1 /*
   2  * Copyright (c) 2001, 2019, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderDataGraph.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "code/codeCache.hpp"
  29 #include "gc/cms/cmsGCStats.hpp"
  30 #include "gc/cms/cmsHeap.hpp"
  31 #include "gc/cms/cmsOopClosures.inline.hpp"
  32 #include "gc/cms/cmsVMOperations.hpp"
  33 #include "gc/cms/compactibleFreeListSpace.hpp"
  34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc/cms/concurrentMarkSweepThread.hpp"
  36 #include "gc/cms/parNewGeneration.hpp"
  37 #include "gc/cms/promotionInfo.inline.hpp"
  38 #include "gc/serial/genMarkSweep.hpp"
  39 #include "gc/serial/tenuredGeneration.hpp"
  40 #include "gc/shared/adaptiveSizePolicy.hpp"
  41 #include "gc/shared/cardGeneration.inline.hpp"
  42 #include "gc/shared/cardTableRS.hpp"
  43 #include "gc/shared/collectedHeap.inline.hpp"
  44 #include "gc/shared/collectorCounters.hpp"
  45 #include "gc/shared/gcLocker.hpp"
  46 #include "gc/shared/gcPolicyCounters.hpp"
  47 #include "gc/shared/gcTimer.hpp"
  48 #include "gc/shared/gcTrace.hpp"
  49 #include "gc/shared/gcTraceTime.inline.hpp"
  50 #include "gc/shared/genCollectedHeap.hpp"
  51 #include "gc/shared/genOopClosures.inline.hpp"
  52 #include "gc/shared/isGCActiveMark.hpp"
  53 #include "gc/shared/owstTaskTerminator.hpp"
  54 #include "gc/shared/referencePolicy.hpp"
  55 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  56 #include "gc/shared/space.inline.hpp"
  57 #include "gc/shared/strongRootsScope.hpp"
  58 #include "gc/shared/taskqueue.inline.hpp"
  59 #include "gc/shared/weakProcessor.hpp"
  60 #include "gc/shared/workerPolicy.hpp"
  61 #include "logging/log.hpp"
  62 #include "logging/logStream.hpp"
  63 #include "memory/allocation.hpp"
  64 #include "memory/binaryTreeDictionary.inline.hpp"
  65 #include "memory/iterator.inline.hpp"
  66 #include "memory/padded.hpp"
  67 #include "memory/resourceArea.hpp"
  68 #include "memory/universe.hpp"
  69 #include "oops/access.inline.hpp"
  70 #include "oops/oop.inline.hpp"
  71 #include "prims/jvmtiExport.hpp"
  72 #include "runtime/atomic.hpp"
  73 #include "runtime/flags/flagSetting.hpp"
  74 #include "runtime/globals_extension.hpp"
  75 #include "runtime/handles.inline.hpp"
  76 #include "runtime/java.hpp"
  77 #include "runtime/orderAccess.hpp"
  78 #include "runtime/timer.hpp"
  79 #include "runtime/vmThread.hpp"
  80 #include "services/memoryService.hpp"
  81 #include "services/runtimeService.hpp"
  82 #include "utilities/align.hpp"
  83 #include "utilities/stack.inline.hpp"
  84 #if INCLUDE_JVMCI
  85 #include "jvmci/jvmci.hpp"
  86 #endif
  87 
  88 // statics
  89 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  90 bool CMSCollector::_full_gc_requested = false;
  91 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  92 
  93 //////////////////////////////////////////////////////////////////
  94 // In support of CMS/VM thread synchronization
  95 //////////////////////////////////////////////////////////////////
  96 // We split use of the CGC_lock into 2 "levels".
  97 // The low-level locking is of the usual CGC_lock monitor. We introduce
  98 // a higher level "token" (hereafter "CMS token") built on top of the
  99 // low level monitor (hereafter "CGC lock").
 100 // The token-passing protocol gives priority to the VM thread. The
 101 // CMS-lock doesn't provide any fairness guarantees, but clients
 102 // should ensure that it is only held for very short, bounded
 103 // durations.
 104 //
 105 // When either of the CMS thread or the VM thread is involved in
 106 // collection operations during which it does not want the other
 107 // thread to interfere, it obtains the CMS token.
 108 //
 109 // If either thread tries to get the token while the other has
 110 // it, that thread waits. However, if the VM thread and CMS thread
 111 // both want the token, then the VM thread gets priority while the
 112 // CMS thread waits. This ensures, for instance, that the "concurrent"
 113 // phases of the CMS thread's work do not block out the VM thread
 114 // for long periods of time as the CMS thread continues to hog
 115 // the token. (See bug 4616232).
 116 //
 117 // The baton-passing functions are, however, controlled by the
 118 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 119 // and here the low-level CMS lock, not the high level token,
 120 // ensures mutual exclusion.
 121 //
 122 // Two important conditions that we have to satisfy:
 123 // 1. if a thread does a low-level wait on the CMS lock, then it
 124 //    relinquishes the CMS token if it were holding that token
 125 //    when it acquired the low-level CMS lock.
 126 // 2. any low-level notifications on the low-level lock
 127 //    should only be sent when a thread has relinquished the token.
 128 //
 129 // In the absence of either property, we'd have potential deadlock.
 130 //
 131 // We protect each of the CMS (concurrent and sequential) phases
 132 // with the CMS _token_, not the CMS _lock_.
 133 //
 134 // The only code protected by CMS lock is the token acquisition code
 135 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 136 // baton-passing code.
 137 //
 138 // Unfortunately, i couldn't come up with a good abstraction to factor and
 139 // hide the naked CGC_lock manipulation in the baton-passing code
 140 // further below. That's something we should try to do. Also, the proof
 141 // of correctness of this 2-level locking scheme is far from obvious,
 142 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 143 // that there may be a theoretical possibility of delay/starvation in the
 144 // low-level lock/wait/notify scheme used for the baton-passing because of
 145 // potential interference with the priority scheme embodied in the
 146 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 147 // invocation further below and marked with "XXX 20011219YSR".
 148 // Indeed, as we note elsewhere, this may become yet more slippery
 149 // in the presence of multiple CMS and/or multiple VM threads. XXX
 150 
 151 class CMSTokenSync: public StackObj {
 152  private:
 153   bool _is_cms_thread;
 154  public:
 155   CMSTokenSync(bool is_cms_thread):
 156     _is_cms_thread(is_cms_thread) {
 157     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 158            "Incorrect argument to constructor");
 159     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 160   }
 161 
 162   ~CMSTokenSync() {
 163     assert(_is_cms_thread ?
 164              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 165              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 166           "Incorrect state");
 167     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 168   }
 169 };
 170 
 171 // Convenience class that does a CMSTokenSync, and then acquires
 172 // upto three locks.
 173 class CMSTokenSyncWithLocks: public CMSTokenSync {
 174  private:
 175   // Note: locks are acquired in textual declaration order
 176   // and released in the opposite order
 177   MutexLocker _locker1, _locker2, _locker3;
 178  public:
 179   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 180                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 181     CMSTokenSync(is_cms_thread),
 182     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 183     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 184     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 185   { }
 186 };
 187 
 188 
 189 //////////////////////////////////////////////////////////////////
 190 //  Concurrent Mark-Sweep Generation /////////////////////////////
 191 //////////////////////////////////////////////////////////////////
 192 
 193 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 194 
 195 // This struct contains per-thread things necessary to support parallel
 196 // young-gen collection.
 197 class CMSParGCThreadState: public CHeapObj<mtGC> {
 198  public:
 199   CompactibleFreeListSpaceLAB lab;
 200   PromotionInfo promo;
 201 
 202   // Constructor.
 203   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 204     promo.setSpace(cfls);
 205   }
 206 };
 207 
 208 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 209      ReservedSpace rs,
 210      size_t initial_byte_size,
 211      size_t min_byte_size,
 212      size_t max_byte_size,
 213      CardTableRS* ct) :
 214   CardGeneration(rs, initial_byte_size, ct),
 215   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 216   _did_compact(false)
 217 {
 218   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 219   HeapWord* end    = (HeapWord*) _virtual_space.high();
 220 
 221   _direct_allocated_words = 0;
 222   NOT_PRODUCT(
 223     _numObjectsPromoted = 0;
 224     _numWordsPromoted = 0;
 225     _numObjectsAllocated = 0;
 226     _numWordsAllocated = 0;
 227   )
 228 
 229   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 230   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 231   _cmsSpace->_old_gen = this;
 232 
 233   _gc_stats = new CMSGCStats();
 234 
 235   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 236   // offsets match. The ability to tell free chunks from objects
 237   // depends on this property.
 238   debug_only(
 239     FreeChunk* junk = NULL;
 240     assert(UseCompressedClassPointers ||
 241            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 242            "Offset of FreeChunk::_prev within FreeChunk must match"
 243            "  that of OopDesc::_klass within OopDesc");
 244   )
 245 
 246   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 247   for (uint i = 0; i < ParallelGCThreads; i++) {
 248     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 249   }
 250 
 251   _incremental_collection_failed = false;
 252   // The "dilatation_factor" is the expansion that can occur on
 253   // account of the fact that the minimum object size in the CMS
 254   // generation may be larger than that in, say, a contiguous young
 255   //  generation.
 256   // Ideally, in the calculation below, we'd compute the dilatation
 257   // factor as: MinChunkSize/(promoting_gen's min object size)
 258   // Since we do not have such a general query interface for the
 259   // promoting generation, we'll instead just use the minimum
 260   // object size (which today is a header's worth of space);
 261   // note that all arithmetic is in units of HeapWords.
 262   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 263   assert(_dilatation_factor >= 1.0, "from previous assert");
 264 
 265   initialize_performance_counters(min_byte_size, max_byte_size);
 266 }
 267 
 268 
 269 // The field "_initiating_occupancy" represents the occupancy percentage
 270 // at which we trigger a new collection cycle.  Unless explicitly specified
 271 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 272 // is calculated by:
 273 //
 274 //   Let "f" be MinHeapFreeRatio in
 275 //
 276 //    _initiating_occupancy = 100-f +
 277 //                           f * (CMSTriggerRatio/100)
 278 //   where CMSTriggerRatio is the argument "tr" below.
 279 //
 280 // That is, if we assume the heap is at its desired maximum occupancy at the
 281 // end of a collection, we let CMSTriggerRatio of the (purported) free
 282 // space be allocated before initiating a new collection cycle.
 283 //
 284 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 285   assert(io <= 100 && tr <= 100, "Check the arguments");
 286   if (io >= 0) {
 287     _initiating_occupancy = (double)io / 100.0;
 288   } else {
 289     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 290                              (double)(tr * MinHeapFreeRatio) / 100.0)
 291                             / 100.0;
 292   }
 293 }
 294 
 295 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 296   assert(collector() != NULL, "no collector");
 297   collector()->ref_processor_init();
 298 }
 299 
 300 void CMSCollector::ref_processor_init() {
 301   if (_ref_processor == NULL) {
 302     // Allocate and initialize a reference processor
 303     _ref_processor =
 304       new ReferenceProcessor(&_span_based_discoverer,
 305                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 306                              ParallelGCThreads,                      // mt processing degree
 307                              _cmsGen->refs_discovery_is_mt(),        // mt discovery
 308                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 309                              _cmsGen->refs_discovery_is_atomic(),    // discovery is not atomic
 310                              &_is_alive_closure,                     // closure for liveness info
 311                              false);                                 // disable adjusting number of processing threads
 312     // Initialize the _ref_processor field of CMSGen
 313     _cmsGen->set_ref_processor(_ref_processor);
 314 
 315   }
 316 }
 317 
 318 AdaptiveSizePolicy* CMSCollector::size_policy() {
 319   return CMSHeap::heap()->size_policy();
 320 }
 321 
 322 void ConcurrentMarkSweepGeneration::initialize_performance_counters(size_t min_old_size,
 323                                                                     size_t max_old_size) {
 324 
 325   const char* gen_name = "old";
 326   // Generation Counters - generation 1, 1 subspace
 327   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 328       min_old_size, max_old_size, &_virtual_space);
 329 
 330   _space_counters = new GSpaceCounters(gen_name, 0,
 331                                        _virtual_space.reserved_size(),
 332                                        this, _gen_counters);
 333 }
 334 
 335 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 336   _cms_gen(cms_gen)
 337 {
 338   assert(alpha <= 100, "bad value");
 339   _saved_alpha = alpha;
 340 
 341   // Initialize the alphas to the bootstrap value of 100.
 342   _gc0_alpha = _cms_alpha = 100;
 343 
 344   _cms_begin_time.update();
 345   _cms_end_time.update();
 346 
 347   _gc0_duration = 0.0;
 348   _gc0_period = 0.0;
 349   _gc0_promoted = 0;
 350 
 351   _cms_duration = 0.0;
 352   _cms_period = 0.0;
 353   _cms_allocated = 0;
 354 
 355   _cms_used_at_gc0_begin = 0;
 356   _cms_used_at_gc0_end = 0;
 357   _allow_duty_cycle_reduction = false;
 358   _valid_bits = 0;
 359 }
 360 
 361 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 362   // TBD: CR 6909490
 363   return 1.0;
 364 }
 365 
 366 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 367 }
 368 
 369 // If promotion failure handling is on use
 370 // the padded average size of the promotion for each
 371 // young generation collection.
 372 double CMSStats::time_until_cms_gen_full() const {
 373   size_t cms_free = _cms_gen->cmsSpace()->free();
 374   CMSHeap* heap = CMSHeap::heap();
 375   size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
 376                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 377   if (cms_free > expected_promotion) {
 378     // Start a cms collection if there isn't enough space to promote
 379     // for the next young collection.  Use the padded average as
 380     // a safety factor.
 381     cms_free -= expected_promotion;
 382 
 383     // Adjust by the safety factor.
 384     double cms_free_dbl = (double)cms_free;
 385     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 386     // Apply a further correction factor which tries to adjust
 387     // for recent occurance of concurrent mode failures.
 388     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 389     cms_free_dbl = cms_free_dbl * cms_adjustment;
 390 
 391     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 392                   cms_free, expected_promotion);
 393     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 394     // Add 1 in case the consumption rate goes to zero.
 395     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 396   }
 397   return 0.0;
 398 }
 399 
 400 // Compare the duration of the cms collection to the
 401 // time remaining before the cms generation is empty.
 402 // Note that the time from the start of the cms collection
 403 // to the start of the cms sweep (less than the total
 404 // duration of the cms collection) can be used.  This
 405 // has been tried and some applications experienced
 406 // promotion failures early in execution.  This was
 407 // possibly because the averages were not accurate
 408 // enough at the beginning.
 409 double CMSStats::time_until_cms_start() const {
 410   // We add "gc0_period" to the "work" calculation
 411   // below because this query is done (mostly) at the
 412   // end of a scavenge, so we need to conservatively
 413   // account for that much possible delay
 414   // in the query so as to avoid concurrent mode failures
 415   // due to starting the collection just a wee bit too
 416   // late.
 417   double work = cms_duration() + gc0_period();
 418   double deadline = time_until_cms_gen_full();
 419   // If a concurrent mode failure occurred recently, we want to be
 420   // more conservative and halve our expected time_until_cms_gen_full()
 421   if (work > deadline) {
 422     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 423                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 424     return 0.0;
 425   }
 426   return work - deadline;
 427 }
 428 
 429 #ifndef PRODUCT
 430 void CMSStats::print_on(outputStream *st) const {
 431   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 432   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 433                gc0_duration(), gc0_period(), gc0_promoted());
 434   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 435             cms_duration(), cms_period(), cms_allocated());
 436   st->print(",cms_since_beg=%g,cms_since_end=%g",
 437             cms_time_since_begin(), cms_time_since_end());
 438   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 439             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 440 
 441   if (valid()) {
 442     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 443               promotion_rate(), cms_allocation_rate());
 444     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 445               cms_consumption_rate(), time_until_cms_gen_full());
 446   }
 447   st->cr();
 448 }
 449 #endif // #ifndef PRODUCT
 450 
 451 CMSCollector::CollectorState CMSCollector::_collectorState =
 452                              CMSCollector::Idling;
 453 bool CMSCollector::_foregroundGCIsActive = false;
 454 bool CMSCollector::_foregroundGCShouldWait = false;
 455 
 456 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 457                            CardTableRS*                   ct):
 458   _overflow_list(NULL),
 459   _conc_workers(NULL),     // may be set later
 460   _completed_initialization(false),
 461   _collection_count_start(0),
 462   _should_unload_classes(CMSClassUnloadingEnabled),
 463   _concurrent_cycles_since_last_unload(0),
 464   _roots_scanning_options(GenCollectedHeap::SO_None),
 465   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 466   _verifying(false),
 467   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 468   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 469   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 470   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 471   _cms_start_registered(false),
 472   _cmsGen(cmsGen),
 473   // Adjust span to cover old (cms) gen
 474   _span(cmsGen->reserved()),
 475   _ct(ct),
 476   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 477   _modUnionTable((CardTable::card_shift - LogHeapWordSize),
 478                  -1 /* lock-free */, "No_lock" /* dummy */),
 479   _restart_addr(NULL),
 480   _ser_pmc_preclean_ovflw(0),
 481   _ser_pmc_remark_ovflw(0),
 482   _par_pmc_remark_ovflw(0),
 483   _ser_kac_preclean_ovflw(0),
 484   _ser_kac_ovflw(0),
 485   _par_kac_ovflw(0),
 486 #ifndef PRODUCT
 487   _num_par_pushes(0),
 488 #endif
 489   _span_based_discoverer(_span),
 490   _ref_processor(NULL),    // will be set later
 491   // Construct the is_alive_closure with _span & markBitMap
 492   _is_alive_closure(_span, &_markBitMap),
 493   _modUnionClosurePar(&_modUnionTable),
 494   _between_prologue_and_epilogue(false),
 495   _abort_preclean(false),
 496   _start_sampling(false),
 497   _stats(cmsGen),
 498   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 499                              //verify that this lock should be acquired with safepoint check.
 500                              Monitor::_safepoint_check_never)),
 501   _eden_chunk_array(NULL),     // may be set in ctor body
 502   _eden_chunk_index(0),        // -- ditto --
 503   _eden_chunk_capacity(0),     // -- ditto --
 504   _survivor_chunk_array(NULL), // -- ditto --
 505   _survivor_chunk_index(0),    // -- ditto --
 506   _survivor_chunk_capacity(0), // -- ditto --
 507   _survivor_plab_array(NULL)   // -- ditto --
 508 {
 509   // Now expand the span and allocate the collection support structures
 510   // (MUT, marking bit map etc.) to cover both generations subject to
 511   // collection.
 512 
 513   // For use by dirty card to oop closures.
 514   _cmsGen->cmsSpace()->set_collector(this);
 515 
 516   // Allocate MUT and marking bit map
 517   {
 518     MutexLocker x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 519     if (!_markBitMap.allocate(_span)) {
 520       log_warning(gc)("Failed to allocate CMS Bit Map");
 521       return;
 522     }
 523     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 524   }
 525   {
 526     _modUnionTable.allocate(_span);
 527     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 528   }
 529 
 530   if (!_markStack.allocate(MarkStackSize)) {
 531     log_warning(gc)("Failed to allocate CMS Marking Stack");
 532     return;
 533   }
 534 
 535   // Support for multi-threaded concurrent phases
 536   if (CMSConcurrentMTEnabled) {
 537     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 538       // just for now
 539       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 540     }
 541     if (ConcGCThreads > 1) {
 542       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 543                                  ConcGCThreads, true);
 544       if (_conc_workers == NULL) {
 545         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 546         CMSConcurrentMTEnabled = false;
 547       } else {
 548         _conc_workers->initialize_workers();
 549       }
 550     } else {
 551       CMSConcurrentMTEnabled = false;
 552     }
 553   }
 554   if (!CMSConcurrentMTEnabled) {
 555     ConcGCThreads = 0;
 556   } else {
 557     // Turn off CMSCleanOnEnter optimization temporarily for
 558     // the MT case where it's not fixed yet; see 6178663.
 559     CMSCleanOnEnter = false;
 560   }
 561   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 562          "Inconsistency");
 563   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 564   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 565 
 566   // Parallel task queues; these are shared for the
 567   // concurrent and stop-world phases of CMS, but
 568   // are not shared with parallel scavenge (ParNew).
 569   {
 570     uint i;
 571     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 572 
 573     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 574          || ParallelRefProcEnabled)
 575         && num_queues > 0) {
 576       _task_queues = new OopTaskQueueSet(num_queues);
 577       if (_task_queues == NULL) {
 578         log_warning(gc)("task_queues allocation failure.");
 579         return;
 580       }
 581       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 582       for (i = 0; i < num_queues; i++) {
 583         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 584         if (q == NULL) {
 585           log_warning(gc)("work_queue allocation failure.");
 586           return;
 587         }
 588         _task_queues->register_queue(i, q);
 589       }
 590       for (i = 0; i < num_queues; i++) {
 591         _task_queues->queue(i)->initialize();
 592       }
 593     }
 594   }
 595 
 596   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 597 
 598   // Clip CMSBootstrapOccupancy between 0 and 100.
 599   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 600 
 601   // Now tell CMS generations the identity of their collector
 602   ConcurrentMarkSweepGeneration::set_collector(this);
 603 
 604   // Create & start a CMS thread for this CMS collector
 605   _cmsThread = ConcurrentMarkSweepThread::start(this);
 606   assert(cmsThread() != NULL, "CMS Thread should have been created");
 607   assert(cmsThread()->collector() == this,
 608          "CMS Thread should refer to this gen");
 609   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 610 
 611   // Support for parallelizing young gen rescan
 612   CMSHeap* heap = CMSHeap::heap();
 613   _young_gen = heap->young_gen();
 614   if (heap->supports_inline_contig_alloc()) {
 615     _top_addr = heap->top_addr();
 616     _end_addr = heap->end_addr();
 617     assert(_young_gen != NULL, "no _young_gen");
 618     _eden_chunk_index = 0;
 619     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 620     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 621   }
 622 
 623   // Support for parallelizing survivor space rescan
 624   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 625     const size_t max_plab_samples =
 626       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 627 
 628     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 629     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 630     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 631     _survivor_chunk_capacity = max_plab_samples;
 632     for (uint i = 0; i < ParallelGCThreads; i++) {
 633       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 634       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 635       assert(cur->end() == 0, "Should be 0");
 636       assert(cur->array() == vec, "Should be vec");
 637       assert(cur->capacity() == max_plab_samples, "Error");
 638     }
 639   }
 640 
 641   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 642   _gc_counters = new CollectorCounters("CMS full collection pauses", 1);
 643   _cgc_counters = new CollectorCounters("CMS concurrent cycle pauses", 2);
 644   _completed_initialization = true;
 645   _inter_sweep_timer.start();  // start of time
 646 }
 647 
 648 const char* ConcurrentMarkSweepGeneration::name() const {
 649   return "concurrent mark-sweep generation";
 650 }
 651 void ConcurrentMarkSweepGeneration::update_counters() {
 652   if (UsePerfData) {
 653     _space_counters->update_all();
 654     _gen_counters->update_all();
 655   }
 656 }
 657 
 658 // this is an optimized version of update_counters(). it takes the
 659 // used value as a parameter rather than computing it.
 660 //
 661 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 662   if (UsePerfData) {
 663     _space_counters->update_used(used);
 664     _space_counters->update_capacity();
 665     _gen_counters->update_all();
 666   }
 667 }
 668 
 669 void ConcurrentMarkSweepGeneration::print() const {
 670   Generation::print();
 671   cmsSpace()->print();
 672 }
 673 
 674 #ifndef PRODUCT
 675 void ConcurrentMarkSweepGeneration::print_statistics() {
 676   cmsSpace()->printFLCensus(0);
 677 }
 678 #endif
 679 
 680 size_t
 681 ConcurrentMarkSweepGeneration::contiguous_available() const {
 682   // dld proposes an improvement in precision here. If the committed
 683   // part of the space ends in a free block we should add that to
 684   // uncommitted size in the calculation below. Will make this
 685   // change later, staying with the approximation below for the
 686   // time being. -- ysr.
 687   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 688 }
 689 
 690 size_t
 691 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 692   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 693 }
 694 
 695 size_t ConcurrentMarkSweepGeneration::used_stable() const {
 696   return cmsSpace()->used_stable();
 697 }
 698 
 699 size_t ConcurrentMarkSweepGeneration::max_available() const {
 700   return free() + _virtual_space.uncommitted_size();
 701 }
 702 
 703 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 704   size_t available = max_available();
 705   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 706   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 707   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 708                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 709   return res;
 710 }
 711 
 712 // At a promotion failure dump information on block layout in heap
 713 // (cms old generation).
 714 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 715   Log(gc, promotion) log;
 716   if (log.is_trace()) {
 717     LogStream ls(log.trace());
 718     cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
 719   }
 720 }
 721 
 722 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 723   // Clear the promotion information.  These pointers can be adjusted
 724   // along with all the other pointers into the heap but
 725   // compaction is expected to be a rare event with
 726   // a heap using cms so don't do it without seeing the need.
 727   for (uint i = 0; i < ParallelGCThreads; i++) {
 728     _par_gc_thread_states[i]->promo.reset();
 729   }
 730 }
 731 
 732 void ConcurrentMarkSweepGeneration::compute_new_size() {
 733   assert_locked_or_safepoint(Heap_lock);
 734 
 735   // If incremental collection failed, we just want to expand
 736   // to the limit.
 737   if (incremental_collection_failed()) {
 738     clear_incremental_collection_failed();
 739     grow_to_reserved();
 740     return;
 741   }
 742 
 743   // The heap has been compacted but not reset yet.
 744   // Any metric such as free() or used() will be incorrect.
 745 
 746   CardGeneration::compute_new_size();
 747 
 748   // Reset again after a possible resizing
 749   if (did_compact()) {
 750     cmsSpace()->reset_after_compaction();
 751   }
 752 }
 753 
 754 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 755   assert_locked_or_safepoint(Heap_lock);
 756 
 757   // If incremental collection failed, we just want to expand
 758   // to the limit.
 759   if (incremental_collection_failed()) {
 760     clear_incremental_collection_failed();
 761     grow_to_reserved();
 762     return;
 763   }
 764 
 765   double free_percentage = ((double) free()) / capacity();
 766   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 767   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 768 
 769   // compute expansion delta needed for reaching desired free percentage
 770   if (free_percentage < desired_free_percentage) {
 771     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 772     assert(desired_capacity >= capacity(), "invalid expansion size");
 773     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 774     Log(gc) log;
 775     if (log.is_trace()) {
 776       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 777       log.trace("From compute_new_size: ");
 778       log.trace("  Free fraction %f", free_percentage);
 779       log.trace("  Desired free fraction %f", desired_free_percentage);
 780       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 781       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 782       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 783       CMSHeap* heap = CMSHeap::heap();
 784       size_t young_size = heap->young_gen()->capacity();
 785       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 786       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 787       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 788       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 789     }
 790     // safe if expansion fails
 791     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 792     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 793   } else {
 794     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 795     assert(desired_capacity <= capacity(), "invalid expansion size");
 796     size_t shrink_bytes = capacity() - desired_capacity;
 797     // Don't shrink unless the delta is greater than the minimum shrink we want
 798     if (shrink_bytes >= MinHeapDeltaBytes) {
 799       shrink_free_list_by(shrink_bytes);
 800     }
 801   }
 802 }
 803 
 804 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 805   return cmsSpace()->freelistLock();
 806 }
 807 
 808 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 809   CMSSynchronousYieldRequest yr;
 810   MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
 811   return have_lock_and_allocate(size, tlab);
 812 }
 813 
 814 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 815                                                                 bool   tlab /* ignored */) {
 816   assert_lock_strong(freelistLock());
 817   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 818   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 819   // Allocate the object live (grey) if the background collector has
 820   // started marking. This is necessary because the marker may
 821   // have passed this address and consequently this object will
 822   // not otherwise be greyed and would be incorrectly swept up.
 823   // Note that if this object contains references, the writing
 824   // of those references will dirty the card containing this object
 825   // allowing the object to be blackened (and its references scanned)
 826   // either during a preclean phase or at the final checkpoint.
 827   if (res != NULL) {
 828     // We may block here with an uninitialized object with
 829     // its mark-bit or P-bits not yet set. Such objects need
 830     // to be safely navigable by block_start().
 831     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 832     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 833     collector()->direct_allocated(res, adjustedSize);
 834     _direct_allocated_words += adjustedSize;
 835     // allocation counters
 836     NOT_PRODUCT(
 837       _numObjectsAllocated++;
 838       _numWordsAllocated += (int)adjustedSize;
 839     )
 840   }
 841   return res;
 842 }
 843 
 844 // In the case of direct allocation by mutators in a generation that
 845 // is being concurrently collected, the object must be allocated
 846 // live (grey) if the background collector has started marking.
 847 // This is necessary because the marker may
 848 // have passed this address and consequently this object will
 849 // not otherwise be greyed and would be incorrectly swept up.
 850 // Note that if this object contains references, the writing
 851 // of those references will dirty the card containing this object
 852 // allowing the object to be blackened (and its references scanned)
 853 // either during a preclean phase or at the final checkpoint.
 854 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 855   assert(_markBitMap.covers(start, size), "Out of bounds");
 856   if (_collectorState >= Marking) {
 857     MutexLocker y(_markBitMap.lock(),
 858                   Mutex::_no_safepoint_check_flag);
 859     // [see comments preceding SweepClosure::do_blk() below for details]
 860     //
 861     // Can the P-bits be deleted now?  JJJ
 862     //
 863     // 1. need to mark the object as live so it isn't collected
 864     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 865     // 3. need to mark the end of the object so marking, precleaning or sweeping
 866     //    can skip over uninitialized or unparsable objects. An allocated
 867     //    object is considered uninitialized for our purposes as long as
 868     //    its klass word is NULL.  All old gen objects are parsable
 869     //    as soon as they are initialized.)
 870     _markBitMap.mark(start);          // object is live
 871     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 872     _markBitMap.mark(start + size - 1);
 873                                       // mark end of object
 874   }
 875   // check that oop looks uninitialized
 876   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 877 }
 878 
 879 void CMSCollector::promoted(bool par, HeapWord* start,
 880                             bool is_obj_array, size_t obj_size) {
 881   assert(_markBitMap.covers(start), "Out of bounds");
 882   // See comment in direct_allocated() about when objects should
 883   // be allocated live.
 884   if (_collectorState >= Marking) {
 885     // we already hold the marking bit map lock, taken in
 886     // the prologue
 887     if (par) {
 888       _markBitMap.par_mark(start);
 889     } else {
 890       _markBitMap.mark(start);
 891     }
 892     // We don't need to mark the object as uninitialized (as
 893     // in direct_allocated above) because this is being done with the
 894     // world stopped and the object will be initialized by the
 895     // time the marking, precleaning or sweeping get to look at it.
 896     // But see the code for copying objects into the CMS generation,
 897     // where we need to ensure that concurrent readers of the
 898     // block offset table are able to safely navigate a block that
 899     // is in flux from being free to being allocated (and in
 900     // transition while being copied into) and subsequently
 901     // becoming a bona-fide object when the copy/promotion is complete.
 902     assert(SafepointSynchronize::is_at_safepoint(),
 903            "expect promotion only at safepoints");
 904 
 905     if (_collectorState < Sweeping) {
 906       // Mark the appropriate cards in the modUnionTable, so that
 907       // this object gets scanned before the sweep. If this is
 908       // not done, CMS generation references in the object might
 909       // not get marked.
 910       // For the case of arrays, which are otherwise precisely
 911       // marked, we need to dirty the entire array, not just its head.
 912       if (is_obj_array) {
 913         // The [par_]mark_range() method expects mr.end() below to
 914         // be aligned to the granularity of a bit's representation
 915         // in the heap. In the case of the MUT below, that's a
 916         // card size.
 917         MemRegion mr(start,
 918                      align_up(start + obj_size,
 919                               CardTable::card_size /* bytes */));
 920         if (par) {
 921           _modUnionTable.par_mark_range(mr);
 922         } else {
 923           _modUnionTable.mark_range(mr);
 924         }
 925       } else {  // not an obj array; we can just mark the head
 926         if (par) {
 927           _modUnionTable.par_mark(start);
 928         } else {
 929           _modUnionTable.mark(start);
 930         }
 931       }
 932     }
 933   }
 934 }
 935 
 936 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 937   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 938   // allocate, copy and if necessary update promoinfo --
 939   // delegate to underlying space.
 940   assert_lock_strong(freelistLock());
 941 
 942 #ifndef PRODUCT
 943   if (CMSHeap::heap()->promotion_should_fail()) {
 944     return NULL;
 945   }
 946 #endif  // #ifndef PRODUCT
 947 
 948   oop res = _cmsSpace->promote(obj, obj_size);
 949   if (res == NULL) {
 950     // expand and retry
 951     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 952     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 953     // Since this is the old generation, we don't try to promote
 954     // into a more senior generation.
 955     res = _cmsSpace->promote(obj, obj_size);
 956   }
 957   if (res != NULL) {
 958     // See comment in allocate() about when objects should
 959     // be allocated live.
 960     assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
 961     collector()->promoted(false,           // Not parallel
 962                           (HeapWord*)res, obj->is_objArray(), obj_size);
 963     // promotion counters
 964     NOT_PRODUCT(
 965       _numObjectsPromoted++;
 966       _numWordsPromoted +=
 967         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 968     )
 969   }
 970   return res;
 971 }
 972 
 973 
 974 // IMPORTANT: Notes on object size recognition in CMS.
 975 // ---------------------------------------------------
 976 // A block of storage in the CMS generation is always in
 977 // one of three states. A free block (FREE), an allocated
 978 // object (OBJECT) whose size() method reports the correct size,
 979 // and an intermediate state (TRANSIENT) in which its size cannot
 980 // be accurately determined.
 981 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 982 // -----------------------------------------------------
 983 // FREE:      klass_word & 1 == 1; mark_word holds block size
 984 //
 985 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 986 //            obj->size() computes correct size
 987 //
 988 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 989 //
 990 // STATE IDENTIFICATION: (64 bit+COOPS)
 991 // ------------------------------------
 992 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 993 //
 994 // OBJECT:    klass_word installed; klass_word != 0;
 995 //            obj->size() computes correct size
 996 //
 997 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 998 //
 999 //
1000 // STATE TRANSITION DIAGRAM
1001 //
1002 //        mut / parnew                     mut  /  parnew
1003 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1004 //  ^                                                                   |
1005 //  |------------------------ DEAD <------------------------------------|
1006 //         sweep                            mut
1007 //
1008 // While a block is in TRANSIENT state its size cannot be determined
1009 // so readers will either need to come back later or stall until
1010 // the size can be determined. Note that for the case of direct
1011 // allocation, P-bits, when available, may be used to determine the
1012 // size of an object that may not yet have been initialized.
1013 
1014 // Things to support parallel young-gen collection.
1015 oop
1016 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1017                                            oop old, markOop m,
1018                                            size_t word_sz) {
1019 #ifndef PRODUCT
1020   if (CMSHeap::heap()->promotion_should_fail()) {
1021     return NULL;
1022   }
1023 #endif  // #ifndef PRODUCT
1024 
1025   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1026   PromotionInfo* promoInfo = &ps->promo;
1027   // if we are tracking promotions, then first ensure space for
1028   // promotion (including spooling space for saving header if necessary).
1029   // then allocate and copy, then track promoted info if needed.
1030   // When tracking (see PromotionInfo::track()), the mark word may
1031   // be displaced and in this case restoration of the mark word
1032   // occurs in the (oop_since_save_marks_)iterate phase.
1033   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1034     // Out of space for allocating spooling buffers;
1035     // try expanding and allocating spooling buffers.
1036     if (!expand_and_ensure_spooling_space(promoInfo)) {
1037       return NULL;
1038     }
1039   }
1040   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1041   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1042   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1043   if (obj_ptr == NULL) {
1044      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1045      if (obj_ptr == NULL) {
1046        return NULL;
1047      }
1048   }
1049   oop obj = oop(obj_ptr);
1050   OrderAccess::storestore();
1051   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1052   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1053   // IMPORTANT: See note on object initialization for CMS above.
