1 /*
   2  * Copyright (c) 2001, 2017, 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   // Now expand the span and allocate the collection support structures
 492   // (MUT, marking bit map etc.) to cover both generations subject to
 493   // collection.
 494 
 495   // For use by dirty card to oop closures.
 496   _cmsGen->cmsSpace()->set_collector(this);
 497 
 498   // Allocate MUT and marking bit map
 499   {
 500     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 501     if (!_markBitMap.allocate(_span)) {
 502       log_warning(gc)("Failed to allocate CMS Bit Map");
 503       return;
 504     }
 505     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 506   }
 507   {
 508     _modUnionTable.allocate(_span);
 509     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 510   }
 511 
 512   if (!_markStack.allocate(MarkStackSize)) {
 513     log_warning(gc)("Failed to allocate CMS Marking Stack");
 514     return;
 515   }
 516 
 517   // Support for multi-threaded concurrent phases
 518   if (CMSConcurrentMTEnabled) {
 519     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 520       // just for now
 521       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 522     }
 523     if (ConcGCThreads > 1) {
 524       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 525                                  ConcGCThreads, true);
 526       if (_conc_workers == NULL) {
 527         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 528         CMSConcurrentMTEnabled = false;
 529       } else {
 530         _conc_workers->initialize_workers();
 531       }
 532     } else {
 533       CMSConcurrentMTEnabled = false;
 534     }
 535   }
 536   if (!CMSConcurrentMTEnabled) {
 537     ConcGCThreads = 0;
 538   } else {
 539     // Turn off CMSCleanOnEnter optimization temporarily for
 540     // the MT case where it's not fixed yet; see 6178663.
 541     CMSCleanOnEnter = false;
 542   }
 543   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 544          "Inconsistency");
 545   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 546   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 547 
 548   // Parallel task queues; these are shared for the
 549   // concurrent and stop-world phases of CMS, but
 550   // are not shared with parallel scavenge (ParNew).
 551   {
 552     uint i;
 553     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 554 
 555     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 556          || ParallelRefProcEnabled)
 557         && num_queues > 0) {
 558       _task_queues = new OopTaskQueueSet(num_queues);
 559       if (_task_queues == NULL) {
 560         log_warning(gc)("task_queues allocation failure.");
 561         return;
 562       }
 563       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 564       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 565       for (i = 0; i < num_queues; i++) {
 566         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 567         if (q == NULL) {
 568           log_warning(gc)("work_queue allocation failure.");
 569           return;
 570         }
 571         _task_queues->register_queue(i, q);
 572       }
 573       for (i = 0; i < num_queues; i++) {
 574         _task_queues->queue(i)->initialize();
 575         _hash_seed[i] = 17;  // copied from ParNew
 576       }
 577     }
 578   }
 579 
 580   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 581 
 582   // Clip CMSBootstrapOccupancy between 0 and 100.
 583   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 584 
 585   // Now tell CMS generations the identity of their collector
 586   ConcurrentMarkSweepGeneration::set_collector(this);
 587 
 588   // Create & start a CMS thread for this CMS collector
 589   _cmsThread = ConcurrentMarkSweepThread::start(this);
 590   assert(cmsThread() != NULL, "CMS Thread should have been created");
 591   assert(cmsThread()->collector() == this,
 592          "CMS Thread should refer to this gen");
 593   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 594 
 595   // Support for parallelizing young gen rescan
 596   GenCollectedHeap* gch = GenCollectedHeap::heap();
 597   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 598   _young_gen = (ParNewGeneration*)gch->young_gen();
 599   if (gch->supports_inline_contig_alloc()) {
 600     _top_addr = gch->top_addr();
 601     _end_addr = gch->end_addr();
 602     assert(_young_gen != NULL, "no _young_gen");
 603     _eden_chunk_index = 0;
 604     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 605     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 606   }
 607 
 608   // Support for parallelizing survivor space rescan
 609   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 610     const size_t max_plab_samples =
 611       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 612 
 613     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 614     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 615     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 616     _survivor_chunk_capacity = max_plab_samples;
 617     for (uint i = 0; i < ParallelGCThreads; i++) {
 618       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 619       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 620       assert(cur->end() == 0, "Should be 0");
 621       assert(cur->array() == vec, "Should be vec");
 622       assert(cur->capacity() == max_plab_samples, "Error");
 623     }
 624   }
 625 
 626   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 627   _gc_counters = new CollectorCounters("CMS", 1);
 628   _completed_initialization = true;
 629   _inter_sweep_timer.start();  // start of time
 630 }
 631 
 632 const char* ConcurrentMarkSweepGeneration::name() const {
 633   return "concurrent mark-sweep generation";
 634 }
 635 void ConcurrentMarkSweepGeneration::update_counters() {
 636   if (UsePerfData) {
 637     _space_counters->update_all();
 638     _gen_counters->update_all();
 639   }
 640 }
 641 
 642 // this is an optimized version of update_counters(). it takes the
 643 // used value as a parameter rather than computing it.
 644 //
 645 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 646   if (UsePerfData) {
 647     _space_counters->update_used(used);
 648     _space_counters->update_capacity();
 649     _gen_counters->update_all();
 650   }
 651 }
 652 
 653 void ConcurrentMarkSweepGeneration::print() const {
 654   Generation::print();
 655   cmsSpace()->print();
 656 }
 657 
 658 #ifndef PRODUCT
 659 void ConcurrentMarkSweepGeneration::print_statistics() {
 660   cmsSpace()->printFLCensus(0);
 661 }
 662 #endif
 663 
 664 size_t
 665 ConcurrentMarkSweepGeneration::contiguous_available() const {
 666   // dld proposes an improvement in precision here. If the committed
 667   // part of the space ends in a free block we should add that to
 668   // uncommitted size in the calculation below. Will make this
 669   // change later, staying with the approximation below for the
 670   // time being. -- ysr.
 671   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 672 }
 673 
 674 size_t
 675 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 676   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 677 }
 678 
 679 size_t ConcurrentMarkSweepGeneration::max_available() const {
 680   return free() + _virtual_space.uncommitted_size();
 681 }
 682 
 683 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 684   size_t available = max_available();
 685   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 686   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 687   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 688                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 689   return res;
 690 }
 691 
 692 // At a promotion failure dump information on block layout in heap
 693 // (cms old generation).
 694 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 695   Log(gc, promotion) log;
 696   if (log.is_trace()) {
 697     ResourceMark rm;
 698     cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
 699   }
 700 }
 701 
 702 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 703   // Clear the promotion information.  These pointers can be adjusted
 704   // along with all the other pointers into the heap but
 705   // compaction is expected to be a rare event with
 706   // a heap using cms so don't do it without seeing the need.
 707   for (uint i = 0; i < ParallelGCThreads; i++) {
 708     _par_gc_thread_states[i]->promo.reset();
 709   }
 710 }
 711 
 712 void ConcurrentMarkSweepGeneration::compute_new_size() {
 713   assert_locked_or_safepoint(Heap_lock);
 714 
 715   // If incremental collection failed, we just want to expand
 716   // to the limit.
 717   if (incremental_collection_failed()) {
 718     clear_incremental_collection_failed();
 719     grow_to_reserved();
 720     return;
 721   }
 722 
 723   // The heap has been compacted but not reset yet.
 724   // Any metric such as free() or used() will be incorrect.
 725 
 726   CardGeneration::compute_new_size();
 727 
 728   // Reset again after a possible resizing
 729   if (did_compact()) {
 730     cmsSpace()->reset_after_compaction();
 731   }
 732 }
 733 
 734 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 735   assert_locked_or_safepoint(Heap_lock);
 736 
 737   // If incremental collection failed, we just want to expand
 738   // to the limit.
 739   if (incremental_collection_failed()) {
 740     clear_incremental_collection_failed();
 741     grow_to_reserved();
 742     return;
 743   }
 744 
 745   double free_percentage = ((double) free()) / capacity();
 746   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 747   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 748 
 749   // compute expansion delta needed for reaching desired free percentage
 750   if (free_percentage < desired_free_percentage) {
 751     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 752     assert(desired_capacity >= capacity(), "invalid expansion size");
 753     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 754     Log(gc) log;
 755     if (log.is_trace()) {
 756       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 757       log.trace("From compute_new_size: ");
 758       log.trace("  Free fraction %f", free_percentage);
 759       log.trace("  Desired free fraction %f", desired_free_percentage);
 760       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 761       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 762       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 763       GenCollectedHeap* gch = GenCollectedHeap::heap();
 764       assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
 765       size_t young_size = gch->young_gen()->capacity();
 766       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 767       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 768       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 769       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 770     }
 771     // safe if expansion fails
 772     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 773     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 774   } else {
 775     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 776     assert(desired_capacity <= capacity(), "invalid expansion size");
 777     size_t shrink_bytes = capacity() - desired_capacity;
 778     // Don't shrink unless the delta is greater than the minimum shrink we want
 779     if (shrink_bytes >= MinHeapDeltaBytes) {
 780       shrink_free_list_by(shrink_bytes);
 781     }
 782   }
 783 }
 784 
 785 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 786   return cmsSpace()->freelistLock();
 787 }
 788 
 789 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 790   CMSSynchronousYieldRequest yr;
 791   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 792   return have_lock_and_allocate(size, tlab);
 793 }
 794 
 795 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 796                                                                 bool   tlab /* ignored */) {
 797   assert_lock_strong(freelistLock());
 798   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 799   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 800   // Allocate the object live (grey) if the background collector has
 801   // started marking. This is necessary because the marker may
 802   // have passed this address and consequently this object will
 803   // not otherwise be greyed and would be incorrectly swept up.
 804   // Note that if this object contains references, the writing
 805   // of those references will dirty the card containing this object
 806   // allowing the object to be blackened (and its references scanned)
 807   // either during a preclean phase or at the final checkpoint.
 808   if (res != NULL) {
 809     // We may block here with an uninitialized object with
 810     // its mark-bit or P-bits not yet set. Such objects need
 811     // to be safely navigable by block_start().
 812     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 813     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 814     collector()->direct_allocated(res, adjustedSize);
 815     _direct_allocated_words += adjustedSize;
 816     // allocation counters
 817     NOT_PRODUCT(
 818       _numObjectsAllocated++;
 819       _numWordsAllocated += (int)adjustedSize;
 820     )
 821   }
 822   return res;
 823 }
 824 
 825 // In the case of direct allocation by mutators in a generation that
 826 // is being concurrently collected, the object must be allocated
 827 // live (grey) if the background collector has started marking.
 828 // This is necessary because the marker may
 829 // have passed this address and consequently this object will
 830 // not otherwise be greyed and would be incorrectly swept up.
 831 // Note that if this object contains references, the writing
 832 // of those references will dirty the card containing this object
 833 // allowing the object to be blackened (and its references scanned)
 834 // either during a preclean phase or at the final checkpoint.
 835 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 836   assert(_markBitMap.covers(start, size), "Out of bounds");
 837   if (_collectorState >= Marking) {
 838     MutexLockerEx y(_markBitMap.lock(),
 839                     Mutex::_no_safepoint_check_flag);
 840     // [see comments preceding SweepClosure::do_blk() below for details]
 841     //
 842     // Can the P-bits be deleted now?  JJJ
 843     //
 844     // 1. need to mark the object as live so it isn't collected
 845     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 846     // 3. need to mark the end of the object so marking, precleaning or sweeping
 847     //    can skip over uninitialized or unparsable objects. An allocated
 848     //    object is considered uninitialized for our purposes as long as
 849     //    its klass word is NULL.  All old gen objects are parsable
 850     //    as soon as they are initialized.)
 851     _markBitMap.mark(start);          // object is live
 852     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 853     _markBitMap.mark(start + size - 1);
 854                                       // mark end of object
 855   }
 856   // check that oop looks uninitialized
 857   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 858 }
 859 
 860 void CMSCollector::promoted(bool par, HeapWord* start,
 861                             bool is_obj_array, size_t obj_size) {
 862   assert(_markBitMap.covers(start), "Out of bounds");
 863   // See comment in direct_allocated() about when objects should
 864   // be allocated live.
 865   if (_collectorState >= Marking) {
 866     // we already hold the marking bit map lock, taken in
 867     // the prologue
 868     if (par) {
 869       _markBitMap.par_mark(start);
 870     } else {
 871       _markBitMap.mark(start);
 872     }
 873     // We don't need to mark the object as uninitialized (as
 874     // in direct_allocated above) because this is being done with the
 875     // world stopped and the object will be initialized by the
 876     // time the marking, precleaning or sweeping get to look at it.
 877     // But see the code for copying objects into the CMS generation,
 878     // where we need to ensure that concurrent readers of the
 879     // block offset table are able to safely navigate a block that
 880     // is in flux from being free to being allocated (and in
 881     // transition while being copied into) and subsequently
 882     // becoming a bona-fide object when the copy/promotion is complete.
 883     assert(SafepointSynchronize::is_at_safepoint(),
 884            "expect promotion only at safepoints");
 885 
 886     if (_collectorState < Sweeping) {
 887       // Mark the appropriate cards in the modUnionTable, so that
 888       // this object gets scanned before the sweep. If this is
 889       // not done, CMS generation references in the object might
 890       // not get marked.
 891       // For the case of arrays, which are otherwise precisely
 892       // marked, we need to dirty the entire array, not just its head.
 893       if (is_obj_array) {
 894         // The [par_]mark_range() method expects mr.end() below to
 895         // be aligned to the granularity of a bit's representation
 896         // in the heap. In the case of the MUT below, that's a
 897         // card size.
 898         MemRegion mr(start,
 899                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 900                         CardTableModRefBS::card_size /* bytes */));
 901         if (par) {
 902           _modUnionTable.par_mark_range(mr);
 903         } else {
 904           _modUnionTable.mark_range(mr);
 905         }
 906       } else {  // not an obj array; we can just mark the head
 907         if (par) {
 908           _modUnionTable.par_mark(start);
 909         } else {
 910           _modUnionTable.mark(start);
 911         }
 912       }
 913     }
 914   }
 915 }
 916 
 917 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 918   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 919   // allocate, copy and if necessary update promoinfo --
 920   // delegate to underlying space.
 921   assert_lock_strong(freelistLock());
 922 
 923 #ifndef PRODUCT
 924   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 925     return NULL;
 926   }
 927 #endif  // #ifndef PRODUCT
 928 
 929   oop res = _cmsSpace->promote(obj, obj_size);
 930   if (res == NULL) {
 931     // expand and retry
 932     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 933     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 934     // Since this is the old generation, we don't try to promote
 935     // into a more senior generation.
 936     res = _cmsSpace->promote(obj, obj_size);
 937   }
 938   if (res != NULL) {
 939     // See comment in allocate() about when objects should
 940     // be allocated live.
 941     assert(obj->is_oop(), "Will dereference klass pointer below");
 942     collector()->promoted(false,           // Not parallel
 943                           (HeapWord*)res, obj->is_objArray(), obj_size);
 944     // promotion counters
 945     NOT_PRODUCT(
 946       _numObjectsPromoted++;
 947       _numWordsPromoted +=
 948         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 949     )
 950   }
 951   return res;
 952 }
 953 
 954 
 955 // IMPORTANT: Notes on object size recognition in CMS.
 956 // ---------------------------------------------------
 957 // A block of storage in the CMS generation is always in
 958 // one of three states. A free block (FREE), an allocated
 959 // object (OBJECT) whose size() method reports the correct size,
 960 // and an intermediate state (TRANSIENT) in which its size cannot
 961 // be accurately determined.
 962 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 963 // -----------------------------------------------------
 964 // FREE:      klass_word & 1 == 1; mark_word holds block size
 965 //
 966 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 967 //            obj->size() computes correct size
 968 //
 969 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 970 //
 971 // STATE IDENTIFICATION: (64 bit+COOPS)
 972 // ------------------------------------
 973 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 974 //
 975 // OBJECT:    klass_word installed; klass_word != 0;
 976 //            obj->size() computes correct size
 977 //
 978 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 979 //
 980 //
 981 // STATE TRANSITION DIAGRAM
 982 //
 983 //        mut / parnew                     mut  /  parnew
 984 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 985 //  ^                                                                   |
 986 //  |------------------------ DEAD <------------------------------------|
 987 //         sweep                            mut
 988 //
 989 // While a block is in TRANSIENT state its size cannot be determined
 990 // so readers will either need to come back later or stall until
 991 // the size can be determined. Note that for the case of direct
 992 // allocation, P-bits, when available, may be used to determine the
 993 // size of an object that may not yet have been initialized.
 994 
 995 // Things to support parallel young-gen collection.
 996 oop
 997 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
 998                                            oop old, markOop m,
 999                                            size_t word_sz) {
1000 #ifndef PRODUCT
1001   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1002     return NULL;
1003   }
1004 #endif  // #ifndef PRODUCT
1005 
1006   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1007   PromotionInfo* promoInfo = &ps->promo;
1008   // if we are tracking promotions, then first ensure space for
1009   // promotion (including spooling space for saving header if necessary).
1010   // then allocate and copy, then track promoted info if needed.
1011   // When tracking (see PromotionInfo::track()), the mark word may
1012   // be displaced and in this case restoration of the mark word
1013   // occurs in the (oop_since_save_marks_)iterate phase.
1014   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1015     // Out of space for allocating spooling buffers;
1016     // try expanding and allocating spooling buffers.
1017     if (!expand_and_ensure_spooling_space(promoInfo)) {
1018       return NULL;
1019     }
1020   }
1021   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1022   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1023   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1024   if (obj_ptr == NULL) {
1025      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1026      if (obj_ptr == NULL) {
1027        return NULL;
1028      }
1029   }
1030   oop obj = oop(obj_ptr);
1031   OrderAccess::storestore();
1032   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1033   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1034   // IMPORTANT: See note on object initialization for CMS above.
1035   // Otherwise, copy the object.  Here we must be careful to insert the
1036   // klass pointer last, since this marks the block as an allocated object.
1037   // Except with compressed oops it's the mark word.
1038   HeapWord* old_ptr = (HeapWord*)old;
1039   // Restore the mark word copied above.
1040   obj->set_mark(m);
1041   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1042   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1043   OrderAccess::storestore();
1044 
1045   if (UseCompressedClassPointers) {
1046     // Copy gap missed by (aligned) header size calculation below
1047     obj->set_klass_gap(old->klass_gap());
1048   }
1049   if (word_sz > (size_t)oopDesc::header_size()) {
1050     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1051                                  obj_ptr + oopDesc::header_size(),
1052                                  word_sz - oopDesc::header_size());
1053   }
1054 
1055   // Now we can track the promoted object, if necessary.  We take care
1056   // to delay the transition from uninitialized to full object
1057   // (i.e., insertion of klass pointer) until after, so that it
1058   // atomically becomes a promoted object.
1059   if (promoInfo->tracking()) {
1060     promoInfo->track((PromotedObject*)obj, old->klass());
1061   }
1062   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1063   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1064   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1065 
1066   // Finally, install the klass pointer (this should be volatile).
1067   OrderAccess::storestore();
1068   obj->set_klass(old->klass());
1069   // We should now be able to calculate the right size for this object
1070   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1071 
1072   collector()->promoted(true,          // parallel
1073                         obj_ptr, old->is_objArray(), word_sz);
1074 
1075   NOT_PRODUCT(
1076     Atomic::inc_ptr(&_numObjectsPromoted);
1077     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1078   )
1079 
1080   return obj;
1081 }
1082 
1083 void
1084 ConcurrentMarkSweepGeneration::
1085 par_promote_alloc_done(int thread_num) {
1086   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1087   ps->lab.retire(thread_num);
1088 }
1089 
1090 void
1091 ConcurrentMarkSweepGeneration::
1092 par_oop_since_save_marks_iterate_done(int thread_num) {
1093   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1094   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1095   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1096 
1097   // Because card-scanning has been completed, subsequent phases
1098   // (e.g., reference processing) will not need to recognize which
1099   // objects have been promoted during this GC. So, we can now disable
1100   // promotion tracking.
1101   ps->promo.stopTrackingPromotions();
1102 }
1103 
1104 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1105                                                    size_t size,
1106                                                    bool   tlab)
1107 {
1108   // We allow a STW collection only if a full
1109   // collection was requested.
1110   return full || should_allocate(size, tlab); // FIX ME !!!
1111   // This and promotion failure handling are connected at the
1112   // hip and should be fixed by untying them.
1113 }
1114 
1115 bool CMSCollector::shouldConcurrentCollect() {
1116   LogTarget(Trace, gc) log;
1117 
1118   if (_full_gc_requested) {
1119     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1120     return true;
1121   }
1122 
1123   FreelistLocker x(this);
1124   // ------------------------------------------------------------------
1125   // Print out lots of information which affects the initiation of
1126   // a collection.
1127   if (log.is_enabled() && stats().valid()) {
1128     log.print("CMSCollector shouldConcurrentCollect: ");
1129 
1130     LogStream out(log);
1131     stats().print_on(&out);
1132 
1133     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1134     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1135     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1136     log.print("promotion_rate=%g", stats().promotion_rate());
1137     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1138     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1139     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1140     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1141     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1142     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1143   }
1144   // ------------------------------------------------------------------
1145 
1146   // If the estimated time to complete a cms collection (cms_duration())
1147   // is less than the estimated time remaining until the cms generation
1148   // is full, start a collection.
1149   if (!UseCMSInitiatingOccupancyOnly) {
1150     if (stats().valid()) {
1151       if (stats().time_until_cms_start() == 0.0) {
1152         return true;
1153       }
1154     } else {
1155       // We want to conservatively collect somewhat early in order
1156       // to try and "bootstrap" our CMS/promotion statistics;
1157       // this branch will not fire after the first successful CMS
1158       // collection because the stats should then be valid.
1159       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1160         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1161                   _cmsGen->occupancy(), _bootstrap_occupancy);
1162         return true;
1163       }
1164     }
1165   }
1166 
1167   // Otherwise, we start a collection cycle if
1168   // old gen want a collection cycle started. Each may use
1169   // an appropriate criterion for making this decision.
1170   // XXX We need to make sure that the gen expansion
1171   // criterion dovetails well with this. XXX NEED TO FIX THIS
1172   if (_cmsGen->should_concurrent_collect()) {
1173     log.print("CMS old gen initiated");
1174     return true;
1175   }
1176 
1177   // We start a collection if we believe an incremental collection may fail;
1178   // this is not likely to be productive in practice because it's probably too
1179   // late anyway.
1180   GenCollectedHeap* gch = GenCollectedHeap::heap();
1181   assert(gch->collector_policy()->is_generation_policy(),
1182          "You may want to check the correctness of the following");
1183   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1184     log.print("CMSCollector: collect because incremental collection will fail ");
1185     return true;
1186   }
1187 
1188   if (MetaspaceGC::should_concurrent_collect()) {
1189     log.print("CMSCollector: collect for metadata allocation ");
1190     return true;
1191   }
1192 
1193   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1194   if (CMSTriggerInterval >= 0) {
1195     if (CMSTriggerInterval == 0) {
1196       // Trigger always
1197       return true;
1198     }
1199 
1200     // Check the CMS time since begin (we do not check the stats validity
1201     // as we want to be able to trigger the first CMS cycle as well)
1202     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1203       if (stats().valid()) {
1204         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1205                   stats().cms_time_since_begin());
1206       } else {
1207         log.print("CMSCollector: collect because of trigger interval (first collection)");
1208       }
1209       return true;
1210     }
1211   }
1212 
1213   return false;
1214 }
1215 
1216 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1217 
1218 // Clear _expansion_cause fields of constituent generations
1219 void CMSCollector::clear_expansion_cause() {
1220   _cmsGen->clear_expansion_cause();
1221 }
1222 
1223 // We should be conservative in starting a collection cycle.  To
1224 // start too eagerly runs the risk of collecting too often in the
1225 // extreme.  To collect too rarely falls back on full collections,
1226 // which works, even if not optimum in terms of concurrent work.
1227 // As a work around for too eagerly collecting, use the flag
1228 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1229 // giving the user an easily understandable way of controlling the
1230 // collections.
1231 // We want to start a new collection cycle if any of the following
1232 // conditions hold:
1233 // . our current occupancy exceeds the configured initiating occupancy
1234 //   for this generation, or
1235 // . we recently needed to expand this space and have not, since that
1236 //   expansion, done a collection of this generation, or
1237 // . the underlying space believes that it may be a good idea to initiate
1238 //   a concurrent collection (this may be based on criteria such as the
1239 //   following: the space uses linear allocation and linear allocation is
1240 //   going to fail, or there is believed to be excessive fragmentation in
1241 //   the generation, etc... or ...
1242 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1243 //   the case of the old generation; see CR 6543076):
1244 //   we may be approaching a point at which allocation requests may fail because
1245 //   we will be out of sufficient free space given allocation rate estimates.]
1246 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1247 
1248   assert_lock_strong(freelistLock());
1249   if (occupancy() > initiating_occupancy()) {
1250     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1251                   short_name(), occupancy(), initiating_occupancy());
1252     return true;
1253   }
1254   if (UseCMSInitiatingOccupancyOnly) {
1255     return false;
1256   }
1257   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1258     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1259     return true;
1260   }
1261   return false;
1262 }
1263 
1264 void ConcurrentMarkSweepGeneration::collect(bool   full,
1265                                             bool   clear_all_soft_refs,
1266                                             size_t size,
1267                                             bool   tlab)
1268 {
1269   collector()->collect(full, clear_all_soft_refs, size, tlab);
1270 }
1271 
1272 void CMSCollector::collect(bool   full,
1273                            bool   clear_all_soft_refs,
1274                            size_t size,
1275                            bool   tlab)
1276 {
1277   // The following "if" branch is present for defensive reasons.
1278   // In the current uses of this interface, it can be replaced with:
1279   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1280   // But I am not placing that assert here to allow future
1281   // generality in invoking this interface.
1282   if (GCLocker::is_active()) {
1283     // A consistency test for GCLocker
1284     assert(GCLocker::needs_gc(), "Should have been set already");
1285     // Skip this foreground collection, instead
1286     // expanding the heap if necessary.
1287     // Need the free list locks for the call to free() in compute_new_size()
1288     compute_new_size();
1289     return;
1290   }
1291   acquire_control_and_collect(full, clear_all_soft_refs);
1292 }
1293 
1294 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1295   GenCollectedHeap* gch = GenCollectedHeap::heap();
1296   unsigned int gc_count = gch->total_full_collections();
1297   if (gc_count == full_gc_count) {
1298     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1299     _full_gc_requested = true;
1300     _full_gc_cause = cause;
1301     CGC_lock->notify();   // nudge CMS thread
1302   } else {
1303     assert(gc_count > full_gc_count, "Error: causal loop");
1304   }
1305 }
1306 
1307 bool CMSCollector::is_external_interruption() {
1308   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1309   return GCCause::is_user_requested_gc(cause) ||
1310          GCCause::is_serviceability_requested_gc(cause);
1311 }
1312 
1313 void CMSCollector::report_concurrent_mode_interruption() {
1314   if (is_external_interruption()) {
1315     log_debug(gc)("Concurrent mode interrupted");
1316   } else {
1317     log_debug(gc)("Concurrent mode failure");
1318     _gc_tracer_cm->report_concurrent_mode_failure();
1319   }
1320 }
1321 
1322 
1323 // The foreground and background collectors need to coordinate in order
1324 // to make sure that they do not mutually interfere with CMS collections.
1325 // When a background collection is active,
1326 // the foreground collector may need to take over (preempt) and
1327 // synchronously complete an ongoing collection. Depending on the
1328 // frequency of the background collections and the heap usage
1329 // of the application, this preemption can be seldom or frequent.
1330 // There are only certain
1331 // points in the background collection that the "collection-baton"
1332 // can be passed to the foreground collector.
1333 //
1334 // The foreground collector will wait for the baton before
1335 // starting any part of the collection.  The foreground collector
1336 // will only wait at one location.
1337 //
1338 // The background collector will yield the baton before starting a new
1339 // phase of the collection (e.g., before initial marking, marking from roots,
1340 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1341 // of the loop which switches the phases. The background collector does some
1342 // of the phases (initial mark, final re-mark) with the world stopped.
1343 // Because of locking involved in stopping the world,
1344 // the foreground collector should not block waiting for the background
1345 // collector when it is doing a stop-the-world phase.  The background
1346 // collector will yield the baton at an additional point just before
1347 // it enters a stop-the-world phase.  Once the world is stopped, the
1348 // background collector checks the phase of the collection.  If the
1349 // phase has not changed, it proceeds with the collection.  If the
1350 // phase has changed, it skips that phase of the collection.  See
1351 // the comments on the use of the Heap_lock in collect_in_background().
1352 //
1353 // Variable used in baton passing.
1354 //   _foregroundGCIsActive - Set to true by the foreground collector when
1355 //      it wants the baton.  The foreground clears it when it has finished
1356 //      the collection.
1357 //   _foregroundGCShouldWait - Set to true by the background collector
1358 //        when it is running.  The foreground collector waits while
1359 //      _foregroundGCShouldWait is true.
1360 //  CGC_lock - monitor used to protect access to the above variables
1361 //      and to notify the foreground and background collectors.
1362 //  _collectorState - current state of the CMS collection.
1363 //
1364 // The foreground collector
1365 //   acquires the CGC_lock
1366 //   sets _foregroundGCIsActive
1367 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1368 //     various locks acquired in preparation for the collection
1369 //     are released so as not to block the background collector
1370 //     that is in the midst of a collection
1371 //   proceeds with the collection
1372 //   clears _foregroundGCIsActive
1373 //   returns
1374 //
1375 // The background collector in a loop iterating on the phases of the
1376 //      collection
1377 //   acquires the CGC_lock
1378 //   sets _foregroundGCShouldWait
1379 //   if _foregroundGCIsActive is set
1380 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1381 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1382 //     and exits the loop.
1383 //   otherwise
1384 //     proceed with that phase of the collection
1385 //     if the phase is a stop-the-world phase,
1386 //       yield the baton once more just before enqueueing
1387 //       the stop-world CMS operation (executed by the VM thread).
1388 //   returns after all phases of the collection are done
1389 //
1390 
1391 void CMSCollector::acquire_control_and_collect(bool full,
1392         bool clear_all_soft_refs) {
1393   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1394   assert(!Thread::current()->is_ConcurrentGC_thread(),
1395          "shouldn't try to acquire control from self!");
1396 
1397   // Start the protocol for acquiring control of the
1398   // collection from the background collector (aka CMS thread).
1399   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1400          "VM thread should have CMS token");
1401   // Remember the possibly interrupted state of an ongoing
1402   // concurrent collection
1403   CollectorState first_state = _collectorState;
1404 
1405   // Signal to a possibly ongoing concurrent collection that
1406   // we want to do a foreground collection.
1407   _foregroundGCIsActive = true;
1408 
1409   // release locks and wait for a notify from the background collector
1410   // releasing the locks in only necessary for phases which
1411   // do yields to improve the granularity of the collection.
1412   assert_lock_strong(bitMapLock());
1413   // We need to lock the Free list lock for the space that we are
1414   // currently collecting.
1415   assert(haveFreelistLocks(), "Must be holding free list locks");
1416   bitMapLock()->unlock();
1417   releaseFreelistLocks();
1418   {
1419     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1420     if (_foregroundGCShouldWait) {
1421       // We are going to be waiting for action for the CMS thread;
1422       // it had better not be gone (for instance at shutdown)!
1423       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1424              "CMS thread must be running");
1425       // Wait here until the background collector gives us the go-ahead
1426       ConcurrentMarkSweepThread::clear_CMS_flag(
1427         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1428       // Get a possibly blocked CMS thread going:
1429       //   Note that we set _foregroundGCIsActive true above,
1430       //   without protection of the CGC_lock.
1431       CGC_lock->notify();
1432       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1433              "Possible deadlock");
1434       while (_foregroundGCShouldWait) {
1435         // wait for notification
1436         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1437         // Possibility of delay/starvation here, since CMS token does
1438         // not know to give priority to VM thread? Actually, i think
1439         // there wouldn't be any delay/starvation, but the proof of
1440         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1441       }
1442       ConcurrentMarkSweepThread::set_CMS_flag(
1443         ConcurrentMarkSweepThread::CMS_vm_has_token);
1444     }
1445   }
1446   // The CMS_token is already held.  Get back the other locks.
1447   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1448          "VM thread should have CMS token");
1449   getFreelistLocks();
1450   bitMapLock()->lock_without_safepoint_check();
1451   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1452                        p2i(Thread::current()), first_state);
1453   log_debug(gc, state)("    gets control with state %d", _collectorState);
1454 
1455   // Inform cms gen if this was due to partial collection failing.
1456   // The CMS gen may use this fact to determine its expansion policy.
1457   GenCollectedHeap* gch = GenCollectedHeap::heap();
1458   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1459     assert(!_cmsGen->incremental_collection_failed(),
1460            "Should have been noticed, reacted to and cleared");
1461     _cmsGen->set_incremental_collection_failed();
1462   }
1463 
1464   if (first_state > Idling) {
1465     report_concurrent_mode_interruption();
1466   }
1467 
1468   set_did_compact(true);
1469 
1470   // If the collection is being acquired from the background
1471   // collector, there may be references on the discovered
1472   // references lists.  Abandon those references, since some
1473   // of them may have become unreachable after concurrent
1474   // discovery; the STW compacting collector will redo discovery
1475   // more precisely, without being subject to floating garbage.
1476   // Leaving otherwise unreachable references in the discovered
1477   // lists would require special handling.
