1 /*
   2  * Copyright (c) 2001, 2014, 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/cardTableRS.hpp"
  46 #include "memory/collectorPolicy.hpp"
  47 #include "memory/gcLocker.inline.hpp"
  48 #include "memory/genCollectedHeap.hpp"
  49 #include "memory/genMarkSweep.hpp"
  50 #include "memory/genOopClosures.inline.hpp"
  51 #include "memory/iterator.inline.hpp"
  52 #include "memory/padded.hpp"
  53 #include "memory/referencePolicy.hpp"
  54 #include "memory/resourceArea.hpp"
  55 #include "memory/tenuredGeneration.hpp"
  56 #include "oops/oop.inline.hpp"
  57 #include "prims/jvmtiExport.hpp"
  58 #include "runtime/atomic.inline.hpp"
  59 #include "runtime/globals_extension.hpp"
  60 #include "runtime/handles.inline.hpp"
  61 #include "runtime/java.hpp"
  62 #include "runtime/orderAccess.inline.hpp"
  63 #include "runtime/vmThread.hpp"
  64 #include "services/memoryService.hpp"
  65 #include "services/runtimeService.hpp"
  66 
  67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  68 
  69 // statics
  70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  71 bool CMSCollector::_full_gc_requested = false;
  72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  73 
  74 //////////////////////////////////////////////////////////////////
  75 // In support of CMS/VM thread synchronization
  76 //////////////////////////////////////////////////////////////////
  77 // We split use of the CGC_lock into 2 "levels".
  78 // The low-level locking is of the usual CGC_lock monitor. We introduce
  79 // a higher level "token" (hereafter "CMS token") built on top of the
  80 // low level monitor (hereafter "CGC lock").
  81 // The token-passing protocol gives priority to the VM thread. The
  82 // CMS-lock doesn't provide any fairness guarantees, but clients
  83 // should ensure that it is only held for very short, bounded
  84 // durations.
  85 //
  86 // When either of the CMS thread or the VM thread is involved in
  87 // collection operations during which it does not want the other
  88 // thread to interfere, it obtains the CMS token.
  89 //
  90 // If either thread tries to get the token while the other has
  91 // it, that thread waits. However, if the VM thread and CMS thread
  92 // both want the token, then the VM thread gets priority while the
  93 // CMS thread waits. This ensures, for instance, that the "concurrent"
  94 // phases of the CMS thread's work do not block out the VM thread
  95 // for long periods of time as the CMS thread continues to hog
  96 // the token. (See bug 4616232).
  97 //
  98 // The baton-passing functions are, however, controlled by the
  99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 100 // and here the low-level CMS lock, not the high level token,
 101 // ensures mutual exclusion.
 102 //
 103 // Two important conditions that we have to satisfy:
 104 // 1. if a thread does a low-level wait on the CMS lock, then it
 105 //    relinquishes the CMS token if it were holding that token
 106 //    when it acquired the low-level CMS lock.
 107 // 2. any low-level notifications on the low-level lock
 108 //    should only be sent when a thread has relinquished the token.
 109 //
 110 // In the absence of either property, we'd have potential deadlock.
 111 //
 112 // We protect each of the CMS (concurrent and sequential) phases
 113 // with the CMS _token_, not the CMS _lock_.
 114 //
 115 // The only code protected by CMS lock is the token acquisition code
 116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 117 // baton-passing code.
 118 //
 119 // Unfortunately, i couldn't come up with a good abstraction to factor and
 120 // hide the naked CGC_lock manipulation in the baton-passing code
 121 // further below. That's something we should try to do. Also, the proof
 122 // of correctness of this 2-level locking scheme is far from obvious,
 123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 124 // that there may be a theoretical possibility of delay/starvation in the
 125 // low-level lock/wait/notify scheme used for the baton-passing because of
 126 // potential interference with the priority scheme embodied in the
 127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 128 // invocation further below and marked with "XXX 20011219YSR".
 129 // Indeed, as we note elsewhere, this may become yet more slippery
 130 // in the presence of multiple CMS and/or multiple VM threads. XXX
 131 
 132 class CMSTokenSync: public StackObj {
 133  private:
 134   bool _is_cms_thread;
 135  public:
 136   CMSTokenSync(bool is_cms_thread):
 137     _is_cms_thread(is_cms_thread) {
 138     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 139            "Incorrect argument to constructor");
 140     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 141   }
 142 
 143   ~CMSTokenSync() {
 144     assert(_is_cms_thread ?
 145              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 146              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 147           "Incorrect state");
 148     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 149   }
 150 };
 151 
 152 // Convenience class that does a CMSTokenSync, and then acquires
 153 // upto three locks.
 154 class CMSTokenSyncWithLocks: public CMSTokenSync {
 155  private:
 156   // Note: locks are acquired in textual declaration order
 157   // and released in the opposite order
 158   MutexLockerEx _locker1, _locker2, _locker3;
 159  public:
 160   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 161                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 162     CMSTokenSync(is_cms_thread),
 163     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 164     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 165     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 166   { }
 167 };
 168 
 169 
 170 // Wrapper class to temporarily disable icms during a foreground cms collection.
 171 class ICMSDisabler: public StackObj {
 172  public:
 173   // The ctor disables icms and wakes up the thread so it notices the change;
 174   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 175   // CMSIncrementalMode.
 176   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 177   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 178 };
 179 
 180 //////////////////////////////////////////////////////////////////
 181 //  Concurrent Mark-Sweep Generation /////////////////////////////
 182 //////////////////////////////////////////////////////////////////
 183 
 184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 185 
 186 // This struct contains per-thread things necessary to support parallel
 187 // young-gen collection.
 188 class CMSParGCThreadState: public CHeapObj<mtGC> {
 189  public:
 190   CFLS_LAB lab;
 191   PromotionInfo promo;
 192 
 193   // Constructor.
 194   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 195     promo.setSpace(cfls);
 196   }
 197 };
 198 
 199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 200      ReservedSpace rs, size_t initial_byte_size, int level,
 201      CardTableRS* ct, bool use_adaptive_freelists,
 202      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 203   CardGeneration(rs, initial_byte_size, level, ct),
 204   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 205   _debug_collection_type(Concurrent_collection_type),
 206   _did_compact(false)
 207 {
 208   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 209   HeapWord* end    = (HeapWord*) _virtual_space.high();
 210 
 211   _direct_allocated_words = 0;
 212   NOT_PRODUCT(
 213     _numObjectsPromoted = 0;
 214     _numWordsPromoted = 0;
 215     _numObjectsAllocated = 0;
 216     _numWordsAllocated = 0;
 217   )
 218 
 219   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 220                                            use_adaptive_freelists,
 221                                            dictionaryChoice);
 222   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 223   if (_cmsSpace == NULL) {
 224     vm_exit_during_initialization(
 225       "CompactibleFreeListSpace allocation failure");
 226   }
 227   _cmsSpace->_gen = this;
 228 
 229   _gc_stats = new CMSGCStats();
 230 
 231   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 232   // offsets match. The ability to tell free chunks from objects
 233   // depends on this property.
 234   debug_only(
 235     FreeChunk* junk = NULL;
 236     assert(UseCompressedClassPointers ||
 237            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 238            "Offset of FreeChunk::_prev within FreeChunk must match"
 239            "  that of OopDesc::_klass within OopDesc");
 240   )
 241   if (CollectedHeap::use_parallel_gc_threads()) {
 242     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 243     _par_gc_thread_states =
 244       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
 245     if (_par_gc_thread_states == NULL) {
 246       vm_exit_during_initialization("Could not allocate par gc structs");
 247     }
 248     for (uint i = 0; i < ParallelGCThreads; i++) {
 249       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 250       if (_par_gc_thread_states[i] == NULL) {
 251         vm_exit_during_initialization("Could not allocate par gc structs");
 252       }
 253     }
 254   } else {
 255     _par_gc_thread_states = NULL;
 256   }
 257   _incremental_collection_failed = false;
 258   // The "dilatation_factor" is the expansion that can occur on
 259   // account of the fact that the minimum object size in the CMS
 260   // generation may be larger than that in, say, a contiguous young
 261   //  generation.
 262   // Ideally, in the calculation below, we'd compute the dilatation
 263   // factor as: MinChunkSize/(promoting_gen's min object size)
 264   // Since we do not have such a general query interface for the
 265   // promoting generation, we'll instead just use the minimum
 266   // object size (which today is a header's worth of space);
 267   // note that all arithmetic is in units of HeapWords.
 268   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 269   assert(_dilatation_factor >= 1.0, "from previous assert");
 270 }
 271 
 272 
 273 // The field "_initiating_occupancy" represents the occupancy percentage
 274 // at which we trigger a new collection cycle.  Unless explicitly specified
 275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 276 // is calculated by:
 277 //
 278 //   Let "f" be MinHeapFreeRatio in
 279 //
 280 //    _initiating_occupancy = 100-f +
 281 //                           f * (CMSTriggerRatio/100)
 282 //   where CMSTriggerRatio is the argument "tr" below.
 283 //
 284 // That is, if we assume the heap is at its desired maximum occupancy at the
 285 // end of a collection, we let CMSTriggerRatio of the (purported) free
 286 // space be allocated before initiating a new collection cycle.
 287 //
 288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 289   assert(io <= 100 && tr <= 100, "Check the arguments");
 290   if (io >= 0) {
 291     _initiating_occupancy = (double)io / 100.0;
 292   } else {
 293     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 294                              (double)(tr * MinHeapFreeRatio) / 100.0)
 295                             / 100.0;
 296   }
 297 }
 298 
 299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 300   assert(collector() != NULL, "no collector");
 301   collector()->ref_processor_init();
 302 }
 303 
 304 void CMSCollector::ref_processor_init() {
 305   if (_ref_processor == NULL) {
 306     // Allocate and initialize a reference processor
 307     _ref_processor =
 308       new ReferenceProcessor(_span,                               // span
 309                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 310                              (int) ParallelGCThreads,             // mt processing degree
 311                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 312                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 313                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 314                              &_is_alive_closure);                 // closure for liveness info
 315     // Initialize the _ref_processor field of CMSGen
 316     _cmsGen->set_ref_processor(_ref_processor);
 317 
 318   }
 319 }
 320 
 321 AdaptiveSizePolicy* CMSCollector::size_policy() {
 322   GenCollectedHeap* gch = GenCollectedHeap::heap();
 323   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 324     "Wrong type of heap");
 325   return gch->gen_policy()->size_policy();
 326 }
 327 
 328 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 329 
 330   const char* gen_name = "old";
 331 
 332   // Generation Counters - generation 1, 1 subspace
 333   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 334 
 335   _space_counters = new GSpaceCounters(gen_name, 0,
 336                                        _virtual_space.reserved_size(),
 337                                        this, _gen_counters);
 338 }
 339 
 340 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 341   _cms_gen(cms_gen)
 342 {
 343   assert(alpha <= 100, "bad value");
 344   _saved_alpha = alpha;
 345 
 346   // Initialize the alphas to the bootstrap value of 100.
 347   _gc0_alpha = _cms_alpha = 100;
 348 
 349   _cms_begin_time.update();
 350   _cms_end_time.update();
 351 
 352   _gc0_duration = 0.0;
 353   _gc0_period = 0.0;
 354   _gc0_promoted = 0;
 355 
 356   _cms_duration = 0.0;
 357   _cms_period = 0.0;
 358   _cms_allocated = 0;
 359 
 360   _cms_used_at_gc0_begin = 0;
 361   _cms_used_at_gc0_end = 0;
 362   _allow_duty_cycle_reduction = false;
 363   _valid_bits = 0;
 364   _icms_duty_cycle = CMSIncrementalDutyCycle;
 365 }
 366 
 367 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 368   // TBD: CR 6909490
 369   return 1.0;
 370 }
 371 
 372 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 373 }
 374 
 375 // If promotion failure handling is on use
 376 // the padded average size of the promotion for each
 377 // young generation collection.
 378 double CMSStats::time_until_cms_gen_full() const {
 379   size_t cms_free = _cms_gen->cmsSpace()->free();
 380   GenCollectedHeap* gch = GenCollectedHeap::heap();
 381   size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
 382                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 383   if (cms_free > expected_promotion) {
 384     // Start a cms collection if there isn't enough space to promote
 385     // for the next minor collection.  Use the padded average as
 386     // a safety factor.
 387     cms_free -= expected_promotion;
 388 
 389     // Adjust by the safety factor.
 390     double cms_free_dbl = (double)cms_free;
 391     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 392     // Apply a further correction factor which tries to adjust
 393     // for recent occurance of concurrent mode failures.
 394     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 395     cms_free_dbl = cms_free_dbl * cms_adjustment;
 396 
 397     if (PrintGCDetails && Verbose) {
 398       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 399         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 400         cms_free, expected_promotion);
 401       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 402         cms_free_dbl, cms_consumption_rate() + 1.0);
 403     }
 404     // Add 1 in case the consumption rate goes to zero.
 405     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 406   }
 407   return 0.0;
 408 }
 409 
 410 // Compare the duration of the cms collection to the
 411 // time remaining before the cms generation is empty.
 412 // Note that the time from the start of the cms collection
 413 // to the start of the cms sweep (less than the total
 414 // duration of the cms collection) can be used.  This
 415 // has been tried and some applications experienced
 416 // promotion failures early in execution.  This was
 417 // possibly because the averages were not accurate
 418 // enough at the beginning.
 419 double CMSStats::time_until_cms_start() const {
 420   // We add "gc0_period" to the "work" calculation
 421   // below because this query is done (mostly) at the
 422   // end of a scavenge, so we need to conservatively
 423   // account for that much possible delay
 424   // in the query so as to avoid concurrent mode failures
 425   // due to starting the collection just a wee bit too
 426   // late.
 427   double work = cms_duration() + gc0_period();
 428   double deadline = time_until_cms_gen_full();
 429   // If a concurrent mode failure occurred recently, we want to be
 430   // more conservative and halve our expected time_until_cms_gen_full()
 431   if (work > deadline) {
 432     if (Verbose && PrintGCDetails) {
 433       gclog_or_tty->print(
 434         " CMSCollector: collect because of anticipated promotion "
 435         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 436         gc0_period(), time_until_cms_gen_full());
 437     }
 438     return 0.0;
 439   }
 440   return work - deadline;
 441 }
 442 
 443 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 444 // amount of change to prevent wild oscillation.
 445 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 446                                               unsigned int new_duty_cycle) {
 447   assert(old_duty_cycle <= 100, "bad input value");
 448   assert(new_duty_cycle <= 100, "bad input value");
 449 
 450   // Note:  use subtraction with caution since it may underflow (values are
 451   // unsigned).  Addition is safe since we're in the range 0-100.
 452   unsigned int damped_duty_cycle = new_duty_cycle;
 453   if (new_duty_cycle < old_duty_cycle) {
 454     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 455     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 456       damped_duty_cycle = old_duty_cycle - largest_delta;
 457     }
 458   } else if (new_duty_cycle > old_duty_cycle) {
 459     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 460     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 461       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 462     }
 463   }
 464   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 465 
 466   if (CMSTraceIncrementalPacing) {
 467     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 468                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 469   }
 470   return damped_duty_cycle;
 471 }
 472 
 473 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 474   assert(CMSIncrementalPacing && valid(),
 475          "should be handled in icms_update_duty_cycle()");
 476 
 477   double cms_time_so_far = cms_timer().seconds();
 478   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 479   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 480 
 481   // Avoid division by 0.
 482   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 483   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 484 
 485   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 486   if (new_duty_cycle > _icms_duty_cycle) {
 487     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 488     if (new_duty_cycle > 2) {
 489       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 490                                                 new_duty_cycle);
 491     }
 492   } else if (_allow_duty_cycle_reduction) {
 493     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 494     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 495     // Respect the minimum duty cycle.
 496     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 497     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 498   }
 499 
 500   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 501     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 502   }
 503 
 504   _allow_duty_cycle_reduction = false;
 505   return _icms_duty_cycle;
 506 }
 507 
 508 #ifndef PRODUCT
 509 void CMSStats::print_on(outputStream *st) const {
 510   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 511   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 512                gc0_duration(), gc0_period(), gc0_promoted());
 513   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 514             cms_duration(), cms_duration_per_mb(),
 515             cms_period(), cms_allocated());
 516   st->print(",cms_since_beg=%g,cms_since_end=%g",
 517             cms_time_since_begin(), cms_time_since_end());
 518   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 519             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 520   if (CMSIncrementalMode) {
 521     st->print(",dc=%d", icms_duty_cycle());
 522   }
 523 
 524   if (valid()) {
 525     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 526               promotion_rate(), cms_allocation_rate());
 527     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 528               cms_consumption_rate(), time_until_cms_gen_full());
 529   }
 530   st->print(" ");
 531 }
 532 #endif // #ifndef PRODUCT
 533 
 534 CMSCollector::CollectorState CMSCollector::_collectorState =
 535                              CMSCollector::Idling;
 536 bool CMSCollector::_foregroundGCIsActive = false;
 537 bool CMSCollector::_foregroundGCShouldWait = false;
 538 
 539 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 540                            CardTableRS*                   ct,
 541                            ConcurrentMarkSweepPolicy*     cp):
 542   _cmsGen(cmsGen),
 543   _ct(ct),
 544   _ref_processor(NULL),    // will be set later
 545   _conc_workers(NULL),     // may be set later
 546   _abort_preclean(false),
 547   _start_sampling(false),
 548   _between_prologue_and_epilogue(false),
 549   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 550   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 551                  -1 /* lock-free */, "No_lock" /* dummy */),
 552   _modUnionClosure(&_modUnionTable),
 553   _modUnionClosurePar(&_modUnionTable),
 554   // Adjust my span to cover old (cms) gen
 555   _span(cmsGen->reserved()),
 556   // Construct the is_alive_closure with _span & markBitMap
 557   _is_alive_closure(_span, &_markBitMap),
 558   _restart_addr(NULL),
 559   _overflow_list(NULL),
 560   _stats(cmsGen),
 561   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
 562   _eden_chunk_array(NULL),     // may be set in ctor body
 563   _eden_chunk_capacity(0),     // -- ditto --
 564   _eden_chunk_index(0),        // -- ditto --
 565   _survivor_plab_array(NULL),  // -- ditto --
 566   _survivor_chunk_array(NULL), // -- ditto --
 567   _survivor_chunk_capacity(0), // -- ditto --
 568   _survivor_chunk_index(0),    // -- ditto --
 569   _ser_pmc_preclean_ovflw(0),
 570   _ser_kac_preclean_ovflw(0),
 571   _ser_pmc_remark_ovflw(0),
 572   _par_pmc_remark_ovflw(0),
 573   _ser_kac_ovflw(0),
 574   _par_kac_ovflw(0),
 575 #ifndef PRODUCT
 576   _num_par_pushes(0),
 577 #endif
 578   _collection_count_start(0),
 579   _verifying(false),
 580   _icms_start_limit(NULL),
 581   _icms_stop_limit(NULL),
 582   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 583   _completed_initialization(false),
 584   _collector_policy(cp),
 585   _should_unload_classes(CMSClassUnloadingEnabled),
 586   _concurrent_cycles_since_last_unload(0),
 587   _roots_scanning_options(SharedHeap::SO_None),
 588   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 589   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 590   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 591   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 592   _cms_start_registered(false)
 593 {
 594   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 595     ExplicitGCInvokesConcurrent = true;
 596   }
 597   // Now expand the span and allocate the collection support structures
 598   // (MUT, marking bit map etc.) to cover both generations subject to
 599   // collection.
 600 
 601   // For use by dirty card to oop closures.
 602   _cmsGen->cmsSpace()->set_collector(this);
 603 
 604   // Allocate MUT and marking bit map
 605   {
 606     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 607     if (!_markBitMap.allocate(_span)) {
 608       warning("Failed to allocate CMS Bit Map");
 609       return;
 610     }
 611     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 612   }
 613   {
 614     _modUnionTable.allocate(_span);
 615     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 616   }
 617 
 618   if (!_markStack.allocate(MarkStackSize)) {
 619     warning("Failed to allocate CMS Marking Stack");
 620     return;
 621   }
 622 
 623   // Support for multi-threaded concurrent phases
 624   if (CMSConcurrentMTEnabled) {
 625     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 626       // just for now
 627       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 628     }
 629     if (ConcGCThreads > 1) {
 630       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 631                                  ConcGCThreads, true);
 632       if (_conc_workers == NULL) {
 633         warning("GC/CMS: _conc_workers allocation failure: "
 634               "forcing -CMSConcurrentMTEnabled");
 635         CMSConcurrentMTEnabled = false;
 636       } else {
 637         _conc_workers->initialize_workers();
 638       }
 639     } else {
 640       CMSConcurrentMTEnabled = false;
 641     }
 642   }
 643   if (!CMSConcurrentMTEnabled) {
 644     ConcGCThreads = 0;
 645   } else {
 646     // Turn off CMSCleanOnEnter optimization temporarily for
 647     // the MT case where it's not fixed yet; see 6178663.
 648     CMSCleanOnEnter = false;
 649   }
 650   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 651          "Inconsistency");
 652 
 653   // Parallel task queues; these are shared for the
 654   // concurrent and stop-world phases of CMS, but
 655   // are not shared with parallel scavenge (ParNew).
 656   {
 657     uint i;
 658     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 659 
 660     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 661          || ParallelRefProcEnabled)
 662         && num_queues > 0) {
 663       _task_queues = new OopTaskQueueSet(num_queues);
 664       if (_task_queues == NULL) {
 665         warning("task_queues allocation failure.");
 666         return;
 667       }
 668       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 669       if (_hash_seed == NULL) {
 670         warning("_hash_seed array allocation failure");
 671         return;
 672       }
 673 
 674       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 675       for (i = 0; i < num_queues; i++) {
 676         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 677         if (q == NULL) {
 678           warning("work_queue allocation failure.");
 679           return;
 680         }
 681         _task_queues->register_queue(i, q);
 682       }
 683       for (i = 0; i < num_queues; i++) {
 684         _task_queues->queue(i)->initialize();
 685         _hash_seed[i] = 17;  // copied from ParNew
 686       }
 687     }
 688   }
 689 
 690   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 691 
 692   // Clip CMSBootstrapOccupancy between 0 and 100.
 693   _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
 694 
 695   _full_gcs_since_conc_gc = 0;
 696 
 697   // Now tell CMS generations the identity of their collector
 698   ConcurrentMarkSweepGeneration::set_collector(this);
 699 
 700   // Create & start a CMS thread for this CMS collector
 701   _cmsThread = ConcurrentMarkSweepThread::start(this);
 702   assert(cmsThread() != NULL, "CMS Thread should have been created");
 703   assert(cmsThread()->collector() == this,
 704          "CMS Thread should refer to this gen");
 705   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 706 
 707   // Support for parallelizing young gen rescan
 708   GenCollectedHeap* gch = GenCollectedHeap::heap();
 709   _young_gen = gch->prev_gen(_cmsGen);
 710   if (gch->supports_inline_contig_alloc()) {
 711     _top_addr = gch->top_addr();
 712     _end_addr = gch->end_addr();
 713     assert(_young_gen != NULL, "no _young_gen");
 714     _eden_chunk_index = 0;
 715     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 716     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 717     if (_eden_chunk_array == NULL) {
 718       _eden_chunk_capacity = 0;
 719       warning("GC/CMS: _eden_chunk_array allocation failure");
 720     }
 721   }
 722   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 723 
 724   // Support for parallelizing survivor space rescan
 725   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 726     const size_t max_plab_samples =
 727       ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
 728 
 729     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 730     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 731     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 732     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 733         || _cursor == NULL) {
 734       warning("Failed to allocate survivor plab/chunk array");
 735       if (_survivor_plab_array  != NULL) {
 736         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 737         _survivor_plab_array = NULL;
 738       }
 739       if (_survivor_chunk_array != NULL) {
 740         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 741         _survivor_chunk_array = NULL;
 742       }
 743       if (_cursor != NULL) {
 744         FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
 745         _cursor = NULL;
 746       }
 747     } else {
 748       _survivor_chunk_capacity = 2*max_plab_samples;
 749       for (uint i = 0; i < ParallelGCThreads; i++) {
 750         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 751         if (vec == NULL) {
 752           warning("Failed to allocate survivor plab array");
 753           for (int j = i; j > 0; j--) {
 754             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
 755           }
 756           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 757           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 758           _survivor_plab_array = NULL;
 759           _survivor_chunk_array = NULL;
 760           _survivor_chunk_capacity = 0;
 761           break;
 762         } else {
 763           ChunkArray* cur =
 764             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 765                                                         max_plab_samples);
 766           assert(cur->end() == 0, "Should be 0");
 767           assert(cur->array() == vec, "Should be vec");
 768           assert(cur->capacity() == max_plab_samples, "Error");
 769         }
 770       }
 771     }
 772   }
 773   assert(   (   _survivor_plab_array  != NULL
 774              && _survivor_chunk_array != NULL)
 775          || (   _survivor_chunk_capacity == 0
 776              && _survivor_chunk_index == 0),
 777          "Error");
 778 
 779   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 780   _gc_counters = new CollectorCounters("CMS", 1);
 781   _completed_initialization = true;
 782   _inter_sweep_timer.start();  // start of time
 783 }
 784 
 785 const char* ConcurrentMarkSweepGeneration::name() const {
 786   return "concurrent mark-sweep generation";
 787 }
 788 void ConcurrentMarkSweepGeneration::update_counters() {
 789   if (UsePerfData) {
 790     _space_counters->update_all();
 791     _gen_counters->update_all();
 792   }
 793 }
 794 
 795 // this is an optimized version of update_counters(). it takes the
 796 // used value as a parameter rather than computing it.
 797 //
 798 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 799   if (UsePerfData) {
 800     _space_counters->update_used(used);
 801     _space_counters->update_capacity();
 802     _gen_counters->update_all();
 803   }
 804 }
 805 
 806 void ConcurrentMarkSweepGeneration::print() const {
 807   Generation::print();
 808   cmsSpace()->print();
 809 }
 810 
 811 #ifndef PRODUCT
 812 void ConcurrentMarkSweepGeneration::print_statistics() {
 813   cmsSpace()->printFLCensus(0);
 814 }
 815 #endif
 816 
 817 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 818   GenCollectedHeap* gch = GenCollectedHeap::heap();
 819   if (PrintGCDetails) {
 820     if (Verbose) {
 821       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 822         level(), short_name(), s, used(), capacity());
 823     } else {
 824       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 825         level(), short_name(), s, used() / K, capacity() / K);
 826     }
 827   }
 828   if (Verbose) {
 829     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 830               gch->used(), gch->capacity());
 831   } else {
 832     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 833               gch->used() / K, gch->capacity() / K);
 834   }
 835 }
 836 
 837 size_t
 838 ConcurrentMarkSweepGeneration::contiguous_available() const {
 839   // dld proposes an improvement in precision here. If the committed
 840   // part of the space ends in a free block we should add that to
 841   // uncommitted size in the calculation below. Will make this
 842   // change later, staying with the approximation below for the
 843   // time being. -- ysr.
 844   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 845 }
 846 
 847 size_t
 848 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 849   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 850 }
 851 
 852 size_t ConcurrentMarkSweepGeneration::max_available() const {
 853   return free() + _virtual_space.uncommitted_size();
 854 }
 855 
 856 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 857   size_t available = max_available();
 858   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 859   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 860   if (Verbose && PrintGCDetails) {
 861     gclog_or_tty->print_cr(
 862       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 863       "max_promo("SIZE_FORMAT")",
 864       res? "":" not", available, res? ">=":"<",
 865       av_promo, max_promotion_in_bytes);
 866   }
 867   return res;
 868 }
 869 
 870 // At a promotion failure dump information on block layout in heap
 871 // (cms old generation).
 872 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 873   if (CMSDumpAtPromotionFailure) {
 874     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 875   }
 876 }
 877 
 878 CompactibleSpace*
 879 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 880   return _cmsSpace;
 881 }
 882 
 883 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 884   // Clear the promotion information.  These pointers can be adjusted
 885   // along with all the other pointers into the heap but
 886   // compaction is expected to be a rare event with
 887   // a heap using cms so don't do it without seeing the need.
 888   if (CollectedHeap::use_parallel_gc_threads()) {
 889     for (uint i = 0; i < ParallelGCThreads; i++) {
 890       _par_gc_thread_states[i]->promo.reset();
 891     }
 892   }
 893 }
 894 
 895 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 896   blk->do_space(_cmsSpace);
 897 }
 898 
 899 void ConcurrentMarkSweepGeneration::compute_new_size() {
 900   assert_locked_or_safepoint(Heap_lock);
 901 
 902   // If incremental collection failed, we just want to expand
 903   // to the limit.
 904   if (incremental_collection_failed()) {
 905     clear_incremental_collection_failed();
 906     grow_to_reserved();
 907     return;
 908   }
 909 
 910   // The heap has been compacted but not reset yet.
 911   // Any metric such as free() or used() will be incorrect.
 912 
 913   CardGeneration::compute_new_size();
 914 
 915   // Reset again after a possible resizing
 916   if (did_compact()) {
 917     cmsSpace()->reset_after_compaction();
 918   }
 919 }
 920 
 921 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 922   assert_locked_or_safepoint(Heap_lock);
 923 
 924   // If incremental collection failed, we just want to expand
 925   // to the limit.
 926   if (incremental_collection_failed()) {
 927     clear_incremental_collection_failed();
 928     grow_to_reserved();
 929     return;
 930   }
 931 
 932   double free_percentage = ((double) free()) / capacity();
 933   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 934   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 935 
 936   // compute expansion delta needed for reaching desired free percentage
 937   if (free_percentage < desired_free_percentage) {
 938     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 939     assert(desired_capacity >= capacity(), "invalid expansion size");
 940     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 941     if (PrintGCDetails && Verbose) {
 942       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 943       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 944       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 945       gclog_or_tty->print_cr("  Desired free fraction %f",
 946         desired_free_percentage);
 947       gclog_or_tty->print_cr("  Maximum free fraction %f",
 948         maximum_free_percentage);
 949       gclog_or_tty->print_cr("  Capacity "SIZE_FORMAT, capacity()/1000);
 950       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 951         desired_capacity/1000);
 952       int prev_level = level() - 1;
 953       if (prev_level >= 0) {
 954         size_t prev_size = 0;
 955         GenCollectedHeap* gch = GenCollectedHeap::heap();
 956         Generation* prev_gen = gch->_gens[prev_level];
 957         prev_size = prev_gen->capacity();
 958           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 959                                  prev_size/1000);
 960       }
 961       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 962         unsafe_max_alloc_nogc()/1000);
 963       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 964         contiguous_available()/1000);
 965       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 966         expand_bytes);
 967     }
 968     // safe if expansion fails
 969     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 970     if (PrintGCDetails && Verbose) {
 971       gclog_or_tty->print_cr("  Expanded free fraction %f",
 972         ((double) free()) / capacity());
 973     }
 974   } else {
 975     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 976     assert(desired_capacity <= capacity(), "invalid expansion size");
 977     size_t shrink_bytes = capacity() - desired_capacity;
 978     // Don't shrink unless the delta is greater than the minimum shrink we want
 979     if (shrink_bytes >= MinHeapDeltaBytes) {
 980       shrink_free_list_by(shrink_bytes);
 981     }
 982   }
 983 }
 984 
 985 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 986   return cmsSpace()->freelistLock();
 987 }
 988 
 989 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 990                                                   bool   tlab) {
 991   CMSSynchronousYieldRequest yr;
 992   MutexLockerEx x(freelistLock(),
 993                   Mutex::_no_safepoint_check_flag);
 994   return have_lock_and_allocate(size, tlab);
 995 }
 996 
 997 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 998                                                   bool   tlab /* ignored */) {
 999   assert_lock_strong(freelistLock());
1000   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1001   HeapWord* res = cmsSpace()->allocate(adjustedSize);
1002   // Allocate the object live (grey) if the background collector has
1003   // started marking. This is necessary because the marker may
1004   // have passed this address and consequently this object will
1005   // not otherwise be greyed and would be incorrectly swept up.
1006   // Note that if this object contains references, the writing
1007   // of those references will dirty the card containing this object
1008   // allowing the object to be blackened (and its references scanned)
1009   // either during a preclean phase or at the final checkpoint.
1010   if (res != NULL) {
1011     // We may block here with an uninitialized object with
1012     // its mark-bit or P-bits not yet set. Such objects need
1013     // to be safely navigable by block_start().
1014     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1015     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1016     collector()->direct_allocated(res, adjustedSize);
1017     _direct_allocated_words += adjustedSize;
1018     // allocation counters
1019     NOT_PRODUCT(
1020       _numObjectsAllocated++;
1021       _numWordsAllocated += (int)adjustedSize;
1022     )
1023   }
1024   return res;
1025 }
1026 
1027 // In the case of direct allocation by mutators in a generation that
1028 // is being concurrently collected, the object must be allocated
1029 // live (grey) if the background collector has started marking.
1030 // This is necessary because the marker may
1031 // have passed this address and consequently this object will
1032 // not otherwise be greyed and would be incorrectly swept up.
1033 // Note that if this object contains references, the writing
1034 // of those references will dirty the card containing this object
1035 // allowing the object to be blackened (and its references scanned)
1036 // either during a preclean phase or at the final checkpoint.
1037 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1038   assert(_markBitMap.covers(start, size), "Out of bounds");
1039   if (_collectorState >= Marking) {
1040     MutexLockerEx y(_markBitMap.lock(),
1041                     Mutex::_no_safepoint_check_flag);
1042     // [see comments preceding SweepClosure::do_blk() below for details]
1043     //
1044     // Can the P-bits be deleted now?  JJJ
1045     //
1046     // 1. need to mark the object as live so it isn't collected
1047     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1048     // 3. need to mark the end of the object so marking, precleaning or sweeping
1049     //    can skip over uninitialized or unparsable objects. An allocated
1050     //    object is considered uninitialized for our purposes as long as
1051     //    its klass word is NULL.  All old gen objects are parsable
1052     //    as soon as they are initialized.)
1053     _markBitMap.mark(start);          // object is live
1054     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1055     _markBitMap.mark(start + size - 1);
1056                                       // mark end of object
1057   }
1058   // check that oop looks uninitialized
1059   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1060 }
1061 
1062 void CMSCollector::promoted(bool par, HeapWord* start,
1063                             bool is_obj_array, size_t obj_size) {
1064   assert(_markBitMap.covers(start), "Out of bounds");
1065   // See comment in direct_allocated() about when objects should
1066   // be allocated live.
1067   if (_collectorState >= Marking) {
1068     // we already hold the marking bit map lock, taken in
1069     // the prologue
1070     if (par) {
1071       _markBitMap.par_mark(start);
1072     } else {
1073       _markBitMap.mark(start);
1074     }
1075     // We don't need to mark the object as uninitialized (as
1076     // in direct_allocated above) because this is being done with the
1077     // world stopped and the object will be initialized by the
1078     // time the marking, precleaning or sweeping get to look at it.
1079     // But see the code for copying objects into the CMS generation,
1080     // where we need to ensure that concurrent readers of the
1081     // block offset table are able to safely navigate a block that
1082     // is in flux from being free to being allocated (and in
1083     // transition while being copied into) and subsequently
1084     // becoming a bona-fide object when the copy/promotion is complete.
1085     assert(SafepointSynchronize::is_at_safepoint(),
1086            "expect promotion only at safepoints");
1087 
1088     if (_collectorState < Sweeping) {
1089       // Mark the appropriate cards in the modUnionTable, so that
1090       // this object gets scanned before the sweep. If this is
1091       // not done, CMS generation references in the object might
1092       // not get marked.
1093       // For the case of arrays, which are otherwise precisely
1094       // marked, we need to dirty the entire array, not just its head.
1095       if (is_obj_array) {
1096         // The [par_]mark_range() method expects mr.end() below to
1097         // be aligned to the granularity of a bit's representation
1098         // in the heap. In the case of the MUT below, that's a
1099         // card size.
1100         MemRegion mr(start,
1101                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1102                         CardTableModRefBS::card_size /* bytes */));
1103         if (par) {
1104           _modUnionTable.par_mark_range(mr);
1105         } else {
1106           _modUnionTable.mark_range(mr);
1107         }
1108       } else {  // not an obj array; we can just mark the head
1109         if (par) {
1110           _modUnionTable.par_mark(start);
1111         } else {
1112           _modUnionTable.mark(start);
1113         }
1114       }
1115     }
1116   }
1117 }
1118 
1119 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1120 {
1121   size_t delta = pointer_delta(addr, space->bottom());
1122   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1123 }
1124 
1125 void CMSCollector::icms_update_allocation_limits()
1126 {
1127   Generation* young = GenCollectedHeap::heap()->get_gen(0);
1128   EdenSpace* eden = young->as_DefNewGeneration()->eden();
1129 
1130   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1131   if (CMSTraceIncrementalPacing) {
1132     stats().print();
1133   }
1134 
1135   assert(duty_cycle <= 100, "invalid duty cycle");
1136   if (duty_cycle != 0) {
1137     // The duty_cycle is a percentage between 0 and 100; convert to words and
1138     // then compute the offset from the endpoints of the space.
1139     size_t free_words = eden->free() / HeapWordSize;
1140     double free_words_dbl = (double)free_words;
1141     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1142     size_t offset_words = (free_words - duty_cycle_words) / 2;
1143 
1144     _icms_start_limit = eden->top() + offset_words;
1145     _icms_stop_limit = eden->end() - offset_words;
1146 
1147     // The limits may be adjusted (shifted to the right) by
1148     // CMSIncrementalOffset, to allow the application more mutator time after a
1149     // young gen gc (when all mutators were stopped) and before CMS starts and
1150     // takes away one or more cpus.
1151     if (CMSIncrementalOffset != 0) {
1152       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1153       size_t adjustment = (size_t)adjustment_dbl;
1154       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1155       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1156         _icms_start_limit += adjustment;
1157         _icms_stop_limit = tmp_stop;
1158       }
1159     }
1160   }
1161   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1162     _icms_start_limit = _icms_stop_limit = eden->end();
1163   }
1164 
1165   // Install the new start limit.
1166   eden->set_soft_end(_icms_start_limit);
1167 
1168   if (CMSTraceIncrementalMode) {
1169     gclog_or_tty->print(" icms alloc limits:  "
1170                            PTR_FORMAT "," PTR_FORMAT
1171                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1172                            p2i(_icms_start_limit), p2i(_icms_stop_limit),
1173                            percent_of_space(eden, _icms_start_limit),
1174                            percent_of_space(eden, _icms_stop_limit));
1175     if (Verbose) {
1176       gclog_or_tty->print("eden:  ");
1177       eden->print_on(gclog_or_tty);
1178     }
1179   }
1180 }
1181 
1182 // Any changes here should try to maintain the invariant
1183 // that if this method is called with _icms_start_limit
1184 // and _icms_stop_limit both NULL, then it should return NULL
1185 // and not notify the icms thread.
1186 HeapWord*
1187 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1188                                        size_t word_size)
1189 {
1190   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1191   // nop.
1192   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1193     if (top <= _icms_start_limit) {
1194       if (CMSTraceIncrementalMode) {
1195         space->print_on(gclog_or_tty);
1196         gclog_or_tty->stamp();
1197         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1198                                ", new limit=" PTR_FORMAT
1199                                " (" SIZE_FORMAT "%%)",
1200                                p2i(top), p2i(_icms_stop_limit),
1201                                percent_of_space(space, _icms_stop_limit));
1202       }
1203       ConcurrentMarkSweepThread::start_icms();
1204       assert(top < _icms_stop_limit, "Tautology");
1205       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1206         return _icms_stop_limit;
1207       }
1208 
1209       // The allocation will cross both the _start and _stop limits, so do the
1210       // stop notification also and return end().
1211       if (CMSTraceIncrementalMode) {
1212         space->print_on(gclog_or_tty);
1213         gclog_or_tty->stamp();
1214         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1215                                ", new limit=" PTR_FORMAT
1216                                " (" SIZE_FORMAT "%%)",
1217                                p2i(top), p2i(space->end()),
1218                                percent_of_space(space, space->end()));
1219       }
1220       ConcurrentMarkSweepThread::stop_icms();
1221       return space->end();
1222     }
1223 
1224     if (top <= _icms_stop_limit) {
1225       if (CMSTraceIncrementalMode) {
1226         space->print_on(gclog_or_tty);
1227         gclog_or_tty->stamp();
1228         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1229                                ", new limit=" PTR_FORMAT
1230                                " (" SIZE_FORMAT "%%)",
1231                                top, space->end(),
1232                                percent_of_space(space, space->end()));
1233       }
1234       ConcurrentMarkSweepThread::stop_icms();
1235       return space->end();
1236     }
1237 
1238     if (CMSTraceIncrementalMode) {
1239       space->print_on(gclog_or_tty);
1240       gclog_or_tty->stamp();
1241       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1242                              ", new limit=" PTR_FORMAT,
1243                              top, NULL);
1244     }
1245   }
1246 
1247   return NULL;
1248 }
1249 
1250 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1251   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1252   // allocate, copy and if necessary update promoinfo --
1253   // delegate to underlying space.
