1 /*
   2  * Copyright 2001-2007 Sun Microsystems, Inc.  All Rights Reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  20  * CA 95054 USA or visit www.sun.com if you need additional information or
  21  * have any questions.
  22  *
  23  */
  24 
  25 # include "incls/_precompiled.incl"
  26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
  27 
  28 // statics
  29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  30 bool          CMSCollector::_full_gc_requested          = false;
  31 
  32 //////////////////////////////////////////////////////////////////
  33 // In support of CMS/VM thread synchronization
  34 //////////////////////////////////////////////////////////////////
  35 // We split use of the CGC_lock into 2 "levels".
  36 // The low-level locking is of the usual CGC_lock monitor. We introduce
  37 // a higher level "token" (hereafter "CMS token") built on top of the
  38 // low level monitor (hereafter "CGC lock").
  39 // The token-passing protocol gives priority to the VM thread. The
  40 // CMS-lock doesn't provide any fairness guarantees, but clients
  41 // should ensure that it is only held for very short, bounded
  42 // durations.
  43 //
  44 // When either of the CMS thread or the VM thread is involved in
  45 // collection operations during which it does not want the other
  46 // thread to interfere, it obtains the CMS token.
  47 //
  48 // If either thread tries to get the token while the other has
  49 // it, that thread waits. However, if the VM thread and CMS thread
  50 // both want the token, then the VM thread gets priority while the
  51 // CMS thread waits. This ensures, for instance, that the "concurrent"
  52 // phases of the CMS thread's work do not block out the VM thread
  53 // for long periods of time as the CMS thread continues to hog
  54 // the token. (See bug 4616232).
  55 //
  56 // The baton-passing functions are, however, controlled by the
  57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
  58 // and here the low-level CMS lock, not the high level token,
  59 // ensures mutual exclusion.
  60 //
  61 // Two important conditions that we have to satisfy:
  62 // 1. if a thread does a low-level wait on the CMS lock, then it
  63 //    relinquishes the CMS token if it were holding that token
  64 //    when it acquired the low-level CMS lock.
  65 // 2. any low-level notifications on the low-level lock
  66 //    should only be sent when a thread has relinquished the token.
  67 //
  68 // In the absence of either property, we'd have potential deadlock.
  69 //
  70 // We protect each of the CMS (concurrent and sequential) phases
  71 // with the CMS _token_, not the CMS _lock_.
  72 //
  73 // The only code protected by CMS lock is the token acquisition code
  74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
  75 // baton-passing code.
  76 //
  77 // Unfortunately, i couldn't come up with a good abstraction to factor and
  78 // hide the naked CGC_lock manipulation in the baton-passing code
  79 // further below. That's something we should try to do. Also, the proof
  80 // of correctness of this 2-level locking scheme is far from obvious,
  81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
  82 // that there may be a theoretical possibility of delay/starvation in the
  83 // low-level lock/wait/notify scheme used for the baton-passing because of
  84 // potential intereference with the priority scheme embodied in the
  85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
  86 // invocation further below and marked with "XXX 20011219YSR".
  87 // Indeed, as we note elsewhere, this may become yet more slippery
  88 // in the presence of multiple CMS and/or multiple VM threads. XXX
  89 
  90 class CMSTokenSync: public StackObj {
  91  private:
  92   bool _is_cms_thread;
  93  public:
  94   CMSTokenSync(bool is_cms_thread):
  95     _is_cms_thread(is_cms_thread) {
  96     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
  97            "Incorrect argument to constructor");
  98     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
  99   }
 100 
 101   ~CMSTokenSync() {
 102     assert(_is_cms_thread ?
 103              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 104              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 105           "Incorrect state");
 106     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 107   }
 108 };
 109 
 110 // Convenience class that does a CMSTokenSync, and then acquires
 111 // upto three locks.
 112 class CMSTokenSyncWithLocks: public CMSTokenSync {
 113  private:
 114   // Note: locks are acquired in textual declaration order
 115   // and released in the opposite order
 116   MutexLockerEx _locker1, _locker2, _locker3;
 117  public:
 118   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 119                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 120     CMSTokenSync(is_cms_thread),
 121     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 122     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 123     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 124   { }
 125 };
 126 
 127 
 128 // Wrapper class to temporarily disable icms during a foreground cms collection.
 129 class ICMSDisabler: public StackObj {
 130  public:
 131   // The ctor disables icms and wakes up the thread so it notices the change;
 132   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 133   // CMSIncrementalMode.
 134   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 135   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 136 };
 137 
 138 //////////////////////////////////////////////////////////////////
 139 //  Concurrent Mark-Sweep Generation /////////////////////////////
 140 //////////////////////////////////////////////////////////////////
 141 
 142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 143 
 144 // This struct contains per-thread things necessary to support parallel
 145 // young-gen collection.
 146 class CMSParGCThreadState: public CHeapObj {
 147  public:
 148   CFLS_LAB lab;
 149   PromotionInfo promo;
 150 
 151   // Constructor.
 152   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 153     promo.setSpace(cfls);
 154   }
 155 };
 156 
 157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 158      ReservedSpace rs, size_t initial_byte_size, int level,
 159      CardTableRS* ct, bool use_adaptive_freelists,
 160      FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
 161   CardGeneration(rs, initial_byte_size, level, ct),
 162   _dilatation_factor(((double)MinChunkSize)/((double)(oopDesc::header_size()))),
 163   _debug_collection_type(Concurrent_collection_type)
 164 {
 165   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 166   HeapWord* end    = (HeapWord*) _virtual_space.high();
 167 
 168   _direct_allocated_words = 0;
 169   NOT_PRODUCT(
 170     _numObjectsPromoted = 0;
 171     _numWordsPromoted = 0;
 172     _numObjectsAllocated = 0;
 173     _numWordsAllocated = 0;
 174   )
 175 
 176   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 177                                            use_adaptive_freelists,
 178                                            dictionaryChoice);
 179   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 180   if (_cmsSpace == NULL) {
 181     vm_exit_during_initialization(
 182       "CompactibleFreeListSpace allocation failure");
 183   }
 184   _cmsSpace->_gen = this;
 185 
 186   _gc_stats = new CMSGCStats();
 187 
 188   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 189   // offsets match. The ability to tell free chunks from objects
 190   // depends on this property.
 191   debug_only(
 192     FreeChunk* junk = NULL;
 193     assert(junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 194            "Offset of FreeChunk::_prev within FreeChunk must match"
 195            "  that of OopDesc::_klass within OopDesc");
 196   )
 197   if (ParallelGCThreads > 0) {
 198     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 199     _par_gc_thread_states =
 200       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
 201     if (_par_gc_thread_states == NULL) {
 202       vm_exit_during_initialization("Could not allocate par gc structs");
 203     }
 204     for (uint i = 0; i < ParallelGCThreads; i++) {
 205       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 206       if (_par_gc_thread_states[i] == NULL) {
 207         vm_exit_during_initialization("Could not allocate par gc structs");
 208       }
 209     }
 210   } else {
 211     _par_gc_thread_states = NULL;
 212   }
 213   _incremental_collection_failed = false;
 214   // The "dilatation_factor" is the expansion that can occur on
 215   // account of the fact that the minimum object size in the CMS
 216   // generation may be larger than that in, say, a contiguous young
 217   //  generation.
 218   // Ideally, in the calculation below, we'd compute the dilatation
 219   // factor as: MinChunkSize/(promoting_gen's min object size)
 220   // Since we do not have such a general query interface for the
 221   // promoting generation, we'll instead just use the mimimum
 222   // object size (which today is a header's worth of space);
 223   // note that all arithmetic is in units of HeapWords.
 224   assert(MinChunkSize >= oopDesc::header_size(), "just checking");
 225   assert(_dilatation_factor >= 1.0, "from previous assert");
 226 }
 227 
 228 
 229 // The field "_initiating_occupancy" represents the occupancy percentage
 230 // at which we trigger a new collection cycle.  Unless explicitly specified
 231 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
 232 // is calculated by:
 233 //
 234 //   Let "f" be MinHeapFreeRatio in
 235 //
 236 //    _intiating_occupancy = 100-f +
 237 //                           f * (CMSTrigger[Perm]Ratio/100)
 238 //   where CMSTrigger[Perm]Ratio is the argument "tr" below.
 239 //
 240 // That is, if we assume the heap is at its desired maximum occupancy at the
 241 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
 242 // space be allocated before initiating a new collection cycle.
 243 //
 244 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
 245   assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
 246   if (io >= 0) {
 247     _initiating_occupancy = (double)io / 100.0;
 248   } else {
 249     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 250                              (double)(tr * MinHeapFreeRatio) / 100.0)
 251                             / 100.0;
 252   }
 253 }
 254 
 255 
 256 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 257   assert(collector() != NULL, "no collector");
 258   collector()->ref_processor_init();
 259 }
 260 
 261 void CMSCollector::ref_processor_init() {
 262   if (_ref_processor == NULL) {
 263     // Allocate and initialize a reference processor
 264     _ref_processor = ReferenceProcessor::create_ref_processor(
 265         _span,                               // span
 266         _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
 267         _cmsGen->refs_discovery_is_mt(),     // mt_discovery
 268         &_is_alive_closure,
 269         ParallelGCThreads,
 270         ParallelRefProcEnabled);
 271     // Initialize the _ref_processor field of CMSGen
 272     _cmsGen->set_ref_processor(_ref_processor);
 273 
 274     // Allocate a dummy ref processor for perm gen.
 275     ReferenceProcessor* rp2 = new ReferenceProcessor();
 276     if (rp2 == NULL) {
 277       vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
 278     }
 279     _permGen->set_ref_processor(rp2);
 280   }
 281 }
 282 
 283 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 284   GenCollectedHeap* gch = GenCollectedHeap::heap();
 285   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 286     "Wrong type of heap");
 287   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 288     gch->gen_policy()->size_policy();
 289   assert(sp->is_gc_cms_adaptive_size_policy(),
 290     "Wrong type of size policy");
 291   return sp;
 292 }
 293 
 294 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 295   CMSGCAdaptivePolicyCounters* results =
 296     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 297   assert(
 298     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 299     "Wrong gc policy counter kind");
 300   return results;
 301 }
 302 
 303 
 304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 305 
 306   const char* gen_name = "old";
 307 
 308   // Generation Counters - generation 1, 1 subspace
 309   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 310 
 311   _space_counters = new GSpaceCounters(gen_name, 0,
 312                                        _virtual_space.reserved_size(),
 313                                        this, _gen_counters);
 314 }
 315 
 316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 317   _cms_gen(cms_gen)
 318 {
 319   assert(alpha <= 100, "bad value");
 320   _saved_alpha = alpha;
 321 
 322   // Initialize the alphas to the bootstrap value of 100.
 323   _gc0_alpha = _cms_alpha = 100;
 324 
 325   _cms_begin_time.update();
 326   _cms_end_time.update();
 327 
 328   _gc0_duration = 0.0;
 329   _gc0_period = 0.0;
 330   _gc0_promoted = 0;
 331 
 332   _cms_duration = 0.0;
 333   _cms_period = 0.0;
 334   _cms_allocated = 0;
 335 
 336   _cms_used_at_gc0_begin = 0;
 337   _cms_used_at_gc0_end = 0;
 338   _allow_duty_cycle_reduction = false;
 339   _valid_bits = 0;
 340   _icms_duty_cycle = CMSIncrementalDutyCycle;
 341 }
 342 
 343 // If promotion failure handling is on use
 344 // the padded average size of the promotion for each
 345 // young generation collection.
 346 double CMSStats::time_until_cms_gen_full() const {
 347   size_t cms_free = _cms_gen->cmsSpace()->free();
 348   GenCollectedHeap* gch = GenCollectedHeap::heap();
 349   size_t expected_promotion = gch->get_gen(0)->capacity();
 350   if (HandlePromotionFailure) {
 351     expected_promotion = MIN2(
 352         (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
 353         expected_promotion);
 354   }
 355   if (cms_free > expected_promotion) {
 356     // Start a cms collection if there isn't enough space to promote
 357     // for the next minor collection.  Use the padded average as
 358     // a safety factor.
 359     cms_free -= expected_promotion;
 360 
 361     // Adjust by the safety factor.
 362     double cms_free_dbl = (double)cms_free;
 363     cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 364 
 365     if (PrintGCDetails && Verbose) {
 366       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 367         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 368         cms_free, expected_promotion);
 369       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 370         cms_free_dbl, cms_consumption_rate() + 1.0);
 371     }
 372     // Add 1 in case the consumption rate goes to zero.
 373     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 374   }
 375   return 0.0;
 376 }
 377 
 378 // Compare the duration of the cms collection to the
 379 // time remaining before the cms generation is empty.
 380 // Note that the time from the start of the cms collection
 381 // to the start of the cms sweep (less than the total
 382 // duration of the cms collection) can be used.  This
 383 // has been tried and some applications experienced
 384 // promotion failures early in execution.  This was
 385 // possibly because the averages were not accurate
 386 // enough at the beginning.
 387 double CMSStats::time_until_cms_start() const {
 388   // We add "gc0_period" to the "work" calculation
 389   // below because this query is done (mostly) at the
 390   // end of a scavenge, so we need to conservatively
 391   // account for that much possible delay
 392   // in the query so as to avoid concurrent mode failures
 393   // due to starting the collection just a wee bit too
 394   // late.
 395   double work = cms_duration() + gc0_period();
 396   double deadline = time_until_cms_gen_full();
 397   if (work > deadline) {
 398     if (Verbose && PrintGCDetails) {
 399       gclog_or_tty->print(
 400         " CMSCollector: collect because of anticipated promotion "
 401         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 402         gc0_period(), time_until_cms_gen_full());
 403     }
 404     return 0.0;
 405   }
 406   return work - deadline;
 407 }
 408 
 409 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 410 // amount of change to prevent wild oscillation.
 411 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 412                                               unsigned int new_duty_cycle) {
 413   assert(old_duty_cycle <= 100, "bad input value");
 414   assert(new_duty_cycle <= 100, "bad input value");
 415 
 416   // Note:  use subtraction with caution since it may underflow (values are
 417   // unsigned).  Addition is safe since we're in the range 0-100.
 418   unsigned int damped_duty_cycle = new_duty_cycle;
 419   if (new_duty_cycle < old_duty_cycle) {
 420     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 421     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 422       damped_duty_cycle = old_duty_cycle - largest_delta;
 423     }
 424   } else if (new_duty_cycle > old_duty_cycle) {
 425     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 426     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 427       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 428     }
 429   }
 430   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 431 
 432   if (CMSTraceIncrementalPacing) {
 433     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 434                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 435   }
 436   return damped_duty_cycle;
 437 }
 438 
 439 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 440   assert(CMSIncrementalPacing && valid(),
 441          "should be handled in icms_update_duty_cycle()");
 442 
 443   double cms_time_so_far = cms_timer().seconds();
 444   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 445   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 446 
 447   // Avoid division by 0.
 448   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 449   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 450 
 451   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 452   if (new_duty_cycle > _icms_duty_cycle) {
 453     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 454     if (new_duty_cycle > 2) {
 455       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 456                                                 new_duty_cycle);
 457     }
 458   } else if (_allow_duty_cycle_reduction) {
 459     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 460     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 461     // Respect the minimum duty cycle.
 462     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 463     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 464   }
 465 
 466   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 467     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 468   }
 469 
 470   _allow_duty_cycle_reduction = false;
 471   return _icms_duty_cycle;
 472 }
 473 
 474 #ifndef PRODUCT
 475 void CMSStats::print_on(outputStream *st) const {
 476   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 477   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 478                gc0_duration(), gc0_period(), gc0_promoted());
 479   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 480             cms_duration(), cms_duration_per_mb(),
 481             cms_period(), cms_allocated());
 482   st->print(",cms_since_beg=%g,cms_since_end=%g",
 483             cms_time_since_begin(), cms_time_since_end());
 484   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 485             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 486   if (CMSIncrementalMode) {
 487     st->print(",dc=%d", icms_duty_cycle());
 488   }
 489 
 490   if (valid()) {
 491     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 492               promotion_rate(), cms_allocation_rate());
 493     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 494               cms_consumption_rate(), time_until_cms_gen_full());
 495   }
 496   st->print(" ");
 497 }
 498 #endif // #ifndef PRODUCT
 499 
 500 CMSCollector::CollectorState CMSCollector::_collectorState =
 501                              CMSCollector::Idling;
 502 bool CMSCollector::_foregroundGCIsActive = false;
 503 bool CMSCollector::_foregroundGCShouldWait = false;
 504 
 505 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 506                            ConcurrentMarkSweepGeneration* permGen,
 507                            CardTableRS*                   ct,
 508                            ConcurrentMarkSweepPolicy*     cp):
 509   _cmsGen(cmsGen),
 510   _permGen(permGen),
 511   _ct(ct),
 512   _ref_processor(NULL),    // will be set later
 513   _conc_workers(NULL),     // may be set later
 514   _abort_preclean(false),
 515   _start_sampling(false),
 516   _between_prologue_and_epilogue(false),
 517   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 518   _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
 519   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 520                  -1 /* lock-free */, "No_lock" /* dummy */),
 521   _modUnionClosure(&_modUnionTable),
 522   _modUnionClosurePar(&_modUnionTable),
 523   _is_alive_closure(&_markBitMap),
 524   _restart_addr(NULL),
 525   _overflow_list(NULL),
 526   _preserved_oop_stack(NULL),
 527   _preserved_mark_stack(NULL),
 528   _stats(cmsGen),
 529   _eden_chunk_array(NULL),     // may be set in ctor body
 530   _eden_chunk_capacity(0),     // -- ditto --
 531   _eden_chunk_index(0),        // -- ditto --
 532   _survivor_plab_array(NULL),  // -- ditto --
 533   _survivor_chunk_array(NULL), // -- ditto --
 534   _survivor_chunk_capacity(0), // -- ditto --
 535   _survivor_chunk_index(0),    // -- ditto --
 536   _ser_pmc_preclean_ovflw(0),
 537   _ser_pmc_remark_ovflw(0),
 538   _par_pmc_remark_ovflw(0),
 539   _ser_kac_ovflw(0),
 540   _par_kac_ovflw(0),
 541 #ifndef PRODUCT
 542   _num_par_pushes(0),
 543 #endif
 544   _collection_count_start(0),
 545   _verifying(false),
 546   _icms_start_limit(NULL),
 547   _icms_stop_limit(NULL),
 548   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 549   _completed_initialization(false),
 550   _collector_policy(cp),
 551   _should_unload_classes(false),
 552   _concurrent_cycles_since_last_unload(0),
 553   _sweep_count(0),
 554   _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
 555 {
 556   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 557     ExplicitGCInvokesConcurrent = true;
 558   }
 559   // Now expand the span and allocate the collection support structures
 560   // (MUT, marking bit map etc.) to cover both generations subject to
 561   // collection.
 562 
 563   // First check that _permGen is adjacent to _cmsGen and above it.
 564   assert(   _cmsGen->reserved().word_size()  > 0
 565          && _permGen->reserved().word_size() > 0,
 566          "generations should not be of zero size");
 567   assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
 568          "_cmsGen and _permGen should not overlap");
 569   assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
 570          "_cmsGen->end() different from _permGen->start()");
 571 
 572   // For use by dirty card to oop closures.
 573   _cmsGen->cmsSpace()->set_collector(this);
 574   _permGen->cmsSpace()->set_collector(this);
 575 
 576   // Adjust my span to cover old (cms) gen and perm gen
 577   _span = _cmsGen->reserved()._union(_permGen->reserved());
 578   // Initialize the span of is_alive_closure
 579   _is_alive_closure.set_span(_span);
 580 
 581   // Allocate MUT and marking bit map
 582   {
 583     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 584     if (!_markBitMap.allocate(_span)) {
 585       warning("Failed to allocate CMS Bit Map");
 586       return;
 587     }
 588     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 589   }
 590   {
 591     _modUnionTable.allocate(_span);
 592     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 593   }
 594 
 595   if (!_markStack.allocate(CMSMarkStackSize)) {
 596     warning("Failed to allocate CMS Marking Stack");
 597     return;
 598   }
 599   if (!_revisitStack.allocate(CMSRevisitStackSize)) {
 600     warning("Failed to allocate CMS Revisit Stack");
 601     return;
 602   }
 603 
 604   // Support for multi-threaded concurrent phases
 605   if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
 606     if (FLAG_IS_DEFAULT(ParallelCMSThreads)) {
 607       // just for now
 608       FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4);
 609     }
 610     if (ParallelCMSThreads > 1) {
 611       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 612                                  ParallelCMSThreads, true);
 613       if (_conc_workers == NULL) {
 614         warning("GC/CMS: _conc_workers allocation failure: "
 615               "forcing -CMSConcurrentMTEnabled");
 616         CMSConcurrentMTEnabled = false;
 617       }
 618     } else {
 619       CMSConcurrentMTEnabled = false;
 620     }
 621   }
 622   if (!CMSConcurrentMTEnabled) {
 623     ParallelCMSThreads = 0;
 624   } else {
 625     // Turn off CMSCleanOnEnter optimization temporarily for
 626     // the MT case where it's not fixed yet; see 6178663.
 627     CMSCleanOnEnter = false;
 628   }
 629   assert((_conc_workers != NULL) == (ParallelCMSThreads > 1),
 630          "Inconsistency");
 631 
 632   // Parallel task queues; these are shared for the
 633   // concurrent and stop-world phases of CMS, but
 634   // are not shared with parallel scavenge (ParNew).
 635   {
 636     uint i;
 637     uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads);
 638 
 639     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 640          || ParallelRefProcEnabled)
 641         && num_queues > 0) {
 642       _task_queues = new OopTaskQueueSet(num_queues);
 643       if (_task_queues == NULL) {
 644         warning("task_queues allocation failure.");
 645         return;
 646       }
 647       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
 648       if (_hash_seed == NULL) {
 649         warning("_hash_seed array allocation failure");
 650         return;
 651       }
 652 
 653       // XXX use a global constant instead of 64!
 654       typedef struct OopTaskQueuePadded {
 655         OopTaskQueue work_queue;
 656         char pad[64 - sizeof(OopTaskQueue)];  // prevent false sharing
 657       } OopTaskQueuePadded;
 658 
 659       for (i = 0; i < num_queues; i++) {
 660         OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
 661         if (q_padded == NULL) {
 662           warning("work_queue allocation failure.");
 663           return;
 664         }
 665         _task_queues->register_queue(i, &q_padded->work_queue);
 666       }
 667       for (i = 0; i < num_queues; i++) {
 668         _task_queues->queue(i)->initialize();
 669         _hash_seed[i] = 17;  // copied from ParNew
 670       }
 671     }
 672   }
 673 
 674   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 675   _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
 676 
 677   // Clip CMSBootstrapOccupancy between 0 and 100.
 678   _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
 679                          /(double)100;
 680 
 681   _full_gcs_since_conc_gc = 0;
 682 
 683   // Now tell CMS generations the identity of their collector
 684   ConcurrentMarkSweepGeneration::set_collector(this);
 685 
 686   // Create & start a CMS thread for this CMS collector
 687   _cmsThread = ConcurrentMarkSweepThread::start(this);
 688   assert(cmsThread() != NULL, "CMS Thread should have been created");
 689   assert(cmsThread()->collector() == this,
 690          "CMS Thread should refer to this gen");
 691   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 692 
 693   // Support for parallelizing young gen rescan
 694   GenCollectedHeap* gch = GenCollectedHeap::heap();
 695   _young_gen = gch->prev_gen(_cmsGen);
 696   if (gch->supports_inline_contig_alloc()) {
 697     _top_addr = gch->top_addr();
 698     _end_addr = gch->end_addr();
 699     assert(_young_gen != NULL, "no _young_gen");
 700     _eden_chunk_index = 0;
 701     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 702     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
 703     if (_eden_chunk_array == NULL) {
 704       _eden_chunk_capacity = 0;
 705       warning("GC/CMS: _eden_chunk_array allocation failure");
 706     }
 707   }
 708   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 709 
 710   // Support for parallelizing survivor space rescan
 711   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 712     size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize);
 713     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
 714     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
 715     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
 716     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 717         || _cursor == NULL) {
 718       warning("Failed to allocate survivor plab/chunk array");
 719       if (_survivor_plab_array  != NULL) {
 720         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
 721         _survivor_plab_array = NULL;
 722       }
 723       if (_survivor_chunk_array != NULL) {
 724         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
 725         _survivor_chunk_array = NULL;
 726       }
 727       if (_cursor != NULL) {
 728         FREE_C_HEAP_ARRAY(size_t, _cursor);
 729         _cursor = NULL;
 730       }
 731     } else {
 732       _survivor_chunk_capacity = 2*max_plab_samples;
 733       for (uint i = 0; i < ParallelGCThreads; i++) {
 734         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
 735         if (vec == NULL) {
 736           warning("Failed to allocate survivor plab array");
 737           for (int j = i; j > 0; j--) {
 738             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
 739           }
 740           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
 741           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
 742           _survivor_plab_array = NULL;
 743           _survivor_chunk_array = NULL;
 744           _survivor_chunk_capacity = 0;
 745           break;
 746         } else {
 747           ChunkArray* cur =
 748             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 749                                                         max_plab_samples);
 750           assert(cur->end() == 0, "Should be 0");
 751           assert(cur->array() == vec, "Should be vec");
 752           assert(cur->capacity() == max_plab_samples, "Error");
 753         }
 754       }
 755     }
 756   }
 757   assert(   (   _survivor_plab_array  != NULL
 758              && _survivor_chunk_array != NULL)
 759          || (   _survivor_chunk_capacity == 0
 760              && _survivor_chunk_index == 0),
 761          "Error");
 762 
 763   // Choose what strong roots should be scanned depending on verification options
 764   // and perm gen collection mode.
 765   if (!CMSClassUnloadingEnabled) {
 766     // If class unloading is disabled we want to include all classes into the root set.
 767     add_root_scanning_option(SharedHeap::SO_AllClasses);
 768   } else {
 769     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 770   }
 771 
 772   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 773   _gc_counters = new CollectorCounters("CMS", 1);
 774   _completed_initialization = true;
 775   _sweep_timer.start();  // start of time
 776 }
 777 
 778 const char* ConcurrentMarkSweepGeneration::name() const {
 779   return "concurrent mark-sweep generation";
 780 }
 781 void ConcurrentMarkSweepGeneration::update_counters() {
 782   if (UsePerfData) {
 783     _space_counters->update_all();
 784     _gen_counters->update_all();
 785   }
 786 }
 787 
 788 // this is an optimized version of update_counters(). it takes the
 789 // used value as a parameter rather than computing it.
 790 //
 791 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 792   if (UsePerfData) {
 793     _space_counters->update_used(used);
 794     _space_counters->update_capacity();
 795     _gen_counters->update_all();
 796   }
 797 }
 798 
 799 void ConcurrentMarkSweepGeneration::print() const {
 800   Generation::print();
 801   cmsSpace()->print();
 802 }
 803 
 804 #ifndef PRODUCT
 805 void ConcurrentMarkSweepGeneration::print_statistics() {
 806   cmsSpace()->printFLCensus(0);
 807 }
 808 #endif
 809 
 810 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 811   GenCollectedHeap* gch = GenCollectedHeap::heap();
 812   if (PrintGCDetails) {
 813     if (Verbose) {
 814       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 815         level(), short_name(), s, used(), capacity());
 816     } else {
 817       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 818         level(), short_name(), s, used() / K, capacity() / K);
 819     }
 820   }
 821   if (Verbose) {
 822     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 823               gch->used(), gch->capacity());
 824   } else {
 825     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 826               gch->used() / K, gch->capacity() / K);
 827   }
 828 }
 829 
 830 size_t
 831 ConcurrentMarkSweepGeneration::contiguous_available() const {
 832   // dld proposes an improvement in precision here. If the committed
 833   // part of the space ends in a free block we should add that to
 834   // uncommitted size in the calculation below. Will make this
 835   // change later, staying with the approximation below for the
 836   // time being. -- ysr.
 837   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 838 }
 839 
 840 size_t
 841 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 842   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 843 }
 844 
 845 size_t ConcurrentMarkSweepGeneration::max_available() const {
 846   return free() + _virtual_space.uncommitted_size();
 847 }
 848 
 849 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
 850     size_t max_promotion_in_bytes,
 851     bool younger_handles_promotion_failure) const {
 852 
 853   // This is the most conservative test.  Full promotion is
 854   // guaranteed if this is used. The multiplicative factor is to
 855   // account for the worst case "dilatation".
 856   double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
 857   if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
 858     adjusted_max_promo_bytes = (double)max_uintx;
 859   }
 860   bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
 861 
 862   if (younger_handles_promotion_failure && !result) {
 863     // Full promotion is not guaranteed because fragmentation
 864     // of the cms generation can prevent the full promotion.
 865     result = (max_available() >= (size_t)adjusted_max_promo_bytes);
 866 
 867     if (!result) {
 868       // With promotion failure handling the test for the ability
 869       // to support the promotion does not have to be guaranteed.
 870       // Use an average of the amount promoted.
 871       result = max_available() >= (size_t)
 872         gc_stats()->avg_promoted()->padded_average();
 873       if (PrintGC && Verbose && result) {
 874         gclog_or_tty->print_cr(
 875           "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 876           " max_available: " SIZE_FORMAT
 877           " avg_promoted: " SIZE_FORMAT,
 878           max_available(), (size_t)
 879           gc_stats()->avg_promoted()->padded_average());
 880       }
 881     } else {
 882       if (PrintGC && Verbose) {
 883         gclog_or_tty->print_cr(
 884           "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 885           " max_available: " SIZE_FORMAT
 886           " adj_max_promo_bytes: " SIZE_FORMAT,
 887           max_available(), (size_t)adjusted_max_promo_bytes);
 888       }
 889     }
 890   } else {
 891     if (PrintGC && Verbose) {
 892       gclog_or_tty->print_cr(
 893         "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 894         " contiguous_available: " SIZE_FORMAT
 895         " adj_max_promo_bytes: " SIZE_FORMAT,
 896         max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
 897     }
 898   }
 899   return result;
 900 }
 901 
 902 CompactibleSpace*
 903 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 904   return _cmsSpace;
 905 }
 906 
 907 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 908   // Clear the promotion information.  These pointers can be adjusted
 909   // along with all the other pointers into the heap but
 910   // compaction is expected to be a rare event with
 911   // a heap using cms so don't do it without seeing the need.
 912   if (ParallelGCThreads > 0) {
 913     for (uint i = 0; i < ParallelGCThreads; i++) {
 914       _par_gc_thread_states[i]->promo.reset();
 915     }
 916   }
 917 }
 918 
 919 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 920   blk->do_space(_cmsSpace);
 921 }
 922 
 923 void ConcurrentMarkSweepGeneration::compute_new_size() {
 924   assert_locked_or_safepoint(Heap_lock);
 925 
 926   // If incremental collection failed, we just want to expand
 927   // to the limit.
 928   if (incremental_collection_failed()) {
 929     clear_incremental_collection_failed();
 930     grow_to_reserved();
 931     return;
 932   }
 933 
 934   size_t expand_bytes = 0;
 935   double free_percentage = ((double) free()) / capacity();
 936   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 937   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 938 
 939   // compute expansion delta needed for reaching desired free percentage
 940   if (free_percentage < desired_free_percentage) {
 941     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 942     assert(desired_capacity >= capacity(), "invalid expansion size");
 943     expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 944   }
 945   if (expand_bytes > 0) {
 946     if (PrintGCDetails && Verbose) {
 947       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 948       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 949       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 950       gclog_or_tty->print_cr("  Desired free fraction %f",
 951         desired_free_percentage);
 952       gclog_or_tty->print_cr("  Maximum free fraction %f",
 953         maximum_free_percentage);
 954       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 955       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 956         desired_capacity/1000);
 957       int prev_level = level() - 1;
 958       if (prev_level >= 0) {
 959         size_t prev_size = 0;
 960         GenCollectedHeap* gch = GenCollectedHeap::heap();
 961         Generation* prev_gen = gch->_gens[prev_level];
 962         prev_size = prev_gen->capacity();
 963           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 964                                  prev_size/1000);
 965       }
 966       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 967         unsafe_max_alloc_nogc()/1000);
 968       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 969         contiguous_available()/1000);
 970       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 971         expand_bytes);
 972     }
 973     // safe if expansion fails
 974     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 975     if (PrintGCDetails && Verbose) {
 976       gclog_or_tty->print_cr("  Expanded free fraction %f",
 977         ((double) free()) / capacity());
 978     }
 979   }
 980 }
 981 
 982 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 983   return cmsSpace()->freelistLock();
 984 }
 985 
 986 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 987                                                   bool   tlab) {
 988   CMSSynchronousYieldRequest yr;
 989   MutexLockerEx x(freelistLock(),
 990                   Mutex::_no_safepoint_check_flag);
 991   return have_lock_and_allocate(size, tlab);
 992 }
 993 
 994 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 995                                                   bool   tlab) {
 996   assert_lock_strong(freelistLock());
 997   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 998   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 999   // Allocate the object live (grey) if the background collector has
1000   // started marking. This is necessary because the marker may
1001   // have passed this address and consequently this object will
1002   // not otherwise be greyed and would be incorrectly swept up.
1003   // Note that if this object contains references, the writing
1004   // of those references will dirty the card containing this object
1005   // allowing the object to be blackened (and its references scanned)
1006   // either during a preclean phase or at the final checkpoint.
1007   if (res != NULL) {
1008     collector()->direct_allocated(res, adjustedSize);
1009     _direct_allocated_words += adjustedSize;
1010     // allocation counters
1011     NOT_PRODUCT(
1012       _numObjectsAllocated++;
1013       _numWordsAllocated += (int)adjustedSize;
1014     )
1015   }
1016   return res;
1017 }
1018 
1019 // In the case of direct allocation by mutators in a generation that
1020 // is being concurrently collected, the object must be allocated
1021 // live (grey) if the background collector has started marking.
1022 // This is necessary because the marker may
1023 // have passed this address and consequently this object will
1024 // not otherwise be greyed and would be incorrectly swept up.
1025 // Note that if this object contains references, the writing
1026 // of those references will dirty the card containing this object
1027 // allowing the object to be blackened (and its references scanned)
1028 // either during a preclean phase or at the final checkpoint.
1029 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1030   assert(_markBitMap.covers(start, size), "Out of bounds");
1031   if (_collectorState >= Marking) {
1032     MutexLockerEx y(_markBitMap.lock(),
1033                     Mutex::_no_safepoint_check_flag);
1034     // [see comments preceding SweepClosure::do_blk() below for details]
1035     // 1. need to mark the object as live so it isn't collected
1036     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1037     // 3. need to mark the end of the object so sweeper can skip over it
1038     //    if it's uninitialized when the sweeper reaches it.
1039     _markBitMap.mark(start);          // object is live
1040     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1041     _markBitMap.mark(start + size - 1);
1042                                       // mark end of object
1043   }
1044   // check that oop looks uninitialized
1045   assert(oop(start)->klass() == NULL, "_klass should be NULL");
1046 }
1047 
1048 void CMSCollector::promoted(bool par, HeapWord* start,
1049                             bool is_obj_array, size_t obj_size) {
1050   assert(_markBitMap.covers(start), "Out of bounds");
1051   // See comment in direct_allocated() about when objects should
1052   // be allocated live.
1053   if (_collectorState >= Marking) {
1054     // we already hold the marking bit map lock, taken in
1055     // the prologue
1056     if (par) {
1057       _markBitMap.par_mark(start);
1058     } else {
1059       _markBitMap.mark(start);
1060     }
1061     // We don't need to mark the object as uninitialized (as
1062     // in direct_allocated above) because this is being done with the
1063     // world stopped and the object will be initialized by the
1064     // time the sweeper gets to look at it.
1065     assert(SafepointSynchronize::is_at_safepoint(),
1066            "expect promotion only at safepoints");
1067 
1068     if (_collectorState < Sweeping) {
1069       // Mark the appropriate cards in the modUnionTable, so that
1070       // this object gets scanned before the sweep. If this is
1071       // not done, CMS generation references in the object might
1072       // not get marked.
1073       // For the case of arrays, which are otherwise precisely
1074       // marked, we need to dirty the entire array, not just its head.
1075       if (is_obj_array) {
1076         // The [par_]mark_range() method expects mr.end() below to
1077         // be aligned to the granularity of a bit's representation
1078         // in the heap. In the case of the MUT below, that's a
1079         // card size.
1080         MemRegion mr(start,
1081                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1082                         CardTableModRefBS::card_size /* bytes */));
1083         if (par) {
1084           _modUnionTable.par_mark_range(mr);
1085         } else {
1086           _modUnionTable.mark_range(mr);
1087         }
1088       } else {  // not an obj array; we can just mark the head
1089         if (par) {
1090           _modUnionTable.par_mark(start);
1091         } else {
1092           _modUnionTable.mark(start);
1093         }
1094       }
1095     }
1096   }
1097 }
1098 
1099 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1100 {
1101   size_t delta = pointer_delta(addr, space->bottom());
1102   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1103 }
1104 
1105 void CMSCollector::icms_update_allocation_limits()
1106 {
1107   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1108   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1109 
1110   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1111   if (CMSTraceIncrementalPacing) {
1112     stats().print();
1113   }
1114 
1115   assert(duty_cycle <= 100, "invalid duty cycle");
1116   if (duty_cycle != 0) {
1117     // The duty_cycle is a percentage between 0 and 100; convert to words and
1118     // then compute the offset from the endpoints of the space.
1119     size_t free_words = eden->free() / HeapWordSize;
1120     double free_words_dbl = (double)free_words;
1121     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1122     size_t offset_words = (free_words - duty_cycle_words) / 2;
1123 
1124     _icms_start_limit = eden->top() + offset_words;
1125     _icms_stop_limit = eden->end() - offset_words;
1126 
1127     // The limits may be adjusted (shifted to the right) by
1128     // CMSIncrementalOffset, to allow the application more mutator time after a
1129     // young gen gc (when all mutators were stopped) and before CMS starts and
1130     // takes away one or more cpus.
1131     if (CMSIncrementalOffset != 0) {
1132       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1133       size_t adjustment = (size_t)adjustment_dbl;
1134       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1135       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1136         _icms_start_limit += adjustment;
1137         _icms_stop_limit = tmp_stop;
1138       }
1139     }
1140   }
1141   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1142     _icms_start_limit = _icms_stop_limit = eden->end();
1143   }
1144 
1145   // Install the new start limit.
1146   eden->set_soft_end(_icms_start_limit);
1147 
1148   if (CMSTraceIncrementalMode) {
1149     gclog_or_tty->print(" icms alloc limits:  "
1150                            PTR_FORMAT "," PTR_FORMAT
1151                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1152                            _icms_start_limit, _icms_stop_limit,
1153                            percent_of_space(eden, _icms_start_limit),
1154                            percent_of_space(eden, _icms_stop_limit));
1155     if (Verbose) {
1156       gclog_or_tty->print("eden:  ");
1157       eden->print_on(gclog_or_tty);
1158     }
1159   }
1160 }
1161 
1162 // Any changes here should try to maintain the invariant
1163 // that if this method is called with _icms_start_limit
1164 // and _icms_stop_limit both NULL, then it should return NULL
1165 // and not notify the icms thread.
1166 HeapWord*
1167 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1168                                        size_t word_size)
1169 {
1170   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1171   // nop.
1172   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1173     if (top <= _icms_start_limit) {
1174       if (CMSTraceIncrementalMode) {
1175         space->print_on(gclog_or_tty);
1176         gclog_or_tty->stamp();
1177         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1178                                ", new limit=" PTR_FORMAT
1179                                " (" SIZE_FORMAT "%%)",
1180                                top, _icms_stop_limit,
1181                                percent_of_space(space, _icms_stop_limit));
1182       }
1183       ConcurrentMarkSweepThread::start_icms();
1184       assert(top < _icms_stop_limit, "Tautology");
1185       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1186         return _icms_stop_limit;
1187       }
1188 
1189       // The allocation will cross both the _start and _stop limits, so do the
1190       // stop notification also and return end().