1478   ref_processor()->disable_discovery();
1479   ref_processor()->abandon_partial_discovery();
1480   ref_processor()->verify_no_references_recorded();
1481 
1482   if (first_state > Idling) {
1483     save_heap_summary();
1484   }
1485 
1486   do_compaction_work(clear_all_soft_refs);
1487 
1488   // Has the GC time limit been exceeded?
1489   size_t max_eden_size = _young_gen->max_eden_size();
1490   GCCause::Cause gc_cause = gch->gc_cause();
1491   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1492                                          _young_gen->eden()->used(),
1493                                          _cmsGen->max_capacity(),
1494                                          max_eden_size,
1495                                          full,
1496                                          gc_cause,
1497                                          gch->collector_policy());
1498 
1499   // Reset the expansion cause, now that we just completed
1500   // a collection cycle.
1501   clear_expansion_cause();
1502   _foregroundGCIsActive = false;
1503   return;
1504 }
1505 
1506 // Resize the tenured generation
1507 // after obtaining the free list locks for the
1508 // two generations.
1509 void CMSCollector::compute_new_size() {
1510   assert_locked_or_safepoint(Heap_lock);
1511   FreelistLocker z(this);
1512   MetaspaceGC::compute_new_size();
1513   _cmsGen->compute_new_size_free_list();
1514 }
1515 
1516 // A work method used by the foreground collector to do
1517 // a mark-sweep-compact.
1518 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1519   GenCollectedHeap* gch = GenCollectedHeap::heap();
1520 
1521   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1522   gc_timer->register_gc_start();
1523 
1524   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1525   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1526 
1527   gch->pre_full_gc_dump(gc_timer);
1528 
1529   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1530 
1531   // Temporarily widen the span of the weak reference processing to
1532   // the entire heap.
1533   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1534   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1535   // Temporarily, clear the "is_alive_non_header" field of the
1536   // reference processor.
1537   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1538   // Temporarily make reference _processing_ single threaded (non-MT).
1539   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1540   // Temporarily make refs discovery atomic
1541   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1542   // Temporarily make reference _discovery_ single threaded (non-MT)
1543   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1544 
1545   ref_processor()->set_enqueuing_is_done(false);
1546   ref_processor()->enable_discovery();
1547   ref_processor()->setup_policy(clear_all_soft_refs);
1548   // If an asynchronous collection finishes, the _modUnionTable is
1549   // all clear.  If we are assuming the collection from an asynchronous
1550   // collection, clear the _modUnionTable.
1551   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1552     "_modUnionTable should be clear if the baton was not passed");
1553   _modUnionTable.clear_all();
1554   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1555     "mod union for klasses should be clear if the baton was passed");
1556   _ct->klass_rem_set()->clear_mod_union();
1557 
1558   // We must adjust the allocation statistics being maintained
1559   // in the free list space. We do so by reading and clearing
1560   // the sweep timer and updating the block flux rate estimates below.
1561   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1562   if (_inter_sweep_timer.is_active()) {
1563     _inter_sweep_timer.stop();
1564     // Note that we do not use this sample to update the _inter_sweep_estimate.
1565     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1566                                             _inter_sweep_estimate.padded_average(),
1567                                             _intra_sweep_estimate.padded_average());
1568   }
1569 
1570   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1571   #ifdef ASSERT
1572     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1573     size_t free_size = cms_space->free();
1574     assert(free_size ==
1575            pointer_delta(cms_space->end(), cms_space->compaction_top())
1576            * HeapWordSize,
1577       "All the free space should be compacted into one chunk at top");
1578     assert(cms_space->dictionary()->total_chunk_size(
1579                                       debug_only(cms_space->freelistLock())) == 0 ||
1580            cms_space->totalSizeInIndexedFreeLists() == 0,
1581       "All the free space should be in a single chunk");
1582     size_t num = cms_space->totalCount();
1583     assert((free_size == 0 && num == 0) ||
1584            (free_size > 0  && (num == 1 || num == 2)),
1585          "There should be at most 2 free chunks after compaction");
1586   #endif // ASSERT
1587   _collectorState = Resetting;
1588   assert(_restart_addr == NULL,
1589          "Should have been NULL'd before baton was passed");
1590   reset_stw();
1591   _cmsGen->reset_after_compaction();
1592   _concurrent_cycles_since_last_unload = 0;
1593 
1594   // Clear any data recorded in the PLAB chunk arrays.
1595   if (_survivor_plab_array != NULL) {
1596     reset_survivor_plab_arrays();
1597   }
1598 
1599   // Adjust the per-size allocation stats for the next epoch.
1600   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1601   // Restart the "inter sweep timer" for the next epoch.
1602   _inter_sweep_timer.reset();
1603   _inter_sweep_timer.start();
1604 
1605   // No longer a need to do a concurrent collection for Metaspace.
1606   MetaspaceGC::set_should_concurrent_collect(false);
1607 
1608   gch->post_full_gc_dump(gc_timer);
1609 
1610   gc_timer->register_gc_end();
1611 
1612   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1613 
1614   // For a mark-sweep-compact, compute_new_size() will be called
1615   // in the heap's do_collection() method.
1616 }
1617 
1618 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1619   Log(gc, heap) log;
1620   if (!log.is_trace()) {
1621     return;
1622   }
1623 
1624   ContiguousSpace* eden_space = _young_gen->eden();
1625   ContiguousSpace* from_space = _young_gen->from();
1626   ContiguousSpace* to_space   = _young_gen->to();
1627   // Eden
1628   if (_eden_chunk_array != NULL) {
1629     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1630               p2i(eden_space->bottom()), p2i(eden_space->top()),
1631               p2i(eden_space->end()), eden_space->capacity());
1632     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1633               _eden_chunk_index, _eden_chunk_capacity);
1634     for (size_t i = 0; i < _eden_chunk_index; i++) {
1635       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1636     }
1637   }
1638   // Survivor
1639   if (_survivor_chunk_array != NULL) {
1640     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1641               p2i(from_space->bottom()), p2i(from_space->top()),
1642               p2i(from_space->end()), from_space->capacity());
1643     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1644               _survivor_chunk_index, _survivor_chunk_capacity);
1645     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1646       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1647     }
1648   }
1649 }
1650 
1651 void CMSCollector::getFreelistLocks() const {
1652   // Get locks for all free lists in all generations that this
1653   // collector is responsible for
1654   _cmsGen->freelistLock()->lock_without_safepoint_check();
1655 }
1656 
1657 void CMSCollector::releaseFreelistLocks() const {
1658   // Release locks for all free lists in all generations that this
1659   // collector is responsible for
1660   _cmsGen->freelistLock()->unlock();
1661 }
1662 
1663 bool CMSCollector::haveFreelistLocks() const {
1664   // Check locks for all free lists in all generations that this
1665   // collector is responsible for
1666   assert_lock_strong(_cmsGen->freelistLock());
1667   PRODUCT_ONLY(ShouldNotReachHere());
1668   return true;
1669 }
1670 
1671 // A utility class that is used by the CMS collector to
1672 // temporarily "release" the foreground collector from its
1673 // usual obligation to wait for the background collector to
1674 // complete an ongoing phase before proceeding.
1675 class ReleaseForegroundGC: public StackObj {
1676  private:
1677   CMSCollector* _c;
1678  public:
1679   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1680     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1681     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1682     // allow a potentially blocked foreground collector to proceed
1683     _c->_foregroundGCShouldWait = false;
1684     if (_c->_foregroundGCIsActive) {
1685       CGC_lock->notify();
1686     }
1687     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1688            "Possible deadlock");
1689   }
1690 
1691   ~ReleaseForegroundGC() {
1692     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1693     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1694     _c->_foregroundGCShouldWait = true;
1695   }
1696 };
1697 
1698 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1699   assert(Thread::current()->is_ConcurrentGC_thread(),
1700     "A CMS asynchronous collection is only allowed on a CMS thread.");
1701 
1702   GenCollectedHeap* gch = GenCollectedHeap::heap();
1703   {
1704     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1705     MutexLockerEx hl(Heap_lock, safepoint_check);
1706     FreelistLocker fll(this);
1707     MutexLockerEx x(CGC_lock, safepoint_check);
1708     if (_foregroundGCIsActive) {
1709       // The foreground collector is. Skip this
1710       // background collection.
1711       assert(!_foregroundGCShouldWait, "Should be clear");
1712       return;
1713     } else {
1714       assert(_collectorState == Idling, "Should be idling before start.");
1715       _collectorState = InitialMarking;
1716       register_gc_start(cause);
1717       // Reset the expansion cause, now that we are about to begin
1718       // a new cycle.
1719       clear_expansion_cause();
1720 
1721       // Clear the MetaspaceGC flag since a concurrent collection
1722       // is starting but also clear it after the collection.
1723       MetaspaceGC::set_should_concurrent_collect(false);
1724     }
1725     // Decide if we want to enable class unloading as part of the
1726     // ensuing concurrent GC cycle.
1727     update_should_unload_classes();
1728     _full_gc_requested = false;           // acks all outstanding full gc requests
1729     _full_gc_cause = GCCause::_no_gc;
1730     // Signal that we are about to start a collection
1731     gch->increment_total_full_collections();  // ... starting a collection cycle
1732     _collection_count_start = gch->total_full_collections();
1733   }
1734 
1735   size_t prev_used = _cmsGen->used();
1736 
1737   // The change of the collection state is normally done at this level;
1738   // the exceptions are phases that are executed while the world is
1739   // stopped.  For those phases the change of state is done while the
1740   // world is stopped.  For baton passing purposes this allows the
1741   // background collector to finish the phase and change state atomically.
1742   // The foreground collector cannot wait on a phase that is done
1743   // while the world is stopped because the foreground collector already
1744   // has the world stopped and would deadlock.
1745   while (_collectorState != Idling) {
1746     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1747                          p2i(Thread::current()), _collectorState);
1748     // The foreground collector
1749     //   holds the Heap_lock throughout its collection.
1750     //   holds the CMS token (but not the lock)
1751     //     except while it is waiting for the background collector to yield.
1752     //
1753     // The foreground collector should be blocked (not for long)
1754     //   if the background collector is about to start a phase
1755     //   executed with world stopped.  If the background
1756     //   collector has already started such a phase, the
1757     //   foreground collector is blocked waiting for the
1758     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1759     //   are executed in the VM thread.
1760     //
1761     // The locking order is
1762     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1763     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1764     //   CMS token  (claimed in
1765     //                stop_world_and_do() -->
1766     //                  safepoint_synchronize() -->
1767     //                    CMSThread::synchronize())
1768 
1769     {
1770       // Check if the FG collector wants us to yield.
1771       CMSTokenSync x(true); // is cms thread
1772       if (waitForForegroundGC()) {
1773         // We yielded to a foreground GC, nothing more to be
1774         // done this round.
1775         assert(_foregroundGCShouldWait == false, "We set it to false in "
1776                "waitForForegroundGC()");
1777         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1778                              p2i(Thread::current()), _collectorState);
1779         return;
1780       } else {
1781         // The background collector can run but check to see if the
1782         // foreground collector has done a collection while the
1783         // background collector was waiting to get the CGC_lock
1784         // above.  If yes, break so that _foregroundGCShouldWait
1785         // is cleared before returning.
1786         if (_collectorState == Idling) {
1787           break;
1788         }
1789       }
1790     }
1791 
1792     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1793       "should be waiting");
1794 
1795     switch (_collectorState) {
1796       case InitialMarking:
1797         {
1798           ReleaseForegroundGC x(this);
1799           stats().record_cms_begin();
1800           VM_CMS_Initial_Mark initial_mark_op(this);
1801           VMThread::execute(&initial_mark_op);
1802         }
1803         // The collector state may be any legal state at this point
1804         // since the background collector may have yielded to the
1805         // foreground collector.
1806         break;
1807       case Marking:
1808         // initial marking in checkpointRootsInitialWork has been completed
1809         if (markFromRoots()) { // we were successful
1810           assert(_collectorState == Precleaning, "Collector state should "
1811             "have changed");
1812         } else {
1813           assert(_foregroundGCIsActive, "Internal state inconsistency");
1814         }
1815         break;
1816       case Precleaning:
1817         // marking from roots in markFromRoots has been completed
1818         preclean();
1819         assert(_collectorState == AbortablePreclean ||
1820                _collectorState == FinalMarking,
1821                "Collector state should have changed");
1822         break;
1823       case AbortablePreclean:
1824         abortable_preclean();
1825         assert(_collectorState == FinalMarking, "Collector state should "
1826           "have changed");
1827         break;
1828       case FinalMarking:
1829         {
1830           ReleaseForegroundGC x(this);
1831 
1832           VM_CMS_Final_Remark final_remark_op(this);
1833           VMThread::execute(&final_remark_op);
1834         }
1835         assert(_foregroundGCShouldWait, "block post-condition");
1836         break;
1837       case Sweeping:
1838         // final marking in checkpointRootsFinal has been completed
1839         sweep();
1840         assert(_collectorState == Resizing, "Collector state change "
1841           "to Resizing must be done under the free_list_lock");
1842 
1843       case Resizing: {
1844         // Sweeping has been completed...
1845         // At this point the background collection has completed.
1846         // Don't move the call to compute_new_size() down
1847         // into code that might be executed if the background
1848         // collection was preempted.
1849         {
1850           ReleaseForegroundGC x(this);   // unblock FG collection
1851           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1852           CMSTokenSync        z(true);   // not strictly needed.
1853           if (_collectorState == Resizing) {
1854             compute_new_size();
1855             save_heap_summary();
1856             _collectorState = Resetting;
1857           } else {
1858             assert(_collectorState == Idling, "The state should only change"
1859                    " because the foreground collector has finished the collection");
1860           }
1861         }
1862         break;
1863       }
1864       case Resetting:
1865         // CMS heap resizing has been completed
1866         reset_concurrent();
1867         assert(_collectorState == Idling, "Collector state should "
1868           "have changed");
1869 
1870         MetaspaceGC::set_should_concurrent_collect(false);
1871 
1872         stats().record_cms_end();
1873         // Don't move the concurrent_phases_end() and compute_new_size()
1874         // calls to here because a preempted background collection
1875         // has it's state set to "Resetting".
1876         break;
1877       case Idling:
1878       default:
1879         ShouldNotReachHere();
1880         break;
1881     }
1882     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1883                          p2i(Thread::current()), _collectorState);
1884     assert(_foregroundGCShouldWait, "block post-condition");
1885   }
1886 
1887   // Should this be in gc_epilogue?
1888   collector_policy()->counters()->update_counters();
1889 
1890   {
1891     // Clear _foregroundGCShouldWait and, in the event that the
1892     // foreground collector is waiting, notify it, before
1893     // returning.
1894     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1895     _foregroundGCShouldWait = false;
1896     if (_foregroundGCIsActive) {
1897       CGC_lock->notify();
1898     }
1899     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1900            "Possible deadlock");
1901   }
1902   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1903                        p2i(Thread::current()), _collectorState);
1904   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1905                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1906 }
1907 
1908 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1909   _cms_start_registered = true;
1910   _gc_timer_cm->register_gc_start();
1911   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1912 }
1913 
1914 void CMSCollector::register_gc_end() {
1915   if (_cms_start_registered) {
1916     report_heap_summary(GCWhen::AfterGC);
1917 
1918     _gc_timer_cm->register_gc_end();
1919     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1920     _cms_start_registered = false;
1921   }
1922 }
1923 
1924 void CMSCollector::save_heap_summary() {
1925   GenCollectedHeap* gch = GenCollectedHeap::heap();
1926   _last_heap_summary = gch->create_heap_summary();
1927   _last_metaspace_summary = gch->create_metaspace_summary();
1928 }
1929 
1930 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1931   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1932   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1933 }
1934 
1935 bool CMSCollector::waitForForegroundGC() {
1936   bool res = false;
1937   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1938          "CMS thread should have CMS token");
1939   // Block the foreground collector until the
1940   // background collectors decides whether to
1941   // yield.
1942   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1943   _foregroundGCShouldWait = true;
1944   if (_foregroundGCIsActive) {
1945     // The background collector yields to the
1946     // foreground collector and returns a value
1947     // indicating that it has yielded.  The foreground
1948     // collector can proceed.
1949     res = true;
1950     _foregroundGCShouldWait = false;
1951     ConcurrentMarkSweepThread::clear_CMS_flag(
1952       ConcurrentMarkSweepThread::CMS_cms_has_token);
1953     ConcurrentMarkSweepThread::set_CMS_flag(
1954       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1955     // Get a possibly blocked foreground thread going
1956     CGC_lock->notify();
1957     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1958                          p2i(Thread::current()), _collectorState);
1959     while (_foregroundGCIsActive) {
1960       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1961     }
1962     ConcurrentMarkSweepThread::set_CMS_flag(
1963       ConcurrentMarkSweepThread::CMS_cms_has_token);
1964     ConcurrentMarkSweepThread::clear_CMS_flag(
1965       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1966   }
1967   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1968                        p2i(Thread::current()), _collectorState);
1969   return res;
1970 }
1971 
1972 // Because of the need to lock the free lists and other structures in
1973 // the collector, common to all the generations that the collector is
1974 // collecting, we need the gc_prologues of individual CMS generations
1975 // delegate to their collector. It may have been simpler had the
1976 // current infrastructure allowed one to call a prologue on a
1977 // collector. In the absence of that we have the generation's
1978 // prologue delegate to the collector, which delegates back
1979 // some "local" work to a worker method in the individual generations
1980 // that it's responsible for collecting, while itself doing any
1981 // work common to all generations it's responsible for. A similar
1982 // comment applies to the  gc_epilogue()'s.
1983 // The role of the variable _between_prologue_and_epilogue is to
1984 // enforce the invocation protocol.
1985 void CMSCollector::gc_prologue(bool full) {
1986   // Call gc_prologue_work() for the CMSGen
1987   // we are responsible for.
1988 
1989   // The following locking discipline assumes that we are only called
1990   // when the world is stopped.
1991   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1992 
1993   // The CMSCollector prologue must call the gc_prologues for the
1994   // "generations" that it's responsible
1995   // for.
1996 
1997   assert(   Thread::current()->is_VM_thread()
1998          || (   CMSScavengeBeforeRemark
1999              && Thread::current()->is_ConcurrentGC_thread()),
2000          "Incorrect thread type for prologue execution");
2001 
2002   if (_between_prologue_and_epilogue) {
2003     // We have already been invoked; this is a gc_prologue delegation
2004     // from yet another CMS generation that we are responsible for, just
2005     // ignore it since all relevant work has already been done.
2006     return;
2007   }
2008 
2009   // set a bit saying prologue has been called; cleared in epilogue
2010   _between_prologue_and_epilogue = true;
2011   // Claim locks for common data structures, then call gc_prologue_work()
2012   // for each CMSGen.
2013 
2014   getFreelistLocks();   // gets free list locks on constituent spaces
2015   bitMapLock()->lock_without_safepoint_check();
2016 
2017   // Should call gc_prologue_work() for all cms gens we are responsible for
2018   bool duringMarking =    _collectorState >= Marking
2019                          && _collectorState < Sweeping;
2020 
2021   // The young collections clear the modified oops state, which tells if
2022   // there are any modified oops in the class. The remark phase also needs
2023   // that information. Tell the young collection to save the union of all
2024   // modified klasses.
2025   if (duringMarking) {
2026     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2027   }
2028 
2029   bool registerClosure = duringMarking;
2030 
2031   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2032 
2033   if (!full) {
2034     stats().record_gc0_begin();
2035   }
2036 }
2037 
2038 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2039 
2040   _capacity_at_prologue = capacity();
2041   _used_at_prologue = used();
2042 
2043   // We enable promotion tracking so that card-scanning can recognize
2044   // which objects have been promoted during this GC and skip them.
2045   for (uint i = 0; i < ParallelGCThreads; i++) {
2046     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2047   }
2048 
2049   // Delegate to CMScollector which knows how to coordinate between
2050   // this and any other CMS generations that it is responsible for
2051   // collecting.
2052   collector()->gc_prologue(full);
2053 }
2054 
2055 // This is a "private" interface for use by this generation's CMSCollector.
2056 // Not to be called directly by any other entity (for instance,
2057 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2058 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2059   bool registerClosure, ModUnionClosure* modUnionClosure) {
2060   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2061   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2062     "Should be NULL");
2063   if (registerClosure) {
2064     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2065   }
2066   cmsSpace()->gc_prologue();
2067   // Clear stat counters
2068   NOT_PRODUCT(
2069     assert(_numObjectsPromoted == 0, "check");
2070     assert(_numWordsPromoted   == 0, "check");
2071     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2072                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2073     _numObjectsAllocated = 0;
2074     _numWordsAllocated   = 0;
2075   )
2076 }
2077 
2078 void CMSCollector::gc_epilogue(bool full) {
2079   // The following locking discipline assumes that we are only called
2080   // when the world is stopped.
2081   assert(SafepointSynchronize::is_at_safepoint(),
2082          "world is stopped assumption");
2083 
2084   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2085   // if linear allocation blocks need to be appropriately marked to allow the
2086   // the blocks to be parsable. We also check here whether we need to nudge the
2087   // CMS collector thread to start a new cycle (if it's not already active).
2088   assert(   Thread::current()->is_VM_thread()
2089          || (   CMSScavengeBeforeRemark
2090              && Thread::current()->is_ConcurrentGC_thread()),
2091          "Incorrect thread type for epilogue execution");
2092 
2093   if (!_between_prologue_and_epilogue) {
2094     // We have already been invoked; this is a gc_epilogue delegation
2095     // from yet another CMS generation that we are responsible for, just
2096     // ignore it since all relevant work has already been done.
2097     return;
2098   }
2099   assert(haveFreelistLocks(), "must have freelist locks");
2100   assert_lock_strong(bitMapLock());
2101 
2102   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2103 
2104   _cmsGen->gc_epilogue_work(full);
2105 
2106   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2107     // in case sampling was not already enabled, enable it
2108     _start_sampling = true;
2109   }
2110   // reset _eden_chunk_array so sampling starts afresh
2111   _eden_chunk_index = 0;
2112 
2113   size_t cms_used   = _cmsGen->cmsSpace()->used();
2114 
2115   // update performance counters - this uses a special version of
2116   // update_counters() that allows the utilization to be passed as a
2117   // parameter, avoiding multiple calls to used().
2118   //
2119   _cmsGen->update_counters(cms_used);
2120 
2121   bitMapLock()->unlock();
2122   releaseFreelistLocks();
2123 
2124   if (!CleanChunkPoolAsync) {
2125     Chunk::clean_chunk_pool();
2126   }
2127 
2128   set_did_compact(false);
2129   _between_prologue_and_epilogue = false;  // ready for next cycle
2130 }
2131 
2132 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2133   collector()->gc_epilogue(full);
2134 
2135   // When using ParNew, promotion tracking should have already been
2136   // disabled. However, the prologue (which enables promotion
2137   // tracking) and epilogue are called irrespective of the type of
2138   // GC. So they will also be called before and after Full GCs, during
2139   // which promotion tracking will not be explicitly disabled. So,
2140   // it's safer to also disable it here too (to be symmetric with
2141   // enabling it in the prologue).
2142   for (uint i = 0; i < ParallelGCThreads; i++) {
2143     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2144   }
2145 }
2146 
2147 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2148   assert(!incremental_collection_failed(), "Should have been cleared");
2149   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2150   cmsSpace()->gc_epilogue();
2151     // Print stat counters
2152   NOT_PRODUCT(
2153     assert(_numObjectsAllocated == 0, "check");
2154     assert(_numWordsAllocated == 0, "check");
2155     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2156                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2157     _numObjectsPromoted = 0;
2158     _numWordsPromoted   = 0;
2159   )
2160 
2161   // Call down the chain in contiguous_available needs the freelistLock
2162   // so print this out before releasing the freeListLock.
2163   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2164 }
2165 
2166 #ifndef PRODUCT
2167 bool CMSCollector::have_cms_token() {
2168   Thread* thr = Thread::current();
2169   if (thr->is_VM_thread()) {
2170     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2171   } else if (thr->is_ConcurrentGC_thread()) {
2172     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2173   } else if (thr->is_GC_task_thread()) {
2174     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2175            ParGCRareEvent_lock->owned_by_self();
2176   }
2177   return false;
2178 }
2179 
2180 // Check reachability of the given heap address in CMS generation,
2181 // treating all other generations as roots.
2182 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2183   // We could "guarantee" below, rather than assert, but I'll
2184   // leave these as "asserts" so that an adventurous debugger
2185   // could try this in the product build provided some subset of
2186   // the conditions were met, provided they were interested in the
2187   // results and knew that the computation below wouldn't interfere
2188   // with other concurrent computations mutating the structures
2189   // being read or written.
2190   assert(SafepointSynchronize::is_at_safepoint(),
2191          "Else mutations in object graph will make answer suspect");
2192   assert(have_cms_token(), "Should hold cms token");
2193   assert(haveFreelistLocks(), "must hold free list locks");
2194   assert_lock_strong(bitMapLock());
2195 
2196   // Clear the marking bit map array before starting, but, just
2197   // for kicks, first report if the given address is already marked
2198   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2199                 _markBitMap.isMarked(addr) ? "" : " not");
2200 
2201   if (verify_after_remark()) {
2202     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2203     bool result = verification_mark_bm()->isMarked(addr);
2204     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2205                   result ? "IS" : "is NOT");
2206     return result;
2207   } else {
2208     tty->print_cr("Could not compute result");
2209     return false;
2210   }
2211 }
2212 #endif
2213 
2214 void
2215 CMSCollector::print_on_error(outputStream* st) {
2216   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2217   if (collector != NULL) {
2218     CMSBitMap* bitmap = &collector->_markBitMap;
2219     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2220     bitmap->print_on_error(st, " Bits: ");
2221 
2222     st->cr();
2223 
2224     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2225     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2226     mut_bitmap->print_on_error(st, " Bits: ");
2227   }
2228 }
2229 
2230 ////////////////////////////////////////////////////////
2231 // CMS Verification Support
2232 ////////////////////////////////////////////////////////
2233 // Following the remark phase, the following invariant
2234 // should hold -- each object in the CMS heap which is
2235 // marked in markBitMap() should be marked in the verification_mark_bm().
2236 
2237 class VerifyMarkedClosure: public BitMapClosure {
2238   CMSBitMap* _marks;
2239   bool       _failed;
2240 
2241  public:
2242   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2243 
2244   bool do_bit(size_t offset) {
2245     HeapWord* addr = _marks->offsetToHeapWord(offset);
2246     if (!_marks->isMarked(addr)) {
2247       Log(gc, verify) log;
2248       ResourceMark rm;
2249       oop(addr)->print_on(log.error_stream());
2250       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2251       _failed = true;
2252     }
2253     return true;
2254   }
2255 
2256   bool failed() { return _failed; }
2257 };
2258 
2259 bool CMSCollector::verify_after_remark() {
2260   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2261   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2262   static bool init = false;
2263 
2264   assert(SafepointSynchronize::is_at_safepoint(),
2265          "Else mutations in object graph will make answer suspect");
2266   assert(have_cms_token(),
2267          "Else there may be mutual interference in use of "
2268          " verification data structures");
2269   assert(_collectorState > Marking && _collectorState <= Sweeping,
2270          "Else marking info checked here may be obsolete");
2271   assert(haveFreelistLocks(), "must hold free list locks");
2272   assert_lock_strong(bitMapLock());
2273 
2274 
2275   // Allocate marking bit map if not already allocated
2276   if (!init) { // first time
2277     if (!verification_mark_bm()->allocate(_span)) {
2278       return false;
2279     }
2280     init = true;
2281   }
2282 
2283   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2284 
2285   // Turn off refs discovery -- so we will be tracing through refs.
2286   // This is as intended, because by this time
2287   // GC must already have cleared any refs that need to be cleared,
2288   // and traced those that need to be marked; moreover,
2289   // the marking done here is not going to interfere in any
2290   // way with the marking information used by GC.
2291   NoRefDiscovery no_discovery(ref_processor());
2292 
2293 #if defined(COMPILER2) || INCLUDE_JVMCI
2294   DerivedPointerTableDeactivate dpt_deact;
2295 #endif
2296 
2297   // Clear any marks from a previous round
2298   verification_mark_bm()->clear_all();
2299   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2300   verify_work_stacks_empty();
2301 
2302   GenCollectedHeap* gch = GenCollectedHeap::heap();
2303   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2304   // Update the saved marks which may affect the root scans.
2305   gch->save_marks();
2306 
2307   if (CMSRemarkVerifyVariant == 1) {
2308     // In this first variant of verification, we complete
2309     // all marking, then check if the new marks-vector is
2310     // a subset of the CMS marks-vector.
2311     verify_after_remark_work_1();
2312   } else {
2313     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2314     // In this second variant of verification, we flag an error
2315     // (i.e. an object reachable in the new marks-vector not reachable
2316     // in the CMS marks-vector) immediately, also indicating the
2317     // identify of an object (A) that references the unmarked object (B) --
2318     // presumably, a mutation to A failed to be picked up by preclean/remark?
2319     verify_after_remark_work_2();
2320   }
2321 
2322   return true;
2323 }
2324 
2325 void CMSCollector::verify_after_remark_work_1() {
2326   ResourceMark rm;
2327   HandleMark  hm;
2328   GenCollectedHeap* gch = GenCollectedHeap::heap();
2329 
2330   // Get a clear set of claim bits for the roots processing to work with.
2331   ClassLoaderDataGraph::clear_claimed_marks();
2332 
2333   // Mark from roots one level into CMS
2334   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2335   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2336 
2337   {
2338     StrongRootsScope srs(1);
2339 
2340     gch->cms_process_roots(&srs,
2341                            true,   // young gen as roots
2342                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2343                            should_unload_classes(),
2344                            &notOlder,
2345                            NULL);
2346   }
2347 
2348   // Now mark from the roots
2349   MarkFromRootsClosure markFromRootsClosure(this, _span,
2350     verification_mark_bm(), verification_mark_stack(),
2351     false /* don't yield */, true /* verifying */);
2352   assert(_restart_addr == NULL, "Expected pre-condition");
2353   verification_mark_bm()->iterate(&markFromRootsClosure);
2354   while (_restart_addr != NULL) {
2355     // Deal with stack overflow: by restarting at the indicated
2356     // address.
2357     HeapWord* ra = _restart_addr;
2358     markFromRootsClosure.reset(ra);
2359     _restart_addr = NULL;
2360     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2361   }
2362   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2363   verify_work_stacks_empty();
2364 
2365   // Marking completed -- now verify that each bit marked in
2366   // verification_mark_bm() is also marked in markBitMap(); flag all
2367   // errors by printing corresponding objects.
2368   VerifyMarkedClosure vcl(markBitMap());
2369   verification_mark_bm()->iterate(&vcl);
2370   if (vcl.failed()) {
2371     Log(gc, verify) log;
2372     log.error("Failed marking verification after remark");
2373     ResourceMark rm;
2374     gch->print_on(log.error_stream());
2375     fatal("CMS: failed marking verification after remark");
2376   }
2377 }
2378 
2379 class VerifyKlassOopsKlassClosure : public KlassClosure {
2380   class VerifyKlassOopsClosure : public OopClosure {
2381     CMSBitMap* _bitmap;
2382    public:
2383     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2384     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2385     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2386   } _oop_closure;
2387  public:
2388   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2389   void do_klass(Klass* k) {
2390     k->oops_do(&_oop_closure);
2391   }
2392 };
2393 
2394 void CMSCollector::verify_after_remark_work_2() {
2395   ResourceMark rm;
2396   HandleMark  hm;
2397   GenCollectedHeap* gch = GenCollectedHeap::heap();
2398 
2399   // Get a clear set of claim bits for the roots processing to work with.
2400   ClassLoaderDataGraph::clear_claimed_marks();
2401 
2402   // Mark from roots one level into CMS
2403   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2404                                      markBitMap());
2405   CLDToOopClosure cld_closure(&notOlder, true);
2406 
2407   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2408 
2409   {
2410     StrongRootsScope srs(1);
2411 
2412     gch->cms_process_roots(&srs,
2413                            true,   // young gen as roots
2414                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2415                            should_unload_classes(),
2416                            &notOlder,
2417                            &cld_closure);
2418   }
2419 
2420   // Now mark from the roots
2421   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2422     verification_mark_bm(), markBitMap(), verification_mark_stack());
2423   assert(_restart_addr == NULL, "Expected pre-condition");
2424   verification_mark_bm()->iterate(&markFromRootsClosure);
2425   while (_restart_addr != NULL) {
2426     // Deal with stack overflow: by restarting at the indicated
2427     // address.
2428     HeapWord* ra = _restart_addr;
2429     markFromRootsClosure.reset(ra);
2430     _restart_addr = NULL;
2431     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2432   }
2433   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2434   verify_work_stacks_empty();
2435 
2436   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2437   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2438 
2439   // Marking completed -- now verify that each bit marked in
2440   // verification_mark_bm() is also marked in markBitMap(); flag all
2441   // errors by printing corresponding objects.
