1 /*
   2  * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "gc/cms/cmsCollectorPolicy.hpp"
  32 #include "gc/cms/cmsOopClosures.inline.hpp"
  33 #include "gc/cms/compactibleFreeListSpace.hpp"
  34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc/cms/concurrentMarkSweepThread.hpp"
  36 #include "gc/cms/parNewGeneration.hpp"
  37 #include "gc/cms/vmCMSOperations.hpp"
  38 #include "gc/serial/genMarkSweep.hpp"
  39 #include "gc/serial/tenuredGeneration.hpp"
  40 #include "gc/shared/adaptiveSizePolicy.hpp"
  41 #include "gc/shared/cardGeneration.inline.hpp"
  42 #include "gc/shared/cardTableRS.hpp"
  43 #include "gc/shared/collectedHeap.inline.hpp"
  44 #include "gc/shared/collectorCounters.hpp"
  45 #include "gc/shared/collectorPolicy.hpp"
  46 #include "gc/shared/gcLocker.inline.hpp"
  47 #include "gc/shared/gcPolicyCounters.hpp"
  48 #include "gc/shared/gcTimer.hpp"
  49 #include "gc/shared/gcTrace.hpp"
  50 #include "gc/shared/gcTraceTime.inline.hpp"
  51 #include "gc/shared/genCollectedHeap.hpp"
  52 #include "gc/shared/genOopClosures.inline.hpp"
  53 #include "gc/shared/isGCActiveMark.hpp"
  54 #include "gc/shared/referencePolicy.hpp"
  55 #include "gc/shared/strongRootsScope.hpp"
  56 #include "gc/shared/taskqueue.inline.hpp"
  57 #include "logging/log.hpp"
  58 #include "memory/allocation.hpp"
  59 #include "memory/iterator.inline.hpp"
  60 #include "memory/padded.hpp"
  61 #include "memory/resourceArea.hpp"
  62 #include "oops/oop.inline.hpp"
  63 #include "prims/jvmtiExport.hpp"
  64 #include "runtime/atomic.inline.hpp"
  65 #include "runtime/globals_extension.hpp"
  66 #include "runtime/handles.inline.hpp"
  67 #include "runtime/java.hpp"
  68 #include "runtime/orderAccess.inline.hpp"
  69 #include "runtime/timer.hpp"
  70 #include "runtime/vmThread.hpp"
  71 #include "services/memoryService.hpp"
  72 #include "services/runtimeService.hpp"
  73 #include "utilities/stack.inline.hpp"
  74 
  75 // statics
  76 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  77 bool CMSCollector::_full_gc_requested = false;
  78 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  79 
  80 //////////////////////////////////////////////////////////////////
  81 // In support of CMS/VM thread synchronization
  82 //////////////////////////////////////////////////////////////////
  83 // We split use of the CGC_lock into 2 "levels".
  84 // The low-level locking is of the usual CGC_lock monitor. We introduce
  85 // a higher level "token" (hereafter "CMS token") built on top of the
  86 // low level monitor (hereafter "CGC lock").
  87 // The token-passing protocol gives priority to the VM thread. The
  88 // CMS-lock doesn't provide any fairness guarantees, but clients
  89 // should ensure that it is only held for very short, bounded
  90 // durations.
  91 //
  92 // When either of the CMS thread or the VM thread is involved in
  93 // collection operations during which it does not want the other
  94 // thread to interfere, it obtains the CMS token.
  95 //
  96 // If either thread tries to get the token while the other has
  97 // it, that thread waits. However, if the VM thread and CMS thread
  98 // both want the token, then the VM thread gets priority while the
  99 // CMS thread waits. This ensures, for instance, that the "concurrent"
 100 // phases of the CMS thread's work do not block out the VM thread
 101 // for long periods of time as the CMS thread continues to hog
 102 // the token. (See bug 4616232).
 103 //
 104 // The baton-passing functions are, however, controlled by the
 105 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 106 // and here the low-level CMS lock, not the high level token,
 107 // ensures mutual exclusion.
 108 //
 109 // Two important conditions that we have to satisfy:
 110 // 1. if a thread does a low-level wait on the CMS lock, then it
 111 //    relinquishes the CMS token if it were holding that token
 112 //    when it acquired the low-level CMS lock.
 113 // 2. any low-level notifications on the low-level lock
 114 //    should only be sent when a thread has relinquished the token.
 115 //
 116 // In the absence of either property, we'd have potential deadlock.
 117 //
 118 // We protect each of the CMS (concurrent and sequential) phases
 119 // with the CMS _token_, not the CMS _lock_.
 120 //
 121 // The only code protected by CMS lock is the token acquisition code
 122 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 123 // baton-passing code.
 124 //
 125 // Unfortunately, i couldn't come up with a good abstraction to factor and
 126 // hide the naked CGC_lock manipulation in the baton-passing code
 127 // further below. That's something we should try to do. Also, the proof
 128 // of correctness of this 2-level locking scheme is far from obvious,
 129 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 130 // that there may be a theoretical possibility of delay/starvation in the
 131 // low-level lock/wait/notify scheme used for the baton-passing because of
 132 // potential interference with the priority scheme embodied in the
 133 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 134 // invocation further below and marked with "XXX 20011219YSR".
 135 // Indeed, as we note elsewhere, this may become yet more slippery
 136 // in the presence of multiple CMS and/or multiple VM threads. XXX
 137 
 138 class CMSTokenSync: public StackObj {
 139  private:
 140   bool _is_cms_thread;
 141  public:
 142   CMSTokenSync(bool is_cms_thread):
 143     _is_cms_thread(is_cms_thread) {
 144     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 145            "Incorrect argument to constructor");
 146     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 147   }
 148 
 149   ~CMSTokenSync() {
 150     assert(_is_cms_thread ?
 151              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 152              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 153           "Incorrect state");
 154     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 155   }
 156 };
 157 
 158 // Convenience class that does a CMSTokenSync, and then acquires
 159 // upto three locks.
 160 class CMSTokenSyncWithLocks: public CMSTokenSync {
 161  private:
 162   // Note: locks are acquired in textual declaration order
 163   // and released in the opposite order
 164   MutexLockerEx _locker1, _locker2, _locker3;
 165  public:
 166   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 167                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 168     CMSTokenSync(is_cms_thread),
 169     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 170     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 171     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 172   { }
 173 };
 174 
 175 
 176 //////////////////////////////////////////////////////////////////
 177 //  Concurrent Mark-Sweep Generation /////////////////////////////
 178 //////////////////////////////////////////////////////////////////
 179 
 180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 181 
 182 // This struct contains per-thread things necessary to support parallel
 183 // young-gen collection.
 184 class CMSParGCThreadState: public CHeapObj<mtGC> {
 185  public:
 186   CFLS_LAB 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->print(" ");
 429 }
 430 #endif // #ifndef PRODUCT
 431 
 432 CMSCollector::CollectorState CMSCollector::_collectorState =
 433                              CMSCollector::Idling;
 434 bool CMSCollector::_foregroundGCIsActive = false;
 435 bool CMSCollector::_foregroundGCShouldWait = false;
 436 
 437 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 438                            CardTableRS*                   ct,
 439                            ConcurrentMarkSweepPolicy*     cp):
 440   _cmsGen(cmsGen),
 441   _ct(ct),
 442   _ref_processor(NULL),    // will be set later
 443   _conc_workers(NULL),     // may be set later
 444   _abort_preclean(false),
 445   _start_sampling(false),
 446   _between_prologue_and_epilogue(false),
 447   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 448   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 449                  -1 /* lock-free */, "No_lock" /* dummy */),
 450   _modUnionClosurePar(&_modUnionTable),
 451   // Adjust my span to cover old (cms) gen
 452   _span(cmsGen->reserved()),
 453   // Construct the is_alive_closure with _span & markBitMap
 454   _is_alive_closure(_span, &_markBitMap),
 455   _restart_addr(NULL),
 456   _overflow_list(NULL),
 457   _stats(cmsGen),
 458   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 459                              //verify that this lock should be acquired with safepoint check.
 460                              Monitor::_safepoint_check_sometimes)),
 461   _eden_chunk_array(NULL),     // may be set in ctor body
 462   _eden_chunk_capacity(0),     // -- ditto --
 463   _eden_chunk_index(0),        // -- ditto --
 464   _survivor_plab_array(NULL),  // -- ditto --
 465   _survivor_chunk_array(NULL), // -- ditto --
 466   _survivor_chunk_capacity(0), // -- ditto --
 467   _survivor_chunk_index(0),    // -- ditto --
 468   _ser_pmc_preclean_ovflw(0),
 469   _ser_kac_preclean_ovflw(0),
 470   _ser_pmc_remark_ovflw(0),
 471   _par_pmc_remark_ovflw(0),
 472   _ser_kac_ovflw(0),
 473   _par_kac_ovflw(0),
 474 #ifndef PRODUCT
 475   _num_par_pushes(0),
 476 #endif
 477   _collection_count_start(0),
 478   _verifying(false),
 479   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 480   _completed_initialization(false),
 481   _collector_policy(cp),
 482   _should_unload_classes(CMSClassUnloadingEnabled),
 483   _concurrent_cycles_since_last_unload(0),
 484   _roots_scanning_options(GenCollectedHeap::SO_None),
 485   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 486   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 487   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 488   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 489   _cms_start_registered(false)
 490 {
 491   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 492     ExplicitGCInvokesConcurrent = true;
 493   }
 494   // Now expand the span and allocate the collection support structures
 495   // (MUT, marking bit map etc.) to cover both generations subject to
 496   // collection.
 497 
 498   // For use by dirty card to oop closures.
 499   _cmsGen->cmsSpace()->set_collector(this);
 500 
 501   // Allocate MUT and marking bit map
 502   {
 503     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 504     if (!_markBitMap.allocate(_span)) {
 505       warning("Failed to allocate CMS Bit Map");
 506       return;
 507     }
 508     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 509   }
 510   {
 511     _modUnionTable.allocate(_span);
 512     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 513   }
 514 
 515   if (!_markStack.allocate(MarkStackSize)) {
 516     warning("Failed to allocate CMS Marking Stack");
 517     return;
 518   }
 519 
 520   // Support for multi-threaded concurrent phases
 521   if (CMSConcurrentMTEnabled) {
 522     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 523       // just for now
 524       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 525     }
 526     if (ConcGCThreads > 1) {
 527       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 528                                  ConcGCThreads, true);
 529       if (_conc_workers == NULL) {
 530         warning("GC/CMS: _conc_workers allocation failure: "
 531               "forcing -CMSConcurrentMTEnabled");
 532         CMSConcurrentMTEnabled = false;
 533       } else {
 534         _conc_workers->initialize_workers();
 535       }
 536     } else {
 537       CMSConcurrentMTEnabled = false;
 538     }
 539   }
 540   if (!CMSConcurrentMTEnabled) {
 541     ConcGCThreads = 0;
 542   } else {
 543     // Turn off CMSCleanOnEnter optimization temporarily for
 544     // the MT case where it's not fixed yet; see 6178663.
 545     CMSCleanOnEnter = false;
 546   }
 547   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 548          "Inconsistency");
 549 
 550   // Parallel task queues; these are shared for the
 551   // concurrent and stop-world phases of CMS, but
 552   // are not shared with parallel scavenge (ParNew).
 553   {
 554     uint i;
 555     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 556 
 557     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 558          || ParallelRefProcEnabled)
 559         && num_queues > 0) {
 560       _task_queues = new OopTaskQueueSet(num_queues);
 561       if (_task_queues == NULL) {
 562         warning("task_queues allocation failure.");
 563         return;
 564       }
 565       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 566       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 567       for (i = 0; i < num_queues; i++) {
 568         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 569         if (q == NULL) {
 570           warning("work_queue allocation failure.");
 571           return;
 572         }
 573         _task_queues->register_queue(i, q);
 574       }
 575       for (i = 0; i < num_queues; i++) {
 576         _task_queues->queue(i)->initialize();
 577         _hash_seed[i] = 17;  // copied from ParNew
 578       }
 579     }
 580   }
 581 
 582   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 583 
 584   // Clip CMSBootstrapOccupancy between 0 and 100.
 585   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 586 
 587   // Now tell CMS generations the identity of their collector
 588   ConcurrentMarkSweepGeneration::set_collector(this);
 589 
 590   // Create & start a CMS thread for this CMS collector
 591   _cmsThread = ConcurrentMarkSweepThread::start(this);
 592   assert(cmsThread() != NULL, "CMS Thread should have been created");
 593   assert(cmsThread()->collector() == this,
 594          "CMS Thread should refer to this gen");
 595   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 596 
 597   // Support for parallelizing young gen rescan
 598   GenCollectedHeap* gch = GenCollectedHeap::heap();
 599   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 600   _young_gen = (ParNewGeneration*)gch->young_gen();
 601   if (gch->supports_inline_contig_alloc()) {
 602     _top_addr = gch->top_addr();
 603     _end_addr = gch->end_addr();
 604     assert(_young_gen != NULL, "no _young_gen");
 605     _eden_chunk_index = 0;
 606     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 607     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 608   }
 609 
 610   // Support for parallelizing survivor space rescan
 611   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 612     const size_t max_plab_samples =
 613       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 614 
 615     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 616     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 617     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 618     _survivor_chunk_capacity = max_plab_samples;
 619     for (uint i = 0; i < ParallelGCThreads; i++) {
 620       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 621       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 622       assert(cur->end() == 0, "Should be 0");
 623       assert(cur->array() == vec, "Should be vec");
 624       assert(cur->capacity() == max_plab_samples, "Error");
 625     }
 626   }
 627 
 628   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 629   _gc_counters = new CollectorCounters("CMS", 1);
 630   _completed_initialization = true;
 631   _inter_sweep_timer.start();  // start of time
 632 }
 633 
 634 const char* ConcurrentMarkSweepGeneration::name() const {
 635   return "concurrent mark-sweep generation";
 636 }
 637 void ConcurrentMarkSweepGeneration::update_counters() {
 638   if (UsePerfData) {
 639     _space_counters->update_all();
 640     _gen_counters->update_all();
 641   }
 642 }
 643 
 644 // this is an optimized version of update_counters(). it takes the
 645 // used value as a parameter rather than computing it.
 646 //
 647 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 648   if (UsePerfData) {
 649     _space_counters->update_used(used);
 650     _space_counters->update_capacity();
 651     _gen_counters->update_all();
 652   }
 653 }
 654 
 655 void ConcurrentMarkSweepGeneration::print() const {
 656   Generation::print();
 657   cmsSpace()->print();
 658 }
 659 
 660 #ifndef PRODUCT
 661 void ConcurrentMarkSweepGeneration::print_statistics() {
 662   cmsSpace()->printFLCensus(0);
 663 }
 664 #endif
 665 
 666 size_t
 667 ConcurrentMarkSweepGeneration::contiguous_available() const {
 668   // dld proposes an improvement in precision here. If the committed
 669   // part of the space ends in a free block we should add that to
 670   // uncommitted size in the calculation below. Will make this
 671   // change later, staying with the approximation below for the
 672   // time being. -- ysr.
 673   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 674 }
 675 
 676 size_t
 677 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 678   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 679 }
 680 
 681 size_t ConcurrentMarkSweepGeneration::max_available() const {
 682   return free() + _virtual_space.uncommitted_size();
 683 }
 684 
 685 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 686   size_t available = max_available();
 687   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 688   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 689   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 690                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 691   return res;
 692 }
 693 
 694 // At a promotion failure dump information on block layout in heap
 695 // (cms old generation).
 696 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 697   LogHandle(gc, promotion) log;
 698   if (log.is_trace()) {
 699     ResourceMark rm;
 700     cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
 701   }
 702 }
 703 
 704 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 705   // Clear the promotion information.  These pointers can be adjusted
 706   // along with all the other pointers into the heap but
 707   // compaction is expected to be a rare event with
 708   // a heap using cms so don't do it without seeing the need.
 709   for (uint i = 0; i < ParallelGCThreads; i++) {
 710     _par_gc_thread_states[i]->promo.reset();
 711   }
 712 }
 713 
 714 void ConcurrentMarkSweepGeneration::compute_new_size() {
 715   assert_locked_or_safepoint(Heap_lock);
 716 
 717   // If incremental collection failed, we just want to expand
 718   // to the limit.
 719   if (incremental_collection_failed()) {
 720     clear_incremental_collection_failed();
 721     grow_to_reserved();
 722     return;
 723   }
 724 
 725   // The heap has been compacted but not reset yet.
 726   // Any metric such as free() or used() will be incorrect.
 727 
 728   CardGeneration::compute_new_size();
 729 
 730   // Reset again after a possible resizing
 731   if (did_compact()) {
 732     cmsSpace()->reset_after_compaction();
 733   }
 734 }
 735 
 736 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 737   assert_locked_or_safepoint(Heap_lock);
 738 
 739   // If incremental collection failed, we just want to expand
 740   // to the limit.
 741   if (incremental_collection_failed()) {
 742     clear_incremental_collection_failed();
 743     grow_to_reserved();
 744     return;
 745   }
 746 
 747   double free_percentage = ((double) free()) / capacity();
 748   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 749   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 750 
 751   // compute expansion delta needed for reaching desired free percentage
 752   if (free_percentage < desired_free_percentage) {
 753     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 754     assert(desired_capacity >= capacity(), "invalid expansion size");
 755     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 756     LogHandle(gc) log;
 757     if (log.is_trace()) {
 758       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 759       log.trace("From compute_new_size: ");
 760       log.trace("  Free fraction %f", free_percentage);
 761       log.trace("  Desired free fraction %f", desired_free_percentage);
 762       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 763       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 764       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 765       GenCollectedHeap* gch = GenCollectedHeap::heap();
 766       assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
 767       size_t young_size = gch->young_gen()->capacity();
 768       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 769       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 770       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 771       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 772     }
 773     // safe if expansion fails
 774     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 775     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 776   } else {
 777     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 778     assert(desired_capacity <= capacity(), "invalid expansion size");
 779     size_t shrink_bytes = capacity() - desired_capacity;
 780     // Don't shrink unless the delta is greater than the minimum shrink we want
 781     if (shrink_bytes >= MinHeapDeltaBytes) {
 782       shrink_free_list_by(shrink_bytes);
 783     }
 784   }
 785 }
 786 
 787 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 788   return cmsSpace()->freelistLock();
 789 }
 790 
 791 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 792   CMSSynchronousYieldRequest yr;
 793   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 794   return have_lock_and_allocate(size, tlab);
 795 }
 796 
 797 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 798                                                                 bool   tlab /* ignored */) {
 799   assert_lock_strong(freelistLock());
 800   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 801   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 802   // Allocate the object live (grey) if the background collector has
 803   // started marking. This is necessary because the marker may
 804   // have passed this address and consequently this object will
 805   // not otherwise be greyed and would be incorrectly swept up.
 806   // Note that if this object contains references, the writing
 807   // of those references will dirty the card containing this object
 808   // allowing the object to be blackened (and its references scanned)
 809   // either during a preclean phase or at the final checkpoint.
 810   if (res != NULL) {
 811     // We may block here with an uninitialized object with
 812     // its mark-bit or P-bits not yet set. Such objects need
 813     // to be safely navigable by block_start().
 814     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 815     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 816     collector()->direct_allocated(res, adjustedSize);
 817     _direct_allocated_words += adjustedSize;
 818     // allocation counters
 819     NOT_PRODUCT(
 820       _numObjectsAllocated++;
 821       _numWordsAllocated += (int)adjustedSize;
 822     )
 823   }
 824   return res;
 825 }
 826 
 827 // In the case of direct allocation by mutators in a generation that
 828 // is being concurrently collected, the object must be allocated
 829 // live (grey) if the background collector has started marking.
 830 // This is necessary because the marker may
 831 // have passed this address and consequently this object will
 832 // not otherwise be greyed and would be incorrectly swept up.
 833 // Note that if this object contains references, the writing
 834 // of those references will dirty the card containing this object
 835 // allowing the object to be blackened (and its references scanned)
 836 // either during a preclean phase or at the final checkpoint.
 837 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 838   assert(_markBitMap.covers(start, size), "Out of bounds");
 839   if (_collectorState >= Marking) {
 840     MutexLockerEx y(_markBitMap.lock(),
 841                     Mutex::_no_safepoint_check_flag);
 842     // [see comments preceding SweepClosure::do_blk() below for details]
 843     //
 844     // Can the P-bits be deleted now?  JJJ
 845     //
 846     // 1. need to mark the object as live so it isn't collected
 847     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 848     // 3. need to mark the end of the object so marking, precleaning or sweeping
 849     //    can skip over uninitialized or unparsable objects. An allocated
 850     //    object is considered uninitialized for our purposes as long as
 851     //    its klass word is NULL.  All old gen objects are parsable
 852     //    as soon as they are initialized.)
 853     _markBitMap.mark(start);          // object is live
 854     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 855     _markBitMap.mark(start + size - 1);
 856                                       // mark end of object
 857   }
 858   // check that oop looks uninitialized
 859   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 860 }
 861 
 862 void CMSCollector::promoted(bool par, HeapWord* start,
 863                             bool is_obj_array, size_t obj_size) {
 864   assert(_markBitMap.covers(start), "Out of bounds");
 865   // See comment in direct_allocated() about when objects should
 866   // be allocated live.
 867   if (_collectorState >= Marking) {
 868     // we already hold the marking bit map lock, taken in
 869     // the prologue
 870     if (par) {
 871       _markBitMap.par_mark(start);
 872     } else {
 873       _markBitMap.mark(start);
 874     }
 875     // We don't need to mark the object as uninitialized (as
 876     // in direct_allocated above) because this is being done with the
 877     // world stopped and the object will be initialized by the
 878     // time the marking, precleaning or sweeping get to look at it.
 879     // But see the code for copying objects into the CMS generation,
 880     // where we need to ensure that concurrent readers of the
 881     // block offset table are able to safely navigate a block that
 882     // is in flux from being free to being allocated (and in
 883     // transition while being copied into) and subsequently
 884     // becoming a bona-fide object when the copy/promotion is complete.
 885     assert(SafepointSynchronize::is_at_safepoint(),
 886            "expect promotion only at safepoints");
 887 
 888     if (_collectorState < Sweeping) {
 889       // Mark the appropriate cards in the modUnionTable, so that
 890       // this object gets scanned before the sweep. If this is
 891       // not done, CMS generation references in the object might
 892       // not get marked.
 893       // For the case of arrays, which are otherwise precisely
 894       // marked, we need to dirty the entire array, not just its head.
 895       if (is_obj_array) {
 896         // The [par_]mark_range() method expects mr.end() below to
 897         // be aligned to the granularity of a bit's representation
 898         // in the heap. In the case of the MUT below, that's a
 899         // card size.
 900         MemRegion mr(start,
 901                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 902                         CardTableModRefBS::card_size /* bytes */));
 903         if (par) {
 904           _modUnionTable.par_mark_range(mr);
 905         } else {
 906           _modUnionTable.mark_range(mr);
 907         }
 908       } else {  // not an obj array; we can just mark the head
 909         if (par) {
 910           _modUnionTable.par_mark(start);
 911         } else {
 912           _modUnionTable.mark(start);
 913         }
 914       }
 915     }
 916   }
 917 }
 918 
 919 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 920   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 921   // allocate, copy and if necessary update promoinfo --
 922   // delegate to underlying space.
 923   assert_lock_strong(freelistLock());
 924 
 925 #ifndef PRODUCT
 926   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 927     return NULL;
 928   }
 929 #endif  // #ifndef PRODUCT
 930 
 931   oop res = _cmsSpace->promote(obj, obj_size);
 932   if (res == NULL) {
 933     // expand and retry
 934     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 935     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 936     // Since this is the old generation, we don't try to promote
 937     // into a more senior generation.
 938     res = _cmsSpace->promote(obj, obj_size);
 939   }
 940   if (res != NULL) {
 941     // See comment in allocate() about when objects should
 942     // be allocated live.
 943     assert(obj->is_oop(), "Will dereference klass pointer below");
 944     collector()->promoted(false,           // Not parallel
 945                           (HeapWord*)res, obj->is_objArray(), obj_size);
 946     // promotion counters
 947     NOT_PRODUCT(
 948       _numObjectsPromoted++;
 949       _numWordsPromoted +=
 950         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 951     )
 952   }
 953   return res;
 954 }
 955 
 956 
 957 // IMPORTANT: Notes on object size recognition in CMS.
 958 // ---------------------------------------------------
 959 // A block of storage in the CMS generation is always in
 960 // one of three states. A free block (FREE), an allocated
 961 // object (OBJECT) whose size() method reports the correct size,
 962 // and an intermediate state (TRANSIENT) in which its size cannot
 963 // be accurately determined.
 964 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 965 // -----------------------------------------------------
 966 // FREE:      klass_word & 1 == 1; mark_word holds block size
 967 //
 968 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 969 //            obj->size() computes correct size
 970 //
 971 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 972 //
 973 // STATE IDENTIFICATION: (64 bit+COOPS)
 974 // ------------------------------------
 975 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 976 //
 977 // OBJECT:    klass_word installed; klass_word != 0;
 978 //            obj->size() computes correct size
 979 //
 980 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 981 //
 982 //
 983 // STATE TRANSITION DIAGRAM
 984 //
 985 //        mut / parnew                     mut  /  parnew
 986 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 987 //  ^                                                                   |
 988 //  |------------------------ DEAD <------------------------------------|
 989 //         sweep                            mut
 990 //
 991 // While a block is in TRANSIENT state its size cannot be determined
 992 // so readers will either need to come back later or stall until
 993 // the size can be determined. Note that for the case of direct
 994 // allocation, P-bits, when available, may be used to determine the
 995 // size of an object that may not yet have been initialized.
 996 
 997 // Things to support parallel young-gen collection.
 998 oop
 999 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1000                                            oop old, markOop m,
1001                                            size_t word_sz) {
1002 #ifndef PRODUCT
1003   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1004     return NULL;
1005   }
1006 #endif  // #ifndef PRODUCT
1007 
1008   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1009   PromotionInfo* promoInfo = &ps->promo;
1010   // if we are tracking promotions, then first ensure space for
1011   // promotion (including spooling space for saving header if necessary).
1012   // then allocate and copy, then track promoted info if needed.
1013   // When tracking (see PromotionInfo::track()), the mark word may
1014   // be displaced and in this case restoration of the mark word
1015   // occurs in the (oop_since_save_marks_)iterate phase.
1016   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1017     // Out of space for allocating spooling buffers;
1018     // try expanding and allocating spooling buffers.
1019     if (!expand_and_ensure_spooling_space(promoInfo)) {
1020       return NULL;
1021     }
1022   }
1023   assert(promoInfo->has_spooling_space(), "Control point invariant");
1024   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1025   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1026   if (obj_ptr == NULL) {
1027      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1028      if (obj_ptr == NULL) {
1029        return NULL;
1030      }
1031   }
1032   oop obj = oop(obj_ptr);
1033   OrderAccess::storestore();
1034   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1035   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1036   // IMPORTANT: See note on object initialization for CMS above.
1037   // Otherwise, copy the object.  Here we must be careful to insert the
1038   // klass pointer last, since this marks the block as an allocated object.
1039   // Except with compressed oops it's the mark word.
1040   HeapWord* old_ptr = (HeapWord*)old;
1041   // Restore the mark word copied above.
1042   obj->set_mark(m);
1043   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1044   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1045   OrderAccess::storestore();
1046 
1047   if (UseCompressedClassPointers) {
1048     // Copy gap missed by (aligned) header size calculation below
1049     obj->set_klass_gap(old->klass_gap());
1050   }
1051   if (word_sz > (size_t)oopDesc::header_size()) {
1052     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1053                                  obj_ptr + oopDesc::header_size(),
1054                                  word_sz - oopDesc::header_size());
1055   }
1056 
1057   // Now we can track the promoted object, if necessary.  We take care
1058   // to delay the transition from uninitialized to full object
1059   // (i.e., insertion of klass pointer) until after, so that it
1060   // atomically becomes a promoted object.
1061   if (promoInfo->tracking()) {
1062     promoInfo->track((PromotedObject*)obj, old->klass());
1063   }
1064   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1065   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1066   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1067 
1068   // Finally, install the klass pointer (this should be volatile).
1069   OrderAccess::storestore();
1070   obj->set_klass(old->klass());
1071   // We should now be able to calculate the right size for this object
1072   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1073 
1074   collector()->promoted(true,          // parallel
1075                         obj_ptr, old->is_objArray(), word_sz);
1076 
1077   NOT_PRODUCT(
1078     Atomic::inc_ptr(&_numObjectsPromoted);
1079     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1080   )
1081 
1082   return obj;
1083 }
1084 
1085 void
1086 ConcurrentMarkSweepGeneration::
1087 par_promote_alloc_done(int thread_num) {
1088   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1089   ps->lab.retire(thread_num);
1090 }
1091 
1092 void
1093 ConcurrentMarkSweepGeneration::
1094 par_oop_since_save_marks_iterate_done(int thread_num) {
1095   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1096   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1097   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1098 }
1099 
1100 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1101                                                    size_t size,
1102                                                    bool   tlab)
1103 {
1104   // We allow a STW collection only if a full
1105   // collection was requested.
1106   return full || should_allocate(size, tlab); // FIX ME !!!
1107   // This and promotion failure handling are connected at the
1108   // hip and should be fixed by untying them.
1109 }
1110 
1111 bool CMSCollector::shouldConcurrentCollect() {
1112   if (_full_gc_requested) {
1113     log_trace(gc)("CMSCollector: collect because of explicit  gc request (or gc_locker)");
1114     return true;
1115   }
1116 
1117   FreelistLocker x(this);
1118   // ------------------------------------------------------------------
1119   // Print out lots of information which affects the initiation of
1120   // a collection.
1121   LogHandle(gc) log;
1122   if (log.is_trace() && stats().valid()) {
1123     log.trace("CMSCollector shouldConcurrentCollect: ");
1124     ResourceMark rm;
1125     stats().print_on(log.debug_stream());
1126     log.trace("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1127     log.trace("free=" SIZE_FORMAT, _cmsGen->free());
1128     log.trace("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1129     log.trace("promotion_rate=%g", stats().promotion_rate());
1130     log.trace("cms_allocation_rate=%g", stats().cms_allocation_rate());
1131     log.trace("occupancy=%3.7f", _cmsGen->occupancy());
1132     log.trace("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1133     log.trace("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1134     log.trace("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1135     log.trace("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1136   }
1137   // ------------------------------------------------------------------
1138 
1139   // If the estimated time to complete a cms collection (cms_duration())
1140   // is less than the estimated time remaining until the cms generation
1141   // is full, start a collection.
1142   if (!UseCMSInitiatingOccupancyOnly) {
1143     if (stats().valid()) {
1144       if (stats().time_until_cms_start() == 0.0) {
1145         return true;
1146       }
1147     } else {
1148       // We want to conservatively collect somewhat early in order
1149       // to try and "bootstrap" our CMS/promotion statistics;
1150       // this branch will not fire after the first successful CMS
1151       // collection because the stats should then be valid.
1152       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1153         log_trace(gc)(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1154                       _cmsGen->occupancy(), _bootstrap_occupancy);
1155         return true;
1156       }
1157     }
1158   }
1159 
1160   // Otherwise, we start a collection cycle if
1161   // old gen want a collection cycle started. Each may use
1162   // an appropriate criterion for making this decision.
1163   // XXX We need to make sure that the gen expansion
1164   // criterion dovetails well with this. XXX NEED TO FIX THIS
1165   if (_cmsGen->should_concurrent_collect()) {
1166     log_trace(gc)("CMS old gen initiated");
1167     return true;
1168   }
1169 
1170   // We start a collection if we believe an incremental collection may fail;
1171   // this is not likely to be productive in practice because it's probably too
1172   // late anyway.
1173   GenCollectedHeap* gch = GenCollectedHeap::heap();
1174   assert(gch->collector_policy()->is_generation_policy(),
1175          "You may want to check the correctness of the following");
1176   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1177     log_trace(gc)("CMSCollector: collect because incremental collection will fail ");
1178     return true;
1179   }
1180 
1181   if (MetaspaceGC::should_concurrent_collect()) {
1182     log_trace(gc)("CMSCollector: collect for metadata allocation ");
1183     return true;
1184   }
1185 
1186   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1187   if (CMSTriggerInterval >= 0) {
1188     if (CMSTriggerInterval == 0) {
1189       // Trigger always
1190       return true;
1191     }
1192 
1193     // Check the CMS time since begin (we do not check the stats validity
1194     // as we want to be able to trigger the first CMS cycle as well)
1195     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1196       if (stats().valid()) {
1197         log_trace(gc)("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1198                       stats().cms_time_since_begin());
1199       } else {
1200         log_trace(gc)("CMSCollector: collect because of trigger interval (first collection)");
1201       }
1202       return true;
1203     }
1204   }
1205 
1206   return false;
1207 }
1208 
1209 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1210 
1211 // Clear _expansion_cause fields of constituent generations
1212 void CMSCollector::clear_expansion_cause() {
1213   _cmsGen->clear_expansion_cause();
1214 }
1215 
1216 // We should be conservative in starting a collection cycle.  To
1217 // start too eagerly runs the risk of collecting too often in the
1218 // extreme.  To collect too rarely falls back on full collections,
1219 // which works, even if not optimum in terms of concurrent work.
1220 // As a work around for too eagerly collecting, use the flag
1221 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1222 // giving the user an easily understandable way of controlling the
1223 // collections.
1224 // We want to start a new collection cycle if any of the following
1225 // conditions hold:
1226 // . our current occupancy exceeds the configured initiating occupancy
1227 //   for this generation, or
1228 // . we recently needed to expand this space and have not, since that
1229 //   expansion, done a collection of this generation, or
1230 // . the underlying space believes that it may be a good idea to initiate
1231 //   a concurrent collection (this may be based on criteria such as the
1232 //   following: the space uses linear allocation and linear allocation is
1233 //   going to fail, or there is believed to be excessive fragmentation in
1234 //   the generation, etc... or ...
1235 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1236 //   the case of the old generation; see CR 6543076):
1237 //   we may be approaching a point at which allocation requests may fail because
1238 //   we will be out of sufficient free space given allocation rate estimates.]
1239 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1240 
1241   assert_lock_strong(freelistLock());
1242   if (occupancy() > initiating_occupancy()) {
1243     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1244                   short_name(), occupancy(), initiating_occupancy());
1245     return true;
1246   }
1247   if (UseCMSInitiatingOccupancyOnly) {
1248     return false;
1249   }
1250   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1251     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1252     return true;
1253   }
1254   return false;
1255 }
1256 
1257 void ConcurrentMarkSweepGeneration::collect(bool   full,
1258                                             bool   clear_all_soft_refs,
1259                                             size_t size,
1260                                             bool   tlab)
1261 {
1262   collector()->collect(full, clear_all_soft_refs, size, tlab);
1263 }
1264 
1265 void CMSCollector::collect(bool   full,
1266                            bool   clear_all_soft_refs,
1267                            size_t size,
1268                            bool   tlab)
1269 {
1270   // The following "if" branch is present for defensive reasons.
