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/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "gc/cms/cmsCollectorPolicy.hpp"
  31 #include "gc/cms/cmsOopClosures.inline.hpp"
  32 #include "gc/cms/compactibleFreeListSpace.hpp"
  33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  34 #include "gc/cms/concurrentMarkSweepThread.hpp"
  35 #include "gc/cms/parNewGeneration.hpp"
  36 #include "gc/cms/vmCMSOperations.hpp"
  37 #include "gc/serial/genMarkSweep.hpp"
  38 #include "gc/serial/tenuredGeneration.hpp"
  39 #include "gc/shared/adaptiveSizePolicy.hpp"
  40 #include "gc/shared/cardGeneration.inline.hpp"
  41 #include "gc/shared/cardTableRS.hpp"
  42 #include "gc/shared/collectedHeap.inline.hpp"
  43 #include "gc/shared/collectorCounters.hpp"
  44 #include "gc/shared/collectorPolicy.hpp"
  45 #include "gc/shared/gcLocker.inline.hpp"
  46 #include "gc/shared/gcPolicyCounters.hpp"
  47 #include "gc/shared/gcTimer.hpp"
  48 #include "gc/shared/gcTrace.hpp"
  49 #include "gc/shared/gcTraceTime.hpp"
  50 #include "gc/shared/genCollectedHeap.hpp"
  51 #include "gc/shared/genOopClosures.inline.hpp"
  52 #include "gc/shared/isGCActiveMark.hpp"
  53 #include "gc/shared/referencePolicy.hpp"
  54 #include "gc/shared/strongRootsScope.hpp"
  55 #include "gc/shared/taskqueue.inline.hpp"
  56 #include "memory/allocation.hpp"
  57 #include "memory/iterator.inline.hpp"
  58 #include "memory/padded.hpp"
  59 #include "memory/resourceArea.hpp"
  60 #include "oops/oop.inline.hpp"
  61 #include "prims/jvmtiExport.hpp"
  62 #include "runtime/atomic.inline.hpp"
  63 #include "runtime/globals_extension.hpp"
  64 #include "runtime/handles.inline.hpp"
  65 #include "runtime/java.hpp"
  66 #include "runtime/orderAccess.inline.hpp"
  67 #include "runtime/vmThread.hpp"
  68 #include "services/memoryService.hpp"
  69 #include "services/runtimeService.hpp"
  70 #include "utilities/stack.inline.hpp"
  71 
  72 // statics
  73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  74 bool CMSCollector::_full_gc_requested = false;
  75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  76 
  77 //////////////////////////////////////////////////////////////////
  78 // In support of CMS/VM thread synchronization
  79 //////////////////////////////////////////////////////////////////
  80 // We split use of the CGC_lock into 2 "levels".
  81 // The low-level locking is of the usual CGC_lock monitor. We introduce
  82 // a higher level "token" (hereafter "CMS token") built on top of the
  83 // low level monitor (hereafter "CGC lock").
  84 // The token-passing protocol gives priority to the VM thread. The
  85 // CMS-lock doesn't provide any fairness guarantees, but clients
  86 // should ensure that it is only held for very short, bounded
  87 // durations.
  88 //
  89 // When either of the CMS thread or the VM thread is involved in
  90 // collection operations during which it does not want the other
  91 // thread to interfere, it obtains the CMS token.
  92 //
  93 // If either thread tries to get the token while the other has
  94 // it, that thread waits. However, if the VM thread and CMS thread
  95 // both want the token, then the VM thread gets priority while the
  96 // CMS thread waits. This ensures, for instance, that the "concurrent"
  97 // phases of the CMS thread's work do not block out the VM thread
  98 // for long periods of time as the CMS thread continues to hog
  99 // the token. (See bug 4616232).
 100 //
 101 // The baton-passing functions are, however, controlled by the
 102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 103 // and here the low-level CMS lock, not the high level token,
 104 // ensures mutual exclusion.
 105 //
 106 // Two important conditions that we have to satisfy:
 107 // 1. if a thread does a low-level wait on the CMS lock, then it
 108 //    relinquishes the CMS token if it were holding that token
 109 //    when it acquired the low-level CMS lock.
 110 // 2. any low-level notifications on the low-level lock
 111 //    should only be sent when a thread has relinquished the token.
 112 //
 113 // In the absence of either property, we'd have potential deadlock.
 114 //
 115 // We protect each of the CMS (concurrent and sequential) phases
 116 // with the CMS _token_, not the CMS _lock_.
 117 //
 118 // The only code protected by CMS lock is the token acquisition code
 119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 120 // baton-passing code.
 121 //
 122 // Unfortunately, i couldn't come up with a good abstraction to factor and
 123 // hide the naked CGC_lock manipulation in the baton-passing code
 124 // further below. That's something we should try to do. Also, the proof
 125 // of correctness of this 2-level locking scheme is far from obvious,
 126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 127 // that there may be a theoretical possibility of delay/starvation in the
 128 // low-level lock/wait/notify scheme used for the baton-passing because of
 129 // potential interference with the priority scheme embodied in the
 130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 131 // invocation further below and marked with "XXX 20011219YSR".
 132 // Indeed, as we note elsewhere, this may become yet more slippery
 133 // in the presence of multiple CMS and/or multiple VM threads. XXX
 134 
 135 class CMSTokenSync: public StackObj {
 136  private:
 137   bool _is_cms_thread;
 138  public:
 139   CMSTokenSync(bool is_cms_thread):
 140     _is_cms_thread(is_cms_thread) {
 141     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 142            "Incorrect argument to constructor");
 143     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 144   }
 145 
 146   ~CMSTokenSync() {
 147     assert(_is_cms_thread ?
 148              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 149              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 150           "Incorrect state");
 151     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 152   }
 153 };
 154 
 155 // Convenience class that does a CMSTokenSync, and then acquires
 156 // upto three locks.
 157 class CMSTokenSyncWithLocks: public CMSTokenSync {
 158  private:
 159   // Note: locks are acquired in textual declaration order
 160   // and released in the opposite order
 161   MutexLockerEx _locker1, _locker2, _locker3;
 162  public:
 163   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 164                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 165     CMSTokenSync(is_cms_thread),
 166     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 167     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 168     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 169   { }
 170 };
 171 
 172 
 173 //////////////////////////////////////////////////////////////////
 174 //  Concurrent Mark-Sweep Generation /////////////////////////////
 175 //////////////////////////////////////////////////////////////////
 176 
 177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 178 
 179 // This struct contains per-thread things necessary to support parallel
 180 // young-gen collection.
 181 class CMSParGCThreadState: public CHeapObj<mtGC> {
 182  public:
 183   CFLS_LAB lab;
 184   PromotionInfo promo;
 185 
 186   // Constructor.
 187   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 188     promo.setSpace(cfls);
 189   }
 190 };
 191 
 192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 193      ReservedSpace rs, size_t initial_byte_size,
 194      CardTableRS* ct, bool use_adaptive_freelists,
 195      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 196   CardGeneration(rs, initial_byte_size, ct),
 197   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 198   _did_compact(false)
 199 {
 200   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 201   HeapWord* end    = (HeapWord*) _virtual_space.high();
 202 
 203   _direct_allocated_words = 0;
 204   NOT_PRODUCT(
 205     _numObjectsPromoted = 0;
 206     _numWordsPromoted = 0;
 207     _numObjectsAllocated = 0;
 208     _numWordsAllocated = 0;
 209   )
 210 
 211   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 212                                            use_adaptive_freelists,
 213                                            dictionaryChoice);
 214   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 215   _cmsSpace->_old_gen = this;
 216 
 217   _gc_stats = new CMSGCStats();
 218 
 219   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 220   // offsets match. The ability to tell free chunks from objects
 221   // depends on this property.
 222   debug_only(
 223     FreeChunk* junk = NULL;
 224     assert(UseCompressedClassPointers ||
 225            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 226            "Offset of FreeChunk::_prev within FreeChunk must match"
 227            "  that of OopDesc::_klass within OopDesc");
 228   )
 229 
 230   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 231   for (uint i = 0; i < ParallelGCThreads; i++) {
 232     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 233   }
 234 
 235   _incremental_collection_failed = false;
 236   // The "dilatation_factor" is the expansion that can occur on
 237   // account of the fact that the minimum object size in the CMS
 238   // generation may be larger than that in, say, a contiguous young
 239   //  generation.
 240   // Ideally, in the calculation below, we'd compute the dilatation
 241   // factor as: MinChunkSize/(promoting_gen's min object size)
 242   // Since we do not have such a general query interface for the
 243   // promoting generation, we'll instead just use the minimum
 244   // object size (which today is a header's worth of space);
 245   // note that all arithmetic is in units of HeapWords.
 246   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 247   assert(_dilatation_factor >= 1.0, "from previous assert");
 248 }
 249 
 250 
 251 // The field "_initiating_occupancy" represents the occupancy percentage
 252 // at which we trigger a new collection cycle.  Unless explicitly specified
 253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 254 // is calculated by:
 255 //
 256 //   Let "f" be MinHeapFreeRatio in
 257 //
 258 //    _initiating_occupancy = 100-f +
 259 //                           f * (CMSTriggerRatio/100)
 260 //   where CMSTriggerRatio is the argument "tr" below.
 261 //
 262 // That is, if we assume the heap is at its desired maximum occupancy at the
 263 // end of a collection, we let CMSTriggerRatio of the (purported) free
 264 // space be allocated before initiating a new collection cycle.
 265 //
 266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 267   assert(io <= 100 && tr <= 100, "Check the arguments");
 268   if (io >= 0) {
 269     _initiating_occupancy = (double)io / 100.0;
 270   } else {
 271     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 272                              (double)(tr * MinHeapFreeRatio) / 100.0)
 273                             / 100.0;
 274   }
 275 }
 276 
 277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 278   assert(collector() != NULL, "no collector");
 279   collector()->ref_processor_init();
 280 }
 281 
 282 void CMSCollector::ref_processor_init() {
 283   if (_ref_processor == NULL) {
 284     // Allocate and initialize a reference processor
 285     _ref_processor =
 286       new ReferenceProcessor(_span,                               // span
 287                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 288                              ParallelGCThreads,                   // mt processing degree
 289                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 290                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 291                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 292                              &_is_alive_closure);                 // closure for liveness info
 293     // Initialize the _ref_processor field of CMSGen
 294     _cmsGen->set_ref_processor(_ref_processor);
 295 
 296   }
 297 }
 298 
 299 AdaptiveSizePolicy* CMSCollector::size_policy() {
 300   GenCollectedHeap* gch = GenCollectedHeap::heap();
 301   return gch->gen_policy()->size_policy();
 302 }
 303 
 304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 305 
 306   const char* gen_name = "old";
 307   GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
 308   // Generation Counters - generation 1, 1 subspace
 309   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 310       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 311 
 312   _space_counters = new GSpaceCounters(gen_name, 0,
 313                                        _virtual_space.reserved_size(),
 314                                        this, _gen_counters);
 315 }
 316 
 317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 318   _cms_gen(cms_gen)
 319 {
 320   assert(alpha <= 100, "bad value");
 321   _saved_alpha = alpha;
 322 
 323   // Initialize the alphas to the bootstrap value of 100.
 324   _gc0_alpha = _cms_alpha = 100;
 325 
 326   _cms_begin_time.update();
 327   _cms_end_time.update();
 328 
 329   _gc0_duration = 0.0;
 330   _gc0_period = 0.0;
 331   _gc0_promoted = 0;
 332 
 333   _cms_duration = 0.0;
 334   _cms_period = 0.0;
 335   _cms_allocated = 0;
 336 
 337   _cms_used_at_gc0_begin = 0;
 338   _cms_used_at_gc0_end = 0;
 339   _allow_duty_cycle_reduction = false;
 340   _valid_bits = 0;
 341 }
 342 
 343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 344   // TBD: CR 6909490
 345   return 1.0;
 346 }
 347 
 348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 349 }
 350 
 351 // If promotion failure handling is on use
 352 // the padded average size of the promotion for each
 353 // young generation collection.
 354 double CMSStats::time_until_cms_gen_full() const {
 355   size_t cms_free = _cms_gen->cmsSpace()->free();
 356   GenCollectedHeap* gch = GenCollectedHeap::heap();
 357   size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
 358                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 359   if (cms_free > expected_promotion) {
 360     // Start a cms collection if there isn't enough space to promote
 361     // for the next young collection.  Use the padded average as
 362     // a safety factor.
 363     cms_free -= expected_promotion;
 364 
 365     // Adjust by the safety factor.
 366     double cms_free_dbl = (double)cms_free;
 367     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 368     // Apply a further correction factor which tries to adjust
 369     // for recent occurance of concurrent mode failures.
 370     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 371     cms_free_dbl = cms_free_dbl * cms_adjustment;
 372 
 373     if (PrintGCDetails && Verbose) {
 374       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 375         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 376         cms_free, expected_promotion);
 377       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 378         cms_free_dbl, cms_consumption_rate() + 1.0);
 379     }
 380     // Add 1 in case the consumption rate goes to zero.
 381     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 382   }
 383   return 0.0;
 384 }
 385 
 386 // Compare the duration of the cms collection to the
 387 // time remaining before the cms generation is empty.
 388 // Note that the time from the start of the cms collection
 389 // to the start of the cms sweep (less than the total
 390 // duration of the cms collection) can be used.  This
 391 // has been tried and some applications experienced
 392 // promotion failures early in execution.  This was
 393 // possibly because the averages were not accurate
 394 // enough at the beginning.
 395 double CMSStats::time_until_cms_start() const {
 396   // We add "gc0_period" to the "work" calculation
 397   // below because this query is done (mostly) at the
 398   // end of a scavenge, so we need to conservatively
 399   // account for that much possible delay
 400   // in the query so as to avoid concurrent mode failures
 401   // due to starting the collection just a wee bit too
 402   // late.
 403   double work = cms_duration() + gc0_period();
 404   double deadline = time_until_cms_gen_full();
 405   // If a concurrent mode failure occurred recently, we want to be
 406   // more conservative and halve our expected time_until_cms_gen_full()
 407   if (work > deadline) {
 408     if (Verbose && PrintGCDetails) {
 409       gclog_or_tty->print(
 410         " CMSCollector: collect because of anticipated promotion "
 411         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 412         gc0_period(), time_until_cms_gen_full());
 413     }
 414     return 0.0;
 415   }
 416   return work - deadline;
 417 }
 418 
 419 #ifndef PRODUCT
 420 void CMSStats::print_on(outputStream *st) const {
 421   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 422   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 423                gc0_duration(), gc0_period(), gc0_promoted());
 424   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 425             cms_duration(), cms_period(), cms_allocated());
 426   st->print(",cms_since_beg=%g,cms_since_end=%g",
 427             cms_time_since_begin(), cms_time_since_end());
 428   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 429             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 430 
 431   if (valid()) {
 432     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 433               promotion_rate(), cms_allocation_rate());
 434     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 435               cms_consumption_rate(), time_until_cms_gen_full());
 436   }
 437   st->print(" ");
 438 }
 439 #endif // #ifndef PRODUCT
 440 
 441 CMSCollector::CollectorState CMSCollector::_collectorState =
 442                              CMSCollector::Idling;
 443 bool CMSCollector::_foregroundGCIsActive = false;
 444 bool CMSCollector::_foregroundGCShouldWait = false;
 445 
 446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 447                            CardTableRS*                   ct,
 448                            ConcurrentMarkSweepPolicy*     cp):
 449   _cmsGen(cmsGen),
 450   _ct(ct),
 451   _ref_processor(NULL),    // will be set later
 452   _conc_workers(NULL),     // may be set later
 453   _abort_preclean(false),
 454   _start_sampling(false),
 455   _between_prologue_and_epilogue(false),
 456   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 457   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 458                  -1 /* lock-free */, "No_lock" /* dummy */),
 459   _modUnionClosurePar(&_modUnionTable),
 460   // Adjust my span to cover old (cms) gen
 461   _span(cmsGen->reserved()),
 462   // Construct the is_alive_closure with _span & markBitMap
 463   _is_alive_closure(_span, &_markBitMap),
 464   _restart_addr(NULL),
 465   _overflow_list(NULL),
 466   _stats(cmsGen),
 467   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 468                              //verify that this lock should be acquired with safepoint check.
 469                              Monitor::_safepoint_check_sometimes)),
 470   _eden_chunk_array(NULL),     // may be set in ctor body
 471   _eden_chunk_capacity(0),     // -- ditto --
 472   _eden_chunk_index(0),        // -- ditto --
 473   _survivor_plab_array(NULL),  // -- ditto --
 474   _survivor_chunk_array(NULL), // -- ditto --
 475   _survivor_chunk_capacity(0), // -- ditto --
 476   _survivor_chunk_index(0),    // -- ditto --
 477   _ser_pmc_preclean_ovflw(0),
 478   _ser_kac_preclean_ovflw(0),
 479   _ser_pmc_remark_ovflw(0),
 480   _par_pmc_remark_ovflw(0),
 481   _ser_kac_ovflw(0),
 482   _par_kac_ovflw(0),
 483 #ifndef PRODUCT
 484   _num_par_pushes(0),
 485 #endif
 486   _collection_count_start(0),
 487   _verifying(false),
 488   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 489   _completed_initialization(false),
 490   _collector_policy(cp),
 491   _should_unload_classes(CMSClassUnloadingEnabled),
 492   _concurrent_cycles_since_last_unload(0),
 493   _roots_scanning_options(GenCollectedHeap::SO_None),
 494   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 495   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 496   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 497   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 498   _cms_start_registered(false)
 499 {
 500   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 501     ExplicitGCInvokesConcurrent = true;
 502   }
 503   // Now expand the span and allocate the collection support structures
 504   // (MUT, marking bit map etc.) to cover both generations subject to
 505   // collection.
 506 
 507   // For use by dirty card to oop closures.
 508   _cmsGen->cmsSpace()->set_collector(this);
 509 
 510   // Allocate MUT and marking bit map
 511   {
 512     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 513     if (!_markBitMap.allocate(_span)) {
 514       warning("Failed to allocate CMS Bit Map");
 515       return;
 516     }
 517     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 518   }
 519   {
 520     _modUnionTable.allocate(_span);
 521     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 522   }
 523 
 524   if (!_markStack.allocate(MarkStackSize)) {
 525     warning("Failed to allocate CMS Marking Stack");
 526     return;
 527   }
 528 
 529   // Support for multi-threaded concurrent phases
 530   if (CMSConcurrentMTEnabled) {
 531     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 532       // just for now
 533       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 534     }
 535     if (ConcGCThreads > 1) {
 536       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 537                                  ConcGCThreads, true);
 538       if (_conc_workers == NULL) {
 539         warning("GC/CMS: _conc_workers allocation failure: "
 540               "forcing -CMSConcurrentMTEnabled");
 541         CMSConcurrentMTEnabled = false;
 542       } else {
 543         _conc_workers->initialize_workers();
 544       }
 545     } else {
 546       CMSConcurrentMTEnabled = false;
 547     }
 548   }
 549   if (!CMSConcurrentMTEnabled) {
 550     ConcGCThreads = 0;
 551   } else {
 552     // Turn off CMSCleanOnEnter optimization temporarily for
 553     // the MT case where it's not fixed yet; see 6178663.
 554     CMSCleanOnEnter = false;
 555   }
 556   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 557          "Inconsistency");
 558 
 559   // Parallel task queues; these are shared for the
 560   // concurrent and stop-world phases of CMS, but
 561   // are not shared with parallel scavenge (ParNew).
 562   {
 563     uint i;
 564     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 565 
 566     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 567          || ParallelRefProcEnabled)
 568         && num_queues > 0) {
 569       _task_queues = new OopTaskQueueSet(num_queues);
 570       if (_task_queues == NULL) {
 571         warning("task_queues allocation failure.");
 572         return;
 573       }
 574       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 575       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 576       for (i = 0; i < num_queues; i++) {
 577         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 578         if (q == NULL) {
 579           warning("work_queue allocation failure.");
 580           return;
 581         }
 582         _task_queues->register_queue(i, q);
 583       }
 584       for (i = 0; i < num_queues; i++) {
 585         _task_queues->queue(i)->initialize();
 586         _hash_seed[i] = 17;  // copied from ParNew
 587       }
 588     }
 589   }
 590 
 591   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 592 
 593   // Clip CMSBootstrapOccupancy between 0 and 100.
 594   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 595 
 596   // Now tell CMS generations the identity of their collector
 597   ConcurrentMarkSweepGeneration::set_collector(this);
 598 
 599   // Create & start a CMS thread for this CMS collector
 600   _cmsThread = ConcurrentMarkSweepThread::start(this);
 601   assert(cmsThread() != NULL, "CMS Thread should have been created");
 602   assert(cmsThread()->collector() == this,
 603          "CMS Thread should refer to this gen");
 604   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 605 
 606   // Support for parallelizing young gen rescan
 607   GenCollectedHeap* gch = GenCollectedHeap::heap();
 608   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 609   _young_gen = (ParNewGeneration*)gch->young_gen();
 610   if (gch->supports_inline_contig_alloc()) {
 611     _top_addr = gch->top_addr();
 612     _end_addr = gch->end_addr();
 613     assert(_young_gen != NULL, "no _young_gen");
 614     _eden_chunk_index = 0;
 615     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 616     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 617   }
 618 
 619   // Support for parallelizing survivor space rescan
 620   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 621     const size_t max_plab_samples =
 622       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 623 
 624     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 625     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 626     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 627     _survivor_chunk_capacity = max_plab_samples;
 628     for (uint i = 0; i < ParallelGCThreads; i++) {
 629       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 630       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 631       assert(cur->end() == 0, "Should be 0");
 632       assert(cur->array() == vec, "Should be vec");
 633       assert(cur->capacity() == max_plab_samples, "Error");
 634     }
 635   }
 636 
 637   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 638   _gc_counters = new CollectorCounters("CMS", 1);
 639   _completed_initialization = true;
 640   _inter_sweep_timer.start();  // start of time
 641 }
 642 
 643 const char* ConcurrentMarkSweepGeneration::name() const {
 644   return "concurrent mark-sweep generation";
 645 }
 646 void ConcurrentMarkSweepGeneration::update_counters() {
 647   if (UsePerfData) {
 648     _space_counters->update_all();
 649     _gen_counters->update_all();
 650   }
 651 }
 652 
 653 // this is an optimized version of update_counters(). it takes the
 654 // used value as a parameter rather than computing it.
 655 //
 656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 657   if (UsePerfData) {
 658     _space_counters->update_used(used);
 659     _space_counters->update_capacity();
 660     _gen_counters->update_all();
 661   }
 662 }
 663 
 664 void ConcurrentMarkSweepGeneration::print() const {
 665   Generation::print();
 666   cmsSpace()->print();
 667 }
 668 
 669 #ifndef PRODUCT
 670 void ConcurrentMarkSweepGeneration::print_statistics() {
 671   cmsSpace()->printFLCensus(0);
 672 }
 673 #endif
 674 
 675 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 676   GenCollectedHeap* gch = GenCollectedHeap::heap();
 677   if (PrintGCDetails) {
 678     // I didn't want to change the logging when removing the level concept,
 679     // but I guess this logging could say "old" or something instead of "1".
 680     assert(gch->is_old_gen(this),
 681            "The CMS generation should be the old generation");
 682     uint level = 1;
 683     if (Verbose) {
 684       gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
 685         level, short_name(), s, used(), capacity());
 686     } else {
 687       gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
 688         level, short_name(), s, used() / K, capacity() / K);
 689     }
 690   }
 691   if (Verbose) {
 692     gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
 693               gch->used(), gch->capacity());
 694   } else {
 695     gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
 696               gch->used() / K, gch->capacity() / K);
 697   }
 698 }
 699 
 700 size_t
 701 ConcurrentMarkSweepGeneration::contiguous_available() const {
 702   // dld proposes an improvement in precision here. If the committed
 703   // part of the space ends in a free block we should add that to
 704   // uncommitted size in the calculation below. Will make this
 705   // change later, staying with the approximation below for the
 706   // time being. -- ysr.
 707   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 708 }
 709 
 710 size_t
 711 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 712   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 713 }
 714 
 715 size_t ConcurrentMarkSweepGeneration::max_available() const {
 716   return free() + _virtual_space.uncommitted_size();
 717 }
 718 
 719 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 720   size_t available = max_available();
 721   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 722   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 723   if (Verbose && PrintGCDetails) {
 724     gclog_or_tty->print_cr(
 725       "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
 726       "max_promo(" SIZE_FORMAT ")",
 727       res? "":" not", available, res? ">=":"<",
 728       av_promo, max_promotion_in_bytes);
 729   }
 730   return res;
 731 }
 732 
 733 // At a promotion failure dump information on block layout in heap
 734 // (cms old generation).
 735 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 736   if (CMSDumpAtPromotionFailure) {
 737     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 738   }
 739 }
 740 
 741 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 742   // Clear the promotion information.  These pointers can be adjusted
 743   // along with all the other pointers into the heap but
 744   // compaction is expected to be a rare event with
 745   // a heap using cms so don't do it without seeing the need.
 746   for (uint i = 0; i < ParallelGCThreads; i++) {
 747     _par_gc_thread_states[i]->promo.reset();
 748   }
 749 }
 750 
 751 void ConcurrentMarkSweepGeneration::compute_new_size() {
 752   assert_locked_or_safepoint(Heap_lock);
 753 
 754   // If incremental collection failed, we just want to expand
 755   // to the limit.
 756   if (incremental_collection_failed()) {
 757     clear_incremental_collection_failed();
 758     grow_to_reserved();
 759     return;
 760   }
 761 
 762   // The heap has been compacted but not reset yet.
 763   // Any metric such as free() or used() will be incorrect.
 764 
 765   CardGeneration::compute_new_size();
 766 
 767   // Reset again after a possible resizing
 768   if (did_compact()) {
 769     cmsSpace()->reset_after_compaction();
 770   }
 771 }
 772 
 773 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 774   assert_locked_or_safepoint(Heap_lock);
 775 
 776   // If incremental collection failed, we just want to expand
 777   // to the limit.
 778   if (incremental_collection_failed()) {
 779     clear_incremental_collection_failed();
 780     grow_to_reserved();
 781     return;
 782   }
 783 
 784   double free_percentage = ((double) free()) / capacity();
 785   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 786   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 787 
 788   // compute expansion delta needed for reaching desired free percentage
 789   if (free_percentage < desired_free_percentage) {
 790     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 791     assert(desired_capacity >= capacity(), "invalid expansion size");
 792     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 793     if (PrintGCDetails && Verbose) {
 794       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 795       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 796       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 797       gclog_or_tty->print_cr("  Desired free fraction %f", desired_free_percentage);
 798       gclog_or_tty->print_cr("  Maximum free fraction %f", maximum_free_percentage);
 799       gclog_or_tty->print_cr("  Capacity " SIZE_FORMAT, capacity() / 1000);
 800       gclog_or_tty->print_cr("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 801       GenCollectedHeap* gch = GenCollectedHeap::heap();
 802       assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
 803       size_t young_size = gch->young_gen()->capacity();
 804       gclog_or_tty->print_cr("  Young gen size " SIZE_FORMAT, young_size / 1000);
 805       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 806       gclog_or_tty->print_cr("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 807       gclog_or_tty->print_cr("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 808     }
 809     // safe if expansion fails
 810     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 811     if (PrintGCDetails && Verbose) {
 812       gclog_or_tty->print_cr("  Expanded free fraction %f", ((double) free()) / capacity());
 813     }
 814   } else {
 815     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 816     assert(desired_capacity <= capacity(), "invalid expansion size");
 817     size_t shrink_bytes = capacity() - desired_capacity;
 818     // Don't shrink unless the delta is greater than the minimum shrink we want
 819     if (shrink_bytes >= MinHeapDeltaBytes) {
 820       shrink_free_list_by(shrink_bytes);
 821     }
 822   }
 823 }
 824 
 825 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 826   return cmsSpace()->freelistLock();
 827 }
 828 
 829 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 830   CMSSynchronousYieldRequest yr;
 831   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 832   return have_lock_and_allocate(size, tlab);
 833 }
 834 
 835 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 836                                                                 bool   tlab /* ignored */) {
 837   assert_lock_strong(freelistLock());
 838   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 839   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 840   // Allocate the object live (grey) if the background collector has
 841   // started marking. This is necessary because the marker may
 842   // have passed this address and consequently this object will
 843   // not otherwise be greyed and would be incorrectly swept up.
 844   // Note that if this object contains references, the writing
 845   // of those references will dirty the card containing this object
 846   // allowing the object to be blackened (and its references scanned)
 847   // either during a preclean phase or at the final checkpoint.
 848   if (res != NULL) {
 849     // We may block here with an uninitialized object with
 850     // its mark-bit or P-bits not yet set. Such objects need
 851     // to be safely navigable by block_start().
 852     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 853     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 854     collector()->direct_allocated(res, adjustedSize);
 855     _direct_allocated_words += adjustedSize;
 856     // allocation counters
 857     NOT_PRODUCT(
 858       _numObjectsAllocated++;
 859       _numWordsAllocated += (int)adjustedSize;
 860     )
 861   }
 862   return res;
 863 }
 864 
 865 // In the case of direct allocation by mutators in a generation that
 866 // is being concurrently collected, the object must be allocated
 867 // live (grey) if the background collector has started marking.
 868 // This is necessary because the marker may
 869 // have passed this address and consequently this object will
 870 // not otherwise be greyed and would be incorrectly swept up.
 871 // Note that if this object contains references, the writing
 872 // of those references will dirty the card containing this object
 873 // allowing the object to be blackened (and its references scanned)
 874 // either during a preclean phase or at the final checkpoint.
 875 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 876   assert(_markBitMap.covers(start, size), "Out of bounds");
 877   if (_collectorState >= Marking) {
 878     MutexLockerEx y(_markBitMap.lock(),
 879                     Mutex::_no_safepoint_check_flag);
 880     // [see comments preceding SweepClosure::do_blk() below for details]
 881     //
 882     // Can the P-bits be deleted now?  JJJ
 883     //
 884     // 1. need to mark the object as live so it isn't collected
 885     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 886     // 3. need to mark the end of the object so marking, precleaning or sweeping
 887     //    can skip over uninitialized or unparsable objects. An allocated
 888     //    object is considered uninitialized for our purposes as long as
 889     //    its klass word is NULL.  All old gen objects are parsable
 890     //    as soon as they are initialized.)
 891     _markBitMap.mark(start);          // object is live
 892     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 893     _markBitMap.mark(start + size - 1);
 894                                       // mark end of object
 895   }
 896   // check that oop looks uninitialized
 897   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 898 }
 899 
 900 void CMSCollector::promoted(bool par, HeapWord* start,
 901                             bool is_obj_array, size_t obj_size) {
 902   assert(_markBitMap.covers(start), "Out of bounds");
 903   // See comment in direct_allocated() about when objects should
 904   // be allocated live.
 905   if (_collectorState >= Marking) {
 906     // we already hold the marking bit map lock, taken in
 907     // the prologue
 908     if (par) {
 909       _markBitMap.par_mark(start);
 910     } else {
 911       _markBitMap.mark(start);
 912     }
 913     // We don't need to mark the object as uninitialized (as
 914     // in direct_allocated above) because this is being done with the
 915     // world stopped and the object will be initialized by the
 916     // time the marking, precleaning or sweeping get to look at it.
 917     // But see the code for copying objects into the CMS generation,
 918     // where we need to ensure that concurrent readers of the
 919     // block offset table are able to safely navigate a block that
 920     // is in flux from being free to being allocated (and in
 921     // transition while being copied into) and subsequently
 922     // becoming a bona-fide object when the copy/promotion is complete.
 923     assert(SafepointSynchronize::is_at_safepoint(),
 924            "expect promotion only at safepoints");
 925 
 926     if (_collectorState < Sweeping) {
 927       // Mark the appropriate cards in the modUnionTable, so that
 928       // this object gets scanned before the sweep. If this is
 929       // not done, CMS generation references in the object might
 930       // not get marked.
 931       // For the case of arrays, which are otherwise precisely
 932       // marked, we need to dirty the entire array, not just its head.
 933       if (is_obj_array) {
 934         // The [par_]mark_range() method expects mr.end() below to
 935         // be aligned to the granularity of a bit's representation
 936         // in the heap. In the case of the MUT below, that's a
 937         // card size.
 938         MemRegion mr(start,
 939                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 940                         CardTableModRefBS::card_size /* bytes */));
 941         if (par) {
 942           _modUnionTable.par_mark_range(mr);
 943         } else {
 944           _modUnionTable.mark_range(mr);
 945         }
 946       } else {  // not an obj array; we can just mark the head
 947         if (par) {
 948           _modUnionTable.par_mark(start);
 949         } else {
 950           _modUnionTable.mark(start);
 951         }
 952       }
 953     }
 954   }
 955 }
 956 
 957 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 958   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 959   // allocate, copy and if necessary update promoinfo --
 960   // delegate to underlying space.
 961   assert_lock_strong(freelistLock());
 962 
 963 #ifndef PRODUCT
 964   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 965     return NULL;
 966   }
 967 #endif  // #ifndef PRODUCT
 968 
 969   oop res = _cmsSpace->promote(obj, obj_size);
 970   if (res == NULL) {
 971     // expand and retry
 972     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 973     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 974     // Since this is the old generation, we don't try to promote
 975     // into a more senior generation.
 976     res = _cmsSpace->promote(obj, obj_size);
 977   }
 978   if (res != NULL) {
 979     // See comment in allocate() about when objects should
 980     // be allocated live.
 981     assert(obj->is_oop(), "Will dereference klass pointer below");
 982     collector()->promoted(false,           // Not parallel
 983                           (HeapWord*)res, obj->is_objArray(), obj_size);
 984     // promotion counters
 985     NOT_PRODUCT(
 986       _numObjectsPromoted++;
 987       _numWordsPromoted +=
 988         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 989     )
 990   }
 991   return res;
 992 }
 993 
 994 
 995 // IMPORTANT: Notes on object size recognition in CMS.
 996 // ---------------------------------------------------
 997 // A block of storage in the CMS generation is always in
 998 // one of three states. A free block (FREE), an allocated
 999 // object (OBJECT) whose size() method reports the correct size,
1000 // and an intermediate state (TRANSIENT) in which its size cannot
1001 // be accurately determined.
1002 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1003 // -----------------------------------------------------
1004 // FREE:      klass_word & 1 == 1; mark_word holds block size
1005 //
1006 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1007 //            obj->size() computes correct size
1008 //
1009 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1010 //
1011 // STATE IDENTIFICATION: (64 bit+COOPS)
1012 // ------------------------------------
1013 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1014 //
1015 // OBJECT:    klass_word installed; klass_word != 0;
1016 //            obj->size() computes correct size
1017 //
1018 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1019 //
1020 //
1021 // STATE TRANSITION DIAGRAM
1022 //
1023 //        mut / parnew                     mut  /  parnew
1024 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1025 //  ^                                                                   |
1026 //  |------------------------ DEAD <------------------------------------|
1027 //         sweep                            mut
1028 //
1029 // While a block is in TRANSIENT state its size cannot be determined
1030 // so readers will either need to come back later or stall until
1031 // the size can be determined. Note that for the case of direct
1032 // allocation, P-bits, when available, may be used to determine the
1033 // size of an object that may not yet have been initialized.
1034 
1035 // Things to support parallel young-gen collection.
1036 oop
1037 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1038                                            oop old, markOop m,
1039                                            size_t word_sz) {
1040 #ifndef PRODUCT
1041   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1042     return NULL;
1043   }
1044 #endif  // #ifndef PRODUCT
1045 
1046   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1047   PromotionInfo* promoInfo = &ps->promo;
1048   // if we are tracking promotions, then first ensure space for
1049   // promotion (including spooling space for saving header if necessary).
1050   // then allocate and copy, then track promoted info if needed.
1051   // When tracking (see PromotionInfo::track()), the mark word may
1052   // be displaced and in this case restoration of the mark word
1053   // occurs in the (oop_since_save_marks_)iterate phase.
1054   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1055     // Out of space for allocating spooling buffers;
1056     // try expanding and allocating spooling buffers.
1057     if (!expand_and_ensure_spooling_space(promoInfo)) {
1058       return NULL;
1059     }
1060   }
1061   assert(promoInfo->has_spooling_space(), "Control point invariant");
1062   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1063   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1064   if (obj_ptr == NULL) {
1065      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1066      if (obj_ptr == NULL) {
1067        return NULL;
1068      }
1069   }
1070   oop obj = oop(obj_ptr);
1071   OrderAccess::storestore();
1072   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074   // IMPORTANT: See note on object initialization for CMS above.
1075   // Otherwise, copy the object.  Here we must be careful to insert the
1076   // klass pointer last, since this marks the block as an allocated object.
1077   // Except with compressed oops it's the mark word.
1078   HeapWord* old_ptr = (HeapWord*)old;
1079   // Restore the mark word copied above.
