rev 11970 : [mq]: base_volatiles

   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.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 the total workers is greater than 1, then multiple workers
2892       // may be used at some time and the initialization has been set
2893       // such that the single threaded path cannot be used.
2894       if (workers->total_workers() > 1) {
2895         workers->run_task(&tsk);
2896       } else {
2897         tsk.work(0);
2898       }
2899     } else {
2900       // The serial version.
2901       CLDToOopClosure cld_closure(&notOlder, true);
2902       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2903 
2904       StrongRootsScope srs(1);
2905 
2906       gch->gen_process_roots(&srs,
2907                              GenCollectedHeap::OldGen,
2908                              true,   // young gen as roots
2909                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2910                              should_unload_classes(),
2911                              &notOlder,
2912                              NULL,
2913                              &cld_closure);
2914     }
2915   }
2916 
2917   // Clear mod-union table; it will be dirtied in the prologue of
2918   // CMS generation per each young generation collection.
2919 
2920   assert(_modUnionTable.isAllClear(),
2921        "Was cleared in most recent final checkpoint phase"
2922        " or no bits are set in the gc_prologue before the start of the next "
2923        "subsequent marking phase.");
2924 
2925   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2926 
2927   // Save the end of the used_region of the constituent generations
2928   // to be used to limit the extent of sweep in each generation.
2929   save_sweep_limits();
2930   verify_overflow_empty();
2931 }
2932 
2933 bool CMSCollector::markFromRoots() {
2934   // we might be tempted to assert that:
2935   // assert(!SafepointSynchronize::is_at_safepoint(),
2936   //        "inconsistent argument?");
2937   // However that wouldn't be right, because it's possible that
2938   // a safepoint is indeed in progress as a young generation
2939   // stop-the-world GC happens even as we mark in this generation.
2940   assert(_collectorState == Marking, "inconsistent state?");
2941   check_correct_thread_executing();
2942   verify_overflow_empty();
2943 
2944   // Weak ref discovery note: We may be discovering weak
2945   // refs in this generation concurrent (but interleaved) with
2946   // weak ref discovery by the young generation collector.
2947 
2948   CMSTokenSyncWithLocks ts(true, bitMapLock());
2949   GCTraceCPUTime tcpu;
2950   CMSPhaseAccounting pa(this, "Concurrent Mark");
2951   bool res = markFromRootsWork();
2952   if (res) {
2953     _collectorState = Precleaning;
2954   } else { // We failed and a foreground collection wants to take over
2955     assert(_foregroundGCIsActive, "internal state inconsistency");
2956     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2957     log_debug(gc)("bailing out to foreground collection");
2958   }
2959   verify_overflow_empty();
2960   return res;
2961 }
2962 
2963 bool CMSCollector::markFromRootsWork() {
2964   // iterate over marked bits in bit map, doing a full scan and mark
2965   // from these roots using the following algorithm:
2966   // . if oop is to the right of the current scan pointer,
2967   //   mark corresponding bit (we'll process it later)
2968   // . else (oop is to left of current scan pointer)
2969   //   push oop on marking stack
2970   // . drain the marking stack
2971 
2972   // Note that when we do a marking step we need to hold the
2973   // bit map lock -- recall that direct allocation (by mutators)
2974   // and promotion (by the young generation collector) is also
2975   // marking the bit map. [the so-called allocate live policy.]
2976   // Because the implementation of bit map marking is not
2977   // robust wrt simultaneous marking of bits in the same word,
2978   // we need to make sure that there is no such interference
2979   // between concurrent such updates.
2980 
2981   // already have locks
2982   assert_lock_strong(bitMapLock());
2983 
2984   verify_work_stacks_empty();
2985   verify_overflow_empty();
2986   bool result = false;
2987   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2988     result = do_marking_mt();
2989   } else {
2990     result = do_marking_st();
2991   }
2992   return result;
2993 }
2994 
2995 // Forward decl
2996 class CMSConcMarkingTask;
2997 
2998 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2999   CMSCollector*       _collector;
3000   CMSConcMarkingTask* _task;
3001  public:
3002   virtual void yield();
3003 
3004   // "n_threads" is the number of threads to be terminated.
3005   // "queue_set" is a set of work queues of other threads.
3006   // "collector" is the CMS collector associated with this task terminator.
3007   // "yield" indicates whether we need the gang as a whole to yield.
3008   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3009     ParallelTaskTerminator(n_threads, queue_set),
3010     _collector(collector) { }
3011 
3012   void set_task(CMSConcMarkingTask* task) {
3013     _task = task;
3014   }
3015 };
3016 
3017 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3018   CMSConcMarkingTask* _task;
3019  public:
3020   bool should_exit_termination();
3021   void set_task(CMSConcMarkingTask* task) {
3022     _task = task;
3023   }
3024 };
3025 
3026 // MT Concurrent Marking Task
3027 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3028   CMSCollector* _collector;
3029   uint          _n_workers;       // requested/desired # workers
3030   bool          _result;
3031   CompactibleFreeListSpace*  _cms_space;
3032   char          _pad_front[64];   // padding to ...
3033   HeapWord*     _global_finger;   // ... avoid sharing cache line
3034   char          _pad_back[64];
3035   HeapWord*     _restart_addr;
3036 
3037   //  Exposed here for yielding support
3038   Mutex* const _bit_map_lock;
3039 
3040   // The per thread work queues, available here for stealing
3041   OopTaskQueueSet*  _task_queues;
3042 
3043   // Termination (and yielding) support
3044   CMSConcMarkingTerminator _term;
3045   CMSConcMarkingTerminatorTerminator _term_term;
3046 
3047  public:
3048   CMSConcMarkingTask(CMSCollector* collector,
3049                  CompactibleFreeListSpace* cms_space,
3050                  YieldingFlexibleWorkGang* workers,
3051                  OopTaskQueueSet* task_queues):
3052     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3053     _collector(collector),
3054     _cms_space(cms_space),
3055     _n_workers(0), _result(true),
3056     _task_queues(task_queues),
3057     _term(_n_workers, task_queues, _collector),
3058     _bit_map_lock(collector->bitMapLock())
3059   {
3060     _requested_size = _n_workers;
3061     _term.set_task(this);
3062     _term_term.set_task(this);
3063     _restart_addr = _global_finger = _cms_space->bottom();
3064   }
3065 
3066 
3067   OopTaskQueueSet* task_queues()  { return _task_queues; }
3068 
3069   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3070 
3071   HeapWord** global_finger_addr() { return &_global_finger; }
3072 
3073   CMSConcMarkingTerminator* terminator() { return &_term; }
3074 
3075   virtual void set_for_termination(uint active_workers) {
3076     terminator()->reset_for_reuse(active_workers);
3077   }
3078 
3079   void work(uint worker_id);
3080   bool should_yield() {
3081     return    ConcurrentMarkSweepThread::should_yield()
3082            && !_collector->foregroundGCIsActive();
3083   }
3084 
3085   virtual void coordinator_yield();  // stuff done by coordinator
3086   bool result() { return _result; }
3087 
3088   void reset(HeapWord* ra) {
3089     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3090     _restart_addr = _global_finger = ra;
3091     _term.reset_for_reuse();
3092   }
3093 
3094   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3095                                            OopTaskQueue* work_q);
3096 
3097  private:
3098   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3099   void do_work_steal(int i);
3100   void bump_global_finger(HeapWord* f);
3101 };
3102 
3103 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3104   assert(_task != NULL, "Error");
3105   return _task->yielding();
3106   // Note that we do not need the disjunct || _task->should_yield() above
3107   // because we want terminating threads to yield only if the task
3108   // is already in the midst of yielding, which happens only after at least one
3109   // thread has yielded.
3110 }
3111 
3112 void CMSConcMarkingTerminator::yield() {
3113   if (_task->should_yield()) {
3114     _task->yield();
3115   } else {
3116     ParallelTaskTerminator::yield();
3117   }
3118 }
3119 
3120 ////////////////////////////////////////////////////////////////
3121 // Concurrent Marking Algorithm Sketch
3122 ////////////////////////////////////////////////////////////////
3123 // Until all tasks exhausted (both spaces):
3124 // -- claim next available chunk
3125 // -- bump global finger via CAS
3126 // -- find first object that starts in this chunk
3127 //    and start scanning bitmap from that position
3128 // -- scan marked objects for oops
3129 // -- CAS-mark target, and if successful:
3130 //    . if target oop is above global finger (volatile read)
3131 //      nothing to do
3132 //    . if target oop is in chunk and above local finger
3133 //        then nothing to do
3134 //    . else push on work-queue
3135 // -- Deal with possible overflow issues:
3136 //    . local work-queue overflow causes stuff to be pushed on
3137 //      global (common) overflow queue
3138 //    . always first empty local work queue
3139 //    . then get a batch of oops from global work queue if any
3140 //    . then do work stealing
3141 // -- When all tasks claimed (both spaces)
3142 //    and local work queue empty,
3143 //    then in a loop do:
3144 //    . check global overflow stack; steal a batch of oops and trace
3145 //    . try to steal from other threads oif GOS is empty
3146 //    . if neither is available, offer termination
3147 // -- Terminate and return result
3148 //
3149 void CMSConcMarkingTask::work(uint worker_id) {
3150   elapsedTimer _timer;
3151   ResourceMark rm;
3152   HandleMark hm;
3153 
3154   DEBUG_ONLY(_collector->verify_overflow_empty();)
3155 
3156   // Before we begin work, our work queue should be empty
3157   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3158   // Scan the bitmap covering _cms_space, tracing through grey objects.
3159   _timer.start();
3160   do_scan_and_mark(worker_id, _cms_space);
3161   _timer.stop();
3162   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3163 
3164   // ... do work stealing
3165   _timer.reset();
3166   _timer.start();
3167   do_work_steal(worker_id);
3168   _timer.stop();
3169   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3170   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3171   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3172   // Note that under the current task protocol, the
3173   // following assertion is true even of the spaces
3174   // expanded since the completion of the concurrent
3175   // marking. XXX This will likely change under a strict
3176   // ABORT semantics.
3177   // After perm removal the comparison was changed to
3178   // greater than or equal to from strictly greater than.
3179   // Before perm removal the highest address sweep would
3180   // have been at the end of perm gen but now is at the
3181   // end of the tenured gen.
3182   assert(_global_finger >=  _cms_space->end(),
3183          "All tasks have been completed");
3184   DEBUG_ONLY(_collector->verify_overflow_empty();)
3185 }
3186 
3187 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3188   HeapWord* read = _global_finger;
3189   HeapWord* cur  = read;
3190   while (f > read) {
3191     cur = read;
3192     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3193     if (cur == read) {
3194       // our cas succeeded
3195       assert(_global_finger >= f, "protocol consistency");
3196       break;
3197     }
3198   }
3199 }
3200 
3201 // This is really inefficient, and should be redone by
3202 // using (not yet available) block-read and -write interfaces to the
3203 // stack and the work_queue. XXX FIX ME !!!
3204 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3205                                                       OopTaskQueue* work_q) {
3206   // Fast lock-free check
3207   if (ovflw_stk->length() == 0) {
3208     return false;
3209   }
3210   assert(work_q->size() == 0, "Shouldn't steal");
3211   MutexLockerEx ml(ovflw_stk->par_lock(),
3212                    Mutex::_no_safepoint_check_flag);
3213   // Grab up to 1/4 the size of the work queue
3214   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3215                     (size_t)ParGCDesiredObjsFromOverflowList);
3216   num = MIN2(num, ovflw_stk->length());
3217   for (int i = (int) num; i > 0; i--) {
3218     oop cur = ovflw_stk->pop();
3219     assert(cur != NULL, "Counted wrong?");
3220     work_q->push(cur);
3221   }
3222   return num > 0;
3223 }
3224 
3225 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3226   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3227   int n_tasks = pst->n_tasks();
3228   // We allow that there may be no tasks to do here because
3229   // we are restarting after a stack overflow.
3230   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3231   uint nth_task = 0;
3232 
3233   HeapWord* aligned_start = sp->bottom();
3234   if (sp->used_region().contains(_restart_addr)) {
3235     // Align down to a card boundary for the start of 0th task
3236     // for this space.
3237     aligned_start =
3238       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3239                                  CardTableModRefBS::card_size);
3240   }
3241 
3242   size_t chunk_size = sp->marking_task_size();
3243   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3244     // Having claimed the nth task in this space,
3245     // compute the chunk that it corresponds to:
3246     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3247                                aligned_start + (nth_task+1)*chunk_size);
3248     // Try and bump the global finger via a CAS;
3249     // note that we need to do the global finger bump
3250     // _before_ taking the intersection below, because
3251     // the task corresponding to that region will be
3252     // deemed done even if the used_region() expands
3253     // because of allocation -- as it almost certainly will
3254     // during start-up while the threads yield in the
3255     // closure below.
3256     HeapWord* finger = span.end();
3257     bump_global_finger(finger);   // atomically
3258     // There are null tasks here corresponding to chunks
3259     // beyond the "top" address of the space.
3260     span = span.intersection(sp->used_region());
3261     if (!span.is_empty()) {  // Non-null task
3262       HeapWord* prev_obj;
3263       assert(!span.contains(_restart_addr) || nth_task == 0,
3264              "Inconsistency");
3265       if (nth_task == 0) {
3266         // For the 0th task, we'll not need to compute a block_start.
3267         if (span.contains(_restart_addr)) {
3268           // In the case of a restart because of stack overflow,
3269           // we might additionally skip a chunk prefix.
3270           prev_obj = _restart_addr;
3271         } else {
3272           prev_obj = span.start();
3273         }
3274       } else {
3275         // We want to skip the first object because
3276         // the protocol is to scan any object in its entirety
3277         // that _starts_ in this span; a fortiori, any
3278         // object starting in an earlier span is scanned
3279         // as part of an earlier claimed task.
3280         // Below we use the "careful" version of block_start
3281         // so we do not try to navigate uninitialized objects.
3282         prev_obj = sp->block_start_careful(span.start());
3283         // Below we use a variant of block_size that uses the
3284         // Printezis bits to avoid waiting for allocated
3285         // objects to become initialized/parsable.
3286         while (prev_obj < span.start()) {
3287           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3288           if (sz > 0) {
3289             prev_obj += sz;
3290           } else {
3291             // In this case we may end up doing a bit of redundant
3292             // scanning, but that appears unavoidable, short of
3293             // locking the free list locks; see bug 6324141.
3294             break;
3295           }
3296         }
3297       }
3298       if (prev_obj < span.end()) {
3299         MemRegion my_span = MemRegion(prev_obj, span.end());
3300         // Do the marking work within a non-empty span --
3301         // the last argument to the constructor indicates whether the
3302         // iteration should be incremental with periodic yields.
3303         ParMarkFromRootsClosure cl(this, _collector, my_span,
3304                                    &_collector->_markBitMap,
3305                                    work_queue(i),
3306                                    &_collector->_markStack);
3307         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3308       } // else nothing to do for this task
3309     }   // else nothing to do for this task
3310   }
3311   // We'd be tempted to assert here that since there are no
3312   // more tasks left to claim in this space, the global_finger
3313   // must exceed space->top() and a fortiori space->end(). However,
3314   // that would not quite be correct because the bumping of
3315   // global_finger occurs strictly after the claiming of a task,
3316   // so by the time we reach here the global finger may not yet
3317   // have been bumped up by the thread that claimed the last
3318   // task.
3319   pst->all_tasks_completed();
3320 }
3321 
3322 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3323  private:
3324   CMSCollector* _collector;
3325   CMSConcMarkingTask* _task;
3326   MemRegion     _span;
3327   CMSBitMap*    _bit_map;
3328   CMSMarkStack* _overflow_stack;
3329   OopTaskQueue* _work_queue;
3330  protected:
3331   DO_OOP_WORK_DEFN
3332  public:
3333   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3334                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3335     MetadataAwareOopClosure(collector->ref_processor()),
3336     _collector(collector),
3337     _task(task),
3338     _span(collector->_span),
3339     _work_queue(work_queue),
3340     _bit_map(bit_map),
3341     _overflow_stack(overflow_stack)
3342   { }
3343   virtual void do_oop(oop* p);
3344   virtual void do_oop(narrowOop* p);
3345 
3346   void trim_queue(size_t max);
3347   void handle_stack_overflow(HeapWord* lost);
3348   void do_yield_check() {
3349     if (_task->should_yield()) {
3350       _task->yield();
3351     }
3352   }
3353 };
3354 
3355 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3356 
3357 // Grey object scanning during work stealing phase --
3358 // the salient assumption here is that any references
3359 // that are in these stolen objects being scanned must
3360 // already have been initialized (else they would not have
3361 // been published), so we do not need to check for
3362 // uninitialized objects before pushing here.
3363 void ParConcMarkingClosure::do_oop(oop obj) {
3364   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3365   HeapWord* addr = (HeapWord*)obj;
3366   // Check if oop points into the CMS generation
3367   // and is not marked
3368   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3369     // a white object ...
3370     // If we manage to "claim" the object, by being the
3371     // first thread to mark it, then we push it on our
3372     // marking stack
3373     if (_bit_map->par_mark(addr)) {     // ... now grey
3374       // push on work queue (grey set)
3375       bool simulate_overflow = false;
3376       NOT_PRODUCT(
3377         if (CMSMarkStackOverflowALot &&
3378             _collector->simulate_overflow()) {
3379           // simulate a stack overflow
3380           simulate_overflow = true;
3381         }
3382       )
3383       if (simulate_overflow ||
3384           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3385         // stack overflow
3386         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3387         // We cannot assert that the overflow stack is full because
3388         // it may have been emptied since.
3389         assert(simulate_overflow ||
3390                _work_queue->size() == _work_queue->max_elems(),
3391               "Else push should have succeeded");
3392         handle_stack_overflow(addr);
3393       }
3394     } // Else, some other thread got there first
3395     do_yield_check();
3396   }
3397 }
3398 
3399 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3400 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3401 
3402 void ParConcMarkingClosure::trim_queue(size_t max) {
3403   while (_work_queue->size() > max) {
3404     oop new_oop;
3405     if (_work_queue->pop_local(new_oop)) {
3406       assert(new_oop->is_oop(), "Should be an oop");
3407       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3408       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3409       new_oop->oop_iterate(this);  // do_oop() above
3410       do_yield_check();
3411     }
3412   }
3413 }
3414 
3415 // Upon stack overflow, we discard (part of) the stack,
3416 // remembering the least address amongst those discarded
3417 // in CMSCollector's _restart_address.
3418 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3419   // We need to do this under a mutex to prevent other
3420   // workers from interfering with the work done below.
3421   MutexLockerEx ml(_overflow_stack->par_lock(),
3422                    Mutex::_no_safepoint_check_flag);
3423   // Remember the least grey address discarded
3424   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3425   _collector->lower_restart_addr(ra);
3426   _overflow_stack->reset();  // discard stack contents
3427   _overflow_stack->expand(); // expand the stack if possible
3428 }
3429 
3430 
3431 void CMSConcMarkingTask::do_work_steal(int i) {
3432   OopTaskQueue* work_q = work_queue(i);
3433   oop obj_to_scan;
3434   CMSBitMap* bm = &(_collector->_markBitMap);
3435   CMSMarkStack* ovflw = &(_collector->_markStack);
3436   int* seed = _collector->hash_seed(i);
3437   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3438   while (true) {
3439     cl.trim_queue(0);
3440     assert(work_q->size() == 0, "Should have been emptied above");
3441     if (get_work_from_overflow_stack(ovflw, work_q)) {
3442       // Can't assert below because the work obtained from the
3443       // overflow stack may already have been stolen from us.
3444       // assert(work_q->size() > 0, "Work from overflow stack");
3445       continue;
3446     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3447       assert(obj_to_scan->is_oop(), "Should be an oop");
3448       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3449       obj_to_scan->oop_iterate(&cl);
3450     } else if (terminator()->offer_termination(&_term_term)) {
3451       assert(work_q->size() == 0, "Impossible!");
3452       break;
3453     } else if (yielding() || should_yield()) {
3454       yield();
3455     }
3456   }
3457 }
3458 
3459 // This is run by the CMS (coordinator) thread.
3460 void CMSConcMarkingTask::coordinator_yield() {
3461   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3462          "CMS thread should hold CMS token");
3463   // First give up the locks, then yield, then re-lock
3464   // We should probably use a constructor/destructor idiom to
3465   // do this unlock/lock or modify the MutexUnlocker class to
3466   // serve our purpose. XXX
3467   assert_lock_strong(_bit_map_lock);
3468   _bit_map_lock->unlock();
3469   ConcurrentMarkSweepThread::desynchronize(true);
3470   _collector->stopTimer();
3471   _collector->incrementYields();
3472 
3473   // It is possible for whichever thread initiated the yield request
3474   // not to get a chance to wake up and take the bitmap lock between
3475   // this thread releasing it and reacquiring it. So, while the
3476   // should_yield() flag is on, let's sleep for a bit to give the
3477   // other thread a chance to wake up. The limit imposed on the number
3478   // of iterations is defensive, to avoid any unforseen circumstances
3479   // putting us into an infinite loop. Since it's always been this
3480   // (coordinator_yield()) method that was observed to cause the
3481   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3482   // which is by default non-zero. For the other seven methods that
3483   // also perform the yield operation, as are using a different
3484   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3485   // can enable the sleeping for those methods too, if necessary.
3486   // See 6442774.
3487   //
3488   // We really need to reconsider the synchronization between the GC
3489   // thread and the yield-requesting threads in the future and we
3490   // should really use wait/notify, which is the recommended
3491   // way of doing this type of interaction. Additionally, we should
3492   // consolidate the eight methods that do the yield operation and they
3493   // are almost identical into one for better maintainability and
3494   // readability. See 6445193.
3495   //
3496   // Tony 2006.06.29
3497   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3498                    ConcurrentMarkSweepThread::should_yield() &&
3499                    !CMSCollector::foregroundGCIsActive(); ++i) {
3500     os::sleep(Thread::current(), 1, false);
3501   }
3502 
3503   ConcurrentMarkSweepThread::synchronize(true);
3504   _bit_map_lock->lock_without_safepoint_check();
3505   _collector->startTimer();
3506 }
3507 
3508 bool CMSCollector::do_marking_mt() {
3509   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3510   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3511                                                                   conc_workers()->active_workers(),
3512                                                                   Threads::number_of_non_daemon_threads());
3513   num_workers = conc_workers()->update_active_workers(num_workers);
3514   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3515 
3516   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3517 
3518   CMSConcMarkingTask tsk(this,
3519                          cms_space,
3520                          conc_workers(),
3521                          task_queues());
3522 
3523   // Since the actual number of workers we get may be different
3524   // from the number we requested above, do we need to do anything different
3525   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3526   // class?? XXX
3527   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3528 
3529   // Refs discovery is already non-atomic.
3530   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3531   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3532   conc_workers()->start_task(&tsk);
3533   while (tsk.yielded()) {
3534     tsk.coordinator_yield();
3535     conc_workers()->continue_task(&tsk);
3536   }
3537   // If the task was aborted, _restart_addr will be non-NULL
3538   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3539   while (_restart_addr != NULL) {
3540     // XXX For now we do not make use of ABORTED state and have not
3541     // yet implemented the right abort semantics (even in the original
3542     // single-threaded CMS case). That needs some more investigation
3543     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3544     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3545     // If _restart_addr is non-NULL, a marking stack overflow
3546     // occurred; we need to do a fresh marking iteration from the
3547     // indicated restart address.
3548     if (_foregroundGCIsActive) {
3549       // We may be running into repeated stack overflows, having
3550       // reached the limit of the stack size, while making very
3551       // slow forward progress. It may be best to bail out and
3552       // let the foreground collector do its job.