1191       if (CMSTraceIncrementalMode) {
1192         space->print_on(gclog_or_tty);
1193         gclog_or_tty->stamp();
1194         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1195                                ", new limit=" PTR_FORMAT
1196                                " (" SIZE_FORMAT "%%)",
1197                                top, space->end(),
1198                                percent_of_space(space, space->end()));
1199       }
1200       ConcurrentMarkSweepThread::stop_icms();
1201       return space->end();
1202     }
1203 
1204     if (top <= _icms_stop_limit) {
1205       if (CMSTraceIncrementalMode) {
1206         space->print_on(gclog_or_tty);
1207         gclog_or_tty->stamp();
1208         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1209                                ", new limit=" PTR_FORMAT
1210                                " (" SIZE_FORMAT "%%)",
1211                                top, space->end(),
1212                                percent_of_space(space, space->end()));
1213       }
1214       ConcurrentMarkSweepThread::stop_icms();
1215       return space->end();
1216     }
1217 
1218     if (CMSTraceIncrementalMode) {
1219       space->print_on(gclog_or_tty);
1220       gclog_or_tty->stamp();
1221       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1222                              ", new limit=" PTR_FORMAT,
1223                              top, NULL);
1224     }
1225   }
1226 
1227   return NULL;
1228 }
1229 
1230 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size, oop* ref) {
1231   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1232   // allocate, copy and if necessary update promoinfo --
1233   // delegate to underlying space.
1234   assert_lock_strong(freelistLock());
1235 
1236 #ifndef PRODUCT
1237   if (Universe::heap()->promotion_should_fail()) {
1238     return NULL;
1239   }
1240 #endif  // #ifndef PRODUCT
1241 
1242   oop res = _cmsSpace->promote(obj, obj_size, ref);
1243   if (res == NULL) {
1244     // expand and retry
1245     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1246     expand(s*HeapWordSize, MinHeapDeltaBytes,
1247       CMSExpansionCause::_satisfy_promotion);
1248     // Since there's currently no next generation, we don't try to promote
1249     // into a more senior generation.
1250     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1251                                "is made to pass on a possibly failing "
1252                                "promotion to next generation");
1253     res = _cmsSpace->promote(obj, obj_size, ref);
1254   }
1255   if (res != NULL) {
1256     // See comment in allocate() about when objects should
1257     // be allocated live.
1258     assert(obj->is_oop(), "Will dereference klass pointer below");
1259     collector()->promoted(false,           // Not parallel
1260                           (HeapWord*)res, obj->is_objArray(), obj_size);
1261     // promotion counters
1262     NOT_PRODUCT(
1263       _numObjectsPromoted++;
1264       _numWordsPromoted +=
1265         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1266     )
1267   }
1268   return res;
1269 }
1270 
1271 
1272 HeapWord*
1273 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1274                                              HeapWord* top,
1275                                              size_t word_sz)
1276 {
1277   return collector()->allocation_limit_reached(space, top, word_sz);
1278 }
1279 
1280 // Things to support parallel young-gen collection.
1281 oop
1282 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1283                                            oop old, markOop m,
1284                                            size_t word_sz) {
1285 #ifndef PRODUCT
1286   if (Universe::heap()->promotion_should_fail()) {
1287     return NULL;
1288   }
1289 #endif  // #ifndef PRODUCT
1290 
1291   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1292   PromotionInfo* promoInfo = &ps->promo;
1293   // if we are tracking promotions, then first ensure space for
1294   // promotion (including spooling space for saving header if necessary).
1295   // then allocate and copy, then track promoted info if needed.
1296   // When tracking (see PromotionInfo::track()), the mark word may
1297   // be displaced and in this case restoration of the mark word
1298   // occurs in the (oop_since_save_marks_)iterate phase.
1299   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1300     // Out of space for allocating spooling buffers;
1301     // try expanding and allocating spooling buffers.
1302     if (!expand_and_ensure_spooling_space(promoInfo)) {
1303       return NULL;
1304     }
1305   }
1306   assert(promoInfo->has_spooling_space(), "Control point invariant");
1307   HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1308   if (obj_ptr == NULL) {
1309      obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1310      if (obj_ptr == NULL) {
1311        return NULL;
1312      }
1313   }
1314   oop obj = oop(obj_ptr);
1315   assert(obj->klass() == NULL, "Object should be uninitialized here.");
1316   // Otherwise, copy the object.  Here we must be careful to insert the
1317   // klass pointer last, since this marks the block as an allocated object.
1318   HeapWord* old_ptr = (HeapWord*)old;
1319   if (word_sz > (size_t)oopDesc::header_size()) {
1320     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1321                                  obj_ptr + oopDesc::header_size(),
1322                                  word_sz - oopDesc::header_size());
1323   }
1324   // Restore the mark word copied above.
1325   obj->set_mark(m);
1326   // Now we can track the promoted object, if necessary.  We take care
1327   // To delay the transition from uninitialized to full object
1328   // (i.e., insertion of klass pointer) until after, so that it
1329   // atomically becomes a promoted object.
1330   if (promoInfo->tracking()) {
1331     promoInfo->track((PromotedObject*)obj, old->klass());
1332   }
1333   // Finally, install the klass pointer.
1334   obj->set_klass(old->klass());
1335 
1336   assert(old->is_oop(), "Will dereference klass ptr below");
1337   collector()->promoted(true,          // parallel
1338                         obj_ptr, old->is_objArray(), word_sz);
1339 
1340   NOT_PRODUCT(
1341     Atomic::inc(&_numObjectsPromoted);
1342     Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1343                 &_numWordsPromoted);
1344   )
1345 
1346   return obj;
1347 }
1348 
1349 void
1350 ConcurrentMarkSweepGeneration::
1351 par_promote_alloc_undo(int thread_num,
1352                        HeapWord* obj, size_t word_sz) {
1353   // CMS does not support promotion undo.
1354   ShouldNotReachHere();
1355 }
1356 
1357 void
1358 ConcurrentMarkSweepGeneration::
1359 par_promote_alloc_done(int thread_num) {
1360   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1361   ps->lab.retire();
1362 #if CFLS_LAB_REFILL_STATS
1363   if (thread_num == 0) {
1364     _cmsSpace->print_par_alloc_stats();
1365   }
1366 #endif
1367 }
1368 
1369 void
1370 ConcurrentMarkSweepGeneration::
1371 par_oop_since_save_marks_iterate_done(int thread_num) {
1372   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1373   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1374   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1375 }
1376 
1377 // XXXPERM
1378 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1379                                                    size_t size,
1380                                                    bool   tlab)
1381 {
1382   // We allow a STW collection only if a full
1383   // collection was requested.
1384   return full || should_allocate(size, tlab); // FIX ME !!!
1385   // This and promotion failure handling are connected at the
1386   // hip and should be fixed by untying them.
1387 }
1388 
1389 bool CMSCollector::shouldConcurrentCollect() {
1390   if (_full_gc_requested) {
1391     assert(ExplicitGCInvokesConcurrent, "Unexpected state");
1392     if (Verbose && PrintGCDetails) {
1393       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1394                              " gc request");
1395     }
1396     return true;
1397   }
1398 
1399   // For debugging purposes, change the type of collection.
1400   // If the rotation is not on the concurrent collection
1401   // type, don't start a concurrent collection.
1402   NOT_PRODUCT(
1403     if (RotateCMSCollectionTypes &&
1404         (_cmsGen->debug_collection_type() !=
1405           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1406       assert(_cmsGen->debug_collection_type() !=
1407         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1408         "Bad cms collection type");
1409       return false;
1410     }
1411   )
1412 
1413   FreelistLocker x(this);
1414   // ------------------------------------------------------------------
1415   // Print out lots of information which affects the initiation of
1416   // a collection.
1417   if (PrintCMSInitiationStatistics && stats().valid()) {
1418     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1419     gclog_or_tty->stamp();
1420     gclog_or_tty->print_cr("");
1421     stats().print_on(gclog_or_tty);
1422     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1423       stats().time_until_cms_gen_full());
1424     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1425     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1426                            _cmsGen->contiguous_available());
1427     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1428     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1429     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1430     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1431     gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1432   }
1433   // ------------------------------------------------------------------
1434 
1435   // If the estimated time to complete a cms collection (cms_duration())
1436   // is less than the estimated time remaining until the cms generation
1437   // is full, start a collection.
1438   if (!UseCMSInitiatingOccupancyOnly) {
1439     if (stats().valid()) {
1440       if (stats().time_until_cms_start() == 0.0) {
1441         return true;
1442       }
1443     } else {
1444       // We want to conservatively collect somewhat early in order
1445       // to try and "bootstrap" our CMS/promotion statistics;
1446       // this branch will not fire after the first successful CMS
1447       // collection because the stats should then be valid.
1448       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1449         if (Verbose && PrintGCDetails) {
1450           gclog_or_tty->print_cr(
1451             " CMSCollector: collect for bootstrapping statistics:"
1452             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1453             _bootstrap_occupancy);
1454         }
1455         return true;
1456       }
1457     }
1458   }
1459 
1460   // Otherwise, we start a collection cycle if either the perm gen or
1461   // old gen want a collection cycle started. Each may use
1462   // an appropriate criterion for making this decision.
1463   // XXX We need to make sure that the gen expansion
1464   // criterion dovetails well with this. XXX NEED TO FIX THIS
1465   if (_cmsGen->should_concurrent_collect()) {
1466     if (Verbose && PrintGCDetails) {
1467       gclog_or_tty->print_cr("CMS old gen initiated");
1468     }
1469     return true;
1470   }
1471 
1472   // We start a collection if we believe an incremental collection may fail;
1473   // this is not likely to be productive in practice because it's probably too
1474   // late anyway.
1475   GenCollectedHeap* gch = GenCollectedHeap::heap();
1476   assert(gch->collector_policy()->is_two_generation_policy(),
1477          "You may want to check the correctness of the following");
1478   if (gch->incremental_collection_will_fail()) {
1479     if (PrintGCDetails && Verbose) {
1480       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1481     }
1482     return true;
1483   }
1484 
1485   if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1486     bool res = update_should_unload_classes();
1487     if (res) {
1488       if (Verbose && PrintGCDetails) {
1489         gclog_or_tty->print_cr("CMS perm gen initiated");
1490       }
1491       return true;
1492     }
1493   }
1494   return false;
1495 }
1496 
1497 // Clear _expansion_cause fields of constituent generations
1498 void CMSCollector::clear_expansion_cause() {
1499   _cmsGen->clear_expansion_cause();
1500   _permGen->clear_expansion_cause();
1501 }
1502 
1503 // We should be conservative in starting a collection cycle.  To
1504 // start too eagerly runs the risk of collecting too often in the
1505 // extreme.  To collect too rarely falls back on full collections,
1506 // which works, even if not optimum in terms of concurrent work.
1507 // As a work around for too eagerly collecting, use the flag
1508 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1509 // giving the user an easily understandable way of controlling the
1510 // collections.
1511 // We want to start a new collection cycle if any of the following
1512 // conditions hold:
1513 // . our current occupancy exceeds the configured initiating occupancy
1514 //   for this generation, or
1515 // . we recently needed to expand this space and have not, since that
1516 //   expansion, done a collection of this generation, or
1517 // . the underlying space believes that it may be a good idea to initiate
1518 //   a concurrent collection (this may be based on criteria such as the
1519 //   following: the space uses linear allocation and linear allocation is
1520 //   going to fail, or there is believed to be excessive fragmentation in
1521 //   the generation, etc... or ...
1522 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1523 //   the case of the old generation, not the perm generation; see CR 6543076):
1524 //   we may be approaching a point at which allocation requests may fail because
1525 //   we will be out of sufficient free space given allocation rate estimates.]
1526 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1527 
1528   assert_lock_strong(freelistLock());
1529   if (occupancy() > initiating_occupancy()) {
1530     if (PrintGCDetails && Verbose) {
1531       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1532         short_name(), occupancy(), initiating_occupancy());
1533     }
1534     return true;
1535   }
1536   if (UseCMSInitiatingOccupancyOnly) {
1537     return false;
1538   }
1539   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1540     if (PrintGCDetails && Verbose) {
1541       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1542         short_name());
1543     }
1544     return true;
1545   }
1546   if (_cmsSpace->should_concurrent_collect()) {
1547     if (PrintGCDetails && Verbose) {
1548       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1549         short_name());
1550     }
1551     return true;
1552   }
1553   return false;
1554 }
1555 
1556 void ConcurrentMarkSweepGeneration::collect(bool   full,
1557                                             bool   clear_all_soft_refs,
1558                                             size_t size,
1559                                             bool   tlab)
1560 {
1561   collector()->collect(full, clear_all_soft_refs, size, tlab);
1562 }
1563 
1564 void CMSCollector::collect(bool   full,
1565                            bool   clear_all_soft_refs,
1566                            size_t size,
1567                            bool   tlab)
1568 {
1569   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1570     // For debugging purposes skip the collection if the state
1571     // is not currently idle
1572     if (TraceCMSState) {
1573       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1574         Thread::current(), full, _collectorState);
1575     }
1576     return;
1577   }
1578 
1579   // The following "if" branch is present for defensive reasons.
1580   // In the current uses of this interface, it can be replaced with:
1581   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1582   // But I am not placing that assert here to allow future
1583   // generality in invoking this interface.
1584   if (GC_locker::is_active()) {
1585     // A consistency test for GC_locker
1586     assert(GC_locker::needs_gc(), "Should have been set already");
1587     // Skip this foreground collection, instead
1588     // expanding the heap if necessary.
1589     // Need the free list locks for the call to free() in compute_new_size()
1590     compute_new_size();
1591     return;
1592   }
1593   acquire_control_and_collect(full, clear_all_soft_refs);
1594   _full_gcs_since_conc_gc++;
1595 
1596 }
1597 
1598 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1599   GenCollectedHeap* gch = GenCollectedHeap::heap();
1600   unsigned int gc_count = gch->total_full_collections();
1601   if (gc_count == full_gc_count) {
1602     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1603     _full_gc_requested = true;
1604     CGC_lock->notify();   // nudge CMS thread
1605   }
1606 }
1607 
1608 
1609 // The foreground and background collectors need to coordinate in order
1610 // to make sure that they do not mutually interfere with CMS collections.
1611 // When a background collection is active,
1612 // the foreground collector may need to take over (preempt) and
1613 // synchronously complete an ongoing collection. Depending on the
1614 // frequency of the background collections and the heap usage
1615 // of the application, this preemption can be seldom or frequent.
1616 // There are only certain
1617 // points in the background collection that the "collection-baton"
1618 // can be passed to the foreground collector.
1619 //
1620 // The foreground collector will wait for the baton before
1621 // starting any part of the collection.  The foreground collector
1622 // will only wait at one location.
1623 //
1624 // The background collector will yield the baton before starting a new
1625 // phase of the collection (e.g., before initial marking, marking from roots,
1626 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1627 // of the loop which switches the phases. The background collector does some
1628 // of the phases (initial mark, final re-mark) with the world stopped.
1629 // Because of locking involved in stopping the world,
1630 // the foreground collector should not block waiting for the background
1631 // collector when it is doing a stop-the-world phase.  The background
1632 // collector will yield the baton at an additional point just before
1633 // it enters a stop-the-world phase.  Once the world is stopped, the
1634 // background collector checks the phase of the collection.  If the
1635 // phase has not changed, it proceeds with the collection.  If the
1636 // phase has changed, it skips that phase of the collection.  See
1637 // the comments on the use of the Heap_lock in collect_in_background().
1638 //
1639 // Variable used in baton passing.
1640 //   _foregroundGCIsActive - Set to true by the foreground collector when
1641 //      it wants the baton.  The foreground clears it when it has finished
1642 //      the collection.
1643 //   _foregroundGCShouldWait - Set to true by the background collector
1644 //        when it is running.  The foreground collector waits while
1645 //      _foregroundGCShouldWait is true.
1646 //  CGC_lock - monitor used to protect access to the above variables
1647 //      and to notify the foreground and background collectors.
1648 //  _collectorState - current state of the CMS collection.
1649 //
1650 // The foreground collector
1651 //   acquires the CGC_lock
1652 //   sets _foregroundGCIsActive
1653 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1654 //     various locks acquired in preparation for the collection
1655 //     are released so as not to block the background collector
1656 //     that is in the midst of a collection
1657 //   proceeds with the collection
1658 //   clears _foregroundGCIsActive
1659 //   returns
1660 //
1661 // The background collector in a loop iterating on the phases of the
1662 //      collection
1663 //   acquires the CGC_lock
1664 //   sets _foregroundGCShouldWait
1665 //   if _foregroundGCIsActive is set
1666 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1667 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1668 //     and exits the loop.
1669 //   otherwise
1670 //     proceed with that phase of the collection
1671 //     if the phase is a stop-the-world phase,
1672 //       yield the baton once more just before enqueueing
1673 //       the stop-world CMS operation (executed by the VM thread).
1674 //   returns after all phases of the collection are done
1675 //
1676 
1677 void CMSCollector::acquire_control_and_collect(bool full,
1678         bool clear_all_soft_refs) {
1679   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1680   assert(!Thread::current()->is_ConcurrentGC_thread(),
1681          "shouldn't try to acquire control from self!");
1682 
1683   // Start the protocol for acquiring control of the
1684   // collection from the background collector (aka CMS thread).
1685   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1686          "VM thread should have CMS token");
1687   // Remember the possibly interrupted state of an ongoing
1688   // concurrent collection
1689   CollectorState first_state = _collectorState;
1690 
1691   // Signal to a possibly ongoing concurrent collection that
1692   // we want to do a foreground collection.
1693   _foregroundGCIsActive = true;
1694 
1695   // Disable incremental mode during a foreground collection.
1696   ICMSDisabler icms_disabler;
1697 
1698   // release locks and wait for a notify from the background collector
1699   // releasing the locks in only necessary for phases which
1700   // do yields to improve the granularity of the collection.
1701   assert_lock_strong(bitMapLock());
1702   // We need to lock the Free list lock for the space that we are
1703   // currently collecting.
1704   assert(haveFreelistLocks(), "Must be holding free list locks");
1705   bitMapLock()->unlock();
1706   releaseFreelistLocks();
1707   {
1708     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1709     if (_foregroundGCShouldWait) {
1710       // We are going to be waiting for action for the CMS thread;
1711       // it had better not be gone (for instance at shutdown)!
1712       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1713              "CMS thread must be running");
1714       // Wait here until the background collector gives us the go-ahead
1715       ConcurrentMarkSweepThread::clear_CMS_flag(
1716         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1717       // Get a possibly blocked CMS thread going:
1718       //   Note that we set _foregroundGCIsActive true above,
1719       //   without protection of the CGC_lock.
1720       CGC_lock->notify();
1721       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1722              "Possible deadlock");
1723       while (_foregroundGCShouldWait) {
1724         // wait for notification
1725         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1726         // Possibility of delay/starvation here, since CMS token does
1727         // not know to give priority to VM thread? Actually, i think
1728         // there wouldn't be any delay/starvation, but the proof of
1729         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1730       }
1731       ConcurrentMarkSweepThread::set_CMS_flag(
1732         ConcurrentMarkSweepThread::CMS_vm_has_token);
1733     }
1734   }
1735   // The CMS_token is already held.  Get back the other locks.
1736   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1737          "VM thread should have CMS token");
1738   getFreelistLocks();
1739   bitMapLock()->lock_without_safepoint_check();
1740   if (TraceCMSState) {
1741     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1742       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1743     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1744   }
1745 
1746   // Check if we need to do a compaction, or if not, whether
1747   // we need to start the mark-sweep from scratch.
1748   bool should_compact    = false;
1749   bool should_start_over = false;
1750   decide_foreground_collection_type(clear_all_soft_refs,
1751     &should_compact, &should_start_over);
1752 
1753 NOT_PRODUCT(
1754   if (RotateCMSCollectionTypes) {
1755     if (_cmsGen->debug_collection_type() ==
1756         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1757       should_compact = true;
1758     } else if (_cmsGen->debug_collection_type() ==
1759                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1760       should_compact = false;
1761     }
1762   }
1763 )
1764 
1765   if (PrintGCDetails && first_state > Idling) {
1766     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1767     if (GCCause::is_user_requested_gc(cause) ||
1768         GCCause::is_serviceability_requested_gc(cause)) {
1769       gclog_or_tty->print(" (concurrent mode interrupted)");
1770     } else {
1771       gclog_or_tty->print(" (concurrent mode failure)");
1772     }
1773   }
1774 
1775   if (should_compact) {
1776     // If the collection is being acquired from the background
1777     // collector, there may be references on the discovered
1778     // references lists that have NULL referents (being those
1779     // that were concurrently cleared by a mutator) or
1780     // that are no longer active (having been enqueued concurrently
1781     // by the mutator).
1782     // Scrub the list of those references because Mark-Sweep-Compact
1783     // code assumes referents are not NULL and that all discovered
1784     // Reference objects are active.
1785     ref_processor()->clean_up_discovered_references();
1786 
1787     do_compaction_work(clear_all_soft_refs);
1788 
1789     // Has the GC time limit been exceeded?
1790     check_gc_time_limit();
1791 
1792   } else {
1793     do_mark_sweep_work(clear_all_soft_refs, first_state,
1794       should_start_over);
1795   }
1796   // Reset the expansion cause, now that we just completed
1797   // a collection cycle.
1798   clear_expansion_cause();
1799   _foregroundGCIsActive = false;
1800   return;
1801 }
1802 
1803 void CMSCollector::check_gc_time_limit() {
1804 
1805   // Ignore explicit GC's.  Exiting here does not set the flag and
1806   // does not reset the count.  Updating of the averages for system
1807   // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
1808   GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause();
1809   if (GCCause::is_user_requested_gc(gc_cause) ||
1810       GCCause::is_serviceability_requested_gc(gc_cause)) {
1811     return;
1812   }
1813 
1814   // Calculate the fraction of the CMS generation was freed during
1815   // the last collection.
1816   // Only consider the STW compacting cost for now.
1817   //
1818   // Note that the gc time limit test only works for the collections
1819   // of the young gen + tenured gen and not for collections of the
1820   // permanent gen.  That is because the calculation of the space
1821   // freed by the collection is the free space in the young gen +
1822   // tenured gen.
1823 
1824   double fraction_free =
1825     ((double)_cmsGen->free())/((double)_cmsGen->max_capacity());
1826   if ((100.0 * size_policy()->compacting_gc_cost()) >
1827          ((double) GCTimeLimit) &&
1828         ((fraction_free * 100) < GCHeapFreeLimit)) {
1829     size_policy()->inc_gc_time_limit_count();
1830     if (UseGCOverheadLimit &&
1831         (size_policy()->gc_time_limit_count() >
1832          AdaptiveSizePolicyGCTimeLimitThreshold)) {
1833       size_policy()->set_gc_time_limit_exceeded(true);
1834       // Avoid consecutive OOM due to the gc time limit by resetting
1835       // the counter.
1836       size_policy()->reset_gc_time_limit_count();
1837       if (PrintGCDetails) {
1838         gclog_or_tty->print_cr("      GC is exceeding overhead limit "
1839           "of %d%%", GCTimeLimit);
1840       }
1841     } else {
1842       if (PrintGCDetails) {
1843         gclog_or_tty->print_cr("      GC would exceed overhead limit "
1844           "of %d%%", GCTimeLimit);
1845       }
1846     }
1847   } else {
1848     size_policy()->reset_gc_time_limit_count();
1849   }
1850 }
1851 
1852 // Resize the perm generation and the tenured generation
1853 // after obtaining the free list locks for the
1854 // two generations.
1855 void CMSCollector::compute_new_size() {
1856   assert_locked_or_safepoint(Heap_lock);
1857   FreelistLocker z(this);
1858   _permGen->compute_new_size();
1859   _cmsGen->compute_new_size();
1860 }
1861 
1862 // A work method used by foreground collection to determine
1863 // what type of collection (compacting or not, continuing or fresh)
1864 // it should do.
1865 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1866 // and CMSCompactWhenClearAllSoftRefs the default in the future
1867 // and do away with the flags after a suitable period.
1868 void CMSCollector::decide_foreground_collection_type(
1869   bool clear_all_soft_refs, bool* should_compact,
1870   bool* should_start_over) {
1871   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1872   // flag is set, and we have either requested a System.gc() or
1873   // the number of full gc's since the last concurrent cycle
1874   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1875   // or if an incremental collection has failed
1876   GenCollectedHeap* gch = GenCollectedHeap::heap();
1877   assert(gch->collector_policy()->is_two_generation_policy(),
1878          "You may want to check the correctness of the following");
1879   // Inform cms gen if this was due to partial collection failing.
1880   // The CMS gen may use this fact to determine its expansion policy.
1881   if (gch->incremental_collection_will_fail()) {
1882     assert(!_cmsGen->incremental_collection_failed(),
1883            "Should have been noticed, reacted to and cleared");
1884     _cmsGen->set_incremental_collection_failed();
1885   }
1886   *should_compact =
1887     UseCMSCompactAtFullCollection &&
1888     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1889      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1890      gch->incremental_collection_will_fail());
1891   *should_start_over = false;
1892   if (clear_all_soft_refs && !*should_compact) {
1893     // We are about to do a last ditch collection attempt
1894     // so it would normally make sense to do a compaction
1895     // to reclaim as much space as possible.
1896     if (CMSCompactWhenClearAllSoftRefs) {
1897       // Default: The rationale is that in this case either
1898       // we are past the final marking phase, in which case
1899       // we'd have to start over, or so little has been done
1900       // that there's little point in saving that work. Compaction
1901       // appears to be the sensible choice in either case.
1902       *should_compact = true;
1903     } else {
1904       // We have been asked to clear all soft refs, but not to
1905       // compact. Make sure that we aren't past the final checkpoint
1906       // phase, for that is where we process soft refs. If we are already
1907       // past that phase, we'll need to redo the refs discovery phase and
1908       // if necessary clear soft refs that weren't previously
1909       // cleared. We do so by remembering the phase in which
1910       // we came in, and if we are past the refs processing
1911       // phase, we'll choose to just redo the mark-sweep
1912       // collection from scratch.
1913       if (_collectorState > FinalMarking) {
1914         // We are past the refs processing phase;
1915         // start over and do a fresh synchronous CMS cycle
1916         _collectorState = Resetting; // skip to reset to start new cycle
1917         reset(false /* == !asynch */);
1918         *should_start_over = true;
1919       } // else we can continue a possibly ongoing current cycle
1920     }
1921   }
1922 }
1923 
1924 // A work method used by the foreground collector to do
1925 // a mark-sweep-compact.
1926 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1927   GenCollectedHeap* gch = GenCollectedHeap::heap();
1928   TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1929   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1930     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1931       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1932   }
1933 
1934   // Sample collection interval time and reset for collection pause.
1935   if (UseAdaptiveSizePolicy) {
1936     size_policy()->msc_collection_begin();
1937   }
1938 
1939   // Temporarily widen the span of the weak reference processing to
1940   // the entire heap.
1941   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1942   ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1943 
1944   // Temporarily, clear the "is_alive_non_header" field of the
1945   // reference processor.
1946   ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1947 
1948   // Temporarily make reference _processing_ single threaded (non-MT).
1949   ReferenceProcessorMTProcMutator z(ref_processor(), false);
1950 
1951   // Temporarily make refs discovery atomic
1952   ReferenceProcessorAtomicMutator w(ref_processor(), true);
1953 
1954   ref_processor()->set_enqueuing_is_done(false);
1955   ref_processor()->enable_discovery();
1956   // If an asynchronous collection finishes, the _modUnionTable is
1957   // all clear.  If we are assuming the collection from an asynchronous
1958   // collection, clear the _modUnionTable.
1959   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1960     "_modUnionTable should be clear if the baton was not passed");
1961   _modUnionTable.clear_all();
1962 
1963   // We must adjust the allocation statistics being maintained
1964   // in the free list space. We do so by reading and clearing
1965   // the sweep timer and updating the block flux rate estimates below.
1966   assert(_sweep_timer.is_active(), "We should never see the timer inactive");
1967   _sweep_timer.stop();
1968   // Note that we do not use this sample to update the _sweep_estimate.
1969   _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
1970                                           _sweep_estimate.padded_average());
1971 
1972   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1973     ref_processor(), clear_all_soft_refs);
1974   #ifdef ASSERT
1975     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1976     size_t free_size = cms_space->free();
1977     assert(free_size ==
1978            pointer_delta(cms_space->end(), cms_space->compaction_top())
1979            * HeapWordSize,
1980       "All the free space should be compacted into one chunk at top");
1981     assert(cms_space->dictionary()->totalChunkSize(
1982                                       debug_only(cms_space->freelistLock())) == 0 ||
1983            cms_space->totalSizeInIndexedFreeLists() == 0,
1984       "All the free space should be in a single chunk");
1985     size_t num = cms_space->totalCount();
1986     assert((free_size == 0 && num == 0) ||
1987            (free_size > 0  && (num == 1 || num == 2)),
1988          "There should be at most 2 free chunks after compaction");
1989   #endif // ASSERT
1990   _collectorState = Resetting;
1991   assert(_restart_addr == NULL,
1992          "Should have been NULL'd before baton was passed");
1993   reset(false /* == !asynch */);
1994   _cmsGen->reset_after_compaction();
1995   _concurrent_cycles_since_last_unload = 0;
1996 
1997   if (verifying() && !should_unload_classes()) {
1998     perm_gen_verify_bit_map()->clear_all();
1999   }
2000 
2001   // Clear any data recorded in the PLAB chunk arrays.
2002   if (_survivor_plab_array != NULL) {
2003     reset_survivor_plab_arrays();
2004   }
2005 
2006   // Adjust the per-size allocation stats for the next epoch.
2007   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2008   // Restart the "sweep timer" for next epoch.
2009   _sweep_timer.reset();
2010   _sweep_timer.start();
2011 
2012   // Sample collection pause time and reset for collection interval.
2013   if (UseAdaptiveSizePolicy) {
2014     size_policy()->msc_collection_end(gch->gc_cause());
2015   }
2016 
2017   // For a mark-sweep-compact, compute_new_size() will be called
2018   // in the heap's do_collection() method.
2019 }
2020 
2021 // A work method used by the foreground collector to do
2022 // a mark-sweep, after taking over from a possibly on-going
2023 // concurrent mark-sweep collection.
2024 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2025   CollectorState first_state, bool should_start_over) {
2026   if (PrintGC && Verbose) {
2027     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2028       "collector with count %d",
2029       _full_gcs_since_conc_gc);
2030   }
2031   switch (_collectorState) {
2032     case Idling:
2033       if (first_state == Idling || should_start_over) {
2034         // The background GC was not active, or should
2035         // restarted from scratch;  start the cycle.
2036         _collectorState = InitialMarking;
2037       }
2038       // If first_state was not Idling, then a background GC
2039       // was in progress and has now finished.  No need to do it
2040       // again.  Leave the state as Idling.
2041       break;
2042     case Precleaning:
2043       // In the foreground case don't do the precleaning since
2044       // it is not done concurrently and there is extra work
2045       // required.
2046       _collectorState = FinalMarking;
2047   }
2048   if (PrintGCDetails &&
2049       (_collectorState > Idling ||
2050        !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2051     gclog_or_tty->print(" (concurrent mode failure)");
2052   }
2053   collect_in_foreground(clear_all_soft_refs);
2054 
2055   // For a mark-sweep, compute_new_size() will be called
2056   // in the heap's do_collection() method.
2057 }
2058 
2059 
2060 void CMSCollector::getFreelistLocks() const {
2061   // Get locks for all free lists in all generations that this
2062   // collector is responsible for
2063   _cmsGen->freelistLock()->lock_without_safepoint_check();
2064   _permGen->freelistLock()->lock_without_safepoint_check();
2065 }
2066 
2067 void CMSCollector::releaseFreelistLocks() const {
2068   // Release locks for all free lists in all generations that this
2069   // collector is responsible for
2070   _cmsGen->freelistLock()->unlock();
2071   _permGen->freelistLock()->unlock();
2072 }
2073 
2074 bool CMSCollector::haveFreelistLocks() const {
2075   // Check locks for all free lists in all generations that this
2076   // collector is responsible for
2077   assert_lock_strong(_cmsGen->freelistLock());
2078   assert_lock_strong(_permGen->freelistLock());
2079   PRODUCT_ONLY(ShouldNotReachHere());
2080   return true;
2081 }
2082 
2083 // A utility class that is used by the CMS collector to
2084 // temporarily "release" the foreground collector from its
2085 // usual obligation to wait for the background collector to
2086 // complete an ongoing phase before proceeding.
2087 class ReleaseForegroundGC: public StackObj {
2088  private:
2089   CMSCollector* _c;
2090  public:
2091   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2092     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2093     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2094     // allow a potentially blocked foreground collector to proceed
2095     _c->_foregroundGCShouldWait = false;
2096     if (_c->_foregroundGCIsActive) {
2097       CGC_lock->notify();
2098     }
2099     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2100            "Possible deadlock");
2101   }
2102 
2103   ~ReleaseForegroundGC() {
2104     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2105     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2106     _c->_foregroundGCShouldWait = true;
2107   }
2108 };
2109 
2110 // There are separate collect_in_background and collect_in_foreground because of
2111 // the different locking requirements of the background collector and the
2112 // foreground collector.  There was originally an attempt to share
2113 // one "collect" method between the background collector and the foreground
2114 // collector but the if-then-else required made it cleaner to have
2115 // separate methods.
2116 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2117   assert(Thread::current()->is_ConcurrentGC_thread(),
2118     "A CMS asynchronous collection is only allowed on a CMS thread.");
2119 
2120   GenCollectedHeap* gch = GenCollectedHeap::heap();
2121   {
2122     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2123     MutexLockerEx hl(Heap_lock, safepoint_check);
2124     FreelistLocker fll(this);
2125     MutexLockerEx x(CGC_lock, safepoint_check);
2126     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2127       // The foreground collector is active or we're
2128       // not using asynchronous collections.  Skip this
2129       // background collection.
2130       assert(!_foregroundGCShouldWait, "Should be clear");
2131       return;
2132     } else {
2133       assert(_collectorState == Idling, "Should be idling before start.");
2134       _collectorState = InitialMarking;
2135       // Reset the expansion cause, now that we are about to begin
2136       // a new cycle.
2137       clear_expansion_cause();
2138     }
2139     // Decide if we want to enable class unloading as part of the
2140     // ensuing concurrent GC cycle.
2141     update_should_unload_classes(); 
2142     _full_gc_requested = false;           // acks all outstanding full gc requests
2143     // Signal that we are about to start a collection
2144     gch->increment_total_full_collections();  // ... starting a collection cycle
2145     _collection_count_start = gch->total_full_collections();
2146   }
2147 
2148   // Used for PrintGC
2149   size_t prev_used;
2150   if (PrintGC && Verbose) {
2151     prev_used = _cmsGen->used(); // XXXPERM
2152   }
2153 
2154   // The change of the collection state is normally done at this level;
2155   // the exceptions are phases that are executed while the world is
2156   // stopped.  For those phases the change of state is done while the
2157   // world is stopped.  For baton passing purposes this allows the
2158   // background collector to finish the phase and change state atomically.
2159   // The foreground collector cannot wait on a phase that is done
2160   // while the world is stopped because the foreground collector already
2161   // has the world stopped and would deadlock.
2162   while (_collectorState != Idling) {
2163     if (TraceCMSState) {
2164       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2165         Thread::current(), _collectorState);
2166     }
2167     // The foreground collector
2168     //   holds the Heap_lock throughout its collection.
2169     //   holds the CMS token (but not the lock)
2170     //     except while it is waiting for the background collector to yield.
2171     //
2172     // The foreground collector should be blocked (not for long)
2173     //   if the background collector is about to start a phase
2174     //   executed with world stopped.  If the background
2175     //   collector has already started such a phase, the
2176     //   foreground collector is blocked waiting for the
2177     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2178     //   are executed in the VM thread.
2179     //
2180     // The locking order is
2181     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2182     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2183     //   CMS token  (claimed in
2184     //                stop_world_and_do() -->
2185     //                  safepoint_synchronize() -->
2186     //                    CMSThread::synchronize())
2187 
2188     {
2189       // Check if the FG collector wants us to yield.
2190       CMSTokenSync x(true); // is cms thread
2191       if (waitForForegroundGC()) {
2192         // We yielded to a foreground GC, nothing more to be
2193         // done this round.
2194         assert(_foregroundGCShouldWait == false, "We set it to false in "
2195                "waitForForegroundGC()");
2196         if (TraceCMSState) {
2197           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2198             " exiting collection CMS state %d",
2199             Thread::current(), _collectorState);
2200         }
2201         return;
2202       } else {
2203         // The background collector can run but check to see if the
2204         // foreground collector has done a collection while the
2205         // background collector was waiting to get the CGC_lock
2206         // above.  If yes, break so that _foregroundGCShouldWait
2207         // is cleared before returning.
2208         if (_collectorState == Idling) {
2209           break;
2210         }
2211       }
2212     }
2213 
2214     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2215       "should be waiting");
2216 
2217     switch (_collectorState) {
2218       case InitialMarking:
2219         {
2220           ReleaseForegroundGC x(this);
2221           stats().record_cms_begin();
2222 
2223           VM_CMS_Initial_Mark initial_mark_op(this);
2224           VMThread::execute(&initial_mark_op);
2225         }
2226         // The collector state may be any legal state at this point
2227         // since the background collector may have yielded to the
2228         // foreground collector.
2229         break;
2230       case Marking:
2231         // initial marking in checkpointRootsInitialWork has been completed
2232         if (markFromRoots(true)) { // we were successful
2233           assert(_collectorState == Precleaning, "Collector state should "
2234             "have changed");
2235         } else {
2236           assert(_foregroundGCIsActive, "Internal state inconsistency");
2237         }
2238         break;
2239       case Precleaning:
2240         if (UseAdaptiveSizePolicy) {
2241           size_policy()->concurrent_precleaning_begin();
2242         }
2243         // marking from roots in markFromRoots has been completed
2244         preclean();
2245         if (UseAdaptiveSizePolicy) {
2246           size_policy()->concurrent_precleaning_end();
2247         }
2248         assert(_collectorState == AbortablePreclean ||
2249                _collectorState == FinalMarking,
2250                "Collector state should have changed");
2251         break;
2252       case AbortablePreclean:
2253         if (UseAdaptiveSizePolicy) {
2254         size_policy()->concurrent_phases_resume();
2255         }
2256         abortable_preclean();
2257         if (UseAdaptiveSizePolicy) {
2258           size_policy()->concurrent_precleaning_end();
2259         }
2260         assert(_collectorState == FinalMarking, "Collector state should "
2261           "have changed");
2262         break;
2263       case FinalMarking:
2264         {
2265           ReleaseForegroundGC x(this);
2266 
2267           VM_CMS_Final_Remark final_remark_op(this);
2268           VMThread::execute(&final_remark_op);
2269           }
2270         assert(_foregroundGCShouldWait, "block post-condition");
2271         break;
2272       case Sweeping:
2273         if (UseAdaptiveSizePolicy) {
2274           size_policy()->concurrent_sweeping_begin();
2275         }
2276         // final marking in checkpointRootsFinal has been completed
2277         sweep(true);
2278         assert(_collectorState == Resizing, "Collector state change "
2279           "to Resizing must be done under the free_list_lock");
2280         _full_gcs_since_conc_gc = 0;
2281 
2282         // Stop the timers for adaptive size policy for the concurrent phases
2283         if (UseAdaptiveSizePolicy) {
2284           size_policy()->concurrent_sweeping_end();
2285           size_policy()->concurrent_phases_end(gch->gc_cause(),
2286                                              gch->prev_gen(_cmsGen)->capacity(),
2287                                              _cmsGen->free());
2288         }
2289 
2290       case Resizing: {
2291         // Sweeping has been completed...
