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_implementation/shared/adaptiveSizePolicy.hpp"
  31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
  32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
  33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
  34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
  37 #include "gc_implementation/parNew/parNewGeneration.hpp"
  38 #include "gc_implementation/shared/collectorCounters.hpp"
  39 #include "gc_implementation/shared/gcTimer.hpp"
  40 #include "gc_implementation/shared/gcTrace.hpp"
  41 #include "gc_implementation/shared/gcTraceTime.hpp"
  42 #include "gc_implementation/shared/isGCActiveMark.hpp"
  43 #include "gc_interface/collectedHeap.inline.hpp"
  44 #include "memory/allocation.hpp"
  45 #include "memory/cardGeneration.inline.hpp"
  46 #include "memory/cardTableRS.hpp"
  47 #include "memory/collectorPolicy.hpp"
  48 #include "memory/gcLocker.inline.hpp"
  49 #include "memory/genCollectedHeap.hpp"
  50 #include "memory/genMarkSweep.hpp"
  51 #include "memory/genOopClosures.inline.hpp"
  52 #include "memory/iterator.inline.hpp"
  53 #include "memory/padded.hpp"
  54 #include "memory/referencePolicy.hpp"
  55 #include "memory/resourceArea.hpp"
  56 #include "memory/strongRootsScope.hpp"
  57 #include "memory/tenuredGeneration.hpp"
  58 #include "oops/oop.inline.hpp"
  59 #include "prims/jvmtiExport.hpp"
  60 #include "runtime/atomic.inline.hpp"
  61 #include "runtime/globals_extension.hpp"
  62 #include "runtime/handles.inline.hpp"
  63 #include "runtime/java.hpp"
  64 #include "runtime/orderAccess.inline.hpp"
  65 #include "runtime/vmThread.hpp"
  66 #include "services/memoryService.hpp"
  67 #include "services/runtimeService.hpp"
  68 #include "utilities/stack.inline.hpp"
  69 #include "utilities/taskqueue.inline.hpp"
  70 
  71 // statics
  72 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  73 bool CMSCollector::_full_gc_requested = false;
  74 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  75 
  76 //////////////////////////////////////////////////////////////////
  77 // In support of CMS/VM thread synchronization
  78 //////////////////////////////////////////////////////////////////
  79 // We split use of the CGC_lock into 2 "levels".
  80 // The low-level locking is of the usual CGC_lock monitor. We introduce
  81 // a higher level "token" (hereafter "CMS token") built on top of the
  82 // low level monitor (hereafter "CGC lock").
  83 // The token-passing protocol gives priority to the VM thread. The
  84 // CMS-lock doesn't provide any fairness guarantees, but clients
  85 // should ensure that it is only held for very short, bounded
  86 // durations.
  87 //
  88 // When either of the CMS thread or the VM thread is involved in
  89 // collection operations during which it does not want the other
  90 // thread to interfere, it obtains the CMS token.
  91 //
  92 // If either thread tries to get the token while the other has
  93 // it, that thread waits. However, if the VM thread and CMS thread
  94 // both want the token, then the VM thread gets priority while the
  95 // CMS thread waits. This ensures, for instance, that the "concurrent"
  96 // phases of the CMS thread's work do not block out the VM thread
  97 // for long periods of time as the CMS thread continues to hog
  98 // the token. (See bug 4616232).
  99 //
 100 // The baton-passing functions are, however, controlled by the
 101 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 102 // and here the low-level CMS lock, not the high level token,
 103 // ensures mutual exclusion.
 104 //
 105 // Two important conditions that we have to satisfy:
 106 // 1. if a thread does a low-level wait on the CMS lock, then it
 107 //    relinquishes the CMS token if it were holding that token
 108 //    when it acquired the low-level CMS lock.
 109 // 2. any low-level notifications on the low-level lock
 110 //    should only be sent when a thread has relinquished the token.
 111 //
 112 // In the absence of either property, we'd have potential deadlock.
 113 //
 114 // We protect each of the CMS (concurrent and sequential) phases
 115 // with the CMS _token_, not the CMS _lock_.
 116 //
 117 // The only code protected by CMS lock is the token acquisition code
 118 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 119 // baton-passing code.
 120 //
 121 // Unfortunately, i couldn't come up with a good abstraction to factor and
 122 // hide the naked CGC_lock manipulation in the baton-passing code
 123 // further below. That's something we should try to do. Also, the proof
 124 // of correctness of this 2-level locking scheme is far from obvious,
 125 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 126 // that there may be a theoretical possibility of delay/starvation in the
 127 // low-level lock/wait/notify scheme used for the baton-passing because of
 128 // potential interference with the priority scheme embodied in the
 129 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 130 // invocation further below and marked with "XXX 20011219YSR".
 131 // Indeed, as we note elsewhere, this may become yet more slippery
 132 // in the presence of multiple CMS and/or multiple VM threads. XXX
 133 
 134 class CMSTokenSync: public StackObj {
 135  private:
 136   bool _is_cms_thread;
 137  public:
 138   CMSTokenSync(bool is_cms_thread):
 139     _is_cms_thread(is_cms_thread) {
 140     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 141            "Incorrect argument to constructor");
 142     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 143   }
 144 
 145   ~CMSTokenSync() {
 146     assert(_is_cms_thread ?
 147              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 148              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 149           "Incorrect state");
 150     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 151   }
 152 };
 153 
 154 // Convenience class that does a CMSTokenSync, and then acquires
 155 // upto three locks.
 156 class CMSTokenSyncWithLocks: public CMSTokenSync {
 157  private:
 158   // Note: locks are acquired in textual declaration order
 159   // and released in the opposite order
 160   MutexLockerEx _locker1, _locker2, _locker3;
 161  public:
 162   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 163                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 164     CMSTokenSync(is_cms_thread),
 165     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 166     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 167     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 168   { }
 169 };
 170 
 171 
 172 //////////////////////////////////////////////////////////////////
 173 //  Concurrent Mark-Sweep Generation /////////////////////////////
 174 //////////////////////////////////////////////////////////////////
 175 
 176 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 177 
 178 // This struct contains per-thread things necessary to support parallel
 179 // young-gen collection.
 180 class CMSParGCThreadState: public CHeapObj<mtGC> {
 181  public:
 182   CFLS_LAB lab;
 183   PromotionInfo promo;
 184 
 185   // Constructor.
 186   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 187     promo.setSpace(cfls);
 188   }
 189 };
 190 
 191 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 192      ReservedSpace rs, size_t initial_byte_size, int level,
 193      CardTableRS* ct, bool use_adaptive_freelists,
 194      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 195   CardGeneration(rs, initial_byte_size, level, ct),
 196   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 197   _did_compact(false)
 198 {
 199   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 200   HeapWord* end    = (HeapWord*) _virtual_space.high();
 201 
 202   _direct_allocated_words = 0;
 203   NOT_PRODUCT(
 204     _numObjectsPromoted = 0;
 205     _numWordsPromoted = 0;
 206     _numObjectsAllocated = 0;
 207     _numWordsAllocated = 0;
 208   )
 209 
 210   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 211                                            use_adaptive_freelists,
 212                                            dictionaryChoice);
 213   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 214   _cmsSpace->_gen = this;
 215 
 216   _gc_stats = new CMSGCStats();
 217 
 218   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 219   // offsets match. The ability to tell free chunks from objects
 220   // depends on this property.
 221   debug_only(
 222     FreeChunk* junk = NULL;
 223     assert(UseCompressedClassPointers ||
 224            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 225            "Offset of FreeChunk::_prev within FreeChunk must match"
 226            "  that of OopDesc::_klass within OopDesc");
 227   )
 228 
 229   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 230   for (uint i = 0; i < ParallelGCThreads; i++) {
 231     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 232   }
 233 
 234   _incremental_collection_failed = false;
 235   // The "dilatation_factor" is the expansion that can occur on
 236   // account of the fact that the minimum object size in the CMS
 237   // generation may be larger than that in, say, a contiguous young
 238   //  generation.
 239   // Ideally, in the calculation below, we'd compute the dilatation
 240   // factor as: MinChunkSize/(promoting_gen's min object size)
 241   // Since we do not have such a general query interface for the
 242   // promoting generation, we'll instead just use the minimum
 243   // object size (which today is a header's worth of space);
 244   // note that all arithmetic is in units of HeapWords.
 245   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 246   assert(_dilatation_factor >= 1.0, "from previous assert");
 247 }
 248 
 249 
 250 // The field "_initiating_occupancy" represents the occupancy percentage
 251 // at which we trigger a new collection cycle.  Unless explicitly specified
 252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 253 // is calculated by:
 254 //
 255 //   Let "f" be MinHeapFreeRatio in
 256 //
 257 //    _initiating_occupancy = 100-f +
 258 //                           f * (CMSTriggerRatio/100)
 259 //   where CMSTriggerRatio is the argument "tr" below.
 260 //
 261 // That is, if we assume the heap is at its desired maximum occupancy at the
 262 // end of a collection, we let CMSTriggerRatio of the (purported) free
 263 // space be allocated before initiating a new collection cycle.
 264 //
 265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 266   assert(io <= 100 && tr <= 100, "Check the arguments");
 267   if (io >= 0) {
 268     _initiating_occupancy = (double)io / 100.0;
 269   } else {
 270     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 271                              (double)(tr * MinHeapFreeRatio) / 100.0)
 272                             / 100.0;
 273   }
 274 }
 275 
 276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 277   assert(collector() != NULL, "no collector");
 278   collector()->ref_processor_init();
 279 }
 280 
 281 void CMSCollector::ref_processor_init() {
 282   if (_ref_processor == NULL) {
 283     // Allocate and initialize a reference processor
 284     _ref_processor =
 285       new ReferenceProcessor(_span,                               // span
 286                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 287                              (int) ParallelGCThreads,             // mt processing degree
 288                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 289                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 290                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 291                              &_is_alive_closure);                 // closure for liveness info
 292     // Initialize the _ref_processor field of CMSGen
 293     _cmsGen->set_ref_processor(_ref_processor);
 294 
 295   }
 296 }
 297 
 298 AdaptiveSizePolicy* CMSCollector::size_policy() {
 299   GenCollectedHeap* gch = GenCollectedHeap::heap();
 300   return gch->gen_policy()->size_policy();
 301 }
 302 
 303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 304 
 305   const char* gen_name = "old";
 306   GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
 307 
 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 minor 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 = (uint) 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 = ((double)CMSBootstrapOccupancy)/(double)100;
 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       ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
 623 
 624     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 625     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 626     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 627     _survivor_chunk_capacity = 2*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 size_t CMSCollector::plab_sample_minimum_size() {
 644   // The default value of MinTLABSize is 2k, but there is
 645   // no way to get the default value if the flag has been overridden.
 646   return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
 647 }
 648 
 649 const char* ConcurrentMarkSweepGeneration::name() const {
 650   return "concurrent mark-sweep generation";
 651 }
 652 void ConcurrentMarkSweepGeneration::update_counters() {
 653   if (UsePerfData) {
 654     _space_counters->update_all();
 655     _gen_counters->update_all();
 656   }
 657 }
 658 
 659 // this is an optimized version of update_counters(). it takes the
 660 // used value as a parameter rather than computing it.
 661 //
 662 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 663   if (UsePerfData) {
 664     _space_counters->update_used(used);
 665     _space_counters->update_capacity();
 666     _gen_counters->update_all();
 667   }
 668 }
 669 
 670 void ConcurrentMarkSweepGeneration::print() const {
 671   Generation::print();
 672   cmsSpace()->print();
 673 }
 674 
 675 #ifndef PRODUCT
 676 void ConcurrentMarkSweepGeneration::print_statistics() {
 677   cmsSpace()->printFLCensus(0);
 678 }
 679 #endif
 680 
 681 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 682   GenCollectedHeap* gch = GenCollectedHeap::heap();
 683   if (PrintGCDetails) {
 684     if (Verbose) {
 685       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 686         level(), short_name(), s, used(), capacity());
 687     } else {
 688       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 689         level(), short_name(), s, used() / K, capacity() / K);
 690     }
 691   }
 692   if (Verbose) {
 693     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 694               gch->used(), gch->capacity());
 695   } else {
 696     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 697               gch->used() / K, gch->capacity() / K);
 698   }
 699 }
 700 
 701 size_t
 702 ConcurrentMarkSweepGeneration::contiguous_available() const {
 703   // dld proposes an improvement in precision here. If the committed
 704   // part of the space ends in a free block we should add that to
 705   // uncommitted size in the calculation below. Will make this
 706   // change later, staying with the approximation below for the
 707   // time being. -- ysr.
 708   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 709 }
 710 
 711 size_t
 712 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 713   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 714 }
 715 
 716 size_t ConcurrentMarkSweepGeneration::max_available() const {
 717   return free() + _virtual_space.uncommitted_size();
 718 }
 719 
 720 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 721   size_t available = max_available();
 722   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 723   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 724   if (Verbose && PrintGCDetails) {
 725     gclog_or_tty->print_cr(
 726       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 727       "max_promo("SIZE_FORMAT")",
 728       res? "":" not", available, res? ">=":"<",
 729       av_promo, max_promotion_in_bytes);
 730   }
 731   return res;
 732 }
 733 
 734 // At a promotion failure dump information on block layout in heap
 735 // (cms old generation).
 736 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 737   if (CMSDumpAtPromotionFailure) {
 738     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 739   }
 740 }
 741 
 742 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 743   // Clear the promotion information.  These pointers can be adjusted
 744   // along with all the other pointers into the heap but
 745   // compaction is expected to be a rare event with
 746   // a heap using cms so don't do it without seeing the need.
 747   for (uint i = 0; i < ParallelGCThreads; i++) {
 748     _par_gc_thread_states[i]->promo.reset();
 749   }
 750 }
 751 
 752 void ConcurrentMarkSweepGeneration::compute_new_size() {
 753   assert_locked_or_safepoint(Heap_lock);
 754 
 755   // If incremental collection failed, we just want to expand
 756   // to the limit.
 757   if (incremental_collection_failed()) {
 758     clear_incremental_collection_failed();
 759     grow_to_reserved();
 760     return;
 761   }
 762 
 763   // The heap has been compacted but not reset yet.
 764   // Any metric such as free() or used() will be incorrect.
 765 
 766   CardGeneration::compute_new_size();
 767 
 768   // Reset again after a possible resizing
 769   if (did_compact()) {
 770     cmsSpace()->reset_after_compaction();
 771   }
 772 }
 773 
 774 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 775   assert_locked_or_safepoint(Heap_lock);
 776 
 777   // If incremental collection failed, we just want to expand
 778   // to the limit.
 779   if (incremental_collection_failed()) {
 780     clear_incremental_collection_failed();
 781     grow_to_reserved();
 782     return;
 783   }
 784 
 785   double free_percentage = ((double) free()) / capacity();
 786   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 787   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 788 
 789   // compute expansion delta needed for reaching desired free percentage
 790   if (free_percentage < desired_free_percentage) {
 791     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 792     assert(desired_capacity >= capacity(), "invalid expansion size");
 793     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 794     if (PrintGCDetails && Verbose) {
 795       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 796       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 797       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 798       gclog_or_tty->print_cr("  Desired free fraction %f",
 799         desired_free_percentage);
 800       gclog_or_tty->print_cr("  Maximum free fraction %f",
 801         maximum_free_percentage);
 802       gclog_or_tty->print_cr("  Capacity "SIZE_FORMAT, capacity()/1000);
 803       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 804         desired_capacity/1000);
 805       int prev_level = level() - 1;
 806       if (prev_level >= 0) {
 807         size_t prev_size = 0;
 808         GenCollectedHeap* gch = GenCollectedHeap::heap();
 809         Generation* prev_gen = gch->young_gen();
 810         prev_size = prev_gen->capacity();
 811           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 812                                  prev_size/1000);
 813       }
 814       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 815         unsafe_max_alloc_nogc()/1000);
 816       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 817         contiguous_available()/1000);
 818       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 819         expand_bytes);
 820     }
 821     // safe if expansion fails
 822     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 823     if (PrintGCDetails && Verbose) {
 824       gclog_or_tty->print_cr("  Expanded free fraction %f",
 825         ((double) free()) / capacity());
 826     }
 827   } else {
 828     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 829     assert(desired_capacity <= capacity(), "invalid expansion size");
 830     size_t shrink_bytes = capacity() - desired_capacity;
 831     // Don't shrink unless the delta is greater than the minimum shrink we want
 832     if (shrink_bytes >= MinHeapDeltaBytes) {
 833       shrink_free_list_by(shrink_bytes);
 834     }
 835   }
 836 }
 837 
 838 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 839   return cmsSpace()->freelistLock();
 840 }
 841 
 842 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 843                                                   bool   tlab) {
 844   CMSSynchronousYieldRequest yr;
 845   MutexLockerEx x(freelistLock(),
 846                   Mutex::_no_safepoint_check_flag);
 847   return have_lock_and_allocate(size, tlab);
 848 }
 849 
 850 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 851                                                   bool   tlab /* ignored */) {
 852   assert_lock_strong(freelistLock());
 853   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 854   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 855   // Allocate the object live (grey) if the background collector has
 856   // started marking. This is necessary because the marker may
 857   // have passed this address and consequently this object will
 858   // not otherwise be greyed and would be incorrectly swept up.
 859   // Note that if this object contains references, the writing
 860   // of those references will dirty the card containing this object
 861   // allowing the object to be blackened (and its references scanned)
 862   // either during a preclean phase or at the final checkpoint.
 863   if (res != NULL) {
 864     // We may block here with an uninitialized object with
 865     // its mark-bit or P-bits not yet set. Such objects need
 866     // to be safely navigable by block_start().
 867     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 868     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 869     collector()->direct_allocated(res, adjustedSize);
 870     _direct_allocated_words += adjustedSize;
 871     // allocation counters
 872     NOT_PRODUCT(
 873       _numObjectsAllocated++;
 874       _numWordsAllocated += (int)adjustedSize;
 875     )
 876   }
 877   return res;
 878 }
 879 
 880 // In the case of direct allocation by mutators in a generation that
 881 // is being concurrently collected, the object must be allocated
 882 // live (grey) if the background collector has started marking.
 883 // This is necessary because the marker may
 884 // have passed this address and consequently this object will
 885 // not otherwise be greyed and would be incorrectly swept up.
 886 // Note that if this object contains references, the writing
 887 // of those references will dirty the card containing this object
 888 // allowing the object to be blackened (and its references scanned)
 889 // either during a preclean phase or at the final checkpoint.
 890 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 891   assert(_markBitMap.covers(start, size), "Out of bounds");
 892   if (_collectorState >= Marking) {
 893     MutexLockerEx y(_markBitMap.lock(),
 894                     Mutex::_no_safepoint_check_flag);
 895     // [see comments preceding SweepClosure::do_blk() below for details]
 896     //
 897     // Can the P-bits be deleted now?  JJJ
 898     //
 899     // 1. need to mark the object as live so it isn't collected
 900     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 901     // 3. need to mark the end of the object so marking, precleaning or sweeping
 902     //    can skip over uninitialized or unparsable objects. An allocated
 903     //    object is considered uninitialized for our purposes as long as
 904     //    its klass word is NULL.  All old gen objects are parsable
 905     //    as soon as they are initialized.)
 906     _markBitMap.mark(start);          // object is live
 907     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 908     _markBitMap.mark(start + size - 1);
 909                                       // mark end of object
 910   }
 911   // check that oop looks uninitialized
 912   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 913 }
 914 
 915 void CMSCollector::promoted(bool par, HeapWord* start,
 916                             bool is_obj_array, size_t obj_size) {
 917   assert(_markBitMap.covers(start), "Out of bounds");
 918   // See comment in direct_allocated() about when objects should
 919   // be allocated live.
 920   if (_collectorState >= Marking) {
 921     // we already hold the marking bit map lock, taken in
 922     // the prologue
 923     if (par) {
 924       _markBitMap.par_mark(start);
 925     } else {
 926       _markBitMap.mark(start);
 927     }
 928     // We don't need to mark the object as uninitialized (as
 929     // in direct_allocated above) because this is being done with the
 930     // world stopped and the object will be initialized by the
 931     // time the marking, precleaning or sweeping get to look at it.
 932     // But see the code for copying objects into the CMS generation,
 933     // where we need to ensure that concurrent readers of the
 934     // block offset table are able to safely navigate a block that
 935     // is in flux from being free to being allocated (and in
 936     // transition while being copied into) and subsequently
 937     // becoming a bona-fide object when the copy/promotion is complete.
 938     assert(SafepointSynchronize::is_at_safepoint(),
 939            "expect promotion only at safepoints");
 940 
 941     if (_collectorState < Sweeping) {
 942       // Mark the appropriate cards in the modUnionTable, so that
 943       // this object gets scanned before the sweep. If this is
 944       // not done, CMS generation references in the object might
 945       // not get marked.
 946       // For the case of arrays, which are otherwise precisely
 947       // marked, we need to dirty the entire array, not just its head.
 948       if (is_obj_array) {
 949         // The [par_]mark_range() method expects mr.end() below to
 950         // be aligned to the granularity of a bit's representation
 951         // in the heap. In the case of the MUT below, that's a
 952         // card size.
 953         MemRegion mr(start,
 954                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 955                         CardTableModRefBS::card_size /* bytes */));
 956         if (par) {
 957           _modUnionTable.par_mark_range(mr);
 958         } else {
 959           _modUnionTable.mark_range(mr);
 960         }
 961       } else {  // not an obj array; we can just mark the head
 962         if (par) {
 963           _modUnionTable.par_mark(start);
 964         } else {
 965           _modUnionTable.mark(start);
 966         }
 967       }
 968     }
 969   }
 970 }
 971 
 972 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 973   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 974   // allocate, copy and if necessary update promoinfo --
 975   // delegate to underlying space.
 976   assert_lock_strong(freelistLock());
 977 
 978 #ifndef PRODUCT
 979   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 980     return NULL;
 981   }
 982 #endif  // #ifndef PRODUCT
 983 
 984   oop res = _cmsSpace->promote(obj, obj_size);
 985   if (res == NULL) {
 986     // expand and retry
 987     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 988     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 989     // Since this is the old generation, we don't try to promote
 990     // into a more senior generation.
 991     res = _cmsSpace->promote(obj, obj_size);
 992   }
 993   if (res != NULL) {
 994     // See comment in allocate() about when objects should
 995     // be allocated live.
 996     assert(obj->is_oop(), "Will dereference klass pointer below");
 997     collector()->promoted(false,           // Not parallel
 998                           (HeapWord*)res, obj->is_objArray(), obj_size);
 999     // promotion counters
1000     NOT_PRODUCT(
1001       _numObjectsPromoted++;
1002       _numWordsPromoted +=
1003         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1004     )
1005   }
1006   return res;
1007 }
1008 
1009 
1010 // IMPORTANT: Notes on object size recognition in CMS.
1011 // ---------------------------------------------------
1012 // A block of storage in the CMS generation is always in
1013 // one of three states. A free block (FREE), an allocated
1014 // object (OBJECT) whose size() method reports the correct size,
1015 // and an intermediate state (TRANSIENT) in which its size cannot
1016 // be accurately determined.
1017 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1018 // -----------------------------------------------------
1019 // FREE:      klass_word & 1 == 1; mark_word holds block size
1020 //
1021 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1022 //            obj->size() computes correct size
1023 //
1024 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1025 //
1026 // STATE IDENTIFICATION: (64 bit+COOPS)
1027 // ------------------------------------
1028 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1029 //
1030 // OBJECT:    klass_word installed; klass_word != 0;
1031 //            obj->size() computes correct size
1032 //
1033 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1034 //
1035 //
1036 // STATE TRANSITION DIAGRAM
1037 //
1038 //        mut / parnew                     mut  /  parnew
1039 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1040 //  ^                                                                   |
1041 //  |------------------------ DEAD <------------------------------------|
1042 //         sweep                            mut
1043 //
1044 // While a block is in TRANSIENT state its size cannot be determined
1045 // so readers will either need to come back later or stall until
1046 // the size can be determined. Note that for the case of direct
1047 // allocation, P-bits, when available, may be used to determine the
1048 // size of an object that may not yet have been initialized.
1049 
1050 // Things to support parallel young-gen collection.
1051 oop
1052 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1053                                            oop old, markOop m,
1054                                            size_t word_sz) {
1055 #ifndef PRODUCT
1056   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1057     return NULL;
1058   }
1059 #endif  // #ifndef PRODUCT
1060 
1061   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1062   PromotionInfo* promoInfo = &ps->promo;
1063   // if we are tracking promotions, then first ensure space for
1064   // promotion (including spooling space for saving header if necessary).
1065   // then allocate and copy, then track promoted info if needed.
1066   // When tracking (see PromotionInfo::track()), the mark word may
1067   // be displaced and in this case restoration of the mark word
1068   // occurs in the (oop_since_save_marks_)iterate phase.
1069   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1070     // Out of space for allocating spooling buffers;
1071     // try expanding and allocating spooling buffers.
1072     if (!expand_and_ensure_spooling_space(promoInfo)) {
1073       return NULL;
1074     }
1075   }
1076   assert(promoInfo->has_spooling_space(), "Control point invariant");
1077   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1078   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1079   if (obj_ptr == NULL) {
1080      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1081      if (obj_ptr == NULL) {
1082        return NULL;
1083      }
1084   }
1085   oop obj = oop(obj_ptr);
1086   OrderAccess::storestore();
1087   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1088   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1089   // IMPORTANT: See note on object initialization for CMS above.
1090   // Otherwise, copy the object.  Here we must be careful to insert the
1091   // klass pointer last, since this marks the block as an allocated object.
1092   // Except with compressed oops it's the mark word.
1093   HeapWord* old_ptr = (HeapWord*)old;
1094   // Restore the mark word copied above.
1095   obj->set_mark(m);
1096   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1097   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1098   OrderAccess::storestore();
1099 
1100   if (UseCompressedClassPointers) {
1101     // Copy gap missed by (aligned) header size calculation below
1102     obj->set_klass_gap(old->klass_gap());
1103   }
1104   if (word_sz > (size_t)oopDesc::header_size()) {
1105     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1106                                  obj_ptr + oopDesc::header_size(),
1107                                  word_sz - oopDesc::header_size());
1108   }
1109 
1110   // Now we can track the promoted object, if necessary.  We take care
1111   // to delay the transition from uninitialized to full object
1112   // (i.e., insertion of klass pointer) until after, so that it
1113   // atomically becomes a promoted object.
1114   if (promoInfo->tracking()) {
1115     promoInfo->track((PromotedObject*)obj, old->klass());
1116   }
1117   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1118   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1119   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1120 
1121   // Finally, install the klass pointer (this should be volatile).
1122   OrderAccess::storestore();
1123   obj->set_klass(old->klass());
1124   // We should now be able to calculate the right size for this object
1125   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1126 
1127   collector()->promoted(true,          // parallel
1128                         obj_ptr, old->is_objArray(), word_sz);
1129 
1130   NOT_PRODUCT(
1131     Atomic::inc_ptr(&_numObjectsPromoted);
1132     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1133   )
1134 
1135   return obj;
1136 }
1137 
1138 void
1139 ConcurrentMarkSweepGeneration::
1140 par_promote_alloc_done(int thread_num) {
1141   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1142   ps->lab.retire(thread_num);
1143 }
1144 
1145 void
1146 ConcurrentMarkSweepGeneration::
1147 par_oop_since_save_marks_iterate_done(int thread_num) {
1148   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1149   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1150   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1151 }
1152 
1153 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1154                                                    size_t size,
1155                                                    bool   tlab)
1156 {
1157   // We allow a STW collection only if a full
1158   // collection was requested.
1159   return full || should_allocate(size, tlab); // FIX ME !!!
1160   // This and promotion failure handling are connected at the
1161   // hip and should be fixed by untying them.
1162 }
1163 
1164 bool CMSCollector::shouldConcurrentCollect() {
1165   if (_full_gc_requested) {
1166     if (Verbose && PrintGCDetails) {
1167       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1168                              " gc request (or gc_locker)");
1169     }
1170     return true;
1171   }
1172 
1173   FreelistLocker x(this);
1174   // ------------------------------------------------------------------
1175   // Print out lots of information which affects the initiation of
1176   // a collection.
1177   if (PrintCMSInitiationStatistics && stats().valid()) {
1178     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1179     gclog_or_tty->stamp();
1180     gclog_or_tty->cr();
1181     stats().print_on(gclog_or_tty);
1182     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1183       stats().time_until_cms_gen_full());
1184     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1185     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1186                            _cmsGen->contiguous_available());
1187     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1188     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1189     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1190     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1191     gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1192     gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1193     gclog_or_tty->print_cr("metadata initialized %d",
1194       MetaspaceGC::should_concurrent_collect());
1195   }
1196   // ------------------------------------------------------------------
1197 
1198   // If the estimated time to complete a cms collection (cms_duration())
1199   // is less than the estimated time remaining until the cms generation
1200   // is full, start a collection.
1201   if (!UseCMSInitiatingOccupancyOnly) {
1202     if (stats().valid()) {
1203       if (stats().time_until_cms_start() == 0.0) {
1204         return true;
1205       }
1206     } else {
1207       // We want to conservatively collect somewhat early in order
1208       // to try and "bootstrap" our CMS/promotion statistics;
1209       // this branch will not fire after the first successful CMS
1210       // collection because the stats should then be valid.
1211       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1212         if (Verbose && PrintGCDetails) {
1213           gclog_or_tty->print_cr(
1214             " CMSCollector: collect for bootstrapping statistics:"
1215             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1216             _bootstrap_occupancy);
1217         }
1218         return true;
1219       }
1220     }
1221   }
1222 
1223   // Otherwise, we start a collection cycle if
1224   // old gen want a collection cycle started. Each may use
1225   // an appropriate criterion for making this decision.
1226   // XXX We need to make sure that the gen expansion
1227   // criterion dovetails well with this. XXX NEED TO FIX THIS
1228   if (_cmsGen->should_concurrent_collect()) {
1229     if (Verbose && PrintGCDetails) {
1230       gclog_or_tty->print_cr("CMS old gen initiated");
1231     }
1232     return true;
1233   }
1234 
1235   // We start a collection if we believe an incremental collection may fail;
1236   // this is not likely to be productive in practice because it's probably too
1237   // late anyway.
1238   GenCollectedHeap* gch = GenCollectedHeap::heap();
1239   assert(gch->collector_policy()->is_generation_policy(),
1240          "You may want to check the correctness of the following");
1241   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1242     if (Verbose && PrintGCDetails) {
1243       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1244     }
1245     return true;
1246   }
1247 
1248   if (MetaspaceGC::should_concurrent_collect()) {
1249     if (Verbose && PrintGCDetails) {
1250       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1251     }
1252     return true;
1253   }
1254 
1255   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1256   if (CMSTriggerInterval >= 0) {
1257     if (CMSTriggerInterval == 0) {
1258       // Trigger always
1259       return true;
1260     }
1261 
1262     // Check the CMS time since begin (we do not check the stats validity
1263     // as we want to be able to trigger the first CMS cycle as well)
1264     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1265       if (Verbose && PrintGCDetails) {
1266         if (stats().valid()) {
1267           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1268                                  stats().cms_time_since_begin());
1269         } else {
1270           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1271         }
1272       }
1273       return true;
1274     }
1275   }
1276 
1277   return false;
1278 }
1279 
1280 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1281 
1282 // Clear _expansion_cause fields of constituent generations
1283 void CMSCollector::clear_expansion_cause() {
1284   _cmsGen->clear_expansion_cause();
1285 }
1286 
1287 // We should be conservative in starting a collection cycle.  To
1288 // start too eagerly runs the risk of collecting too often in the
1289 // extreme.  To collect too rarely falls back on full collections,
1290 // which works, even if not optimum in terms of concurrent work.
1291 // As a work around for too eagerly collecting, use the flag
1292 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1293 // giving the user an easily understandable way of controlling the
1294 // collections.
1295 // We want to start a new collection cycle if any of the following
1296 // conditions hold:
1297 // . our current occupancy exceeds the configured initiating occupancy
1298 //   for this generation, or
1299 // . we recently needed to expand this space and have not, since that
1300 //   expansion, done a collection of this generation, or
1301 // . the underlying space believes that it may be a good idea to initiate
1302 //   a concurrent collection (this may be based on criteria such as the
1303 //   following: the space uses linear allocation and linear allocation is
1304 //   going to fail, or there is believed to be excessive fragmentation in
1305 //   the generation, etc... or ...
1306 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1307 //   the case of the old generation; see CR 6543076):
1308 //   we may be approaching a point at which allocation requests may fail because
1309 //   we will be out of sufficient free space given allocation rate estimates.]
1310 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1311 
1312   assert_lock_strong(freelistLock());
1313   if (occupancy() > initiating_occupancy()) {
1314     if (PrintGCDetails && Verbose) {
1315       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1316         short_name(), occupancy(), initiating_occupancy());
1317     }
1318     return true;
1319   }
1320   if (UseCMSInitiatingOccupancyOnly) {
1321     return false;
1322   }
1323   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1324     if (PrintGCDetails && Verbose) {
1325       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1326         short_name());
1327     }
1328     return true;
1329   }
1330   if (_cmsSpace->should_concurrent_collect()) {
1331     if (PrintGCDetails && Verbose) {
1332       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1333         short_name());
1334     }
1335     return true;
1336   }
1337   return false;
1338 }
1339 
1340 void ConcurrentMarkSweepGeneration::collect(bool   full,
1341                                             bool   clear_all_soft_refs,
1342                                             size_t size,
1343                                             bool   tlab)
1344 {
1345   collector()->collect(full, clear_all_soft_refs, size, tlab);
1346 }
1347 
1348 void CMSCollector::collect(bool   full,
1349                            bool   clear_all_soft_refs,
1350                            size_t size,
1351                            bool   tlab)
1352 {
1353   // The following "if" branch is present for defensive reasons.
1354   // In the current uses of this interface, it can be replaced with:
1355   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1356   // But I am not placing that assert here to allow future
1357   // generality in invoking this interface.
1358   if (GC_locker::is_active()) {
1359     // A consistency test for GC_locker
1360     assert(GC_locker::needs_gc(), "Should have been set already");
1361     // Skip this foreground collection, instead
1362     // expanding the heap if necessary.
1363     // Need the free list locks for the call to free() in compute_new_size()
1364     compute_new_size();
1365     return;
1366   }
1367   acquire_control_and_collect(full, clear_all_soft_refs);
1368 }
1369 
1370 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1371   GenCollectedHeap* gch = GenCollectedHeap::heap();
1372   unsigned int gc_count = gch->total_full_collections();
1373   if (gc_count == full_gc_count) {
1374     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1375     _full_gc_requested = true;
1376     _full_gc_cause = cause;
1377     CGC_lock->notify();   // nudge CMS thread
1378   } else {
1379     assert(gc_count > full_gc_count, "Error: causal loop");
1380   }
1381 }
1382 
1383 bool CMSCollector::is_external_interruption() {
1384   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1385   return GCCause::is_user_requested_gc(cause) ||
1386          GCCause::is_serviceability_requested_gc(cause);
1387 }
1388 
1389 void CMSCollector::report_concurrent_mode_interruption() {
1390   if (is_external_interruption()) {
1391     if (PrintGCDetails) {
1392       gclog_or_tty->print(" (concurrent mode interrupted)");
1393     }
1394   } else {
1395     if (PrintGCDetails) {
1396       gclog_or_tty->print(" (concurrent mode failure)");
1397     }
1398     _gc_tracer_cm->report_concurrent_mode_failure();
1399   }
1400 }
1401 
1402 
1403 // The foreground and background collectors need to coordinate in order
1404 // to make sure that they do not mutually interfere with CMS collections.
1405 // When a background collection is active,
1406 // the foreground collector may need to take over (preempt) and
1407 // synchronously complete an ongoing collection. Depending on the
1408 // frequency of the background collections and the heap usage
1409 // of the application, this preemption can be seldom or frequent.
