1 /* 2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/classLoaderData.hpp" 27 #include "classfile/stringTable.hpp" 28 #include "classfile/symbolTable.hpp" 29 #include "classfile/systemDictionary.hpp" 30 #include "code/codeCache.hpp" 31 #include "gc/cms/cmsCollectorPolicy.hpp" 32 #include "gc/cms/cmsOopClosures.inline.hpp" 33 #include "gc/cms/compactibleFreeListSpace.hpp" 34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp" 35 #include "gc/cms/concurrentMarkSweepThread.hpp" 36 #include "gc/cms/parNewGeneration.hpp" 37 #include "gc/cms/vmCMSOperations.hpp" 38 #include "gc/serial/genMarkSweep.hpp" 39 #include "gc/serial/tenuredGeneration.hpp" 40 #include "gc/shared/adaptiveSizePolicy.hpp" 41 #include "gc/shared/cardGeneration.inline.hpp" 42 #include "gc/shared/cardTableRS.hpp" 43 #include "gc/shared/collectedHeap.inline.hpp" 44 #include "gc/shared/collectorCounters.hpp" 45 #include "gc/shared/collectorPolicy.hpp" 46 #include "gc/shared/gcLocker.inline.hpp" 47 #include "gc/shared/gcPolicyCounters.hpp" 48 #include "gc/shared/gcTimer.hpp" 49 #include "gc/shared/gcTrace.hpp" 50 #include "gc/shared/gcTraceTime.inline.hpp" 51 #include "gc/shared/genCollectedHeap.hpp" 52 #include "gc/shared/genOopClosures.inline.hpp" 53 #include "gc/shared/isGCActiveMark.hpp" 54 #include "gc/shared/referencePolicy.hpp" 55 #include "gc/shared/strongRootsScope.hpp" 56 #include "gc/shared/taskqueue.inline.hpp" 57 #include "logging/log.hpp" 58 #include "memory/allocation.hpp" 59 #include "memory/iterator.inline.hpp" 60 #include "memory/padded.hpp" 61 #include "memory/resourceArea.hpp" 62 #include "oops/oop.inline.hpp" 63 #include "prims/jvmtiExport.hpp" 64 #include "runtime/atomic.inline.hpp" 65 #include "runtime/globals_extension.hpp" 66 #include "runtime/handles.inline.hpp" 67 #include "runtime/java.hpp" 68 #include "runtime/orderAccess.inline.hpp" 69 #include "runtime/timer.hpp" 70 #include "runtime/vmThread.hpp" 71 #include "services/memoryService.hpp" 72 #include "services/runtimeService.hpp" 73 #include "utilities/stack.inline.hpp" 74 75 // statics 76 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; 77 bool CMSCollector::_full_gc_requested = false; 78 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc; 79 80 ////////////////////////////////////////////////////////////////// 81 // In support of CMS/VM thread synchronization 82 ////////////////////////////////////////////////////////////////// 83 // We split use of the CGC_lock into 2 "levels". 84 // The low-level locking is of the usual CGC_lock monitor. We introduce 85 // a higher level "token" (hereafter "CMS token") built on top of the 86 // low level monitor (hereafter "CGC lock"). 87 // The token-passing protocol gives priority to the VM thread. The 88 // CMS-lock doesn't provide any fairness guarantees, but clients 89 // should ensure that it is only held for very short, bounded 90 // durations. 91 // 92 // When either of the CMS thread or the VM thread is involved in 93 // collection operations during which it does not want the other 94 // thread to interfere, it obtains the CMS token. 95 // 96 // If either thread tries to get the token while the other has 97 // it, that thread waits. However, if the VM thread and CMS thread 98 // both want the token, then the VM thread gets priority while the 99 // CMS thread waits. This ensures, for instance, that the "concurrent" 100 // phases of the CMS thread's work do not block out the VM thread 101 // for long periods of time as the CMS thread continues to hog 102 // the token. (See bug 4616232). 103 // 104 // The baton-passing functions are, however, controlled by the 105 // flags _foregroundGCShouldWait and _foregroundGCIsActive, 106 // and here the low-level CMS lock, not the high level token, 107 // ensures mutual exclusion. 108 // 109 // Two important conditions that we have to satisfy: 110 // 1. if a thread does a low-level wait on the CMS lock, then it 111 // relinquishes the CMS token if it were holding that token 112 // when it acquired the low-level CMS lock. 113 // 2. any low-level notifications on the low-level lock 114 // should only be sent when a thread has relinquished the token. 115 // 116 // In the absence of either property, we'd have potential deadlock. 117 // 118 // We protect each of the CMS (concurrent and sequential) phases 119 // with the CMS _token_, not the CMS _lock_. 120 // 121 // The only code protected by CMS lock is the token acquisition code 122 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the 123 // baton-passing code. 124 // 125 // Unfortunately, i couldn't come up with a good abstraction to factor and 126 // hide the naked CGC_lock manipulation in the baton-passing code 127 // further below. That's something we should try to do. Also, the proof 128 // of correctness of this 2-level locking scheme is far from obvious, 129 // and potentially quite slippery. We have an uneasy suspicion, for instance, 130 // that there may be a theoretical possibility of delay/starvation in the 131 // low-level lock/wait/notify scheme used for the baton-passing because of 132 // potential interference with the priority scheme embodied in the 133 // CMS-token-passing protocol. See related comments at a CGC_lock->wait() 134 // invocation further below and marked with "XXX 20011219YSR". 135 // Indeed, as we note elsewhere, this may become yet more slippery 136 // in the presence of multiple CMS and/or multiple VM threads. XXX 137 138 class CMSTokenSync: public StackObj { 139 private: 140 bool _is_cms_thread; 141 public: 142 CMSTokenSync(bool is_cms_thread): 143 _is_cms_thread(is_cms_thread) { 144 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), 145 "Incorrect argument to constructor"); 146 ConcurrentMarkSweepThread::synchronize(_is_cms_thread); 147 } 148 149 ~CMSTokenSync() { 150 assert(_is_cms_thread ? 151 ConcurrentMarkSweepThread::cms_thread_has_cms_token() : 152 ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 153 "Incorrect state"); 154 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); 155 } 156 }; 157 158 // Convenience class that does a CMSTokenSync, and then acquires 159 // upto three locks. 160 class CMSTokenSyncWithLocks: public CMSTokenSync { 161 private: 162 // Note: locks are acquired in textual declaration order 163 // and released in the opposite order 164 MutexLockerEx _locker1, _locker2, _locker3; 165 public: 166 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, 167 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): 168 CMSTokenSync(is_cms_thread), 169 _locker1(mutex1, Mutex::_no_safepoint_check_flag), 170 _locker2(mutex2, Mutex::_no_safepoint_check_flag), 171 _locker3(mutex3, Mutex::_no_safepoint_check_flag) 172 { } 173 }; 174 175 176 ////////////////////////////////////////////////////////////////// 177 // Concurrent Mark-Sweep Generation ///////////////////////////// 178 ////////////////////////////////////////////////////////////////// 179 180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) 181 182 // This struct contains per-thread things necessary to support parallel 183 // young-gen collection. 184 class CMSParGCThreadState: public CHeapObj<mtGC> { 185 public: 186 CompactibleFreeListSpaceLAB lab; 187 PromotionInfo promo; 188 189 // Constructor. 190 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { 191 promo.setSpace(cfls); 192 } 193 }; 194 195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( 196 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) : 197 CardGeneration(rs, initial_byte_size, ct), 198 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), 199 _did_compact(false) 200 { 201 HeapWord* bottom = (HeapWord*) _virtual_space.low(); 202 HeapWord* end = (HeapWord*) _virtual_space.high(); 203 204 _direct_allocated_words = 0; 205 NOT_PRODUCT( 206 _numObjectsPromoted = 0; 207 _numWordsPromoted = 0; 208 _numObjectsAllocated = 0; 209 _numWordsAllocated = 0; 210 ) 211 212 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end)); 213 NOT_PRODUCT(debug_cms_space = _cmsSpace;) 214 _cmsSpace->_old_gen = this; 215 216 _gc_stats = new CMSGCStats(); 217 218 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass 219 // offsets match. The ability to tell free chunks from objects 220 // depends on this property. 221 debug_only( 222 FreeChunk* junk = NULL; 223 assert(UseCompressedClassPointers || 224 junk->prev_addr() == (void*)(oop(junk)->klass_addr()), 225 "Offset of FreeChunk::_prev within FreeChunk must match" 226 " that of OopDesc::_klass within OopDesc"); 227 ) 228 229 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC); 230 for (uint i = 0; i < ParallelGCThreads; i++) { 231 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); 232 } 233 234 _incremental_collection_failed = false; 235 // The "dilatation_factor" is the expansion that can occur on 236 // account of the fact that the minimum object size in the CMS 237 // generation may be larger than that in, say, a contiguous young 238 // generation. 