1271   // In the current uses of this interface, it can be replaced with:
1272   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1273   // But I am not placing that assert here to allow future
1274   // generality in invoking this interface.
1275   if (GC_locker::is_active()) {
1276     // A consistency test for GC_locker
1277     assert(GC_locker::needs_gc(), "Should have been set already");
1278     // Skip this foreground collection, instead
1279     // expanding the heap if necessary.
1280     // Need the free list locks for the call to free() in compute_new_size()
1281     compute_new_size();
1282     return;
1283   }
1284   acquire_control_and_collect(full, clear_all_soft_refs);
1285 }
1286 
1287 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1288   GenCollectedHeap* gch = GenCollectedHeap::heap();
1289   unsigned int gc_count = gch->total_full_collections();
1290   if (gc_count == full_gc_count) {
1291     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1292     _full_gc_requested = true;
1293     _full_gc_cause = cause;
1294     CGC_lock->notify();   // nudge CMS thread
1295   } else {
1296     assert(gc_count > full_gc_count, "Error: causal loop");
1297   }
1298 }
1299 
1300 bool CMSCollector::is_external_interruption() {
1301   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1302   return GCCause::is_user_requested_gc(cause) ||
1303          GCCause::is_serviceability_requested_gc(cause);
1304 }
1305 
1306 void CMSCollector::report_concurrent_mode_interruption() {
1307   if (is_external_interruption()) {
1308     log_debug(gc)("Concurrent mode interrupted");
1309   } else {
1310     log_debug(gc)("Concurrent mode failure");
1311     _gc_tracer_cm->report_concurrent_mode_failure();
1312   }
1313 }
1314 
1315 
1316 // The foreground and background collectors need to coordinate in order
1317 // to make sure that they do not mutually interfere with CMS collections.
1318 // When a background collection is active,
1319 // the foreground collector may need to take over (preempt) and
1320 // synchronously complete an ongoing collection. Depending on the
1321 // frequency of the background collections and the heap usage
1322 // of the application, this preemption can be seldom or frequent.
1323 // There are only certain
1324 // points in the background collection that the "collection-baton"
1325 // can be passed to the foreground collector.
1326 //
1327 // The foreground collector will wait for the baton before
1328 // starting any part of the collection.  The foreground collector
1329 // will only wait at one location.
1330 //
1331 // The background collector will yield the baton before starting a new
1332 // phase of the collection (e.g., before initial marking, marking from roots,
1333 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1334 // of the loop which switches the phases. The background collector does some
1335 // of the phases (initial mark, final re-mark) with the world stopped.
1336 // Because of locking involved in stopping the world,
1337 // the foreground collector should not block waiting for the background
1338 // collector when it is doing a stop-the-world phase.  The background
1339 // collector will yield the baton at an additional point just before
1340 // it enters a stop-the-world phase.  Once the world is stopped, the
1341 // background collector checks the phase of the collection.  If the
1342 // phase has not changed, it proceeds with the collection.  If the
1343 // phase has changed, it skips that phase of the collection.  See
1344 // the comments on the use of the Heap_lock in collect_in_background().
1345 //
1346 // Variable used in baton passing.
1347 //   _foregroundGCIsActive - Set to true by the foreground collector when
1348 //      it wants the baton.  The foreground clears it when it has finished
1349 //      the collection.
1350 //   _foregroundGCShouldWait - Set to true by the background collector
1351 //        when it is running.  The foreground collector waits while
1352 //      _foregroundGCShouldWait is true.
1353 //  CGC_lock - monitor used to protect access to the above variables
1354 //      and to notify the foreground and background collectors.
1355 //  _collectorState - current state of the CMS collection.
1356 //
1357 // The foreground collector
1358 //   acquires the CGC_lock
1359 //   sets _foregroundGCIsActive
1360 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1361 //     various locks acquired in preparation for the collection
1362 //     are released so as not to block the background collector
1363 //     that is in the midst of a collection
1364 //   proceeds with the collection
1365 //   clears _foregroundGCIsActive
1366 //   returns
1367 //
1368 // The background collector in a loop iterating on the phases of the
1369 //      collection
1370 //   acquires the CGC_lock
1371 //   sets _foregroundGCShouldWait
1372 //   if _foregroundGCIsActive is set
1373 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1374 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1375 //     and exits the loop.
1376 //   otherwise
1377 //     proceed with that phase of the collection
1378 //     if the phase is a stop-the-world phase,
1379 //       yield the baton once more just before enqueueing
1380 //       the stop-world CMS operation (executed by the VM thread).
1381 //   returns after all phases of the collection are done
1382 //
1383 
1384 void CMSCollector::acquire_control_and_collect(bool full,
1385         bool clear_all_soft_refs) {
1386   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1387   assert(!Thread::current()->is_ConcurrentGC_thread(),
1388          "shouldn't try to acquire control from self!");
1389 
1390   // Start the protocol for acquiring control of the
1391   // collection from the background collector (aka CMS thread).
1392   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1393          "VM thread should have CMS token");
1394   // Remember the possibly interrupted state of an ongoing
1395   // concurrent collection
1396   CollectorState first_state = _collectorState;
1397 
1398   // Signal to a possibly ongoing concurrent collection that
1399   // we want to do a foreground collection.
1400   _foregroundGCIsActive = true;
1401 
1402   // release locks and wait for a notify from the background collector
1403   // releasing the locks in only necessary for phases which
1404   // do yields to improve the granularity of the collection.
1405   assert_lock_strong(bitMapLock());
1406   // We need to lock the Free list lock for the space that we are
1407   // currently collecting.
1408   assert(haveFreelistLocks(), "Must be holding free list locks");
1409   bitMapLock()->unlock();
1410   releaseFreelistLocks();
1411   {
1412     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1413     if (_foregroundGCShouldWait) {
1414       // We are going to be waiting for action for the CMS thread;
1415       // it had better not be gone (for instance at shutdown)!
1416       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1417              "CMS thread must be running");
1418       // Wait here until the background collector gives us the go-ahead
1419       ConcurrentMarkSweepThread::clear_CMS_flag(
1420         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1421       // Get a possibly blocked CMS thread going:
1422       //   Note that we set _foregroundGCIsActive true above,
1423       //   without protection of the CGC_lock.
1424       CGC_lock->notify();
1425       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1426              "Possible deadlock");
1427       while (_foregroundGCShouldWait) {
1428         // wait for notification
1429         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1430         // Possibility of delay/starvation here, since CMS token does
1431         // not know to give priority to VM thread? Actually, i think
1432         // there wouldn't be any delay/starvation, but the proof of
1433         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1434       }
1435       ConcurrentMarkSweepThread::set_CMS_flag(
1436         ConcurrentMarkSweepThread::CMS_vm_has_token);
1437     }
1438   }
1439   // The CMS_token is already held.  Get back the other locks.
1440   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1441          "VM thread should have CMS token");
1442   getFreelistLocks();
1443   bitMapLock()->lock_without_safepoint_check();
1444   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1445                        p2i(Thread::current()), first_state);
1446   log_debug(gc, state)("    gets control with state %d", _collectorState);
1447 
1448   // Inform cms gen if this was due to partial collection failing.
1449   // The CMS gen may use this fact to determine its expansion policy.
1450   GenCollectedHeap* gch = GenCollectedHeap::heap();
1451   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1452     assert(!_cmsGen->incremental_collection_failed(),
1453            "Should have been noticed, reacted to and cleared");
1454     _cmsGen->set_incremental_collection_failed();
1455   }
1456 
1457   if (first_state > Idling) {
1458     report_concurrent_mode_interruption();
1459   }
1460 
1461   set_did_compact(true);
1462 
1463   // If the collection is being acquired from the background
1464   // collector, there may be references on the discovered
1465   // references lists.  Abandon those references, since some
1466   // of them may have become unreachable after concurrent
1467   // discovery; the STW compacting collector will redo discovery
1468   // more precisely, without being subject to floating garbage.
1469   // Leaving otherwise unreachable references in the discovered
1470   // lists would require special handling.
1471   ref_processor()->disable_discovery();
1472   ref_processor()->abandon_partial_discovery();
1473   ref_processor()->verify_no_references_recorded();
1474 
1475   if (first_state > Idling) {
1476     save_heap_summary();
1477   }
1478 
1479   do_compaction_work(clear_all_soft_refs);
1480 
1481   // Has the GC time limit been exceeded?
1482   size_t max_eden_size = _young_gen->max_eden_size();
1483   GCCause::Cause gc_cause = gch->gc_cause();
1484   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1485                                          _young_gen->eden()->used(),
1486                                          _cmsGen->max_capacity(),
1487                                          max_eden_size,
1488                                          full,
1489                                          gc_cause,
1490                                          gch->collector_policy());
1491 
1492   // Reset the expansion cause, now that we just completed
1493   // a collection cycle.
1494   clear_expansion_cause();
1495   _foregroundGCIsActive = false;
1496   return;
1497 }
1498 
1499 // Resize the tenured generation
1500 // after obtaining the free list locks for the
1501 // two generations.
1502 void CMSCollector::compute_new_size() {
1503   assert_locked_or_safepoint(Heap_lock);
1504   FreelistLocker z(this);
1505   MetaspaceGC::compute_new_size();
1506   _cmsGen->compute_new_size_free_list();
1507 }
1508 
1509 // A work method used by the foreground collector to do
1510 // a mark-sweep-compact.
1511 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1512   GenCollectedHeap* gch = GenCollectedHeap::heap();
1513 
1514   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1515   gc_timer->register_gc_start();
1516 
1517   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1518   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1519 
1520   GCTraceTime(Trace, gc) t("CMS:MSC");
1521 
1522   // Temporarily widen the span of the weak reference processing to
1523   // the entire heap.
1524   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1525   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1526   // Temporarily, clear the "is_alive_non_header" field of the
1527   // reference processor.
1528   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1529   // Temporarily make reference _processing_ single threaded (non-MT).
1530   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1531   // Temporarily make refs discovery atomic
1532   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1533   // Temporarily make reference _discovery_ single threaded (non-MT)
1534   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1535 
1536   ref_processor()->set_enqueuing_is_done(false);
1537   ref_processor()->enable_discovery();
1538   ref_processor()->setup_policy(clear_all_soft_refs);
1539   // If an asynchronous collection finishes, the _modUnionTable is
1540   // all clear.  If we are assuming the collection from an asynchronous
1541   // collection, clear the _modUnionTable.
1542   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1543     "_modUnionTable should be clear if the baton was not passed");
1544   _modUnionTable.clear_all();
1545   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1546     "mod union for klasses should be clear if the baton was passed");
1547   _ct->klass_rem_set()->clear_mod_union();
1548 
1549   // We must adjust the allocation statistics being maintained
1550   // in the free list space. We do so by reading and clearing
1551   // the sweep timer and updating the block flux rate estimates below.
1552   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1553   if (_inter_sweep_timer.is_active()) {
1554     _inter_sweep_timer.stop();
1555     // Note that we do not use this sample to update the _inter_sweep_estimate.
1556     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1557                                             _inter_sweep_estimate.padded_average(),
1558                                             _intra_sweep_estimate.padded_average());
1559   }
1560 
1561   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1562   #ifdef ASSERT
1563     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1564     size_t free_size = cms_space->free();
1565     assert(free_size ==
1566            pointer_delta(cms_space->end(), cms_space->compaction_top())
1567            * HeapWordSize,
1568       "All the free space should be compacted into one chunk at top");
1569     assert(cms_space->dictionary()->total_chunk_size(
1570                                       debug_only(cms_space->freelistLock())) == 0 ||
1571            cms_space->totalSizeInIndexedFreeLists() == 0,
1572       "All the free space should be in a single chunk");
1573     size_t num = cms_space->totalCount();
1574     assert((free_size == 0 && num == 0) ||
1575            (free_size > 0  && (num == 1 || num == 2)),
1576          "There should be at most 2 free chunks after compaction");
1577   #endif // ASSERT
1578   _collectorState = Resetting;
1579   assert(_restart_addr == NULL,
1580          "Should have been NULL'd before baton was passed");
1581   reset_stw();
1582   _cmsGen->reset_after_compaction();
1583   _concurrent_cycles_since_last_unload = 0;
1584 
1585   // Clear any data recorded in the PLAB chunk arrays.
1586   if (_survivor_plab_array != NULL) {
1587     reset_survivor_plab_arrays();
1588   }
1589 
1590   // Adjust the per-size allocation stats for the next epoch.
1591   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1592   // Restart the "inter sweep timer" for the next epoch.
1593   _inter_sweep_timer.reset();
1594   _inter_sweep_timer.start();
1595 
1596   gc_timer->register_gc_end();
1597 
1598   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1599 
1600   // For a mark-sweep-compact, compute_new_size() will be called
1601   // in the heap's do_collection() method.
1602 }
1603 
1604 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1605   LogHandle(gc, heap) log;
1606   if (!log.is_trace()) {
1607     return;
1608   }
1609 
1610   ContiguousSpace* eden_space = _young_gen->eden();
1611   ContiguousSpace* from_space = _young_gen->from();
1612   ContiguousSpace* to_space   = _young_gen->to();
1613   // Eden
1614   if (_eden_chunk_array != NULL) {
1615     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1616               p2i(eden_space->bottom()), p2i(eden_space->top()),
1617               p2i(eden_space->end()), eden_space->capacity());
1618     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1619               _eden_chunk_index, _eden_chunk_capacity);
1620     for (size_t i = 0; i < _eden_chunk_index; i++) {
1621       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1622     }
1623   }
1624   // Survivor
1625   if (_survivor_chunk_array != NULL) {
1626     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1627               p2i(from_space->bottom()), p2i(from_space->top()),
1628               p2i(from_space->end()), from_space->capacity());
1629     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1630               _survivor_chunk_index, _survivor_chunk_capacity);
1631     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1632       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1633     }
1634   }
1635 }
1636 
1637 void CMSCollector::getFreelistLocks() const {
1638   // Get locks for all free lists in all generations that this
1639   // collector is responsible for
1640   _cmsGen->freelistLock()->lock_without_safepoint_check();
1641 }
1642 
1643 void CMSCollector::releaseFreelistLocks() const {
1644   // Release locks for all free lists in all generations that this
1645   // collector is responsible for
1646   _cmsGen->freelistLock()->unlock();
1647 }
1648 
1649 bool CMSCollector::haveFreelistLocks() const {
1650   // Check locks for all free lists in all generations that this
1651   // collector is responsible for
1652   assert_lock_strong(_cmsGen->freelistLock());
1653   PRODUCT_ONLY(ShouldNotReachHere());
1654   return true;
1655 }
1656 
1657 // A utility class that is used by the CMS collector to
1658 // temporarily "release" the foreground collector from its
1659 // usual obligation to wait for the background collector to
1660 // complete an ongoing phase before proceeding.
1661 class ReleaseForegroundGC: public StackObj {
1662  private:
1663   CMSCollector* _c;
1664  public:
1665   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1666     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1667     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1668     // allow a potentially blocked foreground collector to proceed
1669     _c->_foregroundGCShouldWait = false;
1670     if (_c->_foregroundGCIsActive) {
1671       CGC_lock->notify();
1672     }
1673     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1674            "Possible deadlock");
1675   }
1676 
1677   ~ReleaseForegroundGC() {
1678     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1679     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1680     _c->_foregroundGCShouldWait = true;
1681   }
1682 };
1683 
1684 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1685   assert(Thread::current()->is_ConcurrentGC_thread(),
1686     "A CMS asynchronous collection is only allowed on a CMS thread.");
1687 
1688   GenCollectedHeap* gch = GenCollectedHeap::heap();
1689   {
1690     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1691     MutexLockerEx hl(Heap_lock, safepoint_check);
1692     FreelistLocker fll(this);
1693     MutexLockerEx x(CGC_lock, safepoint_check);
1694     if (_foregroundGCIsActive) {
1695       // The foreground collector is. Skip this
1696       // background collection.
1697       assert(!_foregroundGCShouldWait, "Should be clear");
1698       return;
1699     } else {
1700       assert(_collectorState == Idling, "Should be idling before start.");
1701       _collectorState = InitialMarking;
1702       register_gc_start(cause);
1703       // Reset the expansion cause, now that we are about to begin
1704       // a new cycle.
1705       clear_expansion_cause();
1706 
1707       // Clear the MetaspaceGC flag since a concurrent collection
1708       // is starting but also clear it after the collection.
1709       MetaspaceGC::set_should_concurrent_collect(false);
1710     }
1711     // Decide if we want to enable class unloading as part of the
1712     // ensuing concurrent GC cycle.
1713     update_should_unload_classes();
1714     _full_gc_requested = false;           // acks all outstanding full gc requests
1715     _full_gc_cause = GCCause::_no_gc;
1716     // Signal that we are about to start a collection
1717     gch->increment_total_full_collections();  // ... starting a collection cycle
1718     _collection_count_start = gch->total_full_collections();
1719   }
1720 
1721   size_t prev_used = _cmsGen->used();
1722 
1723   // The change of the collection state is normally done at this level;
1724   // the exceptions are phases that are executed while the world is
1725   // stopped.  For those phases the change of state is done while the
1726   // world is stopped.  For baton passing purposes this allows the
1727   // background collector to finish the phase and change state atomically.
1728   // The foreground collector cannot wait on a phase that is done
1729   // while the world is stopped because the foreground collector already
1730   // has the world stopped and would deadlock.
1731   while (_collectorState != Idling) {
1732     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1733                          p2i(Thread::current()), _collectorState);
1734     // The foreground collector
1735     //   holds the Heap_lock throughout its collection.
1736     //   holds the CMS token (but not the lock)
1737     //     except while it is waiting for the background collector to yield.
1738     //
1739     // The foreground collector should be blocked (not for long)
1740     //   if the background collector is about to start a phase
1741     //   executed with world stopped.  If the background
1742     //   collector has already started such a phase, the
1743     //   foreground collector is blocked waiting for the
1744     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1745     //   are executed in the VM thread.
1746     //
1747     // The locking order is
1748     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1749     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1750     //   CMS token  (claimed in
1751     //                stop_world_and_do() -->
1752     //                  safepoint_synchronize() -->
1753     //                    CMSThread::synchronize())
1754 
1755     {
1756       // Check if the FG collector wants us to yield.
1757       CMSTokenSync x(true); // is cms thread
1758       if (waitForForegroundGC()) {
1759         // We yielded to a foreground GC, nothing more to be
1760         // done this round.
1761         assert(_foregroundGCShouldWait == false, "We set it to false in "
1762                "waitForForegroundGC()");
1763         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1764                              p2i(Thread::current()), _collectorState);
1765         return;
1766       } else {
1767         // The background collector can run but check to see if the
1768         // foreground collector has done a collection while the
1769         // background collector was waiting to get the CGC_lock
1770         // above.  If yes, break so that _foregroundGCShouldWait
1771         // is cleared before returning.
1772         if (_collectorState == Idling) {
1773           break;
1774         }
1775       }
1776     }
1777 
1778     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1779       "should be waiting");
1780 
1781     switch (_collectorState) {
1782       case InitialMarking:
1783         {
1784           ReleaseForegroundGC x(this);
1785           stats().record_cms_begin();
1786           VM_CMS_Initial_Mark initial_mark_op(this);
1787           VMThread::execute(&initial_mark_op);
1788         }
1789         // The collector state may be any legal state at this point
1790         // since the background collector may have yielded to the
1791         // foreground collector.
1792         break;
1793       case Marking:
1794         // initial marking in checkpointRootsInitialWork has been completed
1795         if (markFromRoots()) { // we were successful
1796           assert(_collectorState == Precleaning, "Collector state should "
1797             "have changed");
1798         } else {
1799           assert(_foregroundGCIsActive, "Internal state inconsistency");
1800         }
1801         break;
1802       case Precleaning:
1803         // marking from roots in markFromRoots has been completed
1804         preclean();
1805         assert(_collectorState == AbortablePreclean ||
1806                _collectorState == FinalMarking,
1807                "Collector state should have changed");
1808         break;
1809       case AbortablePreclean:
1810         abortable_preclean();
1811         assert(_collectorState == FinalMarking, "Collector state should "
1812           "have changed");
1813         break;
1814       case FinalMarking:
1815         {
1816           ReleaseForegroundGC x(this);
1817 
1818           VM_CMS_Final_Remark final_remark_op(this);
1819           VMThread::execute(&final_remark_op);
1820         }
1821         assert(_foregroundGCShouldWait, "block post-condition");
1822         break;
1823       case Sweeping:
1824         // final marking in checkpointRootsFinal has been completed
1825         sweep();
1826         assert(_collectorState == Resizing, "Collector state change "
1827           "to Resizing must be done under the free_list_lock");
1828 
1829       case Resizing: {
1830         // Sweeping has been completed...
1831         // At this point the background collection has completed.
1832         // Don't move the call to compute_new_size() down
1833         // into code that might be executed if the background
1834         // collection was preempted.
1835         {
1836           ReleaseForegroundGC x(this);   // unblock FG collection
1837           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1838           CMSTokenSync        z(true);   // not strictly needed.
1839           if (_collectorState == Resizing) {
1840             compute_new_size();
1841             save_heap_summary();
1842             _collectorState = Resetting;
1843           } else {
1844             assert(_collectorState == Idling, "The state should only change"
1845                    " because the foreground collector has finished the collection");
1846           }
1847         }
1848         break;
1849       }
1850       case Resetting:
1851         // CMS heap resizing has been completed
1852         reset_concurrent();
1853         assert(_collectorState == Idling, "Collector state should "
1854           "have changed");
1855 
1856         MetaspaceGC::set_should_concurrent_collect(false);
1857 
1858         stats().record_cms_end();
1859         // Don't move the concurrent_phases_end() and compute_new_size()
1860         // calls to here because a preempted background collection
1861         // has it's state set to "Resetting".
1862         break;
1863       case Idling:
1864       default:
1865         ShouldNotReachHere();
1866         break;
1867     }
1868     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1869                          p2i(Thread::current()), _collectorState);
1870     assert(_foregroundGCShouldWait, "block post-condition");
1871   }
1872 
1873   // Should this be in gc_epilogue?
1874   collector_policy()->counters()->update_counters();
1875 
1876   {
1877     // Clear _foregroundGCShouldWait and, in the event that the
1878     // foreground collector is waiting, notify it, before
1879     // returning.
1880     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1881     _foregroundGCShouldWait = false;
1882     if (_foregroundGCIsActive) {
1883       CGC_lock->notify();
1884     }
1885     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1886            "Possible deadlock");
1887   }
1888   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1889                        p2i(Thread::current()), _collectorState);
1890   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1891                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1892 }
1893 
1894 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1895   _cms_start_registered = true;
1896   _gc_timer_cm->register_gc_start();
1897   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1898 }
1899 
1900 void CMSCollector::register_gc_end() {
1901   if (_cms_start_registered) {
1902     report_heap_summary(GCWhen::AfterGC);
1903 
1904     _gc_timer_cm->register_gc_end();
1905     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1906     _cms_start_registered = false;
1907   }
1908 }
1909 
1910 void CMSCollector::save_heap_summary() {
1911   GenCollectedHeap* gch = GenCollectedHeap::heap();
1912   _last_heap_summary = gch->create_heap_summary();
1913   _last_metaspace_summary = gch->create_metaspace_summary();
1914 }
1915 
1916 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1917   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1918   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1919 }
1920 
1921 bool CMSCollector::waitForForegroundGC() {
1922   bool res = false;
1923   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1924          "CMS thread should have CMS token");
1925   // Block the foreground collector until the
1926   // background collectors decides whether to
1927   // yield.
1928   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1929   _foregroundGCShouldWait = true;
1930   if (_foregroundGCIsActive) {
1931     // The background collector yields to the
1932     // foreground collector and returns a value
1933     // indicating that it has yielded.  The foreground
1934     // collector can proceed.
1935     res = true;
1936     _foregroundGCShouldWait = false;
1937     ConcurrentMarkSweepThread::clear_CMS_flag(
1938       ConcurrentMarkSweepThread::CMS_cms_has_token);
1939     ConcurrentMarkSweepThread::set_CMS_flag(
1940       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1941     // Get a possibly blocked foreground thread going
1942     CGC_lock->notify();
1943     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1944                          p2i(Thread::current()), _collectorState);
1945     while (_foregroundGCIsActive) {
1946       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1947     }
1948     ConcurrentMarkSweepThread::set_CMS_flag(
1949       ConcurrentMarkSweepThread::CMS_cms_has_token);
1950     ConcurrentMarkSweepThread::clear_CMS_flag(
1951       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1952   }
1953   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1954                        p2i(Thread::current()), _collectorState);
1955   return res;
1956 }
1957 
1958 // Because of the need to lock the free lists and other structures in
1959 // the collector, common to all the generations that the collector is
1960 // collecting, we need the gc_prologues of individual CMS generations
1961 // delegate to their collector. It may have been simpler had the
1962 // current infrastructure allowed one to call a prologue on a
1963 // collector. In the absence of that we have the generation's
1964 // prologue delegate to the collector, which delegates back
1965 // some "local" work to a worker method in the individual generations
1966 // that it's responsible for collecting, while itself doing any
1967 // work common to all generations it's responsible for. A similar
1968 // comment applies to the  gc_epilogue()'s.
1969 // The role of the variable _between_prologue_and_epilogue is to
1970 // enforce the invocation protocol.
1971 void CMSCollector::gc_prologue(bool full) {
1972   // Call gc_prologue_work() for the CMSGen
1973   // we are responsible for.
1974 
1975   // The following locking discipline assumes that we are only called
1976   // when the world is stopped.
1977   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1978 
1979   // The CMSCollector prologue must call the gc_prologues for the
1980   // "generations" that it's responsible
1981   // for.
1982 
1983   assert(   Thread::current()->is_VM_thread()
1984          || (   CMSScavengeBeforeRemark
1985              && Thread::current()->is_ConcurrentGC_thread()),
1986          "Incorrect thread type for prologue execution");
1987 
1988   if (_between_prologue_and_epilogue) {
1989     // We have already been invoked; this is a gc_prologue delegation
1990     // from yet another CMS generation that we are responsible for, just
1991     // ignore it since all relevant work has already been done.
1992     return;
1993   }
1994 
1995   // set a bit saying prologue has been called; cleared in epilogue
1996   _between_prologue_and_epilogue = true;
1997   // Claim locks for common data structures, then call gc_prologue_work()
1998   // for each CMSGen.
1999 
2000   getFreelistLocks();   // gets free list locks on constituent spaces
2001   bitMapLock()->lock_without_safepoint_check();
2002 
2003   // Should call gc_prologue_work() for all cms gens we are responsible for
2004   bool duringMarking =    _collectorState >= Marking
2005                          && _collectorState < Sweeping;
2006 
2007   // The young collections clear the modified oops state, which tells if
2008   // there are any modified oops in the class. The remark phase also needs
2009   // that information. Tell the young collection to save the union of all
2010   // modified klasses.
2011   if (duringMarking) {
2012     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2013   }
2014 
2015   bool registerClosure = duringMarking;
2016 
2017   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2018 
2019   if (!full) {
2020     stats().record_gc0_begin();
2021   }
2022 }
2023 
2024 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2025 
2026   _capacity_at_prologue = capacity();
2027   _used_at_prologue = used();
2028 
2029   // Delegate to CMScollector which knows how to coordinate between
2030   // this and any other CMS generations that it is responsible for
2031   // collecting.
2032   collector()->gc_prologue(full);
2033 }
2034 
2035 // This is a "private" interface for use by this generation's CMSCollector.
2036 // Not to be called directly by any other entity (for instance,
2037 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2038 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2039   bool registerClosure, ModUnionClosure* modUnionClosure) {
2040   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2041   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2042     "Should be NULL");
2043   if (registerClosure) {
2044     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2045   }
2046   cmsSpace()->gc_prologue();
2047   // Clear stat counters
2048   NOT_PRODUCT(
2049     assert(_numObjectsPromoted == 0, "check");
2050     assert(_numWordsPromoted   == 0, "check");
2051     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2052                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2053     _numObjectsAllocated = 0;
2054     _numWordsAllocated   = 0;
2055   )
2056 }
2057 
2058 void CMSCollector::gc_epilogue(bool full) {
2059   // The following locking discipline assumes that we are only called
2060   // when the world is stopped.
2061   assert(SafepointSynchronize::is_at_safepoint(),
2062          "world is stopped assumption");
2063 
2064   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2065   // if linear allocation blocks need to be appropriately marked to allow the
2066   // the blocks to be parsable. We also check here whether we need to nudge the
2067   // CMS collector thread to start a new cycle (if it's not already active).
2068   assert(   Thread::current()->is_VM_thread()
2069          || (   CMSScavengeBeforeRemark
2070              && Thread::current()->is_ConcurrentGC_thread()),
2071          "Incorrect thread type for epilogue execution");
2072 
2073   if (!_between_prologue_and_epilogue) {
2074     // We have already been invoked; this is a gc_epilogue delegation
2075     // from yet another CMS generation that we are responsible for, just
2076     // ignore it since all relevant work has already been done.
2077     return;
2078   }
2079   assert(haveFreelistLocks(), "must have freelist locks");
2080   assert_lock_strong(bitMapLock());
2081 
2082   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2083 
2084   _cmsGen->gc_epilogue_work(full);
2085 
2086   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2087     // in case sampling was not already enabled, enable it
2088     _start_sampling = true;
2089   }
2090   // reset _eden_chunk_array so sampling starts afresh
2091   _eden_chunk_index = 0;
2092 
2093   size_t cms_used   = _cmsGen->cmsSpace()->used();
2094 
2095   // update performance counters - this uses a special version of
2096   // update_counters() that allows the utilization to be passed as a
2097   // parameter, avoiding multiple calls to used().
2098   //
2099   _cmsGen->update_counters(cms_used);
2100 
2101   bitMapLock()->unlock();
2102   releaseFreelistLocks();
2103 
2104   if (!CleanChunkPoolAsync) {
2105     Chunk::clean_chunk_pool();
2106   }
2107 
2108   set_did_compact(false);
2109   _between_prologue_and_epilogue = false;  // ready for next cycle
2110 }
2111 
2112 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2113   collector()->gc_epilogue(full);
2114 
2115   // Also reset promotion tracking in par gc thread states.
2116   for (uint i = 0; i < ParallelGCThreads; i++) {
2117     _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2118   }
2119 }
2120 
2121 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2122   assert(!incremental_collection_failed(), "Should have been cleared");
2123   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2124   cmsSpace()->gc_epilogue();
2125     // Print stat counters
2126   NOT_PRODUCT(
2127     assert(_numObjectsAllocated == 0, "check");
2128     assert(_numWordsAllocated == 0, "check");
2129     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2130                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2131     _numObjectsPromoted = 0;
2132     _numWordsPromoted   = 0;
2133   )
2134 
2135   // Call down the chain in contiguous_available needs the freelistLock
2136   // so print this out before releasing the freeListLock.
2137   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2138 }
2139 
2140 #ifndef PRODUCT
2141 bool CMSCollector::have_cms_token() {
2142   Thread* thr = Thread::current();
2143   if (thr->is_VM_thread()) {
2144     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2145   } else if (thr->is_ConcurrentGC_thread()) {
2146     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2147   } else if (thr->is_GC_task_thread()) {
2148     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2149            ParGCRareEvent_lock->owned_by_self();
2150   }
2151   return false;
2152 }
2153 
2154 // Check reachability of the given heap address in CMS generation,
2155 // treating all other generations as roots.
2156 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2157   // We could "guarantee" below, rather than assert, but I'll
2158   // leave these as "asserts" so that an adventurous debugger
2159   // could try this in the product build provided some subset of
2160   // the conditions were met, provided they were interested in the
2161   // results and knew that the computation below wouldn't interfere
2162   // with other concurrent computations mutating the structures
2163   // being read or written.
2164   assert(SafepointSynchronize::is_at_safepoint(),
2165          "Else mutations in object graph will make answer suspect");
2166   assert(have_cms_token(), "Should hold cms token");
2167   assert(haveFreelistLocks(), "must hold free list locks");
2168   assert_lock_strong(bitMapLock());
2169 
2170   // Clear the marking bit map array before starting, but, just
2171   // for kicks, first report if the given address is already marked
2172   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2173                 _markBitMap.isMarked(addr) ? "" : " not");
2174 
2175   if (verify_after_remark()) {
2176     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2177     bool result = verification_mark_bm()->isMarked(addr);
2178     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2179                   result ? "IS" : "is NOT");
2180     return result;
2181   } else {
2182     tty->print_cr("Could not compute result");
2183     return false;
2184   }
2185 }
2186 #endif
2187 
2188 void
2189 CMSCollector::print_on_error(outputStream* st) {
2190   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2191   if (collector != NULL) {
2192     CMSBitMap* bitmap = &collector->_markBitMap;
2193     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2194     bitmap->print_on_error(st, " Bits: ");
2195 
2196     st->cr();
2197 
2198     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2199     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2200     mut_bitmap->print_on_error(st, " Bits: ");
2201   }
2202 }
2203 
2204 ////////////////////////////////////////////////////////
2205 // CMS Verification Support
2206 ////////////////////////////////////////////////////////
2207 // Following the remark phase, the following invariant
2208 // should hold -- each object in the CMS heap which is
2209 // marked in markBitMap() should be marked in the verification_mark_bm().
2210 
2211 class VerifyMarkedClosure: public BitMapClosure {
2212   CMSBitMap* _marks;
2213   bool       _failed;
2214 
2215  public:
2216   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2217 
2218   bool do_bit(size_t offset) {
2219     HeapWord* addr = _marks->offsetToHeapWord(offset);
2220     if (!_marks->isMarked(addr)) {
2221       LogHandle(gc, verify) log;
2222       ResourceMark rm;
2223       oop(addr)->print_on(log.info_stream());
2224       log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2225       _failed = true;
2226     }
2227     return true;
2228   }
2229 
2230   bool failed() { return _failed; }
2231 };
2232 
2233 bool CMSCollector::verify_after_remark() {
2234   GCTraceTime(Info, gc, verify) tm("Verifying CMS Marking.");
2235   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2236   static bool init = false;
2237 
2238   assert(SafepointSynchronize::is_at_safepoint(),
2239          "Else mutations in object graph will make answer suspect");
2240   assert(have_cms_token(),
2241          "Else there may be mutual interference in use of "
2242          " verification data structures");
2243   assert(_collectorState > Marking && _collectorState <= Sweeping,
2244          "Else marking info checked here may be obsolete");
2245   assert(haveFreelistLocks(), "must hold free list locks");
2246   assert_lock_strong(bitMapLock());
2247 
2248 
2249   // Allocate marking bit map if not already allocated
2250   if (!init) { // first time
2251     if (!verification_mark_bm()->allocate(_span)) {
2252       return false;
2253     }
2254     init = true;
2255   }
2256 
2257   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2258 
2259   // Turn off refs discovery -- so we will be tracing through refs.