1410 // There are only certain
1411 // points in the background collection that the "collection-baton"
1412 // can be passed to the foreground collector.
1413 //
1414 // The foreground collector will wait for the baton before
1415 // starting any part of the collection.  The foreground collector
1416 // will only wait at one location.
1417 //
1418 // The background collector will yield the baton before starting a new
1419 // phase of the collection (e.g., before initial marking, marking from roots,
1420 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1421 // of the loop which switches the phases. The background collector does some
1422 // of the phases (initial mark, final re-mark) with the world stopped.
1423 // Because of locking involved in stopping the world,
1424 // the foreground collector should not block waiting for the background
1425 // collector when it is doing a stop-the-world phase.  The background
1426 // collector will yield the baton at an additional point just before
1427 // it enters a stop-the-world phase.  Once the world is stopped, the
1428 // background collector checks the phase of the collection.  If the
1429 // phase has not changed, it proceeds with the collection.  If the
1430 // phase has changed, it skips that phase of the collection.  See
1431 // the comments on the use of the Heap_lock in collect_in_background().
1432 //
1433 // Variable used in baton passing.
1434 //   _foregroundGCIsActive - Set to true by the foreground collector when
1435 //      it wants the baton.  The foreground clears it when it has finished
1436 //      the collection.
1437 //   _foregroundGCShouldWait - Set to true by the background collector
1438 //        when it is running.  The foreground collector waits while
1439 //      _foregroundGCShouldWait is true.
1440 //  CGC_lock - monitor used to protect access to the above variables
1441 //      and to notify the foreground and background collectors.
1442 //  _collectorState - current state of the CMS collection.
1443 //
1444 // The foreground collector
1445 //   acquires the CGC_lock
1446 //   sets _foregroundGCIsActive
1447 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1448 //     various locks acquired in preparation for the collection
1449 //     are released so as not to block the background collector
1450 //     that is in the midst of a collection
1451 //   proceeds with the collection
1452 //   clears _foregroundGCIsActive
1453 //   returns
1454 //
1455 // The background collector in a loop iterating on the phases of the
1456 //      collection
1457 //   acquires the CGC_lock
1458 //   sets _foregroundGCShouldWait
1459 //   if _foregroundGCIsActive is set
1460 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1461 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1462 //     and exits the loop.
1463 //   otherwise
1464 //     proceed with that phase of the collection
1465 //     if the phase is a stop-the-world phase,
1466 //       yield the baton once more just before enqueueing
1467 //       the stop-world CMS operation (executed by the VM thread).
1468 //   returns after all phases of the collection are done
1469 //
1470 
1471 void CMSCollector::acquire_control_and_collect(bool full,
1472         bool clear_all_soft_refs) {
1473   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1474   assert(!Thread::current()->is_ConcurrentGC_thread(),
1475          "shouldn't try to acquire control from self!");
1476 
1477   // Start the protocol for acquiring control of the
1478   // collection from the background collector (aka CMS thread).
1479   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1480          "VM thread should have CMS token");
1481   // Remember the possibly interrupted state of an ongoing
1482   // concurrent collection
1483   CollectorState first_state = _collectorState;
1484 
1485   // Signal to a possibly ongoing concurrent collection that
1486   // we want to do a foreground collection.
1487   _foregroundGCIsActive = true;
1488 
1489   // release locks and wait for a notify from the background collector
1490   // releasing the locks in only necessary for phases which
1491   // do yields to improve the granularity of the collection.
1492   assert_lock_strong(bitMapLock());
1493   // We need to lock the Free list lock for the space that we are
1494   // currently collecting.
1495   assert(haveFreelistLocks(), "Must be holding free list locks");
1496   bitMapLock()->unlock();
1497   releaseFreelistLocks();
1498   {
1499     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1500     if (_foregroundGCShouldWait) {
1501       // We are going to be waiting for action for the CMS thread;
1502       // it had better not be gone (for instance at shutdown)!
1503       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1504              "CMS thread must be running");
1505       // Wait here until the background collector gives us the go-ahead
1506       ConcurrentMarkSweepThread::clear_CMS_flag(
1507         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1508       // Get a possibly blocked CMS thread going:
1509       //   Note that we set _foregroundGCIsActive true above,
1510       //   without protection of the CGC_lock.
1511       CGC_lock->notify();
1512       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1513              "Possible deadlock");
1514       while (_foregroundGCShouldWait) {
1515         // wait for notification
1516         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1517         // Possibility of delay/starvation here, since CMS token does
1518         // not know to give priority to VM thread? Actually, i think
1519         // there wouldn't be any delay/starvation, but the proof of
1520         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1521       }
1522       ConcurrentMarkSweepThread::set_CMS_flag(
1523         ConcurrentMarkSweepThread::CMS_vm_has_token);
1524     }
1525   }
1526   // The CMS_token is already held.  Get back the other locks.
1527   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1528          "VM thread should have CMS token");
1529   getFreelistLocks();
1530   bitMapLock()->lock_without_safepoint_check();
1531   if (TraceCMSState) {
1532     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1533       INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1534     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1535   }
1536 
1537   // Inform cms gen if this was due to partial collection failing.
1538   // The CMS gen may use this fact to determine its expansion policy.
1539   GenCollectedHeap* gch = GenCollectedHeap::heap();
1540   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1541     assert(!_cmsGen->incremental_collection_failed(),
1542            "Should have been noticed, reacted to and cleared");
1543     _cmsGen->set_incremental_collection_failed();
1544   }
1545 
1546   if (first_state > Idling) {
1547     report_concurrent_mode_interruption();
1548   }
1549 
1550   set_did_compact(true);
1551 
1552   // If the collection is being acquired from the background
1553   // collector, there may be references on the discovered
1554   // references lists.  Abandon those references, since some
1555   // of them may have become unreachable after concurrent
1556   // discovery; the STW compacting collector will redo discovery
1557   // more precisely, without being subject to floating garbage.
1558   // Leaving otherwise unreachable references in the discovered
1559   // lists would require special handling.
1560   ref_processor()->disable_discovery();
1561   ref_processor()->abandon_partial_discovery();
1562   ref_processor()->verify_no_references_recorded();
1563 
1564   if (first_state > Idling) {
1565     save_heap_summary();
1566   }
1567 
1568   do_compaction_work(clear_all_soft_refs);
1569 
1570   // Has the GC time limit been exceeded?
1571   size_t max_eden_size = _young_gen->max_capacity() -
1572                          _young_gen->to()->capacity() -
1573                          _young_gen->from()->capacity();
1574   GCCause::Cause gc_cause = gch->gc_cause();
1575   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1576                                          _young_gen->eden()->used(),
1577                                          _cmsGen->max_capacity(),
1578                                          max_eden_size,
1579                                          full,
1580                                          gc_cause,
1581                                          gch->collector_policy());
1582 
1583   // Reset the expansion cause, now that we just completed
1584   // a collection cycle.
1585   clear_expansion_cause();
1586   _foregroundGCIsActive = false;
1587   return;
1588 }
1589 
1590 // Resize the tenured generation
1591 // after obtaining the free list locks for the
1592 // two generations.
1593 void CMSCollector::compute_new_size() {
1594   assert_locked_or_safepoint(Heap_lock);
1595   FreelistLocker z(this);
1596   MetaspaceGC::compute_new_size();
1597   _cmsGen->compute_new_size_free_list();
1598 }
1599 
1600 // A work method used by the foreground collector to do
1601 // a mark-sweep-compact.
1602 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1603   GenCollectedHeap* gch = GenCollectedHeap::heap();
1604 
1605   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1606   gc_timer->register_gc_start();
1607 
1608   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1609   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1610 
1611   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1612 
1613   // Temporarily widen the span of the weak reference processing to
1614   // the entire heap.
1615   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1616   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1617   // Temporarily, clear the "is_alive_non_header" field of the
1618   // reference processor.
1619   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1620   // Temporarily make reference _processing_ single threaded (non-MT).
1621   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1622   // Temporarily make refs discovery atomic
1623   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1624   // Temporarily make reference _discovery_ single threaded (non-MT)
1625   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1626 
1627   ref_processor()->set_enqueuing_is_done(false);
1628   ref_processor()->enable_discovery();
1629   ref_processor()->setup_policy(clear_all_soft_refs);
1630   // If an asynchronous collection finishes, the _modUnionTable is
1631   // all clear.  If we are assuming the collection from an asynchronous
1632   // collection, clear the _modUnionTable.
1633   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1634     "_modUnionTable should be clear if the baton was not passed");
1635   _modUnionTable.clear_all();
1636   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1637     "mod union for klasses should be clear if the baton was passed");
1638   _ct->klass_rem_set()->clear_mod_union();
1639 
1640   // We must adjust the allocation statistics being maintained
1641   // in the free list space. We do so by reading and clearing
1642   // the sweep timer and updating the block flux rate estimates below.
1643   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1644   if (_inter_sweep_timer.is_active()) {
1645     _inter_sweep_timer.stop();
1646     // Note that we do not use this sample to update the _inter_sweep_estimate.
1647     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1648                                             _inter_sweep_estimate.padded_average(),
1649                                             _intra_sweep_estimate.padded_average());
1650   }
1651 
1652   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1653     ref_processor(), clear_all_soft_refs);
1654   #ifdef ASSERT
1655     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1656     size_t free_size = cms_space->free();
1657     assert(free_size ==
1658            pointer_delta(cms_space->end(), cms_space->compaction_top())
1659            * HeapWordSize,
1660       "All the free space should be compacted into one chunk at top");
1661     assert(cms_space->dictionary()->total_chunk_size(
1662                                       debug_only(cms_space->freelistLock())) == 0 ||
1663            cms_space->totalSizeInIndexedFreeLists() == 0,
1664       "All the free space should be in a single chunk");
1665     size_t num = cms_space->totalCount();
1666     assert((free_size == 0 && num == 0) ||
1667            (free_size > 0  && (num == 1 || num == 2)),
1668          "There should be at most 2 free chunks after compaction");
1669   #endif // ASSERT
1670   _collectorState = Resetting;
1671   assert(_restart_addr == NULL,
1672          "Should have been NULL'd before baton was passed");
1673   reset(false /* == !concurrent */);
1674   _cmsGen->reset_after_compaction();
1675   _concurrent_cycles_since_last_unload = 0;
1676 
1677   // Clear any data recorded in the PLAB chunk arrays.
1678   if (_survivor_plab_array != NULL) {
1679     reset_survivor_plab_arrays();
1680   }
1681 
1682   // Adjust the per-size allocation stats for the next epoch.
1683   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1684   // Restart the "inter sweep timer" for the next epoch.
1685   _inter_sweep_timer.reset();
1686   _inter_sweep_timer.start();
1687 
1688   gc_timer->register_gc_end();
1689 
1690   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1691 
1692   // For a mark-sweep-compact, compute_new_size() will be called
1693   // in the heap's do_collection() method.
1694 }
1695 
1696 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1697   ContiguousSpace* eden_space = _young_gen->eden();
1698   ContiguousSpace* from_space = _young_gen->from();
1699   ContiguousSpace* to_space   = _young_gen->to();
1700   // Eden
1701   if (_eden_chunk_array != NULL) {
1702     gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1703                            p2i(eden_space->bottom()), p2i(eden_space->top()),
1704                            p2i(eden_space->end()), eden_space->capacity());
1705     gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1706                            "_eden_chunk_capacity=" SIZE_FORMAT,
1707                            _eden_chunk_index, _eden_chunk_capacity);
1708     for (size_t i = 0; i < _eden_chunk_index; i++) {
1709       gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1710                              i, p2i(_eden_chunk_array[i]));
1711     }
1712   }
1713   // Survivor
1714   if (_survivor_chunk_array != NULL) {
1715     gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1716                            p2i(from_space->bottom()), p2i(from_space->top()),
1717                            p2i(from_space->end()), from_space->capacity());
1718     gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1719                            "_survivor_chunk_capacity=" SIZE_FORMAT,
1720                            _survivor_chunk_index, _survivor_chunk_capacity);
1721     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1722       gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1723                              i, p2i(_survivor_chunk_array[i]));
1724     }
1725   }
1726 }
1727 
1728 void CMSCollector::getFreelistLocks() const {
1729   // Get locks for all free lists in all generations that this
1730   // collector is responsible for
1731   _cmsGen->freelistLock()->lock_without_safepoint_check();
1732 }
1733 
1734 void CMSCollector::releaseFreelistLocks() const {
1735   // Release locks for all free lists in all generations that this
1736   // collector is responsible for
1737   _cmsGen->freelistLock()->unlock();
1738 }
1739 
1740 bool CMSCollector::haveFreelistLocks() const {
1741   // Check locks for all free lists in all generations that this
1742   // collector is responsible for
1743   assert_lock_strong(_cmsGen->freelistLock());
1744   PRODUCT_ONLY(ShouldNotReachHere());
1745   return true;
1746 }
1747 
1748 // A utility class that is used by the CMS collector to
1749 // temporarily "release" the foreground collector from its
1750 // usual obligation to wait for the background collector to
1751 // complete an ongoing phase before proceeding.
1752 class ReleaseForegroundGC: public StackObj {
1753  private:
1754   CMSCollector* _c;
1755  public:
1756   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1757     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1758     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1759     // allow a potentially blocked foreground collector to proceed
1760     _c->_foregroundGCShouldWait = false;
1761     if (_c->_foregroundGCIsActive) {
1762       CGC_lock->notify();
1763     }
1764     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1765            "Possible deadlock");
1766   }
1767 
1768   ~ReleaseForegroundGC() {
1769     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1770     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1771     _c->_foregroundGCShouldWait = true;
1772   }
1773 };
1774 
1775 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1776   assert(Thread::current()->is_ConcurrentGC_thread(),
1777     "A CMS asynchronous collection is only allowed on a CMS thread.");
1778 
1779   GenCollectedHeap* gch = GenCollectedHeap::heap();
1780   {
1781     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1782     MutexLockerEx hl(Heap_lock, safepoint_check);
1783     FreelistLocker fll(this);
1784     MutexLockerEx x(CGC_lock, safepoint_check);
1785     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1786       // The foreground collector is active or we're
1787       // not using asynchronous collections.  Skip this
1788       // background collection.
1789       assert(!_foregroundGCShouldWait, "Should be clear");
1790       return;
1791     } else {
1792       assert(_collectorState == Idling, "Should be idling before start.");
1793       _collectorState = InitialMarking;
1794       register_gc_start(cause);
1795       // Reset the expansion cause, now that we are about to begin
1796       // a new cycle.
1797       clear_expansion_cause();
1798 
1799       // Clear the MetaspaceGC flag since a concurrent collection
1800       // is starting but also clear it after the collection.
1801       MetaspaceGC::set_should_concurrent_collect(false);
1802     }
1803     // Decide if we want to enable class unloading as part of the
1804     // ensuing concurrent GC cycle.
1805     update_should_unload_classes();
1806     _full_gc_requested = false;           // acks all outstanding full gc requests
1807     _full_gc_cause = GCCause::_no_gc;
1808     // Signal that we are about to start a collection
1809     gch->increment_total_full_collections();  // ... starting a collection cycle
1810     _collection_count_start = gch->total_full_collections();
1811   }
1812 
1813   // Used for PrintGC
1814   size_t prev_used;
1815   if (PrintGC && Verbose) {
1816     prev_used = _cmsGen->used();
1817   }
1818 
1819   // The change of the collection state is normally done at this level;
1820   // the exceptions are phases that are executed while the world is
1821   // stopped.  For those phases the change of state is done while the
1822   // world is stopped.  For baton passing purposes this allows the
1823   // background collector to finish the phase and change state atomically.
1824   // The foreground collector cannot wait on a phase that is done
1825   // while the world is stopped because the foreground collector already
1826   // has the world stopped and would deadlock.
1827   while (_collectorState != Idling) {
1828     if (TraceCMSState) {
1829       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1830         p2i(Thread::current()), _collectorState);
1831     }
1832     // The foreground collector
1833     //   holds the Heap_lock throughout its collection.
1834     //   holds the CMS token (but not the lock)
1835     //     except while it is waiting for the background collector to yield.
1836     //
1837     // The foreground collector should be blocked (not for long)
1838     //   if the background collector is about to start a phase
1839     //   executed with world stopped.  If the background
1840     //   collector has already started such a phase, the
1841     //   foreground collector is blocked waiting for the
1842     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1843     //   are executed in the VM thread.
1844     //
1845     // The locking order is
1846     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1847     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1848     //   CMS token  (claimed in
1849     //                stop_world_and_do() -->
1850     //                  safepoint_synchronize() -->
1851     //                    CMSThread::synchronize())
1852 
1853     {
1854       // Check if the FG collector wants us to yield.
1855       CMSTokenSync x(true); // is cms thread
1856       if (waitForForegroundGC()) {
1857         // We yielded to a foreground GC, nothing more to be
1858         // done this round.
1859         assert(_foregroundGCShouldWait == false, "We set it to false in "
1860                "waitForForegroundGC()");
1861         if (TraceCMSState) {
1862           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1863             " exiting collection CMS state %d",
1864             p2i(Thread::current()), _collectorState);
1865         }
1866         return;
1867       } else {
1868         // The background collector can run but check to see if the
1869         // foreground collector has done a collection while the
1870         // background collector was waiting to get the CGC_lock
1871         // above.  If yes, break so that _foregroundGCShouldWait
1872         // is cleared before returning.
1873         if (_collectorState == Idling) {
1874           break;
1875         }
1876       }
1877     }
1878 
1879     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1880       "should be waiting");
1881 
1882     switch (_collectorState) {
1883       case InitialMarking:
1884         {
1885           ReleaseForegroundGC x(this);
1886           stats().record_cms_begin();
1887           VM_CMS_Initial_Mark initial_mark_op(this);
1888           VMThread::execute(&initial_mark_op);
1889         }
1890         // The collector state may be any legal state at this point
1891         // since the background collector may have yielded to the
1892         // foreground collector.
1893         break;
1894       case Marking:
1895         // initial marking in checkpointRootsInitialWork has been completed
1896         if (markFromRoots()) { // we were successful
1897           assert(_collectorState == Precleaning, "Collector state should "
1898             "have changed");
1899         } else {
1900           assert(_foregroundGCIsActive, "Internal state inconsistency");
1901         }
1902         break;
1903       case Precleaning:
1904         // marking from roots in markFromRoots has been completed
1905         preclean();
1906         assert(_collectorState == AbortablePreclean ||
1907                _collectorState == FinalMarking,
1908                "Collector state should have changed");
1909         break;
1910       case AbortablePreclean:
1911         abortable_preclean();
1912         assert(_collectorState == FinalMarking, "Collector state should "
1913           "have changed");
1914         break;
1915       case FinalMarking:
1916         {
1917           ReleaseForegroundGC x(this);
1918 
1919           VM_CMS_Final_Remark final_remark_op(this);
1920           VMThread::execute(&final_remark_op);
1921         }
1922         assert(_foregroundGCShouldWait, "block post-condition");
1923         break;
1924       case Sweeping:
1925         // final marking in checkpointRootsFinal has been completed
1926         sweep();
1927         assert(_collectorState == Resizing, "Collector state change "
1928           "to Resizing must be done under the free_list_lock");
1929 
1930       case Resizing: {
1931         // Sweeping has been completed...
1932         // At this point the background collection has completed.
1933         // Don't move the call to compute_new_size() down
1934         // into code that might be executed if the background
1935         // collection was preempted.
1936         {
1937           ReleaseForegroundGC x(this);   // unblock FG collection
1938           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1939           CMSTokenSync        z(true);   // not strictly needed.
1940           if (_collectorState == Resizing) {
1941             compute_new_size();
1942             save_heap_summary();
1943             _collectorState = Resetting;
1944           } else {
1945             assert(_collectorState == Idling, "The state should only change"
1946                    " because the foreground collector has finished the collection");
1947           }
1948         }
1949         break;
1950       }
1951       case Resetting:
1952         // CMS heap resizing has been completed
1953         reset(true);
1954         assert(_collectorState == Idling, "Collector state should "
1955           "have changed");
1956 
1957         MetaspaceGC::set_should_concurrent_collect(false);
1958 
1959         stats().record_cms_end();
1960         // Don't move the concurrent_phases_end() and compute_new_size()
1961         // calls to here because a preempted background collection
1962         // has it's state set to "Resetting".
1963         break;
1964       case Idling:
1965       default:
1966         ShouldNotReachHere();
1967         break;
1968     }
1969     if (TraceCMSState) {
1970       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1971         p2i(Thread::current()), _collectorState);
1972     }
1973     assert(_foregroundGCShouldWait, "block post-condition");
1974   }
1975 
1976   // Should this be in gc_epilogue?
1977   collector_policy()->counters()->update_counters();
1978 
1979   {
1980     // Clear _foregroundGCShouldWait and, in the event that the
1981     // foreground collector is waiting, notify it, before
1982     // returning.
1983     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1984     _foregroundGCShouldWait = false;
1985     if (_foregroundGCIsActive) {
1986       CGC_lock->notify();
1987     }
1988     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1989            "Possible deadlock");
1990   }
1991   if (TraceCMSState) {
1992     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1993       " exiting collection CMS state %d",
1994       p2i(Thread::current()), _collectorState);
1995   }
1996   if (PrintGC && Verbose) {
1997     _cmsGen->print_heap_change(prev_used);
1998   }
1999 }
2000 
2001 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2002   _cms_start_registered = true;
2003   _gc_timer_cm->register_gc_start();
2004   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2005 }
2006 
2007 void CMSCollector::register_gc_end() {
2008   if (_cms_start_registered) {
2009     report_heap_summary(GCWhen::AfterGC);
2010 
2011     _gc_timer_cm->register_gc_end();
2012     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2013     _cms_start_registered = false;
2014   }
2015 }
2016 
2017 void CMSCollector::save_heap_summary() {
2018   GenCollectedHeap* gch = GenCollectedHeap::heap();
2019   _last_heap_summary = gch->create_heap_summary();
2020   _last_metaspace_summary = gch->create_metaspace_summary();
2021 }
2022 
2023 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2024   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2025   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2026 }
2027 
2028 bool CMSCollector::waitForForegroundGC() {
2029   bool res = false;
2030   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2031          "CMS thread should have CMS token");
2032   // Block the foreground collector until the
2033   // background collectors decides whether to
2034   // yield.
2035   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2036   _foregroundGCShouldWait = true;
2037   if (_foregroundGCIsActive) {
2038     // The background collector yields to the
2039     // foreground collector and returns a value
2040     // indicating that it has yielded.  The foreground
2041     // collector can proceed.
2042     res = true;
2043     _foregroundGCShouldWait = false;
2044     ConcurrentMarkSweepThread::clear_CMS_flag(
2045       ConcurrentMarkSweepThread::CMS_cms_has_token);
2046     ConcurrentMarkSweepThread::set_CMS_flag(
2047       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2048     // Get a possibly blocked foreground thread going
2049     CGC_lock->notify();
2050     if (TraceCMSState) {
2051       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2052         p2i(Thread::current()), _collectorState);
2053     }
2054     while (_foregroundGCIsActive) {
2055       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2056     }
2057     ConcurrentMarkSweepThread::set_CMS_flag(
2058       ConcurrentMarkSweepThread::CMS_cms_has_token);
2059     ConcurrentMarkSweepThread::clear_CMS_flag(
2060       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2061   }
2062   if (TraceCMSState) {
2063     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2064       p2i(Thread::current()), _collectorState);
2065   }
2066   return res;
2067 }
2068 
2069 // Because of the need to lock the free lists and other structures in
2070 // the collector, common to all the generations that the collector is
2071 // collecting, we need the gc_prologues of individual CMS generations
2072 // delegate to their collector. It may have been simpler had the
2073 // current infrastructure allowed one to call a prologue on a
2074 // collector. In the absence of that we have the generation's
2075 // prologue delegate to the collector, which delegates back
2076 // some "local" work to a worker method in the individual generations
2077 // that it's responsible for collecting, while itself doing any
2078 // work common to all generations it's responsible for. A similar
2079 // comment applies to the  gc_epilogue()'s.
2080 // The role of the variable _between_prologue_and_epilogue is to
2081 // enforce the invocation protocol.
2082 void CMSCollector::gc_prologue(bool full) {
2083   // Call gc_prologue_work() for the CMSGen
2084   // we are responsible for.
2085 
2086   // The following locking discipline assumes that we are only called
2087   // when the world is stopped.
2088   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2089 
2090   // The CMSCollector prologue must call the gc_prologues for the
2091   // "generations" that it's responsible
2092   // for.
2093 
2094   assert(   Thread::current()->is_VM_thread()
2095          || (   CMSScavengeBeforeRemark
2096              && Thread::current()->is_ConcurrentGC_thread()),
2097          "Incorrect thread type for prologue execution");
2098 
2099   if (_between_prologue_and_epilogue) {
2100     // We have already been invoked; this is a gc_prologue delegation
2101     // from yet another CMS generation that we are responsible for, just
2102     // ignore it since all relevant work has already been done.
2103     return;
2104   }
2105 
2106   // set a bit saying prologue has been called; cleared in epilogue
2107   _between_prologue_and_epilogue = true;
2108   // Claim locks for common data structures, then call gc_prologue_work()
2109   // for each CMSGen.
2110 
2111   getFreelistLocks();   // gets free list locks on constituent spaces
2112   bitMapLock()->lock_without_safepoint_check();
2113 
2114   // Should call gc_prologue_work() for all cms gens we are responsible for
2115   bool duringMarking =    _collectorState >= Marking
2116                          && _collectorState < Sweeping;
2117 
2118   // The young collections clear the modified oops state, which tells if
2119   // there are any modified oops in the class. The remark phase also needs
2120   // that information. Tell the young collection to save the union of all
2121   // modified klasses.
2122   if (duringMarking) {
2123     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2124   }
2125 
2126   bool registerClosure = duringMarking;
2127 
2128   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2129 
2130   if (!full) {
2131     stats().record_gc0_begin();
2132   }
2133 }
2134 
2135 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2136 
2137   _capacity_at_prologue = capacity();
2138   _used_at_prologue = used();
2139 
2140   // Delegate to CMScollector which knows how to coordinate between
2141   // this and any other CMS generations that it is responsible for
2142   // collecting.
2143   collector()->gc_prologue(full);
2144 }
2145 
2146 // This is a "private" interface for use by this generation's CMSCollector.
2147 // Not to be called directly by any other entity (for instance,
2148 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2149 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2150   bool registerClosure, ModUnionClosure* modUnionClosure) {
2151   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2152   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2153     "Should be NULL");
2154   if (registerClosure) {
2155     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2156   }
2157   cmsSpace()->gc_prologue();
2158   // Clear stat counters
2159   NOT_PRODUCT(
2160     assert(_numObjectsPromoted == 0, "check");
2161     assert(_numWordsPromoted   == 0, "check");
2162     if (Verbose && PrintGC) {
2163       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2164                           SIZE_FORMAT" bytes concurrently",
2165       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2166     }
2167     _numObjectsAllocated = 0;
2168     _numWordsAllocated   = 0;
2169   )
2170 }
2171 
2172 void CMSCollector::gc_epilogue(bool full) {
2173   // The following locking discipline assumes that we are only called
2174   // when the world is stopped.
2175   assert(SafepointSynchronize::is_at_safepoint(),
2176          "world is stopped assumption");
2177 
2178   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2179   // if linear allocation blocks need to be appropriately marked to allow the
2180   // the blocks to be parsable. We also check here whether we need to nudge the
2181   // CMS collector thread to start a new cycle (if it's not already active).
2182   assert(   Thread::current()->is_VM_thread()
2183          || (   CMSScavengeBeforeRemark
2184              && Thread::current()->is_ConcurrentGC_thread()),
2185          "Incorrect thread type for epilogue execution");
2186 
2187   if (!_between_prologue_and_epilogue) {
2188     // We have already been invoked; this is a gc_epilogue delegation
2189     // from yet another CMS generation that we are responsible for, just
2190     // ignore it since all relevant work has already been done.
2191     return;
2192   }
2193   assert(haveFreelistLocks(), "must have freelist locks");
2194   assert_lock_strong(bitMapLock());
2195 
2196   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2197 
2198   _cmsGen->gc_epilogue_work(full);
2199 
2200   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2201     // in case sampling was not already enabled, enable it
2202     _start_sampling = true;
2203   }
2204   // reset _eden_chunk_array so sampling starts afresh
2205   _eden_chunk_index = 0;
2206 
2207   size_t cms_used   = _cmsGen->cmsSpace()->used();
2208 
2209   // update performance counters - this uses a special version of
2210   // update_counters() that allows the utilization to be passed as a
2211   // parameter, avoiding multiple calls to used().
2212   //
2213   _cmsGen->update_counters(cms_used);
2214 
2215   bitMapLock()->unlock();
2216   releaseFreelistLocks();
2217 
2218   if (!CleanChunkPoolAsync) {
2219     Chunk::clean_chunk_pool();
2220   }
2221 
2222   set_did_compact(false);
2223   _between_prologue_and_epilogue = false;  // ready for next cycle
2224 }
2225 
2226 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2227   collector()->gc_epilogue(full);
2228 
2229   // Also reset promotion tracking in par gc thread states.
2230   for (uint i = 0; i < ParallelGCThreads; i++) {
2231     _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2232   }
2233 }
2234 
2235 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2236   assert(!incremental_collection_failed(), "Should have been cleared");
2237   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2238   cmsSpace()->gc_epilogue();
2239     // Print stat counters
2240   NOT_PRODUCT(
2241     assert(_numObjectsAllocated == 0, "check");
2242     assert(_numWordsAllocated == 0, "check");
2243     if (Verbose && PrintGC) {
2244       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2245                           SIZE_FORMAT" bytes",
2246                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2247     }
2248     _numObjectsPromoted = 0;
2249     _numWordsPromoted   = 0;
2250   )
2251 
2252   if (PrintGC && Verbose) {
2253     // Call down the chain in contiguous_available needs the freelistLock
2254     // so print this out before releasing the freeListLock.
2255     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2256                         contiguous_available());
2257   }
2258 }
2259 
2260 #ifndef PRODUCT
2261 bool CMSCollector::have_cms_token() {
2262   Thread* thr = Thread::current();
2263   if (thr->is_VM_thread()) {
2264     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2265   } else if (thr->is_ConcurrentGC_thread()) {
2266     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2267   } else if (thr->is_GC_task_thread()) {
2268     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2269            ParGCRareEvent_lock->owned_by_self();
2270   }
2271   return false;
2272 }
2273 #endif
2274 
2275 // Check reachability of the given heap address in CMS generation,
2276 // treating all other generations as roots.
2277 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2278   // We could "guarantee" below, rather than assert, but I'll
2279   // leave these as "asserts" so that an adventurous debugger
2280   // could try this in the product build provided some subset of
2281   // the conditions were met, provided they were interested in the
2282   // results and knew that the computation below wouldn't interfere
2283   // with other concurrent computations mutating the structures
2284   // being read or written.
2285   assert(SafepointSynchronize::is_at_safepoint(),
2286          "Else mutations in object graph will make answer suspect");
2287   assert(have_cms_token(), "Should hold cms token");
2288   assert(haveFreelistLocks(), "must hold free list locks");
2289   assert_lock_strong(bitMapLock());
2290 
2291   // Clear the marking bit map array before starting, but, just
2292   // for kicks, first report if the given address is already marked
2293   gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2294                 _markBitMap.isMarked(addr) ? "" : " not");
2295 
2296   if (verify_after_remark()) {
2297     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2298     bool result = verification_mark_bm()->isMarked(addr);
2299     gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2300                            result ? "IS" : "is NOT");
2301     return result;
2302   } else {
2303     gclog_or_tty->print_cr("Could not compute result");
2304     return false;
2305   }
2306 }
2307 
2308 
2309 void
2310 CMSCollector::print_on_error(outputStream* st) {
2311   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2312   if (collector != NULL) {
2313     CMSBitMap* bitmap = &collector->_markBitMap;
2314     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2315     bitmap->print_on_error(st, " Bits: ");
2316 
2317     st->cr();
2318 
2319     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2320     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2321     mut_bitmap->print_on_error(st, " Bits: ");
2322   }
2323 }
2324 
2325 ////////////////////////////////////////////////////////
2326 // CMS Verification Support
2327 ////////////////////////////////////////////////////////
2328 // Following the remark phase, the following invariant
2329 // should hold -- each object in the CMS heap which is
2330 // marked in markBitMap() should be marked in the verification_mark_bm().
2331 
2332 class VerifyMarkedClosure: public BitMapClosure {
2333   CMSBitMap* _marks;
2334   bool       _failed;
2335 
2336  public:
2337   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2338 
2339   bool do_bit(size_t offset) {
2340     HeapWord* addr = _marks->offsetToHeapWord(offset);
2341     if (!_marks->isMarked(addr)) {
2342       oop(addr)->print_on(gclog_or_tty);
2343       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2344       _failed = true;
2345     }
2346     return true;
2347   }
2348 
2349   bool failed() { return _failed; }
2350 };
2351 
2352 bool CMSCollector::verify_after_remark(bool silent) {
2353   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2354   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2355   static bool init = false;
2356 
2357   assert(SafepointSynchronize::is_at_safepoint(),
2358          "Else mutations in object graph will make answer suspect");
2359   assert(have_cms_token(),
2360          "Else there may be mutual interference in use of "
2361          " verification data structures");
2362   assert(_collectorState > Marking && _collectorState <= Sweeping,
2363          "Else marking info checked here may be obsolete");
2364   assert(haveFreelistLocks(), "must hold free list locks");
2365   assert_lock_strong(bitMapLock());
2366 
2367 
2368   // Allocate marking bit map if not already allocated
2369   if (!init) { // first time
2370     if (!verification_mark_bm()->allocate(_span)) {
2371       return false;
2372     }
2373     init = true;
2374   }
2375 
2376   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2377 
2378   // Turn off refs discovery -- so we will be tracing through refs.
2379   // This is as intended, because by this time
2380   // GC must already have cleared any refs that need to be cleared,
2381   // and traced those that need to be marked; moreover,
2382   // the marking done here is not going to interfere in any
2383   // way with the marking information used by GC.
2384   NoRefDiscovery no_discovery(ref_processor());
2385 
2386   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2387 
2388   // Clear any marks from a previous round
2389   verification_mark_bm()->clear_all();
2390   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2391   verify_work_stacks_empty();
2392 
2393   GenCollectedHeap* gch = GenCollectedHeap::heap();
2394   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2395   // Update the saved marks which may affect the root scans.
2396   gch->save_marks();
2397 
2398   if (CMSRemarkVerifyVariant == 1) {
2399     // In this first variant of verification, we complete
2400     // all marking, then check if the new marks-vector is
2401     // a subset of the CMS marks-vector.
2402     verify_after_remark_work_1();
2403   } else if (CMSRemarkVerifyVariant == 2) {
2404     // In this second variant of verification, we flag an error
2405     // (i.e. an object reachable in the new marks-vector not reachable
2406     // in the CMS marks-vector) immediately, also indicating the
2407     // identify of an object (A) that references the unmarked object (B) --
2408     // presumably, a mutation to A failed to be picked up by preclean/remark?
2409     verify_after_remark_work_2();
2410   } else {
2411     warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2412             CMSRemarkVerifyVariant);
2413   }
2414   if (!silent) gclog_or_tty->print(" done] ");
2415   return true;
2416 }
2417 
2418 void CMSCollector::verify_after_remark_work_1() {
2419   ResourceMark rm;
2420   HandleMark  hm;
2421   GenCollectedHeap* gch = GenCollectedHeap::heap();
2422 
2423   // Get a clear set of claim bits for the roots processing to work with.
