1 /* 2 * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/classLoaderData.hpp" 27 #include "classfile/stringTable.hpp" 28 #include "classfile/symbolTable.hpp" 29 #include "classfile/systemDictionary.hpp" 30 #include "code/codeCache.hpp" 31 #include "gc/cms/cmsCollectorPolicy.hpp" 32 #include "gc/cms/cmsGCStats.hpp" 33 #include "gc/cms/cmsHeap.hpp" 34 #include "gc/cms/cmsOopClosures.inline.hpp" 35 #include "gc/cms/compactibleFreeListSpace.hpp" 36 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp" 37 #include "gc/cms/concurrentMarkSweepThread.hpp" 38 #include "gc/cms/parNewGeneration.hpp" 39 #include "gc/cms/vmCMSOperations.hpp" 40 #include "gc/serial/genMarkSweep.hpp" 41 #include "gc/serial/tenuredGeneration.hpp" 42 #include "gc/shared/adaptiveSizePolicy.hpp" 43 #include "gc/shared/cardGeneration.inline.hpp" 44 #include "gc/shared/cardTableRS.hpp" 45 #include "gc/shared/collectedHeap.inline.hpp" 46 #include "gc/shared/collectorCounters.hpp" 47 #include "gc/shared/collectorPolicy.hpp" 48 #include "gc/shared/gcLocker.hpp" 49 #include "gc/shared/gcPolicyCounters.hpp" 50 #include "gc/shared/gcTimer.hpp" 51 #include "gc/shared/gcTrace.hpp" 52 #include "gc/shared/gcTraceTime.inline.hpp" 53 #include "gc/shared/genCollectedHeap.hpp" 54 #include "gc/shared/genOopClosures.inline.hpp" 55 #include "gc/shared/isGCActiveMark.hpp" 56 #include "gc/shared/referencePolicy.hpp" 57 #include "gc/shared/strongRootsScope.hpp" 58 #include "gc/shared/taskqueue.inline.hpp" 59 #include "gc/shared/weakProcessor.hpp" 60 #include "logging/log.hpp" 61 #include "logging/logStream.hpp" 62 #include "memory/allocation.hpp" 63 #include "memory/binaryTreeDictionary.inline.hpp" 64 #include "memory/iterator.inline.hpp" 65 #include "memory/padded.hpp" 66 #include "memory/resourceArea.hpp" 67 #include "oops/access.inline.hpp" 68 #include "oops/oop.inline.hpp" 69 #include "prims/jvmtiExport.hpp" 70 #include "runtime/atomic.hpp" 71 #include "runtime/flags/flagSetting.hpp" 72 #include "runtime/globals_extension.hpp" 73 #include "runtime/handles.inline.hpp" 74 #include "runtime/java.hpp" 75 #include "runtime/orderAccess.inline.hpp" 76 #include "runtime/timer.hpp" 77 #include "runtime/vmThread.hpp" 78 #include "services/memoryService.hpp" 79 #include "services/runtimeService.hpp" 80 #include "utilities/align.hpp" 81 #include "utilities/stack.inline.hpp" 82 83 // statics 84 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; 85 bool CMSCollector::_full_gc_requested = false; 86 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc; 87 88 ////////////////////////////////////////////////////////////////// 89 // In support of CMS/VM thread synchronization 90 ////////////////////////////////////////////////////////////////// 91 // We split use of the CGC_lock into 2 "levels". 92 // The low-level locking is of the usual CGC_lock monitor. We introduce 93 // a higher level "token" (hereafter "CMS token") built on top of the 94 // low level monitor (hereafter "CGC lock"). 95 // The token-passing protocol gives priority to the VM thread. The 96 // CMS-lock doesn't provide any fairness guarantees, but clients 97 // should ensure that it is only held for very short, bounded 98 // durations. 99 // 100 // When either of the CMS thread or the VM thread is involved in 101 // collection operations during which it does not want the other 102 // thread to interfere, it obtains the CMS token. 103 // 104 // If either thread tries to get the token while the other has 105 // it, that thread waits. However, if the VM thread and CMS thread 106 // both want the token, then the VM thread gets priority while the 107 // CMS thread waits. This ensures, for instance, that the "concurrent" 108 // phases of the CMS thread's work do not block out the VM thread 109 // for long periods of time as the CMS thread continues to hog 110 // the token. (See bug 4616232). 111 // 112 // The baton-passing functions are, however, controlled by the 113 // flags _foregroundGCShouldWait and _foregroundGCIsActive, 114 // and here the low-level CMS lock, not the high level token, 115 // ensures mutual exclusion. 116 // 117 // Two important conditions that we have to satisfy: 118 // 1. if a thread does a low-level wait on the CMS lock, then it 119 // relinquishes the CMS token if it were holding that token 120 // when it acquired the low-level CMS lock. 121 // 2. any low-level notifications on the low-level lock 122 // should only be sent when a thread has relinquished the token. 123 // 124 // In the absence of either property, we'd have potential deadlock. 125 // 126 // We protect each of the CMS (concurrent and sequential) phases 127 // with the CMS _token_, not the CMS _lock_. 128 // 129 // The only code protected by CMS lock is the token acquisition code 130 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the 131 // baton-passing code. 132 // 133 // Unfortunately, i couldn't come up with a good abstraction to factor and 134 // hide the naked CGC_lock manipulation in the baton-passing code 135 // further below. That's something we should try to do. Also, the proof 136 // of correctness of this 2-level locking scheme is far from obvious, 137 // and potentially quite slippery. We have an uneasy suspicion, for instance, 138 // that there may be a theoretical possibility of delay/starvation in the 139 // low-level lock/wait/notify scheme used for the baton-passing because of 140 // potential interference with the priority scheme embodied in the 141 // CMS-token-passing protocol. See related comments at a CGC_lock->wait() 142 // invocation further below and marked with "XXX 20011219YSR". 143 // Indeed, as we note elsewhere, this may become yet more slippery 144 // in the presence of multiple CMS and/or multiple VM threads. XXX 145 146 class CMSTokenSync: public StackObj { 147 private: 148 bool _is_cms_thread; 149 public: 150 CMSTokenSync(bool is_cms_thread): 151 _is_cms_thread(is_cms_thread) { 152 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), 153 "Incorrect argument to constructor"); 154 ConcurrentMarkSweepThread::synchronize(_is_cms_thread); 155 } 156 157 ~CMSTokenSync() { 158 assert(_is_cms_thread ? 159 ConcurrentMarkSweepThread::cms_thread_has_cms_token() : 160 ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 161 "Incorrect state"); 162 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); 163 } 164 }; 165 166 // Convenience class that does a CMSTokenSync, and then acquires 167 // upto three locks. 168 class CMSTokenSyncWithLocks: public CMSTokenSync { 169 private: 170 // Note: locks are acquired in textual declaration order 171 // and released in the opposite order 172 MutexLockerEx _locker1, _locker2, _locker3; 173 public: 174 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, 175 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): 176 CMSTokenSync(is_cms_thread), 177 _locker1(mutex1, Mutex::_no_safepoint_check_flag), 178 _locker2(mutex2, Mutex::_no_safepoint_check_flag), 179 _locker3(mutex3, Mutex::_no_safepoint_check_flag) 180 { } 181 }; 182 183 184 ////////////////////////////////////////////////////////////////// 185 // Concurrent Mark-Sweep Generation ///////////////////////////// 186 ////////////////////////////////////////////////////////////////// 187 188 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) 189 190 // This struct contains per-thread things necessary to support parallel 191 // young-gen collection. 192 class CMSParGCThreadState: public CHeapObj<mtGC> { 193 public: 194 CompactibleFreeListSpaceLAB lab; 195 PromotionInfo promo; 196 197 // Constructor. 198 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { 199 promo.setSpace(cfls); 200 } 201 }; 202 203 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( 204 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) : 205 CardGeneration(rs, initial_byte_size, ct), 206 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), 207 _did_compact(false) 208 { 209 HeapWord* bottom = (HeapWord*) _virtual_space.low(); 210 HeapWord* end = (HeapWord*) _virtual_space.high(); 211 212 _direct_allocated_words = 0; 213 NOT_PRODUCT( 214 _numObjectsPromoted = 0; 215 _numWordsPromoted = 0; 216 _numObjectsAllocated = 0; 217 _numWordsAllocated = 0; 218 ) 219 220 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end)); 221 NOT_PRODUCT(debug_cms_space = _cmsSpace;) 222 _cmsSpace->_old_gen = this; 223 224 _gc_stats = new CMSGCStats(); 225 226 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass 227 // offsets match. The ability to tell free chunks from objects 228 // depends on this property. 229 debug_only( 230 FreeChunk* junk = NULL; 231 assert(UseCompressedClassPointers || 232 junk->prev_addr() == (void*)(oop(junk)->klass_addr()), 233 "Offset of FreeChunk::_prev within FreeChunk must match" 234 " that of OopDesc::_klass within OopDesc"); 235 ) 236 237 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC); 238 for (uint i = 0; i < ParallelGCThreads; i++) { 239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); 240 } 241 242 _incremental_collection_failed = false; 243 // The "dilatation_factor" is the expansion that can occur on 244 // account of the fact that the minimum object size in the CMS 245 // generation may be larger than that in, say, a contiguous young 246 // generation. 247 // Ideally, in the calculation below, we'd compute the dilatation 248 // factor as: MinChunkSize/(promoting_gen's min object size) 249 // Since we do not have such a general query interface for the 250 // promoting generation, we'll instead just use the minimum 251 // object size (which today is a header's worth of space); 252 // note that all arithmetic is in units of HeapWords. 253 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking"); 254 assert(_dilatation_factor >= 1.0, "from previous assert"); 255 } 256 257 258 // The field "_initiating_occupancy" represents the occupancy percentage 259 // at which we trigger a new collection cycle. Unless explicitly specified 260 // via CMSInitiatingOccupancyFraction (argument "io" below), it 261 // is calculated by: 262 // 263 // Let "f" be MinHeapFreeRatio in 264 // 265 // _initiating_occupancy = 100-f + 266 // f * (CMSTriggerRatio/100) 267 // where CMSTriggerRatio is the argument "tr" below. 268 // 269 // That is, if we assume the heap is at its desired maximum occupancy at the 270 // end of a collection, we let CMSTriggerRatio of the (purported) free 271 // space be allocated before initiating a new collection cycle. 272 // 273 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) { 274 assert(io <= 100 && tr <= 100, "Check the arguments"); 275 if (io >= 0) { 276 _initiating_occupancy = (double)io / 100.0; 277 } else { 278 _initiating_occupancy = ((100 - MinHeapFreeRatio) + 279 (double)(tr * MinHeapFreeRatio) / 100.0) 280 / 100.0; 281 } 282 } 283 284 void ConcurrentMarkSweepGeneration::ref_processor_init() { 285 assert(collector() != NULL, "no collector"); 286 collector()->ref_processor_init(); 287 } 288 289 void CMSCollector::ref_processor_init() { 290 if (_ref_processor == NULL) { 291 // Allocate and initialize a reference processor 292 _ref_processor = 293 new ReferenceProcessor(_span, // span 294 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing 295 ParallelGCThreads, // mt processing degree 296 _cmsGen->refs_discovery_is_mt(), // mt discovery 297 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree 298 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic 299 &_is_alive_closure); // closure for liveness info 300 // Initialize the _ref_processor field of CMSGen 301 _cmsGen->set_ref_processor(_ref_processor); 302 303 } 304 } 305 306 AdaptiveSizePolicy* CMSCollector::size_policy() { 307 return CMSHeap::heap()->size_policy(); 308 } 309 310 void ConcurrentMarkSweepGeneration::initialize_performance_counters() { 311 312 const char* gen_name = "old"; 313 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy(); 314 // Generation Counters - generation 1, 1 subspace 315 _gen_counters = new GenerationCounters(gen_name, 1, 1, 316 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space); 317 318 _space_counters = new GSpaceCounters(gen_name, 0, 319 _virtual_space.reserved_size(), 320 this, _gen_counters); 321 } 322 323 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): 324 _cms_gen(cms_gen) 325 { 326 assert(alpha <= 100, "bad value"); 327 _saved_alpha = alpha; 328 329 // Initialize the alphas to the bootstrap value of 100. 330 _gc0_alpha = _cms_alpha = 100; 331 332 _cms_begin_time.update(); 333 _cms_end_time.update(); 334 335 _gc0_duration = 0.0; 336 _gc0_period = 0.0; 337 _gc0_promoted = 0; 338 339 _cms_duration = 0.0; 340 _cms_period = 0.0; 341 _cms_allocated = 0; 342 343 _cms_used_at_gc0_begin = 0; 344 _cms_used_at_gc0_end = 0; 345 _allow_duty_cycle_reduction = false; 346 _valid_bits = 0; 347 } 348 349 double CMSStats::cms_free_adjustment_factor(size_t free) const { 350 // TBD: CR 6909490 351 return 1.0; 352 } 353 354 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) { 355 } 356 357 // If promotion failure handling is on use 358 // the padded average size of the promotion for each 359 // young generation collection. 360 double CMSStats::time_until_cms_gen_full() const { 361 size_t cms_free = _cms_gen->cmsSpace()->free(); 362 CMSHeap* heap = CMSHeap::heap(); 363 size_t expected_promotion = MIN2(heap->young_gen()->capacity(), 364 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average()); 365 if (cms_free > expected_promotion) { 366 // Start a cms collection if there isn't enough space to promote 367 // for the next young collection. Use the padded average as 368 // a safety factor. 369 cms_free -= expected_promotion; 370 371 // Adjust by the safety factor. 372 double cms_free_dbl = (double)cms_free; 373 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0; 374 // Apply a further correction factor which tries to adjust 375 // for recent occurance of concurrent mode failures. 376 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free); 377 cms_free_dbl = cms_free_dbl * cms_adjustment; 378 379 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT, 380 cms_free, expected_promotion); 381 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0); 382 // Add 1 in case the consumption rate goes to zero. 383 return cms_free_dbl / (cms_consumption_rate() + 1.0); 384 } 385 return 0.0; 386 } 387 388 // Compare the duration of the cms collection to the 389 // time remaining before the cms generation is empty. 390 // Note that the time from the start of the cms collection 391 // to the start of the cms sweep (less than the total 392 // duration of the cms collection) can be used. This 393 // has been tried and some applications experienced 394 // promotion failures early in execution. This was 395 // possibly because the averages were not accurate 396 // enough at the beginning. 397 double CMSStats::time_until_cms_start() const { 398 // We add "gc0_period" to the "work" calculation 399 // below because this query is done (mostly) at the 400 // end of a scavenge, so we need to conservatively 401 // account for that much possible delay 402 // in the query so as to avoid concurrent mode failures 403 // due to starting the collection just a wee bit too 404 // late. 405 double work = cms_duration() + gc0_period(); 406 double deadline = time_until_cms_gen_full(); 407 // If a concurrent mode failure occurred recently, we want to be 408 // more conservative and halve our expected time_until_cms_gen_full() 409 if (work > deadline) { 410 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ", 411 cms_duration(), gc0_period(), time_until_cms_gen_full()); 412 return 0.0; 413 } 414 return work - deadline; 415 } 416 417 #ifndef PRODUCT 418 void CMSStats::print_on(outputStream *st) const { 419 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); 420 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT, 421 gc0_duration(), gc0_period(), gc0_promoted()); 422 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, 423 cms_duration(), cms_period(), cms_allocated()); 424 st->print(",cms_since_beg=%g,cms_since_end=%g", 425 cms_time_since_begin(), cms_time_since_end()); 426 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT, 427 _cms_used_at_gc0_begin, _cms_used_at_gc0_end); 428 429 if (valid()) { 430 st->print(",promo_rate=%g,cms_alloc_rate=%g", 431 promotion_rate(), cms_allocation_rate()); 432 st->print(",cms_consumption_rate=%g,time_until_full=%g", 433 cms_consumption_rate(), time_until_cms_gen_full()); 434 } 435 st->cr(); 436 } 437 #endif // #ifndef PRODUCT 438 439 CMSCollector::CollectorState CMSCollector::_collectorState = 440 CMSCollector::Idling; 441 bool CMSCollector::_foregroundGCIsActive = false; 442 bool CMSCollector::_foregroundGCShouldWait = false; 443 444 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, 445 CardTableRS* ct, 446 ConcurrentMarkSweepPolicy* cp): 447 _cmsGen(cmsGen), 448 _ct(ct), 449 _ref_processor(NULL), // will be set later 450 _conc_workers(NULL), // may be set later 451 _abort_preclean(false), 452 _start_sampling(false), 453 _between_prologue_and_epilogue(false), 454 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), 455 _modUnionTable((CardTable::card_shift - LogHeapWordSize), 456 -1 /* lock-free */, "No_lock" /* dummy */), 457 _modUnionClosurePar(&_modUnionTable), 458 // Adjust my span to cover old (cms) gen 459 _span(cmsGen->reserved()), 460 // Construct the is_alive_closure with _span & markBitMap 461 _is_alive_closure(_span, &_markBitMap), 462 _restart_addr(NULL), 463 _overflow_list(NULL), 464 _stats(cmsGen), 465 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true, 466 //verify that this lock should be acquired with safepoint check. 467 Monitor::_safepoint_check_sometimes)), 468 _eden_chunk_array(NULL), // may be set in ctor body 469 _eden_chunk_capacity(0), // -- ditto -- 470 _eden_chunk_index(0), // -- ditto -- 471 _survivor_plab_array(NULL), // -- ditto -- 472 _survivor_chunk_array(NULL), // -- ditto -- 473 _survivor_chunk_capacity(0), // -- ditto -- 474 _survivor_chunk_index(0), // -- ditto -- 475 _ser_pmc_preclean_ovflw(0), 476 _ser_kac_preclean_ovflw(0), 477 _ser_pmc_remark_ovflw(0), 478 _par_pmc_remark_ovflw(0), 479 _ser_kac_ovflw(0), 480 _par_kac_ovflw(0), 481 #ifndef PRODUCT 482 _num_par_pushes(0), 483 #endif 484 _collection_count_start(0), 485 _verifying(false), 486 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), 487 _completed_initialization(false), 488 _collector_policy(cp), 489 _should_unload_classes(CMSClassUnloadingEnabled), 490 _concurrent_cycles_since_last_unload(0), 491 _roots_scanning_options(GenCollectedHeap::SO_None), 492 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), 493 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), 494 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()), 495 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()), 496 _cms_start_registered(false) 497 { 498 // Now expand the span and allocate the collection support structures 499 // (MUT, marking bit map etc.) to cover both generations subject to 500 // collection. 501 502 // For use by dirty card to oop closures. 503 _cmsGen->cmsSpace()->set_collector(this); 504 505 // Allocate MUT and marking bit map 506 { 507 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); 508 if (!_markBitMap.allocate(_span)) { 509 log_warning(gc)("Failed to allocate CMS Bit Map"); 510 return; 511 } 512 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); 513 } 514 { 515 _modUnionTable.allocate(_span); 516 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); 517 } 518 519 if (!_markStack.allocate(MarkStackSize)) { 520 log_warning(gc)("Failed to allocate CMS Marking Stack"); 521 return; 522 } 523 524 // Support for multi-threaded concurrent phases 525 if (CMSConcurrentMTEnabled) { 526 if (FLAG_IS_DEFAULT(ConcGCThreads)) { 527 // just for now 528 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4); 529 } 530 if (ConcGCThreads > 1) { 531 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread", 532 ConcGCThreads, true); 533 if (_conc_workers == NULL) { 534 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled"); 535 CMSConcurrentMTEnabled = false; 536 } else { 537 _conc_workers->initialize_workers(); 538 } 539 } else { 540 CMSConcurrentMTEnabled = false; 541 } 542 } 543 if (!CMSConcurrentMTEnabled) { 544 ConcGCThreads = 0; 545 } else { 546 // Turn off CMSCleanOnEnter optimization temporarily for 547 // the MT case where it's not fixed yet; see 6178663. 548 CMSCleanOnEnter = false; 549 } 550 assert((_conc_workers != NULL) == (ConcGCThreads > 1), 551 "Inconsistency"); 552 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads); 553 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads); 554 555 // Parallel task queues; these are shared for the 556 // concurrent and stop-world phases of CMS, but 557 // are not shared with parallel scavenge (ParNew). 558 { 559 uint i; 560 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads); 561 562 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled 563 || ParallelRefProcEnabled) 564 && num_queues > 0) { 565 _task_queues = new OopTaskQueueSet(num_queues); 566 if (_task_queues == NULL) { 567 log_warning(gc)("task_queues allocation failure."); 568 return; 569 } 570 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC); 571 typedef Padded<OopTaskQueue> PaddedOopTaskQueue; 572 for (i = 0; i < num_queues; i++) { 573 PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); 574 if (q == NULL) { 575 log_warning(gc)("work_queue allocation failure."); 576 return; 577 } 578 _task_queues->register_queue(i, q); 579 } 580 for (i = 0; i < num_queues; i++) { 581 _task_queues->queue(i)->initialize(); 582 _hash_seed[i] = 17; // copied from ParNew 583 } 584 } 585 } 586 587 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); 588 589 // Clip CMSBootstrapOccupancy between 0 and 100. 590 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0; 591 592 // Now tell CMS generations the identity of their collector 593 ConcurrentMarkSweepGeneration::set_collector(this); 594 595 // Create & start a CMS thread for this CMS collector 596 _cmsThread = ConcurrentMarkSweepThread::start(this); 597 assert(cmsThread() != NULL, "CMS Thread should have been created"); 598 assert(cmsThread()->collector() == this, 599 "CMS Thread should refer to this gen"); 600 assert(CGC_lock != NULL, "Where's the CGC_lock?"); 601 602 // Support for parallelizing young gen rescan 603 CMSHeap* heap = CMSHeap::heap(); 604 assert(heap->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew"); 605 _young_gen = (ParNewGeneration*)heap->young_gen(); 606 if (heap->supports_inline_contig_alloc()) { 607 _top_addr = heap->top_addr(); 608 _end_addr = heap->end_addr(); 609 assert(_young_gen != NULL, "no _young_gen"); 610 _eden_chunk_index = 0; 611 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain; 612 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC); 613 } 614 615 // Support for parallelizing survivor space rescan 616 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) { 617 const size_t max_plab_samples = 618 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize); 619 620 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC); 621 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); 622 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC); 623 _survivor_chunk_capacity = max_plab_samples; 624 for (uint i = 0; i < ParallelGCThreads; i++) { 625 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); 626 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples); 627 assert(cur->end() == 0, "Should be 0"); 628 assert(cur->array() == vec, "Should be vec"); 629 assert(cur->capacity() == max_plab_samples, "Error"); 630 } 631 } 632 633 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) 634 _gc_counters = new CollectorCounters("CMS", 1); 635 _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2); 636 _completed_initialization = true; 637 _inter_sweep_timer.start(); // start of time 638 } 639 640 const char* ConcurrentMarkSweepGeneration::name() const { 641 return "concurrent mark-sweep generation"; 642 } 643 void ConcurrentMarkSweepGeneration::update_counters() { 644 if (UsePerfData) { 645 _space_counters->update_all(); 646 _gen_counters->update_all(); 647 } 648 } 649 650 // this is an optimized version of update_counters(). it takes the 651 // used value as a parameter rather than computing it. 652 // 653 void ConcurrentMarkSweepGeneration::update_counters(size_t used) { 654 if (UsePerfData) { 655 _space_counters->update_used(used); 656 _space_counters->update_capacity(); 657 _gen_counters->update_all(); 658 } 659 } 660 661 void ConcurrentMarkSweepGeneration::print() const { 662 Generation::print(); 663 cmsSpace()->print(); 664 } 665 666 #ifndef PRODUCT 667 void ConcurrentMarkSweepGeneration::print_statistics() { 668 cmsSpace()->printFLCensus(0); 669 } 670 #endif 671 672 size_t 673 ConcurrentMarkSweepGeneration::contiguous_available() const { 674 // dld proposes an improvement in precision here. If the committed 675 // part of the space ends in a free block we should add that to 676 // uncommitted size in the calculation below. Will make this 677 // change later, staying with the approximation below for the 678 // time being. -- ysr. 679 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); 680 } 681 682 size_t 683 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { 684 return _cmsSpace->max_alloc_in_words() * HeapWordSize; 685 } 686 687 size_t ConcurrentMarkSweepGeneration::max_available() const { 688 return free() + _virtual_space.uncommitted_size(); 689 } 690 691 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const { 692 size_t available = max_available(); 693 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average(); 694 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes); 695 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")", 696 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes); 697 return res; 698 } 699 700 // At a promotion failure dump information on block layout in heap 701 // (cms old generation). 702 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() { 703 Log(gc, promotion) log; 704 if (log.is_trace()) { 705 LogStream ls(log.trace()); 706 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls); 707 } 708 } 709 710 void ConcurrentMarkSweepGeneration::reset_after_compaction() { 711 // Clear the promotion information. These pointers can be adjusted 712 // along with all the other pointers into the heap but 713 // compaction is expected to be a rare event with 714 // a heap using cms so don't do it without seeing the need. 715 for (uint i = 0; i < ParallelGCThreads; i++) { 716 _par_gc_thread_states[i]->promo.reset(); 717 } 718 } 719 720 void ConcurrentMarkSweepGeneration::compute_new_size() { 721 assert_locked_or_safepoint(Heap_lock); 722 723 // If incremental collection failed, we just want to expand 724 // to the limit. 725 if (incremental_collection_failed()) { 726 clear_incremental_collection_failed(); 727 grow_to_reserved(); 728 return; 729 } 730 731 // The heap has been compacted but not reset yet. 732 // Any metric such as free() or used() will be incorrect. 733 734 CardGeneration::compute_new_size(); 735 736 // Reset again after a possible resizing 737 if (did_compact()) { 738 cmsSpace()->reset_after_compaction(); 739 } 740 } 741 742 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() { 743 assert_locked_or_safepoint(Heap_lock); 744 745 // If incremental collection failed, we just want to expand 746 // to the limit. 747 if (incremental_collection_failed()) { 748 clear_incremental_collection_failed(); 749 grow_to_reserved(); 750 return; 751 } 752 753 double free_percentage = ((double) free()) / capacity(); 754 double desired_free_percentage = (double) MinHeapFreeRatio / 100; 755 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; 756 757 // compute expansion delta needed for reaching desired free percentage 758 if (free_percentage < desired_free_percentage) { 759 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 760 assert(desired_capacity >= capacity(), "invalid expansion size"); 761 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); 762 Log(gc) log; 763 if (log.is_trace()) { 764 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 765 log.trace("From compute_new_size: "); 766 log.trace(" Free fraction %f", free_percentage); 767 log.trace(" Desired free fraction %f", desired_free_percentage); 768 log.trace(" Maximum free fraction %f", maximum_free_percentage); 769 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000); 770 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000); 771 CMSHeap* heap = CMSHeap::heap(); 772 assert(heap->is_old_gen(this), "The CMS generation should always be the old generation"); 773 size_t young_size = heap->young_gen()->capacity(); 774 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000); 775 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000); 776 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000); 777 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes); 778 } 779 // safe if expansion fails 780 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); 781 log.trace(" Expanded free fraction %f", ((double) free()) / capacity()); 782 } else { 783 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 784 assert(desired_capacity <= capacity(), "invalid expansion size"); 785 size_t shrink_bytes = capacity() - desired_capacity; 786 // Don't shrink unless the delta is greater than the minimum shrink we want 787 if (shrink_bytes >= MinHeapDeltaBytes) { 788 shrink_free_list_by(shrink_bytes); 789 } 790 } 791 } 792 793 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { 794 return cmsSpace()->freelistLock(); 795 } 796 797 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) { 798 CMSSynchronousYieldRequest yr; 799 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 800 return have_lock_and_allocate(size, tlab); 801 } 802 803 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, 804 bool tlab /* ignored */) { 805 assert_lock_strong(freelistLock()); 806 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); 807 HeapWord* res = cmsSpace()->allocate(adjustedSize); 808 // Allocate the object live (grey) if the background collector has 809 // started marking. This is necessary because the marker may 810 // have passed this address and consequently this object will 811 // not otherwise be greyed and would be incorrectly swept up. 812 // Note that if this object contains references, the writing 813 // of those references will dirty the card containing this object 814 // allowing the object to be blackened (and its references scanned) 815 // either during a preclean phase or at the final checkpoint. 816 if (res != NULL) { 817 // We may block here with an uninitialized object with 818 // its mark-bit or P-bits not yet set. Such objects need 819 // to be safely navigable by block_start(). 820 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here."); 821 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size"); 822 collector()->direct_allocated(res, adjustedSize); 823 _direct_allocated_words += adjustedSize; 824 // allocation counters 825 NOT_PRODUCT( 826 _numObjectsAllocated++; 827 _numWordsAllocated += (int)adjustedSize; 828 ) 829 } 830 return res; 831 } 832 833 // In the case of direct allocation by mutators in a generation that 834 // is being concurrently collected, the object must be allocated 835 // live (grey) if the background collector has started marking. 836 // This is necessary because the marker may 837 // have passed this address and consequently this object will 838 // not otherwise be greyed and would be incorrectly swept up. 839 // Note that if this object contains references, the writing 840 // of those references will dirty the card containing this object 841 // allowing the object to be blackened (and its references scanned) 842 // either during a preclean phase or at the final checkpoint. 843 void CMSCollector::direct_allocated(HeapWord* start, size_t size) { 844 assert(_markBitMap.covers(start, size), "Out of bounds"); 845 if (_collectorState >= Marking) { 846 MutexLockerEx y(_markBitMap.lock(), 847 Mutex::_no_safepoint_check_flag); 848 // [see comments preceding SweepClosure::do_blk() below for details] 849 // 850 // Can the P-bits be deleted now? JJJ 851 // 852 // 1. need to mark the object as live so it isn't collected 853 // 2. need to mark the 2nd bit to indicate the object may be uninitialized 854 // 3. need to mark the end of the object so marking, precleaning or sweeping 855 // can skip over uninitialized or unparsable objects. An allocated 856 // object is considered uninitialized for our purposes as long as 857 // its klass word is NULL. All old gen objects are parsable 858 // as soon as they are initialized.) 859 _markBitMap.mark(start); // object is live 860 _markBitMap.mark(start + 1); // object is potentially uninitialized? 861 _markBitMap.mark(start + size - 1); 862 // mark end of object 863 } 864 // check that oop looks uninitialized 865 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL"); 866 } 867 868 void CMSCollector::promoted(bool par, HeapWord* start, 869 bool is_obj_array, size_t obj_size) { 870 assert(_markBitMap.covers(start), "Out of bounds"); 871 // See comment in direct_allocated() about when objects should 872 // be allocated live. 873 if (_collectorState >= Marking) { 874 // we already hold the marking bit map lock, taken in 875 // the prologue 876 if (par) { 877 _markBitMap.par_mark(start); 878 } else { 879 _markBitMap.mark(start); 880 } 881 // We don't need to mark the object as uninitialized (as 882 // in direct_allocated above) because this is being done with the 883 // world stopped and the object will be initialized by the 884 // time the marking, precleaning or sweeping get to look at it. 885 // But see the code for copying objects into the CMS generation, 886 // where we need to ensure that concurrent readers of the 887 // block offset table are able to safely navigate a block that 888 // is in flux from being free to being allocated (and in 889 // transition while being copied into) and subsequently 890 // becoming a bona-fide object when the copy/promotion is complete. 891 assert(SafepointSynchronize::is_at_safepoint(), 892 "expect promotion only at safepoints"); 893 894 if (_collectorState < Sweeping) { 895 // Mark the appropriate cards in the modUnionTable, so that 896 // this object gets scanned before the sweep. If this is 897 // not done, CMS generation references in the object might 898 // not get marked. 899 // For the case of arrays, which are otherwise precisely 900 // marked, we need to dirty the entire array, not just its head. 901 if (is_obj_array) { 902 // The [par_]mark_range() method expects mr.end() below to 903 // be aligned to the granularity of a bit's representation 904 // in the heap. In the case of the MUT below, that's a 905 // card size. 906 MemRegion mr(start, 907 align_up(start + obj_size, 908 CardTable::card_size /* bytes */)); 909 if (par) { 910 _modUnionTable.par_mark_range(mr); 911 } else { 912 _modUnionTable.mark_range(mr); 913 } 914 } else { // not an obj array; we can just mark the head 915 if (par) { 916 _modUnionTable.par_mark(start); 917 } else { 918 _modUnionTable.mark(start); 919 } 920 } 921 } 922 } 923 } 924 925 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) { 926 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); 927 // allocate, copy and if necessary update promoinfo -- 928 // delegate to underlying space. 929 assert_lock_strong(freelistLock()); 930 931 #ifndef PRODUCT 932 if (CMSHeap::heap()->promotion_should_fail()) { 933 return NULL; 934 } 935 #endif // #ifndef PRODUCT 936 937 oop res = _cmsSpace->promote(obj, obj_size); 938 if (res == NULL) { 939 // expand and retry 940 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords 941 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion); 942 // Since this is the old generation, we don't try to promote 943 // into a more senior generation. 944 res = _cmsSpace->promote(obj, obj_size); 945 } 946 if (res != NULL) { 947 // See comment in allocate() about when objects should 948 // be allocated live. 949 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below"); 950 collector()->promoted(false, // Not parallel 951 (HeapWord*)res, obj->is_objArray(), obj_size); 952 // promotion counters 953 NOT_PRODUCT( 954 _numObjectsPromoted++; 955 _numWordsPromoted += 956 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); 957 ) 958 } 959 return res; 960 } 961 962 963 // IMPORTANT: Notes on object size recognition in CMS. 964 // --------------------------------------------------- 965 // A block of storage in the CMS generation is always in 966 // one of three states. A free block (FREE), an allocated 967 // object (OBJECT) whose size() method reports the correct size, 968 // and an intermediate state (TRANSIENT) in which its size cannot 969 // be accurately determined. 970 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS) 971 // ----------------------------------------------------- 972 // FREE: klass_word & 1 == 1; mark_word holds block size 973 // 974 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0; 975 // obj->size() computes correct size 976 // 977 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT 978 // 979 // STATE IDENTIFICATION: (64 bit+COOPS) 980 // ------------------------------------ 981 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size 982 // 983 // OBJECT: klass_word installed; klass_word != 0; 984 // obj->size() computes correct size 985 // 986 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT 987 // 988 // 989 // STATE TRANSITION DIAGRAM 990 // 991 // mut / parnew mut / parnew 992 // FREE --------------------> TRANSIENT ---------------------> OBJECT --| 993 // ^ | 994 // |------------------------ DEAD <------------------------------------| 995 // sweep mut 996 // 997 // While a block is in TRANSIENT state its size cannot be determined 998 // so readers will either need to come back later or stall until 999 // the size can be determined. Note that for the case of direct 1000 // allocation, P-bits, when available, may be used to determine the 1001 // size of an object that may not yet have been initialized. 1002 1003 // Things to support parallel young-gen collection. 1004 oop 1005 ConcurrentMarkSweepGeneration::par_promote(int thread_num, 1006 oop old, markOop m, 1007 size_t word_sz) { 1008 #ifndef PRODUCT 1009 if (CMSHeap::heap()->promotion_should_fail()) { 1010 return NULL; 1011 } 1012 #endif // #ifndef PRODUCT 1013 1014 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1015 PromotionInfo* promoInfo = &ps->promo; 1016 // if we are tracking promotions, then first ensure space for 1017 // promotion (including spooling space for saving header if necessary). 1018 // then allocate and copy, then track promoted info if needed. 1019 // When tracking (see PromotionInfo::track()), the mark word may 1020 // be displaced and in this case restoration of the mark word 1021 // occurs in the (oop_since_save_marks_)iterate phase. 1022 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { 1023 // Out of space for allocating spooling buffers; 1024 // try expanding and allocating spooling buffers. 1025 if (!expand_and_ensure_spooling_space(promoInfo)) { 1026 return NULL; 1027 } 1028 } 1029 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant"); 1030 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz); 1031 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz); 1032 if (obj_ptr == NULL) { 1033 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz); 1034 if (obj_ptr == NULL) { 1035 return NULL; 1036 } 1037 } 1038 oop obj = oop(obj_ptr); 1039 OrderAccess::storestore(); 1040 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1041 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1042 // IMPORTANT: See note on object initialization for CMS above. 1043 // Otherwise, copy the object. Here we must be careful to insert the 1044 // klass pointer last, since this marks the block as an allocated object. 