2442   VerifyMarkedClosure vcl(markBitMap());
2443   verification_mark_bm()->iterate(&vcl);
2444   assert(!vcl.failed(), "Else verification above should not have succeeded");
2445 }
2446 
2447 void ConcurrentMarkSweepGeneration::save_marks() {
2448   // delegate to CMS space
2449   cmsSpace()->save_marks();
2450 }
2451 
2452 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2453   return cmsSpace()->no_allocs_since_save_marks();
2454 }
2455 
2456 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2457                                                                 \
2458 void ConcurrentMarkSweepGeneration::                            \
2459 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2460   cl->set_generation(this);                                     \
2461   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2462   cl->reset_generation();                                       \
2463   save_marks();                                                 \
2464 }
2465 
2466 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2467 
2468 void
2469 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2470   if (freelistLock()->owned_by_self()) {
2471     Generation::oop_iterate(cl);
2472   } else {
2473     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2474     Generation::oop_iterate(cl);
2475   }
2476 }
2477 
2478 void
2479 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2480   if (freelistLock()->owned_by_self()) {
2481     Generation::object_iterate(cl);
2482   } else {
2483     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2484     Generation::object_iterate(cl);
2485   }
2486 }
2487 
2488 void
2489 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2490   if (freelistLock()->owned_by_self()) {
2491     Generation::safe_object_iterate(cl);
2492   } else {
2493     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2494     Generation::safe_object_iterate(cl);
2495   }
2496 }
2497 
2498 void
2499 ConcurrentMarkSweepGeneration::post_compact() {
2500 }
2501 
2502 void
2503 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2504   // Fix the linear allocation blocks to look like free blocks.
2505 
2506   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2507   // are not called when the heap is verified during universe initialization and
2508   // at vm shutdown.
2509   if (freelistLock()->owned_by_self()) {
2510     cmsSpace()->prepare_for_verify();
2511   } else {
2512     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2513     cmsSpace()->prepare_for_verify();
2514   }
2515 }
2516 
2517 void
2518 ConcurrentMarkSweepGeneration::verify() {
2519   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2520   // are not called when the heap is verified during universe initialization and
2521   // at vm shutdown.
2522   if (freelistLock()->owned_by_self()) {
2523     cmsSpace()->verify();
2524   } else {
2525     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2526     cmsSpace()->verify();
2527   }
2528 }
2529 
2530 void CMSCollector::verify() {
2531   _cmsGen->verify();
2532 }
2533 
2534 #ifndef PRODUCT
2535 bool CMSCollector::overflow_list_is_empty() const {
2536   assert(_num_par_pushes >= 0, "Inconsistency");
2537   if (_overflow_list == NULL) {
2538     assert(_num_par_pushes == 0, "Inconsistency");
2539   }
2540   return _overflow_list == NULL;
2541 }
2542 
2543 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2544 // merely consolidate assertion checks that appear to occur together frequently.
2545 void CMSCollector::verify_work_stacks_empty() const {
2546   assert(_markStack.isEmpty(), "Marking stack should be empty");
2547   assert(overflow_list_is_empty(), "Overflow list should be empty");
2548 }
2549 
2550 void CMSCollector::verify_overflow_empty() const {
2551   assert(overflow_list_is_empty(), "Overflow list should be empty");
2552   assert(no_preserved_marks(), "No preserved marks");
2553 }
2554 #endif // PRODUCT
2555 
2556 // Decide if we want to enable class unloading as part of the
2557 // ensuing concurrent GC cycle. We will collect and
2558 // unload classes if it's the case that:
2559 //  (a) class unloading is enabled at the command line, and
2560 //  (b) old gen is getting really full
2561 // NOTE: Provided there is no change in the state of the heap between
2562 // calls to this method, it should have idempotent results. Moreover,
2563 // its results should be monotonically increasing (i.e. going from 0 to 1,
2564 // but not 1 to 0) between successive calls between which the heap was
2565 // not collected. For the implementation below, it must thus rely on
2566 // the property that concurrent_cycles_since_last_unload()
2567 // will not decrease unless a collection cycle happened and that
2568 // _cmsGen->is_too_full() are
2569 // themselves also monotonic in that sense. See check_monotonicity()
2570 // below.
2571 void CMSCollector::update_should_unload_classes() {
2572   _should_unload_classes = false;
2573   if (CMSClassUnloadingEnabled) {
2574     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2575                               CMSClassUnloadingMaxInterval)
2576                            || _cmsGen->is_too_full();
2577   }
2578 }
2579 
2580 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2581   bool res = should_concurrent_collect();
2582   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2583   return res;
2584 }
2585 
2586 void CMSCollector::setup_cms_unloading_and_verification_state() {
2587   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2588                              || VerifyBeforeExit;
2589   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2590 
2591   // We set the proper root for this CMS cycle here.
2592   if (should_unload_classes()) {   // Should unload classes this cycle
2593     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2594     set_verifying(should_verify);    // Set verification state for this cycle
2595     return;                            // Nothing else needs to be done at this time
2596   }
2597 
2598   // Not unloading classes this cycle
2599   assert(!should_unload_classes(), "Inconsistency!");
2600 
2601   // If we are not unloading classes then add SO_AllCodeCache to root
2602   // scanning options.
2603   add_root_scanning_option(rso);
2604 
2605   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2606     set_verifying(true);
2607   } else if (verifying() && !should_verify) {
2608     // We were verifying, but some verification flags got disabled.
2609     set_verifying(false);
2610     // Exclude symbols, strings and code cache elements from root scanning to
2611     // reduce IM and RM pauses.
2612     remove_root_scanning_option(rso);
2613   }
2614 }
2615 
2616 
2617 #ifndef PRODUCT
2618 HeapWord* CMSCollector::block_start(const void* p) const {
2619   const HeapWord* addr = (HeapWord*)p;
2620   if (_span.contains(p)) {
2621     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2622       return _cmsGen->cmsSpace()->block_start(p);
2623     }
2624   }
2625   return NULL;
2626 }
2627 #endif
2628 
2629 HeapWord*
2630 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2631                                                    bool   tlab,
2632                                                    bool   parallel) {
2633   CMSSynchronousYieldRequest yr;
2634   assert(!tlab, "Can't deal with TLAB allocation");
2635   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2636   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2637   if (GCExpandToAllocateDelayMillis > 0) {
2638     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2639   }
2640   return have_lock_and_allocate(word_size, tlab);
2641 }
2642 
2643 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2644     size_t bytes,
2645     size_t expand_bytes,
2646     CMSExpansionCause::Cause cause)
2647 {
2648 
2649   bool success = expand(bytes, expand_bytes);
2650 
2651   // remember why we expanded; this information is used
2652   // by shouldConcurrentCollect() when making decisions on whether to start
2653   // a new CMS cycle.
2654   if (success) {
2655     set_expansion_cause(cause);
2656     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2657   }
2658 }
2659 
2660 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2661   HeapWord* res = NULL;
2662   MutexLocker x(ParGCRareEvent_lock);
2663   while (true) {
2664     // Expansion by some other thread might make alloc OK now:
2665     res = ps->lab.alloc(word_sz);
2666     if (res != NULL) return res;
2667     // If there's not enough expansion space available, give up.
2668     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2669       return NULL;
2670     }
2671     // Otherwise, we try expansion.
2672     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2673     // Now go around the loop and try alloc again;
2674     // A competing par_promote might beat us to the expansion space,
2675     // so we may go around the loop again if promotion fails again.
2676     if (GCExpandToAllocateDelayMillis > 0) {
2677       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2678     }
2679   }
2680 }
2681 
2682 
2683 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2684   PromotionInfo* promo) {
2685   MutexLocker x(ParGCRareEvent_lock);
2686   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2687   while (true) {
2688     // Expansion by some other thread might make alloc OK now:
2689     if (promo->ensure_spooling_space()) {
2690       assert(promo->has_spooling_space(),
2691              "Post-condition of successful ensure_spooling_space()");
2692       return true;
2693     }
2694     // If there's not enough expansion space available, give up.
2695     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2696       return false;
2697     }
2698     // Otherwise, we try expansion.
2699     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2700     // Now go around the loop and try alloc again;
2701     // A competing allocation might beat us to the expansion space,
2702     // so we may go around the loop again if allocation fails again.
2703     if (GCExpandToAllocateDelayMillis > 0) {
2704       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2705     }
2706   }
2707 }
2708 
2709 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2710   // Only shrink if a compaction was done so that all the free space
2711   // in the generation is in a contiguous block at the end.
2712   if (did_compact()) {
2713     CardGeneration::shrink(bytes);
2714   }
2715 }
2716 
2717 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2718   assert_locked_or_safepoint(Heap_lock);
2719 }
2720 
2721 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2722   assert_locked_or_safepoint(Heap_lock);
2723   assert_lock_strong(freelistLock());
2724   log_trace(gc)("Shrinking of CMS not yet implemented");
2725   return;
2726 }
2727 
2728 
2729 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2730 // phases.
2731 class CMSPhaseAccounting: public StackObj {
2732  public:
2733   CMSPhaseAccounting(CMSCollector *collector,
2734                      const char *title);
2735   ~CMSPhaseAccounting();
2736 
2737  private:
2738   CMSCollector *_collector;
2739   const char *_title;
2740   GCTraceConcTime(Info, gc) _trace_time;
2741 
2742  public:
2743   // Not MT-safe; so do not pass around these StackObj's
2744   // where they may be accessed by other threads.
2745   double wallclock_millis() {
2746     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2747   }
2748 };
2749 
2750 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2751                                        const char *title) :
2752   _collector(collector), _title(title), _trace_time(title) {
2753 
2754   _collector->resetYields();
2755   _collector->resetTimer();
2756   _collector->startTimer();
2757   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2758 }
2759 
2760 CMSPhaseAccounting::~CMSPhaseAccounting() {
2761   _collector->gc_timer_cm()->register_gc_concurrent_end();
2762   _collector->stopTimer();
2763   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2764   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2765 }
2766 
2767 // CMS work
2768 
2769 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2770 class CMSParMarkTask : public AbstractGangTask {
2771  protected:
2772   CMSCollector*     _collector;
2773   uint              _n_workers;
2774   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2775       AbstractGangTask(name),
2776       _collector(collector),
2777       _n_workers(n_workers) {}
2778   // Work method in support of parallel rescan ... of young gen spaces
2779   void do_young_space_rescan(OopsInGenClosure* cl,
2780                              ContiguousSpace* space,
2781                              HeapWord** chunk_array, size_t chunk_top);
2782   void work_on_young_gen_roots(OopsInGenClosure* cl);
2783 };
2784 
2785 // Parallel initial mark task
2786 class CMSParInitialMarkTask: public CMSParMarkTask {
2787   StrongRootsScope* _strong_roots_scope;
2788  public:
2789   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2790       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2791       _strong_roots_scope(strong_roots_scope) {}
2792   void work(uint worker_id);
2793 };
2794 
2795 // Checkpoint the roots into this generation from outside
2796 // this generation. [Note this initial checkpoint need only
2797 // be approximate -- we'll do a catch up phase subsequently.]
2798 void CMSCollector::checkpointRootsInitial() {
2799   assert(_collectorState == InitialMarking, "Wrong collector state");
2800   check_correct_thread_executing();
2801   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2802 
2803   save_heap_summary();
2804   report_heap_summary(GCWhen::BeforeGC);
2805 
2806   ReferenceProcessor* rp = ref_processor();
2807   assert(_restart_addr == NULL, "Control point invariant");
2808   {
2809     // acquire locks for subsequent manipulations
2810     MutexLockerEx x(bitMapLock(),
2811                     Mutex::_no_safepoint_check_flag);
2812     checkpointRootsInitialWork();
2813     // enable ("weak") refs discovery
2814     rp->enable_discovery();
2815     _collectorState = Marking;
2816   }
2817 }
2818 
2819 void CMSCollector::checkpointRootsInitialWork() {
2820   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2821   assert(_collectorState == InitialMarking, "just checking");
2822 
2823   // Already have locks.
2824   assert_lock_strong(bitMapLock());
2825   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2826 
2827   // Setup the verification and class unloading state for this
2828   // CMS collection cycle.
2829   setup_cms_unloading_and_verification_state();
2830 
2831   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2832 
2833   // Reset all the PLAB chunk arrays if necessary.
2834   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2835     reset_survivor_plab_arrays();
2836   }
2837 
2838   ResourceMark rm;
2839   HandleMark  hm;
2840 
2841   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2842   GenCollectedHeap* gch = GenCollectedHeap::heap();
2843 
2844   verify_work_stacks_empty();
2845   verify_overflow_empty();
2846 
2847   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2848   // Update the saved marks which may affect the root scans.
2849   gch->save_marks();
2850 
2851   // weak reference processing has not started yet.
2852   ref_processor()->set_enqueuing_is_done(false);
2853 
2854   // Need to remember all newly created CLDs,
2855   // so that we can guarantee that the remark finds them.
2856   ClassLoaderDataGraph::remember_new_clds(true);
2857 
2858   // Whenever a CLD is found, it will be claimed before proceeding to mark
2859   // the klasses. The claimed marks need to be cleared before marking starts.
2860   ClassLoaderDataGraph::clear_claimed_marks();
2861 
2862   print_eden_and_survivor_chunk_arrays();
2863 
2864   {
2865 #if defined(COMPILER2) || INCLUDE_JVMCI
2866     DerivedPointerTableDeactivate dpt_deact;
2867 #endif
2868     if (CMSParallelInitialMarkEnabled) {
2869       // The parallel version.
2870       WorkGang* workers = gch->workers();
2871       assert(workers != NULL, "Need parallel worker threads.");
2872       uint n_workers = workers->active_workers();
2873 
2874       StrongRootsScope srs(n_workers);
2875 
2876       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2877       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2878       // If the total workers is greater than 1, then multiple workers
2879       // may be used at some time and the initialization has been set
2880       // such that the single threaded path cannot be used.
2881       if (workers->total_workers() > 1) {
2882         workers->run_task(&tsk);
2883       } else {
2884         tsk.work(0);
2885       }
2886     } else {
2887       // The serial version.
2888       CLDToOopClosure cld_closure(&notOlder, true);
2889       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2890 
2891       StrongRootsScope srs(1);
2892 
2893       gch->cms_process_roots(&srs,
2894                              true,   // young gen as roots
2895                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2896                              should_unload_classes(),
2897                              &notOlder,
2898                              &cld_closure);
2899     }
2900   }
2901 
2902   // Clear mod-union table; it will be dirtied in the prologue of
2903   // CMS generation per each young generation collection.
2904 
2905   assert(_modUnionTable.isAllClear(),
2906        "Was cleared in most recent final checkpoint phase"
2907        " or no bits are set in the gc_prologue before the start of the next "
2908        "subsequent marking phase.");
2909 
2910   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2911 
2912   // Save the end of the used_region of the constituent generations
2913   // to be used to limit the extent of sweep in each generation.
2914   save_sweep_limits();
2915   verify_overflow_empty();
2916 }
2917 
2918 bool CMSCollector::markFromRoots() {
2919   // we might be tempted to assert that:
2920   // assert(!SafepointSynchronize::is_at_safepoint(),
2921   //        "inconsistent argument?");
2922   // However that wouldn't be right, because it's possible that
2923   // a safepoint is indeed in progress as a young generation
2924   // stop-the-world GC happens even as we mark in this generation.
2925   assert(_collectorState == Marking, "inconsistent state?");
2926   check_correct_thread_executing();
2927   verify_overflow_empty();
2928 
2929   // Weak ref discovery note: We may be discovering weak
2930   // refs in this generation concurrent (but interleaved) with
2931   // weak ref discovery by the young generation collector.
2932 
2933   CMSTokenSyncWithLocks ts(true, bitMapLock());
2934   GCTraceCPUTime tcpu;
2935   CMSPhaseAccounting pa(this, "Concurrent Mark");
2936   bool res = markFromRootsWork();
2937   if (res) {
2938     _collectorState = Precleaning;
2939   } else { // We failed and a foreground collection wants to take over
2940     assert(_foregroundGCIsActive, "internal state inconsistency");
2941     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2942     log_debug(gc)("bailing out to foreground collection");
2943   }
2944   verify_overflow_empty();
2945   return res;
2946 }
2947 
2948 bool CMSCollector::markFromRootsWork() {
2949   // iterate over marked bits in bit map, doing a full scan and mark
2950   // from these roots using the following algorithm:
2951   // . if oop is to the right of the current scan pointer,
2952   //   mark corresponding bit (we'll process it later)
2953   // . else (oop is to left of current scan pointer)
2954   //   push oop on marking stack
2955   // . drain the marking stack
2956 
2957   // Note that when we do a marking step we need to hold the
2958   // bit map lock -- recall that direct allocation (by mutators)
2959   // and promotion (by the young generation collector) is also
2960   // marking the bit map. [the so-called allocate live policy.]
2961   // Because the implementation of bit map marking is not
2962   // robust wrt simultaneous marking of bits in the same word,
2963   // we need to make sure that there is no such interference
2964   // between concurrent such updates.
2965 
2966   // already have locks
2967   assert_lock_strong(bitMapLock());
2968 
2969   verify_work_stacks_empty();
2970   verify_overflow_empty();
2971   bool result = false;
2972   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2973     result = do_marking_mt();
2974   } else {
2975     result = do_marking_st();
2976   }
2977   return result;
2978 }
2979 
2980 // Forward decl
2981 class CMSConcMarkingTask;
2982 
2983 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2984   CMSCollector*       _collector;
2985   CMSConcMarkingTask* _task;
2986  public:
2987   virtual void yield();
2988 
2989   // "n_threads" is the number of threads to be terminated.
2990   // "queue_set" is a set of work queues of other threads.
2991   // "collector" is the CMS collector associated with this task terminator.
2992   // "yield" indicates whether we need the gang as a whole to yield.
2993   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2994     ParallelTaskTerminator(n_threads, queue_set),
2995     _collector(collector) { }
2996 
2997   void set_task(CMSConcMarkingTask* task) {
2998     _task = task;
2999   }
3000 };
3001 
3002 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3003   CMSConcMarkingTask* _task;
3004  public:
3005   bool should_exit_termination();
3006   void set_task(CMSConcMarkingTask* task) {
3007     _task = task;
3008   }
3009 };
3010 
3011 // MT Concurrent Marking Task
3012 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3013   CMSCollector*             _collector;
3014   uint                      _n_workers;      // requested/desired # workers
3015   bool                      _result;
3016   CompactibleFreeListSpace* _cms_space;
3017   char                      _pad_front[64];   // padding to ...
3018   HeapWord* volatile        _global_finger;   // ... avoid sharing cache line
3019   char                      _pad_back[64];
3020   HeapWord*                 _restart_addr;
3021 
3022   //  Exposed here for yielding support
3023   Mutex* const _bit_map_lock;
3024 
3025   // The per thread work queues, available here for stealing
3026   OopTaskQueueSet*  _task_queues;
3027 
3028   // Termination (and yielding) support
3029   CMSConcMarkingTerminator _term;
3030   CMSConcMarkingTerminatorTerminator _term_term;
3031 
3032  public:
3033   CMSConcMarkingTask(CMSCollector* collector,
3034                  CompactibleFreeListSpace* cms_space,
3035                  YieldingFlexibleWorkGang* workers,
3036                  OopTaskQueueSet* task_queues):
3037     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3038     _collector(collector),
3039     _cms_space(cms_space),
3040     _n_workers(0), _result(true),
3041     _task_queues(task_queues),
3042     _term(_n_workers, task_queues, _collector),
3043     _bit_map_lock(collector->bitMapLock())
3044   {
3045     _requested_size = _n_workers;
3046     _term.set_task(this);
3047     _term_term.set_task(this);
3048     _restart_addr = _global_finger = _cms_space->bottom();
3049   }
3050 
3051 
3052   OopTaskQueueSet* task_queues()  { return _task_queues; }
3053 
3054   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3055 
3056   HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3057 
3058   CMSConcMarkingTerminator* terminator() { return &_term; }
3059 
3060   virtual void set_for_termination(uint active_workers) {
3061     terminator()->reset_for_reuse(active_workers);
3062   }
3063 
3064   void work(uint worker_id);
3065   bool should_yield() {
3066     return    ConcurrentMarkSweepThread::should_yield()
3067            && !_collector->foregroundGCIsActive();
3068   }
3069 
3070   virtual void coordinator_yield();  // stuff done by coordinator
3071   bool result() { return _result; }
3072 
3073   void reset(HeapWord* ra) {
3074     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3075     _restart_addr = _global_finger = ra;
3076     _term.reset_for_reuse();
3077   }
3078 
3079   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3080                                            OopTaskQueue* work_q);
3081 
3082  private:
3083   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3084   void do_work_steal(int i);
3085   void bump_global_finger(HeapWord* f);
3086 };
3087 
3088 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3089   assert(_task != NULL, "Error");
3090   return _task->yielding();
3091   // Note that we do not need the disjunct || _task->should_yield() above
3092   // because we want terminating threads to yield only if the task
3093   // is already in the midst of yielding, which happens only after at least one
3094   // thread has yielded.
3095 }
3096 
3097 void CMSConcMarkingTerminator::yield() {
3098   if (_task->should_yield()) {
3099     _task->yield();
3100   } else {
3101     ParallelTaskTerminator::yield();
3102   }
3103 }
3104 
3105 ////////////////////////////////////////////////////////////////
3106 // Concurrent Marking Algorithm Sketch
3107 ////////////////////////////////////////////////////////////////
3108 // Until all tasks exhausted (both spaces):
3109 // -- claim next available chunk
3110 // -- bump global finger via CAS
3111 // -- find first object that starts in this chunk
3112 //    and start scanning bitmap from that position
3113 // -- scan marked objects for oops
3114 // -- CAS-mark target, and if successful:
3115 //    . if target oop is above global finger (volatile read)
3116 //      nothing to do
3117 //    . if target oop is in chunk and above local finger
3118 //        then nothing to do
3119 //    . else push on work-queue
3120 // -- Deal with possible overflow issues:
3121 //    . local work-queue overflow causes stuff to be pushed on
3122 //      global (common) overflow queue
3123 //    . always first empty local work queue
3124 //    . then get a batch of oops from global work queue if any
3125 //    . then do work stealing
3126 // -- When all tasks claimed (both spaces)
3127 //    and local work queue empty,
3128 //    then in a loop do:
3129 //    . check global overflow stack; steal a batch of oops and trace
3130 //    . try to steal from other threads oif GOS is empty
3131 //    . if neither is available, offer termination
3132 // -- Terminate and return result
3133 //
3134 void CMSConcMarkingTask::work(uint worker_id) {
3135   elapsedTimer _timer;
3136   ResourceMark rm;
3137   HandleMark hm;
3138 
3139   DEBUG_ONLY(_collector->verify_overflow_empty();)
3140 
3141   // Before we begin work, our work queue should be empty
3142   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3143   // Scan the bitmap covering _cms_space, tracing through grey objects.
3144   _timer.start();
3145   do_scan_and_mark(worker_id, _cms_space);
3146   _timer.stop();
3147   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3148 
3149   // ... do work stealing
3150   _timer.reset();
3151   _timer.start();
3152   do_work_steal(worker_id);
3153   _timer.stop();
3154   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3155   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3156   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3157   // Note that under the current task protocol, the
3158   // following assertion is true even of the spaces
3159   // expanded since the completion of the concurrent
3160   // marking. XXX This will likely change under a strict
3161   // ABORT semantics.
3162   // After perm removal the comparison was changed to
3163   // greater than or equal to from strictly greater than.
3164   // Before perm removal the highest address sweep would
3165   // have been at the end of perm gen but now is at the
3166   // end of the tenured gen.
3167   assert(_global_finger >=  _cms_space->end(),
3168          "All tasks have been completed");
3169   DEBUG_ONLY(_collector->verify_overflow_empty();)
3170 }
3171 
3172 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3173   HeapWord* read = _global_finger;
3174   HeapWord* cur  = read;
3175   while (f > read) {
3176     cur = read;
3177     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3178     if (cur == read) {
3179       // our cas succeeded
3180       assert(_global_finger >= f, "protocol consistency");
3181       break;
3182     }
3183   }
3184 }
3185 
3186 // This is really inefficient, and should be redone by
3187 // using (not yet available) block-read and -write interfaces to the
3188 // stack and the work_queue. XXX FIX ME !!!
3189 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3190                                                       OopTaskQueue* work_q) {
3191   // Fast lock-free check
3192   if (ovflw_stk->length() == 0) {
3193     return false;
3194   }
3195   assert(work_q->size() == 0, "Shouldn't steal");
3196   MutexLockerEx ml(ovflw_stk->par_lock(),
3197                    Mutex::_no_safepoint_check_flag);
3198   // Grab up to 1/4 the size of the work queue
3199   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3200                     (size_t)ParGCDesiredObjsFromOverflowList);
3201   num = MIN2(num, ovflw_stk->length());
3202   for (int i = (int) num; i > 0; i--) {
3203     oop cur = ovflw_stk->pop();
3204     assert(cur != NULL, "Counted wrong?");
3205     work_q->push(cur);
3206   }
3207   return num > 0;
3208 }
3209 
3210 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3211   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3212   int n_tasks = pst->n_tasks();
3213   // We allow that there may be no tasks to do here because
3214   // we are restarting after a stack overflow.
3215   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3216   uint nth_task = 0;
3217 
3218   HeapWord* aligned_start = sp->bottom();
3219   if (sp->used_region().contains(_restart_addr)) {
3220     // Align down to a card boundary for the start of 0th task
3221     // for this space.
3222     aligned_start = align_down(_restart_addr, CardTableModRefBS::card_size);
3223   }
3224 
3225   size_t chunk_size = sp->marking_task_size();
3226   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3227     // Having claimed the nth task in this space,
3228     // compute the chunk that it corresponds to:
3229     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3230                                aligned_start + (nth_task+1)*chunk_size);
3231     // Try and bump the global finger via a CAS;
3232     // note that we need to do the global finger bump
3233     // _before_ taking the intersection below, because
3234     // the task corresponding to that region will be
3235     // deemed done even if the used_region() expands
3236     // because of allocation -- as it almost certainly will
3237     // during start-up while the threads yield in the
3238     // closure below.
3239     HeapWord* finger = span.end();
3240     bump_global_finger(finger);   // atomically
3241     // There are null tasks here corresponding to chunks
3242     // beyond the "top" address of the space.
3243     span = span.intersection(sp->used_region());
3244     if (!span.is_empty()) {  // Non-null task
3245       HeapWord* prev_obj;
3246       assert(!span.contains(_restart_addr) || nth_task == 0,
3247              "Inconsistency");
3248       if (nth_task == 0) {
3249         // For the 0th task, we'll not need to compute a block_start.
3250         if (span.contains(_restart_addr)) {
3251           // In the case of a restart because of stack overflow,
3252           // we might additionally skip a chunk prefix.
3253           prev_obj = _restart_addr;
3254         } else {
3255           prev_obj = span.start();
3256         }
3257       } else {
3258         // We want to skip the first object because
3259         // the protocol is to scan any object in its entirety
3260         // that _starts_ in this span; a fortiori, any
3261         // object starting in an earlier span is scanned
3262         // as part of an earlier claimed task.
3263         // Below we use the "careful" version of block_start
3264         // so we do not try to navigate uninitialized objects.
3265         prev_obj = sp->block_start_careful(span.start());
3266         // Below we use a variant of block_size that uses the
3267         // Printezis bits to avoid waiting for allocated
3268         // objects to become initialized/parsable.
3269         while (prev_obj < span.start()) {
3270           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3271           if (sz > 0) {
3272             prev_obj += sz;
3273           } else {
3274             // In this case we may end up doing a bit of redundant
3275             // scanning, but that appears unavoidable, short of
3276             // locking the free list locks; see bug 6324141.
3277             break;
3278           }
3279         }
3280       }
3281       if (prev_obj < span.end()) {
3282         MemRegion my_span = MemRegion(prev_obj, span.end());
3283         // Do the marking work within a non-empty span --
3284         // the last argument to the constructor indicates whether the
3285         // iteration should be incremental with periodic yields.
3286         ParMarkFromRootsClosure cl(this, _collector, my_span,
3287                                    &_collector->_markBitMap,
3288                                    work_queue(i),
3289                                    &_collector->_markStack);
3290         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3291       } // else nothing to do for this task
3292     }   // else nothing to do for this task
3293   }
3294   // We'd be tempted to assert here that since there are no
3295   // more tasks left to claim in this space, the global_finger
3296   // must exceed space->top() and a fortiori space->end(). However,
3297   // that would not quite be correct because the bumping of
3298   // global_finger occurs strictly after the claiming of a task,
3299   // so by the time we reach here the global finger may not yet
3300   // have been bumped up by the thread that claimed the last
3301   // task.
3302   pst->all_tasks_completed();
3303 }
3304 
3305 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3306  private:
3307   CMSCollector* _collector;
3308   CMSConcMarkingTask* _task;
3309   MemRegion     _span;
3310   CMSBitMap*    _bit_map;
3311   CMSMarkStack* _overflow_stack;
3312   OopTaskQueue* _work_queue;
3313  protected:
3314   DO_OOP_WORK_DEFN
3315  public:
3316   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3317                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3318     MetadataAwareOopClosure(collector->ref_processor()),
3319     _collector(collector),
3320     _task(task),
3321     _span(collector->_span),
3322     _work_queue(work_queue),
3323     _bit_map(bit_map),
3324     _overflow_stack(overflow_stack)
3325   { }
3326   virtual void do_oop(oop* p);
3327   virtual void do_oop(narrowOop* p);
3328 
3329   void trim_queue(size_t max);
3330   void handle_stack_overflow(HeapWord* lost);
3331   void do_yield_check() {
3332     if (_task->should_yield()) {
3333       _task->yield();
3334     }
3335   }
3336 };
3337 
3338 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3339 
3340 // Grey object scanning during work stealing phase --
3341 // the salient assumption here is that any references
3342 // that are in these stolen objects being scanned must
3343 // already have been initialized (else they would not have
3344 // been published), so we do not need to check for
3345 // uninitialized objects before pushing here.
3346 void ParConcMarkingClosure::do_oop(oop obj) {
3347   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3348   HeapWord* addr = (HeapWord*)obj;
3349   // Check if oop points into the CMS generation
3350   // and is not marked
3351   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3352     // a white object ...
3353     // If we manage to "claim" the object, by being the
3354     // first thread to mark it, then we push it on our
3355     // marking stack
3356     if (_bit_map->par_mark(addr)) {     // ... now grey
3357       // push on work queue (grey set)
3358       bool simulate_overflow = false;
3359       NOT_PRODUCT(
3360         if (CMSMarkStackOverflowALot &&
3361             _collector->simulate_overflow()) {
3362           // simulate a stack overflow
3363           simulate_overflow = true;
3364         }
3365       )
3366       if (simulate_overflow ||
3367           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3368         // stack overflow
3369         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3370         // We cannot assert that the overflow stack is full because
3371         // it may have been emptied since.
3372         assert(simulate_overflow ||
3373                _work_queue->size() == _work_queue->max_elems(),
3374               "Else push should have succeeded");
3375         handle_stack_overflow(addr);
3376       }
3377     } // Else, some other thread got there first
3378     do_yield_check();
3379   }
3380 }
3381 
3382 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3383 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3384 
3385 void ParConcMarkingClosure::trim_queue(size_t max) {
3386   while (_work_queue->size() > max) {
3387     oop new_oop;
3388     if (_work_queue->pop_local(new_oop)) {
3389       assert(new_oop->is_oop(), "Should be an oop");
3390       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3391       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3392       new_oop->oop_iterate(this);  // do_oop() above
3393       do_yield_check();
3394     }
3395   }
3396 }
3397 
3398 // Upon stack overflow, we discard (part of) the stack,
3399 // remembering the least address amongst those discarded
3400 // in CMSCollector's _restart_address.
3401 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3402   // We need to do this under a mutex to prevent other
3403   // workers from interfering with the work done below.
3404   MutexLockerEx ml(_overflow_stack->par_lock(),
3405                    Mutex::_no_safepoint_check_flag);
3406   // Remember the least grey address discarded
3407   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3408   _collector->lower_restart_addr(ra);
3409   _overflow_stack->reset();  // discard stack contents
3410   _overflow_stack->expand(); // expand the stack if possible
3411 }
3412 
3413 
3414 void CMSConcMarkingTask::do_work_steal(int i) {
3415   OopTaskQueue* work_q = work_queue(i);
3416   oop obj_to_scan;
3417   CMSBitMap* bm = &(_collector->_markBitMap);
3418   CMSMarkStack* ovflw = &(_collector->_markStack);
3419   int* seed = _collector->hash_seed(i);
3420   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3421   while (true) {
3422     cl.trim_queue(0);
3423     assert(work_q->size() == 0, "Should have been emptied above");
3424     if (get_work_from_overflow_stack(ovflw, work_q)) {
3425       // Can't assert below because the work obtained from the
3426       // overflow stack may already have been stolen from us.
3427       // assert(work_q->size() > 0, "Work from overflow stack");
3428       continue;
3429     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3430       assert(obj_to_scan->is_oop(), "Should be an oop");
3431       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3432       obj_to_scan->oop_iterate(&cl);
3433     } else if (terminator()->offer_termination(&_term_term)) {
3434       assert(work_q->size() == 0, "Impossible!");
3435       break;
3436     } else if (yielding() || should_yield()) {
3437       yield();
3438     }
3439   }
3440 }
3441 
3442 // This is run by the CMS (coordinator) thread.
3443 void CMSConcMarkingTask::coordinator_yield() {
3444   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3445          "CMS thread should hold CMS token");
3446   // First give up the locks, then yield, then re-lock
3447   // We should probably use a constructor/destructor idiom to
3448   // do this unlock/lock or modify the MutexUnlocker class to
3449   // serve our purpose. XXX
3450   assert_lock_strong(_bit_map_lock);
3451   _bit_map_lock->unlock();
3452   ConcurrentMarkSweepThread::desynchronize(true);
3453   _collector->stopTimer();
3454   _collector->incrementYields();
3455 
3456   // It is possible for whichever thread initiated the yield request
3457   // not to get a chance to wake up and take the bitmap lock between
3458   // this thread releasing it and reacquiring it. So, while the
3459   // should_yield() flag is on, let's sleep for a bit to give the
3460   // other thread a chance to wake up. The limit imposed on the number
3461   // of iterations is defensive, to avoid any unforseen circumstances
3462   // putting us into an infinite loop. Since it's always been this
3463   // (coordinator_yield()) method that was observed to cause the
3464   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3465   // which is by default non-zero. For the other seven methods that
3466   // also perform the yield operation, as are using a different
3467   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3468   // can enable the sleeping for those methods too, if necessary.