1254   assert_lock_strong(freelistLock());
1255 
1256 #ifndef PRODUCT
1257   if (Universe::heap()->promotion_should_fail()) {
1258     return NULL;
1259   }
1260 #endif  // #ifndef PRODUCT
1261 
1262   oop res = _cmsSpace->promote(obj, obj_size);
1263   if (res == NULL) {
1264     // expand and retry
1265     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1266     expand(s*HeapWordSize, MinHeapDeltaBytes,
1267       CMSExpansionCause::_satisfy_promotion);
1268     // Since there's currently no next generation, we don't try to promote
1269     // into a more senior generation.
1270     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1271                                "is made to pass on a possibly failing "
1272                                "promotion to next generation");
1273     res = _cmsSpace->promote(obj, obj_size);
1274   }
1275   if (res != NULL) {
1276     // See comment in allocate() about when objects should
1277     // be allocated live.
1278     assert(obj->is_oop(), "Will dereference klass pointer below");
1279     collector()->promoted(false,           // Not parallel
1280                           (HeapWord*)res, obj->is_objArray(), obj_size);
1281     // promotion counters
1282     NOT_PRODUCT(
1283       _numObjectsPromoted++;
1284       _numWordsPromoted +=
1285         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1286     )
1287   }
1288   return res;
1289 }
1290 
1291 
1292 HeapWord*
1293 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1294                                              HeapWord* top,
1295                                              size_t word_sz)
1296 {
1297   return collector()->allocation_limit_reached(space, top, word_sz);
1298 }
1299 
1300 // IMPORTANT: Notes on object size recognition in CMS.
1301 // ---------------------------------------------------
1302 // A block of storage in the CMS generation is always in
1303 // one of three states. A free block (FREE), an allocated
1304 // object (OBJECT) whose size() method reports the correct size,
1305 // and an intermediate state (TRANSIENT) in which its size cannot
1306 // be accurately determined.
1307 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1308 // -----------------------------------------------------
1309 // FREE:      klass_word & 1 == 1; mark_word holds block size
1310 //
1311 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1312 //            obj->size() computes correct size
1313 //
1314 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1315 //
1316 // STATE IDENTIFICATION: (64 bit+COOPS)
1317 // ------------------------------------
1318 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1319 //
1320 // OBJECT:    klass_word installed; klass_word != 0;
1321 //            obj->size() computes correct size
1322 //
1323 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1324 //
1325 //
1326 // STATE TRANSITION DIAGRAM
1327 //
1328 //        mut / parnew                     mut  /  parnew
1329 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1330 //  ^                                                                   |
1331 //  |------------------------ DEAD <------------------------------------|
1332 //         sweep                            mut
1333 //
1334 // While a block is in TRANSIENT state its size cannot be determined
1335 // so readers will either need to come back later or stall until
1336 // the size can be determined. Note that for the case of direct
1337 // allocation, P-bits, when available, may be used to determine the
1338 // size of an object that may not yet have been initialized.
1339 
1340 // Things to support parallel young-gen collection.
1341 oop
1342 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1343                                            oop old, markOop m,
1344                                            size_t word_sz) {
1345 #ifndef PRODUCT
1346   if (Universe::heap()->promotion_should_fail()) {
1347     return NULL;
1348   }
1349 #endif  // #ifndef PRODUCT
1350 
1351   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1352   PromotionInfo* promoInfo = &ps->promo;
1353   // if we are tracking promotions, then first ensure space for
1354   // promotion (including spooling space for saving header if necessary).
1355   // then allocate and copy, then track promoted info if needed.
1356   // When tracking (see PromotionInfo::track()), the mark word may
1357   // be displaced and in this case restoration of the mark word
1358   // occurs in the (oop_since_save_marks_)iterate phase.
1359   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1360     // Out of space for allocating spooling buffers;
1361     // try expanding and allocating spooling buffers.
1362     if (!expand_and_ensure_spooling_space(promoInfo)) {
1363       return NULL;
1364     }
1365   }
1366   assert(promoInfo->has_spooling_space(), "Control point invariant");
1367   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1368   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1369   if (obj_ptr == NULL) {
1370      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1371      if (obj_ptr == NULL) {
1372        return NULL;
1373      }
1374   }
1375   oop obj = oop(obj_ptr);
1376   OrderAccess::storestore();
1377   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1378   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1379   // IMPORTANT: See note on object initialization for CMS above.
1380   // Otherwise, copy the object.  Here we must be careful to insert the
1381   // klass pointer last, since this marks the block as an allocated object.
1382   // Except with compressed oops it's the mark word.
1383   HeapWord* old_ptr = (HeapWord*)old;
1384   // Restore the mark word copied above.
1385   obj->set_mark(m);
1386   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1387   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1388   OrderAccess::storestore();
1389 
1390   if (UseCompressedClassPointers) {
1391     // Copy gap missed by (aligned) header size calculation below
1392     obj->set_klass_gap(old->klass_gap());
1393   }
1394   if (word_sz > (size_t)oopDesc::header_size()) {
1395     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1396                                  obj_ptr + oopDesc::header_size(),
1397                                  word_sz - oopDesc::header_size());
1398   }
1399 
1400   // Now we can track the promoted object, if necessary.  We take care
1401   // to delay the transition from uninitialized to full object
1402   // (i.e., insertion of klass pointer) until after, so that it
1403   // atomically becomes a promoted object.
1404   if (promoInfo->tracking()) {
1405     promoInfo->track((PromotedObject*)obj, old->klass());
1406   }
1407   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1408   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1409   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1410 
1411   // Finally, install the klass pointer (this should be volatile).
1412   OrderAccess::storestore();
1413   obj->set_klass(old->klass());
1414   // We should now be able to calculate the right size for this object
1415   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1416 
1417   collector()->promoted(true,          // parallel
1418                         obj_ptr, old->is_objArray(), word_sz);
1419 
1420   NOT_PRODUCT(
1421     Atomic::inc_ptr(&_numObjectsPromoted);
1422     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1423   )
1424 
1425   return obj;
1426 }
1427 
1428 void
1429 ConcurrentMarkSweepGeneration::
1430 par_promote_alloc_undo(int thread_num,
1431                        HeapWord* obj, size_t word_sz) {
1432   // CMS does not support promotion undo.
1433   ShouldNotReachHere();
1434 }
1435 
1436 void
1437 ConcurrentMarkSweepGeneration::
1438 par_promote_alloc_done(int thread_num) {
1439   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1440   ps->lab.retire(thread_num);
1441 }
1442 
1443 void
1444 ConcurrentMarkSweepGeneration::
1445 par_oop_since_save_marks_iterate_done(int thread_num) {
1446   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1447   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1448   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1449 }
1450 
1451 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1452                                                    size_t size,
1453                                                    bool   tlab)
1454 {
1455   // We allow a STW collection only if a full
1456   // collection was requested.
1457   return full || should_allocate(size, tlab); // FIX ME !!!
1458   // This and promotion failure handling are connected at the
1459   // hip and should be fixed by untying them.
1460 }
1461 
1462 bool CMSCollector::shouldConcurrentCollect() {
1463   if (_full_gc_requested) {
1464     if (Verbose && PrintGCDetails) {
1465       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1466                              " gc request (or gc_locker)");
1467     }
1468     return true;
1469   }
1470 
1471   // For debugging purposes, change the type of collection.
1472   // If the rotation is not on the concurrent collection
1473   // type, don't start a concurrent collection.
1474   NOT_PRODUCT(
1475     if (RotateCMSCollectionTypes &&
1476         (_cmsGen->debug_collection_type() !=
1477           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1478       assert(_cmsGen->debug_collection_type() !=
1479         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1480         "Bad cms collection type");
1481       return false;
1482     }
1483   )
1484 
1485   FreelistLocker x(this);
1486   // ------------------------------------------------------------------
1487   // Print out lots of information which affects the initiation of
1488   // a collection.
1489   if (PrintCMSInitiationStatistics && stats().valid()) {
1490     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1491     gclog_or_tty->stamp();
1492     gclog_or_tty->cr();
1493     stats().print_on(gclog_or_tty);
1494     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1495       stats().time_until_cms_gen_full());
1496     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1497     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1498                            _cmsGen->contiguous_available());
1499     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1500     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1501     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1502     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1503     gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1504     gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1505     gclog_or_tty->print_cr("metadata initialized %d",
1506       MetaspaceGC::should_concurrent_collect());
1507   }
1508   // ------------------------------------------------------------------
1509 
1510   // If the estimated time to complete a cms collection (cms_duration())
1511   // is less than the estimated time remaining until the cms generation
1512   // is full, start a collection.
1513   if (!UseCMSInitiatingOccupancyOnly) {
1514     if (stats().valid()) {
1515       if (stats().time_until_cms_start() == 0.0) {
1516         return true;
1517       }
1518     } else {
1519       // We want to conservatively collect somewhat early in order
1520       // to try and "bootstrap" our CMS/promotion statistics;
1521       // this branch will not fire after the first successful CMS
1522       // collection because the stats should then be valid.
1523       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1524         if (Verbose && PrintGCDetails) {
1525           gclog_or_tty->print_cr(
1526             " CMSCollector: collect for bootstrapping statistics:"
1527             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1528             _bootstrap_occupancy);
1529         }
1530         return true;
1531       }
1532     }
1533   }
1534 
1535   // Otherwise, we start a collection cycle if
1536   // old gen want a collection cycle started. Each may use
1537   // an appropriate criterion for making this decision.
1538   // XXX We need to make sure that the gen expansion
1539   // criterion dovetails well with this. XXX NEED TO FIX THIS
1540   if (_cmsGen->should_concurrent_collect()) {
1541     if (Verbose && PrintGCDetails) {
1542       gclog_or_tty->print_cr("CMS old gen initiated");
1543     }
1544     return true;
1545   }
1546 
1547   // We start a collection if we believe an incremental collection may fail;
1548   // this is not likely to be productive in practice because it's probably too
1549   // late anyway.
1550   GenCollectedHeap* gch = GenCollectedHeap::heap();
1551   assert(gch->collector_policy()->is_generation_policy(),
1552          "You may want to check the correctness of the following");
1553   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1554     if (Verbose && PrintGCDetails) {
1555       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1556     }
1557     return true;
1558   }
1559 
1560   if (MetaspaceGC::should_concurrent_collect()) {
1561     if (Verbose && PrintGCDetails) {
1562       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1563     }
1564     return true;
1565   }
1566 
1567   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1568   if (CMSTriggerInterval >= 0) {
1569     if (CMSTriggerInterval == 0) {
1570       // Trigger always
1571       return true;
1572     }
1573 
1574     // Check the CMS time since begin (we do not check the stats validity
1575     // as we want to be able to trigger the first CMS cycle as well)
1576     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1577       if (Verbose && PrintGCDetails) {
1578         if (stats().valid()) {
1579           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1580                                  stats().cms_time_since_begin());
1581         } else {
1582           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1583         }
1584       }
1585       return true;
1586     }
1587   }
1588 
1589   return false;
1590 }
1591 
1592 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1593 
1594 // Clear _expansion_cause fields of constituent generations
1595 void CMSCollector::clear_expansion_cause() {
1596   _cmsGen->clear_expansion_cause();
1597 }
1598 
1599 // We should be conservative in starting a collection cycle.  To
1600 // start too eagerly runs the risk of collecting too often in the
1601 // extreme.  To collect too rarely falls back on full collections,
1602 // which works, even if not optimum in terms of concurrent work.
1603 // As a work around for too eagerly collecting, use the flag
1604 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1605 // giving the user an easily understandable way of controlling the
1606 // collections.
1607 // We want to start a new collection cycle if any of the following
1608 // conditions hold:
1609 // . our current occupancy exceeds the configured initiating occupancy
1610 //   for this generation, or
1611 // . we recently needed to expand this space and have not, since that
1612 //   expansion, done a collection of this generation, or
1613 // . the underlying space believes that it may be a good idea to initiate
1614 //   a concurrent collection (this may be based on criteria such as the
1615 //   following: the space uses linear allocation and linear allocation is
1616 //   going to fail, or there is believed to be excessive fragmentation in
1617 //   the generation, etc... or ...
1618 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1619 //   the case of the old generation; see CR 6543076):
1620 //   we may be approaching a point at which allocation requests may fail because
1621 //   we will be out of sufficient free space given allocation rate estimates.]
1622 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1623 
1624   assert_lock_strong(freelistLock());
1625   if (occupancy() > initiating_occupancy()) {
1626     if (PrintGCDetails && Verbose) {
1627       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1628         short_name(), occupancy(), initiating_occupancy());
1629     }
1630     return true;
1631   }
1632   if (UseCMSInitiatingOccupancyOnly) {
1633     return false;
1634   }
1635   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1636     if (PrintGCDetails && Verbose) {
1637       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1638         short_name());
1639     }
1640     return true;
1641   }
1642   if (_cmsSpace->should_concurrent_collect()) {
1643     if (PrintGCDetails && Verbose) {
1644       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1645         short_name());
1646     }
1647     return true;
1648   }
1649   return false;
1650 }
1651 
1652 void ConcurrentMarkSweepGeneration::collect(bool   full,
1653                                             bool   clear_all_soft_refs,
1654                                             size_t size,
1655                                             bool   tlab)
1656 {
1657   collector()->collect(full, clear_all_soft_refs, size, tlab);
1658 }
1659 
1660 void CMSCollector::collect(bool   full,
1661                            bool   clear_all_soft_refs,
1662                            size_t size,
1663                            bool   tlab)
1664 {
1665   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1666     // For debugging purposes skip the collection if the state
1667     // is not currently idle
1668     if (TraceCMSState) {
1669       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1670         Thread::current(), full, _collectorState);
1671     }
1672     return;
1673   }
1674 
1675   // The following "if" branch is present for defensive reasons.
1676   // In the current uses of this interface, it can be replaced with:
1677   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1678   // But I am not placing that assert here to allow future
1679   // generality in invoking this interface.
1680   if (GC_locker::is_active()) {
1681     // A consistency test for GC_locker
1682     assert(GC_locker::needs_gc(), "Should have been set already");
1683     // Skip this foreground collection, instead
1684     // expanding the heap if necessary.
1685     // Need the free list locks for the call to free() in compute_new_size()
1686     compute_new_size();
1687     return;
1688   }
1689   acquire_control_and_collect(full, clear_all_soft_refs);
1690   _full_gcs_since_conc_gc++;
1691 }
1692 
1693 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1694   GenCollectedHeap* gch = GenCollectedHeap::heap();
1695   unsigned int gc_count = gch->total_full_collections();
1696   if (gc_count == full_gc_count) {
1697     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1698     _full_gc_requested = true;
1699     _full_gc_cause = cause;
1700     CGC_lock->notify();   // nudge CMS thread
1701   } else {
1702     assert(gc_count > full_gc_count, "Error: causal loop");
1703   }
1704 }
1705 
1706 bool CMSCollector::is_external_interruption() {
1707   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1708   return GCCause::is_user_requested_gc(cause) ||
1709          GCCause::is_serviceability_requested_gc(cause);
1710 }
1711 
1712 void CMSCollector::report_concurrent_mode_interruption() {
1713   if (is_external_interruption()) {
1714     if (PrintGCDetails) {
1715       gclog_or_tty->print(" (concurrent mode interrupted)");
1716     }
1717   } else {
1718     if (PrintGCDetails) {
1719       gclog_or_tty->print(" (concurrent mode failure)");
1720     }
1721     _gc_tracer_cm->report_concurrent_mode_failure();
1722   }
1723 }
1724 
1725 
1726 // The foreground and background collectors need to coordinate in order
1727 // to make sure that they do not mutually interfere with CMS collections.
1728 // When a background collection is active,
1729 // the foreground collector may need to take over (preempt) and
1730 // synchronously complete an ongoing collection. Depending on the
1731 // frequency of the background collections and the heap usage
1732 // of the application, this preemption can be seldom or frequent.
1733 // There are only certain
1734 // points in the background collection that the "collection-baton"
1735 // can be passed to the foreground collector.
1736 //
1737 // The foreground collector will wait for the baton before
1738 // starting any part of the collection.  The foreground collector
1739 // will only wait at one location.
1740 //
1741 // The background collector will yield the baton before starting a new
1742 // phase of the collection (e.g., before initial marking, marking from roots,
1743 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1744 // of the loop which switches the phases. The background collector does some
1745 // of the phases (initial mark, final re-mark) with the world stopped.
1746 // Because of locking involved in stopping the world,
1747 // the foreground collector should not block waiting for the background
1748 // collector when it is doing a stop-the-world phase.  The background
1749 // collector will yield the baton at an additional point just before
1750 // it enters a stop-the-world phase.  Once the world is stopped, the
1751 // background collector checks the phase of the collection.  If the
1752 // phase has not changed, it proceeds with the collection.  If the
1753 // phase has changed, it skips that phase of the collection.  See
1754 // the comments on the use of the Heap_lock in collect_in_background().
1755 //
1756 // Variable used in baton passing.
1757 //   _foregroundGCIsActive - Set to true by the foreground collector when
1758 //      it wants the baton.  The foreground clears it when it has finished
1759 //      the collection.
1760 //   _foregroundGCShouldWait - Set to true by the background collector
1761 //        when it is running.  The foreground collector waits while
1762 //      _foregroundGCShouldWait is true.
1763 //  CGC_lock - monitor used to protect access to the above variables
1764 //      and to notify the foreground and background collectors.
1765 //  _collectorState - current state of the CMS collection.
1766 //
1767 // The foreground collector
1768 //   acquires the CGC_lock
1769 //   sets _foregroundGCIsActive
1770 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1771 //     various locks acquired in preparation for the collection
1772 //     are released so as not to block the background collector
1773 //     that is in the midst of a collection
1774 //   proceeds with the collection
1775 //   clears _foregroundGCIsActive
1776 //   returns
1777 //
1778 // The background collector in a loop iterating on the phases of the
1779 //      collection
1780 //   acquires the CGC_lock
1781 //   sets _foregroundGCShouldWait
1782 //   if _foregroundGCIsActive is set
1783 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1784 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1785 //     and exits the loop.
1786 //   otherwise
1787 //     proceed with that phase of the collection
1788 //     if the phase is a stop-the-world phase,
1789 //       yield the baton once more just before enqueueing
1790 //       the stop-world CMS operation (executed by the VM thread).
1791 //   returns after all phases of the collection are done
1792 //
1793 
1794 void CMSCollector::acquire_control_and_collect(bool full,
1795         bool clear_all_soft_refs) {
1796   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1797   assert(!Thread::current()->is_ConcurrentGC_thread(),
1798          "shouldn't try to acquire control from self!");
1799 
1800   // Start the protocol for acquiring control of the
1801   // collection from the background collector (aka CMS thread).
1802   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1803          "VM thread should have CMS token");
1804   // Remember the possibly interrupted state of an ongoing
1805   // concurrent collection
1806   CollectorState first_state = _collectorState;
1807 
1808   // Signal to a possibly ongoing concurrent collection that
1809   // we want to do a foreground collection.
1810   _foregroundGCIsActive = true;
1811 
1812   // Disable incremental mode during a foreground collection.
1813   ICMSDisabler icms_disabler;
1814 
1815   // release locks and wait for a notify from the background collector
1816   // releasing the locks in only necessary for phases which
1817   // do yields to improve the granularity of the collection.
1818   assert_lock_strong(bitMapLock());
1819   // We need to lock the Free list lock for the space that we are
1820   // currently collecting.
1821   assert(haveFreelistLocks(), "Must be holding free list locks");
1822   bitMapLock()->unlock();
1823   releaseFreelistLocks();
1824   {
1825     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1826     if (_foregroundGCShouldWait) {
1827       // We are going to be waiting for action for the CMS thread;
1828       // it had better not be gone (for instance at shutdown)!
1829       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1830              "CMS thread must be running");
1831       // Wait here until the background collector gives us the go-ahead
1832       ConcurrentMarkSweepThread::clear_CMS_flag(
1833         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1834       // Get a possibly blocked CMS thread going:
1835       //   Note that we set _foregroundGCIsActive true above,
1836       //   without protection of the CGC_lock.
1837       CGC_lock->notify();
1838       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1839              "Possible deadlock");
1840       while (_foregroundGCShouldWait) {
1841         // wait for notification
1842         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1843         // Possibility of delay/starvation here, since CMS token does
1844         // not know to give priority to VM thread? Actually, i think
1845         // there wouldn't be any delay/starvation, but the proof of
1846         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1847       }
1848       ConcurrentMarkSweepThread::set_CMS_flag(
1849         ConcurrentMarkSweepThread::CMS_vm_has_token);
1850     }
1851   }
1852   // The CMS_token is already held.  Get back the other locks.
1853   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1854          "VM thread should have CMS token");
1855   getFreelistLocks();
1856   bitMapLock()->lock_without_safepoint_check();
1857   if (TraceCMSState) {
1858     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1859       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1860     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1861   }
1862 
1863   // Check if we need to do a compaction, or if not, whether
1864   // we need to start the mark-sweep from scratch.
1865   bool should_compact    = false;
1866   bool should_start_over = false;
1867   decide_foreground_collection_type(clear_all_soft_refs,
1868     &should_compact, &should_start_over);
1869 
1870 NOT_PRODUCT(
1871   if (RotateCMSCollectionTypes) {
1872     if (_cmsGen->debug_collection_type() ==
1873         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1874       should_compact = true;
1875     } else if (_cmsGen->debug_collection_type() ==
1876                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1877       should_compact = false;
1878     }
1879   }
1880 )
1881 
1882   if (first_state > Idling) {
1883     report_concurrent_mode_interruption();
1884   }
1885 
1886   set_did_compact(should_compact);
1887   if (should_compact) {
1888     // If the collection is being acquired from the background
1889     // collector, there may be references on the discovered
1890     // references lists that have NULL referents (being those
1891     // that were concurrently cleared by a mutator) or
1892     // that are no longer active (having been enqueued concurrently
1893     // by the mutator).
1894     // Scrub the list of those references because Mark-Sweep-Compact
1895     // code assumes referents are not NULL and that all discovered
1896     // Reference objects are active.
1897     ref_processor()->clean_up_discovered_references();
1898 
1899     if (first_state > Idling) {
1900       save_heap_summary();
1901     }
1902 
1903     do_compaction_work(clear_all_soft_refs);
1904 
1905     // Has the GC time limit been exceeded?
1906     DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1907     size_t max_eden_size = young_gen->max_capacity() -
1908                            young_gen->to()->capacity() -
1909                            young_gen->from()->capacity();
1910     GenCollectedHeap* gch = GenCollectedHeap::heap();
1911     GCCause::Cause gc_cause = gch->gc_cause();
1912     size_policy()->check_gc_overhead_limit(_young_gen->used(),
1913                                            young_gen->eden()->used(),
1914                                            _cmsGen->max_capacity(),
1915                                            max_eden_size,
1916                                            full,
1917                                            gc_cause,
1918                                            gch->collector_policy());
1919   } else {
1920     do_mark_sweep_work(clear_all_soft_refs, first_state,
1921       should_start_over);
1922   }
1923   // Reset the expansion cause, now that we just completed
1924   // a collection cycle.
1925   clear_expansion_cause();
1926   _foregroundGCIsActive = false;
1927   return;
1928 }
1929 
1930 // Resize the tenured generation
1931 // after obtaining the free list locks for the
1932 // two generations.
1933 void CMSCollector::compute_new_size() {
1934   assert_locked_or_safepoint(Heap_lock);
1935   FreelistLocker z(this);
1936   MetaspaceGC::compute_new_size();
1937   _cmsGen->compute_new_size_free_list();
1938 }
1939 
1940 // A work method used by foreground collection to determine
1941 // what type of collection (compacting or not, continuing or fresh)
1942 // it should do.
1943 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1944 // and CMSCompactWhenClearAllSoftRefs the default in the future
1945 // and do away with the flags after a suitable period.
1946 void CMSCollector::decide_foreground_collection_type(
1947   bool clear_all_soft_refs, bool* should_compact,
1948   bool* should_start_over) {
1949   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1950   // flag is set, and we have either requested a System.gc() or
1951   // the number of full gc's since the last concurrent cycle
1952   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1953   // or if an incremental collection has failed
1954   GenCollectedHeap* gch = GenCollectedHeap::heap();
1955   assert(gch->collector_policy()->is_generation_policy(),
1956          "You may want to check the correctness of the following");
1957   // Inform cms gen if this was due to partial collection failing.
1958   // The CMS gen may use this fact to determine its expansion policy.
1959   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1960     assert(!_cmsGen->incremental_collection_failed(),
1961            "Should have been noticed, reacted to and cleared");
1962     _cmsGen->set_incremental_collection_failed();
1963   }
1964   *should_compact =
1965     UseCMSCompactAtFullCollection &&
1966     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1967      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1968      gch->incremental_collection_will_fail(true /* consult_young */));
1969   *should_start_over = false;
1970   if (clear_all_soft_refs && !*should_compact) {
1971     // We are about to do a last ditch collection attempt
1972     // so it would normally make sense to do a compaction
1973     // to reclaim as much space as possible.
1974     if (CMSCompactWhenClearAllSoftRefs) {
1975       // Default: The rationale is that in this case either
1976       // we are past the final marking phase, in which case
1977       // we'd have to start over, or so little has been done
1978       // that there's little point in saving that work. Compaction
1979       // appears to be the sensible choice in either case.
1980       *should_compact = true;
1981     } else {
1982       // We have been asked to clear all soft refs, but not to
1983       // compact. Make sure that we aren't past the final checkpoint
1984       // phase, for that is where we process soft refs. If we are already
1985       // past that phase, we'll need to redo the refs discovery phase and
1986       // if necessary clear soft refs that weren't previously
1987       // cleared. We do so by remembering the phase in which
1988       // we came in, and if we are past the refs processing
1989       // phase, we'll choose to just redo the mark-sweep
1990       // collection from scratch.
1991       if (_collectorState > FinalMarking) {
1992         // We are past the refs processing phase;
1993         // start over and do a fresh synchronous CMS cycle
1994         _collectorState = Resetting; // skip to reset to start new cycle
1995         reset(false /* == !asynch */);
1996         *should_start_over = true;
1997       } // else we can continue a possibly ongoing current cycle
1998     }
1999   }
2000 }
2001 
2002 // A work method used by the foreground collector to do
2003 // a mark-sweep-compact.
2004 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2005   GenCollectedHeap* gch = GenCollectedHeap::heap();
2006 
2007   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2008   gc_timer->register_gc_start();
2009 
2010   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2011   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2012 
2013   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2014   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2015     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2016       "collections passed to foreground collector", _full_gcs_since_conc_gc);
2017   }
2018 
2019   // Temporarily widen the span of the weak reference processing to
2020   // the entire heap.
2021   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2022   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2023   // Temporarily, clear the "is_alive_non_header" field of the
2024   // reference processor.
2025   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2026   // Temporarily make reference _processing_ single threaded (non-MT).
2027   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2028   // Temporarily make refs discovery atomic
2029   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2030   // Temporarily make reference _discovery_ single threaded (non-MT)
2031   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2032 
2033   ref_processor()->set_enqueuing_is_done(false);
2034   ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2035   ref_processor()->setup_policy(clear_all_soft_refs);
2036   // If an asynchronous collection finishes, the _modUnionTable is
2037   // all clear.  If we are assuming the collection from an asynchronous
2038   // collection, clear the _modUnionTable.
2039   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2040     "_modUnionTable should be clear if the baton was not passed");
2041   _modUnionTable.clear_all();
2042   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2043     "mod union for klasses should be clear if the baton was passed");
2044   _ct->klass_rem_set()->clear_mod_union();
2045 
2046   // We must adjust the allocation statistics being maintained
2047   // in the free list space. We do so by reading and clearing
2048   // the sweep timer and updating the block flux rate estimates below.
2049   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2050   if (_inter_sweep_timer.is_active()) {
2051     _inter_sweep_timer.stop();
2052     // Note that we do not use this sample to update the _inter_sweep_estimate.
2053     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2054                                             _inter_sweep_estimate.padded_average(),
2055                                             _intra_sweep_estimate.padded_average());
2056   }
2057 
2058   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2059     ref_processor(), clear_all_soft_refs);
2060   #ifdef ASSERT
2061     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2062     size_t free_size = cms_space->free();
2063     assert(free_size ==
2064            pointer_delta(cms_space->end(), cms_space->compaction_top())
2065            * HeapWordSize,
2066       "All the free space should be compacted into one chunk at top");
2067     assert(cms_space->dictionary()->total_chunk_size(
2068                                       debug_only(cms_space->freelistLock())) == 0 ||
2069            cms_space->totalSizeInIndexedFreeLists() == 0,
2070       "All the free space should be in a single chunk");
2071     size_t num = cms_space->totalCount();
2072     assert((free_size == 0 && num == 0) ||
2073            (free_size > 0  && (num == 1 || num == 2)),
2074          "There should be at most 2 free chunks after compaction");
2075   #endif // ASSERT
2076   _collectorState = Resetting;
2077   assert(_restart_addr == NULL,
2078          "Should have been NULL'd before baton was passed");
2079   reset(false /* == !asynch */);
2080   _cmsGen->reset_after_compaction();
2081   _concurrent_cycles_since_last_unload = 0;
2082 
2083   // Clear any data recorded in the PLAB chunk arrays.
2084   if (_survivor_plab_array != NULL) {
2085     reset_survivor_plab_arrays();
2086   }
2087 
2088   // Adjust the per-size allocation stats for the next epoch.
2089   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2090   // Restart the "inter sweep timer" for the next epoch.
2091   _inter_sweep_timer.reset();
2092   _inter_sweep_timer.start();
2093 
2094   gc_timer->register_gc_end();
2095 
2096   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2097 
2098   // For a mark-sweep-compact, compute_new_size() will be called
2099   // in the heap's do_collection() method.
2100 }
2101 
2102 // A work method used by the foreground collector to do
2103 // a mark-sweep, after taking over from a possibly on-going
2104 // concurrent mark-sweep collection.
2105 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2106   CollectorState first_state, bool should_start_over) {
2107   if (PrintGC && Verbose) {
2108     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2109       "collector with count %d",
2110       _full_gcs_since_conc_gc);
2111   }
2112   switch (_collectorState) {
2113     case Idling:
2114       if (first_state == Idling || should_start_over) {
2115         // The background GC was not active, or should
2116         // restarted from scratch;  start the cycle.
2117         _collectorState = InitialMarking;
2118       }
2119       // If first_state was not Idling, then a background GC
2120       // was in progress and has now finished.  No need to do it
2121       // again.  Leave the state as Idling.
2122       break;
2123     case Precleaning:
2124       // In the foreground case don't do the precleaning since
2125       // it is not done concurrently and there is extra work
2126       // required.
2127       _collectorState = FinalMarking;
2128   }
2129   collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2130 
2131   // For a mark-sweep, compute_new_size() will be called
2132   // in the heap's do_collection() method.
2133 }
2134 
2135 
2136 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2137   DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2138   EdenSpace* eden_space = dng->eden();
2139   ContiguousSpace* from_space = dng->from();
2140   ContiguousSpace* to_space   = dng->to();
2141   // Eden
2142   if (_eden_chunk_array != NULL) {
2143     gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2144                            eden_space->bottom(), eden_space->top(),
2145                            eden_space->end(), eden_space->capacity());
2146     gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2147                            "_eden_chunk_capacity=" SIZE_FORMAT,
2148                            _eden_chunk_index, _eden_chunk_capacity);
2149     for (size_t i = 0; i < _eden_chunk_index; i++) {
2150       gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2151                              i, _eden_chunk_array[i]);
2152     }
2153   }
2154   // Survivor
2155   if (_survivor_chunk_array != NULL) {
2156     gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2157                            from_space->bottom(), from_space->top(),
2158                            from_space->end(), from_space->capacity());
2159     gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2160                            "_survivor_chunk_capacity=" SIZE_FORMAT,
2161                            _survivor_chunk_index, _survivor_chunk_capacity);
2162     for (size_t i = 0; i < _survivor_chunk_index; i++) {
2163       gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2164                              i, _survivor_chunk_array[i]);
2165     }
2166   }
2167 }
2168 
2169 void CMSCollector::getFreelistLocks() const {
2170   // Get locks for all free lists in all generations that this
2171   // collector is responsible for
2172   _cmsGen->freelistLock()->lock_without_safepoint_check();
2173 }
2174 
2175 void CMSCollector::releaseFreelistLocks() const {
2176   // Release locks for all free lists in all generations that this
2177   // collector is responsible for
2178   _cmsGen->freelistLock()->unlock();
2179 }
2180 
2181 bool CMSCollector::haveFreelistLocks() const {
2182   // Check locks for all free lists in all generations that this
2183   // collector is responsible for
2184   assert_lock_strong(_cmsGen->freelistLock());
2185   PRODUCT_ONLY(ShouldNotReachHere());
2186   return true;
2187 }
2188 
2189 // A utility class that is used by the CMS collector to
2190 // temporarily "release" the foreground collector from its
2191 // usual obligation to wait for the background collector to
2192 // complete an ongoing phase before proceeding.
2193 class ReleaseForegroundGC: public StackObj {
2194  private:
2195   CMSCollector* _c;
2196  public:
2197   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2198     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2199     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2200     // allow a potentially blocked foreground collector to proceed
2201     _c->_foregroundGCShouldWait = false;
2202     if (_c->_foregroundGCIsActive) {
2203       CGC_lock->notify();
2204     }
2205     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2206            "Possible deadlock");
2207   }
2208 
2209   ~ReleaseForegroundGC() {
2210     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2211     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2212     _c->_foregroundGCShouldWait = true;
2213   }
2214 };
2215 
2216 // There are separate collect_in_background and collect_in_foreground because of
2217 // the different locking requirements of the background collector and the
2218 // foreground collector.  There was originally an attempt to share
2219 // one "collect" method between the background collector and the foreground
2220 // collector but the if-then-else required made it cleaner to have
2221 // separate methods.
2222 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2223   assert(Thread::current()->is_ConcurrentGC_thread(),
2224     "A CMS asynchronous collection is only allowed on a CMS thread.");
2225 
2226   GenCollectedHeap* gch = GenCollectedHeap::heap();
2227   {
2228     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2229     MutexLockerEx hl(Heap_lock, safepoint_check);
2230     FreelistLocker fll(this);
2231     MutexLockerEx x(CGC_lock, safepoint_check);
2232     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2233       // The foreground collector is active or we're
2234       // not using asynchronous collections.  Skip this
2235       // background collection.
2236       assert(!_foregroundGCShouldWait, "Should be clear");
2237       return;
2238     } else {
2239       assert(_collectorState == Idling, "Should be idling before start.");
2240       _collectorState = InitialMarking;
2241       register_gc_start(cause);
2242       // Reset the expansion cause, now that we are about to begin
2243       // a new cycle.
2244       clear_expansion_cause();
2245 
2246       // Clear the MetaspaceGC flag since a concurrent collection
2247       // is starting but also clear it after the collection.
2248       MetaspaceGC::set_should_concurrent_collect(false);
2249     }
2250     // Decide if we want to enable class unloading as part of the
2251     // ensuing concurrent GC cycle.
2252     update_should_unload_classes();
2253     _full_gc_requested = false;           // acks all outstanding full gc requests
2254     _full_gc_cause = GCCause::_no_gc;
2255     // Signal that we are about to start a collection
2256     gch->increment_total_full_collections();  // ... starting a collection cycle
2257     _collection_count_start = gch->total_full_collections();
2258   }
2259 
2260   // Used for PrintGC
2261   size_t prev_used;
2262   if (PrintGC && Verbose) {
2263     prev_used = _cmsGen->used(); // XXXPERM
2264   }
2265 
2266   // The change of the collection state is normally done at this level;
2267   // the exceptions are phases that are executed while the world is
2268   // stopped.  For those phases the change of state is done while the
2269   // world is stopped.  For baton passing purposes this allows the
2270   // background collector to finish the phase and change state atomically.
2271   // The foreground collector cannot wait on a phase that is done
2272   // while the world is stopped because the foreground collector already
2273   // has the world stopped and would deadlock.
2274   while (_collectorState != Idling) {
2275     if (TraceCMSState) {
2276       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2277         Thread::current(), _collectorState);
2278     }
2279     // The foreground collector
2280     //   holds the Heap_lock throughout its collection.
2281     //   holds the CMS token (but not the lock)
2282     //     except while it is waiting for the background collector to yield.
2283     //
2284     // The foreground collector should be blocked (not for long)
2285     //   if the background collector is about to start a phase
2286     //   executed with world stopped.  If the background
2287     //   collector has already started such a phase, the
2288     //   foreground collector is blocked waiting for the
2289     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2290     //   are executed in the VM thread.
2291     //
2292     // The locking order is
2293     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2294     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2295     //   CMS token  (claimed in
2296     //                stop_world_and_do() -->
2297     //                  safepoint_synchronize() -->
2298     //                    CMSThread::synchronize())
2299 
2300     {
2301       // Check if the FG collector wants us to yield.
2302       CMSTokenSync x(true); // is cms thread
2303       if (waitForForegroundGC()) {
2304         // We yielded to a foreground GC, nothing more to be
2305         // done this round.
2306         assert(_foregroundGCShouldWait == false, "We set it to false in "
2307                "waitForForegroundGC()");
2308         if (TraceCMSState) {
2309           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2310             " exiting collection CMS state %d",
2311             Thread::current(), _collectorState);
2312         }
2313         return;
2314       } else {
2315         // The background collector can run but check to see if the
2316         // foreground collector has done a collection while the
2317         // background collector was waiting to get the CGC_lock
2318         // above.  If yes, break so that _foregroundGCShouldWait
2319         // is cleared before returning.
2320         if (_collectorState == Idling) {
2321           break;
2322         }
2323       }
2324     }
2325 
2326     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2327       "should be waiting");
2328 
2329     switch (_collectorState) {
2330       case InitialMarking:
2331         {
2332           ReleaseForegroundGC x(this);
2333           stats().record_cms_begin();
2334           VM_CMS_Initial_Mark initial_mark_op(this);
2335           VMThread::execute(&initial_mark_op);
2336         }
2337         // The collector state may be any legal state at this point
2338         // since the background collector may have yielded to the
2339         // foreground collector.
2340         break;
2341       case Marking:
2342         // initial marking in checkpointRootsInitialWork has been completed
2343         if (markFromRoots(true)) { // we were successful
2344           assert(_collectorState == Precleaning, "Collector state should "
2345             "have changed");
2346         } else {
2347           assert(_foregroundGCIsActive, "Internal state inconsistency");
2348         }
2349         break;
2350       case Precleaning:
2351         // marking from roots in markFromRoots has been completed
2352         preclean();
2353         assert(_collectorState == AbortablePreclean ||
2354                _collectorState == FinalMarking,
2355                "Collector state should have changed");
2356         break;
2357       case AbortablePreclean:
2358         abortable_preclean();
2359         assert(_collectorState == FinalMarking, "Collector state should "
2360           "have changed");
2361         break;
2362       case FinalMarking:
2363         {
2364           ReleaseForegroundGC x(this);
2365 
2366           VM_CMS_Final_Remark final_remark_op(this);
2367           VMThread::execute(&final_remark_op);
2368         }
2369         assert(_foregroundGCShouldWait, "block post-condition");
2370         break;
2371       case Sweeping:
2372         // final marking in checkpointRootsFinal has been completed
2373         sweep(true);
2374         assert(_collectorState == Resizing, "Collector state change "
2375           "to Resizing must be done under the free_list_lock");
2376         _full_gcs_since_conc_gc = 0;
2377 
2378       case Resizing: {
2379         // Sweeping has been completed...
2380         // At this point the background collection has completed.
2381         // Don't move the call to compute_new_size() down
2382         // into code that might be executed if the background
2383         // collection was preempted.
2384         {
2385           ReleaseForegroundGC x(this);   // unblock FG collection
2386           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2387           CMSTokenSync        z(true);   // not strictly needed.