239 // Ideally, in the calculation below, we'd compute the dilatation 240 // factor as: MinChunkSize/(promoting_gen's min object size) 241 // Since we do not have such a general query interface for the 242 // promoting generation, we'll instead just use the minimum 243 // object size (which today is a header's worth of space); 244 // note that all arithmetic is in units of HeapWords. 245 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking"); 246 assert(_dilatation_factor >= 1.0, "from previous assert"); 247 } 248 249 250 // The field "_initiating_occupancy" represents the occupancy percentage 251 // at which we trigger a new collection cycle. Unless explicitly specified 252 // via CMSInitiatingOccupancyFraction (argument "io" below), it 253 // is calculated by: 254 // 255 // Let "f" be MinHeapFreeRatio in 256 // 257 // _initiating_occupancy = 100-f + 258 // f * (CMSTriggerRatio/100) 259 // where CMSTriggerRatio is the argument "tr" below. 260 // 261 // That is, if we assume the heap is at its desired maximum occupancy at the 262 // end of a collection, we let CMSTriggerRatio of the (purported) free 263 // space be allocated before initiating a new collection cycle. 264 // 265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) { 266 assert(io <= 100 && tr <= 100, "Check the arguments"); 267 if (io >= 0) { 268 _initiating_occupancy = (double)io / 100.0; 269 } else { 270 _initiating_occupancy = ((100 - MinHeapFreeRatio) + 271 (double)(tr * MinHeapFreeRatio) / 100.0) 272 / 100.0; 273 } 274 } 275 276 void ConcurrentMarkSweepGeneration::ref_processor_init() { 277 assert(collector() != NULL, "no collector"); 278 collector()->ref_processor_init(); 279 } 280 281 void CMSCollector::ref_processor_init() { 282 if (_ref_processor == NULL) { 283 // Allocate and initialize a reference processor 284 _ref_processor = 285 new ReferenceProcessor(_span, // span 286 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing 287 ParallelGCThreads, // mt processing degree 288 _cmsGen->refs_discovery_is_mt(), // mt discovery 289 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree 290 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic 291 &_is_alive_closure); // closure for liveness info 292 // Initialize the _ref_processor field of CMSGen 293 _cmsGen->set_ref_processor(_ref_processor); 294 295 } 296 } 297 298 AdaptiveSizePolicy* CMSCollector::size_policy() { 299 GenCollectedHeap* gch = GenCollectedHeap::heap(); 300 return gch->gen_policy()->size_policy(); 301 } 302 303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() { 304 305 const char* gen_name = "old"; 306 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy(); 307 // Generation Counters - generation 1, 1 subspace 308 _gen_counters = new GenerationCounters(gen_name, 1, 1, 309 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space); 310 311 _space_counters = new GSpaceCounters(gen_name, 0, 312 _virtual_space.reserved_size(), 313 this, _gen_counters); 314 } 315 316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): 317 _cms_gen(cms_gen) 318 { 319 assert(alpha <= 100, "bad value"); 320 _saved_alpha = alpha; 321 322 // Initialize the alphas to the bootstrap value of 100. 323 _gc0_alpha = _cms_alpha = 100; 324 325 _cms_begin_time.update(); 326 _cms_end_time.update(); 327 328 _gc0_duration = 0.0; 329 _gc0_period = 0.0; 330 _gc0_promoted = 0; 331 332 _cms_duration = 0.0; 333 _cms_period = 0.0; 334 _cms_allocated = 0; 335 336 _cms_used_at_gc0_begin = 0; 337 _cms_used_at_gc0_end = 0; 338 _allow_duty_cycle_reduction = false; 339 _valid_bits = 0; 340 } 341 342 double CMSStats::cms_free_adjustment_factor(size_t free) const { 343 // TBD: CR 6909490 344 return 1.0; 345 } 346 347 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) { 348 } 349 350 // If promotion failure handling is on use 351 // the padded average size of the promotion for each 352 // young generation collection. 353 double CMSStats::time_until_cms_gen_full() const { 354 size_t cms_free = _cms_gen->cmsSpace()->free(); 355 GenCollectedHeap* gch = GenCollectedHeap::heap(); 356 size_t expected_promotion = MIN2(gch->young_gen()->capacity(), 357 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average()); 358 if (cms_free > expected_promotion) { 359 // Start a cms collection if there isn't enough space to promote 360 // for the next young collection. Use the padded average as 361 // a safety factor. 362 cms_free -= expected_promotion; 363 364 // Adjust by the safety factor. 365 double cms_free_dbl = (double)cms_free; 366 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0; 367 // Apply a further correction factor which tries to adjust 368 // for recent occurance of concurrent mode failures. 369 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free); 370 cms_free_dbl = cms_free_dbl * cms_adjustment; 371 372 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT, 373 cms_free, expected_promotion); 374 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0); 375 // Add 1 in case the consumption rate goes to zero. 376 return cms_free_dbl / (cms_consumption_rate() + 1.0); 377 } 378 return 0.0; 379 } 380 381 // Compare the duration of the cms collection to the 382 // time remaining before the cms generation is empty. 383 // Note that the time from the start of the cms collection 384 // to the start of the cms sweep (less than the total 385 // duration of the cms collection) can be used. This 386 // has been tried and some applications experienced 387 // promotion failures early in execution. This was 388 // possibly because the averages were not accurate 389 // enough at the beginning. 390 double CMSStats::time_until_cms_start() const { 391 // We add "gc0_period" to the "work" calculation 392 // below because this query is done (mostly) at the 393 // end of a scavenge, so we need to conservatively 394 // account for that much possible delay 395 // in the query so as to avoid concurrent mode failures 396 // due to starting the collection just a wee bit too 397 // late. 398 double work = cms_duration() + gc0_period(); 399 double deadline = time_until_cms_gen_full(); 400 // If a concurrent mode failure occurred recently, we want to be 401 // more conservative and halve our expected time_until_cms_gen_full() 402 if (work > deadline) { 403 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ", 404 cms_duration(), gc0_period(), time_until_cms_gen_full()); 405 return 0.0; 406 } 407 return work - deadline; 408 } 409 410 #ifndef PRODUCT 411 void CMSStats::print_on(outputStream *st) const { 412 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); 413 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT, 414 gc0_duration(), gc0_period(), gc0_promoted()); 415 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, 416 cms_duration(), cms_period(), cms_allocated()); 417 st->print(",cms_since_beg=%g,cms_since_end=%g", 418 cms_time_since_begin(), cms_time_since_end()); 419 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT, 420 _cms_used_at_gc0_begin, _cms_used_at_gc0_end); 421 422 if (valid()) { 423 st->print(",promo_rate=%g,cms_alloc_rate=%g", 424 promotion_rate(), cms_allocation_rate()); 425 st->print(",cms_consumption_rate=%g,time_until_full=%g", 426 cms_consumption_rate(), time_until_cms_gen_full()); 427 } 428 st->cr(); 429 } 430 #endif // #ifndef PRODUCT 431 432 CMSCollector::CollectorState CMSCollector::_collectorState = 433 CMSCollector::Idling; 434 bool CMSCollector::_foregroundGCIsActive = false; 435 bool CMSCollector::_foregroundGCShouldWait = false; 436 437 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, 438 CardTableRS* ct, 439 ConcurrentMarkSweepPolicy* cp): 440 _cmsGen(cmsGen), 441 _ct(ct), 442 _ref_processor(NULL), // will be set later 443 _conc_workers(NULL), // may be set later 444 _abort_preclean(false), 445 _start_sampling(false), 446 _between_prologue_and_epilogue(false), 447 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), 448 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize), 449 -1 /* lock-free */, "No_lock" /* dummy */), 450 _modUnionClosurePar(&_modUnionTable), 451 // Adjust my span to cover old (cms) gen 452 _span(cmsGen->reserved()), 453 // Construct the is_alive_closure with _span & markBitMap 454 _is_alive_closure(_span, &_markBitMap), 455 _restart_addr(NULL), 456 _overflow_list(NULL), 457 _stats(cmsGen), 458 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true, 459 //verify that this lock should be acquired with safepoint check. 