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 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 229   assert(collector() != NULL, "no collector");
 230   collector()->ref_processor_init();
 231 }
 232 
 233 void CMSCollector::ref_processor_init() {
 234   if (_ref_processor == NULL) {
 235     // Allocate and initialize a reference processor
 236     _ref_processor = ReferenceProcessor::create_ref_processor(
 237         _span,                               // span
 238         _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
 239         _cmsGen->refs_discovery_is_mt(),     // mt_discovery
 240         &_is_alive_closure,
 241         ParallelGCThreads,
 242         ParallelRefProcEnabled);
 243     // Initialize the _ref_processor field of CMSGen
 244     _cmsGen->set_ref_processor(_ref_processor);
 245 
 246     // Allocate a dummy ref processor for perm gen.
 247     ReferenceProcessor* rp2 = new ReferenceProcessor();
 248     if (rp2 == NULL) {
 249       vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
 250     }
 251     _permGen->set_ref_processor(rp2);
 252   }
 253 }
 254 
 255 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 256   GenCollectedHeap* gch = GenCollectedHeap::heap();
 257   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 258     "Wrong type of heap");
 259   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 260     gch->gen_policy()->size_policy();
 261   assert(sp->is_gc_cms_adaptive_size_policy(),
 262     "Wrong type of size policy");
 263   return sp;
 264 }
 265 
 266 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 267   CMSGCAdaptivePolicyCounters* results =
 268     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 269   assert(
 270     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 271     "Wrong gc policy counter kind");
 272   return results;
 273 }
 274 
 275 
 276 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 277 
 278   const char* gen_name = "old";
 279 
 280   // Generation Counters - generation 1, 1 subspace
 281   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 282 
 283   _space_counters = new GSpaceCounters(gen_name, 0,
 284                                        _virtual_space.reserved_size(),
 285                                        this, _gen_counters);
 286 }
 287 
 288 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 289   _cms_gen(cms_gen)
 290 {
 291   assert(alpha <= 100, "bad value");
 292   _saved_alpha = alpha;
 293 
 294   // Initialize the alphas to the bootstrap value of 100.
 295   _gc0_alpha = _cms_alpha = 100;
 296 
 297   _cms_begin_time.update();
 298   _cms_end_time.update();
 299 
 300   _gc0_duration = 0.0;
 301   _gc0_period = 0.0;
 302   _gc0_promoted = 0;
 303 
 304   _cms_duration = 0.0;
 305   _cms_period = 0.0;
 306   _cms_allocated = 0;
 307 
 308   _cms_used_at_gc0_begin = 0;
 309   _cms_used_at_gc0_end = 0;
 310   _allow_duty_cycle_reduction = false;
 311   _valid_bits = 0;
 312   _icms_duty_cycle = CMSIncrementalDutyCycle;
 313 }
 314 
 315 // If promotion failure handling is on use
 316 // the padded average size of the promotion for each
 317 // young generation collection.
 318 double CMSStats::time_until_cms_gen_full() const {
 319   size_t cms_free = _cms_gen->cmsSpace()->free();
 320   GenCollectedHeap* gch = GenCollectedHeap::heap();
 321   size_t expected_promotion = gch->get_gen(0)->capacity();
 322   if (HandlePromotionFailure) {
 323     expected_promotion = MIN2(
 324         (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
 325         expected_promotion);
 326   }
 327   if (cms_free > expected_promotion) {
 328     // Start a cms collection if there isn't enough space to promote
 329     // for the next minor collection.  Use the padded average as
 330     // a safety factor.
 331     cms_free -= expected_promotion;
 332 
 333     // Adjust by the safety factor.
 334     double cms_free_dbl = (double)cms_free;
 335     cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 336 
 337     if (PrintGCDetails && Verbose) {
 338       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 339         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 340         cms_free, expected_promotion);
 341       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 342         cms_free_dbl, cms_consumption_rate() + 1.0);
 343     }
 344     // Add 1 in case the consumption rate goes to zero.
 345     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 346   }
 347   return 0.0;
 348 }
 349 
 350 // Compare the duration of the cms collection to the
 351 // time remaining before the cms generation is empty.
 352 // Note that the time from the start of the cms collection
 353 // to the start of the cms sweep (less than the total
 354 // duration of the cms collection) can be used.  This
 355 // has been tried and some applications experienced
 356 // promotion failures early in execution.  This was
 357 // possibly because the averages were not accurate
 358 // enough at the beginning.
 359 double CMSStats::time_until_cms_start() const {
 360   // We add "gc0_period" to the "work" calculation
 361   // below because this query is done (mostly) at the
 362   // end of a scavenge, so we need to conservatively
 363   // account for that much possible delay
 364   // in the query so as to avoid concurrent mode failures
 365   // due to starting the collection just a wee bit too
 366   // late.
 367   double work = cms_duration() + gc0_period();
 368   double deadline = time_until_cms_gen_full();
 369   if (work > deadline) {
 370     if (Verbose && PrintGCDetails) {
 371       gclog_or_tty->print(
 372         " CMSCollector: collect because of anticipated promotion "
 373         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 374         gc0_period(), time_until_cms_gen_full());
 375     }
 376     return 0.0;
 377   }
 378   return work - deadline;
 379 }
 380 
 381 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 382 // amount of change to prevent wild oscillation.
 383 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 384                                               unsigned int new_duty_cycle) {
 385   assert(old_duty_cycle <= 100, "bad input value");
 386   assert(new_duty_cycle <= 100, "bad input value");
 387 
 388   // Note:  use subtraction with caution since it may underflow (values are
 389   // unsigned).  Addition is safe since we're in the range 0-100.
 390   unsigned int damped_duty_cycle = new_duty_cycle;
 391   if (new_duty_cycle < old_duty_cycle) {
 392     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 393     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 394       damped_duty_cycle = old_duty_cycle - largest_delta;
 395     }
 396   } else if (new_duty_cycle > old_duty_cycle) {
 397     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 398     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 399       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 400     }
 401   }
 402   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 403 
 404   if (CMSTraceIncrementalPacing) {
 405     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 406                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 407   }
 408   return damped_duty_cycle;
 409 }
 410 
 411 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 412   assert(CMSIncrementalPacing && valid(),
 413          "should be handled in icms_update_duty_cycle()");
 414 
 415   double cms_time_so_far = cms_timer().seconds();
 416   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 417   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 418 
 419   // Avoid division by 0.
 420   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 421   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 422 
 423   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 424   if (new_duty_cycle > _icms_duty_cycle) {
 425     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 426     if (new_duty_cycle > 2) {
 427       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 428                                                 new_duty_cycle);
 429     }
 430   } else if (_allow_duty_cycle_reduction) {
 431     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 432     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 433     // Respect the minimum duty cycle.
 434     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 435     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 436   }
 437 
 438   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 439     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 440   }
 441 
 442   _allow_duty_cycle_reduction = false;
 443   return _icms_duty_cycle;
 444 }
 445 
 446 #ifndef PRODUCT
 447 void CMSStats::print_on(outputStream *st) const {
 448   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 449   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 450                gc0_duration(), gc0_period(), gc0_promoted());
 451   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 452             cms_duration(), cms_duration_per_mb(),
 453             cms_period(), cms_allocated());
 454   st->print(",cms_since_beg=%g,cms_since_end=%g",
 455             cms_time_since_begin(), cms_time_since_end());
 456   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 457             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 458   if (CMSIncrementalMode) {
 459     st->print(",dc=%d", icms_duty_cycle());
 460   }
 461 
 462   if (valid()) {
 463     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 464               promotion_rate(), cms_allocation_rate());
 465     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 466               cms_consumption_rate(), time_until_cms_gen_full());
 467   }
 468   st->print(" ");
 469 }
 470 #endif // #ifndef PRODUCT
 471 
 472 CMSCollector::CollectorState CMSCollector::_collectorState =
 473                              CMSCollector::Idling;
 474 bool CMSCollector::_foregroundGCIsActive = false;
 475 bool CMSCollector::_foregroundGCShouldWait = false;
 476 
 477 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 478                            ConcurrentMarkSweepGeneration* permGen,
 479                            CardTableRS*                   ct,
 480                            ConcurrentMarkSweepPolicy*     cp):
 481   _cmsGen(cmsGen),
 482   _permGen(permGen),
 483   _ct(ct),
 484   _ref_processor(NULL),    // will be set later
 485   _conc_workers(NULL),     // may be set later
 486   _abort_preclean(false),
 487   _start_sampling(false),
 488   _between_prologue_and_epilogue(false),
 489   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 490   _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
 491   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 492                  -1 /* lock-free */, "No_lock" /* dummy */),
 493   _modUnionClosure(&_modUnionTable),
 494   _modUnionClosurePar(&_modUnionTable),
 495   _is_alive_closure(&_markBitMap),
 496   _restart_addr(NULL),
 497   _overflow_list(NULL),
 498   _preserved_oop_stack(NULL),
 499   _preserved_mark_stack(NULL),
 500   _stats(cmsGen),
 501   _eden_chunk_array(NULL),     // may be set in ctor body
 502   _eden_chunk_capacity(0),     // -- ditto --
 503   _eden_chunk_index(0),        // -- ditto --
 504   _survivor_plab_array(NULL),  // -- ditto --
 505   _survivor_chunk_array(NULL), // -- ditto --
 506   _survivor_chunk_capacity(0), // -- ditto --
 507   _survivor_chunk_index(0),    // -- ditto --
 508   _ser_pmc_preclean_ovflw(0),
 509   _ser_pmc_remark_ovflw(0),
 510   _par_pmc_remark_ovflw(0),
 511   _ser_kac_ovflw(0),
 512   _par_kac_ovflw(0),
 513 #ifndef PRODUCT
 514   _num_par_pushes(0),
 515 #endif
 516   _collection_count_start(0),
 517   _verifying(false),
 518   _icms_start_limit(NULL),
 519   _icms_stop_limit(NULL),
 520   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 521   _completed_initialization(false),
 522   _collector_policy(cp),
 523   _unload_classes(false),
 524   _unloaded_classes_last_cycle(false),
 525   _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
 526 {
 527   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 528     ExplicitGCInvokesConcurrent = true;
 529   }
 530   // Now expand the span and allocate the collection support structures
 531   // (MUT, marking bit map etc.) to cover both generations subject to
 532   // collection.
 533 
 534   // First check that _permGen is adjacent to _cmsGen and above it.
 535   assert(   _cmsGen->reserved().word_size()  > 0
 536          && _permGen->reserved().word_size() > 0,
 537          "generations should not be of zero size");
 538   assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
 539          "_cmsGen and _permGen should not overlap");
 540   assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
 541          "_cmsGen->end() different from _permGen->start()");
 542 
 543   // For use by dirty card to oop closures.
 544   _cmsGen->cmsSpace()->set_collector(this);
 545   _permGen->cmsSpace()->set_collector(this);
 546 
 547   // Adjust my span to cover old (cms) gen and perm gen
 548   _span = _cmsGen->reserved()._union(_permGen->reserved());
 549   // Initialize the span of is_alive_closure
 550   _is_alive_closure.set_span(_span);
 551 
 552   // Allocate MUT and marking bit map
 553   {
 554     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 555     if (!_markBitMap.allocate(_span)) {
 556       warning("Failed to allocate CMS Bit Map");
 557       return;
 558     }
 559     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 560   }
 561   {
 562     _modUnionTable.allocate(_span);
 563     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 564   }
 565 
 566   if (!_markStack.allocate(CMSMarkStackSize)) {
 567     warning("Failed to allocate CMS Marking Stack");
 568     return;
 569   }
 570   if (!_revisitStack.allocate(CMSRevisitStackSize)) {
 571     warning("Failed to allocate CMS Revisit Stack");
 572     return;
 573   }
 574 
 575   // Support for multi-threaded concurrent phases
 576   if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
 577     if (FLAG_IS_DEFAULT(ParallelCMSThreads)) {
 578       // just for now
 579       FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4);
 580     }
 581     if (ParallelCMSThreads > 1) {
 582       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 583                                  ParallelCMSThreads, true);
 584       if (_conc_workers == NULL) {
 585         warning("GC/CMS: _conc_workers allocation failure: "
 586               "forcing -CMSConcurrentMTEnabled");
 587         CMSConcurrentMTEnabled = false;
 588       }
 589     } else {
 590       CMSConcurrentMTEnabled = false;
 591     }
 592   }
 593   if (!CMSConcurrentMTEnabled) {
 594     ParallelCMSThreads = 0;
 595   } else {
 596     // Turn off CMSCleanOnEnter optimization temporarily for
 597     // the MT case where it's not fixed yet; see 6178663.
 598     CMSCleanOnEnter = false;
 599   }
 600   assert((_conc_workers != NULL) == (ParallelCMSThreads > 1),
 601          "Inconsistency");
 602 
 603   // Parallel task queues; these are shared for the
 604   // concurrent and stop-world phases of CMS, but
 605   // are not shared with parallel scavenge (ParNew).
 606   {
 607     uint i;
 608     uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads);
 609 
 610     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 611          || ParallelRefProcEnabled)
 612         && num_queues > 0) {
 613       _task_queues = new OopTaskQueueSet(num_queues);
 614       if (_task_queues == NULL) {
 615         warning("task_queues allocation failure.");
 616         return;
 617       }
 618       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
 619       if (_hash_seed == NULL) {
 620         warning("_hash_seed array allocation failure");
 621         return;
 622       }
 623 
 624       // XXX use a global constant instead of 64!
 625       typedef struct OopTaskQueuePadded {
 626         OopTaskQueue work_queue;
 627         char pad[64 - sizeof(OopTaskQueue)];  // prevent false sharing
 628       } OopTaskQueuePadded;
 629 
 630       for (i = 0; i < num_queues; i++) {
 631         OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
 632         if (q_padded == NULL) {
 633           warning("work_queue allocation failure.");
 634           return;
 635         }
 636         _task_queues->register_queue(i, &q_padded->work_queue);
 637       }
 638       for (i = 0; i < num_queues; i++) {
 639         _task_queues->queue(i)->initialize();
 640         _hash_seed[i] = 17;  // copied from ParNew
 641       }
 642     }
 643   }
 644 
 645   // "initiatingOccupancy" is the occupancy ratio at which we trigger
 646   // a new collection cycle.  Unless explicitly specified via
 647   // CMSTriggerRatio, it is calculated by:
 648   //   Let "f" be MinHeapFreeRatio in
 649   //
 650   //    intiatingOccupancy = 100-f +
 651   //                         f * (CMSTriggerRatio/100)
 652   // That is, if we assume the heap is at its desired maximum occupancy at the
 653   // end of a collection, we let CMSTriggerRatio of the (purported) free
 654   // space be allocated before initiating a new collection cycle.
 655   if (CMSInitiatingOccupancyFraction > 0) {
 656     _initiatingOccupancy = (double)CMSInitiatingOccupancyFraction / 100.0;
 657   } else {
 658     _initiatingOccupancy = ((100 - MinHeapFreeRatio) +
 659                            (double)(CMSTriggerRatio *
 660                                     MinHeapFreeRatio) / 100.0)
 661                            / 100.0;
 662   }
 663   // Clip CMSBootstrapOccupancy between 0 and 100.
 664   _bootstrap_occupancy = ((double)MIN2((intx)100, MAX2((intx)0, CMSBootstrapOccupancy)))
 665                          /(double)100;
 666 
 667   _full_gcs_since_conc_gc = 0;
 668 
 669   // Now tell CMS generations the identity of their collector
 670   ConcurrentMarkSweepGeneration::set_collector(this);
 671 
 672   // Create & start a CMS thread for this CMS collector
 673   _cmsThread = ConcurrentMarkSweepThread::start(this);
 674   assert(cmsThread() != NULL, "CMS Thread should have been created");
 675   assert(cmsThread()->collector() == this,
 676          "CMS Thread should refer to this gen");
 677   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 678 
 679   // Support for parallelizing young gen rescan
 680   GenCollectedHeap* gch = GenCollectedHeap::heap();
 681   _young_gen = gch->prev_gen(_cmsGen);
 682   if (gch->supports_inline_contig_alloc()) {
 683     _top_addr = gch->top_addr();
 684     _end_addr = gch->end_addr();
 685     assert(_young_gen != NULL, "no _young_gen");
 686     _eden_chunk_index = 0;
 687     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 688     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
 689     if (_eden_chunk_array == NULL) {
 690       _eden_chunk_capacity = 0;
 691       warning("GC/CMS: _eden_chunk_array allocation failure");
 692     }
 693   }
 694   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 695 
 696   // Support for parallelizing survivor space rescan
 697   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 698     size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize);
 699     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
 700     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
 701     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
 702     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 703         || _cursor == NULL) {
 704       warning("Failed to allocate survivor plab/chunk array");
 705       if (_survivor_plab_array  != NULL) {
 706         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
 707         _survivor_plab_array = NULL;
 708       }
 709       if (_survivor_chunk_array != NULL) {
 710         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
 711         _survivor_chunk_array = NULL;
 712       }
 713       if (_cursor != NULL) {
 714         FREE_C_HEAP_ARRAY(size_t, _cursor);
 715         _cursor = NULL;
 716       }
 717     } else {
 718       _survivor_chunk_capacity = 2*max_plab_samples;
 719       for (uint i = 0; i < ParallelGCThreads; i++) {
 720         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
 721         if (vec == NULL) {
 722           warning("Failed to allocate survivor plab array");
 723           for (int j = i; j > 0; j--) {
 724             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
 725           }
 726           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
 727           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
 728           _survivor_plab_array = NULL;
 729           _survivor_chunk_array = NULL;
 730           _survivor_chunk_capacity = 0;
 731           break;
 732         } else {
 733           ChunkArray* cur =
 734             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 735                                                         max_plab_samples);
 736           assert(cur->end() == 0, "Should be 0");
 737           assert(cur->array() == vec, "Should be vec");
 738           assert(cur->capacity() == max_plab_samples, "Error");
 739         }
 740       }
 741     }
 742   }
 743   assert(   (   _survivor_plab_array  != NULL
 744              && _survivor_chunk_array != NULL)
 745          || (   _survivor_chunk_capacity == 0
 746              && _survivor_chunk_index == 0),
 747          "Error");
 748 
 749   // Choose what strong roots should be scanned depending on verification options
 750   // and perm gen collection mode.
 751   if (!CMSClassUnloadingEnabled) {
 752     // If class unloading is disabled we want to include all classes into the root set.
 753     add_root_scanning_option(SharedHeap::SO_AllClasses);
 754   } else {
 755     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 756   }
 757 
 758   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 759   _gc_counters = new CollectorCounters("CMS", 1);
 760   _completed_initialization = true;
 761   _sweep_timer.start();  // start of time
 762 }
 763 
 764 const char* ConcurrentMarkSweepGeneration::name() const {
 765   return "concurrent mark-sweep generation";
 766 }
 767 void ConcurrentMarkSweepGeneration::update_counters() {
 768   if (UsePerfData) {
 769     _space_counters->update_all();
 770     _gen_counters->update_all();
 771   }
 772 }
 773 
 774 // this is an optimized version of update_counters(). it takes the
 775 // used value as a parameter rather than computing it.
 776 //
 777 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 778   if (UsePerfData) {
 779     _space_counters->update_used(used);
 780     _space_counters->update_capacity();
 781     _gen_counters->update_all();
 782   }
 783 }
 784 
 785 void ConcurrentMarkSweepGeneration::print() const {
 786   Generation::print();
 787   cmsSpace()->print();
 788 }
 789 
 790 #ifndef PRODUCT
 791 void ConcurrentMarkSweepGeneration::print_statistics() {
 792   cmsSpace()->printFLCensus(0);
 793 }
 794 #endif
 795 
 796 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 797   GenCollectedHeap* gch = GenCollectedHeap::heap();
 798   if (PrintGCDetails) {
 799     if (Verbose) {
 800       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 801         level(), short_name(), s, used(), capacity());
 802     } else {
 803       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 804         level(), short_name(), s, used() / K, capacity() / K);
 805     }
 806   }
 807   if (Verbose) {
 808     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 809               gch->used(), gch->capacity());
 810   } else {
 811     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 812               gch->used() / K, gch->capacity() / K);
 813   }
 814 }
 815 
 816 size_t
 817 ConcurrentMarkSweepGeneration::contiguous_available() const {
 818   // dld proposes an improvement in precision here. If the committed
 819   // part of the space ends in a free block we should add that to
 820   // uncommitted size in the calculation below. Will make this
 821   // change later, staying with the approximation below for the
 822   // time being. -- ysr.
 823   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 824 }
 825 
 826 size_t
 827 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 828   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 829 }
 830 
 831 size_t ConcurrentMarkSweepGeneration::max_available() const {
 832   return free() + _virtual_space.uncommitted_size();
 833 }
 834 
 835 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
 836     size_t max_promotion_in_bytes,
 837     bool younger_handles_promotion_failure) const {
 838 
 839   // This is the most conservative test.  Full promotion is
 840   // guaranteed if this is used. The multiplicative factor is to
 841   // account for the worst case "dilatation".
 842   double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
 843   if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
 844     adjusted_max_promo_bytes = (double)max_uintx;
 845   }
 846   bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
 847 
 848   if (younger_handles_promotion_failure && !result) {
 849     // Full promotion is not guaranteed because fragmentation
 850     // of the cms generation can prevent the full promotion.
 851     result = (max_available() >= (size_t)adjusted_max_promo_bytes);
 852 
 853     if (!result) {
 854       // With promotion failure handling the test for the ability
 855       // to support the promotion does not have to be guaranteed.
 856       // Use an average of the amount promoted.
 857       result = max_available() >= (size_t)
 858         gc_stats()->avg_promoted()->padded_average();
 859       if (PrintGC && Verbose && result) {
 860         gclog_or_tty->print_cr(
 861           "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 862           " max_available: " SIZE_FORMAT
 863           " avg_promoted: " SIZE_FORMAT,
 864           max_available(), (size_t)
 865           gc_stats()->avg_promoted()->padded_average());
 866       }
 867     } else {
 868       if (PrintGC && Verbose) {
 869         gclog_or_tty->print_cr(
 870           "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 871           " max_available: " SIZE_FORMAT
 872           " adj_max_promo_bytes: " SIZE_FORMAT,
 873           max_available(), (size_t)adjusted_max_promo_bytes);
 874       }
 875     }
 876   } else {
 877     if (PrintGC && Verbose) {
 878       gclog_or_tty->print_cr(
 879         "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 880         " contiguous_available: " SIZE_FORMAT
 881         " adj_max_promo_bytes: " SIZE_FORMAT,
 882         max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
 883     }
 884   }
 885   return result;
 886 }
 887 
 888 CompactibleSpace*
 889 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 890   return _cmsSpace;
 891 }
 892 
 893 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 894   // Clear the promotion information.  These pointers can be adjusted
 895   // along with all the other pointers into the heap but
 896   // compaction is expected to be a rare event with
 897   // a heap using cms so don't do it without seeing the need.
 898   if (ParallelGCThreads > 0) {
 899     for (uint i = 0; i < ParallelGCThreads; i++) {
 900       _par_gc_thread_states[i]->promo.reset();
 901     }
 902   }
 903 }
 904 
 905 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 906   blk->do_space(_cmsSpace);
 907 }
 908 
 909 void ConcurrentMarkSweepGeneration::compute_new_size() {
 910   assert_locked_or_safepoint(Heap_lock);
 911 
 912   // If incremental collection failed, we just want to expand
 913   // to the limit.
 914   if (incremental_collection_failed()) {
 915     clear_incremental_collection_failed();
 916     grow_to_reserved();
 917     return;
 918   }
 919 
 920   size_t expand_bytes = 0;
 921   double free_percentage = ((double) free()) / capacity();
 922   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 923   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 924 
 925   // compute expansion delta needed for reaching desired free percentage
 926   if (free_percentage < desired_free_percentage) {
 927     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 928     assert(desired_capacity >= capacity(), "invalid expansion size");
 929     expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 930   }
 931   if (expand_bytes > 0) {
 932     if (PrintGCDetails && Verbose) {
 933       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 934       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 935       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 936       gclog_or_tty->print_cr("  Desired free fraction %f",
 937         desired_free_percentage);
 938       gclog_or_tty->print_cr("  Maximum free fraction %f",
 939         maximum_free_percentage);
 940       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 941       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 942         desired_capacity/1000);
 943       int prev_level = level() - 1;
 944       if (prev_level >= 0) {
 945         size_t prev_size = 0;
 946         GenCollectedHeap* gch = GenCollectedHeap::heap();
 947         Generation* prev_gen = gch->_gens[prev_level];
 948         prev_size = prev_gen->capacity();
 949           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 950                                  prev_size/1000);
 951       }
 952       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 953         unsafe_max_alloc_nogc()/1000);
 954       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 955         contiguous_available()/1000);
 956       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 957         expand_bytes);
 958     }
 959     // safe if expansion fails
 960     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 961     if (PrintGCDetails && Verbose) {
 962       gclog_or_tty->print_cr("  Expanded free fraction %f",
 963         ((double) free()) / capacity());
 964     }
 965   }
 966 }
 967 
 968 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 969   return cmsSpace()->freelistLock();
 970 }
 971 
 972 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 973                                                   bool   tlab) {
 974   CMSSynchronousYieldRequest yr;
 975   MutexLockerEx x(freelistLock(),
 976                   Mutex::_no_safepoint_check_flag);
 977   return have_lock_and_allocate(size, tlab);
 978 }
 979 
 980 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 981                                                   bool   tlab) {
 982   assert_lock_strong(freelistLock());
 983   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 984   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 985   // Allocate the object live (grey) if the background collector has
 986   // started marking. This is necessary because the marker may
 987   // have passed this address and consequently this object will
 988   // not otherwise be greyed and would be incorrectly swept up.
 989   // Note that if this object contains references, the writing
 990   // of those references will dirty the card containing this object
 991   // allowing the object to be blackened (and its references scanned)
 992   // either during a preclean phase or at the final checkpoint.
 993   if (res != NULL) {
 994     collector()->direct_allocated(res, adjustedSize);
 995     _direct_allocated_words += adjustedSize;
 996     // allocation counters
 997     NOT_PRODUCT(
 998       _numObjectsAllocated++;
 999       _numWordsAllocated += (int)adjustedSize;
1000     )
1001   }
1002   return res;
1003 }
1004 
1005 // In the case of direct allocation by mutators in a generation that
1006 // is being concurrently collected, the object must be allocated
1007 // live (grey) if the background collector has started marking.
1008 // This is necessary because the marker may
1009 // have passed this address and consequently this object will
1010 // not otherwise be greyed and would be incorrectly swept up.
1011 // Note that if this object contains references, the writing
1012 // of those references will dirty the card containing this object
1013 // allowing the object to be blackened (and its references scanned)
1014 // either during a preclean phase or at the final checkpoint.
1015 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1016   assert(_markBitMap.covers(start, size), "Out of bounds");
1017   if (_collectorState >= Marking) {
1018     MutexLockerEx y(_markBitMap.lock(),
1019                     Mutex::_no_safepoint_check_flag);
1020     // [see comments preceding SweepClosure::do_blk() below for details]
1021     // 1. need to mark the object as live so it isn't collected
1022     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1023     // 3. need to mark the end of the object so sweeper can skip over it
1024     //    if it's uninitialized when the sweeper reaches it.
1025     _markBitMap.mark(start);          // object is live
1026     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1027     _markBitMap.mark(start + size - 1);
1028                                       // mark end of object
1029   }
1030   // check that oop looks uninitialized
1031   assert(oop(start)->klass() == NULL, "_klass should be NULL");
1032 }
1033 
1034 void CMSCollector::promoted(bool par, HeapWord* start,
1035                             bool is_obj_array, size_t obj_size) {
1036   assert(_markBitMap.covers(start), "Out of bounds");
1037   // See comment in direct_allocated() about when objects should
1038   // be allocated live.
1039   if (_collectorState >= Marking) {
1040     // we already hold the marking bit map lock, taken in
1041     // the prologue
1042     if (par) {
1043       _markBitMap.par_mark(start);
1044     } else {
1045       _markBitMap.mark(start);
1046     }
1047     // We don't need to mark the object as uninitialized (as
1048     // in direct_allocated above) because this is being done with the
1049     // world stopped and the object will be initialized by the
1050     // time the sweeper gets to look at it.
1051     assert(SafepointSynchronize::is_at_safepoint(),
1052            "expect promotion only at safepoints");
1053 
1054     if (_collectorState < Sweeping) {
1055       // Mark the appropriate cards in the modUnionTable, so that
1056       // this object gets scanned before the sweep. If this is
1057       // not done, CMS generation references in the object might
1058       // not get marked.
1059       // For the case of arrays, which are otherwise precisely
1060       // marked, we need to dirty the entire array, not just its head.
1061       if (is_obj_array) {
1062         // The [par_]mark_range() method expects mr.end() below to
1063         // be aligned to the granularity of a bit's representation
1064         // in the heap. In the case of the MUT below, that's a
1065         // card size.
1066         MemRegion mr(start,
1067                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1068                         CardTableModRefBS::card_size /* bytes */));
1069         if (par) {
1070           _modUnionTable.par_mark_range(mr);
1071         } else {
1072           _modUnionTable.mark_range(mr);
1073         }
1074       } else {  // not an obj array; we can just mark the head
1075         if (par) {
1076           _modUnionTable.par_mark(start);
1077         } else {
1078           _modUnionTable.mark(start);
1079         }
1080       }
1081     }
1082   }
1083 }
1084 
1085 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1086 {
1087   size_t delta = pointer_delta(addr, space->bottom());
1088   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1089 }
1090 
1091 void CMSCollector::icms_update_allocation_limits()
1092 {
1093   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1094   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1095 
1096   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1097   if (CMSTraceIncrementalPacing) {
1098     stats().print();
1099   }
1100 
1101   assert(duty_cycle <= 100, "invalid duty cycle");
1102   if (duty_cycle != 0) {
1103     // The duty_cycle is a percentage between 0 and 100; convert to words and
1104     // then compute the offset from the endpoints of the space.
1105     size_t free_words = eden->free() / HeapWordSize;
1106     double free_words_dbl = (double)free_words;
1107     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1108     size_t offset_words = (free_words - duty_cycle_words) / 2;
1109 
1110     _icms_start_limit = eden->top() + offset_words;
1111     _icms_stop_limit = eden->end() - offset_words;
1112 
1113     // The limits may be adjusted (shifted to the right) by
1114     // CMSIncrementalOffset, to allow the application more mutator time after a
1115     // young gen gc (when all mutators were stopped) and before CMS starts and
1116     // takes away one or more cpus.
1117     if (CMSIncrementalOffset != 0) {
1118       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1119       size_t adjustment = (size_t)adjustment_dbl;
1120       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1121       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1122         _icms_start_limit += adjustment;
1123         _icms_stop_limit = tmp_stop;
1124       }
1125     }
1126   }
1127   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1128     _icms_start_limit = _icms_stop_limit = eden->end();
1129   }
1130 
1131   // Install the new start limit.
1132   eden->set_soft_end(_icms_start_limit);
1133 
1134   if (CMSTraceIncrementalMode) {
1135     gclog_or_tty->print(" icms alloc limits:  "
1136                            PTR_FORMAT "," PTR_FORMAT
1137                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1138                            _icms_start_limit, _icms_stop_limit,
1139                            percent_of_space(eden, _icms_start_limit),
1140                            percent_of_space(eden, _icms_stop_limit));
1141     if (Verbose) {
1142       gclog_or_tty->print("eden:  ");
1143       eden->print_on(gclog_or_tty);
1144     }
1145   }
1146 }
1147 
1148 // Any changes here should try to maintain the invariant
1149 // that if this method is called with _icms_start_limit
1150 // and _icms_stop_limit both NULL, then it should return NULL
1151 // and not notify the icms thread.
1152 HeapWord*
1153 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1154                                        size_t word_size)
1155 {
1156   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1157   // nop.
1158   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1159     if (top <= _icms_start_limit) {
1160       if (CMSTraceIncrementalMode) {
1161         space->print_on(gclog_or_tty);
1162         gclog_or_tty->stamp();
1163         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1164                                ", new limit=" PTR_FORMAT
1165                                " (" SIZE_FORMAT "%%)",
1166                                top, _icms_stop_limit,
1167                                percent_of_space(space, _icms_stop_limit));
1168       }
1169       ConcurrentMarkSweepThread::start_icms();
1170       assert(top < _icms_stop_limit, "Tautology");
1171       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1172         return _icms_stop_limit;
1173       }
1174 
1175       // The allocation will cross both the _start and _stop limits, so do the
1176       // stop notification also and return end().
1177       if (CMSTraceIncrementalMode) {
1178         space->print_on(gclog_or_tty);
1179         gclog_or_tty->stamp();
1180         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1181                                ", new limit=" PTR_FORMAT
1182                                " (" SIZE_FORMAT "%%)",
1183                                top, space->end(),
1184                                percent_of_space(space, space->end()));
1185       }
1186       ConcurrentMarkSweepThread::stop_icms();
1187       return space->end();
1188     }
1189 
1190     if (top <= _icms_stop_limit) {
1191       if (CMSTraceIncrementalMode) {
1192         space->print_on(gclog_or_tty);
1193         gclog_or_tty->stamp();
1194         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1195                                ", new limit=" PTR_FORMAT
1196                                " (" SIZE_FORMAT "%%)",
1197                                top, space->end(),
1198                                percent_of_space(space, space->end()));
1199       }
1200       ConcurrentMarkSweepThread::stop_icms();
1201       return space->end();
1202     }
1203 
1204     if (CMSTraceIncrementalMode) {
1205       space->print_on(gclog_or_tty);
1206       gclog_or_tty->stamp();
1207       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1208                              ", new limit=" PTR_FORMAT,
1209                              top, NULL);
1210     }
1211   }
1212 
1213   return NULL;
1214 }
1215 
1216 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size, oop* ref) {
1217   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1218   // allocate, copy and if necessary update promoinfo --
1219   // delegate to underlying space.
1220   assert_lock_strong(freelistLock());
1221 
1222 #ifndef PRODUCT
1223   if (Universe::heap()->promotion_should_fail()) {
1224     return NULL;
1225   }
1226 #endif  // #ifndef PRODUCT
1227 
1228   oop res = _cmsSpace->promote(obj, obj_size, ref);
1229   if (res == NULL) {
1230     // expand and retry
1231     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1232     expand(s*HeapWordSize, MinHeapDeltaBytes,
1233       CMSExpansionCause::_satisfy_promotion);
1234     // Since there's currently no next generation, we don't try to promote
1235     // into a more senior generation.
1236     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1237                                "is made to pass on a possibly failing "
1238                                "promotion to next generation");
1239     res = _cmsSpace->promote(obj, obj_size, ref);
1240   }
1241   if (res != NULL) {
1242     // See comment in allocate() about when objects should
1243     // be allocated live.
1244     assert(obj->is_oop(), "Will dereference klass pointer below");
1245     collector()->promoted(false,           // Not parallel
1246                           (HeapWord*)res, obj->is_objArray(), obj_size);
1247     // promotion counters
1248     NOT_PRODUCT(
1249       _numObjectsPromoted++;
1250       _numWordsPromoted +=
1251         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1252     )
1253   }
1254   return res;
1255 }
1256 
1257 
1258 HeapWord*
1259 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1260                                              HeapWord* top,
1261                                              size_t word_sz)
1262 {
1263   return collector()->allocation_limit_reached(space, top, word_sz);
1264 }
1265 
1266 // Things to support parallel young-gen collection.
1267 oop
1268 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1269                                            oop old, markOop m,
1270                                            size_t word_sz) {
1271 #ifndef PRODUCT
1272   if (Universe::heap()->promotion_should_fail()) {
1273     return NULL;
1274   }
1275 #endif  // #ifndef PRODUCT
1276 
1277   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1278   PromotionInfo* promoInfo = &ps->promo;
1279   // if we are tracking promotions, then first ensure space for
1280   // promotion (including spooling space for saving header if necessary).
1281   // then allocate and copy, then track promoted info if needed.
1282   // When tracking (see PromotionInfo::track()), the mark word may
1283   // be displaced and in this case restoration of the mark word
1284   // occurs in the (oop_since_save_marks_)iterate phase.
1285   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1286     // Out of space for allocating spooling buffers;
1287     // try expanding and allocating spooling buffers.
1288     if (!expand_and_ensure_spooling_space(promoInfo)) {
1289       return NULL;
1290     }
1291   }
1292   assert(promoInfo->has_spooling_space(), "Control point invariant");
1293   HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1294   if (obj_ptr == NULL) {
1295      obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1296      if (obj_ptr == NULL) {
1297        return NULL;
1298      }
1299   }
1300   oop obj = oop(obj_ptr);
1301   assert(obj->klass() == NULL, "Object should be uninitialized here.");
1302   // Otherwise, copy the object.  Here we must be careful to insert the
1303   // klass pointer last, since this marks the block as an allocated object.
1304   HeapWord* old_ptr = (HeapWord*)old;
1305   if (word_sz > (size_t)oopDesc::header_size()) {
1306     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1307                                  obj_ptr + oopDesc::header_size(),
1308                                  word_sz - oopDesc::header_size());
1309   }
1310   // Restore the mark word copied above.
1311   obj->set_mark(m);
1312   // Now we can track the promoted object, if necessary.  We take care
1313   // To delay the transition from uninitialized to full object
1314   // (i.e., insertion of klass pointer) until after, so that it
1315   // atomically becomes a promoted object.
1316   if (promoInfo->tracking()) {
1317     promoInfo->track((PromotedObject*)obj, old->klass());
1318   }
1319   // Finally, install the klass pointer.
1320   obj->set_klass(old->klass());
1321 
1322   assert(old->is_oop(), "Will dereference klass ptr below");
1323   collector()->promoted(true,          // parallel
1324                         obj_ptr, old->is_objArray(), word_sz);
1325 
1326   NOT_PRODUCT(
1327     Atomic::inc(&_numObjectsPromoted);
1328     Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1329                 &_numWordsPromoted);
1330   )
1331 
1332   return obj;
1333 }
1334 
1335 void
1336 ConcurrentMarkSweepGeneration::
1337 par_promote_alloc_undo(int thread_num,
1338                        HeapWord* obj, size_t word_sz) {
1339   // CMS does not support promotion undo.
