1 /*
   2  * Copyright (c) 2001, 2016, 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/classLoaderData.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/cmsOopClosures.inline.hpp"
  33 #include "gc/cms/compactibleFreeListSpace.hpp"
  34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc/cms/concurrentMarkSweepThread.hpp"
  36 #include "gc/cms/parNewGeneration.hpp"
  37 #include "gc/cms/vmCMSOperations.hpp"
  38 #include "gc/serial/genMarkSweep.hpp"
  39 #include "gc/serial/tenuredGeneration.hpp"
  40 #include "gc/shared/adaptiveSizePolicy.hpp"
  41 #include "gc/shared/cardGeneration.inline.hpp"
  42 #include "gc/shared/cardTableRS.hpp"
  43 #include "gc/shared/collectedHeap.inline.hpp"
  44 #include "gc/shared/collectorCounters.hpp"
  45 #include "gc/shared/collectorPolicy.hpp"
  46 #include "gc/shared/gcLocker.inline.hpp"
  47 #include "gc/shared/gcPolicyCounters.hpp"
  48 #include "gc/shared/gcTimer.hpp"
  49 #include "gc/shared/gcTrace.hpp"
  50 #include "gc/shared/gcTraceTime.inline.hpp"
  51 #include "gc/shared/genCollectedHeap.hpp"
  52 #include "gc/shared/genOopClosures.inline.hpp"
  53 #include "gc/shared/isGCActiveMark.hpp"
  54 #include "gc/shared/referencePolicy.hpp"
  55 #include "gc/shared/strongRootsScope.hpp"
  56 #include "gc/shared/taskqueue.inline.hpp"
  57 #include "logging/log.hpp"
  58 #include "memory/allocation.hpp"
  59 #include "memory/iterator.inline.hpp"
  60 #include "memory/padded.hpp"
  61 #include "memory/resourceArea.hpp"
  62 #include "oops/oop.inline.hpp"
  63 #include "prims/jvmtiExport.hpp"
  64 #include "runtime/atomic.inline.hpp"
  65 #include "runtime/globals_extension.hpp"
  66 #include "runtime/handles.inline.hpp"
  67 #include "runtime/java.hpp"
  68 #include "runtime/orderAccess.inline.hpp"
  69 #include "runtime/timer.hpp"
  70 #include "runtime/vmThread.hpp"
  71 #include "services/memoryService.hpp"
  72 #include "services/runtimeService.hpp"
  73 #include "utilities/stack.inline.hpp"
  74 
  75 // statics
  76 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  77 bool CMSCollector::_full_gc_requested = false;
  78 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  79 
  80 //////////////////////////////////////////////////////////////////
  81 // In support of CMS/VM thread synchronization
  82 //////////////////////////////////////////////////////////////////
  83 // We split use of the CGC_lock into 2 "levels".
  84 // The low-level locking is of the usual CGC_lock monitor. We introduce
  85 // a higher level "token" (hereafter "CMS token") built on top of the
  86 // low level monitor (hereafter "CGC lock").
  87 // The token-passing protocol gives priority to the VM thread. The
  88 // CMS-lock doesn't provide any fairness guarantees, but clients
  89 // should ensure that it is only held for very short, bounded
  90 // durations.
  91 //
  92 // When either of the CMS thread or the VM thread is involved in
  93 // collection operations during which it does not want the other
  94 // thread to interfere, it obtains the CMS token.
  95 //
  96 // If either thread tries to get the token while the other has
  97 // it, that thread waits. However, if the VM thread and CMS thread
  98 // both want the token, then the VM thread gets priority while the
  99 // CMS thread waits. This ensures, for instance, that the "concurrent"
 100 // phases of the CMS thread's work do not block out the VM thread
 101 // for long periods of time as the CMS thread continues to hog
 102 // the token. (See bug 4616232).
 103 //
 104 // The baton-passing functions are, however, controlled by the
 105 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 106 // and here the low-level CMS lock, not the high level token,
 107 // ensures mutual exclusion.
 108 //
 109 // Two important conditions that we have to satisfy:
 110 // 1. if a thread does a low-level wait on the CMS lock, then it
 111 //    relinquishes the CMS token if it were holding that token
 112 //    when it acquired the low-level CMS lock.
 113 // 2. any low-level notifications on the low-level lock
 114 //    should only be sent when a thread has relinquished the token.
 115 //
 116 // In the absence of either property, we'd have potential deadlock.
 117 //
 118 // We protect each of the CMS (concurrent and sequential) phases
 119 // with the CMS _token_, not the CMS _lock_.
 120 //
 121 // The only code protected by CMS lock is the token acquisition code
 122 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 123 // baton-passing code.
 124 //
 125 // Unfortunately, i couldn't come up with a good abstraction to factor and
 126 // hide the naked CGC_lock manipulation in the baton-passing code
 127 // further below. That's something we should try to do. Also, the proof
 128 // of correctness of this 2-level locking scheme is far from obvious,
 129 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 130 // that there may be a theoretical possibility of delay/starvation in the
 131 // low-level lock/wait/notify scheme used for the baton-passing because of
 132 // potential interference with the priority scheme embodied in the
 133 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 134 // invocation further below and marked with "XXX 20011219YSR".
 135 // Indeed, as we note elsewhere, this may become yet more slippery
 136 // in the presence of multiple CMS and/or multiple VM threads. XXX
 137 
 138 class CMSTokenSync: public StackObj {
 139  private:
 140   bool _is_cms_thread;
 141  public:
 142   CMSTokenSync(bool is_cms_thread):
 143     _is_cms_thread(is_cms_thread) {
 144     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 145            "Incorrect argument to constructor");
 146     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 147   }
 148 
 149   ~CMSTokenSync() {
 150     assert(_is_cms_thread ?
 151              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 152              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 153           "Incorrect state");
 154     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 155   }
 156 };
 157 
 158 // Convenience class that does a CMSTokenSync, and then acquires
 159 // upto three locks.
 160 class CMSTokenSyncWithLocks: public CMSTokenSync {
 161  private:
 162   // Note: locks are acquired in textual declaration order
 163   // and released in the opposite order
 164   MutexLockerEx _locker1, _locker2, _locker3;
 165  public:
 166   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 167                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 168     CMSTokenSync(is_cms_thread),
 169     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 170     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 171     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 172   { }
 173 };
 174 
 175 
 176 //////////////////////////////////////////////////////////////////
 177 //  Concurrent Mark-Sweep Generation /////////////////////////////
 178 //////////////////////////////////////////////////////////////////
 179 
 180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 181 
 182 // This struct contains per-thread things necessary to support parallel
 183 // young-gen collection.
 184 class CMSParGCThreadState: public CHeapObj<mtGC> {
 185  public:
 186   CompactibleFreeListSpaceLAB lab;
 187   PromotionInfo promo;
 188 
 189   // Constructor.
 190   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 191     promo.setSpace(cfls);
 192   }
 193 };
 194 
 195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 196      ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
 197   CardGeneration(rs, initial_byte_size, ct),
 198   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 199   _did_compact(false)
 200 {
 201   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 202   HeapWord* end    = (HeapWord*) _virtual_space.high();
 203 
 204   _direct_allocated_words = 0;
 205   NOT_PRODUCT(
 206     _numObjectsPromoted = 0;
 207     _numWordsPromoted = 0;
 208     _numObjectsAllocated = 0;
 209     _numWordsAllocated = 0;
 210   )
 211 
 212   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 213   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 214   _cmsSpace->_old_gen = this;
 215 
 216   _gc_stats = new CMSGCStats();
 217 
 218   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 219   // offsets match. The ability to tell free chunks from objects
 220   // depends on this property.
 221   debug_only(
 222     FreeChunk* junk = NULL;
 223     assert(UseCompressedClassPointers ||
 224            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 225            "Offset of FreeChunk::_prev within FreeChunk must match"
 226            "  that of OopDesc::_klass within OopDesc");
 227   )
 228 
 229   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 230   for (uint i = 0; i < ParallelGCThreads; i++) {
 231     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 232   }
 233 
 234   _incremental_collection_failed = false;
 235   // The "dilatation_factor" is the expansion that can occur on
 236   // account of the fact that the minimum object size in the CMS
 237   // generation may be larger than that in, say, a contiguous young
 238   //  generation.
 239   // Ideally, in the calculation below, we'd compute the dilatation
 240   // factor as: MinChunkSize/(promoting_gen's min object size)
 241   // Since we do not have such a general query interface for the
 242   // promoting generation, we'll instead just use the minimum
 243   // object size (which today is a header's worth of space);
 244   // note that all arithmetic is in units of HeapWords.
 245   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 246   assert(_dilatation_factor >= 1.0, "from previous assert");
 247 }
 248 
 249 
 250 // The field "_initiating_occupancy" represents the occupancy percentage
 251 // at which we trigger a new collection cycle.  Unless explicitly specified
 252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 253 // is calculated by:
 254 //
 255 //   Let "f" be MinHeapFreeRatio in
 256 //
 257 //    _initiating_occupancy = 100-f +
 258 //                           f * (CMSTriggerRatio/100)
 259 //   where CMSTriggerRatio is the argument "tr" below.
 260 //
 261 // That is, if we assume the heap is at its desired maximum occupancy at the
 262 // end of a collection, we let CMSTriggerRatio of the (purported) free
 263 // space be allocated before initiating a new collection cycle.
 264 //
 265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 266   assert(io <= 100 && tr <= 100, "Check the arguments");
 267   if (io >= 0) {
 268     _initiating_occupancy = (double)io / 100.0;
 269   } else {
 270     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 271                              (double)(tr * MinHeapFreeRatio) / 100.0)
 272                             / 100.0;
 273   }
 274 }
 275 
 276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 277   assert(collector() != NULL, "no collector");
 278   collector()->ref_processor_init();
 279 }
 280 
 281 void CMSCollector::ref_processor_init() {
 282   if (_ref_processor == NULL) {
 283     // Allocate and initialize a reference processor
 284     _ref_processor =
 285       new ReferenceProcessor(_span,                               // span
 286                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 287                              ParallelGCThreads,                   // mt processing degree
 288                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 289                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 290                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 291                              &_is_alive_closure);                 // closure for liveness info
 292     // Initialize the _ref_processor field of CMSGen
 293     _cmsGen->set_ref_processor(_ref_processor);
 294 
 295   }
 296 }
 297 
 298 AdaptiveSizePolicy* CMSCollector::size_policy() {
 299   GenCollectedHeap* gch = GenCollectedHeap::heap();
 300   return gch->gen_policy()->size_policy();
 301 }
 302 
 303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 304 
 305   const char* gen_name = "old";
 306   GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
 307   // Generation Counters - generation 1, 1 subspace
 308   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 309       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 310 
 311   _space_counters = new GSpaceCounters(gen_name, 0,
 312                                        _virtual_space.reserved_size(),
 313                                        this, _gen_counters);
 314 }
 315 
 316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 317   _cms_gen(cms_gen)
 318 {
 319   assert(alpha <= 100, "bad value");
 320   _saved_alpha = alpha;
 321 
 322   // Initialize the alphas to the bootstrap value of 100.
 323   _gc0_alpha = _cms_alpha = 100;
 324 
 325   _cms_begin_time.update();
 326   _cms_end_time.update();
 327 
 328   _gc0_duration = 0.0;
 329   _gc0_period = 0.0;
 330   _gc0_promoted = 0;
 331 
 332   _cms_duration = 0.0;
 333   _cms_period = 0.0;
 334   _cms_allocated = 0;
 335 
 336   _cms_used_at_gc0_begin = 0;
 337   _cms_used_at_gc0_end = 0;
 338   _allow_duty_cycle_reduction = false;
 339   _valid_bits = 0;
 340 }
 341 
 342 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 343   // TBD: CR 6909490
 344   return 1.0;
 345 }
 346 
 347 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 348 }
 349 
 350 // If promotion failure handling is on use
 351 // the padded average size of the promotion for each
 352 // young generation collection.
 353 double CMSStats::time_until_cms_gen_full() const {
 354   size_t cms_free = _cms_gen->cmsSpace()->free();
 355   GenCollectedHeap* gch = GenCollectedHeap::heap();
 356   size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
 357                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 358   if (cms_free > expected_promotion) {
 359     // Start a cms collection if there isn't enough space to promote
 360     // for the next young collection.  Use the padded average as
 361     // a safety factor.
 362     cms_free -= expected_promotion;
 363 
 364     // Adjust by the safety factor.
 365     double cms_free_dbl = (double)cms_free;
 366     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 367     // Apply a further correction factor which tries to adjust
 368     // for recent occurance of concurrent mode failures.
 369     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 370     cms_free_dbl = cms_free_dbl * cms_adjustment;
 371 
 372     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 373                   cms_free, expected_promotion);
 374     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 375     // Add 1 in case the consumption rate goes to zero.
 376     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 377   }
 378   return 0.0;
 379 }
 380 
 381 // Compare the duration of the cms collection to the
 382 // time remaining before the cms generation is empty.
 383 // Note that the time from the start of the cms collection
 384 // to the start of the cms sweep (less than the total
 385 // duration of the cms collection) can be used.  This
 386 // has been tried and some applications experienced
 387 // promotion failures early in execution.  This was
 388 // possibly because the averages were not accurate
 389 // enough at the beginning.
 390 double CMSStats::time_until_cms_start() const {
 391   // We add "gc0_period" to the "work" calculation
 392   // below because this query is done (mostly) at the
 393   // end of a scavenge, so we need to conservatively
 394   // account for that much possible delay
 395   // in the query so as to avoid concurrent mode failures
 396   // due to starting the collection just a wee bit too
 397   // late.
 398   double work = cms_duration() + gc0_period();
 399   double deadline = time_until_cms_gen_full();
 400   // If a concurrent mode failure occurred recently, we want to be
 401   // more conservative and halve our expected time_until_cms_gen_full()
 402   if (work > deadline) {
 403     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 404                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 405     return 0.0;
 406   }
 407   return work - deadline;
 408 }
 409 
 410 #ifndef PRODUCT
 411 void CMSStats::print_on(outputStream *st) const {
 412   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 413   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 414                gc0_duration(), gc0_period(), gc0_promoted());
 415   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 416             cms_duration(), cms_period(), cms_allocated());
 417   st->print(",cms_since_beg=%g,cms_since_end=%g",
 418             cms_time_since_begin(), cms_time_since_end());
 419   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 420             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 421 
 422   if (valid()) {
 423     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 424               promotion_rate(), cms_allocation_rate());
 425     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 426               cms_consumption_rate(), time_until_cms_gen_full());
 427   }
 428   st->cr();
 429 }
 430 #endif // #ifndef PRODUCT
 431 
 432 CMSCollector::CollectorState CMSCollector::_collectorState =
 433                              CMSCollector::Idling;
 434 bool CMSCollector::_foregroundGCIsActive = false;
 435 bool CMSCollector::_foregroundGCShouldWait = false;
 436 
 437 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 438                            CardTableRS*                   ct,
 439                            ConcurrentMarkSweepPolicy*     cp):
 440   _cmsGen(cmsGen),
 441   _ct(ct),
 442   _ref_processor(NULL),    // will be set later
 443   _conc_workers(NULL),     // may be set later
 444   _abort_preclean(false),
 445   _start_sampling(false),
 446   _between_prologue_and_epilogue(false),
 447   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 448   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 449                  -1 /* lock-free */, "No_lock" /* dummy */),
 450   _modUnionClosurePar(&_modUnionTable),
 451   // Adjust my span to cover old (cms) gen
 452   _span(cmsGen->reserved()),
 453   // Construct the is_alive_closure with _span & markBitMap
 454   _is_alive_closure(_span, &_markBitMap),
 455   _restart_addr(NULL),
 456   _overflow_list(NULL),
 457   _stats(cmsGen),
 458   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 459                              //verify that this lock should be acquired with safepoint check.
 460                              Monitor::_safepoint_check_sometimes)),
 461   _eden_chunk_array(NULL),     // may be set in ctor body
 462   _eden_chunk_capacity(0),     // -- ditto --
 463   _eden_chunk_index(0),        // -- ditto --
 464   _survivor_plab_array(NULL),  // -- ditto --
 465   _survivor_chunk_array(NULL), // -- ditto --
 466   _survivor_chunk_capacity(0), // -- ditto --
 467   _survivor_chunk_index(0),    // -- ditto --
 468   _ser_pmc_preclean_ovflw(0),
 469   _ser_kac_preclean_ovflw(0),
 470   _ser_pmc_remark_ovflw(0),
 471   _par_pmc_remark_ovflw(0),
 472   _ser_kac_ovflw(0),
 473   _par_kac_ovflw(0),
 474 #ifndef PRODUCT
 475   _num_par_pushes(0),
 476 #endif
 477   _collection_count_start(0),
 478   _verifying(false),
 479   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 480   _completed_initialization(false),
 481   _collector_policy(cp),
 482   _should_unload_classes(CMSClassUnloadingEnabled),
 483   _concurrent_cycles_since_last_unload(0),
 484   _roots_scanning_options(GenCollectedHeap::SO_None),
 485   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 486   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 487   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 488   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 489   _cms_start_registered(false)
 490 {
 491   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 492     ExplicitGCInvokesConcurrent = true;
 493   }
 494   // Now expand the span and allocate the collection support structures
 495   // (MUT, marking bit map etc.) to cover both generations subject to
 496   // collection.
 497 
 498   // For use by dirty card to oop closures.
 499   _cmsGen->cmsSpace()->set_collector(this);
 500 
 501   // Allocate MUT and marking bit map
 502   {
 503     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 504     if (!_markBitMap.allocate(_span)) {
 505       log_warning(gc)("Failed to allocate CMS Bit Map");
 506       return;
 507     }
 508     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 509   }
 510   {
 511     _modUnionTable.allocate(_span);
 512     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 513   }
 514 
 515   if (!_markStack.allocate(MarkStackSize)) {
 516     log_warning(gc)("Failed to allocate CMS Marking Stack");
 517     return;
 518   }
 519 
 520   // Support for multi-threaded concurrent phases
 521   if (CMSConcurrentMTEnabled) {
 522     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 523       // just for now
 524       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 525     }
 526     if (ConcGCThreads > 1) {
 527       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 528                                  ConcGCThreads, true);
 529       if (_conc_workers == NULL) {
 530         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 531         CMSConcurrentMTEnabled = false;
 532       } else {
 533         _conc_workers->initialize_workers();
 534       }
 535     } else {
 536       CMSConcurrentMTEnabled = false;
 537     }
 538   }
 539   if (!CMSConcurrentMTEnabled) {
 540     ConcGCThreads = 0;
 541   } else {
 542     // Turn off CMSCleanOnEnter optimization temporarily for
 543     // the MT case where it's not fixed yet; see 6178663.
 544     CMSCleanOnEnter = false;
 545   }
 546   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 547          "Inconsistency");
 548   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 549   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 550 
 551   // Parallel task queues; these are shared for the
 552   // concurrent and stop-world phases of CMS, but
 553   // are not shared with parallel scavenge (ParNew).
 554   {
 555     uint i;
 556     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 557 
 558     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 559          || ParallelRefProcEnabled)
 560         && num_queues > 0) {
 561       _task_queues = new OopTaskQueueSet(num_queues);
 562       if (_task_queues == NULL) {
 563         log_warning(gc)("task_queues allocation failure.");
 564         return;
 565       }
 566       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 567       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 568       for (i = 0; i < num_queues; i++) {
 569         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 570         if (q == NULL) {
 571           log_warning(gc)("work_queue allocation failure.");
 572           return;
 573         }
 574         _task_queues->register_queue(i, q);
 575       }
 576       for (i = 0; i < num_queues; i++) {
 577         _task_queues->queue(i)->initialize();
 578         _hash_seed[i] = 17;  // copied from ParNew
 579       }
 580     }
 581   }
 582 
 583   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 584 
 585   // Clip CMSBootstrapOccupancy between 0 and 100.
 586   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 587 
 588   // Now tell CMS generations the identity of their collector
 589   ConcurrentMarkSweepGeneration::set_collector(this);
 590 
 591   // Create & start a CMS thread for this CMS collector
 592   _cmsThread = ConcurrentMarkSweepThread::start(this);
 593   assert(cmsThread() != NULL, "CMS Thread should have been created");
 594   assert(cmsThread()->collector() == this,
 595          "CMS Thread should refer to this gen");
 596   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 597 
 598   // Support for parallelizing young gen rescan
 599   GenCollectedHeap* gch = GenCollectedHeap::heap();
 600   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 601   _young_gen = (ParNewGeneration*)gch->young_gen();
 602   if (gch->supports_inline_contig_alloc()) {
 603     _top_addr = gch->top_addr();
 604     _end_addr = gch->end_addr();
 605     assert(_young_gen != NULL, "no _young_gen");
 606     _eden_chunk_index = 0;
 607     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 608     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 609   }
 610 
 611   // Support for parallelizing survivor space rescan
 612   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 613     const size_t max_plab_samples =
 614       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 615 
 616     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 617     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 618     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 619     _survivor_chunk_capacity = max_plab_samples;
 620     for (uint i = 0; i < ParallelGCThreads; i++) {
 621       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 622       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 623       assert(cur->end() == 0, "Should be 0");
 624       assert(cur->array() == vec, "Should be vec");
 625       assert(cur->capacity() == max_plab_samples, "Error");
 626     }
 627   }
 628 
 629   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 630   _gc_counters = new CollectorCounters("CMS", 1);
 631   _completed_initialization = true;
 632   _inter_sweep_timer.start();  // start of time
 633 }
 634 
 635 const char* ConcurrentMarkSweepGeneration::name() const {
 636   return "concurrent mark-sweep generation";
 637 }
 638 void ConcurrentMarkSweepGeneration::update_counters() {
 639   if (UsePerfData) {
 640     _space_counters->update_all();
 641     _gen_counters->update_all();
 642   }
 643 }
 644 
 645 // this is an optimized version of update_counters(). it takes the
 646 // used value as a parameter rather than computing it.
 647 //
 648 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 649   if (UsePerfData) {
 650     _space_counters->update_used(used);
 651     _space_counters->update_capacity();
 652     _gen_counters->update_all();
 653   }
 654 }
 655 
 656 void ConcurrentMarkSweepGeneration::print() const {
 657   Generation::print();
 658   cmsSpace()->print();
 659 }
 660 
 661 #ifndef PRODUCT
 662 void ConcurrentMarkSweepGeneration::print_statistics() {
 663   cmsSpace()->printFLCensus(0);
 664 }
 665 #endif
 666 
 667 size_t
 668 ConcurrentMarkSweepGeneration::contiguous_available() const {
 669   // dld proposes an improvement in precision here. If the committed
 670   // part of the space ends in a free block we should add that to
 671   // uncommitted size in the calculation below. Will make this
 672   // change later, staying with the approximation below for the
 673   // time being. -- ysr.
 674   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 675 }
 676 
 677 size_t
 678 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 679   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 680 }
 681 
 682 size_t ConcurrentMarkSweepGeneration::max_available() const {
 683   return free() + _virtual_space.uncommitted_size();
 684 }
 685 
 686 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 687   size_t available = max_available();
 688   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 689   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 690   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 691                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 692   return res;
 693 }
 694 
 695 // At a promotion failure dump information on block layout in heap
 696 // (cms old generation).
 697 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 698   Log(gc, promotion) log;
 699   if (log.is_trace()) {
 700     ResourceMark rm;
 701     cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
 702   }
 703 }
 704 
 705 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 706   // Clear the promotion information.  These pointers can be adjusted
 707   // along with all the other pointers into the heap but
 708   // compaction is expected to be a rare event with
 709   // a heap using cms so don't do it without seeing the need.
 710   for (uint i = 0; i < ParallelGCThreads; i++) {
 711     _par_gc_thread_states[i]->promo.reset();
 712   }
 713 }
 714 
 715 void ConcurrentMarkSweepGeneration::compute_new_size() {
 716   assert_locked_or_safepoint(Heap_lock);
 717 
 718   // If incremental collection failed, we just want to expand
 719   // to the limit.
 720   if (incremental_collection_failed()) {
 721     clear_incremental_collection_failed();
 722     grow_to_reserved();
 723     return;
 724   }
 725 
 726   // The heap has been compacted but not reset yet.
 727   // Any metric such as free() or used() will be incorrect.
 728 
 729   CardGeneration::compute_new_size();
 730 
 731   // Reset again after a possible resizing
 732   if (did_compact()) {
 733     cmsSpace()->reset_after_compaction();
 734   }
 735 }
 736 
 737 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 738   assert_locked_or_safepoint(Heap_lock);
 739 
 740   // If incremental collection failed, we just want to expand
 741   // to the limit.
 742   if (incremental_collection_failed()) {
 743     clear_incremental_collection_failed();
 744     grow_to_reserved();
 745     return;
 746   }
 747 
 748   double free_percentage = ((double) free()) / capacity();
 749   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 750   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 751 
 752   // compute expansion delta needed for reaching desired free percentage
 753   if (free_percentage < desired_free_percentage) {
 754     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 755     assert(desired_capacity >= capacity(), "invalid expansion size");
 756     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 757     Log(gc) log;
 758     if (log.is_trace()) {
 759       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 760       log.trace("From compute_new_size: ");
 761       log.trace("  Free fraction %f", free_percentage);
 762       log.trace("  Desired free fraction %f", desired_free_percentage);
 763       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 764       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 765       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 766       GenCollectedHeap* gch = GenCollectedHeap::heap();
 767       assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
 768       size_t young_size = gch->young_gen()->capacity();
 769       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 770       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 771       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 772       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 773     }
 774     // safe if expansion fails
 775     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 776     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 777   } else {
 778     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 779     assert(desired_capacity <= capacity(), "invalid expansion size");
 780     size_t shrink_bytes = capacity() - desired_capacity;
 781     // Don't shrink unless the delta is greater than the minimum shrink we want
 782     if (shrink_bytes >= MinHeapDeltaBytes) {
 783       shrink_free_list_by(shrink_bytes);
 784     }
 785   }
 786 }
 787 
 788 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 789   return cmsSpace()->freelistLock();
 790 }
 791 
 792 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 793   CMSSynchronousYieldRequest yr;
 794   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 795   return have_lock_and_allocate(size, tlab);
 796 }
 797 
 798 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 799                                                                 bool   tlab /* ignored */) {
 800   assert_lock_strong(freelistLock());
 801   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 802   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 803   // Allocate the object live (grey) if the background collector has
 804   // started marking. This is necessary because the marker may
 805   // have passed this address and consequently this object will
 806   // not otherwise be greyed and would be incorrectly swept up.
 807   // Note that if this object contains references, the writing
 808   // of those references will dirty the card containing this object
 809   // allowing the object to be blackened (and its references scanned)
 810   // either during a preclean phase or at the final checkpoint.
 811   if (res != NULL) {
 812     // We may block here with an uninitialized object with
 813     // its mark-bit or P-bits not yet set. Such objects need
 814     // to be safely navigable by block_start().
 815     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 816     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 817     collector()->direct_allocated(res, adjustedSize);
 818     _direct_allocated_words += adjustedSize;
 819     // allocation counters
 820     NOT_PRODUCT(
 821       _numObjectsAllocated++;
 822       _numWordsAllocated += (int)adjustedSize;
 823     )
 824   }
 825   return res;
 826 }
 827 
 828 // In the case of direct allocation by mutators in a generation that
 829 // is being concurrently collected, the object must be allocated
 830 // live (grey) if the background collector has started marking.
 831 // This is necessary because the marker may
 832 // have passed this address and consequently this object will
 833 // not otherwise be greyed and would be incorrectly swept up.
 834 // Note that if this object contains references, the writing
 835 // of those references will dirty the card containing this object
 836 // allowing the object to be blackened (and its references scanned)
 837 // either during a preclean phase or at the final checkpoint.
 838 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 839   assert(_markBitMap.covers(start, size), "Out of bounds");
 840   if (_collectorState >= Marking) {
 841     MutexLockerEx y(_markBitMap.lock(),
 842                     Mutex::_no_safepoint_check_flag);
 843     // [see comments preceding SweepClosure::do_blk() below for details]
 844     //
 845     // Can the P-bits be deleted now?  JJJ
 846     //
 847     // 1. need to mark the object as live so it isn't collected
 848     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 849     // 3. need to mark the end of the object so marking, precleaning or sweeping
 850     //    can skip over uninitialized or unparsable objects. An allocated
 851     //    object is considered uninitialized for our purposes as long as
 852     //    its klass word is NULL.  All old gen objects are parsable
 853     //    as soon as they are initialized.)
 854     _markBitMap.mark(start);          // object is live
 855     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 856     _markBitMap.mark(start + size - 1);
 857                                       // mark end of object
 858   }
 859   // check that oop looks uninitialized
 860   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 861 }
 862 
 863 void CMSCollector::promoted(bool par, HeapWord* start,
 864                             bool is_obj_array, size_t obj_size) {
 865   assert(_markBitMap.covers(start), "Out of bounds");
 866   // See comment in direct_allocated() about when objects should
 867   // be allocated live.
 868   if (_collectorState >= Marking) {
 869     // we already hold the marking bit map lock, taken in
 870     // the prologue
 871     if (par) {
 872       _markBitMap.par_mark(start);
 873     } else {
 874       _markBitMap.mark(start);
 875     }
 876     // We don't need to mark the object as uninitialized (as
 877     // in direct_allocated above) because this is being done with the
 878     // world stopped and the object will be initialized by the
 879     // time the marking, precleaning or sweeping get to look at it.
 880     // But see the code for copying objects into the CMS generation,
 881     // where we need to ensure that concurrent readers of the
 882     // block offset table are able to safely navigate a block that
 883     // is in flux from being free to being allocated (and in
 884     // transition while being copied into) and subsequently
 885     // becoming a bona-fide object when the copy/promotion is complete.
 886     assert(SafepointSynchronize::is_at_safepoint(),
 887            "expect promotion only at safepoints");
 888 
 889     if (_collectorState < Sweeping) {
 890       // Mark the appropriate cards in the modUnionTable, so that
 891       // this object gets scanned before the sweep. If this is
 892       // not done, CMS generation references in the object might
 893       // not get marked.
 894       // For the case of arrays, which are otherwise precisely
 895       // marked, we need to dirty the entire array, not just its head.
 896       if (is_obj_array) {
 897         // The [par_]mark_range() method expects mr.end() below to
 898         // be aligned to the granularity of a bit's representation
 899         // in the heap. In the case of the MUT below, that's a
 900         // card size.
 901         MemRegion mr(start,
 902                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 903                         CardTableModRefBS::card_size /* bytes */));
 904         if (par) {
 905           _modUnionTable.par_mark_range(mr);
 906         } else {
 907           _modUnionTable.mark_range(mr);
 908         }
 909       } else {  // not an obj array; we can just mark the head
 910         if (par) {
 911           _modUnionTable.par_mark(start);
 912         } else {
 913           _modUnionTable.mark(start);
 914         }
 915       }
 916     }
 917   }
 918 }
 919 
 920 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 921   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 922   // allocate, copy and if necessary update promoinfo --
 923   // delegate to underlying space.
 924   assert_lock_strong(freelistLock());
 925 
 926 #ifndef PRODUCT
 927   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 928     return NULL;
 929   }
 930 #endif  // #ifndef PRODUCT
 931 
 932   oop res = _cmsSpace->promote(obj, obj_size);
 933   if (res == NULL) {
 934     // expand and retry
 935     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 936     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 937     // Since this is the old generation, we don't try to promote
 938     // into a more senior generation.
 939     res = _cmsSpace->promote(obj, obj_size);
 940   }
 941   if (res != NULL) {
 942     // See comment in allocate() about when objects should
 943     // be allocated live.
 944     assert(obj->is_oop(), "Will dereference klass pointer below");
 945     collector()->promoted(false,           // Not parallel
 946                           (HeapWord*)res, obj->is_objArray(), obj_size);
 947     // promotion counters
 948     NOT_PRODUCT(
 949       _numObjectsPromoted++;
 950       _numWordsPromoted +=
 951         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 952     )
 953   }
 954   return res;
 955 }
 956 
 957 
 958 // IMPORTANT: Notes on object size recognition in CMS.
 959 // ---------------------------------------------------
 960 // A block of storage in the CMS generation is always in
 961 // one of three states. A free block (FREE), an allocated
 962 // object (OBJECT) whose size() method reports the correct size,
 963 // and an intermediate state (TRANSIENT) in which its size cannot
 964 // be accurately determined.
 965 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 966 // -----------------------------------------------------
 967 // FREE:      klass_word & 1 == 1; mark_word holds block size
 968 //
 969 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 970 //            obj->size() computes correct size
 971 //
 972 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 973 //
 974 // STATE IDENTIFICATION: (64 bit+COOPS)
 975 // ------------------------------------
 976 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 977 //
 978 // OBJECT:    klass_word installed; klass_word != 0;
 979 //            obj->size() computes correct size
 980 //
 981 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 982 //
 983 //
 984 // STATE TRANSITION DIAGRAM
 985 //
 986 //        mut / parnew                     mut  /  parnew
 987 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 988 //  ^                                                                   |
 989 //  |------------------------ DEAD <------------------------------------|
 990 //         sweep                            mut
 991 //
 992 // While a block is in TRANSIENT state its size cannot be determined
 993 // so readers will either need to come back later or stall until
 994 // the size can be determined. Note that for the case of direct
 995 // allocation, P-bits, when available, may be used to determine the
 996 // size of an object that may not yet have been initialized.
 997 
 998 // Things to support parallel young-gen collection.
 999 oop
1000 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1001                                            oop old, markOop m,
1002                                            size_t word_sz) {
1003 #ifndef PRODUCT
1004   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1005     return NULL;
1006   }
1007 #endif  // #ifndef PRODUCT
1008 
1009   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1010   PromotionInfo* promoInfo = &ps->promo;
1011   // if we are tracking promotions, then first ensure space for
1012   // promotion (including spooling space for saving header if necessary).
1013   // then allocate and copy, then track promoted info if needed.
1014   // When tracking (see PromotionInfo::track()), the mark word may
1015   // be displaced and in this case restoration of the mark word
1016   // occurs in the (oop_since_save_marks_)iterate phase.
1017   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1018     // Out of space for allocating spooling buffers;
1019     // try expanding and allocating spooling buffers.
1020     if (!expand_and_ensure_spooling_space(promoInfo)) {
1021       return NULL;
1022     }
1023   }
1024   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1025   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1026   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1027   if (obj_ptr == NULL) {
1028      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1029      if (obj_ptr == NULL) {
1030        return NULL;
1031      }
1032   }
1033   oop obj = oop(obj_ptr);
1034   OrderAccess::storestore();
1035   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1036   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1037   // IMPORTANT: See note on object initialization for CMS above.
1038   // Otherwise, copy the object.  Here we must be careful to insert the
1039   // klass pointer last, since this marks the block as an allocated object.
1040   // Except with compressed oops it's the mark word.
1041   HeapWord* old_ptr = (HeapWord*)old;
1042   // Restore the mark word copied above.
1043   obj->set_mark(m);
1044   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1045   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1046   OrderAccess::storestore();
1047 
1048   if (UseCompressedClassPointers) {
1049     // Copy gap missed by (aligned) header size calculation below
1050     obj->set_klass_gap(old->klass_gap());
1051   }
1052   if (word_sz > (size_t)oopDesc::header_size()) {
1053     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1054                                  obj_ptr + oopDesc::header_size(),
1055                                  word_sz - oopDesc::header_size());
1056   }
1057 
1058   // Now we can track the promoted object, if necessary.  We take care
1059   // to delay the transition from uninitialized to full object
1060   // (i.e., insertion of klass pointer) until after, so that it
1061   // atomically becomes a promoted object.