2292         // At this point the background collection has completed.
2293         // Don't move the call to compute_new_size() down
2294         // into code that might be executed if the background
2295         // collection was preempted.
2296         {
2297           ReleaseForegroundGC x(this);   // unblock FG collection
2298           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2299           CMSTokenSync        z(true);   // not strictly needed.
2300           if (_collectorState == Resizing) {
2301             compute_new_size();
2302             _collectorState = Resetting;
2303           } else {
2304             assert(_collectorState == Idling, "The state should only change"
2305                    " because the foreground collector has finished the collection");
2306           }
2307         }
2308         break;
2309       }
2310       case Resetting:
2311         // CMS heap resizing has been completed
2312         reset(true);
2313         assert(_collectorState == Idling, "Collector state should "
2314           "have changed");
2315         stats().record_cms_end();
2316         // Don't move the concurrent_phases_end() and compute_new_size()
2317         // calls to here because a preempted background collection
2318         // has it's state set to "Resetting".
2319         break;
2320       case Idling:
2321       default:
2322         ShouldNotReachHere();
2323         break;
2324     }
2325     if (TraceCMSState) {
2326       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2327         Thread::current(), _collectorState);
2328     }
2329     assert(_foregroundGCShouldWait, "block post-condition");
2330   }
2331 
2332   // Should this be in gc_epilogue?
2333   collector_policy()->counters()->update_counters();
2334 
2335   {
2336     // Clear _foregroundGCShouldWait and, in the event that the
2337     // foreground collector is waiting, notify it, before
2338     // returning.
2339     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2340     _foregroundGCShouldWait = false;
2341     if (_foregroundGCIsActive) {
2342       CGC_lock->notify();
2343     }
2344     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2345            "Possible deadlock");
2346   }
2347   if (TraceCMSState) {
2348     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2349       " exiting collection CMS state %d",
2350       Thread::current(), _collectorState);
2351   }
2352   if (PrintGC && Verbose) {
2353     _cmsGen->print_heap_change(prev_used);
2354   }
2355 }
2356 
2357 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2358   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2359          "Foreground collector should be waiting, not executing");
2360   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2361     "may only be done by the VM Thread with the world stopped");
2362   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2363          "VM thread should have CMS token");
2364 
2365   NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2366     true, gclog_or_tty);)
2367   if (UseAdaptiveSizePolicy) {
2368     size_policy()->ms_collection_begin();
2369   }
2370   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2371 
2372   HandleMark hm;  // Discard invalid handles created during verification
2373 
2374   if (VerifyBeforeGC &&
2375       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2376     Universe::verify(true);
2377   }
2378 
2379   bool init_mark_was_synchronous = false; // until proven otherwise
2380   while (_collectorState != Idling) {
2381     if (TraceCMSState) {
2382       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2383         Thread::current(), _collectorState);
2384     }
2385     switch (_collectorState) {
2386       case InitialMarking:
2387         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2388         checkpointRootsInitial(false);
2389         assert(_collectorState == Marking, "Collector state should have changed"
2390           " within checkpointRootsInitial()");
2391         break;
2392       case Marking:
2393         // initial marking in checkpointRootsInitialWork has been completed
2394         if (VerifyDuringGC &&
2395             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2396           gclog_or_tty->print("Verify before initial mark: ");
2397           Universe::verify(true);
2398         }
2399         {
2400           bool res = markFromRoots(false);
2401           assert(res && _collectorState == FinalMarking, "Collector state should "
2402             "have changed");
2403           break;
2404         }
2405       case FinalMarking:
2406         if (VerifyDuringGC &&
2407             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2408           gclog_or_tty->print("Verify before re-mark: ");
2409           Universe::verify(true);
2410         }
2411         checkpointRootsFinal(false, clear_all_soft_refs,
2412                              init_mark_was_synchronous);
2413         assert(_collectorState == Sweeping, "Collector state should not "
2414           "have changed within checkpointRootsFinal()");
2415         break;
2416       case Sweeping:
2417         // final marking in checkpointRootsFinal has been completed
2418         if (VerifyDuringGC &&
2419             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2420           gclog_or_tty->print("Verify before sweep: ");
2421           Universe::verify(true);
2422         }
2423         sweep(false);
2424         assert(_collectorState == Resizing, "Incorrect state");
2425         break;
2426       case Resizing: {
2427         // Sweeping has been completed; the actual resize in this case
2428         // is done separately; nothing to be done in this state.
2429         _collectorState = Resetting;
2430         break;
2431       }
2432       case Resetting:
2433         // The heap has been resized.
2434         if (VerifyDuringGC &&
2435             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2436           gclog_or_tty->print("Verify before reset: ");
2437           Universe::verify(true);
2438         }
2439         reset(false);
2440         assert(_collectorState == Idling, "Collector state should "
2441           "have changed");
2442         break;
2443       case Precleaning:
2444       case AbortablePreclean:
2445         // Elide the preclean phase
2446         _collectorState = FinalMarking;
2447         break;
2448       default:
2449         ShouldNotReachHere();
2450     }
2451     if (TraceCMSState) {
2452       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2453         Thread::current(), _collectorState);
2454     }
2455   }
2456 
2457   if (UseAdaptiveSizePolicy) {
2458     GenCollectedHeap* gch = GenCollectedHeap::heap();
2459     size_policy()->ms_collection_end(gch->gc_cause());
2460   }
2461 
2462   if (VerifyAfterGC &&
2463       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2464     Universe::verify(true);
2465   }
2466   if (TraceCMSState) {
2467     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2468       " exiting collection CMS state %d",
2469       Thread::current(), _collectorState);
2470   }
2471 }
2472 
2473 bool CMSCollector::waitForForegroundGC() {
2474   bool res = false;
2475   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2476          "CMS thread should have CMS token");
2477   // Block the foreground collector until the
2478   // background collectors decides whether to
2479   // yield.
2480   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2481   _foregroundGCShouldWait = true;
2482   if (_foregroundGCIsActive) {
2483     // The background collector yields to the
2484     // foreground collector and returns a value
2485     // indicating that it has yielded.  The foreground
2486     // collector can proceed.
2487     res = true;
2488     _foregroundGCShouldWait = false;
2489     ConcurrentMarkSweepThread::clear_CMS_flag(
2490       ConcurrentMarkSweepThread::CMS_cms_has_token);
2491     ConcurrentMarkSweepThread::set_CMS_flag(
2492       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2493     // Get a possibly blocked foreground thread going
2494     CGC_lock->notify();
2495     if (TraceCMSState) {
2496       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2497         Thread::current(), _collectorState);
2498     }
2499     while (_foregroundGCIsActive) {
2500       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2501     }
2502     ConcurrentMarkSweepThread::set_CMS_flag(
2503       ConcurrentMarkSweepThread::CMS_cms_has_token);
2504     ConcurrentMarkSweepThread::clear_CMS_flag(
2505       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2506   }
2507   if (TraceCMSState) {
2508     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2509       Thread::current(), _collectorState);
2510   }
2511   return res;
2512 }
2513 
2514 // Because of the need to lock the free lists and other structures in
2515 // the collector, common to all the generations that the collector is
2516 // collecting, we need the gc_prologues of individual CMS generations
2517 // delegate to their collector. It may have been simpler had the
2518 // current infrastructure allowed one to call a prologue on a
2519 // collector. In the absence of that we have the generation's
2520 // prologue delegate to the collector, which delegates back
2521 // some "local" work to a worker method in the individual generations
2522 // that it's responsible for collecting, while itself doing any
2523 // work common to all generations it's responsible for. A similar
2524 // comment applies to the  gc_epilogue()'s.
2525 // The role of the varaible _between_prologue_and_epilogue is to
2526 // enforce the invocation protocol.
2527 void CMSCollector::gc_prologue(bool full) {
2528   // Call gc_prologue_work() for each CMSGen and PermGen that
2529   // we are responsible for.
2530 
2531   // The following locking discipline assumes that we are only called
2532   // when the world is stopped.
2533   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2534 
2535   // The CMSCollector prologue must call the gc_prologues for the
2536   // "generations" (including PermGen if any) that it's responsible
2537   // for.
2538 
2539   assert(   Thread::current()->is_VM_thread()
2540          || (   CMSScavengeBeforeRemark
2541              && Thread::current()->is_ConcurrentGC_thread()),
2542          "Incorrect thread type for prologue execution");
2543 
2544   if (_between_prologue_and_epilogue) {
2545     // We have already been invoked; this is a gc_prologue delegation
2546     // from yet another CMS generation that we are responsible for, just
2547     // ignore it since all relevant work has already been done.
2548     return;
2549   }
2550 
2551   // set a bit saying prologue has been called; cleared in epilogue
2552   _between_prologue_and_epilogue = true;
2553   // Claim locks for common data structures, then call gc_prologue_work()
2554   // for each CMSGen and PermGen that we are responsible for.
2555 
2556   getFreelistLocks();   // gets free list locks on constituent spaces
2557   bitMapLock()->lock_without_safepoint_check();
2558 
2559   // Should call gc_prologue_work() for all cms gens we are responsible for
2560   bool registerClosure =    _collectorState >= Marking
2561                          && _collectorState < Sweeping;
2562   ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2563                                                : &_modUnionClosure;
2564   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2565   _permGen->gc_prologue_work(full, registerClosure, muc);
2566 
2567   if (!full) {
2568     stats().record_gc0_begin();
2569   }
2570 }
2571 
2572 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2573   // Delegate to CMScollector which knows how to coordinate between
2574   // this and any other CMS generations that it is responsible for
2575   // collecting.
2576   collector()->gc_prologue(full);
2577 }
2578 
2579 // This is a "private" interface for use by this generation's CMSCollector.
2580 // Not to be called directly by any other entity (for instance,
2581 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2582 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2583   bool registerClosure, ModUnionClosure* modUnionClosure) {
2584   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2585   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2586     "Should be NULL");
2587   if (registerClosure) {
2588     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2589   }
2590   cmsSpace()->gc_prologue();
2591   // Clear stat counters
2592   NOT_PRODUCT(
2593     assert(_numObjectsPromoted == 0, "check");
2594     assert(_numWordsPromoted   == 0, "check");
2595     if (Verbose && PrintGC) {
2596       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2597                           SIZE_FORMAT" bytes concurrently",
2598       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2599     }
2600     _numObjectsAllocated = 0;
2601     _numWordsAllocated   = 0;
2602   )
2603 }
2604 
2605 void CMSCollector::gc_epilogue(bool full) {
2606   // The following locking discipline assumes that we are only called
2607   // when the world is stopped.
2608   assert(SafepointSynchronize::is_at_safepoint(),
2609          "world is stopped assumption");
2610 
2611   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2612   // if linear allocation blocks need to be appropriately marked to allow the
2613   // the blocks to be parsable. We also check here whether we need to nudge the
2614   // CMS collector thread to start a new cycle (if it's not already active).
2615   assert(   Thread::current()->is_VM_thread()
2616          || (   CMSScavengeBeforeRemark
2617              && Thread::current()->is_ConcurrentGC_thread()),
2618          "Incorrect thread type for epilogue execution");
2619 
2620   if (!_between_prologue_and_epilogue) {
2621     // We have already been invoked; this is a gc_epilogue delegation
2622     // from yet another CMS generation that we are responsible for, just
2623     // ignore it since all relevant work has already been done.
2624     return;
2625   }
2626   assert(haveFreelistLocks(), "must have freelist locks");
2627   assert_lock_strong(bitMapLock());
2628 
2629   _cmsGen->gc_epilogue_work(full);
2630   _permGen->gc_epilogue_work(full);
2631 
2632   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2633     // in case sampling was not already enabled, enable it
2634     _start_sampling = true;
2635   }
2636   // reset _eden_chunk_array so sampling starts afresh
2637   _eden_chunk_index = 0;
2638 
2639   size_t cms_used   = _cmsGen->cmsSpace()->used();
2640   size_t perm_used  = _permGen->cmsSpace()->used();
2641 
2642   // update performance counters - this uses a special version of
2643   // update_counters() that allows the utilization to be passed as a
2644   // parameter, avoiding multiple calls to used().
2645   //
2646   _cmsGen->update_counters(cms_used);
2647   _permGen->update_counters(perm_used);
2648 
2649   if (CMSIncrementalMode) {
2650     icms_update_allocation_limits();
2651   }
2652 
2653   bitMapLock()->unlock();
2654   releaseFreelistLocks();
2655 
2656   _between_prologue_and_epilogue = false;  // ready for next cycle
2657 }
2658 
2659 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2660   collector()->gc_epilogue(full);
2661 
2662   // Also reset promotion tracking in par gc thread states.
2663   if (ParallelGCThreads > 0) {
2664     for (uint i = 0; i < ParallelGCThreads; i++) {
2665       _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2666     }
2667   }
2668 }
2669 
2670 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2671   assert(!incremental_collection_failed(), "Should have been cleared");
2672   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2673   cmsSpace()->gc_epilogue();
2674     // Print stat counters
2675   NOT_PRODUCT(
2676     assert(_numObjectsAllocated == 0, "check");
2677     assert(_numWordsAllocated == 0, "check");
2678     if (Verbose && PrintGC) {
2679       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2680                           SIZE_FORMAT" bytes",
2681                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2682     }
2683     _numObjectsPromoted = 0;
2684     _numWordsPromoted   = 0;
2685   )
2686 
2687   if (PrintGC && Verbose) {
2688     // Call down the chain in contiguous_available needs the freelistLock
2689     // so print this out before releasing the freeListLock.
2690     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2691                         contiguous_available());
2692   }
2693 }
2694 
2695 #ifndef PRODUCT
2696 bool CMSCollector::have_cms_token() {
2697   Thread* thr = Thread::current();
2698   if (thr->is_VM_thread()) {
2699     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2700   } else if (thr->is_ConcurrentGC_thread()) {
2701     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2702   } else if (thr->is_GC_task_thread()) {
2703     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2704            ParGCRareEvent_lock->owned_by_self();
2705   }
2706   return false;
2707 }
2708 #endif
2709 
2710 // Check reachability of the given heap address in CMS generation,
2711 // treating all other generations as roots.
2712 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2713   // We could "guarantee" below, rather than assert, but i'll
2714   // leave these as "asserts" so that an adventurous debugger
2715   // could try this in the product build provided some subset of
2716   // the conditions were met, provided they were intersted in the
2717   // results and knew that the computation below wouldn't interfere
2718   // with other concurrent computations mutating the structures
2719   // being read or written.
2720   assert(SafepointSynchronize::is_at_safepoint(),
2721          "Else mutations in object graph will make answer suspect");
2722   assert(have_cms_token(), "Should hold cms token");
2723   assert(haveFreelistLocks(), "must hold free list locks");
2724   assert_lock_strong(bitMapLock());
2725 
2726   // Clear the marking bit map array before starting, but, just
2727   // for kicks, first report if the given address is already marked
2728   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2729                 _markBitMap.isMarked(addr) ? "" : " not");
2730 
2731   if (verify_after_remark()) {
2732     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2733     bool result = verification_mark_bm()->isMarked(addr);
2734     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2735                            result ? "IS" : "is NOT");
2736     return result;
2737   } else {
2738     gclog_or_tty->print_cr("Could not compute result");
2739     return false;
2740   }
2741 }
2742 
2743 ////////////////////////////////////////////////////////
2744 // CMS Verification Support
2745 ////////////////////////////////////////////////////////
2746 // Following the remark phase, the following invariant
2747 // should hold -- each object in the CMS heap which is
2748 // marked in markBitMap() should be marked in the verification_mark_bm().
2749 
2750 class VerifyMarkedClosure: public BitMapClosure {
2751   CMSBitMap* _marks;
2752   bool       _failed;
2753 
2754  public:
2755   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2756 
2757   void do_bit(size_t offset) {
2758     HeapWord* addr = _marks->offsetToHeapWord(offset);
2759     if (!_marks->isMarked(addr)) {
2760       oop(addr)->print();
2761       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2762       _failed = true;
2763     }
2764   }
2765 
2766   bool failed() { return _failed; }
2767 };
2768 
2769 bool CMSCollector::verify_after_remark() {
2770   gclog_or_tty->print(" [Verifying CMS Marking... ");
2771   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2772   static bool init = false;
2773 
2774   assert(SafepointSynchronize::is_at_safepoint(),
2775          "Else mutations in object graph will make answer suspect");
2776   assert(have_cms_token(),
2777          "Else there may be mutual interference in use of "
2778          " verification data structures");
2779   assert(_collectorState > Marking && _collectorState <= Sweeping,
2780          "Else marking info checked here may be obsolete");
2781   assert(haveFreelistLocks(), "must hold free list locks");
2782   assert_lock_strong(bitMapLock());
2783 
2784 
2785   // Allocate marking bit map if not already allocated
2786   if (!init) { // first time
2787     if (!verification_mark_bm()->allocate(_span)) {
2788       return false;
2789     }
2790     init = true;
2791   }
2792 
2793   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2794 
2795   // Turn off refs discovery -- so we will be tracing through refs.
2796   // This is as intended, because by this time
2797   // GC must already have cleared any refs that need to be cleared,
2798   // and traced those that need to be marked; moreover,
2799   // the marking done here is not going to intefere in any
2800   // way with the marking information used by GC.
2801   NoRefDiscovery no_discovery(ref_processor());
2802 
2803   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2804 
2805   // Clear any marks from a previous round
2806   verification_mark_bm()->clear_all();
2807   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2808   assert(overflow_list_is_empty(), "overflow list should be empty");
2809 
2810   GenCollectedHeap* gch = GenCollectedHeap::heap();
2811   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2812   // Update the saved marks which may affect the root scans.
2813   gch->save_marks();
2814 
2815   if (CMSRemarkVerifyVariant == 1) {
2816     // In this first variant of verification, we complete
2817     // all marking, then check if the new marks-verctor is
2818     // a subset of the CMS marks-vector.
2819     verify_after_remark_work_1();
2820   } else if (CMSRemarkVerifyVariant == 2) {
2821     // In this second variant of verification, we flag an error
2822     // (i.e. an object reachable in the new marks-vector not reachable
2823     // in the CMS marks-vector) immediately, also indicating the
2824     // identify of an object (A) that references the unmarked object (B) --
2825     // presumably, a mutation to A failed to be picked up by preclean/remark?
2826     verify_after_remark_work_2();
2827   } else {
2828     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2829             CMSRemarkVerifyVariant);
2830   }
2831   gclog_or_tty->print(" done] ");
2832   return true;
2833 }
2834 
2835 void CMSCollector::verify_after_remark_work_1() {
2836   ResourceMark rm;
2837   HandleMark  hm;
2838   GenCollectedHeap* gch = GenCollectedHeap::heap();
2839 
2840   // Mark from roots one level into CMS
2841   MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */);
2842   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2843 
2844   gch->gen_process_strong_roots(_cmsGen->level(),
2845                                 true,   // younger gens are roots
2846                                 true,   // collecting perm gen
2847                                 SharedHeap::ScanningOption(roots_scanning_options()),
2848                                 NULL, &notOlder);
2849 
2850   // Now mark from the roots
2851   assert(_revisitStack.isEmpty(), "Should be empty");
2852   MarkFromRootsClosure markFromRootsClosure(this, _span,
2853     verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2854     false /* don't yield */, true /* verifying */);
2855   assert(_restart_addr == NULL, "Expected pre-condition");
2856   verification_mark_bm()->iterate(&markFromRootsClosure);
2857   while (_restart_addr != NULL) {
2858     // Deal with stack overflow: by restarting at the indicated
2859     // address.
2860     HeapWord* ra = _restart_addr;
2861     markFromRootsClosure.reset(ra);
2862     _restart_addr = NULL;
2863     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2864   }
2865   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2866   verify_work_stacks_empty();
2867   // Should reset the revisit stack above, since no class tree
2868   // surgery is forthcoming.
2869   _revisitStack.reset(); // throwing away all contents
2870 
2871   // Marking completed -- now verify that each bit marked in
2872   // verification_mark_bm() is also marked in markBitMap(); flag all
2873   // errors by printing corresponding objects.
2874   VerifyMarkedClosure vcl(markBitMap());
2875   verification_mark_bm()->iterate(&vcl);
2876   if (vcl.failed()) {
2877     gclog_or_tty->print("Verification failed");
2878     Universe::heap()->print();
2879     fatal(" ... aborting");
2880   }
2881 }
2882 
2883 void CMSCollector::verify_after_remark_work_2() {
2884   ResourceMark rm;
2885   HandleMark  hm;
2886   GenCollectedHeap* gch = GenCollectedHeap::heap();
2887 
2888   // Mark from roots one level into CMS
2889   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2890                                      markBitMap(), true /* nmethods */);
2891   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2892   gch->gen_process_strong_roots(_cmsGen->level(),
2893                                 true,   // younger gens are roots
2894                                 true,   // collecting perm gen
2895                                 SharedHeap::ScanningOption(roots_scanning_options()),
2896                                 NULL, &notOlder);
2897 
2898   // Now mark from the roots
2899   assert(_revisitStack.isEmpty(), "Should be empty");
2900   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2901     verification_mark_bm(), markBitMap(), verification_mark_stack());
2902   assert(_restart_addr == NULL, "Expected pre-condition");
2903   verification_mark_bm()->iterate(&markFromRootsClosure);
2904   while (_restart_addr != NULL) {
2905     // Deal with stack overflow: by restarting at the indicated
2906     // address.
2907     HeapWord* ra = _restart_addr;
2908     markFromRootsClosure.reset(ra);
2909     _restart_addr = NULL;
2910     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2911   }
2912   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2913   verify_work_stacks_empty();
2914   // Should reset the revisit stack above, since no class tree
2915   // surgery is forthcoming.
2916   _revisitStack.reset(); // throwing away all contents
2917 
2918   // Marking completed -- now verify that each bit marked in
2919   // verification_mark_bm() is also marked in markBitMap(); flag all
2920   // errors by printing corresponding objects.
2921   VerifyMarkedClosure vcl(markBitMap());
2922   verification_mark_bm()->iterate(&vcl);
2923   assert(!vcl.failed(), "Else verification above should not have succeeded");
2924 }
2925 
2926 void ConcurrentMarkSweepGeneration::save_marks() {
2927   // delegate to CMS space
2928   cmsSpace()->save_marks();
2929   for (uint i = 0; i < ParallelGCThreads; i++) {
2930     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2931   }
2932 }
2933 
2934 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2935   return cmsSpace()->no_allocs_since_save_marks();
2936 }
2937 
2938 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2939                                                                 \
2940 void ConcurrentMarkSweepGeneration::                            \
2941 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2942   cl->set_generation(this);                                     \
2943   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2944   cl->reset_generation();                                       \
2945   save_marks();                                                 \
2946 }
2947 
2948 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2949 
2950 void
2951 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2952 {
2953   // Not currently implemented; need to do the following. -- ysr.
2954   // dld -- I think that is used for some sort of allocation profiler.  So it
2955   // really means the objects allocated by the mutator since the last
2956   // GC.  We could potentially implement this cheaply by recording only
2957   // the direct allocations in a side data structure.
2958   //
2959   // I think we probably ought not to be required to support these
2960   // iterations at any arbitrary point; I think there ought to be some
2961   // call to enable/disable allocation profiling in a generation/space,
2962   // and the iterator ought to return the objects allocated in the
2963   // gen/space since the enable call, or the last iterator call (which
2964   // will probably be at a GC.)  That way, for gens like CM&S that would
2965   // require some extra data structure to support this, we only pay the
2966   // cost when it's in use...
2967   cmsSpace()->object_iterate_since_last_GC(blk);
2968 }
2969 
2970 void
2971 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2972   cl->set_generation(this);
2973   younger_refs_in_space_iterate(_cmsSpace, cl);
2974   cl->reset_generation();
2975 }
2976 
2977 void
2978 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2979   if (freelistLock()->owned_by_self()) {
2980     Generation::oop_iterate(mr, cl);
2981   } else {
2982     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2983     Generation::oop_iterate(mr, cl);
2984   }
2985 }
2986 
2987 void
2988 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
2989   if (freelistLock()->owned_by_self()) {
2990     Generation::oop_iterate(cl);
2991   } else {
2992     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2993     Generation::oop_iterate(cl);
2994   }
2995 }
2996 
2997 void
2998 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2999   if (freelistLock()->owned_by_self()) {
3000     Generation::object_iterate(cl);
3001   } else {
3002     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3003     Generation::object_iterate(cl);
3004   }
3005 }
3006 
3007 void
3008 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3009 }
3010 
3011 void
3012 ConcurrentMarkSweepGeneration::post_compact() {
3013 }
3014 
3015 void
3016 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3017   // Fix the linear allocation blocks to look like free blocks.
3018 
3019   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3020   // are not called when the heap is verified during universe initialization and
3021   // at vm shutdown.
3022   if (freelistLock()->owned_by_self()) {
3023     cmsSpace()->prepare_for_verify();
3024   } else {
3025     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3026     cmsSpace()->prepare_for_verify();
3027   }
3028 }
3029 
3030 void
3031 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3032   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3033   // are not called when the heap is verified during universe initialization and
3034   // at vm shutdown.
3035   if (freelistLock()->owned_by_self()) {
3036     cmsSpace()->verify(false /* ignored */);
3037   } else {
3038     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3039     cmsSpace()->verify(false /* ignored */);
3040   }
3041 }
3042 
3043 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3044   _cmsGen->verify(allow_dirty);
3045   _permGen->verify(allow_dirty);
3046 }
3047 
3048 #ifndef PRODUCT
3049 bool CMSCollector::overflow_list_is_empty() const {
3050   assert(_num_par_pushes >= 0, "Inconsistency");
3051   if (_overflow_list == NULL) {
3052     assert(_num_par_pushes == 0, "Inconsistency");
3053   }
3054   return _overflow_list == NULL;
3055 }
3056 
3057 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3058 // merely consolidate assertion checks that appear to occur together frequently.
3059 void CMSCollector::verify_work_stacks_empty() const {
3060   assert(_markStack.isEmpty(), "Marking stack should be empty");
3061   assert(overflow_list_is_empty(), "Overflow list should be empty");
3062 }
3063 
3064 void CMSCollector::verify_overflow_empty() const {
3065   assert(overflow_list_is_empty(), "Overflow list should be empty");
3066   assert(no_preserved_marks(), "No preserved marks");
3067 }
3068 #endif // PRODUCT
3069 
3070 // Decide if we want to enable class unloading as part of the
3071 // ensuing concurrent GC cycle. We will collect the perm gen and
3072 // unload classes if it's the case that:
3073 // (1) an explicit gc request has been made and the flag
3074 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3075 // (2) (a) class unloading is enabled at the command line, and
3076 //     (b) (i)   perm gen threshold has been crossed, or  
3077 //         (ii)  old gen is getting really full, or
3078 //         (iii) the previous N CMS collections did not collect the
3079 //               perm gen
3080 // NOTE: Provided there is no change in the state of the heap between
3081 // calls to this method, it should have idempotent results. Moreover,
3082 // its results should be monotonically increasing (i.e. going from 0 to 1,
3083 // but not 1 to 0) between successive calls between which the heap was
3084 // not collected. For the implementation below, it must thus rely on
3085 // the property that concurrent_cycles_since_last_unload()
3086 // will not decrease unless a collection cycle happened and that
3087 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3088 // themselves also monotonic in that sense. See check_monotonicity()
3089 // below.
3090 bool CMSCollector::update_should_unload_classes() {
3091   // Condition 1 above
3092   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3093     _should_unload_classes = true;
3094   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3095     // Disjuncts 2.b.(i,ii,iii) above
3096     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3097                               CMSClassUnloadingMaxInterval)
3098                            || _permGen->should_concurrent_collect()
3099                            || _cmsGen->is_too_full();
3100   }
3101   return _should_unload_classes;
3102 }
3103 
3104 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3105   bool res = should_concurrent_collect();
3106 #define CMSIsTooFullPercentage 98
3107   res = res && occupancy() > (double)CMSIsTooFullPercentage/100.0;
3108   return res;
3109 }
3110 
3111 void CMSCollector::setup_cms_unloading_and_verification_state() {
3112   const  bool should_verify =    VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3113                              || VerifyBeforeExit;
3114   const  int  rso           =    SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3115                              |   SharedHeap::SO_CodeCache;
3116 
3117   if (should_unload_classes()) {   // Should unload classes this cycle
3118     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3119     set_verifying(should_verify);    // Set verification state for this cycle
3120     return;                            // Nothing else needs to be done at this time
3121   }
3122 
3123   // Not unloading classes this cycle
3124   assert(!should_unload_classes(), "Inconsitency!");
3125   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3126     // We were not verifying, or we _were_ unloading classes in the last cycle,
3127     // AND some verification options are enabled this cycle; in this case,
3128     // we must make sure that the deadness map is allocated if not already so,
3129     // and cleared (if already allocated previously --
3130     // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3131     if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3132       if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3133         warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3134                 "permanent generation verification disabled");
3135         return;  // Note that we leave verification disabled, so we'll retry this
3136                  // allocation next cycle. We _could_ remember this failure
3137                  // and skip further attempts and permanently disable verification
3138                  // attempts if that is considered more desirable.
3139       }
3140       assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3141               "_perm_gen_ver_bit_map inconsistency?");
3142     } else {
3143       perm_gen_verify_bit_map()->clear_all();
3144     }
3145     // Include symbols, strings and code cache elements to prevent their resurrection.
3146     add_root_scanning_option(rso);
3147     set_verifying(true);
3148   } else if (verifying() && !should_verify) {
3149     // We were verifying, but some verification flags got disabled.
3150     set_verifying(false);
3151     // Exclude symbols, strings and code cache elements from root scanning to
3152     // reduce IM and RM pauses.
3153     remove_root_scanning_option(rso);
3154   }
3155 }
3156 
3157 
3158 #ifndef PRODUCT
3159 HeapWord* CMSCollector::block_start(const void* p) const {
3160   const HeapWord* addr = (HeapWord*)p;
3161   if (_span.contains(p)) {
3162     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3163       return _cmsGen->cmsSpace()->block_start(p);
3164     } else {
3165       assert(_permGen->cmsSpace()->is_in_reserved(addr),
3166              "Inconsistent _span?");
3167       return _permGen->cmsSpace()->block_start(p);
3168     }
3169   }
3170   return NULL;
3171 }
3172 #endif
3173 
3174 HeapWord*
3175 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3176                                                    bool   tlab,
3177                                                    bool   parallel) {
3178   assert(!tlab, "Can't deal with TLAB allocation");
3179   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3180   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3181     CMSExpansionCause::_satisfy_allocation);
3182   if (GCExpandToAllocateDelayMillis > 0) {
3183     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3184   }
3185   size_t adj_word_sz = CompactibleFreeListSpace::adjustObjectSize(word_size);
3186   if (parallel) {
3187     return cmsSpace()->par_allocate(adj_word_sz);
3188   } else {
3189     return cmsSpace()->allocate(adj_word_sz);
3190   }
3191 }
3192 
3193 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3194 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3195 // to CardGeneration and share it...
3196 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3197   CMSExpansionCause::Cause cause)
3198 {
3199   assert_locked_or_safepoint(Heap_lock);
3200 
3201   size_t aligned_bytes  = ReservedSpace::page_align_size_up(bytes);
3202   size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
3203   bool success = false;
3204   if (aligned_expand_bytes > aligned_bytes) {
3205     success = grow_by(aligned_expand_bytes);
3206   }
3207   if (!success) {
3208     success = grow_by(aligned_bytes);
3209   }
3210   if (!success) {
3211     size_t remaining_bytes = _virtual_space.uncommitted_size();
3212     if (remaining_bytes > 0) {
3213       success = grow_by(remaining_bytes);
3214     }
3215   }
3216   if (GC_locker::is_active()) {
3217     if (PrintGC && Verbose) {
3218       gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead");
3219     }
3220   }
3221   // remember why we expanded; this information is used
3222   // by shouldConcurrentCollect() when making decisions on whether to start
3223   // a new CMS cycle.
3224   if (success) {
3225     set_expansion_cause(cause);
3226     if (PrintGCDetails && Verbose) {
3227       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3228         CMSExpansionCause::to_string(cause));
3229     }
3230   }
3231 }
3232 
3233 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3234   HeapWord* res = NULL;
3235   MutexLocker x(ParGCRareEvent_lock);
3236   while (true) {
3237     // Expansion by some other thread might make alloc OK now:
3238     res = ps->lab.alloc(word_sz);
3239     if (res != NULL) return res;
3240     // If there's not enough expansion space available, give up.
3241     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3242       return NULL;
3243     }
3244     // Otherwise, we try expansion.
3245     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3246       CMSExpansionCause::_allocate_par_lab);
3247     // Now go around the loop and try alloc again;
3248     // A competing par_promote might beat us to the expansion space,
3249     // so we may go around the loop again if promotion fails agaion.
3250     if (GCExpandToAllocateDelayMillis > 0) {
3251       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3252     }
3253   }
3254 }
3255 
3256 
3257 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3258   PromotionInfo* promo) {
3259   MutexLocker x(ParGCRareEvent_lock);
3260   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3261   while (true) {
3262     // Expansion by some other thread might make alloc OK now:
3263     if (promo->ensure_spooling_space()) {
3264       assert(promo->has_spooling_space(),
3265              "Post-condition of successful ensure_spooling_space()");
3266       return true;
3267     }
3268     // If there's not enough expansion space available, give up.
3269     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3270       return false;
3271     }
3272     // Otherwise, we try expansion.
3273     expand(refill_size_bytes, MinHeapDeltaBytes,
3274       CMSExpansionCause::_allocate_par_spooling_space);
3275     // Now go around the loop and try alloc again;
3276     // A competing allocation might beat us to the expansion space,
3277     // so we may go around the loop again if allocation fails again.
3278     if (GCExpandToAllocateDelayMillis > 0) {
3279       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3280     }
3281   }
3282 }
3283 
3284 
3285 
3286 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3287   assert_locked_or_safepoint(Heap_lock);
3288   size_t size = ReservedSpace::page_align_size_down(bytes);
3289   if (size > 0) {
3290     shrink_by(size);
3291   }
3292 }
3293 
3294 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3295   assert_locked_or_safepoint(Heap_lock);
3296   bool result = _virtual_space.expand_by(bytes);
3297   if (result) {
3298     HeapWord* old_end = _cmsSpace->end();
3299     size_t new_word_size =
3300       heap_word_size(_virtual_space.committed_size());
3301     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3302     _bts->resize(new_word_size);  // resize the block offset shared array
3303     Universe::heap()->barrier_set()->resize_covered_region(mr);
3304     // Hmmmm... why doesn't CFLS::set_end verify locking?
3305     // This is quite ugly; FIX ME XXX
3306     _cmsSpace->assert_locked();
3307     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3308 
3309     // update the space and generation capacity counters
3310     if (UsePerfData) {
3311       _space_counters->update_capacity();
3312       _gen_counters->update_all();
3313     }
3314 
3315     if (Verbose && PrintGC) {
3316       size_t new_mem_size = _virtual_space.committed_size();
3317       size_t old_mem_size = new_mem_size - bytes;
3318       gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3319                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3320     }
3321   }
3322   return result;
3323 }
3324 
3325 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3326   assert_locked_or_safepoint(Heap_lock);
3327   bool success = true;
3328   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3329   if (remaining_bytes > 0) {
3330     success = grow_by(remaining_bytes);
3331     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3332   }
3333   return success;
3334 }
3335 
3336 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3337   assert_locked_or_safepoint(Heap_lock);
3338   assert_lock_strong(freelistLock());
3339   // XXX Fix when compaction is implemented.
3340   warning("Shrinking of CMS not yet implemented");
3341   return;
3342 }
3343 
3344 
3345 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3346 // phases.
3347 class CMSPhaseAccounting: public StackObj {
3348  public:
3349   CMSPhaseAccounting(CMSCollector *collector,
3350                      const char *phase,
3351                      bool print_cr = true);
3352   ~CMSPhaseAccounting();
3353 
3354  private:
3355   CMSCollector *_collector;
3356   const char *_phase;
3357   elapsedTimer _wallclock;
3358   bool _print_cr;
3359 
3360  public:
3361   // Not MT-safe; so do not pass around these StackObj's
3362   // where they may be accessed by other threads.
3363   jlong wallclock_millis() {
3364     assert(_wallclock.is_active(), "Wall clock should not stop");
3365     _wallclock.stop();  // to record time
3366     jlong ret = _wallclock.milliseconds();
3367     _wallclock.start(); // restart
3368     return ret;
3369   }
3370 };
3371 
3372 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3373                                        const char *phase,
3374                                        bool print_cr) :
3375   _collector(collector), _phase(phase), _print_cr(print_cr) {
3376 
3377   if (PrintCMSStatistics != 0) {
3378     _collector->resetYields();
3379   }
3380   if (PrintGCDetails && PrintGCTimeStamps) {
3381     gclog_or_tty->date_stamp(PrintGCDateStamps);
3382     gclog_or_tty->stamp();
3383     gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3384       _collector->cmsGen()->short_name(), _phase);
3385   }
3386   _collector->resetTimer();
3387   _wallclock.start();
3388   _collector->startTimer();
3389 }
3390 
3391 CMSPhaseAccounting::~CMSPhaseAccounting() {
3392   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3393   _collector->stopTimer();
3394   _wallclock.stop();
3395   if (PrintGCDetails) {
3396     gclog_or_tty->date_stamp(PrintGCDateStamps);
3397     if (PrintGCTimeStamps) {
3398       gclog_or_tty->stamp();
3399       gclog_or_tty->print(": ");
3400     }
3401     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3402                  _collector->cmsGen()->short_name(),
3403                  _phase, _collector->timerValue(), _wallclock.seconds());
3404     if (_print_cr) {
3405       gclog_or_tty->print_cr("");
3406     }
3407     if (PrintCMSStatistics != 0) {
3408       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3409                     _collector->yields());
3410     }
3411   }
3412 }
3413 
3414 // CMS work
3415 
3416 // Checkpoint the roots into this generation from outside
3417 // this generation. [Note this initial checkpoint need only
3418 // be approximate -- we'll do a catch up phase subsequently.]
3419 void CMSCollector::checkpointRootsInitial(bool asynch) {
3420   assert(_collectorState == InitialMarking, "Wrong collector state");
3421   check_correct_thread_executing();
3422   ReferenceProcessor* rp = ref_processor();
3423   SpecializationStats::clear();
3424   assert(_restart_addr == NULL, "Control point invariant");
3425   if (asynch) {
3426     // acquire locks for subsequent manipulations
3427     MutexLockerEx x(bitMapLock(),
3428                     Mutex::_no_safepoint_check_flag);
3429     checkpointRootsInitialWork(asynch);
3430     rp->verify_no_references_recorded();
3431     rp->enable_discovery(); // enable ("weak") refs discovery
3432     _collectorState = Marking;
3433   } else {
3434     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3435     // which recognizes if we are a CMS generation, and doesn't try to turn on
3436     // discovery; verify that they aren't meddling.
3437     assert(!rp->discovery_is_atomic(),
3438            "incorrect setting of discovery predicate");
3439     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3440            "ref discovery for this generation kind");
3441     // already have locks
3442     checkpointRootsInitialWork(asynch);
3443     rp->enable_discovery(); // now enable ("weak") refs discovery
3444     _collectorState = Marking;
3445   }
3446   SpecializationStats::print();
3447 }
3448 
3449 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3450   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3451   assert(_collectorState == InitialMarking, "just checking");
3452 
3453   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3454   // precede our marking with a collection of all
3455   // younger generations to keep floating garbage to a minimum.