2388           if (_collectorState == Resizing) {
2389             compute_new_size();
2390             save_heap_summary();
2391             _collectorState = Resetting;
2392           } else {
2393             assert(_collectorState == Idling, "The state should only change"
2394                    " because the foreground collector has finished the collection");
2395           }
2396         }
2397         break;
2398       }
2399       case Resetting:
2400         // CMS heap resizing has been completed
2401         reset(true);
2402         assert(_collectorState == Idling, "Collector state should "
2403           "have changed");
2404 
2405         MetaspaceGC::set_should_concurrent_collect(false);
2406 
2407         stats().record_cms_end();
2408         // Don't move the concurrent_phases_end() and compute_new_size()
2409         // calls to here because a preempted background collection
2410         // has it's state set to "Resetting".
2411         break;
2412       case Idling:
2413       default:
2414         ShouldNotReachHere();
2415         break;
2416     }
2417     if (TraceCMSState) {
2418       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2419         Thread::current(), _collectorState);
2420     }
2421     assert(_foregroundGCShouldWait, "block post-condition");
2422   }
2423 
2424   // Should this be in gc_epilogue?
2425   collector_policy()->counters()->update_counters();
2426 
2427   {
2428     // Clear _foregroundGCShouldWait and, in the event that the
2429     // foreground collector is waiting, notify it, before
2430     // returning.
2431     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2432     _foregroundGCShouldWait = false;
2433     if (_foregroundGCIsActive) {
2434       CGC_lock->notify();
2435     }
2436     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2437            "Possible deadlock");
2438   }
2439   if (TraceCMSState) {
2440     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2441       " exiting collection CMS state %d",
2442       Thread::current(), _collectorState);
2443   }
2444   if (PrintGC && Verbose) {
2445     _cmsGen->print_heap_change(prev_used);
2446   }
2447 }
2448 
2449 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2450   if (!_cms_start_registered) {
2451     register_gc_start(cause);
2452   }
2453 }
2454 
2455 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2456   _cms_start_registered = true;
2457   _gc_timer_cm->register_gc_start();
2458   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2459 }
2460 
2461 void CMSCollector::register_gc_end() {
2462   if (_cms_start_registered) {
2463     report_heap_summary(GCWhen::AfterGC);
2464 
2465     _gc_timer_cm->register_gc_end();
2466     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2467     _cms_start_registered = false;
2468   }
2469 }
2470 
2471 void CMSCollector::save_heap_summary() {
2472   GenCollectedHeap* gch = GenCollectedHeap::heap();
2473   _last_heap_summary = gch->create_heap_summary();
2474   _last_metaspace_summary = gch->create_metaspace_summary();
2475 }
2476 
2477 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2478   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2479   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2480 }
2481 
2482 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2483   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2484          "Foreground collector should be waiting, not executing");
2485   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2486     "may only be done by the VM Thread with the world stopped");
2487   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2488          "VM thread should have CMS token");
2489 
2490   // The gc id is created in register_foreground_gc_start if this collection is synchronous
2491   const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2492   NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2493     true, NULL, gc_id);)
2494   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2495 
2496   HandleMark hm;  // Discard invalid handles created during verification
2497 
2498   if (VerifyBeforeGC &&
2499       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2500     Universe::verify();
2501   }
2502 
2503   // Snapshot the soft reference policy to be used in this collection cycle.
2504   ref_processor()->setup_policy(clear_all_soft_refs);
2505 
2506   // Decide if class unloading should be done
2507   update_should_unload_classes();
2508 
2509   bool init_mark_was_synchronous = false; // until proven otherwise
2510   while (_collectorState != Idling) {
2511     if (TraceCMSState) {
2512       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2513         Thread::current(), _collectorState);
2514     }
2515     switch (_collectorState) {
2516       case InitialMarking:
2517         register_foreground_gc_start(cause);
2518         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2519         checkpointRootsInitial(false);
2520         assert(_collectorState == Marking, "Collector state should have changed"
2521           " within checkpointRootsInitial()");
2522         break;
2523       case Marking:
2524         // initial marking in checkpointRootsInitialWork has been completed
2525         if (VerifyDuringGC &&
2526             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2527           Universe::verify("Verify before initial mark: ");
2528         }
2529         {
2530           bool res = markFromRoots(false);
2531           assert(res && _collectorState == FinalMarking, "Collector state should "
2532             "have changed");
2533           break;
2534         }
2535       case FinalMarking:
2536         if (VerifyDuringGC &&
2537             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2538           Universe::verify("Verify before re-mark: ");
2539         }
2540         checkpointRootsFinal(false, clear_all_soft_refs,
2541                              init_mark_was_synchronous);
2542         assert(_collectorState == Sweeping, "Collector state should not "
2543           "have changed within checkpointRootsFinal()");
2544         break;
2545       case Sweeping:
2546         // final marking in checkpointRootsFinal has been completed
2547         if (VerifyDuringGC &&
2548             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2549           Universe::verify("Verify before sweep: ");
2550         }
2551         sweep(false);
2552         assert(_collectorState == Resizing, "Incorrect state");
2553         break;
2554       case Resizing: {
2555         // Sweeping has been completed; the actual resize in this case
2556         // is done separately; nothing to be done in this state.
2557         _collectorState = Resetting;
2558         break;
2559       }
2560       case Resetting:
2561         // The heap has been resized.
2562         if (VerifyDuringGC &&
2563             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2564           Universe::verify("Verify before reset: ");
2565         }
2566         save_heap_summary();
2567         reset(false);
2568         assert(_collectorState == Idling, "Collector state should "
2569           "have changed");
2570         break;
2571       case Precleaning:
2572       case AbortablePreclean:
2573         // Elide the preclean phase
2574         _collectorState = FinalMarking;
2575         break;
2576       default:
2577         ShouldNotReachHere();
2578     }
2579     if (TraceCMSState) {
2580       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2581         Thread::current(), _collectorState);
2582     }
2583   }
2584 
2585   if (VerifyAfterGC &&
2586       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2587     Universe::verify();
2588   }
2589   if (TraceCMSState) {
2590     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2591       " exiting collection CMS state %d",
2592       Thread::current(), _collectorState);
2593   }
2594 }
2595 
2596 bool CMSCollector::waitForForegroundGC() {
2597   bool res = false;
2598   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2599          "CMS thread should have CMS token");
2600   // Block the foreground collector until the
2601   // background collectors decides whether to
2602   // yield.
2603   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2604   _foregroundGCShouldWait = true;
2605   if (_foregroundGCIsActive) {
2606     // The background collector yields to the
2607     // foreground collector and returns a value
2608     // indicating that it has yielded.  The foreground
2609     // collector can proceed.
2610     res = true;
2611     _foregroundGCShouldWait = false;
2612     ConcurrentMarkSweepThread::clear_CMS_flag(
2613       ConcurrentMarkSweepThread::CMS_cms_has_token);
2614     ConcurrentMarkSweepThread::set_CMS_flag(
2615       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2616     // Get a possibly blocked foreground thread going
2617     CGC_lock->notify();
2618     if (TraceCMSState) {
2619       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2620         Thread::current(), _collectorState);
2621     }
2622     while (_foregroundGCIsActive) {
2623       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2624     }
2625     ConcurrentMarkSweepThread::set_CMS_flag(
2626       ConcurrentMarkSweepThread::CMS_cms_has_token);
2627     ConcurrentMarkSweepThread::clear_CMS_flag(
2628       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2629   }
2630   if (TraceCMSState) {
2631     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2632       Thread::current(), _collectorState);
2633   }
2634   return res;
2635 }
2636 
2637 // Because of the need to lock the free lists and other structures in
2638 // the collector, common to all the generations that the collector is
2639 // collecting, we need the gc_prologues of individual CMS generations
2640 // delegate to their collector. It may have been simpler had the
2641 // current infrastructure allowed one to call a prologue on a
2642 // collector. In the absence of that we have the generation's
2643 // prologue delegate to the collector, which delegates back
2644 // some "local" work to a worker method in the individual generations
2645 // that it's responsible for collecting, while itself doing any
2646 // work common to all generations it's responsible for. A similar
2647 // comment applies to the  gc_epilogue()'s.
2648 // The role of the variable _between_prologue_and_epilogue is to
2649 // enforce the invocation protocol.
2650 void CMSCollector::gc_prologue(bool full) {
2651   // Call gc_prologue_work() for the CMSGen
2652   // we are responsible for.
2653 
2654   // The following locking discipline assumes that we are only called
2655   // when the world is stopped.
2656   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2657 
2658   // The CMSCollector prologue must call the gc_prologues for the
2659   // "generations" that it's responsible
2660   // for.
2661 
2662   assert(   Thread::current()->is_VM_thread()
2663          || (   CMSScavengeBeforeRemark
2664              && Thread::current()->is_ConcurrentGC_thread()),
2665          "Incorrect thread type for prologue execution");
2666 
2667   if (_between_prologue_and_epilogue) {
2668     // We have already been invoked; this is a gc_prologue delegation
2669     // from yet another CMS generation that we are responsible for, just
2670     // ignore it since all relevant work has already been done.
2671     return;
2672   }
2673 
2674   // set a bit saying prologue has been called; cleared in epilogue
2675   _between_prologue_and_epilogue = true;
2676   // Claim locks for common data structures, then call gc_prologue_work()
2677   // for each CMSGen.
2678 
2679   getFreelistLocks();   // gets free list locks on constituent spaces
2680   bitMapLock()->lock_without_safepoint_check();
2681 
2682   // Should call gc_prologue_work() for all cms gens we are responsible for
2683   bool duringMarking =    _collectorState >= Marking
2684                          && _collectorState < Sweeping;
2685 
2686   // The young collections clear the modified oops state, which tells if
2687   // there are any modified oops in the class. The remark phase also needs
2688   // that information. Tell the young collection to save the union of all
2689   // modified klasses.
2690   if (duringMarking) {
2691     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2692   }
2693 
2694   bool registerClosure = duringMarking;
2695 
2696   ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2697                                                &_modUnionClosurePar
2698                                                : &_modUnionClosure;
2699   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2700 
2701   if (!full) {
2702     stats().record_gc0_begin();
2703   }
2704 }
2705 
2706 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2707 
2708   _capacity_at_prologue = capacity();
2709   _used_at_prologue = used();
2710 
2711   // Delegate to CMScollector which knows how to coordinate between
2712   // this and any other CMS generations that it is responsible for
2713   // collecting.
2714   collector()->gc_prologue(full);
2715 }
2716 
2717 // This is a "private" interface for use by this generation's CMSCollector.
2718 // Not to be called directly by any other entity (for instance,
2719 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2720 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2721   bool registerClosure, ModUnionClosure* modUnionClosure) {
2722   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2723   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2724     "Should be NULL");
2725   if (registerClosure) {
2726     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2727   }
2728   cmsSpace()->gc_prologue();
2729   // Clear stat counters
2730   NOT_PRODUCT(
2731     assert(_numObjectsPromoted == 0, "check");
2732     assert(_numWordsPromoted   == 0, "check");
2733     if (Verbose && PrintGC) {
2734       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2735                           SIZE_FORMAT" bytes concurrently",
2736       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2737     }
2738     _numObjectsAllocated = 0;
2739     _numWordsAllocated   = 0;
2740   )
2741 }
2742 
2743 void CMSCollector::gc_epilogue(bool full) {
2744   // The following locking discipline assumes that we are only called
2745   // when the world is stopped.
2746   assert(SafepointSynchronize::is_at_safepoint(),
2747          "world is stopped assumption");
2748 
2749   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2750   // if linear allocation blocks need to be appropriately marked to allow the
2751   // the blocks to be parsable. We also check here whether we need to nudge the
2752   // CMS collector thread to start a new cycle (if it's not already active).
2753   assert(   Thread::current()->is_VM_thread()
2754          || (   CMSScavengeBeforeRemark
2755              && Thread::current()->is_ConcurrentGC_thread()),
2756          "Incorrect thread type for epilogue execution");
2757 
2758   if (!_between_prologue_and_epilogue) {
2759     // We have already been invoked; this is a gc_epilogue delegation
2760     // from yet another CMS generation that we are responsible for, just
2761     // ignore it since all relevant work has already been done.
2762     return;
2763   }
2764   assert(haveFreelistLocks(), "must have freelist locks");
2765   assert_lock_strong(bitMapLock());
2766 
2767   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2768 
2769   _cmsGen->gc_epilogue_work(full);
2770 
2771   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2772     // in case sampling was not already enabled, enable it
2773     _start_sampling = true;
2774   }
2775   // reset _eden_chunk_array so sampling starts afresh
2776   _eden_chunk_index = 0;
2777 
2778   size_t cms_used   = _cmsGen->cmsSpace()->used();
2779 
2780   // update performance counters - this uses a special version of
2781   // update_counters() that allows the utilization to be passed as a
2782   // parameter, avoiding multiple calls to used().
2783   //
2784   _cmsGen->update_counters(cms_used);
2785 
2786   if (CMSIncrementalMode) {
2787     icms_update_allocation_limits();
2788   }
2789 
2790   bitMapLock()->unlock();
2791   releaseFreelistLocks();
2792 
2793   if (!CleanChunkPoolAsync) {
2794     Chunk::clean_chunk_pool();
2795   }
2796 
2797   set_did_compact(false);
2798   _between_prologue_and_epilogue = false;  // ready for next cycle
2799 }
2800 
2801 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2802   collector()->gc_epilogue(full);
2803 
2804   // Also reset promotion tracking in par gc thread states.
2805   if (CollectedHeap::use_parallel_gc_threads()) {
2806     for (uint i = 0; i < ParallelGCThreads; i++) {
2807       _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2808     }
2809   }
2810 }
2811 
2812 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2813   assert(!incremental_collection_failed(), "Should have been cleared");
2814   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2815   cmsSpace()->gc_epilogue();
2816     // Print stat counters
2817   NOT_PRODUCT(
2818     assert(_numObjectsAllocated == 0, "check");
2819     assert(_numWordsAllocated == 0, "check");
2820     if (Verbose && PrintGC) {
2821       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2822                           SIZE_FORMAT" bytes",
2823                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2824     }
2825     _numObjectsPromoted = 0;
2826     _numWordsPromoted   = 0;
2827   )
2828 
2829   if (PrintGC && Verbose) {
2830     // Call down the chain in contiguous_available needs the freelistLock
2831     // so print this out before releasing the freeListLock.
2832     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2833                         contiguous_available());
2834   }
2835 }
2836 
2837 #ifndef PRODUCT
2838 bool CMSCollector::have_cms_token() {
2839   Thread* thr = Thread::current();
2840   if (thr->is_VM_thread()) {
2841     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2842   } else if (thr->is_ConcurrentGC_thread()) {
2843     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2844   } else if (thr->is_GC_task_thread()) {
2845     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2846            ParGCRareEvent_lock->owned_by_self();
2847   }
2848   return false;
2849 }
2850 #endif
2851 
2852 // Check reachability of the given heap address in CMS generation,
2853 // treating all other generations as roots.
2854 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2855   // We could "guarantee" below, rather than assert, but I'll
2856   // leave these as "asserts" so that an adventurous debugger
2857   // could try this in the product build provided some subset of
2858   // the conditions were met, provided they were interested in the
2859   // results and knew that the computation below wouldn't interfere
2860   // with other concurrent computations mutating the structures
2861   // being read or written.
2862   assert(SafepointSynchronize::is_at_safepoint(),
2863          "Else mutations in object graph will make answer suspect");
2864   assert(have_cms_token(), "Should hold cms token");
2865   assert(haveFreelistLocks(), "must hold free list locks");
2866   assert_lock_strong(bitMapLock());
2867 
2868   // Clear the marking bit map array before starting, but, just
2869   // for kicks, first report if the given address is already marked
2870   gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2871                 _markBitMap.isMarked(addr) ? "" : " not");
2872 
2873   if (verify_after_remark()) {
2874     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2875     bool result = verification_mark_bm()->isMarked(addr);
2876     gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2877                            result ? "IS" : "is NOT");
2878     return result;
2879   } else {
2880     gclog_or_tty->print_cr("Could not compute result");
2881     return false;
2882   }
2883 }
2884 
2885 
2886 void
2887 CMSCollector::print_on_error(outputStream* st) {
2888   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2889   if (collector != NULL) {
2890     CMSBitMap* bitmap = &collector->_markBitMap;
2891     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2892     bitmap->print_on_error(st, " Bits: ");
2893 
2894     st->cr();
2895 
2896     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2897     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2898     mut_bitmap->print_on_error(st, " Bits: ");
2899   }
2900 }
2901 
2902 ////////////////////////////////////////////////////////
2903 // CMS Verification Support
2904 ////////////////////////////////////////////////////////
2905 // Following the remark phase, the following invariant
2906 // should hold -- each object in the CMS heap which is
2907 // marked in markBitMap() should be marked in the verification_mark_bm().
2908 
2909 class VerifyMarkedClosure: public BitMapClosure {
2910   CMSBitMap* _marks;
2911   bool       _failed;
2912 
2913  public:
2914   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2915 
2916   bool do_bit(size_t offset) {
2917     HeapWord* addr = _marks->offsetToHeapWord(offset);
2918     if (!_marks->isMarked(addr)) {
2919       oop(addr)->print_on(gclog_or_tty);
2920       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2921       _failed = true;
2922     }
2923     return true;
2924   }
2925 
2926   bool failed() { return _failed; }
2927 };
2928 
2929 bool CMSCollector::verify_after_remark(bool silent) {
2930   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2931   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2932   static bool init = false;
2933 
2934   assert(SafepointSynchronize::is_at_safepoint(),
2935          "Else mutations in object graph will make answer suspect");
2936   assert(have_cms_token(),
2937          "Else there may be mutual interference in use of "
2938          " verification data structures");
2939   assert(_collectorState > Marking && _collectorState <= Sweeping,
2940          "Else marking info checked here may be obsolete");
2941   assert(haveFreelistLocks(), "must hold free list locks");
2942   assert_lock_strong(bitMapLock());
2943 
2944 
2945   // Allocate marking bit map if not already allocated
2946   if (!init) { // first time
2947     if (!verification_mark_bm()->allocate(_span)) {
2948       return false;
2949     }
2950     init = true;
2951   }
2952 
2953   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2954 
2955   // Turn off refs discovery -- so we will be tracing through refs.
2956   // This is as intended, because by this time
2957   // GC must already have cleared any refs that need to be cleared,
2958   // and traced those that need to be marked; moreover,
2959   // the marking done here is not going to interfere in any
2960   // way with the marking information used by GC.
2961   NoRefDiscovery no_discovery(ref_processor());
2962 
2963   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2964 
2965   // Clear any marks from a previous round
2966   verification_mark_bm()->clear_all();
2967   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2968   verify_work_stacks_empty();
2969 
2970   GenCollectedHeap* gch = GenCollectedHeap::heap();
2971   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2972   // Update the saved marks which may affect the root scans.
2973   gch->save_marks();
2974 
2975   if (CMSRemarkVerifyVariant == 1) {
2976     // In this first variant of verification, we complete
2977     // all marking, then check if the new marks-vector is
2978     // a subset of the CMS marks-vector.
2979     verify_after_remark_work_1();
2980   } else if (CMSRemarkVerifyVariant == 2) {
2981     // In this second variant of verification, we flag an error
2982     // (i.e. an object reachable in the new marks-vector not reachable
2983     // in the CMS marks-vector) immediately, also indicating the
2984     // identify of an object (A) that references the unmarked object (B) --
2985     // presumably, a mutation to A failed to be picked up by preclean/remark?
2986     verify_after_remark_work_2();
2987   } else {
2988     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2989             CMSRemarkVerifyVariant);
2990   }
2991   if (!silent) gclog_or_tty->print(" done] ");
2992   return true;
2993 }
2994 
2995 void CMSCollector::verify_after_remark_work_1() {
2996   ResourceMark rm;
2997   HandleMark  hm;
2998   GenCollectedHeap* gch = GenCollectedHeap::heap();
2999 
3000   // Get a clear set of claim bits for the roots processing to work with.
3001   ClassLoaderDataGraph::clear_claimed_marks();
3002 
3003   // Mark from roots one level into CMS
3004   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3005   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3006 
3007   gch->gen_process_roots(_cmsGen->level(),
3008                          true,   // younger gens are roots
3009                          true,   // activate StrongRootsScope
3010                          SharedHeap::ScanningOption(roots_scanning_options()),
3011                          should_unload_classes(),
3012                          &notOlder,
3013                          NULL,
3014                          NULL);  // SSS: Provide correct closure
3015 
3016   // Now mark from the roots
3017   MarkFromRootsClosure markFromRootsClosure(this, _span,
3018     verification_mark_bm(), verification_mark_stack(),
3019     false /* don't yield */, true /* verifying */);
3020   assert(_restart_addr == NULL, "Expected pre-condition");
3021   verification_mark_bm()->iterate(&markFromRootsClosure);
3022   while (_restart_addr != NULL) {
3023     // Deal with stack overflow: by restarting at the indicated
3024     // address.
3025     HeapWord* ra = _restart_addr;
3026     markFromRootsClosure.reset(ra);
3027     _restart_addr = NULL;
3028     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3029   }
3030   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3031   verify_work_stacks_empty();
3032 
3033   // Marking completed -- now verify that each bit marked in
3034   // verification_mark_bm() is also marked in markBitMap(); flag all
3035   // errors by printing corresponding objects.
3036   VerifyMarkedClosure vcl(markBitMap());
3037   verification_mark_bm()->iterate(&vcl);
3038   if (vcl.failed()) {
3039     gclog_or_tty->print("Verification failed");
3040     Universe::heap()->print_on(gclog_or_tty);
3041     fatal("CMS: failed marking verification after remark");
3042   }
3043 }
3044 
3045 class VerifyKlassOopsKlassClosure : public KlassClosure {
3046   class VerifyKlassOopsClosure : public OopClosure {
3047     CMSBitMap* _bitmap;
3048    public:
3049     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3050     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3051     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3052   } _oop_closure;
3053  public:
3054   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3055   void do_klass(Klass* k) {
3056     k->oops_do(&_oop_closure);
3057   }
3058 };
3059 
3060 void CMSCollector::verify_after_remark_work_2() {
3061   ResourceMark rm;
3062   HandleMark  hm;
3063   GenCollectedHeap* gch = GenCollectedHeap::heap();
3064 
3065   // Get a clear set of claim bits for the roots processing to work with.
3066   ClassLoaderDataGraph::clear_claimed_marks();
3067 
3068   // Mark from roots one level into CMS
3069   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3070                                      markBitMap());
3071   CLDToOopClosure cld_closure(&notOlder, true);
3072 
3073   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3074 
3075   gch->gen_process_roots(_cmsGen->level(),
3076                          true,   // younger gens are roots
3077                          true,   // activate StrongRootsScope
3078                          SharedHeap::ScanningOption(roots_scanning_options()),
3079                          should_unload_classes(),
3080                          &notOlder,
3081                          NULL,
3082                          &cld_closure);
3083 
3084   // Now mark from the roots
3085   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3086     verification_mark_bm(), markBitMap(), verification_mark_stack());
3087   assert(_restart_addr == NULL, "Expected pre-condition");
3088   verification_mark_bm()->iterate(&markFromRootsClosure);
3089   while (_restart_addr != NULL) {
3090     // Deal with stack overflow: by restarting at the indicated
3091     // address.
3092     HeapWord* ra = _restart_addr;
3093     markFromRootsClosure.reset(ra);
3094     _restart_addr = NULL;
3095     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3096   }
3097   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3098   verify_work_stacks_empty();
3099 
3100   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3101   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3102 
3103   // Marking completed -- now verify that each bit marked in
3104   // verification_mark_bm() is also marked in markBitMap(); flag all
3105   // errors by printing corresponding objects.
3106   VerifyMarkedClosure vcl(markBitMap());
3107   verification_mark_bm()->iterate(&vcl);
3108   assert(!vcl.failed(), "Else verification above should not have succeeded");
3109 }
3110 
3111 void ConcurrentMarkSweepGeneration::save_marks() {
3112   // delegate to CMS space
3113   cmsSpace()->save_marks();
3114   for (uint i = 0; i < ParallelGCThreads; i++) {
3115     _par_gc_thread_states[i]->promo.startTrackingPromotions();
3116   }
3117 }
3118 
3119 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3120   return cmsSpace()->no_allocs_since_save_marks();
3121 }
3122 
3123 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
3124                                                                 \
3125 void ConcurrentMarkSweepGeneration::                            \
3126 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
3127   cl->set_generation(this);                                     \
3128   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
3129   cl->reset_generation();                                       \
3130   save_marks();                                                 \
3131 }
3132 
3133 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3134 
3135 void
3136 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3137   cl->set_generation(this);
3138   younger_refs_in_space_iterate(_cmsSpace, cl);
3139   cl->reset_generation();
3140 }
3141 
3142 void
3143 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3144   if (freelistLock()->owned_by_self()) {
3145     Generation::oop_iterate(cl);
3146   } else {
3147     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3148     Generation::oop_iterate(cl);
3149   }
3150 }
3151 
3152 void
3153 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3154   if (freelistLock()->owned_by_self()) {
3155     Generation::object_iterate(cl);
3156   } else {
3157     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3158     Generation::object_iterate(cl);
3159   }
3160 }
3161 
3162 void
3163 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3164   if (freelistLock()->owned_by_self()) {
3165     Generation::safe_object_iterate(cl);
3166   } else {
3167     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3168     Generation::safe_object_iterate(cl);
3169   }
3170 }
3171 
3172 void
3173 ConcurrentMarkSweepGeneration::post_compact() {
3174 }
3175 
3176 void
3177 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3178   // Fix the linear allocation blocks to look like free blocks.
3179 
3180   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3181   // are not called when the heap is verified during universe initialization and
3182   // at vm shutdown.
3183   if (freelistLock()->owned_by_self()) {
3184     cmsSpace()->prepare_for_verify();
3185   } else {
3186     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3187     cmsSpace()->prepare_for_verify();
3188   }
3189 }
3190 
3191 void
3192 ConcurrentMarkSweepGeneration::verify() {
3193   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3194   // are not called when the heap is verified during universe initialization and
3195   // at vm shutdown.
3196   if (freelistLock()->owned_by_self()) {
3197     cmsSpace()->verify();
3198   } else {
3199     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3200     cmsSpace()->verify();
3201   }
3202 }
3203 
3204 void CMSCollector::verify() {
3205   _cmsGen->verify();
3206 }
3207 
3208 #ifndef PRODUCT
3209 bool CMSCollector::overflow_list_is_empty() const {
3210   assert(_num_par_pushes >= 0, "Inconsistency");
3211   if (_overflow_list == NULL) {
3212     assert(_num_par_pushes == 0, "Inconsistency");
3213   }
3214   return _overflow_list == NULL;
3215 }
3216 
3217 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3218 // merely consolidate assertion checks that appear to occur together frequently.
3219 void CMSCollector::verify_work_stacks_empty() const {
3220   assert(_markStack.isEmpty(), "Marking stack should be empty");
3221   assert(overflow_list_is_empty(), "Overflow list should be empty");
3222 }
3223 
3224 void CMSCollector::verify_overflow_empty() const {
3225   assert(overflow_list_is_empty(), "Overflow list should be empty");
3226   assert(no_preserved_marks(), "No preserved marks");
3227 }
3228 #endif // PRODUCT
3229 
3230 // Decide if we want to enable class unloading as part of the
3231 // ensuing concurrent GC cycle. We will collect and
3232 // unload classes if it's the case that:
3233 // (1) an explicit gc request has been made and the flag
3234 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3235 // (2) (a) class unloading is enabled at the command line, and
3236 //     (b) old gen is getting really full
3237 // NOTE: Provided there is no change in the state of the heap between
3238 // calls to this method, it should have idempotent results. Moreover,
3239 // its results should be monotonically increasing (i.e. going from 0 to 1,
3240 // but not 1 to 0) between successive calls between which the heap was
3241 // not collected. For the implementation below, it must thus rely on
3242 // the property that concurrent_cycles_since_last_unload()
3243 // will not decrease unless a collection cycle happened and that
3244 // _cmsGen->is_too_full() are
3245 // themselves also monotonic in that sense. See check_monotonicity()
3246 // below.
3247 void CMSCollector::update_should_unload_classes() {
3248   _should_unload_classes = false;
3249   // Condition 1 above
3250   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3251     _should_unload_classes = true;
3252   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3253     // Disjuncts 2.b.(i,ii,iii) above
3254     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3255                               CMSClassUnloadingMaxInterval)
3256                            || _cmsGen->is_too_full();
3257   }
3258 }
3259 
3260 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3261   bool res = should_concurrent_collect();
3262   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3263   return res;
3264 }
3265 
3266 void CMSCollector::setup_cms_unloading_and_verification_state() {
3267   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3268                              || VerifyBeforeExit;
3269   const  int  rso           =   SharedHeap::SO_AllCodeCache;
3270 
3271   // We set the proper root for this CMS cycle here.
3272   if (should_unload_classes()) {   // Should unload classes this cycle
3273     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3274     set_verifying(should_verify);    // Set verification state for this cycle
3275     return;                            // Nothing else needs to be done at this time
3276   }
3277 
3278   // Not unloading classes this cycle
3279   assert(!should_unload_classes(), "Inconsistency!");
3280 
3281   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3282     // Include symbols, strings and code cache elements to prevent their resurrection.
3283     add_root_scanning_option(rso);
3284     set_verifying(true);
3285   } else if (verifying() && !should_verify) {
3286     // We were verifying, but some verification flags got disabled.
3287     set_verifying(false);
3288     // Exclude symbols, strings and code cache elements from root scanning to
3289     // reduce IM and RM pauses.
3290     remove_root_scanning_option(rso);
3291   }
3292 }
3293 
3294 
3295 #ifndef PRODUCT
3296 HeapWord* CMSCollector::block_start(const void* p) const {
3297   const HeapWord* addr = (HeapWord*)p;
3298   if (_span.contains(p)) {
3299     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3300       return _cmsGen->cmsSpace()->block_start(p);
3301     }
3302   }
3303   return NULL;
3304 }
3305 #endif
3306 
3307 HeapWord*
3308 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3309                                                    bool   tlab,
3310                                                    bool   parallel) {
3311   CMSSynchronousYieldRequest yr;
3312   assert(!tlab, "Can't deal with TLAB allocation");
3313   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3314   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3315     CMSExpansionCause::_satisfy_allocation);
3316   if (GCExpandToAllocateDelayMillis > 0) {
3317     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3318   }
3319   return have_lock_and_allocate(word_size, tlab);
3320 }
3321 
3322 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3323 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3324 // to CardGeneration and share it...
3325 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3326   return CardGeneration::expand(bytes, expand_bytes);
3327 }
3328 
3329 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3330   CMSExpansionCause::Cause cause)
3331 {
3332 
3333   bool success = expand(bytes, expand_bytes);
3334 
3335   // remember why we expanded; this information is used
3336   // by shouldConcurrentCollect() when making decisions on whether to start
3337   // a new CMS cycle.
3338   if (success) {
3339     set_expansion_cause(cause);
3340     if (PrintGCDetails && Verbose) {
3341       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3342         CMSExpansionCause::to_string(cause));
3343     }
3344   }
3345 }
3346 
3347 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3348   HeapWord* res = NULL;
3349   MutexLocker x(ParGCRareEvent_lock);
3350   while (true) {
3351     // Expansion by some other thread might make alloc OK now:
3352     res = ps->lab.alloc(word_sz);
3353     if (res != NULL) return res;
3354     // If there's not enough expansion space available, give up.
3355     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3356       return NULL;
3357     }
3358     // Otherwise, we try expansion.
3359     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3360       CMSExpansionCause::_allocate_par_lab);
3361     // Now go around the loop and try alloc again;
3362     // A competing par_promote might beat us to the expansion space,
3363     // so we may go around the loop again if promotion fails again.
3364     if (GCExpandToAllocateDelayMillis > 0) {
3365       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3366     }
3367   }
3368 }
3369 
3370 
3371 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3372   PromotionInfo* promo) {
3373   MutexLocker x(ParGCRareEvent_lock);
3374   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3375   while (true) {
3376     // Expansion by some other thread might make alloc OK now:
3377     if (promo->ensure_spooling_space()) {
3378       assert(promo->has_spooling_space(),
3379              "Post-condition of successful ensure_spooling_space()");
3380       return true;
3381     }
3382     // If there's not enough expansion space available, give up.
3383     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3384       return false;
3385     }
3386     // Otherwise, we try expansion.
3387     expand(refill_size_bytes, MinHeapDeltaBytes,
3388       CMSExpansionCause::_allocate_par_spooling_space);
3389     // Now go around the loop and try alloc again;
3390     // A competing allocation might beat us to the expansion space,
3391     // so we may go around the loop again if allocation fails again.
3392     if (GCExpandToAllocateDelayMillis > 0) {
3393       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3394     }
3395   }
3396 }
3397 
3398 
3399 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3400   assert_locked_or_safepoint(ExpandHeap_lock);
3401   // Shrink committed space
3402   _virtual_space.shrink_by(bytes);
3403   // Shrink space; this also shrinks the space's BOT
3404   _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3405   size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3406   // Shrink the shared block offset array
3407   _bts->resize(new_word_size);
3408   MemRegion mr(_cmsSpace->bottom(), new_word_size);
3409   // Shrink the card table
3410   Universe::heap()->barrier_set()->resize_covered_region(mr);
3411 
3412   if (Verbose && PrintGC) {
3413     size_t new_mem_size = _virtual_space.committed_size();
3414     size_t old_mem_size = new_mem_size + bytes;
3415     gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3416                   name(), old_mem_size/K, new_mem_size/K);
3417   }
3418 }
3419 
3420 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3421   assert_locked_or_safepoint(Heap_lock);
3422   size_t size = ReservedSpace::page_align_size_down(bytes);
3423   // Only shrink if a compaction was done so that all the free space
3424   // in the generation is in a contiguous block at the end.
3425   if (size > 0 && did_compact()) {
3426     shrink_by(size);
3427   }
3428 }
3429 
3430 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3431   assert_locked_or_safepoint(Heap_lock);
3432   bool result = _virtual_space.expand_by(bytes);
3433   if (result) {
3434     size_t new_word_size =
3435       heap_word_size(_virtual_space.committed_size());
3436     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3437     _bts->resize(new_word_size);  // resize the block offset shared array
3438     Universe::heap()->barrier_set()->resize_covered_region(mr);
3439     // Hmmmm... why doesn't CFLS::set_end verify locking?
3440     // This is quite ugly; FIX ME XXX
3441     _cmsSpace->assert_locked(freelistLock());
3442     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3443 
3444     // update the space and generation capacity counters
3445     if (UsePerfData) {
3446       _space_counters->update_capacity();
3447       _gen_counters->update_all();
3448     }
3449 
3450     if (Verbose && PrintGC) {
3451       size_t new_mem_size = _virtual_space.committed_size();
3452       size_t old_mem_size = new_mem_size - bytes;
3453       gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3454                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3455     }
3456   }
3457   return result;
3458 }
3459 
3460 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3461   assert_locked_or_safepoint(Heap_lock);
3462   bool success = true;
3463   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3464   if (remaining_bytes > 0) {
3465     success = grow_by(remaining_bytes);
3466     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3467   }
3468   return success;
3469 }
3470 
3471 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3472   assert_locked_or_safepoint(Heap_lock);
3473   assert_lock_strong(freelistLock());
3474   if (PrintGCDetails && Verbose) {
3475     warning("Shrinking of CMS not yet implemented");
3476   }
3477   return;
3478 }
3479 
3480 
3481 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3482 // phases.
3483 class CMSPhaseAccounting: public StackObj {
3484  public:
3485   CMSPhaseAccounting(CMSCollector *collector,
3486                      const char *phase,
3487                      const GCId gc_id,
3488                      bool print_cr = true);
3489   ~CMSPhaseAccounting();
3490 
3491  private:
3492   CMSCollector *_collector;
3493   const char *_phase;
3494   elapsedTimer _wallclock;
3495   bool _print_cr;
3496   const GCId _gc_id;
3497 
3498  public:
3499   // Not MT-safe; so do not pass around these StackObj's
3500   // where they may be accessed by other threads.
3501   jlong wallclock_millis() {
3502     assert(_wallclock.is_active(), "Wall clock should not stop");
3503     _wallclock.stop();  // to record time
3504     jlong ret = _wallclock.milliseconds();
3505     _wallclock.start(); // restart
3506     return ret;
3507   }
3508 };
3509 
3510 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3511                                        const char *phase,
3512                                        const GCId gc_id,
3513                                        bool print_cr) :
3514   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3515 
3516   if (PrintCMSStatistics != 0) {
3517     _collector->resetYields();
3518   }
3519   if (PrintGCDetails) {
3520     gclog_or_tty->gclog_stamp(_gc_id);
3521     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3522       _collector->cmsGen()->short_name(), _phase);
3523   }
3524   _collector->resetTimer();
3525   _wallclock.start();
3526   _collector->startTimer();
3527 }
3528 
3529 CMSPhaseAccounting::~CMSPhaseAccounting() {
3530   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3531   _collector->stopTimer();
3532   _wallclock.stop();
3533   if (PrintGCDetails) {
3534     gclog_or_tty->gclog_stamp(_gc_id);
3535     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3536                  _collector->cmsGen()->short_name(),
3537                  _phase, _collector->timerValue(), _wallclock.seconds());
3538     if (_print_cr) {
3539       gclog_or_tty->cr();
3540     }
3541     if (PrintCMSStatistics != 0) {
3542       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3543                     _collector->yields());
3544     }
3545   }
3546 }
3547 
3548 // CMS work
3549 
3550 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3551 class CMSParMarkTask : public AbstractGangTask {
3552  protected:
3553   CMSCollector*     _collector;
3554   int               _n_workers;
3555   CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3556       AbstractGangTask(name),
3557       _collector(collector),
3558       _n_workers(n_workers) {}
3559   // Work method in support of parallel rescan ... of young gen spaces
3560   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3561                              ContiguousSpace* space,
3562                              HeapWord** chunk_array, size_t chunk_top);
3563   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3564 };
3565 
3566 // Parallel initial mark task
3567 class CMSParInitialMarkTask: public CMSParMarkTask {
3568  public:
3569   CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3570       CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3571                      collector, n_workers) {}
3572   void work(uint worker_id);
3573 };
3574 
3575 // Checkpoint the roots into this generation from outside
3576 // this generation. [Note this initial checkpoint need only
3577 // be approximate -- we'll do a catch up phase subsequently.]
3578 void CMSCollector::checkpointRootsInitial(bool asynch) {
3579   assert(_collectorState == InitialMarking, "Wrong collector state");
3580   check_correct_thread_executing();
3581   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3582 
3583   save_heap_summary();
3584   report_heap_summary(GCWhen::BeforeGC);
3585 
3586   ReferenceProcessor* rp = ref_processor();
3587   SpecializationStats::clear();
3588   assert(_restart_addr == NULL, "Control point invariant");
3589   if (asynch) {
3590     // acquire locks for subsequent manipulations
3591     MutexLockerEx x(bitMapLock(),
3592                     Mutex::_no_safepoint_check_flag);
3593     checkpointRootsInitialWork(asynch);
3594     // enable ("weak") refs discovery
3595     rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3596     _collectorState = Marking;
3597   } else {
3598     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3599     // which recognizes if we are a CMS generation, and doesn't try to turn on
3600     // discovery; verify that they aren't meddling.
3601     assert(!rp->discovery_is_atomic(),
3602            "incorrect setting of discovery predicate");
3603     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3604            "ref discovery for this generation kind");
3605     // already have locks
3606     checkpointRootsInitialWork(asynch);
3607     // now enable ("weak") refs discovery
3608     rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3609     _collectorState = Marking;
3610   }
3611   SpecializationStats::print();
3612 }
3613 
3614 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3615   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3616   assert(_collectorState == InitialMarking, "just checking");
3617 
3618   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3619   // precede our marking with a collection of all
3620   // younger generations to keep floating garbage to a minimum.
3621   // XXX: we won't do this for now -- it's an optimization to be done later.
3622 
3623   // already have locks
3624   assert_lock_strong(bitMapLock());
3625   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3626 
3627   // Setup the verification and class unloading state for this
3628   // CMS collection cycle.
3629   setup_cms_unloading_and_verification_state();
3630 
3631   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3632     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3633 
3634   // Reset all the PLAB chunk arrays if necessary.
3635   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3636     reset_survivor_plab_arrays();
3637   }
3638 
3639   ResourceMark rm;
3640   HandleMark  hm;
3641 
3642   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3643   GenCollectedHeap* gch = GenCollectedHeap::heap();
3644 
3645   verify_work_stacks_empty();
3646   verify_overflow_empty();
3647 
3648   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3649   // Update the saved marks which may affect the root scans.