1062   if (promoInfo->tracking()) {
1063     promoInfo->track((PromotedObject*)obj, old->klass());
1064   }
1065   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1066   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1067   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1068 
1069   // Finally, install the klass pointer (this should be volatile).
1070   OrderAccess::storestore();
1071   obj->set_klass(old->klass());
1072   // We should now be able to calculate the right size for this object
1073   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1074 
1075   collector()->promoted(true,          // parallel
1076                         obj_ptr, old->is_objArray(), word_sz);
1077 
1078   NOT_PRODUCT(
1079     Atomic::inc_ptr(&_numObjectsPromoted);
1080     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1081   )
1082 
1083   return obj;
1084 }
1085 
1086 void
1087 ConcurrentMarkSweepGeneration::
1088 par_promote_alloc_done(int thread_num) {
1089   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1090   ps->lab.retire(thread_num);
1091 }
1092 
1093 void
1094 ConcurrentMarkSweepGeneration::
1095 par_oop_since_save_marks_iterate_done(int thread_num) {
1096   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1097   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1098   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1099 
1100   // Because card-scanning has been completed, subsequent phases
1101   // (e.g., reference processing) will not need to recognize which
1102   // objects have been promoted during this GC. So, we can now disable
1103   // promotion tracking.
1104   ps->promo.stopTrackingPromotions();
1105 }
1106 
1107 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1108                                                    size_t size,
1109                                                    bool   tlab)
1110 {
1111   // We allow a STW collection only if a full
1112   // collection was requested.
1113   return full || should_allocate(size, tlab); // FIX ME !!!
1114   // This and promotion failure handling are connected at the
1115   // hip and should be fixed by untying them.
1116 }
1117 
1118 bool CMSCollector::shouldConcurrentCollect() {
1119   LogTarget(Trace, gc) log;
1120 
1121   if (_full_gc_requested) {
1122     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1123     return true;
1124   }
1125 
1126   FreelistLocker x(this);
1127   // ------------------------------------------------------------------
1128   // Print out lots of information which affects the initiation of
1129   // a collection.
1130   if (log.is_enabled() && stats().valid()) {
1131     log.print("CMSCollector shouldConcurrentCollect: ");
1132 
1133     LogStream out(log);
1134     stats().print_on(&out);
1135 
1136     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1137     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1138     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1139     log.print("promotion_rate=%g", stats().promotion_rate());
1140     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1141     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1142     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1143     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1144     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1145     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1146   }
1147   // ------------------------------------------------------------------
1148 
1149   // If the estimated time to complete a cms collection (cms_duration())
1150   // is less than the estimated time remaining until the cms generation
1151   // is full, start a collection.
1152   if (!UseCMSInitiatingOccupancyOnly) {
1153     if (stats().valid()) {
1154       if (stats().time_until_cms_start() == 0.0) {
1155         return true;
1156       }
1157     } else {
1158       // We want to conservatively collect somewhat early in order
1159       // to try and "bootstrap" our CMS/promotion statistics;
1160       // this branch will not fire after the first successful CMS
1161       // collection because the stats should then be valid.
1162       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1163         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1164                   _cmsGen->occupancy(), _bootstrap_occupancy);
1165         return true;
1166       }
1167     }
1168   }
1169 
1170   // Otherwise, we start a collection cycle if
1171   // old gen want a collection cycle started. Each may use
1172   // an appropriate criterion for making this decision.
1173   // XXX We need to make sure that the gen expansion
1174   // criterion dovetails well with this. XXX NEED TO FIX THIS
1175   if (_cmsGen->should_concurrent_collect()) {
1176     log.print("CMS old gen initiated");
1177     return true;
1178   }
1179 
1180   // We start a collection if we believe an incremental collection may fail;
1181   // this is not likely to be productive in practice because it's probably too
1182   // late anyway.
1183   GenCollectedHeap* gch = GenCollectedHeap::heap();
1184   assert(gch->collector_policy()->is_generation_policy(),
1185          "You may want to check the correctness of the following");
1186   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1187     log.print("CMSCollector: collect because incremental collection will fail ");
1188     return true;
1189   }
1190 
1191   if (MetaspaceGC::should_concurrent_collect()) {
1192     log.print("CMSCollector: collect for metadata allocation ");
1193     return true;
1194   }
1195 
1196   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1197   if (CMSTriggerInterval >= 0) {
1198     if (CMSTriggerInterval == 0) {
1199       // Trigger always
1200       return true;
1201     }
1202 
1203     // Check the CMS time since begin (we do not check the stats validity
1204     // as we want to be able to trigger the first CMS cycle as well)
1205     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1206       if (stats().valid()) {
1207         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1208                   stats().cms_time_since_begin());
1209       } else {
1210         log.print("CMSCollector: collect because of trigger interval (first collection)");
1211       }
1212       return true;
1213     }
1214   }
1215 
1216   return false;
1217 }
1218 
1219 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1220 
1221 // Clear _expansion_cause fields of constituent generations
1222 void CMSCollector::clear_expansion_cause() {
1223   _cmsGen->clear_expansion_cause();
1224 }
1225 
1226 // We should be conservative in starting a collection cycle.  To
1227 // start too eagerly runs the risk of collecting too often in the
1228 // extreme.  To collect too rarely falls back on full collections,
1229 // which works, even if not optimum in terms of concurrent work.
1230 // As a work around for too eagerly collecting, use the flag
1231 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1232 // giving the user an easily understandable way of controlling the
1233 // collections.
1234 // We want to start a new collection cycle if any of the following
1235 // conditions hold:
1236 // . our current occupancy exceeds the configured initiating occupancy
1237 //   for this generation, or
1238 // . we recently needed to expand this space and have not, since that
1239 //   expansion, done a collection of this generation, or
1240 // . the underlying space believes that it may be a good idea to initiate
1241 //   a concurrent collection (this may be based on criteria such as the
1242 //   following: the space uses linear allocation and linear allocation is
1243 //   going to fail, or there is believed to be excessive fragmentation in
1244 //   the generation, etc... or ...
1245 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1246 //   the case of the old generation; see CR 6543076):
1247 //   we may be approaching a point at which allocation requests may fail because
1248 //   we will be out of sufficient free space given allocation rate estimates.]
1249 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1250 
1251   assert_lock_strong(freelistLock());
1252   if (occupancy() > initiating_occupancy()) {
1253     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1254                   short_name(), occupancy(), initiating_occupancy());
1255     return true;
1256   }
1257   if (UseCMSInitiatingOccupancyOnly) {
1258     return false;
1259   }
1260   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1261     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1262     return true;
1263   }
1264   return false;
1265 }
1266 
1267 void ConcurrentMarkSweepGeneration::collect(bool   full,
1268                                             bool   clear_all_soft_refs,
1269                                             size_t size,
1270                                             bool   tlab)
1271 {
1272   collector()->collect(full, clear_all_soft_refs, size, tlab);
1273 }
1274 
1275 void CMSCollector::collect(bool   full,
1276                            bool   clear_all_soft_refs,
1277                            size_t size,
1278                            bool   tlab)
1279 {
1280   // The following "if" branch is present for defensive reasons.
1281   // In the current uses of this interface, it can be replaced with:
1282   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1283   // But I am not placing that assert here to allow future
1284   // generality in invoking this interface.
1285   if (GCLocker::is_active()) {
1286     // A consistency test for GCLocker
1287     assert(GCLocker::needs_gc(), "Should have been set already");
1288     // Skip this foreground collection, instead
1289     // expanding the heap if necessary.
1290     // Need the free list locks for the call to free() in compute_new_size()
1291     compute_new_size();
1292     return;
1293   }
1294   acquire_control_and_collect(full, clear_all_soft_refs);
1295 }
1296 
1297 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1298   GenCollectedHeap* gch = GenCollectedHeap::heap();
1299   unsigned int gc_count = gch->total_full_collections();
1300   if (gc_count == full_gc_count) {
1301     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1302     _full_gc_requested = true;
1303     _full_gc_cause = cause;
1304     CGC_lock->notify();   // nudge CMS thread
1305   } else {
1306     assert(gc_count > full_gc_count, "Error: causal loop");
1307   }
1308 }
1309 
1310 bool CMSCollector::is_external_interruption() {
1311   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1312   return GCCause::is_user_requested_gc(cause) ||
1313          GCCause::is_serviceability_requested_gc(cause);
1314 }
1315 
1316 void CMSCollector::report_concurrent_mode_interruption() {
1317   if (is_external_interruption()) {
1318     log_debug(gc)("Concurrent mode interrupted");
1319   } else {
1320     log_debug(gc)("Concurrent mode failure");
1321     _gc_tracer_cm->report_concurrent_mode_failure();
1322   }
1323 }
1324 
1325 
1326 // The foreground and background collectors need to coordinate in order
1327 // to make sure that they do not mutually interfere with CMS collections.
1328 // When a background collection is active,
1329 // the foreground collector may need to take over (preempt) and
1330 // synchronously complete an ongoing collection. Depending on the
1331 // frequency of the background collections and the heap usage
1332 // of the application, this preemption can be seldom or frequent.
1333 // There are only certain
1334 // points in the background collection that the "collection-baton"
1335 // can be passed to the foreground collector.
1336 //
1337 // The foreground collector will wait for the baton before
1338 // starting any part of the collection.  The foreground collector
1339 // will only wait at one location.
1340 //
1341 // The background collector will yield the baton before starting a new
1342 // phase of the collection (e.g., before initial marking, marking from roots,
1343 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1344 // of the loop which switches the phases. The background collector does some
1345 // of the phases (initial mark, final re-mark) with the world stopped.
1346 // Because of locking involved in stopping the world,
1347 // the foreground collector should not block waiting for the background
1348 // collector when it is doing a stop-the-world phase.  The background
1349 // collector will yield the baton at an additional point just before
1350 // it enters a stop-the-world phase.  Once the world is stopped, the
1351 // background collector checks the phase of the collection.  If the
1352 // phase has not changed, it proceeds with the collection.  If the
1353 // phase has changed, it skips that phase of the collection.  See
1354 // the comments on the use of the Heap_lock in collect_in_background().
1355 //
1356 // Variable used in baton passing.
1357 //   _foregroundGCIsActive - Set to true by the foreground collector when
1358 //      it wants the baton.  The foreground clears it when it has finished
1359 //      the collection.
1360 //   _foregroundGCShouldWait - Set to true by the background collector
1361 //        when it is running.  The foreground collector waits while
1362 //      _foregroundGCShouldWait is true.
1363 //  CGC_lock - monitor used to protect access to the above variables
1364 //      and to notify the foreground and background collectors.
1365 //  _collectorState - current state of the CMS collection.
1366 //
1367 // The foreground collector
1368 //   acquires the CGC_lock
1369 //   sets _foregroundGCIsActive
1370 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1371 //     various locks acquired in preparation for the collection
1372 //     are released so as not to block the background collector
1373 //     that is in the midst of a collection
1374 //   proceeds with the collection
1375 //   clears _foregroundGCIsActive
1376 //   returns
1377 //
1378 // The background collector in a loop iterating on the phases of the
1379 //      collection
1380 //   acquires the CGC_lock
1381 //   sets _foregroundGCShouldWait
1382 //   if _foregroundGCIsActive is set
1383 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1384 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1385 //     and exits the loop.
1386 //   otherwise
1387 //     proceed with that phase of the collection
1388 //     if the phase is a stop-the-world phase,
1389 //       yield the baton once more just before enqueueing
1390 //       the stop-world CMS operation (executed by the VM thread).
1391 //   returns after all phases of the collection are done
1392 //
1393 
1394 void CMSCollector::acquire_control_and_collect(bool full,
1395         bool clear_all_soft_refs) {
1396   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1397   assert(!Thread::current()->is_ConcurrentGC_thread(),
1398          "shouldn't try to acquire control from self!");
1399 
1400   // Start the protocol for acquiring control of the
1401   // collection from the background collector (aka CMS thread).
1402   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1403          "VM thread should have CMS token");
1404   // Remember the possibly interrupted state of an ongoing
1405   // concurrent collection
1406   CollectorState first_state = _collectorState;
1407 
1408   // Signal to a possibly ongoing concurrent collection that
1409   // we want to do a foreground collection.
1410   _foregroundGCIsActive = true;
1411 
1412   // release locks and wait for a notify from the background collector
1413   // releasing the locks in only necessary for phases which
1414   // do yields to improve the granularity of the collection.
1415   assert_lock_strong(bitMapLock());
1416   // We need to lock the Free list lock for the space that we are
1417   // currently collecting.
1418   assert(haveFreelistLocks(), "Must be holding free list locks");
1419   bitMapLock()->unlock();
1420   releaseFreelistLocks();
1421   {
1422     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1423     if (_foregroundGCShouldWait) {
1424       // We are going to be waiting for action for the CMS thread;
1425       // it had better not be gone (for instance at shutdown)!
1426       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1427              "CMS thread must be running");
1428       // Wait here until the background collector gives us the go-ahead
1429       ConcurrentMarkSweepThread::clear_CMS_flag(
1430         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1431       // Get a possibly blocked CMS thread going:
1432       //   Note that we set _foregroundGCIsActive true above,
1433       //   without protection of the CGC_lock.
1434       CGC_lock->notify();
1435       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1436              "Possible deadlock");
1437       while (_foregroundGCShouldWait) {
1438         // wait for notification
1439         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1440         // Possibility of delay/starvation here, since CMS token does
1441         // not know to give priority to VM thread? Actually, i think
1442         // there wouldn't be any delay/starvation, but the proof of
1443         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1444       }
1445       ConcurrentMarkSweepThread::set_CMS_flag(
1446         ConcurrentMarkSweepThread::CMS_vm_has_token);
1447     }
1448   }
1449   // The CMS_token is already held.  Get back the other locks.
1450   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1451          "VM thread should have CMS token");
1452   getFreelistLocks();
1453   bitMapLock()->lock_without_safepoint_check();
1454   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1455                        p2i(Thread::current()), first_state);
1456   log_debug(gc, state)("    gets control with state %d", _collectorState);
1457 
1458   // Inform cms gen if this was due to partial collection failing.
1459   // The CMS gen may use this fact to determine its expansion policy.
1460   GenCollectedHeap* gch = GenCollectedHeap::heap();
1461   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1462     assert(!_cmsGen->incremental_collection_failed(),
1463            "Should have been noticed, reacted to and cleared");
1464     _cmsGen->set_incremental_collection_failed();
1465   }
1466 
1467   if (first_state > Idling) {
1468     report_concurrent_mode_interruption();
1469   }
1470 
1471   set_did_compact(true);
1472 
1473   // If the collection is being acquired from the background
1474   // collector, there may be references on the discovered
1475   // references lists.  Abandon those references, since some
1476   // of them may have become unreachable after concurrent
1477   // discovery; the STW compacting collector will redo discovery
1478   // more precisely, without being subject to floating garbage.
1479   // Leaving otherwise unreachable references in the discovered
1480   // lists would require special handling.
1481   ref_processor()->disable_discovery();
1482   ref_processor()->abandon_partial_discovery();
1483   ref_processor()->verify_no_references_recorded();
1484 
1485   if (first_state > Idling) {
1486     save_heap_summary();
1487   }
1488 
1489   do_compaction_work(clear_all_soft_refs);
1490 
1491   // Has the GC time limit been exceeded?
1492   size_t max_eden_size = _young_gen->max_eden_size();
1493   GCCause::Cause gc_cause = gch->gc_cause();
1494   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1495                                          _young_gen->eden()->used(),
1496                                          _cmsGen->max_capacity(),
1497                                          max_eden_size,
1498                                          full,
1499                                          gc_cause,
1500                                          gch->collector_policy());
1501 
1502   // Reset the expansion cause, now that we just completed
1503   // a collection cycle.
1504   clear_expansion_cause();
1505   _foregroundGCIsActive = false;
1506   return;
1507 }
1508 
1509 // Resize the tenured generation
1510 // after obtaining the free list locks for the
1511 // two generations.
1512 void CMSCollector::compute_new_size() {
1513   assert_locked_or_safepoint(Heap_lock);
1514   FreelistLocker z(this);
1515   MetaspaceGC::compute_new_size();
1516   _cmsGen->compute_new_size_free_list();
1517 }
1518 
1519 // A work method used by the foreground collector to do
1520 // a mark-sweep-compact.
1521 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1522   GenCollectedHeap* gch = GenCollectedHeap::heap();
1523 
1524   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1525   gc_timer->register_gc_start();
1526 
1527   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1528   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1529 
1530   gch->pre_full_gc_dump(gc_timer);
1531 
1532   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1533 
1534   // Temporarily widen the span of the weak reference processing to
1535   // the entire heap.
1536   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1537   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1538   // Temporarily, clear the "is_alive_non_header" field of the
1539   // reference processor.
1540   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1541   // Temporarily make reference _processing_ single threaded (non-MT).
1542   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1543   // Temporarily make refs discovery atomic
1544   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1545   // Temporarily make reference _discovery_ single threaded (non-MT)
1546   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1547 
1548   ref_processor()->set_enqueuing_is_done(false);
1549   ref_processor()->enable_discovery();
1550   ref_processor()->setup_policy(clear_all_soft_refs);
1551   // If an asynchronous collection finishes, the _modUnionTable is
1552   // all clear.  If we are assuming the collection from an asynchronous
1553   // collection, clear the _modUnionTable.
1554   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1555     "_modUnionTable should be clear if the baton was not passed");
1556   _modUnionTable.clear_all();
1557   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1558     "mod union for klasses should be clear if the baton was passed");
1559   _ct->klass_rem_set()->clear_mod_union();
1560 
1561   // We must adjust the allocation statistics being maintained
1562   // in the free list space. We do so by reading and clearing
1563   // the sweep timer and updating the block flux rate estimates below.
1564   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1565   if (_inter_sweep_timer.is_active()) {
1566     _inter_sweep_timer.stop();
1567     // Note that we do not use this sample to update the _inter_sweep_estimate.
1568     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1569                                             _inter_sweep_estimate.padded_average(),
1570                                             _intra_sweep_estimate.padded_average());
1571   }
1572 
1573   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1574   #ifdef ASSERT
1575     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1576     size_t free_size = cms_space->free();
1577     assert(free_size ==
1578            pointer_delta(cms_space->end(), cms_space->compaction_top())
1579            * HeapWordSize,
1580       "All the free space should be compacted into one chunk at top");
1581     assert(cms_space->dictionary()->total_chunk_size(
1582                                       debug_only(cms_space->freelistLock())) == 0 ||
1583            cms_space->totalSizeInIndexedFreeLists() == 0,
1584       "All the free space should be in a single chunk");
1585     size_t num = cms_space->totalCount();
1586     assert((free_size == 0 && num == 0) ||
1587            (free_size > 0  && (num == 1 || num == 2)),
1588          "There should be at most 2 free chunks after compaction");
1589   #endif // ASSERT
1590   _collectorState = Resetting;
1591   assert(_restart_addr == NULL,
1592          "Should have been NULL'd before baton was passed");
1593   reset_stw();
1594   _cmsGen->reset_after_compaction();
1595   _concurrent_cycles_since_last_unload = 0;
1596 
1597   // Clear any data recorded in the PLAB chunk arrays.
1598   if (_survivor_plab_array != NULL) {
1599     reset_survivor_plab_arrays();
1600   }
1601 
1602   // Adjust the per-size allocation stats for the next epoch.
1603   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1604   // Restart the "inter sweep timer" for the next epoch.
1605   _inter_sweep_timer.reset();
1606   _inter_sweep_timer.start();
1607 
1608   // No longer a need to do a concurrent collection for Metaspace.
1609   MetaspaceGC::set_should_concurrent_collect(false);
1610 
1611   gch->post_full_gc_dump(gc_timer);
1612 
1613   gc_timer->register_gc_end();
1614 
1615   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1616 
1617   // For a mark-sweep-compact, compute_new_size() will be called
1618   // in the heap's do_collection() method.
1619 }
1620 
1621 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1622   Log(gc, heap) log;
1623   if (!log.is_trace()) {
1624     return;
1625   }
1626 
1627   ContiguousSpace* eden_space = _young_gen->eden();
1628   ContiguousSpace* from_space = _young_gen->from();
1629   ContiguousSpace* to_space   = _young_gen->to();
1630   // Eden
1631   if (_eden_chunk_array != NULL) {
1632     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1633               p2i(eden_space->bottom()), p2i(eden_space->top()),
1634               p2i(eden_space->end()), eden_space->capacity());
1635     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1636               _eden_chunk_index, _eden_chunk_capacity);
1637     for (size_t i = 0; i < _eden_chunk_index; i++) {
1638       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1639     }
1640   }
1641   // Survivor
1642   if (_survivor_chunk_array != NULL) {
1643     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1644               p2i(from_space->bottom()), p2i(from_space->top()),
1645               p2i(from_space->end()), from_space->capacity());
1646     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1647               _survivor_chunk_index, _survivor_chunk_capacity);
1648     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1649       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1650     }
1651   }
1652 }
1653 
1654 void CMSCollector::getFreelistLocks() const {
1655   // Get locks for all free lists in all generations that this
1656   // collector is responsible for
1657   _cmsGen->freelistLock()->lock_without_safepoint_check();
1658 }
1659 
1660 void CMSCollector::releaseFreelistLocks() const {
1661   // Release locks for all free lists in all generations that this
1662   // collector is responsible for
1663   _cmsGen->freelistLock()->unlock();
1664 }
1665 
1666 bool CMSCollector::haveFreelistLocks() const {
1667   // Check locks for all free lists in all generations that this
1668   // collector is responsible for
1669   assert_lock_strong(_cmsGen->freelistLock());
1670   PRODUCT_ONLY(ShouldNotReachHere());
1671   return true;
1672 }
1673 
1674 // A utility class that is used by the CMS collector to
1675 // temporarily "release" the foreground collector from its
1676 // usual obligation to wait for the background collector to
1677 // complete an ongoing phase before proceeding.
1678 class ReleaseForegroundGC: public StackObj {
1679  private:
1680   CMSCollector* _c;
1681  public:
1682   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1683     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1684     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1685     // allow a potentially blocked foreground collector to proceed
1686     _c->_foregroundGCShouldWait = false;
1687     if (_c->_foregroundGCIsActive) {
1688       CGC_lock->notify();
1689     }
1690     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1691            "Possible deadlock");
1692   }
1693 
1694   ~ReleaseForegroundGC() {
1695     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1696     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1697     _c->_foregroundGCShouldWait = true;
1698   }
1699 };
1700 
1701 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1702   assert(Thread::current()->is_ConcurrentGC_thread(),
1703     "A CMS asynchronous collection is only allowed on a CMS thread.");
1704 
1705   GenCollectedHeap* gch = GenCollectedHeap::heap();
1706   {
1707     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1708     MutexLockerEx hl(Heap_lock, safepoint_check);
1709     FreelistLocker fll(this);
1710     MutexLockerEx x(CGC_lock, safepoint_check);
1711     if (_foregroundGCIsActive) {
1712       // The foreground collector is. Skip this
1713       // background collection.
1714       assert(!_foregroundGCShouldWait, "Should be clear");
1715       return;
1716     } else {
1717       assert(_collectorState == Idling, "Should be idling before start.");
1718       _collectorState = InitialMarking;
1719       register_gc_start(cause);
1720       // Reset the expansion cause, now that we are about to begin
1721       // a new cycle.
1722       clear_expansion_cause();
1723 
1724       // Clear the MetaspaceGC flag since a concurrent collection
1725       // is starting but also clear it after the collection.
1726       MetaspaceGC::set_should_concurrent_collect(false);
1727     }
1728     // Decide if we want to enable class unloading as part of the
1729     // ensuing concurrent GC cycle.
1730     update_should_unload_classes();
1731     _full_gc_requested = false;           // acks all outstanding full gc requests
1732     _full_gc_cause = GCCause::_no_gc;
1733     // Signal that we are about to start a collection
1734     gch->increment_total_full_collections();  // ... starting a collection cycle
1735     _collection_count_start = gch->total_full_collections();
1736   }
1737 
1738   size_t prev_used = _cmsGen->used();
1739 
1740   // The change of the collection state is normally done at this level;
1741   // the exceptions are phases that are executed while the world is
1742   // stopped.  For those phases the change of state is done while the
1743   // world is stopped.  For baton passing purposes this allows the
1744   // background collector to finish the phase and change state atomically.
1745   // The foreground collector cannot wait on a phase that is done
1746   // while the world is stopped because the foreground collector already
1747   // has the world stopped and would deadlock.
1748   while (_collectorState != Idling) {
1749     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1750                          p2i(Thread::current()), _collectorState);
1751     // The foreground collector
1752     //   holds the Heap_lock throughout its collection.
1753     //   holds the CMS token (but not the lock)
1754     //     except while it is waiting for the background collector to yield.
1755     //
1756     // The foreground collector should be blocked (not for long)
1757     //   if the background collector is about to start a phase
1758     //   executed with world stopped.  If the background
1759     //   collector has already started such a phase, the
1760     //   foreground collector is blocked waiting for the
1761     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1762     //   are executed in the VM thread.
1763     //
1764     // The locking order is
1765     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1766     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1767     //   CMS token  (claimed in
1768     //                stop_world_and_do() -->
1769     //                  safepoint_synchronize() -->
1770     //                    CMSThread::synchronize())
1771 
1772     {
1773       // Check if the FG collector wants us to yield.
1774       CMSTokenSync x(true); // is cms thread
1775       if (waitForForegroundGC()) {
1776         // We yielded to a foreground GC, nothing more to be
1777         // done this round.
1778         assert(_foregroundGCShouldWait == false, "We set it to false in "
1779                "waitForForegroundGC()");
1780         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1781                              p2i(Thread::current()), _collectorState);
1782         return;
1783       } else {
1784         // The background collector can run but check to see if the
1785         // foreground collector has done a collection while the
1786         // background collector was waiting to get the CGC_lock
1787         // above.  If yes, break so that _foregroundGCShouldWait
1788         // is cleared before returning.
1789         if (_collectorState == Idling) {
1790           break;
1791         }
1792       }
1793     }
1794 
1795     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1796       "should be waiting");
1797 
1798     switch (_collectorState) {
1799       case InitialMarking:
1800         {
1801           ReleaseForegroundGC x(this);
1802           stats().record_cms_begin();
1803           VM_CMS_Initial_Mark initial_mark_op(this);
1804           VMThread::execute(&initial_mark_op);
1805         }
1806         // The collector state may be any legal state at this point
1807         // since the background collector may have yielded to the
1808         // foreground collector.
1809         break;
1810       case Marking:
1811         // initial marking in checkpointRootsInitialWork has been completed
1812         if (markFromRoots()) { // we were successful
1813           assert(_collectorState == Precleaning, "Collector state should "
1814             "have changed");
1815         } else {
1816           assert(_foregroundGCIsActive, "Internal state inconsistency");
1817         }
1818         break;
1819       case Precleaning:
1820         // marking from roots in markFromRoots has been completed
1821         preclean();
1822         assert(_collectorState == AbortablePreclean ||
1823                _collectorState == FinalMarking,
1824                "Collector state should have changed");
1825         break;
1826       case AbortablePreclean:
1827         abortable_preclean();
1828         assert(_collectorState == FinalMarking, "Collector state should "
1829           "have changed");
1830         break;
1831       case FinalMarking:
1832         {
1833           ReleaseForegroundGC x(this);
1834 
1835           VM_CMS_Final_Remark final_remark_op(this);
1836           VMThread::execute(&final_remark_op);
1837         }
1838         assert(_foregroundGCShouldWait, "block post-condition");
1839         break;
1840       case Sweeping:
1841         // final marking in checkpointRootsFinal has been completed
1842         sweep();
1843         assert(_collectorState == Resizing, "Collector state change "
1844           "to Resizing must be done under the free_list_lock");
1845 
1846       case Resizing: {
1847         // Sweeping has been completed...
1848         // At this point the background collection has completed.
1849         // Don't move the call to compute_new_size() down
1850         // into code that might be executed if the background
1851         // collection was preempted.
1852         {
1853           ReleaseForegroundGC x(this);   // unblock FG collection
1854           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1855           CMSTokenSync        z(true);   // not strictly needed.
1856           if (_collectorState == Resizing) {
1857             compute_new_size();
1858             save_heap_summary();
1859             _collectorState = Resetting;
1860           } else {
1861             assert(_collectorState == Idling, "The state should only change"
1862                    " because the foreground collector has finished the collection");
1863           }
1864         }
1865         break;
1866       }
1867       case Resetting:
1868         // CMS heap resizing has been completed
1869         reset_concurrent();
1870         assert(_collectorState == Idling, "Collector state should "
1871           "have changed");
1872 
1873         MetaspaceGC::set_should_concurrent_collect(false);
1874 
1875         stats().record_cms_end();
1876         // Don't move the concurrent_phases_end() and compute_new_size()
1877         // calls to here because a preempted background collection
1878         // has it's state set to "Resetting".
1879         break;
1880       case Idling:
1881       default:
1882         ShouldNotReachHere();
1883         break;
1884     }
1885     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1886                          p2i(Thread::current()), _collectorState);
1887     assert(_foregroundGCShouldWait, "block post-condition");
1888   }
1889 
1890   // Should this be in gc_epilogue?
1891   collector_policy()->counters()->update_counters();
1892 
1893   {
1894     // Clear _foregroundGCShouldWait and, in the event that the
1895     // foreground collector is waiting, notify it, before
1896     // returning.
1897     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1898     _foregroundGCShouldWait = false;
1899     if (_foregroundGCIsActive) {
1900       CGC_lock->notify();
1901     }
1902     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1903            "Possible deadlock");
1904   }
1905   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1906                        p2i(Thread::current()), _collectorState);
1907   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1908                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1909 }
1910 
1911 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1912   _cms_start_registered = true;
1913   _gc_timer_cm->register_gc_start();
1914   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1915 }
1916 
1917 void CMSCollector::register_gc_end() {
1918   if (_cms_start_registered) {
1919     report_heap_summary(GCWhen::AfterGC);
1920 
1921     _gc_timer_cm->register_gc_end();
1922     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1923     _cms_start_registered = false;
1924   }
1925 }
1926 
1927 void CMSCollector::save_heap_summary() {
1928   GenCollectedHeap* gch = GenCollectedHeap::heap();
1929   _last_heap_summary = gch->create_heap_summary();
1930   _last_metaspace_summary = gch->create_metaspace_summary();
1931 }
1932 
1933 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1934   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1935   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1936 }
1937 
1938 bool CMSCollector::waitForForegroundGC() {
1939   bool res = false;
1940   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1941          "CMS thread should have CMS token");
1942   // Block the foreground collector until the
1943   // background collectors decides whether to
1944   // yield.
1945   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1946   _foregroundGCShouldWait = true;
1947   if (_foregroundGCIsActive) {
1948     // The background collector yields to the
1949     // foreground collector and returns a value
1950     // indicating that it has yielded.  The foreground
1951     // collector can proceed.
1952     res = true;
1953     _foregroundGCShouldWait = false;
1954     ConcurrentMarkSweepThread::clear_CMS_flag(
1955       ConcurrentMarkSweepThread::CMS_cms_has_token);
1956     ConcurrentMarkSweepThread::set_CMS_flag(
1957       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1958     // Get a possibly blocked foreground thread going
1959     CGC_lock->notify();
1960     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1961                          p2i(Thread::current()), _collectorState);
1962     while (_foregroundGCIsActive) {
1963       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1964     }
1965     ConcurrentMarkSweepThread::set_CMS_flag(
1966       ConcurrentMarkSweepThread::CMS_cms_has_token);
1967     ConcurrentMarkSweepThread::clear_CMS_flag(
1968       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1969   }
1970   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1971                        p2i(Thread::current()), _collectorState);
1972   return res;
1973 }
1974 
1975 // Because of the need to lock the free lists and other structures in
1976 // the collector, common to all the generations that the collector is
1977 // collecting, we need the gc_prologues of individual CMS generations
1978 // delegate to their collector. It may have been simpler had the
1979 // current infrastructure allowed one to call a prologue on a
1980 // collector. In the absence of that we have the generation's
1981 // prologue delegate to the collector, which delegates back
1982 // some "local" work to a worker method in the individual generations
1983 // that it's responsible for collecting, while itself doing any
1984 // work common to all generations it's responsible for. A similar
1985 // comment applies to the  gc_epilogue()'s.
1986 // The role of the variable _between_prologue_and_epilogue is to
1987 // enforce the invocation protocol.
1988 void CMSCollector::gc_prologue(bool full) {
1989   // Call gc_prologue_work() for the CMSGen
1990   // we are responsible for.
1991 
1992   // The following locking discipline assumes that we are only called
1993   // when the world is stopped.
1994   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1995 
1996   // The CMSCollector prologue must call the gc_prologues for the
1997   // "generations" that it's responsible
1998   // for.
1999 
2000   assert(   Thread::current()->is_VM_thread()
2001          || (   CMSScavengeBeforeRemark
2002              && Thread::current()->is_ConcurrentGC_thread()),
2003          "Incorrect thread type for prologue execution");
2004 
2005   if (_between_prologue_and_epilogue) {
2006     // We have already been invoked; this is a gc_prologue delegation
2007     // from yet another CMS generation that we are responsible for, just
2008     // ignore it since all relevant work has already been done.
2009     return;
2010   }
2011 
2012   // set a bit saying prologue has been called; cleared in epilogue
2013   _between_prologue_and_epilogue = true;
2014   // Claim locks for common data structures, then call gc_prologue_work()
2015   // for each CMSGen.
2016 
2017   getFreelistLocks();   // gets free list locks on constituent spaces
2018   bitMapLock()->lock_without_safepoint_check();
2019 
2020   // Should call gc_prologue_work() for all cms gens we are responsible for
2021   bool duringMarking =    _collectorState >= Marking
2022                          && _collectorState < Sweeping;
2023 
2024   // The young collections clear the modified oops state, which tells if
2025   // there are any modified oops in the class. The remark phase also needs
2026   // that information. Tell the young collection to save the union of all
2027   // modified klasses.
2028   if (duringMarking) {
2029     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2030   }
2031 
2032   bool registerClosure = duringMarking;
2033 
2034   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2035 
2036   if (!full) {
2037     stats().record_gc0_begin();
2038   }
2039 }
2040 
2041 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2042 
2043   _capacity_at_prologue = capacity();
2044   _used_at_prologue = used();
2045 
2046   // We enable promotion tracking so that card-scanning can recognize
2047   // which objects have been promoted during this GC and skip them.
2048   for (uint i = 0; i < ParallelGCThreads; i++) {
2049     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2050   }
2051 
2052   // Delegate to CMScollector which knows how to coordinate between
2053   // this and any other CMS generations that it is responsible for
2054   // collecting.
2055   collector()->gc_prologue(full);
2056 }
2057 
2058 // This is a "private" interface for use by this generation's CMSCollector.
2059 // Not to be called directly by any other entity (for instance,
2060 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2061 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2062   bool registerClosure, ModUnionClosure* modUnionClosure) {
2063   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2064   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2065     "Should be NULL");
2066   if (registerClosure) {
2067     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2068   }
2069   cmsSpace()->gc_prologue();
2070   // Clear stat counters
2071   NOT_PRODUCT(
2072     assert(_numObjectsPromoted == 0, "check");
2073     assert(_numWordsPromoted   == 0, "check");
2074     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2075                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2076     _numObjectsAllocated = 0;
2077     _numWordsAllocated   = 0;
2078   )
2079 }
2080 
2081 void CMSCollector::gc_epilogue(bool full) {
2082   // The following locking discipline assumes that we are only called
2083   // when the world is stopped.