2424   ClassLoaderDataGraph::clear_claimed_marks();
2425 
2426   // Mark from roots one level into CMS
2427   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2428   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2429 
2430   {
2431     StrongRootsScope srs(1);
2432 
2433     gch->gen_process_roots(&srs,
2434                            _cmsGen->level(),
2435                            true,   // younger gens are roots

2436                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2437                            should_unload_classes(),
2438                            &notOlder,
2439                            NULL,
2440                            NULL);
2441   }
2442 
2443   // Now mark from the roots
2444   MarkFromRootsClosure markFromRootsClosure(this, _span,
2445     verification_mark_bm(), verification_mark_stack(),
2446     false /* don't yield */, true /* verifying */);
2447   assert(_restart_addr == NULL, "Expected pre-condition");
2448   verification_mark_bm()->iterate(&markFromRootsClosure);
2449   while (_restart_addr != NULL) {
2450     // Deal with stack overflow: by restarting at the indicated
2451     // address.
2452     HeapWord* ra = _restart_addr;
2453     markFromRootsClosure.reset(ra);
2454     _restart_addr = NULL;
2455     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2456   }
2457   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2458   verify_work_stacks_empty();
2459 
2460   // Marking completed -- now verify that each bit marked in
2461   // verification_mark_bm() is also marked in markBitMap(); flag all
2462   // errors by printing corresponding objects.
2463   VerifyMarkedClosure vcl(markBitMap());
2464   verification_mark_bm()->iterate(&vcl);
2465   if (vcl.failed()) {
2466     gclog_or_tty->print("Verification failed");
2467     gch->print_on(gclog_or_tty);
2468     fatal("CMS: failed marking verification after remark");
2469   }
2470 }
2471 
2472 class VerifyKlassOopsKlassClosure : public KlassClosure {
2473   class VerifyKlassOopsClosure : public OopClosure {
2474     CMSBitMap* _bitmap;
2475    public:
2476     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2477     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2478     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2479   } _oop_closure;
2480  public:
2481   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2482   void do_klass(Klass* k) {
2483     k->oops_do(&_oop_closure);
2484   }
2485 };
2486 
2487 void CMSCollector::verify_after_remark_work_2() {
2488   ResourceMark rm;
2489   HandleMark  hm;
2490   GenCollectedHeap* gch = GenCollectedHeap::heap();
2491 
2492   // Get a clear set of claim bits for the roots processing to work with.
2493   ClassLoaderDataGraph::clear_claimed_marks();
2494 
2495   // Mark from roots one level into CMS
2496   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2497                                      markBitMap());
2498   CLDToOopClosure cld_closure(&notOlder, true);
2499 
2500   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2501 
2502   {
2503     StrongRootsScope srs(1);
2504 
2505     gch->gen_process_roots(&srs,
2506                            _cmsGen->level(),
2507                            true,   // younger gens are roots

2508                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2509                            should_unload_classes(),
2510                            &notOlder,
2511                            NULL,
2512                            &cld_closure);
2513   }
2514 
2515   // Now mark from the roots
2516   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2517     verification_mark_bm(), markBitMap(), verification_mark_stack());
2518   assert(_restart_addr == NULL, "Expected pre-condition");
2519   verification_mark_bm()->iterate(&markFromRootsClosure);
2520   while (_restart_addr != NULL) {
2521     // Deal with stack overflow: by restarting at the indicated
2522     // address.
2523     HeapWord* ra = _restart_addr;
2524     markFromRootsClosure.reset(ra);
2525     _restart_addr = NULL;
2526     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2527   }
2528   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2529   verify_work_stacks_empty();
2530 
2531   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2532   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2533 
2534   // Marking completed -- now verify that each bit marked in
2535   // verification_mark_bm() is also marked in markBitMap(); flag all
2536   // errors by printing corresponding objects.
2537   VerifyMarkedClosure vcl(markBitMap());
2538   verification_mark_bm()->iterate(&vcl);
2539   assert(!vcl.failed(), "Else verification above should not have succeeded");
2540 }
2541 
2542 void ConcurrentMarkSweepGeneration::save_marks() {
2543   // delegate to CMS space
2544   cmsSpace()->save_marks();
2545   for (uint i = 0; i < ParallelGCThreads; i++) {
2546     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2547   }
2548 }
2549 
2550 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2551   return cmsSpace()->no_allocs_since_save_marks();
2552 }
2553 
2554 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2555                                                                 \
2556 void ConcurrentMarkSweepGeneration::                            \
2557 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2558   cl->set_generation(this);                                     \
2559   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2560   cl->reset_generation();                                       \
2561   save_marks();                                                 \
2562 }
2563 
2564 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2565 
2566 void
2567 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2568   if (freelistLock()->owned_by_self()) {
2569     Generation::oop_iterate(cl);
2570   } else {
2571     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2572     Generation::oop_iterate(cl);
2573   }
2574 }
2575 
2576 void
2577 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2578   if (freelistLock()->owned_by_self()) {
2579     Generation::object_iterate(cl);
2580   } else {
2581     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2582     Generation::object_iterate(cl);
2583   }
2584 }
2585 
2586 void
2587 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2588   if (freelistLock()->owned_by_self()) {
2589     Generation::safe_object_iterate(cl);
2590   } else {
2591     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2592     Generation::safe_object_iterate(cl);
2593   }
2594 }
2595 
2596 void
2597 ConcurrentMarkSweepGeneration::post_compact() {
2598 }
2599 
2600 void
2601 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2602   // Fix the linear allocation blocks to look like free blocks.
2603 
2604   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2605   // are not called when the heap is verified during universe initialization and
2606   // at vm shutdown.
2607   if (freelistLock()->owned_by_self()) {
2608     cmsSpace()->prepare_for_verify();
2609   } else {
2610     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2611     cmsSpace()->prepare_for_verify();
2612   }
2613 }
2614 
2615 void
2616 ConcurrentMarkSweepGeneration::verify() {
2617   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2618   // are not called when the heap is verified during universe initialization and
2619   // at vm shutdown.
2620   if (freelistLock()->owned_by_self()) {
2621     cmsSpace()->verify();
2622   } else {
2623     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2624     cmsSpace()->verify();
2625   }
2626 }
2627 
2628 void CMSCollector::verify() {
2629   _cmsGen->verify();
2630 }
2631 
2632 #ifndef PRODUCT
2633 bool CMSCollector::overflow_list_is_empty() const {
2634   assert(_num_par_pushes >= 0, "Inconsistency");
2635   if (_overflow_list == NULL) {
2636     assert(_num_par_pushes == 0, "Inconsistency");
2637   }
2638   return _overflow_list == NULL;
2639 }
2640 
2641 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2642 // merely consolidate assertion checks that appear to occur together frequently.
2643 void CMSCollector::verify_work_stacks_empty() const {
2644   assert(_markStack.isEmpty(), "Marking stack should be empty");
2645   assert(overflow_list_is_empty(), "Overflow list should be empty");
2646 }
2647 
2648 void CMSCollector::verify_overflow_empty() const {
2649   assert(overflow_list_is_empty(), "Overflow list should be empty");
2650   assert(no_preserved_marks(), "No preserved marks");
2651 }
2652 #endif // PRODUCT
2653 
2654 // Decide if we want to enable class unloading as part of the
2655 // ensuing concurrent GC cycle. We will collect and
2656 // unload classes if it's the case that:
2657 // (1) an explicit gc request has been made and the flag
2658 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2659 // (2) (a) class unloading is enabled at the command line, and
2660 //     (b) old gen is getting really full
2661 // NOTE: Provided there is no change in the state of the heap between
2662 // calls to this method, it should have idempotent results. Moreover,
2663 // its results should be monotonically increasing (i.e. going from 0 to 1,
2664 // but not 1 to 0) between successive calls between which the heap was
2665 // not collected. For the implementation below, it must thus rely on
2666 // the property that concurrent_cycles_since_last_unload()
2667 // will not decrease unless a collection cycle happened and that
2668 // _cmsGen->is_too_full() are
2669 // themselves also monotonic in that sense. See check_monotonicity()
2670 // below.
2671 void CMSCollector::update_should_unload_classes() {
2672   _should_unload_classes = false;
2673   // Condition 1 above
2674   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2675     _should_unload_classes = true;
2676   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2677     // Disjuncts 2.b.(i,ii,iii) above
2678     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2679                               CMSClassUnloadingMaxInterval)
2680                            || _cmsGen->is_too_full();
2681   }
2682 }
2683 
2684 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2685   bool res = should_concurrent_collect();
2686   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2687   return res;
2688 }
2689 
2690 void CMSCollector::setup_cms_unloading_and_verification_state() {
2691   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2692                              || VerifyBeforeExit;
2693   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2694 
2695   // We set the proper root for this CMS cycle here.
2696   if (should_unload_classes()) {   // Should unload classes this cycle
2697     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2698     set_verifying(should_verify);    // Set verification state for this cycle
2699     return;                            // Nothing else needs to be done at this time
2700   }
2701 
2702   // Not unloading classes this cycle
2703   assert(!should_unload_classes(), "Inconsistency!");
2704 
2705   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2706     // Include symbols, strings and code cache elements to prevent their resurrection.
2707     add_root_scanning_option(rso);
2708     set_verifying(true);
2709   } else if (verifying() && !should_verify) {
2710     // We were verifying, but some verification flags got disabled.
2711     set_verifying(false);
2712     // Exclude symbols, strings and code cache elements from root scanning to
2713     // reduce IM and RM pauses.
2714     remove_root_scanning_option(rso);
2715   }
2716 }
2717 
2718 
2719 #ifndef PRODUCT
2720 HeapWord* CMSCollector::block_start(const void* p) const {
2721   const HeapWord* addr = (HeapWord*)p;
2722   if (_span.contains(p)) {
2723     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2724       return _cmsGen->cmsSpace()->block_start(p);
2725     }
2726   }
2727   return NULL;
2728 }
2729 #endif
2730 
2731 HeapWord*
2732 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2733                                                    bool   tlab,
2734                                                    bool   parallel) {
2735   CMSSynchronousYieldRequest yr;
2736   assert(!tlab, "Can't deal with TLAB allocation");
2737   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2738   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2739   if (GCExpandToAllocateDelayMillis > 0) {
2740     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2741   }
2742   return have_lock_and_allocate(word_size, tlab);
2743 }
2744 
2745 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2746     size_t bytes,
2747     size_t expand_bytes,
2748     CMSExpansionCause::Cause cause)
2749 {
2750 
2751   bool success = expand(bytes, expand_bytes);
2752 
2753   // remember why we expanded; this information is used
2754   // by shouldConcurrentCollect() when making decisions on whether to start
2755   // a new CMS cycle.
2756   if (success) {
2757     set_expansion_cause(cause);
2758     if (PrintGCDetails && Verbose) {
2759       gclog_or_tty->print_cr("Expanded CMS gen for %s",
2760         CMSExpansionCause::to_string(cause));
2761     }
2762   }
2763 }
2764 
2765 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2766   HeapWord* res = NULL;
2767   MutexLocker x(ParGCRareEvent_lock);
2768   while (true) {
2769     // Expansion by some other thread might make alloc OK now:
2770     res = ps->lab.alloc(word_sz);
2771     if (res != NULL) return res;
2772     // If there's not enough expansion space available, give up.
2773     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2774       return NULL;
2775     }
2776     // Otherwise, we try expansion.
2777     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2778     // Now go around the loop and try alloc again;
2779     // A competing par_promote might beat us to the expansion space,
2780     // so we may go around the loop again if promotion fails again.
2781     if (GCExpandToAllocateDelayMillis > 0) {
2782       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2783     }
2784   }
2785 }
2786 
2787 
2788 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2789   PromotionInfo* promo) {
2790   MutexLocker x(ParGCRareEvent_lock);
2791   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2792   while (true) {
2793     // Expansion by some other thread might make alloc OK now:
2794     if (promo->ensure_spooling_space()) {
2795       assert(promo->has_spooling_space(),
2796              "Post-condition of successful ensure_spooling_space()");
2797       return true;
2798     }
2799     // If there's not enough expansion space available, give up.
2800     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2801       return false;
2802     }
2803     // Otherwise, we try expansion.
2804     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2805     // Now go around the loop and try alloc again;
2806     // A competing allocation might beat us to the expansion space,
2807     // so we may go around the loop again if allocation fails again.
2808     if (GCExpandToAllocateDelayMillis > 0) {
2809       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2810     }
2811   }
2812 }
2813 
2814 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2815   // Only shrink if a compaction was done so that all the free space
2816   // in the generation is in a contiguous block at the end.
2817   if (did_compact()) {
2818     CardGeneration::shrink(bytes);
2819   }
2820 }
2821 
2822 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2823   assert_locked_or_safepoint(Heap_lock);
2824 }
2825 
2826 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2827   assert_locked_or_safepoint(Heap_lock);
2828   assert_lock_strong(freelistLock());
2829   if (PrintGCDetails && Verbose) {
2830     warning("Shrinking of CMS not yet implemented");
2831   }
2832   return;
2833 }
2834 
2835 
2836 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2837 // phases.
2838 class CMSPhaseAccounting: public StackObj {
2839  public:
2840   CMSPhaseAccounting(CMSCollector *collector,
2841                      const char *phase,
2842                      const GCId gc_id,
2843                      bool print_cr = true);
2844   ~CMSPhaseAccounting();
2845 
2846  private:
2847   CMSCollector *_collector;
2848   const char *_phase;
2849   elapsedTimer _wallclock;
2850   bool _print_cr;
2851   const GCId _gc_id;
2852 
2853  public:
2854   // Not MT-safe; so do not pass around these StackObj's
2855   // where they may be accessed by other threads.
2856   jlong wallclock_millis() {
2857     assert(_wallclock.is_active(), "Wall clock should not stop");
2858     _wallclock.stop();  // to record time
2859     jlong ret = _wallclock.milliseconds();
2860     _wallclock.start(); // restart
2861     return ret;
2862   }
2863 };
2864 
2865 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2866                                        const char *phase,
2867                                        const GCId gc_id,
2868                                        bool print_cr) :
2869   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2870 
2871   if (PrintCMSStatistics != 0) {
2872     _collector->resetYields();
2873   }
2874   if (PrintGCDetails) {
2875     gclog_or_tty->gclog_stamp(_gc_id);
2876     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2877       _collector->cmsGen()->short_name(), _phase);
2878   }
2879   _collector->resetTimer();
2880   _wallclock.start();
2881   _collector->startTimer();
2882 }
2883 
2884 CMSPhaseAccounting::~CMSPhaseAccounting() {
2885   assert(_wallclock.is_active(), "Wall clock should not have stopped");
2886   _collector->stopTimer();
2887   _wallclock.stop();
2888   if (PrintGCDetails) {
2889     gclog_or_tty->gclog_stamp(_gc_id);
2890     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2891                  _collector->cmsGen()->short_name(),
2892                  _phase, _collector->timerValue(), _wallclock.seconds());
2893     if (_print_cr) {
2894       gclog_or_tty->cr();
2895     }
2896     if (PrintCMSStatistics != 0) {
2897       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2898                     _collector->yields());
2899     }
2900   }
2901 }
2902 
2903 // CMS work
2904 
2905 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2906 class CMSParMarkTask : public AbstractGangTask {
2907  protected:
2908   CMSCollector*     _collector;
2909   uint              _n_workers;
2910   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2911       AbstractGangTask(name),
2912       _collector(collector),
2913       _n_workers(n_workers) {}
2914   // Work method in support of parallel rescan ... of young gen spaces
2915   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2916                              ContiguousSpace* space,
2917                              HeapWord** chunk_array, size_t chunk_top);
2918   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2919 };
2920 
2921 // Parallel initial mark task
2922 class CMSParInitialMarkTask: public CMSParMarkTask {
2923   StrongRootsScope* _strong_roots_scope;
2924  public:
2925   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2926       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2927       _strong_roots_scope(strong_roots_scope) {}
2928   void work(uint worker_id);
2929 };
2930 
2931 // Checkpoint the roots into this generation from outside
2932 // this generation. [Note this initial checkpoint need only
2933 // be approximate -- we'll do a catch up phase subsequently.]
2934 void CMSCollector::checkpointRootsInitial() {
2935   assert(_collectorState == InitialMarking, "Wrong collector state");
2936   check_correct_thread_executing();
2937   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2938 
2939   save_heap_summary();
2940   report_heap_summary(GCWhen::BeforeGC);
2941 
2942   ReferenceProcessor* rp = ref_processor();
2943   assert(_restart_addr == NULL, "Control point invariant");
2944   {
2945     // acquire locks for subsequent manipulations
2946     MutexLockerEx x(bitMapLock(),
2947                     Mutex::_no_safepoint_check_flag);
2948     checkpointRootsInitialWork();
2949     // enable ("weak") refs discovery
2950     rp->enable_discovery();
2951     _collectorState = Marking;
2952   }
2953 }
2954 
2955 void CMSCollector::checkpointRootsInitialWork() {
2956   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2957   assert(_collectorState == InitialMarking, "just checking");
2958 
2959   // If there has not been a GC[n-1] since last GC[n] cycle completed,
2960   // precede our marking with a collection of all
2961   // younger generations to keep floating garbage to a minimum.
2962   // XXX: we won't do this for now -- it's an optimization to be done later.
2963 
2964   // already have locks
2965   assert_lock_strong(bitMapLock());
2966   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2967 
2968   // Setup the verification and class unloading state for this
2969   // CMS collection cycle.
2970   setup_cms_unloading_and_verification_state();
2971 
2972   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2973     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2974 
2975   // Reset all the PLAB chunk arrays if necessary.
2976   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2977     reset_survivor_plab_arrays();
2978   }
2979 
2980   ResourceMark rm;
2981   HandleMark  hm;
2982 
2983   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2984   GenCollectedHeap* gch = GenCollectedHeap::heap();
2985 
2986   verify_work_stacks_empty();
2987   verify_overflow_empty();
2988 
2989   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2990   // Update the saved marks which may affect the root scans.
2991   gch->save_marks();
2992 
2993   // weak reference processing has not started yet.
2994   ref_processor()->set_enqueuing_is_done(false);
2995 
2996   // Need to remember all newly created CLDs,
2997   // so that we can guarantee that the remark finds them.
2998   ClassLoaderDataGraph::remember_new_clds(true);
2999 
3000   // Whenever a CLD is found, it will be claimed before proceeding to mark
3001   // the klasses. The claimed marks need to be cleared before marking starts.
3002   ClassLoaderDataGraph::clear_claimed_marks();
3003 
3004   if (CMSPrintEdenSurvivorChunks) {
3005     print_eden_and_survivor_chunk_arrays();
3006   }
3007 
3008   {
3009     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3010     if (CMSParallelInitialMarkEnabled) {
3011       // The parallel version.
3012       FlexibleWorkGang* workers = gch->workers();
3013       assert(workers != NULL, "Need parallel worker threads.");
3014       uint n_workers = workers->active_workers();
3015 
3016       StrongRootsScope srs(n_workers);
3017 
3018       CMSParInitialMarkTask tsk(this, &srs, n_workers);
3019       gch->set_par_threads(n_workers);
3020       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3021       if (n_workers > 1) {

3022         workers->run_task(&tsk);
3023       } else {

3024         tsk.work(0);
3025       }
3026       gch->set_par_threads(0);
3027     } else {
3028       // The serial version.
3029       CLDToOopClosure cld_closure(&notOlder, true);
3030       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3031 
3032       StrongRootsScope srs(1);
3033 
3034       gch->gen_process_roots(&srs,
3035                              _cmsGen->level(),
3036                              true,   // younger gens are roots

3037                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
3038                              should_unload_classes(),
3039                              &notOlder,
3040                              NULL,
3041                              &cld_closure);
3042     }
3043   }
3044 
3045   // Clear mod-union table; it will be dirtied in the prologue of
3046   // CMS generation per each younger generation collection.
3047 
3048   assert(_modUnionTable.isAllClear(),
3049        "Was cleared in most recent final checkpoint phase"
3050        " or no bits are set in the gc_prologue before the start of the next "
3051        "subsequent marking phase.");
3052 
3053   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3054 
3055   // Save the end of the used_region of the constituent generations
3056   // to be used to limit the extent of sweep in each generation.
3057   save_sweep_limits();
3058   verify_overflow_empty();
3059 }
3060 
3061 bool CMSCollector::markFromRoots() {
3062   // we might be tempted to assert that:
3063   // assert(!SafepointSynchronize::is_at_safepoint(),
3064   //        "inconsistent argument?");
3065   // However that wouldn't be right, because it's possible that
3066   // a safepoint is indeed in progress as a younger generation
3067   // stop-the-world GC happens even as we mark in this generation.
3068   assert(_collectorState == Marking, "inconsistent state?");
3069   check_correct_thread_executing();
3070   verify_overflow_empty();
3071 
3072   // Weak ref discovery note: We may be discovering weak
3073   // refs in this generation concurrent (but interleaved) with
3074   // weak ref discovery by a younger generation collector.
3075 
3076   CMSTokenSyncWithLocks ts(true, bitMapLock());
3077   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3078   CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3079   bool res = markFromRootsWork();
3080   if (res) {
3081     _collectorState = Precleaning;
3082   } else { // We failed and a foreground collection wants to take over
3083     assert(_foregroundGCIsActive, "internal state inconsistency");
3084     assert(_restart_addr == NULL,  "foreground will restart from scratch");
3085     if (PrintGCDetails) {
3086       gclog_or_tty->print_cr("bailing out to foreground collection");
3087     }
3088   }
3089   verify_overflow_empty();
3090   return res;
3091 }
3092 
3093 bool CMSCollector::markFromRootsWork() {
3094   // iterate over marked bits in bit map, doing a full scan and mark
3095   // from these roots using the following algorithm:
3096   // . if oop is to the right of the current scan pointer,
3097   //   mark corresponding bit (we'll process it later)
3098   // . else (oop is to left of current scan pointer)
3099   //   push oop on marking stack
3100   // . drain the marking stack
3101 
3102   // Note that when we do a marking step we need to hold the
3103   // bit map lock -- recall that direct allocation (by mutators)
3104   // and promotion (by younger generation collectors) is also
3105   // marking the bit map. [the so-called allocate live policy.]
3106   // Because the implementation of bit map marking is not
3107   // robust wrt simultaneous marking of bits in the same word,
3108   // we need to make sure that there is no such interference
3109   // between concurrent such updates.
3110 
3111   // already have locks
3112   assert_lock_strong(bitMapLock());
3113 
3114   verify_work_stacks_empty();
3115   verify_overflow_empty();
3116   bool result = false;
3117   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3118     result = do_marking_mt();
3119   } else {
3120     result = do_marking_st();
3121   }
3122   return result;
3123 }
3124 
3125 // Forward decl
3126 class CMSConcMarkingTask;
3127 
3128 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3129   CMSCollector*       _collector;
3130   CMSConcMarkingTask* _task;
3131  public:
3132   virtual void yield();
3133 
3134   // "n_threads" is the number of threads to be terminated.
3135   // "queue_set" is a set of work queues of other threads.
3136   // "collector" is the CMS collector associated with this task terminator.
3137   // "yield" indicates whether we need the gang as a whole to yield.
3138   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3139     ParallelTaskTerminator(n_threads, queue_set),
3140     _collector(collector) { }
3141 
3142   void set_task(CMSConcMarkingTask* task) {
3143     _task = task;
3144   }
3145 };
3146 
3147 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3148   CMSConcMarkingTask* _task;
3149  public:
3150   bool should_exit_termination();
3151   void set_task(CMSConcMarkingTask* task) {
3152     _task = task;
3153   }
3154 };
3155 
3156 // MT Concurrent Marking Task
3157 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3158   CMSCollector* _collector;
3159   uint          _n_workers;       // requested/desired # workers
3160   bool          _result;
3161   CompactibleFreeListSpace*  _cms_space;
3162   char          _pad_front[64];   // padding to ...
3163   HeapWord*     _global_finger;   // ... avoid sharing cache line
3164   char          _pad_back[64];
3165   HeapWord*     _restart_addr;
3166 
3167   //  Exposed here for yielding support
3168   Mutex* const _bit_map_lock;
3169 
3170   // The per thread work queues, available here for stealing
3171   OopTaskQueueSet*  _task_queues;
3172 
3173   // Termination (and yielding) support
3174   CMSConcMarkingTerminator _term;
3175   CMSConcMarkingTerminatorTerminator _term_term;
3176 
3177  public:
3178   CMSConcMarkingTask(CMSCollector* collector,
3179                  CompactibleFreeListSpace* cms_space,
3180                  YieldingFlexibleWorkGang* workers,
3181                  OopTaskQueueSet* task_queues):
3182     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3183     _collector(collector),
3184     _cms_space(cms_space),
3185     _n_workers(0), _result(true),
3186     _task_queues(task_queues),
3187     _term(_n_workers, task_queues, _collector),
3188     _bit_map_lock(collector->bitMapLock())
3189   {
3190     _requested_size = _n_workers;
3191     _term.set_task(this);
3192     _term_term.set_task(this);
3193     _restart_addr = _global_finger = _cms_space->bottom();
3194   }
3195 
3196 
3197   OopTaskQueueSet* task_queues()  { return _task_queues; }
3198 
3199   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3200 
3201   HeapWord** global_finger_addr() { return &_global_finger; }
3202 
3203   CMSConcMarkingTerminator* terminator() { return &_term; }
3204 
3205   virtual void set_for_termination(uint active_workers) {
3206     terminator()->reset_for_reuse(active_workers);
3207   }
3208 
3209   void work(uint worker_id);
3210   bool should_yield() {
3211     return    ConcurrentMarkSweepThread::should_yield()
3212            && !_collector->foregroundGCIsActive();
3213   }
3214 
3215   virtual void coordinator_yield();  // stuff done by coordinator
3216   bool result() { return _result; }
3217 
3218   void reset(HeapWord* ra) {
3219     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3220     _restart_addr = _global_finger = ra;
3221     _term.reset_for_reuse();
3222   }
3223 
3224   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3225                                            OopTaskQueue* work_q);
3226 
3227  private:
3228   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3229   void do_work_steal(int i);
3230   void bump_global_finger(HeapWord* f);
3231 };
3232 
3233 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3234   assert(_task != NULL, "Error");
3235   return _task->yielding();
3236   // Note that we do not need the disjunct || _task->should_yield() above
3237   // because we want terminating threads to yield only if the task
3238   // is already in the midst of yielding, which happens only after at least one
3239   // thread has yielded.
3240 }
3241 
3242 void CMSConcMarkingTerminator::yield() {
3243   if (_task->should_yield()) {
3244     _task->yield();
3245   } else {
3246     ParallelTaskTerminator::yield();
3247   }
3248 }
3249 
3250 ////////////////////////////////////////////////////////////////
3251 // Concurrent Marking Algorithm Sketch
3252 ////////////////////////////////////////////////////////////////
3253 // Until all tasks exhausted (both spaces):
3254 // -- claim next available chunk
3255 // -- bump global finger via CAS
3256 // -- find first object that starts in this chunk
3257 //    and start scanning bitmap from that position
3258 // -- scan marked objects for oops
3259 // -- CAS-mark target, and if successful:
3260 //    . if target oop is above global finger (volatile read)
3261 //      nothing to do
3262 //    . if target oop is in chunk and above local finger
3263 //        then nothing to do
3264 //    . else push on work-queue
3265 // -- Deal with possible overflow issues:
3266 //    . local work-queue overflow causes stuff to be pushed on
3267 //      global (common) overflow queue
3268 //    . always first empty local work queue
3269 //    . then get a batch of oops from global work queue if any
3270 //    . then do work stealing
3271 // -- When all tasks claimed (both spaces)
3272 //    and local work queue empty,
3273 //    then in a loop do:
3274 //    . check global overflow stack; steal a batch of oops and trace
3275 //    . try to steal from other threads oif GOS is empty
3276 //    . if neither is available, offer termination
3277 // -- Terminate and return result
3278 //
3279 void CMSConcMarkingTask::work(uint worker_id) {
3280   elapsedTimer _timer;
3281   ResourceMark rm;
3282   HandleMark hm;
3283 
3284   DEBUG_ONLY(_collector->verify_overflow_empty();)
3285 
3286   // Before we begin work, our work queue should be empty
3287   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3288   // Scan the bitmap covering _cms_space, tracing through grey objects.
3289   _timer.start();
3290   do_scan_and_mark(worker_id, _cms_space);
3291   _timer.stop();
3292   if (PrintCMSStatistics != 0) {
3293     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3294       worker_id, _timer.seconds());
3295       // XXX: need xxx/xxx type of notation, two timers
3296   }
3297 
3298   // ... do work stealing
3299   _timer.reset();
3300   _timer.start();
3301   do_work_steal(worker_id);
3302   _timer.stop();
3303   if (PrintCMSStatistics != 0) {
3304     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3305       worker_id, _timer.seconds());
3306       // XXX: need xxx/xxx type of notation, two timers
3307   }
3308   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3309   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3310   // Note that under the current task protocol, the
3311   // following assertion is true even of the spaces
3312   // expanded since the completion of the concurrent
3313   // marking. XXX This will likely change under a strict
3314   // ABORT semantics.
3315   // After perm removal the comparison was changed to
3316   // greater than or equal to from strictly greater than.
3317   // Before perm removal the highest address sweep would
3318   // have been at the end of perm gen but now is at the
3319   // end of the tenured gen.
3320   assert(_global_finger >=  _cms_space->end(),
3321          "All tasks have been completed");
3322   DEBUG_ONLY(_collector->verify_overflow_empty();)
3323 }
3324 
3325 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3326   HeapWord* read = _global_finger;
3327   HeapWord* cur  = read;
3328   while (f > read) {
3329     cur = read;
3330     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3331     if (cur == read) {
3332       // our cas succeeded
3333       assert(_global_finger >= f, "protocol consistency");
3334       break;
3335     }
3336   }
3337 }
3338 
3339 // This is really inefficient, and should be redone by
3340 // using (not yet available) block-read and -write interfaces to the
3341 // stack and the work_queue. XXX FIX ME !!!
3342 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3343                                                       OopTaskQueue* work_q) {
3344   // Fast lock-free check
3345   if (ovflw_stk->length() == 0) {
3346     return false;
3347   }
3348   assert(work_q->size() == 0, "Shouldn't steal");
3349   MutexLockerEx ml(ovflw_stk->par_lock(),
3350                    Mutex::_no_safepoint_check_flag);
3351   // Grab up to 1/4 the size of the work queue
3352   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3353                     (size_t)ParGCDesiredObjsFromOverflowList);
3354   num = MIN2(num, ovflw_stk->length());
3355   for (int i = (int) num; i > 0; i--) {
3356     oop cur = ovflw_stk->pop();
3357     assert(cur != NULL, "Counted wrong?");
3358     work_q->push(cur);
3359   }
3360   return num > 0;
3361 }
3362 
3363 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3364   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3365   int n_tasks = pst->n_tasks();
3366   // We allow that there may be no tasks to do here because
3367   // we are restarting after a stack overflow.
3368   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3369   uint nth_task = 0;
3370 
3371   HeapWord* aligned_start = sp->bottom();
3372   if (sp->used_region().contains(_restart_addr)) {
3373     // Align down to a card boundary for the start of 0th task
3374     // for this space.
3375     aligned_start =
3376       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3377                                  CardTableModRefBS::card_size);
3378   }
3379 
3380   size_t chunk_size = sp->marking_task_size();
3381   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3382     // Having claimed the nth task in this space,
3383     // compute the chunk that it corresponds to:
3384     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3385                                aligned_start + (nth_task+1)*chunk_size);
3386     // Try and bump the global finger via a CAS;
3387     // note that we need to do the global finger bump
3388     // _before_ taking the intersection below, because
3389     // the task corresponding to that region will be
3390     // deemed done even if the used_region() expands
3391     // because of allocation -- as it almost certainly will
3392     // during start-up while the threads yield in the
3393     // closure below.
3394     HeapWord* finger = span.end();
3395     bump_global_finger(finger);   // atomically
3396     // There are null tasks here corresponding to chunks
3397     // beyond the "top" address of the space.
3398     span = span.intersection(sp->used_region());
3399     if (!span.is_empty()) {  // Non-null task
3400       HeapWord* prev_obj;
3401       assert(!span.contains(_restart_addr) || nth_task == 0,
3402              "Inconsistency");
3403       if (nth_task == 0) {
3404         // For the 0th task, we'll not need to compute a block_start.
3405         if (span.contains(_restart_addr)) {
3406           // In the case of a restart because of stack overflow,
3407           // we might additionally skip a chunk prefix.
3408           prev_obj = _restart_addr;
3409         } else {
3410           prev_obj = span.start();
3411         }
3412       } else {
3413         // We want to skip the first object because
3414         // the protocol is to scan any object in its entirety
3415         // that _starts_ in this span; a fortiori, any
3416         // object starting in an earlier span is scanned
3417         // as part of an earlier claimed task.
3418         // Below we use the "careful" version of block_start
3419         // so we do not try to navigate uninitialized objects.
3420         prev_obj = sp->block_start_careful(span.start());
3421         // Below we use a variant of block_size that uses the
3422         // Printezis bits to avoid waiting for allocated
3423         // objects to become initialized/parsable.
3424         while (prev_obj < span.start()) {
3425           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3426           if (sz > 0) {
3427             prev_obj += sz;
3428           } else {
3429             // In this case we may end up doing a bit of redundant
3430             // scanning, but that appears unavoidable, short of
3431             // locking the free list locks; see bug 6324141.
3432             break;
3433           }
3434         }
3435       }
3436       if (prev_obj < span.end()) {
3437         MemRegion my_span = MemRegion(prev_obj, span.end());
3438         // Do the marking work within a non-empty span --
3439         // the last argument to the constructor indicates whether the
3440         // iteration should be incremental with periodic yields.
3441         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3442                                     &_collector->_markBitMap,
3443                                     work_queue(i),
3444                                     &_collector->_markStack);
3445         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3446       } // else nothing to do for this task
3447     }   // else nothing to do for this task
3448   }
3449   // We'd be tempted to assert here that since there are no
3450   // more tasks left to claim in this space, the global_finger
3451   // must exceed space->top() and a fortiori space->end(). However,
3452   // that would not quite be correct because the bumping of
3453   // global_finger occurs strictly after the claiming of a task,
3454   // so by the time we reach here the global finger may not yet
3455   // have been bumped up by the thread that claimed the last
3456   // task.
3457   pst->all_tasks_completed();
3458 }
3459 
3460 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3461  private:
3462   CMSCollector* _collector;
3463   CMSConcMarkingTask* _task;
3464   MemRegion     _span;
3465   CMSBitMap*    _bit_map;
3466   CMSMarkStack* _overflow_stack;
3467   OopTaskQueue* _work_queue;
3468  protected:
3469   DO_OOP_WORK_DEFN
3470  public:
3471   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3472                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3473     MetadataAwareOopClosure(collector->ref_processor()),
3474     _collector(collector),
3475     _task(task),
3476     _span(collector->_span),
3477     _work_queue(work_queue),
3478     _bit_map(bit_map),
3479     _overflow_stack(overflow_stack)
3480   { }
3481   virtual void do_oop(oop* p);
3482   virtual void do_oop(narrowOop* p);
3483 
3484   void trim_queue(size_t max);
3485   void handle_stack_overflow(HeapWord* lost);
3486   void do_yield_check() {
3487     if (_task->should_yield()) {
3488       _task->yield();
3489     }
3490   }
3491 };
3492 
3493 // Grey object scanning during work stealing phase --
3494 // the salient assumption here is that any references
3495 // that are in these stolen objects being scanned must
3496 // already have been initialized (else they would not have
3497 // been published), so we do not need to check for
3498 // uninitialized objects before pushing here.
3499 void Par_ConcMarkingClosure::do_oop(oop obj) {
3500   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3501   HeapWord* addr = (HeapWord*)obj;
3502   // Check if oop points into the CMS generation
3503   // and is not marked
3504   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3505     // a white object ...