2260   // This is as intended, because by this time
2261   // GC must already have cleared any refs that need to be cleared,
2262   // and traced those that need to be marked; moreover,
2263   // the marking done here is not going to interfere in any
2264   // way with the marking information used by GC.
2265   NoRefDiscovery no_discovery(ref_processor());
2266 
2267 #if defined(COMPILER2) || INCLUDE_JVMCI
2268   DerivedPointerTableDeactivate dpt_deact;
2269 #endif
2270 
2271   // Clear any marks from a previous round
2272   verification_mark_bm()->clear_all();
2273   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2274   verify_work_stacks_empty();
2275 
2276   GenCollectedHeap* gch = GenCollectedHeap::heap();
2277   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2278   // Update the saved marks which may affect the root scans.
2279   gch->save_marks();
2280 
2281   if (CMSRemarkVerifyVariant == 1) {
2282     // In this first variant of verification, we complete
2283     // all marking, then check if the new marks-vector is
2284     // a subset of the CMS marks-vector.
2285     verify_after_remark_work_1();
2286   } else if (CMSRemarkVerifyVariant == 2) {
2287     // In this second variant of verification, we flag an error
2288     // (i.e. an object reachable in the new marks-vector not reachable
2289     // in the CMS marks-vector) immediately, also indicating the
2290     // identify of an object (A) that references the unmarked object (B) --
2291     // presumably, a mutation to A failed to be picked up by preclean/remark?
2292     verify_after_remark_work_2();
2293   } else {
2294     warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2295             CMSRemarkVerifyVariant);
2296   }
2297   return true;
2298 }
2299 
2300 void CMSCollector::verify_after_remark_work_1() {
2301   ResourceMark rm;
2302   HandleMark  hm;
2303   GenCollectedHeap* gch = GenCollectedHeap::heap();
2304 
2305   // Get a clear set of claim bits for the roots processing to work with.
2306   ClassLoaderDataGraph::clear_claimed_marks();
2307 
2308   // Mark from roots one level into CMS
2309   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2310   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2311 
2312   {
2313     StrongRootsScope srs(1);
2314 
2315     gch->gen_process_roots(&srs,
2316                            GenCollectedHeap::OldGen,
2317                            true,   // young gen as roots
2318                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2319                            should_unload_classes(),
2320                            &notOlder,
2321                            NULL,
2322                            NULL);
2323   }
2324 
2325   // Now mark from the roots
2326   MarkFromRootsClosure markFromRootsClosure(this, _span,
2327     verification_mark_bm(), verification_mark_stack(),
2328     false /* don't yield */, true /* verifying */);
2329   assert(_restart_addr == NULL, "Expected pre-condition");
2330   verification_mark_bm()->iterate(&markFromRootsClosure);
2331   while (_restart_addr != NULL) {
2332     // Deal with stack overflow: by restarting at the indicated
2333     // address.
2334     HeapWord* ra = _restart_addr;
2335     markFromRootsClosure.reset(ra);
2336     _restart_addr = NULL;
2337     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2338   }
2339   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2340   verify_work_stacks_empty();
2341 
2342   // Marking completed -- now verify that each bit marked in
2343   // verification_mark_bm() is also marked in markBitMap(); flag all
2344   // errors by printing corresponding objects.
2345   VerifyMarkedClosure vcl(markBitMap());
2346   verification_mark_bm()->iterate(&vcl);
2347   if (vcl.failed()) {
2348     LogHandle(gc, verify) log;
2349     log.info("Verification failed");
2350     ResourceMark rm;
2351     gch->print_on(log.info_stream());
2352     fatal("CMS: failed marking verification after remark");
2353   }
2354 }
2355 
2356 class VerifyKlassOopsKlassClosure : public KlassClosure {
2357   class VerifyKlassOopsClosure : public OopClosure {
2358     CMSBitMap* _bitmap;
2359    public:
2360     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2361     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2362     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2363   } _oop_closure;
2364  public:
2365   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2366   void do_klass(Klass* k) {
2367     k->oops_do(&_oop_closure);
2368   }
2369 };
2370 
2371 void CMSCollector::verify_after_remark_work_2() {
2372   ResourceMark rm;
2373   HandleMark  hm;
2374   GenCollectedHeap* gch = GenCollectedHeap::heap();
2375 
2376   // Get a clear set of claim bits for the roots processing to work with.
2377   ClassLoaderDataGraph::clear_claimed_marks();
2378 
2379   // Mark from roots one level into CMS
2380   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2381                                      markBitMap());
2382   CLDToOopClosure cld_closure(&notOlder, true);
2383 
2384   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2385 
2386   {
2387     StrongRootsScope srs(1);
2388 
2389     gch->gen_process_roots(&srs,
2390                            GenCollectedHeap::OldGen,
2391                            true,   // young gen as roots
2392                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2393                            should_unload_classes(),
2394                            &notOlder,
2395                            NULL,
2396                            &cld_closure);
2397   }
2398 
2399   // Now mark from the roots
2400   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2401     verification_mark_bm(), markBitMap(), verification_mark_stack());
2402   assert(_restart_addr == NULL, "Expected pre-condition");
2403   verification_mark_bm()->iterate(&markFromRootsClosure);
2404   while (_restart_addr != NULL) {
2405     // Deal with stack overflow: by restarting at the indicated
2406     // address.
2407     HeapWord* ra = _restart_addr;
2408     markFromRootsClosure.reset(ra);
2409     _restart_addr = NULL;
2410     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2411   }
2412   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2413   verify_work_stacks_empty();
2414 
2415   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2416   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2417 
2418   // Marking completed -- now verify that each bit marked in
2419   // verification_mark_bm() is also marked in markBitMap(); flag all
2420   // errors by printing corresponding objects.
2421   VerifyMarkedClosure vcl(markBitMap());
2422   verification_mark_bm()->iterate(&vcl);
2423   assert(!vcl.failed(), "Else verification above should not have succeeded");
2424 }
2425 
2426 void ConcurrentMarkSweepGeneration::save_marks() {
2427   // delegate to CMS space
2428   cmsSpace()->save_marks();
2429   for (uint i = 0; i < ParallelGCThreads; i++) {
2430     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2431   }
2432 }
2433 
2434 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2435   return cmsSpace()->no_allocs_since_save_marks();
2436 }
2437 
2438 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2439                                                                 \
2440 void ConcurrentMarkSweepGeneration::                            \
2441 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2442   cl->set_generation(this);                                     \
2443   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2444   cl->reset_generation();                                       \
2445   save_marks();                                                 \
2446 }
2447 
2448 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2449 
2450 void
2451 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2452   if (freelistLock()->owned_by_self()) {
2453     Generation::oop_iterate(cl);
2454   } else {
2455     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2456     Generation::oop_iterate(cl);
2457   }
2458 }
2459 
2460 void
2461 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2462   if (freelistLock()->owned_by_self()) {
2463     Generation::object_iterate(cl);
2464   } else {
2465     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2466     Generation::object_iterate(cl);
2467   }
2468 }
2469 
2470 void
2471 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2472   if (freelistLock()->owned_by_self()) {
2473     Generation::safe_object_iterate(cl);
2474   } else {
2475     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2476     Generation::safe_object_iterate(cl);
2477   }
2478 }
2479 
2480 void
2481 ConcurrentMarkSweepGeneration::post_compact() {
2482 }
2483 
2484 void
2485 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2486   // Fix the linear allocation blocks to look like free blocks.
2487 
2488   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2489   // are not called when the heap is verified during universe initialization and
2490   // at vm shutdown.
2491   if (freelistLock()->owned_by_self()) {
2492     cmsSpace()->prepare_for_verify();
2493   } else {
2494     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2495     cmsSpace()->prepare_for_verify();
2496   }
2497 }
2498 
2499 void
2500 ConcurrentMarkSweepGeneration::verify() {
2501   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2502   // are not called when the heap is verified during universe initialization and
2503   // at vm shutdown.
2504   if (freelistLock()->owned_by_self()) {
2505     cmsSpace()->verify();
2506   } else {
2507     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2508     cmsSpace()->verify();
2509   }
2510 }
2511 
2512 void CMSCollector::verify() {
2513   _cmsGen->verify();
2514 }
2515 
2516 #ifndef PRODUCT
2517 bool CMSCollector::overflow_list_is_empty() const {
2518   assert(_num_par_pushes >= 0, "Inconsistency");
2519   if (_overflow_list == NULL) {
2520     assert(_num_par_pushes == 0, "Inconsistency");
2521   }
2522   return _overflow_list == NULL;
2523 }
2524 
2525 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2526 // merely consolidate assertion checks that appear to occur together frequently.
2527 void CMSCollector::verify_work_stacks_empty() const {
2528   assert(_markStack.isEmpty(), "Marking stack should be empty");
2529   assert(overflow_list_is_empty(), "Overflow list should be empty");
2530 }
2531 
2532 void CMSCollector::verify_overflow_empty() const {
2533   assert(overflow_list_is_empty(), "Overflow list should be empty");
2534   assert(no_preserved_marks(), "No preserved marks");
2535 }
2536 #endif // PRODUCT
2537 
2538 // Decide if we want to enable class unloading as part of the
2539 // ensuing concurrent GC cycle. We will collect and
2540 // unload classes if it's the case that:
2541 // (1) an explicit gc request has been made and the flag
2542 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2543 // (2) (a) class unloading is enabled at the command line, and
2544 //     (b) old gen is getting really full
2545 // NOTE: Provided there is no change in the state of the heap between
2546 // calls to this method, it should have idempotent results. Moreover,
2547 // its results should be monotonically increasing (i.e. going from 0 to 1,
2548 // but not 1 to 0) between successive calls between which the heap was
2549 // not collected. For the implementation below, it must thus rely on
2550 // the property that concurrent_cycles_since_last_unload()
2551 // will not decrease unless a collection cycle happened and that
2552 // _cmsGen->is_too_full() are
2553 // themselves also monotonic in that sense. See check_monotonicity()
2554 // below.
2555 void CMSCollector::update_should_unload_classes() {
2556   _should_unload_classes = false;
2557   // Condition 1 above
2558   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2559     _should_unload_classes = true;
2560   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2561     // Disjuncts 2.b.(i,ii,iii) above
2562     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2563                               CMSClassUnloadingMaxInterval)
2564                            || _cmsGen->is_too_full();
2565   }
2566 }
2567 
2568 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2569   bool res = should_concurrent_collect();
2570   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2571   return res;
2572 }
2573 
2574 void CMSCollector::setup_cms_unloading_and_verification_state() {
2575   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2576                              || VerifyBeforeExit;
2577   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2578 
2579   // We set the proper root for this CMS cycle here.
2580   if (should_unload_classes()) {   // Should unload classes this cycle
2581     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2582     set_verifying(should_verify);    // Set verification state for this cycle
2583     return;                            // Nothing else needs to be done at this time
2584   }
2585 
2586   // Not unloading classes this cycle
2587   assert(!should_unload_classes(), "Inconsistency!");
2588 
2589   // If we are not unloading classes then add SO_AllCodeCache to root
2590   // scanning options.
2591   add_root_scanning_option(rso);
2592 
2593   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2594     set_verifying(true);
2595   } else if (verifying() && !should_verify) {
2596     // We were verifying, but some verification flags got disabled.
2597     set_verifying(false);
2598     // Exclude symbols, strings and code cache elements from root scanning to
2599     // reduce IM and RM pauses.
2600     remove_root_scanning_option(rso);
2601   }
2602 }
2603 
2604 
2605 #ifndef PRODUCT
2606 HeapWord* CMSCollector::block_start(const void* p) const {
2607   const HeapWord* addr = (HeapWord*)p;
2608   if (_span.contains(p)) {
2609     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2610       return _cmsGen->cmsSpace()->block_start(p);
2611     }
2612   }
2613   return NULL;
2614 }
2615 #endif
2616 
2617 HeapWord*
2618 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2619                                                    bool   tlab,
2620                                                    bool   parallel) {
2621   CMSSynchronousYieldRequest yr;
2622   assert(!tlab, "Can't deal with TLAB allocation");
2623   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2624   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2625   if (GCExpandToAllocateDelayMillis > 0) {
2626     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2627   }
2628   return have_lock_and_allocate(word_size, tlab);
2629 }
2630 
2631 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2632     size_t bytes,
2633     size_t expand_bytes,
2634     CMSExpansionCause::Cause cause)
2635 {
2636 
2637   bool success = expand(bytes, expand_bytes);
2638 
2639   // remember why we expanded; this information is used
2640   // by shouldConcurrentCollect() when making decisions on whether to start
2641   // a new CMS cycle.
2642   if (success) {
2643     set_expansion_cause(cause);
2644     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2645   }
2646 }
2647 
2648 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2649   HeapWord* res = NULL;
2650   MutexLocker x(ParGCRareEvent_lock);
2651   while (true) {
2652     // Expansion by some other thread might make alloc OK now:
2653     res = ps->lab.alloc(word_sz);
2654     if (res != NULL) return res;
2655     // If there's not enough expansion space available, give up.
2656     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2657       return NULL;
2658     }
2659     // Otherwise, we try expansion.
2660     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2661     // Now go around the loop and try alloc again;
2662     // A competing par_promote might beat us to the expansion space,
2663     // so we may go around the loop again if promotion fails again.
2664     if (GCExpandToAllocateDelayMillis > 0) {
2665       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2666     }
2667   }
2668 }
2669 
2670 
2671 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2672   PromotionInfo* promo) {
2673   MutexLocker x(ParGCRareEvent_lock);
2674   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2675   while (true) {
2676     // Expansion by some other thread might make alloc OK now:
2677     if (promo->ensure_spooling_space()) {
2678       assert(promo->has_spooling_space(),
2679              "Post-condition of successful ensure_spooling_space()");
2680       return true;
2681     }
2682     // If there's not enough expansion space available, give up.
2683     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2684       return false;
2685     }
2686     // Otherwise, we try expansion.
2687     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2688     // Now go around the loop and try alloc again;
2689     // A competing allocation might beat us to the expansion space,
2690     // so we may go around the loop again if allocation fails again.
2691     if (GCExpandToAllocateDelayMillis > 0) {
2692       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2693     }
2694   }
2695 }
2696 
2697 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2698   // Only shrink if a compaction was done so that all the free space
2699   // in the generation is in a contiguous block at the end.
2700   if (did_compact()) {
2701     CardGeneration::shrink(bytes);
2702   }
2703 }
2704 
2705 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2706   assert_locked_or_safepoint(Heap_lock);
2707 }
2708 
2709 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2710   assert_locked_or_safepoint(Heap_lock);
2711   assert_lock_strong(freelistLock());
2712   log_trace(gc)("Shrinking of CMS not yet implemented");
2713   return;
2714 }
2715 
2716 
2717 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2718 // phases.
2719 class CMSPhaseAccounting: public StackObj {
2720  public:
2721   CMSPhaseAccounting(CMSCollector *collector,
2722                      const char *title);
2723   ~CMSPhaseAccounting();
2724 
2725  private:
2726   CMSCollector *_collector;
2727   const char *_title;
2728   GCTraceConcTime(Info, gc) _trace_time;
2729 
2730  public:
2731   // Not MT-safe; so do not pass around these StackObj's
2732   // where they may be accessed by other threads.
2733   jlong wallclock_millis() {
2734     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2735   }
2736 };
2737 
2738 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2739                                        const char *title) :
2740   _collector(collector), _title(title), _trace_time(title) {
2741 
2742   _collector->resetYields();
2743   _collector->resetTimer();
2744   _collector->startTimer();
2745 }
2746 
2747 CMSPhaseAccounting::~CMSPhaseAccounting() {
2748   _collector->stopTimer();
2749   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2750   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2751 }
2752 
2753 // CMS work
2754 
2755 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2756 class CMSParMarkTask : public AbstractGangTask {
2757  protected:
2758   CMSCollector*     _collector;
2759   uint              _n_workers;
2760   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2761       AbstractGangTask(name),
2762       _collector(collector),
2763       _n_workers(n_workers) {}
2764   // Work method in support of parallel rescan ... of young gen spaces
2765   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2766                              ContiguousSpace* space,
2767                              HeapWord** chunk_array, size_t chunk_top);
2768   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2769 };
2770 
2771 // Parallel initial mark task
2772 class CMSParInitialMarkTask: public CMSParMarkTask {
2773   StrongRootsScope* _strong_roots_scope;
2774  public:
2775   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2776       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2777       _strong_roots_scope(strong_roots_scope) {}
2778   void work(uint worker_id);
2779 };
2780 
2781 // Checkpoint the roots into this generation from outside
2782 // this generation. [Note this initial checkpoint need only
2783 // be approximate -- we'll do a catch up phase subsequently.]
2784 void CMSCollector::checkpointRootsInitial() {
2785   assert(_collectorState == InitialMarking, "Wrong collector state");
2786   check_correct_thread_executing();
2787   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2788 
2789   save_heap_summary();
2790   report_heap_summary(GCWhen::BeforeGC);
2791 
2792   ReferenceProcessor* rp = ref_processor();
2793   assert(_restart_addr == NULL, "Control point invariant");
2794   {
2795     // acquire locks for subsequent manipulations
2796     MutexLockerEx x(bitMapLock(),
2797                     Mutex::_no_safepoint_check_flag);
2798     checkpointRootsInitialWork();
2799     // enable ("weak") refs discovery
2800     rp->enable_discovery();
2801     _collectorState = Marking;
2802   }
2803 }
2804 
2805 void CMSCollector::checkpointRootsInitialWork() {
2806   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2807   assert(_collectorState == InitialMarking, "just checking");
2808 
2809   // Already have locks.
2810   assert_lock_strong(bitMapLock());
2811   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2812 
2813   // Setup the verification and class unloading state for this
2814   // CMS collection cycle.
2815   setup_cms_unloading_and_verification_state();
2816 
2817   GCTraceTime(Trace, gc) ts("checkpointRootsInitialWork", _gc_timer_cm);
2818 
2819   // Reset all the PLAB chunk arrays if necessary.
2820   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2821     reset_survivor_plab_arrays();
2822   }
2823 
2824   ResourceMark rm;
2825   HandleMark  hm;
2826 
2827   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2828   GenCollectedHeap* gch = GenCollectedHeap::heap();
2829 
2830   verify_work_stacks_empty();
2831   verify_overflow_empty();
2832 
2833   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2834   // Update the saved marks which may affect the root scans.
2835   gch->save_marks();
2836 
2837   // weak reference processing has not started yet.
2838   ref_processor()->set_enqueuing_is_done(false);
2839 
2840   // Need to remember all newly created CLDs,
2841   // so that we can guarantee that the remark finds them.
2842   ClassLoaderDataGraph::remember_new_clds(true);
2843 
2844   // Whenever a CLD is found, it will be claimed before proceeding to mark
2845   // the klasses. The claimed marks need to be cleared before marking starts.
2846   ClassLoaderDataGraph::clear_claimed_marks();
2847 
2848   print_eden_and_survivor_chunk_arrays();
2849 
2850   {
2851 #if defined(COMPILER2) || INCLUDE_JVMCI
2852     DerivedPointerTableDeactivate dpt_deact;
2853 #endif
2854     if (CMSParallelInitialMarkEnabled) {
2855       // The parallel version.
2856       WorkGang* workers = gch->workers();
2857       assert(workers != NULL, "Need parallel worker threads.");
2858       uint n_workers = workers->active_workers();
2859 
2860       StrongRootsScope srs(n_workers);
2861 
2862       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2863       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2864       if (n_workers > 1) {
2865         workers->run_task(&tsk);
2866       } else {
2867         tsk.work(0);
2868       }
2869     } else {
2870       // The serial version.
2871       CLDToOopClosure cld_closure(&notOlder, true);
2872       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2873 
2874       StrongRootsScope srs(1);
2875 
2876       gch->gen_process_roots(&srs,
2877                              GenCollectedHeap::OldGen,
2878                              true,   // young gen as roots
2879                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2880                              should_unload_classes(),
2881                              &notOlder,
2882                              NULL,
2883                              &cld_closure);
2884     }
2885   }
2886 
2887   // Clear mod-union table; it will be dirtied in the prologue of
2888   // CMS generation per each young generation collection.
2889 
2890   assert(_modUnionTable.isAllClear(),
2891        "Was cleared in most recent final checkpoint phase"
2892        " or no bits are set in the gc_prologue before the start of the next "
2893        "subsequent marking phase.");
2894 
2895   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2896 
2897   // Save the end of the used_region of the constituent generations
2898   // to be used to limit the extent of sweep in each generation.
2899   save_sweep_limits();
2900   verify_overflow_empty();
2901 }
2902 
2903 bool CMSCollector::markFromRoots() {
2904   // we might be tempted to assert that:
2905   // assert(!SafepointSynchronize::is_at_safepoint(),
2906   //        "inconsistent argument?");
2907   // However that wouldn't be right, because it's possible that
2908   // a safepoint is indeed in progress as a young generation
2909   // stop-the-world GC happens even as we mark in this generation.
2910   assert(_collectorState == Marking, "inconsistent state?");
2911   _gc_timer_cm->register_gc_concurrent_start("Concurrent Mark");
2912   check_correct_thread_executing();
2913   verify_overflow_empty();
2914 
2915   // Weak ref discovery note: We may be discovering weak
2916   // refs in this generation concurrent (but interleaved) with
2917   // weak ref discovery by the young generation collector.
2918 
2919   CMSTokenSyncWithLocks ts(true, bitMapLock());
2920   GCTraceCPUTime tcpu;
2921   CMSPhaseAccounting pa(this, "Concrurrent Mark");
2922   bool res = markFromRootsWork();
2923   if (res) {
2924     _collectorState = Precleaning;
2925   } else { // We failed and a foreground collection wants to take over
2926     assert(_foregroundGCIsActive, "internal state inconsistency");
2927     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2928     log_debug(gc)("bailing out to foreground collection");
2929   }
2930   verify_overflow_empty();
2931   _gc_timer_cm->register_gc_concurrent_end();
2932   return res;
2933 }
2934 
2935 bool CMSCollector::markFromRootsWork() {
2936   // iterate over marked bits in bit map, doing a full scan and mark
2937   // from these roots using the following algorithm:
2938   // . if oop is to the right of the current scan pointer,
2939   //   mark corresponding bit (we'll process it later)
2940   // . else (oop is to left of current scan pointer)
2941   //   push oop on marking stack
2942   // . drain the marking stack
2943 
2944   // Note that when we do a marking step we need to hold the
2945   // bit map lock -- recall that direct allocation (by mutators)
2946   // and promotion (by the young generation collector) is also
2947   // marking the bit map. [the so-called allocate live policy.]
2948   // Because the implementation of bit map marking is not
2949   // robust wrt simultaneous marking of bits in the same word,
2950   // we need to make sure that there is no such interference
2951   // between concurrent such updates.
2952 
2953   // already have locks
2954   assert_lock_strong(bitMapLock());
2955 
2956   verify_work_stacks_empty();
2957   verify_overflow_empty();
2958   bool result = false;
2959   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2960     result = do_marking_mt();
2961   } else {
2962     result = do_marking_st();
2963   }
2964   return result;
2965 }
2966 
2967 // Forward decl
2968 class CMSConcMarkingTask;
2969 
2970 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2971   CMSCollector*       _collector;
2972   CMSConcMarkingTask* _task;
2973  public:
2974   virtual void yield();
2975 
2976   // "n_threads" is the number of threads to be terminated.
2977   // "queue_set" is a set of work queues of other threads.
2978   // "collector" is the CMS collector associated with this task terminator.
2979   // "yield" indicates whether we need the gang as a whole to yield.
2980   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2981     ParallelTaskTerminator(n_threads, queue_set),
2982     _collector(collector) { }
2983 
2984   void set_task(CMSConcMarkingTask* task) {
2985     _task = task;
2986   }
2987 };
2988 
2989 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
2990   CMSConcMarkingTask* _task;
2991  public:
2992   bool should_exit_termination();
2993   void set_task(CMSConcMarkingTask* task) {
2994     _task = task;
2995   }
2996 };
2997 
2998 // MT Concurrent Marking Task
2999 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3000   CMSCollector* _collector;
3001   uint          _n_workers;       // requested/desired # workers
3002   bool          _result;
3003   CompactibleFreeListSpace*  _cms_space;
3004   char          _pad_front[64];   // padding to ...
3005   HeapWord*     _global_finger;   // ... avoid sharing cache line
3006   char          _pad_back[64];
3007   HeapWord*     _restart_addr;
3008 
3009   //  Exposed here for yielding support
3010   Mutex* const _bit_map_lock;
3011 
3012   // The per thread work queues, available here for stealing
3013   OopTaskQueueSet*  _task_queues;
3014 
3015   // Termination (and yielding) support
3016   CMSConcMarkingTerminator _term;
3017   CMSConcMarkingTerminatorTerminator _term_term;
3018 
3019  public:
3020   CMSConcMarkingTask(CMSCollector* collector,
3021                  CompactibleFreeListSpace* cms_space,
3022                  YieldingFlexibleWorkGang* workers,
3023                  OopTaskQueueSet* task_queues):
3024     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3025     _collector(collector),
3026     _cms_space(cms_space),
3027     _n_workers(0), _result(true),
3028     _task_queues(task_queues),
3029     _term(_n_workers, task_queues, _collector),
3030     _bit_map_lock(collector->bitMapLock())
3031   {
3032     _requested_size = _n_workers;
3033     _term.set_task(this);
3034     _term_term.set_task(this);
3035     _restart_addr = _global_finger = _cms_space->bottom();
3036   }
3037 
3038 
3039   OopTaskQueueSet* task_queues()  { return _task_queues; }
3040 
3041   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3042 
3043   HeapWord** global_finger_addr() { return &_global_finger; }
3044 
3045   CMSConcMarkingTerminator* terminator() { return &_term; }
3046 
3047   virtual void set_for_termination(uint active_workers) {
3048     terminator()->reset_for_reuse(active_workers);
3049   }
3050 
3051   void work(uint worker_id);
3052   bool should_yield() {
3053     return    ConcurrentMarkSweepThread::should_yield()
3054            && !_collector->foregroundGCIsActive();
3055   }
3056 
3057   virtual void coordinator_yield();  // stuff done by coordinator
3058   bool result() { return _result; }
3059 
3060   void reset(HeapWord* ra) {
3061     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3062     _restart_addr = _global_finger = ra;
3063     _term.reset_for_reuse();
3064   }
3065 
3066   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3067                                            OopTaskQueue* work_q);
3068 
3069  private:
3070   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3071   void do_work_steal(int i);
3072   void bump_global_finger(HeapWord* f);
3073 };
3074 
3075 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3076   assert(_task != NULL, "Error");
3077   return _task->yielding();
3078   // Note that we do not need the disjunct || _task->should_yield() above
3079   // because we want terminating threads to yield only if the task
3080   // is already in the midst of yielding, which happens only after at least one
3081   // thread has yielded.
3082 }
3083 
3084 void CMSConcMarkingTerminator::yield() {
3085   if (_task->should_yield()) {
3086     _task->yield();
3087   } else {
3088     ParallelTaskTerminator::yield();
3089   }
3090 }
3091 
3092 ////////////////////////////////////////////////////////////////
3093 // Concurrent Marking Algorithm Sketch
3094 ////////////////////////////////////////////////////////////////
3095 // Until all tasks exhausted (both spaces):
3096 // -- claim next available chunk
3097 // -- bump global finger via CAS
3098 // -- find first object that starts in this chunk
3099 //    and start scanning bitmap from that position
3100 // -- scan marked objects for oops
3101 // -- CAS-mark target, and if successful:
3102 //    . if target oop is above global finger (volatile read)
3103 //      nothing to do
3104 //    . if target oop is in chunk and above local finger
3105 //        then nothing to do
3106 //    . else push on work-queue
3107 // -- Deal with possible overflow issues:
3108 //    . local work-queue overflow causes stuff to be pushed on
3109 //      global (common) overflow queue
3110 //    . always first empty local work queue
3111 //    . then get a batch of oops from global work queue if any
3112 //    . then do work stealing
3113 // -- When all tasks claimed (both spaces)
3114 //    and local work queue empty,
3115 //    then in a loop do:
3116 //    . check global overflow stack; steal a batch of oops and trace
3117 //    . try to steal from other threads oif GOS is empty
3118 //    . if neither is available, offer termination
3119 // -- Terminate and return result
3120 //
3121 void CMSConcMarkingTask::work(uint worker_id) {
3122   elapsedTimer _timer;
3123   ResourceMark rm;
3124   HandleMark hm;
3125 
3126   DEBUG_ONLY(_collector->verify_overflow_empty();)
3127 
3128   // Before we begin work, our work queue should be empty
3129   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3130   // Scan the bitmap covering _cms_space, tracing through grey objects.
3131   _timer.start();
3132   do_scan_and_mark(worker_id, _cms_space);
3133   _timer.stop();
3134   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3135 
3136   // ... do work stealing
3137   _timer.reset();
3138   _timer.start();
3139   do_work_steal(worker_id);
3140   _timer.stop();
3141   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3142   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3143   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3144   // Note that under the current task protocol, the
3145   // following assertion is true even of the spaces
3146   // expanded since the completion of the concurrent
3147   // marking. XXX This will likely change under a strict
3148   // ABORT semantics.
3149   // After perm removal the comparison was changed to
3150   // greater than or equal to from strictly greater than.
3151   // Before perm removal the highest address sweep would
3152   // have been at the end of perm gen but now is at the
3153   // end of the tenured gen.
3154   assert(_global_finger >=  _cms_space->end(),
3155          "All tasks have been completed");
3156   DEBUG_ONLY(_collector->verify_overflow_empty();)
3157 }
3158 
3159 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3160   HeapWord* read = _global_finger;
3161   HeapWord* cur  = read;
3162   while (f > read) {
3163     cur = read;
3164     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3165     if (cur == read) {
3166       // our cas succeeded
3167       assert(_global_finger >= f, "protocol consistency");
3168       break;
3169     }
3170   }
3171 }
3172 
3173 // This is really inefficient, and should be redone by
3174 // using (not yet available) block-read and -write interfaces to the
3175 // stack and the work_queue. XXX FIX ME !!!
3176 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3177                                                       OopTaskQueue* work_q) {
3178   // Fast lock-free check
3179   if (ovflw_stk->length() == 0) {
3180     return false;
3181   }
3182   assert(work_q->size() == 0, "Shouldn't steal");
3183   MutexLockerEx ml(ovflw_stk->par_lock(),
3184                    Mutex::_no_safepoint_check_flag);
3185   // Grab up to 1/4 the size of the work queue
3186   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3187                     (size_t)ParGCDesiredObjsFromOverflowList);
3188   num = MIN2(num, ovflw_stk->length());
3189   for (int i = (int) num; i > 0; i--) {
3190     oop cur = ovflw_stk->pop();
3191     assert(cur != NULL, "Counted wrong?");
3192     work_q->push(cur);
3193   }
3194   return num > 0;
3195 }
3196 
3197 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3198   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3199   int n_tasks = pst->n_tasks();
3200   // We allow that there may be no tasks to do here because
3201   // we are restarting after a stack overflow.
3202   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3203   uint nth_task = 0;
3204 
3205   HeapWord* aligned_start = sp->bottom();
3206   if (sp->used_region().contains(_restart_addr)) {
3207     // Align down to a card boundary for the start of 0th task
3208     // for this space.
3209     aligned_start =
3210       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3211                                  CardTableModRefBS::card_size);
3212   }
3213 
3214   size_t chunk_size = sp->marking_task_size();
3215   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3216     // Having claimed the nth task in this space,
3217     // compute the chunk that it corresponds to:
3218     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3219                                aligned_start + (nth_task+1)*chunk_size);
3220     // Try and bump the global finger via a CAS;
3221     // note that we need to do the global finger bump
3222     // _before_ taking the intersection below, because
3223     // the task corresponding to that region will be
3224     // deemed done even if the used_region() expands
3225     // because of allocation -- as it almost certainly will
3226     // during start-up while the threads yield in the
3227     // closure below.
3228     HeapWord* finger = span.end();
3229     bump_global_finger(finger);   // atomically
3230     // There are null tasks here corresponding to chunks
3231     // beyond the "top" address of the space.
3232     span = span.intersection(sp->used_region());
3233     if (!span.is_empty()) {  // Non-null task
3234       HeapWord* prev_obj;
3235       assert(!span.contains(_restart_addr) || nth_task == 0,
3236              "Inconsistency");
3237       if (nth_task == 0) {
3238         // For the 0th task, we'll not need to compute a block_start.
3239         if (span.contains(_restart_addr)) {
3240           // In the case of a restart because of stack overflow,
3241           // we might additionally skip a chunk prefix.
3242           prev_obj = _restart_addr;
3243         } else {
3244           prev_obj = span.start();
3245         }
3246       } else {
3247         // We want to skip the first object because
3248         // the protocol is to scan any object in its entirety
3249         // that _starts_ in this span; a fortiori, any
3250         // object starting in an earlier span is scanned
3251         // as part of an earlier claimed task.
3252         // Below we use the "careful" version of block_start
3253         // so we do not try to navigate uninitialized objects.
3254         prev_obj = sp->block_start_careful(span.start());
3255         // Below we use a variant of block_size that uses the
3256         // Printezis bits to avoid waiting for allocated
3257         // objects to become initialized/parsable.
3258         while (prev_obj < span.start()) {
3259           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3260           if (sz > 0) {
3261             prev_obj += sz;
3262           } else {
3263             // In this case we may end up doing a bit of redundant
3264             // scanning, but that appears unavoidable, short of
3265             // locking the free list locks; see bug 6324141.
3266             break;
3267           }
3268         }
3269       }
3270       if (prev_obj < span.end()) {
3271         MemRegion my_span = MemRegion(prev_obj, span.end());
3272         // Do the marking work within a non-empty span --
3273         // the last argument to the constructor indicates whether the
3274         // iteration should be incremental with periodic yields.
3275         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3276                                     &_collector->_markBitMap,
3277                                     work_queue(i),
3278                                     &_collector->_markStack);
3279         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3280       } // else nothing to do for this task
3281     }   // else nothing to do for this task
3282   }
3283   // We'd be tempted to assert here that since there are no
3284   // more tasks left to claim in this space, the global_finger
3285   // must exceed space->top() and a fortiori space->end(). However,
3286   // that would not quite be correct because the bumping of
3287   // global_finger occurs strictly after the claiming of a task,
3288   // so by the time we reach here the global finger may not yet
3289   // have been bumped up by the thread that claimed the last
3290   // task.