2084   assert(SafepointSynchronize::is_at_safepoint(),
2085          "world is stopped assumption");
2086 
2087   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2088   // if linear allocation blocks need to be appropriately marked to allow the
2089   // the blocks to be parsable. We also check here whether we need to nudge the
2090   // CMS collector thread to start a new cycle (if it's not already active).
2091   assert(   Thread::current()->is_VM_thread()
2092          || (   CMSScavengeBeforeRemark
2093              && Thread::current()->is_ConcurrentGC_thread()),
2094          "Incorrect thread type for epilogue execution");
2095 
2096   if (!_between_prologue_and_epilogue) {
2097     // We have already been invoked; this is a gc_epilogue delegation
2098     // from yet another CMS generation that we are responsible for, just
2099     // ignore it since all relevant work has already been done.
2100     return;
2101   }
2102   assert(haveFreelistLocks(), "must have freelist locks");
2103   assert_lock_strong(bitMapLock());
2104 
2105   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2106 
2107   _cmsGen->gc_epilogue_work(full);
2108 
2109   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2110     // in case sampling was not already enabled, enable it
2111     _start_sampling = true;
2112   }
2113   // reset _eden_chunk_array so sampling starts afresh
2114   _eden_chunk_index = 0;
2115 
2116   size_t cms_used   = _cmsGen->cmsSpace()->used();
2117 
2118   // update performance counters - this uses a special version of
2119   // update_counters() that allows the utilization to be passed as a
2120   // parameter, avoiding multiple calls to used().
2121   //
2122   _cmsGen->update_counters(cms_used);
2123 
2124   bitMapLock()->unlock();
2125   releaseFreelistLocks();
2126 
2127   if (!CleanChunkPoolAsync) {
2128     Chunk::clean_chunk_pool();
2129   }
2130 
2131   set_did_compact(false);
2132   _between_prologue_and_epilogue = false;  // ready for next cycle
2133 }
2134 
2135 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2136   collector()->gc_epilogue(full);
2137 
2138   // When using ParNew, promotion tracking should have already been
2139   // disabled. However, the prologue (which enables promotion
2140   // tracking) and epilogue are called irrespective of the type of
2141   // GC. So they will also be called before and after Full GCs, during
2142   // which promotion tracking will not be explicitly disabled. So,
2143   // it's safer to also disable it here too (to be symmetric with
2144   // enabling it in the prologue).
2145   for (uint i = 0; i < ParallelGCThreads; i++) {
2146     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2147   }
2148 }
2149 
2150 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2151   assert(!incremental_collection_failed(), "Should have been cleared");
2152   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2153   cmsSpace()->gc_epilogue();
2154     // Print stat counters
2155   NOT_PRODUCT(
2156     assert(_numObjectsAllocated == 0, "check");
2157     assert(_numWordsAllocated == 0, "check");
2158     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2159                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2160     _numObjectsPromoted = 0;
2161     _numWordsPromoted   = 0;
2162   )
2163 
2164   // Call down the chain in contiguous_available needs the freelistLock
2165   // so print this out before releasing the freeListLock.
2166   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2167 }
2168 
2169 #ifndef PRODUCT
2170 bool CMSCollector::have_cms_token() {
2171   Thread* thr = Thread::current();
2172   if (thr->is_VM_thread()) {
2173     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2174   } else if (thr->is_ConcurrentGC_thread()) {
2175     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2176   } else if (thr->is_GC_task_thread()) {
2177     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2178            ParGCRareEvent_lock->owned_by_self();
2179   }
2180   return false;
2181 }
2182 
2183 // Check reachability of the given heap address in CMS generation,
2184 // treating all other generations as roots.
2185 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2186   // We could "guarantee" below, rather than assert, but I'll
2187   // leave these as "asserts" so that an adventurous debugger
2188   // could try this in the product build provided some subset of
2189   // the conditions were met, provided they were interested in the
2190   // results and knew that the computation below wouldn't interfere
2191   // with other concurrent computations mutating the structures
2192   // being read or written.
2193   assert(SafepointSynchronize::is_at_safepoint(),
2194          "Else mutations in object graph will make answer suspect");
2195   assert(have_cms_token(), "Should hold cms token");
2196   assert(haveFreelistLocks(), "must hold free list locks");
2197   assert_lock_strong(bitMapLock());
2198 
2199   // Clear the marking bit map array before starting, but, just
2200   // for kicks, first report if the given address is already marked
2201   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2202                 _markBitMap.isMarked(addr) ? "" : " not");
2203 
2204   if (verify_after_remark()) {
2205     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2206     bool result = verification_mark_bm()->isMarked(addr);
2207     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2208                   result ? "IS" : "is NOT");
2209     return result;
2210   } else {
2211     tty->print_cr("Could not compute result");
2212     return false;
2213   }
2214 }
2215 #endif
2216 
2217 void
2218 CMSCollector::print_on_error(outputStream* st) {
2219   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2220   if (collector != NULL) {
2221     CMSBitMap* bitmap = &collector->_markBitMap;
2222     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2223     bitmap->print_on_error(st, " Bits: ");
2224 
2225     st->cr();
2226 
2227     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2228     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2229     mut_bitmap->print_on_error(st, " Bits: ");
2230   }
2231 }
2232 
2233 ////////////////////////////////////////////////////////
2234 // CMS Verification Support
2235 ////////////////////////////////////////////////////////
2236 // Following the remark phase, the following invariant
2237 // should hold -- each object in the CMS heap which is
2238 // marked in markBitMap() should be marked in the verification_mark_bm().
2239 
2240 class VerifyMarkedClosure: public BitMapClosure {
2241   CMSBitMap* _marks;
2242   bool       _failed;
2243 
2244  public:
2245   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2246 
2247   bool do_bit(size_t offset) {
2248     HeapWord* addr = _marks->offsetToHeapWord(offset);
2249     if (!_marks->isMarked(addr)) {
2250       Log(gc, verify) log;
2251       ResourceMark rm;
2252       oop(addr)->print_on(log.error_stream());
2253       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2254       _failed = true;
2255     }
2256     return true;
2257   }
2258 
2259   bool failed() { return _failed; }
2260 };
2261 
2262 bool CMSCollector::verify_after_remark() {
2263   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2264   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2265   static bool init = false;
2266 
2267   assert(SafepointSynchronize::is_at_safepoint(),
2268          "Else mutations in object graph will make answer suspect");
2269   assert(have_cms_token(),
2270          "Else there may be mutual interference in use of "
2271          " verification data structures");
2272   assert(_collectorState > Marking && _collectorState <= Sweeping,
2273          "Else marking info checked here may be obsolete");
2274   assert(haveFreelistLocks(), "must hold free list locks");
2275   assert_lock_strong(bitMapLock());
2276 
2277 
2278   // Allocate marking bit map if not already allocated
2279   if (!init) { // first time
2280     if (!verification_mark_bm()->allocate(_span)) {
2281       return false;
2282     }
2283     init = true;
2284   }
2285 
2286   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2287 
2288   // Turn off refs discovery -- so we will be tracing through refs.
2289   // This is as intended, because by this time
2290   // GC must already have cleared any refs that need to be cleared,
2291   // and traced those that need to be marked; moreover,
2292   // the marking done here is not going to interfere in any
2293   // way with the marking information used by GC.
2294   NoRefDiscovery no_discovery(ref_processor());
2295 
2296 #if defined(COMPILER2) || INCLUDE_JVMCI
2297   DerivedPointerTableDeactivate dpt_deact;
2298 #endif
2299 
2300   // Clear any marks from a previous round
2301   verification_mark_bm()->clear_all();
2302   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2303   verify_work_stacks_empty();
2304 
2305   GenCollectedHeap* gch = GenCollectedHeap::heap();
2306   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2307   // Update the saved marks which may affect the root scans.
2308   gch->save_marks();
2309 
2310   if (CMSRemarkVerifyVariant == 1) {
2311     // In this first variant of verification, we complete
2312     // all marking, then check if the new marks-vector is
2313     // a subset of the CMS marks-vector.
2314     verify_after_remark_work_1();
2315   } else {
2316     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2317     // In this second variant of verification, we flag an error
2318     // (i.e. an object reachable in the new marks-vector not reachable
2319     // in the CMS marks-vector) immediately, also indicating the
2320     // identify of an object (A) that references the unmarked object (B) --
2321     // presumably, a mutation to A failed to be picked up by preclean/remark?
2322     verify_after_remark_work_2();
2323   }
2324 
2325   return true;
2326 }
2327 
2328 void CMSCollector::verify_after_remark_work_1() {
2329   ResourceMark rm;
2330   HandleMark  hm;
2331   GenCollectedHeap* gch = GenCollectedHeap::heap();
2332 
2333   // Get a clear set of claim bits for the roots processing to work with.
2334   ClassLoaderDataGraph::clear_claimed_marks();
2335 
2336   // Mark from roots one level into CMS
2337   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2338   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2339 
2340   {
2341     StrongRootsScope srs(1);
2342 
2343     gch->gen_process_roots(&srs,
2344                            GenCollectedHeap::OldGen,
2345                            true,   // young gen as roots
2346                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2347                            should_unload_classes(),
2348                            &notOlder,
2349                            NULL,
2350                            NULL);
2351   }
2352 
2353   // Now mark from the roots
2354   MarkFromRootsClosure markFromRootsClosure(this, _span,
2355     verification_mark_bm(), verification_mark_stack(),
2356     false /* don't yield */, true /* verifying */);
2357   assert(_restart_addr == NULL, "Expected pre-condition");
2358   verification_mark_bm()->iterate(&markFromRootsClosure);
2359   while (_restart_addr != NULL) {
2360     // Deal with stack overflow: by restarting at the indicated
2361     // address.
2362     HeapWord* ra = _restart_addr;
2363     markFromRootsClosure.reset(ra);
2364     _restart_addr = NULL;
2365     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2366   }
2367   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2368   verify_work_stacks_empty();
2369 
2370   // Marking completed -- now verify that each bit marked in
2371   // verification_mark_bm() is also marked in markBitMap(); flag all
2372   // errors by printing corresponding objects.
2373   VerifyMarkedClosure vcl(markBitMap());
2374   verification_mark_bm()->iterate(&vcl);
2375   if (vcl.failed()) {
2376     Log(gc, verify) log;
2377     log.error("Failed marking verification after remark");
2378     ResourceMark rm;
2379     gch->print_on(log.error_stream());
2380     fatal("CMS: failed marking verification after remark");
2381   }
2382 }
2383 
2384 class VerifyKlassOopsKlassClosure : public KlassClosure {
2385   class VerifyKlassOopsClosure : public OopClosure {
2386     CMSBitMap* _bitmap;
2387    public:
2388     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2389     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2390     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2391   } _oop_closure;
2392  public:
2393   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2394   void do_klass(Klass* k) {
2395     k->oops_do(&_oop_closure);
2396   }
2397 };
2398 
2399 void CMSCollector::verify_after_remark_work_2() {
2400   ResourceMark rm;
2401   HandleMark  hm;
2402   GenCollectedHeap* gch = GenCollectedHeap::heap();
2403 
2404   // Get a clear set of claim bits for the roots processing to work with.
2405   ClassLoaderDataGraph::clear_claimed_marks();
2406 
2407   // Mark from roots one level into CMS
2408   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2409                                      markBitMap());
2410   CLDToOopClosure cld_closure(&notOlder, true);
2411 
2412   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2413 
2414   {
2415     StrongRootsScope srs(1);
2416 
2417     gch->gen_process_roots(&srs,
2418                            GenCollectedHeap::OldGen,
2419                            true,   // young gen as roots
2420                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2421                            should_unload_classes(),
2422                            &notOlder,
2423                            NULL,
2424                            &cld_closure);
2425   }
2426 
2427   // Now mark from the roots
2428   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2429     verification_mark_bm(), markBitMap(), verification_mark_stack());
2430   assert(_restart_addr == NULL, "Expected pre-condition");
2431   verification_mark_bm()->iterate(&markFromRootsClosure);
2432   while (_restart_addr != NULL) {
2433     // Deal with stack overflow: by restarting at the indicated
2434     // address.
2435     HeapWord* ra = _restart_addr;
2436     markFromRootsClosure.reset(ra);
2437     _restart_addr = NULL;
2438     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2439   }
2440   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2441   verify_work_stacks_empty();
2442 
2443   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2444   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2445 
2446   // Marking completed -- now verify that each bit marked in
2447   // verification_mark_bm() is also marked in markBitMap(); flag all
2448   // errors by printing corresponding objects.
2449   VerifyMarkedClosure vcl(markBitMap());
2450   verification_mark_bm()->iterate(&vcl);
2451   assert(!vcl.failed(), "Else verification above should not have succeeded");
2452 }
2453 
2454 void ConcurrentMarkSweepGeneration::save_marks() {
2455   // delegate to CMS space
2456   cmsSpace()->save_marks();
2457 }
2458 
2459 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2460   return cmsSpace()->no_allocs_since_save_marks();
2461 }
2462 
2463 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2464                                                                 \
2465 void ConcurrentMarkSweepGeneration::                            \
2466 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2467   cl->set_generation(this);                                     \
2468   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2469   cl->reset_generation();                                       \
2470   save_marks();                                                 \
2471 }
2472 
2473 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2474 
2475 void
2476 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2477   if (freelistLock()->owned_by_self()) {
2478     Generation::oop_iterate(cl);
2479   } else {
2480     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2481     Generation::oop_iterate(cl);
2482   }
2483 }
2484 
2485 void
2486 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2487   if (freelistLock()->owned_by_self()) {
2488     Generation::object_iterate(cl);
2489   } else {
2490     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2491     Generation::object_iterate(cl);
2492   }
2493 }
2494 
2495 void
2496 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2497   if (freelistLock()->owned_by_self()) {
2498     Generation::safe_object_iterate(cl);
2499   } else {
2500     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2501     Generation::safe_object_iterate(cl);
2502   }
2503 }
2504 
2505 void
2506 ConcurrentMarkSweepGeneration::post_compact() {
2507 }
2508 
2509 void
2510 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2511   // Fix the linear allocation blocks to look like free blocks.
2512 
2513   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2514   // are not called when the heap is verified during universe initialization and
2515   // at vm shutdown.
2516   if (freelistLock()->owned_by_self()) {
2517     cmsSpace()->prepare_for_verify();
2518   } else {
2519     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2520     cmsSpace()->prepare_for_verify();
2521   }
2522 }
2523 
2524 void
2525 ConcurrentMarkSweepGeneration::verify() {
2526   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2527   // are not called when the heap is verified during universe initialization and
2528   // at vm shutdown.
2529   if (freelistLock()->owned_by_self()) {
2530     cmsSpace()->verify();
2531   } else {
2532     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2533     cmsSpace()->verify();
2534   }
2535 }
2536 
2537 void CMSCollector::verify() {
2538   _cmsGen->verify();
2539 }
2540 
2541 #ifndef PRODUCT
2542 bool CMSCollector::overflow_list_is_empty() const {
2543   assert(_num_par_pushes >= 0, "Inconsistency");
2544   if (_overflow_list == NULL) {
2545     assert(_num_par_pushes == 0, "Inconsistency");
2546   }
2547   return _overflow_list == NULL;
2548 }
2549 
2550 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2551 // merely consolidate assertion checks that appear to occur together frequently.
2552 void CMSCollector::verify_work_stacks_empty() const {
2553   assert(_markStack.isEmpty(), "Marking stack should be empty");
2554   assert(overflow_list_is_empty(), "Overflow list should be empty");
2555 }
2556 
2557 void CMSCollector::verify_overflow_empty() const {
2558   assert(overflow_list_is_empty(), "Overflow list should be empty");
2559   assert(no_preserved_marks(), "No preserved marks");
2560 }
2561 #endif // PRODUCT
2562 
2563 // Decide if we want to enable class unloading as part of the
2564 // ensuing concurrent GC cycle. We will collect and
2565 // unload classes if it's the case that:
2566 // (1) an explicit gc request has been made and the flag
2567 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2568 // (2) (a) class unloading is enabled at the command line, and
2569 //     (b) old gen is getting really full
2570 // NOTE: Provided there is no change in the state of the heap between
2571 // calls to this method, it should have idempotent results. Moreover,
2572 // its results should be monotonically increasing (i.e. going from 0 to 1,
2573 // but not 1 to 0) between successive calls between which the heap was
2574 // not collected. For the implementation below, it must thus rely on
2575 // the property that concurrent_cycles_since_last_unload()
2576 // will not decrease unless a collection cycle happened and that
2577 // _cmsGen->is_too_full() are
2578 // themselves also monotonic in that sense. See check_monotonicity()
2579 // below.
2580 void CMSCollector::update_should_unload_classes() {
2581   _should_unload_classes = false;
2582   // Condition 1 above
2583   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2584     _should_unload_classes = true;
2585   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2586     // Disjuncts 2.b.(i,ii,iii) above
2587     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2588                               CMSClassUnloadingMaxInterval)
2589                            || _cmsGen->is_too_full();
2590   }
2591 }
2592 
2593 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2594   bool res = should_concurrent_collect();
2595   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2596   return res;
2597 }
2598 
2599 void CMSCollector::setup_cms_unloading_and_verification_state() {
2600   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2601                              || VerifyBeforeExit;
2602   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2603 
2604   // We set the proper root for this CMS cycle here.
2605   if (should_unload_classes()) {   // Should unload classes this cycle
2606     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2607     set_verifying(should_verify);    // Set verification state for this cycle
2608     return;                            // Nothing else needs to be done at this time
2609   }
2610 
2611   // Not unloading classes this cycle
2612   assert(!should_unload_classes(), "Inconsistency!");
2613 
2614   // If we are not unloading classes then add SO_AllCodeCache to root
2615   // scanning options.
2616   add_root_scanning_option(rso);
2617 
2618   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2619     set_verifying(true);
2620   } else if (verifying() && !should_verify) {
2621     // We were verifying, but some verification flags got disabled.
2622     set_verifying(false);
2623     // Exclude symbols, strings and code cache elements from root scanning to
2624     // reduce IM and RM pauses.
2625     remove_root_scanning_option(rso);
2626   }
2627 }
2628 
2629 
2630 #ifndef PRODUCT
2631 HeapWord* CMSCollector::block_start(const void* p) const {
2632   const HeapWord* addr = (HeapWord*)p;
2633   if (_span.contains(p)) {
2634     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2635       return _cmsGen->cmsSpace()->block_start(p);
2636     }
2637   }
2638   return NULL;
2639 }
2640 #endif
2641 
2642 HeapWord*
2643 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2644                                                    bool   tlab,
2645                                                    bool   parallel) {
2646   CMSSynchronousYieldRequest yr;
2647   assert(!tlab, "Can't deal with TLAB allocation");
2648   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2649   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2650   if (GCExpandToAllocateDelayMillis > 0) {
2651     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2652   }
2653   return have_lock_and_allocate(word_size, tlab);
2654 }
2655 
2656 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2657     size_t bytes,
2658     size_t expand_bytes,
2659     CMSExpansionCause::Cause cause)
2660 {
2661 
2662   bool success = expand(bytes, expand_bytes);
2663 
2664   // remember why we expanded; this information is used
2665   // by shouldConcurrentCollect() when making decisions on whether to start
2666   // a new CMS cycle.
2667   if (success) {
2668     set_expansion_cause(cause);
2669     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2670   }
2671 }
2672 
2673 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2674   HeapWord* res = NULL;
2675   MutexLocker x(ParGCRareEvent_lock);
2676   while (true) {
2677     // Expansion by some other thread might make alloc OK now:
2678     res = ps->lab.alloc(word_sz);
2679     if (res != NULL) return res;
2680     // If there's not enough expansion space available, give up.
2681     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2682       return NULL;
2683     }
2684     // Otherwise, we try expansion.
2685     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2686     // Now go around the loop and try alloc again;
2687     // A competing par_promote might beat us to the expansion space,
2688     // so we may go around the loop again if promotion fails again.
2689     if (GCExpandToAllocateDelayMillis > 0) {
2690       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2691     }
2692   }
2693 }
2694 
2695 
2696 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2697   PromotionInfo* promo) {
2698   MutexLocker x(ParGCRareEvent_lock);
2699   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2700   while (true) {
2701     // Expansion by some other thread might make alloc OK now:
2702     if (promo->ensure_spooling_space()) {
2703       assert(promo->has_spooling_space(),
2704              "Post-condition of successful ensure_spooling_space()");
2705       return true;
2706     }
2707     // If there's not enough expansion space available, give up.
2708     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2709       return false;
2710     }
2711     // Otherwise, we try expansion.
2712     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2713     // Now go around the loop and try alloc again;
2714     // A competing allocation might beat us to the expansion space,
2715     // so we may go around the loop again if allocation fails again.
2716     if (GCExpandToAllocateDelayMillis > 0) {
2717       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2718     }
2719   }
2720 }
2721 
2722 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2723   // Only shrink if a compaction was done so that all the free space
2724   // in the generation is in a contiguous block at the end.
2725   if (did_compact()) {
2726     CardGeneration::shrink(bytes);
2727   }
2728 }
2729 
2730 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2731   assert_locked_or_safepoint(Heap_lock);
2732 }
2733 
2734 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2735   assert_locked_or_safepoint(Heap_lock);
2736   assert_lock_strong(freelistLock());
2737   log_trace(gc)("Shrinking of CMS not yet implemented");
2738   return;
2739 }
2740 
2741 
2742 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2743 // phases.
2744 class CMSPhaseAccounting: public StackObj {
2745  public:
2746   CMSPhaseAccounting(CMSCollector *collector,
2747                      const char *title);
2748   ~CMSPhaseAccounting();
2749 
2750  private:
2751   CMSCollector *_collector;
2752   const char *_title;
2753   GCTraceConcTime(Info, gc) _trace_time;
2754 
2755  public:
2756   // Not MT-safe; so do not pass around these StackObj's
2757   // where they may be accessed by other threads.
2758   double wallclock_millis() {
2759     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2760   }
2761 };
2762 
2763 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2764                                        const char *title) :
2765   _collector(collector), _title(title), _trace_time(title) {
2766 
2767   _collector->resetYields();
2768   _collector->resetTimer();
2769   _collector->startTimer();
2770   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2771 }
2772 
2773 CMSPhaseAccounting::~CMSPhaseAccounting() {
2774   _collector->gc_timer_cm()->register_gc_concurrent_end();
2775   _collector->stopTimer();
2776   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2777   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2778 }
2779 
2780 // CMS work
2781 
2782 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2783 class CMSParMarkTask : public AbstractGangTask {
2784  protected:
2785   CMSCollector*     _collector;
2786   uint              _n_workers;
2787   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2788       AbstractGangTask(name),
2789       _collector(collector),
2790       _n_workers(n_workers) {}
2791   // Work method in support of parallel rescan ... of young gen spaces
2792   void do_young_space_rescan(OopsInGenClosure* cl,
2793                              ContiguousSpace* space,
2794                              HeapWord** chunk_array, size_t chunk_top);
2795   void work_on_young_gen_roots(OopsInGenClosure* cl);
2796 };
2797 
2798 // Parallel initial mark task
2799 class CMSParInitialMarkTask: public CMSParMarkTask {
2800   StrongRootsScope* _strong_roots_scope;
2801  public:
2802   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2803       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2804       _strong_roots_scope(strong_roots_scope) {}
2805   void work(uint worker_id);
2806 };
2807 
2808 // Checkpoint the roots into this generation from outside
2809 // this generation. [Note this initial checkpoint need only
2810 // be approximate -- we'll do a catch up phase subsequently.]
2811 void CMSCollector::checkpointRootsInitial() {
2812   assert(_collectorState == InitialMarking, "Wrong collector state");
2813   check_correct_thread_executing();
2814   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2815 
2816   save_heap_summary();
2817   report_heap_summary(GCWhen::BeforeGC);
2818 
2819   ReferenceProcessor* rp = ref_processor();
2820   assert(_restart_addr == NULL, "Control point invariant");
2821   {
2822     // acquire locks for subsequent manipulations
2823     MutexLockerEx x(bitMapLock(),
2824                     Mutex::_no_safepoint_check_flag);
2825     checkpointRootsInitialWork();
2826     // enable ("weak") refs discovery
2827     rp->enable_discovery();
2828     _collectorState = Marking;
2829   }
2830 }
2831 
2832 void CMSCollector::checkpointRootsInitialWork() {
2833   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2834   assert(_collectorState == InitialMarking, "just checking");
2835 
2836   // Already have locks.
2837   assert_lock_strong(bitMapLock());
2838   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2839 
2840   // Setup the verification and class unloading state for this
2841   // CMS collection cycle.
2842   setup_cms_unloading_and_verification_state();
2843 
2844   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2845 
2846   // Reset all the PLAB chunk arrays if necessary.
2847   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2848     reset_survivor_plab_arrays();
2849   }
2850 
2851   ResourceMark rm;
2852   HandleMark  hm;
2853 
2854   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2855   GenCollectedHeap* gch = GenCollectedHeap::heap();
2856 
2857   verify_work_stacks_empty();
2858   verify_overflow_empty();
2859 
2860   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2861   // Update the saved marks which may affect the root scans.
2862   gch->save_marks();
2863 
2864   // weak reference processing has not started yet.
2865   ref_processor()->set_enqueuing_is_done(false);
2866 
2867   // Need to remember all newly created CLDs,
2868   // so that we can guarantee that the remark finds them.
2869   ClassLoaderDataGraph::remember_new_clds(true);
2870 
2871   // Whenever a CLD is found, it will be claimed before proceeding to mark
2872   // the klasses. The claimed marks need to be cleared before marking starts.
2873   ClassLoaderDataGraph::clear_claimed_marks();
2874 
2875   print_eden_and_survivor_chunk_arrays();
2876 
2877   {
2878 #if defined(COMPILER2) || INCLUDE_JVMCI
2879     DerivedPointerTableDeactivate dpt_deact;
2880 #endif
2881     if (CMSParallelInitialMarkEnabled) {
2882       // The parallel version.
2883       WorkGang* workers = gch->workers();
2884       assert(workers != NULL, "Need parallel worker threads.");
2885       uint n_workers = workers->active_workers();
2886 
2887       StrongRootsScope srs(n_workers);
2888 
2889       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2890       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2891       if (n_workers > 1) {
2892         workers->run_task(&tsk);
2893       } else {
2894         tsk.work(0);
2895       }
2896     } else {
2897       // The serial version.
2898       CLDToOopClosure cld_closure(&notOlder, true);
2899       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2900 
2901       StrongRootsScope srs(1);
2902 
2903       gch->gen_process_roots(&srs,
2904                              GenCollectedHeap::OldGen,
2905                              true,   // young gen as roots
2906                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2907                              should_unload_classes(),
2908                              &notOlder,
2909                              NULL,
2910                              &cld_closure);
2911     }
2912   }
2913 
2914   // Clear mod-union table; it will be dirtied in the prologue of
2915   // CMS generation per each young generation collection.
2916 
2917   assert(_modUnionTable.isAllClear(),
2918        "Was cleared in most recent final checkpoint phase"
2919        " or no bits are set in the gc_prologue before the start of the next "
2920        "subsequent marking phase.");
2921 
2922   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2923 
2924   // Save the end of the used_region of the constituent generations
2925   // to be used to limit the extent of sweep in each generation.
2926   save_sweep_limits();
2927   verify_overflow_empty();
2928 }
2929 
2930 bool CMSCollector::markFromRoots() {
2931   // we might be tempted to assert that:
2932   // assert(!SafepointSynchronize::is_at_safepoint(),
2933   //        "inconsistent argument?");
2934   // However that wouldn't be right, because it's possible that
2935   // a safepoint is indeed in progress as a young generation
2936   // stop-the-world GC happens even as we mark in this generation.
2937   assert(_collectorState == Marking, "inconsistent state?");
2938   check_correct_thread_executing();
2939   verify_overflow_empty();
2940 
2941   // Weak ref discovery note: We may be discovering weak
2942   // refs in this generation concurrent (but interleaved) with
2943   // weak ref discovery by the young generation collector.
2944 
2945   CMSTokenSyncWithLocks ts(true, bitMapLock());
2946   GCTraceCPUTime tcpu;
2947   CMSPhaseAccounting pa(this, "Concurrent Mark");
2948   bool res = markFromRootsWork();
2949   if (res) {
2950     _collectorState = Precleaning;
2951   } else { // We failed and a foreground collection wants to take over
2952     assert(_foregroundGCIsActive, "internal state inconsistency");
2953     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2954     log_debug(gc)("bailing out to foreground collection");
2955   }
2956   verify_overflow_empty();
2957   return res;
2958 }
2959 
2960 bool CMSCollector::markFromRootsWork() {
2961   // iterate over marked bits in bit map, doing a full scan and mark
2962   // from these roots using the following algorithm:
2963   // . if oop is to the right of the current scan pointer,
2964   //   mark corresponding bit (we'll process it later)
2965   // . else (oop is to left of current scan pointer)
2966   //   push oop on marking stack
2967   // . drain the marking stack
2968 
2969   // Note that when we do a marking step we need to hold the
2970   // bit map lock -- recall that direct allocation (by mutators)
2971   // and promotion (by the young generation collector) is also
2972   // marking the bit map. [the so-called allocate live policy.]
2973   // Because the implementation of bit map marking is not
2974   // robust wrt simultaneous marking of bits in the same word,
2975   // we need to make sure that there is no such interference
2976   // between concurrent such updates.
2977 
2978   // already have locks
2979   assert_lock_strong(bitMapLock());
2980 
2981   verify_work_stacks_empty();
2982   verify_overflow_empty();
2983   bool result = false;
2984   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2985     result = do_marking_mt();
2986   } else {
2987     result = do_marking_st();
2988   }
2989   return result;
2990 }
2991 
2992 // Forward decl
2993 class CMSConcMarkingTask;
2994 
2995 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2996   CMSCollector*       _collector;
2997   CMSConcMarkingTask* _task;
2998  public:
2999   virtual void yield();
3000 
3001   // "n_threads" is the number of threads to be terminated.
3002   // "queue_set" is a set of work queues of other threads.
3003   // "collector" is the CMS collector associated with this task terminator.
3004   // "yield" indicates whether we need the gang as a whole to yield.
3005   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3006     ParallelTaskTerminator(n_threads, queue_set),
3007     _collector(collector) { }
3008 
3009   void set_task(CMSConcMarkingTask* task) {
3010     _task = task;
3011   }
3012 };
3013 
3014 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3015   CMSConcMarkingTask* _task;
3016  public:
3017   bool should_exit_termination();
3018   void set_task(CMSConcMarkingTask* task) {
3019     _task = task;
3020   }
3021 };
3022 
3023 // MT Concurrent Marking Task
3024 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3025   CMSCollector* _collector;
3026   uint          _n_workers;       // requested/desired # workers
3027   bool          _result;
3028   CompactibleFreeListSpace*  _cms_space;
3029   char          _pad_front[64];   // padding to ...
3030   HeapWord*     _global_finger;   // ... avoid sharing cache line
3031   char          _pad_back[64];
3032   HeapWord*     _restart_addr;
3033 
3034   //  Exposed here for yielding support
3035   Mutex* const _bit_map_lock;
3036 
3037   // The per thread work queues, available here for stealing
3038   OopTaskQueueSet*  _task_queues;
3039 
3040   // Termination (and yielding) support
3041   CMSConcMarkingTerminator _term;
3042   CMSConcMarkingTerminatorTerminator _term_term;
3043 
3044  public:
3045   CMSConcMarkingTask(CMSCollector* collector,
3046                  CompactibleFreeListSpace* cms_space,
3047                  YieldingFlexibleWorkGang* workers,
3048                  OopTaskQueueSet* task_queues):
3049     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3050     _collector(collector),
3051     _cms_space(cms_space),
3052     _n_workers(0), _result(true),
3053     _task_queues(task_queues),
3054     _term(_n_workers, task_queues, _collector),
3055     _bit_map_lock(collector->bitMapLock())
3056   {
3057     _requested_size = _n_workers;
3058     _term.set_task(this);
3059     _term_term.set_task(this);
3060     _restart_addr = _global_finger = _cms_space->bottom();
3061   }
3062 
3063 
3064   OopTaskQueueSet* task_queues()  { return _task_queues; }
3065 
3066   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3067 
3068   HeapWord** global_finger_addr() { return &_global_finger; }
3069 
3070   CMSConcMarkingTerminator* terminator() { return &_term; }
3071 
3072   virtual void set_for_termination(uint active_workers) {
3073     terminator()->reset_for_reuse(active_workers);
3074   }
3075 
3076   void work(uint worker_id);
3077   bool should_yield() {
3078     return    ConcurrentMarkSweepThread::should_yield()
3079            && !_collector->foregroundGCIsActive();
3080   }
3081 
3082   virtual void coordinator_yield();  // stuff done by coordinator
3083   bool result() { return _result; }
3084 
3085   void reset(HeapWord* ra) {
3086     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3087     _restart_addr = _global_finger = ra;
3088     _term.reset_for_reuse();
3089   }
3090 
3091   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3092                                            OopTaskQueue* work_q);
3093 
3094  private:
3095   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3096   void do_work_steal(int i);
3097   void bump_global_finger(HeapWord* f);
3098 };
3099 
3100 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3101   assert(_task != NULL, "Error");
3102   return _task->yielding();
3103   // Note that we do not need the disjunct || _task->should_yield() above
3104   // because we want terminating threads to yield only if the task
3105   // is already in the midst of yielding, which happens only after at least one
3106   // thread has yielded.
3107 }
3108 
3109 void CMSConcMarkingTerminator::yield() {
3110   if (_task->should_yield()) {
3111     _task->yield();
3112   } else {
3113     ParallelTaskTerminator::yield();
3114   }
3115 }
3116 
3117 ////////////////////////////////////////////////////////////////
3118 // Concurrent Marking Algorithm Sketch
3119 ////////////////////////////////////////////////////////////////
3120 // Until all tasks exhausted (both spaces):
3121 // -- claim next available chunk
3122 // -- bump global finger via CAS
3123 // -- find first object that starts in this chunk
3124 //    and start scanning bitmap from that position
3125 // -- scan marked objects for oops
3126 // -- CAS-mark target, and if successful:
3127 //    . if target oop is above global finger (volatile read)
3128 //      nothing to do
3129 //    . if target oop is in chunk and above local finger
3130 //        then nothing to do
3131 //    . else push on work-queue
3132 // -- Deal with possible overflow issues:
3133 //    . local work-queue overflow causes stuff to be pushed on
3134 //      global (common) overflow queue
3135 //    . always first empty local work queue
3136 //    . then get a batch of oops from global work queue if any
3137 //    . then do work stealing
3138 // -- When all tasks claimed (both spaces)
3139 //    and local work queue empty,
3140 //    then in a loop do:
3141 //    . check global overflow stack; steal a batch of oops and trace
3142 //    . try to steal from other threads oif GOS is empty
3143 //    . if neither is available, offer termination
3144 // -- Terminate and return result
3145 //
3146 void CMSConcMarkingTask::work(uint worker_id) {
3147   elapsedTimer _timer;
3148   ResourceMark rm;
3149   HandleMark hm;
3150 
3151   DEBUG_ONLY(_collector->verify_overflow_empty();)
3152 
3153   // Before we begin work, our work queue should be empty
3154   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3155   // Scan the bitmap covering _cms_space, tracing through grey objects.
3156   _timer.start();
3157   do_scan_and_mark(worker_id, _cms_space);
3158   _timer.stop();
3159   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3160 
3161   // ... do work stealing
3162   _timer.reset();
3163   _timer.start();
3164   do_work_steal(worker_id);
3165   _timer.stop();
3166   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3167   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3168   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3169   // Note that under the current task protocol, the
3170   // following assertion is true even of the spaces
3171   // expanded since the completion of the concurrent
3172   // marking. XXX This will likely change under a strict
3173   // ABORT semantics.