3456   // XXX: we won't do this for now -- it's an optimization to be done later.
3457 
3458   // already have locks
3459   assert_lock_strong(bitMapLock());
3460   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3461 
3462   // Setup the verification and class unloading state for this
3463   // CMS collection cycle.
3464   setup_cms_unloading_and_verification_state();
3465 
3466   NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3467     PrintGCDetails && Verbose, true, gclog_or_tty);)
3468   if (UseAdaptiveSizePolicy) {
3469     size_policy()->checkpoint_roots_initial_begin();
3470   }
3471 
3472   // Reset all the PLAB chunk arrays if necessary.
3473   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3474     reset_survivor_plab_arrays();
3475   }
3476 
3477   ResourceMark rm;
3478   HandleMark  hm;
3479 
3480   FalseClosure falseClosure;
3481   // In the case of a synchronous collection, we will elide the
3482   // remark step, so it's important to catch all the nmethod oops
3483   // in this step; hence the last argument to the constrcutor below.
3484   MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */);
3485   GenCollectedHeap* gch = GenCollectedHeap::heap();
3486 
3487   verify_work_stacks_empty();
3488   verify_overflow_empty();
3489 
3490   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3491   // Update the saved marks which may affect the root scans.
3492   gch->save_marks();
3493 
3494   // weak reference processing has not started yet.
3495   ref_processor()->set_enqueuing_is_done(false);
3496 
3497   {
3498     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3499     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3500     gch->gen_process_strong_roots(_cmsGen->level(),
3501                                   true,   // younger gens are roots
3502                                   true,   // collecting perm gen
3503                                   SharedHeap::ScanningOption(roots_scanning_options()),
3504                                   NULL, &notOlder);
3505   }
3506 
3507   // Clear mod-union table; it will be dirtied in the prologue of
3508   // CMS generation per each younger generation collection.
3509 
3510   assert(_modUnionTable.isAllClear(),
3511        "Was cleared in most recent final checkpoint phase"
3512        " or no bits are set in the gc_prologue before the start of the next "
3513        "subsequent marking phase.");
3514 
3515   // Temporarily disabled, since pre/post-consumption closures don't
3516   // care about precleaned cards
3517   #if 0
3518   {
3519     MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3520                              (HeapWord*)_virtual_space.high());
3521     _ct->ct_bs()->preclean_dirty_cards(mr);
3522   }
3523   #endif
3524 
3525   // Save the end of the used_region of the constituent generations
3526   // to be used to limit the extent of sweep in each generation.
3527   save_sweep_limits();
3528   if (UseAdaptiveSizePolicy) {
3529     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3530   }
3531   verify_overflow_empty();
3532 }
3533 
3534 bool CMSCollector::markFromRoots(bool asynch) {
3535   // we might be tempted to assert that:
3536   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3537   //        "inconsistent argument?");
3538   // However that wouldn't be right, because it's possible that
3539   // a safepoint is indeed in progress as a younger generation
3540   // stop-the-world GC happens even as we mark in this generation.
3541   assert(_collectorState == Marking, "inconsistent state?");
3542   check_correct_thread_executing();
3543   verify_overflow_empty();
3544 
3545   bool res;
3546   if (asynch) {
3547 
3548     // Start the timers for adaptive size policy for the concurrent phases
3549     // Do it here so that the foreground MS can use the concurrent
3550     // timer since a foreground MS might has the sweep done concurrently
3551     // or STW.
3552     if (UseAdaptiveSizePolicy) {
3553       size_policy()->concurrent_marking_begin();
3554     }
3555 
3556     // Weak ref discovery note: We may be discovering weak
3557     // refs in this generation concurrent (but interleaved) with
3558     // weak ref discovery by a younger generation collector.
3559 
3560     CMSTokenSyncWithLocks ts(true, bitMapLock());
3561     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3562     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3563     res = markFromRootsWork(asynch);
3564     if (res) {
3565       _collectorState = Precleaning;
3566     } else { // We failed and a foreground collection wants to take over
3567       assert(_foregroundGCIsActive, "internal state inconsistency");
3568       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3569       if (PrintGCDetails) {
3570         gclog_or_tty->print_cr("bailing out to foreground collection");
3571       }
3572     }
3573     if (UseAdaptiveSizePolicy) {
3574       size_policy()->concurrent_marking_end();
3575     }
3576   } else {
3577     assert(SafepointSynchronize::is_at_safepoint(),
3578            "inconsistent with asynch == false");
3579     if (UseAdaptiveSizePolicy) {
3580       size_policy()->ms_collection_marking_begin();
3581     }
3582     // already have locks
3583     res = markFromRootsWork(asynch);
3584     _collectorState = FinalMarking;
3585     if (UseAdaptiveSizePolicy) {
3586       GenCollectedHeap* gch = GenCollectedHeap::heap();
3587       size_policy()->ms_collection_marking_end(gch->gc_cause());
3588     }
3589   }
3590   verify_overflow_empty();
3591   return res;
3592 }
3593 
3594 bool CMSCollector::markFromRootsWork(bool asynch) {
3595   // iterate over marked bits in bit map, doing a full scan and mark
3596   // from these roots using the following algorithm:
3597   // . if oop is to the right of the current scan pointer,
3598   //   mark corresponding bit (we'll process it later)
3599   // . else (oop is to left of current scan pointer)
3600   //   push oop on marking stack
3601   // . drain the marking stack
3602 
3603   // Note that when we do a marking step we need to hold the
3604   // bit map lock -- recall that direct allocation (by mutators)
3605   // and promotion (by younger generation collectors) is also
3606   // marking the bit map. [the so-called allocate live policy.]
3607   // Because the implementation of bit map marking is not
3608   // robust wrt simultaneous marking of bits in the same word,
3609   // we need to make sure that there is no such interference
3610   // between concurrent such updates.
3611 
3612   // already have locks
3613   assert_lock_strong(bitMapLock());
3614 
3615   // Clear the revisit stack, just in case there are any
3616   // obsolete contents from a short-circuited previous CMS cycle.
3617   _revisitStack.reset();
3618   verify_work_stacks_empty();
3619   verify_overflow_empty();
3620   assert(_revisitStack.isEmpty(), "tabula rasa");
3621 
3622   bool result = false;
3623   if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) {
3624     result = do_marking_mt(asynch);
3625   } else {
3626     result = do_marking_st(asynch);
3627   }
3628   return result;
3629 }
3630 
3631 // Forward decl
3632 class CMSConcMarkingTask;
3633 
3634 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3635   CMSCollector*       _collector;
3636   CMSConcMarkingTask* _task;
3637   bool _yield;
3638  protected:
3639   virtual void yield();
3640  public:
3641   // "n_threads" is the number of threads to be terminated.
3642   // "queue_set" is a set of work queues of other threads.
3643   // "collector" is the CMS collector associated with this task terminator.
3644   // "yield" indicates whether we need the gang as a whole to yield.
3645   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3646                            CMSCollector* collector, bool yield) :
3647     ParallelTaskTerminator(n_threads, queue_set),
3648     _collector(collector),
3649     _yield(yield) { }
3650 
3651   void set_task(CMSConcMarkingTask* task) {
3652     _task = task;
3653   }
3654 };
3655 
3656 // MT Concurrent Marking Task
3657 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3658   CMSCollector* _collector;
3659   YieldingFlexibleWorkGang* _workers;        // the whole gang
3660   int           _n_workers;                  // requested/desired # workers
3661   bool          _asynch;
3662   bool          _result;
3663   CompactibleFreeListSpace*  _cms_space;
3664   CompactibleFreeListSpace* _perm_space;
3665   HeapWord*     _global_finger;
3666 
3667   //  Exposed here for yielding support
3668   Mutex* const _bit_map_lock;
3669 
3670   // The per thread work queues, available here for stealing
3671   OopTaskQueueSet*  _task_queues;
3672   CMSConcMarkingTerminator _term;
3673 
3674  public:
3675   CMSConcMarkingTask(CMSCollector* collector,
3676                  CompactibleFreeListSpace* cms_space,
3677                  CompactibleFreeListSpace* perm_space,
3678                  bool asynch, int n_workers,
3679                  YieldingFlexibleWorkGang* workers,
3680                  OopTaskQueueSet* task_queues):
3681     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3682     _collector(collector),
3683     _cms_space(cms_space),
3684     _perm_space(perm_space),
3685     _asynch(asynch), _n_workers(n_workers), _result(true),
3686     _workers(workers), _task_queues(task_queues),
3687     _term(n_workers, task_queues, _collector, asynch),
3688     _bit_map_lock(collector->bitMapLock())
3689   {
3690     assert(n_workers <= workers->total_workers(),
3691            "Else termination won't work correctly today"); // XXX FIX ME!
3692     _requested_size = n_workers;
3693     _term.set_task(this);
3694     assert(_cms_space->bottom() < _perm_space->bottom(),
3695            "Finger incorrectly initialized below");
3696     _global_finger = _cms_space->bottom();
3697   }
3698 
3699 
3700   OopTaskQueueSet* task_queues()  { return _task_queues; }
3701 
3702   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3703 
3704   HeapWord** global_finger_addr() { return &_global_finger; }
3705 
3706   CMSConcMarkingTerminator* terminator() { return &_term; }
3707 
3708   void work(int i);
3709 
3710   virtual void coordinator_yield();  // stuff done by coordinator
3711   bool result() { return _result; }
3712 
3713   void reset(HeapWord* ra) {
3714     _term.reset_for_reuse();
3715   }
3716 
3717   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3718                                            OopTaskQueue* work_q);
3719 
3720  private:
3721   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3722   void do_work_steal(int i);
3723   void bump_global_finger(HeapWord* f);
3724 };
3725 
3726 void CMSConcMarkingTerminator::yield() {
3727   if (ConcurrentMarkSweepThread::should_yield() &&
3728       !_collector->foregroundGCIsActive() &&
3729       _yield) {
3730     _task->yield();
3731   } else {
3732     ParallelTaskTerminator::yield();
3733   }
3734 }
3735 
3736 ////////////////////////////////////////////////////////////////
3737 // Concurrent Marking Algorithm Sketch
3738 ////////////////////////////////////////////////////////////////
3739 // Until all tasks exhausted (both spaces):
3740 // -- claim next available chunk
3741 // -- bump global finger via CAS
3742 // -- find first object that starts in this chunk
3743 //    and start scanning bitmap from that position
3744 // -- scan marked objects for oops
3745 // -- CAS-mark target, and if successful:
3746 //    . if target oop is above global finger (volatile read)
3747 //      nothing to do
3748 //    . if target oop is in chunk and above local finger
3749 //        then nothing to do
3750 //    . else push on work-queue
3751 // -- Deal with possible overflow issues:
3752 //    . local work-queue overflow causes stuff to be pushed on
3753 //      global (common) overflow queue
3754 //    . always first empty local work queue
3755 //    . then get a batch of oops from global work queue if any
3756 //    . then do work stealing
3757 // -- When all tasks claimed (both spaces)
3758 //    and local work queue empty,
3759 //    then in a loop do:
3760 //    . check global overflow stack; steal a batch of oops and trace
3761 //    . try to steal from other threads oif GOS is empty
3762 //    . if neither is available, offer termination
3763 // -- Terminate and return result
3764 //
3765 void CMSConcMarkingTask::work(int i) {
3766   elapsedTimer _timer;
3767   ResourceMark rm;
3768   HandleMark hm;
3769 
3770   DEBUG_ONLY(_collector->verify_overflow_empty();)
3771 
3772   // Before we begin work, our work queue should be empty
3773   assert(work_queue(i)->size() == 0, "Expected to be empty");
3774   // Scan the bitmap covering _cms_space, tracing through grey objects.
3775   _timer.start();
3776   do_scan_and_mark(i, _cms_space);
3777   _timer.stop();
3778   if (PrintCMSStatistics != 0) {
3779     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3780       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3781   }
3782 
3783   // ... do the same for the _perm_space
3784   _timer.reset();
3785   _timer.start();
3786   do_scan_and_mark(i, _perm_space);
3787   _timer.stop();
3788   if (PrintCMSStatistics != 0) {
3789     gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3790       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3791   }
3792 
3793   // ... do work stealing
3794   _timer.reset();
3795   _timer.start();
3796   do_work_steal(i);
3797   _timer.stop();
3798   if (PrintCMSStatistics != 0) {
3799     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3800       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3801   }
3802   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3803   assert(work_queue(i)->size() == 0, "Should have been emptied");
3804   // Note that under the current task protocol, the
3805   // following assertion is true even of the spaces
3806   // expanded since the completion of the concurrent
3807   // marking. XXX This will likely change under a strict
3808   // ABORT semantics.
3809   assert(_global_finger >  _cms_space->end() &&
3810          _global_finger >= _perm_space->end(),
3811          "All tasks have been completed");
3812   DEBUG_ONLY(_collector->verify_overflow_empty();)
3813 }
3814 
3815 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3816   HeapWord* read = _global_finger;
3817   HeapWord* cur  = read;
3818   while (f > read) {
3819     cur = read;
3820     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3821     if (cur == read) {
3822       // our cas succeeded
3823       assert(_global_finger >= f, "protocol consistency");
3824       break;
3825     }
3826   }
3827 }
3828 
3829 // This is really inefficient, and should be redone by
3830 // using (not yet available) block-read and -write interfaces to the
3831 // stack and the work_queue. XXX FIX ME !!!
3832 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3833                                                       OopTaskQueue* work_q) {
3834   // Fast lock-free check
3835   if (ovflw_stk->length() == 0) {
3836     return false;
3837   }
3838   assert(work_q->size() == 0, "Shouldn't steal");
3839   MutexLockerEx ml(ovflw_stk->par_lock(),
3840                    Mutex::_no_safepoint_check_flag);
3841   // Grab up to 1/4 the size of the work queue
3842   size_t num = MIN2((size_t)work_q->max_elems()/4,
3843                     (size_t)ParGCDesiredObjsFromOverflowList);
3844   num = MIN2(num, ovflw_stk->length());
3845   for (int i = (int) num; i > 0; i--) {
3846     oop cur = ovflw_stk->pop();
3847     assert(cur != NULL, "Counted wrong?");
3848     work_q->push(cur);
3849   }
3850   return num > 0;
3851 }
3852 
3853 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3854   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3855   int n_tasks = pst->n_tasks();
3856   // We allow that there may be no tasks to do here because
3857   // we are restarting after a stack overflow.
3858   assert(pst->valid() || n_tasks == 0, "Uninitializd use?");
3859   int nth_task = 0;
3860 
3861   HeapWord* start = sp->bottom();
3862   size_t chunk_size = sp->marking_task_size();
3863   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3864     // Having claimed the nth task in this space,
3865     // compute the chunk that it corresponds to:
3866     MemRegion span = MemRegion(start + nth_task*chunk_size,
3867                                start + (nth_task+1)*chunk_size);
3868     // Try and bump the global finger via a CAS;
3869     // note that we need to do the global finger bump
3870     // _before_ taking the intersection below, because
3871     // the task corresponding to that region will be
3872     // deemed done even if the used_region() expands
3873     // because of allocation -- as it almost certainly will
3874     // during start-up while the threads yield in the
3875     // closure below.
3876     HeapWord* finger = span.end();
3877     bump_global_finger(finger);   // atomically
3878     // There are null tasks here corresponding to chunks
3879     // beyond the "top" address of the space.
3880     span = span.intersection(sp->used_region());
3881     if (!span.is_empty()) {  // Non-null task
3882       // We want to skip the first object because
3883       // the protocol is to scan any object in its entirety
3884       // that _starts_ in this span; a fortiori, any
3885       // object starting in an earlier span is scanned
3886       // as part of an earlier claimed task.
3887       // Below we use the "careful" version of block_start
3888       // so we do not try to navigate uninitialized objects.
3889       HeapWord* prev_obj = sp->block_start_careful(span.start());
3890       // Below we use a variant of block_size that uses the
3891       // Printezis bits to avoid waiting for allocated
3892       // objects to become initialized/parsable.
3893       while (prev_obj < span.start()) {
3894         size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3895         if (sz > 0) {
3896           prev_obj += sz;
3897         } else {
3898           // In this case we may end up doing a bit of redundant
3899           // scanning, but that appears unavoidable, short of
3900           // locking the free list locks; see bug 6324141.
3901           break;
3902         }
3903       }
3904       if (prev_obj < span.end()) {
3905         MemRegion my_span = MemRegion(prev_obj, span.end());
3906         // Do the marking work within a non-empty span --
3907         // the last argument to the constructor indicates whether the
3908         // iteration should be incremental with periodic yields.
3909         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3910                                     &_collector->_markBitMap,
3911                                     work_queue(i),
3912                                     &_collector->_markStack,
3913                                     &_collector->_revisitStack,
3914                                     _asynch);
3915         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3916       } // else nothing to do for this task
3917     }   // else nothing to do for this task
3918   }
3919   // We'd be tempted to assert here that since there are no
3920   // more tasks left to claim in this space, the global_finger
3921   // must exceed space->top() and a fortiori space->end(). However,
3922   // that would not quite be correct because the bumping of
3923   // global_finger occurs strictly after the claiming of a task,
3924   // so by the time we reach here the global finger may not yet
3925   // have been bumped up by the thread that claimed the last
3926   // task.
3927   pst->all_tasks_completed();
3928 }
3929 
3930 class Par_ConcMarkingClosure: public OopClosure {
3931   CMSCollector* _collector;
3932   MemRegion     _span;
3933   CMSBitMap*    _bit_map;
3934   CMSMarkStack* _overflow_stack;
3935   CMSMarkStack* _revisit_stack;     // XXXXXX Check proper use
3936   OopTaskQueue* _work_queue;
3937 
3938  public:
3939   Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3940                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3941     _collector(collector),
3942     _span(_collector->_span),
3943     _work_queue(work_queue),
3944     _bit_map(bit_map),
3945     _overflow_stack(overflow_stack) { }   // need to initialize revisit stack etc.
3946 
3947   void do_oop(oop* p);
3948   void trim_queue(size_t max);
3949   void handle_stack_overflow(HeapWord* lost);
3950 };
3951 
3952 // Grey object rescan during work stealing phase --
3953 // the salient assumption here is that stolen oops must
3954 // always be initialized, so we do not need to check for
3955 // uninitialized objects before scanning here.
3956 void Par_ConcMarkingClosure::do_oop(oop* p) {
3957   oop    this_oop = *p;
3958   assert(this_oop->is_oop_or_null(),
3959          "expected an oop or NULL");
3960   HeapWord* addr = (HeapWord*)this_oop;
3961   // Check if oop points into the CMS generation
3962   // and is not marked
3963   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3964     // a white object ...
3965     // If we manage to "claim" the object, by being the
3966     // first thread to mark it, then we push it on our
3967     // marking stack
3968     if (_bit_map->par_mark(addr)) {     // ... now grey
3969       // push on work queue (grey set)
3970       bool simulate_overflow = false;
3971       NOT_PRODUCT(
3972         if (CMSMarkStackOverflowALot &&
3973             _collector->simulate_overflow()) {
3974           // simulate a stack overflow
3975           simulate_overflow = true;
3976         }
3977       )
3978       if (simulate_overflow ||
3979           !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) {
3980         // stack overflow
3981         if (PrintCMSStatistics != 0) {
3982           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3983                                  SIZE_FORMAT, _overflow_stack->capacity());
3984         }
3985         // We cannot assert that the overflow stack is full because
3986         // it may have been emptied since.
3987         assert(simulate_overflow ||
3988                _work_queue->size() == _work_queue->max_elems(),
3989               "Else push should have succeeded");
3990         handle_stack_overflow(addr);
3991       }
3992     } // Else, some other thread got there first
3993   }
3994 }
3995 
3996 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3997   while (_work_queue->size() > max) {
3998     oop new_oop;
3999     if (_work_queue->pop_local(new_oop)) {
4000       assert(new_oop->is_oop(), "Should be an oop");
4001       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4002       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4003       assert(new_oop->is_parsable(), "Should be parsable");
4004       new_oop->oop_iterate(this);  // do_oop() above
4005     }
4006   }
4007 }
4008 
4009 // Upon stack overflow, we discard (part of) the stack,
4010 // remembering the least address amongst those discarded
4011 // in CMSCollector's _restart_address.
4012 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4013   // We need to do this under a mutex to prevent other
4014   // workers from interfering with the expansion below.
4015   MutexLockerEx ml(_overflow_stack->par_lock(),
4016                    Mutex::_no_safepoint_check_flag);
4017   // Remember the least grey address discarded
4018   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4019   _collector->lower_restart_addr(ra);
4020   _overflow_stack->reset();  // discard stack contents
4021   _overflow_stack->expand(); // expand the stack if possible
4022 }
4023 
4024 
4025 void CMSConcMarkingTask::do_work_steal(int i) {
4026   OopTaskQueue* work_q = work_queue(i);
4027   oop obj_to_scan;
4028   CMSBitMap* bm = &(_collector->_markBitMap);
4029   CMSMarkStack* ovflw = &(_collector->_markStack);
4030   int* seed = _collector->hash_seed(i);
4031   Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw);
4032   while (true) {
4033     cl.trim_queue(0);
4034     assert(work_q->size() == 0, "Should have been emptied above");
4035     if (get_work_from_overflow_stack(ovflw, work_q)) {
4036       // Can't assert below because the work obtained from the
4037       // overflow stack may already have been stolen from us.
4038       // assert(work_q->size() > 0, "Work from overflow stack");
4039       continue;
4040     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4041       assert(obj_to_scan->is_oop(), "Should be an oop");
4042       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4043       obj_to_scan->oop_iterate(&cl);
4044     } else if (terminator()->offer_termination()) {
4045       assert(work_q->size() == 0, "Impossible!");
4046       break;
4047     }
4048   }
4049 }
4050 
4051 // This is run by the CMS (coordinator) thread.
4052 void CMSConcMarkingTask::coordinator_yield() {
4053   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4054          "CMS thread should hold CMS token");
4055 
4056   // First give up the locks, then yield, then re-lock
4057   // We should probably use a constructor/destructor idiom to
4058   // do this unlock/lock or modify the MutexUnlocker class to
4059   // serve our purpose. XXX
4060   assert_lock_strong(_bit_map_lock);
4061   _bit_map_lock->unlock();
4062   ConcurrentMarkSweepThread::desynchronize(true);
4063   ConcurrentMarkSweepThread::acknowledge_yield_request();
4064   _collector->stopTimer();
4065   if (PrintCMSStatistics != 0) {
4066     _collector->incrementYields();
4067   }
4068   _collector->icms_wait();
4069 
4070   // It is possible for whichever thread initiated the yield request
4071   // not to get a chance to wake up and take the bitmap lock between
4072   // this thread releasing it and reacquiring it. So, while the
4073   // should_yield() flag is on, let's sleep for a bit to give the
4074   // other thread a chance to wake up. The limit imposed on the number
4075   // of iterations is defensive, to avoid any unforseen circumstances
4076   // putting us into an infinite loop. Since it's always been this
4077   // (coordinator_yield()) method that was observed to cause the
4078   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4079   // which is by default non-zero. For the other seven methods that
4080   // also perform the yield operation, as are using a different
4081   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4082   // can enable the sleeping for those methods too, if necessary.
4083   // See 6442774.
4084   //
4085   // We really need to reconsider the synchronization between the GC
4086   // thread and the yield-requesting threads in the future and we
4087   // should really use wait/notify, which is the recommended
4088   // way of doing this type of interaction. Additionally, we should
4089   // consolidate the eight methods that do the yield operation and they
4090   // are almost identical into one for better maintenability and
4091   // readability. See 6445193.
4092   //
4093   // Tony 2006.06.29
4094   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4095                        ConcurrentMarkSweepThread::should_yield() &&
4096                        !CMSCollector::foregroundGCIsActive(); ++i) {
4097     os::sleep(Thread::current(), 1, false);
4098     ConcurrentMarkSweepThread::acknowledge_yield_request();
4099   }
4100 
4101   ConcurrentMarkSweepThread::synchronize(true);
4102   _bit_map_lock->lock_without_safepoint_check();
4103   _collector->startTimer();
4104 }
4105 
4106 bool CMSCollector::do_marking_mt(bool asynch) {
4107   assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition");
4108   // In the future this would be determined ergonomically, based
4109   // on #cpu's, # active mutator threads (and load), and mutation rate.
4110   int num_workers = ParallelCMSThreads;
4111 
4112   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4113   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4114 
4115   CMSConcMarkingTask tsk(this, cms_space, perm_space,
4116                          asynch, num_workers /* number requested XXX */,
4117                          conc_workers(), task_queues());
4118 
4119   // Since the actual number of workers we get may be different
4120   // from the number we requested above, do we need to do anything different
4121   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4122   // class?? XXX
4123   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4124   perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4125 
4126   // Refs discovery is already non-atomic.
4127   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4128   // Mutate the Refs discovery so it is MT during the
4129   // multi-threaded marking phase.
4130   ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4131 
4132   conc_workers()->start_task(&tsk);
4133   while (tsk.yielded()) {
4134     tsk.coordinator_yield();
4135     conc_workers()->continue_task(&tsk);
4136   }
4137   // If the task was aborted, _restart_addr will be non-NULL
4138   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4139   while (_restart_addr != NULL) {
4140     // XXX For now we do not make use of ABORTED state and have not
4141     // yet implemented the right abort semantics (even in the original
4142     // single-threaded CMS case). That needs some more investigation
4143     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4144     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4145     // If _restart_addr is non-NULL, a marking stack overflow
4146     // occured; we need to do a fresh marking iteration from the
4147     // indicated restart address.
4148     if (_foregroundGCIsActive && asynch) {
4149       // We may be running into repeated stack overflows, having
4150       // reached the limit of the stack size, while making very
4151       // slow forward progress. It may be best to bail out and
4152       // let the foreground collector do its job.
4153       // Clear _restart_addr, so that foreground GC
4154       // works from scratch. This avoids the headache of
4155       // a "rescan" which would otherwise be needed because
4156       // of the dirty mod union table & card table.
4157       _restart_addr = NULL;
4158       return false;
4159     }
4160     // Adjust the task to restart from _restart_addr
4161     tsk.reset(_restart_addr);
4162     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4163                   _restart_addr);
4164     perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4165                   _restart_addr);
4166     _restart_addr = NULL;
4167     // Get the workers going again
4168     conc_workers()->start_task(&tsk);
4169     while (tsk.yielded()) {
4170       tsk.coordinator_yield();
4171       conc_workers()->continue_task(&tsk);
4172     }
4173   }
4174   assert(tsk.completed(), "Inconsistency");
4175   assert(tsk.result() == true, "Inconsistency");
4176   return true;
4177 }
4178 
4179 bool CMSCollector::do_marking_st(bool asynch) {
4180   ResourceMark rm;
4181   HandleMark   hm;
4182 
4183   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4184     &_markStack, &_revisitStack, CMSYield && asynch);
4185   // the last argument to iterate indicates whether the iteration
4186   // should be incremental with periodic yields.
4187   _markBitMap.iterate(&markFromRootsClosure);
4188   // If _restart_addr is non-NULL, a marking stack overflow
4189   // occured; we need to do a fresh iteration from the
4190   // indicated restart address.
4191   while (_restart_addr != NULL) {
4192     if (_foregroundGCIsActive && asynch) {
4193       // We may be running into repeated stack overflows, having
4194       // reached the limit of the stack size, while making very
4195       // slow forward progress. It may be best to bail out and
4196       // let the foreground collector do its job.
4197       // Clear _restart_addr, so that foreground GC
4198       // works from scratch. This avoids the headache of
4199       // a "rescan" which would otherwise be needed because
4200       // of the dirty mod union table & card table.
4201       _restart_addr = NULL;
4202       return false;  // indicating failure to complete marking
4203     }
4204     // Deal with stack overflow:
4205     // we restart marking from _restart_addr
4206     HeapWord* ra = _restart_addr;
4207     markFromRootsClosure.reset(ra);
4208     _restart_addr = NULL;
4209     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4210   }
4211   return true;
4212 }
4213 
4214 void CMSCollector::preclean() {
4215   check_correct_thread_executing();
4216   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4217   verify_work_stacks_empty();
4218   verify_overflow_empty();
4219   _abort_preclean = false;
4220   if (CMSPrecleaningEnabled) {
4221     _eden_chunk_index = 0;
4222     size_t used = get_eden_used();
4223     size_t capacity = get_eden_capacity();
4224     // Don't start sampling unless we will get sufficiently
4225     // many samples.
4226     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4227                 * CMSScheduleRemarkEdenPenetration)) {
4228       _start_sampling = true;
4229     } else {
4230       _start_sampling = false;
4231     }
4232     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4233     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4234     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4235   }
4236   CMSTokenSync x(true); // is cms thread
4237   if (CMSPrecleaningEnabled) {
4238     sample_eden();
4239     _collectorState = AbortablePreclean;
4240   } else {
4241     _collectorState = FinalMarking;
4242   }
4243   verify_work_stacks_empty();
4244   verify_overflow_empty();
4245 }
4246 
4247 // Try and schedule the remark such that young gen
4248 // occupancy is CMSScheduleRemarkEdenPenetration %.
4249 void CMSCollector::abortable_preclean() {
4250   check_correct_thread_executing();
4251   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4252   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4253 
4254   // If Eden's current occupancy is below this threshold,
4255   // immediately schedule the remark; else preclean
4256   // past the next scavenge in an effort to
4257   // schedule the pause as described avove. By choosing
4258   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4259   // we will never do an actual abortable preclean cycle.
4260   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4261     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4262     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4263     // We need more smarts in the abortable preclean
4264     // loop below to deal with cases where allocation
4265     // in young gen is very very slow, and our precleaning
4266     // is running a losing race against a horde of
4267     // mutators intent on flooding us with CMS updates
4268     // (dirty cards).
4269     // One, admittedly dumb, strategy is to give up
4270     // after a certain number of abortable precleaning loops
4271     // or after a certain maximum time. We want to make
4272     // this smarter in the next iteration.
4273     // XXX FIX ME!!! YSR
4274     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4275     while (!(should_abort_preclean() ||
4276              ConcurrentMarkSweepThread::should_terminate())) {
4277       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4278       cumworkdone += workdone;
4279       loops++;
4280       // Voluntarily terminate abortable preclean phase if we have
4281       // been at it for too long.
4282       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4283           loops >= CMSMaxAbortablePrecleanLoops) {
4284         if (PrintGCDetails) {
4285           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4286         }
4287         break;
4288       }
4289       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4290         if (PrintGCDetails) {
4291           gclog_or_tty->print(" CMS: abort preclean due to time ");
4292         }
4293         break;
4294       }
4295       // If we are doing little work each iteration, we should
4296       // take a short break.
4297       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4298         // Sleep for some time, waiting for work to accumulate
4299         stopTimer();
4300         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4301         startTimer();
4302         waited++;
4303       }
4304     }
4305     if (PrintCMSStatistics > 0) {
4306       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4307                           loops, waited, cumworkdone);
4308     }
4309   }
4310   CMSTokenSync x(true); // is cms thread
4311   if (_collectorState != Idling) {
4312     assert(_collectorState == AbortablePreclean,
4313            "Spontaneous state transition?");
4314     _collectorState = FinalMarking;
4315   } // Else, a foreground collection completed this CMS cycle.
4316   return;
4317 }
4318 
4319 // Respond to an Eden sampling opportunity
4320 void CMSCollector::sample_eden() {
4321   // Make sure a young gc cannot sneak in between our
4322   // reading and recording of a sample.
4323   assert(Thread::current()->is_ConcurrentGC_thread(),
4324          "Only the cms thread may collect Eden samples");
4325   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4326          "Should collect samples while holding CMS token");
4327   if (!_start_sampling) {
4328     return;
4329   }
4330   if (_eden_chunk_array) {
4331     if (_eden_chunk_index < _eden_chunk_capacity) {
4332       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4333       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4334              "Unexpected state of Eden");
4335       // We'd like to check that what we just sampled is an oop-start address;
4336       // however, we cannot do that here since the object may not yet have been
4337       // initialized. So we'll instead do the check when we _use_ this sample
4338       // later.
4339       if (_eden_chunk_index == 0 ||
4340           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4341                          _eden_chunk_array[_eden_chunk_index-1])
4342            >= CMSSamplingGrain)) {
4343         _eden_chunk_index++;  // commit sample
4344       }
4345     }
4346   }
4347   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4348     size_t used = get_eden_used();
4349     size_t capacity = get_eden_capacity();
4350     assert(used <= capacity, "Unexpected state of Eden");
4351     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4352       _abort_preclean = true;
4353     }
4354   }
4355 }
4356 
4357 
4358 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4359   assert(_collectorState == Precleaning ||
4360          _collectorState == AbortablePreclean, "incorrect state");
4361   ResourceMark rm;
4362   HandleMark   hm;
4363   // Do one pass of scrubbing the discovered reference lists
4364   // to remove any reference objects with strongly-reachable
4365   // referents.
4366   if (clean_refs) {
4367     ReferenceProcessor* rp = ref_processor();
4368     CMSPrecleanRefsYieldClosure yield_cl(this);
4369     assert(rp->span().equals(_span), "Spans should be equal");
4370     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4371                                    &_markStack);
4372     CMSDrainMarkingStackClosure complete_trace(this,
4373                                   _span, &_markBitMap, &_markStack,
4374                                   &keep_alive);
4375 
4376     // We don't want this step to interfere with a young
4377     // collection because we don't want to take CPU
4378     // or memory bandwidth away from the young GC threads
4379     // (which may be as many as there are CPUs).
4380     // Note that we don't need to protect ourselves from
4381     // interference with mutators because they can't
4382     // manipulate the discovered reference lists nor affect
4383     // the computed reachability of the referents, the
4384     // only properties manipulated by the precleaning
4385     // of these reference lists.
4386     stopTimer();
4387     CMSTokenSyncWithLocks x(true /* is cms thread */,
4388                             bitMapLock());
4389     startTimer();
4390     sample_eden();
4391     // The following will yield to allow foreground
4392     // collection to proceed promptly. XXX YSR:
4393     // The code in this method may need further
4394     // tweaking for better performance and some restructuring
4395     // for cleaner interfaces.
4396     rp->preclean_discovered_references(
4397           rp->is_alive_non_header(), &keep_alive, &complete_trace,
4398           &yield_cl);
4399   }
4400 
4401   if (clean_survivor) {  // preclean the active survivor space(s)
4402     assert(_young_gen->kind() == Generation::DefNew ||
4403            _young_gen->kind() == Generation::ParNew ||
4404            _young_gen->kind() == Generation::ASParNew,
4405          "incorrect type for cast");
4406     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4407     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4408                              &_markBitMap, &_modUnionTable,
4409                              &_markStack, &_revisitStack,
4410                              true /* precleaning phase */);
4411     stopTimer();
4412     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4413                              bitMapLock());
4414     startTimer();
4415     unsigned int before_count =
4416       GenCollectedHeap::heap()->total_collections();
4417     SurvivorSpacePrecleanClosure
4418       sss_cl(this, _span, &_markBitMap, &_markStack,
4419              &pam_cl, before_count, CMSYield);
4420     dng->from()->object_iterate_careful(&sss_cl);
4421     dng->to()->object_iterate_careful(&sss_cl);
4422   }
4423   MarkRefsIntoAndScanClosure
4424     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4425              &_markStack, &_revisitStack, this, CMSYield,
4426              true /* precleaning phase */);
4427   // CAUTION: The following closure has persistent state that may need to
4428   // be reset upon a decrease in the sequence of addresses it
4429   // processes.
4430   ScanMarkedObjectsAgainCarefullyClosure
4431     smoac_cl(this, _span,
4432       &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4433 
4434   // Preclean dirty cards in ModUnionTable and CardTable using
4435   // appropriate convergence criterion;
4436   // repeat CMSPrecleanIter times unless we find that
4437   // we are losing.
4438   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4439   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4440          "Bad convergence multiplier");
4441   assert(CMSPrecleanThreshold >= 100,
4442          "Unreasonably low CMSPrecleanThreshold");
4443 
4444   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4445   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4446        numIter < CMSPrecleanIter;
4447        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4448     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4449     if (CMSPermGenPrecleaningEnabled) {
4450       curNumCards  += preclean_mod_union_table(_permGen, &smoac_cl);
4451     }
4452     if (Verbose && PrintGCDetails) {
4453       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4454     }
4455     // Either there are very few dirty cards, so re-mark
4456     // pause will be small anyway, or our pre-cleaning isn't
4457     // that much faster than the rate at which cards are being
4458     // dirtied, so we might as well stop and re-mark since
4459     // precleaning won't improve our re-mark time by much.
4460     if (curNumCards <= CMSPrecleanThreshold ||
4461         (numIter > 0 &&
4462          (curNumCards * CMSPrecleanDenominator >
4463          lastNumCards * CMSPrecleanNumerator))) {
4464       numIter++;
4465       cumNumCards += curNumCards;
4466       break;
4467     }
4468   }
4469   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4470   if (CMSPermGenPrecleaningEnabled) {
4471     curNumCards += preclean_card_table(_permGen, &smoac_cl);
4472   }
4473   cumNumCards += curNumCards;
4474   if (PrintGCDetails && PrintCMSStatistics != 0) {
4475     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4476                   curNumCards, cumNumCards, numIter);
4477   }
4478   return cumNumCards;   // as a measure of useful work done
4479 }
4480 
4481 // PRECLEANING NOTES:
4482 // Precleaning involves:
4483 // . reading the bits of the modUnionTable and clearing the set bits.
4484 // . For the cards corresponding to the set bits, we scan the
4485 //   objects on those cards. This means we need the free_list_lock
4486 //   so that we can safely iterate over the CMS space when scanning
4487 //   for oops.
4488 // . When we scan the objects, we'll be both reading and setting
4489 //   marks in the marking bit map, so we'll need the marking bit map.
4490 // . For protecting _collector_state transitions, we take the CGC_lock.
4491 //   Note that any races in the reading of of card table entries by the
4492 //   CMS thread on the one hand and the clearing of those entries by the
4493 //   VM thread or the setting of those entries by the mutator threads on the
4494 //   other are quite benign. However, for efficiency it makes sense to keep
4495 //   the VM thread from racing with the CMS thread while the latter is
4496 //   dirty card info to the modUnionTable. We therefore also use the
4497 //   CGC_lock to protect the reading of the card table and the mod union
4498 //   table by the CM thread.
4499 // . We run concurrently with mutator updates, so scanning
4500 //   needs to be done carefully  -- we should not try to scan
4501 //   potentially uninitialized objects.
4502 //
4503 // Locking strategy: While holding the CGC_lock, we scan over and
4504 // reset a maximal dirty range of the mod union / card tables, then lock
4505 // the free_list_lock and bitmap lock to do a full marking, then
4506 // release these locks; and repeat the cycle. This allows for a
4507 // certain amount of fairness in the sharing of these locks between
4508 // the CMS collector on the one hand, and the VM thread and the
4509 // mutators on the other.
4510 
4511 // NOTE: preclean_mod_union_table() and preclean_card_table()
4512 // further below are largely identical; if you need to modify
4513 // one of these methods, please check the other method too.
4514 
4515 size_t CMSCollector::preclean_mod_union_table(
4516   ConcurrentMarkSweepGeneration* gen,
4517   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4518   verify_work_stacks_empty();
4519   verify_overflow_empty();
4520 
4521   // strategy: starting with the first card, accumulate contiguous
4522   // ranges of dirty cards; clear these cards, then scan the region
4523   // covered by these cards.
4524 
4525   // Since all of the MUT is committed ahead, we can just use
4526   // that, in case the generations expand while we are precleaning.
