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