1340   ShouldNotReachHere();
1341 }
1342 
1343 void
1344 ConcurrentMarkSweepGeneration::
1345 par_promote_alloc_done(int thread_num) {
1346   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1347   ps->lab.retire();
1348 #if CFLS_LAB_REFILL_STATS
1349   if (thread_num == 0) {
1350     _cmsSpace->print_par_alloc_stats();
1351   }
1352 #endif
1353 }
1354 
1355 void
1356 ConcurrentMarkSweepGeneration::
1357 par_oop_since_save_marks_iterate_done(int thread_num) {
1358   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1359   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1360   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1361 }
1362 
1363 // XXXPERM
1364 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1365                                                    size_t size,
1366                                                    bool   tlab)
1367 {
1368   // We allow a STW collection only if a full
1369   // collection was requested.
1370   return full || should_allocate(size, tlab); // FIX ME !!!
1371   // This and promotion failure handling are connected at the
1372   // hip and should be fixed by untying them.
1373 }
1374 
1375 bool CMSCollector::shouldConcurrentCollect() {
1376   if (_full_gc_requested) {
1377     assert(ExplicitGCInvokesConcurrent, "Unexpected state");
1378     if (Verbose && PrintGCDetails) {
1379       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1380                              " gc request");
1381     }
1382     return true;
1383   }
1384 
1385   // For debugging purposes, change the type of collection.
1386   // If the rotation is not on the concurrent collection
1387   // type, don't start a concurrent collection.
1388   NOT_PRODUCT(
1389     if (RotateCMSCollectionTypes &&
1390         (_cmsGen->debug_collection_type() !=
1391           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1392       assert(_cmsGen->debug_collection_type() !=
1393         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1394         "Bad cms collection type");
1395       return false;
1396     }
1397   )
1398 
1399   FreelistLocker x(this);
1400   // ------------------------------------------------------------------
1401   // Print out lots of information which affects the initiation of
1402   // a collection.
1403   if (PrintCMSInitiationStatistics && stats().valid()) {
1404     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1405     gclog_or_tty->stamp();
1406     gclog_or_tty->print_cr("");
1407     stats().print_on(gclog_or_tty);
1408     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1409       stats().time_until_cms_gen_full());
1410     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1411     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1412                            _cmsGen->contiguous_available());
1413     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1414     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1415     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1416     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", initiatingOccupancy());
1417   }
1418   // ------------------------------------------------------------------
1419 
1420   // If the estimated time to complete a cms collection (cms_duration())
1421   // is less than the estimated time remaining until the cms generation
1422   // is full, start a collection.
1423   if (!UseCMSInitiatingOccupancyOnly) {
1424     if (stats().valid()) {
1425       if (stats().time_until_cms_start() == 0.0) {
1426         return true;
1427       }
1428     } else {
1429       // We want to conservatively collect somewhat early in order
1430       // to try and "bootstrap" our CMS/promotion statistics;
1431       // this branch will not fire after the first successful CMS
1432       // collection because the stats should then be valid.
1433       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1434         if (Verbose && PrintGCDetails) {
1435           gclog_or_tty->print_cr(
1436             " CMSCollector: collect for bootstrapping statistics:"
1437             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1438             _bootstrap_occupancy);
1439         }
1440         return true;
1441       }
1442     }
1443   }
1444 
1445   // Otherwise, we start a collection cycle if either the perm gen or
1446   // old gen want a collection cycle started. Each may use
1447   // an appropriate criterion for making this decision.
1448   // XXX We need to make sure that the gen expansion
1449   // criterion dovetails well with this.
1450   if (_cmsGen->shouldConcurrentCollect(initiatingOccupancy())) {
1451     if (Verbose && PrintGCDetails) {
1452       gclog_or_tty->print_cr("CMS old gen initiated");
1453     }
1454     return true;
1455   }
1456 
1457   if (cms_should_unload_classes() &&
1458       _permGen->shouldConcurrentCollect(initiatingOccupancy())) {
1459     if (Verbose && PrintGCDetails) {
1460      gclog_or_tty->print_cr("CMS perm gen initiated");
1461     }
1462     return true;
1463   }
1464 
1465   return false;
1466 }
1467 
1468 // Clear _expansion_cause fields of constituent generations
1469 void CMSCollector::clear_expansion_cause() {
1470   _cmsGen->clear_expansion_cause();
1471   _permGen->clear_expansion_cause();
1472 }
1473 
1474 bool ConcurrentMarkSweepGeneration::shouldConcurrentCollect(
1475   double initiatingOccupancy) {
1476   // We should be conservative in starting a collection cycle.  To
1477   // start too eagerly runs the risk of collecting too often in the
1478   // extreme.  To collect too rarely falls back on full collections,
1479   // which works, even if not optimum in terms of concurrent work.
1480   // As a work around for too eagerly collecting, use the flag
1481   // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1482   // giving the user an easily understandable way of controlling the
1483   // collections.
1484   // We want to start a new collection cycle if any of the following
1485   // conditions hold:
1486   // . our current occupancy exceeds the initiating occupancy, or
1487   // . we recently needed to expand and have not since that expansion,
1488   //   collected, or
1489   // . we are not using adaptive free lists and linear allocation is
1490   //   going to fail, or
1491   // . (for old gen) incremental collection has already failed or
1492   //   may soon fail in the near future as we may not be able to absorb
1493   //   promotions.
1494   assert_lock_strong(freelistLock());
1495 
1496   if (occupancy() > initiatingOccupancy) {
1497     if (PrintGCDetails && Verbose) {
1498       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1499         short_name(), occupancy(), initiatingOccupancy);
1500     }
1501     return true;
1502   }
1503   if (UseCMSInitiatingOccupancyOnly) {
1504     return false;
1505   }
1506   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1507     if (PrintGCDetails && Verbose) {
1508       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1509         short_name());
1510     }
1511     return true;
1512   }
1513   GenCollectedHeap* gch = GenCollectedHeap::heap();
1514   assert(gch->collector_policy()->is_two_generation_policy(),
1515          "You may want to check the correctness of the following");
1516   if (gch->incremental_collection_will_fail()) {
1517     if (PrintGCDetails && Verbose) {
1518       gclog_or_tty->print(" %s: collect because incremental collection will fail ",
1519         short_name());
1520     }
1521     return true;
1522   }
1523   if (!_cmsSpace->adaptive_freelists() &&
1524       _cmsSpace->linearAllocationWouldFail()) {
1525     if (PrintGCDetails && Verbose) {
1526       gclog_or_tty->print(" %s: collect because of linAB ",
1527         short_name());
1528     }
1529     return true;
1530   }
1531   return false;
1532 }
1533 
1534 void ConcurrentMarkSweepGeneration::collect(bool   full,
1535                                             bool   clear_all_soft_refs,
1536                                             size_t size,
1537                                             bool   tlab)
1538 {
1539   collector()->collect(full, clear_all_soft_refs, size, tlab);
1540 }
1541 
1542 void CMSCollector::collect(bool   full,
1543                            bool   clear_all_soft_refs,
1544                            size_t size,
1545                            bool   tlab)
1546 {
1547   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1548     // For debugging purposes skip the collection if the state
1549     // is not currently idle
1550     if (TraceCMSState) {
1551       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1552         Thread::current(), full, _collectorState);
1553     }
1554     return;
1555   }
1556 
1557   // The following "if" branch is present for defensive reasons.
1558   // In the current uses of this interface, it can be replaced with:
1559   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1560   // But I am not placing that assert here to allow future
1561   // generality in invoking this interface.
1562   if (GC_locker::is_active()) {
1563     // A consistency test for GC_locker
1564     assert(GC_locker::needs_gc(), "Should have been set already");
1565     // Skip this foreground collection, instead
1566     // expanding the heap if necessary.
1567     // Need the free list locks for the call to free() in compute_new_size()
1568     compute_new_size();
1569     return;
1570   }
1571   acquire_control_and_collect(full, clear_all_soft_refs);
1572   _full_gcs_since_conc_gc++;
1573 
1574 }
1575 
1576 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1577   GenCollectedHeap* gch = GenCollectedHeap::heap();
1578   unsigned int gc_count = gch->total_full_collections();
1579   if (gc_count == full_gc_count) {
1580     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1581     _full_gc_requested = true;
1582     CGC_lock->notify();   // nudge CMS thread
1583   }
1584 }
1585 
1586 
1587 // The foreground and background collectors need to coordinate in order
1588 // to make sure that they do not mutually interfere with CMS collections.
1589 // When a background collection is active,
1590 // the foreground collector may need to take over (preempt) and
1591 // synchronously complete an ongoing collection. Depending on the
1592 // frequency of the background collections and the heap usage
1593 // of the application, this preemption can be seldom or frequent.
1594 // There are only certain
1595 // points in the background collection that the "collection-baton"
1596 // can be passed to the foreground collector.
1597 //
1598 // The foreground collector will wait for the baton before
1599 // starting any part of the collection.  The foreground collector
1600 // will only wait at one location.
1601 //
1602 // The background collector will yield the baton before starting a new
1603 // phase of the collection (e.g., before initial marking, marking from roots,
1604 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1605 // of the loop which switches the phases. The background collector does some
1606 // of the phases (initial mark, final re-mark) with the world stopped.
1607 // Because of locking involved in stopping the world,
1608 // the foreground collector should not block waiting for the background
1609 // collector when it is doing a stop-the-world phase.  The background
1610 // collector will yield the baton at an additional point just before
1611 // it enters a stop-the-world phase.  Once the world is stopped, the
1612 // background collector checks the phase of the collection.  If the
1613 // phase has not changed, it proceeds with the collection.  If the
1614 // phase has changed, it skips that phase of the collection.  See
1615 // the comments on the use of the Heap_lock in collect_in_background().
1616 //
1617 // Variable used in baton passing.
1618 //   _foregroundGCIsActive - Set to true by the foreground collector when
1619 //      it wants the baton.  The foreground clears it when it has finished
1620 //      the collection.
1621 //   _foregroundGCShouldWait - Set to true by the background collector
1622 //        when it is running.  The foreground collector waits while
1623 //      _foregroundGCShouldWait is true.
1624 //  CGC_lock - monitor used to protect access to the above variables
1625 //      and to notify the foreground and background collectors.
1626 //  _collectorState - current state of the CMS collection.
1627 //
1628 // The foreground collector
1629 //   acquires the CGC_lock
1630 //   sets _foregroundGCIsActive
1631 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1632 //     various locks acquired in preparation for the collection
1633 //     are released so as not to block the background collector
1634 //     that is in the midst of a collection
1635 //   proceeds with the collection
1636 //   clears _foregroundGCIsActive
1637 //   returns
1638 //
1639 // The background collector in a loop iterating on the phases of the
1640 //      collection
1641 //   acquires the CGC_lock
1642 //   sets _foregroundGCShouldWait
1643 //   if _foregroundGCIsActive is set
1644 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1645 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1646 //     and exits the loop.
1647 //   otherwise
1648 //     proceed with that phase of the collection
1649 //     if the phase is a stop-the-world phase,
1650 //       yield the baton once more just before enqueueing
1651 //       the stop-world CMS operation (executed by the VM thread).
1652 //   returns after all phases of the collection are done
1653 //
1654 
1655 void CMSCollector::acquire_control_and_collect(bool full,
1656         bool clear_all_soft_refs) {
1657   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1658   assert(!Thread::current()->is_ConcurrentGC_thread(),
1659          "shouldn't try to acquire control from self!");
1660 
1661   // Start the protocol for acquiring control of the
1662   // collection from the background collector (aka CMS thread).
1663   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1664          "VM thread should have CMS token");
1665   // Remember the possibly interrupted state of an ongoing
1666   // concurrent collection
1667   CollectorState first_state = _collectorState;
1668 
1669   // Signal to a possibly ongoing concurrent collection that
1670   // we want to do a foreground collection.
1671   _foregroundGCIsActive = true;
1672 
1673   // Disable incremental mode during a foreground collection.
1674   ICMSDisabler icms_disabler;
1675 
1676   // release locks and wait for a notify from the background collector
1677   // releasing the locks in only necessary for phases which
1678   // do yields to improve the granularity of the collection.
1679   assert_lock_strong(bitMapLock());
1680   // We need to lock the Free list lock for the space that we are
1681   // currently collecting.
1682   assert(haveFreelistLocks(), "Must be holding free list locks");
1683   bitMapLock()->unlock();
1684   releaseFreelistLocks();
1685   {
1686     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1687     if (_foregroundGCShouldWait) {
1688       // We are going to be waiting for action for the CMS thread;
1689       // it had better not be gone (for instance at shutdown)!
1690       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1691              "CMS thread must be running");
1692       // Wait here until the background collector gives us the go-ahead
1693       ConcurrentMarkSweepThread::clear_CMS_flag(
1694         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1695       // Get a possibly blocked CMS thread going:
1696       //   Note that we set _foregroundGCIsActive true above,
1697       //   without protection of the CGC_lock.
1698       CGC_lock->notify();
1699       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1700              "Possible deadlock");
1701       while (_foregroundGCShouldWait) {
1702         // wait for notification
1703         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1704         // Possibility of delay/starvation here, since CMS token does
1705         // not know to give priority to VM thread? Actually, i think
1706         // there wouldn't be any delay/starvation, but the proof of
1707         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1708       }
1709       ConcurrentMarkSweepThread::set_CMS_flag(
1710         ConcurrentMarkSweepThread::CMS_vm_has_token);
1711     }
1712   }
1713   // The CMS_token is already held.  Get back the other locks.
1714   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1715          "VM thread should have CMS token");
1716   getFreelistLocks();
1717   bitMapLock()->lock_without_safepoint_check();
1718   if (TraceCMSState) {
1719     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1720       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1721     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1722   }
1723 
1724   // Check if we need to do a compaction, or if not, whether
1725   // we need to start the mark-sweep from scratch.
1726   bool should_compact    = false;
1727   bool should_start_over = false;
1728   decide_foreground_collection_type(clear_all_soft_refs,
1729     &should_compact, &should_start_over);
1730 
1731 NOT_PRODUCT(
1732   if (RotateCMSCollectionTypes) {
1733     if (_cmsGen->debug_collection_type() ==
1734         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1735       should_compact = true;
1736     } else if (_cmsGen->debug_collection_type() ==
1737                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1738       should_compact = false;
1739     }
1740   }
1741 )
1742 
1743   if (PrintGCDetails && first_state > Idling) {
1744     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1745     if (GCCause::is_user_requested_gc(cause) ||
1746         GCCause::is_serviceability_requested_gc(cause)) {
1747       gclog_or_tty->print(" (concurrent mode interrupted)");
1748     } else {
1749       gclog_or_tty->print(" (concurrent mode failure)");
1750     }
1751   }
1752 
1753   if (should_compact) {
1754     // If the collection is being acquired from the background
1755     // collector, there may be references on the discovered
1756     // references lists that have NULL referents (being those
1757     // that were concurrently cleared by a mutator) or
1758     // that are no longer active (having been enqueued concurrently
1759     // by the mutator).
1760     // Scrub the list of those references because Mark-Sweep-Compact
1761     // code assumes referents are not NULL and that all discovered
1762     // Reference objects are active.
1763     ref_processor()->clean_up_discovered_references();
1764 
1765     do_compaction_work(clear_all_soft_refs);
1766 
1767     // Has the GC time limit been exceeded?
1768     check_gc_time_limit();
1769 
1770   } else {
1771     do_mark_sweep_work(clear_all_soft_refs, first_state,
1772       should_start_over);
1773   }
1774   // Reset the expansion cause, now that we just completed
1775   // a collection cycle.
1776   clear_expansion_cause();
1777   _foregroundGCIsActive = false;
1778   return;
1779 }
1780 
1781 void CMSCollector::check_gc_time_limit() {
1782 
1783   // Ignore explicit GC's.  Exiting here does not set the flag and
1784   // does not reset the count.  Updating of the averages for system
1785   // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
1786   GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause();
1787   if (GCCause::is_user_requested_gc(gc_cause) ||
1788       GCCause::is_serviceability_requested_gc(gc_cause)) {
1789     return;
1790   }
1791 
1792   // Calculate the fraction of the CMS generation was freed during
1793   // the last collection.
1794   // Only consider the STW compacting cost for now.
1795   //
1796   // Note that the gc time limit test only works for the collections
1797   // of the young gen + tenured gen and not for collections of the
1798   // permanent gen.  That is because the calculation of the space
1799   // freed by the collection is the free space in the young gen +
1800   // tenured gen.
1801 
1802   double fraction_free =
1803     ((double)_cmsGen->free())/((double)_cmsGen->max_capacity());
1804   if ((100.0 * size_policy()->compacting_gc_cost()) >
1805          ((double) GCTimeLimit) &&
1806         ((fraction_free * 100) < GCHeapFreeLimit)) {
1807     size_policy()->inc_gc_time_limit_count();
1808     if (UseGCOverheadLimit &&
1809         (size_policy()->gc_time_limit_count() >
1810          AdaptiveSizePolicyGCTimeLimitThreshold)) {
1811       size_policy()->set_gc_time_limit_exceeded(true);
1812       // Avoid consecutive OOM due to the gc time limit by resetting
1813       // the counter.
1814       size_policy()->reset_gc_time_limit_count();
1815       if (PrintGCDetails) {
1816         gclog_or_tty->print_cr("      GC is exceeding overhead limit "
1817           "of %d%%", GCTimeLimit);
1818       }
1819     } else {
1820       if (PrintGCDetails) {
1821         gclog_or_tty->print_cr("      GC would exceed overhead limit "
1822           "of %d%%", GCTimeLimit);
1823       }
1824     }
1825   } else {
1826     size_policy()->reset_gc_time_limit_count();
1827   }
1828 }
1829 
1830 // Resize the perm generation and the tenured generation
1831 // after obtaining the free list locks for the
1832 // two generations.
1833 void CMSCollector::compute_new_size() {
1834   assert_locked_or_safepoint(Heap_lock);
1835   FreelistLocker z(this);
1836   _permGen->compute_new_size();
1837   _cmsGen->compute_new_size();
1838 }
1839 
1840 // A work method used by foreground collection to determine
1841 // what type of collection (compacting or not, continuing or fresh)
1842 // it should do.
1843 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1844 // and CMSCompactWhenClearAllSoftRefs the default in the future
1845 // and do away with the flags after a suitable period.
1846 void CMSCollector::decide_foreground_collection_type(
1847   bool clear_all_soft_refs, bool* should_compact,
1848   bool* should_start_over) {
1849   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1850   // flag is set, and we have either requested a System.gc() or
1851   // the number of full gc's since the last concurrent cycle
1852   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1853   // or if an incremental collection has failed
1854   GenCollectedHeap* gch = GenCollectedHeap::heap();
1855   assert(gch->collector_policy()->is_two_generation_policy(),
1856          "You may want to check the correctness of the following");
1857   // Inform cms gen if this was due to partial collection failing.
1858   // The CMS gen may use this fact to determine its expansion policy.
1859   if (gch->incremental_collection_will_fail()) {
1860     assert(!_cmsGen->incremental_collection_failed(),
1861            "Should have been noticed, reacted to and cleared");
1862     _cmsGen->set_incremental_collection_failed();
1863   }
1864   *should_compact =
1865     UseCMSCompactAtFullCollection &&
1866     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1867      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1868      gch->incremental_collection_will_fail());
1869   *should_start_over = false;
1870   if (clear_all_soft_refs && !*should_compact) {
1871     // We are about to do a last ditch collection attempt
1872     // so it would normally make sense to do a compaction
1873     // to reclaim as much space as possible.
1874     if (CMSCompactWhenClearAllSoftRefs) {
1875       // Default: The rationale is that in this case either
1876       // we are past the final marking phase, in which case
1877       // we'd have to start over, or so little has been done
1878       // that there's little point in saving that work. Compaction
1879       // appears to be the sensible choice in either case.
1880       *should_compact = true;
1881     } else {
1882       // We have been asked to clear all soft refs, but not to
1883       // compact. Make sure that we aren't past the final checkpoint
1884       // phase, for that is where we process soft refs. If we are already
1885       // past that phase, we'll need to redo the refs discovery phase and
1886       // if necessary clear soft refs that weren't previously
1887       // cleared. We do so by remembering the phase in which
1888       // we came in, and if we are past the refs processing
1889       // phase, we'll choose to just redo the mark-sweep
1890       // collection from scratch.
1891       if (_collectorState > FinalMarking) {
1892         // We are past the refs processing phase;
1893         // start over and do a fresh synchronous CMS cycle
1894         _collectorState = Resetting; // skip to reset to start new cycle
1895         reset(false /* == !asynch */);
1896         *should_start_over = true;
1897       } // else we can continue a possibly ongoing current cycle
1898     }
1899   }
1900 }
1901 
1902 // A work method used by the foreground collector to do
1903 // a mark-sweep-compact.
1904 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1905   GenCollectedHeap* gch = GenCollectedHeap::heap();
1906   TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1907   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1908     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1909       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1910   }
1911 
1912   // Sample collection interval time and reset for collection pause.
1913   if (UseAdaptiveSizePolicy) {
1914     size_policy()->msc_collection_begin();
1915   }
1916 
1917   // Temporarily widen the span of the weak reference processing to
1918   // the entire heap.
1919   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1920   ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1921 
1922   // Temporarily, clear the "is_alive_non_header" field of the
1923   // reference processor.
1924   ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1925 
1926   // Temporarily make reference _processing_ single threaded (non-MT).
1927   ReferenceProcessorMTProcMutator z(ref_processor(), false);
1928 
1929   // Temporarily make refs discovery atomic
1930   ReferenceProcessorAtomicMutator w(ref_processor(), true);
1931 
1932   ref_processor()->set_enqueuing_is_done(false);
1933   ref_processor()->enable_discovery();
1934   // If an asynchronous collection finishes, the _modUnionTable is
1935   // all clear.  If we are assuming the collection from an asynchronous
1936   // collection, clear the _modUnionTable.
1937   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1938     "_modUnionTable should be clear if the baton was not passed");
1939   _modUnionTable.clear_all();
1940 
1941   // We must adjust the allocation statistics being maintained
1942   // in the free list space. We do so by reading and clearing
1943   // the sweep timer and updating the block flux rate estimates below.
1944   assert(_sweep_timer.is_active(), "We should never see the timer inactive");
1945   _sweep_timer.stop();
1946   // Note that we do not use this sample to update the _sweep_estimate.
1947   _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
1948                                           _sweep_estimate.padded_average());
1949 
1950   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1951     ref_processor(), clear_all_soft_refs);
1952   #ifdef ASSERT
1953     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1954     size_t free_size = cms_space->free();
1955     assert(free_size ==
1956            pointer_delta(cms_space->end(), cms_space->compaction_top())
1957            * HeapWordSize,
1958       "All the free space should be compacted into one chunk at top");
1959     assert(cms_space->dictionary()->totalChunkSize(
1960                                       debug_only(cms_space->freelistLock())) == 0 ||
1961            cms_space->totalSizeInIndexedFreeLists() == 0,
1962       "All the free space should be in a single chunk");
1963     size_t num = cms_space->totalCount();
1964     assert((free_size == 0 && num == 0) ||
1965            (free_size > 0  && (num == 1 || num == 2)),
1966          "There should be at most 2 free chunks after compaction");
1967   #endif // ASSERT
1968   _collectorState = Resetting;
1969   assert(_restart_addr == NULL,
1970          "Should have been NULL'd before baton was passed");
1971   reset(false /* == !asynch */);
1972   _cmsGen->reset_after_compaction();
1973 
1974   if (verifying() && !cms_should_unload_classes()) {
1975     perm_gen_verify_bit_map()->clear_all();
1976   }
1977 
1978   // Clear any data recorded in the PLAB chunk arrays.
1979   if (_survivor_plab_array != NULL) {
1980     reset_survivor_plab_arrays();
1981   }
1982 
1983   // Adjust the per-size allocation stats for the next epoch.
1984   _cmsGen->cmsSpace()->endSweepFLCensus(sweepCount() /* fake */);
1985   // Restart the "sweep timer" for next epoch.
1986   _sweep_timer.reset();
1987   _sweep_timer.start();
1988 
1989   // Sample collection pause time and reset for collection interval.
1990   if (UseAdaptiveSizePolicy) {
1991     size_policy()->msc_collection_end(gch->gc_cause());
1992   }
1993 
1994   // For a mark-sweep-compact, compute_new_size() will be called
1995   // in the heap's do_collection() method.
1996 }
1997 
1998 // A work method used by the foreground collector to do
1999 // a mark-sweep, after taking over from a possibly on-going
2000 // concurrent mark-sweep collection.
2001 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2002   CollectorState first_state, bool should_start_over) {
2003   if (PrintGC && Verbose) {
2004     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2005       "collector with count %d",
2006       _full_gcs_since_conc_gc);
2007   }
2008   switch (_collectorState) {
2009     case Idling:
2010       if (first_state == Idling || should_start_over) {
2011         // The background GC was not active, or should
2012         // restarted from scratch;  start the cycle.
2013         _collectorState = InitialMarking;
2014       }
2015       // If first_state was not Idling, then a background GC
2016       // was in progress and has now finished.  No need to do it
2017       // again.  Leave the state as Idling.
2018       break;
2019     case Precleaning:
2020       // In the foreground case don't do the precleaning since
2021       // it is not done concurrently and there is extra work
2022       // required.
2023       _collectorState = FinalMarking;
2024   }
2025   if (PrintGCDetails &&
2026       (_collectorState > Idling ||
2027        !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2028     gclog_or_tty->print(" (concurrent mode failure)");
2029   }
2030   collect_in_foreground(clear_all_soft_refs);
2031 
2032   // For a mark-sweep, compute_new_size() will be called
2033   // in the heap's do_collection() method.
2034 }
2035 
2036 
2037 void CMSCollector::getFreelistLocks() const {
2038   // Get locks for all free lists in all generations that this
2039   // collector is responsible for
2040   _cmsGen->freelistLock()->lock_without_safepoint_check();
2041   _permGen->freelistLock()->lock_without_safepoint_check();
2042 }
2043 
2044 void CMSCollector::releaseFreelistLocks() const {
2045   // Release locks for all free lists in all generations that this
2046   // collector is responsible for
2047   _cmsGen->freelistLock()->unlock();
2048   _permGen->freelistLock()->unlock();
2049 }
2050 
2051 bool CMSCollector::haveFreelistLocks() const {
2052   // Check locks for all free lists in all generations that this
2053   // collector is responsible for
2054   assert_lock_strong(_cmsGen->freelistLock());
2055   assert_lock_strong(_permGen->freelistLock());
2056   PRODUCT_ONLY(ShouldNotReachHere());
2057   return true;
2058 }
2059 
2060 // A utility class that is used by the CMS collector to
2061 // temporarily "release" the foreground collector from its
2062 // usual obligation to wait for the background collector to
2063 // complete an ongoing phase before proceeding.
2064 class ReleaseForegroundGC: public StackObj {
2065  private:
2066   CMSCollector* _c;
2067  public:
2068   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2069     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2070     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2071     // allow a potentially blocked foreground collector to proceed
2072     _c->_foregroundGCShouldWait = false;
2073     if (_c->_foregroundGCIsActive) {
2074       CGC_lock->notify();
2075     }
2076     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2077            "Possible deadlock");
2078   }
2079 
2080   ~ReleaseForegroundGC() {
2081     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2082     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2083     _c->_foregroundGCShouldWait = true;
2084   }
2085 };
2086 
2087 // There are separate collect_in_background and collect_in_foreground because of
2088 // the different locking requirements of the background collector and the
2089 // foreground collector.  There was originally an attempt to share
2090 // one "collect" method between the background collector and the foreground
2091 // collector but the if-then-else required made it cleaner to have
2092 // separate methods.
2093 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2094   assert(Thread::current()->is_ConcurrentGC_thread(),
2095     "A CMS asynchronous collection is only allowed on a CMS thread.");
2096 
2097   GenCollectedHeap* gch = GenCollectedHeap::heap();
2098   {
2099     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2100     MutexLockerEx hl(Heap_lock, safepoint_check);
2101     MutexLockerEx x(CGC_lock, safepoint_check);
2102     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2103       // The foreground collector is active or we're
2104       // not using asynchronous collections.  Skip this
2105       // background collection.
2106       assert(!_foregroundGCShouldWait, "Should be clear");
2107       return;
2108     } else {
2109       assert(_collectorState == Idling, "Should be idling before start.");
2110       _collectorState = InitialMarking;
2111       // Reset the expansion cause, now that we are about to begin
2112       // a new cycle.
2113       clear_expansion_cause();
2114     }
2115     _unloaded_classes_last_cycle = cms_should_unload_classes(); // ... from last cycle
2116     // This controls class unloading in response to an explicit gc request.
2117     // If ExplicitGCInvokesConcurrentAndUnloadsClasses is set, then
2118     // we will unload classes even if CMSClassUnloadingEnabled is not set.
2119     // See CR 6541037 and related CRs.
2120     _unload_classes = _full_gc_requested                      // ... for this cycle
2121                       && ExplicitGCInvokesConcurrentAndUnloadsClasses;
2122     _full_gc_requested = false;           // acks all outstanding full gc requests
2123     // Signal that we are about to start a collection
2124     gch->increment_total_full_collections();  // ... starting a collection cycle
2125     _collection_count_start = gch->total_full_collections();
2126   }
2127 
2128   // Used for PrintGC
2129   size_t prev_used;
2130   if (PrintGC && Verbose) {
2131     prev_used = _cmsGen->used(); // XXXPERM
2132   }
2133 
2134   // The change of the collection state is normally done at this level;
2135   // the exceptions are phases that are executed while the world is
2136   // stopped.  For those phases the change of state is done while the
2137   // world is stopped.  For baton passing purposes this allows the
2138   // background collector to finish the phase and change state atomically.
2139   // The foreground collector cannot wait on a phase that is done
2140   // while the world is stopped because the foreground collector already
2141   // has the world stopped and would deadlock.
2142   while (_collectorState != Idling) {
2143     if (TraceCMSState) {
2144       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2145         Thread::current(), _collectorState);
2146     }
2147     // The foreground collector
2148     //   holds the Heap_lock throughout its collection.
2149     //   holds the CMS token (but not the lock)
2150     //     except while it is waiting for the background collector to yield.
2151     //
2152     // The foreground collector should be blocked (not for long)
2153     //   if the background collector is about to start a phase
2154     //   executed with world stopped.  If the background
2155     //   collector has already started such a phase, the
2156     //   foreground collector is blocked waiting for the
2157     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2158     //   are executed in the VM thread.
2159     //
2160     // The locking order is
2161     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2162     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2163     //   CMS token  (claimed in
2164     //                stop_world_and_do() -->
2165     //                  safepoint_synchronize() -->
2166     //                    CMSThread::synchronize())
2167 
2168     {
2169       // Check if the FG collector wants us to yield.
2170       CMSTokenSync x(true); // is cms thread
2171       if (waitForForegroundGC()) {
2172         // We yielded to a foreground GC, nothing more to be
2173         // done this round.
2174         assert(_foregroundGCShouldWait == false, "We set it to false in "
2175                "waitForForegroundGC()");
2176         if (TraceCMSState) {
2177           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2178             " exiting collection CMS state %d",
2179             Thread::current(), _collectorState);
2180         }
2181         return;
2182       } else {
2183         // The background collector can run but check to see if the
2184         // foreground collector has done a collection while the
2185         // background collector was waiting to get the CGC_lock
2186         // above.  If yes, break so that _foregroundGCShouldWait
2187         // is cleared before returning.
2188         if (_collectorState == Idling) {
2189           break;
2190         }
2191       }
2192     }
2193 
2194     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2195       "should be waiting");
2196 
2197     switch (_collectorState) {
2198       case InitialMarking:
2199         {
2200           ReleaseForegroundGC x(this);
2201           stats().record_cms_begin();
2202 
2203           VM_CMS_Initial_Mark initial_mark_op(this);
2204           VMThread::execute(&initial_mark_op);
2205         }
2206         // The collector state may be any legal state at this point
2207         // since the background collector may have yielded to the
2208         // foreground collector.
2209         break;
2210       case Marking:
2211         // initial marking in checkpointRootsInitialWork has been completed
2212         if (markFromRoots(true)) { // we were successful
2213           assert(_collectorState == Precleaning, "Collector state should "
2214             "have changed");
2215         } else {
2216           assert(_foregroundGCIsActive, "Internal state inconsistency");
2217         }
2218         break;
2219       case Precleaning:
2220         if (UseAdaptiveSizePolicy) {
2221           size_policy()->concurrent_precleaning_begin();
2222         }
2223         // marking from roots in markFromRoots has been completed
2224         preclean();
2225         if (UseAdaptiveSizePolicy) {
2226           size_policy()->concurrent_precleaning_end();
2227         }
2228         assert(_collectorState == AbortablePreclean ||
2229                _collectorState == FinalMarking,
2230                "Collector state should have changed");
2231         break;
2232       case AbortablePreclean:
2233         if (UseAdaptiveSizePolicy) {
2234         size_policy()->concurrent_phases_resume();
2235         }
2236         abortable_preclean();
2237         if (UseAdaptiveSizePolicy) {
2238           size_policy()->concurrent_precleaning_end();
2239         }
2240         assert(_collectorState == FinalMarking, "Collector state should "
2241           "have changed");
2242         break;
2243       case FinalMarking:
2244         {
2245           ReleaseForegroundGC x(this);
2246 
2247           VM_CMS_Final_Remark final_remark_op(this);
2248           VMThread::execute(&final_remark_op);
2249           }
2250         assert(_foregroundGCShouldWait, "block post-condition");
2251         break;
2252       case Sweeping:
2253         if (UseAdaptiveSizePolicy) {
2254           size_policy()->concurrent_sweeping_begin();
2255         }
2256         // final marking in checkpointRootsFinal has been completed
2257         sweep(true);
2258         assert(_collectorState == Resizing, "Collector state change "
2259           "to Resizing must be done under the free_list_lock");
2260         _full_gcs_since_conc_gc = 0;
2261 
2262         // Stop the timers for adaptive size policy for the concurrent phases
2263         if (UseAdaptiveSizePolicy) {
2264           size_policy()->concurrent_sweeping_end();
2265           size_policy()->concurrent_phases_end(gch->gc_cause(),
2266                                              gch->prev_gen(_cmsGen)->capacity(),
2267                                              _cmsGen->free());
2268         }
2269 
2270       case Resizing: {
2271         // Sweeping has been completed...
2272         // At this point the background collection has completed.
2273         // Don't move the call to compute_new_size() down
2274         // into code that might be executed if the background
2275         // collection was preempted.
2276         {
2277           ReleaseForegroundGC x(this);   // unblock FG collection
2278           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2279           CMSTokenSync        z(true);   // not strictly needed.
2280           if (_collectorState == Resizing) {
2281             compute_new_size();
2282             _collectorState = Resetting;
2283           } else {
2284             assert(_collectorState == Idling, "The state should only change"
2285                    " because the foreground collector has finished the collection");
2286           }
2287         }
2288         break;
2289       }
2290       case Resetting:
2291         // CMS heap resizing has been completed
2292         reset(true);
2293         assert(_collectorState == Idling, "Collector state should "
2294           "have changed");
2295         stats().record_cms_end();
2296         // Don't move the concurrent_phases_end() and compute_new_size()
2297         // calls to here because a preempted background collection
2298         // has it's state set to "Resetting".
2299         break;
2300       case Idling:
2301       default:
2302         ShouldNotReachHere();
2303         break;
2304     }
2305     if (TraceCMSState) {
2306       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2307         Thread::current(), _collectorState);
2308     }
2309     assert(_foregroundGCShouldWait, "block post-condition");
2310   }
2311 
2312   // Should this be in gc_epilogue?
2313   collector_policy()->counters()->update_counters();
2314 
2315   {
2316     // Clear _foregroundGCShouldWait and, in the event that the
2317     // foreground collector is waiting, notify it, before
2318     // returning.
2319     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2320     _foregroundGCShouldWait = false;
2321     if (_foregroundGCIsActive) {
2322       CGC_lock->notify();
2323     }
2324     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2325            "Possible deadlock");
2326   }
2327   if (TraceCMSState) {
2328     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2329       " exiting collection CMS state %d",
2330       Thread::current(), _collectorState);
2331   }
2332   if (PrintGC && Verbose) {
2333     _cmsGen->print_heap_change(prev_used);
2334   }
2335 }
2336 
2337 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2338   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2339          "Foreground collector should be waiting, not executing");
2340   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2341     "may only be done by the VM Thread with the world stopped");
2342   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2343          "VM thread should have CMS token");
2344 
2345   NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2346     true, gclog_or_tty);)
2347   if (UseAdaptiveSizePolicy) {
2348     size_policy()->ms_collection_begin();
2349   }
2350   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2351 
2352   HandleMark hm;  // Discard invalid handles created during verification
2353 
2354   if (VerifyBeforeGC &&
2355       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2356     Universe::verify(true);
2357   }
2358 
2359   bool init_mark_was_synchronous = false; // until proven otherwise
2360   while (_collectorState != Idling) {
2361     if (TraceCMSState) {
2362       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2363         Thread::current(), _collectorState);
2364     }
2365     switch (_collectorState) {
2366       case InitialMarking:
2367         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2368         checkpointRootsInitial(false);
2369         assert(_collectorState == Marking, "Collector state should have changed"
2370           " within checkpointRootsInitial()");
2371         break;
2372       case Marking:
2373         // initial marking in checkpointRootsInitialWork has been completed
2374         if (VerifyDuringGC &&
2375             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2376           gclog_or_tty->print("Verify before initial mark: ");
2377           Universe::verify(true);
2378         }
2379         {
2380           bool res = markFromRoots(false);
2381           assert(res && _collectorState == FinalMarking, "Collector state should "
2382             "have changed");
2383           break;
2384         }
2385       case FinalMarking:
2386         if (VerifyDuringGC &&
2387             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2388           gclog_or_tty->print("Verify before re-mark: ");
2389           Universe::verify(true);
2390         }
2391         checkpointRootsFinal(false, clear_all_soft_refs,
2392                              init_mark_was_synchronous);
2393         assert(_collectorState == Sweeping, "Collector state should not "
2394           "have changed within checkpointRootsFinal()");
2395         break;
2396       case Sweeping:
2397         // final marking in checkpointRootsFinal has been completed
2398         if (VerifyDuringGC &&
2399             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2400           gclog_or_tty->print("Verify before sweep: ");
2401           Universe::verify(true);
2402         }
2403         sweep(false);
2404         assert(_collectorState == Resizing, "Incorrect state");
2405         break;
2406       case Resizing: {
2407         // Sweeping has been completed; the actual resize in this case
2408         // is done separately; nothing to be done in this state.
2409         _collectorState = Resetting;
2410         break;
2411       }
2412       case Resetting:
2413         // The heap has been resized.