1080   obj->set_mark(m);
1081   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083   OrderAccess::storestore();
1084 
1085   if (UseCompressedClassPointers) {
1086     // Copy gap missed by (aligned) header size calculation below
1087     obj->set_klass_gap(old->klass_gap());
1088   }
1089   if (word_sz > (size_t)oopDesc::header_size()) {
1090     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1091                                  obj_ptr + oopDesc::header_size(),
1092                                  word_sz - oopDesc::header_size());
1093   }
1094 
1095   // Now we can track the promoted object, if necessary.  We take care
1096   // to delay the transition from uninitialized to full object
1097   // (i.e., insertion of klass pointer) until after, so that it
1098   // atomically becomes a promoted object.
1099   if (promoInfo->tracking()) {
1100     promoInfo->track((PromotedObject*)obj, old->klass());
1101   }
1102   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1103   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1104   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1105 
1106   // Finally, install the klass pointer (this should be volatile).
1107   OrderAccess::storestore();
1108   obj->set_klass(old->klass());
1109   // We should now be able to calculate the right size for this object
1110   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1111 
1112   collector()->promoted(true,          // parallel
1113                         obj_ptr, old->is_objArray(), word_sz);
1114 
1115   NOT_PRODUCT(
1116     Atomic::inc_ptr(&_numObjectsPromoted);
1117     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1118   )
1119 
1120   return obj;
1121 }
1122 
1123 void
1124 ConcurrentMarkSweepGeneration::
1125 par_promote_alloc_done(int thread_num) {
1126   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1127   ps->lab.retire(thread_num);
1128 }
1129 
1130 void
1131 ConcurrentMarkSweepGeneration::
1132 par_oop_since_save_marks_iterate_done(int thread_num) {
1133   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1134   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1135   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1136 }
1137 
1138 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1139                                                    size_t size,
1140                                                    bool   tlab)
1141 {
1142   // We allow a STW collection only if a full
1143   // collection was requested.
1144   return full || should_allocate(size, tlab); // FIX ME !!!
1145   // This and promotion failure handling are connected at the
1146   // hip and should be fixed by untying them.
1147 }
1148 
1149 bool CMSCollector::shouldConcurrentCollect() {
1150   if (_full_gc_requested) {
1151     if (Verbose && PrintGCDetails) {
1152       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1153                              " gc request (or gc_locker)");
1154     }
1155     return true;
1156   }
1157 
1158   FreelistLocker x(this);
1159   // ------------------------------------------------------------------
1160   // Print out lots of information which affects the initiation of
1161   // a collection.
1162   if (PrintCMSInitiationStatistics && stats().valid()) {
1163     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1164     gclog_or_tty->stamp();
1165     gclog_or_tty->cr();
1166     stats().print_on(gclog_or_tty);
1167     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1168       stats().time_until_cms_gen_full());
1169     gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1170     gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1171                            _cmsGen->contiguous_available());
1172     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1173     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1174     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1175     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1176     gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1177     gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1178     gclog_or_tty->print_cr("metadata initialized %d",
1179       MetaspaceGC::should_concurrent_collect());
1180   }
1181   // ------------------------------------------------------------------
1182 
1183   // If the estimated time to complete a cms collection (cms_duration())
1184   // is less than the estimated time remaining until the cms generation
1185   // is full, start a collection.
1186   if (!UseCMSInitiatingOccupancyOnly) {
1187     if (stats().valid()) {
1188       if (stats().time_until_cms_start() == 0.0) {
1189         return true;
1190       }
1191     } else {
1192       // We want to conservatively collect somewhat early in order
1193       // to try and "bootstrap" our CMS/promotion statistics;
1194       // this branch will not fire after the first successful CMS
1195       // collection because the stats should then be valid.
1196       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1197         if (Verbose && PrintGCDetails) {
1198           gclog_or_tty->print_cr(
1199             " CMSCollector: collect for bootstrapping statistics:"
1200             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1201             _bootstrap_occupancy);
1202         }
1203         return true;
1204       }
1205     }
1206   }
1207 
1208   // Otherwise, we start a collection cycle if
1209   // old gen want a collection cycle started. Each may use
1210   // an appropriate criterion for making this decision.
1211   // XXX We need to make sure that the gen expansion
1212   // criterion dovetails well with this. XXX NEED TO FIX THIS
1213   if (_cmsGen->should_concurrent_collect()) {
1214     if (Verbose && PrintGCDetails) {
1215       gclog_or_tty->print_cr("CMS old gen initiated");
1216     }
1217     return true;
1218   }
1219 
1220   // We start a collection if we believe an incremental collection may fail;
1221   // this is not likely to be productive in practice because it's probably too
1222   // late anyway.
1223   GenCollectedHeap* gch = GenCollectedHeap::heap();
1224   assert(gch->collector_policy()->is_generation_policy(),
1225          "You may want to check the correctness of the following");
1226   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1227     if (Verbose && PrintGCDetails) {
1228       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1229     }
1230     return true;
1231   }
1232 
1233   if (MetaspaceGC::should_concurrent_collect()) {
1234     if (Verbose && PrintGCDetails) {
1235       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1236     }
1237     return true;
1238   }
1239 
1240   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1241   if (CMSTriggerInterval >= 0) {
1242     if (CMSTriggerInterval == 0) {
1243       // Trigger always
1244       return true;
1245     }
1246 
1247     // Check the CMS time since begin (we do not check the stats validity
1248     // as we want to be able to trigger the first CMS cycle as well)
1249     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1250       if (Verbose && PrintGCDetails) {
1251         if (stats().valid()) {
1252           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1253                                  stats().cms_time_since_begin());
1254         } else {
1255           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1256         }
1257       }
1258       return true;
1259     }
1260   }
1261 
1262   return false;
1263 }
1264 
1265 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1266 
1267 // Clear _expansion_cause fields of constituent generations
1268 void CMSCollector::clear_expansion_cause() {
1269   _cmsGen->clear_expansion_cause();
1270 }
1271 
1272 // We should be conservative in starting a collection cycle.  To
1273 // start too eagerly runs the risk of collecting too often in the
1274 // extreme.  To collect too rarely falls back on full collections,
1275 // which works, even if not optimum in terms of concurrent work.
1276 // As a work around for too eagerly collecting, use the flag
1277 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1278 // giving the user an easily understandable way of controlling the
1279 // collections.
1280 // We want to start a new collection cycle if any of the following
1281 // conditions hold:
1282 // . our current occupancy exceeds the configured initiating occupancy
1283 //   for this generation, or
1284 // . we recently needed to expand this space and have not, since that
1285 //   expansion, done a collection of this generation, or
1286 // . the underlying space believes that it may be a good idea to initiate
1287 //   a concurrent collection (this may be based on criteria such as the
1288 //   following: the space uses linear allocation and linear allocation is
1289 //   going to fail, or there is believed to be excessive fragmentation in
1290 //   the generation, etc... or ...
1291 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1292 //   the case of the old generation; see CR 6543076):
1293 //   we may be approaching a point at which allocation requests may fail because
1294 //   we will be out of sufficient free space given allocation rate estimates.]
1295 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1296 
1297   assert_lock_strong(freelistLock());
1298   if (occupancy() > initiating_occupancy()) {
1299     if (PrintGCDetails && Verbose) {
1300       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1301         short_name(), occupancy(), initiating_occupancy());
1302     }
1303     return true;
1304   }
1305   if (UseCMSInitiatingOccupancyOnly) {
1306     return false;
1307   }
1308   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1309     if (PrintGCDetails && Verbose) {
1310       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1311         short_name());
1312     }
1313     return true;
1314   }
1315   if (_cmsSpace->should_concurrent_collect()) {
1316     if (PrintGCDetails && Verbose) {
1317       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1318         short_name());
1319     }
1320     return true;
1321   }
1322   return false;
1323 }
1324 
1325 void ConcurrentMarkSweepGeneration::collect(bool   full,
1326                                             bool   clear_all_soft_refs,
1327                                             size_t size,
1328                                             bool   tlab)
1329 {
1330   collector()->collect(full, clear_all_soft_refs, size, tlab);
1331 }
1332 
1333 void CMSCollector::collect(bool   full,
1334                            bool   clear_all_soft_refs,
1335                            size_t size,
1336                            bool   tlab)
1337 {
1338   // The following "if" branch is present for defensive reasons.
1339   // In the current uses of this interface, it can be replaced with:
1340   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1341   // But I am not placing that assert here to allow future
1342   // generality in invoking this interface.
1343   if (GC_locker::is_active()) {
1344     // A consistency test for GC_locker
1345     assert(GC_locker::needs_gc(), "Should have been set already");
1346     // Skip this foreground collection, instead
1347     // expanding the heap if necessary.
1348     // Need the free list locks for the call to free() in compute_new_size()
1349     compute_new_size();
1350     return;
1351   }
1352   acquire_control_and_collect(full, clear_all_soft_refs);
1353 }
1354 
1355 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1356   GenCollectedHeap* gch = GenCollectedHeap::heap();
1357   unsigned int gc_count = gch->total_full_collections();
1358   if (gc_count == full_gc_count) {
1359     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1360     _full_gc_requested = true;
1361     _full_gc_cause = cause;
1362     CGC_lock->notify();   // nudge CMS thread
1363   } else {
1364     assert(gc_count > full_gc_count, "Error: causal loop");
1365   }
1366 }
1367 
1368 bool CMSCollector::is_external_interruption() {
1369   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1370   return GCCause::is_user_requested_gc(cause) ||
1371          GCCause::is_serviceability_requested_gc(cause);
1372 }
1373 
1374 void CMSCollector::report_concurrent_mode_interruption() {
1375   if (is_external_interruption()) {
1376     if (PrintGCDetails) {
1377       gclog_or_tty->print(" (concurrent mode interrupted)");
1378     }
1379   } else {
1380     if (PrintGCDetails) {
1381       gclog_or_tty->print(" (concurrent mode failure)");
1382     }
1383     _gc_tracer_cm->report_concurrent_mode_failure();
1384   }
1385 }
1386 
1387 
1388 // The foreground and background collectors need to coordinate in order
1389 // to make sure that they do not mutually interfere with CMS collections.
1390 // When a background collection is active,
1391 // the foreground collector may need to take over (preempt) and
1392 // synchronously complete an ongoing collection. Depending on the
1393 // frequency of the background collections and the heap usage
1394 // of the application, this preemption can be seldom or frequent.
1395 // There are only certain
1396 // points in the background collection that the "collection-baton"
1397 // can be passed to the foreground collector.
1398 //
1399 // The foreground collector will wait for the baton before
1400 // starting any part of the collection.  The foreground collector
1401 // will only wait at one location.
1402 //
1403 // The background collector will yield the baton before starting a new
1404 // phase of the collection (e.g., before initial marking, marking from roots,
1405 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1406 // of the loop which switches the phases. The background collector does some
1407 // of the phases (initial mark, final re-mark) with the world stopped.
1408 // Because of locking involved in stopping the world,
1409 // the foreground collector should not block waiting for the background
1410 // collector when it is doing a stop-the-world phase.  The background
1411 // collector will yield the baton at an additional point just before
1412 // it enters a stop-the-world phase.  Once the world is stopped, the
1413 // background collector checks the phase of the collection.  If the
1414 // phase has not changed, it proceeds with the collection.  If the
1415 // phase has changed, it skips that phase of the collection.  See
1416 // the comments on the use of the Heap_lock in collect_in_background().
1417 //
1418 // Variable used in baton passing.
1419 //   _foregroundGCIsActive - Set to true by the foreground collector when
1420 //      it wants the baton.  The foreground clears it when it has finished
1421 //      the collection.
1422 //   _foregroundGCShouldWait - Set to true by the background collector
1423 //        when it is running.  The foreground collector waits while
1424 //      _foregroundGCShouldWait is true.
1425 //  CGC_lock - monitor used to protect access to the above variables
1426 //      and to notify the foreground and background collectors.
1427 //  _collectorState - current state of the CMS collection.
1428 //
1429 // The foreground collector
1430 //   acquires the CGC_lock
1431 //   sets _foregroundGCIsActive
1432 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1433 //     various locks acquired in preparation for the collection
1434 //     are released so as not to block the background collector
1435 //     that is in the midst of a collection
1436 //   proceeds with the collection
1437 //   clears _foregroundGCIsActive
1438 //   returns
1439 //
1440 // The background collector in a loop iterating on the phases of the
1441 //      collection
1442 //   acquires the CGC_lock
1443 //   sets _foregroundGCShouldWait
1444 //   if _foregroundGCIsActive is set
1445 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1446 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1447 //     and exits the loop.
1448 //   otherwise
1449 //     proceed with that phase of the collection
1450 //     if the phase is a stop-the-world phase,
1451 //       yield the baton once more just before enqueueing
1452 //       the stop-world CMS operation (executed by the VM thread).
1453 //   returns after all phases of the collection are done
1454 //
1455 
1456 void CMSCollector::acquire_control_and_collect(bool full,
1457         bool clear_all_soft_refs) {
1458   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1459   assert(!Thread::current()->is_ConcurrentGC_thread(),
1460          "shouldn't try to acquire control from self!");
1461 
1462   // Start the protocol for acquiring control of the
1463   // collection from the background collector (aka CMS thread).
1464   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1465          "VM thread should have CMS token");
1466   // Remember the possibly interrupted state of an ongoing
1467   // concurrent collection
1468   CollectorState first_state = _collectorState;
1469 
1470   // Signal to a possibly ongoing concurrent collection that
1471   // we want to do a foreground collection.
1472   _foregroundGCIsActive = true;
1473 
1474   // release locks and wait for a notify from the background collector
1475   // releasing the locks in only necessary for phases which
1476   // do yields to improve the granularity of the collection.
1477   assert_lock_strong(bitMapLock());
1478   // We need to lock the Free list lock for the space that we are
1479   // currently collecting.
1480   assert(haveFreelistLocks(), "Must be holding free list locks");
1481   bitMapLock()->unlock();
1482   releaseFreelistLocks();
1483   {
1484     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1485     if (_foregroundGCShouldWait) {
1486       // We are going to be waiting for action for the CMS thread;
1487       // it had better not be gone (for instance at shutdown)!
1488       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1489              "CMS thread must be running");
1490       // Wait here until the background collector gives us the go-ahead
1491       ConcurrentMarkSweepThread::clear_CMS_flag(
1492         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1493       // Get a possibly blocked CMS thread going:
1494       //   Note that we set _foregroundGCIsActive true above,
1495       //   without protection of the CGC_lock.
1496       CGC_lock->notify();
1497       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1498              "Possible deadlock");
1499       while (_foregroundGCShouldWait) {
1500         // wait for notification
1501         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1502         // Possibility of delay/starvation here, since CMS token does
1503         // not know to give priority to VM thread? Actually, i think
1504         // there wouldn't be any delay/starvation, but the proof of
1505         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1506       }
1507       ConcurrentMarkSweepThread::set_CMS_flag(
1508         ConcurrentMarkSweepThread::CMS_vm_has_token);
1509     }
1510   }
1511   // The CMS_token is already held.  Get back the other locks.
1512   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1513          "VM thread should have CMS token");
1514   getFreelistLocks();
1515   bitMapLock()->lock_without_safepoint_check();
1516   if (TraceCMSState) {
1517     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1518       INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1519     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1520   }
1521 
1522   // Inform cms gen if this was due to partial collection failing.
1523   // The CMS gen may use this fact to determine its expansion policy.
1524   GenCollectedHeap* gch = GenCollectedHeap::heap();
1525   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1526     assert(!_cmsGen->incremental_collection_failed(),
1527            "Should have been noticed, reacted to and cleared");
1528     _cmsGen->set_incremental_collection_failed();
1529   }
1530 
1531   if (first_state > Idling) {
1532     report_concurrent_mode_interruption();
1533   }
1534 
1535   set_did_compact(true);
1536 
1537   // If the collection is being acquired from the background
1538   // collector, there may be references on the discovered
1539   // references lists.  Abandon those references, since some
1540   // of them may have become unreachable after concurrent
1541   // discovery; the STW compacting collector will redo discovery
1542   // more precisely, without being subject to floating garbage.
1543   // Leaving otherwise unreachable references in the discovered
1544   // lists would require special handling.
1545   ref_processor()->disable_discovery();
1546   ref_processor()->abandon_partial_discovery();
1547   ref_processor()->verify_no_references_recorded();
1548 
1549   if (first_state > Idling) {
1550     save_heap_summary();
1551   }
1552 
1553   do_compaction_work(clear_all_soft_refs);
1554 
1555   // Has the GC time limit been exceeded?
1556   size_t max_eden_size = _young_gen->max_capacity() -
1557                          _young_gen->to()->capacity() -
1558                          _young_gen->from()->capacity();
1559   GCCause::Cause gc_cause = gch->gc_cause();
1560   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1561                                          _young_gen->eden()->used(),
1562                                          _cmsGen->max_capacity(),
1563                                          max_eden_size,
1564                                          full,
1565                                          gc_cause,
1566                                          gch->collector_policy());
1567 
1568   // Reset the expansion cause, now that we just completed
1569   // a collection cycle.
1570   clear_expansion_cause();
1571   _foregroundGCIsActive = false;
1572   return;
1573 }
1574 
1575 // Resize the tenured generation
1576 // after obtaining the free list locks for the
1577 // two generations.
1578 void CMSCollector::compute_new_size() {
1579   assert_locked_or_safepoint(Heap_lock);
1580   FreelistLocker z(this);
1581   MetaspaceGC::compute_new_size();
1582   _cmsGen->compute_new_size_free_list();
1583 }
1584 
1585 // A work method used by the foreground collector to do
1586 // a mark-sweep-compact.
1587 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1588   GenCollectedHeap* gch = GenCollectedHeap::heap();
1589 
1590   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1591   gc_timer->register_gc_start();
1592 
1593   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1594   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1595 
1596   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1597 
1598   // Temporarily widen the span of the weak reference processing to
1599   // the entire heap.
1600   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1601   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1602   // Temporarily, clear the "is_alive_non_header" field of the
1603   // reference processor.
1604   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1605   // Temporarily make reference _processing_ single threaded (non-MT).
1606   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1607   // Temporarily make refs discovery atomic
1608   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1609   // Temporarily make reference _discovery_ single threaded (non-MT)
1610   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1611 
1612   ref_processor()->set_enqueuing_is_done(false);
1613   ref_processor()->enable_discovery();
1614   ref_processor()->setup_policy(clear_all_soft_refs);
1615   // If an asynchronous collection finishes, the _modUnionTable is
1616   // all clear.  If we are assuming the collection from an asynchronous
1617   // collection, clear the _modUnionTable.
1618   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1619     "_modUnionTable should be clear if the baton was not passed");
1620   _modUnionTable.clear_all();
1621   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1622     "mod union for klasses should be clear if the baton was passed");
1623   _ct->klass_rem_set()->clear_mod_union();
1624 
1625   // We must adjust the allocation statistics being maintained
1626   // in the free list space. We do so by reading and clearing
1627   // the sweep timer and updating the block flux rate estimates below.
1628   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1629   if (_inter_sweep_timer.is_active()) {
1630     _inter_sweep_timer.stop();
1631     // Note that we do not use this sample to update the _inter_sweep_estimate.
1632     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1633                                             _inter_sweep_estimate.padded_average(),
1634                                             _intra_sweep_estimate.padded_average());
1635   }
1636 
1637   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1638   #ifdef ASSERT
1639     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1640     size_t free_size = cms_space->free();
1641     assert(free_size ==
1642            pointer_delta(cms_space->end(), cms_space->compaction_top())
1643            * HeapWordSize,
1644       "All the free space should be compacted into one chunk at top");
1645     assert(cms_space->dictionary()->total_chunk_size(
1646                                       debug_only(cms_space->freelistLock())) == 0 ||
1647            cms_space->totalSizeInIndexedFreeLists() == 0,
1648       "All the free space should be in a single chunk");
1649     size_t num = cms_space->totalCount();
1650     assert((free_size == 0 && num == 0) ||
1651            (free_size > 0  && (num == 1 || num == 2)),
1652          "There should be at most 2 free chunks after compaction");
1653   #endif // ASSERT
1654   _collectorState = Resetting;
1655   assert(_restart_addr == NULL,
1656          "Should have been NULL'd before baton was passed");
1657   reset(false /* == !concurrent */);
1658   _cmsGen->reset_after_compaction();
1659   _concurrent_cycles_since_last_unload = 0;
1660 
1661   // Clear any data recorded in the PLAB chunk arrays.
1662   if (_survivor_plab_array != NULL) {
1663     reset_survivor_plab_arrays();
1664   }
1665 
1666   // Adjust the per-size allocation stats for the next epoch.
1667   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1668   // Restart the "inter sweep timer" for the next epoch.
1669   _inter_sweep_timer.reset();
1670   _inter_sweep_timer.start();
1671 
1672   gc_timer->register_gc_end();
1673 
1674   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1675 
1676   // For a mark-sweep-compact, compute_new_size() will be called
1677   // in the heap's do_collection() method.
1678 }
1679 
1680 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1681   ContiguousSpace* eden_space = _young_gen->eden();
1682   ContiguousSpace* from_space = _young_gen->from();
1683   ContiguousSpace* to_space   = _young_gen->to();
1684   // Eden
1685   if (_eden_chunk_array != NULL) {
1686     gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1687                            p2i(eden_space->bottom()), p2i(eden_space->top()),
1688                            p2i(eden_space->end()), eden_space->capacity());
1689     gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1690                            "_eden_chunk_capacity=" SIZE_FORMAT,
1691                            _eden_chunk_index, _eden_chunk_capacity);
1692     for (size_t i = 0; i < _eden_chunk_index; i++) {
1693       gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1694                              i, p2i(_eden_chunk_array[i]));
1695     }
1696   }
1697   // Survivor
1698   if (_survivor_chunk_array != NULL) {
1699     gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1700                            p2i(from_space->bottom()), p2i(from_space->top()),
1701                            p2i(from_space->end()), from_space->capacity());
1702     gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1703                            "_survivor_chunk_capacity=" SIZE_FORMAT,
1704                            _survivor_chunk_index, _survivor_chunk_capacity);
1705     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1706       gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1707                              i, p2i(_survivor_chunk_array[i]));
1708     }
1709   }
1710 }
1711 
1712 void CMSCollector::getFreelistLocks() const {
1713   // Get locks for all free lists in all generations that this
1714   // collector is responsible for
1715   _cmsGen->freelistLock()->lock_without_safepoint_check();
1716 }
1717 
1718 void CMSCollector::releaseFreelistLocks() const {
1719   // Release locks for all free lists in all generations that this
1720   // collector is responsible for
1721   _cmsGen->freelistLock()->unlock();
1722 }
1723 
1724 bool CMSCollector::haveFreelistLocks() const {
1725   // Check locks for all free lists in all generations that this
1726   // collector is responsible for
1727   assert_lock_strong(_cmsGen->freelistLock());
1728   PRODUCT_ONLY(ShouldNotReachHere());
1729   return true;
1730 }
1731 
1732 // A utility class that is used by the CMS collector to
1733 // temporarily "release" the foreground collector from its
1734 // usual obligation to wait for the background collector to
1735 // complete an ongoing phase before proceeding.
1736 class ReleaseForegroundGC: public StackObj {
1737  private:
1738   CMSCollector* _c;
1739  public:
1740   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1741     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1742     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1743     // allow a potentially blocked foreground collector to proceed
1744     _c->_foregroundGCShouldWait = false;
1745     if (_c->_foregroundGCIsActive) {
1746       CGC_lock->notify();
1747     }
1748     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1749            "Possible deadlock");
1750   }
1751 
1752   ~ReleaseForegroundGC() {
1753     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1754     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1755     _c->_foregroundGCShouldWait = true;
1756   }
1757 };
1758 
1759 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1760   assert(Thread::current()->is_ConcurrentGC_thread(),
1761     "A CMS asynchronous collection is only allowed on a CMS thread.");
1762 
1763   GenCollectedHeap* gch = GenCollectedHeap::heap();
1764   {
1765     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1766     MutexLockerEx hl(Heap_lock, safepoint_check);
1767     FreelistLocker fll(this);
1768     MutexLockerEx x(CGC_lock, safepoint_check);
1769     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1770       // The foreground collector is active or we're
1771       // not using asynchronous collections.  Skip this
1772       // background collection.
1773       assert(!_foregroundGCShouldWait, "Should be clear");
1774       return;
1775     } else {
1776       assert(_collectorState == Idling, "Should be idling before start.");
1777       _collectorState = InitialMarking;
1778       register_gc_start(cause);
1779       // Reset the expansion cause, now that we are about to begin
1780       // a new cycle.
1781       clear_expansion_cause();
1782 
1783       // Clear the MetaspaceGC flag since a concurrent collection
1784       // is starting but also clear it after the collection.
1785       MetaspaceGC::set_should_concurrent_collect(false);
1786     }
1787     // Decide if we want to enable class unloading as part of the
1788     // ensuing concurrent GC cycle.
1789     update_should_unload_classes();
1790     _full_gc_requested = false;           // acks all outstanding full gc requests
1791     _full_gc_cause = GCCause::_no_gc;
1792     // Signal that we are about to start a collection
1793     gch->increment_total_full_collections();  // ... starting a collection cycle
1794     _collection_count_start = gch->total_full_collections();
1795   }
1796 
1797   // Used for PrintGC
1798   size_t prev_used;
1799   if (PrintGC && Verbose) {
1800     prev_used = _cmsGen->used();
1801   }
1802 
1803   // The change of the collection state is normally done at this level;
1804   // the exceptions are phases that are executed while the world is
1805   // stopped.  For those phases the change of state is done while the
1806   // world is stopped.  For baton passing purposes this allows the
1807   // background collector to finish the phase and change state atomically.
1808   // The foreground collector cannot wait on a phase that is done
1809   // while the world is stopped because the foreground collector already
1810   // has the world stopped and would deadlock.
1811   while (_collectorState != Idling) {
1812     if (TraceCMSState) {
1813       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1814         p2i(Thread::current()), _collectorState);
1815     }
1816     // The foreground collector
1817     //   holds the Heap_lock throughout its collection.
1818     //   holds the CMS token (but not the lock)
1819     //     except while it is waiting for the background collector to yield.
1820     //
1821     // The foreground collector should be blocked (not for long)
1822     //   if the background collector is about to start a phase
1823     //   executed with world stopped.  If the background
1824     //   collector has already started such a phase, the
1825     //   foreground collector is blocked waiting for the
1826     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1827     //   are executed in the VM thread.
1828     //
1829     // The locking order is
1830     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1831     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1832     //   CMS token  (claimed in
1833     //                stop_world_and_do() -->
1834     //                  safepoint_synchronize() -->
1835     //                    CMSThread::synchronize())
1836 
1837     {
1838       // Check if the FG collector wants us to yield.
1839       CMSTokenSync x(true); // is cms thread
1840       if (waitForForegroundGC()) {
1841         // We yielded to a foreground GC, nothing more to be
1842         // done this round.
1843         assert(_foregroundGCShouldWait == false, "We set it to false in "
1844                "waitForForegroundGC()");
1845         if (TraceCMSState) {
1846           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1847             " exiting collection CMS state %d",
1848             p2i(Thread::current()), _collectorState);
1849         }
1850         return;
1851       } else {
1852         // The background collector can run but check to see if the
1853         // foreground collector has done a collection while the
1854         // background collector was waiting to get the CGC_lock
1855         // above.  If yes, break so that _foregroundGCShouldWait
1856         // is cleared before returning.
1857         if (_collectorState == Idling) {
1858           break;
1859         }
1860       }
1861     }
1862 
1863     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1864       "should be waiting");
1865 
1866     switch (_collectorState) {
1867       case InitialMarking:
1868         {
1869           ReleaseForegroundGC x(this);
1870           stats().record_cms_begin();
1871           VM_CMS_Initial_Mark initial_mark_op(this);
1872           VMThread::execute(&initial_mark_op);
1873         }
1874         // The collector state may be any legal state at this point
1875         // since the background collector may have yielded to the
1876         // foreground collector.
1877         break;
1878       case Marking:
1879         // initial marking in checkpointRootsInitialWork has been completed
1880         if (markFromRoots()) { // we were successful
1881           assert(_collectorState == Precleaning, "Collector state should "
1882             "have changed");
1883         } else {
1884           assert(_foregroundGCIsActive, "Internal state inconsistency");
1885         }
1886         break;
1887       case Precleaning:
1888         // marking from roots in markFromRoots has been completed
1889         preclean();
1890         assert(_collectorState == AbortablePreclean ||
1891                _collectorState == FinalMarking,
1892                "Collector state should have changed");
1893         break;
1894       case AbortablePreclean:
1895         abortable_preclean();
1896         assert(_collectorState == FinalMarking, "Collector state should "
1897           "have changed");
1898         break;
1899       case FinalMarking:
1900         {
1901           ReleaseForegroundGC x(this);
1902 
1903           VM_CMS_Final_Remark final_remark_op(this);
1904           VMThread::execute(&final_remark_op);
1905         }
1906         assert(_foregroundGCShouldWait, "block post-condition");
1907         break;
1908       case Sweeping:
1909         // final marking in checkpointRootsFinal has been completed
1910         sweep();
1911         assert(_collectorState == Resizing, "Collector state change "
1912           "to Resizing must be done under the free_list_lock");
1913 
1914       case Resizing: {
1915         // Sweeping has been completed...
1916         // At this point the background collection has completed.
1917         // Don't move the call to compute_new_size() down
1918         // into code that might be executed if the background
1919         // collection was preempted.
1920         {
1921           ReleaseForegroundGC x(this);   // unblock FG collection
1922           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1923           CMSTokenSync        z(true);   // not strictly needed.
1924           if (_collectorState == Resizing) {
1925             compute_new_size();
1926             save_heap_summary();
1927             _collectorState = Resetting;
1928           } else {
1929             assert(_collectorState == Idling, "The state should only change"
1930                    " because the foreground collector has finished the collection");
1931           }
1932         }
1933         break;
1934       }
1935       case Resetting:
1936         // CMS heap resizing has been completed
1937         reset(true);
1938         assert(_collectorState == Idling, "Collector state should "
1939           "have changed");
1940 
1941         MetaspaceGC::set_should_concurrent_collect(false);
1942 
1943         stats().record_cms_end();
1944         // Don't move the concurrent_phases_end() and compute_new_size()
1945         // calls to here because a preempted background collection
1946         // has it's state set to "Resetting".
1947         break;
1948       case Idling:
1949       default:
1950         ShouldNotReachHere();
1951         break;
1952     }
1953     if (TraceCMSState) {
1954       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1955         p2i(Thread::current()), _collectorState);
1956     }
1957     assert(_foregroundGCShouldWait, "block post-condition");
1958   }
1959 
1960   // Should this be in gc_epilogue?
1961   collector_policy()->counters()->update_counters();
1962 
1963   {
1964     // Clear _foregroundGCShouldWait and, in the event that the
1965     // foreground collector is waiting, notify it, before
1966     // returning.
1967     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1968     _foregroundGCShouldWait = false;
1969     if (_foregroundGCIsActive) {
1970       CGC_lock->notify();
1971     }
1972     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1973            "Possible deadlock");
1974   }
1975   if (TraceCMSState) {
1976     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1977       " exiting collection CMS state %d",
1978       p2i(Thread::current()), _collectorState);
1979   }
1980   if (PrintGC && Verbose) {
1981     _cmsGen->print_heap_change(prev_used);
1982   }
1983 }
1984 
1985 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1986   _cms_start_registered = true;
1987   _gc_timer_cm->register_gc_start();
1988   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1989 }
1990 
1991 void CMSCollector::register_gc_end() {
1992   if (_cms_start_registered) {
1993     report_heap_summary(GCWhen::AfterGC);
1994 
1995     _gc_timer_cm->register_gc_end();
1996     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1997     _cms_start_registered = false;
1998   }
1999 }
2000 
2001 void CMSCollector::save_heap_summary() {
2002   GenCollectedHeap* gch = GenCollectedHeap::heap();
2003   _last_heap_summary = gch->create_heap_summary();
2004   _last_metaspace_summary = gch->create_metaspace_summary();
2005 }
2006 
2007 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2008   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2009   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2010 }
2011 
2012 bool CMSCollector::waitForForegroundGC() {
2013   bool res = false;
2014   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2015          "CMS thread should have CMS token");
2016   // Block the foreground collector until the
2017   // background collectors decides whether to
2018   // yield.
2019   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2020   _foregroundGCShouldWait = true;
2021   if (_foregroundGCIsActive) {
2022     // The background collector yields to the
2023     // foreground collector and returns a value
2024     // indicating that it has yielded.  The foreground
2025     // collector can proceed.
2026     res = true;
2027     _foregroundGCShouldWait = false;
2028     ConcurrentMarkSweepThread::clear_CMS_flag(
2029       ConcurrentMarkSweepThread::CMS_cms_has_token);
2030     ConcurrentMarkSweepThread::set_CMS_flag(
2031       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2032     // Get a possibly blocked foreground thread going
2033     CGC_lock->notify();
2034     if (TraceCMSState) {
2035       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2036         p2i(Thread::current()), _collectorState);
2037     }
2038     while (_foregroundGCIsActive) {
2039       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2040     }
2041     ConcurrentMarkSweepThread::set_CMS_flag(
2042       ConcurrentMarkSweepThread::CMS_cms_has_token);
2043     ConcurrentMarkSweepThread::clear_CMS_flag(
2044       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2045   }
2046   if (TraceCMSState) {
2047     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2048       p2i(Thread::current()), _collectorState);
2049   }
2050   return res;
2051 }
2052 
2053 // Because of the need to lock the free lists and other structures in
2054 // the collector, common to all the generations that the collector is
2055 // collecting, we need the gc_prologues of individual CMS generations
2056 // delegate to their collector. It may have been simpler had the
2057 // current infrastructure allowed one to call a prologue on a
2058 // collector. In the absence of that we have the generation's
2059 // prologue delegate to the collector, which delegates back
2060 // some "local" work to a worker method in the individual generations
2061 // that it's responsible for collecting, while itself doing any
2062 // work common to all generations it's responsible for. A similar
2063 // comment applies to the  gc_epilogue()'s.
2064 // The role of the variable _between_prologue_and_epilogue is to
2065 // enforce the invocation protocol.
2066 void CMSCollector::gc_prologue(bool full) {
2067   // Call gc_prologue_work() for the CMSGen
2068   // we are responsible for.
2069 
2070   // The following locking discipline assumes that we are only called
2071   // when the world is stopped.
2072   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2073 
2074   // The CMSCollector prologue must call the gc_prologues for the
2075   // "generations" that it's responsible
2076   // for.
2077 
2078   assert(   Thread::current()->is_VM_thread()
2079          || (   CMSScavengeBeforeRemark
2080              && Thread::current()->is_ConcurrentGC_thread()),
2081          "Incorrect thread type for prologue execution");
2082 
2083   if (_between_prologue_and_epilogue) {
2084     // We have already been invoked; this is a gc_prologue delegation
2085     // from yet another CMS generation that we are responsible for, just
2086     // ignore it since all relevant work has already been done.
2087     return;
2088   }
2089 
2090   // set a bit saying prologue has been called; cleared in epilogue
2091   _between_prologue_and_epilogue = true;
2092   // Claim locks for common data structures, then call gc_prologue_work()
2093   // for each CMSGen.
2094 
2095   getFreelistLocks();   // gets free list locks on constituent spaces
2096   bitMapLock()->lock_without_safepoint_check();
2097 
2098   // Should call gc_prologue_work() for all cms gens we are responsible for
2099   bool duringMarking =    _collectorState >= Marking
2100                          && _collectorState < Sweeping;
2101 
2102   // The young collections clear the modified oops state, which tells if
2103   // there are any modified oops in the class. The remark phase also needs
2104   // that information. Tell the young collection to save the union of all
2105   // modified klasses.
2106   if (duringMarking) {
2107     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2108   }
2109 
2110   bool registerClosure = duringMarking;
2111 
2112   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2113 
2114   if (!full) {
2115     stats().record_gc0_begin();
2116   }
2117 }
2118 
2119 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2120 
2121   _capacity_at_prologue = capacity();
2122   _used_at_prologue = used();
2123 
2124   // Delegate to CMScollector which knows how to coordinate between
2125   // this and any other CMS generations that it is responsible for
2126   // collecting.
2127   collector()->gc_prologue(full);
2128 }
2129 
2130 // This is a "private" interface for use by this generation's CMSCollector.
2131 // Not to be called directly by any other entity (for instance,
2132 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2133 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2134   bool registerClosure, ModUnionClosure* modUnionClosure) {
2135   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2136   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2137     "Should be NULL");
2138   if (registerClosure) {
2139     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2140   }
2141   cmsSpace()->gc_prologue();
2142   // Clear stat counters
2143   NOT_PRODUCT(
2144     assert(_numObjectsPromoted == 0, "check");
2145     assert(_numWordsPromoted   == 0, "check");
2146     if (Verbose && PrintGC) {
2147       gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2148                           SIZE_FORMAT " bytes concurrently",
2149       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2150     }
2151     _numObjectsAllocated = 0;
2152     _numWordsAllocated   = 0;
2153   )
2154 }
2155 
2156 void CMSCollector::gc_epilogue(bool full) {
2157   // The following locking discipline assumes that we are only called
2158   // when the world is stopped.
2159   assert(SafepointSynchronize::is_at_safepoint(),
2160          "world is stopped assumption");
2161 
2162   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2163   // if linear allocation blocks need to be appropriately marked to allow the
2164   // the blocks to be parsable. We also check here whether we need to nudge the
2165   // CMS collector thread to start a new cycle (if it's not already active).