3291   pst->all_tasks_completed();
3292 }
3293 
3294 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3295  private:
3296   CMSCollector* _collector;
3297   CMSConcMarkingTask* _task;
3298   MemRegion     _span;
3299   CMSBitMap*    _bit_map;
3300   CMSMarkStack* _overflow_stack;
3301   OopTaskQueue* _work_queue;
3302  protected:
3303   DO_OOP_WORK_DEFN
3304  public:
3305   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3306                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3307     MetadataAwareOopClosure(collector->ref_processor()),
3308     _collector(collector),
3309     _task(task),
3310     _span(collector->_span),
3311     _work_queue(work_queue),
3312     _bit_map(bit_map),
3313     _overflow_stack(overflow_stack)
3314   { }
3315   virtual void do_oop(oop* p);
3316   virtual void do_oop(narrowOop* p);
3317 
3318   void trim_queue(size_t max);
3319   void handle_stack_overflow(HeapWord* lost);
3320   void do_yield_check() {
3321     if (_task->should_yield()) {
3322       _task->yield();
3323     }
3324   }
3325 };
3326 
3327 // Grey object scanning during work stealing phase --
3328 // the salient assumption here is that any references
3329 // that are in these stolen objects being scanned must
3330 // already have been initialized (else they would not have
3331 // been published), so we do not need to check for
3332 // uninitialized objects before pushing here.
3333 void Par_ConcMarkingClosure::do_oop(oop obj) {
3334   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3335   HeapWord* addr = (HeapWord*)obj;
3336   // Check if oop points into the CMS generation
3337   // and is not marked
3338   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3339     // a white object ...
3340     // If we manage to "claim" the object, by being the
3341     // first thread to mark it, then we push it on our
3342     // marking stack
3343     if (_bit_map->par_mark(addr)) {     // ... now grey
3344       // push on work queue (grey set)
3345       bool simulate_overflow = false;
3346       NOT_PRODUCT(
3347         if (CMSMarkStackOverflowALot &&
3348             _collector->simulate_overflow()) {
3349           // simulate a stack overflow
3350           simulate_overflow = true;
3351         }
3352       )
3353       if (simulate_overflow ||
3354           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3355         // stack overflow
3356         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3357         // We cannot assert that the overflow stack is full because
3358         // it may have been emptied since.
3359         assert(simulate_overflow ||
3360                _work_queue->size() == _work_queue->max_elems(),
3361               "Else push should have succeeded");
3362         handle_stack_overflow(addr);
3363       }
3364     } // Else, some other thread got there first
3365     do_yield_check();
3366   }
3367 }
3368 
3369 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3370 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3371 
3372 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3373   while (_work_queue->size() > max) {
3374     oop new_oop;
3375     if (_work_queue->pop_local(new_oop)) {
3376       assert(new_oop->is_oop(), "Should be an oop");
3377       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3378       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3379       new_oop->oop_iterate(this);  // do_oop() above
3380       do_yield_check();
3381     }
3382   }
3383 }
3384 
3385 // Upon stack overflow, we discard (part of) the stack,
3386 // remembering the least address amongst those discarded
3387 // in CMSCollector's _restart_address.
3388 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3389   // We need to do this under a mutex to prevent other
3390   // workers from interfering with the work done below.
3391   MutexLockerEx ml(_overflow_stack->par_lock(),
3392                    Mutex::_no_safepoint_check_flag);
3393   // Remember the least grey address discarded
3394   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3395   _collector->lower_restart_addr(ra);
3396   _overflow_stack->reset();  // discard stack contents
3397   _overflow_stack->expand(); // expand the stack if possible
3398 }
3399 
3400 
3401 void CMSConcMarkingTask::do_work_steal(int i) {
3402   OopTaskQueue* work_q = work_queue(i);
3403   oop obj_to_scan;
3404   CMSBitMap* bm = &(_collector->_markBitMap);
3405   CMSMarkStack* ovflw = &(_collector->_markStack);
3406   int* seed = _collector->hash_seed(i);
3407   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3408   while (true) {
3409     cl.trim_queue(0);
3410     assert(work_q->size() == 0, "Should have been emptied above");
3411     if (get_work_from_overflow_stack(ovflw, work_q)) {
3412       // Can't assert below because the work obtained from the
3413       // overflow stack may already have been stolen from us.
3414       // assert(work_q->size() > 0, "Work from overflow stack");
3415       continue;
3416     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3417       assert(obj_to_scan->is_oop(), "Should be an oop");
3418       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3419       obj_to_scan->oop_iterate(&cl);
3420     } else if (terminator()->offer_termination(&_term_term)) {
3421       assert(work_q->size() == 0, "Impossible!");
3422       break;
3423     } else if (yielding() || should_yield()) {
3424       yield();
3425     }
3426   }
3427 }
3428 
3429 // This is run by the CMS (coordinator) thread.
3430 void CMSConcMarkingTask::coordinator_yield() {
3431   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3432          "CMS thread should hold CMS token");
3433   // First give up the locks, then yield, then re-lock
3434   // We should probably use a constructor/destructor idiom to
3435   // do this unlock/lock or modify the MutexUnlocker class to
3436   // serve our purpose. XXX
3437   assert_lock_strong(_bit_map_lock);
3438   _bit_map_lock->unlock();
3439   ConcurrentMarkSweepThread::desynchronize(true);
3440   _collector->stopTimer();
3441   _collector->incrementYields();
3442 
3443   // It is possible for whichever thread initiated the yield request
3444   // not to get a chance to wake up and take the bitmap lock between
3445   // this thread releasing it and reacquiring it. So, while the
3446   // should_yield() flag is on, let's sleep for a bit to give the
3447   // other thread a chance to wake up. The limit imposed on the number
3448   // of iterations is defensive, to avoid any unforseen circumstances
3449   // putting us into an infinite loop. Since it's always been this
3450   // (coordinator_yield()) method that was observed to cause the
3451   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3452   // which is by default non-zero. For the other seven methods that
3453   // also perform the yield operation, as are using a different
3454   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3455   // can enable the sleeping for those methods too, if necessary.
3456   // See 6442774.
3457   //
3458   // We really need to reconsider the synchronization between the GC
3459   // thread and the yield-requesting threads in the future and we
3460   // should really use wait/notify, which is the recommended
3461   // way of doing this type of interaction. Additionally, we should
3462   // consolidate the eight methods that do the yield operation and they
3463   // are almost identical into one for better maintainability and
3464   // readability. See 6445193.
3465   //
3466   // Tony 2006.06.29
3467   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3468                    ConcurrentMarkSweepThread::should_yield() &&
3469                    !CMSCollector::foregroundGCIsActive(); ++i) {
3470     os::sleep(Thread::current(), 1, false);
3471   }
3472 
3473   ConcurrentMarkSweepThread::synchronize(true);
3474   _bit_map_lock->lock_without_safepoint_check();
3475   _collector->startTimer();
3476 }
3477 
3478 bool CMSCollector::do_marking_mt() {
3479   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3480   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3481                                                                   conc_workers()->active_workers(),
3482                                                                   Threads::number_of_non_daemon_threads());
3483   conc_workers()->set_active_workers(num_workers);
3484 
3485   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3486 
3487   CMSConcMarkingTask tsk(this,
3488                          cms_space,
3489                          conc_workers(),
3490                          task_queues());
3491 
3492   // Since the actual number of workers we get may be different
3493   // from the number we requested above, do we need to do anything different
3494   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3495   // class?? XXX
3496   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3497 
3498   // Refs discovery is already non-atomic.
3499   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3500   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3501   conc_workers()->start_task(&tsk);
3502   while (tsk.yielded()) {
3503     tsk.coordinator_yield();
3504     conc_workers()->continue_task(&tsk);
3505   }
3506   // If the task was aborted, _restart_addr will be non-NULL
3507   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3508   while (_restart_addr != NULL) {
3509     // XXX For now we do not make use of ABORTED state and have not
3510     // yet implemented the right abort semantics (even in the original
3511     // single-threaded CMS case). That needs some more investigation
3512     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3513     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3514     // If _restart_addr is non-NULL, a marking stack overflow
3515     // occurred; we need to do a fresh marking iteration from the
3516     // indicated restart address.
3517     if (_foregroundGCIsActive) {
3518       // We may be running into repeated stack overflows, having
3519       // reached the limit of the stack size, while making very
3520       // slow forward progress. It may be best to bail out and
3521       // let the foreground collector do its job.
3522       // Clear _restart_addr, so that foreground GC
3523       // works from scratch. This avoids the headache of
3524       // a "rescan" which would otherwise be needed because
3525       // of the dirty mod union table & card table.
3526       _restart_addr = NULL;
3527       return false;
3528     }
3529     // Adjust the task to restart from _restart_addr
3530     tsk.reset(_restart_addr);
3531     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3532                   _restart_addr);
3533     _restart_addr = NULL;
3534     // Get the workers going again
3535     conc_workers()->start_task(&tsk);
3536     while (tsk.yielded()) {
3537       tsk.coordinator_yield();
3538       conc_workers()->continue_task(&tsk);
3539     }
3540   }
3541   assert(tsk.completed(), "Inconsistency");
3542   assert(tsk.result() == true, "Inconsistency");
3543   return true;
3544 }
3545 
3546 bool CMSCollector::do_marking_st() {
3547   ResourceMark rm;
3548   HandleMark   hm;
3549 
3550   // Temporarily make refs discovery single threaded (non-MT)
3551   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3552   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3553     &_markStack, CMSYield);
3554   // the last argument to iterate indicates whether the iteration
3555   // should be incremental with periodic yields.
3556   _markBitMap.iterate(&markFromRootsClosure);
3557   // If _restart_addr is non-NULL, a marking stack overflow
3558   // occurred; we need to do a fresh iteration from the
3559   // indicated restart address.
3560   while (_restart_addr != NULL) {
3561     if (_foregroundGCIsActive) {
3562       // We may be running into repeated stack overflows, having
3563       // reached the limit of the stack size, while making very
3564       // slow forward progress. It may be best to bail out and
3565       // let the foreground collector do its job.
3566       // Clear _restart_addr, so that foreground GC
3567       // works from scratch. This avoids the headache of
3568       // a "rescan" which would otherwise be needed because
3569       // of the dirty mod union table & card table.
3570       _restart_addr = NULL;
3571       return false;  // indicating failure to complete marking
3572     }
3573     // Deal with stack overflow:
3574     // we restart marking from _restart_addr
3575     HeapWord* ra = _restart_addr;
3576     markFromRootsClosure.reset(ra);
3577     _restart_addr = NULL;
3578     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3579   }
3580   return true;
3581 }
3582 
3583 void CMSCollector::preclean() {
3584   check_correct_thread_executing();
3585   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3586   verify_work_stacks_empty();
3587   verify_overflow_empty();
3588   _abort_preclean = false;
3589   if (CMSPrecleaningEnabled) {
3590     if (!CMSEdenChunksRecordAlways) {
3591       _eden_chunk_index = 0;
3592     }
3593     size_t used = get_eden_used();
3594     size_t capacity = get_eden_capacity();
3595     // Don't start sampling unless we will get sufficiently
3596     // many samples.
3597     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3598                 * CMSScheduleRemarkEdenPenetration)) {
3599       _start_sampling = true;
3600     } else {
3601       _start_sampling = false;
3602     }
3603     GCTraceCPUTime tcpu;
3604     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3605     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3606   }
3607   CMSTokenSync x(true); // is cms thread
3608   if (CMSPrecleaningEnabled) {
3609     sample_eden();
3610     _collectorState = AbortablePreclean;
3611   } else {
3612     _collectorState = FinalMarking;
3613   }
3614   verify_work_stacks_empty();
3615   verify_overflow_empty();
3616 }
3617 
3618 // Try and schedule the remark such that young gen
3619 // occupancy is CMSScheduleRemarkEdenPenetration %.
3620 void CMSCollector::abortable_preclean() {
3621   check_correct_thread_executing();
3622   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3623   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3624 
3625   // If Eden's current occupancy is below this threshold,
3626   // immediately schedule the remark; else preclean
3627   // past the next scavenge in an effort to
3628   // schedule the pause as described above. By choosing
3629   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3630   // we will never do an actual abortable preclean cycle.
3631   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3632     GCTraceCPUTime tcpu;
3633     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3634     // We need more smarts in the abortable preclean
3635     // loop below to deal with cases where allocation
3636     // in young gen is very very slow, and our precleaning
3637     // is running a losing race against a horde of
3638     // mutators intent on flooding us with CMS updates
3639     // (dirty cards).
3640     // One, admittedly dumb, strategy is to give up
3641     // after a certain number of abortable precleaning loops
3642     // or after a certain maximum time. We want to make
3643     // this smarter in the next iteration.
3644     // XXX FIX ME!!! YSR
3645     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3646     while (!(should_abort_preclean() ||
3647              ConcurrentMarkSweepThread::should_terminate())) {
3648       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3649       cumworkdone += workdone;
3650       loops++;
3651       // Voluntarily terminate abortable preclean phase if we have
3652       // been at it for too long.
3653       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3654           loops >= CMSMaxAbortablePrecleanLoops) {
3655         log_debug(gc)(" CMS: abort preclean due to loops ");
3656         break;
3657       }
3658       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3659         log_debug(gc)(" CMS: abort preclean due to time ");
3660         break;
3661       }
3662       // If we are doing little work each iteration, we should
3663       // take a short break.
3664       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3665         // Sleep for some time, waiting for work to accumulate
3666         stopTimer();
3667         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3668         startTimer();
3669         waited++;
3670       }
3671     }
3672     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3673                                loops, waited, cumworkdone);
3674   }
3675   CMSTokenSync x(true); // is cms thread
3676   if (_collectorState != Idling) {
3677     assert(_collectorState == AbortablePreclean,
3678            "Spontaneous state transition?");
3679     _collectorState = FinalMarking;
3680   } // Else, a foreground collection completed this CMS cycle.
3681   return;
3682 }
3683 
3684 // Respond to an Eden sampling opportunity
3685 void CMSCollector::sample_eden() {
3686   // Make sure a young gc cannot sneak in between our
3687   // reading and recording of a sample.
3688   assert(Thread::current()->is_ConcurrentGC_thread(),
3689          "Only the cms thread may collect Eden samples");
3690   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3691          "Should collect samples while holding CMS token");
3692   if (!_start_sampling) {
3693     return;
3694   }
3695   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3696   // is populated by the young generation.
3697   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3698     if (_eden_chunk_index < _eden_chunk_capacity) {
3699       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3700       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3701              "Unexpected state of Eden");
3702       // We'd like to check that what we just sampled is an oop-start address;
3703       // however, we cannot do that here since the object may not yet have been
3704       // initialized. So we'll instead do the check when we _use_ this sample
3705       // later.
3706       if (_eden_chunk_index == 0 ||
3707           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3708                          _eden_chunk_array[_eden_chunk_index-1])
3709            >= CMSSamplingGrain)) {
3710         _eden_chunk_index++;  // commit sample
3711       }
3712     }
3713   }
3714   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3715     size_t used = get_eden_used();
3716     size_t capacity = get_eden_capacity();
3717     assert(used <= capacity, "Unexpected state of Eden");
3718     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3719       _abort_preclean = true;
3720     }
3721   }
3722 }
3723 
3724 
3725 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3726   assert(_collectorState == Precleaning ||
3727          _collectorState == AbortablePreclean, "incorrect state");
3728   ResourceMark rm;
3729   HandleMark   hm;
3730 
3731   // Precleaning is currently not MT but the reference processor
3732   // may be set for MT.  Disable it temporarily here.
3733   ReferenceProcessor* rp = ref_processor();
3734   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3735 
3736   // Do one pass of scrubbing the discovered reference lists
3737   // to remove any reference objects with strongly-reachable
3738   // referents.
3739   if (clean_refs) {
3740     CMSPrecleanRefsYieldClosure yield_cl(this);
3741     assert(rp->span().equals(_span), "Spans should be equal");
3742     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3743                                    &_markStack, true /* preclean */);
3744     CMSDrainMarkingStackClosure complete_trace(this,
3745                                    _span, &_markBitMap, &_markStack,
3746                                    &keep_alive, true /* preclean */);
3747 
3748     // We don't want this step to interfere with a young
3749     // collection because we don't want to take CPU
3750     // or memory bandwidth away from the young GC threads
3751     // (which may be as many as there are CPUs).
3752     // Note that we don't need to protect ourselves from
3753     // interference with mutators because they can't
3754     // manipulate the discovered reference lists nor affect
3755     // the computed reachability of the referents, the
3756     // only properties manipulated by the precleaning
3757     // of these reference lists.
3758     stopTimer();
3759     CMSTokenSyncWithLocks x(true /* is cms thread */,
3760                             bitMapLock());
3761     startTimer();
3762     sample_eden();
3763 
3764     // The following will yield to allow foreground
3765     // collection to proceed promptly. XXX YSR:
3766     // The code in this method may need further
3767     // tweaking for better performance and some restructuring
3768     // for cleaner interfaces.
3769     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3770     rp->preclean_discovered_references(
3771           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3772           gc_timer);
3773   }
3774 
3775   if (clean_survivor) {  // preclean the active survivor space(s)
3776     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3777                              &_markBitMap, &_modUnionTable,
3778                              &_markStack, true /* precleaning phase */);
3779     stopTimer();
3780     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3781                              bitMapLock());
3782     startTimer();
3783     unsigned int before_count =
3784       GenCollectedHeap::heap()->total_collections();
3785     SurvivorSpacePrecleanClosure
3786       sss_cl(this, _span, &_markBitMap, &_markStack,
3787              &pam_cl, before_count, CMSYield);
3788     _young_gen->from()->object_iterate_careful(&sss_cl);
3789     _young_gen->to()->object_iterate_careful(&sss_cl);
3790   }
3791   MarkRefsIntoAndScanClosure
3792     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3793              &_markStack, this, CMSYield,
3794              true /* precleaning phase */);
3795   // CAUTION: The following closure has persistent state that may need to
3796   // be reset upon a decrease in the sequence of addresses it
3797   // processes.
3798   ScanMarkedObjectsAgainCarefullyClosure
3799     smoac_cl(this, _span,
3800       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3801 
3802   // Preclean dirty cards in ModUnionTable and CardTable using
3803   // appropriate convergence criterion;
3804   // repeat CMSPrecleanIter times unless we find that
3805   // we are losing.
3806   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3807   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3808          "Bad convergence multiplier");
3809   assert(CMSPrecleanThreshold >= 100,
3810          "Unreasonably low CMSPrecleanThreshold");
3811 
3812   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3813   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3814        numIter < CMSPrecleanIter;
3815        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3816     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3817     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3818     // Either there are very few dirty cards, so re-mark
3819     // pause will be small anyway, or our pre-cleaning isn't
3820     // that much faster than the rate at which cards are being
3821     // dirtied, so we might as well stop and re-mark since
3822     // precleaning won't improve our re-mark time by much.
3823     if (curNumCards <= CMSPrecleanThreshold ||
3824         (numIter > 0 &&
3825          (curNumCards * CMSPrecleanDenominator >
3826          lastNumCards * CMSPrecleanNumerator))) {
3827       numIter++;
3828       cumNumCards += curNumCards;
3829       break;
3830     }
3831   }
3832 
3833   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3834 
3835   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3836   cumNumCards += curNumCards;
3837   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3838                              curNumCards, cumNumCards, numIter);
3839   return cumNumCards;   // as a measure of useful work done
3840 }
3841 
3842 // PRECLEANING NOTES:
3843 // Precleaning involves:
3844 // . reading the bits of the modUnionTable and clearing the set bits.
3845 // . For the cards corresponding to the set bits, we scan the
3846 //   objects on those cards. This means we need the free_list_lock
3847 //   so that we can safely iterate over the CMS space when scanning
3848 //   for oops.
3849 // . When we scan the objects, we'll be both reading and setting
3850 //   marks in the marking bit map, so we'll need the marking bit map.
3851 // . For protecting _collector_state transitions, we take the CGC_lock.
3852 //   Note that any races in the reading of of card table entries by the
3853 //   CMS thread on the one hand and the clearing of those entries by the
3854 //   VM thread or the setting of those entries by the mutator threads on the
3855 //   other are quite benign. However, for efficiency it makes sense to keep
3856 //   the VM thread from racing with the CMS thread while the latter is
3857 //   dirty card info to the modUnionTable. We therefore also use the
3858 //   CGC_lock to protect the reading of the card table and the mod union
3859 //   table by the CM thread.
3860 // . We run concurrently with mutator updates, so scanning
3861 //   needs to be done carefully  -- we should not try to scan
3862 //   potentially uninitialized objects.
3863 //
3864 // Locking strategy: While holding the CGC_lock, we scan over and
3865 // reset a maximal dirty range of the mod union / card tables, then lock
3866 // the free_list_lock and bitmap lock to do a full marking, then
3867 // release these locks; and repeat the cycle. This allows for a
3868 // certain amount of fairness in the sharing of these locks between
3869 // the CMS collector on the one hand, and the VM thread and the
3870 // mutators on the other.
3871 
3872 // NOTE: preclean_mod_union_table() and preclean_card_table()
3873 // further below are largely identical; if you need to modify
3874 // one of these methods, please check the other method too.
3875 
3876 size_t CMSCollector::preclean_mod_union_table(
3877   ConcurrentMarkSweepGeneration* old_gen,
3878   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3879   verify_work_stacks_empty();
3880   verify_overflow_empty();
3881 
3882   // strategy: starting with the first card, accumulate contiguous
3883   // ranges of dirty cards; clear these cards, then scan the region
3884   // covered by these cards.
3885 
3886   // Since all of the MUT is committed ahead, we can just use
3887   // that, in case the generations expand while we are precleaning.
3888   // It might also be fine to just use the committed part of the
3889   // generation, but we might potentially miss cards when the
3890   // generation is rapidly expanding while we are in the midst
3891   // of precleaning.
3892   HeapWord* startAddr = old_gen->reserved().start();
3893   HeapWord* endAddr   = old_gen->reserved().end();
3894 
3895   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3896 
3897   size_t numDirtyCards, cumNumDirtyCards;
3898   HeapWord *nextAddr, *lastAddr;
3899   for (cumNumDirtyCards = numDirtyCards = 0,
3900        nextAddr = lastAddr = startAddr;
3901        nextAddr < endAddr;
3902        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3903 
3904     ResourceMark rm;
3905     HandleMark   hm;
3906 
3907     MemRegion dirtyRegion;
3908     {
3909       stopTimer();
3910       // Potential yield point
3911       CMSTokenSync ts(true);
3912       startTimer();
3913       sample_eden();
3914       // Get dirty region starting at nextOffset (inclusive),
3915       // simultaneously clearing it.
3916       dirtyRegion =
3917         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3918       assert(dirtyRegion.start() >= nextAddr,
3919              "returned region inconsistent?");
3920     }
3921     // Remember where the next search should begin.
3922     // The returned region (if non-empty) is a right open interval,
3923     // so lastOffset is obtained from the right end of that
3924     // interval.
3925     lastAddr = dirtyRegion.end();
3926     // Should do something more transparent and less hacky XXX
3927     numDirtyCards =
3928       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3929 
3930     // We'll scan the cards in the dirty region (with periodic
3931     // yields for foreground GC as needed).
3932     if (!dirtyRegion.is_empty()) {
3933       assert(numDirtyCards > 0, "consistency check");
3934       HeapWord* stop_point = NULL;
3935       stopTimer();
3936       // Potential yield point
3937       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3938                                bitMapLock());
3939       startTimer();
3940       {
3941         verify_work_stacks_empty();
3942         verify_overflow_empty();
3943         sample_eden();
3944         stop_point =
3945           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3946       }
3947       if (stop_point != NULL) {
3948         // The careful iteration stopped early either because it found an
3949         // uninitialized object, or because we were in the midst of an
3950         // "abortable preclean", which should now be aborted. Redirty
3951         // the bits corresponding to the partially-scanned or unscanned
3952         // cards. We'll either restart at the next block boundary or
3953         // abort the preclean.
3954         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3955                "Should only be AbortablePreclean.");
3956         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3957         if (should_abort_preclean()) {
3958           break; // out of preclean loop
3959         } else {
3960           // Compute the next address at which preclean should pick up;
3961           // might need bitMapLock in order to read P-bits.
3962           lastAddr = next_card_start_after_block(stop_point);
3963         }
3964       }
3965     } else {
3966       assert(lastAddr == endAddr, "consistency check");
3967       assert(numDirtyCards == 0, "consistency check");
3968       break;
3969     }
3970   }
3971   verify_work_stacks_empty();
3972   verify_overflow_empty();
3973   return cumNumDirtyCards;
3974 }
3975 
3976 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3977 // below are largely identical; if you need to modify
3978 // one of these methods, please check the other method too.
3979 
3980 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3981   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3982   // strategy: it's similar to precleamModUnionTable above, in that
3983   // we accumulate contiguous ranges of dirty cards, mark these cards
3984   // precleaned, then scan the region covered by these cards.
3985   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
3986   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3987 
3988   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3989 
3990   size_t numDirtyCards, cumNumDirtyCards;
3991   HeapWord *lastAddr, *nextAddr;
3992 
3993   for (cumNumDirtyCards = numDirtyCards = 0,
3994        nextAddr = lastAddr = startAddr;
3995        nextAddr < endAddr;
3996        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3997 
3998     ResourceMark rm;
3999     HandleMark   hm;
4000 
4001     MemRegion dirtyRegion;
4002     {
4003       // See comments in "Precleaning notes" above on why we
4004       // do this locking. XXX Could the locking overheads be
4005       // too high when dirty cards are sparse? [I don't think so.]
4006       stopTimer();
4007       CMSTokenSync x(true); // is cms thread
4008       startTimer();
4009       sample_eden();
4010       // Get and clear dirty region from card table
4011       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4012                                     MemRegion(nextAddr, endAddr),
4013                                     true,
4014                                     CardTableModRefBS::precleaned_card_val());
4015 
4016       assert(dirtyRegion.start() >= nextAddr,
4017              "returned region inconsistent?");
4018     }
4019     lastAddr = dirtyRegion.end();
4020     numDirtyCards =
4021       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4022 
4023     if (!dirtyRegion.is_empty()) {
4024       stopTimer();
4025       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4026       startTimer();
4027       sample_eden();
4028       verify_work_stacks_empty();
4029       verify_overflow_empty();
4030       HeapWord* stop_point =
4031         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4032       if (stop_point != NULL) {
4033         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4034                "Should only be AbortablePreclean.");
4035         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4036         if (should_abort_preclean()) {
4037           break; // out of preclean loop
4038         } else {
4039           // Compute the next address at which preclean should pick up.
4040           lastAddr = next_card_start_after_block(stop_point);
4041         }
4042       }
4043     } else {
4044       break;
4045     }
4046   }
4047   verify_work_stacks_empty();
4048   verify_overflow_empty();
4049   return cumNumDirtyCards;
4050 }
4051 
4052 class PrecleanKlassClosure : public KlassClosure {
4053   KlassToOopClosure _cm_klass_closure;
4054  public:
4055   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4056   void do_klass(Klass* k) {
4057     if (k->has_accumulated_modified_oops()) {
4058       k->clear_accumulated_modified_oops();
4059 
4060       _cm_klass_closure.do_klass(k);
4061     }
4062   }
4063 };
4064 
4065 // The freelist lock is needed to prevent asserts, is it really needed?
4066 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4067 
4068   cl->set_freelistLock(freelistLock);
4069 
4070   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4071 
4072   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4073   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4074   PrecleanKlassClosure preclean_klass_closure(cl);
4075   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4076 
4077   verify_work_stacks_empty();
4078   verify_overflow_empty();
4079 }
4080 
4081 void CMSCollector::checkpointRootsFinal() {
4082   assert(_collectorState == FinalMarking, "incorrect state transition?");
4083   check_correct_thread_executing();
4084   // world is stopped at this checkpoint
4085   assert(SafepointSynchronize::is_at_safepoint(),
4086          "world should be stopped");
4087   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4088 
4089   verify_work_stacks_empty();
4090   verify_overflow_empty();
4091 
4092   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4093                 _young_gen->used() / K, _young_gen->capacity() / K);
4094   {
4095     if (CMSScavengeBeforeRemark) {
4096       GenCollectedHeap* gch = GenCollectedHeap::heap();
4097       // Temporarily set flag to false, GCH->do_collection will
4098       // expect it to be false and set to true
4099       FlagSetting fl(gch->_is_gc_active, false);
4100 
4101       GCTraceTime(Trace, gc) tm("Pause Scavenge Before Remark", _gc_timer_cm);
4102 
4103       gch->do_collection(true,                      // full (i.e. force, see below)
4104                          false,                     // !clear_all_soft_refs
4105                          0,                         // size
4106                          false,                     // is_tlab
4107                          GenCollectedHeap::YoungGen // type
4108         );
4109     }
4110     FreelistLocker x(this);
4111     MutexLockerEx y(bitMapLock(),
4112                     Mutex::_no_safepoint_check_flag);
4113     checkpointRootsFinalWork();
4114   }
4115   verify_work_stacks_empty();
4116   verify_overflow_empty();
4117 }
4118 
4119 void CMSCollector::checkpointRootsFinalWork() {
4120   GCTraceTime(Trace, gc) tm("checkpointRootsFinalWork", _gc_timer_cm);
4121 
4122   assert(haveFreelistLocks(), "must have free list locks");
4123   assert_lock_strong(bitMapLock());
4124 
4125   ResourceMark rm;
4126   HandleMark   hm;
4127 
4128   GenCollectedHeap* gch = GenCollectedHeap::heap();
4129 
4130   if (should_unload_classes()) {
4131     CodeCache::gc_prologue();
4132   }
4133   assert(haveFreelistLocks(), "must have free list locks");
4134   assert_lock_strong(bitMapLock());
4135 
4136   // We might assume that we need not fill TLAB's when
4137   // CMSScavengeBeforeRemark is set, because we may have just done
4138   // a scavenge which would have filled all TLAB's -- and besides
4139   // Eden would be empty. This however may not always be the case --
4140   // for instance although we asked for a scavenge, it may not have
4141   // happened because of a JNI critical section. We probably need
4142   // a policy for deciding whether we can in that case wait until
4143   // the critical section releases and then do the remark following
4144   // the scavenge, and skip it here. In the absence of that policy,
4145   // or of an indication of whether the scavenge did indeed occur,
4146   // we cannot rely on TLAB's having been filled and must do
4147   // so here just in case a scavenge did not happen.
4148   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4149   // Update the saved marks which may affect the root scans.
4150   gch->save_marks();
4151 
4152   print_eden_and_survivor_chunk_arrays();
4153 
4154   {
4155 #if defined(COMPILER2) || INCLUDE_JVMCI
4156     DerivedPointerTableDeactivate dpt_deact;
4157 #endif
4158 
4159     // Note on the role of the mod union table:
4160     // Since the marker in "markFromRoots" marks concurrently with
4161     // mutators, it is possible for some reachable objects not to have been
4162     // scanned. For instance, an only reference to an object A was
4163     // placed in object B after the marker scanned B. Unless B is rescanned,
4164     // A would be collected. Such updates to references in marked objects
4165     // are detected via the mod union table which is the set of all cards
4166     // dirtied since the first checkpoint in this GC cycle and prior to
4167     // the most recent young generation GC, minus those cleaned up by the
4168     // concurrent precleaning.
4169     if (CMSParallelRemarkEnabled) {
4170       GCTraceTime(Debug, gc) t("Rescan (parallel)", _gc_timer_cm);
4171       do_remark_parallel();
4172     } else {
4173       GCTraceTime(Debug, gc) t("Rescan (non-parallel)", _gc_timer_cm);
4174       do_remark_non_parallel();
4175     }
4176   }
4177   verify_work_stacks_empty();
4178   verify_overflow_empty();
4179 
4180   {
4181     GCTraceTime(Trace, gc) ts("refProcessingWork", _gc_timer_cm);
4182     refProcessingWork();
4183   }
4184   verify_work_stacks_empty();
4185   verify_overflow_empty();
4186 
4187   if (should_unload_classes()) {
4188     CodeCache::gc_epilogue();
4189   }
4190   JvmtiExport::gc_epilogue();
4191 
4192   // If we encountered any (marking stack / work queue) overflow
4193   // events during the current CMS cycle, take appropriate
4194   // remedial measures, where possible, so as to try and avoid
4195   // recurrence of that condition.
4196   assert(_markStack.isEmpty(), "No grey objects");
4197   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4198                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4199   if (ser_ovflw > 0) {
4200     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4201                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4202     _markStack.expand();
4203     _ser_pmc_remark_ovflw = 0;
4204     _ser_pmc_preclean_ovflw = 0;
4205     _ser_kac_preclean_ovflw = 0;
4206     _ser_kac_ovflw = 0;
4207   }
4208   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4209      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4210                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4211      _par_pmc_remark_ovflw = 0;
4212     _par_kac_ovflw = 0;
4213   }
4214    if (_markStack._hit_limit > 0) {
4215      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4216                           _markStack._hit_limit);
4217    }
4218    if (_markStack._failed_double > 0) {
4219      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4220                           _markStack._failed_double, _markStack.capacity());
4221    }
4222   _markStack._hit_limit = 0;
4223   _markStack._failed_double = 0;
4224 
4225   if ((VerifyAfterGC || VerifyDuringGC) &&
4226       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4227     verify_after_remark();
4228   }
4229 
4230   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4231 
4232   // Change under the freelistLocks.
4233   _collectorState = Sweeping;
4234   // Call isAllClear() under bitMapLock
4235   assert(_modUnionTable.isAllClear(),
4236       "Should be clear by end of the final marking");
4237   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4238       "Should be clear by end of the final marking");
4239 }
4240 
4241 void CMSParInitialMarkTask::work(uint worker_id) {
4242   elapsedTimer _timer;
4243   ResourceMark rm;
4244   HandleMark   hm;
4245 
4246   // ---------- scan from roots --------------
4247   _timer.start();
4248   GenCollectedHeap* gch = GenCollectedHeap::heap();
4249   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4250 
4251   // ---------- young gen roots --------------
4252   {
4253     work_on_young_gen_roots(worker_id, &par_mri_cl);
4254     _timer.stop();
4255     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4256   }
4257 
4258   // ---------- remaining roots --------------
4259   _timer.reset();
4260   _timer.start();
4261 
4262   CLDToOopClosure cld_closure(&par_mri_cl, true);
4263 
4264   gch->gen_process_roots(_strong_roots_scope,
4265                          GenCollectedHeap::OldGen,
4266                          false,     // yg was scanned above
4267                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4268                          _collector->should_unload_classes(),
4269                          &par_mri_cl,
4270                          NULL,
4271                          &cld_closure);
4272   assert(_collector->should_unload_classes()
4273          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4274          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4275   _timer.stop();
4276   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4277 }
4278 
4279 // Parallel remark task
4280 class CMSParRemarkTask: public CMSParMarkTask {
4281   CompactibleFreeListSpace* _cms_space;
4282 
4283   // The per-thread work queues, available here for stealing.