3469   // See 6442774.
3470   //
3471   // We really need to reconsider the synchronization between the GC
3472   // thread and the yield-requesting threads in the future and we
3473   // should really use wait/notify, which is the recommended
3474   // way of doing this type of interaction. Additionally, we should
3475   // consolidate the eight methods that do the yield operation and they
3476   // are almost identical into one for better maintainability and
3477   // readability. See 6445193.
3478   //
3479   // Tony 2006.06.29
3480   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3481                    ConcurrentMarkSweepThread::should_yield() &&
3482                    !CMSCollector::foregroundGCIsActive(); ++i) {
3483     os::sleep(Thread::current(), 1, false);
3484   }
3485 
3486   ConcurrentMarkSweepThread::synchronize(true);
3487   _bit_map_lock->lock_without_safepoint_check();
3488   _collector->startTimer();
3489 }
3490 
3491 bool CMSCollector::do_marking_mt() {
3492   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3493   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3494                                                                   conc_workers()->active_workers(),
3495                                                                   Threads::number_of_non_daemon_threads());
3496   num_workers = conc_workers()->update_active_workers(num_workers);
3497   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3498 
3499   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3500 
3501   CMSConcMarkingTask tsk(this,
3502                          cms_space,
3503                          conc_workers(),
3504                          task_queues());
3505 
3506   // Since the actual number of workers we get may be different
3507   // from the number we requested above, do we need to do anything different
3508   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3509   // class?? XXX
3510   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3511 
3512   // Refs discovery is already non-atomic.
3513   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3514   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3515   conc_workers()->start_task(&tsk);
3516   while (tsk.yielded()) {
3517     tsk.coordinator_yield();
3518     conc_workers()->continue_task(&tsk);
3519   }
3520   // If the task was aborted, _restart_addr will be non-NULL
3521   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3522   while (_restart_addr != NULL) {
3523     // XXX For now we do not make use of ABORTED state and have not
3524     // yet implemented the right abort semantics (even in the original
3525     // single-threaded CMS case). That needs some more investigation
3526     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3527     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3528     // If _restart_addr is non-NULL, a marking stack overflow
3529     // occurred; we need to do a fresh marking iteration from the
3530     // indicated restart address.
3531     if (_foregroundGCIsActive) {
3532       // We may be running into repeated stack overflows, having
3533       // reached the limit of the stack size, while making very
3534       // slow forward progress. It may be best to bail out and
3535       // let the foreground collector do its job.
3536       // Clear _restart_addr, so that foreground GC
3537       // works from scratch. This avoids the headache of
3538       // a "rescan" which would otherwise be needed because
3539       // of the dirty mod union table & card table.
3540       _restart_addr = NULL;
3541       return false;
3542     }
3543     // Adjust the task to restart from _restart_addr
3544     tsk.reset(_restart_addr);
3545     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3546                   _restart_addr);
3547     _restart_addr = NULL;
3548     // Get the workers going again
3549     conc_workers()->start_task(&tsk);
3550     while (tsk.yielded()) {
3551       tsk.coordinator_yield();
3552       conc_workers()->continue_task(&tsk);
3553     }
3554   }
3555   assert(tsk.completed(), "Inconsistency");
3556   assert(tsk.result() == true, "Inconsistency");
3557   return true;
3558 }
3559 
3560 bool CMSCollector::do_marking_st() {
3561   ResourceMark rm;
3562   HandleMark   hm;
3563 
3564   // Temporarily make refs discovery single threaded (non-MT)
3565   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3566   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3567     &_markStack, CMSYield);
3568   // the last argument to iterate indicates whether the iteration
3569   // should be incremental with periodic yields.
3570   _markBitMap.iterate(&markFromRootsClosure);
3571   // If _restart_addr is non-NULL, a marking stack overflow
3572   // occurred; we need to do a fresh iteration from the
3573   // indicated restart address.
3574   while (_restart_addr != NULL) {
3575     if (_foregroundGCIsActive) {
3576       // We may be running into repeated stack overflows, having
3577       // reached the limit of the stack size, while making very
3578       // slow forward progress. It may be best to bail out and
3579       // let the foreground collector do its job.
3580       // Clear _restart_addr, so that foreground GC
3581       // works from scratch. This avoids the headache of
3582       // a "rescan" which would otherwise be needed because
3583       // of the dirty mod union table & card table.
3584       _restart_addr = NULL;
3585       return false;  // indicating failure to complete marking
3586     }
3587     // Deal with stack overflow:
3588     // we restart marking from _restart_addr
3589     HeapWord* ra = _restart_addr;
3590     markFromRootsClosure.reset(ra);
3591     _restart_addr = NULL;
3592     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3593   }
3594   return true;
3595 }
3596 
3597 void CMSCollector::preclean() {
3598   check_correct_thread_executing();
3599   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3600   verify_work_stacks_empty();
3601   verify_overflow_empty();
3602   _abort_preclean = false;
3603   if (CMSPrecleaningEnabled) {
3604     if (!CMSEdenChunksRecordAlways) {
3605       _eden_chunk_index = 0;
3606     }
3607     size_t used = get_eden_used();
3608     size_t capacity = get_eden_capacity();
3609     // Don't start sampling unless we will get sufficiently
3610     // many samples.
3611     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3612                 * CMSScheduleRemarkEdenPenetration)) {
3613       _start_sampling = true;
3614     } else {
3615       _start_sampling = false;
3616     }
3617     GCTraceCPUTime tcpu;
3618     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3619     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3620   }
3621   CMSTokenSync x(true); // is cms thread
3622   if (CMSPrecleaningEnabled) {
3623     sample_eden();
3624     _collectorState = AbortablePreclean;
3625   } else {
3626     _collectorState = FinalMarking;
3627   }
3628   verify_work_stacks_empty();
3629   verify_overflow_empty();
3630 }
3631 
3632 // Try and schedule the remark such that young gen
3633 // occupancy is CMSScheduleRemarkEdenPenetration %.
3634 void CMSCollector::abortable_preclean() {
3635   check_correct_thread_executing();
3636   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3637   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3638 
3639   // If Eden's current occupancy is below this threshold,
3640   // immediately schedule the remark; else preclean
3641   // past the next scavenge in an effort to
3642   // schedule the pause as described above. By choosing
3643   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3644   // we will never do an actual abortable preclean cycle.
3645   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3646     GCTraceCPUTime tcpu;
3647     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3648     // We need more smarts in the abortable preclean
3649     // loop below to deal with cases where allocation
3650     // in young gen is very very slow, and our precleaning
3651     // is running a losing race against a horde of
3652     // mutators intent on flooding us with CMS updates
3653     // (dirty cards).
3654     // One, admittedly dumb, strategy is to give up
3655     // after a certain number of abortable precleaning loops
3656     // or after a certain maximum time. We want to make
3657     // this smarter in the next iteration.
3658     // XXX FIX ME!!! YSR
3659     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3660     while (!(should_abort_preclean() ||
3661              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3662       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3663       cumworkdone += workdone;
3664       loops++;
3665       // Voluntarily terminate abortable preclean phase if we have
3666       // been at it for too long.
3667       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3668           loops >= CMSMaxAbortablePrecleanLoops) {
3669         log_debug(gc)(" CMS: abort preclean due to loops ");
3670         break;
3671       }
3672       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3673         log_debug(gc)(" CMS: abort preclean due to time ");
3674         break;
3675       }
3676       // If we are doing little work each iteration, we should
3677       // take a short break.
3678       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3679         // Sleep for some time, waiting for work to accumulate
3680         stopTimer();
3681         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3682         startTimer();
3683         waited++;
3684       }
3685     }
3686     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3687                                loops, waited, cumworkdone);
3688   }
3689   CMSTokenSync x(true); // is cms thread
3690   if (_collectorState != Idling) {
3691     assert(_collectorState == AbortablePreclean,
3692            "Spontaneous state transition?");
3693     _collectorState = FinalMarking;
3694   } // Else, a foreground collection completed this CMS cycle.
3695   return;
3696 }
3697 
3698 // Respond to an Eden sampling opportunity
3699 void CMSCollector::sample_eden() {
3700   // Make sure a young gc cannot sneak in between our
3701   // reading and recording of a sample.
3702   assert(Thread::current()->is_ConcurrentGC_thread(),
3703          "Only the cms thread may collect Eden samples");
3704   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3705          "Should collect samples while holding CMS token");
3706   if (!_start_sampling) {
3707     return;
3708   }
3709   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3710   // is populated by the young generation.
3711   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3712     if (_eden_chunk_index < _eden_chunk_capacity) {
3713       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3714       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3715              "Unexpected state of Eden");
3716       // We'd like to check that what we just sampled is an oop-start address;
3717       // however, we cannot do that here since the object may not yet have been
3718       // initialized. So we'll instead do the check when we _use_ this sample
3719       // later.
3720       if (_eden_chunk_index == 0 ||
3721           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3722                          _eden_chunk_array[_eden_chunk_index-1])
3723            >= CMSSamplingGrain)) {
3724         _eden_chunk_index++;  // commit sample
3725       }
3726     }
3727   }
3728   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3729     size_t used = get_eden_used();
3730     size_t capacity = get_eden_capacity();
3731     assert(used <= capacity, "Unexpected state of Eden");
3732     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3733       _abort_preclean = true;
3734     }
3735   }
3736 }
3737 
3738 
3739 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3740   assert(_collectorState == Precleaning ||
3741          _collectorState == AbortablePreclean, "incorrect state");
3742   ResourceMark rm;
3743   HandleMark   hm;
3744 
3745   // Precleaning is currently not MT but the reference processor
3746   // may be set for MT.  Disable it temporarily here.
3747   ReferenceProcessor* rp = ref_processor();
3748   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3749 
3750   // Do one pass of scrubbing the discovered reference lists
3751   // to remove any reference objects with strongly-reachable
3752   // referents.
3753   if (clean_refs) {
3754     CMSPrecleanRefsYieldClosure yield_cl(this);
3755     assert(rp->span().equals(_span), "Spans should be equal");
3756     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3757                                    &_markStack, true /* preclean */);
3758     CMSDrainMarkingStackClosure complete_trace(this,
3759                                    _span, &_markBitMap, &_markStack,
3760                                    &keep_alive, true /* preclean */);
3761 
3762     // We don't want this step to interfere with a young
3763     // collection because we don't want to take CPU
3764     // or memory bandwidth away from the young GC threads
3765     // (which may be as many as there are CPUs).
3766     // Note that we don't need to protect ourselves from
3767     // interference with mutators because they can't
3768     // manipulate the discovered reference lists nor affect
3769     // the computed reachability of the referents, the
3770     // only properties manipulated by the precleaning
3771     // of these reference lists.
3772     stopTimer();
3773     CMSTokenSyncWithLocks x(true /* is cms thread */,
3774                             bitMapLock());
3775     startTimer();
3776     sample_eden();
3777 
3778     // The following will yield to allow foreground
3779     // collection to proceed promptly. XXX YSR:
3780     // The code in this method may need further
3781     // tweaking for better performance and some restructuring
3782     // for cleaner interfaces.
3783     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3784     rp->preclean_discovered_references(
3785           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3786           gc_timer);
3787   }
3788 
3789   if (clean_survivor) {  // preclean the active survivor space(s)
3790     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3791                              &_markBitMap, &_modUnionTable,
3792                              &_markStack, true /* precleaning phase */);
3793     stopTimer();
3794     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3795                              bitMapLock());
3796     startTimer();
3797     unsigned int before_count =
3798       GenCollectedHeap::heap()->total_collections();
3799     SurvivorSpacePrecleanClosure
3800       sss_cl(this, _span, &_markBitMap, &_markStack,
3801              &pam_cl, before_count, CMSYield);
3802     _young_gen->from()->object_iterate_careful(&sss_cl);
3803     _young_gen->to()->object_iterate_careful(&sss_cl);
3804   }
3805   MarkRefsIntoAndScanClosure
3806     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3807              &_markStack, this, CMSYield,
3808              true /* precleaning phase */);
3809   // CAUTION: The following closure has persistent state that may need to
3810   // be reset upon a decrease in the sequence of addresses it
3811   // processes.
3812   ScanMarkedObjectsAgainCarefullyClosure
3813     smoac_cl(this, _span,
3814       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3815 
3816   // Preclean dirty cards in ModUnionTable and CardTable using
3817   // appropriate convergence criterion;
3818   // repeat CMSPrecleanIter times unless we find that
3819   // we are losing.
3820   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3821   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3822          "Bad convergence multiplier");
3823   assert(CMSPrecleanThreshold >= 100,
3824          "Unreasonably low CMSPrecleanThreshold");
3825 
3826   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3827   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3828        numIter < CMSPrecleanIter;
3829        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3830     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3831     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3832     // Either there are very few dirty cards, so re-mark
3833     // pause will be small anyway, or our pre-cleaning isn't
3834     // that much faster than the rate at which cards are being
3835     // dirtied, so we might as well stop and re-mark since
3836     // precleaning won't improve our re-mark time by much.
3837     if (curNumCards <= CMSPrecleanThreshold ||
3838         (numIter > 0 &&
3839          (curNumCards * CMSPrecleanDenominator >
3840          lastNumCards * CMSPrecleanNumerator))) {
3841       numIter++;
3842       cumNumCards += curNumCards;
3843       break;
3844     }
3845   }
3846 
3847   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3848 
3849   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3850   cumNumCards += curNumCards;
3851   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3852                              curNumCards, cumNumCards, numIter);
3853   return cumNumCards;   // as a measure of useful work done
3854 }
3855 
3856 // PRECLEANING NOTES:
3857 // Precleaning involves:
3858 // . reading the bits of the modUnionTable and clearing the set bits.
3859 // . For the cards corresponding to the set bits, we scan the
3860 //   objects on those cards. This means we need the free_list_lock
3861 //   so that we can safely iterate over the CMS space when scanning
3862 //   for oops.
3863 // . When we scan the objects, we'll be both reading and setting
3864 //   marks in the marking bit map, so we'll need the marking bit map.
3865 // . For protecting _collector_state transitions, we take the CGC_lock.
3866 //   Note that any races in the reading of of card table entries by the
3867 //   CMS thread on the one hand and the clearing of those entries by the
3868 //   VM thread or the setting of those entries by the mutator threads on the
3869 //   other are quite benign. However, for efficiency it makes sense to keep
3870 //   the VM thread from racing with the CMS thread while the latter is
3871 //   dirty card info to the modUnionTable. We therefore also use the
3872 //   CGC_lock to protect the reading of the card table and the mod union
3873 //   table by the CM thread.
3874 // . We run concurrently with mutator updates, so scanning
3875 //   needs to be done carefully  -- we should not try to scan
3876 //   potentially uninitialized objects.
3877 //
3878 // Locking strategy: While holding the CGC_lock, we scan over and
3879 // reset a maximal dirty range of the mod union / card tables, then lock
3880 // the free_list_lock and bitmap lock to do a full marking, then
3881 // release these locks; and repeat the cycle. This allows for a
3882 // certain amount of fairness in the sharing of these locks between
3883 // the CMS collector on the one hand, and the VM thread and the
3884 // mutators on the other.
3885 
3886 // NOTE: preclean_mod_union_table() and preclean_card_table()
3887 // further below are largely identical; if you need to modify
3888 // one of these methods, please check the other method too.
3889 
3890 size_t CMSCollector::preclean_mod_union_table(
3891   ConcurrentMarkSweepGeneration* old_gen,
3892   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3893   verify_work_stacks_empty();
3894   verify_overflow_empty();
3895 
3896   // strategy: starting with the first card, accumulate contiguous
3897   // ranges of dirty cards; clear these cards, then scan the region
3898   // covered by these cards.
3899 
3900   // Since all of the MUT is committed ahead, we can just use
3901   // that, in case the generations expand while we are precleaning.
3902   // It might also be fine to just use the committed part of the
3903   // generation, but we might potentially miss cards when the
3904   // generation is rapidly expanding while we are in the midst
3905   // of precleaning.
3906   HeapWord* startAddr = old_gen->reserved().start();
3907   HeapWord* endAddr   = old_gen->reserved().end();
3908 
3909   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3910 
3911   size_t numDirtyCards, cumNumDirtyCards;
3912   HeapWord *nextAddr, *lastAddr;
3913   for (cumNumDirtyCards = numDirtyCards = 0,
3914        nextAddr = lastAddr = startAddr;
3915        nextAddr < endAddr;
3916        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3917 
3918     ResourceMark rm;
3919     HandleMark   hm;
3920 
3921     MemRegion dirtyRegion;
3922     {
3923       stopTimer();
3924       // Potential yield point
3925       CMSTokenSync ts(true);
3926       startTimer();
3927       sample_eden();
3928       // Get dirty region starting at nextOffset (inclusive),
3929       // simultaneously clearing it.
3930       dirtyRegion =
3931         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3932       assert(dirtyRegion.start() >= nextAddr,
3933              "returned region inconsistent?");
3934     }
3935     // Remember where the next search should begin.
3936     // The returned region (if non-empty) is a right open interval,
3937     // so lastOffset is obtained from the right end of that
3938     // interval.
3939     lastAddr = dirtyRegion.end();
3940     // Should do something more transparent and less hacky XXX
3941     numDirtyCards =
3942       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3943 
3944     // We'll scan the cards in the dirty region (with periodic
3945     // yields for foreground GC as needed).
3946     if (!dirtyRegion.is_empty()) {
3947       assert(numDirtyCards > 0, "consistency check");
3948       HeapWord* stop_point = NULL;
3949       stopTimer();
3950       // Potential yield point
3951       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3952                                bitMapLock());
3953       startTimer();
3954       {
3955         verify_work_stacks_empty();
3956         verify_overflow_empty();
3957         sample_eden();
3958         stop_point =
3959           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3960       }
3961       if (stop_point != NULL) {
3962         // The careful iteration stopped early either because it found an
3963         // uninitialized object, or because we were in the midst of an
3964         // "abortable preclean", which should now be aborted. Redirty
3965         // the bits corresponding to the partially-scanned or unscanned
3966         // cards. We'll either restart at the next block boundary or
3967         // abort the preclean.
3968         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3969                "Should only be AbortablePreclean.");
3970         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3971         if (should_abort_preclean()) {
3972           break; // out of preclean loop
3973         } else {
3974           // Compute the next address at which preclean should pick up;
3975           // might need bitMapLock in order to read P-bits.
3976           lastAddr = next_card_start_after_block(stop_point);
3977         }
3978       }
3979     } else {
3980       assert(lastAddr == endAddr, "consistency check");
3981       assert(numDirtyCards == 0, "consistency check");
3982       break;
3983     }
3984   }
3985   verify_work_stacks_empty();
3986   verify_overflow_empty();
3987   return cumNumDirtyCards;
3988 }
3989 
3990 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3991 // below are largely identical; if you need to modify
3992 // one of these methods, please check the other method too.
3993 
3994 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3995   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3996   // strategy: it's similar to precleamModUnionTable above, in that
3997   // we accumulate contiguous ranges of dirty cards, mark these cards
3998   // precleaned, then scan the region covered by these cards.
3999   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4000   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4001 
4002   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4003 
4004   size_t numDirtyCards, cumNumDirtyCards;
4005   HeapWord *lastAddr, *nextAddr;
4006 
4007   for (cumNumDirtyCards = numDirtyCards = 0,
4008        nextAddr = lastAddr = startAddr;
4009        nextAddr < endAddr;
4010        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4011 
4012     ResourceMark rm;
4013     HandleMark   hm;
4014 
4015     MemRegion dirtyRegion;
4016     {
4017       // See comments in "Precleaning notes" above on why we
4018       // do this locking. XXX Could the locking overheads be
4019       // too high when dirty cards are sparse? [I don't think so.]
4020       stopTimer();
4021       CMSTokenSync x(true); // is cms thread
4022       startTimer();
4023       sample_eden();
4024       // Get and clear dirty region from card table
4025       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4026                                     MemRegion(nextAddr, endAddr),
4027                                     true,
4028                                     CardTableModRefBS::precleaned_card_val());
4029 
4030       assert(dirtyRegion.start() >= nextAddr,
4031              "returned region inconsistent?");
4032     }
4033     lastAddr = dirtyRegion.end();
4034     numDirtyCards =
4035       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4036 
4037     if (!dirtyRegion.is_empty()) {
4038       stopTimer();
4039       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4040       startTimer();
4041       sample_eden();
4042       verify_work_stacks_empty();
4043       verify_overflow_empty();
4044       HeapWord* stop_point =
4045         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4046       if (stop_point != NULL) {
4047         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4048                "Should only be AbortablePreclean.");
4049         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4050         if (should_abort_preclean()) {
4051           break; // out of preclean loop
4052         } else {
4053           // Compute the next address at which preclean should pick up.
4054           lastAddr = next_card_start_after_block(stop_point);
4055         }
4056       }
4057     } else {
4058       break;
4059     }
4060   }
4061   verify_work_stacks_empty();
4062   verify_overflow_empty();
4063   return cumNumDirtyCards;
4064 }
4065 
4066 class PrecleanKlassClosure : public KlassClosure {
4067   KlassToOopClosure _cm_klass_closure;
4068  public:
4069   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4070   void do_klass(Klass* k) {
4071     if (k->has_accumulated_modified_oops()) {
4072       k->clear_accumulated_modified_oops();
4073 
4074       _cm_klass_closure.do_klass(k);
4075     }
4076   }
4077 };
4078 
4079 // The freelist lock is needed to prevent asserts, is it really needed?
4080 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4081 
4082   cl->set_freelistLock(freelistLock);
4083 
4084   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4085 
4086   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4087   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4088   PrecleanKlassClosure preclean_klass_closure(cl);
4089   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4090 
4091   verify_work_stacks_empty();
4092   verify_overflow_empty();
4093 }
4094 
4095 void CMSCollector::checkpointRootsFinal() {
4096   assert(_collectorState == FinalMarking, "incorrect state transition?");
4097   check_correct_thread_executing();
4098   // world is stopped at this checkpoint
4099   assert(SafepointSynchronize::is_at_safepoint(),
4100          "world should be stopped");
4101   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4102 
4103   verify_work_stacks_empty();
4104   verify_overflow_empty();
4105 
4106   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4107                 _young_gen->used() / K, _young_gen->capacity() / K);
4108   {
4109     if (CMSScavengeBeforeRemark) {
4110       GenCollectedHeap* gch = GenCollectedHeap::heap();
4111       // Temporarily set flag to false, GCH->do_collection will
4112       // expect it to be false and set to true
4113       FlagSetting fl(gch->_is_gc_active, false);
4114 
4115       gch->do_collection(true,                      // full (i.e. force, see below)
4116                          false,                     // !clear_all_soft_refs
4117                          0,                         // size
4118                          false,                     // is_tlab
4119                          GenCollectedHeap::YoungGen // type
4120         );
4121     }
4122     FreelistLocker x(this);
4123     MutexLockerEx y(bitMapLock(),
4124                     Mutex::_no_safepoint_check_flag);
4125     checkpointRootsFinalWork();
4126   }
4127   verify_work_stacks_empty();
4128   verify_overflow_empty();
4129 }
4130 
4131 void CMSCollector::checkpointRootsFinalWork() {
4132   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4133 
4134   assert(haveFreelistLocks(), "must have free list locks");
4135   assert_lock_strong(bitMapLock());
4136 
4137   ResourceMark rm;
4138   HandleMark   hm;
4139 
4140   GenCollectedHeap* gch = GenCollectedHeap::heap();
4141 
4142   if (should_unload_classes()) {
4143     CodeCache::gc_prologue();
4144   }
4145   assert(haveFreelistLocks(), "must have free list locks");
4146   assert_lock_strong(bitMapLock());
4147 
4148   // We might assume that we need not fill TLAB's when
4149   // CMSScavengeBeforeRemark is set, because we may have just done
4150   // a scavenge which would have filled all TLAB's -- and besides
4151   // Eden would be empty. This however may not always be the case --
4152   // for instance although we asked for a scavenge, it may not have
4153   // happened because of a JNI critical section. We probably need
4154   // a policy for deciding whether we can in that case wait until
4155   // the critical section releases and then do the remark following
4156   // the scavenge, and skip it here. In the absence of that policy,
4157   // or of an indication of whether the scavenge did indeed occur,
4158   // we cannot rely on TLAB's having been filled and must do
4159   // so here just in case a scavenge did not happen.
4160   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4161   // Update the saved marks which may affect the root scans.
4162   gch->save_marks();
4163 
4164   print_eden_and_survivor_chunk_arrays();
4165 
4166   {
4167 #if defined(COMPILER2) || INCLUDE_JVMCI
4168     DerivedPointerTableDeactivate dpt_deact;
4169 #endif
4170 
4171     // Note on the role of the mod union table:
4172     // Since the marker in "markFromRoots" marks concurrently with
4173     // mutators, it is possible for some reachable objects not to have been
4174     // scanned. For instance, an only reference to an object A was
4175     // placed in object B after the marker scanned B. Unless B is rescanned,
4176     // A would be collected. Such updates to references in marked objects
4177     // are detected via the mod union table which is the set of all cards
4178     // dirtied since the first checkpoint in this GC cycle and prior to
4179     // the most recent young generation GC, minus those cleaned up by the
4180     // concurrent precleaning.
4181     if (CMSParallelRemarkEnabled) {
4182       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4183       do_remark_parallel();
4184     } else {
4185       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4186       do_remark_non_parallel();
4187     }
4188   }
4189   verify_work_stacks_empty();
4190   verify_overflow_empty();
4191 
4192   {
4193     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4194     refProcessingWork();
4195   }
4196   verify_work_stacks_empty();
4197   verify_overflow_empty();
4198 
4199   if (should_unload_classes()) {
4200     CodeCache::gc_epilogue();
4201   }
4202   JvmtiExport::gc_epilogue();
4203 
4204   // If we encountered any (marking stack / work queue) overflow
4205   // events during the current CMS cycle, take appropriate
4206   // remedial measures, where possible, so as to try and avoid
4207   // recurrence of that condition.
4208   assert(_markStack.isEmpty(), "No grey objects");
4209   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4210                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4211   if (ser_ovflw > 0) {
4212     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4213                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4214     _markStack.expand();
4215     _ser_pmc_remark_ovflw = 0;
4216     _ser_pmc_preclean_ovflw = 0;
4217     _ser_kac_preclean_ovflw = 0;
4218     _ser_kac_ovflw = 0;
4219   }
4220   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4221      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4222                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4223      _par_pmc_remark_ovflw = 0;
4224     _par_kac_ovflw = 0;
4225   }
4226    if (_markStack._hit_limit > 0) {
4227      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4228                           _markStack._hit_limit);
4229    }
4230    if (_markStack._failed_double > 0) {
4231      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4232                           _markStack._failed_double, _markStack.capacity());
4233    }
4234   _markStack._hit_limit = 0;
4235   _markStack._failed_double = 0;
4236 
4237   if ((VerifyAfterGC || VerifyDuringGC) &&
4238       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4239     verify_after_remark();
4240   }
4241 
4242   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4243 
4244   // Change under the freelistLocks.
4245   _collectorState = Sweeping;
4246   // Call isAllClear() under bitMapLock
4247   assert(_modUnionTable.isAllClear(),
4248       "Should be clear by end of the final marking");
4249   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4250       "Should be clear by end of the final marking");
4251 }
4252 
4253 void CMSParInitialMarkTask::work(uint worker_id) {
4254   elapsedTimer _timer;
4255   ResourceMark rm;
4256   HandleMark   hm;
4257 
4258   // ---------- scan from roots --------------
4259   _timer.start();
4260   GenCollectedHeap* gch = GenCollectedHeap::heap();
4261   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4262 
4263   // ---------- young gen roots --------------
4264   {
4265     work_on_young_gen_roots(&par_mri_cl);
4266     _timer.stop();
4267     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4268   }
4269 
4270   // ---------- remaining roots --------------
4271   _timer.reset();
4272   _timer.start();
4273 
4274   CLDToOopClosure cld_closure(&par_mri_cl, true);
4275 
4276   gch->cms_process_roots(_strong_roots_scope,
4277                          false,     // yg was scanned above
4278                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4279                          _collector->should_unload_classes(),
4280                          &par_mri_cl,
4281                          &cld_closure);
4282   assert(_collector->should_unload_classes()
4283          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4284          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4285   _timer.stop();
4286   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4287 }
4288 
4289 // Parallel remark task
4290 class CMSParRemarkTask: public CMSParMarkTask {
4291   CompactibleFreeListSpace* _cms_space;
4292 
4293   // The per-thread work queues, available here for stealing.
4294   OopTaskQueueSet*       _task_queues;
4295   ParallelTaskTerminator _term;
4296   StrongRootsScope*      _strong_roots_scope;
4297 
4298  public:
4299   // A value of 0 passed to n_workers will cause the number of
4300   // workers to be taken from the active workers in the work gang.
4301   CMSParRemarkTask(CMSCollector* collector,
4302                    CompactibleFreeListSpace* cms_space,
4303                    uint n_workers, WorkGang* workers,
4304                    OopTaskQueueSet* task_queues,
4305                    StrongRootsScope* strong_roots_scope):
4306     CMSParMarkTask("Rescan roots and grey objects in parallel",
4307                    collector, n_workers),
4308     _cms_space(cms_space),
4309     _task_queues(task_queues),
4310     _term(n_workers, task_queues),
4311     _strong_roots_scope(strong_roots_scope) { }
4312 
4313   OopTaskQueueSet* task_queues() { return _task_queues; }
4314 
4315   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4316 
4317   ParallelTaskTerminator* terminator() { return &_term; }
4318   uint n_workers() { return _n_workers; }
4319 
4320   void work(uint worker_id);
4321 
4322  private:
4323   // ... of  dirty cards in old space
4324   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4325                                   ParMarkRefsIntoAndScanClosure* cl);
4326 
4327   // ... work stealing for the above
4328   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4329 };
4330 
4331 class RemarkKlassClosure : public KlassClosure {
4332   KlassToOopClosure _cm_klass_closure;
4333  public:
4334   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4335   void do_klass(Klass* k) {
4336     // Check if we have modified any oops in the Klass during the concurrent marking.
4337     if (k->has_accumulated_modified_oops()) {
4338       k->clear_accumulated_modified_oops();
4339 
4340       // We could have transfered the current modified marks to the accumulated marks,
4341       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4342     } else if (k->has_modified_oops()) {
4343       // Don't clear anything, this info is needed by the next young collection.
4344     } else {
4345       // No modified oops in the Klass.
4346       return;
4347     }
4348 
4349     // The klass has modified fields, need to scan the klass.
4350     _cm_klass_closure.do_klass(k);
4351   }
4352 };
4353 
4354 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4355   ParNewGeneration* young_gen = _collector->_young_gen;
4356   ContiguousSpace* eden_space = young_gen->eden();
4357   ContiguousSpace* from_space = young_gen->from();
4358   ContiguousSpace* to_space   = young_gen->to();
4359 
4360   HeapWord** eca = _collector->_eden_chunk_array;
4361   size_t     ect = _collector->_eden_chunk_index;
4362   HeapWord** sca = _collector->_survivor_chunk_array;
4363   size_t     sct = _collector->_survivor_chunk_index;
4364 
4365   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4366   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4367 
4368   do_young_space_rescan(cl, to_space, NULL, 0);
4369   do_young_space_rescan(cl, from_space, sca, sct);
4370   do_young_space_rescan(cl, eden_space, eca, ect);
4371 }
4372 
4373 // work_queue(i) is passed to the closure
4374 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4375 // also is passed to do_dirty_card_rescan_tasks() and to
4376 // do_work_steal() to select the i-th task_queue.
4377 
4378 void CMSParRemarkTask::work(uint worker_id) {
4379   elapsedTimer _timer;
4380   ResourceMark rm;
4381   HandleMark   hm;
4382 
4383   // ---------- rescan from roots --------------
4384   _timer.start();
4385   GenCollectedHeap* gch = GenCollectedHeap::heap();
4386   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4387     _collector->_span, _collector->ref_processor(),
4388     &(_collector->_markBitMap),
4389     work_queue(worker_id));
4390 
4391   // Rescan young gen roots first since these are likely
4392   // coarsely partitioned and may, on that account, constitute
4393   // the critical path; thus, it's best to start off that
4394   // work first.
4395   // ---------- young gen roots --------------
4396   {
4397     work_on_young_gen_roots(&par_mrias_cl);
4398     _timer.stop();
4399     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4400   }
4401 
4402   // ---------- remaining roots --------------
4403   _timer.reset();
4404   _timer.start();
4405   gch->cms_process_roots(_strong_roots_scope,
4406                          false,     // yg was scanned above
4407                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4408                          _collector->should_unload_classes(),
4409                          &par_mrias_cl,
4410                          NULL);     // The dirty klasses will be handled below
4411 
4412   assert(_collector->should_unload_classes()
4413          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4414          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4415   _timer.stop();
4416   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4417 
4418   // ---------- unhandled CLD scanning ----------
4419   if (worker_id == 0) { // Single threaded at the moment.