3506     // If we manage to "claim" the object, by being the
3507     // first thread to mark it, then we push it on our
3508     // marking stack
3509     if (_bit_map->par_mark(addr)) {     // ... now grey
3510       // push on work queue (grey set)
3511       bool simulate_overflow = false;
3512       NOT_PRODUCT(
3513         if (CMSMarkStackOverflowALot &&
3514             _collector->simulate_overflow()) {
3515           // simulate a stack overflow
3516           simulate_overflow = true;
3517         }
3518       )
3519       if (simulate_overflow ||
3520           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3521         // stack overflow
3522         if (PrintCMSStatistics != 0) {
3523           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3524                                  SIZE_FORMAT, _overflow_stack->capacity());
3525         }
3526         // We cannot assert that the overflow stack is full because
3527         // it may have been emptied since.
3528         assert(simulate_overflow ||
3529                _work_queue->size() == _work_queue->max_elems(),
3530               "Else push should have succeeded");
3531         handle_stack_overflow(addr);
3532       }
3533     } // Else, some other thread got there first
3534     do_yield_check();
3535   }
3536 }
3537 
3538 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3539 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3540 
3541 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3542   while (_work_queue->size() > max) {
3543     oop new_oop;
3544     if (_work_queue->pop_local(new_oop)) {
3545       assert(new_oop->is_oop(), "Should be an oop");
3546       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3547       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3548       new_oop->oop_iterate(this);  // do_oop() above
3549       do_yield_check();
3550     }
3551   }
3552 }
3553 
3554 // Upon stack overflow, we discard (part of) the stack,
3555 // remembering the least address amongst those discarded
3556 // in CMSCollector's _restart_address.
3557 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3558   // We need to do this under a mutex to prevent other
3559   // workers from interfering with the work done below.
3560   MutexLockerEx ml(_overflow_stack->par_lock(),
3561                    Mutex::_no_safepoint_check_flag);
3562   // Remember the least grey address discarded
3563   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3564   _collector->lower_restart_addr(ra);
3565   _overflow_stack->reset();  // discard stack contents
3566   _overflow_stack->expand(); // expand the stack if possible
3567 }
3568 
3569 
3570 void CMSConcMarkingTask::do_work_steal(int i) {
3571   OopTaskQueue* work_q = work_queue(i);
3572   oop obj_to_scan;
3573   CMSBitMap* bm = &(_collector->_markBitMap);
3574   CMSMarkStack* ovflw = &(_collector->_markStack);
3575   int* seed = _collector->hash_seed(i);
3576   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3577   while (true) {
3578     cl.trim_queue(0);
3579     assert(work_q->size() == 0, "Should have been emptied above");
3580     if (get_work_from_overflow_stack(ovflw, work_q)) {
3581       // Can't assert below because the work obtained from the
3582       // overflow stack may already have been stolen from us.
3583       // assert(work_q->size() > 0, "Work from overflow stack");
3584       continue;
3585     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3586       assert(obj_to_scan->is_oop(), "Should be an oop");
3587       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3588       obj_to_scan->oop_iterate(&cl);
3589     } else if (terminator()->offer_termination(&_term_term)) {
3590       assert(work_q->size() == 0, "Impossible!");
3591       break;
3592     } else if (yielding() || should_yield()) {
3593       yield();
3594     }
3595   }
3596 }
3597 
3598 // This is run by the CMS (coordinator) thread.
3599 void CMSConcMarkingTask::coordinator_yield() {
3600   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3601          "CMS thread should hold CMS token");
3602   // First give up the locks, then yield, then re-lock
3603   // We should probably use a constructor/destructor idiom to
3604   // do this unlock/lock or modify the MutexUnlocker class to
3605   // serve our purpose. XXX
3606   assert_lock_strong(_bit_map_lock);
3607   _bit_map_lock->unlock();
3608   ConcurrentMarkSweepThread::desynchronize(true);
3609   _collector->stopTimer();
3610   if (PrintCMSStatistics != 0) {
3611     _collector->incrementYields();
3612   }
3613 
3614   // It is possible for whichever thread initiated the yield request
3615   // not to get a chance to wake up and take the bitmap lock between
3616   // this thread releasing it and reacquiring it. So, while the
3617   // should_yield() flag is on, let's sleep for a bit to give the
3618   // other thread a chance to wake up. The limit imposed on the number
3619   // of iterations is defensive, to avoid any unforseen circumstances
3620   // putting us into an infinite loop. Since it's always been this
3621   // (coordinator_yield()) method that was observed to cause the
3622   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3623   // which is by default non-zero. For the other seven methods that
3624   // also perform the yield operation, as are using a different
3625   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3626   // can enable the sleeping for those methods too, if necessary.
3627   // See 6442774.
3628   //
3629   // We really need to reconsider the synchronization between the GC
3630   // thread and the yield-requesting threads in the future and we
3631   // should really use wait/notify, which is the recommended
3632   // way of doing this type of interaction. Additionally, we should
3633   // consolidate the eight methods that do the yield operation and they
3634   // are almost identical into one for better maintainability and
3635   // readability. See 6445193.
3636   //
3637   // Tony 2006.06.29
3638   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3639                    ConcurrentMarkSweepThread::should_yield() &&
3640                    !CMSCollector::foregroundGCIsActive(); ++i) {
3641     os::sleep(Thread::current(), 1, false);
3642   }
3643 
3644   ConcurrentMarkSweepThread::synchronize(true);
3645   _bit_map_lock->lock_without_safepoint_check();
3646   _collector->startTimer();
3647 }
3648 
3649 bool CMSCollector::do_marking_mt() {
3650   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3651   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3652                                                                   conc_workers()->active_workers(),
3653                                                                   Threads::number_of_non_daemon_threads());
3654   conc_workers()->set_active_workers(num_workers);
3655 
3656   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3657 
3658   CMSConcMarkingTask tsk(this,
3659                          cms_space,
3660                          conc_workers(),
3661                          task_queues());
3662 
3663   // Since the actual number of workers we get may be different
3664   // from the number we requested above, do we need to do anything different
3665   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3666   // class?? XXX
3667   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3668 
3669   // Refs discovery is already non-atomic.
3670   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3671   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3672   conc_workers()->start_task(&tsk);
3673   while (tsk.yielded()) {
3674     tsk.coordinator_yield();
3675     conc_workers()->continue_task(&tsk);
3676   }
3677   // If the task was aborted, _restart_addr will be non-NULL
3678   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3679   while (_restart_addr != NULL) {
3680     // XXX For now we do not make use of ABORTED state and have not
3681     // yet implemented the right abort semantics (even in the original
3682     // single-threaded CMS case). That needs some more investigation
3683     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3684     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3685     // If _restart_addr is non-NULL, a marking stack overflow
3686     // occurred; we need to do a fresh marking iteration from the
3687     // indicated restart address.
3688     if (_foregroundGCIsActive) {
3689       // We may be running into repeated stack overflows, having
3690       // reached the limit of the stack size, while making very
3691       // slow forward progress. It may be best to bail out and
3692       // let the foreground collector do its job.
3693       // Clear _restart_addr, so that foreground GC
3694       // works from scratch. This avoids the headache of
3695       // a "rescan" which would otherwise be needed because
3696       // of the dirty mod union table & card table.
3697       _restart_addr = NULL;
3698       return false;
3699     }
3700     // Adjust the task to restart from _restart_addr
3701     tsk.reset(_restart_addr);
3702     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3703                   _restart_addr);
3704     _restart_addr = NULL;
3705     // Get the workers going again
3706     conc_workers()->start_task(&tsk);
3707     while (tsk.yielded()) {
3708       tsk.coordinator_yield();
3709       conc_workers()->continue_task(&tsk);
3710     }
3711   }
3712   assert(tsk.completed(), "Inconsistency");
3713   assert(tsk.result() == true, "Inconsistency");
3714   return true;
3715 }
3716 
3717 bool CMSCollector::do_marking_st() {
3718   ResourceMark rm;
3719   HandleMark   hm;
3720 
3721   // Temporarily make refs discovery single threaded (non-MT)
3722   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3723   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3724     &_markStack, CMSYield);
3725   // the last argument to iterate indicates whether the iteration
3726   // should be incremental with periodic yields.
3727   _markBitMap.iterate(&markFromRootsClosure);
3728   // If _restart_addr is non-NULL, a marking stack overflow
3729   // occurred; we need to do a fresh iteration from the
3730   // indicated restart address.
3731   while (_restart_addr != NULL) {
3732     if (_foregroundGCIsActive) {
3733       // We may be running into repeated stack overflows, having
3734       // reached the limit of the stack size, while making very
3735       // slow forward progress. It may be best to bail out and
3736       // let the foreground collector do its job.
3737       // Clear _restart_addr, so that foreground GC
3738       // works from scratch. This avoids the headache of
3739       // a "rescan" which would otherwise be needed because
3740       // of the dirty mod union table & card table.
3741       _restart_addr = NULL;
3742       return false;  // indicating failure to complete marking
3743     }
3744     // Deal with stack overflow:
3745     // we restart marking from _restart_addr
3746     HeapWord* ra = _restart_addr;
3747     markFromRootsClosure.reset(ra);
3748     _restart_addr = NULL;
3749     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3750   }
3751   return true;
3752 }
3753 
3754 void CMSCollector::preclean() {
3755   check_correct_thread_executing();
3756   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3757   verify_work_stacks_empty();
3758   verify_overflow_empty();
3759   _abort_preclean = false;
3760   if (CMSPrecleaningEnabled) {
3761     if (!CMSEdenChunksRecordAlways) {
3762       _eden_chunk_index = 0;
3763     }
3764     size_t used = get_eden_used();
3765     size_t capacity = get_eden_capacity();
3766     // Don't start sampling unless we will get sufficiently
3767     // many samples.
3768     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3769                 * CMSScheduleRemarkEdenPenetration)) {
3770       _start_sampling = true;
3771     } else {
3772       _start_sampling = false;
3773     }
3774     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3775     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3776     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3777   }
3778   CMSTokenSync x(true); // is cms thread
3779   if (CMSPrecleaningEnabled) {
3780     sample_eden();
3781     _collectorState = AbortablePreclean;
3782   } else {
3783     _collectorState = FinalMarking;
3784   }
3785   verify_work_stacks_empty();
3786   verify_overflow_empty();
3787 }
3788 
3789 // Try and schedule the remark such that young gen
3790 // occupancy is CMSScheduleRemarkEdenPenetration %.
3791 void CMSCollector::abortable_preclean() {
3792   check_correct_thread_executing();
3793   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3794   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3795 
3796   // If Eden's current occupancy is below this threshold,
3797   // immediately schedule the remark; else preclean
3798   // past the next scavenge in an effort to
3799   // schedule the pause as described above. By choosing
3800   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3801   // we will never do an actual abortable preclean cycle.
3802   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3803     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3804     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3805     // We need more smarts in the abortable preclean
3806     // loop below to deal with cases where allocation
3807     // in young gen is very very slow, and our precleaning
3808     // is running a losing race against a horde of
3809     // mutators intent on flooding us with CMS updates
3810     // (dirty cards).
3811     // One, admittedly dumb, strategy is to give up
3812     // after a certain number of abortable precleaning loops
3813     // or after a certain maximum time. We want to make
3814     // this smarter in the next iteration.
3815     // XXX FIX ME!!! YSR
3816     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3817     while (!(should_abort_preclean() ||
3818              ConcurrentMarkSweepThread::should_terminate())) {
3819       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3820       cumworkdone += workdone;
3821       loops++;
3822       // Voluntarily terminate abortable preclean phase if we have
3823       // been at it for too long.
3824       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3825           loops >= CMSMaxAbortablePrecleanLoops) {
3826         if (PrintGCDetails) {
3827           gclog_or_tty->print(" CMS: abort preclean due to loops ");
3828         }
3829         break;
3830       }
3831       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3832         if (PrintGCDetails) {
3833           gclog_or_tty->print(" CMS: abort preclean due to time ");
3834         }
3835         break;
3836       }
3837       // If we are doing little work each iteration, we should
3838       // take a short break.
3839       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3840         // Sleep for some time, waiting for work to accumulate
3841         stopTimer();
3842         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3843         startTimer();
3844         waited++;
3845       }
3846     }
3847     if (PrintCMSStatistics > 0) {
3848       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3849                           loops, waited, cumworkdone);
3850     }
3851   }
3852   CMSTokenSync x(true); // is cms thread
3853   if (_collectorState != Idling) {
3854     assert(_collectorState == AbortablePreclean,
3855            "Spontaneous state transition?");
3856     _collectorState = FinalMarking;
3857   } // Else, a foreground collection completed this CMS cycle.
3858   return;
3859 }
3860 
3861 // Respond to an Eden sampling opportunity
3862 void CMSCollector::sample_eden() {
3863   // Make sure a young gc cannot sneak in between our
3864   // reading and recording of a sample.
3865   assert(Thread::current()->is_ConcurrentGC_thread(),
3866          "Only the cms thread may collect Eden samples");
3867   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3868          "Should collect samples while holding CMS token");
3869   if (!_start_sampling) {
3870     return;
3871   }
3872   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3873   // is populated by the young generation.
3874   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3875     if (_eden_chunk_index < _eden_chunk_capacity) {
3876       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3877       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3878              "Unexpected state of Eden");
3879       // We'd like to check that what we just sampled is an oop-start address;
3880       // however, we cannot do that here since the object may not yet have been
3881       // initialized. So we'll instead do the check when we _use_ this sample
3882       // later.
3883       if (_eden_chunk_index == 0 ||
3884           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3885                          _eden_chunk_array[_eden_chunk_index-1])
3886            >= CMSSamplingGrain)) {
3887         _eden_chunk_index++;  // commit sample
3888       }
3889     }
3890   }
3891   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3892     size_t used = get_eden_used();
3893     size_t capacity = get_eden_capacity();
3894     assert(used <= capacity, "Unexpected state of Eden");
3895     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3896       _abort_preclean = true;
3897     }
3898   }
3899 }
3900 
3901 
3902 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3903   assert(_collectorState == Precleaning ||
3904          _collectorState == AbortablePreclean, "incorrect state");
3905   ResourceMark rm;
3906   HandleMark   hm;
3907 
3908   // Precleaning is currently not MT but the reference processor
3909   // may be set for MT.  Disable it temporarily here.
3910   ReferenceProcessor* rp = ref_processor();
3911   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3912 
3913   // Do one pass of scrubbing the discovered reference lists
3914   // to remove any reference objects with strongly-reachable
3915   // referents.
3916   if (clean_refs) {
3917     CMSPrecleanRefsYieldClosure yield_cl(this);
3918     assert(rp->span().equals(_span), "Spans should be equal");
3919     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3920                                    &_markStack, true /* preclean */);
3921     CMSDrainMarkingStackClosure complete_trace(this,
3922                                    _span, &_markBitMap, &_markStack,
3923                                    &keep_alive, true /* preclean */);
3924 
3925     // We don't want this step to interfere with a young
3926     // collection because we don't want to take CPU
3927     // or memory bandwidth away from the young GC threads
3928     // (which may be as many as there are CPUs).
3929     // Note that we don't need to protect ourselves from
3930     // interference with mutators because they can't
3931     // manipulate the discovered reference lists nor affect
3932     // the computed reachability of the referents, the
3933     // only properties manipulated by the precleaning
3934     // of these reference lists.
3935     stopTimer();
3936     CMSTokenSyncWithLocks x(true /* is cms thread */,
3937                             bitMapLock());
3938     startTimer();
3939     sample_eden();
3940 
3941     // The following will yield to allow foreground
3942     // collection to proceed promptly. XXX YSR:
3943     // The code in this method may need further
3944     // tweaking for better performance and some restructuring
3945     // for cleaner interfaces.
3946     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3947     rp->preclean_discovered_references(
3948           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3949           gc_timer, _gc_tracer_cm->gc_id());
3950   }
3951 
3952   if (clean_survivor) {  // preclean the active survivor space(s)
3953     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3954                              &_markBitMap, &_modUnionTable,
3955                              &_markStack, true /* precleaning phase */);
3956     stopTimer();
3957     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3958                              bitMapLock());
3959     startTimer();
3960     unsigned int before_count =
3961       GenCollectedHeap::heap()->total_collections();
3962     SurvivorSpacePrecleanClosure
3963       sss_cl(this, _span, &_markBitMap, &_markStack,
3964              &pam_cl, before_count, CMSYield);
3965     _young_gen->from()->object_iterate_careful(&sss_cl);
3966     _young_gen->to()->object_iterate_careful(&sss_cl);
3967   }
3968   MarkRefsIntoAndScanClosure
3969     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3970              &_markStack, this, CMSYield,
3971              true /* precleaning phase */);
3972   // CAUTION: The following closure has persistent state that may need to
3973   // be reset upon a decrease in the sequence of addresses it
3974   // processes.
3975   ScanMarkedObjectsAgainCarefullyClosure
3976     smoac_cl(this, _span,
3977       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3978 
3979   // Preclean dirty cards in ModUnionTable and CardTable using
3980   // appropriate convergence criterion;
3981   // repeat CMSPrecleanIter times unless we find that
3982   // we are losing.
3983   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3984   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3985          "Bad convergence multiplier");
3986   assert(CMSPrecleanThreshold >= 100,
3987          "Unreasonably low CMSPrecleanThreshold");
3988 
3989   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3990   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3991        numIter < CMSPrecleanIter;
3992        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3993     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3994     if (Verbose && PrintGCDetails) {
3995       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3996     }
3997     // Either there are very few dirty cards, so re-mark
3998     // pause will be small anyway, or our pre-cleaning isn't
3999     // that much faster than the rate at which cards are being
4000     // dirtied, so we might as well stop and re-mark since
4001     // precleaning won't improve our re-mark time by much.
4002     if (curNumCards <= CMSPrecleanThreshold ||
4003         (numIter > 0 &&
4004          (curNumCards * CMSPrecleanDenominator >
4005          lastNumCards * CMSPrecleanNumerator))) {
4006       numIter++;
4007       cumNumCards += curNumCards;
4008       break;
4009     }
4010   }
4011 
4012   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4013 
4014   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4015   cumNumCards += curNumCards;
4016   if (PrintGCDetails && PrintCMSStatistics != 0) {
4017     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4018                   curNumCards, cumNumCards, numIter);
4019   }
4020   return cumNumCards;   // as a measure of useful work done
4021 }
4022 
4023 // PRECLEANING NOTES:
4024 // Precleaning involves:
4025 // . reading the bits of the modUnionTable and clearing the set bits.
4026 // . For the cards corresponding to the set bits, we scan the
4027 //   objects on those cards. This means we need the free_list_lock
4028 //   so that we can safely iterate over the CMS space when scanning
4029 //   for oops.
4030 // . When we scan the objects, we'll be both reading and setting
4031 //   marks in the marking bit map, so we'll need the marking bit map.
4032 // . For protecting _collector_state transitions, we take the CGC_lock.
4033 //   Note that any races in the reading of of card table entries by the
4034 //   CMS thread on the one hand and the clearing of those entries by the
4035 //   VM thread or the setting of those entries by the mutator threads on the
4036 //   other are quite benign. However, for efficiency it makes sense to keep
4037 //   the VM thread from racing with the CMS thread while the latter is
4038 //   dirty card info to the modUnionTable. We therefore also use the
4039 //   CGC_lock to protect the reading of the card table and the mod union
4040 //   table by the CM thread.
4041 // . We run concurrently with mutator updates, so scanning
4042 //   needs to be done carefully  -- we should not try to scan
4043 //   potentially uninitialized objects.
4044 //
4045 // Locking strategy: While holding the CGC_lock, we scan over and
4046 // reset a maximal dirty range of the mod union / card tables, then lock
4047 // the free_list_lock and bitmap lock to do a full marking, then
4048 // release these locks; and repeat the cycle. This allows for a
4049 // certain amount of fairness in the sharing of these locks between
4050 // the CMS collector on the one hand, and the VM thread and the
4051 // mutators on the other.
4052 
4053 // NOTE: preclean_mod_union_table() and preclean_card_table()
4054 // further below are largely identical; if you need to modify
4055 // one of these methods, please check the other method too.
4056 
4057 size_t CMSCollector::preclean_mod_union_table(
4058   ConcurrentMarkSweepGeneration* gen,
4059   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4060   verify_work_stacks_empty();
4061   verify_overflow_empty();
4062 
4063   // strategy: starting with the first card, accumulate contiguous
4064   // ranges of dirty cards; clear these cards, then scan the region
4065   // covered by these cards.
4066 
4067   // Since all of the MUT is committed ahead, we can just use
4068   // that, in case the generations expand while we are precleaning.
4069   // It might also be fine to just use the committed part of the
4070   // generation, but we might potentially miss cards when the
4071   // generation is rapidly expanding while we are in the midst
4072   // of precleaning.
4073   HeapWord* startAddr = gen->reserved().start();
4074   HeapWord* endAddr   = gen->reserved().end();
4075 
4076   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4077 
4078   size_t numDirtyCards, cumNumDirtyCards;
4079   HeapWord *nextAddr, *lastAddr;
4080   for (cumNumDirtyCards = numDirtyCards = 0,
4081        nextAddr = lastAddr = startAddr;
4082        nextAddr < endAddr;
4083        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4084 
4085     ResourceMark rm;
4086     HandleMark   hm;
4087 
4088     MemRegion dirtyRegion;
4089     {
4090       stopTimer();
4091       // Potential yield point
4092       CMSTokenSync ts(true);
4093       startTimer();
4094       sample_eden();
4095       // Get dirty region starting at nextOffset (inclusive),
4096       // simultaneously clearing it.
4097       dirtyRegion =
4098         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4099       assert(dirtyRegion.start() >= nextAddr,
4100              "returned region inconsistent?");
4101     }
4102     // Remember where the next search should begin.
4103     // The returned region (if non-empty) is a right open interval,
4104     // so lastOffset is obtained from the right end of that
4105     // interval.
4106     lastAddr = dirtyRegion.end();
4107     // Should do something more transparent and less hacky XXX
4108     numDirtyCards =
4109       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4110 
4111     // We'll scan the cards in the dirty region (with periodic
4112     // yields for foreground GC as needed).
4113     if (!dirtyRegion.is_empty()) {
4114       assert(numDirtyCards > 0, "consistency check");
4115       HeapWord* stop_point = NULL;
4116       stopTimer();
4117       // Potential yield point
4118       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4119                                bitMapLock());
4120       startTimer();
4121       {
4122         verify_work_stacks_empty();
4123         verify_overflow_empty();
4124         sample_eden();
4125         stop_point =
4126           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4127       }
4128       if (stop_point != NULL) {
4129         // The careful iteration stopped early either because it found an
4130         // uninitialized object, or because we were in the midst of an
4131         // "abortable preclean", which should now be aborted. Redirty
4132         // the bits corresponding to the partially-scanned or unscanned
4133         // cards. We'll either restart at the next block boundary or
4134         // abort the preclean.
4135         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4136                "Should only be AbortablePreclean.");
4137         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4138         if (should_abort_preclean()) {
4139           break; // out of preclean loop
4140         } else {
4141           // Compute the next address at which preclean should pick up;
4142           // might need bitMapLock in order to read P-bits.
4143           lastAddr = next_card_start_after_block(stop_point);
4144         }
4145       }
4146     } else {
4147       assert(lastAddr == endAddr, "consistency check");
4148       assert(numDirtyCards == 0, "consistency check");
4149       break;
4150     }
4151   }
4152   verify_work_stacks_empty();
4153   verify_overflow_empty();
4154   return cumNumDirtyCards;
4155 }
4156 
4157 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4158 // below are largely identical; if you need to modify
4159 // one of these methods, please check the other method too.
4160 
4161 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4162   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4163   // strategy: it's similar to precleamModUnionTable above, in that
4164   // we accumulate contiguous ranges of dirty cards, mark these cards
4165   // precleaned, then scan the region covered by these cards.
4166   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4167   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4168 
4169   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4170 
4171   size_t numDirtyCards, cumNumDirtyCards;
4172   HeapWord *lastAddr, *nextAddr;
4173 
4174   for (cumNumDirtyCards = numDirtyCards = 0,
4175        nextAddr = lastAddr = startAddr;
4176        nextAddr < endAddr;
4177        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4178 
4179     ResourceMark rm;
4180     HandleMark   hm;
4181 
4182     MemRegion dirtyRegion;
4183     {
4184       // See comments in "Precleaning notes" above on why we
4185       // do this locking. XXX Could the locking overheads be
4186       // too high when dirty cards are sparse? [I don't think so.]
4187       stopTimer();
4188       CMSTokenSync x(true); // is cms thread
4189       startTimer();
4190       sample_eden();
4191       // Get and clear dirty region from card table
4192       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4193                                     MemRegion(nextAddr, endAddr),
4194                                     true,
4195                                     CardTableModRefBS::precleaned_card_val());
4196 
4197       assert(dirtyRegion.start() >= nextAddr,
4198              "returned region inconsistent?");
4199     }
4200     lastAddr = dirtyRegion.end();
4201     numDirtyCards =
4202       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4203 
4204     if (!dirtyRegion.is_empty()) {
4205       stopTimer();
4206       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4207       startTimer();
4208       sample_eden();
4209       verify_work_stacks_empty();
4210       verify_overflow_empty();
4211       HeapWord* stop_point =
4212         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4213       if (stop_point != NULL) {
4214         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4215                "Should only be AbortablePreclean.");
4216         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4217         if (should_abort_preclean()) {
4218           break; // out of preclean loop
4219         } else {
4220           // Compute the next address at which preclean should pick up.
4221           lastAddr = next_card_start_after_block(stop_point);
4222         }
4223       }
4224     } else {
4225       break;
4226     }
4227   }
4228   verify_work_stacks_empty();
4229   verify_overflow_empty();
4230   return cumNumDirtyCards;
4231 }
4232 
4233 class PrecleanKlassClosure : public KlassClosure {
4234   KlassToOopClosure _cm_klass_closure;
4235  public:
4236   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4237   void do_klass(Klass* k) {
4238     if (k->has_accumulated_modified_oops()) {
4239       k->clear_accumulated_modified_oops();
4240 
4241       _cm_klass_closure.do_klass(k);
4242     }
4243   }
4244 };
4245 
4246 // The freelist lock is needed to prevent asserts, is it really needed?
4247 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4248 
4249   cl->set_freelistLock(freelistLock);
4250 
4251   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4252 
4253   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4254   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4255   PrecleanKlassClosure preclean_klass_closure(cl);
4256   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4257 
4258   verify_work_stacks_empty();
4259   verify_overflow_empty();
4260 }
4261 
4262 void CMSCollector::checkpointRootsFinal() {
4263   assert(_collectorState == FinalMarking, "incorrect state transition?");
4264   check_correct_thread_executing();
4265   // world is stopped at this checkpoint
4266   assert(SafepointSynchronize::is_at_safepoint(),
4267          "world should be stopped");
4268   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4269 
4270   verify_work_stacks_empty();
4271   verify_overflow_empty();
4272 
4273   if (PrintGCDetails) {
4274     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4275                         _young_gen->used() / K,
4276                         _young_gen->capacity() / K);
4277   }
4278   {
4279     if (CMSScavengeBeforeRemark) {
4280       GenCollectedHeap* gch = GenCollectedHeap::heap();
4281       // Temporarily set flag to false, GCH->do_collection will
4282       // expect it to be false and set to true
4283       FlagSetting fl(gch->_is_gc_active, false);
4284       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4285         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4286       int level = _cmsGen->level() - 1;
4287       if (level >= 0) {
4288         gch->do_collection(true,        // full (i.e. force, see below)
4289                            false,       // !clear_all_soft_refs
4290                            0,           // size
4291                            false,       // is_tlab
4292                            level        // max_level
4293                           );
4294       }
4295     }
4296     FreelistLocker x(this);
4297     MutexLockerEx y(bitMapLock(),
4298                     Mutex::_no_safepoint_check_flag);
4299     checkpointRootsFinalWork();
4300   }
4301   verify_work_stacks_empty();
4302   verify_overflow_empty();
4303 }
4304 
4305 void CMSCollector::checkpointRootsFinalWork() {
4306   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4307 
4308   assert(haveFreelistLocks(), "must have free list locks");
4309   assert_lock_strong(bitMapLock());
4310 
4311   ResourceMark rm;
4312   HandleMark   hm;
4313 
4314   GenCollectedHeap* gch = GenCollectedHeap::heap();
4315 
4316   if (should_unload_classes()) {
4317     CodeCache::gc_prologue();
4318   }
4319   assert(haveFreelistLocks(), "must have free list locks");
4320   assert_lock_strong(bitMapLock());
4321 
4322   // We might assume that we need not fill TLAB's when
4323   // CMSScavengeBeforeRemark is set, because we may have just done
4324   // a scavenge which would have filled all TLAB's -- and besides
4325   // Eden would be empty. This however may not always be the case --
4326   // for instance although we asked for a scavenge, it may not have
4327   // happened because of a JNI critical section. We probably need
4328   // a policy for deciding whether we can in that case wait until
4329   // the critical section releases and then do the remark following
4330   // the scavenge, and skip it here. In the absence of that policy,
4331   // or of an indication of whether the scavenge did indeed occur,
4332   // we cannot rely on TLAB's having been filled and must do
4333   // so here just in case a scavenge did not happen.
4334   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4335   // Update the saved marks which may affect the root scans.
4336   gch->save_marks();
4337 
4338   if (CMSPrintEdenSurvivorChunks) {
4339     print_eden_and_survivor_chunk_arrays();
4340   }
4341 
4342   {
4343     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4344 
4345     // Note on the role of the mod union table:
4346     // Since the marker in "markFromRoots" marks concurrently with
4347     // mutators, it is possible for some reachable objects not to have been
4348     // scanned. For instance, an only reference to an object A was
4349     // placed in object B after the marker scanned B. Unless B is rescanned,
4350     // A would be collected. Such updates to references in marked objects
4351     // are detected via the mod union table which is the set of all cards
4352     // dirtied since the first checkpoint in this GC cycle and prior to
4353     // the most recent young generation GC, minus those cleaned up by the
4354     // concurrent precleaning.
4355     if (CMSParallelRemarkEnabled) {
4356       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4357       do_remark_parallel();
4358     } else {
4359       GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4360                   _gc_timer_cm, _gc_tracer_cm->gc_id());
4361       do_remark_non_parallel();
4362     }
4363   }
4364   verify_work_stacks_empty();
4365   verify_overflow_empty();
4366 
4367   {
4368     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4369     refProcessingWork();
4370   }
4371   verify_work_stacks_empty();
4372   verify_overflow_empty();
4373 
4374   if (should_unload_classes()) {
4375     CodeCache::gc_epilogue();
4376   }
4377   JvmtiExport::gc_epilogue();
4378 
4379   // If we encountered any (marking stack / work queue) overflow
4380   // events during the current CMS cycle, take appropriate
4381   // remedial measures, where possible, so as to try and avoid
4382   // recurrence of that condition.
4383   assert(_markStack.isEmpty(), "No grey objects");
4384   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4385                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4386   if (ser_ovflw > 0) {
4387     if (PrintCMSStatistics != 0) {
4388       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4389         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4390         ", kac_preclean="SIZE_FORMAT")",
4391         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4392         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4393     }
4394     _markStack.expand();
4395     _ser_pmc_remark_ovflw = 0;
4396     _ser_pmc_preclean_ovflw = 0;
4397     _ser_kac_preclean_ovflw = 0;
4398     _ser_kac_ovflw = 0;
4399   }
4400   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4401     if (PrintCMSStatistics != 0) {
4402       gclog_or_tty->print_cr("Work queue overflow (benign) "
4403         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4404         _par_pmc_remark_ovflw, _par_kac_ovflw);
4405     }
4406     _par_pmc_remark_ovflw = 0;
4407     _par_kac_ovflw = 0;
4408   }
4409   if (PrintCMSStatistics != 0) {
4410      if (_markStack._hit_limit > 0) {
4411        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4412                               _markStack._hit_limit);
4413      }
4414      if (_markStack._failed_double > 0) {
4415        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4416                               " current capacity "SIZE_FORMAT,
4417                               _markStack._failed_double,
4418                               _markStack.capacity());
4419      }
4420   }
4421   _markStack._hit_limit = 0;
4422   _markStack._failed_double = 0;
4423 
4424   if ((VerifyAfterGC || VerifyDuringGC) &&
4425       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4426     verify_after_remark();
4427   }
4428 
4429   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4430 
4431   // Change under the freelistLocks.
4432   _collectorState = Sweeping;
4433   // Call isAllClear() under bitMapLock
4434   assert(_modUnionTable.isAllClear(),
4435       "Should be clear by end of the final marking");
4436   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4437       "Should be clear by end of the final marking");
4438 }
4439 
4440 void CMSParInitialMarkTask::work(uint worker_id) {
4441   elapsedTimer _timer;
4442   ResourceMark rm;
4443   HandleMark   hm;
4444 
4445   // ---------- scan from roots --------------
4446   _timer.start();
4447   GenCollectedHeap* gch = GenCollectedHeap::heap();
4448   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4449 
4450   // ---------- young gen roots --------------
4451   {
4452     work_on_young_gen_roots(worker_id, &par_mri_cl);
4453     _timer.stop();
4454     if (PrintCMSStatistics != 0) {
4455       gclog_or_tty->print_cr(
4456         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4457         worker_id, _timer.seconds());
4458     }
4459   }
4460 
4461   // ---------- remaining roots --------------
4462   _timer.reset();
4463   _timer.start();
4464 
4465   CLDToOopClosure cld_closure(&par_mri_cl, true);
4466 
4467   gch->gen_process_roots(_strong_roots_scope,
4468                          _collector->_cmsGen->level(),
4469                          false,     // yg was scanned above

4470                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4471                          _collector->should_unload_classes(),
4472                          &par_mri_cl,
4473                          NULL,
4474                          &cld_closure);
4475   assert(_collector->should_unload_classes()
4476          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4477          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4478   _timer.stop();
4479   if (PrintCMSStatistics != 0) {
4480     gclog_or_tty->print_cr(
4481       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4482       worker_id, _timer.seconds());
4483   }
4484 }
4485 
4486 // Parallel remark task
4487 class CMSParRemarkTask: public CMSParMarkTask {
4488   CompactibleFreeListSpace* _cms_space;
4489 
4490   // The per-thread work queues, available here for stealing.
4491   OopTaskQueueSet*       _task_queues;
4492   ParallelTaskTerminator _term;
4493   StrongRootsScope*      _strong_roots_scope;
4494 
4495  public:
4496   // A value of 0 passed to n_workers will cause the number of
4497   // workers to be taken from the active workers in the work gang.
4498   CMSParRemarkTask(CMSCollector* collector,
4499                    CompactibleFreeListSpace* cms_space,
4500                    uint n_workers, FlexibleWorkGang* workers,
4501                    OopTaskQueueSet* task_queues,
4502                    StrongRootsScope* strong_roots_scope):
4503     CMSParMarkTask("Rescan roots and grey objects in parallel",
4504                    collector, n_workers),
4505     _cms_space(cms_space),
4506     _task_queues(task_queues),
4507     _term(n_workers, task_queues),
4508     _strong_roots_scope(strong_roots_scope) { }
4509 
4510   OopTaskQueueSet* task_queues() { return _task_queues; }
4511 
4512   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4513 
4514   ParallelTaskTerminator* terminator() { return &_term; }
4515   uint n_workers() { return _n_workers; }
4516 
4517   void work(uint worker_id);
4518 
4519  private:
4520   // ... of  dirty cards in old space
4521   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4522                                   Par_MarkRefsIntoAndScanClosure* cl);
4523 
4524   // ... work stealing for the above
4525   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4526 };
4527 
4528 class RemarkKlassClosure : public KlassClosure {
4529   KlassToOopClosure _cm_klass_closure;
4530  public:
4531   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4532   void do_klass(Klass* k) {
4533     // Check if we have modified any oops in the Klass during the concurrent marking.