2414         if (VerifyDuringGC &&
2415             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2416           gclog_or_tty->print("Verify before reset: ");
2417           Universe::verify(true);
2418         }
2419         reset(false);
2420         assert(_collectorState == Idling, "Collector state should "
2421           "have changed");
2422         break;
2423       case Precleaning:
2424       case AbortablePreclean:
2425         // Elide the preclean phase
2426         _collectorState = FinalMarking;
2427         break;
2428       default:
2429         ShouldNotReachHere();
2430     }
2431     if (TraceCMSState) {
2432       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2433         Thread::current(), _collectorState);
2434     }
2435   }
2436 
2437   if (UseAdaptiveSizePolicy) {
2438     GenCollectedHeap* gch = GenCollectedHeap::heap();
2439     size_policy()->ms_collection_end(gch->gc_cause());
2440   }
2441 
2442   if (VerifyAfterGC &&
2443       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2444     Universe::verify(true);
2445   }
2446   if (TraceCMSState) {
2447     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2448       " exiting collection CMS state %d",
2449       Thread::current(), _collectorState);
2450   }
2451 }
2452 
2453 bool CMSCollector::waitForForegroundGC() {
2454   bool res = false;
2455   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2456          "CMS thread should have CMS token");
2457   // Block the foreground collector until the
2458   // background collectors decides whether to
2459   // yield.
2460   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2461   _foregroundGCShouldWait = true;
2462   if (_foregroundGCIsActive) {
2463     // The background collector yields to the
2464     // foreground collector and returns a value
2465     // indicating that it has yielded.  The foreground
2466     // collector can proceed.
2467     res = true;
2468     _foregroundGCShouldWait = false;
2469     ConcurrentMarkSweepThread::clear_CMS_flag(
2470       ConcurrentMarkSweepThread::CMS_cms_has_token);
2471     ConcurrentMarkSweepThread::set_CMS_flag(
2472       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2473     // Get a possibly blocked foreground thread going
2474     CGC_lock->notify();
2475     if (TraceCMSState) {
2476       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2477         Thread::current(), _collectorState);
2478     }
2479     while (_foregroundGCIsActive) {
2480       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2481     }
2482     ConcurrentMarkSweepThread::set_CMS_flag(
2483       ConcurrentMarkSweepThread::CMS_cms_has_token);
2484     ConcurrentMarkSweepThread::clear_CMS_flag(
2485       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2486   }
2487   if (TraceCMSState) {
2488     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2489       Thread::current(), _collectorState);
2490   }
2491   return res;
2492 }
2493 
2494 // Because of the need to lock the free lists and other structures in
2495 // the collector, common to all the generations that the collector is
2496 // collecting, we need the gc_prologues of individual CMS generations
2497 // delegate to their collector. It may have been simpler had the
2498 // current infrastructure allowed one to call a prologue on a
2499 // collector. In the absence of that we have the generation's
2500 // prologue delegate to the collector, which delegates back
2501 // some "local" work to a worker method in the individual generations
2502 // that it's responsible for collecting, while itself doing any
2503 // work common to all generations it's responsible for. A similar
2504 // comment applies to the  gc_epilogue()'s.
2505 // The role of the varaible _between_prologue_and_epilogue is to
2506 // enforce the invocation protocol.
2507 void CMSCollector::gc_prologue(bool full) {
2508   // Call gc_prologue_work() for each CMSGen and PermGen that
2509   // we are responsible for.
2510 
2511   // The following locking discipline assumes that we are only called
2512   // when the world is stopped.
2513   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2514 
2515   // The CMSCollector prologue must call the gc_prologues for the
2516   // "generations" (including PermGen if any) that it's responsible
2517   // for.
2518 
2519   assert(   Thread::current()->is_VM_thread()
2520          || (   CMSScavengeBeforeRemark
2521              && Thread::current()->is_ConcurrentGC_thread()),
2522          "Incorrect thread type for prologue execution");
2523 
2524   if (_between_prologue_and_epilogue) {
2525     // We have already been invoked; this is a gc_prologue delegation
2526     // from yet another CMS generation that we are responsible for, just
2527     // ignore it since all relevant work has already been done.
2528     return;
2529   }
2530 
2531   // set a bit saying prologue has been called; cleared in epilogue
2532   _between_prologue_and_epilogue = true;
2533   // Claim locks for common data structures, then call gc_prologue_work()
2534   // for each CMSGen and PermGen that we are responsible for.
2535 
2536   getFreelistLocks();   // gets free list locks on constituent spaces
2537   bitMapLock()->lock_without_safepoint_check();
2538 
2539   // Should call gc_prologue_work() for all cms gens we are responsible for
2540   bool registerClosure =    _collectorState >= Marking
2541                          && _collectorState < Sweeping;
2542   ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2543                                                : &_modUnionClosure;
2544   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2545   _permGen->gc_prologue_work(full, registerClosure, muc);
2546 
2547   if (!full) {
2548     stats().record_gc0_begin();
2549   }
2550 }
2551 
2552 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2553   // Delegate to CMScollector which knows how to coordinate between
2554   // this and any other CMS generations that it is responsible for
2555   // collecting.
2556   collector()->gc_prologue(full);
2557 }
2558 
2559 // This is a "private" interface for use by this generation's CMSCollector.
2560 // Not to be called directly by any other entity (for instance,
2561 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2562 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2563   bool registerClosure, ModUnionClosure* modUnionClosure) {
2564   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2565   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2566     "Should be NULL");
2567   if (registerClosure) {
2568     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2569   }
2570   cmsSpace()->gc_prologue();
2571   // Clear stat counters
2572   NOT_PRODUCT(
2573     assert(_numObjectsPromoted == 0, "check");
2574     assert(_numWordsPromoted   == 0, "check");
2575     if (Verbose && PrintGC) {
2576       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2577                           SIZE_FORMAT" bytes concurrently",
2578       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2579     }
2580     _numObjectsAllocated = 0;
2581     _numWordsAllocated   = 0;
2582   )
2583 }
2584 
2585 void CMSCollector::gc_epilogue(bool full) {
2586   // The following locking discipline assumes that we are only called
2587   // when the world is stopped.
2588   assert(SafepointSynchronize::is_at_safepoint(),
2589          "world is stopped assumption");
2590 
2591   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2592   // if linear allocation blocks need to be appropriately marked to allow the
2593   // the blocks to be parsable. We also check here whether we need to nudge the
2594   // CMS collector thread to start a new cycle (if it's not already active).
2595   assert(   Thread::current()->is_VM_thread()
2596          || (   CMSScavengeBeforeRemark
2597              && Thread::current()->is_ConcurrentGC_thread()),
2598          "Incorrect thread type for epilogue execution");
2599 
2600   if (!_between_prologue_and_epilogue) {
2601     // We have already been invoked; this is a gc_epilogue delegation
2602     // from yet another CMS generation that we are responsible for, just
2603     // ignore it since all relevant work has already been done.
2604     return;
2605   }
2606   assert(haveFreelistLocks(), "must have freelist locks");
2607   assert_lock_strong(bitMapLock());
2608 
2609   _cmsGen->gc_epilogue_work(full);
2610   _permGen->gc_epilogue_work(full);
2611 
2612   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2613     // in case sampling was not already enabled, enable it
2614     _start_sampling = true;
2615   }
2616   // reset _eden_chunk_array so sampling starts afresh
2617   _eden_chunk_index = 0;
2618 
2619   size_t cms_used   = _cmsGen->cmsSpace()->used();
2620   size_t perm_used  = _permGen->cmsSpace()->used();
2621 
2622   // update performance counters - this uses a special version of
2623   // update_counters() that allows the utilization to be passed as a
2624   // parameter, avoiding multiple calls to used().
2625   //
2626   _cmsGen->update_counters(cms_used);
2627   _permGen->update_counters(perm_used);
2628 
2629   if (CMSIncrementalMode) {
2630     icms_update_allocation_limits();
2631   }
2632 
2633   bitMapLock()->unlock();
2634   releaseFreelistLocks();
2635 
2636   _between_prologue_and_epilogue = false;  // ready for next cycle
2637 }
2638 
2639 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2640   collector()->gc_epilogue(full);
2641 
2642   // Also reset promotion tracking in par gc thread states.
2643   if (ParallelGCThreads > 0) {
2644     for (uint i = 0; i < ParallelGCThreads; i++) {
2645       _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2646     }
2647   }
2648 }
2649 
2650 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2651   assert(!incremental_collection_failed(), "Should have been cleared");
2652   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2653   cmsSpace()->gc_epilogue();
2654     // Print stat counters
2655   NOT_PRODUCT(
2656     assert(_numObjectsAllocated == 0, "check");
2657     assert(_numWordsAllocated == 0, "check");
2658     if (Verbose && PrintGC) {
2659       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2660                           SIZE_FORMAT" bytes",
2661                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2662     }
2663     _numObjectsPromoted = 0;
2664     _numWordsPromoted   = 0;
2665   )
2666 
2667   if (PrintGC && Verbose) {
2668     // Call down the chain in contiguous_available needs the freelistLock
2669     // so print this out before releasing the freeListLock.
2670     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2671                         contiguous_available());
2672   }
2673 }
2674 
2675 #ifndef PRODUCT
2676 bool CMSCollector::have_cms_token() {
2677   Thread* thr = Thread::current();
2678   if (thr->is_VM_thread()) {
2679     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2680   } else if (thr->is_ConcurrentGC_thread()) {
2681     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2682   } else if (thr->is_GC_task_thread()) {
2683     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2684            ParGCRareEvent_lock->owned_by_self();
2685   }
2686   return false;
2687 }
2688 #endif
2689 
2690 // Check reachability of the given heap address in CMS generation,
2691 // treating all other generations as roots.
2692 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2693   // We could "guarantee" below, rather than assert, but i'll
2694   // leave these as "asserts" so that an adventurous debugger
2695   // could try this in the product build provided some subset of
2696   // the conditions were met, provided they were intersted in the
2697   // results and knew that the computation below wouldn't interfere
2698   // with other concurrent computations mutating the structures
2699   // being read or written.
2700   assert(SafepointSynchronize::is_at_safepoint(),
2701          "Else mutations in object graph will make answer suspect");
2702   assert(have_cms_token(), "Should hold cms token");
2703   assert(haveFreelistLocks(), "must hold free list locks");
2704   assert_lock_strong(bitMapLock());
2705 
2706   // Clear the marking bit map array before starting, but, just
2707   // for kicks, first report if the given address is already marked
2708   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2709                 _markBitMap.isMarked(addr) ? "" : " not");
2710 
2711   if (verify_after_remark()) {
2712     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2713     bool result = verification_mark_bm()->isMarked(addr);
2714     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2715                            result ? "IS" : "is NOT");
2716     return result;
2717   } else {
2718     gclog_or_tty->print_cr("Could not compute result");
2719     return false;
2720   }
2721 }
2722 
2723 ////////////////////////////////////////////////////////
2724 // CMS Verification Support
2725 ////////////////////////////////////////////////////////
2726 // Following the remark phase, the following invariant
2727 // should hold -- each object in the CMS heap which is
2728 // marked in markBitMap() should be marked in the verification_mark_bm().
2729 
2730 class VerifyMarkedClosure: public BitMapClosure {
2731   CMSBitMap* _marks;
2732   bool       _failed;
2733 
2734  public:
2735   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2736 
2737   void do_bit(size_t offset) {
2738     HeapWord* addr = _marks->offsetToHeapWord(offset);
2739     if (!_marks->isMarked(addr)) {
2740       oop(addr)->print();
2741       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2742       _failed = true;
2743     }
2744   }
2745 
2746   bool failed() { return _failed; }
2747 };
2748 
2749 bool CMSCollector::verify_after_remark() {
2750   gclog_or_tty->print(" [Verifying CMS Marking... ");
2751   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2752   static bool init = false;
2753 
2754   assert(SafepointSynchronize::is_at_safepoint(),
2755          "Else mutations in object graph will make answer suspect");
2756   assert(have_cms_token(),
2757          "Else there may be mutual interference in use of "
2758          " verification data structures");
2759   assert(_collectorState > Marking && _collectorState <= Sweeping,
2760          "Else marking info checked here may be obsolete");
2761   assert(haveFreelistLocks(), "must hold free list locks");
2762   assert_lock_strong(bitMapLock());
2763 
2764 
2765   // Allocate marking bit map if not already allocated
2766   if (!init) { // first time
2767     if (!verification_mark_bm()->allocate(_span)) {
2768       return false;
2769     }
2770     init = true;
2771   }
2772 
2773   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2774 
2775   // Turn off refs discovery -- so we will be tracing through refs.
2776   // This is as intended, because by this time
2777   // GC must already have cleared any refs that need to be cleared,
2778   // and traced those that need to be marked; moreover,
2779   // the marking done here is not going to intefere in any
2780   // way with the marking information used by GC.
2781   NoRefDiscovery no_discovery(ref_processor());
2782 
2783   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2784 
2785   // Clear any marks from a previous round
2786   verification_mark_bm()->clear_all();
2787   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2788   assert(overflow_list_is_empty(), "overflow list should be empty");
2789 
2790   GenCollectedHeap* gch = GenCollectedHeap::heap();
2791   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2792   // Update the saved marks which may affect the root scans.
2793   gch->save_marks();
2794 
2795   if (CMSRemarkVerifyVariant == 1) {
2796     // In this first variant of verification, we complete
2797     // all marking, then check if the new marks-verctor is
2798     // a subset of the CMS marks-vector.
2799     verify_after_remark_work_1();
2800   } else if (CMSRemarkVerifyVariant == 2) {
2801     // In this second variant of verification, we flag an error
2802     // (i.e. an object reachable in the new marks-vector not reachable
2803     // in the CMS marks-vector) immediately, also indicating the
2804     // identify of an object (A) that references the unmarked object (B) --
2805     // presumably, a mutation to A failed to be picked up by preclean/remark?
2806     verify_after_remark_work_2();
2807   } else {
2808     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2809             CMSRemarkVerifyVariant);
2810   }
2811   gclog_or_tty->print(" done] ");
2812   return true;
2813 }
2814 
2815 void CMSCollector::verify_after_remark_work_1() {
2816   ResourceMark rm;
2817   HandleMark  hm;
2818   GenCollectedHeap* gch = GenCollectedHeap::heap();
2819 
2820   // Mark from roots one level into CMS
2821   MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */);
2822   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2823 
2824   gch->gen_process_strong_roots(_cmsGen->level(),
2825                                 true,   // younger gens are roots
2826                                 true,   // collecting perm gen
2827                                 SharedHeap::ScanningOption(roots_scanning_options()),
2828                                 NULL, &notOlder);
2829 
2830   // Now mark from the roots
2831   assert(_revisitStack.isEmpty(), "Should be empty");
2832   MarkFromRootsClosure markFromRootsClosure(this, _span,
2833     verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2834     false /* don't yield */, true /* verifying */);
2835   assert(_restart_addr == NULL, "Expected pre-condition");
2836   verification_mark_bm()->iterate(&markFromRootsClosure);
2837   while (_restart_addr != NULL) {
2838     // Deal with stack overflow: by restarting at the indicated
2839     // address.
2840     HeapWord* ra = _restart_addr;
2841     markFromRootsClosure.reset(ra);
2842     _restart_addr = NULL;
2843     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2844   }
2845   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2846   verify_work_stacks_empty();
2847   // Should reset the revisit stack above, since no class tree
2848   // surgery is forthcoming.
2849   _revisitStack.reset(); // throwing away all contents
2850 
2851   // Marking completed -- now verify that each bit marked in
2852   // verification_mark_bm() is also marked in markBitMap(); flag all
2853   // errors by printing corresponding objects.
2854   VerifyMarkedClosure vcl(markBitMap());
2855   verification_mark_bm()->iterate(&vcl);
2856   if (vcl.failed()) {
2857     gclog_or_tty->print("Verification failed");
2858     Universe::heap()->print();
2859     fatal(" ... aborting");
2860   }
2861 }
2862 
2863 void CMSCollector::verify_after_remark_work_2() {
2864   ResourceMark rm;
2865   HandleMark  hm;
2866   GenCollectedHeap* gch = GenCollectedHeap::heap();
2867 
2868   // Mark from roots one level into CMS
2869   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2870                                      markBitMap(), true /* nmethods */);
2871   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2872   gch->gen_process_strong_roots(_cmsGen->level(),
2873                                 true,   // younger gens are roots
2874                                 true,   // collecting perm gen
2875                                 SharedHeap::ScanningOption(roots_scanning_options()),
2876                                 NULL, &notOlder);
2877 
2878   // Now mark from the roots
2879   assert(_revisitStack.isEmpty(), "Should be empty");
2880   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2881     verification_mark_bm(), markBitMap(), verification_mark_stack());
2882   assert(_restart_addr == NULL, "Expected pre-condition");
2883   verification_mark_bm()->iterate(&markFromRootsClosure);
2884   while (_restart_addr != NULL) {
2885     // Deal with stack overflow: by restarting at the indicated
2886     // address.
2887     HeapWord* ra = _restart_addr;
2888     markFromRootsClosure.reset(ra);
2889     _restart_addr = NULL;
2890     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2891   }
2892   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2893   verify_work_stacks_empty();
2894   // Should reset the revisit stack above, since no class tree
2895   // surgery is forthcoming.
2896   _revisitStack.reset(); // throwing away all contents
2897 
2898   // Marking completed -- now verify that each bit marked in
2899   // verification_mark_bm() is also marked in markBitMap(); flag all
2900   // errors by printing corresponding objects.
2901   VerifyMarkedClosure vcl(markBitMap());
2902   verification_mark_bm()->iterate(&vcl);
2903   assert(!vcl.failed(), "Else verification above should not have succeeded");
2904 }
2905 
2906 void ConcurrentMarkSweepGeneration::save_marks() {
2907   // delegate to CMS space
2908   cmsSpace()->save_marks();
2909   for (uint i = 0; i < ParallelGCThreads; i++) {
2910     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2911   }
2912 }
2913 
2914 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2915   return cmsSpace()->no_allocs_since_save_marks();
2916 }
2917 
2918 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2919                                                                 \
2920 void ConcurrentMarkSweepGeneration::                            \
2921 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2922   cl->set_generation(this);                                     \
2923   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2924   cl->reset_generation();                                       \
2925   save_marks();                                                 \
2926 }
2927 
2928 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2929 
2930 void
2931 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2932 {
2933   // Not currently implemented; need to do the following. -- ysr.
2934   // dld -- I think that is used for some sort of allocation profiler.  So it
2935   // really means the objects allocated by the mutator since the last
2936   // GC.  We could potentially implement this cheaply by recording only
2937   // the direct allocations in a side data structure.
2938   //
2939   // I think we probably ought not to be required to support these
2940   // iterations at any arbitrary point; I think there ought to be some
2941   // call to enable/disable allocation profiling in a generation/space,
2942   // and the iterator ought to return the objects allocated in the
2943   // gen/space since the enable call, or the last iterator call (which
2944   // will probably be at a GC.)  That way, for gens like CM&S that would
2945   // require some extra data structure to support this, we only pay the
2946   // cost when it's in use...
2947   cmsSpace()->object_iterate_since_last_GC(blk);
2948 }
2949 
2950 void
2951 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2952   cl->set_generation(this);
2953   younger_refs_in_space_iterate(_cmsSpace, cl);
2954   cl->reset_generation();
2955 }
2956 
2957 void
2958 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2959   if (freelistLock()->owned_by_self()) {
2960     Generation::oop_iterate(mr, cl);
2961   } else {
2962     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2963     Generation::oop_iterate(mr, cl);
2964   }
2965 }
2966 
2967 void
2968 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
2969   if (freelistLock()->owned_by_self()) {
2970     Generation::oop_iterate(cl);
2971   } else {
2972     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2973     Generation::oop_iterate(cl);
2974   }
2975 }
2976 
2977 void
2978 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2979   if (freelistLock()->owned_by_self()) {
2980     Generation::object_iterate(cl);
2981   } else {
2982     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2983     Generation::object_iterate(cl);
2984   }
2985 }
2986 
2987 void
2988 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
2989 }
2990 
2991 void
2992 ConcurrentMarkSweepGeneration::post_compact() {
2993 }
2994 
2995 void
2996 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2997   // Fix the linear allocation blocks to look like free blocks.
2998 
2999   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3000   // are not called when the heap is verified during universe initialization and
3001   // at vm shutdown.
3002   if (freelistLock()->owned_by_self()) {
3003     cmsSpace()->prepare_for_verify();
3004   } else {
3005     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3006     cmsSpace()->prepare_for_verify();
3007   }
3008 }
3009 
3010 void
3011 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3012   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3013   // are not called when the heap is verified during universe initialization and
3014   // at vm shutdown.
3015   if (freelistLock()->owned_by_self()) {
3016     cmsSpace()->verify(false /* ignored */);
3017   } else {
3018     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3019     cmsSpace()->verify(false /* ignored */);
3020   }
3021 }
3022 
3023 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3024   _cmsGen->verify(allow_dirty);
3025   _permGen->verify(allow_dirty);
3026 }
3027 
3028 #ifndef PRODUCT
3029 bool CMSCollector::overflow_list_is_empty() const {
3030   assert(_num_par_pushes >= 0, "Inconsistency");
3031   if (_overflow_list == NULL) {
3032     assert(_num_par_pushes == 0, "Inconsistency");
3033   }
3034   return _overflow_list == NULL;
3035 }
3036 
3037 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3038 // merely consolidate assertion checks that appear to occur together frequently.
3039 void CMSCollector::verify_work_stacks_empty() const {
3040   assert(_markStack.isEmpty(), "Marking stack should be empty");
3041   assert(overflow_list_is_empty(), "Overflow list should be empty");
3042 }
3043 
3044 void CMSCollector::verify_overflow_empty() const {
3045   assert(overflow_list_is_empty(), "Overflow list should be empty");
3046   assert(no_preserved_marks(), "No preserved marks");
3047 }
3048 #endif // PRODUCT
3049 
3050 void CMSCollector::setup_cms_unloading_and_verification_state() {
3051   const  bool should_verify =    VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3052                              || VerifyBeforeExit;
3053   const  int  rso           =    SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3054                              |   SharedHeap::SO_CodeCache;
3055 
3056   if (cms_should_unload_classes()) {   // Should unload classes this cycle
3057     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3058     set_verifying(should_verify);    // Set verification state for this cycle
3059     return;                            // Nothing else needs to be done at this time
3060   }
3061 
3062   // Not unloading classes this cycle
3063   assert(!cms_should_unload_classes(), "Inconsitency!");
3064   if ((!verifying() || cms_unloaded_classes_last_cycle()) && should_verify) {
3065     // We were not verifying, or we _were_ unloading classes in the last cycle,
3066     // AND some verification options are enabled this cycle; in this case,
3067     // we must make sure that the deadness map is allocated if not already so,
3068     // and cleared (if already allocated previously --
3069     // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3070     if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3071       if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3072         warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3073                 "permanent generation verification disabled");
3074         return;  // Note that we leave verification disabled, so we'll retry this
3075                  // allocation next cycle. We _could_ remember this failure
3076                  // and skip further attempts and permanently disable verification
3077                  // attempts if that is considered more desirable.
3078       }
3079       assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3080               "_perm_gen_ver_bit_map inconsistency?");
3081     } else {
3082       perm_gen_verify_bit_map()->clear_all();
3083     }
3084     // Include symbols, strings and code cache elements to prevent their resurrection.
3085     add_root_scanning_option(rso);
3086     set_verifying(true);
3087   } else if (verifying() && !should_verify) {
3088     // We were verifying, but some verification flags got disabled.
3089     set_verifying(false);
3090     // Exclude symbols, strings and code cache elements from root scanning to
3091     // reduce IM and RM pauses.
3092     remove_root_scanning_option(rso);
3093   }
3094 }
3095 
3096 
3097 #ifndef PRODUCT
3098 HeapWord* CMSCollector::block_start(const void* p) const {
3099   const HeapWord* addr = (HeapWord*)p;
3100   if (_span.contains(p)) {
3101     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3102       return _cmsGen->cmsSpace()->block_start(p);
3103     } else {
3104       assert(_permGen->cmsSpace()->is_in_reserved(addr),
3105              "Inconsistent _span?");
3106       return _permGen->cmsSpace()->block_start(p);
3107     }
3108   }
3109   return NULL;
3110 }
3111 #endif
3112 
3113 HeapWord*
3114 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3115                                                    bool   tlab,
3116                                                    bool   parallel) {
3117   assert(!tlab, "Can't deal with TLAB allocation");
3118   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3119   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3120     CMSExpansionCause::_satisfy_allocation);
3121   if (GCExpandToAllocateDelayMillis > 0) {
3122     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3123   }
3124   size_t adj_word_sz = CompactibleFreeListSpace::adjustObjectSize(word_size);
3125   if (parallel) {
3126     return cmsSpace()->par_allocate(adj_word_sz);
3127   } else {
3128     return cmsSpace()->allocate(adj_word_sz);
3129   }
3130 }
3131 
3132 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3133 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3134 // to CardGeneration and share it...
3135 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3136   CMSExpansionCause::Cause cause)
3137 {
3138   assert_locked_or_safepoint(Heap_lock);
3139 
3140   size_t aligned_bytes  = ReservedSpace::page_align_size_up(bytes);
3141   size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
3142   bool success = false;
3143   if (aligned_expand_bytes > aligned_bytes) {
3144     success = grow_by(aligned_expand_bytes);
3145   }
3146   if (!success) {
3147     success = grow_by(aligned_bytes);
3148   }
3149   if (!success) {
3150     size_t remaining_bytes = _virtual_space.uncommitted_size();
3151     if (remaining_bytes > 0) {
3152       success = grow_by(remaining_bytes);
3153     }
3154   }
3155   if (GC_locker::is_active()) {
3156     if (PrintGC && Verbose) {
3157       gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead");
3158     }
3159   }
3160   // remember why we expanded; this information is used
3161   // by shouldConcurrentCollect() when making decisions on whether to start
3162   // a new CMS cycle.
3163   if (success) {
3164     set_expansion_cause(cause);
3165     if (PrintGCDetails && Verbose) {
3166       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3167         CMSExpansionCause::to_string(cause));
3168     }
3169   }
3170 }
3171 
3172 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3173   HeapWord* res = NULL;
3174   MutexLocker x(ParGCRareEvent_lock);
3175   while (true) {
3176     // Expansion by some other thread might make alloc OK now:
3177     res = ps->lab.alloc(word_sz);
3178     if (res != NULL) return res;
3179     // If there's not enough expansion space available, give up.
3180     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3181       return NULL;
3182     }
3183     // Otherwise, we try expansion.
3184     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3185       CMSExpansionCause::_allocate_par_lab);
3186     // Now go around the loop and try alloc again;
3187     // A competing par_promote might beat us to the expansion space,
3188     // so we may go around the loop again if promotion fails agaion.
3189     if (GCExpandToAllocateDelayMillis > 0) {
3190       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3191     }
3192   }
3193 }
3194 
3195 
3196 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3197   PromotionInfo* promo) {
3198   MutexLocker x(ParGCRareEvent_lock);
3199   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3200   while (true) {
3201     // Expansion by some other thread might make alloc OK now:
3202     if (promo->ensure_spooling_space()) {
3203       assert(promo->has_spooling_space(),
3204              "Post-condition of successful ensure_spooling_space()");
3205       return true;
3206     }
3207     // If there's not enough expansion space available, give up.
3208     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3209       return false;
3210     }
3211     // Otherwise, we try expansion.
3212     expand(refill_size_bytes, MinHeapDeltaBytes,
3213       CMSExpansionCause::_allocate_par_spooling_space);
3214     // Now go around the loop and try alloc again;
3215     // A competing allocation might beat us to the expansion space,
3216     // so we may go around the loop again if allocation fails again.
3217     if (GCExpandToAllocateDelayMillis > 0) {
3218       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3219     }
3220   }
3221 }
3222 
3223 
3224 
3225 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3226   assert_locked_or_safepoint(Heap_lock);
3227   size_t size = ReservedSpace::page_align_size_down(bytes);
3228   if (size > 0) {
3229     shrink_by(size);
3230   }
3231 }
3232 
3233 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3234   assert_locked_or_safepoint(Heap_lock);
3235   bool result = _virtual_space.expand_by(bytes);
3236   if (result) {
3237     HeapWord* old_end = _cmsSpace->end();
3238     size_t new_word_size =
3239       heap_word_size(_virtual_space.committed_size());
3240     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3241     _bts->resize(new_word_size);  // resize the block offset shared array
3242     Universe::heap()->barrier_set()->resize_covered_region(mr);
3243     // Hmmmm... why doesn't CFLS::set_end verify locking?
3244     // This is quite ugly; FIX ME XXX
3245     _cmsSpace->assert_locked();
3246     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3247 
3248     // update the space and generation capacity counters
3249     if (UsePerfData) {
3250       _space_counters->update_capacity();
3251       _gen_counters->update_all();
3252     }
3253 
3254     if (Verbose && PrintGC) {
3255       size_t new_mem_size = _virtual_space.committed_size();
3256       size_t old_mem_size = new_mem_size - bytes;
3257       gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3258                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3259     }
3260   }
3261   return result;
3262 }
3263 
3264 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3265   assert_locked_or_safepoint(Heap_lock);
3266   bool success = true;
3267   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3268   if (remaining_bytes > 0) {
3269     success = grow_by(remaining_bytes);
3270     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3271   }
3272   return success;
3273 }
3274 
3275 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3276   assert_locked_or_safepoint(Heap_lock);
3277   assert_lock_strong(freelistLock());
3278   // XXX Fix when compaction is implemented.
3279   warning("Shrinking of CMS not yet implemented");
3280   return;
3281 }
3282 
3283 
3284 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3285 // phases.
3286 class CMSPhaseAccounting: public StackObj {
3287  public:
3288   CMSPhaseAccounting(CMSCollector *collector,
3289                      const char *phase,
3290                      bool print_cr = true);
3291   ~CMSPhaseAccounting();
3292 
3293  private:
3294   CMSCollector *_collector;
3295   const char *_phase;
3296   elapsedTimer _wallclock;
3297   bool _print_cr;
3298 
3299  public:
3300   // Not MT-safe; so do not pass around these StackObj's
3301   // where they may be accessed by other threads.
3302   jlong wallclock_millis() {
3303     assert(_wallclock.is_active(), "Wall clock should not stop");
3304     _wallclock.stop();  // to record time
3305     jlong ret = _wallclock.milliseconds();
3306     _wallclock.start(); // restart
3307     return ret;
3308   }
3309 };
3310 
3311 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3312                                        const char *phase,
3313                                        bool print_cr) :
3314   _collector(collector), _phase(phase), _print_cr(print_cr) {
3315 
3316   if (PrintCMSStatistics != 0) {
3317     _collector->resetYields();
3318   }
3319   if (PrintGCDetails && PrintGCTimeStamps) {
3320     gclog_or_tty->date_stamp(PrintGCDateStamps);
3321     gclog_or_tty->stamp();
3322     gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3323       _collector->cmsGen()->short_name(), _phase);
3324   }
3325   _collector->resetTimer();
3326   _wallclock.start();
3327   _collector->startTimer();
3328 }
3329 
3330 CMSPhaseAccounting::~CMSPhaseAccounting() {
3331   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3332   _collector->stopTimer();
3333   _wallclock.stop();
3334   if (PrintGCDetails) {
3335     gclog_or_tty->date_stamp(PrintGCDateStamps);
3336     if (PrintGCTimeStamps) {
3337       gclog_or_tty->stamp();
3338       gclog_or_tty->print(": ");
3339     }
3340     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3341                  _collector->cmsGen()->short_name(),
3342                  _phase, _collector->timerValue(), _wallclock.seconds());
3343     if (_print_cr) {
3344       gclog_or_tty->print_cr("");
3345     }
3346     if (PrintCMSStatistics != 0) {
3347       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3348                     _collector->yields());
3349     }
3350   }
3351 }
3352 
3353 // CMS work
3354 
3355 // Checkpoint the roots into this generation from outside
3356 // this generation. [Note this initial checkpoint need only
3357 // be approximate -- we'll do a catch up phase subsequently.]
3358 void CMSCollector::checkpointRootsInitial(bool asynch) {
3359   assert(_collectorState == InitialMarking, "Wrong collector state");
3360   check_correct_thread_executing();
3361   ReferenceProcessor* rp = ref_processor();
3362   SpecializationStats::clear();
3363   assert(_restart_addr == NULL, "Control point invariant");
3364   if (asynch) {
3365     // acquire locks for subsequent manipulations
3366     MutexLockerEx x(bitMapLock(),
3367                     Mutex::_no_safepoint_check_flag);
3368     checkpointRootsInitialWork(asynch);
3369     rp->verify_no_references_recorded();
3370     rp->enable_discovery(); // enable ("weak") refs discovery
3371     _collectorState = Marking;
3372   } else {
3373     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3374     // which recognizes if we are a CMS generation, and doesn't try to turn on
3375     // discovery; verify that they aren't meddling.
3376     assert(!rp->discovery_is_atomic(),
3377            "incorrect setting of discovery predicate");
3378     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3379            "ref discovery for this generation kind");
3380     // already have locks
3381     checkpointRootsInitialWork(asynch);
3382     rp->enable_discovery(); // now enable ("weak") refs discovery
3383     _collectorState = Marking;
3384   }
3385   SpecializationStats::print();
3386 }
3387 
3388 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3389   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3390   assert(_collectorState == InitialMarking, "just checking");
3391 
3392   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3393   // precede our marking with a collection of all
3394   // younger generations to keep floating garbage to a minimum.
3395   // XXX: we won't do this for now -- it's an optimization to be done later.
3396 
3397   // already have locks
3398   assert_lock_strong(bitMapLock());
3399   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3400 
3401   // Setup the verification and class unloading state for this
3402   // CMS collection cycle.
3403   setup_cms_unloading_and_verification_state();
3404 
3405   NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3406     PrintGCDetails && Verbose, true, gclog_or_tty);)
3407   if (UseAdaptiveSizePolicy) {
3408     size_policy()->checkpoint_roots_initial_begin();
3409   }
3410 
3411   // Reset all the PLAB chunk arrays if necessary.
3412   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3413     reset_survivor_plab_arrays();
3414   }
3415 
3416   ResourceMark rm;
3417   HandleMark  hm;
3418 
3419   FalseClosure falseClosure;
3420   // In the case of a synchronous collection, we will elide the
3421   // remark step, so it's important to catch all the nmethod oops
3422   // in this step; hence the last argument to the constrcutor below.
3423   MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */);
3424   GenCollectedHeap* gch = GenCollectedHeap::heap();
3425 
3426   verify_work_stacks_empty();
3427   verify_overflow_empty();
3428 
3429   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3430   // Update the saved marks which may affect the root scans.
3431   gch->save_marks();
3432 
3433   // weak reference processing has not started yet.
3434   ref_processor()->set_enqueuing_is_done(false);
3435 
3436   {
3437     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3438     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3439     gch->gen_process_strong_roots(_cmsGen->level(),
3440                                   true,   // younger gens are roots
3441                                   true,   // collecting perm gen
3442                                   SharedHeap::ScanningOption(roots_scanning_options()),
3443                                   NULL, &notOlder);
3444   }
3445 
3446   // Clear mod-union table; it will be dirtied in the prologue of
3447   // CMS generation per each younger generation collection.
3448 
3449   assert(_modUnionTable.isAllClear(),
3450        "Was cleared in most recent final checkpoint phase"
3451        " or no bits are set in the gc_prologue before the start of the next "
3452        "subsequent marking phase.");
3453 
3454   // Temporarily disabled, since pre/post-consumption closures don't
3455   // care about precleaned cards
3456   #if 0
3457   {
3458     MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3459                              (HeapWord*)_virtual_space.high());
3460     _ct->ct_bs()->preclean_dirty_cards(mr);
3461   }
3462   #endif
3463 
3464   // Save the end of the used_region of the constituent generations
3465   // to be used to limit the extent of sweep in each generation.
3466   save_sweep_limits();
3467   if (UseAdaptiveSizePolicy) {
3468     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3469   }
3470   verify_overflow_empty();
3471 }
3472 
3473 bool CMSCollector::markFromRoots(bool asynch) {
3474   // we might be tempted to assert that:
3475   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3476   //        "inconsistent argument?");
3477   // However that wouldn't be right, because it's possible that
3478   // a safepoint is indeed in progress as a younger generation
3479   // stop-the-world GC happens even as we mark in this generation.
3480   assert(_collectorState == Marking, "inconsistent state?");
3481   check_correct_thread_executing();
3482   verify_overflow_empty();
3483 
3484   bool res;
3485   if (asynch) {
3486 
3487     // Start the timers for adaptive size policy for the concurrent phases
3488     // Do it here so that the foreground MS can use the concurrent
3489     // timer since a foreground MS might has the sweep done concurrently
3490     // or STW.
3491     if (UseAdaptiveSizePolicy) {
3492       size_policy()->concurrent_marking_begin();
3493     }
3494 
3495     // Weak ref discovery note: We may be discovering weak
3496     // refs in this generation concurrent (but interleaved) with
3497     // weak ref discovery by a younger generation collector.
3498 
3499     CMSTokenSyncWithLocks ts(true, bitMapLock());
3500     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3501     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3502     res = markFromRootsWork(asynch);
3503     if (res) {
3504       _collectorState = Precleaning;
3505     } else { // We failed and a foreground collection wants to take over
3506       assert(_foregroundGCIsActive, "internal state inconsistency");
3507       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3508       if (PrintGCDetails) {
3509         gclog_or_tty->print_cr("bailing out to foreground collection");
3510       }
3511     }
3512     if (UseAdaptiveSizePolicy) {
3513       size_policy()->concurrent_marking_end();
3514     }
3515   } else {
3516     assert(SafepointSynchronize::is_at_safepoint(),
3517            "inconsistent with asynch == false");
3518     if (UseAdaptiveSizePolicy) {
3519       size_policy()->ms_collection_marking_begin();
3520     }
3521     // already have locks
3522     res = markFromRootsWork(asynch);
3523     _collectorState = FinalMarking;
3524     if (UseAdaptiveSizePolicy) {
3525       GenCollectedHeap* gch = GenCollectedHeap::heap();
3526       size_policy()->ms_collection_marking_end(gch->gc_cause());
3527     }
3528   }
3529   verify_overflow_empty();
3530   return res;
3531 }
3532 
3533 bool CMSCollector::markFromRootsWork(bool asynch) {
3534   // iterate over marked bits in bit map, doing a full scan and mark
3535   // from these roots using the following algorithm:
3536   // . if oop is to the right of the current scan pointer,
3537   //   mark corresponding bit (we'll process it later)
3538   // . else (oop is to left of current scan pointer)
3539   //   push oop on marking stack
3540   // . drain the marking stack
3541 
3542   // Note that when we do a marking step we need to hold the
3543   // bit map lock -- recall that direct allocation (by mutators)
3544   // and promotion (by younger generation collectors) is also
3545   // marking the bit map. [the so-called allocate live policy.]