460 Monitor::_safepoint_check_sometimes)), 461 _eden_chunk_array(NULL), // may be set in ctor body 462 _eden_chunk_capacity(0), // -- ditto -- 463 _eden_chunk_index(0), // -- ditto -- 464 _survivor_plab_array(NULL), // -- ditto -- 465 _survivor_chunk_array(NULL), // -- ditto -- 466 _survivor_chunk_capacity(0), // -- ditto -- 467 _survivor_chunk_index(0), // -- ditto -- 468 _ser_pmc_preclean_ovflw(0), 469 _ser_kac_preclean_ovflw(0), 470 _ser_pmc_remark_ovflw(0), 471 _par_pmc_remark_ovflw(0), 472 _ser_kac_ovflw(0), 473 _par_kac_ovflw(0), 474 #ifndef PRODUCT 475 _num_par_pushes(0), 476 #endif 477 _collection_count_start(0), 478 _verifying(false), 479 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), 480 _completed_initialization(false), 481 _collector_policy(cp), 482 _should_unload_classes(CMSClassUnloadingEnabled), 483 _concurrent_cycles_since_last_unload(0), 484 _roots_scanning_options(GenCollectedHeap::SO_None), 485 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), 486 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), 487 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()), 488 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()), 489 _cms_start_registered(false) 490 { 491 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) { 492 ExplicitGCInvokesConcurrent = true; 493 } 494 // Now expand the span and allocate the collection support structures 495 // (MUT, marking bit map etc.) to cover both generations subject to 496 // collection. 497 498 // For use by dirty card to oop closures. 499 _cmsGen->cmsSpace()->set_collector(this); 500 501 // Allocate MUT and marking bit map 502 { 503 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); 504 if (!_markBitMap.allocate(_span)) { 505 log_warning(gc)("Failed to allocate CMS Bit Map"); 506 return; 507 } 508 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); 509 } 510 { 511 _modUnionTable.allocate(_span); 512 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); 513 } 514 515 if (!_markStack.allocate(MarkStackSize)) { 516 log_warning(gc)("Failed to allocate CMS Marking Stack"); 517 return; 518 } 519 520 // Support for multi-threaded concurrent phases 521 if (CMSConcurrentMTEnabled) { 522 if (FLAG_IS_DEFAULT(ConcGCThreads)) { 523 // just for now 524 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4); 525 } 526 if (ConcGCThreads > 1) { 527 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread", 528 ConcGCThreads, true); 529 if (_conc_workers == NULL) { 530 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled"); 531 CMSConcurrentMTEnabled = false; 532 } else { 533 _conc_workers->initialize_workers(); 534 } 535 } else { 536 CMSConcurrentMTEnabled = false; 537 } 538 } 539 if (!CMSConcurrentMTEnabled) { 540 ConcGCThreads = 0; 541 } else { 542 // Turn off CMSCleanOnEnter optimization temporarily for 543 // the MT case where it's not fixed yet; see 6178663. 544 CMSCleanOnEnter = false; 545 } 546 assert((_conc_workers != NULL) == (ConcGCThreads > 1), 547 "Inconsistency"); 548 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads); 549 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads); 550 551 // Parallel task queues; these are shared for the 552 // concurrent and stop-world phases of CMS, but 553 // are not shared with parallel scavenge (ParNew). 554 { 555 uint i; 556 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads); 557 558 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled 559 || ParallelRefProcEnabled) 560 && num_queues > 0) { 561 _task_queues = new OopTaskQueueSet(num_queues); 562 if (_task_queues == NULL) { 563 log_warning(gc)("task_queues allocation failure."); 564 return; 565 } 566 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC); 567 typedef Padded<OopTaskQueue> PaddedOopTaskQueue; 568 for (i = 0; i < num_queues; i++) { 569 PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); 570 if (q == NULL) { 571 log_warning(gc)("work_queue allocation failure."); 572 return; 573 } 574 _task_queues->register_queue(i, q); 575 } 576 for (i = 0; i < num_queues; i++) { 577 _task_queues->queue(i)->initialize(); 578 _hash_seed[i] = 17; // copied from ParNew 579 } 580 } 581 } 582 583 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); 584 585 // Clip CMSBootstrapOccupancy between 0 and 100. 586 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0; 587 588 // Now tell CMS generations the identity of their collector 589 ConcurrentMarkSweepGeneration::set_collector(this); 590 591 // Create & start a CMS thread for this CMS collector 592 _cmsThread = ConcurrentMarkSweepThread::start(this); 593 assert(cmsThread() != NULL, "CMS Thread should have been created"); 594 assert(cmsThread()->collector() == this, 595 "CMS Thread should refer to this gen"); 596 assert(CGC_lock != NULL, "Where's the CGC_lock?"); 597 598 // Support for parallelizing young gen rescan 599 GenCollectedHeap* gch = GenCollectedHeap::heap(); 600 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew"); 601 _young_gen = (ParNewGeneration*)gch->young_gen(); 602 if (gch->supports_inline_contig_alloc()) { 603 _top_addr = gch->top_addr(); 604 _end_addr = gch->end_addr(); 605 assert(_young_gen != NULL, "no _young_gen"); 606 _eden_chunk_index = 0; 607 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain; 608 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC); 609 } 610 611 // Support for parallelizing survivor space rescan 612 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) { 613 const size_t max_plab_samples = 614 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize); 615 616 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC); 617 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); 618 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC); 619 _survivor_chunk_capacity = max_plab_samples; 620 for (uint i = 0; i < ParallelGCThreads; i++) { 621 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); 622 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples); 623 assert(cur->end() == 0, "Should be 0"); 624 assert(cur->array() == vec, "Should be vec"); 625 assert(cur->capacity() == max_plab_samples, "Error"); 626 } 627 } 628 629 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) 630 _gc_counters = new CollectorCounters("CMS", 1); 631 _completed_initialization = true; 632 _inter_sweep_timer.start(); // start of time 633 } 634 635 const char* ConcurrentMarkSweepGeneration::name() const { 636 return "concurrent mark-sweep generation"; 637 } 638 void ConcurrentMarkSweepGeneration::update_counters() { 639 if (UsePerfData) { 640 _space_counters->update_all(); 641 _gen_counters->update_all(); 642 } 643 } 644 645 // this is an optimized version of update_counters(). it takes the 646 // used value as a parameter rather than computing it. 647 // 648 void ConcurrentMarkSweepGeneration::update_counters(size_t used) { 649 if (UsePerfData) { 650 _space_counters->update_used(used); 651 _space_counters->update_capacity(); 652 _gen_counters->update_all(); 653 } 654 } 655 656 void ConcurrentMarkSweepGeneration::print() const { 657 Generation::print(); 658 cmsSpace()->print(); 659 } 660 661 #ifndef PRODUCT 662 void ConcurrentMarkSweepGeneration::print_statistics() { 663 cmsSpace()->printFLCensus(0); 664 } 665 #endif 666 667 size_t 668 ConcurrentMarkSweepGeneration::contiguous_available() const { 669 // dld proposes an improvement in precision here. If the committed 670 // part of the space ends in a free block we should add that to 671 // uncommitted size in the calculation below. Will make this 672 // change later, staying with the approximation below for the 673 // time being. -- ysr. 674 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); 675 } 676 677 size_t 678 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { 679 return _cmsSpace->max_alloc_in_words() * HeapWordSize; 680 } 681 682 size_t ConcurrentMarkSweepGeneration::max_available() const { 683 return free() + _virtual_space.uncommitted_size(); 684 } 685 686 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const { 687 size_t available = max_available(); 688 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average(); 689 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes); 690 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")", 691 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes); 692 return res; 693 } 694 695 // At a promotion failure dump information on block layout in heap 696 // (cms old generation). 697 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() { 698 Log(gc, promotion) log; 699 if (log.is_trace()) { 700 ResourceMark rm; 701 cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream()); 702 } 703 } 704 705 void ConcurrentMarkSweepGeneration::reset_after_compaction() { 706 // Clear the promotion information. These pointers can be adjusted 707 // along with all the other pointers into the heap but 708 // compaction is expected to be a rare event with 709 // a heap using cms so don't do it without seeing the need. 710 for (uint i = 0; i < ParallelGCThreads; i++) { 711 _par_gc_thread_states[i]->promo.reset(); 712 } 713 } 714 715 void ConcurrentMarkSweepGeneration::compute_new_size() { 716 assert_locked_or_safepoint(Heap_lock); 717 718 // If incremental collection failed, we just want to expand 719 // to the limit. 720 if (incremental_collection_failed()) { 721 clear_incremental_collection_failed(); 722 grow_to_reserved(); 723 return; 724 } 725 726 // The heap has been compacted but not reset yet. 727 // Any metric such as free() or used() will be incorrect. 