4420     _timer.reset();
4421     _timer.start();
4422 
4423     // Scan all new class loader data objects and new dependencies that were
4424     // introduced during concurrent marking.
4425     ResourceMark rm;
4426     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4427     for (int i = 0; i < array->length(); i++) {
4428       par_mrias_cl.do_cld_nv(array->at(i));
4429     }
4430 
4431     // We don't need to keep track of new CLDs anymore.
4432     ClassLoaderDataGraph::remember_new_clds(false);
4433 
4434     _timer.stop();
4435     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4436   }
4437 
4438   // ---------- dirty klass scanning ----------
4439   if (worker_id == 0) { // Single threaded at the moment.
4440     _timer.reset();
4441     _timer.start();
4442 
4443     // Scan all classes that was dirtied during the concurrent marking phase.
4444     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4445     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4446 
4447     _timer.stop();
4448     log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4449   }
4450 
4451   // We might have added oops to ClassLoaderData::_handles during the
4452   // concurrent marking phase. These oops point to newly allocated objects
4453   // that are guaranteed to be kept alive. Either by the direct allocation
4454   // code, or when the young collector processes the roots. Hence,
4455   // we don't have to revisit the _handles block during the remark phase.
4456 
4457   // ---------- rescan dirty cards ------------
4458   _timer.reset();
4459   _timer.start();
4460 
4461   // Do the rescan tasks for each of the two spaces
4462   // (cms_space) in turn.
4463   // "worker_id" is passed to select the task_queue for "worker_id"
4464   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4465   _timer.stop();
4466   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4467 
4468   // ---------- steal work from other threads ...
4469   // ---------- ... and drain overflow list.
4470   _timer.reset();
4471   _timer.start();
4472   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4473   _timer.stop();
4474   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4475 }
4476 
4477 void
4478 CMSParMarkTask::do_young_space_rescan(
4479   OopsInGenClosure* cl, ContiguousSpace* space,
4480   HeapWord** chunk_array, size_t chunk_top) {
4481   // Until all tasks completed:
4482   // . claim an unclaimed task
4483   // . compute region boundaries corresponding to task claimed
4484   //   using chunk_array
4485   // . par_oop_iterate(cl) over that region
4486 
4487   ResourceMark rm;
4488   HandleMark   hm;
4489 
4490   SequentialSubTasksDone* pst = space->par_seq_tasks();
4491 
4492   uint nth_task = 0;
4493   uint n_tasks  = pst->n_tasks();
4494 
4495   if (n_tasks > 0) {
4496     assert(pst->valid(), "Uninitialized use?");
4497     HeapWord *start, *end;
4498     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4499       // We claimed task # nth_task; compute its boundaries.
4500       if (chunk_top == 0) {  // no samples were taken
4501         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4502         start = space->bottom();
4503         end   = space->top();
4504       } else if (nth_task == 0) {
4505         start = space->bottom();
4506         end   = chunk_array[nth_task];
4507       } else if (nth_task < (uint)chunk_top) {
4508         assert(nth_task >= 1, "Control point invariant");
4509         start = chunk_array[nth_task - 1];
4510         end   = chunk_array[nth_task];
4511       } else {
4512         assert(nth_task == (uint)chunk_top, "Control point invariant");
4513         start = chunk_array[chunk_top - 1];
4514         end   = space->top();
4515       }
4516       MemRegion mr(start, end);
4517       // Verify that mr is in space
4518       assert(mr.is_empty() || space->used_region().contains(mr),
4519              "Should be in space");
4520       // Verify that "start" is an object boundary
4521       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4522              "Should be an oop");
4523       space->par_oop_iterate(mr, cl);
4524     }
4525     pst->all_tasks_completed();
4526   }
4527 }
4528 
4529 void
4530 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4531   CompactibleFreeListSpace* sp, int i,
4532   ParMarkRefsIntoAndScanClosure* cl) {
4533   // Until all tasks completed:
4534   // . claim an unclaimed task
4535   // . compute region boundaries corresponding to task claimed
4536   // . transfer dirty bits ct->mut for that region
4537   // . apply rescanclosure to dirty mut bits for that region
4538 
4539   ResourceMark rm;
4540   HandleMark   hm;
4541 
4542   OopTaskQueue* work_q = work_queue(i);
4543   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4544   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4545   // CAUTION: This closure has state that persists across calls to
4546   // the work method dirty_range_iterate_clear() in that it has
4547   // embedded in it a (subtype of) UpwardsObjectClosure. The
4548   // use of that state in the embedded UpwardsObjectClosure instance
4549   // assumes that the cards are always iterated (even if in parallel
4550   // by several threads) in monotonically increasing order per each
4551   // thread. This is true of the implementation below which picks
4552   // card ranges (chunks) in monotonically increasing order globally
4553   // and, a-fortiori, in monotonically increasing order per thread
4554   // (the latter order being a subsequence of the former).
4555   // If the work code below is ever reorganized into a more chaotic
4556   // work-partitioning form than the current "sequential tasks"
4557   // paradigm, the use of that persistent state will have to be
4558   // revisited and modified appropriately. See also related
4559   // bug 4756801 work on which should examine this code to make
4560   // sure that the changes there do not run counter to the
4561   // assumptions made here and necessary for correctness and
4562   // efficiency. Note also that this code might yield inefficient
4563   // behavior in the case of very large objects that span one or
4564   // more work chunks. Such objects would potentially be scanned
4565   // several times redundantly. Work on 4756801 should try and
4566   // address that performance anomaly if at all possible. XXX
4567   MemRegion  full_span  = _collector->_span;
4568   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4569   MarkFromDirtyCardsClosure
4570     greyRescanClosure(_collector, full_span, // entire span of interest
4571                       sp, bm, work_q, cl);
4572 
4573   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4574   assert(pst->valid(), "Uninitialized use?");
4575   uint nth_task = 0;
4576   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4577   MemRegion span = sp->used_region();
4578   HeapWord* start_addr = span.start();
4579   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4580                                            alignment);
4581   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4582   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4583          start_addr, "Check alignment");
4584   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4585          chunk_size, "Check alignment");
4586 
4587   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4588     // Having claimed the nth_task, compute corresponding mem-region,
4589     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4590     // The alignment restriction ensures that we do not need any
4591     // synchronization with other gang-workers while setting or
4592     // clearing bits in thus chunk of the MUT.
4593     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4594                                     start_addr + (nth_task+1)*chunk_size);
4595     // The last chunk's end might be way beyond end of the
4596     // used region. In that case pull back appropriately.
4597     if (this_span.end() > end_addr) {
4598       this_span.set_end(end_addr);
4599       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4600     }
4601     // Iterate over the dirty cards covering this chunk, marking them
4602     // precleaned, and setting the corresponding bits in the mod union
4603     // table. Since we have been careful to partition at Card and MUT-word
4604     // boundaries no synchronization is needed between parallel threads.
4605     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4606                                                  &modUnionClosure);
4607 
4608     // Having transferred these marks into the modUnionTable,
4609     // rescan the marked objects on the dirty cards in the modUnionTable.
4610     // Even if this is at a synchronous collection, the initial marking
4611     // may have been done during an asynchronous collection so there
4612     // may be dirty bits in the mod-union table.
4613     _collector->_modUnionTable.dirty_range_iterate_clear(
4614                   this_span, &greyRescanClosure);
4615     _collector->_modUnionTable.verifyNoOneBitsInRange(
4616                                  this_span.start(),
4617                                  this_span.end());
4618   }
4619   pst->all_tasks_completed();  // declare that i am done
4620 }
4621 
4622 // . see if we can share work_queues with ParNew? XXX
4623 void
4624 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4625                                 int* seed) {
4626   OopTaskQueue* work_q = work_queue(i);
4627   NOT_PRODUCT(int num_steals = 0;)
4628   oop obj_to_scan;
4629   CMSBitMap* bm = &(_collector->_markBitMap);
4630 
4631   while (true) {
4632     // Completely finish any left over work from (an) earlier round(s)
4633     cl->trim_queue(0);
4634     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4635                                          (size_t)ParGCDesiredObjsFromOverflowList);
4636     // Now check if there's any work in the overflow list
4637     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4638     // only affects the number of attempts made to get work from the
4639     // overflow list and does not affect the number of workers.  Just
4640     // pass ParallelGCThreads so this behavior is unchanged.
4641     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4642                                                 work_q,
4643                                                 ParallelGCThreads)) {
4644       // found something in global overflow list;
4645       // not yet ready to go stealing work from others.
4646       // We'd like to assert(work_q->size() != 0, ...)
4647       // because we just took work from the overflow list,
4648       // but of course we can't since all of that could have
4649       // been already stolen from us.
4650       // "He giveth and He taketh away."
4651       continue;
4652     }
4653     // Verify that we have no work before we resort to stealing
4654     assert(work_q->size() == 0, "Have work, shouldn't steal");
4655     // Try to steal from other queues that have work
4656     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4657       NOT_PRODUCT(num_steals++;)
4658       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4659       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4660       // Do scanning work
4661       obj_to_scan->oop_iterate(cl);
4662       // Loop around, finish this work, and try to steal some more
4663     } else if (terminator()->offer_termination()) {
4664         break;  // nirvana from the infinite cycle
4665     }
4666   }
4667   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4668   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4669          "Else our work is not yet done");
4670 }
4671 
4672 // Record object boundaries in _eden_chunk_array by sampling the eden
4673 // top in the slow-path eden object allocation code path and record
4674 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4675 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4676 // sampling in sample_eden() that activates during the part of the
4677 // preclean phase.
4678 void CMSCollector::sample_eden_chunk() {
4679   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4680     if (_eden_chunk_lock->try_lock()) {
4681       // Record a sample. This is the critical section. The contents
4682       // of the _eden_chunk_array have to be non-decreasing in the
4683       // address order.
4684       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4685       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4686              "Unexpected state of Eden");
4687       if (_eden_chunk_index == 0 ||
4688           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4689            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4690                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4691         _eden_chunk_index++;  // commit sample
4692       }
4693       _eden_chunk_lock->unlock();
4694     }
4695   }
4696 }
4697 
4698 // Return a thread-local PLAB recording array, as appropriate.
4699 void* CMSCollector::get_data_recorder(int thr_num) {
4700   if (_survivor_plab_array != NULL &&
4701       (CMSPLABRecordAlways ||
4702        (_collectorState > Marking && _collectorState < FinalMarking))) {
4703     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4704     ChunkArray* ca = &_survivor_plab_array[thr_num];
4705     ca->reset();   // clear it so that fresh data is recorded
4706     return (void*) ca;
4707   } else {
4708     return NULL;
4709   }
4710 }
4711 
4712 // Reset all the thread-local PLAB recording arrays
4713 void CMSCollector::reset_survivor_plab_arrays() {
4714   for (uint i = 0; i < ParallelGCThreads; i++) {
4715     _survivor_plab_array[i].reset();
4716   }
4717 }
4718 
4719 // Merge the per-thread plab arrays into the global survivor chunk
4720 // array which will provide the partitioning of the survivor space
4721 // for CMS initial scan and rescan.
4722 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4723                                               int no_of_gc_threads) {
4724   assert(_survivor_plab_array  != NULL, "Error");
4725   assert(_survivor_chunk_array != NULL, "Error");
4726   assert(_collectorState == FinalMarking ||
4727          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4728   for (int j = 0; j < no_of_gc_threads; j++) {
4729     _cursor[j] = 0;
4730   }
4731   HeapWord* top = surv->top();
4732   size_t i;
4733   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4734     HeapWord* min_val = top;          // Higher than any PLAB address
4735     uint      min_tid = 0;            // position of min_val this round
4736     for (int j = 0; j < no_of_gc_threads; j++) {
4737       ChunkArray* cur_sca = &_survivor_plab_array[j];
4738       if (_cursor[j] == cur_sca->end()) {
4739         continue;
4740       }
4741       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4742       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4743       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4744       if (cur_val < min_val) {
4745         min_tid = j;
4746         min_val = cur_val;
4747       } else {
4748         assert(cur_val < top, "All recorded addresses should be less");
4749       }
4750     }
4751     // At this point min_val and min_tid are respectively
4752     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4753     // and the thread (j) that witnesses that address.
4754     // We record this address in the _survivor_chunk_array[i]
4755     // and increment _cursor[min_tid] prior to the next round i.
4756     if (min_val == top) {
4757       break;
4758     }
4759     _survivor_chunk_array[i] = min_val;
4760     _cursor[min_tid]++;
4761   }
4762   // We are all done; record the size of the _survivor_chunk_array
4763   _survivor_chunk_index = i; // exclusive: [0, i)
4764   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4765   // Verify that we used up all the recorded entries
4766   #ifdef ASSERT
4767     size_t total = 0;
4768     for (int j = 0; j < no_of_gc_threads; j++) {
4769       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4770       total += _cursor[j];
4771     }
4772     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4773     // Check that the merged array is in sorted order
4774     if (total > 0) {
4775       for (size_t i = 0; i < total - 1; i++) {
4776         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4777                                      i, p2i(_survivor_chunk_array[i]));
4778         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4779                "Not sorted");
4780       }
4781     }
4782   #endif // ASSERT
4783 }
4784 
4785 // Set up the space's par_seq_tasks structure for work claiming
4786 // for parallel initial scan and rescan of young gen.
4787 // See ParRescanTask where this is currently used.
4788 void
4789 CMSCollector::
4790 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4791   assert(n_threads > 0, "Unexpected n_threads argument");
4792 
4793   // Eden space
4794   if (!_young_gen->eden()->is_empty()) {
4795     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4796     assert(!pst->valid(), "Clobbering existing data?");
4797     // Each valid entry in [0, _eden_chunk_index) represents a task.
4798     size_t n_tasks = _eden_chunk_index + 1;
4799     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4800     // Sets the condition for completion of the subtask (how many threads
4801     // need to finish in order to be done).
4802     pst->set_n_threads(n_threads);
4803     pst->set_n_tasks((int)n_tasks);
4804   }
4805 
4806   // Merge the survivor plab arrays into _survivor_chunk_array
4807   if (_survivor_plab_array != NULL) {
4808     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4809   } else {
4810     assert(_survivor_chunk_index == 0, "Error");
4811   }
4812 
4813   // To space
4814   {
4815     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4816     assert(!pst->valid(), "Clobbering existing data?");
4817     // Sets the condition for completion of the subtask (how many threads
4818     // need to finish in order to be done).
4819     pst->set_n_threads(n_threads);
4820     pst->set_n_tasks(1);
4821     assert(pst->valid(), "Error");
4822   }
4823 
4824   // From space
4825   {
4826     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4827     assert(!pst->valid(), "Clobbering existing data?");
4828     size_t n_tasks = _survivor_chunk_index + 1;
4829     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4830     // Sets the condition for completion of the subtask (how many threads
4831     // need to finish in order to be done).
4832     pst->set_n_threads(n_threads);
4833     pst->set_n_tasks((int)n_tasks);
4834     assert(pst->valid(), "Error");
4835   }
4836 }
4837 
4838 // Parallel version of remark
4839 void CMSCollector::do_remark_parallel() {
4840   GenCollectedHeap* gch = GenCollectedHeap::heap();
4841   WorkGang* workers = gch->workers();
4842   assert(workers != NULL, "Need parallel worker threads.");
4843   // Choose to use the number of GC workers most recently set
4844   // into "active_workers".
4845   uint n_workers = workers->active_workers();
4846 
4847   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4848 
4849   StrongRootsScope srs(n_workers);
4850 
4851   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4852 
4853   // We won't be iterating over the cards in the card table updating
4854   // the younger_gen cards, so we shouldn't call the following else
4855   // the verification code as well as subsequent younger_refs_iterate
4856   // code would get confused. XXX
4857   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4858 
4859   // The young gen rescan work will not be done as part of
4860   // process_roots (which currently doesn't know how to
4861   // parallelize such a scan), but rather will be broken up into
4862   // a set of parallel tasks (via the sampling that the [abortable]
4863   // preclean phase did of eden, plus the [two] tasks of
4864   // scanning the [two] survivor spaces. Further fine-grain
4865   // parallelization of the scanning of the survivor spaces
4866   // themselves, and of precleaning of the young gen itself
4867   // is deferred to the future.
4868   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4869 
4870   // The dirty card rescan work is broken up into a "sequence"
4871   // of parallel tasks (per constituent space) that are dynamically
4872   // claimed by the parallel threads.
4873   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4874 
4875   // It turns out that even when we're using 1 thread, doing the work in a
4876   // separate thread causes wide variance in run times.  We can't help this
4877   // in the multi-threaded case, but we special-case n=1 here to get
4878   // repeatable measurements of the 1-thread overhead of the parallel code.
4879   if (n_workers > 1) {
4880     // Make refs discovery MT-safe, if it isn't already: it may not
4881     // necessarily be so, since it's possible that we are doing
4882     // ST marking.
4883     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4884     workers->run_task(&tsk);
4885   } else {
4886     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4887     tsk.work(0);
4888   }
4889 
4890   // restore, single-threaded for now, any preserved marks
4891   // as a result of work_q overflow
4892   restore_preserved_marks_if_any();
4893 }
4894 
4895 // Non-parallel version of remark
4896 void CMSCollector::do_remark_non_parallel() {
4897   ResourceMark rm;
4898   HandleMark   hm;
4899   GenCollectedHeap* gch = GenCollectedHeap::heap();
4900   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4901 
4902   MarkRefsIntoAndScanClosure
4903     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4904              &_markStack, this,
4905              false /* should_yield */, false /* not precleaning */);
4906   MarkFromDirtyCardsClosure
4907     markFromDirtyCardsClosure(this, _span,
4908                               NULL,  // space is set further below
4909                               &_markBitMap, &_markStack, &mrias_cl);
4910   {
4911     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4912     // Iterate over the dirty cards, setting the corresponding bits in the
4913     // mod union table.
4914     {
4915       ModUnionClosure modUnionClosure(&_modUnionTable);
4916       _ct->ct_bs()->dirty_card_iterate(
4917                       _cmsGen->used_region(),
4918                       &modUnionClosure);
4919     }
4920     // Having transferred these marks into the modUnionTable, we just need
4921     // to rescan the marked objects on the dirty cards in the modUnionTable.
4922     // The initial marking may have been done during an asynchronous
4923     // collection so there may be dirty bits in the mod-union table.
4924     const int alignment =
4925       CardTableModRefBS::card_size * BitsPerWord;
4926     {
4927       // ... First handle dirty cards in CMS gen
4928       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4929       MemRegion ur = _cmsGen->used_region();
4930       HeapWord* lb = ur.start();
4931       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4932       MemRegion cms_span(lb, ub);
4933       _modUnionTable.dirty_range_iterate_clear(cms_span,
4934                                                &markFromDirtyCardsClosure);
4935       verify_work_stacks_empty();
4936       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4937     }
4938   }
4939   if (VerifyDuringGC &&
4940       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4941     HandleMark hm;  // Discard invalid handles created during verification
4942     Universe::verify();
4943   }
4944   {
4945     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4946 
4947     verify_work_stacks_empty();
4948 
4949     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4950     StrongRootsScope srs(1);
4951 
4952     gch->cms_process_roots(&srs,
4953                            true,  // young gen as roots
4954                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
4955                            should_unload_classes(),
4956                            &mrias_cl,
4957                            NULL); // The dirty klasses will be handled below
4958 
4959     assert(should_unload_classes()
4960            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4961            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4962   }
4963 
4964   {
4965     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4966 
4967     verify_work_stacks_empty();
4968 
4969     // Scan all class loader data objects that might have been introduced
4970     // during concurrent marking.
4971     ResourceMark rm;
4972     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4973     for (int i = 0; i < array->length(); i++) {
4974       mrias_cl.do_cld_nv(array->at(i));
4975     }
4976 
4977     // We don't need to keep track of new CLDs anymore.
4978     ClassLoaderDataGraph::remember_new_clds(false);
4979 
4980     verify_work_stacks_empty();
4981   }
4982 
4983   {
4984     GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
4985 
4986     verify_work_stacks_empty();
4987 
4988     RemarkKlassClosure remark_klass_closure(&mrias_cl);
4989     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4990 
4991     verify_work_stacks_empty();
4992   }
4993 
4994   // We might have added oops to ClassLoaderData::_handles during the
4995   // concurrent marking phase. These oops point to newly allocated objects
4996   // that are guaranteed to be kept alive. Either by the direct allocation
4997   // code, or when the young collector processes the roots. Hence,
4998   // we don't have to revisit the _handles block during the remark phase.
4999 
5000   verify_work_stacks_empty();
5001   // Restore evacuated mark words, if any, used for overflow list links
5002   restore_preserved_marks_if_any();
5003 
5004   verify_overflow_empty();
5005 }
5006 
5007 ////////////////////////////////////////////////////////
5008 // Parallel Reference Processing Task Proxy Class
5009 ////////////////////////////////////////////////////////
5010 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5011   OopTaskQueueSet*       _queues;
5012   ParallelTaskTerminator _terminator;
5013  public:
5014   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5015     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5016   ParallelTaskTerminator* terminator() { return &_terminator; }
5017   OopTaskQueueSet* queues() { return _queues; }
5018 };
5019 
5020 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5021   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5022   CMSCollector*          _collector;
5023   CMSBitMap*             _mark_bit_map;
5024   const MemRegion        _span;
5025   ProcessTask&           _task;
5026 
5027 public:
5028   CMSRefProcTaskProxy(ProcessTask&     task,
5029                       CMSCollector*    collector,
5030                       const MemRegion& span,
5031                       CMSBitMap*       mark_bit_map,
5032                       AbstractWorkGang* workers,
5033                       OopTaskQueueSet* task_queues):
5034     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5035       task_queues,
5036       workers->active_workers()),
5037     _task(task),
5038     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5039   {
5040     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5041            "Inconsistency in _span");
5042   }
5043 
5044   OopTaskQueueSet* task_queues() { return queues(); }
5045 
5046   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5047 
5048   void do_work_steal(int i,
5049                      CMSParDrainMarkingStackClosure* drain,
5050                      CMSParKeepAliveClosure* keep_alive,
5051                      int* seed);
5052 
5053   virtual void work(uint worker_id);
5054 };
5055 
5056 void CMSRefProcTaskProxy::work(uint worker_id) {
5057   ResourceMark rm;
5058   HandleMark hm;
5059   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5060   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5061                                         _mark_bit_map,
5062                                         work_queue(worker_id));
5063   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5064                                                  _mark_bit_map,
5065                                                  work_queue(worker_id));
5066   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5067   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5068   if (_task.marks_oops_alive()) {
5069     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5070                   _collector->hash_seed(worker_id));
5071   }
5072   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5073   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5074 }
5075 
5076 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5077   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5078   EnqueueTask& _task;
5079 
5080 public:
5081   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5082     : AbstractGangTask("Enqueue reference objects in parallel"),
5083       _task(task)
5084   { }
5085 
5086   virtual void work(uint worker_id)
5087   {
5088     _task.work(worker_id);
5089   }
5090 };
5091 
5092 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5093   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5094    _span(span),
5095    _bit_map(bit_map),
5096    _work_queue(work_queue),
5097    _mark_and_push(collector, span, bit_map, work_queue),
5098    _low_water_mark(MIN2((work_queue->max_elems()/4),
5099                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5100 { }
5101 
5102 // . see if we can share work_queues with ParNew? XXX
5103 void CMSRefProcTaskProxy::do_work_steal(int i,
5104   CMSParDrainMarkingStackClosure* drain,
5105   CMSParKeepAliveClosure* keep_alive,
5106   int* seed) {
5107   OopTaskQueue* work_q = work_queue(i);
5108   NOT_PRODUCT(int num_steals = 0;)
5109   oop obj_to_scan;
5110 
5111   while (true) {
5112     // Completely finish any left over work from (an) earlier round(s)
5113     drain->trim_queue(0);
5114     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5115                                          (size_t)ParGCDesiredObjsFromOverflowList);
5116     // Now check if there's any work in the overflow list
5117     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5118     // only affects the number of attempts made to get work from the
5119     // overflow list and does not affect the number of workers.  Just
5120     // pass ParallelGCThreads so this behavior is unchanged.
5121     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5122                                                 work_q,
5123                                                 ParallelGCThreads)) {
5124       // Found something in global overflow list;
5125       // not yet ready to go stealing work from others.
5126       // We'd like to assert(work_q->size() != 0, ...)
5127       // because we just took work from the overflow list,
5128       // but of course we can't, since all of that might have
5129       // been already stolen from us.
5130       continue;
5131     }
5132     // Verify that we have no work before we resort to stealing
5133     assert(work_q->size() == 0, "Have work, shouldn't steal");
5134     // Try to steal from other queues that have work
5135     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5136       NOT_PRODUCT(num_steals++;)
5137       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5138       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5139       // Do scanning work
5140       obj_to_scan->oop_iterate(keep_alive);
5141       // Loop around, finish this work, and try to steal some more
5142     } else if (terminator()->offer_termination()) {
5143       break;  // nirvana from the infinite cycle
5144     }
5145   }
5146   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5147 }
5148 
5149 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5150 {
5151   GenCollectedHeap* gch = GenCollectedHeap::heap();
5152   WorkGang* workers = gch->workers();
5153   assert(workers != NULL, "Need parallel worker threads.");
5154   CMSRefProcTaskProxy rp_task(task, &_collector,
5155                               _collector.ref_processor()->span(),
5156                               _collector.markBitMap(),
5157                               workers, _collector.task_queues());
5158   workers->run_task(&rp_task);
5159 }
5160 
5161 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5162 {
5163 
5164   GenCollectedHeap* gch = GenCollectedHeap::heap();
5165   WorkGang* workers = gch->workers();
5166   assert(workers != NULL, "Need parallel worker threads.");
5167   CMSRefEnqueueTaskProxy enq_task(task);
5168   workers->run_task(&enq_task);
5169 }
5170 
5171 void CMSCollector::refProcessingWork() {
5172   ResourceMark rm;
5173   HandleMark   hm;
5174 
5175   ReferenceProcessor* rp = ref_processor();
5176   assert(rp->span().equals(_span), "Spans should be equal");
5177   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5178   // Process weak references.
5179   rp->setup_policy(false);
5180   verify_work_stacks_empty();
5181 
5182   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5183                                           &_markStack, false /* !preclean */);
5184   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5185                                 _span, &_markBitMap, &_markStack,
5186                                 &cmsKeepAliveClosure, false /* !preclean */);
5187   {
5188     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5189 
5190     ReferenceProcessorStats stats;
5191     if (rp->processing_is_mt()) {
5192       // Set the degree of MT here.  If the discovery is done MT, there
5193       // may have been a different number of threads doing the discovery
5194       // and a different number of discovered lists may have Ref objects.
5195       // That is OK as long as the Reference lists are balanced (see
5196       // balance_all_queues() and balance_queues()).
5197       GenCollectedHeap* gch = GenCollectedHeap::heap();
5198       uint active_workers = ParallelGCThreads;
5199       WorkGang* workers = gch->workers();
5200       if (workers != NULL) {
5201         active_workers = workers->active_workers();
5202         // The expectation is that active_workers will have already
5203         // been set to a reasonable value.  If it has not been set,
5204         // investigate.
5205         assert(active_workers > 0, "Should have been set during scavenge");
5206       }
5207       rp->set_active_mt_degree(active_workers);
5208       CMSRefProcTaskExecutor task_executor(*this);
5209       stats = rp->process_discovered_references(&_is_alive_closure,
5210                                         &cmsKeepAliveClosure,
5211                                         &cmsDrainMarkingStackClosure,
5212                                         &task_executor,
5213                                         _gc_timer_cm);
5214     } else {
5215       stats = rp->process_discovered_references(&_is_alive_closure,
5216                                         &cmsKeepAliveClosure,
5217                                         &cmsDrainMarkingStackClosure,
5218                                         NULL,
5219                                         _gc_timer_cm);
5220     }
5221     _gc_tracer_cm->report_gc_reference_stats(stats);
5222 
5223   }
5224 
5225   // This is the point where the entire marking should have completed.
5226   verify_work_stacks_empty();
5227 
5228   if (should_unload_classes()) {
5229     {
5230       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5231 
5232       // Unload classes and purge the SystemDictionary.
5233       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5234 
5235       // Unload nmethods.
5236       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5237 
5238       // Prune dead klasses from subklass/sibling/implementor lists.
5239       Klass::clean_weak_klass_links(&_is_alive_closure);
5240     }
5241 
5242     {
5243       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5244       // Clean up unreferenced symbols in symbol table.
5245       SymbolTable::unlink();
5246     }
5247 
5248     {
5249       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5250       // Delete entries for dead interned strings.
5251       StringTable::unlink(&_is_alive_closure);
5252     }
5253   }
5254 
5255   // Restore any preserved marks as a result of mark stack or
5256   // work queue overflow
5257   restore_preserved_marks_if_any();  // done single-threaded for now
5258 
5259   rp->set_enqueuing_is_done(true);
5260   if (rp->processing_is_mt()) {
5261     rp->balance_all_queues();
5262     CMSRefProcTaskExecutor task_executor(*this);
5263     rp->enqueue_discovered_references(&task_executor);
5264   } else {
5265     rp->enqueue_discovered_references(NULL);
5266   }
5267   rp->verify_no_references_recorded();
5268   assert(!rp->discovery_enabled(), "should have been disabled");
5269 }
5270 
5271 #ifndef PRODUCT
5272 void CMSCollector::check_correct_thread_executing() {
5273   Thread* t = Thread::current();
5274   // Only the VM thread or the CMS thread should be here.
5275   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5276          "Unexpected thread type");
5277   // If this is the vm thread, the foreground process
5278   // should not be waiting.  Note that _foregroundGCIsActive is
5279   // true while the foreground collector is waiting.
5280   if (_foregroundGCShouldWait) {
5281     // We cannot be the VM thread
5282     assert(t->is_ConcurrentGC_thread(),
5283            "Should be CMS thread");
5284   } else {
5285     // We can be the CMS thread only if we are in a stop-world
5286     // phase of CMS collection.
5287     if (t->is_ConcurrentGC_thread()) {
5288       assert(_collectorState == InitialMarking ||
5289              _collectorState == FinalMarking,
5290              "Should be a stop-world phase");
5291       // The CMS thread should be holding the CMS_token.
5292       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5293              "Potential interference with concurrently "
5294              "executing VM thread");
5295     }
5296   }
5297 }
5298 #endif
5299 
5300 void CMSCollector::sweep() {
5301   assert(_collectorState == Sweeping, "just checking");
5302   check_correct_thread_executing();
5303   verify_work_stacks_empty();
5304   verify_overflow_empty();
5305   increment_sweep_count();
5306   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5307 
5308   _inter_sweep_timer.stop();
5309   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5310 
5311   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5312   _intra_sweep_timer.reset();
5313   _intra_sweep_timer.start();
5314   {
5315     GCTraceCPUTime tcpu;
5316     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5317     // First sweep the old gen
5318     {
5319       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5320                                bitMapLock());
5321       sweepWork(_cmsGen);
5322     }
5323 
5324     // Update Universe::_heap_*_at_gc figures.
5325     // We need all the free list locks to make the abstract state
5326     // transition from Sweeping to Resetting. See detailed note
5327     // further below.
5328     {
5329       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5330       // Update heap occupancy information which is used as
5331       // input to soft ref clearing policy at the next gc.
5332       Universe::update_heap_info_at_gc();
5333       _collectorState = Resizing;
5334     }
5335   }
5336   verify_work_stacks_empty();
5337   verify_overflow_empty();
5338 
5339   if (should_unload_classes()) {
5340     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5341     // requires that the virtual spaces are stable and not deleted.
5342     ClassLoaderDataGraph::set_should_purge(true);
5343   }
5344 
5345   _intra_sweep_timer.stop();
5346   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5347 
5348   _inter_sweep_timer.reset();
5349   _inter_sweep_timer.start();
5350 
5351   // We need to use a monotonically non-decreasing time in ms
5352   // or we will see time-warp warnings and os::javaTimeMillis()
5353   // does not guarantee monotonicity.
5354   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5355   update_time_of_last_gc(now);
5356 
5357   // NOTE on abstract state transitions:
5358   // Mutators allocate-live and/or mark the mod-union table dirty
5359   // based on the state of the collection.  The former is done in
5360   // the interval [Marking, Sweeping] and the latter in the interval
5361   // [Marking, Sweeping).  Thus the transitions into the Marking state
5362   // and out of the Sweeping state must be synchronously visible
5363   // globally to the mutators.
5364   // The transition into the Marking state happens with the world
5365   // stopped so the mutators will globally see it.  Sweeping is
5366   // done asynchronously by the background collector so the transition
5367   // from the Sweeping state to the Resizing state must be done
5368   // under the freelistLock (as is the check for whether to
5369   // allocate-live and whether to dirty the mod-union table).
5370   assert(_collectorState == Resizing, "Change of collector state to"
5371     " Resizing must be done under the freelistLocks (plural)");
5372 
5373   // Now that sweeping has been completed, we clear
5374   // the incremental_collection_failed flag,
5375   // thus inviting a younger gen collection to promote into
5376   // this generation. If such a promotion may still fail,
5377   // the flag will be set again when a young collection is
5378   // attempted.
5379   GenCollectedHeap* gch = GenCollectedHeap::heap();
5380   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5381   gch->update_full_collections_completed(_collection_count_start);
5382 }
5383 
5384 // FIX ME!!! Looks like this belongs in CFLSpace, with
5385 // CMSGen merely delegating to it.
5386 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5387   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5388   HeapWord*  minAddr        = _cmsSpace->bottom();
5389   HeapWord*  largestAddr    =
5390     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5391   if (largestAddr == NULL) {
5392     // The dictionary appears to be empty.  In this case
5393     // try to coalesce at the end of the heap.