4527   // It might also be fine to just use the committed part of the
4528   // generation, but we might potentially miss cards when the
4529   // generation is rapidly expanding while we are in the midst
4530   // of precleaning.
4531   HeapWord* startAddr = gen->reserved().start();
4532   HeapWord* endAddr   = gen->reserved().end();
4533 
4534   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4535 
4536   size_t numDirtyCards, cumNumDirtyCards;
4537   HeapWord *nextAddr, *lastAddr;
4538   for (cumNumDirtyCards = numDirtyCards = 0,
4539        nextAddr = lastAddr = startAddr;
4540        nextAddr < endAddr;
4541        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4542 
4543     ResourceMark rm;
4544     HandleMark   hm;
4545 
4546     MemRegion dirtyRegion;
4547     {
4548       stopTimer();
4549       CMSTokenSync ts(true);
4550       startTimer();
4551       sample_eden();
4552       // Get dirty region starting at nextOffset (inclusive),
4553       // simultaneously clearing it.
4554       dirtyRegion =
4555         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4556       assert(dirtyRegion.start() >= nextAddr,
4557              "returned region inconsistent?");
4558     }
4559     // Remember where the next search should begin.
4560     // The returned region (if non-empty) is a right open interval,
4561     // so lastOffset is obtained from the right end of that
4562     // interval.
4563     lastAddr = dirtyRegion.end();
4564     // Should do something more transparent and less hacky XXX
4565     numDirtyCards =
4566       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4567 
4568     // We'll scan the cards in the dirty region (with periodic
4569     // yields for foreground GC as needed).
4570     if (!dirtyRegion.is_empty()) {
4571       assert(numDirtyCards > 0, "consistency check");
4572       HeapWord* stop_point = NULL;
4573       {
4574         stopTimer();
4575         CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4576                                  bitMapLock());
4577         startTimer();
4578         verify_work_stacks_empty();
4579         verify_overflow_empty();
4580         sample_eden();
4581         stop_point =
4582           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4583       }
4584       if (stop_point != NULL) {
4585         // The careful iteration stopped early either because it found an
4586         // uninitialized object, or because we were in the midst of an
4587         // "abortable preclean", which should now be aborted. Redirty
4588         // the bits corresponding to the partially-scanned or unscanned
4589         // cards. We'll either restart at the next block boundary or
4590         // abort the preclean.
4591         assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4592                (_collectorState == AbortablePreclean && should_abort_preclean()),
4593                "Unparsable objects should only be in perm gen.");
4594 
4595         stopTimer();
4596         CMSTokenSyncWithLocks ts(true, bitMapLock());
4597         startTimer();
4598         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4599         if (should_abort_preclean()) {
4600           break; // out of preclean loop
4601         } else {
4602           // Compute the next address at which preclean should pick up;
4603           // might need bitMapLock in order to read P-bits.
4604           lastAddr = next_card_start_after_block(stop_point);
4605         }
4606       }
4607     } else {
4608       assert(lastAddr == endAddr, "consistency check");
4609       assert(numDirtyCards == 0, "consistency check");
4610       break;
4611     }
4612   }
4613   verify_work_stacks_empty();
4614   verify_overflow_empty();
4615   return cumNumDirtyCards;
4616 }
4617 
4618 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4619 // below are largely identical; if you need to modify
4620 // one of these methods, please check the other method too.
4621 
4622 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4623   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4624   // strategy: it's similar to precleamModUnionTable above, in that
4625   // we accumulate contiguous ranges of dirty cards, mark these cards
4626   // precleaned, then scan the region covered by these cards.
4627   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4628   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4629 
4630   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4631 
4632   size_t numDirtyCards, cumNumDirtyCards;
4633   HeapWord *lastAddr, *nextAddr;
4634 
4635   for (cumNumDirtyCards = numDirtyCards = 0,
4636        nextAddr = lastAddr = startAddr;
4637        nextAddr < endAddr;
4638        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4639 
4640     ResourceMark rm;
4641     HandleMark   hm;
4642 
4643     MemRegion dirtyRegion;
4644     {
4645       // See comments in "Precleaning notes" above on why we
4646       // do this locking. XXX Could the locking overheads be
4647       // too high when dirty cards are sparse? [I don't think so.]
4648       stopTimer();
4649       CMSTokenSync x(true); // is cms thread
4650       startTimer();
4651       sample_eden();
4652       // Get and clear dirty region from card table
4653       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_preclean(
4654                                     MemRegion(nextAddr, endAddr));
4655       assert(dirtyRegion.start() >= nextAddr,
4656              "returned region inconsistent?");
4657     }
4658     lastAddr = dirtyRegion.end();
4659     numDirtyCards =
4660       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4661 
4662     if (!dirtyRegion.is_empty()) {
4663       stopTimer();
4664       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4665       startTimer();
4666       sample_eden();
4667       verify_work_stacks_empty();
4668       verify_overflow_empty();
4669       HeapWord* stop_point =
4670         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4671       if (stop_point != NULL) {
4672         // The careful iteration stopped early because it found an
4673         // uninitialized object.  Redirty the bits corresponding to the
4674         // partially-scanned or unscanned cards, and start again at the
4675         // next block boundary.
4676         assert(CMSPermGenPrecleaningEnabled ||
4677                (_collectorState == AbortablePreclean && should_abort_preclean()),
4678                "Unparsable objects should only be in perm gen.");
4679         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4680         if (should_abort_preclean()) {
4681           break; // out of preclean loop
4682         } else {
4683           // Compute the next address at which preclean should pick up.
4684           lastAddr = next_card_start_after_block(stop_point);
4685         }
4686       }
4687     } else {
4688       break;
4689     }
4690   }
4691   verify_work_stacks_empty();
4692   verify_overflow_empty();
4693   return cumNumDirtyCards;
4694 }
4695 
4696 void CMSCollector::checkpointRootsFinal(bool asynch,
4697   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4698   assert(_collectorState == FinalMarking, "incorrect state transition?");
4699   check_correct_thread_executing();
4700   // world is stopped at this checkpoint
4701   assert(SafepointSynchronize::is_at_safepoint(),
4702          "world should be stopped");
4703   verify_work_stacks_empty();
4704   verify_overflow_empty();
4705 
4706   SpecializationStats::clear();
4707   if (PrintGCDetails) {
4708     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4709                         _young_gen->used() / K,
4710                         _young_gen->capacity() / K);
4711   }
4712   if (asynch) {
4713     if (CMSScavengeBeforeRemark) {
4714       GenCollectedHeap* gch = GenCollectedHeap::heap();
4715       // Temporarily set flag to false, GCH->do_collection will
4716       // expect it to be false and set to true
4717       FlagSetting fl(gch->_is_gc_active, false);
4718       NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4719         PrintGCDetails && Verbose, true, gclog_or_tty);)
4720       int level = _cmsGen->level() - 1;
4721       if (level >= 0) {
4722         gch->do_collection(true,        // full (i.e. force, see below)
4723                            false,       // !clear_all_soft_refs
4724                            0,           // size
4725                            false,       // is_tlab
4726                            level        // max_level
4727                           );
4728       }
4729     }
4730     FreelistLocker x(this);
4731     MutexLockerEx y(bitMapLock(),
4732                     Mutex::_no_safepoint_check_flag);
4733     assert(!init_mark_was_synchronous, "but that's impossible!");
4734     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4735   } else {
4736     // already have all the locks
4737     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4738                              init_mark_was_synchronous);
4739   }
4740   verify_work_stacks_empty();
4741   verify_overflow_empty();
4742   SpecializationStats::print();
4743 }
4744 
4745 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4746   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4747 
4748   NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4749 
4750   assert(haveFreelistLocks(), "must have free list locks");
4751   assert_lock_strong(bitMapLock());
4752 
4753   if (UseAdaptiveSizePolicy) {
4754     size_policy()->checkpoint_roots_final_begin();
4755   }
4756 
4757   ResourceMark rm;
4758   HandleMark   hm;
4759 
4760   GenCollectedHeap* gch = GenCollectedHeap::heap();
4761 
4762   if (should_unload_classes()) {
4763     CodeCache::gc_prologue();
4764   }
4765   assert(haveFreelistLocks(), "must have free list locks");
4766   assert_lock_strong(bitMapLock());
4767 
4768   if (!init_mark_was_synchronous) {
4769     // We might assume that we need not fill TLAB's when
4770     // CMSScavengeBeforeRemark is set, because we may have just done
4771     // a scavenge which would have filled all TLAB's -- and besides
4772     // Eden would be empty. This however may not always be the case --
4773     // for instance although we asked for a scavenge, it may not have
4774     // happened because of a JNI critical section. We probably need
4775     // a policy for deciding whether we can in that case wait until
4776     // the critical section releases and then do the remark following
4777     // the scavenge, and skip it here. In the absence of that policy,
4778     // or of an indication of whether the scavenge did indeed occur,
4779     // we cannot rely on TLAB's having been filled and must do
4780     // so here just in case a scavenge did not happen.
4781     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4782     // Update the saved marks which may affect the root scans.
4783     gch->save_marks();
4784 
4785     {
4786       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4787 
4788       // Note on the role of the mod union table:
4789       // Since the marker in "markFromRoots" marks concurrently with
4790       // mutators, it is possible for some reachable objects not to have been
4791       // scanned. For instance, an only reference to an object A was
4792       // placed in object B after the marker scanned B. Unless B is rescanned,
4793       // A would be collected. Such updates to references in marked objects
4794       // are detected via the mod union table which is the set of all cards
4795       // dirtied since the first checkpoint in this GC cycle and prior to
4796       // the most recent young generation GC, minus those cleaned up by the
4797       // concurrent precleaning.
4798       if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4799         TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4800         do_remark_parallel();
4801       } else {
4802         TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4803                     gclog_or_tty);
4804         do_remark_non_parallel();
4805       }
4806     }
4807   } else {
4808     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4809     // The initial mark was stop-world, so there's no rescanning to
4810     // do; go straight on to the next step below.
4811   }
4812   verify_work_stacks_empty();
4813   verify_overflow_empty();
4814 
4815   {
4816     NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4817     refProcessingWork(asynch, clear_all_soft_refs);
4818   }
4819   verify_work_stacks_empty();
4820   verify_overflow_empty();
4821 
4822   if (should_unload_classes()) {
4823     CodeCache::gc_epilogue();
4824   }
4825 
4826   // If we encountered any (marking stack / work queue) overflow
4827   // events during the current CMS cycle, take appropriate
4828   // remedial measures, where possible, so as to try and avoid
4829   // recurrence of that condition.
4830   assert(_markStack.isEmpty(), "No grey objects");
4831   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4832                      _ser_kac_ovflw;
4833   if (ser_ovflw > 0) {
4834     if (PrintCMSStatistics != 0) {
4835       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4836         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4837         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4838         _ser_kac_ovflw);
4839     }
4840     _markStack.expand();
4841     _ser_pmc_remark_ovflw = 0;
4842     _ser_pmc_preclean_ovflw = 0;
4843     _ser_kac_ovflw = 0;
4844   }
4845   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4846     if (PrintCMSStatistics != 0) {
4847       gclog_or_tty->print_cr("Work queue overflow (benign) "
4848         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4849         _par_pmc_remark_ovflw, _par_kac_ovflw);
4850     }
4851     _par_pmc_remark_ovflw = 0;
4852     _par_kac_ovflw = 0;
4853   }
4854   if (PrintCMSStatistics != 0) {
4855      if (_markStack._hit_limit > 0) {
4856        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4857                               _markStack._hit_limit);
4858      }
4859      if (_markStack._failed_double > 0) {
4860        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4861                               " current capacity "SIZE_FORMAT,
4862                               _markStack._failed_double,
4863                               _markStack.capacity());
4864      }
4865   }
4866   _markStack._hit_limit = 0;
4867   _markStack._failed_double = 0;
4868 
4869   if ((VerifyAfterGC || VerifyDuringGC) &&
4870       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4871     verify_after_remark();
4872   }
4873 
4874   // Change under the freelistLocks.
4875   _collectorState = Sweeping;
4876   // Call isAllClear() under bitMapLock
4877   assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4878     " final marking");
4879   if (UseAdaptiveSizePolicy) {
4880     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4881   }
4882 }
4883 
4884 // Parallel remark task
4885 class CMSParRemarkTask: public AbstractGangTask {
4886   CMSCollector* _collector;
4887   WorkGang*     _workers;
4888   int           _n_workers;
4889   CompactibleFreeListSpace* _cms_space;
4890   CompactibleFreeListSpace* _perm_space;
4891 
4892   // The per-thread work queues, available here for stealing.
4893   OopTaskQueueSet*       _task_queues;
4894   ParallelTaskTerminator _term;
4895 
4896  public:
4897   CMSParRemarkTask(CMSCollector* collector,
4898                    CompactibleFreeListSpace* cms_space,
4899                    CompactibleFreeListSpace* perm_space,
4900                    int n_workers, WorkGang* workers,
4901                    OopTaskQueueSet* task_queues):
4902     AbstractGangTask("Rescan roots and grey objects in parallel"),
4903     _collector(collector),
4904     _cms_space(cms_space), _perm_space(perm_space),
4905     _n_workers(n_workers),
4906     _workers(workers),
4907     _task_queues(task_queues),
4908     _term(workers->total_workers(), task_queues) { }
4909 
4910   OopTaskQueueSet* task_queues() { return _task_queues; }
4911 
4912   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4913 
4914   ParallelTaskTerminator* terminator() { return &_term; }
4915 
4916   void work(int i);
4917 
4918  private:
4919   // Work method in support of parallel rescan ... of young gen spaces
4920   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4921                              ContiguousSpace* space,
4922                              HeapWord** chunk_array, size_t chunk_top);
4923 
4924   // ... of  dirty cards in old space
4925   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4926                                   Par_MarkRefsIntoAndScanClosure* cl);
4927 
4928   // ... work stealing for the above
4929   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4930 };
4931 
4932 void CMSParRemarkTask::work(int i) {
4933   elapsedTimer _timer;
4934   ResourceMark rm;
4935   HandleMark   hm;
4936 
4937   // ---------- rescan from roots --------------
4938   _timer.start();
4939   GenCollectedHeap* gch = GenCollectedHeap::heap();
4940   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4941     _collector->_span, _collector->ref_processor(),
4942     &(_collector->_markBitMap),
4943     work_queue(i), &(_collector->_revisitStack));
4944 
4945   // Rescan young gen roots first since these are likely
4946   // coarsely partitioned and may, on that account, constitute
4947   // the critical path; thus, it's best to start off that
4948   // work first.
4949   // ---------- young gen roots --------------
4950   {
4951     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
4952     EdenSpace* eden_space = dng->eden();
4953     ContiguousSpace* from_space = dng->from();
4954     ContiguousSpace* to_space   = dng->to();
4955 
4956     HeapWord** eca = _collector->_eden_chunk_array;
4957     size_t     ect = _collector->_eden_chunk_index;
4958     HeapWord** sca = _collector->_survivor_chunk_array;
4959     size_t     sct = _collector->_survivor_chunk_index;
4960 
4961     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4962     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4963 
4964     do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
4965     do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
4966     do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
4967 
4968     _timer.stop();
4969     if (PrintCMSStatistics != 0) {
4970       gclog_or_tty->print_cr(
4971         "Finished young gen rescan work in %dth thread: %3.3f sec",
4972         i, _timer.seconds());
4973     }
4974   }
4975 
4976   // ---------- remaining roots --------------
4977   _timer.reset();
4978   _timer.start();
4979   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
4980                                 false,     // yg was scanned above
4981                                 true,      // collecting perm gen
4982                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4983                                 NULL, &par_mrias_cl);
4984   _timer.stop();
4985   if (PrintCMSStatistics != 0) {
4986     gclog_or_tty->print_cr(
4987       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4988       i, _timer.seconds());
4989   }
4990 
4991   // ---------- rescan dirty cards ------------
4992   _timer.reset();
4993   _timer.start();
4994 
4995   // Do the rescan tasks for each of the two spaces
4996   // (cms_space and perm_space) in turn.
4997   do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
4998   do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
4999   _timer.stop();
5000   if (PrintCMSStatistics != 0) {
5001     gclog_or_tty->print_cr(
5002       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5003       i, _timer.seconds());
5004   }
5005 
5006   // ---------- steal work from other threads ...
5007   // ---------- ... and drain overflow list.
5008   _timer.reset();
5009   _timer.start();
5010   do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5011   _timer.stop();
5012   if (PrintCMSStatistics != 0) {
5013     gclog_or_tty->print_cr(
5014       "Finished work stealing in %dth thread: %3.3f sec",
5015       i, _timer.seconds());
5016   }
5017 }
5018 
5019 void
5020 CMSParRemarkTask::do_young_space_rescan(int i,
5021   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5022   HeapWord** chunk_array, size_t chunk_top) {
5023   // Until all tasks completed:
5024   // . claim an unclaimed task
5025   // . compute region boundaries corresponding to task claimed
5026   //   using chunk_array
5027   // . par_oop_iterate(cl) over that region
5028 
5029   ResourceMark rm;
5030   HandleMark   hm;
5031 
5032   SequentialSubTasksDone* pst = space->par_seq_tasks();
5033   assert(pst->valid(), "Uninitialized use?");
5034 
5035   int nth_task = 0;
5036   int n_tasks  = pst->n_tasks();
5037 
5038   HeapWord *start, *end;
5039   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5040     // We claimed task # nth_task; compute its boundaries.
5041     if (chunk_top == 0) {  // no samples were taken
5042       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5043       start = space->bottom();
5044       end   = space->top();
5045     } else if (nth_task == 0) {
5046       start = space->bottom();
5047       end   = chunk_array[nth_task];
5048     } else if (nth_task < (jint)chunk_top) {
5049       assert(nth_task >= 1, "Control point invariant");
5050       start = chunk_array[nth_task - 1];
5051       end   = chunk_array[nth_task];
5052     } else {
5053       assert(nth_task == (jint)chunk_top, "Control point invariant");
5054       start = chunk_array[chunk_top - 1];
5055       end   = space->top();
5056     }
5057     MemRegion mr(start, end);
5058     // Verify that mr is in space
5059     assert(mr.is_empty() || space->used_region().contains(mr),
5060            "Should be in space");
5061     // Verify that "start" is an object boundary
5062     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5063            "Should be an oop");
5064     space->par_oop_iterate(mr, cl);
5065   }
5066   pst->all_tasks_completed();
5067 }
5068 
5069 void
5070 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5071   CompactibleFreeListSpace* sp, int i,
5072   Par_MarkRefsIntoAndScanClosure* cl) {
5073   // Until all tasks completed:
5074   // . claim an unclaimed task
5075   // . compute region boundaries corresponding to task claimed
5076   // . transfer dirty bits ct->mut for that region
5077   // . apply rescanclosure to dirty mut bits for that region
5078 
5079   ResourceMark rm;
5080   HandleMark   hm;
5081 
5082   OopTaskQueue* work_q = work_queue(i);
5083   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5084   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5085   // CAUTION: This closure has state that persists across calls to
5086   // the work method dirty_range_iterate_clear() in that it has
5087   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5088   // use of that state in the imbedded UpwardsObjectClosure instance
5089   // assumes that the cards are always iterated (even if in parallel
5090   // by several threads) in monotonically increasing order per each
5091   // thread. This is true of the implementation below which picks
5092   // card ranges (chunks) in monotonically increasing order globally
5093   // and, a-fortiori, in monotonically increasing order per thread
5094   // (the latter order being a subsequence of the former).
5095   // If the work code below is ever reorganized into a more chaotic
5096   // work-partitioning form than the current "sequential tasks"
5097   // paradigm, the use of that persistent state will have to be
5098   // revisited and modified appropriately. See also related
5099   // bug 4756801 work on which should examine this code to make
5100   // sure that the changes there do not run counter to the
5101   // assumptions made here and necessary for correctness and
5102   // efficiency. Note also that this code might yield inefficient
5103   // behaviour in the case of very large objects that span one or
5104   // more work chunks. Such objects would potentially be scanned
5105   // several times redundantly. Work on 4756801 should try and
5106   // address that performance anomaly if at all possible. XXX
5107   MemRegion  full_span  = _collector->_span;
5108   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5109   CMSMarkStack* rs = &(_collector->_revisitStack);   // shared
5110   MarkFromDirtyCardsClosure
5111     greyRescanClosure(_collector, full_span, // entire span of interest
5112                       sp, bm, work_q, rs, cl);
5113 
5114   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5115   assert(pst->valid(), "Uninitialized use?");
5116   int nth_task = 0;
5117   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5118   MemRegion span = sp->used_region();
5119   HeapWord* start_addr = span.start();
5120   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5121                                            alignment);
5122   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5123   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5124          start_addr, "Check alignment");
5125   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5126          chunk_size, "Check alignment");
5127 
5128   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5129     // Having claimed the nth_task, compute corresponding mem-region,
5130     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5131     // The alignment restriction ensures that we do not need any
5132     // synchronization with other gang-workers while setting or
5133     // clearing bits in thus chunk of the MUT.
5134     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5135                                     start_addr + (nth_task+1)*chunk_size);
5136     // The last chunk's end might be way beyond end of the
5137     // used region. In that case pull back appropriately.
5138     if (this_span.end() > end_addr) {
5139       this_span.set_end(end_addr);
5140       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5141     }
5142     // Iterate over the dirty cards covering this chunk, marking them
5143     // precleaned, and setting the corresponding bits in the mod union
5144     // table. Since we have been careful to partition at Card and MUT-word
5145     // boundaries no synchronization is needed between parallel threads.
5146     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5147                                                  &modUnionClosure);
5148 
5149     // Having transferred these marks into the modUnionTable,
5150     // rescan the marked objects on the dirty cards in the modUnionTable.
5151     // Even if this is at a synchronous collection, the initial marking
5152     // may have been done during an asynchronous collection so there
5153     // may be dirty bits in the mod-union table.
5154     _collector->_modUnionTable.dirty_range_iterate_clear(
5155                   this_span, &greyRescanClosure);
5156     _collector->_modUnionTable.verifyNoOneBitsInRange(
5157                                  this_span.start(),
5158                                  this_span.end());
5159   }
5160   pst->all_tasks_completed();  // declare that i am done
5161 }
5162 
5163 // . see if we can share work_queues with ParNew? XXX
5164 void
5165 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5166                                 int* seed) {
5167   OopTaskQueue* work_q = work_queue(i);
5168   NOT_PRODUCT(int num_steals = 0;)
5169   oop obj_to_scan;
5170   CMSBitMap* bm = &(_collector->_markBitMap);
5171   size_t num_from_overflow_list =
5172            MIN2((size_t)work_q->max_elems()/4,
5173                 (size_t)ParGCDesiredObjsFromOverflowList);
5174 
5175   while (true) {
5176     // Completely finish any left over work from (an) earlier round(s)
5177     cl->trim_queue(0);
5178     // Now check if there's any work in the overflow list
5179     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5180                                                 work_q)) {
5181       // found something in global overflow list;
5182       // not yet ready to go stealing work from others.
5183       // We'd like to assert(work_q->size() != 0, ...)
5184       // because we just took work from the overflow list,
5185       // but of course we can't since all of that could have
5186       // been already stolen from us.
5187       // "He giveth and He taketh away."
5188       continue;
5189     }
5190     // Verify that we have no work before we resort to stealing
5191     assert(work_q->size() == 0, "Have work, shouldn't steal");
5192     // Try to steal from other queues that have work
5193     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5194       NOT_PRODUCT(num_steals++;)
5195       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5196       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5197       // Do scanning work
5198       obj_to_scan->oop_iterate(cl);
5199       // Loop around, finish this work, and try to steal some more
5200     } else if (terminator()->offer_termination()) {
5201         break;  // nirvana from the infinite cycle
5202     }
5203   }
5204   NOT_PRODUCT(
5205     if (PrintCMSStatistics != 0) {
5206       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5207     }
5208   )
5209   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5210          "Else our work is not yet done");
5211 }
5212 
5213 // Return a thread-local PLAB recording array, as appropriate.
5214 void* CMSCollector::get_data_recorder(int thr_num) {
5215   if (_survivor_plab_array != NULL &&
5216       (CMSPLABRecordAlways ||
5217        (_collectorState > Marking && _collectorState < FinalMarking))) {
5218     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5219     ChunkArray* ca = &_survivor_plab_array[thr_num];
5220     ca->reset();   // clear it so that fresh data is recorded
5221     return (void*) ca;
5222   } else {
5223     return NULL;
5224   }
5225 }
5226 
5227 // Reset all the thread-local PLAB recording arrays
5228 void CMSCollector::reset_survivor_plab_arrays() {
5229   for (uint i = 0; i < ParallelGCThreads; i++) {
5230     _survivor_plab_array[i].reset();
5231   }
5232 }
5233 
5234 // Merge the per-thread plab arrays into the global survivor chunk
5235 // array which will provide the partitioning of the survivor space
5236 // for CMS rescan.
5237 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5238   assert(_survivor_plab_array  != NULL, "Error");
5239   assert(_survivor_chunk_array != NULL, "Error");
5240   assert(_collectorState == FinalMarking, "Error");
5241   for (uint j = 0; j < ParallelGCThreads; j++) {
5242     _cursor[j] = 0;
5243   }
5244   HeapWord* top = surv->top();
5245   size_t i;
5246   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5247     HeapWord* min_val = top;          // Higher than any PLAB address
5248     uint      min_tid = 0;            // position of min_val this round
5249     for (uint j = 0; j < ParallelGCThreads; j++) {
5250       ChunkArray* cur_sca = &_survivor_plab_array[j];
5251       if (_cursor[j] == cur_sca->end()) {
5252         continue;
5253       }
5254       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5255       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5256       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5257       if (cur_val < min_val) {
5258         min_tid = j;
5259         min_val = cur_val;
5260       } else {
5261         assert(cur_val < top, "All recorded addresses should be less");
5262       }
5263     }
5264     // At this point min_val and min_tid are respectively
5265     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5266     // and the thread (j) that witnesses that address.
5267     // We record this address in the _survivor_chunk_array[i]
5268     // and increment _cursor[min_tid] prior to the next round i.
5269     if (min_val == top) {
5270       break;
5271     }
5272     _survivor_chunk_array[i] = min_val;
5273     _cursor[min_tid]++;
5274   }
5275   // We are all done; record the size of the _survivor_chunk_array
5276   _survivor_chunk_index = i; // exclusive: [0, i)
5277   if (PrintCMSStatistics > 0) {
5278     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5279   }
5280   // Verify that we used up all the recorded entries
5281   #ifdef ASSERT
5282     size_t total = 0;
5283     for (uint j = 0; j < ParallelGCThreads; j++) {
5284       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5285       total += _cursor[j];
5286     }
5287     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5288     // Check that the merged array is in sorted order
5289     if (total > 0) {
5290       for (size_t i = 0; i < total - 1; i++) {
5291         if (PrintCMSStatistics > 0) {
5292           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5293                               i, _survivor_chunk_array[i]);
5294         }
5295         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5296                "Not sorted");
5297       }
5298     }
5299   #endif // ASSERT
5300 }
5301 
5302 // Set up the space's par_seq_tasks structure for work claiming
5303 // for parallel rescan of young gen.
5304 // See ParRescanTask where this is currently used.
5305 void
5306 CMSCollector::
5307 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5308   assert(n_threads > 0, "Unexpected n_threads argument");
5309   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5310 
5311   // Eden space
5312   {
5313     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5314     assert(!pst->valid(), "Clobbering existing data?");
5315     // Each valid entry in [0, _eden_chunk_index) represents a task.
5316     size_t n_tasks = _eden_chunk_index + 1;
5317     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5318     pst->set_par_threads(n_threads);
5319     pst->set_n_tasks((int)n_tasks);
5320   }
5321 
5322   // Merge the survivor plab arrays into _survivor_chunk_array
5323   if (_survivor_plab_array != NULL) {
5324     merge_survivor_plab_arrays(dng->from());
5325   } else {
5326     assert(_survivor_chunk_index == 0, "Error");
5327   }
5328 
5329   // To space
5330   {
5331     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5332     assert(!pst->valid(), "Clobbering existing data?");
5333     pst->set_par_threads(n_threads);
5334     pst->set_n_tasks(1);
5335     assert(pst->valid(), "Error");
5336   }
5337 
5338   // From space
5339   {
5340     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5341     assert(!pst->valid(), "Clobbering existing data?");
5342     size_t n_tasks = _survivor_chunk_index + 1;
5343     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5344     pst->set_par_threads(n_threads);
5345     pst->set_n_tasks((int)n_tasks);
5346     assert(pst->valid(), "Error");
5347   }
5348 }
5349 
5350 // Parallel version of remark
5351 void CMSCollector::do_remark_parallel() {
5352   GenCollectedHeap* gch = GenCollectedHeap::heap();
5353   WorkGang* workers = gch->workers();
5354   assert(workers != NULL, "Need parallel worker threads.");
5355   int n_workers = workers->total_workers();
5356   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5357   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5358 
5359   CMSParRemarkTask tsk(this,
5360     cms_space, perm_space,
5361     n_workers, workers, task_queues());
5362 
5363   // Set up for parallel process_strong_roots work.
5364   gch->set_par_threads(n_workers);
5365   gch->change_strong_roots_parity();
5366   // We won't be iterating over the cards in the card table updating
5367   // the younger_gen cards, so we shouldn't call the following else
5368   // the verification code as well as subsequent younger_refs_iterate
5369   // code would get confused. XXX
5370   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5371 
5372   // The young gen rescan work will not be done as part of
5373   // process_strong_roots (which currently doesn't knw how to
5374   // parallelize such a scan), but rather will be broken up into
5375   // a set of parallel tasks (via the sampling that the [abortable]
5376   // preclean phase did of EdenSpace, plus the [two] tasks of
5377   // scanning the [two] survivor spaces. Further fine-grain
5378   // parallelization of the scanning of the survivor spaces
5379   // themselves, and of precleaning of the younger gen itself
5380   // is deferred to the future.
5381   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5382 
5383   // The dirty card rescan work is broken up into a "sequence"
5384   // of parallel tasks (per constituent space) that are dynamically
5385   // claimed by the parallel threads.
5386   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5387   perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5388 
5389   // It turns out that even when we're using 1 thread, doing the work in a
5390   // separate thread causes wide variance in run times.  We can't help this
5391   // in the multi-threaded case, but we special-case n=1 here to get
5392   // repeatable measurements of the 1-thread overhead of the parallel code.
5393   if (n_workers > 1) {
5394     // Make refs discovery MT-safe
5395     ReferenceProcessorMTMutator mt(ref_processor(), true);
5396     workers->run_task(&tsk);
5397   } else {
5398     tsk.work(0);
5399   }
5400   gch->set_par_threads(0);  // 0 ==> non-parallel.
5401   // restore, single-threaded for now, any preserved marks
5402   // as a result of work_q overflow
5403   restore_preserved_marks_if_any();
5404 }
5405 
5406 // Non-parallel version of remark
5407 void CMSCollector::do_remark_non_parallel() {
5408   ResourceMark rm;
5409   HandleMark   hm;
5410   GenCollectedHeap* gch = GenCollectedHeap::heap();
5411   MarkRefsIntoAndScanClosure
5412     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5413              &_markStack, &_revisitStack, this,
5414              false /* should_yield */, false /* not precleaning */);
5415   MarkFromDirtyCardsClosure
5416     markFromDirtyCardsClosure(this, _span,
5417                               NULL,  // space is set further below
5418                               &_markBitMap, &_markStack, &_revisitStack,
5419                               &mrias_cl);
5420   {
5421     TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5422     // Iterate over the dirty cards, marking them precleaned, and
5423     // setting the corresponding bits in the mod union table.
5424     {
5425       ModUnionClosure modUnionClosure(&_modUnionTable);
5426       _ct->ct_bs()->dirty_card_iterate(
5427                       _cmsGen->used_region(),
5428                       &modUnionClosure);
5429       _ct->ct_bs()->dirty_card_iterate(
5430                       _permGen->used_region(),
5431                       &modUnionClosure);
5432     }
5433     // Having transferred these marks into the modUnionTable, we just need
5434     // to rescan the marked objects on the dirty cards in the modUnionTable.
5435     // The initial marking may have been done during an asynchronous
5436     // collection so there may be dirty bits in the mod-union table.
5437     const int alignment =
5438       CardTableModRefBS::card_size * BitsPerWord;
5439     {
5440       // ... First handle dirty cards in CMS gen
5441       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5442       MemRegion ur = _cmsGen->used_region();
5443       HeapWord* lb = ur.start();
5444       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5445       MemRegion cms_span(lb, ub);
5446       _modUnionTable.dirty_range_iterate_clear(cms_span,
5447                                                &markFromDirtyCardsClosure);
5448       verify_work_stacks_empty();
5449       if (PrintCMSStatistics != 0) {
5450         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5451           markFromDirtyCardsClosure.num_dirty_cards());
5452       }
5453     }
5454     {
5455       // .. and then repeat for dirty cards in perm gen
5456       markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5457       MemRegion ur = _permGen->used_region();
5458       HeapWord* lb = ur.start();
5459       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5460       MemRegion perm_span(lb, ub);
5461       _modUnionTable.dirty_range_iterate_clear(perm_span,
5462                                                &markFromDirtyCardsClosure);
5463       verify_work_stacks_empty();
5464       if (PrintCMSStatistics != 0) {
5465         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5466           markFromDirtyCardsClosure.num_dirty_cards());
5467       }
5468     }
5469   }
5470   if (VerifyDuringGC &&
5471       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5472     HandleMark hm;  // Discard invalid handles created during verification
5473     Universe::verify(true);
5474   }
5475   {
5476     TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5477 
5478     verify_work_stacks_empty();
5479 
5480     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5481     gch->gen_process_strong_roots(_cmsGen->level(),
5482                                   true,  // younger gens as roots
5483                                   true,  // collecting perm gen
5484                                   SharedHeap::ScanningOption(roots_scanning_options()),
5485                                   NULL, &mrias_cl);
5486   }
5487   verify_work_stacks_empty();
5488   // Restore evacuated mark words, if any, used for overflow list links
5489   if (!CMSOverflowEarlyRestoration) {
5490     restore_preserved_marks_if_any();
5491   }
5492   verify_overflow_empty();
5493 }
5494 
5495 ////////////////////////////////////////////////////////
5496 // Parallel Reference Processing Task Proxy Class
5497 ////////////////////////////////////////////////////////
5498 class CMSRefProcTaskProxy: public AbstractGangTask {
5499   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5500   CMSCollector*          _collector;
5501   CMSBitMap*             _mark_bit_map;
5502   MemRegion              _span;
5503   OopTaskQueueSet*       _task_queues;
5504   ParallelTaskTerminator _term;
5505   ProcessTask&           _task;
5506 
5507 public:
5508   CMSRefProcTaskProxy(ProcessTask&     task,
5509                       CMSCollector*    collector,
5510                       const MemRegion& span,
5511                       CMSBitMap*       mark_bit_map,
5512                       int              total_workers,
5513                       OopTaskQueueSet* task_queues):
5514     AbstractGangTask("Process referents by policy in parallel"),
5515     _task(task),
5516     _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5517     _task_queues(task_queues),
5518     _term(total_workers, task_queues)
5519     { }
5520 
5521   OopTaskQueueSet* task_queues() { return _task_queues; }
5522 
5523   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5524 
5525   ParallelTaskTerminator* terminator() { return &_term; }
5526 
5527   void do_work_steal(int i,
5528                      CMSParDrainMarkingStackClosure* drain,
5529                      CMSParKeepAliveClosure* keep_alive,
5530                      int* seed);
5531 
5532   virtual void work(int i);
5533 };
5534 
5535 void CMSRefProcTaskProxy::work(int i) {
5536   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5537                                         _mark_bit_map, work_queue(i));
5538   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5539                                                  _mark_bit_map, work_queue(i));
5540   CMSIsAliveClosure is_alive_closure(_mark_bit_map);
5541   _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5542   if (_task.marks_oops_alive()) {
5543     do_work_steal(i, &par_drain_stack, &par_keep_alive,
5544                   _collector->hash_seed(i));
5545   }
5546   assert(work_queue(i)->size() == 0, "work_queue should be empty");
5547   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5548 }
5549 
5550 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5551   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5552   EnqueueTask& _task;
5553 
5554 public:
5555   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5556     : AbstractGangTask("Enqueue reference objects in parallel"),
5557       _task(task)
5558   { }
5559 
5560   virtual void work(int i)
5561   {
5562     _task.work(i);
5563   }
5564 };
5565 
5566 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5567   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5568    _collector(collector),
5569    _span(span),
5570    _bit_map(bit_map),
5571    _work_queue(work_queue),
5572    _mark_and_push(collector, span, bit_map, work_queue),
5573    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5574                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5575 { }
5576 
5577 // . see if we can share work_queues with ParNew? XXX
5578 void CMSRefProcTaskProxy::do_work_steal(int i,
5579   CMSParDrainMarkingStackClosure* drain,
5580   CMSParKeepAliveClosure* keep_alive,
5581   int* seed) {
5582   OopTaskQueue* work_q = work_queue(i);
5583   NOT_PRODUCT(int num_steals = 0;)
5584   oop obj_to_scan;
5585   size_t num_from_overflow_list =
5586            MIN2((size_t)work_q->max_elems()/4,
5587                 (size_t)ParGCDesiredObjsFromOverflowList);
5588 
5589   while (true) {
5590     // Completely finish any left over work from (an) earlier round(s)
5591     drain->trim_queue(0);
5592     // Now check if there's any work in the overflow list
5593     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5594                                                 work_q)) {
5595       // Found something in global overflow list;
5596       // not yet ready to go stealing work from others.
5597       // We'd like to assert(work_q->size() != 0, ...)
5598       // because we just took work from the overflow list,
5599       // but of course we can't, since all of that might have
5600       // been already stolen from us.
5601       continue;
5602     }
5603     // Verify that we have no work before we resort to stealing
5604     assert(work_q->size() == 0, "Have work, shouldn't steal");
5605     // Try to steal from other queues that have work
5606     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5607       NOT_PRODUCT(num_steals++;)
5608       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5609       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5610       // Do scanning work
5611       obj_to_scan->oop_iterate(keep_alive);
5612       // Loop around, finish this work, and try to steal some more
5613     } else if (terminator()->offer_termination()) {
5614       break;  // nirvana from the infinite cycle
5615     }
5616   }
5617   NOT_PRODUCT(
5618     if (PrintCMSStatistics != 0) {
5619       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5620     }
5621   )
5622 }
5623 
5624 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5625 {
5626   GenCollectedHeap* gch = GenCollectedHeap::heap();
5627   WorkGang* workers = gch->workers();
5628   assert(workers != NULL, "Need parallel worker threads.");
5629   int n_workers = workers->total_workers();
5630   CMSRefProcTaskProxy rp_task(task, &_collector,
5631                               _collector.ref_processor()->span(),
5632                               _collector.markBitMap(),
5633                               n_workers, _collector.task_queues());
5634   workers->run_task(&rp_task);
5635 }
5636 
5637 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5638 {
5639 
5640   GenCollectedHeap* gch = GenCollectedHeap::heap();
5641   WorkGang* workers = gch->workers();
5642   assert(workers != NULL, "Need parallel worker threads.");
5643   CMSRefEnqueueTaskProxy enq_task(task);
5644   workers->run_task(&enq_task);
5645 }
5646 
5647 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5648 
5649   ResourceMark rm;
5650   HandleMark   hm;
5651   ReferencePolicy* soft_ref_policy;
5652 
5653   assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete");
5654   // Process weak references.