4534     if (k->has_accumulated_modified_oops()) {
4535       k->clear_accumulated_modified_oops();
4536 
4537       // We could have transfered the current modified marks to the accumulated marks,
4538       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4539     } else if (k->has_modified_oops()) {
4540       // Don't clear anything, this info is needed by the next young collection.
4541     } else {
4542       // No modified oops in the Klass.
4543       return;
4544     }
4545 
4546     // The klass has modified fields, need to scan the klass.
4547     _cm_klass_closure.do_klass(k);
4548   }
4549 };
4550 
4551 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4552   ParNewGeneration* young_gen = _collector->_young_gen;
4553   ContiguousSpace* eden_space = young_gen->eden();
4554   ContiguousSpace* from_space = young_gen->from();
4555   ContiguousSpace* to_space   = young_gen->to();
4556 
4557   HeapWord** eca = _collector->_eden_chunk_array;
4558   size_t     ect = _collector->_eden_chunk_index;
4559   HeapWord** sca = _collector->_survivor_chunk_array;
4560   size_t     sct = _collector->_survivor_chunk_index;
4561 
4562   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4563   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4564 
4565   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4566   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4567   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4568 }
4569 
4570 // work_queue(i) is passed to the closure
4571 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4572 // also is passed to do_dirty_card_rescan_tasks() and to
4573 // do_work_steal() to select the i-th task_queue.
4574 
4575 void CMSParRemarkTask::work(uint worker_id) {
4576   elapsedTimer _timer;
4577   ResourceMark rm;
4578   HandleMark   hm;
4579 
4580   // ---------- rescan from roots --------------
4581   _timer.start();
4582   GenCollectedHeap* gch = GenCollectedHeap::heap();
4583   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4584     _collector->_span, _collector->ref_processor(),
4585     &(_collector->_markBitMap),
4586     work_queue(worker_id));
4587 
4588   // Rescan young gen roots first since these are likely
4589   // coarsely partitioned and may, on that account, constitute
4590   // the critical path; thus, it's best to start off that
4591   // work first.
4592   // ---------- young gen roots --------------
4593   {
4594     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4595     _timer.stop();
4596     if (PrintCMSStatistics != 0) {
4597       gclog_or_tty->print_cr(
4598         "Finished young gen rescan work in %dth thread: %3.3f sec",
4599         worker_id, _timer.seconds());
4600     }
4601   }
4602 
4603   // ---------- remaining roots --------------
4604   _timer.reset();
4605   _timer.start();
4606   gch->gen_process_roots(_strong_roots_scope,
4607                          _collector->_cmsGen->level(),
4608                          false,     // yg was scanned above

4609                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4610                          _collector->should_unload_classes(),
4611                          &par_mrias_cl,
4612                          NULL,
4613                          NULL);     // The dirty klasses will be handled below
4614 
4615   assert(_collector->should_unload_classes()
4616          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4617          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4618   _timer.stop();
4619   if (PrintCMSStatistics != 0) {
4620     gclog_or_tty->print_cr(
4621       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4622       worker_id, _timer.seconds());
4623   }
4624 
4625   // ---------- unhandled CLD scanning ----------
4626   if (worker_id == 0) { // Single threaded at the moment.
4627     _timer.reset();
4628     _timer.start();
4629 
4630     // Scan all new class loader data objects and new dependencies that were
4631     // introduced during concurrent marking.
4632     ResourceMark rm;
4633     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4634     for (int i = 0; i < array->length(); i++) {
4635       par_mrias_cl.do_class_loader_data(array->at(i));
4636     }
4637 
4638     // We don't need to keep track of new CLDs anymore.
4639     ClassLoaderDataGraph::remember_new_clds(false);
4640 
4641     _timer.stop();
4642     if (PrintCMSStatistics != 0) {
4643       gclog_or_tty->print_cr(
4644           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4645           worker_id, _timer.seconds());
4646     }
4647   }
4648 
4649   // ---------- dirty klass scanning ----------
4650   if (worker_id == 0) { // Single threaded at the moment.
4651     _timer.reset();
4652     _timer.start();
4653 
4654     // Scan all classes that was dirtied during the concurrent marking phase.
4655     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4656     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4657 
4658     _timer.stop();
4659     if (PrintCMSStatistics != 0) {
4660       gclog_or_tty->print_cr(
4661           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4662           worker_id, _timer.seconds());
4663     }
4664   }
4665 
4666   // We might have added oops to ClassLoaderData::_handles during the
4667   // concurrent marking phase. These oops point to newly allocated objects
4668   // that are guaranteed to be kept alive. Either by the direct allocation
4669   // code, or when the young collector processes the roots. Hence,
4670   // we don't have to revisit the _handles block during the remark phase.
4671 
4672   // ---------- rescan dirty cards ------------
4673   _timer.reset();
4674   _timer.start();
4675 
4676   // Do the rescan tasks for each of the two spaces
4677   // (cms_space) in turn.
4678   // "worker_id" is passed to select the task_queue for "worker_id"
4679   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4680   _timer.stop();
4681   if (PrintCMSStatistics != 0) {
4682     gclog_or_tty->print_cr(
4683       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4684       worker_id, _timer.seconds());
4685   }
4686 
4687   // ---------- steal work from other threads ...
4688   // ---------- ... and drain overflow list.
4689   _timer.reset();
4690   _timer.start();
4691   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4692   _timer.stop();
4693   if (PrintCMSStatistics != 0) {
4694     gclog_or_tty->print_cr(
4695       "Finished work stealing in %dth thread: %3.3f sec",
4696       worker_id, _timer.seconds());
4697   }
4698 }
4699 
4700 // Note that parameter "i" is not used.
4701 void
4702 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4703   OopsInGenClosure* cl, ContiguousSpace* space,
4704   HeapWord** chunk_array, size_t chunk_top) {
4705   // Until all tasks completed:
4706   // . claim an unclaimed task
4707   // . compute region boundaries corresponding to task claimed
4708   //   using chunk_array
4709   // . par_oop_iterate(cl) over that region
4710 
4711   ResourceMark rm;
4712   HandleMark   hm;
4713 
4714   SequentialSubTasksDone* pst = space->par_seq_tasks();
4715 
4716   uint nth_task = 0;
4717   uint n_tasks  = pst->n_tasks();
4718 
4719   if (n_tasks > 0) {
4720     assert(pst->valid(), "Uninitialized use?");
4721     HeapWord *start, *end;
4722     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4723       // We claimed task # nth_task; compute its boundaries.
4724       if (chunk_top == 0) {  // no samples were taken
4725         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4726         start = space->bottom();
4727         end   = space->top();
4728       } else if (nth_task == 0) {
4729         start = space->bottom();
4730         end   = chunk_array[nth_task];
4731       } else if (nth_task < (uint)chunk_top) {
4732         assert(nth_task >= 1, "Control point invariant");
4733         start = chunk_array[nth_task - 1];
4734         end   = chunk_array[nth_task];
4735       } else {
4736         assert(nth_task == (uint)chunk_top, "Control point invariant");
4737         start = chunk_array[chunk_top - 1];
4738         end   = space->top();
4739       }
4740       MemRegion mr(start, end);
4741       // Verify that mr is in space
4742       assert(mr.is_empty() || space->used_region().contains(mr),
4743              "Should be in space");
4744       // Verify that "start" is an object boundary
4745       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4746              "Should be an oop");
4747       space->par_oop_iterate(mr, cl);
4748     }
4749     pst->all_tasks_completed();
4750   }
4751 }
4752 
4753 void
4754 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4755   CompactibleFreeListSpace* sp, int i,
4756   Par_MarkRefsIntoAndScanClosure* cl) {
4757   // Until all tasks completed:
4758   // . claim an unclaimed task
4759   // . compute region boundaries corresponding to task claimed
4760   // . transfer dirty bits ct->mut for that region
4761   // . apply rescanclosure to dirty mut bits for that region
4762 
4763   ResourceMark rm;
4764   HandleMark   hm;
4765 
4766   OopTaskQueue* work_q = work_queue(i);
4767   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4768   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4769   // CAUTION: This closure has state that persists across calls to
4770   // the work method dirty_range_iterate_clear() in that it has
4771   // embedded in it a (subtype of) UpwardsObjectClosure. The
4772   // use of that state in the embedded UpwardsObjectClosure instance
4773   // assumes that the cards are always iterated (even if in parallel
4774   // by several threads) in monotonically increasing order per each
4775   // thread. This is true of the implementation below which picks
4776   // card ranges (chunks) in monotonically increasing order globally
4777   // and, a-fortiori, in monotonically increasing order per thread
4778   // (the latter order being a subsequence of the former).
4779   // If the work code below is ever reorganized into a more chaotic
4780   // work-partitioning form than the current "sequential tasks"
4781   // paradigm, the use of that persistent state will have to be
4782   // revisited and modified appropriately. See also related
4783   // bug 4756801 work on which should examine this code to make
4784   // sure that the changes there do not run counter to the
4785   // assumptions made here and necessary for correctness and
4786   // efficiency. Note also that this code might yield inefficient
4787   // behavior in the case of very large objects that span one or
4788   // more work chunks. Such objects would potentially be scanned
4789   // several times redundantly. Work on 4756801 should try and
4790   // address that performance anomaly if at all possible. XXX
4791   MemRegion  full_span  = _collector->_span;
4792   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4793   MarkFromDirtyCardsClosure
4794     greyRescanClosure(_collector, full_span, // entire span of interest
4795                       sp, bm, work_q, cl);
4796 
4797   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4798   assert(pst->valid(), "Uninitialized use?");
4799   uint nth_task = 0;
4800   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4801   MemRegion span = sp->used_region();
4802   HeapWord* start_addr = span.start();
4803   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4804                                            alignment);
4805   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4806   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4807          start_addr, "Check alignment");
4808   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4809          chunk_size, "Check alignment");
4810 
4811   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4812     // Having claimed the nth_task, compute corresponding mem-region,
4813     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4814     // The alignment restriction ensures that we do not need any
4815     // synchronization with other gang-workers while setting or
4816     // clearing bits in thus chunk of the MUT.
4817     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4818                                     start_addr + (nth_task+1)*chunk_size);
4819     // The last chunk's end might be way beyond end of the
4820     // used region. In that case pull back appropriately.
4821     if (this_span.end() > end_addr) {
4822       this_span.set_end(end_addr);
4823       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4824     }
4825     // Iterate over the dirty cards covering this chunk, marking them
4826     // precleaned, and setting the corresponding bits in the mod union
4827     // table. Since we have been careful to partition at Card and MUT-word
4828     // boundaries no synchronization is needed between parallel threads.
4829     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4830                                                  &modUnionClosure);
4831 
4832     // Having transferred these marks into the modUnionTable,
4833     // rescan the marked objects on the dirty cards in the modUnionTable.
4834     // Even if this is at a synchronous collection, the initial marking
4835     // may have been done during an asynchronous collection so there
4836     // may be dirty bits in the mod-union table.
4837     _collector->_modUnionTable.dirty_range_iterate_clear(
4838                   this_span, &greyRescanClosure);
4839     _collector->_modUnionTable.verifyNoOneBitsInRange(
4840                                  this_span.start(),
4841                                  this_span.end());
4842   }
4843   pst->all_tasks_completed();  // declare that i am done
4844 }
4845 
4846 // . see if we can share work_queues with ParNew? XXX
4847 void
4848 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4849                                 int* seed) {
4850   OopTaskQueue* work_q = work_queue(i);
4851   NOT_PRODUCT(int num_steals = 0;)
4852   oop obj_to_scan;
4853   CMSBitMap* bm = &(_collector->_markBitMap);
4854 
4855   while (true) {
4856     // Completely finish any left over work from (an) earlier round(s)
4857     cl->trim_queue(0);
4858     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4859                                          (size_t)ParGCDesiredObjsFromOverflowList);
4860     // Now check if there's any work in the overflow list
4861     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4862     // only affects the number of attempts made to get work from the
4863     // overflow list and does not affect the number of workers.  Just
4864     // pass ParallelGCThreads so this behavior is unchanged.
4865     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4866                                                 work_q,
4867                                                 ParallelGCThreads)) {
4868       // found something in global overflow list;
4869       // not yet ready to go stealing work from others.
4870       // We'd like to assert(work_q->size() != 0, ...)
4871       // because we just took work from the overflow list,
4872       // but of course we can't since all of that could have
4873       // been already stolen from us.
4874       // "He giveth and He taketh away."
4875       continue;
4876     }
4877     // Verify that we have no work before we resort to stealing
4878     assert(work_q->size() == 0, "Have work, shouldn't steal");
4879     // Try to steal from other queues that have work
4880     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4881       NOT_PRODUCT(num_steals++;)
4882       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4883       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4884       // Do scanning work
4885       obj_to_scan->oop_iterate(cl);
4886       // Loop around, finish this work, and try to steal some more
4887     } else if (terminator()->offer_termination()) {
4888         break;  // nirvana from the infinite cycle
4889     }
4890   }
4891   NOT_PRODUCT(
4892     if (PrintCMSStatistics != 0) {
4893       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4894     }
4895   )
4896   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4897          "Else our work is not yet done");
4898 }
4899 
4900 // Record object boundaries in _eden_chunk_array by sampling the eden
4901 // top in the slow-path eden object allocation code path and record
4902 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4903 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4904 // sampling in sample_eden() that activates during the part of the
4905 // preclean phase.
4906 void CMSCollector::sample_eden_chunk() {
4907   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4908     if (_eden_chunk_lock->try_lock()) {
4909       // Record a sample. This is the critical section. The contents
4910       // of the _eden_chunk_array have to be non-decreasing in the
4911       // address order.
4912       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4913       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4914              "Unexpected state of Eden");
4915       if (_eden_chunk_index == 0 ||
4916           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4917            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4918                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4919         _eden_chunk_index++;  // commit sample
4920       }
4921       _eden_chunk_lock->unlock();
4922     }
4923   }
4924 }
4925 
4926 // Return a thread-local PLAB recording array, as appropriate.
4927 void* CMSCollector::get_data_recorder(int thr_num) {
4928   if (_survivor_plab_array != NULL &&
4929       (CMSPLABRecordAlways ||
4930        (_collectorState > Marking && _collectorState < FinalMarking))) {
4931     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4932     ChunkArray* ca = &_survivor_plab_array[thr_num];
4933     ca->reset();   // clear it so that fresh data is recorded
4934     return (void*) ca;
4935   } else {
4936     return NULL;
4937   }
4938 }
4939 
4940 // Reset all the thread-local PLAB recording arrays
4941 void CMSCollector::reset_survivor_plab_arrays() {
4942   for (uint i = 0; i < ParallelGCThreads; i++) {
4943     _survivor_plab_array[i].reset();
4944   }
4945 }
4946 
4947 // Merge the per-thread plab arrays into the global survivor chunk
4948 // array which will provide the partitioning of the survivor space
4949 // for CMS initial scan and rescan.
4950 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4951                                               int no_of_gc_threads) {
4952   assert(_survivor_plab_array  != NULL, "Error");
4953   assert(_survivor_chunk_array != NULL, "Error");
4954   assert(_collectorState == FinalMarking ||
4955          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4956   for (int j = 0; j < no_of_gc_threads; j++) {
4957     _cursor[j] = 0;
4958   }
4959   HeapWord* top = surv->top();
4960   size_t i;
4961   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4962     HeapWord* min_val = top;          // Higher than any PLAB address
4963     uint      min_tid = 0;            // position of min_val this round
4964     for (int j = 0; j < no_of_gc_threads; j++) {
4965       ChunkArray* cur_sca = &_survivor_plab_array[j];
4966       if (_cursor[j] == cur_sca->end()) {
4967         continue;
4968       }
4969       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4970       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4971       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4972       if (cur_val < min_val) {
4973         min_tid = j;
4974         min_val = cur_val;
4975       } else {
4976         assert(cur_val < top, "All recorded addresses should be less");
4977       }
4978     }
4979     // At this point min_val and min_tid are respectively
4980     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4981     // and the thread (j) that witnesses that address.
4982     // We record this address in the _survivor_chunk_array[i]
4983     // and increment _cursor[min_tid] prior to the next round i.
4984     if (min_val == top) {
4985       break;
4986     }
4987     _survivor_chunk_array[i] = min_val;
4988     _cursor[min_tid]++;
4989   }
4990   // We are all done; record the size of the _survivor_chunk_array
4991   _survivor_chunk_index = i; // exclusive: [0, i)
4992   if (PrintCMSStatistics > 0) {
4993     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4994   }
4995   // Verify that we used up all the recorded entries
4996   #ifdef ASSERT
4997     size_t total = 0;
4998     for (int j = 0; j < no_of_gc_threads; j++) {
4999       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5000       total += _cursor[j];
5001     }
5002     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5003     // Check that the merged array is in sorted order
5004     if (total > 0) {
5005       for (size_t i = 0; i < total - 1; i++) {
5006         if (PrintCMSStatistics > 0) {
5007           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5008                               i, p2i(_survivor_chunk_array[i]));
5009         }
5010         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5011                "Not sorted");
5012       }
5013     }
5014   #endif // ASSERT
5015 }
5016 
5017 // Set up the space's par_seq_tasks structure for work claiming
5018 // for parallel initial scan and rescan of young gen.
5019 // See ParRescanTask where this is currently used.
5020 void
5021 CMSCollector::
5022 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5023   assert(n_threads > 0, "Unexpected n_threads argument");
5024 
5025   // Eden space
5026   if (!_young_gen->eden()->is_empty()) {
5027     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5028     assert(!pst->valid(), "Clobbering existing data?");
5029     // Each valid entry in [0, _eden_chunk_index) represents a task.
5030     size_t n_tasks = _eden_chunk_index + 1;
5031     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5032     // Sets the condition for completion of the subtask (how many threads
5033     // need to finish in order to be done).
5034     pst->set_n_threads(n_threads);
5035     pst->set_n_tasks((int)n_tasks);
5036   }
5037 
5038   // Merge the survivor plab arrays into _survivor_chunk_array
5039   if (_survivor_plab_array != NULL) {
5040     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5041   } else {
5042     assert(_survivor_chunk_index == 0, "Error");
5043   }
5044 
5045   // To space
5046   {
5047     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5048     assert(!pst->valid(), "Clobbering existing data?");
5049     // Sets the condition for completion of the subtask (how many threads
5050     // need to finish in order to be done).
5051     pst->set_n_threads(n_threads);
5052     pst->set_n_tasks(1);
5053     assert(pst->valid(), "Error");
5054   }
5055 
5056   // From space
5057   {
5058     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5059     assert(!pst->valid(), "Clobbering existing data?");
5060     size_t n_tasks = _survivor_chunk_index + 1;
5061     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5062     // Sets the condition for completion of the subtask (how many threads
5063     // need to finish in order to be done).
5064     pst->set_n_threads(n_threads);
5065     pst->set_n_tasks((int)n_tasks);
5066     assert(pst->valid(), "Error");
5067   }
5068 }
5069 
5070 // Parallel version of remark
5071 void CMSCollector::do_remark_parallel() {
5072   GenCollectedHeap* gch = GenCollectedHeap::heap();
5073   FlexibleWorkGang* workers = gch->workers();
5074   assert(workers != NULL, "Need parallel worker threads.");
5075   // Choose to use the number of GC workers most recently set
5076   // into "active_workers".  If active_workers is not set, set it
5077   // to ParallelGCThreads.
5078   uint n_workers = workers->active_workers();
5079   if (n_workers == 0) {
5080     assert(n_workers > 0, "Should have been set during scavenge");
5081     n_workers = ParallelGCThreads;
5082     workers->set_active_workers(n_workers);
5083   }
5084   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5085 
5086   StrongRootsScope srs(n_workers);
5087 
5088   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5089 
5090   // Set up for parallel process_roots work.
5091   gch->set_par_threads(n_workers);
5092   // We won't be iterating over the cards in the card table updating
5093   // the younger_gen cards, so we shouldn't call the following else
5094   // the verification code as well as subsequent younger_refs_iterate
5095   // code would get confused. XXX
5096   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5097 
5098   // The young gen rescan work will not be done as part of
5099   // process_roots (which currently doesn't know how to
5100   // parallelize such a scan), but rather will be broken up into
5101   // a set of parallel tasks (via the sampling that the [abortable]
5102   // preclean phase did of eden, plus the [two] tasks of
5103   // scanning the [two] survivor spaces. Further fine-grain
5104   // parallelization of the scanning of the survivor spaces
5105   // themselves, and of precleaning of the younger gen itself
5106   // is deferred to the future.
5107   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5108 
5109   // The dirty card rescan work is broken up into a "sequence"
5110   // of parallel tasks (per constituent space) that are dynamically
5111   // claimed by the parallel threads.
5112   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5113 
5114   // It turns out that even when we're using 1 thread, doing the work in a
5115   // separate thread causes wide variance in run times.  We can't help this
5116   // in the multi-threaded case, but we special-case n=1 here to get
5117   // repeatable measurements of the 1-thread overhead of the parallel code.
5118   if (n_workers > 1) {
5119     // Make refs discovery MT-safe, if it isn't already: it may not
5120     // necessarily be so, since it's possible that we are doing
5121     // ST marking.
5122     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);

5123     workers->run_task(&tsk);
5124   } else {
5125     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);

5126     tsk.work(0);
5127   }
5128 
5129   gch->set_par_threads(0);  // 0 ==> non-parallel.
5130   // restore, single-threaded for now, any preserved marks
5131   // as a result of work_q overflow
5132   restore_preserved_marks_if_any();
5133 }
5134 
5135 // Non-parallel version of remark
5136 void CMSCollector::do_remark_non_parallel() {
5137   ResourceMark rm;
5138   HandleMark   hm;
5139   GenCollectedHeap* gch = GenCollectedHeap::heap();
5140   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5141 
5142   MarkRefsIntoAndScanClosure
5143     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5144              &_markStack, this,
5145              false /* should_yield */, false /* not precleaning */);
5146   MarkFromDirtyCardsClosure
5147     markFromDirtyCardsClosure(this, _span,
5148                               NULL,  // space is set further below
5149                               &_markBitMap, &_markStack, &mrias_cl);
5150   {
5151     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5152     // Iterate over the dirty cards, setting the corresponding bits in the
5153     // mod union table.
5154     {
5155       ModUnionClosure modUnionClosure(&_modUnionTable);
5156       _ct->ct_bs()->dirty_card_iterate(
5157                       _cmsGen->used_region(),
5158                       &modUnionClosure);
5159     }
5160     // Having transferred these marks into the modUnionTable, we just need
5161     // to rescan the marked objects on the dirty cards in the modUnionTable.
5162     // The initial marking may have been done during an asynchronous
5163     // collection so there may be dirty bits in the mod-union table.
5164     const int alignment =
5165       CardTableModRefBS::card_size * BitsPerWord;
5166     {
5167       // ... First handle dirty cards in CMS gen
5168       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5169       MemRegion ur = _cmsGen->used_region();
5170       HeapWord* lb = ur.start();
5171       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5172       MemRegion cms_span(lb, ub);
5173       _modUnionTable.dirty_range_iterate_clear(cms_span,
5174                                                &markFromDirtyCardsClosure);
5175       verify_work_stacks_empty();
5176       if (PrintCMSStatistics != 0) {
5177         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5178           markFromDirtyCardsClosure.num_dirty_cards());
5179       }
5180     }
5181   }
5182   if (VerifyDuringGC &&
5183       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5184     HandleMark hm;  // Discard invalid handles created during verification
5185     Universe::verify();
5186   }
5187   {
5188     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5189 
5190     verify_work_stacks_empty();
5191 
5192     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5193     StrongRootsScope srs(1);
5194 
5195     gch->gen_process_roots(&srs,
5196                            _cmsGen->level(),
5197                            true,  // younger gens as roots

5198                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
5199                            should_unload_classes(),
5200                            &mrias_cl,
5201                            NULL,
5202                            NULL); // The dirty klasses will be handled below
5203 
5204     assert(should_unload_classes()
5205            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5206            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5207   }
5208 
5209   {
5210     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5211 
5212     verify_work_stacks_empty();
5213 
5214     // Scan all class loader data objects that might have been introduced
5215     // during concurrent marking.
5216     ResourceMark rm;
5217     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5218     for (int i = 0; i < array->length(); i++) {
5219       mrias_cl.do_class_loader_data(array->at(i));
5220     }
5221 
5222     // We don't need to keep track of new CLDs anymore.
5223     ClassLoaderDataGraph::remember_new_clds(false);
5224 
5225     verify_work_stacks_empty();
5226   }
5227 
5228   {
5229     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5230 
5231     verify_work_stacks_empty();
5232 
5233     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5234     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5235 
5236     verify_work_stacks_empty();
5237   }
5238 
5239   // We might have added oops to ClassLoaderData::_handles during the
5240   // concurrent marking phase. These oops point to newly allocated objects
5241   // that are guaranteed to be kept alive. Either by the direct allocation
5242   // code, or when the young collector processes the roots. Hence,
5243   // we don't have to revisit the _handles block during the remark phase.
5244 
5245   verify_work_stacks_empty();
5246   // Restore evacuated mark words, if any, used for overflow list links
5247   if (!CMSOverflowEarlyRestoration) {
5248     restore_preserved_marks_if_any();
5249   }
5250   verify_overflow_empty();
5251 }
5252 
5253 ////////////////////////////////////////////////////////
5254 // Parallel Reference Processing Task Proxy Class
5255 ////////////////////////////////////////////////////////
5256 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5257   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5258   CMSCollector*          _collector;
5259   CMSBitMap*             _mark_bit_map;
5260   const MemRegion        _span;
5261   ProcessTask&           _task;
5262 
5263 public:
5264   CMSRefProcTaskProxy(ProcessTask&     task,
5265                       CMSCollector*    collector,
5266                       const MemRegion& span,
5267                       CMSBitMap*       mark_bit_map,
5268                       AbstractWorkGang* workers,
5269                       OopTaskQueueSet* task_queues):
5270     // XXX Should superclass AGTWOQ also know about AWG since it knows
5271     // about the task_queues used by the AWG? Then it could initialize
5272     // the terminator() object. See 6984287. The set_for_termination()
5273     // below is a temporary band-aid for the regression in 6984287.
5274     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5275       task_queues),
5276     _task(task),
5277     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5278   {
5279     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5280            "Inconsistency in _span");
5281     set_for_termination(workers->active_workers());
5282   }
5283 
5284   OopTaskQueueSet* task_queues() { return queues(); }
5285 
5286   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5287 
5288   void do_work_steal(int i,
5289                      CMSParDrainMarkingStackClosure* drain,
5290                      CMSParKeepAliveClosure* keep_alive,
5291                      int* seed);
5292 
5293   virtual void work(uint worker_id);
5294 };
5295 
5296 void CMSRefProcTaskProxy::work(uint worker_id) {
5297   ResourceMark rm;
5298   HandleMark hm;
5299   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5300   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5301                                         _mark_bit_map,
5302                                         work_queue(worker_id));
5303   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5304                                                  _mark_bit_map,
5305                                                  work_queue(worker_id));
5306   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5307   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5308   if (_task.marks_oops_alive()) {
5309     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5310                   _collector->hash_seed(worker_id));
5311   }
5312   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5313   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5314 }
5315 
5316 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5317   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5318   EnqueueTask& _task;
5319 
5320 public:
5321   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5322     : AbstractGangTask("Enqueue reference objects in parallel"),
5323       _task(task)
5324   { }
5325 
5326   virtual void work(uint worker_id)
5327   {
5328     _task.work(worker_id);
5329   }
5330 };
5331 
5332 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5333   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5334    _span(span),
5335    _bit_map(bit_map),
5336    _work_queue(work_queue),
5337    _mark_and_push(collector, span, bit_map, work_queue),
5338    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5339                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5340 { }
5341 
5342 // . see if we can share work_queues with ParNew? XXX
5343 void CMSRefProcTaskProxy::do_work_steal(int i,
5344   CMSParDrainMarkingStackClosure* drain,
5345   CMSParKeepAliveClosure* keep_alive,
5346   int* seed) {
5347   OopTaskQueue* work_q = work_queue(i);
5348   NOT_PRODUCT(int num_steals = 0;)
5349   oop obj_to_scan;
5350 
5351   while (true) {
5352     // Completely finish any left over work from (an) earlier round(s)
5353     drain->trim_queue(0);
5354     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5355                                          (size_t)ParGCDesiredObjsFromOverflowList);
5356     // Now check if there's any work in the overflow list
5357     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5358     // only affects the number of attempts made to get work from the
5359     // overflow list and does not affect the number of workers.  Just
5360     // pass ParallelGCThreads so this behavior is unchanged.
5361     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5362                                                 work_q,
5363                                                 ParallelGCThreads)) {
5364       // Found something in global overflow list;
5365       // not yet ready to go stealing work from others.
5366       // We'd like to assert(work_q->size() != 0, ...)
5367       // because we just took work from the overflow list,
5368       // but of course we can't, since all of that might have
5369       // been already stolen from us.
5370       continue;
5371     }
5372     // Verify that we have no work before we resort to stealing
5373     assert(work_q->size() == 0, "Have work, shouldn't steal");
5374     // Try to steal from other queues that have work
5375     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5376       NOT_PRODUCT(num_steals++;)
5377       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5378       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5379       // Do scanning work
5380       obj_to_scan->oop_iterate(keep_alive);
5381       // Loop around, finish this work, and try to steal some more
5382     } else if (terminator()->offer_termination()) {
5383       break;  // nirvana from the infinite cycle
5384     }
5385   }
5386   NOT_PRODUCT(
5387     if (PrintCMSStatistics != 0) {
5388       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5389     }
5390   )
5391 }
5392 
5393 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5394 {
5395   GenCollectedHeap* gch = GenCollectedHeap::heap();
5396   FlexibleWorkGang* workers = gch->workers();
5397   assert(workers != NULL, "Need parallel worker threads.");
5398   CMSRefProcTaskProxy rp_task(task, &_collector,
5399                               _collector.ref_processor()->span(),
5400                               _collector.markBitMap(),
5401                               workers, _collector.task_queues());
5402   workers->run_task(&rp_task);
5403 }
5404 
5405 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5406 {
5407 
5408   GenCollectedHeap* gch = GenCollectedHeap::heap();
5409   FlexibleWorkGang* workers = gch->workers();
5410   assert(workers != NULL, "Need parallel worker threads.");
5411   CMSRefEnqueueTaskProxy enq_task(task);
5412   workers->run_task(&enq_task);
5413 }
5414 
5415 void CMSCollector::refProcessingWork() {
5416   ResourceMark rm;
5417   HandleMark   hm;
5418 
5419   ReferenceProcessor* rp = ref_processor();
5420   assert(rp->span().equals(_span), "Spans should be equal");
5421   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5422   // Process weak references.
5423   rp->setup_policy(false);
5424   verify_work_stacks_empty();
5425 
5426   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5427                                           &_markStack, false /* !preclean */);
5428   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5429                                 _span, &_markBitMap, &_markStack,
5430                                 &cmsKeepAliveClosure, false /* !preclean */);
5431   {
5432     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5433 
5434     ReferenceProcessorStats stats;
5435     if (rp->processing_is_mt()) {
5436       // Set the degree of MT here.  If the discovery is done MT, there
5437       // may have been a different number of threads doing the discovery
5438       // and a different number of discovered lists may have Ref objects.
5439       // That is OK as long as the Reference lists are balanced (see
5440       // balance_all_queues() and balance_queues()).
5441       GenCollectedHeap* gch = GenCollectedHeap::heap();
5442       uint active_workers = ParallelGCThreads;
5443       FlexibleWorkGang* workers = gch->workers();
5444       if (workers != NULL) {
5445         active_workers = workers->active_workers();
5446         // The expectation is that active_workers will have already
5447         // been set to a reasonable value.  If it has not been set,
5448         // investigate.
5449         assert(active_workers > 0, "Should have been set during scavenge");
5450       }
5451       rp->set_active_mt_degree(active_workers);
5452       CMSRefProcTaskExecutor task_executor(*this);
5453       stats = rp->process_discovered_references(&_is_alive_closure,
5454                                         &cmsKeepAliveClosure,
5455                                         &cmsDrainMarkingStackClosure,
5456                                         &task_executor,
5457                                         _gc_timer_cm,
5458                                         _gc_tracer_cm->gc_id());
5459     } else {
5460       stats = rp->process_discovered_references(&_is_alive_closure,
5461                                         &cmsKeepAliveClosure,
5462                                         &cmsDrainMarkingStackClosure,
5463                                         NULL,
5464                                         _gc_timer_cm,
5465                                         _gc_tracer_cm->gc_id());
5466     }
5467     _gc_tracer_cm->report_gc_reference_stats(stats);
5468 
5469   }
5470 
5471   // This is the point where the entire marking should have completed.
5472   verify_work_stacks_empty();
5473 
5474   if (should_unload_classes()) {
5475     {
5476       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5477 
5478       // Unload classes and purge the SystemDictionary.
5479       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5480 
5481       // Unload nmethods.
5482       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5483 
5484       // Prune dead klasses from subklass/sibling/implementor lists.
5485       Klass::clean_weak_klass_links(&_is_alive_closure);
5486     }
5487 
5488     {
5489       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5490       // Clean up unreferenced symbols in symbol table.
5491       SymbolTable::unlink();
5492     }
5493 
5494     {
5495       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5496       // Delete entries for dead interned strings.
5497       StringTable::unlink(&_is_alive_closure);
5498     }
5499   }
5500 
5501 
5502   // Restore any preserved marks as a result of mark stack or
5503   // work queue overflow
5504   restore_preserved_marks_if_any();  // done single-threaded for now
5505 
5506   rp->set_enqueuing_is_done(true);
5507   if (rp->processing_is_mt()) {
5508     rp->balance_all_queues();
5509     CMSRefProcTaskExecutor task_executor(*this);
5510     rp->enqueue_discovered_references(&task_executor);
5511   } else {
5512     rp->enqueue_discovered_references(NULL);
5513   }
5514   rp->verify_no_references_recorded();
5515   assert(!rp->discovery_enabled(), "should have been disabled");
5516 }
5517 
5518 #ifndef PRODUCT
5519 void CMSCollector::check_correct_thread_executing() {
5520   Thread* t = Thread::current();
5521   // Only the VM thread or the CMS thread should be here.
5522   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5523          "Unexpected thread type");
5524   // If this is the vm thread, the foreground process
5525   // should not be waiting.  Note that _foregroundGCIsActive is
5526   // true while the foreground collector is waiting.
5527   if (_foregroundGCShouldWait) {
5528     // We cannot be the VM thread
5529     assert(t->is_ConcurrentGC_thread(),
5530            "Should be CMS thread");
5531   } else {
5532     // We can be the CMS thread only if we are in a stop-world
5533     // phase of CMS collection.
5534     if (t->is_ConcurrentGC_thread()) {
5535       assert(_collectorState == InitialMarking ||
5536              _collectorState == FinalMarking,
5537              "Should be a stop-world phase");
5538       // The CMS thread should be holding the CMS_token.
5539       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5540              "Potential interference with concurrently "
5541              "executing VM thread");
5542     }
5543   }
5544 }
5545 #endif
5546 
5547 void CMSCollector::sweep() {
5548   assert(_collectorState == Sweeping, "just checking");
5549   check_correct_thread_executing();
5550   verify_work_stacks_empty();
5551   verify_overflow_empty();
5552   increment_sweep_count();
5553   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5554 
5555   _inter_sweep_timer.stop();
5556   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5557 
5558   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5559   _intra_sweep_timer.reset();
5560   _intra_sweep_timer.start();
5561   {
5562     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5563     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5564     // First sweep the old gen
5565     {
5566       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5567                                bitMapLock());
5568       sweepWork(_cmsGen);
5569     }
5570 
5571     // Update Universe::_heap_*_at_gc figures.
5572     // We need all the free list locks to make the abstract state
5573     // transition from Sweeping to Resetting. See detailed note
5574     // further below.