5394     largestAddr = _cmsSpace->end();
5395   }
5396   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5397   size_t nearLargestOffset =
5398     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5399   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5400                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5401   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5402 }
5403 
5404 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5405   return addr >= _cmsSpace->nearLargestChunk();
5406 }
5407 
5408 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5409   return _cmsSpace->find_chunk_at_end();
5410 }
5411 
5412 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5413                                                     bool full) {
5414   // If the young generation has been collected, gather any statistics
5415   // that are of interest at this point.
5416   bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5417   if (!full && current_is_young) {
5418     // Gather statistics on the young generation collection.
5419     collector()->stats().record_gc0_end(used());
5420   }
5421 }
5422 
5423 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5424   // We iterate over the space(s) underlying this generation,
5425   // checking the mark bit map to see if the bits corresponding
5426   // to specific blocks are marked or not. Blocks that are
5427   // marked are live and are not swept up. All remaining blocks
5428   // are swept up, with coalescing on-the-fly as we sweep up
5429   // contiguous free and/or garbage blocks:
5430   // We need to ensure that the sweeper synchronizes with allocators
5431   // and stop-the-world collectors. In particular, the following
5432   // locks are used:
5433   // . CMS token: if this is held, a stop the world collection cannot occur
5434   // . freelistLock: if this is held no allocation can occur from this
5435   //                 generation by another thread
5436   // . bitMapLock: if this is held, no other thread can access or update
5437   //
5438 
5439   // Note that we need to hold the freelistLock if we use
5440   // block iterate below; else the iterator might go awry if
5441   // a mutator (or promotion) causes block contents to change
5442   // (for instance if the allocator divvies up a block).
5443   // If we hold the free list lock, for all practical purposes
5444   // young generation GC's can't occur (they'll usually need to
5445   // promote), so we might as well prevent all young generation
5446   // GC's while we do a sweeping step. For the same reason, we might
5447   // as well take the bit map lock for the entire duration
5448 
5449   // check that we hold the requisite locks
5450   assert(have_cms_token(), "Should hold cms token");
5451   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5452   assert_lock_strong(old_gen->freelistLock());
5453   assert_lock_strong(bitMapLock());
5454 
5455   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5456   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5457   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5458                                           _inter_sweep_estimate.padded_average(),
5459                                           _intra_sweep_estimate.padded_average());
5460   old_gen->setNearLargestChunk();
5461 
5462   {
5463     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5464     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5465     // We need to free-up/coalesce garbage/blocks from a
5466     // co-terminal free run. This is done in the SweepClosure
5467     // destructor; so, do not remove this scope, else the
5468     // end-of-sweep-census below will be off by a little bit.
5469   }
5470   old_gen->cmsSpace()->sweep_completed();
5471   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5472   if (should_unload_classes()) {                // unloaded classes this cycle,
5473     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5474   } else {                                      // did not unload classes,
5475     _concurrent_cycles_since_last_unload++;     // ... increment count
5476   }
5477 }
5478 
5479 // Reset CMS data structures (for now just the marking bit map)
5480 // preparatory for the next cycle.
5481 void CMSCollector::reset_concurrent() {
5482   CMSTokenSyncWithLocks ts(true, bitMapLock());
5483 
5484   // If the state is not "Resetting", the foreground  thread
5485   // has done a collection and the resetting.
5486   if (_collectorState != Resetting) {
5487     assert(_collectorState == Idling, "The state should only change"
5488       " because the foreground collector has finished the collection");
5489     return;
5490   }
5491 
5492   {
5493     // Clear the mark bitmap (no grey objects to start with)
5494     // for the next cycle.
5495     GCTraceCPUTime tcpu;
5496     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5497 
5498     HeapWord* curAddr = _markBitMap.startWord();
5499     while (curAddr < _markBitMap.endWord()) {
5500       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5501       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5502       _markBitMap.clear_large_range(chunk);
5503       if (ConcurrentMarkSweepThread::should_yield() &&
5504           !foregroundGCIsActive() &&
5505           CMSYield) {
5506         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5507                "CMS thread should hold CMS token");
5508         assert_lock_strong(bitMapLock());
5509         bitMapLock()->unlock();
5510         ConcurrentMarkSweepThread::desynchronize(true);
5511         stopTimer();
5512         incrementYields();
5513 
5514         // See the comment in coordinator_yield()
5515         for (unsigned i = 0; i < CMSYieldSleepCount &&
5516                          ConcurrentMarkSweepThread::should_yield() &&
5517                          !CMSCollector::foregroundGCIsActive(); ++i) {
5518           os::sleep(Thread::current(), 1, false);
5519         }
5520 
5521         ConcurrentMarkSweepThread::synchronize(true);
5522         bitMapLock()->lock_without_safepoint_check();
5523         startTimer();
5524       }
5525       curAddr = chunk.end();
5526     }
5527     // A successful mostly concurrent collection has been done.
5528     // Because only the full (i.e., concurrent mode failure) collections
5529     // are being measured for gc overhead limits, clean the "near" flag
5530     // and count.
5531     size_policy()->reset_gc_overhead_limit_count();
5532     _collectorState = Idling;
5533   }
5534 
5535   register_gc_end();
5536 }
5537 
5538 // Same as above but for STW paths
5539 void CMSCollector::reset_stw() {
5540   // already have the lock
5541   assert(_collectorState == Resetting, "just checking");
5542   assert_lock_strong(bitMapLock());
5543   GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5544   _markBitMap.clear_all();
5545   _collectorState = Idling;
5546   register_gc_end();
5547 }
5548 
5549 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5550   GCTraceCPUTime tcpu;
5551   TraceCollectorStats tcs(counters());
5552 
5553   switch (op) {
5554     case CMS_op_checkpointRootsInitial: {
5555       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5556       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5557       checkpointRootsInitial();
5558       break;
5559     }
5560     case CMS_op_checkpointRootsFinal: {
5561       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5562       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5563       checkpointRootsFinal();
5564       break;
5565     }
5566     default:
5567       fatal("No such CMS_op");
5568   }
5569 }
5570 
5571 #ifndef PRODUCT
5572 size_t const CMSCollector::skip_header_HeapWords() {
5573   return FreeChunk::header_size();
5574 }
5575 
5576 // Try and collect here conditions that should hold when
5577 // CMS thread is exiting. The idea is that the foreground GC
5578 // thread should not be blocked if it wants to terminate
5579 // the CMS thread and yet continue to run the VM for a while
5580 // after that.
5581 void CMSCollector::verify_ok_to_terminate() const {
5582   assert(Thread::current()->is_ConcurrentGC_thread(),
5583          "should be called by CMS thread");
5584   assert(!_foregroundGCShouldWait, "should be false");
5585   // We could check here that all the various low-level locks
5586   // are not held by the CMS thread, but that is overkill; see
5587   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5588   // is checked.
5589 }
5590 #endif
5591 
5592 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5593    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5594           "missing Printezis mark?");
5595   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5596   size_t size = pointer_delta(nextOneAddr + 1, addr);
5597   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5598          "alignment problem");
5599   assert(size >= 3, "Necessary for Printezis marks to work");
5600   return size;
5601 }
5602 
5603 // A variant of the above (block_size_using_printezis_bits()) except
5604 // that we return 0 if the P-bits are not yet set.
5605 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5606   if (_markBitMap.isMarked(addr + 1)) {
5607     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5608     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5609     size_t size = pointer_delta(nextOneAddr + 1, addr);
5610     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5611            "alignment problem");
5612     assert(size >= 3, "Necessary for Printezis marks to work");
5613     return size;
5614   }
5615   return 0;
5616 }
5617 
5618 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5619   size_t sz = 0;
5620   oop p = (oop)addr;
5621   if (p->klass_or_null_acquire() != NULL) {
5622     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5623   } else {
5624     sz = block_size_using_printezis_bits(addr);
5625   }
5626   assert(sz > 0, "size must be nonzero");
5627   HeapWord* next_block = addr + sz;
5628   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5629                                              CardTableModRefBS::card_size);
5630   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5631          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5632          "must be different cards");
5633   return next_card;
5634 }
5635 
5636 
5637 // CMS Bit Map Wrapper /////////////////////////////////////////
5638 
5639 // Construct a CMS bit map infrastructure, but don't create the
5640 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5641 // further below.
5642 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5643   _bm(),
5644   _shifter(shifter),
5645   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5646                                     Monitor::_safepoint_check_sometimes) : NULL)
5647 {
5648   _bmStartWord = 0;
5649   _bmWordSize  = 0;
5650 }
5651 
5652 bool CMSBitMap::allocate(MemRegion mr) {
5653   _bmStartWord = mr.start();
5654   _bmWordSize  = mr.word_size();
5655   ReservedSpace brs(ReservedSpace::allocation_align_up(
5656                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5657   if (!brs.is_reserved()) {
5658     log_warning(gc)("CMS bit map allocation failure");
5659     return false;
5660   }
5661   // For now we'll just commit all of the bit map up front.
5662   // Later on we'll try to be more parsimonious with swap.
5663   if (!_virtual_space.initialize(brs, brs.size())) {
5664     log_warning(gc)("CMS bit map backing store failure");
5665     return false;
5666   }
5667   assert(_virtual_space.committed_size() == brs.size(),
5668          "didn't reserve backing store for all of CMS bit map?");
5669   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5670          _bmWordSize, "inconsistency in bit map sizing");
5671   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5672 
5673   // bm.clear(); // can we rely on getting zero'd memory? verify below
5674   assert(isAllClear(),
5675          "Expected zero'd memory from ReservedSpace constructor");
5676   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5677          "consistency check");
5678   return true;
5679 }
5680 
5681 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5682   HeapWord *next_addr, *end_addr, *last_addr;
5683   assert_locked();
5684   assert(covers(mr), "out-of-range error");
5685   // XXX assert that start and end are appropriately aligned
5686   for (next_addr = mr.start(), end_addr = mr.end();
5687        next_addr < end_addr; next_addr = last_addr) {
5688     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5689     last_addr = dirty_region.end();
5690     if (!dirty_region.is_empty()) {
5691       cl->do_MemRegion(dirty_region);
5692     } else {
5693       assert(last_addr == end_addr, "program logic");
5694       return;
5695     }
5696   }
5697 }
5698 
5699 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5700   _bm.print_on_error(st, prefix);
5701 }
5702 
5703 #ifndef PRODUCT
5704 void CMSBitMap::assert_locked() const {
5705   CMSLockVerifier::assert_locked(lock());
5706 }
5707 
5708 bool CMSBitMap::covers(MemRegion mr) const {
5709   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5710   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5711          "size inconsistency");
5712   return (mr.start() >= _bmStartWord) &&
5713          (mr.end()   <= endWord());
5714 }
5715 
5716 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5717     return (start >= _bmStartWord && (start + size) <= endWord());
5718 }
5719 
5720 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5721   // verify that there are no 1 bits in the interval [left, right)
5722   FalseBitMapClosure falseBitMapClosure;
5723   iterate(&falseBitMapClosure, left, right);
5724 }
5725 
5726 void CMSBitMap::region_invariant(MemRegion mr)
5727 {
5728   assert_locked();
5729   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5730   assert(!mr.is_empty(), "unexpected empty region");
5731   assert(covers(mr), "mr should be covered by bit map");
5732   // convert address range into offset range
5733   size_t start_ofs = heapWordToOffset(mr.start());
5734   // Make sure that end() is appropriately aligned
5735   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5736                         (1 << (_shifter+LogHeapWordSize))),
5737          "Misaligned mr.end()");
5738   size_t end_ofs   = heapWordToOffset(mr.end());
5739   assert(end_ofs > start_ofs, "Should mark at least one bit");
5740 }
5741 
5742 #endif
5743 
5744 bool CMSMarkStack::allocate(size_t size) {
5745   // allocate a stack of the requisite depth
5746   ReservedSpace rs(ReservedSpace::allocation_align_up(
5747                    size * sizeof(oop)));
5748   if (!rs.is_reserved()) {
5749     log_warning(gc)("CMSMarkStack allocation failure");
5750     return false;
5751   }
5752   if (!_virtual_space.initialize(rs, rs.size())) {
5753     log_warning(gc)("CMSMarkStack backing store failure");
5754     return false;
5755   }
5756   assert(_virtual_space.committed_size() == rs.size(),
5757          "didn't reserve backing store for all of CMS stack?");
5758   _base = (oop*)(_virtual_space.low());
5759   _index = 0;
5760   _capacity = size;
5761   NOT_PRODUCT(_max_depth = 0);
5762   return true;
5763 }
5764 
5765 // XXX FIX ME !!! In the MT case we come in here holding a
5766 // leaf lock. For printing we need to take a further lock
5767 // which has lower rank. We need to recalibrate the two
5768 // lock-ranks involved in order to be able to print the
5769 // messages below. (Or defer the printing to the caller.
5770 // For now we take the expedient path of just disabling the
5771 // messages for the problematic case.)
5772 void CMSMarkStack::expand() {
5773   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5774   if (_capacity == MarkStackSizeMax) {
5775     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5776       // We print a warning message only once per CMS cycle.
5777       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5778     }
5779     return;
5780   }
5781   // Double capacity if possible
5782   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5783   // Do not give up existing stack until we have managed to
5784   // get the double capacity that we desired.
5785   ReservedSpace rs(ReservedSpace::allocation_align_up(
5786                    new_capacity * sizeof(oop)));
5787   if (rs.is_reserved()) {
5788     // Release the backing store associated with old stack
5789     _virtual_space.release();
5790     // Reinitialize virtual space for new stack
5791     if (!_virtual_space.initialize(rs, rs.size())) {
5792       fatal("Not enough swap for expanded marking stack");
5793     }
5794     _base = (oop*)(_virtual_space.low());
5795     _index = 0;
5796     _capacity = new_capacity;
5797   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5798     // Failed to double capacity, continue;
5799     // we print a detail message only once per CMS cycle.
5800     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5801                         _capacity / K, new_capacity / K);
5802   }
5803 }
5804 
5805 
5806 // Closures
5807 // XXX: there seems to be a lot of code  duplication here;
5808 // should refactor and consolidate common code.
5809 
5810 // This closure is used to mark refs into the CMS generation in
5811 // the CMS bit map. Called at the first checkpoint. This closure
5812 // assumes that we do not need to re-mark dirty cards; if the CMS
5813 // generation on which this is used is not an oldest
5814 // generation then this will lose younger_gen cards!
5815 
5816 MarkRefsIntoClosure::MarkRefsIntoClosure(
5817   MemRegion span, CMSBitMap* bitMap):
5818     _span(span),
5819     _bitMap(bitMap)
5820 {
5821   assert(ref_processor() == NULL, "deliberately left NULL");
5822   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5823 }
5824 
5825 void MarkRefsIntoClosure::do_oop(oop obj) {
5826   // if p points into _span, then mark corresponding bit in _markBitMap
5827   assert(obj->is_oop(), "expected an oop");
5828   HeapWord* addr = (HeapWord*)obj;
5829   if (_span.contains(addr)) {
5830     // this should be made more efficient
5831     _bitMap->mark(addr);
5832   }
5833 }
5834 
5835 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5836 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5837 
5838 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5839   MemRegion span, CMSBitMap* bitMap):
5840     _span(span),
5841     _bitMap(bitMap)
5842 {
5843   assert(ref_processor() == NULL, "deliberately left NULL");
5844   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5845 }
5846 
5847 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5848   // if p points into _span, then mark corresponding bit in _markBitMap
5849   assert(obj->is_oop(), "expected an oop");
5850   HeapWord* addr = (HeapWord*)obj;
5851   if (_span.contains(addr)) {
5852     // this should be made more efficient
5853     _bitMap->par_mark(addr);
5854   }
5855 }
5856 
5857 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5858 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5859 
5860 // A variant of the above, used for CMS marking verification.
5861 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5862   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5863     _span(span),
5864     _verification_bm(verification_bm),
5865     _cms_bm(cms_bm)
5866 {
5867   assert(ref_processor() == NULL, "deliberately left NULL");
5868   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5869 }
5870 
5871 void MarkRefsIntoVerifyClosure::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     _verification_bm->mark(addr);
5877     if (!_cms_bm->isMarked(addr)) {
5878       Log(gc, verify) log;
5879       ResourceMark rm;
5880       oop(addr)->print_on(log.error_stream());
5881       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5882       fatal("... aborting");
5883     }
5884   }
5885 }
5886 
5887 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5888 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5889 
5890 //////////////////////////////////////////////////
5891 // MarkRefsIntoAndScanClosure
5892 //////////////////////////////////////////////////
5893 
5894 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5895                                                        ReferenceProcessor* rp,
5896                                                        CMSBitMap* bit_map,
5897                                                        CMSBitMap* mod_union_table,
5898                                                        CMSMarkStack*  mark_stack,
5899                                                        CMSCollector* collector,
5900                                                        bool should_yield,
5901                                                        bool concurrent_precleaning):
5902   _collector(collector),
5903   _span(span),
5904   _bit_map(bit_map),
5905   _mark_stack(mark_stack),
5906   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5907                       mark_stack, concurrent_precleaning),
5908   _yield(should_yield),
5909   _concurrent_precleaning(concurrent_precleaning),
5910   _freelistLock(NULL)
5911 {
5912   // FIXME: Should initialize in base class constructor.
5913   assert(rp != NULL, "ref_processor shouldn't be NULL");
5914   set_ref_processor_internal(rp);
5915 }
5916 
5917 // This closure is used to mark refs into the CMS generation at the
5918 // second (final) checkpoint, and to scan and transitively follow
5919 // the unmarked oops. It is also used during the concurrent precleaning
5920 // phase while scanning objects on dirty cards in the CMS generation.
5921 // The marks are made in the marking bit map and the marking stack is
5922 // used for keeping the (newly) grey objects during the scan.
5923 // The parallel version (Par_...) appears further below.
5924 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5925   if (obj != NULL) {
5926     assert(obj->is_oop(), "expected an oop");
5927     HeapWord* addr = (HeapWord*)obj;
5928     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5929     assert(_collector->overflow_list_is_empty(),
5930            "overflow list should be empty");
5931     if (_span.contains(addr) &&
5932         !_bit_map->isMarked(addr)) {
5933       // mark bit map (object is now grey)
5934       _bit_map->mark(addr);
5935       // push on marking stack (stack should be empty), and drain the
5936       // stack by applying this closure to the oops in the oops popped
5937       // from the stack (i.e. blacken the grey objects)
5938       bool res = _mark_stack->push(obj);
5939       assert(res, "Should have space to push on empty stack");
5940       do {
5941         oop new_oop = _mark_stack->pop();
5942         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5943         assert(_bit_map->isMarked((HeapWord*)new_oop),
5944                "only grey objects on this stack");
5945         // iterate over the oops in this oop, marking and pushing
5946         // the ones in CMS heap (i.e. in _span).
5947         new_oop->oop_iterate(&_pushAndMarkClosure);
5948         // check if it's time to yield
5949         do_yield_check();
5950       } while (!_mark_stack->isEmpty() ||
5951                (!_concurrent_precleaning && take_from_overflow_list()));
5952         // if marking stack is empty, and we are not doing this
5953         // during precleaning, then check the overflow list
5954     }
5955     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5956     assert(_collector->overflow_list_is_empty(),
5957            "overflow list was drained above");
5958 
5959     assert(_collector->no_preserved_marks(),
5960            "All preserved marks should have been restored above");
5961   }
5962 }
5963 
5964 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5965 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5966 
5967 void MarkRefsIntoAndScanClosure::do_yield_work() {
5968   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5969          "CMS thread should hold CMS token");
5970   assert_lock_strong(_freelistLock);
5971   assert_lock_strong(_bit_map->lock());
5972   // relinquish the free_list_lock and bitMaplock()
5973   _bit_map->lock()->unlock();
5974   _freelistLock->unlock();
5975   ConcurrentMarkSweepThread::desynchronize(true);
5976   _collector->stopTimer();
5977   _collector->incrementYields();
5978 
5979   // See the comment in coordinator_yield()
5980   for (unsigned i = 0;
5981        i < CMSYieldSleepCount &&
5982        ConcurrentMarkSweepThread::should_yield() &&
5983        !CMSCollector::foregroundGCIsActive();
5984        ++i) {
5985     os::sleep(Thread::current(), 1, false);
5986   }
5987 
5988   ConcurrentMarkSweepThread::synchronize(true);
5989   _freelistLock->lock_without_safepoint_check();
5990   _bit_map->lock()->lock_without_safepoint_check();
5991   _collector->startTimer();
5992 }
5993 
5994 ///////////////////////////////////////////////////////////
5995 // ParMarkRefsIntoAndScanClosure: a parallel version of
5996 //                                MarkRefsIntoAndScanClosure
5997 ///////////////////////////////////////////////////////////
5998 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
5999   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6000   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6001   _span(span),
6002   _bit_map(bit_map),
6003   _work_queue(work_queue),
6004   _low_water_mark(MIN2((work_queue->max_elems()/4),
6005                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6006   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6007 {
6008   // FIXME: Should initialize in base class constructor.
6009   assert(rp != NULL, "ref_processor shouldn't be NULL");
6010   set_ref_processor_internal(rp);
6011 }
6012 
6013 // This closure is used to mark refs into the CMS generation at the
6014 // second (final) checkpoint, and to scan and transitively follow
6015 // the unmarked oops. The marks are made in the marking bit map and
6016 // the work_queue is used for keeping the (newly) grey objects during
6017 // the scan phase whence they are also available for stealing by parallel
6018 // threads. Since the marking bit map is shared, updates are
6019 // synchronized (via CAS).
6020 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6021   if (obj != NULL) {
6022     // Ignore mark word because this could be an already marked oop
6023     // that may be chained at the end of the overflow list.
6024     assert(obj->is_oop(true), "expected an oop");
6025     HeapWord* addr = (HeapWord*)obj;
6026     if (_span.contains(addr) &&
6027         !_bit_map->isMarked(addr)) {
6028       // mark bit map (object will become grey):
6029       // It is possible for several threads to be
6030       // trying to "claim" this object concurrently;
6031       // the unique thread that succeeds in marking the
6032       // object first will do the subsequent push on
6033       // to the work queue (or overflow list).
6034       if (_bit_map->par_mark(addr)) {
6035         // push on work_queue (which may not be empty), and trim the
6036         // queue to an appropriate length by applying this closure to
6037         // the oops in the oops popped from the stack (i.e. blacken the
6038         // grey objects)
6039         bool res = _work_queue->push(obj);
6040         assert(res, "Low water mark should be less than capacity?");
6041         trim_queue(_low_water_mark);
6042       } // Else, another thread claimed the object
6043     }
6044   }
6045 }
6046 
6047 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p)       { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6048 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6049 
6050 // This closure is used to rescan the marked objects on the dirty cards
6051 // in the mod union table and the card table proper.
6052 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6053   oop p, MemRegion mr) {
6054 
6055   size_t size = 0;
6056   HeapWord* addr = (HeapWord*)p;
6057   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6058   assert(_span.contains(addr), "we are scanning the CMS generation");
6059   // check if it's time to yield
6060   if (do_yield_check()) {
6061     // We yielded for some foreground stop-world work,
6062     // and we have been asked to abort this ongoing preclean cycle.
6063     return 0;
6064   }
6065   if (_bitMap->isMarked(addr)) {
6066     // it's marked; is it potentially uninitialized?
6067     if (p->klass_or_null_acquire() != NULL) {
6068         // an initialized object; ignore mark word in verification below
6069         // since we are running concurrent with mutators
6070         assert(p->is_oop(true), "should be an oop");
6071         if (p->is_objArray()) {
6072           // objArrays are precisely marked; restrict scanning
6073           // to dirty cards only.
6074           size = CompactibleFreeListSpace::adjustObjectSize(
6075                    p->oop_iterate_size(_scanningClosure, mr));
6076         } else {
6077           // A non-array may have been imprecisely marked; we need
6078           // to scan object in its entirety.
6079           size = CompactibleFreeListSpace::adjustObjectSize(
6080                    p->oop_iterate_size(_scanningClosure));
6081         }
6082       #ifdef ASSERT
6083         size_t direct_size =
6084           CompactibleFreeListSpace::adjustObjectSize(p->size());
6085         assert(size == direct_size, "Inconsistency in size");
6086         assert(size >= 3, "Necessary for Printezis marks to work");
6087         HeapWord* start_pbit = addr + 1;
6088         HeapWord* end_pbit = addr + size - 1;
6089         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6090                "inconsistent Printezis mark");
6091         // Verify inner mark bits (between Printezis bits) are clear,
6092         // but don't repeat if there are multiple dirty regions for
6093         // the same object, to avoid potential O(N^2) performance.
6094         if (addr != _last_scanned_object) {
6095           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6096           _last_scanned_object = addr;
6097         }
6098       #endif // ASSERT
6099     } else {
6100       // An uninitialized object.
6101       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6102       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6103       size = pointer_delta(nextOneAddr + 1, addr);
6104       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6105              "alignment problem");
6106       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6107       // will dirty the card when the klass pointer is installed in the
6108       // object (signaling the completion of initialization).
6109     }
6110   } else {
6111     // Either a not yet marked object or an uninitialized object
6112     if (p->klass_or_null_acquire() == NULL) {
6113       // An uninitialized object, skip to the next card, since
6114       // we may not be able to read its P-bits yet.
6115       assert(size == 0, "Initial value");
6116     } else {
6117       // An object not (yet) reached by marking: we merely need to
6118       // compute its size so as to go look at the next block.
6119       assert(p->is_oop(true), "should be an oop");
6120       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6121     }
6122   }
6123   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6124   return size;
6125 }
6126 
6127 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6128   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6129          "CMS thread should hold CMS token");
6130   assert_lock_strong(_freelistLock);
6131   assert_lock_strong(_bitMap->lock());
6132   // relinquish the free_list_lock and bitMaplock()
6133   _bitMap->lock()->unlock();
6134   _freelistLock->unlock();
6135   ConcurrentMarkSweepThread::desynchronize(true);
6136   _collector->stopTimer();
6137   _collector->incrementYields();
6138 
6139   // See the comment in coordinator_yield()
6140   for (unsigned i = 0; i < CMSYieldSleepCount &&
6141                    ConcurrentMarkSweepThread::should_yield() &&
6142                    !CMSCollector::foregroundGCIsActive(); ++i) {
6143     os::sleep(Thread::current(), 1, false);
6144   }
6145 
6146   ConcurrentMarkSweepThread::synchronize(true);
6147   _freelistLock->lock_without_safepoint_check();
6148   _bitMap->lock()->lock_without_safepoint_check();
6149   _collector->startTimer();
6150 }
6151 
6152 
6153 //////////////////////////////////////////////////////////////////
6154 // SurvivorSpacePrecleanClosure
6155 //////////////////////////////////////////////////////////////////
6156 // This (single-threaded) closure is used to preclean the oops in
6157 // the survivor spaces.
6158 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6159 
6160   HeapWord* addr = (HeapWord*)p;
6161   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6162   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6163   assert(p->klass_or_null() != NULL, "object should be initialized");
6164   // an initialized object; ignore mark word in verification below
6165   // since we are running concurrent with mutators
6166   assert(p->is_oop(true), "should be an oop");
6167   // Note that we do not yield while we iterate over
6168   // the interior oops of p, pushing the relevant ones
6169   // on our marking stack.
6170   size_t size = p->oop_iterate_size(_scanning_closure);
6171   do_yield_check();
6172   // Observe that below, we do not abandon the preclean
6173   // phase as soon as we should; rather we empty the
6174   // marking stack before returning. This is to satisfy
6175   // some existing assertions. In general, it may be a
6176   // good idea to abort immediately and complete the marking
6177   // from the grey objects at a later time.
6178   while (!_mark_stack->isEmpty()) {
6179     oop new_oop = _mark_stack->pop();
6180     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6181     assert(_bit_map->isMarked((HeapWord*)new_oop),
6182            "only grey objects on this stack");
6183     // iterate over the oops in this oop, marking and pushing
6184     // the ones in CMS heap (i.e. in _span).
6185     new_oop->oop_iterate(_scanning_closure);
6186     // check if it's time to yield
6187     do_yield_check();
6188   }
6189   unsigned int after_count =
6190     GenCollectedHeap::heap()->total_collections();
6191   bool abort = (_before_count != after_count) ||
6192                _collector->should_abort_preclean();
6193   return abort ? 0 : size;
6194 }
6195 
6196 void SurvivorSpacePrecleanClosure::do_yield_work() {
6197   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6198          "CMS thread should hold CMS token");
6199   assert_lock_strong(_bit_map->lock());
6200   // Relinquish the bit map lock
6201   _bit_map->lock()->unlock();
6202   ConcurrentMarkSweepThread::desynchronize(true);
6203   _collector->stopTimer();
6204   _collector->incrementYields();
6205 
6206   // See the comment in coordinator_yield()
6207   for (unsigned i = 0; i < CMSYieldSleepCount &&
6208                        ConcurrentMarkSweepThread::should_yield() &&
6209                        !CMSCollector::foregroundGCIsActive(); ++i) {
6210     os::sleep(Thread::current(), 1, false);
6211   }
6212 
6213   ConcurrentMarkSweepThread::synchronize(true);
6214   _bit_map->lock()->lock_without_safepoint_check();
6215   _collector->startTimer();
6216 }
6217 
6218 // This closure is used to rescan the marked objects on the dirty cards
6219 // in the mod union table and the card table proper. In the parallel
6220 // case, although the bitMap is shared, we do a single read so the
6221 // isMarked() query is "safe".
6222 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6223   // Ignore mark word because we are running concurrent with mutators
6224   assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6225   HeapWord* addr = (HeapWord*)p;
6226   assert(_span.contains(addr), "we are scanning the CMS generation");
6227   bool is_obj_array = false;
6228   #ifdef ASSERT
6229     if (!_parallel) {
6230       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6231       assert(_collector->overflow_list_is_empty(),
6232              "overflow list should be empty");
6233 
6234     }
6235   #endif // ASSERT
6236   if (_bit_map->isMarked(addr)) {
6237     // Obj arrays are precisely marked, non-arrays are not;
6238     // so we scan objArrays precisely and non-arrays in their
6239     // entirety.
6240     if (p->is_objArray()) {
6241       is_obj_array = true;
6242       if (_parallel) {
6243         p->oop_iterate(_par_scan_closure, mr);
6244       } else {
6245         p->oop_iterate(_scan_closure, mr);
6246       }
6247     } else {
6248       if (_parallel) {
6249         p->oop_iterate(_par_scan_closure);
6250       } else {
6251         p->oop_iterate(_scan_closure);
6252       }
6253     }
6254   }
6255   #ifdef ASSERT
6256     if (!_parallel) {
6257       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6258       assert(_collector->overflow_list_is_empty(),
6259              "overflow list should be empty");
6260 
6261     }
6262   #endif // ASSERT
6263   return is_obj_array;
6264 }
6265 
6266 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6267                         MemRegion span,
6268                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6269                         bool should_yield, bool verifying):
6270   _collector(collector),
6271   _span(span),
6272   _bitMap(bitMap),
6273   _mut(&collector->_modUnionTable),
6274   _markStack(markStack),
6275   _yield(should_yield),
6276   _skipBits(0)
6277 {
6278   assert(_markStack->isEmpty(), "stack should be empty");
6279   _finger = _bitMap->startWord();
6280   _threshold = _finger;
6281   assert(_collector->_restart_addr == NULL, "Sanity check");
6282   assert(_span.contains(_finger), "Out of bounds _finger?");
6283   DEBUG_ONLY(_verifying = verifying;)
6284 }
6285 
6286 void MarkFromRootsClosure::reset(HeapWord* addr) {
6287   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6288   assert(_span.contains(addr), "Out of bounds _finger?");
6289   _finger = addr;
6290   _threshold = (HeapWord*)round_to(
6291                  (intptr_t)_finger, CardTableModRefBS::card_size);
6292 }
6293 
6294 // Should revisit to see if this should be restructured for
6295 // greater efficiency.
6296 bool MarkFromRootsClosure::do_bit(size_t offset) {
6297   if (_skipBits > 0) {
6298     _skipBits--;
6299     return true;
6300   }
6301   // convert offset into a HeapWord*
6302   HeapWord* addr = _bitMap->startWord() + offset;
6303   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6304          "address out of range");
6305   assert(_bitMap->isMarked(addr), "tautology");
6306   if (_bitMap->isMarked(addr+1)) {
6307     // this is an allocated but not yet initialized object
6308     assert(_skipBits == 0, "tautology");
6309     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6310     oop p = oop(addr);
6311     if (p->klass_or_null_acquire() == NULL) {
6312       DEBUG_ONLY(if (!_verifying) {)
6313         // We re-dirty the cards on which this object lies and increase
6314         // the _threshold so that we'll come back to scan this object
6315         // during the preclean or remark phase. (CMSCleanOnEnter)
6316         if (CMSCleanOnEnter) {
6317           size_t sz = _collector->block_size_using_printezis_bits(addr);
6318           HeapWord* end_card_addr   = (HeapWord*)round_to(
6319                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6320           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6321           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6322           // Bump _threshold to end_card_addr; note that
6323           // _threshold cannot possibly exceed end_card_addr, anyhow.
6324           // This prevents future clearing of the card as the scan proceeds
6325           // to the right.
6326           assert(_threshold <= end_card_addr,
6327                  "Because we are just scanning into this object");
6328           if (_threshold < end_card_addr) {
6329             _threshold = end_card_addr;
6330           }
6331           if (p->klass_or_null_acquire() != NULL) {
6332             // Redirty the range of cards...