5655   if (clear_all_soft_refs) {
5656     soft_ref_policy = new AlwaysClearPolicy();
5657   } else {
5658 #ifdef COMPILER2
5659     soft_ref_policy = new LRUMaxHeapPolicy();
5660 #else
5661     soft_ref_policy = new LRUCurrentHeapPolicy();
5662 #endif // COMPILER2
5663   }
5664   verify_work_stacks_empty();
5665 
5666   ReferenceProcessor* rp = ref_processor();
5667   assert(rp->span().equals(_span), "Spans should be equal");
5668   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5669                                           &_markStack);
5670   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5671                                 _span, &_markBitMap, &_markStack,
5672                                 &cmsKeepAliveClosure);
5673   {
5674     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5675     if (rp->processing_is_mt()) {
5676       CMSRefProcTaskExecutor task_executor(*this);
5677       rp->process_discovered_references(soft_ref_policy,
5678                                         &_is_alive_closure,
5679                                         &cmsKeepAliveClosure,
5680                                         &cmsDrainMarkingStackClosure,
5681                                         &task_executor);
5682     } else {
5683       rp->process_discovered_references(soft_ref_policy,
5684                                         &_is_alive_closure,
5685                                         &cmsKeepAliveClosure,
5686                                         &cmsDrainMarkingStackClosure,
5687                                         NULL);
5688     }
5689     verify_work_stacks_empty();
5690   }
5691 
5692   if (should_unload_classes()) {
5693     {
5694       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5695 
5696       // Follow SystemDictionary roots and unload classes
5697       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5698 
5699       // Follow CodeCache roots and unload any methods marked for unloading
5700       CodeCache::do_unloading(&_is_alive_closure,
5701                               &cmsKeepAliveClosure,
5702                               purged_class);
5703 
5704       cmsDrainMarkingStackClosure.do_void();
5705       verify_work_stacks_empty();
5706 
5707       // Update subklass/sibling/implementor links in KlassKlass descendants
5708       assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5709       oop k;
5710       while ((k = _revisitStack.pop()) != NULL) {
5711         ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5712                        &_is_alive_closure,
5713                        &cmsKeepAliveClosure);
5714       }
5715       assert(!ClassUnloading ||
5716              (_markStack.isEmpty() && overflow_list_is_empty()),
5717              "Should not have found new reachable objects");
5718       assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5719       cmsDrainMarkingStackClosure.do_void();
5720       verify_work_stacks_empty();
5721     }
5722 
5723     {
5724       TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5725       // Now clean up stale oops in SymbolTable and StringTable
5726       SymbolTable::unlink(&_is_alive_closure);
5727       StringTable::unlink(&_is_alive_closure);
5728     }
5729   }
5730 
5731   verify_work_stacks_empty();
5732   // Restore any preserved marks as a result of mark stack or
5733   // work queue overflow
5734   restore_preserved_marks_if_any();  // done single-threaded for now
5735 
5736   rp->set_enqueuing_is_done(true);
5737   if (rp->processing_is_mt()) {
5738     CMSRefProcTaskExecutor task_executor(*this);
5739     rp->enqueue_discovered_references(&task_executor);
5740   } else {
5741     rp->enqueue_discovered_references(NULL);
5742   }
5743   rp->verify_no_references_recorded();
5744   assert(!rp->discovery_enabled(), "should have been disabled");
5745 
5746   // JVMTI object tagging is based on JNI weak refs. If any of these
5747   // refs were cleared then JVMTI needs to update its maps and
5748   // maybe post ObjectFrees to agents.
5749   JvmtiExport::cms_ref_processing_epilogue();
5750 }
5751 
5752 #ifndef PRODUCT
5753 void CMSCollector::check_correct_thread_executing() {
5754   Thread* t = Thread::current();
5755   // Only the VM thread or the CMS thread should be here.
5756   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5757          "Unexpected thread type");
5758   // If this is the vm thread, the foreground process
5759   // should not be waiting.  Note that _foregroundGCIsActive is
5760   // true while the foreground collector is waiting.
5761   if (_foregroundGCShouldWait) {
5762     // We cannot be the VM thread
5763     assert(t->is_ConcurrentGC_thread(),
5764            "Should be CMS thread");
5765   } else {
5766     // We can be the CMS thread only if we are in a stop-world
5767     // phase of CMS collection.
5768     if (t->is_ConcurrentGC_thread()) {
5769       assert(_collectorState == InitialMarking ||
5770              _collectorState == FinalMarking,
5771              "Should be a stop-world phase");
5772       // The CMS thread should be holding the CMS_token.
5773       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5774              "Potential interference with concurrently "
5775              "executing VM thread");
5776     }
5777   }
5778 }
5779 #endif
5780 
5781 void CMSCollector::sweep(bool asynch) {
5782   assert(_collectorState == Sweeping, "just checking");
5783   check_correct_thread_executing();
5784   verify_work_stacks_empty();
5785   verify_overflow_empty();
5786   increment_sweep_count();
5787   _sweep_timer.stop();
5788   _sweep_estimate.sample(_sweep_timer.seconds());
5789   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5790 
5791   // PermGen verification support: If perm gen sweeping is disabled in
5792   // this cycle, we preserve the perm gen object "deadness" information
5793   // in the perm_gen_verify_bit_map. In order to do that we traverse
5794   // all blocks in perm gen and mark all dead objects.
5795   if (verifying() && !should_unload_classes()) {
5796     assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5797            "Should have already been allocated");
5798     MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5799                                markBitMap(), perm_gen_verify_bit_map());
5800     if (asynch) {
5801       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5802                                bitMapLock());
5803       _permGen->cmsSpace()->blk_iterate(&mdo);
5804     } else {
5805       // In the case of synchronous sweep, we already have
5806       // the requisite locks/tokens.
5807       _permGen->cmsSpace()->blk_iterate(&mdo);
5808     }
5809   }
5810 
5811   if (asynch) {
5812     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5813     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5814     // First sweep the old gen then the perm gen
5815     {
5816       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5817                                bitMapLock());
5818       sweepWork(_cmsGen, asynch);
5819     }
5820 
5821     // Now repeat for perm gen
5822     if (should_unload_classes()) {
5823       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5824                              bitMapLock());
5825       sweepWork(_permGen, asynch);
5826     }
5827 
5828     // Update Universe::_heap_*_at_gc figures.
5829     // We need all the free list locks to make the abstract state
5830     // transition from Sweeping to Resetting. See detailed note
5831     // further below.
5832     {
5833       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5834                                _permGen->freelistLock());
5835       // Update heap occupancy information which is used as
5836       // input to soft ref clearing policy at the next gc.
5837       Universe::update_heap_info_at_gc();
5838       _collectorState = Resizing;
5839     }
5840   } else {
5841     // already have needed locks
5842     sweepWork(_cmsGen,  asynch);
5843 
5844     if (should_unload_classes()) {
5845       sweepWork(_permGen, asynch);
5846     }
5847     // Update heap occupancy information which is used as
5848     // input to soft ref clearing policy at the next gc.
5849     Universe::update_heap_info_at_gc();
5850     _collectorState = Resizing;
5851   }
5852   verify_work_stacks_empty();
5853   verify_overflow_empty();
5854 
5855   _sweep_timer.reset();
5856   _sweep_timer.start();
5857 
5858   update_time_of_last_gc(os::javaTimeMillis());
5859 
5860   // NOTE on abstract state transitions:
5861   // Mutators allocate-live and/or mark the mod-union table dirty
5862   // based on the state of the collection.  The former is done in
5863   // the interval [Marking, Sweeping] and the latter in the interval
5864   // [Marking, Sweeping).  Thus the transitions into the Marking state
5865   // and out of the Sweeping state must be synchronously visible
5866   // globally to the mutators.
5867   // The transition into the Marking state happens with the world
5868   // stopped so the mutators will globally see it.  Sweeping is
5869   // done asynchronously by the background collector so the transition
5870   // from the Sweeping state to the Resizing state must be done
5871   // under the freelistLock (as is the check for whether to
5872   // allocate-live and whether to dirty the mod-union table).
5873   assert(_collectorState == Resizing, "Change of collector state to"
5874     " Resizing must be done under the freelistLocks (plural)");
5875 
5876   // Now that sweeping has been completed, if the GCH's
5877   // incremental_collection_will_fail flag is set, clear it,
5878   // thus inviting a younger gen collection to promote into
5879   // this generation. If such a promotion may still fail,
5880   // the flag will be set again when a young collection is
5881   // attempted.
5882   // I think the incremental_collection_will_fail flag's use
5883   // is specific to a 2 generation collection policy, so i'll
5884   // assert that that's the configuration we are operating within.
5885   // The use of the flag can and should be generalized appropriately
5886   // in the future to deal with a general n-generation system.
5887 
5888   GenCollectedHeap* gch = GenCollectedHeap::heap();
5889   assert(gch->collector_policy()->is_two_generation_policy(),
5890          "Resetting of incremental_collection_will_fail flag"
5891          " may be incorrect otherwise");
5892   gch->clear_incremental_collection_will_fail();
5893   gch->update_full_collections_completed(_collection_count_start);
5894 }
5895 
5896 // FIX ME!!! Looks like this belongs in CFLSpace, with
5897 // CMSGen merely delegating to it.
5898 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5899   double nearLargestPercent = 0.999;
5900   HeapWord*  minAddr        = _cmsSpace->bottom();
5901   HeapWord*  largestAddr    =
5902     (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5903   if (largestAddr == 0) {
5904     // The dictionary appears to be empty.  In this case
5905     // try to coalesce at the end of the heap.
5906     largestAddr = _cmsSpace->end();
5907   }
5908   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5909   size_t nearLargestOffset =
5910     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5911   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5912 }
5913 
5914 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5915   return addr >= _cmsSpace->nearLargestChunk();
5916 }
5917 
5918 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5919   return _cmsSpace->find_chunk_at_end();
5920 }
5921 
5922 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5923                                                     bool full) {
5924   // The next lower level has been collected.  Gather any statistics
5925   // that are of interest at this point.
5926   if (!full && (current_level + 1) == level()) {
5927     // Gather statistics on the young generation collection.
5928     collector()->stats().record_gc0_end(used());
5929   }
5930 }
5931 
5932 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
5933   GenCollectedHeap* gch = GenCollectedHeap::heap();
5934   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
5935     "Wrong type of heap");
5936   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
5937     gch->gen_policy()->size_policy();
5938   assert(sp->is_gc_cms_adaptive_size_policy(),
5939     "Wrong type of size policy");
5940   return sp;
5941 }
5942 
5943 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
5944   if (PrintGCDetails && Verbose) {
5945     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
5946   }
5947   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
5948   _debug_collection_type =
5949     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
5950   if (PrintGCDetails && Verbose) {
5951     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
5952   }
5953 }
5954 
5955 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
5956   bool asynch) {
5957   // We iterate over the space(s) underlying this generation,
5958   // checking the mark bit map to see if the bits corresponding
5959   // to specific blocks are marked or not. Blocks that are
5960   // marked are live and are not swept up. All remaining blocks
5961   // are swept up, with coalescing on-the-fly as we sweep up
5962   // contiguous free and/or garbage blocks:
5963   // We need to ensure that the sweeper synchronizes with allocators
5964   // and stop-the-world collectors. In particular, the following
5965   // locks are used:
5966   // . CMS token: if this is held, a stop the world collection cannot occur
5967   // . freelistLock: if this is held no allocation can occur from this
5968   //                 generation by another thread
5969   // . bitMapLock: if this is held, no other thread can access or update
5970   //
5971 
5972   // Note that we need to hold the freelistLock if we use
5973   // block iterate below; else the iterator might go awry if
5974   // a mutator (or promotion) causes block contents to change
5975   // (for instance if the allocator divvies up a block).
5976   // If we hold the free list lock, for all practical purposes
5977   // young generation GC's can't occur (they'll usually need to
5978   // promote), so we might as well prevent all young generation
5979   // GC's while we do a sweeping step. For the same reason, we might
5980   // as well take the bit map lock for the entire duration
5981 
5982   // check that we hold the requisite locks
5983   assert(have_cms_token(), "Should hold cms token");
5984   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
5985          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
5986         "Should possess CMS token to sweep");
5987   assert_lock_strong(gen->freelistLock());
5988   assert_lock_strong(bitMapLock());
5989 
5990   assert(!_sweep_timer.is_active(), "Was switched off in an outer context");
5991   gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
5992                                       _sweep_estimate.padded_average());
5993   gen->setNearLargestChunk();
5994 
5995   {
5996     SweepClosure sweepClosure(this, gen, &_markBitMap,
5997                             CMSYield && asynch);
5998     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5999     // We need to free-up/coalesce garbage/blocks from a
6000     // co-terminal free run. This is done in the SweepClosure
6001     // destructor; so, do not remove this scope, else the
6002     // end-of-sweep-census below will be off by a little bit.
6003   }
6004   gen->cmsSpace()->sweep_completed();
6005   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6006   if (should_unload_classes()) {                // unloaded classes this cycle,
6007     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6008   } else {                                      // did not unload classes,
6009     _concurrent_cycles_since_last_unload++;     // ... increment count
6010   }
6011 }
6012 
6013 // Reset CMS data structures (for now just the marking bit map)
6014 // preparatory for the next cycle.
6015 void CMSCollector::reset(bool asynch) {
6016   GenCollectedHeap* gch = GenCollectedHeap::heap();
6017   CMSAdaptiveSizePolicy* sp = size_policy();
6018   AdaptiveSizePolicyOutput(sp, gch->total_collections());
6019   if (asynch) {
6020     CMSTokenSyncWithLocks ts(true, bitMapLock());
6021 
6022     // If the state is not "Resetting", the foreground  thread
6023     // has done a collection and the resetting.
6024     if (_collectorState != Resetting) {
6025       assert(_collectorState == Idling, "The state should only change"
6026         " because the foreground collector has finished the collection");
6027       return;
6028     }
6029 
6030     // Clear the mark bitmap (no grey objects to start with)
6031     // for the next cycle.
6032     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6033     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6034 
6035     HeapWord* curAddr = _markBitMap.startWord();
6036     while (curAddr < _markBitMap.endWord()) {
6037       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6038       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6039       _markBitMap.clear_large_range(chunk);
6040       if (ConcurrentMarkSweepThread::should_yield() &&
6041           !foregroundGCIsActive() &&
6042           CMSYield) {
6043         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6044                "CMS thread should hold CMS token");
6045         assert_lock_strong(bitMapLock());
6046         bitMapLock()->unlock();
6047         ConcurrentMarkSweepThread::desynchronize(true);
6048         ConcurrentMarkSweepThread::acknowledge_yield_request();
6049         stopTimer();
6050         if (PrintCMSStatistics != 0) {
6051           incrementYields();
6052         }
6053         icms_wait();
6054 
6055         // See the comment in coordinator_yield()
6056         for (unsigned i = 0; i < CMSYieldSleepCount &&
6057                         ConcurrentMarkSweepThread::should_yield() &&
6058                         !CMSCollector::foregroundGCIsActive(); ++i) {
6059           os::sleep(Thread::current(), 1, false);
6060           ConcurrentMarkSweepThread::acknowledge_yield_request();
6061         }
6062 
6063         ConcurrentMarkSweepThread::synchronize(true);
6064         bitMapLock()->lock_without_safepoint_check();
6065         startTimer();
6066       }
6067       curAddr = chunk.end();
6068     }
6069     _collectorState = Idling;
6070   } else {
6071     // already have the lock
6072     assert(_collectorState == Resetting, "just checking");
6073     assert_lock_strong(bitMapLock());
6074     _markBitMap.clear_all();
6075     _collectorState = Idling;
6076   }
6077 
6078   // Stop incremental mode after a cycle completes, so that any future cycles
6079   // are triggered by allocation.
6080   stop_icms();
6081 
6082   NOT_PRODUCT(
6083     if (RotateCMSCollectionTypes) {
6084       _cmsGen->rotate_debug_collection_type();
6085     }
6086   )
6087 }
6088 
6089 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6090   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6091   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6092   TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6093   TraceCollectorStats tcs(counters());
6094 
6095   switch (op) {
6096     case CMS_op_checkpointRootsInitial: {
6097       checkpointRootsInitial(true);       // asynch
6098       if (PrintGC) {
6099         _cmsGen->printOccupancy("initial-mark");
6100       }
6101       break;
6102     }
6103     case CMS_op_checkpointRootsFinal: {
6104       checkpointRootsFinal(true,    // asynch
6105                            false,   // !clear_all_soft_refs
6106                            false);  // !init_mark_was_synchronous
6107       if (PrintGC) {
6108         _cmsGen->printOccupancy("remark");
6109       }
6110       break;
6111     }
6112     default:
6113       fatal("No such CMS_op");
6114   }
6115 }
6116 
6117 #ifndef PRODUCT
6118 size_t const CMSCollector::skip_header_HeapWords() {
6119   return FreeChunk::header_size();
6120 }
6121 
6122 // Try and collect here conditions that should hold when
6123 // CMS thread is exiting. The idea is that the foreground GC
6124 // thread should not be blocked if it wants to terminate
6125 // the CMS thread and yet continue to run the VM for a while
6126 // after that.
6127 void CMSCollector::verify_ok_to_terminate() const {
6128   assert(Thread::current()->is_ConcurrentGC_thread(),
6129          "should be called by CMS thread");
6130   assert(!_foregroundGCShouldWait, "should be false");
6131   // We could check here that all the various low-level locks
6132   // are not held by the CMS thread, but that is overkill; see
6133   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6134   // is checked.
6135 }
6136 #endif
6137 
6138 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6139   assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6140          "missing Printezis mark?");
6141   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6142   size_t size = pointer_delta(nextOneAddr + 1, addr);
6143   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6144          "alignment problem");
6145   assert(size >= 3, "Necessary for Printezis marks to work");
6146   return size;
6147 }
6148 
6149 // A variant of the above (block_size_using_printezis_bits()) except
6150 // that we return 0 if the P-bits are not yet set.
6151 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6152   if (_markBitMap.isMarked(addr)) {
6153     assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6154     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6155     size_t size = pointer_delta(nextOneAddr + 1, addr);
6156     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6157            "alignment problem");
6158     assert(size >= 3, "Necessary for Printezis marks to work");
6159     return size;
6160   } else {
6161     assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6162     return 0;
6163   }
6164 }
6165 
6166 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6167   size_t sz = 0;
6168   oop p = (oop)addr;
6169   if (p->klass() != NULL && p->is_parsable()) {
6170     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6171   } else {
6172     sz = block_size_using_printezis_bits(addr);
6173   }
6174   assert(sz > 0, "size must be nonzero");
6175   HeapWord* next_block = addr + sz;
6176   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6177                                              CardTableModRefBS::card_size);
6178   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6179          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6180          "must be different cards");
6181   return next_card;
6182 }
6183 
6184 
6185 // CMS Bit Map Wrapper /////////////////////////////////////////
6186 
6187 // Construct a CMS bit map infrastructure, but don't create the
6188 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6189 // further below.
6190 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6191   _bm(NULL,0),
6192   _shifter(shifter),
6193   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6194 {
6195   _bmStartWord = 0;
6196   _bmWordSize  = 0;
6197 }
6198 
6199 bool CMSBitMap::allocate(MemRegion mr) {
6200   _bmStartWord = mr.start();
6201   _bmWordSize  = mr.word_size();
6202   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6203                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6204   if (!brs.is_reserved()) {
6205     warning("CMS bit map allocation failure");
6206     return false;
6207   }
6208   // For now we'll just commit all of the bit map up fromt.
6209   // Later on we'll try to be more parsimonious with swap.
6210   if (!_virtual_space.initialize(brs, brs.size())) {
6211     warning("CMS bit map backing store failure");
6212     return false;
6213   }
6214   assert(_virtual_space.committed_size() == brs.size(),
6215          "didn't reserve backing store for all of CMS bit map?");
6216   _bm.set_map((uintptr_t*)_virtual_space.low());
6217   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6218          _bmWordSize, "inconsistency in bit map sizing");
6219   _bm.set_size(_bmWordSize >> _shifter);
6220 
6221   // bm.clear(); // can we rely on getting zero'd memory? verify below
6222   assert(isAllClear(),
6223          "Expected zero'd memory from ReservedSpace constructor");
6224   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6225          "consistency check");
6226   return true;
6227 }
6228 
6229 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6230   HeapWord *next_addr, *end_addr, *last_addr;
6231   assert_locked();
6232   assert(covers(mr), "out-of-range error");
6233   // XXX assert that start and end are appropriately aligned
6234   for (next_addr = mr.start(), end_addr = mr.end();
6235        next_addr < end_addr; next_addr = last_addr) {
6236     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6237     last_addr = dirty_region.end();
6238     if (!dirty_region.is_empty()) {
6239       cl->do_MemRegion(dirty_region);
6240     } else {
6241       assert(last_addr == end_addr, "program logic");
6242       return;
6243     }
6244   }
6245 }
6246 
6247 #ifndef PRODUCT
6248 void CMSBitMap::assert_locked() const {
6249   CMSLockVerifier::assert_locked(lock());
6250 }
6251 
6252 bool CMSBitMap::covers(MemRegion mr) const {
6253   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6254   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6255          "size inconsistency");
6256   return (mr.start() >= _bmStartWord) &&
6257          (mr.end()   <= endWord());
6258 }
6259 
6260 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6261     return (start >= _bmStartWord && (start + size) <= endWord());
6262 }
6263 
6264 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6265   // verify that there are no 1 bits in the interval [left, right)
6266   FalseBitMapClosure falseBitMapClosure;
6267   iterate(&falseBitMapClosure, left, right);
6268 }
6269 
6270 void CMSBitMap::region_invariant(MemRegion mr)
6271 {
6272   assert_locked();
6273   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6274   assert(!mr.is_empty(), "unexpected empty region");
6275   assert(covers(mr), "mr should be covered by bit map");
6276   // convert address range into offset range
6277   size_t start_ofs = heapWordToOffset(mr.start());
6278   // Make sure that end() is appropriately aligned
6279   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6280                         (1 << (_shifter+LogHeapWordSize))),
6281          "Misaligned mr.end()");
6282   size_t end_ofs   = heapWordToOffset(mr.end());
6283   assert(end_ofs > start_ofs, "Should mark at least one bit");
6284 }
6285 
6286 #endif
6287 
6288 bool CMSMarkStack::allocate(size_t size) {
6289   // allocate a stack of the requisite depth
6290   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6291                    size * sizeof(oop)));
6292   if (!rs.is_reserved()) {
6293     warning("CMSMarkStack allocation failure");
6294     return false;
6295   }
6296   if (!_virtual_space.initialize(rs, rs.size())) {
6297     warning("CMSMarkStack backing store failure");
6298     return false;
6299   }
6300   assert(_virtual_space.committed_size() == rs.size(),
6301          "didn't reserve backing store for all of CMS stack?");
6302   _base = (oop*)(_virtual_space.low());
6303   _index = 0;
6304   _capacity = size;
6305   NOT_PRODUCT(_max_depth = 0);
6306   return true;
6307 }
6308 
6309 // XXX FIX ME !!! In the MT case we come in here holding a
6310 // leaf lock. For printing we need to take a further lock
6311 // which has lower rank. We need to recallibrate the two
6312 // lock-ranks involved in order to be able to rpint the
6313 // messages below. (Or defer the printing to the caller.
6314 // For now we take the expedient path of just disabling the
6315 // messages for the problematic case.)
6316 void CMSMarkStack::expand() {
6317   assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted");
6318   if (_capacity == CMSMarkStackSizeMax) {
6319     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6320       // We print a warning message only once per CMS cycle.
6321       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6322     }
6323     return;
6324   }
6325   // Double capacity if possible
6326   size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax);
6327   // Do not give up existing stack until we have managed to
6328   // get the double capacity that we desired.
6329   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6330                    new_capacity * sizeof(oop)));
6331   if (rs.is_reserved()) {
6332     // Release the backing store associated with old stack
6333     _virtual_space.release();
6334     // Reinitialize virtual space for new stack
6335     if (!_virtual_space.initialize(rs, rs.size())) {
6336       fatal("Not enough swap for expanded marking stack");
6337     }
6338     _base = (oop*)(_virtual_space.low());
6339     _index = 0;
6340     _capacity = new_capacity;
6341   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6342     // Failed to double capacity, continue;
6343     // we print a detail message only once per CMS cycle.
6344     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6345             SIZE_FORMAT"K",
6346             _capacity / K, new_capacity / K);
6347   }
6348 }
6349 
6350 
6351 // Closures
6352 // XXX: there seems to be a lot of code  duplication here;
6353 // should refactor and consolidate common code.
6354 
6355 // This closure is used to mark refs into the CMS generation in
6356 // the CMS bit map. Called at the first checkpoint. This closure
6357 // assumes that we do not need to re-mark dirty cards; if the CMS
6358 // generation on which this is used is not an oldest (modulo perm gen)
6359 // generation then this will lose younger_gen cards!
6360 
6361 MarkRefsIntoClosure::MarkRefsIntoClosure(
6362   MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods):
6363     _span(span),
6364     _bitMap(bitMap),
6365     _should_do_nmethods(should_do_nmethods)
6366 {
6367     assert(_ref_processor == NULL, "deliberately left NULL");
6368     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6369 }
6370 
6371 void MarkRefsIntoClosure::do_oop(oop* p) {
6372   // if p points into _span, then mark corresponding bit in _markBitMap
6373   oop thisOop = *p;
6374   if (thisOop != NULL) {
6375     assert(thisOop->is_oop(), "expected an oop");
6376     HeapWord* addr = (HeapWord*)thisOop;
6377     if (_span.contains(addr)) {
6378       // this should be made more efficient
6379       _bitMap->mark(addr);
6380     }
6381   }
6382 }
6383 
6384 // A variant of the above, used for CMS marking verification.
6385 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6386   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6387   bool should_do_nmethods):
6388     _span(span),
6389     _verification_bm(verification_bm),
6390     _cms_bm(cms_bm),
6391     _should_do_nmethods(should_do_nmethods) {
6392     assert(_ref_processor == NULL, "deliberately left NULL");
6393     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6394 }
6395 
6396 void MarkRefsIntoVerifyClosure::do_oop(oop* p) {
6397   // if p points into _span, then mark corresponding bit in _markBitMap
6398   oop this_oop = *p;
6399   if (this_oop != NULL) {
6400     assert(this_oop->is_oop(), "expected an oop");
6401     HeapWord* addr = (HeapWord*)this_oop;
6402     if (_span.contains(addr)) {
6403       _verification_bm->mark(addr);
6404       if (!_cms_bm->isMarked(addr)) {
6405         oop(addr)->print();
6406         gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
6407         fatal("... aborting");
6408       }
6409     }
6410   }
6411 }
6412 
6413 //////////////////////////////////////////////////
6414 // MarkRefsIntoAndScanClosure
6415 //////////////////////////////////////////////////
6416 
6417 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6418                                                        ReferenceProcessor* rp,
6419                                                        CMSBitMap* bit_map,
6420                                                        CMSBitMap* mod_union_table,
6421                                                        CMSMarkStack*  mark_stack,
6422                                                        CMSMarkStack*  revisit_stack,
6423                                                        CMSCollector* collector,
6424                                                        bool should_yield,
6425                                                        bool concurrent_precleaning):
6426   _collector(collector),
6427   _span(span),
6428   _bit_map(bit_map),
6429   _mark_stack(mark_stack),
6430   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6431                       mark_stack, revisit_stack, concurrent_precleaning),
6432   _yield(should_yield),
6433   _concurrent_precleaning(concurrent_precleaning),
6434   _freelistLock(NULL)
6435 {
6436   _ref_processor = rp;
6437   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6438 }
6439 
6440 // This closure is used to mark refs into the CMS generation at the
6441 // second (final) checkpoint, and to scan and transitively follow
6442 // the unmarked oops. It is also used during the concurrent precleaning
6443 // phase while scanning objects on dirty cards in the CMS generation.
6444 // The marks are made in the marking bit map and the marking stack is
6445 // used for keeping the (newly) grey objects during the scan.
6446 // The parallel version (Par_...) appears further below.
6447 void MarkRefsIntoAndScanClosure::do_oop(oop* p) {
6448   oop this_oop = *p;
6449   if (this_oop != NULL) {
6450     assert(this_oop->is_oop(), "expected an oop");
6451     HeapWord* addr = (HeapWord*)this_oop;
6452     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6453     assert(_collector->overflow_list_is_empty(), "should be empty");
6454     if (_span.contains(addr) &&
6455         !_bit_map->isMarked(addr)) {
6456       // mark bit map (object is now grey)
6457       _bit_map->mark(addr);
6458       // push on marking stack (stack should be empty), and drain the
6459       // stack by applying this closure to the oops in the oops popped
6460       // from the stack (i.e. blacken the grey objects)
6461       bool res = _mark_stack->push(this_oop);
6462       assert(res, "Should have space to push on empty stack");
6463       do {
6464         oop new_oop = _mark_stack->pop();
6465         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6466         assert(new_oop->is_parsable(), "Found unparsable oop");
6467         assert(_bit_map->isMarked((HeapWord*)new_oop),
6468                "only grey objects on this stack");
6469         // iterate over the oops in this oop, marking and pushing
6470         // the ones in CMS heap (i.e. in _span).
6471         new_oop->oop_iterate(&_pushAndMarkClosure);
6472         // check if it's time to yield
6473         do_yield_check();
6474       } while (!_mark_stack->isEmpty() ||
6475                (!_concurrent_precleaning && take_from_overflow_list()));
6476         // if marking stack is empty, and we are not doing this
6477         // during precleaning, then check the overflow list
6478     }
6479     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6480     assert(_collector->overflow_list_is_empty(),
6481            "overflow list was drained above");
6482     // We could restore evacuated mark words, if any, used for
6483     // overflow list links here because the overflow list is
6484     // provably empty here. That would reduce the maximum
6485     // size requirements for preserved_{oop,mark}_stack.
6486     // But we'll just postpone it until we are all done
6487     // so we can just stream through.
6488     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6489       _collector->restore_preserved_marks_if_any();
6490       assert(_collector->no_preserved_marks(), "No preserved marks");
6491     }
6492     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6493            "All preserved marks should have been restored above");
6494   }
6495 }
6496 
6497 void MarkRefsIntoAndScanClosure::do_yield_work() {
6498   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6499          "CMS thread should hold CMS token");
6500   assert_lock_strong(_freelistLock);
6501   assert_lock_strong(_bit_map->lock());
6502   // relinquish the free_list_lock and bitMaplock()
6503   _bit_map->lock()->unlock();
6504   _freelistLock->unlock();
6505   ConcurrentMarkSweepThread::desynchronize(true);
6506   ConcurrentMarkSweepThread::acknowledge_yield_request();
6507   _collector->stopTimer();
6508   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6509   if (PrintCMSStatistics != 0) {
6510     _collector->incrementYields();
6511   }
6512   _collector->icms_wait();
6513 
6514   // See the comment in coordinator_yield()
6515   for (unsigned i = 0; i < CMSYieldSleepCount &&
6516                        ConcurrentMarkSweepThread::should_yield() &&
6517                        !CMSCollector::foregroundGCIsActive(); ++i) {
6518     os::sleep(Thread::current(), 1, false);
6519     ConcurrentMarkSweepThread::acknowledge_yield_request();
6520   }
6521 
6522   ConcurrentMarkSweepThread::synchronize(true);
6523   _freelistLock->lock_without_safepoint_check();
6524   _bit_map->lock()->lock_without_safepoint_check();
6525   _collector->startTimer();
6526 }
6527 
6528 ///////////////////////////////////////////////////////////
6529 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6530 //                                 MarkRefsIntoAndScanClosure
6531 ///////////////////////////////////////////////////////////
6532 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6533   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6534   CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack*  revisit_stack):
6535   _span(span),
6536   _bit_map(bit_map),
6537   _work_queue(work_queue),
6538   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6539                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6540   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6541                           revisit_stack)
6542 {
6543   _ref_processor = rp;
6544   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6545 }
6546 
6547 // This closure is used to mark refs into the CMS generation at the
6548 // second (final) checkpoint, and to scan and transitively follow
6549 // the unmarked oops. The marks are made in the marking bit map and
6550 // the work_queue is used for keeping the (newly) grey objects during
6551 // the scan phase whence they are also available for stealing by parallel
6552 // threads. Since the marking bit map is shared, updates are
6553 // synchronized (via CAS).
6554 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) {
6555   oop this_oop = *p;
6556   if (this_oop != NULL) {
6557     // Ignore mark word because this could be an already marked oop
6558     // that may be chained at the end of the overflow list.
6559     assert(this_oop->is_oop(true /* ignore mark word */), "expected an oop");
6560     HeapWord* addr = (HeapWord*)this_oop;
6561     if (_span.contains(addr) &&
6562         !_bit_map->isMarked(addr)) {
6563       // mark bit map (object will become grey):
6564       // It is possible for several threads to be
6565       // trying to "claim" this object concurrently;
6566       // the unique thread that succeeds in marking the
6567       // object first will do the subsequent push on
6568       // to the work queue (or overflow list).
6569       if (_bit_map->par_mark(addr)) {
6570         // push on work_queue (which may not be empty), and trim the
6571         // queue to an appropriate length by applying this closure to
6572         // the oops in the oops popped from the stack (i.e. blacken the
6573         // grey objects)
6574         bool res = _work_queue->push(this_oop);
6575         assert(res, "Low water mark should be less than capacity?");
6576         trim_queue(_low_water_mark);
6577       } // Else, another thread claimed the object
6578     }
6579   }
6580 }
6581 
6582 // This closure is used to rescan the marked objects on the dirty cards
6583 // in the mod union table and the card table proper.
6584 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6585   oop p, MemRegion mr) {
6586 
6587   size_t size = 0;
6588   HeapWord* addr = (HeapWord*)p;
6589   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6590   assert(_span.contains(addr), "we are scanning the CMS generation");
6591   // check if it's time to yield
6592   if (do_yield_check()) {
6593     // We yielded for some foreground stop-world work,
6594     // and we have been asked to abort this ongoing preclean cycle.
6595     return 0;
6596   }
6597   if (_bitMap->isMarked(addr)) {
6598     // it's marked; is it potentially uninitialized?
6599     if (p->klass() != NULL) {
6600       if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
6601         // Signal precleaning to redirty the card since
6602         // the klass pointer is already installed.
6603         assert(size == 0, "Initial value");
6604       } else {
6605         assert(p->is_parsable(), "must be parsable.");
6606         // an initialized object; ignore mark word in verification below
6607         // since we are running concurrent with mutators
6608         assert(p->is_oop(true), "should be an oop");
6609         if (p->is_objArray()) {
6610           // objArrays are precisely marked; restrict scanning
6611           // to dirty cards only.
6612           size = p->oop_iterate(_scanningClosure, mr);
6613           assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6614                  "adjustObjectSize should be the identity for array sizes, "
6615                  "which are necessarily larger than minimum object size of "
6616                  "two heap words");
6617         } else {
6618           // A non-array may have been imprecisely marked; we need
6619           // to scan object in its entirety.
6620           size = CompactibleFreeListSpace::adjustObjectSize(
6621                    p->oop_iterate(_scanningClosure));
6622         }
6623         #ifdef DEBUG
6624           size_t direct_size =
6625             CompactibleFreeListSpace::adjustObjectSize(p->size());
6626           assert(size == direct_size, "Inconsistency in size");
6627           assert(size >= 3, "Necessary for Printezis marks to work");
6628           if (!_bitMap->isMarked(addr+1)) {
6629             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6630           } else {
6631             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6632             assert(_bitMap->isMarked(addr+size-1),
6633                    "inconsistent Printezis mark");
6634           }
6635         #endif // DEBUG
6636       }
6637     } else {
6638       // an unitialized object
6639       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6640       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6641       size = pointer_delta(nextOneAddr + 1, addr);
6642       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6643              "alignment problem");
6644       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6645       // will dirty the card when the klass pointer is installed in the
6646       // object (signalling the completion of initialization).
6647     }
6648   } else {
6649     // Either a not yet marked object or an uninitialized object
6650     if (p->klass() == NULL || !p->is_parsable()) {
6651       // An uninitialized object, skip to the next card, since
6652       // we may not be able to read its P-bits yet.
6653       assert(size == 0, "Initial value");
6654     } else {
6655       // An object not (yet) reached by marking: we merely need to
6656       // compute its size so as to go look at the next block.
6657       assert(p->is_oop(true), "should be an oop");
6658       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6659     }
6660   }
6661   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6662   return size;
6663 }
6664 
6665 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6666   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6667          "CMS thread should hold CMS token");
6668   assert_lock_strong(_freelistLock);
6669   assert_lock_strong(_bitMap->lock());
6670   // relinquish the free_list_lock and bitMaplock()
6671   _bitMap->lock()->unlock();
6672   _freelistLock->unlock();
6673   ConcurrentMarkSweepThread::desynchronize(true);
6674   ConcurrentMarkSweepThread::acknowledge_yield_request();
6675   _collector->stopTimer();
6676   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6677   if (PrintCMSStatistics != 0) {
6678     _collector->incrementYields();
6679   }
6680   _collector->icms_wait();
6681 
6682   // See the comment in coordinator_yield()
6683   for (unsigned i = 0; i < CMSYieldSleepCount &&
6684                        ConcurrentMarkSweepThread::should_yield() &&
6685                        !CMSCollector::foregroundGCIsActive(); ++i) {
6686     os::sleep(Thread::current(), 1, false);
6687     ConcurrentMarkSweepThread::acknowledge_yield_request();
6688   }
6689 
6690   ConcurrentMarkSweepThread::synchronize(true);
6691   _freelistLock->lock_without_safepoint_check();
6692   _bitMap->lock()->lock_without_safepoint_check();
6693   _collector->startTimer();
6694 }
6695 
6696 
6697 //////////////////////////////////////////////////////////////////
6698 // SurvivorSpacePrecleanClosure
6699 //////////////////////////////////////////////////////////////////
6700 // This (single-threaded) closure is used to preclean the oops in
6701 // the survivor spaces.
6702 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6703 
6704   HeapWord* addr = (HeapWord*)p;
6705   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6706   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6707   assert(p->klass() != NULL, "object should be initializd");
6708   assert(p->is_parsable(), "must be parsable.");
6709   // an initialized object; ignore mark word in verification below
6710   // since we are running concurrent with mutators
6711   assert(p->is_oop(true), "should be an oop");
6712   // Note that we do not yield while we iterate over
6713   // the interior oops of p, pushing the relevant ones
6714   // on our marking stack.
6715   size_t size = p->oop_iterate(_scanning_closure);
6716   do_yield_check();
6717   // Observe that below, we do not abandon the preclean
6718   // phase as soon as we should; rather we empty the
6719   // marking stack before returning. This is to satisfy
6720   // some existing assertions. In general, it may be a
6721   // good idea to abort immediately and complete the marking
6722   // from the grey objects at a later time.
6723   while (!_mark_stack->isEmpty()) {
6724     oop new_oop = _mark_stack->pop();
6725     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6726     assert(new_oop->is_parsable(), "Found unparsable oop");
6727     assert(_bit_map->isMarked((HeapWord*)new_oop),
6728            "only grey objects on this stack");
6729     // iterate over the oops in this oop, marking and pushing
6730     // the ones in CMS heap (i.e. in _span).