2166   assert(   Thread::current()->is_VM_thread()
2167          || (   CMSScavengeBeforeRemark
2168              && Thread::current()->is_ConcurrentGC_thread()),
2169          "Incorrect thread type for epilogue execution");
2170 
2171   if (!_between_prologue_and_epilogue) {
2172     // We have already been invoked; this is a gc_epilogue delegation
2173     // from yet another CMS generation that we are responsible for, just
2174     // ignore it since all relevant work has already been done.
2175     return;
2176   }
2177   assert(haveFreelistLocks(), "must have freelist locks");
2178   assert_lock_strong(bitMapLock());
2179 
2180   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2181 
2182   _cmsGen->gc_epilogue_work(full);
2183 
2184   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2185     // in case sampling was not already enabled, enable it
2186     _start_sampling = true;
2187   }
2188   // reset _eden_chunk_array so sampling starts afresh
2189   _eden_chunk_index = 0;
2190 
2191   size_t cms_used   = _cmsGen->cmsSpace()->used();
2192 
2193   // update performance counters - this uses a special version of
2194   // update_counters() that allows the utilization to be passed as a
2195   // parameter, avoiding multiple calls to used().
2196   //
2197   _cmsGen->update_counters(cms_used);
2198 
2199   bitMapLock()->unlock();
2200   releaseFreelistLocks();
2201 
2202   if (!CleanChunkPoolAsync) {
2203     Chunk::clean_chunk_pool();
2204   }
2205 
2206   set_did_compact(false);
2207   _between_prologue_and_epilogue = false;  // ready for next cycle
2208 }
2209 
2210 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2211   collector()->gc_epilogue(full);
2212 
2213   // Also reset promotion tracking in par gc thread states.
2214   for (uint i = 0; i < ParallelGCThreads; i++) {
2215     _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2216   }
2217 }
2218 
2219 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2220   assert(!incremental_collection_failed(), "Should have been cleared");
2221   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2222   cmsSpace()->gc_epilogue();
2223     // Print stat counters
2224   NOT_PRODUCT(
2225     assert(_numObjectsAllocated == 0, "check");
2226     assert(_numWordsAllocated == 0, "check");
2227     if (Verbose && PrintGC) {
2228       gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2229                           SIZE_FORMAT " bytes",
2230                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2231     }
2232     _numObjectsPromoted = 0;
2233     _numWordsPromoted   = 0;
2234   )
2235 
2236   if (PrintGC && Verbose) {
2237     // Call down the chain in contiguous_available needs the freelistLock
2238     // so print this out before releasing the freeListLock.
2239     gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2240                         contiguous_available());
2241   }
2242 }
2243 
2244 #ifndef PRODUCT
2245 bool CMSCollector::have_cms_token() {
2246   Thread* thr = Thread::current();
2247   if (thr->is_VM_thread()) {
2248     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2249   } else if (thr->is_ConcurrentGC_thread()) {
2250     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2251   } else if (thr->is_GC_task_thread()) {
2252     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2253            ParGCRareEvent_lock->owned_by_self();
2254   }
2255   return false;
2256 }
2257 #endif
2258 
2259 // Check reachability of the given heap address in CMS generation,
2260 // treating all other generations as roots.
2261 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2262   // We could "guarantee" below, rather than assert, but I'll
2263   // leave these as "asserts" so that an adventurous debugger
2264   // could try this in the product build provided some subset of
2265   // the conditions were met, provided they were interested in the
2266   // results and knew that the computation below wouldn't interfere
2267   // with other concurrent computations mutating the structures
2268   // being read or written.
2269   assert(SafepointSynchronize::is_at_safepoint(),
2270          "Else mutations in object graph will make answer suspect");
2271   assert(have_cms_token(), "Should hold cms token");
2272   assert(haveFreelistLocks(), "must hold free list locks");
2273   assert_lock_strong(bitMapLock());
2274 
2275   // Clear the marking bit map array before starting, but, just
2276   // for kicks, first report if the given address is already marked
2277   gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2278                 _markBitMap.isMarked(addr) ? "" : " not");
2279 
2280   if (verify_after_remark()) {
2281     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2282     bool result = verification_mark_bm()->isMarked(addr);
2283     gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2284                            result ? "IS" : "is NOT");
2285     return result;
2286   } else {
2287     gclog_or_tty->print_cr("Could not compute result");
2288     return false;
2289   }
2290 }
2291 
2292 
2293 void
2294 CMSCollector::print_on_error(outputStream* st) {
2295   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2296   if (collector != NULL) {
2297     CMSBitMap* bitmap = &collector->_markBitMap;
2298     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2299     bitmap->print_on_error(st, " Bits: ");
2300 
2301     st->cr();
2302 
2303     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2304     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2305     mut_bitmap->print_on_error(st, " Bits: ");
2306   }
2307 }
2308 
2309 ////////////////////////////////////////////////////////
2310 // CMS Verification Support
2311 ////////////////////////////////////////////////////////
2312 // Following the remark phase, the following invariant
2313 // should hold -- each object in the CMS heap which is
2314 // marked in markBitMap() should be marked in the verification_mark_bm().
2315 
2316 class VerifyMarkedClosure: public BitMapClosure {
2317   CMSBitMap* _marks;
2318   bool       _failed;
2319 
2320  public:
2321   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2322 
2323   bool do_bit(size_t offset) {
2324     HeapWord* addr = _marks->offsetToHeapWord(offset);
2325     if (!_marks->isMarked(addr)) {
2326       oop(addr)->print_on(gclog_or_tty);
2327       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2328       _failed = true;
2329     }
2330     return true;
2331   }
2332 
2333   bool failed() { return _failed; }
2334 };
2335 
2336 bool CMSCollector::verify_after_remark(bool silent) {
2337   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2338   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2339   static bool init = false;
2340 
2341   assert(SafepointSynchronize::is_at_safepoint(),
2342          "Else mutations in object graph will make answer suspect");
2343   assert(have_cms_token(),
2344          "Else there may be mutual interference in use of "
2345          " verification data structures");
2346   assert(_collectorState > Marking && _collectorState <= Sweeping,
2347          "Else marking info checked here may be obsolete");
2348   assert(haveFreelistLocks(), "must hold free list locks");
2349   assert_lock_strong(bitMapLock());
2350 
2351 
2352   // Allocate marking bit map if not already allocated
2353   if (!init) { // first time
2354     if (!verification_mark_bm()->allocate(_span)) {
2355       return false;
2356     }
2357     init = true;
2358   }
2359 
2360   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2361 
2362   // Turn off refs discovery -- so we will be tracing through refs.
2363   // This is as intended, because by this time
2364   // GC must already have cleared any refs that need to be cleared,
2365   // and traced those that need to be marked; moreover,
2366   // the marking done here is not going to interfere in any
2367   // way with the marking information used by GC.
2368   NoRefDiscovery no_discovery(ref_processor());
2369 
2370 #if defined(COMPILER2) || INCLUDE_JVMCI
2371   DerivedPointerTableDeactivate dpt_deact;
2372 #endif
2373 
2374   // Clear any marks from a previous round
2375   verification_mark_bm()->clear_all();
2376   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2377   verify_work_stacks_empty();
2378 
2379   GenCollectedHeap* gch = GenCollectedHeap::heap();
2380   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2381   // Update the saved marks which may affect the root scans.
2382   gch->save_marks();
2383 
2384   if (CMSRemarkVerifyVariant == 1) {
2385     // In this first variant of verification, we complete
2386     // all marking, then check if the new marks-vector is
2387     // a subset of the CMS marks-vector.
2388     verify_after_remark_work_1();
2389   } else if (CMSRemarkVerifyVariant == 2) {
2390     // In this second variant of verification, we flag an error
2391     // (i.e. an object reachable in the new marks-vector not reachable
2392     // in the CMS marks-vector) immediately, also indicating the
2393     // identify of an object (A) that references the unmarked object (B) --
2394     // presumably, a mutation to A failed to be picked up by preclean/remark?
2395     verify_after_remark_work_2();
2396   } else {
2397     warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2398             CMSRemarkVerifyVariant);
2399   }
2400   if (!silent) gclog_or_tty->print(" done] ");
2401   return true;
2402 }
2403 
2404 void CMSCollector::verify_after_remark_work_1() {
2405   ResourceMark rm;
2406   HandleMark  hm;
2407   GenCollectedHeap* gch = GenCollectedHeap::heap();
2408 
2409   // Get a clear set of claim bits for the roots processing to work with.
2410   ClassLoaderDataGraph::clear_claimed_marks();
2411 
2412   // Mark from roots one level into CMS
2413   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2414   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2415 
2416   {
2417     StrongRootsScope srs(1);
2418 
2419     gch->gen_process_roots(&srs,
2420                            GenCollectedHeap::OldGen,
2421                            true,   // young gen as roots
2422                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2423                            should_unload_classes(),
2424                            &notOlder,
2425                            NULL,
2426                            NULL);
2427   }
2428 
2429   // Now mark from the roots
2430   MarkFromRootsClosure markFromRootsClosure(this, _span,
2431     verification_mark_bm(), verification_mark_stack(),
2432     false /* don't yield */, true /* verifying */);
2433   assert(_restart_addr == NULL, "Expected pre-condition");
2434   verification_mark_bm()->iterate(&markFromRootsClosure);
2435   while (_restart_addr != NULL) {
2436     // Deal with stack overflow: by restarting at the indicated
2437     // address.
2438     HeapWord* ra = _restart_addr;
2439     markFromRootsClosure.reset(ra);
2440     _restart_addr = NULL;
2441     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2442   }
2443   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2444   verify_work_stacks_empty();
2445 
2446   // Marking completed -- now verify that each bit marked in
2447   // verification_mark_bm() is also marked in markBitMap(); flag all
2448   // errors by printing corresponding objects.
2449   VerifyMarkedClosure vcl(markBitMap());
2450   verification_mark_bm()->iterate(&vcl);
2451   if (vcl.failed()) {
2452     gclog_or_tty->print("Verification failed");
2453     gch->print_on(gclog_or_tty);
2454     fatal("CMS: failed marking verification after remark");
2455   }
2456 }
2457 
2458 class VerifyKlassOopsKlassClosure : public KlassClosure {
2459   class VerifyKlassOopsClosure : public OopClosure {
2460     CMSBitMap* _bitmap;
2461    public:
2462     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2463     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2464     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2465   } _oop_closure;
2466  public:
2467   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2468   void do_klass(Klass* k) {
2469     k->oops_do(&_oop_closure);
2470   }
2471 };
2472 
2473 void CMSCollector::verify_after_remark_work_2() {
2474   ResourceMark rm;
2475   HandleMark  hm;
2476   GenCollectedHeap* gch = GenCollectedHeap::heap();
2477 
2478   // Get a clear set of claim bits for the roots processing to work with.
2479   ClassLoaderDataGraph::clear_claimed_marks();
2480 
2481   // Mark from roots one level into CMS
2482   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2483                                      markBitMap());
2484   CLDToOopClosure cld_closure(&notOlder, true);
2485 
2486   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2487 
2488   {
2489     StrongRootsScope srs(1);
2490 
2491     gch->gen_process_roots(&srs,
2492                            GenCollectedHeap::OldGen,
2493                            true,   // young gen as roots
2494                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2495                            should_unload_classes(),
2496                            &notOlder,
2497                            NULL,
2498                            &cld_closure);
2499   }
2500 
2501   // Now mark from the roots
2502   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2503     verification_mark_bm(), markBitMap(), verification_mark_stack());
2504   assert(_restart_addr == NULL, "Expected pre-condition");
2505   verification_mark_bm()->iterate(&markFromRootsClosure);
2506   while (_restart_addr != NULL) {
2507     // Deal with stack overflow: by restarting at the indicated
2508     // address.
2509     HeapWord* ra = _restart_addr;
2510     markFromRootsClosure.reset(ra);
2511     _restart_addr = NULL;
2512     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2513   }
2514   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2515   verify_work_stacks_empty();
2516 
2517   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2518   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2519 
2520   // Marking completed -- now verify that each bit marked in
2521   // verification_mark_bm() is also marked in markBitMap(); flag all
2522   // errors by printing corresponding objects.
2523   VerifyMarkedClosure vcl(markBitMap());
2524   verification_mark_bm()->iterate(&vcl);
2525   assert(!vcl.failed(), "Else verification above should not have succeeded");
2526 }
2527 
2528 void ConcurrentMarkSweepGeneration::save_marks() {
2529   // delegate to CMS space
2530   cmsSpace()->save_marks();
2531   for (uint i = 0; i < ParallelGCThreads; i++) {
2532     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2533   }
2534 }
2535 
2536 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2537   return cmsSpace()->no_allocs_since_save_marks();
2538 }
2539 
2540 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2541                                                                 \
2542 void ConcurrentMarkSweepGeneration::                            \
2543 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2544   cl->set_generation(this);                                     \
2545   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2546   cl->reset_generation();                                       \
2547   save_marks();                                                 \
2548 }
2549 
2550 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2551 
2552 void
2553 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2554   if (freelistLock()->owned_by_self()) {
2555     Generation::oop_iterate(cl);
2556   } else {
2557     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2558     Generation::oop_iterate(cl);
2559   }
2560 }
2561 
2562 void
2563 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2564   if (freelistLock()->owned_by_self()) {
2565     Generation::object_iterate(cl);
2566   } else {
2567     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2568     Generation::object_iterate(cl);
2569   }
2570 }
2571 
2572 void
2573 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2574   if (freelistLock()->owned_by_self()) {
2575     Generation::safe_object_iterate(cl);
2576   } else {
2577     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2578     Generation::safe_object_iterate(cl);
2579   }
2580 }
2581 
2582 void
2583 ConcurrentMarkSweepGeneration::post_compact() {
2584 }
2585 
2586 void
2587 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2588   // Fix the linear allocation blocks to look like free blocks.
2589 
2590   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2591   // are not called when the heap is verified during universe initialization and
2592   // at vm shutdown.
2593   if (freelistLock()->owned_by_self()) {
2594     cmsSpace()->prepare_for_verify();
2595   } else {
2596     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2597     cmsSpace()->prepare_for_verify();
2598   }
2599 }
2600 
2601 void
2602 ConcurrentMarkSweepGeneration::verify() {
2603   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2604   // are not called when the heap is verified during universe initialization and
2605   // at vm shutdown.
2606   if (freelistLock()->owned_by_self()) {
2607     cmsSpace()->verify();
2608   } else {
2609     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2610     cmsSpace()->verify();
2611   }
2612 }
2613 
2614 void CMSCollector::verify() {
2615   _cmsGen->verify();
2616 }
2617 
2618 #ifndef PRODUCT
2619 bool CMSCollector::overflow_list_is_empty() const {
2620   assert(_num_par_pushes >= 0, "Inconsistency");
2621   if (_overflow_list == NULL) {
2622     assert(_num_par_pushes == 0, "Inconsistency");
2623   }
2624   return _overflow_list == NULL;
2625 }
2626 
2627 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2628 // merely consolidate assertion checks that appear to occur together frequently.
2629 void CMSCollector::verify_work_stacks_empty() const {
2630   assert(_markStack.isEmpty(), "Marking stack should be empty");
2631   assert(overflow_list_is_empty(), "Overflow list should be empty");
2632 }
2633 
2634 void CMSCollector::verify_overflow_empty() const {
2635   assert(overflow_list_is_empty(), "Overflow list should be empty");
2636   assert(no_preserved_marks(), "No preserved marks");
2637 }
2638 #endif // PRODUCT
2639 
2640 // Decide if we want to enable class unloading as part of the
2641 // ensuing concurrent GC cycle. We will collect and
2642 // unload classes if it's the case that:
2643 // (1) an explicit gc request has been made and the flag
2644 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2645 // (2) (a) class unloading is enabled at the command line, and
2646 //     (b) old gen is getting really full
2647 // NOTE: Provided there is no change in the state of the heap between
2648 // calls to this method, it should have idempotent results. Moreover,
2649 // its results should be monotonically increasing (i.e. going from 0 to 1,
2650 // but not 1 to 0) between successive calls between which the heap was
2651 // not collected. For the implementation below, it must thus rely on
2652 // the property that concurrent_cycles_since_last_unload()
2653 // will not decrease unless a collection cycle happened and that
2654 // _cmsGen->is_too_full() are
2655 // themselves also monotonic in that sense. See check_monotonicity()
2656 // below.
2657 void CMSCollector::update_should_unload_classes() {
2658   _should_unload_classes = false;
2659   // Condition 1 above
2660   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2661     _should_unload_classes = true;
2662   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2663     // Disjuncts 2.b.(i,ii,iii) above
2664     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2665                               CMSClassUnloadingMaxInterval)
2666                            || _cmsGen->is_too_full();
2667   }
2668 }
2669 
2670 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2671   bool res = should_concurrent_collect();
2672   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2673   return res;
2674 }
2675 
2676 void CMSCollector::setup_cms_unloading_and_verification_state() {
2677   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2678                              || VerifyBeforeExit;
2679   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2680 
2681   // We set the proper root for this CMS cycle here.
2682   if (should_unload_classes()) {   // Should unload classes this cycle
2683     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2684     set_verifying(should_verify);    // Set verification state for this cycle
2685     return;                            // Nothing else needs to be done at this time
2686   }
2687 
2688   // Not unloading classes this cycle
2689   assert(!should_unload_classes(), "Inconsistency!");
2690 
2691   // If we are not unloading classes then add SO_AllCodeCache to root
2692   // scanning options.
2693   add_root_scanning_option(rso);
2694 
2695   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2696     set_verifying(true);
2697   } else if (verifying() && !should_verify) {
2698     // We were verifying, but some verification flags got disabled.
2699     set_verifying(false);
2700     // Exclude symbols, strings and code cache elements from root scanning to
2701     // reduce IM and RM pauses.
2702     remove_root_scanning_option(rso);
2703   }
2704 }
2705 
2706 
2707 #ifndef PRODUCT
2708 HeapWord* CMSCollector::block_start(const void* p) const {
2709   const HeapWord* addr = (HeapWord*)p;
2710   if (_span.contains(p)) {
2711     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2712       return _cmsGen->cmsSpace()->block_start(p);
2713     }
2714   }
2715   return NULL;
2716 }
2717 #endif
2718 
2719 HeapWord*
2720 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2721                                                    bool   tlab,
2722                                                    bool   parallel) {
2723   CMSSynchronousYieldRequest yr;
2724   assert(!tlab, "Can't deal with TLAB allocation");
2725   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2726   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2727   if (GCExpandToAllocateDelayMillis > 0) {
2728     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2729   }
2730   return have_lock_and_allocate(word_size, tlab);
2731 }
2732 
2733 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2734     size_t bytes,
2735     size_t expand_bytes,
2736     CMSExpansionCause::Cause cause)
2737 {
2738 
2739   bool success = expand(bytes, expand_bytes);
2740 
2741   // remember why we expanded; this information is used
2742   // by shouldConcurrentCollect() when making decisions on whether to start
2743   // a new CMS cycle.
2744   if (success) {
2745     set_expansion_cause(cause);
2746     if (PrintGCDetails && Verbose) {
2747       gclog_or_tty->print_cr("Expanded CMS gen for %s",
2748         CMSExpansionCause::to_string(cause));
2749     }
2750   }
2751 }
2752 
2753 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2754   HeapWord* res = NULL;
2755   MutexLocker x(ParGCRareEvent_lock);
2756   while (true) {
2757     // Expansion by some other thread might make alloc OK now:
2758     res = ps->lab.alloc(word_sz);
2759     if (res != NULL) return res;
2760     // If there's not enough expansion space available, give up.
2761     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2762       return NULL;
2763     }
2764     // Otherwise, we try expansion.
2765     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2766     // Now go around the loop and try alloc again;
2767     // A competing par_promote might beat us to the expansion space,
2768     // so we may go around the loop again if promotion fails again.
2769     if (GCExpandToAllocateDelayMillis > 0) {
2770       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2771     }
2772   }
2773 }
2774 
2775 
2776 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2777   PromotionInfo* promo) {
2778   MutexLocker x(ParGCRareEvent_lock);
2779   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2780   while (true) {
2781     // Expansion by some other thread might make alloc OK now:
2782     if (promo->ensure_spooling_space()) {
2783       assert(promo->has_spooling_space(),
2784              "Post-condition of successful ensure_spooling_space()");
2785       return true;
2786     }
2787     // If there's not enough expansion space available, give up.
2788     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2789       return false;
2790     }
2791     // Otherwise, we try expansion.
2792     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2793     // Now go around the loop and try alloc again;
2794     // A competing allocation might beat us to the expansion space,
2795     // so we may go around the loop again if allocation fails again.
2796     if (GCExpandToAllocateDelayMillis > 0) {
2797       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2798     }
2799   }
2800 }
2801 
2802 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2803   // Only shrink if a compaction was done so that all the free space
2804   // in the generation is in a contiguous block at the end.
2805   if (did_compact()) {
2806     CardGeneration::shrink(bytes);
2807   }
2808 }
2809 
2810 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2811   assert_locked_or_safepoint(Heap_lock);
2812 }
2813 
2814 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2815   assert_locked_or_safepoint(Heap_lock);
2816   assert_lock_strong(freelistLock());
2817   if (PrintGCDetails && Verbose) {
2818     warning("Shrinking of CMS not yet implemented");
2819   }
2820   return;
2821 }
2822 
2823 
2824 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2825 // phases.
2826 class CMSPhaseAccounting: public StackObj {
2827  public:
2828   CMSPhaseAccounting(CMSCollector *collector,
2829                      const char *phase,
2830                      const GCId gc_id,
2831                      bool print_cr = true);
2832   ~CMSPhaseAccounting();
2833 
2834  private:
2835   CMSCollector *_collector;
2836   const char *_phase;
2837   elapsedTimer _wallclock;
2838   bool _print_cr;
2839   const GCId _gc_id;
2840 
2841  public:
2842   // Not MT-safe; so do not pass around these StackObj's
2843   // where they may be accessed by other threads.
2844   jlong wallclock_millis() {
2845     assert(_wallclock.is_active(), "Wall clock should not stop");
2846     _wallclock.stop();  // to record time
2847     jlong ret = _wallclock.milliseconds();
2848     _wallclock.start(); // restart
2849     return ret;
2850   }
2851 };
2852 
2853 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2854                                        const char *phase,
2855                                        const GCId gc_id,
2856                                        bool print_cr) :
2857   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2858 
2859   if (PrintCMSStatistics != 0) {
2860     _collector->resetYields();
2861   }
2862   if (PrintGCDetails) {
2863     gclog_or_tty->gclog_stamp(_gc_id);
2864     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2865       _collector->cmsGen()->short_name(), _phase);
2866   }
2867   _collector->resetTimer();
2868   _wallclock.start();
2869   _collector->startTimer();
2870 }
2871 
2872 CMSPhaseAccounting::~CMSPhaseAccounting() {
2873   assert(_wallclock.is_active(), "Wall clock should not have stopped");
2874   _collector->stopTimer();
2875   _wallclock.stop();
2876   if (PrintGCDetails) {
2877     gclog_or_tty->gclog_stamp(_gc_id);
2878     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2879                  _collector->cmsGen()->short_name(),
2880                  _phase, _collector->timerValue(), _wallclock.seconds());
2881     if (_print_cr) {
2882       gclog_or_tty->cr();
2883     }
2884     if (PrintCMSStatistics != 0) {
2885       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2886                     _collector->yields());
2887     }
2888   }
2889 }
2890 
2891 // CMS work
2892 
2893 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2894 class CMSParMarkTask : public AbstractGangTask {
2895  protected:
2896   CMSCollector*     _collector;
2897   uint              _n_workers;
2898   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2899       AbstractGangTask(name),
2900       _collector(collector),
2901       _n_workers(n_workers) {}
2902   // Work method in support of parallel rescan ... of young gen spaces
2903   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2904                              ContiguousSpace* space,
2905                              HeapWord** chunk_array, size_t chunk_top);
2906   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2907 };
2908 
2909 // Parallel initial mark task
2910 class CMSParInitialMarkTask: public CMSParMarkTask {
2911   StrongRootsScope* _strong_roots_scope;
2912  public:
2913   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2914       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2915       _strong_roots_scope(strong_roots_scope) {}
2916   void work(uint worker_id);
2917 };
2918 
2919 // Checkpoint the roots into this generation from outside
2920 // this generation. [Note this initial checkpoint need only
2921 // be approximate -- we'll do a catch up phase subsequently.]
2922 void CMSCollector::checkpointRootsInitial() {
2923   assert(_collectorState == InitialMarking, "Wrong collector state");
2924   check_correct_thread_executing();
2925   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2926 
2927   save_heap_summary();
2928   report_heap_summary(GCWhen::BeforeGC);
2929 
2930   ReferenceProcessor* rp = ref_processor();
2931   assert(_restart_addr == NULL, "Control point invariant");
2932   {
2933     // acquire locks for subsequent manipulations
2934     MutexLockerEx x(bitMapLock(),
2935                     Mutex::_no_safepoint_check_flag);
2936     checkpointRootsInitialWork();
2937     // enable ("weak") refs discovery
2938     rp->enable_discovery();
2939     _collectorState = Marking;
2940   }
2941 }
2942 
2943 void CMSCollector::checkpointRootsInitialWork() {
2944   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2945   assert(_collectorState == InitialMarking, "just checking");
2946 
2947   // Already have locks.
2948   assert_lock_strong(bitMapLock());
2949   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2950 
2951   // Setup the verification and class unloading state for this
2952   // CMS collection cycle.
2953   setup_cms_unloading_and_verification_state();
2954 
2955   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2956     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2957 
2958   // Reset all the PLAB chunk arrays if necessary.
2959   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2960     reset_survivor_plab_arrays();
2961   }
2962 
2963   ResourceMark rm;
2964   HandleMark  hm;
2965 
2966   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2967   GenCollectedHeap* gch = GenCollectedHeap::heap();
2968 
2969   verify_work_stacks_empty();
2970   verify_overflow_empty();
2971 
2972   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2973   // Update the saved marks which may affect the root scans.
2974   gch->save_marks();
2975 
2976   // weak reference processing has not started yet.
2977   ref_processor()->set_enqueuing_is_done(false);
2978 
2979   // Need to remember all newly created CLDs,
2980   // so that we can guarantee that the remark finds them.
2981   ClassLoaderDataGraph::remember_new_clds(true);
2982 
2983   // Whenever a CLD is found, it will be claimed before proceeding to mark
2984   // the klasses. The claimed marks need to be cleared before marking starts.
2985   ClassLoaderDataGraph::clear_claimed_marks();
2986 
2987   if (CMSPrintEdenSurvivorChunks) {
2988     print_eden_and_survivor_chunk_arrays();
2989   }
2990 
2991   {
2992 #if defined(COMPILER2) || INCLUDE_JVMCI
2993     DerivedPointerTableDeactivate dpt_deact;
2994 #endif
2995     if (CMSParallelInitialMarkEnabled) {
2996       // The parallel version.
2997       WorkGang* workers = gch->workers();
2998       assert(workers != NULL, "Need parallel worker threads.");
2999       uint n_workers = workers->active_workers();
3000 
3001       StrongRootsScope srs(n_workers);
3002 
3003       CMSParInitialMarkTask tsk(this, &srs, n_workers);
3004       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3005       if (n_workers > 1) {
3006         workers->run_task(&tsk);
3007       } else {
3008         tsk.work(0);
3009       }
3010     } else {
3011       // The serial version.
3012       CLDToOopClosure cld_closure(&notOlder, true);
3013       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3014 
3015       StrongRootsScope srs(1);
3016 
3017       gch->gen_process_roots(&srs,
3018                              GenCollectedHeap::OldGen,
3019                              true,   // young gen as roots
3020                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
3021                              should_unload_classes(),
3022                              &notOlder,
3023                              NULL,
3024                              &cld_closure);
3025     }
3026   }
3027 
3028   // Clear mod-union table; it will be dirtied in the prologue of
3029   // CMS generation per each young generation collection.
3030 
3031   assert(_modUnionTable.isAllClear(),
3032        "Was cleared in most recent final checkpoint phase"
3033        " or no bits are set in the gc_prologue before the start of the next "
3034        "subsequent marking phase.");
3035 
3036   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3037 
3038   // Save the end of the used_region of the constituent generations
3039   // to be used to limit the extent of sweep in each generation.
3040   save_sweep_limits();
3041   verify_overflow_empty();
3042 }
3043 
3044 bool CMSCollector::markFromRoots() {
3045   // we might be tempted to assert that:
3046   // assert(!SafepointSynchronize::is_at_safepoint(),
3047   //        "inconsistent argument?");
3048   // However that wouldn't be right, because it's possible that
3049   // a safepoint is indeed in progress as a young generation
3050   // stop-the-world GC happens even as we mark in this generation.
3051   assert(_collectorState == Marking, "inconsistent state?");
3052   check_correct_thread_executing();
3053   verify_overflow_empty();
3054 
3055   // Weak ref discovery note: We may be discovering weak
3056   // refs in this generation concurrent (but interleaved) with
3057   // weak ref discovery by the young generation collector.
3058 
3059   CMSTokenSyncWithLocks ts(true, bitMapLock());
3060   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3061   CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3062   bool res = markFromRootsWork();
3063   if (res) {
3064     _collectorState = Precleaning;
3065   } else { // We failed and a foreground collection wants to take over
3066     assert(_foregroundGCIsActive, "internal state inconsistency");
3067     assert(_restart_addr == NULL,  "foreground will restart from scratch");
3068     if (PrintGCDetails) {
3069       gclog_or_tty->print_cr("bailing out to foreground collection");
3070     }
3071   }
3072   verify_overflow_empty();
3073   return res;
3074 }
3075 
3076 bool CMSCollector::markFromRootsWork() {
3077   // iterate over marked bits in bit map, doing a full scan and mark
3078   // from these roots using the following algorithm:
3079   // . if oop is to the right of the current scan pointer,
3080   //   mark corresponding bit (we'll process it later)
3081   // . else (oop is to left of current scan pointer)
3082   //   push oop on marking stack
3083   // . drain the marking stack
3084 
3085   // Note that when we do a marking step we need to hold the
3086   // bit map lock -- recall that direct allocation (by mutators)
3087   // and promotion (by the young generation collector) is also
3088   // marking the bit map. [the so-called allocate live policy.]
3089   // Because the implementation of bit map marking is not
3090   // robust wrt simultaneous marking of bits in the same word,
3091   // we need to make sure that there is no such interference
3092   // between concurrent such updates.
3093 
3094   // already have locks
3095   assert_lock_strong(bitMapLock());
3096 
3097   verify_work_stacks_empty();
3098   verify_overflow_empty();
3099   bool result = false;
3100   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3101     result = do_marking_mt();
3102   } else {
3103     result = do_marking_st();
3104   }
3105   return result;
3106 }
3107 
3108 // Forward decl
3109 class CMSConcMarkingTask;
3110 
3111 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3112   CMSCollector*       _collector;
3113   CMSConcMarkingTask* _task;
3114  public:
3115   virtual void yield();
3116 
3117   // "n_threads" is the number of threads to be terminated.
3118   // "queue_set" is a set of work queues of other threads.
3119   // "collector" is the CMS collector associated with this task terminator.
3120   // "yield" indicates whether we need the gang as a whole to yield.
3121   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3122     ParallelTaskTerminator(n_threads, queue_set),
3123     _collector(collector) { }
3124 
3125   void set_task(CMSConcMarkingTask* task) {
3126     _task = task;
3127   }
3128 };
3129 
3130 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3131   CMSConcMarkingTask* _task;
3132  public:
3133   bool should_exit_termination();
3134   void set_task(CMSConcMarkingTask* task) {
3135     _task = task;
3136   }
3137 };
3138 
3139 // MT Concurrent Marking Task
3140 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3141   CMSCollector* _collector;
3142   uint          _n_workers;       // requested/desired # workers
3143   bool          _result;
3144   CompactibleFreeListSpace*  _cms_space;
3145   char          _pad_front[64];   // padding to ...
3146   HeapWord*     _global_finger;   // ... avoid sharing cache line
3147   char          _pad_back[64];
3148   HeapWord*     _restart_addr;
3149 
3150   //  Exposed here for yielding support
3151   Mutex* const _bit_map_lock;
3152 
3153   // The per thread work queues, available here for stealing
3154   OopTaskQueueSet*  _task_queues;
3155 
3156   // Termination (and yielding) support
3157   CMSConcMarkingTerminator _term;
3158   CMSConcMarkingTerminatorTerminator _term_term;
3159 
3160  public:
3161   CMSConcMarkingTask(CMSCollector* collector,
3162                  CompactibleFreeListSpace* cms_space,
3163                  YieldingFlexibleWorkGang* workers,
3164                  OopTaskQueueSet* task_queues):
3165     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3166     _collector(collector),
3167     _cms_space(cms_space),
3168     _n_workers(0), _result(true),
3169     _task_queues(task_queues),
3170     _term(_n_workers, task_queues, _collector),
3171     _bit_map_lock(collector->bitMapLock())
3172   {
3173     _requested_size = _n_workers;
3174     _term.set_task(this);
3175     _term_term.set_task(this);
3176     _restart_addr = _global_finger = _cms_space->bottom();
3177   }
3178 
3179 
3180   OopTaskQueueSet* task_queues()  { return _task_queues; }
3181 
3182   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3183 
3184   HeapWord** global_finger_addr() { return &_global_finger; }
3185 
3186   CMSConcMarkingTerminator* terminator() { return &_term; }
3187 
3188   virtual void set_for_termination(uint active_workers) {
3189     terminator()->reset_for_reuse(active_workers);
3190   }
3191 
3192   void work(uint worker_id);
3193   bool should_yield() {
3194     return    ConcurrentMarkSweepThread::should_yield()
3195            && !_collector->foregroundGCIsActive();
3196   }
3197 
3198   virtual void coordinator_yield();  // stuff done by coordinator
3199   bool result() { return _result; }
3200 
3201   void reset(HeapWord* ra) {
3202     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3203     _restart_addr = _global_finger = ra;
3204     _term.reset_for_reuse();
3205   }
3206 
3207   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3208                                            OopTaskQueue* work_q);
3209 
3210  private:
3211   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3212   void do_work_steal(int i);
3213   void bump_global_finger(HeapWord* f);
3214 };
3215 
3216 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3217   assert(_task != NULL, "Error");
3218   return _task->yielding();
3219   // Note that we do not need the disjunct || _task->should_yield() above
3220   // because we want terminating threads to yield only if the task
3221   // is already in the midst of yielding, which happens only after at least one
3222   // thread has yielded.
3223 }
3224 
3225 void CMSConcMarkingTerminator::yield() {
3226   if (_task->should_yield()) {
3227     _task->yield();
3228   } else {
3229     ParallelTaskTerminator::yield();
3230   }
3231 }
3232 
3233 ////////////////////////////////////////////////////////////////
3234 // Concurrent Marking Algorithm Sketch
3235 ////////////////////////////////////////////////////////////////
3236 // Until all tasks exhausted (both spaces):
3237 // -- claim next available chunk
3238 // -- bump global finger via CAS
3239 // -- find first object that starts in this chunk
3240 //    and start scanning bitmap from that position
3241 // -- scan marked objects for oops
3242 // -- CAS-mark target, and if successful:
3243 //    . if target oop is above global finger (volatile read)
3244 //      nothing to do
3245 //    . if target oop is in chunk and above local finger
3246 //        then nothing to do
3247 //    . else push on work-queue
3248 // -- Deal with possible overflow issues:
3249 //    . local work-queue overflow causes stuff to be pushed on
3250 //      global (common) overflow queue
3251 //    . always first empty local work queue
3252 //    . then get a batch of oops from global work queue if any
3253 //    . then do work stealing
3254 // -- When all tasks claimed (both spaces)
3255 //    and local work queue empty,
3256 //    then in a loop do:
3257 //    . check global overflow stack; steal a batch of oops and trace
3258 //    . try to steal from other threads oif GOS is empty
3259 //    . if neither is available, offer termination
3260 // -- Terminate and return result
3261 //
3262 void CMSConcMarkingTask::work(uint worker_id) {
3263   elapsedTimer _timer;
3264   ResourceMark rm;
3265   HandleMark hm;
3266 
3267   DEBUG_ONLY(_collector->verify_overflow_empty();)
3268 
3269   // Before we begin work, our work queue should be empty
3270   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3271   // Scan the bitmap covering _cms_space, tracing through grey objects.
3272   _timer.start();
3273   do_scan_and_mark(worker_id, _cms_space);
3274   _timer.stop();
3275   if (PrintCMSStatistics != 0) {
3276     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3277       worker_id, _timer.seconds());
3278       // XXX: need xxx/xxx type of notation, two timers
3279   }
3280 
3281   // ... do work stealing
3282   _timer.reset();
3283   _timer.start();
3284   do_work_steal(worker_id);
3285   _timer.stop();
3286   if (PrintCMSStatistics != 0) {
3287     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3288       worker_id, _timer.seconds());
3289       // XXX: need xxx/xxx type of notation, two timers
3290   }
3291   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3292   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3293   // Note that under the current task protocol, the
3294   // following assertion is true even of the spaces
3295   // expanded since the completion of the concurrent
3296   // marking. XXX This will likely change under a strict
3297   // ABORT semantics.