3553       // Clear _restart_addr, so that foreground GC
3554       // works from scratch. This avoids the headache of
3555       // a "rescan" which would otherwise be needed because
3556       // of the dirty mod union table & card table.
3557       _restart_addr = NULL;
3558       return false;
3559     }
3560     // Adjust the task to restart from _restart_addr
3561     tsk.reset(_restart_addr);
3562     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3563                   _restart_addr);
3564     _restart_addr = NULL;
3565     // Get the workers going again
3566     conc_workers()->start_task(&tsk);
3567     while (tsk.yielded()) {
3568       tsk.coordinator_yield();
3569       conc_workers()->continue_task(&tsk);
3570     }
3571   }
3572   assert(tsk.completed(), "Inconsistency");
3573   assert(tsk.result() == true, "Inconsistency");
3574   return true;
3575 }
3576 
3577 bool CMSCollector::do_marking_st() {
3578   ResourceMark rm;
3579   HandleMark   hm;
3580 
3581   // Temporarily make refs discovery single threaded (non-MT)
3582   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3583   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3584     &_markStack, CMSYield);
3585   // the last argument to iterate indicates whether the iteration
3586   // should be incremental with periodic yields.
3587   _markBitMap.iterate(&markFromRootsClosure);
3588   // If _restart_addr is non-NULL, a marking stack overflow
3589   // occurred; we need to do a fresh iteration from the
3590   // indicated restart address.
3591   while (_restart_addr != NULL) {
3592     if (_foregroundGCIsActive) {
3593       // We may be running into repeated stack overflows, having
3594       // reached the limit of the stack size, while making very
3595       // slow forward progress. It may be best to bail out and
3596       // let the foreground collector do its job.
3597       // Clear _restart_addr, so that foreground GC
3598       // works from scratch. This avoids the headache of
3599       // a "rescan" which would otherwise be needed because
3600       // of the dirty mod union table & card table.
3601       _restart_addr = NULL;
3602       return false;  // indicating failure to complete marking
3603     }
3604     // Deal with stack overflow:
3605     // we restart marking from _restart_addr
3606     HeapWord* ra = _restart_addr;
3607     markFromRootsClosure.reset(ra);
3608     _restart_addr = NULL;
3609     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3610   }
3611   return true;
3612 }
3613 
3614 void CMSCollector::preclean() {
3615   check_correct_thread_executing();
3616   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3617   verify_work_stacks_empty();
3618   verify_overflow_empty();
3619   _abort_preclean = false;
3620   if (CMSPrecleaningEnabled) {
3621     if (!CMSEdenChunksRecordAlways) {
3622       _eden_chunk_index = 0;
3623     }
3624     size_t used = get_eden_used();
3625     size_t capacity = get_eden_capacity();
3626     // Don't start sampling unless we will get sufficiently
3627     // many samples.
3628     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3629                 * CMSScheduleRemarkEdenPenetration)) {
3630       _start_sampling = true;
3631     } else {
3632       _start_sampling = false;
3633     }
3634     GCTraceCPUTime tcpu;
3635     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3636     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3637   }
3638   CMSTokenSync x(true); // is cms thread
3639   if (CMSPrecleaningEnabled) {
3640     sample_eden();
3641     _collectorState = AbortablePreclean;
3642   } else {
3643     _collectorState = FinalMarking;
3644   }
3645   verify_work_stacks_empty();
3646   verify_overflow_empty();
3647 }
3648 
3649 // Try and schedule the remark such that young gen
3650 // occupancy is CMSScheduleRemarkEdenPenetration %.
3651 void CMSCollector::abortable_preclean() {
3652   check_correct_thread_executing();
3653   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3654   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3655 
3656   // If Eden's current occupancy is below this threshold,
3657   // immediately schedule the remark; else preclean
3658   // past the next scavenge in an effort to
3659   // schedule the pause as described above. By choosing
3660   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3661   // we will never do an actual abortable preclean cycle.
3662   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3663     GCTraceCPUTime tcpu;
3664     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3665     // We need more smarts in the abortable preclean
3666     // loop below to deal with cases where allocation
3667     // in young gen is very very slow, and our precleaning
3668     // is running a losing race against a horde of
3669     // mutators intent on flooding us with CMS updates
3670     // (dirty cards).
3671     // One, admittedly dumb, strategy is to give up
3672     // after a certain number of abortable precleaning loops
3673     // or after a certain maximum time. We want to make
3674     // this smarter in the next iteration.
3675     // XXX FIX ME!!! YSR
3676     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3677     while (!(should_abort_preclean() ||
3678              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3679       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3680       cumworkdone += workdone;
3681       loops++;
3682       // Voluntarily terminate abortable preclean phase if we have
3683       // been at it for too long.
3684       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3685           loops >= CMSMaxAbortablePrecleanLoops) {
3686         log_debug(gc)(" CMS: abort preclean due to loops ");
3687         break;
3688       }
3689       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3690         log_debug(gc)(" CMS: abort preclean due to time ");
3691         break;
3692       }
3693       // If we are doing little work each iteration, we should
3694       // take a short break.
3695       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3696         // Sleep for some time, waiting for work to accumulate
3697         stopTimer();
3698         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3699         startTimer();
3700         waited++;
3701       }
3702     }
3703     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3704                                loops, waited, cumworkdone);
3705   }
3706   CMSTokenSync x(true); // is cms thread
3707   if (_collectorState != Idling) {
3708     assert(_collectorState == AbortablePreclean,
3709            "Spontaneous state transition?");
3710     _collectorState = FinalMarking;
3711   } // Else, a foreground collection completed this CMS cycle.
3712   return;
3713 }
3714 
3715 // Respond to an Eden sampling opportunity
3716 void CMSCollector::sample_eden() {
3717   // Make sure a young gc cannot sneak in between our
3718   // reading and recording of a sample.
3719   assert(Thread::current()->is_ConcurrentGC_thread(),
3720          "Only the cms thread may collect Eden samples");
3721   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3722          "Should collect samples while holding CMS token");
3723   if (!_start_sampling) {
3724     return;
3725   }
3726   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3727   // is populated by the young generation.
3728   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3729     if (_eden_chunk_index < _eden_chunk_capacity) {
3730       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3731       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3732              "Unexpected state of Eden");
3733       // We'd like to check that what we just sampled is an oop-start address;
3734       // however, we cannot do that here since the object may not yet have been
3735       // initialized. So we'll instead do the check when we _use_ this sample
3736       // later.
3737       if (_eden_chunk_index == 0 ||
3738           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3739                          _eden_chunk_array[_eden_chunk_index-1])
3740            >= CMSSamplingGrain)) {
3741         _eden_chunk_index++;  // commit sample
3742       }
3743     }
3744   }
3745   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3746     size_t used = get_eden_used();
3747     size_t capacity = get_eden_capacity();
3748     assert(used <= capacity, "Unexpected state of Eden");
3749     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3750       _abort_preclean = true;
3751     }
3752   }
3753 }
3754 
3755 
3756 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3757   assert(_collectorState == Precleaning ||
3758          _collectorState == AbortablePreclean, "incorrect state");
3759   ResourceMark rm;
3760   HandleMark   hm;
3761 
3762   // Precleaning is currently not MT but the reference processor
3763   // may be set for MT.  Disable it temporarily here.
3764   ReferenceProcessor* rp = ref_processor();
3765   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3766 
3767   // Do one pass of scrubbing the discovered reference lists
3768   // to remove any reference objects with strongly-reachable
3769   // referents.
3770   if (clean_refs) {
3771     CMSPrecleanRefsYieldClosure yield_cl(this);
3772     assert(rp->span().equals(_span), "Spans should be equal");
3773     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3774                                    &_markStack, true /* preclean */);
3775     CMSDrainMarkingStackClosure complete_trace(this,
3776                                    _span, &_markBitMap, &_markStack,
3777                                    &keep_alive, true /* preclean */);
3778 
3779     // We don't want this step to interfere with a young
3780     // collection because we don't want to take CPU
3781     // or memory bandwidth away from the young GC threads
3782     // (which may be as many as there are CPUs).
3783     // Note that we don't need to protect ourselves from
3784     // interference with mutators because they can't
3785     // manipulate the discovered reference lists nor affect
3786     // the computed reachability of the referents, the
3787     // only properties manipulated by the precleaning
3788     // of these reference lists.
3789     stopTimer();
3790     CMSTokenSyncWithLocks x(true /* is cms thread */,
3791                             bitMapLock());
3792     startTimer();
3793     sample_eden();
3794 
3795     // The following will yield to allow foreground
3796     // collection to proceed promptly. XXX YSR:
3797     // The code in this method may need further
3798     // tweaking for better performance and some restructuring
3799     // for cleaner interfaces.
3800     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3801     rp->preclean_discovered_references(
3802           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3803           gc_timer);
3804   }
3805 
3806   if (clean_survivor) {  // preclean the active survivor space(s)
3807     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3808                              &_markBitMap, &_modUnionTable,
3809                              &_markStack, true /* precleaning phase */);
3810     stopTimer();
3811     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3812                              bitMapLock());
3813     startTimer();
3814     unsigned int before_count =
3815       GenCollectedHeap::heap()->total_collections();
3816     SurvivorSpacePrecleanClosure
3817       sss_cl(this, _span, &_markBitMap, &_markStack,
3818              &pam_cl, before_count, CMSYield);
3819     _young_gen->from()->object_iterate_careful(&sss_cl);
3820     _young_gen->to()->object_iterate_careful(&sss_cl);
3821   }
3822   MarkRefsIntoAndScanClosure
3823     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3824              &_markStack, this, CMSYield,
3825              true /* precleaning phase */);
3826   // CAUTION: The following closure has persistent state that may need to
3827   // be reset upon a decrease in the sequence of addresses it
3828   // processes.
3829   ScanMarkedObjectsAgainCarefullyClosure
3830     smoac_cl(this, _span,
3831       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3832 
3833   // Preclean dirty cards in ModUnionTable and CardTable using
3834   // appropriate convergence criterion;
3835   // repeat CMSPrecleanIter times unless we find that
3836   // we are losing.
3837   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3838   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3839          "Bad convergence multiplier");
3840   assert(CMSPrecleanThreshold >= 100,
3841          "Unreasonably low CMSPrecleanThreshold");
3842 
3843   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3844   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3845        numIter < CMSPrecleanIter;
3846        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3847     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3848     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3849     // Either there are very few dirty cards, so re-mark
3850     // pause will be small anyway, or our pre-cleaning isn't
3851     // that much faster than the rate at which cards are being
3852     // dirtied, so we might as well stop and re-mark since
3853     // precleaning won't improve our re-mark time by much.
3854     if (curNumCards <= CMSPrecleanThreshold ||
3855         (numIter > 0 &&
3856          (curNumCards * CMSPrecleanDenominator >
3857          lastNumCards * CMSPrecleanNumerator))) {
3858       numIter++;
3859       cumNumCards += curNumCards;
3860       break;
3861     }
3862   }
3863 
3864   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3865 
3866   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3867   cumNumCards += curNumCards;
3868   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3869                              curNumCards, cumNumCards, numIter);
3870   return cumNumCards;   // as a measure of useful work done
3871 }
3872 
3873 // PRECLEANING NOTES:
3874 // Precleaning involves:
3875 // . reading the bits of the modUnionTable and clearing the set bits.
3876 // . For the cards corresponding to the set bits, we scan the
3877 //   objects on those cards. This means we need the free_list_lock
3878 //   so that we can safely iterate over the CMS space when scanning
3879 //   for oops.
3880 // . When we scan the objects, we'll be both reading and setting
3881 //   marks in the marking bit map, so we'll need the marking bit map.
3882 // . For protecting _collector_state transitions, we take the CGC_lock.
3883 //   Note that any races in the reading of of card table entries by the
3884 //   CMS thread on the one hand and the clearing of those entries by the
3885 //   VM thread or the setting of those entries by the mutator threads on the
3886 //   other are quite benign. However, for efficiency it makes sense to keep
3887 //   the VM thread from racing with the CMS thread while the latter is
3888 //   dirty card info to the modUnionTable. We therefore also use the
3889 //   CGC_lock to protect the reading of the card table and the mod union
3890 //   table by the CM thread.
3891 // . We run concurrently with mutator updates, so scanning
3892 //   needs to be done carefully  -- we should not try to scan
3893 //   potentially uninitialized objects.
3894 //
3895 // Locking strategy: While holding the CGC_lock, we scan over and
3896 // reset a maximal dirty range of the mod union / card tables, then lock
3897 // the free_list_lock and bitmap lock to do a full marking, then
3898 // release these locks; and repeat the cycle. This allows for a
3899 // certain amount of fairness in the sharing of these locks between
3900 // the CMS collector on the one hand, and the VM thread and the
3901 // mutators on the other.
3902 
3903 // NOTE: preclean_mod_union_table() and preclean_card_table()
3904 // further below are largely identical; if you need to modify
3905 // one of these methods, please check the other method too.
3906 
3907 size_t CMSCollector::preclean_mod_union_table(
3908   ConcurrentMarkSweepGeneration* old_gen,
3909   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3910   verify_work_stacks_empty();
3911   verify_overflow_empty();
3912 
3913   // strategy: starting with the first card, accumulate contiguous
3914   // ranges of dirty cards; clear these cards, then scan the region
3915   // covered by these cards.
3916 
3917   // Since all of the MUT is committed ahead, we can just use
3918   // that, in case the generations expand while we are precleaning.
3919   // It might also be fine to just use the committed part of the
3920   // generation, but we might potentially miss cards when the
3921   // generation is rapidly expanding while we are in the midst
3922   // of precleaning.
3923   HeapWord* startAddr = old_gen->reserved().start();
3924   HeapWord* endAddr   = old_gen->reserved().end();
3925 
3926   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3927 
3928   size_t numDirtyCards, cumNumDirtyCards;
3929   HeapWord *nextAddr, *lastAddr;
3930   for (cumNumDirtyCards = numDirtyCards = 0,
3931        nextAddr = lastAddr = startAddr;
3932        nextAddr < endAddr;
3933        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3934 
3935     ResourceMark rm;
3936     HandleMark   hm;
3937 
3938     MemRegion dirtyRegion;
3939     {
3940       stopTimer();
3941       // Potential yield point
3942       CMSTokenSync ts(true);
3943       startTimer();
3944       sample_eden();
3945       // Get dirty region starting at nextOffset (inclusive),
3946       // simultaneously clearing it.
3947       dirtyRegion =
3948         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3949       assert(dirtyRegion.start() >= nextAddr,
3950              "returned region inconsistent?");
3951     }
3952     // Remember where the next search should begin.
3953     // The returned region (if non-empty) is a right open interval,
3954     // so lastOffset is obtained from the right end of that
3955     // interval.
3956     lastAddr = dirtyRegion.end();
3957     // Should do something more transparent and less hacky XXX
3958     numDirtyCards =
3959       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3960 
3961     // We'll scan the cards in the dirty region (with periodic
3962     // yields for foreground GC as needed).
3963     if (!dirtyRegion.is_empty()) {
3964       assert(numDirtyCards > 0, "consistency check");
3965       HeapWord* stop_point = NULL;
3966       stopTimer();
3967       // Potential yield point
3968       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3969                                bitMapLock());
3970       startTimer();
3971       {
3972         verify_work_stacks_empty();
3973         verify_overflow_empty();
3974         sample_eden();
3975         stop_point =
3976           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3977       }
3978       if (stop_point != NULL) {
3979         // The careful iteration stopped early either because it found an
3980         // uninitialized object, or because we were in the midst of an
3981         // "abortable preclean", which should now be aborted. Redirty
3982         // the bits corresponding to the partially-scanned or unscanned
3983         // cards. We'll either restart at the next block boundary or
3984         // abort the preclean.
3985         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3986                "Should only be AbortablePreclean.");
3987         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3988         if (should_abort_preclean()) {
3989           break; // out of preclean loop
3990         } else {
3991           // Compute the next address at which preclean should pick up;
3992           // might need bitMapLock in order to read P-bits.
3993           lastAddr = next_card_start_after_block(stop_point);
3994         }
3995       }
3996     } else {
3997       assert(lastAddr == endAddr, "consistency check");
3998       assert(numDirtyCards == 0, "consistency check");
3999       break;
4000     }
4001   }
4002   verify_work_stacks_empty();
4003   verify_overflow_empty();
4004   return cumNumDirtyCards;
4005 }
4006 
4007 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4008 // below are largely identical; if you need to modify
4009 // one of these methods, please check the other method too.
4010 
4011 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4012   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4013   // strategy: it's similar to precleamModUnionTable above, in that
4014   // we accumulate contiguous ranges of dirty cards, mark these cards
4015   // precleaned, then scan the region covered by these cards.
4016   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4017   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4018 
4019   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4020 
4021   size_t numDirtyCards, cumNumDirtyCards;
4022   HeapWord *lastAddr, *nextAddr;
4023 
4024   for (cumNumDirtyCards = numDirtyCards = 0,
4025        nextAddr = lastAddr = startAddr;
4026        nextAddr < endAddr;
4027        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4028 
4029     ResourceMark rm;
4030     HandleMark   hm;
4031 
4032     MemRegion dirtyRegion;
4033     {
4034       // See comments in "Precleaning notes" above on why we
4035       // do this locking. XXX Could the locking overheads be
4036       // too high when dirty cards are sparse? [I don't think so.]
4037       stopTimer();
4038       CMSTokenSync x(true); // is cms thread
4039       startTimer();
4040       sample_eden();
4041       // Get and clear dirty region from card table
4042       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4043                                     MemRegion(nextAddr, endAddr),
4044                                     true,
4045                                     CardTableModRefBS::precleaned_card_val());
4046 
4047       assert(dirtyRegion.start() >= nextAddr,
4048              "returned region inconsistent?");
4049     }
4050     lastAddr = dirtyRegion.end();
4051     numDirtyCards =
4052       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4053 
4054     if (!dirtyRegion.is_empty()) {
4055       stopTimer();
4056       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4057       startTimer();
4058       sample_eden();
4059       verify_work_stacks_empty();
4060       verify_overflow_empty();
4061       HeapWord* stop_point =
4062         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4063       if (stop_point != NULL) {
4064         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4065                "Should only be AbortablePreclean.");
4066         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4067         if (should_abort_preclean()) {
4068           break; // out of preclean loop
4069         } else {
4070           // Compute the next address at which preclean should pick up.
4071           lastAddr = next_card_start_after_block(stop_point);
4072         }
4073       }
4074     } else {
4075       break;
4076     }
4077   }
4078   verify_work_stacks_empty();
4079   verify_overflow_empty();
4080   return cumNumDirtyCards;
4081 }
4082 
4083 class PrecleanKlassClosure : public KlassClosure {
4084   KlassToOopClosure _cm_klass_closure;
4085  public:
4086   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4087   void do_klass(Klass* k) {
4088     if (k->has_accumulated_modified_oops()) {
4089       k->clear_accumulated_modified_oops();
4090 
4091       _cm_klass_closure.do_klass(k);
4092     }
4093   }
4094 };
4095 
4096 // The freelist lock is needed to prevent asserts, is it really needed?
4097 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4098 
4099   cl->set_freelistLock(freelistLock);
4100 
4101   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4102 
4103   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4104   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4105   PrecleanKlassClosure preclean_klass_closure(cl);
4106   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4107 
4108   verify_work_stacks_empty();
4109   verify_overflow_empty();
4110 }
4111 
4112 void CMSCollector::checkpointRootsFinal() {
4113   assert(_collectorState == FinalMarking, "incorrect state transition?");
4114   check_correct_thread_executing();
4115   // world is stopped at this checkpoint
4116   assert(SafepointSynchronize::is_at_safepoint(),
4117          "world should be stopped");
4118   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4119 
4120   verify_work_stacks_empty();
4121   verify_overflow_empty();
4122 
4123   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4124                 _young_gen->used() / K, _young_gen->capacity() / K);
4125   {
4126     if (CMSScavengeBeforeRemark) {
4127       GenCollectedHeap* gch = GenCollectedHeap::heap();
4128       // Temporarily set flag to false, GCH->do_collection will
4129       // expect it to be false and set to true
4130       FlagSetting fl(gch->_is_gc_active, false);
4131 
4132       gch->do_collection(true,                      // full (i.e. force, see below)
4133                          false,                     // !clear_all_soft_refs
4134                          0,                         // size
4135                          false,                     // is_tlab
4136                          GenCollectedHeap::YoungGen // type
4137         );
4138     }
4139     FreelistLocker x(this);
4140     MutexLockerEx y(bitMapLock(),
4141                     Mutex::_no_safepoint_check_flag);
4142     checkpointRootsFinalWork();
4143   }
4144   verify_work_stacks_empty();
4145   verify_overflow_empty();
4146 }
4147 
4148 void CMSCollector::checkpointRootsFinalWork() {
4149   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4150 
4151   assert(haveFreelistLocks(), "must have free list locks");
4152   assert_lock_strong(bitMapLock());
4153 
4154   ResourceMark rm;
4155   HandleMark   hm;
4156 
4157   GenCollectedHeap* gch = GenCollectedHeap::heap();
4158 
4159   if (should_unload_classes()) {
4160     CodeCache::gc_prologue();
4161   }
4162   assert(haveFreelistLocks(), "must have free list locks");
4163   assert_lock_strong(bitMapLock());
4164 
4165   // We might assume that we need not fill TLAB's when
4166   // CMSScavengeBeforeRemark is set, because we may have just done
4167   // a scavenge which would have filled all TLAB's -- and besides
4168   // Eden would be empty. This however may not always be the case --
4169   // for instance although we asked for a scavenge, it may not have
4170   // happened because of a JNI critical section. We probably need
4171   // a policy for deciding whether we can in that case wait until
4172   // the critical section releases and then do the remark following
4173   // the scavenge, and skip it here. In the absence of that policy,
4174   // or of an indication of whether the scavenge did indeed occur,
4175   // we cannot rely on TLAB's having been filled and must do
4176   // so here just in case a scavenge did not happen.
4177   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4178   // Update the saved marks which may affect the root scans.
4179   gch->save_marks();
4180 
4181   print_eden_and_survivor_chunk_arrays();
4182 
4183   {
4184 #if defined(COMPILER2) || INCLUDE_JVMCI
4185     DerivedPointerTableDeactivate dpt_deact;
4186 #endif
4187 
4188     // Note on the role of the mod union table:
4189     // Since the marker in "markFromRoots" marks concurrently with
4190     // mutators, it is possible for some reachable objects not to have been
4191     // scanned. For instance, an only reference to an object A was
4192     // placed in object B after the marker scanned B. Unless B is rescanned,
4193     // A would be collected. Such updates to references in marked objects
4194     // are detected via the mod union table which is the set of all cards
4195     // dirtied since the first checkpoint in this GC cycle and prior to
4196     // the most recent young generation GC, minus those cleaned up by the
4197     // concurrent precleaning.
4198     if (CMSParallelRemarkEnabled) {
4199       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4200       do_remark_parallel();
4201     } else {
4202       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4203       do_remark_non_parallel();
4204     }
4205   }
4206   verify_work_stacks_empty();
4207   verify_overflow_empty();
4208 
4209   {
4210     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4211     refProcessingWork();
4212   }
4213   verify_work_stacks_empty();
4214   verify_overflow_empty();
4215 
4216   if (should_unload_classes()) {
4217     CodeCache::gc_epilogue();
4218   }
4219   JvmtiExport::gc_epilogue();
4220 
4221   // If we encountered any (marking stack / work queue) overflow
4222   // events during the current CMS cycle, take appropriate
4223   // remedial measures, where possible, so as to try and avoid
4224   // recurrence of that condition.