6731     new_oop->oop_iterate(_scanning_closure);
6732     // check if it's time to yield
6733     do_yield_check();
6734   }
6735   unsigned int after_count =
6736     GenCollectedHeap::heap()->total_collections();
6737   bool abort = (_before_count != after_count) ||
6738                _collector->should_abort_preclean();
6739   return abort ? 0 : size;
6740 }
6741 
6742 void SurvivorSpacePrecleanClosure::do_yield_work() {
6743   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6744          "CMS thread should hold CMS token");
6745   assert_lock_strong(_bit_map->lock());
6746   // Relinquish the bit map lock
6747   _bit_map->lock()->unlock();
6748   ConcurrentMarkSweepThread::desynchronize(true);
6749   ConcurrentMarkSweepThread::acknowledge_yield_request();
6750   _collector->stopTimer();
6751   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6752   if (PrintCMSStatistics != 0) {
6753     _collector->incrementYields();
6754   }
6755   _collector->icms_wait();
6756 
6757   // See the comment in coordinator_yield()
6758   for (unsigned i = 0; i < CMSYieldSleepCount &&
6759                        ConcurrentMarkSweepThread::should_yield() &&
6760                        !CMSCollector::foregroundGCIsActive(); ++i) {
6761     os::sleep(Thread::current(), 1, false);
6762     ConcurrentMarkSweepThread::acknowledge_yield_request();
6763   }
6764 
6765   ConcurrentMarkSweepThread::synchronize(true);
6766   _bit_map->lock()->lock_without_safepoint_check();
6767   _collector->startTimer();
6768 }
6769 
6770 // This closure is used to rescan the marked objects on the dirty cards
6771 // in the mod union table and the card table proper. In the parallel
6772 // case, although the bitMap is shared, we do a single read so the
6773 // isMarked() query is "safe".
6774 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6775   // Ignore mark word because we are running concurrent with mutators
6776   assert(p->is_oop_or_null(true), "expected an oop or null");
6777   HeapWord* addr = (HeapWord*)p;
6778   assert(_span.contains(addr), "we are scanning the CMS generation");
6779   bool is_obj_array = false;
6780   #ifdef DEBUG
6781     if (!_parallel) {
6782       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6783       assert(_collector->overflow_list_is_empty(),
6784              "overflow list should be empty");
6785 
6786     }
6787   #endif // DEBUG
6788   if (_bit_map->isMarked(addr)) {
6789     // Obj arrays are precisely marked, non-arrays are not;
6790     // so we scan objArrays precisely and non-arrays in their
6791     // entirety.
6792     if (p->is_objArray()) {
6793       is_obj_array = true;
6794       if (_parallel) {
6795         p->oop_iterate(_par_scan_closure, mr);
6796       } else {
6797         p->oop_iterate(_scan_closure, mr);
6798       }
6799     } else {
6800       if (_parallel) {
6801         p->oop_iterate(_par_scan_closure);
6802       } else {
6803         p->oop_iterate(_scan_closure);
6804       }
6805     }
6806   }
6807   #ifdef DEBUG
6808     if (!_parallel) {
6809       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6810       assert(_collector->overflow_list_is_empty(),
6811              "overflow list should be empty");
6812 
6813     }
6814   #endif // DEBUG
6815   return is_obj_array;
6816 }
6817 
6818 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6819                         MemRegion span,
6820                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6821                         CMSMarkStack*  revisitStack,
6822                         bool should_yield, bool verifying):
6823   _collector(collector),
6824   _span(span),
6825   _bitMap(bitMap),
6826   _mut(&collector->_modUnionTable),
6827   _markStack(markStack),
6828   _revisitStack(revisitStack),
6829   _yield(should_yield),
6830   _skipBits(0)
6831 {
6832   assert(_markStack->isEmpty(), "stack should be empty");
6833   _finger = _bitMap->startWord();
6834   _threshold = _finger;
6835   assert(_collector->_restart_addr == NULL, "Sanity check");
6836   assert(_span.contains(_finger), "Out of bounds _finger?");
6837   DEBUG_ONLY(_verifying = verifying;)
6838 }
6839 
6840 void MarkFromRootsClosure::reset(HeapWord* addr) {
6841   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6842   assert(_span.contains(addr), "Out of bounds _finger?");
6843   _finger = addr;
6844   _threshold = (HeapWord*)round_to(
6845                  (intptr_t)_finger, CardTableModRefBS::card_size);
6846 }
6847 
6848 // Should revisit to see if this should be restructured for
6849 // greater efficiency.
6850 void MarkFromRootsClosure::do_bit(size_t offset) {
6851   if (_skipBits > 0) {
6852     _skipBits--;
6853     return;
6854   }
6855   // convert offset into a HeapWord*
6856   HeapWord* addr = _bitMap->startWord() + offset;
6857   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6858          "address out of range");
6859   assert(_bitMap->isMarked(addr), "tautology");
6860   if (_bitMap->isMarked(addr+1)) {
6861     // this is an allocated but not yet initialized object
6862     assert(_skipBits == 0, "tautology");
6863     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6864     oop p = oop(addr);
6865     if (p->klass() == NULL || !p->is_parsable()) {
6866       DEBUG_ONLY(if (!_verifying) {)
6867         // We re-dirty the cards on which this object lies and increase
6868         // the _threshold so that we'll come back to scan this object
6869         // during the preclean or remark phase. (CMSCleanOnEnter)
6870         if (CMSCleanOnEnter) {
6871           size_t sz = _collector->block_size_using_printezis_bits(addr);
6872           HeapWord* start_card_addr = (HeapWord*)round_down(
6873                                          (intptr_t)addr, CardTableModRefBS::card_size);
6874           HeapWord* end_card_addr   = (HeapWord*)round_to(
6875                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6876           MemRegion redirty_range = MemRegion(start_card_addr, end_card_addr);
6877           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6878           // Bump _threshold to end_card_addr; note that
6879           // _threshold cannot possibly exceed end_card_addr, anyhow.
6880           // This prevents future clearing of the card as the scan proceeds
6881           // to the right.
6882           assert(_threshold <= end_card_addr,
6883                  "Because we are just scanning into this object");
6884           if (_threshold < end_card_addr) {
6885             _threshold = end_card_addr;
6886           }
6887           if (p->klass() != NULL) {
6888             // Redirty the range of cards...
6889             _mut->mark_range(redirty_range);
6890           } // ...else the setting of klass will dirty the card anyway.
6891         }
6892       DEBUG_ONLY(})
6893       return;
6894     }
6895   }
6896   scanOopsInOop(addr);
6897 }
6898 
6899 // We take a break if we've been at this for a while,
6900 // so as to avoid monopolizing the locks involved.
6901 void MarkFromRootsClosure::do_yield_work() {
6902   // First give up the locks, then yield, then re-lock
6903   // We should probably use a constructor/destructor idiom to
6904   // do this unlock/lock or modify the MutexUnlocker class to
6905   // serve our purpose. XXX
6906   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6907          "CMS thread should hold CMS token");
6908   assert_lock_strong(_bitMap->lock());
6909   _bitMap->lock()->unlock();
6910   ConcurrentMarkSweepThread::desynchronize(true);
6911   ConcurrentMarkSweepThread::acknowledge_yield_request();
6912   _collector->stopTimer();
6913   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6914   if (PrintCMSStatistics != 0) {
6915     _collector->incrementYields();
6916   }
6917   _collector->icms_wait();
6918 
6919   // See the comment in coordinator_yield()
6920   for (unsigned i = 0; i < CMSYieldSleepCount &&
6921                        ConcurrentMarkSweepThread::should_yield() &&
6922                        !CMSCollector::foregroundGCIsActive(); ++i) {
6923     os::sleep(Thread::current(), 1, false);
6924     ConcurrentMarkSweepThread::acknowledge_yield_request();
6925   }
6926 
6927   ConcurrentMarkSweepThread::synchronize(true);
6928   _bitMap->lock()->lock_without_safepoint_check();
6929   _collector->startTimer();
6930 }
6931 
6932 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6933   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6934   assert(_markStack->isEmpty(),
6935          "should drain stack to limit stack usage");
6936   // convert ptr to an oop preparatory to scanning
6937   oop this_oop = oop(ptr);
6938   // Ignore mark word in verification below, since we
6939   // may be running concurrent with mutators.
6940   assert(this_oop->is_oop(true), "should be an oop");
6941   assert(_finger <= ptr, "_finger runneth ahead");
6942   // advance the finger to right end of this object
6943   _finger = ptr + this_oop->size();
6944   assert(_finger > ptr, "we just incremented it above");
6945   // On large heaps, it may take us some time to get through
6946   // the marking phase (especially if running iCMS). During
6947   // this time it's possible that a lot of mutations have
6948   // accumulated in the card table and the mod union table --
6949   // these mutation records are redundant until we have
6950   // actually traced into the corresponding card.
6951   // Here, we check whether advancing the finger would make
6952   // us cross into a new card, and if so clear corresponding
6953   // cards in the MUT (preclean them in the card-table in the
6954   // future).
6955 
6956   DEBUG_ONLY(if (!_verifying) {)
6957     // The clean-on-enter optimization is disabled by default,
6958     // until we fix 6178663.
6959     if (CMSCleanOnEnter && (_finger > _threshold)) {
6960       // [_threshold, _finger) represents the interval
6961       // of cards to be cleared  in MUT (or precleaned in card table).
6962       // The set of cards to be cleared is all those that overlap
6963       // with the interval [_threshold, _finger); note that
6964       // _threshold is always kept card-aligned but _finger isn't
6965       // always card-aligned.
6966       HeapWord* old_threshold = _threshold;
6967       assert(old_threshold == (HeapWord*)round_to(
6968               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6969              "_threshold should always be card-aligned");
6970       _threshold = (HeapWord*)round_to(
6971                      (intptr_t)_finger, CardTableModRefBS::card_size);
6972       MemRegion mr(old_threshold, _threshold);
6973       assert(!mr.is_empty(), "Control point invariant");
6974       assert(_span.contains(mr), "Should clear within span");
6975       // XXX When _finger crosses from old gen into perm gen
6976       // we may be doing unnecessary cleaning; do better in the
6977       // future by detecting that condition and clearing fewer
6978       // MUT/CT entries.
6979       _mut->clear_range(mr);
6980     }
6981   DEBUG_ONLY(})
6982 
6983   // Note: the finger doesn't advance while we drain
6984   // the stack below.
6985   PushOrMarkClosure pushOrMarkClosure(_collector,
6986                                       _span, _bitMap, _markStack,
6987                                       _revisitStack,
6988                                       _finger, this);
6989   bool res = _markStack->push(this_oop);
6990   assert(res, "Empty non-zero size stack should have space for single push");
6991   while (!_markStack->isEmpty()) {
6992     oop new_oop = _markStack->pop();
6993     // Skip verifying header mark word below because we are
6994     // running concurrent with mutators.
6995     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6996     // now scan this oop's oops
6997     new_oop->oop_iterate(&pushOrMarkClosure);
6998     do_yield_check();
6999   }
7000   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7001 }
7002 
7003 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7004                        CMSCollector* collector, MemRegion span,
7005                        CMSBitMap* bit_map,
7006                        OopTaskQueue* work_queue,
7007                        CMSMarkStack*  overflow_stack,
7008                        CMSMarkStack*  revisit_stack,
7009                        bool should_yield):
7010   _collector(collector),
7011   _whole_span(collector->_span),
7012   _span(span),
7013   _bit_map(bit_map),
7014   _mut(&collector->_modUnionTable),
7015   _work_queue(work_queue),
7016   _overflow_stack(overflow_stack),
7017   _revisit_stack(revisit_stack),
7018   _yield(should_yield),
7019   _skip_bits(0),
7020   _task(task)
7021 {
7022   assert(_work_queue->size() == 0, "work_queue should be empty");
7023   _finger = span.start();
7024   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7025   assert(_span.contains(_finger), "Out of bounds _finger?");
7026 }
7027 
7028 // Should revisit to see if this should be restructured for
7029 // greater efficiency.
7030 void Par_MarkFromRootsClosure::do_bit(size_t offset) {
7031   if (_skip_bits > 0) {
7032     _skip_bits--;
7033     return;
7034   }
7035   // convert offset into a HeapWord*
7036   HeapWord* addr = _bit_map->startWord() + offset;
7037   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7038          "address out of range");
7039   assert(_bit_map->isMarked(addr), "tautology");
7040   if (_bit_map->isMarked(addr+1)) {
7041     // this is an allocated object that might not yet be initialized
7042     assert(_skip_bits == 0, "tautology");
7043     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7044     oop p = oop(addr);
7045     if (p->klass() == NULL || !p->is_parsable()) {
7046       // in the case of Clean-on-Enter optimization, redirty card
7047       // and avoid clearing card by increasing  the threshold.
7048       return;
7049     }
7050   }
7051   scan_oops_in_oop(addr);
7052 }
7053 
7054 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7055   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7056   // Should we assert that our work queue is empty or
7057   // below some drain limit?
7058   assert(_work_queue->size() == 0,
7059          "should drain stack to limit stack usage");
7060   // convert ptr to an oop preparatory to scanning
7061   oop this_oop = oop(ptr);
7062   // Ignore mark word in verification below, since we
7063   // may be running concurrent with mutators.
7064   assert(this_oop->is_oop(true), "should be an oop");
7065   assert(_finger <= ptr, "_finger runneth ahead");
7066   // advance the finger to right end of this object
7067   _finger = ptr + this_oop->size();
7068   assert(_finger > ptr, "we just incremented it above");
7069   // On large heaps, it may take us some time to get through
7070   // the marking phase (especially if running iCMS). During
7071   // this time it's possible that a lot of mutations have
7072   // accumulated in the card table and the mod union table --
7073   // these mutation records are redundant until we have
7074   // actually traced into the corresponding card.
7075   // Here, we check whether advancing the finger would make
7076   // us cross into a new card, and if so clear corresponding
7077   // cards in the MUT (preclean them in the card-table in the
7078   // future).
7079 
7080   // The clean-on-enter optimization is disabled by default,
7081   // until we fix 6178663.
7082   if (CMSCleanOnEnter && (_finger > _threshold)) {
7083     // [_threshold, _finger) represents the interval
7084     // of cards to be cleared  in MUT (or precleaned in card table).
7085     // The set of cards to be cleared is all those that overlap
7086     // with the interval [_threshold, _finger); note that
7087     // _threshold is always kept card-aligned but _finger isn't
7088     // always card-aligned.
7089     HeapWord* old_threshold = _threshold;
7090     assert(old_threshold == (HeapWord*)round_to(
7091             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7092            "_threshold should always be card-aligned");
7093     _threshold = (HeapWord*)round_to(
7094                    (intptr_t)_finger, CardTableModRefBS::card_size);
7095     MemRegion mr(old_threshold, _threshold);
7096     assert(!mr.is_empty(), "Control point invariant");
7097     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7098     // XXX When _finger crosses from old gen into perm gen
7099     // we may be doing unnecessary cleaning; do better in the
7100     // future by detecting that condition and clearing fewer
7101     // MUT/CT entries.
7102     _mut->clear_range(mr);
7103   }
7104 
7105   // Note: the local finger doesn't advance while we drain
7106   // the stack below, but the global finger sure can and will.
7107   HeapWord** gfa = _task->global_finger_addr();
7108   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7109                                       _span, _bit_map,
7110                                       _work_queue,
7111                                       _overflow_stack,
7112                                       _revisit_stack,
7113                                       _finger,
7114                                       gfa, this);
7115   bool res = _work_queue->push(this_oop);   // overflow could occur here
7116   assert(res, "Will hold once we use workqueues");
7117   while (true) {
7118     oop new_oop;
7119     if (!_work_queue->pop_local(new_oop)) {
7120       // We emptied our work_queue; check if there's stuff that can
7121       // be gotten from the overflow stack.
7122       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7123             _overflow_stack, _work_queue)) {
7124         do_yield_check();
7125         continue;
7126       } else {  // done
7127         break;
7128       }
7129     }
7130     // Skip verifying header mark word below because we are
7131     // running concurrent with mutators.
7132     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7133     // now scan this oop's oops
7134     new_oop->oop_iterate(&pushOrMarkClosure);
7135     do_yield_check();
7136   }
7137   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7138 }
7139 
7140 // Yield in response to a request from VM Thread or
7141 // from mutators.
7142 void Par_MarkFromRootsClosure::do_yield_work() {
7143   assert(_task != NULL, "sanity");
7144   _task->yield();
7145 }
7146 
7147 // A variant of the above used for verifying CMS marking work.
7148 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7149                         MemRegion span,
7150                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7151                         CMSMarkStack*  mark_stack):
7152   _collector(collector),
7153   _span(span),
7154   _verification_bm(verification_bm),
7155   _cms_bm(cms_bm),
7156   _mark_stack(mark_stack),
7157   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7158                       mark_stack)
7159 {
7160   assert(_mark_stack->isEmpty(), "stack should be empty");
7161   _finger = _verification_bm->startWord();
7162   assert(_collector->_restart_addr == NULL, "Sanity check");
7163   assert(_span.contains(_finger), "Out of bounds _finger?");
7164 }
7165 
7166 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7167   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7168   assert(_span.contains(addr), "Out of bounds _finger?");
7169   _finger = addr;
7170 }
7171 
7172 // Should revisit to see if this should be restructured for
7173 // greater efficiency.
7174 void MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7175   // convert offset into a HeapWord*
7176   HeapWord* addr = _verification_bm->startWord() + offset;
7177   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7178          "address out of range");
7179   assert(_verification_bm->isMarked(addr), "tautology");
7180   assert(_cms_bm->isMarked(addr), "tautology");
7181 
7182   assert(_mark_stack->isEmpty(),
7183          "should drain stack to limit stack usage");
7184   // convert addr to an oop preparatory to scanning
7185   oop this_oop = oop(addr);
7186   assert(this_oop->is_oop(), "should be an oop");
7187   assert(_finger <= addr, "_finger runneth ahead");
7188   // advance the finger to right end of this object
7189   _finger = addr + this_oop->size();
7190   assert(_finger > addr, "we just incremented it above");
7191   // Note: the finger doesn't advance while we drain
7192   // the stack below.
7193   bool res = _mark_stack->push(this_oop);
7194   assert(res, "Empty non-zero size stack should have space for single push");
7195   while (!_mark_stack->isEmpty()) {
7196     oop new_oop = _mark_stack->pop();
7197     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7198     // now scan this oop's oops
7199     new_oop->oop_iterate(&_pam_verify_closure);
7200   }
7201   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7202 }
7203 
7204 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7205   CMSCollector* collector, MemRegion span,
7206   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7207   CMSMarkStack*  mark_stack):
7208   OopClosure(collector->ref_processor()),
7209   _collector(collector),
7210   _span(span),
7211   _verification_bm(verification_bm),
7212   _cms_bm(cms_bm),
7213   _mark_stack(mark_stack)
7214 { }
7215 
7216 
7217 // Upon stack overflow, we discard (part of) the stack,
7218 // remembering the least address amongst those discarded
7219 // in CMSCollector's _restart_address.
7220 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7221   // Remember the least grey address discarded
7222   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7223   _collector->lower_restart_addr(ra);
7224   _mark_stack->reset();  // discard stack contents
7225   _mark_stack->expand(); // expand the stack if possible
7226 }
7227 
7228 void PushAndMarkVerifyClosure::do_oop(oop* p) {
7229   oop    this_oop = *p;
7230   assert(this_oop->is_oop_or_null(), "expected an oop or NULL");
7231   HeapWord* addr = (HeapWord*)this_oop;
7232   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7233     // Oop lies in _span and isn't yet grey or black
7234     _verification_bm->mark(addr);            // now grey
7235     if (!_cms_bm->isMarked(addr)) {
7236       oop(addr)->print();
7237       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
7238       fatal("... aborting");
7239     }
7240 
7241     if (!_mark_stack->push(this_oop)) { // stack overflow
7242       if (PrintCMSStatistics != 0) {
7243         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7244                                SIZE_FORMAT, _mark_stack->capacity());
7245       }
7246       assert(_mark_stack->isFull(), "Else push should have succeeded");
7247       handle_stack_overflow(addr);
7248     }
7249     // anything including and to the right of _finger
7250     // will be scanned as we iterate over the remainder of the
7251     // bit map
7252   }
7253 }
7254 
7255 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7256                      MemRegion span,
7257                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7258                      CMSMarkStack*  revisitStack,
7259                      HeapWord* finger, MarkFromRootsClosure* parent) :
7260   OopClosure(collector->ref_processor()),
7261   _collector(collector),
7262   _span(span),
7263   _bitMap(bitMap),
7264   _markStack(markStack),
7265   _revisitStack(revisitStack),
7266   _finger(finger),
7267   _parent(parent),
7268   _should_remember_klasses(collector->should_unload_classes())
7269 { }
7270 
7271 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7272                      MemRegion span,
7273                      CMSBitMap* bit_map,
7274                      OopTaskQueue* work_queue,
7275                      CMSMarkStack*  overflow_stack,
7276                      CMSMarkStack*  revisit_stack,
7277                      HeapWord* finger,
7278                      HeapWord** global_finger_addr,
7279                      Par_MarkFromRootsClosure* parent) :
7280   OopClosure(collector->ref_processor()),
7281   _collector(collector),
7282   _whole_span(collector->_span),
7283   _span(span),
7284   _bit_map(bit_map),
7285   _work_queue(work_queue),
7286   _overflow_stack(overflow_stack),
7287   _revisit_stack(revisit_stack),
7288   _finger(finger),
7289   _global_finger_addr(global_finger_addr),
7290   _parent(parent),
7291   _should_remember_klasses(collector->should_unload_classes())
7292 { }
7293 
7294 
7295 void CMSCollector::lower_restart_addr(HeapWord* low) {
7296   assert(_span.contains(low), "Out of bounds addr");
7297   if (_restart_addr == NULL) {
7298     _restart_addr = low;
7299   } else {
7300     _restart_addr = MIN2(_restart_addr, low);
7301   }
7302 }
7303 
7304 // Upon stack overflow, we discard (part of) the stack,
7305 // remembering the least address amongst those discarded
7306 // in CMSCollector's _restart_address.
7307 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7308   // Remember the least grey address discarded
7309   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7310   _collector->lower_restart_addr(ra);
7311   _markStack->reset();  // discard stack contents
7312   _markStack->expand(); // expand the stack if possible
7313 }
7314 
7315 // Upon stack overflow, we discard (part of) the stack,
7316 // remembering the least address amongst those discarded
7317 // in CMSCollector's _restart_address.
7318 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7319   // We need to do this under a mutex to prevent other
7320   // workers from interfering with the expansion below.
7321   MutexLockerEx ml(_overflow_stack->par_lock(),
7322                    Mutex::_no_safepoint_check_flag);
7323   // Remember the least grey address discarded
7324   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7325   _collector->lower_restart_addr(ra);
7326   _overflow_stack->reset();  // discard stack contents
7327   _overflow_stack->expand(); // expand the stack if possible
7328 }
7329 
7330 
7331 void PushOrMarkClosure::do_oop(oop* p) {
7332   oop    thisOop = *p;
7333   // Ignore mark word because we are running concurrent with mutators.
7334   assert(thisOop->is_oop_or_null(true), "expected an oop or NULL");
7335   HeapWord* addr = (HeapWord*)thisOop;
7336   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7337     // Oop lies in _span and isn't yet grey or black
7338     _bitMap->mark(addr);            // now grey
7339     if (addr < _finger) {
7340       // the bit map iteration has already either passed, or
7341       // sampled, this bit in the bit map; we'll need to
7342       // use the marking stack to scan this oop's oops.
7343       bool simulate_overflow = false;
7344       NOT_PRODUCT(
7345         if (CMSMarkStackOverflowALot &&
7346             _collector->simulate_overflow()) {
7347           // simulate a stack overflow
7348           simulate_overflow = true;
7349         }
7350       )
7351       if (simulate_overflow || !_markStack->push(thisOop)) { // stack overflow
7352         if (PrintCMSStatistics != 0) {
7353           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7354                                  SIZE_FORMAT, _markStack->capacity());
7355         }
7356         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7357         handle_stack_overflow(addr);
7358       }
7359     }
7360     // anything including and to the right of _finger
7361     // will be scanned as we iterate over the remainder of the
7362     // bit map
7363     do_yield_check();
7364   }
7365 }
7366 
7367 void Par_PushOrMarkClosure::do_oop(oop* p) {
7368   oop    this_oop = *p;
7369   // Ignore mark word because we are running concurrent with mutators.
7370   assert(this_oop->is_oop_or_null(true), "expected an oop or NULL");
7371   HeapWord* addr = (HeapWord*)this_oop;
7372   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7373     // Oop lies in _span and isn't yet grey or black
7374     // We read the global_finger (volatile read) strictly after marking oop
7375     bool res = _bit_map->par_mark(addr);    // now grey
7376     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7377     // Should we push this marked oop on our stack?
7378     // -- if someone else marked it, nothing to do
7379     // -- if target oop is above global finger nothing to do
7380     // -- if target oop is in chunk and above local finger
7381     //      then nothing to do
7382     // -- else push on work queue
7383     if (   !res       // someone else marked it, they will deal with it
7384         || (addr >= *gfa)  // will be scanned in a later task
7385         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7386       return;
7387     }
7388     // the bit map iteration has already either passed, or
7389     // sampled, this bit in the bit map; we'll need to
7390     // use the marking stack to scan this oop's oops.
7391     bool simulate_overflow = false;
7392     NOT_PRODUCT(
7393       if (CMSMarkStackOverflowALot &&
7394           _collector->simulate_overflow()) {
7395         // simulate a stack overflow
7396         simulate_overflow = true;
7397       }
7398     )
7399     if (simulate_overflow ||
7400         !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) {
7401       // stack overflow
7402       if (PrintCMSStatistics != 0) {
7403         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7404                                SIZE_FORMAT, _overflow_stack->capacity());
7405       }
7406       // We cannot assert that the overflow stack is full because
7407       // it may have been emptied since.
7408       assert(simulate_overflow ||
7409              _work_queue->size() == _work_queue->max_elems(),
7410             "Else push should have succeeded");
7411       handle_stack_overflow(addr);
7412     }
7413     do_yield_check();
7414   }
7415 }
7416 
7417 
7418 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7419                                        MemRegion span,
7420                                        ReferenceProcessor* rp,
7421                                        CMSBitMap* bit_map,
7422                                        CMSBitMap* mod_union_table,
7423                                        CMSMarkStack*  mark_stack,
7424                                        CMSMarkStack*  revisit_stack,
7425                                        bool           concurrent_precleaning):
7426   OopClosure(rp),
7427   _collector(collector),
7428   _span(span),
7429   _bit_map(bit_map),
7430   _mod_union_table(mod_union_table),
7431   _mark_stack(mark_stack),
7432   _revisit_stack(revisit_stack),
7433   _concurrent_precleaning(concurrent_precleaning),
7434   _should_remember_klasses(collector->should_unload_classes())
7435 {
7436   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7437 }
7438 
7439 // Grey object rescan during pre-cleaning and second checkpoint phases --
7440 // the non-parallel version (the parallel version appears further below.)
7441 void PushAndMarkClosure::do_oop(oop* p) {
7442   oop    this_oop = *p;
7443   // Ignore mark word verification. If during concurrent precleaning
7444   // the object monitor may be locked. If during the checkpoint
7445   // phases, the object may already have been reached by a  different
7446   // path and may be at the end of the global overflow list (so
7447   // the mark word may be NULL).
7448   assert(this_oop->is_oop_or_null(true/* ignore mark word */),
7449          "expected an oop or NULL");
7450   HeapWord* addr = (HeapWord*)this_oop;
7451   // Check if oop points into the CMS generation
7452   // and is not marked
7453   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7454     // a white object ...
7455     _bit_map->mark(addr);         // ... now grey
7456     // push on the marking stack (grey set)
7457     bool simulate_overflow = false;
7458     NOT_PRODUCT(
7459       if (CMSMarkStackOverflowALot &&
7460           _collector->simulate_overflow()) {
7461         // simulate a stack overflow
7462         simulate_overflow = true;
7463       }
7464     )
7465     if (simulate_overflow || !_mark_stack->push(this_oop)) {
7466       if (_concurrent_precleaning) {
7467          // During precleaning we can just dirty the appropriate card
7468          // in the mod union table, thus ensuring that the object remains
7469          // in the grey set  and continue. Note that no one can be intefering
7470          // with us in this action of dirtying the mod union table, so
7471          // no locking is required.
7472          _mod_union_table->mark(addr);
7473          _collector->_ser_pmc_preclean_ovflw++;
7474       } else {
7475          // During the remark phase, we need to remember this oop
7476          // in the overflow list.
7477          _collector->push_on_overflow_list(this_oop);
7478          _collector->_ser_pmc_remark_ovflw++;
7479       }
7480     }
7481   }
7482 }
7483 
7484 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7485                                                MemRegion span,
7486                                                ReferenceProcessor* rp,
7487                                                CMSBitMap* bit_map,
7488                                                OopTaskQueue* work_queue,
7489                                                CMSMarkStack* revisit_stack):
7490   OopClosure(rp),
7491   _collector(collector),
7492   _span(span),
7493   _bit_map(bit_map),
7494   _work_queue(work_queue),
7495   _revisit_stack(revisit_stack),
7496   _should_remember_klasses(collector->should_unload_classes())
7497 {
7498   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7499 }
7500 
7501 // Grey object rescan during second checkpoint phase --
7502 // the parallel version.
7503 void Par_PushAndMarkClosure::do_oop(oop* p) {
7504   oop    this_oop = *p;
7505   // In the assert below, we ignore the mark word because
7506   // this oop may point to an already visited object that is
7507   // on the overflow stack (in which case the mark word has
7508   // been hijacked for chaining into the overflow stack --
7509   // if this is the last object in the overflow stack then
7510   // its mark word will be NULL). Because this object may
7511   // have been subsequently popped off the global overflow
7512   // stack, and the mark word possibly restored to the prototypical
7513   // value, by the time we get to examined this failing assert in
7514   // the debugger, is_oop_or_null(false) may subsequently start
7515   // to hold.
7516   assert(this_oop->is_oop_or_null(true),
7517          "expected an oop or NULL");
7518   HeapWord* addr = (HeapWord*)this_oop;
7519   // Check if oop points into the CMS generation
7520   // and is not marked
7521   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7522     // a white object ...
7523     // If we manage to "claim" the object, by being the
7524     // first thread to mark it, then we push it on our
7525     // marking stack
7526     if (_bit_map->par_mark(addr)) {     // ... now grey
7527       // push on work queue (grey set)
7528       bool simulate_overflow = false;
7529       NOT_PRODUCT(
7530         if (CMSMarkStackOverflowALot &&
7531             _collector->par_simulate_overflow()) {
7532           // simulate a stack overflow
7533           simulate_overflow = true;
7534         }
7535       )
7536       if (simulate_overflow || !_work_queue->push(this_oop)) {
7537         _collector->par_push_on_overflow_list(this_oop);
7538         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7539       }
7540     } // Else, some other thread got there first
7541   }
7542 }
7543 
7544 void PushAndMarkClosure::remember_klass(Klass* k) {
7545   if (!_revisit_stack->push(oop(k))) {
7546     fatal("Revisit stack overflowed in PushAndMarkClosure");
7547   }
7548 }
7549 
7550 void Par_PushAndMarkClosure::remember_klass(Klass* k) {
7551   if (!_revisit_stack->par_push(oop(k))) {
7552     fatal("Revist stack overflowed in Par_PushAndMarkClosure");
7553   }
7554 }
7555 
7556 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7557   Mutex* bml = _collector->bitMapLock();
7558   assert_lock_strong(bml);
7559   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7560          "CMS thread should hold CMS token");
7561 
7562   bml->unlock();
7563   ConcurrentMarkSweepThread::desynchronize(true);
7564 
7565   ConcurrentMarkSweepThread::acknowledge_yield_request();
7566 
7567   _collector->stopTimer();
7568   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7569   if (PrintCMSStatistics != 0) {
7570     _collector->incrementYields();
7571   }
7572   _collector->icms_wait();
7573 
7574   // See the comment in coordinator_yield()
7575   for (unsigned i = 0; i < CMSYieldSleepCount &&
7576                        ConcurrentMarkSweepThread::should_yield() &&
7577                        !CMSCollector::foregroundGCIsActive(); ++i) {
7578     os::sleep(Thread::current(), 1, false);
7579     ConcurrentMarkSweepThread::acknowledge_yield_request();
7580   }
7581 
7582   ConcurrentMarkSweepThread::synchronize(true);
7583   bml->lock();
7584 
7585   _collector->startTimer();
7586 }
7587 
7588 bool CMSPrecleanRefsYieldClosure::should_return() {
7589   if (ConcurrentMarkSweepThread::should_yield()) {
7590     do_yield_work();
7591   }
7592   return _collector->foregroundGCIsActive();
7593 }
7594 
7595 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7596   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7597          "mr should be aligned to start at a card boundary");
7598   // We'd like to assert:
7599   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7600   //        "mr should be a range of cards");
7601   // However, that would be too strong in one case -- the last
7602   // partition ends at _unallocated_block which, in general, can be
7603   // an arbitrary boundary, not necessarily card aligned.
7604   if (PrintCMSStatistics != 0) {
7605     _num_dirty_cards +=
7606          mr.word_size()/CardTableModRefBS::card_size_in_words;
7607   }
7608   _space->object_iterate_mem(mr, &_scan_cl);
7609 }
7610 
7611 SweepClosure::SweepClosure(CMSCollector* collector,
7612                            ConcurrentMarkSweepGeneration* g,
7613                            CMSBitMap* bitMap, bool should_yield) :
7614   _collector(collector),
7615   _g(g),
7616   _sp(g->cmsSpace()),
7617   _limit(_sp->sweep_limit()),
7618   _freelistLock(_sp->freelistLock()),
7619   _bitMap(bitMap),
7620   _yield(should_yield),
7621   _inFreeRange(false),           // No free range at beginning of sweep
7622   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7623   _lastFreeRangeCoalesced(false),
7624   _freeFinger(g->used_region().start())
7625 {
7626   NOT_PRODUCT(
7627     _numObjectsFreed = 0;
7628     _numWordsFreed   = 0;
7629     _numObjectsLive = 0;
7630     _numWordsLive = 0;
7631     _numObjectsAlreadyFree = 0;
7632     _numWordsAlreadyFree = 0;
7633     _last_fc = NULL;
7634 
7635     _sp->initializeIndexedFreeListArrayReturnedBytes();
7636     _sp->dictionary()->initializeDictReturnedBytes();
7637   )
7638   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7639          "sweep _limit out of bounds");
7640   if (CMSTraceSweeper) {
7641     gclog_or_tty->print("\n====================\nStarting new sweep\n");
7642   }
7643 }
7644 
7645 // We need this destructor to reclaim any space at the end
7646 // of the space, which do_blk below may not have added back to
7647 // the free lists. [basically dealing with the "fringe effect"]
7648 SweepClosure::~SweepClosure() {
7649   assert_lock_strong(_freelistLock);
7650   // this should be treated as the end of a free run if any
7651   // The current free range should be returned to the free lists
7652   // as one coalesced chunk.
7653   if (inFreeRange()) {
7654     flushCurFreeChunk(freeFinger(),
7655       pointer_delta(_limit, freeFinger()));
7656     assert(freeFinger() < _limit, "the finger pointeth off base");
7657     if (CMSTraceSweeper) {
7658       gclog_or_tty->print("destructor:");
7659       gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7660                  "[coalesced:"SIZE_FORMAT"]\n",
7661                  freeFinger(), pointer_delta(_limit, freeFinger()),
7662                  lastFreeRangeCoalesced());
7663     }
7664   }
7665   NOT_PRODUCT(
7666     if (Verbose && PrintGC) {
7667       gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7668                           SIZE_FORMAT " bytes",
7669                  _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7670       gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7671                              SIZE_FORMAT" bytes  "
7672         "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7673         _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7674         _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7675       size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7676         sizeof(HeapWord);
7677       gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7678 
7679       if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7680         size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7681         size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7682         size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7683         gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7684         gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7685           indexListReturnedBytes);
7686         gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7687           dictReturnedBytes);
7688       }
7689     }
7690   )
7691   // Now, in debug mode, just null out the sweep_limit
7692   NOT_PRODUCT(_sp->clear_sweep_limit();)
7693   if (CMSTraceSweeper) {
7694     gclog_or_tty->print("end of sweep\n================\n");
7695   }
7696 }
7697 
7698 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7699     bool freeRangeInFreeLists) {
7700   if (CMSTraceSweeper) {
7701     gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7702                freeFinger, _sp->block_size(freeFinger),
7703                freeRangeInFreeLists);
7704   }
7705   assert(!inFreeRange(), "Trampling existing free range");
7706   set_inFreeRange(true);
7707   set_lastFreeRangeCoalesced(false);
7708 
7709   set_freeFinger(freeFinger);
7710   set_freeRangeInFreeLists(freeRangeInFreeLists);
7711   if (CMSTestInFreeList) {
7712     if (freeRangeInFreeLists) {
7713       FreeChunk* fc = (FreeChunk*) freeFinger;
7714       assert(fc->isFree(), "A chunk on the free list should be free.");
7715       assert(fc->size() > 0, "Free range should have a size");
7716       assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7717     }
7718   }
7719 }
7720 
7721 // Note that the sweeper runs concurrently with mutators. Thus,
7722 // it is possible for direct allocation in this generation to happen
7723 // in the middle of the sweep. Note that the sweeper also coalesces
7724 // contiguous free blocks. Thus, unless the sweeper and the allocator
7725 // synchronize appropriately freshly allocated blocks may get swept up.
7726 // This is accomplished by the sweeper locking the free lists while
7727 // it is sweeping. Thus blocks that are determined to be free are
7728 // indeed free. There is however one additional complication:
7729 // blocks that have been allocated since the final checkpoint and
7730 // mark, will not have been marked and so would be treated as
7731 // unreachable and swept up. To prevent this, the allocator marks
7732 // the bit map when allocating during the sweep phase. This leads,
7733 // however, to a further complication -- objects may have been allocated
7734 // but not yet initialized -- in the sense that the header isn't yet
7735 // installed. The sweeper can not then determine the size of the block
7736 // in order to skip over it. To deal with this case, we use a technique
7737 // (due to Printezis) to encode such uninitialized block sizes in the
7738 // bit map. Since the bit map uses a bit per every HeapWord, but the
7739 // CMS generation has a minimum object size of 3 HeapWords, it follows
7740 // that "normal marks" won't be adjacent in the bit map (there will
7741 // always be at least two 0 bits between successive 1 bits). We make use
7742 // of these "unused" bits to represent uninitialized blocks -- the bit
7743 // corresponding to the start of the uninitialized object and the next
7744 // bit are both set. Finally, a 1 bit marks the end of the object that
7745 // started with the two consecutive 1 bits to indicate its potentially
7746 // uninitialized state.
7747 
7748 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7749   FreeChunk* fc = (FreeChunk*)addr;
7750   size_t res;
7751 
7752   // check if we are done sweepinrg
7753   if (addr == _limit) { // we have swept up to the limit, do nothing more
7754     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7755            "sweep _limit out of bounds");
7756     // help the closure application finish
7757     return pointer_delta(_sp->end(), _limit);
7758   }
7759   assert(addr <= _limit, "sweep invariant");
7760 
7761   // check if we should yield
7762   do_yield_check(addr);
7763   if (fc->isFree()) {
7764     // Chunk that is already free
7765     res = fc->size();
7766     doAlreadyFreeChunk(fc);
7767     debug_only(_sp->verifyFreeLists());
7768     assert(res == fc->size(), "Don't expect the size to change");
7769     NOT_PRODUCT(
7770       _numObjectsAlreadyFree++;
7771       _numWordsAlreadyFree += res;
7772     )
7773     NOT_PRODUCT(_last_fc = fc;)
7774   } else if (!_bitMap->isMarked(addr)) {
7775     // Chunk is fresh garbage
7776     res = doGarbageChunk(fc);
7777     debug_only(_sp->verifyFreeLists());
7778     NOT_PRODUCT(
7779       _numObjectsFreed++;
7780       _numWordsFreed += res;
7781     )
7782   } else {
7783     // Chunk that is alive.
7784     res = doLiveChunk(fc);
7785     debug_only(_sp->verifyFreeLists());
7786     NOT_PRODUCT(
7787         _numObjectsLive++;
7788         _numWordsLive += res;
7789     )
7790   }
7791   return res;
7792 }
7793 
7794 // For the smart allocation, record following
7795 //  split deaths - a free chunk is removed from its free list because
7796 //      it is being split into two or more chunks.