1054   // Otherwise, copy the object.  Here we must be careful to insert the
1055   // klass pointer last, since this marks the block as an allocated object.
1056   // Except with compressed oops it's the mark word.
1057   HeapWord* old_ptr = (HeapWord*)old;
1058   // Restore the mark word copied above.
1059   obj->set_mark_raw(m);
1060   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1061   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1062   OrderAccess::storestore();
1063 
1064   if (UseCompressedClassPointers) {
1065     // Copy gap missed by (aligned) header size calculation below
1066     obj->set_klass_gap(old->klass_gap());
1067   }
1068   if (word_sz > (size_t)oopDesc::header_size()) {
1069     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1070                                  obj_ptr + oopDesc::header_size(),
1071                                  word_sz - oopDesc::header_size());
1072   }
1073 
1074   // Now we can track the promoted object, if necessary.  We take care
1075   // to delay the transition from uninitialized to full object
1076   // (i.e., insertion of klass pointer) until after, so that it
1077   // atomically becomes a promoted object.
1078   if (promoInfo->tracking()) {
1079     promoInfo->track((PromotedObject*)obj, old->klass());
1080   }
1081   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083   assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1084 
1085   // Finally, install the klass pointer (this should be volatile).
1086   OrderAccess::storestore();
1087   obj->set_klass(old->klass());
1088   // We should now be able to calculate the right size for this object
1089   assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1090 
1091   collector()->promoted(true,          // parallel
1092                         obj_ptr, old->is_objArray(), word_sz);
1093 
1094   NOT_PRODUCT(
1095     Atomic::inc(&_numObjectsPromoted);
1096     Atomic::add(alloc_sz, &_numWordsPromoted);
1097   )
1098 
1099   return obj;
1100 }
1101 
1102 void
1103 ConcurrentMarkSweepGeneration::
1104 par_promote_alloc_done(int thread_num) {
1105   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1106   ps->lab.retire(thread_num);
1107 }
1108 
1109 void
1110 ConcurrentMarkSweepGeneration::
1111 par_oop_since_save_marks_iterate_done(int thread_num) {
1112   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1113   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1114   ps->promo.promoted_oops_iterate(dummy_cl);
1115 
1116   // Because card-scanning has been completed, subsequent phases
1117   // (e.g., reference processing) will not need to recognize which
1118   // objects have been promoted during this GC. So, we can now disable
1119   // promotion tracking.
1120   ps->promo.stopTrackingPromotions();
1121 }
1122 
1123 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1124                                                    size_t size,
1125                                                    bool   tlab)
1126 {
1127   // We allow a STW collection only if a full
1128   // collection was requested.
1129   return full || should_allocate(size, tlab); // FIX ME !!!
1130   // This and promotion failure handling are connected at the
1131   // hip and should be fixed by untying them.
1132 }
1133 
1134 bool CMSCollector::shouldConcurrentCollect() {
1135   LogTarget(Trace, gc) log;
1136 
1137   if (_full_gc_requested) {
1138     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1139     return true;
1140   }
1141 
1142   FreelistLocker x(this);
1143   // ------------------------------------------------------------------
1144   // Print out lots of information which affects the initiation of
1145   // a collection.
1146   if (log.is_enabled() && stats().valid()) {
1147     log.print("CMSCollector shouldConcurrentCollect: ");
1148 
1149     LogStream out(log);
1150     stats().print_on(&out);
1151 
1152     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1153     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1154     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1155     log.print("promotion_rate=%g", stats().promotion_rate());
1156     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1157     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1158     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1159     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1160     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1161     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1162   }
1163   // ------------------------------------------------------------------
1164 
1165   // If the estimated time to complete a cms collection (cms_duration())
1166   // is less than the estimated time remaining until the cms generation
1167   // is full, start a collection.
1168   if (!UseCMSInitiatingOccupancyOnly) {
1169     if (stats().valid()) {
1170       if (stats().time_until_cms_start() == 0.0) {
1171         return true;
1172       }
1173     } else {
1174       // We want to conservatively collect somewhat early in order
1175       // to try and "bootstrap" our CMS/promotion statistics;
1176       // this branch will not fire after the first successful CMS
1177       // collection because the stats should then be valid.
1178       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1179         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1180                   _cmsGen->occupancy(), _bootstrap_occupancy);
1181         return true;
1182       }
1183     }
1184   }
1185 
1186   // Otherwise, we start a collection cycle if
1187   // old gen want a collection cycle started. Each may use
1188   // an appropriate criterion for making this decision.
1189   // XXX We need to make sure that the gen expansion
1190   // criterion dovetails well with this. XXX NEED TO FIX THIS
1191   if (_cmsGen->should_concurrent_collect()) {
1192     log.print("CMS old gen initiated");
1193     return true;
1194   }
1195 
1196   // We start a collection if we believe an incremental collection may fail;
1197   // this is not likely to be productive in practice because it's probably too
1198   // late anyway.
1199   CMSHeap* heap = CMSHeap::heap();
1200   if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1201     log.print("CMSCollector: collect because incremental collection will fail ");
1202     return true;
1203   }
1204 
1205   if (MetaspaceGC::should_concurrent_collect()) {
1206     log.print("CMSCollector: collect for metadata allocation ");
1207     return true;
1208   }
1209 
1210   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1211   if (CMSTriggerInterval >= 0) {
1212     if (CMSTriggerInterval == 0) {
1213       // Trigger always
1214       return true;
1215     }
1216 
1217     // Check the CMS time since begin (we do not check the stats validity
1218     // as we want to be able to trigger the first CMS cycle as well)
1219     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1220       if (stats().valid()) {
1221         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1222                   stats().cms_time_since_begin());
1223       } else {
1224         log.print("CMSCollector: collect because of trigger interval (first collection)");
1225       }
1226       return true;
1227     }
1228   }
1229 
1230   return false;
1231 }
1232 
1233 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1234 
1235 // Clear _expansion_cause fields of constituent generations
1236 void CMSCollector::clear_expansion_cause() {
1237   _cmsGen->clear_expansion_cause();
1238 }
1239 
1240 // We should be conservative in starting a collection cycle.  To
1241 // start too eagerly runs the risk of collecting too often in the
1242 // extreme.  To collect too rarely falls back on full collections,
1243 // which works, even if not optimum in terms of concurrent work.
1244 // As a work around for too eagerly collecting, use the flag
1245 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1246 // giving the user an easily understandable way of controlling the
1247 // collections.
1248 // We want to start a new collection cycle if any of the following
1249 // conditions hold:
1250 // . our current occupancy exceeds the configured initiating occupancy
1251 //   for this generation, or
1252 // . we recently needed to expand this space and have not, since that
1253 //   expansion, done a collection of this generation, or
1254 // . the underlying space believes that it may be a good idea to initiate
1255 //   a concurrent collection (this may be based on criteria such as the
1256 //   following: the space uses linear allocation and linear allocation is
1257 //   going to fail, or there is believed to be excessive fragmentation in
1258 //   the generation, etc... or ...
1259 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1260 //   the case of the old generation; see CR 6543076):
1261 //   we may be approaching a point at which allocation requests may fail because
1262 //   we will be out of sufficient free space given allocation rate estimates.]
1263 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1264 
1265   assert_lock_strong(freelistLock());
1266   if (occupancy() > initiating_occupancy()) {
1267     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1268                   short_name(), occupancy(), initiating_occupancy());
1269     return true;
1270   }
1271   if (UseCMSInitiatingOccupancyOnly) {
1272     return false;
1273   }
1274   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1275     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1276     return true;
1277   }
1278   return false;
1279 }
1280 
1281 void ConcurrentMarkSweepGeneration::collect(bool   full,
1282                                             bool   clear_all_soft_refs,
1283                                             size_t size,
1284                                             bool   tlab)
1285 {
1286   collector()->collect(full, clear_all_soft_refs, size, tlab);
1287 }
1288 
1289 void CMSCollector::collect(bool   full,
1290                            bool   clear_all_soft_refs,
1291                            size_t size,
1292                            bool   tlab)
1293 {
1294   // The following "if" branch is present for defensive reasons.
1295   // In the current uses of this interface, it can be replaced with:
1296   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1297   // But I am not placing that assert here to allow future
1298   // generality in invoking this interface.
1299   if (GCLocker::is_active()) {
1300     // A consistency test for GCLocker
1301     assert(GCLocker::needs_gc(), "Should have been set already");
1302     // Skip this foreground collection, instead
1303     // expanding the heap if necessary.
1304     // Need the free list locks for the call to free() in compute_new_size()
1305     compute_new_size();
1306     return;
1307   }
1308   acquire_control_and_collect(full, clear_all_soft_refs);
1309 }
1310 
1311 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1312   CMSHeap* heap = CMSHeap::heap();
1313   unsigned int gc_count = heap->total_full_collections();
1314   if (gc_count == full_gc_count) {
1315     MutexLocker y(CGC_lock, Mutex::_no_safepoint_check_flag);
1316     _full_gc_requested = true;
1317     _full_gc_cause = cause;
1318     CGC_lock->notify();   // nudge CMS thread
1319   } else {
1320     assert(gc_count > full_gc_count, "Error: causal loop");
1321   }
1322 }
1323 
1324 bool CMSCollector::is_external_interruption() {
1325   GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1326   return GCCause::is_user_requested_gc(cause) ||
1327          GCCause::is_serviceability_requested_gc(cause);
1328 }
1329 
1330 void CMSCollector::report_concurrent_mode_interruption() {
1331   if (is_external_interruption()) {
1332     log_debug(gc)("Concurrent mode interrupted");
1333   } else {
1334     log_debug(gc)("Concurrent mode failure");
1335     _gc_tracer_cm->report_concurrent_mode_failure();
1336   }
1337 }
1338 
1339 
1340 // The foreground and background collectors need to coordinate in order
1341 // to make sure that they do not mutually interfere with CMS collections.
1342 // When a background collection is active,
1343 // the foreground collector may need to take over (preempt) and
1344 // synchronously complete an ongoing collection. Depending on the
1345 // frequency of the background collections and the heap usage
1346 // of the application, this preemption can be seldom or frequent.
1347 // There are only certain
1348 // points in the background collection that the "collection-baton"
1349 // can be passed to the foreground collector.
1350 //
1351 // The foreground collector will wait for the baton before
1352 // starting any part of the collection.  The foreground collector
1353 // will only wait at one location.
1354 //
1355 // The background collector will yield the baton before starting a new
1356 // phase of the collection (e.g., before initial marking, marking from roots,
1357 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1358 // of the loop which switches the phases. The background collector does some
1359 // of the phases (initial mark, final re-mark) with the world stopped.
1360 // Because of locking involved in stopping the world,
1361 // the foreground collector should not block waiting for the background
1362 // collector when it is doing a stop-the-world phase.  The background
1363 // collector will yield the baton at an additional point just before
1364 // it enters a stop-the-world phase.  Once the world is stopped, the
1365 // background collector checks the phase of the collection.  If the
1366 // phase has not changed, it proceeds with the collection.  If the
1367 // phase has changed, it skips that phase of the collection.  See
1368 // the comments on the use of the Heap_lock in collect_in_background().
1369 //
1370 // Variable used in baton passing.
1371 //   _foregroundGCIsActive - Set to true by the foreground collector when
1372 //      it wants the baton.  The foreground clears it when it has finished
1373 //      the collection.
1374 //   _foregroundGCShouldWait - Set to true by the background collector
1375 //        when it is running.  The foreground collector waits while
1376 //      _foregroundGCShouldWait is true.
1377 //  CGC_lock - monitor used to protect access to the above variables
1378 //      and to notify the foreground and background collectors.
1379 //  _collectorState - current state of the CMS collection.
1380 //
1381 // The foreground collector
1382 //   acquires the CGC_lock
1383 //   sets _foregroundGCIsActive
1384 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1385 //     various locks acquired in preparation for the collection
1386 //     are released so as not to block the background collector
1387 //     that is in the midst of a collection
1388 //   proceeds with the collection
1389 //   clears _foregroundGCIsActive
1390 //   returns
1391 //
1392 // The background collector in a loop iterating on the phases of the
1393 //      collection
1394 //   acquires the CGC_lock
1395 //   sets _foregroundGCShouldWait
1396 //   if _foregroundGCIsActive is set
1397 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1398 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1399 //     and exits the loop.
1400 //   otherwise
1401 //     proceed with that phase of the collection
1402 //     if the phase is a stop-the-world phase,
1403 //       yield the baton once more just before enqueueing
1404 //       the stop-world CMS operation (executed by the VM thread).
1405 //   returns after all phases of the collection are done
1406 //
1407 
1408 void CMSCollector::acquire_control_and_collect(bool full,
1409         bool clear_all_soft_refs) {
1410   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1411   assert(!Thread::current()->is_ConcurrentGC_thread(),
1412          "shouldn't try to acquire control from self!");
1413 
1414   // Start the protocol for acquiring control of the
1415   // collection from the background collector (aka CMS thread).
1416   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1417          "VM thread should have CMS token");
1418   // Remember the possibly interrupted state of an ongoing
1419   // concurrent collection
1420   CollectorState first_state = _collectorState;
1421 
1422   // Signal to a possibly ongoing concurrent collection that
1423   // we want to do a foreground collection.
1424   _foregroundGCIsActive = true;
1425 
1426   // release locks and wait for a notify from the background collector
1427   // releasing the locks in only necessary for phases which
1428   // do yields to improve the granularity of the collection.
1429   assert_lock_strong(bitMapLock());
1430   // We need to lock the Free list lock for the space that we are
1431   // currently collecting.
1432   assert(haveFreelistLocks(), "Must be holding free list locks");
1433   bitMapLock()->unlock();
1434   releaseFreelistLocks();
1435   {
1436     MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1437     if (_foregroundGCShouldWait) {
1438       // We are going to be waiting for action for the CMS thread;
1439       // it had better not be gone (for instance at shutdown)!
1440       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1441              "CMS thread must be running");
1442       // Wait here until the background collector gives us the go-ahead
1443       ConcurrentMarkSweepThread::clear_CMS_flag(
1444         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1445       // Get a possibly blocked CMS thread going:
1446       //   Note that we set _foregroundGCIsActive true above,
1447       //   without protection of the CGC_lock.
1448       CGC_lock->notify();
1449       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1450              "Possible deadlock");
1451       while (_foregroundGCShouldWait) {
1452         // wait for notification
1453         CGC_lock->wait_without_safepoint_check();
1454         // Possibility of delay/starvation here, since CMS token does
1455         // not know to give priority to VM thread? Actually, i think
1456         // there wouldn't be any delay/starvation, but the proof of
1457         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1458       }
1459       ConcurrentMarkSweepThread::set_CMS_flag(
1460         ConcurrentMarkSweepThread::CMS_vm_has_token);
1461     }
1462   }
1463   // The CMS_token is already held.  Get back the other locks.
1464   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1465          "VM thread should have CMS token");
1466   getFreelistLocks();
1467   bitMapLock()->lock_without_safepoint_check();
1468   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1469                        p2i(Thread::current()), first_state);
1470   log_debug(gc, state)("    gets control with state %d", _collectorState);
1471 
1472   // Inform cms gen if this was due to partial collection failing.
1473   // The CMS gen may use this fact to determine its expansion policy.
1474   CMSHeap* heap = CMSHeap::heap();
1475   if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1476     assert(!_cmsGen->incremental_collection_failed(),
1477            "Should have been noticed, reacted to and cleared");
1478     _cmsGen->set_incremental_collection_failed();
1479   }
1480 
1481   if (first_state > Idling) {
1482     report_concurrent_mode_interruption();
1483   }
1484 
1485   set_did_compact(true);
1486 
1487   // If the collection is being acquired from the background
1488   // collector, there may be references on the discovered
1489   // references lists.  Abandon those references, since some
1490   // of them may have become unreachable after concurrent
1491   // discovery; the STW compacting collector will redo discovery
1492   // more precisely, without being subject to floating garbage.
1493   // Leaving otherwise unreachable references in the discovered
1494   // lists would require special handling.
1495   ref_processor()->disable_discovery();
1496   ref_processor()->abandon_partial_discovery();
1497   ref_processor()->verify_no_references_recorded();
1498 
1499   if (first_state > Idling) {
1500     save_heap_summary();
1501   }
1502 
1503   do_compaction_work(clear_all_soft_refs);
1504 
1505   // Has the GC time limit been exceeded?
1506   size_t max_eden_size = _young_gen->max_eden_size();
1507   GCCause::Cause gc_cause = heap->gc_cause();
1508   size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(),
1509                                          _cmsGen->max_capacity(),
1510                                          max_eden_size,
1511                                          full,
1512                                          gc_cause,
1513                                          heap->soft_ref_policy());
1514 
1515   // Reset the expansion cause, now that we just completed
1516   // a collection cycle.
1517   clear_expansion_cause();
1518   _foregroundGCIsActive = false;
1519   return;
1520 }
1521 
1522 // Resize the tenured generation
1523 // after obtaining the free list locks for the
1524 // two generations.
1525 void CMSCollector::compute_new_size() {
1526   assert_locked_or_safepoint(Heap_lock);
1527   FreelistLocker z(this);
1528   MetaspaceGC::compute_new_size();
1529   _cmsGen->compute_new_size_free_list();
1530   // recalculate CMS used space after CMS collection
1531   _cmsGen->cmsSpace()->recalculate_used_stable();
1532 }
1533 
1534 // A work method used by the foreground collector to do
1535 // a mark-sweep-compact.
1536 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1537   CMSHeap* heap = CMSHeap::heap();
1538 
1539   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1540   gc_timer->register_gc_start();
1541 
1542   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1543   gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1544 
1545   heap->pre_full_gc_dump(gc_timer);
1546 
1547   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1548 
1549   // Temporarily widen the span of the weak reference processing to
1550   // the entire heap.
1551   MemRegion new_span(CMSHeap::heap()->reserved_region());
1552   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1553   // Temporarily, clear the "is_alive_non_header" field of the
1554   // reference processor.
1555   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1556   // Temporarily make reference _processing_ single threaded (non-MT).
1557   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1558   // Temporarily make refs discovery atomic
1559   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1560   // Temporarily make reference _discovery_ single threaded (non-MT)
1561   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1562 
1563   ref_processor()->set_enqueuing_is_done(false);
1564   ref_processor()->enable_discovery();
1565   ref_processor()->setup_policy(clear_all_soft_refs);
1566   // If an asynchronous collection finishes, the _modUnionTable is
1567   // all clear.  If we are assuming the collection from an asynchronous
1568   // collection, clear the _modUnionTable.
1569   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1570     "_modUnionTable should be clear if the baton was not passed");
1571   _modUnionTable.clear_all();
1572   assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1573     "mod union for klasses should be clear if the baton was passed");
1574   _ct->cld_rem_set()->clear_mod_union();
1575 
1576 
1577   // We must adjust the allocation statistics being maintained
1578   // in the free list space. We do so by reading and clearing
1579   // the sweep timer and updating the block flux rate estimates below.
1580   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1581   if (_inter_sweep_timer.is_active()) {
1582     _inter_sweep_timer.stop();
1583     // Note that we do not use this sample to update the _inter_sweep_estimate.
1584     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1585                                             _inter_sweep_estimate.padded_average(),
1586                                             _intra_sweep_estimate.padded_average());
1587   }
1588 
1589   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1590   #ifdef ASSERT
1591     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1592     size_t free_size = cms_space->free();
1593     assert(free_size ==
1594            pointer_delta(cms_space->end(), cms_space->compaction_top())
1595            * HeapWordSize,
1596       "All the free space should be compacted into one chunk at top");
1597     assert(cms_space->dictionary()->total_chunk_size(
1598                                       debug_only(cms_space->freelistLock())) == 0 ||
1599            cms_space->totalSizeInIndexedFreeLists() == 0,
1600       "All the free space should be in a single chunk");
1601     size_t num = cms_space->totalCount();
1602     assert((free_size == 0 && num == 0) ||
1603            (free_size > 0  && (num == 1 || num == 2)),
1604          "There should be at most 2 free chunks after compaction");
1605   #endif // ASSERT
1606   _collectorState = Resetting;
1607   assert(_restart_addr == NULL,
1608          "Should have been NULL'd before baton was passed");
1609   reset_stw();
1610   _cmsGen->reset_after_compaction();
1611   _concurrent_cycles_since_last_unload = 0;
1612 
1613   // Clear any data recorded in the PLAB chunk arrays.
1614   if (_survivor_plab_array != NULL) {
1615     reset_survivor_plab_arrays();
1616   }
1617 
1618   // Adjust the per-size allocation stats for the next epoch.
1619   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1620   // Restart the "inter sweep timer" for the next epoch.
1621   _inter_sweep_timer.reset();
1622   _inter_sweep_timer.start();
1623 
1624   // No longer a need to do a concurrent collection for Metaspace.
1625   MetaspaceGC::set_should_concurrent_collect(false);
1626 
1627   heap->post_full_gc_dump(gc_timer);
1628 
1629   gc_timer->register_gc_end();
1630 
1631   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1632 
1633   // For a mark-sweep-compact, compute_new_size() will be called
1634   // in the heap's do_collection() method.
1635 }
1636 
1637 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1638   Log(gc, heap) log;
1639   if (!log.is_trace()) {
1640     return;
1641   }
1642 
1643   ContiguousSpace* eden_space = _young_gen->eden();
1644   ContiguousSpace* from_space = _young_gen->from();
1645   ContiguousSpace* to_space   = _young_gen->to();
1646   // Eden
1647   if (_eden_chunk_array != NULL) {
1648     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1649               p2i(eden_space->bottom()), p2i(eden_space->top()),
1650               p2i(eden_space->end()), eden_space->capacity());
1651     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1652               _eden_chunk_index, _eden_chunk_capacity);
1653     for (size_t i = 0; i < _eden_chunk_index; i++) {
1654       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1655     }
1656   }
1657   // Survivor
1658   if (_survivor_chunk_array != NULL) {
1659     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1660               p2i(from_space->bottom()), p2i(from_space->top()),
1661               p2i(from_space->end()), from_space->capacity());
1662     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1663               _survivor_chunk_index, _survivor_chunk_capacity);
1664     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1665       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1666     }
1667   }
1668 }
1669 
1670 void CMSCollector::getFreelistLocks() const {
1671   // Get locks for all free lists in all generations that this
1672   // collector is responsible for
1673   _cmsGen->freelistLock()->lock_without_safepoint_check();
1674 }
1675 
1676 void CMSCollector::releaseFreelistLocks() const {
1677   // Release locks for all free lists in all generations that this
1678   // collector is responsible for
1679   _cmsGen->freelistLock()->unlock();
1680 }
1681 
1682 bool CMSCollector::haveFreelistLocks() const {
1683   // Check locks for all free lists in all generations that this
1684   // collector is responsible for
1685   assert_lock_strong(_cmsGen->freelistLock());
1686   PRODUCT_ONLY(ShouldNotReachHere());
1687   return true;
1688 }
1689 
1690 // A utility class that is used by the CMS collector to
1691 // temporarily "release" the foreground collector from its
1692 // usual obligation to wait for the background collector to
1693 // complete an ongoing phase before proceeding.
1694 class ReleaseForegroundGC: public StackObj {
1695  private:
1696   CMSCollector* _c;
1697  public:
1698   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1699     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1700     MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1701     // allow a potentially blocked foreground collector to proceed
1702     _c->_foregroundGCShouldWait = false;
1703     if (_c->_foregroundGCIsActive) {
1704       CGC_lock->notify();
1705     }
1706     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1707            "Possible deadlock");
1708   }
1709 
1710   ~ReleaseForegroundGC() {
1711     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1712     MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1713     _c->_foregroundGCShouldWait = true;
1714   }
1715 };
1716 
1717 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1718   assert(Thread::current()->is_ConcurrentGC_thread(),
1719     "A CMS asynchronous collection is only allowed on a CMS thread.");
1720 
1721   CMSHeap* heap = CMSHeap::heap();
1722   {
1723     MutexLocker hl(Heap_lock, Mutex::_no_safepoint_check_flag);
1724     FreelistLocker fll(this);
1725     MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1726     if (_foregroundGCIsActive) {
1727       // The foreground collector is. Skip this
1728       // background collection.
1729       assert(!_foregroundGCShouldWait, "Should be clear");
1730       return;
1731     } else {
1732       assert(_collectorState == Idling, "Should be idling before start.");
1733       _collectorState = InitialMarking;
1734       register_gc_start(cause);
1735       // Reset the expansion cause, now that we are about to begin
1736       // a new cycle.
1737       clear_expansion_cause();
1738 
1739       // Clear the MetaspaceGC flag since a concurrent collection
1740       // is starting but also clear it after the collection.
1741       MetaspaceGC::set_should_concurrent_collect(false);
1742     }
1743     // Decide if we want to enable class unloading as part of the
1744     // ensuing concurrent GC cycle.
1745     update_should_unload_classes();
1746     _full_gc_requested = false;           // acks all outstanding full gc requests
1747     _full_gc_cause = GCCause::_no_gc;
1748     // Signal that we are about to start a collection
1749     heap->increment_total_full_collections();  // ... starting a collection cycle
1750     _collection_count_start = heap->total_full_collections();
1751   }
1752 
1753   size_t prev_used = _cmsGen->used();
1754 
1755   // The change of the collection state is normally done at this level;
1756   // the exceptions are phases that are executed while the world is
1757   // stopped.  For those phases the change of state is done while the
1758   // world is stopped.  For baton passing purposes this allows the
1759   // background collector to finish the phase and change state atomically.
1760   // The foreground collector cannot wait on a phase that is done
1761   // while the world is stopped because the foreground collector already
1762   // has the world stopped and would deadlock.
1763   while (_collectorState != Idling) {
1764     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1765                          p2i(Thread::current()), _collectorState);
1766     // The foreground collector
1767     //   holds the Heap_lock throughout its collection.
1768     //   holds the CMS token (but not the lock)
1769     //     except while it is waiting for the background collector to yield.
1770     //
1771     // The foreground collector should be blocked (not for long)
1772     //   if the background collector is about to start a phase
1773     //   executed with world stopped.  If the background
1774     //   collector has already started such a phase, the
1775     //   foreground collector is blocked waiting for the
1776     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1777     //   are executed in the VM thread.
1778     //
1779     // The locking order is
1780     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1781     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1782     //   CMS token  (claimed in
1783     //                stop_world_and_do() -->
1784     //                  safepoint_synchronize() -->
1785     //                    CMSThread::synchronize())
1786 
1787     {
1788       // Check if the FG collector wants us to yield.
1789       CMSTokenSync x(true); // is cms thread
1790       if (waitForForegroundGC()) {
1791         // We yielded to a foreground GC, nothing more to be
1792         // done this round.
1793         assert(_foregroundGCShouldWait == false, "We set it to false in "
1794                "waitForForegroundGC()");
1795         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1796                              p2i(Thread::current()), _collectorState);
1797         return;
1798       } else {
1799         // The background collector can run but check to see if the
1800         // foreground collector has done a collection while the
1801         // background collector was waiting to get the CGC_lock
1802         // above.  If yes, break so that _foregroundGCShouldWait
1803         // is cleared before returning.
1804         if (_collectorState == Idling) {
1805           break;
1806         }
1807       }
1808     }
1809 
1810     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1811       "should be waiting");
1812 
1813     switch (_collectorState) {
1814       case InitialMarking:
1815         {
1816           ReleaseForegroundGC x(this);
1817           stats().record_cms_begin();
1818           VM_CMS_Initial_Mark initial_mark_op(this);
1819           VMThread::execute(&initial_mark_op);
1820         }
1821         // The collector state may be any legal state at this point
1822         // since the background collector may have yielded to the
1823         // foreground collector.
1824         break;
1825       case Marking:
1826         // initial marking in checkpointRootsInitialWork has been completed
1827         if (markFromRoots()) { // we were successful
1828           assert(_collectorState == Precleaning, "Collector state should "
1829             "have changed");
1830         } else {
1831           assert(_foregroundGCIsActive, "Internal state inconsistency");
1832         }
1833         break;
1834       case Precleaning:
1835         // marking from roots in markFromRoots has been completed
1836         preclean();
1837         assert(_collectorState == AbortablePreclean ||
1838                _collectorState == FinalMarking,
1839                "Collector state should have changed");
1840         break;
1841       case AbortablePreclean:
1842         abortable_preclean();
1843         assert(_collectorState == FinalMarking, "Collector state should "
1844           "have changed");
1845         break;
1846       case FinalMarking:
1847         {
1848           ReleaseForegroundGC x(this);
1849 
1850           VM_CMS_Final_Remark final_remark_op(this);
1851           VMThread::execute(&final_remark_op);
1852         }
1853         assert(_foregroundGCShouldWait, "block post-condition");
1854         break;
1855       case Sweeping:
1856         // final marking in checkpointRootsFinal has been completed
1857         sweep();
1858         assert(_collectorState == Resizing, "Collector state change "
1859           "to Resizing must be done under the free_list_lock");
1860 
1861       case Resizing: {
1862         // Sweeping has been completed...
1863         // At this point the background collection has completed.
1864         // Don't move the call to compute_new_size() down
1865         // into code that might be executed if the background
1866         // collection was preempted.
1867         {
1868           ReleaseForegroundGC x(this);   // unblock FG collection
1869           MutexLocker         y(Heap_lock, Mutex::_no_safepoint_check_flag);
1870           CMSTokenSync        z(true);   // not strictly needed.
1871           if (_collectorState == Resizing) {
1872             compute_new_size();
1873             save_heap_summary();
1874             _collectorState = Resetting;
1875           } else {
1876             assert(_collectorState == Idling, "The state should only change"
1877                    " because the foreground collector has finished the collection");
1878           }
1879         }
1880         break;
1881       }
1882       case Resetting:
1883         // CMS heap resizing has been completed
1884         reset_concurrent();
1885         assert(_collectorState == Idling, "Collector state should "
1886           "have changed");
1887 
1888         MetaspaceGC::set_should_concurrent_collect(false);
1889 
1890         stats().record_cms_end();
1891         // Don't move the concurrent_phases_end() and compute_new_size()
1892         // calls to here because a preempted background collection
1893         // has it's state set to "Resetting".
1894         break;
1895       case Idling:
1896       default:
1897         ShouldNotReachHere();
1898         break;
1899     }
1900     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1901                          p2i(Thread::current()), _collectorState);
1902     assert(_foregroundGCShouldWait, "block post-condition");
1903   }
1904 
1905   // Should this be in gc_epilogue?
1906   heap->counters()->update_counters();
1907 
1908   {
1909     // Clear _foregroundGCShouldWait and, in the event that the
1910     // foreground collector is waiting, notify it, before
1911     // returning.
1912     MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1913     _foregroundGCShouldWait = false;
1914     if (_foregroundGCIsActive) {
1915       CGC_lock->notify();
1916     }
1917     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1918            "Possible deadlock");
1919   }
1920   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1921                        p2i(Thread::current()), _collectorState);
1922   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1923                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1924 }
1925 
1926 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1927   _cms_start_registered = true;
1928   _gc_timer_cm->register_gc_start();
1929   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1930 }
1931 
1932 void CMSCollector::register_gc_end() {
1933   if (_cms_start_registered) {
1934     report_heap_summary(GCWhen::AfterGC);
1935 
1936     _gc_timer_cm->register_gc_end();
1937     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1938     _cms_start_registered = false;
1939   }
1940 }
1941 
1942 void CMSCollector::save_heap_summary() {
1943   CMSHeap* heap = CMSHeap::heap();
1944   _last_heap_summary = heap->create_heap_summary();
1945   _last_metaspace_summary = heap->create_metaspace_summary();
1946 }
1947 
1948 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1949   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1950   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1951 }
1952 
1953 bool CMSCollector::waitForForegroundGC() {
1954   bool res = false;
1955   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1956          "CMS thread should have CMS token");
1957   // Block the foreground collector until the
1958   // background collectors decides whether to
1959   // yield.
1960   MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1961   _foregroundGCShouldWait = true;
1962   if (_foregroundGCIsActive) {
1963     // The background collector yields to the
1964     // foreground collector and returns a value
1965     // indicating that it has yielded.  The foreground
1966     // collector can proceed.
1967     res = true;
1968     _foregroundGCShouldWait = false;
1969     ConcurrentMarkSweepThread::clear_CMS_flag(
1970       ConcurrentMarkSweepThread::CMS_cms_has_token);
1971     ConcurrentMarkSweepThread::set_CMS_flag(
1972       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1973     // Get a possibly blocked foreground thread going
1974     CGC_lock->notify();
1975     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1976                          p2i(Thread::current()), _collectorState);
1977     while (_foregroundGCIsActive) {
1978       CGC_lock->wait_without_safepoint_check();
1979     }
1980     ConcurrentMarkSweepThread::set_CMS_flag(
1981       ConcurrentMarkSweepThread::CMS_cms_has_token);
1982     ConcurrentMarkSweepThread::clear_CMS_flag(
1983       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1984   }
1985   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1986                        p2i(Thread::current()), _collectorState);
1987   return res;
1988 }
1989 
1990 // Because of the need to lock the free lists and other structures in
1991 // the collector, common to all the generations that the collector is
1992 // collecting, we need the gc_prologues of individual CMS generations
1993 // delegate to their collector. It may have been simpler had the
1994 // current infrastructure allowed one to call a prologue on a
1995 // collector. In the absence of that we have the generation's
1996 // prologue delegate to the collector, which delegates back
1997 // some "local" work to a worker method in the individual generations
1998 // that it's responsible for collecting, while itself doing any
1999 // work common to all generations it's responsible for. A similar
2000 // comment applies to the  gc_epilogue()'s.
2001 // The role of the variable _between_prologue_and_epilogue is to
2002 // enforce the invocation protocol.
2003 void CMSCollector::gc_prologue(bool full) {
2004   // Call gc_prologue_work() for the CMSGen
2005   // we are responsible for.
2006 
2007   // The following locking discipline assumes that we are only called
2008   // when the world is stopped.
2009   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2010 
2011   // The CMSCollector prologue must call the gc_prologues for the
2012   // "generations" that it's responsible
2013   // for.
2014 
2015   assert(   Thread::current()->is_VM_thread()
2016          || (   CMSScavengeBeforeRemark
2017              && Thread::current()->is_ConcurrentGC_thread()),
2018          "Incorrect thread type for prologue execution");
2019 
2020   if (_between_prologue_and_epilogue) {
2021     // We have already been invoked; this is a gc_prologue delegation
2022     // from yet another CMS generation that we are responsible for, just
2023     // ignore it since all relevant work has already been done.
2024     return;
2025   }
2026 
2027   // set a bit saying prologue has been called; cleared in epilogue
2028   _between_prologue_and_epilogue = true;
2029   // Claim locks for common data structures, then call gc_prologue_work()
2030   // for each CMSGen.
2031 
2032   getFreelistLocks();   // gets free list locks on constituent spaces
2033   bitMapLock()->lock_without_safepoint_check();
2034 
2035   // Should call gc_prologue_work() for all cms gens we are responsible for
2036   bool duringMarking =    _collectorState >= Marking
2037                          && _collectorState < Sweeping;
2038 
2039   // The young collections clear the modified oops state, which tells if
2040   // there are any modified oops in the class. The remark phase also needs
2041   // that information. Tell the young collection to save the union of all
2042   // modified klasses.
2043   if (duringMarking) {
2044     _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2045   }
2046 
2047   bool registerClosure = duringMarking;
2048 
2049   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2050 
2051   if (!full) {
2052     stats().record_gc0_begin();
2053   }
2054 }
2055 
2056 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2057 
2058   _capacity_at_prologue = capacity();
2059   _used_at_prologue = used();
2060   _cmsSpace->recalculate_used_stable();
2061 
2062   // We enable promotion tracking so that card-scanning can recognize
2063   // which objects have been promoted during this GC and skip them.