3174   // After perm removal the comparison was changed to
3175   // greater than or equal to from strictly greater than.
3176   // Before perm removal the highest address sweep would
3177   // have been at the end of perm gen but now is at the
3178   // end of the tenured gen.
3179   assert(_global_finger >=  _cms_space->end(),
3180          "All tasks have been completed");
3181   DEBUG_ONLY(_collector->verify_overflow_empty();)
3182 }
3183 
3184 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3185   HeapWord* read = _global_finger;
3186   HeapWord* cur  = read;
3187   while (f > read) {
3188     cur = read;
3189     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3190     if (cur == read) {
3191       // our cas succeeded
3192       assert(_global_finger >= f, "protocol consistency");
3193       break;
3194     }
3195   }
3196 }
3197 
3198 // This is really inefficient, and should be redone by
3199 // using (not yet available) block-read and -write interfaces to the
3200 // stack and the work_queue. XXX FIX ME !!!
3201 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3202                                                       OopTaskQueue* work_q) {
3203   // Fast lock-free check
3204   if (ovflw_stk->length() == 0) {
3205     return false;
3206   }
3207   assert(work_q->size() == 0, "Shouldn't steal");
3208   MutexLockerEx ml(ovflw_stk->par_lock(),
3209                    Mutex::_no_safepoint_check_flag);
3210   // Grab up to 1/4 the size of the work queue
3211   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3212                     (size_t)ParGCDesiredObjsFromOverflowList);
3213   num = MIN2(num, ovflw_stk->length());
3214   for (int i = (int) num; i > 0; i--) {
3215     oop cur = ovflw_stk->pop();
3216     assert(cur != NULL, "Counted wrong?");
3217     work_q->push(cur);
3218   }
3219   return num > 0;
3220 }
3221 
3222 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3223   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3224   int n_tasks = pst->n_tasks();
3225   // We allow that there may be no tasks to do here because
3226   // we are restarting after a stack overflow.
3227   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3228   uint nth_task = 0;
3229 
3230   HeapWord* aligned_start = sp->bottom();
3231   if (sp->used_region().contains(_restart_addr)) {
3232     // Align down to a card boundary for the start of 0th task
3233     // for this space.
3234     aligned_start =
3235       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3236                                  CardTableModRefBS::card_size);
3237   }
3238 
3239   size_t chunk_size = sp->marking_task_size();
3240   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3241     // Having claimed the nth task in this space,
3242     // compute the chunk that it corresponds to:
3243     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3244                                aligned_start + (nth_task+1)*chunk_size);
3245     // Try and bump the global finger via a CAS;
3246     // note that we need to do the global finger bump
3247     // _before_ taking the intersection below, because
3248     // the task corresponding to that region will be
3249     // deemed done even if the used_region() expands
3250     // because of allocation -- as it almost certainly will
3251     // during start-up while the threads yield in the
3252     // closure below.
3253     HeapWord* finger = span.end();
3254     bump_global_finger(finger);   // atomically
3255     // There are null tasks here corresponding to chunks
3256     // beyond the "top" address of the space.
3257     span = span.intersection(sp->used_region());
3258     if (!span.is_empty()) {  // Non-null task
3259       HeapWord* prev_obj;
3260       assert(!span.contains(_restart_addr) || nth_task == 0,
3261              "Inconsistency");
3262       if (nth_task == 0) {
3263         // For the 0th task, we'll not need to compute a block_start.
3264         if (span.contains(_restart_addr)) {
3265           // In the case of a restart because of stack overflow,
3266           // we might additionally skip a chunk prefix.
3267           prev_obj = _restart_addr;
3268         } else {
3269           prev_obj = span.start();
3270         }
3271       } else {
3272         // We want to skip the first object because
3273         // the protocol is to scan any object in its entirety
3274         // that _starts_ in this span; a fortiori, any
3275         // object starting in an earlier span is scanned
3276         // as part of an earlier claimed task.
3277         // Below we use the "careful" version of block_start
3278         // so we do not try to navigate uninitialized objects.
3279         prev_obj = sp->block_start_careful(span.start());
3280         // Below we use a variant of block_size that uses the
3281         // Printezis bits to avoid waiting for allocated
3282         // objects to become initialized/parsable.
3283         while (prev_obj < span.start()) {
3284           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3285           if (sz > 0) {
3286             prev_obj += sz;
3287           } else {
3288             // In this case we may end up doing a bit of redundant
3289             // scanning, but that appears unavoidable, short of
3290             // locking the free list locks; see bug 6324141.
3291             break;
3292           }
3293         }
3294       }
3295       if (prev_obj < span.end()) {
3296         MemRegion my_span = MemRegion(prev_obj, span.end());
3297         // Do the marking work within a non-empty span --
3298         // the last argument to the constructor indicates whether the
3299         // iteration should be incremental with periodic yields.
3300         ParMarkFromRootsClosure cl(this, _collector, my_span,
3301                                    &_collector->_markBitMap,
3302                                    work_queue(i),
3303                                    &_collector->_markStack);
3304         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3305       } // else nothing to do for this task
3306     }   // else nothing to do for this task
3307   }
3308   // We'd be tempted to assert here that since there are no
3309   // more tasks left to claim in this space, the global_finger
3310   // must exceed space->top() and a fortiori space->end(). However,
3311   // that would not quite be correct because the bumping of
3312   // global_finger occurs strictly after the claiming of a task,
3313   // so by the time we reach here the global finger may not yet
3314   // have been bumped up by the thread that claimed the last
3315   // task.
3316   pst->all_tasks_completed();
3317 }
3318 
3319 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3320  private:
3321   CMSCollector* _collector;
3322   CMSConcMarkingTask* _task;
3323   MemRegion     _span;
3324   CMSBitMap*    _bit_map;
3325   CMSMarkStack* _overflow_stack;
3326   OopTaskQueue* _work_queue;
3327  protected:
3328   DO_OOP_WORK_DEFN
3329  public:
3330   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3331                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3332     MetadataAwareOopClosure(collector->ref_processor()),
3333     _collector(collector),
3334     _task(task),
3335     _span(collector->_span),
3336     _work_queue(work_queue),
3337     _bit_map(bit_map),
3338     _overflow_stack(overflow_stack)
3339   { }
3340   virtual void do_oop(oop* p);
3341   virtual void do_oop(narrowOop* p);
3342 
3343   void trim_queue(size_t max);
3344   void handle_stack_overflow(HeapWord* lost);
3345   void do_yield_check() {
3346     if (_task->should_yield()) {
3347       _task->yield();
3348     }
3349   }
3350 };
3351 
3352 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3353 
3354 // Grey object scanning during work stealing phase --
3355 // the salient assumption here is that any references
3356 // that are in these stolen objects being scanned must
3357 // already have been initialized (else they would not have
3358 // been published), so we do not need to check for
3359 // uninitialized objects before pushing here.
3360 void ParConcMarkingClosure::do_oop(oop obj) {
3361   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3362   HeapWord* addr = (HeapWord*)obj;
3363   // Check if oop points into the CMS generation
3364   // and is not marked
3365   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3366     // a white object ...
3367     // If we manage to "claim" the object, by being the
3368     // first thread to mark it, then we push it on our
3369     // marking stack
3370     if (_bit_map->par_mark(addr)) {     // ... now grey
3371       // push on work queue (grey set)
3372       bool simulate_overflow = false;
3373       NOT_PRODUCT(
3374         if (CMSMarkStackOverflowALot &&
3375             _collector->simulate_overflow()) {
3376           // simulate a stack overflow
3377           simulate_overflow = true;
3378         }
3379       )
3380       if (simulate_overflow ||
3381           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3382         // stack overflow
3383         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3384         // We cannot assert that the overflow stack is full because
3385         // it may have been emptied since.
3386         assert(simulate_overflow ||
3387                _work_queue->size() == _work_queue->max_elems(),
3388               "Else push should have succeeded");
3389         handle_stack_overflow(addr);
3390       }
3391     } // Else, some other thread got there first
3392     do_yield_check();
3393   }
3394 }
3395 
3396 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3397 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3398 
3399 void ParConcMarkingClosure::trim_queue(size_t max) {
3400   while (_work_queue->size() > max) {
3401     oop new_oop;
3402     if (_work_queue->pop_local(new_oop)) {
3403       assert(new_oop->is_oop(), "Should be an oop");
3404       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3405       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3406       new_oop->oop_iterate(this);  // do_oop() above
3407       do_yield_check();
3408     }
3409   }
3410 }
3411 
3412 // Upon stack overflow, we discard (part of) the stack,
3413 // remembering the least address amongst those discarded
3414 // in CMSCollector's _restart_address.
3415 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3416   // We need to do this under a mutex to prevent other
3417   // workers from interfering with the work done below.
3418   MutexLockerEx ml(_overflow_stack->par_lock(),
3419                    Mutex::_no_safepoint_check_flag);
3420   // Remember the least grey address discarded
3421   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3422   _collector->lower_restart_addr(ra);
3423   _overflow_stack->reset();  // discard stack contents
3424   _overflow_stack->expand(); // expand the stack if possible
3425 }
3426 
3427 
3428 void CMSConcMarkingTask::do_work_steal(int i) {
3429   OopTaskQueue* work_q = work_queue(i);
3430   oop obj_to_scan;
3431   CMSBitMap* bm = &(_collector->_markBitMap);
3432   CMSMarkStack* ovflw = &(_collector->_markStack);
3433   int* seed = _collector->hash_seed(i);
3434   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3435   while (true) {
3436     cl.trim_queue(0);
3437     assert(work_q->size() == 0, "Should have been emptied above");
3438     if (get_work_from_overflow_stack(ovflw, work_q)) {
3439       // Can't assert below because the work obtained from the
3440       // overflow stack may already have been stolen from us.
3441       // assert(work_q->size() > 0, "Work from overflow stack");
3442       continue;
3443     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3444       assert(obj_to_scan->is_oop(), "Should be an oop");
3445       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3446       obj_to_scan->oop_iterate(&cl);
3447     } else if (terminator()->offer_termination(&_term_term)) {
3448       assert(work_q->size() == 0, "Impossible!");
3449       break;
3450     } else if (yielding() || should_yield()) {
3451       yield();
3452     }
3453   }
3454 }
3455 
3456 // This is run by the CMS (coordinator) thread.
3457 void CMSConcMarkingTask::coordinator_yield() {
3458   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3459          "CMS thread should hold CMS token");
3460   // First give up the locks, then yield, then re-lock
3461   // We should probably use a constructor/destructor idiom to
3462   // do this unlock/lock or modify the MutexUnlocker class to
3463   // serve our purpose. XXX
3464   assert_lock_strong(_bit_map_lock);
3465   _bit_map_lock->unlock();
3466   ConcurrentMarkSweepThread::desynchronize(true);
3467   _collector->stopTimer();
3468   _collector->incrementYields();
3469 
3470   // It is possible for whichever thread initiated the yield request
3471   // not to get a chance to wake up and take the bitmap lock between
3472   // this thread releasing it and reacquiring it. So, while the
3473   // should_yield() flag is on, let's sleep for a bit to give the
3474   // other thread a chance to wake up. The limit imposed on the number
3475   // of iterations is defensive, to avoid any unforseen circumstances
3476   // putting us into an infinite loop. Since it's always been this
3477   // (coordinator_yield()) method that was observed to cause the
3478   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3479   // which is by default non-zero. For the other seven methods that
3480   // also perform the yield operation, as are using a different
3481   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3482   // can enable the sleeping for those methods too, if necessary.
3483   // See 6442774.
3484   //
3485   // We really need to reconsider the synchronization between the GC
3486   // thread and the yield-requesting threads in the future and we
3487   // should really use wait/notify, which is the recommended
3488   // way of doing this type of interaction. Additionally, we should
3489   // consolidate the eight methods that do the yield operation and they
3490   // are almost identical into one for better maintainability and
3491   // readability. See 6445193.
3492   //
3493   // Tony 2006.06.29
3494   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3495                    ConcurrentMarkSweepThread::should_yield() &&
3496                    !CMSCollector::foregroundGCIsActive(); ++i) {
3497     os::sleep(Thread::current(), 1, false);
3498   }
3499 
3500   ConcurrentMarkSweepThread::synchronize(true);
3501   _bit_map_lock->lock_without_safepoint_check();
3502   _collector->startTimer();
3503 }
3504 
3505 bool CMSCollector::do_marking_mt() {
3506   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3507   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3508                                                                   conc_workers()->active_workers(),
3509                                                                   Threads::number_of_non_daemon_threads());
3510   conc_workers()->set_active_workers(num_workers);
3511 
3512   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3513 
3514   CMSConcMarkingTask tsk(this,
3515                          cms_space,
3516                          conc_workers(),
3517                          task_queues());
3518 
3519   // Since the actual number of workers we get may be different
3520   // from the number we requested above, do we need to do anything different
3521   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3522   // class?? XXX
3523   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3524 
3525   // Refs discovery is already non-atomic.
3526   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3527   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3528   conc_workers()->start_task(&tsk);
3529   while (tsk.yielded()) {
3530     tsk.coordinator_yield();
3531     conc_workers()->continue_task(&tsk);
3532   }
3533   // If the task was aborted, _restart_addr will be non-NULL
3534   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3535   while (_restart_addr != NULL) {
3536     // XXX For now we do not make use of ABORTED state and have not
3537     // yet implemented the right abort semantics (even in the original
3538     // single-threaded CMS case). That needs some more investigation
3539     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3540     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3541     // If _restart_addr is non-NULL, a marking stack overflow
3542     // occurred; we need to do a fresh marking iteration from the
3543     // indicated restart address.
3544     if (_foregroundGCIsActive) {
3545       // We may be running into repeated stack overflows, having
3546       // reached the limit of the stack size, while making very
3547       // slow forward progress. It may be best to bail out and
3548       // let the foreground collector do its job.
3549       // Clear _restart_addr, so that foreground GC
3550       // works from scratch. This avoids the headache of
3551       // a "rescan" which would otherwise be needed because
3552       // of the dirty mod union table & card table.
3553       _restart_addr = NULL;
3554       return false;
3555     }
3556     // Adjust the task to restart from _restart_addr
3557     tsk.reset(_restart_addr);
3558     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3559                   _restart_addr);
3560     _restart_addr = NULL;
3561     // Get the workers going again
3562     conc_workers()->start_task(&tsk);
3563     while (tsk.yielded()) {
3564       tsk.coordinator_yield();
3565       conc_workers()->continue_task(&tsk);
3566     }
3567   }
3568   assert(tsk.completed(), "Inconsistency");
3569   assert(tsk.result() == true, "Inconsistency");
3570   return true;
3571 }
3572 
3573 bool CMSCollector::do_marking_st() {
3574   ResourceMark rm;
3575   HandleMark   hm;
3576 
3577   // Temporarily make refs discovery single threaded (non-MT)
3578   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3579   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3580     &_markStack, CMSYield);
3581   // the last argument to iterate indicates whether the iteration
3582   // should be incremental with periodic yields.
3583   _markBitMap.iterate(&markFromRootsClosure);
3584   // If _restart_addr is non-NULL, a marking stack overflow
3585   // occurred; we need to do a fresh iteration from the
3586   // indicated restart address.
3587   while (_restart_addr != NULL) {
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;  // indicating failure to complete marking
3599     }
3600     // Deal with stack overflow:
3601     // we restart marking from _restart_addr
3602     HeapWord* ra = _restart_addr;
3603     markFromRootsClosure.reset(ra);
3604     _restart_addr = NULL;
3605     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3606   }
3607   return true;
3608 }
3609 
3610 void CMSCollector::preclean() {
3611   check_correct_thread_executing();
3612   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3613   verify_work_stacks_empty();
3614   verify_overflow_empty();
3615   _abort_preclean = false;
3616   if (CMSPrecleaningEnabled) {
3617     if (!CMSEdenChunksRecordAlways) {
3618       _eden_chunk_index = 0;
3619     }
3620     size_t used = get_eden_used();
3621     size_t capacity = get_eden_capacity();
3622     // Don't start sampling unless we will get sufficiently
3623     // many samples.
3624     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3625                 * CMSScheduleRemarkEdenPenetration)) {
3626       _start_sampling = true;
3627     } else {
3628       _start_sampling = false;
3629     }
3630     GCTraceCPUTime tcpu;
3631     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3632     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3633   }
3634   CMSTokenSync x(true); // is cms thread
3635   if (CMSPrecleaningEnabled) {
3636     sample_eden();
3637     _collectorState = AbortablePreclean;
3638   } else {
3639     _collectorState = FinalMarking;
3640   }
3641   verify_work_stacks_empty();
3642   verify_overflow_empty();
3643 }
3644 
3645 // Try and schedule the remark such that young gen
3646 // occupancy is CMSScheduleRemarkEdenPenetration %.
3647 void CMSCollector::abortable_preclean() {
3648   check_correct_thread_executing();
3649   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3650   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3651 
3652   // If Eden's current occupancy is below this threshold,
3653   // immediately schedule the remark; else preclean
3654   // past the next scavenge in an effort to
3655   // schedule the pause as described above. By choosing
3656   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3657   // we will never do an actual abortable preclean cycle.
3658   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3659     GCTraceCPUTime tcpu;
3660     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3661     // We need more smarts in the abortable preclean
3662     // loop below to deal with cases where allocation
3663     // in young gen is very very slow, and our precleaning
3664     // is running a losing race against a horde of
3665     // mutators intent on flooding us with CMS updates
3666     // (dirty cards).
3667     // One, admittedly dumb, strategy is to give up
3668     // after a certain number of abortable precleaning loops
3669     // or after a certain maximum time. We want to make
3670     // this smarter in the next iteration.
3671     // XXX FIX ME!!! YSR
3672     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3673     while (!(should_abort_preclean() ||
3674              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3675       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3676       cumworkdone += workdone;
3677       loops++;
3678       // Voluntarily terminate abortable preclean phase if we have
3679       // been at it for too long.
3680       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3681           loops >= CMSMaxAbortablePrecleanLoops) {
3682         log_debug(gc)(" CMS: abort preclean due to loops ");
3683         break;
3684       }
3685       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3686         log_debug(gc)(" CMS: abort preclean due to time ");
3687         break;
3688       }
3689       // If we are doing little work each iteration, we should
3690       // take a short break.
3691       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3692         // Sleep for some time, waiting for work to accumulate
3693         stopTimer();
3694         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3695         startTimer();
3696         waited++;
3697       }
3698     }
3699     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3700                                loops, waited, cumworkdone);
3701   }
3702   CMSTokenSync x(true); // is cms thread
3703   if (_collectorState != Idling) {
3704     assert(_collectorState == AbortablePreclean,
3705            "Spontaneous state transition?");
3706     _collectorState = FinalMarking;
3707   } // Else, a foreground collection completed this CMS cycle.
3708   return;
3709 }
3710 
3711 // Respond to an Eden sampling opportunity
3712 void CMSCollector::sample_eden() {
3713   // Make sure a young gc cannot sneak in between our
3714   // reading and recording of a sample.
3715   assert(Thread::current()->is_ConcurrentGC_thread(),
3716          "Only the cms thread may collect Eden samples");
3717   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3718          "Should collect samples while holding CMS token");
3719   if (!_start_sampling) {
3720     return;
3721   }
3722   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3723   // is populated by the young generation.
3724   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3725     if (_eden_chunk_index < _eden_chunk_capacity) {
3726       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3727       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3728              "Unexpected state of Eden");
3729       // We'd like to check that what we just sampled is an oop-start address;
3730       // however, we cannot do that here since the object may not yet have been
3731       // initialized. So we'll instead do the check when we _use_ this sample
3732       // later.
3733       if (_eden_chunk_index == 0 ||
3734           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3735                          _eden_chunk_array[_eden_chunk_index-1])
3736            >= CMSSamplingGrain)) {
3737         _eden_chunk_index++;  // commit sample
3738       }
3739     }
3740   }
3741   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3742     size_t used = get_eden_used();
3743     size_t capacity = get_eden_capacity();
3744     assert(used <= capacity, "Unexpected state of Eden");
3745     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3746       _abort_preclean = true;
3747     }
3748   }
3749 }
3750 
3751 
3752 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3753   assert(_collectorState == Precleaning ||
3754          _collectorState == AbortablePreclean, "incorrect state");
3755   ResourceMark rm;
3756   HandleMark   hm;
3757 
3758   // Precleaning is currently not MT but the reference processor
3759   // may be set for MT.  Disable it temporarily here.
3760   ReferenceProcessor* rp = ref_processor();
3761   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3762 
3763   // Do one pass of scrubbing the discovered reference lists
3764   // to remove any reference objects with strongly-reachable
3765   // referents.
3766   if (clean_refs) {
3767     CMSPrecleanRefsYieldClosure yield_cl(this);
3768     assert(rp->span().equals(_span), "Spans should be equal");
3769     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3770                                    &_markStack, true /* preclean */);
3771     CMSDrainMarkingStackClosure complete_trace(this,
3772                                    _span, &_markBitMap, &_markStack,
3773                                    &keep_alive, true /* preclean */);
3774 
3775     // We don't want this step to interfere with a young
3776     // collection because we don't want to take CPU
3777     // or memory bandwidth away from the young GC threads
3778     // (which may be as many as there are CPUs).
3779     // Note that we don't need to protect ourselves from
3780     // interference with mutators because they can't
3781     // manipulate the discovered reference lists nor affect
3782     // the computed reachability of the referents, the
3783     // only properties manipulated by the precleaning
3784     // of these reference lists.
3785     stopTimer();
3786     CMSTokenSyncWithLocks x(true /* is cms thread */,
3787                             bitMapLock());
3788     startTimer();
3789     sample_eden();
3790 
3791     // The following will yield to allow foreground
3792     // collection to proceed promptly. XXX YSR:
3793     // The code in this method may need further
3794     // tweaking for better performance and some restructuring
3795     // for cleaner interfaces.
3796     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3797     rp->preclean_discovered_references(
3798           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3799           gc_timer);
3800   }
3801 
3802   if (clean_survivor) {  // preclean the active survivor space(s)
3803     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3804                              &_markBitMap, &_modUnionTable,
3805                              &_markStack, true /* precleaning phase */);
3806     stopTimer();
3807     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3808                              bitMapLock());
3809     startTimer();
3810     unsigned int before_count =
3811       GenCollectedHeap::heap()->total_collections();
3812     SurvivorSpacePrecleanClosure
3813       sss_cl(this, _span, &_markBitMap, &_markStack,
3814              &pam_cl, before_count, CMSYield);
3815     _young_gen->from()->object_iterate_careful(&sss_cl);
3816     _young_gen->to()->object_iterate_careful(&sss_cl);
3817   }
3818   MarkRefsIntoAndScanClosure
3819     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3820              &_markStack, this, CMSYield,
3821              true /* precleaning phase */);
3822   // CAUTION: The following closure has persistent state that may need to
3823   // be reset upon a decrease in the sequence of addresses it
3824   // processes.
3825   ScanMarkedObjectsAgainCarefullyClosure
3826     smoac_cl(this, _span,
3827       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3828 
3829   // Preclean dirty cards in ModUnionTable and CardTable using
3830   // appropriate convergence criterion;
3831   // repeat CMSPrecleanIter times unless we find that
3832   // we are losing.
3833   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3834   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3835          "Bad convergence multiplier");
3836   assert(CMSPrecleanThreshold >= 100,
3837          "Unreasonably low CMSPrecleanThreshold");
3838 
3839   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3840   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3841        numIter < CMSPrecleanIter;
3842        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3843     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3844     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3845     // Either there are very few dirty cards, so re-mark
3846     // pause will be small anyway, or our pre-cleaning isn't
3847     // that much faster than the rate at which cards are being
3848     // dirtied, so we might as well stop and re-mark since
3849     // precleaning won't improve our re-mark time by much.
3850     if (curNumCards <= CMSPrecleanThreshold ||
3851         (numIter > 0 &&
3852          (curNumCards * CMSPrecleanDenominator >
3853          lastNumCards * CMSPrecleanNumerator))) {
3854       numIter++;
3855       cumNumCards += curNumCards;
3856       break;
3857     }
3858   }
3859 
3860   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3861 
3862   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3863   cumNumCards += curNumCards;
3864   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3865                              curNumCards, cumNumCards, numIter);
3866   return cumNumCards;   // as a measure of useful work done
3867 }
3868 
3869 // PRECLEANING NOTES:
3870 // Precleaning involves:
3871 // . reading the bits of the modUnionTable and clearing the set bits.
3872 // . For the cards corresponding to the set bits, we scan the
3873 //   objects on those cards. This means we need the free_list_lock
3874 //   so that we can safely iterate over the CMS space when scanning
3875 //   for oops.
3876 // . When we scan the objects, we'll be both reading and setting
3877 //   marks in the marking bit map, so we'll need the marking bit map.
3878 // . For protecting _collector_state transitions, we take the CGC_lock.
3879 //   Note that any races in the reading of of card table entries by the
3880 //   CMS thread on the one hand and the clearing of those entries by the
3881 //   VM thread or the setting of those entries by the mutator threads on the
3882 //   other are quite benign. However, for efficiency it makes sense to keep
3883 //   the VM thread from racing with the CMS thread while the latter is
3884 //   dirty card info to the modUnionTable. We therefore also use the
3885 //   CGC_lock to protect the reading of the card table and the mod union
3886 //   table by the CM thread.
3887 // . We run concurrently with mutator updates, so scanning
3888 //   needs to be done carefully  -- we should not try to scan
3889 //   potentially uninitialized objects.
3890 //
3891 // Locking strategy: While holding the CGC_lock, we scan over and
3892 // reset a maximal dirty range of the mod union / card tables, then lock
3893 // the free_list_lock and bitmap lock to do a full marking, then
3894 // release these locks; and repeat the cycle. This allows for a
3895 // certain amount of fairness in the sharing of these locks between
3896 // the CMS collector on the one hand, and the VM thread and the
3897 // mutators on the other.
3898 
3899 // NOTE: preclean_mod_union_table() and preclean_card_table()
3900 // further below are largely identical; if you need to modify
3901 // one of these methods, please check the other method too.
3902 
3903 size_t CMSCollector::preclean_mod_union_table(
3904   ConcurrentMarkSweepGeneration* old_gen,
3905   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3906   verify_work_stacks_empty();
3907   verify_overflow_empty();
3908 
3909   // strategy: starting with the first card, accumulate contiguous
3910   // ranges of dirty cards; clear these cards, then scan the region
3911   // covered by these cards.
3912 
3913   // Since all of the MUT is committed ahead, we can just use
3914   // that, in case the generations expand while we are precleaning.
3915   // It might also be fine to just use the committed part of the
3916   // generation, but we might potentially miss cards when the
3917   // generation is rapidly expanding while we are in the midst
3918   // of precleaning.
3919   HeapWord* startAddr = old_gen->reserved().start();
3920   HeapWord* endAddr   = old_gen->reserved().end();
3921 
3922   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3923 
3924   size_t numDirtyCards, cumNumDirtyCards;
3925   HeapWord *nextAddr, *lastAddr;
3926   for (cumNumDirtyCards = numDirtyCards = 0,
3927        nextAddr = lastAddr = startAddr;
3928        nextAddr < endAddr;
3929        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3930 
3931     ResourceMark rm;
3932     HandleMark   hm;
3933 
3934     MemRegion dirtyRegion;
3935     {
3936       stopTimer();
3937       // Potential yield point
3938       CMSTokenSync ts(true);
3939       startTimer();
3940       sample_eden();
3941       // Get dirty region starting at nextOffset (inclusive),
3942       // simultaneously clearing it.
3943       dirtyRegion =
3944         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3945       assert(dirtyRegion.start() >= nextAddr,
3946              "returned region inconsistent?");
3947     }
3948     // Remember where the next search should begin.
3949     // The returned region (if non-empty) is a right open interval,
3950     // so lastOffset is obtained from the right end of that
3951     // interval.
3952     lastAddr = dirtyRegion.end();
3953     // Should do something more transparent and less hacky XXX
3954     numDirtyCards =
3955       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3956 
3957     // We'll scan the cards in the dirty region (with periodic
3958     // yields for foreground GC as needed).
3959     if (!dirtyRegion.is_empty()) {
3960       assert(numDirtyCards > 0, "consistency check");
3961       HeapWord* stop_point = NULL;
3962       stopTimer();
3963       // Potential yield point
3964       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3965                                bitMapLock());
3966       startTimer();
3967       {
3968         verify_work_stacks_empty();
3969         verify_overflow_empty();
3970         sample_eden();
3971         stop_point =
3972           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3973       }
3974       if (stop_point != NULL) {
3975         // The careful iteration stopped early either because it found an
3976         // uninitialized object, or because we were in the midst of an
3977         // "abortable preclean", which should now be aborted. Redirty
3978         // the bits corresponding to the partially-scanned or unscanned
3979         // cards. We'll either restart at the next block boundary or
3980         // abort the preclean.
3981         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3982                "Should only be AbortablePreclean.");
3983         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3984         if (should_abort_preclean()) {
3985           break; // out of preclean loop
3986         } else {
3987           // Compute the next address at which preclean should pick up;
3988           // might need bitMapLock in order to read P-bits.
3989           lastAddr = next_card_start_after_block(stop_point);
3990         }
3991       }
3992     } else {
3993       assert(lastAddr == endAddr, "consistency check");
3994       assert(numDirtyCards == 0, "consistency check");
3995       break;
3996     }
3997   }
3998   verify_work_stacks_empty();
3999   verify_overflow_empty();
4000   return cumNumDirtyCards;
4001 }
4002 
4003 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4004 // below are largely identical; if you need to modify
4005 // one of these methods, please check the other method too.
4006 
4007 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4008   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4009   // strategy: it's similar to precleamModUnionTable above, in that
4010   // we accumulate contiguous ranges of dirty cards, mark these cards
4011   // precleaned, then scan the region covered by these cards.
4012   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4013   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4014 
4015   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4016 
4017   size_t numDirtyCards, cumNumDirtyCards;
4018   HeapWord *lastAddr, *nextAddr;
4019 
4020   for (cumNumDirtyCards = numDirtyCards = 0,
4021        nextAddr = lastAddr = startAddr;
4022        nextAddr < endAddr;
4023        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4024 
4025     ResourceMark rm;
4026     HandleMark   hm;
4027 
4028     MemRegion dirtyRegion;
4029     {
4030       // See comments in "Precleaning notes" above on why we
4031       // do this locking. XXX Could the locking overheads be
4032       // too high when dirty cards are sparse? [I don't think so.]
4033       stopTimer();
4034       CMSTokenSync x(true); // is cms thread
4035       startTimer();
4036       sample_eden();
4037       // Get and clear dirty region from card table
4038       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4039                                     MemRegion(nextAddr, endAddr),
4040                                     true,
4041                                     CardTableModRefBS::precleaned_card_val());
4042 
4043       assert(dirtyRegion.start() >= nextAddr,
4044              "returned region inconsistent?");
4045     }
4046     lastAddr = dirtyRegion.end();
4047     numDirtyCards =
4048       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4049 
4050     if (!dirtyRegion.is_empty()) {
4051       stopTimer();
4052       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4053       startTimer();
4054       sample_eden();
4055       verify_work_stacks_empty();
4056       verify_overflow_empty();
4057       HeapWord* stop_point =
4058         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4059       if (stop_point != NULL) {
4060         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4061                "Should only be AbortablePreclean.");
4062         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4063         if (should_abort_preclean()) {
4064           break; // out of preclean loop
4065         } else {
4066           // Compute the next address at which preclean should pick up.
4067           lastAddr = next_card_start_after_block(stop_point);
4068         }
4069       }
4070     } else {
4071       break;
4072     }
4073   }
4074   verify_work_stacks_empty();
4075   verify_overflow_empty();
4076   return cumNumDirtyCards;
4077 }
4078 
4079 class PrecleanKlassClosure : public KlassClosure {
4080   KlassToOopClosure _cm_klass_closure;
4081  public:
4082   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4083   void do_klass(Klass* k) {
4084     if (k->has_accumulated_modified_oops()) {
4085       k->clear_accumulated_modified_oops();
4086 
4087       _cm_klass_closure.do_klass(k);
4088     }
4089   }
4090 };
4091 
4092 // The freelist lock is needed to prevent asserts, is it really needed?
4093 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4094 
4095   cl->set_freelistLock(freelistLock);
4096 
4097   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4098 
4099   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4100   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4101   PrecleanKlassClosure preclean_klass_closure(cl);
4102   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4103 
4104   verify_work_stacks_empty();
4105   verify_overflow_empty();
4106 }
4107 
4108 void CMSCollector::checkpointRootsFinal() {
4109   assert(_collectorState == FinalMarking, "incorrect state transition?");
4110   check_correct_thread_executing();
4111   // world is stopped at this checkpoint
4112   assert(SafepointSynchronize::is_at_safepoint(),
4113          "world should be stopped");
4114   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4115 
4116   verify_work_stacks_empty();
4117   verify_overflow_empty();
4118 
4119   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4120                 _young_gen->used() / K, _young_gen->capacity() / K);
4121   {
4122     if (CMSScavengeBeforeRemark) {
4123       GenCollectedHeap* gch = GenCollectedHeap::heap();
4124       // Temporarily set flag to false, GCH->do_collection will
4125       // expect it to be false and set to true
4126       FlagSetting fl(gch->_is_gc_active, false);
4127 
4128       gch->do_collection(true,                      // full (i.e. force, see below)
4129                          false,                     // !clear_all_soft_refs
4130                          0,                         // size
4131                          false,                     // is_tlab
4132                          GenCollectedHeap::YoungGen // type
4133         );
4134     }
4135     FreelistLocker x(this);
4136     MutexLockerEx y(bitMapLock(),
4137                     Mutex::_no_safepoint_check_flag);
4138     checkpointRootsFinalWork();
4139   }
4140   verify_work_stacks_empty();
4141   verify_overflow_empty();
4142 }
4143 
4144 void CMSCollector::checkpointRootsFinalWork() {
4145   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4146 
4147   assert(haveFreelistLocks(), "must have free list locks");
4148   assert_lock_strong(bitMapLock());
4149 
4150   ResourceMark rm;
4151   HandleMark   hm;
4152 
4153   GenCollectedHeap* gch = GenCollectedHeap::heap();
4154 
4155   if (should_unload_classes()) {
4156     CodeCache::gc_prologue();
4157   }
4158   assert(haveFreelistLocks(), "must have free list locks");
4159   assert_lock_strong(bitMapLock());
4160 
4161   // We might assume that we need not fill TLAB's when
4162   // CMSScavengeBeforeRemark is set, because we may have just done
4163   // a scavenge which would have filled all TLAB's -- and besides
4164   // Eden would be empty. This however may not always be the case --
4165   // for instance although we asked for a scavenge, it may not have
4166   // happened because of a JNI critical section. We probably need
4167   // a policy for deciding whether we can in that case wait until
4168   // the critical section releases and then do the remark following
4169   // the scavenge, and skip it here. In the absence of that policy,
4170   // or of an indication of whether the scavenge did indeed occur,
4171   // we cannot rely on TLAB's having been filled and must do
4172   // so here just in case a scavenge did not happen.
4173   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4174   // Update the saved marks which may affect the root scans.
4175   gch->save_marks();
4176 
4177   print_eden_and_survivor_chunk_arrays();
4178 
4179   {
4180 #if defined(COMPILER2) || INCLUDE_JVMCI
4181     DerivedPointerTableDeactivate dpt_deact;
4182 #endif
4183 
4184     // Note on the role of the mod union table:
4185     // Since the marker in "markFromRoots" marks concurrently with
4186     // mutators, it is possible for some reachable objects not to have been
4187     // scanned. For instance, an only reference to an object A was
4188     // placed in object B after the marker scanned B. Unless B is rescanned,
4189     // A would be collected. Such updates to references in marked objects
4190     // are detected via the mod union table which is the set of all cards
4191     // dirtied since the first checkpoint in this GC cycle and prior to
4192     // the most recent young generation GC, minus those cleaned up by the
4193     // concurrent precleaning.