728 729 CardGeneration::compute_new_size(); 730 731 // Reset again after a possible resizing 732 if (did_compact()) { 733 cmsSpace()->reset_after_compaction(); 734 } 735 } 736 737 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() { 738 assert_locked_or_safepoint(Heap_lock); 739 740 // If incremental collection failed, we just want to expand 741 // to the limit. 742 if (incremental_collection_failed()) { 743 clear_incremental_collection_failed(); 744 grow_to_reserved(); 745 return; 746 } 747 748 double free_percentage = ((double) free()) / capacity(); 749 double desired_free_percentage = (double) MinHeapFreeRatio / 100; 750 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; 751 752 // compute expansion delta needed for reaching desired free percentage 753 if (free_percentage < desired_free_percentage) { 754 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 755 assert(desired_capacity >= capacity(), "invalid expansion size"); 756 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); 757 Log(gc) log; 758 if (log.is_trace()) { 759 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 760 log.trace("From compute_new_size: "); 761 log.trace(" Free fraction %f", free_percentage); 762 log.trace(" Desired free fraction %f", desired_free_percentage); 763 log.trace(" Maximum free fraction %f", maximum_free_percentage); 764 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000); 765 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000); 766 GenCollectedHeap* gch = GenCollectedHeap::heap(); 767 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation"); 768 size_t young_size = gch->young_gen()->capacity(); 769 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000); 770 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000); 771 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000); 772 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes); 773 } 774 // safe if expansion fails 775 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); 776 log.trace(" Expanded free fraction %f", ((double) free()) / capacity()); 777 } else { 778 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 779 assert(desired_capacity <= capacity(), "invalid expansion size"); 780 size_t shrink_bytes = capacity() - desired_capacity; 781 // Don't shrink unless the delta is greater than the minimum shrink we want 782 if (shrink_bytes >= MinHeapDeltaBytes) { 783 shrink_free_list_by(shrink_bytes); 784 } 785 } 786 } 787 788 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { 789 return cmsSpace()->freelistLock(); 790 } 791 792 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) { 793 CMSSynchronousYieldRequest yr; 794 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 795 return have_lock_and_allocate(size, tlab); 796 } 797 798 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, 799 bool tlab /* ignored */) { 800 assert_lock_strong(freelistLock()); 801 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); 802 HeapWord* res = cmsSpace()->allocate(adjustedSize); 803 // Allocate the object live (grey) if the background collector has 804 // started marking. This is necessary because the marker may 805 // have passed this address and consequently this object will 806 // not otherwise be greyed and would be incorrectly swept up. 807 // Note that if this object contains references, the writing 808 // of those references will dirty the card containing this object 809 // allowing the object to be blackened (and its references scanned) 810 // either during a preclean phase or at the final checkpoint. 811 if (res != NULL) { 812 // We may block here with an uninitialized object with 813 // its mark-bit or P-bits not yet set. Such objects need 814 // to be safely navigable by block_start(). 815 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here."); 816 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size"); 817 collector()->direct_allocated(res, adjustedSize); 818 _direct_allocated_words += adjustedSize; 819 // allocation counters 820 NOT_PRODUCT( 821 _numObjectsAllocated++; 822 _numWordsAllocated += (int)adjustedSize; 823 ) 824 } 825 return res; 826 } 827 828 // In the case of direct allocation by mutators in a generation that 829 // is being concurrently collected, the object must be allocated 830 // live (grey) if the background collector has started marking. 831 // This is necessary because the marker may 832 // have passed this address and consequently this object will 833 // not otherwise be greyed and would be incorrectly swept up. 834 // Note that if this object contains references, the writing 835 // of those references will dirty the card containing this object 836 // allowing the object to be blackened (and its references scanned) 837 // either during a preclean phase or at the final checkpoint. 838 void CMSCollector::direct_allocated(HeapWord* start, size_t size) { 839 assert(_markBitMap.covers(start, size), "Out of bounds"); 840 if (_collectorState >= Marking) { 841 MutexLockerEx y(_markBitMap.lock(), 842 Mutex::_no_safepoint_check_flag); 843 // [see comments preceding SweepClosure::do_blk() below for details] 844 // 845 // Can the P-bits be deleted now? JJJ 846 // 847 // 1. need to mark the object as live so it isn't collected 848 // 2. need to mark the 2nd bit to indicate the object may be uninitialized 849 // 3. need to mark the end of the object so marking, precleaning or sweeping 850 // can skip over uninitialized or unparsable objects. An allocated 851 // object is considered uninitialized for our purposes as long as 852 // its klass word is NULL. All old gen objects are parsable 853 // as soon as they are initialized.) 854 _markBitMap.mark(start); // object is live 855 _markBitMap.mark(start + 1); // object is potentially uninitialized? 856 _markBitMap.mark(start + size - 1); 857 // mark end of object 858 } 859 // check that oop looks uninitialized 860 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL"); 861 } 862 863 void CMSCollector::promoted(bool par, HeapWord* start, 864 bool is_obj_array, size_t obj_size) { 865 assert(_markBitMap.covers(start), "Out of bounds"); 866 // See comment in direct_allocated() about when objects should 867 // be allocated live. 868 if (_collectorState >= Marking) { 869 // we already hold the marking bit map lock, taken in 870 // the prologue 871 if (par) { 872 _markBitMap.par_mark(start); 873 } else { 874 _markBitMap.mark(start); 875 } 876 // We don't need to mark the object as uninitialized (as 877 // in direct_allocated above) because this is being done with the 878 // world stopped and the object will be initialized by the 879 // time the marking, precleaning or sweeping get to look at it. 880 // But see the code for copying objects into the CMS generation, 881 // where we need to ensure that concurrent readers of the 882 // block offset table are able to safely navigate a block that 883 // is in flux from being free to being allocated (and in 884 // transition while being copied into) and subsequently 885 // becoming a bona-fide object when the copy/promotion is complete. 886 assert(SafepointSynchronize::is_at_safepoint(), 887 "expect promotion only at safepoints"); 888 889 if (_collectorState < Sweeping) { 890 // Mark the appropriate cards in the modUnionTable, so that 891 // this object gets scanned before the sweep. If this is 892 // not done, CMS generation references in the object might 893 // not get marked. 894 // For the case of arrays, which are otherwise precisely 895 // marked, we need to dirty the entire array, not just its head. 896 if (is_obj_array) { 897 // The [par_]mark_range() method expects mr.end() below to 898 // be aligned to the granularity of a bit's representation 899 // in the heap. In the case of the MUT below, that's a 900 // card size. 901 MemRegion mr(start, 902 (HeapWord*)round_to((intptr_t)(start + obj_size), 903 CardTableModRefBS::card_size /* bytes */)); 904 if (par) { 905 _modUnionTable.par_mark_range(mr); 906 } else { 907 _modUnionTable.mark_range(mr); 908 } 909 } else { // not an obj array; we can just mark the head 910 if (par) { 911 _modUnionTable.par_mark(start); 912 } else { 913 _modUnionTable.mark(start); 914 } 915 } 916 } 917 } 918 } 919 920 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) { 921 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); 922 // allocate, copy and if necessary update promoinfo -- 923 // delegate to underlying space. 924 assert_lock_strong(freelistLock()); 925 926 #ifndef PRODUCT 927 if (GenCollectedHeap::heap()->promotion_should_fail()) { 928 return NULL; 929 } 930 #endif // #ifndef PRODUCT 931 932 oop res = _cmsSpace->promote(obj, obj_size); 933 if (res == NULL) { 934 // expand and retry 935 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords 936 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion); 937 // Since this is the old generation, we don't try to promote 938 // into a more senior generation. 