2064   for (uint i = 0; i < ParallelGCThreads; i++) {
2065     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2066   }
2067 
2068   // Delegate to CMScollector which knows how to coordinate between
2069   // this and any other CMS generations that it is responsible for
2070   // collecting.
2071   collector()->gc_prologue(full);
2072 }
2073 
2074 // This is a "private" interface for use by this generation's CMSCollector.
2075 // Not to be called directly by any other entity (for instance,
2076 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2077 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2078   bool registerClosure, ModUnionClosure* modUnionClosure) {
2079   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2080   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2081     "Should be NULL");
2082   if (registerClosure) {
2083     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2084   }
2085   cmsSpace()->gc_prologue();
2086   // Clear stat counters
2087   NOT_PRODUCT(
2088     assert(_numObjectsPromoted == 0, "check");
2089     assert(_numWordsPromoted   == 0, "check");
2090     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2091                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2092     _numObjectsAllocated = 0;
2093     _numWordsAllocated   = 0;
2094   )
2095 }
2096 
2097 void CMSCollector::gc_epilogue(bool full) {
2098   // The following locking discipline assumes that we are only called
2099   // when the world is stopped.
2100   assert(SafepointSynchronize::is_at_safepoint(),
2101          "world is stopped assumption");
2102 
2103   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2104   // if linear allocation blocks need to be appropriately marked to allow the
2105   // the blocks to be parsable. We also check here whether we need to nudge the
2106   // CMS collector thread to start a new cycle (if it's not already active).
2107   assert(   Thread::current()->is_VM_thread()
2108          || (   CMSScavengeBeforeRemark
2109              && Thread::current()->is_ConcurrentGC_thread()),
2110          "Incorrect thread type for epilogue execution");
2111 
2112   if (!_between_prologue_and_epilogue) {
2113     // We have already been invoked; this is a gc_epilogue delegation
2114     // from yet another CMS generation that we are responsible for, just
2115     // ignore it since all relevant work has already been done.
2116     return;
2117   }
2118   assert(haveFreelistLocks(), "must have freelist locks");
2119   assert_lock_strong(bitMapLock());
2120 
2121   _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2122 
2123   _cmsGen->gc_epilogue_work(full);
2124 
2125   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2126     // in case sampling was not already enabled, enable it
2127     _start_sampling = true;
2128   }
2129   // reset _eden_chunk_array so sampling starts afresh
2130   _eden_chunk_index = 0;
2131 
2132   size_t cms_used   = _cmsGen->cmsSpace()->used();
2133   _cmsGen->cmsSpace()->recalculate_used_stable();
2134 
2135   // update performance counters - this uses a special version of
2136   // update_counters() that allows the utilization to be passed as a
2137   // parameter, avoiding multiple calls to used().
2138   //
2139   _cmsGen->update_counters(cms_used);
2140 
2141   bitMapLock()->unlock();
2142   releaseFreelistLocks();
2143 
2144   if (!CleanChunkPoolAsync) {
2145     Chunk::clean_chunk_pool();
2146   }
2147 
2148   set_did_compact(false);
2149   _between_prologue_and_epilogue = false;  // ready for next cycle
2150 }
2151 
2152 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2153   collector()->gc_epilogue(full);
2154 
2155   // When using ParNew, promotion tracking should have already been
2156   // disabled. However, the prologue (which enables promotion
2157   // tracking) and epilogue are called irrespective of the type of
2158   // GC. So they will also be called before and after Full GCs, during
2159   // which promotion tracking will not be explicitly disabled. So,
2160   // it's safer to also disable it here too (to be symmetric with
2161   // enabling it in the prologue).
2162   for (uint i = 0; i < ParallelGCThreads; i++) {
2163     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2164   }
2165 }
2166 
2167 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2168   assert(!incremental_collection_failed(), "Should have been cleared");
2169   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2170   cmsSpace()->gc_epilogue();
2171     // Print stat counters
2172   NOT_PRODUCT(
2173     assert(_numObjectsAllocated == 0, "check");
2174     assert(_numWordsAllocated == 0, "check");
2175     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2176                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2177     _numObjectsPromoted = 0;
2178     _numWordsPromoted   = 0;
2179   )
2180 
2181   // Call down the chain in contiguous_available needs the freelistLock
2182   // so print this out before releasing the freeListLock.
2183   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2184 }
2185 
2186 #ifndef PRODUCT
2187 bool CMSCollector::have_cms_token() {
2188   Thread* thr = Thread::current();
2189   if (thr->is_VM_thread()) {
2190     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2191   } else if (thr->is_ConcurrentGC_thread()) {
2192     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2193   } else if (thr->is_GC_task_thread()) {
2194     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2195            ParGCRareEvent_lock->owned_by_self();
2196   }
2197   return false;
2198 }
2199 
2200 // Check reachability of the given heap address in CMS generation,
2201 // treating all other generations as roots.
2202 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2203   // We could "guarantee" below, rather than assert, but I'll
2204   // leave these as "asserts" so that an adventurous debugger
2205   // could try this in the product build provided some subset of
2206   // the conditions were met, provided they were interested in the
2207   // results and knew that the computation below wouldn't interfere
2208   // with other concurrent computations mutating the structures
2209   // being read or written.
2210   assert(SafepointSynchronize::is_at_safepoint(),
2211          "Else mutations in object graph will make answer suspect");
2212   assert(have_cms_token(), "Should hold cms token");
2213   assert(haveFreelistLocks(), "must hold free list locks");
2214   assert_lock_strong(bitMapLock());
2215 
2216   // Clear the marking bit map array before starting, but, just
2217   // for kicks, first report if the given address is already marked
2218   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2219                 _markBitMap.isMarked(addr) ? "" : " not");
2220 
2221   if (verify_after_remark()) {
2222     MutexLocker x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2223     bool result = verification_mark_bm()->isMarked(addr);
2224     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2225                   result ? "IS" : "is NOT");
2226     return result;
2227   } else {
2228     tty->print_cr("Could not compute result");
2229     return false;
2230   }
2231 }
2232 #endif
2233 
2234 void
2235 CMSCollector::print_on_error(outputStream* st) {
2236   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2237   if (collector != NULL) {
2238     CMSBitMap* bitmap = &collector->_markBitMap;
2239     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2240     bitmap->print_on_error(st, " Bits: ");
2241 
2242     st->cr();
2243 
2244     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2245     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2246     mut_bitmap->print_on_error(st, " Bits: ");
2247   }
2248 }
2249 
2250 ////////////////////////////////////////////////////////
2251 // CMS Verification Support
2252 ////////////////////////////////////////////////////////
2253 // Following the remark phase, the following invariant
2254 // should hold -- each object in the CMS heap which is
2255 // marked in markBitMap() should be marked in the verification_mark_bm().
2256 
2257 class VerifyMarkedClosure: public BitMapClosure {
2258   CMSBitMap* _marks;
2259   bool       _failed;
2260 
2261  public:
2262   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2263 
2264   bool do_bit(size_t offset) {
2265     HeapWord* addr = _marks->offsetToHeapWord(offset);
2266     if (!_marks->isMarked(addr)) {
2267       Log(gc, verify) log;
2268       ResourceMark rm;
2269       LogStream ls(log.error());
2270       oop(addr)->print_on(&ls);
2271       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2272       _failed = true;
2273     }
2274     return true;
2275   }
2276 
2277   bool failed() { return _failed; }
2278 };
2279 
2280 bool CMSCollector::verify_after_remark() {
2281   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2282   MutexLocker ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2283   static bool init = false;
2284 
2285   assert(SafepointSynchronize::is_at_safepoint(),
2286          "Else mutations in object graph will make answer suspect");
2287   assert(have_cms_token(),
2288          "Else there may be mutual interference in use of "
2289          " verification data structures");
2290   assert(_collectorState > Marking && _collectorState <= Sweeping,
2291          "Else marking info checked here may be obsolete");
2292   assert(haveFreelistLocks(), "must hold free list locks");
2293   assert_lock_strong(bitMapLock());
2294 
2295 
2296   // Allocate marking bit map if not already allocated
2297   if (!init) { // first time
2298     if (!verification_mark_bm()->allocate(_span)) {
2299       return false;
2300     }
2301     init = true;
2302   }
2303 
2304   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2305 
2306   // Turn off refs discovery -- so we will be tracing through refs.
2307   // This is as intended, because by this time
2308   // GC must already have cleared any refs that need to be cleared,
2309   // and traced those that need to be marked; moreover,
2310   // the marking done here is not going to interfere in any
2311   // way with the marking information used by GC.
2312   NoRefDiscovery no_discovery(ref_processor());
2313 
2314 #if COMPILER2_OR_JVMCI
2315   DerivedPointerTableDeactivate dpt_deact;
2316 #endif
2317 
2318   // Clear any marks from a previous round
2319   verification_mark_bm()->clear_all();
2320   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2321   verify_work_stacks_empty();
2322 
2323   CMSHeap* heap = CMSHeap::heap();
2324   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2325   // Update the saved marks which may affect the root scans.
2326   heap->save_marks();
2327 
2328   if (CMSRemarkVerifyVariant == 1) {
2329     // In this first variant of verification, we complete
2330     // all marking, then check if the new marks-vector is
2331     // a subset of the CMS marks-vector.
2332     verify_after_remark_work_1();
2333   } else {
2334     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2335     // In this second variant of verification, we flag an error
2336     // (i.e. an object reachable in the new marks-vector not reachable
2337     // in the CMS marks-vector) immediately, also indicating the
2338     // identify of an object (A) that references the unmarked object (B) --
2339     // presumably, a mutation to A failed to be picked up by preclean/remark?
2340     verify_after_remark_work_2();
2341   }
2342 
2343   return true;
2344 }
2345 
2346 void CMSCollector::verify_after_remark_work_1() {
2347   ResourceMark rm;
2348   HandleMark  hm;
2349   CMSHeap* heap = CMSHeap::heap();
2350 
2351   // Get a clear set of claim bits for the roots processing to work with.
2352   ClassLoaderDataGraph::clear_claimed_marks();
2353 
2354   // Mark from roots one level into CMS
2355   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2356   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2357 
2358   {
2359     StrongRootsScope srs(1);
2360 
2361     heap->cms_process_roots(&srs,
2362                            true,   // young gen as roots
2363                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2364                            should_unload_classes(),
2365                            &notOlder,
2366                            NULL);
2367   }
2368 
2369   // Now mark from the roots
2370   MarkFromRootsClosure markFromRootsClosure(this, _span,
2371     verification_mark_bm(), verification_mark_stack(),
2372     false /* don't yield */, true /* verifying */);
2373   assert(_restart_addr == NULL, "Expected pre-condition");
2374   verification_mark_bm()->iterate(&markFromRootsClosure);
2375   while (_restart_addr != NULL) {
2376     // Deal with stack overflow: by restarting at the indicated
2377     // address.
2378     HeapWord* ra = _restart_addr;
2379     markFromRootsClosure.reset(ra);
2380     _restart_addr = NULL;
2381     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2382   }
2383   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2384   verify_work_stacks_empty();
2385 
2386   // Marking completed -- now verify that each bit marked in
2387   // verification_mark_bm() is also marked in markBitMap(); flag all
2388   // errors by printing corresponding objects.
2389   VerifyMarkedClosure vcl(markBitMap());
2390   verification_mark_bm()->iterate(&vcl);
2391   if (vcl.failed()) {
2392     Log(gc, verify) log;
2393     log.error("Failed marking verification after remark");
2394     ResourceMark rm;
2395     LogStream ls(log.error());
2396     heap->print_on(&ls);
2397     fatal("CMS: failed marking verification after remark");
2398   }
2399 }
2400 
2401 class VerifyCLDOopsCLDClosure : public CLDClosure {
2402   class VerifyCLDOopsClosure : public OopClosure {
2403     CMSBitMap* _bitmap;
2404    public:
2405     VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2406     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2407     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2408   } _oop_closure;
2409  public:
2410   VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2411   void do_cld(ClassLoaderData* cld) {
2412     cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2413   }
2414 };
2415 
2416 void CMSCollector::verify_after_remark_work_2() {
2417   ResourceMark rm;
2418   HandleMark  hm;
2419   CMSHeap* heap = CMSHeap::heap();
2420 
2421   // Get a clear set of claim bits for the roots processing to work with.
2422   ClassLoaderDataGraph::clear_claimed_marks();
2423 
2424   // Mark from roots one level into CMS
2425   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2426                                      markBitMap());
2427   CLDToOopClosure cld_closure(&notOlder, ClassLoaderData::_claim_strong);
2428 
2429   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2430 
2431   {
2432     StrongRootsScope srs(1);
2433 
2434     heap->cms_process_roots(&srs,
2435                            true,   // young gen as roots
2436                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2437                            should_unload_classes(),
2438                            &notOlder,
2439                            &cld_closure);
2440   }
2441 
2442   // Now mark from the roots
2443   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2444     verification_mark_bm(), markBitMap(), verification_mark_stack());
2445   assert(_restart_addr == NULL, "Expected pre-condition");
2446   verification_mark_bm()->iterate(&markFromRootsClosure);
2447   while (_restart_addr != NULL) {
2448     // Deal with stack overflow: by restarting at the indicated
2449     // address.
2450     HeapWord* ra = _restart_addr;
2451     markFromRootsClosure.reset(ra);
2452     _restart_addr = NULL;
2453     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2454   }
2455   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2456   verify_work_stacks_empty();
2457 
2458   VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2459   ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2460 
2461   // Marking completed -- now verify that each bit marked in
2462   // verification_mark_bm() is also marked in markBitMap(); flag all
2463   // errors by printing corresponding objects.
2464   VerifyMarkedClosure vcl(markBitMap());
2465   verification_mark_bm()->iterate(&vcl);
2466   assert(!vcl.failed(), "Else verification above should not have succeeded");
2467 }
2468 
2469 void ConcurrentMarkSweepGeneration::save_marks() {
2470   // delegate to CMS space
2471   cmsSpace()->save_marks();
2472 }
2473 
2474 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2475   return cmsSpace()->no_allocs_since_save_marks();
2476 }
2477 
2478 void
2479 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2480   if (freelistLock()->owned_by_self()) {
2481     Generation::oop_iterate(cl);
2482   } else {
2483     MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2484     Generation::oop_iterate(cl);
2485   }
2486 }
2487 
2488 void
2489 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2490   if (freelistLock()->owned_by_self()) {
2491     Generation::object_iterate(cl);
2492   } else {
2493     MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2494     Generation::object_iterate(cl);
2495   }
2496 }
2497 
2498 void
2499 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2500   if (freelistLock()->owned_by_self()) {
2501     Generation::safe_object_iterate(cl);
2502   } else {
2503     MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2504     Generation::safe_object_iterate(cl);
2505   }
2506 }
2507 
2508 void
2509 ConcurrentMarkSweepGeneration::post_compact() {
2510 }
2511 
2512 void
2513 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2514   // Fix the linear allocation blocks to look like free blocks.
2515 
2516   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2517   // are not called when the heap is verified during universe initialization and
2518   // at vm shutdown.
2519   if (freelistLock()->owned_by_self()) {
2520     cmsSpace()->prepare_for_verify();
2521   } else {
2522     MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2523     cmsSpace()->prepare_for_verify();
2524   }
2525 }
2526 
2527 void
2528 ConcurrentMarkSweepGeneration::verify() {
2529   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2530   // are not called when the heap is verified during universe initialization and
2531   // at vm shutdown.
2532   if (freelistLock()->owned_by_self()) {
2533     cmsSpace()->verify();
2534   } else {
2535     MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2536     cmsSpace()->verify();
2537   }
2538 }
2539 
2540 void CMSCollector::verify() {
2541   _cmsGen->verify();
2542 }
2543 
2544 #ifndef PRODUCT
2545 bool CMSCollector::overflow_list_is_empty() const {
2546   assert(_num_par_pushes >= 0, "Inconsistency");
2547   if (_overflow_list == NULL) {
2548     assert(_num_par_pushes == 0, "Inconsistency");
2549   }
2550   return _overflow_list == NULL;
2551 }
2552 
2553 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2554 // merely consolidate assertion checks that appear to occur together frequently.
2555 void CMSCollector::verify_work_stacks_empty() const {
2556   assert(_markStack.isEmpty(), "Marking stack should be empty");
2557   assert(overflow_list_is_empty(), "Overflow list should be empty");
2558 }
2559 
2560 void CMSCollector::verify_overflow_empty() const {
2561   assert(overflow_list_is_empty(), "Overflow list should be empty");
2562   assert(no_preserved_marks(), "No preserved marks");
2563 }
2564 #endif // PRODUCT
2565 
2566 // Decide if we want to enable class unloading as part of the
2567 // ensuing concurrent GC cycle. We will collect and
2568 // unload classes if it's the case that:
2569 //  (a) class unloading is enabled at the command line, and
2570 //  (b) old gen is getting really full
2571 // NOTE: Provided there is no change in the state of the heap between
2572 // calls to this method, it should have idempotent results. Moreover,
2573 // its results should be monotonically increasing (i.e. going from 0 to 1,
2574 // but not 1 to 0) between successive calls between which the heap was
2575 // not collected. For the implementation below, it must thus rely on
2576 // the property that concurrent_cycles_since_last_unload()
2577 // will not decrease unless a collection cycle happened and that
2578 // _cmsGen->is_too_full() are
2579 // themselves also monotonic in that sense. See check_monotonicity()
2580 // below.
2581 void CMSCollector::update_should_unload_classes() {
2582   _should_unload_classes = false;
2583   if (CMSClassUnloadingEnabled) {
2584     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2585                               CMSClassUnloadingMaxInterval)
2586                            || _cmsGen->is_too_full();
2587   }
2588 }
2589 
2590 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2591   bool res = should_concurrent_collect();
2592   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2593   return res;
2594 }
2595 
2596 void CMSCollector::setup_cms_unloading_and_verification_state() {
2597   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2598                              || VerifyBeforeExit;
2599   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2600 
2601   // We set the proper root for this CMS cycle here.
2602   if (should_unload_classes()) {   // Should unload classes this cycle
2603     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2604     set_verifying(should_verify);    // Set verification state for this cycle
2605     return;                            // Nothing else needs to be done at this time
2606   }
2607 
2608   // Not unloading classes this cycle
2609   assert(!should_unload_classes(), "Inconsistency!");
2610 
2611   // If we are not unloading classes then add SO_AllCodeCache to root
2612   // scanning options.
2613   add_root_scanning_option(rso);
2614 
2615   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2616     set_verifying(true);
2617   } else if (verifying() && !should_verify) {
2618     // We were verifying, but some verification flags got disabled.
2619     set_verifying(false);
2620     // Exclude symbols, strings and code cache elements from root scanning to
2621     // reduce IM and RM pauses.
2622     remove_root_scanning_option(rso);
2623   }
2624 }
2625 
2626 
2627 #ifndef PRODUCT
2628 HeapWord* CMSCollector::block_start(const void* p) const {
2629   const HeapWord* addr = (HeapWord*)p;
2630   if (_span.contains(p)) {
2631     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2632       return _cmsGen->cmsSpace()->block_start(p);
2633     }
2634   }
2635   return NULL;
2636 }
2637 #endif
2638 
2639 HeapWord*
2640 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2641                                                    bool   tlab,
2642                                                    bool   parallel) {
2643   CMSSynchronousYieldRequest yr;
2644   assert(!tlab, "Can't deal with TLAB allocation");
2645   MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2646   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2647   if (GCExpandToAllocateDelayMillis > 0) {
2648     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2649   }
2650   return have_lock_and_allocate(word_size, tlab);
2651 }
2652 
2653 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2654     size_t bytes,
2655     size_t expand_bytes,
2656     CMSExpansionCause::Cause cause)
2657 {
2658 
2659   bool success = expand(bytes, expand_bytes);
2660 
2661   // remember why we expanded; this information is used
2662   // by shouldConcurrentCollect() when making decisions on whether to start
2663   // a new CMS cycle.
2664   if (success) {
2665     set_expansion_cause(cause);
2666     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2667   }
2668 }
2669 
2670 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2671   HeapWord* res = NULL;
2672   MutexLocker x(ParGCRareEvent_lock);
2673   while (true) {
2674     // Expansion by some other thread might make alloc OK now:
2675     res = ps->lab.alloc(word_sz);
2676     if (res != NULL) return res;
2677     // If there's not enough expansion space available, give up.
2678     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2679       return NULL;
2680     }
2681     // Otherwise, we try expansion.
2682     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2683     // Now go around the loop and try alloc again;
2684     // A competing par_promote might beat us to the expansion space,
2685     // so we may go around the loop again if promotion fails again.
2686     if (GCExpandToAllocateDelayMillis > 0) {
2687       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2688     }
2689   }
2690 }
2691 
2692 
2693 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2694   PromotionInfo* promo) {
2695   MutexLocker x(ParGCRareEvent_lock);
2696   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2697   while (true) {
2698     // Expansion by some other thread might make alloc OK now:
2699     if (promo->ensure_spooling_space()) {
2700       assert(promo->has_spooling_space(),
2701              "Post-condition of successful ensure_spooling_space()");
2702       return true;
2703     }
2704     // If there's not enough expansion space available, give up.
2705     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2706       return false;
2707     }
2708     // Otherwise, we try expansion.
2709     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2710     // Now go around the loop and try alloc again;
2711     // A competing allocation might beat us to the expansion space,
2712     // so we may go around the loop again if allocation fails again.
2713     if (GCExpandToAllocateDelayMillis > 0) {
2714       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2715     }
2716   }
2717 }
2718 
2719 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2720   // Only shrink if a compaction was done so that all the free space
2721   // in the generation is in a contiguous block at the end.
2722   if (did_compact()) {
2723     CardGeneration::shrink(bytes);
2724   }
2725 }
2726 
2727 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2728   assert_locked_or_safepoint(Heap_lock);
2729 }
2730 
2731 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2732   assert_locked_or_safepoint(Heap_lock);
2733   assert_lock_strong(freelistLock());
2734   log_trace(gc)("Shrinking of CMS not yet implemented");
2735   return;
2736 }
2737 
2738 
2739 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2740 // phases.
2741 class CMSPhaseAccounting: public StackObj {
2742  public:
2743   CMSPhaseAccounting(CMSCollector *collector,
2744                      const char *title);
2745   ~CMSPhaseAccounting();
2746 
2747  private:
2748   CMSCollector *_collector;
2749   const char *_title;
2750   GCTraceConcTime(Info, gc) _trace_time;
2751 
2752  public:
2753   // Not MT-safe; so do not pass around these StackObj's
2754   // where they may be accessed by other threads.
2755   double wallclock_millis() {
2756     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2757   }
2758 };
2759 
2760 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2761                                        const char *title) :
2762   _collector(collector), _title(title), _trace_time(title) {
2763 
2764   _collector->resetYields();
2765   _collector->resetTimer();
2766   _collector->startTimer();
2767   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2768 }
2769 
2770 CMSPhaseAccounting::~CMSPhaseAccounting() {
2771   _collector->gc_timer_cm()->register_gc_concurrent_end();
2772   _collector->stopTimer();
2773   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_millis(_collector->timerTicks()));
2774   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2775 }
2776 
2777 // CMS work
2778 
2779 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2780 class CMSParMarkTask : public AbstractGangTask {
2781  protected:
2782   CMSCollector*     _collector;
2783   uint              _n_workers;
2784   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2785       AbstractGangTask(name),
2786       _collector(collector),
2787       _n_workers(n_workers) {}
2788   // Work method in support of parallel rescan ... of young gen spaces
2789   void do_young_space_rescan(OopsInGenClosure* cl,
2790                              ContiguousSpace* space,
2791                              HeapWord** chunk_array, size_t chunk_top);
2792   void work_on_young_gen_roots(OopsInGenClosure* cl);
2793 };
2794 
2795 // Parallel initial mark task
2796 class CMSParInitialMarkTask: public CMSParMarkTask {
2797   StrongRootsScope* _strong_roots_scope;
2798  public:
2799   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2800       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2801       _strong_roots_scope(strong_roots_scope) {}
2802   void work(uint worker_id);
2803 };
2804 
2805 // Checkpoint the roots into this generation from outside
2806 // this generation. [Note this initial checkpoint need only
2807 // be approximate -- we'll do a catch up phase subsequently.]
2808 void CMSCollector::checkpointRootsInitial() {
2809   assert(_collectorState == InitialMarking, "Wrong collector state");
2810   check_correct_thread_executing();
2811   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2812 
2813   save_heap_summary();
2814   report_heap_summary(GCWhen::BeforeGC);
2815 
2816   ReferenceProcessor* rp = ref_processor();
2817   assert(_restart_addr == NULL, "Control point invariant");
2818   {
2819     // acquire locks for subsequent manipulations
2820     MutexLocker x(bitMapLock(),
2821                   Mutex::_no_safepoint_check_flag);
2822     checkpointRootsInitialWork();
2823     // enable ("weak") refs discovery
2824     rp->enable_discovery();
2825     _collectorState = Marking;
2826   }
2827 
2828   _cmsGen->cmsSpace()->recalculate_used_stable();
2829 }
2830 
2831 void CMSCollector::checkpointRootsInitialWork() {
2832   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2833   assert(_collectorState == InitialMarking, "just checking");
2834 
2835   // Already have locks.
2836   assert_lock_strong(bitMapLock());
2837   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2838 
2839   // Setup the verification and class unloading state for this
2840   // CMS collection cycle.
2841   setup_cms_unloading_and_verification_state();
2842 
2843   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2844 
2845   // Reset all the PLAB chunk arrays if necessary.
2846   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2847     reset_survivor_plab_arrays();
2848   }
2849 
2850   ResourceMark rm;
2851   HandleMark  hm;
2852 
2853   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2854   CMSHeap* heap = CMSHeap::heap();
2855 
2856   verify_work_stacks_empty();
2857   verify_overflow_empty();
2858 
2859   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2860   // Update the saved marks which may affect the root scans.
2861   heap->save_marks();
2862 
2863   // weak reference processing has not started yet.
2864   ref_processor()->set_enqueuing_is_done(false);
2865 
2866   // Need to remember all newly created CLDs,
2867   // so that we can guarantee that the remark finds them.
2868   ClassLoaderDataGraph::remember_new_clds(true);
2869 
2870   // Whenever a CLD is found, it will be claimed before proceeding to mark
2871   // the klasses. The claimed marks need to be cleared before marking starts.
2872   ClassLoaderDataGraph::clear_claimed_marks();
2873 
2874   print_eden_and_survivor_chunk_arrays();
2875 
2876   {
2877 #if COMPILER2_OR_JVMCI
2878     DerivedPointerTableDeactivate dpt_deact;
2879 #endif
2880     if (CMSParallelInitialMarkEnabled) {
2881       // The parallel version.
2882       WorkGang* workers = heap->workers();
2883       assert(workers != NULL, "Need parallel worker threads.");
2884       uint n_workers = workers->active_workers();
2885 
2886       StrongRootsScope srs(n_workers);
2887 
2888       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2889       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2890       // If the total workers is greater than 1, then multiple workers
2891       // may be used at some time and the initialization has been set
2892       // such that the single threaded path cannot be used.
2893       if (workers->total_workers() > 1) {
2894         workers->run_task(&tsk);
2895       } else {
2896         tsk.work(0);
2897       }
2898     } else {
2899       // The serial version.
2900       CLDToOopClosure cld_closure(&notOlder, ClassLoaderData::_claim_strong);
2901       heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2902 
2903       StrongRootsScope srs(1);
2904 
2905       heap->cms_process_roots(&srs,
2906                              true,   // young gen as roots
2907                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2908                              should_unload_classes(),
2909                              &notOlder,
2910                              &cld_closure);
2911     }
2912   }
2913 
2914   // Clear mod-union table; it will be dirtied in the prologue of
2915   // CMS generation per each young generation collection.
2916 
2917   assert(_modUnionTable.isAllClear(),
2918        "Was cleared in most recent final checkpoint phase"
2919        " or no bits are set in the gc_prologue before the start of the next "
2920        "subsequent marking phase.");
2921 
2922   assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2923 
2924   // Save the end of the used_region of the constituent generations
2925   // to be used to limit the extent of sweep in each generation.
2926   save_sweep_limits();
2927   verify_overflow_empty();
2928 }
2929 
2930 bool CMSCollector::markFromRoots() {
2931   // we might be tempted to assert that:
2932   // assert(!SafepointSynchronize::is_at_safepoint(),
2933   //        "inconsistent argument?");
2934   // However that wouldn't be right, because it's possible that
2935   // a safepoint is indeed in progress as a young generation
2936   // stop-the-world GC happens even as we mark in this generation.
2937   assert(_collectorState == Marking, "inconsistent state?");
2938   check_correct_thread_executing();
2939   verify_overflow_empty();
2940 
2941   // Weak ref discovery note: We may be discovering weak
2942   // refs in this generation concurrent (but interleaved) with
2943   // weak ref discovery by the young generation collector.
2944 
2945   CMSTokenSyncWithLocks ts(true, bitMapLock());
2946   GCTraceCPUTime tcpu;
2947   CMSPhaseAccounting pa(this, "Concurrent Mark");
2948   bool res = markFromRootsWork();
2949   if (res) {
2950     _collectorState = Precleaning;
2951   } else { // We failed and a foreground collection wants to take over
2952     assert(_foregroundGCIsActive, "internal state inconsistency");
2953     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2954     log_debug(gc)("bailing out to foreground collection");
2955   }
2956   verify_overflow_empty();
2957   return res;
2958 }
2959 
2960 bool CMSCollector::markFromRootsWork() {
2961   // iterate over marked bits in bit map, doing a full scan and mark
2962   // from these roots using the following algorithm:
2963   // . if oop is to the right of the current scan pointer,
2964   //   mark corresponding bit (we'll process it later)
2965   // . else (oop is to left of current scan pointer)
2966   //   push oop on marking stack
2967   // . drain the marking stack
2968 
2969   // Note that when we do a marking step we need to hold the
2970   // bit map lock -- recall that direct allocation (by mutators)
2971   // and promotion (by the young generation collector) is also
2972   // marking the bit map. [the so-called allocate live policy.]
2973   // Because the implementation of bit map marking is not
2974   // robust wrt simultaneous marking of bits in the same word,
2975   // we need to make sure that there is no such interference
2976   // between concurrent such updates.
2977 
2978   // already have locks
2979   assert_lock_strong(bitMapLock());
2980 
2981   verify_work_stacks_empty();
2982   verify_overflow_empty();
2983   bool result = false;
2984   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2985     result = do_marking_mt();
2986   } else {
2987     result = do_marking_st();
2988   }
2989   return result;
2990 }
2991 
2992 // Forward decl
2993 class CMSConcMarkingTask;
2994 
2995 class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator {
2996   CMSCollector*       _collector;
2997   CMSConcMarkingTask* _task;
2998  public:
2999   virtual void yield();
3000 
3001   // "n_threads" is the number of threads to be terminated.
3002   // "queue_set" is a set of work queues of other threads.
3003   // "collector" is the CMS collector associated with this task terminator.
3004   // "yield" indicates whether we need the gang as a whole to yield.
3005   CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3006     ParallelTaskTerminator(n_threads, queue_set),
3007     _collector(collector) { }
3008 
3009   void set_task(CMSConcMarkingTask* task) {
3010     _task = task;
3011   }
3012 };
3013 
3014 class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator {
3015   CMSCollector*       _collector;
3016   CMSConcMarkingTask* _task;
3017  public:
3018   virtual void yield();
3019 
3020   // "n_threads" is the number of threads to be terminated.
3021   // "queue_set" is a set of work queues of other threads.
3022   // "collector" is the CMS collector associated with this task terminator.
3023   // "yield" indicates whether we need the gang as a whole to yield.
3024   CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3025     OWSTTaskTerminator(n_threads, queue_set),
3026     _collector(collector) { }
3027 
3028   void set_task(CMSConcMarkingTask* task) {
3029     _task = task;
3030   }
3031 };
3032 
3033 class CMSConcMarkingTaskTerminator {
3034  private:
3035   ParallelTaskTerminator* _term;
3036  public:
3037   CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) {
3038     if (UseOWSTTaskTerminator) {
3039       _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector);
3040     } else {
3041       _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector);
3042     }
3043   }
3044   ~CMSConcMarkingTaskTerminator() {
3045     assert(_term != NULL, "Must not be NULL");
3046     delete _term;
3047   }
3048 
3049   void set_task(CMSConcMarkingTask* task);
3050   ParallelTaskTerminator* terminator() const { return _term; }
3051 };
3052 
3053 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3054   CMSConcMarkingTask* _task;
3055  public:
3056   bool should_exit_termination();
3057   void set_task(CMSConcMarkingTask* task) {
3058     _task = task;
3059   }
3060 };
3061 
3062 // MT Concurrent Marking Task
3063 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3064   CMSCollector*             _collector;
3065   uint                      _n_workers;      // requested/desired # workers
3066   bool                      _result;
3067   CompactibleFreeListSpace* _cms_space;
3068   char                      _pad_front[64];   // padding to ...
3069   HeapWord* volatile        _global_finger;   // ... avoid sharing cache line
3070   char                      _pad_back[64];
3071   HeapWord*                 _restart_addr;
3072 
3073   //  Exposed here for yielding support
3074   Mutex* const _bit_map_lock;
3075 
3076   // The per thread work queues, available here for stealing
3077   OopTaskQueueSet*  _task_queues;
3078 
3079   // Termination (and yielding) support
3080   CMSConcMarkingTaskTerminator       _term;
3081   CMSConcMarkingTerminatorTerminator _term_term;
3082 
3083  public:
3084   CMSConcMarkingTask(CMSCollector* collector,
3085                  CompactibleFreeListSpace* cms_space,
3086                  YieldingFlexibleWorkGang* workers,
3087                  OopTaskQueueSet* task_queues):
3088     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3089     _collector(collector),
3090     _n_workers(0),
3091     _result(true),
3092     _cms_space(cms_space),
3093     _bit_map_lock(collector->bitMapLock()),
3094     _task_queues(task_queues),
3095     _term(_n_workers, task_queues, _collector)
3096   {
3097     _requested_size = _n_workers;
3098     _term.set_task(this);
3099     _term_term.set_task(this);
3100     _restart_addr = _global_finger = _cms_space->bottom();
3101   }
3102 
3103 
3104   OopTaskQueueSet* task_queues()  { return _task_queues; }
3105 
3106   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3107 
3108   HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3109 
3110   ParallelTaskTerminator* terminator() { return _term.terminator(); }
3111 
3112   virtual void set_for_termination(uint active_workers) {
3113     terminator()->reset_for_reuse(active_workers);
3114   }
3115 
3116   void work(uint worker_id);
3117   bool should_yield() {
3118     return    ConcurrentMarkSweepThread::should_yield()
3119            && !_collector->foregroundGCIsActive();
3120   }
3121 
3122   virtual void coordinator_yield();  // stuff done by coordinator
3123   bool result() { return _result; }
3124 
3125   void reset(HeapWord* ra) {
3126     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3127     _restart_addr = _global_finger = ra;
3128     _term.terminator()->reset_for_reuse();
3129   }
3130 
3131   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3132                                            OopTaskQueue* work_q);
3133 
3134  private:
3135   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3136   void do_work_steal(int i);
3137   void bump_global_finger(HeapWord* f);
3138 };
3139 
3140 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3141   assert(_task != NULL, "Error");
3142   return _task->yielding();
3143   // Note that we do not need the disjunct || _task->should_yield() above
3144   // because we want terminating threads to yield only if the task
3145   // is already in the midst of yielding, which happens only after at least one
3146   // thread has yielded.