6333             _mut->mark_range(redirty_range);
6334           } // ...else the setting of klass will dirty the card anyway.
6335         }
6336       DEBUG_ONLY(})
6337       return true;
6338     }
6339   }
6340   scanOopsInOop(addr);
6341   return true;
6342 }
6343 
6344 // We take a break if we've been at this for a while,
6345 // so as to avoid monopolizing the locks involved.
6346 void MarkFromRootsClosure::do_yield_work() {
6347   // First give up the locks, then yield, then re-lock
6348   // We should probably use a constructor/destructor idiom to
6349   // do this unlock/lock or modify the MutexUnlocker class to
6350   // serve our purpose. XXX
6351   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6352          "CMS thread should hold CMS token");
6353   assert_lock_strong(_bitMap->lock());
6354   _bitMap->lock()->unlock();
6355   ConcurrentMarkSweepThread::desynchronize(true);
6356   _collector->stopTimer();
6357   _collector->incrementYields();
6358 
6359   // See the comment in coordinator_yield()
6360   for (unsigned i = 0; i < CMSYieldSleepCount &&
6361                        ConcurrentMarkSweepThread::should_yield() &&
6362                        !CMSCollector::foregroundGCIsActive(); ++i) {
6363     os::sleep(Thread::current(), 1, false);
6364   }
6365 
6366   ConcurrentMarkSweepThread::synchronize(true);
6367   _bitMap->lock()->lock_without_safepoint_check();
6368   _collector->startTimer();
6369 }
6370 
6371 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6372   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6373   assert(_markStack->isEmpty(),
6374          "should drain stack to limit stack usage");
6375   // convert ptr to an oop preparatory to scanning
6376   oop obj = oop(ptr);
6377   // Ignore mark word in verification below, since we
6378   // may be running concurrent with mutators.
6379   assert(obj->is_oop(true), "should be an oop");
6380   assert(_finger <= ptr, "_finger runneth ahead");
6381   // advance the finger to right end of this object
6382   _finger = ptr + obj->size();
6383   assert(_finger > ptr, "we just incremented it above");
6384   // On large heaps, it may take us some time to get through
6385   // the marking phase. During
6386   // this time it's possible that a lot of mutations have
6387   // accumulated in the card table and the mod union table --
6388   // these mutation records are redundant until we have
6389   // actually traced into the corresponding card.
6390   // Here, we check whether advancing the finger would make
6391   // us cross into a new card, and if so clear corresponding
6392   // cards in the MUT (preclean them in the card-table in the
6393   // future).
6394 
6395   DEBUG_ONLY(if (!_verifying) {)
6396     // The clean-on-enter optimization is disabled by default,
6397     // until we fix 6178663.
6398     if (CMSCleanOnEnter && (_finger > _threshold)) {
6399       // [_threshold, _finger) represents the interval
6400       // of cards to be cleared  in MUT (or precleaned in card table).
6401       // The set of cards to be cleared is all those that overlap
6402       // with the interval [_threshold, _finger); note that
6403       // _threshold is always kept card-aligned but _finger isn't
6404       // always card-aligned.
6405       HeapWord* old_threshold = _threshold;
6406       assert(old_threshold == (HeapWord*)round_to(
6407               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6408              "_threshold should always be card-aligned");
6409       _threshold = (HeapWord*)round_to(
6410                      (intptr_t)_finger, CardTableModRefBS::card_size);
6411       MemRegion mr(old_threshold, _threshold);
6412       assert(!mr.is_empty(), "Control point invariant");
6413       assert(_span.contains(mr), "Should clear within span");
6414       _mut->clear_range(mr);
6415     }
6416   DEBUG_ONLY(})
6417   // Note: the finger doesn't advance while we drain
6418   // the stack below.
6419   PushOrMarkClosure pushOrMarkClosure(_collector,
6420                                       _span, _bitMap, _markStack,
6421                                       _finger, this);
6422   bool res = _markStack->push(obj);
6423   assert(res, "Empty non-zero size stack should have space for single push");
6424   while (!_markStack->isEmpty()) {
6425     oop new_oop = _markStack->pop();
6426     // Skip verifying header mark word below because we are
6427     // running concurrent with mutators.
6428     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6429     // now scan this oop's oops
6430     new_oop->oop_iterate(&pushOrMarkClosure);
6431     do_yield_check();
6432   }
6433   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6434 }
6435 
6436 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6437                        CMSCollector* collector, MemRegion span,
6438                        CMSBitMap* bit_map,
6439                        OopTaskQueue* work_queue,
6440                        CMSMarkStack*  overflow_stack):
6441   _collector(collector),
6442   _whole_span(collector->_span),
6443   _span(span),
6444   _bit_map(bit_map),
6445   _mut(&collector->_modUnionTable),
6446   _work_queue(work_queue),
6447   _overflow_stack(overflow_stack),
6448   _skip_bits(0),
6449   _task(task)
6450 {
6451   assert(_work_queue->size() == 0, "work_queue should be empty");
6452   _finger = span.start();
6453   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6454   assert(_span.contains(_finger), "Out of bounds _finger?");
6455 }
6456 
6457 // Should revisit to see if this should be restructured for
6458 // greater efficiency.
6459 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6460   if (_skip_bits > 0) {
6461     _skip_bits--;
6462     return true;
6463   }
6464   // convert offset into a HeapWord*
6465   HeapWord* addr = _bit_map->startWord() + offset;
6466   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6467          "address out of range");
6468   assert(_bit_map->isMarked(addr), "tautology");
6469   if (_bit_map->isMarked(addr+1)) {
6470     // this is an allocated object that might not yet be initialized
6471     assert(_skip_bits == 0, "tautology");
6472     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6473     oop p = oop(addr);
6474     if (p->klass_or_null_acquire() == NULL) {
6475       // in the case of Clean-on-Enter optimization, redirty card
6476       // and avoid clearing card by increasing  the threshold.
6477       return true;
6478     }
6479   }
6480   scan_oops_in_oop(addr);
6481   return true;
6482 }
6483 
6484 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6485   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6486   // Should we assert that our work queue is empty or
6487   // below some drain limit?
6488   assert(_work_queue->size() == 0,
6489          "should drain stack to limit stack usage");
6490   // convert ptr to an oop preparatory to scanning
6491   oop obj = oop(ptr);
6492   // Ignore mark word in verification below, since we
6493   // may be running concurrent with mutators.
6494   assert(obj->is_oop(true), "should be an oop");
6495   assert(_finger <= ptr, "_finger runneth ahead");
6496   // advance the finger to right end of this object
6497   _finger = ptr + obj->size();
6498   assert(_finger > ptr, "we just incremented it above");
6499   // On large heaps, it may take us some time to get through
6500   // the marking phase. During
6501   // this time it's possible that a lot of mutations have
6502   // accumulated in the card table and the mod union table --
6503   // these mutation records are redundant until we have
6504   // actually traced into the corresponding card.
6505   // Here, we check whether advancing the finger would make
6506   // us cross into a new card, and if so clear corresponding
6507   // cards in the MUT (preclean them in the card-table in the
6508   // future).
6509 
6510   // The clean-on-enter optimization is disabled by default,
6511   // until we fix 6178663.
6512   if (CMSCleanOnEnter && (_finger > _threshold)) {
6513     // [_threshold, _finger) represents the interval
6514     // of cards to be cleared  in MUT (or precleaned in card table).
6515     // The set of cards to be cleared is all those that overlap
6516     // with the interval [_threshold, _finger); note that
6517     // _threshold is always kept card-aligned but _finger isn't
6518     // always card-aligned.
6519     HeapWord* old_threshold = _threshold;
6520     assert(old_threshold == (HeapWord*)round_to(
6521             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6522            "_threshold should always be card-aligned");
6523     _threshold = (HeapWord*)round_to(
6524                    (intptr_t)_finger, CardTableModRefBS::card_size);
6525     MemRegion mr(old_threshold, _threshold);
6526     assert(!mr.is_empty(), "Control point invariant");
6527     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6528     _mut->clear_range(mr);
6529   }
6530 
6531   // Note: the local finger doesn't advance while we drain
6532   // the stack below, but the global finger sure can and will.
6533   HeapWord* volatile* gfa = _task->global_finger_addr();
6534   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6535                                          _span, _bit_map,
6536                                          _work_queue,
6537                                          _overflow_stack,
6538                                          _finger,
6539                                          gfa, this);
6540   bool res = _work_queue->push(obj);   // overflow could occur here
6541   assert(res, "Will hold once we use workqueues");
6542   while (true) {
6543     oop new_oop;
6544     if (!_work_queue->pop_local(new_oop)) {
6545       // We emptied our work_queue; check if there's stuff that can
6546       // be gotten from the overflow stack.
6547       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6548             _overflow_stack, _work_queue)) {
6549         do_yield_check();
6550         continue;
6551       } else {  // done
6552         break;
6553       }
6554     }
6555     // Skip verifying header mark word below because we are
6556     // running concurrent with mutators.
6557     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6558     // now scan this oop's oops
6559     new_oop->oop_iterate(&pushOrMarkClosure);
6560     do_yield_check();
6561   }
6562   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6563 }
6564 
6565 // Yield in response to a request from VM Thread or
6566 // from mutators.
6567 void ParMarkFromRootsClosure::do_yield_work() {
6568   assert(_task != NULL, "sanity");
6569   _task->yield();
6570 }
6571 
6572 // A variant of the above used for verifying CMS marking work.
6573 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6574                         MemRegion span,
6575                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6576                         CMSMarkStack*  mark_stack):
6577   _collector(collector),
6578   _span(span),
6579   _verification_bm(verification_bm),
6580   _cms_bm(cms_bm),
6581   _mark_stack(mark_stack),
6582   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6583                       mark_stack)
6584 {
6585   assert(_mark_stack->isEmpty(), "stack should be empty");
6586   _finger = _verification_bm->startWord();
6587   assert(_collector->_restart_addr == NULL, "Sanity check");
6588   assert(_span.contains(_finger), "Out of bounds _finger?");
6589 }
6590 
6591 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6592   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6593   assert(_span.contains(addr), "Out of bounds _finger?");
6594   _finger = addr;
6595 }
6596 
6597 // Should revisit to see if this should be restructured for
6598 // greater efficiency.
6599 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6600   // convert offset into a HeapWord*
6601   HeapWord* addr = _verification_bm->startWord() + offset;
6602   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6603          "address out of range");
6604   assert(_verification_bm->isMarked(addr), "tautology");
6605   assert(_cms_bm->isMarked(addr), "tautology");
6606 
6607   assert(_mark_stack->isEmpty(),
6608          "should drain stack to limit stack usage");
6609   // convert addr to an oop preparatory to scanning
6610   oop obj = oop(addr);
6611   assert(obj->is_oop(), "should be an oop");
6612   assert(_finger <= addr, "_finger runneth ahead");
6613   // advance the finger to right end of this object
6614   _finger = addr + obj->size();
6615   assert(_finger > addr, "we just incremented it above");
6616   // Note: the finger doesn't advance while we drain
6617   // the stack below.
6618   bool res = _mark_stack->push(obj);
6619   assert(res, "Empty non-zero size stack should have space for single push");
6620   while (!_mark_stack->isEmpty()) {
6621     oop new_oop = _mark_stack->pop();
6622     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6623     // now scan this oop's oops
6624     new_oop->oop_iterate(&_pam_verify_closure);
6625   }
6626   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6627   return true;
6628 }
6629 
6630 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6631   CMSCollector* collector, MemRegion span,
6632   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6633   CMSMarkStack*  mark_stack):
6634   MetadataAwareOopClosure(collector->ref_processor()),
6635   _collector(collector),
6636   _span(span),
6637   _verification_bm(verification_bm),
6638   _cms_bm(cms_bm),
6639   _mark_stack(mark_stack)
6640 { }
6641 
6642 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6643 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6644 
6645 // Upon stack overflow, we discard (part of) the stack,
6646 // remembering the least address amongst those discarded
6647 // in CMSCollector's _restart_address.
6648 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6649   // Remember the least grey address discarded
6650   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6651   _collector->lower_restart_addr(ra);
6652   _mark_stack->reset();  // discard stack contents
6653   _mark_stack->expand(); // expand the stack if possible
6654 }
6655 
6656 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6657   assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6658   HeapWord* addr = (HeapWord*)obj;
6659   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6660     // Oop lies in _span and isn't yet grey or black
6661     _verification_bm->mark(addr);            // now grey
6662     if (!_cms_bm->isMarked(addr)) {
6663       Log(gc, verify) log;
6664       ResourceMark rm;
6665       oop(addr)->print_on(log.error_stream());
6666       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6667       fatal("... aborting");
6668     }
6669 
6670     if (!_mark_stack->push(obj)) { // stack overflow
6671       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6672       assert(_mark_stack->isFull(), "Else push should have succeeded");
6673       handle_stack_overflow(addr);
6674     }
6675     // anything including and to the right of _finger
6676     // will be scanned as we iterate over the remainder of the
6677     // bit map
6678   }
6679 }
6680 
6681 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6682                      MemRegion span,
6683                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6684                      HeapWord* finger, MarkFromRootsClosure* parent) :
6685   MetadataAwareOopClosure(collector->ref_processor()),
6686   _collector(collector),
6687   _span(span),
6688   _bitMap(bitMap),
6689   _markStack(markStack),
6690   _finger(finger),
6691   _parent(parent)
6692 { }
6693 
6694 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6695                                            MemRegion span,
6696                                            CMSBitMap* bit_map,
6697                                            OopTaskQueue* work_queue,
6698                                            CMSMarkStack*  overflow_stack,
6699                                            HeapWord* finger,
6700                                            HeapWord* volatile* global_finger_addr,
6701                                            ParMarkFromRootsClosure* parent) :
6702   MetadataAwareOopClosure(collector->ref_processor()),
6703   _collector(collector),
6704   _whole_span(collector->_span),
6705   _span(span),
6706   _bit_map(bit_map),
6707   _work_queue(work_queue),
6708   _overflow_stack(overflow_stack),
6709   _finger(finger),
6710   _global_finger_addr(global_finger_addr),
6711   _parent(parent)
6712 { }
6713 
6714 // Assumes thread-safe access by callers, who are
6715 // responsible for mutual exclusion.
6716 void CMSCollector::lower_restart_addr(HeapWord* low) {
6717   assert(_span.contains(low), "Out of bounds addr");
6718   if (_restart_addr == NULL) {
6719     _restart_addr = low;
6720   } else {
6721     _restart_addr = MIN2(_restart_addr, low);
6722   }
6723 }
6724 
6725 // Upon stack overflow, we discard (part of) the stack,
6726 // remembering the least address amongst those discarded
6727 // in CMSCollector's _restart_address.
6728 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6729   // Remember the least grey address discarded
6730   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6731   _collector->lower_restart_addr(ra);
6732   _markStack->reset();  // discard stack contents
6733   _markStack->expand(); // expand the stack if possible
6734 }
6735 
6736 // Upon stack overflow, we discard (part of) the stack,
6737 // remembering the least address amongst those discarded
6738 // in CMSCollector's _restart_address.
6739 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6740   // We need to do this under a mutex to prevent other
6741   // workers from interfering with the work done below.
6742   MutexLockerEx ml(_overflow_stack->par_lock(),
6743                    Mutex::_no_safepoint_check_flag);
6744   // Remember the least grey address discarded
6745   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6746   _collector->lower_restart_addr(ra);
6747   _overflow_stack->reset();  // discard stack contents
6748   _overflow_stack->expand(); // expand the stack if possible
6749 }
6750 
6751 void PushOrMarkClosure::do_oop(oop obj) {
6752   // Ignore mark word because we are running concurrent with mutators.
6753   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6754   HeapWord* addr = (HeapWord*)obj;
6755   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6756     // Oop lies in _span and isn't yet grey or black
6757     _bitMap->mark(addr);            // now grey
6758     if (addr < _finger) {
6759       // the bit map iteration has already either passed, or
6760       // sampled, this bit in the bit map; we'll need to
6761       // use the marking stack to scan this oop's oops.
6762       bool simulate_overflow = false;
6763       NOT_PRODUCT(
6764         if (CMSMarkStackOverflowALot &&
6765             _collector->simulate_overflow()) {
6766           // simulate a stack overflow
6767           simulate_overflow = true;
6768         }
6769       )
6770       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6771         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6772         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6773         handle_stack_overflow(addr);
6774       }
6775     }
6776     // anything including and to the right of _finger
6777     // will be scanned as we iterate over the remainder of the
6778     // bit map
6779     do_yield_check();
6780   }
6781 }
6782 
6783 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6784 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6785 
6786 void ParPushOrMarkClosure::do_oop(oop obj) {
6787   // Ignore mark word because we are running concurrent with mutators.
6788   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6789   HeapWord* addr = (HeapWord*)obj;
6790   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6791     // Oop lies in _span and isn't yet grey or black
6792     // We read the global_finger (volatile read) strictly after marking oop
6793     bool res = _bit_map->par_mark(addr);    // now grey
6794     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6795     // Should we push this marked oop on our stack?
6796     // -- if someone else marked it, nothing to do
6797     // -- if target oop is above global finger nothing to do
6798     // -- if target oop is in chunk and above local finger
6799     //      then nothing to do
6800     // -- else push on work queue
6801     if (   !res       // someone else marked it, they will deal with it
6802         || (addr >= *gfa)  // will be scanned in a later task
6803         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6804       return;
6805     }
6806     // the bit map iteration has already either passed, or
6807     // sampled, this bit in the bit map; we'll need to
6808     // use the marking stack to scan this oop's oops.
6809     bool simulate_overflow = false;
6810     NOT_PRODUCT(
6811       if (CMSMarkStackOverflowALot &&
6812           _collector->simulate_overflow()) {
6813         // simulate a stack overflow
6814         simulate_overflow = true;
6815       }
6816     )
6817     if (simulate_overflow ||
6818         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6819       // stack overflow
6820       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6821       // We cannot assert that the overflow stack is full because
6822       // it may have been emptied since.
6823       assert(simulate_overflow ||
6824              _work_queue->size() == _work_queue->max_elems(),
6825             "Else push should have succeeded");
6826       handle_stack_overflow(addr);
6827     }
6828     do_yield_check();
6829   }
6830 }
6831 
6832 void ParPushOrMarkClosure::do_oop(oop* p)       { ParPushOrMarkClosure::do_oop_work(p); }
6833 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6834 
6835 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6836                                        MemRegion span,
6837                                        ReferenceProcessor* rp,
6838                                        CMSBitMap* bit_map,
6839                                        CMSBitMap* mod_union_table,
6840                                        CMSMarkStack*  mark_stack,
6841                                        bool           concurrent_precleaning):
6842   MetadataAwareOopClosure(rp),
6843   _collector(collector),
6844   _span(span),
6845   _bit_map(bit_map),
6846   _mod_union_table(mod_union_table),
6847   _mark_stack(mark_stack),
6848   _concurrent_precleaning(concurrent_precleaning)
6849 {
6850   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6851 }
6852 
6853 // Grey object rescan during pre-cleaning and second checkpoint phases --
6854 // the non-parallel version (the parallel version appears further below.)
6855 void PushAndMarkClosure::do_oop(oop obj) {
6856   // Ignore mark word verification. If during concurrent precleaning,
6857   // the object monitor may be locked. If during the checkpoint
6858   // phases, the object may already have been reached by a  different
6859   // path and may be at the end of the global overflow list (so
6860   // the mark word may be NULL).
6861   assert(obj->is_oop_or_null(true /* ignore mark word */),
6862          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6863   HeapWord* addr = (HeapWord*)obj;
6864   // Check if oop points into the CMS generation
6865   // and is not marked
6866   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6867     // a white object ...
6868     _bit_map->mark(addr);         // ... now grey
6869     // push on the marking stack (grey set)
6870     bool simulate_overflow = false;
6871     NOT_PRODUCT(
6872       if (CMSMarkStackOverflowALot &&
6873           _collector->simulate_overflow()) {
6874         // simulate a stack overflow
6875         simulate_overflow = true;
6876       }
6877     )
6878     if (simulate_overflow || !_mark_stack->push(obj)) {
6879       if (_concurrent_precleaning) {
6880          // During precleaning we can just dirty the appropriate card(s)
6881          // in the mod union table, thus ensuring that the object remains
6882          // in the grey set  and continue. In the case of object arrays
6883          // we need to dirty all of the cards that the object spans,
6884          // since the rescan of object arrays will be limited to the
6885          // dirty cards.
6886          // Note that no one can be interfering with us in this action
6887          // of dirtying the mod union table, so no locking or atomics
6888          // are required.
6889          if (obj->is_objArray()) {
6890            size_t sz = obj->size();
6891            HeapWord* end_card_addr = (HeapWord*)round_to(
6892                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6893            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6894            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6895            _mod_union_table->mark_range(redirty_range);
6896          } else {
6897            _mod_union_table->mark(addr);
6898          }
6899          _collector->_ser_pmc_preclean_ovflw++;
6900       } else {
6901          // During the remark phase, we need to remember this oop
6902          // in the overflow list.
6903          _collector->push_on_overflow_list(obj);
6904          _collector->_ser_pmc_remark_ovflw++;
6905       }
6906     }
6907   }
6908 }
6909 
6910 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6911                                              MemRegion span,
6912                                              ReferenceProcessor* rp,
6913                                              CMSBitMap* bit_map,
6914                                              OopTaskQueue* work_queue):
6915   MetadataAwareOopClosure(rp),
6916   _collector(collector),
6917   _span(span),
6918   _bit_map(bit_map),
6919   _work_queue(work_queue)
6920 {
6921   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6922 }
6923 
6924 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6925 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6926 
6927 // Grey object rescan during second checkpoint phase --
6928 // the parallel version.
6929 void ParPushAndMarkClosure::do_oop(oop obj) {
6930   // In the assert below, we ignore the mark word because
6931   // this oop may point to an already visited object that is
6932   // on the overflow stack (in which case the mark word has
6933   // been hijacked for chaining into the overflow stack --
6934   // if this is the last object in the overflow stack then
6935   // its mark word will be NULL). Because this object may
6936   // have been subsequently popped off the global overflow
6937   // stack, and the mark word possibly restored to the prototypical
6938   // value, by the time we get to examined this failing assert in
6939   // the debugger, is_oop_or_null(false) may subsequently start
6940   // to hold.
6941   assert(obj->is_oop_or_null(true),
6942          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6943   HeapWord* addr = (HeapWord*)obj;
6944   // Check if oop points into the CMS generation
6945   // and is not marked
6946   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6947     // a white object ...
6948     // If we manage to "claim" the object, by being the
6949     // first thread to mark it, then we push it on our
6950     // marking stack
6951     if (_bit_map->par_mark(addr)) {     // ... now grey
6952       // push on work queue (grey set)
6953       bool simulate_overflow = false;
6954       NOT_PRODUCT(
6955         if (CMSMarkStackOverflowALot &&
6956             _collector->par_simulate_overflow()) {
6957           // simulate a stack overflow
6958           simulate_overflow = true;
6959         }
6960       )
6961       if (simulate_overflow || !_work_queue->push(obj)) {
6962         _collector->par_push_on_overflow_list(obj);
6963         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6964       }
6965     } // Else, some other thread got there first
6966   }
6967 }
6968 
6969 void ParPushAndMarkClosure::do_oop(oop* p)       { ParPushAndMarkClosure::do_oop_work(p); }
6970 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6971 
6972 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6973   Mutex* bml = _collector->bitMapLock();
6974   assert_lock_strong(bml);
6975   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6976          "CMS thread should hold CMS token");
6977 
6978   bml->unlock();
6979   ConcurrentMarkSweepThread::desynchronize(true);
6980 
6981   _collector->stopTimer();
6982   _collector->incrementYields();
6983 
6984   // See the comment in coordinator_yield()
6985   for (unsigned i = 0; i < CMSYieldSleepCount &&
6986                        ConcurrentMarkSweepThread::should_yield() &&
6987                        !CMSCollector::foregroundGCIsActive(); ++i) {
6988     os::sleep(Thread::current(), 1, false);
6989   }
6990 
6991   ConcurrentMarkSweepThread::synchronize(true);
6992   bml->lock();
6993 
6994   _collector->startTimer();
6995 }
6996 
6997 bool CMSPrecleanRefsYieldClosure::should_return() {
6998   if (ConcurrentMarkSweepThread::should_yield()) {
6999     do_yield_work();
7000   }
7001   return _collector->foregroundGCIsActive();
7002 }
7003 
7004 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7005   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7006          "mr should be aligned to start at a card boundary");
7007   // We'd like to assert:
7008   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7009   //        "mr should be a range of cards");
7010   // However, that would be too strong in one case -- the last
7011   // partition ends at _unallocated_block which, in general, can be
7012   // an arbitrary boundary, not necessarily card aligned.
7013   _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7014   _space->object_iterate_mem(mr, &_scan_cl);
7015 }
7016 
7017 SweepClosure::SweepClosure(CMSCollector* collector,
7018                            ConcurrentMarkSweepGeneration* g,
7019                            CMSBitMap* bitMap, bool should_yield) :
7020   _collector(collector),
7021   _g(g),
7022   _sp(g->cmsSpace()),
7023   _limit(_sp->sweep_limit()),
7024   _freelistLock(_sp->freelistLock()),
7025   _bitMap(bitMap),
7026   _yield(should_yield),
7027   _inFreeRange(false),           // No free range at beginning of sweep
7028   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7029   _lastFreeRangeCoalesced(false),
7030   _freeFinger(g->used_region().start())
7031 {
7032   NOT_PRODUCT(
7033     _numObjectsFreed = 0;
7034     _numWordsFreed   = 0;
7035     _numObjectsLive = 0;
7036     _numWordsLive = 0;
7037     _numObjectsAlreadyFree = 0;
7038     _numWordsAlreadyFree = 0;
7039     _last_fc = NULL;
7040 
7041     _sp->initializeIndexedFreeListArrayReturnedBytes();
7042     _sp->dictionary()->initialize_dict_returned_bytes();
7043   )
7044   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7045          "sweep _limit out of bounds");
7046   log_develop_trace(gc, sweep)("====================");
7047   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7048 }
7049 
7050 void SweepClosure::print_on(outputStream* st) const {
7051   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7052                p2i(_sp->bottom()), p2i(_sp->end()));
7053   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7054   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7055   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7056   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7057                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7058 }
7059 
7060 #ifndef PRODUCT
7061 // Assertion checking only:  no useful work in product mode --
7062 // however, if any of the flags below become product flags,
7063 // you may need to review this code to see if it needs to be
7064 // enabled in product mode.
7065 SweepClosure::~SweepClosure() {
7066   assert_lock_strong(_freelistLock);
7067   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7068          "sweep _limit out of bounds");
7069   if (inFreeRange()) {
7070     Log(gc, sweep) log;
7071     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7072     ResourceMark rm;
7073     print_on(log.error_stream());
7074     ShouldNotReachHere();
7075   }
7076 
7077   if (log_is_enabled(Debug, gc, sweep)) {
7078     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7079                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7080     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7081                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7082     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7083     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7084   }
7085 
7086   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7087     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7088     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7089     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7090     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7091                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7092   }
7093   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7094   log_develop_trace(gc, sweep)("================");
7095 }
7096 #endif  // PRODUCT
7097 
7098 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7099     bool freeRangeInFreeLists) {
7100   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7101                                p2i(freeFinger), freeRangeInFreeLists);
7102   assert(!inFreeRange(), "Trampling existing free range");
7103   set_inFreeRange(true);
7104   set_lastFreeRangeCoalesced(false);
7105 
7106   set_freeFinger(freeFinger);
7107   set_freeRangeInFreeLists(freeRangeInFreeLists);
7108   if (CMSTestInFreeList) {
7109     if (freeRangeInFreeLists) {
7110       FreeChunk* fc = (FreeChunk*) freeFinger;
7111       assert(fc->is_free(), "A chunk on the free list should be free.");
7112       assert(fc->size() > 0, "Free range should have a size");
7113       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7114     }
7115   }
7116 }
7117 
7118 // Note that the sweeper runs concurrently with mutators. Thus,
7119 // it is possible for direct allocation in this generation to happen
7120 // in the middle of the sweep. Note that the sweeper also coalesces
7121 // contiguous free blocks. Thus, unless the sweeper and the allocator
7122 // synchronize appropriately freshly allocated blocks may get swept up.
7123 // This is accomplished by the sweeper locking the free lists while
7124 // it is sweeping. Thus blocks that are determined to be free are
7125 // indeed free. There is however one additional complication:
7126 // blocks that have been allocated since the final checkpoint and
7127 // mark, will not have been marked and so would be treated as
7128 // unreachable and swept up. To prevent this, the allocator marks
7129 // the bit map when allocating during the sweep phase. This leads,
7130 // however, to a further complication -- objects may have been allocated
7131 // but not yet initialized -- in the sense that the header isn't yet
7132 // installed. The sweeper can not then determine the size of the block
7133 // in order to skip over it. To deal with this case, we use a technique
7134 // (due to Printezis) to encode such uninitialized block sizes in the
7135 // bit map. Since the bit map uses a bit per every HeapWord, but the
7136 // CMS generation has a minimum object size of 3 HeapWords, it follows
7137 // that "normal marks" won't be adjacent in the bit map (there will
7138 // always be at least two 0 bits between successive 1 bits). We make use
7139 // of these "unused" bits to represent uninitialized blocks -- the bit
7140 // corresponding to the start of the uninitialized object and the next
7141 // bit are both set. Finally, a 1 bit marks the end of the object that
7142 // started with the two consecutive 1 bits to indicate its potentially
7143 // uninitialized state.
7144 
7145 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7146   FreeChunk* fc = (FreeChunk*)addr;
7147   size_t res;
7148 
7149   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7150   // than "addr == _limit" because although _limit was a block boundary when
7151   // we started the sweep, it may no longer be one because heap expansion
7152   // may have caused us to coalesce the block ending at the address _limit
7153   // with a newly expanded chunk (this happens when _limit was set to the
7154   // previous _end of the space), so we may have stepped past _limit:
7155   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7156   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7157     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7158            "sweep _limit out of bounds");
7159     assert(addr < _sp->end(), "addr out of bounds");
7160     // Flush any free range we might be holding as a single
7161     // coalesced chunk to the appropriate free list.
7162     if (inFreeRange()) {
7163       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7164              "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7165       flush_cur_free_chunk(freeFinger(),
7166                            pointer_delta(addr, freeFinger()));
7167       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7168                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7169                                    lastFreeRangeCoalesced() ? 1 : 0);
7170     }
7171 
7172     // help the iterator loop finish
7173     return pointer_delta(_sp->end(), addr);
7174   }
7175 
7176   assert(addr < _limit, "sweep invariant");
7177   // check if we should yield
7178   do_yield_check(addr);
7179   if (fc->is_free()) {
7180     // Chunk that is already free
7181     res = fc->size();
7182     do_already_free_chunk(fc);
7183     debug_only(_sp->verifyFreeLists());
7184     // If we flush the chunk at hand in lookahead_and_flush()
7185     // and it's coalesced with a preceding chunk, then the
7186     // process of "mangling" the payload of the coalesced block
7187     // will cause erasure of the size information from the
7188     // (erstwhile) header of all the coalesced blocks but the
7189     // first, so the first disjunct in the assert will not hold
7190     // in that specific case (in which case the second disjunct
7191     // will hold).
7192     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7193            "Otherwise the size info doesn't change at this step");
7194     NOT_PRODUCT(
7195       _numObjectsAlreadyFree++;
7196       _numWordsAlreadyFree += res;
7197     )
7198     NOT_PRODUCT(_last_fc = fc;)
7199   } else if (!_bitMap->isMarked(addr)) {
7200     // Chunk is fresh garbage
7201     res = do_garbage_chunk(fc);
7202     debug_only(_sp->verifyFreeLists());
7203     NOT_PRODUCT(
7204       _numObjectsFreed++;
7205       _numWordsFreed += res;
7206     )
7207   } else {
7208     // Chunk that is alive.
7209     res = do_live_chunk(fc);
7210     debug_only(_sp->verifyFreeLists());
7211     NOT_PRODUCT(
7212         _numObjectsLive++;
7213         _numWordsLive += res;
7214     )
7215   }
7216   return res;
7217 }
7218 
7219 // For the smart allocation, record following
7220 //  split deaths - a free chunk is removed from its free list because
7221 //      it is being split into two or more chunks.
7222 //  split birth - a free chunk is being added to its free list because
7223 //      a larger free chunk has been split and resulted in this free chunk.
7224 //  coal death - a free chunk is being removed from its free list because
7225 //      it is being coalesced into a large free chunk.
7226 //  coal birth - a free chunk is being added to its free list because
7227 //      it was created when two or more free chunks where coalesced into
7228 //      this free chunk.
7229 //
7230 // These statistics are used to determine the desired number of free
7231 // chunks of a given size.  The desired number is chosen to be relative
7232 // to the end of a CMS sweep.  The desired number at the end of a sweep
7233 // is the
7234 //      count-at-end-of-previous-sweep (an amount that was enough)
7235 //              - count-at-beginning-of-current-sweep  (the excess)
7236 //              + split-births  (gains in this size during interval)
7237 //              - split-deaths  (demands on this size during interval)
7238 // where the interval is from the end of one sweep to the end of the
7239 // next.
7240 //
7241 // When sweeping the sweeper maintains an accumulated chunk which is
7242 // the chunk that is made up of chunks that have been coalesced.  That
7243 // will be termed the left-hand chunk.  A new chunk of garbage that
7244 // is being considered for coalescing will be referred to as the
7245 // right-hand chunk.