3298   // After perm removal the comparison was changed to
3299   // greater than or equal to from strictly greater than.
3300   // Before perm removal the highest address sweep would
3301   // have been at the end of perm gen but now is at the
3302   // end of the tenured gen.
3303   assert(_global_finger >=  _cms_space->end(),
3304          "All tasks have been completed");
3305   DEBUG_ONLY(_collector->verify_overflow_empty();)
3306 }
3307 
3308 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3309   HeapWord* read = _global_finger;
3310   HeapWord* cur  = read;
3311   while (f > read) {
3312     cur = read;
3313     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3314     if (cur == read) {
3315       // our cas succeeded
3316       assert(_global_finger >= f, "protocol consistency");
3317       break;
3318     }
3319   }
3320 }
3321 
3322 // This is really inefficient, and should be redone by
3323 // using (not yet available) block-read and -write interfaces to the
3324 // stack and the work_queue. XXX FIX ME !!!
3325 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3326                                                       OopTaskQueue* work_q) {
3327   // Fast lock-free check
3328   if (ovflw_stk->length() == 0) {
3329     return false;
3330   }
3331   assert(work_q->size() == 0, "Shouldn't steal");
3332   MutexLockerEx ml(ovflw_stk->par_lock(),
3333                    Mutex::_no_safepoint_check_flag);
3334   // Grab up to 1/4 the size of the work queue
3335   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3336                     (size_t)ParGCDesiredObjsFromOverflowList);
3337   num = MIN2(num, ovflw_stk->length());
3338   for (int i = (int) num; i > 0; i--) {
3339     oop cur = ovflw_stk->pop();
3340     assert(cur != NULL, "Counted wrong?");
3341     work_q->push(cur);
3342   }
3343   return num > 0;
3344 }
3345 
3346 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3347   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3348   int n_tasks = pst->n_tasks();
3349   // We allow that there may be no tasks to do here because
3350   // we are restarting after a stack overflow.
3351   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3352   uint nth_task = 0;
3353 
3354   HeapWord* aligned_start = sp->bottom();
3355   if (sp->used_region().contains(_restart_addr)) {
3356     // Align down to a card boundary for the start of 0th task
3357     // for this space.
3358     aligned_start =
3359       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3360                                  CardTableModRefBS::card_size);
3361   }
3362 
3363   size_t chunk_size = sp->marking_task_size();
3364   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3365     // Having claimed the nth task in this space,
3366     // compute the chunk that it corresponds to:
3367     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3368                                aligned_start + (nth_task+1)*chunk_size);
3369     // Try and bump the global finger via a CAS;
3370     // note that we need to do the global finger bump
3371     // _before_ taking the intersection below, because
3372     // the task corresponding to that region will be
3373     // deemed done even if the used_region() expands
3374     // because of allocation -- as it almost certainly will
3375     // during start-up while the threads yield in the
3376     // closure below.
3377     HeapWord* finger = span.end();
3378     bump_global_finger(finger);   // atomically
3379     // There are null tasks here corresponding to chunks
3380     // beyond the "top" address of the space.
3381     span = span.intersection(sp->used_region());
3382     if (!span.is_empty()) {  // Non-null task
3383       HeapWord* prev_obj;
3384       assert(!span.contains(_restart_addr) || nth_task == 0,
3385              "Inconsistency");
3386       if (nth_task == 0) {
3387         // For the 0th task, we'll not need to compute a block_start.
3388         if (span.contains(_restart_addr)) {
3389           // In the case of a restart because of stack overflow,
3390           // we might additionally skip a chunk prefix.
3391           prev_obj = _restart_addr;
3392         } else {
3393           prev_obj = span.start();
3394         }
3395       } else {
3396         // We want to skip the first object because
3397         // the protocol is to scan any object in its entirety
3398         // that _starts_ in this span; a fortiori, any
3399         // object starting in an earlier span is scanned
3400         // as part of an earlier claimed task.
3401         // Below we use the "careful" version of block_start
3402         // so we do not try to navigate uninitialized objects.
3403         prev_obj = sp->block_start_careful(span.start());
3404         // Below we use a variant of block_size that uses the
3405         // Printezis bits to avoid waiting for allocated
3406         // objects to become initialized/parsable.
3407         while (prev_obj < span.start()) {
3408           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3409           if (sz > 0) {
3410             prev_obj += sz;
3411           } else {
3412             // In this case we may end up doing a bit of redundant
3413             // scanning, but that appears unavoidable, short of
3414             // locking the free list locks; see bug 6324141.
3415             break;
3416           }
3417         }
3418       }
3419       if (prev_obj < span.end()) {
3420         MemRegion my_span = MemRegion(prev_obj, span.end());
3421         // Do the marking work within a non-empty span --
3422         // the last argument to the constructor indicates whether the
3423         // iteration should be incremental with periodic yields.
3424         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3425                                     &_collector->_markBitMap,
3426                                     work_queue(i),
3427                                     &_collector->_markStack);
3428         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3429       } // else nothing to do for this task
3430     }   // else nothing to do for this task
3431   }
3432   // We'd be tempted to assert here that since there are no
3433   // more tasks left to claim in this space, the global_finger
3434   // must exceed space->top() and a fortiori space->end(). However,
3435   // that would not quite be correct because the bumping of
3436   // global_finger occurs strictly after the claiming of a task,
3437   // so by the time we reach here the global finger may not yet
3438   // have been bumped up by the thread that claimed the last
3439   // task.
3440   pst->all_tasks_completed();
3441 }
3442 
3443 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3444  private:
3445   CMSCollector* _collector;
3446   CMSConcMarkingTask* _task;
3447   MemRegion     _span;
3448   CMSBitMap*    _bit_map;
3449   CMSMarkStack* _overflow_stack;
3450   OopTaskQueue* _work_queue;
3451  protected:
3452   DO_OOP_WORK_DEFN
3453  public:
3454   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3455                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3456     MetadataAwareOopClosure(collector->ref_processor()),
3457     _collector(collector),
3458     _task(task),
3459     _span(collector->_span),
3460     _work_queue(work_queue),
3461     _bit_map(bit_map),
3462     _overflow_stack(overflow_stack)
3463   { }
3464   virtual void do_oop(oop* p);
3465   virtual void do_oop(narrowOop* p);
3466 
3467   void trim_queue(size_t max);
3468   void handle_stack_overflow(HeapWord* lost);
3469   void do_yield_check() {
3470     if (_task->should_yield()) {
3471       _task->yield();
3472     }
3473   }
3474 };
3475 
3476 // Grey object scanning during work stealing phase --
3477 // the salient assumption here is that any references
3478 // that are in these stolen objects being scanned must
3479 // already have been initialized (else they would not have
3480 // been published), so we do not need to check for
3481 // uninitialized objects before pushing here.
3482 void Par_ConcMarkingClosure::do_oop(oop obj) {
3483   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3484   HeapWord* addr = (HeapWord*)obj;
3485   // Check if oop points into the CMS generation
3486   // and is not marked
3487   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3488     // a white object ...
3489     // If we manage to "claim" the object, by being the
3490     // first thread to mark it, then we push it on our
3491     // marking stack
3492     if (_bit_map->par_mark(addr)) {     // ... now grey
3493       // push on work queue (grey set)
3494       bool simulate_overflow = false;
3495       NOT_PRODUCT(
3496         if (CMSMarkStackOverflowALot &&
3497             _collector->simulate_overflow()) {
3498           // simulate a stack overflow
3499           simulate_overflow = true;
3500         }
3501       )
3502       if (simulate_overflow ||
3503           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3504         // stack overflow
3505         if (PrintCMSStatistics != 0) {
3506           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3507                                  SIZE_FORMAT, _overflow_stack->capacity());
3508         }
3509         // We cannot assert that the overflow stack is full because
3510         // it may have been emptied since.
3511         assert(simulate_overflow ||
3512                _work_queue->size() == _work_queue->max_elems(),
3513               "Else push should have succeeded");
3514         handle_stack_overflow(addr);
3515       }
3516     } // Else, some other thread got there first
3517     do_yield_check();
3518   }
3519 }
3520 
3521 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3522 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3523 
3524 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3525   while (_work_queue->size() > max) {
3526     oop new_oop;
3527     if (_work_queue->pop_local(new_oop)) {
3528       assert(new_oop->is_oop(), "Should be an oop");
3529       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3530       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3531       new_oop->oop_iterate(this);  // do_oop() above
3532       do_yield_check();
3533     }
3534   }
3535 }
3536 
3537 // Upon stack overflow, we discard (part of) the stack,
3538 // remembering the least address amongst those discarded
3539 // in CMSCollector's _restart_address.
3540 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3541   // We need to do this under a mutex to prevent other
3542   // workers from interfering with the work done below.
3543   MutexLockerEx ml(_overflow_stack->par_lock(),
3544                    Mutex::_no_safepoint_check_flag);
3545   // Remember the least grey address discarded
3546   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3547   _collector->lower_restart_addr(ra);
3548   _overflow_stack->reset();  // discard stack contents
3549   _overflow_stack->expand(); // expand the stack if possible
3550 }
3551 
3552 
3553 void CMSConcMarkingTask::do_work_steal(int i) {
3554   OopTaskQueue* work_q = work_queue(i);
3555   oop obj_to_scan;
3556   CMSBitMap* bm = &(_collector->_markBitMap);
3557   CMSMarkStack* ovflw = &(_collector->_markStack);
3558   int* seed = _collector->hash_seed(i);
3559   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3560   while (true) {
3561     cl.trim_queue(0);
3562     assert(work_q->size() == 0, "Should have been emptied above");
3563     if (get_work_from_overflow_stack(ovflw, work_q)) {
3564       // Can't assert below because the work obtained from the
3565       // overflow stack may already have been stolen from us.
3566       // assert(work_q->size() > 0, "Work from overflow stack");
3567       continue;
3568     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3569       assert(obj_to_scan->is_oop(), "Should be an oop");
3570       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3571       obj_to_scan->oop_iterate(&cl);
3572     } else if (terminator()->offer_termination(&_term_term)) {
3573       assert(work_q->size() == 0, "Impossible!");
3574       break;
3575     } else if (yielding() || should_yield()) {
3576       yield();
3577     }
3578   }
3579 }
3580 
3581 // This is run by the CMS (coordinator) thread.
3582 void CMSConcMarkingTask::coordinator_yield() {
3583   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3584          "CMS thread should hold CMS token");
3585   // First give up the locks, then yield, then re-lock
3586   // We should probably use a constructor/destructor idiom to
3587   // do this unlock/lock or modify the MutexUnlocker class to
3588   // serve our purpose. XXX
3589   assert_lock_strong(_bit_map_lock);
3590   _bit_map_lock->unlock();
3591   ConcurrentMarkSweepThread::desynchronize(true);
3592   _collector->stopTimer();
3593   if (PrintCMSStatistics != 0) {
3594     _collector->incrementYields();
3595   }
3596 
3597   // It is possible for whichever thread initiated the yield request
3598   // not to get a chance to wake up and take the bitmap lock between
3599   // this thread releasing it and reacquiring it. So, while the
3600   // should_yield() flag is on, let's sleep for a bit to give the
3601   // other thread a chance to wake up. The limit imposed on the number
3602   // of iterations is defensive, to avoid any unforseen circumstances
3603   // putting us into an infinite loop. Since it's always been this
3604   // (coordinator_yield()) method that was observed to cause the
3605   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3606   // which is by default non-zero. For the other seven methods that
3607   // also perform the yield operation, as are using a different
3608   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3609   // can enable the sleeping for those methods too, if necessary.
3610   // See 6442774.
3611   //
3612   // We really need to reconsider the synchronization between the GC
3613   // thread and the yield-requesting threads in the future and we
3614   // should really use wait/notify, which is the recommended
3615   // way of doing this type of interaction. Additionally, we should
3616   // consolidate the eight methods that do the yield operation and they
3617   // are almost identical into one for better maintainability and
3618   // readability. See 6445193.
3619   //
3620   // Tony 2006.06.29
3621   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3622                    ConcurrentMarkSweepThread::should_yield() &&
3623                    !CMSCollector::foregroundGCIsActive(); ++i) {
3624     os::sleep(Thread::current(), 1, false);
3625   }
3626 
3627   ConcurrentMarkSweepThread::synchronize(true);
3628   _bit_map_lock->lock_without_safepoint_check();
3629   _collector->startTimer();
3630 }
3631 
3632 bool CMSCollector::do_marking_mt() {
3633   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3634   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3635                                                                   conc_workers()->active_workers(),
3636                                                                   Threads::number_of_non_daemon_threads());
3637   conc_workers()->set_active_workers(num_workers);
3638 
3639   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3640 
3641   CMSConcMarkingTask tsk(this,
3642                          cms_space,
3643                          conc_workers(),
3644                          task_queues());
3645 
3646   // Since the actual number of workers we get may be different
3647   // from the number we requested above, do we need to do anything different
3648   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3649   // class?? XXX
3650   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3651 
3652   // Refs discovery is already non-atomic.
3653   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3654   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3655   conc_workers()->start_task(&tsk);
3656   while (tsk.yielded()) {
3657     tsk.coordinator_yield();
3658     conc_workers()->continue_task(&tsk);
3659   }
3660   // If the task was aborted, _restart_addr will be non-NULL
3661   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3662   while (_restart_addr != NULL) {
3663     // XXX For now we do not make use of ABORTED state and have not
3664     // yet implemented the right abort semantics (even in the original
3665     // single-threaded CMS case). That needs some more investigation
3666     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3667     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3668     // If _restart_addr is non-NULL, a marking stack overflow
3669     // occurred; we need to do a fresh marking iteration from the
3670     // indicated restart address.
3671     if (_foregroundGCIsActive) {
3672       // We may be running into repeated stack overflows, having
3673       // reached the limit of the stack size, while making very
3674       // slow forward progress. It may be best to bail out and
3675       // let the foreground collector do its job.
3676       // Clear _restart_addr, so that foreground GC
3677       // works from scratch. This avoids the headache of
3678       // a "rescan" which would otherwise be needed because
3679       // of the dirty mod union table & card table.
3680       _restart_addr = NULL;
3681       return false;
3682     }
3683     // Adjust the task to restart from _restart_addr
3684     tsk.reset(_restart_addr);
3685     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3686                   _restart_addr);
3687     _restart_addr = NULL;
3688     // Get the workers going again
3689     conc_workers()->start_task(&tsk);
3690     while (tsk.yielded()) {
3691       tsk.coordinator_yield();
3692       conc_workers()->continue_task(&tsk);
3693     }
3694   }
3695   assert(tsk.completed(), "Inconsistency");
3696   assert(tsk.result() == true, "Inconsistency");
3697   return true;
3698 }
3699 
3700 bool CMSCollector::do_marking_st() {
3701   ResourceMark rm;
3702   HandleMark   hm;
3703 
3704   // Temporarily make refs discovery single threaded (non-MT)
3705   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3706   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3707     &_markStack, CMSYield);
3708   // the last argument to iterate indicates whether the iteration
3709   // should be incremental with periodic yields.
3710   _markBitMap.iterate(&markFromRootsClosure);
3711   // If _restart_addr is non-NULL, a marking stack overflow
3712   // occurred; we need to do a fresh iteration from the
3713   // indicated restart address.
3714   while (_restart_addr != NULL) {
3715     if (_foregroundGCIsActive) {
3716       // We may be running into repeated stack overflows, having
3717       // reached the limit of the stack size, while making very
3718       // slow forward progress. It may be best to bail out and
3719       // let the foreground collector do its job.
3720       // Clear _restart_addr, so that foreground GC
3721       // works from scratch. This avoids the headache of
3722       // a "rescan" which would otherwise be needed because
3723       // of the dirty mod union table & card table.
3724       _restart_addr = NULL;
3725       return false;  // indicating failure to complete marking
3726     }
3727     // Deal with stack overflow:
3728     // we restart marking from _restart_addr
3729     HeapWord* ra = _restart_addr;
3730     markFromRootsClosure.reset(ra);
3731     _restart_addr = NULL;
3732     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3733   }
3734   return true;
3735 }
3736 
3737 void CMSCollector::preclean() {
3738   check_correct_thread_executing();
3739   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3740   verify_work_stacks_empty();
3741   verify_overflow_empty();
3742   _abort_preclean = false;
3743   if (CMSPrecleaningEnabled) {
3744     if (!CMSEdenChunksRecordAlways) {
3745       _eden_chunk_index = 0;
3746     }
3747     size_t used = get_eden_used();
3748     size_t capacity = get_eden_capacity();
3749     // Don't start sampling unless we will get sufficiently
3750     // many samples.
3751     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3752                 * CMSScheduleRemarkEdenPenetration)) {
3753       _start_sampling = true;
3754     } else {
3755       _start_sampling = false;
3756     }
3757     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3758     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3759     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3760   }
3761   CMSTokenSync x(true); // is cms thread
3762   if (CMSPrecleaningEnabled) {
3763     sample_eden();
3764     _collectorState = AbortablePreclean;
3765   } else {
3766     _collectorState = FinalMarking;
3767   }
3768   verify_work_stacks_empty();
3769   verify_overflow_empty();
3770 }
3771 
3772 // Try and schedule the remark such that young gen
3773 // occupancy is CMSScheduleRemarkEdenPenetration %.
3774 void CMSCollector::abortable_preclean() {
3775   check_correct_thread_executing();
3776   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3777   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3778 
3779   // If Eden's current occupancy is below this threshold,
3780   // immediately schedule the remark; else preclean
3781   // past the next scavenge in an effort to
3782   // schedule the pause as described above. By choosing
3783   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3784   // we will never do an actual abortable preclean cycle.
3785   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3786     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3787     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3788     // We need more smarts in the abortable preclean
3789     // loop below to deal with cases where allocation
3790     // in young gen is very very slow, and our precleaning
3791     // is running a losing race against a horde of
3792     // mutators intent on flooding us with CMS updates
3793     // (dirty cards).
3794     // One, admittedly dumb, strategy is to give up
3795     // after a certain number of abortable precleaning loops
3796     // or after a certain maximum time. We want to make
3797     // this smarter in the next iteration.
3798     // XXX FIX ME!!! YSR
3799     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3800     while (!(should_abort_preclean() ||
3801              ConcurrentMarkSweepThread::should_terminate())) {
3802       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3803       cumworkdone += workdone;
3804       loops++;
3805       // Voluntarily terminate abortable preclean phase if we have
3806       // been at it for too long.
3807       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3808           loops >= CMSMaxAbortablePrecleanLoops) {
3809         if (PrintGCDetails) {
3810           gclog_or_tty->print(" CMS: abort preclean due to loops ");
3811         }
3812         break;
3813       }
3814       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3815         if (PrintGCDetails) {
3816           gclog_or_tty->print(" CMS: abort preclean due to time ");
3817         }
3818         break;
3819       }
3820       // If we are doing little work each iteration, we should
3821       // take a short break.
3822       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3823         // Sleep for some time, waiting for work to accumulate
3824         stopTimer();
3825         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3826         startTimer();
3827         waited++;
3828       }
3829     }
3830     if (PrintCMSStatistics > 0) {
3831       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3832                           loops, waited, cumworkdone);
3833     }
3834   }
3835   CMSTokenSync x(true); // is cms thread
3836   if (_collectorState != Idling) {
3837     assert(_collectorState == AbortablePreclean,
3838            "Spontaneous state transition?");
3839     _collectorState = FinalMarking;
3840   } // Else, a foreground collection completed this CMS cycle.
3841   return;
3842 }
3843 
3844 // Respond to an Eden sampling opportunity
3845 void CMSCollector::sample_eden() {
3846   // Make sure a young gc cannot sneak in between our
3847   // reading and recording of a sample.
3848   assert(Thread::current()->is_ConcurrentGC_thread(),
3849          "Only the cms thread may collect Eden samples");
3850   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3851          "Should collect samples while holding CMS token");
3852   if (!_start_sampling) {
3853     return;
3854   }
3855   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3856   // is populated by the young generation.
3857   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3858     if (_eden_chunk_index < _eden_chunk_capacity) {
3859       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3860       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3861              "Unexpected state of Eden");
3862       // We'd like to check that what we just sampled is an oop-start address;
3863       // however, we cannot do that here since the object may not yet have been
3864       // initialized. So we'll instead do the check when we _use_ this sample
3865       // later.
3866       if (_eden_chunk_index == 0 ||
3867           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3868                          _eden_chunk_array[_eden_chunk_index-1])
3869            >= CMSSamplingGrain)) {
3870         _eden_chunk_index++;  // commit sample
3871       }
3872     }
3873   }
3874   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3875     size_t used = get_eden_used();
3876     size_t capacity = get_eden_capacity();
3877     assert(used <= capacity, "Unexpected state of Eden");
3878     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3879       _abort_preclean = true;
3880     }
3881   }
3882 }
3883 
3884 
3885 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3886   assert(_collectorState == Precleaning ||
3887          _collectorState == AbortablePreclean, "incorrect state");
3888   ResourceMark rm;
3889   HandleMark   hm;
3890 
3891   // Precleaning is currently not MT but the reference processor
3892   // may be set for MT.  Disable it temporarily here.
3893   ReferenceProcessor* rp = ref_processor();
3894   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3895 
3896   // Do one pass of scrubbing the discovered reference lists
3897   // to remove any reference objects with strongly-reachable
3898   // referents.
3899   if (clean_refs) {
3900     CMSPrecleanRefsYieldClosure yield_cl(this);
3901     assert(rp->span().equals(_span), "Spans should be equal");
3902     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3903                                    &_markStack, true /* preclean */);
3904     CMSDrainMarkingStackClosure complete_trace(this,
3905                                    _span, &_markBitMap, &_markStack,
3906                                    &keep_alive, true /* preclean */);
3907 
3908     // We don't want this step to interfere with a young
3909     // collection because we don't want to take CPU
3910     // or memory bandwidth away from the young GC threads
3911     // (which may be as many as there are CPUs).
3912     // Note that we don't need to protect ourselves from
3913     // interference with mutators because they can't
3914     // manipulate the discovered reference lists nor affect
3915     // the computed reachability of the referents, the
3916     // only properties manipulated by the precleaning
3917     // of these reference lists.
3918     stopTimer();
3919     CMSTokenSyncWithLocks x(true /* is cms thread */,
3920                             bitMapLock());
3921     startTimer();
3922     sample_eden();
3923 
3924     // The following will yield to allow foreground
3925     // collection to proceed promptly. XXX YSR:
3926     // The code in this method may need further
3927     // tweaking for better performance and some restructuring
3928     // for cleaner interfaces.
3929     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3930     rp->preclean_discovered_references(
3931           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3932           gc_timer, _gc_tracer_cm->gc_id());
3933   }
3934 
3935   if (clean_survivor) {  // preclean the active survivor space(s)
3936     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3937                              &_markBitMap, &_modUnionTable,
3938                              &_markStack, true /* precleaning phase */);
3939     stopTimer();
3940     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3941                              bitMapLock());
3942     startTimer();
3943     unsigned int before_count =
3944       GenCollectedHeap::heap()->total_collections();
3945     SurvivorSpacePrecleanClosure
3946       sss_cl(this, _span, &_markBitMap, &_markStack,
3947              &pam_cl, before_count, CMSYield);
3948     _young_gen->from()->object_iterate_careful(&sss_cl);
3949     _young_gen->to()->object_iterate_careful(&sss_cl);
3950   }
3951   MarkRefsIntoAndScanClosure
3952     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3953              &_markStack, this, CMSYield,
3954              true /* precleaning phase */);
3955   // CAUTION: The following closure has persistent state that may need to
3956   // be reset upon a decrease in the sequence of addresses it
3957   // processes.
3958   ScanMarkedObjectsAgainCarefullyClosure
3959     smoac_cl(this, _span,
3960       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3961 
3962   // Preclean dirty cards in ModUnionTable and CardTable using
3963   // appropriate convergence criterion;
3964   // repeat CMSPrecleanIter times unless we find that
3965   // we are losing.
3966   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3967   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3968          "Bad convergence multiplier");
3969   assert(CMSPrecleanThreshold >= 100,
3970          "Unreasonably low CMSPrecleanThreshold");
3971 
3972   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3973   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3974        numIter < CMSPrecleanIter;
3975        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3976     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3977     if (Verbose && PrintGCDetails) {
3978       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3979     }
3980     // Either there are very few dirty cards, so re-mark
3981     // pause will be small anyway, or our pre-cleaning isn't
3982     // that much faster than the rate at which cards are being
3983     // dirtied, so we might as well stop and re-mark since
3984     // precleaning won't improve our re-mark time by much.
3985     if (curNumCards <= CMSPrecleanThreshold ||
3986         (numIter > 0 &&
3987          (curNumCards * CMSPrecleanDenominator >
3988          lastNumCards * CMSPrecleanNumerator))) {
3989       numIter++;
3990       cumNumCards += curNumCards;
3991       break;
3992     }
3993   }
3994 
3995   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3996 
3997   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3998   cumNumCards += curNumCards;
3999   if (PrintGCDetails && PrintCMSStatistics != 0) {
4000     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4001                   curNumCards, cumNumCards, numIter);
4002   }
4003   return cumNumCards;   // as a measure of useful work done
4004 }
4005 
4006 // PRECLEANING NOTES:
4007 // Precleaning involves:
4008 // . reading the bits of the modUnionTable and clearing the set bits.
4009 // . For the cards corresponding to the set bits, we scan the
4010 //   objects on those cards. This means we need the free_list_lock
4011 //   so that we can safely iterate over the CMS space when scanning
4012 //   for oops.
4013 // . When we scan the objects, we'll be both reading and setting
4014 //   marks in the marking bit map, so we'll need the marking bit map.
4015 // . For protecting _collector_state transitions, we take the CGC_lock.
4016 //   Note that any races in the reading of of card table entries by the
4017 //   CMS thread on the one hand and the clearing of those entries by the
4018 //   VM thread or the setting of those entries by the mutator threads on the
4019 //   other are quite benign. However, for efficiency it makes sense to keep
4020 //   the VM thread from racing with the CMS thread while the latter is
4021 //   dirty card info to the modUnionTable. We therefore also use the
4022 //   CGC_lock to protect the reading of the card table and the mod union
4023 //   table by the CM thread.
4024 // . We run concurrently with mutator updates, so scanning
4025 //   needs to be done carefully  -- we should not try to scan
4026 //   potentially uninitialized objects.
4027 //
4028 // Locking strategy: While holding the CGC_lock, we scan over and
4029 // reset a maximal dirty range of the mod union / card tables, then lock
4030 // the free_list_lock and bitmap lock to do a full marking, then
4031 // release these locks; and repeat the cycle. This allows for a
4032 // certain amount of fairness in the sharing of these locks between
4033 // the CMS collector on the one hand, and the VM thread and the
4034 // mutators on the other.
4035 
4036 // NOTE: preclean_mod_union_table() and preclean_card_table()
4037 // further below are largely identical; if you need to modify
4038 // one of these methods, please check the other method too.
4039 
4040 size_t CMSCollector::preclean_mod_union_table(
4041   ConcurrentMarkSweepGeneration* old_gen,
4042   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4043   verify_work_stacks_empty();
4044   verify_overflow_empty();
4045 
4046   // strategy: starting with the first card, accumulate contiguous
4047   // ranges of dirty cards; clear these cards, then scan the region
4048   // covered by these cards.
4049 
4050   // Since all of the MUT is committed ahead, we can just use
4051   // that, in case the generations expand while we are precleaning.
4052   // It might also be fine to just use the committed part of the
4053   // generation, but we might potentially miss cards when the
4054   // generation is rapidly expanding while we are in the midst
4055   // of precleaning.
4056   HeapWord* startAddr = old_gen->reserved().start();
4057   HeapWord* endAddr   = old_gen->reserved().end();
4058 
4059   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4060 
4061   size_t numDirtyCards, cumNumDirtyCards;
4062   HeapWord *nextAddr, *lastAddr;
4063   for (cumNumDirtyCards = numDirtyCards = 0,
4064        nextAddr = lastAddr = startAddr;
4065        nextAddr < endAddr;
4066        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4067 
4068     ResourceMark rm;
4069     HandleMark   hm;
4070 
4071     MemRegion dirtyRegion;
4072     {
4073       stopTimer();
4074       // Potential yield point
4075       CMSTokenSync ts(true);
4076       startTimer();
4077       sample_eden();
4078       // Get dirty region starting at nextOffset (inclusive),
4079       // simultaneously clearing it.
4080       dirtyRegion =
4081         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4082       assert(dirtyRegion.start() >= nextAddr,
4083              "returned region inconsistent?");
4084     }
4085     // Remember where the next search should begin.
4086     // The returned region (if non-empty) is a right open interval,
4087     // so lastOffset is obtained from the right end of that
4088     // interval.
4089     lastAddr = dirtyRegion.end();
4090     // Should do something more transparent and less hacky XXX
4091     numDirtyCards =
4092       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4093 
4094     // We'll scan the cards in the dirty region (with periodic
4095     // yields for foreground GC as needed).
4096     if (!dirtyRegion.is_empty()) {
4097       assert(numDirtyCards > 0, "consistency check");
4098       HeapWord* stop_point = NULL;
4099       stopTimer();
4100       // Potential yield point
4101       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4102                                bitMapLock());
4103       startTimer();
4104       {
4105         verify_work_stacks_empty();
4106         verify_overflow_empty();
4107         sample_eden();
4108         stop_point =
4109           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4110       }
4111       if (stop_point != NULL) {
4112         // The careful iteration stopped early either because it found an
4113         // uninitialized object, or because we were in the midst of an
4114         // "abortable preclean", which should now be aborted. Redirty
4115         // the bits corresponding to the partially-scanned or unscanned
4116         // cards. We'll either restart at the next block boundary or
4117         // abort the preclean.
4118         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4119                "Should only be AbortablePreclean.");
4120         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4121         if (should_abort_preclean()) {
4122           break; // out of preclean loop
4123         } else {
4124           // Compute the next address at which preclean should pick up;
4125           // might need bitMapLock in order to read P-bits.
4126           lastAddr = next_card_start_after_block(stop_point);
4127         }
4128       }
4129     } else {
4130       assert(lastAddr == endAddr, "consistency check");
4131       assert(numDirtyCards == 0, "consistency check");
4132       break;
4133     }
4134   }
4135   verify_work_stacks_empty();
4136   verify_overflow_empty();
4137   return cumNumDirtyCards;
4138 }
4139 
4140 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4141 // below are largely identical; if you need to modify
4142 // one of these methods, please check the other method too.
4143 
4144 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4145   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4146   // strategy: it's similar to precleamModUnionTable above, in that
4147   // we accumulate contiguous ranges of dirty cards, mark these cards
4148   // precleaned, then scan the region covered by these cards.
4149   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4150   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4151 
4152   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4153 
4154   size_t numDirtyCards, cumNumDirtyCards;
4155   HeapWord *lastAddr, *nextAddr;
4156 
4157   for (cumNumDirtyCards = numDirtyCards = 0,
4158        nextAddr = lastAddr = startAddr;
4159        nextAddr < endAddr;
4160        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4161 
4162     ResourceMark rm;
4163     HandleMark   hm;
4164 
4165     MemRegion dirtyRegion;
4166     {
4167       // See comments in "Precleaning notes" above on why we
4168       // do this locking. XXX Could the locking overheads be
4169       // too high when dirty cards are sparse? [I don't think so.]
4170       stopTimer();
4171       CMSTokenSync x(true); // is cms thread
4172       startTimer();
4173       sample_eden();
4174       // Get and clear dirty region from card table
4175       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4176                                     MemRegion(nextAddr, endAddr),
4177                                     true,
4178                                     CardTableModRefBS::precleaned_card_val());
4179 
4180       assert(dirtyRegion.start() >= nextAddr,
4181              "returned region inconsistent?");
4182     }
4183     lastAddr = dirtyRegion.end();
4184     numDirtyCards =
4185       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4186 
4187     if (!dirtyRegion.is_empty()) {
4188       stopTimer();
4189       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4190       startTimer();
4191       sample_eden();
4192       verify_work_stacks_empty();
4193       verify_overflow_empty();
4194       HeapWord* stop_point =
4195         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4196       if (stop_point != NULL) {
4197         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4198                "Should only be AbortablePreclean.");
4199         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4200         if (should_abort_preclean()) {
4201           break; // out of preclean loop
4202         } else {
4203           // Compute the next address at which preclean should pick up.
4204           lastAddr = next_card_start_after_block(stop_point);
4205         }
4206       }
4207     } else {
4208       break;
4209     }
4210   }
4211   verify_work_stacks_empty();
4212   verify_overflow_empty();
4213   return cumNumDirtyCards;
4214 }
4215 
4216 class PrecleanKlassClosure : public KlassClosure {
4217   KlassToOopClosure _cm_klass_closure;
4218  public:
4219   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4220   void do_klass(Klass* k) {
4221     if (k->has_accumulated_modified_oops()) {
4222       k->clear_accumulated_modified_oops();
4223 
4224       _cm_klass_closure.do_klass(k);
4225     }
4226   }
4227 };
4228 
4229 // The freelist lock is needed to prevent asserts, is it really needed?
4230 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4231 
4232   cl->set_freelistLock(freelistLock);
4233 
4234   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4235 
4236   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4237   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4238   PrecleanKlassClosure preclean_klass_closure(cl);
4239   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4240 
4241   verify_work_stacks_empty();
4242   verify_overflow_empty();
4243 }
4244 
4245 void CMSCollector::checkpointRootsFinal() {
4246   assert(_collectorState == FinalMarking, "incorrect state transition?");
4247   check_correct_thread_executing();
4248   // world is stopped at this checkpoint
4249   assert(SafepointSynchronize::is_at_safepoint(),
4250          "world should be stopped");
4251   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4252 
4253   verify_work_stacks_empty();
4254   verify_overflow_empty();
4255 
4256   if (PrintGCDetails) {
4257     gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4258                         _young_gen->used() / K,
4259                         _young_gen->capacity() / K);
4260   }
4261   {
4262     if (CMSScavengeBeforeRemark) {
4263       GenCollectedHeap* gch = GenCollectedHeap::heap();
4264       // Temporarily set flag to false, GCH->do_collection will
4265       // expect it to be false and set to true
4266       FlagSetting fl(gch->_is_gc_active, false);
4267       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4268         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4269       gch->do_collection(true,                      // full (i.e. force, see below)
4270                          false,                     // !clear_all_soft_refs
4271                          0,                         // size
4272                          false,                     // is_tlab
4273                          GenCollectedHeap::YoungGen // type
4274         );
4275     }
4276     FreelistLocker x(this);
4277     MutexLockerEx y(bitMapLock(),
4278                     Mutex::_no_safepoint_check_flag);
4279     checkpointRootsFinalWork();
4280   }
4281   verify_work_stacks_empty();
4282   verify_overflow_empty();
4283 }
4284 
4285 void CMSCollector::checkpointRootsFinalWork() {
4286   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4287 
4288   assert(haveFreelistLocks(), "must have free list locks");
4289   assert_lock_strong(bitMapLock());
4290 
4291   ResourceMark rm;
4292   HandleMark   hm;
4293 
4294   GenCollectedHeap* gch = GenCollectedHeap::heap();
4295 
4296   if (should_unload_classes()) {
4297     CodeCache::gc_prologue();
4298   }
4299   assert(haveFreelistLocks(), "must have free list locks");
4300   assert_lock_strong(bitMapLock());
4301 
4302   // We might assume that we need not fill TLAB's when
4303   // CMSScavengeBeforeRemark is set, because we may have just done
4304   // a scavenge which would have filled all TLAB's -- and besides
4305   // Eden would be empty. This however may not always be the case --
4306   // for instance although we asked for a scavenge, it may not have
4307   // happened because of a JNI critical section. We probably need
4308   // a policy for deciding whether we can in that case wait until
4309   // the critical section releases and then do the remark following
4310   // the scavenge, and skip it here. In the absence of that policy,
4311   // or of an indication of whether the scavenge did indeed occur,
4312   // we cannot rely on TLAB's having been filled and must do
4313   // so here just in case a scavenge did not happen.
4314   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4315   // Update the saved marks which may affect the root scans.
4316   gch->save_marks();
4317 
4318   if (CMSPrintEdenSurvivorChunks) {
4319     print_eden_and_survivor_chunk_arrays();
4320   }
4321 
4322   {
4323 #if defined(COMPILER2) || INCLUDE_JVMCI
4324     DerivedPointerTableDeactivate dpt_deact;
4325 #endif
4326 
4327     // Note on the role of the mod union table:
4328     // Since the marker in "markFromRoots" marks concurrently with
4329     // mutators, it is possible for some reachable objects not to have been
4330     // scanned. For instance, an only reference to an object A was
4331     // placed in object B after the marker scanned B. Unless B is rescanned,
4332     // A would be collected. Such updates to references in marked objects
4333     // are detected via the mod union table which is the set of all cards
4334     // dirtied since the first checkpoint in this GC cycle and prior to
4335     // the most recent young generation GC, minus those cleaned up by the
4336     // concurrent precleaning.