1045 // Except with compressed oops it's the mark word. 1046 HeapWord* old_ptr = (HeapWord*)old; 1047 // Restore the mark word copied above. 1048 obj->set_mark_raw(m); 1049 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1050 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1051 OrderAccess::storestore(); 1052 1053 if (UseCompressedClassPointers) { 1054 // Copy gap missed by (aligned) header size calculation below 1055 obj->set_klass_gap(old->klass_gap()); 1056 } 1057 if (word_sz > (size_t)oopDesc::header_size()) { 1058 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), 1059 obj_ptr + oopDesc::header_size(), 1060 word_sz - oopDesc::header_size()); 1061 } 1062 1063 // Now we can track the promoted object, if necessary. We take care 1064 // to delay the transition from uninitialized to full object 1065 // (i.e., insertion of klass pointer) until after, so that it 1066 // atomically becomes a promoted object. 1067 if (promoInfo->tracking()) { 1068 promoInfo->track((PromotedObject*)obj, old->klass()); 1069 } 1070 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1071 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1072 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below"); 1073 1074 // Finally, install the klass pointer (this should be volatile). 1075 OrderAccess::storestore(); 1076 obj->set_klass(old->klass()); 1077 // We should now be able to calculate the right size for this object 1078 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object"); 1079 1080 collector()->promoted(true, // parallel 1081 obj_ptr, old->is_objArray(), word_sz); 1082 1083 NOT_PRODUCT( 1084 Atomic::inc(&_numObjectsPromoted); 1085 Atomic::add(alloc_sz, &_numWordsPromoted); 1086 ) 1087 1088 return obj; 1089 } 1090 1091 void 1092 ConcurrentMarkSweepGeneration:: 1093 par_promote_alloc_done(int thread_num) { 1094 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1095 ps->lab.retire(thread_num); 1096 } 1097 1098 void 1099 ConcurrentMarkSweepGeneration:: 1100 par_oop_since_save_marks_iterate_done(int thread_num) { 1101 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1102 ParScanWithoutBarrierClosure* dummy_cl = NULL; 1103 ps->promo.promoted_oops_iterate_nv(dummy_cl); 1104 1105 // Because card-scanning has been completed, subsequent phases 1106 // (e.g., reference processing) will not need to recognize which 1107 // objects have been promoted during this GC. So, we can now disable 1108 // promotion tracking. 1109 ps->promo.stopTrackingPromotions(); 1110 } 1111 1112 bool ConcurrentMarkSweepGeneration::should_collect(bool full, 1113 size_t size, 1114 bool tlab) 1115 { 1116 // We allow a STW collection only if a full 1117 // collection was requested. 1118 return full || should_allocate(size, tlab); // FIX ME !!! 1119 // This and promotion failure handling are connected at the 1120 // hip and should be fixed by untying them. 1121 } 1122 1123 bool CMSCollector::shouldConcurrentCollect() { 1124 LogTarget(Trace, gc) log; 1125 1126 if (_full_gc_requested) { 1127 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)"); 1128 return true; 1129 } 1130 1131 FreelistLocker x(this); 1132 // ------------------------------------------------------------------ 1133 // Print out lots of information which affects the initiation of 1134 // a collection. 1135 if (log.is_enabled() && stats().valid()) { 1136 log.print("CMSCollector shouldConcurrentCollect: "); 1137 1138 LogStream out(log); 1139 stats().print_on(&out); 1140 1141 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full()); 1142 log.print("free=" SIZE_FORMAT, _cmsGen->free()); 1143 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available()); 1144 log.print("promotion_rate=%g", stats().promotion_rate()); 1145 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate()); 1146 log.print("occupancy=%3.7f", _cmsGen->occupancy()); 1147 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); 1148 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin()); 1149 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end()); 1150 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect()); 1151 } 1152 // ------------------------------------------------------------------ 1153 1154 // If the estimated time to complete a cms collection (cms_duration()) 1155 // is less than the estimated time remaining until the cms generation 1156 // is full, start a collection. 1157 if (!UseCMSInitiatingOccupancyOnly) { 1158 if (stats().valid()) { 1159 if (stats().time_until_cms_start() == 0.0) { 1160 return true; 1161 } 1162 } else { 1163 // We want to conservatively collect somewhat early in order 1164 // to try and "bootstrap" our CMS/promotion statistics; 1165 // this branch will not fire after the first successful CMS 1166 // collection because the stats should then be valid. 1167 if (_cmsGen->occupancy() >= _bootstrap_occupancy) { 1168 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f", 1169 _cmsGen->occupancy(), _bootstrap_occupancy); 1170 return true; 1171 } 1172 } 1173 } 1174 1175 // Otherwise, we start a collection cycle if 1176 // old gen want a collection cycle started. Each may use 1177 // an appropriate criterion for making this decision. 1178 // XXX We need to make sure that the gen expansion 1179 // criterion dovetails well with this. XXX NEED TO FIX THIS 1180 if (_cmsGen->should_concurrent_collect()) { 1181 log.print("CMS old gen initiated"); 1182 return true; 1183 } 1184 1185 // We start a collection if we believe an incremental collection may fail; 1186 // this is not likely to be productive in practice because it's probably too 1187 // late anyway. 1188 CMSHeap* heap = CMSHeap::heap(); 1189 if (heap->incremental_collection_will_fail(true /* consult_young */)) { 1190 log.print("CMSCollector: collect because incremental collection will fail "); 1191 return true; 1192 } 1193 1194 if (MetaspaceGC::should_concurrent_collect()) { 1195 log.print("CMSCollector: collect for metadata allocation "); 1196 return true; 1197 } 1198 1199 // CMSTriggerInterval starts a CMS cycle if enough time has passed. 1200 if (CMSTriggerInterval >= 0) { 1201 if (CMSTriggerInterval == 0) { 1202 // Trigger always 1203 return true; 1204 } 1205 1206 // Check the CMS time since begin (we do not check the stats validity 1207 // as we want to be able to trigger the first CMS cycle as well) 1208 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) { 1209 if (stats().valid()) { 1210 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)", 1211 stats().cms_time_since_begin()); 1212 } else { 1213 log.print("CMSCollector: collect because of trigger interval (first collection)"); 1214 } 1215 return true; 1216 } 1217 } 1218 1219 return false; 1220 } 1221 1222 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); } 1223 1224 // Clear _expansion_cause fields of constituent generations 1225 void CMSCollector::clear_expansion_cause() { 1226 _cmsGen->clear_expansion_cause(); 1227 } 1228 1229 // We should be conservative in starting a collection cycle. To 1230 // start too eagerly runs the risk of collecting too often in the 1231 // extreme. To collect too rarely falls back on full collections, 1232 // which works, even if not optimum in terms of concurrent work. 1233 // As a work around for too eagerly collecting, use the flag 1234 // UseCMSInitiatingOccupancyOnly. This also has the advantage of 1235 // giving the user an easily understandable way of controlling the 1236 // collections. 1237 // We want to start a new collection cycle if any of the following 1238 // conditions hold: 1239 // . our current occupancy exceeds the configured initiating occupancy 1240 // for this generation, or 1241 // . we recently needed to expand this space and have not, since that 1242 // expansion, done a collection of this generation, or 1243 // . the underlying space believes that it may be a good idea to initiate 1244 // a concurrent collection (this may be based on criteria such as the 1245 // following: the space uses linear allocation and linear allocation is 1246 // going to fail, or there is believed to be excessive fragmentation in 1247 // the generation, etc... or ... 1248 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for 1249 // the case of the old generation; see CR 6543076): 1250 // we may be approaching a point at which allocation requests may fail because 1251 // we will be out of sufficient free space given allocation rate estimates.] 1252 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const { 1253 1254 assert_lock_strong(freelistLock()); 1255 if (occupancy() > initiating_occupancy()) { 1256 log_trace(gc)(" %s: collect because of occupancy %f / %f ", 1257 short_name(), occupancy(), initiating_occupancy()); 1258 return true; 1259 } 1260 if (UseCMSInitiatingOccupancyOnly) { 1261 return false; 1262 } 1263 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { 1264 log_trace(gc)(" %s: collect because expanded for allocation ", short_name()); 1265 return true; 1266 } 1267 return false; 1268 } 1269 1270 void ConcurrentMarkSweepGeneration::collect(bool full, 1271 bool clear_all_soft_refs, 1272 size_t size, 1273 bool tlab) 1274 { 1275 collector()->collect(full, clear_all_soft_refs, size, tlab); 1276 } 1277 1278 void CMSCollector::collect(bool full, 1279 bool clear_all_soft_refs, 1280 size_t size, 1281 bool tlab) 1282 { 1283 // The following "if" branch is present for defensive reasons. 1284 // In the current uses of this interface, it can be replaced with: 1285 // assert(!GCLocker.is_active(), "Can't be called otherwise"); 1286 // But I am not placing that assert here to allow future 1287 // generality in invoking this interface. 1288 if (GCLocker::is_active()) { 1289 // A consistency test for GCLocker 1290 assert(GCLocker::needs_gc(), "Should have been set already"); 1291 // Skip this foreground collection, instead 1292 // expanding the heap if necessary. 1293 // Need the free list locks for the call to free() in compute_new_size() 1294 compute_new_size(); 1295 return; 1296 } 1297 acquire_control_and_collect(full, clear_all_soft_refs); 1298 } 1299 1300 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) { 1301 CMSHeap* heap = CMSHeap::heap(); 1302 unsigned int gc_count = heap->total_full_collections(); 1303 if (gc_count == full_gc_count) { 1304 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag); 1305 _full_gc_requested = true; 1306 _full_gc_cause = cause; 1307 CGC_lock->notify(); // nudge CMS thread 1308 } else { 1309 assert(gc_count > full_gc_count, "Error: causal loop"); 1310 } 1311 } 1312 1313 bool CMSCollector::is_external_interruption() { 1314 GCCause::Cause cause = CMSHeap::heap()->gc_cause(); 1315 return GCCause::is_user_requested_gc(cause) || 1316 GCCause::is_serviceability_requested_gc(cause); 1317 } 1318 1319 void CMSCollector::report_concurrent_mode_interruption() { 1320 if (is_external_interruption()) { 1321 log_debug(gc)("Concurrent mode interrupted"); 1322 } else { 1323 log_debug(gc)("Concurrent mode failure"); 1324 _gc_tracer_cm->report_concurrent_mode_failure(); 1325 } 1326 } 1327 1328 1329 // The foreground and background collectors need to coordinate in order 1330 // to make sure that they do not mutually interfere with CMS collections. 1331 // When a background collection is active, 1332 // the foreground collector may need to take over (preempt) and 1333 // synchronously complete an ongoing collection. Depending on the 1334 // frequency of the background collections and the heap usage 1335 // of the application, this preemption can be seldom or frequent. 1336 // There are only certain 1337 // points in the background collection that the "collection-baton" 1338 // can be passed to the foreground collector. 1339 // 1340 // The foreground collector will wait for the baton before 1341 // starting any part of the collection. The foreground collector 1342 // will only wait at one location. 1343 // 1344 // The background collector will yield the baton before starting a new 1345 // phase of the collection (e.g., before initial marking, marking from roots, 1346 // precleaning, final re-mark, sweep etc.) This is normally done at the head 1347 // of the loop which switches the phases. The background collector does some 1348 // of the phases (initial mark, final re-mark) with the world stopped. 1349 // Because of locking involved in stopping the world, 1350 // the foreground collector should not block waiting for the background 1351 // collector when it is doing a stop-the-world phase. The background 1352 // collector will yield the baton at an additional point just before 1353 // it enters a stop-the-world phase. Once the world is stopped, the 1354 // background collector checks the phase of the collection. If the 1355 // phase has not changed, it proceeds with the collection. If the 1356 // phase has changed, it skips that phase of the collection. See 1357 // the comments on the use of the Heap_lock in collect_in_background(). 1358 // 1359 // Variable used in baton passing. 1360 // _foregroundGCIsActive - Set to true by the foreground collector when 1361 // it wants the baton. The foreground clears it when it has finished 1362 // the collection. 1363 // _foregroundGCShouldWait - Set to true by the background collector 1364 // when it is running. The foreground collector waits while 1365 // _foregroundGCShouldWait is true. 1366 // CGC_lock - monitor used to protect access to the above variables 1367 // and to notify the foreground and background collectors. 1368 // _collectorState - current state of the CMS collection. 1369 // 1370 // The foreground collector 1371 // acquires the CGC_lock 1372 // sets _foregroundGCIsActive 1373 // waits on the CGC_lock for _foregroundGCShouldWait to be false 1374 // various locks acquired in preparation for the collection 1375 // are released so as not to block the background collector 1376 // that is in the midst of a collection 1377 // proceeds with the collection 1378 // clears _foregroundGCIsActive 1379 // returns 1380 // 1381 // The background collector in a loop iterating on the phases of the 1382 // collection 1383 // acquires the CGC_lock 1384 // sets _foregroundGCShouldWait 1385 // if _foregroundGCIsActive is set 1386 // clears _foregroundGCShouldWait, notifies _CGC_lock 1387 // waits on _CGC_lock for _foregroundGCIsActive to become false 1388 // and exits the loop. 1389 // otherwise 1390 // proceed with that phase of the collection 1391 // if the phase is a stop-the-world phase, 1392 // yield the baton once more just before enqueueing 1393 // the stop-world CMS operation (executed by the VM thread). 1394 // returns after all phases of the collection are done 1395 // 1396 1397 void CMSCollector::acquire_control_and_collect(bool full, 1398 bool clear_all_soft_refs) { 1399 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); 1400 assert(!Thread::current()->is_ConcurrentGC_thread(), 1401 "shouldn't try to acquire control from self!"); 1402 1403 // Start the protocol for acquiring control of the 1404 // collection from the background collector (aka CMS thread). 1405 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 1406 "VM thread should have CMS token"); 1407 // Remember the possibly interrupted state of an ongoing 1408 // concurrent collection 1409 CollectorState first_state = _collectorState; 1410 1411 // Signal to a possibly ongoing concurrent collection that 1412 // we want to do a foreground collection. 1413 _foregroundGCIsActive = true; 1414 1415 // release locks and wait for a notify from the background collector 1416 // releasing the locks in only necessary for phases which 1417 // do yields to improve the granularity of the collection. 1418 assert_lock_strong(bitMapLock()); 1419 // We need to lock the Free list lock for the space that we are 1420 // currently collecting. 1421 assert(haveFreelistLocks(), "Must be holding free list locks"); 1422 bitMapLock()->unlock(); 1423 releaseFreelistLocks(); 1424 { 1425 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1426 if (_foregroundGCShouldWait) { 1427 // We are going to be waiting for action for the CMS thread; 1428 // it had better not be gone (for instance at shutdown)! 1429 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(), 1430 "CMS thread must be running"); 1431 // Wait here until the background collector gives us the go-ahead 1432 ConcurrentMarkSweepThread::clear_CMS_flag( 1433 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token 1434 // Get a possibly blocked CMS thread going: 1435 // Note that we set _foregroundGCIsActive true above, 1436 // without protection of the CGC_lock. 1437 CGC_lock->notify(); 1438 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), 1439 "Possible deadlock"); 1440 while (_foregroundGCShouldWait) { 1441 // wait for notification 1442 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 1443 // Possibility of delay/starvation here, since CMS token does 1444 // not know to give priority to VM thread? Actually, i think 1445 // there wouldn't be any delay/starvation, but the proof of 1446 // that "fact" (?) appears non-trivial. XXX 20011219YSR 1447 } 1448 ConcurrentMarkSweepThread::set_CMS_flag( 1449 ConcurrentMarkSweepThread::CMS_vm_has_token); 1450 } 1451 } 1452 // The CMS_token is already held. Get back the other locks. 1453 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 1454 "VM thread should have CMS token"); 1455 getFreelistLocks(); 1456 bitMapLock()->lock_without_safepoint_check(); 1457 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d", 1458 p2i(Thread::current()), first_state); 1459 log_debug(gc, state)(" gets control with state %d", _collectorState); 1460 1461 // Inform cms gen if this was due to partial collection failing. 1462 // The CMS gen may use this fact to determine its expansion policy. 1463 CMSHeap* heap = CMSHeap::heap(); 1464 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) { 1465 assert(!_cmsGen->incremental_collection_failed(), 1466 "Should have been noticed, reacted to and cleared"); 1467 _cmsGen->set_incremental_collection_failed(); 1468 } 1469 1470 if (first_state > Idling) { 1471 report_concurrent_mode_interruption(); 1472 } 1473 1474 set_did_compact(true); 1475 1476 // If the collection is being acquired from the background 1477 // collector, there may be references on the discovered 1478 // references lists. Abandon those references, since some 1479 // of them may have become unreachable after concurrent 1480 // discovery; the STW compacting collector will redo discovery 1481 // more precisely, without being subject to floating garbage. 1482 // Leaving otherwise unreachable references in the discovered 1483 // lists would require special handling. 1484 ref_processor()->disable_discovery(); 1485 ref_processor()->abandon_partial_discovery(); 1486 ref_processor()->verify_no_references_recorded(); 1487 1488 if (first_state > Idling) { 1489 save_heap_summary(); 1490 } 1491 1492 do_compaction_work(clear_all_soft_refs); 1493 1494 // Has the GC time limit been exceeded? 1495 size_t max_eden_size = _young_gen->max_eden_size(); 1496 GCCause::Cause gc_cause = heap->gc_cause(); 1497 size_policy()->check_gc_overhead_limit(_young_gen->used(), 1498 _young_gen->eden()->used(), 1499 _cmsGen->max_capacity(), 1500 max_eden_size, 1501 full, 1502 gc_cause, 1503 heap->soft_ref_policy()); 1504 1505 // Reset the expansion cause, now that we just completed 1506 // a collection cycle. 1507 clear_expansion_cause(); 1508 _foregroundGCIsActive = false; 1509 return; 1510 } 1511 1512 // Resize the tenured generation 1513 // after obtaining the free list locks for the 1514 // two generations. 1515 void CMSCollector::compute_new_size() { 1516 assert_locked_or_safepoint(Heap_lock); 1517 FreelistLocker z(this); 1518 MetaspaceGC::compute_new_size(); 1519 _cmsGen->compute_new_size_free_list(); 1520 } 1521 1522 // A work method used by the foreground collector to do 1523 // a mark-sweep-compact. 1524 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { 1525 CMSHeap* heap = CMSHeap::heap(); 1526 1527 STWGCTimer* gc_timer = GenMarkSweep::gc_timer(); 1528 gc_timer->register_gc_start(); 1529 1530 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer(); 1531 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start()); 1532 1533 heap->pre_full_gc_dump(gc_timer); 1534 1535 GCTraceTime(Trace, gc, phases) t("CMS:MSC"); 1536 1537 // Temporarily widen the span of the weak reference processing to 1538 // the entire heap. 1539 MemRegion new_span(CMSHeap::heap()->reserved_region()); 1540 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span); 1541 // Temporarily, clear the "is_alive_non_header" field of the 1542 // reference processor. 1543 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL); 1544 // Temporarily make reference _processing_ single threaded (non-MT). 1545 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false); 1546 // Temporarily make refs discovery atomic 1547 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true); 1548 // Temporarily make reference _discovery_ single threaded (non-MT) 1549 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); 1550 1551 ref_processor()->set_enqueuing_is_done(false); 1552 ref_processor()->enable_discovery(); 1553 ref_processor()->setup_policy(clear_all_soft_refs); 1554 // If an asynchronous collection finishes, the _modUnionTable is 1555 // all clear. If we are assuming the collection from an asynchronous 1556 // collection, clear the _modUnionTable. 1557 assert(_collectorState != Idling || _modUnionTable.isAllClear(), 1558 "_modUnionTable should be clear if the baton was not passed"); 1559 _modUnionTable.clear_all(); 1560 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(), 1561 "mod union for klasses should be clear if the baton was passed"); 1562 _ct->cld_rem_set()->clear_mod_union(); 1563 1564 1565 // We must adjust the allocation statistics being maintained 1566 // in the free list space. We do so by reading and clearing 1567 // the sweep timer and updating the block flux rate estimates below. 1568 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive"); 1569 if (_inter_sweep_timer.is_active()) { 1570 _inter_sweep_timer.stop(); 1571 // Note that we do not use this sample to update the _inter_sweep_estimate. 1572 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), 1573 _inter_sweep_estimate.padded_average(), 1574 _intra_sweep_estimate.padded_average()); 1575 } 1576 1577 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs); 1578 #ifdef ASSERT 1579 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 1580 size_t free_size = cms_space->free(); 1581 assert(free_size == 1582 pointer_delta(cms_space->end(), cms_space->compaction_top()) 1583 * HeapWordSize, 1584 "All the free space should be compacted into one chunk at top"); 1585 assert(cms_space->dictionary()->total_chunk_size( 1586 debug_only(cms_space->freelistLock())) == 0 || 1587 cms_space->totalSizeInIndexedFreeLists() == 0, 1588 "All the free space should be in a single chunk"); 1589 size_t num = cms_space->totalCount(); 1590 assert((free_size == 0 && num == 0) || 1591 (free_size > 0 && (num == 1 || num == 2)), 1592 "There should be at most 2 free chunks after compaction"); 1593 #endif // ASSERT 1594 _collectorState = Resetting; 1595 assert(_restart_addr == NULL, 1596 "Should have been NULL'd before baton was passed"); 1597 reset_stw(); 1598 _cmsGen->reset_after_compaction(); 1599 _concurrent_cycles_since_last_unload = 0; 1600 1601 // Clear any data recorded in the PLAB chunk arrays. 1602 if (_survivor_plab_array != NULL) { 1603 reset_survivor_plab_arrays(); 1604 } 1605 1606 // Adjust the per-size allocation stats for the next epoch. 1607 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */); 1608 // Restart the "inter sweep timer" for the next epoch. 1609 _inter_sweep_timer.reset(); 1610 _inter_sweep_timer.start(); 1611 1612 // No longer a need to do a concurrent collection for Metaspace. 1613 MetaspaceGC::set_should_concurrent_collect(false); 1614 1615 heap->post_full_gc_dump(gc_timer); 1616 1617 gc_timer->register_gc_end(); 1618 1619 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions()); 1620 1621 // For a mark-sweep-compact, compute_new_size() will be called 1622 // in the heap's do_collection() method. 1623 } 1624 1625 void CMSCollector::print_eden_and_survivor_chunk_arrays() { 1626 Log(gc, heap) log; 1627 if (!log.is_trace()) { 1628 return; 1629 } 1630 1631 ContiguousSpace* eden_space = _young_gen->eden(); 1632 ContiguousSpace* from_space = _young_gen->from(); 1633 ContiguousSpace* to_space = _young_gen->to(); 1634 // Eden 1635 if (_eden_chunk_array != NULL) { 1636 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", 1637 p2i(eden_space->bottom()), p2i(eden_space->top()), 1638 p2i(eden_space->end()), eden_space->capacity()); 1639 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT, 1640 _eden_chunk_index, _eden_chunk_capacity); 1641 for (size_t i = 0; i < _eden_chunk_index; i++) { 1642 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i])); 1643 } 1644 } 1645 // Survivor 1646 if (_survivor_chunk_array != NULL) { 1647 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", 1648 p2i(from_space->bottom()), p2i(from_space->top()), 1649 p2i(from_space->end()), from_space->capacity()); 1650 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT, 1651 _survivor_chunk_index, _survivor_chunk_capacity); 1652 for (size_t i = 0; i < _survivor_chunk_index; i++) { 1653 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i])); 1654 } 1655 } 1656 } 1657 1658 void CMSCollector::getFreelistLocks() const { 1659 // Get locks for all free lists in all generations that this 1660 // collector is responsible for 1661 _cmsGen->freelistLock()->lock_without_safepoint_check(); 1662 } 1663 1664 void CMSCollector::releaseFreelistLocks() const { 1665 // Release locks for all free lists in all generations that this 1666 // collector is responsible for 1667 _cmsGen->freelistLock()->unlock(); 1668 } 1669 1670 bool CMSCollector::haveFreelistLocks() const { 1671 // Check locks for all free lists in all generations that this 1672 // collector is responsible for 1673 assert_lock_strong(_cmsGen->freelistLock()); 1674 PRODUCT_ONLY(ShouldNotReachHere()); 1675 return true; 1676 } 1677 1678 // A utility class that is used by the CMS collector to 1679 // temporarily "release" the foreground collector from its 1680 // usual obligation to wait for the background collector to 1681 // complete an ongoing phase before proceeding. 1682 class ReleaseForegroundGC: public StackObj { 1683 private: 1684 CMSCollector* _c; 1685 public: 1686 ReleaseForegroundGC(CMSCollector* c) : _c(c) { 1687 assert(_c->_foregroundGCShouldWait, "Else should not need to call"); 1688 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1689 // allow a potentially blocked foreground collector to proceed 1690 _c->_foregroundGCShouldWait = false; 1691 if (_c->_foregroundGCIsActive) { 1692 CGC_lock->notify(); 1693 } 1694 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 1695 "Possible deadlock"); 1696 } 1697 1698 ~ReleaseForegroundGC() { 1699 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); 1700 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1701 _c->_foregroundGCShouldWait = true; 1702 } 1703 }; 1704 1705 void CMSCollector::collect_in_background(GCCause::Cause cause) { 1706 assert(Thread::current()->is_ConcurrentGC_thread(), 1707 "A CMS asynchronous collection is only allowed on a CMS thread."); 1708 1709 CMSHeap* heap = CMSHeap::heap(); 1710 { 1711 bool safepoint_check = Mutex::_no_safepoint_check_flag; 1712 MutexLockerEx hl(Heap_lock, safepoint_check); 1713 FreelistLocker fll(this); 1714 MutexLockerEx x(CGC_lock, safepoint_check); 1715 if (_foregroundGCIsActive) { 1716 // The foreground collector is. Skip this 1717 // background collection. 1718 assert(!_foregroundGCShouldWait, "Should be clear"); 1719 return; 1720 } else { 1721 assert(_collectorState == Idling, "Should be idling before start."); 1722 _collectorState = InitialMarking; 1723 register_gc_start(cause); 1724 // Reset the expansion cause, now that we are about to begin 1725 // a new cycle. 1726 clear_expansion_cause(); 1727 1728 // Clear the MetaspaceGC flag since a concurrent collection 1729 // is starting but also clear it after the collection. 1730 MetaspaceGC::set_should_concurrent_collect(false); 1731 } 1732 // Decide if we want to enable class unloading as part of the 1733 // ensuing concurrent GC cycle. 1734 update_should_unload_classes(); 1735 _full_gc_requested = false; // acks all outstanding full gc requests 1736 _full_gc_cause = GCCause::_no_gc; 1737 // Signal that we are about to start a collection 1738 heap->increment_total_full_collections(); // ... starting a collection cycle 1739 _collection_count_start = heap->total_full_collections(); 1740 } 1741 1742 size_t prev_used = _cmsGen->used(); 1743 1744 // The change of the collection state is normally done at this level; 1745 // the exceptions are phases that are executed while the world is 1746 // stopped. For those phases the change of state is done while the 1747 // world is stopped. For baton passing purposes this allows the 1748 // background collector to finish the phase and change state atomically. 1749 // The foreground collector cannot wait on a phase that is done 1750 // while the world is stopped because the foreground collector already 1751 // has the world stopped and would deadlock. 1752 while (_collectorState != Idling) { 1753 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d", 1754 p2i(Thread::current()), _collectorState); 1755 // The foreground collector 1756 // holds the Heap_lock throughout its collection. 1757 // holds the CMS token (but not the lock) 1758 // except while it is waiting for the background collector to yield. 1759 // 1760 // The foreground collector should be blocked (not for long) 1761 // if the background collector is about to start a phase 1762 // executed with world stopped. If the background 1763 // collector has already started such a phase, the 1764 // foreground collector is blocked waiting for the 1765 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) 1766 // are executed in the VM thread. 1767 // 1768 // The locking order is 1769 // PendingListLock (PLL) -- if applicable (FinalMarking) 1770 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) 1771 // CMS token (claimed in 1772 // stop_world_and_do() --> 1773 // safepoint_synchronize() --> 1774 // CMSThread::synchronize()) 1775 1776 { 1777 // Check if the FG collector wants us to yield. 1778 CMSTokenSync x(true); // is cms thread 1779 if (waitForForegroundGC()) { 1780 // We yielded to a foreground GC, nothing more to be 1781 // done this round. 1782 assert(_foregroundGCShouldWait == false, "We set it to false in " 1783 "waitForForegroundGC()"); 1784 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d", 1785 p2i(Thread::current()), _collectorState); 1786 return; 1787 } else { 1788 // The background collector can run but check to see if the 1789 // foreground collector has done a collection while the 1790 // background collector was waiting to get the CGC_lock 1791 // above. If yes, break so that _foregroundGCShouldWait 1792 // is cleared before returning. 1793 if (_collectorState == Idling) { 1794 break; 1795 } 1796 } 1797 } 1798 1799 assert(_foregroundGCShouldWait, "Foreground collector, if active, " 1800 "should be waiting"); 1801 1802 switch (_collectorState) { 1803 case InitialMarking: 1804 { 1805 ReleaseForegroundGC x(this); 1806 stats().record_cms_begin(); 1807 VM_CMS_Initial_Mark initial_mark_op(this); 1808 VMThread::execute(&initial_mark_op); 1809 } 1810 // The collector state may be any legal state at this point 1811 // since the background collector may have yielded to the 1812 // foreground collector. 1813 break; 1814 case Marking: 1815 // initial marking in checkpointRootsInitialWork has been completed 1816 if (markFromRoots()) { // we were successful 1817 assert(_collectorState == Precleaning, "Collector state should " 1818 "have changed"); 1819 } else { 1820 assert(_foregroundGCIsActive, "Internal state inconsistency"); 1821 } 1822 break; 1823 case Precleaning: 1824 // marking from roots in markFromRoots has been completed 1825 preclean(); 1826 assert(_collectorState == AbortablePreclean || 1827 _collectorState == FinalMarking, 1828 "Collector state should have changed"); 1829 break; 1830 case AbortablePreclean: 1831 abortable_preclean(); 1832 assert(_collectorState == FinalMarking, "Collector state should " 1833 "have changed"); 1834 break; 1835 case FinalMarking: 1836 { 1837 ReleaseForegroundGC x(this); 1838 1839 VM_CMS_Final_Remark final_remark_op(this); 1840 VMThread::execute(&final_remark_op); 1841 } 1842 assert(_foregroundGCShouldWait, "block post-condition"); 1843 break; 1844 case Sweeping: 1845 // final marking in checkpointRootsFinal has been completed 1846 sweep(); 1847 assert(_collectorState == Resizing, "Collector state change " 1848 "to Resizing must be done under the free_list_lock"); 1849 1850 case Resizing: { 1851 // Sweeping has been completed... 1852 // At this point the background collection has completed. 1853 // Don't move the call to compute_new_size() down 1854 // into code that might be executed if the background 1855 // collection was preempted. 1856 { 1857 ReleaseForegroundGC x(this); // unblock FG collection 1858 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag); 1859 CMSTokenSync z(true); // not strictly needed. 1860 if (_collectorState == Resizing) { 1861 compute_new_size(); 1862 save_heap_summary(); 1863 _collectorState = Resetting; 1864 } else { 1865 assert(_collectorState == Idling, "The state should only change" 1866 " because the foreground collector has finished the collection"); 1867 } 1868 } 1869 break; 1870 } 1871 case Resetting: 1872 // CMS heap resizing has been completed 1873 reset_concurrent(); 1874 assert(_collectorState == Idling, "Collector state should " 1875 "have changed"); 1876 1877 MetaspaceGC::set_should_concurrent_collect(false); 1878 1879 stats().record_cms_end(); 1880 // Don't move the concurrent_phases_end() and compute_new_size() 1881 // calls to here because a preempted background collection 1882 // has it's state set to "Resetting". 1883 break; 1884 case Idling: 1885 default: 1886 ShouldNotReachHere(); 1887 break; 1888 } 1889 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d", 1890 p2i(Thread::current()), _collectorState); 1891 assert(_foregroundGCShouldWait, "block post-condition"); 1892 } 1893 1894 // Should this be in gc_epilogue? 1895 heap->counters()->update_counters(); 1896 1897 { 1898 // Clear _foregroundGCShouldWait and, in the event that the 1899 // foreground collector is waiting, notify it, before 1900 // returning. 1901 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1902 _foregroundGCShouldWait = false; 1903 if (_foregroundGCIsActive) { 1904 CGC_lock->notify(); 1905 } 1906 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 1907 "Possible deadlock"); 1908 } 1909 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d", 1910 p2i(Thread::current()), _collectorState); 1911 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)", 1912 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K); 1913 } 1914 1915 void CMSCollector::register_gc_start(GCCause::Cause cause) { 1916 _cms_start_registered = true; 1917 _gc_timer_cm->register_gc_start(); 1918 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start()); 1919 } 1920 1921 void CMSCollector::register_gc_end() { 1922 if (_cms_start_registered) { 1923 report_heap_summary(GCWhen::AfterGC); 1924 1925 _gc_timer_cm->register_gc_end(); 1926 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions()); 1927 _cms_start_registered = false; 1928 } 1929 } 1930 1931 void CMSCollector::save_heap_summary() { 1932 CMSHeap* heap = CMSHeap::heap(); 1933 _last_heap_summary = heap->create_heap_summary(); 1934 _last_metaspace_summary = heap->create_metaspace_summary(); 1935 } 1936 1937 void CMSCollector::report_heap_summary(GCWhen::Type when) { 1938 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary); 1939 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary); 1940 } 1941 1942 bool CMSCollector::waitForForegroundGC() { 1943 bool res = false; 1944 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 1945 "CMS thread should have CMS token"); 1946 // Block the foreground collector until the 1947 // background collectors decides whether to 1948 // yield. 1949 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1950 _foregroundGCShouldWait = true; 1951 if (_foregroundGCIsActive) { 1952 // The background collector yields to the 1953 // foreground collector and returns a value 1954 // indicating that it has yielded. The foreground 1955 // collector can proceed. 1956 res = true; 1957 _foregroundGCShouldWait = false; 1958 ConcurrentMarkSweepThread::clear_CMS_flag( 1959 ConcurrentMarkSweepThread::CMS_cms_has_token); 1960 ConcurrentMarkSweepThread::set_CMS_flag( 1961 ConcurrentMarkSweepThread::CMS_cms_wants_token); 1962 // Get a possibly blocked foreground thread going 1963 CGC_lock->notify(); 1964 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", 1965 p2i(Thread::current()), _collectorState); 1966 while (_foregroundGCIsActive) { 1967 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 1968 } 1969 ConcurrentMarkSweepThread::set_CMS_flag( 1970 ConcurrentMarkSweepThread::CMS_cms_has_token); 1971 ConcurrentMarkSweepThread::clear_CMS_flag( 1972 ConcurrentMarkSweepThread::CMS_cms_wants_token); 1973 } 1974 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", 1975 p2i(Thread::current()), _collectorState); 1976 return res; 1977 } 1978 1979 // Because of the need to lock the free lists and other structures in 1980 // the collector, common to all the generations that the collector is 1981 // collecting, we need the gc_prologues of individual CMS generations 1982 // delegate to their collector. It may have been simpler had the 1983 // current infrastructure allowed one to call a prologue on a 1984 // collector. In the absence of that we have the generation's 1985 // prologue delegate to the collector, which delegates back 1986 // some "local" work to a worker method in the individual generations 1987 // that it's responsible for collecting, while itself doing any 1988 // work common to all generations it's responsible for. A similar 1989 // comment applies to the gc_epilogue()'s. 1990 // The role of the variable _between_prologue_and_epilogue is to 1991 // enforce the invocation protocol. 1992 void CMSCollector::gc_prologue(bool full) { 1993 // Call gc_prologue_work() for the CMSGen 1994 // we are responsible for. 1995 1996 // The following locking discipline assumes that we are only called 1997 // when the world is stopped. 1998 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); 1999 2000 // The CMSCollector prologue must call the gc_prologues for the 2001 // "generations" that it's responsible 2002 // for. 2003 2004 assert( Thread::current()->is_VM_thread() 2005 || ( CMSScavengeBeforeRemark 2006 && Thread::current()->is_ConcurrentGC_thread()), 2007 "Incorrect thread type for prologue execution"); 2008 2009 if (_between_prologue_and_epilogue) { 2010 // We have already been invoked; this is a gc_prologue delegation 2011 // from yet another CMS generation that we are responsible for, just 2012 // ignore it since all relevant work has already been done. 2013 return; 2014 } 2015 2016 // set a bit saying prologue has been called; cleared in epilogue 2017 _between_prologue_and_epilogue = true; 2018 // Claim locks for common data structures, then call gc_prologue_work() 2019 // for each CMSGen. 2020 2021 getFreelistLocks(); // gets free list locks on constituent spaces 2022 bitMapLock()->lock_without_safepoint_check(); 2023 2024 // Should call gc_prologue_work() for all cms gens we are responsible for 2025 bool duringMarking = _collectorState >= Marking 2026 && _collectorState < Sweeping; 2027 2028 // The young collections clear the modified oops state, which tells if 2029 // there are any modified oops in the class. The remark phase also needs 2030 // that information. Tell the young collection to save the union of all 2031 // modified klasses. 