3147 }
3148 
3149 void CMSConcMarkingParallelTerminator::yield() {
3150   if (_task->should_yield()) {
3151     _task->yield();
3152   } else {
3153     ParallelTaskTerminator::yield();
3154   }
3155 }
3156 
3157 void CMSConcMarkingOWSTTerminator::yield() {
3158   if (_task->should_yield()) {
3159     _task->yield();
3160   } else {
3161     OWSTTaskTerminator::yield();
3162   }
3163 }
3164 
3165 void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) {
3166   if (UseOWSTTaskTerminator) {
3167     ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task);
3168   } else {
3169     ((CMSConcMarkingParallelTerminator*)_term)->set_task(task);
3170   }
3171 }
3172 
3173 ////////////////////////////////////////////////////////////////
3174 // Concurrent Marking Algorithm Sketch
3175 ////////////////////////////////////////////////////////////////
3176 // Until all tasks exhausted (both spaces):
3177 // -- claim next available chunk
3178 // -- bump global finger via CAS
3179 // -- find first object that starts in this chunk
3180 //    and start scanning bitmap from that position
3181 // -- scan marked objects for oops
3182 // -- CAS-mark target, and if successful:
3183 //    . if target oop is above global finger (volatile read)
3184 //      nothing to do
3185 //    . if target oop is in chunk and above local finger
3186 //        then nothing to do
3187 //    . else push on work-queue
3188 // -- Deal with possible overflow issues:
3189 //    . local work-queue overflow causes stuff to be pushed on
3190 //      global (common) overflow queue
3191 //    . always first empty local work queue
3192 //    . then get a batch of oops from global work queue if any
3193 //    . then do work stealing
3194 // -- When all tasks claimed (both spaces)
3195 //    and local work queue empty,
3196 //    then in a loop do:
3197 //    . check global overflow stack; steal a batch of oops and trace
3198 //    . try to steal from other threads oif GOS is empty
3199 //    . if neither is available, offer termination
3200 // -- Terminate and return result
3201 //
3202 void CMSConcMarkingTask::work(uint worker_id) {
3203   elapsedTimer _timer;
3204   ResourceMark rm;
3205   HandleMark hm;
3206 
3207   DEBUG_ONLY(_collector->verify_overflow_empty();)
3208 
3209   // Before we begin work, our work queue should be empty
3210   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3211   // Scan the bitmap covering _cms_space, tracing through grey objects.
3212   _timer.start();
3213   do_scan_and_mark(worker_id, _cms_space);
3214   _timer.stop();
3215   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3216 
3217   // ... do work stealing
3218   _timer.reset();
3219   _timer.start();
3220   do_work_steal(worker_id);
3221   _timer.stop();
3222   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3223   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3224   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3225   // Note that under the current task protocol, the
3226   // following assertion is true even of the spaces
3227   // expanded since the completion of the concurrent
3228   // marking. XXX This will likely change under a strict
3229   // ABORT semantics.
3230   // After perm removal the comparison was changed to
3231   // greater than or equal to from strictly greater than.
3232   // Before perm removal the highest address sweep would
3233   // have been at the end of perm gen but now is at the
3234   // end of the tenured gen.
3235   assert(_global_finger >=  _cms_space->end(),
3236          "All tasks have been completed");
3237   DEBUG_ONLY(_collector->verify_overflow_empty();)
3238 }
3239 
3240 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3241   HeapWord* read = _global_finger;
3242   HeapWord* cur  = read;
3243   while (f > read) {
3244     cur = read;
3245     read = Atomic::cmpxchg(f, &_global_finger, cur);
3246     if (cur == read) {
3247       // our cas succeeded
3248       assert(_global_finger >= f, "protocol consistency");
3249       break;
3250     }
3251   }
3252 }
3253 
3254 // This is really inefficient, and should be redone by
3255 // using (not yet available) block-read and -write interfaces to the
3256 // stack and the work_queue. XXX FIX ME !!!
3257 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3258                                                       OopTaskQueue* work_q) {
3259   // Fast lock-free check
3260   if (ovflw_stk->length() == 0) {
3261     return false;
3262   }
3263   assert(work_q->size() == 0, "Shouldn't steal");
3264   MutexLocker ml(ovflw_stk->par_lock(),
3265                  Mutex::_no_safepoint_check_flag);
3266   // Grab up to 1/4 the size of the work queue
3267   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3268                     (size_t)ParGCDesiredObjsFromOverflowList);
3269   num = MIN2(num, ovflw_stk->length());
3270   for (int i = (int) num; i > 0; i--) {
3271     oop cur = ovflw_stk->pop();
3272     assert(cur != NULL, "Counted wrong?");
3273     work_q->push(cur);
3274   }
3275   return num > 0;
3276 }
3277 
3278 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3279   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3280   int n_tasks = pst->n_tasks();
3281   // We allow that there may be no tasks to do here because
3282   // we are restarting after a stack overflow.
3283   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3284   uint nth_task = 0;
3285 
3286   HeapWord* aligned_start = sp->bottom();
3287   if (sp->used_region().contains(_restart_addr)) {
3288     // Align down to a card boundary for the start of 0th task
3289     // for this space.
3290     aligned_start = align_down(_restart_addr, CardTable::card_size);
3291   }
3292 
3293   size_t chunk_size = sp->marking_task_size();
3294   while (pst->try_claim_task(/* reference */ nth_task)) {
3295     // Having claimed the nth task in this space,
3296     // compute the chunk that it corresponds to:
3297     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3298                                aligned_start + (nth_task+1)*chunk_size);
3299     // Try and bump the global finger via a CAS;
3300     // note that we need to do the global finger bump
3301     // _before_ taking the intersection below, because
3302     // the task corresponding to that region will be
3303     // deemed done even if the used_region() expands
3304     // because of allocation -- as it almost certainly will
3305     // during start-up while the threads yield in the
3306     // closure below.
3307     HeapWord* finger = span.end();
3308     bump_global_finger(finger);   // atomically
3309     // There are null tasks here corresponding to chunks
3310     // beyond the "top" address of the space.
3311     span = span.intersection(sp->used_region());
3312     if (!span.is_empty()) {  // Non-null task
3313       HeapWord* prev_obj;
3314       assert(!span.contains(_restart_addr) || nth_task == 0,
3315              "Inconsistency");
3316       if (nth_task == 0) {
3317         // For the 0th task, we'll not need to compute a block_start.
3318         if (span.contains(_restart_addr)) {
3319           // In the case of a restart because of stack overflow,
3320           // we might additionally skip a chunk prefix.
3321           prev_obj = _restart_addr;
3322         } else {
3323           prev_obj = span.start();
3324         }
3325       } else {
3326         // We want to skip the first object because
3327         // the protocol is to scan any object in its entirety
3328         // that _starts_ in this span; a fortiori, any
3329         // object starting in an earlier span is scanned
3330         // as part of an earlier claimed task.
3331         // Below we use the "careful" version of block_start
3332         // so we do not try to navigate uninitialized objects.
3333         prev_obj = sp->block_start_careful(span.start());
3334         // Below we use a variant of block_size that uses the
3335         // Printezis bits to avoid waiting for allocated
3336         // objects to become initialized/parsable.
3337         while (prev_obj < span.start()) {
3338           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3339           if (sz > 0) {
3340             prev_obj += sz;
3341           } else {
3342             // In this case we may end up doing a bit of redundant
3343             // scanning, but that appears unavoidable, short of
3344             // locking the free list locks; see bug 6324141.
3345             break;
3346           }
3347         }
3348       }
3349       if (prev_obj < span.end()) {
3350         MemRegion my_span = MemRegion(prev_obj, span.end());
3351         // Do the marking work within a non-empty span --
3352         // the last argument to the constructor indicates whether the
3353         // iteration should be incremental with periodic yields.
3354         ParMarkFromRootsClosure cl(this, _collector, my_span,
3355                                    &_collector->_markBitMap,
3356                                    work_queue(i),
3357                                    &_collector->_markStack);
3358         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3359       } // else nothing to do for this task
3360     }   // else nothing to do for this task
3361   }
3362   // We'd be tempted to assert here that since there are no
3363   // more tasks left to claim in this space, the global_finger
3364   // must exceed space->top() and a fortiori space->end(). However,
3365   // that would not quite be correct because the bumping of
3366   // global_finger occurs strictly after the claiming of a task,
3367   // so by the time we reach here the global finger may not yet
3368   // have been bumped up by the thread that claimed the last
3369   // task.
3370   pst->all_tasks_completed();
3371 }
3372 
3373 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3374  private:
3375   CMSCollector* _collector;
3376   CMSConcMarkingTask* _task;
3377   MemRegion     _span;
3378   CMSBitMap*    _bit_map;
3379   CMSMarkStack* _overflow_stack;
3380   OopTaskQueue* _work_queue;
3381  protected:
3382   DO_OOP_WORK_DEFN
3383  public:
3384   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3385                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3386     MetadataVisitingOopIterateClosure(collector->ref_processor()),
3387     _collector(collector),
3388     _task(task),
3389     _span(collector->_span),
3390     _bit_map(bit_map),
3391     _overflow_stack(overflow_stack),
3392     _work_queue(work_queue)
3393   { }
3394   virtual void do_oop(oop* p);
3395   virtual void do_oop(narrowOop* p);
3396 
3397   void trim_queue(size_t max);
3398   void handle_stack_overflow(HeapWord* lost);
3399   void do_yield_check() {
3400     if (_task->should_yield()) {
3401       _task->yield();
3402     }
3403   }
3404 };
3405 
3406 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3407 
3408 // Grey object scanning during work stealing phase --
3409 // the salient assumption here is that any references
3410 // that are in these stolen objects being scanned must
3411 // already have been initialized (else they would not have
3412 // been published), so we do not need to check for
3413 // uninitialized objects before pushing here.
3414 void ParConcMarkingClosure::do_oop(oop obj) {
3415   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3416   HeapWord* addr = (HeapWord*)obj;
3417   // Check if oop points into the CMS generation
3418   // and is not marked
3419   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3420     // a white object ...
3421     // If we manage to "claim" the object, by being the
3422     // first thread to mark it, then we push it on our
3423     // marking stack
3424     if (_bit_map->par_mark(addr)) {     // ... now grey
3425       // push on work queue (grey set)
3426       bool simulate_overflow = false;
3427       NOT_PRODUCT(
3428         if (CMSMarkStackOverflowALot &&
3429             _collector->simulate_overflow()) {
3430           // simulate a stack overflow
3431           simulate_overflow = true;
3432         }
3433       )
3434       if (simulate_overflow ||
3435           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3436         // stack overflow
3437         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3438         // We cannot assert that the overflow stack is full because
3439         // it may have been emptied since.
3440         assert(simulate_overflow ||
3441                _work_queue->size() == _work_queue->max_elems(),
3442               "Else push should have succeeded");
3443         handle_stack_overflow(addr);
3444       }
3445     } // Else, some other thread got there first
3446     do_yield_check();
3447   }
3448 }
3449 
3450 void ParConcMarkingClosure::trim_queue(size_t max) {
3451   while (_work_queue->size() > max) {
3452     oop new_oop;
3453     if (_work_queue->pop_local(new_oop)) {
3454       assert(oopDesc::is_oop(new_oop), "Should be an oop");
3455       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3456       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3457       new_oop->oop_iterate(this);  // do_oop() above
3458       do_yield_check();
3459     }
3460   }
3461 }
3462 
3463 // Upon stack overflow, we discard (part of) the stack,
3464 // remembering the least address amongst those discarded
3465 // in CMSCollector's _restart_address.
3466 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3467   // We need to do this under a mutex to prevent other
3468   // workers from interfering with the work done below.
3469   MutexLocker ml(_overflow_stack->par_lock(),
3470                  Mutex::_no_safepoint_check_flag);
3471   // Remember the least grey address discarded
3472   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3473   _collector->lower_restart_addr(ra);
3474   _overflow_stack->reset();  // discard stack contents
3475   _overflow_stack->expand(); // expand the stack if possible
3476 }
3477 
3478 
3479 void CMSConcMarkingTask::do_work_steal(int i) {
3480   OopTaskQueue* work_q = work_queue(i);
3481   oop obj_to_scan;
3482   CMSBitMap* bm = &(_collector->_markBitMap);
3483   CMSMarkStack* ovflw = &(_collector->_markStack);
3484   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3485   while (true) {
3486     cl.trim_queue(0);
3487     assert(work_q->size() == 0, "Should have been emptied above");
3488     if (get_work_from_overflow_stack(ovflw, work_q)) {
3489       // Can't assert below because the work obtained from the
3490       // overflow stack may already have been stolen from us.
3491       // assert(work_q->size() > 0, "Work from overflow stack");
3492       continue;
3493     } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3494       assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3495       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3496       obj_to_scan->oop_iterate(&cl);
3497     } else if (terminator()->offer_termination(&_term_term)) {
3498       assert(work_q->size() == 0, "Impossible!");
3499       break;
3500     } else if (yielding() || should_yield()) {
3501       yield();
3502     }
3503   }
3504 }
3505 
3506 // This is run by the CMS (coordinator) thread.
3507 void CMSConcMarkingTask::coordinator_yield() {
3508   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3509          "CMS thread should hold CMS token");
3510   // First give up the locks, then yield, then re-lock
3511   // We should probably use a constructor/destructor idiom to
3512   // do this unlock/lock or modify the MutexUnlocker class to
3513   // serve our purpose. XXX
3514   assert_lock_strong(_bit_map_lock);
3515   _bit_map_lock->unlock();
3516   ConcurrentMarkSweepThread::desynchronize(true);
3517   _collector->stopTimer();
3518   _collector->incrementYields();
3519 
3520   // It is possible for whichever thread initiated the yield request
3521   // not to get a chance to wake up and take the bitmap lock between
3522   // this thread releasing it and reacquiring it. So, while the
3523   // should_yield() flag is on, let's sleep for a bit to give the
3524   // other thread a chance to wake up. The limit imposed on the number
3525   // of iterations is defensive, to avoid any unforseen circumstances
3526   // putting us into an infinite loop. Since it's always been this
3527   // (coordinator_yield()) method that was observed to cause the
3528   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3529   // which is by default non-zero. For the other seven methods that
3530   // also perform the yield operation, as are using a different
3531   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3532   // can enable the sleeping for those methods too, if necessary.
3533   // See 6442774.
3534   //
3535   // We really need to reconsider the synchronization between the GC
3536   // thread and the yield-requesting threads in the future and we
3537   // should really use wait/notify, which is the recommended
3538   // way of doing this type of interaction. Additionally, we should
3539   // consolidate the eight methods that do the yield operation and they
3540   // are almost identical into one for better maintainability and
3541   // readability. See 6445193.
3542   //
3543   // Tony 2006.06.29
3544   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3545                    ConcurrentMarkSweepThread::should_yield() &&
3546                    !CMSCollector::foregroundGCIsActive(); ++i) {
3547     os::sleep(Thread::current(), 1, false);
3548   }
3549 
3550   ConcurrentMarkSweepThread::synchronize(true);
3551   _bit_map_lock->lock_without_safepoint_check();
3552   _collector->startTimer();
3553 }
3554 
3555 bool CMSCollector::do_marking_mt() {
3556   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3557   uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3558                                                             conc_workers()->active_workers(),
3559                                                             Threads::number_of_non_daemon_threads());
3560   num_workers = conc_workers()->update_active_workers(num_workers);
3561   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3562 
3563   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3564 
3565   CMSConcMarkingTask tsk(this,
3566                          cms_space,
3567                          conc_workers(),
3568                          task_queues());
3569 
3570   // Since the actual number of workers we get may be different
3571   // from the number we requested above, do we need to do anything different
3572   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3573   // class?? XXX
3574   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3575 
3576   // Refs discovery is already non-atomic.
3577   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3578   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3579   conc_workers()->start_task(&tsk);
3580   while (tsk.yielded()) {
3581     tsk.coordinator_yield();
3582     conc_workers()->continue_task(&tsk);
3583   }
3584   // If the task was aborted, _restart_addr will be non-NULL
3585   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3586   while (_restart_addr != NULL) {
3587     // XXX For now we do not make use of ABORTED state and have not
3588     // yet implemented the right abort semantics (even in the original
3589     // single-threaded CMS case). That needs some more investigation
3590     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3591     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3592     // If _restart_addr is non-NULL, a marking stack overflow
3593     // occurred; we need to do a fresh marking iteration from the
3594     // indicated restart address.
3595     if (_foregroundGCIsActive) {
3596       // We may be running into repeated stack overflows, having
3597       // reached the limit of the stack size, while making very
3598       // slow forward progress. It may be best to bail out and
3599       // let the foreground collector do its job.
3600       // Clear _restart_addr, so that foreground GC
3601       // works from scratch. This avoids the headache of
3602       // a "rescan" which would otherwise be needed because
3603       // of the dirty mod union table & card table.
3604       _restart_addr = NULL;
3605       return false;
3606     }
3607     // Adjust the task to restart from _restart_addr
3608     tsk.reset(_restart_addr);
3609     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3610                   _restart_addr);
3611     _restart_addr = NULL;
3612     // Get the workers going again
3613     conc_workers()->start_task(&tsk);
3614     while (tsk.yielded()) {
3615       tsk.coordinator_yield();
3616       conc_workers()->continue_task(&tsk);
3617     }
3618   }
3619   assert(tsk.completed(), "Inconsistency");
3620   assert(tsk.result() == true, "Inconsistency");
3621   return true;
3622 }
3623 
3624 bool CMSCollector::do_marking_st() {
3625   ResourceMark rm;
3626   HandleMark   hm;
3627 
3628   // Temporarily make refs discovery single threaded (non-MT)
3629   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3630   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3631     &_markStack, CMSYield);
3632   // the last argument to iterate indicates whether the iteration
3633   // should be incremental with periodic yields.
3634   _markBitMap.iterate(&markFromRootsClosure);
3635   // If _restart_addr is non-NULL, a marking stack overflow
3636   // occurred; we need to do a fresh iteration from the
3637   // indicated restart address.
3638   while (_restart_addr != NULL) {
3639     if (_foregroundGCIsActive) {
3640       // We may be running into repeated stack overflows, having
3641       // reached the limit of the stack size, while making very
3642       // slow forward progress. It may be best to bail out and
3643       // let the foreground collector do its job.
3644       // Clear _restart_addr, so that foreground GC
3645       // works from scratch. This avoids the headache of
3646       // a "rescan" which would otherwise be needed because
3647       // of the dirty mod union table & card table.
3648       _restart_addr = NULL;
3649       return false;  // indicating failure to complete marking
3650     }
3651     // Deal with stack overflow:
3652     // we restart marking from _restart_addr
3653     HeapWord* ra = _restart_addr;
3654     markFromRootsClosure.reset(ra);
3655     _restart_addr = NULL;
3656     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3657   }
3658   return true;
3659 }
3660 
3661 void CMSCollector::preclean() {
3662   check_correct_thread_executing();
3663   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3664   verify_work_stacks_empty();
3665   verify_overflow_empty();
3666   _abort_preclean = false;
3667   if (CMSPrecleaningEnabled) {
3668     if (!CMSEdenChunksRecordAlways) {
3669       _eden_chunk_index = 0;
3670     }
3671     size_t used = get_eden_used();
3672     size_t capacity = get_eden_capacity();
3673     // Don't start sampling unless we will get sufficiently
3674     // many samples.
3675     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3676                 * CMSScheduleRemarkEdenPenetration)) {
3677       _start_sampling = true;
3678     } else {
3679       _start_sampling = false;
3680     }
3681     GCTraceCPUTime tcpu;
3682     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3683     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3684   }
3685   CMSTokenSync x(true); // is cms thread
3686   if (CMSPrecleaningEnabled) {
3687     sample_eden();
3688     _collectorState = AbortablePreclean;
3689   } else {
3690     _collectorState = FinalMarking;
3691   }
3692   verify_work_stacks_empty();
3693   verify_overflow_empty();
3694 }
3695 
3696 // Try and schedule the remark such that young gen
3697 // occupancy is CMSScheduleRemarkEdenPenetration %.
3698 void CMSCollector::abortable_preclean() {
3699   check_correct_thread_executing();
3700   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3701   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3702 
3703   // If Eden's current occupancy is below this threshold,
3704   // immediately schedule the remark; else preclean
3705   // past the next scavenge in an effort to
3706   // schedule the pause as described above. By choosing
3707   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3708   // we will never do an actual abortable preclean cycle.
3709   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3710     GCTraceCPUTime tcpu;
3711     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3712     // We need more smarts in the abortable preclean
3713     // loop below to deal with cases where allocation
3714     // in young gen is very very slow, and our precleaning
3715     // is running a losing race against a horde of
3716     // mutators intent on flooding us with CMS updates
3717     // (dirty cards).
3718     // One, admittedly dumb, strategy is to give up
3719     // after a certain number of abortable precleaning loops
3720     // or after a certain maximum time. We want to make
3721     // this smarter in the next iteration.
3722     // XXX FIX ME!!! YSR
3723     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3724     while (!(should_abort_preclean() ||
3725              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3726       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3727       cumworkdone += workdone;
3728       loops++;
3729       // Voluntarily terminate abortable preclean phase if we have
3730       // been at it for too long.
3731       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3732           loops >= CMSMaxAbortablePrecleanLoops) {
3733         log_debug(gc)(" CMS: abort preclean due to loops ");
3734         break;
3735       }
3736       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3737         log_debug(gc)(" CMS: abort preclean due to time ");
3738         break;
3739       }
3740       // If we are doing little work each iteration, we should
3741       // take a short break.
3742       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3743         // Sleep for some time, waiting for work to accumulate
3744         stopTimer();
3745         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3746         startTimer();
3747         waited++;
3748       }
3749     }
3750     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3751                                loops, waited, cumworkdone);
3752   }
3753   CMSTokenSync x(true); // is cms thread
3754   if (_collectorState != Idling) {
3755     assert(_collectorState == AbortablePreclean,
3756            "Spontaneous state transition?");
3757     _collectorState = FinalMarking;
3758   } // Else, a foreground collection completed this CMS cycle.
3759   return;
3760 }
3761 
3762 // Respond to an Eden sampling opportunity
3763 void CMSCollector::sample_eden() {
3764   // Make sure a young gc cannot sneak in between our
3765   // reading and recording of a sample.
3766   assert(Thread::current()->is_ConcurrentGC_thread(),
3767          "Only the cms thread may collect Eden samples");
3768   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3769          "Should collect samples while holding CMS token");
3770   if (!_start_sampling) {
3771     return;
3772   }
3773   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3774   // is populated by the young generation.
3775   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3776     if (_eden_chunk_index < _eden_chunk_capacity) {
3777       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3778       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3779              "Unexpected state of Eden");
3780       // We'd like to check that what we just sampled is an oop-start address;
3781       // however, we cannot do that here since the object may not yet have been
3782       // initialized. So we'll instead do the check when we _use_ this sample
3783       // later.
3784       if (_eden_chunk_index == 0 ||
3785           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3786                          _eden_chunk_array[_eden_chunk_index-1])
3787            >= CMSSamplingGrain)) {
3788         _eden_chunk_index++;  // commit sample
3789       }
3790     }
3791   }
3792   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3793     size_t used = get_eden_used();
3794     size_t capacity = get_eden_capacity();
3795     assert(used <= capacity, "Unexpected state of Eden");
3796     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3797       _abort_preclean = true;
3798     }
3799   }
3800 }
3801 
3802 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3803   assert(_collectorState == Precleaning ||
3804          _collectorState == AbortablePreclean, "incorrect state");
3805   ResourceMark rm;
3806   HandleMark   hm;
3807 
3808   // Precleaning is currently not MT but the reference processor
3809   // may be set for MT.  Disable it temporarily here.
3810   ReferenceProcessor* rp = ref_processor();
3811   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3812 
3813   // Do one pass of scrubbing the discovered reference lists
3814   // to remove any reference objects with strongly-reachable
3815   // referents.
3816   if (clean_refs) {
3817     CMSPrecleanRefsYieldClosure yield_cl(this);
3818     assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3819     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3820                                    &_markStack, true /* preclean */);
3821     CMSDrainMarkingStackClosure complete_trace(this,
3822                                    _span, &_markBitMap, &_markStack,
3823                                    &keep_alive, true /* preclean */);
3824 
3825     // We don't want this step to interfere with a young
3826     // collection because we don't want to take CPU
3827     // or memory bandwidth away from the young GC threads
3828     // (which may be as many as there are CPUs).
3829     // Note that we don't need to protect ourselves from
3830     // interference with mutators because they can't
3831     // manipulate the discovered reference lists nor affect
3832     // the computed reachability of the referents, the
3833     // only properties manipulated by the precleaning
3834     // of these reference lists.
3835     stopTimer();
3836     CMSTokenSyncWithLocks x(true /* is cms thread */,
3837                             bitMapLock());
3838     startTimer();
3839     sample_eden();
3840 
3841     // The following will yield to allow foreground
3842     // collection to proceed promptly. XXX YSR:
3843     // The code in this method may need further
3844     // tweaking for better performance and some restructuring
3845     // for cleaner interfaces.
3846     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3847     rp->preclean_discovered_references(
3848           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3849           gc_timer);
3850   }
3851 
3852   if (clean_survivor) {  // preclean the active survivor space(s)
3853     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3854                              &_markBitMap, &_modUnionTable,
3855                              &_markStack, true /* precleaning phase */);
3856     stopTimer();
3857     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3858                              bitMapLock());
3859     startTimer();
3860     unsigned int before_count =
3861       CMSHeap::heap()->total_collections();
3862     SurvivorSpacePrecleanClosure
3863       sss_cl(this, _span, &_markBitMap, &_markStack,
3864              &pam_cl, before_count, CMSYield);
3865     _young_gen->from()->object_iterate_careful(&sss_cl);
3866     _young_gen->to()->object_iterate_careful(&sss_cl);
3867   }
3868   MarkRefsIntoAndScanClosure
3869     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3870              &_markStack, this, CMSYield,
3871              true /* precleaning phase */);
3872   // CAUTION: The following closure has persistent state that may need to
3873   // be reset upon a decrease in the sequence of addresses it
3874   // processes.
3875   ScanMarkedObjectsAgainCarefullyClosure
3876     smoac_cl(this, _span,
3877       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3878 
3879   // Preclean dirty cards in ModUnionTable and CardTable using
3880   // appropriate convergence criterion;
3881   // repeat CMSPrecleanIter times unless we find that
3882   // we are losing.
3883   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3884   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3885          "Bad convergence multiplier");
3886   assert(CMSPrecleanThreshold >= 100,
3887          "Unreasonably low CMSPrecleanThreshold");
3888 
3889   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3890   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3891        numIter < CMSPrecleanIter;
3892        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3893     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3894     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3895     // Either there are very few dirty cards, so re-mark
3896     // pause will be small anyway, or our pre-cleaning isn't
3897     // that much faster than the rate at which cards are being
3898     // dirtied, so we might as well stop and re-mark since
3899     // precleaning won't improve our re-mark time by much.
3900     if (curNumCards <= CMSPrecleanThreshold ||
3901         (numIter > 0 &&
3902          (curNumCards * CMSPrecleanDenominator >
3903          lastNumCards * CMSPrecleanNumerator))) {
3904       numIter++;
3905       cumNumCards += curNumCards;
3906       break;
3907     }
3908   }
3909 
3910   preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3911 
3912   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3913   cumNumCards += curNumCards;
3914   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3915                              curNumCards, cumNumCards, numIter);
3916   return cumNumCards;   // as a measure of useful work done
3917 }
3918 
3919 // PRECLEANING NOTES:
3920 // Precleaning involves:
3921 // . reading the bits of the modUnionTable and clearing the set bits.
3922 // . For the cards corresponding to the set bits, we scan the
3923 //   objects on those cards. This means we need the free_list_lock
3924 //   so that we can safely iterate over the CMS space when scanning
3925 //   for oops.
3926 // . When we scan the objects, we'll be both reading and setting
3927 //   marks in the marking bit map, so we'll need the marking bit map.
3928 // . For protecting _collector_state transitions, we take the CGC_lock.
3929 //   Note that any races in the reading of of card table entries by the
3930 //   CMS thread on the one hand and the clearing of those entries by the
3931 //   VM thread or the setting of those entries by the mutator threads on the
3932 //   other are quite benign. However, for efficiency it makes sense to keep
3933 //   the VM thread from racing with the CMS thread while the latter is
3934 //   dirty card info to the modUnionTable. We therefore also use the
3935 //   CGC_lock to protect the reading of the card table and the mod union
3936 //   table by the CM thread.
3937 // . We run concurrently with mutator updates, so scanning
3938 //   needs to be done carefully  -- we should not try to scan
3939 //   potentially uninitialized objects.
3940 //
3941 // Locking strategy: While holding the CGC_lock, we scan over and
3942 // reset a maximal dirty range of the mod union / card tables, then lock
3943 // the free_list_lock and bitmap lock to do a full marking, then
3944 // release these locks; and repeat the cycle. This allows for a
3945 // certain amount of fairness in the sharing of these locks between
3946 // the CMS collector on the one hand, and the VM thread and the
3947 // mutators on the other.
3948 
3949 // NOTE: preclean_mod_union_table() and preclean_card_table()
3950 // further below are largely identical; if you need to modify
3951 // one of these methods, please check the other method too.
3952 
3953 size_t CMSCollector::preclean_mod_union_table(
3954   ConcurrentMarkSweepGeneration* old_gen,
3955   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3956   verify_work_stacks_empty();
3957   verify_overflow_empty();
3958 
3959   // strategy: starting with the first card, accumulate contiguous
3960   // ranges of dirty cards; clear these cards, then scan the region
3961   // covered by these cards.
3962 
3963   // Since all of the MUT is committed ahead, we can just use
3964   // that, in case the generations expand while we are precleaning.
3965   // It might also be fine to just use the committed part of the
3966   // generation, but we might potentially miss cards when the
3967   // generation is rapidly expanding while we are in the midst
3968   // of precleaning.
3969   HeapWord* startAddr = old_gen->reserved().start();
3970   HeapWord* endAddr   = old_gen->reserved().end();
3971 
3972   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3973 
3974   size_t numDirtyCards, cumNumDirtyCards;
3975   HeapWord *nextAddr, *lastAddr;
3976   for (cumNumDirtyCards = numDirtyCards = 0,
3977        nextAddr = lastAddr = startAddr;
3978        nextAddr < endAddr;
3979        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3980 
3981     ResourceMark rm;
3982     HandleMark   hm;
3983 
3984     MemRegion dirtyRegion;
3985     {
3986       stopTimer();
3987       // Potential yield point
3988       CMSTokenSync ts(true);
3989       startTimer();
3990       sample_eden();
3991       // Get dirty region starting at nextOffset (inclusive),
3992       // simultaneously clearing it.
3993       dirtyRegion =
3994         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3995       assert(dirtyRegion.start() >= nextAddr,
3996              "returned region inconsistent?");
3997     }
3998     // Remember where the next search should begin.
3999     // The returned region (if non-empty) is a right open interval,
4000     // so lastOffset is obtained from the right end of that
4001     // interval.
4002     lastAddr = dirtyRegion.end();
4003     // Should do something more transparent and less hacky XXX
4004     numDirtyCards =
4005       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4006 
4007     // We'll scan the cards in the dirty region (with periodic
4008     // yields for foreground GC as needed).
4009     if (!dirtyRegion.is_empty()) {
4010       assert(numDirtyCards > 0, "consistency check");
4011       HeapWord* stop_point = NULL;
4012       stopTimer();
4013       // Potential yield point
4014       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4015                                bitMapLock());
4016       startTimer();
4017       {
4018         verify_work_stacks_empty();
4019         verify_overflow_empty();
4020         sample_eden();
4021         stop_point =
4022           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4023       }
4024       if (stop_point != NULL) {
4025         // The careful iteration stopped early either because it found an
4026         // uninitialized object, or because we were in the midst of an
4027         // "abortable preclean", which should now be aborted. Redirty
4028         // the bits corresponding to the partially-scanned or unscanned
4029         // cards. We'll either restart at the next block boundary or
4030         // abort the preclean.
4031         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4032                "Should only be AbortablePreclean.");
4033         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4034         if (should_abort_preclean()) {
4035           break; // out of preclean loop
4036         } else {
4037           // Compute the next address at which preclean should pick up;
4038           // might need bitMapLock in order to read P-bits.
4039           lastAddr = next_card_start_after_block(stop_point);
4040         }
4041       }
4042     } else {
4043       assert(lastAddr == endAddr, "consistency check");
4044       assert(numDirtyCards == 0, "consistency check");
4045       break;
4046     }
4047   }
4048   verify_work_stacks_empty();
4049   verify_overflow_empty();
4050   return cumNumDirtyCards;
4051 }
4052 
4053 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4054 // below are largely identical; if you need to modify
4055 // one of these methods, please check the other method too.
4056 
4057 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4058   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4059   // strategy: it's similar to precleamModUnionTable above, in that
4060   // we accumulate contiguous ranges of dirty cards, mark these cards
4061   // precleaned, then scan the region covered by these cards.
4062   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4063   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4064 
4065   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4066 
4067   size_t numDirtyCards, cumNumDirtyCards;
4068   HeapWord *lastAddr, *nextAddr;
4069 
4070   for (cumNumDirtyCards = numDirtyCards = 0,
4071        nextAddr = lastAddr = startAddr;
4072        nextAddr < endAddr;
4073        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4074 
4075     ResourceMark rm;
4076     HandleMark   hm;
4077 
4078     MemRegion dirtyRegion;
4079     {
4080       // See comments in "Precleaning notes" above on why we
4081       // do this locking. XXX Could the locking overheads be
4082       // too high when dirty cards are sparse? [I don't think so.]
4083       stopTimer();
4084       CMSTokenSync x(true); // is cms thread
4085       startTimer();
4086       sample_eden();
4087       // Get and clear dirty region from card table
4088       dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4089                                                       true,
4090                                                       CardTable::precleaned_card_val());
4091 
4092       assert(dirtyRegion.start() >= nextAddr,
4093              "returned region inconsistent?");
4094     }
4095     lastAddr = dirtyRegion.end();
4096     numDirtyCards =
4097       dirtyRegion.word_size()/CardTable::card_size_in_words;
4098 
4099     if (!dirtyRegion.is_empty()) {
4100       stopTimer();
4101       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4102       startTimer();
4103       sample_eden();
4104       verify_work_stacks_empty();
4105       verify_overflow_empty();
4106       HeapWord* stop_point =
4107         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4108       if (stop_point != NULL) {
4109         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4110                "Should only be AbortablePreclean.");
4111         _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4112         if (should_abort_preclean()) {
4113           break; // out of preclean loop
4114         } else {
4115           // Compute the next address at which preclean should pick up.
4116           lastAddr = next_card_start_after_block(stop_point);
4117         }
4118       }
4119     } else {
4120       break;
4121     }
4122   }
4123   verify_work_stacks_empty();
4124   verify_overflow_empty();
4125   return cumNumDirtyCards;
4126 }
4127 
4128 class PrecleanCLDClosure : public CLDClosure {
4129   MetadataVisitingOopsInGenClosure* _cm_closure;
4130  public:
4131   PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4132   void do_cld(ClassLoaderData* cld) {
4133     if (cld->has_accumulated_modified_oops()) {
4134       cld->clear_accumulated_modified_oops();
4135 
4136       _cm_closure->do_cld(cld);
4137     }
4138   }
4139 };
4140 
4141 // The freelist lock is needed to prevent asserts, is it really needed?