3650   gch->save_marks();
3651 
3652   // weak reference processing has not started yet.
3653   ref_processor()->set_enqueuing_is_done(false);
3654 
3655   // Need to remember all newly created CLDs,
3656   // so that we can guarantee that the remark finds them.
3657   ClassLoaderDataGraph::remember_new_clds(true);
3658 
3659   // Whenever a CLD is found, it will be claimed before proceeding to mark
3660   // the klasses. The claimed marks need to be cleared before marking starts.
3661   ClassLoaderDataGraph::clear_claimed_marks();
3662 
3663   if (CMSPrintEdenSurvivorChunks) {
3664     print_eden_and_survivor_chunk_arrays();
3665   }
3666 
3667   {
3668     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3669     if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3670       // The parallel version.
3671       FlexibleWorkGang* workers = gch->workers();
3672       assert(workers != NULL, "Need parallel worker threads.");
3673       int n_workers = workers->active_workers();
3674       CMSParInitialMarkTask tsk(this, n_workers);
3675       gch->set_par_threads(n_workers);
3676       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3677       if (n_workers > 1) {
3678         GenCollectedHeap::StrongRootsScope srs(gch);
3679         workers->run_task(&tsk);
3680       } else {
3681         GenCollectedHeap::StrongRootsScope srs(gch);
3682         tsk.work(0);
3683       }
3684       gch->set_par_threads(0);
3685     } else {
3686       // The serial version.
3687       CLDToOopClosure cld_closure(&notOlder, true);
3688       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3689       gch->gen_process_roots(_cmsGen->level(),
3690                              true,   // younger gens are roots
3691                              true,   // activate StrongRootsScope
3692                              SharedHeap::ScanningOption(roots_scanning_options()),
3693                              should_unload_classes(),
3694                              &notOlder,
3695                              NULL,
3696                              &cld_closure);
3697     }
3698   }
3699 
3700   // Clear mod-union table; it will be dirtied in the prologue of
3701   // CMS generation per each younger generation collection.
3702 
3703   assert(_modUnionTable.isAllClear(),
3704        "Was cleared in most recent final checkpoint phase"
3705        " or no bits are set in the gc_prologue before the start of the next "
3706        "subsequent marking phase.");
3707 
3708   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3709 
3710   // Save the end of the used_region of the constituent generations
3711   // to be used to limit the extent of sweep in each generation.
3712   save_sweep_limits();
3713   verify_overflow_empty();
3714 }
3715 
3716 bool CMSCollector::markFromRoots(bool asynch) {
3717   // we might be tempted to assert that:
3718   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3719   //        "inconsistent argument?");
3720   // However that wouldn't be right, because it's possible that
3721   // a safepoint is indeed in progress as a younger generation
3722   // stop-the-world GC happens even as we mark in this generation.
3723   assert(_collectorState == Marking, "inconsistent state?");
3724   check_correct_thread_executing();
3725   verify_overflow_empty();
3726 
3727   bool res;
3728   if (asynch) {
3729     // Weak ref discovery note: We may be discovering weak
3730     // refs in this generation concurrent (but interleaved) with
3731     // weak ref discovery by a younger generation collector.
3732 
3733     CMSTokenSyncWithLocks ts(true, bitMapLock());
3734     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3735     CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3736     res = markFromRootsWork(asynch);
3737     if (res) {
3738       _collectorState = Precleaning;
3739     } else { // We failed and a foreground collection wants to take over
3740       assert(_foregroundGCIsActive, "internal state inconsistency");
3741       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3742       if (PrintGCDetails) {
3743         gclog_or_tty->print_cr("bailing out to foreground collection");
3744       }
3745     }
3746   } else {
3747     assert(SafepointSynchronize::is_at_safepoint(),
3748            "inconsistent with asynch == false");
3749     // already have locks
3750     res = markFromRootsWork(asynch);
3751     _collectorState = FinalMarking;
3752   }
3753   verify_overflow_empty();
3754   return res;
3755 }
3756 
3757 bool CMSCollector::markFromRootsWork(bool asynch) {
3758   // iterate over marked bits in bit map, doing a full scan and mark
3759   // from these roots using the following algorithm:
3760   // . if oop is to the right of the current scan pointer,
3761   //   mark corresponding bit (we'll process it later)
3762   // . else (oop is to left of current scan pointer)
3763   //   push oop on marking stack
3764   // . drain the marking stack
3765 
3766   // Note that when we do a marking step we need to hold the
3767   // bit map lock -- recall that direct allocation (by mutators)
3768   // and promotion (by younger generation collectors) is also
3769   // marking the bit map. [the so-called allocate live policy.]
3770   // Because the implementation of bit map marking is not
3771   // robust wrt simultaneous marking of bits in the same word,
3772   // we need to make sure that there is no such interference
3773   // between concurrent such updates.
3774 
3775   // already have locks
3776   assert_lock_strong(bitMapLock());
3777 
3778   verify_work_stacks_empty();
3779   verify_overflow_empty();
3780   bool result = false;
3781   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3782     result = do_marking_mt(asynch);
3783   } else {
3784     result = do_marking_st(asynch);
3785   }
3786   return result;
3787 }
3788 
3789 // Forward decl
3790 class CMSConcMarkingTask;
3791 
3792 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3793   CMSCollector*       _collector;
3794   CMSConcMarkingTask* _task;
3795  public:
3796   virtual void yield();
3797 
3798   // "n_threads" is the number of threads to be terminated.
3799   // "queue_set" is a set of work queues of other threads.
3800   // "collector" is the CMS collector associated with this task terminator.
3801   // "yield" indicates whether we need the gang as a whole to yield.
3802   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3803     ParallelTaskTerminator(n_threads, queue_set),
3804     _collector(collector) { }
3805 
3806   void set_task(CMSConcMarkingTask* task) {
3807     _task = task;
3808   }
3809 };
3810 
3811 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3812   CMSConcMarkingTask* _task;
3813  public:
3814   bool should_exit_termination();
3815   void set_task(CMSConcMarkingTask* task) {
3816     _task = task;
3817   }
3818 };
3819 
3820 // MT Concurrent Marking Task
3821 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3822   CMSCollector* _collector;
3823   int           _n_workers;                  // requested/desired # workers
3824   bool          _asynch;
3825   bool          _result;
3826   CompactibleFreeListSpace*  _cms_space;
3827   char          _pad_front[64];   // padding to ...
3828   HeapWord*     _global_finger;   // ... avoid sharing cache line
3829   char          _pad_back[64];
3830   HeapWord*     _restart_addr;
3831 
3832   //  Exposed here for yielding support
3833   Mutex* const _bit_map_lock;
3834 
3835   // The per thread work queues, available here for stealing
3836   OopTaskQueueSet*  _task_queues;
3837 
3838   // Termination (and yielding) support
3839   CMSConcMarkingTerminator _term;
3840   CMSConcMarkingTerminatorTerminator _term_term;
3841 
3842  public:
3843   CMSConcMarkingTask(CMSCollector* collector,
3844                  CompactibleFreeListSpace* cms_space,
3845                  bool asynch,
3846                  YieldingFlexibleWorkGang* workers,
3847                  OopTaskQueueSet* task_queues):
3848     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3849     _collector(collector),
3850     _cms_space(cms_space),
3851     _asynch(asynch), _n_workers(0), _result(true),
3852     _task_queues(task_queues),
3853     _term(_n_workers, task_queues, _collector),
3854     _bit_map_lock(collector->bitMapLock())
3855   {
3856     _requested_size = _n_workers;
3857     _term.set_task(this);
3858     _term_term.set_task(this);
3859     _restart_addr = _global_finger = _cms_space->bottom();
3860   }
3861 
3862 
3863   OopTaskQueueSet* task_queues()  { return _task_queues; }
3864 
3865   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3866 
3867   HeapWord** global_finger_addr() { return &_global_finger; }
3868 
3869   CMSConcMarkingTerminator* terminator() { return &_term; }
3870 
3871   virtual void set_for_termination(int active_workers) {
3872     terminator()->reset_for_reuse(active_workers);
3873   }
3874 
3875   void work(uint worker_id);
3876   bool should_yield() {
3877     return    ConcurrentMarkSweepThread::should_yield()
3878            && !_collector->foregroundGCIsActive()
3879            && _asynch;
3880   }
3881 
3882   virtual void coordinator_yield();  // stuff done by coordinator
3883   bool result() { return _result; }
3884 
3885   void reset(HeapWord* ra) {
3886     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3887     _restart_addr = _global_finger = ra;
3888     _term.reset_for_reuse();
3889   }
3890 
3891   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3892                                            OopTaskQueue* work_q);
3893 
3894  private:
3895   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3896   void do_work_steal(int i);
3897   void bump_global_finger(HeapWord* f);
3898 };
3899 
3900 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3901   assert(_task != NULL, "Error");
3902   return _task->yielding();
3903   // Note that we do not need the disjunct || _task->should_yield() above
3904   // because we want terminating threads to yield only if the task
3905   // is already in the midst of yielding, which happens only after at least one
3906   // thread has yielded.
3907 }
3908 
3909 void CMSConcMarkingTerminator::yield() {
3910   if (_task->should_yield()) {
3911     _task->yield();
3912   } else {
3913     ParallelTaskTerminator::yield();
3914   }
3915 }
3916 
3917 ////////////////////////////////////////////////////////////////
3918 // Concurrent Marking Algorithm Sketch
3919 ////////////////////////////////////////////////////////////////
3920 // Until all tasks exhausted (both spaces):
3921 // -- claim next available chunk
3922 // -- bump global finger via CAS
3923 // -- find first object that starts in this chunk
3924 //    and start scanning bitmap from that position
3925 // -- scan marked objects for oops
3926 // -- CAS-mark target, and if successful:
3927 //    . if target oop is above global finger (volatile read)
3928 //      nothing to do
3929 //    . if target oop is in chunk and above local finger
3930 //        then nothing to do
3931 //    . else push on work-queue
3932 // -- Deal with possible overflow issues:
3933 //    . local work-queue overflow causes stuff to be pushed on
3934 //      global (common) overflow queue
3935 //    . always first empty local work queue
3936 //    . then get a batch of oops from global work queue if any
3937 //    . then do work stealing
3938 // -- When all tasks claimed (both spaces)
3939 //    and local work queue empty,
3940 //    then in a loop do:
3941 //    . check global overflow stack; steal a batch of oops and trace
3942 //    . try to steal from other threads oif GOS is empty
3943 //    . if neither is available, offer termination
3944 // -- Terminate and return result
3945 //
3946 void CMSConcMarkingTask::work(uint worker_id) {
3947   elapsedTimer _timer;
3948   ResourceMark rm;
3949   HandleMark hm;
3950 
3951   DEBUG_ONLY(_collector->verify_overflow_empty();)
3952 
3953   // Before we begin work, our work queue should be empty
3954   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3955   // Scan the bitmap covering _cms_space, tracing through grey objects.
3956   _timer.start();
3957   do_scan_and_mark(worker_id, _cms_space);
3958   _timer.stop();
3959   if (PrintCMSStatistics != 0) {
3960     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3961       worker_id, _timer.seconds());
3962       // XXX: need xxx/xxx type of notation, two timers
3963   }
3964 
3965   // ... do work stealing
3966   _timer.reset();
3967   _timer.start();
3968   do_work_steal(worker_id);
3969   _timer.stop();
3970   if (PrintCMSStatistics != 0) {
3971     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3972       worker_id, _timer.seconds());
3973       // XXX: need xxx/xxx type of notation, two timers
3974   }
3975   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3976   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3977   // Note that under the current task protocol, the
3978   // following assertion is true even of the spaces
3979   // expanded since the completion of the concurrent
3980   // marking. XXX This will likely change under a strict
3981   // ABORT semantics.
3982   // After perm removal the comparison was changed to
3983   // greater than or equal to from strictly greater than.
3984   // Before perm removal the highest address sweep would
3985   // have been at the end of perm gen but now is at the
3986   // end of the tenured gen.
3987   assert(_global_finger >=  _cms_space->end(),
3988          "All tasks have been completed");
3989   DEBUG_ONLY(_collector->verify_overflow_empty();)
3990 }
3991 
3992 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3993   HeapWord* read = _global_finger;
3994   HeapWord* cur  = read;
3995   while (f > read) {
3996     cur = read;
3997     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3998     if (cur == read) {
3999       // our cas succeeded
4000       assert(_global_finger >= f, "protocol consistency");
4001       break;
4002     }
4003   }
4004 }
4005 
4006 // This is really inefficient, and should be redone by
4007 // using (not yet available) block-read and -write interfaces to the
4008 // stack and the work_queue. XXX FIX ME !!!
4009 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4010                                                       OopTaskQueue* work_q) {
4011   // Fast lock-free check
4012   if (ovflw_stk->length() == 0) {
4013     return false;
4014   }
4015   assert(work_q->size() == 0, "Shouldn't steal");
4016   MutexLockerEx ml(ovflw_stk->par_lock(),
4017                    Mutex::_no_safepoint_check_flag);
4018   // Grab up to 1/4 the size of the work queue
4019   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4020                     (size_t)ParGCDesiredObjsFromOverflowList);
4021   num = MIN2(num, ovflw_stk->length());
4022   for (int i = (int) num; i > 0; i--) {
4023     oop cur = ovflw_stk->pop();
4024     assert(cur != NULL, "Counted wrong?");
4025     work_q->push(cur);
4026   }
4027   return num > 0;
4028 }
4029 
4030 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4031   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4032   int n_tasks = pst->n_tasks();
4033   // We allow that there may be no tasks to do here because
4034   // we are restarting after a stack overflow.
4035   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4036   uint nth_task = 0;
4037 
4038   HeapWord* aligned_start = sp->bottom();
4039   if (sp->used_region().contains(_restart_addr)) {
4040     // Align down to a card boundary for the start of 0th task
4041     // for this space.
4042     aligned_start =
4043       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4044                                  CardTableModRefBS::card_size);
4045   }
4046 
4047   size_t chunk_size = sp->marking_task_size();
4048   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4049     // Having claimed the nth task in this space,
4050     // compute the chunk that it corresponds to:
4051     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4052                                aligned_start + (nth_task+1)*chunk_size);
4053     // Try and bump the global finger via a CAS;
4054     // note that we need to do the global finger bump
4055     // _before_ taking the intersection below, because
4056     // the task corresponding to that region will be
4057     // deemed done even if the used_region() expands
4058     // because of allocation -- as it almost certainly will
4059     // during start-up while the threads yield in the
4060     // closure below.
4061     HeapWord* finger = span.end();
4062     bump_global_finger(finger);   // atomically
4063     // There are null tasks here corresponding to chunks
4064     // beyond the "top" address of the space.
4065     span = span.intersection(sp->used_region());
4066     if (!span.is_empty()) {  // Non-null task
4067       HeapWord* prev_obj;
4068       assert(!span.contains(_restart_addr) || nth_task == 0,
4069              "Inconsistency");
4070       if (nth_task == 0) {
4071         // For the 0th task, we'll not need to compute a block_start.
4072         if (span.contains(_restart_addr)) {
4073           // In the case of a restart because of stack overflow,
4074           // we might additionally skip a chunk prefix.
4075           prev_obj = _restart_addr;
4076         } else {
4077           prev_obj = span.start();
4078         }
4079       } else {
4080         // We want to skip the first object because
4081         // the protocol is to scan any object in its entirety
4082         // that _starts_ in this span; a fortiori, any
4083         // object starting in an earlier span is scanned
4084         // as part of an earlier claimed task.
4085         // Below we use the "careful" version of block_start
4086         // so we do not try to navigate uninitialized objects.
4087         prev_obj = sp->block_start_careful(span.start());
4088         // Below we use a variant of block_size that uses the
4089         // Printezis bits to avoid waiting for allocated
4090         // objects to become initialized/parsable.
4091         while (prev_obj < span.start()) {
4092           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4093           if (sz > 0) {
4094             prev_obj += sz;
4095           } else {
4096             // In this case we may end up doing a bit of redundant
4097             // scanning, but that appears unavoidable, short of
4098             // locking the free list locks; see bug 6324141.
4099             break;
4100           }
4101         }
4102       }
4103       if (prev_obj < span.end()) {
4104         MemRegion my_span = MemRegion(prev_obj, span.end());
4105         // Do the marking work within a non-empty span --
4106         // the last argument to the constructor indicates whether the
4107         // iteration should be incremental with periodic yields.
4108         Par_MarkFromRootsClosure cl(this, _collector, my_span,
4109                                     &_collector->_markBitMap,
4110                                     work_queue(i),
4111                                     &_collector->_markStack,
4112                                     _asynch);
4113         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4114       } // else nothing to do for this task
4115     }   // else nothing to do for this task
4116   }
4117   // We'd be tempted to assert here that since there are no
4118   // more tasks left to claim in this space, the global_finger
4119   // must exceed space->top() and a fortiori space->end(). However,
4120   // that would not quite be correct because the bumping of
4121   // global_finger occurs strictly after the claiming of a task,
4122   // so by the time we reach here the global finger may not yet
4123   // have been bumped up by the thread that claimed the last
4124   // task.
4125   pst->all_tasks_completed();
4126 }
4127 
4128 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4129  private:
4130   CMSCollector* _collector;
4131   CMSConcMarkingTask* _task;
4132   MemRegion     _span;
4133   CMSBitMap*    _bit_map;
4134   CMSMarkStack* _overflow_stack;
4135   OopTaskQueue* _work_queue;
4136  protected:
4137   DO_OOP_WORK_DEFN
4138  public:
4139   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4140                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4141     MetadataAwareOopClosure(collector->ref_processor()),
4142     _collector(collector),
4143     _task(task),
4144     _span(collector->_span),
4145     _work_queue(work_queue),
4146     _bit_map(bit_map),
4147     _overflow_stack(overflow_stack)
4148   { }
4149   virtual void do_oop(oop* p);
4150   virtual void do_oop(narrowOop* p);
4151 
4152   void trim_queue(size_t max);
4153   void handle_stack_overflow(HeapWord* lost);
4154   void do_yield_check() {
4155     if (_task->should_yield()) {
4156       _task->yield();
4157     }
4158   }
4159 };
4160 
4161 // Grey object scanning during work stealing phase --
4162 // the salient assumption here is that any references
4163 // that are in these stolen objects being scanned must
4164 // already have been initialized (else they would not have
4165 // been published), so we do not need to check for
4166 // uninitialized objects before pushing here.
4167 void Par_ConcMarkingClosure::do_oop(oop obj) {
4168   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4169   HeapWord* addr = (HeapWord*)obj;
4170   // Check if oop points into the CMS generation
4171   // and is not marked
4172   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4173     // a white object ...
4174     // If we manage to "claim" the object, by being the
4175     // first thread to mark it, then we push it on our
4176     // marking stack
4177     if (_bit_map->par_mark(addr)) {     // ... now grey
4178       // push on work queue (grey set)
4179       bool simulate_overflow = false;
4180       NOT_PRODUCT(
4181         if (CMSMarkStackOverflowALot &&
4182             _collector->simulate_overflow()) {
4183           // simulate a stack overflow
4184           simulate_overflow = true;
4185         }
4186       )
4187       if (simulate_overflow ||
4188           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4189         // stack overflow
4190         if (PrintCMSStatistics != 0) {
4191           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4192                                  SIZE_FORMAT, _overflow_stack->capacity());
4193         }
4194         // We cannot assert that the overflow stack is full because
4195         // it may have been emptied since.
4196         assert(simulate_overflow ||
4197                _work_queue->size() == _work_queue->max_elems(),
4198               "Else push should have succeeded");
4199         handle_stack_overflow(addr);
4200       }
4201     } // Else, some other thread got there first
4202     do_yield_check();
4203   }
4204 }
4205 
4206 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
4207 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4208 
4209 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4210   while (_work_queue->size() > max) {
4211     oop new_oop;
4212     if (_work_queue->pop_local(new_oop)) {
4213       assert(new_oop->is_oop(), "Should be an oop");
4214       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4215       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4216       new_oop->oop_iterate(this);  // do_oop() above
4217       do_yield_check();
4218     }
4219   }
4220 }
4221 
4222 // Upon stack overflow, we discard (part of) the stack,
4223 // remembering the least address amongst those discarded
4224 // in CMSCollector's _restart_address.
4225 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4226   // We need to do this under a mutex to prevent other
4227   // workers from interfering with the work done below.
4228   MutexLockerEx ml(_overflow_stack->par_lock(),
4229                    Mutex::_no_safepoint_check_flag);
4230   // Remember the least grey address discarded
4231   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4232   _collector->lower_restart_addr(ra);
4233   _overflow_stack->reset();  // discard stack contents
4234   _overflow_stack->expand(); // expand the stack if possible
4235 }
4236 
4237 
4238 void CMSConcMarkingTask::do_work_steal(int i) {
4239   OopTaskQueue* work_q = work_queue(i);
4240   oop obj_to_scan;
4241   CMSBitMap* bm = &(_collector->_markBitMap);
4242   CMSMarkStack* ovflw = &(_collector->_markStack);
4243   int* seed = _collector->hash_seed(i);
4244   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4245   while (true) {
4246     cl.trim_queue(0);
4247     assert(work_q->size() == 0, "Should have been emptied above");
4248     if (get_work_from_overflow_stack(ovflw, work_q)) {
4249       // Can't assert below because the work obtained from the
4250       // overflow stack may already have been stolen from us.
4251       // assert(work_q->size() > 0, "Work from overflow stack");
4252       continue;
4253     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4254       assert(obj_to_scan->is_oop(), "Should be an oop");
4255       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4256       obj_to_scan->oop_iterate(&cl);
4257     } else if (terminator()->offer_termination(&_term_term)) {
4258       assert(work_q->size() == 0, "Impossible!");
4259       break;
4260     } else if (yielding() || should_yield()) {
4261       yield();
4262     }
4263   }
4264 }
4265 
4266 // This is run by the CMS (coordinator) thread.
4267 void CMSConcMarkingTask::coordinator_yield() {
4268   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4269          "CMS thread should hold CMS token");
4270   // First give up the locks, then yield, then re-lock
4271   // We should probably use a constructor/destructor idiom to
4272   // do this unlock/lock or modify the MutexUnlocker class to
4273   // serve our purpose. XXX
4274   assert_lock_strong(_bit_map_lock);
4275   _bit_map_lock->unlock();
4276   ConcurrentMarkSweepThread::desynchronize(true);
4277   ConcurrentMarkSweepThread::acknowledge_yield_request();
4278   _collector->stopTimer();
4279   if (PrintCMSStatistics != 0) {
4280     _collector->incrementYields();
4281   }
4282   _collector->icms_wait();
4283 
4284   // It is possible for whichever thread initiated the yield request
4285   // not to get a chance to wake up and take the bitmap lock between
4286   // this thread releasing it and reacquiring it. So, while the
4287   // should_yield() flag is on, let's sleep for a bit to give the
4288   // other thread a chance to wake up. The limit imposed on the number
4289   // of iterations is defensive, to avoid any unforseen circumstances
4290   // putting us into an infinite loop. Since it's always been this
4291   // (coordinator_yield()) method that was observed to cause the
4292   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4293   // which is by default non-zero. For the other seven methods that
4294   // also perform the yield operation, as are using a different
4295   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4296   // can enable the sleeping for those methods too, if necessary.
4297   // See 6442774.
4298   //
4299   // We really need to reconsider the synchronization between the GC
4300   // thread and the yield-requesting threads in the future and we
4301   // should really use wait/notify, which is the recommended
4302   // way of doing this type of interaction. Additionally, we should
4303   // consolidate the eight methods that do the yield operation and they
4304   // are almost identical into one for better maintainability and
4305   // readability. See 6445193.
4306   //
4307   // Tony 2006.06.29
4308   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4309                    ConcurrentMarkSweepThread::should_yield() &&
4310                    !CMSCollector::foregroundGCIsActive(); ++i) {
4311     os::sleep(Thread::current(), 1, false);
4312     ConcurrentMarkSweepThread::acknowledge_yield_request();
4313   }
4314 
4315   ConcurrentMarkSweepThread::synchronize(true);
4316   _bit_map_lock->lock_without_safepoint_check();
4317   _collector->startTimer();
4318 }
4319 
4320 bool CMSCollector::do_marking_mt(bool asynch) {
4321   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4322   int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4323                                        conc_workers()->total_workers(),
4324                                        conc_workers()->active_workers(),
4325                                        Threads::number_of_non_daemon_threads());
4326   conc_workers()->set_active_workers(num_workers);
4327 
4328   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4329 
4330   CMSConcMarkingTask tsk(this,
4331                          cms_space,
4332                          asynch,
4333                          conc_workers(),
4334                          task_queues());
4335 
4336   // Since the actual number of workers we get may be different
4337   // from the number we requested above, do we need to do anything different
4338   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4339   // class?? XXX
4340   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4341 
4342   // Refs discovery is already non-atomic.
4343   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4344   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4345   conc_workers()->start_task(&tsk);
4346   while (tsk.yielded()) {
4347     tsk.coordinator_yield();
4348     conc_workers()->continue_task(&tsk);
4349   }
4350   // If the task was aborted, _restart_addr will be non-NULL
4351   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4352   while (_restart_addr != NULL) {
4353     // XXX For now we do not make use of ABORTED state and have not
4354     // yet implemented the right abort semantics (even in the original
4355     // single-threaded CMS case). That needs some more investigation
4356     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4357     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4358     // If _restart_addr is non-NULL, a marking stack overflow
4359     // occurred; we need to do a fresh marking iteration from the
4360     // indicated restart address.
4361     if (_foregroundGCIsActive && asynch) {
4362       // We may be running into repeated stack overflows, having
4363       // reached the limit of the stack size, while making very
4364       // slow forward progress. It may be best to bail out and
4365       // let the foreground collector do its job.
4366       // Clear _restart_addr, so that foreground GC
4367       // works from scratch. This avoids the headache of
4368       // a "rescan" which would otherwise be needed because
4369       // of the dirty mod union table & card table.
4370       _restart_addr = NULL;
4371       return false;
4372     }
4373     // Adjust the task to restart from _restart_addr
4374     tsk.reset(_restart_addr);
4375     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4376                   _restart_addr);
4377     _restart_addr = NULL;
4378     // Get the workers going again
4379     conc_workers()->start_task(&tsk);
4380     while (tsk.yielded()) {
4381       tsk.coordinator_yield();
4382       conc_workers()->continue_task(&tsk);
4383     }
4384   }
4385   assert(tsk.completed(), "Inconsistency");
4386   assert(tsk.result() == true, "Inconsistency");
4387   return true;
4388 }
4389 
4390 bool CMSCollector::do_marking_st(bool asynch) {
4391   ResourceMark rm;
4392   HandleMark   hm;
4393 
4394   // Temporarily make refs discovery single threaded (non-MT)
4395   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4396   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4397     &_markStack, CMSYield && asynch);
4398   // the last argument to iterate indicates whether the iteration
4399   // should be incremental with periodic yields.
4400   _markBitMap.iterate(&markFromRootsClosure);
4401   // If _restart_addr is non-NULL, a marking stack overflow
4402   // occurred; we need to do a fresh iteration from the
4403   // indicated restart address.
4404   while (_restart_addr != NULL) {
4405     if (_foregroundGCIsActive && asynch) {
4406       // We may be running into repeated stack overflows, having
4407       // reached the limit of the stack size, while making very
4408       // slow forward progress. It may be best to bail out and
4409       // let the foreground collector do its job.
4410       // Clear _restart_addr, so that foreground GC
4411       // works from scratch. This avoids the headache of
4412       // a "rescan" which would otherwise be needed because
4413       // of the dirty mod union table & card table.
4414       _restart_addr = NULL;
4415       return false;  // indicating failure to complete marking
4416     }
4417     // Deal with stack overflow:
4418     // we restart marking from _restart_addr
4419     HeapWord* ra = _restart_addr;
4420     markFromRootsClosure.reset(ra);
4421     _restart_addr = NULL;
4422     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4423   }
4424   return true;
4425 }
4426 
4427 void CMSCollector::preclean() {
4428   check_correct_thread_executing();
4429   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4430   verify_work_stacks_empty();
4431   verify_overflow_empty();
4432   _abort_preclean = false;
4433   if (CMSPrecleaningEnabled) {
4434     if (!CMSEdenChunksRecordAlways) {
4435       _eden_chunk_index = 0;
4436     }
4437     size_t used = get_eden_used();
4438     size_t capacity = get_eden_capacity();
4439     // Don't start sampling unless we will get sufficiently
4440     // many samples.
4441     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4442                 * CMSScheduleRemarkEdenPenetration)) {
4443       _start_sampling = true;
4444     } else {
4445       _start_sampling = false;
4446     }
4447     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4448     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4449     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4450   }
4451   CMSTokenSync x(true); // is cms thread
4452   if (CMSPrecleaningEnabled) {
4453     sample_eden();
4454     _collectorState = AbortablePreclean;
4455   } else {
4456     _collectorState = FinalMarking;
4457   }
4458   verify_work_stacks_empty();
4459   verify_overflow_empty();
4460 }
4461 
4462 // Try and schedule the remark such that young gen
4463 // occupancy is CMSScheduleRemarkEdenPenetration %.
4464 void CMSCollector::abortable_preclean() {
4465   check_correct_thread_executing();
4466   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4467   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4468 
4469   // If Eden's current occupancy is below this threshold,
4470   // immediately schedule the remark; else preclean
4471   // past the next scavenge in an effort to
4472   // schedule the pause as described above. By choosing
4473   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4474   // we will never do an actual abortable preclean cycle.
4475   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4476     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4477     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4478     // We need more smarts in the abortable preclean
4479     // loop below to deal with cases where allocation
4480     // in young gen is very very slow, and our precleaning
4481     // is running a losing race against a horde of
4482     // mutators intent on flooding us with CMS updates
4483     // (dirty cards).
4484     // One, admittedly dumb, strategy is to give up
4485     // after a certain number of abortable precleaning loops
4486     // or after a certain maximum time. We want to make
4487     // this smarter in the next iteration.
4488     // XXX FIX ME!!! YSR
4489     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4490     while (!(should_abort_preclean() ||
4491              ConcurrentMarkSweepThread::should_terminate())) {
4492       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4493       cumworkdone += workdone;
4494       loops++;
4495       // Voluntarily terminate abortable preclean phase if we have
4496       // been at it for too long.
4497       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4498           loops >= CMSMaxAbortablePrecleanLoops) {
4499         if (PrintGCDetails) {
4500           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4501         }
4502         break;
4503       }
4504       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4505         if (PrintGCDetails) {
4506           gclog_or_tty->print(" CMS: abort preclean due to time ");
4507         }
4508         break;
4509       }
4510       // If we are doing little work each iteration, we should
4511       // take a short break.
4512       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4513         // Sleep for some time, waiting for work to accumulate
4514         stopTimer();
4515         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4516         startTimer();
4517         waited++;
4518       }
4519     }
4520     if (PrintCMSStatistics > 0) {
4521       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4522                           loops, waited, cumworkdone);
4523     }
4524   }
4525   CMSTokenSync x(true); // is cms thread
4526   if (_collectorState != Idling) {
4527     assert(_collectorState == AbortablePreclean,
4528            "Spontaneous state transition?");
4529     _collectorState = FinalMarking;
4530   } // Else, a foreground collection completed this CMS cycle.
4531   return;
4532 }
4533 
4534 // Respond to an Eden sampling opportunity
4535 void CMSCollector::sample_eden() {
4536   // Make sure a young gc cannot sneak in between our
4537   // reading and recording of a sample.
4538   assert(Thread::current()->is_ConcurrentGC_thread(),
4539          "Only the cms thread may collect Eden samples");
4540   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4541          "Should collect samples while holding CMS token");
4542   if (!_start_sampling) {
4543     return;
4544   }
4545   // When CMSEdenChunksRecordAlways is true, the eden chunk array
4546   // is populated by the young generation.
4547   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4548     if (_eden_chunk_index < _eden_chunk_capacity) {
4549       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4550       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4551              "Unexpected state of Eden");
4552       // We'd like to check that what we just sampled is an oop-start address;
4553       // however, we cannot do that here since the object may not yet have been
4554       // initialized. So we'll instead do the check when we _use_ this sample
4555       // later.
4556       if (_eden_chunk_index == 0 ||
4557           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4558                          _eden_chunk_array[_eden_chunk_index-1])
4559            >= CMSSamplingGrain)) {
4560         _eden_chunk_index++;  // commit sample
4561       }
4562     }
4563   }
4564   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4565     size_t used = get_eden_used();
4566     size_t capacity = get_eden_capacity();
4567     assert(used <= capacity, "Unexpected state of Eden");
4568     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4569       _abort_preclean = true;
4570     }
4571   }
4572 }
4573 
4574 
4575 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4576   assert(_collectorState == Precleaning ||
4577          _collectorState == AbortablePreclean, "incorrect state");
4578   ResourceMark rm;
4579   HandleMark   hm;
4580 
4581   // Precleaning is currently not MT but the reference processor
4582   // may be set for MT.  Disable it temporarily here.
4583   ReferenceProcessor* rp = ref_processor();
4584   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4585 
4586   // Do one pass of scrubbing the discovered reference lists
4587   // to remove any reference objects with strongly-reachable
4588   // referents.
4589   if (clean_refs) {
4590     CMSPrecleanRefsYieldClosure yield_cl(this);
4591     assert(rp->span().equals(_span), "Spans should be equal");
4592     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4593                                    &_markStack, true /* preclean */);
4594     CMSDrainMarkingStackClosure complete_trace(this,
4595                                    _span, &_markBitMap, &_markStack,
4596                                    &keep_alive, true /* preclean */);
4597 
4598     // We don't want this step to interfere with a young
4599     // collection because we don't want to take CPU
4600     // or memory bandwidth away from the young GC threads
4601     // (which may be as many as there are CPUs).
4602     // Note that we don't need to protect ourselves from
4603     // interference with mutators because they can't
4604     // manipulate the discovered reference lists nor affect
4605     // the computed reachability of the referents, the
4606     // only properties manipulated by the precleaning
4607     // of these reference lists.
4608     stopTimer();
4609     CMSTokenSyncWithLocks x(true /* is cms thread */,
4610                             bitMapLock());
4611     startTimer();
4612     sample_eden();
4613 
4614     // The following will yield to allow foreground
4615     // collection to proceed promptly. XXX YSR:
4616     // The code in this method may need further
4617     // tweaking for better performance and some restructuring
4618     // for cleaner interfaces.
4619     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4620     rp->preclean_discovered_references(
4621           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4622           gc_timer, _gc_tracer_cm->gc_id());
4623   }
4624 
4625   if (clean_survivor) {  // preclean the active survivor space(s)
4626     assert(_young_gen->kind() == Generation::DefNew ||
4627            _young_gen->kind() == Generation::ParNew,
4628          "incorrect type for cast");
4629     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4630     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4631                              &_markBitMap, &_modUnionTable,
4632                              &_markStack, true /* precleaning phase */);
4633     stopTimer();
4634     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4635                              bitMapLock());
4636     startTimer();
4637     unsigned int before_count =
4638       GenCollectedHeap::heap()->total_collections();
4639     SurvivorSpacePrecleanClosure
4640       sss_cl(this, _span, &_markBitMap, &_markStack,
4641              &pam_cl, before_count, CMSYield);
4642     dng->from()->object_iterate_careful(&sss_cl);
4643     dng->to()->object_iterate_careful(&sss_cl);
4644   }
4645   MarkRefsIntoAndScanClosure
4646     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4647              &_markStack, this, CMSYield,
4648              true /* precleaning phase */);
4649   // CAUTION: The following closure has persistent state that may need to
4650   // be reset upon a decrease in the sequence of addresses it
4651   // processes.
4652   ScanMarkedObjectsAgainCarefullyClosure
4653     smoac_cl(this, _span,
4654       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4655 
4656   // Preclean dirty cards in ModUnionTable and CardTable using
4657   // appropriate convergence criterion;
4658   // repeat CMSPrecleanIter times unless we find that
4659   // we are losing.
4660   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4661   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4662          "Bad convergence multiplier");
4663   assert(CMSPrecleanThreshold >= 100,
4664          "Unreasonably low CMSPrecleanThreshold");
4665 
4666   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4667   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4668        numIter < CMSPrecleanIter;
4669        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4670     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4671     if (Verbose && PrintGCDetails) {
4672       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4673     }
4674     // Either there are very few dirty cards, so re-mark
4675     // pause will be small anyway, or our pre-cleaning isn't
4676     // that much faster than the rate at which cards are being
4677     // dirtied, so we might as well stop and re-mark since
4678     // precleaning won't improve our re-mark time by much.
4679     if (curNumCards <= CMSPrecleanThreshold ||
4680         (numIter > 0 &&
4681          (curNumCards * CMSPrecleanDenominator >
4682          lastNumCards * CMSPrecleanNumerator))) {
4683       numIter++;
4684       cumNumCards += curNumCards;
4685       break;
4686     }
4687   }
4688 
4689   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4690 
4691   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4692   cumNumCards += curNumCards;
4693   if (PrintGCDetails && PrintCMSStatistics != 0) {
4694     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4695                   curNumCards, cumNumCards, numIter);
4696   }
4697   return cumNumCards;   // as a measure of useful work done
4698 }
4699 
4700 // PRECLEANING NOTES:
4701 // Precleaning involves:
4702 // . reading the bits of the modUnionTable and clearing the set bits.
4703 // . For the cards corresponding to the set bits, we scan the
4704 //   objects on those cards. This means we need the free_list_lock
4705 //   so that we can safely iterate over the CMS space when scanning
4706 //   for oops.
4707 // . When we scan the objects, we'll be both reading and setting
4708 //   marks in the marking bit map, so we'll need the marking bit map.
4709 // . For protecting _collector_state transitions, we take the CGC_lock.
4710 //   Note that any races in the reading of of card table entries by the
4711 //   CMS thread on the one hand and the clearing of those entries by the
4712 //   VM thread or the setting of those entries by the mutator threads on the
4713 //   other are quite benign. However, for efficiency it makes sense to keep
4714 //   the VM thread from racing with the CMS thread while the latter is
4715 //   dirty card info to the modUnionTable. We therefore also use the
4716 //   CGC_lock to protect the reading of the card table and the mod union
4717 //   table by the CM thread.
4718 // . We run concurrently with mutator updates, so scanning
4719 //   needs to be done carefully  -- we should not try to scan
4720 //   potentially uninitialized objects.
4721 //
4722 // Locking strategy: While holding the CGC_lock, we scan over and
4723 // reset a maximal dirty range of the mod union / card tables, then lock
4724 // the free_list_lock and bitmap lock to do a full marking, then
4725 // release these locks; and repeat the cycle. This allows for a
4726 // certain amount of fairness in the sharing of these locks between
4727 // the CMS collector on the one hand, and the VM thread and the
4728 // mutators on the other.
4729 
4730 // NOTE: preclean_mod_union_table() and preclean_card_table()
4731 // further below are largely identical; if you need to modify
4732 // one of these methods, please check the other method too.
4733 
4734 size_t CMSCollector::preclean_mod_union_table(
4735   ConcurrentMarkSweepGeneration* gen,
4736   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4737   verify_work_stacks_empty();
4738   verify_overflow_empty();
4739 
4740   // strategy: starting with the first card, accumulate contiguous
4741   // ranges of dirty cards; clear these cards, then scan the region
4742   // covered by these cards.
4743 
4744   // Since all of the MUT is committed ahead, we can just use
4745   // that, in case the generations expand while we are precleaning.
4746   // It might also be fine to just use the committed part of the
4747   // generation, but we might potentially miss cards when the
4748   // generation is rapidly expanding while we are in the midst
4749   // of precleaning.
4750   HeapWord* startAddr = gen->reserved().start();
4751   HeapWord* endAddr   = gen->reserved().end();
4752 
4753   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4754 
4755   size_t numDirtyCards, cumNumDirtyCards;
4756   HeapWord *nextAddr, *lastAddr;
4757   for (cumNumDirtyCards = numDirtyCards = 0,
4758        nextAddr = lastAddr = startAddr;
4759        nextAddr < endAddr;
4760        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4761 
4762     ResourceMark rm;
4763     HandleMark   hm;
4764 
4765     MemRegion dirtyRegion;
4766     {
4767       stopTimer();
4768       // Potential yield point
4769       CMSTokenSync ts(true);
4770       startTimer();
4771       sample_eden();
4772       // Get dirty region starting at nextOffset (inclusive),
4773       // simultaneously clearing it.