2032 if (duringMarking) { 2033 _ct->cld_rem_set()->set_accumulate_modified_oops(true); 2034 } 2035 2036 bool registerClosure = duringMarking; 2037 2038 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar); 2039 2040 if (!full) { 2041 stats().record_gc0_begin(); 2042 } 2043 } 2044 2045 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { 2046 2047 _capacity_at_prologue = capacity(); 2048 _used_at_prologue = used(); 2049 2050 // We enable promotion tracking so that card-scanning can recognize 2051 // which objects have been promoted during this GC and skip them. 2052 for (uint i = 0; i < ParallelGCThreads; i++) { 2053 _par_gc_thread_states[i]->promo.startTrackingPromotions(); 2054 } 2055 2056 // Delegate to CMScollector which knows how to coordinate between 2057 // this and any other CMS generations that it is responsible for 2058 // collecting. 2059 collector()->gc_prologue(full); 2060 } 2061 2062 // This is a "private" interface for use by this generation's CMSCollector. 2063 // Not to be called directly by any other entity (for instance, 2064 // GenCollectedHeap, which calls the "public" gc_prologue method above). 2065 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, 2066 bool registerClosure, ModUnionClosure* modUnionClosure) { 2067 assert(!incremental_collection_failed(), "Shouldn't be set yet"); 2068 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, 2069 "Should be NULL"); 2070 if (registerClosure) { 2071 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); 2072 } 2073 cmsSpace()->gc_prologue(); 2074 // Clear stat counters 2075 NOT_PRODUCT( 2076 assert(_numObjectsPromoted == 0, "check"); 2077 assert(_numWordsPromoted == 0, "check"); 2078 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently", 2079 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); 2080 _numObjectsAllocated = 0; 2081 _numWordsAllocated = 0; 2082 ) 2083 } 2084 2085 void CMSCollector::gc_epilogue(bool full) { 2086 // The following locking discipline assumes that we are only called 2087 // when the world is stopped. 2088 assert(SafepointSynchronize::is_at_safepoint(), 2089 "world is stopped assumption"); 2090 2091 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks 2092 // if linear allocation blocks need to be appropriately marked to allow the 2093 // the blocks to be parsable. We also check here whether we need to nudge the 2094 // CMS collector thread to start a new cycle (if it's not already active). 2095 assert( Thread::current()->is_VM_thread() 2096 || ( CMSScavengeBeforeRemark 2097 && Thread::current()->is_ConcurrentGC_thread()), 2098 "Incorrect thread type for epilogue execution"); 2099 2100 if (!_between_prologue_and_epilogue) { 2101 // We have already been invoked; this is a gc_epilogue delegation 2102 // from yet another CMS generation that we are responsible for, just 2103 // ignore it since all relevant work has already been done. 2104 return; 2105 } 2106 assert(haveFreelistLocks(), "must have freelist locks"); 2107 assert_lock_strong(bitMapLock()); 2108 2109 _ct->cld_rem_set()->set_accumulate_modified_oops(false); 2110 2111 _cmsGen->gc_epilogue_work(full); 2112 2113 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { 2114 // in case sampling was not already enabled, enable it 2115 _start_sampling = true; 2116 } 2117 // reset _eden_chunk_array so sampling starts afresh 2118 _eden_chunk_index = 0; 2119 2120 size_t cms_used = _cmsGen->cmsSpace()->used(); 2121 2122 // update performance counters - this uses a special version of 2123 // update_counters() that allows the utilization to be passed as a 2124 // parameter, avoiding multiple calls to used(). 2125 // 2126 _cmsGen->update_counters(cms_used); 2127 2128 bitMapLock()->unlock(); 2129 releaseFreelistLocks(); 2130 2131 if (!CleanChunkPoolAsync) { 2132 Chunk::clean_chunk_pool(); 2133 } 2134 2135 set_did_compact(false); 2136 _between_prologue_and_epilogue = false; // ready for next cycle 2137 } 2138 2139 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { 2140 collector()->gc_epilogue(full); 2141 2142 // When using ParNew, promotion tracking should have already been 2143 // disabled. However, the prologue (which enables promotion 2144 // tracking) and epilogue are called irrespective of the type of 2145 // GC. So they will also be called before and after Full GCs, during 2146 // which promotion tracking will not be explicitly disabled. So, 2147 // it's safer to also disable it here too (to be symmetric with 2148 // enabling it in the prologue). 2149 for (uint i = 0; i < ParallelGCThreads; i++) { 2150 _par_gc_thread_states[i]->promo.stopTrackingPromotions(); 2151 } 2152 } 2153 2154 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { 2155 assert(!incremental_collection_failed(), "Should have been cleared"); 2156 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); 2157 cmsSpace()->gc_epilogue(); 2158 // Print stat counters 2159 NOT_PRODUCT( 2160 assert(_numObjectsAllocated == 0, "check"); 2161 assert(_numWordsAllocated == 0, "check"); 2162 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", 2163 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); 2164 _numObjectsPromoted = 0; 2165 _numWordsPromoted = 0; 2166 ) 2167 2168 // Call down the chain in contiguous_available needs the freelistLock 2169 // so print this out before releasing the freeListLock. 2170 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available()); 2171 } 2172 2173 #ifndef PRODUCT 2174 bool CMSCollector::have_cms_token() { 2175 Thread* thr = Thread::current(); 2176 if (thr->is_VM_thread()) { 2177 return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); 2178 } else if (thr->is_ConcurrentGC_thread()) { 2179 return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); 2180 } else if (thr->is_GC_task_thread()) { 2181 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && 2182 ParGCRareEvent_lock->owned_by_self(); 2183 } 2184 return false; 2185 } 2186 2187 // Check reachability of the given heap address in CMS generation, 2188 // treating all other generations as roots. 2189 bool CMSCollector::is_cms_reachable(HeapWord* addr) { 2190 // We could "guarantee" below, rather than assert, but I'll 2191 // leave these as "asserts" so that an adventurous debugger 2192 // could try this in the product build provided some subset of 2193 // the conditions were met, provided they were interested in the 2194 // results and knew that the computation below wouldn't interfere 2195 // with other concurrent computations mutating the structures 2196 // being read or written. 2197 assert(SafepointSynchronize::is_at_safepoint(), 2198 "Else mutations in object graph will make answer suspect"); 2199 assert(have_cms_token(), "Should hold cms token"); 2200 assert(haveFreelistLocks(), "must hold free list locks"); 2201 assert_lock_strong(bitMapLock()); 2202 2203 // Clear the marking bit map array before starting, but, just 2204 // for kicks, first report if the given address is already marked 2205 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr), 2206 _markBitMap.isMarked(addr) ? "" : " not"); 2207 2208 if (verify_after_remark()) { 2209 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); 2210 bool result = verification_mark_bm()->isMarked(addr); 2211 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr), 2212 result ? "IS" : "is NOT"); 2213 return result; 2214 } else { 2215 tty->print_cr("Could not compute result"); 2216 return false; 2217 } 2218 } 2219 #endif 2220 2221 void 2222 CMSCollector::print_on_error(outputStream* st) { 2223 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector; 2224 if (collector != NULL) { 2225 CMSBitMap* bitmap = &collector->_markBitMap; 2226 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap)); 2227 bitmap->print_on_error(st, " Bits: "); 2228 2229 st->cr(); 2230 2231 CMSBitMap* mut_bitmap = &collector->_modUnionTable; 2232 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap)); 2233 mut_bitmap->print_on_error(st, " Bits: "); 2234 } 2235 } 2236 2237 //////////////////////////////////////////////////////// 2238 // CMS Verification Support 2239 //////////////////////////////////////////////////////// 2240 // Following the remark phase, the following invariant 2241 // should hold -- each object in the CMS heap which is 2242 // marked in markBitMap() should be marked in the verification_mark_bm(). 2243 2244 class VerifyMarkedClosure: public BitMapClosure { 2245 CMSBitMap* _marks; 2246 bool _failed; 2247 2248 public: 2249 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} 2250 2251 bool do_bit(size_t offset) { 2252 HeapWord* addr = _marks->offsetToHeapWord(offset); 2253 if (!_marks->isMarked(addr)) { 2254 Log(gc, verify) log; 2255 ResourceMark rm; 2256 LogStream ls(log.error()); 2257 oop(addr)->print_on(&ls); 2258 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); 2259 _failed = true; 2260 } 2261 return true; 2262 } 2263 2264 bool failed() { return _failed; } 2265 }; 2266 2267 bool CMSCollector::verify_after_remark() { 2268 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking."); 2269 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); 2270 static bool init = false; 2271 2272 assert(SafepointSynchronize::is_at_safepoint(), 2273 "Else mutations in object graph will make answer suspect"); 2274 assert(have_cms_token(), 2275 "Else there may be mutual interference in use of " 2276 " verification data structures"); 2277 assert(_collectorState > Marking && _collectorState <= Sweeping, 2278 "Else marking info checked here may be obsolete"); 2279 assert(haveFreelistLocks(), "must hold free list locks"); 2280 assert_lock_strong(bitMapLock()); 2281 2282 2283 // Allocate marking bit map if not already allocated 2284 if (!init) { // first time 2285 if (!verification_mark_bm()->allocate(_span)) { 2286 return false; 2287 } 2288 init = true; 2289 } 2290 2291 assert(verification_mark_stack()->isEmpty(), "Should be empty"); 2292 2293 // Turn off refs discovery -- so we will be tracing through refs. 2294 // This is as intended, because by this time 2295 // GC must already have cleared any refs that need to be cleared, 2296 // and traced those that need to be marked; moreover, 2297 // the marking done here is not going to interfere in any 2298 // way with the marking information used by GC. 2299 NoRefDiscovery no_discovery(ref_processor()); 2300 2301 #if COMPILER2_OR_JVMCI 2302 DerivedPointerTableDeactivate dpt_deact; 2303 #endif 2304 2305 // Clear any marks from a previous round 2306 verification_mark_bm()->clear_all(); 2307 assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); 2308 verify_work_stacks_empty(); 2309 2310 CMSHeap* heap = CMSHeap::heap(); 2311 heap->ensure_parsability(false); // fill TLABs, but no need to retire them 2312 // Update the saved marks which may affect the root scans. 2313 heap->save_marks(); 2314 2315 if (CMSRemarkVerifyVariant == 1) { 2316 // In this first variant of verification, we complete 2317 // all marking, then check if the new marks-vector is 2318 // a subset of the CMS marks-vector. 2319 verify_after_remark_work_1(); 2320 } else { 2321 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2"); 2322 // In this second variant of verification, we flag an error 2323 // (i.e. an object reachable in the new marks-vector not reachable 2324 // in the CMS marks-vector) immediately, also indicating the 2325 // identify of an object (A) that references the unmarked object (B) -- 2326 // presumably, a mutation to A failed to be picked up by preclean/remark? 2327 verify_after_remark_work_2(); 2328 } 2329 2330 return true; 2331 } 2332 2333 void CMSCollector::verify_after_remark_work_1() { 2334 ResourceMark rm; 2335 HandleMark hm; 2336 CMSHeap* heap = CMSHeap::heap(); 2337 2338 // Get a clear set of claim bits for the roots processing to work with. 2339 ClassLoaderDataGraph::clear_claimed_marks(); 2340 2341 // Mark from roots one level into CMS 2342 MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); 2343 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 2344 2345 { 2346 StrongRootsScope srs(1); 2347 2348 heap->cms_process_roots(&srs, 2349 true, // young gen as roots 2350 GenCollectedHeap::ScanningOption(roots_scanning_options()), 2351 should_unload_classes(), 2352 ¬Older, 2353 NULL); 2354 } 2355 2356 // Now mark from the roots 2357 MarkFromRootsClosure markFromRootsClosure(this, _span, 2358 verification_mark_bm(), verification_mark_stack(), 2359 false /* don't yield */, true /* verifying */); 2360 assert(_restart_addr == NULL, "Expected pre-condition"); 2361 verification_mark_bm()->iterate(&markFromRootsClosure); 2362 while (_restart_addr != NULL) { 2363 // Deal with stack overflow: by restarting at the indicated 2364 // address. 2365 HeapWord* ra = _restart_addr; 2366 markFromRootsClosure.reset(ra); 2367 _restart_addr = NULL; 2368 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); 2369 } 2370 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); 2371 verify_work_stacks_empty(); 2372 2373 // Marking completed -- now verify that each bit marked in 2374 // verification_mark_bm() is also marked in markBitMap(); flag all 2375 // errors by printing corresponding objects. 2376 VerifyMarkedClosure vcl(markBitMap()); 2377 verification_mark_bm()->iterate(&vcl); 2378 if (vcl.failed()) { 2379 Log(gc, verify) log; 2380 log.error("Failed marking verification after remark"); 2381 ResourceMark rm; 2382 LogStream ls(log.error()); 2383 heap->print_on(&ls); 2384 fatal("CMS: failed marking verification after remark"); 2385 } 2386 } 2387 2388 class VerifyCLDOopsCLDClosure : public CLDClosure { 2389 class VerifyCLDOopsClosure : public OopClosure { 2390 CMSBitMap* _bitmap; 2391 public: 2392 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { } 2393 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); } 2394 void do_oop(narrowOop* p) { ShouldNotReachHere(); } 2395 } _oop_closure; 2396 public: 2397 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {} 2398 void do_cld(ClassLoaderData* cld) { 2399 cld->oops_do(&_oop_closure, false, false); 2400 } 2401 }; 2402 2403 void CMSCollector::verify_after_remark_work_2() { 2404 ResourceMark rm; 2405 HandleMark hm; 2406 CMSHeap* heap = CMSHeap::heap(); 2407 2408 // Get a clear set of claim bits for the roots processing to work with. 2409 ClassLoaderDataGraph::clear_claimed_marks(); 2410 2411 // Mark from roots one level into CMS 2412 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), 2413 markBitMap()); 2414 CLDToOopClosure cld_closure(¬Older, true); 2415 2416 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 2417 2418 { 2419 StrongRootsScope srs(1); 2420 2421 heap->cms_process_roots(&srs, 2422 true, // young gen as roots 2423 GenCollectedHeap::ScanningOption(roots_scanning_options()), 2424 should_unload_classes(), 2425 ¬Older, 2426 &cld_closure); 2427 } 2428 2429 // Now mark from the roots 2430 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, 2431 verification_mark_bm(), markBitMap(), verification_mark_stack()); 2432 assert(_restart_addr == NULL, "Expected pre-condition"); 2433 verification_mark_bm()->iterate(&markFromRootsClosure); 2434 while (_restart_addr != NULL) { 2435 // Deal with stack overflow: by restarting at the indicated 2436 // address. 2437 HeapWord* ra = _restart_addr; 2438 markFromRootsClosure.reset(ra); 2439 _restart_addr = NULL; 2440 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); 2441 } 2442 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); 2443 verify_work_stacks_empty(); 2444 2445 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm()); 2446 ClassLoaderDataGraph::cld_do(&verify_cld_oops); 2447 2448 // Marking completed -- now verify that each bit marked in 2449 // verification_mark_bm() is also marked in markBitMap(); flag all 2450 // errors by printing corresponding objects. 2451 VerifyMarkedClosure vcl(markBitMap()); 2452 verification_mark_bm()->iterate(&vcl); 2453 assert(!vcl.failed(), "Else verification above should not have succeeded"); 2454 } 2455 2456 void ConcurrentMarkSweepGeneration::save_marks() { 2457 // delegate to CMS space 2458 cmsSpace()->save_marks(); 2459 } 2460 2461 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { 2462 return cmsSpace()->no_allocs_since_save_marks(); 2463 } 2464 2465 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \ 2466 \ 2467 void ConcurrentMarkSweepGeneration:: \ 2468 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ 2469 cl->set_generation(this); \ 2470 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \ 2471 cl->reset_generation(); \ 2472 save_marks(); \ 2473 } 2474 2475 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN) 2476 2477 void 2478 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) { 2479 if (freelistLock()->owned_by_self()) { 2480 Generation::oop_iterate(cl); 2481 } else { 2482 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2483 Generation::oop_iterate(cl); 2484 } 2485 } 2486 2487 void 2488 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { 2489 if (freelistLock()->owned_by_self()) { 2490 Generation::object_iterate(cl); 2491 } else { 2492 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2493 Generation::object_iterate(cl); 2494 } 2495 } 2496 2497 void 2498 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) { 2499 if (freelistLock()->owned_by_self()) { 2500 Generation::safe_object_iterate(cl); 2501 } else { 2502 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2503 Generation::safe_object_iterate(cl); 2504 } 2505 } 2506 2507 void 2508 ConcurrentMarkSweepGeneration::post_compact() { 2509 } 2510 2511 void 2512 ConcurrentMarkSweepGeneration::prepare_for_verify() { 2513 // Fix the linear allocation blocks to look like free blocks. 2514 2515 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those 2516 // are not called when the heap is verified during universe initialization and 2517 // at vm shutdown. 2518 if (freelistLock()->owned_by_self()) { 2519 cmsSpace()->prepare_for_verify(); 2520 } else { 2521 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); 2522 cmsSpace()->prepare_for_verify(); 2523 } 2524 } 2525 2526 void 2527 ConcurrentMarkSweepGeneration::verify() { 2528 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those 2529 // are not called when the heap is verified during universe initialization and 2530 // at vm shutdown. 2531 if (freelistLock()->owned_by_self()) { 2532 cmsSpace()->verify(); 2533 } else { 2534 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); 2535 cmsSpace()->verify(); 2536 } 2537 } 2538 2539 void CMSCollector::verify() { 2540 _cmsGen->verify(); 2541 } 2542 2543 #ifndef PRODUCT 2544 bool CMSCollector::overflow_list_is_empty() const { 2545 assert(_num_par_pushes >= 0, "Inconsistency"); 2546 if (_overflow_list == NULL) { 2547 assert(_num_par_pushes == 0, "Inconsistency"); 2548 } 2549 return _overflow_list == NULL; 2550 } 2551 2552 // The methods verify_work_stacks_empty() and verify_overflow_empty() 2553 // merely consolidate assertion checks that appear to occur together frequently. 2554 void CMSCollector::verify_work_stacks_empty() const { 2555 assert(_markStack.isEmpty(), "Marking stack should be empty"); 2556 assert(overflow_list_is_empty(), "Overflow list should be empty"); 2557 } 2558 2559 void CMSCollector::verify_overflow_empty() const { 2560 assert(overflow_list_is_empty(), "Overflow list should be empty"); 2561 assert(no_preserved_marks(), "No preserved marks"); 2562 } 2563 #endif // PRODUCT 2564 2565 // Decide if we want to enable class unloading as part of the 2566 // ensuing concurrent GC cycle. We will collect and 2567 // unload classes if it's the case that: 2568 // (a) class unloading is enabled at the command line, and 2569 // (b) old gen is getting really full 2570 // NOTE: Provided there is no change in the state of the heap between 2571 // calls to this method, it should have idempotent results. Moreover, 2572 // its results should be monotonically increasing (i.e. going from 0 to 1, 2573 // but not 1 to 0) between successive calls between which the heap was 2574 // not collected. For the implementation below, it must thus rely on 2575 // the property that concurrent_cycles_since_last_unload() 2576 // will not decrease unless a collection cycle happened and that 2577 // _cmsGen->is_too_full() are 2578 // themselves also monotonic in that sense. See check_monotonicity() 2579 // below. 2580 void CMSCollector::update_should_unload_classes() { 2581 _should_unload_classes = false; 2582 if (CMSClassUnloadingEnabled) { 2583 _should_unload_classes = (concurrent_cycles_since_last_unload() >= 2584 CMSClassUnloadingMaxInterval) 2585 || _cmsGen->is_too_full(); 2586 } 2587 } 2588 2589 bool ConcurrentMarkSweepGeneration::is_too_full() const { 2590 bool res = should_concurrent_collect(); 2591 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0); 2592 return res; 2593 } 2594 2595 void CMSCollector::setup_cms_unloading_and_verification_state() { 2596 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC 2597 || VerifyBeforeExit; 2598 const int rso = GenCollectedHeap::SO_AllCodeCache; 2599 2600 // We set the proper root for this CMS cycle here. 2601 if (should_unload_classes()) { // Should unload classes this cycle 2602 remove_root_scanning_option(rso); // Shrink the root set appropriately 2603 set_verifying(should_verify); // Set verification state for this cycle 2604 return; // Nothing else needs to be done at this time 2605 } 2606 2607 // Not unloading classes this cycle 2608 assert(!should_unload_classes(), "Inconsistency!"); 2609 2610 // If we are not unloading classes then add SO_AllCodeCache to root 2611 // scanning options. 2612 add_root_scanning_option(rso); 2613 2614 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { 2615 set_verifying(true); 2616 } else if (verifying() && !should_verify) { 2617 // We were verifying, but some verification flags got disabled. 2618 set_verifying(false); 2619 // Exclude symbols, strings and code cache elements from root scanning to 2620 // reduce IM and RM pauses. 2621 remove_root_scanning_option(rso); 2622 } 2623 } 2624 2625 2626 #ifndef PRODUCT 2627 HeapWord* CMSCollector::block_start(const void* p) const { 2628 const HeapWord* addr = (HeapWord*)p; 2629 if (_span.contains(p)) { 2630 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { 2631 return _cmsGen->cmsSpace()->block_start(p); 2632 } 2633 } 2634 return NULL; 2635 } 2636 #endif 2637 2638 HeapWord* 2639 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, 2640 bool tlab, 2641 bool parallel) { 2642 CMSSynchronousYieldRequest yr; 2643 assert(!tlab, "Can't deal with TLAB allocation"); 2644 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2645 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation); 2646 if (GCExpandToAllocateDelayMillis > 0) { 2647 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 2648 } 2649 return have_lock_and_allocate(word_size, tlab); 2650 } 2651 2652 void ConcurrentMarkSweepGeneration::expand_for_gc_cause( 2653 size_t bytes, 2654 size_t expand_bytes, 2655 CMSExpansionCause::Cause cause) 2656 { 2657 2658 bool success = expand(bytes, expand_bytes); 2659 2660 // remember why we expanded; this information is used 2661 // by shouldConcurrentCollect() when making decisions on whether to start 2662 // a new CMS cycle. 2663 if (success) { 2664 set_expansion_cause(cause); 2665 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause)); 2666 } 2667 } 2668 2669 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { 2670 HeapWord* res = NULL; 2671 MutexLocker x(ParGCRareEvent_lock); 2672 while (true) { 2673 // Expansion by some other thread might make alloc OK now: 2674 res = ps->lab.alloc(word_sz); 2675 if (res != NULL) return res; 2676 // If there's not enough expansion space available, give up. 2677 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { 2678 return NULL; 2679 } 2680 // Otherwise, we try expansion. 2681 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab); 2682 // Now go around the loop and try alloc again; 2683 // A competing par_promote might beat us to the expansion space, 2684 // so we may go around the loop again if promotion fails again. 2685 if (GCExpandToAllocateDelayMillis > 0) { 2686 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 2687 } 2688 } 2689 } 2690 2691 2692 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( 2693 PromotionInfo* promo) { 2694 MutexLocker x(ParGCRareEvent_lock); 2695 size_t refill_size_bytes = promo->refillSize() * HeapWordSize; 2696 while (true) { 2697 // Expansion by some other thread might make alloc OK now: 2698 if (promo->ensure_spooling_space()) { 2699 assert(promo->has_spooling_space(), 2700 "Post-condition of successful ensure_spooling_space()"); 2701 return true; 2702 } 2703 // If there's not enough expansion space available, give up. 2704 if (_virtual_space.uncommitted_size() < refill_size_bytes) { 2705 return false; 2706 } 2707 // Otherwise, we try expansion. 2708 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space); 2709 // Now go around the loop and try alloc again; 2710 // A competing allocation might beat us to the expansion space, 2711 // so we may go around the loop again if allocation fails again. 2712 if (GCExpandToAllocateDelayMillis > 0) { 2713 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 2714 } 2715 } 2716 } 2717 2718 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { 2719 // Only shrink if a compaction was done so that all the free space 2720 // in the generation is in a contiguous block at the end. 2721 if (did_compact()) { 2722 CardGeneration::shrink(bytes); 2723 } 2724 } 2725 2726 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() { 2727 assert_locked_or_safepoint(Heap_lock); 2728 } 2729 2730 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) { 2731 assert_locked_or_safepoint(Heap_lock); 2732 assert_lock_strong(freelistLock()); 2733 log_trace(gc)("Shrinking of CMS not yet implemented"); 2734 return; 2735 } 2736 2737 2738 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent 2739 // phases. 2740 class CMSPhaseAccounting: public StackObj { 2741 public: 2742 CMSPhaseAccounting(CMSCollector *collector, 2743 const char *title); 2744 ~CMSPhaseAccounting(); 2745 2746 private: 2747 CMSCollector *_collector; 2748 const char *_title; 2749 GCTraceConcTime(Info, gc) _trace_time; 2750 2751 public: 2752 // Not MT-safe; so do not pass around these StackObj's 2753 // where they may be accessed by other threads. 2754 double wallclock_millis() { 2755 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time()); 2756 } 2757 }; 2758 2759 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, 2760 const char *title) : 2761 _collector(collector), _title(title), _trace_time(title) { 2762 2763 _collector->resetYields(); 2764 _collector->resetTimer(); 2765 _collector->startTimer(); 2766 _collector->gc_timer_cm()->register_gc_concurrent_start(title); 2767 } 2768 2769 CMSPhaseAccounting::~CMSPhaseAccounting() { 2770 _collector->gc_timer_cm()->register_gc_concurrent_end(); 2771 _collector->stopTimer(); 2772 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks())); 2773 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields()); 2774 } 2775 2776 // CMS work 2777 2778 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask. 2779 class CMSParMarkTask : public AbstractGangTask { 2780 protected: 2781 CMSCollector* _collector; 2782 uint _n_workers; 2783 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) : 2784 AbstractGangTask(name), 2785 _collector(collector), 2786 _n_workers(n_workers) {} 2787 // Work method in support of parallel rescan ... of young gen spaces 2788 void do_young_space_rescan(OopsInGenClosure* cl, 2789 ContiguousSpace* space, 2790 HeapWord** chunk_array, size_t chunk_top); 2791 void work_on_young_gen_roots(OopsInGenClosure* cl); 2792 }; 2793 2794 // Parallel initial mark task 2795 class CMSParInitialMarkTask: public CMSParMarkTask { 2796 StrongRootsScope* _strong_roots_scope; 2797 public: 2798 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) : 2799 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers), 2800 _strong_roots_scope(strong_roots_scope) {} 2801 void work(uint worker_id); 2802 }; 2803 2804 // Checkpoint the roots into this generation from outside 2805 // this generation. [Note this initial checkpoint need only 2806 // be approximate -- we'll do a catch up phase subsequently.] 2807 void CMSCollector::checkpointRootsInitial() { 2808 assert(_collectorState == InitialMarking, "Wrong collector state"); 2809 check_correct_thread_executing(); 2810 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); 2811 2812 save_heap_summary(); 2813 report_heap_summary(GCWhen::BeforeGC); 2814 2815 ReferenceProcessor* rp = ref_processor(); 2816 assert(_restart_addr == NULL, "Control point invariant"); 2817 { 2818 // acquire locks for subsequent manipulations 2819 MutexLockerEx x(bitMapLock(), 2820 Mutex::_no_safepoint_check_flag); 2821 checkpointRootsInitialWork(); 2822 // enable ("weak") refs discovery 2823 rp->enable_discovery(); 2824 _collectorState = Marking; 2825 } 2826 } 2827 2828 void CMSCollector::checkpointRootsInitialWork() { 2829 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); 2830 assert(_collectorState == InitialMarking, "just checking"); 2831 2832 // Already have locks. 2833 assert_lock_strong(bitMapLock()); 2834 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); 2835 2836 // Setup the verification and class unloading state for this 2837 // CMS collection cycle. 2838 setup_cms_unloading_and_verification_state(); 2839 2840 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm); 2841 2842 // Reset all the PLAB chunk arrays if necessary. 2843 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { 2844 reset_survivor_plab_arrays(); 2845 } 2846 2847 ResourceMark rm; 2848 HandleMark hm; 2849 2850 MarkRefsIntoClosure notOlder(_span, &_markBitMap); 2851 CMSHeap* heap = CMSHeap::heap(); 2852 2853 verify_work_stacks_empty(); 2854 verify_overflow_empty(); 2855 2856 heap->ensure_parsability(false); // fill TLABs, but no need to retire them 2857 // Update the saved marks which may affect the root scans. 2858 heap->save_marks(); 2859 2860 // weak reference processing has not started yet. 2861 ref_processor()->set_enqueuing_is_done(false); 2862 2863 // Need to remember all newly created CLDs, 2864 // so that we can guarantee that the remark finds them. 2865 ClassLoaderDataGraph::remember_new_clds(true); 2866 2867 // Whenever a CLD is found, it will be claimed before proceeding to mark 2868 // the klasses. The claimed marks need to be cleared before marking starts. 2869 ClassLoaderDataGraph::clear_claimed_marks(); 2870 2871 print_eden_and_survivor_chunk_arrays(); 2872 2873 { 2874 #if COMPILER2_OR_JVMCI 2875 DerivedPointerTableDeactivate dpt_deact; 2876 #endif 2877 if (CMSParallelInitialMarkEnabled) { 2878 // The parallel version. 2879 WorkGang* workers = heap->workers(); 2880 assert(workers != NULL, "Need parallel worker threads."); 2881 uint n_workers = workers->active_workers(); 2882 2883 StrongRootsScope srs(n_workers); 2884 2885 CMSParInitialMarkTask tsk(this, &srs, n_workers); 2886 initialize_sequential_subtasks_for_young_gen_rescan(n_workers); 2887 // If the total workers is greater than 1, then multiple workers 2888 // may be used at some time and the initialization has been set 2889 // such that the single threaded path cannot be used. 2890 if (workers->total_workers() > 1) { 2891 workers->run_task(&tsk); 2892 } else { 2893 tsk.work(0); 2894 } 2895 } else { 2896 // The serial version. 2897 CLDToOopClosure cld_closure(¬Older, true); 2898 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 2899 2900 StrongRootsScope srs(1); 2901 2902 heap->cms_process_roots(&srs, 2903 true, // young gen as roots 2904 GenCollectedHeap::ScanningOption(roots_scanning_options()), 2905 should_unload_classes(), 2906 ¬Older, 2907 &cld_closure); 2908 } 2909 } 2910 2911 // Clear mod-union table; it will be dirtied in the prologue of 2912 // CMS generation per each young generation collection. 2913 2914 assert(_modUnionTable.isAllClear(), 2915 "Was cleared in most recent final checkpoint phase" 2916 " or no bits are set in the gc_prologue before the start of the next " 2917 "subsequent marking phase."); 2918 2919 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be"); 2920 2921 // Save the end of the used_region of the constituent generations 2922 // to be used to limit the extent of sweep in each generation. 2923 save_sweep_limits(); 2924 verify_overflow_empty(); 2925 } 2926 2927 bool CMSCollector::markFromRoots() { 2928 // we might be tempted to assert that: 2929 // assert(!SafepointSynchronize::is_at_safepoint(), 2930 // "inconsistent argument?"); 2931 // However that wouldn't be right, because it's possible that 2932 // a safepoint is indeed in progress as a young generation 2933 // stop-the-world GC happens even as we mark in this generation. 2934 assert(_collectorState == Marking, "inconsistent state?"); 2935 check_correct_thread_executing(); 2936 verify_overflow_empty(); 2937 2938 // Weak ref discovery note: We may be discovering weak 2939 // refs in this generation concurrent (but interleaved) with 2940 // weak ref discovery by the young generation collector. 2941 2942 CMSTokenSyncWithLocks ts(true, bitMapLock()); 2943 GCTraceCPUTime tcpu; 2944 CMSPhaseAccounting pa(this, "Concurrent Mark"); 2945 bool res = markFromRootsWork(); 2946 if (res) { 2947 _collectorState = Precleaning; 2948 } else { // We failed and a foreground collection wants to take over 2949 assert(_foregroundGCIsActive, "internal state inconsistency"); 2950 assert(_restart_addr == NULL, "foreground will restart from scratch"); 2951 log_debug(gc)("bailing out to foreground collection"); 2952 } 2953 verify_overflow_empty(); 2954 return res; 2955 } 2956 2957 bool CMSCollector::markFromRootsWork() { 2958 // iterate over marked bits in bit map, doing a full scan and mark 2959 // from these roots using the following algorithm: 2960 // . if oop is to the right of the current scan pointer, 2961 // mark corresponding bit (we'll process it later) 2962 // . else (oop is to left of current scan pointer) 2963 // push oop on marking stack 2964 // . drain the marking stack 2965 2966 // Note that when we do a marking step we need to hold the 2967 // bit map lock -- recall that direct allocation (by mutators) 2968 // and promotion (by the young generation collector) is also 2969 // marking the bit map. [the so-called allocate live policy.] 2970 // Because the implementation of bit map marking is not 2971 // robust wrt simultaneous marking of bits in the same word, 2972 // we need to make sure that there is no such interference 2973 // between concurrent such updates. 2974 2975 // already have locks 2976 assert_lock_strong(bitMapLock()); 2977 2978 verify_work_stacks_empty(); 2979 verify_overflow_empty(); 2980 bool result = false; 2981 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) { 2982 result = do_marking_mt(); 2983 } else { 2984 result = do_marking_st(); 2985 } 2986 return result; 2987 } 2988 2989 // Forward decl 2990 class CMSConcMarkingTask; 2991 2992 class CMSConcMarkingTerminator: public ParallelTaskTerminator { 2993 CMSCollector* _collector; 2994 CMSConcMarkingTask* _task; 2995 public: 2996 virtual void yield(); 2997 2998 // "n_threads" is the number of threads to be terminated. 2999 // "queue_set" is a set of work queues of other threads. 3000 // "collector" is the CMS collector associated with this task terminator. 3001 // "yield" indicates whether we need the gang as a whole to yield. 3002 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : 3003 ParallelTaskTerminator(n_threads, queue_set), 3004 _collector(collector) { } 3005 3006 void set_task(CMSConcMarkingTask* task) { 3007 _task = task; 3008 } 3009 }; 3010 3011 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator { 3012 CMSConcMarkingTask* _task; 3013 public: 3014 bool should_exit_termination(); 3015 void set_task(CMSConcMarkingTask* task) { 3016 _task = task; 3017 } 3018 }; 3019 3020 // MT Concurrent Marking Task 3021 class CMSConcMarkingTask: public YieldingFlexibleGangTask { 3022 CMSCollector* _collector; 3023 uint _n_workers; // requested/desired # workers 3024 bool _result; 3025 CompactibleFreeListSpace* _cms_space; 3026 char _pad_front[64]; // padding to ... 3027 HeapWord* volatile _global_finger; // ... avoid sharing cache line 3028 char _pad_back[64]; 3029 HeapWord* _restart_addr; 3030 3031 // Exposed here for yielding support 3032 Mutex* const _bit_map_lock; 3033 3034 // The per thread work queues, available here for stealing 3035 OopTaskQueueSet* _task_queues; 3036 3037 // Termination (and yielding) support 3038 CMSConcMarkingTerminator _term; 3039 CMSConcMarkingTerminatorTerminator _term_term; 3040 3041 public: 3042 CMSConcMarkingTask(CMSCollector* collector, 3043 CompactibleFreeListSpace* cms_space, 3044 YieldingFlexibleWorkGang* workers, 3045 OopTaskQueueSet* task_queues): 3046 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), 3047 _collector(collector), 3048 _cms_space(cms_space), 3049 _n_workers(0), _result(true), 3050 _task_queues(task_queues), 3051 _term(_n_workers, task_queues, _collector), 3052 _bit_map_lock(collector->bitMapLock()) 3053 { 3054 _requested_size = _n_workers; 3055 _term.set_task(this); 3056 _term_term.set_task(this); 3057 _restart_addr = _global_finger = _cms_space->bottom(); 3058 } 3059 3060 3061 OopTaskQueueSet* task_queues() { return _task_queues; } 3062 3063 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 3064 3065 HeapWord* volatile* global_finger_addr() { return &_global_finger; } 3066 3067 CMSConcMarkingTerminator* terminator() { return &_term; } 3068 3069 virtual void set_for_termination(uint active_workers) { 3070 terminator()->reset_for_reuse(active_workers); 3071 } 3072 3073 void work(uint worker_id); 3074 bool should_yield() { 3075 return ConcurrentMarkSweepThread::should_yield() 3076 && !_collector->foregroundGCIsActive(); 3077 } 3078 3079 virtual void coordinator_yield(); // stuff done by coordinator 3080 bool result() { return _result; } 3081 3082 void reset(HeapWord* ra) { 3083 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)"); 3084 _restart_addr = _global_finger = ra; 3085 _term.reset_for_reuse(); 3086 } 3087 3088 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, 3089 OopTaskQueue* work_q); 3090 3091 private: 3092 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); 3093 void do_work_steal(int i); 3094 void bump_global_finger(HeapWord* f); 3095 }; 3096 3097 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() { 3098 assert(_task != NULL, "Error"); 3099 return _task->yielding(); 3100 // Note that we do not need the disjunct || _task->should_yield() above 3101 // because we want terminating threads to yield only if the task 3102 // is already in the midst of yielding, which happens only after at least one 3103 // thread has yielded. 3104 } 3105 3106 void CMSConcMarkingTerminator::yield() { 3107 if (_task->should_yield()) { 3108 _task->yield(); 3109 } else { 3110 ParallelTaskTerminator::yield(); 3111 } 3112 } 3113 3114 //////////////////////////////////////////////////////////////// 3115 // Concurrent Marking Algorithm Sketch 3116 //////////////////////////////////////////////////////////////// 3117 // Until all tasks exhausted (both spaces): 3118 // -- claim next available chunk 3119 // -- bump global finger via CAS 3120 // -- find first object that starts in this chunk 3121 // and start scanning bitmap from that position 3122 // -- scan marked objects for oops 3123 // -- CAS-mark target, and if successful: 3124 // . if target oop is above global finger (volatile read) 3125 // nothing to do 3126 // . if target oop is in chunk and above local finger 3127 // then nothing to do 3128 // . else push on work-queue 3129 // -- Deal with possible overflow issues: 3130 // . local work-queue overflow causes stuff to be pushed on 3131 // global (common) overflow queue 3132 // . always first empty local work queue 3133 // . then get a batch of oops from global work queue if any 3134 // . then do work stealing 3135 // -- When all tasks claimed (both spaces) 3136 // and local work queue empty, 3137 // then in a loop do: 3138 // . check global overflow stack; steal a batch of oops and trace 3139 // . try to steal from other threads oif GOS is empty 3140 // . if neither is available, offer termination 3141 // -- Terminate and return result 3142 // 3143 void CMSConcMarkingTask::work(uint worker_id) { 3144 elapsedTimer _timer; 3145 ResourceMark rm; 3146 HandleMark hm; 3147 3148 DEBUG_ONLY(_collector->verify_overflow_empty();) 3149 3150 // Before we begin work, our work queue should be empty 3151 assert(work_queue(worker_id)->size() == 0, "Expected to be empty"); 3152 // Scan the bitmap covering _cms_space, tracing through grey objects. 