4284   OopTaskQueueSet*       _task_queues;
4285   ParallelTaskTerminator _term;
4286   StrongRootsScope*      _strong_roots_scope;
4287 
4288  public:
4289   // A value of 0 passed to n_workers will cause the number of
4290   // workers to be taken from the active workers in the work gang.
4291   CMSParRemarkTask(CMSCollector* collector,
4292                    CompactibleFreeListSpace* cms_space,
4293                    uint n_workers, WorkGang* workers,
4294                    OopTaskQueueSet* task_queues,
4295                    StrongRootsScope* strong_roots_scope):
4296     CMSParMarkTask("Rescan roots and grey objects in parallel",
4297                    collector, n_workers),
4298     _cms_space(cms_space),
4299     _task_queues(task_queues),
4300     _term(n_workers, task_queues),
4301     _strong_roots_scope(strong_roots_scope) { }
4302 
4303   OopTaskQueueSet* task_queues() { return _task_queues; }
4304 
4305   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4306 
4307   ParallelTaskTerminator* terminator() { return &_term; }
4308   uint n_workers() { return _n_workers; }
4309 
4310   void work(uint worker_id);
4311 
4312  private:
4313   // ... of  dirty cards in old space
4314   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4315                                   Par_MarkRefsIntoAndScanClosure* cl);
4316 
4317   // ... work stealing for the above
4318   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4319 };
4320 
4321 class RemarkKlassClosure : public KlassClosure {
4322   KlassToOopClosure _cm_klass_closure;
4323  public:
4324   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4325   void do_klass(Klass* k) {
4326     // Check if we have modified any oops in the Klass during the concurrent marking.
4327     if (k->has_accumulated_modified_oops()) {
4328       k->clear_accumulated_modified_oops();
4329 
4330       // We could have transfered the current modified marks to the accumulated marks,
4331       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4332     } else if (k->has_modified_oops()) {
4333       // Don't clear anything, this info is needed by the next young collection.
4334     } else {
4335       // No modified oops in the Klass.
4336       return;
4337     }
4338 
4339     // The klass has modified fields, need to scan the klass.
4340     _cm_klass_closure.do_klass(k);
4341   }
4342 };
4343 
4344 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4345   ParNewGeneration* young_gen = _collector->_young_gen;
4346   ContiguousSpace* eden_space = young_gen->eden();
4347   ContiguousSpace* from_space = young_gen->from();
4348   ContiguousSpace* to_space   = young_gen->to();
4349 
4350   HeapWord** eca = _collector->_eden_chunk_array;
4351   size_t     ect = _collector->_eden_chunk_index;
4352   HeapWord** sca = _collector->_survivor_chunk_array;
4353   size_t     sct = _collector->_survivor_chunk_index;
4354 
4355   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4356   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4357 
4358   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4359   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4360   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4361 }
4362 
4363 // work_queue(i) is passed to the closure
4364 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4365 // also is passed to do_dirty_card_rescan_tasks() and to
4366 // do_work_steal() to select the i-th task_queue.
4367 
4368 void CMSParRemarkTask::work(uint worker_id) {
4369   elapsedTimer _timer;
4370   ResourceMark rm;
4371   HandleMark   hm;
4372 
4373   // ---------- rescan from roots --------------
4374   _timer.start();
4375   GenCollectedHeap* gch = GenCollectedHeap::heap();
4376   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4377     _collector->_span, _collector->ref_processor(),
4378     &(_collector->_markBitMap),
4379     work_queue(worker_id));
4380 
4381   // Rescan young gen roots first since these are likely
4382   // coarsely partitioned and may, on that account, constitute
4383   // the critical path; thus, it's best to start off that
4384   // work first.
4385   // ---------- young gen roots --------------
4386   {
4387     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4388     _timer.stop();
4389     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4390   }
4391 
4392   // ---------- remaining roots --------------
4393   _timer.reset();
4394   _timer.start();
4395   gch->gen_process_roots(_strong_roots_scope,
4396                          GenCollectedHeap::OldGen,
4397                          false,     // yg was scanned above
4398                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4399                          _collector->should_unload_classes(),
4400                          &par_mrias_cl,
4401                          NULL,
4402                          NULL);     // The dirty klasses will be handled below
4403 
4404   assert(_collector->should_unload_classes()
4405          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4406          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4407   _timer.stop();
4408   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4409 
4410   // ---------- unhandled CLD scanning ----------
4411   if (worker_id == 0) { // Single threaded at the moment.
4412     _timer.reset();
4413     _timer.start();
4414 
4415     // Scan all new class loader data objects and new dependencies that were
4416     // introduced during concurrent marking.
4417     ResourceMark rm;
4418     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4419     for (int i = 0; i < array->length(); i++) {
4420       par_mrias_cl.do_cld_nv(array->at(i));
4421     }
4422 
4423     // We don't need to keep track of new CLDs anymore.
4424     ClassLoaderDataGraph::remember_new_clds(false);
4425 
4426     _timer.stop();
4427     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4428   }
4429 
4430   // ---------- dirty klass scanning ----------
4431   if (worker_id == 0) { // Single threaded at the moment.
4432     _timer.reset();
4433     _timer.start();
4434 
4435     // Scan all classes that was dirtied during the concurrent marking phase.
4436     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4437     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4438 
4439     _timer.stop();
4440     log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4441   }
4442 
4443   // We might have added oops to ClassLoaderData::_handles during the
4444   // concurrent marking phase. These oops point to newly allocated objects
4445   // that are guaranteed to be kept alive. Either by the direct allocation
4446   // code, or when the young collector processes the roots. Hence,
4447   // we don't have to revisit the _handles block during the remark phase.
4448 
4449   // ---------- rescan dirty cards ------------
4450   _timer.reset();
4451   _timer.start();
4452 
4453   // Do the rescan tasks for each of the two spaces
4454   // (cms_space) in turn.
4455   // "worker_id" is passed to select the task_queue for "worker_id"
4456   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4457   _timer.stop();
4458   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4459 
4460   // ---------- steal work from other threads ...
4461   // ---------- ... and drain overflow list.
4462   _timer.reset();
4463   _timer.start();
4464   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4465   _timer.stop();
4466   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4467 }
4468 
4469 // Note that parameter "i" is not used.
4470 void
4471 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4472   OopsInGenClosure* cl, ContiguousSpace* space,
4473   HeapWord** chunk_array, size_t chunk_top) {
4474   // Until all tasks completed:
4475   // . claim an unclaimed task
4476   // . compute region boundaries corresponding to task claimed
4477   //   using chunk_array
4478   // . par_oop_iterate(cl) over that region
4479 
4480   ResourceMark rm;
4481   HandleMark   hm;
4482 
4483   SequentialSubTasksDone* pst = space->par_seq_tasks();
4484 
4485   uint nth_task = 0;
4486   uint n_tasks  = pst->n_tasks();
4487 
4488   if (n_tasks > 0) {
4489     assert(pst->valid(), "Uninitialized use?");
4490     HeapWord *start, *end;
4491     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4492       // We claimed task # nth_task; compute its boundaries.
4493       if (chunk_top == 0) {  // no samples were taken
4494         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4495         start = space->bottom();
4496         end   = space->top();
4497       } else if (nth_task == 0) {
4498         start = space->bottom();
4499         end   = chunk_array[nth_task];
4500       } else if (nth_task < (uint)chunk_top) {
4501         assert(nth_task >= 1, "Control point invariant");
4502         start = chunk_array[nth_task - 1];
4503         end   = chunk_array[nth_task];
4504       } else {
4505         assert(nth_task == (uint)chunk_top, "Control point invariant");
4506         start = chunk_array[chunk_top - 1];
4507         end   = space->top();
4508       }
4509       MemRegion mr(start, end);
4510       // Verify that mr is in space
4511       assert(mr.is_empty() || space->used_region().contains(mr),
4512              "Should be in space");
4513       // Verify that "start" is an object boundary
4514       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4515              "Should be an oop");
4516       space->par_oop_iterate(mr, cl);
4517     }
4518     pst->all_tasks_completed();
4519   }
4520 }
4521 
4522 void
4523 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4524   CompactibleFreeListSpace* sp, int i,
4525   Par_MarkRefsIntoAndScanClosure* cl) {
4526   // Until all tasks completed:
4527   // . claim an unclaimed task
4528   // . compute region boundaries corresponding to task claimed
4529   // . transfer dirty bits ct->mut for that region
4530   // . apply rescanclosure to dirty mut bits for that region
4531 
4532   ResourceMark rm;
4533   HandleMark   hm;
4534 
4535   OopTaskQueue* work_q = work_queue(i);
4536   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4537   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4538   // CAUTION: This closure has state that persists across calls to
4539   // the work method dirty_range_iterate_clear() in that it has
4540   // embedded in it a (subtype of) UpwardsObjectClosure. The
4541   // use of that state in the embedded UpwardsObjectClosure instance
4542   // assumes that the cards are always iterated (even if in parallel
4543   // by several threads) in monotonically increasing order per each
4544   // thread. This is true of the implementation below which picks
4545   // card ranges (chunks) in monotonically increasing order globally
4546   // and, a-fortiori, in monotonically increasing order per thread
4547   // (the latter order being a subsequence of the former).
4548   // If the work code below is ever reorganized into a more chaotic
4549   // work-partitioning form than the current "sequential tasks"
4550   // paradigm, the use of that persistent state will have to be
4551   // revisited and modified appropriately. See also related
4552   // bug 4756801 work on which should examine this code to make
4553   // sure that the changes there do not run counter to the
4554   // assumptions made here and necessary for correctness and
4555   // efficiency. Note also that this code might yield inefficient
4556   // behavior in the case of very large objects that span one or
4557   // more work chunks. Such objects would potentially be scanned
4558   // several times redundantly. Work on 4756801 should try and
4559   // address that performance anomaly if at all possible. XXX
4560   MemRegion  full_span  = _collector->_span;
4561   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4562   MarkFromDirtyCardsClosure
4563     greyRescanClosure(_collector, full_span, // entire span of interest
4564                       sp, bm, work_q, cl);
4565 
4566   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4567   assert(pst->valid(), "Uninitialized use?");
4568   uint nth_task = 0;
4569   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4570   MemRegion span = sp->used_region();
4571   HeapWord* start_addr = span.start();
4572   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4573                                            alignment);
4574   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4575   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4576          start_addr, "Check alignment");
4577   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4578          chunk_size, "Check alignment");
4579 
4580   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4581     // Having claimed the nth_task, compute corresponding mem-region,
4582     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4583     // The alignment restriction ensures that we do not need any
4584     // synchronization with other gang-workers while setting or
4585     // clearing bits in thus chunk of the MUT.
4586     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4587                                     start_addr + (nth_task+1)*chunk_size);
4588     // The last chunk's end might be way beyond end of the
4589     // used region. In that case pull back appropriately.
4590     if (this_span.end() > end_addr) {
4591       this_span.set_end(end_addr);
4592       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4593     }
4594     // Iterate over the dirty cards covering this chunk, marking them
4595     // precleaned, and setting the corresponding bits in the mod union
4596     // table. Since we have been careful to partition at Card and MUT-word
4597     // boundaries no synchronization is needed between parallel threads.
4598     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4599                                                  &modUnionClosure);
4600 
4601     // Having transferred these marks into the modUnionTable,
4602     // rescan the marked objects on the dirty cards in the modUnionTable.
4603     // Even if this is at a synchronous collection, the initial marking
4604     // may have been done during an asynchronous collection so there
4605     // may be dirty bits in the mod-union table.
4606     _collector->_modUnionTable.dirty_range_iterate_clear(
4607                   this_span, &greyRescanClosure);
4608     _collector->_modUnionTable.verifyNoOneBitsInRange(
4609                                  this_span.start(),
4610                                  this_span.end());
4611   }
4612   pst->all_tasks_completed();  // declare that i am done
4613 }
4614 
4615 // . see if we can share work_queues with ParNew? XXX
4616 void
4617 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4618                                 int* seed) {
4619   OopTaskQueue* work_q = work_queue(i);
4620   NOT_PRODUCT(int num_steals = 0;)
4621   oop obj_to_scan;
4622   CMSBitMap* bm = &(_collector->_markBitMap);
4623 
4624   while (true) {
4625     // Completely finish any left over work from (an) earlier round(s)
4626     cl->trim_queue(0);
4627     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4628                                          (size_t)ParGCDesiredObjsFromOverflowList);
4629     // Now check if there's any work in the overflow list
4630     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4631     // only affects the number of attempts made to get work from the
4632     // overflow list and does not affect the number of workers.  Just
4633     // pass ParallelGCThreads so this behavior is unchanged.
4634     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4635                                                 work_q,
4636                                                 ParallelGCThreads)) {
4637       // found something in global overflow list;
4638       // not yet ready to go stealing work from others.
4639       // We'd like to assert(work_q->size() != 0, ...)
4640       // because we just took work from the overflow list,
4641       // but of course we can't since all of that could have
4642       // been already stolen from us.
4643       // "He giveth and He taketh away."
4644       continue;
4645     }
4646     // Verify that we have no work before we resort to stealing
4647     assert(work_q->size() == 0, "Have work, shouldn't steal");
4648     // Try to steal from other queues that have work
4649     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4650       NOT_PRODUCT(num_steals++;)
4651       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4652       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4653       // Do scanning work
4654       obj_to_scan->oop_iterate(cl);
4655       // Loop around, finish this work, and try to steal some more
4656     } else if (terminator()->offer_termination()) {
4657         break;  // nirvana from the infinite cycle
4658     }
4659   }
4660   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4661   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4662          "Else our work is not yet done");
4663 }
4664 
4665 // Record object boundaries in _eden_chunk_array by sampling the eden
4666 // top in the slow-path eden object allocation code path and record
4667 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4668 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4669 // sampling in sample_eden() that activates during the part of the
4670 // preclean phase.
4671 void CMSCollector::sample_eden_chunk() {
4672   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4673     if (_eden_chunk_lock->try_lock()) {
4674       // Record a sample. This is the critical section. The contents
4675       // of the _eden_chunk_array have to be non-decreasing in the
4676       // address order.
4677       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4678       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4679              "Unexpected state of Eden");
4680       if (_eden_chunk_index == 0 ||
4681           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4682            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4683                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4684         _eden_chunk_index++;  // commit sample
4685       }
4686       _eden_chunk_lock->unlock();
4687     }
4688   }
4689 }
4690 
4691 // Return a thread-local PLAB recording array, as appropriate.
4692 void* CMSCollector::get_data_recorder(int thr_num) {
4693   if (_survivor_plab_array != NULL &&
4694       (CMSPLABRecordAlways ||
4695        (_collectorState > Marking && _collectorState < FinalMarking))) {
4696     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4697     ChunkArray* ca = &_survivor_plab_array[thr_num];
4698     ca->reset();   // clear it so that fresh data is recorded
4699     return (void*) ca;
4700   } else {
4701     return NULL;
4702   }
4703 }
4704 
4705 // Reset all the thread-local PLAB recording arrays
4706 void CMSCollector::reset_survivor_plab_arrays() {
4707   for (uint i = 0; i < ParallelGCThreads; i++) {
4708     _survivor_plab_array[i].reset();
4709   }
4710 }
4711 
4712 // Merge the per-thread plab arrays into the global survivor chunk
4713 // array which will provide the partitioning of the survivor space
4714 // for CMS initial scan and rescan.
4715 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4716                                               int no_of_gc_threads) {
4717   assert(_survivor_plab_array  != NULL, "Error");
4718   assert(_survivor_chunk_array != NULL, "Error");
4719   assert(_collectorState == FinalMarking ||
4720          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4721   for (int j = 0; j < no_of_gc_threads; j++) {
4722     _cursor[j] = 0;
4723   }
4724   HeapWord* top = surv->top();
4725   size_t i;
4726   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4727     HeapWord* min_val = top;          // Higher than any PLAB address
4728     uint      min_tid = 0;            // position of min_val this round
4729     for (int j = 0; j < no_of_gc_threads; j++) {
4730       ChunkArray* cur_sca = &_survivor_plab_array[j];
4731       if (_cursor[j] == cur_sca->end()) {
4732         continue;
4733       }
4734       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4735       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4736       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4737       if (cur_val < min_val) {
4738         min_tid = j;
4739         min_val = cur_val;
4740       } else {
4741         assert(cur_val < top, "All recorded addresses should be less");
4742       }
4743     }
4744     // At this point min_val and min_tid are respectively
4745     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4746     // and the thread (j) that witnesses that address.
4747     // We record this address in the _survivor_chunk_array[i]
4748     // and increment _cursor[min_tid] prior to the next round i.
4749     if (min_val == top) {
4750       break;
4751     }
4752     _survivor_chunk_array[i] = min_val;
4753     _cursor[min_tid]++;
4754   }
4755   // We are all done; record the size of the _survivor_chunk_array
4756   _survivor_chunk_index = i; // exclusive: [0, i)
4757   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4758   // Verify that we used up all the recorded entries
4759   #ifdef ASSERT
4760     size_t total = 0;
4761     for (int j = 0; j < no_of_gc_threads; j++) {
4762       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4763       total += _cursor[j];
4764     }
4765     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4766     // Check that the merged array is in sorted order
4767     if (total > 0) {
4768       for (size_t i = 0; i < total - 1; i++) {
4769         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4770                                      i, p2i(_survivor_chunk_array[i]));
4771         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4772                "Not sorted");
4773       }
4774     }
4775   #endif // ASSERT
4776 }
4777 
4778 // Set up the space's par_seq_tasks structure for work claiming
4779 // for parallel initial scan and rescan of young gen.
4780 // See ParRescanTask where this is currently used.
4781 void
4782 CMSCollector::
4783 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4784   assert(n_threads > 0, "Unexpected n_threads argument");
4785 
4786   // Eden space
4787   if (!_young_gen->eden()->is_empty()) {
4788     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4789     assert(!pst->valid(), "Clobbering existing data?");
4790     // Each valid entry in [0, _eden_chunk_index) represents a task.
4791     size_t n_tasks = _eden_chunk_index + 1;
4792     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4793     // Sets the condition for completion of the subtask (how many threads
4794     // need to finish in order to be done).
4795     pst->set_n_threads(n_threads);
4796     pst->set_n_tasks((int)n_tasks);
4797   }
4798 
4799   // Merge the survivor plab arrays into _survivor_chunk_array
4800   if (_survivor_plab_array != NULL) {
4801     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4802   } else {
4803     assert(_survivor_chunk_index == 0, "Error");
4804   }
4805 
4806   // To space
4807   {
4808     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4809     assert(!pst->valid(), "Clobbering existing data?");
4810     // Sets the condition for completion of the subtask (how many threads
4811     // need to finish in order to be done).
4812     pst->set_n_threads(n_threads);
4813     pst->set_n_tasks(1);
4814     assert(pst->valid(), "Error");
4815   }
4816 
4817   // From space
4818   {
4819     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4820     assert(!pst->valid(), "Clobbering existing data?");
4821     size_t n_tasks = _survivor_chunk_index + 1;
4822     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4823     // Sets the condition for completion of the subtask (how many threads
4824     // need to finish in order to be done).
4825     pst->set_n_threads(n_threads);
4826     pst->set_n_tasks((int)n_tasks);
4827     assert(pst->valid(), "Error");
4828   }
4829 }
4830 
4831 // Parallel version of remark
4832 void CMSCollector::do_remark_parallel() {
4833   GenCollectedHeap* gch = GenCollectedHeap::heap();
4834   WorkGang* workers = gch->workers();
4835   assert(workers != NULL, "Need parallel worker threads.");
4836   // Choose to use the number of GC workers most recently set
4837   // into "active_workers".
4838   uint n_workers = workers->active_workers();
4839 
4840   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4841 
4842   StrongRootsScope srs(n_workers);
4843 
4844   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4845 
4846   // We won't be iterating over the cards in the card table updating
4847   // the younger_gen cards, so we shouldn't call the following else
4848   // the verification code as well as subsequent younger_refs_iterate
4849   // code would get confused. XXX
4850   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4851 
4852   // The young gen rescan work will not be done as part of
4853   // process_roots (which currently doesn't know how to
4854   // parallelize such a scan), but rather will be broken up into
4855   // a set of parallel tasks (via the sampling that the [abortable]
4856   // preclean phase did of eden, plus the [two] tasks of
4857   // scanning the [two] survivor spaces. Further fine-grain
4858   // parallelization of the scanning of the survivor spaces
4859   // themselves, and of precleaning of the young gen itself
4860   // is deferred to the future.
4861   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4862 
4863   // The dirty card rescan work is broken up into a "sequence"
4864   // of parallel tasks (per constituent space) that are dynamically
4865   // claimed by the parallel threads.
4866   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4867 
4868   // It turns out that even when we're using 1 thread, doing the work in a
4869   // separate thread causes wide variance in run times.  We can't help this
4870   // in the multi-threaded case, but we special-case n=1 here to get
4871   // repeatable measurements of the 1-thread overhead of the parallel code.
4872   if (n_workers > 1) {
4873     // Make refs discovery MT-safe, if it isn't already: it may not
4874     // necessarily be so, since it's possible that we are doing
4875     // ST marking.
4876     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4877     workers->run_task(&tsk);
4878   } else {
4879     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4880     tsk.work(0);
4881   }
4882 
4883   // restore, single-threaded for now, any preserved marks
4884   // as a result of work_q overflow
4885   restore_preserved_marks_if_any();
4886 }
4887 
4888 // Non-parallel version of remark
4889 void CMSCollector::do_remark_non_parallel() {
4890   ResourceMark rm;
4891   HandleMark   hm;
4892   GenCollectedHeap* gch = GenCollectedHeap::heap();
4893   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4894 
4895   MarkRefsIntoAndScanClosure
4896     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4897              &_markStack, this,
4898              false /* should_yield */, false /* not precleaning */);
4899   MarkFromDirtyCardsClosure
4900     markFromDirtyCardsClosure(this, _span,
4901                               NULL,  // space is set further below
4902                               &_markBitMap, &_markStack, &mrias_cl);
4903   {
4904     GCTraceTime(Trace, gc) t("Grey Object Rescan", _gc_timer_cm);
4905     // Iterate over the dirty cards, setting the corresponding bits in the
4906     // mod union table.
4907     {
4908       ModUnionClosure modUnionClosure(&_modUnionTable);
4909       _ct->ct_bs()->dirty_card_iterate(
4910                       _cmsGen->used_region(),
4911                       &modUnionClosure);
4912     }
4913     // Having transferred these marks into the modUnionTable, we just need
4914     // to rescan the marked objects on the dirty cards in the modUnionTable.
4915     // The initial marking may have been done during an asynchronous
4916     // collection so there may be dirty bits in the mod-union table.
4917     const int alignment =
4918       CardTableModRefBS::card_size * BitsPerWord;
4919     {
4920       // ... First handle dirty cards in CMS gen
4921       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4922       MemRegion ur = _cmsGen->used_region();
4923       HeapWord* lb = ur.start();
4924       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4925       MemRegion cms_span(lb, ub);
4926       _modUnionTable.dirty_range_iterate_clear(cms_span,
4927                                                &markFromDirtyCardsClosure);
4928       verify_work_stacks_empty();
4929       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4930     }
4931   }
4932   if (VerifyDuringGC &&
4933       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4934     HandleMark hm;  // Discard invalid handles created during verification
4935     Universe::verify();
4936   }
4937   {
4938     GCTraceTime(Trace, gc) t("Root Rescan", _gc_timer_cm);
4939 
4940     verify_work_stacks_empty();
4941 
4942     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4943     StrongRootsScope srs(1);
4944 
4945     gch->gen_process_roots(&srs,
4946                            GenCollectedHeap::OldGen,
4947                            true,  // young gen as roots
4948                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
4949                            should_unload_classes(),
4950                            &mrias_cl,
4951                            NULL,
4952                            NULL); // The dirty klasses will be handled below
4953 
4954     assert(should_unload_classes()
4955            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4956            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4957   }
4958 
4959   {
4960     GCTraceTime(Trace, gc) t("Visit Unhandled CLDs", _gc_timer_cm);
4961 
4962     verify_work_stacks_empty();
4963 
4964     // Scan all class loader data objects that might have been introduced
4965     // during concurrent marking.
4966     ResourceMark rm;
4967     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4968     for (int i = 0; i < array->length(); i++) {
4969       mrias_cl.do_cld_nv(array->at(i));
4970     }
4971 
4972     // We don't need to keep track of new CLDs anymore.
4973     ClassLoaderDataGraph::remember_new_clds(false);
4974 
4975     verify_work_stacks_empty();
4976   }
4977 
4978   {
4979     GCTraceTime(Trace, gc) t("Dirty Klass Scan", _gc_timer_cm);
4980 
4981     verify_work_stacks_empty();
4982 
4983     RemarkKlassClosure remark_klass_closure(&mrias_cl);
4984     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4985 
4986     verify_work_stacks_empty();
4987   }
4988 
4989   // We might have added oops to ClassLoaderData::_handles during the
4990   // concurrent marking phase. These oops point to newly allocated objects
4991   // that are guaranteed to be kept alive. Either by the direct allocation
4992   // code, or when the young collector processes the roots. Hence,
4993   // we don't have to revisit the _handles block during the remark phase.
4994 
4995   verify_work_stacks_empty();
4996   // Restore evacuated mark words, if any, used for overflow list links
4997   restore_preserved_marks_if_any();
4998 
4999   verify_overflow_empty();
5000 }
5001 
5002 ////////////////////////////////////////////////////////
5003 // Parallel Reference Processing Task Proxy Class
5004 ////////////////////////////////////////////////////////
5005 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5006   OopTaskQueueSet*       _queues;
5007   ParallelTaskTerminator _terminator;
5008  public:
5009   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5010     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5011   ParallelTaskTerminator* terminator() { return &_terminator; }
5012   OopTaskQueueSet* queues() { return _queues; }
5013 };
5014 
5015 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5016   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5017   CMSCollector*          _collector;
5018   CMSBitMap*             _mark_bit_map;
5019   const MemRegion        _span;
5020   ProcessTask&           _task;
5021 
5022 public:
5023   CMSRefProcTaskProxy(ProcessTask&     task,
5024                       CMSCollector*    collector,
5025                       const MemRegion& span,
5026                       CMSBitMap*       mark_bit_map,
5027                       AbstractWorkGang* workers,
5028                       OopTaskQueueSet* task_queues):
5029     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5030       task_queues,
5031       workers->active_workers()),
5032     _task(task),
5033     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5034   {
5035     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5036            "Inconsistency in _span");
5037   }
5038 
5039   OopTaskQueueSet* task_queues() { return queues(); }
5040 
5041   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5042 
5043   void do_work_steal(int i,
5044                      CMSParDrainMarkingStackClosure* drain,
5045                      CMSParKeepAliveClosure* keep_alive,
5046                      int* seed);
5047 
5048   virtual void work(uint worker_id);
5049 };
5050 
5051 void CMSRefProcTaskProxy::work(uint worker_id) {
5052   ResourceMark rm;
5053   HandleMark hm;
5054   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5055   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5056                                         _mark_bit_map,
5057                                         work_queue(worker_id));
5058   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5059                                                  _mark_bit_map,
5060                                                  work_queue(worker_id));
5061   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5062   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5063   if (_task.marks_oops_alive()) {
5064     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5065                   _collector->hash_seed(worker_id));
5066   }
5067   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5068   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5069 }
5070 
5071 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5072   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5073   EnqueueTask& _task;
5074 
5075 public:
5076   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5077     : AbstractGangTask("Enqueue reference objects in parallel"),
5078       _task(task)
5079   { }
5080 
5081   virtual void work(uint worker_id)
5082   {
5083     _task.work(worker_id);
5084   }
5085 };
5086 
5087 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5088   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5089    _span(span),
5090    _bit_map(bit_map),
5091    _work_queue(work_queue),
5092    _mark_and_push(collector, span, bit_map, work_queue),
5093    _low_water_mark(MIN2((work_queue->max_elems()/4),
5094                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5095 { }
5096 
5097 // . see if we can share work_queues with ParNew? XXX
5098 void CMSRefProcTaskProxy::do_work_steal(int i,
5099   CMSParDrainMarkingStackClosure* drain,
5100   CMSParKeepAliveClosure* keep_alive,
5101   int* seed) {
5102   OopTaskQueue* work_q = work_queue(i);
5103   NOT_PRODUCT(int num_steals = 0;)
5104   oop obj_to_scan;
5105 
5106   while (true) {
5107     // Completely finish any left over work from (an) earlier round(s)
5108     drain->trim_queue(0);
5109     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5110                                          (size_t)ParGCDesiredObjsFromOverflowList);
5111     // Now check if there's any work in the overflow list
5112     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5113     // only affects the number of attempts made to get work from the
5114     // overflow list and does not affect the number of workers.  Just
5115     // pass ParallelGCThreads so this behavior is unchanged.
5116     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5117                                                 work_q,
5118                                                 ParallelGCThreads)) {
5119       // Found something in global overflow list;
5120       // not yet ready to go stealing work from others.
5121       // We'd like to assert(work_q->size() != 0, ...)
5122       // because we just took work from the overflow list,
5123       // but of course we can't, since all of that might have
5124       // been already stolen from us.
5125       continue;
5126     }
5127     // Verify that we have no work before we resort to stealing
5128     assert(work_q->size() == 0, "Have work, shouldn't steal");
5129     // Try to steal from other queues that have work
5130     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5131       NOT_PRODUCT(num_steals++;)
5132       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5133       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5134       // Do scanning work
5135       obj_to_scan->oop_iterate(keep_alive);
5136       // Loop around, finish this work, and try to steal some more
5137     } else if (terminator()->offer_termination()) {
5138       break;  // nirvana from the infinite cycle
5139     }
5140   }
5141   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5142 }
5143 
5144 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5145 {
5146   GenCollectedHeap* gch = GenCollectedHeap::heap();
5147   WorkGang* workers = gch->workers();
5148   assert(workers != NULL, "Need parallel worker threads.");
5149   CMSRefProcTaskProxy rp_task(task, &_collector,
5150                               _collector.ref_processor()->span(),
5151                               _collector.markBitMap(),
5152                               workers, _collector.task_queues());
5153   workers->run_task(&rp_task);
5154 }
5155 
5156 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5157 {
5158 
5159   GenCollectedHeap* gch = GenCollectedHeap::heap();
5160   WorkGang* workers = gch->workers();
5161   assert(workers != NULL, "Need parallel worker threads.");
5162   CMSRefEnqueueTaskProxy enq_task(task);
5163   workers->run_task(&enq_task);
5164 }
5165 
5166 void CMSCollector::refProcessingWork() {
5167   ResourceMark rm;
5168   HandleMark   hm;
5169 
5170   ReferenceProcessor* rp = ref_processor();
5171   assert(rp->span().equals(_span), "Spans should be equal");
5172   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5173   // Process weak references.
5174   rp->setup_policy(false);
5175   verify_work_stacks_empty();
5176 
5177   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5178                                           &_markStack, false /* !preclean */);
5179   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5180                                 _span, &_markBitMap, &_markStack,
5181                                 &cmsKeepAliveClosure, false /* !preclean */);
5182   {
5183     GCTraceTime(Debug, gc) t("Weak Refs Processing", _gc_timer_cm);
5184 
5185     ReferenceProcessorStats stats;
5186     if (rp->processing_is_mt()) {
5187       // Set the degree of MT here.  If the discovery is done MT, there
5188       // may have been a different number of threads doing the discovery
5189       // and a different number of discovered lists may have Ref objects.
5190       // That is OK as long as the Reference lists are balanced (see
5191       // balance_all_queues() and balance_queues()).
5192       GenCollectedHeap* gch = GenCollectedHeap::heap();
5193       uint active_workers = ParallelGCThreads;
5194       WorkGang* workers = gch->workers();
5195       if (workers != NULL) {
5196         active_workers = workers->active_workers();
5197         // The expectation is that active_workers will have already
5198         // been set to a reasonable value.  If it has not been set,
5199         // investigate.
5200         assert(active_workers > 0, "Should have been set during scavenge");
5201       }
5202       rp->set_active_mt_degree(active_workers);
5203       CMSRefProcTaskExecutor task_executor(*this);
5204       stats = rp->process_discovered_references(&_is_alive_closure,
5205                                         &cmsKeepAliveClosure,
5206                                         &cmsDrainMarkingStackClosure,
5207                                         &task_executor,
5208                                         _gc_timer_cm);
5209     } else {
5210       stats = rp->process_discovered_references(&_is_alive_closure,
5211                                         &cmsKeepAliveClosure,
5212                                         &cmsDrainMarkingStackClosure,
5213                                         NULL,
5214                                         _gc_timer_cm);
5215     }
5216     _gc_tracer_cm->report_gc_reference_stats(stats);
5217 
5218   }
5219 
5220   // This is the point where the entire marking should have completed.
5221   verify_work_stacks_empty();
5222 
5223   if (should_unload_classes()) {
5224     {
5225       GCTraceTime(Debug, gc) t("Class Unloading", _gc_timer_cm);
5226 
5227       // Unload classes and purge the SystemDictionary.
5228       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5229 
5230       // Unload nmethods.
5231       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5232 
5233       // Prune dead klasses from subklass/sibling/implementor lists.
5234       Klass::clean_weak_klass_links(&_is_alive_closure);
5235     }
5236 
5237     {
5238       GCTraceTime(Debug, gc) t("Scrub Symbol Table", _gc_timer_cm);
5239       // Clean up unreferenced symbols in symbol table.
5240       SymbolTable::unlink();
5241     }
5242 
5243     {
5244       GCTraceTime(Debug, gc) t("Scrub String Table", _gc_timer_cm);
5245       // Delete entries for dead interned strings.
5246       StringTable::unlink(&_is_alive_closure);
5247     }
5248   }
5249 
5250 
5251   // Restore any preserved marks as a result of mark stack or
5252   // work queue overflow
5253   restore_preserved_marks_if_any();  // done single-threaded for now
5254 
5255   rp->set_enqueuing_is_done(true);
5256   if (rp->processing_is_mt()) {
5257     rp->balance_all_queues();
5258     CMSRefProcTaskExecutor task_executor(*this);
5259     rp->enqueue_discovered_references(&task_executor);
5260   } else {
5261     rp->enqueue_discovered_references(NULL);
5262   }
5263   rp->verify_no_references_recorded();
5264   assert(!rp->discovery_enabled(), "should have been disabled");
5265 }
5266 
5267 #ifndef PRODUCT
5268 void CMSCollector::check_correct_thread_executing() {
5269   Thread* t = Thread::current();
5270   // Only the VM thread or the CMS thread should be here.