3546   // Because the implementation of bit map marking is not
3547   // robust wrt simultaneous marking of bits in the same word,
3548   // we need to make sure that there is no such interference
3549   // between concurrent such updates.
3550 
3551   // already have locks
3552   assert_lock_strong(bitMapLock());
3553 
3554   // Clear the revisit stack, just in case there are any
3555   // obsolete contents from a short-circuited previous CMS cycle.
3556   _revisitStack.reset();
3557   verify_work_stacks_empty();
3558   verify_overflow_empty();
3559   assert(_revisitStack.isEmpty(), "tabula rasa");
3560 
3561   bool result = false;
3562   if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) {
3563     result = do_marking_mt(asynch);
3564   } else {
3565     result = do_marking_st(asynch);
3566   }
3567   return result;
3568 }
3569 
3570 // Forward decl
3571 class CMSConcMarkingTask;
3572 
3573 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3574   CMSCollector*       _collector;
3575   CMSConcMarkingTask* _task;
3576   bool _yield;
3577  protected:
3578   virtual void yield();
3579  public:
3580   // "n_threads" is the number of threads to be terminated.
3581   // "queue_set" is a set of work queues of other threads.
3582   // "collector" is the CMS collector associated with this task terminator.
3583   // "yield" indicates whether we need the gang as a whole to yield.
3584   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3585                            CMSCollector* collector, bool yield) :
3586     ParallelTaskTerminator(n_threads, queue_set),
3587     _collector(collector),
3588     _yield(yield) { }
3589 
3590   void set_task(CMSConcMarkingTask* task) {
3591     _task = task;
3592   }
3593 };
3594 
3595 // MT Concurrent Marking Task
3596 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3597   CMSCollector* _collector;
3598   YieldingFlexibleWorkGang* _workers;        // the whole gang
3599   int           _n_workers;                  // requested/desired # workers
3600   bool          _asynch;
3601   bool          _result;
3602   CompactibleFreeListSpace*  _cms_space;
3603   CompactibleFreeListSpace* _perm_space;
3604   HeapWord*     _global_finger;
3605 
3606   //  Exposed here for yielding support
3607   Mutex* const _bit_map_lock;
3608 
3609   // The per thread work queues, available here for stealing
3610   OopTaskQueueSet*  _task_queues;
3611   CMSConcMarkingTerminator _term;
3612 
3613  public:
3614   CMSConcMarkingTask(CMSCollector* collector,
3615                  CompactibleFreeListSpace* cms_space,
3616                  CompactibleFreeListSpace* perm_space,
3617                  bool asynch, int n_workers,
3618                  YieldingFlexibleWorkGang* workers,
3619                  OopTaskQueueSet* task_queues):
3620     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3621     _collector(collector),
3622     _cms_space(cms_space),
3623     _perm_space(perm_space),
3624     _asynch(asynch), _n_workers(n_workers), _result(true),
3625     _workers(workers), _task_queues(task_queues),
3626     _term(n_workers, task_queues, _collector, asynch),
3627     _bit_map_lock(collector->bitMapLock())
3628   {
3629     assert(n_workers <= workers->total_workers(),
3630            "Else termination won't work correctly today"); // XXX FIX ME!
3631     _requested_size = n_workers;
3632     _term.set_task(this);
3633     assert(_cms_space->bottom() < _perm_space->bottom(),
3634            "Finger incorrectly initialized below");
3635     _global_finger = _cms_space->bottom();
3636   }
3637 
3638 
3639   OopTaskQueueSet* task_queues()  { return _task_queues; }
3640 
3641   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3642 
3643   HeapWord** global_finger_addr() { return &_global_finger; }
3644 
3645   CMSConcMarkingTerminator* terminator() { return &_term; }
3646 
3647   void work(int i);
3648 
3649   virtual void coordinator_yield();  // stuff done by coordinator
3650   bool result() { return _result; }
3651 
3652   void reset(HeapWord* ra) {
3653     _term.reset_for_reuse();
3654   }
3655 
3656   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3657                                            OopTaskQueue* work_q);
3658 
3659  private:
3660   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3661   void do_work_steal(int i);
3662   void bump_global_finger(HeapWord* f);
3663 };
3664 
3665 void CMSConcMarkingTerminator::yield() {
3666   if (ConcurrentMarkSweepThread::should_yield() &&
3667       !_collector->foregroundGCIsActive() &&
3668       _yield) {
3669     _task->yield();
3670   } else {
3671     ParallelTaskTerminator::yield();
3672   }
3673 }
3674 
3675 ////////////////////////////////////////////////////////////////
3676 // Concurrent Marking Algorithm Sketch
3677 ////////////////////////////////////////////////////////////////
3678 // Until all tasks exhausted (both spaces):
3679 // -- claim next available chunk
3680 // -- bump global finger via CAS
3681 // -- find first object that starts in this chunk
3682 //    and start scanning bitmap from that position
3683 // -- scan marked objects for oops
3684 // -- CAS-mark target, and if successful:
3685 //    . if target oop is above global finger (volatile read)
3686 //      nothing to do
3687 //    . if target oop is in chunk and above local finger
3688 //        then nothing to do
3689 //    . else push on work-queue
3690 // -- Deal with possible overflow issues:
3691 //    . local work-queue overflow causes stuff to be pushed on
3692 //      global (common) overflow queue
3693 //    . always first empty local work queue
3694 //    . then get a batch of oops from global work queue if any
3695 //    . then do work stealing
3696 // -- When all tasks claimed (both spaces)
3697 //    and local work queue empty,
3698 //    then in a loop do:
3699 //    . check global overflow stack; steal a batch of oops and trace
3700 //    . try to steal from other threads oif GOS is empty
3701 //    . if neither is available, offer termination
3702 // -- Terminate and return result
3703 //
3704 void CMSConcMarkingTask::work(int i) {
3705   elapsedTimer _timer;
3706   ResourceMark rm;
3707   HandleMark hm;
3708 
3709   DEBUG_ONLY(_collector->verify_overflow_empty();)
3710 
3711   // Before we begin work, our work queue should be empty
3712   assert(work_queue(i)->size() == 0, "Expected to be empty");
3713   // Scan the bitmap covering _cms_space, tracing through grey objects.
3714   _timer.start();
3715   do_scan_and_mark(i, _cms_space);
3716   _timer.stop();
3717   if (PrintCMSStatistics != 0) {
3718     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3719       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3720   }
3721 
3722   // ... do the same for the _perm_space
3723   _timer.reset();
3724   _timer.start();
3725   do_scan_and_mark(i, _perm_space);
3726   _timer.stop();
3727   if (PrintCMSStatistics != 0) {
3728     gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3729       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3730   }
3731 
3732   // ... do work stealing
3733   _timer.reset();
3734   _timer.start();
3735   do_work_steal(i);
3736   _timer.stop();
3737   if (PrintCMSStatistics != 0) {
3738     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3739       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3740   }
3741   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3742   assert(work_queue(i)->size() == 0, "Should have been emptied");
3743   // Note that under the current task protocol, the
3744   // following assertion is true even of the spaces
3745   // expanded since the completion of the concurrent
3746   // marking. XXX This will likely change under a strict
3747   // ABORT semantics.
3748   assert(_global_finger >  _cms_space->end() &&
3749          _global_finger >= _perm_space->end(),
3750          "All tasks have been completed");
3751   DEBUG_ONLY(_collector->verify_overflow_empty();)
3752 }
3753 
3754 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3755   HeapWord* read = _global_finger;
3756   HeapWord* cur  = read;
3757   while (f > read) {
3758     cur = read;
3759     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3760     if (cur == read) {
3761       // our cas succeeded
3762       assert(_global_finger >= f, "protocol consistency");
3763       break;
3764     }
3765   }
3766 }
3767 
3768 // This is really inefficient, and should be redone by
3769 // using (not yet available) block-read and -write interfaces to the
3770 // stack and the work_queue. XXX FIX ME !!!
3771 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3772                                                       OopTaskQueue* work_q) {
3773   // Fast lock-free check
3774   if (ovflw_stk->length() == 0) {
3775     return false;
3776   }
3777   assert(work_q->size() == 0, "Shouldn't steal");
3778   MutexLockerEx ml(ovflw_stk->par_lock(),
3779                    Mutex::_no_safepoint_check_flag);
3780   // Grab up to 1/4 the size of the work queue
3781   size_t num = MIN2((size_t)work_q->max_elems()/4,
3782                     (size_t)ParGCDesiredObjsFromOverflowList);
3783   num = MIN2(num, ovflw_stk->length());
3784   for (int i = (int) num; i > 0; i--) {
3785     oop cur = ovflw_stk->pop();
3786     assert(cur != NULL, "Counted wrong?");
3787     work_q->push(cur);
3788   }
3789   return num > 0;
3790 }
3791 
3792 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3793   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3794   int n_tasks = pst->n_tasks();
3795   // We allow that there may be no tasks to do here because
3796   // we are restarting after a stack overflow.
3797   assert(pst->valid() || n_tasks == 0, "Uninitializd use?");
3798   int nth_task = 0;
3799 
3800   HeapWord* start = sp->bottom();
3801   size_t chunk_size = sp->marking_task_size();
3802   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3803     // Having claimed the nth task in this space,
3804     // compute the chunk that it corresponds to:
3805     MemRegion span = MemRegion(start + nth_task*chunk_size,
3806                                start + (nth_task+1)*chunk_size);
3807     // Try and bump the global finger via a CAS;
3808     // note that we need to do the global finger bump
3809     // _before_ taking the intersection below, because
3810     // the task corresponding to that region will be
3811     // deemed done even if the used_region() expands
3812     // because of allocation -- as it almost certainly will
3813     // during start-up while the threads yield in the
3814     // closure below.
3815     HeapWord* finger = span.end();
3816     bump_global_finger(finger);   // atomically
3817     // There are null tasks here corresponding to chunks
3818     // beyond the "top" address of the space.
3819     span = span.intersection(sp->used_region());
3820     if (!span.is_empty()) {  // Non-null task
3821       // We want to skip the first object because
3822       // the protocol is to scan any object in its entirety
3823       // that _starts_ in this span; a fortiori, any
3824       // object starting in an earlier span is scanned
3825       // as part of an earlier claimed task.
3826       // Below we use the "careful" version of block_start
3827       // so we do not try to navigate uninitialized objects.
3828       HeapWord* prev_obj = sp->block_start_careful(span.start());
3829       // Below we use a variant of block_size that uses the
3830       // Printezis bits to avoid waiting for allocated
3831       // objects to become initialized/parsable.
3832       while (prev_obj < span.start()) {
3833         size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3834         if (sz > 0) {
3835           prev_obj += sz;
3836         } else {
3837           // In this case we may end up doing a bit of redundant
3838           // scanning, but that appears unavoidable, short of
3839           // locking the free list locks; see bug 6324141.
3840           break;
3841         }
3842       }
3843       if (prev_obj < span.end()) {
3844         MemRegion my_span = MemRegion(prev_obj, span.end());
3845         // Do the marking work within a non-empty span --
3846         // the last argument to the constructor indicates whether the
3847         // iteration should be incremental with periodic yields.
3848         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3849                                     &_collector->_markBitMap,
3850                                     work_queue(i),
3851                                     &_collector->_markStack,
3852                                     &_collector->_revisitStack,
3853                                     _asynch);
3854         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3855       } // else nothing to do for this task
3856     }   // else nothing to do for this task
3857   }
3858   // We'd be tempted to assert here that since there are no
3859   // more tasks left to claim in this space, the global_finger
3860   // must exceed space->top() and a fortiori space->end(). However,
3861   // that would not quite be correct because the bumping of
3862   // global_finger occurs strictly after the claiming of a task,
3863   // so by the time we reach here the global finger may not yet
3864   // have been bumped up by the thread that claimed the last
3865   // task.
3866   pst->all_tasks_completed();
3867 }
3868 
3869 class Par_ConcMarkingClosure: public OopClosure {
3870   CMSCollector* _collector;
3871   MemRegion     _span;
3872   CMSBitMap*    _bit_map;
3873   CMSMarkStack* _overflow_stack;
3874   CMSMarkStack* _revisit_stack;     // XXXXXX Check proper use
3875   OopTaskQueue* _work_queue;
3876 
3877  public:
3878   Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3879                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3880     _collector(collector),
3881     _span(_collector->_span),
3882     _work_queue(work_queue),
3883     _bit_map(bit_map),
3884     _overflow_stack(overflow_stack) { }   // need to initialize revisit stack etc.
3885 
3886   void do_oop(oop* p);
3887   void trim_queue(size_t max);
3888   void handle_stack_overflow(HeapWord* lost);
3889 };
3890 
3891 // Grey object rescan during work stealing phase --
3892 // the salient assumption here is that stolen oops must
3893 // always be initialized, so we do not need to check for
3894 // uninitialized objects before scanning here.
3895 void Par_ConcMarkingClosure::do_oop(oop* p) {
3896   oop    this_oop = *p;
3897   assert(this_oop->is_oop_or_null(),
3898          "expected an oop or NULL");
3899   HeapWord* addr = (HeapWord*)this_oop;
3900   // Check if oop points into the CMS generation
3901   // and is not marked
3902   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3903     // a white object ...
3904     // If we manage to "claim" the object, by being the
3905     // first thread to mark it, then we push it on our
3906     // marking stack
3907     if (_bit_map->par_mark(addr)) {     // ... now grey
3908       // push on work queue (grey set)
3909       bool simulate_overflow = false;
3910       NOT_PRODUCT(
3911         if (CMSMarkStackOverflowALot &&
3912             _collector->simulate_overflow()) {
3913           // simulate a stack overflow
3914           simulate_overflow = true;
3915         }
3916       )
3917       if (simulate_overflow ||
3918           !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) {
3919         // stack overflow
3920         if (PrintCMSStatistics != 0) {
3921           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3922                                  SIZE_FORMAT, _overflow_stack->capacity());
3923         }
3924         // We cannot assert that the overflow stack is full because
3925         // it may have been emptied since.
3926         assert(simulate_overflow ||
3927                _work_queue->size() == _work_queue->max_elems(),
3928               "Else push should have succeeded");
3929         handle_stack_overflow(addr);
3930       }
3931     } // Else, some other thread got there first
3932   }
3933 }
3934 
3935 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3936   while (_work_queue->size() > max) {
3937     oop new_oop;
3938     if (_work_queue->pop_local(new_oop)) {
3939       assert(new_oop->is_oop(), "Should be an oop");
3940       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3941       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3942       assert(new_oop->is_parsable(), "Should be parsable");
3943       new_oop->oop_iterate(this);  // do_oop() above
3944     }
3945   }
3946 }
3947 
3948 // Upon stack overflow, we discard (part of) the stack,
3949 // remembering the least address amongst those discarded
3950 // in CMSCollector's _restart_address.
3951 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3952   // We need to do this under a mutex to prevent other
3953   // workers from interfering with the expansion below.
3954   MutexLockerEx ml(_overflow_stack->par_lock(),
3955                    Mutex::_no_safepoint_check_flag);
3956   // Remember the least grey address discarded
3957   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3958   _collector->lower_restart_addr(ra);
3959   _overflow_stack->reset();  // discard stack contents
3960   _overflow_stack->expand(); // expand the stack if possible
3961 }
3962 
3963 
3964 void CMSConcMarkingTask::do_work_steal(int i) {
3965   OopTaskQueue* work_q = work_queue(i);
3966   oop obj_to_scan;
3967   CMSBitMap* bm = &(_collector->_markBitMap);
3968   CMSMarkStack* ovflw = &(_collector->_markStack);
3969   int* seed = _collector->hash_seed(i);
3970   Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw);
3971   while (true) {
3972     cl.trim_queue(0);
3973     assert(work_q->size() == 0, "Should have been emptied above");
3974     if (get_work_from_overflow_stack(ovflw, work_q)) {
3975       // Can't assert below because the work obtained from the
3976       // overflow stack may already have been stolen from us.
3977       // assert(work_q->size() > 0, "Work from overflow stack");
3978       continue;
3979     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3980       assert(obj_to_scan->is_oop(), "Should be an oop");
3981       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3982       obj_to_scan->oop_iterate(&cl);
3983     } else if (terminator()->offer_termination()) {
3984       assert(work_q->size() == 0, "Impossible!");
3985       break;
3986     }
3987   }
3988 }
3989 
3990 // This is run by the CMS (coordinator) thread.
3991 void CMSConcMarkingTask::coordinator_yield() {
3992   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3993          "CMS thread should hold CMS token");
3994 
3995   // First give up the locks, then yield, then re-lock
3996   // We should probably use a constructor/destructor idiom to
3997   // do this unlock/lock or modify the MutexUnlocker class to
3998   // serve our purpose. XXX
3999   assert_lock_strong(_bit_map_lock);
4000   _bit_map_lock->unlock();
4001   ConcurrentMarkSweepThread::desynchronize(true);
4002   ConcurrentMarkSweepThread::acknowledge_yield_request();
4003   _collector->stopTimer();
4004   if (PrintCMSStatistics != 0) {
4005     _collector->incrementYields();
4006   }
4007   _collector->icms_wait();
4008 
4009   // It is possible for whichever thread initiated the yield request
4010   // not to get a chance to wake up and take the bitmap lock between
4011   // this thread releasing it and reacquiring it. So, while the
4012   // should_yield() flag is on, let's sleep for a bit to give the
4013   // other thread a chance to wake up. The limit imposed on the number
4014   // of iterations is defensive, to avoid any unforseen circumstances
4015   // putting us into an infinite loop. Since it's always been this
4016   // (coordinator_yield()) method that was observed to cause the
4017   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4018   // which is by default non-zero. For the other seven methods that
4019   // also perform the yield operation, as are using a different
4020   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4021   // can enable the sleeping for those methods too, if necessary.
4022   // See 6442774.
4023   //
4024   // We really need to reconsider the synchronization between the GC
4025   // thread and the yield-requesting threads in the future and we
4026   // should really use wait/notify, which is the recommended
4027   // way of doing this type of interaction. Additionally, we should
4028   // consolidate the eight methods that do the yield operation and they
4029   // are almost identical into one for better maintenability and
4030   // readability. See 6445193.
4031   //
4032   // Tony 2006.06.29
4033   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4034                        ConcurrentMarkSweepThread::should_yield() &&
4035                        !CMSCollector::foregroundGCIsActive(); ++i) {
4036     os::sleep(Thread::current(), 1, false);
4037     ConcurrentMarkSweepThread::acknowledge_yield_request();
4038   }
4039 
4040   ConcurrentMarkSweepThread::synchronize(true);
4041   _bit_map_lock->lock_without_safepoint_check();
4042   _collector->startTimer();
4043 }
4044 
4045 bool CMSCollector::do_marking_mt(bool asynch) {
4046   assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition");
4047   // In the future this would be determined ergonomically, based
4048   // on #cpu's, # active mutator threads (and load), and mutation rate.
4049   int num_workers = ParallelCMSThreads;
4050 
4051   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4052   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4053 
4054   CMSConcMarkingTask tsk(this, cms_space, perm_space,
4055                          asynch, num_workers /* number requested XXX */,
4056                          conc_workers(), task_queues());
4057 
4058   // Since the actual number of workers we get may be different
4059   // from the number we requested above, do we need to do anything different
4060   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4061   // class?? XXX
4062   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4063   perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4064 
4065   // Refs discovery is already non-atomic.
4066   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4067   // Mutate the Refs discovery so it is MT during the
4068   // multi-threaded marking phase.
4069   ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4070 
4071   conc_workers()->start_task(&tsk);
4072   while (tsk.yielded()) {
4073     tsk.coordinator_yield();
4074     conc_workers()->continue_task(&tsk);
4075   }
4076   // If the task was aborted, _restart_addr will be non-NULL
4077   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4078   while (_restart_addr != NULL) {
4079     // XXX For now we do not make use of ABORTED state and have not
4080     // yet implemented the right abort semantics (even in the original
4081     // single-threaded CMS case). That needs some more investigation
4082     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4083     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4084     // If _restart_addr is non-NULL, a marking stack overflow
4085     // occured; we need to do a fresh marking iteration from the
4086     // indicated restart address.
4087     if (_foregroundGCIsActive && asynch) {
4088       // We may be running into repeated stack overflows, having
4089       // reached the limit of the stack size, while making very
4090       // slow forward progress. It may be best to bail out and
4091       // let the foreground collector do its job.
4092       // Clear _restart_addr, so that foreground GC
4093       // works from scratch. This avoids the headache of
4094       // a "rescan" which would otherwise be needed because
4095       // of the dirty mod union table & card table.
4096       _restart_addr = NULL;
4097       return false;
4098     }
4099     // Adjust the task to restart from _restart_addr
4100     tsk.reset(_restart_addr);
4101     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4102                   _restart_addr);
4103     perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4104                   _restart_addr);
4105     _restart_addr = NULL;
4106     // Get the workers going again
4107     conc_workers()->start_task(&tsk);
4108     while (tsk.yielded()) {
4109       tsk.coordinator_yield();
4110       conc_workers()->continue_task(&tsk);
4111     }
4112   }
4113   assert(tsk.completed(), "Inconsistency");
4114   assert(tsk.result() == true, "Inconsistency");
4115   return true;
4116 }
4117 
4118 bool CMSCollector::do_marking_st(bool asynch) {
4119   ResourceMark rm;
4120   HandleMark   hm;
4121 
4122   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4123     &_markStack, &_revisitStack, CMSYield && asynch);
4124   // the last argument to iterate indicates whether the iteration
4125   // should be incremental with periodic yields.
4126   _markBitMap.iterate(&markFromRootsClosure);
4127   // If _restart_addr is non-NULL, a marking stack overflow
4128   // occured; we need to do a fresh iteration from the
4129   // indicated restart address.
4130   while (_restart_addr != NULL) {
4131     if (_foregroundGCIsActive && asynch) {
4132       // We may be running into repeated stack overflows, having
4133       // reached the limit of the stack size, while making very
4134       // slow forward progress. It may be best to bail out and
4135       // let the foreground collector do its job.
4136       // Clear _restart_addr, so that foreground GC
4137       // works from scratch. This avoids the headache of
4138       // a "rescan" which would otherwise be needed because
4139       // of the dirty mod union table & card table.
4140       _restart_addr = NULL;
4141       return false;  // indicating failure to complete marking
4142     }
4143     // Deal with stack overflow:
4144     // we restart marking from _restart_addr
4145     HeapWord* ra = _restart_addr;
4146     markFromRootsClosure.reset(ra);
4147     _restart_addr = NULL;
4148     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4149   }
4150   return true;
4151 }
4152 
4153 void CMSCollector::preclean() {
4154   check_correct_thread_executing();
4155   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4156   verify_work_stacks_empty();
4157   verify_overflow_empty();
4158   _abort_preclean = false;
4159   if (CMSPrecleaningEnabled) {
4160     _eden_chunk_index = 0;
4161     size_t used = get_eden_used();
4162     size_t capacity = get_eden_capacity();
4163     // Don't start sampling unless we will get sufficiently
4164     // many samples.
4165     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4166                 * CMSScheduleRemarkEdenPenetration)) {
4167       _start_sampling = true;
4168     } else {
4169       _start_sampling = false;
4170     }
4171     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4172     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4173     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4174   }
4175   CMSTokenSync x(true); // is cms thread
4176   if (CMSPrecleaningEnabled) {
4177     sample_eden();
4178     _collectorState = AbortablePreclean;
4179   } else {
4180     _collectorState = FinalMarking;
4181   }
4182   verify_work_stacks_empty();
4183   verify_overflow_empty();
4184 }
4185 
4186 // Try and schedule the remark such that young gen
4187 // occupancy is CMSScheduleRemarkEdenPenetration %.
4188 void CMSCollector::abortable_preclean() {
4189   check_correct_thread_executing();
4190   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4191   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4192 
4193   // If Eden's current occupancy is below this threshold,
4194   // immediately schedule the remark; else preclean
4195   // past the next scavenge in an effort to
4196   // schedule the pause as described avove. By choosing
4197   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4198   // we will never do an actual abortable preclean cycle.
4199   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4200     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4201     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4202     // We need more smarts in the abortable preclean
4203     // loop below to deal with cases where allocation
4204     // in young gen is very very slow, and our precleaning
4205     // is running a losing race against a horde of
4206     // mutators intent on flooding us with CMS updates
4207     // (dirty cards).
4208     // One, admittedly dumb, strategy is to give up
4209     // after a certain number of abortable precleaning loops
4210     // or after a certain maximum time. We want to make
4211     // this smarter in the next iteration.
4212     // XXX FIX ME!!! YSR
4213     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4214     while (!(should_abort_preclean() ||
4215              ConcurrentMarkSweepThread::should_terminate())) {
4216       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4217       cumworkdone += workdone;
4218       loops++;
4219       // Voluntarily terminate abortable preclean phase if we have
4220       // been at it for too long.
4221       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4222           loops >= CMSMaxAbortablePrecleanLoops) {
4223         if (PrintGCDetails) {
4224           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4225         }
4226         break;
4227       }
4228       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4229         if (PrintGCDetails) {
4230           gclog_or_tty->print(" CMS: abort preclean due to time ");
4231         }
4232         break;
4233       }
4234       // If we are doing little work each iteration, we should
4235       // take a short break.
4236       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4237         // Sleep for some time, waiting for work to accumulate
4238         stopTimer();
4239         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4240         startTimer();
4241         waited++;
4242       }
4243     }
4244     if (PrintCMSStatistics > 0) {
4245       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4246                           loops, waited, cumworkdone);
4247     }
4248   }
4249   CMSTokenSync x(true); // is cms thread
4250   if (_collectorState != Idling) {
4251     assert(_collectorState == AbortablePreclean,
4252            "Spontaneous state transition?");
4253     _collectorState = FinalMarking;
4254   } // Else, a foreground collection completed this CMS cycle.
4255   return;
4256 }
4257 
4258 // Respond to an Eden sampling opportunity
4259 void CMSCollector::sample_eden() {
4260   // Make sure a young gc cannot sneak in between our
4261   // reading and recording of a sample.
4262   assert(Thread::current()->is_ConcurrentGC_thread(),
4263          "Only the cms thread may collect Eden samples");
4264   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4265          "Should collect samples while holding CMS token");
4266   if (!_start_sampling) {
4267     return;
4268   }
4269   if (_eden_chunk_array) {
4270     if (_eden_chunk_index < _eden_chunk_capacity) {
4271       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4272       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4273              "Unexpected state of Eden");
4274       // We'd like to check that what we just sampled is an oop-start address;
4275       // however, we cannot do that here since the object may not yet have been
4276       // initialized. So we'll instead do the check when we _use_ this sample
4277       // later.
4278       if (_eden_chunk_index == 0 ||
4279           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4280                          _eden_chunk_array[_eden_chunk_index-1])
4281            >= CMSSamplingGrain)) {
4282         _eden_chunk_index++;  // commit sample
4283       }
4284     }
4285   }
4286   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4287     size_t used = get_eden_used();
4288     size_t capacity = get_eden_capacity();
4289     assert(used <= capacity, "Unexpected state of Eden");
4290     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4291       _abort_preclean = true;
4292     }
4293   }
4294 }
4295 
4296 
4297 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4298   assert(_collectorState == Precleaning ||
4299          _collectorState == AbortablePreclean, "incorrect state");
4300   ResourceMark rm;
4301   HandleMark   hm;
4302   // Do one pass of scrubbing the discovered reference lists
4303   // to remove any reference objects with strongly-reachable
4304   // referents.
4305   if (clean_refs) {
4306     ReferenceProcessor* rp = ref_processor();
4307     CMSPrecleanRefsYieldClosure yield_cl(this);
4308     assert(rp->span().equals(_span), "Spans should be equal");
4309     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4310                                    &_markStack);
4311     CMSDrainMarkingStackClosure complete_trace(this,
4312                                   _span, &_markBitMap, &_markStack,
4313                                   &keep_alive);
4314 
4315     // We don't want this step to interfere with a young
4316     // collection because we don't want to take CPU
4317     // or memory bandwidth away from the young GC threads
4318     // (which may be as many as there are CPUs).
4319     // Note that we don't need to protect ourselves from
4320     // interference with mutators because they can't
4321     // manipulate the discovered reference lists nor affect
4322     // the computed reachability of the referents, the
4323     // only properties manipulated by the precleaning
4324     // of these reference lists.
4325     stopTimer();
4326     CMSTokenSyncWithLocks x(true /* is cms thread */,
4327                             bitMapLock());
4328     startTimer();
4329     sample_eden();
4330     // The following will yield to allow foreground
4331     // collection to proceed promptly. XXX YSR:
4332     // The code in this method may need further
4333     // tweaking for better performance and some restructuring
4334     // for cleaner interfaces.
4335     rp->preclean_discovered_references(
4336           rp->is_alive_non_header(), &keep_alive, &complete_trace,
4337           &yield_cl);
4338   }
4339 
4340   if (clean_survivor) {  // preclean the active survivor space(s)
4341     assert(_young_gen->kind() == Generation::DefNew ||
4342            _young_gen->kind() == Generation::ParNew ||
4343            _young_gen->kind() == Generation::ASParNew,
4344          "incorrect type for cast");
4345     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4346     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4347                              &_markBitMap, &_modUnionTable,
4348                              &_markStack, &_revisitStack,
4349                              true /* precleaning phase */);
4350     stopTimer();
4351     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4352                              bitMapLock());
4353     startTimer();
4354     unsigned int before_count =
4355       GenCollectedHeap::heap()->total_collections();
4356     SurvivorSpacePrecleanClosure
4357       sss_cl(this, _span, &_markBitMap, &_markStack,
4358              &pam_cl, before_count, CMSYield);
4359     dng->from()->object_iterate_careful(&sss_cl);
4360     dng->to()->object_iterate_careful(&sss_cl);
4361   }
4362   MarkRefsIntoAndScanClosure
4363     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4364              &_markStack, &_revisitStack, this, CMSYield,
4365              true /* precleaning phase */);
4366   // CAUTION: The following closure has persistent state that may need to
4367   // be reset upon a decrease in the sequence of addresses it
4368   // processes.
4369   ScanMarkedObjectsAgainCarefullyClosure
4370     smoac_cl(this, _span,
4371       &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4372 
4373   // Preclean dirty cards in ModUnionTable and CardTable using
4374   // appropriate convergence criterion;
4375   // repeat CMSPrecleanIter times unless we find that
4376   // we are losing.
4377   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4378   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4379          "Bad convergence multiplier");
4380   assert(CMSPrecleanThreshold >= 100,
4381          "Unreasonably low CMSPrecleanThreshold");
4382 
4383   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4384   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4385        numIter < CMSPrecleanIter;
4386        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4387     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4388     if (CMSPermGenPrecleaningEnabled) {
4389       curNumCards  += preclean_mod_union_table(_permGen, &smoac_cl);
4390     }
4391     if (Verbose && PrintGCDetails) {
4392       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4393     }
4394     // Either there are very few dirty cards, so re-mark
4395     // pause will be small anyway, or our pre-cleaning isn't
4396     // that much faster than the rate at which cards are being
4397     // dirtied, so we might as well stop and re-mark since
4398     // precleaning won't improve our re-mark time by much.
4399     if (curNumCards <= CMSPrecleanThreshold ||
4400         (numIter > 0 &&
4401          (curNumCards * CMSPrecleanDenominator >
4402          lastNumCards * CMSPrecleanNumerator))) {
4403       numIter++;
4404       cumNumCards += curNumCards;
4405       break;
4406     }
4407   }
4408   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4409   if (CMSPermGenPrecleaningEnabled) {
4410     curNumCards += preclean_card_table(_permGen, &smoac_cl);
4411   }
4412   cumNumCards += curNumCards;
4413   if (PrintGCDetails && PrintCMSStatistics != 0) {
4414     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4415                   curNumCards, cumNumCards, numIter);
4416   }
4417   return cumNumCards;   // as a measure of useful work done
4418 }
4419 
4420 // PRECLEANING NOTES:
4421 // Precleaning involves:
4422 // . reading the bits of the modUnionTable and clearing the set bits.
4423 // . For the cards corresponding to the set bits, we scan the
4424 //   objects on those cards. This means we need the free_list_lock
4425 //   so that we can safely iterate over the CMS space when scanning
4426 //   for oops.
4427 // . When we scan the objects, we'll be both reading and setting
4428 //   marks in the marking bit map, so we'll need the marking bit map.
4429 // . For protecting _collector_state transitions, we take the CGC_lock.
4430 //   Note that any races in the reading of of card table entries by the
4431 //   CMS thread on the one hand and the clearing of those entries by the
4432 //   VM thread or the setting of those entries by the mutator threads on the
4433 //   other are quite benign. However, for efficiency it makes sense to keep
4434 //   the VM thread from racing with the CMS thread while the latter is
4435 //   dirty card info to the modUnionTable. We therefore also use the
4436 //   CGC_lock to protect the reading of the card table and the mod union
4437 //   table by the CM thread.
4438 // . We run concurrently with mutator updates, so scanning
4439 //   needs to be done carefully  -- we should not try to scan
4440 //   potentially uninitialized objects.
4441 //
4442 // Locking strategy: While holding the CGC_lock, we scan over and
4443 // reset a maximal dirty range of the mod union / card tables, then lock
4444 // the free_list_lock and bitmap lock to do a full marking, then
4445 // release these locks; and repeat the cycle. This allows for a
4446 // certain amount of fairness in the sharing of these locks between
4447 // the CMS collector on the one hand, and the VM thread and the
4448 // mutators on the other.
4449 
4450 // NOTE: preclean_mod_union_table() and preclean_card_table()
4451 // further below are largely identical; if you need to modify
4452 // one of these methods, please check the other method too.
4453 
4454 size_t CMSCollector::preclean_mod_union_table(
4455   ConcurrentMarkSweepGeneration* gen,
4456   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4457   verify_work_stacks_empty();
4458   verify_overflow_empty();
4459 
4460   // strategy: starting with the first card, accumulate contiguous
4461   // ranges of dirty cards; clear these cards, then scan the region
4462   // covered by these cards.
4463 
4464   // Since all of the MUT is committed ahead, we can just use
4465   // that, in case the generations expand while we are precleaning.
4466   // It might also be fine to just use the committed part of the
4467   // generation, but we might potentially miss cards when the
4468   // generation is rapidly expanding while we are in the midst
4469   // of precleaning.
4470   HeapWord* startAddr = gen->reserved().start();
4471   HeapWord* endAddr   = gen->reserved().end();
4472 
4473   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4474 
4475   size_t numDirtyCards, cumNumDirtyCards;
4476   HeapWord *nextAddr, *lastAddr;
4477   for (cumNumDirtyCards = numDirtyCards = 0,
4478        nextAddr = lastAddr = startAddr;
4479        nextAddr < endAddr;
4480        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4481 
4482     ResourceMark rm;
4483     HandleMark   hm;
4484 
4485     MemRegion dirtyRegion;
4486     {
4487       stopTimer();
4488       CMSTokenSync ts(true);
4489       startTimer();
4490       sample_eden();
4491       // Get dirty region starting at nextOffset (inclusive),
4492       // simultaneously clearing it.
4493       dirtyRegion =
4494         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4495       assert(dirtyRegion.start() >= nextAddr,
4496              "returned region inconsistent?");
4497     }
4498     // Remember where the next search should begin.
4499     // The returned region (if non-empty) is a right open interval,
4500     // so lastOffset is obtained from the right end of that
4501     // interval.
4502     lastAddr = dirtyRegion.end();
4503     // Should do something more transparent and less hacky XXX
4504     numDirtyCards =
4505       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4506 
4507     // We'll scan the cards in the dirty region (with periodic
4508     // yields for foreground GC as needed).
4509     if (!dirtyRegion.is_empty()) {
4510       assert(numDirtyCards > 0, "consistency check");
4511       HeapWord* stop_point = NULL;
4512       {
4513         stopTimer();
4514         CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4515                                  bitMapLock());
4516         startTimer();
4517         verify_work_stacks_empty();
4518         verify_overflow_empty();
4519         sample_eden();
4520         stop_point =
4521           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4522       }
4523       if (stop_point != NULL) {
4524         // The careful iteration stopped early either because it found an
4525         // uninitialized object, or because we were in the midst of an
4526         // "abortable preclean", which should now be aborted. Redirty
4527         // the bits corresponding to the partially-scanned or unscanned
4528         // cards. We'll either restart at the next block boundary or
4529         // abort the preclean.
4530         assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4531                (_collectorState == AbortablePreclean && should_abort_preclean()),
4532                "Unparsable objects should only be in perm gen.");
4533 
4534         stopTimer();
4535         CMSTokenSyncWithLocks ts(true, bitMapLock());
4536         startTimer();
4537         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4538         if (should_abort_preclean()) {
4539           break; // out of preclean loop
4540         } else {
4541           // Compute the next address at which preclean should pick up;
4542           // might need bitMapLock in order to read P-bits.
4543           lastAddr = next_card_start_after_block(stop_point);
4544         }
4545       }
4546     } else {
4547       assert(lastAddr == endAddr, "consistency check");
4548       assert(numDirtyCards == 0, "consistency check");
4549       break;
4550     }
4551   }
4552   verify_work_stacks_empty();
4553   verify_overflow_empty();
4554   return cumNumDirtyCards;
4555 }
4556 
4557 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4558 // below are largely identical; if you need to modify
4559 // one of these methods, please check the other method too.
4560 
4561 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4562   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4563   // strategy: it's similar to precleamModUnionTable above, in that
4564   // we accumulate contiguous ranges of dirty cards, mark these cards
4565   // precleaned, then scan the region covered by these cards.
4566   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4567   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4568 
4569   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4570 
4571   size_t numDirtyCards, cumNumDirtyCards;
4572   HeapWord *lastAddr, *nextAddr;
4573 
4574   for (cumNumDirtyCards = numDirtyCards = 0,
4575        nextAddr = lastAddr = startAddr;
4576        nextAddr < endAddr;
4577        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4578 
4579     ResourceMark rm;
4580     HandleMark   hm;
4581 
4582     MemRegion dirtyRegion;
4583     {
4584       // See comments in "Precleaning notes" above on why we
4585       // do this locking. XXX Could the locking overheads be
4586       // too high when dirty cards are sparse? [I don't think so.]