3153 _timer.start(); 3154 do_scan_and_mark(worker_id, _cms_space); 3155 _timer.stop(); 3156 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 3157 3158 // ... do work stealing 3159 _timer.reset(); 3160 _timer.start(); 3161 do_work_steal(worker_id); 3162 _timer.stop(); 3163 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 3164 assert(_collector->_markStack.isEmpty(), "Should have been emptied"); 3165 assert(work_queue(worker_id)->size() == 0, "Should have been emptied"); 3166 // Note that under the current task protocol, the 3167 // following assertion is true even of the spaces 3168 // expanded since the completion of the concurrent 3169 // marking. XXX This will likely change under a strict 3170 // ABORT semantics. 3171 // After perm removal the comparison was changed to 3172 // greater than or equal to from strictly greater than. 3173 // Before perm removal the highest address sweep would 3174 // have been at the end of perm gen but now is at the 3175 // end of the tenured gen. 3176 assert(_global_finger >= _cms_space->end(), 3177 "All tasks have been completed"); 3178 DEBUG_ONLY(_collector->verify_overflow_empty();) 3179 } 3180 3181 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { 3182 HeapWord* read = _global_finger; 3183 HeapWord* cur = read; 3184 while (f > read) { 3185 cur = read; 3186 read = Atomic::cmpxchg(f, &_global_finger, cur); 3187 if (cur == read) { 3188 // our cas succeeded 3189 assert(_global_finger >= f, "protocol consistency"); 3190 break; 3191 } 3192 } 3193 } 3194 3195 // This is really inefficient, and should be redone by 3196 // using (not yet available) block-read and -write interfaces to the 3197 // stack and the work_queue. XXX FIX ME !!! 3198 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, 3199 OopTaskQueue* work_q) { 3200 // Fast lock-free check 3201 if (ovflw_stk->length() == 0) { 3202 return false; 3203 } 3204 assert(work_q->size() == 0, "Shouldn't steal"); 3205 MutexLockerEx ml(ovflw_stk->par_lock(), 3206 Mutex::_no_safepoint_check_flag); 3207 // Grab up to 1/4 the size of the work queue 3208 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 3209 (size_t)ParGCDesiredObjsFromOverflowList); 3210 num = MIN2(num, ovflw_stk->length()); 3211 for (int i = (int) num; i > 0; i--) { 3212 oop cur = ovflw_stk->pop(); 3213 assert(cur != NULL, "Counted wrong?"); 3214 work_q->push(cur); 3215 } 3216 return num > 0; 3217 } 3218 3219 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { 3220 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); 3221 int n_tasks = pst->n_tasks(); 3222 // We allow that there may be no tasks to do here because 3223 // we are restarting after a stack overflow. 3224 assert(pst->valid() || n_tasks == 0, "Uninitialized use?"); 3225 uint nth_task = 0; 3226 3227 HeapWord* aligned_start = sp->bottom(); 3228 if (sp->used_region().contains(_restart_addr)) { 3229 // Align down to a card boundary for the start of 0th task 3230 // for this space. 3231 aligned_start = align_down(_restart_addr, CardTable::card_size); 3232 } 3233 3234 size_t chunk_size = sp->marking_task_size(); 3235 while (!pst->is_task_claimed(/* reference */ nth_task)) { 3236 // Having claimed the nth task in this space, 3237 // compute the chunk that it corresponds to: 3238 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size, 3239 aligned_start + (nth_task+1)*chunk_size); 3240 // Try and bump the global finger via a CAS; 3241 // note that we need to do the global finger bump 3242 // _before_ taking the intersection below, because 3243 // the task corresponding to that region will be 3244 // deemed done even if the used_region() expands 3245 // because of allocation -- as it almost certainly will 3246 // during start-up while the threads yield in the 3247 // closure below. 3248 HeapWord* finger = span.end(); 3249 bump_global_finger(finger); // atomically 3250 // There are null tasks here corresponding to chunks 3251 // beyond the "top" address of the space. 3252 span = span.intersection(sp->used_region()); 3253 if (!span.is_empty()) { // Non-null task 3254 HeapWord* prev_obj; 3255 assert(!span.contains(_restart_addr) || nth_task == 0, 3256 "Inconsistency"); 3257 if (nth_task == 0) { 3258 // For the 0th task, we'll not need to compute a block_start. 3259 if (span.contains(_restart_addr)) { 3260 // In the case of a restart because of stack overflow, 3261 // we might additionally skip a chunk prefix. 3262 prev_obj = _restart_addr; 3263 } else { 3264 prev_obj = span.start(); 3265 } 3266 } else { 3267 // We want to skip the first object because 3268 // the protocol is to scan any object in its entirety 3269 // that _starts_ in this span; a fortiori, any 3270 // object starting in an earlier span is scanned 3271 // as part of an earlier claimed task. 3272 // Below we use the "careful" version of block_start 3273 // so we do not try to navigate uninitialized objects. 3274 prev_obj = sp->block_start_careful(span.start()); 3275 // Below we use a variant of block_size that uses the 3276 // Printezis bits to avoid waiting for allocated 3277 // objects to become initialized/parsable. 3278 while (prev_obj < span.start()) { 3279 size_t sz = sp->block_size_no_stall(prev_obj, _collector); 3280 if (sz > 0) { 3281 prev_obj += sz; 3282 } else { 3283 // In this case we may end up doing a bit of redundant 3284 // scanning, but that appears unavoidable, short of 3285 // locking the free list locks; see bug 6324141. 3286 break; 3287 } 3288 } 3289 } 3290 if (prev_obj < span.end()) { 3291 MemRegion my_span = MemRegion(prev_obj, span.end()); 3292 // Do the marking work within a non-empty span -- 3293 // the last argument to the constructor indicates whether the 3294 // iteration should be incremental with periodic yields. 3295 ParMarkFromRootsClosure cl(this, _collector, my_span, 3296 &_collector->_markBitMap, 3297 work_queue(i), 3298 &_collector->_markStack); 3299 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); 3300 } // else nothing to do for this task 3301 } // else nothing to do for this task 3302 } 3303 // We'd be tempted to assert here that since there are no 3304 // more tasks left to claim in this space, the global_finger 3305 // must exceed space->top() and a fortiori space->end(). However, 3306 // that would not quite be correct because the bumping of 3307 // global_finger occurs strictly after the claiming of a task, 3308 // so by the time we reach here the global finger may not yet 3309 // have been bumped up by the thread that claimed the last 3310 // task. 3311 pst->all_tasks_completed(); 3312 } 3313 3314 class ParConcMarkingClosure: public MetadataAwareOopClosure { 3315 private: 3316 CMSCollector* _collector; 3317 CMSConcMarkingTask* _task; 3318 MemRegion _span; 3319 CMSBitMap* _bit_map; 3320 CMSMarkStack* _overflow_stack; 3321 OopTaskQueue* _work_queue; 3322 protected: 3323 DO_OOP_WORK_DEFN 3324 public: 3325 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, 3326 CMSBitMap* bit_map, CMSMarkStack* overflow_stack): 3327 MetadataAwareOopClosure(collector->ref_processor()), 3328 _collector(collector), 3329 _task(task), 3330 _span(collector->_span), 3331 _work_queue(work_queue), 3332 _bit_map(bit_map), 3333 _overflow_stack(overflow_stack) 3334 { } 3335 virtual void do_oop(oop* p); 3336 virtual void do_oop(narrowOop* p); 3337 3338 void trim_queue(size_t max); 3339 void handle_stack_overflow(HeapWord* lost); 3340 void do_yield_check() { 3341 if (_task->should_yield()) { 3342 _task->yield(); 3343 } 3344 } 3345 }; 3346 3347 DO_OOP_WORK_IMPL(ParConcMarkingClosure) 3348 3349 // Grey object scanning during work stealing phase -- 3350 // the salient assumption here is that any references 3351 // that are in these stolen objects being scanned must 3352 // already have been initialized (else they would not have 3353 // been published), so we do not need to check for 3354 // uninitialized objects before pushing here. 3355 void ParConcMarkingClosure::do_oop(oop obj) { 3356 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 3357 HeapWord* addr = (HeapWord*)obj; 3358 // Check if oop points into the CMS generation 3359 // and is not marked 3360 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 3361 // a white object ... 3362 // If we manage to "claim" the object, by being the 3363 // first thread to mark it, then we push it on our 3364 // marking stack 3365 if (_bit_map->par_mark(addr)) { // ... now grey 3366 // push on work queue (grey set) 3367 bool simulate_overflow = false; 3368 NOT_PRODUCT( 3369 if (CMSMarkStackOverflowALot && 3370 _collector->simulate_overflow()) { 3371 // simulate a stack overflow 3372 simulate_overflow = true; 3373 } 3374 ) 3375 if (simulate_overflow || 3376 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { 3377 // stack overflow 3378 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity()); 3379 // We cannot assert that the overflow stack is full because 3380 // it may have been emptied since. 3381 assert(simulate_overflow || 3382 _work_queue->size() == _work_queue->max_elems(), 3383 "Else push should have succeeded"); 3384 handle_stack_overflow(addr); 3385 } 3386 } // Else, some other thread got there first 3387 do_yield_check(); 3388 } 3389 } 3390 3391 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); } 3392 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); } 3393 3394 void ParConcMarkingClosure::trim_queue(size_t max) { 3395 while (_work_queue->size() > max) { 3396 oop new_oop; 3397 if (_work_queue->pop_local(new_oop)) { 3398 assert(oopDesc::is_oop(new_oop), "Should be an oop"); 3399 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); 3400 assert(_span.contains((HeapWord*)new_oop), "Not in span"); 3401 new_oop->oop_iterate(this); // do_oop() above 3402 do_yield_check(); 3403 } 3404 } 3405 } 3406 3407 // Upon stack overflow, we discard (part of) the stack, 3408 // remembering the least address amongst those discarded 3409 // in CMSCollector's _restart_address. 3410 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { 3411 // We need to do this under a mutex to prevent other 3412 // workers from interfering with the work done below. 3413 MutexLockerEx ml(_overflow_stack->par_lock(), 3414 Mutex::_no_safepoint_check_flag); 3415 // Remember the least grey address discarded 3416 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); 3417 _collector->lower_restart_addr(ra); 3418 _overflow_stack->reset(); // discard stack contents 3419 _overflow_stack->expand(); // expand the stack if possible 3420 } 3421 3422 3423 void CMSConcMarkingTask::do_work_steal(int i) { 3424 OopTaskQueue* work_q = work_queue(i); 3425 oop obj_to_scan; 3426 CMSBitMap* bm = &(_collector->_markBitMap); 3427 CMSMarkStack* ovflw = &(_collector->_markStack); 3428 int* seed = _collector->hash_seed(i); 3429 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw); 3430 while (true) { 3431 cl.trim_queue(0); 3432 assert(work_q->size() == 0, "Should have been emptied above"); 3433 if (get_work_from_overflow_stack(ovflw, work_q)) { 3434 // Can't assert below because the work obtained from the 3435 // overflow stack may already have been stolen from us. 3436 // assert(work_q->size() > 0, "Work from overflow stack"); 3437 continue; 3438 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 3439 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop"); 3440 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); 3441 obj_to_scan->oop_iterate(&cl); 3442 } else if (terminator()->offer_termination(&_term_term)) { 3443 assert(work_q->size() == 0, "Impossible!"); 3444 break; 3445 } else if (yielding() || should_yield()) { 3446 yield(); 3447 } 3448 } 3449 } 3450 3451 // This is run by the CMS (coordinator) thread. 3452 void CMSConcMarkingTask::coordinator_yield() { 3453 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 3454 "CMS thread should hold CMS token"); 3455 // First give up the locks, then yield, then re-lock 3456 // We should probably use a constructor/destructor idiom to 3457 // do this unlock/lock or modify the MutexUnlocker class to 3458 // serve our purpose. XXX 3459 assert_lock_strong(_bit_map_lock); 3460 _bit_map_lock->unlock(); 3461 ConcurrentMarkSweepThread::desynchronize(true); 3462 _collector->stopTimer(); 3463 _collector->incrementYields(); 3464 3465 // It is possible for whichever thread initiated the yield request 3466 // not to get a chance to wake up and take the bitmap lock between 3467 // this thread releasing it and reacquiring it. So, while the 3468 // should_yield() flag is on, let's sleep for a bit to give the 3469 // other thread a chance to wake up. The limit imposed on the number 3470 // of iterations is defensive, to avoid any unforseen circumstances 3471 // putting us into an infinite loop. Since it's always been this 3472 // (coordinator_yield()) method that was observed to cause the 3473 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) 3474 // which is by default non-zero. For the other seven methods that 3475 // also perform the yield operation, as are using a different 3476 // parameter (CMSYieldSleepCount) which is by default zero. This way we 3477 // can enable the sleeping for those methods too, if necessary. 3478 // See 6442774. 3479 // 3480 // We really need to reconsider the synchronization between the GC 3481 // thread and the yield-requesting threads in the future and we 3482 // should really use wait/notify, which is the recommended 3483 // way of doing this type of interaction. Additionally, we should 3484 // consolidate the eight methods that do the yield operation and they 3485 // are almost identical into one for better maintainability and 3486 // readability. See 6445193. 3487 // 3488 // Tony 2006.06.29 3489 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && 3490 ConcurrentMarkSweepThread::should_yield() && 3491 !CMSCollector::foregroundGCIsActive(); ++i) { 3492 os::sleep(Thread::current(), 1, false); 3493 } 3494 3495 ConcurrentMarkSweepThread::synchronize(true); 3496 _bit_map_lock->lock_without_safepoint_check(); 3497 _collector->startTimer(); 3498 } 3499 3500 bool CMSCollector::do_marking_mt() { 3501 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); 3502 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(), 3503 conc_workers()->active_workers(), 3504 Threads::number_of_non_daemon_threads()); 3505 num_workers = conc_workers()->update_active_workers(num_workers); 3506 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers()); 3507 3508 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 3509 3510 CMSConcMarkingTask tsk(this, 3511 cms_space, 3512 conc_workers(), 3513 task_queues()); 3514 3515 // Since the actual number of workers we get may be different 3516 // from the number we requested above, do we need to do anything different 3517 // below? In particular, may be we need to subclass the SequantialSubTasksDone 3518 // class?? XXX 3519 cms_space ->initialize_sequential_subtasks_for_marking(num_workers); 3520 3521 // Refs discovery is already non-atomic. 3522 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); 3523 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT"); 3524 conc_workers()->start_task(&tsk); 3525 while (tsk.yielded()) { 3526 tsk.coordinator_yield(); 3527 conc_workers()->continue_task(&tsk); 3528 } 3529 // If the task was aborted, _restart_addr will be non-NULL 3530 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); 3531 while (_restart_addr != NULL) { 3532 // XXX For now we do not make use of ABORTED state and have not 3533 // yet implemented the right abort semantics (even in the original 3534 // single-threaded CMS case). That needs some more investigation 3535 // and is deferred for now; see CR# TBF. 07252005YSR. XXX 3536 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); 3537 // If _restart_addr is non-NULL, a marking stack overflow 3538 // occurred; we need to do a fresh marking iteration from the 3539 // indicated restart address. 3540 if (_foregroundGCIsActive) { 3541 // We may be running into repeated stack overflows, having 3542 // reached the limit of the stack size, while making very 3543 // slow forward progress. It may be best to bail out and 3544 // let the foreground collector do its job. 3545 // Clear _restart_addr, so that foreground GC 3546 // works from scratch. This avoids the headache of 3547 // a "rescan" which would otherwise be needed because 3548 // of the dirty mod union table & card table. 3549 _restart_addr = NULL; 3550 return false; 3551 } 3552 // Adjust the task to restart from _restart_addr 3553 tsk.reset(_restart_addr); 3554 cms_space ->initialize_sequential_subtasks_for_marking(num_workers, 3555 _restart_addr); 3556 _restart_addr = NULL; 3557 // Get the workers going again 3558 conc_workers()->start_task(&tsk); 3559 while (tsk.yielded()) { 3560 tsk.coordinator_yield(); 3561 conc_workers()->continue_task(&tsk); 3562 } 3563 } 3564 assert(tsk.completed(), "Inconsistency"); 3565 assert(tsk.result() == true, "Inconsistency"); 3566 return true; 3567 } 3568 3569 bool CMSCollector::do_marking_st() { 3570 ResourceMark rm; 3571 HandleMark hm; 3572 3573 // Temporarily make refs discovery single threaded (non-MT) 3574 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); 3575 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, 3576 &_markStack, CMSYield); 3577 // the last argument to iterate indicates whether the iteration 3578 // should be incremental with periodic yields. 3579 _markBitMap.iterate(&markFromRootsClosure); 3580 // If _restart_addr is non-NULL, a marking stack overflow 3581 // occurred; we need to do a fresh iteration from the 3582 // indicated restart address. 3583 while (_restart_addr != NULL) { 3584 if (_foregroundGCIsActive) { 3585 // We may be running into repeated stack overflows, having 3586 // reached the limit of the stack size, while making very 3587 // slow forward progress. It may be best to bail out and 3588 // let the foreground collector do its job. 3589 // Clear _restart_addr, so that foreground GC 3590 // works from scratch. This avoids the headache of 3591 // a "rescan" which would otherwise be needed because 3592 // of the dirty mod union table & card table. 3593 _restart_addr = NULL; 3594 return false; // indicating failure to complete marking 3595 } 3596 // Deal with stack overflow: 3597 // we restart marking from _restart_addr 3598 HeapWord* ra = _restart_addr; 3599 markFromRootsClosure.reset(ra); 3600 _restart_addr = NULL; 3601 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); 3602 } 3603 return true; 3604 } 3605 3606 void CMSCollector::preclean() { 3607 check_correct_thread_executing(); 3608 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); 3609 verify_work_stacks_empty(); 3610 verify_overflow_empty(); 3611 _abort_preclean = false; 3612 if (CMSPrecleaningEnabled) { 3613 if (!CMSEdenChunksRecordAlways) { 3614 _eden_chunk_index = 0; 3615 } 3616 size_t used = get_eden_used(); 3617 size_t capacity = get_eden_capacity(); 3618 // Don't start sampling unless we will get sufficiently 3619 // many samples. 3620 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100) 3621 * CMSScheduleRemarkEdenPenetration)) { 3622 _start_sampling = true; 3623 } else { 3624 _start_sampling = false; 3625 } 3626 GCTraceCPUTime tcpu; 3627 CMSPhaseAccounting pa(this, "Concurrent Preclean"); 3628 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); 3629 } 3630 CMSTokenSync x(true); // is cms thread 3631 if (CMSPrecleaningEnabled) { 3632 sample_eden(); 3633 _collectorState = AbortablePreclean; 3634 } else { 3635 _collectorState = FinalMarking; 3636 } 3637 verify_work_stacks_empty(); 3638 verify_overflow_empty(); 3639 } 3640 3641 // Try and schedule the remark such that young gen 3642 // occupancy is CMSScheduleRemarkEdenPenetration %. 3643 void CMSCollector::abortable_preclean() { 3644 check_correct_thread_executing(); 3645 assert(CMSPrecleaningEnabled, "Inconsistent control state"); 3646 assert(_collectorState == AbortablePreclean, "Inconsistent control state"); 3647 3648 // If Eden's current occupancy is below this threshold, 3649 // immediately schedule the remark; else preclean 3650 // past the next scavenge in an effort to 3651 // schedule the pause as described above. By choosing 3652 // CMSScheduleRemarkEdenSizeThreshold >= max eden size 3653 // we will never do an actual abortable preclean cycle. 3654 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { 3655 GCTraceCPUTime tcpu; 3656 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean"); 3657 // We need more smarts in the abortable preclean 3658 // loop below to deal with cases where allocation 3659 // in young gen is very very slow, and our precleaning 3660 // is running a losing race against a horde of 3661 // mutators intent on flooding us with CMS updates 3662 // (dirty cards). 3663 // One, admittedly dumb, strategy is to give up 3664 // after a certain number of abortable precleaning loops 3665 // or after a certain maximum time. We want to make 3666 // this smarter in the next iteration. 3667 // XXX FIX ME!!! YSR 3668 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; 3669 while (!(should_abort_preclean() || 3670 ConcurrentMarkSweepThread::cmst()->should_terminate())) { 3671 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); 3672 cumworkdone += workdone; 3673 loops++; 3674 // Voluntarily terminate abortable preclean phase if we have 3675 // been at it for too long. 3676 if ((CMSMaxAbortablePrecleanLoops != 0) && 3677 loops >= CMSMaxAbortablePrecleanLoops) { 3678 log_debug(gc)(" CMS: abort preclean due to loops "); 3679 break; 3680 } 3681 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { 3682 log_debug(gc)(" CMS: abort preclean due to time "); 3683 break; 3684 } 3685 // If we are doing little work each iteration, we should 3686 // take a short break. 3687 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { 3688 // Sleep for some time, waiting for work to accumulate 3689 stopTimer(); 3690 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); 3691 startTimer(); 3692 waited++; 3693 } 3694 } 3695 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ", 3696 loops, waited, cumworkdone); 3697 } 3698 CMSTokenSync x(true); // is cms thread 3699 if (_collectorState != Idling) { 3700 assert(_collectorState == AbortablePreclean, 3701 "Spontaneous state transition?"); 3702 _collectorState = FinalMarking; 3703 } // Else, a foreground collection completed this CMS cycle. 3704 return; 3705 } 3706 3707 // Respond to an Eden sampling opportunity 3708 void CMSCollector::sample_eden() { 3709 // Make sure a young gc cannot sneak in between our 3710 // reading and recording of a sample. 3711 assert(Thread::current()->is_ConcurrentGC_thread(), 3712 "Only the cms thread may collect Eden samples"); 3713 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 3714 "Should collect samples while holding CMS token"); 3715 if (!_start_sampling) { 3716 return; 3717 } 3718 // When CMSEdenChunksRecordAlways is true, the eden chunk array 3719 // is populated by the young generation. 3720 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) { 3721 if (_eden_chunk_index < _eden_chunk_capacity) { 3722 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample 3723 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, 3724 "Unexpected state of Eden"); 3725 // We'd like to check that what we just sampled is an oop-start address; 3726 // however, we cannot do that here since the object may not yet have been 3727 // initialized. So we'll instead do the check when we _use_ this sample 3728 // later. 3729 if (_eden_chunk_index == 0 || 3730 (pointer_delta(_eden_chunk_array[_eden_chunk_index], 3731 _eden_chunk_array[_eden_chunk_index-1]) 3732 >= CMSSamplingGrain)) { 3733 _eden_chunk_index++; // commit sample 3734 } 3735 } 3736 } 3737 if ((_collectorState == AbortablePreclean) && !_abort_preclean) { 3738 size_t used = get_eden_used(); 3739 size_t capacity = get_eden_capacity(); 3740 assert(used <= capacity, "Unexpected state of Eden"); 3741 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { 3742 _abort_preclean = true; 3743 } 3744 } 3745 } 3746 3747 3748 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { 3749 assert(_collectorState == Precleaning || 3750 _collectorState == AbortablePreclean, "incorrect state"); 3751 ResourceMark rm; 3752 HandleMark hm; 3753 3754 // Precleaning is currently not MT but the reference processor 3755 // may be set for MT. Disable it temporarily here. 3756 ReferenceProcessor* rp = ref_processor(); 3757 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false); 3758 3759 // Do one pass of scrubbing the discovered reference lists 3760 // to remove any reference objects with strongly-reachable 3761 // referents. 3762 if (clean_refs) { 3763 CMSPrecleanRefsYieldClosure yield_cl(this); 3764 assert(rp->span().equals(_span), "Spans should be equal"); 3765 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, 3766 &_markStack, true /* preclean */); 3767 CMSDrainMarkingStackClosure complete_trace(this, 3768 _span, &_markBitMap, &_markStack, 3769 &keep_alive, true /* preclean */); 3770 3771 // We don't want this step to interfere with a young 3772 // collection because we don't want to take CPU 3773 // or memory bandwidth away from the young GC threads 3774 // (which may be as many as there are CPUs). 3775 // Note that we don't need to protect ourselves from 3776 // interference with mutators because they can't 3777 // manipulate the discovered reference lists nor affect 3778 // the computed reachability of the referents, the 3779 // only properties manipulated by the precleaning 3780 // of these reference lists. 3781 stopTimer(); 3782 CMSTokenSyncWithLocks x(true /* is cms thread */, 3783 bitMapLock()); 3784 startTimer(); 3785 sample_eden(); 3786 3787 // The following will yield to allow foreground 3788 // collection to proceed promptly. XXX YSR: 3789 // The code in this method may need further 3790 // tweaking for better performance and some restructuring 3791 // for cleaner interfaces. 3792 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases 3793 rp->preclean_discovered_references( 3794 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl, 3795 gc_timer); 3796 } 3797 3798 if (clean_survivor) { // preclean the active survivor space(s) 3799 PushAndMarkClosure pam_cl(this, _span, ref_processor(), 3800 &_markBitMap, &_modUnionTable, 3801 &_markStack, true /* precleaning phase */); 3802 stopTimer(); 3803 CMSTokenSyncWithLocks ts(true /* is cms thread */, 3804 bitMapLock()); 3805 startTimer(); 3806 unsigned int before_count = 3807 CMSHeap::heap()->total_collections(); 3808 SurvivorSpacePrecleanClosure 3809 sss_cl(this, _span, &_markBitMap, &_markStack, 3810 &pam_cl, before_count, CMSYield); 3811 _young_gen->from()->object_iterate_careful(&sss_cl); 3812 _young_gen->to()->object_iterate_careful(&sss_cl); 3813 } 3814 MarkRefsIntoAndScanClosure 3815 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, 3816 &_markStack, this, CMSYield, 3817 true /* precleaning phase */); 3818 // CAUTION: The following closure has persistent state that may need to 3819 // be reset upon a decrease in the sequence of addresses it 3820 // processes. 3821 ScanMarkedObjectsAgainCarefullyClosure 3822 smoac_cl(this, _span, 3823 &_markBitMap, &_markStack, &mrias_cl, CMSYield); 3824 3825 // Preclean dirty cards in ModUnionTable and CardTable using 3826 // appropriate convergence criterion; 3827 // repeat CMSPrecleanIter times unless we find that 3828 // we are losing. 3829 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); 3830 assert(CMSPrecleanNumerator < CMSPrecleanDenominator, 3831 "Bad convergence multiplier"); 3832 assert(CMSPrecleanThreshold >= 100, 3833 "Unreasonably low CMSPrecleanThreshold"); 3834 3835 size_t numIter, cumNumCards, lastNumCards, curNumCards; 3836 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; 3837 numIter < CMSPrecleanIter; 3838 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { 3839 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); 3840 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards); 3841 // Either there are very few dirty cards, so re-mark 3842 // pause will be small anyway, or our pre-cleaning isn't 3843 // that much faster than the rate at which cards are being 3844 // dirtied, so we might as well stop and re-mark since 3845 // precleaning won't improve our re-mark time by much. 3846 if (curNumCards <= CMSPrecleanThreshold || 3847 (numIter > 0 && 3848 (curNumCards * CMSPrecleanDenominator > 3849 lastNumCards * CMSPrecleanNumerator))) { 3850 numIter++; 3851 cumNumCards += curNumCards; 3852 break; 3853 } 3854 } 3855 3856 preclean_cld(&mrias_cl, _cmsGen->freelistLock()); 3857 3858 curNumCards = preclean_card_table(_cmsGen, &smoac_cl); 3859 cumNumCards += curNumCards; 3860 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)", 3861 curNumCards, cumNumCards, numIter); 3862 return cumNumCards; // as a measure of useful work done 3863 } 3864 3865 // PRECLEANING NOTES: 3866 // Precleaning involves: 3867 // . reading the bits of the modUnionTable and clearing the set bits. 3868 // . For the cards corresponding to the set bits, we scan the 3869 // objects on those cards. This means we need the free_list_lock 3870 // so that we can safely iterate over the CMS space when scanning 3871 // for oops. 3872 // . When we scan the objects, we'll be both reading and setting 3873 // marks in the marking bit map, so we'll need the marking bit map. 3874 // . For protecting _collector_state transitions, we take the CGC_lock. 3875 // Note that any races in the reading of of card table entries by the 3876 // CMS thread on the one hand and the clearing of those entries by the 3877 // VM thread or the setting of those entries by the mutator threads on the 3878 // other are quite benign. However, for efficiency it makes sense to keep 3879 // the VM thread from racing with the CMS thread while the latter is 3880 // dirty card info to the modUnionTable. We therefore also use the 3881 // CGC_lock to protect the reading of the card table and the mod union 3882 // table by the CM thread. 3883 // . We run concurrently with mutator updates, so scanning 3884 // needs to be done carefully -- we should not try to scan 3885 // potentially uninitialized objects. 3886 // 3887 // Locking strategy: While holding the CGC_lock, we scan over and 3888 // reset a maximal dirty range of the mod union / card tables, then lock 3889 // the free_list_lock and bitmap lock to do a full marking, then 3890 // release these locks; and repeat the cycle. This allows for a 3891 // certain amount of fairness in the sharing of these locks between 3892 // the CMS collector on the one hand, and the VM thread and the 3893 // mutators on the other. 3894 3895 // NOTE: preclean_mod_union_table() and preclean_card_table() 3896 // further below are largely identical; if you need to modify 3897 // one of these methods, please check the other method too. 3898 3899 size_t CMSCollector::preclean_mod_union_table( 3900 ConcurrentMarkSweepGeneration* old_gen, 3901 ScanMarkedObjectsAgainCarefullyClosure* cl) { 3902 verify_work_stacks_empty(); 3903 verify_overflow_empty(); 3904 3905 // strategy: starting with the first card, accumulate contiguous 3906 // ranges of dirty cards; clear these cards, then scan the region 3907 // covered by these cards. 3908 3909 // Since all of the MUT is committed ahead, we can just use 3910 // that, in case the generations expand while we are precleaning. 3911 // It might also be fine to just use the committed part of the 3912 // generation, but we might potentially miss cards when the 3913 // generation is rapidly expanding while we are in the midst 3914 // of precleaning. 3915 HeapWord* startAddr = old_gen->reserved().start(); 3916 HeapWord* endAddr = old_gen->reserved().end(); 3917 3918 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding 3919 3920 size_t numDirtyCards, cumNumDirtyCards; 3921 HeapWord *nextAddr, *lastAddr; 3922 for (cumNumDirtyCards = numDirtyCards = 0, 3923 nextAddr = lastAddr = startAddr; 3924 nextAddr < endAddr; 3925 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { 3926 3927 ResourceMark rm; 3928 HandleMark hm; 3929 3930 MemRegion dirtyRegion; 3931 { 3932 stopTimer(); 3933 // Potential yield point 3934 CMSTokenSync ts(true); 3935 startTimer(); 3936 sample_eden(); 3937 // Get dirty region starting at nextOffset (inclusive), 3938 // simultaneously clearing it. 3939 dirtyRegion = 3940 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); 3941 assert(dirtyRegion.start() >= nextAddr, 3942 "returned region inconsistent?"); 3943 } 3944 // Remember where the next search should begin. 3945 // The returned region (if non-empty) is a right open interval, 3946 // so lastOffset is obtained from the right end of that 3947 // interval. 3948 lastAddr = dirtyRegion.end(); 3949 // Should do something more transparent and less hacky XXX 3950 numDirtyCards = 3951 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); 3952 3953 // We'll scan the cards in the dirty region (with periodic 3954 // yields for foreground GC as needed). 3955 if (!dirtyRegion.is_empty()) { 3956 assert(numDirtyCards > 0, "consistency check"); 3957 HeapWord* stop_point = NULL; 3958 stopTimer(); 3959 // Potential yield point 3960 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), 3961 bitMapLock()); 3962 startTimer(); 3963 { 3964 verify_work_stacks_empty(); 3965 verify_overflow_empty(); 3966 sample_eden(); 3967 stop_point = 3968 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); 3969 } 3970 if (stop_point != NULL) { 3971 // The careful iteration stopped early either because it found an 3972 // uninitialized object, or because we were in the midst of an 3973 // "abortable preclean", which should now be aborted. Redirty 3974 // the bits corresponding to the partially-scanned or unscanned 3975 // cards. We'll either restart at the next block boundary or 3976 // abort the preclean. 3977 assert((_collectorState == AbortablePreclean && should_abort_preclean()), 3978 "Should only be AbortablePreclean."); 3979 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); 3980 if (should_abort_preclean()) { 3981 break; // out of preclean loop 3982 } else { 3983 // Compute the next address at which preclean should pick up; 3984 // might need bitMapLock in order to read P-bits. 3985 lastAddr = next_card_start_after_block(stop_point); 3986 } 3987 } 3988 } else { 3989 assert(lastAddr == endAddr, "consistency check"); 3990 assert(numDirtyCards == 0, "consistency check"); 3991 break; 3992 } 3993 } 3994 verify_work_stacks_empty(); 3995 verify_overflow_empty(); 3996 return cumNumDirtyCards; 3997 } 3998 3999 // NOTE: preclean_mod_union_table() above and preclean_card_table() 4000 // below are largely identical; if you need to modify 4001 // one of these methods, please check the other method too. 4002 4003 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen, 4004 ScanMarkedObjectsAgainCarefullyClosure* cl) { 4005 // strategy: it's similar to precleamModUnionTable above, in that 4006 // we accumulate contiguous ranges of dirty cards, mark these cards 4007 // precleaned, then scan the region covered by these cards. 4008 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high()); 4009 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low()); 4010 4011 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding 4012 4013 size_t numDirtyCards, cumNumDirtyCards; 4014 HeapWord *lastAddr, *nextAddr; 4015 4016 for (cumNumDirtyCards = numDirtyCards = 0, 4017 nextAddr = lastAddr = startAddr; 4018 nextAddr < endAddr; 4019 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { 4020 4021 ResourceMark rm; 4022 HandleMark hm; 4023 4024 MemRegion dirtyRegion; 4025 { 4026 // See comments in "Precleaning notes" above on why we 4027 // do this locking. XXX Could the locking overheads be 4028 // too high when dirty cards are sparse? [I don't think so.] 4029 stopTimer(); 4030 CMSTokenSync x(true); // is cms thread 4031 startTimer(); 4032 sample_eden(); 4033 // Get and clear dirty region from card table 4034 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr), 4035 true, 4036 CardTable::precleaned_card_val()); 4037 4038 assert(dirtyRegion.start() >= nextAddr, 4039 "returned region inconsistent?"); 4040 } 4041 lastAddr = dirtyRegion.end(); 4042 numDirtyCards = 4043 dirtyRegion.word_size()/CardTable::card_size_in_words; 4044 4045 if (!dirtyRegion.is_empty()) { 4046 stopTimer(); 4047 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock()); 4048 startTimer(); 4049 sample_eden(); 4050 verify_work_stacks_empty(); 4051 verify_overflow_empty(); 4052 HeapWord* stop_point = 4053 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); 4054 if (stop_point != NULL) { 4055 assert((_collectorState == AbortablePreclean && should_abort_preclean()), 4056 "Should only be AbortablePreclean."); 4057 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end())); 4058 if (should_abort_preclean()) { 4059 break; // out of preclean loop 4060 } else { 4061 // Compute the next address at which preclean should pick up. 4062 lastAddr = next_card_start_after_block(stop_point); 4063 } 4064 } 4065 } else { 4066 break; 4067 } 4068 } 4069 verify_work_stacks_empty(); 4070 verify_overflow_empty(); 4071 return cumNumDirtyCards; 4072 } 4073 4074 class PrecleanCLDClosure : public CLDClosure { 4075 MetadataAwareOopsInGenClosure* _cm_closure; 4076 public: 4077 PrecleanCLDClosure(MetadataAwareOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {} 4078 void do_cld(ClassLoaderData* cld) { 4079 if (cld->has_accumulated_modified_oops()) { 4080 cld->clear_accumulated_modified_oops(); 4081 4082 _cm_closure->do_cld(cld); 4083 } 4084 } 4085 }; 4086 4087 // The freelist lock is needed to prevent asserts, is it really needed? 4088 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) { 4089 4090 cl->set_freelistLock(freelistLock); 4091 4092 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock()); 4093 4094 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean? 4095 // SSS: We should probably check if precleaning should be aborted, at suitable intervals? 