4337     if (CMSParallelRemarkEnabled) {
4338       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4339       do_remark_parallel();
4340     } else {
4341       GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4342                   _gc_timer_cm, _gc_tracer_cm->gc_id());
4343       do_remark_non_parallel();
4344     }
4345   }
4346   verify_work_stacks_empty();
4347   verify_overflow_empty();
4348 
4349   {
4350     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4351     refProcessingWork();
4352   }
4353   verify_work_stacks_empty();
4354   verify_overflow_empty();
4355 
4356   if (should_unload_classes()) {
4357     CodeCache::gc_epilogue();
4358   }
4359   JvmtiExport::gc_epilogue();
4360 
4361   // If we encountered any (marking stack / work queue) overflow
4362   // events during the current CMS cycle, take appropriate
4363   // remedial measures, where possible, so as to try and avoid
4364   // recurrence of that condition.
4365   assert(_markStack.isEmpty(), "No grey objects");
4366   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4367                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4368   if (ser_ovflw > 0) {
4369     if (PrintCMSStatistics != 0) {
4370       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4371         "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4372         ", kac_preclean=" SIZE_FORMAT ")",
4373         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4374         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4375     }
4376     _markStack.expand();
4377     _ser_pmc_remark_ovflw = 0;
4378     _ser_pmc_preclean_ovflw = 0;
4379     _ser_kac_preclean_ovflw = 0;
4380     _ser_kac_ovflw = 0;
4381   }
4382   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4383     if (PrintCMSStatistics != 0) {
4384       gclog_or_tty->print_cr("Work queue overflow (benign) "
4385         "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4386         _par_pmc_remark_ovflw, _par_kac_ovflw);
4387     }
4388     _par_pmc_remark_ovflw = 0;
4389     _par_kac_ovflw = 0;
4390   }
4391   if (PrintCMSStatistics != 0) {
4392      if (_markStack._hit_limit > 0) {
4393        gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4394                               _markStack._hit_limit);
4395      }
4396      if (_markStack._failed_double > 0) {
4397        gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4398                               " current capacity " SIZE_FORMAT,
4399                               _markStack._failed_double,
4400                               _markStack.capacity());
4401      }
4402   }
4403   _markStack._hit_limit = 0;
4404   _markStack._failed_double = 0;
4405 
4406   if ((VerifyAfterGC || VerifyDuringGC) &&
4407       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4408     verify_after_remark();
4409   }
4410 
4411   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4412 
4413   // Change under the freelistLocks.
4414   _collectorState = Sweeping;
4415   // Call isAllClear() under bitMapLock
4416   assert(_modUnionTable.isAllClear(),
4417       "Should be clear by end of the final marking");
4418   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4419       "Should be clear by end of the final marking");
4420 }
4421 
4422 void CMSParInitialMarkTask::work(uint worker_id) {
4423   elapsedTimer _timer;
4424   ResourceMark rm;
4425   HandleMark   hm;
4426 
4427   // ---------- scan from roots --------------
4428   _timer.start();
4429   GenCollectedHeap* gch = GenCollectedHeap::heap();
4430   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4431 
4432   // ---------- young gen roots --------------
4433   {
4434     work_on_young_gen_roots(worker_id, &par_mri_cl);
4435     _timer.stop();
4436     if (PrintCMSStatistics != 0) {
4437       gclog_or_tty->print_cr(
4438         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4439         worker_id, _timer.seconds());
4440     }
4441   }
4442 
4443   // ---------- remaining roots --------------
4444   _timer.reset();
4445   _timer.start();
4446 
4447   CLDToOopClosure cld_closure(&par_mri_cl, true);
4448 
4449   gch->gen_process_roots(_strong_roots_scope,
4450                          GenCollectedHeap::OldGen,
4451                          false,     // yg was scanned above
4452                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4453                          _collector->should_unload_classes(),
4454                          &par_mri_cl,
4455                          NULL,
4456                          &cld_closure);
4457   assert(_collector->should_unload_classes()
4458          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4459          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4460   _timer.stop();
4461   if (PrintCMSStatistics != 0) {
4462     gclog_or_tty->print_cr(
4463       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4464       worker_id, _timer.seconds());
4465   }
4466 }
4467 
4468 // Parallel remark task
4469 class CMSParRemarkTask: public CMSParMarkTask {
4470   CompactibleFreeListSpace* _cms_space;
4471 
4472   // The per-thread work queues, available here for stealing.
4473   OopTaskQueueSet*       _task_queues;
4474   ParallelTaskTerminator _term;
4475   StrongRootsScope*      _strong_roots_scope;
4476 
4477  public:
4478   // A value of 0 passed to n_workers will cause the number of
4479   // workers to be taken from the active workers in the work gang.
4480   CMSParRemarkTask(CMSCollector* collector,
4481                    CompactibleFreeListSpace* cms_space,
4482                    uint n_workers, WorkGang* workers,
4483                    OopTaskQueueSet* task_queues,
4484                    StrongRootsScope* strong_roots_scope):
4485     CMSParMarkTask("Rescan roots and grey objects in parallel",
4486                    collector, n_workers),
4487     _cms_space(cms_space),
4488     _task_queues(task_queues),
4489     _term(n_workers, task_queues),
4490     _strong_roots_scope(strong_roots_scope) { }
4491 
4492   OopTaskQueueSet* task_queues() { return _task_queues; }
4493 
4494   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4495 
4496   ParallelTaskTerminator* terminator() { return &_term; }
4497   uint n_workers() { return _n_workers; }
4498 
4499   void work(uint worker_id);
4500 
4501  private:
4502   // ... of  dirty cards in old space
4503   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4504                                   Par_MarkRefsIntoAndScanClosure* cl);
4505 
4506   // ... work stealing for the above
4507   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4508 };
4509 
4510 class RemarkKlassClosure : public KlassClosure {
4511   KlassToOopClosure _cm_klass_closure;
4512  public:
4513   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4514   void do_klass(Klass* k) {
4515     // Check if we have modified any oops in the Klass during the concurrent marking.
4516     if (k->has_accumulated_modified_oops()) {
4517       k->clear_accumulated_modified_oops();
4518 
4519       // We could have transfered the current modified marks to the accumulated marks,
4520       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4521     } else if (k->has_modified_oops()) {
4522       // Don't clear anything, this info is needed by the next young collection.
4523     } else {
4524       // No modified oops in the Klass.
4525       return;
4526     }
4527 
4528     // The klass has modified fields, need to scan the klass.
4529     _cm_klass_closure.do_klass(k);
4530   }
4531 };
4532 
4533 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4534   ParNewGeneration* young_gen = _collector->_young_gen;
4535   ContiguousSpace* eden_space = young_gen->eden();
4536   ContiguousSpace* from_space = young_gen->from();
4537   ContiguousSpace* to_space   = young_gen->to();
4538 
4539   HeapWord** eca = _collector->_eden_chunk_array;
4540   size_t     ect = _collector->_eden_chunk_index;
4541   HeapWord** sca = _collector->_survivor_chunk_array;
4542   size_t     sct = _collector->_survivor_chunk_index;
4543 
4544   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4545   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4546 
4547   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4548   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4549   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4550 }
4551 
4552 // work_queue(i) is passed to the closure
4553 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4554 // also is passed to do_dirty_card_rescan_tasks() and to
4555 // do_work_steal() to select the i-th task_queue.
4556 
4557 void CMSParRemarkTask::work(uint worker_id) {
4558   elapsedTimer _timer;
4559   ResourceMark rm;
4560   HandleMark   hm;
4561 
4562   // ---------- rescan from roots --------------
4563   _timer.start();
4564   GenCollectedHeap* gch = GenCollectedHeap::heap();
4565   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4566     _collector->_span, _collector->ref_processor(),
4567     &(_collector->_markBitMap),
4568     work_queue(worker_id));
4569 
4570   // Rescan young gen roots first since these are likely
4571   // coarsely partitioned and may, on that account, constitute
4572   // the critical path; thus, it's best to start off that
4573   // work first.
4574   // ---------- young gen roots --------------
4575   {
4576     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4577     _timer.stop();
4578     if (PrintCMSStatistics != 0) {
4579       gclog_or_tty->print_cr(
4580         "Finished young gen rescan work in %dth thread: %3.3f sec",
4581         worker_id, _timer.seconds());
4582     }
4583   }
4584 
4585   // ---------- remaining roots --------------
4586   _timer.reset();
4587   _timer.start();
4588   gch->gen_process_roots(_strong_roots_scope,
4589                          GenCollectedHeap::OldGen,
4590                          false,     // yg was scanned above
4591                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4592                          _collector->should_unload_classes(),
4593                          &par_mrias_cl,
4594                          NULL,
4595                          NULL);     // The dirty klasses will be handled below
4596 
4597   assert(_collector->should_unload_classes()
4598          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4599          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4600   _timer.stop();
4601   if (PrintCMSStatistics != 0) {
4602     gclog_or_tty->print_cr(
4603       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4604       worker_id, _timer.seconds());
4605   }
4606 
4607   // ---------- unhandled CLD scanning ----------
4608   if (worker_id == 0) { // Single threaded at the moment.
4609     _timer.reset();
4610     _timer.start();
4611 
4612     // Scan all new class loader data objects and new dependencies that were
4613     // introduced during concurrent marking.
4614     ResourceMark rm;
4615     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4616     for (int i = 0; i < array->length(); i++) {
4617       par_mrias_cl.do_cld_nv(array->at(i));
4618     }
4619 
4620     // We don't need to keep track of new CLDs anymore.
4621     ClassLoaderDataGraph::remember_new_clds(false);
4622 
4623     _timer.stop();
4624     if (PrintCMSStatistics != 0) {
4625       gclog_or_tty->print_cr(
4626           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4627           worker_id, _timer.seconds());
4628     }
4629   }
4630 
4631   // ---------- dirty klass scanning ----------
4632   if (worker_id == 0) { // Single threaded at the moment.
4633     _timer.reset();
4634     _timer.start();
4635 
4636     // Scan all classes that was dirtied during the concurrent marking phase.
4637     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4638     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4639 
4640     _timer.stop();
4641     if (PrintCMSStatistics != 0) {
4642       gclog_or_tty->print_cr(
4643           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4644           worker_id, _timer.seconds());
4645     }
4646   }
4647 
4648   // We might have added oops to ClassLoaderData::_handles during the
4649   // concurrent marking phase. These oops point to newly allocated objects
4650   // that are guaranteed to be kept alive. Either by the direct allocation
4651   // code, or when the young collector processes the roots. Hence,
4652   // we don't have to revisit the _handles block during the remark phase.
4653 
4654   // ---------- rescan dirty cards ------------
4655   _timer.reset();
4656   _timer.start();
4657 
4658   // Do the rescan tasks for each of the two spaces
4659   // (cms_space) in turn.
4660   // "worker_id" is passed to select the task_queue for "worker_id"
4661   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4662   _timer.stop();
4663   if (PrintCMSStatistics != 0) {
4664     gclog_or_tty->print_cr(
4665       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4666       worker_id, _timer.seconds());
4667   }
4668 
4669   // ---------- steal work from other threads ...
4670   // ---------- ... and drain overflow list.
4671   _timer.reset();
4672   _timer.start();
4673   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4674   _timer.stop();
4675   if (PrintCMSStatistics != 0) {
4676     gclog_or_tty->print_cr(
4677       "Finished work stealing in %dth thread: %3.3f sec",
4678       worker_id, _timer.seconds());
4679   }
4680 }
4681 
4682 // Note that parameter "i" is not used.
4683 void
4684 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4685   OopsInGenClosure* cl, ContiguousSpace* space,
4686   HeapWord** chunk_array, size_t chunk_top) {
4687   // Until all tasks completed:
4688   // . claim an unclaimed task
4689   // . compute region boundaries corresponding to task claimed
4690   //   using chunk_array
4691   // . par_oop_iterate(cl) over that region
4692 
4693   ResourceMark rm;
4694   HandleMark   hm;
4695 
4696   SequentialSubTasksDone* pst = space->par_seq_tasks();
4697 
4698   uint nth_task = 0;
4699   uint n_tasks  = pst->n_tasks();
4700 
4701   if (n_tasks > 0) {
4702     assert(pst->valid(), "Uninitialized use?");
4703     HeapWord *start, *end;
4704     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4705       // We claimed task # nth_task; compute its boundaries.
4706       if (chunk_top == 0) {  // no samples were taken
4707         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4708         start = space->bottom();
4709         end   = space->top();
4710       } else if (nth_task == 0) {
4711         start = space->bottom();
4712         end   = chunk_array[nth_task];
4713       } else if (nth_task < (uint)chunk_top) {
4714         assert(nth_task >= 1, "Control point invariant");
4715         start = chunk_array[nth_task - 1];
4716         end   = chunk_array[nth_task];
4717       } else {
4718         assert(nth_task == (uint)chunk_top, "Control point invariant");
4719         start = chunk_array[chunk_top - 1];
4720         end   = space->top();
4721       }
4722       MemRegion mr(start, end);
4723       // Verify that mr is in space
4724       assert(mr.is_empty() || space->used_region().contains(mr),
4725              "Should be in space");
4726       // Verify that "start" is an object boundary
4727       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4728              "Should be an oop");
4729       space->par_oop_iterate(mr, cl);
4730     }
4731     pst->all_tasks_completed();
4732   }
4733 }
4734 
4735 void
4736 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4737   CompactibleFreeListSpace* sp, int i,
4738   Par_MarkRefsIntoAndScanClosure* cl) {
4739   // Until all tasks completed:
4740   // . claim an unclaimed task
4741   // . compute region boundaries corresponding to task claimed
4742   // . transfer dirty bits ct->mut for that region
4743   // . apply rescanclosure to dirty mut bits for that region
4744 
4745   ResourceMark rm;
4746   HandleMark   hm;
4747 
4748   OopTaskQueue* work_q = work_queue(i);
4749   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4750   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4751   // CAUTION: This closure has state that persists across calls to
4752   // the work method dirty_range_iterate_clear() in that it has
4753   // embedded in it a (subtype of) UpwardsObjectClosure. The
4754   // use of that state in the embedded UpwardsObjectClosure instance
4755   // assumes that the cards are always iterated (even if in parallel
4756   // by several threads) in monotonically increasing order per each
4757   // thread. This is true of the implementation below which picks
4758   // card ranges (chunks) in monotonically increasing order globally
4759   // and, a-fortiori, in monotonically increasing order per thread
4760   // (the latter order being a subsequence of the former).
4761   // If the work code below is ever reorganized into a more chaotic
4762   // work-partitioning form than the current "sequential tasks"
4763   // paradigm, the use of that persistent state will have to be
4764   // revisited and modified appropriately. See also related
4765   // bug 4756801 work on which should examine this code to make
4766   // sure that the changes there do not run counter to the
4767   // assumptions made here and necessary for correctness and
4768   // efficiency. Note also that this code might yield inefficient
4769   // behavior in the case of very large objects that span one or
4770   // more work chunks. Such objects would potentially be scanned
4771   // several times redundantly. Work on 4756801 should try and
4772   // address that performance anomaly if at all possible. XXX
4773   MemRegion  full_span  = _collector->_span;
4774   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4775   MarkFromDirtyCardsClosure
4776     greyRescanClosure(_collector, full_span, // entire span of interest
4777                       sp, bm, work_q, cl);
4778 
4779   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4780   assert(pst->valid(), "Uninitialized use?");
4781   uint nth_task = 0;
4782   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4783   MemRegion span = sp->used_region();
4784   HeapWord* start_addr = span.start();
4785   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4786                                            alignment);
4787   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4788   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4789          start_addr, "Check alignment");
4790   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4791          chunk_size, "Check alignment");
4792 
4793   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4794     // Having claimed the nth_task, compute corresponding mem-region,
4795     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4796     // The alignment restriction ensures that we do not need any
4797     // synchronization with other gang-workers while setting or
4798     // clearing bits in thus chunk of the MUT.
4799     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4800                                     start_addr + (nth_task+1)*chunk_size);
4801     // The last chunk's end might be way beyond end of the
4802     // used region. In that case pull back appropriately.
4803     if (this_span.end() > end_addr) {
4804       this_span.set_end(end_addr);
4805       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4806     }
4807     // Iterate over the dirty cards covering this chunk, marking them
4808     // precleaned, and setting the corresponding bits in the mod union
4809     // table. Since we have been careful to partition at Card and MUT-word
4810     // boundaries no synchronization is needed between parallel threads.
4811     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4812                                                  &modUnionClosure);
4813 
4814     // Having transferred these marks into the modUnionTable,
4815     // rescan the marked objects on the dirty cards in the modUnionTable.
4816     // Even if this is at a synchronous collection, the initial marking
4817     // may have been done during an asynchronous collection so there
4818     // may be dirty bits in the mod-union table.
4819     _collector->_modUnionTable.dirty_range_iterate_clear(
4820                   this_span, &greyRescanClosure);
4821     _collector->_modUnionTable.verifyNoOneBitsInRange(
4822                                  this_span.start(),
4823                                  this_span.end());
4824   }
4825   pst->all_tasks_completed();  // declare that i am done
4826 }
4827 
4828 // . see if we can share work_queues with ParNew? XXX
4829 void
4830 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4831                                 int* seed) {
4832   OopTaskQueue* work_q = work_queue(i);
4833   NOT_PRODUCT(int num_steals = 0;)
4834   oop obj_to_scan;
4835   CMSBitMap* bm = &(_collector->_markBitMap);
4836 
4837   while (true) {
4838     // Completely finish any left over work from (an) earlier round(s)
4839     cl->trim_queue(0);
4840     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4841                                          (size_t)ParGCDesiredObjsFromOverflowList);
4842     // Now check if there's any work in the overflow list
4843     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4844     // only affects the number of attempts made to get work from the
4845     // overflow list and does not affect the number of workers.  Just
4846     // pass ParallelGCThreads so this behavior is unchanged.
4847     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4848                                                 work_q,
4849                                                 ParallelGCThreads)) {
4850       // found something in global overflow list;
4851       // not yet ready to go stealing work from others.
4852       // We'd like to assert(work_q->size() != 0, ...)
4853       // because we just took work from the overflow list,
4854       // but of course we can't since all of that could have
4855       // been already stolen from us.
4856       // "He giveth and He taketh away."
4857       continue;
4858     }
4859     // Verify that we have no work before we resort to stealing
4860     assert(work_q->size() == 0, "Have work, shouldn't steal");
4861     // Try to steal from other queues that have work
4862     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4863       NOT_PRODUCT(num_steals++;)
4864       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4865       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4866       // Do scanning work
4867       obj_to_scan->oop_iterate(cl);
4868       // Loop around, finish this work, and try to steal some more
4869     } else if (terminator()->offer_termination()) {
4870         break;  // nirvana from the infinite cycle
4871     }
4872   }
4873   NOT_PRODUCT(
4874     if (PrintCMSStatistics != 0) {
4875       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4876     }
4877   )
4878   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4879          "Else our work is not yet done");
4880 }
4881 
4882 // Record object boundaries in _eden_chunk_array by sampling the eden
4883 // top in the slow-path eden object allocation code path and record
4884 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4885 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4886 // sampling in sample_eden() that activates during the part of the
4887 // preclean phase.
4888 void CMSCollector::sample_eden_chunk() {
4889   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4890     if (_eden_chunk_lock->try_lock()) {
4891       // Record a sample. This is the critical section. The contents
4892       // of the _eden_chunk_array have to be non-decreasing in the
4893       // address order.
4894       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4895       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4896              "Unexpected state of Eden");
4897       if (_eden_chunk_index == 0 ||
4898           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4899            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4900                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4901         _eden_chunk_index++;  // commit sample
4902       }
4903       _eden_chunk_lock->unlock();
4904     }
4905   }
4906 }
4907 
4908 // Return a thread-local PLAB recording array, as appropriate.
4909 void* CMSCollector::get_data_recorder(int thr_num) {
4910   if (_survivor_plab_array != NULL &&
4911       (CMSPLABRecordAlways ||
4912        (_collectorState > Marking && _collectorState < FinalMarking))) {
4913     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4914     ChunkArray* ca = &_survivor_plab_array[thr_num];
4915     ca->reset();   // clear it so that fresh data is recorded
4916     return (void*) ca;
4917   } else {
4918     return NULL;
4919   }
4920 }
4921 
4922 // Reset all the thread-local PLAB recording arrays
4923 void CMSCollector::reset_survivor_plab_arrays() {
4924   for (uint i = 0; i < ParallelGCThreads; i++) {
4925     _survivor_plab_array[i].reset();
4926   }
4927 }
4928 
4929 // Merge the per-thread plab arrays into the global survivor chunk
4930 // array which will provide the partitioning of the survivor space
4931 // for CMS initial scan and rescan.
4932 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4933                                               int no_of_gc_threads) {
4934   assert(_survivor_plab_array  != NULL, "Error");
4935   assert(_survivor_chunk_array != NULL, "Error");
4936   assert(_collectorState == FinalMarking ||
4937          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4938   for (int j = 0; j < no_of_gc_threads; j++) {
4939     _cursor[j] = 0;
4940   }
4941   HeapWord* top = surv->top();
4942   size_t i;
4943   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4944     HeapWord* min_val = top;          // Higher than any PLAB address
4945     uint      min_tid = 0;            // position of min_val this round
4946     for (int j = 0; j < no_of_gc_threads; j++) {
4947       ChunkArray* cur_sca = &_survivor_plab_array[j];
4948       if (_cursor[j] == cur_sca->end()) {
4949         continue;
4950       }
4951       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4952       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4953       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4954       if (cur_val < min_val) {
4955         min_tid = j;
4956         min_val = cur_val;
4957       } else {
4958         assert(cur_val < top, "All recorded addresses should be less");
4959       }
4960     }
4961     // At this point min_val and min_tid are respectively
4962     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4963     // and the thread (j) that witnesses that address.
4964     // We record this address in the _survivor_chunk_array[i]
4965     // and increment _cursor[min_tid] prior to the next round i.
4966     if (min_val == top) {
4967       break;
4968     }
4969     _survivor_chunk_array[i] = min_val;
4970     _cursor[min_tid]++;
4971   }
4972   // We are all done; record the size of the _survivor_chunk_array
4973   _survivor_chunk_index = i; // exclusive: [0, i)
4974   if (PrintCMSStatistics > 0) {
4975     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4976   }
4977   // Verify that we used up all the recorded entries
4978   #ifdef ASSERT
4979     size_t total = 0;
4980     for (int j = 0; j < no_of_gc_threads; j++) {
4981       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4982       total += _cursor[j];
4983     }
4984     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4985     // Check that the merged array is in sorted order
4986     if (total > 0) {
4987       for (size_t i = 0; i < total - 1; i++) {
4988         if (PrintCMSStatistics > 0) {
4989           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4990                               i, p2i(_survivor_chunk_array[i]));
4991         }
4992         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4993                "Not sorted");
4994       }
4995     }
4996   #endif // ASSERT
4997 }
4998 
4999 // Set up the space's par_seq_tasks structure for work claiming
5000 // for parallel initial scan and rescan of young gen.
5001 // See ParRescanTask where this is currently used.
5002 void
5003 CMSCollector::
5004 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5005   assert(n_threads > 0, "Unexpected n_threads argument");
5006 
5007   // Eden space
5008   if (!_young_gen->eden()->is_empty()) {
5009     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5010     assert(!pst->valid(), "Clobbering existing data?");
5011     // Each valid entry in [0, _eden_chunk_index) represents a task.
5012     size_t n_tasks = _eden_chunk_index + 1;
5013     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5014     // Sets the condition for completion of the subtask (how many threads
5015     // need to finish in order to be done).
5016     pst->set_n_threads(n_threads);
5017     pst->set_n_tasks((int)n_tasks);
5018   }
5019 
5020   // Merge the survivor plab arrays into _survivor_chunk_array
5021   if (_survivor_plab_array != NULL) {
5022     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5023   } else {
5024     assert(_survivor_chunk_index == 0, "Error");
5025   }
5026 
5027   // To space
5028   {
5029     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5030     assert(!pst->valid(), "Clobbering existing data?");
5031     // Sets the condition for completion of the subtask (how many threads
5032     // need to finish in order to be done).
5033     pst->set_n_threads(n_threads);
5034     pst->set_n_tasks(1);
5035     assert(pst->valid(), "Error");
5036   }
5037 
5038   // From space
5039   {
5040     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5041     assert(!pst->valid(), "Clobbering existing data?");
5042     size_t n_tasks = _survivor_chunk_index + 1;
5043     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5044     // Sets the condition for completion of the subtask (how many threads
5045     // need to finish in order to be done).
5046     pst->set_n_threads(n_threads);
5047     pst->set_n_tasks((int)n_tasks);
5048     assert(pst->valid(), "Error");
5049   }
5050 }
5051 
5052 // Parallel version of remark
5053 void CMSCollector::do_remark_parallel() {
5054   GenCollectedHeap* gch = GenCollectedHeap::heap();
5055   WorkGang* workers = gch->workers();
5056   assert(workers != NULL, "Need parallel worker threads.");
5057   // Choose to use the number of GC workers most recently set
5058   // into "active_workers".
5059   uint n_workers = workers->active_workers();
5060 
5061   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5062 
5063   StrongRootsScope srs(n_workers);
5064 
5065   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5066 
5067   // We won't be iterating over the cards in the card table updating
5068   // the younger_gen cards, so we shouldn't call the following else
5069   // the verification code as well as subsequent younger_refs_iterate
5070   // code would get confused. XXX
5071   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5072 
5073   // The young gen rescan work will not be done as part of
5074   // process_roots (which currently doesn't know how to
5075   // parallelize such a scan), but rather will be broken up into
5076   // a set of parallel tasks (via the sampling that the [abortable]
5077   // preclean phase did of eden, plus the [two] tasks of
5078   // scanning the [two] survivor spaces. Further fine-grain
5079   // parallelization of the scanning of the survivor spaces
5080   // themselves, and of precleaning of the young gen itself
5081   // is deferred to the future.
5082   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5083 
5084   // The dirty card rescan work is broken up into a "sequence"
5085   // of parallel tasks (per constituent space) that are dynamically
5086   // claimed by the parallel threads.
5087   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5088 
5089   // It turns out that even when we're using 1 thread, doing the work in a
5090   // separate thread causes wide variance in run times.  We can't help this
5091   // in the multi-threaded case, but we special-case n=1 here to get
5092   // repeatable measurements of the 1-thread overhead of the parallel code.
5093   if (n_workers > 1) {
5094     // Make refs discovery MT-safe, if it isn't already: it may not
5095     // necessarily be so, since it's possible that we are doing
5096     // ST marking.
5097     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5098     workers->run_task(&tsk);
5099   } else {
5100     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5101     tsk.work(0);
5102   }
5103 
5104   // restore, single-threaded for now, any preserved marks
5105   // as a result of work_q overflow
5106   restore_preserved_marks_if_any();
5107 }
5108 
5109 // Non-parallel version of remark
5110 void CMSCollector::do_remark_non_parallel() {
5111   ResourceMark rm;
5112   HandleMark   hm;
5113   GenCollectedHeap* gch = GenCollectedHeap::heap();
5114   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5115 
5116   MarkRefsIntoAndScanClosure
5117     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5118              &_markStack, this,
5119              false /* should_yield */, false /* not precleaning */);
5120   MarkFromDirtyCardsClosure
5121     markFromDirtyCardsClosure(this, _span,
5122                               NULL,  // space is set further below
5123                               &_markBitMap, &_markStack, &mrias_cl);
5124   {
5125     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5126     // Iterate over the dirty cards, setting the corresponding bits in the
5127     // mod union table.
5128     {
5129       ModUnionClosure modUnionClosure(&_modUnionTable);
5130       _ct->ct_bs()->dirty_card_iterate(
5131                       _cmsGen->used_region(),
5132                       &modUnionClosure);
5133     }
5134     // Having transferred these marks into the modUnionTable, we just need
5135     // to rescan the marked objects on the dirty cards in the modUnionTable.
5136     // The initial marking may have been done during an asynchronous
5137     // collection so there may be dirty bits in the mod-union table.
5138     const int alignment =
5139       CardTableModRefBS::card_size * BitsPerWord;
5140     {
5141       // ... First handle dirty cards in CMS gen
5142       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5143       MemRegion ur = _cmsGen->used_region();
5144       HeapWord* lb = ur.start();
5145       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5146       MemRegion cms_span(lb, ub);
5147       _modUnionTable.dirty_range_iterate_clear(cms_span,
5148                                                &markFromDirtyCardsClosure);
5149       verify_work_stacks_empty();
5150       if (PrintCMSStatistics != 0) {
5151         gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5152           markFromDirtyCardsClosure.num_dirty_cards());
5153       }
5154     }
5155   }
5156   if (VerifyDuringGC &&
5157       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5158     HandleMark hm;  // Discard invalid handles created during verification
5159     Universe::verify();
5160   }
5161   {
5162     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5163 
5164     verify_work_stacks_empty();
5165 
5166     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5167     StrongRootsScope srs(1);
5168 
5169     gch->gen_process_roots(&srs,
5170                            GenCollectedHeap::OldGen,
5171                            true,  // young gen as roots
5172                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
5173                            should_unload_classes(),
5174                            &mrias_cl,
5175                            NULL,
5176                            NULL); // The dirty klasses will be handled below
5177 
5178     assert(should_unload_classes()
5179            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5180            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5181   }
5182 
5183   {
5184     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5185 
5186     verify_work_stacks_empty();
5187 
5188     // Scan all class loader data objects that might have been introduced
5189     // during concurrent marking.
5190     ResourceMark rm;
5191     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5192     for (int i = 0; i < array->length(); i++) {
5193       mrias_cl.do_cld_nv(array->at(i));
5194     }
5195 
5196     // We don't need to keep track of new CLDs anymore.
5197     ClassLoaderDataGraph::remember_new_clds(false);
5198 
5199     verify_work_stacks_empty();
5200   }
5201 
5202   {
5203     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5204 
5205     verify_work_stacks_empty();
5206 
5207     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5208     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5209 
5210     verify_work_stacks_empty();
5211   }
5212 
5213   // We might have added oops to ClassLoaderData::_handles during the
5214   // concurrent marking phase. These oops point to newly allocated objects
5215   // that are guaranteed to be kept alive. Either by the direct allocation
5216   // code, or when the young collector processes the roots. Hence,
5217   // we don't have to revisit the _handles block during the remark phase.
5218 
5219   verify_work_stacks_empty();
5220   // Restore evacuated mark words, if any, used for overflow list links
5221   if (!CMSOverflowEarlyRestoration) {
5222     restore_preserved_marks_if_any();
5223   }
5224   verify_overflow_empty();
5225 }
5226 
5227 ////////////////////////////////////////////////////////
5228 // Parallel Reference Processing Task Proxy Class
5229 ////////////////////////////////////////////////////////
5230 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5231   OopTaskQueueSet*       _queues;
5232   ParallelTaskTerminator _terminator;
5233  public:
5234   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5235     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5236   ParallelTaskTerminator* terminator() { return &_terminator; }
5237   OopTaskQueueSet* queues() { return _queues; }
5238 };
5239 
5240 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5241   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5242   CMSCollector*          _collector;
5243   CMSBitMap*             _mark_bit_map;
5244   const MemRegion        _span;
5245   ProcessTask&           _task;
5246 
5247 public:
5248   CMSRefProcTaskProxy(ProcessTask&     task,
5249                       CMSCollector*    collector,
5250                       const MemRegion& span,
5251                       CMSBitMap*       mark_bit_map,
5252                       AbstractWorkGang* workers,
5253                       OopTaskQueueSet* task_queues):
5254     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5255       task_queues,
5256       workers->active_workers()),
5257     _task(task),
5258     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5259   {
5260     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5261            "Inconsistency in _span");
5262   }
5263 
5264   OopTaskQueueSet* task_queues() { return queues(); }
5265 
5266   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5267 
5268   void do_work_steal(int i,
5269                      CMSParDrainMarkingStackClosure* drain,
5270                      CMSParKeepAliveClosure* keep_alive,
5271                      int* seed);
5272 
5273   virtual void work(uint worker_id);
5274 };
5275 
5276 void CMSRefProcTaskProxy::work(uint worker_id) {
5277   ResourceMark rm;
5278   HandleMark hm;
5279   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5280   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5281                                         _mark_bit_map,
5282                                         work_queue(worker_id));
5283   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5284                                                  _mark_bit_map,
5285                                                  work_queue(worker_id));
5286   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5287   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5288   if (_task.marks_oops_alive()) {
5289     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5290                   _collector->hash_seed(worker_id));
5291   }
5292   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5293   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5294 }
5295 
5296 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5297   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5298   EnqueueTask& _task;
5299 
5300 public:
5301   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5302     : AbstractGangTask("Enqueue reference objects in parallel"),
5303       _task(task)
5304   { }
5305 
5306   virtual void work(uint worker_id)
5307   {
5308     _task.work(worker_id);
5309   }
5310 };
5311 
5312 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5313   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5314    _span(span),
5315    _bit_map(bit_map),
5316    _work_queue(work_queue),
5317    _mark_and_push(collector, span, bit_map, work_queue),
5318    _low_water_mark(MIN2((work_queue->max_elems()/4),
5319                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5320 { }
5321 
5322 // . see if we can share work_queues with ParNew? XXX
5323 void CMSRefProcTaskProxy::do_work_steal(int i,
5324   CMSParDrainMarkingStackClosure* drain,
5325   CMSParKeepAliveClosure* keep_alive,
5326   int* seed) {
5327   OopTaskQueue* work_q = work_queue(i);
5328   NOT_PRODUCT(int num_steals = 0;)
5329   oop obj_to_scan;
5330 
5331   while (true) {
5332     // Completely finish any left over work from (an) earlier round(s)
5333     drain->trim_queue(0);
5334     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5335                                          (size_t)ParGCDesiredObjsFromOverflowList);
5336     // Now check if there's any work in the overflow list
5337     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5338     // only affects the number of attempts made to get work from the
5339     // overflow list and does not affect the number of workers.  Just
5340     // pass ParallelGCThreads so this behavior is unchanged.
5341     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5342                                                 work_q,
5343                                                 ParallelGCThreads)) {
5344       // Found something in global overflow list;
5345       // not yet ready to go stealing work from others.
5346       // We'd like to assert(work_q->size() != 0, ...)
5347       // because we just took work from the overflow list,
5348       // but of course we can't, since all of that might have
5349       // been already stolen from us.
5350       continue;
5351     }
5352     // Verify that we have no work before we resort to stealing
5353     assert(work_q->size() == 0, "Have work, shouldn't steal");
5354     // Try to steal from other queues that have work
5355     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5356       NOT_PRODUCT(num_steals++;)
5357       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5358       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5359       // Do scanning work
5360       obj_to_scan->oop_iterate(keep_alive);
5361       // Loop around, finish this work, and try to steal some more
5362     } else if (terminator()->offer_termination()) {
5363       break;  // nirvana from the infinite cycle
5364     }
5365   }
5366   NOT_PRODUCT(
5367     if (PrintCMSStatistics != 0) {
5368       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5369     }
5370   )
5371 }
5372 
5373 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5374 {
5375   GenCollectedHeap* gch = GenCollectedHeap::heap();
5376   WorkGang* workers = gch->workers();
5377   assert(workers != NULL, "Need parallel worker threads.");
5378   CMSRefProcTaskProxy rp_task(task, &_collector,
5379                               _collector.ref_processor()->span(),
5380                               _collector.markBitMap(),
5381                               workers, _collector.task_queues());
5382   workers->run_task(&rp_task);
5383 }
5384 
5385 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5386 {
5387 
5388   GenCollectedHeap* gch = GenCollectedHeap::heap();
5389   WorkGang* workers = gch->workers();
5390   assert(workers != NULL, "Need parallel worker threads.");
5391   CMSRefEnqueueTaskProxy enq_task(task);
5392   workers->run_task(&enq_task);
5393 }
5394 
5395 void CMSCollector::refProcessingWork() {
5396   ResourceMark rm;
5397   HandleMark   hm;
5398 
5399   ReferenceProcessor* rp = ref_processor();
5400   assert(rp->span().equals(_span), "Spans should be equal");
5401   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5402   // Process weak references.
5403   rp->setup_policy(false);
5404   verify_work_stacks_empty();
5405 
5406   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5407                                           &_markStack, false /* !preclean */);
5408   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5409                                 _span, &_markBitMap, &_markStack,
5410                                 &cmsKeepAliveClosure, false /* !preclean */);
5411   {
5412     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5413 
5414     ReferenceProcessorStats stats;
5415     if (rp->processing_is_mt()) {
5416       // Set the degree of MT here.  If the discovery is done MT, there
5417       // may have been a different number of threads doing the discovery
5418       // and a different number of discovered lists may have Ref objects.
5419       // That is OK as long as the Reference lists are balanced (see
5420       // balance_all_queues() and balance_queues()).
5421       GenCollectedHeap* gch = GenCollectedHeap::heap();
5422       uint active_workers = ParallelGCThreads;
5423       WorkGang* workers = gch->workers();
5424       if (workers != NULL) {
5425         active_workers = workers->active_workers();
5426         // The expectation is that active_workers will have already
5427         // been set to a reasonable value.  If it has not been set,
5428         // investigate.