4774       dirtyRegion =
4775         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4776       assert(dirtyRegion.start() >= nextAddr,
4777              "returned region inconsistent?");
4778     }
4779     // Remember where the next search should begin.
4780     // The returned region (if non-empty) is a right open interval,
4781     // so lastOffset is obtained from the right end of that
4782     // interval.
4783     lastAddr = dirtyRegion.end();
4784     // Should do something more transparent and less hacky XXX
4785     numDirtyCards =
4786       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4787 
4788     // We'll scan the cards in the dirty region (with periodic
4789     // yields for foreground GC as needed).
4790     if (!dirtyRegion.is_empty()) {
4791       assert(numDirtyCards > 0, "consistency check");
4792       HeapWord* stop_point = NULL;
4793       stopTimer();
4794       // Potential yield point
4795       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4796                                bitMapLock());
4797       startTimer();
4798       {
4799         verify_work_stacks_empty();
4800         verify_overflow_empty();
4801         sample_eden();
4802         stop_point =
4803           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4804       }
4805       if (stop_point != NULL) {
4806         // The careful iteration stopped early either because it found an
4807         // uninitialized object, or because we were in the midst of an
4808         // "abortable preclean", which should now be aborted. Redirty
4809         // the bits corresponding to the partially-scanned or unscanned
4810         // cards. We'll either restart at the next block boundary or
4811         // abort the preclean.
4812         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4813                "Should only be AbortablePreclean.");
4814         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4815         if (should_abort_preclean()) {
4816           break; // out of preclean loop
4817         } else {
4818           // Compute the next address at which preclean should pick up;
4819           // might need bitMapLock in order to read P-bits.
4820           lastAddr = next_card_start_after_block(stop_point);
4821         }
4822       }
4823     } else {
4824       assert(lastAddr == endAddr, "consistency check");
4825       assert(numDirtyCards == 0, "consistency check");
4826       break;
4827     }
4828   }
4829   verify_work_stacks_empty();
4830   verify_overflow_empty();
4831   return cumNumDirtyCards;
4832 }
4833 
4834 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4835 // below are largely identical; if you need to modify
4836 // one of these methods, please check the other method too.
4837 
4838 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4839   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4840   // strategy: it's similar to precleamModUnionTable above, in that
4841   // we accumulate contiguous ranges of dirty cards, mark these cards
4842   // precleaned, then scan the region covered by these cards.
4843   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4844   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4845 
4846   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4847 
4848   size_t numDirtyCards, cumNumDirtyCards;
4849   HeapWord *lastAddr, *nextAddr;
4850 
4851   for (cumNumDirtyCards = numDirtyCards = 0,
4852        nextAddr = lastAddr = startAddr;
4853        nextAddr < endAddr;
4854        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4855 
4856     ResourceMark rm;
4857     HandleMark   hm;
4858 
4859     MemRegion dirtyRegion;
4860     {
4861       // See comments in "Precleaning notes" above on why we
4862       // do this locking. XXX Could the locking overheads be
4863       // too high when dirty cards are sparse? [I don't think so.]
4864       stopTimer();
4865       CMSTokenSync x(true); // is cms thread
4866       startTimer();
4867       sample_eden();
4868       // Get and clear dirty region from card table
4869       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4870                                     MemRegion(nextAddr, endAddr),
4871                                     true,
4872                                     CardTableModRefBS::precleaned_card_val());
4873 
4874       assert(dirtyRegion.start() >= nextAddr,
4875              "returned region inconsistent?");
4876     }
4877     lastAddr = dirtyRegion.end();
4878     numDirtyCards =
4879       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4880 
4881     if (!dirtyRegion.is_empty()) {
4882       stopTimer();
4883       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4884       startTimer();
4885       sample_eden();
4886       verify_work_stacks_empty();
4887       verify_overflow_empty();
4888       HeapWord* stop_point =
4889         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4890       if (stop_point != NULL) {
4891         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4892                "Should only be AbortablePreclean.");
4893         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4894         if (should_abort_preclean()) {
4895           break; // out of preclean loop
4896         } else {
4897           // Compute the next address at which preclean should pick up.
4898           lastAddr = next_card_start_after_block(stop_point);
4899         }
4900       }
4901     } else {
4902       break;
4903     }
4904   }
4905   verify_work_stacks_empty();
4906   verify_overflow_empty();
4907   return cumNumDirtyCards;
4908 }
4909 
4910 class PrecleanKlassClosure : public KlassClosure {
4911   KlassToOopClosure _cm_klass_closure;
4912  public:
4913   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4914   void do_klass(Klass* k) {
4915     if (k->has_accumulated_modified_oops()) {
4916       k->clear_accumulated_modified_oops();
4917 
4918       _cm_klass_closure.do_klass(k);
4919     }
4920   }
4921 };
4922 
4923 // The freelist lock is needed to prevent asserts, is it really needed?
4924 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4925 
4926   cl->set_freelistLock(freelistLock);
4927 
4928   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4929 
4930   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4931   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4932   PrecleanKlassClosure preclean_klass_closure(cl);
4933   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4934 
4935   verify_work_stacks_empty();
4936   verify_overflow_empty();
4937 }
4938 
4939 void CMSCollector::checkpointRootsFinal(bool asynch,
4940   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4941   assert(_collectorState == FinalMarking, "incorrect state transition?");
4942   check_correct_thread_executing();
4943   // world is stopped at this checkpoint
4944   assert(SafepointSynchronize::is_at_safepoint(),
4945          "world should be stopped");
4946   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4947 
4948   verify_work_stacks_empty();
4949   verify_overflow_empty();
4950 
4951   SpecializationStats::clear();
4952   if (PrintGCDetails) {
4953     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4954                         _young_gen->used() / K,
4955                         _young_gen->capacity() / K);
4956   }
4957   if (asynch) {
4958     if (CMSScavengeBeforeRemark) {
4959       GenCollectedHeap* gch = GenCollectedHeap::heap();
4960       // Temporarily set flag to false, GCH->do_collection will
4961       // expect it to be false and set to true
4962       FlagSetting fl(gch->_is_gc_active, false);
4963       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4964         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4965       int level = _cmsGen->level() - 1;
4966       if (level >= 0) {
4967         gch->do_collection(true,        // full (i.e. force, see below)
4968                            false,       // !clear_all_soft_refs
4969                            0,           // size
4970                            false,       // is_tlab
4971                            level        // max_level
4972                           );
4973       }
4974     }
4975     FreelistLocker x(this);
4976     MutexLockerEx y(bitMapLock(),
4977                     Mutex::_no_safepoint_check_flag);
4978     assert(!init_mark_was_synchronous, "but that's impossible!");
4979     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4980   } else {
4981     // already have all the locks
4982     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4983                              init_mark_was_synchronous);
4984   }
4985   verify_work_stacks_empty();
4986   verify_overflow_empty();
4987   SpecializationStats::print();
4988 }
4989 
4990 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4991   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4992 
4993   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4994 
4995   assert(haveFreelistLocks(), "must have free list locks");
4996   assert_lock_strong(bitMapLock());
4997 
4998   ResourceMark rm;
4999   HandleMark   hm;
5000 
5001   GenCollectedHeap* gch = GenCollectedHeap::heap();
5002 
5003   if (should_unload_classes()) {
5004     CodeCache::gc_prologue();
5005   }
5006   assert(haveFreelistLocks(), "must have free list locks");
5007   assert_lock_strong(bitMapLock());
5008 
5009   if (!init_mark_was_synchronous) {
5010     // We might assume that we need not fill TLAB's when
5011     // CMSScavengeBeforeRemark is set, because we may have just done
5012     // a scavenge which would have filled all TLAB's -- and besides
5013     // Eden would be empty. This however may not always be the case --
5014     // for instance although we asked for a scavenge, it may not have
5015     // happened because of a JNI critical section. We probably need
5016     // a policy for deciding whether we can in that case wait until
5017     // the critical section releases and then do the remark following
5018     // the scavenge, and skip it here. In the absence of that policy,
5019     // or of an indication of whether the scavenge did indeed occur,
5020     // we cannot rely on TLAB's having been filled and must do
5021     // so here just in case a scavenge did not happen.
5022     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
5023     // Update the saved marks which may affect the root scans.
5024     gch->save_marks();
5025 
5026     if (CMSPrintEdenSurvivorChunks) {
5027       print_eden_and_survivor_chunk_arrays();
5028     }
5029 
5030     {
5031       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5032 
5033       // Note on the role of the mod union table:
5034       // Since the marker in "markFromRoots" marks concurrently with
5035       // mutators, it is possible for some reachable objects not to have been
5036       // scanned. For instance, an only reference to an object A was
5037       // placed in object B after the marker scanned B. Unless B is rescanned,
5038       // A would be collected. Such updates to references in marked objects
5039       // are detected via the mod union table which is the set of all cards
5040       // dirtied since the first checkpoint in this GC cycle and prior to
5041       // the most recent young generation GC, minus those cleaned up by the
5042       // concurrent precleaning.
5043       if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5044         GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5045         do_remark_parallel();
5046       } else {
5047         GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5048                     _gc_timer_cm, _gc_tracer_cm->gc_id());
5049         do_remark_non_parallel();
5050       }
5051     }
5052   } else {
5053     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5054     // The initial mark was stop-world, so there's no rescanning to
5055     // do; go straight on to the next step below.
5056   }
5057   verify_work_stacks_empty();
5058   verify_overflow_empty();
5059 
5060   {
5061     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5062     refProcessingWork(asynch, clear_all_soft_refs);
5063   }
5064   verify_work_stacks_empty();
5065   verify_overflow_empty();
5066 
5067   if (should_unload_classes()) {
5068     CodeCache::gc_epilogue();
5069   }
5070   JvmtiExport::gc_epilogue();
5071 
5072   // If we encountered any (marking stack / work queue) overflow
5073   // events during the current CMS cycle, take appropriate
5074   // remedial measures, where possible, so as to try and avoid
5075   // recurrence of that condition.
5076   assert(_markStack.isEmpty(), "No grey objects");
5077   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5078                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
5079   if (ser_ovflw > 0) {
5080     if (PrintCMSStatistics != 0) {
5081       gclog_or_tty->print_cr("Marking stack overflow (benign) "
5082         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5083         ", kac_preclean="SIZE_FORMAT")",
5084         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5085         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5086     }
5087     _markStack.expand();
5088     _ser_pmc_remark_ovflw = 0;
5089     _ser_pmc_preclean_ovflw = 0;
5090     _ser_kac_preclean_ovflw = 0;
5091     _ser_kac_ovflw = 0;
5092   }
5093   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5094     if (PrintCMSStatistics != 0) {
5095       gclog_or_tty->print_cr("Work queue overflow (benign) "
5096         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5097         _par_pmc_remark_ovflw, _par_kac_ovflw);
5098     }
5099     _par_pmc_remark_ovflw = 0;
5100     _par_kac_ovflw = 0;
5101   }
5102   if (PrintCMSStatistics != 0) {
5103      if (_markStack._hit_limit > 0) {
5104        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5105                               _markStack._hit_limit);
5106      }
5107      if (_markStack._failed_double > 0) {
5108        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5109                               " current capacity "SIZE_FORMAT,
5110                               _markStack._failed_double,
5111                               _markStack.capacity());
5112      }
5113   }
5114   _markStack._hit_limit = 0;
5115   _markStack._failed_double = 0;
5116 
5117   if ((VerifyAfterGC || VerifyDuringGC) &&
5118       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5119     verify_after_remark();
5120   }
5121 
5122   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5123 
5124   // Change under the freelistLocks.
5125   _collectorState = Sweeping;
5126   // Call isAllClear() under bitMapLock
5127   assert(_modUnionTable.isAllClear(),
5128       "Should be clear by end of the final marking");
5129   assert(_ct->klass_rem_set()->mod_union_is_clear(),
5130       "Should be clear by end of the final marking");
5131 }
5132 
5133 void CMSParInitialMarkTask::work(uint worker_id) {
5134   elapsedTimer _timer;
5135   ResourceMark rm;
5136   HandleMark   hm;
5137 
5138   // ---------- scan from roots --------------
5139   _timer.start();
5140   GenCollectedHeap* gch = GenCollectedHeap::heap();
5141   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5142 
5143   // ---------- young gen roots --------------
5144   {
5145     work_on_young_gen_roots(worker_id, &par_mri_cl);
5146     _timer.stop();
5147     if (PrintCMSStatistics != 0) {
5148       gclog_or_tty->print_cr(
5149         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5150         worker_id, _timer.seconds());
5151     }
5152   }
5153 
5154   // ---------- remaining roots --------------
5155   _timer.reset();
5156   _timer.start();
5157 
5158   CLDToOopClosure cld_closure(&par_mri_cl, true);
5159 
5160   gch->gen_process_roots(_collector->_cmsGen->level(),
5161                          false,     // yg was scanned above
5162                          false,     // this is parallel code
5163                          SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5164                          _collector->should_unload_classes(),
5165                          &par_mri_cl,
5166                          NULL,
5167                          &cld_closure);
5168   assert(_collector->should_unload_classes()
5169          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5170          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5171   _timer.stop();
5172   if (PrintCMSStatistics != 0) {
5173     gclog_or_tty->print_cr(
5174       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5175       worker_id, _timer.seconds());
5176   }
5177 }
5178 
5179 // Parallel remark task
5180 class CMSParRemarkTask: public CMSParMarkTask {
5181   CompactibleFreeListSpace* _cms_space;
5182 
5183   // The per-thread work queues, available here for stealing.
5184   OopTaskQueueSet*       _task_queues;
5185   ParallelTaskTerminator _term;
5186 
5187  public:
5188   // A value of 0 passed to n_workers will cause the number of
5189   // workers to be taken from the active workers in the work gang.
5190   CMSParRemarkTask(CMSCollector* collector,
5191                    CompactibleFreeListSpace* cms_space,
5192                    int n_workers, FlexibleWorkGang* workers,
5193                    OopTaskQueueSet* task_queues):
5194     CMSParMarkTask("Rescan roots and grey objects in parallel",
5195                    collector, n_workers),
5196     _cms_space(cms_space),
5197     _task_queues(task_queues),
5198     _term(n_workers, task_queues) { }
5199 
5200   OopTaskQueueSet* task_queues() { return _task_queues; }
5201 
5202   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5203 
5204   ParallelTaskTerminator* terminator() { return &_term; }
5205   int n_workers() { return _n_workers; }
5206 
5207   void work(uint worker_id);
5208 
5209  private:
5210   // ... of  dirty cards in old space
5211   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5212                                   Par_MarkRefsIntoAndScanClosure* cl);
5213 
5214   // ... work stealing for the above
5215   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5216 };
5217 
5218 class RemarkKlassClosure : public KlassClosure {
5219   KlassToOopClosure _cm_klass_closure;
5220  public:
5221   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5222   void do_klass(Klass* k) {
5223     // Check if we have modified any oops in the Klass during the concurrent marking.
5224     if (k->has_accumulated_modified_oops()) {
5225       k->clear_accumulated_modified_oops();
5226 
5227       // We could have transfered the current modified marks to the accumulated marks,
5228       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5229     } else if (k->has_modified_oops()) {
5230       // Don't clear anything, this info is needed by the next young collection.
5231     } else {
5232       // No modified oops in the Klass.
5233       return;
5234     }
5235 
5236     // The klass has modified fields, need to scan the klass.
5237     _cm_klass_closure.do_klass(k);
5238   }
5239 };
5240 
5241 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5242   DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5243   EdenSpace* eden_space = dng->eden();
5244   ContiguousSpace* from_space = dng->from();
5245   ContiguousSpace* to_space   = dng->to();
5246 
5247   HeapWord** eca = _collector->_eden_chunk_array;
5248   size_t     ect = _collector->_eden_chunk_index;
5249   HeapWord** sca = _collector->_survivor_chunk_array;
5250   size_t     sct = _collector->_survivor_chunk_index;
5251 
5252   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5253   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5254 
5255   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5256   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5257   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5258 }
5259 
5260 // work_queue(i) is passed to the closure
5261 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
5262 // also is passed to do_dirty_card_rescan_tasks() and to
5263 // do_work_steal() to select the i-th task_queue.
5264 
5265 void CMSParRemarkTask::work(uint worker_id) {
5266   elapsedTimer _timer;
5267   ResourceMark rm;
5268   HandleMark   hm;
5269 
5270   // ---------- rescan from roots --------------
5271   _timer.start();
5272   GenCollectedHeap* gch = GenCollectedHeap::heap();
5273   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5274     _collector->_span, _collector->ref_processor(),
5275     &(_collector->_markBitMap),
5276     work_queue(worker_id));
5277 
5278   // Rescan young gen roots first since these are likely
5279   // coarsely partitioned and may, on that account, constitute
5280   // the critical path; thus, it's best to start off that
5281   // work first.
5282   // ---------- young gen roots --------------
5283   {
5284     work_on_young_gen_roots(worker_id, &par_mrias_cl);
5285     _timer.stop();
5286     if (PrintCMSStatistics != 0) {
5287       gclog_or_tty->print_cr(
5288         "Finished young gen rescan work in %dth thread: %3.3f sec",
5289         worker_id, _timer.seconds());
5290     }
5291   }
5292 
5293   // ---------- remaining roots --------------
5294   _timer.reset();
5295   _timer.start();
5296   gch->gen_process_roots(_collector->_cmsGen->level(),
5297                          false,     // yg was scanned above
5298                          false,     // this is parallel code
5299                          SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5300                          _collector->should_unload_classes(),
5301                          &par_mrias_cl,
5302                          NULL,
5303                          NULL);     // The dirty klasses will be handled below
5304 
5305   assert(_collector->should_unload_classes()
5306          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5307          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5308   _timer.stop();
5309   if (PrintCMSStatistics != 0) {
5310     gclog_or_tty->print_cr(
5311       "Finished remaining root rescan work in %dth thread: %3.3f sec",
5312       worker_id, _timer.seconds());
5313   }
5314 
5315   // ---------- unhandled CLD scanning ----------
5316   if (worker_id == 0) { // Single threaded at the moment.
5317     _timer.reset();
5318     _timer.start();
5319 
5320     // Scan all new class loader data objects and new dependencies that were
5321     // introduced during concurrent marking.
5322     ResourceMark rm;
5323     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5324     for (int i = 0; i < array->length(); i++) {
5325       par_mrias_cl.do_class_loader_data(array->at(i));
5326     }
5327 
5328     // We don't need to keep track of new CLDs anymore.
5329     ClassLoaderDataGraph::remember_new_clds(false);
5330 
5331     _timer.stop();
5332     if (PrintCMSStatistics != 0) {
5333       gclog_or_tty->print_cr(
5334           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5335           worker_id, _timer.seconds());
5336     }
5337   }
5338 
5339   // ---------- dirty klass scanning ----------
5340   if (worker_id == 0) { // Single threaded at the moment.
5341     _timer.reset();
5342     _timer.start();
5343 
5344     // Scan all classes that was dirtied during the concurrent marking phase.
5345     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5346     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5347 
5348     _timer.stop();
5349     if (PrintCMSStatistics != 0) {
5350       gclog_or_tty->print_cr(
5351           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5352           worker_id, _timer.seconds());
5353     }
5354   }
5355 
5356   // We might have added oops to ClassLoaderData::_handles during the
5357   // concurrent marking phase. These oops point to newly allocated objects
5358   // that are guaranteed to be kept alive. Either by the direct allocation
5359   // code, or when the young collector processes the roots. Hence,
5360   // we don't have to revisit the _handles block during the remark phase.
5361 
5362   // ---------- rescan dirty cards ------------
5363   _timer.reset();
5364   _timer.start();
5365 
5366   // Do the rescan tasks for each of the two spaces
5367   // (cms_space) in turn.
5368   // "worker_id" is passed to select the task_queue for "worker_id"
5369   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5370   _timer.stop();
5371   if (PrintCMSStatistics != 0) {
5372     gclog_or_tty->print_cr(
5373       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5374       worker_id, _timer.seconds());
5375   }
5376 
5377   // ---------- steal work from other threads ...
5378   // ---------- ... and drain overflow list.
5379   _timer.reset();
5380   _timer.start();
5381   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5382   _timer.stop();
5383   if (PrintCMSStatistics != 0) {
5384     gclog_or_tty->print_cr(
5385       "Finished work stealing in %dth thread: %3.3f sec",
5386       worker_id, _timer.seconds());
5387   }
5388 }
5389 
5390 // Note that parameter "i" is not used.
5391 void
5392 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5393   OopsInGenClosure* cl, ContiguousSpace* space,
5394   HeapWord** chunk_array, size_t chunk_top) {
5395   // Until all tasks completed:
5396   // . claim an unclaimed task
5397   // . compute region boundaries corresponding to task claimed
5398   //   using chunk_array
5399   // . par_oop_iterate(cl) over that region
5400 
5401   ResourceMark rm;
5402   HandleMark   hm;
5403 
5404   SequentialSubTasksDone* pst = space->par_seq_tasks();
5405 
5406   uint nth_task = 0;
5407   uint n_tasks  = pst->n_tasks();
5408 
5409   if (n_tasks > 0) {
5410     assert(pst->valid(), "Uninitialized use?");
5411     HeapWord *start, *end;
5412     while (!pst->is_task_claimed(/* reference */ nth_task)) {
5413       // We claimed task # nth_task; compute its boundaries.
5414       if (chunk_top == 0) {  // no samples were taken
5415         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5416         start = space->bottom();
5417         end   = space->top();
5418       } else if (nth_task == 0) {
5419         start = space->bottom();
5420         end   = chunk_array[nth_task];
5421       } else if (nth_task < (uint)chunk_top) {
5422         assert(nth_task >= 1, "Control point invariant");
5423         start = chunk_array[nth_task - 1];
5424         end   = chunk_array[nth_task];
5425       } else {
5426         assert(nth_task == (uint)chunk_top, "Control point invariant");
5427         start = chunk_array[chunk_top - 1];
5428         end   = space->top();
5429       }
5430       MemRegion mr(start, end);
5431       // Verify that mr is in space
5432       assert(mr.is_empty() || space->used_region().contains(mr),
5433              "Should be in space");
5434       // Verify that "start" is an object boundary
5435       assert(mr.is_empty() || oop(mr.start())->is_oop(),
5436              "Should be an oop");
5437       space->par_oop_iterate(mr, cl);
5438     }
5439     pst->all_tasks_completed();
5440   }
5441 }
5442 
5443 void
5444 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5445   CompactibleFreeListSpace* sp, int i,
5446   Par_MarkRefsIntoAndScanClosure* cl) {
5447   // Until all tasks completed:
5448   // . claim an unclaimed task
5449   // . compute region boundaries corresponding to task claimed
5450   // . transfer dirty bits ct->mut for that region
5451   // . apply rescanclosure to dirty mut bits for that region
5452 
5453   ResourceMark rm;
5454   HandleMark   hm;
5455 
5456   OopTaskQueue* work_q = work_queue(i);
5457   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5458   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5459   // CAUTION: This closure has state that persists across calls to
5460   // the work method dirty_range_iterate_clear() in that it has
5461   // embedded in it a (subtype of) UpwardsObjectClosure. The
5462   // use of that state in the embedded UpwardsObjectClosure instance
5463   // assumes that the cards are always iterated (even if in parallel
5464   // by several threads) in monotonically increasing order per each
5465   // thread. This is true of the implementation below which picks
5466   // card ranges (chunks) in monotonically increasing order globally
5467   // and, a-fortiori, in monotonically increasing order per thread
5468   // (the latter order being a subsequence of the former).
5469   // If the work code below is ever reorganized into a more chaotic
5470   // work-partitioning form than the current "sequential tasks"
5471   // paradigm, the use of that persistent state will have to be
5472   // revisited and modified appropriately. See also related
5473   // bug 4756801 work on which should examine this code to make
5474   // sure that the changes there do not run counter to the
5475   // assumptions made here and necessary for correctness and
5476   // efficiency. Note also that this code might yield inefficient
5477   // behavior in the case of very large objects that span one or
5478   // more work chunks. Such objects would potentially be scanned
5479   // several times redundantly. Work on 4756801 should try and
5480   // address that performance anomaly if at all possible. XXX
5481   MemRegion  full_span  = _collector->_span;
5482   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5483   MarkFromDirtyCardsClosure
5484     greyRescanClosure(_collector, full_span, // entire span of interest
5485                       sp, bm, work_q, cl);
5486 
5487   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5488   assert(pst->valid(), "Uninitialized use?");
5489   uint nth_task = 0;
5490   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5491   MemRegion span = sp->used_region();
5492   HeapWord* start_addr = span.start();
5493   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5494                                            alignment);
5495   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5496   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5497          start_addr, "Check alignment");
5498   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5499          chunk_size, "Check alignment");
5500 
5501   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5502     // Having claimed the nth_task, compute corresponding mem-region,
5503     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5504     // The alignment restriction ensures that we do not need any
5505     // synchronization with other gang-workers while setting or
5506     // clearing bits in thus chunk of the MUT.
5507     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5508                                     start_addr + (nth_task+1)*chunk_size);
5509     // The last chunk's end might be way beyond end of the
5510     // used region. In that case pull back appropriately.
5511     if (this_span.end() > end_addr) {
5512       this_span.set_end(end_addr);
5513       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5514     }
5515     // Iterate over the dirty cards covering this chunk, marking them
5516     // precleaned, and setting the corresponding bits in the mod union
5517     // table. Since we have been careful to partition at Card and MUT-word
5518     // boundaries no synchronization is needed between parallel threads.
5519     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5520                                                  &modUnionClosure);
5521 
5522     // Having transferred these marks into the modUnionTable,
5523     // rescan the marked objects on the dirty cards in the modUnionTable.
5524     // Even if this is at a synchronous collection, the initial marking
5525     // may have been done during an asynchronous collection so there
5526     // may be dirty bits in the mod-union table.
5527     _collector->_modUnionTable.dirty_range_iterate_clear(
5528                   this_span, &greyRescanClosure);
5529     _collector->_modUnionTable.verifyNoOneBitsInRange(
5530                                  this_span.start(),
5531                                  this_span.end());
5532   }
5533   pst->all_tasks_completed();  // declare that i am done
5534 }
5535 
5536 // . see if we can share work_queues with ParNew? XXX
5537 void
5538 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5539                                 int* seed) {
5540   OopTaskQueue* work_q = work_queue(i);
5541   NOT_PRODUCT(int num_steals = 0;)
5542   oop obj_to_scan;
5543   CMSBitMap* bm = &(_collector->_markBitMap);
5544 
5545   while (true) {
5546     // Completely finish any left over work from (an) earlier round(s)
5547     cl->trim_queue(0);
5548     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5549                                          (size_t)ParGCDesiredObjsFromOverflowList);
5550     // Now check if there's any work in the overflow list
5551     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5552     // only affects the number of attempts made to get work from the
5553     // overflow list and does not affect the number of workers.  Just
5554     // pass ParallelGCThreads so this behavior is unchanged.
5555     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5556                                                 work_q,
5557                                                 ParallelGCThreads)) {
5558       // found something in global overflow list;
5559       // not yet ready to go stealing work from others.
5560       // We'd like to assert(work_q->size() != 0, ...)
5561       // because we just took work from the overflow list,
5562       // but of course we can't since all of that could have
5563       // been already stolen from us.
5564       // "He giveth and He taketh away."
5565       continue;
5566     }
5567     // Verify that we have no work before we resort to stealing
5568     assert(work_q->size() == 0, "Have work, shouldn't steal");
5569     // Try to steal from other queues that have work
5570     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5571       NOT_PRODUCT(num_steals++;)
5572       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5573       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5574       // Do scanning work
5575       obj_to_scan->oop_iterate(cl);
5576       // Loop around, finish this work, and try to steal some more
5577     } else if (terminator()->offer_termination()) {
5578         break;  // nirvana from the infinite cycle
5579     }
5580   }
5581   NOT_PRODUCT(
5582     if (PrintCMSStatistics != 0) {
5583       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5584     }
5585   )
5586   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5587          "Else our work is not yet done");
5588 }
5589 
5590 // Record object boundaries in _eden_chunk_array by sampling the eden
5591 // top in the slow-path eden object allocation code path and record
5592 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5593 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5594 // sampling in sample_eden() that activates during the part of the
5595 // preclean phase.
5596 void CMSCollector::sample_eden_chunk() {
5597   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5598     if (_eden_chunk_lock->try_lock()) {
5599       // Record a sample. This is the critical section. The contents
5600       // of the _eden_chunk_array have to be non-decreasing in the
5601       // address order.
5602       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5603       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5604              "Unexpected state of Eden");
5605       if (_eden_chunk_index == 0 ||
5606           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5607            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5608                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5609         _eden_chunk_index++;  // commit sample
5610       }
5611       _eden_chunk_lock->unlock();
5612     }
5613   }
5614 }
5615 
5616 // Return a thread-local PLAB recording array, as appropriate.
5617 void* CMSCollector::get_data_recorder(int thr_num) {
5618   if (_survivor_plab_array != NULL &&
5619       (CMSPLABRecordAlways ||
5620        (_collectorState > Marking && _collectorState < FinalMarking))) {
5621     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5622     ChunkArray* ca = &_survivor_plab_array[thr_num];
5623     ca->reset();   // clear it so that fresh data is recorded
5624     return (void*) ca;
5625   } else {
5626     return NULL;
5627   }
5628 }
5629 
5630 // Reset all the thread-local PLAB recording arrays
5631 void CMSCollector::reset_survivor_plab_arrays() {
5632   for (uint i = 0; i < ParallelGCThreads; i++) {
5633     _survivor_plab_array[i].reset();
5634   }
5635 }
5636 
5637 // Merge the per-thread plab arrays into the global survivor chunk
5638 // array which will provide the partitioning of the survivor space
5639 // for CMS initial scan and rescan.
5640 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5641                                               int no_of_gc_threads) {
5642   assert(_survivor_plab_array  != NULL, "Error");
5643   assert(_survivor_chunk_array != NULL, "Error");
5644   assert(_collectorState == FinalMarking ||
5645          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5646   for (int j = 0; j < no_of_gc_threads; j++) {
5647     _cursor[j] = 0;
5648   }
5649   HeapWord* top = surv->top();
5650   size_t i;
5651   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5652     HeapWord* min_val = top;          // Higher than any PLAB address
5653     uint      min_tid = 0;            // position of min_val this round
5654     for (int j = 0; j < no_of_gc_threads; j++) {
5655       ChunkArray* cur_sca = &_survivor_plab_array[j];
5656       if (_cursor[j] == cur_sca->end()) {
5657         continue;
5658       }
5659       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5660       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5661       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5662       if (cur_val < min_val) {
5663         min_tid = j;
5664         min_val = cur_val;
5665       } else {
5666         assert(cur_val < top, "All recorded addresses should be less");
5667       }
5668     }
5669     // At this point min_val and min_tid are respectively
5670     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5671     // and the thread (j) that witnesses that address.
5672     // We record this address in the _survivor_chunk_array[i]
5673     // and increment _cursor[min_tid] prior to the next round i.
5674     if (min_val == top) {
5675       break;
5676     }
5677     _survivor_chunk_array[i] = min_val;
5678     _cursor[min_tid]++;
5679   }
5680   // We are all done; record the size of the _survivor_chunk_array
5681   _survivor_chunk_index = i; // exclusive: [0, i)
5682   if (PrintCMSStatistics > 0) {
5683     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5684   }
5685   // Verify that we used up all the recorded entries
5686   #ifdef ASSERT
5687     size_t total = 0;
5688     for (int j = 0; j < no_of_gc_threads; j++) {
5689       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5690       total += _cursor[j];
5691     }
5692     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5693     // Check that the merged array is in sorted order
5694     if (total > 0) {
5695       for (size_t i = 0; i < total - 1; i++) {
5696         if (PrintCMSStatistics > 0) {
5697           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5698                               i, _survivor_chunk_array[i]);
5699         }
5700         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5701                "Not sorted");
5702       }
5703     }
5704   #endif // ASSERT
5705 }
5706 
5707 // Set up the space's par_seq_tasks structure for work claiming
5708 // for parallel initial scan and rescan of young gen.
5709 // See ParRescanTask where this is currently used.
5710 void
5711 CMSCollector::
5712 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5713   assert(n_threads > 0, "Unexpected n_threads argument");
5714   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5715 
5716   // Eden space
5717   if (!dng->eden()->is_empty()) {
5718     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5719     assert(!pst->valid(), "Clobbering existing data?");
5720     // Each valid entry in [0, _eden_chunk_index) represents a task.
5721     size_t n_tasks = _eden_chunk_index + 1;
5722     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5723     // Sets the condition for completion of the subtask (how many threads
5724     // need to finish in order to be done).
5725     pst->set_n_threads(n_threads);
5726     pst->set_n_tasks((int)n_tasks);
5727   }
5728 
5729   // Merge the survivor plab arrays into _survivor_chunk_array
5730   if (_survivor_plab_array != NULL) {
5731     merge_survivor_plab_arrays(dng->from(), n_threads);
5732   } else {
5733     assert(_survivor_chunk_index == 0, "Error");
5734   }
5735 
5736   // To space
5737   {
5738     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5739     assert(!pst->valid(), "Clobbering existing data?");
5740     // Sets the condition for completion of the subtask (how many threads
5741     // need to finish in order to be done).
5742     pst->set_n_threads(n_threads);
5743     pst->set_n_tasks(1);
5744     assert(pst->valid(), "Error");
5745   }
5746 
5747   // From space
5748   {
5749     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5750     assert(!pst->valid(), "Clobbering existing data?");
5751     size_t n_tasks = _survivor_chunk_index + 1;
5752     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5753     // Sets the condition for completion of the subtask (how many threads
5754     // need to finish in order to be done).
5755     pst->set_n_threads(n_threads);
5756     pst->set_n_tasks((int)n_tasks);
5757     assert(pst->valid(), "Error");
5758   }
5759 }
5760 
5761 // Parallel version of remark
5762 void CMSCollector::do_remark_parallel() {
5763   GenCollectedHeap* gch = GenCollectedHeap::heap();
5764   FlexibleWorkGang* workers = gch->workers();
5765   assert(workers != NULL, "Need parallel worker threads.");
5766   // Choose to use the number of GC workers most recently set
5767   // into "active_workers".  If active_workers is not set, set it
5768   // to ParallelGCThreads.
5769   int n_workers = workers->active_workers();
5770   if (n_workers == 0) {
5771     assert(n_workers > 0, "Should have been set during scavenge");
5772     n_workers = ParallelGCThreads;
5773     workers->set_active_workers(n_workers);
5774   }
5775   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5776 
5777   CMSParRemarkTask tsk(this,
5778     cms_space,
5779     n_workers, workers, task_queues());
5780 
5781   // Set up for parallel process_roots work.
5782   gch->set_par_threads(n_workers);
5783   // We won't be iterating over the cards in the card table updating
5784   // the younger_gen cards, so we shouldn't call the following else
5785   // the verification code as well as subsequent younger_refs_iterate
5786   // code would get confused. XXX
5787   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5788 
5789   // The young gen rescan work will not be done as part of
5790   // process_roots (which currently doesn't know how to
5791   // parallelize such a scan), but rather will be broken up into
5792   // a set of parallel tasks (via the sampling that the [abortable]
5793   // preclean phase did of EdenSpace, plus the [two] tasks of
5794   // scanning the [two] survivor spaces. Further fine-grain
5795   // parallelization of the scanning of the survivor spaces
5796   // themselves, and of precleaning of the younger gen itself
5797   // is deferred to the future.
5798   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5799 
5800   // The dirty card rescan work is broken up into a "sequence"
5801   // of parallel tasks (per constituent space) that are dynamically
5802   // claimed by the parallel threads.
5803   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5804 
5805   // It turns out that even when we're using 1 thread, doing the work in a
5806   // separate thread causes wide variance in run times.  We can't help this
5807   // in the multi-threaded case, but we special-case n=1 here to get
5808   // repeatable measurements of the 1-thread overhead of the parallel code.
5809   if (n_workers > 1) {
5810     // Make refs discovery MT-safe, if it isn't already: it may not
5811     // necessarily be so, since it's possible that we are doing
5812     // ST marking.
5813     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5814     GenCollectedHeap::StrongRootsScope srs(gch);
5815     workers->run_task(&tsk);
5816   } else {
5817     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5818     GenCollectedHeap::StrongRootsScope srs(gch);
5819     tsk.work(0);
5820   }
5821 
5822   gch->set_par_threads(0);  // 0 ==> non-parallel.
5823   // restore, single-threaded for now, any preserved marks
5824   // as a result of work_q overflow
5825   restore_preserved_marks_if_any();
5826 }
5827 
5828 // Non-parallel version of remark
5829 void CMSCollector::do_remark_non_parallel() {
5830   ResourceMark rm;
5831   HandleMark   hm;
5832   GenCollectedHeap* gch = GenCollectedHeap::heap();
5833   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5834 
5835   MarkRefsIntoAndScanClosure
5836     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5837              &_markStack, this,
5838              false /* should_yield */, false /* not precleaning */);
5839   MarkFromDirtyCardsClosure
5840     markFromDirtyCardsClosure(this, _span,
5841                               NULL,  // space is set further below
5842                               &_markBitMap, &_markStack, &mrias_cl);
5843   {
5844     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5845     // Iterate over the dirty cards, setting the corresponding bits in the
5846     // mod union table.
5847     {
5848       ModUnionClosure modUnionClosure(&_modUnionTable);
5849       _ct->ct_bs()->dirty_card_iterate(
5850                       _cmsGen->used_region(),
5851                       &modUnionClosure);
5852     }
5853     // Having transferred these marks into the modUnionTable, we just need
5854     // to rescan the marked objects on the dirty cards in the modUnionTable.
5855     // The initial marking may have been done during an asynchronous
5856     // collection so there may be dirty bits in the mod-union table.
5857     const int alignment =
5858       CardTableModRefBS::card_size * BitsPerWord;
5859     {
5860       // ... First handle dirty cards in CMS gen
5861       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5862       MemRegion ur = _cmsGen->used_region();
5863       HeapWord* lb = ur.start();
5864       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5865       MemRegion cms_span(lb, ub);
5866       _modUnionTable.dirty_range_iterate_clear(cms_span,
5867                                                &markFromDirtyCardsClosure);
5868       verify_work_stacks_empty();
5869       if (PrintCMSStatistics != 0) {
5870         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5871           markFromDirtyCardsClosure.num_dirty_cards());
5872       }
5873     }
5874   }
5875   if (VerifyDuringGC &&
5876       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5877     HandleMark hm;  // Discard invalid handles created during verification
5878     Universe::verify();
5879   }
5880   {
5881     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5882 
5883     verify_work_stacks_empty();
5884 
5885     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5886     GenCollectedHeap::StrongRootsScope srs(gch);
5887 
5888     gch->gen_process_roots(_cmsGen->level(),
5889                            true,  // younger gens as roots
5890                            false, // use the local StrongRootsScope
5891                            SharedHeap::ScanningOption(roots_scanning_options()),
5892                            should_unload_classes(),
5893                            &mrias_cl,
5894                            NULL,
5895                            NULL); // The dirty klasses will be handled below
5896 
5897     assert(should_unload_classes()
5898            || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5899            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5900   }
5901 
5902   {
5903     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5904 
5905     verify_work_stacks_empty();
5906 
5907     // Scan all class loader data objects that might have been introduced
5908     // during concurrent marking.
5909     ResourceMark rm;
5910     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5911     for (int i = 0; i < array->length(); i++) {
5912       mrias_cl.do_class_loader_data(array->at(i));
5913     }
5914 
5915     // We don't need to keep track of new CLDs anymore.
5916     ClassLoaderDataGraph::remember_new_clds(false);
5917 
5918     verify_work_stacks_empty();
5919   }
5920 
5921   {
5922     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5923 
5924     verify_work_stacks_empty();
5925 
5926     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5927     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5928 
5929     verify_work_stacks_empty();
5930   }
5931 
5932   // We might have added oops to ClassLoaderData::_handles during the
5933   // concurrent marking phase. These oops point to newly allocated objects
5934   // that are guaranteed to be kept alive. Either by the direct allocation
5935   // code, or when the young collector processes the roots. Hence,
5936   // we don't have to revisit the _handles block during the remark phase.