4096 PrecleanCLDClosure preclean_closure(cl); 4097 ClassLoaderDataGraph::cld_do(&preclean_closure); 4098 4099 verify_work_stacks_empty(); 4100 verify_overflow_empty(); 4101 } 4102 4103 void CMSCollector::checkpointRootsFinal() { 4104 assert(_collectorState == FinalMarking, "incorrect state transition?"); 4105 check_correct_thread_executing(); 4106 // world is stopped at this checkpoint 4107 assert(SafepointSynchronize::is_at_safepoint(), 4108 "world should be stopped"); 4109 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); 4110 4111 verify_work_stacks_empty(); 4112 verify_overflow_empty(); 4113 4114 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)", 4115 _young_gen->used() / K, _young_gen->capacity() / K); 4116 { 4117 if (CMSScavengeBeforeRemark) { 4118 CMSHeap* heap = CMSHeap::heap(); 4119 // Temporarily set flag to false, GCH->do_collection will 4120 // expect it to be false and set to true 4121 FlagSetting fl(heap->_is_gc_active, false); 4122 4123 heap->do_collection(true, // full (i.e. force, see below) 4124 false, // !clear_all_soft_refs 4125 0, // size 4126 false, // is_tlab 4127 GenCollectedHeap::YoungGen // type 4128 ); 4129 } 4130 FreelistLocker x(this); 4131 MutexLockerEx y(bitMapLock(), 4132 Mutex::_no_safepoint_check_flag); 4133 checkpointRootsFinalWork(); 4134 } 4135 verify_work_stacks_empty(); 4136 verify_overflow_empty(); 4137 } 4138 4139 void CMSCollector::checkpointRootsFinalWork() { 4140 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm); 4141 4142 assert(haveFreelistLocks(), "must have free list locks"); 4143 assert_lock_strong(bitMapLock()); 4144 4145 ResourceMark rm; 4146 HandleMark hm; 4147 4148 CMSHeap* heap = CMSHeap::heap(); 4149 4150 if (should_unload_classes()) { 4151 CodeCache::gc_prologue(); 4152 } 4153 assert(haveFreelistLocks(), "must have free list locks"); 4154 assert_lock_strong(bitMapLock()); 4155 4156 // We might assume that we need not fill TLAB's when 4157 // CMSScavengeBeforeRemark is set, because we may have just done 4158 // a scavenge which would have filled all TLAB's -- and besides 4159 // Eden would be empty. This however may not always be the case -- 4160 // for instance although we asked for a scavenge, it may not have 4161 // happened because of a JNI critical section. We probably need 4162 // a policy for deciding whether we can in that case wait until 4163 // the critical section releases and then do the remark following 4164 // the scavenge, and skip it here. In the absence of that policy, 4165 // or of an indication of whether the scavenge did indeed occur, 4166 // we cannot rely on TLAB's having been filled and must do 4167 // so here just in case a scavenge did not happen. 4168 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them 4169 // Update the saved marks which may affect the root scans. 4170 heap->save_marks(); 4171 4172 print_eden_and_survivor_chunk_arrays(); 4173 4174 { 4175 #if COMPILER2_OR_JVMCI 4176 DerivedPointerTableDeactivate dpt_deact; 4177 #endif 4178 4179 // Note on the role of the mod union table: 4180 // Since the marker in "markFromRoots" marks concurrently with 4181 // mutators, it is possible for some reachable objects not to have been 4182 // scanned. For instance, an only reference to an object A was 4183 // placed in object B after the marker scanned B. Unless B is rescanned, 4184 // A would be collected. Such updates to references in marked objects 4185 // are detected via the mod union table which is the set of all cards 4186 // dirtied since the first checkpoint in this GC cycle and prior to 4187 // the most recent young generation GC, minus those cleaned up by the 4188 // concurrent precleaning. 4189 if (CMSParallelRemarkEnabled) { 4190 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm); 4191 do_remark_parallel(); 4192 } else { 4193 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm); 4194 do_remark_non_parallel(); 4195 } 4196 } 4197 verify_work_stacks_empty(); 4198 verify_overflow_empty(); 4199 4200 { 4201 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm); 4202 refProcessingWork(); 4203 } 4204 verify_work_stacks_empty(); 4205 verify_overflow_empty(); 4206 4207 if (should_unload_classes()) { 4208 CodeCache::gc_epilogue(); 4209 } 4210 JvmtiExport::gc_epilogue(); 4211 4212 // If we encountered any (marking stack / work queue) overflow 4213 // events during the current CMS cycle, take appropriate 4214 // remedial measures, where possible, so as to try and avoid 4215 // recurrence of that condition. 4216 assert(_markStack.isEmpty(), "No grey objects"); 4217 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + 4218 _ser_kac_ovflw + _ser_kac_preclean_ovflw; 4219 if (ser_ovflw > 0) { 4220 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")", 4221 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw); 4222 _markStack.expand(); 4223 _ser_pmc_remark_ovflw = 0; 4224 _ser_pmc_preclean_ovflw = 0; 4225 _ser_kac_preclean_ovflw = 0; 4226 _ser_kac_ovflw = 0; 4227 } 4228 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { 4229 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")", 4230 _par_pmc_remark_ovflw, _par_kac_ovflw); 4231 _par_pmc_remark_ovflw = 0; 4232 _par_kac_ovflw = 0; 4233 } 4234 if (_markStack._hit_limit > 0) { 4235 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")", 4236 _markStack._hit_limit); 4237 } 4238 if (_markStack._failed_double > 0) { 4239 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT, 4240 _markStack._failed_double, _markStack.capacity()); 4241 } 4242 _markStack._hit_limit = 0; 4243 _markStack._failed_double = 0; 4244 4245 if ((VerifyAfterGC || VerifyDuringGC) && 4246 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) { 4247 verify_after_remark(); 4248 } 4249 4250 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure); 4251 4252 // Change under the freelistLocks. 4253 _collectorState = Sweeping; 4254 // Call isAllClear() under bitMapLock 4255 assert(_modUnionTable.isAllClear(), 4256 "Should be clear by end of the final marking"); 4257 assert(_ct->cld_rem_set()->mod_union_is_clear(), 4258 "Should be clear by end of the final marking"); 4259 } 4260 4261 void CMSParInitialMarkTask::work(uint worker_id) { 4262 elapsedTimer _timer; 4263 ResourceMark rm; 4264 HandleMark hm; 4265 4266 // ---------- scan from roots -------------- 4267 _timer.start(); 4268 CMSHeap* heap = CMSHeap::heap(); 4269 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap)); 4270 4271 // ---------- young gen roots -------------- 4272 { 4273 work_on_young_gen_roots(&par_mri_cl); 4274 _timer.stop(); 4275 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4276 } 4277 4278 // ---------- remaining roots -------------- 4279 _timer.reset(); 4280 _timer.start(); 4281 4282 CLDToOopClosure cld_closure(&par_mri_cl, true); 4283 4284 heap->cms_process_roots(_strong_roots_scope, 4285 false, // yg was scanned above 4286 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), 4287 _collector->should_unload_classes(), 4288 &par_mri_cl, 4289 &cld_closure); 4290 assert(_collector->should_unload_classes() 4291 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), 4292 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 4293 _timer.stop(); 4294 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4295 } 4296 4297 // Parallel remark task 4298 class CMSParRemarkTask: public CMSParMarkTask { 4299 CompactibleFreeListSpace* _cms_space; 4300 4301 // The per-thread work queues, available here for stealing. 4302 OopTaskQueueSet* _task_queues; 4303 ParallelTaskTerminator _term; 4304 StrongRootsScope* _strong_roots_scope; 4305 4306 public: 4307 // A value of 0 passed to n_workers will cause the number of 4308 // workers to be taken from the active workers in the work gang. 4309 CMSParRemarkTask(CMSCollector* collector, 4310 CompactibleFreeListSpace* cms_space, 4311 uint n_workers, WorkGang* workers, 4312 OopTaskQueueSet* task_queues, 4313 StrongRootsScope* strong_roots_scope): 4314 CMSParMarkTask("Rescan roots and grey objects in parallel", 4315 collector, n_workers), 4316 _cms_space(cms_space), 4317 _task_queues(task_queues), 4318 _term(n_workers, task_queues), 4319 _strong_roots_scope(strong_roots_scope) { } 4320 4321 OopTaskQueueSet* task_queues() { return _task_queues; } 4322 4323 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 4324 4325 ParallelTaskTerminator* terminator() { return &_term; } 4326 uint n_workers() { return _n_workers; } 4327 4328 void work(uint worker_id); 4329 4330 private: 4331 // ... of dirty cards in old space 4332 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, 4333 ParMarkRefsIntoAndScanClosure* cl); 4334 4335 // ... work stealing for the above 4336 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed); 4337 }; 4338 4339 class RemarkCLDClosure : public CLDClosure { 4340 CLDToOopClosure _cm_closure; 4341 public: 4342 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure) {} 4343 void do_cld(ClassLoaderData* cld) { 4344 // Check if we have modified any oops in the CLD during the concurrent marking. 4345 if (cld->has_accumulated_modified_oops()) { 4346 cld->clear_accumulated_modified_oops(); 4347 4348 // We could have transfered the current modified marks to the accumulated marks, 4349 // like we do with the Card Table to Mod Union Table. But it's not really necessary. 4350 } else if (cld->has_modified_oops()) { 4351 // Don't clear anything, this info is needed by the next young collection. 4352 } else { 4353 // No modified oops in the ClassLoaderData. 4354 return; 4355 } 4356 4357 // The klass has modified fields, need to scan the klass. 4358 _cm_closure.do_cld(cld); 4359 } 4360 }; 4361 4362 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) { 4363 ParNewGeneration* young_gen = _collector->_young_gen; 4364 ContiguousSpace* eden_space = young_gen->eden(); 4365 ContiguousSpace* from_space = young_gen->from(); 4366 ContiguousSpace* to_space = young_gen->to(); 4367 4368 HeapWord** eca = _collector->_eden_chunk_array; 4369 size_t ect = _collector->_eden_chunk_index; 4370 HeapWord** sca = _collector->_survivor_chunk_array; 4371 size_t sct = _collector->_survivor_chunk_index; 4372 4373 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); 4374 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); 4375 4376 do_young_space_rescan(cl, to_space, NULL, 0); 4377 do_young_space_rescan(cl, from_space, sca, sct); 4378 do_young_space_rescan(cl, eden_space, eca, ect); 4379 } 4380 4381 // work_queue(i) is passed to the closure 4382 // ParMarkRefsIntoAndScanClosure. The "i" parameter 4383 // also is passed to do_dirty_card_rescan_tasks() and to 4384 // do_work_steal() to select the i-th task_queue. 4385 4386 void CMSParRemarkTask::work(uint worker_id) { 4387 elapsedTimer _timer; 4388 ResourceMark rm; 4389 HandleMark hm; 4390 4391 // ---------- rescan from roots -------------- 4392 _timer.start(); 4393 CMSHeap* heap = CMSHeap::heap(); 4394 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector, 4395 _collector->_span, _collector->ref_processor(), 4396 &(_collector->_markBitMap), 4397 work_queue(worker_id)); 4398 4399 // Rescan young gen roots first since these are likely 4400 // coarsely partitioned and may, on that account, constitute 4401 // the critical path; thus, it's best to start off that 4402 // work first. 4403 // ---------- young gen roots -------------- 4404 { 4405 work_on_young_gen_roots(&par_mrias_cl); 4406 _timer.stop(); 4407 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4408 } 4409 4410 // ---------- remaining roots -------------- 4411 _timer.reset(); 4412 _timer.start(); 4413 heap->cms_process_roots(_strong_roots_scope, 4414 false, // yg was scanned above 4415 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), 4416 _collector->should_unload_classes(), 4417 &par_mrias_cl, 4418 NULL); // The dirty klasses will be handled below 4419 4420 assert(_collector->should_unload_classes() 4421 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), 4422 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 4423 _timer.stop(); 4424 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4425 4426 // ---------- unhandled CLD scanning ---------- 4427 if (worker_id == 0) { // Single threaded at the moment. 4428 _timer.reset(); 4429 _timer.start(); 4430 4431 // Scan all new class loader data objects and new dependencies that were 4432 // introduced during concurrent marking. 4433 ResourceMark rm; 4434 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); 4435 for (int i = 0; i < array->length(); i++) { 4436 par_mrias_cl.do_cld_nv(array->at(i)); 4437 } 4438 4439 // We don't need to keep track of new CLDs anymore. 4440 ClassLoaderDataGraph::remember_new_clds(false); 4441 4442 _timer.stop(); 4443 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4444 } 4445 4446 // We might have added oops to ClassLoaderData::_handles during the 4447 // concurrent marking phase. These oops do not always point to newly allocated objects 4448 // that are guaranteed to be kept alive. Hence, 4449 // we do have to revisit the _handles block during the remark phase. 4450 4451 // ---------- dirty CLD scanning ---------- 4452 if (worker_id == 0) { // Single threaded at the moment. 4453 _timer.reset(); 4454 _timer.start(); 4455 4456 // Scan all classes that was dirtied during the concurrent marking phase. 4457 RemarkCLDClosure remark_closure(&par_mrias_cl); 4458 ClassLoaderDataGraph::cld_do(&remark_closure); 4459 4460 _timer.stop(); 4461 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4462 } 4463 4464 4465 // ---------- rescan dirty cards ------------ 4466 _timer.reset(); 4467 _timer.start(); 4468 4469 // Do the rescan tasks for each of the two spaces 4470 // (cms_space) in turn. 4471 // "worker_id" is passed to select the task_queue for "worker_id" 4472 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl); 4473 _timer.stop(); 4474 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4475 4476 // ---------- steal work from other threads ... 4477 // ---------- ... and drain overflow list. 4478 _timer.reset(); 4479 _timer.start(); 4480 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id)); 4481 _timer.stop(); 4482 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4483 } 4484 4485 void 4486 CMSParMarkTask::do_young_space_rescan( 4487 OopsInGenClosure* cl, ContiguousSpace* space, 4488 HeapWord** chunk_array, size_t chunk_top) { 4489 // Until all tasks completed: 4490 // . claim an unclaimed task 4491 // . compute region boundaries corresponding to task claimed 4492 // using chunk_array 4493 // . par_oop_iterate(cl) over that region 4494 4495 ResourceMark rm; 4496 HandleMark hm; 4497 4498 SequentialSubTasksDone* pst = space->par_seq_tasks(); 4499 4500 uint nth_task = 0; 4501 uint n_tasks = pst->n_tasks(); 4502 4503 if (n_tasks > 0) { 4504 assert(pst->valid(), "Uninitialized use?"); 4505 HeapWord *start, *end; 4506 while (!pst->is_task_claimed(/* reference */ nth_task)) { 4507 // We claimed task # nth_task; compute its boundaries. 4508 if (chunk_top == 0) { // no samples were taken 4509 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task"); 4510 start = space->bottom(); 4511 end = space->top(); 4512 } else if (nth_task == 0) { 4513 start = space->bottom(); 4514 end = chunk_array[nth_task]; 4515 } else if (nth_task < (uint)chunk_top) { 4516 assert(nth_task >= 1, "Control point invariant"); 4517 start = chunk_array[nth_task - 1]; 4518 end = chunk_array[nth_task]; 4519 } else { 4520 assert(nth_task == (uint)chunk_top, "Control point invariant"); 4521 start = chunk_array[chunk_top - 1]; 4522 end = space->top(); 4523 } 4524 MemRegion mr(start, end); 4525 // Verify that mr is in space 4526 assert(mr.is_empty() || space->used_region().contains(mr), 4527 "Should be in space"); 4528 // Verify that "start" is an object boundary 4529 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())), 4530 "Should be an oop"); 4531 space->par_oop_iterate(mr, cl); 4532 } 4533 pst->all_tasks_completed(); 4534 } 4535 } 4536 4537 void 4538 CMSParRemarkTask::do_dirty_card_rescan_tasks( 4539 CompactibleFreeListSpace* sp, int i, 4540 ParMarkRefsIntoAndScanClosure* cl) { 4541 // Until all tasks completed: 4542 // . claim an unclaimed task 4543 // . compute region boundaries corresponding to task claimed 4544 // . transfer dirty bits ct->mut for that region 4545 // . apply rescanclosure to dirty mut bits for that region 4546 4547 ResourceMark rm; 4548 HandleMark hm; 4549 4550 OopTaskQueue* work_q = work_queue(i); 4551 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); 4552 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! 4553 // CAUTION: This closure has state that persists across calls to 4554 // the work method dirty_range_iterate_clear() in that it has 4555 // embedded in it a (subtype of) UpwardsObjectClosure. The 4556 // use of that state in the embedded UpwardsObjectClosure instance 4557 // assumes that the cards are always iterated (even if in parallel 4558 // by several threads) in monotonically increasing order per each 4559 // thread. This is true of the implementation below which picks 4560 // card ranges (chunks) in monotonically increasing order globally 4561 // and, a-fortiori, in monotonically increasing order per thread 4562 // (the latter order being a subsequence of the former). 4563 // If the work code below is ever reorganized into a more chaotic 4564 // work-partitioning form than the current "sequential tasks" 4565 // paradigm, the use of that persistent state will have to be 4566 // revisited and modified appropriately. See also related 4567 // bug 4756801 work on which should examine this code to make 4568 // sure that the changes there do not run counter to the 4569 // assumptions made here and necessary for correctness and 4570 // efficiency. Note also that this code might yield inefficient 4571 // behavior in the case of very large objects that span one or 4572 // more work chunks. Such objects would potentially be scanned 4573 // several times redundantly. Work on 4756801 should try and 4574 // address that performance anomaly if at all possible. XXX 4575 MemRegion full_span = _collector->_span; 4576 CMSBitMap* bm = &(_collector->_markBitMap); // shared 4577 MarkFromDirtyCardsClosure 4578 greyRescanClosure(_collector, full_span, // entire span of interest 4579 sp, bm, work_q, cl); 4580 4581 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); 4582 assert(pst->valid(), "Uninitialized use?"); 4583 uint nth_task = 0; 4584 const int alignment = CardTable::card_size * BitsPerWord; 4585 MemRegion span = sp->used_region(); 4586 HeapWord* start_addr = span.start(); 4587 HeapWord* end_addr = align_up(span.end(), alignment); 4588 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units 4589 assert(is_aligned(start_addr, alignment), "Check alignment"); 4590 assert(is_aligned(chunk_size, alignment), "Check alignment"); 4591 4592 while (!pst->is_task_claimed(/* reference */ nth_task)) { 4593 // Having claimed the nth_task, compute corresponding mem-region, 4594 // which is a-fortiori aligned correctly (i.e. at a MUT boundary). 4595 // The alignment restriction ensures that we do not need any 4596 // synchronization with other gang-workers while setting or 4597 // clearing bits in thus chunk of the MUT. 4598 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, 4599 start_addr + (nth_task+1)*chunk_size); 4600 // The last chunk's end might be way beyond end of the 4601 // used region. In that case pull back appropriately. 4602 if (this_span.end() > end_addr) { 4603 this_span.set_end(end_addr); 4604 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); 4605 } 4606 // Iterate over the dirty cards covering this chunk, marking them 4607 // precleaned, and setting the corresponding bits in the mod union 4608 // table. Since we have been careful to partition at Card and MUT-word 4609 // boundaries no synchronization is needed between parallel threads. 4610 _collector->_ct->dirty_card_iterate(this_span, 4611 &modUnionClosure); 4612 4613 // Having transferred these marks into the modUnionTable, 4614 // rescan the marked objects on the dirty cards in the modUnionTable. 4615 // Even if this is at a synchronous collection, the initial marking 4616 // may have been done during an asynchronous collection so there 4617 // may be dirty bits in the mod-union table. 4618 _collector->_modUnionTable.dirty_range_iterate_clear( 4619 this_span, &greyRescanClosure); 4620 _collector->_modUnionTable.verifyNoOneBitsInRange( 4621 this_span.start(), 4622 this_span.end()); 4623 } 4624 pst->all_tasks_completed(); // declare that i am done 4625 } 4626 4627 // . see if we can share work_queues with ParNew? XXX 4628 void 4629 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, 4630 int* seed) { 4631 OopTaskQueue* work_q = work_queue(i); 4632 NOT_PRODUCT(int num_steals = 0;) 4633 oop obj_to_scan; 4634 CMSBitMap* bm = &(_collector->_markBitMap); 4635 4636 while (true) { 4637 // Completely finish any left over work from (an) earlier round(s) 4638 cl->trim_queue(0); 4639 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 4640 (size_t)ParGCDesiredObjsFromOverflowList); 4641 // Now check if there's any work in the overflow list 4642 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, 4643 // only affects the number of attempts made to get work from the 4644 // overflow list and does not affect the number of workers. Just 4645 // pass ParallelGCThreads so this behavior is unchanged. 4646 if (_collector->par_take_from_overflow_list(num_from_overflow_list, 4647 work_q, 4648 ParallelGCThreads)) { 4649 // found something in global overflow list; 4650 // not yet ready to go stealing work from others. 4651 // We'd like to assert(work_q->size() != 0, ...) 4652 // because we just took work from the overflow list, 4653 // but of course we can't since all of that could have 4654 // been already stolen from us. 4655 // "He giveth and He taketh away." 4656 continue; 4657 } 4658 // Verify that we have no work before we resort to stealing 4659 assert(work_q->size() == 0, "Have work, shouldn't steal"); 4660 // Try to steal from other queues that have work 4661 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 4662 NOT_PRODUCT(num_steals++;) 4663 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!"); 4664 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); 4665 // Do scanning work 4666 obj_to_scan->oop_iterate(cl); 4667 // Loop around, finish this work, and try to steal some more 4668 } else if (terminator()->offer_termination()) { 4669 break; // nirvana from the infinite cycle 4670 } 4671 } 4672 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); 4673 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), 4674 "Else our work is not yet done"); 4675 } 4676 4677 // Record object boundaries in _eden_chunk_array by sampling the eden 4678 // top in the slow-path eden object allocation code path and record 4679 // the boundaries, if CMSEdenChunksRecordAlways is true. If 4680 // CMSEdenChunksRecordAlways is false, we use the other asynchronous 4681 // sampling in sample_eden() that activates during the part of the 4682 // preclean phase. 4683 void CMSCollector::sample_eden_chunk() { 4684 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) { 4685 if (_eden_chunk_lock->try_lock()) { 4686 // Record a sample. This is the critical section. The contents 4687 // of the _eden_chunk_array have to be non-decreasing in the 4688 // address order. 4689 _eden_chunk_array[_eden_chunk_index] = *_top_addr; 4690 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, 4691 "Unexpected state of Eden"); 4692 if (_eden_chunk_index == 0 || 4693 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) && 4694 (pointer_delta(_eden_chunk_array[_eden_chunk_index], 4695 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) { 4696 _eden_chunk_index++; // commit sample 4697 } 4698 _eden_chunk_lock->unlock(); 4699 } 4700 } 4701 } 4702 4703 // Return a thread-local PLAB recording array, as appropriate. 4704 void* CMSCollector::get_data_recorder(int thr_num) { 4705 if (_survivor_plab_array != NULL && 4706 (CMSPLABRecordAlways || 4707 (_collectorState > Marking && _collectorState < FinalMarking))) { 4708 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); 4709 ChunkArray* ca = &_survivor_plab_array[thr_num]; 4710 ca->reset(); // clear it so that fresh data is recorded 4711 return (void*) ca; 4712 } else { 4713 return NULL; 4714 } 4715 } 4716 4717 // Reset all the thread-local PLAB recording arrays 4718 void CMSCollector::reset_survivor_plab_arrays() { 4719 for (uint i = 0; i < ParallelGCThreads; i++) { 4720 _survivor_plab_array[i].reset(); 4721 } 4722 } 4723 4724 // Merge the per-thread plab arrays into the global survivor chunk 4725 // array which will provide the partitioning of the survivor space 4726 // for CMS initial scan and rescan. 4727 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv, 4728 int no_of_gc_threads) { 4729 assert(_survivor_plab_array != NULL, "Error"); 4730 assert(_survivor_chunk_array != NULL, "Error"); 4731 assert(_collectorState == FinalMarking || 4732 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error"); 4733 for (int j = 0; j < no_of_gc_threads; j++) { 4734 _cursor[j] = 0; 4735 } 4736 HeapWord* top = surv->top(); 4737 size_t i; 4738 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries 4739 HeapWord* min_val = top; // Higher than any PLAB address 4740 uint min_tid = 0; // position of min_val this round 4741 for (int j = 0; j < no_of_gc_threads; j++) { 4742 ChunkArray* cur_sca = &_survivor_plab_array[j]; 4743 if (_cursor[j] == cur_sca->end()) { 4744 continue; 4745 } 4746 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); 4747 HeapWord* cur_val = cur_sca->nth(_cursor[j]); 4748 assert(surv->used_region().contains(cur_val), "Out of bounds value"); 4749 if (cur_val < min_val) { 4750 min_tid = j; 4751 min_val = cur_val; 4752 } else { 4753 assert(cur_val < top, "All recorded addresses should be less"); 4754 } 4755 } 4756 // At this point min_val and min_tid are respectively 4757 // the least address in _survivor_plab_array[j]->nth(_cursor[j]) 4758 // and the thread (j) that witnesses that address. 4759 // We record this address in the _survivor_chunk_array[i] 4760 // and increment _cursor[min_tid] prior to the next round i. 4761 if (min_val == top) { 4762 break; 4763 } 4764 _survivor_chunk_array[i] = min_val; 4765 _cursor[min_tid]++; 4766 } 4767 // We are all done; record the size of the _survivor_chunk_array 4768 _survivor_chunk_index = i; // exclusive: [0, i) 4769 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i); 4770 // Verify that we used up all the recorded entries 4771 #ifdef ASSERT 4772 size_t total = 0; 4773 for (int j = 0; j < no_of_gc_threads; j++) { 4774 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); 4775 total += _cursor[j]; 4776 } 4777 assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); 4778 // Check that the merged array is in sorted order 4779 if (total > 0) { 4780 for (size_t i = 0; i < total - 1; i++) { 4781 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", 4782 i, p2i(_survivor_chunk_array[i])); 4783 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], 4784 "Not sorted"); 4785 } 4786 } 4787 #endif // ASSERT 4788 } 4789 4790 // Set up the space's par_seq_tasks structure for work claiming 4791 // for parallel initial scan and rescan of young gen. 4792 // See ParRescanTask where this is currently used. 4793 void 4794 CMSCollector:: 4795 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { 4796 assert(n_threads > 0, "Unexpected n_threads argument"); 4797 4798 // Eden space 4799 if (!_young_gen->eden()->is_empty()) { 4800 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks(); 4801 assert(!pst->valid(), "Clobbering existing data?"); 4802 // Each valid entry in [0, _eden_chunk_index) represents a task. 4803 size_t n_tasks = _eden_chunk_index + 1; 4804 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); 4805 // Sets the condition for completion of the subtask (how many threads 4806 // need to finish in order to be done). 4807 pst->set_n_threads(n_threads); 4808 pst->set_n_tasks((int)n_tasks); 4809 } 4810 4811 // Merge the survivor plab arrays into _survivor_chunk_array 4812 if (_survivor_plab_array != NULL) { 4813 merge_survivor_plab_arrays(_young_gen->from(), n_threads); 4814 } else { 4815 assert(_survivor_chunk_index == 0, "Error"); 4816 } 4817 4818 // To space 4819 { 4820 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks(); 4821 assert(!pst->valid(), "Clobbering existing data?"); 4822 // Sets the condition for completion of the subtask (how many threads 4823 // need to finish in order to be done). 4824 pst->set_n_threads(n_threads); 4825 pst->set_n_tasks(1); 4826 assert(pst->valid(), "Error"); 4827 } 4828 4829 // From space 4830 { 4831 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks(); 4832 assert(!pst->valid(), "Clobbering existing data?"); 4833 size_t n_tasks = _survivor_chunk_index + 1; 4834 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); 4835 // Sets the condition for completion of the subtask (how many threads 4836 // need to finish in order to be done). 4837 pst->set_n_threads(n_threads); 4838 pst->set_n_tasks((int)n_tasks); 4839 assert(pst->valid(), "Error"); 4840 } 4841 } 4842 4843 // Parallel version of remark 4844 void CMSCollector::do_remark_parallel() { 4845 CMSHeap* heap = CMSHeap::heap(); 4846 WorkGang* workers = heap->workers(); 4847 assert(workers != NULL, "Need parallel worker threads."); 4848 // Choose to use the number of GC workers most recently set 4849 // into "active_workers". 4850 uint n_workers = workers->active_workers(); 4851 4852 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 4853 4854 StrongRootsScope srs(n_workers); 4855 4856 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs); 4857 4858 // We won't be iterating over the cards in the card table updating 4859 // the younger_gen cards, so we shouldn't call the following else 4860 // the verification code as well as subsequent younger_refs_iterate 4861 // code would get confused. XXX 4862 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel 4863 4864 // The young gen rescan work will not be done as part of 4865 // process_roots (which currently doesn't know how to 4866 // parallelize such a scan), but rather will be broken up into 4867 // a set of parallel tasks (via the sampling that the [abortable] 4868 // preclean phase did of eden, plus the [two] tasks of 4869 // scanning the [two] survivor spaces. Further fine-grain 4870 // parallelization of the scanning of the survivor spaces 4871 // themselves, and of precleaning of the young gen itself 4872 // is deferred to the future. 4873 initialize_sequential_subtasks_for_young_gen_rescan(n_workers); 4874 4875 // The dirty card rescan work is broken up into a "sequence" 4876 // of parallel tasks (per constituent space) that are dynamically 4877 // claimed by the parallel threads. 4878 cms_space->initialize_sequential_subtasks_for_rescan(n_workers); 4879 4880 // It turns out that even when we're using 1 thread, doing the work in a 4881 // separate thread causes wide variance in run times. We can't help this 4882 // in the multi-threaded case, but we special-case n=1 here to get 4883 // repeatable measurements of the 1-thread overhead of the parallel code. 4884 if (n_workers > 1) { 4885 // Make refs discovery MT-safe, if it isn't already: it may not 4886 // necessarily be so, since it's possible that we are doing 4887 // ST marking. 4888 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true); 4889 workers->run_task(&tsk); 4890 } else { 4891 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); 4892 tsk.work(0); 4893 } 4894 4895 // restore, single-threaded for now, any preserved marks 4896 // as a result of work_q overflow 4897 restore_preserved_marks_if_any(); 4898 } 4899 4900 // Non-parallel version of remark 4901 void CMSCollector::do_remark_non_parallel() { 4902 ResourceMark rm; 4903 HandleMark hm; 4904 CMSHeap* heap = CMSHeap::heap(); 4905 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); 4906 4907 MarkRefsIntoAndScanClosure 4908 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */, 4909 &_markStack, this, 4910 false /* should_yield */, false /* not precleaning */); 4911 MarkFromDirtyCardsClosure 4912 markFromDirtyCardsClosure(this, _span, 4913 NULL, // space is set further below 4914 &_markBitMap, &_markStack, &mrias_cl); 4915 { 4916 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm); 4917 // Iterate over the dirty cards, setting the corresponding bits in the 4918 // mod union table. 4919 { 4920 ModUnionClosure modUnionClosure(&_modUnionTable); 4921 _ct->dirty_card_iterate(_cmsGen->used_region(), 4922 &modUnionClosure); 4923 } 4924 // Having transferred these marks into the modUnionTable, we just need 4925 // to rescan the marked objects on the dirty cards in the modUnionTable. 4926 // The initial marking may have been done during an asynchronous 4927 // collection so there may be dirty bits in the mod-union table. 4928 const int alignment = CardTable::card_size * BitsPerWord; 4929 { 4930 // ... First handle dirty cards in CMS gen 4931 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); 4932 MemRegion ur = _cmsGen->used_region(); 4933 HeapWord* lb = ur.start(); 4934 HeapWord* ub = align_up(ur.end(), alignment); 4935 MemRegion cms_span(lb, ub); 4936 _modUnionTable.dirty_range_iterate_clear(cms_span, 4937 &markFromDirtyCardsClosure); 4938 verify_work_stacks_empty(); 4939 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards()); 4940 } 4941 } 4942 if (VerifyDuringGC && 4943 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) { 4944 HandleMark hm; // Discard invalid handles created during verification 4945 Universe::verify(); 4946 } 4947 { 4948 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm); 4949 4950 verify_work_stacks_empty(); 4951 4952 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 4953 StrongRootsScope srs(1); 4954 4955 heap->cms_process_roots(&srs, 4956 true, // young gen as roots 4957 GenCollectedHeap::ScanningOption(roots_scanning_options()), 4958 should_unload_classes(), 4959 &mrias_cl, 4960 NULL); // The dirty klasses will be handled below 4961 4962 assert(should_unload_classes() 4963 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), 4964 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 4965 } 4966 4967 { 4968 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm); 4969 4970 verify_work_stacks_empty(); 4971 4972 // Scan all class loader data objects that might have been introduced 4973 // during concurrent marking. 4974 ResourceMark rm; 4975 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); 4976 for (int i = 0; i < array->length(); i++) { 4977 mrias_cl.do_cld_nv(array->at(i)); 4978 } 4979 4980 // We don't need to keep track of new CLDs anymore. 4981 ClassLoaderDataGraph::remember_new_clds(false); 4982 4983 verify_work_stacks_empty(); 4984 } 4985 4986 // We might have added oops to ClassLoaderData::_handles during the 4987 // concurrent marking phase. These oops do not point to newly allocated objects 4988 // that are guaranteed to be kept alive. Hence, 4989 // we do have to revisit the _handles block during the remark phase. 4990 { 4991 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm); 4992 4993 verify_work_stacks_empty(); 4994 4995 RemarkCLDClosure remark_closure(&mrias_cl); 4996 ClassLoaderDataGraph::cld_do(&remark_closure); 4997 4998 verify_work_stacks_empty(); 4999 } 5000 5001 verify_work_stacks_empty(); 5002 // Restore evacuated mark words, if any, used for overflow list links 5003 restore_preserved_marks_if_any(); 5004 5005 verify_overflow_empty(); 5006 } 5007 5008 //////////////////////////////////////////////////////// 5009 // Parallel Reference Processing Task Proxy Class 5010 //////////////////////////////////////////////////////// 5011 class AbstractGangTaskWOopQueues : public AbstractGangTask { 5012 OopTaskQueueSet* _queues; 5013 ParallelTaskTerminator _terminator; 5014 public: 5015 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) : 5016 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {} 5017 ParallelTaskTerminator* terminator() { return &_terminator; } 5018 OopTaskQueueSet* queues() { return _queues; } 5019 }; 5020 5021 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues { 5022 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 5023 CMSCollector* _collector; 5024 CMSBitMap* _mark_bit_map; 5025 const MemRegion _span; 5026 ProcessTask& _task; 5027 5028 public: 5029 CMSRefProcTaskProxy(ProcessTask& task, 5030 CMSCollector* collector, 5031 const MemRegion& span, 5032 CMSBitMap* mark_bit_map, 5033 AbstractWorkGang* workers, 5034 OopTaskQueueSet* task_queues): 5035 AbstractGangTaskWOopQueues("Process referents by policy in parallel", 5036 task_queues, 5037 workers->active_workers()), 5038 _task(task), 5039 _collector(collector), _span(span), _mark_bit_map(mark_bit_map) 5040 { 5041 assert(_collector->_span.equals(_span) && !_span.is_empty(), 5042 "Inconsistency in _span"); 5043 } 5044 5045 OopTaskQueueSet* task_queues() { return queues(); } 5046 5047 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 5048 5049 void do_work_steal(int i, 5050 CMSParDrainMarkingStackClosure* drain, 5051 CMSParKeepAliveClosure* keep_alive, 5052 int* seed); 5053 5054 virtual void work(uint worker_id); 5055 }; 5056 5057 void CMSRefProcTaskProxy::work(uint worker_id) { 5058 ResourceMark rm; 5059 HandleMark hm; 5060 assert(_collector->_span.equals(_span), "Inconsistency in _span"); 5061 CMSParKeepAliveClosure par_keep_alive(_collector, _span, 5062 _mark_bit_map, 5063 work_queue(worker_id)); 5064 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, 5065 _mark_bit_map, 5066 work_queue(worker_id)); 5067 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map); 5068 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack); 5069 if (_task.marks_oops_alive()) { 5070 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive, 5071 _collector->hash_seed(worker_id)); 5072 } 5073 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); 5074 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); 5075 } 5076 5077 class CMSRefEnqueueTaskProxy: public AbstractGangTask { 5078 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 5079 EnqueueTask& _task; 5080 5081 public: 5082 CMSRefEnqueueTaskProxy(EnqueueTask& task) 5083 : AbstractGangTask("Enqueue reference objects in parallel"), 5084 _task(task) 5085 { } 5086 5087 virtual void work(uint worker_id) 5088 { 5089 _task.work(worker_id); 5090 } 5091 }; 5092 5093 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, 5094 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): 5095 _span(span), 5096 _bit_map(bit_map), 5097 _work_queue(work_queue), 5098 _mark_and_push(collector, span, bit_map, work_queue), 5099 _low_water_mark(MIN2((work_queue->max_elems()/4), 5100 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))) 5101 { } 5102 5103 // . see if we can share work_queues with ParNew? XXX 5104 void CMSRefProcTaskProxy::do_work_steal(int i, 5105 CMSParDrainMarkingStackClosure* drain, 5106 CMSParKeepAliveClosure* keep_alive, 5107 int* seed) { 5108 OopTaskQueue* work_q = work_queue(i); 5109 NOT_PRODUCT(int num_steals = 0;) 5110 oop obj_to_scan; 5111 5112 while (true) { 5113 // Completely finish any left over work from (an) earlier round(s) 5114 drain->trim_queue(0); 5115 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 5116 (size_t)ParGCDesiredObjsFromOverflowList); 5117 // Now check if there's any work in the overflow list 5118 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, 5119 // only affects the number of attempts made to get work from the 5120 // overflow list and does not affect the number of workers. Just 5121 // pass ParallelGCThreads so this behavior is unchanged. 5122 if (_collector->par_take_from_overflow_list(num_from_overflow_list, 5123 work_q, 5124 ParallelGCThreads)) { 5125 // Found something in global overflow list; 5126 // not yet ready to go stealing work from others. 5127 // We'd like to assert(work_q->size() != 0, ...) 5128 // because we just took work from the overflow list, 5129 // but of course we can't, since all of that might have 5130 // been already stolen from us. 5131 continue; 5132 } 5133 // Verify that we have no work before we resort to stealing 5134 assert(work_q->size() == 0, "Have work, shouldn't steal"); 5135 // Try to steal from other queues that have work 5136 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 5137 NOT_PRODUCT(num_steals++;) 5138 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!"); 5139 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); 5140 // Do scanning work 5141 obj_to_scan->oop_iterate(keep_alive); 5142 // Loop around, finish this work, and try to steal some more 5143 } else if (terminator()->offer_termination()) { 5144 break; // nirvana from the infinite cycle 5145 } 5146 } 5147 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); 5148 } 5149 5150 void CMSRefProcTaskExecutor::execute(ProcessTask& task) 5151 { 5152 CMSHeap* heap = CMSHeap::heap(); 5153 WorkGang* workers = heap->workers(); 5154 assert(workers != NULL, "Need parallel worker threads."); 5155 CMSRefProcTaskProxy rp_task(task, &_collector, 5156 _collector.ref_processor()->span(), 5157 _collector.markBitMap(), 5158 workers, _collector.task_queues()); 5159 workers->run_task(&rp_task); 5160 } 5161 5162 void CMSRefProcTaskExecutor::execute(EnqueueTask& task) 5163 { 5164 5165 CMSHeap* heap = CMSHeap::heap(); 5166 WorkGang* workers = heap->workers(); 5167 assert(workers != NULL, "Need parallel worker threads."); 5168 CMSRefEnqueueTaskProxy enq_task(task); 5169 workers->run_task(&enq_task); 5170 } 5171 5172 void CMSCollector::refProcessingWork() { 5173 ResourceMark rm; 5174 HandleMark hm; 5175 5176 ReferenceProcessor* rp = ref_processor(); 5177 assert(rp->span().equals(_span), "Spans should be equal"); 5178 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); 5179 // Process weak references. 