939 res = _cmsSpace->promote(obj, obj_size); 940 } 941 if (res != NULL) { 942 // See comment in allocate() about when objects should 943 // be allocated live. 944 assert(obj->is_oop(), "Will dereference klass pointer below"); 945 collector()->promoted(false, // Not parallel 946 (HeapWord*)res, obj->is_objArray(), obj_size); 947 // promotion counters 948 NOT_PRODUCT( 949 _numObjectsPromoted++; 950 _numWordsPromoted += 951 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); 952 ) 953 } 954 return res; 955 } 956 957 958 // IMPORTANT: Notes on object size recognition in CMS. 959 // --------------------------------------------------- 960 // A block of storage in the CMS generation is always in 961 // one of three states. A free block (FREE), an allocated 962 // object (OBJECT) whose size() method reports the correct size, 963 // and an intermediate state (TRANSIENT) in which its size cannot 964 // be accurately determined. 965 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS) 966 // ----------------------------------------------------- 967 // FREE: klass_word & 1 == 1; mark_word holds block size 968 // 969 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0; 970 // obj->size() computes correct size 971 // 972 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT 973 // 974 // STATE IDENTIFICATION: (64 bit+COOPS) 975 // ------------------------------------ 976 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size 977 // 978 // OBJECT: klass_word installed; klass_word != 0; 979 // obj->size() computes correct size 980 // 981 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT 982 // 983 // 984 // STATE TRANSITION DIAGRAM 985 // 986 // mut / parnew mut / parnew 987 // FREE --------------------> TRANSIENT ---------------------> OBJECT --| 988 // ^ | 989 // |------------------------ DEAD <------------------------------------| 990 // sweep mut 991 // 992 // While a block is in TRANSIENT state its size cannot be determined 993 // so readers will either need to come back later or stall until 994 // the size can be determined. Note that for the case of direct 995 // allocation, P-bits, when available, may be used to determine the 996 // size of an object that may not yet have been initialized. 997 998 // Things to support parallel young-gen collection. 999 oop 1000 ConcurrentMarkSweepGeneration::par_promote(int thread_num, 1001 oop old, markOop m, 1002 size_t word_sz) { 1003 #ifndef PRODUCT 1004 if (GenCollectedHeap::heap()->promotion_should_fail()) { 1005 return NULL; 1006 } 1007 #endif // #ifndef PRODUCT 1008 1009 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1010 PromotionInfo* promoInfo = &ps->promo; 1011 // if we are tracking promotions, then first ensure space for 1012 // promotion (including spooling space for saving header if necessary). 1013 // then allocate and copy, then track promoted info if needed. 1014 // When tracking (see PromotionInfo::track()), the mark word may 1015 // be displaced and in this case restoration of the mark word 1016 // occurs in the (oop_since_save_marks_)iterate phase. 1017 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { 1018 // Out of space for allocating spooling buffers; 1019 // try expanding and allocating spooling buffers. 1020 if (!expand_and_ensure_spooling_space(promoInfo)) { 1021 return NULL; 1022 } 1023 } 1024 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant"); 1025 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz); 1026 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz); 1027 if (obj_ptr == NULL) { 1028 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz); 1029 if (obj_ptr == NULL) { 1030 return NULL; 1031 } 1032 } 1033 oop obj = oop(obj_ptr); 1034 OrderAccess::storestore(); 1035 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1036 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1037 // IMPORTANT: See note on object initialization for CMS above. 1038 // Otherwise, copy the object. Here we must be careful to insert the 1039 // klass pointer last, since this marks the block as an allocated object. 1040 // Except with compressed oops it's the mark word. 1041 HeapWord* old_ptr = (HeapWord*)old; 1042 // Restore the mark word copied above. 1043 obj->set_mark(m); 1044 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1045 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1046 OrderAccess::storestore(); 1047 1048 if (UseCompressedClassPointers) { 1049 // Copy gap missed by (aligned) header size calculation below 1050 obj->set_klass_gap(old->klass_gap()); 1051 } 1052 if (word_sz > (size_t)oopDesc::header_size()) { 1053 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), 1054 obj_ptr + oopDesc::header_size(), 1055 word_sz - oopDesc::header_size()); 1056 } 1057 1058 // Now we can track the promoted object, if necessary. We take care 1059 // to delay the transition from uninitialized to full object 1060 // (i.e., insertion of klass pointer) until after, so that it 1061 // atomically becomes a promoted object. 1062 if (promoInfo->tracking()) { 1063 promoInfo->track((PromotedObject*)obj, old->klass()); 1064 } 1065 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1066 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1067 assert(old->is_oop(), "Will use and dereference old klass ptr below"); 1068 1069 // Finally, install the klass pointer (this should be volatile). 1070 OrderAccess::storestore(); 1071 obj->set_klass(old->klass()); 1072 // We should now be able to calculate the right size for this object 1073 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object"); 1074 1075 collector()->promoted(true, // parallel 1076 obj_ptr, old->is_objArray(), word_sz); 1077 1078 NOT_PRODUCT( 1079 Atomic::inc_ptr(&_numObjectsPromoted); 1080 Atomic::add_ptr(alloc_sz, &_numWordsPromoted); 1081 ) 1082 1083 return obj; 1084 } 1085 1086 void 1087 ConcurrentMarkSweepGeneration:: 1088 par_promote_alloc_done(int thread_num) { 1089 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1090 ps->lab.retire(thread_num); 1091 } 1092 1093 void 1094 ConcurrentMarkSweepGeneration:: 1095 par_oop_since_save_marks_iterate_done(int thread_num) { 1096 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1097 ParScanWithoutBarrierClosure* dummy_cl = NULL; 1098 ps->promo.promoted_oops_iterate_nv(dummy_cl); 1099 1100 // Because card-scanning has been completed, subsequent phases 1101 // (e.g., reference processing) will not need to recognize which 1102 // objects have been promoted during this GC. So, we can now disable 1103 // promotion tracking. 1104 ps->promo.stopTrackingPromotions(); 1105 } 1106 1107 bool ConcurrentMarkSweepGeneration::should_collect(bool full, 1108 size_t size, 1109 bool tlab) 1110 { 1111 // We allow a STW collection only if a full 1112 // collection was requested. 1113 return full || should_allocate(size, tlab); // FIX ME !!! 1114 // This and promotion failure handling are connected at the 1115 // hip and should be fixed by untying them. 1116 } 1117 1118 bool CMSCollector::shouldConcurrentCollect() { 1119 LogTarget(Trace, gc) log; 1120 1121 if (_full_gc_requested) { 1122 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)"); 1123 return true; 1124 } 1125 1126 FreelistLocker x(this); 1127 // ------------------------------------------------------------------ 1128 // Print out lots of information which affects the initiation of 1129 // a collection. 1130 if (log.is_enabled() && stats().valid()) { 1131 log.print("CMSCollector shouldConcurrentCollect: "); 1132 1133 LogStream out(log); 1134 stats().print_on(&out); 1135 1136 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full()); 1137 log.print("free=" SIZE_FORMAT, _cmsGen->free()); 1138 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available()); 1139 log.print("promotion_rate=%g", stats().promotion_rate()); 1140 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate()); 1141 log.print("occupancy=%3.7f", _cmsGen->occupancy()); 1142 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); 1143 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin()); 1144 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end()); 1145 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect()); 1146 } 1147 // ------------------------------------------------------------------ 1148 1149 // If the estimated time to complete a cms collection (cms_duration()) 1150 // is less than the estimated time remaining until the cms generation 1151 // is full, start a collection. 1152 if (!UseCMSInitiatingOccupancyOnly) { 1153 if (stats().valid()) { 1154 if (stats().time_until_cms_start() == 0.0) { 1155 return true; 1156 } 1157 } else { 1158 // We want to conservatively collect somewhat early in order 1159 // to try and "bootstrap" our CMS/promotion statistics; 1160 // this branch will not fire after the first successful CMS 1161 // collection because the stats should then be valid. 1162 if (_cmsGen->occupancy() >= _bootstrap_occupancy) { 1163 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f", 1164 _cmsGen->occupancy(), _bootstrap_occupancy); 1165 return true; 1166 } 1167 } 1168 } 1169 1170 // Otherwise, we start a collection cycle if 1171 // old gen want a collection cycle started. Each may use 1172 // an appropriate criterion for making this decision. 