4142 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4143   // Needed to walk CLDG
4144   MutexLocker ml(ClassLoaderDataGraph_lock);
4145 
4146   cl->set_freelistLock(freelistLock);
4147 
4148   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4149 
4150   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4151   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4152   PrecleanCLDClosure preclean_closure(cl);
4153   ClassLoaderDataGraph::cld_do(&preclean_closure);
4154 
4155   verify_work_stacks_empty();
4156   verify_overflow_empty();
4157 }
4158 
4159 void CMSCollector::checkpointRootsFinal() {
4160   assert(_collectorState == FinalMarking, "incorrect state transition?");
4161   check_correct_thread_executing();
4162   // world is stopped at this checkpoint
4163   assert(SafepointSynchronize::is_at_safepoint(),
4164          "world should be stopped");
4165   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4166 
4167   verify_work_stacks_empty();
4168   verify_overflow_empty();
4169 
4170   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4171                 _young_gen->used() / K, _young_gen->capacity() / K);
4172   {
4173     if (CMSScavengeBeforeRemark) {
4174       CMSHeap* heap = CMSHeap::heap();
4175       // Temporarily set flag to false, GCH->do_collection will
4176       // expect it to be false and set to true
4177       FlagSetting fl(heap->_is_gc_active, false);
4178 
4179       heap->do_collection(true,                      // full (i.e. force, see below)
4180                           false,                     // !clear_all_soft_refs
4181                           0,                         // size
4182                           false,                     // is_tlab
4183                           GenCollectedHeap::YoungGen // type
4184         );
4185     }
4186     FreelistLocker x(this);
4187     MutexLocker y(bitMapLock(),
4188                   Mutex::_no_safepoint_check_flag);
4189     checkpointRootsFinalWork();
4190     _cmsGen->cmsSpace()->recalculate_used_stable();
4191   }
4192   verify_work_stacks_empty();
4193   verify_overflow_empty();
4194 }
4195 
4196 void CMSCollector::checkpointRootsFinalWork() {
4197   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4198 
4199   assert(haveFreelistLocks(), "must have free list locks");
4200   assert_lock_strong(bitMapLock());
4201 
4202   ResourceMark rm;
4203   HandleMark   hm;
4204 
4205   CMSHeap* heap = CMSHeap::heap();
4206 
4207   assert(haveFreelistLocks(), "must have free list locks");
4208   assert_lock_strong(bitMapLock());
4209 
4210   // We might assume that we need not fill TLAB's when
4211   // CMSScavengeBeforeRemark is set, because we may have just done
4212   // a scavenge which would have filled all TLAB's -- and besides
4213   // Eden would be empty. This however may not always be the case --
4214   // for instance although we asked for a scavenge, it may not have
4215   // happened because of a JNI critical section. We probably need
4216   // a policy for deciding whether we can in that case wait until
4217   // the critical section releases and then do the remark following
4218   // the scavenge, and skip it here. In the absence of that policy,
4219   // or of an indication of whether the scavenge did indeed occur,
4220   // we cannot rely on TLAB's having been filled and must do
4221   // so here just in case a scavenge did not happen.
4222   heap->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4223   // Update the saved marks which may affect the root scans.
4224   heap->save_marks();
4225 
4226   print_eden_and_survivor_chunk_arrays();
4227 
4228   {
4229 #if COMPILER2_OR_JVMCI
4230     DerivedPointerTableDeactivate dpt_deact;
4231 #endif
4232 
4233     // Note on the role of the mod union table:
4234     // Since the marker in "markFromRoots" marks concurrently with
4235     // mutators, it is possible for some reachable objects not to have been
4236     // scanned. For instance, an only reference to an object A was
4237     // placed in object B after the marker scanned B. Unless B is rescanned,
4238     // A would be collected. Such updates to references in marked objects
4239     // are detected via the mod union table which is the set of all cards
4240     // dirtied since the first checkpoint in this GC cycle and prior to
4241     // the most recent young generation GC, minus those cleaned up by the
4242     // concurrent precleaning.
4243     if (CMSParallelRemarkEnabled) {
4244       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4245       do_remark_parallel();
4246     } else {
4247       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4248       do_remark_non_parallel();
4249     }
4250   }
4251   verify_work_stacks_empty();
4252   verify_overflow_empty();
4253 
4254   {
4255     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4256     refProcessingWork();
4257   }
4258   verify_work_stacks_empty();
4259   verify_overflow_empty();
4260 
4261   if (should_unload_classes()) {
4262     heap->prune_scavengable_nmethods();
4263   }
4264   JvmtiExport::gc_epilogue();
4265 
4266   // If we encountered any (marking stack / work queue) overflow
4267   // events during the current CMS cycle, take appropriate
4268   // remedial measures, where possible, so as to try and avoid
4269   // recurrence of that condition.
4270   assert(_markStack.isEmpty(), "No grey objects");
4271   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4272                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4273   if (ser_ovflw > 0) {
4274     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4275                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4276     _markStack.expand();
4277     _ser_pmc_remark_ovflw = 0;
4278     _ser_pmc_preclean_ovflw = 0;
4279     _ser_kac_preclean_ovflw = 0;
4280     _ser_kac_ovflw = 0;
4281   }
4282   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4283      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4284                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4285      _par_pmc_remark_ovflw = 0;
4286     _par_kac_ovflw = 0;
4287   }
4288    if (_markStack._hit_limit > 0) {
4289      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4290                           _markStack._hit_limit);
4291    }
4292    if (_markStack._failed_double > 0) {
4293      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4294                           _markStack._failed_double, _markStack.capacity());
4295    }
4296   _markStack._hit_limit = 0;
4297   _markStack._failed_double = 0;
4298 
4299   if ((VerifyAfterGC || VerifyDuringGC) &&
4300       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4301     verify_after_remark();
4302   }
4303 
4304   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4305 
4306   // Change under the freelistLocks.
4307   _collectorState = Sweeping;
4308   // Call isAllClear() under bitMapLock
4309   assert(_modUnionTable.isAllClear(),
4310       "Should be clear by end of the final marking");
4311   assert(_ct->cld_rem_set()->mod_union_is_clear(),
4312       "Should be clear by end of the final marking");
4313 }
4314 
4315 void CMSParInitialMarkTask::work(uint worker_id) {
4316   elapsedTimer _timer;
4317   ResourceMark rm;
4318   HandleMark   hm;
4319 
4320   // ---------- scan from roots --------------
4321   _timer.start();
4322   CMSHeap* heap = CMSHeap::heap();
4323   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4324 
4325   // ---------- young gen roots --------------
4326   {
4327     work_on_young_gen_roots(&par_mri_cl);
4328     _timer.stop();
4329     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4330   }
4331 
4332   // ---------- remaining roots --------------
4333   _timer.reset();
4334   _timer.start();
4335 
4336   CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4337 
4338   heap->cms_process_roots(_strong_roots_scope,
4339                           false,     // yg was scanned above
4340                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4341                           _collector->should_unload_classes(),
4342                           &par_mri_cl,
4343                           &cld_closure);
4344 
4345   assert(_collector->should_unload_classes()
4346          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4347          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4348   _timer.stop();
4349   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4350 }
4351 
4352 // Parallel remark task
4353 class CMSParRemarkTask: public CMSParMarkTask {
4354   CompactibleFreeListSpace* _cms_space;
4355 
4356   // The per-thread work queues, available here for stealing.
4357   OopTaskQueueSet*       _task_queues;
4358   TaskTerminator         _term;
4359   StrongRootsScope*      _strong_roots_scope;
4360 
4361  public:
4362   // A value of 0 passed to n_workers will cause the number of
4363   // workers to be taken from the active workers in the work gang.
4364   CMSParRemarkTask(CMSCollector* collector,
4365                    CompactibleFreeListSpace* cms_space,
4366                    uint n_workers, WorkGang* workers,
4367                    OopTaskQueueSet* task_queues,
4368                    StrongRootsScope* strong_roots_scope):
4369     CMSParMarkTask("Rescan roots and grey objects in parallel",
4370                    collector, n_workers),
4371     _cms_space(cms_space),
4372     _task_queues(task_queues),
4373     _term(n_workers, task_queues),
4374     _strong_roots_scope(strong_roots_scope) { }
4375 
4376   OopTaskQueueSet* task_queues() { return _task_queues; }
4377 
4378   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4379 
4380   ParallelTaskTerminator* terminator() { return _term.terminator(); }
4381   uint n_workers() { return _n_workers; }
4382 
4383   void work(uint worker_id);
4384 
4385  private:
4386   // ... of  dirty cards in old space
4387   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4388                                   ParMarkRefsIntoAndScanClosure* cl);
4389 
4390   // ... work stealing for the above
4391   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4392 };
4393 
4394 class RemarkCLDClosure : public CLDClosure {
4395   CLDToOopClosure _cm_closure;
4396  public:
4397   RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4398   void do_cld(ClassLoaderData* cld) {
4399     // Check if we have modified any oops in the CLD during the concurrent marking.
4400     if (cld->has_accumulated_modified_oops()) {
4401       cld->clear_accumulated_modified_oops();
4402 
4403       // We could have transfered the current modified marks to the accumulated marks,
4404       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4405     } else if (cld->has_modified_oops()) {
4406       // Don't clear anything, this info is needed by the next young collection.
4407     } else {
4408       // No modified oops in the ClassLoaderData.
4409       return;
4410     }
4411 
4412     // The klass has modified fields, need to scan the klass.
4413     _cm_closure.do_cld(cld);
4414   }
4415 };
4416 
4417 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4418   ParNewGeneration* young_gen = _collector->_young_gen;
4419   ContiguousSpace* eden_space = young_gen->eden();
4420   ContiguousSpace* from_space = young_gen->from();
4421   ContiguousSpace* to_space   = young_gen->to();
4422 
4423   HeapWord** eca = _collector->_eden_chunk_array;
4424   size_t     ect = _collector->_eden_chunk_index;
4425   HeapWord** sca = _collector->_survivor_chunk_array;
4426   size_t     sct = _collector->_survivor_chunk_index;
4427 
4428   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4429   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4430 
4431   do_young_space_rescan(cl, to_space, NULL, 0);
4432   do_young_space_rescan(cl, from_space, sca, sct);
4433   do_young_space_rescan(cl, eden_space, eca, ect);
4434 }
4435 
4436 // work_queue(i) is passed to the closure
4437 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4438 // also is passed to do_dirty_card_rescan_tasks() and to
4439 // do_work_steal() to select the i-th task_queue.
4440 
4441 void CMSParRemarkTask::work(uint worker_id) {
4442   elapsedTimer _timer;
4443   ResourceMark rm;
4444   HandleMark   hm;
4445 
4446   // ---------- rescan from roots --------------
4447   _timer.start();
4448   CMSHeap* heap = CMSHeap::heap();
4449   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4450     _collector->_span, _collector->ref_processor(),
4451     &(_collector->_markBitMap),
4452     work_queue(worker_id));
4453 
4454   // Rescan young gen roots first since these are likely
4455   // coarsely partitioned and may, on that account, constitute
4456   // the critical path; thus, it's best to start off that
4457   // work first.
4458   // ---------- young gen roots --------------
4459   {
4460     work_on_young_gen_roots(&par_mrias_cl);
4461     _timer.stop();
4462     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4463   }
4464 
4465   // ---------- remaining roots --------------
4466   _timer.reset();
4467   _timer.start();
4468   heap->cms_process_roots(_strong_roots_scope,
4469                           false,     // yg was scanned above
4470                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4471                           _collector->should_unload_classes(),
4472                           &par_mrias_cl,
4473                           NULL);     // The dirty klasses will be handled below
4474 
4475   assert(_collector->should_unload_classes()
4476          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4477          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4478   _timer.stop();
4479   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4480 
4481   // ---------- unhandled CLD scanning ----------
4482   if (worker_id == 0) { // Single threaded at the moment.
4483     _timer.reset();
4484     _timer.start();
4485 
4486     // Scan all new class loader data objects and new dependencies that were
4487     // introduced during concurrent marking.
4488     ResourceMark rm;
4489     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4490     for (int i = 0; i < array->length(); i++) {
4491       Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4492     }
4493 
4494     // We don't need to keep track of new CLDs anymore.
4495     ClassLoaderDataGraph::remember_new_clds(false);
4496 
4497     _timer.stop();
4498     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4499   }
4500 
4501   // We might have added oops to ClassLoaderData::_handles during the
4502   // concurrent marking phase. These oops do not always point to newly allocated objects
4503   // that are guaranteed to be kept alive.  Hence,
4504   // we do have to revisit the _handles block during the remark phase.
4505 
4506   // ---------- dirty CLD scanning ----------
4507   if (worker_id == 0) { // Single threaded at the moment.
4508     _timer.reset();
4509     _timer.start();
4510 
4511     // Scan all classes that was dirtied during the concurrent marking phase.
4512     RemarkCLDClosure remark_closure(&par_mrias_cl);
4513     ClassLoaderDataGraph::cld_do(&remark_closure);
4514 
4515     _timer.stop();
4516     log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4517   }
4518 
4519 
4520   // ---------- rescan dirty cards ------------
4521   _timer.reset();
4522   _timer.start();
4523 
4524   // Do the rescan tasks for each of the two spaces
4525   // (cms_space) in turn.
4526   // "worker_id" is passed to select the task_queue for "worker_id"
4527   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4528   _timer.stop();
4529   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4530 
4531   // ---------- steal work from other threads ...
4532   // ---------- ... and drain overflow list.
4533   _timer.reset();
4534   _timer.start();
4535   do_work_steal(worker_id, &par_mrias_cl);
4536   _timer.stop();
4537   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4538 }
4539 
4540 void
4541 CMSParMarkTask::do_young_space_rescan(
4542   OopsInGenClosure* cl, ContiguousSpace* space,
4543   HeapWord** chunk_array, size_t chunk_top) {
4544   // Until all tasks completed:
4545   // . claim an unclaimed task
4546   // . compute region boundaries corresponding to task claimed
4547   //   using chunk_array
4548   // . par_oop_iterate(cl) over that region
4549 
4550   ResourceMark rm;
4551   HandleMark   hm;
4552 
4553   SequentialSubTasksDone* pst = space->par_seq_tasks();
4554 
4555   uint nth_task = 0;
4556   uint n_tasks  = pst->n_tasks();
4557 
4558   if (n_tasks > 0) {
4559     assert(pst->valid(), "Uninitialized use?");
4560     HeapWord *start, *end;
4561     while (pst->try_claim_task(/* reference */ nth_task)) {
4562       // We claimed task # nth_task; compute its boundaries.
4563       if (chunk_top == 0) {  // no samples were taken
4564         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4565         start = space->bottom();
4566         end   = space->top();
4567       } else if (nth_task == 0) {
4568         start = space->bottom();
4569         end   = chunk_array[nth_task];
4570       } else if (nth_task < (uint)chunk_top) {
4571         assert(nth_task >= 1, "Control point invariant");
4572         start = chunk_array[nth_task - 1];
4573         end   = chunk_array[nth_task];
4574       } else {
4575         assert(nth_task == (uint)chunk_top, "Control point invariant");
4576         start = chunk_array[chunk_top - 1];
4577         end   = space->top();
4578       }
4579       MemRegion mr(start, end);
4580       // Verify that mr is in space
4581       assert(mr.is_empty() || space->used_region().contains(mr),
4582              "Should be in space");
4583       // Verify that "start" is an object boundary
4584       assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4585              "Should be an oop");
4586       space->par_oop_iterate(mr, cl);
4587     }
4588     pst->all_tasks_completed();
4589   }
4590 }
4591 
4592 void
4593 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4594   CompactibleFreeListSpace* sp, int i,
4595   ParMarkRefsIntoAndScanClosure* cl) {
4596   // Until all tasks completed:
4597   // . claim an unclaimed task
4598   // . compute region boundaries corresponding to task claimed
4599   // . transfer dirty bits ct->mut for that region
4600   // . apply rescanclosure to dirty mut bits for that region
4601 
4602   ResourceMark rm;
4603   HandleMark   hm;
4604 
4605   OopTaskQueue* work_q = work_queue(i);
4606   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4607   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4608   // CAUTION: This closure has state that persists across calls to
4609   // the work method dirty_range_iterate_clear() in that it has
4610   // embedded in it a (subtype of) UpwardsObjectClosure. The
4611   // use of that state in the embedded UpwardsObjectClosure instance
4612   // assumes that the cards are always iterated (even if in parallel
4613   // by several threads) in monotonically increasing order per each
4614   // thread. This is true of the implementation below which picks
4615   // card ranges (chunks) in monotonically increasing order globally
4616   // and, a-fortiori, in monotonically increasing order per thread
4617   // (the latter order being a subsequence of the former).
4618   // If the work code below is ever reorganized into a more chaotic
4619   // work-partitioning form than the current "sequential tasks"
4620   // paradigm, the use of that persistent state will have to be
4621   // revisited and modified appropriately. See also related
4622   // bug 4756801 work on which should examine this code to make
4623   // sure that the changes there do not run counter to the
4624   // assumptions made here and necessary for correctness and
4625   // efficiency. Note also that this code might yield inefficient
4626   // behavior in the case of very large objects that span one or
4627   // more work chunks. Such objects would potentially be scanned
4628   // several times redundantly. Work on 4756801 should try and
4629   // address that performance anomaly if at all possible. XXX
4630   MemRegion  full_span  = _collector->_span;
4631   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4632   MarkFromDirtyCardsClosure
4633     greyRescanClosure(_collector, full_span, // entire span of interest
4634                       sp, bm, work_q, cl);
4635 
4636   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4637   assert(pst->valid(), "Uninitialized use?");
4638   uint nth_task = 0;
4639   const int alignment = CardTable::card_size * BitsPerWord;
4640   MemRegion span = sp->used_region();
4641   HeapWord* start_addr = span.start();
4642   HeapWord* end_addr = align_up(span.end(), alignment);
4643   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4644   assert(is_aligned(start_addr, alignment), "Check alignment");
4645   assert(is_aligned(chunk_size, alignment), "Check alignment");
4646 
4647   while (pst->try_claim_task(/* reference */ nth_task)) {
4648     // Having claimed the nth_task, compute corresponding mem-region,
4649     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4650     // The alignment restriction ensures that we do not need any
4651     // synchronization with other gang-workers while setting or
4652     // clearing bits in thus chunk of the MUT.
4653     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4654                                     start_addr + (nth_task+1)*chunk_size);
4655     // The last chunk's end might be way beyond end of the
4656     // used region. In that case pull back appropriately.
4657     if (this_span.end() > end_addr) {
4658       this_span.set_end(end_addr);
4659       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4660     }
4661     // Iterate over the dirty cards covering this chunk, marking them
4662     // precleaned, and setting the corresponding bits in the mod union
4663     // table. Since we have been careful to partition at Card and MUT-word
4664     // boundaries no synchronization is needed between parallel threads.
4665     _collector->_ct->dirty_card_iterate(this_span,
4666                                                  &modUnionClosure);
4667 
4668     // Having transferred these marks into the modUnionTable,
4669     // rescan the marked objects on the dirty cards in the modUnionTable.
4670     // Even if this is at a synchronous collection, the initial marking
4671     // may have been done during an asynchronous collection so there
4672     // may be dirty bits in the mod-union table.
4673     _collector->_modUnionTable.dirty_range_iterate_clear(
4674                   this_span, &greyRescanClosure);
4675     _collector->_modUnionTable.verifyNoOneBitsInRange(
4676                                  this_span.start(),
4677                                  this_span.end());
4678   }
4679   pst->all_tasks_completed();  // declare that i am done
4680 }
4681 
4682 // . see if we can share work_queues with ParNew? XXX
4683 void
4684 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4685   OopTaskQueue* work_q = work_queue(i);
4686   NOT_PRODUCT(int num_steals = 0;)
4687   oop obj_to_scan;
4688   CMSBitMap* bm = &(_collector->_markBitMap);
4689 
4690   while (true) {
4691     // Completely finish any left over work from (an) earlier round(s)
4692     cl->trim_queue(0);
4693     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4694                                          (size_t)ParGCDesiredObjsFromOverflowList);
4695     // Now check if there's any work in the overflow list
4696     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4697     // only affects the number of attempts made to get work from the
4698     // overflow list and does not affect the number of workers.  Just
4699     // pass ParallelGCThreads so this behavior is unchanged.
4700     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4701                                                 work_q,
4702                                                 ParallelGCThreads)) {
4703       // found something in global overflow list;
4704       // not yet ready to go stealing work from others.
4705       // We'd like to assert(work_q->size() != 0, ...)
4706       // because we just took work from the overflow list,
4707       // but of course we can't since all of that could have
4708       // been already stolen from us.
4709       // "He giveth and He taketh away."
4710       continue;
4711     }
4712     // Verify that we have no work before we resort to stealing
4713     assert(work_q->size() == 0, "Have work, shouldn't steal");
4714     // Try to steal from other queues that have work
4715     if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4716       NOT_PRODUCT(num_steals++;)
4717       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4718       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4719       // Do scanning work
4720       obj_to_scan->oop_iterate(cl);
4721       // Loop around, finish this work, and try to steal some more
4722     } else if (terminator()->offer_termination()) {
4723         break;  // nirvana from the infinite cycle
4724     }
4725   }
4726   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4727   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4728          "Else our work is not yet done");
4729 }
4730 
4731 // Record object boundaries in _eden_chunk_array by sampling the eden
4732 // top in the slow-path eden object allocation code path and record
4733 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4734 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4735 // sampling in sample_eden() that activates during the part of the
4736 // preclean phase.
4737 void CMSCollector::sample_eden_chunk() {
4738   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4739     if (_eden_chunk_lock->try_lock()) {
4740       // Record a sample. This is the critical section. The contents
4741       // of the _eden_chunk_array have to be non-decreasing in the
4742       // address order.
4743       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4744       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4745              "Unexpected state of Eden");
4746       if (_eden_chunk_index == 0 ||
4747           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4748            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4749                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4750         _eden_chunk_index++;  // commit sample
4751       }
4752       _eden_chunk_lock->unlock();
4753     }
4754   }
4755 }
4756 
4757 // Return a thread-local PLAB recording array, as appropriate.
4758 void* CMSCollector::get_data_recorder(int thr_num) {
4759   if (_survivor_plab_array != NULL &&
4760       (CMSPLABRecordAlways ||
4761        (_collectorState > Marking && _collectorState < FinalMarking))) {
4762     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4763     ChunkArray* ca = &_survivor_plab_array[thr_num];
4764     ca->reset();   // clear it so that fresh data is recorded
4765     return (void*) ca;
4766   } else {
4767     return NULL;
4768   }
4769 }
4770 
4771 // Reset all the thread-local PLAB recording arrays
4772 void CMSCollector::reset_survivor_plab_arrays() {
4773   for (uint i = 0; i < ParallelGCThreads; i++) {
4774     _survivor_plab_array[i].reset();
4775   }
4776 }
4777 
4778 // Merge the per-thread plab arrays into the global survivor chunk
4779 // array which will provide the partitioning of the survivor space
4780 // for CMS initial scan and rescan.
4781 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4782                                               int no_of_gc_threads) {
4783   assert(_survivor_plab_array  != NULL, "Error");
4784   assert(_survivor_chunk_array != NULL, "Error");
4785   assert(_collectorState == FinalMarking ||
4786          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4787   for (int j = 0; j < no_of_gc_threads; j++) {
4788     _cursor[j] = 0;
4789   }
4790   HeapWord* top = surv->top();
4791   size_t i;
4792   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4793     HeapWord* min_val = top;          // Higher than any PLAB address
4794     uint      min_tid = 0;            // position of min_val this round
4795     for (int j = 0; j < no_of_gc_threads; j++) {
4796       ChunkArray* cur_sca = &_survivor_plab_array[j];
4797       if (_cursor[j] == cur_sca->end()) {
4798         continue;
4799       }
4800       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4801       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4802       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4803       if (cur_val < min_val) {
4804         min_tid = j;
4805         min_val = cur_val;
4806       } else {
4807         assert(cur_val < top, "All recorded addresses should be less");
4808       }
4809     }
4810     // At this point min_val and min_tid are respectively
4811     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4812     // and the thread (j) that witnesses that address.
4813     // We record this address in the _survivor_chunk_array[i]
4814     // and increment _cursor[min_tid] prior to the next round i.
4815     if (min_val == top) {
4816       break;
4817     }
4818     _survivor_chunk_array[i] = min_val;
4819     _cursor[min_tid]++;
4820   }
4821   // We are all done; record the size of the _survivor_chunk_array
4822   _survivor_chunk_index = i; // exclusive: [0, i)
4823   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4824   // Verify that we used up all the recorded entries
4825   #ifdef ASSERT
4826     size_t total = 0;
4827     for (int j = 0; j < no_of_gc_threads; j++) {
4828       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4829       total += _cursor[j];
4830     }
4831     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4832     // Check that the merged array is in sorted order
4833     if (total > 0) {
4834       for (size_t i = 0; i < total - 1; i++) {
4835         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4836                                      i, p2i(_survivor_chunk_array[i]));
4837         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4838                "Not sorted");
4839       }
4840     }
4841   #endif // ASSERT
4842 }
4843 
4844 // Set up the space's par_seq_tasks structure for work claiming
4845 // for parallel initial scan and rescan of young gen.
4846 // See ParRescanTask where this is currently used.
4847 void
4848 CMSCollector::
4849 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4850   assert(n_threads > 0, "Unexpected n_threads argument");
4851 
4852   // Eden space
4853   if (!_young_gen->eden()->is_empty()) {
4854     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4855     assert(!pst->valid(), "Clobbering existing data?");
4856     // Each valid entry in [0, _eden_chunk_index) represents a task.
4857     size_t n_tasks = _eden_chunk_index + 1;
4858     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4859     // Sets the condition for completion of the subtask (how many threads
4860     // need to finish in order to be done).
4861     pst->set_n_threads(n_threads);
4862     pst->set_n_tasks((int)n_tasks);
4863   }
4864 
4865   // Merge the survivor plab arrays into _survivor_chunk_array
4866   if (_survivor_plab_array != NULL) {
4867     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4868   } else {
4869     assert(_survivor_chunk_index == 0, "Error");
4870   }
4871 
4872   // To space
4873   {
4874     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4875     assert(!pst->valid(), "Clobbering existing data?");
4876     // Sets the condition for completion of the subtask (how many threads
4877     // need to finish in order to be done).
4878     pst->set_n_threads(n_threads);
4879     pst->set_n_tasks(1);
4880     assert(pst->valid(), "Error");
4881   }
4882 
4883   // From space
4884   {
4885     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4886     assert(!pst->valid(), "Clobbering existing data?");
4887     size_t n_tasks = _survivor_chunk_index + 1;
4888     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4889     // Sets the condition for completion of the subtask (how many threads
4890     // need to finish in order to be done).
4891     pst->set_n_threads(n_threads);
4892     pst->set_n_tasks((int)n_tasks);
4893     assert(pst->valid(), "Error");
4894   }
4895 }
4896 
4897 // Parallel version of remark
4898 void CMSCollector::do_remark_parallel() {
4899   CMSHeap* heap = CMSHeap::heap();
4900   WorkGang* workers = heap->workers();
4901   assert(workers != NULL, "Need parallel worker threads.");
4902   // Choose to use the number of GC workers most recently set
4903   // into "active_workers".
4904   uint n_workers = workers->active_workers();
4905 
4906   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4907 
4908   StrongRootsScope srs(n_workers);
4909 
4910   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4911 
4912   // We won't be iterating over the cards in the card table updating
4913   // the younger_gen cards, so we shouldn't call the following else
4914   // the verification code as well as subsequent younger_refs_iterate
4915   // code would get confused. XXX
4916   // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4917 
4918   // The young gen rescan work will not be done as part of
4919   // process_roots (which currently doesn't know how to
4920   // parallelize such a scan), but rather will be broken up into
4921   // a set of parallel tasks (via the sampling that the [abortable]
4922   // preclean phase did of eden, plus the [two] tasks of
4923   // scanning the [two] survivor spaces. Further fine-grain
4924   // parallelization of the scanning of the survivor spaces
4925   // themselves, and of precleaning of the young gen itself
4926   // is deferred to the future.
4927   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4928 
4929   // The dirty card rescan work is broken up into a "sequence"
4930   // of parallel tasks (per constituent space) that are dynamically
4931   // claimed by the parallel threads.
4932   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4933 
4934   // It turns out that even when we're using 1 thread, doing the work in a
4935   // separate thread causes wide variance in run times.  We can't help this
4936   // in the multi-threaded case, but we special-case n=1 here to get
4937   // repeatable measurements of the 1-thread overhead of the parallel code.
4938   if (n_workers > 1) {
4939     // Make refs discovery MT-safe, if it isn't already: it may not
4940     // necessarily be so, since it's possible that we are doing
4941     // ST marking.
4942     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4943     workers->run_task(&tsk);
4944   } else {
4945     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4946     tsk.work(0);
4947   }
4948 
4949   // restore, single-threaded for now, any preserved marks
4950   // as a result of work_q overflow
4951   restore_preserved_marks_if_any();
4952 }
4953 
4954 // Non-parallel version of remark
4955 void CMSCollector::do_remark_non_parallel() {
4956   ResourceMark rm;
4957   HandleMark   hm;
4958   CMSHeap* heap = CMSHeap::heap();
4959   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4960 
4961   MarkRefsIntoAndScanClosure
4962     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4963              &_markStack, this,
4964              false /* should_yield */, false /* not precleaning */);
4965   MarkFromDirtyCardsClosure
4966     markFromDirtyCardsClosure(this, _span,
4967                               NULL,  // space is set further below
4968                               &_markBitMap, &_markStack, &mrias_cl);
4969   {
4970     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4971     // Iterate over the dirty cards, setting the corresponding bits in the
4972     // mod union table.
4973     {
4974       ModUnionClosure modUnionClosure(&_modUnionTable);
4975       _ct->dirty_card_iterate(_cmsGen->used_region(),
4976                               &modUnionClosure);
4977     }
4978     // Having transferred these marks into the modUnionTable, we just need
4979     // to rescan the marked objects on the dirty cards in the modUnionTable.
4980     // The initial marking may have been done during an asynchronous
4981     // collection so there may be dirty bits in the mod-union table.
4982     const int alignment = CardTable::card_size * BitsPerWord;
4983     {
4984       // ... First handle dirty cards in CMS gen
4985       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4986       MemRegion ur = _cmsGen->used_region();
4987       HeapWord* lb = ur.start();
4988       HeapWord* ub = align_up(ur.end(), alignment);
4989       MemRegion cms_span(lb, ub);
4990       _modUnionTable.dirty_range_iterate_clear(cms_span,
4991                                                &markFromDirtyCardsClosure);
4992       verify_work_stacks_empty();
4993       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4994     }
4995   }
4996   if (VerifyDuringGC &&
4997       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4998     HandleMark hm;  // Discard invalid handles created during verification
4999     Universe::verify();
5000   }
5001   {
5002     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
5003 
5004     verify_work_stacks_empty();
5005 
5006     heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5007     StrongRootsScope srs(1);
5008 
5009     heap->cms_process_roots(&srs,
5010                             true,  // young gen as roots
5011                             GenCollectedHeap::ScanningOption(roots_scanning_options()),
5012                             should_unload_classes(),
5013                             &mrias_cl,
5014                             NULL); // The dirty klasses will be handled below
5015 
5016     assert(should_unload_classes()
5017            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5018            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5019   }
5020 
5021   {
5022     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
5023 
5024     verify_work_stacks_empty();
5025 
5026     // Scan all class loader data objects that might have been introduced
5027     // during concurrent marking.
5028     ResourceMark rm;
5029     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5030     for (int i = 0; i < array->length(); i++) {
5031       Devirtualizer::do_cld(&mrias_cl, array->at(i));
5032     }
5033 
5034     // We don't need to keep track of new CLDs anymore.
5035     ClassLoaderDataGraph::remember_new_clds(false);
5036 
5037     verify_work_stacks_empty();
5038   }
5039 
5040   // We might have added oops to ClassLoaderData::_handles during the
5041   // concurrent marking phase. These oops do not point to newly allocated objects
5042   // that are guaranteed to be kept alive.  Hence,
5043   // we do have to revisit the _handles block during the remark phase.
5044   {
5045     GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
5046 
5047     verify_work_stacks_empty();
5048 
5049     RemarkCLDClosure remark_closure(&mrias_cl);
5050     ClassLoaderDataGraph::cld_do(&remark_closure);
5051 
5052     verify_work_stacks_empty();
5053   }
5054 
5055   verify_work_stacks_empty();
5056   // Restore evacuated mark words, if any, used for overflow list links
5057   restore_preserved_marks_if_any();
5058 
5059   verify_overflow_empty();
5060 }
5061 
5062 ////////////////////////////////////////////////////////
5063 // Parallel Reference Processing Task Proxy Class
5064 ////////////////////////////////////////////////////////
5065 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5066   OopTaskQueueSet*       _queues;
5067   TaskTerminator         _terminator;
5068  public:
5069   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5070     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5071   ParallelTaskTerminator* terminator() { return _terminator.terminator(); }
5072   OopTaskQueueSet* queues() { return _queues; }
5073 };
5074 
5075 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5076   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5077   CMSCollector*          _collector;
5078   CMSBitMap*             _mark_bit_map;
5079   const MemRegion        _span;
5080   ProcessTask&           _task;
5081 
5082 public:
5083   CMSRefProcTaskProxy(ProcessTask&     task,
5084                       CMSCollector*    collector,
5085                       const MemRegion& span,
5086                       CMSBitMap*       mark_bit_map,
5087                       AbstractWorkGang* workers,
5088                       OopTaskQueueSet* task_queues):
5089     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5090       task_queues,
5091       workers->active_workers()),
5092     _collector(collector),
5093     _mark_bit_map(mark_bit_map),
5094     _span(span),
5095     _task(task)
5096   {
5097     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5098            "Inconsistency in _span");
5099   }
5100 
5101   OopTaskQueueSet* task_queues() { return queues(); }
5102 
5103   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5104 
5105   void do_work_steal(int i,
5106                      CMSParDrainMarkingStackClosure* drain,
5107                      CMSParKeepAliveClosure* keep_alive);
5108 
5109   virtual void work(uint worker_id);
5110 };
5111 
5112 void CMSRefProcTaskProxy::work(uint worker_id) {
5113   ResourceMark rm;
5114   HandleMark hm;
5115   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5116   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5117                                         _mark_bit_map,
5118                                         work_queue(worker_id));
5119   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5120                                                  _mark_bit_map,
5121                                                  work_queue(worker_id));
5122   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5123   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5124   if (_task.marks_oops_alive()) {
5125     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5126   }
5127   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5128   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5129 }
5130 
5131 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5132   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5133    _span(span),
5134    _work_queue(work_queue),
5135    _bit_map(bit_map),
5136    _mark_and_push(collector, span, bit_map, work_queue),
5137    _low_water_mark(MIN2((work_queue->max_elems()/4),
5138                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5139 { }
5140 
5141 // . see if we can share work_queues with ParNew? XXX
5142 void CMSRefProcTaskProxy::do_work_steal(int i,
5143   CMSParDrainMarkingStackClosure* drain,
5144   CMSParKeepAliveClosure* keep_alive) {
5145   OopTaskQueue* work_q = work_queue(i);
5146   NOT_PRODUCT(int num_steals = 0;)
5147   oop obj_to_scan;
5148 
5149   while (true) {
5150     // Completely finish any left over work from (an) earlier round(s)
5151     drain->trim_queue(0);
5152     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5153                                          (size_t)ParGCDesiredObjsFromOverflowList);
5154     // Now check if there's any work in the overflow list
5155     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5156     // only affects the number of attempts made to get work from the
5157     // overflow list and does not affect the number of workers.  Just
5158     // pass ParallelGCThreads so this behavior is unchanged.
5159     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5160                                                 work_q,
5161                                                 ParallelGCThreads)) {
5162       // Found something in global overflow list;
5163       // not yet ready to go stealing work from others.
5164       // We'd like to assert(work_q->size() != 0, ...)
5165       // because we just took work from the overflow list,
5166       // but of course we can't, since all of that might have
5167       // been already stolen from us.
5168       continue;
5169     }
5170     // Verify that we have no work before we resort to stealing
5171     assert(work_q->size() == 0, "Have work, shouldn't steal");
5172     // Try to steal from other queues that have work
5173     if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5174       NOT_PRODUCT(num_steals++;)
5175       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5176       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5177       // Do scanning work
5178       obj_to_scan->oop_iterate(keep_alive);
5179       // Loop around, finish this work, and try to steal some more
5180     } else if (terminator()->offer_termination()) {
5181       break;  // nirvana from the infinite cycle
5182     }
5183   }
5184   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5185 }
5186 
5187 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5188   CMSHeap* heap = CMSHeap::heap();
5189   WorkGang* workers = heap->workers();
5190   assert(workers != NULL, "Need parallel worker threads.");
5191   assert(workers->active_workers() == ergo_workers,
5192          "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5193          ergo_workers, workers->active_workers());
5194   CMSRefProcTaskProxy rp_task(task, &_collector,
5195                               _collector.ref_processor_span(),
5196                               _collector.markBitMap(),
5197                               workers, _collector.task_queues());
5198   workers->run_task(&rp_task, workers->active_workers());
5199 }
5200 
5201 void CMSCollector::refProcessingWork() {
5202   ResourceMark rm;
5203   HandleMark   hm;
5204 
5205   ReferenceProcessor* rp = ref_processor();
5206   assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5207   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5208   // Process weak references.