5180 rp->setup_policy(false); 5181 verify_work_stacks_empty(); 5182 5183 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->num_q()); 5184 { 5185 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm); 5186 5187 // Setup keep_alive and complete closures. 5188 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, 5189 &_markStack, false /* !preclean */); 5190 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, 5191 _span, &_markBitMap, &_markStack, 5192 &cmsKeepAliveClosure, false /* !preclean */); 5193 5194 ReferenceProcessorStats stats; 5195 if (rp->processing_is_mt()) { 5196 // Set the degree of MT here. If the discovery is done MT, there 5197 // may have been a different number of threads doing the discovery 5198 // and a different number of discovered lists may have Ref objects. 5199 // That is OK as long as the Reference lists are balanced (see 5200 // balance_all_queues() and balance_queues()). 5201 CMSHeap* heap = CMSHeap::heap(); 5202 uint active_workers = ParallelGCThreads; 5203 WorkGang* workers = heap->workers(); 5204 if (workers != NULL) { 5205 active_workers = workers->active_workers(); 5206 // The expectation is that active_workers will have already 5207 // been set to a reasonable value. If it has not been set, 5208 // investigate. 5209 assert(active_workers > 0, "Should have been set during scavenge"); 5210 } 5211 rp->set_active_mt_degree(active_workers); 5212 CMSRefProcTaskExecutor task_executor(*this); 5213 stats = rp->process_discovered_references(&_is_alive_closure, 5214 &cmsKeepAliveClosure, 5215 &cmsDrainMarkingStackClosure, 5216 &task_executor, 5217 &pt); 5218 } else { 5219 stats = rp->process_discovered_references(&_is_alive_closure, 5220 &cmsKeepAliveClosure, 5221 &cmsDrainMarkingStackClosure, 5222 NULL, 5223 &pt); 5224 } 5225 _gc_tracer_cm->report_gc_reference_stats(stats); 5226 pt.print_all_references(); 5227 } 5228 5229 // This is the point where the entire marking should have completed. 5230 verify_work_stacks_empty(); 5231 5232 { 5233 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm); 5234 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl); 5235 } 5236 5237 if (should_unload_classes()) { 5238 { 5239 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm); 5240 5241 // Unload classes and purge the SystemDictionary. 5242 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm); 5243 5244 // Unload nmethods. 5245 CodeCache::do_unloading(&_is_alive_closure, purged_class); 5246 5247 // Prune dead klasses from subklass/sibling/implementor lists. 5248 Klass::clean_weak_klass_links(); 5249 } 5250 5251 { 5252 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm); 5253 // Clean up unreferenced symbols in symbol table. 5254 SymbolTable::unlink(); 5255 } 5256 5257 { 5258 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm); 5259 // Delete entries for dead interned strings. 5260 StringTable::unlink(&_is_alive_closure); 5261 } 5262 } 5263 5264 // Restore any preserved marks as a result of mark stack or 5265 // work queue overflow 5266 restore_preserved_marks_if_any(); // done single-threaded for now 5267 5268 rp->set_enqueuing_is_done(true); 5269 if (rp->processing_is_mt()) { 5270 rp->balance_all_queues(); 5271 CMSRefProcTaskExecutor task_executor(*this); 5272 rp->enqueue_discovered_references(&task_executor, &pt); 5273 } else { 5274 rp->enqueue_discovered_references(NULL, &pt); 5275 } 5276 rp->verify_no_references_recorded(); 5277 pt.print_enqueue_phase(); 5278 assert(!rp->discovery_enabled(), "should have been disabled"); 5279 } 5280 5281 #ifndef PRODUCT 5282 void CMSCollector::check_correct_thread_executing() { 5283 Thread* t = Thread::current(); 5284 // Only the VM thread or the CMS thread should be here. 5285 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), 5286 "Unexpected thread type"); 5287 // If this is the vm thread, the foreground process 5288 // should not be waiting. Note that _foregroundGCIsActive is 5289 // true while the foreground collector is waiting. 5290 if (_foregroundGCShouldWait) { 5291 // We cannot be the VM thread 5292 assert(t->is_ConcurrentGC_thread(), 5293 "Should be CMS thread"); 5294 } else { 5295 // We can be the CMS thread only if we are in a stop-world 5296 // phase of CMS collection. 5297 if (t->is_ConcurrentGC_thread()) { 5298 assert(_collectorState == InitialMarking || 5299 _collectorState == FinalMarking, 5300 "Should be a stop-world phase"); 5301 // The CMS thread should be holding the CMS_token. 5302 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 5303 "Potential interference with concurrently " 5304 "executing VM thread"); 5305 } 5306 } 5307 } 5308 #endif 5309 5310 void CMSCollector::sweep() { 5311 assert(_collectorState == Sweeping, "just checking"); 5312 check_correct_thread_executing(); 5313 verify_work_stacks_empty(); 5314 verify_overflow_empty(); 5315 increment_sweep_count(); 5316 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); 5317 5318 _inter_sweep_timer.stop(); 5319 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); 5320 5321 assert(!_intra_sweep_timer.is_active(), "Should not be active"); 5322 _intra_sweep_timer.reset(); 5323 _intra_sweep_timer.start(); 5324 { 5325 GCTraceCPUTime tcpu; 5326 CMSPhaseAccounting pa(this, "Concurrent Sweep"); 5327 // First sweep the old gen 5328 { 5329 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), 5330 bitMapLock()); 5331 sweepWork(_cmsGen); 5332 } 5333 5334 // Update Universe::_heap_*_at_gc figures. 5335 // We need all the free list locks to make the abstract state 5336 // transition from Sweeping to Resetting. See detailed note 5337 // further below. 5338 { 5339 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock()); 5340 // Update heap occupancy information which is used as 5341 // input to soft ref clearing policy at the next gc. 5342 Universe::update_heap_info_at_gc(); 5343 _collectorState = Resizing; 5344 } 5345 } 5346 verify_work_stacks_empty(); 5347 verify_overflow_empty(); 5348 5349 if (should_unload_classes()) { 5350 // Delay purge to the beginning of the next safepoint. Metaspace::contains 5351 // requires that the virtual spaces are stable and not deleted. 5352 ClassLoaderDataGraph::set_should_purge(true); 5353 } 5354 5355 _intra_sweep_timer.stop(); 5356 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds()); 5357 5358 _inter_sweep_timer.reset(); 5359 _inter_sweep_timer.start(); 5360 5361 // We need to use a monotonically non-decreasing time in ms 5362 // or we will see time-warp warnings and os::javaTimeMillis() 5363 // does not guarantee monotonicity. 5364 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 5365 update_time_of_last_gc(now); 5366 5367 // NOTE on abstract state transitions: 5368 // Mutators allocate-live and/or mark the mod-union table dirty 5369 // based on the state of the collection. The former is done in 5370 // the interval [Marking, Sweeping] and the latter in the interval 5371 // [Marking, Sweeping). Thus the transitions into the Marking state 5372 // and out of the Sweeping state must be synchronously visible 5373 // globally to the mutators. 5374 // The transition into the Marking state happens with the world 5375 // stopped so the mutators will globally see it. Sweeping is 5376 // done asynchronously by the background collector so the transition 5377 // from the Sweeping state to the Resizing state must be done 5378 // under the freelistLock (as is the check for whether to 5379 // allocate-live and whether to dirty the mod-union table). 5380 assert(_collectorState == Resizing, "Change of collector state to" 5381 " Resizing must be done under the freelistLocks (plural)"); 5382 5383 // Now that sweeping has been completed, we clear 5384 // the incremental_collection_failed flag, 5385 // thus inviting a younger gen collection to promote into 5386 // this generation. If such a promotion may still fail, 5387 // the flag will be set again when a young collection is 5388 // attempted. 5389 CMSHeap* heap = CMSHeap::heap(); 5390 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up 5391 heap->update_full_collections_completed(_collection_count_start); 5392 } 5393 5394 // FIX ME!!! Looks like this belongs in CFLSpace, with 5395 // CMSGen merely delegating to it. 5396 void ConcurrentMarkSweepGeneration::setNearLargestChunk() { 5397 double nearLargestPercent = FLSLargestBlockCoalesceProximity; 5398 HeapWord* minAddr = _cmsSpace->bottom(); 5399 HeapWord* largestAddr = 5400 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict(); 5401 if (largestAddr == NULL) { 5402 // The dictionary appears to be empty. In this case 5403 // try to coalesce at the end of the heap. 5404 largestAddr = _cmsSpace->end(); 5405 } 5406 size_t largestOffset = pointer_delta(largestAddr, minAddr); 5407 size_t nearLargestOffset = 5408 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; 5409 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT, 5410 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset)); 5411 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); 5412 } 5413 5414 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { 5415 return addr >= _cmsSpace->nearLargestChunk(); 5416 } 5417 5418 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { 5419 return _cmsSpace->find_chunk_at_end(); 5420 } 5421 5422 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation, 5423 bool full) { 5424 // If the young generation has been collected, gather any statistics 5425 // that are of interest at this point. 5426 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation); 5427 if (!full && current_is_young) { 5428 // Gather statistics on the young generation collection. 5429 collector()->stats().record_gc0_end(used()); 5430 } 5431 } 5432 5433 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) { 5434 // We iterate over the space(s) underlying this generation, 5435 // checking the mark bit map to see if the bits corresponding 5436 // to specific blocks are marked or not. Blocks that are 5437 // marked are live and are not swept up. All remaining blocks 5438 // are swept up, with coalescing on-the-fly as we sweep up 5439 // contiguous free and/or garbage blocks: 5440 // We need to ensure that the sweeper synchronizes with allocators 5441 // and stop-the-world collectors. In particular, the following 5442 // locks are used: 5443 // . CMS token: if this is held, a stop the world collection cannot occur 5444 // . freelistLock: if this is held no allocation can occur from this 5445 // generation by another thread 5446 // . bitMapLock: if this is held, no other thread can access or update 5447 // 5448 5449 // Note that we need to hold the freelistLock if we use 5450 // block iterate below; else the iterator might go awry if 5451 // a mutator (or promotion) causes block contents to change 5452 // (for instance if the allocator divvies up a block). 5453 // If we hold the free list lock, for all practical purposes 5454 // young generation GC's can't occur (they'll usually need to 5455 // promote), so we might as well prevent all young generation 5456 // GC's while we do a sweeping step. For the same reason, we might 5457 // as well take the bit map lock for the entire duration 5458 5459 // check that we hold the requisite locks 5460 assert(have_cms_token(), "Should hold cms token"); 5461 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep"); 5462 assert_lock_strong(old_gen->freelistLock()); 5463 assert_lock_strong(bitMapLock()); 5464 5465 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context"); 5466 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context"); 5467 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), 5468 _inter_sweep_estimate.padded_average(), 5469 _intra_sweep_estimate.padded_average()); 5470 old_gen->setNearLargestChunk(); 5471 5472 { 5473 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield); 5474 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure); 5475 // We need to free-up/coalesce garbage/blocks from a 5476 // co-terminal free run. This is done in the SweepClosure 5477 // destructor; so, do not remove this scope, else the 5478 // end-of-sweep-census below will be off by a little bit. 5479 } 5480 old_gen->cmsSpace()->sweep_completed(); 5481 old_gen->cmsSpace()->endSweepFLCensus(sweep_count()); 5482 if (should_unload_classes()) { // unloaded classes this cycle, 5483 _concurrent_cycles_since_last_unload = 0; // ... reset count 5484 } else { // did not unload classes, 5485 _concurrent_cycles_since_last_unload++; // ... increment count 5486 } 5487 } 5488 5489 // Reset CMS data structures (for now just the marking bit map) 5490 // preparatory for the next cycle. 5491 void CMSCollector::reset_concurrent() { 5492 CMSTokenSyncWithLocks ts(true, bitMapLock()); 5493 5494 // If the state is not "Resetting", the foreground thread 5495 // has done a collection and the resetting. 5496 if (_collectorState != Resetting) { 5497 assert(_collectorState == Idling, "The state should only change" 5498 " because the foreground collector has finished the collection"); 5499 return; 5500 } 5501 5502 { 5503 // Clear the mark bitmap (no grey objects to start with) 5504 // for the next cycle. 5505 GCTraceCPUTime tcpu; 5506 CMSPhaseAccounting cmspa(this, "Concurrent Reset"); 5507 5508 HeapWord* curAddr = _markBitMap.startWord(); 5509 while (curAddr < _markBitMap.endWord()) { 5510 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); 5511 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); 5512 _markBitMap.clear_large_range(chunk); 5513 if (ConcurrentMarkSweepThread::should_yield() && 5514 !foregroundGCIsActive() && 5515 CMSYield) { 5516 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 5517 "CMS thread should hold CMS token"); 5518 assert_lock_strong(bitMapLock()); 5519 bitMapLock()->unlock(); 5520 ConcurrentMarkSweepThread::desynchronize(true); 5521 stopTimer(); 5522 incrementYields(); 5523 5524 // See the comment in coordinator_yield() 5525 for (unsigned i = 0; i < CMSYieldSleepCount && 5526 ConcurrentMarkSweepThread::should_yield() && 5527 !CMSCollector::foregroundGCIsActive(); ++i) { 5528 os::sleep(Thread::current(), 1, false); 5529 } 5530 5531 ConcurrentMarkSweepThread::synchronize(true); 5532 bitMapLock()->lock_without_safepoint_check(); 5533 startTimer(); 5534 } 5535 curAddr = chunk.end(); 5536 } 5537 // A successful mostly concurrent collection has been done. 5538 // Because only the full (i.e., concurrent mode failure) collections 5539 // are being measured for gc overhead limits, clean the "near" flag 5540 // and count. 5541 size_policy()->reset_gc_overhead_limit_count(); 5542 _collectorState = Idling; 5543 } 5544 5545 register_gc_end(); 5546 } 5547 5548 // Same as above but for STW paths 5549 void CMSCollector::reset_stw() { 5550 // already have the lock 5551 assert(_collectorState == Resetting, "just checking"); 5552 assert_lock_strong(bitMapLock()); 5553 GCIdMark gc_id_mark(_cmsThread->gc_id()); 5554 _markBitMap.clear_all(); 5555 _collectorState = Idling; 5556 register_gc_end(); 5557 } 5558 5559 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) { 5560 GCTraceCPUTime tcpu; 5561 TraceCollectorStats tcs_cgc(cgc_counters()); 5562 5563 switch (op) { 5564 case CMS_op_checkpointRootsInitial: { 5565 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true); 5566 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT); 5567 checkpointRootsInitial(); 5568 break; 5569 } 5570 case CMS_op_checkpointRootsFinal: { 5571 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true); 5572 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT); 5573 checkpointRootsFinal(); 5574 break; 5575 } 5576 default: 5577 fatal("No such CMS_op"); 5578 } 5579 } 5580 5581 #ifndef PRODUCT 5582 size_t const CMSCollector::skip_header_HeapWords() { 5583 return FreeChunk::header_size(); 5584 } 5585 5586 // Try and collect here conditions that should hold when 5587 // CMS thread is exiting. The idea is that the foreground GC 5588 // thread should not be blocked if it wants to terminate 5589 // the CMS thread and yet continue to run the VM for a while 5590 // after that. 5591 void CMSCollector::verify_ok_to_terminate() const { 5592 assert(Thread::current()->is_ConcurrentGC_thread(), 5593 "should be called by CMS thread"); 5594 assert(!_foregroundGCShouldWait, "should be false"); 5595 // We could check here that all the various low-level locks 5596 // are not held by the CMS thread, but that is overkill; see 5597 // also CMSThread::verify_ok_to_terminate() where the CGC_lock 5598 // is checked. 5599 } 5600 #endif 5601 5602 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { 5603 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), 5604 "missing Printezis mark?"); 5605 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); 5606 size_t size = pointer_delta(nextOneAddr + 1, addr); 5607 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 5608 "alignment problem"); 5609 assert(size >= 3, "Necessary for Printezis marks to work"); 5610 return size; 5611 } 5612 5613 // A variant of the above (block_size_using_printezis_bits()) except 5614 // that we return 0 if the P-bits are not yet set. 5615 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { 5616 if (_markBitMap.isMarked(addr + 1)) { 5617 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects"); 5618 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); 5619 size_t size = pointer_delta(nextOneAddr + 1, addr); 5620 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 5621 "alignment problem"); 5622 assert(size >= 3, "Necessary for Printezis marks to work"); 5623 return size; 5624 } 5625 return 0; 5626 } 5627 5628 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { 5629 size_t sz = 0; 5630 oop p = (oop)addr; 5631 if (p->klass_or_null_acquire() != NULL) { 5632 sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); 5633 } else { 5634 sz = block_size_using_printezis_bits(addr); 5635 } 5636 assert(sz > 0, "size must be nonzero"); 5637 HeapWord* next_block = addr + sz; 5638 HeapWord* next_card = align_up(next_block, CardTable::card_size); 5639 assert(align_down((uintptr_t)addr, CardTable::card_size) < 5640 align_down((uintptr_t)next_card, CardTable::card_size), 5641 "must be different cards"); 5642 return next_card; 5643 } 5644 5645 5646 // CMS Bit Map Wrapper ///////////////////////////////////////// 5647 5648 // Construct a CMS bit map infrastructure, but don't create the 5649 // bit vector itself. That is done by a separate call CMSBitMap::allocate() 5650 // further below. 5651 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): 5652 _bm(), 5653 _shifter(shifter), 5654 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true, 5655 Monitor::_safepoint_check_sometimes) : NULL) 5656 { 5657 _bmStartWord = 0; 5658 _bmWordSize = 0; 5659 } 5660 5661 bool CMSBitMap::allocate(MemRegion mr) { 5662 _bmStartWord = mr.start(); 5663 _bmWordSize = mr.word_size(); 5664 ReservedSpace brs(ReservedSpace::allocation_align_size_up( 5665 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); 5666 if (!brs.is_reserved()) { 5667 log_warning(gc)("CMS bit map allocation failure"); 5668 return false; 5669 } 5670 // For now we'll just commit all of the bit map up front. 5671 // Later on we'll try to be more parsimonious with swap. 5672 if (!_virtual_space.initialize(brs, brs.size())) { 5673 log_warning(gc)("CMS bit map backing store failure"); 5674 return false; 5675 } 5676 assert(_virtual_space.committed_size() == brs.size(), 5677 "didn't reserve backing store for all of CMS bit map?"); 5678 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= 5679 _bmWordSize, "inconsistency in bit map sizing"); 5680 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter); 5681 5682 // bm.clear(); // can we rely on getting zero'd memory? verify below 5683 assert(isAllClear(), 5684 "Expected zero'd memory from ReservedSpace constructor"); 5685 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), 5686 "consistency check"); 5687 return true; 5688 } 5689 5690 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { 5691 HeapWord *next_addr, *end_addr, *last_addr; 5692 assert_locked(); 5693 assert(covers(mr), "out-of-range error"); 5694 // XXX assert that start and end are appropriately aligned 5695 for (next_addr = mr.start(), end_addr = mr.end(); 5696 next_addr < end_addr; next_addr = last_addr) { 5697 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); 5698 last_addr = dirty_region.end(); 5699 if (!dirty_region.is_empty()) { 5700 cl->do_MemRegion(dirty_region); 5701 } else { 5702 assert(last_addr == end_addr, "program logic"); 5703 return; 5704 } 5705 } 5706 } 5707 5708 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const { 5709 _bm.print_on_error(st, prefix); 5710 } 5711 5712 #ifndef PRODUCT 5713 void CMSBitMap::assert_locked() const { 5714 CMSLockVerifier::assert_locked(lock()); 5715 } 5716 5717 bool CMSBitMap::covers(MemRegion mr) const { 5718 // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); 5719 assert((size_t)_bm.size() == (_bmWordSize >> _shifter), 5720 "size inconsistency"); 5721 return (mr.start() >= _bmStartWord) && 5722 (mr.end() <= endWord()); 5723 } 5724 5725 bool CMSBitMap::covers(HeapWord* start, size_t size) const { 5726 return (start >= _bmStartWord && (start + size) <= endWord()); 5727 } 5728 5729 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { 5730 // verify that there are no 1 bits in the interval [left, right) 5731 FalseBitMapClosure falseBitMapClosure; 5732 iterate(&falseBitMapClosure, left, right); 5733 } 5734 5735 void CMSBitMap::region_invariant(MemRegion mr) 5736 { 5737 assert_locked(); 5738 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); 5739 assert(!mr.is_empty(), "unexpected empty region"); 5740 assert(covers(mr), "mr should be covered by bit map"); 5741 // convert address range into offset range 5742 size_t start_ofs = heapWordToOffset(mr.start()); 5743 // Make sure that end() is appropriately aligned 5744 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))), 5745 "Misaligned mr.end()"); 5746 size_t end_ofs = heapWordToOffset(mr.end()); 5747 assert(end_ofs > start_ofs, "Should mark at least one bit"); 5748 } 5749 5750 #endif 5751 5752 bool CMSMarkStack::allocate(size_t size) { 5753 // allocate a stack of the requisite depth 5754 ReservedSpace rs(ReservedSpace::allocation_align_size_up( 5755 size * sizeof(oop))); 5756 if (!rs.is_reserved()) { 5757 log_warning(gc)("CMSMarkStack allocation failure"); 5758 return false; 5759 } 5760 if (!_virtual_space.initialize(rs, rs.size())) { 5761 log_warning(gc)("CMSMarkStack backing store failure"); 5762 return false; 5763 } 5764 assert(_virtual_space.committed_size() == rs.size(), 5765 "didn't reserve backing store for all of CMS stack?"); 5766 _base = (oop*)(_virtual_space.low()); 5767 _index = 0; 5768 _capacity = size; 5769 NOT_PRODUCT(_max_depth = 0); 5770 return true; 5771 } 5772 5773 // XXX FIX ME !!! In the MT case we come in here holding a 5774 // leaf lock. For printing we need to take a further lock 5775 // which has lower rank. We need to recalibrate the two 5776 // lock-ranks involved in order to be able to print the 5777 // messages below. (Or defer the printing to the caller. 5778 // For now we take the expedient path of just disabling the 5779 // messages for the problematic case.) 5780 void CMSMarkStack::expand() { 5781 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted"); 5782 if (_capacity == MarkStackSizeMax) { 5783 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) { 5784 // We print a warning message only once per CMS cycle. 5785 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit"); 5786 } 5787 return; 5788 } 5789 // Double capacity if possible 5790 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax); 5791 // Do not give up existing stack until we have managed to 5792 // get the double capacity that we desired. 5793 ReservedSpace rs(ReservedSpace::allocation_align_size_up( 5794 new_capacity * sizeof(oop))); 5795 if (rs.is_reserved()) { 5796 // Release the backing store associated with old stack 5797 _virtual_space.release(); 5798 // Reinitialize virtual space for new stack 5799 if (!_virtual_space.initialize(rs, rs.size())) { 5800 fatal("Not enough swap for expanded marking stack"); 5801 } 5802 _base = (oop*)(_virtual_space.low()); 5803 _index = 0; 5804 _capacity = new_capacity; 5805 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) { 5806 // Failed to double capacity, continue; 5807 // we print a detail message only once per CMS cycle. 5808 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K", 5809 _capacity / K, new_capacity / K); 5810 } 5811 } 5812 5813 5814 // Closures 5815 // XXX: there seems to be a lot of code duplication here; 5816 // should refactor and consolidate common code. 5817 5818 // This closure is used to mark refs into the CMS generation in 5819 // the CMS bit map. Called at the first checkpoint. This closure 5820 // assumes that we do not need to re-mark dirty cards; if the CMS 5821 // generation on which this is used is not an oldest 5822 // generation then this will lose younger_gen cards! 5823 5824 MarkRefsIntoClosure::MarkRefsIntoClosure( 5825 MemRegion span, CMSBitMap* bitMap): 5826 _span(span), 5827 _bitMap(bitMap) 5828 { 5829 assert(ref_discoverer() == NULL, "deliberately left NULL"); 5830 assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); 5831 } 5832 5833 void MarkRefsIntoClosure::do_oop(oop obj) { 5834 // if p points into _span, then mark corresponding bit in _markBitMap 5835 assert(oopDesc::is_oop(obj), "expected an oop"); 5836 HeapWord* addr = (HeapWord*)obj; 5837 if (_span.contains(addr)) { 5838 // this should be made more efficient 5839 _bitMap->mark(addr); 5840 } 5841 } 5842 5843 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); } 5844 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); } 5845 5846 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure( 5847 MemRegion span, CMSBitMap* bitMap): 5848 _span(span), 5849 _bitMap(bitMap) 5850 { 5851 assert(ref_discoverer() == NULL, "deliberately left NULL"); 5852 assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); 5853 } 5854 5855 void ParMarkRefsIntoClosure::do_oop(oop obj) { 5856 // if p points into _span, then mark corresponding bit in _markBitMap 5857 assert(oopDesc::is_oop(obj), "expected an oop"); 5858 HeapWord* addr = (HeapWord*)obj; 5859 if (_span.contains(addr)) { 5860 // this should be made more efficient 5861 _bitMap->par_mark(addr); 5862 } 5863 } 5864 5865 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); } 5866 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); } 5867 5868 // A variant of the above, used for CMS marking verification. 5869 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( 5870 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm): 5871 _span(span), 5872 _verification_bm(verification_bm), 5873 _cms_bm(cms_bm) 5874 { 5875 assert(ref_discoverer() == NULL, "deliberately left NULL"); 5876 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); 5877 } 5878 5879 void MarkRefsIntoVerifyClosure::do_oop(oop obj) { 5880 // if p points into _span, then mark corresponding bit in _markBitMap 5881 assert(oopDesc::is_oop(obj), "expected an oop"); 5882 HeapWord* addr = (HeapWord*)obj; 5883 if (_span.contains(addr)) { 5884 _verification_bm->mark(addr); 5885 if (!_cms_bm->isMarked(addr)) { 5886 Log(gc, verify) log; 5887 ResourceMark rm; 5888 LogStream ls(log.error()); 5889 oop(addr)->print_on(&ls); 5890 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); 5891 fatal("... aborting"); 5892 } 5893 } 5894 } 5895 5896 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } 5897 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } 5898 5899 ////////////////////////////////////////////////// 5900 // MarkRefsIntoAndScanClosure 5901 ////////////////////////////////////////////////// 5902 5903 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, 5904 ReferenceDiscoverer* rd, 5905 CMSBitMap* bit_map, 5906 CMSBitMap* mod_union_table, 5907 CMSMarkStack* mark_stack, 5908 CMSCollector* collector, 5909 bool should_yield, 5910 bool concurrent_precleaning): 5911 _collector(collector), 5912 _span(span), 5913 _bit_map(bit_map), 5914 _mark_stack(mark_stack), 5915 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table, 5916 mark_stack, concurrent_precleaning), 5917 _yield(should_yield), 5918 _concurrent_precleaning(concurrent_precleaning), 5919 _freelistLock(NULL) 5920 { 5921 // FIXME: Should initialize in base class constructor. 5922 assert(rd != NULL, "ref_discoverer shouldn't be NULL"); 5923 set_ref_discoverer_internal(rd); 5924 } 5925 5926 // This closure is used to mark refs into the CMS generation at the 5927 // second (final) checkpoint, and to scan and transitively follow 5928 // the unmarked oops. It is also used during the concurrent precleaning 5929 // phase while scanning objects on dirty cards in the CMS generation. 5930 // The marks are made in the marking bit map and the marking stack is 5931 // used for keeping the (newly) grey objects during the scan. 5932 // The parallel version (Par_...) appears further below. 5933 void MarkRefsIntoAndScanClosure::do_oop(oop obj) { 5934 if (obj != NULL) { 5935 assert(oopDesc::is_oop(obj), "expected an oop"); 5936 HeapWord* addr = (HeapWord*)obj; 5937 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); 5938 assert(_collector->overflow_list_is_empty(), 5939 "overflow list should be empty"); 5940 if (_span.contains(addr) && 5941 !_bit_map->isMarked(addr)) { 5942 // mark bit map (object is now grey) 5943 _bit_map->mark(addr); 5944 // push on marking stack (stack should be empty), and drain the 5945 // stack by applying this closure to the oops in the oops popped 5946 // from the stack (i.e. blacken the grey objects) 5947 bool res = _mark_stack->push(obj); 5948 assert(res, "Should have space to push on empty stack"); 5949 do { 5950 oop new_oop = _mark_stack->pop(); 5951 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); 5952 assert(_bit_map->isMarked((HeapWord*)new_oop), 5953 "only grey objects on this stack"); 5954 // iterate over the oops in this oop, marking and pushing 5955 // the ones in CMS heap (i.e. in _span). 5956 new_oop->oop_iterate(&_pushAndMarkClosure); 5957 // check if it's time to yield 5958 do_yield_check(); 5959 } while (!_mark_stack->isEmpty() || 5960 (!_concurrent_precleaning && take_from_overflow_list())); 5961 // if marking stack is empty, and we are not doing this 5962 // during precleaning, then check the overflow list 5963 } 5964 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); 5965 assert(_collector->overflow_list_is_empty(), 5966 "overflow list was drained above"); 5967 5968 assert(_collector->no_preserved_marks(), 5969 "All preserved marks should have been restored above"); 5970 } 5971 } 5972 5973 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } 5974 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } 5975 5976 void MarkRefsIntoAndScanClosure::do_yield_work() { 5977 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 5978 "CMS thread should hold CMS token"); 5979 assert_lock_strong(_freelistLock); 5980 assert_lock_strong(_bit_map->lock()); 5981 // relinquish the free_list_lock and bitMaplock() 5982 _bit_map->lock()->unlock(); 5983 _freelistLock->unlock(); 5984 ConcurrentMarkSweepThread::desynchronize(true); 5985 _collector->stopTimer(); 5986 _collector->incrementYields(); 5987 5988 // See the comment in coordinator_yield() 5989 for (unsigned i = 0; 5990 i < CMSYieldSleepCount && 5991 ConcurrentMarkSweepThread::should_yield() && 5992 !CMSCollector::foregroundGCIsActive(); 5993 ++i) { 5994 os::sleep(Thread::current(), 1, false); 5995 } 5996 5997 ConcurrentMarkSweepThread::synchronize(true); 5998 _freelistLock->lock_without_safepoint_check(); 5999 _bit_map->lock()->lock_without_safepoint_check(); 6000 _collector->startTimer(); 6001 } 6002 6003 /////////////////////////////////////////////////////////// 6004 // ParMarkRefsIntoAndScanClosure: a parallel version of 6005 // MarkRefsIntoAndScanClosure 6006 /////////////////////////////////////////////////////////// 6007 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure( 6008 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd, 6009 CMSBitMap* bit_map, OopTaskQueue* work_queue): 6010 _span(span), 6011 _bit_map(bit_map), 6012 _work_queue(work_queue), 6013 _low_water_mark(MIN2((work_queue->max_elems()/4), 6014 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))), 6015 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue) 6016 { 6017 // FIXME: Should initialize in base class constructor. 6018 assert(rd != NULL, "ref_discoverer shouldn't be NULL"); 6019 set_ref_discoverer_internal(rd); 6020 } 6021 6022 // This closure is used to mark refs into the CMS generation at the 6023 // second (final) checkpoint, and to scan and transitively follow 6024 // the unmarked oops. The marks are made in the marking bit map and 6025 // the work_queue is used for keeping the (newly) grey objects during 6026 // the scan phase whence they are also available for stealing by parallel 6027 // threads. Since the marking bit map is shared, updates are 6028 // synchronized (via CAS). 6029 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) { 6030 if (obj != NULL) { 6031 // Ignore mark word because this could be an already marked oop 6032 // that may be chained at the end of the overflow list. 6033 assert(oopDesc::is_oop(obj, true), "expected an oop"); 6034 HeapWord* addr = (HeapWord*)obj; 6035 if (_span.contains(addr) && 6036 !_bit_map->isMarked(addr)) { 6037 // mark bit map (object will become grey): 6038 // It is possible for several threads to be 6039 // trying to "claim" this object concurrently; 6040 // the unique thread that succeeds in marking the 6041 // object first will do the subsequent push on 6042 // to the work queue (or overflow list). 6043 if (_bit_map->par_mark(addr)) { 6044 // push on work_queue (which may not be empty), and trim the 6045 // queue to an appropriate length by applying this closure to 6046 // the oops in the oops popped from the stack (i.e. blacken the 6047 // grey objects) 6048 bool res = _work_queue->push(obj); 6049 assert(res, "Low water mark should be less than capacity?"); 6050 trim_queue(_low_water_mark); 6051 } // Else, another thread claimed the object 6052 } 6053 } 6054 } 6055 6056 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); } 6057 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); } 6058 6059 // This closure is used to rescan the marked objects on the dirty cards 6060 // in the mod union table and the card table proper. 6061 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( 6062 oop p, MemRegion mr) { 6063 6064 size_t size = 0; 6065 HeapWord* addr = (HeapWord*)p; 6066 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6067 assert(_span.contains(addr), "we are scanning the CMS generation"); 6068 // check if it's time to yield 6069 if (do_yield_check()) { 6070 // We yielded for some foreground stop-world work, 6071 // and we have been asked to abort this ongoing preclean cycle. 6072 return 0; 6073 } 6074 if (_bitMap->isMarked(addr)) { 6075 // it's marked; is it potentially uninitialized? 6076 if (p->klass_or_null_acquire() != NULL) { 6077 // an initialized object; ignore mark word in verification below 6078 // since we are running concurrent with mutators 6079 assert(oopDesc::is_oop(p, true), "should be an oop"); 6080 if (p->is_objArray()) { 6081 // objArrays are precisely marked; restrict scanning 6082 // to dirty cards only. 6083 size = CompactibleFreeListSpace::adjustObjectSize( 6084 p->oop_iterate_size(_scanningClosure, mr)); 6085 } else { 6086 // A non-array may have been imprecisely marked; we need 6087 // to scan object in its entirety. 6088 size = CompactibleFreeListSpace::adjustObjectSize( 6089 p->oop_iterate_size(_scanningClosure)); 6090 } 6091 #ifdef ASSERT 6092 size_t direct_size = 6093 CompactibleFreeListSpace::adjustObjectSize(p->size()); 6094 assert(size == direct_size, "Inconsistency in size"); 6095 assert(size >= 3, "Necessary for Printezis marks to work"); 6096 HeapWord* start_pbit = addr + 1; 6097 HeapWord* end_pbit = addr + size - 1; 6098 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit), 6099 "inconsistent Printezis mark"); 6100 // Verify inner mark bits (between Printezis bits) are clear, 6101 // but don't repeat if there are multiple dirty regions for 6102 // the same object, to avoid potential O(N^2) performance. 6103 if (addr != _last_scanned_object) { 6104 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit); 6105 _last_scanned_object = addr; 6106 } 6107 #endif // ASSERT 6108 } else { 6109 // An uninitialized object. 6110 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); 6111 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); 6112 size = pointer_delta(nextOneAddr + 1, addr); 6113 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 6114 "alignment problem"); 6115 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() 6116 // will dirty the card when the klass pointer is installed in the 6117 // object (signaling the completion of initialization). 6118 } 6119 } else { 6120 // Either a not yet marked object or an uninitialized object 6121 if (p->klass_or_null_acquire() == NULL) { 6122 // An uninitialized object, skip to the next card, since 6123 // we may not be able to read its P-bits yet. 6124 assert(size == 0, "Initial value"); 6125 } else { 6126 // An object not (yet) reached by marking: we merely need to 6127 // compute its size so as to go look at the next block. 6128 assert(oopDesc::is_oop(p, true), "should be an oop"); 6129 size = CompactibleFreeListSpace::adjustObjectSize(p->size()); 6130 } 6131 } 6132 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6133 return size; 6134 } 6135 6136 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { 6137 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6138 "CMS thread should hold CMS token"); 6139 assert_lock_strong(_freelistLock); 6140 assert_lock_strong(_bitMap->lock()); 6141 // relinquish the free_list_lock and bitMaplock() 6142 _bitMap->lock()->unlock(); 6143 _freelistLock->unlock(); 6144 ConcurrentMarkSweepThread::desynchronize(true); 6145 _collector->stopTimer(); 6146 _collector->incrementYields(); 6147 6148 // See the comment in coordinator_yield() 6149 for (unsigned i = 0; i < CMSYieldSleepCount && 6150 ConcurrentMarkSweepThread::should_yield() && 6151 !CMSCollector::foregroundGCIsActive(); ++i) { 6152 os::sleep(Thread::current(), 1, false); 6153 } 6154 6155 ConcurrentMarkSweepThread::synchronize(true); 6156 _freelistLock->lock_without_safepoint_check(); 6157 _bitMap->lock()->lock_without_safepoint_check(); 6158 _collector->startTimer(); 6159 } 6160 6161 6162 ////////////////////////////////////////////////////////////////// 6163 // SurvivorSpacePrecleanClosure 6164 ////////////////////////////////////////////////////////////////// 6165 // This (single-threaded) closure is used to preclean the oops in 6166 // the survivor spaces. 6167 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { 6168 6169 HeapWord* addr = (HeapWord*)p; 6170 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6171 assert(!