7797 //  split birth - a free chunk is being added to its free list because
7798 //      a larger free chunk has been split and resulted in this free chunk.
7799 //  coal death - a free chunk is being removed from its free list because
7800 //      it is being coalesced into a large free chunk.
7801 //  coal birth - a free chunk is being added to its free list because
7802 //      it was created when two or more free chunks where coalesced into
7803 //      this free chunk.
7804 //
7805 // These statistics are used to determine the desired number of free
7806 // chunks of a given size.  The desired number is chosen to be relative
7807 // to the end of a CMS sweep.  The desired number at the end of a sweep
7808 // is the
7809 //      count-at-end-of-previous-sweep (an amount that was enough)
7810 //              - count-at-beginning-of-current-sweep  (the excess)
7811 //              + split-births  (gains in this size during interval)
7812 //              - split-deaths  (demands on this size during interval)
7813 // where the interval is from the end of one sweep to the end of the
7814 // next.
7815 //
7816 // When sweeping the sweeper maintains an accumulated chunk which is
7817 // the chunk that is made up of chunks that have been coalesced.  That
7818 // will be termed the left-hand chunk.  A new chunk of garbage that
7819 // is being considered for coalescing will be referred to as the
7820 // right-hand chunk.
7821 //
7822 // When making a decision on whether to coalesce a right-hand chunk with
7823 // the current left-hand chunk, the current count vs. the desired count
7824 // of the left-hand chunk is considered.  Also if the right-hand chunk
7825 // is near the large chunk at the end of the heap (see
7826 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7827 // left-hand chunk is coalesced.
7828 //
7829 // When making a decision about whether to split a chunk, the desired count
7830 // vs. the current count of the candidate to be split is also considered.
7831 // If the candidate is underpopulated (currently fewer chunks than desired)
7832 // a chunk of an overpopulated (currently more chunks than desired) size may
7833 // be chosen.  The "hint" associated with a free list, if non-null, points
7834 // to a free list which may be overpopulated.
7835 //
7836 
7837 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7838   size_t size = fc->size();
7839   // Chunks that cannot be coalesced are not in the
7840   // free lists.
7841   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7842     assert(_sp->verifyChunkInFreeLists(fc),
7843       "free chunk should be in free lists");
7844   }
7845   // a chunk that is already free, should not have been
7846   // marked in the bit map
7847   HeapWord* addr = (HeapWord*) fc;
7848   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7849   // Verify that the bit map has no bits marked between
7850   // addr and purported end of this block.
7851   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7852 
7853   // Some chunks cannot be coalesced in under any circumstances.
7854   // See the definition of cantCoalesce().
7855   if (!fc->cantCoalesce()) {
7856     // This chunk can potentially be coalesced.
7857     if (_sp->adaptive_freelists()) {
7858       // All the work is done in
7859       doPostIsFreeOrGarbageChunk(fc, size);
7860     } else {  // Not adaptive free lists
7861       // this is a free chunk that can potentially be coalesced by the sweeper;
7862       if (!inFreeRange()) {
7863         // if the next chunk is a free block that can't be coalesced
7864         // it doesn't make sense to remove this chunk from the free lists
7865         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7866         assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7867         if ((HeapWord*)nextChunk < _limit  &&    // there's a next chunk...
7868             nextChunk->isFree()    &&            // which is free...
7869             nextChunk->cantCoalesce()) {         // ... but cant be coalesced
7870           // nothing to do
7871         } else {
7872           // Potentially the start of a new free range:
7873           // Don't eagerly remove it from the free lists.
7874           // No need to remove it if it will just be put
7875           // back again.  (Also from a pragmatic point of view
7876           // if it is a free block in a region that is beyond
7877           // any allocated blocks, an assertion will fail)
7878           // Remember the start of a free run.
7879           initialize_free_range(addr, true);
7880           // end - can coalesce with next chunk
7881         }
7882       } else {
7883         // the midst of a free range, we are coalescing
7884         debug_only(record_free_block_coalesced(fc);)
7885         if (CMSTraceSweeper) {
7886           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
7887         }
7888         // remove it from the free lists
7889         _sp->removeFreeChunkFromFreeLists(fc);
7890         set_lastFreeRangeCoalesced(true);
7891         // If the chunk is being coalesced and the current free range is
7892         // in the free lists, remove the current free range so that it
7893         // will be returned to the free lists in its entirety - all
7894         // the coalesced pieces included.
7895         if (freeRangeInFreeLists()) {
7896           FreeChunk* ffc = (FreeChunk*) freeFinger();
7897           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7898             "Size of free range is inconsistent with chunk size.");
7899           if (CMSTestInFreeList) {
7900             assert(_sp->verifyChunkInFreeLists(ffc),
7901               "free range is not in free lists");
7902           }
7903           _sp->removeFreeChunkFromFreeLists(ffc);
7904           set_freeRangeInFreeLists(false);
7905         }
7906       }
7907     }
7908   } else {
7909     // Code path common to both original and adaptive free lists.
7910 
7911     // cant coalesce with previous block; this should be treated
7912     // as the end of a free run if any
7913     if (inFreeRange()) {
7914       // we kicked some butt; time to pick up the garbage
7915       assert(freeFinger() < addr, "the finger pointeth off base");
7916       flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
7917     }
7918     // else, nothing to do, just continue
7919   }
7920 }
7921 
7922 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
7923   // This is a chunk of garbage.  It is not in any free list.
7924   // Add it to a free list or let it possibly be coalesced into
7925   // a larger chunk.
7926   HeapWord* addr = (HeapWord*) fc;
7927   size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7928 
7929   if (_sp->adaptive_freelists()) {
7930     // Verify that the bit map has no bits marked between
7931     // addr and purported end of just dead object.
7932     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7933 
7934     doPostIsFreeOrGarbageChunk(fc, size);
7935   } else {
7936     if (!inFreeRange()) {
7937       // start of a new free range
7938       assert(size > 0, "A free range should have a size");
7939       initialize_free_range(addr, false);
7940 
7941     } else {
7942       // this will be swept up when we hit the end of the
7943       // free range
7944       if (CMSTraceSweeper) {
7945         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
7946       }
7947       // If the chunk is being coalesced and the current free range is
7948       // in the free lists, remove the current free range so that it
7949       // will be returned to the free lists in its entirety - all
7950       // the coalesced pieces included.
7951       if (freeRangeInFreeLists()) {
7952         FreeChunk* ffc = (FreeChunk*)freeFinger();
7953         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7954           "Size of free range is inconsistent with chunk size.");
7955         if (CMSTestInFreeList) {
7956           assert(_sp->verifyChunkInFreeLists(ffc),
7957             "free range is not in free lists");
7958         }
7959         _sp->removeFreeChunkFromFreeLists(ffc);
7960         set_freeRangeInFreeLists(false);
7961       }
7962       set_lastFreeRangeCoalesced(true);
7963     }
7964     // this will be swept up when we hit the end of the free range
7965 
7966     // Verify that the bit map has no bits marked between
7967     // addr and purported end of just dead object.
7968     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7969   }
7970   return size;
7971 }
7972 
7973 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
7974   HeapWord* addr = (HeapWord*) fc;
7975   // The sweeper has just found a live object. Return any accumulated
7976   // left hand chunk to the free lists.
7977   if (inFreeRange()) {
7978     if (_sp->adaptive_freelists()) {
7979       flushCurFreeChunk(freeFinger(),
7980                         pointer_delta(addr, freeFinger()));
7981     } else { // not adaptive freelists
7982       set_inFreeRange(false);
7983       // Add the free range back to the free list if it is not already
7984       // there.
7985       if (!freeRangeInFreeLists()) {
7986         assert(freeFinger() < addr, "the finger pointeth off base");
7987         if (CMSTraceSweeper) {
7988           gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
7989             "[coalesced:%d]\n",
7990             freeFinger(), pointer_delta(addr, freeFinger()),
7991             lastFreeRangeCoalesced());
7992         }
7993         _sp->addChunkAndRepairOffsetTable(freeFinger(),
7994           pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
7995       }
7996     }
7997   }
7998 
7999   // Common code path for original and adaptive free lists.
8000 
8001   // this object is live: we'd normally expect this to be
8002   // an oop, and like to assert the following:
8003   // assert(oop(addr)->is_oop(), "live block should be an oop");
8004   // However, as we commented above, this may be an object whose
8005   // header hasn't yet been initialized.
8006   size_t size;
8007   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8008   if (_bitMap->isMarked(addr + 1)) {
8009     // Determine the size from the bit map, rather than trying to
8010     // compute it from the object header.
8011     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8012     size = pointer_delta(nextOneAddr + 1, addr);
8013     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8014            "alignment problem");
8015 
8016     #ifdef DEBUG
8017       if (oop(addr)->klass() != NULL &&
8018           (   !_collector->should_unload_classes()
8019            || oop(addr)->is_parsable())) {
8020         // Ignore mark word because we are running concurrent with mutators
8021         assert(oop(addr)->is_oop(true), "live block should be an oop");
8022         assert(size ==
8023                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8024                "P-mark and computed size do not agree");
8025       }
8026     #endif
8027 
8028   } else {
8029     // This should be an initialized object that's alive.
8030     assert(oop(addr)->klass() != NULL &&
8031            (!_collector->should_unload_classes()
8032             || oop(addr)->is_parsable()),
8033            "Should be an initialized object");
8034     // Ignore mark word because we are running concurrent with mutators
8035     assert(oop(addr)->is_oop(true), "live block should be an oop");
8036     // Verify that the bit map has no bits marked between
8037     // addr and purported end of this block.
8038     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8039     assert(size >= 3, "Necessary for Printezis marks to work");
8040     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8041     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8042   }
8043   return size;
8044 }
8045 
8046 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8047                                             size_t chunkSize) {
8048   // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8049   // scheme.
8050   bool fcInFreeLists = fc->isFree();
8051   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8052   assert((HeapWord*)fc <= _limit, "sweep invariant");
8053   if (CMSTestInFreeList && fcInFreeLists) {
8054     assert(_sp->verifyChunkInFreeLists(fc),
8055       "free chunk is not in free lists");
8056   }
8057 
8058 
8059   if (CMSTraceSweeper) {
8060     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8061   }
8062 
8063   HeapWord* addr = (HeapWord*) fc;
8064 
8065   bool coalesce;
8066   size_t left  = pointer_delta(addr, freeFinger());
8067   size_t right = chunkSize;
8068   switch (FLSCoalescePolicy) {
8069     // numeric value forms a coalition aggressiveness metric
8070     case 0:  { // never coalesce
8071       coalesce = false;
8072       break;
8073     }
8074     case 1: { // coalesce if left & right chunks on overpopulated lists
8075       coalesce = _sp->coalOverPopulated(left) &&
8076                  _sp->coalOverPopulated(right);
8077       break;
8078     }
8079     case 2: { // coalesce if left chunk on overpopulated list (default)
8080       coalesce = _sp->coalOverPopulated(left);
8081       break;
8082     }
8083     case 3: { // coalesce if left OR right chunk on overpopulated list
8084       coalesce = _sp->coalOverPopulated(left) ||
8085                  _sp->coalOverPopulated(right);
8086       break;
8087     }
8088     case 4: { // always coalesce
8089       coalesce = true;
8090       break;
8091     }
8092     default:
8093      ShouldNotReachHere();
8094   }
8095 
8096   // Should the current free range be coalesced?
8097   // If the chunk is in a free range and either we decided to coalesce above
8098   // or the chunk is near the large block at the end of the heap
8099   // (isNearLargestChunk() returns true), then coalesce this chunk.
8100   bool doCoalesce = inFreeRange() &&
8101     (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8102   if (doCoalesce) {
8103     // Coalesce the current free range on the left with the new
8104     // chunk on the right.  If either is on a free list,
8105     // it must be removed from the list and stashed in the closure.
8106     if (freeRangeInFreeLists()) {
8107       FreeChunk* ffc = (FreeChunk*)freeFinger();
8108       assert(ffc->size() == pointer_delta(addr, freeFinger()),
8109         "Size of free range is inconsistent with chunk size.");
8110       if (CMSTestInFreeList) {
8111         assert(_sp->verifyChunkInFreeLists(ffc),
8112           "Chunk is not in free lists");
8113       }
8114       _sp->coalDeath(ffc->size());
8115       _sp->removeFreeChunkFromFreeLists(ffc);
8116       set_freeRangeInFreeLists(false);
8117     }
8118     if (fcInFreeLists) {
8119       _sp->coalDeath(chunkSize);
8120       assert(fc->size() == chunkSize,
8121         "The chunk has the wrong size or is not in the free lists");
8122       _sp->removeFreeChunkFromFreeLists(fc);
8123     }
8124     set_lastFreeRangeCoalesced(true);
8125   } else {  // not in a free range and/or should not coalesce
8126     // Return the current free range and start a new one.
8127     if (inFreeRange()) {
8128       // In a free range but cannot coalesce with the right hand chunk.
8129       // Put the current free range into the free lists.
8130       flushCurFreeChunk(freeFinger(),
8131         pointer_delta(addr, freeFinger()));
8132     }
8133     // Set up for new free range.  Pass along whether the right hand
8134     // chunk is in the free lists.
8135     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8136   }
8137 }
8138 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8139   assert(inFreeRange(), "Should only be called if currently in a free range.");
8140   assert(size > 0,
8141     "A zero sized chunk cannot be added to the free lists.");
8142   if (!freeRangeInFreeLists()) {
8143     if(CMSTestInFreeList) {
8144       FreeChunk* fc = (FreeChunk*) chunk;
8145       fc->setSize(size);
8146       assert(!_sp->verifyChunkInFreeLists(fc),
8147         "chunk should not be in free lists yet");
8148     }
8149     if (CMSTraceSweeper) {
8150       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8151                     chunk, size);
8152     }
8153     // A new free range is going to be starting.  The current
8154     // free range has not been added to the free lists yet or
8155     // was removed so add it back.
8156     // If the current free range was coalesced, then the death
8157     // of the free range was recorded.  Record a birth now.
8158     if (lastFreeRangeCoalesced()) {
8159       _sp->coalBirth(size);
8160     }
8161     _sp->addChunkAndRepairOffsetTable(chunk, size,
8162             lastFreeRangeCoalesced());
8163   }
8164   set_inFreeRange(false);
8165   set_freeRangeInFreeLists(false);
8166 }
8167 
8168 // We take a break if we've been at this for a while,
8169 // so as to avoid monopolizing the locks involved.
8170 void SweepClosure::do_yield_work(HeapWord* addr) {
8171   // Return current free chunk being used for coalescing (if any)
8172   // to the appropriate freelist.  After yielding, the next
8173   // free block encountered will start a coalescing range of
8174   // free blocks.  If the next free block is adjacent to the
8175   // chunk just flushed, they will need to wait for the next
8176   // sweep to be coalesced.
8177   if (inFreeRange()) {
8178     flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8179   }
8180 
8181   // First give up the locks, then yield, then re-lock.
8182   // We should probably use a constructor/destructor idiom to
8183   // do this unlock/lock or modify the MutexUnlocker class to
8184   // serve our purpose. XXX
8185   assert_lock_strong(_bitMap->lock());
8186   assert_lock_strong(_freelistLock);
8187   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8188          "CMS thread should hold CMS token");
8189   _bitMap->lock()->unlock();
8190   _freelistLock->unlock();
8191   ConcurrentMarkSweepThread::desynchronize(true);
8192   ConcurrentMarkSweepThread::acknowledge_yield_request();
8193   _collector->stopTimer();
8194   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8195   if (PrintCMSStatistics != 0) {
8196     _collector->incrementYields();
8197   }
8198   _collector->icms_wait();
8199 
8200   // See the comment in coordinator_yield()
8201   for (unsigned i = 0; i < CMSYieldSleepCount &&
8202                        ConcurrentMarkSweepThread::should_yield() &&
8203                        !CMSCollector::foregroundGCIsActive(); ++i) {
8204     os::sleep(Thread::current(), 1, false);
8205     ConcurrentMarkSweepThread::acknowledge_yield_request();
8206   }
8207 
8208   ConcurrentMarkSweepThread::synchronize(true);
8209   _freelistLock->lock();
8210   _bitMap->lock()->lock_without_safepoint_check();
8211   _collector->startTimer();
8212 }
8213 
8214 #ifndef PRODUCT
8215 // This is actually very useful in a product build if it can
8216 // be called from the debugger.  Compile it into the product
8217 // as needed.
8218 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8219   return debug_cms_space->verifyChunkInFreeLists(fc);
8220 }
8221 
8222 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8223   if (CMSTraceSweeper) {
8224     gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8225   }
8226 }
8227 #endif
8228 
8229 // CMSIsAliveClosure
8230 bool CMSIsAliveClosure::do_object_b(oop obj) {
8231   HeapWord* addr = (HeapWord*)obj;
8232   return addr != NULL &&
8233          (!_span.contains(addr) || _bit_map->isMarked(addr));
8234 }
8235 
8236 // CMSKeepAliveClosure: the serial version
8237 void CMSKeepAliveClosure::do_oop(oop* p) {
8238   oop this_oop = *p;
8239   HeapWord* addr = (HeapWord*)this_oop;
8240   if (_span.contains(addr) &&
8241       !_bit_map->isMarked(addr)) {
8242     _bit_map->mark(addr);
8243     bool simulate_overflow = false;
8244     NOT_PRODUCT(
8245       if (CMSMarkStackOverflowALot &&
8246           _collector->simulate_overflow()) {
8247         // simulate a stack overflow
8248         simulate_overflow = true;
8249       }
8250     )
8251     if (simulate_overflow || !_mark_stack->push(this_oop)) {
8252       _collector->push_on_overflow_list(this_oop);
8253       _collector->_ser_kac_ovflw++;
8254     }
8255   }
8256 }
8257 
8258 // CMSParKeepAliveClosure: a parallel version of the above.
8259 // The work queues are private to each closure (thread),
8260 // but (may be) available for stealing by other threads.
8261 void CMSParKeepAliveClosure::do_oop(oop* p) {
8262   oop this_oop = *p;
8263   HeapWord* addr = (HeapWord*)this_oop;
8264   if (_span.contains(addr) &&
8265       !_bit_map->isMarked(addr)) {
8266     // In general, during recursive tracing, several threads
8267     // may be concurrently getting here; the first one to
8268     // "tag" it, claims it.
8269     if (_bit_map->par_mark(addr)) {
8270       bool res = _work_queue->push(this_oop);
8271       assert(res, "Low water mark should be much less than capacity");
8272       // Do a recursive trim in the hope that this will keep
8273       // stack usage lower, but leave some oops for potential stealers
8274       trim_queue(_low_water_mark);
8275     } // Else, another thread got there first
8276   }
8277 }
8278 
8279 void CMSParKeepAliveClosure::trim_queue(uint max) {
8280   while (_work_queue->size() > max) {
8281     oop new_oop;
8282     if (_work_queue->pop_local(new_oop)) {
8283       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8284       assert(_bit_map->isMarked((HeapWord*)new_oop),
8285              "no white objects on this stack!");
8286       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8287       // iterate over the oops in this oop, marking and pushing
8288       // the ones in CMS heap (i.e. in _span).
8289       new_oop->oop_iterate(&_mark_and_push);
8290     }
8291   }
8292 }
8293 
8294 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) {
8295   oop this_oop = *p;
8296   HeapWord* addr = (HeapWord*)this_oop;
8297   if (_span.contains(addr) &&
8298       !_bit_map->isMarked(addr)) {
8299     if (_bit_map->par_mark(addr)) {
8300       bool simulate_overflow = false;
8301       NOT_PRODUCT(
8302         if (CMSMarkStackOverflowALot &&
8303             _collector->par_simulate_overflow()) {
8304           // simulate a stack overflow
8305           simulate_overflow = true;
8306         }
8307       )
8308       if (simulate_overflow || !_work_queue->push(this_oop)) {
8309         _collector->par_push_on_overflow_list(this_oop);
8310         _collector->_par_kac_ovflw++;
8311       }
8312     } // Else another thread got there already
8313   }
8314 }
8315 
8316 //////////////////////////////////////////////////////////////////
8317 //  CMSExpansionCause                /////////////////////////////
8318 //////////////////////////////////////////////////////////////////
8319 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8320   switch (cause) {
8321     case _no_expansion:
8322       return "No expansion";
8323     case _satisfy_free_ratio:
8324       return "Free ratio";
8325     case _satisfy_promotion:
8326       return "Satisfy promotion";
8327     case _satisfy_allocation:
8328       return "allocation";
8329     case _allocate_par_lab:
8330       return "Par LAB";
8331     case _allocate_par_spooling_space:
8332       return "Par Spooling Space";
8333     case _adaptive_size_policy:
8334       return "Ergonomics";
8335     default:
8336       return "unknown";
8337   }
8338 }
8339 
8340 void CMSDrainMarkingStackClosure::do_void() {
8341   // the max number to take from overflow list at a time
8342   const size_t num = _mark_stack->capacity()/4;
8343   while (!_mark_stack->isEmpty() ||
8344          // if stack is empty, check the overflow list
8345          _collector->take_from_overflow_list(num, _mark_stack)) {
8346     oop this_oop = _mark_stack->pop();
8347     HeapWord* addr = (HeapWord*)this_oop;
8348     assert(_span.contains(addr), "Should be within span");
8349     assert(_bit_map->isMarked(addr), "Should be marked");
8350     assert(this_oop->is_oop(), "Should be an oop");
8351     this_oop->oop_iterate(_keep_alive);
8352   }
8353 }
8354 
8355 void CMSParDrainMarkingStackClosure::do_void() {
8356   // drain queue
8357   trim_queue(0);
8358 }
8359 
8360 // Trim our work_queue so its length is below max at return
8361 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8362   while (_work_queue->size() > max) {
8363     oop new_oop;
8364     if (_work_queue->pop_local(new_oop)) {
8365       assert(new_oop->is_oop(), "Expected an oop");
8366       assert(_bit_map->isMarked((HeapWord*)new_oop),
8367              "no white objects on this stack!");
8368       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8369       // iterate over the oops in this oop, marking and pushing
8370       // the ones in CMS heap (i.e. in _span).
8371       new_oop->oop_iterate(&_mark_and_push);
8372     }
8373   }
8374 }
8375 
8376 ////////////////////////////////////////////////////////////////////
8377 // Support for Marking Stack Overflow list handling and related code
8378 ////////////////////////////////////////////////////////////////////
8379 // Much of the following code is similar in shape and spirit to the
8380 // code used in ParNewGC. We should try and share that code
8381 // as much as possible in the future.
8382 
8383 #ifndef PRODUCT
8384 // Debugging support for CMSStackOverflowALot
8385 
8386 // It's OK to call this multi-threaded;  the worst thing
8387 // that can happen is that we'll get a bunch of closely
8388 // spaced simulated oveflows, but that's OK, in fact
8389 // probably good as it would exercise the overflow code
8390 // under contention.
8391 bool CMSCollector::simulate_overflow() {
8392   if (_overflow_counter-- <= 0) { // just being defensive
8393     _overflow_counter = CMSMarkStackOverflowInterval;
8394     return true;
8395   } else {
8396     return false;
8397   }
8398 }
8399 
8400 bool CMSCollector::par_simulate_overflow() {
8401   return simulate_overflow();
8402 }
8403 #endif
8404 
8405 // Single-threaded
8406 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8407   assert(stack->isEmpty(), "Expected precondition");
8408   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8409   size_t i = num;
8410   oop  cur = _overflow_list;
8411   const markOop proto = markOopDesc::prototype();
8412   NOT_PRODUCT(size_t n = 0;)
8413   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8414     next = oop(cur->mark());
8415     cur->set_mark(proto);   // until proven otherwise
8416     assert(cur->is_oop(), "Should be an oop");
8417     bool res = stack->push(cur);
8418     assert(res, "Bit off more than can chew?");
8419     NOT_PRODUCT(n++;)
8420   }
8421   _overflow_list = cur;
8422 #ifndef PRODUCT
8423   assert(_num_par_pushes >= n, "Too many pops?");
8424   _num_par_pushes -=n;
8425 #endif
8426   return !stack->isEmpty();
8427 }
8428 
8429 // Multi-threaded; use CAS to break off a prefix
8430 bool CMSCollector::par_take_from_overflow_list(size_t num,
8431                                                OopTaskQueue* work_q) {
8432   assert(work_q->size() == 0, "That's the current policy");
8433   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8434   if (_overflow_list == NULL) {
8435     return false;
8436   }
8437   // Grab the entire list; we'll put back a suffix
8438   oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list);
8439   if (prefix == NULL) {  // someone grabbed it before we did ...
8440     // ... we could spin for a short while, but for now we don't
8441     return false;
8442   }
8443   size_t i = num;
8444   oop cur = prefix;
8445   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8446   if (cur->mark() != NULL) {
8447     oop suffix_head = cur->mark(); // suffix will be put back on global list
8448     cur->set_mark(NULL);           // break off suffix
8449     // Find tail of suffix so we can prepend suffix to global list
8450     for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8451     oop suffix_tail = cur;
8452     assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8453            "Tautology");
8454     oop observed_overflow_list = _overflow_list;
8455     do {
8456       cur = observed_overflow_list;
8457       suffix_tail->set_mark(markOop(cur));
8458       observed_overflow_list =
8459         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur);
8460     } while (cur != observed_overflow_list);
8461   }
8462 
8463   // Push the prefix elements on work_q
8464   assert(prefix != NULL, "control point invariant");
8465   const markOop proto = markOopDesc::prototype();
8466   oop next;
8467   NOT_PRODUCT(size_t n = 0;)
8468   for (cur = prefix; cur != NULL; cur = next) {
8469     next = oop(cur->mark());
8470     cur->set_mark(proto);   // until proven otherwise
8471     assert(cur->is_oop(), "Should be an oop");
8472     bool res = work_q->push(cur);
8473     assert(res, "Bit off more than we can chew?");
8474     NOT_PRODUCT(n++;)
8475   }
8476 #ifndef PRODUCT
8477   assert(_num_par_pushes >= n, "Too many pops?");
8478   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8479 #endif
8480   return true;
8481 }
8482 
8483 // Single-threaded
8484 void CMSCollector::push_on_overflow_list(oop p) {
8485   NOT_PRODUCT(_num_par_pushes++;)
8486   assert(p->is_oop(), "Not an oop");
8487   preserve_mark_if_necessary(p);
8488   p->set_mark((markOop)_overflow_list);
8489   _overflow_list = p;
8490 }
8491 
8492 // Multi-threaded; use CAS to prepend to overflow list
8493 void CMSCollector::par_push_on_overflow_list(oop p) {
8494   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8495   assert(p->is_oop(), "Not an oop");
8496   par_preserve_mark_if_necessary(p);
8497   oop observed_overflow_list = _overflow_list;
8498   oop cur_overflow_list;
8499   do {
8500     cur_overflow_list = observed_overflow_list;
8501     p->set_mark(markOop(cur_overflow_list));
8502     observed_overflow_list =
8503       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8504   } while (cur_overflow_list != observed_overflow_list);
8505 }
8506 
8507 // Single threaded
8508 // General Note on GrowableArray: pushes may silently fail
8509 // because we are (temporarily) out of C-heap for expanding
8510 // the stack. The problem is quite ubiquitous and affects
8511 // a lot of code in the JVM. The prudent thing for GrowableArray
8512 // to do (for now) is to exit with an error. However, that may
8513 // be too draconian in some cases because the caller may be
8514 // able to recover without much harm. For suych cases, we
8515 // should probably introduce a "soft_push" method which returns
8516 // an indication of success or failure with the assumption that
8517 // the caller may be able to recover from a failure; code in
8518 // the VM can then be changed, incrementally, to deal with such
8519 // failures where possible, thus, incrementally hardening the VM
8520 // in such low resource situations.
8521 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8522   int PreserveMarkStackSize = 128;
8523 
8524   if (_preserved_oop_stack == NULL) {
8525     assert(_preserved_mark_stack == NULL,
8526            "bijection with preserved_oop_stack");
8527     // Allocate the stacks
8528     _preserved_oop_stack  = new (ResourceObj::C_HEAP)
8529       GrowableArray<oop>(PreserveMarkStackSize, true);
8530     _preserved_mark_stack = new (ResourceObj::C_HEAP)
8531       GrowableArray<markOop>(PreserveMarkStackSize, true);
8532     if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8533       vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8534                             "Preserved Mark/Oop Stack for CMS (C-heap)");
8535     }
8536   }
8537   _preserved_oop_stack->push(p);
8538   _preserved_mark_stack->push(m);
8539   assert(m == p->mark(), "Mark word changed");
8540   assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8541          "bijection");
8542 }
8543 
8544 // Single threaded
8545 void CMSCollector::preserve_mark_if_necessary(oop p) {
8546   markOop m = p->mark();
8547   if (m->must_be_preserved(p)) {
8548     preserve_mark_work(p, m);
8549   }
8550 }
8551 
8552 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8553   markOop m = p->mark();
8554   if (m->must_be_preserved(p)) {
8555     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8556     // Even though we read the mark word without holding
8557     // the lock, we are assured that it will not change
8558     // because we "own" this oop, so no other thread can
8559     // be trying to push it on the overflow list; see
8560     // the assertion in preserve_mark_work() that checks
8561     // that m == p->mark().
8562     preserve_mark_work(p, m);
8563   }
8564 }
8565 
8566 // We should be able to do this multi-threaded,
8567 // a chunk of stack being a task (this is
8568 // correct because each oop only ever appears
8569 // once in the overflow list. However, it's
8570 // not very easy to completely overlap this with
8571 // other operations, so will generally not be done
8572 // until all work's been completed. Because we
8573 // expect the preserved oop stack (set) to be small,
8574 // it's probably fine to do this single-threaded.
8575 // We can explore cleverer concurrent/overlapped/parallel
8576 // processing of preserved marks if we feel the
8577 // need for this in the future. Stack overflow should
8578 // be so rare in practice and, when it happens, its
8579 // effect on performance so great that this will
8580 // likely just be in the noise anyway.
8581 void CMSCollector::restore_preserved_marks_if_any() {
8582   if (_preserved_oop_stack == NULL) {
8583     assert(_preserved_mark_stack == NULL,
8584            "bijection with preserved_oop_stack");
8585     return;
8586   }
8587 
8588   assert(SafepointSynchronize::is_at_safepoint(),
8589          "world should be stopped");
8590   assert(Thread::current()->is_ConcurrentGC_thread() ||
8591          Thread::current()->is_VM_thread(),
8592          "should be single-threaded");
8593 
8594   int length = _preserved_oop_stack->length();
8595   assert(_preserved_mark_stack->length() == length, "bijection");
8596   for (int i = 0; i < length; i++) {
8597     oop p = _preserved_oop_stack->at(i);
8598     assert(p->is_oop(), "Should be an oop");
8599     assert(_span.contains(p), "oop should be in _span");
8600     assert(p->mark() == markOopDesc::prototype(),
8601            "Set when taken from overflow list");
8602     markOop m = _preserved_mark_stack->at(i);
8603     p->set_mark(m);
8604   }
8605   _preserved_mark_stack->clear();
8606   _preserved_oop_stack->clear();
8607   assert(_preserved_mark_stack->is_empty() &&
8608          _preserved_oop_stack->is_empty(),
8609          "stacks were cleared above");
8610 }
8611 
8612 #ifndef PRODUCT
8613 bool CMSCollector::no_preserved_marks() const {
8614   return (   (   _preserved_mark_stack == NULL
8615               && _preserved_oop_stack == NULL)
8616           || (   _preserved_mark_stack->is_empty()
8617               && _preserved_oop_stack->is_empty()));
8618 }
8619 #endif
8620 
8621 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8622 {
8623   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8624   CMSAdaptiveSizePolicy* size_policy =
8625     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8626   assert(size_policy->is_gc_cms_adaptive_size_policy(),
8627     "Wrong type for size policy");
8628   return size_policy;
8629 }
8630 
8631 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8632                                            size_t desired_promo_size) {
8633   if (cur_promo_size < desired_promo_size) {
8634     size_t expand_bytes = desired_promo_size - cur_promo_size;
8635     if (PrintAdaptiveSizePolicy && Verbose) {
8636       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8637         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8638         expand_bytes);
8639     }
8640     expand(expand_bytes,
8641            MinHeapDeltaBytes,
8642            CMSExpansionCause::_adaptive_size_policy);
8643   } else if (desired_promo_size < cur_promo_size) {
8644     size_t shrink_bytes = cur_promo_size - desired_promo_size;
8645     if (PrintAdaptiveSizePolicy && Verbose) {
8646       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8647         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8648         shrink_bytes);
8649     }
8650     shrink(shrink_bytes);
8651   }
8652 }
8653 
8654 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8655   GenCollectedHeap* gch = GenCollectedHeap::heap();
8656   CMSGCAdaptivePolicyCounters* counters =
8657     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8658   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8659     "Wrong kind of counters");
8660   return counters;
8661 }
8662 
8663 
8664 void ASConcurrentMarkSweepGeneration::update_counters() {
8665   if (UsePerfData) {
8666     _space_counters->update_all();
8667     _gen_counters->update_all();
8668     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8669     GenCollectedHeap* gch = GenCollectedHeap::heap();
8670     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8671     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8672       "Wrong gc statistics type");
8673     counters->update_counters(gc_stats_l);
8674   }
8675 }
8676 
8677 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8678   if (UsePerfData) {
8679     _space_counters->update_used(used);
8680     _space_counters->update_capacity();
8681     _gen_counters->update_all();
8682 
8683     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8684     GenCollectedHeap* gch = GenCollectedHeap::heap();
8685     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8686     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8687       "Wrong gc statistics type");
8688     counters->update_counters(gc_stats_l);
8689   }
8690 }
8691 
8692 // The desired expansion delta is computed so that:
8693 // . desired free percentage or greater is used
8694 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8695   assert_locked_or_safepoint(Heap_lock);
8696 
8697   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8698 
8699   // If incremental collection failed, we just want to expand
8700   // to the limit.
8701   if (incremental_collection_failed()) {
8702     clear_incremental_collection_failed();
8703     grow_to_reserved();
8704     return;
8705   }
8706 
8707   assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8708 
8709   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8710     "Wrong type of heap");
8711   int prev_level = level() - 1;
8712   assert(prev_level >= 0, "The cms generation is the lowest generation");
8713   Generation* prev_gen = gch->get_gen(prev_level);
8714   assert(prev_gen->kind() == Generation::ASParNew,
8715     "Wrong type of young generation");
8716   ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8717   size_t cur_eden = younger_gen->eden()->capacity();
8718   CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8719   size_t cur_promo = free();
8720   size_policy->compute_tenured_generation_free_space(cur_promo,
8721                                                        max_available(),
8722                                                        cur_eden);
8723   resize(cur_promo, size_policy->promo_size());
8724 
8725   // Record the new size of the space in the cms generation
8726   // that is available for promotions.  This is temporary.
8727   // It should be the desired promo size.
8728   size_policy->avg_cms_promo()->sample(free());
8729   size_policy->avg_old_live()->sample(used());
8730 
8731   if (UsePerfData) {
8732     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8733     counters->update_cms_capacity_counter(capacity());
8734   }
8735 }
8736 
8737 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
8738   assert_locked_or_safepoint(Heap_lock);
8739   assert_lock_strong(freelistLock());
8740   HeapWord* old_end = _cmsSpace->end();
8741   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
8742   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
8743   FreeChunk* chunk_at_end = find_chunk_at_end();
8744   if (chunk_at_end == NULL) {
8745     // No room to shrink
8746     if (PrintGCDetails && Verbose) {
8747       gclog_or_tty->print_cr("No room to shrink: old_end  "
8748         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
8749         " chunk_at_end  " PTR_FORMAT,
8750         old_end, unallocated_start, chunk_at_end);
8751     }
8752     return;
8753   } else {
8754 
8755     // Find the chunk at the end of the space and determine
8756     // how much it can be shrunk.
8757     size_t shrinkable_size_in_bytes = chunk_at_end->size();
8758     size_t aligned_shrinkable_size_in_bytes =
8759       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
8760     assert(unallocated_start <= chunk_at_end->end(),
8761       "Inconsistent chunk at end of space");
8762     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
8763     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
8764 
8765     // Shrink the underlying space
8766     _virtual_space.shrink_by(bytes);
8767     if (PrintGCDetails && Verbose) {
8768       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
8769         " desired_bytes " SIZE_FORMAT
8770         " shrinkable_size_in_bytes " SIZE_FORMAT
8771         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
8772         "  bytes  " SIZE_FORMAT,
8773         desired_bytes, shrinkable_size_in_bytes,
8774         aligned_shrinkable_size_in_bytes, bytes);
8775       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
8776         "  unallocated_start  " SIZE_FORMAT,
8777         old_end, unallocated_start);
8778     }
8779 
8780     // If the space did shrink (shrinking is not guaranteed),
8781     // shrink the chunk at the end by the appropriate amount.
8782     if (((HeapWord*)_virtual_space.high()) < old_end) {
8783       size_t new_word_size =
8784         heap_word_size(_virtual_space.committed_size());
8785 
8786       // Have to remove the chunk from the dictionary because it is changing
8787       // size and might be someplace elsewhere in the dictionary.
8788 
8789       // Get the chunk at end, shrink it, and put it
8790       // back.
8791       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
8792       size_t word_size_change = word_size_before - new_word_size;
8793       size_t chunk_at_end_old_size = chunk_at_end->size();
8794       assert(chunk_at_end_old_size >= word_size_change,
8795         "Shrink is too large");
8796       chunk_at_end->setSize(chunk_at_end_old_size -
8797                           word_size_change);
8798       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
8799         word_size_change);
8800 
8801       _cmsSpace->returnChunkToDictionary(chunk_at_end);
8802 
8803       MemRegion mr(_cmsSpace->bottom(), new_word_size);
8804       _bts->resize(new_word_size);  // resize the block offset shared array
8805       Universe::heap()->barrier_set()->resize_covered_region(mr);
8806       _cmsSpace->assert_locked();
8807       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
8808 
8809       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
8810 
8811       // update the space and generation capacity counters
8812       if (UsePerfData) {
8813         _space_counters->update_capacity();
8814         _gen_counters->update_all();
8815       }
8816 
8817       if (Verbose && PrintGCDetails) {
8818         size_t new_mem_size = _virtual_space.committed_size();
8819         size_t old_mem_size = new_mem_size + bytes;
8820         gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
8821                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
8822       }
8823     }
8824 
8825     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
8826       "Inconsistency at end of space");
8827     assert(chunk_at_end->end() == _cmsSpace->end(),
8828       "Shrinking is inconsistent");
8829     return;
8830   }
8831 }
8832 
8833 // Transfer some number of overflown objects to usual marking
8834 // stack. Return true if some objects were transferred.
8835 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8836   size_t num = MIN2((size_t)_mark_stack->capacity()/4,
8837                     (size_t)ParGCDesiredObjsFromOverflowList);
8838 
8839   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8840   assert(_collector->overflow_list_is_empty() || res,
8841          "If list is not empty, we should have taken something");
8842   assert(!res || !_mark_stack->isEmpty(),
8843          "If we took something, it should now be on our stack");
8844   return res;
8845 }
8846 
8847 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8848   size_t res = _sp->block_size_no_stall(addr, _collector);
8849   assert(res != 0, "Should always be able to compute a size");
8850   if (_sp->block_is_obj(addr)) {
8851     if (_live_bit_map->isMarked(addr)) {
8852       // It can't have been dead in a previous cycle
8853       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8854     } else {
8855       _dead_bit_map->mark(addr);      // mark the dead object
8856     }
8857   }
8858   return res;
8859 }