5209   rp->setup_policy(false);
5210   verify_work_stacks_empty();
5211 
5212   ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5213   {
5214     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5215 
5216     // Setup keep_alive and complete closures.
5217     CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5218                                             &_markStack, false /* !preclean */);
5219     CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5220                                   _span, &_markBitMap, &_markStack,
5221                                   &cmsKeepAliveClosure, false /* !preclean */);
5222 
5223     ReferenceProcessorStats stats;
5224     if (rp->processing_is_mt()) {
5225       // Set the degree of MT here.  If the discovery is done MT, there
5226       // may have been a different number of threads doing the discovery
5227       // and a different number of discovered lists may have Ref objects.
5228       // That is OK as long as the Reference lists are balanced (see
5229       // balance_all_queues() and balance_queues()).
5230       CMSHeap* heap = CMSHeap::heap();
5231       uint active_workers = ParallelGCThreads;
5232       WorkGang* workers = heap->workers();
5233       if (workers != NULL) {
5234         active_workers = workers->active_workers();
5235         // The expectation is that active_workers will have already
5236         // been set to a reasonable value.  If it has not been set,
5237         // investigate.
5238         assert(active_workers > 0, "Should have been set during scavenge");
5239       }
5240       rp->set_active_mt_degree(active_workers);
5241       CMSRefProcTaskExecutor task_executor(*this);
5242       stats = rp->process_discovered_references(&_is_alive_closure,
5243                                         &cmsKeepAliveClosure,
5244                                         &cmsDrainMarkingStackClosure,
5245                                         &task_executor,
5246                                         &pt);
5247     } else {
5248       stats = rp->process_discovered_references(&_is_alive_closure,
5249                                         &cmsKeepAliveClosure,
5250                                         &cmsDrainMarkingStackClosure,
5251                                         NULL,
5252                                         &pt);
5253     }
5254     _gc_tracer_cm->report_gc_reference_stats(stats);
5255     pt.print_all_references();
5256   }
5257 
5258   // This is the point where the entire marking should have completed.
5259   verify_work_stacks_empty();
5260 
5261   {
5262     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5263     WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5264   }
5265 
5266   if (should_unload_classes()) {
5267     {
5268       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5269 
5270       // Unload classes and purge the SystemDictionary.
5271       bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5272 
5273       // Unload nmethods.
5274       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5275 
5276       // Prune dead klasses from subklass/sibling/implementor lists.
5277       Klass::clean_weak_klass_links(purged_class);
5278 
5279       // Clean JVMCI metadata handles.
5280       JVMCI_ONLY(JVMCI::do_unloading(purged_class));
5281     }
5282   }
5283 
5284   // Restore any preserved marks as a result of mark stack or
5285   // work queue overflow
5286   restore_preserved_marks_if_any();  // done single-threaded for now
5287 
5288   rp->set_enqueuing_is_done(true);
5289   rp->verify_no_references_recorded();
5290 }
5291 
5292 #ifndef PRODUCT
5293 void CMSCollector::check_correct_thread_executing() {
5294   Thread* t = Thread::current();
5295   // Only the VM thread or the CMS thread should be here.
5296   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5297          "Unexpected thread type");
5298   // If this is the vm thread, the foreground process
5299   // should not be waiting.  Note that _foregroundGCIsActive is
5300   // true while the foreground collector is waiting.
5301   if (_foregroundGCShouldWait) {
5302     // We cannot be the VM thread
5303     assert(t->is_ConcurrentGC_thread(),
5304            "Should be CMS thread");
5305   } else {
5306     // We can be the CMS thread only if we are in a stop-world
5307     // phase of CMS collection.
5308     if (t->is_ConcurrentGC_thread()) {
5309       assert(_collectorState == InitialMarking ||
5310              _collectorState == FinalMarking,
5311              "Should be a stop-world phase");
5312       // The CMS thread should be holding the CMS_token.
5313       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5314              "Potential interference with concurrently "
5315              "executing VM thread");
5316     }
5317   }
5318 }
5319 #endif
5320 
5321 void CMSCollector::sweep() {
5322   assert(_collectorState == Sweeping, "just checking");
5323   check_correct_thread_executing();
5324   verify_work_stacks_empty();
5325   verify_overflow_empty();
5326   increment_sweep_count();
5327   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5328 
5329   _inter_sweep_timer.stop();
5330   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5331 
5332   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5333   _intra_sweep_timer.reset();
5334   _intra_sweep_timer.start();
5335   {
5336     GCTraceCPUTime tcpu;
5337     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5338     // First sweep the old gen
5339     {
5340       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5341                                bitMapLock());
5342       sweepWork(_cmsGen);
5343     }
5344 
5345     // Update Universe::_heap_*_at_gc figures.
5346     // We need all the free list locks to make the abstract state
5347     // transition from Sweeping to Resetting. See detailed note
5348     // further below.
5349     {
5350       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5351       
5352       // Update heap occupancy information which is used as
5353       // input to soft ref clearing policy at the next gc.
5354       Universe::update_heap_info_at_gc();
5355    
5356       // recalculate CMS used space after CMS collection
5357       _cmsGen->cmsSpace()->recalculate_used_stable();
5358  
5359       _collectorState = Resizing;
5360     }
5361   }
5362   verify_work_stacks_empty();
5363   verify_overflow_empty();
5364 
5365   if (should_unload_classes()) {
5366     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5367     // requires that the virtual spaces are stable and not deleted.
5368     ClassLoaderDataGraph::set_should_purge(true);
5369   }
5370 
5371   _intra_sweep_timer.stop();
5372   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5373 
5374   _inter_sweep_timer.reset();
5375   _inter_sweep_timer.start();
5376 
5377   // We need to use a monotonically non-decreasing time in ms
5378   // or we will see time-warp warnings and os::javaTimeMillis()
5379   // does not guarantee monotonicity.
5380   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5381   update_time_of_last_gc(now);
5382 
5383   // NOTE on abstract state transitions:
5384   // Mutators allocate-live and/or mark the mod-union table dirty
5385   // based on the state of the collection.  The former is done in
5386   // the interval [Marking, Sweeping] and the latter in the interval
5387   // [Marking, Sweeping).  Thus the transitions into the Marking state
5388   // and out of the Sweeping state must be synchronously visible
5389   // globally to the mutators.
5390   // The transition into the Marking state happens with the world
5391   // stopped so the mutators will globally see it.  Sweeping is
5392   // done asynchronously by the background collector so the transition
5393   // from the Sweeping state to the Resizing state must be done
5394   // under the freelistLock (as is the check for whether to
5395   // allocate-live and whether to dirty the mod-union table).
5396   assert(_collectorState == Resizing, "Change of collector state to"
5397     " Resizing must be done under the freelistLocks (plural)");
5398 
5399   // Now that sweeping has been completed, we clear
5400   // the incremental_collection_failed flag,
5401   // thus inviting a younger gen collection to promote into
5402   // this generation. If such a promotion may still fail,
5403   // the flag will be set again when a young collection is
5404   // attempted.
5405   CMSHeap* heap = CMSHeap::heap();
5406   heap->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5407   heap->update_full_collections_completed(_collection_count_start);
5408 }
5409 
5410 // FIX ME!!! Looks like this belongs in CFLSpace, with
5411 // CMSGen merely delegating to it.
5412 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5413   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5414   HeapWord*  minAddr        = _cmsSpace->bottom();
5415   HeapWord*  largestAddr    =
5416     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5417   if (largestAddr == NULL) {
5418     // The dictionary appears to be empty.  In this case
5419     // try to coalesce at the end of the heap.
5420     largestAddr = _cmsSpace->end();
5421   }
5422   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5423   size_t nearLargestOffset =
5424     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5425   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5426                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5427   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5428 }
5429 
5430 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5431   return addr >= _cmsSpace->nearLargestChunk();
5432 }
5433 
5434 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5435   return _cmsSpace->find_chunk_at_end();
5436 }
5437 
5438 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5439                                                     bool full) {
5440   // If the young generation has been collected, gather any statistics
5441   // that are of interest at this point.
5442   bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5443   if (!full && current_is_young) {
5444     // Gather statistics on the young generation collection.
5445     collector()->stats().record_gc0_end(used());
5446   }
5447   _cmsSpace->recalculate_used_stable();
5448 }
5449 
5450 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5451   // We iterate over the space(s) underlying this generation,
5452   // checking the mark bit map to see if the bits corresponding
5453   // to specific blocks are marked or not. Blocks that are
5454   // marked are live and are not swept up. All remaining blocks
5455   // are swept up, with coalescing on-the-fly as we sweep up
5456   // contiguous free and/or garbage blocks:
5457   // We need to ensure that the sweeper synchronizes with allocators
5458   // and stop-the-world collectors. In particular, the following
5459   // locks are used:
5460   // . CMS token: if this is held, a stop the world collection cannot occur
5461   // . freelistLock: if this is held no allocation can occur from this
5462   //                 generation by another thread
5463   // . bitMapLock: if this is held, no other thread can access or update
5464   //
5465 
5466   // Note that we need to hold the freelistLock if we use
5467   // block iterate below; else the iterator might go awry if
5468   // a mutator (or promotion) causes block contents to change
5469   // (for instance if the allocator divvies up a block).
5470   // If we hold the free list lock, for all practical purposes
5471   // young generation GC's can't occur (they'll usually need to
5472   // promote), so we might as well prevent all young generation
5473   // GC's while we do a sweeping step. For the same reason, we might
5474   // as well take the bit map lock for the entire duration
5475 
5476   // check that we hold the requisite locks
5477   assert(have_cms_token(), "Should hold cms token");
5478   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5479   assert_lock_strong(old_gen->freelistLock());
5480   assert_lock_strong(bitMapLock());
5481 
5482   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5483   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5484   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5485                                           _inter_sweep_estimate.padded_average(),
5486                                           _intra_sweep_estimate.padded_average());
5487   old_gen->setNearLargestChunk();
5488 
5489   {
5490     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5491     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5492     // We need to free-up/coalesce garbage/blocks from a
5493     // co-terminal free run. This is done in the SweepClosure
5494     // destructor; so, do not remove this scope, else the
5495     // end-of-sweep-census below will be off by a little bit.
5496   }
5497   old_gen->cmsSpace()->sweep_completed();
5498   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5499   if (should_unload_classes()) {                // unloaded classes this cycle,
5500     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5501   } else {                                      // did not unload classes,
5502     _concurrent_cycles_since_last_unload++;     // ... increment count
5503   }
5504 }
5505 
5506 // Reset CMS data structures (for now just the marking bit map)
5507 // preparatory for the next cycle.
5508 void CMSCollector::reset_concurrent() {
5509   CMSTokenSyncWithLocks ts(true, bitMapLock());
5510 
5511   // If the state is not "Resetting", the foreground  thread
5512   // has done a collection and the resetting.
5513   if (_collectorState != Resetting) {
5514     assert(_collectorState == Idling, "The state should only change"
5515       " because the foreground collector has finished the collection");
5516     return;
5517   }
5518 
5519   {
5520     // Clear the mark bitmap (no grey objects to start with)
5521     // for the next cycle.
5522     GCTraceCPUTime tcpu;
5523     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5524 
5525     HeapWord* curAddr = _markBitMap.startWord();
5526     while (curAddr < _markBitMap.endWord()) {
5527       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5528       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5529       _markBitMap.clear_large_range(chunk);
5530       if (ConcurrentMarkSweepThread::should_yield() &&
5531           !foregroundGCIsActive() &&
5532           CMSYield) {
5533         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5534                "CMS thread should hold CMS token");
5535         assert_lock_strong(bitMapLock());
5536         bitMapLock()->unlock();
5537         ConcurrentMarkSweepThread::desynchronize(true);
5538         stopTimer();
5539         incrementYields();
5540 
5541         // See the comment in coordinator_yield()
5542         for (unsigned i = 0; i < CMSYieldSleepCount &&
5543                          ConcurrentMarkSweepThread::should_yield() &&
5544                          !CMSCollector::foregroundGCIsActive(); ++i) {
5545           os::sleep(Thread::current(), 1, false);
5546         }
5547 
5548         ConcurrentMarkSweepThread::synchronize(true);
5549         bitMapLock()->lock_without_safepoint_check();
5550         startTimer();
5551       }
5552       curAddr = chunk.end();
5553     }
5554     // A successful mostly concurrent collection has been done.
5555     // Because only the full (i.e., concurrent mode failure) collections
5556     // are being measured for gc overhead limits, clean the "near" flag
5557     // and count.
5558     size_policy()->reset_gc_overhead_limit_count();
5559     _collectorState = Idling;
5560   }
5561 
5562   register_gc_end();
5563 }
5564 
5565 // Same as above but for STW paths
5566 void CMSCollector::reset_stw() {
5567   // already have the lock
5568   assert(_collectorState == Resetting, "just checking");
5569   assert_lock_strong(bitMapLock());
5570   GCIdMark gc_id_mark(_cmsThread->gc_id());
5571   _markBitMap.clear_all();
5572   _collectorState = Idling;
5573   register_gc_end();
5574 }
5575 
5576 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5577   GCTraceCPUTime tcpu;
5578   TraceCollectorStats tcs_cgc(cgc_counters());
5579 
5580   switch (op) {
5581     case CMS_op_checkpointRootsInitial: {
5582       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5583       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5584       checkpointRootsInitial();
5585       break;
5586     }
5587     case CMS_op_checkpointRootsFinal: {
5588       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5589       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5590       checkpointRootsFinal();
5591       break;
5592     }
5593     default:
5594       fatal("No such CMS_op");
5595   }
5596 }
5597 
5598 #ifndef PRODUCT
5599 size_t const CMSCollector::skip_header_HeapWords() {
5600   return FreeChunk::header_size();
5601 }
5602 
5603 // Try and collect here conditions that should hold when
5604 // CMS thread is exiting. The idea is that the foreground GC
5605 // thread should not be blocked if it wants to terminate
5606 // the CMS thread and yet continue to run the VM for a while
5607 // after that.
5608 void CMSCollector::verify_ok_to_terminate() const {
5609   assert(Thread::current()->is_ConcurrentGC_thread(),
5610          "should be called by CMS thread");
5611   assert(!_foregroundGCShouldWait, "should be false");
5612   // We could check here that all the various low-level locks
5613   // are not held by the CMS thread, but that is overkill; see
5614   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5615   // is checked.
5616 }
5617 #endif
5618 
5619 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5620    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5621           "missing Printezis mark?");
5622   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5623   size_t size = pointer_delta(nextOneAddr + 1, addr);
5624   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5625          "alignment problem");
5626   assert(size >= 3, "Necessary for Printezis marks to work");
5627   return size;
5628 }
5629 
5630 // A variant of the above (block_size_using_printezis_bits()) except
5631 // that we return 0 if the P-bits are not yet set.
5632 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5633   if (_markBitMap.isMarked(addr + 1)) {
5634     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5635     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5636     size_t size = pointer_delta(nextOneAddr + 1, addr);
5637     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5638            "alignment problem");
5639     assert(size >= 3, "Necessary for Printezis marks to work");
5640     return size;
5641   }
5642   return 0;
5643 }
5644 
5645 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5646   size_t sz = 0;
5647   oop p = (oop)addr;
5648   if (p->klass_or_null_acquire() != NULL) {
5649     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5650   } else {
5651     sz = block_size_using_printezis_bits(addr);
5652   }
5653   assert(sz > 0, "size must be nonzero");
5654   HeapWord* next_block = addr + sz;
5655   HeapWord* next_card  = align_up(next_block, CardTable::card_size);
5656   assert(align_down((uintptr_t)addr,      CardTable::card_size) <
5657          align_down((uintptr_t)next_card, CardTable::card_size),
5658          "must be different cards");
5659   return next_card;
5660 }
5661 
5662 
5663 // CMS Bit Map Wrapper /////////////////////////////////////////
5664 
5665 // Construct a CMS bit map infrastructure, but don't create the
5666 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5667 // further below.
5668 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5669   _shifter(shifter),
5670   _bm(),
5671   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5672                                     Monitor::_safepoint_check_never) : NULL)
5673 {
5674   _bmStartWord = 0;
5675   _bmWordSize  = 0;
5676 }
5677 
5678 bool CMSBitMap::allocate(MemRegion mr) {
5679   _bmStartWord = mr.start();
5680   _bmWordSize  = mr.word_size();
5681   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5682                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5683   if (!brs.is_reserved()) {
5684     log_warning(gc)("CMS bit map allocation failure");
5685     return false;
5686   }
5687   // For now we'll just commit all of the bit map up front.
5688   // Later on we'll try to be more parsimonious with swap.
5689   if (!_virtual_space.initialize(brs, brs.size())) {
5690     log_warning(gc)("CMS bit map backing store failure");
5691     return false;
5692   }
5693   assert(_virtual_space.committed_size() == brs.size(),
5694          "didn't reserve backing store for all of CMS bit map?");
5695   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5696          _bmWordSize, "inconsistency in bit map sizing");
5697   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5698 
5699   // bm.clear(); // can we rely on getting zero'd memory? verify below
5700   assert(isAllClear(),
5701          "Expected zero'd memory from ReservedSpace constructor");
5702   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5703          "consistency check");
5704   return true;
5705 }
5706 
5707 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5708   HeapWord *next_addr, *end_addr, *last_addr;
5709   assert_locked();
5710   assert(covers(mr), "out-of-range error");
5711   // XXX assert that start and end are appropriately aligned
5712   for (next_addr = mr.start(), end_addr = mr.end();
5713        next_addr < end_addr; next_addr = last_addr) {
5714     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5715     last_addr = dirty_region.end();
5716     if (!dirty_region.is_empty()) {
5717       cl->do_MemRegion(dirty_region);
5718     } else {
5719       assert(last_addr == end_addr, "program logic");
5720       return;
5721     }
5722   }
5723 }
5724 
5725 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5726   _bm.print_on_error(st, prefix);
5727 }
5728 
5729 #ifndef PRODUCT
5730 void CMSBitMap::assert_locked() const {
5731   CMSLockVerifier::assert_locked(lock());
5732 }
5733 
5734 bool CMSBitMap::covers(MemRegion mr) const {
5735   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5736   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5737          "size inconsistency");
5738   return (mr.start() >= _bmStartWord) &&
5739          (mr.end()   <= endWord());
5740 }
5741 
5742 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5743     return (start >= _bmStartWord && (start + size) <= endWord());
5744 }
5745 
5746 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5747   // verify that there are no 1 bits in the interval [left, right)
5748   FalseBitMapClosure falseBitMapClosure;
5749   iterate(&falseBitMapClosure, left, right);
5750 }
5751 
5752 void CMSBitMap::region_invariant(MemRegion mr)
5753 {
5754   assert_locked();
5755   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5756   assert(!mr.is_empty(), "unexpected empty region");
5757   assert(covers(mr), "mr should be covered by bit map");
5758   // convert address range into offset range
5759   size_t start_ofs = heapWordToOffset(mr.start());
5760   // Make sure that end() is appropriately aligned
5761   assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5762          "Misaligned mr.end()");
5763   size_t end_ofs   = heapWordToOffset(mr.end());
5764   assert(end_ofs > start_ofs, "Should mark at least one bit");
5765 }
5766 
5767 #endif
5768 
5769 bool CMSMarkStack::allocate(size_t size) {
5770   // allocate a stack of the requisite depth
5771   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5772                    size * sizeof(oop)));
5773   if (!rs.is_reserved()) {
5774     log_warning(gc)("CMSMarkStack allocation failure");
5775     return false;
5776   }
5777   if (!_virtual_space.initialize(rs, rs.size())) {
5778     log_warning(gc)("CMSMarkStack backing store failure");
5779     return false;
5780   }
5781   assert(_virtual_space.committed_size() == rs.size(),
5782          "didn't reserve backing store for all of CMS stack?");
5783   _base = (oop*)(_virtual_space.low());
5784   _index = 0;
5785   _capacity = size;
5786   NOT_PRODUCT(_max_depth = 0);
5787   return true;
5788 }
5789 
5790 // XXX FIX ME !!! In the MT case we come in here holding a
5791 // leaf lock. For printing we need to take a further lock
5792 // which has lower rank. We need to recalibrate the two
5793 // lock-ranks involved in order to be able to print the
5794 // messages below. (Or defer the printing to the caller.
5795 // For now we take the expedient path of just disabling the
5796 // messages for the problematic case.)
5797 void CMSMarkStack::expand() {
5798   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5799   if (_capacity == MarkStackSizeMax) {
5800     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5801       // We print a warning message only once per CMS cycle.
5802       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5803     }
5804     return;
5805   }
5806   // Double capacity if possible
5807   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5808   // Do not give up existing stack until we have managed to
5809   // get the double capacity that we desired.
5810   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5811                    new_capacity * sizeof(oop)));
5812   if (rs.is_reserved()) {
5813     // Release the backing store associated with old stack
5814     _virtual_space.release();
5815     // Reinitialize virtual space for new stack
5816     if (!_virtual_space.initialize(rs, rs.size())) {
5817       fatal("Not enough swap for expanded marking stack");
5818     }
5819     _base = (oop*)(_virtual_space.low());
5820     _index = 0;
5821     _capacity = new_capacity;
5822   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5823     // Failed to double capacity, continue;
5824     // we print a detail message only once per CMS cycle.
5825     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5826                         _capacity / K, new_capacity / K);
5827   }
5828 }
5829 
5830 
5831 // Closures
5832 // XXX: there seems to be a lot of code  duplication here;
5833 // should refactor and consolidate common code.
5834 
5835 // This closure is used to mark refs into the CMS generation in
5836 // the CMS bit map. Called at the first checkpoint. This closure
5837 // assumes that we do not need to re-mark dirty cards; if the CMS
5838 // generation on which this is used is not an oldest
5839 // generation then this will lose younger_gen cards!
5840 
5841 MarkRefsIntoClosure::MarkRefsIntoClosure(
5842   MemRegion span, CMSBitMap* bitMap):
5843     _span(span),
5844     _bitMap(bitMap)
5845 {
5846   assert(ref_discoverer() == NULL, "deliberately left NULL");
5847   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5848 }
5849 
5850 void MarkRefsIntoClosure::do_oop(oop obj) {
5851   // if p points into _span, then mark corresponding bit in _markBitMap
5852   assert(oopDesc::is_oop(obj), "expected an oop");
5853   HeapWord* addr = (HeapWord*)obj;
5854   if (_span.contains(addr)) {
5855     // this should be made more efficient
5856     _bitMap->mark(addr);
5857   }
5858 }
5859 
5860 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5861   MemRegion span, CMSBitMap* bitMap):
5862     _span(span),
5863     _bitMap(bitMap)
5864 {
5865   assert(ref_discoverer() == NULL, "deliberately left NULL");
5866   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5867 }
5868 
5869 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5870   // if p points into _span, then mark corresponding bit in _markBitMap
5871   assert(oopDesc::is_oop(obj), "expected an oop");
5872   HeapWord* addr = (HeapWord*)obj;
5873   if (_span.contains(addr)) {
5874     // this should be made more efficient
5875     _bitMap->par_mark(addr);
5876   }
5877 }
5878 
5879 // A variant of the above, used for CMS marking verification.
5880 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5881   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5882     _span(span),
5883     _verification_bm(verification_bm),
5884     _cms_bm(cms_bm)
5885 {
5886   assert(ref_discoverer() == NULL, "deliberately left NULL");
5887   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5888 }
5889 
5890 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5891   // if p points into _span, then mark corresponding bit in _markBitMap
5892   assert(oopDesc::is_oop(obj), "expected an oop");
5893   HeapWord* addr = (HeapWord*)obj;
5894   if (_span.contains(addr)) {
5895     _verification_bm->mark(addr);
5896     if (!_cms_bm->isMarked(addr)) {
5897       Log(gc, verify) log;
5898       ResourceMark rm;
5899       LogStream ls(log.error());
5900       oop(addr)->print_on(&ls);
5901       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5902       fatal("... aborting");
5903     }
5904   }
5905 }
5906 
5907 //////////////////////////////////////////////////
5908 // MarkRefsIntoAndScanClosure
5909 //////////////////////////////////////////////////
5910 
5911 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5912                                                        ReferenceDiscoverer* rd,
5913                                                        CMSBitMap* bit_map,
5914                                                        CMSBitMap* mod_union_table,
5915                                                        CMSMarkStack*  mark_stack,
5916                                                        CMSCollector* collector,
5917                                                        bool should_yield,
5918                                                        bool concurrent_precleaning):
5919   _span(span),
5920   _bit_map(bit_map),
5921   _mark_stack(mark_stack),
5922   _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5923                       mark_stack, concurrent_precleaning),
5924   _collector(collector),
5925   _freelistLock(NULL),
5926   _yield(should_yield),
5927   _concurrent_precleaning(concurrent_precleaning)
5928 {
5929   // FIXME: Should initialize in base class constructor.
5930   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5931   set_ref_discoverer_internal(rd);
5932 }
5933 
5934 // This closure is used to mark refs into the CMS generation at the
5935 // second (final) checkpoint, and to scan and transitively follow
5936 // the unmarked oops. It is also used during the concurrent precleaning
5937 // phase while scanning objects on dirty cards in the CMS generation.
5938 // The marks are made in the marking bit map and the marking stack is
5939 // used for keeping the (newly) grey objects during the scan.
5940 // The parallel version (Par_...) appears further below.
5941 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5942   if (obj != NULL) {
5943     assert(oopDesc::is_oop(obj), "expected an oop");
5944     HeapWord* addr = (HeapWord*)obj;
5945     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5946     assert(_collector->overflow_list_is_empty(),
5947            "overflow list should be empty");
5948     if (_span.contains(addr) &&
5949         !_bit_map->isMarked(addr)) {
5950       // mark bit map (object is now grey)
5951       _bit_map->mark(addr);
5952       // push on marking stack (stack should be empty), and drain the
5953       // stack by applying this closure to the oops in the oops popped
5954       // from the stack (i.e. blacken the grey objects)
5955       bool res = _mark_stack->push(obj);
5956       assert(res, "Should have space to push on empty stack");
5957       do {
5958         oop new_oop = _mark_stack->pop();
5959         assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5960         assert(_bit_map->isMarked((HeapWord*)new_oop),
5961                "only grey objects on this stack");
5962         // iterate over the oops in this oop, marking and pushing
5963         // the ones in CMS heap (i.e. in _span).
5964         new_oop->oop_iterate(&_pushAndMarkClosure);
5965         // check if it's time to yield
5966         do_yield_check();
5967       } while (!_mark_stack->isEmpty() ||
5968                (!_concurrent_precleaning && take_from_overflow_list()));
5969         // if marking stack is empty, and we are not doing this
5970         // during precleaning, then check the overflow list
5971     }
5972     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5973     assert(_collector->overflow_list_is_empty(),
5974            "overflow list was drained above");
5975 
5976     assert(_collector->no_preserved_marks(),
5977            "All preserved marks should have been restored above");
5978   }
5979 }
5980 
5981 void MarkRefsIntoAndScanClosure::do_yield_work() {
5982   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5983          "CMS thread should hold CMS token");
5984   assert_lock_strong(_freelistLock);
5985   assert_lock_strong(_bit_map->lock());
5986   // relinquish the free_list_lock and bitMaplock()
5987   _bit_map->lock()->unlock();
5988   _freelistLock->unlock();
5989   ConcurrentMarkSweepThread::desynchronize(true);
5990   _collector->stopTimer();
5991   _collector->incrementYields();
5992 
5993   // See the comment in coordinator_yield()
5994   for (unsigned i = 0;
5995        i < CMSYieldSleepCount &&
5996        ConcurrentMarkSweepThread::should_yield() &&
5997        !CMSCollector::foregroundGCIsActive();
5998        ++i) {
5999     os::sleep(Thread::current(), 1, false);
6000   }
6001 
6002   ConcurrentMarkSweepThread::synchronize(true);
6003   _freelistLock->lock_without_safepoint_check();
6004   _bit_map->lock()->lock_without_safepoint_check();
6005   _collector->startTimer();
6006 }
6007 
6008 ///////////////////////////////////////////////////////////
6009 // ParMarkRefsIntoAndScanClosure: a parallel version of
6010 //                                MarkRefsIntoAndScanClosure
6011 ///////////////////////////////////////////////////////////
6012 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6013   CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
6014   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6015   _span(span),
6016   _bit_map(bit_map),
6017   _work_queue(work_queue),
6018   _low_water_mark(MIN2((work_queue->max_elems()/4),
6019                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6020   _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
6021 {
6022   // FIXME: Should initialize in base class constructor.
6023   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
6024   set_ref_discoverer_internal(rd);
6025 }
6026 
6027 // This closure is used to mark refs into the CMS generation at the
6028 // second (final) checkpoint, and to scan and transitively follow
6029 // the unmarked oops. The marks are made in the marking bit map and
6030 // the work_queue is used for keeping the (newly) grey objects during
6031 // the scan phase whence they are also available for stealing by parallel
6032 // threads. Since the marking bit map is shared, updates are
6033 // synchronized (via CAS).
6034 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6035   if (obj != NULL) {
6036     // Ignore mark word because this could be an already marked oop
6037     // that may be chained at the end of the overflow list.
6038     assert(oopDesc::is_oop(obj, true), "expected an oop");
6039     HeapWord* addr = (HeapWord*)obj;
6040     if (_span.contains(addr) &&
6041         !_bit_map->isMarked(addr)) {
6042       // mark bit map (object will become grey):
6043       // It is possible for several threads to be
6044       // trying to "claim" this object concurrently;
6045       // the unique thread that succeeds in marking the
6046       // object first will do the subsequent push on
6047       // to the work queue (or overflow list).
6048       if (_bit_map->par_mark(addr)) {
6049         // push on work_queue (which may not be empty), and trim the
6050         // queue to an appropriate length by applying this closure to
6051         // the oops in the oops popped from the stack (i.e. blacken the
6052         // grey objects)
6053         bool res = _work_queue->push(obj);
6054         assert(res, "Low water mark should be less than capacity?");
6055         trim_queue(_low_water_mark);
6056       } // Else, another thread claimed the object
6057     }
6058   }
6059 }
6060 
6061 // This closure is used to rescan the marked objects on the dirty cards
6062 // in the mod union table and the card table proper.
6063 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6064   oop p, MemRegion mr) {
6065 
6066   size_t size = 0;
6067   HeapWord* addr = (HeapWord*)p;
6068   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6069   assert(_span.contains(addr), "we are scanning the CMS generation");
6070   // check if it's time to yield
6071   if (do_yield_check()) {
6072     // We yielded for some foreground stop-world work,
6073     // and we have been asked to abort this ongoing preclean cycle.
6074     return 0;
6075   }
6076   if (_bitMap->isMarked(addr)) {
6077     // it's marked; is it potentially uninitialized?
6078     if (p->klass_or_null_acquire() != NULL) {
6079         // an initialized object; ignore mark word in verification below
6080         // since we are running concurrent with mutators
6081         assert(oopDesc::is_oop(p, true), "should be an oop");
6082         if (p->is_objArray()) {
6083           // objArrays are precisely marked; restrict scanning
6084           // to dirty cards only.
6085           size = CompactibleFreeListSpace::adjustObjectSize(
6086                    p->oop_iterate_size(_scanningClosure, mr));
6087         } else {
6088           // A non-array may have been imprecisely marked; we need
6089           // to scan object in its entirety.
6090           size = CompactibleFreeListSpace::adjustObjectSize(
6091                    p->oop_iterate_size(_scanningClosure));
6092         }
6093       #ifdef ASSERT
6094         size_t direct_size =
6095           CompactibleFreeListSpace::adjustObjectSize(p->size());
6096         assert(size == direct_size, "Inconsistency in size");
6097         assert(size >= 3, "Necessary for Printezis marks to work");
6098         HeapWord* start_pbit = addr + 1;
6099         HeapWord* end_pbit = addr + size - 1;
6100         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6101                "inconsistent Printezis mark");
6102         // Verify inner mark bits (between Printezis bits) are clear,
6103         // but don't repeat if there are multiple dirty regions for
6104         // the same object, to avoid potential O(N^2) performance.
6105         if (addr != _last_scanned_object) {
6106           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6107           _last_scanned_object = addr;
6108         }
6109       #endif // ASSERT
6110     } else {
6111       // An uninitialized object.
6112       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6113       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6114       size = pointer_delta(nextOneAddr + 1, addr);
6115       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6116              "alignment problem");
6117       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6118       // will dirty the card when the klass pointer is installed in the
6119       // object (signaling the completion of initialization).
6120     }
6121   } else {
6122     // Either a not yet marked object or an uninitialized object
6123     if (p->klass_or_null_acquire() == NULL) {
6124       // An uninitialized object, skip to the next card, since
6125       // we may not be able to read its P-bits yet.
6126       assert(size == 0, "Initial value");
6127     } else {
6128       // An object not (yet) reached by marking: we merely need to
6129       // compute its size so as to go look at the next block.
6130       assert(oopDesc::is_oop(p, true), "should be an oop");
6131       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6132     }
6133   }
6134   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6135   return size;
6136 }
6137 
6138 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6139   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6140          "CMS thread should hold CMS token");
6141   assert_lock_strong(_freelistLock);
6142   assert_lock_strong(_bitMap->lock());
6143   // relinquish the free_list_lock and bitMaplock()
6144   _bitMap->lock()->unlock();
6145   _freelistLock->unlock();
6146   ConcurrentMarkSweepThread::desynchronize(true);
6147   _collector->stopTimer();
6148   _collector->incrementYields();
6149 
6150   // See the comment in coordinator_yield()
6151   for (unsigned i = 0; i < CMSYieldSleepCount &&
6152                    ConcurrentMarkSweepThread::should_yield() &&
6153                    !CMSCollector::foregroundGCIsActive(); ++i) {
6154     os::sleep(Thread::current(), 1, false);
6155   }
6156 
6157   ConcurrentMarkSweepThread::synchronize(true);
6158   _freelistLock->lock_without_safepoint_check();
6159   _bitMap->lock()->lock_without_safepoint_check();
6160   _collector->startTimer();
6161 }
6162 
6163 
6164 //////////////////////////////////////////////////////////////////
6165 // SurvivorSpacePrecleanClosure
6166 //////////////////////////////////////////////////////////////////
6167 // This (single-threaded) closure is used to preclean the oops in
6168 // the survivor spaces.
6169 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6170 
6171   HeapWord* addr = (HeapWord*)p;
6172   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6173   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6174   assert(p->klass_or_null() != NULL, "object should be initialized");
6175   // an initialized object; ignore mark word in verification below
6176   // since we are running concurrent with mutators
6177   assert(oopDesc::is_oop(p, true), "should be an oop");
6178   // Note that we do not yield while we iterate over
6179   // the interior oops of p, pushing the relevant ones
6180   // on our marking stack.
6181   size_t size = p->oop_iterate_size(_scanning_closure);
6182   do_yield_check();
6183   // Observe that below, we do not abandon the preclean
6184   // phase as soon as we should; rather we empty the
6185   // marking stack before returning. This is to satisfy
6186   // some existing assertions. In general, it may be a
6187   // good idea to abort immediately and complete the marking
6188   // from the grey objects at a later time.
6189   while (!_mark_stack->isEmpty()) {
6190     oop new_oop = _mark_stack->pop();
6191     assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6192     assert(_bit_map->isMarked((HeapWord*)new_oop),
6193            "only grey objects on this stack");
6194     // iterate over the oops in this oop, marking and pushing
6195     // the ones in CMS heap (i.e. in _span).