4194     if (CMSParallelRemarkEnabled) {
4195       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4196       do_remark_parallel();
4197     } else {
4198       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4199       do_remark_non_parallel();
4200     }
4201   }
4202   verify_work_stacks_empty();
4203   verify_overflow_empty();
4204 
4205   {
4206     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4207     refProcessingWork();
4208   }
4209   verify_work_stacks_empty();
4210   verify_overflow_empty();
4211 
4212   if (should_unload_classes()) {
4213     CodeCache::gc_epilogue();
4214   }
4215   JvmtiExport::gc_epilogue();
4216 
4217   // If we encountered any (marking stack / work queue) overflow
4218   // events during the current CMS cycle, take appropriate
4219   // remedial measures, where possible, so as to try and avoid
4220   // recurrence of that condition.
4221   assert(_markStack.isEmpty(), "No grey objects");
4222   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4223                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4224   if (ser_ovflw > 0) {
4225     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4226                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4227     _markStack.expand();
4228     _ser_pmc_remark_ovflw = 0;
4229     _ser_pmc_preclean_ovflw = 0;
4230     _ser_kac_preclean_ovflw = 0;
4231     _ser_kac_ovflw = 0;
4232   }
4233   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4234      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4235                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4236      _par_pmc_remark_ovflw = 0;
4237     _par_kac_ovflw = 0;
4238   }
4239    if (_markStack._hit_limit > 0) {
4240      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4241                           _markStack._hit_limit);
4242    }
4243    if (_markStack._failed_double > 0) {
4244      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4245                           _markStack._failed_double, _markStack.capacity());
4246    }
4247   _markStack._hit_limit = 0;
4248   _markStack._failed_double = 0;
4249 
4250   if ((VerifyAfterGC || VerifyDuringGC) &&
4251       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4252     verify_after_remark();
4253   }
4254 
4255   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4256 
4257   // Change under the freelistLocks.
4258   _collectorState = Sweeping;
4259   // Call isAllClear() under bitMapLock
4260   assert(_modUnionTable.isAllClear(),
4261       "Should be clear by end of the final marking");
4262   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4263       "Should be clear by end of the final marking");
4264 }
4265 
4266 void CMSParInitialMarkTask::work(uint worker_id) {
4267   elapsedTimer _timer;
4268   ResourceMark rm;
4269   HandleMark   hm;
4270 
4271   // ---------- scan from roots --------------
4272   _timer.start();
4273   GenCollectedHeap* gch = GenCollectedHeap::heap();
4274   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4275 
4276   // ---------- young gen roots --------------
4277   {
4278     work_on_young_gen_roots(&par_mri_cl);
4279     _timer.stop();
4280     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4281   }
4282 
4283   // ---------- remaining roots --------------
4284   _timer.reset();
4285   _timer.start();
4286 
4287   CLDToOopClosure cld_closure(&par_mri_cl, true);
4288 
4289   gch->gen_process_roots(_strong_roots_scope,
4290                          GenCollectedHeap::OldGen,
4291                          false,     // yg was scanned above
4292                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4293                          _collector->should_unload_classes(),
4294                          &par_mri_cl,
4295                          NULL,
4296                          &cld_closure);
4297   assert(_collector->should_unload_classes()
4298          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4299          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4300   _timer.stop();
4301   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4302 }
4303 
4304 // Parallel remark task
4305 class CMSParRemarkTask: public CMSParMarkTask {
4306   CompactibleFreeListSpace* _cms_space;
4307 
4308   // The per-thread work queues, available here for stealing.
4309   OopTaskQueueSet*       _task_queues;
4310   ParallelTaskTerminator _term;
4311   StrongRootsScope*      _strong_roots_scope;
4312 
4313  public:
4314   // A value of 0 passed to n_workers will cause the number of
4315   // workers to be taken from the active workers in the work gang.
4316   CMSParRemarkTask(CMSCollector* collector,
4317                    CompactibleFreeListSpace* cms_space,
4318                    uint n_workers, WorkGang* workers,
4319                    OopTaskQueueSet* task_queues,
4320                    StrongRootsScope* strong_roots_scope):
4321     CMSParMarkTask("Rescan roots and grey objects in parallel",
4322                    collector, n_workers),
4323     _cms_space(cms_space),
4324     _task_queues(task_queues),
4325     _term(n_workers, task_queues),
4326     _strong_roots_scope(strong_roots_scope) { }
4327 
4328   OopTaskQueueSet* task_queues() { return _task_queues; }
4329 
4330   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4331 
4332   ParallelTaskTerminator* terminator() { return &_term; }
4333   uint n_workers() { return _n_workers; }
4334 
4335   void work(uint worker_id);
4336 
4337  private:
4338   // ... of  dirty cards in old space
4339   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4340                                   ParMarkRefsIntoAndScanClosure* cl);
4341 
4342   // ... work stealing for the above
4343   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4344 };
4345 
4346 class RemarkKlassClosure : public KlassClosure {
4347   KlassToOopClosure _cm_klass_closure;
4348  public:
4349   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4350   void do_klass(Klass* k) {
4351     // Check if we have modified any oops in the Klass during the concurrent marking.
4352     if (k->has_accumulated_modified_oops()) {
4353       k->clear_accumulated_modified_oops();
4354 
4355       // We could have transfered the current modified marks to the accumulated marks,
4356       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4357     } else if (k->has_modified_oops()) {
4358       // Don't clear anything, this info is needed by the next young collection.
4359     } else {
4360       // No modified oops in the Klass.
4361       return;
4362     }
4363 
4364     // The klass has modified fields, need to scan the klass.
4365     _cm_klass_closure.do_klass(k);
4366   }
4367 };
4368 
4369 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4370   ParNewGeneration* young_gen = _collector->_young_gen;
4371   ContiguousSpace* eden_space = young_gen->eden();
4372   ContiguousSpace* from_space = young_gen->from();
4373   ContiguousSpace* to_space   = young_gen->to();
4374 
4375   HeapWord** eca = _collector->_eden_chunk_array;
4376   size_t     ect = _collector->_eden_chunk_index;
4377   HeapWord** sca = _collector->_survivor_chunk_array;
4378   size_t     sct = _collector->_survivor_chunk_index;
4379 
4380   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4381   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4382 
4383   do_young_space_rescan(cl, to_space, NULL, 0);
4384   do_young_space_rescan(cl, from_space, sca, sct);
4385   do_young_space_rescan(cl, eden_space, eca, ect);
4386 }
4387 
4388 // work_queue(i) is passed to the closure
4389 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4390 // also is passed to do_dirty_card_rescan_tasks() and to
4391 // do_work_steal() to select the i-th task_queue.
4392 
4393 void CMSParRemarkTask::work(uint worker_id) {
4394   elapsedTimer _timer;
4395   ResourceMark rm;
4396   HandleMark   hm;
4397 
4398   // ---------- rescan from roots --------------
4399   _timer.start();
4400   GenCollectedHeap* gch = GenCollectedHeap::heap();
4401   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4402     _collector->_span, _collector->ref_processor(),
4403     &(_collector->_markBitMap),
4404     work_queue(worker_id));
4405 
4406   // Rescan young gen roots first since these are likely
4407   // coarsely partitioned and may, on that account, constitute
4408   // the critical path; thus, it's best to start off that
4409   // work first.
4410   // ---------- young gen roots --------------
4411   {
4412     work_on_young_gen_roots(&par_mrias_cl);
4413     _timer.stop();
4414     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4415   }
4416 
4417   // ---------- remaining roots --------------
4418   _timer.reset();
4419   _timer.start();
4420   gch->gen_process_roots(_strong_roots_scope,
4421                          GenCollectedHeap::OldGen,
4422                          false,     // yg was scanned above
4423                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4424                          _collector->should_unload_classes(),
4425                          &par_mrias_cl,
4426                          NULL,
4427                          NULL);     // The dirty klasses will be handled below
4428 
4429   assert(_collector->should_unload_classes()
4430          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4431          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4432   _timer.stop();
4433   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4434 
4435   // ---------- unhandled CLD scanning ----------
4436   if (worker_id == 0) { // Single threaded at the moment.
4437     _timer.reset();
4438     _timer.start();
4439 
4440     // Scan all new class loader data objects and new dependencies that were
4441     // introduced during concurrent marking.
4442     ResourceMark rm;
4443     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4444     for (int i = 0; i < array->length(); i++) {
4445       par_mrias_cl.do_cld_nv(array->at(i));
4446     }
4447 
4448     // We don't need to keep track of new CLDs anymore.
4449     ClassLoaderDataGraph::remember_new_clds(false);
4450 
4451     _timer.stop();
4452     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4453   }
4454 
4455   // ---------- dirty klass scanning ----------
4456   if (worker_id == 0) { // Single threaded at the moment.
4457     _timer.reset();
4458     _timer.start();
4459 
4460     // Scan all classes that was dirtied during the concurrent marking phase.
4461     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4462     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4463 
4464     _timer.stop();
4465     log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4466   }
4467 
4468   // We might have added oops to ClassLoaderData::_handles during the
4469   // concurrent marking phase. These oops point to newly allocated objects
4470   // that are guaranteed to be kept alive. Either by the direct allocation
4471   // code, or when the young collector processes the roots. Hence,
4472   // we don't have to revisit the _handles block during the remark phase.
4473 
4474   // ---------- rescan dirty cards ------------
4475   _timer.reset();
4476   _timer.start();
4477 
4478   // Do the rescan tasks for each of the two spaces
4479   // (cms_space) in turn.
4480   // "worker_id" is passed to select the task_queue for "worker_id"
4481   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4482   _timer.stop();
4483   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4484 
4485   // ---------- steal work from other threads ...
4486   // ---------- ... and drain overflow list.
4487   _timer.reset();
4488   _timer.start();
4489   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4490   _timer.stop();
4491   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4492 }
4493 
4494 void
4495 CMSParMarkTask::do_young_space_rescan(
4496   OopsInGenClosure* cl, ContiguousSpace* space,
4497   HeapWord** chunk_array, size_t chunk_top) {
4498   // Until all tasks completed:
4499   // . claim an unclaimed task
4500   // . compute region boundaries corresponding to task claimed
4501   //   using chunk_array
4502   // . par_oop_iterate(cl) over that region
4503 
4504   ResourceMark rm;
4505   HandleMark   hm;
4506 
4507   SequentialSubTasksDone* pst = space->par_seq_tasks();
4508 
4509   uint nth_task = 0;
4510   uint n_tasks  = pst->n_tasks();
4511 
4512   if (n_tasks > 0) {
4513     assert(pst->valid(), "Uninitialized use?");
4514     HeapWord *start, *end;
4515     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4516       // We claimed task # nth_task; compute its boundaries.
4517       if (chunk_top == 0) {  // no samples were taken
4518         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4519         start = space->bottom();
4520         end   = space->top();
4521       } else if (nth_task == 0) {
4522         start = space->bottom();
4523         end   = chunk_array[nth_task];
4524       } else if (nth_task < (uint)chunk_top) {
4525         assert(nth_task >= 1, "Control point invariant");
4526         start = chunk_array[nth_task - 1];
4527         end   = chunk_array[nth_task];
4528       } else {
4529         assert(nth_task == (uint)chunk_top, "Control point invariant");
4530         start = chunk_array[chunk_top - 1];
4531         end   = space->top();
4532       }
4533       MemRegion mr(start, end);
4534       // Verify that mr is in space
4535       assert(mr.is_empty() || space->used_region().contains(mr),
4536              "Should be in space");
4537       // Verify that "start" is an object boundary
4538       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4539              "Should be an oop");
4540       space->par_oop_iterate(mr, cl);
4541     }
4542     pst->all_tasks_completed();
4543   }
4544 }
4545 
4546 void
4547 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4548   CompactibleFreeListSpace* sp, int i,
4549   ParMarkRefsIntoAndScanClosure* cl) {
4550   // Until all tasks completed:
4551   // . claim an unclaimed task
4552   // . compute region boundaries corresponding to task claimed
4553   // . transfer dirty bits ct->mut for that region
4554   // . apply rescanclosure to dirty mut bits for that region
4555 
4556   ResourceMark rm;
4557   HandleMark   hm;
4558 
4559   OopTaskQueue* work_q = work_queue(i);
4560   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4561   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4562   // CAUTION: This closure has state that persists across calls to
4563   // the work method dirty_range_iterate_clear() in that it has
4564   // embedded in it a (subtype of) UpwardsObjectClosure. The
4565   // use of that state in the embedded UpwardsObjectClosure instance
4566   // assumes that the cards are always iterated (even if in parallel
4567   // by several threads) in monotonically increasing order per each
4568   // thread. This is true of the implementation below which picks
4569   // card ranges (chunks) in monotonically increasing order globally
4570   // and, a-fortiori, in monotonically increasing order per thread
4571   // (the latter order being a subsequence of the former).
4572   // If the work code below is ever reorganized into a more chaotic
4573   // work-partitioning form than the current "sequential tasks"
4574   // paradigm, the use of that persistent state will have to be
4575   // revisited and modified appropriately. See also related
4576   // bug 4756801 work on which should examine this code to make
4577   // sure that the changes there do not run counter to the
4578   // assumptions made here and necessary for correctness and
4579   // efficiency. Note also that this code might yield inefficient
4580   // behavior in the case of very large objects that span one or
4581   // more work chunks. Such objects would potentially be scanned
4582   // several times redundantly. Work on 4756801 should try and
4583   // address that performance anomaly if at all possible. XXX
4584   MemRegion  full_span  = _collector->_span;
4585   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4586   MarkFromDirtyCardsClosure
4587     greyRescanClosure(_collector, full_span, // entire span of interest
4588                       sp, bm, work_q, cl);
4589 
4590   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4591   assert(pst->valid(), "Uninitialized use?");
4592   uint nth_task = 0;
4593   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4594   MemRegion span = sp->used_region();
4595   HeapWord* start_addr = span.start();
4596   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4597                                            alignment);
4598   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4599   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4600          start_addr, "Check alignment");
4601   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4602          chunk_size, "Check alignment");
4603 
4604   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4605     // Having claimed the nth_task, compute corresponding mem-region,
4606     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4607     // The alignment restriction ensures that we do not need any
4608     // synchronization with other gang-workers while setting or
4609     // clearing bits in thus chunk of the MUT.
4610     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4611                                     start_addr + (nth_task+1)*chunk_size);
4612     // The last chunk's end might be way beyond end of the
4613     // used region. In that case pull back appropriately.
4614     if (this_span.end() > end_addr) {
4615       this_span.set_end(end_addr);
4616       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4617     }
4618     // Iterate over the dirty cards covering this chunk, marking them
4619     // precleaned, and setting the corresponding bits in the mod union
4620     // table. Since we have been careful to partition at Card and MUT-word
4621     // boundaries no synchronization is needed between parallel threads.
4622     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4623                                                  &modUnionClosure);
4624 
4625     // Having transferred these marks into the modUnionTable,
4626     // rescan the marked objects on the dirty cards in the modUnionTable.
4627     // Even if this is at a synchronous collection, the initial marking
4628     // may have been done during an asynchronous collection so there
4629     // may be dirty bits in the mod-union table.
4630     _collector->_modUnionTable.dirty_range_iterate_clear(
4631                   this_span, &greyRescanClosure);
4632     _collector->_modUnionTable.verifyNoOneBitsInRange(
4633                                  this_span.start(),
4634                                  this_span.end());
4635   }
4636   pst->all_tasks_completed();  // declare that i am done
4637 }
4638 
4639 // . see if we can share work_queues with ParNew? XXX
4640 void
4641 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4642                                 int* seed) {
4643   OopTaskQueue* work_q = work_queue(i);
4644   NOT_PRODUCT(int num_steals = 0;)
4645   oop obj_to_scan;
4646   CMSBitMap* bm = &(_collector->_markBitMap);
4647 
4648   while (true) {
4649     // Completely finish any left over work from (an) earlier round(s)
4650     cl->trim_queue(0);
4651     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4652                                          (size_t)ParGCDesiredObjsFromOverflowList);
4653     // Now check if there's any work in the overflow list
4654     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4655     // only affects the number of attempts made to get work from the
4656     // overflow list and does not affect the number of workers.  Just
4657     // pass ParallelGCThreads so this behavior is unchanged.
4658     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4659                                                 work_q,
4660                                                 ParallelGCThreads)) {
4661       // found something in global overflow list;
4662       // not yet ready to go stealing work from others.
4663       // We'd like to assert(work_q->size() != 0, ...)
4664       // because we just took work from the overflow list,
4665       // but of course we can't since all of that could have
4666       // been already stolen from us.
4667       // "He giveth and He taketh away."
4668       continue;
4669     }
4670     // Verify that we have no work before we resort to stealing
4671     assert(work_q->size() == 0, "Have work, shouldn't steal");
4672     // Try to steal from other queues that have work
4673     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4674       NOT_PRODUCT(num_steals++;)
4675       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4676       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4677       // Do scanning work
4678       obj_to_scan->oop_iterate(cl);
4679       // Loop around, finish this work, and try to steal some more
4680     } else if (terminator()->offer_termination()) {
4681         break;  // nirvana from the infinite cycle
4682     }
4683   }
4684   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4685   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4686          "Else our work is not yet done");
4687 }
4688 
4689 // Record object boundaries in _eden_chunk_array by sampling the eden
4690 // top in the slow-path eden object allocation code path and record
4691 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4692 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4693 // sampling in sample_eden() that activates during the part of the
4694 // preclean phase.
4695 void CMSCollector::sample_eden_chunk() {
4696   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4697     if (_eden_chunk_lock->try_lock()) {
4698       // Record a sample. This is the critical section. The contents
4699       // of the _eden_chunk_array have to be non-decreasing in the
4700       // address order.
4701       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4702       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4703              "Unexpected state of Eden");
4704       if (_eden_chunk_index == 0 ||
4705           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4706            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4707                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4708         _eden_chunk_index++;  // commit sample
4709       }
4710       _eden_chunk_lock->unlock();
4711     }
4712   }
4713 }
4714 
4715 // Return a thread-local PLAB recording array, as appropriate.
4716 void* CMSCollector::get_data_recorder(int thr_num) {
4717   if (_survivor_plab_array != NULL &&
4718       (CMSPLABRecordAlways ||
4719        (_collectorState > Marking && _collectorState < FinalMarking))) {
4720     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4721     ChunkArray* ca = &_survivor_plab_array[thr_num];
4722     ca->reset();   // clear it so that fresh data is recorded
4723     return (void*) ca;
4724   } else {
4725     return NULL;
4726   }
4727 }
4728 
4729 // Reset all the thread-local PLAB recording arrays
4730 void CMSCollector::reset_survivor_plab_arrays() {
4731   for (uint i = 0; i < ParallelGCThreads; i++) {
4732     _survivor_plab_array[i].reset();
4733   }
4734 }
4735 
4736 // Merge the per-thread plab arrays into the global survivor chunk
4737 // array which will provide the partitioning of the survivor space
4738 // for CMS initial scan and rescan.
4739 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4740                                               int no_of_gc_threads) {
4741   assert(_survivor_plab_array  != NULL, "Error");
4742   assert(_survivor_chunk_array != NULL, "Error");
4743   assert(_collectorState == FinalMarking ||
4744          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4745   for (int j = 0; j < no_of_gc_threads; j++) {
4746     _cursor[j] = 0;
4747   }
4748   HeapWord* top = surv->top();
4749   size_t i;
4750   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4751     HeapWord* min_val = top;          // Higher than any PLAB address
4752     uint      min_tid = 0;            // position of min_val this round
4753     for (int j = 0; j < no_of_gc_threads; j++) {
4754       ChunkArray* cur_sca = &_survivor_plab_array[j];
4755       if (_cursor[j] == cur_sca->end()) {
4756         continue;
4757       }
4758       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4759       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4760       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4761       if (cur_val < min_val) {
4762         min_tid = j;
4763         min_val = cur_val;
4764       } else {
4765         assert(cur_val < top, "All recorded addresses should be less");
4766       }
4767     }
4768     // At this point min_val and min_tid are respectively
4769     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4770     // and the thread (j) that witnesses that address.
4771     // We record this address in the _survivor_chunk_array[i]
4772     // and increment _cursor[min_tid] prior to the next round i.
4773     if (min_val == top) {
4774       break;
4775     }
4776     _survivor_chunk_array[i] = min_val;
4777     _cursor[min_tid]++;
4778   }
4779   // We are all done; record the size of the _survivor_chunk_array
4780   _survivor_chunk_index = i; // exclusive: [0, i)
4781   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4782   // Verify that we used up all the recorded entries
4783   #ifdef ASSERT
4784     size_t total = 0;
4785     for (int j = 0; j < no_of_gc_threads; j++) {
4786       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4787       total += _cursor[j];
4788     }
4789     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4790     // Check that the merged array is in sorted order
4791     if (total > 0) {
4792       for (size_t i = 0; i < total - 1; i++) {
4793         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4794                                      i, p2i(_survivor_chunk_array[i]));
4795         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4796                "Not sorted");
4797       }
4798     }
4799   #endif // ASSERT
4800 }
4801 
4802 // Set up the space's par_seq_tasks structure for work claiming
4803 // for parallel initial scan and rescan of young gen.
4804 // See ParRescanTask where this is currently used.
4805 void
4806 CMSCollector::
4807 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4808   assert(n_threads > 0, "Unexpected n_threads argument");
4809 
4810   // Eden space
4811   if (!_young_gen->eden()->is_empty()) {
4812     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4813     assert(!pst->valid(), "Clobbering existing data?");
4814     // Each valid entry in [0, _eden_chunk_index) represents a task.
4815     size_t n_tasks = _eden_chunk_index + 1;
4816     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4817     // Sets the condition for completion of the subtask (how many threads
4818     // need to finish in order to be done).
4819     pst->set_n_threads(n_threads);
4820     pst->set_n_tasks((int)n_tasks);
4821   }
4822 
4823   // Merge the survivor plab arrays into _survivor_chunk_array
4824   if (_survivor_plab_array != NULL) {
4825     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4826   } else {
4827     assert(_survivor_chunk_index == 0, "Error");
4828   }
4829 
4830   // To space
4831   {
4832     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4833     assert(!pst->valid(), "Clobbering existing data?");
4834     // Sets the condition for completion of the subtask (how many threads
4835     // need to finish in order to be done).
4836     pst->set_n_threads(n_threads);
4837     pst->set_n_tasks(1);
4838     assert(pst->valid(), "Error");
4839   }
4840 
4841   // From space
4842   {
4843     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4844     assert(!pst->valid(), "Clobbering existing data?");
4845     size_t n_tasks = _survivor_chunk_index + 1;
4846     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4847     // Sets the condition for completion of the subtask (how many threads
4848     // need to finish in order to be done).
4849     pst->set_n_threads(n_threads);
4850     pst->set_n_tasks((int)n_tasks);
4851     assert(pst->valid(), "Error");
4852   }
4853 }
4854 
4855 // Parallel version of remark
4856 void CMSCollector::do_remark_parallel() {
4857   GenCollectedHeap* gch = GenCollectedHeap::heap();
4858   WorkGang* workers = gch->workers();
4859   assert(workers != NULL, "Need parallel worker threads.");
4860   // Choose to use the number of GC workers most recently set
4861   // into "active_workers".
4862   uint n_workers = workers->active_workers();
4863 
4864   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4865 
4866   StrongRootsScope srs(n_workers);
4867 
4868   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4869 
4870   // We won't be iterating over the cards in the card table updating
4871   // the younger_gen cards, so we shouldn't call the following else
4872   // the verification code as well as subsequent younger_refs_iterate
4873   // code would get confused. XXX
4874   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4875 
4876   // The young gen rescan work will not be done as part of
4877   // process_roots (which currently doesn't know how to
4878   // parallelize such a scan), but rather will be broken up into
4879   // a set of parallel tasks (via the sampling that the [abortable]
4880   // preclean phase did of eden, plus the [two] tasks of
4881   // scanning the [two] survivor spaces. Further fine-grain
4882   // parallelization of the scanning of the survivor spaces
4883   // themselves, and of precleaning of the young gen itself
4884   // is deferred to the future.
4885   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4886 
4887   // The dirty card rescan work is broken up into a "sequence"
4888   // of parallel tasks (per constituent space) that are dynamically
4889   // claimed by the parallel threads.
4890   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4891 
4892   // It turns out that even when we're using 1 thread, doing the work in a
4893   // separate thread causes wide variance in run times.  We can't help this
4894   // in the multi-threaded case, but we special-case n=1 here to get
4895   // repeatable measurements of the 1-thread overhead of the parallel code.
4896   if (n_workers > 1) {
4897     // Make refs discovery MT-safe, if it isn't already: it may not
4898     // necessarily be so, since it's possible that we are doing
4899     // ST marking.
4900     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4901     workers->run_task(&tsk);
4902   } else {
4903     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4904     tsk.work(0);
4905   }
4906 
4907   // restore, single-threaded for now, any preserved marks
4908   // as a result of work_q overflow
4909   restore_preserved_marks_if_any();
4910 }
4911 
4912 // Non-parallel version of remark
4913 void CMSCollector::do_remark_non_parallel() {
4914   ResourceMark rm;
4915   HandleMark   hm;
4916   GenCollectedHeap* gch = GenCollectedHeap::heap();
4917   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4918 
4919   MarkRefsIntoAndScanClosure
4920     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4921              &_markStack, this,
4922              false /* should_yield */, false /* not precleaning */);
4923   MarkFromDirtyCardsClosure
4924     markFromDirtyCardsClosure(this, _span,
4925                               NULL,  // space is set further below
4926                               &_markBitMap, &_markStack, &mrias_cl);
4927   {
4928     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4929     // Iterate over the dirty cards, setting the corresponding bits in the
4930     // mod union table.
4931     {
4932       ModUnionClosure modUnionClosure(&_modUnionTable);
4933       _ct->ct_bs()->dirty_card_iterate(
4934                       _cmsGen->used_region(),
4935                       &modUnionClosure);
4936     }
4937     // Having transferred these marks into the modUnionTable, we just need
4938     // to rescan the marked objects on the dirty cards in the modUnionTable.
4939     // The initial marking may have been done during an asynchronous
4940     // collection so there may be dirty bits in the mod-union table.
4941     const int alignment =
4942       CardTableModRefBS::card_size * BitsPerWord;
4943     {
4944       // ... First handle dirty cards in CMS gen
4945       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4946       MemRegion ur = _cmsGen->used_region();
4947       HeapWord* lb = ur.start();
4948       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4949       MemRegion cms_span(lb, ub);
4950       _modUnionTable.dirty_range_iterate_clear(cms_span,
4951                                                &markFromDirtyCardsClosure);
4952       verify_work_stacks_empty();
4953       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4954     }
4955   }
4956   if (VerifyDuringGC &&
4957       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4958     HandleMark hm;  // Discard invalid handles created during verification
4959     Universe::verify();
4960   }
4961   {
4962     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4963 
4964     verify_work_stacks_empty();
4965 
4966     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4967     StrongRootsScope srs(1);
4968 
4969     gch->gen_process_roots(&srs,
4970                            GenCollectedHeap::OldGen,
4971                            true,  // young gen as roots
4972                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
4973                            should_unload_classes(),
4974                            &mrias_cl,
4975                            NULL,
4976                            NULL); // The dirty klasses will be handled below
4977 
4978     assert(should_unload_classes()
4979            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4980            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4981   }
4982 
4983   {
4984     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4985 
4986     verify_work_stacks_empty();
4987 
4988     // Scan all class loader data objects that might have been introduced
4989     // during concurrent marking.
4990     ResourceMark rm;
4991     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4992     for (int i = 0; i < array->length(); i++) {
4993       mrias_cl.do_cld_nv(array->at(i));
4994     }
4995 
4996     // We don't need to keep track of new CLDs anymore.
4997     ClassLoaderDataGraph::remember_new_clds(false);
4998 
4999     verify_work_stacks_empty();
5000   }
5001 
5002   {
5003     GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
5004 
5005     verify_work_stacks_empty();
5006 
5007     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5008     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5009 
5010     verify_work_stacks_empty();
5011   }
5012 
5013   // We might have added oops to ClassLoaderData::_handles during the
5014   // concurrent marking phase. These oops point to newly allocated objects
5015   // that are guaranteed to be kept alive. Either by the direct allocation
5016   // code, or when the young collector processes the roots. Hence,
5017   // we don't have to revisit the _handles block during the remark phase.
5018 
5019   verify_work_stacks_empty();
5020   // Restore evacuated mark words, if any, used for overflow list links
5021   restore_preserved_marks_if_any();
5022 
5023   verify_overflow_empty();
5024 }
5025 
5026 ////////////////////////////////////////////////////////
5027 // Parallel Reference Processing Task Proxy Class
5028 ////////////////////////////////////////////////////////
5029 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5030   OopTaskQueueSet*       _queues;
5031   ParallelTaskTerminator _terminator;
5032  public:
5033   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5034     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5035   ParallelTaskTerminator* terminator() { return &_terminator; }
5036   OopTaskQueueSet* queues() { return _queues; }
5037 };
5038 
5039 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5040   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5041   CMSCollector*          _collector;
5042   CMSBitMap*             _mark_bit_map;
5043   const MemRegion        _span;
5044   ProcessTask&           _task;
5045 
5046 public:
5047   CMSRefProcTaskProxy(ProcessTask&     task,
5048                       CMSCollector*    collector,
5049                       const MemRegion& span,
5050                       CMSBitMap*       mark_bit_map,
5051                       AbstractWorkGang* workers,
5052                       OopTaskQueueSet* task_queues):
5053     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5054       task_queues,
5055       workers->active_workers()),
5056     _task(task),
5057     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5058   {
5059     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5060            "Inconsistency in _span");
5061   }
5062 
5063   OopTaskQueueSet* task_queues() { return queues(); }
5064 
5065   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5066 
5067   void do_work_steal(int i,
5068                      CMSParDrainMarkingStackClosure* drain,
5069                      CMSParKeepAliveClosure* keep_alive,
5070                      int* seed);
5071 
5072   virtual void work(uint worker_id);
5073 };
5074 
5075 void CMSRefProcTaskProxy::work(uint worker_id) {
5076   ResourceMark rm;
5077   HandleMark hm;
5078   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5079   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5080                                         _mark_bit_map,
5081                                         work_queue(worker_id));
5082   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5083                                                  _mark_bit_map,
5084                                                  work_queue(worker_id));
5085   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5086   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5087   if (_task.marks_oops_alive()) {
5088     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5089                   _collector->hash_seed(worker_id));
5090   }
5091   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5092   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5093 }
5094 
5095 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5096   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5097   EnqueueTask& _task;
5098 
5099 public:
5100   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5101     : AbstractGangTask("Enqueue reference objects in parallel"),
5102       _task(task)
5103   { }
5104 
5105   virtual void work(uint worker_id)
5106   {
5107     _task.work(worker_id);
5108   }
5109 };
5110 
5111 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5112   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5113    _span(span),
5114    _bit_map(bit_map),
5115    _work_queue(work_queue),
5116    _mark_and_push(collector, span, bit_map, work_queue),
5117    _low_water_mark(MIN2((work_queue->max_elems()/4),
5118                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5119 { }
5120 
5121 // . see if we can share work_queues with ParNew? XXX
5122 void CMSRefProcTaskProxy::do_work_steal(int i,
5123   CMSParDrainMarkingStackClosure* drain,
5124   CMSParKeepAliveClosure* keep_alive,
5125   int* seed) {
5126   OopTaskQueue* work_q = work_queue(i);
5127   NOT_PRODUCT(int num_steals = 0;)
5128   oop obj_to_scan;
5129 
5130   while (true) {
5131     // Completely finish any left over work from (an) earlier round(s)
5132     drain->trim_queue(0);
5133     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5134                                          (size_t)ParGCDesiredObjsFromOverflowList);
5135     // Now check if there's any work in the overflow list
5136     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5137     // only affects the number of attempts made to get work from the
5138     // overflow list and does not affect the number of workers.  Just
5139     // pass ParallelGCThreads so this behavior is unchanged.
5140     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5141                                                 work_q,
5142                                                 ParallelGCThreads)) {
5143       // Found something in global overflow list;
5144       // not yet ready to go stealing work from others.
5145       // We'd like to assert(work_q->size() != 0, ...)
5146       // because we just took work from the overflow list,
5147       // but of course we can't, since all of that might have
5148       // been already stolen from us.
5149       continue;
5150     }
5151     // Verify that we have no work before we resort to stealing
5152     assert(work_q->size() == 0, "Have work, shouldn't steal");
5153     // Try to steal from other queues that have work
5154     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5155       NOT_PRODUCT(num_steals++;)
5156       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5157       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5158       // Do scanning work
5159       obj_to_scan->oop_iterate(keep_alive);
5160       // Loop around, finish this work, and try to steal some more
5161     } else if (terminator()->offer_termination()) {
5162       break;  // nirvana from the infinite cycle
5163     }
5164   }
5165   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5166 }
5167 
5168 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5169 {
5170   GenCollectedHeap* gch = GenCollectedHeap::heap();
5171   WorkGang* workers = gch->workers();
5172   assert(workers != NULL, "Need parallel worker threads.");
5173   CMSRefProcTaskProxy rp_task(task, &_collector,
5174                               _collector.ref_processor()->span(),
5175                               _collector.markBitMap(),
5176                               workers, _collector.task_queues());
5177   workers->run_task(&rp_task);
5178 }
5179 
5180 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5181 {
5182 
5183   GenCollectedHeap* gch = GenCollectedHeap::heap();
5184   WorkGang* workers = gch->workers();
5185   assert(workers != NULL, "Need parallel worker threads.");
5186   CMSRefEnqueueTaskProxy enq_task(task);
5187   workers->run_task(&enq_task);
5188 }
5189 
5190 void CMSCollector::refProcessingWork() {
5191   ResourceMark rm;
5192   HandleMark   hm;
5193 
5194   ReferenceProcessor* rp = ref_processor();
5195   assert(rp->span().equals(_span), "Spans should be equal");
5196   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5197   // Process weak references.
5198   rp->setup_policy(false);
5199   verify_work_stacks_empty();
5200 
5201   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5202                                           &_markStack, false /* !preclean */);
5203   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5204                                 _span, &_markBitMap, &_markStack,
5205                                 &cmsKeepAliveClosure, false /* !preclean */);
5206   {
5207     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5208 
5209     ReferenceProcessorStats stats;
5210     if (rp->processing_is_mt()) {
5211       // Set the degree of MT here.  If the discovery is done MT, there
5212       // may have been a different number of threads doing the discovery
5213       // and a different number of discovered lists may have Ref objects.
5214       // That is OK as long as the Reference lists are balanced (see
5215       // balance_all_queues() and balance_queues()).
5216       GenCollectedHeap* gch = GenCollectedHeap::heap();
5217       uint active_workers = ParallelGCThreads;
5218       WorkGang* workers = gch->workers();
5219       if (workers != NULL) {
5220         active_workers = workers->active_workers();
5221         // The expectation is that active_workers will have already
5222         // been set to a reasonable value.  If it has not been set,
5223         // investigate.