5271   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5272          "Unexpected thread type");
5273   // If this is the vm thread, the foreground process
5274   // should not be waiting.  Note that _foregroundGCIsActive is
5275   // true while the foreground collector is waiting.
5276   if (_foregroundGCShouldWait) {
5277     // We cannot be the VM thread
5278     assert(t->is_ConcurrentGC_thread(),
5279            "Should be CMS thread");
5280   } else {
5281     // We can be the CMS thread only if we are in a stop-world
5282     // phase of CMS collection.
5283     if (t->is_ConcurrentGC_thread()) {
5284       assert(_collectorState == InitialMarking ||
5285              _collectorState == FinalMarking,
5286              "Should be a stop-world phase");
5287       // The CMS thread should be holding the CMS_token.
5288       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5289              "Potential interference with concurrently "
5290              "executing VM thread");
5291     }
5292   }
5293 }
5294 #endif
5295 
5296 void CMSCollector::sweep() {
5297   assert(_collectorState == Sweeping, "just checking");
5298   _gc_timer_cm->register_gc_concurrent_start("Concurrent Sweep");
5299   check_correct_thread_executing();
5300   verify_work_stacks_empty();
5301   verify_overflow_empty();
5302   increment_sweep_count();
5303   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5304 
5305   _inter_sweep_timer.stop();
5306   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5307 
5308   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5309   _intra_sweep_timer.reset();
5310   _intra_sweep_timer.start();
5311   {
5312     GCTraceCPUTime tcpu;
5313     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5314     // First sweep the old gen
5315     {
5316       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5317                                bitMapLock());
5318       sweepWork(_cmsGen);
5319     }
5320 
5321     // Update Universe::_heap_*_at_gc figures.
5322     // We need all the free list locks to make the abstract state
5323     // transition from Sweeping to Resetting. See detailed note
5324     // further below.
5325     {
5326       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5327       // Update heap occupancy information which is used as
5328       // input to soft ref clearing policy at the next gc.
5329       Universe::update_heap_info_at_gc();
5330       _collectorState = Resizing;
5331     }
5332   }
5333   verify_work_stacks_empty();
5334   verify_overflow_empty();
5335 
5336   if (should_unload_classes()) {
5337     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5338     // requires that the virtual spaces are stable and not deleted.
5339     ClassLoaderDataGraph::set_should_purge(true);
5340   }
5341 
5342   _intra_sweep_timer.stop();
5343   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5344 
5345   _inter_sweep_timer.reset();
5346   _inter_sweep_timer.start();
5347 
5348   // We need to use a monotonically non-decreasing time in ms
5349   // or we will see time-warp warnings and os::javaTimeMillis()
5350   // does not guarantee monotonicity.
5351   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5352   update_time_of_last_gc(now);
5353 
5354   // NOTE on abstract state transitions:
5355   // Mutators allocate-live and/or mark the mod-union table dirty
5356   // based on the state of the collection.  The former is done in
5357   // the interval [Marking, Sweeping] and the latter in the interval
5358   // [Marking, Sweeping).  Thus the transitions into the Marking state
5359   // and out of the Sweeping state must be synchronously visible
5360   // globally to the mutators.
5361   // The transition into the Marking state happens with the world
5362   // stopped so the mutators will globally see it.  Sweeping is
5363   // done asynchronously by the background collector so the transition
5364   // from the Sweeping state to the Resizing state must be done
5365   // under the freelistLock (as is the check for whether to
5366   // allocate-live and whether to dirty the mod-union table).
5367   assert(_collectorState == Resizing, "Change of collector state to"
5368     " Resizing must be done under the freelistLocks (plural)");
5369 
5370   // Now that sweeping has been completed, we clear
5371   // the incremental_collection_failed flag,
5372   // thus inviting a younger gen collection to promote into
5373   // this generation. If such a promotion may still fail,
5374   // the flag will be set again when a young collection is
5375   // attempted.
5376   GenCollectedHeap* gch = GenCollectedHeap::heap();
5377   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5378   gch->update_full_collections_completed(_collection_count_start);
5379   _gc_timer_cm->register_gc_concurrent_end();
5380 }
5381 
5382 // FIX ME!!! Looks like this belongs in CFLSpace, with
5383 // CMSGen merely delegating to it.
5384 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5385   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5386   HeapWord*  minAddr        = _cmsSpace->bottom();
5387   HeapWord*  largestAddr    =
5388     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5389   if (largestAddr == NULL) {
5390     // The dictionary appears to be empty.  In this case
5391     // try to coalesce at the end of the heap.
5392     largestAddr = _cmsSpace->end();
5393   }
5394   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5395   size_t nearLargestOffset =
5396     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5397   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5398                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5399   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5400 }
5401 
5402 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5403   return addr >= _cmsSpace->nearLargestChunk();
5404 }
5405 
5406 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5407   return _cmsSpace->find_chunk_at_end();
5408 }
5409 
5410 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5411                                                     bool full) {
5412   // If the young generation has been collected, gather any statistics
5413   // that are of interest at this point.
5414   bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5415   if (!full && current_is_young) {
5416     // Gather statistics on the young generation collection.
5417     collector()->stats().record_gc0_end(used());
5418   }
5419 }
5420 
5421 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5422   // We iterate over the space(s) underlying this generation,
5423   // checking the mark bit map to see if the bits corresponding
5424   // to specific blocks are marked or not. Blocks that are
5425   // marked are live and are not swept up. All remaining blocks
5426   // are swept up, with coalescing on-the-fly as we sweep up
5427   // contiguous free and/or garbage blocks:
5428   // We need to ensure that the sweeper synchronizes with allocators
5429   // and stop-the-world collectors. In particular, the following
5430   // locks are used:
5431   // . CMS token: if this is held, a stop the world collection cannot occur
5432   // . freelistLock: if this is held no allocation can occur from this
5433   //                 generation by another thread
5434   // . bitMapLock: if this is held, no other thread can access or update
5435   //
5436 
5437   // Note that we need to hold the freelistLock if we use
5438   // block iterate below; else the iterator might go awry if
5439   // a mutator (or promotion) causes block contents to change
5440   // (for instance if the allocator divvies up a block).
5441   // If we hold the free list lock, for all practical purposes
5442   // young generation GC's can't occur (they'll usually need to
5443   // promote), so we might as well prevent all young generation
5444   // GC's while we do a sweeping step. For the same reason, we might
5445   // as well take the bit map lock for the entire duration
5446 
5447   // check that we hold the requisite locks
5448   assert(have_cms_token(), "Should hold cms token");
5449   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5450   assert_lock_strong(old_gen->freelistLock());
5451   assert_lock_strong(bitMapLock());
5452 
5453   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5454   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5455   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5456                                           _inter_sweep_estimate.padded_average(),
5457                                           _intra_sweep_estimate.padded_average());
5458   old_gen->setNearLargestChunk();
5459 
5460   {
5461     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5462     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5463     // We need to free-up/coalesce garbage/blocks from a
5464     // co-terminal free run. This is done in the SweepClosure
5465     // destructor; so, do not remove this scope, else the
5466     // end-of-sweep-census below will be off by a little bit.
5467   }
5468   old_gen->cmsSpace()->sweep_completed();
5469   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5470   if (should_unload_classes()) {                // unloaded classes this cycle,
5471     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5472   } else {                                      // did not unload classes,
5473     _concurrent_cycles_since_last_unload++;     // ... increment count
5474   }
5475 }
5476 
5477 // Reset CMS data structures (for now just the marking bit map)
5478 // preparatory for the next cycle.
5479 void CMSCollector::reset_concurrent() {
5480   CMSTokenSyncWithLocks ts(true, bitMapLock());
5481 
5482   // If the state is not "Resetting", the foreground  thread
5483   // has done a collection and the resetting.
5484   if (_collectorState != Resetting) {
5485     assert(_collectorState == Idling, "The state should only change"
5486       " because the foreground collector has finished the collection");
5487     return;
5488   }
5489 
5490   // Clear the mark bitmap (no grey objects to start with)
5491   // for the next cycle.
5492   GCTraceCPUTime tcpu;
5493   CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5494 
5495   HeapWord* curAddr = _markBitMap.startWord();
5496   while (curAddr < _markBitMap.endWord()) {
5497     size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5498     MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5499     _markBitMap.clear_large_range(chunk);
5500     if (ConcurrentMarkSweepThread::should_yield() &&
5501         !foregroundGCIsActive() &&
5502         CMSYield) {
5503       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5504              "CMS thread should hold CMS token");
5505       assert_lock_strong(bitMapLock());
5506       bitMapLock()->unlock();
5507       ConcurrentMarkSweepThread::desynchronize(true);
5508       stopTimer();
5509       incrementYields();
5510 
5511       // See the comment in coordinator_yield()
5512       for (unsigned i = 0; i < CMSYieldSleepCount &&
5513                        ConcurrentMarkSweepThread::should_yield() &&
5514                        !CMSCollector::foregroundGCIsActive(); ++i) {
5515         os::sleep(Thread::current(), 1, false);
5516       }
5517 
5518       ConcurrentMarkSweepThread::synchronize(true);
5519       bitMapLock()->lock_without_safepoint_check();
5520       startTimer();
5521     }
5522     curAddr = chunk.end();
5523   }
5524   // A successful mostly concurrent collection has been done.
5525   // Because only the full (i.e., concurrent mode failure) collections
5526   // are being measured for gc overhead limits, clean the "near" flag
5527   // and count.
5528   size_policy()->reset_gc_overhead_limit_count();
5529   _collectorState = Idling;
5530 
5531   register_gc_end();
5532 }
5533 
5534 // Same as above but for STW paths
5535 void CMSCollector::reset_stw() {
5536   // already have the lock
5537   assert(_collectorState == Resetting, "just checking");
5538   assert_lock_strong(bitMapLock());
5539   GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5540   _markBitMap.clear_all();
5541   _collectorState = Idling;
5542   register_gc_end();
5543 }
5544 
5545 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5546   GCTraceCPUTime tcpu;
5547   TraceCollectorStats tcs(counters());
5548 
5549   switch (op) {
5550     case CMS_op_checkpointRootsInitial: {
5551       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5552       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5553       checkpointRootsInitial();
5554       break;
5555     }
5556     case CMS_op_checkpointRootsFinal: {
5557       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5558       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5559       checkpointRootsFinal();
5560       break;
5561     }
5562     default:
5563       fatal("No such CMS_op");
5564   }
5565 }
5566 
5567 #ifndef PRODUCT
5568 size_t const CMSCollector::skip_header_HeapWords() {
5569   return FreeChunk::header_size();
5570 }
5571 
5572 // Try and collect here conditions that should hold when
5573 // CMS thread is exiting. The idea is that the foreground GC
5574 // thread should not be blocked if it wants to terminate
5575 // the CMS thread and yet continue to run the VM for a while
5576 // after that.
5577 void CMSCollector::verify_ok_to_terminate() const {
5578   assert(Thread::current()->is_ConcurrentGC_thread(),
5579          "should be called by CMS thread");
5580   assert(!_foregroundGCShouldWait, "should be false");
5581   // We could check here that all the various low-level locks
5582   // are not held by the CMS thread, but that is overkill; see
5583   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5584   // is checked.
5585 }
5586 #endif
5587 
5588 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5589    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5590           "missing Printezis mark?");
5591   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5592   size_t size = pointer_delta(nextOneAddr + 1, addr);
5593   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5594          "alignment problem");
5595   assert(size >= 3, "Necessary for Printezis marks to work");
5596   return size;
5597 }
5598 
5599 // A variant of the above (block_size_using_printezis_bits()) except
5600 // that we return 0 if the P-bits are not yet set.
5601 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5602   if (_markBitMap.isMarked(addr + 1)) {
5603     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5604     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5605     size_t size = pointer_delta(nextOneAddr + 1, addr);
5606     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5607            "alignment problem");
5608     assert(size >= 3, "Necessary for Printezis marks to work");
5609     return size;
5610   }
5611   return 0;
5612 }
5613 
5614 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5615   size_t sz = 0;
5616   oop p = (oop)addr;
5617   if (p->klass_or_null() != NULL) {
5618     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5619   } else {
5620     sz = block_size_using_printezis_bits(addr);
5621   }
5622   assert(sz > 0, "size must be nonzero");
5623   HeapWord* next_block = addr + sz;
5624   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5625                                              CardTableModRefBS::card_size);
5626   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5627          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5628          "must be different cards");
5629   return next_card;
5630 }
5631 
5632 
5633 // CMS Bit Map Wrapper /////////////////////////////////////////
5634 
5635 // Construct a CMS bit map infrastructure, but don't create the
5636 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5637 // further below.
5638 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5639   _bm(),
5640   _shifter(shifter),
5641   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5642                                     Monitor::_safepoint_check_sometimes) : NULL)
5643 {
5644   _bmStartWord = 0;
5645   _bmWordSize  = 0;
5646 }
5647 
5648 bool CMSBitMap::allocate(MemRegion mr) {
5649   _bmStartWord = mr.start();
5650   _bmWordSize  = mr.word_size();
5651   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5652                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5653   if (!brs.is_reserved()) {
5654     warning("CMS bit map allocation failure");
5655     return false;
5656   }
5657   // For now we'll just commit all of the bit map up front.
5658   // Later on we'll try to be more parsimonious with swap.
5659   if (!_virtual_space.initialize(brs, brs.size())) {
5660     warning("CMS bit map backing store failure");
5661     return false;
5662   }
5663   assert(_virtual_space.committed_size() == brs.size(),
5664          "didn't reserve backing store for all of CMS bit map?");
5665   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5666   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5667          _bmWordSize, "inconsistency in bit map sizing");
5668   _bm.set_size(_bmWordSize >> _shifter);
5669 
5670   // bm.clear(); // can we rely on getting zero'd memory? verify below
5671   assert(isAllClear(),
5672          "Expected zero'd memory from ReservedSpace constructor");
5673   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5674          "consistency check");
5675   return true;
5676 }
5677 
5678 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5679   HeapWord *next_addr, *end_addr, *last_addr;
5680   assert_locked();
5681   assert(covers(mr), "out-of-range error");
5682   // XXX assert that start and end are appropriately aligned
5683   for (next_addr = mr.start(), end_addr = mr.end();
5684        next_addr < end_addr; next_addr = last_addr) {
5685     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5686     last_addr = dirty_region.end();
5687     if (!dirty_region.is_empty()) {
5688       cl->do_MemRegion(dirty_region);
5689     } else {
5690       assert(last_addr == end_addr, "program logic");
5691       return;
5692     }
5693   }
5694 }
5695 
5696 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5697   _bm.print_on_error(st, prefix);
5698 }
5699 
5700 #ifndef PRODUCT
5701 void CMSBitMap::assert_locked() const {
5702   CMSLockVerifier::assert_locked(lock());
5703 }
5704 
5705 bool CMSBitMap::covers(MemRegion mr) const {
5706   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5707   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5708          "size inconsistency");
5709   return (mr.start() >= _bmStartWord) &&
5710          (mr.end()   <= endWord());
5711 }
5712 
5713 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5714     return (start >= _bmStartWord && (start + size) <= endWord());
5715 }
5716 
5717 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5718   // verify that there are no 1 bits in the interval [left, right)
5719   FalseBitMapClosure falseBitMapClosure;
5720   iterate(&falseBitMapClosure, left, right);
5721 }
5722 
5723 void CMSBitMap::region_invariant(MemRegion mr)
5724 {
5725   assert_locked();
5726   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5727   assert(!mr.is_empty(), "unexpected empty region");
5728   assert(covers(mr), "mr should be covered by bit map");
5729   // convert address range into offset range
5730   size_t start_ofs = heapWordToOffset(mr.start());
5731   // Make sure that end() is appropriately aligned
5732   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5733                         (1 << (_shifter+LogHeapWordSize))),
5734          "Misaligned mr.end()");
5735   size_t end_ofs   = heapWordToOffset(mr.end());
5736   assert(end_ofs > start_ofs, "Should mark at least one bit");
5737 }
5738 
5739 #endif
5740 
5741 bool CMSMarkStack::allocate(size_t size) {
5742   // allocate a stack of the requisite depth
5743   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5744                    size * sizeof(oop)));
5745   if (!rs.is_reserved()) {
5746     warning("CMSMarkStack allocation failure");
5747     return false;
5748   }
5749   if (!_virtual_space.initialize(rs, rs.size())) {
5750     warning("CMSMarkStack backing store failure");
5751     return false;
5752   }
5753   assert(_virtual_space.committed_size() == rs.size(),
5754          "didn't reserve backing store for all of CMS stack?");
5755   _base = (oop*)(_virtual_space.low());
5756   _index = 0;
5757   _capacity = size;
5758   NOT_PRODUCT(_max_depth = 0);
5759   return true;
5760 }
5761 
5762 // XXX FIX ME !!! In the MT case we come in here holding a
5763 // leaf lock. For printing we need to take a further lock
5764 // which has lower rank. We need to recalibrate the two
5765 // lock-ranks involved in order to be able to print the
5766 // messages below. (Or defer the printing to the caller.
5767 // For now we take the expedient path of just disabling the
5768 // messages for the problematic case.)
5769 void CMSMarkStack::expand() {
5770   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5771   if (_capacity == MarkStackSizeMax) {
5772     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5773       // We print a warning message only once per CMS cycle.
5774       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5775     }
5776     return;
5777   }
5778   // Double capacity if possible
5779   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5780   // Do not give up existing stack until we have managed to
5781   // get the double capacity that we desired.
5782   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5783                    new_capacity * sizeof(oop)));
5784   if (rs.is_reserved()) {
5785     // Release the backing store associated with old stack
5786     _virtual_space.release();
5787     // Reinitialize virtual space for new stack
5788     if (!_virtual_space.initialize(rs, rs.size())) {
5789       fatal("Not enough swap for expanded marking stack");
5790     }
5791     _base = (oop*)(_virtual_space.low());
5792     _index = 0;
5793     _capacity = new_capacity;
5794   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5795     // Failed to double capacity, continue;
5796     // we print a detail message only once per CMS cycle.
5797     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5798                         _capacity / K, new_capacity / K);
5799   }
5800 }
5801 
5802 
5803 // Closures
5804 // XXX: there seems to be a lot of code  duplication here;
5805 // should refactor and consolidate common code.
5806 
5807 // This closure is used to mark refs into the CMS generation in
5808 // the CMS bit map. Called at the first checkpoint. This closure
5809 // assumes that we do not need to re-mark dirty cards; if the CMS
5810 // generation on which this is used is not an oldest
5811 // generation then this will lose younger_gen cards!
5812 
5813 MarkRefsIntoClosure::MarkRefsIntoClosure(
5814   MemRegion span, CMSBitMap* bitMap):
5815     _span(span),
5816     _bitMap(bitMap)
5817 {
5818   assert(ref_processor() == NULL, "deliberately left NULL");
5819   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5820 }
5821 
5822 void MarkRefsIntoClosure::do_oop(oop obj) {
5823   // if p points into _span, then mark corresponding bit in _markBitMap
5824   assert(obj->is_oop(), "expected an oop");
5825   HeapWord* addr = (HeapWord*)obj;
5826   if (_span.contains(addr)) {
5827     // this should be made more efficient
5828     _bitMap->mark(addr);
5829   }
5830 }
5831 
5832 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5833 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5834 
5835 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
5836   MemRegion span, CMSBitMap* bitMap):
5837     _span(span),
5838     _bitMap(bitMap)
5839 {
5840   assert(ref_processor() == NULL, "deliberately left NULL");
5841   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5842 }
5843 
5844 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
5845   // if p points into _span, then mark corresponding bit in _markBitMap
5846   assert(obj->is_oop(), "expected an oop");
5847   HeapWord* addr = (HeapWord*)obj;
5848   if (_span.contains(addr)) {
5849     // this should be made more efficient
5850     _bitMap->par_mark(addr);
5851   }
5852 }
5853 
5854 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
5855 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
5856 
5857 // A variant of the above, used for CMS marking verification.
5858 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5859   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5860     _span(span),
5861     _verification_bm(verification_bm),
5862     _cms_bm(cms_bm)
5863 {
5864   assert(ref_processor() == NULL, "deliberately left NULL");
5865   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5866 }
5867 
5868 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5869   // if p points into _span, then mark corresponding bit in _markBitMap
5870   assert(obj->is_oop(), "expected an oop");
5871   HeapWord* addr = (HeapWord*)obj;
5872   if (_span.contains(addr)) {
5873     _verification_bm->mark(addr);
5874     if (!_cms_bm->isMarked(addr)) {
5875       LogHandle(gc, verify) log;
5876       ResourceMark rm;
5877       oop(addr)->print_on(log.info_stream());
5878       log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5879       fatal("... aborting");
5880     }
5881   }
5882 }
5883 
5884 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5885 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5886 
5887 //////////////////////////////////////////////////
5888 // MarkRefsIntoAndScanClosure
5889 //////////////////////////////////////////////////
5890 
5891 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5892                                                        ReferenceProcessor* rp,
5893                                                        CMSBitMap* bit_map,
5894                                                        CMSBitMap* mod_union_table,
5895                                                        CMSMarkStack*  mark_stack,
5896                                                        CMSCollector* collector,
5897                                                        bool should_yield,
5898                                                        bool concurrent_precleaning):
5899   _collector(collector),
5900   _span(span),
5901   _bit_map(bit_map),
5902   _mark_stack(mark_stack),
5903   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5904                       mark_stack, concurrent_precleaning),
5905   _yield(should_yield),
5906   _concurrent_precleaning(concurrent_precleaning),
5907   _freelistLock(NULL)
5908 {
5909   // FIXME: Should initialize in base class constructor.
5910   assert(rp != NULL, "ref_processor shouldn't be NULL");
5911   set_ref_processor_internal(rp);
5912 }
5913 
5914 // This closure is used to mark refs into the CMS generation at the
5915 // second (final) checkpoint, and to scan and transitively follow
5916 // the unmarked oops. It is also used during the concurrent precleaning
5917 // phase while scanning objects on dirty cards in the CMS generation.
5918 // The marks are made in the marking bit map and the marking stack is
5919 // used for keeping the (newly) grey objects during the scan.
5920 // The parallel version (Par_...) appears further below.
5921 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5922   if (obj != NULL) {
5923     assert(obj->is_oop(), "expected an oop");
5924     HeapWord* addr = (HeapWord*)obj;
5925     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5926     assert(_collector->overflow_list_is_empty(),
5927            "overflow list should be empty");
5928     if (_span.contains(addr) &&
5929         !_bit_map->isMarked(addr)) {
5930       // mark bit map (object is now grey)
5931       _bit_map->mark(addr);
5932       // push on marking stack (stack should be empty), and drain the
5933       // stack by applying this closure to the oops in the oops popped
5934       // from the stack (i.e. blacken the grey objects)
5935       bool res = _mark_stack->push(obj);
5936       assert(res, "Should have space to push on empty stack");
5937       do {
5938         oop new_oop = _mark_stack->pop();
5939         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5940         assert(_bit_map->isMarked((HeapWord*)new_oop),
5941                "only grey objects on this stack");
5942         // iterate over the oops in this oop, marking and pushing
5943         // the ones in CMS heap (i.e. in _span).
5944         new_oop->oop_iterate(&_pushAndMarkClosure);
5945         // check if it's time to yield
5946         do_yield_check();
5947       } while (!_mark_stack->isEmpty() ||
5948                (!_concurrent_precleaning && take_from_overflow_list()));
5949         // if marking stack is empty, and we are not doing this
5950         // during precleaning, then check the overflow list
5951     }
5952     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5953     assert(_collector->overflow_list_is_empty(),
5954            "overflow list was drained above");
5955 
5956     assert(_collector->no_preserved_marks(),
5957            "All preserved marks should have been restored above");
5958   }
5959 }
5960 
5961 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5962 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5963 
5964 void MarkRefsIntoAndScanClosure::do_yield_work() {
5965   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5966          "CMS thread should hold CMS token");
5967   assert_lock_strong(_freelistLock);
5968   assert_lock_strong(_bit_map->lock());
5969   // relinquish the free_list_lock and bitMaplock()
5970   _bit_map->lock()->unlock();
5971   _freelistLock->unlock();
5972   ConcurrentMarkSweepThread::desynchronize(true);
5973   _collector->stopTimer();
5974   _collector->incrementYields();
5975 
5976   // See the comment in coordinator_yield()
5977   for (unsigned i = 0;
5978        i < CMSYieldSleepCount &&
5979        ConcurrentMarkSweepThread::should_yield() &&
5980        !CMSCollector::foregroundGCIsActive();
5981        ++i) {
5982     os::sleep(Thread::current(), 1, false);
5983   }
5984 
5985   ConcurrentMarkSweepThread::synchronize(true);
5986   _freelistLock->lock_without_safepoint_check();
5987   _bit_map->lock()->lock_without_safepoint_check();
5988   _collector->startTimer();
5989 }
5990 
5991 ///////////////////////////////////////////////////////////
5992 // Par_MarkRefsIntoAndScanClosure: a parallel version of
5993 //                                 MarkRefsIntoAndScanClosure
5994 ///////////////////////////////////////////////////////////
5995 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
5996   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
5997   CMSBitMap* bit_map, OopTaskQueue* work_queue):
5998   _span(span),
5999   _bit_map(bit_map),
6000   _work_queue(work_queue),
6001   _low_water_mark(MIN2((work_queue->max_elems()/4),
6002                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6003   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6004 {
6005   // FIXME: Should initialize in base class constructor.
6006   assert(rp != NULL, "ref_processor shouldn't be NULL");
6007   set_ref_processor_internal(rp);
6008 }
6009 
6010 // This closure is used to mark refs into the CMS generation at the
6011 // second (final) checkpoint, and to scan and transitively follow
6012 // the unmarked oops. The marks are made in the marking bit map and
6013 // the work_queue is used for keeping the (newly) grey objects during
6014 // the scan phase whence they are also available for stealing by parallel
6015 // threads. Since the marking bit map is shared, updates are
6016 // synchronized (via CAS).
6017 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6018   if (obj != NULL) {
6019     // Ignore mark word because this could be an already marked oop
6020     // that may be chained at the end of the overflow list.
6021     assert(obj->is_oop(true), "expected an oop");
6022     HeapWord* addr = (HeapWord*)obj;
6023     if (_span.contains(addr) &&
6024         !_bit_map->isMarked(addr)) {
6025       // mark bit map (object will become grey):
6026       // It is possible for several threads to be
6027       // trying to "claim" this object concurrently;
6028       // the unique thread that succeeds in marking the
6029       // object first will do the subsequent push on
6030       // to the work queue (or overflow list).
6031       if (_bit_map->par_mark(addr)) {
6032         // push on work_queue (which may not be empty), and trim the
6033         // queue to an appropriate length by applying this closure to
6034         // the oops in the oops popped from the stack (i.e. blacken the
6035         // grey objects)
6036         bool res = _work_queue->push(obj);
6037         assert(res, "Low water mark should be less than capacity?");
6038         trim_queue(_low_water_mark);
6039       } // Else, another thread claimed the object
6040     }
6041   }
6042 }
6043 
6044 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6045 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6046 
6047 // This closure is used to rescan the marked objects on the dirty cards
6048 // in the mod union table and the card table proper.
6049 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6050   oop p, MemRegion mr) {
6051 
6052   size_t size = 0;
6053   HeapWord* addr = (HeapWord*)p;
6054   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6055   assert(_span.contains(addr), "we are scanning the CMS generation");
6056   // check if it's time to yield
6057   if (do_yield_check()) {
6058     // We yielded for some foreground stop-world work,
6059     // and we have been asked to abort this ongoing preclean cycle.
6060     return 0;
6061   }
6062   if (_bitMap->isMarked(addr)) {
6063     // it's marked; is it potentially uninitialized?
6064     if (p->klass_or_null() != NULL) {
6065         // an initialized object; ignore mark word in verification below
6066         // since we are running concurrent with mutators
6067         assert(p->is_oop(true), "should be an oop");
6068         if (p->is_objArray()) {
6069           // objArrays are precisely marked; restrict scanning
6070           // to dirty cards only.
6071           size = CompactibleFreeListSpace::adjustObjectSize(
6072                    p->oop_iterate_size(_scanningClosure, mr));
6073         } else {
6074           // A non-array may have been imprecisely marked; we need
6075           // to scan object in its entirety.
6076           size = CompactibleFreeListSpace::adjustObjectSize(
6077                    p->oop_iterate_size(_scanningClosure));
6078         }
6079         #ifdef ASSERT
6080           size_t direct_size =
6081             CompactibleFreeListSpace::adjustObjectSize(p->size());
6082           assert(size == direct_size, "Inconsistency in size");
6083           assert(size >= 3, "Necessary for Printezis marks to work");
6084           if (!_bitMap->isMarked(addr+1)) {
6085             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6086           } else {
6087             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6088             assert(_bitMap->isMarked(addr+size-1),
6089                    "inconsistent Printezis mark");
6090           }
6091         #endif // ASSERT
6092     } else {
6093       // An uninitialized object.
6094       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6095       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6096       size = pointer_delta(nextOneAddr + 1, addr);
6097       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6098              "alignment problem");
6099       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6100       // will dirty the card when the klass pointer is installed in the
6101       // object (signaling the completion of initialization).
6102     }
6103   } else {
6104     // Either a not yet marked object or an uninitialized object
6105     if (p->klass_or_null() == NULL) {
6106       // An uninitialized object, skip to the next card, since
6107       // we may not be able to read its P-bits yet.
6108       assert(size == 0, "Initial value");
6109     } else {
6110       // An object not (yet) reached by marking: we merely need to
6111       // compute its size so as to go look at the next block.
6112       assert(p->is_oop(true), "should be an oop");
6113       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6114     }
6115   }
6116   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6117   return size;
6118 }
6119 
6120 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6121   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6122          "CMS thread should hold CMS token");
6123   assert_lock_strong(_freelistLock);
6124   assert_lock_strong(_bitMap->lock());
6125   // relinquish the free_list_lock and bitMaplock()
6126   _bitMap->lock()->unlock();
6127   _freelistLock->unlock();
6128   ConcurrentMarkSweepThread::desynchronize(true);
6129   _collector->stopTimer();
6130   _collector->incrementYields();
6131 
6132   // See the comment in coordinator_yield()
6133   for (unsigned i = 0; i < CMSYieldSleepCount &&
6134                    ConcurrentMarkSweepThread::should_yield() &&
6135                    !CMSCollector::foregroundGCIsActive(); ++i) {
6136     os::sleep(Thread::current(), 1, false);
6137   }
6138 
6139   ConcurrentMarkSweepThread::synchronize(true);
6140   _freelistLock->lock_without_safepoint_check();
6141   _bitMap->lock()->lock_without_safepoint_check();
6142   _collector->startTimer();
6143 }
6144 
6145 
6146 //////////////////////////////////////////////////////////////////
6147 // SurvivorSpacePrecleanClosure
6148 //////////////////////////////////////////////////////////////////
6149 // This (single-threaded) closure is used to preclean the oops in
6150 // the survivor spaces.
6151 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6152 
6153   HeapWord* addr = (HeapWord*)p;
6154   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6155   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6156   assert(p->klass_or_null() != NULL, "object should be initialized");
6157   // an initialized object; ignore mark word in verification below
6158   // since we are running concurrent with mutators
6159   assert(p->is_oop(true), "should be an oop");
6160   // Note that we do not yield while we iterate over
6161   // the interior oops of p, pushing the relevant ones
6162   // on our marking stack.
6163   size_t size = p->oop_iterate_size(_scanning_closure);
6164   do_yield_check();
6165   // Observe that below, we do not abandon the preclean
6166   // phase as soon as we should; rather we empty the
6167   // marking stack before returning. This is to satisfy
6168   // some existing assertions. In general, it may be a
6169   // good idea to abort immediately and complete the marking
6170   // from the grey objects at a later time.
6171   while (!_mark_stack->isEmpty()) {
6172     oop new_oop = _mark_stack->pop();
6173     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6174     assert(_bit_map->isMarked((HeapWord*)new_oop),
6175            "only grey objects on this stack");
6176     // iterate over the oops in this oop, marking and pushing
6177     // the ones in CMS heap (i.e. in _span).
6178     new_oop->oop_iterate(_scanning_closure);
6179     // check if it's time to yield
6180     do_yield_check();
6181   }
6182   unsigned int after_count =
6183     GenCollectedHeap::heap()->total_collections();
6184   bool abort = (_before_count != after_count) ||
6185                _collector->should_abort_preclean();
6186   return abort ? 0 : size;
6187 }
6188 
6189 void SurvivorSpacePrecleanClosure::do_yield_work() {
6190   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6191          "CMS thread should hold CMS token");
6192   assert_lock_strong(_bit_map->lock());
6193   // Relinquish the bit map lock
6194   _bit_map->lock()->unlock();
6195   ConcurrentMarkSweepThread::desynchronize(true);
6196   _collector->stopTimer();
6197   _collector->incrementYields();
6198 
6199   // See the comment in coordinator_yield()
6200   for (unsigned i = 0; i < CMSYieldSleepCount &&
6201                        ConcurrentMarkSweepThread::should_yield() &&
6202                        !CMSCollector::foregroundGCIsActive(); ++i) {
6203     os::sleep(Thread::current(), 1, false);
6204   }
6205 
6206   ConcurrentMarkSweepThread::synchronize(true);
6207   _bit_map->lock()->lock_without_safepoint_check();
6208   _collector->startTimer();
6209 }
6210 
6211 // This closure is used to rescan the marked objects on the dirty cards
6212 // in the mod union table and the card table proper. In the parallel
6213 // case, although the bitMap is shared, we do a single read so the
6214 // isMarked() query is "safe".
6215 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6216   // Ignore mark word because we are running concurrent with mutators
6217   assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6218   HeapWord* addr = (HeapWord*)p;
6219   assert(_span.contains(addr), "we are scanning the CMS generation");
6220   bool is_obj_array = false;
6221   #ifdef ASSERT
6222     if (!_parallel) {
6223       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6224       assert(_collector->overflow_list_is_empty(),
6225              "overflow list should be empty");
6226 
6227     }
6228   #endif // ASSERT
6229   if (_bit_map->isMarked(addr)) {
6230     // Obj arrays are precisely marked, non-arrays are not;
6231     // so we scan objArrays precisely and non-arrays in their
6232     // entirety.