1173 // XXX We need to make sure that the gen expansion 1174 // criterion dovetails well with this. XXX NEED TO FIX THIS 1175 if (_cmsGen->should_concurrent_collect()) { 1176 log.print("CMS old gen initiated"); 1177 return true; 1178 } 1179 1180 // We start a collection if we believe an incremental collection may fail; 1181 // this is not likely to be productive in practice because it's probably too 1182 // late anyway. 1183 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1184 assert(gch->collector_policy()->is_generation_policy(), 1185 "You may want to check the correctness of the following"); 1186 if (gch->incremental_collection_will_fail(true /* consult_young */)) { 1187 log.print("CMSCollector: collect because incremental collection will fail "); 1188 return true; 1189 } 1190 1191 if (MetaspaceGC::should_concurrent_collect()) { 1192 log.print("CMSCollector: collect for metadata allocation "); 1193 return true; 1194 } 1195 1196 // CMSTriggerInterval starts a CMS cycle if enough time has passed. 1197 if (CMSTriggerInterval >= 0) { 1198 if (CMSTriggerInterval == 0) { 1199 // Trigger always 1200 return true; 1201 } 1202 1203 // Check the CMS time since begin (we do not check the stats validity 1204 // as we want to be able to trigger the first CMS cycle as well) 1205 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) { 1206 if (stats().valid()) { 1207 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)", 1208 stats().cms_time_since_begin()); 1209 } else { 1210 log.print("CMSCollector: collect because of trigger interval (first collection)"); 1211 } 1212 return true; 1213 } 1214 } 1215 1216 return false; 1217 } 1218 1219 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); } 1220 1221 // Clear _expansion_cause fields of constituent generations 1222 void CMSCollector::clear_expansion_cause() { 1223 _cmsGen->clear_expansion_cause(); 1224 } 1225 1226 // We should be conservative in starting a collection cycle. To 1227 // start too eagerly runs the risk of collecting too often in the 1228 // extreme. To collect too rarely falls back on full collections, 1229 // which works, even if not optimum in terms of concurrent work. 1230 // As a work around for too eagerly collecting, use the flag 1231 // UseCMSInitiatingOccupancyOnly. This also has the advantage of 1232 // giving the user an easily understandable way of controlling the 1233 // collections. 1234 // We want to start a new collection cycle if any of the following 1235 // conditions hold: 1236 // . our current occupancy exceeds the configured initiating occupancy 1237 // for this generation, or 1238 // . we recently needed to expand this space and have not, since that 1239 // expansion, done a collection of this generation, or 1240 // . the underlying space believes that it may be a good idea to initiate 1241 // a concurrent collection (this may be based on criteria such as the 1242 // following: the space uses linear allocation and linear allocation is 1243 // going to fail, or there is believed to be excessive fragmentation in 1244 // the generation, etc... or ... 1245 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for 1246 // the case of the old generation; see CR 6543076): 1247 // we may be approaching a point at which allocation requests may fail because 1248 // we will be out of sufficient free space given allocation rate estimates.] 1249 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const { 1250 1251 assert_lock_strong(freelistLock()); 1252 if (occupancy() > initiating_occupancy()) { 1253 log_trace(gc)(" %s: collect because of occupancy %f / %f ", 1254 short_name(), occupancy(), initiating_occupancy()); 1255 return true; 1256 } 1257 if (UseCMSInitiatingOccupancyOnly) { 1258 return false; 1259 } 1260 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { 1261 log_trace(gc)(" %s: collect because expanded for allocation ", short_name()); 1262 return true; 1263 } 1264 return false; 1265 } 1266 1267 void ConcurrentMarkSweepGeneration::collect(bool full, 1268 bool clear_all_soft_refs, 1269 size_t size, 1270 bool tlab) 1271 { 1272 collector()->collect(full, clear_all_soft_refs, size, tlab); 1273 } 1274 1275 void CMSCollector::collect(bool full, 1276 bool clear_all_soft_refs, 1277 size_t size, 1278 bool tlab) 1279 { 1280 // The following "if" branch is present for defensive reasons. 1281 // In the current uses of this interface, it can be replaced with: 1282 // assert(!GCLocker.is_active(), "Can't be called otherwise"); 1283 // But I am not placing that assert here to allow future 1284 // generality in invoking this interface. 1285 if (GCLocker::is_active()) { 1286 // A consistency test for GCLocker 1287 assert(GCLocker::needs_gc(), "Should have been set already"); 1288 // Skip this foreground collection, instead 1289 // expanding the heap if necessary. 1290 // Need the free list locks for the call to free() in compute_new_size() 1291 compute_new_size(); 1292 return; 1293 } 1294 acquire_control_and_collect(full, clear_all_soft_refs); 1295 } 1296 1297 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) { 1298 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1299 unsigned int gc_count = gch->total_full_collections(); 1300 if (gc_count == full_gc_count) { 1301 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag); 1302 _full_gc_requested = true; 1303 _full_gc_cause = cause; 1304 CGC_lock->notify(); // nudge CMS thread 1305 } else { 1306 assert(gc_count > full_gc_count, "Error: causal loop"); 1307 } 1308 } 1309 1310 bool CMSCollector::is_external_interruption() { 1311 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause(); 1312 return GCCause::is_user_requested_gc(cause) || 1313 GCCause::is_serviceability_requested_gc(cause); 1314 } 1315 1316 void CMSCollector::report_concurrent_mode_interruption() { 1317 if (is_external_interruption()) { 1318 log_debug(gc)("Concurrent mode interrupted"); 1319 } else { 1320 log_debug(gc)("Concurrent mode failure"); 1321 _gc_tracer_cm->report_concurrent_mode_failure(); 1322 } 1323 } 1324 1325 1326 // The foreground and background collectors need to coordinate in order 1327 // to make sure that they do not mutually interfere with CMS collections. 1328 // When a background collection is active, 1329 // the foreground collector may need to take over (preempt) and 1330 // synchronously complete an ongoing collection. Depending on the 1331 // frequency of the background collections and the heap usage 1332 // of the application, this preemption can be seldom or frequent. 1333 // There are only certain 1334 // points in the background collection that the "collection-baton" 1335 // can be passed to the foreground collector. 1336 // 1337 // The foreground collector will wait for the baton before 1338 // starting any part of the collection. The foreground collector 1339 // will only wait at one location. 1340 // 1341 // The background collector will yield the baton before starting a new 1342 // phase of the collection (e.g., before initial marking, marking from roots, 1343 // precleaning, final re-mark, sweep etc.) This is normally done at the head 1344 // of the loop which switches the phases. The background collector does some 1345 // of the phases (initial mark, final re-mark) with the world stopped. 1346 // Because of locking involved in stopping the world, 1347 // the foreground collector should not block waiting for the background 1348 // collector when it is doing a stop-the-world phase. The background 1349 // collector will yield the baton at an additional point just before 1350 // it enters a stop-the-world phase. Once the world is stopped, the 1351 // background collector checks the phase of the collection. If the 1352 // phase has not changed, it proceeds with the collection. If the 1353 // phase has changed, it skips that phase of the collection. See 1354 // the comments on the use of the Heap_lock in collect_in_background(). 1355 // 1356 // Variable used in baton passing. 1357 // _foregroundGCIsActive - Set to true by the foreground collector when 1358 // it wants the baton. The foreground clears it when it has finished 1359 // the collection. 1360 // _foregroundGCShouldWait - Set to true by the background collector 1361 // when it is running. The foreground collector waits while 1362 // _foregroundGCShouldWait is true. 1363 // CGC_lock - monitor used to protect access to the above variables 1364 // and to notify the foreground and background collectors. 1365 // _collectorState - current state of the CMS collection. 1366 // 1367 // The foreground collector 1368 // acquires the CGC_lock 1369 // sets _foregroundGCIsActive 1370 // waits on the CGC_lock for _foregroundGCShouldWait to be false 1371 // various locks acquired in preparation for the collection 1372 // are released so as not to block the background collector 1373 // that is in the midst of a collection 1374 // proceeds with the collection 1375 // clears _foregroundGCIsActive 1376 // returns 1377 // 1378 // The background collector in a loop iterating on the phases of the 1379 // collection 1380 // acquires the CGC_lock 1381 // sets _foregroundGCShouldWait 1382 // if _foregroundGCIsActive is set 1383 // clears _foregroundGCShouldWait, notifies _CGC_lock 1384 // waits on _CGC_lock for _foregroundGCIsActive to become false 1385 // and exits the loop. 1386 // otherwise 1387 // proceed with that phase of the collection 1388 // if the phase is a stop-the-world phase, 1389 // yield the baton once more just before enqueueing 1390 // the stop-world CMS operation (executed by the VM thread). 