4225   assert(_markStack.isEmpty(), "No grey objects");
4226   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4227                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4228   if (ser_ovflw > 0) {
4229     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4230                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4231     _markStack.expand();
4232     _ser_pmc_remark_ovflw = 0;
4233     _ser_pmc_preclean_ovflw = 0;
4234     _ser_kac_preclean_ovflw = 0;
4235     _ser_kac_ovflw = 0;
4236   }
4237   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4238      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4239                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4240      _par_pmc_remark_ovflw = 0;
4241     _par_kac_ovflw = 0;
4242   }
4243    if (_markStack._hit_limit > 0) {
4244      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4245                           _markStack._hit_limit);
4246    }
4247    if (_markStack._failed_double > 0) {
4248      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4249                           _markStack._failed_double, _markStack.capacity());
4250    }
4251   _markStack._hit_limit = 0;
4252   _markStack._failed_double = 0;
4253 
4254   if ((VerifyAfterGC || VerifyDuringGC) &&
4255       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4256     verify_after_remark();
4257   }
4258 
4259   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4260 
4261   // Change under the freelistLocks.
4262   _collectorState = Sweeping;
4263   // Call isAllClear() under bitMapLock
4264   assert(_modUnionTable.isAllClear(),
4265       "Should be clear by end of the final marking");
4266   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4267       "Should be clear by end of the final marking");
4268 }
4269 
4270 void CMSParInitialMarkTask::work(uint worker_id) {
4271   elapsedTimer _timer;
4272   ResourceMark rm;
4273   HandleMark   hm;
4274 
4275   // ---------- scan from roots --------------
4276   _timer.start();
4277   GenCollectedHeap* gch = GenCollectedHeap::heap();
4278   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4279 
4280   // ---------- young gen roots --------------
4281   {
4282     work_on_young_gen_roots(&par_mri_cl);
4283     _timer.stop();
4284     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4285   }
4286 
4287   // ---------- remaining roots --------------
4288   _timer.reset();
4289   _timer.start();
4290 
4291   CLDToOopClosure cld_closure(&par_mri_cl, true);
4292 
4293   gch->gen_process_roots(_strong_roots_scope,
4294                          GenCollectedHeap::OldGen,
4295                          false,     // yg was scanned above
4296                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4297                          _collector->should_unload_classes(),
4298                          &par_mri_cl,
4299                          NULL,
4300                          &cld_closure);
4301   assert(_collector->should_unload_classes()
4302          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4303          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4304   _timer.stop();
4305   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4306 }
4307 
4308 // Parallel remark task
4309 class CMSParRemarkTask: public CMSParMarkTask {
4310   CompactibleFreeListSpace* _cms_space;
4311 
4312   // The per-thread work queues, available here for stealing.
4313   OopTaskQueueSet*       _task_queues;
4314   ParallelTaskTerminator _term;
4315   StrongRootsScope*      _strong_roots_scope;
4316 
4317  public:
4318   // A value of 0 passed to n_workers will cause the number of
4319   // workers to be taken from the active workers in the work gang.
4320   CMSParRemarkTask(CMSCollector* collector,
4321                    CompactibleFreeListSpace* cms_space,
4322                    uint n_workers, WorkGang* workers,
4323                    OopTaskQueueSet* task_queues,
4324                    StrongRootsScope* strong_roots_scope):
4325     CMSParMarkTask("Rescan roots and grey objects in parallel",
4326                    collector, n_workers),
4327     _cms_space(cms_space),
4328     _task_queues(task_queues),
4329     _term(n_workers, task_queues),
4330     _strong_roots_scope(strong_roots_scope) { }
4331 
4332   OopTaskQueueSet* task_queues() { return _task_queues; }
4333 
4334   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4335 
4336   ParallelTaskTerminator* terminator() { return &_term; }
4337   uint n_workers() { return _n_workers; }
4338 
4339   void work(uint worker_id);
4340 
4341  private:
4342   // ... of  dirty cards in old space
4343   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4344                                   ParMarkRefsIntoAndScanClosure* cl);
4345 
4346   // ... work stealing for the above
4347   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4348 };
4349 
4350 class RemarkKlassClosure : public KlassClosure {
4351   KlassToOopClosure _cm_klass_closure;
4352  public:
4353   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4354   void do_klass(Klass* k) {
4355     // Check if we have modified any oops in the Klass during the concurrent marking.
4356     if (k->has_accumulated_modified_oops()) {
4357       k->clear_accumulated_modified_oops();
4358 
4359       // We could have transfered the current modified marks to the accumulated marks,
4360       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4361     } else if (k->has_modified_oops()) {
4362       // Don't clear anything, this info is needed by the next young collection.
4363     } else {
4364       // No modified oops in the Klass.
4365       return;
4366     }
4367 
4368     // The klass has modified fields, need to scan the klass.
4369     _cm_klass_closure.do_klass(k);
4370   }
4371 };
4372 
4373 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4374   ParNewGeneration* young_gen = _collector->_young_gen;
4375   ContiguousSpace* eden_space = young_gen->eden();
4376   ContiguousSpace* from_space = young_gen->from();
4377   ContiguousSpace* to_space   = young_gen->to();
4378 
4379   HeapWord** eca = _collector->_eden_chunk_array;
4380   size_t     ect = _collector->_eden_chunk_index;
4381   HeapWord** sca = _collector->_survivor_chunk_array;
4382   size_t     sct = _collector->_survivor_chunk_index;
4383 
4384   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4385   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4386 
4387   do_young_space_rescan(cl, to_space, NULL, 0);
4388   do_young_space_rescan(cl, from_space, sca, sct);
4389   do_young_space_rescan(cl, eden_space, eca, ect);
4390 }
4391 
4392 // work_queue(i) is passed to the closure
4393 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4394 // also is passed to do_dirty_card_rescan_tasks() and to
4395 // do_work_steal() to select the i-th task_queue.
4396 
4397 void CMSParRemarkTask::work(uint worker_id) {
4398   elapsedTimer _timer;
4399   ResourceMark rm;
4400   HandleMark   hm;
4401 
4402   // ---------- rescan from roots --------------
4403   _timer.start();
4404   GenCollectedHeap* gch = GenCollectedHeap::heap();
4405   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4406     _collector->_span, _collector->ref_processor(),
4407     &(_collector->_markBitMap),
4408     work_queue(worker_id));
4409 
4410   // Rescan young gen roots first since these are likely
4411   // coarsely partitioned and may, on that account, constitute
4412   // the critical path; thus, it's best to start off that
4413   // work first.
4414   // ---------- young gen roots --------------
4415   {
4416     work_on_young_gen_roots(&par_mrias_cl);
4417     _timer.stop();
4418     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4419   }
4420 
4421   // ---------- remaining roots --------------
4422   _timer.reset();
4423   _timer.start();
4424   gch->gen_process_roots(_strong_roots_scope,
4425                          GenCollectedHeap::OldGen,
4426                          false,     // yg was scanned above
4427                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4428                          _collector->should_unload_classes(),
4429                          &par_mrias_cl,
4430                          NULL,
4431                          NULL);     // The dirty klasses will be handled below
4432 
4433   assert(_collector->should_unload_classes()
4434          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4435          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4436   _timer.stop();
4437   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4438 
4439   // ---------- unhandled CLD scanning ----------
4440   if (worker_id == 0) { // Single threaded at the moment.
4441     _timer.reset();
4442     _timer.start();
4443 
4444     // Scan all new class loader data objects and new dependencies that were
4445     // introduced during concurrent marking.
4446     ResourceMark rm;
4447     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4448     for (int i = 0; i < array->length(); i++) {
4449       par_mrias_cl.do_cld_nv(array->at(i));
4450     }
4451 
4452     // We don't need to keep track of new CLDs anymore.
4453     ClassLoaderDataGraph::remember_new_clds(false);
4454 
4455     _timer.stop();
4456     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4457   }
4458 
4459   // ---------- dirty klass scanning ----------
4460   if (worker_id == 0) { // Single threaded at the moment.
4461     _timer.reset();
4462     _timer.start();
4463 
4464     // Scan all classes that was dirtied during the concurrent marking phase.
4465     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4466     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4467 
4468     _timer.stop();
4469     log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4470   }
4471 
4472   // We might have added oops to ClassLoaderData::_handles during the
4473   // concurrent marking phase. These oops point to newly allocated objects
4474   // that are guaranteed to be kept alive. Either by the direct allocation
4475   // code, or when the young collector processes the roots. Hence,
4476   // we don't have to revisit the _handles block during the remark phase.
4477 
4478   // ---------- rescan dirty cards ------------
4479   _timer.reset();
4480   _timer.start();
4481 
4482   // Do the rescan tasks for each of the two spaces
4483   // (cms_space) in turn.
4484   // "worker_id" is passed to select the task_queue for "worker_id"
4485   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4486   _timer.stop();
4487   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4488 
4489   // ---------- steal work from other threads ...
4490   // ---------- ... and drain overflow list.
4491   _timer.reset();
4492   _timer.start();
4493   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4494   _timer.stop();
4495   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4496 }
4497 
4498 void
4499 CMSParMarkTask::do_young_space_rescan(
4500   OopsInGenClosure* cl, ContiguousSpace* space,
4501   HeapWord** chunk_array, size_t chunk_top) {
4502   // Until all tasks completed:
4503   // . claim an unclaimed task
4504   // . compute region boundaries corresponding to task claimed
4505   //   using chunk_array
4506   // . par_oop_iterate(cl) over that region
4507 
4508   ResourceMark rm;
4509   HandleMark   hm;
4510 
4511   SequentialSubTasksDone* pst = space->par_seq_tasks();
4512 
4513   uint nth_task = 0;
4514   uint n_tasks  = pst->n_tasks();
4515 
4516   if (n_tasks > 0) {
4517     assert(pst->valid(), "Uninitialized use?");
4518     HeapWord *start, *end;
4519     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4520       // We claimed task # nth_task; compute its boundaries.
4521       if (chunk_top == 0) {  // no samples were taken
4522         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4523         start = space->bottom();
4524         end   = space->top();
4525       } else if (nth_task == 0) {
4526         start = space->bottom();
4527         end   = chunk_array[nth_task];
4528       } else if (nth_task < (uint)chunk_top) {
4529         assert(nth_task >= 1, "Control point invariant");
4530         start = chunk_array[nth_task - 1];
4531         end   = chunk_array[nth_task];
4532       } else {
4533         assert(nth_task == (uint)chunk_top, "Control point invariant");
4534         start = chunk_array[chunk_top - 1];
4535         end   = space->top();
4536       }
4537       MemRegion mr(start, end);
4538       // Verify that mr is in space
4539       assert(mr.is_empty() || space->used_region().contains(mr),
4540              "Should be in space");
4541       // Verify that "start" is an object boundary
4542       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4543              "Should be an oop");
4544       space->par_oop_iterate(mr, cl);
4545     }
4546     pst->all_tasks_completed();
4547   }
4548 }
4549 
4550 void
4551 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4552   CompactibleFreeListSpace* sp, int i,
4553   ParMarkRefsIntoAndScanClosure* cl) {
4554   // Until all tasks completed:
4555   // . claim an unclaimed task
4556   // . compute region boundaries corresponding to task claimed
4557   // . transfer dirty bits ct->mut for that region
4558   // . apply rescanclosure to dirty mut bits for that region
4559 
4560   ResourceMark rm;
4561   HandleMark   hm;
4562 
4563   OopTaskQueue* work_q = work_queue(i);
4564   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4565   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4566   // CAUTION: This closure has state that persists across calls to
4567   // the work method dirty_range_iterate_clear() in that it has
4568   // embedded in it a (subtype of) UpwardsObjectClosure. The
4569   // use of that state in the embedded UpwardsObjectClosure instance
4570   // assumes that the cards are always iterated (even if in parallel
4571   // by several threads) in monotonically increasing order per each
4572   // thread. This is true of the implementation below which picks
4573   // card ranges (chunks) in monotonically increasing order globally
4574   // and, a-fortiori, in monotonically increasing order per thread
4575   // (the latter order being a subsequence of the former).
4576   // If the work code below is ever reorganized into a more chaotic
4577   // work-partitioning form than the current "sequential tasks"
4578   // paradigm, the use of that persistent state will have to be
4579   // revisited and modified appropriately. See also related
4580   // bug 4756801 work on which should examine this code to make
4581   // sure that the changes there do not run counter to the
4582   // assumptions made here and necessary for correctness and
4583   // efficiency. Note also that this code might yield inefficient
4584   // behavior in the case of very large objects that span one or
4585   // more work chunks. Such objects would potentially be scanned
4586   // several times redundantly. Work on 4756801 should try and
4587   // address that performance anomaly if at all possible. XXX
4588   MemRegion  full_span  = _collector->_span;
4589   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4590   MarkFromDirtyCardsClosure
4591     greyRescanClosure(_collector, full_span, // entire span of interest
4592                       sp, bm, work_q, cl);
4593 
4594   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4595   assert(pst->valid(), "Uninitialized use?");
4596   uint nth_task = 0;
4597   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4598   MemRegion span = sp->used_region();
4599   HeapWord* start_addr = span.start();
4600   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4601                                            alignment);
4602   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4603   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4604          start_addr, "Check alignment");
4605   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4606          chunk_size, "Check alignment");
4607 
4608   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4609     // Having claimed the nth_task, compute corresponding mem-region,
4610     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4611     // The alignment restriction ensures that we do not need any
4612     // synchronization with other gang-workers while setting or
4613     // clearing bits in thus chunk of the MUT.
4614     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4615                                     start_addr + (nth_task+1)*chunk_size);
4616     // The last chunk's end might be way beyond end of the
4617     // used region. In that case pull back appropriately.
4618     if (this_span.end() > end_addr) {
4619       this_span.set_end(end_addr);
4620       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4621     }
4622     // Iterate over the dirty cards covering this chunk, marking them
4623     // precleaned, and setting the corresponding bits in the mod union
4624     // table. Since we have been careful to partition at Card and MUT-word
4625     // boundaries no synchronization is needed between parallel threads.
4626     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4627                                                  &modUnionClosure);
4628 
4629     // Having transferred these marks into the modUnionTable,
4630     // rescan the marked objects on the dirty cards in the modUnionTable.
4631     // Even if this is at a synchronous collection, the initial marking
4632     // may have been done during an asynchronous collection so there
4633     // may be dirty bits in the mod-union table.
4634     _collector->_modUnionTable.dirty_range_iterate_clear(
4635                   this_span, &greyRescanClosure);
4636     _collector->_modUnionTable.verifyNoOneBitsInRange(
4637                                  this_span.start(),
4638                                  this_span.end());
4639   }
4640   pst->all_tasks_completed();  // declare that i am done
4641 }
4642 
4643 // . see if we can share work_queues with ParNew? XXX
4644 void
4645 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4646                                 int* seed) {
4647   OopTaskQueue* work_q = work_queue(i);
4648   NOT_PRODUCT(int num_steals = 0;)
4649   oop obj_to_scan;
4650   CMSBitMap* bm = &(_collector->_markBitMap);
4651 
4652   while (true) {
4653     // Completely finish any left over work from (an) earlier round(s)
4654     cl->trim_queue(0);
4655     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4656                                          (size_t)ParGCDesiredObjsFromOverflowList);
4657     // Now check if there's any work in the overflow list
4658     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4659     // only affects the number of attempts made to get work from the
4660     // overflow list and does not affect the number of workers.  Just
4661     // pass ParallelGCThreads so this behavior is unchanged.
4662     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4663                                                 work_q,
4664                                                 ParallelGCThreads)) {
4665       // found something in global overflow list;
4666       // not yet ready to go stealing work from others.
4667       // We'd like to assert(work_q->size() != 0, ...)
4668       // because we just took work from the overflow list,
4669       // but of course we can't since all of that could have
4670       // been already stolen from us.
4671       // "He giveth and He taketh away."
4672       continue;
4673     }
4674     // Verify that we have no work before we resort to stealing
4675     assert(work_q->size() == 0, "Have work, shouldn't steal");
4676     // Try to steal from other queues that have work
4677     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4678       NOT_PRODUCT(num_steals++;)
4679       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4680       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4681       // Do scanning work
4682       obj_to_scan->oop_iterate(cl);
4683       // Loop around, finish this work, and try to steal some more
4684     } else if (terminator()->offer_termination()) {
4685         break;  // nirvana from the infinite cycle
4686     }
4687   }
4688   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4689   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4690          "Else our work is not yet done");
4691 }
4692 
4693 // Record object boundaries in _eden_chunk_array by sampling the eden
4694 // top in the slow-path eden object allocation code path and record
4695 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4696 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4697 // sampling in sample_eden() that activates during the part of the
4698 // preclean phase.
4699 void CMSCollector::sample_eden_chunk() {
4700   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4701     if (_eden_chunk_lock->try_lock()) {
4702       // Record a sample. This is the critical section. The contents
4703       // of the _eden_chunk_array have to be non-decreasing in the
4704       // address order.
4705       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4706       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4707              "Unexpected state of Eden");
4708       if (_eden_chunk_index == 0 ||
4709           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4710            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4711                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4712         _eden_chunk_index++;  // commit sample
4713       }
4714       _eden_chunk_lock->unlock();
4715     }
4716   }
4717 }
4718 
4719 // Return a thread-local PLAB recording array, as appropriate.
4720 void* CMSCollector::get_data_recorder(int thr_num) {
4721   if (_survivor_plab_array != NULL &&
4722       (CMSPLABRecordAlways ||
4723        (_collectorState > Marking && _collectorState < FinalMarking))) {
4724     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4725     ChunkArray* ca = &_survivor_plab_array[thr_num];
4726     ca->reset();   // clear it so that fresh data is recorded
4727     return (void*) ca;
4728   } else {
4729     return NULL;
4730   }
4731 }
4732 
4733 // Reset all the thread-local PLAB recording arrays
4734 void CMSCollector::reset_survivor_plab_arrays() {
4735   for (uint i = 0; i < ParallelGCThreads; i++) {
4736     _survivor_plab_array[i].reset();
4737   }
4738 }
4739 
4740 // Merge the per-thread plab arrays into the global survivor chunk
4741 // array which will provide the partitioning of the survivor space
4742 // for CMS initial scan and rescan.
4743 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4744                                               int no_of_gc_threads) {
4745   assert(_survivor_plab_array  != NULL, "Error");
4746   assert(_survivor_chunk_array != NULL, "Error");
4747   assert(_collectorState == FinalMarking ||
4748          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4749   for (int j = 0; j < no_of_gc_threads; j++) {
4750     _cursor[j] = 0;
4751   }
4752   HeapWord* top = surv->top();
4753   size_t i;
4754   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4755     HeapWord* min_val = top;          // Higher than any PLAB address
4756     uint      min_tid = 0;            // position of min_val this round
4757     for (int j = 0; j < no_of_gc_threads; j++) {
4758       ChunkArray* cur_sca = &_survivor_plab_array[j];
4759       if (_cursor[j] == cur_sca->end()) {
4760         continue;
4761       }
4762       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4763       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4764       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4765       if (cur_val < min_val) {
4766         min_tid = j;
4767         min_val = cur_val;
4768       } else {
4769         assert(cur_val < top, "All recorded addresses should be less");
4770       }
4771     }
4772     // At this point min_val and min_tid are respectively
4773     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4774     // and the thread (j) that witnesses that address.
4775     // We record this address in the _survivor_chunk_array[i]
4776     // and increment _cursor[min_tid] prior to the next round i.
4777     if (min_val == top) {
4778       break;
4779     }
4780     _survivor_chunk_array[i] = min_val;
4781     _cursor[min_tid]++;
4782   }
4783   // We are all done; record the size of the _survivor_chunk_array
4784   _survivor_chunk_index = i; // exclusive: [0, i)
4785   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4786   // Verify that we used up all the recorded entries
4787   #ifdef ASSERT
4788     size_t total = 0;
4789     for (int j = 0; j < no_of_gc_threads; j++) {
4790       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4791       total += _cursor[j];
4792     }
4793     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4794     // Check that the merged array is in sorted order
4795     if (total > 0) {
4796       for (size_t i = 0; i < total - 1; i++) {
4797         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4798                                      i, p2i(_survivor_chunk_array[i]));
4799         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4800                "Not sorted");
4801       }
4802     }
4803   #endif // ASSERT
4804 }
4805 
4806 // Set up the space's par_seq_tasks structure for work claiming
4807 // for parallel initial scan and rescan of young gen.
4808 // See ParRescanTask where this is currently used.
4809 void
4810 CMSCollector::
4811 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4812   assert(n_threads > 0, "Unexpected n_threads argument");
4813 
4814   // Eden space
4815   if (!_young_gen->eden()->is_empty()) {
4816     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4817     assert(!pst->valid(), "Clobbering existing data?");
4818     // Each valid entry in [0, _eden_chunk_index) represents a task.
4819     size_t n_tasks = _eden_chunk_index + 1;
4820     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4821     // Sets the condition for completion of the subtask (how many threads
4822     // need to finish in order to be done).
4823     pst->set_n_threads(n_threads);
4824     pst->set_n_tasks((int)n_tasks);
4825   }
4826 
4827   // Merge the survivor plab arrays into _survivor_chunk_array
4828   if (_survivor_plab_array != NULL) {
4829     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4830   } else {
4831     assert(_survivor_chunk_index == 0, "Error");
4832   }
4833 
4834   // To space
4835   {
4836     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4837     assert(!pst->valid(), "Clobbering existing data?");
4838     // Sets the condition for completion of the subtask (how many threads
4839     // need to finish in order to be done).
4840     pst->set_n_threads(n_threads);
4841     pst->set_n_tasks(1);
4842     assert(pst->valid(), "Error");
4843   }
4844 
4845   // From space
4846   {
4847     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4848     assert(!pst->valid(), "Clobbering existing data?");
4849     size_t n_tasks = _survivor_chunk_index + 1;
4850     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4851     // Sets the condition for completion of the subtask (how many threads
4852     // need to finish in order to be done).
4853     pst->set_n_threads(n_threads);
4854     pst->set_n_tasks((int)n_tasks);
4855     assert(pst->valid(), "Error");
4856   }
4857 }
4858 
4859 // Parallel version of remark
4860 void CMSCollector::do_remark_parallel() {
4861   GenCollectedHeap* gch = GenCollectedHeap::heap();
4862   WorkGang* workers = gch->workers();
4863   assert(workers != NULL, "Need parallel worker threads.");
4864   // Choose to use the number of GC workers most recently set
4865   // into "active_workers".
4866   uint n_workers = workers->active_workers();
4867 
4868   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4869 
4870   StrongRootsScope srs(n_workers);
4871 
4872   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4873 
4874   // We won't be iterating over the cards in the card table updating
4875   // the younger_gen cards, so we shouldn't call the following else
4876   // the verification code as well as subsequent younger_refs_iterate
4877   // code would get confused. XXX
4878   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4879 
4880   // The young gen rescan work will not be done as part of
4881   // process_roots (which currently doesn't know how to
4882   // parallelize such a scan), but rather will be broken up into
4883   // a set of parallel tasks (via the sampling that the [abortable]
4884   // preclean phase did of eden, plus the [two] tasks of
4885   // scanning the [two] survivor spaces. Further fine-grain
4886   // parallelization of the scanning of the survivor spaces
4887   // themselves, and of precleaning of the young gen itself
4888   // is deferred to the future.
4889   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4890 
4891   // The dirty card rescan work is broken up into a "sequence"
4892   // of parallel tasks (per constituent space) that are dynamically
4893   // claimed by the parallel threads.