4587       stopTimer();
4588       CMSTokenSync x(true); // is cms thread
4589       startTimer();
4590       sample_eden();
4591       // Get and clear dirty region from card table
4592       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_preclean(
4593                                     MemRegion(nextAddr, endAddr));
4594       assert(dirtyRegion.start() >= nextAddr,
4595              "returned region inconsistent?");
4596     }
4597     lastAddr = dirtyRegion.end();
4598     numDirtyCards =
4599       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4600 
4601     if (!dirtyRegion.is_empty()) {
4602       stopTimer();
4603       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4604       startTimer();
4605       sample_eden();
4606       verify_work_stacks_empty();
4607       verify_overflow_empty();
4608       HeapWord* stop_point =
4609         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4610       if (stop_point != NULL) {
4611         // The careful iteration stopped early because it found an
4612         // uninitialized object.  Redirty the bits corresponding to the
4613         // partially-scanned or unscanned cards, and start again at the
4614         // next block boundary.
4615         assert(CMSPermGenPrecleaningEnabled ||
4616                (_collectorState == AbortablePreclean && should_abort_preclean()),
4617                "Unparsable objects should only be in perm gen.");
4618         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4619         if (should_abort_preclean()) {
4620           break; // out of preclean loop
4621         } else {
4622           // Compute the next address at which preclean should pick up.
4623           lastAddr = next_card_start_after_block(stop_point);
4624         }
4625       }
4626     } else {
4627       break;
4628     }
4629   }
4630   verify_work_stacks_empty();
4631   verify_overflow_empty();
4632   return cumNumDirtyCards;
4633 }
4634 
4635 void CMSCollector::checkpointRootsFinal(bool asynch,
4636   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4637   assert(_collectorState == FinalMarking, "incorrect state transition?");
4638   check_correct_thread_executing();
4639   // world is stopped at this checkpoint
4640   assert(SafepointSynchronize::is_at_safepoint(),
4641          "world should be stopped");
4642   verify_work_stacks_empty();
4643   verify_overflow_empty();
4644 
4645   SpecializationStats::clear();
4646   if (PrintGCDetails) {
4647     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4648                         _young_gen->used() / K,
4649                         _young_gen->capacity() / K);
4650   }
4651   if (asynch) {
4652     if (CMSScavengeBeforeRemark) {
4653       GenCollectedHeap* gch = GenCollectedHeap::heap();
4654       // Temporarily set flag to false, GCH->do_collection will
4655       // expect it to be false and set to true
4656       FlagSetting fl(gch->_is_gc_active, false);
4657       NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4658         PrintGCDetails && Verbose, true, gclog_or_tty);)
4659       int level = _cmsGen->level() - 1;
4660       if (level >= 0) {
4661         gch->do_collection(true,        // full (i.e. force, see below)
4662                            false,       // !clear_all_soft_refs
4663                            0,           // size
4664                            false,       // is_tlab
4665                            level        // max_level
4666                           );
4667       }
4668     }
4669     FreelistLocker x(this);
4670     MutexLockerEx y(bitMapLock(),
4671                     Mutex::_no_safepoint_check_flag);
4672     assert(!init_mark_was_synchronous, "but that's impossible!");
4673     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4674   } else {
4675     // already have all the locks
4676     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4677                              init_mark_was_synchronous);
4678   }
4679   verify_work_stacks_empty();
4680   verify_overflow_empty();
4681   SpecializationStats::print();
4682 }
4683 
4684 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4685   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4686 
4687   NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4688 
4689   assert(haveFreelistLocks(), "must have free list locks");
4690   assert_lock_strong(bitMapLock());
4691 
4692   if (UseAdaptiveSizePolicy) {
4693     size_policy()->checkpoint_roots_final_begin();
4694   }
4695 
4696   ResourceMark rm;
4697   HandleMark   hm;
4698 
4699   GenCollectedHeap* gch = GenCollectedHeap::heap();
4700 
4701   if (cms_should_unload_classes()) {
4702     CodeCache::gc_prologue();
4703   }
4704   assert(haveFreelistLocks(), "must have free list locks");
4705   assert_lock_strong(bitMapLock());
4706 
4707   if (!init_mark_was_synchronous) {
4708     // We might assume that we need not fill TLAB's when
4709     // CMSScavengeBeforeRemark is set, because we may have just done
4710     // a scavenge which would have filled all TLAB's -- and besides
4711     // Eden would be empty. This however may not always be the case --
4712     // for instance although we asked for a scavenge, it may not have
4713     // happened because of a JNI critical section. We probably need
4714     // a policy for deciding whether we can in that case wait until
4715     // the critical section releases and then do the remark following
4716     // the scavenge, and skip it here. In the absence of that policy,
4717     // or of an indication of whether the scavenge did indeed occur,
4718     // we cannot rely on TLAB's having been filled and must do
4719     // so here just in case a scavenge did not happen.
4720     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4721     // Update the saved marks which may affect the root scans.
4722     gch->save_marks();
4723 
4724     {
4725       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4726 
4727       // Note on the role of the mod union table:
4728       // Since the marker in "markFromRoots" marks concurrently with
4729       // mutators, it is possible for some reachable objects not to have been
4730       // scanned. For instance, an only reference to an object A was
4731       // placed in object B after the marker scanned B. Unless B is rescanned,
4732       // A would be collected. Such updates to references in marked objects
4733       // are detected via the mod union table which is the set of all cards
4734       // dirtied since the first checkpoint in this GC cycle and prior to
4735       // the most recent young generation GC, minus those cleaned up by the
4736       // concurrent precleaning.
4737       if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4738         TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4739         do_remark_parallel();
4740       } else {
4741         TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4742                     gclog_or_tty);
4743         do_remark_non_parallel();
4744       }
4745     }
4746   } else {
4747     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4748     // The initial mark was stop-world, so there's no rescanning to
4749     // do; go straight on to the next step below.
4750   }
4751   verify_work_stacks_empty();
4752   verify_overflow_empty();
4753 
4754   {
4755     NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4756     refProcessingWork(asynch, clear_all_soft_refs);
4757   }
4758   verify_work_stacks_empty();
4759   verify_overflow_empty();
4760 
4761   if (cms_should_unload_classes()) {
4762     CodeCache::gc_epilogue();
4763   }
4764 
4765   // If we encountered any (marking stack / work queue) overflow
4766   // events during the current CMS cycle, take appropriate
4767   // remedial measures, where possible, so as to try and avoid
4768   // recurrence of that condition.
4769   assert(_markStack.isEmpty(), "No grey objects");
4770   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4771                      _ser_kac_ovflw;
4772   if (ser_ovflw > 0) {
4773     if (PrintCMSStatistics != 0) {
4774       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4775         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4776         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4777         _ser_kac_ovflw);
4778     }
4779     _markStack.expand();
4780     _ser_pmc_remark_ovflw = 0;
4781     _ser_pmc_preclean_ovflw = 0;
4782     _ser_kac_ovflw = 0;
4783   }
4784   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4785     if (PrintCMSStatistics != 0) {
4786       gclog_or_tty->print_cr("Work queue overflow (benign) "
4787         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4788         _par_pmc_remark_ovflw, _par_kac_ovflw);
4789     }
4790     _par_pmc_remark_ovflw = 0;
4791     _par_kac_ovflw = 0;
4792   }
4793   if (PrintCMSStatistics != 0) {
4794      if (_markStack._hit_limit > 0) {
4795        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4796                               _markStack._hit_limit);
4797      }
4798      if (_markStack._failed_double > 0) {
4799        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4800                               " current capacity "SIZE_FORMAT,
4801                               _markStack._failed_double,
4802                               _markStack.capacity());
4803      }
4804   }
4805   _markStack._hit_limit = 0;
4806   _markStack._failed_double = 0;
4807 
4808   if ((VerifyAfterGC || VerifyDuringGC) &&
4809       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4810     verify_after_remark();
4811   }
4812 
4813   // Change under the freelistLocks.
4814   _collectorState = Sweeping;
4815   // Call isAllClear() under bitMapLock
4816   assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4817     " final marking");
4818   if (UseAdaptiveSizePolicy) {
4819     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4820   }
4821 }
4822 
4823 // Parallel remark task
4824 class CMSParRemarkTask: public AbstractGangTask {
4825   CMSCollector* _collector;
4826   WorkGang*     _workers;
4827   int           _n_workers;
4828   CompactibleFreeListSpace* _cms_space;
4829   CompactibleFreeListSpace* _perm_space;
4830 
4831   // The per-thread work queues, available here for stealing.
4832   OopTaskQueueSet*       _task_queues;
4833   ParallelTaskTerminator _term;
4834 
4835  public:
4836   CMSParRemarkTask(CMSCollector* collector,
4837                    CompactibleFreeListSpace* cms_space,
4838                    CompactibleFreeListSpace* perm_space,
4839                    int n_workers, WorkGang* workers,
4840                    OopTaskQueueSet* task_queues):
4841     AbstractGangTask("Rescan roots and grey objects in parallel"),
4842     _collector(collector),
4843     _cms_space(cms_space), _perm_space(perm_space),
4844     _n_workers(n_workers),
4845     _workers(workers),
4846     _task_queues(task_queues),
4847     _term(workers->total_workers(), task_queues) { }
4848 
4849   OopTaskQueueSet* task_queues() { return _task_queues; }
4850 
4851   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4852 
4853   ParallelTaskTerminator* terminator() { return &_term; }
4854 
4855   void work(int i);
4856 
4857  private:
4858   // Work method in support of parallel rescan ... of young gen spaces
4859   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4860                              ContiguousSpace* space,
4861                              HeapWord** chunk_array, size_t chunk_top);
4862 
4863   // ... of  dirty cards in old space
4864   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4865                                   Par_MarkRefsIntoAndScanClosure* cl);
4866 
4867   // ... work stealing for the above
4868   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4869 };
4870 
4871 void CMSParRemarkTask::work(int i) {
4872   elapsedTimer _timer;
4873   ResourceMark rm;
4874   HandleMark   hm;
4875 
4876   // ---------- rescan from roots --------------
4877   _timer.start();
4878   GenCollectedHeap* gch = GenCollectedHeap::heap();
4879   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4880     _collector->_span, _collector->ref_processor(),
4881     &(_collector->_markBitMap),
4882     work_queue(i), &(_collector->_revisitStack));
4883 
4884   // Rescan young gen roots first since these are likely
4885   // coarsely partitioned and may, on that account, constitute
4886   // the critical path; thus, it's best to start off that
4887   // work first.
4888   // ---------- young gen roots --------------
4889   {
4890     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
4891     EdenSpace* eden_space = dng->eden();
4892     ContiguousSpace* from_space = dng->from();
4893     ContiguousSpace* to_space   = dng->to();
4894 
4895     HeapWord** eca = _collector->_eden_chunk_array;
4896     size_t     ect = _collector->_eden_chunk_index;
4897     HeapWord** sca = _collector->_survivor_chunk_array;
4898     size_t     sct = _collector->_survivor_chunk_index;
4899 
4900     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4901     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4902 
4903     do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
4904     do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
4905     do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
4906 
4907     _timer.stop();
4908     if (PrintCMSStatistics != 0) {
4909       gclog_or_tty->print_cr(
4910         "Finished young gen rescan work in %dth thread: %3.3f sec",
4911         i, _timer.seconds());
4912     }
4913   }
4914 
4915   // ---------- remaining roots --------------
4916   _timer.reset();
4917   _timer.start();
4918   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
4919                                 false,     // yg was scanned above
4920                                 true,      // collecting perm gen
4921                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4922                                 NULL, &par_mrias_cl);
4923   _timer.stop();
4924   if (PrintCMSStatistics != 0) {
4925     gclog_or_tty->print_cr(
4926       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4927       i, _timer.seconds());
4928   }
4929 
4930   // ---------- rescan dirty cards ------------
4931   _timer.reset();
4932   _timer.start();
4933 
4934   // Do the rescan tasks for each of the two spaces
4935   // (cms_space and perm_space) in turn.
4936   do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
4937   do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
4938   _timer.stop();
4939   if (PrintCMSStatistics != 0) {
4940     gclog_or_tty->print_cr(
4941       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4942       i, _timer.seconds());
4943   }
4944 
4945   // ---------- steal work from other threads ...
4946   // ---------- ... and drain overflow list.
4947   _timer.reset();
4948   _timer.start();
4949   do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
4950   _timer.stop();
4951   if (PrintCMSStatistics != 0) {
4952     gclog_or_tty->print_cr(
4953       "Finished work stealing in %dth thread: %3.3f sec",
4954       i, _timer.seconds());
4955   }
4956 }
4957 
4958 void
4959 CMSParRemarkTask::do_young_space_rescan(int i,
4960   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
4961   HeapWord** chunk_array, size_t chunk_top) {
4962   // Until all tasks completed:
4963   // . claim an unclaimed task
4964   // . compute region boundaries corresponding to task claimed
4965   //   using chunk_array
4966   // . par_oop_iterate(cl) over that region
4967 
4968   ResourceMark rm;
4969   HandleMark   hm;
4970 
4971   SequentialSubTasksDone* pst = space->par_seq_tasks();
4972   assert(pst->valid(), "Uninitialized use?");
4973 
4974   int nth_task = 0;
4975   int n_tasks  = pst->n_tasks();
4976 
4977   HeapWord *start, *end;
4978   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4979     // We claimed task # nth_task; compute its boundaries.
4980     if (chunk_top == 0) {  // no samples were taken
4981       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
4982       start = space->bottom();
4983       end   = space->top();
4984     } else if (nth_task == 0) {
4985       start = space->bottom();
4986       end   = chunk_array[nth_task];
4987     } else if (nth_task < (jint)chunk_top) {
4988       assert(nth_task >= 1, "Control point invariant");
4989       start = chunk_array[nth_task - 1];
4990       end   = chunk_array[nth_task];
4991     } else {
4992       assert(nth_task == (jint)chunk_top, "Control point invariant");
4993       start = chunk_array[chunk_top - 1];
4994       end   = space->top();
4995     }
4996     MemRegion mr(start, end);
4997     // Verify that mr is in space
4998     assert(mr.is_empty() || space->used_region().contains(mr),
4999            "Should be in space");
5000     // Verify that "start" is an object boundary
5001     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5002            "Should be an oop");
5003     space->par_oop_iterate(mr, cl);
5004   }
5005   pst->all_tasks_completed();
5006 }
5007 
5008 void
5009 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5010   CompactibleFreeListSpace* sp, int i,
5011   Par_MarkRefsIntoAndScanClosure* cl) {
5012   // Until all tasks completed:
5013   // . claim an unclaimed task
5014   // . compute region boundaries corresponding to task claimed
5015   // . transfer dirty bits ct->mut for that region
5016   // . apply rescanclosure to dirty mut bits for that region
5017 
5018   ResourceMark rm;
5019   HandleMark   hm;
5020 
5021   OopTaskQueue* work_q = work_queue(i);
5022   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5023   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5024   // CAUTION: This closure has state that persists across calls to
5025   // the work method dirty_range_iterate_clear() in that it has
5026   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5027   // use of that state in the imbedded UpwardsObjectClosure instance
5028   // assumes that the cards are always iterated (even if in parallel
5029   // by several threads) in monotonically increasing order per each
5030   // thread. This is true of the implementation below which picks
5031   // card ranges (chunks) in monotonically increasing order globally
5032   // and, a-fortiori, in monotonically increasing order per thread
5033   // (the latter order being a subsequence of the former).
5034   // If the work code below is ever reorganized into a more chaotic
5035   // work-partitioning form than the current "sequential tasks"
5036   // paradigm, the use of that persistent state will have to be
5037   // revisited and modified appropriately. See also related
5038   // bug 4756801 work on which should examine this code to make
5039   // sure that the changes there do not run counter to the
5040   // assumptions made here and necessary for correctness and
5041   // efficiency. Note also that this code might yield inefficient
5042   // behaviour in the case of very large objects that span one or
5043   // more work chunks. Such objects would potentially be scanned
5044   // several times redundantly. Work on 4756801 should try and
5045   // address that performance anomaly if at all possible. XXX
5046   MemRegion  full_span  = _collector->_span;
5047   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5048   CMSMarkStack* rs = &(_collector->_revisitStack);   // shared
5049   MarkFromDirtyCardsClosure
5050     greyRescanClosure(_collector, full_span, // entire span of interest
5051                       sp, bm, work_q, rs, cl);
5052 
5053   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5054   assert(pst->valid(), "Uninitialized use?");
5055   int nth_task = 0;
5056   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5057   MemRegion span = sp->used_region();
5058   HeapWord* start_addr = span.start();
5059   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5060                                            alignment);
5061   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5062   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5063          start_addr, "Check alignment");
5064   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5065          chunk_size, "Check alignment");
5066 
5067   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5068     // Having claimed the nth_task, compute corresponding mem-region,
5069     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5070     // The alignment restriction ensures that we do not need any
5071     // synchronization with other gang-workers while setting or
5072     // clearing bits in thus chunk of the MUT.
5073     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5074                                     start_addr + (nth_task+1)*chunk_size);
5075     // The last chunk's end might be way beyond end of the
5076     // used region. In that case pull back appropriately.
5077     if (this_span.end() > end_addr) {
5078       this_span.set_end(end_addr);
5079       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5080     }
5081     // Iterate over the dirty cards covering this chunk, marking them
5082     // precleaned, and setting the corresponding bits in the mod union
5083     // table. Since we have been careful to partition at Card and MUT-word
5084     // boundaries no synchronization is needed between parallel threads.
5085     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5086                                                  &modUnionClosure);
5087 
5088     // Having transferred these marks into the modUnionTable,
5089     // rescan the marked objects on the dirty cards in the modUnionTable.
5090     // Even if this is at a synchronous collection, the initial marking
5091     // may have been done during an asynchronous collection so there
5092     // may be dirty bits in the mod-union table.
5093     _collector->_modUnionTable.dirty_range_iterate_clear(
5094                   this_span, &greyRescanClosure);
5095     _collector->_modUnionTable.verifyNoOneBitsInRange(
5096                                  this_span.start(),
5097                                  this_span.end());
5098   }
5099   pst->all_tasks_completed();  // declare that i am done
5100 }
5101 
5102 // . see if we can share work_queues with ParNew? XXX
5103 void
5104 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5105                                 int* seed) {
5106   OopTaskQueue* work_q = work_queue(i);
5107   NOT_PRODUCT(int num_steals = 0;)
5108   oop obj_to_scan;
5109   CMSBitMap* bm = &(_collector->_markBitMap);
5110   size_t num_from_overflow_list =
5111            MIN2((size_t)work_q->max_elems()/4,
5112                 (size_t)ParGCDesiredObjsFromOverflowList);
5113 
5114   while (true) {
5115     // Completely finish any left over work from (an) earlier round(s)
5116     cl->trim_queue(0);
5117     // Now check if there's any work in the overflow list
5118     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5119                                                 work_q)) {
5120       // found something in global overflow list;
5121       // not yet ready to go stealing work from others.
5122       // We'd like to assert(work_q->size() != 0, ...)
5123       // because we just took work from the overflow list,
5124       // but of course we can't since all of that could have
5125       // been already stolen from us.
5126       // "He giveth and He taketh away."
5127       continue;
5128     }
5129     // Verify that we have no work before we resort to stealing
5130     assert(work_q->size() == 0, "Have work, shouldn't steal");
5131     // Try to steal from other queues that have work
5132     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5133       NOT_PRODUCT(num_steals++;)
5134       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5135       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5136       // Do scanning work
5137       obj_to_scan->oop_iterate(cl);
5138       // Loop around, finish this work, and try to steal some more
5139     } else if (terminator()->offer_termination()) {
5140         break;  // nirvana from the infinite cycle
5141     }
5142   }
5143   NOT_PRODUCT(
5144     if (PrintCMSStatistics != 0) {
5145       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5146     }
5147   )
5148   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5149          "Else our work is not yet done");
5150 }
5151 
5152 // Return a thread-local PLAB recording array, as appropriate.
5153 void* CMSCollector::get_data_recorder(int thr_num) {
5154   if (_survivor_plab_array != NULL &&
5155       (CMSPLABRecordAlways ||
5156        (_collectorState > Marking && _collectorState < FinalMarking))) {
5157     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5158     ChunkArray* ca = &_survivor_plab_array[thr_num];
5159     ca->reset();   // clear it so that fresh data is recorded
5160     return (void*) ca;
5161   } else {
5162     return NULL;
5163   }
5164 }
5165 
5166 // Reset all the thread-local PLAB recording arrays
5167 void CMSCollector::reset_survivor_plab_arrays() {
5168   for (uint i = 0; i < ParallelGCThreads; i++) {
5169     _survivor_plab_array[i].reset();
5170   }
5171 }
5172 
5173 // Merge the per-thread plab arrays into the global survivor chunk
5174 // array which will provide the partitioning of the survivor space
5175 // for CMS rescan.
5176 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5177   assert(_survivor_plab_array  != NULL, "Error");
5178   assert(_survivor_chunk_array != NULL, "Error");
5179   assert(_collectorState == FinalMarking, "Error");
5180   for (uint j = 0; j < ParallelGCThreads; j++) {
5181     _cursor[j] = 0;
5182   }
5183   HeapWord* top = surv->top();
5184   size_t i;
5185   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5186     HeapWord* min_val = top;          // Higher than any PLAB address
5187     uint      min_tid = 0;            // position of min_val this round
5188     for (uint j = 0; j < ParallelGCThreads; j++) {
5189       ChunkArray* cur_sca = &_survivor_plab_array[j];
5190       if (_cursor[j] == cur_sca->end()) {
5191         continue;
5192       }
5193       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5194       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5195       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5196       if (cur_val < min_val) {
5197         min_tid = j;
5198         min_val = cur_val;
5199       } else {
5200         assert(cur_val < top, "All recorded addresses should be less");
5201       }
5202     }
5203     // At this point min_val and min_tid are respectively
5204     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5205     // and the thread (j) that witnesses that address.
5206     // We record this address in the _survivor_chunk_array[i]
5207     // and increment _cursor[min_tid] prior to the next round i.
5208     if (min_val == top) {
5209       break;
5210     }
5211     _survivor_chunk_array[i] = min_val;
5212     _cursor[min_tid]++;
5213   }
5214   // We are all done; record the size of the _survivor_chunk_array
5215   _survivor_chunk_index = i; // exclusive: [0, i)
5216   if (PrintCMSStatistics > 0) {
5217     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5218   }
5219   // Verify that we used up all the recorded entries
5220   #ifdef ASSERT
5221     size_t total = 0;
5222     for (uint j = 0; j < ParallelGCThreads; j++) {
5223       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5224       total += _cursor[j];
5225     }
5226     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5227     // Check that the merged array is in sorted order
5228     if (total > 0) {
5229       for (size_t i = 0; i < total - 1; i++) {
5230         if (PrintCMSStatistics > 0) {
5231           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5232                               i, _survivor_chunk_array[i]);
5233         }
5234         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5235                "Not sorted");
5236       }
5237     }
5238   #endif // ASSERT
5239 }
5240 
5241 // Set up the space's par_seq_tasks structure for work claiming
5242 // for parallel rescan of young gen.
5243 // See ParRescanTask where this is currently used.
5244 void
5245 CMSCollector::
5246 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5247   assert(n_threads > 0, "Unexpected n_threads argument");
5248   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5249 
5250   // Eden space
5251   {
5252     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5253     assert(!pst->valid(), "Clobbering existing data?");
5254     // Each valid entry in [0, _eden_chunk_index) represents a task.
5255     size_t n_tasks = _eden_chunk_index + 1;
5256     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5257     pst->set_par_threads(n_threads);
5258     pst->set_n_tasks((int)n_tasks);
5259   }
5260 
5261   // Merge the survivor plab arrays into _survivor_chunk_array
5262   if (_survivor_plab_array != NULL) {
5263     merge_survivor_plab_arrays(dng->from());
5264   } else {
5265     assert(_survivor_chunk_index == 0, "Error");
5266   }
5267 
5268   // To space
5269   {
5270     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5271     assert(!pst->valid(), "Clobbering existing data?");
5272     pst->set_par_threads(n_threads);
5273     pst->set_n_tasks(1);
5274     assert(pst->valid(), "Error");
5275   }
5276 
5277   // From space
5278   {
5279     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5280     assert(!pst->valid(), "Clobbering existing data?");
5281     size_t n_tasks = _survivor_chunk_index + 1;
5282     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5283     pst->set_par_threads(n_threads);
5284     pst->set_n_tasks((int)n_tasks);
5285     assert(pst->valid(), "Error");
5286   }
5287 }
5288 
5289 // Parallel version of remark
5290 void CMSCollector::do_remark_parallel() {
5291   GenCollectedHeap* gch = GenCollectedHeap::heap();
5292   WorkGang* workers = gch->workers();
5293   assert(workers != NULL, "Need parallel worker threads.");
5294   int n_workers = workers->total_workers();
5295   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5296   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5297 
5298   CMSParRemarkTask tsk(this,
5299     cms_space, perm_space,
5300     n_workers, workers, task_queues());
5301 
5302   // Set up for parallel process_strong_roots work.
5303   gch->set_par_threads(n_workers);
5304   gch->change_strong_roots_parity();
5305   // We won't be iterating over the cards in the card table updating
5306   // the younger_gen cards, so we shouldn't call the following else
5307   // the verification code as well as subsequent younger_refs_iterate
5308   // code would get confused. XXX
5309   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5310 
5311   // The young gen rescan work will not be done as part of
5312   // process_strong_roots (which currently doesn't knw how to
5313   // parallelize such a scan), but rather will be broken up into
5314   // a set of parallel tasks (via the sampling that the [abortable]
5315   // preclean phase did of EdenSpace, plus the [two] tasks of
5316   // scanning the [two] survivor spaces. Further fine-grain
5317   // parallelization of the scanning of the survivor spaces
5318   // themselves, and of precleaning of the younger gen itself
5319   // is deferred to the future.
5320   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5321 
5322   // The dirty card rescan work is broken up into a "sequence"
5323   // of parallel tasks (per constituent space) that are dynamically
5324   // claimed by the parallel threads.
5325   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5326   perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5327 
5328   // It turns out that even when we're using 1 thread, doing the work in a
5329   // separate thread causes wide variance in run times.  We can't help this
5330   // in the multi-threaded case, but we special-case n=1 here to get
5331   // repeatable measurements of the 1-thread overhead of the parallel code.
5332   if (n_workers > 1) {
5333     // Make refs discovery MT-safe
5334     ReferenceProcessorMTMutator mt(ref_processor(), true);
5335     workers->run_task(&tsk);
5336   } else {
5337     tsk.work(0);
5338   }
5339   gch->set_par_threads(0);  // 0 ==> non-parallel.
5340   // restore, single-threaded for now, any preserved marks
5341   // as a result of work_q overflow
5342   restore_preserved_marks_if_any();
5343 }
5344 
5345 // Non-parallel version of remark
5346 void CMSCollector::do_remark_non_parallel() {
5347   ResourceMark rm;
5348   HandleMark   hm;
5349   GenCollectedHeap* gch = GenCollectedHeap::heap();
5350   MarkRefsIntoAndScanClosure
5351     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5352              &_markStack, &_revisitStack, this,
5353              false /* should_yield */, false /* not precleaning */);
5354   MarkFromDirtyCardsClosure
5355     markFromDirtyCardsClosure(this, _span,
5356                               NULL,  // space is set further below
5357                               &_markBitMap, &_markStack, &_revisitStack,
5358                               &mrias_cl);
5359   {
5360     TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5361     // Iterate over the dirty cards, marking them precleaned, and
5362     // setting the corresponding bits in the mod union table.
5363     {
5364       ModUnionClosure modUnionClosure(&_modUnionTable);
5365       _ct->ct_bs()->dirty_card_iterate(
5366                       _cmsGen->used_region(),
5367                       &modUnionClosure);
5368       _ct->ct_bs()->dirty_card_iterate(
5369                       _permGen->used_region(),
5370                       &modUnionClosure);
5371     }
5372     // Having transferred these marks into the modUnionTable, we just need
5373     // to rescan the marked objects on the dirty cards in the modUnionTable.
5374     // The initial marking may have been done during an asynchronous
5375     // collection so there may be dirty bits in the mod-union table.
5376     const int alignment =
5377       CardTableModRefBS::card_size * BitsPerWord;
5378     {
5379       // ... First handle dirty cards in CMS gen
5380       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5381       MemRegion ur = _cmsGen->used_region();
5382       HeapWord* lb = ur.start();
5383       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5384       MemRegion cms_span(lb, ub);
5385       _modUnionTable.dirty_range_iterate_clear(cms_span,
5386                                                &markFromDirtyCardsClosure);
5387       verify_work_stacks_empty();
5388       if (PrintCMSStatistics != 0) {
5389         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5390           markFromDirtyCardsClosure.num_dirty_cards());
5391       }
5392     }
5393     {
5394       // .. and then repeat for dirty cards in perm gen
5395       markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5396       MemRegion ur = _permGen->used_region();
5397       HeapWord* lb = ur.start();
5398       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5399       MemRegion perm_span(lb, ub);
5400       _modUnionTable.dirty_range_iterate_clear(perm_span,
5401                                                &markFromDirtyCardsClosure);
5402       verify_work_stacks_empty();
5403       if (PrintCMSStatistics != 0) {
5404         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5405           markFromDirtyCardsClosure.num_dirty_cards());
5406       }
5407     }
5408   }
5409   if (VerifyDuringGC &&
5410       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5411     HandleMark hm;  // Discard invalid handles created during verification
5412     Universe::verify(true);
5413   }
5414   {
5415     TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5416 
5417     verify_work_stacks_empty();
5418 
5419     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5420     gch->gen_process_strong_roots(_cmsGen->level(),
5421                                   true,  // younger gens as roots
5422                                   true,  // collecting perm gen
5423                                   SharedHeap::ScanningOption(roots_scanning_options()),
5424                                   NULL, &mrias_cl);
5425   }
5426   verify_work_stacks_empty();
5427   // Restore evacuated mark words, if any, used for overflow list links
5428   if (!CMSOverflowEarlyRestoration) {
5429     restore_preserved_marks_if_any();
5430   }
5431   verify_overflow_empty();
5432 }
5433 
5434 ////////////////////////////////////////////////////////
5435 // Parallel Reference Processing Task Proxy Class
5436 ////////////////////////////////////////////////////////
5437 class CMSRefProcTaskProxy: public AbstractGangTask {
5438   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5439   CMSCollector*          _collector;
5440   CMSBitMap*             _mark_bit_map;
5441   MemRegion              _span;
5442   OopTaskQueueSet*       _task_queues;
5443   ParallelTaskTerminator _term;
5444   ProcessTask&           _task;
5445 
5446 public:
5447   CMSRefProcTaskProxy(ProcessTask&     task,
5448                       CMSCollector*    collector,
5449                       const MemRegion& span,
5450                       CMSBitMap*       mark_bit_map,
5451                       int              total_workers,
5452                       OopTaskQueueSet* task_queues):
5453     AbstractGangTask("Process referents by policy in parallel"),
5454     _task(task),
5455     _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5456     _task_queues(task_queues),
5457     _term(total_workers, task_queues)
5458     { }
5459 
5460   OopTaskQueueSet* task_queues() { return _task_queues; }
5461 
5462   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5463 
5464   ParallelTaskTerminator* terminator() { return &_term; }
5465 
5466   void do_work_steal(int i,
5467                      CMSParDrainMarkingStackClosure* drain,
5468                      CMSParKeepAliveClosure* keep_alive,
5469                      int* seed);
5470 
5471   virtual void work(int i);
5472 };
5473 
5474 void CMSRefProcTaskProxy::work(int i) {
5475   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5476                                         _mark_bit_map, work_queue(i));
5477   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5478                                                  _mark_bit_map, work_queue(i));
5479   CMSIsAliveClosure is_alive_closure(_mark_bit_map);
5480   _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5481   if (_task.marks_oops_alive()) {
5482     do_work_steal(i, &par_drain_stack, &par_keep_alive,
5483                   _collector->hash_seed(i));
5484   }
5485   assert(work_queue(i)->size() == 0, "work_queue should be empty");
5486   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5487 }
5488 
5489 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5490   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5491   EnqueueTask& _task;
5492 
5493 public:
5494   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5495     : AbstractGangTask("Enqueue reference objects in parallel"),
5496       _task(task)
5497   { }
5498 
5499   virtual void work(int i)
5500   {
5501     _task.work(i);
5502   }
5503 };
5504 
5505 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5506   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5507    _collector(collector),
5508    _span(span),
5509    _bit_map(bit_map),
5510    _work_queue(work_queue),
5511    _mark_and_push(collector, span, bit_map, work_queue),
5512    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5513                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5514 { }
5515 
5516 // . see if we can share work_queues with ParNew? XXX
5517 void CMSRefProcTaskProxy::do_work_steal(int i,
5518   CMSParDrainMarkingStackClosure* drain,
5519   CMSParKeepAliveClosure* keep_alive,
5520   int* seed) {
5521   OopTaskQueue* work_q = work_queue(i);
5522   NOT_PRODUCT(int num_steals = 0;)
5523   oop obj_to_scan;
5524   size_t num_from_overflow_list =
5525            MIN2((size_t)work_q->max_elems()/4,
5526                 (size_t)ParGCDesiredObjsFromOverflowList);
5527 
5528   while (true) {
5529     // Completely finish any left over work from (an) earlier round(s)
5530     drain->trim_queue(0);
5531     // Now check if there's any work in the overflow list
5532     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5533                                                 work_q)) {
5534       // Found something in global overflow list;
5535       // not yet ready to go stealing work from others.
5536       // We'd like to assert(work_q->size() != 0, ...)
5537       // because we just took work from the overflow list,
5538       // but of course we can't, since all of that might have
5539       // been already stolen from us.
5540       continue;
5541     }
5542     // Verify that we have no work before we resort to stealing
5543     assert(work_q->size() == 0, "Have work, shouldn't steal");
5544     // Try to steal from other queues that have work
5545     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5546       NOT_PRODUCT(num_steals++;)
5547       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5548       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5549       // Do scanning work
5550       obj_to_scan->oop_iterate(keep_alive);
5551       // Loop around, finish this work, and try to steal some more
5552     } else if (terminator()->offer_termination()) {
5553       break;  // nirvana from the infinite cycle
5554     }
5555   }
5556   NOT_PRODUCT(
5557     if (PrintCMSStatistics != 0) {
5558       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5559     }
5560   )
5561 }
5562 
5563 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5564 {
5565   GenCollectedHeap* gch = GenCollectedHeap::heap();
5566   WorkGang* workers = gch->workers();
5567   assert(workers != NULL, "Need parallel worker threads.");
5568   int n_workers = workers->total_workers();
5569   CMSRefProcTaskProxy rp_task(task, &_collector,
5570                               _collector.ref_processor()->span(),
5571                               _collector.markBitMap(),
5572                               n_workers, _collector.task_queues());
5573   workers->run_task(&rp_task);
5574 }
5575 
5576 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5577 {
5578 
5579   GenCollectedHeap* gch = GenCollectedHeap::heap();
5580   WorkGang* workers = gch->workers();
5581   assert(workers != NULL, "Need parallel worker threads.");
5582   CMSRefEnqueueTaskProxy enq_task(task);
5583   workers->run_task(&enq_task);
5584 }
5585 
5586 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5587 
5588   ResourceMark rm;
5589   HandleMark   hm;
5590   ReferencePolicy* soft_ref_policy;
5591 
5592   assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete");
5593   // Process weak references.
5594   if (clear_all_soft_refs) {
5595     soft_ref_policy = new AlwaysClearPolicy();
5596   } else {
5597 #ifdef COMPILER2
5598     soft_ref_policy = new LRUMaxHeapPolicy();
5599 #else
5600     soft_ref_policy = new LRUCurrentHeapPolicy();
5601 #endif // COMPILER2
5602   }
5603   verify_work_stacks_empty();
5604 
5605   ReferenceProcessor* rp = ref_processor();
5606   assert(rp->span().equals(_span), "Spans should be equal");
5607   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5608                                           &_markStack);
5609   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5610                                 _span, &_markBitMap, &_markStack,
5611                                 &cmsKeepAliveClosure);
5612   {
5613     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5614     if (rp->processing_is_mt()) {
5615       CMSRefProcTaskExecutor task_executor(*this);
5616       rp->process_discovered_references(soft_ref_policy,
5617                                         &_is_alive_closure,
5618                                         &cmsKeepAliveClosure,
5619                                         &cmsDrainMarkingStackClosure,
5620                                         &task_executor);
5621     } else {
5622       rp->process_discovered_references(soft_ref_policy,
5623                                         &_is_alive_closure,
5624                                         &cmsKeepAliveClosure,
5625                                         &cmsDrainMarkingStackClosure,
5626                                         NULL);
5627     }
5628     verify_work_stacks_empty();
5629   }
5630 
5631   if (cms_should_unload_classes()) {
5632     {
5633       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5634 
5635       // Follow SystemDictionary roots and unload classes
5636       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5637 
5638       // Follow CodeCache roots and unload any methods marked for unloading
5639       CodeCache::do_unloading(&_is_alive_closure,
5640                               &cmsKeepAliveClosure,
5641                               purged_class);
5642 
5643       cmsDrainMarkingStackClosure.do_void();
5644       verify_work_stacks_empty();
5645 
5646       // Update subklass/sibling/implementor links in KlassKlass descendants
5647       assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5648       oop k;
5649       while ((k = _revisitStack.pop()) != NULL) {
5650         ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5651                        &_is_alive_closure,
5652                        &cmsKeepAliveClosure);
5653       }
5654       assert(!ClassUnloading ||
5655              (_markStack.isEmpty() && overflow_list_is_empty()),
5656              "Should not have found new reachable objects");
5657       assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5658       cmsDrainMarkingStackClosure.do_void();
5659       verify_work_stacks_empty();
5660     }
5661 
5662     {
5663       TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5664       // Now clean up stale oops in SymbolTable and StringTable
5665       SymbolTable::unlink(&_is_alive_closure);
5666       StringTable::unlink(&_is_alive_closure);
5667     }
5668   }
5669 
5670   verify_work_stacks_empty();
5671   // Restore any preserved marks as a result of mark stack or
5672   // work queue overflow
5673   restore_preserved_marks_if_any();  // done single-threaded for now
5674 
5675   rp->set_enqueuing_is_done(true);
5676   if (rp->processing_is_mt()) {
5677     CMSRefProcTaskExecutor task_executor(*this);
5678     rp->enqueue_discovered_references(&task_executor);
5679   } else {
5680     rp->enqueue_discovered_references(NULL);
5681   }
5682   rp->verify_no_references_recorded();
5683   assert(!rp->discovery_enabled(), "should have been disabled");
5684 
5685   // JVMTI object tagging is based on JNI weak refs. If any of these
5686   // refs were cleared then JVMTI needs to update its maps and
5687   // maybe post ObjectFrees to agents.