5575     {
5576       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5577       // Update heap occupancy information which is used as
5578       // input to soft ref clearing policy at the next gc.
5579       Universe::update_heap_info_at_gc();
5580       _collectorState = Resizing;
5581     }
5582   }
5583   verify_work_stacks_empty();
5584   verify_overflow_empty();
5585 
5586   if (should_unload_classes()) {
5587     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5588     // requires that the virtual spaces are stable and not deleted.
5589     ClassLoaderDataGraph::set_should_purge(true);
5590   }
5591 
5592   _intra_sweep_timer.stop();
5593   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5594 
5595   _inter_sweep_timer.reset();
5596   _inter_sweep_timer.start();
5597 
5598   // We need to use a monotonically non-decreasing time in ms
5599   // or we will see time-warp warnings and os::javaTimeMillis()
5600   // does not guarantee monotonicity.
5601   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5602   update_time_of_last_gc(now);
5603 
5604   // NOTE on abstract state transitions:
5605   // Mutators allocate-live and/or mark the mod-union table dirty
5606   // based on the state of the collection.  The former is done in
5607   // the interval [Marking, Sweeping] and the latter in the interval
5608   // [Marking, Sweeping).  Thus the transitions into the Marking state
5609   // and out of the Sweeping state must be synchronously visible
5610   // globally to the mutators.
5611   // The transition into the Marking state happens with the world
5612   // stopped so the mutators will globally see it.  Sweeping is
5613   // done asynchronously by the background collector so the transition
5614   // from the Sweeping state to the Resizing state must be done
5615   // under the freelistLock (as is the check for whether to
5616   // allocate-live and whether to dirty the mod-union table).
5617   assert(_collectorState == Resizing, "Change of collector state to"
5618     " Resizing must be done under the freelistLocks (plural)");
5619 
5620   // Now that sweeping has been completed, we clear
5621   // the incremental_collection_failed flag,
5622   // thus inviting a younger gen collection to promote into
5623   // this generation. If such a promotion may still fail,
5624   // the flag will be set again when a young collection is
5625   // attempted.
5626   GenCollectedHeap* gch = GenCollectedHeap::heap();
5627   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5628   gch->update_full_collections_completed(_collection_count_start);
5629 }
5630 
5631 // FIX ME!!! Looks like this belongs in CFLSpace, with
5632 // CMSGen merely delegating to it.
5633 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5634   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5635   HeapWord*  minAddr        = _cmsSpace->bottom();
5636   HeapWord*  largestAddr    =
5637     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5638   if (largestAddr == NULL) {
5639     // The dictionary appears to be empty.  In this case
5640     // try to coalesce at the end of the heap.
5641     largestAddr = _cmsSpace->end();
5642   }
5643   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5644   size_t nearLargestOffset =
5645     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5646   if (PrintFLSStatistics != 0) {
5647     gclog_or_tty->print_cr(
5648       "CMS: Large Block: " PTR_FORMAT ";"
5649       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5650       p2i(largestAddr),
5651       p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5652   }
5653   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5654 }
5655 
5656 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5657   return addr >= _cmsSpace->nearLargestChunk();
5658 }
5659 
5660 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5661   return _cmsSpace->find_chunk_at_end();
5662 }
5663 
5664 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5665                                                     bool full) {
5666   // The next lower level has been collected.  Gather any statistics
5667   // that are of interest at this point.
5668   if (!full && (current_level + 1) == level()) {
5669     // Gather statistics on the young generation collection.
5670     collector()->stats().record_gc0_end(used());
5671   }
5672 }
5673 
5674 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5675   // We iterate over the space(s) underlying this generation,
5676   // checking the mark bit map to see if the bits corresponding
5677   // to specific blocks are marked or not. Blocks that are
5678   // marked are live and are not swept up. All remaining blocks
5679   // are swept up, with coalescing on-the-fly as we sweep up
5680   // contiguous free and/or garbage blocks:
5681   // We need to ensure that the sweeper synchronizes with allocators
5682   // and stop-the-world collectors. In particular, the following
5683   // locks are used:
5684   // . CMS token: if this is held, a stop the world collection cannot occur
5685   // . freelistLock: if this is held no allocation can occur from this
5686   //                 generation by another thread
5687   // . bitMapLock: if this is held, no other thread can access or update
5688   //
5689 
5690   // Note that we need to hold the freelistLock if we use
5691   // block iterate below; else the iterator might go awry if
5692   // a mutator (or promotion) causes block contents to change
5693   // (for instance if the allocator divvies up a block).
5694   // If we hold the free list lock, for all practical purposes
5695   // young generation GC's can't occur (they'll usually need to
5696   // promote), so we might as well prevent all young generation
5697   // GC's while we do a sweeping step. For the same reason, we might
5698   // as well take the bit map lock for the entire duration
5699 
5700   // check that we hold the requisite locks
5701   assert(have_cms_token(), "Should hold cms token");
5702   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5703   assert_lock_strong(gen->freelistLock());
5704   assert_lock_strong(bitMapLock());
5705 
5706   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5707   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5708   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5709                                       _inter_sweep_estimate.padded_average(),
5710                                       _intra_sweep_estimate.padded_average());
5711   gen->setNearLargestChunk();
5712 
5713   {
5714     SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5715     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5716     // We need to free-up/coalesce garbage/blocks from a
5717     // co-terminal free run. This is done in the SweepClosure
5718     // destructor; so, do not remove this scope, else the
5719     // end-of-sweep-census below will be off by a little bit.
5720   }
5721   gen->cmsSpace()->sweep_completed();
5722   gen->cmsSpace()->endSweepFLCensus(sweep_count());
5723   if (should_unload_classes()) {                // unloaded classes this cycle,
5724     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5725   } else {                                      // did not unload classes,
5726     _concurrent_cycles_since_last_unload++;     // ... increment count
5727   }
5728 }
5729 
5730 // Reset CMS data structures (for now just the marking bit map)
5731 // preparatory for the next cycle.
5732 void CMSCollector::reset(bool concurrent) {
5733   if (concurrent) {
5734     CMSTokenSyncWithLocks ts(true, bitMapLock());
5735 
5736     // If the state is not "Resetting", the foreground  thread
5737     // has done a collection and the resetting.
5738     if (_collectorState != Resetting) {
5739       assert(_collectorState == Idling, "The state should only change"
5740         " because the foreground collector has finished the collection");
5741       return;
5742     }
5743 
5744     // Clear the mark bitmap (no grey objects to start with)
5745     // for the next cycle.
5746     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5747     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5748 
5749     HeapWord* curAddr = _markBitMap.startWord();
5750     while (curAddr < _markBitMap.endWord()) {
5751       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5752       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5753       _markBitMap.clear_large_range(chunk);
5754       if (ConcurrentMarkSweepThread::should_yield() &&
5755           !foregroundGCIsActive() &&
5756           CMSYield) {
5757         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5758                "CMS thread should hold CMS token");
5759         assert_lock_strong(bitMapLock());
5760         bitMapLock()->unlock();
5761         ConcurrentMarkSweepThread::desynchronize(true);
5762         stopTimer();
5763         if (PrintCMSStatistics != 0) {
5764           incrementYields();
5765         }
5766 
5767         // See the comment in coordinator_yield()
5768         for (unsigned i = 0; i < CMSYieldSleepCount &&
5769                          ConcurrentMarkSweepThread::should_yield() &&
5770                          !CMSCollector::foregroundGCIsActive(); ++i) {
5771           os::sleep(Thread::current(), 1, false);
5772         }
5773 
5774         ConcurrentMarkSweepThread::synchronize(true);
5775         bitMapLock()->lock_without_safepoint_check();
5776         startTimer();
5777       }
5778       curAddr = chunk.end();
5779     }
5780     // A successful mostly concurrent collection has been done.
5781     // Because only the full (i.e., concurrent mode failure) collections
5782     // are being measured for gc overhead limits, clean the "near" flag
5783     // and count.
5784     size_policy()->reset_gc_overhead_limit_count();
5785     _collectorState = Idling;
5786   } else {
5787     // already have the lock
5788     assert(_collectorState == Resetting, "just checking");
5789     assert_lock_strong(bitMapLock());
5790     _markBitMap.clear_all();
5791     _collectorState = Idling;
5792   }
5793 
5794   register_gc_end();
5795 }
5796 
5797 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5798   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5799   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5800   TraceCollectorStats tcs(counters());
5801 
5802   switch (op) {
5803     case CMS_op_checkpointRootsInitial: {
5804       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5805       checkpointRootsInitial();
5806       if (PrintGC) {
5807         _cmsGen->printOccupancy("initial-mark");
5808       }
5809       break;
5810     }
5811     case CMS_op_checkpointRootsFinal: {
5812       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5813       checkpointRootsFinal();
5814       if (PrintGC) {
5815         _cmsGen->printOccupancy("remark");
5816       }
5817       break;
5818     }
5819     default:
5820       fatal("No such CMS_op");
5821   }
5822 }
5823 
5824 #ifndef PRODUCT
5825 size_t const CMSCollector::skip_header_HeapWords() {
5826   return FreeChunk::header_size();
5827 }
5828 
5829 // Try and collect here conditions that should hold when
5830 // CMS thread is exiting. The idea is that the foreground GC
5831 // thread should not be blocked if it wants to terminate
5832 // the CMS thread and yet continue to run the VM for a while
5833 // after that.
5834 void CMSCollector::verify_ok_to_terminate() const {
5835   assert(Thread::current()->is_ConcurrentGC_thread(),
5836          "should be called by CMS thread");
5837   assert(!_foregroundGCShouldWait, "should be false");
5838   // We could check here that all the various low-level locks
5839   // are not held by the CMS thread, but that is overkill; see
5840   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5841   // is checked.
5842 }
5843 #endif
5844 
5845 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5846    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5847           "missing Printezis mark?");
5848   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5849   size_t size = pointer_delta(nextOneAddr + 1, addr);
5850   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5851          "alignment problem");
5852   assert(size >= 3, "Necessary for Printezis marks to work");
5853   return size;
5854 }
5855 
5856 // A variant of the above (block_size_using_printezis_bits()) except
5857 // that we return 0 if the P-bits are not yet set.
5858 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5859   if (_markBitMap.isMarked(addr + 1)) {
5860     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5861     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5862     size_t size = pointer_delta(nextOneAddr + 1, addr);
5863     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5864            "alignment problem");
5865     assert(size >= 3, "Necessary for Printezis marks to work");
5866     return size;
5867   }
5868   return 0;
5869 }
5870 
5871 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5872   size_t sz = 0;
5873   oop p = (oop)addr;
5874   if (p->klass_or_null() != NULL) {
5875     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5876   } else {
5877     sz = block_size_using_printezis_bits(addr);
5878   }
5879   assert(sz > 0, "size must be nonzero");
5880   HeapWord* next_block = addr + sz;
5881   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5882                                              CardTableModRefBS::card_size);
5883   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5884          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5885          "must be different cards");
5886   return next_card;
5887 }
5888 
5889 
5890 // CMS Bit Map Wrapper /////////////////////////////////////////
5891 
5892 // Construct a CMS bit map infrastructure, but don't create the
5893 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5894 // further below.
5895 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5896   _bm(),
5897   _shifter(shifter),
5898   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5899                                     Monitor::_safepoint_check_sometimes) : NULL)
5900 {
5901   _bmStartWord = 0;
5902   _bmWordSize  = 0;
5903 }
5904 
5905 bool CMSBitMap::allocate(MemRegion mr) {
5906   _bmStartWord = mr.start();
5907   _bmWordSize  = mr.word_size();
5908   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5909                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5910   if (!brs.is_reserved()) {
5911     warning("CMS bit map allocation failure");
5912     return false;
5913   }
5914   // For now we'll just commit all of the bit map up front.
5915   // Later on we'll try to be more parsimonious with swap.
5916   if (!_virtual_space.initialize(brs, brs.size())) {
5917     warning("CMS bit map backing store failure");
5918     return false;
5919   }
5920   assert(_virtual_space.committed_size() == brs.size(),
5921          "didn't reserve backing store for all of CMS bit map?");
5922   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5923   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5924          _bmWordSize, "inconsistency in bit map sizing");
5925   _bm.set_size(_bmWordSize >> _shifter);
5926 
5927   // bm.clear(); // can we rely on getting zero'd memory? verify below
5928   assert(isAllClear(),
5929          "Expected zero'd memory from ReservedSpace constructor");
5930   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5931          "consistency check");
5932   return true;
5933 }
5934 
5935 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5936   HeapWord *next_addr, *end_addr, *last_addr;
5937   assert_locked();
5938   assert(covers(mr), "out-of-range error");
5939   // XXX assert that start and end are appropriately aligned
5940   for (next_addr = mr.start(), end_addr = mr.end();
5941        next_addr < end_addr; next_addr = last_addr) {
5942     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5943     last_addr = dirty_region.end();
5944     if (!dirty_region.is_empty()) {
5945       cl->do_MemRegion(dirty_region);
5946     } else {
5947       assert(last_addr == end_addr, "program logic");
5948       return;
5949     }
5950   }
5951 }
5952 
5953 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5954   _bm.print_on_error(st, prefix);
5955 }
5956 
5957 #ifndef PRODUCT
5958 void CMSBitMap::assert_locked() const {
5959   CMSLockVerifier::assert_locked(lock());
5960 }
5961 
5962 bool CMSBitMap::covers(MemRegion mr) const {
5963   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5964   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5965          "size inconsistency");
5966   return (mr.start() >= _bmStartWord) &&
5967          (mr.end()   <= endWord());
5968 }
5969 
5970 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5971     return (start >= _bmStartWord && (start + size) <= endWord());
5972 }
5973 
5974 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5975   // verify that there are no 1 bits in the interval [left, right)
5976   FalseBitMapClosure falseBitMapClosure;
5977   iterate(&falseBitMapClosure, left, right);
5978 }
5979 
5980 void CMSBitMap::region_invariant(MemRegion mr)
5981 {
5982   assert_locked();
5983   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5984   assert(!mr.is_empty(), "unexpected empty region");
5985   assert(covers(mr), "mr should be covered by bit map");
5986   // convert address range into offset range
5987   size_t start_ofs = heapWordToOffset(mr.start());
5988   // Make sure that end() is appropriately aligned
5989   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5990                         (1 << (_shifter+LogHeapWordSize))),
5991          "Misaligned mr.end()");
5992   size_t end_ofs   = heapWordToOffset(mr.end());
5993   assert(end_ofs > start_ofs, "Should mark at least one bit");
5994 }
5995 
5996 #endif
5997 
5998 bool CMSMarkStack::allocate(size_t size) {
5999   // allocate a stack of the requisite depth
6000   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6001                    size * sizeof(oop)));
6002   if (!rs.is_reserved()) {
6003     warning("CMSMarkStack allocation failure");
6004     return false;
6005   }
6006   if (!_virtual_space.initialize(rs, rs.size())) {
6007     warning("CMSMarkStack backing store failure");
6008     return false;
6009   }
6010   assert(_virtual_space.committed_size() == rs.size(),
6011          "didn't reserve backing store for all of CMS stack?");
6012   _base = (oop*)(_virtual_space.low());
6013   _index = 0;
6014   _capacity = size;
6015   NOT_PRODUCT(_max_depth = 0);
6016   return true;
6017 }
6018 
6019 // XXX FIX ME !!! In the MT case we come in here holding a
6020 // leaf lock. For printing we need to take a further lock
6021 // which has lower rank. We need to recalibrate the two
6022 // lock-ranks involved in order to be able to print the
6023 // messages below. (Or defer the printing to the caller.
6024 // For now we take the expedient path of just disabling the
6025 // messages for the problematic case.)
6026 void CMSMarkStack::expand() {
6027   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6028   if (_capacity == MarkStackSizeMax) {
6029     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6030       // We print a warning message only once per CMS cycle.
6031       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6032     }
6033     return;
6034   }
6035   // Double capacity if possible
6036   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6037   // Do not give up existing stack until we have managed to
6038   // get the double capacity that we desired.
6039   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6040                    new_capacity * sizeof(oop)));
6041   if (rs.is_reserved()) {
6042     // Release the backing store associated with old stack
6043     _virtual_space.release();
6044     // Reinitialize virtual space for new stack
6045     if (!_virtual_space.initialize(rs, rs.size())) {
6046       fatal("Not enough swap for expanded marking stack");
6047     }
6048     _base = (oop*)(_virtual_space.low());
6049     _index = 0;
6050     _capacity = new_capacity;
6051   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6052     // Failed to double capacity, continue;
6053     // we print a detail message only once per CMS cycle.
6054     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6055             SIZE_FORMAT"K",
6056             _capacity / K, new_capacity / K);
6057   }
6058 }
6059 
6060 
6061 // Closures
6062 // XXX: there seems to be a lot of code  duplication here;
6063 // should refactor and consolidate common code.
6064 
6065 // This closure is used to mark refs into the CMS generation in
6066 // the CMS bit map. Called at the first checkpoint. This closure
6067 // assumes that we do not need to re-mark dirty cards; if the CMS
6068 // generation on which this is used is not an oldest
6069 // generation then this will lose younger_gen cards!
6070 
6071 MarkRefsIntoClosure::MarkRefsIntoClosure(
6072   MemRegion span, CMSBitMap* bitMap):
6073     _span(span),
6074     _bitMap(bitMap)
6075 {
6076     assert(_ref_processor == NULL, "deliberately left NULL");
6077     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6078 }
6079 
6080 void MarkRefsIntoClosure::do_oop(oop obj) {
6081   // if p points into _span, then mark corresponding bit in _markBitMap
6082   assert(obj->is_oop(), "expected an oop");
6083   HeapWord* addr = (HeapWord*)obj;
6084   if (_span.contains(addr)) {
6085     // this should be made more efficient
6086     _bitMap->mark(addr);
6087   }
6088 }
6089 
6090 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6091 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6092 
6093 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6094   MemRegion span, CMSBitMap* bitMap):
6095     _span(span),
6096     _bitMap(bitMap)
6097 {
6098     assert(_ref_processor == NULL, "deliberately left NULL");
6099     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6100 }
6101 
6102 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6103   // if p points into _span, then mark corresponding bit in _markBitMap
6104   assert(obj->is_oop(), "expected an oop");
6105   HeapWord* addr = (HeapWord*)obj;
6106   if (_span.contains(addr)) {
6107     // this should be made more efficient
6108     _bitMap->par_mark(addr);
6109   }
6110 }
6111 
6112 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6113 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6114 
6115 // A variant of the above, used for CMS marking verification.
6116 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6117   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6118     _span(span),
6119     _verification_bm(verification_bm),
6120     _cms_bm(cms_bm)
6121 {
6122     assert(_ref_processor == NULL, "deliberately left NULL");
6123     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6124 }
6125 
6126 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6127   // if p points into _span, then mark corresponding bit in _markBitMap
6128   assert(obj->is_oop(), "expected an oop");
6129   HeapWord* addr = (HeapWord*)obj;
6130   if (_span.contains(addr)) {
6131     _verification_bm->mark(addr);
6132     if (!_cms_bm->isMarked(addr)) {
6133       oop(addr)->print();
6134       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6135       fatal("... aborting");
6136     }
6137   }
6138 }
6139 
6140 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6141 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6142 
6143 //////////////////////////////////////////////////
6144 // MarkRefsIntoAndScanClosure
6145 //////////////////////////////////////////////////
6146 
6147 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6148                                                        ReferenceProcessor* rp,
6149                                                        CMSBitMap* bit_map,
6150                                                        CMSBitMap* mod_union_table,
6151                                                        CMSMarkStack*  mark_stack,
6152                                                        CMSCollector* collector,
6153                                                        bool should_yield,
6154                                                        bool concurrent_precleaning):
6155   _collector(collector),
6156   _span(span),
6157   _bit_map(bit_map),
6158   _mark_stack(mark_stack),
6159   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6160                       mark_stack, concurrent_precleaning),
6161   _yield(should_yield),
6162   _concurrent_precleaning(concurrent_precleaning),
6163   _freelistLock(NULL)
6164 {
6165   _ref_processor = rp;
6166   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6167 }
6168 
6169 // This closure is used to mark refs into the CMS generation at the
6170 // second (final) checkpoint, and to scan and transitively follow
6171 // the unmarked oops. It is also used during the concurrent precleaning
6172 // phase while scanning objects on dirty cards in the CMS generation.
6173 // The marks are made in the marking bit map and the marking stack is
6174 // used for keeping the (newly) grey objects during the scan.
6175 // The parallel version (Par_...) appears further below.
6176 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6177   if (obj != NULL) {
6178     assert(obj->is_oop(), "expected an oop");
6179     HeapWord* addr = (HeapWord*)obj;
6180     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6181     assert(_collector->overflow_list_is_empty(),
6182            "overflow list should be empty");
6183     if (_span.contains(addr) &&
6184         !_bit_map->isMarked(addr)) {
6185       // mark bit map (object is now grey)
6186       _bit_map->mark(addr);
6187       // push on marking stack (stack should be empty), and drain the
6188       // stack by applying this closure to the oops in the oops popped
6189       // from the stack (i.e. blacken the grey objects)
6190       bool res = _mark_stack->push(obj);
6191       assert(res, "Should have space to push on empty stack");
6192       do {
6193         oop new_oop = _mark_stack->pop();
6194         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6195         assert(_bit_map->isMarked((HeapWord*)new_oop),
6196                "only grey objects on this stack");
6197         // iterate over the oops in this oop, marking and pushing
6198         // the ones in CMS heap (i.e. in _span).
6199         new_oop->oop_iterate(&_pushAndMarkClosure);
6200         // check if it's time to yield
6201         do_yield_check();
6202       } while (!_mark_stack->isEmpty() ||
6203                (!_concurrent_precleaning && take_from_overflow_list()));
6204         // if marking stack is empty, and we are not doing this
6205         // during precleaning, then check the overflow list
6206     }
6207     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6208     assert(_collector->overflow_list_is_empty(),
6209            "overflow list was drained above");
6210     // We could restore evacuated mark words, if any, used for
6211     // overflow list links here because the overflow list is
6212     // provably empty here. That would reduce the maximum
6213     // size requirements for preserved_{oop,mark}_stack.
6214     // But we'll just postpone it until we are all done
6215     // so we can just stream through.
6216     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6217       _collector->restore_preserved_marks_if_any();
6218       assert(_collector->no_preserved_marks(), "No preserved marks");
6219     }
6220     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6221            "All preserved marks should have been restored above");
6222   }
6223 }
6224 
6225 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6226 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6227 
6228 void MarkRefsIntoAndScanClosure::do_yield_work() {
6229   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6230          "CMS thread should hold CMS token");
6231   assert_lock_strong(_freelistLock);
6232   assert_lock_strong(_bit_map->lock());
6233   // relinquish the free_list_lock and bitMaplock()
6234   _bit_map->lock()->unlock();
6235   _freelistLock->unlock();
6236   ConcurrentMarkSweepThread::desynchronize(true);
6237   _collector->stopTimer();
6238   if (PrintCMSStatistics != 0) {
6239     _collector->incrementYields();
6240   }
6241 
6242   // See the comment in coordinator_yield()
6243   for (unsigned i = 0;
6244        i < CMSYieldSleepCount &&
6245        ConcurrentMarkSweepThread::should_yield() &&
6246        !CMSCollector::foregroundGCIsActive();
6247        ++i) {
6248     os::sleep(Thread::current(), 1, false);
6249   }
6250 
6251   ConcurrentMarkSweepThread::synchronize(true);
6252   _freelistLock->lock_without_safepoint_check();
6253   _bit_map->lock()->lock_without_safepoint_check();
6254   _collector->startTimer();
6255 }
6256 
6257 ///////////////////////////////////////////////////////////
6258 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6259 //                                 MarkRefsIntoAndScanClosure
6260 ///////////////////////////////////////////////////////////
6261 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6262   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6263   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6264   _span(span),
6265   _bit_map(bit_map),
6266   _work_queue(work_queue),
6267   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6268                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6269   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6270 {
6271   _ref_processor = rp;
6272   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6273 }
6274 
6275 // This closure is used to mark refs into the CMS generation at the
6276 // second (final) checkpoint, and to scan and transitively follow
6277 // the unmarked oops. The marks are made in the marking bit map and
6278 // the work_queue is used for keeping the (newly) grey objects during
6279 // the scan phase whence they are also available for stealing by parallel
6280 // threads. Since the marking bit map is shared, updates are
6281 // synchronized (via CAS).
6282 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6283   if (obj != NULL) {
6284     // Ignore mark word because this could be an already marked oop
6285     // that may be chained at the end of the overflow list.
6286     assert(obj->is_oop(true), "expected an oop");
6287     HeapWord* addr = (HeapWord*)obj;
6288     if (_span.contains(addr) &&
6289         !_bit_map->isMarked(addr)) {
6290       // mark bit map (object will become grey):
6291       // It is possible for several threads to be
6292       // trying to "claim" this object concurrently;
6293       // the unique thread that succeeds in marking the
6294       // object first will do the subsequent push on
6295       // to the work queue (or overflow list).
6296       if (_bit_map->par_mark(addr)) {
6297         // push on work_queue (which may not be empty), and trim the
6298         // queue to an appropriate length by applying this closure to
6299         // the oops in the oops popped from the stack (i.e. blacken the
6300         // grey objects)
6301         bool res = _work_queue->push(obj);
6302         assert(res, "Low water mark should be less than capacity?");
6303         trim_queue(_low_water_mark);
6304       } // Else, another thread claimed the object
6305     }
6306   }
6307 }
6308 
6309 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6310 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6311 
6312 // This closure is used to rescan the marked objects on the dirty cards
6313 // in the mod union table and the card table proper.
6314 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6315   oop p, MemRegion mr) {
6316 
6317   size_t size = 0;
6318   HeapWord* addr = (HeapWord*)p;
6319   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6320   assert(_span.contains(addr), "we are scanning the CMS generation");
6321   // check if it's time to yield
6322   if (do_yield_check()) {
6323     // We yielded for some foreground stop-world work,
6324     // and we have been asked to abort this ongoing preclean cycle.
6325     return 0;
6326   }
6327   if (_bitMap->isMarked(addr)) {
6328     // it's marked; is it potentially uninitialized?
6329     if (p->klass_or_null() != NULL) {
6330         // an initialized object; ignore mark word in verification below
6331         // since we are running concurrent with mutators
6332         assert(p->is_oop(true), "should be an oop");
6333         if (p->is_objArray()) {
6334           // objArrays are precisely marked; restrict scanning
6335           // to dirty cards only.
6336           size = CompactibleFreeListSpace::adjustObjectSize(
6337                    p->oop_iterate(_scanningClosure, mr));
6338         } else {
6339           // A non-array may have been imprecisely marked; we need
6340           // to scan object in its entirety.
6341           size = CompactibleFreeListSpace::adjustObjectSize(
6342                    p->oop_iterate(_scanningClosure));
6343         }
6344         #ifdef ASSERT
6345           size_t direct_size =
6346             CompactibleFreeListSpace::adjustObjectSize(p->size());
6347           assert(size == direct_size, "Inconsistency in size");
6348           assert(size >= 3, "Necessary for Printezis marks to work");
6349           if (!_bitMap->isMarked(addr+1)) {
6350             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6351           } else {
6352             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6353             assert(_bitMap->isMarked(addr+size-1),
6354                    "inconsistent Printezis mark");
6355           }
6356         #endif // ASSERT
6357     } else {
6358       // An uninitialized object.
6359       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6360       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6361       size = pointer_delta(nextOneAddr + 1, addr);
6362       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6363              "alignment problem");
6364       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6365       // will dirty the card when the klass pointer is installed in the
6366       // object (signaling the completion of initialization).
6367     }
6368   } else {
6369     // Either a not yet marked object or an uninitialized object
6370     if (p->klass_or_null() == NULL) {
6371       // An uninitialized object, skip to the next card, since
6372       // we may not be able to read its P-bits yet.
6373       assert(size == 0, "Initial value");
6374     } else {
6375       // An object not (yet) reached by marking: we merely need to
6376       // compute its size so as to go look at the next block.
6377       assert(p->is_oop(true), "should be an oop");
6378       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6379     }
6380   }
6381   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6382   return size;
6383 }
6384 
6385 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6386   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6387          "CMS thread should hold CMS token");
6388   assert_lock_strong(_freelistLock);
6389   assert_lock_strong(_bitMap->lock());
6390   // relinquish the free_list_lock and bitMaplock()
6391   _bitMap->lock()->unlock();
6392   _freelistLock->unlock();
6393   ConcurrentMarkSweepThread::desynchronize(true);
6394   _collector->stopTimer();
6395   if (PrintCMSStatistics != 0) {
6396     _collector->incrementYields();
6397   }
6398 
6399   // See the comment in coordinator_yield()
6400   for (unsigned i = 0; i < CMSYieldSleepCount &&
6401                    ConcurrentMarkSweepThread::should_yield() &&
6402                    !CMSCollector::foregroundGCIsActive(); ++i) {
6403     os::sleep(Thread::current(), 1, false);
6404   }
6405 
6406   ConcurrentMarkSweepThread::synchronize(true);
6407   _freelistLock->lock_without_safepoint_check();
6408   _bitMap->lock()->lock_without_safepoint_check();
6409   _collector->startTimer();
6410 }
6411 
6412 
6413 //////////////////////////////////////////////////////////////////
6414 // SurvivorSpacePrecleanClosure
6415 //////////////////////////////////////////////////////////////////
6416 // This (single-threaded) closure is used to preclean the oops in
6417 // the survivor spaces.
6418 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6419 
6420   HeapWord* addr = (HeapWord*)p;
6421   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6422   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6423   assert(p->klass_or_null() != NULL, "object should be initialized");
6424   // an initialized object; ignore mark word in verification below
6425   // since we are running concurrent with mutators
6426   assert(p->is_oop(true), "should be an oop");
6427   // Note that we do not yield while we iterate over
6428   // the interior oops of p, pushing the relevant ones
6429   // on our marking stack.
6430   size_t size = p->oop_iterate(_scanning_closure);
6431   do_yield_check();
6432   // Observe that below, we do not abandon the preclean
6433   // phase as soon as we should; rather we empty the
6434   // marking stack before returning. This is to satisfy
6435   // some existing assertions. In general, it may be a
6436   // good idea to abort immediately and complete the marking
6437   // from the grey objects at a later time.
6438   while (!_mark_stack->isEmpty()) {
6439     oop new_oop = _mark_stack->pop();
6440     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6441     assert(_bit_map->isMarked((HeapWord*)new_oop),
6442            "only grey objects on this stack");
6443     // iterate over the oops in this oop, marking and pushing
6444     // the ones in CMS heap (i.e. in _span).
6445     new_oop->oop_iterate(_scanning_closure);
6446     // check if it's time to yield
6447     do_yield_check();
6448   }
6449   unsigned int after_count =
6450     GenCollectedHeap::heap()->total_collections();
6451   bool abort = (_before_count != after_count) ||
6452                _collector->should_abort_preclean();
6453   return abort ? 0 : size;
6454 }
6455 
6456 void SurvivorSpacePrecleanClosure::do_yield_work() {
6457   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6458          "CMS thread should hold CMS token");
6459   assert_lock_strong(_bit_map->lock());
6460   // Relinquish the bit map lock
6461   _bit_map->lock()->unlock();
6462   ConcurrentMarkSweepThread::desynchronize(true);
6463   _collector->stopTimer();
6464   if (PrintCMSStatistics != 0) {
6465     _collector->incrementYields();
6466   }
6467 
6468   // See the comment in coordinator_yield()
6469   for (unsigned i = 0; i < CMSYieldSleepCount &&
6470                        ConcurrentMarkSweepThread::should_yield() &&
6471                        !CMSCollector::foregroundGCIsActive(); ++i) {
6472     os::sleep(Thread::current(), 1, false);
6473   }
6474 
6475   ConcurrentMarkSweepThread::synchronize(true);
6476   _bit_map->lock()->lock_without_safepoint_check();
6477   _collector->startTimer();
6478 }
6479 
6480 // This closure is used to rescan the marked objects on the dirty cards
6481 // in the mod union table and the card table proper. In the parallel
6482 // case, although the bitMap is shared, we do a single read so the
6483 // isMarked() query is "safe".
6484 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6485   // Ignore mark word because we are running concurrent with mutators
6486   assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6487   HeapWord* addr = (HeapWord*)p;
6488   assert(_span.contains(addr), "we are scanning the CMS generation");
6489   bool is_obj_array = false;
6490   #ifdef ASSERT
6491     if (!_parallel) {
6492       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6493       assert(_collector->overflow_list_is_empty(),
6494              "overflow list should be empty");
6495 
6496     }
6497   #endif // ASSERT
6498   if (_bit_map->isMarked(addr)) {
6499     // Obj arrays are precisely marked, non-arrays are not;
6500     // so we scan objArrays precisely and non-arrays in their
6501     // entirety.
6502     if (p->is_objArray()) {
6503       is_obj_array = true;
6504       if (_parallel) {
6505         p->oop_iterate(_par_scan_closure, mr);
6506       } else {
6507         p->oop_iterate(_scan_closure, mr);
6508       }
6509     } else {
6510       if (_parallel) {
6511         p->oop_iterate(_par_scan_closure);
6512       } else {
6513         p->oop_iterate(_scan_closure);
6514       }
6515     }
6516   }
6517   #ifdef ASSERT
6518     if (!_parallel) {
6519       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6520       assert(_collector->overflow_list_is_empty(),
6521              "overflow list should be empty");
6522 
6523     }
6524   #endif // ASSERT
6525   return is_obj_array;
6526 }
6527 
6528 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6529                         MemRegion span,
6530                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6531                         bool should_yield, bool verifying):
6532   _collector(collector),
6533   _span(span),
6534   _bitMap(bitMap),
6535   _mut(&collector->_modUnionTable),
6536   _markStack(markStack),
6537   _yield(should_yield),
6538   _skipBits(0)
6539 {
6540   assert(_markStack->isEmpty(), "stack should be empty");
6541   _finger = _bitMap->startWord();
6542   _threshold = _finger;
6543   assert(_collector->_restart_addr == NULL, "Sanity check");
6544   assert(_span.contains(_finger), "Out of bounds _finger?");
6545   DEBUG_ONLY(_verifying = verifying;)
6546 }
6547 
6548 void MarkFromRootsClosure::reset(HeapWord* addr) {
6549   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6550   assert(_span.contains(addr), "Out of bounds _finger?");
6551   _finger = addr;
6552   _threshold = (HeapWord*)round_to(
6553                  (intptr_t)_finger, CardTableModRefBS::card_size);
6554 }
6555 
6556 // Should revisit to see if this should be restructured for
6557 // greater efficiency.
6558 bool MarkFromRootsClosure::do_bit(size_t offset) {
6559   if (_skipBits > 0) {
6560     _skipBits--;
6561     return true;
6562   }
6563   // convert offset into a HeapWord*
6564   HeapWord* addr = _bitMap->startWord() + offset;
6565   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6566          "address out of range");
6567   assert(_bitMap->isMarked(addr), "tautology");
6568   if (_bitMap->isMarked(addr+1)) {
6569     // this is an allocated but not yet initialized object
6570     assert(_skipBits == 0, "tautology");
6571     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6572     oop p = oop(addr);
6573     if (p->klass_or_null() == NULL) {
6574       DEBUG_ONLY(if (!_verifying) {)
6575         // We re-dirty the cards on which this object lies and increase
6576         // the _threshold so that we'll come back to scan this object
6577         // during the preclean or remark phase. (CMSCleanOnEnter)
6578         if (CMSCleanOnEnter) {
6579           size_t sz = _collector->block_size_using_printezis_bits(addr);
6580           HeapWord* end_card_addr   = (HeapWord*)round_to(
6581                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6582           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6583           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6584           // Bump _threshold to end_card_addr; note that
6585           // _threshold cannot possibly exceed end_card_addr, anyhow.