5224         assert(active_workers > 0, "Should have been set during scavenge");
5225       }
5226       rp->set_active_mt_degree(active_workers);
5227       CMSRefProcTaskExecutor task_executor(*this);
5228       stats = rp->process_discovered_references(&_is_alive_closure,
5229                                         &cmsKeepAliveClosure,
5230                                         &cmsDrainMarkingStackClosure,
5231                                         &task_executor,
5232                                         _gc_timer_cm);
5233     } else {
5234       stats = rp->process_discovered_references(&_is_alive_closure,
5235                                         &cmsKeepAliveClosure,
5236                                         &cmsDrainMarkingStackClosure,
5237                                         NULL,
5238                                         _gc_timer_cm);
5239     }
5240     _gc_tracer_cm->report_gc_reference_stats(stats);
5241 
5242   }
5243 
5244   // This is the point where the entire marking should have completed.
5245   verify_work_stacks_empty();
5246 
5247   if (should_unload_classes()) {
5248     {
5249       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5250 
5251       // Unload classes and purge the SystemDictionary.
5252       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5253 
5254       // Unload nmethods.
5255       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5256 
5257       // Prune dead klasses from subklass/sibling/implementor lists.
5258       Klass::clean_weak_klass_links(&_is_alive_closure);
5259     }
5260 
5261     {
5262       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5263       // Clean up unreferenced symbols in symbol table.
5264       SymbolTable::unlink();
5265     }
5266 
5267     {
5268       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5269       // Delete entries for dead interned strings.
5270       StringTable::unlink(&_is_alive_closure);
5271     }
5272   }
5273 
5274 
5275   // Restore any preserved marks as a result of mark stack or
5276   // work queue overflow
5277   restore_preserved_marks_if_any();  // done single-threaded for now
5278 
5279   rp->set_enqueuing_is_done(true);
5280   if (rp->processing_is_mt()) {
5281     rp->balance_all_queues();
5282     CMSRefProcTaskExecutor task_executor(*this);
5283     rp->enqueue_discovered_references(&task_executor);
5284   } else {
5285     rp->enqueue_discovered_references(NULL);
5286   }
5287   rp->verify_no_references_recorded();
5288   assert(!rp->discovery_enabled(), "should have been disabled");
5289 }
5290 
5291 #ifndef PRODUCT
5292 void CMSCollector::check_correct_thread_executing() {
5293   Thread* t = Thread::current();
5294   // Only the VM thread or the CMS thread should be here.
5295   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5296          "Unexpected thread type");
5297   // If this is the vm thread, the foreground process
5298   // should not be waiting.  Note that _foregroundGCIsActive is
5299   // true while the foreground collector is waiting.
5300   if (_foregroundGCShouldWait) {
5301     // We cannot be the VM thread
5302     assert(t->is_ConcurrentGC_thread(),
5303            "Should be CMS thread");
5304   } else {
5305     // We can be the CMS thread only if we are in a stop-world
5306     // phase of CMS collection.
5307     if (t->is_ConcurrentGC_thread()) {
5308       assert(_collectorState == InitialMarking ||
5309              _collectorState == FinalMarking,
5310              "Should be a stop-world phase");
5311       // The CMS thread should be holding the CMS_token.
5312       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5313              "Potential interference with concurrently "
5314              "executing VM thread");
5315     }
5316   }
5317 }
5318 #endif
5319 
5320 void CMSCollector::sweep() {
5321   assert(_collectorState == Sweeping, "just checking");
5322   check_correct_thread_executing();
5323   verify_work_stacks_empty();
5324   verify_overflow_empty();
5325   increment_sweep_count();
5326   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5327 
5328   _inter_sweep_timer.stop();
5329   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5330 
5331   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5332   _intra_sweep_timer.reset();
5333   _intra_sweep_timer.start();
5334   {
5335     GCTraceCPUTime tcpu;
5336     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5337     // First sweep the old gen
5338     {
5339       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5340                                bitMapLock());
5341       sweepWork(_cmsGen);
5342     }
5343 
5344     // Update Universe::_heap_*_at_gc figures.
5345     // We need all the free list locks to make the abstract state
5346     // transition from Sweeping to Resetting. See detailed note
5347     // further below.
5348     {
5349       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5350       // Update heap occupancy information which is used as
5351       // input to soft ref clearing policy at the next gc.
5352       Universe::update_heap_info_at_gc();
5353       _collectorState = Resizing;
5354     }
5355   }
5356   verify_work_stacks_empty();
5357   verify_overflow_empty();
5358 
5359   if (should_unload_classes()) {
5360     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5361     // requires that the virtual spaces are stable and not deleted.
5362     ClassLoaderDataGraph::set_should_purge(true);
5363   }
5364 
5365   _intra_sweep_timer.stop();
5366   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5367 
5368   _inter_sweep_timer.reset();
5369   _inter_sweep_timer.start();
5370 
5371   // We need to use a monotonically non-decreasing time in ms
5372   // or we will see time-warp warnings and os::javaTimeMillis()
5373   // does not guarantee monotonicity.
5374   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5375   update_time_of_last_gc(now);
5376 
5377   // NOTE on abstract state transitions:
5378   // Mutators allocate-live and/or mark the mod-union table dirty
5379   // based on the state of the collection.  The former is done in
5380   // the interval [Marking, Sweeping] and the latter in the interval
5381   // [Marking, Sweeping).  Thus the transitions into the Marking state
5382   // and out of the Sweeping state must be synchronously visible
5383   // globally to the mutators.
5384   // The transition into the Marking state happens with the world
5385   // stopped so the mutators will globally see it.  Sweeping is
5386   // done asynchronously by the background collector so the transition
5387   // from the Sweeping state to the Resizing state must be done
5388   // under the freelistLock (as is the check for whether to
5389   // allocate-live and whether to dirty the mod-union table).
5390   assert(_collectorState == Resizing, "Change of collector state to"
5391     " Resizing must be done under the freelistLocks (plural)");
5392 
5393   // Now that sweeping has been completed, we clear
5394   // the incremental_collection_failed flag,
5395   // thus inviting a younger gen collection to promote into
5396   // this generation. If such a promotion may still fail,
5397   // the flag will be set again when a young collection is
5398   // attempted.
5399   GenCollectedHeap* gch = GenCollectedHeap::heap();
5400   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5401   gch->update_full_collections_completed(_collection_count_start);
5402 }
5403 
5404 // FIX ME!!! Looks like this belongs in CFLSpace, with
5405 // CMSGen merely delegating to it.
5406 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5407   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5408   HeapWord*  minAddr        = _cmsSpace->bottom();
5409   HeapWord*  largestAddr    =
5410     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5411   if (largestAddr == NULL) {
5412     // The dictionary appears to be empty.  In this case
5413     // try to coalesce at the end of the heap.
5414     largestAddr = _cmsSpace->end();
5415   }
5416   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5417   size_t nearLargestOffset =
5418     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5419   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5420                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5421   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5422 }
5423 
5424 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5425   return addr >= _cmsSpace->nearLargestChunk();
5426 }
5427 
5428 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5429   return _cmsSpace->find_chunk_at_end();
5430 }
5431 
5432 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5433                                                     bool full) {
5434   // If the young generation has been collected, gather any statistics
5435   // that are of interest at this point.
5436   bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5437   if (!full && current_is_young) {
5438     // Gather statistics on the young generation collection.
5439     collector()->stats().record_gc0_end(used());
5440   }
5441 }
5442 
5443 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5444   // We iterate over the space(s) underlying this generation,
5445   // checking the mark bit map to see if the bits corresponding
5446   // to specific blocks are marked or not. Blocks that are
5447   // marked are live and are not swept up. All remaining blocks
5448   // are swept up, with coalescing on-the-fly as we sweep up
5449   // contiguous free and/or garbage blocks:
5450   // We need to ensure that the sweeper synchronizes with allocators
5451   // and stop-the-world collectors. In particular, the following
5452   // locks are used:
5453   // . CMS token: if this is held, a stop the world collection cannot occur
5454   // . freelistLock: if this is held no allocation can occur from this
5455   //                 generation by another thread
5456   // . bitMapLock: if this is held, no other thread can access or update
5457   //
5458 
5459   // Note that we need to hold the freelistLock if we use
5460   // block iterate below; else the iterator might go awry if
5461   // a mutator (or promotion) causes block contents to change
5462   // (for instance if the allocator divvies up a block).
5463   // If we hold the free list lock, for all practical purposes
5464   // young generation GC's can't occur (they'll usually need to
5465   // promote), so we might as well prevent all young generation
5466   // GC's while we do a sweeping step. For the same reason, we might
5467   // as well take the bit map lock for the entire duration
5468 
5469   // check that we hold the requisite locks
5470   assert(have_cms_token(), "Should hold cms token");
5471   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5472   assert_lock_strong(old_gen->freelistLock());
5473   assert_lock_strong(bitMapLock());
5474 
5475   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5476   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5477   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5478                                           _inter_sweep_estimate.padded_average(),
5479                                           _intra_sweep_estimate.padded_average());
5480   old_gen->setNearLargestChunk();
5481 
5482   {
5483     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5484     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5485     // We need to free-up/coalesce garbage/blocks from a
5486     // co-terminal free run. This is done in the SweepClosure
5487     // destructor; so, do not remove this scope, else the
5488     // end-of-sweep-census below will be off by a little bit.
5489   }
5490   old_gen->cmsSpace()->sweep_completed();
5491   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5492   if (should_unload_classes()) {                // unloaded classes this cycle,
5493     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5494   } else {                                      // did not unload classes,
5495     _concurrent_cycles_since_last_unload++;     // ... increment count
5496   }
5497 }
5498 
5499 // Reset CMS data structures (for now just the marking bit map)
5500 // preparatory for the next cycle.
5501 void CMSCollector::reset_concurrent() {
5502   CMSTokenSyncWithLocks ts(true, bitMapLock());
5503 
5504   // If the state is not "Resetting", the foreground  thread
5505   // has done a collection and the resetting.
5506   if (_collectorState != Resetting) {
5507     assert(_collectorState == Idling, "The state should only change"
5508       " because the foreground collector has finished the collection");
5509     return;
5510   }
5511 
5512   {
5513     // Clear the mark bitmap (no grey objects to start with)
5514     // for the next cycle.
5515     GCTraceCPUTime tcpu;
5516     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5517 
5518     HeapWord* curAddr = _markBitMap.startWord();
5519     while (curAddr < _markBitMap.endWord()) {
5520       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5521       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5522       _markBitMap.clear_large_range(chunk);
5523       if (ConcurrentMarkSweepThread::should_yield() &&
5524           !foregroundGCIsActive() &&
5525           CMSYield) {
5526         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5527                "CMS thread should hold CMS token");
5528         assert_lock_strong(bitMapLock());
5529         bitMapLock()->unlock();
5530         ConcurrentMarkSweepThread::desynchronize(true);
5531         stopTimer();
5532         incrementYields();
5533 
5534         // See the comment in coordinator_yield()
5535         for (unsigned i = 0; i < CMSYieldSleepCount &&
5536                          ConcurrentMarkSweepThread::should_yield() &&
5537                          !CMSCollector::foregroundGCIsActive(); ++i) {
5538           os::sleep(Thread::current(), 1, false);
5539         }
5540 
5541         ConcurrentMarkSweepThread::synchronize(true);
5542         bitMapLock()->lock_without_safepoint_check();
5543         startTimer();
5544       }
5545       curAddr = chunk.end();
5546     }
5547     // A successful mostly concurrent collection has been done.
5548     // Because only the full (i.e., concurrent mode failure) collections
5549     // are being measured for gc overhead limits, clean the "near" flag
5550     // and count.
5551     size_policy()->reset_gc_overhead_limit_count();
5552     _collectorState = Idling;
5553   }
5554 
5555   register_gc_end();
5556 }
5557 
5558 // Same as above but for STW paths
5559 void CMSCollector::reset_stw() {
5560   // already have the lock
5561   assert(_collectorState == Resetting, "just checking");
5562   assert_lock_strong(bitMapLock());
5563   GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5564   _markBitMap.clear_all();
5565   _collectorState = Idling;
5566   register_gc_end();
5567 }
5568 
5569 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5570   GCTraceCPUTime tcpu;
5571   TraceCollectorStats tcs(counters());
5572 
5573   switch (op) {
5574     case CMS_op_checkpointRootsInitial: {
5575       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5576       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5577       checkpointRootsInitial();
5578       break;
5579     }
5580     case CMS_op_checkpointRootsFinal: {
5581       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5582       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5583       checkpointRootsFinal();
5584       break;
5585     }
5586     default:
5587       fatal("No such CMS_op");
5588   }
5589 }
5590 
5591 #ifndef PRODUCT
5592 size_t const CMSCollector::skip_header_HeapWords() {
5593   return FreeChunk::header_size();
5594 }
5595 
5596 // Try and collect here conditions that should hold when
5597 // CMS thread is exiting. The idea is that the foreground GC
5598 // thread should not be blocked if it wants to terminate
5599 // the CMS thread and yet continue to run the VM for a while
5600 // after that.
5601 void CMSCollector::verify_ok_to_terminate() const {
5602   assert(Thread::current()->is_ConcurrentGC_thread(),
5603          "should be called by CMS thread");
5604   assert(!_foregroundGCShouldWait, "should be false");
5605   // We could check here that all the various low-level locks
5606   // are not held by the CMS thread, but that is overkill; see
5607   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5608   // is checked.
5609 }
5610 #endif
5611 
5612 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5613    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5614           "missing Printezis mark?");
5615   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5616   size_t size = pointer_delta(nextOneAddr + 1, addr);
5617   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5618          "alignment problem");
5619   assert(size >= 3, "Necessary for Printezis marks to work");
5620   return size;
5621 }
5622 
5623 // A variant of the above (block_size_using_printezis_bits()) except
5624 // that we return 0 if the P-bits are not yet set.
5625 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5626   if (_markBitMap.isMarked(addr + 1)) {
5627     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5628     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5629     size_t size = pointer_delta(nextOneAddr + 1, addr);
5630     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5631            "alignment problem");
5632     assert(size >= 3, "Necessary for Printezis marks to work");
5633     return size;
5634   }
5635   return 0;
5636 }
5637 
5638 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5639   size_t sz = 0;
5640   oop p = (oop)addr;
5641   if (p->klass_or_null() != NULL) {
5642     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5643   } else {
5644     sz = block_size_using_printezis_bits(addr);
5645   }
5646   assert(sz > 0, "size must be nonzero");
5647   HeapWord* next_block = addr + sz;
5648   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5649                                              CardTableModRefBS::card_size);
5650   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5651          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5652          "must be different cards");
5653   return next_card;
5654 }
5655 
5656 
5657 // CMS Bit Map Wrapper /////////////////////////////////////////
5658 
5659 // Construct a CMS bit map infrastructure, but don't create the
5660 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5661 // further below.
5662 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5663   _bm(),
5664   _shifter(shifter),
5665   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5666                                     Monitor::_safepoint_check_sometimes) : NULL)
5667 {
5668   _bmStartWord = 0;
5669   _bmWordSize  = 0;
5670 }
5671 
5672 bool CMSBitMap::allocate(MemRegion mr) {
5673   _bmStartWord = mr.start();
5674   _bmWordSize  = mr.word_size();
5675   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5676                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5677   if (!brs.is_reserved()) {
5678     log_warning(gc)("CMS bit map allocation failure");
5679     return false;
5680   }
5681   // For now we'll just commit all of the bit map up front.
5682   // Later on we'll try to be more parsimonious with swap.
5683   if (!_virtual_space.initialize(brs, brs.size())) {
5684     log_warning(gc)("CMS bit map backing store failure");
5685     return false;
5686   }
5687   assert(_virtual_space.committed_size() == brs.size(),
5688          "didn't reserve backing store for all of CMS bit map?");
5689   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5690          _bmWordSize, "inconsistency in bit map sizing");
5691   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5692 
5693   // bm.clear(); // can we rely on getting zero'd memory? verify below
5694   assert(isAllClear(),
5695          "Expected zero'd memory from ReservedSpace constructor");
5696   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5697          "consistency check");
5698   return true;
5699 }
5700 
5701 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5702   HeapWord *next_addr, *end_addr, *last_addr;
5703   assert_locked();
5704   assert(covers(mr), "out-of-range error");
5705   // XXX assert that start and end are appropriately aligned
5706   for (next_addr = mr.start(), end_addr = mr.end();
5707        next_addr < end_addr; next_addr = last_addr) {
5708     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5709     last_addr = dirty_region.end();
5710     if (!dirty_region.is_empty()) {
5711       cl->do_MemRegion(dirty_region);
5712     } else {
5713       assert(last_addr == end_addr, "program logic");
5714       return;
5715     }
5716   }
5717 }
5718 
5719 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5720   _bm.print_on_error(st, prefix);
5721 }
5722 
5723 #ifndef PRODUCT
5724 void CMSBitMap::assert_locked() const {
5725   CMSLockVerifier::assert_locked(lock());
5726 }
5727 
5728 bool CMSBitMap::covers(MemRegion mr) const {
5729   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5730   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5731          "size inconsistency");
5732   return (mr.start() >= _bmStartWord) &&
5733          (mr.end()   <= endWord());
5734 }
5735 
5736 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5737     return (start >= _bmStartWord && (start + size) <= endWord());
5738 }
5739 
5740 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5741   // verify that there are no 1 bits in the interval [left, right)
5742   FalseBitMapClosure falseBitMapClosure;
5743   iterate(&falseBitMapClosure, left, right);
5744 }
5745 
5746 void CMSBitMap::region_invariant(MemRegion mr)
5747 {
5748   assert_locked();
5749   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5750   assert(!mr.is_empty(), "unexpected empty region");
5751   assert(covers(mr), "mr should be covered by bit map");
5752   // convert address range into offset range
5753   size_t start_ofs = heapWordToOffset(mr.start());
5754   // Make sure that end() is appropriately aligned
5755   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5756                         (1 << (_shifter+LogHeapWordSize))),
5757          "Misaligned mr.end()");
5758   size_t end_ofs   = heapWordToOffset(mr.end());
5759   assert(end_ofs > start_ofs, "Should mark at least one bit");
5760 }
5761 
5762 #endif
5763 
5764 bool CMSMarkStack::allocate(size_t size) {
5765   // allocate a stack of the requisite depth
5766   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5767                    size * sizeof(oop)));
5768   if (!rs.is_reserved()) {
5769     log_warning(gc)("CMSMarkStack allocation failure");
5770     return false;
5771   }
5772   if (!_virtual_space.initialize(rs, rs.size())) {
5773     log_warning(gc)("CMSMarkStack backing store failure");
5774     return false;
5775   }
5776   assert(_virtual_space.committed_size() == rs.size(),
5777          "didn't reserve backing store for all of CMS stack?");
5778   _base = (oop*)(_virtual_space.low());
5779   _index = 0;
5780   _capacity = size;
5781   NOT_PRODUCT(_max_depth = 0);
5782   return true;
5783 }
5784 
5785 // XXX FIX ME !!! In the MT case we come in here holding a
5786 // leaf lock. For printing we need to take a further lock
5787 // which has lower rank. We need to recalibrate the two
5788 // lock-ranks involved in order to be able to print the
5789 // messages below. (Or defer the printing to the caller.
5790 // For now we take the expedient path of just disabling the
5791 // messages for the problematic case.)
5792 void CMSMarkStack::expand() {
5793   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5794   if (_capacity == MarkStackSizeMax) {
5795     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5796       // We print a warning message only once per CMS cycle.
5797       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5798     }
5799     return;
5800   }
5801   // Double capacity if possible
5802   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5803   // Do not give up existing stack until we have managed to
5804   // get the double capacity that we desired.
5805   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5806                    new_capacity * sizeof(oop)));
5807   if (rs.is_reserved()) {
5808     // Release the backing store associated with old stack
5809     _virtual_space.release();
5810     // Reinitialize virtual space for new stack
5811     if (!_virtual_space.initialize(rs, rs.size())) {
5812       fatal("Not enough swap for expanded marking stack");
5813     }
5814     _base = (oop*)(_virtual_space.low());
5815     _index = 0;
5816     _capacity = new_capacity;
5817   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5818     // Failed to double capacity, continue;
5819     // we print a detail message only once per CMS cycle.
5820     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5821                         _capacity / K, new_capacity / K);
5822   }
5823 }
5824 
5825 
5826 // Closures
5827 // XXX: there seems to be a lot of code  duplication here;
5828 // should refactor and consolidate common code.
5829 
5830 // This closure is used to mark refs into the CMS generation in
5831 // the CMS bit map. Called at the first checkpoint. This closure
5832 // assumes that we do not need to re-mark dirty cards; if the CMS
5833 // generation on which this is used is not an oldest
5834 // generation then this will lose younger_gen cards!
5835 
5836 MarkRefsIntoClosure::MarkRefsIntoClosure(
5837   MemRegion span, CMSBitMap* bitMap):
5838     _span(span),
5839     _bitMap(bitMap)
5840 {
5841   assert(ref_processor() == NULL, "deliberately left NULL");
5842   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5843 }
5844 
5845 void MarkRefsIntoClosure::do_oop(oop obj) {
5846   // if p points into _span, then mark corresponding bit in _markBitMap
5847   assert(obj->is_oop(), "expected an oop");
5848   HeapWord* addr = (HeapWord*)obj;
5849   if (_span.contains(addr)) {
5850     // this should be made more efficient
5851     _bitMap->mark(addr);
5852   }
5853 }
5854 
5855 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5856 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5857 
5858 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5859   MemRegion span, CMSBitMap* bitMap):
5860     _span(span),
5861     _bitMap(bitMap)
5862 {
5863   assert(ref_processor() == NULL, "deliberately left NULL");
5864   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5865 }
5866 
5867 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5868   // if p points into _span, then mark corresponding bit in _markBitMap
5869   assert(obj->is_oop(), "expected an oop");
5870   HeapWord* addr = (HeapWord*)obj;
5871   if (_span.contains(addr)) {
5872     // this should be made more efficient
5873     _bitMap->par_mark(addr);
5874   }
5875 }
5876 
5877 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5878 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5879 
5880 // A variant of the above, used for CMS marking verification.
5881 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5882   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5883     _span(span),
5884     _verification_bm(verification_bm),
5885     _cms_bm(cms_bm)
5886 {
5887   assert(ref_processor() == NULL, "deliberately left NULL");
5888   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5889 }
5890 
5891 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5892   // if p points into _span, then mark corresponding bit in _markBitMap
5893   assert(obj->is_oop(), "expected an oop");
5894   HeapWord* addr = (HeapWord*)obj;
5895   if (_span.contains(addr)) {
5896     _verification_bm->mark(addr);
5897     if (!_cms_bm->isMarked(addr)) {
5898       Log(gc, verify) log;
5899       ResourceMark rm;
5900       oop(addr)->print_on(log.error_stream());
5901       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5902       fatal("... aborting");
5903     }
5904   }
5905 }
5906 
5907 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5908 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5909 
5910 //////////////////////////////////////////////////
5911 // MarkRefsIntoAndScanClosure
5912 //////////////////////////////////////////////////
5913 
5914 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5915                                                        ReferenceProcessor* rp,
5916                                                        CMSBitMap* bit_map,
5917                                                        CMSBitMap* mod_union_table,
5918                                                        CMSMarkStack*  mark_stack,
5919                                                        CMSCollector* collector,
5920                                                        bool should_yield,
5921                                                        bool concurrent_precleaning):
5922   _collector(collector),
5923   _span(span),
5924   _bit_map(bit_map),
5925   _mark_stack(mark_stack),
5926   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5927                       mark_stack, concurrent_precleaning),
5928   _yield(should_yield),
5929   _concurrent_precleaning(concurrent_precleaning),
5930   _freelistLock(NULL)
5931 {
5932   // FIXME: Should initialize in base class constructor.
5933   assert(rp != NULL, "ref_processor shouldn't be NULL");
5934   set_ref_processor_internal(rp);
5935 }
5936 
5937 // This closure is used to mark refs into the CMS generation at the
5938 // second (final) checkpoint, and to scan and transitively follow
5939 // the unmarked oops. It is also used during the concurrent precleaning
5940 // phase while scanning objects on dirty cards in the CMS generation.
5941 // The marks are made in the marking bit map and the marking stack is
5942 // used for keeping the (newly) grey objects during the scan.
5943 // The parallel version (Par_...) appears further below.
5944 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5945   if (obj != NULL) {
5946     assert(obj->is_oop(), "expected an oop");
5947     HeapWord* addr = (HeapWord*)obj;
5948     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5949     assert(_collector->overflow_list_is_empty(),
5950            "overflow list should be empty");
5951     if (_span.contains(addr) &&
5952         !_bit_map->isMarked(addr)) {
5953       // mark bit map (object is now grey)
5954       _bit_map->mark(addr);
5955       // push on marking stack (stack should be empty), and drain the
5956       // stack by applying this closure to the oops in the oops popped
5957       // from the stack (i.e. blacken the grey objects)
5958       bool res = _mark_stack->push(obj);
5959       assert(res, "Should have space to push on empty stack");
5960       do {
5961         oop new_oop = _mark_stack->pop();
5962         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5963         assert(_bit_map->isMarked((HeapWord*)new_oop),
5964                "only grey objects on this stack");
5965         // iterate over the oops in this oop, marking and pushing
5966         // the ones in CMS heap (i.e. in _span).
5967         new_oop->oop_iterate(&_pushAndMarkClosure);
5968         // check if it's time to yield
5969         do_yield_check();
5970       } while (!_mark_stack->isEmpty() ||
5971                (!_concurrent_precleaning && take_from_overflow_list()));
5972         // if marking stack is empty, and we are not doing this
5973         // during precleaning, then check the overflow list
5974     }
5975     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5976     assert(_collector->overflow_list_is_empty(),
5977            "overflow list was drained above");
5978 
5979     assert(_collector->no_preserved_marks(),
5980            "All preserved marks should have been restored above");
5981   }
5982 }
5983 
5984 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5985 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5986 
5987 void MarkRefsIntoAndScanClosure::do_yield_work() {
5988   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5989          "CMS thread should hold CMS token");
5990   assert_lock_strong(_freelistLock);
5991   assert_lock_strong(_bit_map->lock());
5992   // relinquish the free_list_lock and bitMaplock()
5993   _bit_map->lock()->unlock();
5994   _freelistLock->unlock();
5995   ConcurrentMarkSweepThread::desynchronize(true);
5996   _collector->stopTimer();
5997   _collector->incrementYields();
5998 
5999   // See the comment in coordinator_yield()
6000   for (unsigned i = 0;
6001        i < CMSYieldSleepCount &&
6002        ConcurrentMarkSweepThread::should_yield() &&
6003        !CMSCollector::foregroundGCIsActive();
6004        ++i) {
6005     os::sleep(Thread::current(), 1, false);
6006   }
6007 
6008   ConcurrentMarkSweepThread::synchronize(true);
6009   _freelistLock->lock_without_safepoint_check();
6010   _bit_map->lock()->lock_without_safepoint_check();
6011   _collector->startTimer();
6012 }
6013 
6014 ///////////////////////////////////////////////////////////
6015 // ParMarkRefsIntoAndScanClosure: a parallel version of
6016 //                                MarkRefsIntoAndScanClosure
6017 ///////////////////////////////////////////////////////////
6018 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6019   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6020   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6021   _span(span),
6022   _bit_map(bit_map),
6023   _work_queue(work_queue),
6024   _low_water_mark(MIN2((work_queue->max_elems()/4),
6025                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6026   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6027 {
6028   // FIXME: Should initialize in base class constructor.
6029   assert(rp != NULL, "ref_processor shouldn't be NULL");
6030   set_ref_processor_internal(rp);
6031 }
6032 
6033 // This closure is used to mark refs into the CMS generation at the
6034 // second (final) checkpoint, and to scan and transitively follow
6035 // the unmarked oops. The marks are made in the marking bit map and
6036 // the work_queue is used for keeping the (newly) grey objects during
6037 // the scan phase whence they are also available for stealing by parallel
6038 // threads. Since the marking bit map is shared, updates are
6039 // synchronized (via CAS).
6040 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6041   if (obj != NULL) {
6042     // Ignore mark word because this could be an already marked oop
6043     // that may be chained at the end of the overflow list.
6044     assert(obj->is_oop(true), "expected an oop");
6045     HeapWord* addr = (HeapWord*)obj;
6046     if (_span.contains(addr) &&
6047         !_bit_map->isMarked(addr)) {
6048       // mark bit map (object will become grey):
6049       // It is possible for several threads to be
6050       // trying to "claim" this object concurrently;
6051       // the unique thread that succeeds in marking the
6052       // object first will do the subsequent push on
6053       // to the work queue (or overflow list).
6054       if (_bit_map->par_mark(addr)) {
6055         // push on work_queue (which may not be empty), and trim the
6056         // queue to an appropriate length by applying this closure to
6057         // the oops in the oops popped from the stack (i.e. blacken the
6058         // grey objects)
6059         bool res = _work_queue->push(obj);
6060         assert(res, "Low water mark should be less than capacity?");
6061         trim_queue(_low_water_mark);
6062       } // Else, another thread claimed the object
6063     }
6064   }
6065 }
6066 
6067 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p)       { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6068 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6069 
6070 // This closure is used to rescan the marked objects on the dirty cards
6071 // in the mod union table and the card table proper.
6072 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6073   oop p, MemRegion mr) {
6074 
6075   size_t size = 0;
6076   HeapWord* addr = (HeapWord*)p;
6077   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6078   assert(_span.contains(addr), "we are scanning the CMS generation");
6079   // check if it's time to yield
6080   if (do_yield_check()) {
6081     // We yielded for some foreground stop-world work,
6082     // and we have been asked to abort this ongoing preclean cycle.
6083     return 0;
6084   }
6085   if (_bitMap->isMarked(addr)) {
6086     // it's marked; is it potentially uninitialized?
6087     if (p->klass_or_null() != NULL) {
6088         // an initialized object; ignore mark word in verification below
6089         // since we are running concurrent with mutators
6090         assert(p->is_oop(true), "should be an oop");
6091         if (p->is_objArray()) {
6092           // objArrays are precisely marked; restrict scanning
6093           // to dirty cards only.
6094           size = CompactibleFreeListSpace::adjustObjectSize(
6095                    p->oop_iterate_size(_scanningClosure, mr));
6096         } else {
6097           // A non-array may have been imprecisely marked; we need
6098           // to scan object in its entirety.
6099           size = CompactibleFreeListSpace::adjustObjectSize(
6100                    p->oop_iterate_size(_scanningClosure));
6101         }
6102       #ifdef ASSERT
6103         size_t direct_size =
6104           CompactibleFreeListSpace::adjustObjectSize(p->size());
6105         assert(size == direct_size, "Inconsistency in size");
6106         assert(size >= 3, "Necessary for Printezis marks to work");
6107         HeapWord* start_pbit = addr + 1;
6108         HeapWord* end_pbit = addr + size - 1;
6109         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6110                "inconsistent Printezis mark");
6111         // Verify inner mark bits (between Printezis bits) are clear,
6112         // but don't repeat if there are multiple dirty regions for
6113         // the same object, to avoid potential O(N^2) performance.
6114         if (addr != _last_scanned_object) {
6115           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6116           _last_scanned_object = addr;
6117         }
6118       #endif // ASSERT
6119     } else {
6120       // An uninitialized object.
6121       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6122       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6123       size = pointer_delta(nextOneAddr + 1, addr);
6124       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6125              "alignment problem");
6126       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6127       // will dirty the card when the klass pointer is installed in the
6128       // object (signaling the completion of initialization).
6129     }
6130   } else {
6131     // Either a not yet marked object or an uninitialized object
6132     if (p->klass_or_null() == NULL) {
6133       // An uninitialized object, skip to the next card, since
6134       // we may not be able to read its P-bits yet.
6135       assert(size == 0, "Initial value");
6136     } else {
6137       // An object not (yet) reached by marking: we merely need to
6138       // compute its size so as to go look at the next block.
6139       assert(p->is_oop(true), "should be an oop");
6140       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6141     }
6142   }
6143   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6144   return size;
6145 }
6146 
6147 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6148   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6149          "CMS thread should hold CMS token");
6150   assert_lock_strong(_freelistLock);
6151   assert_lock_strong(_bitMap->lock());
6152   // relinquish the free_list_lock and bitMaplock()
6153   _bitMap->lock()->unlock();
6154   _freelistLock->unlock();
6155   ConcurrentMarkSweepThread::desynchronize(true);
6156   _collector->stopTimer();
6157   _collector->incrementYields();
6158 
6159   // See the comment in coordinator_yield()
6160   for (unsigned i = 0; i < CMSYieldSleepCount &&
6161                    ConcurrentMarkSweepThread::should_yield() &&
6162                    !CMSCollector::foregroundGCIsActive(); ++i) {
6163     os::sleep(Thread::current(), 1, false);
6164   }
6165 
6166   ConcurrentMarkSweepThread::synchronize(true);
6167   _freelistLock->lock_without_safepoint_check();
6168   _bitMap->lock()->lock_without_safepoint_check();
6169   _collector->startTimer();
6170 }
6171 
6172 
6173 //////////////////////////////////////////////////////////////////
6174 // SurvivorSpacePrecleanClosure
6175 //////////////////////////////////////////////////////////////////
6176 // This (single-threaded) closure is used to preclean the oops in
6177 // the survivor spaces.
6178 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6179 
6180   HeapWord* addr = (HeapWord*)p;
6181   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6182   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6183   assert(p->klass_or_null() != NULL, "object should be initialized");
6184   // an initialized object; ignore mark word in verification below
6185   // since we are running concurrent with mutators
6186   assert(p->is_oop(true), "should be an oop");
6187   // Note that we do not yield while we iterate over
6188   // the interior oops of p, pushing the relevant ones
6189   // on our marking stack.
6190   size_t size = p->oop_iterate_size(_scanning_closure);
6191   do_yield_check();
6192   // Observe that below, we do not abandon the preclean
6193   // phase as soon as we should; rather we empty the
6194   // marking stack before returning. This is to satisfy
6195   // some existing assertions. In general, it may be a
6196   // good idea to abort immediately and complete the marking
6197   // from the grey objects at a later time.
6198   while (!_mark_stack->isEmpty()) {
6199     oop new_oop = _mark_stack->pop();
6200     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6201     assert(_bit_map->isMarked((HeapWord*)new_oop),
6202            "only grey objects on this stack");
6203     // iterate over the oops in this oop, marking and pushing
6204     // the ones in CMS heap (i.e. in _span).
6205     new_oop->oop_iterate(_scanning_closure);
6206     // check if it's time to yield
6207     do_yield_check();
6208   }
6209   unsigned int after_count =
6210     GenCollectedHeap::heap()->total_collections();
6211   bool abort = (_before_count != after_count) ||
6212                _collector->should_abort_preclean();
6213   return abort ? 0 : size;
6214 }
6215 
6216 void SurvivorSpacePrecleanClosure::do_yield_work() {
6217   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6218          "CMS thread should hold CMS token");
6219   assert_lock_strong(_bit_map->lock());
6220   // Relinquish the bit map lock
6221   _bit_map->lock()->unlock();
6222   ConcurrentMarkSweepThread::desynchronize(true);
6223   _collector->stopTimer();
6224   _collector->incrementYields();
6225 
6226   // See the comment in coordinator_yield()
6227   for (unsigned i = 0; i < CMSYieldSleepCount &&
6228                        ConcurrentMarkSweepThread::should_yield() &&
6229                        !CMSCollector::foregroundGCIsActive(); ++i) {
6230     os::sleep(Thread::current(), 1, false);
6231   }
6232 
6233   ConcurrentMarkSweepThread::synchronize(true);
6234   _bit_map->lock()->lock_without_safepoint_check();
6235   _collector->startTimer();
6236 }
6237 
6238 // This closure is used to rescan the marked objects on the dirty cards
6239 // in the mod union table and the card table proper. In the parallel
6240 // case, although the bitMap is shared, we do a single read so the
6241 // isMarked() query is "safe".