5688   JvmtiExport::cms_ref_processing_epilogue();
5689 }
5690 
5691 #ifndef PRODUCT
5692 void CMSCollector::check_correct_thread_executing() {
5693   Thread* t = Thread::current();
5694   // Only the VM thread or the CMS thread should be here.
5695   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5696          "Unexpected thread type");
5697   // If this is the vm thread, the foreground process
5698   // should not be waiting.  Note that _foregroundGCIsActive is
5699   // true while the foreground collector is waiting.
5700   if (_foregroundGCShouldWait) {
5701     // We cannot be the VM thread
5702     assert(t->is_ConcurrentGC_thread(),
5703            "Should be CMS thread");
5704   } else {
5705     // We can be the CMS thread only if we are in a stop-world
5706     // phase of CMS collection.
5707     if (t->is_ConcurrentGC_thread()) {
5708       assert(_collectorState == InitialMarking ||
5709              _collectorState == FinalMarking,
5710              "Should be a stop-world phase");
5711       // The CMS thread should be holding the CMS_token.
5712       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5713              "Potential interference with concurrently "
5714              "executing VM thread");
5715     }
5716   }
5717 }
5718 #endif
5719 
5720 void CMSCollector::sweep(bool asynch) {
5721   assert(_collectorState == Sweeping, "just checking");
5722   check_correct_thread_executing();
5723   verify_work_stacks_empty();
5724   verify_overflow_empty();
5725   incrementSweepCount();
5726   _sweep_timer.stop();
5727   _sweep_estimate.sample(_sweep_timer.seconds());
5728   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5729 
5730   // PermGen verification support: If perm gen sweeping is disabled in
5731   // this cycle, we preserve the perm gen object "deadness" information
5732   // in the perm_gen_verify_bit_map. In order to do that we traverse
5733   // all blocks in perm gen and mark all dead objects.
5734   if (verifying() && !cms_should_unload_classes()) {
5735     CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5736                              bitMapLock());
5737     assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5738            "Should have already been allocated");
5739     MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5740                                markBitMap(), perm_gen_verify_bit_map());
5741     _permGen->cmsSpace()->blk_iterate(&mdo);
5742   }
5743 
5744   if (asynch) {
5745     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5746     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5747     // First sweep the old gen then the perm gen
5748     {
5749       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5750                                bitMapLock());
5751       sweepWork(_cmsGen, asynch);
5752     }
5753 
5754     // Now repeat for perm gen
5755     if (cms_should_unload_classes()) {
5756       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5757                              bitMapLock());
5758       sweepWork(_permGen, asynch);
5759     }
5760 
5761     // Update Universe::_heap_*_at_gc figures.
5762     // We need all the free list locks to make the abstract state
5763     // transition from Sweeping to Resetting. See detailed note
5764     // further below.
5765     {
5766       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5767                                _permGen->freelistLock());
5768       // Update heap occupancy information which is used as
5769       // input to soft ref clearing policy at the next gc.
5770       Universe::update_heap_info_at_gc();
5771       _collectorState = Resizing;
5772     }
5773   } else {
5774     // already have needed locks
5775     sweepWork(_cmsGen,  asynch);
5776 
5777     if (cms_should_unload_classes()) {
5778       sweepWork(_permGen, asynch);
5779     }
5780     // Update heap occupancy information which is used as
5781     // input to soft ref clearing policy at the next gc.
5782     Universe::update_heap_info_at_gc();
5783     _collectorState = Resizing;
5784   }
5785   verify_work_stacks_empty();
5786   verify_overflow_empty();
5787 
5788   _sweep_timer.reset();
5789   _sweep_timer.start();
5790 
5791   update_time_of_last_gc(os::javaTimeMillis());
5792 
5793   // NOTE on abstract state transitions:
5794   // Mutators allocate-live and/or mark the mod-union table dirty
5795   // based on the state of the collection.  The former is done in
5796   // the interval [Marking, Sweeping] and the latter in the interval
5797   // [Marking, Sweeping).  Thus the transitions into the Marking state
5798   // and out of the Sweeping state must be synchronously visible
5799   // globally to the mutators.
5800   // The transition into the Marking state happens with the world
5801   // stopped so the mutators will globally see it.  Sweeping is
5802   // done asynchronously by the background collector so the transition
5803   // from the Sweeping state to the Resizing state must be done
5804   // under the freelistLock (as is the check for whether to
5805   // allocate-live and whether to dirty the mod-union table).
5806   assert(_collectorState == Resizing, "Change of collector state to"
5807     " Resizing must be done under the freelistLocks (plural)");
5808 
5809   // Now that sweeping has been completed, if the GCH's
5810   // incremental_collection_will_fail flag is set, clear it,
5811   // thus inviting a younger gen collection to promote into
5812   // this generation. If such a promotion may still fail,
5813   // the flag will be set again when a young collection is
5814   // attempted.
5815   // I think the incremental_collection_will_fail flag's use
5816   // is specific to a 2 generation collection policy, so i'll
5817   // assert that that's the configuration we are operating within.
5818   // The use of the flag can and should be generalized appropriately
5819   // in the future to deal with a general n-generation system.
5820 
5821   GenCollectedHeap* gch = GenCollectedHeap::heap();
5822   assert(gch->collector_policy()->is_two_generation_policy(),
5823          "Resetting of incremental_collection_will_fail flag"
5824          " may be incorrect otherwise");
5825   gch->clear_incremental_collection_will_fail();
5826   gch->update_full_collections_completed(_collection_count_start);
5827 }
5828 
5829 // FIX ME!!! Looks like this belongs in CFLSpace, with
5830 // CMSGen merely delegating to it.
5831 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5832   double nearLargestPercent = 0.999;
5833   HeapWord*  minAddr        = _cmsSpace->bottom();
5834   HeapWord*  largestAddr    =
5835     (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5836   if (largestAddr == 0) {
5837     // The dictionary appears to be empty.  In this case
5838     // try to coalesce at the end of the heap.
5839     largestAddr = _cmsSpace->end();
5840   }
5841   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5842   size_t nearLargestOffset =
5843     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5844   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5845 }
5846 
5847 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5848   return addr >= _cmsSpace->nearLargestChunk();
5849 }
5850 
5851 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5852   return _cmsSpace->find_chunk_at_end();
5853 }
5854 
5855 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5856                                                     bool full) {
5857   // The next lower level has been collected.  Gather any statistics
5858   // that are of interest at this point.
5859   if (!full && (current_level + 1) == level()) {
5860     // Gather statistics on the young generation collection.
5861     collector()->stats().record_gc0_end(used());
5862   }
5863 }
5864 
5865 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
5866   GenCollectedHeap* gch = GenCollectedHeap::heap();
5867   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
5868     "Wrong type of heap");
5869   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
5870     gch->gen_policy()->size_policy();
5871   assert(sp->is_gc_cms_adaptive_size_policy(),
5872     "Wrong type of size policy");
5873   return sp;
5874 }
5875 
5876 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
5877   if (PrintGCDetails && Verbose) {
5878     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
5879   }
5880   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
5881   _debug_collection_type =
5882     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
5883   if (PrintGCDetails && Verbose) {
5884     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
5885   }
5886 }
5887 
5888 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
5889   bool asynch) {
5890   // We iterate over the space(s) underlying this generation,
5891   // checking the mark bit map to see if the bits corresponding
5892   // to specific blocks are marked or not. Blocks that are
5893   // marked are live and are not swept up. All remaining blocks
5894   // are swept up, with coalescing on-the-fly as we sweep up
5895   // contiguous free and/or garbage blocks:
5896   // We need to ensure that the sweeper synchronizes with allocators
5897   // and stop-the-world collectors. In particular, the following
5898   // locks are used:
5899   // . CMS token: if this is held, a stop the world collection cannot occur
5900   // . freelistLock: if this is held no allocation can occur from this
5901   //                 generation by another thread
5902   // . bitMapLock: if this is held, no other thread can access or update
5903   //
5904 
5905   // Note that we need to hold the freelistLock if we use
5906   // block iterate below; else the iterator might go awry if
5907   // a mutator (or promotion) causes block contents to change
5908   // (for instance if the allocator divvies up a block).
5909   // If we hold the free list lock, for all practical purposes
5910   // young generation GC's can't occur (they'll usually need to
5911   // promote), so we might as well prevent all young generation
5912   // GC's while we do a sweeping step. For the same reason, we might
5913   // as well take the bit map lock for the entire duration
5914 
5915   // check that we hold the requisite locks
5916   assert(have_cms_token(), "Should hold cms token");
5917   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
5918          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
5919         "Should possess CMS token to sweep");
5920   assert_lock_strong(gen->freelistLock());
5921   assert_lock_strong(bitMapLock());
5922 
5923   assert(!_sweep_timer.is_active(), "Was switched off in an outer context");
5924   gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
5925                                       _sweep_estimate.padded_average());
5926   gen->setNearLargestChunk();
5927 
5928   {
5929     SweepClosure sweepClosure(this, gen, &_markBitMap,
5930                             CMSYield && asynch);
5931     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5932     // We need to free-up/coalesce garbage/blocks from a
5933     // co-terminal free run. This is done in the SweepClosure
5934     // destructor; so, do not remove this scope, else the
5935     // end-of-sweep-census below will be off by a little bit.
5936   }
5937   gen->cmsSpace()->sweep_completed();
5938   gen->cmsSpace()->endSweepFLCensus(sweepCount());
5939 }
5940 
5941 // Reset CMS data structures (for now just the marking bit map)
5942 // preparatory for the next cycle.
5943 void CMSCollector::reset(bool asynch) {
5944   GenCollectedHeap* gch = GenCollectedHeap::heap();
5945   CMSAdaptiveSizePolicy* sp = size_policy();
5946   AdaptiveSizePolicyOutput(sp, gch->total_collections());
5947   if (asynch) {
5948     CMSTokenSyncWithLocks ts(true, bitMapLock());
5949 
5950     // If the state is not "Resetting", the foreground  thread
5951     // has done a collection and the resetting.
5952     if (_collectorState != Resetting) {
5953       assert(_collectorState == Idling, "The state should only change"
5954         " because the foreground collector has finished the collection");
5955       return;
5956     }
5957 
5958     // Clear the mark bitmap (no grey objects to start with)
5959     // for the next cycle.
5960     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5961     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5962 
5963     HeapWord* curAddr = _markBitMap.startWord();
5964     while (curAddr < _markBitMap.endWord()) {
5965       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5966       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5967       _markBitMap.clear_large_range(chunk);
5968       if (ConcurrentMarkSweepThread::should_yield() &&
5969           !foregroundGCIsActive() &&
5970           CMSYield) {
5971         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5972                "CMS thread should hold CMS token");
5973         assert_lock_strong(bitMapLock());
5974         bitMapLock()->unlock();
5975         ConcurrentMarkSweepThread::desynchronize(true);
5976         ConcurrentMarkSweepThread::acknowledge_yield_request();
5977         stopTimer();
5978         if (PrintCMSStatistics != 0) {
5979           incrementYields();
5980         }
5981         icms_wait();
5982 
5983         // See the comment in coordinator_yield()
5984         for (unsigned i = 0; i < CMSYieldSleepCount &&
5985                         ConcurrentMarkSweepThread::should_yield() &&
5986                         !CMSCollector::foregroundGCIsActive(); ++i) {
5987           os::sleep(Thread::current(), 1, false);
5988           ConcurrentMarkSweepThread::acknowledge_yield_request();
5989         }
5990 
5991         ConcurrentMarkSweepThread::synchronize(true);
5992         bitMapLock()->lock_without_safepoint_check();
5993         startTimer();
5994       }
5995       curAddr = chunk.end();
5996     }
5997     _collectorState = Idling;
5998   } else {
5999     // already have the lock
6000     assert(_collectorState == Resetting, "just checking");
6001     assert_lock_strong(bitMapLock());
6002     _markBitMap.clear_all();
6003     _collectorState = Idling;
6004   }
6005 
6006   // Stop incremental mode after a cycle completes, so that any future cycles
6007   // are triggered by allocation.
6008   stop_icms();
6009 
6010   NOT_PRODUCT(
6011     if (RotateCMSCollectionTypes) {
6012       _cmsGen->rotate_debug_collection_type();
6013     }
6014   )
6015 }
6016 
6017 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6018   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6019   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6020   TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6021   TraceCollectorStats tcs(counters());
6022 
6023   switch (op) {
6024     case CMS_op_checkpointRootsInitial: {
6025       checkpointRootsInitial(true);       // asynch
6026       if (PrintGC) {
6027         _cmsGen->printOccupancy("initial-mark");
6028       }
6029       break;
6030     }
6031     case CMS_op_checkpointRootsFinal: {
6032       checkpointRootsFinal(true,    // asynch
6033                            false,   // !clear_all_soft_refs
6034                            false);  // !init_mark_was_synchronous
6035       if (PrintGC) {
6036         _cmsGen->printOccupancy("remark");
6037       }
6038       break;
6039     }
6040     default:
6041       fatal("No such CMS_op");
6042   }
6043 }
6044 
6045 #ifndef PRODUCT
6046 size_t const CMSCollector::skip_header_HeapWords() {
6047   return FreeChunk::header_size();
6048 }
6049 
6050 // Try and collect here conditions that should hold when
6051 // CMS thread is exiting. The idea is that the foreground GC
6052 // thread should not be blocked if it wants to terminate
6053 // the CMS thread and yet continue to run the VM for a while
6054 // after that.
6055 void CMSCollector::verify_ok_to_terminate() const {
6056   assert(Thread::current()->is_ConcurrentGC_thread(),
6057          "should be called by CMS thread");
6058   assert(!_foregroundGCShouldWait, "should be false");
6059   // We could check here that all the various low-level locks
6060   // are not held by the CMS thread, but that is overkill; see
6061   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6062   // is checked.
6063 }
6064 #endif
6065 
6066 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6067   assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6068          "missing Printezis mark?");
6069   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6070   size_t size = pointer_delta(nextOneAddr + 1, addr);
6071   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6072          "alignment problem");
6073   assert(size >= 3, "Necessary for Printezis marks to work");
6074   return size;
6075 }
6076 
6077 // A variant of the above (block_size_using_printezis_bits()) except
6078 // that we return 0 if the P-bits are not yet set.
6079 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6080   if (_markBitMap.isMarked(addr)) {
6081     assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6082     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6083     size_t size = pointer_delta(nextOneAddr + 1, addr);
6084     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6085            "alignment problem");
6086     assert(size >= 3, "Necessary for Printezis marks to work");
6087     return size;
6088   } else {
6089     assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6090     return 0;
6091   }
6092 }
6093 
6094 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6095   size_t sz = 0;
6096   oop p = (oop)addr;
6097   if (p->klass() != NULL && p->is_parsable()) {
6098     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6099   } else {
6100     sz = block_size_using_printezis_bits(addr);
6101   }
6102   assert(sz > 0, "size must be nonzero");
6103   HeapWord* next_block = addr + sz;
6104   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6105                                              CardTableModRefBS::card_size);
6106   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6107          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6108          "must be different cards");
6109   return next_card;
6110 }
6111 
6112 
6113 // CMS Bit Map Wrapper /////////////////////////////////////////
6114 
6115 // Construct a CMS bit map infrastructure, but don't create the
6116 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6117 // further below.
6118 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6119   _bm(NULL,0),
6120   _shifter(shifter),
6121   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6122 {
6123   _bmStartWord = 0;
6124   _bmWordSize  = 0;
6125 }
6126 
6127 bool CMSBitMap::allocate(MemRegion mr) {
6128   _bmStartWord = mr.start();
6129   _bmWordSize  = mr.word_size();
6130   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6131                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6132   if (!brs.is_reserved()) {
6133     warning("CMS bit map allocation failure");
6134     return false;
6135   }
6136   // For now we'll just commit all of the bit map up fromt.
6137   // Later on we'll try to be more parsimonious with swap.
6138   if (!_virtual_space.initialize(brs, brs.size())) {
6139     warning("CMS bit map backing store failure");
6140     return false;
6141   }
6142   assert(_virtual_space.committed_size() == brs.size(),
6143          "didn't reserve backing store for all of CMS bit map?");
6144   _bm.set_map((uintptr_t*)_virtual_space.low());
6145   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6146          _bmWordSize, "inconsistency in bit map sizing");
6147   _bm.set_size(_bmWordSize >> _shifter);
6148 
6149   // bm.clear(); // can we rely on getting zero'd memory? verify below
6150   assert(isAllClear(),
6151          "Expected zero'd memory from ReservedSpace constructor");
6152   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6153          "consistency check");
6154   return true;
6155 }
6156 
6157 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6158   HeapWord *next_addr, *end_addr, *last_addr;
6159   assert_locked();
6160   assert(covers(mr), "out-of-range error");
6161   // XXX assert that start and end are appropriately aligned
6162   for (next_addr = mr.start(), end_addr = mr.end();
6163        next_addr < end_addr; next_addr = last_addr) {
6164     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6165     last_addr = dirty_region.end();
6166     if (!dirty_region.is_empty()) {
6167       cl->do_MemRegion(dirty_region);
6168     } else {
6169       assert(last_addr == end_addr, "program logic");
6170       return;
6171     }
6172   }
6173 }
6174 
6175 #ifndef PRODUCT
6176 void CMSBitMap::assert_locked() const {
6177   CMSLockVerifier::assert_locked(lock());
6178 }
6179 
6180 bool CMSBitMap::covers(MemRegion mr) const {
6181   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6182   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6183          "size inconsistency");
6184   return (mr.start() >= _bmStartWord) &&
6185          (mr.end()   <= endWord());
6186 }
6187 
6188 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6189     return (start >= _bmStartWord && (start + size) <= endWord());
6190 }
6191 
6192 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6193   // verify that there are no 1 bits in the interval [left, right)
6194   FalseBitMapClosure falseBitMapClosure;
6195   iterate(&falseBitMapClosure, left, right);
6196 }
6197 
6198 void CMSBitMap::region_invariant(MemRegion mr)
6199 {
6200   assert_locked();
6201   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6202   assert(!mr.is_empty(), "unexpected empty region");
6203   assert(covers(mr), "mr should be covered by bit map");
6204   // convert address range into offset range
6205   size_t start_ofs = heapWordToOffset(mr.start());
6206   // Make sure that end() is appropriately aligned
6207   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6208                         (1 << (_shifter+LogHeapWordSize))),
6209          "Misaligned mr.end()");
6210   size_t end_ofs   = heapWordToOffset(mr.end());
6211   assert(end_ofs > start_ofs, "Should mark at least one bit");
6212 }
6213 
6214 #endif
6215 
6216 bool CMSMarkStack::allocate(size_t size) {
6217   // allocate a stack of the requisite depth
6218   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6219                    size * sizeof(oop)));
6220   if (!rs.is_reserved()) {
6221     warning("CMSMarkStack allocation failure");
6222     return false;
6223   }
6224   if (!_virtual_space.initialize(rs, rs.size())) {
6225     warning("CMSMarkStack backing store failure");
6226     return false;
6227   }
6228   assert(_virtual_space.committed_size() == rs.size(),
6229          "didn't reserve backing store for all of CMS stack?");
6230   _base = (oop*)(_virtual_space.low());
6231   _index = 0;
6232   _capacity = size;
6233   NOT_PRODUCT(_max_depth = 0);
6234   return true;
6235 }
6236 
6237 // XXX FIX ME !!! In the MT case we come in here holding a
6238 // leaf lock. For printing we need to take a further lock
6239 // which has lower rank. We need to recallibrate the two
6240 // lock-ranks involved in order to be able to rpint the
6241 // messages below. (Or defer the printing to the caller.
6242 // For now we take the expedient path of just disabling the
6243 // messages for the problematic case.)
6244 void CMSMarkStack::expand() {
6245   assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted");
6246   if (_capacity == CMSMarkStackSizeMax) {
6247     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6248       // We print a warning message only once per CMS cycle.
6249       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6250     }
6251     return;
6252   }
6253   // Double capacity if possible
6254   size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax);
6255   // Do not give up existing stack until we have managed to
6256   // get the double capacity that we desired.
6257   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6258                    new_capacity * sizeof(oop)));
6259   if (rs.is_reserved()) {
6260     // Release the backing store associated with old stack
6261     _virtual_space.release();
6262     // Reinitialize virtual space for new stack
6263     if (!_virtual_space.initialize(rs, rs.size())) {
6264       fatal("Not enough swap for expanded marking stack");
6265     }
6266     _base = (oop*)(_virtual_space.low());
6267     _index = 0;
6268     _capacity = new_capacity;
6269   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6270     // Failed to double capacity, continue;
6271     // we print a detail message only once per CMS cycle.
6272     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6273             SIZE_FORMAT"K",
6274             _capacity / K, new_capacity / K);
6275   }
6276 }
6277 
6278 
6279 // Closures
6280 // XXX: there seems to be a lot of code  duplication here;
6281 // should refactor and consolidate common code.
6282 
6283 // This closure is used to mark refs into the CMS generation in
6284 // the CMS bit map. Called at the first checkpoint. This closure
6285 // assumes that we do not need to re-mark dirty cards; if the CMS
6286 // generation on which this is used is not an oldest (modulo perm gen)
6287 // generation then this will lose younger_gen cards!
6288 
6289 MarkRefsIntoClosure::MarkRefsIntoClosure(
6290   MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods):
6291     _span(span),
6292     _bitMap(bitMap),
6293     _should_do_nmethods(should_do_nmethods)
6294 {
6295     assert(_ref_processor == NULL, "deliberately left NULL");
6296     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6297 }
6298 
6299 void MarkRefsIntoClosure::do_oop(oop* p) {
6300   // if p points into _span, then mark corresponding bit in _markBitMap
6301   oop thisOop = *p;
6302   if (thisOop != NULL) {
6303     assert(thisOop->is_oop(), "expected an oop");
6304     HeapWord* addr = (HeapWord*)thisOop;
6305     if (_span.contains(addr)) {
6306       // this should be made more efficient
6307       _bitMap->mark(addr);
6308     }
6309   }
6310 }
6311 
6312 // A variant of the above, used for CMS marking verification.
6313 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6314   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6315   bool should_do_nmethods):
6316     _span(span),
6317     _verification_bm(verification_bm),
6318     _cms_bm(cms_bm),
6319     _should_do_nmethods(should_do_nmethods) {
6320     assert(_ref_processor == NULL, "deliberately left NULL");
6321     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6322 }
6323 
6324 void MarkRefsIntoVerifyClosure::do_oop(oop* p) {
6325   // if p points into _span, then mark corresponding bit in _markBitMap
6326   oop this_oop = *p;
6327   if (this_oop != NULL) {
6328     assert(this_oop->is_oop(), "expected an oop");
6329     HeapWord* addr = (HeapWord*)this_oop;
6330     if (_span.contains(addr)) {
6331       _verification_bm->mark(addr);
6332       if (!_cms_bm->isMarked(addr)) {
6333         oop(addr)->print();
6334         gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
6335         fatal("... aborting");
6336       }
6337     }
6338   }
6339 }
6340 
6341 //////////////////////////////////////////////////
6342 // MarkRefsIntoAndScanClosure
6343 //////////////////////////////////////////////////
6344 
6345 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6346                                                        ReferenceProcessor* rp,
6347                                                        CMSBitMap* bit_map,
6348                                                        CMSBitMap* mod_union_table,
6349                                                        CMSMarkStack*  mark_stack,
6350                                                        CMSMarkStack*  revisit_stack,
6351                                                        CMSCollector* collector,
6352                                                        bool should_yield,
6353                                                        bool concurrent_precleaning):
6354   _collector(collector),
6355   _span(span),
6356   _bit_map(bit_map),
6357   _mark_stack(mark_stack),
6358   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6359                       mark_stack, revisit_stack, concurrent_precleaning),
6360   _yield(should_yield),
6361   _concurrent_precleaning(concurrent_precleaning),
6362   _freelistLock(NULL)
6363 {
6364   _ref_processor = rp;
6365   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6366 }
6367 
6368 // This closure is used to mark refs into the CMS generation at the
6369 // second (final) checkpoint, and to scan and transitively follow
6370 // the unmarked oops. It is also used during the concurrent precleaning
6371 // phase while scanning objects on dirty cards in the CMS generation.
6372 // The marks are made in the marking bit map and the marking stack is
6373 // used for keeping the (newly) grey objects during the scan.
6374 // The parallel version (Par_...) appears further below.
6375 void MarkRefsIntoAndScanClosure::do_oop(oop* p) {
6376   oop this_oop = *p;
6377   if (this_oop != NULL) {
6378     assert(this_oop->is_oop(), "expected an oop");
6379     HeapWord* addr = (HeapWord*)this_oop;
6380     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6381     assert(_collector->overflow_list_is_empty(), "should be empty");
6382     if (_span.contains(addr) &&
6383         !_bit_map->isMarked(addr)) {
6384       // mark bit map (object is now grey)
6385       _bit_map->mark(addr);
6386       // push on marking stack (stack should be empty), and drain the
6387       // stack by applying this closure to the oops in the oops popped
6388       // from the stack (i.e. blacken the grey objects)
6389       bool res = _mark_stack->push(this_oop);
6390       assert(res, "Should have space to push on empty stack");
6391       do {
6392         oop new_oop = _mark_stack->pop();
6393         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6394         assert(new_oop->is_parsable(), "Found unparsable oop");
6395         assert(_bit_map->isMarked((HeapWord*)new_oop),
6396                "only grey objects on this stack");
6397         // iterate over the oops in this oop, marking and pushing
6398         // the ones in CMS heap (i.e. in _span).
6399         new_oop->oop_iterate(&_pushAndMarkClosure);
6400         // check if it's time to yield
6401         do_yield_check();
6402       } while (!_mark_stack->isEmpty() ||
6403                (!_concurrent_precleaning && take_from_overflow_list()));
6404         // if marking stack is empty, and we are not doing this
6405         // during precleaning, then check the overflow list
6406     }
6407     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6408     assert(_collector->overflow_list_is_empty(),
6409            "overflow list was drained above");
6410     // We could restore evacuated mark words, if any, used for
6411     // overflow list links here because the overflow list is
6412     // provably empty here. That would reduce the maximum
6413     // size requirements for preserved_{oop,mark}_stack.
6414     // But we'll just postpone it until we are all done
6415     // so we can just stream through.
6416     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6417       _collector->restore_preserved_marks_if_any();
6418       assert(_collector->no_preserved_marks(), "No preserved marks");
6419     }
6420     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6421            "All preserved marks should have been restored above");
6422   }
6423 }
6424 
6425 void MarkRefsIntoAndScanClosure::do_yield_work() {
6426   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6427          "CMS thread should hold CMS token");
6428   assert_lock_strong(_freelistLock);
6429   assert_lock_strong(_bit_map->lock());
6430   // relinquish the free_list_lock and bitMaplock()
6431   _bit_map->lock()->unlock();
6432   _freelistLock->unlock();
6433   ConcurrentMarkSweepThread::desynchronize(true);
6434   ConcurrentMarkSweepThread::acknowledge_yield_request();
6435   _collector->stopTimer();
6436   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6437   if (PrintCMSStatistics != 0) {
6438     _collector->incrementYields();
6439   }
6440   _collector->icms_wait();
6441 
6442   // See the comment in coordinator_yield()
6443   for (unsigned i = 0; i < CMSYieldSleepCount &&
6444                        ConcurrentMarkSweepThread::should_yield() &&
6445                        !CMSCollector::foregroundGCIsActive(); ++i) {
6446     os::sleep(Thread::current(), 1, false);
6447     ConcurrentMarkSweepThread::acknowledge_yield_request();
6448   }
6449 
6450   ConcurrentMarkSweepThread::synchronize(true);
6451   _freelistLock->lock_without_safepoint_check();
6452   _bit_map->lock()->lock_without_safepoint_check();
6453   _collector->startTimer();
6454 }
6455 
6456 ///////////////////////////////////////////////////////////
6457 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6458 //                                 MarkRefsIntoAndScanClosure
6459 ///////////////////////////////////////////////////////////
6460 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6461   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6462   CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack*  revisit_stack):
6463   _span(span),
6464   _bit_map(bit_map),
6465   _work_queue(work_queue),
6466   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6467                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6468   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6469                           revisit_stack)
6470 {
6471   _ref_processor = rp;
6472   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6473 }
6474 
6475 // This closure is used to mark refs into the CMS generation at the
6476 // second (final) checkpoint, and to scan and transitively follow
6477 // the unmarked oops. The marks are made in the marking bit map and
6478 // the work_queue is used for keeping the (newly) grey objects during
6479 // the scan phase whence they are also available for stealing by parallel
6480 // threads. Since the marking bit map is shared, updates are
6481 // synchronized (via CAS).
6482 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) {
6483   oop this_oop = *p;
6484   if (this_oop != NULL) {
6485     // Ignore mark word because this could be an already marked oop
6486     // that may be chained at the end of the overflow list.
6487     assert(this_oop->is_oop(true /* ignore mark word */), "expected an oop");
6488     HeapWord* addr = (HeapWord*)this_oop;
6489     if (_span.contains(addr) &&
6490         !_bit_map->isMarked(addr)) {
6491       // mark bit map (object will become grey):
6492       // It is possible for several threads to be
6493       // trying to "claim" this object concurrently;
6494       // the unique thread that succeeds in marking the
6495       // object first will do the subsequent push on
6496       // to the work queue (or overflow list).
6497       if (_bit_map->par_mark(addr)) {
6498         // push on work_queue (which may not be empty), and trim the
6499         // queue to an appropriate length by applying this closure to
6500         // the oops in the oops popped from the stack (i.e. blacken the
6501         // grey objects)
6502         bool res = _work_queue->push(this_oop);
6503         assert(res, "Low water mark should be less than capacity?");
6504         trim_queue(_low_water_mark);
6505       } // Else, another thread claimed the object
6506     }
6507   }
6508 }
6509 
6510 // This closure is used to rescan the marked objects on the dirty cards
6511 // in the mod union table and the card table proper.
6512 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6513   oop p, MemRegion mr) {
6514 
6515   size_t size = 0;
6516   HeapWord* addr = (HeapWord*)p;
6517   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6518   assert(_span.contains(addr), "we are scanning the CMS generation");
6519   // check if it's time to yield
6520   if (do_yield_check()) {
6521     // We yielded for some foreground stop-world work,
6522     // and we have been asked to abort this ongoing preclean cycle.
6523     return 0;
6524   }
6525   if (_bitMap->isMarked(addr)) {
6526     // it's marked; is it potentially uninitialized?
6527     if (p->klass() != NULL) {
6528       if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
6529         // Signal precleaning to redirty the card since
6530         // the klass pointer is already installed.
6531         assert(size == 0, "Initial value");
6532       } else {
6533         assert(p->is_parsable(), "must be parsable.");
6534         // an initialized object; ignore mark word in verification below
6535         // since we are running concurrent with mutators
6536         assert(p->is_oop(true), "should be an oop");
6537         if (p->is_objArray()) {
6538           // objArrays are precisely marked; restrict scanning
6539           // to dirty cards only.
6540           size = p->oop_iterate(_scanningClosure, mr);
6541           assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6542                  "adjustObjectSize should be the identity for array sizes, "
6543                  "which are necessarily larger than minimum object size of "
6544                  "two heap words");
6545         } else {
6546           // A non-array may have been imprecisely marked; we need
6547           // to scan object in its entirety.
6548           size = CompactibleFreeListSpace::adjustObjectSize(
6549                    p->oop_iterate(_scanningClosure));
6550         }
6551         #ifdef DEBUG
6552           size_t direct_size =
6553             CompactibleFreeListSpace::adjustObjectSize(p->size());
6554           assert(size == direct_size, "Inconsistency in size");
6555           assert(size >= 3, "Necessary for Printezis marks to work");
6556           if (!_bitMap->isMarked(addr+1)) {
6557             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6558           } else {
6559             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6560             assert(_bitMap->isMarked(addr+size-1),
6561                    "inconsistent Printezis mark");
6562           }
6563         #endif // DEBUG
6564       }
6565     } else {
6566       // an unitialized object
6567       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6568       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6569       size = pointer_delta(nextOneAddr + 1, addr);
6570       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6571              "alignment problem");
6572       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6573       // will dirty the card when the klass pointer is installed in the
6574       // object (signalling the completion of initialization).
6575     }
6576   } else {
6577     // Either a not yet marked object or an uninitialized object
6578     if (p->klass() == NULL || !p->is_parsable()) {
6579       // An uninitialized object, skip to the next card, since
6580       // we may not be able to read its P-bits yet.
6581       assert(size == 0, "Initial value");
6582     } else {
6583       // An object not (yet) reached by marking: we merely need to
6584       // compute its size so as to go look at the next block.
6585       assert(p->is_oop(true), "should be an oop");
6586       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6587     }
6588   }
6589   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6590   return size;
6591 }
6592 
6593 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6594   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6595          "CMS thread should hold CMS token");
6596   assert_lock_strong(_freelistLock);
6597   assert_lock_strong(_bitMap->lock());
6598   // relinquish the free_list_lock and bitMaplock()
6599   _bitMap->lock()->unlock();
6600   _freelistLock->unlock();
6601   ConcurrentMarkSweepThread::desynchronize(true);
6602   ConcurrentMarkSweepThread::acknowledge_yield_request();
6603   _collector->stopTimer();
6604   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6605   if (PrintCMSStatistics != 0) {
6606     _collector->incrementYields();
6607   }
6608   _collector->icms_wait();
6609 
6610   // See the comment in coordinator_yield()
6611   for (unsigned i = 0; i < CMSYieldSleepCount &&
6612                        ConcurrentMarkSweepThread::should_yield() &&
6613                        !CMSCollector::foregroundGCIsActive(); ++i) {
6614     os::sleep(Thread::current(), 1, false);
6615     ConcurrentMarkSweepThread::acknowledge_yield_request();
6616   }
6617 
6618   ConcurrentMarkSweepThread::synchronize(true);
6619   _freelistLock->lock_without_safepoint_check();
6620   _bitMap->lock()->lock_without_safepoint_check();
6621   _collector->startTimer();
6622 }
6623 
6624 
6625 //////////////////////////////////////////////////////////////////
6626 // SurvivorSpacePrecleanClosure
6627 //////////////////////////////////////////////////////////////////
6628 // This (single-threaded) closure is used to preclean the oops in
6629 // the survivor spaces.
6630 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6631 
6632   HeapWord* addr = (HeapWord*)p;
6633   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6634   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6635   assert(p->klass() != NULL, "object should be initializd");
6636   assert(p->is_parsable(), "must be parsable.");
6637   // an initialized object; ignore mark word in verification below
6638   // since we are running concurrent with mutators
6639   assert(p->is_oop(true), "should be an oop");
6640   // Note that we do not yield while we iterate over
6641   // the interior oops of p, pushing the relevant ones
6642   // on our marking stack.
6643   size_t size = p->oop_iterate(_scanning_closure);
6644   do_yield_check();
6645   // Observe that below, we do not abandon the preclean
6646   // phase as soon as we should; rather we empty the
6647   // marking stack before returning. This is to satisfy
6648   // some existing assertions. In general, it may be a
6649   // good idea to abort immediately and complete the marking
6650   // from the grey objects at a later time.
6651   while (!_mark_stack->isEmpty()) {
6652     oop new_oop = _mark_stack->pop();
6653     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6654     assert(new_oop->is_parsable(), "Found unparsable oop");
6655     assert(_bit_map->isMarked((HeapWord*)new_oop),
6656            "only grey objects on this stack");
6657     // iterate over the oops in this oop, marking and pushing
6658     // the ones in CMS heap (i.e. in _span).
6659     new_oop->oop_iterate(_scanning_closure);
6660     // check if it's time to yield
6661     do_yield_check();
6662   }
6663   unsigned int after_count =
6664     GenCollectedHeap::heap()->total_collections();
6665   bool abort = (_before_count != after_count) ||
6666                _collector->should_abort_preclean();
6667   return abort ? 0 : size;
6668 }
6669 
6670 void SurvivorSpacePrecleanClosure::do_yield_work() {
6671   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6672          "CMS thread should hold CMS token");
6673   assert_lock_strong(_bit_map->lock());
6674   // Relinquish the bit map lock
6675   _bit_map->lock()->unlock();
6676   ConcurrentMarkSweepThread::desynchronize(true);
6677   ConcurrentMarkSweepThread::acknowledge_yield_request();
6678   _collector->stopTimer();
6679   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6680   if (PrintCMSStatistics != 0) {
6681     _collector->incrementYields();
6682   }
6683   _collector->icms_wait();
6684 
6685   // See the comment in coordinator_yield()
6686   for (unsigned i = 0; i < CMSYieldSleepCount &&
6687                        ConcurrentMarkSweepThread::should_yield() &&
6688                        !CMSCollector::foregroundGCIsActive(); ++i) {
6689     os::sleep(Thread::current(), 1, false);
6690     ConcurrentMarkSweepThread::acknowledge_yield_request();
6691   }
6692 
6693   ConcurrentMarkSweepThread::synchronize(true);
6694   _bit_map->lock()->lock_without_safepoint_check();
6695   _collector->startTimer();
6696 }
6697 
6698 // This closure is used to rescan the marked objects on the dirty cards
6699 // in the mod union table and the card table proper. In the parallel
6700 // case, although the bitMap is shared, we do a single read so the
6701 // isMarked() query is "safe".
6702 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6703   // Ignore mark word because we are running concurrent with mutators
6704   assert(p->is_oop_or_null(true), "expected an oop or null");
6705   HeapWord* addr = (HeapWord*)p;
6706   assert(_span.contains(addr), "we are scanning the CMS generation");
6707   bool is_obj_array = false;
6708   #ifdef DEBUG
6709     if (!_parallel) {
6710       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6711       assert(_collector->overflow_list_is_empty(),
6712              "overflow list should be empty");
6713 
6714     }
6715   #endif // DEBUG
6716   if (_bit_map->isMarked(addr)) {
6717     // Obj arrays are precisely marked, non-arrays are not;
6718     // so we scan objArrays precisely and non-arrays in their
6719     // entirety.