1391 // returns after all phases of the collection are done 1392 // 1393 1394 void CMSCollector::acquire_control_and_collect(bool full, 1395 bool clear_all_soft_refs) { 1396 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); 1397 assert(!Thread::current()->is_ConcurrentGC_thread(), 1398 "shouldn't try to acquire control from self!"); 1399 1400 // Start the protocol for acquiring control of the 1401 // collection from the background collector (aka CMS thread). 1402 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 1403 "VM thread should have CMS token"); 1404 // Remember the possibly interrupted state of an ongoing 1405 // concurrent collection 1406 CollectorState first_state = _collectorState; 1407 1408 // Signal to a possibly ongoing concurrent collection that 1409 // we want to do a foreground collection. 1410 _foregroundGCIsActive = true; 1411 1412 // release locks and wait for a notify from the background collector 1413 // releasing the locks in only necessary for phases which 1414 // do yields to improve the granularity of the collection. 1415 assert_lock_strong(bitMapLock()); 1416 // We need to lock the Free list lock for the space that we are 1417 // currently collecting. 1418 assert(haveFreelistLocks(), "Must be holding free list locks"); 1419 bitMapLock()->unlock(); 1420 releaseFreelistLocks(); 1421 { 1422 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1423 if (_foregroundGCShouldWait) { 1424 // We are going to be waiting for action for the CMS thread; 1425 // it had better not be gone (for instance at shutdown)! 1426 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(), 1427 "CMS thread must be running"); 1428 // Wait here until the background collector gives us the go-ahead 1429 ConcurrentMarkSweepThread::clear_CMS_flag( 1430 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token 1431 // Get a possibly blocked CMS thread going: 1432 // Note that we set _foregroundGCIsActive true above, 1433 // without protection of the CGC_lock. 1434 CGC_lock->notify(); 1435 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), 1436 "Possible deadlock"); 1437 while (_foregroundGCShouldWait) { 1438 // wait for notification 1439 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 1440 // Possibility of delay/starvation here, since CMS token does 1441 // not know to give priority to VM thread? Actually, i think 1442 // there wouldn't be any delay/starvation, but the proof of 1443 // that "fact" (?) appears non-trivial. XXX 20011219YSR 1444 } 1445 ConcurrentMarkSweepThread::set_CMS_flag( 1446 ConcurrentMarkSweepThread::CMS_vm_has_token); 1447 } 1448 } 1449 // The CMS_token is already held. Get back the other locks. 1450 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 1451 "VM thread should have CMS token"); 1452 getFreelistLocks(); 1453 bitMapLock()->lock_without_safepoint_check(); 1454 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d", 1455 p2i(Thread::current()), first_state); 1456 log_debug(gc, state)(" gets control with state %d", _collectorState); 1457 1458 // Inform cms gen if this was due to partial collection failing. 1459 // The CMS gen may use this fact to determine its expansion policy. 1460 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1461 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) { 1462 assert(!_cmsGen->incremental_collection_failed(), 1463 "Should have been noticed, reacted to and cleared"); 1464 _cmsGen->set_incremental_collection_failed(); 1465 } 1466 1467 if (first_state > Idling) { 1468 report_concurrent_mode_interruption(); 1469 } 1470 1471 set_did_compact(true); 1472 1473 // If the collection is being acquired from the background 1474 // collector, there may be references on the discovered 1475 // references lists. Abandon those references, since some 1476 // of them may have become unreachable after concurrent 1477 // discovery; the STW compacting collector will redo discovery 1478 // more precisely, without being subject to floating garbage. 1479 // Leaving otherwise unreachable references in the discovered 1480 // lists would require special handling. 1481 ref_processor()->disable_discovery(); 1482 ref_processor()->abandon_partial_discovery(); 1483 ref_processor()->verify_no_references_recorded(); 1484 1485 if (first_state > Idling) { 1486 save_heap_summary(); 1487 } 1488 1489 do_compaction_work(clear_all_soft_refs); 1490 1491 // Has the GC time limit been exceeded? 1492 size_t max_eden_size = _young_gen->max_eden_size(); 1493 GCCause::Cause gc_cause = gch->gc_cause(); 1494 size_policy()->check_gc_overhead_limit(_young_gen->used(), 1495 _young_gen->eden()->used(), 1496 _cmsGen->max_capacity(), 1497 max_eden_size, 1498 full, 1499 gc_cause, 1500 gch->collector_policy()); 1501 1502 // Reset the expansion cause, now that we just completed 1503 // a collection cycle. 1504 clear_expansion_cause(); 1505 _foregroundGCIsActive = false; 1506 return; 1507 } 1508 1509 // Resize the tenured generation 1510 // after obtaining the free list locks for the 1511 // two generations. 1512 void CMSCollector::compute_new_size() { 1513 assert_locked_or_safepoint(Heap_lock); 1514 FreelistLocker z(this); 1515 MetaspaceGC::compute_new_size(); 1516 _cmsGen->compute_new_size_free_list(); 1517 } 1518 1519 // A work method used by the foreground collector to do 1520 // a mark-sweep-compact. 1521 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { 1522 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1523 1524 STWGCTimer* gc_timer = GenMarkSweep::gc_timer(); 1525 gc_timer->register_gc_start(); 1526 1527 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer(); 1528 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start()); 1529 1530 gch->pre_full_gc_dump(gc_timer); 1531 1532 GCTraceTime(Trace, gc, phases) t("CMS:MSC"); 1533 1534 // Temporarily widen the span of the weak reference processing to 1535 // the entire heap. 1536 MemRegion new_span(GenCollectedHeap::heap()->reserved_region()); 1537 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span); 1538 // Temporarily, clear the "is_alive_non_header" field of the 1539 // reference processor. 1540 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL); 1541 // Temporarily make reference _processing_ single threaded (non-MT). 1542 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false); 1543 // Temporarily make refs discovery atomic 1544 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true); 1545 // Temporarily make reference _discovery_ single threaded (non-MT) 1546 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); 1547 1548 ref_processor()->set_enqueuing_is_done(false); 1549 ref_processor()->enable_discovery(); 1550 ref_processor()->setup_policy(clear_all_soft_refs); 1551 // If an asynchronous collection finishes, the _modUnionTable is 1552 // all clear. If we are assuming the collection from an asynchronous 1553 // collection, clear the _modUnionTable. 1554 assert(_collectorState != Idling || _modUnionTable.isAllClear(), 1555 "_modUnionTable should be clear if the baton was not passed"); 1556 _modUnionTable.clear_all(); 1557 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(), 1558 "mod union for klasses should be clear if the baton was passed"); 1559 _ct->klass_rem_set()->clear_mod_union(); 1560 1561 // We must adjust the allocation statistics being maintained 1562 // in the free list space. We do so by reading and clearing 1563 // the sweep timer and updating the block flux rate estimates below. 1564 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive"); 1565 if (_inter_sweep_timer.is_active()) { 1566 _inter_sweep_timer.stop(); 1567 // Note that we do not use this sample to update the _inter_sweep_estimate. 1568 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), 1569 _inter_sweep_estimate.padded_average(), 1570 _intra_sweep_estimate.padded_average()); 1571 } 1572 1573 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs); 1574 #ifdef ASSERT 1575 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 1576 size_t free_size = cms_space->free(); 1577 assert(free_size == 1578 pointer_delta(cms_space->end(), cms_space->compaction_top()) 1579 * HeapWordSize, 1580 "All the free space should be compacted into one chunk at top"); 1581 assert(cms_space->dictionary()->total_chunk_size( 1582 debug_only(cms_space->freelistLock())) == 0 || 1583 cms_space->totalSizeInIndexedFreeLists() == 0, 1584 "All the free space should be in a single chunk"); 1585 size_t num = cms_space->totalCount(); 1586 assert((free_size == 0 && num == 0) || 1587 (free_size > 0 && (num == 1 || num == 2)), 1588 "There should be at most 2 free chunks after compaction"); 1589 #endif // ASSERT 1590 _collectorState = Resetting; 1591 assert(_restart_addr == NULL, 1592 "Should have been NULL'd before baton was passed"); 1593 reset_stw(); 1594 _cmsGen->reset_after_compaction(); 1595 _concurrent_cycles_since_last_unload = 0; 1596 1597 // Clear any data recorded in the PLAB chunk arrays. 