_span.contains(addr), "we are scanning the survivor spaces"); 6172 assert(p->klass_or_null() != NULL, "object should be initialized"); 6173 // an initialized object; ignore mark word in verification below 6174 // since we are running concurrent with mutators 6175 assert(oopDesc::is_oop(p, true), "should be an oop"); 6176 // Note that we do not yield while we iterate over 6177 // the interior oops of p, pushing the relevant ones 6178 // on our marking stack. 6179 size_t size = p->oop_iterate_size(_scanning_closure); 6180 do_yield_check(); 6181 // Observe that below, we do not abandon the preclean 6182 // phase as soon as we should; rather we empty the 6183 // marking stack before returning. This is to satisfy 6184 // some existing assertions. In general, it may be a 6185 // good idea to abort immediately and complete the marking 6186 // from the grey objects at a later time. 6187 while (!_mark_stack->isEmpty()) { 6188 oop new_oop = _mark_stack->pop(); 6189 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); 6190 assert(_bit_map->isMarked((HeapWord*)new_oop), 6191 "only grey objects on this stack"); 6192 // iterate over the oops in this oop, marking and pushing 6193 // the ones in CMS heap (i.e. in _span). 6194 new_oop->oop_iterate(_scanning_closure); 6195 // check if it's time to yield 6196 do_yield_check(); 6197 } 6198 unsigned int after_count = 6199 CMSHeap::heap()->total_collections(); 6200 bool abort = (_before_count != after_count) || 6201 _collector->should_abort_preclean(); 6202 return abort ? 0 : size; 6203 } 6204 6205 void SurvivorSpacePrecleanClosure::do_yield_work() { 6206 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6207 "CMS thread should hold CMS token"); 6208 assert_lock_strong(_bit_map->lock()); 6209 // Relinquish the bit map lock 6210 _bit_map->lock()->unlock(); 6211 ConcurrentMarkSweepThread::desynchronize(true); 6212 _collector->stopTimer(); 6213 _collector->incrementYields(); 6214 6215 // See the comment in coordinator_yield() 6216 for (unsigned i = 0; i < CMSYieldSleepCount && 6217 ConcurrentMarkSweepThread::should_yield() && 6218 !CMSCollector::foregroundGCIsActive(); ++i) { 6219 os::sleep(Thread::current(), 1, false); 6220 } 6221 6222 ConcurrentMarkSweepThread::synchronize(true); 6223 _bit_map->lock()->lock_without_safepoint_check(); 6224 _collector->startTimer(); 6225 } 6226 6227 // This closure is used to rescan the marked objects on the dirty cards 6228 // in the mod union table and the card table proper. In the parallel 6229 // case, although the bitMap is shared, we do a single read so the 6230 // isMarked() query is "safe". 6231 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { 6232 // Ignore mark word because we are running concurrent with mutators 6233 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p)); 6234 HeapWord* addr = (HeapWord*)p; 6235 assert(_span.contains(addr), "we are scanning the CMS generation"); 6236 bool is_obj_array = false; 6237 #ifdef ASSERT 6238 if (!_parallel) { 6239 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); 6240 assert(_collector->overflow_list_is_empty(), 6241 "overflow list should be empty"); 6242 6243 } 6244 #endif // ASSERT 6245 if (_bit_map->isMarked(addr)) { 6246 // Obj arrays are precisely marked, non-arrays are not; 6247 // so we scan objArrays precisely and non-arrays in their 6248 // entirety. 6249 if (p->is_objArray()) { 6250 is_obj_array = true; 6251 if (_parallel) { 6252 p->oop_iterate(_par_scan_closure, mr); 6253 } else { 6254 p->oop_iterate(_scan_closure, mr); 6255 } 6256 } else { 6257 if (_parallel) { 6258 p->oop_iterate(_par_scan_closure); 6259 } else { 6260 p->oop_iterate(_scan_closure); 6261 } 6262 } 6263 } 6264 #ifdef ASSERT 6265 if (!_parallel) { 6266 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); 6267 assert(_collector->overflow_list_is_empty(), 6268 "overflow list should be empty"); 6269 6270 } 6271 #endif // ASSERT 6272 return is_obj_array; 6273 } 6274 6275 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, 6276 MemRegion span, 6277 CMSBitMap* bitMap, CMSMarkStack* markStack, 6278 bool should_yield, bool verifying): 6279 _collector(collector), 6280 _span(span), 6281 _bitMap(bitMap), 6282 _mut(&collector->_modUnionTable), 6283 _markStack(markStack), 6284 _yield(should_yield), 6285 _skipBits(0) 6286 { 6287 assert(_markStack->isEmpty(), "stack should be empty"); 6288 _finger = _bitMap->startWord(); 6289 _threshold = _finger; 6290 assert(_collector->_restart_addr == NULL, "Sanity check"); 6291 assert(_span.contains(_finger), "Out of bounds _finger?"); 6292 DEBUG_ONLY(_verifying = verifying;) 6293 } 6294 6295 void MarkFromRootsClosure::reset(HeapWord* addr) { 6296 assert(_markStack->isEmpty(), "would cause duplicates on stack"); 6297 assert(_span.contains(addr), "Out of bounds _finger?"); 6298 _finger = addr; 6299 _threshold = align_up(_finger, CardTable::card_size); 6300 } 6301 6302 // Should revisit to see if this should be restructured for 6303 // greater efficiency. 6304 bool MarkFromRootsClosure::do_bit(size_t offset) { 6305 if (_skipBits > 0) { 6306 _skipBits--; 6307 return true; 6308 } 6309 // convert offset into a HeapWord* 6310 HeapWord* addr = _bitMap->startWord() + offset; 6311 assert(_bitMap->endWord() && addr < _bitMap->endWord(), 6312 "address out of range"); 6313 assert(_bitMap->isMarked(addr), "tautology"); 6314 if (_bitMap->isMarked(addr+1)) { 6315 // this is an allocated but not yet initialized object 6316 assert(_skipBits == 0, "tautology"); 6317 _skipBits = 2; // skip next two marked bits ("Printezis-marks") 6318 oop p = oop(addr); 6319 if (p->klass_or_null_acquire() == NULL) { 6320 DEBUG_ONLY(if (!_verifying) {) 6321 // We re-dirty the cards on which this object lies and increase 6322 // the _threshold so that we'll come back to scan this object 6323 // during the preclean or remark phase. (CMSCleanOnEnter) 6324 if (CMSCleanOnEnter) { 6325 size_t sz = _collector->block_size_using_printezis_bits(addr); 6326 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); 6327 MemRegion redirty_range = MemRegion(addr, end_card_addr); 6328 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 6329 // Bump _threshold to end_card_addr; note that 6330 // _threshold cannot possibly exceed end_card_addr, anyhow. 6331 // This prevents future clearing of the card as the scan proceeds 6332 // to the right. 6333 assert(_threshold <= end_card_addr, 6334 "Because we are just scanning into this object"); 6335 if (_threshold < end_card_addr) { 6336 _threshold = end_card_addr; 6337 } 6338 if (p->klass_or_null_acquire() != NULL) { 6339 // Redirty the range of cards... 6340 _mut->mark_range(redirty_range); 6341 } // ...else the setting of klass will dirty the card anyway. 6342 } 6343 DEBUG_ONLY(}) 6344 return true; 6345 } 6346 } 6347 scanOopsInOop(addr); 6348 return true; 6349 } 6350 6351 // We take a break if we've been at this for a while, 6352 // so as to avoid monopolizing the locks involved. 6353 void MarkFromRootsClosure::do_yield_work() { 6354 // First give up the locks, then yield, then re-lock 6355 // We should probably use a constructor/destructor idiom to 6356 // do this unlock/lock or modify the MutexUnlocker class to 6357 // serve our purpose. XXX 6358 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6359 "CMS thread should hold CMS token"); 6360 assert_lock_strong(_bitMap->lock()); 6361 _bitMap->lock()->unlock(); 6362 ConcurrentMarkSweepThread::desynchronize(true); 6363 _collector->stopTimer(); 6364 _collector->incrementYields(); 6365 6366 // See the comment in coordinator_yield() 6367 for (unsigned i = 0; i < CMSYieldSleepCount && 6368 ConcurrentMarkSweepThread::should_yield() && 6369 !CMSCollector::foregroundGCIsActive(); ++i) { 6370 os::sleep(Thread::current(), 1, false); 6371 } 6372 6373 ConcurrentMarkSweepThread::synchronize(true); 6374 _bitMap->lock()->lock_without_safepoint_check(); 6375 _collector->startTimer(); 6376 } 6377 6378 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { 6379 assert(_bitMap->isMarked(ptr), "expected bit to be set"); 6380 assert(_markStack->isEmpty(), 6381 "should drain stack to limit stack usage"); 6382 // convert ptr to an oop preparatory to scanning 6383 oop obj = oop(ptr); 6384 // Ignore mark word in verification below, since we 6385 // may be running concurrent with mutators. 6386 assert(oopDesc::is_oop(obj, true), "should be an oop"); 6387 assert(_finger <= ptr, "_finger runneth ahead"); 6388 // advance the finger to right end of this object 6389 _finger = ptr + obj->size(); 6390 assert(_finger > ptr, "we just incremented it above"); 6391 // On large heaps, it may take us some time to get through 6392 // the marking phase. During 6393 // this time it's possible that a lot of mutations have 6394 // accumulated in the card table and the mod union table -- 6395 // these mutation records are redundant until we have 6396 // actually traced into the corresponding card. 6397 // Here, we check whether advancing the finger would make 6398 // us cross into a new card, and if so clear corresponding 6399 // cards in the MUT (preclean them in the card-table in the 6400 // future). 6401 6402 DEBUG_ONLY(if (!_verifying) {) 6403 // The clean-on-enter optimization is disabled by default, 6404 // until we fix 6178663. 6405 if (CMSCleanOnEnter && (_finger > _threshold)) { 6406 // [_threshold, _finger) represents the interval 6407 // of cards to be cleared in MUT (or precleaned in card table). 6408 // The set of cards to be cleared is all those that overlap 6409 // with the interval [_threshold, _finger); note that 6410 // _threshold is always kept card-aligned but _finger isn't 6411 // always card-aligned. 6412 HeapWord* old_threshold = _threshold; 6413 assert(is_aligned(old_threshold, CardTable::card_size), 6414 "_threshold should always be card-aligned"); 6415 _threshold = align_up(_finger, CardTable::card_size); 6416 MemRegion mr(old_threshold, _threshold); 6417 assert(!mr.is_empty(), "Control point invariant"); 6418 assert(_span.contains(mr), "Should clear within span"); 6419 _mut->clear_range(mr); 6420 } 6421 DEBUG_ONLY(}) 6422 // Note: the finger doesn't advance while we drain 6423 // the stack below. 6424 PushOrMarkClosure pushOrMarkClosure(_collector, 6425 _span, _bitMap, _markStack, 6426 _finger, this); 6427 bool res = _markStack->push(obj); 6428 assert(res, "Empty non-zero size stack should have space for single push"); 6429 while (!_markStack->isEmpty()) { 6430 oop new_oop = _markStack->pop(); 6431 // Skip verifying header mark word below because we are 6432 // running concurrent with mutators. 6433 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop"); 6434 // now scan this oop's oops 6435 new_oop->oop_iterate(&pushOrMarkClosure); 6436 do_yield_check(); 6437 } 6438 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); 6439 } 6440 6441 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task, 6442 CMSCollector* collector, MemRegion span, 6443 CMSBitMap* bit_map, 6444 OopTaskQueue* work_queue, 6445 CMSMarkStack* overflow_stack): 6446 _collector(collector), 6447 _whole_span(collector->_span), 6448 _span(span), 6449 _bit_map(bit_map), 6450 _mut(&collector->_modUnionTable), 6451 _work_queue(work_queue), 6452 _overflow_stack(overflow_stack), 6453 _skip_bits(0), 6454 _task(task) 6455 { 6456 assert(_work_queue->size() == 0, "work_queue should be empty"); 6457 _finger = span.start(); 6458 _threshold = _finger; // XXX Defer clear-on-enter optimization for now 6459 assert(_span.contains(_finger), "Out of bounds _finger?"); 6460 } 6461 6462 // Should revisit to see if this should be restructured for 6463 // greater efficiency. 6464 bool ParMarkFromRootsClosure::do_bit(size_t offset) { 6465 if (_skip_bits > 0) { 6466 _skip_bits--; 6467 return true; 6468 } 6469 // convert offset into a HeapWord* 6470 HeapWord* addr = _bit_map->startWord() + offset; 6471 assert(_bit_map->endWord() && addr < _bit_map->endWord(), 6472 "address out of range"); 6473 assert(_bit_map->isMarked(addr), "tautology"); 6474 if (_bit_map->isMarked(addr+1)) { 6475 // this is an allocated object that might not yet be initialized 6476 assert(_skip_bits == 0, "tautology"); 6477 _skip_bits = 2; // skip next two marked bits ("Printezis-marks") 6478 oop p = oop(addr); 6479 if (p->klass_or_null_acquire() == NULL) { 6480 // in the case of Clean-on-Enter optimization, redirty card 6481 // and avoid clearing card by increasing the threshold. 6482 return true; 6483 } 6484 } 6485 scan_oops_in_oop(addr); 6486 return true; 6487 } 6488 6489 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { 6490 assert(_bit_map->isMarked(ptr), "expected bit to be set"); 6491 // Should we assert that our work queue is empty or 6492 // below some drain limit? 6493 assert(_work_queue->size() == 0, 6494 "should drain stack to limit stack usage"); 6495 // convert ptr to an oop preparatory to scanning 6496 oop obj = oop(ptr); 6497 // Ignore mark word in verification below, since we 6498 // may be running concurrent with mutators. 6499 assert(oopDesc::is_oop(obj, true), "should be an oop"); 6500 assert(_finger <= ptr, "_finger runneth ahead"); 6501 // advance the finger to right end of this object 6502 _finger = ptr + obj->size(); 6503 assert(_finger > ptr, "we just incremented it above"); 6504 // On large heaps, it may take us some time to get through 6505 // the marking phase. During 6506 // this time it's possible that a lot of mutations have 6507 // accumulated in the card table and the mod union table -- 6508 // these mutation records are redundant until we have 6509 // actually traced into the corresponding card. 6510 // Here, we check whether advancing the finger would make 6511 // us cross into a new card, and if so clear corresponding 6512 // cards in the MUT (preclean them in the card-table in the 6513 // future). 6514 6515 // The clean-on-enter optimization is disabled by default, 6516 // until we fix 6178663. 6517 if (CMSCleanOnEnter && (_finger > _threshold)) { 6518 // [_threshold, _finger) represents the interval 6519 // of cards to be cleared in MUT (or precleaned in card table). 6520 // The set of cards to be cleared is all those that overlap 6521 // with the interval [_threshold, _finger); note that 6522 // _threshold is always kept card-aligned but _finger isn't 6523 // always card-aligned. 6524 HeapWord* old_threshold = _threshold; 6525 assert(is_aligned(old_threshold, CardTable::card_size), 6526 "_threshold should always be card-aligned"); 6527 _threshold = align_up(_finger, CardTable::card_size); 6528 MemRegion mr(old_threshold, _threshold); 6529 assert(!mr.is_empty(), "Control point invariant"); 6530 assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? 6531 _mut->clear_range(mr); 6532 } 6533 6534 // Note: the local finger doesn't advance while we drain 6535 // the stack below, but the global finger sure can and will. 6536 HeapWord* volatile* gfa = _task->global_finger_addr(); 6537 ParPushOrMarkClosure pushOrMarkClosure(_collector, 6538 _span, _bit_map, 6539 _work_queue, 6540 _overflow_stack, 6541 _finger, 6542 gfa, this); 6543 bool res = _work_queue->push(obj); // overflow could occur here 6544 assert(res, "Will hold once we use workqueues"); 6545 while (true) { 6546 oop new_oop; 6547 if (!_work_queue->pop_local(new_oop)) { 6548 // We emptied our work_queue; check if there's stuff that can 6549 // be gotten from the overflow stack. 6550 if (CMSConcMarkingTask::get_work_from_overflow_stack( 6551 _overflow_stack, _work_queue)) { 6552 do_yield_check(); 6553 continue; 6554 } else { // done 6555 break; 6556 } 6557 } 6558 // Skip verifying header mark word below because we are 6559 // running concurrent with mutators. 6560 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop"); 6561 // now scan this oop's oops 6562 new_oop->oop_iterate(&pushOrMarkClosure); 6563 do_yield_check(); 6564 } 6565 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); 6566 } 6567 6568 // Yield in response to a request from VM Thread or 6569 // from mutators. 6570 void ParMarkFromRootsClosure::do_yield_work() { 6571 assert(_task != NULL, "sanity"); 6572 _task->yield(); 6573 } 6574 6575 // A variant of the above used for verifying CMS marking work. 6576 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, 6577 MemRegion span, 6578 CMSBitMap* verification_bm, CMSBitMap* cms_bm, 6579 CMSMarkStack* mark_stack): 6580 _collector(collector), 6581 _span(span), 6582 _verification_bm(verification_bm), 6583 _cms_bm(cms_bm), 6584 _mark_stack(mark_stack), 6585 _pam_verify_closure(collector, span, verification_bm, cms_bm, 6586 mark_stack) 6587 { 6588 assert(_mark_stack->isEmpty(), "stack should be empty"); 6589 _finger = _verification_bm->startWord(); 6590 assert(_collector->_restart_addr == NULL, "Sanity check"); 6591 assert(_span.contains(_finger), "Out of bounds _finger?"); 6592 } 6593 6594 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { 6595 assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); 6596 assert(_span.contains(addr), "Out of bounds _finger?"); 6597 _finger = addr; 6598 } 6599 6600 // Should revisit to see if this should be restructured for 6601 // greater efficiency. 6602 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) { 6603 // convert offset into a HeapWord* 6604 HeapWord* addr = _verification_bm->startWord() + offset; 6605 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), 6606 "address out of range"); 6607 assert(_verification_bm->isMarked(addr), "tautology"); 6608 assert(_cms_bm->isMarked(addr), "tautology"); 6609 6610 assert(_mark_stack->isEmpty(), 6611 "should drain stack to limit stack usage"); 6612 // convert addr to an oop preparatory to scanning 6613 oop obj = oop(addr); 6614 assert(oopDesc::is_oop(obj), "should be an oop"); 6615 assert(_finger <= addr, "_finger runneth ahead"); 6616 // advance the finger to right end of this object 6617 _finger = addr + obj->size(); 6618 assert(_finger > addr, "we just incremented it above"); 6619 // Note: the finger doesn't advance while we drain 6620 // the stack below. 6621 bool res = _mark_stack->push(obj); 6622 assert(res, "Empty non-zero size stack should have space for single push"); 6623 while (!_mark_stack->isEmpty()) { 6624 oop new_oop = _mark_stack->pop(); 6625 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop"); 6626 // now scan this oop's oops 6627 new_oop->oop_iterate(&_pam_verify_closure); 6628 } 6629 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); 6630 return true; 6631 } 6632 6633 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( 6634 CMSCollector* collector, MemRegion span, 6635 CMSBitMap* verification_bm, CMSBitMap* cms_bm, 6636 CMSMarkStack* mark_stack): 6637 MetadataAwareOopClosure(collector->ref_processor()), 6638 _collector(collector), 6639 _span(span), 6640 _verification_bm(verification_bm), 6641 _cms_bm(cms_bm), 6642 _mark_stack(mark_stack) 6643 { } 6644 6645 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) { 6646 oop obj = RawAccess<>::oop_load(p); 6647 do_oop(obj); 6648 } 6649 6650 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } 6651 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } 6652 6653 // Upon stack overflow, we discard (part of) the stack, 6654 // remembering the least address amongst those discarded 6655 // in CMSCollector's _restart_address. 6656 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { 6657 // Remember the least grey address discarded 6658 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); 6659 _collector->lower_restart_addr(ra); 6660 _mark_stack->reset(); // discard stack contents 6661 _mark_stack->expand(); // expand the stack if possible 6662 } 6663 6664 void PushAndMarkVerifyClosure::do_oop(oop obj) { 6665 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6666 HeapWord* addr = (HeapWord*)obj; 6667 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { 6668 // Oop lies in _span and isn't yet grey or black 6669 _verification_bm->mark(addr); // now grey 6670 if (!_cms_bm->isMarked(addr)) { 6671 Log(gc, verify) log; 6672 ResourceMark rm; 6673 LogStream ls(log.error()); 6674 oop(addr)->print_on(&ls); 6675 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); 6676 fatal("... aborting"); 6677 } 6678 6679 if (!_mark_stack->push(obj)) { // stack overflow 6680 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity()); 6681 assert(_mark_stack->isFull(), "Else push should have succeeded"); 6682 handle_stack_overflow(addr); 6683 } 6684 // anything including and to the right of _finger 6685 // will be scanned as we iterate over the remainder of the 6686 // bit map 6687 } 6688 } 6689 6690 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, 6691 MemRegion span, 6692 CMSBitMap* bitMap, CMSMarkStack* markStack, 6693 HeapWord* finger, MarkFromRootsClosure* parent) : 6694 MetadataAwareOopClosure(collector->ref_processor()), 6695 _collector(collector), 6696 _span(span), 6697 _bitMap(bitMap), 6698 _markStack(markStack), 6699 _finger(finger), 6700 _parent(parent) 6701 { } 6702 6703 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector, 6704 MemRegion span, 6705 CMSBitMap* bit_map, 6706 OopTaskQueue* work_queue, 6707 CMSMarkStack* overflow_stack, 6708 HeapWord* finger, 6709 HeapWord* volatile* global_finger_addr, 6710 ParMarkFromRootsClosure* parent) : 6711 MetadataAwareOopClosure(collector->ref_processor()), 6712 _collector(collector), 6713 _whole_span(collector->_span), 6714 _span(span), 6715 _bit_map(bit_map), 6716 _work_queue(work_queue), 6717 _overflow_stack(overflow_stack), 6718 _finger(finger), 6719 _global_finger_addr(global_finger_addr), 6720 _parent(parent) 6721 { } 6722 6723 // Assumes thread-safe access by callers, who are 6724 // responsible for mutual exclusion. 6725 void CMSCollector::lower_restart_addr(HeapWord* low) { 6726 assert(_span.contains(low), "Out of bounds addr"); 6727 if (_restart_addr == NULL) { 6728 _restart_addr = low; 6729 } else { 6730 _restart_addr = MIN2(_restart_addr, low); 6731 } 6732 } 6733 6734 // Upon stack overflow, we discard (part of) the stack, 6735 // remembering the least address amongst those discarded 6736 // in CMSCollector's _restart_address. 6737 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { 6738 // Remember the least grey address discarded 6739 HeapWord* ra = (HeapWord*)_markStack->least_value(lost); 6740 _collector->lower_restart_addr(ra); 6741 _markStack->reset(); // discard stack contents 6742 _markStack->expand(); // expand the stack if possible 6743 } 6744 6745 // Upon stack overflow, we discard (part of) the stack, 6746 // remembering the least address amongst those discarded 6747 // in CMSCollector's _restart_address. 6748 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { 6749 // We need to do this under a mutex to prevent other 6750 // workers from interfering with the work done below. 6751 MutexLockerEx ml(_overflow_stack->par_lock(), 6752 Mutex::_no_safepoint_check_flag); 6753 // Remember the least grey address discarded 6754 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); 6755 _collector->lower_restart_addr(ra); 6756 _overflow_stack->reset(); // discard stack contents 6757 _overflow_stack->expand(); // expand the stack if possible 6758 } 6759 6760 void PushOrMarkClosure::do_oop(oop obj) { 6761 // Ignore mark word because we are running concurrent with mutators. 6762 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6763 HeapWord* addr = (HeapWord*)obj; 6764 if (_span.contains(addr) && !_bitMap->isMarked(addr)) { 6765 // Oop lies in _span and isn't yet grey or black 6766 _bitMap->mark(addr); // now grey 6767 if (addr < _finger) { 6768 // the bit map iteration has already either passed, or 6769 // sampled, this bit in the bit map; we'll need to 6770 // use the marking stack to scan this oop's oops. 6771 bool simulate_overflow = false; 6772 NOT_PRODUCT( 6773 if (CMSMarkStackOverflowALot && 6774 _collector->simulate_overflow()) { 6775 // simulate a stack overflow 6776 simulate_overflow = true; 6777 } 6778 ) 6779 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow 6780 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity()); 6781 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); 6782 handle_stack_overflow(addr); 6783 } 6784 } 6785 // anything including and to the right of _finger 6786 // will be scanned as we iterate over the remainder of the 6787 // bit map 6788 do_yield_check(); 6789 } 6790 } 6791 6792 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); } 6793 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); } 6794 6795 void ParPushOrMarkClosure::do_oop(oop obj) { 6796 // Ignore mark word because we are running concurrent with mutators. 6797 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6798 HeapWord* addr = (HeapWord*)obj; 6799 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { 6800 // Oop lies in _span and isn't yet grey or black 6801 // We read the global_finger (volatile read) strictly after marking oop 6802 bool res = _bit_map->par_mark(addr); // now grey 6803 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; 6804 // Should we push this marked oop on our stack? 6805 // -- if someone else marked it, nothing to do 6806 // -- if target oop is above global finger nothing to do 6807 // -- if target oop is in chunk and above local finger 6808 // then nothing to do 6809 // -- else push on work queue 6810 if ( !res // someone else marked it, they will deal with it 6811 || (addr >= *gfa) // will be scanned in a later task 6812 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk 6813 return; 6814 } 6815 // the bit map iteration has already either passed, or 6816 // sampled, this bit in the bit map; we'll need to 6817 // use the marking stack to scan this oop's oops. 6818 bool simulate_overflow = false; 6819 NOT_PRODUCT( 6820 if (CMSMarkStackOverflowALot && 6821 _collector->simulate_overflow()) { 6822 // simulate a stack overflow 6823 simulate_overflow = true; 6824 } 6825 ) 6826 if (simulate_overflow || 6827 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { 6828 // stack overflow 6829 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity()); 6830 // We cannot assert that the overflow stack is full because 6831 // it may have been emptied since. 6832 assert(simulate_overflow || 6833 _work_queue->size() == _work_queue->max_elems(), 6834 "Else push should have succeeded"); 6835 handle_stack_overflow(addr); 6836 } 6837 do_yield_check(); 6838 } 6839 } 6840 6841 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); } 6842 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); } 6843 6844 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, 6845 MemRegion span, 6846 ReferenceDiscoverer* rd, 6847 CMSBitMap* bit_map, 6848 CMSBitMap* mod_union_table, 6849 CMSMarkStack* mark_stack, 6850 bool concurrent_precleaning): 6851 MetadataAwareOopClosure(rd), 6852 _collector(collector), 6853 _span(span), 6854 _bit_map(bit_map), 6855 _mod_union_table(mod_union_table), 6856 _mark_stack(mark_stack), 6857 _concurrent_precleaning(concurrent_precleaning) 6858 { 6859 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL"); 6860 } 6861 6862 // Grey object rescan during pre-cleaning and second checkpoint phases -- 6863 // the non-parallel version (the parallel version appears further below.) 6864 void PushAndMarkClosure::do_oop(oop obj) { 6865 // Ignore mark word verification. If during concurrent precleaning, 6866 // the object monitor may be locked. If during the checkpoint 6867 // phases, the object may already have been reached by a different 6868 // path and may be at the end of the global overflow list (so 6869 // the mark word may be NULL). 6870 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */), 6871 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6872 HeapWord* addr = (HeapWord*)obj; 6873 // Check if oop points into the CMS generation 6874 // and is not marked 6875 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 6876 // a white object ... 6877 _bit_map->mark(addr); // ... now grey 6878 // push on the marking stack (grey set) 6879 bool simulate_overflow = false; 6880 NOT_PRODUCT( 6881 if (CMSMarkStackOverflowALot && 6882 _collector->simulate_overflow()) { 6883 // simulate a stack overflow 6884 simulate_overflow = true; 6885 } 6886 ) 6887 if (simulate_overflow || !_mark_stack->push(obj)) { 6888 if (_concurrent_precleaning) { 6889 // During precleaning we can just dirty the appropriate card(s) 6890 // in the mod union table, thus ensuring that the object remains 6891 // in the grey set and continue. In the case of object arrays 6892 // we need to dirty all of the cards that the object spans, 6893 // since the rescan of object arrays will be limited to the 6894 // dirty cards. 6895 // Note that no one can be interfering with us in this action 6896 // of dirtying the mod union table, so no locking or atomics 6897 // are required. 6898 if (obj->is_objArray()) { 6899 size_t sz = obj->size(); 6900 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); 6901 MemRegion redirty_range = MemRegion(addr, end_card_addr); 6902 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 6903 _mod_union_table->mark_range(redirty_range); 6904 } else { 6905 _mod_union_table->mark(addr); 6906 } 6907 _collector->_ser_pmc_preclean_ovflw++; 6908 } else { 6909 // During the remark phase, we need to remember this oop 6910 // in the overflow list. 6911 _collector->push_on_overflow_list(obj); 6912 _collector->_ser_pmc_remark_ovflw++; 6913 } 6914 } 6915 } 6916 } 6917 6918 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector, 6919 MemRegion span, 6920 ReferenceDiscoverer* rd, 6921 CMSBitMap* bit_map, 6922 OopTaskQueue* work_queue): 6923 MetadataAwareOopClosure(rd), 6924 _collector(collector), 6925 _span(span), 6926 _bit_map(bit_map), 6927 _work_queue(work_queue) 6928 { 6929 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL"); 6930 } 6931 6932 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); } 6933 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); } 6934 6935 // Grey object rescan during second checkpoint phase -- 6936 // the parallel version. 6937 void ParPushAndMarkClosure::do_oop(oop obj) { 6938 // In the assert below, we ignore the mark word because 6939 // this oop may point to an already visited object that is 6940 // on the overflow stack (in which case the mark word has 6941 // been hijacked for chaining into the overflow stack -- 6942 // if this is the last object in the overflow stack then 6943 // its mark word will be NULL). Because this object may 6944 // have been subsequently popped off the global overflow 6945 // stack, and the mark word possibly restored to the prototypical 6946 // value, by the time we get to examined this failing assert in 6947 // the debugger, is_oop_or_null(false) may subsequently start 6948 // to hold. 6949 assert(oopDesc::is_oop_or_null(obj, true), 6950 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6951 HeapWord* addr = (HeapWord*)obj; 6952 // Check if oop points into the CMS generation 6953 // and is not marked 6954 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 6955 // a white object ... 6956 // If we manage to "claim" the object, by being the 6957 // first thread to mark it, then we push it on our 6958 // marking stack 6959 if (_bit_map->par_mark(addr)) { // ... now grey 6960 // push on work queue (grey set) 6961 bool simulate_overflow = false; 6962 NOT_PRODUCT( 6963 if (CMSMarkStackOverflowALot && 6964 _collector->par_simulate_overflow()) { 6965 // simulate a stack overflow 6966 simulate_overflow = true; 6967 } 6968 ) 6969 if (simulate_overflow || !_work_queue->push(obj)) { 6970 _collector->par_push_on_overflow_list(obj); 6971 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS 6972 } 6973 } // Else, some other thread got there first 6974 } 6975 } 6976 6977 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); } 6978 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); } 6979 6980 void CMSPrecleanRefsYieldClosure::do_yield_work() { 6981 Mutex* bml = _collector->bitMapLock(); 6982 assert_lock_strong(bml); 6983 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6984 "CMS thread should hold CMS token"); 6985 6986 bml->unlock(); 6987 ConcurrentMarkSweepThread::desynchronize(true); 6988 6989 _collector->stopTimer(); 6990 _collector->incrementYields(); 6991 6992 // See the comment in coordinator_yield() 6993 for (unsigned i = 0; i < CMSYieldSleepCount && 6994 ConcurrentMarkSweepThread::should_yield() && 6995 !CMSCollector::foregroundGCIsActive(); ++i) { 6996 os::sleep(Thread::current(), 1, false); 6997 } 6998 6999 ConcurrentMarkSweepThread::synchronize(true); 7000 bml->lock(); 7001 7002 _collector->startTimer(); 7003 } 7004 7005 bool CMSPrecleanRefsYieldClosure::should_return() { 7006 if (ConcurrentMarkSweepThread::should_yield()) { 7007 do_yield_work(); 7008 } 7009 return _collector->foregroundGCIsActive(); 7010 } 7011 7012 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { 7013 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0, 7014 "mr should be aligned to start at a card boundary"); 7015 // We'd like to assert: 7016 // assert(mr.word_size()%CardTable::card_size_in_words == 0, 7017 // "mr should be a range of cards"); 7018 // However, that would be too strong in one case -- the last 7019 // partition ends at _unallocated_block which, in general, can be 7020 // an arbitrary boundary, not necessarily card aligned. 7021 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words; 7022 _space->object_iterate_mem(mr, &_scan_cl); 7023 } 7024 7025 SweepClosure::SweepClosure(CMSCollector* collector, 7026 ConcurrentMarkSweepGeneration* g, 7027 CMSBitMap* bitMap, bool should_yield) : 7028 _collector(collector), 7029 _g(g), 7030 _sp(g->cmsSpace()), 7031 _limit(_sp->sweep_limit()), 7032 _freelistLock(_sp->freelistLock()), 7033 _bitMap(bitMap), 7034 _yield(should_yield), 7035 _inFreeRange(false), // No free range at beginning of sweep 7036 _freeRangeInFreeLists(false), // No free range at beginning of sweep 7037 _lastFreeRangeCoalesced(false), 7038 _freeFinger(g->used_region().start()) 7039 { 7040 NOT_PRODUCT( 7041 _numObjectsFreed = 0; 7042 _numWordsFreed = 0; 7043 _numObjectsLive = 0; 7044 _numWordsLive = 0; 7045 _numObjectsAlreadyFree = 0; 7046 _numWordsAlreadyFree = 0; 7047 _last_fc = NULL; 7048 7049 _sp->initializeIndexedFreeListArrayReturnedBytes(); 7050 _sp->dictionary()->initialize_dict_returned_bytes(); 7051 ) 7052 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 7053 "sweep _limit out of bounds"); 7054 log_develop_trace(gc, sweep)("===================="); 7055 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit)); 7056 } 7057 7058 void SweepClosure::print_on(outputStream* st) const { 7059 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")", 7060 p2i(_sp->bottom()), p2i(_sp->end())); 7061 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit)); 7062 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger)); 7063 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));) 7064 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d", 7065 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced); 7066 } 7067 7068 #ifndef PRODUCT 7069 // Assertion checking only: no useful work in product mode -- 7070 // however, if any of the flags below become product flags, 7071 // you may need to review this code to see if it needs to be 7072 // enabled in product mode. 7073 SweepClosure::~SweepClosure() { 7074 assert_lock_strong(_freelistLock); 7075 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 7076 "sweep _limit out of bounds"); 7077 if (inFreeRange()) { 7078 Log(gc, sweep) log; 7079 log.error("inFreeRange() should have been reset; dumping state of SweepClosure"); 7080 ResourceMark rm; 7081 LogStream ls(log.error()); 7082 print_on(&ls); 7083 ShouldNotReachHere(); 7084 } 7085 7086 if (log_is_enabled(Debug, gc, sweep)) { 7087 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", 7088 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); 7089 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", 7090 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); 7091 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord); 7092 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes); 7093 } 7094 7095 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) { 7096 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); 7097 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes(); 7098 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes; 7099 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes", 7100 returned_bytes, indexListReturnedBytes, dict_returned_bytes); 7101 } 7102 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit)); 7103 log_develop_trace(gc, sweep)("================"); 7104 } 7105 #endif // PRODUCT 7106 7107 void SweepClosure::initialize_free_range(HeapWord* freeFinger, 7108 bool freeRangeInFreeLists) { 7109 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)", 7110 p2i(freeFinger), freeRangeInFreeLists); 7111 assert(!inFreeRange(), "Trampling existing free range"); 7112 set_inFreeRange(true); 7113 set_lastFreeRangeCoalesced(false); 7114 7115 set_freeFinger(freeFinger); 7116 set_freeRangeInFreeLists(freeRangeInFreeLists); 7117 if (CMSTestInFreeList) { 7118 if (freeRangeInFreeLists) { 7119 FreeChunk* fc = (FreeChunk*) freeFinger; 7120 assert(fc->is_free(), "A chunk on the free list should be free."); 7121 assert(fc->size() > 0, "Free range should have a size"); 7122 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists"); 7123 } 7124 } 7125 } 7126 7127 // Note that the sweeper runs concurrently with mutators. Thus, 7128 // it is possible for direct allocation in this generation to happen 7129 // in the middle of the sweep. Note that the sweeper also coalesces 7130 // contiguous free blocks. Thus, unless the sweeper and the allocator 7131 // synchronize appropriately freshly allocated blocks may get swept up. 7132 // This is accomplished by the sweeper locking the free lists while 7133 // it is sweeping. Thus blocks that are determined to be free are 7134 // indeed free. There is however one additional complication: 7135 // blocks that have been allocated since the final checkpoint and 7136 // mark, will not have been marked and so would be treated as 7137 // unreachable and swept up. To prevent this, the allocator marks 7138 // the bit map when allocating during the sweep phase. This leads, 7139 // however, to a further complication -- objects may have been allocated 7140 // but not yet initialized -- in the sense that the header isn't yet 7141 // installed. The sweeper can not then determine the size of the block 7142 // in order to skip over it. To deal with this case, we use a technique 7143 // (due to Printezis) to encode such uninitialized block sizes in the 7144 // bit map. Since the bit map uses a bit per every HeapWord, but the 7145 // CMS generation has a minimum object size of 3 HeapWords, it follows 7146 // that "normal marks" won't be adjacent in the bit map (there will 7147 // always be at least two 0 bits between successive 1 bits). We make use 7148 // of these "unused" bits to represent uninitialized blocks -- the bit 7149 // corresponding to the start of the uninitialized object and the next 7150 // bit are both set. Finally, a 1 bit marks the end of the object that 7151 // started with the two consecutive 1 bits to indicate its potentially 7152 // uninitialized state. 7153 7154 size_t SweepClosure::do_blk_careful(HeapWord* addr) { 7155 FreeChunk* fc = (FreeChunk*)addr; 7156 size_t res; 7157 7158 // Check if we are done sweeping. Below we check "addr >= _limit" rather 7159 // than "addr == _limit" because although _limit was a block boundary when 7160 // we started the sweep, it may no longer be one because heap expansion 7161 // may have caused us to coalesce the block ending at the address _limit 7162 // with a newly expanded chunk (this happens when _limit was set to the 7163 // previous _end of the space), so we may have stepped past _limit: 7164 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740. 