6720     if (p->is_objArray()) {
6721       is_obj_array = true;
6722       if (_parallel) {
6723         p->oop_iterate(_par_scan_closure, mr);
6724       } else {
6725         p->oop_iterate(_scan_closure, mr);
6726       }
6727     } else {
6728       if (_parallel) {
6729         p->oop_iterate(_par_scan_closure);
6730       } else {
6731         p->oop_iterate(_scan_closure);
6732       }
6733     }
6734   }
6735   #ifdef DEBUG
6736     if (!_parallel) {
6737       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6738       assert(_collector->overflow_list_is_empty(),
6739              "overflow list should be empty");
6740 
6741     }
6742   #endif // DEBUG
6743   return is_obj_array;
6744 }
6745 
6746 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6747                         MemRegion span,
6748                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6749                         CMSMarkStack*  revisitStack,
6750                         bool should_yield, bool verifying):
6751   _collector(collector),
6752   _span(span),
6753   _bitMap(bitMap),
6754   _mut(&collector->_modUnionTable),
6755   _markStack(markStack),
6756   _revisitStack(revisitStack),
6757   _yield(should_yield),
6758   _skipBits(0)
6759 {
6760   assert(_markStack->isEmpty(), "stack should be empty");
6761   _finger = _bitMap->startWord();
6762   _threshold = _finger;
6763   assert(_collector->_restart_addr == NULL, "Sanity check");
6764   assert(_span.contains(_finger), "Out of bounds _finger?");
6765   DEBUG_ONLY(_verifying = verifying;)
6766 }
6767 
6768 void MarkFromRootsClosure::reset(HeapWord* addr) {
6769   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6770   assert(_span.contains(addr), "Out of bounds _finger?");
6771   _finger = addr;
6772   _threshold = (HeapWord*)round_to(
6773                  (intptr_t)_finger, CardTableModRefBS::card_size);
6774 }
6775 
6776 // Should revisit to see if this should be restructured for
6777 // greater efficiency.
6778 void MarkFromRootsClosure::do_bit(size_t offset) {
6779   if (_skipBits > 0) {
6780     _skipBits--;
6781     return;
6782   }
6783   // convert offset into a HeapWord*
6784   HeapWord* addr = _bitMap->startWord() + offset;
6785   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6786          "address out of range");
6787   assert(_bitMap->isMarked(addr), "tautology");
6788   if (_bitMap->isMarked(addr+1)) {
6789     // this is an allocated but not yet initialized object
6790     assert(_skipBits == 0, "tautology");
6791     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6792     oop p = oop(addr);
6793     if (p->klass() == NULL || !p->is_parsable()) {
6794       DEBUG_ONLY(if (!_verifying) {)
6795         // We re-dirty the cards on which this object lies and increase
6796         // the _threshold so that we'll come back to scan this object
6797         // during the preclean or remark phase. (CMSCleanOnEnter)
6798         if (CMSCleanOnEnter) {
6799           size_t sz = _collector->block_size_using_printezis_bits(addr);
6800           HeapWord* start_card_addr = (HeapWord*)round_down(
6801                                          (intptr_t)addr, CardTableModRefBS::card_size);
6802           HeapWord* end_card_addr   = (HeapWord*)round_to(
6803                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6804           MemRegion redirty_range = MemRegion(start_card_addr, end_card_addr);
6805           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6806           // Bump _threshold to end_card_addr; note that
6807           // _threshold cannot possibly exceed end_card_addr, anyhow.
6808           // This prevents future clearing of the card as the scan proceeds
6809           // to the right.
6810           assert(_threshold <= end_card_addr,
6811                  "Because we are just scanning into this object");
6812           if (_threshold < end_card_addr) {
6813             _threshold = end_card_addr;
6814           }
6815           if (p->klass() != NULL) {
6816             // Redirty the range of cards...
6817             _mut->mark_range(redirty_range);
6818           } // ...else the setting of klass will dirty the card anyway.
6819         }
6820       DEBUG_ONLY(})
6821       return;
6822     }
6823   }
6824   scanOopsInOop(addr);
6825 }
6826 
6827 // We take a break if we've been at this for a while,
6828 // so as to avoid monopolizing the locks involved.
6829 void MarkFromRootsClosure::do_yield_work() {
6830   // First give up the locks, then yield, then re-lock
6831   // We should probably use a constructor/destructor idiom to
6832   // do this unlock/lock or modify the MutexUnlocker class to
6833   // serve our purpose. XXX
6834   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6835          "CMS thread should hold CMS token");
6836   assert_lock_strong(_bitMap->lock());
6837   _bitMap->lock()->unlock();
6838   ConcurrentMarkSweepThread::desynchronize(true);
6839   ConcurrentMarkSweepThread::acknowledge_yield_request();
6840   _collector->stopTimer();
6841   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6842   if (PrintCMSStatistics != 0) {
6843     _collector->incrementYields();
6844   }
6845   _collector->icms_wait();
6846 
6847   // See the comment in coordinator_yield()
6848   for (unsigned i = 0; i < CMSYieldSleepCount &&
6849                        ConcurrentMarkSweepThread::should_yield() &&
6850                        !CMSCollector::foregroundGCIsActive(); ++i) {
6851     os::sleep(Thread::current(), 1, false);
6852     ConcurrentMarkSweepThread::acknowledge_yield_request();
6853   }
6854 
6855   ConcurrentMarkSweepThread::synchronize(true);
6856   _bitMap->lock()->lock_without_safepoint_check();
6857   _collector->startTimer();
6858 }
6859 
6860 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6861   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6862   assert(_markStack->isEmpty(),
6863          "should drain stack to limit stack usage");
6864   // convert ptr to an oop preparatory to scanning
6865   oop this_oop = oop(ptr);
6866   // Ignore mark word in verification below, since we
6867   // may be running concurrent with mutators.
6868   assert(this_oop->is_oop(true), "should be an oop");
6869   assert(_finger <= ptr, "_finger runneth ahead");
6870   // advance the finger to right end of this object
6871   _finger = ptr + this_oop->size();
6872   assert(_finger > ptr, "we just incremented it above");
6873   // On large heaps, it may take us some time to get through
6874   // the marking phase (especially if running iCMS). During
6875   // this time it's possible that a lot of mutations have
6876   // accumulated in the card table and the mod union table --
6877   // these mutation records are redundant until we have
6878   // actually traced into the corresponding card.
6879   // Here, we check whether advancing the finger would make
6880   // us cross into a new card, and if so clear corresponding
6881   // cards in the MUT (preclean them in the card-table in the
6882   // future).
6883 
6884   DEBUG_ONLY(if (!_verifying) {)
6885     // The clean-on-enter optimization is disabled by default,
6886     // until we fix 6178663.
6887     if (CMSCleanOnEnter && (_finger > _threshold)) {
6888       // [_threshold, _finger) represents the interval
6889       // of cards to be cleared  in MUT (or precleaned in card table).
6890       // The set of cards to be cleared is all those that overlap
6891       // with the interval [_threshold, _finger); note that
6892       // _threshold is always kept card-aligned but _finger isn't
6893       // always card-aligned.
6894       HeapWord* old_threshold = _threshold;
6895       assert(old_threshold == (HeapWord*)round_to(
6896               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6897              "_threshold should always be card-aligned");
6898       _threshold = (HeapWord*)round_to(
6899                      (intptr_t)_finger, CardTableModRefBS::card_size);
6900       MemRegion mr(old_threshold, _threshold);
6901       assert(!mr.is_empty(), "Control point invariant");
6902       assert(_span.contains(mr), "Should clear within span");
6903       // XXX When _finger crosses from old gen into perm gen
6904       // we may be doing unnecessary cleaning; do better in the
6905       // future by detecting that condition and clearing fewer
6906       // MUT/CT entries.
6907       _mut->clear_range(mr);
6908     }
6909   DEBUG_ONLY(})
6910 
6911   // Note: the finger doesn't advance while we drain
6912   // the stack below.
6913   PushOrMarkClosure pushOrMarkClosure(_collector,
6914                                       _span, _bitMap, _markStack,
6915                                       _revisitStack,
6916                                       _finger, this);
6917   bool res = _markStack->push(this_oop);
6918   assert(res, "Empty non-zero size stack should have space for single push");
6919   while (!_markStack->isEmpty()) {
6920     oop new_oop = _markStack->pop();
6921     // Skip verifying header mark word below because we are
6922     // running concurrent with mutators.
6923     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6924     // now scan this oop's oops
6925     new_oop->oop_iterate(&pushOrMarkClosure);
6926     do_yield_check();
6927   }
6928   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6929 }
6930 
6931 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6932                        CMSCollector* collector, MemRegion span,
6933                        CMSBitMap* bit_map,
6934                        OopTaskQueue* work_queue,
6935                        CMSMarkStack*  overflow_stack,
6936                        CMSMarkStack*  revisit_stack,
6937                        bool should_yield):
6938   _collector(collector),
6939   _whole_span(collector->_span),
6940   _span(span),
6941   _bit_map(bit_map),
6942   _mut(&collector->_modUnionTable),
6943   _work_queue(work_queue),
6944   _overflow_stack(overflow_stack),
6945   _revisit_stack(revisit_stack),
6946   _yield(should_yield),
6947   _skip_bits(0),
6948   _task(task)
6949 {
6950   assert(_work_queue->size() == 0, "work_queue should be empty");
6951   _finger = span.start();
6952   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6953   assert(_span.contains(_finger), "Out of bounds _finger?");
6954 }
6955 
6956 // Should revisit to see if this should be restructured for
6957 // greater efficiency.
6958 void Par_MarkFromRootsClosure::do_bit(size_t offset) {
6959   if (_skip_bits > 0) {
6960     _skip_bits--;
6961     return;
6962   }
6963   // convert offset into a HeapWord*
6964   HeapWord* addr = _bit_map->startWord() + offset;
6965   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6966          "address out of range");
6967   assert(_bit_map->isMarked(addr), "tautology");
6968   if (_bit_map->isMarked(addr+1)) {
6969     // this is an allocated object that might not yet be initialized
6970     assert(_skip_bits == 0, "tautology");
6971     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6972     oop p = oop(addr);
6973     if (p->klass() == NULL || !p->is_parsable()) {
6974       // in the case of Clean-on-Enter optimization, redirty card
6975       // and avoid clearing card by increasing  the threshold.
6976       return;
6977     }
6978   }
6979   scan_oops_in_oop(addr);
6980 }
6981 
6982 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6983   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6984   // Should we assert that our work queue is empty or
6985   // below some drain limit?
6986   assert(_work_queue->size() == 0,
6987          "should drain stack to limit stack usage");
6988   // convert ptr to an oop preparatory to scanning
6989   oop this_oop = oop(ptr);
6990   // Ignore mark word in verification below, since we
6991   // may be running concurrent with mutators.
6992   assert(this_oop->is_oop(true), "should be an oop");
6993   assert(_finger <= ptr, "_finger runneth ahead");
6994   // advance the finger to right end of this object
6995   _finger = ptr + this_oop->size();
6996   assert(_finger > ptr, "we just incremented it above");
6997   // On large heaps, it may take us some time to get through
6998   // the marking phase (especially if running iCMS). During
6999   // this time it's possible that a lot of mutations have
7000   // accumulated in the card table and the mod union table --
7001   // these mutation records are redundant until we have
7002   // actually traced into the corresponding card.
7003   // Here, we check whether advancing the finger would make
7004   // us cross into a new card, and if so clear corresponding
7005   // cards in the MUT (preclean them in the card-table in the
7006   // future).
7007 
7008   // The clean-on-enter optimization is disabled by default,
7009   // until we fix 6178663.
7010   if (CMSCleanOnEnter && (_finger > _threshold)) {
7011     // [_threshold, _finger) represents the interval
7012     // of cards to be cleared  in MUT (or precleaned in card table).
7013     // The set of cards to be cleared is all those that overlap
7014     // with the interval [_threshold, _finger); note that
7015     // _threshold is always kept card-aligned but _finger isn't
7016     // always card-aligned.
7017     HeapWord* old_threshold = _threshold;
7018     assert(old_threshold == (HeapWord*)round_to(
7019             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7020            "_threshold should always be card-aligned");
7021     _threshold = (HeapWord*)round_to(
7022                    (intptr_t)_finger, CardTableModRefBS::card_size);
7023     MemRegion mr(old_threshold, _threshold);
7024     assert(!mr.is_empty(), "Control point invariant");
7025     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7026     // XXX When _finger crosses from old gen into perm gen
7027     // we may be doing unnecessary cleaning; do better in the
7028     // future by detecting that condition and clearing fewer
7029     // MUT/CT entries.
7030     _mut->clear_range(mr);
7031   }
7032 
7033   // Note: the local finger doesn't advance while we drain
7034   // the stack below, but the global finger sure can and will.
7035   HeapWord** gfa = _task->global_finger_addr();
7036   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7037                                       _span, _bit_map,
7038                                       _work_queue,
7039                                       _overflow_stack,
7040                                       _revisit_stack,
7041                                       _finger,
7042                                       gfa, this);
7043   bool res = _work_queue->push(this_oop);   // overflow could occur here
7044   assert(res, "Will hold once we use workqueues");
7045   while (true) {
7046     oop new_oop;
7047     if (!_work_queue->pop_local(new_oop)) {
7048       // We emptied our work_queue; check if there's stuff that can
7049       // be gotten from the overflow stack.
7050       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7051             _overflow_stack, _work_queue)) {
7052         do_yield_check();
7053         continue;
7054       } else {  // done
7055         break;
7056       }
7057     }
7058     // Skip verifying header mark word below because we are
7059     // running concurrent with mutators.
7060     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7061     // now scan this oop's oops
7062     new_oop->oop_iterate(&pushOrMarkClosure);
7063     do_yield_check();
7064   }
7065   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7066 }
7067 
7068 // Yield in response to a request from VM Thread or
7069 // from mutators.
7070 void Par_MarkFromRootsClosure::do_yield_work() {
7071   assert(_task != NULL, "sanity");
7072   _task->yield();
7073 }
7074 
7075 // A variant of the above used for verifying CMS marking work.
7076 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7077                         MemRegion span,
7078                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7079                         CMSMarkStack*  mark_stack):
7080   _collector(collector),
7081   _span(span),
7082   _verification_bm(verification_bm),
7083   _cms_bm(cms_bm),
7084   _mark_stack(mark_stack),
7085   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7086                       mark_stack)
7087 {
7088   assert(_mark_stack->isEmpty(), "stack should be empty");
7089   _finger = _verification_bm->startWord();
7090   assert(_collector->_restart_addr == NULL, "Sanity check");
7091   assert(_span.contains(_finger), "Out of bounds _finger?");
7092 }
7093 
7094 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7095   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7096   assert(_span.contains(addr), "Out of bounds _finger?");
7097   _finger = addr;
7098 }
7099 
7100 // Should revisit to see if this should be restructured for
7101 // greater efficiency.
7102 void MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7103   // convert offset into a HeapWord*
7104   HeapWord* addr = _verification_bm->startWord() + offset;
7105   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7106          "address out of range");
7107   assert(_verification_bm->isMarked(addr), "tautology");
7108   assert(_cms_bm->isMarked(addr), "tautology");
7109 
7110   assert(_mark_stack->isEmpty(),
7111          "should drain stack to limit stack usage");
7112   // convert addr to an oop preparatory to scanning
7113   oop this_oop = oop(addr);
7114   assert(this_oop->is_oop(), "should be an oop");
7115   assert(_finger <= addr, "_finger runneth ahead");
7116   // advance the finger to right end of this object
7117   _finger = addr + this_oop->size();
7118   assert(_finger > addr, "we just incremented it above");
7119   // Note: the finger doesn't advance while we drain
7120   // the stack below.
7121   bool res = _mark_stack->push(this_oop);
7122   assert(res, "Empty non-zero size stack should have space for single push");
7123   while (!_mark_stack->isEmpty()) {
7124     oop new_oop = _mark_stack->pop();
7125     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7126     // now scan this oop's oops
7127     new_oop->oop_iterate(&_pam_verify_closure);
7128   }
7129   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7130 }
7131 
7132 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7133   CMSCollector* collector, MemRegion span,
7134   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7135   CMSMarkStack*  mark_stack):
7136   OopClosure(collector->ref_processor()),
7137   _collector(collector),
7138   _span(span),
7139   _verification_bm(verification_bm),
7140   _cms_bm(cms_bm),
7141   _mark_stack(mark_stack)
7142 { }
7143 
7144 
7145 // Upon stack overflow, we discard (part of) the stack,
7146 // remembering the least address amongst those discarded
7147 // in CMSCollector's _restart_address.
7148 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7149   // Remember the least grey address discarded
7150   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7151   _collector->lower_restart_addr(ra);
7152   _mark_stack->reset();  // discard stack contents
7153   _mark_stack->expand(); // expand the stack if possible
7154 }
7155 
7156 void PushAndMarkVerifyClosure::do_oop(oop* p) {
7157   oop    this_oop = *p;
7158   assert(this_oop->is_oop_or_null(), "expected an oop or NULL");
7159   HeapWord* addr = (HeapWord*)this_oop;
7160   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7161     // Oop lies in _span and isn't yet grey or black
7162     _verification_bm->mark(addr);            // now grey
7163     if (!_cms_bm->isMarked(addr)) {
7164       oop(addr)->print();
7165       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
7166       fatal("... aborting");
7167     }
7168 
7169     if (!_mark_stack->push(this_oop)) { // stack overflow
7170       if (PrintCMSStatistics != 0) {
7171         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7172                                SIZE_FORMAT, _mark_stack->capacity());
7173       }
7174       assert(_mark_stack->isFull(), "Else push should have succeeded");
7175       handle_stack_overflow(addr);
7176     }
7177     // anything including and to the right of _finger
7178     // will be scanned as we iterate over the remainder of the
7179     // bit map
7180   }
7181 }
7182 
7183 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7184                      MemRegion span,
7185                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7186                      CMSMarkStack*  revisitStack,
7187                      HeapWord* finger, MarkFromRootsClosure* parent) :
7188   OopClosure(collector->ref_processor()),
7189   _collector(collector),
7190   _span(span),
7191   _bitMap(bitMap),
7192   _markStack(markStack),
7193   _revisitStack(revisitStack),
7194   _finger(finger),
7195   _parent(parent),
7196   _should_remember_klasses(collector->cms_should_unload_classes())
7197 { }
7198 
7199 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7200                      MemRegion span,
7201                      CMSBitMap* bit_map,
7202                      OopTaskQueue* work_queue,
7203                      CMSMarkStack*  overflow_stack,
7204                      CMSMarkStack*  revisit_stack,
7205                      HeapWord* finger,
7206                      HeapWord** global_finger_addr,
7207                      Par_MarkFromRootsClosure* parent) :
7208   OopClosure(collector->ref_processor()),
7209   _collector(collector),
7210   _whole_span(collector->_span),
7211   _span(span),
7212   _bit_map(bit_map),
7213   _work_queue(work_queue),
7214   _overflow_stack(overflow_stack),
7215   _revisit_stack(revisit_stack),
7216   _finger(finger),
7217   _global_finger_addr(global_finger_addr),
7218   _parent(parent),
7219   _should_remember_klasses(collector->cms_should_unload_classes())
7220 { }
7221 
7222 
7223 void CMSCollector::lower_restart_addr(HeapWord* low) {
7224   assert(_span.contains(low), "Out of bounds addr");
7225   if (_restart_addr == NULL) {
7226     _restart_addr = low;
7227   } else {
7228     _restart_addr = MIN2(_restart_addr, low);
7229   }
7230 }
7231 
7232 // Upon stack overflow, we discard (part of) the stack,
7233 // remembering the least address amongst those discarded
7234 // in CMSCollector's _restart_address.
7235 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7236   // Remember the least grey address discarded
7237   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7238   _collector->lower_restart_addr(ra);
7239   _markStack->reset();  // discard stack contents
7240   _markStack->expand(); // expand the stack if possible
7241 }
7242 
7243 // Upon stack overflow, we discard (part of) the stack,
7244 // remembering the least address amongst those discarded
7245 // in CMSCollector's _restart_address.
7246 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7247   // We need to do this under a mutex to prevent other
7248   // workers from interfering with the expansion below.
7249   MutexLockerEx ml(_overflow_stack->par_lock(),
7250                    Mutex::_no_safepoint_check_flag);
7251   // Remember the least grey address discarded
7252   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7253   _collector->lower_restart_addr(ra);
7254   _overflow_stack->reset();  // discard stack contents
7255   _overflow_stack->expand(); // expand the stack if possible
7256 }
7257 
7258 
7259 void PushOrMarkClosure::do_oop(oop* p) {
7260   oop    thisOop = *p;
7261   // Ignore mark word because we are running concurrent with mutators.
7262   assert(thisOop->is_oop_or_null(true), "expected an oop or NULL");
7263   HeapWord* addr = (HeapWord*)thisOop;
7264   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7265     // Oop lies in _span and isn't yet grey or black
7266     _bitMap->mark(addr);            // now grey
7267     if (addr < _finger) {
7268       // the bit map iteration has already either passed, or
7269       // sampled, this bit in the bit map; we'll need to
7270       // use the marking stack to scan this oop's oops.
7271       bool simulate_overflow = false;
7272       NOT_PRODUCT(
7273         if (CMSMarkStackOverflowALot &&
7274             _collector->simulate_overflow()) {
7275           // simulate a stack overflow
7276           simulate_overflow = true;
7277         }
7278       )
7279       if (simulate_overflow || !_markStack->push(thisOop)) { // stack overflow
7280         if (PrintCMSStatistics != 0) {
7281           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7282                                  SIZE_FORMAT, _markStack->capacity());
7283         }
7284         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7285         handle_stack_overflow(addr);
7286       }
7287     }
7288     // anything including and to the right of _finger
7289     // will be scanned as we iterate over the remainder of the
7290     // bit map
7291     do_yield_check();
7292   }
7293 }
7294 
7295 void Par_PushOrMarkClosure::do_oop(oop* p) {
7296   oop    this_oop = *p;
7297   // Ignore mark word because we are running concurrent with mutators.
7298   assert(this_oop->is_oop_or_null(true), "expected an oop or NULL");
7299   HeapWord* addr = (HeapWord*)this_oop;
7300   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7301     // Oop lies in _span and isn't yet grey or black
7302     // We read the global_finger (volatile read) strictly after marking oop
7303     bool res = _bit_map->par_mark(addr);    // now grey
7304     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7305     // Should we push this marked oop on our stack?
7306     // -- if someone else marked it, nothing to do
7307     // -- if target oop is above global finger nothing to do
7308     // -- if target oop is in chunk and above local finger
7309     //      then nothing to do
7310     // -- else push on work queue
7311     if (   !res       // someone else marked it, they will deal with it
7312         || (addr >= *gfa)  // will be scanned in a later task
7313         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7314       return;
7315     }
7316     // the bit map iteration has already either passed, or
7317     // sampled, this bit in the bit map; we'll need to
7318     // use the marking stack to scan this oop's oops.
7319     bool simulate_overflow = false;
7320     NOT_PRODUCT(
7321       if (CMSMarkStackOverflowALot &&
7322           _collector->simulate_overflow()) {
7323         // simulate a stack overflow
7324         simulate_overflow = true;
7325       }
7326     )
7327     if (simulate_overflow ||
7328         !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) {
7329       // stack overflow
7330       if (PrintCMSStatistics != 0) {
7331         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7332                                SIZE_FORMAT, _overflow_stack->capacity());
7333       }
7334       // We cannot assert that the overflow stack is full because
7335       // it may have been emptied since.
7336       assert(simulate_overflow ||
7337              _work_queue->size() == _work_queue->max_elems(),
7338             "Else push should have succeeded");
7339       handle_stack_overflow(addr);
7340     }
7341     do_yield_check();
7342   }
7343 }
7344 
7345 
7346 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7347                                        MemRegion span,
7348                                        ReferenceProcessor* rp,
7349                                        CMSBitMap* bit_map,
7350                                        CMSBitMap* mod_union_table,
7351                                        CMSMarkStack*  mark_stack,
7352                                        CMSMarkStack*  revisit_stack,
7353                                        bool           concurrent_precleaning):
7354   OopClosure(rp),
7355   _collector(collector),
7356   _span(span),
7357   _bit_map(bit_map),
7358   _mod_union_table(mod_union_table),
7359   _mark_stack(mark_stack),
7360   _revisit_stack(revisit_stack),
7361   _concurrent_precleaning(concurrent_precleaning),
7362   _should_remember_klasses(collector->cms_should_unload_classes())
7363 {
7364   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7365 }
7366 
7367 // Grey object rescan during pre-cleaning and second checkpoint phases --
7368 // the non-parallel version (the parallel version appears further below.)
7369 void PushAndMarkClosure::do_oop(oop* p) {
7370   oop    this_oop = *p;
7371   // Ignore mark word verification. If during concurrent precleaning
7372   // the object monitor may be locked. If during the checkpoint
7373   // phases, the object may already have been reached by a  different
7374   // path and may be at the end of the global overflow list (so
7375   // the mark word may be NULL).
7376   assert(this_oop->is_oop_or_null(true/* ignore mark word */),
7377          "expected an oop or NULL");
7378   HeapWord* addr = (HeapWord*)this_oop;
7379   // Check if oop points into the CMS generation
7380   // and is not marked
7381   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7382     // a white object ...
7383     _bit_map->mark(addr);         // ... now grey
7384     // push on the marking stack (grey set)
7385     bool simulate_overflow = false;
7386     NOT_PRODUCT(
7387       if (CMSMarkStackOverflowALot &&
7388           _collector->simulate_overflow()) {
7389         // simulate a stack overflow
7390         simulate_overflow = true;
7391       }
7392     )
7393     if (simulate_overflow || !_mark_stack->push(this_oop)) {
7394       if (_concurrent_precleaning) {
7395          // During precleaning we can just dirty the appropriate card
7396          // in the mod union table, thus ensuring that the object remains
7397          // in the grey set  and continue. Note that no one can be intefering
7398          // with us in this action of dirtying the mod union table, so
7399          // no locking is required.
7400          _mod_union_table->mark(addr);
7401          _collector->_ser_pmc_preclean_ovflw++;
7402       } else {
7403          // During the remark phase, we need to remember this oop
7404          // in the overflow list.
7405          _collector->push_on_overflow_list(this_oop);
7406          _collector->_ser_pmc_remark_ovflw++;
7407       }
7408     }
7409   }
7410 }
7411 
7412 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7413                                                MemRegion span,
7414                                                ReferenceProcessor* rp,
7415                                                CMSBitMap* bit_map,
7416                                                OopTaskQueue* work_queue,
7417                                                CMSMarkStack* revisit_stack):
7418   OopClosure(rp),
7419   _collector(collector),
7420   _span(span),
7421   _bit_map(bit_map),
7422   _work_queue(work_queue),
7423   _revisit_stack(revisit_stack),
7424   _should_remember_klasses(collector->cms_should_unload_classes())
7425 {
7426   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7427 }
7428 
7429 // Grey object rescan during second checkpoint phase --
7430 // the parallel version.
7431 void Par_PushAndMarkClosure::do_oop(oop* p) {
7432   oop    this_oop = *p;
7433   // In the assert below, we ignore the mark word because
7434   // this oop may point to an already visited object that is
7435   // on the overflow stack (in which case the mark word has
7436   // been hijacked for chaining into the overflow stack --
7437   // if this is the last object in the overflow stack then
7438   // its mark word will be NULL). Because this object may
7439   // have been subsequently popped off the global overflow
7440   // stack, and the mark word possibly restored to the prototypical
7441   // value, by the time we get to examined this failing assert in
7442   // the debugger, is_oop_or_null(false) may subsequently start
7443   // to hold.
7444   assert(this_oop->is_oop_or_null(true),
7445          "expected an oop or NULL");
7446   HeapWord* addr = (HeapWord*)this_oop;
7447   // Check if oop points into the CMS generation
7448   // and is not marked
7449   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7450     // a white object ...
7451     // If we manage to "claim" the object, by being the
7452     // first thread to mark it, then we push it on our
7453     // marking stack
7454     if (_bit_map->par_mark(addr)) {     // ... now grey
7455       // push on work queue (grey set)
7456       bool simulate_overflow = false;
7457       NOT_PRODUCT(
7458         if (CMSMarkStackOverflowALot &&
7459             _collector->par_simulate_overflow()) {
7460           // simulate a stack overflow
7461           simulate_overflow = true;
7462         }
7463       )
7464       if (simulate_overflow || !_work_queue->push(this_oop)) {
7465         _collector->par_push_on_overflow_list(this_oop);
7466         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7467       }
7468     } // Else, some other thread got there first
7469   }
7470 }
7471 
7472 void PushAndMarkClosure::remember_klass(Klass* k) {
7473   if (!_revisit_stack->push(oop(k))) {
7474     fatal("Revisit stack overflowed in PushAndMarkClosure");
7475   }
7476 }
7477 
7478 void Par_PushAndMarkClosure::remember_klass(Klass* k) {
7479   if (!_revisit_stack->par_push(oop(k))) {
7480     fatal("Revist stack overflowed in Par_PushAndMarkClosure");
7481   }
7482 }
7483 
7484 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7485   Mutex* bml = _collector->bitMapLock();
7486   assert_lock_strong(bml);
7487   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7488          "CMS thread should hold CMS token");
7489 
7490   bml->unlock();
7491   ConcurrentMarkSweepThread::desynchronize(true);
7492 
7493   ConcurrentMarkSweepThread::acknowledge_yield_request();
7494 
7495   _collector->stopTimer();
7496   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7497   if (PrintCMSStatistics != 0) {
7498     _collector->incrementYields();
7499   }
7500   _collector->icms_wait();
7501 
7502   // See the comment in coordinator_yield()
7503   for (unsigned i = 0; i < CMSYieldSleepCount &&
7504                        ConcurrentMarkSweepThread::should_yield() &&
7505                        !CMSCollector::foregroundGCIsActive(); ++i) {
7506     os::sleep(Thread::current(), 1, false);
7507     ConcurrentMarkSweepThread::acknowledge_yield_request();
7508   }
7509 
7510   ConcurrentMarkSweepThread::synchronize(true);
7511   bml->lock();
7512 
7513   _collector->startTimer();
7514 }
7515 
7516 bool CMSPrecleanRefsYieldClosure::should_return() {
7517   if (ConcurrentMarkSweepThread::should_yield()) {
7518     do_yield_work();
7519   }
7520   return _collector->foregroundGCIsActive();
7521 }
7522 
7523 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7524   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7525          "mr should be aligned to start at a card boundary");
7526   // We'd like to assert:
7527   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7528   //        "mr should be a range of cards");
7529   // However, that would be too strong in one case -- the last
7530   // partition ends at _unallocated_block which, in general, can be
7531   // an arbitrary boundary, not necessarily card aligned.
7532   if (PrintCMSStatistics != 0) {
7533     _num_dirty_cards +=
7534          mr.word_size()/CardTableModRefBS::card_size_in_words;
7535   }
7536   _space->object_iterate_mem(mr, &_scan_cl);
7537 }
7538 
7539 SweepClosure::SweepClosure(CMSCollector* collector,
7540                            ConcurrentMarkSweepGeneration* g,
7541                            CMSBitMap* bitMap, bool should_yield) :
7542   _collector(collector),
7543   _g(g),
7544   _sp(g->cmsSpace()),
7545   _limit(_sp->sweep_limit()),
7546   _freelistLock(_sp->freelistLock()),
7547   _bitMap(bitMap),
7548   _yield(should_yield),
7549   _inFreeRange(false),           // No free range at beginning of sweep
7550   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7551   _lastFreeRangeCoalesced(false),
7552   _freeFinger(g->used_region().start())
7553 {
7554   NOT_PRODUCT(
7555     _numObjectsFreed = 0;
7556     _numWordsFreed   = 0;
7557     _numObjectsLive = 0;
7558     _numWordsLive = 0;
7559     _numObjectsAlreadyFree = 0;
7560     _numWordsAlreadyFree = 0;
7561     _last_fc = NULL;
7562 
7563     _sp->initializeIndexedFreeListArrayReturnedBytes();
7564     _sp->dictionary()->initializeDictReturnedBytes();
7565   )
7566   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7567          "sweep _limit out of bounds");
7568   if (CMSTraceSweeper) {
7569     gclog_or_tty->print("\n====================\nStarting new sweep\n");
7570   }
7571 }
7572 
7573 // We need this destructor to reclaim any space at the end
7574 // of the space, which do_blk below may not have added back to
7575 // the free lists. [basically dealing with the "fringe effect"]
7576 SweepClosure::~SweepClosure() {
7577   assert_lock_strong(_freelistLock);
7578   // this should be treated as the end of a free run if any
7579   // The current free range should be returned to the free lists
7580   // as one coalesced chunk.
7581   if (inFreeRange()) {
7582     flushCurFreeChunk(freeFinger(),
7583       pointer_delta(_limit, freeFinger()));
7584     assert(freeFinger() < _limit, "the finger pointeth off base");
7585     if (CMSTraceSweeper) {
7586       gclog_or_tty->print("destructor:");
7587       gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7588                  "[coalesced:"SIZE_FORMAT"]\n",
7589                  freeFinger(), pointer_delta(_limit, freeFinger()),
7590                  lastFreeRangeCoalesced());
7591     }
7592   }
7593   NOT_PRODUCT(
7594     if (Verbose && PrintGC) {
7595       gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7596                           SIZE_FORMAT " bytes",
7597                  _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7598       gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7599                              SIZE_FORMAT" bytes  "
7600         "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7601         _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7602         _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7603       size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7604         sizeof(HeapWord);
7605       gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7606 
7607       if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7608         size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7609         size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7610         size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7611         gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7612         gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7613           indexListReturnedBytes);
7614         gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7615           dictReturnedBytes);
7616       }
7617     }
7618   )
7619   // Now, in debug mode, just null out the sweep_limit
7620   NOT_PRODUCT(_sp->clear_sweep_limit();)
7621   if (CMSTraceSweeper) {
7622     gclog_or_tty->print("end of sweep\n================\n");
7623   }
7624 }
7625 
7626 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7627     bool freeRangeInFreeLists) {
7628   if (CMSTraceSweeper) {
7629     gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7630                freeFinger, _sp->block_size(freeFinger),
7631                freeRangeInFreeLists);
7632   }
7633   assert(!inFreeRange(), "Trampling existing free range");
7634   set_inFreeRange(true);
7635   set_lastFreeRangeCoalesced(false);
7636 
7637   set_freeFinger(freeFinger);
7638   set_freeRangeInFreeLists(freeRangeInFreeLists);
7639   if (CMSTestInFreeList) {
7640     if (freeRangeInFreeLists) {
7641       FreeChunk* fc = (FreeChunk*) freeFinger;
7642       assert(fc->isFree(), "A chunk on the free list should be free.");
7643       assert(fc->size() > 0, "Free range should have a size");
7644       assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7645     }
7646   }
7647 }
7648 
7649 // Note that the sweeper runs concurrently with mutators. Thus,
7650 // it is possible for direct allocation in this generation to happen
7651 // in the middle of the sweep. Note that the sweeper also coalesces
7652 // contiguous free blocks. Thus, unless the sweeper and the allocator
7653 // synchronize appropriately freshly allocated blocks may get swept up.
7654 // This is accomplished by the sweeper locking the free lists while
7655 // it is sweeping. Thus blocks that are determined to be free are
7656 // indeed free. There is however one additional complication:
7657 // blocks that have been allocated since the final checkpoint and
7658 // mark, will not have been marked and so would be treated as
7659 // unreachable and swept up. To prevent this, the allocator marks
7660 // the bit map when allocating during the sweep phase. This leads,
7661 // however, to a further complication -- objects may have been allocated
7662 // but not yet initialized -- in the sense that the header isn't yet
7663 // installed. The sweeper can not then determine the size of the block
7664 // in order to skip over it. To deal with this case, we use a technique
7665 // (due to Printezis) to encode such uninitialized block sizes in the
7666 // bit map. Since the bit map uses a bit per every HeapWord, but the
7667 // CMS generation has a minimum object size of 3 HeapWords, it follows
7668 // that "normal marks" won't be adjacent in the bit map (there will
7669 // always be at least two 0 bits between successive 1 bits). We make use
7670 // of these "unused" bits to represent uninitialized blocks -- the bit
7671 // corresponding to the start of the uninitialized object and the next
7672 // bit are both set. Finally, a 1 bit marks the end of the object that
7673 // started with the two consecutive 1 bits to indicate its potentially
7674 // uninitialized state.
7675 
7676 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7677   FreeChunk* fc = (FreeChunk*)addr;
7678   size_t res;
7679 
7680   // check if we are done sweepinrg
7681   if (addr == _limit) { // we have swept up to the limit, do nothing more
7682     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7683            "sweep _limit out of bounds");
7684     // help the closure application finish
7685     return pointer_delta(_sp->end(), _limit);
7686   }
7687   assert(addr <= _limit, "sweep invariant");
7688 
7689   // check if we should yield
7690   do_yield_check(addr);
7691   if (fc->isFree()) {
7692     // Chunk that is already free
7693     res = fc->size();
7694     doAlreadyFreeChunk(fc);
7695     debug_only(_sp->verifyFreeLists());
7696     assert(res == fc->size(), "Don't expect the size to change");
7697     NOT_PRODUCT(
7698       _numObjectsAlreadyFree++;
7699       _numWordsAlreadyFree += res;
7700     )
7701     NOT_PRODUCT(_last_fc = fc;)
7702   } else if (!_bitMap->isMarked(addr)) {
7703     // Chunk is fresh garbage
7704     res = doGarbageChunk(fc);
7705     debug_only(_sp->verifyFreeLists());
7706     NOT_PRODUCT(
7707       _numObjectsFreed++;
7708       _numWordsFreed += res;
7709     )
7710   } else {
7711     // Chunk that is alive.
7712     res = doLiveChunk(fc);
7713     debug_only(_sp->verifyFreeLists());
7714     NOT_PRODUCT(
7715         _numObjectsLive++;
7716         _numWordsLive += res;
7717     )
7718   }
7719   return res;
7720 }
7721 
7722 // For the smart allocation, record following
7723 //  split deaths - a free chunk is removed from its free list because
7724 //      it is being split into two or more chunks.
7725 //  split birth - a free chunk is being added to its free list because
7726 //      a larger free chunk has been split and resulted in this free chunk.
7727 //  coal death - a free chunk is being removed from its free list because
7728 //      it is being coalesced into a large free chunk.
7729 //  coal birth - a free chunk is being added to its free list because
7730 //      it was created when two or more free chunks where coalesced into
7731 //      this free chunk.
7732 //
7733 // These statistics are used to determine the desired number of free
7734 // chunks of a given size.  The desired number is chosen to be relative
7735 // to the end of a CMS sweep.  The desired number at the end of a sweep
7736 // is the
7737 //      count-at-end-of-previous-sweep (an amount that was enough)
7738 //              - count-at-beginning-of-current-sweep  (the excess)
7739 //              + split-births  (gains in this size during interval)
7740 //              - split-deaths  (demands on this size during interval)
7741 // where the interval is from the end of one sweep to the end of the
7742 // next.