6196     new_oop->oop_iterate(_scanning_closure);
6197     // check if it's time to yield
6198     do_yield_check();
6199   }
6200   unsigned int after_count =
6201     CMSHeap::heap()->total_collections();
6202   bool abort = (_before_count != after_count) ||
6203                _collector->should_abort_preclean();
6204   return abort ? 0 : size;
6205 }
6206 
6207 void SurvivorSpacePrecleanClosure::do_yield_work() {
6208   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6209          "CMS thread should hold CMS token");
6210   assert_lock_strong(_bit_map->lock());
6211   // Relinquish the bit map lock
6212   _bit_map->lock()->unlock();
6213   ConcurrentMarkSweepThread::desynchronize(true);
6214   _collector->stopTimer();
6215   _collector->incrementYields();
6216 
6217   // See the comment in coordinator_yield()
6218   for (unsigned i = 0; i < CMSYieldSleepCount &&
6219                        ConcurrentMarkSweepThread::should_yield() &&
6220                        !CMSCollector::foregroundGCIsActive(); ++i) {
6221     os::sleep(Thread::current(), 1, false);
6222   }
6223 
6224   ConcurrentMarkSweepThread::synchronize(true);
6225   _bit_map->lock()->lock_without_safepoint_check();
6226   _collector->startTimer();
6227 }
6228 
6229 // This closure is used to rescan the marked objects on the dirty cards
6230 // in the mod union table and the card table proper. In the parallel
6231 // case, although the bitMap is shared, we do a single read so the
6232 // isMarked() query is "safe".
6233 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6234   // Ignore mark word because we are running concurrent with mutators
6235   assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6236   HeapWord* addr = (HeapWord*)p;
6237   assert(_span.contains(addr), "we are scanning the CMS generation");
6238   bool is_obj_array = false;
6239   #ifdef ASSERT
6240     if (!_parallel) {
6241       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6242       assert(_collector->overflow_list_is_empty(),
6243              "overflow list should be empty");
6244 
6245     }
6246   #endif // ASSERT
6247   if (_bit_map->isMarked(addr)) {
6248     // Obj arrays are precisely marked, non-arrays are not;
6249     // so we scan objArrays precisely and non-arrays in their
6250     // entirety.
6251     if (p->is_objArray()) {
6252       is_obj_array = true;
6253       if (_parallel) {
6254         p->oop_iterate(_par_scan_closure, mr);
6255       } else {
6256         p->oop_iterate(_scan_closure, mr);
6257       }
6258     } else {
6259       if (_parallel) {
6260         p->oop_iterate(_par_scan_closure);
6261       } else {
6262         p->oop_iterate(_scan_closure);
6263       }
6264     }
6265   }
6266   #ifdef ASSERT
6267     if (!_parallel) {
6268       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6269       assert(_collector->overflow_list_is_empty(),
6270              "overflow list should be empty");
6271 
6272     }
6273   #endif // ASSERT
6274   return is_obj_array;
6275 }
6276 
6277 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6278                         MemRegion span,
6279                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6280                         bool should_yield, bool verifying):
6281   _collector(collector),
6282   _span(span),
6283   _bitMap(bitMap),
6284   _mut(&collector->_modUnionTable),
6285   _markStack(markStack),
6286   _yield(should_yield),
6287   _skipBits(0)
6288 {
6289   assert(_markStack->isEmpty(), "stack should be empty");
6290   _finger = _bitMap->startWord();
6291   _threshold = _finger;
6292   assert(_collector->_restart_addr == NULL, "Sanity check");
6293   assert(_span.contains(_finger), "Out of bounds _finger?");
6294   DEBUG_ONLY(_verifying = verifying;)
6295 }
6296 
6297 void MarkFromRootsClosure::reset(HeapWord* addr) {
6298   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6299   assert(_span.contains(addr), "Out of bounds _finger?");
6300   _finger = addr;
6301   _threshold = align_up(_finger, CardTable::card_size);
6302 }
6303 
6304 // Should revisit to see if this should be restructured for
6305 // greater efficiency.
6306 bool MarkFromRootsClosure::do_bit(size_t offset) {
6307   if (_skipBits > 0) {
6308     _skipBits--;
6309     return true;
6310   }
6311   // convert offset into a HeapWord*
6312   HeapWord* addr = _bitMap->startWord() + offset;
6313   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6314          "address out of range");
6315   assert(_bitMap->isMarked(addr), "tautology");
6316   if (_bitMap->isMarked(addr+1)) {
6317     // this is an allocated but not yet initialized object
6318     assert(_skipBits == 0, "tautology");
6319     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6320     oop p = oop(addr);
6321     if (p->klass_or_null_acquire() == NULL) {
6322       DEBUG_ONLY(if (!_verifying) {)
6323         // We re-dirty the cards on which this object lies and increase
6324         // the _threshold so that we'll come back to scan this object
6325         // during the preclean or remark phase. (CMSCleanOnEnter)
6326         if (CMSCleanOnEnter) {
6327           size_t sz = _collector->block_size_using_printezis_bits(addr);
6328           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6329           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6330           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6331           // Bump _threshold to end_card_addr; note that
6332           // _threshold cannot possibly exceed end_card_addr, anyhow.
6333           // This prevents future clearing of the card as the scan proceeds
6334           // to the right.
6335           assert(_threshold <= end_card_addr,
6336                  "Because we are just scanning into this object");
6337           if (_threshold < end_card_addr) {
6338             _threshold = end_card_addr;
6339           }
6340           if (p->klass_or_null_acquire() != NULL) {
6341             // Redirty the range of cards...
6342             _mut->mark_range(redirty_range);
6343           } // ...else the setting of klass will dirty the card anyway.
6344         }
6345       DEBUG_ONLY(})
6346       return true;
6347     }
6348   }
6349   scanOopsInOop(addr);
6350   return true;
6351 }
6352 
6353 // We take a break if we've been at this for a while,
6354 // so as to avoid monopolizing the locks involved.
6355 void MarkFromRootsClosure::do_yield_work() {
6356   // First give up the locks, then yield, then re-lock
6357   // We should probably use a constructor/destructor idiom to
6358   // do this unlock/lock or modify the MutexUnlocker class to
6359   // serve our purpose. XXX
6360   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6361          "CMS thread should hold CMS token");
6362   assert_lock_strong(_bitMap->lock());
6363   _bitMap->lock()->unlock();
6364   ConcurrentMarkSweepThread::desynchronize(true);
6365   _collector->stopTimer();
6366   _collector->incrementYields();
6367 
6368   // See the comment in coordinator_yield()
6369   for (unsigned i = 0; i < CMSYieldSleepCount &&
6370                        ConcurrentMarkSweepThread::should_yield() &&
6371                        !CMSCollector::foregroundGCIsActive(); ++i) {
6372     os::sleep(Thread::current(), 1, false);
6373   }
6374 
6375   ConcurrentMarkSweepThread::synchronize(true);
6376   _bitMap->lock()->lock_without_safepoint_check();
6377   _collector->startTimer();
6378 }
6379 
6380 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6381   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6382   assert(_markStack->isEmpty(),
6383          "should drain stack to limit stack usage");
6384   // convert ptr to an oop preparatory to scanning
6385   oop obj = oop(ptr);
6386   // Ignore mark word in verification below, since we
6387   // may be running concurrent with mutators.
6388   assert(oopDesc::is_oop(obj, true), "should be an oop");
6389   assert(_finger <= ptr, "_finger runneth ahead");
6390   // advance the finger to right end of this object
6391   _finger = ptr + obj->size();
6392   assert(_finger > ptr, "we just incremented it above");
6393   // On large heaps, it may take us some time to get through
6394   // the marking phase. During
6395   // this time it's possible that a lot of mutations have
6396   // accumulated in the card table and the mod union table --
6397   // these mutation records are redundant until we have
6398   // actually traced into the corresponding card.
6399   // Here, we check whether advancing the finger would make
6400   // us cross into a new card, and if so clear corresponding
6401   // cards in the MUT (preclean them in the card-table in the
6402   // future).
6403 
6404   DEBUG_ONLY(if (!_verifying) {)
6405     // The clean-on-enter optimization is disabled by default,
6406     // until we fix 6178663.
6407     if (CMSCleanOnEnter && (_finger > _threshold)) {
6408       // [_threshold, _finger) represents the interval
6409       // of cards to be cleared  in MUT (or precleaned in card table).
6410       // The set of cards to be cleared is all those that overlap
6411       // with the interval [_threshold, _finger); note that
6412       // _threshold is always kept card-aligned but _finger isn't
6413       // always card-aligned.
6414       HeapWord* old_threshold = _threshold;
6415       assert(is_aligned(old_threshold, CardTable::card_size),
6416              "_threshold should always be card-aligned");
6417       _threshold = align_up(_finger, CardTable::card_size);
6418       MemRegion mr(old_threshold, _threshold);
6419       assert(!mr.is_empty(), "Control point invariant");
6420       assert(_span.contains(mr), "Should clear within span");
6421       _mut->clear_range(mr);
6422     }
6423   DEBUG_ONLY(})
6424   // Note: the finger doesn't advance while we drain
6425   // the stack below.
6426   PushOrMarkClosure pushOrMarkClosure(_collector,
6427                                       _span, _bitMap, _markStack,
6428                                       _finger, this);
6429   bool res = _markStack->push(obj);
6430   assert(res, "Empty non-zero size stack should have space for single push");
6431   while (!_markStack->isEmpty()) {
6432     oop new_oop = _markStack->pop();
6433     // Skip verifying header mark word below because we are
6434     // running concurrent with mutators.
6435     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6436     // now scan this oop's oops
6437     new_oop->oop_iterate(&pushOrMarkClosure);
6438     do_yield_check();
6439   }
6440   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6441 }
6442 
6443 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6444                        CMSCollector* collector, MemRegion span,
6445                        CMSBitMap* bit_map,
6446                        OopTaskQueue* work_queue,
6447                        CMSMarkStack*  overflow_stack):
6448   _collector(collector),
6449   _whole_span(collector->_span),
6450   _span(span),
6451   _bit_map(bit_map),
6452   _mut(&collector->_modUnionTable),
6453   _work_queue(work_queue),
6454   _overflow_stack(overflow_stack),
6455   _skip_bits(0),
6456   _task(task)
6457 {
6458   assert(_work_queue->size() == 0, "work_queue should be empty");
6459   _finger = span.start();
6460   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6461   assert(_span.contains(_finger), "Out of bounds _finger?");
6462 }
6463 
6464 // Should revisit to see if this should be restructured for
6465 // greater efficiency.
6466 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6467   if (_skip_bits > 0) {
6468     _skip_bits--;
6469     return true;
6470   }
6471   // convert offset into a HeapWord*
6472   HeapWord* addr = _bit_map->startWord() + offset;
6473   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6474          "address out of range");
6475   assert(_bit_map->isMarked(addr), "tautology");
6476   if (_bit_map->isMarked(addr+1)) {
6477     // this is an allocated object that might not yet be initialized
6478     assert(_skip_bits == 0, "tautology");
6479     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6480     oop p = oop(addr);
6481     if (p->klass_or_null_acquire() == NULL) {
6482       // in the case of Clean-on-Enter optimization, redirty card
6483       // and avoid clearing card by increasing  the threshold.
6484       return true;
6485     }
6486   }
6487   scan_oops_in_oop(addr);
6488   return true;
6489 }
6490 
6491 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6492   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6493   // Should we assert that our work queue is empty or
6494   // below some drain limit?
6495   assert(_work_queue->size() == 0,
6496          "should drain stack to limit stack usage");
6497   // convert ptr to an oop preparatory to scanning
6498   oop obj = oop(ptr);
6499   // Ignore mark word in verification below, since we
6500   // may be running concurrent with mutators.
6501   assert(oopDesc::is_oop(obj, true), "should be an oop");
6502   assert(_finger <= ptr, "_finger runneth ahead");
6503   // advance the finger to right end of this object
6504   _finger = ptr + obj->size();
6505   assert(_finger > ptr, "we just incremented it above");
6506   // On large heaps, it may take us some time to get through
6507   // the marking phase. During
6508   // this time it's possible that a lot of mutations have
6509   // accumulated in the card table and the mod union table --
6510   // these mutation records are redundant until we have
6511   // actually traced into the corresponding card.
6512   // Here, we check whether advancing the finger would make
6513   // us cross into a new card, and if so clear corresponding
6514   // cards in the MUT (preclean them in the card-table in the
6515   // future).
6516 
6517   // The clean-on-enter optimization is disabled by default,
6518   // until we fix 6178663.
6519   if (CMSCleanOnEnter && (_finger > _threshold)) {
6520     // [_threshold, _finger) represents the interval
6521     // of cards to be cleared  in MUT (or precleaned in card table).
6522     // The set of cards to be cleared is all those that overlap
6523     // with the interval [_threshold, _finger); note that
6524     // _threshold is always kept card-aligned but _finger isn't
6525     // always card-aligned.
6526     HeapWord* old_threshold = _threshold;
6527     assert(is_aligned(old_threshold, CardTable::card_size),
6528            "_threshold should always be card-aligned");
6529     _threshold = align_up(_finger, CardTable::card_size);
6530     MemRegion mr(old_threshold, _threshold);
6531     assert(!mr.is_empty(), "Control point invariant");
6532     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6533     _mut->clear_range(mr);
6534   }
6535 
6536   // Note: the local finger doesn't advance while we drain
6537   // the stack below, but the global finger sure can and will.
6538   HeapWord* volatile* gfa = _task->global_finger_addr();
6539   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6540                                          _span, _bit_map,
6541                                          _work_queue,
6542                                          _overflow_stack,
6543                                          _finger,
6544                                          gfa, this);
6545   bool res = _work_queue->push(obj);   // overflow could occur here
6546   assert(res, "Will hold once we use workqueues");
6547   while (true) {
6548     oop new_oop;
6549     if (!_work_queue->pop_local(new_oop)) {
6550       // We emptied our work_queue; check if there's stuff that can
6551       // be gotten from the overflow stack.
6552       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6553             _overflow_stack, _work_queue)) {
6554         do_yield_check();
6555         continue;
6556       } else {  // done
6557         break;
6558       }
6559     }
6560     // Skip verifying header mark word below because we are
6561     // running concurrent with mutators.
6562     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6563     // now scan this oop's oops
6564     new_oop->oop_iterate(&pushOrMarkClosure);
6565     do_yield_check();
6566   }
6567   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6568 }
6569 
6570 // Yield in response to a request from VM Thread or
6571 // from mutators.
6572 void ParMarkFromRootsClosure::do_yield_work() {
6573   assert(_task != NULL, "sanity");
6574   _task->yield();
6575 }
6576 
6577 // A variant of the above used for verifying CMS marking work.
6578 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6579                         MemRegion span,
6580                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6581                         CMSMarkStack*  mark_stack):
6582   _collector(collector),
6583   _span(span),
6584   _verification_bm(verification_bm),
6585   _cms_bm(cms_bm),
6586   _mark_stack(mark_stack),
6587   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6588                       mark_stack)
6589 {
6590   assert(_mark_stack->isEmpty(), "stack should be empty");
6591   _finger = _verification_bm->startWord();
6592   assert(_collector->_restart_addr == NULL, "Sanity check");
6593   assert(_span.contains(_finger), "Out of bounds _finger?");
6594 }
6595 
6596 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6597   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6598   assert(_span.contains(addr), "Out of bounds _finger?");
6599   _finger = addr;
6600 }
6601 
6602 // Should revisit to see if this should be restructured for
6603 // greater efficiency.
6604 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6605   // convert offset into a HeapWord*
6606   HeapWord* addr = _verification_bm->startWord() + offset;
6607   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6608          "address out of range");
6609   assert(_verification_bm->isMarked(addr), "tautology");
6610   assert(_cms_bm->isMarked(addr), "tautology");
6611 
6612   assert(_mark_stack->isEmpty(),
6613          "should drain stack to limit stack usage");
6614   // convert addr to an oop preparatory to scanning
6615   oop obj = oop(addr);
6616   assert(oopDesc::is_oop(obj), "should be an oop");
6617   assert(_finger <= addr, "_finger runneth ahead");
6618   // advance the finger to right end of this object
6619   _finger = addr + obj->size();
6620   assert(_finger > addr, "we just incremented it above");
6621   // Note: the finger doesn't advance while we drain
6622   // the stack below.
6623   bool res = _mark_stack->push(obj);
6624   assert(res, "Empty non-zero size stack should have space for single push");
6625   while (!_mark_stack->isEmpty()) {
6626     oop new_oop = _mark_stack->pop();
6627     assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6628     // now scan this oop's oops
6629     new_oop->oop_iterate(&_pam_verify_closure);
6630   }
6631   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6632   return true;
6633 }
6634 
6635 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6636   CMSCollector* collector, MemRegion span,
6637   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6638   CMSMarkStack*  mark_stack):
6639   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6640   _collector(collector),
6641   _span(span),
6642   _verification_bm(verification_bm),
6643   _cms_bm(cms_bm),
6644   _mark_stack(mark_stack)
6645 { }
6646 
6647 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6648   oop obj = RawAccess<>::oop_load(p);
6649   do_oop(obj);
6650 }
6651 
6652 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6653 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6654 
6655 // Upon stack overflow, we discard (part of) the stack,
6656 // remembering the least address amongst those discarded
6657 // in CMSCollector's _restart_address.
6658 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6659   // Remember the least grey address discarded
6660   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6661   _collector->lower_restart_addr(ra);
6662   _mark_stack->reset();  // discard stack contents
6663   _mark_stack->expand(); // expand the stack if possible
6664 }
6665 
6666 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6667   assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6668   HeapWord* addr = (HeapWord*)obj;
6669   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6670     // Oop lies in _span and isn't yet grey or black
6671     _verification_bm->mark(addr);            // now grey
6672     if (!_cms_bm->isMarked(addr)) {
6673       Log(gc, verify) log;
6674       ResourceMark rm;
6675       LogStream ls(log.error());
6676       oop(addr)->print_on(&ls);
6677       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6678       fatal("... aborting");
6679     }
6680 
6681     if (!_mark_stack->push(obj)) { // stack overflow
6682       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6683       assert(_mark_stack->isFull(), "Else push should have succeeded");
6684       handle_stack_overflow(addr);
6685     }
6686     // anything including and to the right of _finger
6687     // will be scanned as we iterate over the remainder of the
6688     // bit map
6689   }
6690 }
6691 
6692 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6693                      MemRegion span,
6694                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6695                      HeapWord* finger, MarkFromRootsClosure* parent) :
6696   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6697   _collector(collector),
6698   _span(span),
6699   _bitMap(bitMap),
6700   _markStack(markStack),
6701   _finger(finger),
6702   _parent(parent)
6703 { }
6704 
6705 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6706                                            MemRegion span,
6707                                            CMSBitMap* bit_map,
6708                                            OopTaskQueue* work_queue,
6709                                            CMSMarkStack*  overflow_stack,
6710                                            HeapWord* finger,
6711                                            HeapWord* volatile* global_finger_addr,
6712                                            ParMarkFromRootsClosure* parent) :
6713   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6714   _collector(collector),
6715   _whole_span(collector->_span),
6716   _span(span),
6717   _bit_map(bit_map),
6718   _work_queue(work_queue),
6719   _overflow_stack(overflow_stack),
6720   _finger(finger),
6721   _global_finger_addr(global_finger_addr),
6722   _parent(parent)
6723 { }
6724 
6725 // Assumes thread-safe access by callers, who are
6726 // responsible for mutual exclusion.
6727 void CMSCollector::lower_restart_addr(HeapWord* low) {
6728   assert(_span.contains(low), "Out of bounds addr");
6729   if (_restart_addr == NULL) {
6730     _restart_addr = low;
6731   } else {
6732     _restart_addr = MIN2(_restart_addr, low);
6733   }
6734 }
6735 
6736 // Upon stack overflow, we discard (part of) the stack,
6737 // remembering the least address amongst those discarded
6738 // in CMSCollector's _restart_address.
6739 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6740   // Remember the least grey address discarded
6741   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6742   _collector->lower_restart_addr(ra);
6743   _markStack->reset();  // discard stack contents
6744   _markStack->expand(); // expand the stack if possible
6745 }
6746 
6747 // Upon stack overflow, we discard (part of) the stack,
6748 // remembering the least address amongst those discarded
6749 // in CMSCollector's _restart_address.
6750 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6751   // We need to do this under a mutex to prevent other
6752   // workers from interfering with the work done below.
6753   MutexLocker ml(_overflow_stack->par_lock(),
6754                  Mutex::_no_safepoint_check_flag);
6755   // Remember the least grey address discarded
6756   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6757   _collector->lower_restart_addr(ra);
6758   _overflow_stack->reset();  // discard stack contents
6759   _overflow_stack->expand(); // expand the stack if possible
6760 }
6761 
6762 void PushOrMarkClosure::do_oop(oop obj) {
6763   // Ignore mark word because we are running concurrent with mutators.
6764   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6765   HeapWord* addr = (HeapWord*)obj;
6766   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6767     // Oop lies in _span and isn't yet grey or black
6768     _bitMap->mark(addr);            // now grey
6769     if (addr < _finger) {
6770       // the bit map iteration has already either passed, or
6771       // sampled, this bit in the bit map; we'll need to
6772       // use the marking stack to scan this oop's oops.
6773       bool simulate_overflow = false;
6774       NOT_PRODUCT(
6775         if (CMSMarkStackOverflowALot &&
6776             _collector->simulate_overflow()) {
6777           // simulate a stack overflow
6778           simulate_overflow = true;
6779         }
6780       )
6781       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6782         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6783         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6784         handle_stack_overflow(addr);
6785       }
6786     }
6787     // anything including and to the right of _finger
6788     // will be scanned as we iterate over the remainder of the
6789     // bit map
6790     do_yield_check();
6791   }
6792 }
6793 
6794 void ParPushOrMarkClosure::do_oop(oop obj) {
6795   // Ignore mark word because we are running concurrent with mutators.
6796   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6797   HeapWord* addr = (HeapWord*)obj;
6798   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6799     // Oop lies in _span and isn't yet grey or black
6800     // We read the global_finger (volatile read) strictly after marking oop
6801     bool res = _bit_map->par_mark(addr);    // now grey
6802     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6803     // Should we push this marked oop on our stack?
6804     // -- if someone else marked it, nothing to do
6805     // -- if target oop is above global finger nothing to do
6806     // -- if target oop is in chunk and above local finger
6807     //      then nothing to do
6808     // -- else push on work queue
6809     if (   !res       // someone else marked it, they will deal with it
6810         || (addr >= *gfa)  // will be scanned in a later task
6811         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6812       return;
6813     }
6814     // the bit map iteration has already either passed, or
6815     // sampled, this bit in the bit map; we'll need to
6816     // use the marking stack to scan this oop's oops.
6817     bool simulate_overflow = false;
6818     NOT_PRODUCT(
6819       if (CMSMarkStackOverflowALot &&
6820           _collector->simulate_overflow()) {
6821         // simulate a stack overflow
6822         simulate_overflow = true;
6823       }
6824     )
6825     if (simulate_overflow ||
6826         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6827       // stack overflow
6828       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6829       // We cannot assert that the overflow stack is full because
6830       // it may have been emptied since.
6831       assert(simulate_overflow ||
6832              _work_queue->size() == _work_queue->max_elems(),
6833             "Else push should have succeeded");
6834       handle_stack_overflow(addr);
6835     }
6836     do_yield_check();
6837   }
6838 }
6839 
6840 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6841                                        MemRegion span,
6842                                        ReferenceDiscoverer* rd,
6843                                        CMSBitMap* bit_map,
6844                                        CMSBitMap* mod_union_table,
6845                                        CMSMarkStack*  mark_stack,
6846                                        bool           concurrent_precleaning):
6847   MetadataVisitingOopIterateClosure(rd),
6848   _collector(collector),
6849   _span(span),
6850   _bit_map(bit_map),
6851   _mod_union_table(mod_union_table),
6852   _mark_stack(mark_stack),
6853   _concurrent_precleaning(concurrent_precleaning)
6854 {
6855   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6856 }
6857 
6858 // Grey object rescan during pre-cleaning and second checkpoint phases --
6859 // the non-parallel version (the parallel version appears further below.)
6860 void PushAndMarkClosure::do_oop(oop obj) {
6861   // Ignore mark word verification. If during concurrent precleaning,
6862   // the object monitor may be locked. If during the checkpoint
6863   // phases, the object may already have been reached by a  different
6864   // path and may be at the end of the global overflow list (so
6865   // the mark word may be NULL).
6866   assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6867          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6868   HeapWord* addr = (HeapWord*)obj;
6869   // Check if oop points into the CMS generation
6870   // and is not marked
6871   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6872     // a white object ...
6873     _bit_map->mark(addr);         // ... now grey
6874     // push on the marking stack (grey set)
6875     bool simulate_overflow = false;
6876     NOT_PRODUCT(
6877       if (CMSMarkStackOverflowALot &&
6878           _collector->simulate_overflow()) {
6879         // simulate a stack overflow
6880         simulate_overflow = true;
6881       }
6882     )
6883     if (simulate_overflow || !_mark_stack->push(obj)) {
6884       if (_concurrent_precleaning) {
6885          // During precleaning we can just dirty the appropriate card(s)
6886          // in the mod union table, thus ensuring that the object remains
6887          // in the grey set  and continue. In the case of object arrays
6888          // we need to dirty all of the cards that the object spans,
6889          // since the rescan of object arrays will be limited to the
6890          // dirty cards.
6891          // Note that no one can be interfering with us in this action
6892          // of dirtying the mod union table, so no locking or atomics
6893          // are required.
6894          if (obj->is_objArray()) {
6895            size_t sz = obj->size();
6896            HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6897            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6898            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6899            _mod_union_table->mark_range(redirty_range);
6900          } else {
6901            _mod_union_table->mark(addr);
6902          }
6903          _collector->_ser_pmc_preclean_ovflw++;
6904       } else {
6905          // During the remark phase, we need to remember this oop
6906          // in the overflow list.
6907          _collector->push_on_overflow_list(obj);
6908          _collector->_ser_pmc_remark_ovflw++;
6909       }
6910     }
6911   }
6912 }
6913 
6914 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6915                                              MemRegion span,
6916                                              ReferenceDiscoverer* rd,
6917                                              CMSBitMap* bit_map,
6918                                              OopTaskQueue* work_queue):
6919   MetadataVisitingOopIterateClosure(rd),
6920   _collector(collector),
6921   _span(span),
6922   _bit_map(bit_map),
6923   _work_queue(work_queue)
6924 {
6925   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6926 }
6927 
6928 // Grey object rescan during second checkpoint phase --
6929 // the parallel version.
6930 void ParPushAndMarkClosure::do_oop(oop obj) {
6931   // In the assert below, we ignore the mark word because
6932   // this oop may point to an already visited object that is
6933   // on the overflow stack (in which case the mark word has
6934   // been hijacked for chaining into the overflow stack --
6935   // if this is the last object in the overflow stack then
6936   // its mark word will be NULL). Because this object may
6937   // have been subsequently popped off the global overflow
6938   // stack, and the mark word possibly restored to the prototypical
6939   // value, by the time we get to examined this failing assert in
6940   // the debugger, is_oop_or_null(false) may subsequently start
6941   // to hold.
6942   assert(oopDesc::is_oop_or_null(obj, true),
6943          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6944   HeapWord* addr = (HeapWord*)obj;
6945   // Check if oop points into the CMS generation
6946   // and is not marked
6947   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6948     // a white object ...
6949     // If we manage to "claim" the object, by being the
6950     // first thread to mark it, then we push it on our
6951     // marking stack
6952     if (_bit_map->par_mark(addr)) {     // ... now grey
6953       // push on work queue (grey set)
6954       bool simulate_overflow = false;
6955       NOT_PRODUCT(
6956         if (CMSMarkStackOverflowALot &&
6957             _collector->par_simulate_overflow()) {
6958           // simulate a stack overflow
6959           simulate_overflow = true;
6960         }
6961       )
6962       if (simulate_overflow || !_work_queue->push(obj)) {
6963         _collector->par_push_on_overflow_list(obj);
6964         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6965       }
6966     } // Else, some other thread got there first
6967   }
6968 }
6969 
6970 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6971   Mutex* bml = _collector->bitMapLock();
6972   assert_lock_strong(bml);
6973   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6974          "CMS thread should hold CMS token");
6975 
6976   bml->unlock();
6977   ConcurrentMarkSweepThread::desynchronize(true);
6978 
6979   _collector->stopTimer();
6980   _collector->incrementYields();
6981 
6982   // See the comment in coordinator_yield()
6983   for (unsigned i = 0; i < CMSYieldSleepCount &&
6984                        ConcurrentMarkSweepThread::should_yield() &&
6985                        !CMSCollector::foregroundGCIsActive(); ++i) {
6986     os::sleep(Thread::current(), 1, false);
6987   }
6988 
6989   ConcurrentMarkSweepThread::synchronize(true);
6990   bml->lock();
6991 
6992   _collector->startTimer();
6993 }
6994 
6995 bool CMSPrecleanRefsYieldClosure::should_return() {
6996   if (ConcurrentMarkSweepThread::should_yield()) {
6997     do_yield_work();
6998   }
6999   return _collector->foregroundGCIsActive();
7000 }
7001 
7002 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7003   assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
7004          "mr should be aligned to start at a card boundary");
7005   // We'd like to assert:
7006   // assert(mr.word_size()%CardTable::card_size_in_words == 0,
7007   //        "mr should be a range of cards");
7008   // However, that would be too strong in one case -- the last
7009   // partition ends at _unallocated_block which, in general, can be
7010   // an arbitrary boundary, not necessarily card aligned.
7011   _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
7012   _space->object_iterate_mem(mr, &_scan_cl);
7013 }
7014 
7015 SweepClosure::SweepClosure(CMSCollector* collector,
7016                            ConcurrentMarkSweepGeneration* g,
7017                            CMSBitMap* bitMap, bool should_yield) :
7018   _collector(collector),
7019   _g(g),
7020   _sp(g->cmsSpace()),
7021   _limit(_sp->sweep_limit()),
7022   _freelistLock(_sp->freelistLock()),
7023   _bitMap(bitMap),
7024   _inFreeRange(false),           // No free range at beginning of sweep
7025   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7026   _lastFreeRangeCoalesced(false),
7027   _yield(should_yield),
7028   _freeFinger(g->used_region().start())
7029 {
7030   NOT_PRODUCT(
7031     _numObjectsFreed = 0;
7032     _numWordsFreed   = 0;
7033     _numObjectsLive = 0;
7034     _numWordsLive = 0;
7035     _numObjectsAlreadyFree = 0;
7036     _numWordsAlreadyFree = 0;
7037     _last_fc = NULL;
7038 
7039     _sp->initializeIndexedFreeListArrayReturnedBytes();
7040     _sp->dictionary()->initialize_dict_returned_bytes();
7041   )
7042   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7043          "sweep _limit out of bounds");
7044   log_develop_trace(gc, sweep)("====================");
7045   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7046 }
7047 
7048 void SweepClosure::print_on(outputStream* st) const {
7049   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7050                p2i(_sp->bottom()), p2i(_sp->end()));
7051   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7052   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7053   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7054   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7055                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7056 }
7057 
7058 #ifndef PRODUCT
7059 // Assertion checking only:  no useful work in product mode --
7060 // however, if any of the flags below become product flags,
7061 // you may need to review this code to see if it needs to be
7062 // enabled in product mode.
7063 SweepClosure::~SweepClosure() {
7064   assert_lock_strong(_freelistLock);
7065   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7066          "sweep _limit out of bounds");
7067   if (inFreeRange()) {
7068     Log(gc, sweep) log;
7069     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7070     ResourceMark rm;
7071     LogStream ls(log.error());
7072     print_on(&ls);
7073     ShouldNotReachHere();
7074   }
7075 
7076   if (log_is_enabled(Debug, gc, sweep)) {
7077     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7078                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7079     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7080                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7081     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7082     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7083   }
7084 
7085   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7086     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7087     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7088     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7089     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7090                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7091   }
7092   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7093   log_develop_trace(gc, sweep)("================");
7094 }
7095 #endif  // PRODUCT
7096 
7097 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7098     bool freeRangeInFreeLists) {
7099   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7100                                p2i(freeFinger), freeRangeInFreeLists);
7101   assert(!inFreeRange(), "Trampling existing free range");
7102   set_inFreeRange(true);
7103   set_lastFreeRangeCoalesced(false);
7104 
7105   set_freeFinger(freeFinger);
7106   set_freeRangeInFreeLists(freeRangeInFreeLists);
7107   if (CMSTestInFreeList) {
7108     if (freeRangeInFreeLists) {
7109       FreeChunk* fc = (FreeChunk*) freeFinger;
7110       assert(fc->is_free(), "A chunk on the free list should be free.");
7111       assert(fc->size() > 0, "Free range should have a size");
7112       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7113     }
7114   }
7115 }
7116 
7117 // Note that the sweeper runs concurrently with mutators. Thus,
7118 // it is possible for direct allocation in this generation to happen
7119 // in the middle of the sweep. Note that the sweeper also coalesces
7120 // contiguous free blocks. Thus, unless the sweeper and the allocator
7121 // synchronize appropriately freshly allocated blocks may get swept up.
7122 // This is accomplished by the sweeper locking the free lists while
7123 // it is sweeping. Thus blocks that are determined to be free are
7124 // indeed free. There is however one additional complication:
7125 // blocks that have been allocated since the final checkpoint and
7126 // mark, will not have been marked and so would be treated as
7127 // unreachable and swept up. To prevent this, the allocator marks
7128 // the bit map when allocating during the sweep phase. This leads,
7129 // however, to a further complication -- objects may have been allocated
7130 // but not yet initialized -- in the sense that the header isn't yet
7131 // installed. The sweeper can not then determine the size of the block
7132 // in order to skip over it. To deal with this case, we use a technique
7133 // (due to Printezis) to encode such uninitialized block sizes in the
7134 // bit map. Since the bit map uses a bit per every HeapWord, but the
7135 // CMS generation has a minimum object size of 3 HeapWords, it follows
7136 // that "normal marks" won't be adjacent in the bit map (there will
7137 // always be at least two 0 bits between successive 1 bits). We make use
7138 // of these "unused" bits to represent uninitialized blocks -- the bit
7139 // corresponding to the start of the uninitialized object and the next
7140 // bit are both set. Finally, a 1 bit marks the end of the object that
7141 // started with the two consecutive 1 bits to indicate its potentially
7142 // uninitialized state.
7143 
7144 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7145   FreeChunk* fc = (FreeChunk*)addr;
7146   size_t res;
7147 
7148   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7149   // than "addr == _limit" because although _limit was a block boundary when
7150   // we started the sweep, it may no longer be one because heap expansion
7151   // may have caused us to coalesce the block ending at the address _limit
7152   // with a newly expanded chunk (this happens when _limit was set to the
7153   // previous _end of the space), so we may have stepped past _limit:
7154   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7155   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7156     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7157            "sweep _limit out of bounds");
7158     assert(addr < _sp->end(), "addr out of bounds");
7159     // Flush any free range we might be holding as a single
7160     // coalesced chunk to the appropriate free list.
7161     if (inFreeRange()) {
7162       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7163              "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7164       flush_cur_free_chunk(freeFinger(),
7165                            pointer_delta(addr, freeFinger()));
7166       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7167                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7168                                    lastFreeRangeCoalesced() ? 1 : 0);
7169     }
7170 
7171     // help the iterator loop finish
7172     return pointer_delta(_sp->end(), addr);
7173   }
7174 
7175   assert(addr < _limit, "sweep invariant");
7176   // check if we should yield
7177   do_yield_check(addr);
7178   if (fc->is_free()) {
7179     // Chunk that is already free
7180     res = fc->size();
7181     do_already_free_chunk(fc);
7182     debug_only(_sp->verifyFreeLists());
7183     // If we flush the chunk at hand in lookahead_and_flush()
7184     // and it's coalesced with a preceding chunk, then the
7185     // process of "mangling" the payload of the coalesced block
7186     // will cause erasure of the size information from the
7187     // (erstwhile) header of all the coalesced blocks but the
7188     // first, so the first disjunct in the assert will not hold
7189     // in that specific case (in which case the second disjunct
7190     // will hold).