6242 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6243   // Ignore mark word because we are running concurrent with mutators
6244   assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6245   HeapWord* addr = (HeapWord*)p;
6246   assert(_span.contains(addr), "we are scanning the CMS generation");
6247   bool is_obj_array = false;
6248   #ifdef ASSERT
6249     if (!_parallel) {
6250       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6251       assert(_collector->overflow_list_is_empty(),
6252              "overflow list should be empty");
6253 
6254     }
6255   #endif // ASSERT
6256   if (_bit_map->isMarked(addr)) {
6257     // Obj arrays are precisely marked, non-arrays are not;
6258     // so we scan objArrays precisely and non-arrays in their
6259     // entirety.
6260     if (p->is_objArray()) {
6261       is_obj_array = true;
6262       if (_parallel) {
6263         p->oop_iterate(_par_scan_closure, mr);
6264       } else {
6265         p->oop_iterate(_scan_closure, mr);
6266       }
6267     } else {
6268       if (_parallel) {
6269         p->oop_iterate(_par_scan_closure);
6270       } else {
6271         p->oop_iterate(_scan_closure);
6272       }
6273     }
6274   }
6275   #ifdef ASSERT
6276     if (!_parallel) {
6277       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6278       assert(_collector->overflow_list_is_empty(),
6279              "overflow list should be empty");
6280 
6281     }
6282   #endif // ASSERT
6283   return is_obj_array;
6284 }
6285 
6286 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6287                         MemRegion span,
6288                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6289                         bool should_yield, bool verifying):
6290   _collector(collector),
6291   _span(span),
6292   _bitMap(bitMap),
6293   _mut(&collector->_modUnionTable),
6294   _markStack(markStack),
6295   _yield(should_yield),
6296   _skipBits(0)
6297 {
6298   assert(_markStack->isEmpty(), "stack should be empty");
6299   _finger = _bitMap->startWord();
6300   _threshold = _finger;
6301   assert(_collector->_restart_addr == NULL, "Sanity check");
6302   assert(_span.contains(_finger), "Out of bounds _finger?");
6303   DEBUG_ONLY(_verifying = verifying;)
6304 }
6305 
6306 void MarkFromRootsClosure::reset(HeapWord* addr) {
6307   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6308   assert(_span.contains(addr), "Out of bounds _finger?");
6309   _finger = addr;
6310   _threshold = (HeapWord*)round_to(
6311                  (intptr_t)_finger, CardTableModRefBS::card_size);
6312 }
6313 
6314 // Should revisit to see if this should be restructured for
6315 // greater efficiency.
6316 bool MarkFromRootsClosure::do_bit(size_t offset) {
6317   if (_skipBits > 0) {
6318     _skipBits--;
6319     return true;
6320   }
6321   // convert offset into a HeapWord*
6322   HeapWord* addr = _bitMap->startWord() + offset;
6323   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6324          "address out of range");
6325   assert(_bitMap->isMarked(addr), "tautology");
6326   if (_bitMap->isMarked(addr+1)) {
6327     // this is an allocated but not yet initialized object
6328     assert(_skipBits == 0, "tautology");
6329     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6330     oop p = oop(addr);
6331     if (p->klass_or_null() == NULL) {
6332       DEBUG_ONLY(if (!_verifying) {)
6333         // We re-dirty the cards on which this object lies and increase
6334         // the _threshold so that we'll come back to scan this object
6335         // during the preclean or remark phase. (CMSCleanOnEnter)
6336         if (CMSCleanOnEnter) {
6337           size_t sz = _collector->block_size_using_printezis_bits(addr);
6338           HeapWord* end_card_addr   = (HeapWord*)round_to(
6339                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6340           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6341           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6342           // Bump _threshold to end_card_addr; note that
6343           // _threshold cannot possibly exceed end_card_addr, anyhow.
6344           // This prevents future clearing of the card as the scan proceeds
6345           // to the right.
6346           assert(_threshold <= end_card_addr,
6347                  "Because we are just scanning into this object");
6348           if (_threshold < end_card_addr) {
6349             _threshold = end_card_addr;
6350           }
6351           if (p->klass_or_null() != NULL) {
6352             // Redirty the range of cards...
6353             _mut->mark_range(redirty_range);
6354           } // ...else the setting of klass will dirty the card anyway.
6355         }
6356       DEBUG_ONLY(})
6357       return true;
6358     }
6359   }
6360   scanOopsInOop(addr);
6361   return true;
6362 }
6363 
6364 // We take a break if we've been at this for a while,
6365 // so as to avoid monopolizing the locks involved.
6366 void MarkFromRootsClosure::do_yield_work() {
6367   // First give up the locks, then yield, then re-lock
6368   // We should probably use a constructor/destructor idiom to
6369   // do this unlock/lock or modify the MutexUnlocker class to
6370   // serve our purpose. XXX
6371   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6372          "CMS thread should hold CMS token");
6373   assert_lock_strong(_bitMap->lock());
6374   _bitMap->lock()->unlock();
6375   ConcurrentMarkSweepThread::desynchronize(true);
6376   _collector->stopTimer();
6377   _collector->incrementYields();
6378 
6379   // See the comment in coordinator_yield()
6380   for (unsigned i = 0; i < CMSYieldSleepCount &&
6381                        ConcurrentMarkSweepThread::should_yield() &&
6382                        !CMSCollector::foregroundGCIsActive(); ++i) {
6383     os::sleep(Thread::current(), 1, false);
6384   }
6385 
6386   ConcurrentMarkSweepThread::synchronize(true);
6387   _bitMap->lock()->lock_without_safepoint_check();
6388   _collector->startTimer();
6389 }
6390 
6391 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6392   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6393   assert(_markStack->isEmpty(),
6394          "should drain stack to limit stack usage");
6395   // convert ptr to an oop preparatory to scanning
6396   oop obj = oop(ptr);
6397   // Ignore mark word in verification below, since we
6398   // may be running concurrent with mutators.
6399   assert(obj->is_oop(true), "should be an oop");
6400   assert(_finger <= ptr, "_finger runneth ahead");
6401   // advance the finger to right end of this object
6402   _finger = ptr + obj->size();
6403   assert(_finger > ptr, "we just incremented it above");
6404   // On large heaps, it may take us some time to get through
6405   // the marking phase. During
6406   // this time it's possible that a lot of mutations have
6407   // accumulated in the card table and the mod union table --
6408   // these mutation records are redundant until we have
6409   // actually traced into the corresponding card.
6410   // Here, we check whether advancing the finger would make
6411   // us cross into a new card, and if so clear corresponding
6412   // cards in the MUT (preclean them in the card-table in the
6413   // future).
6414 
6415   DEBUG_ONLY(if (!_verifying) {)
6416     // The clean-on-enter optimization is disabled by default,
6417     // until we fix 6178663.
6418     if (CMSCleanOnEnter && (_finger > _threshold)) {
6419       // [_threshold, _finger) represents the interval
6420       // of cards to be cleared  in MUT (or precleaned in card table).
6421       // The set of cards to be cleared is all those that overlap
6422       // with the interval [_threshold, _finger); note that
6423       // _threshold is always kept card-aligned but _finger isn't
6424       // always card-aligned.
6425       HeapWord* old_threshold = _threshold;
6426       assert(old_threshold == (HeapWord*)round_to(
6427               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6428              "_threshold should always be card-aligned");
6429       _threshold = (HeapWord*)round_to(
6430                      (intptr_t)_finger, CardTableModRefBS::card_size);
6431       MemRegion mr(old_threshold, _threshold);
6432       assert(!mr.is_empty(), "Control point invariant");
6433       assert(_span.contains(mr), "Should clear within span");
6434       _mut->clear_range(mr);
6435     }
6436   DEBUG_ONLY(})
6437   // Note: the finger doesn't advance while we drain
6438   // the stack below.
6439   PushOrMarkClosure pushOrMarkClosure(_collector,
6440                                       _span, _bitMap, _markStack,
6441                                       _finger, this);
6442   bool res = _markStack->push(obj);
6443   assert(res, "Empty non-zero size stack should have space for single push");
6444   while (!_markStack->isEmpty()) {
6445     oop new_oop = _markStack->pop();
6446     // Skip verifying header mark word below because we are
6447     // running concurrent with mutators.
6448     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6449     // now scan this oop's oops
6450     new_oop->oop_iterate(&pushOrMarkClosure);
6451     do_yield_check();
6452   }
6453   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6454 }
6455 
6456 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6457                        CMSCollector* collector, MemRegion span,
6458                        CMSBitMap* bit_map,
6459                        OopTaskQueue* work_queue,
6460                        CMSMarkStack*  overflow_stack):
6461   _collector(collector),
6462   _whole_span(collector->_span),
6463   _span(span),
6464   _bit_map(bit_map),
6465   _mut(&collector->_modUnionTable),
6466   _work_queue(work_queue),
6467   _overflow_stack(overflow_stack),
6468   _skip_bits(0),
6469   _task(task)
6470 {
6471   assert(_work_queue->size() == 0, "work_queue should be empty");
6472   _finger = span.start();
6473   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6474   assert(_span.contains(_finger), "Out of bounds _finger?");
6475 }
6476 
6477 // Should revisit to see if this should be restructured for
6478 // greater efficiency.
6479 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6480   if (_skip_bits > 0) {
6481     _skip_bits--;
6482     return true;
6483   }
6484   // convert offset into a HeapWord*
6485   HeapWord* addr = _bit_map->startWord() + offset;
6486   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6487          "address out of range");
6488   assert(_bit_map->isMarked(addr), "tautology");
6489   if (_bit_map->isMarked(addr+1)) {
6490     // this is an allocated object that might not yet be initialized
6491     assert(_skip_bits == 0, "tautology");
6492     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6493     oop p = oop(addr);
6494     if (p->klass_or_null() == NULL) {
6495       // in the case of Clean-on-Enter optimization, redirty card
6496       // and avoid clearing card by increasing  the threshold.
6497       return true;
6498     }
6499   }
6500   scan_oops_in_oop(addr);
6501   return true;
6502 }
6503 
6504 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6505   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6506   // Should we assert that our work queue is empty or
6507   // below some drain limit?
6508   assert(_work_queue->size() == 0,
6509          "should drain stack to limit stack usage");
6510   // convert ptr to an oop preparatory to scanning
6511   oop obj = oop(ptr);
6512   // Ignore mark word in verification below, since we
6513   // may be running concurrent with mutators.
6514   assert(obj->is_oop(true), "should be an oop");
6515   assert(_finger <= ptr, "_finger runneth ahead");
6516   // advance the finger to right end of this object
6517   _finger = ptr + obj->size();
6518   assert(_finger > ptr, "we just incremented it above");
6519   // On large heaps, it may take us some time to get through
6520   // the marking phase. During
6521   // this time it's possible that a lot of mutations have
6522   // accumulated in the card table and the mod union table --
6523   // these mutation records are redundant until we have
6524   // actually traced into the corresponding card.
6525   // Here, we check whether advancing the finger would make
6526   // us cross into a new card, and if so clear corresponding
6527   // cards in the MUT (preclean them in the card-table in the
6528   // future).
6529 
6530   // The clean-on-enter optimization is disabled by default,
6531   // until we fix 6178663.
6532   if (CMSCleanOnEnter && (_finger > _threshold)) {
6533     // [_threshold, _finger) represents the interval
6534     // of cards to be cleared  in MUT (or precleaned in card table).
6535     // The set of cards to be cleared is all those that overlap
6536     // with the interval [_threshold, _finger); note that
6537     // _threshold is always kept card-aligned but _finger isn't
6538     // always card-aligned.
6539     HeapWord* old_threshold = _threshold;
6540     assert(old_threshold == (HeapWord*)round_to(
6541             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6542            "_threshold should always be card-aligned");
6543     _threshold = (HeapWord*)round_to(
6544                    (intptr_t)_finger, CardTableModRefBS::card_size);
6545     MemRegion mr(old_threshold, _threshold);
6546     assert(!mr.is_empty(), "Control point invariant");
6547     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6548     _mut->clear_range(mr);
6549   }
6550 
6551   // Note: the local finger doesn't advance while we drain
6552   // the stack below, but the global finger sure can and will.
6553   HeapWord** gfa = _task->global_finger_addr();
6554   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6555                                          _span, _bit_map,
6556                                          _work_queue,
6557                                          _overflow_stack,
6558                                          _finger,
6559                                          gfa, this);
6560   bool res = _work_queue->push(obj);   // overflow could occur here
6561   assert(res, "Will hold once we use workqueues");
6562   while (true) {
6563     oop new_oop;
6564     if (!_work_queue->pop_local(new_oop)) {
6565       // We emptied our work_queue; check if there's stuff that can
6566       // be gotten from the overflow stack.
6567       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6568             _overflow_stack, _work_queue)) {
6569         do_yield_check();
6570         continue;
6571       } else {  // done
6572         break;
6573       }
6574     }
6575     // Skip verifying header mark word below because we are
6576     // running concurrent with mutators.
6577     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6578     // now scan this oop's oops
6579     new_oop->oop_iterate(&pushOrMarkClosure);
6580     do_yield_check();
6581   }
6582   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6583 }
6584 
6585 // Yield in response to a request from VM Thread or
6586 // from mutators.
6587 void ParMarkFromRootsClosure::do_yield_work() {
6588   assert(_task != NULL, "sanity");
6589   _task->yield();
6590 }
6591 
6592 // A variant of the above used for verifying CMS marking work.
6593 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6594                         MemRegion span,
6595                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6596                         CMSMarkStack*  mark_stack):
6597   _collector(collector),
6598   _span(span),
6599   _verification_bm(verification_bm),
6600   _cms_bm(cms_bm),
6601   _mark_stack(mark_stack),
6602   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6603                       mark_stack)
6604 {
6605   assert(_mark_stack->isEmpty(), "stack should be empty");
6606   _finger = _verification_bm->startWord();
6607   assert(_collector->_restart_addr == NULL, "Sanity check");
6608   assert(_span.contains(_finger), "Out of bounds _finger?");
6609 }
6610 
6611 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6612   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6613   assert(_span.contains(addr), "Out of bounds _finger?");
6614   _finger = addr;
6615 }
6616 
6617 // Should revisit to see if this should be restructured for
6618 // greater efficiency.
6619 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6620   // convert offset into a HeapWord*
6621   HeapWord* addr = _verification_bm->startWord() + offset;
6622   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6623          "address out of range");
6624   assert(_verification_bm->isMarked(addr), "tautology");
6625   assert(_cms_bm->isMarked(addr), "tautology");
6626 
6627   assert(_mark_stack->isEmpty(),
6628          "should drain stack to limit stack usage");
6629   // convert addr to an oop preparatory to scanning
6630   oop obj = oop(addr);
6631   assert(obj->is_oop(), "should be an oop");
6632   assert(_finger <= addr, "_finger runneth ahead");
6633   // advance the finger to right end of this object
6634   _finger = addr + obj->size();
6635   assert(_finger > addr, "we just incremented it above");
6636   // Note: the finger doesn't advance while we drain
6637   // the stack below.
6638   bool res = _mark_stack->push(obj);
6639   assert(res, "Empty non-zero size stack should have space for single push");
6640   while (!_mark_stack->isEmpty()) {
6641     oop new_oop = _mark_stack->pop();
6642     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6643     // now scan this oop's oops
6644     new_oop->oop_iterate(&_pam_verify_closure);
6645   }
6646   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6647   return true;
6648 }
6649 
6650 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6651   CMSCollector* collector, MemRegion span,
6652   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6653   CMSMarkStack*  mark_stack):
6654   MetadataAwareOopClosure(collector->ref_processor()),
6655   _collector(collector),
6656   _span(span),
6657   _verification_bm(verification_bm),
6658   _cms_bm(cms_bm),
6659   _mark_stack(mark_stack)
6660 { }
6661 
6662 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6663 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6664 
6665 // Upon stack overflow, we discard (part of) the stack,
6666 // remembering the least address amongst those discarded
6667 // in CMSCollector's _restart_address.
6668 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6669   // Remember the least grey address discarded
6670   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6671   _collector->lower_restart_addr(ra);
6672   _mark_stack->reset();  // discard stack contents
6673   _mark_stack->expand(); // expand the stack if possible
6674 }
6675 
6676 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6677   assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6678   HeapWord* addr = (HeapWord*)obj;
6679   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6680     // Oop lies in _span and isn't yet grey or black
6681     _verification_bm->mark(addr);            // now grey
6682     if (!_cms_bm->isMarked(addr)) {
6683       Log(gc, verify) log;
6684       ResourceMark rm;
6685       oop(addr)->print_on(log.error_stream());
6686       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6687       fatal("... aborting");
6688     }
6689 
6690     if (!_mark_stack->push(obj)) { // stack overflow
6691       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6692       assert(_mark_stack->isFull(), "Else push should have succeeded");
6693       handle_stack_overflow(addr);
6694     }
6695     // anything including and to the right of _finger
6696     // will be scanned as we iterate over the remainder of the
6697     // bit map
6698   }
6699 }
6700 
6701 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6702                      MemRegion span,
6703                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6704                      HeapWord* finger, MarkFromRootsClosure* parent) :
6705   MetadataAwareOopClosure(collector->ref_processor()),
6706   _collector(collector),
6707   _span(span),
6708   _bitMap(bitMap),
6709   _markStack(markStack),
6710   _finger(finger),
6711   _parent(parent)
6712 { }
6713 
6714 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6715                                            MemRegion span,
6716                                            CMSBitMap* bit_map,
6717                                            OopTaskQueue* work_queue,
6718                                            CMSMarkStack*  overflow_stack,
6719                                            HeapWord* finger,
6720                                            HeapWord** global_finger_addr,
6721                                            ParMarkFromRootsClosure* parent) :
6722   MetadataAwareOopClosure(collector->ref_processor()),
6723   _collector(collector),
6724   _whole_span(collector->_span),
6725   _span(span),
6726   _bit_map(bit_map),
6727   _work_queue(work_queue),
6728   _overflow_stack(overflow_stack),
6729   _finger(finger),
6730   _global_finger_addr(global_finger_addr),
6731   _parent(parent)
6732 { }
6733 
6734 // Assumes thread-safe access by callers, who are
6735 // responsible for mutual exclusion.
6736 void CMSCollector::lower_restart_addr(HeapWord* low) {
6737   assert(_span.contains(low), "Out of bounds addr");
6738   if (_restart_addr == NULL) {
6739     _restart_addr = low;
6740   } else {
6741     _restart_addr = MIN2(_restart_addr, low);
6742   }
6743 }
6744 
6745 // Upon stack overflow, we discard (part of) the stack,
6746 // remembering the least address amongst those discarded
6747 // in CMSCollector's _restart_address.
6748 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6749   // Remember the least grey address discarded
6750   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6751   _collector->lower_restart_addr(ra);
6752   _markStack->reset();  // discard stack contents
6753   _markStack->expand(); // expand the stack if possible
6754 }
6755 
6756 // Upon stack overflow, we discard (part of) the stack,
6757 // remembering the least address amongst those discarded
6758 // in CMSCollector's _restart_address.
6759 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6760   // We need to do this under a mutex to prevent other
6761   // workers from interfering with the work done below.
6762   MutexLockerEx ml(_overflow_stack->par_lock(),
6763                    Mutex::_no_safepoint_check_flag);
6764   // Remember the least grey address discarded
6765   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6766   _collector->lower_restart_addr(ra);
6767   _overflow_stack->reset();  // discard stack contents
6768   _overflow_stack->expand(); // expand the stack if possible
6769 }
6770 
6771 void PushOrMarkClosure::do_oop(oop obj) {
6772   // Ignore mark word because we are running concurrent with mutators.
6773   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6774   HeapWord* addr = (HeapWord*)obj;
6775   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6776     // Oop lies in _span and isn't yet grey or black
6777     _bitMap->mark(addr);            // now grey
6778     if (addr < _finger) {
6779       // the bit map iteration has already either passed, or
6780       // sampled, this bit in the bit map; we'll need to
6781       // use the marking stack to scan this oop's oops.
6782       bool simulate_overflow = false;
6783       NOT_PRODUCT(
6784         if (CMSMarkStackOverflowALot &&
6785             _collector->simulate_overflow()) {
6786           // simulate a stack overflow
6787           simulate_overflow = true;
6788         }
6789       )
6790       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6791         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6792         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6793         handle_stack_overflow(addr);
6794       }
6795     }
6796     // anything including and to the right of _finger
6797     // will be scanned as we iterate over the remainder of the
6798     // bit map
6799     do_yield_check();
6800   }
6801 }
6802 
6803 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6804 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6805 
6806 void ParPushOrMarkClosure::do_oop(oop obj) {
6807   // Ignore mark word because we are running concurrent with mutators.
6808   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6809   HeapWord* addr = (HeapWord*)obj;
6810   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6811     // Oop lies in _span and isn't yet grey or black
6812     // We read the global_finger (volatile read) strictly after marking oop
6813     bool res = _bit_map->par_mark(addr);    // now grey
6814     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6815     // Should we push this marked oop on our stack?
6816     // -- if someone else marked it, nothing to do
6817     // -- if target oop is above global finger nothing to do
6818     // -- if target oop is in chunk and above local finger
6819     //      then nothing to do
6820     // -- else push on work queue
6821     if (   !res       // someone else marked it, they will deal with it
6822         || (addr >= *gfa)  // will be scanned in a later task
6823         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6824       return;
6825     }
6826     // the bit map iteration has already either passed, or
6827     // sampled, this bit in the bit map; we'll need to
6828     // use the marking stack to scan this oop's oops.
6829     bool simulate_overflow = false;
6830     NOT_PRODUCT(
6831       if (CMSMarkStackOverflowALot &&
6832           _collector->simulate_overflow()) {
6833         // simulate a stack overflow
6834         simulate_overflow = true;
6835       }
6836     )
6837     if (simulate_overflow ||
6838         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6839       // stack overflow
6840       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6841       // We cannot assert that the overflow stack is full because
6842       // it may have been emptied since.
6843       assert(simulate_overflow ||
6844              _work_queue->size() == _work_queue->max_elems(),
6845             "Else push should have succeeded");
6846       handle_stack_overflow(addr);
6847     }
6848     do_yield_check();
6849   }
6850 }
6851 
6852 void ParPushOrMarkClosure::do_oop(oop* p)       { ParPushOrMarkClosure::do_oop_work(p); }
6853 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6854 
6855 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6856                                        MemRegion span,
6857                                        ReferenceProcessor* rp,
6858                                        CMSBitMap* bit_map,
6859                                        CMSBitMap* mod_union_table,
6860                                        CMSMarkStack*  mark_stack,
6861                                        bool           concurrent_precleaning):
6862   MetadataAwareOopClosure(rp),
6863   _collector(collector),
6864   _span(span),
6865   _bit_map(bit_map),
6866   _mod_union_table(mod_union_table),
6867   _mark_stack(mark_stack),
6868   _concurrent_precleaning(concurrent_precleaning)
6869 {
6870   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6871 }
6872 
6873 // Grey object rescan during pre-cleaning and second checkpoint phases --
6874 // the non-parallel version (the parallel version appears further below.)
6875 void PushAndMarkClosure::do_oop(oop obj) {
6876   // Ignore mark word verification. If during concurrent precleaning,
6877   // the object monitor may be locked. If during the checkpoint
6878   // phases, the object may already have been reached by a  different
6879   // path and may be at the end of the global overflow list (so
6880   // the mark word may be NULL).
6881   assert(obj->is_oop_or_null(true /* ignore mark word */),
6882          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6883   HeapWord* addr = (HeapWord*)obj;
6884   // Check if oop points into the CMS generation
6885   // and is not marked
6886   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6887     // a white object ...
6888     _bit_map->mark(addr);         // ... now grey
6889     // push on the marking stack (grey set)
6890     bool simulate_overflow = false;
6891     NOT_PRODUCT(
6892       if (CMSMarkStackOverflowALot &&
6893           _collector->simulate_overflow()) {
6894         // simulate a stack overflow
6895         simulate_overflow = true;
6896       }
6897     )
6898     if (simulate_overflow || !_mark_stack->push(obj)) {
6899       if (_concurrent_precleaning) {
6900          // During precleaning we can just dirty the appropriate card(s)
6901          // in the mod union table, thus ensuring that the object remains
6902          // in the grey set  and continue. In the case of object arrays
6903          // we need to dirty all of the cards that the object spans,
6904          // since the rescan of object arrays will be limited to the
6905          // dirty cards.
6906          // Note that no one can be interfering with us in this action
6907          // of dirtying the mod union table, so no locking or atomics
6908          // are required.
6909          if (obj->is_objArray()) {
6910            size_t sz = obj->size();
6911            HeapWord* end_card_addr = (HeapWord*)round_to(
6912                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6913            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6914            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6915            _mod_union_table->mark_range(redirty_range);
6916          } else {
6917            _mod_union_table->mark(addr);
6918          }
6919          _collector->_ser_pmc_preclean_ovflw++;
6920       } else {
6921          // During the remark phase, we need to remember this oop
6922          // in the overflow list.
6923          _collector->push_on_overflow_list(obj);
6924          _collector->_ser_pmc_remark_ovflw++;
6925       }
6926     }
6927   }
6928 }
6929 
6930 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6931                                              MemRegion span,
6932                                              ReferenceProcessor* rp,
6933                                              CMSBitMap* bit_map,
6934                                              OopTaskQueue* work_queue):
6935   MetadataAwareOopClosure(rp),
6936   _collector(collector),
6937   _span(span),
6938   _bit_map(bit_map),
6939   _work_queue(work_queue)
6940 {
6941   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6942 }
6943 
6944 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6945 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6946 
6947 // Grey object rescan during second checkpoint phase --
6948 // the parallel version.
6949 void ParPushAndMarkClosure::do_oop(oop obj) {
6950   // In the assert below, we ignore the mark word because
6951   // this oop may point to an already visited object that is
6952   // on the overflow stack (in which case the mark word has
6953   // been hijacked for chaining into the overflow stack --
6954   // if this is the last object in the overflow stack then
6955   // its mark word will be NULL). Because this object may
6956   // have been subsequently popped off the global overflow
6957   // stack, and the mark word possibly restored to the prototypical
6958   // value, by the time we get to examined this failing assert in
6959   // the debugger, is_oop_or_null(false) may subsequently start
6960   // to hold.
6961   assert(obj->is_oop_or_null(true),
6962          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6963   HeapWord* addr = (HeapWord*)obj;
6964   // Check if oop points into the CMS generation
6965   // and is not marked
6966   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6967     // a white object ...
6968     // If we manage to "claim" the object, by being the
6969     // first thread to mark it, then we push it on our
6970     // marking stack
6971     if (_bit_map->par_mark(addr)) {     // ... now grey
6972       // push on work queue (grey set)
6973       bool simulate_overflow = false;
6974       NOT_PRODUCT(
6975         if (CMSMarkStackOverflowALot &&
6976             _collector->par_simulate_overflow()) {
6977           // simulate a stack overflow
6978           simulate_overflow = true;
6979         }
6980       )
6981       if (simulate_overflow || !_work_queue->push(obj)) {
6982         _collector->par_push_on_overflow_list(obj);
6983         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6984       }
6985     } // Else, some other thread got there first
6986   }
6987 }
6988 
6989 void ParPushAndMarkClosure::do_oop(oop* p)       { ParPushAndMarkClosure::do_oop_work(p); }
6990 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6991 
6992 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6993   Mutex* bml = _collector->bitMapLock();
6994   assert_lock_strong(bml);
6995   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6996          "CMS thread should hold CMS token");
6997 
6998   bml->unlock();
6999   ConcurrentMarkSweepThread::desynchronize(true);
7000 
7001   _collector->stopTimer();
7002   _collector->incrementYields();
7003 
7004   // See the comment in coordinator_yield()
7005   for (unsigned i = 0; i < CMSYieldSleepCount &&
7006                        ConcurrentMarkSweepThread::should_yield() &&
7007                        !CMSCollector::foregroundGCIsActive(); ++i) {
7008     os::sleep(Thread::current(), 1, false);
7009   }
7010 
7011   ConcurrentMarkSweepThread::synchronize(true);
7012   bml->lock();
7013 
7014   _collector->startTimer();
7015 }
7016 
7017 bool CMSPrecleanRefsYieldClosure::should_return() {
7018   if (ConcurrentMarkSweepThread::should_yield()) {
7019     do_yield_work();
7020   }
7021   return _collector->foregroundGCIsActive();
7022 }
7023 
7024 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7025   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7026          "mr should be aligned to start at a card boundary");
7027   // We'd like to assert:
7028   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7029   //        "mr should be a range of cards");
7030   // However, that would be too strong in one case -- the last
7031   // partition ends at _unallocated_block which, in general, can be
7032   // an arbitrary boundary, not necessarily card aligned.
7033   _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7034   _space->object_iterate_mem(mr, &_scan_cl);
7035 }
7036 
7037 SweepClosure::SweepClosure(CMSCollector* collector,
7038                            ConcurrentMarkSweepGeneration* g,
7039                            CMSBitMap* bitMap, bool should_yield) :
7040   _collector(collector),
7041   _g(g),
7042   _sp(g->cmsSpace()),
7043   _limit(_sp->sweep_limit()),
7044   _freelistLock(_sp->freelistLock()),
7045   _bitMap(bitMap),
7046   _yield(should_yield),
7047   _inFreeRange(false),           // No free range at beginning of sweep
7048   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7049   _lastFreeRangeCoalesced(false),
7050   _freeFinger(g->used_region().start())
7051 {
7052   NOT_PRODUCT(
7053     _numObjectsFreed = 0;
7054     _numWordsFreed   = 0;
7055     _numObjectsLive = 0;
7056     _numWordsLive = 0;
7057     _numObjectsAlreadyFree = 0;
7058     _numWordsAlreadyFree = 0;
7059     _last_fc = NULL;
7060 
7061     _sp->initializeIndexedFreeListArrayReturnedBytes();
7062     _sp->dictionary()->initialize_dict_returned_bytes();
7063   )
7064   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7065          "sweep _limit out of bounds");
7066   log_develop_trace(gc, sweep)("====================");
7067   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7068 }
7069 
7070 void SweepClosure::print_on(outputStream* st) const {
7071   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7072                p2i(_sp->bottom()), p2i(_sp->end()));
7073   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7074   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7075   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7076   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7077                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7078 }
7079 
7080 #ifndef PRODUCT
7081 // Assertion checking only:  no useful work in product mode --
7082 // however, if any of the flags below become product flags,
7083 // you may need to review this code to see if it needs to be
7084 // enabled in product mode.
7085 SweepClosure::~SweepClosure() {
7086   assert_lock_strong(_freelistLock);
7087   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7088          "sweep _limit out of bounds");
7089   if (inFreeRange()) {
7090     Log(gc, sweep) log;
7091     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7092     ResourceMark rm;
7093     print_on(log.error_stream());
7094     ShouldNotReachHere();
7095   }
7096 
7097   if (log_is_enabled(Debug, gc, sweep)) {
7098     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7099                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7100     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7101                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7102     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7103     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7104   }
7105 
7106   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7107     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7108     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7109     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7110     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7111                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7112   }
7113   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7114   log_develop_trace(gc, sweep)("================");
7115 }
7116 #endif  // PRODUCT
7117 
7118 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7119     bool freeRangeInFreeLists) {
7120   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7121                                p2i(freeFinger), freeRangeInFreeLists);
7122   assert(!inFreeRange(), "Trampling existing free range");
7123   set_inFreeRange(true);
7124   set_lastFreeRangeCoalesced(false);
7125 
7126   set_freeFinger(freeFinger);
7127   set_freeRangeInFreeLists(freeRangeInFreeLists);
7128   if (CMSTestInFreeList) {
7129     if (freeRangeInFreeLists) {
7130       FreeChunk* fc = (FreeChunk*) freeFinger;
7131       assert(fc->is_free(), "A chunk on the free list should be free.");
7132       assert(fc->size() > 0, "Free range should have a size");
7133       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7134     }
7135   }
7136 }
7137 
7138 // Note that the sweeper runs concurrently with mutators. Thus,
7139 // it is possible for direct allocation in this generation to happen
7140 // in the middle of the sweep. Note that the sweeper also coalesces
7141 // contiguous free blocks. Thus, unless the sweeper and the allocator
7142 // synchronize appropriately freshly allocated blocks may get swept up.
7143 // This is accomplished by the sweeper locking the free lists while
7144 // it is sweeping. Thus blocks that are determined to be free are
7145 // indeed free. There is however one additional complication:
7146 // blocks that have been allocated since the final checkpoint and
7147 // mark, will not have been marked and so would be treated as
7148 // unreachable and swept up. To prevent this, the allocator marks
7149 // the bit map when allocating during the sweep phase. This leads,
7150 // however, to a further complication -- objects may have been allocated
7151 // but not yet initialized -- in the sense that the header isn't yet
7152 // installed. The sweeper can not then determine the size of the block
7153 // in order to skip over it. To deal with this case, we use a technique
7154 // (due to Printezis) to encode such uninitialized block sizes in the
7155 // bit map. Since the bit map uses a bit per every HeapWord, but the
7156 // CMS generation has a minimum object size of 3 HeapWords, it follows
7157 // that "normal marks" won't be adjacent in the bit map (there will
7158 // always be at least two 0 bits between successive 1 bits). We make use
7159 // of these "unused" bits to represent uninitialized blocks -- the bit
7160 // corresponding to the start of the uninitialized object and the next
7161 // bit are both set. Finally, a 1 bit marks the end of the object that
7162 // started with the two consecutive 1 bits to indicate its potentially
7163 // uninitialized state.
7164 
7165 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7166   FreeChunk* fc = (FreeChunk*)addr;
7167   size_t res;
7168 
7169   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7170   // than "addr == _limit" because although _limit was a block boundary when
7171   // we started the sweep, it may no longer be one because heap expansion
7172   // may have caused us to coalesce the block ending at the address _limit
7173   // with a newly expanded chunk (this happens when _limit was set to the
7174   // previous _end of the space), so we may have stepped past _limit:
7175   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7176   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7177     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7178            "sweep _limit out of bounds");
7179     assert(addr < _sp->end(), "addr out of bounds");
7180     // Flush any free range we might be holding as a single
7181     // coalesced chunk to the appropriate free list.
7182     if (inFreeRange()) {
7183       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7184              "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7185       flush_cur_free_chunk(freeFinger(),
7186                            pointer_delta(addr, freeFinger()));
7187       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7188                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7189                                    lastFreeRangeCoalesced() ? 1 : 0);
7190     }
7191 
7192     // help the iterator loop finish
7193     return pointer_delta(_sp->end(), addr);
7194   }
7195 
7196   assert(addr < _limit, "sweep invariant");
7197   // check if we should yield
7198   do_yield_check(addr);
7199   if (fc->is_free()) {
7200     // Chunk that is already free
7201     res = fc->size();
7202     do_already_free_chunk(fc);
7203     debug_only(_sp->verifyFreeLists());
7204     // If we flush the chunk at hand in lookahead_and_flush()
7205     // and it's coalesced with a preceding chunk, then the
7206     // process of "mangling" the payload of the coalesced block
7207     // will cause erasure of the size information from the
7208     // (erstwhile) header of all the coalesced blocks but the
7209     // first, so the first disjunct in the assert will not hold
7210     // in that specific case (in which case the second disjunct
7211     // will hold).