5937 
5938   verify_work_stacks_empty();
5939   // Restore evacuated mark words, if any, used for overflow list links
5940   if (!CMSOverflowEarlyRestoration) {
5941     restore_preserved_marks_if_any();
5942   }
5943   verify_overflow_empty();
5944 }
5945 
5946 ////////////////////////////////////////////////////////
5947 // Parallel Reference Processing Task Proxy Class
5948 ////////////////////////////////////////////////////////
5949 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5950   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5951   CMSCollector*          _collector;
5952   CMSBitMap*             _mark_bit_map;
5953   const MemRegion        _span;
5954   ProcessTask&           _task;
5955 
5956 public:
5957   CMSRefProcTaskProxy(ProcessTask&     task,
5958                       CMSCollector*    collector,
5959                       const MemRegion& span,
5960                       CMSBitMap*       mark_bit_map,
5961                       AbstractWorkGang* workers,
5962                       OopTaskQueueSet* task_queues):
5963     // XXX Should superclass AGTWOQ also know about AWG since it knows
5964     // about the task_queues used by the AWG? Then it could initialize
5965     // the terminator() object. See 6984287. The set_for_termination()
5966     // below is a temporary band-aid for the regression in 6984287.
5967     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5968       task_queues),
5969     _task(task),
5970     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5971   {
5972     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5973            "Inconsistency in _span");
5974     set_for_termination(workers->active_workers());
5975   }
5976 
5977   OopTaskQueueSet* task_queues() { return queues(); }
5978 
5979   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5980 
5981   void do_work_steal(int i,
5982                      CMSParDrainMarkingStackClosure* drain,
5983                      CMSParKeepAliveClosure* keep_alive,
5984                      int* seed);
5985 
5986   virtual void work(uint worker_id);
5987 };
5988 
5989 void CMSRefProcTaskProxy::work(uint worker_id) {
5990   ResourceMark rm;
5991   HandleMark hm;
5992   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5993   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5994                                         _mark_bit_map,
5995                                         work_queue(worker_id));
5996   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5997                                                  _mark_bit_map,
5998                                                  work_queue(worker_id));
5999   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6000   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6001   if (_task.marks_oops_alive()) {
6002     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6003                   _collector->hash_seed(worker_id));
6004   }
6005   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6006   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6007 }
6008 
6009 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6010   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6011   EnqueueTask& _task;
6012 
6013 public:
6014   CMSRefEnqueueTaskProxy(EnqueueTask& task)
6015     : AbstractGangTask("Enqueue reference objects in parallel"),
6016       _task(task)
6017   { }
6018 
6019   virtual void work(uint worker_id)
6020   {
6021     _task.work(worker_id);
6022   }
6023 };
6024 
6025 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6026   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6027    _span(span),
6028    _bit_map(bit_map),
6029    _work_queue(work_queue),
6030    _mark_and_push(collector, span, bit_map, work_queue),
6031    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6032                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6033 { }
6034 
6035 // . see if we can share work_queues with ParNew? XXX
6036 void CMSRefProcTaskProxy::do_work_steal(int i,
6037   CMSParDrainMarkingStackClosure* drain,
6038   CMSParKeepAliveClosure* keep_alive,
6039   int* seed) {
6040   OopTaskQueue* work_q = work_queue(i);
6041   NOT_PRODUCT(int num_steals = 0;)
6042   oop obj_to_scan;
6043 
6044   while (true) {
6045     // Completely finish any left over work from (an) earlier round(s)
6046     drain->trim_queue(0);
6047     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6048                                          (size_t)ParGCDesiredObjsFromOverflowList);
6049     // Now check if there's any work in the overflow list
6050     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6051     // only affects the number of attempts made to get work from the
6052     // overflow list and does not affect the number of workers.  Just
6053     // pass ParallelGCThreads so this behavior is unchanged.
6054     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6055                                                 work_q,
6056                                                 ParallelGCThreads)) {
6057       // Found something in global overflow list;
6058       // not yet ready to go stealing work from others.
6059       // We'd like to assert(work_q->size() != 0, ...)
6060       // because we just took work from the overflow list,
6061       // but of course we can't, since all of that might have
6062       // been already stolen from us.
6063       continue;
6064     }
6065     // Verify that we have no work before we resort to stealing
6066     assert(work_q->size() == 0, "Have work, shouldn't steal");
6067     // Try to steal from other queues that have work
6068     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6069       NOT_PRODUCT(num_steals++;)
6070       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6071       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6072       // Do scanning work
6073       obj_to_scan->oop_iterate(keep_alive);
6074       // Loop around, finish this work, and try to steal some more
6075     } else if (terminator()->offer_termination()) {
6076       break;  // nirvana from the infinite cycle
6077     }
6078   }
6079   NOT_PRODUCT(
6080     if (PrintCMSStatistics != 0) {
6081       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6082     }
6083   )
6084 }
6085 
6086 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6087 {
6088   GenCollectedHeap* gch = GenCollectedHeap::heap();
6089   FlexibleWorkGang* workers = gch->workers();
6090   assert(workers != NULL, "Need parallel worker threads.");
6091   CMSRefProcTaskProxy rp_task(task, &_collector,
6092                               _collector.ref_processor()->span(),
6093                               _collector.markBitMap(),
6094                               workers, _collector.task_queues());
6095   workers->run_task(&rp_task);
6096 }
6097 
6098 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6099 {
6100 
6101   GenCollectedHeap* gch = GenCollectedHeap::heap();
6102   FlexibleWorkGang* workers = gch->workers();
6103   assert(workers != NULL, "Need parallel worker threads.");
6104   CMSRefEnqueueTaskProxy enq_task(task);
6105   workers->run_task(&enq_task);
6106 }
6107 
6108 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6109 
6110   ResourceMark rm;
6111   HandleMark   hm;
6112 
6113   ReferenceProcessor* rp = ref_processor();
6114   assert(rp->span().equals(_span), "Spans should be equal");
6115   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6116   // Process weak references.
6117   rp->setup_policy(clear_all_soft_refs);
6118   verify_work_stacks_empty();
6119 
6120   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6121                                           &_markStack, false /* !preclean */);
6122   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6123                                 _span, &_markBitMap, &_markStack,
6124                                 &cmsKeepAliveClosure, false /* !preclean */);
6125   {
6126     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6127 
6128     ReferenceProcessorStats stats;
6129     if (rp->processing_is_mt()) {
6130       // Set the degree of MT here.  If the discovery is done MT, there
6131       // may have been a different number of threads doing the discovery
6132       // and a different number of discovered lists may have Ref objects.
6133       // That is OK as long as the Reference lists are balanced (see
6134       // balance_all_queues() and balance_queues()).
6135       GenCollectedHeap* gch = GenCollectedHeap::heap();
6136       int active_workers = ParallelGCThreads;
6137       FlexibleWorkGang* workers = gch->workers();
6138       if (workers != NULL) {
6139         active_workers = workers->active_workers();
6140         // The expectation is that active_workers will have already
6141         // been set to a reasonable value.  If it has not been set,
6142         // investigate.
6143         assert(active_workers > 0, "Should have been set during scavenge");
6144       }
6145       rp->set_active_mt_degree(active_workers);
6146       CMSRefProcTaskExecutor task_executor(*this);
6147       stats = rp->process_discovered_references(&_is_alive_closure,
6148                                         &cmsKeepAliveClosure,
6149                                         &cmsDrainMarkingStackClosure,
6150                                         &task_executor,
6151                                         _gc_timer_cm,
6152                                         _gc_tracer_cm->gc_id());
6153     } else {
6154       stats = rp->process_discovered_references(&_is_alive_closure,
6155                                         &cmsKeepAliveClosure,
6156                                         &cmsDrainMarkingStackClosure,
6157                                         NULL,
6158                                         _gc_timer_cm,
6159                                         _gc_tracer_cm->gc_id());
6160     }
6161     _gc_tracer_cm->report_gc_reference_stats(stats);
6162 
6163   }
6164 
6165   // This is the point where the entire marking should have completed.
6166   verify_work_stacks_empty();
6167 
6168   if (should_unload_classes()) {
6169     {
6170       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6171 
6172       // Unload classes and purge the SystemDictionary.
6173       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6174 
6175       // Unload nmethods.
6176       CodeCache::do_unloading(&_is_alive_closure, purged_class);
6177 
6178       // Prune dead klasses from subklass/sibling/implementor lists.
6179       Klass::clean_weak_klass_links(&_is_alive_closure);
6180     }
6181 
6182     {
6183       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6184       // Clean up unreferenced symbols in symbol table.
6185       SymbolTable::unlink();
6186     }
6187 
6188     {
6189       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6190       // Delete entries for dead interned strings.
6191       StringTable::unlink(&_is_alive_closure);
6192     }
6193   }
6194 
6195 
6196   // Restore any preserved marks as a result of mark stack or
6197   // work queue overflow
6198   restore_preserved_marks_if_any();  // done single-threaded for now
6199 
6200   rp->set_enqueuing_is_done(true);
6201   if (rp->processing_is_mt()) {
6202     rp->balance_all_queues();
6203     CMSRefProcTaskExecutor task_executor(*this);
6204     rp->enqueue_discovered_references(&task_executor);
6205   } else {
6206     rp->enqueue_discovered_references(NULL);
6207   }
6208   rp->verify_no_references_recorded();
6209   assert(!rp->discovery_enabled(), "should have been disabled");
6210 }
6211 
6212 #ifndef PRODUCT
6213 void CMSCollector::check_correct_thread_executing() {
6214   Thread* t = Thread::current();
6215   // Only the VM thread or the CMS thread should be here.
6216   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6217          "Unexpected thread type");
6218   // If this is the vm thread, the foreground process
6219   // should not be waiting.  Note that _foregroundGCIsActive is
6220   // true while the foreground collector is waiting.
6221   if (_foregroundGCShouldWait) {
6222     // We cannot be the VM thread
6223     assert(t->is_ConcurrentGC_thread(),
6224            "Should be CMS thread");
6225   } else {
6226     // We can be the CMS thread only if we are in a stop-world
6227     // phase of CMS collection.
6228     if (t->is_ConcurrentGC_thread()) {
6229       assert(_collectorState == InitialMarking ||
6230              _collectorState == FinalMarking,
6231              "Should be a stop-world phase");
6232       // The CMS thread should be holding the CMS_token.
6233       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6234              "Potential interference with concurrently "
6235              "executing VM thread");
6236     }
6237   }
6238 }
6239 #endif
6240 
6241 void CMSCollector::sweep(bool asynch) {
6242   assert(_collectorState == Sweeping, "just checking");
6243   check_correct_thread_executing();
6244   verify_work_stacks_empty();
6245   verify_overflow_empty();
6246   increment_sweep_count();
6247   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6248 
6249   _inter_sweep_timer.stop();
6250   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6251 
6252   assert(!_intra_sweep_timer.is_active(), "Should not be active");
6253   _intra_sweep_timer.reset();
6254   _intra_sweep_timer.start();
6255   if (asynch) {
6256     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6257     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6258     // First sweep the old gen
6259     {
6260       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6261                                bitMapLock());
6262       sweepWork(_cmsGen, asynch);
6263     }
6264 
6265     // Update Universe::_heap_*_at_gc figures.
6266     // We need all the free list locks to make the abstract state
6267     // transition from Sweeping to Resetting. See detailed note
6268     // further below.
6269     {
6270       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6271       // Update heap occupancy information which is used as
6272       // input to soft ref clearing policy at the next gc.
6273       Universe::update_heap_info_at_gc();
6274       _collectorState = Resizing;
6275     }
6276   } else {
6277     // already have needed locks
6278     sweepWork(_cmsGen,  asynch);
6279     // Update heap occupancy information which is used as
6280     // input to soft ref clearing policy at the next gc.
6281     Universe::update_heap_info_at_gc();
6282     _collectorState = Resizing;
6283   }
6284   verify_work_stacks_empty();
6285   verify_overflow_empty();
6286 
6287   if (should_unload_classes()) {
6288     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
6289     // requires that the virtual spaces are stable and not deleted.
6290     ClassLoaderDataGraph::set_should_purge(true);
6291   }
6292 
6293   _intra_sweep_timer.stop();
6294   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6295 
6296   _inter_sweep_timer.reset();
6297   _inter_sweep_timer.start();
6298 
6299   // We need to use a monotonically non-decreasing time in ms
6300   // or we will see time-warp warnings and os::javaTimeMillis()
6301   // does not guarantee monotonicity.
6302   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6303   update_time_of_last_gc(now);
6304 
6305   // NOTE on abstract state transitions:
6306   // Mutators allocate-live and/or mark the mod-union table dirty
6307   // based on the state of the collection.  The former is done in
6308   // the interval [Marking, Sweeping] and the latter in the interval
6309   // [Marking, Sweeping).  Thus the transitions into the Marking state
6310   // and out of the Sweeping state must be synchronously visible
6311   // globally to the mutators.
6312   // The transition into the Marking state happens with the world
6313   // stopped so the mutators will globally see it.  Sweeping is
6314   // done asynchronously by the background collector so the transition
6315   // from the Sweeping state to the Resizing state must be done
6316   // under the freelistLock (as is the check for whether to
6317   // allocate-live and whether to dirty the mod-union table).
6318   assert(_collectorState == Resizing, "Change of collector state to"
6319     " Resizing must be done under the freelistLocks (plural)");
6320 
6321   // Now that sweeping has been completed, we clear
6322   // the incremental_collection_failed flag,
6323   // thus inviting a younger gen collection to promote into
6324   // this generation. If such a promotion may still fail,
6325   // the flag will be set again when a young collection is
6326   // attempted.
6327   GenCollectedHeap* gch = GenCollectedHeap::heap();
6328   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
6329   gch->update_full_collections_completed(_collection_count_start);
6330 }
6331 
6332 // FIX ME!!! Looks like this belongs in CFLSpace, with
6333 // CMSGen merely delegating to it.
6334 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6335   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6336   HeapWord*  minAddr        = _cmsSpace->bottom();
6337   HeapWord*  largestAddr    =
6338     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6339   if (largestAddr == NULL) {
6340     // The dictionary appears to be empty.  In this case
6341     // try to coalesce at the end of the heap.
6342     largestAddr = _cmsSpace->end();
6343   }
6344   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
6345   size_t nearLargestOffset =
6346     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6347   if (PrintFLSStatistics != 0) {
6348     gclog_or_tty->print_cr(
6349       "CMS: Large Block: " PTR_FORMAT ";"
6350       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6351       largestAddr,
6352       _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6353   }
6354   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6355 }
6356 
6357 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6358   return addr >= _cmsSpace->nearLargestChunk();
6359 }
6360 
6361 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6362   return _cmsSpace->find_chunk_at_end();
6363 }
6364 
6365 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6366                                                     bool full) {
6367   // The next lower level has been collected.  Gather any statistics
6368   // that are of interest at this point.
6369   if (!full && (current_level + 1) == level()) {
6370     // Gather statistics on the young generation collection.
6371     collector()->stats().record_gc0_end(used());
6372   }
6373 }
6374 
6375 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6376   if (PrintGCDetails && Verbose) {
6377     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6378   }
6379   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6380   _debug_collection_type =
6381     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6382   if (PrintGCDetails && Verbose) {
6383     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6384   }
6385 }
6386 
6387 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6388   bool asynch) {
6389   // We iterate over the space(s) underlying this generation,
6390   // checking the mark bit map to see if the bits corresponding
6391   // to specific blocks are marked or not. Blocks that are
6392   // marked are live and are not swept up. All remaining blocks
6393   // are swept up, with coalescing on-the-fly as we sweep up
6394   // contiguous free and/or garbage blocks:
6395   // We need to ensure that the sweeper synchronizes with allocators
6396   // and stop-the-world collectors. In particular, the following
6397   // locks are used:
6398   // . CMS token: if this is held, a stop the world collection cannot occur
6399   // . freelistLock: if this is held no allocation can occur from this
6400   //                 generation by another thread
6401   // . bitMapLock: if this is held, no other thread can access or update
6402   //
6403 
6404   // Note that we need to hold the freelistLock if we use
6405   // block iterate below; else the iterator might go awry if
6406   // a mutator (or promotion) causes block contents to change
6407   // (for instance if the allocator divvies up a block).
6408   // If we hold the free list lock, for all practical purposes
6409   // young generation GC's can't occur (they'll usually need to
6410   // promote), so we might as well prevent all young generation
6411   // GC's while we do a sweeping step. For the same reason, we might
6412   // as well take the bit map lock for the entire duration
6413 
6414   // check that we hold the requisite locks
6415   assert(have_cms_token(), "Should hold cms token");
6416   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6417          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6418         "Should possess CMS token to sweep");
6419   assert_lock_strong(gen->freelistLock());
6420   assert_lock_strong(bitMapLock());
6421 
6422   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6423   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
6424   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6425                                       _inter_sweep_estimate.padded_average(),
6426                                       _intra_sweep_estimate.padded_average());
6427   gen->setNearLargestChunk();
6428 
6429   {
6430     SweepClosure sweepClosure(this, gen, &_markBitMap,
6431                             CMSYield && asynch);
6432     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6433     // We need to free-up/coalesce garbage/blocks from a
6434     // co-terminal free run. This is done in the SweepClosure
6435     // destructor; so, do not remove this scope, else the
6436     // end-of-sweep-census below will be off by a little bit.
6437   }
6438   gen->cmsSpace()->sweep_completed();
6439   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6440   if (should_unload_classes()) {                // unloaded classes this cycle,
6441     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6442   } else {                                      // did not unload classes,
6443     _concurrent_cycles_since_last_unload++;     // ... increment count
6444   }
6445 }
6446 
6447 // Reset CMS data structures (for now just the marking bit map)
6448 // preparatory for the next cycle.
6449 void CMSCollector::reset(bool asynch) {
6450   if (asynch) {
6451     CMSTokenSyncWithLocks ts(true, bitMapLock());
6452 
6453     // If the state is not "Resetting", the foreground  thread
6454     // has done a collection and the resetting.
6455     if (_collectorState != Resetting) {
6456       assert(_collectorState == Idling, "The state should only change"
6457         " because the foreground collector has finished the collection");
6458       return;
6459     }
6460 
6461     // Clear the mark bitmap (no grey objects to start with)
6462     // for the next cycle.
6463     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6464     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6465 
6466     HeapWord* curAddr = _markBitMap.startWord();
6467     while (curAddr < _markBitMap.endWord()) {
6468       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6469       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6470       _markBitMap.clear_large_range(chunk);
6471       if (ConcurrentMarkSweepThread::should_yield() &&
6472           !foregroundGCIsActive() &&
6473           CMSYield) {
6474         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6475                "CMS thread should hold CMS token");
6476         assert_lock_strong(bitMapLock());
6477         bitMapLock()->unlock();
6478         ConcurrentMarkSweepThread::desynchronize(true);
6479         ConcurrentMarkSweepThread::acknowledge_yield_request();
6480         stopTimer();
6481         if (PrintCMSStatistics != 0) {
6482           incrementYields();
6483         }
6484         icms_wait();
6485 
6486         // See the comment in coordinator_yield()
6487         for (unsigned i = 0; i < CMSYieldSleepCount &&
6488                          ConcurrentMarkSweepThread::should_yield() &&
6489                          !CMSCollector::foregroundGCIsActive(); ++i) {
6490           os::sleep(Thread::current(), 1, false);
6491           ConcurrentMarkSweepThread::acknowledge_yield_request();
6492         }
6493 
6494         ConcurrentMarkSweepThread::synchronize(true);
6495         bitMapLock()->lock_without_safepoint_check();
6496         startTimer();
6497       }
6498       curAddr = chunk.end();
6499     }
6500     // A successful mostly concurrent collection has been done.
6501     // Because only the full (i.e., concurrent mode failure) collections
6502     // are being measured for gc overhead limits, clean the "near" flag
6503     // and count.
6504     size_policy()->reset_gc_overhead_limit_count();
6505     _collectorState = Idling;
6506   } else {
6507     // already have the lock
6508     assert(_collectorState == Resetting, "just checking");
6509     assert_lock_strong(bitMapLock());
6510     _markBitMap.clear_all();
6511     _collectorState = Idling;
6512   }
6513 
6514   // Stop incremental mode after a cycle completes, so that any future cycles
6515   // are triggered by allocation.
6516   stop_icms();
6517 
6518   NOT_PRODUCT(
6519     if (RotateCMSCollectionTypes) {
6520       _cmsGen->rotate_debug_collection_type();
6521     }
6522   )
6523 
6524   register_gc_end();
6525 }
6526 
6527 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6528   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6529   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6530   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6531   TraceCollectorStats tcs(counters());
6532 
6533   switch (op) {
6534     case CMS_op_checkpointRootsInitial: {
6535       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6536       checkpointRootsInitial(true);       // asynch
6537       if (PrintGC) {
6538         _cmsGen->printOccupancy("initial-mark");
6539       }
6540       break;
6541     }
6542     case CMS_op_checkpointRootsFinal: {
6543       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6544       checkpointRootsFinal(true,    // asynch
6545                            false,   // !clear_all_soft_refs
6546                            false);  // !init_mark_was_synchronous
6547       if (PrintGC) {
6548         _cmsGen->printOccupancy("remark");
6549       }
6550       break;
6551     }
6552     default:
6553       fatal("No such CMS_op");
6554   }
6555 }
6556 
6557 #ifndef PRODUCT
6558 size_t const CMSCollector::skip_header_HeapWords() {
6559   return FreeChunk::header_size();
6560 }
6561 
6562 // Try and collect here conditions that should hold when
6563 // CMS thread is exiting. The idea is that the foreground GC
6564 // thread should not be blocked if it wants to terminate
6565 // the CMS thread and yet continue to run the VM for a while
6566 // after that.
6567 void CMSCollector::verify_ok_to_terminate() const {
6568   assert(Thread::current()->is_ConcurrentGC_thread(),
6569          "should be called by CMS thread");
6570   assert(!_foregroundGCShouldWait, "should be false");
6571   // We could check here that all the various low-level locks
6572   // are not held by the CMS thread, but that is overkill; see
6573   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6574   // is checked.
6575 }
6576 #endif
6577 
6578 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6579    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6580           "missing Printezis mark?");
6581   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6582   size_t size = pointer_delta(nextOneAddr + 1, addr);
6583   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6584          "alignment problem");
6585   assert(size >= 3, "Necessary for Printezis marks to work");
6586   return size;
6587 }
6588 
6589 // A variant of the above (block_size_using_printezis_bits()) except
6590 // that we return 0 if the P-bits are not yet set.
6591 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6592   if (_markBitMap.isMarked(addr + 1)) {
6593     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6594     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6595     size_t size = pointer_delta(nextOneAddr + 1, addr);
6596     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6597            "alignment problem");
6598     assert(size >= 3, "Necessary for Printezis marks to work");
6599     return size;
6600   }
6601   return 0;
6602 }
6603 
6604 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6605   size_t sz = 0;
6606   oop p = (oop)addr;
6607   if (p->klass_or_null() != NULL) {
6608     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6609   } else {
6610     sz = block_size_using_printezis_bits(addr);
6611   }
6612   assert(sz > 0, "size must be nonzero");
6613   HeapWord* next_block = addr + sz;
6614   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6615                                              CardTableModRefBS::card_size);
6616   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6617          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6618          "must be different cards");
6619   return next_card;
6620 }
6621 
6622 
6623 // CMS Bit Map Wrapper /////////////////////////////////////////
6624 
6625 // Construct a CMS bit map infrastructure, but don't create the
6626 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6627 // further below.
6628 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6629   _bm(),
6630   _shifter(shifter),
6631   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6632 {
6633   _bmStartWord = 0;
6634   _bmWordSize  = 0;
6635 }
6636 
6637 bool CMSBitMap::allocate(MemRegion mr) {
6638   _bmStartWord = mr.start();
6639   _bmWordSize  = mr.word_size();
6640   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6641                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6642   if (!brs.is_reserved()) {
6643     warning("CMS bit map allocation failure");
6644     return false;
6645   }
6646   // For now we'll just commit all of the bit map up front.
6647   // Later on we'll try to be more parsimonious with swap.
6648   if (!_virtual_space.initialize(brs, brs.size())) {
6649     warning("CMS bit map backing store failure");
6650     return false;
6651   }
6652   assert(_virtual_space.committed_size() == brs.size(),
6653          "didn't reserve backing store for all of CMS bit map?");
6654   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6655   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6656          _bmWordSize, "inconsistency in bit map sizing");
6657   _bm.set_size(_bmWordSize >> _shifter);
6658 
6659   // bm.clear(); // can we rely on getting zero'd memory? verify below
6660   assert(isAllClear(),
6661          "Expected zero'd memory from ReservedSpace constructor");
6662   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6663          "consistency check");
6664   return true;
6665 }
6666 
6667 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6668   HeapWord *next_addr, *end_addr, *last_addr;
6669   assert_locked();
6670   assert(covers(mr), "out-of-range error");
6671   // XXX assert that start and end are appropriately aligned
6672   for (next_addr = mr.start(), end_addr = mr.end();
6673        next_addr < end_addr; next_addr = last_addr) {
6674     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6675     last_addr = dirty_region.end();
6676     if (!dirty_region.is_empty()) {
6677       cl->do_MemRegion(dirty_region);
6678     } else {
6679       assert(last_addr == end_addr, "program logic");
6680       return;
6681     }
6682   }
6683 }
6684 
6685 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6686   _bm.print_on_error(st, prefix);
6687 }
6688 
6689 #ifndef PRODUCT
6690 void CMSBitMap::assert_locked() const {
6691   CMSLockVerifier::assert_locked(lock());
6692 }
6693 
6694 bool CMSBitMap::covers(MemRegion mr) const {
6695   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6696   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6697          "size inconsistency");
6698   return (mr.start() >= _bmStartWord) &&
6699          (mr.end()   <= endWord());
6700 }
6701 
6702 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6703     return (start >= _bmStartWord && (start + size) <= endWord());
6704 }
6705 
6706 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6707   // verify that there are no 1 bits in the interval [left, right)
6708   FalseBitMapClosure falseBitMapClosure;
6709   iterate(&falseBitMapClosure, left, right);
6710 }
6711 
6712 void CMSBitMap::region_invariant(MemRegion mr)
6713 {
6714   assert_locked();
6715   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6716   assert(!mr.is_empty(), "unexpected empty region");
6717   assert(covers(mr), "mr should be covered by bit map");
6718   // convert address range into offset range
6719   size_t start_ofs = heapWordToOffset(mr.start());
6720   // Make sure that end() is appropriately aligned
6721   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6722                         (1 << (_shifter+LogHeapWordSize))),
6723          "Misaligned mr.end()");
6724   size_t end_ofs   = heapWordToOffset(mr.end());
6725   assert(end_ofs > start_ofs, "Should mark at least one bit");
6726 }
6727 
6728 #endif
6729 
6730 bool CMSMarkStack::allocate(size_t size) {
6731   // allocate a stack of the requisite depth
6732   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6733                    size * sizeof(oop)));
6734   if (!rs.is_reserved()) {
6735     warning("CMSMarkStack allocation failure");
6736     return false;
6737   }
6738   if (!_virtual_space.initialize(rs, rs.size())) {
6739     warning("CMSMarkStack backing store failure");
6740     return false;
6741   }
6742   assert(_virtual_space.committed_size() == rs.size(),
6743          "didn't reserve backing store for all of CMS stack?");
6744   _base = (oop*)(_virtual_space.low());
6745   _index = 0;
6746   _capacity = size;
6747   NOT_PRODUCT(_max_depth = 0);
6748   return true;
6749 }
6750 
6751 // XXX FIX ME !!! In the MT case we come in here holding a
6752 // leaf lock. For printing we need to take a further lock
6753 // which has lower rank. We need to recalibrate the two
6754 // lock-ranks involved in order to be able to print the
6755 // messages below. (Or defer the printing to the caller.
6756 // For now we take the expedient path of just disabling the
6757 // messages for the problematic case.)
6758 void CMSMarkStack::expand() {
6759   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6760   if (_capacity == MarkStackSizeMax) {
6761     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6762       // We print a warning message only once per CMS cycle.
6763       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6764     }
6765     return;
6766   }
6767   // Double capacity if possible
6768   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6769   // Do not give up existing stack until we have managed to
6770   // get the double capacity that we desired.
6771   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6772                    new_capacity * sizeof(oop)));
6773   if (rs.is_reserved()) {
6774     // Release the backing store associated with old stack
6775     _virtual_space.release();
6776     // Reinitialize virtual space for new stack
6777     if (!_virtual_space.initialize(rs, rs.size())) {
6778       fatal("Not enough swap for expanded marking stack");
6779     }
6780     _base = (oop*)(_virtual_space.low());
6781     _index = 0;
6782     _capacity = new_capacity;
6783   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6784     // Failed to double capacity, continue;
6785     // we print a detail message only once per CMS cycle.
6786     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6787             SIZE_FORMAT"K",
6788             _capacity / K, new_capacity / K);
6789   }
6790 }
6791 
6792 
6793 // Closures
6794 // XXX: there seems to be a lot of code  duplication here;
6795 // should refactor and consolidate common code.
6796 
6797 // This closure is used to mark refs into the CMS generation in
6798 // the CMS bit map. Called at the first checkpoint. This closure
6799 // assumes that we do not need to re-mark dirty cards; if the CMS
6800 // generation on which this is used is not an oldest
6801 // generation then this will lose younger_gen cards!
6802 
6803 MarkRefsIntoClosure::MarkRefsIntoClosure(
6804   MemRegion span, CMSBitMap* bitMap):
6805     _span(span),
6806     _bitMap(bitMap)
6807 {
6808     assert(_ref_processor == NULL, "deliberately left NULL");
6809     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6810 }
6811 
6812 void MarkRefsIntoClosure::do_oop(oop obj) {
6813   // if p points into _span, then mark corresponding bit in _markBitMap
6814   assert(obj->is_oop(), "expected an oop");
6815   HeapWord* addr = (HeapWord*)obj;
6816   if (_span.contains(addr)) {
6817     // this should be made more efficient
6818     _bitMap->mark(addr);
6819   }
6820 }
6821 
6822 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6823 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6824 
6825 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6826   MemRegion span, CMSBitMap* bitMap):
6827     _span(span),
6828     _bitMap(bitMap)
6829 {
6830     assert(_ref_processor == NULL, "deliberately left NULL");
6831     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6832 }
6833 
6834 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6835   // if p points into _span, then mark corresponding bit in _markBitMap
6836   assert(obj->is_oop(), "expected an oop");
6837   HeapWord* addr = (HeapWord*)obj;
6838   if (_span.contains(addr)) {
6839     // this should be made more efficient
6840     _bitMap->par_mark(addr);
6841   }
6842 }
6843 
6844 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6845 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6846 
6847 // A variant of the above, used for CMS marking verification.
6848 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6849   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6850     _span(span),
6851     _verification_bm(verification_bm),
6852     _cms_bm(cms_bm)
6853 {
6854     assert(_ref_processor == NULL, "deliberately left NULL");
6855     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6856 }
6857 
6858 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6859   // if p points into _span, then mark corresponding bit in _markBitMap
6860   assert(obj->is_oop(), "expected an oop");
6861   HeapWord* addr = (HeapWord*)obj;
6862   if (_span.contains(addr)) {
6863     _verification_bm->mark(addr);
6864     if (!_cms_bm->isMarked(addr)) {
6865       oop(addr)->print();
6866       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6867       fatal("... aborting");
6868     }
6869   }
6870 }
6871 
6872 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6873 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6874 
6875 //////////////////////////////////////////////////
6876 // MarkRefsIntoAndScanClosure
6877 //////////////////////////////////////////////////
6878 
6879 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6880                                                        ReferenceProcessor* rp,
6881                                                        CMSBitMap* bit_map,
6882                                                        CMSBitMap* mod_union_table,
6883                                                        CMSMarkStack*  mark_stack,
6884                                                        CMSCollector* collector,
6885                                                        bool should_yield,
6886                                                        bool concurrent_precleaning):
6887   _collector(collector),
6888   _span(span),
6889   _bit_map(bit_map),
6890   _mark_stack(mark_stack),
6891   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6892                       mark_stack, concurrent_precleaning),
6893   _yield(should_yield),
6894   _concurrent_precleaning(concurrent_precleaning),
6895   _freelistLock(NULL)
6896 {
6897   _ref_processor = rp;
6898   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6899 }
6900 
6901 // This closure is used to mark refs into the CMS generation at the
6902 // second (final) checkpoint, and to scan and transitively follow
6903 // the unmarked oops. It is also used during the concurrent precleaning
6904 // phase while scanning objects on dirty cards in the CMS generation.
6905 // The marks are made in the marking bit map and the marking stack is
6906 // used for keeping the (newly) grey objects during the scan.
6907 // The parallel version (Par_...) appears further below.
6908 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6909   if (obj != NULL) {
6910     assert(obj->is_oop(), "expected an oop");
6911     HeapWord* addr = (HeapWord*)obj;
6912     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6913     assert(_collector->overflow_list_is_empty(),
6914            "overflow list should be empty");
6915     if (_span.contains(addr) &&
6916         !_bit_map->isMarked(addr)) {
6917       // mark bit map (object is now grey)
6918       _bit_map->mark(addr);
6919       // push on marking stack (stack should be empty), and drain the
6920       // stack by applying this closure to the oops in the oops popped
6921       // from the stack (i.e. blacken the grey objects)
6922       bool res = _mark_stack->push(obj);
6923       assert(res, "Should have space to push on empty stack");
6924       do {
6925         oop new_oop = _mark_stack->pop();
6926         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6927         assert(_bit_map->isMarked((HeapWord*)new_oop),
6928                "only grey objects on this stack");
6929         // iterate over the oops in this oop, marking and pushing
6930         // the ones in CMS heap (i.e. in _span).
6931         new_oop->oop_iterate(&_pushAndMarkClosure);
6932         // check if it's time to yield
6933         do_yield_check();
6934       } while (!_mark_stack->isEmpty() ||
6935                (!_concurrent_precleaning && take_from_overflow_list()));
6936         // if marking stack is empty, and we are not doing this
6937         // during precleaning, then check the overflow list
6938     }
6939     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6940     assert(_collector->overflow_list_is_empty(),
6941            "overflow list was drained above");
6942     // We could restore evacuated mark words, if any, used for
6943     // overflow list links here because the overflow list is
6944     // provably empty here. That would reduce the maximum
6945     // size requirements for preserved_{oop,mark}_stack.
6946     // But we'll just postpone it until we are all done
6947     // so we can just stream through.
6948     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6949       _collector->restore_preserved_marks_if_any();
6950       assert(_collector->no_preserved_marks(), "No preserved marks");
6951     }
6952     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6953            "All preserved marks should have been restored above");
6954   }
6955 }
6956 
6957 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6958 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6959 
6960 void MarkRefsIntoAndScanClosure::do_yield_work() {
6961   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6962          "CMS thread should hold CMS token");
6963   assert_lock_strong(_freelistLock);
6964   assert_lock_strong(_bit_map->lock());
6965   // relinquish the free_list_lock and bitMaplock()
6966   _bit_map->lock()->unlock();
6967   _freelistLock->unlock();
6968   ConcurrentMarkSweepThread::desynchronize(true);
6969   ConcurrentMarkSweepThread::acknowledge_yield_request();
6970   _collector->stopTimer();
6971   if (PrintCMSStatistics != 0) {
6972     _collector->incrementYields();
6973   }
6974   _collector->icms_wait();
6975 
6976   // See the comment in coordinator_yield()
6977   for (unsigned i = 0;
6978        i < CMSYieldSleepCount &&
6979        ConcurrentMarkSweepThread::should_yield() &&
6980        !CMSCollector::foregroundGCIsActive();
6981        ++i) {
6982     os::sleep(Thread::current(), 1, false);
6983     ConcurrentMarkSweepThread::acknowledge_yield_request();
6984   }
6985 
6986   ConcurrentMarkSweepThread::synchronize(true);
6987   _freelistLock->lock_without_safepoint_check();
6988   _bit_map->lock()->lock_without_safepoint_check();
6989   _collector->startTimer();
6990 }
6991 
6992 ///////////////////////////////////////////////////////////
6993 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6994 //                                 MarkRefsIntoAndScanClosure
6995 ///////////////////////////////////////////////////////////
6996 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6997   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6998   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6999   _span(span),
7000   _bit_map(bit_map),
7001   _work_queue(work_queue),
7002   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7003                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7004   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7005 {
7006   _ref_processor = rp;
7007   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7008 }
7009 
7010 // This closure is used to mark refs into the CMS generation at the
7011 // second (final) checkpoint, and to scan and transitively follow
7012 // the unmarked oops. The marks are made in the marking bit map and
7013 // the work_queue is used for keeping the (newly) grey objects during
7014 // the scan phase whence they are also available for stealing by parallel
7015 // threads. Since the marking bit map is shared, updates are
7016 // synchronized (via CAS).
7017 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7018   if (obj != NULL) {
7019     // Ignore mark word because this could be an already marked oop
7020     // that may be chained at the end of the overflow list.
7021     assert(obj->is_oop(true), "expected an oop");
7022     HeapWord* addr = (HeapWord*)obj;
7023     if (_span.contains(addr) &&
7024         !_bit_map->isMarked(addr)) {
7025       // mark bit map (object will become grey):
7026       // It is possible for several threads to be
7027       // trying to "claim" this object concurrently;
7028       // the unique thread that succeeds in marking the
7029       // object first will do the subsequent push on
7030       // to the work queue (or overflow list).
7031       if (_bit_map->par_mark(addr)) {
7032         // push on work_queue (which may not be empty), and trim the
7033         // queue to an appropriate length by applying this closure to
7034         // the oops in the oops popped from the stack (i.e. blacken the
7035         // grey objects)
7036         bool res = _work_queue->push(obj);
7037         assert(res, "Low water mark should be less than capacity?");
7038         trim_queue(_low_water_mark);
7039       } // Else, another thread claimed the object
7040     }
7041   }
7042 }
7043 
7044 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7045 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7046 
7047 // This closure is used to rescan the marked objects on the dirty cards
7048 // in the mod union table and the card table proper.
7049 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7050   oop p, MemRegion mr) {
7051 
7052   size_t size = 0;
7053   HeapWord* addr = (HeapWord*)p;
7054   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7055   assert(_span.contains(addr), "we are scanning the CMS generation");
7056   // check if it's time to yield
7057   if (do_yield_check()) {
7058     // We yielded for some foreground stop-world work,
7059     // and we have been asked to abort this ongoing preclean cycle.
7060     return 0;
7061   }
7062   if (_bitMap->isMarked(addr)) {
7063     // it's marked; is it potentially uninitialized?
7064     if (p->klass_or_null() != NULL) {
7065         // an initialized object; ignore mark word in verification below
7066         // since we are running concurrent with mutators
7067         assert(p->is_oop(true), "should be an oop");
7068         if (p->is_objArray()) {
7069           // objArrays are precisely marked; restrict scanning
7070           // to dirty cards only.
7071           size = CompactibleFreeListSpace::adjustObjectSize(
7072                    p->oop_iterate(_scanningClosure, mr));
7073         } else {
7074           // A non-array may have been imprecisely marked; we need
7075           // to scan object in its entirety.
7076           size = CompactibleFreeListSpace::adjustObjectSize(
7077                    p->oop_iterate(_scanningClosure));
7078         }
7079         #ifdef ASSERT
7080           size_t direct_size =
7081             CompactibleFreeListSpace::adjustObjectSize(p->size());
7082           assert(size == direct_size, "Inconsistency in size");
7083           assert(size >= 3, "Necessary for Printezis marks to work");
7084           if (!_bitMap->isMarked(addr+1)) {
7085             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7086           } else {
7087             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7088             assert(_bitMap->isMarked(addr+size-1),
7089                    "inconsistent Printezis mark");
7090           }
7091         #endif // ASSERT
7092     } else {
7093       // An uninitialized object.
7094       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7095       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7096       size = pointer_delta(nextOneAddr + 1, addr);
7097       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7098              "alignment problem");
7099       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7100       // will dirty the card when the klass pointer is installed in the
7101       // object (signaling the completion of initialization).
7102     }
7103   } else {
7104     // Either a not yet marked object or an uninitialized object
7105     if (p->klass_or_null() == NULL) {
7106       // An uninitialized object, skip to the next card, since
7107       // we may not be able to read its P-bits yet.
7108       assert(size == 0, "Initial value");
7109     } else {
7110       // An object not (yet) reached by marking: we merely need to
7111       // compute its size so as to go look at the next block.