4894   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4895 
4896   // It turns out that even when we're using 1 thread, doing the work in a
4897   // separate thread causes wide variance in run times.  We can't help this
4898   // in the multi-threaded case, but we special-case n=1 here to get
4899   // repeatable measurements of the 1-thread overhead of the parallel code.
4900   if (n_workers > 1) {
4901     // Make refs discovery MT-safe, if it isn't already: it may not
4902     // necessarily be so, since it's possible that we are doing
4903     // ST marking.
4904     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4905     workers->run_task(&tsk);
4906   } else {
4907     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4908     tsk.work(0);
4909   }
4910 
4911   // restore, single-threaded for now, any preserved marks
4912   // as a result of work_q overflow
4913   restore_preserved_marks_if_any();
4914 }
4915 
4916 // Non-parallel version of remark
4917 void CMSCollector::do_remark_non_parallel() {
4918   ResourceMark rm;
4919   HandleMark   hm;
4920   GenCollectedHeap* gch = GenCollectedHeap::heap();
4921   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4922 
4923   MarkRefsIntoAndScanClosure
4924     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4925              &_markStack, this,
4926              false /* should_yield */, false /* not precleaning */);
4927   MarkFromDirtyCardsClosure
4928     markFromDirtyCardsClosure(this, _span,
4929                               NULL,  // space is set further below
4930                               &_markBitMap, &_markStack, &mrias_cl);
4931   {
4932     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4933     // Iterate over the dirty cards, setting the corresponding bits in the
4934     // mod union table.
4935     {
4936       ModUnionClosure modUnionClosure(&_modUnionTable);
4937       _ct->ct_bs()->dirty_card_iterate(
4938                       _cmsGen->used_region(),
4939                       &modUnionClosure);
4940     }
4941     // Having transferred these marks into the modUnionTable, we just need
4942     // to rescan the marked objects on the dirty cards in the modUnionTable.
4943     // The initial marking may have been done during an asynchronous
4944     // collection so there may be dirty bits in the mod-union table.
4945     const int alignment =
4946       CardTableModRefBS::card_size * BitsPerWord;
4947     {
4948       // ... First handle dirty cards in CMS gen
4949       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4950       MemRegion ur = _cmsGen->used_region();
4951       HeapWord* lb = ur.start();
4952       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4953       MemRegion cms_span(lb, ub);
4954       _modUnionTable.dirty_range_iterate_clear(cms_span,
4955                                                &markFromDirtyCardsClosure);
4956       verify_work_stacks_empty();
4957       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4958     }
4959   }
4960   if (VerifyDuringGC &&
4961       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4962     HandleMark hm;  // Discard invalid handles created during verification
4963     Universe::verify();
4964   }
4965   {
4966     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4967 
4968     verify_work_stacks_empty();
4969 
4970     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4971     StrongRootsScope srs(1);
4972 
4973     gch->gen_process_roots(&srs,
4974                            GenCollectedHeap::OldGen,
4975                            true,  // young gen as roots
4976                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
4977                            should_unload_classes(),
4978                            &mrias_cl,
4979                            NULL,
4980                            NULL); // The dirty klasses will be handled below
4981 
4982     assert(should_unload_classes()
4983            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4984            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4985   }
4986 
4987   {
4988     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4989 
4990     verify_work_stacks_empty();
4991 
4992     // Scan all class loader data objects that might have been introduced
4993     // during concurrent marking.
4994     ResourceMark rm;
4995     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4996     for (int i = 0; i < array->length(); i++) {
4997       mrias_cl.do_cld_nv(array->at(i));
4998     }
4999 
5000     // We don't need to keep track of new CLDs anymore.
5001     ClassLoaderDataGraph::remember_new_clds(false);
5002 
5003     verify_work_stacks_empty();
5004   }
5005 
5006   {
5007     GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
5008 
5009     verify_work_stacks_empty();
5010 
5011     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5012     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5013 
5014     verify_work_stacks_empty();
5015   }
5016 
5017   // We might have added oops to ClassLoaderData::_handles during the
5018   // concurrent marking phase. These oops point to newly allocated objects
5019   // that are guaranteed to be kept alive. Either by the direct allocation
5020   // code, or when the young collector processes the roots. Hence,
5021   // we don't have to revisit the _handles block during the remark phase.
5022 
5023   verify_work_stacks_empty();
5024   // Restore evacuated mark words, if any, used for overflow list links
5025   restore_preserved_marks_if_any();
5026 
5027   verify_overflow_empty();
5028 }
5029 
5030 ////////////////////////////////////////////////////////
5031 // Parallel Reference Processing Task Proxy Class
5032 ////////////////////////////////////////////////////////
5033 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5034   OopTaskQueueSet*       _queues;
5035   ParallelTaskTerminator _terminator;
5036  public:
5037   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5038     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5039   ParallelTaskTerminator* terminator() { return &_terminator; }
5040   OopTaskQueueSet* queues() { return _queues; }
5041 };
5042 
5043 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5044   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5045   CMSCollector*          _collector;
5046   CMSBitMap*             _mark_bit_map;
5047   const MemRegion        _span;
5048   ProcessTask&           _task;
5049 
5050 public:
5051   CMSRefProcTaskProxy(ProcessTask&     task,
5052                       CMSCollector*    collector,
5053                       const MemRegion& span,
5054                       CMSBitMap*       mark_bit_map,
5055                       AbstractWorkGang* workers,
5056                       OopTaskQueueSet* task_queues):
5057     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5058       task_queues,
5059       workers->active_workers()),
5060     _task(task),
5061     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5062   {
5063     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5064            "Inconsistency in _span");
5065   }
5066 
5067   OopTaskQueueSet* task_queues() { return queues(); }
5068 
5069   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5070 
5071   void do_work_steal(int i,
5072                      CMSParDrainMarkingStackClosure* drain,
5073                      CMSParKeepAliveClosure* keep_alive,
5074                      int* seed);
5075 
5076   virtual void work(uint worker_id);
5077 };
5078 
5079 void CMSRefProcTaskProxy::work(uint worker_id) {
5080   ResourceMark rm;
5081   HandleMark hm;
5082   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5083   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5084                                         _mark_bit_map,
5085                                         work_queue(worker_id));
5086   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5087                                                  _mark_bit_map,
5088                                                  work_queue(worker_id));
5089   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5090   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5091   if (_task.marks_oops_alive()) {
5092     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5093                   _collector->hash_seed(worker_id));
5094   }
5095   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5096   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5097 }
5098 
5099 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5100   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5101   EnqueueTask& _task;
5102 
5103 public:
5104   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5105     : AbstractGangTask("Enqueue reference objects in parallel"),
5106       _task(task)
5107   { }
5108 
5109   virtual void work(uint worker_id)
5110   {
5111     _task.work(worker_id);
5112   }
5113 };
5114 
5115 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5116   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5117    _span(span),
5118    _bit_map(bit_map),
5119    _work_queue(work_queue),
5120    _mark_and_push(collector, span, bit_map, work_queue),
5121    _low_water_mark(MIN2((work_queue->max_elems()/4),
5122                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5123 { }
5124 
5125 // . see if we can share work_queues with ParNew? XXX
5126 void CMSRefProcTaskProxy::do_work_steal(int i,
5127   CMSParDrainMarkingStackClosure* drain,
5128   CMSParKeepAliveClosure* keep_alive,
5129   int* seed) {
5130   OopTaskQueue* work_q = work_queue(i);
5131   NOT_PRODUCT(int num_steals = 0;)
5132   oop obj_to_scan;
5133 
5134   while (true) {
5135     // Completely finish any left over work from (an) earlier round(s)
5136     drain->trim_queue(0);
5137     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5138                                          (size_t)ParGCDesiredObjsFromOverflowList);
5139     // Now check if there's any work in the overflow list
5140     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5141     // only affects the number of attempts made to get work from the
5142     // overflow list and does not affect the number of workers.  Just
5143     // pass ParallelGCThreads so this behavior is unchanged.
5144     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5145                                                 work_q,
5146                                                 ParallelGCThreads)) {
5147       // Found something in global overflow list;
5148       // not yet ready to go stealing work from others.
5149       // We'd like to assert(work_q->size() != 0, ...)
5150       // because we just took work from the overflow list,
5151       // but of course we can't, since all of that might have
5152       // been already stolen from us.
5153       continue;
5154     }
5155     // Verify that we have no work before we resort to stealing
5156     assert(work_q->size() == 0, "Have work, shouldn't steal");
5157     // Try to steal from other queues that have work
5158     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5159       NOT_PRODUCT(num_steals++;)
5160       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5161       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5162       // Do scanning work
5163       obj_to_scan->oop_iterate(keep_alive);
5164       // Loop around, finish this work, and try to steal some more
5165     } else if (terminator()->offer_termination()) {
5166       break;  // nirvana from the infinite cycle
5167     }
5168   }
5169   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5170 }
5171 
5172 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5173 {
5174   GenCollectedHeap* gch = GenCollectedHeap::heap();
5175   WorkGang* workers = gch->workers();
5176   assert(workers != NULL, "Need parallel worker threads.");
5177   CMSRefProcTaskProxy rp_task(task, &_collector,
5178                               _collector.ref_processor()->span(),
5179                               _collector.markBitMap(),
5180                               workers, _collector.task_queues());
5181   workers->run_task(&rp_task);
5182 }
5183 
5184 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5185 {
5186 
5187   GenCollectedHeap* gch = GenCollectedHeap::heap();
5188   WorkGang* workers = gch->workers();
5189   assert(workers != NULL, "Need parallel worker threads.");
5190   CMSRefEnqueueTaskProxy enq_task(task);
5191   workers->run_task(&enq_task);
5192 }
5193 
5194 void CMSCollector::refProcessingWork() {
5195   ResourceMark rm;
5196   HandleMark   hm;
5197 
5198   ReferenceProcessor* rp = ref_processor();
5199   assert(rp->span().equals(_span), "Spans should be equal");
5200   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5201   // Process weak references.
5202   rp->setup_policy(false);
5203   verify_work_stacks_empty();
5204 
5205   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5206                                           &_markStack, false /* !preclean */);
5207   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5208                                 _span, &_markBitMap, &_markStack,
5209                                 &cmsKeepAliveClosure, false /* !preclean */);
5210   {
5211     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5212 
5213     ReferenceProcessorStats stats;
5214     if (rp->processing_is_mt()) {
5215       // Set the degree of MT here.  If the discovery is done MT, there
5216       // may have been a different number of threads doing the discovery
5217       // and a different number of discovered lists may have Ref objects.
5218       // That is OK as long as the Reference lists are balanced (see
5219       // balance_all_queues() and balance_queues()).
5220       GenCollectedHeap* gch = GenCollectedHeap::heap();
5221       uint active_workers = ParallelGCThreads;
5222       WorkGang* workers = gch->workers();
5223       if (workers != NULL) {
5224         active_workers = workers->active_workers();
5225         // The expectation is that active_workers will have already
5226         // been set to a reasonable value.  If it has not been set,
5227         // investigate.
5228         assert(active_workers > 0, "Should have been set during scavenge");
5229       }
5230       rp->set_active_mt_degree(active_workers);
5231       CMSRefProcTaskExecutor task_executor(*this);
5232       stats = rp->process_discovered_references(&_is_alive_closure,
5233                                         &cmsKeepAliveClosure,
5234                                         &cmsDrainMarkingStackClosure,
5235                                         &task_executor,
5236                                         _gc_timer_cm);
5237     } else {
5238       stats = rp->process_discovered_references(&_is_alive_closure,
5239                                         &cmsKeepAliveClosure,
5240                                         &cmsDrainMarkingStackClosure,
5241                                         NULL,
5242                                         _gc_timer_cm);
5243     }
5244     _gc_tracer_cm->report_gc_reference_stats(stats);
5245 
5246   }
5247 
5248   // This is the point where the entire marking should have completed.
5249   verify_work_stacks_empty();
5250 
5251   if (should_unload_classes()) {
5252     {
5253       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5254 
5255       // Unload classes and purge the SystemDictionary.
5256       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5257 
5258       // Unload nmethods.
5259       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5260 
5261       // Prune dead klasses from subklass/sibling/implementor lists.
5262       Klass::clean_weak_klass_links(&_is_alive_closure);
5263     }
5264 
5265     {
5266       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5267       // Clean up unreferenced symbols in symbol table.
5268       SymbolTable::unlink();
5269     }
5270 
5271     {
5272       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5273       // Delete entries for dead interned strings.
5274       StringTable::unlink(&_is_alive_closure);
5275     }
5276   }
5277 
5278 
5279   // Restore any preserved marks as a result of mark stack or
5280   // work queue overflow
5281   restore_preserved_marks_if_any();  // done single-threaded for now
5282 
5283   rp->set_enqueuing_is_done(true);
5284   if (rp->processing_is_mt()) {
5285     rp->balance_all_queues();
5286     CMSRefProcTaskExecutor task_executor(*this);
5287     rp->enqueue_discovered_references(&task_executor);
5288   } else {
5289     rp->enqueue_discovered_references(NULL);
5290   }
5291   rp->verify_no_references_recorded();
5292   assert(!rp->discovery_enabled(), "should have been disabled");
5293 }
5294 
5295 #ifndef PRODUCT
5296 void CMSCollector::check_correct_thread_executing() {
5297   Thread* t = Thread::current();
5298   // Only the VM thread or the CMS thread should be here.
5299   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5300          "Unexpected thread type");
5301   // If this is the vm thread, the foreground process
5302   // should not be waiting.  Note that _foregroundGCIsActive is
5303   // true while the foreground collector is waiting.
5304   if (_foregroundGCShouldWait) {
5305     // We cannot be the VM thread
5306     assert(t->is_ConcurrentGC_thread(),
5307            "Should be CMS thread");
5308   } else {
5309     // We can be the CMS thread only if we are in a stop-world
5310     // phase of CMS collection.
5311     if (t->is_ConcurrentGC_thread()) {
5312       assert(_collectorState == InitialMarking ||
5313              _collectorState == FinalMarking,
5314              "Should be a stop-world phase");
5315       // The CMS thread should be holding the CMS_token.
5316       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5317              "Potential interference with concurrently "
5318              "executing VM thread");
5319     }
5320   }
5321 }
5322 #endif
5323 
5324 void CMSCollector::sweep() {
5325   assert(_collectorState == Sweeping, "just checking");
5326   check_correct_thread_executing();
5327   verify_work_stacks_empty();
5328   verify_overflow_empty();
5329   increment_sweep_count();
5330   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5331 
5332   _inter_sweep_timer.stop();
5333   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5334 
5335   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5336   _intra_sweep_timer.reset();
5337   _intra_sweep_timer.start();
5338   {
5339     GCTraceCPUTime tcpu;
5340     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5341     // First sweep the old gen
5342     {
5343       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5344                                bitMapLock());
5345       sweepWork(_cmsGen);
5346     }
5347 
5348     // Update Universe::_heap_*_at_gc figures.
5349     // We need all the free list locks to make the abstract state
5350     // transition from Sweeping to Resetting. See detailed note
5351     // further below.
5352     {
5353       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5354       // Update heap occupancy information which is used as
5355       // input to soft ref clearing policy at the next gc.
5356       Universe::update_heap_info_at_gc();
5357       _collectorState = Resizing;
5358     }
5359   }
5360   verify_work_stacks_empty();
5361   verify_overflow_empty();
5362 
5363   if (should_unload_classes()) {
5364     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5365     // requires that the virtual spaces are stable and not deleted.
5366     ClassLoaderDataGraph::set_should_purge(true);
5367   }
5368 
5369   _intra_sweep_timer.stop();
5370   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5371 
5372   _inter_sweep_timer.reset();
5373   _inter_sweep_timer.start();
5374 
5375   // We need to use a monotonically non-decreasing time in ms
5376   // or we will see time-warp warnings and os::javaTimeMillis()
5377   // does not guarantee monotonicity.
5378   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5379   update_time_of_last_gc(now);
5380 
5381   // NOTE on abstract state transitions:
5382   // Mutators allocate-live and/or mark the mod-union table dirty
5383   // based on the state of the collection.  The former is done in
5384   // the interval [Marking, Sweeping] and the latter in the interval
5385   // [Marking, Sweeping).  Thus the transitions into the Marking state
5386   // and out of the Sweeping state must be synchronously visible
5387   // globally to the mutators.
5388   // The transition into the Marking state happens with the world
5389   // stopped so the mutators will globally see it.  Sweeping is
5390   // done asynchronously by the background collector so the transition
5391   // from the Sweeping state to the Resizing state must be done
5392   // under the freelistLock (as is the check for whether to
5393   // allocate-live and whether to dirty the mod-union table).
5394   assert(_collectorState == Resizing, "Change of collector state to"
5395     " Resizing must be done under the freelistLocks (plural)");
5396 
5397   // Now that sweeping has been completed, we clear
5398   // the incremental_collection_failed flag,
5399   // thus inviting a younger gen collection to promote into
5400   // this generation. If such a promotion may still fail,
5401   // the flag will be set again when a young collection is
5402   // attempted.
5403   GenCollectedHeap* gch = GenCollectedHeap::heap();
5404   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5405   gch->update_full_collections_completed(_collection_count_start);
5406 }
5407 
5408 // FIX ME!!! Looks like this belongs in CFLSpace, with
5409 // CMSGen merely delegating to it.
5410 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5411   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5412   HeapWord*  minAddr        = _cmsSpace->bottom();
5413   HeapWord*  largestAddr    =
5414     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5415   if (largestAddr == NULL) {
5416     // The dictionary appears to be empty.  In this case
5417     // try to coalesce at the end of the heap.
5418     largestAddr = _cmsSpace->end();
5419   }
5420   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5421   size_t nearLargestOffset =
5422     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5423   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5424                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5425   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5426 }
5427 
5428 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5429   return addr >= _cmsSpace->nearLargestChunk();
5430 }
5431 
5432 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5433   return _cmsSpace->find_chunk_at_end();
5434 }
5435 
5436 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5437                                                     bool full) {
5438   // If the young generation has been collected, gather any statistics
5439   // that are of interest at this point.
5440   bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5441   if (!full && current_is_young) {
5442     // Gather statistics on the young generation collection.
5443     collector()->stats().record_gc0_end(used());
5444   }
5445 }
5446 
5447 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5448   // We iterate over the space(s) underlying this generation,
5449   // checking the mark bit map to see if the bits corresponding
5450   // to specific blocks are marked or not. Blocks that are
5451   // marked are live and are not swept up. All remaining blocks
5452   // are swept up, with coalescing on-the-fly as we sweep up
5453   // contiguous free and/or garbage blocks:
5454   // We need to ensure that the sweeper synchronizes with allocators
5455   // and stop-the-world collectors. In particular, the following
5456   // locks are used:
5457   // . CMS token: if this is held, a stop the world collection cannot occur
5458   // . freelistLock: if this is held no allocation can occur from this
5459   //                 generation by another thread
5460   // . bitMapLock: if this is held, no other thread can access or update
5461   //
5462 
5463   // Note that we need to hold the freelistLock if we use
5464   // block iterate below; else the iterator might go awry if
5465   // a mutator (or promotion) causes block contents to change
5466   // (for instance if the allocator divvies up a block).
5467   // If we hold the free list lock, for all practical purposes
5468   // young generation GC's can't occur (they'll usually need to
5469   // promote), so we might as well prevent all young generation
5470   // GC's while we do a sweeping step. For the same reason, we might
5471   // as well take the bit map lock for the entire duration
5472 
5473   // check that we hold the requisite locks
5474   assert(have_cms_token(), "Should hold cms token");
5475   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5476   assert_lock_strong(old_gen->freelistLock());
5477   assert_lock_strong(bitMapLock());
5478 
5479   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5480   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5481   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5482                                           _inter_sweep_estimate.padded_average(),
5483                                           _intra_sweep_estimate.padded_average());
5484   old_gen->setNearLargestChunk();
5485 
5486   {
5487     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5488     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5489     // We need to free-up/coalesce garbage/blocks from a
5490     // co-terminal free run. This is done in the SweepClosure
5491     // destructor; so, do not remove this scope, else the
5492     // end-of-sweep-census below will be off by a little bit.
5493   }
5494   old_gen->cmsSpace()->sweep_completed();
5495   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5496   if (should_unload_classes()) {                // unloaded classes this cycle,
5497     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5498   } else {                                      // did not unload classes,
5499     _concurrent_cycles_since_last_unload++;     // ... increment count
5500   }
5501 }
5502 
5503 // Reset CMS data structures (for now just the marking bit map)
5504 // preparatory for the next cycle.
5505 void CMSCollector::reset_concurrent() {
5506   CMSTokenSyncWithLocks ts(true, bitMapLock());
5507 
5508   // If the state is not "Resetting", the foreground  thread
5509   // has done a collection and the resetting.
5510   if (_collectorState != Resetting) {
5511     assert(_collectorState == Idling, "The state should only change"
5512       " because the foreground collector has finished the collection");
5513     return;
5514   }
5515 
5516   {
5517     // Clear the mark bitmap (no grey objects to start with)
5518     // for the next cycle.
5519     GCTraceCPUTime tcpu;
5520     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5521 
5522     HeapWord* curAddr = _markBitMap.startWord();
5523     while (curAddr < _markBitMap.endWord()) {
5524       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5525       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5526       _markBitMap.clear_large_range(chunk);
5527       if (ConcurrentMarkSweepThread::should_yield() &&
5528           !foregroundGCIsActive() &&
5529           CMSYield) {
5530         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5531                "CMS thread should hold CMS token");
5532         assert_lock_strong(bitMapLock());
5533         bitMapLock()->unlock();
5534         ConcurrentMarkSweepThread::desynchronize(true);
5535         stopTimer();
5536         incrementYields();
5537 
5538         // See the comment in coordinator_yield()
5539         for (unsigned i = 0; i < CMSYieldSleepCount &&
5540                          ConcurrentMarkSweepThread::should_yield() &&
5541                          !CMSCollector::foregroundGCIsActive(); ++i) {
5542           os::sleep(Thread::current(), 1, false);
5543         }
5544 
5545         ConcurrentMarkSweepThread::synchronize(true);
5546         bitMapLock()->lock_without_safepoint_check();
5547         startTimer();
5548       }
5549       curAddr = chunk.end();
5550     }
5551     // A successful mostly concurrent collection has been done.
5552     // Because only the full (i.e., concurrent mode failure) collections
5553     // are being measured for gc overhead limits, clean the "near" flag
5554     // and count.
5555     size_policy()->reset_gc_overhead_limit_count();
5556     _collectorState = Idling;
5557   }
5558 
5559   register_gc_end();
5560 }
5561 
5562 // Same as above but for STW paths
5563 void CMSCollector::reset_stw() {
5564   // already have the lock
5565   assert(_collectorState == Resetting, "just checking");
5566   assert_lock_strong(bitMapLock());
5567   GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5568   _markBitMap.clear_all();
5569   _collectorState = Idling;
5570   register_gc_end();
5571 }
5572 
5573 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5574   GCTraceCPUTime tcpu;
5575   TraceCollectorStats tcs(counters());
5576 
5577   switch (op) {
5578     case CMS_op_checkpointRootsInitial: {
5579       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5580       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5581       checkpointRootsInitial();
5582       break;
5583     }
5584     case CMS_op_checkpointRootsFinal: {
5585       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5586       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5587       checkpointRootsFinal();
5588       break;
5589     }
5590     default:
5591       fatal("No such CMS_op");
5592   }
5593 }
5594 
5595 #ifndef PRODUCT
5596 size_t const CMSCollector::skip_header_HeapWords() {
5597   return FreeChunk::header_size();
5598 }
5599 
5600 // Try and collect here conditions that should hold when
5601 // CMS thread is exiting. The idea is that the foreground GC
5602 // thread should not be blocked if it wants to terminate
5603 // the CMS thread and yet continue to run the VM for a while
5604 // after that.