7246 //
7247 // When making a decision on whether to coalesce a right-hand chunk with
7248 // the current left-hand chunk, the current count vs. the desired count
7249 // of the left-hand chunk is considered.  Also if the right-hand chunk
7250 // is near the large chunk at the end of the heap (see
7251 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7252 // left-hand chunk is coalesced.
7253 //
7254 // When making a decision about whether to split a chunk, the desired count
7255 // vs. the current count of the candidate to be split is also considered.
7256 // If the candidate is underpopulated (currently fewer chunks than desired)
7257 // a chunk of an overpopulated (currently more chunks than desired) size may
7258 // be chosen.  The "hint" associated with a free list, if non-null, points
7259 // to a free list which may be overpopulated.
7260 //
7261 
7262 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7263   const size_t size = fc->size();
7264   // Chunks that cannot be coalesced are not in the
7265   // free lists.
7266   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7267     assert(_sp->verify_chunk_in_free_list(fc),
7268            "free chunk should be in free lists");
7269   }
7270   // a chunk that is already free, should not have been
7271   // marked in the bit map
7272   HeapWord* const addr = (HeapWord*) fc;
7273   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7274   // Verify that the bit map has no bits marked between
7275   // addr and purported end of this block.
7276   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7277 
7278   // Some chunks cannot be coalesced under any circumstances.
7279   // See the definition of cantCoalesce().
7280   if (!fc->cantCoalesce()) {
7281     // This chunk can potentially be coalesced.
7282     // All the work is done in
7283     do_post_free_or_garbage_chunk(fc, size);
7284     // Note that if the chunk is not coalescable (the else arm
7285     // below), we unconditionally flush, without needing to do
7286     // a "lookahead," as we do below.
7287     if (inFreeRange()) lookahead_and_flush(fc, size);
7288   } else {
7289     // Code path common to both original and adaptive free lists.
7290 
7291     // cant coalesce with previous block; this should be treated
7292     // as the end of a free run if any
7293     if (inFreeRange()) {
7294       // we kicked some butt; time to pick up the garbage
7295       assert(freeFinger() < addr, "freeFinger points too high");
7296       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7297     }
7298     // else, nothing to do, just continue
7299   }
7300 }
7301 
7302 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7303   // This is a chunk of garbage.  It is not in any free list.
7304   // Add it to a free list or let it possibly be coalesced into
7305   // a larger chunk.
7306   HeapWord* const addr = (HeapWord*) fc;
7307   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7308 
7309   // Verify that the bit map has no bits marked between
7310   // addr and purported end of just dead object.
7311   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7312   do_post_free_or_garbage_chunk(fc, size);
7313 
7314   assert(_limit >= addr + size,
7315          "A freshly garbage chunk can't possibly straddle over _limit");
7316   if (inFreeRange()) lookahead_and_flush(fc, size);
7317   return size;
7318 }
7319 
7320 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7321   HeapWord* addr = (HeapWord*) fc;
7322   // The sweeper has just found a live object. Return any accumulated
7323   // left hand chunk to the free lists.
7324   if (inFreeRange()) {
7325     assert(freeFinger() < addr, "freeFinger points too high");
7326     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7327   }
7328 
7329   // This object is live: we'd normally expect this to be
7330   // an oop, and like to assert the following:
7331   // assert(oop(addr)->is_oop(), "live block should be an oop");
7332   // However, as we commented above, this may be an object whose
7333   // header hasn't yet been initialized.
7334   size_t size;
7335   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7336   if (_bitMap->isMarked(addr + 1)) {
7337     // Determine the size from the bit map, rather than trying to
7338     // compute it from the object header.
7339     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7340     size = pointer_delta(nextOneAddr + 1, addr);
7341     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7342            "alignment problem");
7343 
7344 #ifdef ASSERT
7345       if (oop(addr)->klass_or_null_acquire() != NULL) {
7346         // Ignore mark word because we are running concurrent with mutators
7347         assert(oop(addr)->is_oop(true), "live block should be an oop");
7348         assert(size ==
7349                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7350                "P-mark and computed size do not agree");
7351       }
7352 #endif
7353 
7354   } else {
7355     // This should be an initialized object that's alive.
7356     assert(oop(addr)->klass_or_null_acquire() != NULL,
7357            "Should be an initialized object");
7358     // Ignore mark word because we are running concurrent with mutators
7359     assert(oop(addr)->is_oop(true), "live block should be an oop");
7360     // Verify that the bit map has no bits marked between
7361     // addr and purported end of this block.
7362     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7363     assert(size >= 3, "Necessary for Printezis marks to work");
7364     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7365     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7366   }
7367   return size;
7368 }
7369 
7370 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7371                                                  size_t chunkSize) {
7372   // do_post_free_or_garbage_chunk() should only be called in the case
7373   // of the adaptive free list allocator.
7374   const bool fcInFreeLists = fc->is_free();
7375   assert((HeapWord*)fc <= _limit, "sweep invariant");
7376   if (CMSTestInFreeList && fcInFreeLists) {
7377     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7378   }
7379 
7380   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7381 
7382   HeapWord* const fc_addr = (HeapWord*) fc;
7383 
7384   bool coalesce = false;
7385   const size_t left  = pointer_delta(fc_addr, freeFinger());
7386   const size_t right = chunkSize;
7387   switch (FLSCoalescePolicy) {
7388     // numeric value forms a coalition aggressiveness metric
7389     case 0:  { // never coalesce
7390       coalesce = false;
7391       break;
7392     }
7393     case 1: { // coalesce if left & right chunks on overpopulated lists
7394       coalesce = _sp->coalOverPopulated(left) &&
7395                  _sp->coalOverPopulated(right);
7396       break;
7397     }
7398     case 2: { // coalesce if left chunk on overpopulated list (default)
7399       coalesce = _sp->coalOverPopulated(left);
7400       break;
7401     }
7402     case 3: { // coalesce if left OR right chunk on overpopulated list
7403       coalesce = _sp->coalOverPopulated(left) ||
7404                  _sp->coalOverPopulated(right);
7405       break;
7406     }
7407     case 4: { // always coalesce
7408       coalesce = true;
7409       break;
7410     }
7411     default:
7412      ShouldNotReachHere();
7413   }
7414 
7415   // Should the current free range be coalesced?
7416   // If the chunk is in a free range and either we decided to coalesce above
7417   // or the chunk is near the large block at the end of the heap
7418   // (isNearLargestChunk() returns true), then coalesce this chunk.
7419   const bool doCoalesce = inFreeRange()
7420                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7421   if (doCoalesce) {
7422     // Coalesce the current free range on the left with the new
7423     // chunk on the right.  If either is on a free list,
7424     // it must be removed from the list and stashed in the closure.
7425     if (freeRangeInFreeLists()) {
7426       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7427       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7428              "Size of free range is inconsistent with chunk size.");
7429       if (CMSTestInFreeList) {
7430         assert(_sp->verify_chunk_in_free_list(ffc),
7431                "Chunk is not in free lists");
7432       }
7433       _sp->coalDeath(ffc->size());
7434       _sp->removeFreeChunkFromFreeLists(ffc);
7435       set_freeRangeInFreeLists(false);
7436     }
7437     if (fcInFreeLists) {
7438       _sp->coalDeath(chunkSize);
7439       assert(fc->size() == chunkSize,
7440         "The chunk has the wrong size or is not in the free lists");
7441       _sp->removeFreeChunkFromFreeLists(fc);
7442     }
7443     set_lastFreeRangeCoalesced(true);
7444     print_free_block_coalesced(fc);
7445   } else {  // not in a free range and/or should not coalesce
7446     // Return the current free range and start a new one.
7447     if (inFreeRange()) {
7448       // In a free range but cannot coalesce with the right hand chunk.
7449       // Put the current free range into the free lists.
7450       flush_cur_free_chunk(freeFinger(),
7451                            pointer_delta(fc_addr, freeFinger()));
7452     }
7453     // Set up for new free range.  Pass along whether the right hand
7454     // chunk is in the free lists.
7455     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7456   }
7457 }
7458 
7459 // Lookahead flush:
7460 // If we are tracking a free range, and this is the last chunk that
7461 // we'll look at because its end crosses past _limit, we'll preemptively
7462 // flush it along with any free range we may be holding on to. Note that
7463 // this can be the case only for an already free or freshly garbage
7464 // chunk. If this block is an object, it can never straddle
7465 // over _limit. The "straddling" occurs when _limit is set at
7466 // the previous end of the space when this cycle started, and
7467 // a subsequent heap expansion caused the previously co-terminal
7468 // free block to be coalesced with the newly expanded portion,
7469 // thus rendering _limit a non-block-boundary making it dangerous
7470 // for the sweeper to step over and examine.
7471 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7472   assert(inFreeRange(), "Should only be called if currently in a free range.");
7473   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7474   assert(_sp->used_region().contains(eob - 1),
7475          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7476          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7477          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7478          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7479   if (eob >= _limit) {
7480     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7481     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7482                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7483                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7484                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7485     // Return the storage we are tracking back into the free lists.
7486     log_develop_trace(gc, sweep)("Flushing ... ");
7487     assert(freeFinger() < eob, "Error");
7488     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7489   }
7490 }
7491 
7492 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7493   assert(inFreeRange(), "Should only be called if currently in a free range.");
7494   assert(size > 0,
7495     "A zero sized chunk cannot be added to the free lists.");
7496   if (!freeRangeInFreeLists()) {
7497     if (CMSTestInFreeList) {
7498       FreeChunk* fc = (FreeChunk*) chunk;
7499       fc->set_size(size);
7500       assert(!_sp->verify_chunk_in_free_list(fc),
7501              "chunk should not be in free lists yet");
7502     }
7503     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7504     // A new free range is going to be starting.  The current
7505     // free range has not been added to the free lists yet or
7506     // was removed so add it back.
7507     // If the current free range was coalesced, then the death
7508     // of the free range was recorded.  Record a birth now.
7509     if (lastFreeRangeCoalesced()) {
7510       _sp->coalBirth(size);
7511     }
7512     _sp->addChunkAndRepairOffsetTable(chunk, size,
7513             lastFreeRangeCoalesced());
7514   } else {
7515     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7516   }
7517   set_inFreeRange(false);
7518   set_freeRangeInFreeLists(false);
7519 }
7520 
7521 // We take a break if we've been at this for a while,
7522 // so as to avoid monopolizing the locks involved.
7523 void SweepClosure::do_yield_work(HeapWord* addr) {
7524   // Return current free chunk being used for coalescing (if any)
7525   // to the appropriate freelist.  After yielding, the next
7526   // free block encountered will start a coalescing range of
7527   // free blocks.  If the next free block is adjacent to the
7528   // chunk just flushed, they will need to wait for the next
7529   // sweep to be coalesced.
7530   if (inFreeRange()) {
7531     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7532   }
7533 
7534   // First give up the locks, then yield, then re-lock.
7535   // We should probably use a constructor/destructor idiom to
7536   // do this unlock/lock or modify the MutexUnlocker class to
7537   // serve our purpose. XXX
7538   assert_lock_strong(_bitMap->lock());
7539   assert_lock_strong(_freelistLock);
7540   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7541          "CMS thread should hold CMS token");
7542   _bitMap->lock()->unlock();
7543   _freelistLock->unlock();
7544   ConcurrentMarkSweepThread::desynchronize(true);
7545   _collector->stopTimer();
7546   _collector->incrementYields();
7547 
7548   // See the comment in coordinator_yield()
7549   for (unsigned i = 0; i < CMSYieldSleepCount &&
7550                        ConcurrentMarkSweepThread::should_yield() &&
7551                        !CMSCollector::foregroundGCIsActive(); ++i) {
7552     os::sleep(Thread::current(), 1, false);
7553   }
7554 
7555   ConcurrentMarkSweepThread::synchronize(true);
7556   _freelistLock->lock();
7557   _bitMap->lock()->lock_without_safepoint_check();
7558   _collector->startTimer();
7559 }
7560 
7561 #ifndef PRODUCT
7562 // This is actually very useful in a product build if it can
7563 // be called from the debugger.  Compile it into the product
7564 // as needed.
7565 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7566   return debug_cms_space->verify_chunk_in_free_list(fc);
7567 }
7568 #endif
7569 
7570 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7571   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7572                                p2i(fc), fc->size());
7573 }
7574 
7575 // CMSIsAliveClosure
7576 bool CMSIsAliveClosure::do_object_b(oop obj) {
7577   HeapWord* addr = (HeapWord*)obj;
7578   return addr != NULL &&
7579          (!_span.contains(addr) || _bit_map->isMarked(addr));
7580 }
7581 
7582 
7583 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7584                       MemRegion span,
7585                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7586                       bool cpc):
7587   _collector(collector),
7588   _span(span),
7589   _bit_map(bit_map),
7590   _mark_stack(mark_stack),
7591   _concurrent_precleaning(cpc) {
7592   assert(!_span.is_empty(), "Empty span could spell trouble");
7593 }
7594 
7595 
7596 // CMSKeepAliveClosure: the serial version
7597 void CMSKeepAliveClosure::do_oop(oop obj) {
7598   HeapWord* addr = (HeapWord*)obj;
7599   if (_span.contains(addr) &&
7600       !_bit_map->isMarked(addr)) {
7601     _bit_map->mark(addr);
7602     bool simulate_overflow = false;
7603     NOT_PRODUCT(
7604       if (CMSMarkStackOverflowALot &&
7605           _collector->simulate_overflow()) {
7606         // simulate a stack overflow
7607         simulate_overflow = true;
7608       }
7609     )
7610     if (simulate_overflow || !_mark_stack->push(obj)) {
7611       if (_concurrent_precleaning) {
7612         // We dirty the overflown object and let the remark
7613         // phase deal with it.
7614         assert(_collector->overflow_list_is_empty(), "Error");
7615         // In the case of object arrays, we need to dirty all of
7616         // the cards that the object spans. No locking or atomics
7617         // are needed since no one else can be mutating the mod union
7618         // table.
7619         if (obj->is_objArray()) {
7620           size_t sz = obj->size();
7621           HeapWord* end_card_addr =
7622             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7623           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7624           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7625           _collector->_modUnionTable.mark_range(redirty_range);
7626         } else {
7627           _collector->_modUnionTable.mark(addr);
7628         }
7629         _collector->_ser_kac_preclean_ovflw++;
7630       } else {
7631         _collector->push_on_overflow_list(obj);
7632         _collector->_ser_kac_ovflw++;
7633       }
7634     }
7635   }
7636 }
7637 
7638 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7639 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7640 
7641 // CMSParKeepAliveClosure: a parallel version of the above.
7642 // The work queues are private to each closure (thread),
7643 // but (may be) available for stealing by other threads.
7644 void CMSParKeepAliveClosure::do_oop(oop obj) {
7645   HeapWord* addr = (HeapWord*)obj;
7646   if (_span.contains(addr) &&
7647       !_bit_map->isMarked(addr)) {
7648     // In general, during recursive tracing, several threads
7649     // may be concurrently getting here; the first one to
7650     // "tag" it, claims it.
7651     if (_bit_map->par_mark(addr)) {
7652       bool res = _work_queue->push(obj);
7653       assert(res, "Low water mark should be much less than capacity");
7654       // Do a recursive trim in the hope that this will keep
7655       // stack usage lower, but leave some oops for potential stealers
7656       trim_queue(_low_water_mark);
7657     } // Else, another thread got there first
7658   }
7659 }
7660 
7661 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7662 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7663 
7664 void CMSParKeepAliveClosure::trim_queue(uint max) {
7665   while (_work_queue->size() > max) {
7666     oop new_oop;
7667     if (_work_queue->pop_local(new_oop)) {
7668       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7669       assert(_bit_map->isMarked((HeapWord*)new_oop),
7670              "no white objects on this stack!");
7671       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7672       // iterate over the oops in this oop, marking and pushing
7673       // the ones in CMS heap (i.e. in _span).
7674       new_oop->oop_iterate(&_mark_and_push);
7675     }
7676   }
7677 }
7678 
7679 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7680                                 CMSCollector* collector,
7681                                 MemRegion span, CMSBitMap* bit_map,
7682                                 OopTaskQueue* work_queue):
7683   _collector(collector),
7684   _span(span),
7685   _bit_map(bit_map),
7686   _work_queue(work_queue) { }
7687 
7688 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7689   HeapWord* addr = (HeapWord*)obj;
7690   if (_span.contains(addr) &&
7691       !_bit_map->isMarked(addr)) {
7692     if (_bit_map->par_mark(addr)) {
7693       bool simulate_overflow = false;
7694       NOT_PRODUCT(
7695         if (CMSMarkStackOverflowALot &&
7696             _collector->par_simulate_overflow()) {
7697           // simulate a stack overflow
7698           simulate_overflow = true;
7699         }
7700       )
7701       if (simulate_overflow || !_work_queue->push(obj)) {
7702         _collector->par_push_on_overflow_list(obj);
7703         _collector->_par_kac_ovflw++;
7704       }
7705     } // Else another thread got there already
7706   }
7707 }
7708 
7709 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7710 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7711 
7712 //////////////////////////////////////////////////////////////////
7713 //  CMSExpansionCause                /////////////////////////////
7714 //////////////////////////////////////////////////////////////////
7715 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7716   switch (cause) {
7717     case _no_expansion:
7718       return "No expansion";
7719     case _satisfy_free_ratio:
7720       return "Free ratio";
7721     case _satisfy_promotion:
7722       return "Satisfy promotion";
7723     case _satisfy_allocation:
7724       return "allocation";
7725     case _allocate_par_lab:
7726       return "Par LAB";
7727     case _allocate_par_spooling_space:
7728       return "Par Spooling Space";
7729     case _adaptive_size_policy:
7730       return "Ergonomics";
7731     default:
7732       return "unknown";
7733   }
7734 }
7735 
7736 void CMSDrainMarkingStackClosure::do_void() {
7737   // the max number to take from overflow list at a time
7738   const size_t num = _mark_stack->capacity()/4;
7739   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7740          "Overflow list should be NULL during concurrent phases");
7741   while (!_mark_stack->isEmpty() ||
7742          // if stack is empty, check the overflow list
7743          _collector->take_from_overflow_list(num, _mark_stack)) {
7744     oop obj = _mark_stack->pop();
7745     HeapWord* addr = (HeapWord*)obj;
7746     assert(_span.contains(addr), "Should be within span");
7747     assert(_bit_map->isMarked(addr), "Should be marked");
7748     assert(obj->is_oop(), "Should be an oop");
7749     obj->oop_iterate(_keep_alive);
7750   }
7751 }
7752 
7753 void CMSParDrainMarkingStackClosure::do_void() {
7754   // drain queue
7755   trim_queue(0);
7756 }
7757 
7758 // Trim our work_queue so its length is below max at return
7759 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7760   while (_work_queue->size() > max) {
7761     oop new_oop;
7762     if (_work_queue->pop_local(new_oop)) {
7763       assert(new_oop->is_oop(), "Expected an oop");
7764       assert(_bit_map->isMarked((HeapWord*)new_oop),
7765              "no white objects on this stack!");
7766       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7767       // iterate over the oops in this oop, marking and pushing
7768       // the ones in CMS heap (i.e. in _span).
7769       new_oop->oop_iterate(&_mark_and_push);
7770     }
7771   }
7772 }
7773 
7774 ////////////////////////////////////////////////////////////////////
7775 // Support for Marking Stack Overflow list handling and related code
7776 ////////////////////////////////////////////////////////////////////
7777 // Much of the following code is similar in shape and spirit to the
7778 // code used in ParNewGC. We should try and share that code
7779 // as much as possible in the future.
7780 
7781 #ifndef PRODUCT
7782 // Debugging support for CMSStackOverflowALot
7783 
7784 // It's OK to call this multi-threaded;  the worst thing
7785 // that can happen is that we'll get a bunch of closely
7786 // spaced simulated overflows, but that's OK, in fact
7787 // probably good as it would exercise the overflow code
7788 // under contention.
7789 bool CMSCollector::simulate_overflow() {
7790   if (_overflow_counter-- <= 0) { // just being defensive
7791     _overflow_counter = CMSMarkStackOverflowInterval;
7792     return true;
7793   } else {
7794     return false;
7795   }
7796 }
7797 
7798 bool CMSCollector::par_simulate_overflow() {
7799   return simulate_overflow();
7800 }
7801 #endif
7802 
7803 // Single-threaded
7804 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7805   assert(stack->isEmpty(), "Expected precondition");
7806   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7807   size_t i = num;
7808   oop  cur = _overflow_list;
7809   const markOop proto = markOopDesc::prototype();
7810   NOT_PRODUCT(ssize_t n = 0;)
7811   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7812     next = oop(cur->mark());
7813     cur->set_mark(proto);   // until proven otherwise
7814     assert(cur->is_oop(), "Should be an oop");
7815     bool res = stack->push(cur);
7816     assert(res, "Bit off more than can chew?");
7817     NOT_PRODUCT(n++;)
7818   }
7819   _overflow_list = cur;
7820 #ifndef PRODUCT
7821   assert(_num_par_pushes >= n, "Too many pops?");
7822   _num_par_pushes -=n;
7823 #endif
7824   return !stack->isEmpty();
7825 }
7826 
7827 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7828 // (MT-safe) Get a prefix of at most "num" from the list.
7829 // The overflow list is chained through the mark word of
7830 // each object in the list. We fetch the entire list,
7831 // break off a prefix of the right size and return the
7832 // remainder. If other threads try to take objects from
7833 // the overflow list at that time, they will wait for
7834 // some time to see if data becomes available. If (and
7835 // only if) another thread places one or more object(s)
7836 // on the global list before we have returned the suffix
7837 // to the global list, we will walk down our local list
7838 // to find its end and append the global list to
7839 // our suffix before returning it. This suffix walk can
7840 // prove to be expensive (quadratic in the amount of traffic)
7841 // when there are many objects in the overflow list and
7842 // there is much producer-consumer contention on the list.
7843 // *NOTE*: The overflow list manipulation code here and
7844 // in ParNewGeneration:: are very similar in shape,
7845 // except that in the ParNew case we use the old (from/eden)
7846 // copy of the object to thread the list via its klass word.
7847 // Because of the common code, if you make any changes in
7848 // the code below, please check the ParNew version to see if
7849 // similar changes might be needed.
7850 // CR 6797058 has been filed to consolidate the common code.
7851 bool CMSCollector::par_take_from_overflow_list(size_t num,
7852                                                OopTaskQueue* work_q,
7853                                                int no_of_gc_threads) {
7854   assert(work_q->size() == 0, "First empty local work queue");
7855   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7856   if (_overflow_list == NULL) {
7857     return false;
7858   }
7859   // Grab the entire list; we'll put back a suffix
7860   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7861   Thread* tid = Thread::current();
7862   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7863   // set to ParallelGCThreads.
7864   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7865   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7866   // If the list is busy, we spin for a short while,
7867   // sleeping between attempts to get the list.
7868   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7869     os::sleep(tid, sleep_time_millis, false);
7870     if (_overflow_list == NULL) {
7871       // Nothing left to take
7872       return false;
7873     } else if (_overflow_list != BUSY) {
7874       // Try and grab the prefix
7875       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7876     }
7877   }
7878   // If the list was found to be empty, or we spun long
7879   // enough, we give up and return empty-handed. If we leave
7880   // the list in the BUSY state below, it must be the case that
7881   // some other thread holds the overflow list and will set it
7882   // to a non-BUSY state in the future.
7883   if (prefix == NULL || prefix == BUSY) {
7884      // Nothing to take or waited long enough
7885      if (prefix == NULL) {
7886        // Write back the NULL in case we overwrote it with BUSY above
7887        // and it is still the same value.
7888        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7889      }
7890      return false;
7891   }
7892   assert(prefix != NULL && prefix != BUSY, "Error");
7893   size_t i = num;
7894   oop cur = prefix;
7895   // Walk down the first "num" objects, unless we reach the end.
7896   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7897   if (cur->mark() == NULL) {
7898     // We have "num" or fewer elements in the list, so there
7899     // is nothing to return to the global list.
7900     // Write back the NULL in lieu of the BUSY we wrote
7901     // above, if it is still the same value.
7902     if (_overflow_list == BUSY) {
7903       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7904     }
7905   } else {
7906     // Chop off the suffix and return it to the global list.
7907     assert(cur->mark() != BUSY, "Error");
7908     oop suffix_head = cur->mark(); // suffix will be put back on global list
7909     cur->set_mark(NULL);           // break off suffix
7910     // It's possible that the list is still in the empty(busy) state
7911     // we left it in a short while ago; in that case we may be
7912     // able to place back the suffix without incurring the cost
7913     // of a walk down the list.
7914     oop observed_overflow_list = _overflow_list;
7915     oop cur_overflow_list = observed_overflow_list;
7916     bool attached = false;
7917     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7918       observed_overflow_list =
7919         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7920       if (cur_overflow_list == observed_overflow_list) {
7921         attached = true;
7922         break;
7923       } else cur_overflow_list = observed_overflow_list;
7924     }
7925     if (!attached) {
7926       // Too bad, someone else sneaked in (at least) an element; we'll need
7927       // to do a splice. Find tail of suffix so we can prepend suffix to global
7928       // list.
7929       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7930       oop suffix_tail = cur;
7931       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7932              "Tautology");
7933       observed_overflow_list = _overflow_list;
7934       do {
7935         cur_overflow_list = observed_overflow_list;
7936         if (cur_overflow_list != BUSY) {
7937           // Do the splice ...
7938           suffix_tail->set_mark(markOop(cur_overflow_list));
7939         } else { // cur_overflow_list == BUSY
7940           suffix_tail->set_mark(NULL);
7941         }
7942         // ... and try to place spliced list back on overflow_list ...
7943         observed_overflow_list =
7944           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7945       } while (cur_overflow_list != observed_overflow_list);
7946       // ... until we have succeeded in doing so.
7947     }
7948   }
7949 
7950   // Push the prefix elements on work_q
7951   assert(prefix != NULL, "control point invariant");
7952   const markOop proto = markOopDesc::prototype();
7953   oop next;
7954   NOT_PRODUCT(ssize_t n = 0;)
7955   for (cur = prefix; cur != NULL; cur = next) {
7956     next = oop(cur->mark());
7957     cur->set_mark(proto);   // until proven otherwise
7958     assert(cur->is_oop(), "Should be an oop");
7959     bool res = work_q->push(cur);
7960     assert(res, "Bit off more than we can chew?");
7961     NOT_PRODUCT(n++;)
7962   }
7963 #ifndef PRODUCT
7964   assert(_num_par_pushes >= n, "Too many pops?");
7965   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7966 #endif
7967   return true;
7968 }
7969 
7970 // Single-threaded
7971 void CMSCollector::push_on_overflow_list(oop p) {
7972   NOT_PRODUCT(_num_par_pushes++;)
7973   assert(p->is_oop(), "Not an oop");
7974   preserve_mark_if_necessary(p);
7975   p->set_mark((markOop)_overflow_list);
7976   _overflow_list = p;
7977 }
7978 
7979 // Multi-threaded; use CAS to prepend to overflow list
7980 void CMSCollector::par_push_on_overflow_list(oop p) {
7981   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7982   assert(p->is_oop(), "Not an oop");
7983   par_preserve_mark_if_necessary(p);
7984   oop observed_overflow_list = _overflow_list;
7985   oop cur_overflow_list;
7986   do {
7987     cur_overflow_list = observed_overflow_list;
7988     if (cur_overflow_list != BUSY) {
7989       p->set_mark(markOop(cur_overflow_list));
7990     } else {
7991       p->set_mark(NULL);
7992     }
7993     observed_overflow_list =
7994       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7995   } while (cur_overflow_list != observed_overflow_list);
7996 }
7997 #undef BUSY
7998 
7999 // Single threaded
8000 // General Note on GrowableArray: pushes may silently fail
8001 // because we are (temporarily) out of C-heap for expanding
8002 // the stack. The problem is quite ubiquitous and affects
8003 // a lot of code in the JVM. The prudent thing for GrowableArray
8004 // to do (for now) is to exit with an error. However, that may
8005 // be too draconian in some cases because the caller may be
8006 // able to recover without much harm. For such cases, we
8007 // should probably introduce a "soft_push" method which returns
8008 // an indication of success or failure with the assumption that
8009 // the caller may be able to recover from a failure; code in
8010 // the VM can then be changed, incrementally, to deal with such
8011 // failures where possible, thus, incrementally hardening the VM
8012 // in such low resource situations.
8013 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8014   _preserved_oop_stack.push(p);
8015   _preserved_mark_stack.push(m);
8016   assert(m == p->mark(), "Mark word changed");
8017   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8018          "bijection");
8019 }
8020 
8021 // Single threaded
8022 void CMSCollector::preserve_mark_if_necessary(oop p) {
8023   markOop m = p->mark();
8024   if (m->must_be_preserved(p)) {
8025     preserve_mark_work(p, m);
8026   }
8027 }
8028 
8029 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8030   markOop m = p->mark();
8031   if (m->must_be_preserved(p)) {
8032     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8033     // Even though we read the mark word without holding
8034     // the lock, we are assured that it will not change
8035     // because we "own" this oop, so no other thread can
8036     // be trying to push it on the overflow list; see
8037     // the assertion in preserve_mark_work() that checks
8038     // that m == p->mark().
8039     preserve_mark_work(p, m);
8040   }
8041 }
8042 
8043 // We should be able to do this multi-threaded,
8044 // a chunk of stack being a task (this is
8045 // correct because each oop only ever appears
8046 // once in the overflow list. However, it's
8047 // not very easy to completely overlap this with
8048 // other operations, so will generally not be done
8049 // until all work's been completed. Because we
8050 // expect the preserved oop stack (set) to be small,
8051 // it's probably fine to do this single-threaded.
8052 // We can explore cleverer concurrent/overlapped/parallel
8053 // processing of preserved marks if we feel the
8054 // need for this in the future. Stack overflow should
8055 // be so rare in practice and, when it happens, its
8056 // effect on performance so great that this will
8057 // likely just be in the noise anyway.
8058 void CMSCollector::restore_preserved_marks_if_any() {
8059   assert(SafepointSynchronize::is_at_safepoint(),
8060          "world should be stopped");
8061   assert(Thread::current()->is_ConcurrentGC_thread() ||
8062          Thread::current()->is_VM_thread(),
8063          "should be single-threaded");
8064   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8065          "bijection");
8066 
8067   while (!_preserved_oop_stack.is_empty()) {
8068     oop p = _preserved_oop_stack.pop();
8069     assert(p->is_oop(), "Should be an oop");
8070     assert(_span.contains(p), "oop should be in _span");
8071     assert(p->mark() == markOopDesc::prototype(),
8072            "Set when taken from overflow list");
8073     markOop m = _preserved_mark_stack.pop();
8074     p->set_mark(m);
8075   }
8076   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8077          "stacks were cleared above");
8078 }
8079 
8080 #ifndef PRODUCT
8081 bool CMSCollector::no_preserved_marks() const {
8082   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8083 }
8084 #endif
8085 
8086 // Transfer some number of overflown objects to usual marking
8087 // stack. Return true if some objects were transferred.
8088 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8089   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8090                     (size_t)ParGCDesiredObjsFromOverflowList);
8091 
8092   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8093   assert(_collector->overflow_list_is_empty() || res,
8094          "If list is not empty, we should have taken something");
8095   assert(!res || !_mark_stack->isEmpty(),
8096          "If we took something, it should now be on our stack");
8097   return res;
8098 }
8099 
8100 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8101   size_t res = _sp->block_size_no_stall(addr, _collector);
8102   if (_sp->block_is_obj(addr)) {
8103     if (_live_bit_map->isMarked(addr)) {
8104       // It can't have been dead in a previous cycle
8105       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8106     } else {
8107       _dead_bit_map->mark(addr);      // mark the dead object
8108     }
8109   }
8110   // Could be 0, if the block size could not be computed without stalling.
8111   return res;
8112 }
8113 
8114 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8115 
8116   switch (phase) {
8117     case CMSCollector::InitialMarking:
8118       initialize(true  /* fullGC */ ,
8119                  cause /* cause of the GC */,
8120                  true  /* recordGCBeginTime */,
8121                  true  /* recordPreGCUsage */,
8122                  false /* recordPeakUsage */,
8123                  false /* recordPostGCusage */,
8124                  true  /* recordAccumulatedGCTime */,
8125                  false /* recordGCEndTime */,
8126                  false /* countCollection */  );
8127       break;
8128 
8129     case CMSCollector::FinalMarking:
8130       initialize(true  /* fullGC */ ,
8131                  cause /* cause of the GC */,
8132                  false /* recordGCBeginTime */,
8133                  false /* recordPreGCUsage */,
8134                  false /* recordPeakUsage */,
8135                  false /* recordPostGCusage */,
8136                  true  /* recordAccumulatedGCTime */,
8137                  false /* recordGCEndTime */,
8138                  false /* countCollection */  );
8139       break;
8140 
8141     case CMSCollector::Sweeping:
8142       initialize(true  /* fullGC */ ,
8143                  cause /* cause of the GC */,
8144                  false /* recordGCBeginTime */,
8145                  false /* recordPreGCUsage */,
8146                  true  /* recordPeakUsage */,
8147                  true  /* recordPostGCusage */,
8148                  false /* recordAccumulatedGCTime */,
8149                  true  /* recordGCEndTime */,
8150                  true  /* countCollection */  );
8151       break;
8152 
8153     default:
8154       ShouldNotReachHere();
8155   }
8156 }