7112       assert(p->is_oop(true), "should be an oop");
7113       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7114     }
7115   }
7116   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7117   return size;
7118 }
7119 
7120 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7121   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7122          "CMS thread should hold CMS token");
7123   assert_lock_strong(_freelistLock);
7124   assert_lock_strong(_bitMap->lock());
7125   // relinquish the free_list_lock and bitMaplock()
7126   _bitMap->lock()->unlock();
7127   _freelistLock->unlock();
7128   ConcurrentMarkSweepThread::desynchronize(true);
7129   ConcurrentMarkSweepThread::acknowledge_yield_request();
7130   _collector->stopTimer();
7131   if (PrintCMSStatistics != 0) {
7132     _collector->incrementYields();
7133   }
7134   _collector->icms_wait();
7135 
7136   // See the comment in coordinator_yield()
7137   for (unsigned i = 0; i < CMSYieldSleepCount &&
7138                    ConcurrentMarkSweepThread::should_yield() &&
7139                    !CMSCollector::foregroundGCIsActive(); ++i) {
7140     os::sleep(Thread::current(), 1, false);
7141     ConcurrentMarkSweepThread::acknowledge_yield_request();
7142   }
7143 
7144   ConcurrentMarkSweepThread::synchronize(true);
7145   _freelistLock->lock_without_safepoint_check();
7146   _bitMap->lock()->lock_without_safepoint_check();
7147   _collector->startTimer();
7148 }
7149 
7150 
7151 //////////////////////////////////////////////////////////////////
7152 // SurvivorSpacePrecleanClosure
7153 //////////////////////////////////////////////////////////////////
7154 // This (single-threaded) closure is used to preclean the oops in
7155 // the survivor spaces.
7156 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7157 
7158   HeapWord* addr = (HeapWord*)p;
7159   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7160   assert(!_span.contains(addr), "we are scanning the survivor spaces");
7161   assert(p->klass_or_null() != NULL, "object should be initialized");
7162   // an initialized object; ignore mark word in verification below
7163   // since we are running concurrent with mutators
7164   assert(p->is_oop(true), "should be an oop");
7165   // Note that we do not yield while we iterate over
7166   // the interior oops of p, pushing the relevant ones
7167   // on our marking stack.
7168   size_t size = p->oop_iterate(_scanning_closure);
7169   do_yield_check();
7170   // Observe that below, we do not abandon the preclean
7171   // phase as soon as we should; rather we empty the
7172   // marking stack before returning. This is to satisfy
7173   // some existing assertions. In general, it may be a
7174   // good idea to abort immediately and complete the marking
7175   // from the grey objects at a later time.
7176   while (!_mark_stack->isEmpty()) {
7177     oop new_oop = _mark_stack->pop();
7178     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7179     assert(_bit_map->isMarked((HeapWord*)new_oop),
7180            "only grey objects on this stack");
7181     // iterate over the oops in this oop, marking and pushing
7182     // the ones in CMS heap (i.e. in _span).
7183     new_oop->oop_iterate(_scanning_closure);
7184     // check if it's time to yield
7185     do_yield_check();
7186   }
7187   unsigned int after_count =
7188     GenCollectedHeap::heap()->total_collections();
7189   bool abort = (_before_count != after_count) ||
7190                _collector->should_abort_preclean();
7191   return abort ? 0 : size;
7192 }
7193 
7194 void SurvivorSpacePrecleanClosure::do_yield_work() {
7195   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7196          "CMS thread should hold CMS token");
7197   assert_lock_strong(_bit_map->lock());
7198   // Relinquish the bit map lock
7199   _bit_map->lock()->unlock();
7200   ConcurrentMarkSweepThread::desynchronize(true);
7201   ConcurrentMarkSweepThread::acknowledge_yield_request();
7202   _collector->stopTimer();
7203   if (PrintCMSStatistics != 0) {
7204     _collector->incrementYields();
7205   }
7206   _collector->icms_wait();
7207 
7208   // See the comment in coordinator_yield()
7209   for (unsigned i = 0; i < CMSYieldSleepCount &&
7210                        ConcurrentMarkSweepThread::should_yield() &&
7211                        !CMSCollector::foregroundGCIsActive(); ++i) {
7212     os::sleep(Thread::current(), 1, false);
7213     ConcurrentMarkSweepThread::acknowledge_yield_request();
7214   }
7215 
7216   ConcurrentMarkSweepThread::synchronize(true);
7217   _bit_map->lock()->lock_without_safepoint_check();
7218   _collector->startTimer();
7219 }
7220 
7221 // This closure is used to rescan the marked objects on the dirty cards
7222 // in the mod union table and the card table proper. In the parallel
7223 // case, although the bitMap is shared, we do a single read so the
7224 // isMarked() query is "safe".
7225 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7226   // Ignore mark word because we are running concurrent with mutators
7227   assert(p->is_oop_or_null(true), "expected an oop or null");
7228   HeapWord* addr = (HeapWord*)p;
7229   assert(_span.contains(addr), "we are scanning the CMS generation");
7230   bool is_obj_array = false;
7231   #ifdef ASSERT
7232     if (!_parallel) {
7233       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7234       assert(_collector->overflow_list_is_empty(),
7235              "overflow list should be empty");
7236 
7237     }
7238   #endif // ASSERT
7239   if (_bit_map->isMarked(addr)) {
7240     // Obj arrays are precisely marked, non-arrays are not;
7241     // so we scan objArrays precisely and non-arrays in their
7242     // entirety.
7243     if (p->is_objArray()) {
7244       is_obj_array = true;
7245       if (_parallel) {
7246         p->oop_iterate(_par_scan_closure, mr);
7247       } else {
7248         p->oop_iterate(_scan_closure, mr);
7249       }
7250     } else {
7251       if (_parallel) {
7252         p->oop_iterate(_par_scan_closure);
7253       } else {
7254         p->oop_iterate(_scan_closure);
7255       }
7256     }
7257   }
7258   #ifdef ASSERT
7259     if (!_parallel) {
7260       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7261       assert(_collector->overflow_list_is_empty(),
7262              "overflow list should be empty");
7263 
7264     }
7265   #endif // ASSERT
7266   return is_obj_array;
7267 }
7268 
7269 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7270                         MemRegion span,
7271                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
7272                         bool should_yield, bool verifying):
7273   _collector(collector),
7274   _span(span),
7275   _bitMap(bitMap),
7276   _mut(&collector->_modUnionTable),
7277   _markStack(markStack),
7278   _yield(should_yield),
7279   _skipBits(0)
7280 {
7281   assert(_markStack->isEmpty(), "stack should be empty");
7282   _finger = _bitMap->startWord();
7283   _threshold = _finger;
7284   assert(_collector->_restart_addr == NULL, "Sanity check");
7285   assert(_span.contains(_finger), "Out of bounds _finger?");
7286   DEBUG_ONLY(_verifying = verifying;)
7287 }
7288 
7289 void MarkFromRootsClosure::reset(HeapWord* addr) {
7290   assert(_markStack->isEmpty(), "would cause duplicates on stack");
7291   assert(_span.contains(addr), "Out of bounds _finger?");
7292   _finger = addr;
7293   _threshold = (HeapWord*)round_to(
7294                  (intptr_t)_finger, CardTableModRefBS::card_size);
7295 }
7296 
7297 // Should revisit to see if this should be restructured for
7298 // greater efficiency.
7299 bool MarkFromRootsClosure::do_bit(size_t offset) {
7300   if (_skipBits > 0) {
7301     _skipBits--;
7302     return true;
7303   }
7304   // convert offset into a HeapWord*
7305   HeapWord* addr = _bitMap->startWord() + offset;
7306   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7307          "address out of range");
7308   assert(_bitMap->isMarked(addr), "tautology");
7309   if (_bitMap->isMarked(addr+1)) {
7310     // this is an allocated but not yet initialized object
7311     assert(_skipBits == 0, "tautology");
7312     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
7313     oop p = oop(addr);
7314     if (p->klass_or_null() == NULL) {
7315       DEBUG_ONLY(if (!_verifying) {)
7316         // We re-dirty the cards on which this object lies and increase
7317         // the _threshold so that we'll come back to scan this object
7318         // during the preclean or remark phase. (CMSCleanOnEnter)
7319         if (CMSCleanOnEnter) {
7320           size_t sz = _collector->block_size_using_printezis_bits(addr);
7321           HeapWord* end_card_addr   = (HeapWord*)round_to(
7322                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7323           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7324           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7325           // Bump _threshold to end_card_addr; note that
7326           // _threshold cannot possibly exceed end_card_addr, anyhow.
7327           // This prevents future clearing of the card as the scan proceeds
7328           // to the right.
7329           assert(_threshold <= end_card_addr,
7330                  "Because we are just scanning into this object");
7331           if (_threshold < end_card_addr) {
7332             _threshold = end_card_addr;
7333           }
7334           if (p->klass_or_null() != NULL) {
7335             // Redirty the range of cards...
7336             _mut->mark_range(redirty_range);
7337           } // ...else the setting of klass will dirty the card anyway.
7338         }
7339       DEBUG_ONLY(})
7340       return true;
7341     }
7342   }
7343   scanOopsInOop(addr);
7344   return true;
7345 }
7346 
7347 // We take a break if we've been at this for a while,
7348 // so as to avoid monopolizing the locks involved.
7349 void MarkFromRootsClosure::do_yield_work() {
7350   // First give up the locks, then yield, then re-lock
7351   // We should probably use a constructor/destructor idiom to
7352   // do this unlock/lock or modify the MutexUnlocker class to
7353   // serve our purpose. XXX
7354   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7355          "CMS thread should hold CMS token");
7356   assert_lock_strong(_bitMap->lock());
7357   _bitMap->lock()->unlock();
7358   ConcurrentMarkSweepThread::desynchronize(true);
7359   ConcurrentMarkSweepThread::acknowledge_yield_request();
7360   _collector->stopTimer();
7361   if (PrintCMSStatistics != 0) {
7362     _collector->incrementYields();
7363   }
7364   _collector->icms_wait();
7365 
7366   // See the comment in coordinator_yield()
7367   for (unsigned i = 0; i < CMSYieldSleepCount &&
7368                        ConcurrentMarkSweepThread::should_yield() &&
7369                        !CMSCollector::foregroundGCIsActive(); ++i) {
7370     os::sleep(Thread::current(), 1, false);
7371     ConcurrentMarkSweepThread::acknowledge_yield_request();
7372   }
7373 
7374   ConcurrentMarkSweepThread::synchronize(true);
7375   _bitMap->lock()->lock_without_safepoint_check();
7376   _collector->startTimer();
7377 }
7378 
7379 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7380   assert(_bitMap->isMarked(ptr), "expected bit to be set");
7381   assert(_markStack->isEmpty(),
7382          "should drain stack to limit stack usage");
7383   // convert ptr to an oop preparatory to scanning
7384   oop obj = oop(ptr);
7385   // Ignore mark word in verification below, since we
7386   // may be running concurrent with mutators.
7387   assert(obj->is_oop(true), "should be an oop");
7388   assert(_finger <= ptr, "_finger runneth ahead");
7389   // advance the finger to right end of this object
7390   _finger = ptr + obj->size();
7391   assert(_finger > ptr, "we just incremented it above");
7392   // On large heaps, it may take us some time to get through
7393   // the marking phase (especially if running iCMS). During
7394   // this time it's possible that a lot of mutations have
7395   // accumulated in the card table and the mod union table --
7396   // these mutation records are redundant until we have
7397   // actually traced into the corresponding card.
7398   // Here, we check whether advancing the finger would make
7399   // us cross into a new card, and if so clear corresponding
7400   // cards in the MUT (preclean them in the card-table in the
7401   // future).
7402 
7403   DEBUG_ONLY(if (!_verifying) {)
7404     // The clean-on-enter optimization is disabled by default,
7405     // until we fix 6178663.
7406     if (CMSCleanOnEnter && (_finger > _threshold)) {
7407       // [_threshold, _finger) represents the interval
7408       // of cards to be cleared  in MUT (or precleaned in card table).
7409       // The set of cards to be cleared is all those that overlap
7410       // with the interval [_threshold, _finger); note that
7411       // _threshold is always kept card-aligned but _finger isn't
7412       // always card-aligned.
7413       HeapWord* old_threshold = _threshold;
7414       assert(old_threshold == (HeapWord*)round_to(
7415               (intptr_t)old_threshold, CardTableModRefBS::card_size),
7416              "_threshold should always be card-aligned");
7417       _threshold = (HeapWord*)round_to(
7418                      (intptr_t)_finger, CardTableModRefBS::card_size);
7419       MemRegion mr(old_threshold, _threshold);
7420       assert(!mr.is_empty(), "Control point invariant");
7421       assert(_span.contains(mr), "Should clear within span");
7422       _mut->clear_range(mr);
7423     }
7424   DEBUG_ONLY(})
7425   // Note: the finger doesn't advance while we drain
7426   // the stack below.
7427   PushOrMarkClosure pushOrMarkClosure(_collector,
7428                                       _span, _bitMap, _markStack,
7429                                       _finger, this);
7430   bool res = _markStack->push(obj);
7431   assert(res, "Empty non-zero size stack should have space for single push");
7432   while (!_markStack->isEmpty()) {
7433     oop new_oop = _markStack->pop();
7434     // Skip verifying header mark word below because we are
7435     // running concurrent with mutators.
7436     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7437     // now scan this oop's oops
7438     new_oop->oop_iterate(&pushOrMarkClosure);
7439     do_yield_check();
7440   }
7441   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7442 }
7443 
7444 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7445                        CMSCollector* collector, MemRegion span,
7446                        CMSBitMap* bit_map,
7447                        OopTaskQueue* work_queue,
7448                        CMSMarkStack*  overflow_stack,
7449                        bool should_yield):
7450   _collector(collector),
7451   _whole_span(collector->_span),
7452   _span(span),
7453   _bit_map(bit_map),
7454   _mut(&collector->_modUnionTable),
7455   _work_queue(work_queue),
7456   _overflow_stack(overflow_stack),
7457   _yield(should_yield),
7458   _skip_bits(0),
7459   _task(task)
7460 {
7461   assert(_work_queue->size() == 0, "work_queue should be empty");
7462   _finger = span.start();
7463   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7464   assert(_span.contains(_finger), "Out of bounds _finger?");
7465 }
7466 
7467 // Should revisit to see if this should be restructured for
7468 // greater efficiency.
7469 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7470   if (_skip_bits > 0) {
7471     _skip_bits--;
7472     return true;
7473   }
7474   // convert offset into a HeapWord*
7475   HeapWord* addr = _bit_map->startWord() + offset;
7476   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7477          "address out of range");
7478   assert(_bit_map->isMarked(addr), "tautology");
7479   if (_bit_map->isMarked(addr+1)) {
7480     // this is an allocated object that might not yet be initialized
7481     assert(_skip_bits == 0, "tautology");
7482     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7483     oop p = oop(addr);
7484     if (p->klass_or_null() == NULL) {
7485       // in the case of Clean-on-Enter optimization, redirty card
7486       // and avoid clearing card by increasing  the threshold.
7487       return true;
7488     }
7489   }
7490   scan_oops_in_oop(addr);
7491   return true;
7492 }
7493 
7494 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7495   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7496   // Should we assert that our work queue is empty or
7497   // below some drain limit?
7498   assert(_work_queue->size() == 0,
7499          "should drain stack to limit stack usage");
7500   // convert ptr to an oop preparatory to scanning
7501   oop obj = oop(ptr);
7502   // Ignore mark word in verification below, since we
7503   // may be running concurrent with mutators.
7504   assert(obj->is_oop(true), "should be an oop");
7505   assert(_finger <= ptr, "_finger runneth ahead");
7506   // advance the finger to right end of this object
7507   _finger = ptr + obj->size();
7508   assert(_finger > ptr, "we just incremented it above");
7509   // On large heaps, it may take us some time to get through
7510   // the marking phase (especially if running iCMS). During
7511   // this time it's possible that a lot of mutations have
7512   // accumulated in the card table and the mod union table --
7513   // these mutation records are redundant until we have
7514   // actually traced into the corresponding card.
7515   // Here, we check whether advancing the finger would make
7516   // us cross into a new card, and if so clear corresponding
7517   // cards in the MUT (preclean them in the card-table in the
7518   // future).
7519 
7520   // The clean-on-enter optimization is disabled by default,
7521   // until we fix 6178663.
7522   if (CMSCleanOnEnter && (_finger > _threshold)) {
7523     // [_threshold, _finger) represents the interval
7524     // of cards to be cleared  in MUT (or precleaned in card table).
7525     // The set of cards to be cleared is all those that overlap
7526     // with the interval [_threshold, _finger); note that
7527     // _threshold is always kept card-aligned but _finger isn't
7528     // always card-aligned.
7529     HeapWord* old_threshold = _threshold;
7530     assert(old_threshold == (HeapWord*)round_to(
7531             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7532            "_threshold should always be card-aligned");
7533     _threshold = (HeapWord*)round_to(
7534                    (intptr_t)_finger, CardTableModRefBS::card_size);
7535     MemRegion mr(old_threshold, _threshold);
7536     assert(!mr.is_empty(), "Control point invariant");
7537     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7538     _mut->clear_range(mr);
7539   }
7540 
7541   // Note: the local finger doesn't advance while we drain
7542   // the stack below, but the global finger sure can and will.
7543   HeapWord** gfa = _task->global_finger_addr();
7544   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7545                                       _span, _bit_map,
7546                                       _work_queue,
7547                                       _overflow_stack,
7548                                       _finger,
7549                                       gfa, this);
7550   bool res = _work_queue->push(obj);   // overflow could occur here
7551   assert(res, "Will hold once we use workqueues");
7552   while (true) {
7553     oop new_oop;
7554     if (!_work_queue->pop_local(new_oop)) {
7555       // We emptied our work_queue; check if there's stuff that can
7556       // be gotten from the overflow stack.
7557       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7558             _overflow_stack, _work_queue)) {
7559         do_yield_check();
7560         continue;
7561       } else {  // done
7562         break;
7563       }
7564     }
7565     // Skip verifying header mark word below because we are
7566     // running concurrent with mutators.
7567     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7568     // now scan this oop's oops
7569     new_oop->oop_iterate(&pushOrMarkClosure);
7570     do_yield_check();
7571   }
7572   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7573 }
7574 
7575 // Yield in response to a request from VM Thread or
7576 // from mutators.
7577 void Par_MarkFromRootsClosure::do_yield_work() {
7578   assert(_task != NULL, "sanity");
7579   _task->yield();
7580 }
7581 
7582 // A variant of the above used for verifying CMS marking work.
7583 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7584                         MemRegion span,
7585                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7586                         CMSMarkStack*  mark_stack):
7587   _collector(collector),
7588   _span(span),
7589   _verification_bm(verification_bm),
7590   _cms_bm(cms_bm),
7591   _mark_stack(mark_stack),
7592   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7593                       mark_stack)
7594 {
7595   assert(_mark_stack->isEmpty(), "stack should be empty");
7596   _finger = _verification_bm->startWord();
7597   assert(_collector->_restart_addr == NULL, "Sanity check");
7598   assert(_span.contains(_finger), "Out of bounds _finger?");
7599 }
7600 
7601 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7602   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7603   assert(_span.contains(addr), "Out of bounds _finger?");
7604   _finger = addr;
7605 }
7606 
7607 // Should revisit to see if this should be restructured for
7608 // greater efficiency.
7609 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7610   // convert offset into a HeapWord*
7611   HeapWord* addr = _verification_bm->startWord() + offset;
7612   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7613          "address out of range");
7614   assert(_verification_bm->isMarked(addr), "tautology");
7615   assert(_cms_bm->isMarked(addr), "tautology");
7616 
7617   assert(_mark_stack->isEmpty(),
7618          "should drain stack to limit stack usage");
7619   // convert addr to an oop preparatory to scanning
7620   oop obj = oop(addr);
7621   assert(obj->is_oop(), "should be an oop");
7622   assert(_finger <= addr, "_finger runneth ahead");
7623   // advance the finger to right end of this object
7624   _finger = addr + obj->size();
7625   assert(_finger > addr, "we just incremented it above");
7626   // Note: the finger doesn't advance while we drain
7627   // the stack below.
7628   bool res = _mark_stack->push(obj);
7629   assert(res, "Empty non-zero size stack should have space for single push");
7630   while (!_mark_stack->isEmpty()) {
7631     oop new_oop = _mark_stack->pop();
7632     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7633     // now scan this oop's oops
7634     new_oop->oop_iterate(&_pam_verify_closure);
7635   }
7636   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7637   return true;
7638 }
7639 
7640 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7641   CMSCollector* collector, MemRegion span,
7642   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7643   CMSMarkStack*  mark_stack):
7644   MetadataAwareOopClosure(collector->ref_processor()),
7645   _collector(collector),
7646   _span(span),
7647   _verification_bm(verification_bm),
7648   _cms_bm(cms_bm),
7649   _mark_stack(mark_stack)
7650 { }
7651 
7652 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
7653 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7654 
7655 // Upon stack overflow, we discard (part of) the stack,
7656 // remembering the least address amongst those discarded
7657 // in CMSCollector's _restart_address.
7658 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7659   // Remember the least grey address discarded
7660   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7661   _collector->lower_restart_addr(ra);
7662   _mark_stack->reset();  // discard stack contents
7663   _mark_stack->expand(); // expand the stack if possible
7664 }
7665 
7666 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7667   assert(obj->is_oop_or_null(), "expected an oop or NULL");
7668   HeapWord* addr = (HeapWord*)obj;
7669   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7670     // Oop lies in _span and isn't yet grey or black
7671     _verification_bm->mark(addr);            // now grey
7672     if (!_cms_bm->isMarked(addr)) {
7673       oop(addr)->print();
7674       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7675                              addr);
7676       fatal("... aborting");
7677     }
7678 
7679     if (!_mark_stack->push(obj)) { // stack overflow
7680       if (PrintCMSStatistics != 0) {
7681         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7682                                SIZE_FORMAT, _mark_stack->capacity());
7683       }
7684       assert(_mark_stack->isFull(), "Else push should have succeeded");
7685       handle_stack_overflow(addr);
7686     }
7687     // anything including and to the right of _finger
7688     // will be scanned as we iterate over the remainder of the
7689     // bit map
7690   }
7691 }
7692 
7693 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7694                      MemRegion span,
7695                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7696                      HeapWord* finger, MarkFromRootsClosure* parent) :
7697   MetadataAwareOopClosure(collector->ref_processor()),
7698   _collector(collector),
7699   _span(span),
7700   _bitMap(bitMap),
7701   _markStack(markStack),
7702   _finger(finger),
7703   _parent(parent)
7704 { }
7705 
7706 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7707                      MemRegion span,
7708                      CMSBitMap* bit_map,
7709                      OopTaskQueue* work_queue,
7710                      CMSMarkStack*  overflow_stack,
7711                      HeapWord* finger,
7712                      HeapWord** global_finger_addr,
7713                      Par_MarkFromRootsClosure* parent) :
7714   MetadataAwareOopClosure(collector->ref_processor()),
7715   _collector(collector),
7716   _whole_span(collector->_span),
7717   _span(span),
7718   _bit_map(bit_map),
7719   _work_queue(work_queue),
7720   _overflow_stack(overflow_stack),
7721   _finger(finger),
7722   _global_finger_addr(global_finger_addr),
7723   _parent(parent)
7724 { }
7725 
7726 // Assumes thread-safe access by callers, who are
7727 // responsible for mutual exclusion.
7728 void CMSCollector::lower_restart_addr(HeapWord* low) {
7729   assert(_span.contains(low), "Out of bounds addr");
7730   if (_restart_addr == NULL) {
7731     _restart_addr = low;
7732   } else {
7733     _restart_addr = MIN2(_restart_addr, low);
7734   }
7735 }
7736 
7737 // Upon stack overflow, we discard (part of) the stack,
7738 // remembering the least address amongst those discarded
7739 // in CMSCollector's _restart_address.
7740 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7741   // Remember the least grey address discarded
7742   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7743   _collector->lower_restart_addr(ra);
7744   _markStack->reset();  // discard stack contents
7745   _markStack->expand(); // expand the stack if possible
7746 }
7747 
7748 // Upon stack overflow, we discard (part of) the stack,
7749 // remembering the least address amongst those discarded
7750 // in CMSCollector's _restart_address.
7751 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7752   // We need to do this under a mutex to prevent other
7753   // workers from interfering with the work done below.
7754   MutexLockerEx ml(_overflow_stack->par_lock(),
7755                    Mutex::_no_safepoint_check_flag);
7756   // Remember the least grey address discarded
7757   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7758   _collector->lower_restart_addr(ra);
7759   _overflow_stack->reset();  // discard stack contents
7760   _overflow_stack->expand(); // expand the stack if possible
7761 }
7762 
7763 void PushOrMarkClosure::do_oop(oop obj) {
7764   // Ignore mark word because we are running concurrent with mutators.
7765   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7766   HeapWord* addr = (HeapWord*)obj;
7767   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7768     // Oop lies in _span and isn't yet grey or black
7769     _bitMap->mark(addr);            // now grey
7770     if (addr < _finger) {
7771       // the bit map iteration has already either passed, or
7772       // sampled, this bit in the bit map; we'll need to
7773       // use the marking stack to scan this oop's oops.
7774       bool simulate_overflow = false;
7775       NOT_PRODUCT(
7776         if (CMSMarkStackOverflowALot &&
7777             _collector->simulate_overflow()) {
7778           // simulate a stack overflow
7779           simulate_overflow = true;
7780         }
7781       )
7782       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7783         if (PrintCMSStatistics != 0) {
7784           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7785                                  SIZE_FORMAT, _markStack->capacity());
7786         }
7787         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7788         handle_stack_overflow(addr);
7789       }
7790     }
7791     // anything including and to the right of _finger
7792     // will be scanned as we iterate over the remainder of the
7793     // bit map
7794     do_yield_check();
7795   }
7796 }
7797 
7798 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7799 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7800 
7801 void Par_PushOrMarkClosure::do_oop(oop obj) {
7802   // Ignore mark word because we are running concurrent with mutators.
7803   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7804   HeapWord* addr = (HeapWord*)obj;
7805   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7806     // Oop lies in _span and isn't yet grey or black
7807     // We read the global_finger (volatile read) strictly after marking oop
7808     bool res = _bit_map->par_mark(addr);    // now grey
7809     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7810     // Should we push this marked oop on our stack?
7811     // -- if someone else marked it, nothing to do
7812     // -- if target oop is above global finger nothing to do
7813     // -- if target oop is in chunk and above local finger
7814     //      then nothing to do
7815     // -- else push on work queue
7816     if (   !res       // someone else marked it, they will deal with it
7817         || (addr >= *gfa)  // will be scanned in a later task
7818         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7819       return;
7820     }
7821     // the bit map iteration has already either passed, or
7822     // sampled, this bit in the bit map; we'll need to
7823     // use the marking stack to scan this oop's oops.
7824     bool simulate_overflow = false;
7825     NOT_PRODUCT(
7826       if (CMSMarkStackOverflowALot &&
7827           _collector->simulate_overflow()) {
7828         // simulate a stack overflow
7829         simulate_overflow = true;
7830       }
7831     )
7832     if (simulate_overflow ||
7833         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7834       // stack overflow
7835       if (PrintCMSStatistics != 0) {
7836         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7837                                SIZE_FORMAT, _overflow_stack->capacity());
7838       }
7839       // We cannot assert that the overflow stack is full because
7840       // it may have been emptied since.
7841       assert(simulate_overflow ||
7842              _work_queue->size() == _work_queue->max_elems(),
7843             "Else push should have succeeded");
7844       handle_stack_overflow(addr);
7845     }
7846     do_yield_check();
7847   }
7848 }
7849 
7850 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7851 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7852 
7853 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7854                                        MemRegion span,
7855                                        ReferenceProcessor* rp,
7856                                        CMSBitMap* bit_map,
7857                                        CMSBitMap* mod_union_table,
7858                                        CMSMarkStack*  mark_stack,
7859                                        bool           concurrent_precleaning):
7860   MetadataAwareOopClosure(rp),
7861   _collector(collector),
7862   _span(span),
7863   _bit_map(bit_map),
7864   _mod_union_table(mod_union_table),
7865   _mark_stack(mark_stack),
7866   _concurrent_precleaning(concurrent_precleaning)
7867 {
7868   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7869 }
7870 
7871 // Grey object rescan during pre-cleaning and second checkpoint phases --
7872 // the non-parallel version (the parallel version appears further below.)
7873 void PushAndMarkClosure::do_oop(oop obj) {
7874   // Ignore mark word verification. If during concurrent precleaning,
7875   // the object monitor may be locked. If during the checkpoint
7876   // phases, the object may already have been reached by a  different
7877   // path and may be at the end of the global overflow list (so
7878   // the mark word may be NULL).
7879   assert(obj->is_oop_or_null(true /* ignore mark word */),
7880          "expected an oop or NULL");
7881   HeapWord* addr = (HeapWord*)obj;
7882   // Check if oop points into the CMS generation
7883   // and is not marked
7884   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7885     // a white object ...
7886     _bit_map->mark(addr);         // ... now grey
7887     // push on the marking stack (grey set)
7888     bool simulate_overflow = false;
7889     NOT_PRODUCT(
7890       if (CMSMarkStackOverflowALot &&
7891           _collector->simulate_overflow()) {
7892         // simulate a stack overflow
7893         simulate_overflow = true;
7894       }
7895     )
7896     if (simulate_overflow || !_mark_stack->push(obj)) {
7897       if (_concurrent_precleaning) {
7898          // During precleaning we can just dirty the appropriate card(s)
7899          // in the mod union table, thus ensuring that the object remains
7900          // in the grey set  and continue. In the case of object arrays
7901          // we need to dirty all of the cards that the object spans,
7902          // since the rescan of object arrays will be limited to the
7903          // dirty cards.
7904          // Note that no one can be interfering with us in this action
7905          // of dirtying the mod union table, so no locking or atomics
7906          // are required.
7907          if (obj->is_objArray()) {
7908            size_t sz = obj->size();
7909            HeapWord* end_card_addr = (HeapWord*)round_to(
7910                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7911            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7912            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7913            _mod_union_table->mark_range(redirty_range);
7914          } else {
7915            _mod_union_table->mark(addr);
7916          }
7917          _collector->_ser_pmc_preclean_ovflw++;
7918       } else {
7919          // During the remark phase, we need to remember this oop
7920          // in the overflow list.
7921          _collector->push_on_overflow_list(obj);
7922          _collector->_ser_pmc_remark_ovflw++;
7923       }
7924     }
7925   }
7926 }
7927 
7928 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7929                                                MemRegion span,
7930                                                ReferenceProcessor* rp,
7931                                                CMSBitMap* bit_map,
7932                                                OopTaskQueue* work_queue):
7933   MetadataAwareOopClosure(rp),
7934   _collector(collector),
7935   _span(span),
7936   _bit_map(bit_map),
7937   _work_queue(work_queue)
7938 {
7939   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7940 }
7941 
7942 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7943 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7944 
7945 // Grey object rescan during second checkpoint phase --
7946 // the parallel version.
7947 void Par_PushAndMarkClosure::do_oop(oop obj) {
7948   // In the assert below, we ignore the mark word because
7949   // this oop may point to an already visited object that is
7950   // on the overflow stack (in which case the mark word has
7951   // been hijacked for chaining into the overflow stack --
7952   // if this is the last object in the overflow stack then
7953   // its mark word will be NULL). Because this object may
7954   // have been subsequently popped off the global overflow
7955   // stack, and the mark word possibly restored to the prototypical
7956   // value, by the time we get to examined this failing assert in
7957   // the debugger, is_oop_or_null(false) may subsequently start
7958   // to hold.
7959   assert(obj->is_oop_or_null(true),
7960          "expected an oop or NULL");
7961   HeapWord* addr = (HeapWord*)obj;
7962   // Check if oop points into the CMS generation
7963   // and is not marked
7964   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7965     // a white object ...
7966     // If we manage to "claim" the object, by being the
7967     // first thread to mark it, then we push it on our
7968     // marking stack
7969     if (_bit_map->par_mark(addr)) {     // ... now grey
7970       // push on work queue (grey set)
7971       bool simulate_overflow = false;
7972       NOT_PRODUCT(
7973         if (CMSMarkStackOverflowALot &&
7974             _collector->par_simulate_overflow()) {
7975           // simulate a stack overflow
7976           simulate_overflow = true;
7977         }
7978       )
7979       if (simulate_overflow || !_work_queue->push(obj)) {
7980         _collector->par_push_on_overflow_list(obj);
7981         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7982       }
7983     } // Else, some other thread got there first
7984   }
7985 }
7986 
7987 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7988 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7989 
7990 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7991   Mutex* bml = _collector->bitMapLock();
7992   assert_lock_strong(bml);
7993   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7994          "CMS thread should hold CMS token");
7995 
7996   bml->unlock();
7997   ConcurrentMarkSweepThread::desynchronize(true);
7998 
7999   ConcurrentMarkSweepThread::acknowledge_yield_request();
8000 
8001   _collector->stopTimer();
8002   if (PrintCMSStatistics != 0) {
8003     _collector->incrementYields();
8004   }
8005   _collector->icms_wait();
8006 
8007   // See the comment in coordinator_yield()
8008   for (unsigned i = 0; i < CMSYieldSleepCount &&
8009                        ConcurrentMarkSweepThread::should_yield() &&
8010                        !CMSCollector::foregroundGCIsActive(); ++i) {
8011     os::sleep(Thread::current(), 1, false);
8012     ConcurrentMarkSweepThread::acknowledge_yield_request();
8013   }
8014 
8015   ConcurrentMarkSweepThread::synchronize(true);
8016   bml->lock();
8017 
8018   _collector->startTimer();
8019 }
8020 
8021 bool CMSPrecleanRefsYieldClosure::should_return() {
8022   if (ConcurrentMarkSweepThread::should_yield()) {
8023     do_yield_work();
8024   }
8025   return _collector->foregroundGCIsActive();
8026 }
8027 
8028 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8029   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8030          "mr should be aligned to start at a card boundary");
8031   // We'd like to assert:
8032   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8033   //        "mr should be a range of cards");
8034   // However, that would be too strong in one case -- the last
8035   // partition ends at _unallocated_block which, in general, can be
8036   // an arbitrary boundary, not necessarily card aligned.
8037   if (PrintCMSStatistics != 0) {
8038     _num_dirty_cards +=
8039          mr.word_size()/CardTableModRefBS::card_size_in_words;
8040   }
8041   _space->object_iterate_mem(mr, &_scan_cl);
8042 }
8043 
8044 SweepClosure::SweepClosure(CMSCollector* collector,
8045                            ConcurrentMarkSweepGeneration* g,
8046                            CMSBitMap* bitMap, bool should_yield) :
8047   _collector(collector),
8048   _g(g),
8049   _sp(g->cmsSpace()),
8050   _limit(_sp->sweep_limit()),
8051   _freelistLock(_sp->freelistLock()),
8052   _bitMap(bitMap),
8053   _yield(should_yield),
8054   _inFreeRange(false),           // No free range at beginning of sweep
8055   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
8056   _lastFreeRangeCoalesced(false),
8057   _freeFinger(g->used_region().start())
8058 {
8059   NOT_PRODUCT(
8060     _numObjectsFreed = 0;
8061     _numWordsFreed   = 0;
8062     _numObjectsLive = 0;
8063     _numWordsLive = 0;
8064     _numObjectsAlreadyFree = 0;
8065     _numWordsAlreadyFree = 0;
8066     _last_fc = NULL;
8067 
8068     _sp->initializeIndexedFreeListArrayReturnedBytes();
8069     _sp->dictionary()->initialize_dict_returned_bytes();
8070   )
8071   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8072          "sweep _limit out of bounds");
8073   if (CMSTraceSweeper) {
8074     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8075                         _limit);
8076   }
8077 }
8078 
8079 void SweepClosure::print_on(outputStream* st) const {
8080   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8081                 _sp->bottom(), _sp->end());
8082   tty->print_cr("_limit = " PTR_FORMAT, _limit);
8083   tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8084   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8085   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8086                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8087 }
8088 
8089 #ifndef PRODUCT
8090 // Assertion checking only:  no useful work in product mode --
8091 // however, if any of the flags below become product flags,
8092 // you may need to review this code to see if it needs to be
8093 // enabled in product mode.
8094 SweepClosure::~SweepClosure() {
8095   assert_lock_strong(_freelistLock);
8096   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8097          "sweep _limit out of bounds");
8098   if (inFreeRange()) {
8099     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8100     print();
8101     ShouldNotReachHere();
8102   }
8103   if (Verbose && PrintGC) {
8104     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8105                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8106     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
8107                            SIZE_FORMAT" bytes  "
8108       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8109       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8110       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8111     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8112                         * sizeof(HeapWord);
8113     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8114 
8115     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8116       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8117       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8118       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8119       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8120       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
8121         indexListReturnedBytes);
8122       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
8123         dict_returned_bytes);
8124     }
8125   }
8126   if (CMSTraceSweeper) {
8127     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8128                            _limit);
8129   }
8130 }
8131 #endif  // PRODUCT
8132 
8133 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8134     bool freeRangeInFreeLists) {
8135   if (CMSTraceSweeper) {
8136     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8137                freeFinger, freeRangeInFreeLists);
8138   }
8139   assert(!inFreeRange(), "Trampling existing free range");
8140   set_inFreeRange(true);
8141   set_lastFreeRangeCoalesced(false);
8142 
8143   set_freeFinger(freeFinger);
8144   set_freeRangeInFreeLists(freeRangeInFreeLists);
8145   if (CMSTestInFreeList) {
8146     if (freeRangeInFreeLists) {
8147       FreeChunk* fc = (FreeChunk*) freeFinger;
8148       assert(fc->is_free(), "A chunk on the free list should be free.");
8149       assert(fc->size() > 0, "Free range should have a size");
8150       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8151     }
8152   }
8153 }
8154 
8155 // Note that the sweeper runs concurrently with mutators. Thus,
8156 // it is possible for direct allocation in this generation to happen
8157 // in the middle of the sweep. Note that the sweeper also coalesces
8158 // contiguous free blocks. Thus, unless the sweeper and the allocator
8159 // synchronize appropriately freshly allocated blocks may get swept up.
8160 // This is accomplished by the sweeper locking the free lists while
8161 // it is sweeping. Thus blocks that are determined to be free are
8162 // indeed free. There is however one additional complication:
8163 // blocks that have been allocated since the final checkpoint and
8164 // mark, will not have been marked and so would be treated as
8165 // unreachable and swept up. To prevent this, the allocator marks
8166 // the bit map when allocating during the sweep phase. This leads,
8167 // however, to a further complication -- objects may have been allocated
8168 // but not yet initialized -- in the sense that the header isn't yet
8169 // installed. The sweeper can not then determine the size of the block
8170 // in order to skip over it. To deal with this case, we use a technique
8171 // (due to Printezis) to encode such uninitialized block sizes in the
8172 // bit map. Since the bit map uses a bit per every HeapWord, but the
8173 // CMS generation has a minimum object size of 3 HeapWords, it follows
8174 // that "normal marks" won't be adjacent in the bit map (there will
8175 // always be at least two 0 bits between successive 1 bits). We make use
8176 // of these "unused" bits to represent uninitialized blocks -- the bit
8177 // corresponding to the start of the uninitialized object and the next
8178 // bit are both set. Finally, a 1 bit marks the end of the object that
8179 // started with the two consecutive 1 bits to indicate its potentially
8180 // uninitialized state.
8181 
8182 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8183   FreeChunk* fc = (FreeChunk*)addr;
8184   size_t res;
8185 
8186   // Check if we are done sweeping. Below we check "addr >= _limit" rather
8187   // than "addr == _limit" because although _limit was a block boundary when
8188   // we started the sweep, it may no longer be one because heap expansion
8189   // may have caused us to coalesce the block ending at the address _limit
8190   // with a newly expanded chunk (this happens when _limit was set to the
8191   // previous _end of the space), so we may have stepped past _limit:
8192   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8193   if (addr >= _limit) { // we have swept up to or past the limit: finish up
8194     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8195            "sweep _limit out of bounds");
8196     assert(addr < _sp->end(), "addr out of bounds");
8197     // Flush any free range we might be holding as a single
8198     // coalesced chunk to the appropriate free list.
8199     if (inFreeRange()) {
8200       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8201              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8202       flush_cur_free_chunk(freeFinger(),
8203                            pointer_delta(addr, freeFinger()));
8204       if (CMSTraceSweeper) {
8205         gclog_or_tty->print("Sweep: last chunk: ");
8206         gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8207                    "[coalesced:%d]\n",
8208                    freeFinger(), pointer_delta(addr, freeFinger()),
8209                    lastFreeRangeCoalesced() ? 1 : 0);
8210       }
8211     }
8212 
8213     // help the iterator loop finish
8214     return pointer_delta(_sp->end(), addr);
8215   }
8216 
8217   assert(addr < _limit, "sweep invariant");
8218   // check if we should yield
8219   do_yield_check(addr);
8220   if (fc->is_free()) {
8221     // Chunk that is already free
8222     res = fc->size();
8223     do_already_free_chunk(fc);
8224     debug_only(_sp->verifyFreeLists());
8225     // If we flush the chunk at hand in lookahead_and_flush()
8226     // and it's coalesced with a preceding chunk, then the
8227     // process of "mangling" the payload of the coalesced block
8228     // will cause erasure of the size information from the
8229     // (erstwhile) header of all the coalesced blocks but the
8230     // first, so the first disjunct in the assert will not hold
8231     // in that specific case (in which case the second disjunct
8232     // will hold).