5429         assert(active_workers > 0, "Should have been set during scavenge");
5430       }
5431       rp->set_active_mt_degree(active_workers);
5432       CMSRefProcTaskExecutor task_executor(*this);
5433       stats = rp->process_discovered_references(&_is_alive_closure,
5434                                         &cmsKeepAliveClosure,
5435                                         &cmsDrainMarkingStackClosure,
5436                                         &task_executor,
5437                                         _gc_timer_cm,
5438                                         _gc_tracer_cm->gc_id());
5439     } else {
5440       stats = rp->process_discovered_references(&_is_alive_closure,
5441                                         &cmsKeepAliveClosure,
5442                                         &cmsDrainMarkingStackClosure,
5443                                         NULL,
5444                                         _gc_timer_cm,
5445                                         _gc_tracer_cm->gc_id());
5446     }
5447     _gc_tracer_cm->report_gc_reference_stats(stats);
5448 
5449   }
5450 
5451   // This is the point where the entire marking should have completed.
5452   verify_work_stacks_empty();
5453 
5454   if (should_unload_classes()) {
5455     {
5456       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5457 
5458       // Unload classes and purge the SystemDictionary.
5459       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5460 
5461       // Unload nmethods.
5462       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5463 
5464       // Prune dead klasses from subklass/sibling/implementor lists.
5465       Klass::clean_weak_klass_links(&_is_alive_closure);
5466     }
5467 
5468     {
5469       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5470       // Clean up unreferenced symbols in symbol table.
5471       SymbolTable::unlink();
5472     }
5473 
5474     {
5475       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5476       // Delete entries for dead interned strings.
5477       StringTable::unlink(&_is_alive_closure);
5478     }
5479   }
5480 
5481 
5482   // Restore any preserved marks as a result of mark stack or
5483   // work queue overflow
5484   restore_preserved_marks_if_any();  // done single-threaded for now
5485 
5486   rp->set_enqueuing_is_done(true);
5487   if (rp->processing_is_mt()) {
5488     rp->balance_all_queues();
5489     CMSRefProcTaskExecutor task_executor(*this);
5490     rp->enqueue_discovered_references(&task_executor);
5491   } else {
5492     rp->enqueue_discovered_references(NULL);
5493   }
5494   rp->verify_no_references_recorded();
5495   assert(!rp->discovery_enabled(), "should have been disabled");
5496 }
5497 
5498 #ifndef PRODUCT
5499 void CMSCollector::check_correct_thread_executing() {
5500   Thread* t = Thread::current();
5501   // Only the VM thread or the CMS thread should be here.
5502   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5503          "Unexpected thread type");
5504   // If this is the vm thread, the foreground process
5505   // should not be waiting.  Note that _foregroundGCIsActive is
5506   // true while the foreground collector is waiting.
5507   if (_foregroundGCShouldWait) {
5508     // We cannot be the VM thread
5509     assert(t->is_ConcurrentGC_thread(),
5510            "Should be CMS thread");
5511   } else {
5512     // We can be the CMS thread only if we are in a stop-world
5513     // phase of CMS collection.
5514     if (t->is_ConcurrentGC_thread()) {
5515       assert(_collectorState == InitialMarking ||
5516              _collectorState == FinalMarking,
5517              "Should be a stop-world phase");
5518       // The CMS thread should be holding the CMS_token.
5519       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5520              "Potential interference with concurrently "
5521              "executing VM thread");
5522     }
5523   }
5524 }
5525 #endif
5526 
5527 void CMSCollector::sweep() {
5528   assert(_collectorState == Sweeping, "just checking");
5529   check_correct_thread_executing();
5530   verify_work_stacks_empty();
5531   verify_overflow_empty();
5532   increment_sweep_count();
5533   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5534 
5535   _inter_sweep_timer.stop();
5536   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5537 
5538   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5539   _intra_sweep_timer.reset();
5540   _intra_sweep_timer.start();
5541   {
5542     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5543     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5544     // First sweep the old gen
5545     {
5546       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5547                                bitMapLock());
5548       sweepWork(_cmsGen);
5549     }
5550 
5551     // Update Universe::_heap_*_at_gc figures.
5552     // We need all the free list locks to make the abstract state
5553     // transition from Sweeping to Resetting. See detailed note
5554     // further below.
5555     {
5556       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5557       // Update heap occupancy information which is used as
5558       // input to soft ref clearing policy at the next gc.
5559       Universe::update_heap_info_at_gc();
5560       _collectorState = Resizing;
5561     }
5562   }
5563   verify_work_stacks_empty();
5564   verify_overflow_empty();
5565 
5566   if (should_unload_classes()) {
5567     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5568     // requires that the virtual spaces are stable and not deleted.
5569     ClassLoaderDataGraph::set_should_purge(true);
5570   }
5571 
5572   _intra_sweep_timer.stop();
5573   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5574 
5575   _inter_sweep_timer.reset();
5576   _inter_sweep_timer.start();
5577 
5578   // We need to use a monotonically non-decreasing time in ms
5579   // or we will see time-warp warnings and os::javaTimeMillis()
5580   // does not guarantee monotonicity.
5581   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5582   update_time_of_last_gc(now);
5583 
5584   // NOTE on abstract state transitions:
5585   // Mutators allocate-live and/or mark the mod-union table dirty
5586   // based on the state of the collection.  The former is done in
5587   // the interval [Marking, Sweeping] and the latter in the interval
5588   // [Marking, Sweeping).  Thus the transitions into the Marking state
5589   // and out of the Sweeping state must be synchronously visible
5590   // globally to the mutators.
5591   // The transition into the Marking state happens with the world
5592   // stopped so the mutators will globally see it.  Sweeping is
5593   // done asynchronously by the background collector so the transition
5594   // from the Sweeping state to the Resizing state must be done
5595   // under the freelistLock (as is the check for whether to
5596   // allocate-live and whether to dirty the mod-union table).
5597   assert(_collectorState == Resizing, "Change of collector state to"
5598     " Resizing must be done under the freelistLocks (plural)");
5599 
5600   // Now that sweeping has been completed, we clear
5601   // the incremental_collection_failed flag,
5602   // thus inviting a younger gen collection to promote into
5603   // this generation. If such a promotion may still fail,
5604   // the flag will be set again when a young collection is
5605   // attempted.
5606   GenCollectedHeap* gch = GenCollectedHeap::heap();
5607   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5608   gch->update_full_collections_completed(_collection_count_start);
5609 }
5610 
5611 // FIX ME!!! Looks like this belongs in CFLSpace, with
5612 // CMSGen merely delegating to it.
5613 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5614   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5615   HeapWord*  minAddr        = _cmsSpace->bottom();
5616   HeapWord*  largestAddr    =
5617     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5618   if (largestAddr == NULL) {
5619     // The dictionary appears to be empty.  In this case
5620     // try to coalesce at the end of the heap.
5621     largestAddr = _cmsSpace->end();
5622   }
5623   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5624   size_t nearLargestOffset =
5625     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5626   if (PrintFLSStatistics != 0) {
5627     gclog_or_tty->print_cr(
5628       "CMS: Large Block: " PTR_FORMAT ";"
5629       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5630       p2i(largestAddr),
5631       p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5632   }
5633   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5634 }
5635 
5636 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5637   return addr >= _cmsSpace->nearLargestChunk();
5638 }
5639 
5640 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5641   return _cmsSpace->find_chunk_at_end();
5642 }
5643 
5644 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5645                                                     bool full) {
5646   // If the young generation has been collected, gather any statistics
5647   // that are of interest at this point.
5648   bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5649   if (!full && current_is_young) {
5650     // Gather statistics on the young generation collection.
5651     collector()->stats().record_gc0_end(used());
5652   }
5653 }
5654 
5655 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5656   // We iterate over the space(s) underlying this generation,
5657   // checking the mark bit map to see if the bits corresponding
5658   // to specific blocks are marked or not. Blocks that are
5659   // marked are live and are not swept up. All remaining blocks
5660   // are swept up, with coalescing on-the-fly as we sweep up
5661   // contiguous free and/or garbage blocks:
5662   // We need to ensure that the sweeper synchronizes with allocators
5663   // and stop-the-world collectors. In particular, the following
5664   // locks are used:
5665   // . CMS token: if this is held, a stop the world collection cannot occur
5666   // . freelistLock: if this is held no allocation can occur from this
5667   //                 generation by another thread
5668   // . bitMapLock: if this is held, no other thread can access or update
5669   //
5670 
5671   // Note that we need to hold the freelistLock if we use
5672   // block iterate below; else the iterator might go awry if
5673   // a mutator (or promotion) causes block contents to change
5674   // (for instance if the allocator divvies up a block).
5675   // If we hold the free list lock, for all practical purposes
5676   // young generation GC's can't occur (they'll usually need to
5677   // promote), so we might as well prevent all young generation
5678   // GC's while we do a sweeping step. For the same reason, we might
5679   // as well take the bit map lock for the entire duration
5680 
5681   // check that we hold the requisite locks
5682   assert(have_cms_token(), "Should hold cms token");
5683   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5684   assert_lock_strong(old_gen->freelistLock());
5685   assert_lock_strong(bitMapLock());
5686 
5687   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5688   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5689   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5690                                           _inter_sweep_estimate.padded_average(),
5691                                           _intra_sweep_estimate.padded_average());
5692   old_gen->setNearLargestChunk();
5693 
5694   {
5695     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5696     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5697     // We need to free-up/coalesce garbage/blocks from a
5698     // co-terminal free run. This is done in the SweepClosure
5699     // destructor; so, do not remove this scope, else the
5700     // end-of-sweep-census below will be off by a little bit.
5701   }
5702   old_gen->cmsSpace()->sweep_completed();
5703   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5704   if (should_unload_classes()) {                // unloaded classes this cycle,
5705     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5706   } else {                                      // did not unload classes,
5707     _concurrent_cycles_since_last_unload++;     // ... increment count
5708   }
5709 }
5710 
5711 // Reset CMS data structures (for now just the marking bit map)
5712 // preparatory for the next cycle.
5713 void CMSCollector::reset(bool concurrent) {
5714   if (concurrent) {
5715     CMSTokenSyncWithLocks ts(true, bitMapLock());
5716 
5717     // If the state is not "Resetting", the foreground  thread
5718     // has done a collection and the resetting.
5719     if (_collectorState != Resetting) {
5720       assert(_collectorState == Idling, "The state should only change"
5721         " because the foreground collector has finished the collection");
5722       return;
5723     }
5724 
5725     // Clear the mark bitmap (no grey objects to start with)
5726     // for the next cycle.
5727     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5728     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5729 
5730     HeapWord* curAddr = _markBitMap.startWord();
5731     while (curAddr < _markBitMap.endWord()) {
5732       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5733       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5734       _markBitMap.clear_large_range(chunk);
5735       if (ConcurrentMarkSweepThread::should_yield() &&
5736           !foregroundGCIsActive() &&
5737           CMSYield) {
5738         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5739                "CMS thread should hold CMS token");
5740         assert_lock_strong(bitMapLock());
5741         bitMapLock()->unlock();
5742         ConcurrentMarkSweepThread::desynchronize(true);
5743         stopTimer();
5744         if (PrintCMSStatistics != 0) {
5745           incrementYields();
5746         }
5747 
5748         // See the comment in coordinator_yield()
5749         for (unsigned i = 0; i < CMSYieldSleepCount &&
5750                          ConcurrentMarkSweepThread::should_yield() &&
5751                          !CMSCollector::foregroundGCIsActive(); ++i) {
5752           os::sleep(Thread::current(), 1, false);
5753         }
5754 
5755         ConcurrentMarkSweepThread::synchronize(true);
5756         bitMapLock()->lock_without_safepoint_check();
5757         startTimer();
5758       }
5759       curAddr = chunk.end();
5760     }
5761     // A successful mostly concurrent collection has been done.
5762     // Because only the full (i.e., concurrent mode failure) collections
5763     // are being measured for gc overhead limits, clean the "near" flag
5764     // and count.
5765     size_policy()->reset_gc_overhead_limit_count();
5766     _collectorState = Idling;
5767   } else {
5768     // already have the lock
5769     assert(_collectorState == Resetting, "just checking");
5770     assert_lock_strong(bitMapLock());
5771     _markBitMap.clear_all();
5772     _collectorState = Idling;
5773   }
5774 
5775   register_gc_end();
5776 }
5777 
5778 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5779   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5780   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5781   TraceCollectorStats tcs(counters());
5782 
5783   switch (op) {
5784     case CMS_op_checkpointRootsInitial: {
5785       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5786       checkpointRootsInitial();
5787       if (PrintGC) {
5788         _cmsGen->printOccupancy("initial-mark");
5789       }
5790       break;
5791     }
5792     case CMS_op_checkpointRootsFinal: {
5793       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5794       checkpointRootsFinal();
5795       if (PrintGC) {
5796         _cmsGen->printOccupancy("remark");
5797       }
5798       break;
5799     }
5800     default:
5801       fatal("No such CMS_op");
5802   }
5803 }
5804 
5805 #ifndef PRODUCT
5806 size_t const CMSCollector::skip_header_HeapWords() {
5807   return FreeChunk::header_size();
5808 }
5809 
5810 // Try and collect here conditions that should hold when
5811 // CMS thread is exiting. The idea is that the foreground GC
5812 // thread should not be blocked if it wants to terminate
5813 // the CMS thread and yet continue to run the VM for a while
5814 // after that.
5815 void CMSCollector::verify_ok_to_terminate() const {
5816   assert(Thread::current()->is_ConcurrentGC_thread(),
5817          "should be called by CMS thread");
5818   assert(!_foregroundGCShouldWait, "should be false");
5819   // We could check here that all the various low-level locks
5820   // are not held by the CMS thread, but that is overkill; see
5821   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5822   // is checked.
5823 }
5824 #endif
5825 
5826 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5827    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5828           "missing Printezis mark?");
5829   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5830   size_t size = pointer_delta(nextOneAddr + 1, addr);
5831   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5832          "alignment problem");
5833   assert(size >= 3, "Necessary for Printezis marks to work");
5834   return size;
5835 }
5836 
5837 // A variant of the above (block_size_using_printezis_bits()) except
5838 // that we return 0 if the P-bits are not yet set.
5839 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5840   if (_markBitMap.isMarked(addr + 1)) {
5841     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5842     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5843     size_t size = pointer_delta(nextOneAddr + 1, addr);
5844     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5845            "alignment problem");
5846     assert(size >= 3, "Necessary for Printezis marks to work");
5847     return size;
5848   }
5849   return 0;
5850 }
5851 
5852 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5853   size_t sz = 0;
5854   oop p = (oop)addr;
5855   if (p->klass_or_null() != NULL) {
5856     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5857   } else {
5858     sz = block_size_using_printezis_bits(addr);
5859   }
5860   assert(sz > 0, "size must be nonzero");
5861   HeapWord* next_block = addr + sz;
5862   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5863                                              CardTableModRefBS::card_size);
5864   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5865          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5866          "must be different cards");
5867   return next_card;
5868 }
5869 
5870 
5871 // CMS Bit Map Wrapper /////////////////////////////////////////
5872 
5873 // Construct a CMS bit map infrastructure, but don't create the
5874 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5875 // further below.
5876 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5877   _bm(),
5878   _shifter(shifter),
5879   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5880                                     Monitor::_safepoint_check_sometimes) : NULL)
5881 {
5882   _bmStartWord = 0;
5883   _bmWordSize  = 0;
5884 }
5885 
5886 bool CMSBitMap::allocate(MemRegion mr) {
5887   _bmStartWord = mr.start();
5888   _bmWordSize  = mr.word_size();
5889   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5890                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5891   if (!brs.is_reserved()) {
5892     warning("CMS bit map allocation failure");
5893     return false;
5894   }
5895   // For now we'll just commit all of the bit map up front.
5896   // Later on we'll try to be more parsimonious with swap.
5897   if (!_virtual_space.initialize(brs, brs.size())) {
5898     warning("CMS bit map backing store failure");
5899     return false;
5900   }
5901   assert(_virtual_space.committed_size() == brs.size(),
5902          "didn't reserve backing store for all of CMS bit map?");
5903   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5904   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5905          _bmWordSize, "inconsistency in bit map sizing");
5906   _bm.set_size(_bmWordSize >> _shifter);
5907 
5908   // bm.clear(); // can we rely on getting zero'd memory? verify below
5909   assert(isAllClear(),
5910          "Expected zero'd memory from ReservedSpace constructor");
5911   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5912          "consistency check");
5913   return true;
5914 }
5915 
5916 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5917   HeapWord *next_addr, *end_addr, *last_addr;
5918   assert_locked();
5919   assert(covers(mr), "out-of-range error");
5920   // XXX assert that start and end are appropriately aligned
5921   for (next_addr = mr.start(), end_addr = mr.end();
5922        next_addr < end_addr; next_addr = last_addr) {
5923     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5924     last_addr = dirty_region.end();
5925     if (!dirty_region.is_empty()) {
5926       cl->do_MemRegion(dirty_region);
5927     } else {
5928       assert(last_addr == end_addr, "program logic");
5929       return;
5930     }
5931   }
5932 }
5933 
5934 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5935   _bm.print_on_error(st, prefix);
5936 }
5937 
5938 #ifndef PRODUCT
5939 void CMSBitMap::assert_locked() const {
5940   CMSLockVerifier::assert_locked(lock());
5941 }
5942 
5943 bool CMSBitMap::covers(MemRegion mr) const {
5944   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5945   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5946          "size inconsistency");
5947   return (mr.start() >= _bmStartWord) &&
5948          (mr.end()   <= endWord());
5949 }
5950 
5951 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5952     return (start >= _bmStartWord && (start + size) <= endWord());
5953 }
5954 
5955 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5956   // verify that there are no 1 bits in the interval [left, right)
5957   FalseBitMapClosure falseBitMapClosure;
5958   iterate(&falseBitMapClosure, left, right);
5959 }
5960 
5961 void CMSBitMap::region_invariant(MemRegion mr)
5962 {
5963   assert_locked();
5964   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5965   assert(!mr.is_empty(), "unexpected empty region");
5966   assert(covers(mr), "mr should be covered by bit map");
5967   // convert address range into offset range
5968   size_t start_ofs = heapWordToOffset(mr.start());
5969   // Make sure that end() is appropriately aligned
5970   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5971                         (1 << (_shifter+LogHeapWordSize))),
5972          "Misaligned mr.end()");
5973   size_t end_ofs   = heapWordToOffset(mr.end());
5974   assert(end_ofs > start_ofs, "Should mark at least one bit");
5975 }
5976 
5977 #endif
5978 
5979 bool CMSMarkStack::allocate(size_t size) {
5980   // allocate a stack of the requisite depth
5981   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5982                    size * sizeof(oop)));
5983   if (!rs.is_reserved()) {
5984     warning("CMSMarkStack allocation failure");
5985     return false;
5986   }
5987   if (!_virtual_space.initialize(rs, rs.size())) {
5988     warning("CMSMarkStack backing store failure");
5989     return false;
5990   }
5991   assert(_virtual_space.committed_size() == rs.size(),
5992          "didn't reserve backing store for all of CMS stack?");
5993   _base = (oop*)(_virtual_space.low());
5994   _index = 0;
5995   _capacity = size;
5996   NOT_PRODUCT(_max_depth = 0);
5997   return true;
5998 }
5999 
6000 // XXX FIX ME !!! In the MT case we come in here holding a
6001 // leaf lock. For printing we need to take a further lock
6002 // which has lower rank. We need to recalibrate the two
6003 // lock-ranks involved in order to be able to print the
6004 // messages below. (Or defer the printing to the caller.
6005 // For now we take the expedient path of just disabling the
6006 // messages for the problematic case.)
6007 void CMSMarkStack::expand() {
6008   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6009   if (_capacity == MarkStackSizeMax) {
6010     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6011       // We print a warning message only once per CMS cycle.
6012       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6013     }
6014     return;
6015   }
6016   // Double capacity if possible
6017   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6018   // Do not give up existing stack until we have managed to
6019   // get the double capacity that we desired.
6020   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6021                    new_capacity * sizeof(oop)));
6022   if (rs.is_reserved()) {
6023     // Release the backing store associated with old stack
6024     _virtual_space.release();
6025     // Reinitialize virtual space for new stack
6026     if (!_virtual_space.initialize(rs, rs.size())) {
6027       fatal("Not enough swap for expanded marking stack");
6028     }
6029     _base = (oop*)(_virtual_space.low());
6030     _index = 0;
6031     _capacity = new_capacity;
6032   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6033     // Failed to double capacity, continue;
6034     // we print a detail message only once per CMS cycle.
6035     gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6036             SIZE_FORMAT "K",
6037             _capacity / K, new_capacity / K);
6038   }
6039 }
6040 
6041 
6042 // Closures
6043 // XXX: there seems to be a lot of code  duplication here;
6044 // should refactor and consolidate common code.
6045 
6046 // This closure is used to mark refs into the CMS generation in
6047 // the CMS bit map. Called at the first checkpoint. This closure
6048 // assumes that we do not need to re-mark dirty cards; if the CMS
6049 // generation on which this is used is not an oldest
6050 // generation then this will lose younger_gen cards!
6051 
6052 MarkRefsIntoClosure::MarkRefsIntoClosure(
6053   MemRegion span, CMSBitMap* bitMap):
6054     _span(span),
6055     _bitMap(bitMap)
6056 {
6057     assert(_ref_processor == NULL, "deliberately left NULL");
6058     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6059 }
6060 
6061 void MarkRefsIntoClosure::do_oop(oop obj) {
6062   // if p points into _span, then mark corresponding bit in _markBitMap
6063   assert(obj->is_oop(), "expected an oop");
6064   HeapWord* addr = (HeapWord*)obj;
6065   if (_span.contains(addr)) {
6066     // this should be made more efficient
6067     _bitMap->mark(addr);
6068   }
6069 }
6070 
6071 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6072 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6073 
6074 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6075   MemRegion span, CMSBitMap* bitMap):
6076     _span(span),
6077     _bitMap(bitMap)
6078 {
6079     assert(_ref_processor == NULL, "deliberately left NULL");
6080     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6081 }
6082 
6083 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6084   // if p points into _span, then mark corresponding bit in _markBitMap
6085   assert(obj->is_oop(), "expected an oop");
6086   HeapWord* addr = (HeapWord*)obj;
6087   if (_span.contains(addr)) {
6088     // this should be made more efficient
6089     _bitMap->par_mark(addr);
6090   }
6091 }
6092 
6093 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6094 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6095 
6096 // A variant of the above, used for CMS marking verification.
6097 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6098   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6099     _span(span),
6100     _verification_bm(verification_bm),
6101     _cms_bm(cms_bm)
6102 {
6103     assert(_ref_processor == NULL, "deliberately left NULL");
6104     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6105 }
6106 
6107 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6108   // if p points into _span, then mark corresponding bit in _markBitMap
6109   assert(obj->is_oop(), "expected an oop");
6110   HeapWord* addr = (HeapWord*)obj;
6111   if (_span.contains(addr)) {
6112     _verification_bm->mark(addr);
6113     if (!_cms_bm->isMarked(addr)) {
6114       oop(addr)->print();
6115       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6116       fatal("... aborting");
6117     }
6118   }
6119 }
6120 
6121 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6122 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6123 
6124 //////////////////////////////////////////////////
6125 // MarkRefsIntoAndScanClosure
6126 //////////////////////////////////////////////////
6127 
6128 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6129                                                        ReferenceProcessor* rp,
6130                                                        CMSBitMap* bit_map,
6131                                                        CMSBitMap* mod_union_table,
6132                                                        CMSMarkStack*  mark_stack,
6133                                                        CMSCollector* collector,
6134                                                        bool should_yield,
6135                                                        bool concurrent_precleaning):
6136   _collector(collector),
6137   _span(span),
6138   _bit_map(bit_map),
6139   _mark_stack(mark_stack),
6140   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6141                       mark_stack, concurrent_precleaning),
6142   _yield(should_yield),
6143   _concurrent_precleaning(concurrent_precleaning),
6144   _freelistLock(NULL)
6145 {
6146   _ref_processor = rp;
6147   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6148 }
6149 
6150 // This closure is used to mark refs into the CMS generation at the
6151 // second (final) checkpoint, and to scan and transitively follow
6152 // the unmarked oops. It is also used during the concurrent precleaning
6153 // phase while scanning objects on dirty cards in the CMS generation.
6154 // The marks are made in the marking bit map and the marking stack is
6155 // used for keeping the (newly) grey objects during the scan.
6156 // The parallel version (Par_...) appears further below.
6157 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6158   if (obj != NULL) {
6159     assert(obj->is_oop(), "expected an oop");
6160     HeapWord* addr = (HeapWord*)obj;
6161     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6162     assert(_collector->overflow_list_is_empty(),
6163            "overflow list should be empty");
6164     if (_span.contains(addr) &&
6165         !_bit_map->isMarked(addr)) {
6166       // mark bit map (object is now grey)
6167       _bit_map->mark(addr);
6168       // push on marking stack (stack should be empty), and drain the
6169       // stack by applying this closure to the oops in the oops popped
6170       // from the stack (i.e. blacken the grey objects)
6171       bool res = _mark_stack->push(obj);
6172       assert(res, "Should have space to push on empty stack");
6173       do {
6174         oop new_oop = _mark_stack->pop();
6175         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6176         assert(_bit_map->isMarked((HeapWord*)new_oop),
6177                "only grey objects on this stack");
6178         // iterate over the oops in this oop, marking and pushing
6179         // the ones in CMS heap (i.e. in _span).
6180         new_oop->oop_iterate(&_pushAndMarkClosure);
6181         // check if it's time to yield
6182         do_yield_check();
6183       } while (!_mark_stack->isEmpty() ||
6184                (!_concurrent_precleaning && take_from_overflow_list()));
6185         // if marking stack is empty, and we are not doing this
6186         // during precleaning, then check the overflow list
6187     }
6188     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6189     assert(_collector->overflow_list_is_empty(),
6190            "overflow list was drained above");
6191     // We could restore evacuated mark words, if any, used for
6192     // overflow list links here because the overflow list is
6193     // provably empty here. That would reduce the maximum
6194     // size requirements for preserved_{oop,mark}_stack.
6195     // But we'll just postpone it until we are all done
6196     // so we can just stream through.
6197     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6198       _collector->restore_preserved_marks_if_any();
6199       assert(_collector->no_preserved_marks(), "No preserved marks");
6200     }
6201     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6202            "All preserved marks should have been restored above");
6203   }
6204 }
6205 
6206 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6207 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6208 
6209 void MarkRefsIntoAndScanClosure::do_yield_work() {
6210   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6211          "CMS thread should hold CMS token");
6212   assert_lock_strong(_freelistLock);
6213   assert_lock_strong(_bit_map->lock());
6214   // relinquish the free_list_lock and bitMaplock()
6215   _bit_map->lock()->unlock();
6216   _freelistLock->unlock();
6217   ConcurrentMarkSweepThread::desynchronize(true);
6218   _collector->stopTimer();
6219   if (PrintCMSStatistics != 0) {
6220     _collector->incrementYields();
6221   }
6222 
6223   // See the comment in coordinator_yield()
6224   for (unsigned i = 0;
6225        i < CMSYieldSleepCount &&
6226        ConcurrentMarkSweepThread::should_yield() &&
6227        !CMSCollector::foregroundGCIsActive();
6228        ++i) {
6229     os::sleep(Thread::current(), 1, false);
6230   }
6231 
6232   ConcurrentMarkSweepThread::synchronize(true);
6233   _freelistLock->lock_without_safepoint_check();
6234   _bit_map->lock()->lock_without_safepoint_check();
6235   _collector->startTimer();
6236 }
6237 
6238 ///////////////////////////////////////////////////////////
6239 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6240 //                                 MarkRefsIntoAndScanClosure
6241 ///////////////////////////////////////////////////////////
6242 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6243   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6244   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6245   _span(span),
6246   _bit_map(bit_map),
6247   _work_queue(work_queue),
6248   _low_water_mark(MIN2((work_queue->max_elems()/4),
6249                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6250   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6251 {
6252   _ref_processor = rp;
6253   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6254 }
6255 
6256 // This closure is used to mark refs into the CMS generation at the
6257 // second (final) checkpoint, and to scan and transitively follow
6258 // the unmarked oops. The marks are made in the marking bit map and
6259 // the work_queue is used for keeping the (newly) grey objects during
6260 // the scan phase whence they are also available for stealing by parallel
6261 // threads. Since the marking bit map is shared, updates are
6262 // synchronized (via CAS).
6263 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6264   if (obj != NULL) {
6265     // Ignore mark word because this could be an already marked oop
6266     // that may be chained at the end of the overflow list.
6267     assert(obj->is_oop(true), "expected an oop");
6268     HeapWord* addr = (HeapWord*)obj;
6269     if (_span.contains(addr) &&
6270         !_bit_map->isMarked(addr)) {
6271       // mark bit map (object will become grey):
6272       // It is possible for several threads to be
6273       // trying to "claim" this object concurrently;
6274       // the unique thread that succeeds in marking the
6275       // object first will do the subsequent push on
6276       // to the work queue (or overflow list).
6277       if (_bit_map->par_mark(addr)) {
6278         // push on work_queue (which may not be empty), and trim the
6279         // queue to an appropriate length by applying this closure to
6280         // the oops in the oops popped from the stack (i.e. blacken the
6281         // grey objects)
6282         bool res = _work_queue->push(obj);
6283         assert(res, "Low water mark should be less than capacity?");
6284         trim_queue(_low_water_mark);
6285       } // Else, another thread claimed the object
6286     }
6287   }
6288 }
6289 
6290 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6291 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6292 
6293 // This closure is used to rescan the marked objects on the dirty cards
6294 // in the mod union table and the card table proper.
6295 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6296   oop p, MemRegion mr) {
6297 
6298   size_t size = 0;
6299   HeapWord* addr = (HeapWord*)p;
6300   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6301   assert(_span.contains(addr), "we are scanning the CMS generation");
6302   // check if it's time to yield
6303   if (do_yield_check()) {
6304     // We yielded for some foreground stop-world work,
6305     // and we have been asked to abort this ongoing preclean cycle.
6306     return 0;
6307   }
6308   if (_bitMap->isMarked(addr)) {
6309     // it's marked; is it potentially uninitialized?
6310     if (p->klass_or_null() != NULL) {
6311         // an initialized object; ignore mark word in verification below
6312         // since we are running concurrent with mutators
6313         assert(p->is_oop(true), "should be an oop");
6314         if (p->is_objArray()) {
6315           // objArrays are precisely marked; restrict scanning
6316           // to dirty cards only.
6317           size = CompactibleFreeListSpace::adjustObjectSize(
6318                    p->oop_iterate_size(_scanningClosure, mr));
6319         } else {
6320           // A non-array may have been imprecisely marked; we need
6321           // to scan object in its entirety.
6322           size = CompactibleFreeListSpace::adjustObjectSize(
6323                    p->oop_iterate_size(_scanningClosure));
6324         }
6325         #ifdef ASSERT
6326           size_t direct_size =
6327             CompactibleFreeListSpace::adjustObjectSize(p->size());
6328           assert(size == direct_size, "Inconsistency in size");
6329           assert(size >= 3, "Necessary for Printezis marks to work");
6330           if (!_bitMap->isMarked(addr+1)) {
6331             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6332           } else {
6333             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6334             assert(_bitMap->isMarked(addr+size-1),
6335                    "inconsistent Printezis mark");
6336           }
6337         #endif // ASSERT
6338     } else {
6339       // An uninitialized object.
6340       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6341       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6342       size = pointer_delta(nextOneAddr + 1, addr);
6343       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6344              "alignment problem");
6345       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6346       // will dirty the card when the klass pointer is installed in the
6347       // object (signaling the completion of initialization).
6348     }
6349   } else {
6350     // Either a not yet marked object or an uninitialized object
6351     if (p->klass_or_null() == NULL) {
6352       // An uninitialized object, skip to the next card, since
6353       // we may not be able to read its P-bits yet.
6354       assert(size == 0, "Initial value");
6355     } else {
6356       // An object not (yet) reached by marking: we merely need to
6357       // compute its size so as to go look at the next block.
6358       assert(p->is_oop(true), "should be an oop");
6359       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6360     }
6361   }
6362   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6363   return size;
6364 }
6365 
6366 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6367   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6368          "CMS thread should hold CMS token");
6369   assert_lock_strong(_freelistLock);
6370   assert_lock_strong(_bitMap->lock());
6371   // relinquish the free_list_lock and bitMaplock()
6372   _bitMap->lock()->unlock();
6373   _freelistLock->unlock();
6374   ConcurrentMarkSweepThread::desynchronize(true);
6375   _collector->stopTimer();
6376   if (PrintCMSStatistics != 0) {
6377     _collector->incrementYields();
6378   }
6379 
6380   // See the comment in coordinator_yield()
6381   for (unsigned i = 0; i < CMSYieldSleepCount &&
6382                    ConcurrentMarkSweepThread::should_yield() &&
6383                    !CMSCollector::foregroundGCIsActive(); ++i) {
6384     os::sleep(Thread::current(), 1, false);
6385   }
6386 
6387   ConcurrentMarkSweepThread::synchronize(true);
6388   _freelistLock->lock_without_safepoint_check();
6389   _bitMap->lock()->lock_without_safepoint_check();
6390   _collector->startTimer();
6391 }
6392 
6393 
6394 //////////////////////////////////////////////////////////////////
6395 // SurvivorSpacePrecleanClosure
6396 //////////////////////////////////////////////////////////////////
6397 // This (single-threaded) closure is used to preclean the oops in
6398 // the survivor spaces.
6399 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6400 
6401   HeapWord* addr = (HeapWord*)p;
6402   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6403   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6404   assert(p->klass_or_null() != NULL, "object should be initialized");
6405   // an initialized object; ignore mark word in verification below
6406   // since we are running concurrent with mutators
6407   assert(p->is_oop(true), "should be an oop");
6408   // Note that we do not yield while we iterate over
6409   // the interior oops of p, pushing the relevant ones
6410   // on our marking stack.
6411   size_t size = p->oop_iterate_size(_scanning_closure);
6412   do_yield_check();
6413   // Observe that below, we do not abandon the preclean
6414   // phase as soon as we should; rather we empty the
6415   // marking stack before returning. This is to satisfy
6416   // some existing assertions. In general, it may be a
6417   // good idea to abort immediately and complete the marking
6418   // from the grey objects at a later time.
6419   while (!_mark_stack->isEmpty()) {
6420     oop new_oop = _mark_stack->pop();
6421     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6422     assert(_bit_map->isMarked((HeapWord*)new_oop),
6423            "only grey objects on this stack");
6424     // iterate over the oops in this oop, marking and pushing
6425     // the ones in CMS heap (i.e. in _span).
6426     new_oop->oop_iterate(_scanning_closure);
6427     // check if it's time to yield
6428     do_yield_check();
6429   }
6430   unsigned int after_count =
6431     GenCollectedHeap::heap()->total_collections();
6432   bool abort = (_before_count != after_count) ||
6433                _collector->should_abort_preclean();
6434   return abort ? 0 : size;
6435 }
6436 
6437 void SurvivorSpacePrecleanClosure::do_yield_work() {
6438   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6439          "CMS thread should hold CMS token");
6440   assert_lock_strong(_bit_map->lock());
6441   // Relinquish the bit map lock
6442   _bit_map->lock()->unlock();
6443   ConcurrentMarkSweepThread::desynchronize(true);
6444   _collector->stopTimer();
6445   if (PrintCMSStatistics != 0) {
6446     _collector->incrementYields();
6447   }
6448 
6449   // See the comment in coordinator_yield()
6450   for (unsigned i = 0; i < CMSYieldSleepCount &&
6451                        ConcurrentMarkSweepThread::should_yield() &&
6452                        !CMSCollector::foregroundGCIsActive(); ++i) {
6453     os::sleep(Thread::current(), 1, false);
6454   }
6455 
6456   ConcurrentMarkSweepThread::synchronize(true);
6457   _bit_map->lock()->lock_without_safepoint_check();
6458   _collector->startTimer();
6459 }
6460 
6461 // This closure is used to rescan the marked objects on the dirty cards
6462 // in the mod union table and the card table proper. In the parallel
6463 // case, although the bitMap is shared, we do a single read so the
6464 // isMarked() query is "safe".
6465 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6466   // Ignore mark word because we are running concurrent with mutators
6467   assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6468   HeapWord* addr = (HeapWord*)p;
6469   assert(_span.contains(addr), "we are scanning the CMS generation");
6470   bool is_obj_array = false;
6471   #ifdef ASSERT
6472     if (!_parallel) {
6473       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6474       assert(_collector->overflow_list_is_empty(),
6475              "overflow list should be empty");
6476 
6477     }
6478   #endif // ASSERT
6479   if (_bit_map->isMarked(addr)) {
6480     // Obj arrays are precisely marked, non-arrays are not;
6481     // so we scan objArrays precisely and non-arrays in their
6482     // entirety.