6233     if (p->is_objArray()) {
6234       is_obj_array = true;
6235       if (_parallel) {
6236         p->oop_iterate(_par_scan_closure, mr);
6237       } else {
6238         p->oop_iterate(_scan_closure, mr);
6239       }
6240     } else {
6241       if (_parallel) {
6242         p->oop_iterate(_par_scan_closure);
6243       } else {
6244         p->oop_iterate(_scan_closure);
6245       }
6246     }
6247   }
6248   #ifdef ASSERT
6249     if (!_parallel) {
6250       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6251       assert(_collector->overflow_list_is_empty(),
6252              "overflow list should be empty");
6253 
6254     }
6255   #endif // ASSERT
6256   return is_obj_array;
6257 }
6258 
6259 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6260                         MemRegion span,
6261                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6262                         bool should_yield, bool verifying):
6263   _collector(collector),
6264   _span(span),
6265   _bitMap(bitMap),
6266   _mut(&collector->_modUnionTable),
6267   _markStack(markStack),
6268   _yield(should_yield),
6269   _skipBits(0)
6270 {
6271   assert(_markStack->isEmpty(), "stack should be empty");
6272   _finger = _bitMap->startWord();
6273   _threshold = _finger;
6274   assert(_collector->_restart_addr == NULL, "Sanity check");
6275   assert(_span.contains(_finger), "Out of bounds _finger?");
6276   DEBUG_ONLY(_verifying = verifying;)
6277 }
6278 
6279 void MarkFromRootsClosure::reset(HeapWord* addr) {
6280   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6281   assert(_span.contains(addr), "Out of bounds _finger?");
6282   _finger = addr;
6283   _threshold = (HeapWord*)round_to(
6284                  (intptr_t)_finger, CardTableModRefBS::card_size);
6285 }
6286 
6287 // Should revisit to see if this should be restructured for
6288 // greater efficiency.
6289 bool MarkFromRootsClosure::do_bit(size_t offset) {
6290   if (_skipBits > 0) {
6291     _skipBits--;
6292     return true;
6293   }
6294   // convert offset into a HeapWord*
6295   HeapWord* addr = _bitMap->startWord() + offset;
6296   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6297          "address out of range");
6298   assert(_bitMap->isMarked(addr), "tautology");
6299   if (_bitMap->isMarked(addr+1)) {
6300     // this is an allocated but not yet initialized object
6301     assert(_skipBits == 0, "tautology");
6302     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6303     oop p = oop(addr);
6304     if (p->klass_or_null() == NULL) {
6305       DEBUG_ONLY(if (!_verifying) {)
6306         // We re-dirty the cards on which this object lies and increase
6307         // the _threshold so that we'll come back to scan this object
6308         // during the preclean or remark phase. (CMSCleanOnEnter)
6309         if (CMSCleanOnEnter) {
6310           size_t sz = _collector->block_size_using_printezis_bits(addr);
6311           HeapWord* end_card_addr   = (HeapWord*)round_to(
6312                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6313           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6314           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6315           // Bump _threshold to end_card_addr; note that
6316           // _threshold cannot possibly exceed end_card_addr, anyhow.
6317           // This prevents future clearing of the card as the scan proceeds
6318           // to the right.
6319           assert(_threshold <= end_card_addr,
6320                  "Because we are just scanning into this object");
6321           if (_threshold < end_card_addr) {
6322             _threshold = end_card_addr;
6323           }
6324           if (p->klass_or_null() != NULL) {
6325             // Redirty the range of cards...
6326             _mut->mark_range(redirty_range);
6327           } // ...else the setting of klass will dirty the card anyway.
6328         }
6329       DEBUG_ONLY(})
6330       return true;
6331     }
6332   }
6333   scanOopsInOop(addr);
6334   return true;
6335 }
6336 
6337 // We take a break if we've been at this for a while,
6338 // so as to avoid monopolizing the locks involved.
6339 void MarkFromRootsClosure::do_yield_work() {
6340   // First give up the locks, then yield, then re-lock
6341   // We should probably use a constructor/destructor idiom to
6342   // do this unlock/lock or modify the MutexUnlocker class to
6343   // serve our purpose. XXX
6344   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6345          "CMS thread should hold CMS token");
6346   assert_lock_strong(_bitMap->lock());
6347   _bitMap->lock()->unlock();
6348   ConcurrentMarkSweepThread::desynchronize(true);
6349   _collector->stopTimer();
6350   _collector->incrementYields();
6351 
6352   // See the comment in coordinator_yield()
6353   for (unsigned i = 0; i < CMSYieldSleepCount &&
6354                        ConcurrentMarkSweepThread::should_yield() &&
6355                        !CMSCollector::foregroundGCIsActive(); ++i) {
6356     os::sleep(Thread::current(), 1, false);
6357   }
6358 
6359   ConcurrentMarkSweepThread::synchronize(true);
6360   _bitMap->lock()->lock_without_safepoint_check();
6361   _collector->startTimer();
6362 }
6363 
6364 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6365   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6366   assert(_markStack->isEmpty(),
6367          "should drain stack to limit stack usage");
6368   // convert ptr to an oop preparatory to scanning
6369   oop obj = oop(ptr);
6370   // Ignore mark word in verification below, since we
6371   // may be running concurrent with mutators.
6372   assert(obj->is_oop(true), "should be an oop");
6373   assert(_finger <= ptr, "_finger runneth ahead");
6374   // advance the finger to right end of this object
6375   _finger = ptr + obj->size();
6376   assert(_finger > ptr, "we just incremented it above");
6377   // On large heaps, it may take us some time to get through
6378   // the marking phase. During
6379   // this time it's possible that a lot of mutations have
6380   // accumulated in the card table and the mod union table --
6381   // these mutation records are redundant until we have
6382   // actually traced into the corresponding card.
6383   // Here, we check whether advancing the finger would make
6384   // us cross into a new card, and if so clear corresponding
6385   // cards in the MUT (preclean them in the card-table in the
6386   // future).
6387 
6388   DEBUG_ONLY(if (!_verifying) {)
6389     // The clean-on-enter optimization is disabled by default,
6390     // until we fix 6178663.
6391     if (CMSCleanOnEnter && (_finger > _threshold)) {
6392       // [_threshold, _finger) represents the interval
6393       // of cards to be cleared  in MUT (or precleaned in card table).
6394       // The set of cards to be cleared is all those that overlap
6395       // with the interval [_threshold, _finger); note that
6396       // _threshold is always kept card-aligned but _finger isn't
6397       // always card-aligned.
6398       HeapWord* old_threshold = _threshold;
6399       assert(old_threshold == (HeapWord*)round_to(
6400               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6401              "_threshold should always be card-aligned");
6402       _threshold = (HeapWord*)round_to(
6403                      (intptr_t)_finger, CardTableModRefBS::card_size);
6404       MemRegion mr(old_threshold, _threshold);
6405       assert(!mr.is_empty(), "Control point invariant");
6406       assert(_span.contains(mr), "Should clear within span");
6407       _mut->clear_range(mr);
6408     }
6409   DEBUG_ONLY(})
6410   // Note: the finger doesn't advance while we drain
6411   // the stack below.
6412   PushOrMarkClosure pushOrMarkClosure(_collector,
6413                                       _span, _bitMap, _markStack,
6414                                       _finger, this);
6415   bool res = _markStack->push(obj);
6416   assert(res, "Empty non-zero size stack should have space for single push");
6417   while (!_markStack->isEmpty()) {
6418     oop new_oop = _markStack->pop();
6419     // Skip verifying header mark word below because we are
6420     // running concurrent with mutators.
6421     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6422     // now scan this oop's oops
6423     new_oop->oop_iterate(&pushOrMarkClosure);
6424     do_yield_check();
6425   }
6426   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6427 }
6428 
6429 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6430                        CMSCollector* collector, MemRegion span,
6431                        CMSBitMap* bit_map,
6432                        OopTaskQueue* work_queue,
6433                        CMSMarkStack*  overflow_stack):
6434   _collector(collector),
6435   _whole_span(collector->_span),
6436   _span(span),
6437   _bit_map(bit_map),
6438   _mut(&collector->_modUnionTable),
6439   _work_queue(work_queue),
6440   _overflow_stack(overflow_stack),
6441   _skip_bits(0),
6442   _task(task)
6443 {
6444   assert(_work_queue->size() == 0, "work_queue should be empty");
6445   _finger = span.start();
6446   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6447   assert(_span.contains(_finger), "Out of bounds _finger?");
6448 }
6449 
6450 // Should revisit to see if this should be restructured for
6451 // greater efficiency.
6452 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6453   if (_skip_bits > 0) {
6454     _skip_bits--;
6455     return true;
6456   }
6457   // convert offset into a HeapWord*
6458   HeapWord* addr = _bit_map->startWord() + offset;
6459   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6460          "address out of range");
6461   assert(_bit_map->isMarked(addr), "tautology");
6462   if (_bit_map->isMarked(addr+1)) {
6463     // this is an allocated object that might not yet be initialized
6464     assert(_skip_bits == 0, "tautology");
6465     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6466     oop p = oop(addr);
6467     if (p->klass_or_null() == NULL) {
6468       // in the case of Clean-on-Enter optimization, redirty card
6469       // and avoid clearing card by increasing  the threshold.
6470       return true;
6471     }
6472   }
6473   scan_oops_in_oop(addr);
6474   return true;
6475 }
6476 
6477 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6478   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6479   // Should we assert that our work queue is empty or
6480   // below some drain limit?
6481   assert(_work_queue->size() == 0,
6482          "should drain stack to limit stack usage");
6483   // convert ptr to an oop preparatory to scanning
6484   oop obj = oop(ptr);
6485   // Ignore mark word in verification below, since we
6486   // may be running concurrent with mutators.
6487   assert(obj->is_oop(true), "should be an oop");
6488   assert(_finger <= ptr, "_finger runneth ahead");
6489   // advance the finger to right end of this object
6490   _finger = ptr + obj->size();
6491   assert(_finger > ptr, "we just incremented it above");
6492   // On large heaps, it may take us some time to get through
6493   // the marking phase. During
6494   // this time it's possible that a lot of mutations have
6495   // accumulated in the card table and the mod union table --
6496   // these mutation records are redundant until we have
6497   // actually traced into the corresponding card.
6498   // Here, we check whether advancing the finger would make
6499   // us cross into a new card, and if so clear corresponding
6500   // cards in the MUT (preclean them in the card-table in the
6501   // future).
6502 
6503   // The clean-on-enter optimization is disabled by default,
6504   // until we fix 6178663.
6505   if (CMSCleanOnEnter && (_finger > _threshold)) {
6506     // [_threshold, _finger) represents the interval
6507     // of cards to be cleared  in MUT (or precleaned in card table).
6508     // The set of cards to be cleared is all those that overlap
6509     // with the interval [_threshold, _finger); note that
6510     // _threshold is always kept card-aligned but _finger isn't
6511     // always card-aligned.
6512     HeapWord* old_threshold = _threshold;
6513     assert(old_threshold == (HeapWord*)round_to(
6514             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6515            "_threshold should always be card-aligned");
6516     _threshold = (HeapWord*)round_to(
6517                    (intptr_t)_finger, CardTableModRefBS::card_size);
6518     MemRegion mr(old_threshold, _threshold);
6519     assert(!mr.is_empty(), "Control point invariant");
6520     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6521     _mut->clear_range(mr);
6522   }
6523 
6524   // Note: the local finger doesn't advance while we drain
6525   // the stack below, but the global finger sure can and will.
6526   HeapWord** gfa = _task->global_finger_addr();
6527   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6528                                       _span, _bit_map,
6529                                       _work_queue,
6530                                       _overflow_stack,
6531                                       _finger,
6532                                       gfa, this);
6533   bool res = _work_queue->push(obj);   // overflow could occur here
6534   assert(res, "Will hold once we use workqueues");
6535   while (true) {
6536     oop new_oop;
6537     if (!_work_queue->pop_local(new_oop)) {
6538       // We emptied our work_queue; check if there's stuff that can
6539       // be gotten from the overflow stack.
6540       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6541             _overflow_stack, _work_queue)) {
6542         do_yield_check();
6543         continue;
6544       } else {  // done
6545         break;
6546       }
6547     }
6548     // Skip verifying header mark word below because we are
6549     // running concurrent with mutators.
6550     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6551     // now scan this oop's oops
6552     new_oop->oop_iterate(&pushOrMarkClosure);
6553     do_yield_check();
6554   }
6555   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6556 }
6557 
6558 // Yield in response to a request from VM Thread or
6559 // from mutators.
6560 void Par_MarkFromRootsClosure::do_yield_work() {
6561   assert(_task != NULL, "sanity");
6562   _task->yield();
6563 }
6564 
6565 // A variant of the above used for verifying CMS marking work.
6566 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6567                         MemRegion span,
6568                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6569                         CMSMarkStack*  mark_stack):
6570   _collector(collector),
6571   _span(span),
6572   _verification_bm(verification_bm),
6573   _cms_bm(cms_bm),
6574   _mark_stack(mark_stack),
6575   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6576                       mark_stack)
6577 {
6578   assert(_mark_stack->isEmpty(), "stack should be empty");
6579   _finger = _verification_bm->startWord();
6580   assert(_collector->_restart_addr == NULL, "Sanity check");
6581   assert(_span.contains(_finger), "Out of bounds _finger?");
6582 }
6583 
6584 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6585   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6586   assert(_span.contains(addr), "Out of bounds _finger?");
6587   _finger = addr;
6588 }
6589 
6590 // Should revisit to see if this should be restructured for
6591 // greater efficiency.
6592 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6593   // convert offset into a HeapWord*
6594   HeapWord* addr = _verification_bm->startWord() + offset;
6595   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6596          "address out of range");
6597   assert(_verification_bm->isMarked(addr), "tautology");
6598   assert(_cms_bm->isMarked(addr), "tautology");
6599 
6600   assert(_mark_stack->isEmpty(),
6601          "should drain stack to limit stack usage");
6602   // convert addr to an oop preparatory to scanning
6603   oop obj = oop(addr);
6604   assert(obj->is_oop(), "should be an oop");
6605   assert(_finger <= addr, "_finger runneth ahead");
6606   // advance the finger to right end of this object
6607   _finger = addr + obj->size();
6608   assert(_finger > addr, "we just incremented it above");
6609   // Note: the finger doesn't advance while we drain
6610   // the stack below.
6611   bool res = _mark_stack->push(obj);
6612   assert(res, "Empty non-zero size stack should have space for single push");
6613   while (!_mark_stack->isEmpty()) {
6614     oop new_oop = _mark_stack->pop();
6615     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6616     // now scan this oop's oops
6617     new_oop->oop_iterate(&_pam_verify_closure);
6618   }
6619   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6620   return true;
6621 }
6622 
6623 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6624   CMSCollector* collector, MemRegion span,
6625   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6626   CMSMarkStack*  mark_stack):
6627   MetadataAwareOopClosure(collector->ref_processor()),
6628   _collector(collector),
6629   _span(span),
6630   _verification_bm(verification_bm),
6631   _cms_bm(cms_bm),
6632   _mark_stack(mark_stack)
6633 { }
6634 
6635 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6636 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6637 
6638 // Upon stack overflow, we discard (part of) the stack,
6639 // remembering the least address amongst those discarded
6640 // in CMSCollector's _restart_address.
6641 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6642   // Remember the least grey address discarded
6643   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6644   _collector->lower_restart_addr(ra);
6645   _mark_stack->reset();  // discard stack contents
6646   _mark_stack->expand(); // expand the stack if possible
6647 }
6648 
6649 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6650   assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6651   HeapWord* addr = (HeapWord*)obj;
6652   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6653     // Oop lies in _span and isn't yet grey or black
6654     _verification_bm->mark(addr);            // now grey
6655     if (!_cms_bm->isMarked(addr)) {
6656       LogHandle(gc, verify) log;
6657       ResourceMark rm;
6658       oop(addr)->print_on(log.info_stream());
6659       log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6660       fatal("... aborting");
6661     }
6662 
6663     if (!_mark_stack->push(obj)) { // stack overflow
6664       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6665       assert(_mark_stack->isFull(), "Else push should have succeeded");
6666       handle_stack_overflow(addr);
6667     }
6668     // anything including and to the right of _finger
6669     // will be scanned as we iterate over the remainder of the
6670     // bit map
6671   }
6672 }
6673 
6674 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6675                      MemRegion span,
6676                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6677                      HeapWord* finger, MarkFromRootsClosure* parent) :
6678   MetadataAwareOopClosure(collector->ref_processor()),
6679   _collector(collector),
6680   _span(span),
6681   _bitMap(bitMap),
6682   _markStack(markStack),
6683   _finger(finger),
6684   _parent(parent)
6685 { }
6686 
6687 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6688                      MemRegion span,
6689                      CMSBitMap* bit_map,
6690                      OopTaskQueue* work_queue,
6691                      CMSMarkStack*  overflow_stack,
6692                      HeapWord* finger,
6693                      HeapWord** global_finger_addr,
6694                      Par_MarkFromRootsClosure* parent) :
6695   MetadataAwareOopClosure(collector->ref_processor()),
6696   _collector(collector),
6697   _whole_span(collector->_span),
6698   _span(span),
6699   _bit_map(bit_map),
6700   _work_queue(work_queue),
6701   _overflow_stack(overflow_stack),
6702   _finger(finger),
6703   _global_finger_addr(global_finger_addr),
6704   _parent(parent)
6705 { }
6706 
6707 // Assumes thread-safe access by callers, who are
6708 // responsible for mutual exclusion.
6709 void CMSCollector::lower_restart_addr(HeapWord* low) {
6710   assert(_span.contains(low), "Out of bounds addr");
6711   if (_restart_addr == NULL) {
6712     _restart_addr = low;
6713   } else {
6714     _restart_addr = MIN2(_restart_addr, low);
6715   }
6716 }
6717 
6718 // Upon stack overflow, we discard (part of) the stack,
6719 // remembering the least address amongst those discarded
6720 // in CMSCollector's _restart_address.
6721 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6722   // Remember the least grey address discarded
6723   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6724   _collector->lower_restart_addr(ra);
6725   _markStack->reset();  // discard stack contents
6726   _markStack->expand(); // expand the stack if possible
6727 }
6728 
6729 // Upon stack overflow, we discard (part of) the stack,
6730 // remembering the least address amongst those discarded
6731 // in CMSCollector's _restart_address.
6732 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6733   // We need to do this under a mutex to prevent other
6734   // workers from interfering with the work done below.
6735   MutexLockerEx ml(_overflow_stack->par_lock(),
6736                    Mutex::_no_safepoint_check_flag);
6737   // Remember the least grey address discarded
6738   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6739   _collector->lower_restart_addr(ra);
6740   _overflow_stack->reset();  // discard stack contents
6741   _overflow_stack->expand(); // expand the stack if possible
6742 }
6743 
6744 void PushOrMarkClosure::do_oop(oop obj) {
6745   // Ignore mark word because we are running concurrent with mutators.
6746   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6747   HeapWord* addr = (HeapWord*)obj;
6748   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6749     // Oop lies in _span and isn't yet grey or black
6750     _bitMap->mark(addr);            // now grey
6751     if (addr < _finger) {
6752       // the bit map iteration has already either passed, or
6753       // sampled, this bit in the bit map; we'll need to
6754       // use the marking stack to scan this oop's oops.
6755       bool simulate_overflow = false;
6756       NOT_PRODUCT(
6757         if (CMSMarkStackOverflowALot &&
6758             _collector->simulate_overflow()) {
6759           // simulate a stack overflow
6760           simulate_overflow = true;
6761         }
6762       )
6763       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6764         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6765         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6766         handle_stack_overflow(addr);
6767       }
6768     }
6769     // anything including and to the right of _finger
6770     // will be scanned as we iterate over the remainder of the
6771     // bit map
6772     do_yield_check();
6773   }
6774 }
6775 
6776 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6777 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6778 
6779 void Par_PushOrMarkClosure::do_oop(oop obj) {
6780   // Ignore mark word because we are running concurrent with mutators.
6781   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6782   HeapWord* addr = (HeapWord*)obj;
6783   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6784     // Oop lies in _span and isn't yet grey or black
6785     // We read the global_finger (volatile read) strictly after marking oop
6786     bool res = _bit_map->par_mark(addr);    // now grey
6787     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6788     // Should we push this marked oop on our stack?
6789     // -- if someone else marked it, nothing to do
6790     // -- if target oop is above global finger nothing to do
6791     // -- if target oop is in chunk and above local finger
6792     //      then nothing to do
6793     // -- else push on work queue
6794     if (   !res       // someone else marked it, they will deal with it
6795         || (addr >= *gfa)  // will be scanned in a later task
6796         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6797       return;
6798     }
6799     // the bit map iteration has already either passed, or
6800     // sampled, this bit in the bit map; we'll need to
6801     // use the marking stack to scan this oop's oops.
6802     bool simulate_overflow = false;
6803     NOT_PRODUCT(
6804       if (CMSMarkStackOverflowALot &&
6805           _collector->simulate_overflow()) {
6806         // simulate a stack overflow
6807         simulate_overflow = true;
6808       }
6809     )
6810     if (simulate_overflow ||
6811         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6812       // stack overflow
6813       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6814       // We cannot assert that the overflow stack is full because
6815       // it may have been emptied since.
6816       assert(simulate_overflow ||
6817              _work_queue->size() == _work_queue->max_elems(),
6818             "Else push should have succeeded");
6819       handle_stack_overflow(addr);
6820     }
6821     do_yield_check();
6822   }
6823 }
6824 
6825 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
6826 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
6827 
6828 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6829                                        MemRegion span,
6830                                        ReferenceProcessor* rp,
6831                                        CMSBitMap* bit_map,
6832                                        CMSBitMap* mod_union_table,
6833                                        CMSMarkStack*  mark_stack,
6834                                        bool           concurrent_precleaning):
6835   MetadataAwareOopClosure(rp),
6836   _collector(collector),
6837   _span(span),
6838   _bit_map(bit_map),
6839   _mod_union_table(mod_union_table),
6840   _mark_stack(mark_stack),
6841   _concurrent_precleaning(concurrent_precleaning)
6842 {
6843   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6844 }
6845 
6846 // Grey object rescan during pre-cleaning and second checkpoint phases --
6847 // the non-parallel version (the parallel version appears further below.)
6848 void PushAndMarkClosure::do_oop(oop obj) {
6849   // Ignore mark word verification. If during concurrent precleaning,
6850   // the object monitor may be locked. If during the checkpoint
6851   // phases, the object may already have been reached by a  different
6852   // path and may be at the end of the global overflow list (so
6853   // the mark word may be NULL).
6854   assert(obj->is_oop_or_null(true /* ignore mark word */),
6855          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6856   HeapWord* addr = (HeapWord*)obj;
6857   // Check if oop points into the CMS generation
6858   // and is not marked
6859   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6860     // a white object ...
6861     _bit_map->mark(addr);         // ... now grey
6862     // push on the marking stack (grey set)
6863     bool simulate_overflow = false;
6864     NOT_PRODUCT(
6865       if (CMSMarkStackOverflowALot &&
6866           _collector->simulate_overflow()) {
6867         // simulate a stack overflow
6868         simulate_overflow = true;
6869       }
6870     )
6871     if (simulate_overflow || !_mark_stack->push(obj)) {
6872       if (_concurrent_precleaning) {
6873          // During precleaning we can just dirty the appropriate card(s)
6874          // in the mod union table, thus ensuring that the object remains
6875          // in the grey set  and continue. In the case of object arrays
6876          // we need to dirty all of the cards that the object spans,
6877          // since the rescan of object arrays will be limited to the
6878          // dirty cards.
6879          // Note that no one can be interfering with us in this action
6880          // of dirtying the mod union table, so no locking or atomics
6881          // are required.
6882          if (obj->is_objArray()) {
6883            size_t sz = obj->size();
6884            HeapWord* end_card_addr = (HeapWord*)round_to(
6885                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6886            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6887            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6888            _mod_union_table->mark_range(redirty_range);
6889          } else {
6890            _mod_union_table->mark(addr);
6891          }
6892          _collector->_ser_pmc_preclean_ovflw++;
6893       } else {
6894          // During the remark phase, we need to remember this oop
6895          // in the overflow list.
6896          _collector->push_on_overflow_list(obj);
6897          _collector->_ser_pmc_remark_ovflw++;
6898       }
6899     }
6900   }
6901 }
6902 
6903 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
6904                                                MemRegion span,
6905                                                ReferenceProcessor* rp,
6906                                                CMSBitMap* bit_map,
6907                                                OopTaskQueue* work_queue):
6908   MetadataAwareOopClosure(rp),
6909   _collector(collector),
6910   _span(span),
6911   _bit_map(bit_map),
6912   _work_queue(work_queue)
6913 {
6914   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6915 }
6916 
6917 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6918 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6919 
6920 // Grey object rescan during second checkpoint phase --
6921 // the parallel version.
6922 void Par_PushAndMarkClosure::do_oop(oop obj) {
6923   // In the assert below, we ignore the mark word because
6924   // this oop may point to an already visited object that is
6925   // on the overflow stack (in which case the mark word has
6926   // been hijacked for chaining into the overflow stack --
6927   // if this is the last object in the overflow stack then
6928   // its mark word will be NULL). Because this object may
6929   // have been subsequently popped off the global overflow
6930   // stack, and the mark word possibly restored to the prototypical
6931   // value, by the time we get to examined this failing assert in
6932   // the debugger, is_oop_or_null(false) may subsequently start
6933   // to hold.
6934   assert(obj->is_oop_or_null(true),
6935          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6936   HeapWord* addr = (HeapWord*)obj;
6937   // Check if oop points into the CMS generation
6938   // and is not marked
6939   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6940     // a white object ...
6941     // If we manage to "claim" the object, by being the
6942     // first thread to mark it, then we push it on our
6943     // marking stack
6944     if (_bit_map->par_mark(addr)) {     // ... now grey
6945       // push on work queue (grey set)
6946       bool simulate_overflow = false;
6947       NOT_PRODUCT(
6948         if (CMSMarkStackOverflowALot &&
6949             _collector->par_simulate_overflow()) {
6950           // simulate a stack overflow
6951           simulate_overflow = true;
6952         }
6953       )
6954       if (simulate_overflow || !_work_queue->push(obj)) {
6955         _collector->par_push_on_overflow_list(obj);
6956         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6957       }
6958     } // Else, some other thread got there first
6959   }
6960 }
6961 
6962 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
6963 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
6964 
6965 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6966   Mutex* bml = _collector->bitMapLock();
6967   assert_lock_strong(bml);
6968   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6969          "CMS thread should hold CMS token");
6970 
6971   bml->unlock();
6972   ConcurrentMarkSweepThread::desynchronize(true);
6973 
6974   _collector->stopTimer();
6975   _collector->incrementYields();
6976 
6977   // See the comment in coordinator_yield()
6978   for (unsigned i = 0; i < CMSYieldSleepCount &&
6979                        ConcurrentMarkSweepThread::should_yield() &&
6980                        !CMSCollector::foregroundGCIsActive(); ++i) {
6981     os::sleep(Thread::current(), 1, false);
6982   }
6983 
6984   ConcurrentMarkSweepThread::synchronize(true);
6985   bml->lock();
6986 
6987   _collector->startTimer();
6988 }
6989 
6990 bool CMSPrecleanRefsYieldClosure::should_return() {
6991   if (ConcurrentMarkSweepThread::should_yield()) {
6992     do_yield_work();
6993   }
6994   return _collector->foregroundGCIsActive();
6995 }
6996 
6997 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6998   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
6999          "mr should be aligned to start at a card boundary");
7000   // We'd like to assert:
7001   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7002   //        "mr should be a range of cards");
7003   // However, that would be too strong in one case -- the last
7004   // partition ends at _unallocated_block which, in general, can be
7005   // an arbitrary boundary, not necessarily card aligned.
7006   _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7007   _space->object_iterate_mem(mr, &_scan_cl);
7008 }
7009 
7010 SweepClosure::SweepClosure(CMSCollector* collector,
7011                            ConcurrentMarkSweepGeneration* g,
7012                            CMSBitMap* bitMap, bool should_yield) :
7013   _collector(collector),
7014   _g(g),
7015   _sp(g->cmsSpace()),
7016   _limit(_sp->sweep_limit()),
7017   _freelistLock(_sp->freelistLock()),
7018   _bitMap(bitMap),
7019   _yield(should_yield),
7020   _inFreeRange(false),           // No free range at beginning of sweep
7021   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7022   _lastFreeRangeCoalesced(false),
7023   _freeFinger(g->used_region().start())
7024 {
7025   NOT_PRODUCT(
7026     _numObjectsFreed = 0;
7027     _numWordsFreed   = 0;
7028     _numObjectsLive = 0;
7029     _numWordsLive = 0;
7030     _numObjectsAlreadyFree = 0;
7031     _numWordsAlreadyFree = 0;
7032     _last_fc = NULL;
7033 
7034     _sp->initializeIndexedFreeListArrayReturnedBytes();
7035     _sp->dictionary()->initialize_dict_returned_bytes();
7036   )
7037   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7038          "sweep _limit out of bounds");
7039   log_develop_trace(gc, sweep)("====================");
7040   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7041 }
7042 
7043 void SweepClosure::print_on(outputStream* st) const {
7044   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7045                 p2i(_sp->bottom()), p2i(_sp->end()));
7046   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7047   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7048   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7049   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7050                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7051 }
7052 
7053 #ifndef PRODUCT
7054 // Assertion checking only:  no useful work in product mode --
7055 // however, if any of the flags below become product flags,
7056 // you may need to review this code to see if it needs to be
7057 // enabled in product mode.
7058 SweepClosure::~SweepClosure() {
7059   assert_lock_strong(_freelistLock);
7060   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7061          "sweep _limit out of bounds");
7062   if (inFreeRange()) {
7063     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7064     print();
7065     ShouldNotReachHere();
7066   }
7067 
7068   if (log_is_enabled(Debug, gc, sweep)) {
7069     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7070                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7071     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7072                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7073     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7074     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7075   }
7076 
7077   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7078     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7079     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7080     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7081     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7082                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7083   }
7084   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7085   log_develop_trace(gc, sweep)("================");
7086 }
7087 #endif  // PRODUCT
7088 
7089 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7090     bool freeRangeInFreeLists) {
7091   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7092                                p2i(freeFinger), freeRangeInFreeLists);
7093   assert(!inFreeRange(), "Trampling existing free range");
7094   set_inFreeRange(true);
7095   set_lastFreeRangeCoalesced(false);
7096 
7097   set_freeFinger(freeFinger);
7098   set_freeRangeInFreeLists(freeRangeInFreeLists);
7099   if (CMSTestInFreeList) {
7100     if (freeRangeInFreeLists) {
7101       FreeChunk* fc = (FreeChunk*) freeFinger;
7102       assert(fc->is_free(), "A chunk on the free list should be free.");
7103       assert(fc->size() > 0, "Free range should have a size");
7104       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7105     }
7106   }
7107 }
7108 
7109 // Note that the sweeper runs concurrently with mutators. Thus,
7110 // it is possible for direct allocation in this generation to happen
7111 // in the middle of the sweep. Note that the sweeper also coalesces
7112 // contiguous free blocks. Thus, unless the sweeper and the allocator
7113 // synchronize appropriately freshly allocated blocks may get swept up.
7114 // This is accomplished by the sweeper locking the free lists while
7115 // it is sweeping. Thus blocks that are determined to be free are
7116 // indeed free. There is however one additional complication:
7117 // blocks that have been allocated since the final checkpoint and
7118 // mark, will not have been marked and so would be treated as
7119 // unreachable and swept up. To prevent this, the allocator marks
7120 // the bit map when allocating during the sweep phase. This leads,
7121 // however, to a further complication -- objects may have been allocated
7122 // but not yet initialized -- in the sense that the header isn't yet
7123 // installed. The sweeper can not then determine the size of the block
7124 // in order to skip over it. To deal with this case, we use a technique
7125 // (due to Printezis) to encode such uninitialized block sizes in the
7126 // bit map. Since the bit map uses a bit per every HeapWord, but the
7127 // CMS generation has a minimum object size of 3 HeapWords, it follows
7128 // that "normal marks" won't be adjacent in the bit map (there will
7129 // always be at least two 0 bits between successive 1 bits). We make use
7130 // of these "unused" bits to represent uninitialized blocks -- the bit
7131 // corresponding to the start of the uninitialized object and the next
7132 // bit are both set. Finally, a 1 bit marks the end of the object that
7133 // started with the two consecutive 1 bits to indicate its potentially
7134 // uninitialized state.
7135 
7136 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7137   FreeChunk* fc = (FreeChunk*)addr;
7138   size_t res;
7139 
7140   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7141   // than "addr == _limit" because although _limit was a block boundary when
7142   // we started the sweep, it may no longer be one because heap expansion
7143   // may have caused us to coalesce the block ending at the address _limit
7144   // with a newly expanded chunk (this happens when _limit was set to the
7145   // previous _end of the space), so we may have stepped past _limit:
7146   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7147   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7148     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7149            "sweep _limit out of bounds");
7150     assert(addr < _sp->end(), "addr out of bounds");
7151     // Flush any free range we might be holding as a single
7152     // coalesced chunk to the appropriate free list.
7153     if (inFreeRange()) {
7154       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7155              "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7156       flush_cur_free_chunk(freeFinger(),
7157                            pointer_delta(addr, freeFinger()));
7158       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7159                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7160                                    lastFreeRangeCoalesced() ? 1 : 0);
7161     }
7162 
7163     // help the iterator loop finish
7164     return pointer_delta(_sp->end(), addr);
7165   }
7166 
7167   assert(addr < _limit, "sweep invariant");
7168   // check if we should yield
7169   do_yield_check(addr);
7170   if (fc->is_free()) {
7171     // Chunk that is already free
7172     res = fc->size();
7173     do_already_free_chunk(fc);
7174     debug_only(_sp->verifyFreeLists());
7175     // If we flush the chunk at hand in lookahead_and_flush()
7176     // and it's coalesced with a preceding chunk, then the
7177     // process of "mangling" the payload of the coalesced block
7178     // will cause erasure of the size information from the
7179     // (erstwhile) header of all the coalesced blocks but the
7180     // first, so the first disjunct in the assert will not hold
7181     // in that specific case (in which case the second disjunct
7182     // will hold).
7183     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7184            "Otherwise the size info doesn't change at this step");
7185     NOT_PRODUCT(
7186       _numObjectsAlreadyFree++;
7187       _numWordsAlreadyFree += res;
7188     )
7189     NOT_PRODUCT(_last_fc = fc;)
7190   } else if (!_bitMap->isMarked(addr)) {
7191     // Chunk is fresh garbage
7192     res = do_garbage_chunk(fc);
7193     debug_only(_sp->verifyFreeLists());
7194     NOT_PRODUCT(
7195       _numObjectsFreed++;
7196       _numWordsFreed += res;
7197     )
7198   } else {
7199     // Chunk that is alive.
7200     res = do_live_chunk(fc);
7201     debug_only(_sp->verifyFreeLists());
7202     NOT_PRODUCT(
7203         _numObjectsLive++;
7204         _numWordsLive += res;
7205     )
7206   }
7207   return res;
7208 }
7209 
7210 // For the smart allocation, record following
7211 //  split deaths - a free chunk is removed from its free list because
7212 //      it is being split into two or more chunks.