7165 if (addr >= _limit) { // we have swept up to or past the limit: finish up 7166 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 7167 "sweep _limit out of bounds"); 7168 assert(addr < _sp->end(), "addr out of bounds"); 7169 // Flush any free range we might be holding as a single 7170 // coalesced chunk to the appropriate free list. 7171 if (inFreeRange()) { 7172 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit, 7173 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger())); 7174 flush_cur_free_chunk(freeFinger(), 7175 pointer_delta(addr, freeFinger())); 7176 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]", 7177 p2i(freeFinger()), pointer_delta(addr, freeFinger()), 7178 lastFreeRangeCoalesced() ? 1 : 0); 7179 } 7180 7181 // help the iterator loop finish 7182 return pointer_delta(_sp->end(), addr); 7183 } 7184 7185 assert(addr < _limit, "sweep invariant"); 7186 // check if we should yield 7187 do_yield_check(addr); 7188 if (fc->is_free()) { 7189 // Chunk that is already free 7190 res = fc->size(); 7191 do_already_free_chunk(fc); 7192 debug_only(_sp->verifyFreeLists()); 7193 // If we flush the chunk at hand in lookahead_and_flush() 7194 // and it's coalesced with a preceding chunk, then the 7195 // process of "mangling" the payload of the coalesced block 7196 // will cause erasure of the size information from the 7197 // (erstwhile) header of all the coalesced blocks but the 7198 // first, so the first disjunct in the assert will not hold 7199 // in that specific case (in which case the second disjunct 7200 // will hold). 7201 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit, 7202 "Otherwise the size info doesn't change at this step"); 7203 NOT_PRODUCT( 7204 _numObjectsAlreadyFree++; 7205 _numWordsAlreadyFree += res; 7206 ) 7207 NOT_PRODUCT(_last_fc = fc;) 7208 } else if (!_bitMap->isMarked(addr)) { 7209 // Chunk is fresh garbage 7210 res = do_garbage_chunk(fc); 7211 debug_only(_sp->verifyFreeLists()); 7212 NOT_PRODUCT( 7213 _numObjectsFreed++; 7214 _numWordsFreed += res; 7215 ) 7216 } else { 7217 // Chunk that is alive. 7218 res = do_live_chunk(fc); 7219 debug_only(_sp->verifyFreeLists()); 7220 NOT_PRODUCT( 7221 _numObjectsLive++; 7222 _numWordsLive += res; 7223 ) 7224 } 7225 return res; 7226 } 7227 7228 // For the smart allocation, record following 7229 // split deaths - a free chunk is removed from its free list because 7230 // it is being split into two or more chunks. 7231 // split birth - a free chunk is being added to its free list because 7232 // a larger free chunk has been split and resulted in this free chunk. 7233 // coal death - a free chunk is being removed from its free list because 7234 // it is being coalesced into a large free chunk. 7235 // coal birth - a free chunk is being added to its free list because 7236 // it was created when two or more free chunks where coalesced into 7237 // this free chunk. 7238 // 7239 // These statistics are used to determine the desired number of free 7240 // chunks of a given size. The desired number is chosen to be relative 7241 // to the end of a CMS sweep. The desired number at the end of a sweep 7242 // is the 7243 // count-at-end-of-previous-sweep (an amount that was enough) 7244 // - count-at-beginning-of-current-sweep (the excess) 7245 // + split-births (gains in this size during interval) 7246 // - split-deaths (demands on this size during interval) 7247 // where the interval is from the end of one sweep to the end of the 7248 // next. 7249 // 7250 // When sweeping the sweeper maintains an accumulated chunk which is 7251 // the chunk that is made up of chunks that have been coalesced. That 7252 // will be termed the left-hand chunk. A new chunk of garbage that 7253 // is being considered for coalescing will be referred to as the 7254 // right-hand chunk. 7255 // 7256 // When making a decision on whether to coalesce a right-hand chunk with 7257 // the current left-hand chunk, the current count vs. the desired count 7258 // of the left-hand chunk is considered. Also if the right-hand chunk 7259 // is near the large chunk at the end of the heap (see 7260 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the 7261 // left-hand chunk is coalesced. 7262 // 7263 // When making a decision about whether to split a chunk, the desired count 7264 // vs. the current count of the candidate to be split is also considered. 7265 // If the candidate is underpopulated (currently fewer chunks than desired) 7266 // a chunk of an overpopulated (currently more chunks than desired) size may 7267 // be chosen. The "hint" associated with a free list, if non-null, points 7268 // to a free list which may be overpopulated. 7269 // 7270 7271 void SweepClosure::do_already_free_chunk(FreeChunk* fc) { 7272 const size_t size = fc->size(); 7273 // Chunks that cannot be coalesced are not in the 7274 // free lists. 7275 if (CMSTestInFreeList && !fc->cantCoalesce()) { 7276 assert(_sp->verify_chunk_in_free_list(fc), 7277 "free chunk should be in free lists"); 7278 } 7279 // a chunk that is already free, should not have been 7280 // marked in the bit map 7281 HeapWord* const addr = (HeapWord*) fc; 7282 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); 7283 // Verify that the bit map has no bits marked between 7284 // addr and purported end of this block. 7285 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 7286 7287 // Some chunks cannot be coalesced under any circumstances. 7288 // See the definition of cantCoalesce(). 7289 if (!fc->cantCoalesce()) { 7290 // This chunk can potentially be coalesced. 7291 // All the work is done in 7292 do_post_free_or_garbage_chunk(fc, size); 7293 // Note that if the chunk is not coalescable (the else arm 7294 // below), we unconditionally flush, without needing to do 7295 // a "lookahead," as we do below. 7296 if (inFreeRange()) lookahead_and_flush(fc, size); 7297 } else { 7298 // Code path common to both original and adaptive free lists. 7299 7300 // cant coalesce with previous block; this should be treated 7301 // as the end of a free run if any 7302 if (inFreeRange()) { 7303 // we kicked some butt; time to pick up the garbage 7304 assert(freeFinger() < addr, "freeFinger points too high"); 7305 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 7306 } 7307 // else, nothing to do, just continue 7308 } 7309 } 7310 7311 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) { 7312 // This is a chunk of garbage. It is not in any free list. 7313 // Add it to a free list or let it possibly be coalesced into 7314 // a larger chunk. 7315 HeapWord* const addr = (HeapWord*) fc; 7316 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); 7317 7318 // Verify that the bit map has no bits marked between 7319 // addr and purported end of just dead object. 7320 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 7321 do_post_free_or_garbage_chunk(fc, size); 7322 7323 assert(_limit >= addr + size, 7324 "A freshly garbage chunk can't possibly straddle over _limit"); 7325 if (inFreeRange()) lookahead_and_flush(fc, size); 7326 return size; 7327 } 7328 7329 size_t SweepClosure::do_live_chunk(FreeChunk* fc) { 7330 HeapWord* addr = (HeapWord*) fc; 7331 // The sweeper has just found a live object. Return any accumulated 7332 // left hand chunk to the free lists. 7333 if (inFreeRange()) { 7334 assert(freeFinger() < addr, "freeFinger points too high"); 7335 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 7336 } 7337 7338 // This object is live: we'd normally expect this to be 7339 // an oop, and like to assert the following: 7340 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop"); 7341 // However, as we commented above, this may be an object whose 7342 // header hasn't yet been initialized. 7343 size_t size; 7344 assert(_bitMap->isMarked(addr), "Tautology for this control point"); 7345 if (_bitMap->isMarked(addr + 1)) { 7346 // Determine the size from the bit map, rather than trying to 7347 // compute it from the object header. 7348 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); 7349 size = pointer_delta(nextOneAddr + 1, addr); 7350 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 7351 "alignment problem"); 7352 7353 #ifdef ASSERT 7354 if (oop(addr)->klass_or_null_acquire() != NULL) { 7355 // Ignore mark word because we are running concurrent with mutators 7356 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop"); 7357 assert(size == 7358 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), 7359 "P-mark and computed size do not agree"); 7360 } 7361 #endif 7362 7363 } else { 7364 // This should be an initialized object that's alive. 7365 assert(oop(addr)->klass_or_null_acquire() != NULL, 7366 "Should be an initialized object"); 7367 // Ignore mark word because we are running concurrent with mutators 7368 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop"); 7369 // Verify that the bit map has no bits marked between 7370 // addr and purported end of this block. 7371 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); 7372 assert(size >= 3, "Necessary for Printezis marks to work"); 7373 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); 7374 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) 7375 } 7376 return size; 7377 } 7378 7379 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc, 7380 size_t chunkSize) { 7381 // do_post_free_or_garbage_chunk() should only be called in the case 7382 // of the adaptive free list allocator. 7383 const bool fcInFreeLists = fc->is_free(); 7384 assert((HeapWord*)fc <= _limit, "sweep invariant"); 7385 if (CMSTestInFreeList && fcInFreeLists) { 7386 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); 7387 } 7388 7389 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize); 7390 7391 HeapWord* const fc_addr = (HeapWord*) fc; 7392 7393 bool coalesce = false; 7394 const size_t left = pointer_delta(fc_addr, freeFinger()); 7395 const size_t right = chunkSize; 7396 switch (FLSCoalescePolicy) { 7397 // numeric value forms a coalition aggressiveness metric 7398 case 0: { // never coalesce 7399 coalesce = false; 7400 break; 7401 } 7402 case 1: { // coalesce if left & right chunks on overpopulated lists 7403 coalesce = _sp->coalOverPopulated(left) && 7404 _sp->coalOverPopulated(right); 7405 break; 7406 } 7407 case 2: { // coalesce if left chunk on overpopulated list (default) 7408 coalesce = _sp->coalOverPopulated(left); 7409 break; 7410 } 7411 case 3: { // coalesce if left OR right chunk on overpopulated list 7412 coalesce = _sp->coalOverPopulated(left) || 7413 _sp->coalOverPopulated(right); 7414 break; 7415 } 7416 case 4: { // always coalesce 7417 coalesce = true; 7418 break; 7419 } 7420 default: 7421 ShouldNotReachHere(); 7422 } 7423 7424 // Should the current free range be coalesced? 7425 // If the chunk is in a free range and either we decided to coalesce above 7426 // or the chunk is near the large block at the end of the heap 7427 // (isNearLargestChunk() returns true), then coalesce this chunk. 7428 const bool doCoalesce = inFreeRange() 7429 && (coalesce || _g->isNearLargestChunk(fc_addr)); 7430 if (doCoalesce) { 7431 // Coalesce the current free range on the left with the new 7432 // chunk on the right. If either is on a free list, 7433 // it must be removed from the list and stashed in the closure. 7434 if (freeRangeInFreeLists()) { 7435 FreeChunk* const ffc = (FreeChunk*)freeFinger(); 7436 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()), 7437 "Size of free range is inconsistent with chunk size."); 7438 if (CMSTestInFreeList) { 7439 assert(_sp->verify_chunk_in_free_list(ffc), 7440 "Chunk is not in free lists"); 7441 } 7442 _sp->coalDeath(ffc->size()); 7443 _sp->removeFreeChunkFromFreeLists(ffc); 7444 set_freeRangeInFreeLists(false); 7445 } 7446 if (fcInFreeLists) { 7447 _sp->coalDeath(chunkSize); 7448 assert(fc->size() == chunkSize, 7449 "The chunk has the wrong size or is not in the free lists"); 7450 _sp->removeFreeChunkFromFreeLists(fc); 7451 } 7452 set_lastFreeRangeCoalesced(true); 7453 print_free_block_coalesced(fc); 7454 } else { // not in a free range and/or should not coalesce 7455 // Return the current free range and start a new one. 7456 if (inFreeRange()) { 7457 // In a free range but cannot coalesce with the right hand chunk. 7458 // Put the current free range into the free lists. 7459 flush_cur_free_chunk(freeFinger(), 7460 pointer_delta(fc_addr, freeFinger())); 7461 } 7462 // Set up for new free range. Pass along whether the right hand 7463 // chunk is in the free lists. 7464 initialize_free_range((HeapWord*)fc, fcInFreeLists); 7465 } 7466 } 7467 7468 // Lookahead flush: 7469 // If we are tracking a free range, and this is the last chunk that 7470 // we'll look at because its end crosses past _limit, we'll preemptively 7471 // flush it along with any free range we may be holding on to. Note that 7472 // this can be the case only for an already free or freshly garbage 7473 // chunk. If this block is an object, it can never straddle 7474 // over _limit. The "straddling" occurs when _limit is set at 7475 // the previous end of the space when this cycle started, and 7476 // a subsequent heap expansion caused the previously co-terminal 7477 // free block to be coalesced with the newly expanded portion, 7478 // thus rendering _limit a non-block-boundary making it dangerous 7479 // for the sweeper to step over and examine. 7480 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) { 7481 assert(inFreeRange(), "Should only be called if currently in a free range."); 7482 HeapWord* const eob = ((HeapWord*)fc) + chunk_size; 7483 assert(_sp->used_region().contains(eob - 1), 7484 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT 7485 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")" 7486 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")", 7487 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size); 7488 if (eob >= _limit) { 7489 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); 7490 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block " 7491 "[" PTR_FORMAT "," PTR_FORMAT ") in space " 7492 "[" PTR_FORMAT "," PTR_FORMAT ")", 7493 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end())); 7494 // Return the storage we are tracking back into the free lists. 7495 log_develop_trace(gc, sweep)("Flushing ... "); 7496 assert(freeFinger() < eob, "Error"); 7497 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger())); 7498 } 7499 } 7500 7501 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) { 7502 assert(inFreeRange(), "Should only be called if currently in a free range."); 7503 assert(size > 0, 7504 "A zero sized chunk cannot be added to the free lists."); 7505 if (!freeRangeInFreeLists()) { 7506 if (CMSTestInFreeList) { 7507 FreeChunk* fc = (FreeChunk*) chunk; 7508 fc->set_size(size); 7509 assert(!_sp->verify_chunk_in_free_list(fc), 7510 "chunk should not be in free lists yet"); 7511 } 7512 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size); 7513 // A new free range is going to be starting. The current 7514 // free range has not been added to the free lists yet or 7515 // was removed so add it back. 7516 // If the current free range was coalesced, then the death 7517 // of the free range was recorded. Record a birth now. 7518 if (lastFreeRangeCoalesced()) { 7519 _sp->coalBirth(size); 7520 } 7521 _sp->addChunkAndRepairOffsetTable(chunk, size, 7522 lastFreeRangeCoalesced()); 7523 } else { 7524 log_develop_trace(gc, sweep)("Already in free list: nothing to flush"); 7525 } 7526 set_inFreeRange(false); 7527 set_freeRangeInFreeLists(false); 7528 } 7529 7530 // We take a break if we've been at this for a while, 7531 // so as to avoid monopolizing the locks involved. 7532 void SweepClosure::do_yield_work(HeapWord* addr) { 7533 // Return current free chunk being used for coalescing (if any) 7534 // to the appropriate freelist. After yielding, the next 7535 // free block encountered will start a coalescing range of 7536 // free blocks. If the next free block is adjacent to the 7537 // chunk just flushed, they will need to wait for the next 7538 // sweep to be coalesced. 7539 if (inFreeRange()) { 7540 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 7541 } 7542 7543 // First give up the locks, then yield, then re-lock. 7544 // We should probably use a constructor/destructor idiom to 7545 // do this unlock/lock or modify the MutexUnlocker class to 7546 // serve our purpose. XXX 7547 assert_lock_strong(_bitMap->lock()); 7548 assert_lock_strong(_freelistLock); 7549 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 7550 "CMS thread should hold CMS token"); 7551 _bitMap->lock()->unlock(); 7552 _freelistLock->unlock(); 7553 ConcurrentMarkSweepThread::desynchronize(true); 7554 _collector->stopTimer(); 7555 _collector->incrementYields(); 7556 7557 // See the comment in coordinator_yield() 7558 for (unsigned i = 0; i < CMSYieldSleepCount && 7559 ConcurrentMarkSweepThread::should_yield() && 7560 !CMSCollector::foregroundGCIsActive(); ++i) { 7561 os::sleep(Thread::current(), 1, false); 7562 } 7563 7564 ConcurrentMarkSweepThread::synchronize(true); 7565 _freelistLock->lock(); 7566 _bitMap->lock()->lock_without_safepoint_check(); 7567 _collector->startTimer(); 7568 } 7569 7570 #ifndef PRODUCT 7571 // This is actually very useful in a product build if it can 7572 // be called from the debugger. Compile it into the product 7573 // as needed. 7574 bool debug_verify_chunk_in_free_list(FreeChunk* fc) { 7575 return debug_cms_space->verify_chunk_in_free_list(fc); 7576 } 7577 #endif 7578 7579 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const { 7580 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")", 7581 p2i(fc), fc->size()); 7582 } 7583 7584 // CMSIsAliveClosure 7585 bool CMSIsAliveClosure::do_object_b(oop obj) { 7586 HeapWord* addr = (HeapWord*)obj; 7587 return addr != NULL && 7588 (!_span.contains(addr) || _bit_map->isMarked(addr)); 7589 } 7590 7591 7592 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector, 7593 MemRegion span, 7594 CMSBitMap* bit_map, CMSMarkStack* mark_stack, 7595 bool cpc): 7596 _collector(collector), 7597 _span(span), 7598 _bit_map(bit_map), 7599 _mark_stack(mark_stack), 7600 _concurrent_precleaning(cpc) { 7601 assert(!_span.is_empty(), "Empty span could spell trouble"); 7602 } 7603 7604 7605 // CMSKeepAliveClosure: the serial version 7606 void CMSKeepAliveClosure::do_oop(oop obj) { 7607 HeapWord* addr = (HeapWord*)obj; 7608 if (_span.contains(addr) && 7609 !_bit_map->isMarked(addr)) { 7610 _bit_map->mark(addr); 7611 bool simulate_overflow = false; 7612 NOT_PRODUCT( 7613 if (CMSMarkStackOverflowALot && 7614 _collector->simulate_overflow()) { 7615 // simulate a stack overflow 7616 simulate_overflow = true; 7617 } 7618 ) 7619 if (simulate_overflow || !_mark_stack->push(obj)) { 7620 if (_concurrent_precleaning) { 7621 // We dirty the overflown object and let the remark 7622 // phase deal with it. 7623 assert(_collector->overflow_list_is_empty(), "Error"); 7624 // In the case of object arrays, we need to dirty all of 7625 // the cards that the object spans. No locking or atomics 7626 // are needed since no one else can be mutating the mod union 7627 // table. 7628 if (obj->is_objArray()) { 7629 size_t sz = obj->size(); 7630 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); 7631 MemRegion redirty_range = MemRegion(addr, end_card_addr); 7632 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 7633 _collector->_modUnionTable.mark_range(redirty_range); 7634 } else { 7635 _collector->_modUnionTable.mark(addr); 7636 } 7637 _collector->_ser_kac_preclean_ovflw++; 7638 } else { 7639 _collector->push_on_overflow_list(obj); 7640 _collector->_ser_kac_ovflw++; 7641 } 7642 } 7643 } 7644 } 7645 7646 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); } 7647 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); } 7648 7649 // CMSParKeepAliveClosure: a parallel version of the above. 7650 // The work queues are private to each closure (thread), 7651 // but (may be) available for stealing by other threads. 7652 void CMSParKeepAliveClosure::do_oop(oop obj) { 7653 HeapWord* addr = (HeapWord*)obj; 7654 if (_span.contains(addr) && 7655 !_bit_map->isMarked(addr)) { 7656 // In general, during recursive tracing, several threads 7657 // may be concurrently getting here; the first one to 7658 // "tag" it, claims it. 7659 if (_bit_map->par_mark(addr)) { 7660 bool res = _work_queue->push(obj); 7661 assert(res, "Low water mark should be much less than capacity"); 7662 // Do a recursive trim in the hope that this will keep 7663 // stack usage lower, but leave some oops for potential stealers 7664 trim_queue(_low_water_mark); 7665 } // Else, another thread got there first 7666 } 7667 } 7668 7669 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); } 7670 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); } 7671 7672 void CMSParKeepAliveClosure::trim_queue(uint max) { 7673 while (_work_queue->size() > max) { 7674 oop new_oop; 7675 if (_work_queue->pop_local(new_oop)) { 7676 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); 7677 assert(_bit_map->isMarked((HeapWord*)new_oop), 7678 "no white objects on this stack!"); 7679 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); 7680 // iterate over the oops in this oop, marking and pushing 7681 // the ones in CMS heap (i.e. in _span). 7682 new_oop->oop_iterate(&_mark_and_push); 7683 } 7684 } 7685 } 7686 7687 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure( 7688 CMSCollector* collector, 7689 MemRegion span, CMSBitMap* bit_map, 7690 OopTaskQueue* work_queue): 7691 _collector(collector), 7692 _span(span), 7693 _bit_map(bit_map), 7694 _work_queue(work_queue) { } 7695 7696 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) { 7697 HeapWord* addr = (HeapWord*)obj; 7698 if (_span.contains(addr) && 7699 !_bit_map->isMarked(addr)) { 7700 if (_bit_map->par_mark(addr)) { 7701 bool simulate_overflow = false; 7702 NOT_PRODUCT( 7703 if (CMSMarkStackOverflowALot && 7704 _collector->par_simulate_overflow()) { 7705 // simulate a stack overflow 7706 simulate_overflow = true; 7707 } 7708 ) 7709 if (simulate_overflow || !_work_queue->push(obj)) { 7710 _collector->par_push_on_overflow_list(obj); 7711 _collector->_par_kac_ovflw++; 7712 } 7713 } // Else another thread got there already 7714 } 7715 } 7716 7717 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } 7718 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } 7719 7720 ////////////////////////////////////////////////////////////////// 7721 // CMSExpansionCause ///////////////////////////// 7722 ////////////////////////////////////////////////////////////////// 7723 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { 7724 switch (cause) { 7725 case _no_expansion: 7726 return "No expansion"; 7727 case _satisfy_free_ratio: 7728 return "Free ratio"; 7729 case _satisfy_promotion: 7730 return "Satisfy promotion"; 7731 case _satisfy_allocation: 7732 return "allocation"; 7733 case _allocate_par_lab: 7734 return "Par LAB"; 7735 case _allocate_par_spooling_space: 7736 return "Par Spooling Space"; 7737 case _adaptive_size_policy: 7738 return "Ergonomics"; 7739 default: 7740 return "unknown"; 7741 } 7742 } 7743 7744 void CMSDrainMarkingStackClosure::do_void() { 7745 // the max number to take from overflow list at a time 7746 const size_t num = _mark_stack->capacity()/4; 7747 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(), 7748 "Overflow list should be NULL during concurrent phases"); 7749 while (!_mark_stack->isEmpty() || 7750 // if stack is empty, check the overflow list 7751 _collector->take_from_overflow_list(num, _mark_stack)) { 7752 oop obj = _mark_stack->pop(); 7753 HeapWord* addr = (HeapWord*)obj; 7754 assert(_span.contains(addr), "Should be within span"); 7755 assert(_bit_map->isMarked(addr), "Should be marked"); 7756 assert(oopDesc::is_oop(obj), "Should be an oop"); 7757 obj->oop_iterate(_keep_alive); 7758 } 7759 } 7760 7761 void CMSParDrainMarkingStackClosure::do_void() { 7762 // drain queue 7763 trim_queue(0); 7764 } 7765 7766 // Trim our work_queue so its length is below max at return 7767 void CMSParDrainMarkingStackClosure::trim_queue(uint max) { 7768 while (_work_queue->size() > max) { 7769 oop new_oop; 7770 if (_work_queue->pop_local(new_oop)) { 7771 assert(oopDesc::is_oop(new_oop), "Expected an oop"); 7772 assert(_bit_map->isMarked((HeapWord*)new_oop), 7773 "no white objects on this stack!"); 7774 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); 7775 // iterate over the oops in this oop, marking and pushing 7776 // the ones in CMS heap (i.e. in _span). 7777 new_oop->oop_iterate(&_mark_and_push); 7778 } 7779 } 7780 } 7781 7782 //////////////////////////////////////////////////////////////////// 7783 // Support for Marking Stack Overflow list handling and related code 7784 //////////////////////////////////////////////////////////////////// 7785 // Much of the following code is similar in shape and spirit to the 7786 // code used in ParNewGC. We should try and share that code 7787 // as much as possible in the future. 7788 7789 #ifndef PRODUCT 7790 // Debugging support for CMSStackOverflowALot 7791 7792 // It's OK to call this multi-threaded; the worst thing 7793 // that can happen is that we'll get a bunch of closely 7794 // spaced simulated overflows, but that's OK, in fact 7795 // probably good as it would exercise the overflow code 7796 // under contention. 7797 bool CMSCollector::simulate_overflow() { 7798 if (_overflow_counter-- <= 0) { // just being defensive 7799 _overflow_counter = CMSMarkStackOverflowInterval; 7800 return true; 7801 } else { 7802 return false; 7803 } 7804 } 7805 7806 bool CMSCollector::par_simulate_overflow() { 7807 return simulate_overflow(); 7808 } 7809 #endif 7810 7811 // Single-threaded 7812 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { 7813 assert(stack->isEmpty(), "Expected precondition"); 7814 assert(stack->capacity() > num, "Shouldn't bite more than can chew"); 7815 size_t i = num; 7816 oop cur = _overflow_list; 7817 const markOop proto = markOopDesc::prototype(); 7818 NOT_PRODUCT(ssize_t n = 0;) 7819 for (oop next; i > 0 && cur != NULL; cur = next, i--) { 7820 next = oop(cur->mark_raw()); 7821 cur->set_mark_raw(proto); // until proven otherwise 7822 assert(oopDesc::is_oop(cur), "Should be an oop"); 7823 bool res = stack->push(cur); 7824 assert(res, "Bit off more than can chew?"); 7825 NOT_PRODUCT(n++;) 7826 } 7827 _overflow_list = cur; 7828 #ifndef PRODUCT 7829 assert(_num_par_pushes >= n, "Too many pops?"); 7830 _num_par_pushes -=n; 7831 #endif 7832 return !stack->isEmpty(); 7833 } 7834 7835 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 7836 // (MT-safe) Get a prefix of at most "num" from the list. 7837 // The overflow list is chained through the mark word of 7838 // each object in the list. We fetch the entire list, 7839 // break off a prefix of the right size and return the 7840 // remainder. If other threads try to take objects from 7841 // the overflow list at that time, they will wait for 7842 // some time to see if data becomes available. If (and 7843 // only if) another thread places one or more object(s) 7844 // on the global list before we have returned the suffix 7845 // to the global list, we will walk down our local list 7846 // to find its end and append the global list to 7847 // our suffix before returning it. This suffix walk can 7848 // prove to be expensive (quadratic in the amount of traffic) 7849 // when there are many objects in the overflow list and 7850 // there is much producer-consumer contention on the list. 7851 // *NOTE*: The overflow list manipulation code here and 7852 // in ParNewGeneration:: are very similar in shape, 7853 // except that in the ParNew case we use the old (from/eden) 7854 // copy of the object to thread the list via its klass word. 7855 // Because of the common code, if you make any changes in 7856 // the code below, please check the ParNew version to see if 7857 // similar changes might be needed. 7858 // CR 6797058 has been filed to consolidate the common code. 7859 bool CMSCollector::par_take_from_overflow_list(size_t num, 7860 OopTaskQueue* work_q, 7861 int no_of_gc_threads) { 7862 assert(work_q->size() == 0, "First empty local work queue"); 7863 assert(num < work_q->max_elems(), "Can't bite more than we can chew"); 7864 if (_overflow_list == NULL) { 7865 return false; 7866 } 7867 // Grab the entire list; we'll put back a suffix 7868 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); 7869 Thread* tid = Thread::current(); 7870 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was 7871 // set to ParallelGCThreads. 7872 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads; 7873 size_t sleep_time_millis = MAX2((size_t)1, num/100); 7874 // If the list is busy, we spin for a short while, 7875 // sleeping between attempts to get the list. 7876 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) { 7877 os::sleep(tid, sleep_time_millis, false); 7878 if (_overflow_list == NULL) { 7879 // Nothing left to take 7880 return false; 7881 } else if (_overflow_list != BUSY) { 7882 // Try and grab the prefix 7883 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); 7884 } 7885 } 7886 // If the list was found to be empty, or we spun long 7887 // enough, we give up and return empty-handed. If we leave 7888 // the list in the BUSY state below, it must be the case that 7889 // some other thread holds the overflow list and will set it 7890 // to a non-BUSY state in the future. 7891 if (prefix == NULL || prefix == BUSY) { 7892 // Nothing to take or waited long enough 7893 if (prefix == NULL) { 7894 // Write back the NULL in case we overwrote it with BUSY above 7895 // and it is still the same value. 7896 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); 7897 } 7898 return false; 7899 } 7900 assert(prefix != NULL && prefix != BUSY, "Error"); 7901 size_t i = num; 7902 oop cur = prefix; 7903 // Walk down the first "num" objects, unless we reach the end. 7904 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--); 7905 if (cur->mark_raw() == NULL) { 7906 // We have "num" or fewer elements in the list, so there 7907 // is nothing to return to the global list. 7908 // Write back the NULL in lieu of the BUSY we wrote 7909 // above, if it is still the same value. 7910 if (_overflow_list == BUSY) { 7911 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); 7912 } 7913 } else { 7914 // Chop off the suffix and return it to the global list. 7915 assert(cur->mark_raw() != BUSY, "Error"); 7916 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list 7917 cur->set_mark_raw(NULL); // break off suffix 7918 // It's possible that the list is still in the empty(busy) state 7919 // we left it in a short while ago; in that case we may be 7920 // able to place back the suffix without incurring the cost 7921 // of a walk down the list. 7922 oop observed_overflow_list = _overflow_list; 7923 oop cur_overflow_list = observed_overflow_list; 7924 bool attached = false; 7925 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 7926 observed_overflow_list = 7927 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list); 7928 if (cur_overflow_list == observed_overflow_list) { 7929 attached = true; 7930 break; 7931 } else cur_overflow_list = observed_overflow_list; 7932 } 7933 if (!attached) { 7934 // Too bad, someone else sneaked in (at least) an element; we'll need 7935 // to do a splice. Find tail of suffix so we can prepend suffix to global 7936 // list. 7937 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw())); 7938 oop suffix_tail = cur; 7939 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL, 7940 "Tautology"); 7941 observed_overflow_list = _overflow_list; 7942 do { 7943 cur_overflow_list = observed_overflow_list; 7944 if (cur_overflow_list != BUSY) { 7945 // Do the splice ... 7946 suffix_tail->set_mark_raw(markOop(cur_overflow_list)); 7947 } else { // cur_overflow_list == BUSY 7948 suffix_tail->set_mark_raw(NULL); 7949 } 7950 // ... and try to place spliced list back on overflow_list ... 7951 observed_overflow_list = 7952 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list); 7953 } while (cur_overflow_list != observed_overflow_list); 7954 // ... until we have succeeded in doing so. 7955 } 7956 } 7957 7958 // Push the prefix elements on work_q 7959 assert(prefix != NULL, "control point invariant"); 7960 const markOop proto = markOopDesc::prototype(); 7961 oop next; 7962 NOT_PRODUCT(ssize_t n = 0;) 7963 for (cur = prefix; cur != NULL; cur = next) { 7964 next = oop(cur->mark_raw()); 7965 cur->set_mark_raw(proto); // until proven otherwise 7966 assert(oopDesc::is_oop(cur), "Should be an oop"); 7967 bool res = work_q->push(cur); 7968 assert(res, "Bit off more than we can chew?"); 7969 NOT_PRODUCT(n++;) 7970 } 7971 #ifndef PRODUCT 7972 assert(_num_par_pushes >= n, "Too many pops?"); 7973 Atomic::sub(n, &_num_par_pushes); 7974 #endif 7975 return true; 7976 } 7977 7978 // Single-threaded 7979 void CMSCollector::push_on_overflow_list(oop p) { 7980 NOT_PRODUCT(_num_par_pushes++;) 7981 assert(oopDesc::is_oop(p), "Not an oop"); 7982 preserve_mark_if_necessary(p); 7983 p->set_mark_raw((markOop)_overflow_list); 7984 _overflow_list = p; 7985 } 7986 7987 // Multi-threaded; use CAS to prepend to overflow list 7988 void CMSCollector::par_push_on_overflow_list(oop p) { 7989 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);) 7990 assert(oopDesc::is_oop(p), "Not an oop"); 7991 par_preserve_mark_if_necessary(p); 7992 oop observed_overflow_list = _overflow_list; 7993 oop cur_overflow_list; 7994 do { 7995 cur_overflow_list = observed_overflow_list; 7996 if (cur_overflow_list != BUSY) { 7997 p->set_mark_raw(markOop(cur_overflow_list)); 7998 } else { 7999 p->set_mark_raw(NULL); 8000 } 8001 observed_overflow_list = 8002 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list); 8003 } while (cur_overflow_list != observed_overflow_list); 8004 } 8005 #undef BUSY 8006 8007 // Single threaded 8008 // General Note on GrowableArray: pushes may silently fail 8009 // because we are (temporarily) out of C-heap for expanding 8010 // the stack. The problem is quite ubiquitous and affects 8011 // a lot of code in the JVM. The prudent thing for GrowableArray 8012 // to do (for now) is to exit with an error. However, that may 8013 // be too draconian in some cases because the caller may be 8014 // able to recover without much harm. For such cases, we 8015 // should probably introduce a "soft_push" method which returns 8016 // an indication of success or failure with the assumption that 8017 // the caller may be able to recover from a failure; code in 8018 // the VM can then be changed, incrementally, to deal with such 8019 // failures where possible, thus, incrementally hardening the VM 8020 // in such low resource situations. 8021 void CMSCollector::preserve_mark_work(oop p, markOop m) { 8022 _preserved_oop_stack.push(p); 8023 _preserved_mark_stack.push(m); 8024 assert(m == p->mark_raw(), "Mark word changed"); 8025 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), 8026 "bijection"); 8027 } 8028 8029 // Single threaded 8030 void CMSCollector::preserve_mark_if_necessary(oop p) { 8031 markOop m = p->mark_raw(); 8032 if (m->must_be_preserved(p)) { 8033 preserve_mark_work(p, m); 8034 } 8035 } 8036 8037 void CMSCollector::par_preserve_mark_if_necessary(oop p) { 8038 markOop m = p->mark_raw(); 8039 if (m->must_be_preserved(p)) { 8040 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); 8041 // Even though we read the mark word without holding 8042 // the lock, we are assured that it will not change 8043 // because we "own" this oop, so no other thread can 8044 // be trying to push it on the overflow list; see 8045 // the assertion in preserve_mark_work() that checks 8046 // that m == p->mark_raw(). 8047 preserve_mark_work(p, m); 8048 } 8049 } 8050 8051 // We should be able to do this multi-threaded, 8052 // a chunk of stack being a task (this is 8053 // correct because each oop only ever appears 8054 // once in the overflow list. However, it's 8055 // not very easy to completely overlap this with 8056 // other operations, so will generally not be done 8057 // until all work's been completed. Because we 8058 // expect the preserved oop stack (set) to be small, 8059 // it's probably fine to do this single-threaded. 8060 // We can explore cleverer concurrent/overlapped/parallel 8061 // processing of preserved marks if we feel the 8062 // need for this in the future. Stack overflow should 8063 // be so rare in practice and, when it happens, its 8064 // effect on performance so great that this will 8065 // likely just be in the noise anyway. 8066 void CMSCollector::restore_preserved_marks_if_any() { 8067 assert(SafepointSynchronize::is_at_safepoint(), 8068 "world should be stopped"); 8069 assert(Thread::current()->is_ConcurrentGC_thread() || 8070 Thread::current()->is_VM_thread(), 8071 "should be single-threaded"); 8072 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), 8073 "bijection"); 8074 8075 while (!_preserved_oop_stack.is_empty()) { 8076 oop p = _preserved_oop_stack.pop(); 8077 assert(oopDesc::is_oop(p), "Should be an oop"); 8078 assert(_span.contains(p), "oop should be in _span"); 8079 assert(p->mark_raw() == markOopDesc::prototype(), 8080 "Set when taken from overflow list"); 8081 markOop m = _preserved_mark_stack.pop(); 8082 p->set_mark_raw(m); 8083 } 8084 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(), 8085 "stacks were cleared above"); 8086 } 8087 8088 #ifndef PRODUCT 8089 bool CMSCollector::no_preserved_marks() const { 8090 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(); 8091 } 8092 #endif 8093 8094 // Transfer some number of overflown objects to usual marking 8095 // stack. Return true if some objects were transferred. 8096 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { 8097 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4, 8098 (size_t)ParGCDesiredObjsFromOverflowList); 8099 8100 bool res = _collector->take_from_overflow_list(num, _mark_stack); 8101 assert(_collector->overflow_list_is_empty() || res, 8102 "If list is not empty, we should have taken something"); 8103 assert(!res || !_mark_stack->isEmpty(), 8104 "If we took something, it should now be on our stack"); 8105 return res; 8106 } 8107 8108 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { 8109 size_t res = _sp->block_size_no_stall(addr, _collector); 8110 if (_sp->block_is_obj(addr)) { 8111 if (_live_bit_map->isMarked(addr)) { 8112 // It can't have been dead in a previous cycle 8113 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); 8114 } else { 8115 _dead_bit_map->mark(addr); // mark the dead object 8116 } 8117 } 8118 // Could be 0, if the block size could not be computed without stalling. 8119 return res; 8120 } 8121 8122 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() { 8123 GCMemoryManager* manager = CMSHeap::heap()->old_manager(); 8124 switch (phase) { 8125 case CMSCollector::InitialMarking: 8126 initialize(manager /* GC manager */ , 8127 cause /* cause of the GC */, 8128 true /* recordGCBeginTime */, 8129 true /* recordPreGCUsage */, 8130 false /* recordPeakUsage */, 8131 false /* recordPostGCusage */, 8132 true /* recordAccumulatedGCTime */, 8133 false /* recordGCEndTime */, 8134 false /* countCollection */ ); 8135 break; 8136 8137 case CMSCollector::FinalMarking: 8138 initialize(manager /* GC manager */ , 8139 cause /* cause of the GC */, 8140 false /* recordGCBeginTime */, 8141 false /* recordPreGCUsage */, 8142 false /* recordPeakUsage */, 8143 false /* recordPostGCusage */, 8144 true /* recordAccumulatedGCTime */, 8145 false /* recordGCEndTime */, 8146 false /* countCollection */ ); 8147 break; 8148 8149 case CMSCollector::Sweeping: 8150 initialize(manager /* GC manager */ , 8151 cause /* cause of the GC */, 8152 false /* recordGCBeginTime */, 8153 false /* recordPreGCUsage */, 8154 true /* recordPeakUsage */, 8155 true /* recordPostGCusage */, 8156 false /* recordAccumulatedGCTime */, 8157 true /* recordGCEndTime */, 8158 true /* countCollection */ ); 8159 break; 8160 8161 default: 8162 ShouldNotReachHere(); 8163 } 8164 }