6483     if (p->is_objArray()) {
6484       is_obj_array = true;
6485       if (_parallel) {
6486         p->oop_iterate(_par_scan_closure, mr);
6487       } else {
6488         p->oop_iterate(_scan_closure, mr);
6489       }
6490     } else {
6491       if (_parallel) {
6492         p->oop_iterate(_par_scan_closure);
6493       } else {
6494         p->oop_iterate(_scan_closure);
6495       }
6496     }
6497   }
6498   #ifdef ASSERT
6499     if (!_parallel) {
6500       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6501       assert(_collector->overflow_list_is_empty(),
6502              "overflow list should be empty");
6503 
6504     }
6505   #endif // ASSERT
6506   return is_obj_array;
6507 }
6508 
6509 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6510                         MemRegion span,
6511                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6512                         bool should_yield, bool verifying):
6513   _collector(collector),
6514   _span(span),
6515   _bitMap(bitMap),
6516   _mut(&collector->_modUnionTable),
6517   _markStack(markStack),
6518   _yield(should_yield),
6519   _skipBits(0)
6520 {
6521   assert(_markStack->isEmpty(), "stack should be empty");
6522   _finger = _bitMap->startWord();
6523   _threshold = _finger;
6524   assert(_collector->_restart_addr == NULL, "Sanity check");
6525   assert(_span.contains(_finger), "Out of bounds _finger?");
6526   DEBUG_ONLY(_verifying = verifying;)
6527 }
6528 
6529 void MarkFromRootsClosure::reset(HeapWord* addr) {
6530   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6531   assert(_span.contains(addr), "Out of bounds _finger?");
6532   _finger = addr;
6533   _threshold = (HeapWord*)round_to(
6534                  (intptr_t)_finger, CardTableModRefBS::card_size);
6535 }
6536 
6537 // Should revisit to see if this should be restructured for
6538 // greater efficiency.
6539 bool MarkFromRootsClosure::do_bit(size_t offset) {
6540   if (_skipBits > 0) {
6541     _skipBits--;
6542     return true;
6543   }
6544   // convert offset into a HeapWord*
6545   HeapWord* addr = _bitMap->startWord() + offset;
6546   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6547          "address out of range");
6548   assert(_bitMap->isMarked(addr), "tautology");
6549   if (_bitMap->isMarked(addr+1)) {
6550     // this is an allocated but not yet initialized object
6551     assert(_skipBits == 0, "tautology");
6552     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6553     oop p = oop(addr);
6554     if (p->klass_or_null() == NULL) {
6555       DEBUG_ONLY(if (!_verifying) {)
6556         // We re-dirty the cards on which this object lies and increase
6557         // the _threshold so that we'll come back to scan this object
6558         // during the preclean or remark phase. (CMSCleanOnEnter)
6559         if (CMSCleanOnEnter) {
6560           size_t sz = _collector->block_size_using_printezis_bits(addr);
6561           HeapWord* end_card_addr   = (HeapWord*)round_to(
6562                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6563           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6564           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6565           // Bump _threshold to end_card_addr; note that
6566           // _threshold cannot possibly exceed end_card_addr, anyhow.
6567           // This prevents future clearing of the card as the scan proceeds
6568           // to the right.
6569           assert(_threshold <= end_card_addr,
6570                  "Because we are just scanning into this object");
6571           if (_threshold < end_card_addr) {
6572             _threshold = end_card_addr;
6573           }
6574           if (p->klass_or_null() != NULL) {
6575             // Redirty the range of cards...
6576             _mut->mark_range(redirty_range);
6577           } // ...else the setting of klass will dirty the card anyway.
6578         }
6579       DEBUG_ONLY(})
6580       return true;
6581     }
6582   }
6583   scanOopsInOop(addr);
6584   return true;
6585 }
6586 
6587 // We take a break if we've been at this for a while,
6588 // so as to avoid monopolizing the locks involved.
6589 void MarkFromRootsClosure::do_yield_work() {
6590   // First give up the locks, then yield, then re-lock
6591   // We should probably use a constructor/destructor idiom to
6592   // do this unlock/lock or modify the MutexUnlocker class to
6593   // serve our purpose. XXX
6594   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6595          "CMS thread should hold CMS token");
6596   assert_lock_strong(_bitMap->lock());
6597   _bitMap->lock()->unlock();
6598   ConcurrentMarkSweepThread::desynchronize(true);
6599   _collector->stopTimer();
6600   if (PrintCMSStatistics != 0) {
6601     _collector->incrementYields();
6602   }
6603 
6604   // See the comment in coordinator_yield()
6605   for (unsigned i = 0; i < CMSYieldSleepCount &&
6606                        ConcurrentMarkSweepThread::should_yield() &&
6607                        !CMSCollector::foregroundGCIsActive(); ++i) {
6608     os::sleep(Thread::current(), 1, false);
6609   }
6610 
6611   ConcurrentMarkSweepThread::synchronize(true);
6612   _bitMap->lock()->lock_without_safepoint_check();
6613   _collector->startTimer();
6614 }
6615 
6616 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6617   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6618   assert(_markStack->isEmpty(),
6619          "should drain stack to limit stack usage");
6620   // convert ptr to an oop preparatory to scanning
6621   oop obj = oop(ptr);
6622   // Ignore mark word in verification below, since we
6623   // may be running concurrent with mutators.
6624   assert(obj->is_oop(true), "should be an oop");
6625   assert(_finger <= ptr, "_finger runneth ahead");
6626   // advance the finger to right end of this object
6627   _finger = ptr + obj->size();
6628   assert(_finger > ptr, "we just incremented it above");
6629   // On large heaps, it may take us some time to get through
6630   // the marking phase. During
6631   // this time it's possible that a lot of mutations have
6632   // accumulated in the card table and the mod union table --
6633   // these mutation records are redundant until we have
6634   // actually traced into the corresponding card.
6635   // Here, we check whether advancing the finger would make
6636   // us cross into a new card, and if so clear corresponding
6637   // cards in the MUT (preclean them in the card-table in the
6638   // future).
6639 
6640   DEBUG_ONLY(if (!_verifying) {)
6641     // The clean-on-enter optimization is disabled by default,
6642     // until we fix 6178663.
6643     if (CMSCleanOnEnter && (_finger > _threshold)) {
6644       // [_threshold, _finger) represents the interval
6645       // of cards to be cleared  in MUT (or precleaned in card table).
6646       // The set of cards to be cleared is all those that overlap
6647       // with the interval [_threshold, _finger); note that
6648       // _threshold is always kept card-aligned but _finger isn't
6649       // always card-aligned.
6650       HeapWord* old_threshold = _threshold;
6651       assert(old_threshold == (HeapWord*)round_to(
6652               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6653              "_threshold should always be card-aligned");
6654       _threshold = (HeapWord*)round_to(
6655                      (intptr_t)_finger, CardTableModRefBS::card_size);
6656       MemRegion mr(old_threshold, _threshold);
6657       assert(!mr.is_empty(), "Control point invariant");
6658       assert(_span.contains(mr), "Should clear within span");
6659       _mut->clear_range(mr);
6660     }
6661   DEBUG_ONLY(})
6662   // Note: the finger doesn't advance while we drain
6663   // the stack below.
6664   PushOrMarkClosure pushOrMarkClosure(_collector,
6665                                       _span, _bitMap, _markStack,
6666                                       _finger, this);
6667   bool res = _markStack->push(obj);
6668   assert(res, "Empty non-zero size stack should have space for single push");
6669   while (!_markStack->isEmpty()) {
6670     oop new_oop = _markStack->pop();
6671     // Skip verifying header mark word below because we are
6672     // running concurrent with mutators.
6673     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6674     // now scan this oop's oops
6675     new_oop->oop_iterate(&pushOrMarkClosure);
6676     do_yield_check();
6677   }
6678   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6679 }
6680 
6681 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6682                        CMSCollector* collector, MemRegion span,
6683                        CMSBitMap* bit_map,
6684                        OopTaskQueue* work_queue,
6685                        CMSMarkStack*  overflow_stack):
6686   _collector(collector),
6687   _whole_span(collector->_span),
6688   _span(span),
6689   _bit_map(bit_map),
6690   _mut(&collector->_modUnionTable),
6691   _work_queue(work_queue),
6692   _overflow_stack(overflow_stack),
6693   _skip_bits(0),
6694   _task(task)
6695 {
6696   assert(_work_queue->size() == 0, "work_queue should be empty");
6697   _finger = span.start();
6698   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6699   assert(_span.contains(_finger), "Out of bounds _finger?");
6700 }
6701 
6702 // Should revisit to see if this should be restructured for
6703 // greater efficiency.
6704 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6705   if (_skip_bits > 0) {
6706     _skip_bits--;
6707     return true;
6708   }
6709   // convert offset into a HeapWord*
6710   HeapWord* addr = _bit_map->startWord() + offset;
6711   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6712          "address out of range");
6713   assert(_bit_map->isMarked(addr), "tautology");
6714   if (_bit_map->isMarked(addr+1)) {
6715     // this is an allocated object that might not yet be initialized
6716     assert(_skip_bits == 0, "tautology");
6717     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6718     oop p = oop(addr);
6719     if (p->klass_or_null() == NULL) {
6720       // in the case of Clean-on-Enter optimization, redirty card
6721       // and avoid clearing card by increasing  the threshold.
6722       return true;
6723     }
6724   }
6725   scan_oops_in_oop(addr);
6726   return true;
6727 }
6728 
6729 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6730   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6731   // Should we assert that our work queue is empty or
6732   // below some drain limit?
6733   assert(_work_queue->size() == 0,
6734          "should drain stack to limit stack usage");
6735   // convert ptr to an oop preparatory to scanning
6736   oop obj = oop(ptr);
6737   // Ignore mark word in verification below, since we
6738   // may be running concurrent with mutators.
6739   assert(obj->is_oop(true), "should be an oop");
6740   assert(_finger <= ptr, "_finger runneth ahead");
6741   // advance the finger to right end of this object
6742   _finger = ptr + obj->size();
6743   assert(_finger > ptr, "we just incremented it above");
6744   // On large heaps, it may take us some time to get through
6745   // the marking phase. During
6746   // this time it's possible that a lot of mutations have
6747   // accumulated in the card table and the mod union table --
6748   // these mutation records are redundant until we have
6749   // actually traced into the corresponding card.
6750   // Here, we check whether advancing the finger would make
6751   // us cross into a new card, and if so clear corresponding
6752   // cards in the MUT (preclean them in the card-table in the
6753   // future).
6754 
6755   // The clean-on-enter optimization is disabled by default,
6756   // until we fix 6178663.
6757   if (CMSCleanOnEnter && (_finger > _threshold)) {
6758     // [_threshold, _finger) represents the interval
6759     // of cards to be cleared  in MUT (or precleaned in card table).
6760     // The set of cards to be cleared is all those that overlap
6761     // with the interval [_threshold, _finger); note that
6762     // _threshold is always kept card-aligned but _finger isn't
6763     // always card-aligned.
6764     HeapWord* old_threshold = _threshold;
6765     assert(old_threshold == (HeapWord*)round_to(
6766             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6767            "_threshold should always be card-aligned");
6768     _threshold = (HeapWord*)round_to(
6769                    (intptr_t)_finger, CardTableModRefBS::card_size);
6770     MemRegion mr(old_threshold, _threshold);
6771     assert(!mr.is_empty(), "Control point invariant");
6772     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6773     _mut->clear_range(mr);
6774   }
6775 
6776   // Note: the local finger doesn't advance while we drain
6777   // the stack below, but the global finger sure can and will.
6778   HeapWord** gfa = _task->global_finger_addr();
6779   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6780                                       _span, _bit_map,
6781                                       _work_queue,
6782                                       _overflow_stack,
6783                                       _finger,
6784                                       gfa, this);
6785   bool res = _work_queue->push(obj);   // overflow could occur here
6786   assert(res, "Will hold once we use workqueues");
6787   while (true) {
6788     oop new_oop;
6789     if (!_work_queue->pop_local(new_oop)) {
6790       // We emptied our work_queue; check if there's stuff that can
6791       // be gotten from the overflow stack.
6792       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6793             _overflow_stack, _work_queue)) {
6794         do_yield_check();
6795         continue;
6796       } else {  // done
6797         break;
6798       }
6799     }
6800     // Skip verifying header mark word below because we are
6801     // running concurrent with mutators.
6802     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6803     // now scan this oop's oops
6804     new_oop->oop_iterate(&pushOrMarkClosure);
6805     do_yield_check();
6806   }
6807   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6808 }
6809 
6810 // Yield in response to a request from VM Thread or
6811 // from mutators.
6812 void Par_MarkFromRootsClosure::do_yield_work() {
6813   assert(_task != NULL, "sanity");
6814   _task->yield();
6815 }
6816 
6817 // A variant of the above used for verifying CMS marking work.
6818 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6819                         MemRegion span,
6820                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6821                         CMSMarkStack*  mark_stack):
6822   _collector(collector),
6823   _span(span),
6824   _verification_bm(verification_bm),
6825   _cms_bm(cms_bm),
6826   _mark_stack(mark_stack),
6827   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6828                       mark_stack)
6829 {
6830   assert(_mark_stack->isEmpty(), "stack should be empty");
6831   _finger = _verification_bm->startWord();
6832   assert(_collector->_restart_addr == NULL, "Sanity check");
6833   assert(_span.contains(_finger), "Out of bounds _finger?");
6834 }
6835 
6836 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6837   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6838   assert(_span.contains(addr), "Out of bounds _finger?");
6839   _finger = addr;
6840 }
6841 
6842 // Should revisit to see if this should be restructured for
6843 // greater efficiency.
6844 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6845   // convert offset into a HeapWord*
6846   HeapWord* addr = _verification_bm->startWord() + offset;
6847   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6848          "address out of range");
6849   assert(_verification_bm->isMarked(addr), "tautology");
6850   assert(_cms_bm->isMarked(addr), "tautology");
6851 
6852   assert(_mark_stack->isEmpty(),
6853          "should drain stack to limit stack usage");
6854   // convert addr to an oop preparatory to scanning
6855   oop obj = oop(addr);
6856   assert(obj->is_oop(), "should be an oop");
6857   assert(_finger <= addr, "_finger runneth ahead");
6858   // advance the finger to right end of this object
6859   _finger = addr + obj->size();
6860   assert(_finger > addr, "we just incremented it above");
6861   // Note: the finger doesn't advance while we drain
6862   // the stack below.
6863   bool res = _mark_stack->push(obj);
6864   assert(res, "Empty non-zero size stack should have space for single push");
6865   while (!_mark_stack->isEmpty()) {
6866     oop new_oop = _mark_stack->pop();
6867     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6868     // now scan this oop's oops
6869     new_oop->oop_iterate(&_pam_verify_closure);
6870   }
6871   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6872   return true;
6873 }
6874 
6875 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6876   CMSCollector* collector, MemRegion span,
6877   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6878   CMSMarkStack*  mark_stack):
6879   MetadataAwareOopClosure(collector->ref_processor()),
6880   _collector(collector),
6881   _span(span),
6882   _verification_bm(verification_bm),
6883   _cms_bm(cms_bm),
6884   _mark_stack(mark_stack)
6885 { }
6886 
6887 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6888 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6889 
6890 // Upon stack overflow, we discard (part of) the stack,
6891 // remembering the least address amongst those discarded
6892 // in CMSCollector's _restart_address.
6893 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6894   // Remember the least grey address discarded
6895   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6896   _collector->lower_restart_addr(ra);
6897   _mark_stack->reset();  // discard stack contents
6898   _mark_stack->expand(); // expand the stack if possible
6899 }
6900 
6901 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6902   assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6903   HeapWord* addr = (HeapWord*)obj;
6904   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6905     // Oop lies in _span and isn't yet grey or black
6906     _verification_bm->mark(addr);            // now grey
6907     if (!_cms_bm->isMarked(addr)) {
6908       oop(addr)->print();
6909       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6910                              p2i(addr));
6911       fatal("... aborting");
6912     }
6913 
6914     if (!_mark_stack->push(obj)) { // stack overflow
6915       if (PrintCMSStatistics != 0) {
6916         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6917                                SIZE_FORMAT, _mark_stack->capacity());
6918       }
6919       assert(_mark_stack->isFull(), "Else push should have succeeded");
6920       handle_stack_overflow(addr);
6921     }
6922     // anything including and to the right of _finger
6923     // will be scanned as we iterate over the remainder of the
6924     // bit map
6925   }
6926 }
6927 
6928 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6929                      MemRegion span,
6930                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6931                      HeapWord* finger, MarkFromRootsClosure* parent) :
6932   MetadataAwareOopClosure(collector->ref_processor()),
6933   _collector(collector),
6934   _span(span),
6935   _bitMap(bitMap),
6936   _markStack(markStack),
6937   _finger(finger),
6938   _parent(parent)
6939 { }
6940 
6941 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6942                      MemRegion span,
6943                      CMSBitMap* bit_map,
6944                      OopTaskQueue* work_queue,
6945                      CMSMarkStack*  overflow_stack,
6946                      HeapWord* finger,
6947                      HeapWord** global_finger_addr,
6948                      Par_MarkFromRootsClosure* parent) :
6949   MetadataAwareOopClosure(collector->ref_processor()),
6950   _collector(collector),
6951   _whole_span(collector->_span),
6952   _span(span),
6953   _bit_map(bit_map),
6954   _work_queue(work_queue),
6955   _overflow_stack(overflow_stack),
6956   _finger(finger),
6957   _global_finger_addr(global_finger_addr),
6958   _parent(parent)
6959 { }
6960 
6961 // Assumes thread-safe access by callers, who are
6962 // responsible for mutual exclusion.
6963 void CMSCollector::lower_restart_addr(HeapWord* low) {
6964   assert(_span.contains(low), "Out of bounds addr");
6965   if (_restart_addr == NULL) {
6966     _restart_addr = low;
6967   } else {
6968     _restart_addr = MIN2(_restart_addr, low);
6969   }
6970 }
6971 
6972 // Upon stack overflow, we discard (part of) the stack,
6973 // remembering the least address amongst those discarded
6974 // in CMSCollector's _restart_address.
6975 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6976   // Remember the least grey address discarded
6977   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6978   _collector->lower_restart_addr(ra);
6979   _markStack->reset();  // discard stack contents
6980   _markStack->expand(); // expand the stack if possible
6981 }
6982 
6983 // Upon stack overflow, we discard (part of) the stack,
6984 // remembering the least address amongst those discarded
6985 // in CMSCollector's _restart_address.
6986 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6987   // We need to do this under a mutex to prevent other
6988   // workers from interfering with the work done below.
6989   MutexLockerEx ml(_overflow_stack->par_lock(),
6990                    Mutex::_no_safepoint_check_flag);
6991   // Remember the least grey address discarded
6992   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6993   _collector->lower_restart_addr(ra);
6994   _overflow_stack->reset();  // discard stack contents
6995   _overflow_stack->expand(); // expand the stack if possible
6996 }
6997 
6998 void PushOrMarkClosure::do_oop(oop obj) {
6999   // Ignore mark word because we are running concurrent with mutators.
7000   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7001   HeapWord* addr = (HeapWord*)obj;
7002   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7003     // Oop lies in _span and isn't yet grey or black
7004     _bitMap->mark(addr);            // now grey
7005     if (addr < _finger) {
7006       // the bit map iteration has already either passed, or
7007       // sampled, this bit in the bit map; we'll need to
7008       // use the marking stack to scan this oop's oops.
7009       bool simulate_overflow = false;
7010       NOT_PRODUCT(
7011         if (CMSMarkStackOverflowALot &&
7012             _collector->simulate_overflow()) {
7013           // simulate a stack overflow
7014           simulate_overflow = true;
7015         }
7016       )
7017       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7018         if (PrintCMSStatistics != 0) {
7019           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7020                                  SIZE_FORMAT, _markStack->capacity());
7021         }
7022         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7023         handle_stack_overflow(addr);
7024       }
7025     }
7026     // anything including and to the right of _finger
7027     // will be scanned as we iterate over the remainder of the
7028     // bit map
7029     do_yield_check();
7030   }
7031 }
7032 
7033 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7034 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7035 
7036 void Par_PushOrMarkClosure::do_oop(oop obj) {
7037   // Ignore mark word because we are running concurrent with mutators.
7038   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7039   HeapWord* addr = (HeapWord*)obj;
7040   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7041     // Oop lies in _span and isn't yet grey or black
7042     // We read the global_finger (volatile read) strictly after marking oop
7043     bool res = _bit_map->par_mark(addr);    // now grey
7044     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7045     // Should we push this marked oop on our stack?
7046     // -- if someone else marked it, nothing to do
7047     // -- if target oop is above global finger nothing to do
7048     // -- if target oop is in chunk and above local finger
7049     //      then nothing to do
7050     // -- else push on work queue
7051     if (   !res       // someone else marked it, they will deal with it
7052         || (addr >= *gfa)  // will be scanned in a later task
7053         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7054       return;
7055     }
7056     // the bit map iteration has already either passed, or
7057     // sampled, this bit in the bit map; we'll need to
7058     // use the marking stack to scan this oop's oops.
7059     bool simulate_overflow = false;
7060     NOT_PRODUCT(
7061       if (CMSMarkStackOverflowALot &&
7062           _collector->simulate_overflow()) {
7063         // simulate a stack overflow
7064         simulate_overflow = true;
7065       }
7066     )
7067     if (simulate_overflow ||
7068         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7069       // stack overflow
7070       if (PrintCMSStatistics != 0) {
7071         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7072                                SIZE_FORMAT, _overflow_stack->capacity());
7073       }
7074       // We cannot assert that the overflow stack is full because
7075       // it may have been emptied since.
7076       assert(simulate_overflow ||
7077              _work_queue->size() == _work_queue->max_elems(),
7078             "Else push should have succeeded");
7079       handle_stack_overflow(addr);
7080     }
7081     do_yield_check();
7082   }
7083 }
7084 
7085 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7086 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7087 
7088 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7089                                        MemRegion span,
7090                                        ReferenceProcessor* rp,
7091                                        CMSBitMap* bit_map,
7092                                        CMSBitMap* mod_union_table,
7093                                        CMSMarkStack*  mark_stack,
7094                                        bool           concurrent_precleaning):
7095   MetadataAwareOopClosure(rp),
7096   _collector(collector),
7097   _span(span),
7098   _bit_map(bit_map),
7099   _mod_union_table(mod_union_table),
7100   _mark_stack(mark_stack),
7101   _concurrent_precleaning(concurrent_precleaning)
7102 {
7103   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7104 }
7105 
7106 // Grey object rescan during pre-cleaning and second checkpoint phases --
7107 // the non-parallel version (the parallel version appears further below.)
7108 void PushAndMarkClosure::do_oop(oop obj) {
7109   // Ignore mark word verification. If during concurrent precleaning,
7110   // the object monitor may be locked. If during the checkpoint
7111   // phases, the object may already have been reached by a  different
7112   // path and may be at the end of the global overflow list (so
7113   // the mark word may be NULL).
7114   assert(obj->is_oop_or_null(true /* ignore mark word */),
7115          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7116   HeapWord* addr = (HeapWord*)obj;
7117   // Check if oop points into the CMS generation
7118   // and is not marked
7119   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7120     // a white object ...
7121     _bit_map->mark(addr);         // ... now grey
7122     // push on the marking stack (grey set)
7123     bool simulate_overflow = false;
7124     NOT_PRODUCT(
7125       if (CMSMarkStackOverflowALot &&
7126           _collector->simulate_overflow()) {
7127         // simulate a stack overflow
7128         simulate_overflow = true;
7129       }
7130     )
7131     if (simulate_overflow || !_mark_stack->push(obj)) {
7132       if (_concurrent_precleaning) {
7133          // During precleaning we can just dirty the appropriate card(s)
7134          // in the mod union table, thus ensuring that the object remains
7135          // in the grey set  and continue. In the case of object arrays
7136          // we need to dirty all of the cards that the object spans,
7137          // since the rescan of object arrays will be limited to the
7138          // dirty cards.
7139          // Note that no one can be interfering with us in this action
7140          // of dirtying the mod union table, so no locking or atomics
7141          // are required.
7142          if (obj->is_objArray()) {
7143            size_t sz = obj->size();
7144            HeapWord* end_card_addr = (HeapWord*)round_to(
7145                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7146            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7147            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7148            _mod_union_table->mark_range(redirty_range);
7149          } else {
7150            _mod_union_table->mark(addr);
7151          }
7152          _collector->_ser_pmc_preclean_ovflw++;
7153       } else {
7154          // During the remark phase, we need to remember this oop
7155          // in the overflow list.
7156          _collector->push_on_overflow_list(obj);
7157          _collector->_ser_pmc_remark_ovflw++;
7158       }
7159     }
7160   }
7161 }
7162 
7163 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7164                                                MemRegion span,
7165                                                ReferenceProcessor* rp,
7166                                                CMSBitMap* bit_map,
7167                                                OopTaskQueue* work_queue):
7168   MetadataAwareOopClosure(rp),
7169   _collector(collector),
7170   _span(span),
7171   _bit_map(bit_map),
7172   _work_queue(work_queue)
7173 {
7174   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7175 }
7176 
7177 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7178 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7179 
7180 // Grey object rescan during second checkpoint phase --
7181 // the parallel version.
7182 void Par_PushAndMarkClosure::do_oop(oop obj) {
7183   // In the assert below, we ignore the mark word because
7184   // this oop may point to an already visited object that is
7185   // on the overflow stack (in which case the mark word has
7186   // been hijacked for chaining into the overflow stack --
7187   // if this is the last object in the overflow stack then
7188   // its mark word will be NULL). Because this object may
7189   // have been subsequently popped off the global overflow
7190   // stack, and the mark word possibly restored to the prototypical
7191   // value, by the time we get to examined this failing assert in
7192   // the debugger, is_oop_or_null(false) may subsequently start
7193   // to hold.
7194   assert(obj->is_oop_or_null(true),
7195          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7196   HeapWord* addr = (HeapWord*)obj;
7197   // Check if oop points into the CMS generation
7198   // and is not marked
7199   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7200     // a white object ...
7201     // If we manage to "claim" the object, by being the
7202     // first thread to mark it, then we push it on our
7203     // marking stack
7204     if (_bit_map->par_mark(addr)) {     // ... now grey
7205       // push on work queue (grey set)
7206       bool simulate_overflow = false;
7207       NOT_PRODUCT(
7208         if (CMSMarkStackOverflowALot &&
7209             _collector->par_simulate_overflow()) {
7210           // simulate a stack overflow
7211           simulate_overflow = true;
7212         }
7213       )
7214       if (simulate_overflow || !_work_queue->push(obj)) {
7215         _collector->par_push_on_overflow_list(obj);
7216         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7217       }
7218     } // Else, some other thread got there first
7219   }
7220 }
7221 
7222 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7223 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7224 
7225 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7226   Mutex* bml = _collector->bitMapLock();
7227   assert_lock_strong(bml);
7228   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7229          "CMS thread should hold CMS token");
7230 
7231   bml->unlock();
7232   ConcurrentMarkSweepThread::desynchronize(true);
7233 
7234   _collector->stopTimer();
7235   if (PrintCMSStatistics != 0) {
7236     _collector->incrementYields();
7237   }
7238 
7239   // See the comment in coordinator_yield()
7240   for (unsigned i = 0; i < CMSYieldSleepCount &&
7241                        ConcurrentMarkSweepThread::should_yield() &&
7242                        !CMSCollector::foregroundGCIsActive(); ++i) {
7243     os::sleep(Thread::current(), 1, false);
7244   }
7245 
7246   ConcurrentMarkSweepThread::synchronize(true);
7247   bml->lock();
7248 
7249   _collector->startTimer();
7250 }
7251 
7252 bool CMSPrecleanRefsYieldClosure::should_return() {
7253   if (ConcurrentMarkSweepThread::should_yield()) {
7254     do_yield_work();
7255   }
7256   return _collector->foregroundGCIsActive();
7257 }
7258 
7259 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7260   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7261          "mr should be aligned to start at a card boundary");
7262   // We'd like to assert:
7263   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7264   //        "mr should be a range of cards");
7265   // However, that would be too strong in one case -- the last
7266   // partition ends at _unallocated_block which, in general, can be
7267   // an arbitrary boundary, not necessarily card aligned.
7268   if (PrintCMSStatistics != 0) {
7269     _num_dirty_cards +=
7270          mr.word_size()/CardTableModRefBS::card_size_in_words;
7271   }
7272   _space->object_iterate_mem(mr, &_scan_cl);
7273 }
7274 
7275 SweepClosure::SweepClosure(CMSCollector* collector,
7276                            ConcurrentMarkSweepGeneration* g,
7277                            CMSBitMap* bitMap, bool should_yield) :
7278   _collector(collector),
7279   _g(g),
7280   _sp(g->cmsSpace()),
7281   _limit(_sp->sweep_limit()),
7282   _freelistLock(_sp->freelistLock()),
7283   _bitMap(bitMap),
7284   _yield(should_yield),
7285   _inFreeRange(false),           // No free range at beginning of sweep
7286   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7287   _lastFreeRangeCoalesced(false),
7288   _freeFinger(g->used_region().start())
7289 {
7290   NOT_PRODUCT(
7291     _numObjectsFreed = 0;
7292     _numWordsFreed   = 0;
7293     _numObjectsLive = 0;
7294     _numWordsLive = 0;
7295     _numObjectsAlreadyFree = 0;
7296     _numWordsAlreadyFree = 0;
7297     _last_fc = NULL;
7298 
7299     _sp->initializeIndexedFreeListArrayReturnedBytes();
7300     _sp->dictionary()->initialize_dict_returned_bytes();
7301   )
7302   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7303          "sweep _limit out of bounds");
7304   if (CMSTraceSweeper) {
7305     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7306                         p2i(_limit));
7307   }
7308 }
7309 
7310 void SweepClosure::print_on(outputStream* st) const {
7311   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7312                 p2i(_sp->bottom()), p2i(_sp->end()));
7313   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7314   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7315   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7316   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7317                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7318 }
7319 
7320 #ifndef PRODUCT
7321 // Assertion checking only:  no useful work in product mode --
7322 // however, if any of the flags below become product flags,
7323 // you may need to review this code to see if it needs to be
7324 // enabled in product mode.
7325 SweepClosure::~SweepClosure() {
7326   assert_lock_strong(_freelistLock);
7327   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7328          "sweep _limit out of bounds");
7329   if (inFreeRange()) {
7330     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7331     print();
7332     ShouldNotReachHere();
7333   }
7334   if (Verbose && PrintGC) {
7335     gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7336                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7337     gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects,  "
7338                            SIZE_FORMAT " bytes  "
7339       "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7340       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7341       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7342     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7343                         * sizeof(HeapWord);
7344     gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7345 
7346     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7347       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7348       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7349       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7350       gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7351       gclog_or_tty->print("   Indexed List Returned " SIZE_FORMAT " bytes",
7352         indexListReturnedBytes);
7353       gclog_or_tty->print_cr("        Dictionary Returned " SIZE_FORMAT " bytes",
7354         dict_returned_bytes);
7355     }
7356   }
7357   if (CMSTraceSweeper) {
7358     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7359                            p2i(_limit));
7360   }
7361 }
7362 #endif  // PRODUCT
7363 
7364 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7365     bool freeRangeInFreeLists) {
7366   if (CMSTraceSweeper) {
7367     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7368                p2i(freeFinger), freeRangeInFreeLists);
7369   }
7370   assert(!inFreeRange(), "Trampling existing free range");
7371   set_inFreeRange(true);
7372   set_lastFreeRangeCoalesced(false);
7373 
7374   set_freeFinger(freeFinger);
7375   set_freeRangeInFreeLists(freeRangeInFreeLists);
7376   if (CMSTestInFreeList) {
7377     if (freeRangeInFreeLists) {
7378       FreeChunk* fc = (FreeChunk*) freeFinger;
7379       assert(fc->is_free(), "A chunk on the free list should be free.");
7380       assert(fc->size() > 0, "Free range should have a size");
7381       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7382     }
7383   }
7384 }
7385 
7386 // Note that the sweeper runs concurrently with mutators. Thus,
7387 // it is possible for direct allocation in this generation to happen
7388 // in the middle of the sweep. Note that the sweeper also coalesces
7389 // contiguous free blocks. Thus, unless the sweeper and the allocator
7390 // synchronize appropriately freshly allocated blocks may get swept up.
7391 // This is accomplished by the sweeper locking the free lists while
7392 // it is sweeping. Thus blocks that are determined to be free are
7393 // indeed free. There is however one additional complication:
7394 // blocks that have been allocated since the final checkpoint and
7395 // mark, will not have been marked and so would be treated as
7396 // unreachable and swept up. To prevent this, the allocator marks
7397 // the bit map when allocating during the sweep phase. This leads,
7398 // however, to a further complication -- objects may have been allocated
7399 // but not yet initialized -- in the sense that the header isn't yet
7400 // installed. The sweeper can not then determine the size of the block
7401 // in order to skip over it. To deal with this case, we use a technique
7402 // (due to Printezis) to encode such uninitialized block sizes in the
7403 // bit map. Since the bit map uses a bit per every HeapWord, but the
7404 // CMS generation has a minimum object size of 3 HeapWords, it follows
7405 // that "normal marks" won't be adjacent in the bit map (there will
7406 // always be at least two 0 bits between successive 1 bits). We make use
7407 // of these "unused" bits to represent uninitialized blocks -- the bit
7408 // corresponding to the start of the uninitialized object and the next
7409 // bit are both set. Finally, a 1 bit marks the end of the object that
7410 // started with the two consecutive 1 bits to indicate its potentially
7411 // uninitialized state.
7412 
7413 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7414   FreeChunk* fc = (FreeChunk*)addr;
7415   size_t res;
7416 
7417   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7418   // than "addr == _limit" because although _limit was a block boundary when
7419   // we started the sweep, it may no longer be one because heap expansion
7420   // may have caused us to coalesce the block ending at the address _limit
7421   // with a newly expanded chunk (this happens when _limit was set to the
7422   // previous _end of the space), so we may have stepped past _limit:
7423   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7424   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7425     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7426            "sweep _limit out of bounds");
7427     assert(addr < _sp->end(), "addr out of bounds");
7428     // Flush any free range we might be holding as a single
7429     // coalesced chunk to the appropriate free list.
7430     if (inFreeRange()) {
7431       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7432              err_msg("freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger())));
7433       flush_cur_free_chunk(freeFinger(),
7434                            pointer_delta(addr, freeFinger()));
7435       if (CMSTraceSweeper) {
7436         gclog_or_tty->print("Sweep: last chunk: ");
7437         gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7438                    "[coalesced:%d]\n",
7439                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7440                    lastFreeRangeCoalesced() ? 1 : 0);
7441       }
7442     }
7443 
7444     // help the iterator loop finish
7445     return pointer_delta(_sp->end(), addr);
7446   }
7447 
7448   assert(addr < _limit, "sweep invariant");
7449   // check if we should yield
7450   do_yield_check(addr);
7451   if (fc->is_free()) {
7452     // Chunk that is already free
7453     res = fc->size();
7454     do_already_free_chunk(fc);
7455     debug_only(_sp->verifyFreeLists());
7456     // If we flush the chunk at hand in lookahead_and_flush()
7457     // and it's coalesced with a preceding chunk, then the
7458     // process of "mangling" the payload of the coalesced block
7459     // will cause erasure of the size information from the
7460     // (erstwhile) header of all the coalesced blocks but the
7461     // first, so the first disjunct in the assert will not hold
7462     // in that specific case (in which case the second disjunct
7463     // will hold).
7464     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7465            "Otherwise the size info doesn't change at this step");
7466     NOT_PRODUCT(
7467       _numObjectsAlreadyFree++;
7468       _numWordsAlreadyFree += res;
7469     )
7470     NOT_PRODUCT(_last_fc = fc;)
7471   } else if (!_bitMap->isMarked(addr)) {
7472     // Chunk is fresh garbage
7473     res = do_garbage_chunk(fc);
7474     debug_only(_sp->verifyFreeLists());
7475     NOT_PRODUCT(
7476       _numObjectsFreed++;
7477       _numWordsFreed += res;
7478     )
7479   } else {
7480     // Chunk that is alive.
7481     res = do_live_chunk(fc);
7482     debug_only(_sp->verifyFreeLists());
7483     NOT_PRODUCT(
7484         _numObjectsLive++;
7485         _numWordsLive += res;
7486     )
7487   }
7488   return res;
7489 }
7490 
7491 // For the smart allocation, record following
7492 //  split deaths - a free chunk is removed from its free list because
7493 //      it is being split into two or more chunks.
7494 //  split birth - a free chunk is being added to its free list because
7495 //      a larger free chunk has been split and resulted in this free chunk.
7496 //  coal death - a free chunk is being removed from its free list because
7497 //      it is being coalesced into a large free chunk.
7498 //  coal birth - a free chunk is being added to its free list because
7499 //      it was created when two or more free chunks where coalesced into
7500 //      this free chunk.
7501 //
7502 // These statistics are used to determine the desired number of free
7503 // chunks of a given size.  The desired number is chosen to be relative
7504 // to the end of a CMS sweep.  The desired number at the end of a sweep
7505 // is the
7506 //      count-at-end-of-previous-sweep (an amount that was enough)
7507 //              - count-at-beginning-of-current-sweep  (the excess)
7508 //              + split-births  (gains in this size during interval)
7509 //              - split-deaths  (demands on this size during interval)
7510 // where the interval is from the end of one sweep to the end of the
7511 // next.
7512 //
7513 // When sweeping the sweeper maintains an accumulated chunk which is
7514 // the chunk that is made up of chunks that have been coalesced.  That
7515 // will be termed the left-hand chunk.  A new chunk of garbage that
7516 // is being considered for coalescing will be referred to as the
7517 // right-hand chunk.