7212     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7213            "Otherwise the size info doesn't change at this step");
7214     NOT_PRODUCT(
7215       _numObjectsAlreadyFree++;
7216       _numWordsAlreadyFree += res;
7217     )
7218     NOT_PRODUCT(_last_fc = fc;)
7219   } else if (!_bitMap->isMarked(addr)) {
7220     // Chunk is fresh garbage
7221     res = do_garbage_chunk(fc);
7222     debug_only(_sp->verifyFreeLists());
7223     NOT_PRODUCT(
7224       _numObjectsFreed++;
7225       _numWordsFreed += res;
7226     )
7227   } else {
7228     // Chunk that is alive.
7229     res = do_live_chunk(fc);
7230     debug_only(_sp->verifyFreeLists());
7231     NOT_PRODUCT(
7232         _numObjectsLive++;
7233         _numWordsLive += res;
7234     )
7235   }
7236   return res;
7237 }
7238 
7239 // For the smart allocation, record following
7240 //  split deaths - a free chunk is removed from its free list because
7241 //      it is being split into two or more chunks.
7242 //  split birth - a free chunk is being added to its free list because
7243 //      a larger free chunk has been split and resulted in this free chunk.
7244 //  coal death - a free chunk is being removed from its free list because
7245 //      it is being coalesced into a large free chunk.
7246 //  coal birth - a free chunk is being added to its free list because
7247 //      it was created when two or more free chunks where coalesced into
7248 //      this free chunk.
7249 //
7250 // These statistics are used to determine the desired number of free
7251 // chunks of a given size.  The desired number is chosen to be relative
7252 // to the end of a CMS sweep.  The desired number at the end of a sweep
7253 // is the
7254 //      count-at-end-of-previous-sweep (an amount that was enough)
7255 //              - count-at-beginning-of-current-sweep  (the excess)
7256 //              + split-births  (gains in this size during interval)
7257 //              - split-deaths  (demands on this size during interval)
7258 // where the interval is from the end of one sweep to the end of the
7259 // next.
7260 //
7261 // When sweeping the sweeper maintains an accumulated chunk which is
7262 // the chunk that is made up of chunks that have been coalesced.  That
7263 // will be termed the left-hand chunk.  A new chunk of garbage that
7264 // is being considered for coalescing will be referred to as the
7265 // right-hand chunk.
7266 //
7267 // When making a decision on whether to coalesce a right-hand chunk with
7268 // the current left-hand chunk, the current count vs. the desired count
7269 // of the left-hand chunk is considered.  Also if the right-hand chunk
7270 // is near the large chunk at the end of the heap (see
7271 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7272 // left-hand chunk is coalesced.
7273 //
7274 // When making a decision about whether to split a chunk, the desired count
7275 // vs. the current count of the candidate to be split is also considered.
7276 // If the candidate is underpopulated (currently fewer chunks than desired)
7277 // a chunk of an overpopulated (currently more chunks than desired) size may
7278 // be chosen.  The "hint" associated with a free list, if non-null, points
7279 // to a free list which may be overpopulated.
7280 //
7281 
7282 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7283   const size_t size = fc->size();
7284   // Chunks that cannot be coalesced are not in the
7285   // free lists.
7286   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7287     assert(_sp->verify_chunk_in_free_list(fc),
7288            "free chunk should be in free lists");
7289   }
7290   // a chunk that is already free, should not have been
7291   // marked in the bit map
7292   HeapWord* const addr = (HeapWord*) fc;
7293   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7294   // Verify that the bit map has no bits marked between
7295   // addr and purported end of this block.
7296   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7297 
7298   // Some chunks cannot be coalesced under any circumstances.
7299   // See the definition of cantCoalesce().
7300   if (!fc->cantCoalesce()) {
7301     // This chunk can potentially be coalesced.
7302     // All the work is done in
7303     do_post_free_or_garbage_chunk(fc, size);
7304     // Note that if the chunk is not coalescable (the else arm
7305     // below), we unconditionally flush, without needing to do
7306     // a "lookahead," as we do below.
7307     if (inFreeRange()) lookahead_and_flush(fc, size);
7308   } else {
7309     // Code path common to both original and adaptive free lists.
7310 
7311     // cant coalesce with previous block; this should be treated
7312     // as the end of a free run if any
7313     if (inFreeRange()) {
7314       // we kicked some butt; time to pick up the garbage
7315       assert(freeFinger() < addr, "freeFinger points too high");
7316       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7317     }
7318     // else, nothing to do, just continue
7319   }
7320 }
7321 
7322 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7323   // This is a chunk of garbage.  It is not in any free list.
7324   // Add it to a free list or let it possibly be coalesced into
7325   // a larger chunk.
7326   HeapWord* const addr = (HeapWord*) fc;
7327   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7328 
7329   // Verify that the bit map has no bits marked between
7330   // addr and purported end of just dead object.
7331   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7332   do_post_free_or_garbage_chunk(fc, size);
7333 
7334   assert(_limit >= addr + size,
7335          "A freshly garbage chunk can't possibly straddle over _limit");
7336   if (inFreeRange()) lookahead_and_flush(fc, size);
7337   return size;
7338 }
7339 
7340 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7341   HeapWord* addr = (HeapWord*) fc;
7342   // The sweeper has just found a live object. Return any accumulated
7343   // left hand chunk to the free lists.
7344   if (inFreeRange()) {
7345     assert(freeFinger() < addr, "freeFinger points too high");
7346     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7347   }
7348 
7349   // This object is live: we'd normally expect this to be
7350   // an oop, and like to assert the following:
7351   // assert(oop(addr)->is_oop(), "live block should be an oop");
7352   // However, as we commented above, this may be an object whose
7353   // header hasn't yet been initialized.
7354   size_t size;
7355   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7356   if (_bitMap->isMarked(addr + 1)) {
7357     // Determine the size from the bit map, rather than trying to
7358     // compute it from the object header.
7359     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7360     size = pointer_delta(nextOneAddr + 1, addr);
7361     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7362            "alignment problem");
7363 
7364 #ifdef ASSERT
7365       if (oop(addr)->klass_or_null() != NULL) {
7366         // Ignore mark word because we are running concurrent with mutators
7367         assert(oop(addr)->is_oop(true), "live block should be an oop");
7368         Klass* k = oop(addr)->klass();
7369 
7370         // It's not always safe to ask for the size of a j.l.Class object,
7371         // if the Class's oop_size hasn't been set yet.
7372         if (!k->is_instance_klass() ||
7373             !InstanceKlass::cast(k)->is_mirror_instance_klass()) {
7374           assert(size ==
7375                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7376                "P-mark and computed size do not agree");
7377         }
7378       }
7379 #endif
7380 
7381   } else {
7382     // This should be an initialized object that's alive.
7383     assert(oop(addr)->klass_or_null() != NULL,
7384            "Should be an initialized object");
7385     // Ignore mark word because we are running concurrent with mutators
7386     assert(oop(addr)->is_oop(true), "live block should be an oop");
7387     // Verify that the bit map has no bits marked between
7388     // addr and purported end of this block.
7389     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7390     assert(size >= 3, "Necessary for Printezis marks to work");
7391     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7392     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7393   }
7394   return size;
7395 }
7396 
7397 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7398                                                  size_t chunkSize) {
7399   // do_post_free_or_garbage_chunk() should only be called in the case
7400   // of the adaptive free list allocator.
7401   const bool fcInFreeLists = fc->is_free();
7402   assert((HeapWord*)fc <= _limit, "sweep invariant");
7403   if (CMSTestInFreeList && fcInFreeLists) {
7404     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7405   }
7406 
7407   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7408 
7409   HeapWord* const fc_addr = (HeapWord*) fc;
7410 
7411   bool coalesce = false;
7412   const size_t left  = pointer_delta(fc_addr, freeFinger());
7413   const size_t right = chunkSize;
7414   switch (FLSCoalescePolicy) {
7415     // numeric value forms a coalition aggressiveness metric
7416     case 0:  { // never coalesce
7417       coalesce = false;
7418       break;
7419     }
7420     case 1: { // coalesce if left & right chunks on overpopulated lists
7421       coalesce = _sp->coalOverPopulated(left) &&
7422                  _sp->coalOverPopulated(right);
7423       break;
7424     }
7425     case 2: { // coalesce if left chunk on overpopulated list (default)
7426       coalesce = _sp->coalOverPopulated(left);
7427       break;
7428     }
7429     case 3: { // coalesce if left OR right chunk on overpopulated list
7430       coalesce = _sp->coalOverPopulated(left) ||
7431                  _sp->coalOverPopulated(right);
7432       break;
7433     }
7434     case 4: { // always coalesce
7435       coalesce = true;
7436       break;
7437     }
7438     default:
7439      ShouldNotReachHere();
7440   }
7441 
7442   // Should the current free range be coalesced?
7443   // If the chunk is in a free range and either we decided to coalesce above
7444   // or the chunk is near the large block at the end of the heap
7445   // (isNearLargestChunk() returns true), then coalesce this chunk.
7446   const bool doCoalesce = inFreeRange()
7447                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7448   if (doCoalesce) {
7449     // Coalesce the current free range on the left with the new
7450     // chunk on the right.  If either is on a free list,
7451     // it must be removed from the list and stashed in the closure.
7452     if (freeRangeInFreeLists()) {
7453       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7454       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7455              "Size of free range is inconsistent with chunk size.");
7456       if (CMSTestInFreeList) {
7457         assert(_sp->verify_chunk_in_free_list(ffc),
7458                "Chunk is not in free lists");
7459       }
7460       _sp->coalDeath(ffc->size());
7461       _sp->removeFreeChunkFromFreeLists(ffc);
7462       set_freeRangeInFreeLists(false);
7463     }
7464     if (fcInFreeLists) {
7465       _sp->coalDeath(chunkSize);
7466       assert(fc->size() == chunkSize,
7467         "The chunk has the wrong size or is not in the free lists");
7468       _sp->removeFreeChunkFromFreeLists(fc);
7469     }
7470     set_lastFreeRangeCoalesced(true);
7471     print_free_block_coalesced(fc);
7472   } else {  // not in a free range and/or should not coalesce
7473     // Return the current free range and start a new one.
7474     if (inFreeRange()) {
7475       // In a free range but cannot coalesce with the right hand chunk.
7476       // Put the current free range into the free lists.
7477       flush_cur_free_chunk(freeFinger(),
7478                            pointer_delta(fc_addr, freeFinger()));
7479     }
7480     // Set up for new free range.  Pass along whether the right hand
7481     // chunk is in the free lists.
7482     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7483   }
7484 }
7485 
7486 // Lookahead flush:
7487 // If we are tracking a free range, and this is the last chunk that
7488 // we'll look at because its end crosses past _limit, we'll preemptively
7489 // flush it along with any free range we may be holding on to. Note that
7490 // this can be the case only for an already free or freshly garbage
7491 // chunk. If this block is an object, it can never straddle
7492 // over _limit. The "straddling" occurs when _limit is set at
7493 // the previous end of the space when this cycle started, and
7494 // a subsequent heap expansion caused the previously co-terminal
7495 // free block to be coalesced with the newly expanded portion,
7496 // thus rendering _limit a non-block-boundary making it dangerous
7497 // for the sweeper to step over and examine.
7498 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7499   assert(inFreeRange(), "Should only be called if currently in a free range.");
7500   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7501   assert(_sp->used_region().contains(eob - 1),
7502          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7503          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7504          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7505          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7506   if (eob >= _limit) {
7507     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7508     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7509                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7510                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7511                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7512     // Return the storage we are tracking back into the free lists.
7513     log_develop_trace(gc, sweep)("Flushing ... ");
7514     assert(freeFinger() < eob, "Error");
7515     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7516   }
7517 }
7518 
7519 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7520   assert(inFreeRange(), "Should only be called if currently in a free range.");
7521   assert(size > 0,
7522     "A zero sized chunk cannot be added to the free lists.");
7523   if (!freeRangeInFreeLists()) {
7524     if (CMSTestInFreeList) {
7525       FreeChunk* fc = (FreeChunk*) chunk;
7526       fc->set_size(size);
7527       assert(!_sp->verify_chunk_in_free_list(fc),
7528              "chunk should not be in free lists yet");
7529     }
7530     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7531     // A new free range is going to be starting.  The current
7532     // free range has not been added to the free lists yet or
7533     // was removed so add it back.
7534     // If the current free range was coalesced, then the death
7535     // of the free range was recorded.  Record a birth now.
7536     if (lastFreeRangeCoalesced()) {
7537       _sp->coalBirth(size);
7538     }
7539     _sp->addChunkAndRepairOffsetTable(chunk, size,
7540             lastFreeRangeCoalesced());
7541   } else {
7542     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7543   }
7544   set_inFreeRange(false);
7545   set_freeRangeInFreeLists(false);
7546 }
7547 
7548 // We take a break if we've been at this for a while,
7549 // so as to avoid monopolizing the locks involved.
7550 void SweepClosure::do_yield_work(HeapWord* addr) {
7551   // Return current free chunk being used for coalescing (if any)
7552   // to the appropriate freelist.  After yielding, the next
7553   // free block encountered will start a coalescing range of
7554   // free blocks.  If the next free block is adjacent to the
7555   // chunk just flushed, they will need to wait for the next
7556   // sweep to be coalesced.
7557   if (inFreeRange()) {
7558     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7559   }
7560 
7561   // First give up the locks, then yield, then re-lock.
7562   // We should probably use a constructor/destructor idiom to
7563   // do this unlock/lock or modify the MutexUnlocker class to
7564   // serve our purpose. XXX
7565   assert_lock_strong(_bitMap->lock());
7566   assert_lock_strong(_freelistLock);
7567   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7568          "CMS thread should hold CMS token");
7569   _bitMap->lock()->unlock();
7570   _freelistLock->unlock();
7571   ConcurrentMarkSweepThread::desynchronize(true);
7572   _collector->stopTimer();
7573   _collector->incrementYields();
7574 
7575   // See the comment in coordinator_yield()
7576   for (unsigned i = 0; i < CMSYieldSleepCount &&
7577                        ConcurrentMarkSweepThread::should_yield() &&
7578                        !CMSCollector::foregroundGCIsActive(); ++i) {
7579     os::sleep(Thread::current(), 1, false);
7580   }
7581 
7582   ConcurrentMarkSweepThread::synchronize(true);
7583   _freelistLock->lock();
7584   _bitMap->lock()->lock_without_safepoint_check();
7585   _collector->startTimer();
7586 }
7587 
7588 #ifndef PRODUCT
7589 // This is actually very useful in a product build if it can
7590 // be called from the debugger.  Compile it into the product
7591 // as needed.
7592 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7593   return debug_cms_space->verify_chunk_in_free_list(fc);
7594 }
7595 #endif
7596 
7597 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7598   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7599                                p2i(fc), fc->size());
7600 }
7601 
7602 // CMSIsAliveClosure
7603 bool CMSIsAliveClosure::do_object_b(oop obj) {
7604   HeapWord* addr = (HeapWord*)obj;
7605   return addr != NULL &&
7606          (!_span.contains(addr) || _bit_map->isMarked(addr));
7607 }
7608 
7609 
7610 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7611                       MemRegion span,
7612                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7613                       bool cpc):
7614   _collector(collector),
7615   _span(span),
7616   _bit_map(bit_map),
7617   _mark_stack(mark_stack),
7618   _concurrent_precleaning(cpc) {
7619   assert(!_span.is_empty(), "Empty span could spell trouble");
7620 }
7621 
7622 
7623 // CMSKeepAliveClosure: the serial version
7624 void CMSKeepAliveClosure::do_oop(oop obj) {
7625   HeapWord* addr = (HeapWord*)obj;
7626   if (_span.contains(addr) &&
7627       !_bit_map->isMarked(addr)) {
7628     _bit_map->mark(addr);
7629     bool simulate_overflow = false;
7630     NOT_PRODUCT(
7631       if (CMSMarkStackOverflowALot &&
7632           _collector->simulate_overflow()) {
7633         // simulate a stack overflow
7634         simulate_overflow = true;
7635       }
7636     )
7637     if (simulate_overflow || !_mark_stack->push(obj)) {
7638       if (_concurrent_precleaning) {
7639         // We dirty the overflown object and let the remark
7640         // phase deal with it.
7641         assert(_collector->overflow_list_is_empty(), "Error");
7642         // In the case of object arrays, we need to dirty all of
7643         // the cards that the object spans. No locking or atomics
7644         // are needed since no one else can be mutating the mod union
7645         // table.
7646         if (obj->is_objArray()) {
7647           size_t sz = obj->size();
7648           HeapWord* end_card_addr =
7649             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7650           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7651           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7652           _collector->_modUnionTable.mark_range(redirty_range);
7653         } else {
7654           _collector->_modUnionTable.mark(addr);
7655         }
7656         _collector->_ser_kac_preclean_ovflw++;
7657       } else {
7658         _collector->push_on_overflow_list(obj);
7659         _collector->_ser_kac_ovflw++;
7660       }
7661     }
7662   }
7663 }
7664 
7665 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7666 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7667 
7668 // CMSParKeepAliveClosure: a parallel version of the above.
7669 // The work queues are private to each closure (thread),
7670 // but (may be) available for stealing by other threads.
7671 void CMSParKeepAliveClosure::do_oop(oop obj) {
7672   HeapWord* addr = (HeapWord*)obj;
7673   if (_span.contains(addr) &&
7674       !_bit_map->isMarked(addr)) {
7675     // In general, during recursive tracing, several threads
7676     // may be concurrently getting here; the first one to
7677     // "tag" it, claims it.
7678     if (_bit_map->par_mark(addr)) {
7679       bool res = _work_queue->push(obj);
7680       assert(res, "Low water mark should be much less than capacity");
7681       // Do a recursive trim in the hope that this will keep
7682       // stack usage lower, but leave some oops for potential stealers
7683       trim_queue(_low_water_mark);
7684     } // Else, another thread got there first
7685   }
7686 }
7687 
7688 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7689 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7690 
7691 void CMSParKeepAliveClosure::trim_queue(uint max) {
7692   while (_work_queue->size() > max) {
7693     oop new_oop;
7694     if (_work_queue->pop_local(new_oop)) {
7695       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7696       assert(_bit_map->isMarked((HeapWord*)new_oop),
7697              "no white objects on this stack!");
7698       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7699       // iterate over the oops in this oop, marking and pushing
7700       // the ones in CMS heap (i.e. in _span).
7701       new_oop->oop_iterate(&_mark_and_push);
7702     }
7703   }
7704 }
7705 
7706 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7707                                 CMSCollector* collector,
7708                                 MemRegion span, CMSBitMap* bit_map,
7709                                 OopTaskQueue* work_queue):
7710   _collector(collector),
7711   _span(span),
7712   _bit_map(bit_map),
7713   _work_queue(work_queue) { }
7714 
7715 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7716   HeapWord* addr = (HeapWord*)obj;
7717   if (_span.contains(addr) &&
7718       !_bit_map->isMarked(addr)) {
7719     if (_bit_map->par_mark(addr)) {
7720       bool simulate_overflow = false;
7721       NOT_PRODUCT(
7722         if (CMSMarkStackOverflowALot &&
7723             _collector->par_simulate_overflow()) {
7724           // simulate a stack overflow
7725           simulate_overflow = true;
7726         }
7727       )
7728       if (simulate_overflow || !_work_queue->push(obj)) {
7729         _collector->par_push_on_overflow_list(obj);
7730         _collector->_par_kac_ovflw++;
7731       }
7732     } // Else another thread got there already
7733   }
7734 }
7735 
7736 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7737 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7738 
7739 //////////////////////////////////////////////////////////////////
7740 //  CMSExpansionCause                /////////////////////////////
7741 //////////////////////////////////////////////////////////////////
7742 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7743   switch (cause) {
7744     case _no_expansion:
7745       return "No expansion";
7746     case _satisfy_free_ratio:
7747       return "Free ratio";
7748     case _satisfy_promotion:
7749       return "Satisfy promotion";
7750     case _satisfy_allocation:
7751       return "allocation";
7752     case _allocate_par_lab:
7753       return "Par LAB";
7754     case _allocate_par_spooling_space:
7755       return "Par Spooling Space";
7756     case _adaptive_size_policy:
7757       return "Ergonomics";
7758     default:
7759       return "unknown";
7760   }
7761 }
7762 
7763 void CMSDrainMarkingStackClosure::do_void() {
7764   // the max number to take from overflow list at a time
7765   const size_t num = _mark_stack->capacity()/4;
7766   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7767          "Overflow list should be NULL during concurrent phases");
7768   while (!_mark_stack->isEmpty() ||
7769          // if stack is empty, check the overflow list
7770          _collector->take_from_overflow_list(num, _mark_stack)) {
7771     oop obj = _mark_stack->pop();
7772     HeapWord* addr = (HeapWord*)obj;
7773     assert(_span.contains(addr), "Should be within span");
7774     assert(_bit_map->isMarked(addr), "Should be marked");
7775     assert(obj->is_oop(), "Should be an oop");
7776     obj->oop_iterate(_keep_alive);
7777   }
7778 }
7779 
7780 void CMSParDrainMarkingStackClosure::do_void() {
7781   // drain queue
7782   trim_queue(0);
7783 }
7784 
7785 // Trim our work_queue so its length is below max at return
7786 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7787   while (_work_queue->size() > max) {
7788     oop new_oop;
7789     if (_work_queue->pop_local(new_oop)) {
7790       assert(new_oop->is_oop(), "Expected an oop");
7791       assert(_bit_map->isMarked((HeapWord*)new_oop),
7792              "no white objects on this stack!");
7793       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7794       // iterate over the oops in this oop, marking and pushing
7795       // the ones in CMS heap (i.e. in _span).
7796       new_oop->oop_iterate(&_mark_and_push);
7797     }
7798   }
7799 }
7800 
7801 ////////////////////////////////////////////////////////////////////
7802 // Support for Marking Stack Overflow list handling and related code
7803 ////////////////////////////////////////////////////////////////////
7804 // Much of the following code is similar in shape and spirit to the
7805 // code used in ParNewGC. We should try and share that code
7806 // as much as possible in the future.
7807 
7808 #ifndef PRODUCT
7809 // Debugging support for CMSStackOverflowALot
7810 
7811 // It's OK to call this multi-threaded;  the worst thing
7812 // that can happen is that we'll get a bunch of closely
7813 // spaced simulated overflows, but that's OK, in fact
7814 // probably good as it would exercise the overflow code
7815 // under contention.
7816 bool CMSCollector::simulate_overflow() {
7817   if (_overflow_counter-- <= 0) { // just being defensive
7818     _overflow_counter = CMSMarkStackOverflowInterval;
7819     return true;
7820   } else {
7821     return false;
7822   }
7823 }
7824 
7825 bool CMSCollector::par_simulate_overflow() {
7826   return simulate_overflow();
7827 }
7828 #endif
7829 
7830 // Single-threaded
7831 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7832   assert(stack->isEmpty(), "Expected precondition");
7833   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7834   size_t i = num;
7835   oop  cur = _overflow_list;
7836   const markOop proto = markOopDesc::prototype();
7837   NOT_PRODUCT(ssize_t n = 0;)
7838   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7839     next = oop(cur->mark());
7840     cur->set_mark(proto);   // until proven otherwise
7841     assert(cur->is_oop(), "Should be an oop");
7842     bool res = stack->push(cur);
7843     assert(res, "Bit off more than can chew?");
7844     NOT_PRODUCT(n++;)
7845   }
7846   _overflow_list = cur;
7847 #ifndef PRODUCT
7848   assert(_num_par_pushes >= n, "Too many pops?");
7849   _num_par_pushes -=n;
7850 #endif
7851   return !stack->isEmpty();
7852 }
7853 
7854 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7855 // (MT-safe) Get a prefix of at most "num" from the list.
7856 // The overflow list is chained through the mark word of
7857 // each object in the list. We fetch the entire list,
7858 // break off a prefix of the right size and return the
7859 // remainder. If other threads try to take objects from
7860 // the overflow list at that time, they will wait for
7861 // some time to see if data becomes available. If (and
7862 // only if) another thread places one or more object(s)
7863 // on the global list before we have returned the suffix
7864 // to the global list, we will walk down our local list
7865 // to find its end and append the global list to
7866 // our suffix before returning it. This suffix walk can
7867 // prove to be expensive (quadratic in the amount of traffic)
7868 // when there are many objects in the overflow list and
7869 // there is much producer-consumer contention on the list.
7870 // *NOTE*: The overflow list manipulation code here and
7871 // in ParNewGeneration:: are very similar in shape,
7872 // except that in the ParNew case we use the old (from/eden)
7873 // copy of the object to thread the list via its klass word.
7874 // Because of the common code, if you make any changes in
7875 // the code below, please check the ParNew version to see if
7876 // similar changes might be needed.
7877 // CR 6797058 has been filed to consolidate the common code.
7878 bool CMSCollector::par_take_from_overflow_list(size_t num,
7879                                                OopTaskQueue* work_q,
7880                                                int no_of_gc_threads) {
7881   assert(work_q->size() == 0, "First empty local work queue");
7882   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7883   if (_overflow_list == NULL) {
7884     return false;
7885   }
7886   // Grab the entire list; we'll put back a suffix
7887   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7888   Thread* tid = Thread::current();
7889   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7890   // set to ParallelGCThreads.
7891   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7892   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7893   // If the list is busy, we spin for a short while,
7894   // sleeping between attempts to get the list.
7895   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7896     os::sleep(tid, sleep_time_millis, false);
7897     if (_overflow_list == NULL) {
7898       // Nothing left to take
7899       return false;
7900     } else if (_overflow_list != BUSY) {
7901       // Try and grab the prefix
7902       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7903     }
7904   }
7905   // If the list was found to be empty, or we spun long
7906   // enough, we give up and return empty-handed. If we leave
7907   // the list in the BUSY state below, it must be the case that
7908   // some other thread holds the overflow list and will set it
7909   // to a non-BUSY state in the future.
7910   if (prefix == NULL || prefix == BUSY) {
7911      // Nothing to take or waited long enough
7912      if (prefix == NULL) {
7913        // Write back the NULL in case we overwrote it with BUSY above
7914        // and it is still the same value.
7915        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7916      }
7917      return false;
7918   }
7919   assert(prefix != NULL && prefix != BUSY, "Error");
7920   size_t i = num;
7921   oop cur = prefix;
7922   // Walk down the first "num" objects, unless we reach the end.
7923   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7924   if (cur->mark() == NULL) {
7925     // We have "num" or fewer elements in the list, so there
7926     // is nothing to return to the global list.
7927     // Write back the NULL in lieu of the BUSY we wrote
7928     // above, if it is still the same value.
7929     if (_overflow_list == BUSY) {
7930       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7931     }
7932   } else {
7933     // Chop off the suffix and return it to the global list.
7934     assert(cur->mark() != BUSY, "Error");
7935     oop suffix_head = cur->mark(); // suffix will be put back on global list
7936     cur->set_mark(NULL);           // break off suffix
7937     // It's possible that the list is still in the empty(busy) state
7938     // we left it in a short while ago; in that case we may be
7939     // able to place back the suffix without incurring the cost
7940     // of a walk down the list.
7941     oop observed_overflow_list = _overflow_list;
7942     oop cur_overflow_list = observed_overflow_list;
7943     bool attached = false;
7944     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7945       observed_overflow_list =
7946         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7947       if (cur_overflow_list == observed_overflow_list) {
7948         attached = true;
7949         break;
7950       } else cur_overflow_list = observed_overflow_list;
7951     }
7952     if (!attached) {
7953       // Too bad, someone else sneaked in (at least) an element; we'll need
7954       // to do a splice. Find tail of suffix so we can prepend suffix to global
7955       // list.
7956       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7957       oop suffix_tail = cur;
7958       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7959              "Tautology");
7960       observed_overflow_list = _overflow_list;
7961       do {
7962         cur_overflow_list = observed_overflow_list;
7963         if (cur_overflow_list != BUSY) {
7964           // Do the splice ...
7965           suffix_tail->set_mark(markOop(cur_overflow_list));
7966         } else { // cur_overflow_list == BUSY
7967           suffix_tail->set_mark(NULL);
7968         }
7969         // ... and try to place spliced list back on overflow_list ...
7970         observed_overflow_list =
7971           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7972       } while (cur_overflow_list != observed_overflow_list);
7973       // ... until we have succeeded in doing so.
7974     }
7975   }
7976 
7977   // Push the prefix elements on work_q
7978   assert(prefix != NULL, "control point invariant");
7979   const markOop proto = markOopDesc::prototype();
7980   oop next;
7981   NOT_PRODUCT(ssize_t n = 0;)
7982   for (cur = prefix; cur != NULL; cur = next) {
7983     next = oop(cur->mark());
7984     cur->set_mark(proto);   // until proven otherwise
7985     assert(cur->is_oop(), "Should be an oop");
7986     bool res = work_q->push(cur);
7987     assert(res, "Bit off more than we can chew?");
7988     NOT_PRODUCT(n++;)
7989   }
7990 #ifndef PRODUCT
7991   assert(_num_par_pushes >= n, "Too many pops?");
7992   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7993 #endif
7994   return true;
7995 }
7996 
7997 // Single-threaded
7998 void CMSCollector::push_on_overflow_list(oop p) {
7999   NOT_PRODUCT(_num_par_pushes++;)
8000   assert(p->is_oop(), "Not an oop");
8001   preserve_mark_if_necessary(p);
8002   p->set_mark((markOop)_overflow_list);
8003   _overflow_list = p;
8004 }
8005 
8006 // Multi-threaded; use CAS to prepend to overflow list
8007 void CMSCollector::par_push_on_overflow_list(oop p) {
8008   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8009   assert(p->is_oop(), "Not an oop");
8010   par_preserve_mark_if_necessary(p);
8011   oop observed_overflow_list = _overflow_list;
8012   oop cur_overflow_list;
8013   do {
8014     cur_overflow_list = observed_overflow_list;
8015     if (cur_overflow_list != BUSY) {
8016       p->set_mark(markOop(cur_overflow_list));
8017     } else {
8018       p->set_mark(NULL);
8019     }
8020     observed_overflow_list =
8021       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8022   } while (cur_overflow_list != observed_overflow_list);
8023 }
8024 #undef BUSY
8025 
8026 // Single threaded
8027 // General Note on GrowableArray: pushes may silently fail
8028 // because we are (temporarily) out of C-heap for expanding
8029 // the stack. The problem is quite ubiquitous and affects
8030 // a lot of code in the JVM. The prudent thing for GrowableArray
8031 // to do (for now) is to exit with an error. However, that may
8032 // be too draconian in some cases because the caller may be
8033 // able to recover without much harm. For such cases, we
8034 // should probably introduce a "soft_push" method which returns
8035 // an indication of success or failure with the assumption that
8036 // the caller may be able to recover from a failure; code in
8037 // the VM can then be changed, incrementally, to deal with such
8038 // failures where possible, thus, incrementally hardening the VM
8039 // in such low resource situations.
8040 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8041   _preserved_oop_stack.push(p);
8042   _preserved_mark_stack.push(m);
8043   assert(m == p->mark(), "Mark word changed");
8044   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8045          "bijection");
8046 }
8047 
8048 // Single threaded
8049 void CMSCollector::preserve_mark_if_necessary(oop p) {
8050   markOop m = p->mark();
8051   if (m->must_be_preserved(p)) {
8052     preserve_mark_work(p, m);
8053   }
8054 }
8055 
8056 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8057   markOop m = p->mark();
8058   if (m->must_be_preserved(p)) {
8059     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8060     // Even though we read the mark word without holding
8061     // the lock, we are assured that it will not change
8062     // because we "own" this oop, so no other thread can
8063     // be trying to push it on the overflow list; see
8064     // the assertion in preserve_mark_work() that checks
8065     // that m == p->mark().
8066     preserve_mark_work(p, m);
8067   }
8068 }
8069 
8070 // We should be able to do this multi-threaded,
8071 // a chunk of stack being a task (this is
8072 // correct because each oop only ever appears
8073 // once in the overflow list. However, it's
8074 // not very easy to completely overlap this with
8075 // other operations, so will generally not be done
8076 // until all work's been completed. Because we
8077 // expect the preserved oop stack (set) to be small,
8078 // it's probably fine to do this single-threaded.
8079 // We can explore cleverer concurrent/overlapped/parallel
8080 // processing of preserved marks if we feel the
8081 // need for this in the future. Stack overflow should
8082 // be so rare in practice and, when it happens, its
8083 // effect on performance so great that this will
8084 // likely just be in the noise anyway.
8085 void CMSCollector::restore_preserved_marks_if_any() {
8086   assert(SafepointSynchronize::is_at_safepoint(),
8087          "world should be stopped");
8088   assert(Thread::current()->is_ConcurrentGC_thread() ||
8089          Thread::current()->is_VM_thread(),
8090          "should be single-threaded");
8091   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8092          "bijection");
8093 
8094   while (!_preserved_oop_stack.is_empty()) {
8095     oop p = _preserved_oop_stack.pop();
8096     assert(p->is_oop(), "Should be an oop");
8097     assert(_span.contains(p), "oop should be in _span");
8098     assert(p->mark() == markOopDesc::prototype(),
8099            "Set when taken from overflow list");
8100     markOop m = _preserved_mark_stack.pop();
8101     p->set_mark(m);
8102   }
8103   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8104          "stacks were cleared above");
8105 }
8106 
8107 #ifndef PRODUCT
8108 bool CMSCollector::no_preserved_marks() const {
8109   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8110 }
8111 #endif
8112 
8113 // Transfer some number of overflown objects to usual marking
8114 // stack. Return true if some objects were transferred.
8115 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8116   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8117                     (size_t)ParGCDesiredObjsFromOverflowList);
8118 
8119   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8120   assert(_collector->overflow_list_is_empty() || res,
8121          "If list is not empty, we should have taken something");
8122   assert(!res || !_mark_stack->isEmpty(),
8123          "If we took something, it should now be on our stack");
8124   return res;
8125 }
8126 
8127 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8128   size_t res = _sp->block_size_no_stall(addr, _collector);
8129   if (_sp->block_is_obj(addr)) {
8130     if (_live_bit_map->isMarked(addr)) {
8131       // It can't have been dead in a previous cycle
8132       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8133     } else {
8134       _dead_bit_map->mark(addr);      // mark the dead object
8135     }
8136   }
8137   // Could be 0, if the block size could not be computed without stalling.
8138   return res;
8139 }
8140 
8141 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8142 
8143   switch (phase) {
8144     case CMSCollector::InitialMarking:
8145       initialize(true  /* fullGC */ ,
8146                  cause /* cause of the GC */,
8147                  true  /* recordGCBeginTime */,
8148                  true  /* recordPreGCUsage */,
8149                  false /* recordPeakUsage */,
8150                  false /* recordPostGCusage */,
8151                  true  /* recordAccumulatedGCTime */,
8152                  false /* recordGCEndTime */,
8153                  false /* countCollection */  );
8154       break;
8155 
8156     case CMSCollector::FinalMarking:
8157       initialize(true  /* fullGC */ ,
8158                  cause /* cause of the GC */,
8159                  false /* recordGCBeginTime */,
8160                  false /* recordPreGCUsage */,
8161                  false /* recordPeakUsage */,
8162                  false /* recordPostGCusage */,
8163                  true  /* recordAccumulatedGCTime */,
8164                  false /* recordGCEndTime */,
8165                  false /* countCollection */  );
8166       break;
8167 
8168     case CMSCollector::Sweeping:
8169       initialize(true  /* fullGC */ ,
8170                  cause /* cause of the GC */,
8171                  false /* recordGCBeginTime */,
8172                  false /* recordPreGCUsage */,
8173                  true  /* recordPeakUsage */,
8174                  true  /* recordPostGCusage */,
8175                  false /* recordAccumulatedGCTime */,
8176                  true  /* recordGCEndTime */,
8177                  true  /* countCollection */  );
8178       break;
8179 
8180     default:
8181       ShouldNotReachHere();
8182   }
8183 }