6586           // This prevents future clearing of the card as the scan proceeds
6587           // to the right.
6588           assert(_threshold <= end_card_addr,
6589                  "Because we are just scanning into this object");
6590           if (_threshold < end_card_addr) {
6591             _threshold = end_card_addr;
6592           }
6593           if (p->klass_or_null() != NULL) {
6594             // Redirty the range of cards...
6595             _mut->mark_range(redirty_range);
6596           } // ...else the setting of klass will dirty the card anyway.
6597         }
6598       DEBUG_ONLY(})
6599       return true;
6600     }
6601   }
6602   scanOopsInOop(addr);
6603   return true;
6604 }
6605 
6606 // We take a break if we've been at this for a while,
6607 // so as to avoid monopolizing the locks involved.
6608 void MarkFromRootsClosure::do_yield_work() {
6609   // First give up the locks, then yield, then re-lock
6610   // We should probably use a constructor/destructor idiom to
6611   // do this unlock/lock or modify the MutexUnlocker class to
6612   // serve our purpose. XXX
6613   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6614          "CMS thread should hold CMS token");
6615   assert_lock_strong(_bitMap->lock());
6616   _bitMap->lock()->unlock();
6617   ConcurrentMarkSweepThread::desynchronize(true);
6618   _collector->stopTimer();
6619   if (PrintCMSStatistics != 0) {
6620     _collector->incrementYields();
6621   }
6622 
6623   // See the comment in coordinator_yield()
6624   for (unsigned i = 0; i < CMSYieldSleepCount &&
6625                        ConcurrentMarkSweepThread::should_yield() &&
6626                        !CMSCollector::foregroundGCIsActive(); ++i) {
6627     os::sleep(Thread::current(), 1, false);
6628   }
6629 
6630   ConcurrentMarkSweepThread::synchronize(true);
6631   _bitMap->lock()->lock_without_safepoint_check();
6632   _collector->startTimer();
6633 }
6634 
6635 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6636   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6637   assert(_markStack->isEmpty(),
6638          "should drain stack to limit stack usage");
6639   // convert ptr to an oop preparatory to scanning
6640   oop obj = oop(ptr);
6641   // Ignore mark word in verification below, since we
6642   // may be running concurrent with mutators.
6643   assert(obj->is_oop(true), "should be an oop");
6644   assert(_finger <= ptr, "_finger runneth ahead");
6645   // advance the finger to right end of this object
6646   _finger = ptr + obj->size();
6647   assert(_finger > ptr, "we just incremented it above");
6648   // On large heaps, it may take us some time to get through
6649   // the marking phase. During
6650   // this time it's possible that a lot of mutations have
6651   // accumulated in the card table and the mod union table --
6652   // these mutation records are redundant until we have
6653   // actually traced into the corresponding card.
6654   // Here, we check whether advancing the finger would make
6655   // us cross into a new card, and if so clear corresponding
6656   // cards in the MUT (preclean them in the card-table in the
6657   // future).
6658 
6659   DEBUG_ONLY(if (!_verifying) {)
6660     // The clean-on-enter optimization is disabled by default,
6661     // until we fix 6178663.
6662     if (CMSCleanOnEnter && (_finger > _threshold)) {
6663       // [_threshold, _finger) represents the interval
6664       // of cards to be cleared  in MUT (or precleaned in card table).
6665       // The set of cards to be cleared is all those that overlap
6666       // with the interval [_threshold, _finger); note that
6667       // _threshold is always kept card-aligned but _finger isn't
6668       // always card-aligned.
6669       HeapWord* old_threshold = _threshold;
6670       assert(old_threshold == (HeapWord*)round_to(
6671               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6672              "_threshold should always be card-aligned");
6673       _threshold = (HeapWord*)round_to(
6674                      (intptr_t)_finger, CardTableModRefBS::card_size);
6675       MemRegion mr(old_threshold, _threshold);
6676       assert(!mr.is_empty(), "Control point invariant");
6677       assert(_span.contains(mr), "Should clear within span");
6678       _mut->clear_range(mr);
6679     }
6680   DEBUG_ONLY(})
6681   // Note: the finger doesn't advance while we drain
6682   // the stack below.
6683   PushOrMarkClosure pushOrMarkClosure(_collector,
6684                                       _span, _bitMap, _markStack,
6685                                       _finger, this);
6686   bool res = _markStack->push(obj);
6687   assert(res, "Empty non-zero size stack should have space for single push");
6688   while (!_markStack->isEmpty()) {
6689     oop new_oop = _markStack->pop();
6690     // Skip verifying header mark word below because we are
6691     // running concurrent with mutators.
6692     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6693     // now scan this oop's oops
6694     new_oop->oop_iterate(&pushOrMarkClosure);
6695     do_yield_check();
6696   }
6697   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6698 }
6699 
6700 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6701                        CMSCollector* collector, MemRegion span,
6702                        CMSBitMap* bit_map,
6703                        OopTaskQueue* work_queue,
6704                        CMSMarkStack*  overflow_stack):
6705   _collector(collector),
6706   _whole_span(collector->_span),
6707   _span(span),
6708   _bit_map(bit_map),
6709   _mut(&collector->_modUnionTable),
6710   _work_queue(work_queue),
6711   _overflow_stack(overflow_stack),
6712   _skip_bits(0),
6713   _task(task)
6714 {
6715   assert(_work_queue->size() == 0, "work_queue should be empty");
6716   _finger = span.start();
6717   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6718   assert(_span.contains(_finger), "Out of bounds _finger?");
6719 }
6720 
6721 // Should revisit to see if this should be restructured for
6722 // greater efficiency.
6723 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6724   if (_skip_bits > 0) {
6725     _skip_bits--;
6726     return true;
6727   }
6728   // convert offset into a HeapWord*
6729   HeapWord* addr = _bit_map->startWord() + offset;
6730   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6731          "address out of range");
6732   assert(_bit_map->isMarked(addr), "tautology");
6733   if (_bit_map->isMarked(addr+1)) {
6734     // this is an allocated object that might not yet be initialized
6735     assert(_skip_bits == 0, "tautology");
6736     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6737     oop p = oop(addr);
6738     if (p->klass_or_null() == NULL) {
6739       // in the case of Clean-on-Enter optimization, redirty card
6740       // and avoid clearing card by increasing  the threshold.
6741       return true;
6742     }
6743   }
6744   scan_oops_in_oop(addr);
6745   return true;
6746 }
6747 
6748 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6749   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6750   // Should we assert that our work queue is empty or
6751   // below some drain limit?
6752   assert(_work_queue->size() == 0,
6753          "should drain stack to limit stack usage");
6754   // convert ptr to an oop preparatory to scanning
6755   oop obj = oop(ptr);
6756   // Ignore mark word in verification below, since we
6757   // may be running concurrent with mutators.
6758   assert(obj->is_oop(true), "should be an oop");
6759   assert(_finger <= ptr, "_finger runneth ahead");
6760   // advance the finger to right end of this object
6761   _finger = ptr + obj->size();
6762   assert(_finger > ptr, "we just incremented it above");
6763   // On large heaps, it may take us some time to get through
6764   // the marking phase. During
6765   // this time it's possible that a lot of mutations have
6766   // accumulated in the card table and the mod union table --
6767   // these mutation records are redundant until we have
6768   // actually traced into the corresponding card.
6769   // Here, we check whether advancing the finger would make
6770   // us cross into a new card, and if so clear corresponding
6771   // cards in the MUT (preclean them in the card-table in the
6772   // future).
6773 
6774   // The clean-on-enter optimization is disabled by default,
6775   // until we fix 6178663.
6776   if (CMSCleanOnEnter && (_finger > _threshold)) {
6777     // [_threshold, _finger) represents the interval
6778     // of cards to be cleared  in MUT (or precleaned in card table).
6779     // The set of cards to be cleared is all those that overlap
6780     // with the interval [_threshold, _finger); note that
6781     // _threshold is always kept card-aligned but _finger isn't
6782     // always card-aligned.
6783     HeapWord* old_threshold = _threshold;
6784     assert(old_threshold == (HeapWord*)round_to(
6785             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6786            "_threshold should always be card-aligned");
6787     _threshold = (HeapWord*)round_to(
6788                    (intptr_t)_finger, CardTableModRefBS::card_size);
6789     MemRegion mr(old_threshold, _threshold);
6790     assert(!mr.is_empty(), "Control point invariant");
6791     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6792     _mut->clear_range(mr);
6793   }
6794 
6795   // Note: the local finger doesn't advance while we drain
6796   // the stack below, but the global finger sure can and will.
6797   HeapWord** gfa = _task->global_finger_addr();
6798   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6799                                       _span, _bit_map,
6800                                       _work_queue,
6801                                       _overflow_stack,
6802                                       _finger,
6803                                       gfa, this);
6804   bool res = _work_queue->push(obj);   // overflow could occur here
6805   assert(res, "Will hold once we use workqueues");
6806   while (true) {
6807     oop new_oop;
6808     if (!_work_queue->pop_local(new_oop)) {
6809       // We emptied our work_queue; check if there's stuff that can
6810       // be gotten from the overflow stack.
6811       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6812             _overflow_stack, _work_queue)) {
6813         do_yield_check();
6814         continue;
6815       } else {  // done
6816         break;
6817       }
6818     }
6819     // Skip verifying header mark word below because we are
6820     // running concurrent with mutators.
6821     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6822     // now scan this oop's oops
6823     new_oop->oop_iterate(&pushOrMarkClosure);
6824     do_yield_check();
6825   }
6826   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6827 }
6828 
6829 // Yield in response to a request from VM Thread or
6830 // from mutators.
6831 void Par_MarkFromRootsClosure::do_yield_work() {
6832   assert(_task != NULL, "sanity");
6833   _task->yield();
6834 }
6835 
6836 // A variant of the above used for verifying CMS marking work.
6837 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6838                         MemRegion span,
6839                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6840                         CMSMarkStack*  mark_stack):
6841   _collector(collector),
6842   _span(span),
6843   _verification_bm(verification_bm),
6844   _cms_bm(cms_bm),
6845   _mark_stack(mark_stack),
6846   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6847                       mark_stack)
6848 {
6849   assert(_mark_stack->isEmpty(), "stack should be empty");
6850   _finger = _verification_bm->startWord();
6851   assert(_collector->_restart_addr == NULL, "Sanity check");
6852   assert(_span.contains(_finger), "Out of bounds _finger?");
6853 }
6854 
6855 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6856   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6857   assert(_span.contains(addr), "Out of bounds _finger?");
6858   _finger = addr;
6859 }
6860 
6861 // Should revisit to see if this should be restructured for
6862 // greater efficiency.
6863 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6864   // convert offset into a HeapWord*
6865   HeapWord* addr = _verification_bm->startWord() + offset;
6866   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6867          "address out of range");
6868   assert(_verification_bm->isMarked(addr), "tautology");
6869   assert(_cms_bm->isMarked(addr), "tautology");
6870 
6871   assert(_mark_stack->isEmpty(),
6872          "should drain stack to limit stack usage");
6873   // convert addr to an oop preparatory to scanning
6874   oop obj = oop(addr);
6875   assert(obj->is_oop(), "should be an oop");
6876   assert(_finger <= addr, "_finger runneth ahead");
6877   // advance the finger to right end of this object
6878   _finger = addr + obj->size();
6879   assert(_finger > addr, "we just incremented it above");
6880   // Note: the finger doesn't advance while we drain
6881   // the stack below.
6882   bool res = _mark_stack->push(obj);
6883   assert(res, "Empty non-zero size stack should have space for single push");
6884   while (!_mark_stack->isEmpty()) {
6885     oop new_oop = _mark_stack->pop();
6886     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6887     // now scan this oop's oops
6888     new_oop->oop_iterate(&_pam_verify_closure);
6889   }
6890   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6891   return true;
6892 }
6893 
6894 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6895   CMSCollector* collector, MemRegion span,
6896   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6897   CMSMarkStack*  mark_stack):
6898   MetadataAwareOopClosure(collector->ref_processor()),
6899   _collector(collector),
6900   _span(span),
6901   _verification_bm(verification_bm),
6902   _cms_bm(cms_bm),
6903   _mark_stack(mark_stack)
6904 { }
6905 
6906 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6907 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6908 
6909 // Upon stack overflow, we discard (part of) the stack,
6910 // remembering the least address amongst those discarded
6911 // in CMSCollector's _restart_address.
6912 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6913   // Remember the least grey address discarded
6914   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6915   _collector->lower_restart_addr(ra);
6916   _mark_stack->reset();  // discard stack contents
6917   _mark_stack->expand(); // expand the stack if possible
6918 }
6919 
6920 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6921   assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6922   HeapWord* addr = (HeapWord*)obj;
6923   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6924     // Oop lies in _span and isn't yet grey or black
6925     _verification_bm->mark(addr);            // now grey
6926     if (!_cms_bm->isMarked(addr)) {
6927       oop(addr)->print();
6928       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6929                              p2i(addr));
6930       fatal("... aborting");
6931     }
6932 
6933     if (!_mark_stack->push(obj)) { // stack overflow
6934       if (PrintCMSStatistics != 0) {
6935         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6936                                SIZE_FORMAT, _mark_stack->capacity());
6937       }
6938       assert(_mark_stack->isFull(), "Else push should have succeeded");
6939       handle_stack_overflow(addr);
6940     }
6941     // anything including and to the right of _finger
6942     // will be scanned as we iterate over the remainder of the
6943     // bit map
6944   }
6945 }
6946 
6947 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6948                      MemRegion span,
6949                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6950                      HeapWord* finger, MarkFromRootsClosure* parent) :
6951   MetadataAwareOopClosure(collector->ref_processor()),
6952   _collector(collector),
6953   _span(span),
6954   _bitMap(bitMap),
6955   _markStack(markStack),
6956   _finger(finger),
6957   _parent(parent)
6958 { }
6959 
6960 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6961                      MemRegion span,
6962                      CMSBitMap* bit_map,
6963                      OopTaskQueue* work_queue,
6964                      CMSMarkStack*  overflow_stack,
6965                      HeapWord* finger,
6966                      HeapWord** global_finger_addr,
6967                      Par_MarkFromRootsClosure* parent) :
6968   MetadataAwareOopClosure(collector->ref_processor()),
6969   _collector(collector),
6970   _whole_span(collector->_span),
6971   _span(span),
6972   _bit_map(bit_map),
6973   _work_queue(work_queue),
6974   _overflow_stack(overflow_stack),
6975   _finger(finger),
6976   _global_finger_addr(global_finger_addr),
6977   _parent(parent)
6978 { }
6979 
6980 // Assumes thread-safe access by callers, who are
6981 // responsible for mutual exclusion.
6982 void CMSCollector::lower_restart_addr(HeapWord* low) {
6983   assert(_span.contains(low), "Out of bounds addr");
6984   if (_restart_addr == NULL) {
6985     _restart_addr = low;
6986   } else {
6987     _restart_addr = MIN2(_restart_addr, low);
6988   }
6989 }
6990 
6991 // Upon stack overflow, we discard (part of) the stack,
6992 // remembering the least address amongst those discarded
6993 // in CMSCollector's _restart_address.
6994 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6995   // Remember the least grey address discarded
6996   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6997   _collector->lower_restart_addr(ra);
6998   _markStack->reset();  // discard stack contents
6999   _markStack->expand(); // expand the stack if possible
7000 }
7001 
7002 // Upon stack overflow, we discard (part of) the stack,
7003 // remembering the least address amongst those discarded
7004 // in CMSCollector's _restart_address.
7005 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7006   // We need to do this under a mutex to prevent other
7007   // workers from interfering with the work done below.
7008   MutexLockerEx ml(_overflow_stack->par_lock(),
7009                    Mutex::_no_safepoint_check_flag);
7010   // Remember the least grey address discarded
7011   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7012   _collector->lower_restart_addr(ra);
7013   _overflow_stack->reset();  // discard stack contents
7014   _overflow_stack->expand(); // expand the stack if possible
7015 }
7016 
7017 void PushOrMarkClosure::do_oop(oop obj) {
7018   // Ignore mark word because we are running concurrent with mutators.
7019   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7020   HeapWord* addr = (HeapWord*)obj;
7021   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7022     // Oop lies in _span and isn't yet grey or black
7023     _bitMap->mark(addr);            // now grey
7024     if (addr < _finger) {
7025       // the bit map iteration has already either passed, or
7026       // sampled, this bit in the bit map; we'll need to
7027       // use the marking stack to scan this oop's oops.
7028       bool simulate_overflow = false;
7029       NOT_PRODUCT(
7030         if (CMSMarkStackOverflowALot &&
7031             _collector->simulate_overflow()) {
7032           // simulate a stack overflow
7033           simulate_overflow = true;
7034         }
7035       )
7036       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7037         if (PrintCMSStatistics != 0) {
7038           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7039                                  SIZE_FORMAT, _markStack->capacity());
7040         }
7041         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7042         handle_stack_overflow(addr);
7043       }
7044     }
7045     // anything including and to the right of _finger
7046     // will be scanned as we iterate over the remainder of the
7047     // bit map
7048     do_yield_check();
7049   }
7050 }
7051 
7052 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7053 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7054 
7055 void Par_PushOrMarkClosure::do_oop(oop obj) {
7056   // Ignore mark word because we are running concurrent with mutators.
7057   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7058   HeapWord* addr = (HeapWord*)obj;
7059   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7060     // Oop lies in _span and isn't yet grey or black
7061     // We read the global_finger (volatile read) strictly after marking oop
7062     bool res = _bit_map->par_mark(addr);    // now grey
7063     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7064     // Should we push this marked oop on our stack?
7065     // -- if someone else marked it, nothing to do
7066     // -- if target oop is above global finger nothing to do
7067     // -- if target oop is in chunk and above local finger
7068     //      then nothing to do
7069     // -- else push on work queue
7070     if (   !res       // someone else marked it, they will deal with it
7071         || (addr >= *gfa)  // will be scanned in a later task
7072         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7073       return;
7074     }
7075     // the bit map iteration has already either passed, or
7076     // sampled, this bit in the bit map; we'll need to
7077     // use the marking stack to scan this oop's oops.
7078     bool simulate_overflow = false;
7079     NOT_PRODUCT(
7080       if (CMSMarkStackOverflowALot &&
7081           _collector->simulate_overflow()) {
7082         // simulate a stack overflow
7083         simulate_overflow = true;
7084       }
7085     )
7086     if (simulate_overflow ||
7087         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7088       // stack overflow
7089       if (PrintCMSStatistics != 0) {
7090         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7091                                SIZE_FORMAT, _overflow_stack->capacity());
7092       }
7093       // We cannot assert that the overflow stack is full because
7094       // it may have been emptied since.
7095       assert(simulate_overflow ||
7096              _work_queue->size() == _work_queue->max_elems(),
7097             "Else push should have succeeded");
7098       handle_stack_overflow(addr);
7099     }
7100     do_yield_check();
7101   }
7102 }
7103 
7104 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7105 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7106 
7107 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7108                                        MemRegion span,
7109                                        ReferenceProcessor* rp,
7110                                        CMSBitMap* bit_map,
7111                                        CMSBitMap* mod_union_table,
7112                                        CMSMarkStack*  mark_stack,
7113                                        bool           concurrent_precleaning):
7114   MetadataAwareOopClosure(rp),
7115   _collector(collector),
7116   _span(span),
7117   _bit_map(bit_map),
7118   _mod_union_table(mod_union_table),
7119   _mark_stack(mark_stack),
7120   _concurrent_precleaning(concurrent_precleaning)
7121 {
7122   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7123 }
7124 
7125 // Grey object rescan during pre-cleaning and second checkpoint phases --
7126 // the non-parallel version (the parallel version appears further below.)
7127 void PushAndMarkClosure::do_oop(oop obj) {
7128   // Ignore mark word verification. If during concurrent precleaning,
7129   // the object monitor may be locked. If during the checkpoint
7130   // phases, the object may already have been reached by a  different
7131   // path and may be at the end of the global overflow list (so
7132   // the mark word may be NULL).
7133   assert(obj->is_oop_or_null(true /* ignore mark word */),
7134          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7135   HeapWord* addr = (HeapWord*)obj;
7136   // Check if oop points into the CMS generation
7137   // and is not marked
7138   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7139     // a white object ...
7140     _bit_map->mark(addr);         // ... now grey
7141     // push on the marking stack (grey set)
7142     bool simulate_overflow = false;
7143     NOT_PRODUCT(
7144       if (CMSMarkStackOverflowALot &&
7145           _collector->simulate_overflow()) {
7146         // simulate a stack overflow
7147         simulate_overflow = true;
7148       }
7149     )
7150     if (simulate_overflow || !_mark_stack->push(obj)) {
7151       if (_concurrent_precleaning) {
7152          // During precleaning we can just dirty the appropriate card(s)
7153          // in the mod union table, thus ensuring that the object remains
7154          // in the grey set  and continue. In the case of object arrays
7155          // we need to dirty all of the cards that the object spans,
7156          // since the rescan of object arrays will be limited to the
7157          // dirty cards.
7158          // Note that no one can be interfering with us in this action
7159          // of dirtying the mod union table, so no locking or atomics
7160          // are required.
7161          if (obj->is_objArray()) {
7162            size_t sz = obj->size();
7163            HeapWord* end_card_addr = (HeapWord*)round_to(
7164                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7165            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7166            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7167            _mod_union_table->mark_range(redirty_range);
7168          } else {
7169            _mod_union_table->mark(addr);
7170          }
7171          _collector->_ser_pmc_preclean_ovflw++;
7172       } else {
7173          // During the remark phase, we need to remember this oop
7174          // in the overflow list.
7175          _collector->push_on_overflow_list(obj);
7176          _collector->_ser_pmc_remark_ovflw++;
7177       }
7178     }
7179   }
7180 }
7181 
7182 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7183                                                MemRegion span,
7184                                                ReferenceProcessor* rp,
7185                                                CMSBitMap* bit_map,
7186                                                OopTaskQueue* work_queue):
7187   MetadataAwareOopClosure(rp),
7188   _collector(collector),
7189   _span(span),
7190   _bit_map(bit_map),
7191   _work_queue(work_queue)
7192 {
7193   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7194 }
7195 
7196 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7197 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7198 
7199 // Grey object rescan during second checkpoint phase --
7200 // the parallel version.
7201 void Par_PushAndMarkClosure::do_oop(oop obj) {
7202   // In the assert below, we ignore the mark word because
7203   // this oop may point to an already visited object that is
7204   // on the overflow stack (in which case the mark word has
7205   // been hijacked for chaining into the overflow stack --
7206   // if this is the last object in the overflow stack then
7207   // its mark word will be NULL). Because this object may
7208   // have been subsequently popped off the global overflow
7209   // stack, and the mark word possibly restored to the prototypical
7210   // value, by the time we get to examined this failing assert in
7211   // the debugger, is_oop_or_null(false) may subsequently start
7212   // to hold.
7213   assert(obj->is_oop_or_null(true),
7214          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7215   HeapWord* addr = (HeapWord*)obj;
7216   // Check if oop points into the CMS generation
7217   // and is not marked
7218   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7219     // a white object ...
7220     // If we manage to "claim" the object, by being the
7221     // first thread to mark it, then we push it on our
7222     // marking stack
7223     if (_bit_map->par_mark(addr)) {     // ... now grey
7224       // push on work queue (grey set)
7225       bool simulate_overflow = false;
7226       NOT_PRODUCT(
7227         if (CMSMarkStackOverflowALot &&
7228             _collector->par_simulate_overflow()) {
7229           // simulate a stack overflow
7230           simulate_overflow = true;
7231         }
7232       )
7233       if (simulate_overflow || !_work_queue->push(obj)) {
7234         _collector->par_push_on_overflow_list(obj);
7235         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7236       }
7237     } // Else, some other thread got there first
7238   }
7239 }
7240 
7241 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7242 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7243 
7244 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7245   Mutex* bml = _collector->bitMapLock();
7246   assert_lock_strong(bml);
7247   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7248          "CMS thread should hold CMS token");
7249 
7250   bml->unlock();
7251   ConcurrentMarkSweepThread::desynchronize(true);
7252 
7253   _collector->stopTimer();
7254   if (PrintCMSStatistics != 0) {
7255     _collector->incrementYields();
7256   }
7257 
7258   // See the comment in coordinator_yield()
7259   for (unsigned i = 0; i < CMSYieldSleepCount &&
7260                        ConcurrentMarkSweepThread::should_yield() &&
7261                        !CMSCollector::foregroundGCIsActive(); ++i) {
7262     os::sleep(Thread::current(), 1, false);
7263   }
7264 
7265   ConcurrentMarkSweepThread::synchronize(true);
7266   bml->lock();
7267 
7268   _collector->startTimer();
7269 }
7270 
7271 bool CMSPrecleanRefsYieldClosure::should_return() {
7272   if (ConcurrentMarkSweepThread::should_yield()) {
7273     do_yield_work();
7274   }
7275   return _collector->foregroundGCIsActive();
7276 }
7277 
7278 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7279   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7280          "mr should be aligned to start at a card boundary");
7281   // We'd like to assert:
7282   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7283   //        "mr should be a range of cards");
7284   // However, that would be too strong in one case -- the last
7285   // partition ends at _unallocated_block which, in general, can be
7286   // an arbitrary boundary, not necessarily card aligned.
7287   if (PrintCMSStatistics != 0) {
7288     _num_dirty_cards +=
7289          mr.word_size()/CardTableModRefBS::card_size_in_words;
7290   }
7291   _space->object_iterate_mem(mr, &_scan_cl);
7292 }
7293 
7294 SweepClosure::SweepClosure(CMSCollector* collector,
7295                            ConcurrentMarkSweepGeneration* g,
7296                            CMSBitMap* bitMap, bool should_yield) :
7297   _collector(collector),
7298   _g(g),
7299   _sp(g->cmsSpace()),
7300   _limit(_sp->sweep_limit()),
7301   _freelistLock(_sp->freelistLock()),
7302   _bitMap(bitMap),
7303   _yield(should_yield),
7304   _inFreeRange(false),           // No free range at beginning of sweep
7305   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7306   _lastFreeRangeCoalesced(false),
7307   _freeFinger(g->used_region().start())
7308 {
7309   NOT_PRODUCT(
7310     _numObjectsFreed = 0;
7311     _numWordsFreed   = 0;
7312     _numObjectsLive = 0;
7313     _numWordsLive = 0;
7314     _numObjectsAlreadyFree = 0;
7315     _numWordsAlreadyFree = 0;
7316     _last_fc = NULL;
7317 
7318     _sp->initializeIndexedFreeListArrayReturnedBytes();
7319     _sp->dictionary()->initialize_dict_returned_bytes();
7320   )
7321   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7322          "sweep _limit out of bounds");
7323   if (CMSTraceSweeper) {
7324     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7325                         p2i(_limit));
7326   }
7327 }
7328 
7329 void SweepClosure::print_on(outputStream* st) const {
7330   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7331                 p2i(_sp->bottom()), p2i(_sp->end()));
7332   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7333   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7334   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7335   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7336                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7337 }
7338 
7339 #ifndef PRODUCT
7340 // Assertion checking only:  no useful work in product mode --
7341 // however, if any of the flags below become product flags,
7342 // you may need to review this code to see if it needs to be
7343 // enabled in product mode.
7344 SweepClosure::~SweepClosure() {
7345   assert_lock_strong(_freelistLock);
7346   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7347          "sweep _limit out of bounds");
7348   if (inFreeRange()) {
7349     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7350     print();
7351     ShouldNotReachHere();
7352   }
7353   if (Verbose && PrintGC) {
7354     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7355                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7356     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7357                            SIZE_FORMAT" bytes  "
7358       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7359       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7360       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7361     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7362                         * sizeof(HeapWord);
7363     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7364 
7365     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7366       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7367       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7368       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7369       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7370       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7371         indexListReturnedBytes);
7372       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7373         dict_returned_bytes);
7374     }
7375   }
7376   if (CMSTraceSweeper) {
7377     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7378                            p2i(_limit));
7379   }
7380 }
7381 #endif  // PRODUCT
7382 
7383 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7384     bool freeRangeInFreeLists) {
7385   if (CMSTraceSweeper) {
7386     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7387                p2i(freeFinger), freeRangeInFreeLists);
7388   }
7389   assert(!inFreeRange(), "Trampling existing free range");
7390   set_inFreeRange(true);
7391   set_lastFreeRangeCoalesced(false);
7392 
7393   set_freeFinger(freeFinger);
7394   set_freeRangeInFreeLists(freeRangeInFreeLists);
7395   if (CMSTestInFreeList) {
7396     if (freeRangeInFreeLists) {
7397       FreeChunk* fc = (FreeChunk*) freeFinger;
7398       assert(fc->is_free(), "A chunk on the free list should be free.");
7399       assert(fc->size() > 0, "Free range should have a size");
7400       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7401     }
7402   }
7403 }
7404 
7405 // Note that the sweeper runs concurrently with mutators. Thus,
7406 // it is possible for direct allocation in this generation to happen
7407 // in the middle of the sweep. Note that the sweeper also coalesces
7408 // contiguous free blocks. Thus, unless the sweeper and the allocator
7409 // synchronize appropriately freshly allocated blocks may get swept up.
7410 // This is accomplished by the sweeper locking the free lists while
7411 // it is sweeping. Thus blocks that are determined to be free are
7412 // indeed free. There is however one additional complication:
7413 // blocks that have been allocated since the final checkpoint and
7414 // mark, will not have been marked and so would be treated as
7415 // unreachable and swept up. To prevent this, the allocator marks
7416 // the bit map when allocating during the sweep phase. This leads,
7417 // however, to a further complication -- objects may have been allocated
7418 // but not yet initialized -- in the sense that the header isn't yet
7419 // installed. The sweeper can not then determine the size of the block
7420 // in order to skip over it. To deal with this case, we use a technique
7421 // (due to Printezis) to encode such uninitialized block sizes in the
7422 // bit map. Since the bit map uses a bit per every HeapWord, but the
7423 // CMS generation has a minimum object size of 3 HeapWords, it follows
7424 // that "normal marks" won't be adjacent in the bit map (there will
7425 // always be at least two 0 bits between successive 1 bits). We make use
7426 // of these "unused" bits to represent uninitialized blocks -- the bit
7427 // corresponding to the start of the uninitialized object and the next
7428 // bit are both set. Finally, a 1 bit marks the end of the object that
7429 // started with the two consecutive 1 bits to indicate its potentially
7430 // uninitialized state.
7431 
7432 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7433   FreeChunk* fc = (FreeChunk*)addr;
7434   size_t res;
7435 
7436   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7437   // than "addr == _limit" because although _limit was a block boundary when
7438   // we started the sweep, it may no longer be one because heap expansion
7439   // may have caused us to coalesce the block ending at the address _limit
7440   // with a newly expanded chunk (this happens when _limit was set to the
7441   // previous _end of the space), so we may have stepped past _limit:
7442   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7443   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7444     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7445            "sweep _limit out of bounds");
7446     assert(addr < _sp->end(), "addr out of bounds");
7447     // Flush any free range we might be holding as a single
7448     // coalesced chunk to the appropriate free list.
7449     if (inFreeRange()) {
7450       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7451              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7452       flush_cur_free_chunk(freeFinger(),
7453                            pointer_delta(addr, freeFinger()));
7454       if (CMSTraceSweeper) {
7455         gclog_or_tty->print("Sweep: last chunk: ");
7456         gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7457                    "[coalesced:%d]\n",
7458                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7459                    lastFreeRangeCoalesced() ? 1 : 0);
7460       }
7461     }
7462 
7463     // help the iterator loop finish
7464     return pointer_delta(_sp->end(), addr);
7465   }
7466 
7467   assert(addr < _limit, "sweep invariant");
7468   // check if we should yield
7469   do_yield_check(addr);
7470   if (fc->is_free()) {
7471     // Chunk that is already free
7472     res = fc->size();
7473     do_already_free_chunk(fc);
7474     debug_only(_sp->verifyFreeLists());
7475     // If we flush the chunk at hand in lookahead_and_flush()
7476     // and it's coalesced with a preceding chunk, then the
7477     // process of "mangling" the payload of the coalesced block
7478     // will cause erasure of the size information from the
7479     // (erstwhile) header of all the coalesced blocks but the
7480     // first, so the first disjunct in the assert will not hold
7481     // in that specific case (in which case the second disjunct
7482     // will hold).
7483     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7484            "Otherwise the size info doesn't change at this step");
7485     NOT_PRODUCT(
7486       _numObjectsAlreadyFree++;
7487       _numWordsAlreadyFree += res;
7488     )
7489     NOT_PRODUCT(_last_fc = fc;)
7490   } else if (!_bitMap->isMarked(addr)) {
7491     // Chunk is fresh garbage
7492     res = do_garbage_chunk(fc);
7493     debug_only(_sp->verifyFreeLists());
7494     NOT_PRODUCT(
7495       _numObjectsFreed++;
7496       _numWordsFreed += res;
7497     )
7498   } else {
7499     // Chunk that is alive.
7500     res = do_live_chunk(fc);
7501     debug_only(_sp->verifyFreeLists());
7502     NOT_PRODUCT(
7503         _numObjectsLive++;
7504         _numWordsLive += res;
7505     )
7506   }
7507   return res;
7508 }
7509 
7510 // For the smart allocation, record following
7511 //  split deaths - a free chunk is removed from its free list because
7512 //      it is being split into two or more chunks.
7513 //  split birth - a free chunk is being added to its free list because
7514 //      a larger free chunk has been split and resulted in this free chunk.
7515 //  coal death - a free chunk is being removed from its free list because
7516 //      it is being coalesced into a large free chunk.
7517 //  coal birth - a free chunk is being added to its free list because
7518 //      it was created when two or more free chunks where coalesced into
7519 //      this free chunk.
7520 //
7521 // These statistics are used to determine the desired number of free
7522 // chunks of a given size.  The desired number is chosen to be relative
7523 // to the end of a CMS sweep.  The desired number at the end of a sweep
7524 // is the
7525 //      count-at-end-of-previous-sweep (an amount that was enough)
7526 //              - count-at-beginning-of-current-sweep  (the excess)
7527 //              + split-births  (gains in this size during interval)
7528 //              - split-deaths  (demands on this size during interval)
7529 // where the interval is from the end of one sweep to the end of the
7530 // next.
7531 //
7532 // When sweeping the sweeper maintains an accumulated chunk which is
7533 // the chunk that is made up of chunks that have been coalesced.  That
7534 // will be termed the left-hand chunk.  A new chunk of garbage that
7535 // is being considered for coalescing will be referred to as the
7536 // right-hand chunk.
7537 //
7538 // When making a decision on whether to coalesce a right-hand chunk with
7539 // the current left-hand chunk, the current count vs. the desired count
7540 // of the left-hand chunk is considered.  Also if the right-hand chunk
7541 // is near the large chunk at the end of the heap (see
7542 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7543 // left-hand chunk is coalesced.
7544 //
7545 // When making a decision about whether to split a chunk, the desired count
7546 // vs. the current count of the candidate to be split is also considered.
7547 // If the candidate is underpopulated (currently fewer chunks than desired)
7548 // a chunk of an overpopulated (currently more chunks than desired) size may
7549 // be chosen.  The "hint" associated with a free list, if non-null, points
7550 // to a free list which may be overpopulated.
7551 //
7552 
7553 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7554   const size_t size = fc->size();
7555   // Chunks that cannot be coalesced are not in the
7556   // free lists.
7557   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7558     assert(_sp->verify_chunk_in_free_list(fc),
7559       "free chunk should be in free lists");
7560   }
7561   // a chunk that is already free, should not have been
7562   // marked in the bit map
7563   HeapWord* const addr = (HeapWord*) fc;
7564   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7565   // Verify that the bit map has no bits marked between
7566   // addr and purported end of this block.
7567   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7568 
7569   // Some chunks cannot be coalesced under any circumstances.