7518 //
7519 // When making a decision on whether to coalesce a right-hand chunk with
7520 // the current left-hand chunk, the current count vs. the desired count
7521 // of the left-hand chunk is considered.  Also if the right-hand chunk
7522 // is near the large chunk at the end of the heap (see
7523 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7524 // left-hand chunk is coalesced.
7525 //
7526 // When making a decision about whether to split a chunk, the desired count
7527 // vs. the current count of the candidate to be split is also considered.
7528 // If the candidate is underpopulated (currently fewer chunks than desired)
7529 // a chunk of an overpopulated (currently more chunks than desired) size may
7530 // be chosen.  The "hint" associated with a free list, if non-null, points
7531 // to a free list which may be overpopulated.
7532 //
7533 
7534 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7535   const size_t size = fc->size();
7536   // Chunks that cannot be coalesced are not in the
7537   // free lists.
7538   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7539     assert(_sp->verify_chunk_in_free_list(fc),
7540       "free chunk should be in free lists");
7541   }
7542   // a chunk that is already free, should not have been
7543   // marked in the bit map
7544   HeapWord* const addr = (HeapWord*) fc;
7545   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7546   // Verify that the bit map has no bits marked between
7547   // addr and purported end of this block.
7548   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7549 
7550   // Some chunks cannot be coalesced under any circumstances.
7551   // See the definition of cantCoalesce().
7552   if (!fc->cantCoalesce()) {
7553     // This chunk can potentially be coalesced.
7554     if (_sp->adaptive_freelists()) {
7555       // All the work is done in
7556       do_post_free_or_garbage_chunk(fc, size);
7557     } else {  // Not adaptive free lists
7558       // this is a free chunk that can potentially be coalesced by the sweeper;
7559       if (!inFreeRange()) {
7560         // if the next chunk is a free block that can't be coalesced
7561         // it doesn't make sense to remove this chunk from the free lists
7562         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7563         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7564         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
7565             nextChunk->is_free()               &&     // ... which is free...
7566             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
7567           // nothing to do
7568         } else {
7569           // Potentially the start of a new free range:
7570           // Don't eagerly remove it from the free lists.
7571           // No need to remove it if it will just be put
7572           // back again.  (Also from a pragmatic point of view
7573           // if it is a free block in a region that is beyond
7574           // any allocated blocks, an assertion will fail)
7575           // Remember the start of a free run.
7576           initialize_free_range(addr, true);
7577           // end - can coalesce with next chunk
7578         }
7579       } else {
7580         // the midst of a free range, we are coalescing
7581         print_free_block_coalesced(fc);
7582         if (CMSTraceSweeper) {
7583           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7584         }
7585         // remove it from the free lists
7586         _sp->removeFreeChunkFromFreeLists(fc);
7587         set_lastFreeRangeCoalesced(true);
7588         // If the chunk is being coalesced and the current free range is
7589         // in the free lists, remove the current free range so that it
7590         // will be returned to the free lists in its entirety - all
7591         // the coalesced pieces included.
7592         if (freeRangeInFreeLists()) {
7593           FreeChunk* ffc = (FreeChunk*) freeFinger();
7594           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7595             "Size of free range is inconsistent with chunk size.");
7596           if (CMSTestInFreeList) {
7597             assert(_sp->verify_chunk_in_free_list(ffc),
7598               "free range is not in free lists");
7599           }
7600           _sp->removeFreeChunkFromFreeLists(ffc);
7601           set_freeRangeInFreeLists(false);
7602         }
7603       }
7604     }
7605     // Note that if the chunk is not coalescable (the else arm
7606     // below), we unconditionally flush, without needing to do
7607     // a "lookahead," as we do below.
7608     if (inFreeRange()) lookahead_and_flush(fc, size);
7609   } else {
7610     // Code path common to both original and adaptive free lists.
7611 
7612     // cant coalesce with previous block; this should be treated
7613     // as the end of a free run if any
7614     if (inFreeRange()) {
7615       // we kicked some butt; time to pick up the garbage
7616       assert(freeFinger() < addr, "freeFinger points too high");
7617       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7618     }
7619     // else, nothing to do, just continue
7620   }
7621 }
7622 
7623 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7624   // This is a chunk of garbage.  It is not in any free list.
7625   // Add it to a free list or let it possibly be coalesced into
7626   // a larger chunk.
7627   HeapWord* const addr = (HeapWord*) fc;
7628   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7629 
7630   if (_sp->adaptive_freelists()) {
7631     // Verify that the bit map has no bits marked between
7632     // addr and purported end of just dead object.
7633     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7634 
7635     do_post_free_or_garbage_chunk(fc, size);
7636   } else {
7637     if (!inFreeRange()) {
7638       // start of a new free range
7639       assert(size > 0, "A free range should have a size");
7640       initialize_free_range(addr, false);
7641     } else {
7642       // this will be swept up when we hit the end of the
7643       // free range
7644       if (CMSTraceSweeper) {
7645         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7646       }
7647       // If the chunk is being coalesced and the current free range is
7648       // in the free lists, remove the current free range so that it
7649       // will be returned to the free lists in its entirety - all
7650       // the coalesced pieces included.
7651       if (freeRangeInFreeLists()) {
7652         FreeChunk* ffc = (FreeChunk*)freeFinger();
7653         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7654           "Size of free range is inconsistent with chunk size.");
7655         if (CMSTestInFreeList) {
7656           assert(_sp->verify_chunk_in_free_list(ffc),
7657             "free range is not in free lists");
7658         }
7659         _sp->removeFreeChunkFromFreeLists(ffc);
7660         set_freeRangeInFreeLists(false);
7661       }
7662       set_lastFreeRangeCoalesced(true);
7663     }
7664     // this will be swept up when we hit the end of the free range
7665 
7666     // Verify that the bit map has no bits marked between
7667     // addr and purported end of just dead object.
7668     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7669   }
7670   assert(_limit >= addr + size,
7671          "A freshly garbage chunk can't possibly straddle over _limit");
7672   if (inFreeRange()) lookahead_and_flush(fc, size);
7673   return size;
7674 }
7675 
7676 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7677   HeapWord* addr = (HeapWord*) fc;
7678   // The sweeper has just found a live object. Return any accumulated
7679   // left hand chunk to the free lists.
7680   if (inFreeRange()) {
7681     assert(freeFinger() < addr, "freeFinger points too high");
7682     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7683   }
7684 
7685   // This object is live: we'd normally expect this to be
7686   // an oop, and like to assert the following:
7687   // assert(oop(addr)->is_oop(), "live block should be an oop");
7688   // However, as we commented above, this may be an object whose
7689   // header hasn't yet been initialized.
7690   size_t size;
7691   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7692   if (_bitMap->isMarked(addr + 1)) {
7693     // Determine the size from the bit map, rather than trying to
7694     // compute it from the object header.
7695     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7696     size = pointer_delta(nextOneAddr + 1, addr);
7697     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7698            "alignment problem");
7699 
7700 #ifdef ASSERT
7701       if (oop(addr)->klass_or_null() != NULL) {
7702         // Ignore mark word because we are running concurrent with mutators
7703         assert(oop(addr)->is_oop(true), "live block should be an oop");
7704         assert(size ==
7705                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7706                "P-mark and computed size do not agree");
7707       }
7708 #endif
7709 
7710   } else {
7711     // This should be an initialized object that's alive.
7712     assert(oop(addr)->klass_or_null() != NULL,
7713            "Should be an initialized object");
7714     // Ignore mark word because we are running concurrent with mutators
7715     assert(oop(addr)->is_oop(true), "live block should be an oop");
7716     // Verify that the bit map has no bits marked between
7717     // addr and purported end of this block.
7718     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7719     assert(size >= 3, "Necessary for Printezis marks to work");
7720     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7721     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7722   }
7723   return size;
7724 }
7725 
7726 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7727                                                  size_t chunkSize) {
7728   // do_post_free_or_garbage_chunk() should only be called in the case
7729   // of the adaptive free list allocator.
7730   const bool fcInFreeLists = fc->is_free();
7731   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7732   assert((HeapWord*)fc <= _limit, "sweep invariant");
7733   if (CMSTestInFreeList && fcInFreeLists) {
7734     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7735   }
7736 
7737   if (CMSTraceSweeper) {
7738     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7739   }
7740 
7741   HeapWord* const fc_addr = (HeapWord*) fc;
7742 
7743   bool coalesce;
7744   const size_t left  = pointer_delta(fc_addr, freeFinger());
7745   const size_t right = chunkSize;
7746   switch (FLSCoalescePolicy) {
7747     // numeric value forms a coalition aggressiveness metric
7748     case 0:  { // never coalesce
7749       coalesce = false;
7750       break;
7751     }
7752     case 1: { // coalesce if left & right chunks on overpopulated lists
7753       coalesce = _sp->coalOverPopulated(left) &&
7754                  _sp->coalOverPopulated(right);
7755       break;
7756     }
7757     case 2: { // coalesce if left chunk on overpopulated list (default)
7758       coalesce = _sp->coalOverPopulated(left);
7759       break;
7760     }
7761     case 3: { // coalesce if left OR right chunk on overpopulated list
7762       coalesce = _sp->coalOverPopulated(left) ||
7763                  _sp->coalOverPopulated(right);
7764       break;
7765     }
7766     case 4: { // always coalesce
7767       coalesce = true;
7768       break;
7769     }
7770     default:
7771      ShouldNotReachHere();
7772   }
7773 
7774   // Should the current free range be coalesced?
7775   // If the chunk is in a free range and either we decided to coalesce above
7776   // or the chunk is near the large block at the end of the heap
7777   // (isNearLargestChunk() returns true), then coalesce this chunk.
7778   const bool doCoalesce = inFreeRange()
7779                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7780   if (doCoalesce) {
7781     // Coalesce the current free range on the left with the new
7782     // chunk on the right.  If either is on a free list,
7783     // it must be removed from the list and stashed in the closure.
7784     if (freeRangeInFreeLists()) {
7785       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7786       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7787         "Size of free range is inconsistent with chunk size.");
7788       if (CMSTestInFreeList) {
7789         assert(_sp->verify_chunk_in_free_list(ffc),
7790           "Chunk is not in free lists");
7791       }
7792       _sp->coalDeath(ffc->size());
7793       _sp->removeFreeChunkFromFreeLists(ffc);
7794       set_freeRangeInFreeLists(false);
7795     }
7796     if (fcInFreeLists) {
7797       _sp->coalDeath(chunkSize);
7798       assert(fc->size() == chunkSize,
7799         "The chunk has the wrong size or is not in the free lists");
7800       _sp->removeFreeChunkFromFreeLists(fc);
7801     }
7802     set_lastFreeRangeCoalesced(true);
7803     print_free_block_coalesced(fc);
7804   } else {  // not in a free range and/or should not coalesce
7805     // Return the current free range and start a new one.
7806     if (inFreeRange()) {
7807       // In a free range but cannot coalesce with the right hand chunk.
7808       // Put the current free range into the free lists.
7809       flush_cur_free_chunk(freeFinger(),
7810                            pointer_delta(fc_addr, freeFinger()));
7811     }
7812     // Set up for new free range.  Pass along whether the right hand
7813     // chunk is in the free lists.
7814     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7815   }
7816 }
7817 
7818 // Lookahead flush:
7819 // If we are tracking a free range, and this is the last chunk that
7820 // we'll look at because its end crosses past _limit, we'll preemptively
7821 // flush it along with any free range we may be holding on to. Note that
7822 // this can be the case only for an already free or freshly garbage
7823 // chunk. If this block is an object, it can never straddle
7824 // over _limit. The "straddling" occurs when _limit is set at
7825 // the previous end of the space when this cycle started, and
7826 // a subsequent heap expansion caused the previously co-terminal
7827 // free block to be coalesced with the newly expanded portion,
7828 // thus rendering _limit a non-block-boundary making it dangerous
7829 // for the sweeper to step over and examine.
7830 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7831   assert(inFreeRange(), "Should only be called if currently in a free range.");
7832   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7833   assert(_sp->used_region().contains(eob - 1),
7834          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7835                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7836                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7837                  p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7838   if (eob >= _limit) {
7839     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7840     if (CMSTraceSweeper) {
7841       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7842                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7843                              "[" PTR_FORMAT "," PTR_FORMAT ")",
7844                              p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7845     }
7846     // Return the storage we are tracking back into the free lists.
7847     if (CMSTraceSweeper) {
7848       gclog_or_tty->print_cr("Flushing ... ");
7849     }
7850     assert(freeFinger() < eob, "Error");
7851     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7852   }
7853 }
7854 
7855 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7856   assert(inFreeRange(), "Should only be called if currently in a free range.");
7857   assert(size > 0,
7858     "A zero sized chunk cannot be added to the free lists.");
7859   if (!freeRangeInFreeLists()) {
7860     if (CMSTestInFreeList) {
7861       FreeChunk* fc = (FreeChunk*) chunk;
7862       fc->set_size(size);
7863       assert(!_sp->verify_chunk_in_free_list(fc),
7864         "chunk should not be in free lists yet");
7865     }
7866     if (CMSTraceSweeper) {
7867       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7868                     p2i(chunk), size);
7869     }
7870     // A new free range is going to be starting.  The current
7871     // free range has not been added to the free lists yet or
7872     // was removed so add it back.
7873     // If the current free range was coalesced, then the death
7874     // of the free range was recorded.  Record a birth now.
7875     if (lastFreeRangeCoalesced()) {
7876       _sp->coalBirth(size);
7877     }
7878     _sp->addChunkAndRepairOffsetTable(chunk, size,
7879             lastFreeRangeCoalesced());
7880   } else if (CMSTraceSweeper) {
7881     gclog_or_tty->print_cr("Already in free list: nothing to flush");
7882   }
7883   set_inFreeRange(false);
7884   set_freeRangeInFreeLists(false);
7885 }
7886 
7887 // We take a break if we've been at this for a while,
7888 // so as to avoid monopolizing the locks involved.
7889 void SweepClosure::do_yield_work(HeapWord* addr) {
7890   // Return current free chunk being used for coalescing (if any)
7891   // to the appropriate freelist.  After yielding, the next
7892   // free block encountered will start a coalescing range of
7893   // free blocks.  If the next free block is adjacent to the
7894   // chunk just flushed, they will need to wait for the next
7895   // sweep to be coalesced.
7896   if (inFreeRange()) {
7897     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7898   }
7899 
7900   // First give up the locks, then yield, then re-lock.
7901   // We should probably use a constructor/destructor idiom to
7902   // do this unlock/lock or modify the MutexUnlocker class to
7903   // serve our purpose. XXX
7904   assert_lock_strong(_bitMap->lock());
7905   assert_lock_strong(_freelistLock);
7906   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7907          "CMS thread should hold CMS token");
7908   _bitMap->lock()->unlock();
7909   _freelistLock->unlock();
7910   ConcurrentMarkSweepThread::desynchronize(true);
7911   _collector->stopTimer();
7912   if (PrintCMSStatistics != 0) {
7913     _collector->incrementYields();
7914   }
7915 
7916   // See the comment in coordinator_yield()
7917   for (unsigned i = 0; i < CMSYieldSleepCount &&
7918                        ConcurrentMarkSweepThread::should_yield() &&
7919                        !CMSCollector::foregroundGCIsActive(); ++i) {
7920     os::sleep(Thread::current(), 1, false);
7921   }
7922 
7923   ConcurrentMarkSweepThread::synchronize(true);
7924   _freelistLock->lock();
7925   _bitMap->lock()->lock_without_safepoint_check();
7926   _collector->startTimer();
7927 }
7928 
7929 #ifndef PRODUCT
7930 // This is actually very useful in a product build if it can
7931 // be called from the debugger.  Compile it into the product
7932 // as needed.
7933 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7934   return debug_cms_space->verify_chunk_in_free_list(fc);
7935 }
7936 #endif
7937 
7938 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7939   if (CMSTraceSweeper) {
7940     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7941                            p2i(fc), fc->size());
7942   }
7943 }
7944 
7945 // CMSIsAliveClosure
7946 bool CMSIsAliveClosure::do_object_b(oop obj) {
7947   HeapWord* addr = (HeapWord*)obj;
7948   return addr != NULL &&
7949          (!_span.contains(addr) || _bit_map->isMarked(addr));
7950 }
7951 
7952 
7953 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7954                       MemRegion span,
7955                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7956                       bool cpc):
7957   _collector(collector),
7958   _span(span),
7959   _bit_map(bit_map),
7960   _mark_stack(mark_stack),
7961   _concurrent_precleaning(cpc) {
7962   assert(!_span.is_empty(), "Empty span could spell trouble");
7963 }
7964 
7965 
7966 // CMSKeepAliveClosure: the serial version
7967 void CMSKeepAliveClosure::do_oop(oop obj) {
7968   HeapWord* addr = (HeapWord*)obj;
7969   if (_span.contains(addr) &&
7970       !_bit_map->isMarked(addr)) {
7971     _bit_map->mark(addr);
7972     bool simulate_overflow = false;
7973     NOT_PRODUCT(
7974       if (CMSMarkStackOverflowALot &&
7975           _collector->simulate_overflow()) {
7976         // simulate a stack overflow
7977         simulate_overflow = true;
7978       }
7979     )
7980     if (simulate_overflow || !_mark_stack->push(obj)) {
7981       if (_concurrent_precleaning) {
7982         // We dirty the overflown object and let the remark
7983         // phase deal with it.
7984         assert(_collector->overflow_list_is_empty(), "Error");
7985         // In the case of object arrays, we need to dirty all of
7986         // the cards that the object spans. No locking or atomics
7987         // are needed since no one else can be mutating the mod union
7988         // table.
7989         if (obj->is_objArray()) {
7990           size_t sz = obj->size();
7991           HeapWord* end_card_addr =
7992             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7993           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7994           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7995           _collector->_modUnionTable.mark_range(redirty_range);
7996         } else {
7997           _collector->_modUnionTable.mark(addr);
7998         }
7999         _collector->_ser_kac_preclean_ovflw++;
8000       } else {
8001         _collector->push_on_overflow_list(obj);
8002         _collector->_ser_kac_ovflw++;
8003       }
8004     }
8005   }
8006 }
8007 
8008 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8009 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8010 
8011 // CMSParKeepAliveClosure: a parallel version of the above.
8012 // The work queues are private to each closure (thread),
8013 // but (may be) available for stealing by other threads.
8014 void CMSParKeepAliveClosure::do_oop(oop obj) {
8015   HeapWord* addr = (HeapWord*)obj;
8016   if (_span.contains(addr) &&
8017       !_bit_map->isMarked(addr)) {
8018     // In general, during recursive tracing, several threads
8019     // may be concurrently getting here; the first one to
8020     // "tag" it, claims it.
8021     if (_bit_map->par_mark(addr)) {
8022       bool res = _work_queue->push(obj);
8023       assert(res, "Low water mark should be much less than capacity");
8024       // Do a recursive trim in the hope that this will keep
8025       // stack usage lower, but leave some oops for potential stealers
8026       trim_queue(_low_water_mark);
8027     } // Else, another thread got there first
8028   }
8029 }
8030 
8031 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8032 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8033 
8034 void CMSParKeepAliveClosure::trim_queue(uint max) {
8035   while (_work_queue->size() > max) {
8036     oop new_oop;
8037     if (_work_queue->pop_local(new_oop)) {
8038       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8039       assert(_bit_map->isMarked((HeapWord*)new_oop),
8040              "no white objects on this stack!");
8041       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8042       // iterate over the oops in this oop, marking and pushing
8043       // the ones in CMS heap (i.e. in _span).
8044       new_oop->oop_iterate(&_mark_and_push);
8045     }
8046   }
8047 }
8048 
8049 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8050                                 CMSCollector* collector,
8051                                 MemRegion span, CMSBitMap* bit_map,
8052                                 OopTaskQueue* work_queue):
8053   _collector(collector),
8054   _span(span),
8055   _bit_map(bit_map),
8056   _work_queue(work_queue) { }
8057 
8058 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8059   HeapWord* addr = (HeapWord*)obj;
8060   if (_span.contains(addr) &&
8061       !_bit_map->isMarked(addr)) {
8062     if (_bit_map->par_mark(addr)) {
8063       bool simulate_overflow = false;
8064       NOT_PRODUCT(
8065         if (CMSMarkStackOverflowALot &&
8066             _collector->par_simulate_overflow()) {
8067           // simulate a stack overflow
8068           simulate_overflow = true;
8069         }
8070       )
8071       if (simulate_overflow || !_work_queue->push(obj)) {
8072         _collector->par_push_on_overflow_list(obj);
8073         _collector->_par_kac_ovflw++;
8074       }
8075     } // Else another thread got there already
8076   }
8077 }
8078 
8079 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8080 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8081 
8082 //////////////////////////////////////////////////////////////////
8083 //  CMSExpansionCause                /////////////////////////////
8084 //////////////////////////////////////////////////////////////////
8085 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8086   switch (cause) {
8087     case _no_expansion:
8088       return "No expansion";
8089     case _satisfy_free_ratio:
8090       return "Free ratio";
8091     case _satisfy_promotion:
8092       return "Satisfy promotion";
8093     case _satisfy_allocation:
8094       return "allocation";
8095     case _allocate_par_lab:
8096       return "Par LAB";
8097     case _allocate_par_spooling_space:
8098       return "Par Spooling Space";
8099     case _adaptive_size_policy:
8100       return "Ergonomics";
8101     default:
8102       return "unknown";
8103   }
8104 }
8105 
8106 void CMSDrainMarkingStackClosure::do_void() {
8107   // the max number to take from overflow list at a time
8108   const size_t num = _mark_stack->capacity()/4;
8109   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8110          "Overflow list should be NULL during concurrent phases");
8111   while (!_mark_stack->isEmpty() ||
8112          // if stack is empty, check the overflow list
8113          _collector->take_from_overflow_list(num, _mark_stack)) {
8114     oop obj = _mark_stack->pop();
8115     HeapWord* addr = (HeapWord*)obj;
8116     assert(_span.contains(addr), "Should be within span");
8117     assert(_bit_map->isMarked(addr), "Should be marked");
8118     assert(obj->is_oop(), "Should be an oop");
8119     obj->oop_iterate(_keep_alive);
8120   }
8121 }
8122 
8123 void CMSParDrainMarkingStackClosure::do_void() {
8124   // drain queue
8125   trim_queue(0);
8126 }
8127 
8128 // Trim our work_queue so its length is below max at return
8129 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8130   while (_work_queue->size() > max) {
8131     oop new_oop;
8132     if (_work_queue->pop_local(new_oop)) {
8133       assert(new_oop->is_oop(), "Expected an oop");
8134       assert(_bit_map->isMarked((HeapWord*)new_oop),
8135              "no white objects on this stack!");
8136       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8137       // iterate over the oops in this oop, marking and pushing
8138       // the ones in CMS heap (i.e. in _span).
8139       new_oop->oop_iterate(&_mark_and_push);
8140     }
8141   }
8142 }
8143 
8144 ////////////////////////////////////////////////////////////////////
8145 // Support for Marking Stack Overflow list handling and related code
8146 ////////////////////////////////////////////////////////////////////
8147 // Much of the following code is similar in shape and spirit to the
8148 // code used in ParNewGC. We should try and share that code
8149 // as much as possible in the future.
8150 
8151 #ifndef PRODUCT
8152 // Debugging support for CMSStackOverflowALot
8153 
8154 // It's OK to call this multi-threaded;  the worst thing
8155 // that can happen is that we'll get a bunch of closely
8156 // spaced simulated overflows, but that's OK, in fact
8157 // probably good as it would exercise the overflow code
8158 // under contention.
8159 bool CMSCollector::simulate_overflow() {
8160   if (_overflow_counter-- <= 0) { // just being defensive
8161     _overflow_counter = CMSMarkStackOverflowInterval;
8162     return true;
8163   } else {
8164     return false;
8165   }
8166 }
8167 
8168 bool CMSCollector::par_simulate_overflow() {
8169   return simulate_overflow();
8170 }
8171 #endif
8172 
8173 // Single-threaded
8174 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8175   assert(stack->isEmpty(), "Expected precondition");
8176   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8177   size_t i = num;
8178   oop  cur = _overflow_list;
8179   const markOop proto = markOopDesc::prototype();
8180   NOT_PRODUCT(ssize_t n = 0;)
8181   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8182     next = oop(cur->mark());
8183     cur->set_mark(proto);   // until proven otherwise
8184     assert(cur->is_oop(), "Should be an oop");
8185     bool res = stack->push(cur);
8186     assert(res, "Bit off more than can chew?");
8187     NOT_PRODUCT(n++;)
8188   }
8189   _overflow_list = cur;
8190 #ifndef PRODUCT
8191   assert(_num_par_pushes >= n, "Too many pops?");
8192   _num_par_pushes -=n;
8193 #endif
8194   return !stack->isEmpty();
8195 }
8196 
8197 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8198 // (MT-safe) Get a prefix of at most "num" from the list.
8199 // The overflow list is chained through the mark word of
8200 // each object in the list. We fetch the entire list,
8201 // break off a prefix of the right size and return the
8202 // remainder. If other threads try to take objects from
8203 // the overflow list at that time, they will wait for
8204 // some time to see if data becomes available. If (and
8205 // only if) another thread places one or more object(s)
8206 // on the global list before we have returned the suffix
8207 // to the global list, we will walk down our local list
8208 // to find its end and append the global list to
8209 // our suffix before returning it. This suffix walk can
8210 // prove to be expensive (quadratic in the amount of traffic)
8211 // when there are many objects in the overflow list and
8212 // there is much producer-consumer contention on the list.
8213 // *NOTE*: The overflow list manipulation code here and
8214 // in ParNewGeneration:: are very similar in shape,
8215 // except that in the ParNew case we use the old (from/eden)
8216 // copy of the object to thread the list via its klass word.
8217 // Because of the common code, if you make any changes in
8218 // the code below, please check the ParNew version to see if
8219 // similar changes might be needed.
8220 // CR 6797058 has been filed to consolidate the common code.
8221 bool CMSCollector::par_take_from_overflow_list(size_t num,
8222                                                OopTaskQueue* work_q,
8223                                                int no_of_gc_threads) {
8224   assert(work_q->size() == 0, "First empty local work queue");
8225   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8226   if (_overflow_list == NULL) {
8227     return false;
8228   }
8229   // Grab the entire list; we'll put back a suffix
8230   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8231   Thread* tid = Thread::current();
8232   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8233   // set to ParallelGCThreads.
8234   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8235   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8236   // If the list is busy, we spin for a short while,
8237   // sleeping between attempts to get the list.
8238   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8239     os::sleep(tid, sleep_time_millis, false);
8240     if (_overflow_list == NULL) {
8241       // Nothing left to take
8242       return false;
8243     } else if (_overflow_list != BUSY) {
8244       // Try and grab the prefix
8245       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8246     }
8247   }
8248   // If the list was found to be empty, or we spun long
8249   // enough, we give up and return empty-handed. If we leave
8250   // the list in the BUSY state below, it must be the case that
8251   // some other thread holds the overflow list and will set it
8252   // to a non-BUSY state in the future.
8253   if (prefix == NULL || prefix == BUSY) {
8254      // Nothing to take or waited long enough
8255      if (prefix == NULL) {
8256        // Write back the NULL in case we overwrote it with BUSY above
8257        // and it is still the same value.
8258        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8259      }
8260      return false;
8261   }
8262   assert(prefix != NULL && prefix != BUSY, "Error");
8263   size_t i = num;
8264   oop cur = prefix;
8265   // Walk down the first "num" objects, unless we reach the end.
8266   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8267   if (cur->mark() == NULL) {
8268     // We have "num" or fewer elements in the list, so there
8269     // is nothing to return to the global list.
8270     // Write back the NULL in lieu of the BUSY we wrote
8271     // above, if it is still the same value.
8272     if (_overflow_list == BUSY) {
8273       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8274     }
8275   } else {
8276     // Chop off the suffix and return it to the global list.
8277     assert(cur->mark() != BUSY, "Error");
8278     oop suffix_head = cur->mark(); // suffix will be put back on global list
8279     cur->set_mark(NULL);           // break off suffix
8280     // It's possible that the list is still in the empty(busy) state
8281     // we left it in a short while ago; in that case we may be
8282     // able to place back the suffix without incurring the cost
8283     // of a walk down the list.
8284     oop observed_overflow_list = _overflow_list;
8285     oop cur_overflow_list = observed_overflow_list;
8286     bool attached = false;
8287     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8288       observed_overflow_list =
8289         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8290       if (cur_overflow_list == observed_overflow_list) {
8291         attached = true;
8292         break;
8293       } else cur_overflow_list = observed_overflow_list;
8294     }
8295     if (!attached) {
8296       // Too bad, someone else sneaked in (at least) an element; we'll need
8297       // to do a splice. Find tail of suffix so we can prepend suffix to global
8298       // list.
8299       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8300       oop suffix_tail = cur;
8301       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8302              "Tautology");
8303       observed_overflow_list = _overflow_list;
8304       do {
8305         cur_overflow_list = observed_overflow_list;
8306         if (cur_overflow_list != BUSY) {
8307           // Do the splice ...
8308           suffix_tail->set_mark(markOop(cur_overflow_list));
8309         } else { // cur_overflow_list == BUSY
8310           suffix_tail->set_mark(NULL);
8311         }
8312         // ... and try to place spliced list back on overflow_list ...
8313         observed_overflow_list =
8314           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8315       } while (cur_overflow_list != observed_overflow_list);
8316       // ... until we have succeeded in doing so.
8317     }
8318   }
8319 
8320   // Push the prefix elements on work_q
8321   assert(prefix != NULL, "control point invariant");
8322   const markOop proto = markOopDesc::prototype();
8323   oop next;
8324   NOT_PRODUCT(ssize_t n = 0;)
8325   for (cur = prefix; cur != NULL; cur = next) {
8326     next = oop(cur->mark());
8327     cur->set_mark(proto);   // until proven otherwise
8328     assert(cur->is_oop(), "Should be an oop");
8329     bool res = work_q->push(cur);
8330     assert(res, "Bit off more than we can chew?");
8331     NOT_PRODUCT(n++;)
8332   }
8333 #ifndef PRODUCT
8334   assert(_num_par_pushes >= n, "Too many pops?");
8335   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8336 #endif
8337   return true;
8338 }
8339 
8340 // Single-threaded
8341 void CMSCollector::push_on_overflow_list(oop p) {
8342   NOT_PRODUCT(_num_par_pushes++;)
8343   assert(p->is_oop(), "Not an oop");
8344   preserve_mark_if_necessary(p);
8345   p->set_mark((markOop)_overflow_list);
8346   _overflow_list = p;
8347 }
8348 
8349 // Multi-threaded; use CAS to prepend to overflow list
8350 void CMSCollector::par_push_on_overflow_list(oop p) {
8351   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8352   assert(p->is_oop(), "Not an oop");
8353   par_preserve_mark_if_necessary(p);
8354   oop observed_overflow_list = _overflow_list;
8355   oop cur_overflow_list;
8356   do {
8357     cur_overflow_list = observed_overflow_list;
8358     if (cur_overflow_list != BUSY) {
8359       p->set_mark(markOop(cur_overflow_list));
8360     } else {
8361       p->set_mark(NULL);
8362     }
8363     observed_overflow_list =
8364       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8365   } while (cur_overflow_list != observed_overflow_list);
8366 }
8367 #undef BUSY
8368 
8369 // Single threaded
8370 // General Note on GrowableArray: pushes may silently fail
8371 // because we are (temporarily) out of C-heap for expanding
8372 // the stack. The problem is quite ubiquitous and affects
8373 // a lot of code in the JVM. The prudent thing for GrowableArray
8374 // to do (for now) is to exit with an error. However, that may
8375 // be too draconian in some cases because the caller may be
8376 // able to recover without much harm. For such cases, we
8377 // should probably introduce a "soft_push" method which returns
8378 // an indication of success or failure with the assumption that
8379 // the caller may be able to recover from a failure; code in
8380 // the VM can then be changed, incrementally, to deal with such
8381 // failures where possible, thus, incrementally hardening the VM
8382 // in such low resource situations.
8383 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8384   _preserved_oop_stack.push(p);
8385   _preserved_mark_stack.push(m);
8386   assert(m == p->mark(), "Mark word changed");
8387   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8388          "bijection");
8389 }
8390 
8391 // Single threaded
8392 void CMSCollector::preserve_mark_if_necessary(oop p) {
8393   markOop m = p->mark();
8394   if (m->must_be_preserved(p)) {
8395     preserve_mark_work(p, m);
8396   }
8397 }
8398 
8399 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8400   markOop m = p->mark();
8401   if (m->must_be_preserved(p)) {
8402     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8403     // Even though we read the mark word without holding
8404     // the lock, we are assured that it will not change
8405     // because we "own" this oop, so no other thread can
8406     // be trying to push it on the overflow list; see
8407     // the assertion in preserve_mark_work() that checks
8408     // that m == p->mark().
8409     preserve_mark_work(p, m);
8410   }
8411 }
8412 
8413 // We should be able to do this multi-threaded,
8414 // a chunk of stack being a task (this is
8415 // correct because each oop only ever appears
8416 // once in the overflow list. However, it's
8417 // not very easy to completely overlap this with
8418 // other operations, so will generally not be done
8419 // until all work's been completed. Because we
8420 // expect the preserved oop stack (set) to be small,
8421 // it's probably fine to do this single-threaded.
8422 // We can explore cleverer concurrent/overlapped/parallel
8423 // processing of preserved marks if we feel the
8424 // need for this in the future. Stack overflow should
8425 // be so rare in practice and, when it happens, its
8426 // effect on performance so great that this will
8427 // likely just be in the noise anyway.
8428 void CMSCollector::restore_preserved_marks_if_any() {
8429   assert(SafepointSynchronize::is_at_safepoint(),
8430          "world should be stopped");
8431   assert(Thread::current()->is_ConcurrentGC_thread() ||
8432          Thread::current()->is_VM_thread(),
8433          "should be single-threaded");
8434   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8435          "bijection");
8436 
8437   while (!_preserved_oop_stack.is_empty()) {
8438     oop p = _preserved_oop_stack.pop();
8439     assert(p->is_oop(), "Should be an oop");
8440     assert(_span.contains(p), "oop should be in _span");
8441     assert(p->mark() == markOopDesc::prototype(),
8442            "Set when taken from overflow list");
8443     markOop m = _preserved_mark_stack.pop();
8444     p->set_mark(m);
8445   }
8446   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8447          "stacks were cleared above");
8448 }
8449 
8450 #ifndef PRODUCT
8451 bool CMSCollector::no_preserved_marks() const {
8452   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8453 }
8454 #endif
8455 
8456 // Transfer some number of overflown objects to usual marking
8457 // stack. Return true if some objects were transferred.
8458 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8459   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8460                     (size_t)ParGCDesiredObjsFromOverflowList);
8461 
8462   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8463   assert(_collector->overflow_list_is_empty() || res,
8464          "If list is not empty, we should have taken something");
8465   assert(!res || !_mark_stack->isEmpty(),
8466          "If we took something, it should now be on our stack");
8467   return res;
8468 }
8469 
8470 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8471   size_t res = _sp->block_size_no_stall(addr, _collector);
8472   if (_sp->block_is_obj(addr)) {
8473     if (_live_bit_map->isMarked(addr)) {
8474       // It can't have been dead in a previous cycle
8475       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8476     } else {
8477       _dead_bit_map->mark(addr);      // mark the dead object
8478     }
8479   }
8480   // Could be 0, if the block size could not be computed without stalling.
8481   return res;
8482 }
8483 
8484 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8485 
8486   switch (phase) {
8487     case CMSCollector::InitialMarking:
8488       initialize(true  /* fullGC */ ,
8489                  cause /* cause of the GC */,
8490                  true  /* recordGCBeginTime */,
8491                  true  /* recordPreGCUsage */,
8492                  false /* recordPeakUsage */,
8493                  false /* recordPostGCusage */,
8494                  true  /* recordAccumulatedGCTime */,
8495                  false /* recordGCEndTime */,
8496                  false /* countCollection */  );
8497       break;
8498 
8499     case CMSCollector::FinalMarking:
8500       initialize(true  /* fullGC */ ,
8501                  cause /* cause of the GC */,
8502                  false /* recordGCBeginTime */,
8503                  false /* recordPreGCUsage */,
8504                  false /* recordPeakUsage */,
8505                  false /* recordPostGCusage */,
8506                  true  /* recordAccumulatedGCTime */,
8507                  false /* recordGCEndTime */,
8508                  false /* countCollection */  );
8509       break;
8510 
8511     case CMSCollector::Sweeping:
8512       initialize(true  /* fullGC */ ,
8513                  cause /* cause of the GC */,
8514                  false /* recordGCBeginTime */,
8515                  false /* recordPreGCUsage */,
8516                  true  /* recordPeakUsage */,
8517                  true  /* recordPostGCusage */,
8518                  false /* recordAccumulatedGCTime */,
8519                  true  /* recordGCEndTime */,
8520                  true  /* countCollection */  );
8521       break;
8522 
8523     default:
8524       ShouldNotReachHere();
8525   }
8526 }