5605 void CMSCollector::verify_ok_to_terminate() const {
5606   assert(Thread::current()->is_ConcurrentGC_thread(),
5607          "should be called by CMS thread");
5608   assert(!_foregroundGCShouldWait, "should be false");
5609   // We could check here that all the various low-level locks
5610   // are not held by the CMS thread, but that is overkill; see
5611   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5612   // is checked.
5613 }
5614 #endif
5615 
5616 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5617    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5618           "missing Printezis mark?");
5619   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5620   size_t size = pointer_delta(nextOneAddr + 1, addr);
5621   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5622          "alignment problem");
5623   assert(size >= 3, "Necessary for Printezis marks to work");
5624   return size;
5625 }
5626 
5627 // A variant of the above (block_size_using_printezis_bits()) except
5628 // that we return 0 if the P-bits are not yet set.
5629 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5630   if (_markBitMap.isMarked(addr + 1)) {
5631     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5632     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5633     size_t size = pointer_delta(nextOneAddr + 1, addr);
5634     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5635            "alignment problem");
5636     assert(size >= 3, "Necessary for Printezis marks to work");
5637     return size;
5638   }
5639   return 0;
5640 }
5641 
5642 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5643   size_t sz = 0;
5644   oop p = (oop)addr;
5645   if (p->klass_or_null() != NULL) {
5646     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5647   } else {
5648     sz = block_size_using_printezis_bits(addr);
5649   }
5650   assert(sz > 0, "size must be nonzero");
5651   HeapWord* next_block = addr + sz;
5652   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5653                                              CardTableModRefBS::card_size);
5654   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5655          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5656          "must be different cards");
5657   return next_card;
5658 }
5659 
5660 
5661 // CMS Bit Map Wrapper /////////////////////////////////////////
5662 
5663 // Construct a CMS bit map infrastructure, but don't create the
5664 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5665 // further below.
5666 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5667   _bm(),
5668   _shifter(shifter),
5669   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5670                                     Monitor::_safepoint_check_sometimes) : NULL)
5671 {
5672   _bmStartWord = 0;
5673   _bmWordSize  = 0;
5674 }
5675 
5676 bool CMSBitMap::allocate(MemRegion mr) {
5677   _bmStartWord = mr.start();
5678   _bmWordSize  = mr.word_size();
5679   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5680                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5681   if (!brs.is_reserved()) {
5682     log_warning(gc)("CMS bit map allocation failure");
5683     return false;
5684   }
5685   // For now we'll just commit all of the bit map up front.
5686   // Later on we'll try to be more parsimonious with swap.
5687   if (!_virtual_space.initialize(brs, brs.size())) {
5688     log_warning(gc)("CMS bit map backing store failure");
5689     return false;
5690   }
5691   assert(_virtual_space.committed_size() == brs.size(),
5692          "didn't reserve backing store for all of CMS bit map?");
5693   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5694          _bmWordSize, "inconsistency in bit map sizing");
5695   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5696 
5697   // bm.clear(); // can we rely on getting zero'd memory? verify below
5698   assert(isAllClear(),
5699          "Expected zero'd memory from ReservedSpace constructor");
5700   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5701          "consistency check");
5702   return true;
5703 }
5704 
5705 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5706   HeapWord *next_addr, *end_addr, *last_addr;
5707   assert_locked();
5708   assert(covers(mr), "out-of-range error");
5709   // XXX assert that start and end are appropriately aligned
5710   for (next_addr = mr.start(), end_addr = mr.end();
5711        next_addr < end_addr; next_addr = last_addr) {
5712     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5713     last_addr = dirty_region.end();
5714     if (!dirty_region.is_empty()) {
5715       cl->do_MemRegion(dirty_region);
5716     } else {
5717       assert(last_addr == end_addr, "program logic");
5718       return;
5719     }
5720   }
5721 }
5722 
5723 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5724   _bm.print_on_error(st, prefix);
5725 }
5726 
5727 #ifndef PRODUCT
5728 void CMSBitMap::assert_locked() const {
5729   CMSLockVerifier::assert_locked(lock());
5730 }
5731 
5732 bool CMSBitMap::covers(MemRegion mr) const {
5733   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5734   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5735          "size inconsistency");
5736   return (mr.start() >= _bmStartWord) &&
5737          (mr.end()   <= endWord());
5738 }
5739 
5740 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5741     return (start >= _bmStartWord && (start + size) <= endWord());
5742 }
5743 
5744 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5745   // verify that there are no 1 bits in the interval [left, right)
5746   FalseBitMapClosure falseBitMapClosure;
5747   iterate(&falseBitMapClosure, left, right);
5748 }
5749 
5750 void CMSBitMap::region_invariant(MemRegion mr)
5751 {
5752   assert_locked();
5753   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5754   assert(!mr.is_empty(), "unexpected empty region");
5755   assert(covers(mr), "mr should be covered by bit map");
5756   // convert address range into offset range
5757   size_t start_ofs = heapWordToOffset(mr.start());
5758   // Make sure that end() is appropriately aligned
5759   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5760                         (1 << (_shifter+LogHeapWordSize))),
5761          "Misaligned mr.end()");
5762   size_t end_ofs   = heapWordToOffset(mr.end());
5763   assert(end_ofs > start_ofs, "Should mark at least one bit");
5764 }
5765 
5766 #endif
5767 
5768 bool CMSMarkStack::allocate(size_t size) {
5769   // allocate a stack of the requisite depth
5770   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5771                    size * sizeof(oop)));
5772   if (!rs.is_reserved()) {
5773     log_warning(gc)("CMSMarkStack allocation failure");
5774     return false;
5775   }
5776   if (!_virtual_space.initialize(rs, rs.size())) {
5777     log_warning(gc)("CMSMarkStack backing store failure");
5778     return false;
5779   }
5780   assert(_virtual_space.committed_size() == rs.size(),
5781          "didn't reserve backing store for all of CMS stack?");
5782   _base = (oop*)(_virtual_space.low());
5783   _index = 0;
5784   _capacity = size;
5785   NOT_PRODUCT(_max_depth = 0);
5786   return true;
5787 }
5788 
5789 // XXX FIX ME !!! In the MT case we come in here holding a
5790 // leaf lock. For printing we need to take a further lock
5791 // which has lower rank. We need to recalibrate the two
5792 // lock-ranks involved in order to be able to print the
5793 // messages below. (Or defer the printing to the caller.
5794 // For now we take the expedient path of just disabling the
5795 // messages for the problematic case.)
5796 void CMSMarkStack::expand() {
5797   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5798   if (_capacity == MarkStackSizeMax) {
5799     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5800       // We print a warning message only once per CMS cycle.
5801       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5802     }
5803     return;
5804   }
5805   // Double capacity if possible
5806   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5807   // Do not give up existing stack until we have managed to
5808   // get the double capacity that we desired.
5809   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5810                    new_capacity * sizeof(oop)));
5811   if (rs.is_reserved()) {
5812     // Release the backing store associated with old stack
5813     _virtual_space.release();
5814     // Reinitialize virtual space for new stack
5815     if (!_virtual_space.initialize(rs, rs.size())) {
5816       fatal("Not enough swap for expanded marking stack");
5817     }
5818     _base = (oop*)(_virtual_space.low());
5819     _index = 0;
5820     _capacity = new_capacity;
5821   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5822     // Failed to double capacity, continue;
5823     // we print a detail message only once per CMS cycle.
5824     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5825                         _capacity / K, new_capacity / K);
5826   }
5827 }
5828 
5829 
5830 // Closures
5831 // XXX: there seems to be a lot of code  duplication here;
5832 // should refactor and consolidate common code.
5833 
5834 // This closure is used to mark refs into the CMS generation in
5835 // the CMS bit map. Called at the first checkpoint. This closure
5836 // assumes that we do not need to re-mark dirty cards; if the CMS
5837 // generation on which this is used is not an oldest
5838 // generation then this will lose younger_gen cards!
5839 
5840 MarkRefsIntoClosure::MarkRefsIntoClosure(
5841   MemRegion span, CMSBitMap* bitMap):
5842     _span(span),
5843     _bitMap(bitMap)
5844 {
5845   assert(ref_processor() == NULL, "deliberately left NULL");
5846   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5847 }
5848 
5849 void MarkRefsIntoClosure::do_oop(oop obj) {
5850   // if p points into _span, then mark corresponding bit in _markBitMap
5851   assert(obj->is_oop(), "expected an oop");
5852   HeapWord* addr = (HeapWord*)obj;
5853   if (_span.contains(addr)) {
5854     // this should be made more efficient
5855     _bitMap->mark(addr);
5856   }
5857 }
5858 
5859 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5860 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5861 
5862 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5863   MemRegion span, CMSBitMap* bitMap):
5864     _span(span),
5865     _bitMap(bitMap)
5866 {
5867   assert(ref_processor() == NULL, "deliberately left NULL");
5868   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5869 }
5870 
5871 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5872   // if p points into _span, then mark corresponding bit in _markBitMap
5873   assert(obj->is_oop(), "expected an oop");
5874   HeapWord* addr = (HeapWord*)obj;
5875   if (_span.contains(addr)) {
5876     // this should be made more efficient
5877     _bitMap->par_mark(addr);
5878   }
5879 }
5880 
5881 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5882 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5883 
5884 // A variant of the above, used for CMS marking verification.
5885 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5886   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5887     _span(span),
5888     _verification_bm(verification_bm),
5889     _cms_bm(cms_bm)
5890 {
5891   assert(ref_processor() == NULL, "deliberately left NULL");
5892   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5893 }
5894 
5895 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5896   // if p points into _span, then mark corresponding bit in _markBitMap
5897   assert(obj->is_oop(), "expected an oop");
5898   HeapWord* addr = (HeapWord*)obj;
5899   if (_span.contains(addr)) {
5900     _verification_bm->mark(addr);
5901     if (!_cms_bm->isMarked(addr)) {
5902       Log(gc, verify) log;
5903       ResourceMark rm;
5904       oop(addr)->print_on(log.error_stream());
5905       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5906       fatal("... aborting");
5907     }
5908   }
5909 }
5910 
5911 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5912 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5913 
5914 //////////////////////////////////////////////////
5915 // MarkRefsIntoAndScanClosure
5916 //////////////////////////////////////////////////
5917 
5918 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5919                                                        ReferenceProcessor* rp,
5920                                                        CMSBitMap* bit_map,
5921                                                        CMSBitMap* mod_union_table,
5922                                                        CMSMarkStack*  mark_stack,
5923                                                        CMSCollector* collector,
5924                                                        bool should_yield,
5925                                                        bool concurrent_precleaning):
5926   _collector(collector),
5927   _span(span),
5928   _bit_map(bit_map),
5929   _mark_stack(mark_stack),
5930   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5931                       mark_stack, concurrent_precleaning),
5932   _yield(should_yield),
5933   _concurrent_precleaning(concurrent_precleaning),
5934   _freelistLock(NULL)
5935 {
5936   // FIXME: Should initialize in base class constructor.
5937   assert(rp != NULL, "ref_processor shouldn't be NULL");
5938   set_ref_processor_internal(rp);
5939 }
5940 
5941 // This closure is used to mark refs into the CMS generation at the
5942 // second (final) checkpoint, and to scan and transitively follow
5943 // the unmarked oops. It is also used during the concurrent precleaning
5944 // phase while scanning objects on dirty cards in the CMS generation.
5945 // The marks are made in the marking bit map and the marking stack is
5946 // used for keeping the (newly) grey objects during the scan.
5947 // The parallel version (Par_...) appears further below.
5948 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5949   if (obj != NULL) {
5950     assert(obj->is_oop(), "expected an oop");
5951     HeapWord* addr = (HeapWord*)obj;
5952     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5953     assert(_collector->overflow_list_is_empty(),
5954            "overflow list should be empty");
5955     if (_span.contains(addr) &&
5956         !_bit_map->isMarked(addr)) {
5957       // mark bit map (object is now grey)
5958       _bit_map->mark(addr);
5959       // push on marking stack (stack should be empty), and drain the
5960       // stack by applying this closure to the oops in the oops popped
5961       // from the stack (i.e. blacken the grey objects)
5962       bool res = _mark_stack->push(obj);
5963       assert(res, "Should have space to push on empty stack");
5964       do {
5965         oop new_oop = _mark_stack->pop();
5966         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5967         assert(_bit_map->isMarked((HeapWord*)new_oop),
5968                "only grey objects on this stack");
5969         // iterate over the oops in this oop, marking and pushing
5970         // the ones in CMS heap (i.e. in _span).
5971         new_oop->oop_iterate(&_pushAndMarkClosure);
5972         // check if it's time to yield
5973         do_yield_check();
5974       } while (!_mark_stack->isEmpty() ||
5975                (!_concurrent_precleaning && take_from_overflow_list()));
5976         // if marking stack is empty, and we are not doing this
5977         // during precleaning, then check the overflow list
5978     }
5979     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5980     assert(_collector->overflow_list_is_empty(),
5981            "overflow list was drained above");
5982 
5983     assert(_collector->no_preserved_marks(),
5984            "All preserved marks should have been restored above");
5985   }
5986 }
5987 
5988 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5989 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5990 
5991 void MarkRefsIntoAndScanClosure::do_yield_work() {
5992   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5993          "CMS thread should hold CMS token");
5994   assert_lock_strong(_freelistLock);
5995   assert_lock_strong(_bit_map->lock());
5996   // relinquish the free_list_lock and bitMaplock()
5997   _bit_map->lock()->unlock();
5998   _freelistLock->unlock();
5999   ConcurrentMarkSweepThread::desynchronize(true);
6000   _collector->stopTimer();
6001   _collector->incrementYields();
6002 
6003   // See the comment in coordinator_yield()
6004   for (unsigned i = 0;
6005        i < CMSYieldSleepCount &&
6006        ConcurrentMarkSweepThread::should_yield() &&
6007        !CMSCollector::foregroundGCIsActive();
6008        ++i) {
6009     os::sleep(Thread::current(), 1, false);
6010   }
6011 
6012   ConcurrentMarkSweepThread::synchronize(true);
6013   _freelistLock->lock_without_safepoint_check();
6014   _bit_map->lock()->lock_without_safepoint_check();
6015   _collector->startTimer();
6016 }
6017 
6018 ///////////////////////////////////////////////////////////
6019 // ParMarkRefsIntoAndScanClosure: a parallel version of
6020 //                                MarkRefsIntoAndScanClosure
6021 ///////////////////////////////////////////////////////////
6022 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6023   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6024   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6025   _span(span),
6026   _bit_map(bit_map),
6027   _work_queue(work_queue),
6028   _low_water_mark(MIN2((work_queue->max_elems()/4),
6029                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6030   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6031 {
6032   // FIXME: Should initialize in base class constructor.
6033   assert(rp != NULL, "ref_processor shouldn't be NULL");
6034   set_ref_processor_internal(rp);
6035 }
6036 
6037 // This closure is used to mark refs into the CMS generation at the
6038 // second (final) checkpoint, and to scan and transitively follow
6039 // the unmarked oops. The marks are made in the marking bit map and
6040 // the work_queue is used for keeping the (newly) grey objects during
6041 // the scan phase whence they are also available for stealing by parallel
6042 // threads. Since the marking bit map is shared, updates are
6043 // synchronized (via CAS).
6044 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6045   if (obj != NULL) {
6046     // Ignore mark word because this could be an already marked oop
6047     // that may be chained at the end of the overflow list.
6048     assert(obj->is_oop(true), "expected an oop");
6049     HeapWord* addr = (HeapWord*)obj;
6050     if (_span.contains(addr) &&
6051         !_bit_map->isMarked(addr)) {
6052       // mark bit map (object will become grey):
6053       // It is possible for several threads to be
6054       // trying to "claim" this object concurrently;
6055       // the unique thread that succeeds in marking the
6056       // object first will do the subsequent push on
6057       // to the work queue (or overflow list).
6058       if (_bit_map->par_mark(addr)) {
6059         // push on work_queue (which may not be empty), and trim the
6060         // queue to an appropriate length by applying this closure to
6061         // the oops in the oops popped from the stack (i.e. blacken the
6062         // grey objects)
6063         bool res = _work_queue->push(obj);
6064         assert(res, "Low water mark should be less than capacity?");
6065         trim_queue(_low_water_mark);
6066       } // Else, another thread claimed the object
6067     }
6068   }
6069 }
6070 
6071 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p)       { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6072 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6073 
6074 // This closure is used to rescan the marked objects on the dirty cards
6075 // in the mod union table and the card table proper.
6076 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6077   oop p, MemRegion mr) {
6078 
6079   size_t size = 0;
6080   HeapWord* addr = (HeapWord*)p;
6081   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6082   assert(_span.contains(addr), "we are scanning the CMS generation");
6083   // check if it's time to yield
6084   if (do_yield_check()) {
6085     // We yielded for some foreground stop-world work,
6086     // and we have been asked to abort this ongoing preclean cycle.
6087     return 0;
6088   }
6089   if (_bitMap->isMarked(addr)) {
6090     // it's marked; is it potentially uninitialized?
6091     if (p->klass_or_null() != NULL) {
6092         // an initialized object; ignore mark word in verification below
6093         // since we are running concurrent with mutators
6094         assert(p->is_oop(true), "should be an oop");
6095         if (p->is_objArray()) {
6096           // objArrays are precisely marked; restrict scanning
6097           // to dirty cards only.
6098           size = CompactibleFreeListSpace::adjustObjectSize(
6099                    p->oop_iterate_size(_scanningClosure, mr));
6100         } else {
6101           // A non-array may have been imprecisely marked; we need
6102           // to scan object in its entirety.
6103           size = CompactibleFreeListSpace::adjustObjectSize(
6104                    p->oop_iterate_size(_scanningClosure));
6105         }
6106       #ifdef ASSERT
6107         size_t direct_size =
6108           CompactibleFreeListSpace::adjustObjectSize(p->size());
6109         assert(size == direct_size, "Inconsistency in size");
6110         assert(size >= 3, "Necessary for Printezis marks to work");
6111         HeapWord* start_pbit = addr + 1;
6112         HeapWord* end_pbit = addr + size - 1;
6113         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6114                "inconsistent Printezis mark");
6115         // Verify inner mark bits (between Printezis bits) are clear,
6116         // but don't repeat if there are multiple dirty regions for
6117         // the same object, to avoid potential O(N^2) performance.
6118         if (addr != _last_scanned_object) {
6119           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6120           _last_scanned_object = addr;
6121         }
6122       #endif // ASSERT
6123     } else {
6124       // An uninitialized object.
6125       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6126       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6127       size = pointer_delta(nextOneAddr + 1, addr);
6128       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6129              "alignment problem");
6130       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6131       // will dirty the card when the klass pointer is installed in the
6132       // object (signaling the completion of initialization).
6133     }
6134   } else {
6135     // Either a not yet marked object or an uninitialized object
6136     if (p->klass_or_null() == NULL) {
6137       // An uninitialized object, skip to the next card, since
6138       // we may not be able to read its P-bits yet.
6139       assert(size == 0, "Initial value");
6140     } else {
6141       // An object not (yet) reached by marking: we merely need to
6142       // compute its size so as to go look at the next block.
6143       assert(p->is_oop(true), "should be an oop");
6144       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6145     }
6146   }
6147   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6148   return size;
6149 }
6150 
6151 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6152   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6153          "CMS thread should hold CMS token");
6154   assert_lock_strong(_freelistLock);
6155   assert_lock_strong(_bitMap->lock());
6156   // relinquish the free_list_lock and bitMaplock()
6157   _bitMap->lock()->unlock();
6158   _freelistLock->unlock();
6159   ConcurrentMarkSweepThread::desynchronize(true);
6160   _collector->stopTimer();
6161   _collector->incrementYields();
6162 
6163   // See the comment in coordinator_yield()
6164   for (unsigned i = 0; i < CMSYieldSleepCount &&
6165                    ConcurrentMarkSweepThread::should_yield() &&
6166                    !CMSCollector::foregroundGCIsActive(); ++i) {
6167     os::sleep(Thread::current(), 1, false);
6168   }
6169 
6170   ConcurrentMarkSweepThread::synchronize(true);
6171   _freelistLock->lock_without_safepoint_check();
6172   _bitMap->lock()->lock_without_safepoint_check();
6173   _collector->startTimer();
6174 }
6175 
6176 
6177 //////////////////////////////////////////////////////////////////
6178 // SurvivorSpacePrecleanClosure
6179 //////////////////////////////////////////////////////////////////
6180 // This (single-threaded) closure is used to preclean the oops in
6181 // the survivor spaces.
6182 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6183 
6184   HeapWord* addr = (HeapWord*)p;
6185   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6186   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6187   assert(p->klass_or_null() != NULL, "object should be initialized");
6188   // an initialized object; ignore mark word in verification below
6189   // since we are running concurrent with mutators
6190   assert(p->is_oop(true), "should be an oop");
6191   // Note that we do not yield while we iterate over
6192   // the interior oops of p, pushing the relevant ones
6193   // on our marking stack.
6194   size_t size = p->oop_iterate_size(_scanning_closure);
6195   do_yield_check();
6196   // Observe that below, we do not abandon the preclean
6197   // phase as soon as we should; rather we empty the
6198   // marking stack before returning. This is to satisfy
6199   // some existing assertions. In general, it may be a
6200   // good idea to abort immediately and complete the marking
6201   // from the grey objects at a later time.
6202   while (!_mark_stack->isEmpty()) {
6203     oop new_oop = _mark_stack->pop();
6204     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6205     assert(_bit_map->isMarked((HeapWord*)new_oop),
6206            "only grey objects on this stack");
6207     // iterate over the oops in this oop, marking and pushing
6208     // the ones in CMS heap (i.e. in _span).
6209     new_oop->oop_iterate(_scanning_closure);
6210     // check if it's time to yield
6211     do_yield_check();
6212   }
6213   unsigned int after_count =
6214     GenCollectedHeap::heap()->total_collections();
6215   bool abort = (_before_count != after_count) ||
6216                _collector->should_abort_preclean();
6217   return abort ? 0 : size;
6218 }
6219 
6220 void SurvivorSpacePrecleanClosure::do_yield_work() {
6221   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6222          "CMS thread should hold CMS token");
6223   assert_lock_strong(_bit_map->lock());
6224   // Relinquish the bit map lock
6225   _bit_map->lock()->unlock();
6226   ConcurrentMarkSweepThread::desynchronize(true);
6227   _collector->stopTimer();
6228   _collector->incrementYields();
6229 
6230   // See the comment in coordinator_yield()
6231   for (unsigned i = 0; i < CMSYieldSleepCount &&
6232                        ConcurrentMarkSweepThread::should_yield() &&
6233                        !CMSCollector::foregroundGCIsActive(); ++i) {
6234     os::sleep(Thread::current(), 1, false);
6235   }
6236 
6237   ConcurrentMarkSweepThread::synchronize(true);
6238   _bit_map->lock()->lock_without_safepoint_check();
6239   _collector->startTimer();
6240 }
6241 
6242 // This closure is used to rescan the marked objects on the dirty cards
6243 // in the mod union table and the card table proper. In the parallel
6244 // case, although the bitMap is shared, we do a single read so the
6245 // isMarked() query is "safe".