7570   // See the definition of cantCoalesce().
7571   if (!fc->cantCoalesce()) {
7572     // This chunk can potentially be coalesced.
7573     if (_sp->adaptive_freelists()) {
7574       // All the work is done in
7575       do_post_free_or_garbage_chunk(fc, size);
7576     } else {  // Not adaptive free lists
7577       // this is a free chunk that can potentially be coalesced by the sweeper;
7578       if (!inFreeRange()) {
7579         // if the next chunk is a free block that can't be coalesced
7580         // it doesn't make sense to remove this chunk from the free lists
7581         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7582         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7583         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
7584             nextChunk->is_free()               &&     // ... which is free...
7585             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
7586           // nothing to do
7587         } else {
7588           // Potentially the start of a new free range:
7589           // Don't eagerly remove it from the free lists.
7590           // No need to remove it if it will just be put
7591           // back again.  (Also from a pragmatic point of view
7592           // if it is a free block in a region that is beyond
7593           // any allocated blocks, an assertion will fail)
7594           // Remember the start of a free run.
7595           initialize_free_range(addr, true);
7596           // end - can coalesce with next chunk
7597         }
7598       } else {
7599         // the midst of a free range, we are coalescing
7600         print_free_block_coalesced(fc);
7601         if (CMSTraceSweeper) {
7602           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7603         }
7604         // remove it from the free lists
7605         _sp->removeFreeChunkFromFreeLists(fc);
7606         set_lastFreeRangeCoalesced(true);
7607         // If the chunk is being coalesced and the current free range is
7608         // in the free lists, remove the current free range so that it
7609         // will be returned to the free lists in its entirety - all
7610         // the coalesced pieces included.
7611         if (freeRangeInFreeLists()) {
7612           FreeChunk* ffc = (FreeChunk*) freeFinger();
7613           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7614             "Size of free range is inconsistent with chunk size.");
7615           if (CMSTestInFreeList) {
7616             assert(_sp->verify_chunk_in_free_list(ffc),
7617               "free range is not in free lists");
7618           }
7619           _sp->removeFreeChunkFromFreeLists(ffc);
7620           set_freeRangeInFreeLists(false);
7621         }
7622       }
7623     }
7624     // Note that if the chunk is not coalescable (the else arm
7625     // below), we unconditionally flush, without needing to do
7626     // a "lookahead," as we do below.
7627     if (inFreeRange()) lookahead_and_flush(fc, size);
7628   } else {
7629     // Code path common to both original and adaptive free lists.
7630 
7631     // cant coalesce with previous block; this should be treated
7632     // as the end of a free run if any
7633     if (inFreeRange()) {
7634       // we kicked some butt; time to pick up the garbage
7635       assert(freeFinger() < addr, "freeFinger points too high");
7636       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7637     }
7638     // else, nothing to do, just continue
7639   }
7640 }
7641 
7642 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7643   // This is a chunk of garbage.  It is not in any free list.
7644   // Add it to a free list or let it possibly be coalesced into
7645   // a larger chunk.
7646   HeapWord* const addr = (HeapWord*) fc;
7647   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7648 
7649   if (_sp->adaptive_freelists()) {
7650     // Verify that the bit map has no bits marked between
7651     // addr and purported end of just dead object.
7652     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7653 
7654     do_post_free_or_garbage_chunk(fc, size);
7655   } else {
7656     if (!inFreeRange()) {
7657       // start of a new free range
7658       assert(size > 0, "A free range should have a size");
7659       initialize_free_range(addr, false);
7660     } else {
7661       // this will be swept up when we hit the end of the
7662       // free range
7663       if (CMSTraceSweeper) {
7664         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7665       }
7666       // If the chunk is being coalesced and the current free range is
7667       // in the free lists, remove the current free range so that it
7668       // will be returned to the free lists in its entirety - all
7669       // the coalesced pieces included.
7670       if (freeRangeInFreeLists()) {
7671         FreeChunk* ffc = (FreeChunk*)freeFinger();
7672         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7673           "Size of free range is inconsistent with chunk size.");
7674         if (CMSTestInFreeList) {
7675           assert(_sp->verify_chunk_in_free_list(ffc),
7676             "free range is not in free lists");
7677         }
7678         _sp->removeFreeChunkFromFreeLists(ffc);
7679         set_freeRangeInFreeLists(false);
7680       }
7681       set_lastFreeRangeCoalesced(true);
7682     }
7683     // this will be swept up when we hit the end of the free range
7684 
7685     // Verify that the bit map has no bits marked between
7686     // addr and purported end of just dead object.
7687     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7688   }
7689   assert(_limit >= addr + size,
7690          "A freshly garbage chunk can't possibly straddle over _limit");
7691   if (inFreeRange()) lookahead_and_flush(fc, size);
7692   return size;
7693 }
7694 
7695 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7696   HeapWord* addr = (HeapWord*) fc;
7697   // The sweeper has just found a live object. Return any accumulated
7698   // left hand chunk to the free lists.
7699   if (inFreeRange()) {
7700     assert(freeFinger() < addr, "freeFinger points too high");
7701     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7702   }
7703 
7704   // This object is live: we'd normally expect this to be
7705   // an oop, and like to assert the following:
7706   // assert(oop(addr)->is_oop(), "live block should be an oop");
7707   // However, as we commented above, this may be an object whose
7708   // header hasn't yet been initialized.
7709   size_t size;
7710   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7711   if (_bitMap->isMarked(addr + 1)) {
7712     // Determine the size from the bit map, rather than trying to
7713     // compute it from the object header.
7714     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7715     size = pointer_delta(nextOneAddr + 1, addr);
7716     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7717            "alignment problem");
7718 
7719 #ifdef ASSERT
7720       if (oop(addr)->klass_or_null() != NULL) {
7721         // Ignore mark word because we are running concurrent with mutators
7722         assert(oop(addr)->is_oop(true), "live block should be an oop");
7723         assert(size ==
7724                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7725                "P-mark and computed size do not agree");
7726       }
7727 #endif
7728 
7729   } else {
7730     // This should be an initialized object that's alive.
7731     assert(oop(addr)->klass_or_null() != NULL,
7732            "Should be an initialized object");
7733     // Ignore mark word because we are running concurrent with mutators
7734     assert(oop(addr)->is_oop(true), "live block should be an oop");
7735     // Verify that the bit map has no bits marked between
7736     // addr and purported end of this block.
7737     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7738     assert(size >= 3, "Necessary for Printezis marks to work");
7739     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7740     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7741   }
7742   return size;
7743 }
7744 
7745 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7746                                                  size_t chunkSize) {
7747   // do_post_free_or_garbage_chunk() should only be called in the case
7748   // of the adaptive free list allocator.
7749   const bool fcInFreeLists = fc->is_free();
7750   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7751   assert((HeapWord*)fc <= _limit, "sweep invariant");
7752   if (CMSTestInFreeList && fcInFreeLists) {
7753     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7754   }
7755 
7756   if (CMSTraceSweeper) {
7757     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7758   }
7759 
7760   HeapWord* const fc_addr = (HeapWord*) fc;
7761 
7762   bool coalesce;
7763   const size_t left  = pointer_delta(fc_addr, freeFinger());
7764   const size_t right = chunkSize;
7765   switch (FLSCoalescePolicy) {
7766     // numeric value forms a coalition aggressiveness metric
7767     case 0:  { // never coalesce
7768       coalesce = false;
7769       break;
7770     }
7771     case 1: { // coalesce if left & right chunks on overpopulated lists
7772       coalesce = _sp->coalOverPopulated(left) &&
7773                  _sp->coalOverPopulated(right);
7774       break;
7775     }
7776     case 2: { // coalesce if left chunk on overpopulated list (default)
7777       coalesce = _sp->coalOverPopulated(left);
7778       break;
7779     }
7780     case 3: { // coalesce if left OR right chunk on overpopulated list
7781       coalesce = _sp->coalOverPopulated(left) ||
7782                  _sp->coalOverPopulated(right);
7783       break;
7784     }
7785     case 4: { // always coalesce
7786       coalesce = true;
7787       break;
7788     }
7789     default:
7790      ShouldNotReachHere();
7791   }
7792 
7793   // Should the current free range be coalesced?
7794   // If the chunk is in a free range and either we decided to coalesce above
7795   // or the chunk is near the large block at the end of the heap
7796   // (isNearLargestChunk() returns true), then coalesce this chunk.
7797   const bool doCoalesce = inFreeRange()
7798                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7799   if (doCoalesce) {
7800     // Coalesce the current free range on the left with the new
7801     // chunk on the right.  If either is on a free list,
7802     // it must be removed from the list and stashed in the closure.
7803     if (freeRangeInFreeLists()) {
7804       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7805       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7806         "Size of free range is inconsistent with chunk size.");
7807       if (CMSTestInFreeList) {
7808         assert(_sp->verify_chunk_in_free_list(ffc),
7809           "Chunk is not in free lists");
7810       }
7811       _sp->coalDeath(ffc->size());
7812       _sp->removeFreeChunkFromFreeLists(ffc);
7813       set_freeRangeInFreeLists(false);
7814     }
7815     if (fcInFreeLists) {
7816       _sp->coalDeath(chunkSize);
7817       assert(fc->size() == chunkSize,
7818         "The chunk has the wrong size or is not in the free lists");
7819       _sp->removeFreeChunkFromFreeLists(fc);
7820     }
7821     set_lastFreeRangeCoalesced(true);
7822     print_free_block_coalesced(fc);
7823   } else {  // not in a free range and/or should not coalesce
7824     // Return the current free range and start a new one.
7825     if (inFreeRange()) {
7826       // In a free range but cannot coalesce with the right hand chunk.
7827       // Put the current free range into the free lists.
7828       flush_cur_free_chunk(freeFinger(),
7829                            pointer_delta(fc_addr, freeFinger()));
7830     }
7831     // Set up for new free range.  Pass along whether the right hand
7832     // chunk is in the free lists.
7833     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7834   }
7835 }
7836 
7837 // Lookahead flush:
7838 // If we are tracking a free range, and this is the last chunk that
7839 // we'll look at because its end crosses past _limit, we'll preemptively
7840 // flush it along with any free range we may be holding on to. Note that
7841 // this can be the case only for an already free or freshly garbage
7842 // chunk. If this block is an object, it can never straddle
7843 // over _limit. The "straddling" occurs when _limit is set at
7844 // the previous end of the space when this cycle started, and
7845 // a subsequent heap expansion caused the previously co-terminal
7846 // free block to be coalesced with the newly expanded portion,
7847 // thus rendering _limit a non-block-boundary making it dangerous
7848 // for the sweeper to step over and examine.
7849 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7850   assert(inFreeRange(), "Should only be called if currently in a free range.");
7851   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7852   assert(_sp->used_region().contains(eob - 1),
7853          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7854                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7855                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7856                  p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7857   if (eob >= _limit) {
7858     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7859     if (CMSTraceSweeper) {
7860       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7861                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7862                              "[" PTR_FORMAT "," PTR_FORMAT ")",
7863                              p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7864     }
7865     // Return the storage we are tracking back into the free lists.
7866     if (CMSTraceSweeper) {
7867       gclog_or_tty->print_cr("Flushing ... ");
7868     }
7869     assert(freeFinger() < eob, "Error");
7870     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7871   }
7872 }
7873 
7874 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7875   assert(inFreeRange(), "Should only be called if currently in a free range.");
7876   assert(size > 0,
7877     "A zero sized chunk cannot be added to the free lists.");
7878   if (!freeRangeInFreeLists()) {
7879     if (CMSTestInFreeList) {
7880       FreeChunk* fc = (FreeChunk*) chunk;
7881       fc->set_size(size);
7882       assert(!_sp->verify_chunk_in_free_list(fc),
7883         "chunk should not be in free lists yet");
7884     }
7885     if (CMSTraceSweeper) {
7886       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7887                     p2i(chunk), size);
7888     }
7889     // A new free range is going to be starting.  The current
7890     // free range has not been added to the free lists yet or
7891     // was removed so add it back.
7892     // If the current free range was coalesced, then the death
7893     // of the free range was recorded.  Record a birth now.
7894     if (lastFreeRangeCoalesced()) {
7895       _sp->coalBirth(size);
7896     }
7897     _sp->addChunkAndRepairOffsetTable(chunk, size,
7898             lastFreeRangeCoalesced());
7899   } else if (CMSTraceSweeper) {
7900     gclog_or_tty->print_cr("Already in free list: nothing to flush");
7901   }
7902   set_inFreeRange(false);
7903   set_freeRangeInFreeLists(false);
7904 }
7905 
7906 // We take a break if we've been at this for a while,
7907 // so as to avoid monopolizing the locks involved.
7908 void SweepClosure::do_yield_work(HeapWord* addr) {
7909   // Return current free chunk being used for coalescing (if any)
7910   // to the appropriate freelist.  After yielding, the next
7911   // free block encountered will start a coalescing range of
7912   // free blocks.  If the next free block is adjacent to the
7913   // chunk just flushed, they will need to wait for the next
7914   // sweep to be coalesced.
7915   if (inFreeRange()) {
7916     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7917   }
7918 
7919   // First give up the locks, then yield, then re-lock.
7920   // We should probably use a constructor/destructor idiom to
7921   // do this unlock/lock or modify the MutexUnlocker class to
7922   // serve our purpose. XXX
7923   assert_lock_strong(_bitMap->lock());
7924   assert_lock_strong(_freelistLock);
7925   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7926          "CMS thread should hold CMS token");
7927   _bitMap->lock()->unlock();
7928   _freelistLock->unlock();
7929   ConcurrentMarkSweepThread::desynchronize(true);
7930   _collector->stopTimer();
7931   if (PrintCMSStatistics != 0) {
7932     _collector->incrementYields();
7933   }
7934 
7935   // See the comment in coordinator_yield()
7936   for (unsigned i = 0; i < CMSYieldSleepCount &&
7937                        ConcurrentMarkSweepThread::should_yield() &&
7938                        !CMSCollector::foregroundGCIsActive(); ++i) {
7939     os::sleep(Thread::current(), 1, false);
7940   }
7941 
7942   ConcurrentMarkSweepThread::synchronize(true);
7943   _freelistLock->lock();
7944   _bitMap->lock()->lock_without_safepoint_check();
7945   _collector->startTimer();
7946 }
7947 
7948 #ifndef PRODUCT
7949 // This is actually very useful in a product build if it can
7950 // be called from the debugger.  Compile it into the product
7951 // as needed.
7952 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7953   return debug_cms_space->verify_chunk_in_free_list(fc);
7954 }
7955 #endif
7956 
7957 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7958   if (CMSTraceSweeper) {
7959     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7960                            p2i(fc), fc->size());
7961   }
7962 }
7963 
7964 // CMSIsAliveClosure
7965 bool CMSIsAliveClosure::do_object_b(oop obj) {
7966   HeapWord* addr = (HeapWord*)obj;
7967   return addr != NULL &&
7968          (!_span.contains(addr) || _bit_map->isMarked(addr));
7969 }
7970 
7971 
7972 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7973                       MemRegion span,
7974                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7975                       bool cpc):
7976   _collector(collector),
7977   _span(span),
7978   _bit_map(bit_map),
7979   _mark_stack(mark_stack),
7980   _concurrent_precleaning(cpc) {
7981   assert(!_span.is_empty(), "Empty span could spell trouble");
7982 }
7983 
7984 
7985 // CMSKeepAliveClosure: the serial version
7986 void CMSKeepAliveClosure::do_oop(oop obj) {
7987   HeapWord* addr = (HeapWord*)obj;
7988   if (_span.contains(addr) &&
7989       !_bit_map->isMarked(addr)) {
7990     _bit_map->mark(addr);
7991     bool simulate_overflow = false;
7992     NOT_PRODUCT(
7993       if (CMSMarkStackOverflowALot &&
7994           _collector->simulate_overflow()) {
7995         // simulate a stack overflow
7996         simulate_overflow = true;
7997       }
7998     )
7999     if (simulate_overflow || !_mark_stack->push(obj)) {
8000       if (_concurrent_precleaning) {
8001         // We dirty the overflown object and let the remark
8002         // phase deal with it.
8003         assert(_collector->overflow_list_is_empty(), "Error");
8004         // In the case of object arrays, we need to dirty all of
8005         // the cards that the object spans. No locking or atomics
8006         // are needed since no one else can be mutating the mod union
8007         // table.
8008         if (obj->is_objArray()) {
8009           size_t sz = obj->size();
8010           HeapWord* end_card_addr =
8011             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8012           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8013           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8014           _collector->_modUnionTable.mark_range(redirty_range);
8015         } else {
8016           _collector->_modUnionTable.mark(addr);
8017         }
8018         _collector->_ser_kac_preclean_ovflw++;
8019       } else {
8020         _collector->push_on_overflow_list(obj);
8021         _collector->_ser_kac_ovflw++;
8022       }
8023     }
8024   }
8025 }
8026 
8027 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8028 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8029 
8030 // CMSParKeepAliveClosure: a parallel version of the above.
8031 // The work queues are private to each closure (thread),
8032 // but (may be) available for stealing by other threads.
8033 void CMSParKeepAliveClosure::do_oop(oop obj) {
8034   HeapWord* addr = (HeapWord*)obj;
8035   if (_span.contains(addr) &&
8036       !_bit_map->isMarked(addr)) {
8037     // In general, during recursive tracing, several threads
8038     // may be concurrently getting here; the first one to
8039     // "tag" it, claims it.
8040     if (_bit_map->par_mark(addr)) {
8041       bool res = _work_queue->push(obj);
8042       assert(res, "Low water mark should be much less than capacity");
8043       // Do a recursive trim in the hope that this will keep
8044       // stack usage lower, but leave some oops for potential stealers
8045       trim_queue(_low_water_mark);
8046     } // Else, another thread got there first
8047   }
8048 }
8049 
8050 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8051 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8052 
8053 void CMSParKeepAliveClosure::trim_queue(uint max) {
8054   while (_work_queue->size() > max) {
8055     oop new_oop;
8056     if (_work_queue->pop_local(new_oop)) {
8057       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8058       assert(_bit_map->isMarked((HeapWord*)new_oop),
8059              "no white objects on this stack!");
8060       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8061       // iterate over the oops in this oop, marking and pushing
8062       // the ones in CMS heap (i.e. in _span).
8063       new_oop->oop_iterate(&_mark_and_push);
8064     }
8065   }
8066 }
8067 
8068 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8069                                 CMSCollector* collector,
8070                                 MemRegion span, CMSBitMap* bit_map,
8071                                 OopTaskQueue* work_queue):
8072   _collector(collector),
8073   _span(span),
8074   _bit_map(bit_map),
8075   _work_queue(work_queue) { }
8076 
8077 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8078   HeapWord* addr = (HeapWord*)obj;
8079   if (_span.contains(addr) &&
8080       !_bit_map->isMarked(addr)) {
8081     if (_bit_map->par_mark(addr)) {
8082       bool simulate_overflow = false;
8083       NOT_PRODUCT(
8084         if (CMSMarkStackOverflowALot &&
8085             _collector->par_simulate_overflow()) {
8086           // simulate a stack overflow
8087           simulate_overflow = true;
8088         }
8089       )
8090       if (simulate_overflow || !_work_queue->push(obj)) {
8091         _collector->par_push_on_overflow_list(obj);
8092         _collector->_par_kac_ovflw++;
8093       }
8094     } // Else another thread got there already
8095   }
8096 }
8097 
8098 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8099 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8100 
8101 //////////////////////////////////////////////////////////////////
8102 //  CMSExpansionCause                /////////////////////////////
8103 //////////////////////////////////////////////////////////////////
8104 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8105   switch (cause) {
8106     case _no_expansion:
8107       return "No expansion";
8108     case _satisfy_free_ratio:
8109       return "Free ratio";
8110     case _satisfy_promotion:
8111       return "Satisfy promotion";
8112     case _satisfy_allocation:
8113       return "allocation";
8114     case _allocate_par_lab:
8115       return "Par LAB";
8116     case _allocate_par_spooling_space:
8117       return "Par Spooling Space";
8118     case _adaptive_size_policy:
8119       return "Ergonomics";
8120     default:
8121       return "unknown";
8122   }
8123 }
8124 
8125 void CMSDrainMarkingStackClosure::do_void() {
8126   // the max number to take from overflow list at a time
8127   const size_t num = _mark_stack->capacity()/4;
8128   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8129          "Overflow list should be NULL during concurrent phases");
8130   while (!_mark_stack->isEmpty() ||
8131          // if stack is empty, check the overflow list
8132          _collector->take_from_overflow_list(num, _mark_stack)) {
8133     oop obj = _mark_stack->pop();
8134     HeapWord* addr = (HeapWord*)obj;
8135     assert(_span.contains(addr), "Should be within span");
8136     assert(_bit_map->isMarked(addr), "Should be marked");
8137     assert(obj->is_oop(), "Should be an oop");
8138     obj->oop_iterate(_keep_alive);
8139   }
8140 }
8141 
8142 void CMSParDrainMarkingStackClosure::do_void() {
8143   // drain queue
8144   trim_queue(0);
8145 }
8146 
8147 // Trim our work_queue so its length is below max at return
8148 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8149   while (_work_queue->size() > max) {
8150     oop new_oop;
8151     if (_work_queue->pop_local(new_oop)) {
8152       assert(new_oop->is_oop(), "Expected an oop");
8153       assert(_bit_map->isMarked((HeapWord*)new_oop),
8154              "no white objects on this stack!");
8155       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8156       // iterate over the oops in this oop, marking and pushing
8157       // the ones in CMS heap (i.e. in _span).
8158       new_oop->oop_iterate(&_mark_and_push);
8159     }
8160   }
8161 }
8162 
8163 ////////////////////////////////////////////////////////////////////
8164 // Support for Marking Stack Overflow list handling and related code
8165 ////////////////////////////////////////////////////////////////////
8166 // Much of the following code is similar in shape and spirit to the
8167 // code used in ParNewGC. We should try and share that code
8168 // as much as possible in the future.
8169 
8170 #ifndef PRODUCT
8171 // Debugging support for CMSStackOverflowALot
8172 
8173 // It's OK to call this multi-threaded;  the worst thing
8174 // that can happen is that we'll get a bunch of closely
8175 // spaced simulated overflows, but that's OK, in fact
8176 // probably good as it would exercise the overflow code
8177 // under contention.
8178 bool CMSCollector::simulate_overflow() {
8179   if (_overflow_counter-- <= 0) { // just being defensive
8180     _overflow_counter = CMSMarkStackOverflowInterval;
8181     return true;
8182   } else {
8183     return false;
8184   }
8185 }
8186 
8187 bool CMSCollector::par_simulate_overflow() {
8188   return simulate_overflow();
8189 }
8190 #endif
8191 
8192 // Single-threaded
8193 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8194   assert(stack->isEmpty(), "Expected precondition");
8195   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8196   size_t i = num;
8197   oop  cur = _overflow_list;
8198   const markOop proto = markOopDesc::prototype();
8199   NOT_PRODUCT(ssize_t n = 0;)
8200   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8201     next = oop(cur->mark());
8202     cur->set_mark(proto);   // until proven otherwise
8203     assert(cur->is_oop(), "Should be an oop");
8204     bool res = stack->push(cur);
8205     assert(res, "Bit off more than can chew?");
8206     NOT_PRODUCT(n++;)
8207   }
8208   _overflow_list = cur;
8209 #ifndef PRODUCT
8210   assert(_num_par_pushes >= n, "Too many pops?");
8211   _num_par_pushes -=n;
8212 #endif
8213   return !stack->isEmpty();
8214 }
8215 
8216 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8217 // (MT-safe) Get a prefix of at most "num" from the list.
8218 // The overflow list is chained through the mark word of
8219 // each object in the list. We fetch the entire list,
8220 // break off a prefix of the right size and return the
8221 // remainder. If other threads try to take objects from
8222 // the overflow list at that time, they will wait for
8223 // some time to see if data becomes available. If (and
8224 // only if) another thread places one or more object(s)
8225 // on the global list before we have returned the suffix
8226 // to the global list, we will walk down our local list
8227 // to find its end and append the global list to
8228 // our suffix before returning it. This suffix walk can
8229 // prove to be expensive (quadratic in the amount of traffic)
8230 // when there are many objects in the overflow list and
8231 // there is much producer-consumer contention on the list.
8232 // *NOTE*: The overflow list manipulation code here and
8233 // in ParNewGeneration:: are very similar in shape,
8234 // except that in the ParNew case we use the old (from/eden)
8235 // copy of the object to thread the list via its klass word.
8236 // Because of the common code, if you make any changes in
8237 // the code below, please check the ParNew version to see if
8238 // similar changes might be needed.
8239 // CR 6797058 has been filed to consolidate the common code.
8240 bool CMSCollector::par_take_from_overflow_list(size_t num,
8241                                                OopTaskQueue* work_q,
8242                                                int no_of_gc_threads) {
8243   assert(work_q->size() == 0, "First empty local work queue");
8244   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8245   if (_overflow_list == NULL) {
8246     return false;
8247   }
8248   // Grab the entire list; we'll put back a suffix
8249   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8250   Thread* tid = Thread::current();
8251   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8252   // set to ParallelGCThreads.
8253   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8254   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8255   // If the list is busy, we spin for a short while,
8256   // sleeping between attempts to get the list.
8257   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8258     os::sleep(tid, sleep_time_millis, false);
8259     if (_overflow_list == NULL) {
8260       // Nothing left to take
8261       return false;
8262     } else if (_overflow_list != BUSY) {
8263       // Try and grab the prefix
8264       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8265     }
8266   }
8267   // If the list was found to be empty, or we spun long
8268   // enough, we give up and return empty-handed. If we leave
8269   // the list in the BUSY state below, it must be the case that
8270   // some other thread holds the overflow list and will set it
8271   // to a non-BUSY state in the future.
8272   if (prefix == NULL || prefix == BUSY) {
8273      // Nothing to take or waited long enough
8274      if (prefix == NULL) {
8275        // Write back the NULL in case we overwrote it with BUSY above
8276        // and it is still the same value.
8277        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8278      }
8279      return false;
8280   }
8281   assert(prefix != NULL && prefix != BUSY, "Error");
8282   size_t i = num;
8283   oop cur = prefix;
8284   // Walk down the first "num" objects, unless we reach the end.
8285   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8286   if (cur->mark() == NULL) {
8287     // We have "num" or fewer elements in the list, so there
8288     // is nothing to return to the global list.
8289     // Write back the NULL in lieu of the BUSY we wrote
8290     // above, if it is still the same value.
8291     if (_overflow_list == BUSY) {
8292       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8293     }
8294   } else {
8295     // Chop off the suffix and return it to the global list.
8296     assert(cur->mark() != BUSY, "Error");
8297     oop suffix_head = cur->mark(); // suffix will be put back on global list
8298     cur->set_mark(NULL);           // break off suffix
8299     // It's possible that the list is still in the empty(busy) state
8300     // we left it in a short while ago; in that case we may be
8301     // able to place back the suffix without incurring the cost
8302     // of a walk down the list.
8303     oop observed_overflow_list = _overflow_list;
8304     oop cur_overflow_list = observed_overflow_list;
8305     bool attached = false;
8306     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8307       observed_overflow_list =
8308         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8309       if (cur_overflow_list == observed_overflow_list) {
8310         attached = true;
8311         break;
8312       } else cur_overflow_list = observed_overflow_list;
8313     }
8314     if (!attached) {
8315       // Too bad, someone else sneaked in (at least) an element; we'll need
8316       // to do a splice. Find tail of suffix so we can prepend suffix to global
8317       // list.
8318       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8319       oop suffix_tail = cur;
8320       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8321              "Tautology");
8322       observed_overflow_list = _overflow_list;
8323       do {
8324         cur_overflow_list = observed_overflow_list;
8325         if (cur_overflow_list != BUSY) {
8326           // Do the splice ...
8327           suffix_tail->set_mark(markOop(cur_overflow_list));
8328         } else { // cur_overflow_list == BUSY
8329           suffix_tail->set_mark(NULL);
8330         }
8331         // ... and try to place spliced list back on overflow_list ...
8332         observed_overflow_list =
8333           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8334       } while (cur_overflow_list != observed_overflow_list);
8335       // ... until we have succeeded in doing so.
8336     }
8337   }
8338 
8339   // Push the prefix elements on work_q
8340   assert(prefix != NULL, "control point invariant");
8341   const markOop proto = markOopDesc::prototype();
8342   oop next;
8343   NOT_PRODUCT(ssize_t n = 0;)
8344   for (cur = prefix; cur != NULL; cur = next) {
8345     next = oop(cur->mark());
8346     cur->set_mark(proto);   // until proven otherwise
8347     assert(cur->is_oop(), "Should be an oop");
8348     bool res = work_q->push(cur);
8349     assert(res, "Bit off more than we can chew?");
8350     NOT_PRODUCT(n++;)
8351   }
8352 #ifndef PRODUCT
8353   assert(_num_par_pushes >= n, "Too many pops?");
8354   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8355 #endif
8356   return true;
8357 }
8358 
8359 // Single-threaded
8360 void CMSCollector::push_on_overflow_list(oop p) {
8361   NOT_PRODUCT(_num_par_pushes++;)
8362   assert(p->is_oop(), "Not an oop");
8363   preserve_mark_if_necessary(p);
8364   p->set_mark((markOop)_overflow_list);
8365   _overflow_list = p;
8366 }
8367 
8368 // Multi-threaded; use CAS to prepend to overflow list
8369 void CMSCollector::par_push_on_overflow_list(oop p) {
8370   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8371   assert(p->is_oop(), "Not an oop");
8372   par_preserve_mark_if_necessary(p);
8373   oop observed_overflow_list = _overflow_list;
8374   oop cur_overflow_list;
8375   do {
8376     cur_overflow_list = observed_overflow_list;
8377     if (cur_overflow_list != BUSY) {
8378       p->set_mark(markOop(cur_overflow_list));
8379     } else {
8380       p->set_mark(NULL);
8381     }
8382     observed_overflow_list =
8383       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8384   } while (cur_overflow_list != observed_overflow_list);
8385 }
8386 #undef BUSY
8387 
8388 // Single threaded
8389 // General Note on GrowableArray: pushes may silently fail
8390 // because we are (temporarily) out of C-heap for expanding
8391 // the stack. The problem is quite ubiquitous and affects
8392 // a lot of code in the JVM. The prudent thing for GrowableArray
8393 // to do (for now) is to exit with an error. However, that may
8394 // be too draconian in some cases because the caller may be
8395 // able to recover without much harm. For such cases, we
8396 // should probably introduce a "soft_push" method which returns
8397 // an indication of success or failure with the assumption that
8398 // the caller may be able to recover from a failure; code in
8399 // the VM can then be changed, incrementally, to deal with such
8400 // failures where possible, thus, incrementally hardening the VM
8401 // in such low resource situations.
8402 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8403   _preserved_oop_stack.push(p);
8404   _preserved_mark_stack.push(m);
8405   assert(m == p->mark(), "Mark word changed");
8406   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8407          "bijection");
8408 }
8409 
8410 // Single threaded
8411 void CMSCollector::preserve_mark_if_necessary(oop p) {
8412   markOop m = p->mark();
8413   if (m->must_be_preserved(p)) {
8414     preserve_mark_work(p, m);
8415   }
8416 }
8417 
8418 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8419   markOop m = p->mark();
8420   if (m->must_be_preserved(p)) {
8421     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8422     // Even though we read the mark word without holding
8423     // the lock, we are assured that it will not change
8424     // because we "own" this oop, so no other thread can
8425     // be trying to push it on the overflow list; see
8426     // the assertion in preserve_mark_work() that checks
8427     // that m == p->mark().
8428     preserve_mark_work(p, m);
8429   }
8430 }
8431 
8432 // We should be able to do this multi-threaded,
8433 // a chunk of stack being a task (this is
8434 // correct because each oop only ever appears
8435 // once in the overflow list. However, it's
8436 // not very easy to completely overlap this with
8437 // other operations, so will generally not be done
8438 // until all work's been completed. Because we
8439 // expect the preserved oop stack (set) to be small,
8440 // it's probably fine to do this single-threaded.
8441 // We can explore cleverer concurrent/overlapped/parallel
8442 // processing of preserved marks if we feel the
8443 // need for this in the future. Stack overflow should
8444 // be so rare in practice and, when it happens, its
8445 // effect on performance so great that this will
8446 // likely just be in the noise anyway.
8447 void CMSCollector::restore_preserved_marks_if_any() {
8448   assert(SafepointSynchronize::is_at_safepoint(),
8449          "world should be stopped");
8450   assert(Thread::current()->is_ConcurrentGC_thread() ||
8451          Thread::current()->is_VM_thread(),
8452          "should be single-threaded");
8453   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8454          "bijection");
8455 
8456   while (!_preserved_oop_stack.is_empty()) {
8457     oop p = _preserved_oop_stack.pop();
8458     assert(p->is_oop(), "Should be an oop");
8459     assert(_span.contains(p), "oop should be in _span");
8460     assert(p->mark() == markOopDesc::prototype(),
8461            "Set when taken from overflow list");
8462     markOop m = _preserved_mark_stack.pop();
8463     p->set_mark(m);
8464   }
8465   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8466          "stacks were cleared above");
8467 }
8468 
8469 #ifndef PRODUCT
8470 bool CMSCollector::no_preserved_marks() const {
8471   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8472 }
8473 #endif
8474 
8475 // Transfer some number of overflown objects to usual marking
8476 // stack. Return true if some objects were transferred.
8477 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8478   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8479                     (size_t)ParGCDesiredObjsFromOverflowList);
8480 
8481   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8482   assert(_collector->overflow_list_is_empty() || res,
8483          "If list is not empty, we should have taken something");
8484   assert(!res || !_mark_stack->isEmpty(),
8485          "If we took something, it should now be on our stack");
8486   return res;
8487 }
8488 
8489 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8490   size_t res = _sp->block_size_no_stall(addr, _collector);
8491   if (_sp->block_is_obj(addr)) {
8492     if (_live_bit_map->isMarked(addr)) {
8493       // It can't have been dead in a previous cycle
8494       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8495     } else {
8496       _dead_bit_map->mark(addr);      // mark the dead object
8497     }
8498   }
8499   // Could be 0, if the block size could not be computed without stalling.
8500   return res;
8501 }
8502 
8503 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8504 
8505   switch (phase) {
8506     case CMSCollector::InitialMarking:
8507       initialize(true  /* fullGC */ ,
8508                  cause /* cause of the GC */,
8509                  true  /* recordGCBeginTime */,
8510                  true  /* recordPreGCUsage */,
8511                  false /* recordPeakUsage */,
8512                  false /* recordPostGCusage */,
8513                  true  /* recordAccumulatedGCTime */,
8514                  false /* recordGCEndTime */,
8515                  false /* countCollection */  );
8516       break;
8517 
8518     case CMSCollector::FinalMarking:
8519       initialize(true  /* fullGC */ ,
8520                  cause /* cause of the GC */,
8521                  false /* recordGCBeginTime */,
8522                  false /* recordPreGCUsage */,
8523                  false /* recordPeakUsage */,
8524                  false /* recordPostGCusage */,
8525                  true  /* recordAccumulatedGCTime */,
8526                  false /* recordGCEndTime */,
8527                  false /* countCollection */  );
8528       break;
8529 
8530     case CMSCollector::Sweeping:
8531       initialize(true  /* fullGC */ ,
8532                  cause /* cause of the GC */,
8533                  false /* recordGCBeginTime */,
8534                  false /* recordPreGCUsage */,
8535                  true  /* recordPeakUsage */,
8536                  true  /* recordPostGCusage */,
8537                  false /* recordAccumulatedGCTime */,
8538                  true  /* recordGCEndTime */,
8539                  true  /* countCollection */  );
8540       break;
8541 
8542     default:
8543       ShouldNotReachHere();
8544   }
8545 }
--- EOF ---