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