6246 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6247   // Ignore mark word because we are running concurrent with mutators
6248   assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6249   HeapWord* addr = (HeapWord*)p;
6250   assert(_span.contains(addr), "we are scanning the CMS generation");
6251   bool is_obj_array = false;
6252   #ifdef ASSERT
6253     if (!_parallel) {
6254       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6255       assert(_collector->overflow_list_is_empty(),
6256              "overflow list should be empty");
6257 
6258     }
6259   #endif // ASSERT
6260   if (_bit_map->isMarked(addr)) {
6261     // Obj arrays are precisely marked, non-arrays are not;
6262     // so we scan objArrays precisely and non-arrays in their
6263     // entirety.
6264     if (p->is_objArray()) {
6265       is_obj_array = true;
6266       if (_parallel) {
6267         p->oop_iterate(_par_scan_closure, mr);
6268       } else {
6269         p->oop_iterate(_scan_closure, mr);
6270       }
6271     } else {
6272       if (_parallel) {
6273         p->oop_iterate(_par_scan_closure);
6274       } else {
6275         p->oop_iterate(_scan_closure);
6276       }
6277     }
6278   }
6279   #ifdef ASSERT
6280     if (!_parallel) {
6281       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6282       assert(_collector->overflow_list_is_empty(),
6283              "overflow list should be empty");
6284 
6285     }
6286   #endif // ASSERT
6287   return is_obj_array;
6288 }
6289 
6290 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6291                         MemRegion span,
6292                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6293                         bool should_yield, bool verifying):
6294   _collector(collector),
6295   _span(span),
6296   _bitMap(bitMap),
6297   _mut(&collector->_modUnionTable),
6298   _markStack(markStack),
6299   _yield(should_yield),
6300   _skipBits(0)
6301 {
6302   assert(_markStack->isEmpty(), "stack should be empty");
6303   _finger = _bitMap->startWord();
6304   _threshold = _finger;
6305   assert(_collector->_restart_addr == NULL, "Sanity check");
6306   assert(_span.contains(_finger), "Out of bounds _finger?");
6307   DEBUG_ONLY(_verifying = verifying;)
6308 }
6309 
6310 void MarkFromRootsClosure::reset(HeapWord* addr) {
6311   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6312   assert(_span.contains(addr), "Out of bounds _finger?");
6313   _finger = addr;
6314   _threshold = (HeapWord*)round_to(
6315                  (intptr_t)_finger, CardTableModRefBS::card_size);
6316 }
6317 
6318 // Should revisit to see if this should be restructured for
6319 // greater efficiency.
6320 bool MarkFromRootsClosure::do_bit(size_t offset) {
6321   if (_skipBits > 0) {
6322     _skipBits--;
6323     return true;
6324   }
6325   // convert offset into a HeapWord*
6326   HeapWord* addr = _bitMap->startWord() + offset;
6327   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6328          "address out of range");
6329   assert(_bitMap->isMarked(addr), "tautology");
6330   if (_bitMap->isMarked(addr+1)) {
6331     // this is an allocated but not yet initialized object
6332     assert(_skipBits == 0, "tautology");
6333     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6334     oop p = oop(addr);
6335     if (p->klass_or_null() == NULL) {
6336       DEBUG_ONLY(if (!_verifying) {)
6337         // We re-dirty the cards on which this object lies and increase
6338         // the _threshold so that we'll come back to scan this object
6339         // during the preclean or remark phase. (CMSCleanOnEnter)
6340         if (CMSCleanOnEnter) {
6341           size_t sz = _collector->block_size_using_printezis_bits(addr);
6342           HeapWord* end_card_addr   = (HeapWord*)round_to(
6343                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6344           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6345           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6346           // Bump _threshold to end_card_addr; note that
6347           // _threshold cannot possibly exceed end_card_addr, anyhow.
6348           // This prevents future clearing of the card as the scan proceeds
6349           // to the right.
6350           assert(_threshold <= end_card_addr,
6351                  "Because we are just scanning into this object");
6352           if (_threshold < end_card_addr) {
6353             _threshold = end_card_addr;
6354           }
6355           if (p->klass_or_null() != NULL) {
6356             // Redirty the range of cards...
6357             _mut->mark_range(redirty_range);
6358           } // ...else the setting of klass will dirty the card anyway.
6359         }
6360       DEBUG_ONLY(})
6361       return true;
6362     }
6363   }
6364   scanOopsInOop(addr);
6365   return true;
6366 }
6367 
6368 // We take a break if we've been at this for a while,
6369 // so as to avoid monopolizing the locks involved.
6370 void MarkFromRootsClosure::do_yield_work() {
6371   // First give up the locks, then yield, then re-lock
6372   // We should probably use a constructor/destructor idiom to
6373   // do this unlock/lock or modify the MutexUnlocker class to
6374   // serve our purpose. XXX
6375   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6376          "CMS thread should hold CMS token");
6377   assert_lock_strong(_bitMap->lock());
6378   _bitMap->lock()->unlock();
6379   ConcurrentMarkSweepThread::desynchronize(true);
6380   _collector->stopTimer();
6381   _collector->incrementYields();
6382 
6383   // See the comment in coordinator_yield()
6384   for (unsigned i = 0; i < CMSYieldSleepCount &&
6385                        ConcurrentMarkSweepThread::should_yield() &&
6386                        !CMSCollector::foregroundGCIsActive(); ++i) {
6387     os::sleep(Thread::current(), 1, false);
6388   }
6389 
6390   ConcurrentMarkSweepThread::synchronize(true);
6391   _bitMap->lock()->lock_without_safepoint_check();
6392   _collector->startTimer();
6393 }
6394 
6395 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6396   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6397   assert(_markStack->isEmpty(),
6398          "should drain stack to limit stack usage");
6399   // convert ptr to an oop preparatory to scanning
6400   oop obj = oop(ptr);
6401   // Ignore mark word in verification below, since we
6402   // may be running concurrent with mutators.
6403   assert(obj->is_oop(true), "should be an oop");
6404   assert(_finger <= ptr, "_finger runneth ahead");
6405   // advance the finger to right end of this object
6406   _finger = ptr + obj->size();
6407   assert(_finger > ptr, "we just incremented it above");
6408   // On large heaps, it may take us some time to get through
6409   // the marking phase. During
6410   // this time it's possible that a lot of mutations have
6411   // accumulated in the card table and the mod union table --
6412   // these mutation records are redundant until we have
6413   // actually traced into the corresponding card.
6414   // Here, we check whether advancing the finger would make
6415   // us cross into a new card, and if so clear corresponding
6416   // cards in the MUT (preclean them in the card-table in the
6417   // future).
6418 
6419   DEBUG_ONLY(if (!_verifying) {)
6420     // The clean-on-enter optimization is disabled by default,
6421     // until we fix 6178663.
6422     if (CMSCleanOnEnter && (_finger > _threshold)) {
6423       // [_threshold, _finger) represents the interval
6424       // of cards to be cleared  in MUT (or precleaned in card table).
6425       // The set of cards to be cleared is all those that overlap
6426       // with the interval [_threshold, _finger); note that
6427       // _threshold is always kept card-aligned but _finger isn't
6428       // always card-aligned.
6429       HeapWord* old_threshold = _threshold;
6430       assert(old_threshold == (HeapWord*)round_to(
6431               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6432              "_threshold should always be card-aligned");
6433       _threshold = (HeapWord*)round_to(
6434                      (intptr_t)_finger, CardTableModRefBS::card_size);
6435       MemRegion mr(old_threshold, _threshold);
6436       assert(!mr.is_empty(), "Control point invariant");
6437       assert(_span.contains(mr), "Should clear within span");
6438       _mut->clear_range(mr);
6439     }
6440   DEBUG_ONLY(})
6441   // Note: the finger doesn't advance while we drain
6442   // the stack below.
6443   PushOrMarkClosure pushOrMarkClosure(_collector,
6444                                       _span, _bitMap, _markStack,
6445                                       _finger, this);
6446   bool res = _markStack->push(obj);
6447   assert(res, "Empty non-zero size stack should have space for single push");
6448   while (!_markStack->isEmpty()) {
6449     oop new_oop = _markStack->pop();
6450     // Skip verifying header mark word below because we are
6451     // running concurrent with mutators.
6452     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6453     // now scan this oop's oops
6454     new_oop->oop_iterate(&pushOrMarkClosure);
6455     do_yield_check();
6456   }
6457   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6458 }
6459 
6460 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6461                        CMSCollector* collector, MemRegion span,
6462                        CMSBitMap* bit_map,
6463                        OopTaskQueue* work_queue,
6464                        CMSMarkStack*  overflow_stack):
6465   _collector(collector),
6466   _whole_span(collector->_span),
6467   _span(span),
6468   _bit_map(bit_map),
6469   _mut(&collector->_modUnionTable),
6470   _work_queue(work_queue),
6471   _overflow_stack(overflow_stack),
6472   _skip_bits(0),
6473   _task(task)
6474 {
6475   assert(_work_queue->size() == 0, "work_queue should be empty");
6476   _finger = span.start();
6477   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6478   assert(_span.contains(_finger), "Out of bounds _finger?");
6479 }
6480 
6481 // Should revisit to see if this should be restructured for
6482 // greater efficiency.
6483 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6484   if (_skip_bits > 0) {
6485     _skip_bits--;
6486     return true;
6487   }
6488   // convert offset into a HeapWord*
6489   HeapWord* addr = _bit_map->startWord() + offset;
6490   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6491          "address out of range");
6492   assert(_bit_map->isMarked(addr), "tautology");
6493   if (_bit_map->isMarked(addr+1)) {
6494     // this is an allocated object that might not yet be initialized
6495     assert(_skip_bits == 0, "tautology");
6496     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6497     oop p = oop(addr);
6498     if (p->klass_or_null() == NULL) {
6499       // in the case of Clean-on-Enter optimization, redirty card
6500       // and avoid clearing card by increasing  the threshold.
6501       return true;
6502     }
6503   }
6504   scan_oops_in_oop(addr);
6505   return true;
6506 }
6507 
6508 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6509   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6510   // Should we assert that our work queue is empty or
6511   // below some drain limit?
6512   assert(_work_queue->size() == 0,
6513          "should drain stack to limit stack usage");
6514   // convert ptr to an oop preparatory to scanning
6515   oop obj = oop(ptr);
6516   // Ignore mark word in verification below, since we
6517   // may be running concurrent with mutators.
6518   assert(obj->is_oop(true), "should be an oop");
6519   assert(_finger <= ptr, "_finger runneth ahead");
6520   // advance the finger to right end of this object
6521   _finger = ptr + obj->size();
6522   assert(_finger > ptr, "we just incremented it above");
6523   // On large heaps, it may take us some time to get through
6524   // the marking phase. During
6525   // this time it's possible that a lot of mutations have
6526   // accumulated in the card table and the mod union table --
6527   // these mutation records are redundant until we have
6528   // actually traced into the corresponding card.
6529   // Here, we check whether advancing the finger would make
6530   // us cross into a new card, and if so clear corresponding
6531   // cards in the MUT (preclean them in the card-table in the
6532   // future).
6533 
6534   // The clean-on-enter optimization is disabled by default,
6535   // until we fix 6178663.
6536   if (CMSCleanOnEnter && (_finger > _threshold)) {
6537     // [_threshold, _finger) represents the interval
6538     // of cards to be cleared  in MUT (or precleaned in card table).
6539     // The set of cards to be cleared is all those that overlap
6540     // with the interval [_threshold, _finger); note that
6541     // _threshold is always kept card-aligned but _finger isn't
6542     // always card-aligned.
6543     HeapWord* old_threshold = _threshold;
6544     assert(old_threshold == (HeapWord*)round_to(
6545             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6546            "_threshold should always be card-aligned");
6547     _threshold = (HeapWord*)round_to(
6548                    (intptr_t)_finger, CardTableModRefBS::card_size);
6549     MemRegion mr(old_threshold, _threshold);
6550     assert(!mr.is_empty(), "Control point invariant");
6551     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6552     _mut->clear_range(mr);
6553   }
6554 
6555   // Note: the local finger doesn't advance while we drain
6556   // the stack below, but the global finger sure can and will.
6557   HeapWord** gfa = _task->global_finger_addr();
6558   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6559                                          _span, _bit_map,
6560                                          _work_queue,
6561                                          _overflow_stack,
6562                                          _finger,
6563                                          gfa, this);
6564   bool res = _work_queue->push(obj);   // overflow could occur here
6565   assert(res, "Will hold once we use workqueues");
6566   while (true) {
6567     oop new_oop;
6568     if (!_work_queue->pop_local(new_oop)) {
6569       // We emptied our work_queue; check if there's stuff that can
6570       // be gotten from the overflow stack.
6571       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6572             _overflow_stack, _work_queue)) {
6573         do_yield_check();
6574         continue;
6575       } else {  // done
6576         break;
6577       }
6578     }
6579     // Skip verifying header mark word below because we are
6580     // running concurrent with mutators.
6581     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6582     // now scan this oop's oops
6583     new_oop->oop_iterate(&pushOrMarkClosure);
6584     do_yield_check();
6585   }
6586   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6587 }
6588 
6589 // Yield in response to a request from VM Thread or
6590 // from mutators.
6591 void ParMarkFromRootsClosure::do_yield_work() {
6592   assert(_task != NULL, "sanity");
6593   _task->yield();
6594 }
6595 
6596 // A variant of the above used for verifying CMS marking work.
6597 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6598                         MemRegion span,
6599                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6600                         CMSMarkStack*  mark_stack):
6601   _collector(collector),
6602   _span(span),
6603   _verification_bm(verification_bm),
6604   _cms_bm(cms_bm),
6605   _mark_stack(mark_stack),
6606   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6607                       mark_stack)
6608 {
6609   assert(_mark_stack->isEmpty(), "stack should be empty");
6610   _finger = _verification_bm->startWord();
6611   assert(_collector->_restart_addr == NULL, "Sanity check");
6612   assert(_span.contains(_finger), "Out of bounds _finger?");
6613 }
6614 
6615 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6616   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6617   assert(_span.contains(addr), "Out of bounds _finger?");
6618   _finger = addr;
6619 }
6620 
6621 // Should revisit to see if this should be restructured for
6622 // greater efficiency.
6623 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6624   // convert offset into a HeapWord*
6625   HeapWord* addr = _verification_bm->startWord() + offset;
6626   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6627          "address out of range");
6628   assert(_verification_bm->isMarked(addr), "tautology");
6629   assert(_cms_bm->isMarked(addr), "tautology");
6630 
6631   assert(_mark_stack->isEmpty(),
6632          "should drain stack to limit stack usage");
6633   // convert addr to an oop preparatory to scanning
6634   oop obj = oop(addr);
6635   assert(obj->is_oop(), "should be an oop");
6636   assert(_finger <= addr, "_finger runneth ahead");
6637   // advance the finger to right end of this object
6638   _finger = addr + obj->size();
6639   assert(_finger > addr, "we just incremented it above");
6640   // Note: the finger doesn't advance while we drain
6641   // the stack below.
6642   bool res = _mark_stack->push(obj);
6643   assert(res, "Empty non-zero size stack should have space for single push");
6644   while (!_mark_stack->isEmpty()) {
6645     oop new_oop = _mark_stack->pop();
6646     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6647     // now scan this oop's oops
6648     new_oop->oop_iterate(&_pam_verify_closure);
6649   }
6650   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6651   return true;
6652 }
6653 
6654 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6655   CMSCollector* collector, MemRegion span,
6656   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6657   CMSMarkStack*  mark_stack):
6658   MetadataAwareOopClosure(collector->ref_processor()),
6659   _collector(collector),
6660   _span(span),
6661   _verification_bm(verification_bm),
6662   _cms_bm(cms_bm),
6663   _mark_stack(mark_stack)
6664 { }
6665 
6666 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6667 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6668 
6669 // Upon stack overflow, we discard (part of) the stack,
6670 // remembering the least address amongst those discarded
6671 // in CMSCollector's _restart_address.
6672 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6673   // Remember the least grey address discarded
6674   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6675   _collector->lower_restart_addr(ra);
6676   _mark_stack->reset();  // discard stack contents
6677   _mark_stack->expand(); // expand the stack if possible
6678 }
6679 
6680 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6681   assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6682   HeapWord* addr = (HeapWord*)obj;
6683   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6684     // Oop lies in _span and isn't yet grey or black
6685     _verification_bm->mark(addr);            // now grey
6686     if (!_cms_bm->isMarked(addr)) {
6687       Log(gc, verify) log;
6688       ResourceMark rm;
6689       oop(addr)->print_on(log.error_stream());
6690       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6691       fatal("... aborting");
6692     }
6693 
6694     if (!_mark_stack->push(obj)) { // stack overflow
6695       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6696       assert(_mark_stack->isFull(), "Else push should have succeeded");
6697       handle_stack_overflow(addr);
6698     }
6699     // anything including and to the right of _finger
6700     // will be scanned as we iterate over the remainder of the
6701     // bit map
6702   }
6703 }
6704 
6705 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6706                      MemRegion span,
6707                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6708                      HeapWord* finger, MarkFromRootsClosure* parent) :
6709   MetadataAwareOopClosure(collector->ref_processor()),
6710   _collector(collector),
6711   _span(span),
6712   _bitMap(bitMap),
6713   _markStack(markStack),
6714   _finger(finger),
6715   _parent(parent)
6716 { }
6717 
6718 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6719                                            MemRegion span,
6720                                            CMSBitMap* bit_map,
6721                                            OopTaskQueue* work_queue,
6722                                            CMSMarkStack*  overflow_stack,
6723                                            HeapWord* finger,
6724                                            HeapWord** global_finger_addr,
6725                                            ParMarkFromRootsClosure* parent) :
6726   MetadataAwareOopClosure(collector->ref_processor()),
6727   _collector(collector),
6728   _whole_span(collector->_span),
6729   _span(span),
6730   _bit_map(bit_map),
6731   _work_queue(work_queue),
6732   _overflow_stack(overflow_stack),
6733   _finger(finger),
6734   _global_finger_addr(global_finger_addr),
6735   _parent(parent)
6736 { }
6737 
6738 // Assumes thread-safe access by callers, who are
6739 // responsible for mutual exclusion.
6740 void CMSCollector::lower_restart_addr(HeapWord* low) {
6741   assert(_span.contains(low), "Out of bounds addr");
6742   if (_restart_addr == NULL) {
6743     _restart_addr = low;
6744   } else {
6745     _restart_addr = MIN2(_restart_addr, low);
6746   }
6747 }
6748 
6749 // Upon stack overflow, we discard (part of) the stack,
6750 // remembering the least address amongst those discarded
6751 // in CMSCollector's _restart_address.
6752 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6753   // Remember the least grey address discarded
6754   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6755   _collector->lower_restart_addr(ra);
6756   _markStack->reset();  // discard stack contents
6757   _markStack->expand(); // expand the stack if possible
6758 }
6759 
6760 // Upon stack overflow, we discard (part of) the stack,
6761 // remembering the least address amongst those discarded
6762 // in CMSCollector's _restart_address.
6763 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6764   // We need to do this under a mutex to prevent other
6765   // workers from interfering with the work done below.
6766   MutexLockerEx ml(_overflow_stack->par_lock(),
6767                    Mutex::_no_safepoint_check_flag);
6768   // Remember the least grey address discarded
6769   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6770   _collector->lower_restart_addr(ra);
6771   _overflow_stack->reset();  // discard stack contents
6772   _overflow_stack->expand(); // expand the stack if possible
6773 }
6774 
6775 void PushOrMarkClosure::do_oop(oop obj) {
6776   // Ignore mark word because we are running concurrent with mutators.
6777   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6778   HeapWord* addr = (HeapWord*)obj;
6779   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6780     // Oop lies in _span and isn't yet grey or black
6781     _bitMap->mark(addr);            // now grey
6782     if (addr < _finger) {
6783       // the bit map iteration has already either passed, or
6784       // sampled, this bit in the bit map; we'll need to
6785       // use the marking stack to scan this oop's oops.
6786       bool simulate_overflow = false;
6787       NOT_PRODUCT(
6788         if (CMSMarkStackOverflowALot &&
6789             _collector->simulate_overflow()) {
6790           // simulate a stack overflow
6791           simulate_overflow = true;
6792         }
6793       )
6794       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6795         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6796         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6797         handle_stack_overflow(addr);
6798       }
6799     }
6800     // anything including and to the right of _finger
6801     // will be scanned as we iterate over the remainder of the
6802     // bit map
6803     do_yield_check();
6804   }
6805 }
6806 
6807 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6808 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6809 
6810 void ParPushOrMarkClosure::do_oop(oop obj) {
6811   // Ignore mark word because we are running concurrent with mutators.
6812   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6813   HeapWord* addr = (HeapWord*)obj;
6814   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6815     // Oop lies in _span and isn't yet grey or black
6816     // We read the global_finger (volatile read) strictly after marking oop
6817     bool res = _bit_map->par_mark(addr);    // now grey
6818     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6819     // Should we push this marked oop on our stack?
6820     // -- if someone else marked it, nothing to do
6821     // -- if target oop is above global finger nothing to do
6822     // -- if target oop is in chunk and above local finger
6823     //      then nothing to do
6824     // -- else push on work queue
6825     if (   !res       // someone else marked it, they will deal with it
6826         || (addr >= *gfa)  // will be scanned in a later task
6827         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6828       return;
6829     }
6830     // the bit map iteration has already either passed, or
6831     // sampled, this bit in the bit map; we'll need to
6832     // use the marking stack to scan this oop's oops.
6833     bool simulate_overflow = false;
6834     NOT_PRODUCT(
6835       if (CMSMarkStackOverflowALot &&
6836           _collector->simulate_overflow()) {
6837         // simulate a stack overflow
6838         simulate_overflow = true;
6839       }
6840     )
6841     if (simulate_overflow ||
6842         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6843       // stack overflow
6844       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6845       // We cannot assert that the overflow stack is full because
6846       // it may have been emptied since.
6847       assert(simulate_overflow ||
6848              _work_queue->size() == _work_queue->max_elems(),
6849             "Else push should have succeeded");
6850       handle_stack_overflow(addr);
6851     }
6852     do_yield_check();
6853   }
6854 }
6855 
6856 void ParPushOrMarkClosure::do_oop(oop* p)       { ParPushOrMarkClosure::do_oop_work(p); }
6857 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6858 
6859 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6860                                        MemRegion span,
6861                                        ReferenceProcessor* rp,
6862                                        CMSBitMap* bit_map,
6863                                        CMSBitMap* mod_union_table,
6864                                        CMSMarkStack*  mark_stack,
6865                                        bool           concurrent_precleaning):
6866   MetadataAwareOopClosure(rp),
6867   _collector(collector),
6868   _span(span),
6869   _bit_map(bit_map),
6870   _mod_union_table(mod_union_table),
6871   _mark_stack(mark_stack),
6872   _concurrent_precleaning(concurrent_precleaning)
6873 {
6874   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6875 }
6876 
6877 // Grey object rescan during pre-cleaning and second checkpoint phases --
6878 // the non-parallel version (the parallel version appears further below.)
6879 void PushAndMarkClosure::do_oop(oop obj) {
6880   // Ignore mark word verification. If during concurrent precleaning,
6881   // the object monitor may be locked. If during the checkpoint
6882   // phases, the object may already have been reached by a  different
6883   // path and may be at the end of the global overflow list (so
6884   // the mark word may be NULL).
6885   assert(obj->is_oop_or_null(true /* ignore mark word */),
6886          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6887   HeapWord* addr = (HeapWord*)obj;
6888   // Check if oop points into the CMS generation
6889   // and is not marked
6890   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6891     // a white object ...