7191     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7192            "Otherwise the size info doesn't change at this step");
7193     NOT_PRODUCT(
7194       _numObjectsAlreadyFree++;
7195       _numWordsAlreadyFree += res;
7196     )
7197     NOT_PRODUCT(_last_fc = fc;)
7198   } else if (!_bitMap->isMarked(addr)) {
7199     // Chunk is fresh garbage
7200     res = do_garbage_chunk(fc);
7201     debug_only(_sp->verifyFreeLists());
7202     NOT_PRODUCT(
7203       _numObjectsFreed++;
7204       _numWordsFreed += res;
7205     )
7206   } else {
7207     // Chunk that is alive.
7208     res = do_live_chunk(fc);
7209     debug_only(_sp->verifyFreeLists());
7210     NOT_PRODUCT(
7211         _numObjectsLive++;
7212         _numWordsLive += res;
7213     )
7214   }
7215   return res;
7216 }
7217 
7218 // For the smart allocation, record following
7219 //  split deaths - a free chunk is removed from its free list because
7220 //      it is being split into two or more chunks.
7221 //  split birth - a free chunk is being added to its free list because
7222 //      a larger free chunk has been split and resulted in this free chunk.
7223 //  coal death - a free chunk is being removed from its free list because
7224 //      it is being coalesced into a large free chunk.
7225 //  coal birth - a free chunk is being added to its free list because
7226 //      it was created when two or more free chunks where coalesced into
7227 //      this free chunk.
7228 //
7229 // These statistics are used to determine the desired number of free
7230 // chunks of a given size.  The desired number is chosen to be relative
7231 // to the end of a CMS sweep.  The desired number at the end of a sweep
7232 // is the
7233 //      count-at-end-of-previous-sweep (an amount that was enough)
7234 //              - count-at-beginning-of-current-sweep  (the excess)
7235 //              + split-births  (gains in this size during interval)
7236 //              - split-deaths  (demands on this size during interval)
7237 // where the interval is from the end of one sweep to the end of the
7238 // next.
7239 //
7240 // When sweeping the sweeper maintains an accumulated chunk which is
7241 // the chunk that is made up of chunks that have been coalesced.  That
7242 // will be termed the left-hand chunk.  A new chunk of garbage that
7243 // is being considered for coalescing will be referred to as the
7244 // right-hand chunk.
7245 //
7246 // When making a decision on whether to coalesce a right-hand chunk with
7247 // the current left-hand chunk, the current count vs. the desired count
7248 // of the left-hand chunk is considered.  Also if the right-hand chunk
7249 // is near the large chunk at the end of the heap (see
7250 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7251 // left-hand chunk is coalesced.
7252 //
7253 // When making a decision about whether to split a chunk, the desired count
7254 // vs. the current count of the candidate to be split is also considered.
7255 // If the candidate is underpopulated (currently fewer chunks than desired)
7256 // a chunk of an overpopulated (currently more chunks than desired) size may
7257 // be chosen.  The "hint" associated with a free list, if non-null, points
7258 // to a free list which may be overpopulated.
7259 //
7260 
7261 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7262   const size_t size = fc->size();
7263   // Chunks that cannot be coalesced are not in the
7264   // free lists.
7265   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7266     assert(_sp->verify_chunk_in_free_list(fc),
7267            "free chunk should be in free lists");
7268   }
7269   // a chunk that is already free, should not have been
7270   // marked in the bit map
7271   HeapWord* const addr = (HeapWord*) fc;
7272   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7273   // Verify that the bit map has no bits marked between
7274   // addr and purported end of this block.
7275   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7276 
7277   // Some chunks cannot be coalesced under any circumstances.
7278   // See the definition of cantCoalesce().
7279   if (!fc->cantCoalesce()) {
7280     // This chunk can potentially be coalesced.
7281     // All the work is done in
7282     do_post_free_or_garbage_chunk(fc, size);
7283     // Note that if the chunk is not coalescable (the else arm
7284     // below), we unconditionally flush, without needing to do
7285     // a "lookahead," as we do below.
7286     if (inFreeRange()) lookahead_and_flush(fc, size);
7287   } else {
7288     // Code path common to both original and adaptive free lists.
7289 
7290     // cant coalesce with previous block; this should be treated
7291     // as the end of a free run if any
7292     if (inFreeRange()) {
7293       // we kicked some butt; time to pick up the garbage
7294       assert(freeFinger() < addr, "freeFinger points too high");
7295       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7296     }
7297     // else, nothing to do, just continue
7298   }
7299 }
7300 
7301 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7302   // This is a chunk of garbage.  It is not in any free list.
7303   // Add it to a free list or let it possibly be coalesced into
7304   // a larger chunk.
7305   HeapWord* const addr = (HeapWord*) fc;
7306   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7307 
7308   // Verify that the bit map has no bits marked between
7309   // addr and purported end of just dead object.
7310   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7311   do_post_free_or_garbage_chunk(fc, size);
7312 
7313   assert(_limit >= addr + size,
7314          "A freshly garbage chunk can't possibly straddle over _limit");
7315   if (inFreeRange()) lookahead_and_flush(fc, size);
7316   return size;
7317 }
7318 
7319 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7320   HeapWord* addr = (HeapWord*) fc;
7321   // The sweeper has just found a live object. Return any accumulated
7322   // left hand chunk to the free lists.
7323   if (inFreeRange()) {
7324     assert(freeFinger() < addr, "freeFinger points too high");
7325     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7326   }
7327 
7328   // This object is live: we'd normally expect this to be
7329   // an oop, and like to assert the following:
7330   // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7331   // However, as we commented above, this may be an object whose
7332   // header hasn't yet been initialized.
7333   size_t size;
7334   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7335   if (_bitMap->isMarked(addr + 1)) {
7336     // Determine the size from the bit map, rather than trying to
7337     // compute it from the object header.
7338     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7339     size = pointer_delta(nextOneAddr + 1, addr);
7340     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7341            "alignment problem");
7342 
7343 #ifdef ASSERT
7344       if (oop(addr)->klass_or_null_acquire() != NULL) {
7345         // Ignore mark word because we are running concurrent with mutators
7346         assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7347         assert(size ==
7348                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7349                "P-mark and computed size do not agree");
7350       }
7351 #endif
7352 
7353   } else {
7354     // This should be an initialized object that's alive.
7355     assert(oop(addr)->klass_or_null_acquire() != NULL,
7356            "Should be an initialized object");
7357     // Ignore mark word because we are running concurrent with mutators
7358     assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7359     // Verify that the bit map has no bits marked between
7360     // addr and purported end of this block.
7361     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7362     assert(size >= 3, "Necessary for Printezis marks to work");
7363     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7364     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7365   }
7366   return size;
7367 }
7368 
7369 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7370                                                  size_t chunkSize) {
7371   // do_post_free_or_garbage_chunk() should only be called in the case
7372   // of the adaptive free list allocator.
7373   const bool fcInFreeLists = fc->is_free();
7374   assert((HeapWord*)fc <= _limit, "sweep invariant");
7375   if (CMSTestInFreeList && fcInFreeLists) {
7376     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7377   }
7378 
7379   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7380 
7381   HeapWord* const fc_addr = (HeapWord*) fc;
7382 
7383   bool coalesce = false;
7384   const size_t left  = pointer_delta(fc_addr, freeFinger());
7385   const size_t right = chunkSize;
7386   switch (FLSCoalescePolicy) {
7387     // numeric value forms a coalition aggressiveness metric
7388     case 0:  { // never coalesce
7389       coalesce = false;
7390       break;
7391     }
7392     case 1: { // coalesce if left & right chunks on overpopulated lists
7393       coalesce = _sp->coalOverPopulated(left) &&
7394                  _sp->coalOverPopulated(right);
7395       break;
7396     }
7397     case 2: { // coalesce if left chunk on overpopulated list (default)
7398       coalesce = _sp->coalOverPopulated(left);
7399       break;
7400     }
7401     case 3: { // coalesce if left OR right chunk on overpopulated list
7402       coalesce = _sp->coalOverPopulated(left) ||
7403                  _sp->coalOverPopulated(right);
7404       break;
7405     }
7406     case 4: { // always coalesce
7407       coalesce = true;
7408       break;
7409     }
7410     default:
7411      ShouldNotReachHere();
7412   }
7413 
7414   // Should the current free range be coalesced?
7415   // If the chunk is in a free range and either we decided to coalesce above
7416   // or the chunk is near the large block at the end of the heap
7417   // (isNearLargestChunk() returns true), then coalesce this chunk.
7418   const bool doCoalesce = inFreeRange()
7419                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7420   if (doCoalesce) {
7421     // Coalesce the current free range on the left with the new
7422     // chunk on the right.  If either is on a free list,
7423     // it must be removed from the list and stashed in the closure.
7424     if (freeRangeInFreeLists()) {
7425       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7426       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7427              "Size of free range is inconsistent with chunk size.");
7428       if (CMSTestInFreeList) {
7429         assert(_sp->verify_chunk_in_free_list(ffc),
7430                "Chunk is not in free lists");
7431       }
7432       _sp->coalDeath(ffc->size());
7433       _sp->removeFreeChunkFromFreeLists(ffc);
7434       set_freeRangeInFreeLists(false);
7435     }
7436     if (fcInFreeLists) {
7437       _sp->coalDeath(chunkSize);
7438       assert(fc->size() == chunkSize,
7439         "The chunk has the wrong size or is not in the free lists");
7440       _sp->removeFreeChunkFromFreeLists(fc);
7441     }
7442     set_lastFreeRangeCoalesced(true);
7443     print_free_block_coalesced(fc);
7444   } else {  // not in a free range and/or should not coalesce
7445     // Return the current free range and start a new one.
7446     if (inFreeRange()) {
7447       // In a free range but cannot coalesce with the right hand chunk.
7448       // Put the current free range into the free lists.
7449       flush_cur_free_chunk(freeFinger(),
7450                            pointer_delta(fc_addr, freeFinger()));
7451     }
7452     // Set up for new free range.  Pass along whether the right hand
7453     // chunk is in the free lists.
7454     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7455   }
7456 }
7457 
7458 // Lookahead flush:
7459 // If we are tracking a free range, and this is the last chunk that
7460 // we'll look at because its end crosses past _limit, we'll preemptively
7461 // flush it along with any free range we may be holding on to. Note that
7462 // this can be the case only for an already free or freshly garbage
7463 // chunk. If this block is an object, it can never straddle
7464 // over _limit. The "straddling" occurs when _limit is set at
7465 // the previous end of the space when this cycle started, and
7466 // a subsequent heap expansion caused the previously co-terminal
7467 // free block to be coalesced with the newly expanded portion,
7468 // thus rendering _limit a non-block-boundary making it dangerous
7469 // for the sweeper to step over and examine.
7470 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7471   assert(inFreeRange(), "Should only be called if currently in a free range.");
7472   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7473   assert(_sp->used_region().contains(eob - 1),
7474          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7475          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7476          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7477          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7478   if (eob >= _limit) {
7479     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7480     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7481                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7482                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7483                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7484     // Return the storage we are tracking back into the free lists.
7485     log_develop_trace(gc, sweep)("Flushing ... ");
7486     assert(freeFinger() < eob, "Error");
7487     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7488   }
7489 }
7490 
7491 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7492   assert(inFreeRange(), "Should only be called if currently in a free range.");
7493   assert(size > 0,
7494     "A zero sized chunk cannot be added to the free lists.");
7495   if (!freeRangeInFreeLists()) {
7496     if (CMSTestInFreeList) {
7497       FreeChunk* fc = (FreeChunk*) chunk;
7498       fc->set_size(size);
7499       assert(!_sp->verify_chunk_in_free_list(fc),
7500              "chunk should not be in free lists yet");
7501     }
7502     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7503     // A new free range is going to be starting.  The current
7504     // free range has not been added to the free lists yet or
7505     // was removed so add it back.
7506     // If the current free range was coalesced, then the death
7507     // of the free range was recorded.  Record a birth now.
7508     if (lastFreeRangeCoalesced()) {
7509       _sp->coalBirth(size);
7510     }
7511     _sp->addChunkAndRepairOffsetTable(chunk, size,
7512             lastFreeRangeCoalesced());
7513   } else {
7514     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7515   }
7516   set_inFreeRange(false);
7517   set_freeRangeInFreeLists(false);
7518 }
7519 
7520 // We take a break if we've been at this for a while,
7521 // so as to avoid monopolizing the locks involved.
7522 void SweepClosure::do_yield_work(HeapWord* addr) {
7523   // Return current free chunk being used for coalescing (if any)
7524   // to the appropriate freelist.  After yielding, the next
7525   // free block encountered will start a coalescing range of
7526   // free blocks.  If the next free block is adjacent to the
7527   // chunk just flushed, they will need to wait for the next
7528   // sweep to be coalesced.
7529   if (inFreeRange()) {
7530     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7531   }
7532 
7533   // First give up the locks, then yield, then re-lock.
7534   // We should probably use a constructor/destructor idiom to
7535   // do this unlock/lock or modify the MutexUnlocker class to
7536   // serve our purpose. XXX
7537   assert_lock_strong(_bitMap->lock());
7538   assert_lock_strong(_freelistLock);
7539   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7540          "CMS thread should hold CMS token");
7541   _bitMap->lock()->unlock();
7542   _freelistLock->unlock();
7543   ConcurrentMarkSweepThread::desynchronize(true);
7544   _collector->stopTimer();
7545   _collector->incrementYields();
7546 
7547   // See the comment in coordinator_yield()
7548   for (unsigned i = 0; i < CMSYieldSleepCount &&
7549                        ConcurrentMarkSweepThread::should_yield() &&
7550                        !CMSCollector::foregroundGCIsActive(); ++i) {
7551     os::sleep(Thread::current(), 1, false);
7552   }
7553 
7554   ConcurrentMarkSweepThread::synchronize(true);
7555   _freelistLock->lock_without_safepoint_check();
7556   _bitMap->lock()->lock_without_safepoint_check();
7557   _collector->startTimer();
7558 }
7559 
7560 #ifndef PRODUCT
7561 // This is actually very useful in a product build if it can
7562 // be called from the debugger.  Compile it into the product
7563 // as needed.
7564 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7565   return debug_cms_space->verify_chunk_in_free_list(fc);
7566 }
7567 #endif
7568 
7569 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7570   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7571                                p2i(fc), fc->size());
7572 }
7573 
7574 // CMSIsAliveClosure
7575 bool CMSIsAliveClosure::do_object_b(oop obj) {
7576   HeapWord* addr = (HeapWord*)obj;
7577   return addr != NULL &&
7578          (!_span.contains(addr) || _bit_map->isMarked(addr));
7579 }
7580 
7581 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7582                       MemRegion span,
7583                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7584                       bool cpc):
7585   _collector(collector),
7586   _span(span),
7587   _mark_stack(mark_stack),
7588   _bit_map(bit_map),
7589   _concurrent_precleaning(cpc) {
7590   assert(!_span.is_empty(), "Empty span could spell trouble");
7591 }
7592 
7593 
7594 // CMSKeepAliveClosure: the serial version
7595 void CMSKeepAliveClosure::do_oop(oop obj) {
7596   HeapWord* addr = (HeapWord*)obj;
7597   if (_span.contains(addr) &&
7598       !_bit_map->isMarked(addr)) {
7599     _bit_map->mark(addr);
7600     bool simulate_overflow = false;
7601     NOT_PRODUCT(
7602       if (CMSMarkStackOverflowALot &&
7603           _collector->simulate_overflow()) {
7604         // simulate a stack overflow
7605         simulate_overflow = true;
7606       }
7607     )
7608     if (simulate_overflow || !_mark_stack->push(obj)) {
7609       if (_concurrent_precleaning) {
7610         // We dirty the overflown object and let the remark
7611         // phase deal with it.
7612         assert(_collector->overflow_list_is_empty(), "Error");
7613         // In the case of object arrays, we need to dirty all of
7614         // the cards that the object spans. No locking or atomics
7615         // are needed since no one else can be mutating the mod union
7616         // table.
7617         if (obj->is_objArray()) {
7618           size_t sz = obj->size();
7619           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7620           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7621           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7622           _collector->_modUnionTable.mark_range(redirty_range);
7623         } else {
7624           _collector->_modUnionTable.mark(addr);
7625         }
7626         _collector->_ser_kac_preclean_ovflw++;
7627       } else {
7628         _collector->push_on_overflow_list(obj);
7629         _collector->_ser_kac_ovflw++;
7630       }
7631     }
7632   }
7633 }
7634 
7635 // CMSParKeepAliveClosure: a parallel version of the above.
7636 // The work queues are private to each closure (thread),
7637 // but (may be) available for stealing by other threads.
7638 void CMSParKeepAliveClosure::do_oop(oop obj) {
7639   HeapWord* addr = (HeapWord*)obj;
7640   if (_span.contains(addr) &&
7641       !_bit_map->isMarked(addr)) {
7642     // In general, during recursive tracing, several threads
7643     // may be concurrently getting here; the first one to
7644     // "tag" it, claims it.
7645     if (_bit_map->par_mark(addr)) {
7646       bool res = _work_queue->push(obj);
7647       assert(res, "Low water mark should be much less than capacity");
7648       // Do a recursive trim in the hope that this will keep
7649       // stack usage lower, but leave some oops for potential stealers
7650       trim_queue(_low_water_mark);
7651     } // Else, another thread got there first
7652   }
7653 }
7654 
7655 void CMSParKeepAliveClosure::trim_queue(uint max) {
7656   while (_work_queue->size() > max) {
7657     oop new_oop;
7658     if (_work_queue->pop_local(new_oop)) {
7659       assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7660       assert(_bit_map->isMarked((HeapWord*)new_oop),
7661              "no white objects on this stack!");
7662       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7663       // iterate over the oops in this oop, marking and pushing
7664       // the ones in CMS heap (i.e. in _span).
7665       new_oop->oop_iterate(&_mark_and_push);
7666     }
7667   }
7668 }
7669 
7670 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7671                                 CMSCollector* collector,
7672                                 MemRegion span, CMSBitMap* bit_map,
7673                                 OopTaskQueue* work_queue):
7674   _collector(collector),
7675   _span(span),
7676   _work_queue(work_queue),
7677   _bit_map(bit_map) { }
7678 
7679 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7680   HeapWord* addr = (HeapWord*)obj;
7681   if (_span.contains(addr) &&
7682       !_bit_map->isMarked(addr)) {
7683     if (_bit_map->par_mark(addr)) {
7684       bool simulate_overflow = false;
7685       NOT_PRODUCT(
7686         if (CMSMarkStackOverflowALot &&
7687             _collector->par_simulate_overflow()) {
7688           // simulate a stack overflow
7689           simulate_overflow = true;
7690         }
7691       )
7692       if (simulate_overflow || !_work_queue->push(obj)) {
7693         _collector->par_push_on_overflow_list(obj);
7694         _collector->_par_kac_ovflw++;
7695       }
7696     } // Else another thread got there already
7697   }
7698 }
7699 
7700 //////////////////////////////////////////////////////////////////
7701 //  CMSExpansionCause                /////////////////////////////
7702 //////////////////////////////////////////////////////////////////
7703 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7704   switch (cause) {
7705     case _no_expansion:
7706       return "No expansion";
7707     case _satisfy_free_ratio:
7708       return "Free ratio";
7709     case _satisfy_promotion:
7710       return "Satisfy promotion";
7711     case _satisfy_allocation:
7712       return "allocation";
7713     case _allocate_par_lab:
7714       return "Par LAB";
7715     case _allocate_par_spooling_space:
7716       return "Par Spooling Space";
7717     case _adaptive_size_policy:
7718       return "Ergonomics";
7719     default:
7720       return "unknown";
7721   }
7722 }
7723 
7724 void CMSDrainMarkingStackClosure::do_void() {
7725   // the max number to take from overflow list at a time
7726   const size_t num = _mark_stack->capacity()/4;
7727   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7728          "Overflow list should be NULL during concurrent phases");
7729   while (!_mark_stack->isEmpty() ||
7730          // if stack is empty, check the overflow list
7731          _collector->take_from_overflow_list(num, _mark_stack)) {
7732     oop obj = _mark_stack->pop();
7733     HeapWord* addr = (HeapWord*)obj;
7734     assert(_span.contains(addr), "Should be within span");
7735     assert(_bit_map->isMarked(addr), "Should be marked");
7736     assert(oopDesc::is_oop(obj), "Should be an oop");
7737     obj->oop_iterate(_keep_alive);
7738   }
7739 }
7740 
7741 void CMSParDrainMarkingStackClosure::do_void() {
7742   // drain queue
7743   trim_queue(0);
7744 }
7745 
7746 // Trim our work_queue so its length is below max at return
7747 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7748   while (_work_queue->size() > max) {
7749     oop new_oop;
7750     if (_work_queue->pop_local(new_oop)) {
7751       assert(oopDesc::is_oop(new_oop), "Expected an oop");
7752       assert(_bit_map->isMarked((HeapWord*)new_oop),
7753              "no white objects on this stack!");
7754       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7755       // iterate over the oops in this oop, marking and pushing
7756       // the ones in CMS heap (i.e. in _span).
7757       new_oop->oop_iterate(&_mark_and_push);
7758     }
7759   }
7760 }
7761 
7762 ////////////////////////////////////////////////////////////////////
7763 // Support for Marking Stack Overflow list handling and related code
7764 ////////////////////////////////////////////////////////////////////
7765 // Much of the following code is similar in shape and spirit to the
7766 // code used in ParNewGC. We should try and share that code
7767 // as much as possible in the future.
7768 
7769 #ifndef PRODUCT
7770 // Debugging support for CMSStackOverflowALot
7771 
7772 // It's OK to call this multi-threaded;  the worst thing
7773 // that can happen is that we'll get a bunch of closely
7774 // spaced simulated overflows, but that's OK, in fact
7775 // probably good as it would exercise the overflow code
7776 // under contention.
7777 bool CMSCollector::simulate_overflow() {
7778   if (_overflow_counter-- <= 0) { // just being defensive
7779     _overflow_counter = CMSMarkStackOverflowInterval;
7780     return true;
7781   } else {
7782     return false;
7783   }
7784 }
7785 
7786 bool CMSCollector::par_simulate_overflow() {
7787   return simulate_overflow();
7788 }
7789 #endif
7790 
7791 // Single-threaded
7792 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7793   assert(stack->isEmpty(), "Expected precondition");
7794   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7795   size_t i = num;
7796   oop  cur = _overflow_list;
7797   const markOop proto = markOopDesc::prototype();
7798   NOT_PRODUCT(ssize_t n = 0;)
7799   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7800     next = oop(cur->mark_raw());
7801     cur->set_mark_raw(proto);   // until proven otherwise
7802     assert(oopDesc::is_oop(cur), "Should be an oop");
7803     bool res = stack->push(cur);
7804     assert(res, "Bit off more than can chew?");
7805     NOT_PRODUCT(n++;)
7806   }
7807   _overflow_list = cur;
7808 #ifndef PRODUCT
7809   assert(_num_par_pushes >= n, "Too many pops?");
7810   _num_par_pushes -=n;
7811 #endif
7812   return !stack->isEmpty();
7813 }
7814 
7815 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7816 // (MT-safe) Get a prefix of at most "num" from the list.
7817 // The overflow list is chained through the mark word of
7818 // each object in the list. We fetch the entire list,
7819 // break off a prefix of the right size and return the
7820 // remainder. If other threads try to take objects from
7821 // the overflow list at that time, they will wait for
7822 // some time to see if data becomes available. If (and
7823 // only if) another thread places one or more object(s)
7824 // on the global list before we have returned the suffix
7825 // to the global list, we will walk down our local list
7826 // to find its end and append the global list to
7827 // our suffix before returning it. This suffix walk can
7828 // prove to be expensive (quadratic in the amount of traffic)
7829 // when there are many objects in the overflow list and
7830 // there is much producer-consumer contention on the list.
7831 // *NOTE*: The overflow list manipulation code here and
7832 // in ParNewGeneration:: are very similar in shape,
7833 // except that in the ParNew case we use the old (from/eden)
7834 // copy of the object to thread the list via its klass word.
7835 // Because of the common code, if you make any changes in
7836 // the code below, please check the ParNew version to see if
7837 // similar changes might be needed.
7838 // CR 6797058 has been filed to consolidate the common code.
7839 bool CMSCollector::par_take_from_overflow_list(size_t num,
7840                                                OopTaskQueue* work_q,
7841                                                int no_of_gc_threads) {
7842   assert(work_q->size() == 0, "First empty local work queue");
7843   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7844   if (_overflow_list == NULL) {
7845     return false;
7846   }
7847   // Grab the entire list; we'll put back a suffix
7848   oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7849   Thread* tid = Thread::current();
7850   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7851   // set to ParallelGCThreads.
7852   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7853   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7854   // If the list is busy, we spin for a short while,
7855   // sleeping between attempts to get the list.
7856   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7857     os::sleep(tid, sleep_time_millis, false);
7858     if (_overflow_list == NULL) {
7859       // Nothing left to take
7860       return false;
7861     } else if (_overflow_list != BUSY) {
7862       // Try and grab the prefix
7863       prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7864     }
7865   }
7866   // If the list was found to be empty, or we spun long
7867   // enough, we give up and return empty-handed. If we leave
7868   // the list in the BUSY state below, it must be the case that
7869   // some other thread holds the overflow list and will set it
7870   // to a non-BUSY state in the future.
7871   if (prefix == NULL || prefix == BUSY) {
7872      // Nothing to take or waited long enough
7873      if (prefix == NULL) {
7874        // Write back the NULL in case we overwrote it with BUSY above
7875        // and it is still the same value.
7876        Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7877      }
7878      return false;
7879   }
7880   assert(prefix != NULL && prefix != BUSY, "Error");
7881   size_t i = num;
7882   oop cur = prefix;
7883   // Walk down the first "num" objects, unless we reach the end.
7884   for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7885   if (cur->mark_raw() == NULL) {
7886     // We have "num" or fewer elements in the list, so there
7887     // is nothing to return to the global list.
7888     // Write back the NULL in lieu of the BUSY we wrote
7889     // above, if it is still the same value.
7890     if (_overflow_list == BUSY) {
7891       Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7892     }
7893   } else {
7894     // Chop off the suffix and return it to the global list.
7895     assert(cur->mark_raw() != BUSY, "Error");
7896     oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7897     cur->set_mark_raw(NULL);           // break off suffix
7898     // It's possible that the list is still in the empty(busy) state
7899     // we left it in a short while ago; in that case we may be
7900     // able to place back the suffix without incurring the cost
7901     // of a walk down the list.
7902     oop observed_overflow_list = _overflow_list;
7903     oop cur_overflow_list = observed_overflow_list;
7904     bool attached = false;
7905     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7906       observed_overflow_list =
7907         Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7908       if (cur_overflow_list == observed_overflow_list) {
7909         attached = true;
7910         break;
7911       } else cur_overflow_list = observed_overflow_list;
7912     }
7913     if (!attached) {
7914       // Too bad, someone else sneaked in (at least) an element; we'll need
7915       // to do a splice. Find tail of suffix so we can prepend suffix to global
7916       // list.
7917       for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7918       oop suffix_tail = cur;
7919       assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7920              "Tautology");
7921       observed_overflow_list = _overflow_list;
7922       do {
7923         cur_overflow_list = observed_overflow_list;
7924         if (cur_overflow_list != BUSY) {
7925           // Do the splice ...
7926           suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7927         } else { // cur_overflow_list == BUSY
7928           suffix_tail->set_mark_raw(NULL);
7929         }
7930         // ... and try to place spliced list back on overflow_list ...
7931         observed_overflow_list =
7932           Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7933       } while (cur_overflow_list != observed_overflow_list);
7934       // ... until we have succeeded in doing so.
7935     }
7936   }
7937 
7938   // Push the prefix elements on work_q
7939   assert(prefix != NULL, "control point invariant");
7940   const markOop proto = markOopDesc::prototype();
7941   oop next;
7942   NOT_PRODUCT(ssize_t n = 0;)
7943   for (cur = prefix; cur != NULL; cur = next) {
7944     next = oop(cur->mark_raw());
7945     cur->set_mark_raw(proto);   // until proven otherwise
7946     assert(oopDesc::is_oop(cur), "Should be an oop");
7947     bool res = work_q->push(cur);
7948     assert(res, "Bit off more than we can chew?");
7949     NOT_PRODUCT(n++;)
7950   }
7951 #ifndef PRODUCT
7952   assert(_num_par_pushes >= n, "Too many pops?");
7953   Atomic::sub(n, &_num_par_pushes);
7954 #endif
7955   return true;
7956 }
7957 
7958 // Single-threaded
7959 void CMSCollector::push_on_overflow_list(oop p) {
7960   NOT_PRODUCT(_num_par_pushes++;)
7961   assert(oopDesc::is_oop(p), "Not an oop");
7962   preserve_mark_if_necessary(p);
7963   p->set_mark_raw((markOop)_overflow_list);
7964   _overflow_list = p;
7965 }
7966 
7967 // Multi-threaded; use CAS to prepend to overflow list
7968 void CMSCollector::par_push_on_overflow_list(oop p) {
7969   NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7970   assert(oopDesc::is_oop(p), "Not an oop");
7971   par_preserve_mark_if_necessary(p);
7972   oop observed_overflow_list = _overflow_list;
7973   oop cur_overflow_list;
7974   do {
7975     cur_overflow_list = observed_overflow_list;
7976     if (cur_overflow_list != BUSY) {
7977       p->set_mark_raw(markOop(cur_overflow_list));
7978     } else {
7979       p->set_mark_raw(NULL);
7980     }
7981     observed_overflow_list =
7982       Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7983   } while (cur_overflow_list != observed_overflow_list);
7984 }
7985 #undef BUSY
7986 
7987 // Single threaded
7988 // General Note on GrowableArray: pushes may silently fail
7989 // because we are (temporarily) out of C-heap for expanding
7990 // the stack. The problem is quite ubiquitous and affects
7991 // a lot of code in the JVM. The prudent thing for GrowableArray
7992 // to do (for now) is to exit with an error. However, that may
7993 // be too draconian in some cases because the caller may be
7994 // able to recover without much harm. For such cases, we
7995 // should probably introduce a "soft_push" method which returns
7996 // an indication of success or failure with the assumption that
7997 // the caller may be able to recover from a failure; code in
7998 // the VM can then be changed, incrementally, to deal with such
7999 // failures where possible, thus, incrementally hardening the VM
8000 // in such low resource situations.
8001 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8002   _preserved_oop_stack.push(p);
8003   _preserved_mark_stack.push(m);
8004   assert(m == p->mark_raw(), "Mark word changed");
8005   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8006          "bijection");
8007 }
8008 
8009 // Single threaded
8010 void CMSCollector::preserve_mark_if_necessary(oop p) {
8011   markOop m = p->mark_raw();
8012   if (m->must_be_preserved(p)) {
8013     preserve_mark_work(p, m);
8014   }
8015 }
8016 
8017 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8018   markOop m = p->mark_raw();
8019   if (m->must_be_preserved(p)) {
8020     MutexLocker x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8021     // Even though we read the mark word without holding
8022     // the lock, we are assured that it will not change
8023     // because we "own" this oop, so no other thread can
8024     // be trying to push it on the overflow list; see
8025     // the assertion in preserve_mark_work() that checks
8026     // that m == p->mark_raw().
8027     preserve_mark_work(p, m);
8028   }
8029 }
8030 
8031 // We should be able to do this multi-threaded,
8032 // a chunk of stack being a task (this is
8033 // correct because each oop only ever appears
8034 // once in the overflow list. However, it's
8035 // not very easy to completely overlap this with
8036 // other operations, so will generally not be done
8037 // until all work's been completed. Because we
8038 // expect the preserved oop stack (set) to be small,
8039 // it's probably fine to do this single-threaded.
8040 // We can explore cleverer concurrent/overlapped/parallel
8041 // processing of preserved marks if we feel the
8042 // need for this in the future. Stack overflow should
8043 // be so rare in practice and, when it happens, its
8044 // effect on performance so great that this will
8045 // likely just be in the noise anyway.
8046 void CMSCollector::restore_preserved_marks_if_any() {
8047   assert(SafepointSynchronize::is_at_safepoint(),
8048          "world should be stopped");
8049   assert(Thread::current()->is_ConcurrentGC_thread() ||
8050          Thread::current()->is_VM_thread(),
8051          "should be single-threaded");
8052   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8053          "bijection");
8054 
8055   while (!_preserved_oop_stack.is_empty()) {
8056     oop p = _preserved_oop_stack.pop();
8057     assert(oopDesc::is_oop(p), "Should be an oop");
8058     assert(_span.contains(p), "oop should be in _span");
8059     assert(p->mark_raw() == markOopDesc::prototype(),
8060            "Set when taken from overflow list");
8061     markOop m = _preserved_mark_stack.pop();
8062     p->set_mark_raw(m);
8063   }
8064   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8065          "stacks were cleared above");
8066 }
8067 
8068 #ifndef PRODUCT
8069 bool CMSCollector::no_preserved_marks() const {
8070   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8071 }
8072 #endif
8073 
8074 // Transfer some number of overflown objects to usual marking
8075 // stack. Return true if some objects were transferred.
8076 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8077   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8078                     (size_t)ParGCDesiredObjsFromOverflowList);
8079 
8080   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8081   assert(_collector->overflow_list_is_empty() || res,
8082          "If list is not empty, we should have taken something");
8083   assert(!res || !_mark_stack->isEmpty(),
8084          "If we took something, it should now be on our stack");
8085   return res;
8086 }
8087 
8088 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8089   size_t res = _sp->block_size_no_stall(addr, _collector);
8090   if (_sp->block_is_obj(addr)) {
8091     if (_live_bit_map->isMarked(addr)) {
8092       // It can't have been dead in a previous cycle
8093       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8094     } else {
8095       _dead_bit_map->mark(addr);      // mark the dead object
8096     }
8097   }
8098   // Could be 0, if the block size could not be computed without stalling.
8099   return res;
8100 }
8101 
8102 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8103   GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8104   switch (phase) {
8105     case CMSCollector::InitialMarking:
8106       initialize(manager /* GC manager */ ,
8107                  cause   /* cause of the GC */,
8108                  true    /* allMemoryPoolsAffected */,
8109                  true    /* recordGCBeginTime */,
8110                  true    /* recordPreGCUsage */,
8111                  false   /* recordPeakUsage */,
8112                  false   /* recordPostGCusage */,
8113                  true    /* recordAccumulatedGCTime */,
8114                  false   /* recordGCEndTime */,
8115                  false   /* countCollection */  );
8116       break;
8117 
8118     case CMSCollector::FinalMarking:
8119       initialize(manager /* GC manager */ ,
8120                  cause   /* cause of the GC */,
8121                  true    /* allMemoryPoolsAffected */,
8122                  false   /* recordGCBeginTime */,
8123                  false   /* recordPreGCUsage */,
8124                  false   /* recordPeakUsage */,
8125                  false   /* recordPostGCusage */,
8126                  true    /* recordAccumulatedGCTime */,
8127                  false   /* recordGCEndTime */,
8128                  false   /* countCollection */  );
8129       break;
8130 
8131     case CMSCollector::Sweeping:
8132       initialize(manager /* GC manager */ ,
8133                  cause   /* cause of the GC */,
8134                  true    /* allMemoryPoolsAffected */,
8135                  false   /* recordGCBeginTime */,
8136                  false   /* recordPreGCUsage */,
8137                  true    /* recordPeakUsage */,
8138                  true    /* recordPostGCusage */,
8139                  false   /* recordAccumulatedGCTime */,
8140                  true    /* recordGCEndTime */,
8141                  true    /* countCollection */  );
8142       break;
8143 
8144     default:
8145       ShouldNotReachHere();
8146   }
8147 }