7213 //  split birth - a free chunk is being added to its free list because
7214 //      a larger free chunk has been split and resulted in this free chunk.
7215 //  coal death - a free chunk is being removed from its free list because
7216 //      it is being coalesced into a large free chunk.
7217 //  coal birth - a free chunk is being added to its free list because
7218 //      it was created when two or more free chunks where coalesced into
7219 //      this free chunk.
7220 //
7221 // These statistics are used to determine the desired number of free
7222 // chunks of a given size.  The desired number is chosen to be relative
7223 // to the end of a CMS sweep.  The desired number at the end of a sweep
7224 // is the
7225 //      count-at-end-of-previous-sweep (an amount that was enough)
7226 //              - count-at-beginning-of-current-sweep  (the excess)
7227 //              + split-births  (gains in this size during interval)
7228 //              - split-deaths  (demands on this size during interval)
7229 // where the interval is from the end of one sweep to the end of the
7230 // next.
7231 //
7232 // When sweeping the sweeper maintains an accumulated chunk which is
7233 // the chunk that is made up of chunks that have been coalesced.  That
7234 // will be termed the left-hand chunk.  A new chunk of garbage that
7235 // is being considered for coalescing will be referred to as the
7236 // right-hand chunk.
7237 //
7238 // When making a decision on whether to coalesce a right-hand chunk with
7239 // the current left-hand chunk, the current count vs. the desired count
7240 // of the left-hand chunk is considered.  Also if the right-hand chunk
7241 // is near the large chunk at the end of the heap (see
7242 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7243 // left-hand chunk is coalesced.
7244 //
7245 // When making a decision about whether to split a chunk, the desired count
7246 // vs. the current count of the candidate to be split is also considered.
7247 // If the candidate is underpopulated (currently fewer chunks than desired)
7248 // a chunk of an overpopulated (currently more chunks than desired) size may
7249 // be chosen.  The "hint" associated with a free list, if non-null, points
7250 // to a free list which may be overpopulated.
7251 //
7252 
7253 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7254   const size_t size = fc->size();
7255   // Chunks that cannot be coalesced are not in the
7256   // free lists.
7257   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7258     assert(_sp->verify_chunk_in_free_list(fc),
7259            "free chunk should be in free lists");
7260   }
7261   // a chunk that is already free, should not have been
7262   // marked in the bit map
7263   HeapWord* const addr = (HeapWord*) fc;
7264   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7265   // Verify that the bit map has no bits marked between
7266   // addr and purported end of this block.
7267   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7268 
7269   // Some chunks cannot be coalesced under any circumstances.
7270   // See the definition of cantCoalesce().
7271   if (!fc->cantCoalesce()) {
7272     // This chunk can potentially be coalesced.
7273     // All the work is done in
7274     do_post_free_or_garbage_chunk(fc, size);
7275     // Note that if the chunk is not coalescable (the else arm
7276     // below), we unconditionally flush, without needing to do
7277     // a "lookahead," as we do below.
7278     if (inFreeRange()) lookahead_and_flush(fc, size);
7279   } else {
7280     // Code path common to both original and adaptive free lists.
7281 
7282     // cant coalesce with previous block; this should be treated
7283     // as the end of a free run if any
7284     if (inFreeRange()) {
7285       // we kicked some butt; time to pick up the garbage
7286       assert(freeFinger() < addr, "freeFinger points too high");
7287       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7288     }
7289     // else, nothing to do, just continue
7290   }
7291 }
7292 
7293 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7294   // This is a chunk of garbage.  It is not in any free list.
7295   // Add it to a free list or let it possibly be coalesced into
7296   // a larger chunk.
7297   HeapWord* const addr = (HeapWord*) fc;
7298   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7299 
7300   // Verify that the bit map has no bits marked between
7301   // addr and purported end of just dead object.
7302   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7303   do_post_free_or_garbage_chunk(fc, size);
7304 
7305   assert(_limit >= addr + size,
7306          "A freshly garbage chunk can't possibly straddle over _limit");
7307   if (inFreeRange()) lookahead_and_flush(fc, size);
7308   return size;
7309 }
7310 
7311 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7312   HeapWord* addr = (HeapWord*) fc;
7313   // The sweeper has just found a live object. Return any accumulated
7314   // left hand chunk to the free lists.
7315   if (inFreeRange()) {
7316     assert(freeFinger() < addr, "freeFinger points too high");
7317     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7318   }
7319 
7320   // This object is live: we'd normally expect this to be
7321   // an oop, and like to assert the following:
7322   // assert(oop(addr)->is_oop(), "live block should be an oop");
7323   // However, as we commented above, this may be an object whose
7324   // header hasn't yet been initialized.
7325   size_t size;
7326   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7327   if (_bitMap->isMarked(addr + 1)) {
7328     // Determine the size from the bit map, rather than trying to
7329     // compute it from the object header.
7330     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7331     size = pointer_delta(nextOneAddr + 1, addr);
7332     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7333            "alignment problem");
7334 
7335 #ifdef ASSERT
7336       if (oop(addr)->klass_or_null() != NULL) {
7337         // Ignore mark word because we are running concurrent with mutators
7338         assert(oop(addr)->is_oop(true), "live block should be an oop");
7339         assert(size ==
7340                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7341                "P-mark and computed size do not agree");
7342       }
7343 #endif
7344 
7345   } else {
7346     // This should be an initialized object that's alive.
7347     assert(oop(addr)->klass_or_null() != NULL,
7348            "Should be an initialized object");
7349     // Ignore mark word because we are running concurrent with mutators
7350     assert(oop(addr)->is_oop(true), "live block should be an oop");
7351     // Verify that the bit map has no bits marked between
7352     // addr and purported end of this block.
7353     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7354     assert(size >= 3, "Necessary for Printezis marks to work");
7355     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7356     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7357   }
7358   return size;
7359 }
7360 
7361 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7362                                                  size_t chunkSize) {
7363   // do_post_free_or_garbage_chunk() should only be called in the case
7364   // of the adaptive free list allocator.
7365   const bool fcInFreeLists = fc->is_free();
7366   assert((HeapWord*)fc <= _limit, "sweep invariant");
7367   if (CMSTestInFreeList && fcInFreeLists) {
7368     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7369   }
7370 
7371   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7372 
7373   HeapWord* const fc_addr = (HeapWord*) fc;
7374 
7375   bool coalesce = false;
7376   const size_t left  = pointer_delta(fc_addr, freeFinger());
7377   const size_t right = chunkSize;
7378   switch (FLSCoalescePolicy) {
7379     // numeric value forms a coalition aggressiveness metric
7380     case 0:  { // never coalesce
7381       coalesce = false;
7382       break;
7383     }
7384     case 1: { // coalesce if left & right chunks on overpopulated lists
7385       coalesce = _sp->coalOverPopulated(left) &&
7386                  _sp->coalOverPopulated(right);
7387       break;
7388     }
7389     case 2: { // coalesce if left chunk on overpopulated list (default)
7390       coalesce = _sp->coalOverPopulated(left);
7391       break;
7392     }
7393     case 3: { // coalesce if left OR right chunk on overpopulated list
7394       coalesce = _sp->coalOverPopulated(left) ||
7395                  _sp->coalOverPopulated(right);
7396       break;
7397     }
7398     case 4: { // always coalesce
7399       coalesce = true;
7400       break;
7401     }
7402     default:
7403      ShouldNotReachHere();
7404   }
7405 
7406   // Should the current free range be coalesced?
7407   // If the chunk is in a free range and either we decided to coalesce above
7408   // or the chunk is near the large block at the end of the heap
7409   // (isNearLargestChunk() returns true), then coalesce this chunk.
7410   const bool doCoalesce = inFreeRange()
7411                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7412   if (doCoalesce) {
7413     // Coalesce the current free range on the left with the new
7414     // chunk on the right.  If either is on a free list,
7415     // it must be removed from the list and stashed in the closure.
7416     if (freeRangeInFreeLists()) {
7417       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7418       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7419              "Size of free range is inconsistent with chunk size.");
7420       if (CMSTestInFreeList) {
7421         assert(_sp->verify_chunk_in_free_list(ffc),
7422                "Chunk is not in free lists");
7423       }
7424       _sp->coalDeath(ffc->size());
7425       _sp->removeFreeChunkFromFreeLists(ffc);
7426       set_freeRangeInFreeLists(false);
7427     }
7428     if (fcInFreeLists) {
7429       _sp->coalDeath(chunkSize);
7430       assert(fc->size() == chunkSize,
7431         "The chunk has the wrong size or is not in the free lists");
7432       _sp->removeFreeChunkFromFreeLists(fc);
7433     }
7434     set_lastFreeRangeCoalesced(true);
7435     print_free_block_coalesced(fc);
7436   } else {  // not in a free range and/or should not coalesce
7437     // Return the current free range and start a new one.
7438     if (inFreeRange()) {
7439       // In a free range but cannot coalesce with the right hand chunk.
7440       // Put the current free range into the free lists.
7441       flush_cur_free_chunk(freeFinger(),
7442                            pointer_delta(fc_addr, freeFinger()));
7443     }
7444     // Set up for new free range.  Pass along whether the right hand
7445     // chunk is in the free lists.
7446     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7447   }
7448 }
7449 
7450 // Lookahead flush:
7451 // If we are tracking a free range, and this is the last chunk that
7452 // we'll look at because its end crosses past _limit, we'll preemptively
7453 // flush it along with any free range we may be holding on to. Note that
7454 // this can be the case only for an already free or freshly garbage
7455 // chunk. If this block is an object, it can never straddle
7456 // over _limit. The "straddling" occurs when _limit is set at
7457 // the previous end of the space when this cycle started, and
7458 // a subsequent heap expansion caused the previously co-terminal
7459 // free block to be coalesced with the newly expanded portion,
7460 // thus rendering _limit a non-block-boundary making it dangerous
7461 // for the sweeper to step over and examine.
7462 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7463   assert(inFreeRange(), "Should only be called if currently in a free range.");
7464   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7465   assert(_sp->used_region().contains(eob - 1),
7466          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7467          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7468          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7469          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7470   if (eob >= _limit) {
7471     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7472     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7473                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7474                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7475                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7476     // Return the storage we are tracking back into the free lists.
7477     log_develop_trace(gc, sweep)("Flushing ... ");
7478     assert(freeFinger() < eob, "Error");
7479     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7480   }
7481 }
7482 
7483 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7484   assert(inFreeRange(), "Should only be called if currently in a free range.");
7485   assert(size > 0,
7486     "A zero sized chunk cannot be added to the free lists.");
7487   if (!freeRangeInFreeLists()) {
7488     if (CMSTestInFreeList) {
7489       FreeChunk* fc = (FreeChunk*) chunk;
7490       fc->set_size(size);
7491       assert(!_sp->verify_chunk_in_free_list(fc),
7492              "chunk should not be in free lists yet");
7493     }
7494     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7495     // A new free range is going to be starting.  The current
7496     // free range has not been added to the free lists yet or
7497     // was removed so add it back.
7498     // If the current free range was coalesced, then the death
7499     // of the free range was recorded.  Record a birth now.
7500     if (lastFreeRangeCoalesced()) {
7501       _sp->coalBirth(size);
7502     }
7503     _sp->addChunkAndRepairOffsetTable(chunk, size,
7504             lastFreeRangeCoalesced());
7505   } else {
7506     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7507   }
7508   set_inFreeRange(false);
7509   set_freeRangeInFreeLists(false);
7510 }
7511 
7512 // We take a break if we've been at this for a while,
7513 // so as to avoid monopolizing the locks involved.
7514 void SweepClosure::do_yield_work(HeapWord* addr) {
7515   // Return current free chunk being used for coalescing (if any)
7516   // to the appropriate freelist.  After yielding, the next
7517   // free block encountered will start a coalescing range of
7518   // free blocks.  If the next free block is adjacent to the
7519   // chunk just flushed, they will need to wait for the next
7520   // sweep to be coalesced.
7521   if (inFreeRange()) {
7522     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7523   }
7524 
7525   // First give up the locks, then yield, then re-lock.
7526   // We should probably use a constructor/destructor idiom to
7527   // do this unlock/lock or modify the MutexUnlocker class to
7528   // serve our purpose. XXX
7529   assert_lock_strong(_bitMap->lock());
7530   assert_lock_strong(_freelistLock);
7531   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7532          "CMS thread should hold CMS token");
7533   _bitMap->lock()->unlock();
7534   _freelistLock->unlock();
7535   ConcurrentMarkSweepThread::desynchronize(true);
7536   _collector->stopTimer();
7537   _collector->incrementYields();
7538 
7539   // See the comment in coordinator_yield()
7540   for (unsigned i = 0; i < CMSYieldSleepCount &&
7541                        ConcurrentMarkSweepThread::should_yield() &&
7542                        !CMSCollector::foregroundGCIsActive(); ++i) {
7543     os::sleep(Thread::current(), 1, false);
7544   }
7545 
7546   ConcurrentMarkSweepThread::synchronize(true);
7547   _freelistLock->lock();
7548   _bitMap->lock()->lock_without_safepoint_check();
7549   _collector->startTimer();
7550 }
7551 
7552 #ifndef PRODUCT
7553 // This is actually very useful in a product build if it can
7554 // be called from the debugger.  Compile it into the product
7555 // as needed.
7556 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7557   return debug_cms_space->verify_chunk_in_free_list(fc);
7558 }
7559 #endif
7560 
7561 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7562   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7563                                p2i(fc), fc->size());
7564 }
7565 
7566 // CMSIsAliveClosure
7567 bool CMSIsAliveClosure::do_object_b(oop obj) {
7568   HeapWord* addr = (HeapWord*)obj;
7569   return addr != NULL &&
7570          (!_span.contains(addr) || _bit_map->isMarked(addr));
7571 }
7572 
7573 
7574 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7575                       MemRegion span,
7576                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7577                       bool cpc):
7578   _collector(collector),
7579   _span(span),
7580   _bit_map(bit_map),
7581   _mark_stack(mark_stack),
7582   _concurrent_precleaning(cpc) {
7583   assert(!_span.is_empty(), "Empty span could spell trouble");
7584 }
7585 
7586 
7587 // CMSKeepAliveClosure: the serial version
7588 void CMSKeepAliveClosure::do_oop(oop obj) {
7589   HeapWord* addr = (HeapWord*)obj;
7590   if (_span.contains(addr) &&
7591       !_bit_map->isMarked(addr)) {
7592     _bit_map->mark(addr);
7593     bool simulate_overflow = false;
7594     NOT_PRODUCT(
7595       if (CMSMarkStackOverflowALot &&
7596           _collector->simulate_overflow()) {
7597         // simulate a stack overflow
7598         simulate_overflow = true;
7599       }
7600     )
7601     if (simulate_overflow || !_mark_stack->push(obj)) {
7602       if (_concurrent_precleaning) {
7603         // We dirty the overflown object and let the remark
7604         // phase deal with it.
7605         assert(_collector->overflow_list_is_empty(), "Error");
7606         // In the case of object arrays, we need to dirty all of
7607         // the cards that the object spans. No locking or atomics
7608         // are needed since no one else can be mutating the mod union
7609         // table.
7610         if (obj->is_objArray()) {
7611           size_t sz = obj->size();
7612           HeapWord* end_card_addr =
7613             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7614           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7615           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7616           _collector->_modUnionTable.mark_range(redirty_range);
7617         } else {
7618           _collector->_modUnionTable.mark(addr);
7619         }
7620         _collector->_ser_kac_preclean_ovflw++;
7621       } else {
7622         _collector->push_on_overflow_list(obj);
7623         _collector->_ser_kac_ovflw++;
7624       }
7625     }
7626   }
7627 }
7628 
7629 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7630 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7631 
7632 // CMSParKeepAliveClosure: a parallel version of the above.
7633 // The work queues are private to each closure (thread),
7634 // but (may be) available for stealing by other threads.
7635 void CMSParKeepAliveClosure::do_oop(oop obj) {
7636   HeapWord* addr = (HeapWord*)obj;
7637   if (_span.contains(addr) &&
7638       !_bit_map->isMarked(addr)) {
7639     // In general, during recursive tracing, several threads
7640     // may be concurrently getting here; the first one to
7641     // "tag" it, claims it.
7642     if (_bit_map->par_mark(addr)) {
7643       bool res = _work_queue->push(obj);
7644       assert(res, "Low water mark should be much less than capacity");
7645       // Do a recursive trim in the hope that this will keep
7646       // stack usage lower, but leave some oops for potential stealers
7647       trim_queue(_low_water_mark);
7648     } // Else, another thread got there first
7649   }
7650 }
7651 
7652 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7653 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7654 
7655 void CMSParKeepAliveClosure::trim_queue(uint max) {
7656   while (_work_queue->size() > max) {
7657     oop new_oop;
7658     if (_work_queue->pop_local(new_oop)) {
7659       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7660       assert(_bit_map->isMarked((HeapWord*)new_oop),
7661              "no white objects on this stack!");
7662       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7663       // iterate over the oops in this oop, marking and pushing
7664       // the ones in CMS heap (i.e. in _span).
7665       new_oop->oop_iterate(&_mark_and_push);
7666     }
7667   }
7668 }
7669 
7670 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7671                                 CMSCollector* collector,
7672                                 MemRegion span, CMSBitMap* bit_map,
7673                                 OopTaskQueue* work_queue):
7674   _collector(collector),
7675   _span(span),
7676   _bit_map(bit_map),
7677   _work_queue(work_queue) { }
7678 
7679 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7680   HeapWord* addr = (HeapWord*)obj;
7681   if (_span.contains(addr) &&
7682       !_bit_map->isMarked(addr)) {
7683     if (_bit_map->par_mark(addr)) {
7684       bool simulate_overflow = false;
7685       NOT_PRODUCT(
7686         if (CMSMarkStackOverflowALot &&
7687             _collector->par_simulate_overflow()) {
7688           // simulate a stack overflow
7689           simulate_overflow = true;
7690         }
7691       )
7692       if (simulate_overflow || !_work_queue->push(obj)) {
7693         _collector->par_push_on_overflow_list(obj);
7694         _collector->_par_kac_ovflw++;
7695       }
7696     } // Else another thread got there already
7697   }
7698 }
7699 
7700 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7701 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7702 
7703 //////////////////////////////////////////////////////////////////
7704 //  CMSExpansionCause                /////////////////////////////
7705 //////////////////////////////////////////////////////////////////
7706 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7707   switch (cause) {
7708     case _no_expansion:
7709       return "No expansion";
7710     case _satisfy_free_ratio:
7711       return "Free ratio";
7712     case _satisfy_promotion:
7713       return "Satisfy promotion";
7714     case _satisfy_allocation:
7715       return "allocation";
7716     case _allocate_par_lab:
7717       return "Par LAB";
7718     case _allocate_par_spooling_space:
7719       return "Par Spooling Space";
7720     case _adaptive_size_policy:
7721       return "Ergonomics";
7722     default:
7723       return "unknown";
7724   }
7725 }
7726 
7727 void CMSDrainMarkingStackClosure::do_void() {
7728   // the max number to take from overflow list at a time
7729   const size_t num = _mark_stack->capacity()/4;
7730   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7731          "Overflow list should be NULL during concurrent phases");
7732   while (!_mark_stack->isEmpty() ||
7733          // if stack is empty, check the overflow list
7734          _collector->take_from_overflow_list(num, _mark_stack)) {
7735     oop obj = _mark_stack->pop();
7736     HeapWord* addr = (HeapWord*)obj;
7737     assert(_span.contains(addr), "Should be within span");
7738     assert(_bit_map->isMarked(addr), "Should be marked");
7739     assert(obj->is_oop(), "Should be an oop");
7740     obj->oop_iterate(_keep_alive);
7741   }
7742 }
7743 
7744 void CMSParDrainMarkingStackClosure::do_void() {
7745   // drain queue
7746   trim_queue(0);
7747 }
7748 
7749 // Trim our work_queue so its length is below max at return
7750 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7751   while (_work_queue->size() > max) {
7752     oop new_oop;
7753     if (_work_queue->pop_local(new_oop)) {
7754       assert(new_oop->is_oop(), "Expected an oop");
7755       assert(_bit_map->isMarked((HeapWord*)new_oop),
7756              "no white objects on this stack!");
7757       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7758       // iterate over the oops in this oop, marking and pushing
7759       // the ones in CMS heap (i.e. in _span).
7760       new_oop->oop_iterate(&_mark_and_push);
7761     }
7762   }
7763 }
7764 
7765 ////////////////////////////////////////////////////////////////////
7766 // Support for Marking Stack Overflow list handling and related code
7767 ////////////////////////////////////////////////////////////////////
7768 // Much of the following code is similar in shape and spirit to the
7769 // code used in ParNewGC. We should try and share that code
7770 // as much as possible in the future.
7771 
7772 #ifndef PRODUCT
7773 // Debugging support for CMSStackOverflowALot
7774 
7775 // It's OK to call this multi-threaded;  the worst thing
7776 // that can happen is that we'll get a bunch of closely
7777 // spaced simulated overflows, but that's OK, in fact
7778 // probably good as it would exercise the overflow code
7779 // under contention.
7780 bool CMSCollector::simulate_overflow() {
7781   if (_overflow_counter-- <= 0) { // just being defensive
7782     _overflow_counter = CMSMarkStackOverflowInterval;
7783     return true;
7784   } else {
7785     return false;
7786   }
7787 }
7788 
7789 bool CMSCollector::par_simulate_overflow() {
7790   return simulate_overflow();
7791 }
7792 #endif
7793 
7794 // Single-threaded
7795 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7796   assert(stack->isEmpty(), "Expected precondition");
7797   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7798   size_t i = num;
7799   oop  cur = _overflow_list;
7800   const markOop proto = markOopDesc::prototype();
7801   NOT_PRODUCT(ssize_t n = 0;)
7802   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7803     next = oop(cur->mark());
7804     cur->set_mark(proto);   // until proven otherwise
7805     assert(cur->is_oop(), "Should be an oop");
7806     bool res = stack->push(cur);
7807     assert(res, "Bit off more than can chew?");
7808     NOT_PRODUCT(n++;)
7809   }
7810   _overflow_list = cur;
7811 #ifndef PRODUCT
7812   assert(_num_par_pushes >= n, "Too many pops?");
7813   _num_par_pushes -=n;
7814 #endif
7815   return !stack->isEmpty();
7816 }
7817 
7818 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7819 // (MT-safe) Get a prefix of at most "num" from the list.
7820 // The overflow list is chained through the mark word of
7821 // each object in the list. We fetch the entire list,
7822 // break off a prefix of the right size and return the
7823 // remainder. If other threads try to take objects from
7824 // the overflow list at that time, they will wait for
7825 // some time to see if data becomes available. If (and
7826 // only if) another thread places one or more object(s)
7827 // on the global list before we have returned the suffix
7828 // to the global list, we will walk down our local list
7829 // to find its end and append the global list to
7830 // our suffix before returning it. This suffix walk can
7831 // prove to be expensive (quadratic in the amount of traffic)
7832 // when there are many objects in the overflow list and
7833 // there is much producer-consumer contention on the list.
7834 // *NOTE*: The overflow list manipulation code here and
7835 // in ParNewGeneration:: are very similar in shape,
7836 // except that in the ParNew case we use the old (from/eden)
7837 // copy of the object to thread the list via its klass word.
7838 // Because of the common code, if you make any changes in
7839 // the code below, please check the ParNew version to see if
7840 // similar changes might be needed.
7841 // CR 6797058 has been filed to consolidate the common code.
7842 bool CMSCollector::par_take_from_overflow_list(size_t num,
7843                                                OopTaskQueue* work_q,
7844                                                int no_of_gc_threads) {
7845   assert(work_q->size() == 0, "First empty local work queue");
7846   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7847   if (_overflow_list == NULL) {
7848     return false;
7849   }
7850   // Grab the entire list; we'll put back a suffix
7851   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7852   Thread* tid = Thread::current();
7853   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7854   // set to ParallelGCThreads.
7855   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7856   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7857   // If the list is busy, we spin for a short while,
7858   // sleeping between attempts to get the list.
7859   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7860     os::sleep(tid, sleep_time_millis, false);
7861     if (_overflow_list == NULL) {
7862       // Nothing left to take
7863       return false;
7864     } else if (_overflow_list != BUSY) {
7865       // Try and grab the prefix
7866       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7867     }
7868   }
7869   // If the list was found to be empty, or we spun long
7870   // enough, we give up and return empty-handed. If we leave
7871   // the list in the BUSY state below, it must be the case that
7872   // some other thread holds the overflow list and will set it
7873   // to a non-BUSY state in the future.
7874   if (prefix == NULL || prefix == BUSY) {
7875      // Nothing to take or waited long enough
7876      if (prefix == NULL) {
7877        // Write back the NULL in case we overwrote it with BUSY above
7878        // and it is still the same value.
7879        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7880      }
7881      return false;
7882   }
7883   assert(prefix != NULL && prefix != BUSY, "Error");
7884   size_t i = num;
7885   oop cur = prefix;
7886   // Walk down the first "num" objects, unless we reach the end.
7887   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7888   if (cur->mark() == NULL) {
7889     // We have "num" or fewer elements in the list, so there
7890     // is nothing to return to the global list.
7891     // Write back the NULL in lieu of the BUSY we wrote
7892     // above, if it is still the same value.
7893     if (_overflow_list == BUSY) {
7894       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7895     }
7896   } else {
7897     // Chop off the suffix and return it to the global list.
7898     assert(cur->mark() != BUSY, "Error");
7899     oop suffix_head = cur->mark(); // suffix will be put back on global list
7900     cur->set_mark(NULL);           // break off suffix
7901     // It's possible that the list is still in the empty(busy) state
7902     // we left it in a short while ago; in that case we may be
7903     // able to place back the suffix without incurring the cost
7904     // of a walk down the list.
7905     oop observed_overflow_list = _overflow_list;
7906     oop cur_overflow_list = observed_overflow_list;
7907     bool attached = false;
7908     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7909       observed_overflow_list =
7910         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7911       if (cur_overflow_list == observed_overflow_list) {
7912         attached = true;
7913         break;
7914       } else cur_overflow_list = observed_overflow_list;
7915     }
7916     if (!attached) {
7917       // Too bad, someone else sneaked in (at least) an element; we'll need
7918       // to do a splice. Find tail of suffix so we can prepend suffix to global
7919       // list.
7920       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7921       oop suffix_tail = cur;
7922       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7923              "Tautology");
7924       observed_overflow_list = _overflow_list;
7925       do {
7926         cur_overflow_list = observed_overflow_list;
7927         if (cur_overflow_list != BUSY) {
7928           // Do the splice ...
7929           suffix_tail->set_mark(markOop(cur_overflow_list));
7930         } else { // cur_overflow_list == BUSY
7931           suffix_tail->set_mark(NULL);
7932         }
7933         // ... and try to place spliced list back on overflow_list ...
7934         observed_overflow_list =
7935           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7936       } while (cur_overflow_list != observed_overflow_list);
7937       // ... until we have succeeded in doing so.
7938     }
7939   }
7940 
7941   // Push the prefix elements on work_q
7942   assert(prefix != NULL, "control point invariant");
7943   const markOop proto = markOopDesc::prototype();
7944   oop next;
7945   NOT_PRODUCT(ssize_t n = 0;)
7946   for (cur = prefix; cur != NULL; cur = next) {
7947     next = oop(cur->mark());
7948     cur->set_mark(proto);   // until proven otherwise
7949     assert(cur->is_oop(), "Should be an oop");
7950     bool res = work_q->push(cur);
7951     assert(res, "Bit off more than we can chew?");
7952     NOT_PRODUCT(n++;)
7953   }
7954 #ifndef PRODUCT
7955   assert(_num_par_pushes >= n, "Too many pops?");
7956   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7957 #endif
7958   return true;
7959 }
7960 
7961 // Single-threaded
7962 void CMSCollector::push_on_overflow_list(oop p) {
7963   NOT_PRODUCT(_num_par_pushes++;)
7964   assert(p->is_oop(), "Not an oop");
7965   preserve_mark_if_necessary(p);
7966   p->set_mark((markOop)_overflow_list);
7967   _overflow_list = p;
7968 }
7969 
7970 // Multi-threaded; use CAS to prepend to overflow list
7971 void CMSCollector::par_push_on_overflow_list(oop p) {
7972   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7973   assert(p->is_oop(), "Not an oop");
7974   par_preserve_mark_if_necessary(p);
7975   oop observed_overflow_list = _overflow_list;
7976   oop cur_overflow_list;
7977   do {
7978     cur_overflow_list = observed_overflow_list;
7979     if (cur_overflow_list != BUSY) {
7980       p->set_mark(markOop(cur_overflow_list));
7981     } else {
7982       p->set_mark(NULL);
7983     }
7984     observed_overflow_list =
7985       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7986   } while (cur_overflow_list != observed_overflow_list);
7987 }
7988 #undef BUSY
7989 
7990 // Single threaded
7991 // General Note on GrowableArray: pushes may silently fail
7992 // because we are (temporarily) out of C-heap for expanding
7993 // the stack. The problem is quite ubiquitous and affects
7994 // a lot of code in the JVM. The prudent thing for GrowableArray
7995 // to do (for now) is to exit with an error. However, that may
7996 // be too draconian in some cases because the caller may be
7997 // able to recover without much harm. For such cases, we
7998 // should probably introduce a "soft_push" method which returns
7999 // an indication of success or failure with the assumption that
8000 // the caller may be able to recover from a failure; code in
8001 // the VM can then be changed, incrementally, to deal with such
8002 // failures where possible, thus, incrementally hardening the VM
8003 // in such low resource situations.
8004 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8005   _preserved_oop_stack.push(p);
8006   _preserved_mark_stack.push(m);
8007   assert(m == p->mark(), "Mark word changed");
8008   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8009          "bijection");
8010 }
8011 
8012 // Single threaded
8013 void CMSCollector::preserve_mark_if_necessary(oop p) {
8014   markOop m = p->mark();
8015   if (m->must_be_preserved(p)) {
8016     preserve_mark_work(p, m);
8017   }
8018 }
8019 
8020 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8021   markOop m = p->mark();
8022   if (m->must_be_preserved(p)) {
8023     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8024     // Even though we read the mark word without holding
8025     // the lock, we are assured that it will not change
8026     // because we "own" this oop, so no other thread can
8027     // be trying to push it on the overflow list; see
8028     // the assertion in preserve_mark_work() that checks
8029     // that m == p->mark().
8030     preserve_mark_work(p, m);
8031   }
8032 }
8033 
8034 // We should be able to do this multi-threaded,
8035 // a chunk of stack being a task (this is
8036 // correct because each oop only ever appears
8037 // once in the overflow list. However, it's
8038 // not very easy to completely overlap this with
8039 // other operations, so will generally not be done
8040 // until all work's been completed. Because we
8041 // expect the preserved oop stack (set) to be small,
8042 // it's probably fine to do this single-threaded.
8043 // We can explore cleverer concurrent/overlapped/parallel
8044 // processing of preserved marks if we feel the
8045 // need for this in the future. Stack overflow should
8046 // be so rare in practice and, when it happens, its
8047 // effect on performance so great that this will
8048 // likely just be in the noise anyway.
8049 void CMSCollector::restore_preserved_marks_if_any() {
8050   assert(SafepointSynchronize::is_at_safepoint(),
8051          "world should be stopped");
8052   assert(Thread::current()->is_ConcurrentGC_thread() ||
8053          Thread::current()->is_VM_thread(),
8054          "should be single-threaded");
8055   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8056          "bijection");
8057 
8058   while (!_preserved_oop_stack.is_empty()) {
8059     oop p = _preserved_oop_stack.pop();
8060     assert(p->is_oop(), "Should be an oop");
8061     assert(_span.contains(p), "oop should be in _span");
8062     assert(p->mark() == markOopDesc::prototype(),
8063            "Set when taken from overflow list");
8064     markOop m = _preserved_mark_stack.pop();
8065     p->set_mark(m);
8066   }
8067   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8068          "stacks were cleared above");
8069 }
8070 
8071 #ifndef PRODUCT
8072 bool CMSCollector::no_preserved_marks() const {
8073   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8074 }
8075 #endif
8076 
8077 // Transfer some number of overflown objects to usual marking
8078 // stack. Return true if some objects were transferred.
8079 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8080   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8081                     (size_t)ParGCDesiredObjsFromOverflowList);
8082 
8083   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8084   assert(_collector->overflow_list_is_empty() || res,
8085          "If list is not empty, we should have taken something");
8086   assert(!res || !_mark_stack->isEmpty(),
8087          "If we took something, it should now be on our stack");
8088   return res;
8089 }
8090 
8091 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8092   size_t res = _sp->block_size_no_stall(addr, _collector);
8093   if (_sp->block_is_obj(addr)) {
8094     if (_live_bit_map->isMarked(addr)) {
8095       // It can't have been dead in a previous cycle
8096       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8097     } else {
8098       _dead_bit_map->mark(addr);      // mark the dead object
8099     }
8100   }
8101   // Could be 0, if the block size could not be computed without stalling.
8102   return res;
8103 }
8104 
8105 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8106 
8107   switch (phase) {
8108     case CMSCollector::InitialMarking:
8109       initialize(true  /* fullGC */ ,
8110                  cause /* cause of the GC */,
8111                  true  /* recordGCBeginTime */,
8112                  true  /* recordPreGCUsage */,
8113                  false /* recordPeakUsage */,
8114                  false /* recordPostGCusage */,
8115                  true  /* recordAccumulatedGCTime */,
8116                  false /* recordGCEndTime */,
8117                  false /* countCollection */  );
8118       break;
8119 
8120     case CMSCollector::FinalMarking:
8121       initialize(true  /* fullGC */ ,
8122                  cause /* cause of the GC */,
8123                  false /* recordGCBeginTime */,
8124                  false /* recordPreGCUsage */,
8125                  false /* recordPeakUsage */,
8126                  false /* recordPostGCusage */,
8127                  true  /* recordAccumulatedGCTime */,
8128                  false /* recordGCEndTime */,
8129                  false /* countCollection */  );
8130       break;
8131 
8132     case CMSCollector::Sweeping:
8133       initialize(true  /* fullGC */ ,
8134                  cause /* cause of the GC */,
8135                  false /* recordGCBeginTime */,
8136                  false /* recordPreGCUsage */,
8137                  true  /* recordPeakUsage */,
8138                  true  /* recordPostGCusage */,
8139                  false /* recordAccumulatedGCTime */,
8140                  true  /* recordGCEndTime */,
8141                  true  /* countCollection */  );
8142       break;
8143 
8144     default:
8145       ShouldNotReachHere();
8146   }
8147 }