6892     _bit_map->mark(addr);         // ... now grey
6893     // push on the marking stack (grey set)
6894     bool simulate_overflow = false;
6895     NOT_PRODUCT(
6896       if (CMSMarkStackOverflowALot &&
6897           _collector->simulate_overflow()) {
6898         // simulate a stack overflow
6899         simulate_overflow = true;
6900       }
6901     )
6902     if (simulate_overflow || !_mark_stack->push(obj)) {
6903       if (_concurrent_precleaning) {
6904          // During precleaning we can just dirty the appropriate card(s)
6905          // in the mod union table, thus ensuring that the object remains
6906          // in the grey set  and continue. In the case of object arrays
6907          // we need to dirty all of the cards that the object spans,
6908          // since the rescan of object arrays will be limited to the
6909          // dirty cards.
6910          // Note that no one can be interfering with us in this action
6911          // of dirtying the mod union table, so no locking or atomics
6912          // are required.
6913          if (obj->is_objArray()) {
6914            size_t sz = obj->size();
6915            HeapWord* end_card_addr = (HeapWord*)round_to(
6916                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6917            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6918            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6919            _mod_union_table->mark_range(redirty_range);
6920          } else {
6921            _mod_union_table->mark(addr);
6922          }
6923          _collector->_ser_pmc_preclean_ovflw++;
6924       } else {
6925          // During the remark phase, we need to remember this oop
6926          // in the overflow list.
6927          _collector->push_on_overflow_list(obj);
6928          _collector->_ser_pmc_remark_ovflw++;
6929       }
6930     }
6931   }
6932 }
6933 
6934 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6935                                              MemRegion span,
6936                                              ReferenceProcessor* rp,
6937                                              CMSBitMap* bit_map,
6938                                              OopTaskQueue* work_queue):
6939   MetadataAwareOopClosure(rp),
6940   _collector(collector),
6941   _span(span),
6942   _bit_map(bit_map),
6943   _work_queue(work_queue)
6944 {
6945   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6946 }
6947 
6948 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6949 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6950 
6951 // Grey object rescan during second checkpoint phase --
6952 // the parallel version.
6953 void ParPushAndMarkClosure::do_oop(oop obj) {
6954   // In the assert below, we ignore the mark word because
6955   // this oop may point to an already visited object that is
6956   // on the overflow stack (in which case the mark word has
6957   // been hijacked for chaining into the overflow stack --
6958   // if this is the last object in the overflow stack then
6959   // its mark word will be NULL). Because this object may
6960   // have been subsequently popped off the global overflow
6961   // stack, and the mark word possibly restored to the prototypical
6962   // value, by the time we get to examined this failing assert in
6963   // the debugger, is_oop_or_null(false) may subsequently start
6964   // to hold.
6965   assert(obj->is_oop_or_null(true),
6966          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6967   HeapWord* addr = (HeapWord*)obj;
6968   // Check if oop points into the CMS generation
6969   // and is not marked
6970   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6971     // a white object ...
6972     // If we manage to "claim" the object, by being the
6973     // first thread to mark it, then we push it on our
6974     // marking stack
6975     if (_bit_map->par_mark(addr)) {     // ... now grey
6976       // push on work queue (grey set)
6977       bool simulate_overflow = false;
6978       NOT_PRODUCT(
6979         if (CMSMarkStackOverflowALot &&
6980             _collector->par_simulate_overflow()) {
6981           // simulate a stack overflow
6982           simulate_overflow = true;
6983         }
6984       )
6985       if (simulate_overflow || !_work_queue->push(obj)) {
6986         _collector->par_push_on_overflow_list(obj);
6987         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6988       }
6989     } // Else, some other thread got there first
6990   }
6991 }
6992 
6993 void ParPushAndMarkClosure::do_oop(oop* p)       { ParPushAndMarkClosure::do_oop_work(p); }
6994 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6995 
6996 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6997   Mutex* bml = _collector->bitMapLock();
6998   assert_lock_strong(bml);
6999   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7000          "CMS thread should hold CMS token");
7001 
7002   bml->unlock();
7003   ConcurrentMarkSweepThread::desynchronize(true);
7004 
7005   _collector->stopTimer();
7006   _collector->incrementYields();
7007 
7008   // See the comment in coordinator_yield()
7009   for (unsigned i = 0; i < CMSYieldSleepCount &&
7010                        ConcurrentMarkSweepThread::should_yield() &&
7011                        !CMSCollector::foregroundGCIsActive(); ++i) {
7012     os::sleep(Thread::current(), 1, false);
7013   }
7014 
7015   ConcurrentMarkSweepThread::synchronize(true);
7016   bml->lock();
7017 
7018   _collector->startTimer();
7019 }
7020 
7021 bool CMSPrecleanRefsYieldClosure::should_return() {
7022   if (ConcurrentMarkSweepThread::should_yield()) {
7023     do_yield_work();
7024   }
7025   return _collector->foregroundGCIsActive();
7026 }
7027 
7028 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7029   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7030          "mr should be aligned to start at a card boundary");
7031   // We'd like to assert:
7032   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7033   //        "mr should be a range of cards");
7034   // However, that would be too strong in one case -- the last
7035   // partition ends at _unallocated_block which, in general, can be
7036   // an arbitrary boundary, not necessarily card aligned.
7037   _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7038   _space->object_iterate_mem(mr, &_scan_cl);
7039 }
7040 
7041 SweepClosure::SweepClosure(CMSCollector* collector,
7042                            ConcurrentMarkSweepGeneration* g,
7043                            CMSBitMap* bitMap, bool should_yield) :
7044   _collector(collector),
7045   _g(g),
7046   _sp(g->cmsSpace()),
7047   _limit(_sp->sweep_limit()),
7048   _freelistLock(_sp->freelistLock()),
7049   _bitMap(bitMap),
7050   _yield(should_yield),
7051   _inFreeRange(false),           // No free range at beginning of sweep
7052   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7053   _lastFreeRangeCoalesced(false),
7054   _freeFinger(g->used_region().start())
7055 {
7056   NOT_PRODUCT(
7057     _numObjectsFreed = 0;
7058     _numWordsFreed   = 0;
7059     _numObjectsLive = 0;
7060     _numWordsLive = 0;
7061     _numObjectsAlreadyFree = 0;
7062     _numWordsAlreadyFree = 0;
7063     _last_fc = NULL;
7064 
7065     _sp->initializeIndexedFreeListArrayReturnedBytes();
7066     _sp->dictionary()->initialize_dict_returned_bytes();
7067   )
7068   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7069          "sweep _limit out of bounds");
7070   log_develop_trace(gc, sweep)("====================");
7071   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7072 }
7073 
7074 void SweepClosure::print_on(outputStream* st) const {
7075   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7076                p2i(_sp->bottom()), p2i(_sp->end()));
7077   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7078   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7079   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7080   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7081                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7082 }
7083 
7084 #ifndef PRODUCT
7085 // Assertion checking only:  no useful work in product mode --
7086 // however, if any of the flags below become product flags,
7087 // you may need to review this code to see if it needs to be
7088 // enabled in product mode.
7089 SweepClosure::~SweepClosure() {
7090   assert_lock_strong(_freelistLock);
7091   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7092          "sweep _limit out of bounds");
7093   if (inFreeRange()) {
7094     Log(gc, sweep) log;
7095     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7096     ResourceMark rm;
7097     print_on(log.error_stream());
7098     ShouldNotReachHere();
7099   }
7100 
7101   if (log_is_enabled(Debug, gc, sweep)) {
7102     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7103                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7104     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7105                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7106     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7107     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7108   }
7109 
7110   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7111     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7112     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7113     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7114     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7115                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7116   }
7117   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7118   log_develop_trace(gc, sweep)("================");
7119 }
7120 #endif  // PRODUCT
7121 
7122 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7123     bool freeRangeInFreeLists) {
7124   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7125                                p2i(freeFinger), freeRangeInFreeLists);
7126   assert(!inFreeRange(), "Trampling existing free range");
7127   set_inFreeRange(true);
7128   set_lastFreeRangeCoalesced(false);
7129 
7130   set_freeFinger(freeFinger);
7131   set_freeRangeInFreeLists(freeRangeInFreeLists);
7132   if (CMSTestInFreeList) {
7133     if (freeRangeInFreeLists) {
7134       FreeChunk* fc = (FreeChunk*) freeFinger;
7135       assert(fc->is_free(), "A chunk on the free list should be free.");
7136       assert(fc->size() > 0, "Free range should have a size");
7137       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7138     }
7139   }
7140 }
7141 
7142 // Note that the sweeper runs concurrently with mutators. Thus,
7143 // it is possible for direct allocation in this generation to happen
7144 // in the middle of the sweep. Note that the sweeper also coalesces
7145 // contiguous free blocks. Thus, unless the sweeper and the allocator
7146 // synchronize appropriately freshly allocated blocks may get swept up.
7147 // This is accomplished by the sweeper locking the free lists while
7148 // it is sweeping. Thus blocks that are determined to be free are
7149 // indeed free. There is however one additional complication:
7150 // blocks that have been allocated since the final checkpoint and
7151 // mark, will not have been marked and so would be treated as
7152 // unreachable and swept up. To prevent this, the allocator marks
7153 // the bit map when allocating during the sweep phase. This leads,
7154 // however, to a further complication -- objects may have been allocated
7155 // but not yet initialized -- in the sense that the header isn't yet
7156 // installed. The sweeper can not then determine the size of the block
7157 // in order to skip over it. To deal with this case, we use a technique
7158 // (due to Printezis) to encode such uninitialized block sizes in the
7159 // bit map. Since the bit map uses a bit per every HeapWord, but the
7160 // CMS generation has a minimum object size of 3 HeapWords, it follows
7161 // that "normal marks" won't be adjacent in the bit map (there will
7162 // always be at least two 0 bits between successive 1 bits). We make use
7163 // of these "unused" bits to represent uninitialized blocks -- the bit
7164 // corresponding to the start of the uninitialized object and the next
7165 // bit are both set. Finally, a 1 bit marks the end of the object that
7166 // started with the two consecutive 1 bits to indicate its potentially
7167 // uninitialized state.
7168 
7169 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7170   FreeChunk* fc = (FreeChunk*)addr;
7171   size_t res;
7172 
7173   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7174   // than "addr == _limit" because although _limit was a block boundary when
7175   // we started the sweep, it may no longer be one because heap expansion
7176   // may have caused us to coalesce the block ending at the address _limit
7177   // with a newly expanded chunk (this happens when _limit was set to the
7178   // previous _end of the space), so we may have stepped past _limit:
7179   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7180   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7181     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7182            "sweep _limit out of bounds");
7183     assert(addr < _sp->end(), "addr out of bounds");
7184     // Flush any free range we might be holding as a single
7185     // coalesced chunk to the appropriate free list.
7186     if (inFreeRange()) {
7187       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7188              "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7189       flush_cur_free_chunk(freeFinger(),
7190                            pointer_delta(addr, freeFinger()));
7191       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7192                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7193                                    lastFreeRangeCoalesced() ? 1 : 0);
7194     }
7195 
7196     // help the iterator loop finish
7197     return pointer_delta(_sp->end(), addr);
7198   }
7199 
7200   assert(addr < _limit, "sweep invariant");
7201   // check if we should yield
7202   do_yield_check(addr);
7203   if (fc->is_free()) {
7204     // Chunk that is already free
7205     res = fc->size();
7206     do_already_free_chunk(fc);
7207     debug_only(_sp->verifyFreeLists());
7208     // If we flush the chunk at hand in lookahead_and_flush()
7209     // and it's coalesced with a preceding chunk, then the
7210     // process of "mangling" the payload of the coalesced block
7211     // will cause erasure of the size information from the
7212     // (erstwhile) header of all the coalesced blocks but the
7213     // first, so the first disjunct in the assert will not hold
7214     // in that specific case (in which case the second disjunct
7215     // will hold).
7216     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7217            "Otherwise the size info doesn't change at this step");
7218     NOT_PRODUCT(
7219       _numObjectsAlreadyFree++;
7220       _numWordsAlreadyFree += res;
7221     )
7222     NOT_PRODUCT(_last_fc = fc;)
7223   } else if (!_bitMap->isMarked(addr)) {
7224     // Chunk is fresh garbage
7225     res = do_garbage_chunk(fc);
7226     debug_only(_sp->verifyFreeLists());
7227     NOT_PRODUCT(
7228       _numObjectsFreed++;
7229       _numWordsFreed += res;
7230     )
7231   } else {
7232     // Chunk that is alive.
7233     res = do_live_chunk(fc);
7234     debug_only(_sp->verifyFreeLists());
7235     NOT_PRODUCT(
7236         _numObjectsLive++;
7237         _numWordsLive += res;
7238     )
7239   }
7240   return res;
7241 }
7242 
7243 // For the smart allocation, record following
7244 //  split deaths - a free chunk is removed from its free list because
7245 //      it is being split into two or more chunks.
7246 //  split birth - a free chunk is being added to its free list because
7247 //      a larger free chunk has been split and resulted in this free chunk.
7248 //  coal death - a free chunk is being removed from its free list because
7249 //      it is being coalesced into a large free chunk.
7250 //  coal birth - a free chunk is being added to its free list because
7251 //      it was created when two or more free chunks where coalesced into
7252 //      this free chunk.
7253 //
7254 // These statistics are used to determine the desired number of free
7255 // chunks of a given size.  The desired number is chosen to be relative
7256 // to the end of a CMS sweep.  The desired number at the end of a sweep
7257 // is the
7258 //      count-at-end-of-previous-sweep (an amount that was enough)
7259 //              - count-at-beginning-of-current-sweep  (the excess)
7260 //              + split-births  (gains in this size during interval)
7261 //              - split-deaths  (demands on this size during interval)
7262 // where the interval is from the end of one sweep to the end of the
7263 // next.
7264 //
7265 // When sweeping the sweeper maintains an accumulated chunk which is
7266 // the chunk that is made up of chunks that have been coalesced.  That
7267 // will be termed the left-hand chunk.  A new chunk of garbage that
7268 // is being considered for coalescing will be referred to as the
7269 // right-hand chunk.
7270 //
7271 // When making a decision on whether to coalesce a right-hand chunk with
7272 // the current left-hand chunk, the current count vs. the desired count
7273 // of the left-hand chunk is considered.  Also if the right-hand chunk
7274 // is near the large chunk at the end of the heap (see
7275 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7276 // left-hand chunk is coalesced.
7277 //
7278 // When making a decision about whether to split a chunk, the desired count
7279 // vs. the current count of the candidate to be split is also considered.
7280 // If the candidate is underpopulated (currently fewer chunks than desired)
7281 // a chunk of an overpopulated (currently more chunks than desired) size may
7282 // be chosen.  The "hint" associated with a free list, if non-null, points
7283 // to a free list which may be overpopulated.
7284 //
7285 
7286 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7287   const size_t size = fc->size();
7288   // Chunks that cannot be coalesced are not in the
7289   // free lists.
7290   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7291     assert(_sp->verify_chunk_in_free_list(fc),
7292            "free chunk should be in free lists");
7293   }
7294   // a chunk that is already free, should not have been
7295   // marked in the bit map
7296   HeapWord* const addr = (HeapWord*) fc;
7297   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7298   // Verify that the bit map has no bits marked between
7299   // addr and purported end of this block.
7300   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7301 
7302   // Some chunks cannot be coalesced under any circumstances.
7303   // See the definition of cantCoalesce().
7304   if (!fc->cantCoalesce()) {
7305     // This chunk can potentially be coalesced.
7306     // All the work is done in
7307     do_post_free_or_garbage_chunk(fc, size);
7308     // Note that if the chunk is not coalescable (the else arm
7309     // below), we unconditionally flush, without needing to do
7310     // a "lookahead," as we do below.
7311     if (inFreeRange()) lookahead_and_flush(fc, size);
7312   } else {
7313     // Code path common to both original and adaptive free lists.
7314 
7315     // cant coalesce with previous block; this should be treated
7316     // as the end of a free run if any
7317     if (inFreeRange()) {
7318       // we kicked some butt; time to pick up the garbage
7319       assert(freeFinger() < addr, "freeFinger points too high");
7320       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7321     }
7322     // else, nothing to do, just continue
7323   }
7324 }
7325 
7326 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7327   // This is a chunk of garbage.  It is not in any free list.
7328   // Add it to a free list or let it possibly be coalesced into
7329   // a larger chunk.
7330   HeapWord* const addr = (HeapWord*) fc;
7331   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7332 
7333   // Verify that the bit map has no bits marked between
7334   // addr and purported end of just dead object.
7335   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7336   do_post_free_or_garbage_chunk(fc, size);
7337 
7338   assert(_limit >= addr + size,
7339          "A freshly garbage chunk can't possibly straddle over _limit");
7340   if (inFreeRange()) lookahead_and_flush(fc, size);
7341   return size;
7342 }
7343 
7344 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7345   HeapWord* addr = (HeapWord*) fc;
7346   // The sweeper has just found a live object. Return any accumulated
7347   // left hand chunk to the free lists.
7348   if (inFreeRange()) {
7349     assert(freeFinger() < addr, "freeFinger points too high");
7350     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7351   }
7352 
7353   // This object is live: we'd normally expect this to be
7354   // an oop, and like to assert the following:
7355   // assert(oop(addr)->is_oop(), "live block should be an oop");
7356   // However, as we commented above, this may be an object whose
7357   // header hasn't yet been initialized.
7358   size_t size;
7359   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7360   if (_bitMap->isMarked(addr + 1)) {
7361     // Determine the size from the bit map, rather than trying to
7362     // compute it from the object header.
7363     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7364     size = pointer_delta(nextOneAddr + 1, addr);
7365     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7366            "alignment problem");
7367 
7368 #ifdef ASSERT
7369       if (oop(addr)->klass_or_null() != NULL) {
7370         // Ignore mark word because we are running concurrent with mutators
7371         assert(oop(addr)->is_oop(true), "live block should be an oop");
7372         assert(size ==
7373                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7374                "P-mark and computed size do not agree");
7375       }
7376 #endif
7377 
7378   } else {
7379     // This should be an initialized object that's alive.
7380     assert(oop(addr)->klass_or_null() != NULL,
7381            "Should be an initialized object");
7382     // Ignore mark word because we are running concurrent with mutators
7383     assert(oop(addr)->is_oop(true), "live block should be an oop");
7384     // Verify that the bit map has no bits marked between
7385     // addr and purported end of this block.
7386     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7387     assert(size >= 3, "Necessary for Printezis marks to work");
7388     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7389     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7390   }
7391   return size;
7392 }
7393 
7394 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7395                                                  size_t chunkSize) {
7396   // do_post_free_or_garbage_chunk() should only be called in the case
7397   // of the adaptive free list allocator.
7398   const bool fcInFreeLists = fc->is_free();
7399   assert((HeapWord*)fc <= _limit, "sweep invariant");
7400   if (CMSTestInFreeList && fcInFreeLists) {
7401     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7402   }
7403 
7404   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7405 
7406   HeapWord* const fc_addr = (HeapWord*) fc;
7407 
7408   bool coalesce = false;
7409   const size_t left  = pointer_delta(fc_addr, freeFinger());
7410   const size_t right = chunkSize;
7411   switch (FLSCoalescePolicy) {
7412     // numeric value forms a coalition aggressiveness metric
7413     case 0:  { // never coalesce
7414       coalesce = false;
7415       break;
7416     }
7417     case 1: { // coalesce if left & right chunks on overpopulated lists
7418       coalesce = _sp->coalOverPopulated(left) &&
7419                  _sp->coalOverPopulated(right);
7420       break;
7421     }
7422     case 2: { // coalesce if left chunk on overpopulated list (default)
7423       coalesce = _sp->coalOverPopulated(left);
7424       break;
7425     }
7426     case 3: { // coalesce if left OR right chunk on overpopulated list
7427       coalesce = _sp->coalOverPopulated(left) ||
7428                  _sp->coalOverPopulated(right);
7429       break;
7430     }
7431     case 4: { // always coalesce
7432       coalesce = true;
7433       break;
7434     }
7435     default:
7436      ShouldNotReachHere();
7437   }
7438 
7439   // Should the current free range be coalesced?
7440   // If the chunk is in a free range and either we decided to coalesce above
7441   // or the chunk is near the large block at the end of the heap
7442   // (isNearLargestChunk() returns true), then coalesce this chunk.
7443   const bool doCoalesce = inFreeRange()
7444                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7445   if (doCoalesce) {
7446     // Coalesce the current free range on the left with the new
7447     // chunk on the right.  If either is on a free list,
7448     // it must be removed from the list and stashed in the closure.
7449     if (freeRangeInFreeLists()) {
7450       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7451       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7452              "Size of free range is inconsistent with chunk size.");
7453       if (CMSTestInFreeList) {
7454         assert(_sp->verify_chunk_in_free_list(ffc),
7455                "Chunk is not in free lists");
7456       }
7457       _sp->coalDeath(ffc->size());
7458       _sp->removeFreeChunkFromFreeLists(ffc);
7459       set_freeRangeInFreeLists(false);
7460     }
7461     if (fcInFreeLists) {
7462       _sp->coalDeath(chunkSize);
7463       assert(fc->size() == chunkSize,
7464         "The chunk has the wrong size or is not in the free lists");
7465       _sp->removeFreeChunkFromFreeLists(fc);
7466     }
7467     set_lastFreeRangeCoalesced(true);
7468     print_free_block_coalesced(fc);
7469   } else {  // not in a free range and/or should not coalesce
7470     // Return the current free range and start a new one.
7471     if (inFreeRange()) {
7472       // In a free range but cannot coalesce with the right hand chunk.
7473       // Put the current free range into the free lists.
7474       flush_cur_free_chunk(freeFinger(),
7475                            pointer_delta(fc_addr, freeFinger()));
7476     }
7477     // Set up for new free range.  Pass along whether the right hand
7478     // chunk is in the free lists.
7479     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7480   }
7481 }
7482 
7483 // Lookahead flush:
7484 // If we are tracking a free range, and this is the last chunk that
7485 // we'll look at because its end crosses past _limit, we'll preemptively
7486 // flush it along with any free range we may be holding on to. Note that
7487 // this can be the case only for an already free or freshly garbage
7488 // chunk. If this block is an object, it can never straddle
7489 // over _limit. The "straddling" occurs when _limit is set at
7490 // the previous end of the space when this cycle started, and
7491 // a subsequent heap expansion caused the previously co-terminal
7492 // free block to be coalesced with the newly expanded portion,
7493 // thus rendering _limit a non-block-boundary making it dangerous
7494 // for the sweeper to step over and examine.
7495 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7496   assert(inFreeRange(), "Should only be called if currently in a free range.");
7497   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7498   assert(_sp->used_region().contains(eob - 1),
7499          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7500          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7501          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7502          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7503   if (eob >= _limit) {
7504     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7505     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7506                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7507                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7508                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7509     // Return the storage we are tracking back into the free lists.
7510     log_develop_trace(gc, sweep)("Flushing ... ");
7511     assert(freeFinger() < eob, "Error");
7512     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7513   }
7514 }
7515 
7516 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7517   assert(inFreeRange(), "Should only be called if currently in a free range.");
7518   assert(size > 0,
7519     "A zero sized chunk cannot be added to the free lists.");
7520   if (!freeRangeInFreeLists()) {
7521     if (CMSTestInFreeList) {
7522       FreeChunk* fc = (FreeChunk*) chunk;
7523       fc->set_size(size);
7524       assert(!_sp->verify_chunk_in_free_list(fc),
7525              "chunk should not be in free lists yet");
7526     }
7527     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7528     // A new free range is going to be starting.  The current
7529     // free range has not been added to the free lists yet or
7530     // was removed so add it back.
7531     // If the current free range was coalesced, then the death
7532     // of the free range was recorded.  Record a birth now.