8233     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8234            "Otherwise the size info doesn't change at this step");
8235     NOT_PRODUCT(
8236       _numObjectsAlreadyFree++;
8237       _numWordsAlreadyFree += res;
8238     )
8239     NOT_PRODUCT(_last_fc = fc;)
8240   } else if (!_bitMap->isMarked(addr)) {
8241     // Chunk is fresh garbage
8242     res = do_garbage_chunk(fc);
8243     debug_only(_sp->verifyFreeLists());
8244     NOT_PRODUCT(
8245       _numObjectsFreed++;
8246       _numWordsFreed += res;
8247     )
8248   } else {
8249     // Chunk that is alive.
8250     res = do_live_chunk(fc);
8251     debug_only(_sp->verifyFreeLists());
8252     NOT_PRODUCT(
8253         _numObjectsLive++;
8254         _numWordsLive += res;
8255     )
8256   }
8257   return res;
8258 }
8259 
8260 // For the smart allocation, record following
8261 //  split deaths - a free chunk is removed from its free list because
8262 //      it is being split into two or more chunks.
8263 //  split birth - a free chunk is being added to its free list because
8264 //      a larger free chunk has been split and resulted in this free chunk.
8265 //  coal death - a free chunk is being removed from its free list because
8266 //      it is being coalesced into a large free chunk.
8267 //  coal birth - a free chunk is being added to its free list because
8268 //      it was created when two or more free chunks where coalesced into
8269 //      this free chunk.
8270 //
8271 // These statistics are used to determine the desired number of free
8272 // chunks of a given size.  The desired number is chosen to be relative
8273 // to the end of a CMS sweep.  The desired number at the end of a sweep
8274 // is the
8275 //      count-at-end-of-previous-sweep (an amount that was enough)
8276 //              - count-at-beginning-of-current-sweep  (the excess)
8277 //              + split-births  (gains in this size during interval)
8278 //              - split-deaths  (demands on this size during interval)
8279 // where the interval is from the end of one sweep to the end of the
8280 // next.
8281 //
8282 // When sweeping the sweeper maintains an accumulated chunk which is
8283 // the chunk that is made up of chunks that have been coalesced.  That
8284 // will be termed the left-hand chunk.  A new chunk of garbage that
8285 // is being considered for coalescing will be referred to as the
8286 // right-hand chunk.
8287 //
8288 // When making a decision on whether to coalesce a right-hand chunk with
8289 // the current left-hand chunk, the current count vs. the desired count
8290 // of the left-hand chunk is considered.  Also if the right-hand chunk
8291 // is near the large chunk at the end of the heap (see
8292 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8293 // left-hand chunk is coalesced.
8294 //
8295 // When making a decision about whether to split a chunk, the desired count
8296 // vs. the current count of the candidate to be split is also considered.
8297 // If the candidate is underpopulated (currently fewer chunks than desired)
8298 // a chunk of an overpopulated (currently more chunks than desired) size may
8299 // be chosen.  The "hint" associated with a free list, if non-null, points
8300 // to a free list which may be overpopulated.
8301 //
8302 
8303 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8304   const size_t size = fc->size();
8305   // Chunks that cannot be coalesced are not in the
8306   // free lists.
8307   if (CMSTestInFreeList && !fc->cantCoalesce()) {
8308     assert(_sp->verify_chunk_in_free_list(fc),
8309       "free chunk should be in free lists");
8310   }
8311   // a chunk that is already free, should not have been
8312   // marked in the bit map
8313   HeapWord* const addr = (HeapWord*) fc;
8314   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8315   // Verify that the bit map has no bits marked between
8316   // addr and purported end of this block.
8317   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8318 
8319   // Some chunks cannot be coalesced under any circumstances.
8320   // See the definition of cantCoalesce().
8321   if (!fc->cantCoalesce()) {
8322     // This chunk can potentially be coalesced.
8323     if (_sp->adaptive_freelists()) {
8324       // All the work is done in
8325       do_post_free_or_garbage_chunk(fc, size);
8326     } else {  // Not adaptive free lists
8327       // this is a free chunk that can potentially be coalesced by the sweeper;
8328       if (!inFreeRange()) {
8329         // if the next chunk is a free block that can't be coalesced
8330         // it doesn't make sense to remove this chunk from the free lists
8331         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8332         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8333         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
8334             nextChunk->is_free()               &&     // ... which is free...
8335             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
8336           // nothing to do
8337         } else {
8338           // Potentially the start of a new free range:
8339           // Don't eagerly remove it from the free lists.
8340           // No need to remove it if it will just be put
8341           // back again.  (Also from a pragmatic point of view
8342           // if it is a free block in a region that is beyond
8343           // any allocated blocks, an assertion will fail)
8344           // Remember the start of a free run.
8345           initialize_free_range(addr, true);
8346           // end - can coalesce with next chunk
8347         }
8348       } else {
8349         // the midst of a free range, we are coalescing
8350         print_free_block_coalesced(fc);
8351         if (CMSTraceSweeper) {
8352           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8353         }
8354         // remove it from the free lists
8355         _sp->removeFreeChunkFromFreeLists(fc);
8356         set_lastFreeRangeCoalesced(true);
8357         // If the chunk is being coalesced and the current free range is
8358         // in the free lists, remove the current free range so that it
8359         // will be returned to the free lists in its entirety - all
8360         // the coalesced pieces included.
8361         if (freeRangeInFreeLists()) {
8362           FreeChunk* ffc = (FreeChunk*) freeFinger();
8363           assert(ffc->size() == pointer_delta(addr, freeFinger()),
8364             "Size of free range is inconsistent with chunk size.");
8365           if (CMSTestInFreeList) {
8366             assert(_sp->verify_chunk_in_free_list(ffc),
8367               "free range is not in free lists");
8368           }
8369           _sp->removeFreeChunkFromFreeLists(ffc);
8370           set_freeRangeInFreeLists(false);
8371         }
8372       }
8373     }
8374     // Note that if the chunk is not coalescable (the else arm
8375     // below), we unconditionally flush, without needing to do
8376     // a "lookahead," as we do below.
8377     if (inFreeRange()) lookahead_and_flush(fc, size);
8378   } else {
8379     // Code path common to both original and adaptive free lists.
8380 
8381     // cant coalesce with previous block; this should be treated
8382     // as the end of a free run if any
8383     if (inFreeRange()) {
8384       // we kicked some butt; time to pick up the garbage
8385       assert(freeFinger() < addr, "freeFinger points too high");
8386       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8387     }
8388     // else, nothing to do, just continue
8389   }
8390 }
8391 
8392 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8393   // This is a chunk of garbage.  It is not in any free list.
8394   // Add it to a free list or let it possibly be coalesced into
8395   // a larger chunk.
8396   HeapWord* const addr = (HeapWord*) fc;
8397   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8398 
8399   if (_sp->adaptive_freelists()) {
8400     // Verify that the bit map has no bits marked between
8401     // addr and purported end of just dead object.
8402     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8403 
8404     do_post_free_or_garbage_chunk(fc, size);
8405   } else {
8406     if (!inFreeRange()) {
8407       // start of a new free range
8408       assert(size > 0, "A free range should have a size");
8409       initialize_free_range(addr, false);
8410     } else {
8411       // this will be swept up when we hit the end of the
8412       // free range
8413       if (CMSTraceSweeper) {
8414         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8415       }
8416       // If the chunk is being coalesced and the current free range is
8417       // in the free lists, remove the current free range so that it
8418       // will be returned to the free lists in its entirety - all
8419       // the coalesced pieces included.
8420       if (freeRangeInFreeLists()) {
8421         FreeChunk* ffc = (FreeChunk*)freeFinger();
8422         assert(ffc->size() == pointer_delta(addr, freeFinger()),
8423           "Size of free range is inconsistent with chunk size.");
8424         if (CMSTestInFreeList) {
8425           assert(_sp->verify_chunk_in_free_list(ffc),
8426             "free range is not in free lists");
8427         }
8428         _sp->removeFreeChunkFromFreeLists(ffc);
8429         set_freeRangeInFreeLists(false);
8430       }
8431       set_lastFreeRangeCoalesced(true);
8432     }
8433     // this will be swept up when we hit the end of the free range
8434 
8435     // Verify that the bit map has no bits marked between
8436     // addr and purported end of just dead object.
8437     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8438   }
8439   assert(_limit >= addr + size,
8440          "A freshly garbage chunk can't possibly straddle over _limit");
8441   if (inFreeRange()) lookahead_and_flush(fc, size);
8442   return size;
8443 }
8444 
8445 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8446   HeapWord* addr = (HeapWord*) fc;
8447   // The sweeper has just found a live object. Return any accumulated
8448   // left hand chunk to the free lists.
8449   if (inFreeRange()) {
8450     assert(freeFinger() < addr, "freeFinger points too high");
8451     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8452   }
8453 
8454   // This object is live: we'd normally expect this to be
8455   // an oop, and like to assert the following:
8456   // assert(oop(addr)->is_oop(), "live block should be an oop");
8457   // However, as we commented above, this may be an object whose
8458   // header hasn't yet been initialized.
8459   size_t size;
8460   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8461   if (_bitMap->isMarked(addr + 1)) {
8462     // Determine the size from the bit map, rather than trying to
8463     // compute it from the object header.
8464     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8465     size = pointer_delta(nextOneAddr + 1, addr);
8466     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8467            "alignment problem");
8468 
8469 #ifdef ASSERT
8470       if (oop(addr)->klass_or_null() != NULL) {
8471         // Ignore mark word because we are running concurrent with mutators
8472         assert(oop(addr)->is_oop(true), "live block should be an oop");
8473         assert(size ==
8474                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8475                "P-mark and computed size do not agree");
8476       }
8477 #endif
8478 
8479   } else {
8480     // This should be an initialized object that's alive.
8481     assert(oop(addr)->klass_or_null() != NULL,
8482            "Should be an initialized object");
8483     // Ignore mark word because we are running concurrent with mutators
8484     assert(oop(addr)->is_oop(true), "live block should be an oop");
8485     // Verify that the bit map has no bits marked between
8486     // addr and purported end of this block.
8487     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8488     assert(size >= 3, "Necessary for Printezis marks to work");
8489     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8490     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8491   }
8492   return size;
8493 }
8494 
8495 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8496                                                  size_t chunkSize) {
8497   // do_post_free_or_garbage_chunk() should only be called in the case
8498   // of the adaptive free list allocator.
8499   const bool fcInFreeLists = fc->is_free();
8500   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8501   assert((HeapWord*)fc <= _limit, "sweep invariant");
8502   if (CMSTestInFreeList && fcInFreeLists) {
8503     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8504   }
8505 
8506   if (CMSTraceSweeper) {
8507     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8508   }
8509 
8510   HeapWord* const fc_addr = (HeapWord*) fc;
8511 
8512   bool coalesce;
8513   const size_t left  = pointer_delta(fc_addr, freeFinger());
8514   const size_t right = chunkSize;
8515   switch (FLSCoalescePolicy) {
8516     // numeric value forms a coalition aggressiveness metric
8517     case 0:  { // never coalesce
8518       coalesce = false;
8519       break;
8520     }
8521     case 1: { // coalesce if left & right chunks on overpopulated lists
8522       coalesce = _sp->coalOverPopulated(left) &&
8523                  _sp->coalOverPopulated(right);
8524       break;
8525     }
8526     case 2: { // coalesce if left chunk on overpopulated list (default)
8527       coalesce = _sp->coalOverPopulated(left);
8528       break;
8529     }
8530     case 3: { // coalesce if left OR right chunk on overpopulated list
8531       coalesce = _sp->coalOverPopulated(left) ||
8532                  _sp->coalOverPopulated(right);
8533       break;
8534     }
8535     case 4: { // always coalesce
8536       coalesce = true;
8537       break;
8538     }
8539     default:
8540      ShouldNotReachHere();
8541   }
8542 
8543   // Should the current free range be coalesced?
8544   // If the chunk is in a free range and either we decided to coalesce above
8545   // or the chunk is near the large block at the end of the heap
8546   // (isNearLargestChunk() returns true), then coalesce this chunk.
8547   const bool doCoalesce = inFreeRange()
8548                           && (coalesce || _g->isNearLargestChunk(fc_addr));
8549   if (doCoalesce) {
8550     // Coalesce the current free range on the left with the new
8551     // chunk on the right.  If either is on a free list,
8552     // it must be removed from the list and stashed in the closure.
8553     if (freeRangeInFreeLists()) {
8554       FreeChunk* const ffc = (FreeChunk*)freeFinger();
8555       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8556         "Size of free range is inconsistent with chunk size.");
8557       if (CMSTestInFreeList) {
8558         assert(_sp->verify_chunk_in_free_list(ffc),
8559           "Chunk is not in free lists");
8560       }
8561       _sp->coalDeath(ffc->size());
8562       _sp->removeFreeChunkFromFreeLists(ffc);
8563       set_freeRangeInFreeLists(false);
8564     }
8565     if (fcInFreeLists) {
8566       _sp->coalDeath(chunkSize);
8567       assert(fc->size() == chunkSize,
8568         "The chunk has the wrong size or is not in the free lists");
8569       _sp->removeFreeChunkFromFreeLists(fc);
8570     }
8571     set_lastFreeRangeCoalesced(true);
8572     print_free_block_coalesced(fc);
8573   } else {  // not in a free range and/or should not coalesce
8574     // Return the current free range and start a new one.
8575     if (inFreeRange()) {
8576       // In a free range but cannot coalesce with the right hand chunk.
8577       // Put the current free range into the free lists.
8578       flush_cur_free_chunk(freeFinger(),
8579                            pointer_delta(fc_addr, freeFinger()));
8580     }
8581     // Set up for new free range.  Pass along whether the right hand
8582     // chunk is in the free lists.
8583     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8584   }
8585 }
8586 
8587 // Lookahead flush:
8588 // If we are tracking a free range, and this is the last chunk that
8589 // we'll look at because its end crosses past _limit, we'll preemptively
8590 // flush it along with any free range we may be holding on to. Note that
8591 // this can be the case only for an already free or freshly garbage
8592 // chunk. If this block is an object, it can never straddle
8593 // over _limit. The "straddling" occurs when _limit is set at
8594 // the previous end of the space when this cycle started, and
8595 // a subsequent heap expansion caused the previously co-terminal
8596 // free block to be coalesced with the newly expanded portion,
8597 // thus rendering _limit a non-block-boundary making it dangerous
8598 // for the sweeper to step over and examine.
8599 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8600   assert(inFreeRange(), "Should only be called if currently in a free range.");
8601   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8602   assert(_sp->used_region().contains(eob - 1),
8603          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8604                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8605                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8606                  eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8607   if (eob >= _limit) {
8608     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8609     if (CMSTraceSweeper) {
8610       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8611                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8612                              "[" PTR_FORMAT "," PTR_FORMAT ")",
8613                              _limit, fc, eob, _sp->bottom(), _sp->end());
8614     }
8615     // Return the storage we are tracking back into the free lists.
8616     if (CMSTraceSweeper) {
8617       gclog_or_tty->print_cr("Flushing ... ");
8618     }
8619     assert(freeFinger() < eob, "Error");
8620     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8621   }
8622 }
8623 
8624 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8625   assert(inFreeRange(), "Should only be called if currently in a free range.");
8626   assert(size > 0,
8627     "A zero sized chunk cannot be added to the free lists.");
8628   if (!freeRangeInFreeLists()) {
8629     if (CMSTestInFreeList) {
8630       FreeChunk* fc = (FreeChunk*) chunk;
8631       fc->set_size(size);
8632       assert(!_sp->verify_chunk_in_free_list(fc),
8633         "chunk should not be in free lists yet");
8634     }
8635     if (CMSTraceSweeper) {
8636       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8637                     chunk, size);
8638     }
8639     // A new free range is going to be starting.  The current
8640     // free range has not been added to the free lists yet or
8641     // was removed so add it back.
8642     // If the current free range was coalesced, then the death
8643     // of the free range was recorded.  Record a birth now.
8644     if (lastFreeRangeCoalesced()) {
8645       _sp->coalBirth(size);
8646     }
8647     _sp->addChunkAndRepairOffsetTable(chunk, size,
8648             lastFreeRangeCoalesced());
8649   } else if (CMSTraceSweeper) {
8650     gclog_or_tty->print_cr("Already in free list: nothing to flush");
8651   }
8652   set_inFreeRange(false);
8653   set_freeRangeInFreeLists(false);
8654 }
8655 
8656 // We take a break if we've been at this for a while,
8657 // so as to avoid monopolizing the locks involved.
8658 void SweepClosure::do_yield_work(HeapWord* addr) {
8659   // Return current free chunk being used for coalescing (if any)
8660   // to the appropriate freelist.  After yielding, the next
8661   // free block encountered will start a coalescing range of
8662   // free blocks.  If the next free block is adjacent to the
8663   // chunk just flushed, they will need to wait for the next
8664   // sweep to be coalesced.
8665   if (inFreeRange()) {
8666     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8667   }
8668 
8669   // First give up the locks, then yield, then re-lock.
8670   // We should probably use a constructor/destructor idiom to
8671   // do this unlock/lock or modify the MutexUnlocker class to
8672   // serve our purpose. XXX
8673   assert_lock_strong(_bitMap->lock());
8674   assert_lock_strong(_freelistLock);
8675   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8676          "CMS thread should hold CMS token");
8677   _bitMap->lock()->unlock();
8678   _freelistLock->unlock();
8679   ConcurrentMarkSweepThread::desynchronize(true);
8680   ConcurrentMarkSweepThread::acknowledge_yield_request();
8681   _collector->stopTimer();
8682   if (PrintCMSStatistics != 0) {
8683     _collector->incrementYields();
8684   }
8685   _collector->icms_wait();
8686 
8687   // See the comment in coordinator_yield()
8688   for (unsigned i = 0; i < CMSYieldSleepCount &&
8689                        ConcurrentMarkSweepThread::should_yield() &&
8690                        !CMSCollector::foregroundGCIsActive(); ++i) {
8691     os::sleep(Thread::current(), 1, false);
8692     ConcurrentMarkSweepThread::acknowledge_yield_request();
8693   }
8694 
8695   ConcurrentMarkSweepThread::synchronize(true);
8696   _freelistLock->lock();
8697   _bitMap->lock()->lock_without_safepoint_check();
8698   _collector->startTimer();
8699 }
8700 
8701 #ifndef PRODUCT
8702 // This is actually very useful in a product build if it can
8703 // be called from the debugger.  Compile it into the product
8704 // as needed.
8705 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8706   return debug_cms_space->verify_chunk_in_free_list(fc);
8707 }
8708 #endif
8709 
8710 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8711   if (CMSTraceSweeper) {
8712     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8713                            fc, fc->size());
8714   }
8715 }
8716 
8717 // CMSIsAliveClosure
8718 bool CMSIsAliveClosure::do_object_b(oop obj) {
8719   HeapWord* addr = (HeapWord*)obj;
8720   return addr != NULL &&
8721          (!_span.contains(addr) || _bit_map->isMarked(addr));
8722 }
8723 
8724 
8725 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8726                       MemRegion span,
8727                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8728                       bool cpc):
8729   _collector(collector),
8730   _span(span),
8731   _bit_map(bit_map),
8732   _mark_stack(mark_stack),
8733   _concurrent_precleaning(cpc) {
8734   assert(!_span.is_empty(), "Empty span could spell trouble");
8735 }
8736 
8737 
8738 // CMSKeepAliveClosure: the serial version
8739 void CMSKeepAliveClosure::do_oop(oop obj) {
8740   HeapWord* addr = (HeapWord*)obj;
8741   if (_span.contains(addr) &&
8742       !_bit_map->isMarked(addr)) {
8743     _bit_map->mark(addr);
8744     bool simulate_overflow = false;
8745     NOT_PRODUCT(
8746       if (CMSMarkStackOverflowALot &&
8747           _collector->simulate_overflow()) {
8748         // simulate a stack overflow
8749         simulate_overflow = true;
8750       }
8751     )
8752     if (simulate_overflow || !_mark_stack->push(obj)) {
8753       if (_concurrent_precleaning) {
8754         // We dirty the overflown object and let the remark
8755         // phase deal with it.
8756         assert(_collector->overflow_list_is_empty(), "Error");
8757         // In the case of object arrays, we need to dirty all of
8758         // the cards that the object spans. No locking or atomics
8759         // are needed since no one else can be mutating the mod union
8760         // table.
8761         if (obj->is_objArray()) {
8762           size_t sz = obj->size();
8763           HeapWord* end_card_addr =
8764             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8765           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8766           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8767           _collector->_modUnionTable.mark_range(redirty_range);
8768         } else {
8769           _collector->_modUnionTable.mark(addr);
8770         }
8771         _collector->_ser_kac_preclean_ovflw++;
8772       } else {
8773         _collector->push_on_overflow_list(obj);
8774         _collector->_ser_kac_ovflw++;
8775       }
8776     }
8777   }
8778 }
8779 
8780 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8781 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8782 
8783 // CMSParKeepAliveClosure: a parallel version of the above.
8784 // The work queues are private to each closure (thread),
8785 // but (may be) available for stealing by other threads.
8786 void CMSParKeepAliveClosure::do_oop(oop obj) {
8787   HeapWord* addr = (HeapWord*)obj;
8788   if (_span.contains(addr) &&
8789       !_bit_map->isMarked(addr)) {
8790     // In general, during recursive tracing, several threads
8791     // may be concurrently getting here; the first one to
8792     // "tag" it, claims it.
8793     if (_bit_map->par_mark(addr)) {
8794       bool res = _work_queue->push(obj);
8795       assert(res, "Low water mark should be much less than capacity");
8796       // Do a recursive trim in the hope that this will keep
8797       // stack usage lower, but leave some oops for potential stealers
8798       trim_queue(_low_water_mark);
8799     } // Else, another thread got there first
8800   }
8801 }
8802 
8803 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8804 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8805 
8806 void CMSParKeepAliveClosure::trim_queue(uint max) {
8807   while (_work_queue->size() > max) {
8808     oop new_oop;
8809     if (_work_queue->pop_local(new_oop)) {
8810       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8811       assert(_bit_map->isMarked((HeapWord*)new_oop),
8812              "no white objects on this stack!");
8813       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8814       // iterate over the oops in this oop, marking and pushing
8815       // the ones in CMS heap (i.e. in _span).
8816       new_oop->oop_iterate(&_mark_and_push);
8817     }
8818   }
8819 }
8820 
8821 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8822                                 CMSCollector* collector,
8823                                 MemRegion span, CMSBitMap* bit_map,
8824                                 OopTaskQueue* work_queue):
8825   _collector(collector),
8826   _span(span),
8827   _bit_map(bit_map),
8828   _work_queue(work_queue) { }
8829 
8830 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8831   HeapWord* addr = (HeapWord*)obj;
8832   if (_span.contains(addr) &&
8833       !_bit_map->isMarked(addr)) {
8834     if (_bit_map->par_mark(addr)) {
8835       bool simulate_overflow = false;
8836       NOT_PRODUCT(
8837         if (CMSMarkStackOverflowALot &&
8838             _collector->par_simulate_overflow()) {
8839           // simulate a stack overflow
8840           simulate_overflow = true;
8841         }
8842       )
8843       if (simulate_overflow || !_work_queue->push(obj)) {
8844         _collector->par_push_on_overflow_list(obj);
8845         _collector->_par_kac_ovflw++;
8846       }
8847     } // Else another thread got there already
8848   }
8849 }
8850 
8851 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8852 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8853 
8854 //////////////////////////////////////////////////////////////////
8855 //  CMSExpansionCause                /////////////////////////////
8856 //////////////////////////////////////////////////////////////////
8857 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8858   switch (cause) {
8859     case _no_expansion:
8860       return "No expansion";
8861     case _satisfy_free_ratio:
8862       return "Free ratio";
8863     case _satisfy_promotion:
8864       return "Satisfy promotion";
8865     case _satisfy_allocation:
8866       return "allocation";
8867     case _allocate_par_lab:
8868       return "Par LAB";
8869     case _allocate_par_spooling_space:
8870       return "Par Spooling Space";
8871     case _adaptive_size_policy:
8872       return "Ergonomics";
8873     default:
8874       return "unknown";
8875   }
8876 }
8877 
8878 void CMSDrainMarkingStackClosure::do_void() {
8879   // the max number to take from overflow list at a time
8880   const size_t num = _mark_stack->capacity()/4;
8881   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8882          "Overflow list should be NULL during concurrent phases");
8883   while (!_mark_stack->isEmpty() ||
8884          // if stack is empty, check the overflow list
8885          _collector->take_from_overflow_list(num, _mark_stack)) {
8886     oop obj = _mark_stack->pop();
8887     HeapWord* addr = (HeapWord*)obj;
8888     assert(_span.contains(addr), "Should be within span");
8889     assert(_bit_map->isMarked(addr), "Should be marked");
8890     assert(obj->is_oop(), "Should be an oop");
8891     obj->oop_iterate(_keep_alive);
8892   }
8893 }
8894 
8895 void CMSParDrainMarkingStackClosure::do_void() {
8896   // drain queue
8897   trim_queue(0);
8898 }
8899 
8900 // Trim our work_queue so its length is below max at return
8901 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8902   while (_work_queue->size() > max) {
8903     oop new_oop;
8904     if (_work_queue->pop_local(new_oop)) {
8905       assert(new_oop->is_oop(), "Expected an oop");
8906       assert(_bit_map->isMarked((HeapWord*)new_oop),
8907              "no white objects on this stack!");
8908       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8909       // iterate over the oops in this oop, marking and pushing
8910       // the ones in CMS heap (i.e. in _span).
8911       new_oop->oop_iterate(&_mark_and_push);
8912     }
8913   }
8914 }
8915 
8916 ////////////////////////////////////////////////////////////////////
8917 // Support for Marking Stack Overflow list handling and related code
8918 ////////////////////////////////////////////////////////////////////
8919 // Much of the following code is similar in shape and spirit to the
8920 // code used in ParNewGC. We should try and share that code
8921 // as much as possible in the future.
8922 
8923 #ifndef PRODUCT
8924 // Debugging support for CMSStackOverflowALot
8925 
8926 // It's OK to call this multi-threaded;  the worst thing
8927 // that can happen is that we'll get a bunch of closely
8928 // spaced simulated overflows, but that's OK, in fact
8929 // probably good as it would exercise the overflow code
8930 // under contention.
8931 bool CMSCollector::simulate_overflow() {
8932   if (_overflow_counter-- <= 0) { // just being defensive
8933     _overflow_counter = CMSMarkStackOverflowInterval;
8934     return true;
8935   } else {
8936     return false;
8937   }
8938 }
8939 
8940 bool CMSCollector::par_simulate_overflow() {
8941   return simulate_overflow();
8942 }
8943 #endif
8944 
8945 // Single-threaded
8946 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8947   assert(stack->isEmpty(), "Expected precondition");
8948   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8949   size_t i = num;
8950   oop  cur = _overflow_list;
8951   const markOop proto = markOopDesc::prototype();
8952   NOT_PRODUCT(ssize_t n = 0;)
8953   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8954     next = oop(cur->mark());
8955     cur->set_mark(proto);   // until proven otherwise
8956     assert(cur->is_oop(), "Should be an oop");
8957     bool res = stack->push(cur);
8958     assert(res, "Bit off more than can chew?");
8959     NOT_PRODUCT(n++;)
8960   }
8961   _overflow_list = cur;
8962 #ifndef PRODUCT
8963   assert(_num_par_pushes >= n, "Too many pops?");
8964   _num_par_pushes -=n;
8965 #endif
8966   return !stack->isEmpty();
8967 }
8968 
8969 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8970 // (MT-safe) Get a prefix of at most "num" from the list.
8971 // The overflow list is chained through the mark word of
8972 // each object in the list. We fetch the entire list,
8973 // break off a prefix of the right size and return the
8974 // remainder. If other threads try to take objects from
8975 // the overflow list at that time, they will wait for
8976 // some time to see if data becomes available. If (and
8977 // only if) another thread places one or more object(s)
8978 // on the global list before we have returned the suffix
8979 // to the global list, we will walk down our local list
8980 // to find its end and append the global list to
8981 // our suffix before returning it. This suffix walk can
8982 // prove to be expensive (quadratic in the amount of traffic)
8983 // when there are many objects in the overflow list and
8984 // there is much producer-consumer contention on the list.
8985 // *NOTE*: The overflow list manipulation code here and
8986 // in ParNewGeneration:: are very similar in shape,
8987 // except that in the ParNew case we use the old (from/eden)
8988 // copy of the object to thread the list via its klass word.
8989 // Because of the common code, if you make any changes in
8990 // the code below, please check the ParNew version to see if
8991 // similar changes might be needed.
8992 // CR 6797058 has been filed to consolidate the common code.
8993 bool CMSCollector::par_take_from_overflow_list(size_t num,
8994                                                OopTaskQueue* work_q,
8995                                                int no_of_gc_threads) {
8996   assert(work_q->size() == 0, "First empty local work queue");
8997   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8998   if (_overflow_list == NULL) {
8999     return false;
9000   }
9001   // Grab the entire list; we'll put back a suffix
9002   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9003   Thread* tid = Thread::current();
9004   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9005   // set to ParallelGCThreads.
9006   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9007   size_t sleep_time_millis = MAX2((size_t)1, num/100);
9008   // If the list is busy, we spin for a short while,
9009   // sleeping between attempts to get the list.
9010   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9011     os::sleep(tid, sleep_time_millis, false);
9012     if (_overflow_list == NULL) {
9013       // Nothing left to take
9014       return false;
9015     } else if (_overflow_list != BUSY) {
9016       // Try and grab the prefix
9017       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9018     }
9019   }
9020   // If the list was found to be empty, or we spun long
9021   // enough, we give up and return empty-handed. If we leave
9022   // the list in the BUSY state below, it must be the case that
9023   // some other thread holds the overflow list and will set it
9024   // to a non-BUSY state in the future.
9025   if (prefix == NULL || prefix == BUSY) {
9026      // Nothing to take or waited long enough
9027      if (prefix == NULL) {
9028        // Write back the NULL in case we overwrote it with BUSY above
9029        // and it is still the same value.
9030        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9031      }
9032      return false;
9033   }
9034   assert(prefix != NULL && prefix != BUSY, "Error");
9035   size_t i = num;
9036   oop cur = prefix;
9037   // Walk down the first "num" objects, unless we reach the end.
9038   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9039   if (cur->mark() == NULL) {
9040     // We have "num" or fewer elements in the list, so there
9041     // is nothing to return to the global list.
9042     // Write back the NULL in lieu of the BUSY we wrote
9043     // above, if it is still the same value.
9044     if (_overflow_list == BUSY) {
9045       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9046     }
9047   } else {
9048     // Chop off the suffix and return it to the global list.
9049     assert(cur->mark() != BUSY, "Error");
9050     oop suffix_head = cur->mark(); // suffix will be put back on global list
9051     cur->set_mark(NULL);           // break off suffix
9052     // It's possible that the list is still in the empty(busy) state
9053     // we left it in a short while ago; in that case we may be
9054     // able to place back the suffix without incurring the cost
9055     // of a walk down the list.
9056     oop observed_overflow_list = _overflow_list;
9057     oop cur_overflow_list = observed_overflow_list;
9058     bool attached = false;
9059     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9060       observed_overflow_list =
9061         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9062       if (cur_overflow_list == observed_overflow_list) {
9063         attached = true;
9064         break;
9065       } else cur_overflow_list = observed_overflow_list;
9066     }
9067     if (!attached) {
9068       // Too bad, someone else sneaked in (at least) an element; we'll need
9069       // to do a splice. Find tail of suffix so we can prepend suffix to global
9070       // list.
9071       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9072       oop suffix_tail = cur;
9073       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9074              "Tautology");
9075       observed_overflow_list = _overflow_list;
9076       do {
9077         cur_overflow_list = observed_overflow_list;
9078         if (cur_overflow_list != BUSY) {
9079           // Do the splice ...
9080           suffix_tail->set_mark(markOop(cur_overflow_list));
9081         } else { // cur_overflow_list == BUSY
9082           suffix_tail->set_mark(NULL);
9083         }
9084         // ... and try to place spliced list back on overflow_list ...
9085         observed_overflow_list =
9086           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9087       } while (cur_overflow_list != observed_overflow_list);
9088       // ... until we have succeeded in doing so.
9089     }
9090   }
9091 
9092   // Push the prefix elements on work_q
9093   assert(prefix != NULL, "control point invariant");
9094   const markOop proto = markOopDesc::prototype();
9095   oop next;
9096   NOT_PRODUCT(ssize_t n = 0;)
9097   for (cur = prefix; cur != NULL; cur = next) {
9098     next = oop(cur->mark());
9099     cur->set_mark(proto);   // until proven otherwise
9100     assert(cur->is_oop(), "Should be an oop");
9101     bool res = work_q->push(cur);
9102     assert(res, "Bit off more than we can chew?");
9103     NOT_PRODUCT(n++;)
9104   }
9105 #ifndef PRODUCT
9106   assert(_num_par_pushes >= n, "Too many pops?");
9107   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9108 #endif
9109   return true;
9110 }
9111 
9112 // Single-threaded
9113 void CMSCollector::push_on_overflow_list(oop p) {
9114   NOT_PRODUCT(_num_par_pushes++;)
9115   assert(p->is_oop(), "Not an oop");
9116   preserve_mark_if_necessary(p);
9117   p->set_mark((markOop)_overflow_list);
9118   _overflow_list = p;
9119 }
9120 
9121 // Multi-threaded; use CAS to prepend to overflow list
9122 void CMSCollector::par_push_on_overflow_list(oop p) {
9123   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9124   assert(p->is_oop(), "Not an oop");
9125   par_preserve_mark_if_necessary(p);
9126   oop observed_overflow_list = _overflow_list;
9127   oop cur_overflow_list;
9128   do {
9129     cur_overflow_list = observed_overflow_list;
9130     if (cur_overflow_list != BUSY) {
9131       p->set_mark(markOop(cur_overflow_list));
9132     } else {
9133       p->set_mark(NULL);
9134     }
9135     observed_overflow_list =
9136       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9137   } while (cur_overflow_list != observed_overflow_list);
9138 }
9139 #undef BUSY
9140 
9141 // Single threaded
9142 // General Note on GrowableArray: pushes may silently fail
9143 // because we are (temporarily) out of C-heap for expanding
9144 // the stack. The problem is quite ubiquitous and affects
9145 // a lot of code in the JVM. The prudent thing for GrowableArray
9146 // to do (for now) is to exit with an error. However, that may
9147 // be too draconian in some cases because the caller may be
9148 // able to recover without much harm. For such cases, we
9149 // should probably introduce a "soft_push" method which returns
9150 // an indication of success or failure with the assumption that
9151 // the caller may be able to recover from a failure; code in
9152 // the VM can then be changed, incrementally, to deal with such
9153 // failures where possible, thus, incrementally hardening the VM
9154 // in such low resource situations.
9155 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9156   _preserved_oop_stack.push(p);
9157   _preserved_mark_stack.push(m);
9158   assert(m == p->mark(), "Mark word changed");
9159   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9160          "bijection");
9161 }
9162 
9163 // Single threaded
9164 void CMSCollector::preserve_mark_if_necessary(oop p) {
9165   markOop m = p->mark();
9166   if (m->must_be_preserved(p)) {
9167     preserve_mark_work(p, m);
9168   }
9169 }
9170 
9171 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9172   markOop m = p->mark();
9173   if (m->must_be_preserved(p)) {
9174     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9175     // Even though we read the mark word without holding
9176     // the lock, we are assured that it will not change
9177     // because we "own" this oop, so no other thread can
9178     // be trying to push it on the overflow list; see
9179     // the assertion in preserve_mark_work() that checks
9180     // that m == p->mark().
9181     preserve_mark_work(p, m);
9182   }
9183 }
9184 
9185 // We should be able to do this multi-threaded,
9186 // a chunk of stack being a task (this is
9187 // correct because each oop only ever appears
9188 // once in the overflow list. However, it's
9189 // not very easy to completely overlap this with
9190 // other operations, so will generally not be done
9191 // until all work's been completed. Because we
9192 // expect the preserved oop stack (set) to be small,
9193 // it's probably fine to do this single-threaded.
9194 // We can explore cleverer concurrent/overlapped/parallel
9195 // processing of preserved marks if we feel the
9196 // need for this in the future. Stack overflow should
9197 // be so rare in practice and, when it happens, its
9198 // effect on performance so great that this will
9199 // likely just be in the noise anyway.
9200 void CMSCollector::restore_preserved_marks_if_any() {
9201   assert(SafepointSynchronize::is_at_safepoint(),
9202          "world should be stopped");
9203   assert(Thread::current()->is_ConcurrentGC_thread() ||
9204          Thread::current()->is_VM_thread(),
9205          "should be single-threaded");
9206   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9207          "bijection");
9208 
9209   while (!_preserved_oop_stack.is_empty()) {
9210     oop p = _preserved_oop_stack.pop();
9211     assert(p->is_oop(), "Should be an oop");
9212     assert(_span.contains(p), "oop should be in _span");
9213     assert(p->mark() == markOopDesc::prototype(),
9214            "Set when taken from overflow list");
9215     markOop m = _preserved_mark_stack.pop();
9216     p->set_mark(m);
9217   }
9218   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9219          "stacks were cleared above");
9220 }
9221 
9222 #ifndef PRODUCT
9223 bool CMSCollector::no_preserved_marks() const {
9224   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9225 }
9226 #endif
9227 
9228 // Transfer some number of overflown objects to usual marking
9229 // stack. Return true if some objects were transferred.
9230 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9231   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9232                     (size_t)ParGCDesiredObjsFromOverflowList);
9233 
9234   bool res = _collector->take_from_overflow_list(num, _mark_stack);
9235   assert(_collector->overflow_list_is_empty() || res,
9236          "If list is not empty, we should have taken something");
9237   assert(!res || !_mark_stack->isEmpty(),
9238          "If we took something, it should now be on our stack");
9239   return res;
9240 }
9241 
9242 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9243   size_t res = _sp->block_size_no_stall(addr, _collector);
9244   if (_sp->block_is_obj(addr)) {
9245     if (_live_bit_map->isMarked(addr)) {
9246       // It can't have been dead in a previous cycle
9247       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9248     } else {
9249       _dead_bit_map->mark(addr);      // mark the dead object
9250     }
9251   }
9252   // Could be 0, if the block size could not be computed without stalling.
9253   return res;
9254 }
9255 
9256 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9257 
9258   switch (phase) {
9259     case CMSCollector::InitialMarking:
9260       initialize(true  /* fullGC */ ,
9261                  cause /* cause of the GC */,
9262                  true  /* recordGCBeginTime */,
9263                  true  /* recordPreGCUsage */,
9264                  false /* recordPeakUsage */,
9265                  false /* recordPostGCusage */,
9266                  true  /* recordAccumulatedGCTime */,
9267                  false /* recordGCEndTime */,
9268                  false /* countCollection */  );
9269       break;
9270 
9271     case CMSCollector::FinalMarking:
9272       initialize(true  /* fullGC */ ,
9273                  cause /* cause of the GC */,
9274                  false /* recordGCBeginTime */,
9275                  false /* recordPreGCUsage */,
9276                  false /* recordPeakUsage */,
9277                  false /* recordPostGCusage */,
9278                  true  /* recordAccumulatedGCTime */,
9279                  false /* recordGCEndTime */,
9280                  false /* countCollection */  );
9281       break;
9282 
9283     case CMSCollector::Sweeping:
9284       initialize(true  /* fullGC */ ,
9285                  cause /* cause of the GC */,
9286                  false /* recordGCBeginTime */,
9287                  false /* recordPreGCUsage */,
9288                  true  /* recordPeakUsage */,
9289                  true  /* recordPostGCusage */,
9290                  false /* recordAccumulatedGCTime */,
9291                  true  /* recordGCEndTime */,
9292                  true  /* countCollection */  );
9293       break;
9294 
9295     default:
9296       ShouldNotReachHere();
9297   }
9298 }