7743 //
7744 // When sweeping the sweeper maintains an accumulated chunk which is
7745 // the chunk that is made up of chunks that have been coalesced.  That
7746 // will be termed the left-hand chunk.  A new chunk of garbage that
7747 // is being considered for coalescing will be referred to as the
7748 // right-hand chunk.
7749 //
7750 // When making a decision on whether to coalesce a right-hand chunk with
7751 // the current left-hand chunk, the current count vs. the desired count
7752 // of the left-hand chunk is considered.  Also if the right-hand chunk
7753 // is near the large chunk at the end of the heap (see
7754 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7755 // left-hand chunk is coalesced.
7756 //
7757 // When making a decision about whether to split a chunk, the desired count
7758 // vs. the current count of the candidate to be split is also considered.
7759 // If the candidate is underpopulated (currently fewer chunks than desired)
7760 // a chunk of an overpopulated (currently more chunks than desired) size may
7761 // be chosen.  The "hint" associated with a free list, if non-null, points
7762 // to a free list which may be overpopulated.
7763 //
7764 
7765 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7766   size_t size = fc->size();
7767   // Chunks that cannot be coalesced are not in the
7768   // free lists.
7769   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7770     assert(_sp->verifyChunkInFreeLists(fc),
7771       "free chunk should be in free lists");
7772   }
7773   // a chunk that is already free, should not have been
7774   // marked in the bit map
7775   HeapWord* addr = (HeapWord*) fc;
7776   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7777   // Verify that the bit map has no bits marked between
7778   // addr and purported end of this block.
7779   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7780 
7781   // Some chunks cannot be coalesced in under any circumstances.
7782   // See the definition of cantCoalesce().
7783   if (!fc->cantCoalesce()) {
7784     // This chunk can potentially be coalesced.
7785     if (_sp->adaptive_freelists()) {
7786       // All the work is done in
7787       doPostIsFreeOrGarbageChunk(fc, size);
7788     } else {  // Not adaptive free lists
7789       // this is a free chunk that can potentially be coalesced by the sweeper;
7790       if (!inFreeRange()) {
7791         // if the next chunk is a free block that can't be coalesced
7792         // it doesn't make sense to remove this chunk from the free lists
7793         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7794         assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7795         if ((HeapWord*)nextChunk < _limit  &&    // there's a next chunk...
7796             nextChunk->isFree()    &&            // which is free...
7797             nextChunk->cantCoalesce()) {         // ... but cant be coalesced
7798           // nothing to do
7799         } else {
7800           // Potentially the start of a new free range:
7801           // Don't eagerly remove it from the free lists.
7802           // No need to remove it if it will just be put
7803           // back again.  (Also from a pragmatic point of view
7804           // if it is a free block in a region that is beyond
7805           // any allocated blocks, an assertion will fail)
7806           // Remember the start of a free run.
7807           initialize_free_range(addr, true);
7808           // end - can coalesce with next chunk
7809         }
7810       } else {
7811         // the midst of a free range, we are coalescing
7812         debug_only(record_free_block_coalesced(fc);)
7813         if (CMSTraceSweeper) {
7814           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
7815         }
7816         // remove it from the free lists
7817         _sp->removeFreeChunkFromFreeLists(fc);
7818         set_lastFreeRangeCoalesced(true);
7819         // If the chunk is being coalesced and the current free range is
7820         // in the free lists, remove the current free range so that it
7821         // will be returned to the free lists in its entirety - all
7822         // the coalesced pieces included.
7823         if (freeRangeInFreeLists()) {
7824           FreeChunk* ffc = (FreeChunk*) freeFinger();
7825           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7826             "Size of free range is inconsistent with chunk size.");
7827           if (CMSTestInFreeList) {
7828             assert(_sp->verifyChunkInFreeLists(ffc),
7829               "free range is not in free lists");
7830           }
7831           _sp->removeFreeChunkFromFreeLists(ffc);
7832           set_freeRangeInFreeLists(false);
7833         }
7834       }
7835     }
7836   } else {
7837     // Code path common to both original and adaptive free lists.
7838 
7839     // cant coalesce with previous block; this should be treated
7840     // as the end of a free run if any
7841     if (inFreeRange()) {
7842       // we kicked some butt; time to pick up the garbage
7843       assert(freeFinger() < addr, "the finger pointeth off base");
7844       flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
7845     }
7846     // else, nothing to do, just continue
7847   }
7848 }
7849 
7850 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
7851   // This is a chunk of garbage.  It is not in any free list.
7852   // Add it to a free list or let it possibly be coalesced into
7853   // a larger chunk.
7854   HeapWord* addr = (HeapWord*) fc;
7855   size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7856 
7857   if (_sp->adaptive_freelists()) {
7858     // Verify that the bit map has no bits marked between
7859     // addr and purported end of just dead object.
7860     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7861 
7862     doPostIsFreeOrGarbageChunk(fc, size);
7863   } else {
7864     if (!inFreeRange()) {
7865       // start of a new free range
7866       assert(size > 0, "A free range should have a size");
7867       initialize_free_range(addr, false);
7868 
7869     } else {
7870       // this will be swept up when we hit the end of the
7871       // free range
7872       if (CMSTraceSweeper) {
7873         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
7874       }
7875       // If the chunk is being coalesced and the current free range is
7876       // in the free lists, remove the current free range so that it
7877       // will be returned to the free lists in its entirety - all
7878       // the coalesced pieces included.
7879       if (freeRangeInFreeLists()) {
7880         FreeChunk* ffc = (FreeChunk*)freeFinger();
7881         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7882           "Size of free range is inconsistent with chunk size.");
7883         if (CMSTestInFreeList) {
7884           assert(_sp->verifyChunkInFreeLists(ffc),
7885             "free range is not in free lists");
7886         }
7887         _sp->removeFreeChunkFromFreeLists(ffc);
7888         set_freeRangeInFreeLists(false);
7889       }
7890       set_lastFreeRangeCoalesced(true);
7891     }
7892     // this will be swept up when we hit the end of the free range
7893 
7894     // Verify that the bit map has no bits marked between
7895     // addr and purported end of just dead object.
7896     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7897   }
7898   return size;
7899 }
7900 
7901 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
7902   HeapWord* addr = (HeapWord*) fc;
7903   // The sweeper has just found a live object. Return any accumulated
7904   // left hand chunk to the free lists.
7905   if (inFreeRange()) {
7906     if (_sp->adaptive_freelists()) {
7907       flushCurFreeChunk(freeFinger(),
7908                         pointer_delta(addr, freeFinger()));
7909     } else { // not adaptive freelists
7910       set_inFreeRange(false);
7911       // Add the free range back to the free list if it is not already
7912       // there.
7913       if (!freeRangeInFreeLists()) {
7914         assert(freeFinger() < addr, "the finger pointeth off base");
7915         if (CMSTraceSweeper) {
7916           gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
7917             "[coalesced:%d]\n",
7918             freeFinger(), pointer_delta(addr, freeFinger()),
7919             lastFreeRangeCoalesced());
7920         }
7921         _sp->addChunkAndRepairOffsetTable(freeFinger(),
7922           pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
7923       }
7924     }
7925   }
7926 
7927   // Common code path for original and adaptive free lists.
7928 
7929   // this object is live: we'd normally expect this to be
7930   // an oop, and like to assert the following:
7931   // assert(oop(addr)->is_oop(), "live block should be an oop");
7932   // However, as we commented above, this may be an object whose
7933   // header hasn't yet been initialized.
7934   size_t size;
7935   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7936   if (_bitMap->isMarked(addr + 1)) {
7937     // Determine the size from the bit map, rather than trying to
7938     // compute it from the object header.
7939     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7940     size = pointer_delta(nextOneAddr + 1, addr);
7941     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7942            "alignment problem");
7943 
7944     #ifdef DEBUG
7945       if (oop(addr)->klass() != NULL &&
7946           (   !_collector->cms_should_unload_classes()
7947            || oop(addr)->is_parsable())) {
7948         // Ignore mark word because we are running concurrent with mutators
7949         assert(oop(addr)->is_oop(true), "live block should be an oop");
7950         assert(size ==
7951                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7952                "P-mark and computed size do not agree");
7953       }
7954     #endif
7955 
7956   } else {
7957     // This should be an initialized object that's alive.
7958     assert(oop(addr)->klass() != NULL &&
7959            (!_collector->cms_should_unload_classes()
7960             || oop(addr)->is_parsable()),
7961            "Should be an initialized object");
7962     // Ignore mark word because we are running concurrent with mutators
7963     assert(oop(addr)->is_oop(true), "live block should be an oop");
7964     // Verify that the bit map has no bits marked between
7965     // addr and purported end of this block.
7966     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7967     assert(size >= 3, "Necessary for Printezis marks to work");
7968     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7969     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7970   }
7971   return size;
7972 }
7973 
7974 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
7975                                             size_t chunkSize) {
7976   // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
7977   // scheme.
7978   bool fcInFreeLists = fc->isFree();
7979   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7980   assert((HeapWord*)fc <= _limit, "sweep invariant");
7981   if (CMSTestInFreeList && fcInFreeLists) {
7982     assert(_sp->verifyChunkInFreeLists(fc),
7983       "free chunk is not in free lists");
7984   }
7985 
7986 
7987   if (CMSTraceSweeper) {
7988     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
7989   }
7990 
7991   HeapWord* addr = (HeapWord*) fc;
7992 
7993   bool coalesce;
7994   size_t left  = pointer_delta(addr, freeFinger());
7995   size_t right = chunkSize;
7996   switch (FLSCoalescePolicy) {
7997     // numeric value forms a coalition aggressiveness metric
7998     case 0:  { // never coalesce
7999       coalesce = false;
8000       break;
8001     }
8002     case 1: { // coalesce if left & right chunks on overpopulated lists
8003       coalesce = _sp->coalOverPopulated(left) &&
8004                  _sp->coalOverPopulated(right);
8005       break;
8006     }
8007     case 2: { // coalesce if left chunk on overpopulated list (default)
8008       coalesce = _sp->coalOverPopulated(left);
8009       break;
8010     }
8011     case 3: { // coalesce if left OR right chunk on overpopulated list
8012       coalesce = _sp->coalOverPopulated(left) ||
8013                  _sp->coalOverPopulated(right);
8014       break;
8015     }
8016     case 4: { // always coalesce
8017       coalesce = true;
8018       break;
8019     }
8020     default:
8021      ShouldNotReachHere();
8022   }
8023 
8024   // Should the current free range be coalesced?
8025   // If the chunk is in a free range and either we decided to coalesce above
8026   // or the chunk is near the large block at the end of the heap
8027   // (isNearLargestChunk() returns true), then coalesce this chunk.
8028   bool doCoalesce = inFreeRange() &&
8029     (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8030   if (doCoalesce) {
8031     // Coalesce the current free range on the left with the new
8032     // chunk on the right.  If either is on a free list,
8033     // it must be removed from the list and stashed in the closure.
8034     if (freeRangeInFreeLists()) {
8035       FreeChunk* ffc = (FreeChunk*)freeFinger();
8036       assert(ffc->size() == pointer_delta(addr, freeFinger()),
8037         "Size of free range is inconsistent with chunk size.");
8038       if (CMSTestInFreeList) {
8039         assert(_sp->verifyChunkInFreeLists(ffc),
8040           "Chunk is not in free lists");
8041       }
8042       _sp->coalDeath(ffc->size());
8043       _sp->removeFreeChunkFromFreeLists(ffc);
8044       set_freeRangeInFreeLists(false);
8045     }
8046     if (fcInFreeLists) {
8047       _sp->coalDeath(chunkSize);
8048       assert(fc->size() == chunkSize,
8049         "The chunk has the wrong size or is not in the free lists");
8050       _sp->removeFreeChunkFromFreeLists(fc);
8051     }
8052     set_lastFreeRangeCoalesced(true);
8053   } else {  // not in a free range and/or should not coalesce
8054     // Return the current free range and start a new one.
8055     if (inFreeRange()) {
8056       // In a free range but cannot coalesce with the right hand chunk.
8057       // Put the current free range into the free lists.
8058       flushCurFreeChunk(freeFinger(),
8059         pointer_delta(addr, freeFinger()));
8060     }
8061     // Set up for new free range.  Pass along whether the right hand
8062     // chunk is in the free lists.
8063     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8064   }
8065 }
8066 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8067   assert(inFreeRange(), "Should only be called if currently in a free range.");
8068   assert(size > 0,
8069     "A zero sized chunk cannot be added to the free lists.");
8070   if (!freeRangeInFreeLists()) {
8071     if(CMSTestInFreeList) {
8072       FreeChunk* fc = (FreeChunk*) chunk;
8073       fc->setSize(size);
8074       assert(!_sp->verifyChunkInFreeLists(fc),
8075         "chunk should not be in free lists yet");
8076     }
8077     if (CMSTraceSweeper) {
8078       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8079                     chunk, size);
8080     }
8081     // A new free range is going to be starting.  The current
8082     // free range has not been added to the free lists yet or
8083     // was removed so add it back.
8084     // If the current free range was coalesced, then the death
8085     // of the free range was recorded.  Record a birth now.
8086     if (lastFreeRangeCoalesced()) {
8087       _sp->coalBirth(size);
8088     }
8089     _sp->addChunkAndRepairOffsetTable(chunk, size,
8090             lastFreeRangeCoalesced());
8091   }
8092   set_inFreeRange(false);
8093   set_freeRangeInFreeLists(false);
8094 }
8095 
8096 // We take a break if we've been at this for a while,
8097 // so as to avoid monopolizing the locks involved.
8098 void SweepClosure::do_yield_work(HeapWord* addr) {
8099   // Return current free chunk being used for coalescing (if any)
8100   // to the appropriate freelist.  After yielding, the next
8101   // free block encountered will start a coalescing range of
8102   // free blocks.  If the next free block is adjacent to the
8103   // chunk just flushed, they will need to wait for the next
8104   // sweep to be coalesced.
8105   if (inFreeRange()) {
8106     flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8107   }
8108 
8109   // First give up the locks, then yield, then re-lock.
8110   // We should probably use a constructor/destructor idiom to
8111   // do this unlock/lock or modify the MutexUnlocker class to
8112   // serve our purpose. XXX
8113   assert_lock_strong(_bitMap->lock());
8114   assert_lock_strong(_freelistLock);
8115   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8116          "CMS thread should hold CMS token");
8117   _bitMap->lock()->unlock();
8118   _freelistLock->unlock();
8119   ConcurrentMarkSweepThread::desynchronize(true);
8120   ConcurrentMarkSweepThread::acknowledge_yield_request();
8121   _collector->stopTimer();
8122   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8123   if (PrintCMSStatistics != 0) {
8124     _collector->incrementYields();
8125   }
8126   _collector->icms_wait();
8127 
8128   // See the comment in coordinator_yield()
8129   for (unsigned i = 0; i < CMSYieldSleepCount &&
8130                        ConcurrentMarkSweepThread::should_yield() &&
8131                        !CMSCollector::foregroundGCIsActive(); ++i) {
8132     os::sleep(Thread::current(), 1, false);
8133     ConcurrentMarkSweepThread::acknowledge_yield_request();
8134   }
8135 
8136   ConcurrentMarkSweepThread::synchronize(true);
8137   _freelistLock->lock();
8138   _bitMap->lock()->lock_without_safepoint_check();
8139   _collector->startTimer();
8140 }
8141 
8142 #ifndef PRODUCT
8143 // This is actually very useful in a product build if it can
8144 // be called from the debugger.  Compile it into the product
8145 // as needed.
8146 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8147   return debug_cms_space->verifyChunkInFreeLists(fc);
8148 }
8149 
8150 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8151   if (CMSTraceSweeper) {
8152     gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8153   }
8154 }
8155 #endif
8156 
8157 // CMSIsAliveClosure
8158 bool CMSIsAliveClosure::do_object_b(oop obj) {
8159   HeapWord* addr = (HeapWord*)obj;
8160   return addr != NULL &&
8161          (!_span.contains(addr) || _bit_map->isMarked(addr));
8162 }
8163 
8164 // CMSKeepAliveClosure: the serial version
8165 void CMSKeepAliveClosure::do_oop(oop* p) {
8166   oop this_oop = *p;
8167   HeapWord* addr = (HeapWord*)this_oop;
8168   if (_span.contains(addr) &&
8169       !_bit_map->isMarked(addr)) {
8170     _bit_map->mark(addr);
8171     bool simulate_overflow = false;
8172     NOT_PRODUCT(
8173       if (CMSMarkStackOverflowALot &&
8174           _collector->simulate_overflow()) {
8175         // simulate a stack overflow
8176         simulate_overflow = true;
8177       }
8178     )
8179     if (simulate_overflow || !_mark_stack->push(this_oop)) {
8180       _collector->push_on_overflow_list(this_oop);
8181       _collector->_ser_kac_ovflw++;
8182     }
8183   }
8184 }
8185 
8186 // CMSParKeepAliveClosure: a parallel version of the above.
8187 // The work queues are private to each closure (thread),
8188 // but (may be) available for stealing by other threads.
8189 void CMSParKeepAliveClosure::do_oop(oop* p) {
8190   oop this_oop = *p;
8191   HeapWord* addr = (HeapWord*)this_oop;
8192   if (_span.contains(addr) &&
8193       !_bit_map->isMarked(addr)) {
8194     // In general, during recursive tracing, several threads
8195     // may be concurrently getting here; the first one to
8196     // "tag" it, claims it.
8197     if (_bit_map->par_mark(addr)) {
8198       bool res = _work_queue->push(this_oop);
8199       assert(res, "Low water mark should be much less than capacity");
8200       // Do a recursive trim in the hope that this will keep
8201       // stack usage lower, but leave some oops for potential stealers
8202       trim_queue(_low_water_mark);
8203     } // Else, another thread got there first
8204   }
8205 }
8206 
8207 void CMSParKeepAliveClosure::trim_queue(uint max) {
8208   while (_work_queue->size() > max) {
8209     oop new_oop;
8210     if (_work_queue->pop_local(new_oop)) {
8211       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8212       assert(_bit_map->isMarked((HeapWord*)new_oop),
8213              "no white objects on this stack!");
8214       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8215       // iterate over the oops in this oop, marking and pushing
8216       // the ones in CMS heap (i.e. in _span).
8217       new_oop->oop_iterate(&_mark_and_push);
8218     }
8219   }
8220 }
8221 
8222 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) {
8223   oop this_oop = *p;
8224   HeapWord* addr = (HeapWord*)this_oop;
8225   if (_span.contains(addr) &&
8226       !_bit_map->isMarked(addr)) {
8227     if (_bit_map->par_mark(addr)) {
8228       bool simulate_overflow = false;
8229       NOT_PRODUCT(
8230         if (CMSMarkStackOverflowALot &&
8231             _collector->par_simulate_overflow()) {
8232           // simulate a stack overflow
8233           simulate_overflow = true;
8234         }
8235       )
8236       if (simulate_overflow || !_work_queue->push(this_oop)) {
8237         _collector->par_push_on_overflow_list(this_oop);
8238         _collector->_par_kac_ovflw++;
8239       }
8240     } // Else another thread got there already
8241   }
8242 }
8243 
8244 //////////////////////////////////////////////////////////////////
8245 //  CMSExpansionCause                /////////////////////////////
8246 //////////////////////////////////////////////////////////////////
8247 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8248   switch (cause) {
8249     case _no_expansion:
8250       return "No expansion";
8251     case _satisfy_free_ratio:
8252       return "Free ratio";
8253     case _satisfy_promotion:
8254       return "Satisfy promotion";
8255     case _satisfy_allocation:
8256       return "allocation";
8257     case _allocate_par_lab:
8258       return "Par LAB";
8259     case _allocate_par_spooling_space:
8260       return "Par Spooling Space";
8261     case _adaptive_size_policy:
8262       return "Ergonomics";
8263     default:
8264       return "unknown";
8265   }
8266 }
8267 
8268 void CMSDrainMarkingStackClosure::do_void() {
8269   // the max number to take from overflow list at a time
8270   const size_t num = _mark_stack->capacity()/4;
8271   while (!_mark_stack->isEmpty() ||
8272          // if stack is empty, check the overflow list
8273          _collector->take_from_overflow_list(num, _mark_stack)) {
8274     oop this_oop = _mark_stack->pop();
8275     HeapWord* addr = (HeapWord*)this_oop;
8276     assert(_span.contains(addr), "Should be within span");
8277     assert(_bit_map->isMarked(addr), "Should be marked");
8278     assert(this_oop->is_oop(), "Should be an oop");
8279     this_oop->oop_iterate(_keep_alive);
8280   }
8281 }
8282 
8283 void CMSParDrainMarkingStackClosure::do_void() {
8284   // drain queue
8285   trim_queue(0);
8286 }
8287 
8288 // Trim our work_queue so its length is below max at return
8289 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8290   while (_work_queue->size() > max) {
8291     oop new_oop;
8292     if (_work_queue->pop_local(new_oop)) {
8293       assert(new_oop->is_oop(), "Expected an oop");
8294       assert(_bit_map->isMarked((HeapWord*)new_oop),
8295              "no white objects on this stack!");
8296       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8297       // iterate over the oops in this oop, marking and pushing
8298       // the ones in CMS heap (i.e. in _span).
8299       new_oop->oop_iterate(&_mark_and_push);
8300     }
8301   }
8302 }
8303 
8304 ////////////////////////////////////////////////////////////////////
8305 // Support for Marking Stack Overflow list handling and related code
8306 ////////////////////////////////////////////////////////////////////
8307 // Much of the following code is similar in shape and spirit to the
8308 // code used in ParNewGC. We should try and share that code
8309 // as much as possible in the future.
8310 
8311 #ifndef PRODUCT
8312 // Debugging support for CMSStackOverflowALot
8313 
8314 // It's OK to call this multi-threaded;  the worst thing
8315 // that can happen is that we'll get a bunch of closely
8316 // spaced simulated oveflows, but that's OK, in fact
8317 // probably good as it would exercise the overflow code
8318 // under contention.
8319 bool CMSCollector::simulate_overflow() {
8320   if (_overflow_counter-- <= 0) { // just being defensive
8321     _overflow_counter = CMSMarkStackOverflowInterval;
8322     return true;
8323   } else {
8324     return false;
8325   }
8326 }
8327 
8328 bool CMSCollector::par_simulate_overflow() {
8329   return simulate_overflow();
8330 }
8331 #endif
8332 
8333 // Single-threaded
8334 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8335   assert(stack->isEmpty(), "Expected precondition");
8336   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8337   size_t i = num;
8338   oop  cur = _overflow_list;
8339   const markOop proto = markOopDesc::prototype();
8340   NOT_PRODUCT(size_t n = 0;)
8341   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8342     next = oop(cur->mark());
8343     cur->set_mark(proto);   // until proven otherwise
8344     assert(cur->is_oop(), "Should be an oop");
8345     bool res = stack->push(cur);
8346     assert(res, "Bit off more than can chew?");
8347     NOT_PRODUCT(n++;)
8348   }
8349   _overflow_list = cur;
8350 #ifndef PRODUCT
8351   assert(_num_par_pushes >= n, "Too many pops?");
8352   _num_par_pushes -=n;
8353 #endif
8354   return !stack->isEmpty();
8355 }
8356 
8357 // Multi-threaded; use CAS to break off a prefix
8358 bool CMSCollector::par_take_from_overflow_list(size_t num,
8359                                                OopTaskQueue* work_q) {
8360   assert(work_q->size() == 0, "That's the current policy");
8361   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8362   if (_overflow_list == NULL) {
8363     return false;
8364   }
8365   // Grab the entire list; we'll put back a suffix
8366   oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list);
8367   if (prefix == NULL) {  // someone grabbed it before we did ...
8368     // ... we could spin for a short while, but for now we don't
8369     return false;
8370   }
8371   size_t i = num;
8372   oop cur = prefix;
8373   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8374   if (cur->mark() != NULL) {
8375     oop suffix_head = cur->mark(); // suffix will be put back on global list
8376     cur->set_mark(NULL);           // break off suffix
8377     // Find tail of suffix so we can prepend suffix to global list
8378     for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8379     oop suffix_tail = cur;
8380     assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8381            "Tautology");
8382     oop observed_overflow_list = _overflow_list;
8383     do {
8384       cur = observed_overflow_list;
8385       suffix_tail->set_mark(markOop(cur));
8386       observed_overflow_list =
8387         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur);
8388     } while (cur != observed_overflow_list);
8389   }
8390 
8391   // Push the prefix elements on work_q
8392   assert(prefix != NULL, "control point invariant");
8393   const markOop proto = markOopDesc::prototype();
8394   oop next;
8395   NOT_PRODUCT(size_t n = 0;)
8396   for (cur = prefix; cur != NULL; cur = next) {
8397     next = oop(cur->mark());
8398     cur->set_mark(proto);   // until proven otherwise
8399     assert(cur->is_oop(), "Should be an oop");
8400     bool res = work_q->push(cur);
8401     assert(res, "Bit off more than we can chew?");
8402     NOT_PRODUCT(n++;)
8403   }
8404 #ifndef PRODUCT
8405   assert(_num_par_pushes >= n, "Too many pops?");
8406   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8407 #endif
8408   return true;
8409 }
8410 
8411 // Single-threaded
8412 void CMSCollector::push_on_overflow_list(oop p) {
8413   NOT_PRODUCT(_num_par_pushes++;)
8414   assert(p->is_oop(), "Not an oop");
8415   preserve_mark_if_necessary(p);
8416   p->set_mark((markOop)_overflow_list);
8417   _overflow_list = p;
8418 }
8419 
8420 // Multi-threaded; use CAS to prepend to overflow list
8421 void CMSCollector::par_push_on_overflow_list(oop p) {
8422   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8423   assert(p->is_oop(), "Not an oop");
8424   par_preserve_mark_if_necessary(p);
8425   oop observed_overflow_list = _overflow_list;
8426   oop cur_overflow_list;
8427   do {
8428     cur_overflow_list = observed_overflow_list;
8429     p->set_mark(markOop(cur_overflow_list));
8430     observed_overflow_list =
8431       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8432   } while (cur_overflow_list != observed_overflow_list);
8433 }
8434 
8435 // Single threaded
8436 // General Note on GrowableArray: pushes may silently fail
8437 // because we are (temporarily) out of C-heap for expanding
8438 // the stack. The problem is quite ubiquitous and affects
8439 // a lot of code in the JVM. The prudent thing for GrowableArray
8440 // to do (for now) is to exit with an error. However, that may
8441 // be too draconian in some cases because the caller may be
8442 // able to recover without much harm. For suych cases, we
8443 // should probably introduce a "soft_push" method which returns
8444 // an indication of success or failure with the assumption that
8445 // the caller may be able to recover from a failure; code in
8446 // the VM can then be changed, incrementally, to deal with such
8447 // failures where possible, thus, incrementally hardening the VM
8448 // in such low resource situations.
8449 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8450   int PreserveMarkStackSize = 128;
8451 
8452   if (_preserved_oop_stack == NULL) {
8453     assert(_preserved_mark_stack == NULL,
8454            "bijection with preserved_oop_stack");
8455     // Allocate the stacks
8456     _preserved_oop_stack  = new (ResourceObj::C_HEAP)
8457       GrowableArray<oop>(PreserveMarkStackSize, true);
8458     _preserved_mark_stack = new (ResourceObj::C_HEAP)
8459       GrowableArray<markOop>(PreserveMarkStackSize, true);
8460     if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8461       vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8462                             "Preserved Mark/Oop Stack for CMS (C-heap)");
8463     }
8464   }
8465   _preserved_oop_stack->push(p);
8466   _preserved_mark_stack->push(m);
8467   assert(m == p->mark(), "Mark word changed");
8468   assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8469          "bijection");
8470 }
8471 
8472 // Single threaded
8473 void CMSCollector::preserve_mark_if_necessary(oop p) {
8474   markOop m = p->mark();
8475   if (m->must_be_preserved(p)) {
8476     preserve_mark_work(p, m);
8477   }
8478 }
8479 
8480 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8481   markOop m = p->mark();
8482   if (m->must_be_preserved(p)) {
8483     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8484     // Even though we read the mark word without holding
8485     // the lock, we are assured that it will not change
8486     // because we "own" this oop, so no other thread can
8487     // be trying to push it on the overflow list; see
8488     // the assertion in preserve_mark_work() that checks
8489     // that m == p->mark().
8490     preserve_mark_work(p, m);
8491   }
8492 }
8493 
8494 // We should be able to do this multi-threaded,
8495 // a chunk of stack being a task (this is
8496 // correct because each oop only ever appears
8497 // once in the overflow list. However, it's
8498 // not very easy to completely overlap this with
8499 // other operations, so will generally not be done
8500 // until all work's been completed. Because we
8501 // expect the preserved oop stack (set) to be small,
8502 // it's probably fine to do this single-threaded.
8503 // We can explore cleverer concurrent/overlapped/parallel
8504 // processing of preserved marks if we feel the
8505 // need for this in the future. Stack overflow should
8506 // be so rare in practice and, when it happens, its
8507 // effect on performance so great that this will
8508 // likely just be in the noise anyway.
8509 void CMSCollector::restore_preserved_marks_if_any() {
8510   if (_preserved_oop_stack == NULL) {
8511     assert(_preserved_mark_stack == NULL,
8512            "bijection with preserved_oop_stack");
8513     return;
8514   }
8515 
8516   assert(SafepointSynchronize::is_at_safepoint(),
8517          "world should be stopped");
8518   assert(Thread::current()->is_ConcurrentGC_thread() ||
8519          Thread::current()->is_VM_thread(),
8520          "should be single-threaded");
8521 
8522   int length = _preserved_oop_stack->length();
8523   assert(_preserved_mark_stack->length() == length, "bijection");
8524   for (int i = 0; i < length; i++) {
8525     oop p = _preserved_oop_stack->at(i);
8526     assert(p->is_oop(), "Should be an oop");
8527     assert(_span.contains(p), "oop should be in _span");
8528     assert(p->mark() == markOopDesc::prototype(),
8529            "Set when taken from overflow list");
8530     markOop m = _preserved_mark_stack->at(i);
8531     p->set_mark(m);
8532   }
8533   _preserved_mark_stack->clear();
8534   _preserved_oop_stack->clear();
8535   assert(_preserved_mark_stack->is_empty() &&
8536          _preserved_oop_stack->is_empty(),
8537          "stacks were cleared above");
8538 }
8539 
8540 #ifndef PRODUCT
8541 bool CMSCollector::no_preserved_marks() const {
8542   return (   (   _preserved_mark_stack == NULL
8543               && _preserved_oop_stack == NULL)
8544           || (   _preserved_mark_stack->is_empty()
8545               && _preserved_oop_stack->is_empty()));
8546 }
8547 #endif
8548 
8549 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8550 {
8551   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8552   CMSAdaptiveSizePolicy* size_policy =
8553     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8554   assert(size_policy->is_gc_cms_adaptive_size_policy(),
8555     "Wrong type for size policy");
8556   return size_policy;
8557 }
8558 
8559 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8560                                            size_t desired_promo_size) {
8561   if (cur_promo_size < desired_promo_size) {
8562     size_t expand_bytes = desired_promo_size - cur_promo_size;
8563     if (PrintAdaptiveSizePolicy && Verbose) {
8564       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8565         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8566         expand_bytes);
8567     }
8568     expand(expand_bytes,
8569            MinHeapDeltaBytes,
8570            CMSExpansionCause::_adaptive_size_policy);
8571   } else if (desired_promo_size < cur_promo_size) {
8572     size_t shrink_bytes = cur_promo_size - desired_promo_size;
8573     if (PrintAdaptiveSizePolicy && Verbose) {
8574       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8575         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8576         shrink_bytes);
8577     }
8578     shrink(shrink_bytes);
8579   }
8580 }
8581 
8582 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8583   GenCollectedHeap* gch = GenCollectedHeap::heap();
8584   CMSGCAdaptivePolicyCounters* counters =
8585     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8586   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8587     "Wrong kind of counters");
8588   return counters;
8589 }
8590 
8591 
8592 void ASConcurrentMarkSweepGeneration::update_counters() {
8593   if (UsePerfData) {
8594     _space_counters->update_all();
8595     _gen_counters->update_all();
8596     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8597     GenCollectedHeap* gch = GenCollectedHeap::heap();
8598     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8599     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8600       "Wrong gc statistics type");
8601     counters->update_counters(gc_stats_l);
8602   }
8603 }
8604 
8605 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8606   if (UsePerfData) {
8607     _space_counters->update_used(used);
8608     _space_counters->update_capacity();
8609     _gen_counters->update_all();
8610 
8611     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8612     GenCollectedHeap* gch = GenCollectedHeap::heap();
8613     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8614     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8615       "Wrong gc statistics type");
8616     counters->update_counters(gc_stats_l);
8617   }
8618 }
8619 
8620 // The desired expansion delta is computed so that:
8621 // . desired free percentage or greater is used
8622 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8623   assert_locked_or_safepoint(Heap_lock);
8624 
8625   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8626 
8627   // If incremental collection failed, we just want to expand
8628   // to the limit.
8629   if (incremental_collection_failed()) {
8630     clear_incremental_collection_failed();
8631     grow_to_reserved();
8632     return;
8633   }
8634 
8635   assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8636 
8637   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8638     "Wrong type of heap");
8639   int prev_level = level() - 1;
8640   assert(prev_level >= 0, "The cms generation is the lowest generation");
8641   Generation* prev_gen = gch->get_gen(prev_level);
8642   assert(prev_gen->kind() == Generation::ASParNew,
8643     "Wrong type of young generation");
8644   ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8645   size_t cur_eden = younger_gen->eden()->capacity();
8646   CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8647   size_t cur_promo = free();
8648   size_policy->compute_tenured_generation_free_space(cur_promo,
8649                                                        max_available(),
8650                                                        cur_eden);
8651   resize(cur_promo, size_policy->promo_size());
8652 
8653   // Record the new size of the space in the cms generation
8654   // that is available for promotions.  This is temporary.
8655   // It should be the desired promo size.
8656   size_policy->avg_cms_promo()->sample(free());
8657   size_policy->avg_old_live()->sample(used());
8658 
8659   if (UsePerfData) {
8660     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8661     counters->update_cms_capacity_counter(capacity());
8662   }
8663 }
8664 
8665 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
8666   assert_locked_or_safepoint(Heap_lock);
8667   assert_lock_strong(freelistLock());
8668   HeapWord* old_end = _cmsSpace->end();
8669   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
8670   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
8671   FreeChunk* chunk_at_end = find_chunk_at_end();
8672   if (chunk_at_end == NULL) {
8673     // No room to shrink
8674     if (PrintGCDetails && Verbose) {
8675       gclog_or_tty->print_cr("No room to shrink: old_end  "
8676         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
8677         " chunk_at_end  " PTR_FORMAT,
8678         old_end, unallocated_start, chunk_at_end);
8679     }
8680     return;
8681   } else {
8682 
8683     // Find the chunk at the end of the space and determine
8684     // how much it can be shrunk.
8685     size_t shrinkable_size_in_bytes = chunk_at_end->size();
8686     size_t aligned_shrinkable_size_in_bytes =
8687       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
8688     assert(unallocated_start <= chunk_at_end->end(),
8689       "Inconsistent chunk at end of space");
8690     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
8691     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
8692 
8693     // Shrink the underlying space
8694     _virtual_space.shrink_by(bytes);
8695     if (PrintGCDetails && Verbose) {
8696       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
8697         " desired_bytes " SIZE_FORMAT
8698         " shrinkable_size_in_bytes " SIZE_FORMAT
8699         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
8700         "  bytes  " SIZE_FORMAT,
8701         desired_bytes, shrinkable_size_in_bytes,
8702         aligned_shrinkable_size_in_bytes, bytes);
8703       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
8704         "  unallocated_start  " SIZE_FORMAT,
8705         old_end, unallocated_start);
8706     }
8707 
8708     // If the space did shrink (shrinking is not guaranteed),
8709     // shrink the chunk at the end by the appropriate amount.
8710     if (((HeapWord*)_virtual_space.high()) < old_end) {
8711       size_t new_word_size =
8712         heap_word_size(_virtual_space.committed_size());
8713 
8714       // Have to remove the chunk from the dictionary because it is changing
8715       // size and might be someplace elsewhere in the dictionary.
8716 
8717       // Get the chunk at end, shrink it, and put it
8718       // back.
8719       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
8720       size_t word_size_change = word_size_before - new_word_size;
8721       size_t chunk_at_end_old_size = chunk_at_end->size();
8722       assert(chunk_at_end_old_size >= word_size_change,
8723         "Shrink is too large");
8724       chunk_at_end->setSize(chunk_at_end_old_size -
8725                           word_size_change);
8726       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
8727         word_size_change);
8728 
8729       _cmsSpace->returnChunkToDictionary(chunk_at_end);
8730 
8731       MemRegion mr(_cmsSpace->bottom(), new_word_size);
8732       _bts->resize(new_word_size);  // resize the block offset shared array
8733       Universe::heap()->barrier_set()->resize_covered_region(mr);
8734       _cmsSpace->assert_locked();
8735       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
8736 
8737       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
8738 
8739       // update the space and generation capacity counters
8740       if (UsePerfData) {
8741         _space_counters->update_capacity();
8742         _gen_counters->update_all();
8743       }
8744 
8745       if (Verbose && PrintGCDetails) {
8746         size_t new_mem_size = _virtual_space.committed_size();
8747         size_t old_mem_size = new_mem_size + bytes;
8748         gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
8749                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
8750       }
8751     }
8752 
8753     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
8754       "Inconsistency at end of space");
8755     assert(chunk_at_end->end() == _cmsSpace->end(),
8756       "Shrinking is inconsistent");
8757     return;
8758   }
8759 }
8760 
8761 // Transfer some number of overflown objects to usual marking
8762 // stack. Return true if some objects were transferred.
8763 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8764   size_t num = MIN2((size_t)_mark_stack->capacity()/4,
8765                     (size_t)ParGCDesiredObjsFromOverflowList);
8766 
8767   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8768   assert(_collector->overflow_list_is_empty() || res,
8769          "If list is not empty, we should have taken something");
8770   assert(!res || !_mark_stack->isEmpty(),
8771          "If we took something, it should now be on our stack");
8772   return res;
8773 }
8774 
8775 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8776   size_t res = _sp->block_size_no_stall(addr, _collector);
8777   assert(res != 0, "Should always be able to compute a size");
8778   if (_sp->block_is_obj(addr)) {
8779     if (_live_bit_map->isMarked(addr)) {
8780       // It can't have been dead in a previous cycle
8781       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8782     } else {
8783       _dead_bit_map->mark(addr);      // mark the dead object
8784     }
8785   }
8786   return res;
8787 }