7533     if (lastFreeRangeCoalesced()) {
7534       _sp->coalBirth(size);
7535     }
7536     _sp->addChunkAndRepairOffsetTable(chunk, size,
7537             lastFreeRangeCoalesced());
7538   } else {
7539     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7540   }
7541   set_inFreeRange(false);
7542   set_freeRangeInFreeLists(false);
7543 }
7544 
7545 // We take a break if we've been at this for a while,
7546 // so as to avoid monopolizing the locks involved.
7547 void SweepClosure::do_yield_work(HeapWord* addr) {
7548   // Return current free chunk being used for coalescing (if any)
7549   // to the appropriate freelist.  After yielding, the next
7550   // free block encountered will start a coalescing range of
7551   // free blocks.  If the next free block is adjacent to the
7552   // chunk just flushed, they will need to wait for the next
7553   // sweep to be coalesced.
7554   if (inFreeRange()) {
7555     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7556   }
7557 
7558   // First give up the locks, then yield, then re-lock.
7559   // We should probably use a constructor/destructor idiom to
7560   // do this unlock/lock or modify the MutexUnlocker class to
7561   // serve our purpose. XXX
7562   assert_lock_strong(_bitMap->lock());
7563   assert_lock_strong(_freelistLock);
7564   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7565          "CMS thread should hold CMS token");
7566   _bitMap->lock()->unlock();
7567   _freelistLock->unlock();
7568   ConcurrentMarkSweepThread::desynchronize(true);
7569   _collector->stopTimer();
7570   _collector->incrementYields();
7571 
7572   // See the comment in coordinator_yield()
7573   for (unsigned i = 0; i < CMSYieldSleepCount &&
7574                        ConcurrentMarkSweepThread::should_yield() &&
7575                        !CMSCollector::foregroundGCIsActive(); ++i) {
7576     os::sleep(Thread::current(), 1, false);
7577   }
7578 
7579   ConcurrentMarkSweepThread::synchronize(true);
7580   _freelistLock->lock();
7581   _bitMap->lock()->lock_without_safepoint_check();
7582   _collector->startTimer();
7583 }
7584 
7585 #ifndef PRODUCT
7586 // This is actually very useful in a product build if it can
7587 // be called from the debugger.  Compile it into the product
7588 // as needed.
7589 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7590   return debug_cms_space->verify_chunk_in_free_list(fc);
7591 }
7592 #endif
7593 
7594 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7595   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7596                                p2i(fc), fc->size());
7597 }
7598 
7599 // CMSIsAliveClosure
7600 bool CMSIsAliveClosure::do_object_b(oop obj) {
7601   HeapWord* addr = (HeapWord*)obj;
7602   return addr != NULL &&
7603          (!_span.contains(addr) || _bit_map->isMarked(addr));
7604 }
7605 
7606 
7607 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7608                       MemRegion span,
7609                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7610                       bool cpc):
7611   _collector(collector),
7612   _span(span),
7613   _bit_map(bit_map),
7614   _mark_stack(mark_stack),
7615   _concurrent_precleaning(cpc) {
7616   assert(!_span.is_empty(), "Empty span could spell trouble");
7617 }
7618 
7619 
7620 // CMSKeepAliveClosure: the serial version
7621 void CMSKeepAliveClosure::do_oop(oop obj) {
7622   HeapWord* addr = (HeapWord*)obj;
7623   if (_span.contains(addr) &&
7624       !_bit_map->isMarked(addr)) {
7625     _bit_map->mark(addr);
7626     bool simulate_overflow = false;
7627     NOT_PRODUCT(
7628       if (CMSMarkStackOverflowALot &&
7629           _collector->simulate_overflow()) {
7630         // simulate a stack overflow
7631         simulate_overflow = true;
7632       }
7633     )
7634     if (simulate_overflow || !_mark_stack->push(obj)) {
7635       if (_concurrent_precleaning) {
7636         // We dirty the overflown object and let the remark
7637         // phase deal with it.
7638         assert(_collector->overflow_list_is_empty(), "Error");
7639         // In the case of object arrays, we need to dirty all of
7640         // the cards that the object spans. No locking or atomics
7641         // are needed since no one else can be mutating the mod union
7642         // table.
7643         if (obj->is_objArray()) {
7644           size_t sz = obj->size();
7645           HeapWord* end_card_addr =
7646             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7647           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7648           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7649           _collector->_modUnionTable.mark_range(redirty_range);
7650         } else {
7651           _collector->_modUnionTable.mark(addr);
7652         }
7653         _collector->_ser_kac_preclean_ovflw++;
7654       } else {
7655         _collector->push_on_overflow_list(obj);
7656         _collector->_ser_kac_ovflw++;
7657       }
7658     }
7659   }
7660 }
7661 
7662 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7663 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7664 
7665 // CMSParKeepAliveClosure: a parallel version of the above.
7666 // The work queues are private to each closure (thread),
7667 // but (may be) available for stealing by other threads.
7668 void CMSParKeepAliveClosure::do_oop(oop obj) {
7669   HeapWord* addr = (HeapWord*)obj;
7670   if (_span.contains(addr) &&
7671       !_bit_map->isMarked(addr)) {
7672     // In general, during recursive tracing, several threads
7673     // may be concurrently getting here; the first one to
7674     // "tag" it, claims it.
7675     if (_bit_map->par_mark(addr)) {
7676       bool res = _work_queue->push(obj);
7677       assert(res, "Low water mark should be much less than capacity");
7678       // Do a recursive trim in the hope that this will keep
7679       // stack usage lower, but leave some oops for potential stealers
7680       trim_queue(_low_water_mark);
7681     } // Else, another thread got there first
7682   }
7683 }
7684 
7685 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7686 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7687 
7688 void CMSParKeepAliveClosure::trim_queue(uint max) {
7689   while (_work_queue->size() > max) {
7690     oop new_oop;
7691     if (_work_queue->pop_local(new_oop)) {
7692       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7693       assert(_bit_map->isMarked((HeapWord*)new_oop),
7694              "no white objects on this stack!");
7695       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7696       // iterate over the oops in this oop, marking and pushing
7697       // the ones in CMS heap (i.e. in _span).
7698       new_oop->oop_iterate(&_mark_and_push);
7699     }
7700   }
7701 }
7702 
7703 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7704                                 CMSCollector* collector,
7705                                 MemRegion span, CMSBitMap* bit_map,
7706                                 OopTaskQueue* work_queue):
7707   _collector(collector),
7708   _span(span),
7709   _bit_map(bit_map),
7710   _work_queue(work_queue) { }
7711 
7712 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7713   HeapWord* addr = (HeapWord*)obj;
7714   if (_span.contains(addr) &&
7715       !_bit_map->isMarked(addr)) {
7716     if (_bit_map->par_mark(addr)) {
7717       bool simulate_overflow = false;
7718       NOT_PRODUCT(
7719         if (CMSMarkStackOverflowALot &&
7720             _collector->par_simulate_overflow()) {
7721           // simulate a stack overflow
7722           simulate_overflow = true;
7723         }
7724       )
7725       if (simulate_overflow || !_work_queue->push(obj)) {
7726         _collector->par_push_on_overflow_list(obj);
7727         _collector->_par_kac_ovflw++;
7728       }
7729     } // Else another thread got there already
7730   }
7731 }
7732 
7733 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7734 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7735 
7736 //////////////////////////////////////////////////////////////////
7737 //  CMSExpansionCause                /////////////////////////////
7738 //////////////////////////////////////////////////////////////////
7739 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7740   switch (cause) {
7741     case _no_expansion:
7742       return "No expansion";
7743     case _satisfy_free_ratio:
7744       return "Free ratio";
7745     case _satisfy_promotion:
7746       return "Satisfy promotion";
7747     case _satisfy_allocation:
7748       return "allocation";
7749     case _allocate_par_lab:
7750       return "Par LAB";
7751     case _allocate_par_spooling_space:
7752       return "Par Spooling Space";
7753     case _adaptive_size_policy:
7754       return "Ergonomics";
7755     default:
7756       return "unknown";
7757   }
7758 }
7759 
7760 void CMSDrainMarkingStackClosure::do_void() {
7761   // the max number to take from overflow list at a time
7762   const size_t num = _mark_stack->capacity()/4;
7763   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7764          "Overflow list should be NULL during concurrent phases");
7765   while (!_mark_stack->isEmpty() ||
7766          // if stack is empty, check the overflow list
7767          _collector->take_from_overflow_list(num, _mark_stack)) {
7768     oop obj = _mark_stack->pop();
7769     HeapWord* addr = (HeapWord*)obj;
7770     assert(_span.contains(addr), "Should be within span");
7771     assert(_bit_map->isMarked(addr), "Should be marked");
7772     assert(obj->is_oop(), "Should be an oop");
7773     obj->oop_iterate(_keep_alive);
7774   }
7775 }
7776 
7777 void CMSParDrainMarkingStackClosure::do_void() {
7778   // drain queue
7779   trim_queue(0);
7780 }
7781 
7782 // Trim our work_queue so its length is below max at return
7783 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7784   while (_work_queue->size() > max) {
7785     oop new_oop;
7786     if (_work_queue->pop_local(new_oop)) {
7787       assert(new_oop->is_oop(), "Expected an oop");
7788       assert(_bit_map->isMarked((HeapWord*)new_oop),
7789              "no white objects on this stack!");
7790       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7791       // iterate over the oops in this oop, marking and pushing
7792       // the ones in CMS heap (i.e. in _span).
7793       new_oop->oop_iterate(&_mark_and_push);
7794     }
7795   }
7796 }
7797 
7798 ////////////////////////////////////////////////////////////////////
7799 // Support for Marking Stack Overflow list handling and related code
7800 ////////////////////////////////////////////////////////////////////
7801 // Much of the following code is similar in shape and spirit to the
7802 // code used in ParNewGC. We should try and share that code
7803 // as much as possible in the future.
7804 
7805 #ifndef PRODUCT
7806 // Debugging support for CMSStackOverflowALot
7807 
7808 // It's OK to call this multi-threaded;  the worst thing
7809 // that can happen is that we'll get a bunch of closely
7810 // spaced simulated overflows, but that's OK, in fact
7811 // probably good as it would exercise the overflow code
7812 // under contention.
7813 bool CMSCollector::simulate_overflow() {
7814   if (_overflow_counter-- <= 0) { // just being defensive
7815     _overflow_counter = CMSMarkStackOverflowInterval;
7816     return true;
7817   } else {
7818     return false;
7819   }
7820 }
7821 
7822 bool CMSCollector::par_simulate_overflow() {
7823   return simulate_overflow();
7824 }
7825 #endif
7826 
7827 // Single-threaded
7828 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7829   assert(stack->isEmpty(), "Expected precondition");
7830   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7831   size_t i = num;
7832   oop  cur = _overflow_list;
7833   const markOop proto = markOopDesc::prototype();
7834   NOT_PRODUCT(ssize_t n = 0;)
7835   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7836     next = oop(cur->mark());
7837     cur->set_mark(proto);   // until proven otherwise
7838     assert(cur->is_oop(), "Should be an oop");
7839     bool res = stack->push(cur);
7840     assert(res, "Bit off more than can chew?");
7841     NOT_PRODUCT(n++;)
7842   }
7843   _overflow_list = cur;
7844 #ifndef PRODUCT
7845   assert(_num_par_pushes >= n, "Too many pops?");
7846   _num_par_pushes -=n;
7847 #endif
7848   return !stack->isEmpty();
7849 }
7850 
7851 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7852 // (MT-safe) Get a prefix of at most "num" from the list.
7853 // The overflow list is chained through the mark word of
7854 // each object in the list. We fetch the entire list,
7855 // break off a prefix of the right size and return the
7856 // remainder. If other threads try to take objects from
7857 // the overflow list at that time, they will wait for
7858 // some time to see if data becomes available. If (and
7859 // only if) another thread places one or more object(s)
7860 // on the global list before we have returned the suffix
7861 // to the global list, we will walk down our local list
7862 // to find its end and append the global list to
7863 // our suffix before returning it. This suffix walk can
7864 // prove to be expensive (quadratic in the amount of traffic)
7865 // when there are many objects in the overflow list and
7866 // there is much producer-consumer contention on the list.
7867 // *NOTE*: The overflow list manipulation code here and
7868 // in ParNewGeneration:: are very similar in shape,
7869 // except that in the ParNew case we use the old (from/eden)
7870 // copy of the object to thread the list via its klass word.
7871 // Because of the common code, if you make any changes in
7872 // the code below, please check the ParNew version to see if
7873 // similar changes might be needed.
7874 // CR 6797058 has been filed to consolidate the common code.
7875 bool CMSCollector::par_take_from_overflow_list(size_t num,
7876                                                OopTaskQueue* work_q,
7877                                                int no_of_gc_threads) {
7878   assert(work_q->size() == 0, "First empty local work queue");
7879   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7880   if (_overflow_list == NULL) {
7881     return false;
7882   }
7883   // Grab the entire list; we'll put back a suffix
7884   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7885   Thread* tid = Thread::current();
7886   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7887   // set to ParallelGCThreads.
7888   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7889   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7890   // If the list is busy, we spin for a short while,
7891   // sleeping between attempts to get the list.
7892   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7893     os::sleep(tid, sleep_time_millis, false);
7894     if (_overflow_list == NULL) {
7895       // Nothing left to take
7896       return false;
7897     } else if (_overflow_list != BUSY) {
7898       // Try and grab the prefix
7899       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7900     }
7901   }
7902   // If the list was found to be empty, or we spun long
7903   // enough, we give up and return empty-handed. If we leave
7904   // the list in the BUSY state below, it must be the case that
7905   // some other thread holds the overflow list and will set it
7906   // to a non-BUSY state in the future.
7907   if (prefix == NULL || prefix == BUSY) {
7908      // Nothing to take or waited long enough
7909      if (prefix == NULL) {
7910        // Write back the NULL in case we overwrote it with BUSY above
7911        // and it is still the same value.
7912        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7913      }
7914      return false;
7915   }
7916   assert(prefix != NULL && prefix != BUSY, "Error");
7917   size_t i = num;
7918   oop cur = prefix;
7919   // Walk down the first "num" objects, unless we reach the end.
7920   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7921   if (cur->mark() == NULL) {
7922     // We have "num" or fewer elements in the list, so there
7923     // is nothing to return to the global list.
7924     // Write back the NULL in lieu of the BUSY we wrote
7925     // above, if it is still the same value.
7926     if (_overflow_list == BUSY) {
7927       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7928     }
7929   } else {
7930     // Chop off the suffix and return it to the global list.
7931     assert(cur->mark() != BUSY, "Error");
7932     oop suffix_head = cur->mark(); // suffix will be put back on global list
7933     cur->set_mark(NULL);           // break off suffix
7934     // It's possible that the list is still in the empty(busy) state
7935     // we left it in a short while ago; in that case we may be
7936     // able to place back the suffix without incurring the cost
7937     // of a walk down the list.
7938     oop observed_overflow_list = _overflow_list;
7939     oop cur_overflow_list = observed_overflow_list;
7940     bool attached = false;
7941     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7942       observed_overflow_list =
7943         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7944       if (cur_overflow_list == observed_overflow_list) {
7945         attached = true;
7946         break;
7947       } else cur_overflow_list = observed_overflow_list;
7948     }
7949     if (!attached) {
7950       // Too bad, someone else sneaked in (at least) an element; we'll need
7951       // to do a splice. Find tail of suffix so we can prepend suffix to global
7952       // list.
7953       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7954       oop suffix_tail = cur;
7955       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7956              "Tautology");
7957       observed_overflow_list = _overflow_list;
7958       do {
7959         cur_overflow_list = observed_overflow_list;
7960         if (cur_overflow_list != BUSY) {
7961           // Do the splice ...
7962           suffix_tail->set_mark(markOop(cur_overflow_list));
7963         } else { // cur_overflow_list == BUSY
7964           suffix_tail->set_mark(NULL);
7965         }
7966         // ... and try to place spliced list back on overflow_list ...
7967         observed_overflow_list =
7968           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7969       } while (cur_overflow_list != observed_overflow_list);
7970       // ... until we have succeeded in doing so.
7971     }
7972   }
7973 
7974   // Push the prefix elements on work_q
7975   assert(prefix != NULL, "control point invariant");
7976   const markOop proto = markOopDesc::prototype();
7977   oop next;
7978   NOT_PRODUCT(ssize_t n = 0;)
7979   for (cur = prefix; cur != NULL; cur = next) {
7980     next = oop(cur->mark());
7981     cur->set_mark(proto);   // until proven otherwise
7982     assert(cur->is_oop(), "Should be an oop");
7983     bool res = work_q->push(cur);
7984     assert(res, "Bit off more than we can chew?");
7985     NOT_PRODUCT(n++;)
7986   }
7987 #ifndef PRODUCT
7988   assert(_num_par_pushes >= n, "Too many pops?");
7989   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7990 #endif
7991   return true;
7992 }
7993 
7994 // Single-threaded
7995 void CMSCollector::push_on_overflow_list(oop p) {
7996   NOT_PRODUCT(_num_par_pushes++;)
7997   assert(p->is_oop(), "Not an oop");
7998   preserve_mark_if_necessary(p);
7999   p->set_mark((markOop)_overflow_list);
8000   _overflow_list = p;
8001 }
8002 
8003 // Multi-threaded; use CAS to prepend to overflow list
8004 void CMSCollector::par_push_on_overflow_list(oop p) {
8005   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8006   assert(p->is_oop(), "Not an oop");
8007   par_preserve_mark_if_necessary(p);
8008   oop observed_overflow_list = _overflow_list;
8009   oop cur_overflow_list;
8010   do {
8011     cur_overflow_list = observed_overflow_list;
8012     if (cur_overflow_list != BUSY) {
8013       p->set_mark(markOop(cur_overflow_list));
8014     } else {
8015       p->set_mark(NULL);
8016     }
8017     observed_overflow_list =
8018       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8019   } while (cur_overflow_list != observed_overflow_list);
8020 }
8021 #undef BUSY
8022 
8023 // Single threaded
8024 // General Note on GrowableArray: pushes may silently fail
8025 // because we are (temporarily) out of C-heap for expanding
8026 // the stack. The problem is quite ubiquitous and affects
8027 // a lot of code in the JVM. The prudent thing for GrowableArray
8028 // to do (for now) is to exit with an error. However, that may
8029 // be too draconian in some cases because the caller may be
8030 // able to recover without much harm. For such cases, we
8031 // should probably introduce a "soft_push" method which returns
8032 // an indication of success or failure with the assumption that
8033 // the caller may be able to recover from a failure; code in
8034 // the VM can then be changed, incrementally, to deal with such
8035 // failures where possible, thus, incrementally hardening the VM
8036 // in such low resource situations.
8037 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8038   _preserved_oop_stack.push(p);
8039   _preserved_mark_stack.push(m);
8040   assert(m == p->mark(), "Mark word changed");
8041   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8042          "bijection");
8043 }
8044 
8045 // Single threaded
8046 void CMSCollector::preserve_mark_if_necessary(oop p) {
8047   markOop m = p->mark();
8048   if (m->must_be_preserved(p)) {
8049     preserve_mark_work(p, m);
8050   }
8051 }
8052 
8053 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8054   markOop m = p->mark();
8055   if (m->must_be_preserved(p)) {
8056     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8057     // Even though we read the mark word without holding
8058     // the lock, we are assured that it will not change
8059     // because we "own" this oop, so no other thread can
8060     // be trying to push it on the overflow list; see
8061     // the assertion in preserve_mark_work() that checks
8062     // that m == p->mark().
8063     preserve_mark_work(p, m);
8064   }
8065 }
8066 
8067 // We should be able to do this multi-threaded,
8068 // a chunk of stack being a task (this is
8069 // correct because each oop only ever appears
8070 // once in the overflow list. However, it's
8071 // not very easy to completely overlap this with
8072 // other operations, so will generally not be done
8073 // until all work's been completed. Because we
8074 // expect the preserved oop stack (set) to be small,
8075 // it's probably fine to do this single-threaded.
8076 // We can explore cleverer concurrent/overlapped/parallel
8077 // processing of preserved marks if we feel the
8078 // need for this in the future. Stack overflow should
8079 // be so rare in practice and, when it happens, its
8080 // effect on performance so great that this will
8081 // likely just be in the noise anyway.
8082 void CMSCollector::restore_preserved_marks_if_any() {
8083   assert(SafepointSynchronize::is_at_safepoint(),
8084          "world should be stopped");
8085   assert(Thread::current()->is_ConcurrentGC_thread() ||
8086          Thread::current()->is_VM_thread(),
8087          "should be single-threaded");
8088   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8089          "bijection");
8090 
8091   while (!_preserved_oop_stack.is_empty()) {
8092     oop p = _preserved_oop_stack.pop();
8093     assert(p->is_oop(), "Should be an oop");
8094     assert(_span.contains(p), "oop should be in _span");
8095     assert(p->mark() == markOopDesc::prototype(),
8096            "Set when taken from overflow list");
8097     markOop m = _preserved_mark_stack.pop();
8098     p->set_mark(m);
8099   }
8100   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8101          "stacks were cleared above");
8102 }
8103 
8104 #ifndef PRODUCT
8105 bool CMSCollector::no_preserved_marks() const {
8106   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8107 }
8108 #endif
8109 
8110 // Transfer some number of overflown objects to usual marking
8111 // stack. Return true if some objects were transferred.
8112 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8113   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8114                     (size_t)ParGCDesiredObjsFromOverflowList);
8115 
8116   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8117   assert(_collector->overflow_list_is_empty() || res,
8118          "If list is not empty, we should have taken something");
8119   assert(!res || !_mark_stack->isEmpty(),
8120          "If we took something, it should now be on our stack");
8121   return res;
8122 }
8123 
8124 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8125   size_t res = _sp->block_size_no_stall(addr, _collector);
8126   if (_sp->block_is_obj(addr)) {
8127     if (_live_bit_map->isMarked(addr)) {
8128       // It can't have been dead in a previous cycle
8129       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8130     } else {
8131       _dead_bit_map->mark(addr);      // mark the dead object
8132     }
8133   }
8134   // Could be 0, if the block size could not be computed without stalling.
8135   return res;
8136 }
8137 
8138 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8139 
8140   switch (phase) {
8141     case CMSCollector::InitialMarking:
8142       initialize(true  /* fullGC */ ,
8143                  cause /* cause of the GC */,
8144                  true  /* recordGCBeginTime */,
8145                  true  /* recordPreGCUsage */,
8146                  false /* recordPeakUsage */,
8147                  false /* recordPostGCusage */,
8148                  true  /* recordAccumulatedGCTime */,
8149                  false /* recordGCEndTime */,
8150                  false /* countCollection */  );
8151       break;
8152 
8153     case CMSCollector::FinalMarking:
8154       initialize(true  /* fullGC */ ,
8155                  cause /* cause of the GC */,
8156                  false /* recordGCBeginTime */,
8157                  false /* recordPreGCUsage */,
8158                  false /* recordPeakUsage */,
8159                  false /* recordPostGCusage */,
8160                  true  /* recordAccumulatedGCTime */,
8161                  false /* recordGCEndTime */,
8162                  false /* countCollection */  );
8163       break;
8164 
8165     case CMSCollector::Sweeping:
8166       initialize(true  /* fullGC */ ,
8167                  cause /* cause of the GC */,
8168                  false /* recordGCBeginTime */,
8169                  false /* recordPreGCUsage */,
8170                  true  /* recordPeakUsage */,
8171                  true  /* recordPostGCusage */,
8172                  false /* recordAccumulatedGCTime */,
8173                  true  /* recordGCEndTime */,
8174                  true  /* countCollection */  );
8175       break;
8176 
8177     default:
8178       ShouldNotReachHere();
8179   }
8180 }
--- EOF ---