1598 if (_survivor_plab_array != NULL) { 1599 reset_survivor_plab_arrays(); 1600 } 1601 1602 // Adjust the per-size allocation stats for the next epoch. 1603 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */); 1604 // Restart the "inter sweep timer" for the next epoch. 1605 _inter_sweep_timer.reset(); 1606 _inter_sweep_timer.start(); 1607 1608 // No longer a need to do a concurrent collection for Metaspace. 1609 MetaspaceGC::set_should_concurrent_collect(false); 1610 1611 gch->post_full_gc_dump(gc_timer); 1612 1613 gc_timer->register_gc_end(); 1614 1615 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions()); 1616 1617 // For a mark-sweep-compact, compute_new_size() will be called 1618 // in the heap's do_collection() method. 1619 } 1620 1621 void CMSCollector::print_eden_and_survivor_chunk_arrays() { 1622 Log(gc, heap) log; 1623 if (!log.is_trace()) { 1624 return; 1625 } 1626 1627 ContiguousSpace* eden_space = _young_gen->eden(); 1628 ContiguousSpace* from_space = _young_gen->from(); 1629 ContiguousSpace* to_space = _young_gen->to(); 1630 // Eden 1631 if (_eden_chunk_array != NULL) { 1632 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", 1633 p2i(eden_space->bottom()), p2i(eden_space->top()), 1634 p2i(eden_space->end()), eden_space->capacity()); 1635 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT, 1636 _eden_chunk_index, _eden_chunk_capacity); 1637 for (size_t i = 0; i < _eden_chunk_index; i++) { 1638 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i])); 1639 } 1640 } 1641 // Survivor 1642 if (_survivor_chunk_array != NULL) { 1643 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", 1644 p2i(from_space->bottom()), p2i(from_space->top()), 1645 p2i(from_space->end()), from_space->capacity()); 1646 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT, 1647 _survivor_chunk_index, _survivor_chunk_capacity); 1648 for (size_t i = 0; i < _survivor_chunk_index; i++) { 1649 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i])); 1650 } 1651 } 1652 } 1653 1654 void CMSCollector::getFreelistLocks() const { 1655 // Get locks for all free lists in all generations that this 1656 // collector is responsible for 1657 _cmsGen->freelistLock()->lock_without_safepoint_check(); 1658 } 1659 1660 void CMSCollector::releaseFreelistLocks() const { 1661 // Release locks for all free lists in all generations that this 1662 // collector is responsible for 1663 _cmsGen->freelistLock()->unlock(); 1664 } 1665 1666 bool CMSCollector::haveFreelistLocks() const { 1667 // Check locks for all free lists in all generations that this 1668 // collector is responsible for 1669 assert_lock_strong(_cmsGen->freelistLock()); 1670 PRODUCT_ONLY(ShouldNotReachHere()); 1671 return true; 1672 } 1673 1674 // A utility class that is used by the CMS collector to 1675 // temporarily "release" the foreground collector from its 1676 // usual obligation to wait for the background collector to 1677 // complete an ongoing phase before proceeding. 1678 class ReleaseForegroundGC: public StackObj { 1679 private: 1680 CMSCollector* _c; 1681 public: 1682 ReleaseForegroundGC(CMSCollector* c) : _c(c) { 1683 assert(_c->_foregroundGCShouldWait, "Else should not need to call"); 1684 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1685 // allow a potentially blocked foreground collector to proceed 1686 _c->_foregroundGCShouldWait = false; 1687 if (_c->_foregroundGCIsActive) { 1688 CGC_lock->notify(); 1689 } 1690 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 1691 "Possible deadlock"); 1692 } 1693 1694 ~ReleaseForegroundGC() { 1695 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); 1696 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1697 _c->_foregroundGCShouldWait = true; 1698 } 1699 }; 1700 1701 void CMSCollector::collect_in_background(GCCause::Cause cause) { 1702 assert(Thread::current()->is_ConcurrentGC_thread(), 1703 "A CMS asynchronous collection is only allowed on a CMS thread."); 1704 1705 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1706 { 1707 bool safepoint_check = Mutex::_no_safepoint_check_flag; 1708 MutexLockerEx hl(Heap_lock, safepoint_check); 1709 FreelistLocker fll(this); 1710 MutexLockerEx x(CGC_lock, safepoint_check); 1711 if (_foregroundGCIsActive) { 1712 // The foreground collector is. Skip this 1713 // background collection. 1714 assert(!_foregroundGCShouldWait, "Should be clear"); 1715 return; 1716 } else { 1717 assert(_collectorState == Idling, "Should be idling before start."); 1718 _collectorState = InitialMarking; 1719 register_gc_start(cause); 1720 // Reset the expansion cause, now that we are about to begin 1721 // a new cycle. 1722 clear_expansion_cause(); 1723 1724 // Clear the MetaspaceGC flag since a concurrent collection 1725 // is starting but also clear it after the collection. 1726 MetaspaceGC::set_should_concurrent_collect(false); 1727 } 1728 // Decide if we want to enable class unloading as part of the 1729 // ensuing concurrent GC cycle. 1730 update_should_unload_classes(); 1731 _full_gc_requested = false; // acks all outstanding full gc requests 1732 _full_gc_cause = GCCause::_no_gc; 1733 // Signal that we are about to start a collection 1734 gch->increment_total_full_collections(); // ... starting a collection cycle 1735 _collection_count_start = gch->total_full_collections(); 1736 } 1737 1738 size_t prev_used = _cmsGen->used(); 1739 1740 // The change of the collection state is normally done at this level; 1741 // the exceptions are phases that are executed while the world is 1742 // stopped. For those phases the change of state is done while the 1743 // world is stopped. For baton passing purposes this allows the 1744 // background collector to finish the phase and change state atomically. 1745 // The foreground collector cannot wait on a phase that is done 1746 // while the world is stopped because the foreground collector already 1747 // has the world stopped and would deadlock. 1748 while (_collectorState != Idling) { 1749 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d", 1750 p2i(Thread::current()), _collectorState); 1751 // The foreground collector 1752 // holds the Heap_lock throughout its collection. 1753 // holds the CMS token (but not the lock) 1754 // except while it is waiting for the background collector to yield. 1755 // 1756 // The foreground collector should be blocked (not for long) 1757 // if the background collector is about to start a phase 1758 // executed with world stopped. If the background 1759 // collector has already started such a phase, the 1760 // foreground collector is blocked waiting for the 1761 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) 1762 // are executed in the VM thread. 1763 // 1764 // The locking order is 1765 // PendingListLock (PLL) -- if applicable (FinalMarking) 1766 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) 1767 // CMS token (claimed in 1768 // stop_world_and_do() --> 1769 // safepoint_synchronize() --> 1770 // CMSThread::synchronize()) 1771 1772 { 1773 // Check if the FG collector wants us to yield. 1774 CMSTokenSync x(true); // is cms thread 1775 if (waitForForegroundGC()) { 1776 // We yielded to a foreground GC, nothing more to be 1777 // done this round. 1778 assert(_foregroundGCShouldWait == false, "We set it to false in " 1779 "waitForForegroundGC()"); 1780 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d", 1781 p2i(Thread::current()), _collectorState); 1782 return; 1783 } else { 1784 // The background collector can run but check to see if the 1785 // foreground collector has done a collection while the 1786 // background collector was waiting to get the CGC_lock 1787 // above. If yes, break so that _foregroundGCShouldWait 1788 // is cleared before returning. 1789 if (_collectorState == Idling) { 1790 break; 1791 } 1792 } 1793 } 1794 1795 assert(_foregroundGCShouldWait, "Foreground collector, if active, " 1796 "should be waiting"); 1797 1798 switch (_collectorState) { 1799 case InitialMarking: 1800 { 1801 ReleaseForegroundGC x(this); 1802 stats().record_cms_begin(); 1803 VM_CMS_Initial_Mark initial_mark_op(this); 1804 VMThread::execute(&initial_mark_op); 1805 } 1806 // The collector state may be any legal state at this point 1807 // since the background collector may have yielded to the 1808 // foreground collector. 1809 break; 1810 case Marking: 1811 // initial marking in checkpointRootsInitialWork has been completed 1812 if (markFromRoots()) { // we were successful 1813 assert(_collectorState == Precleaning, "Collector state should " 1814 "have changed"); 1815 } else { 1816 assert(_foregroundGCIsActive, "Internal state inconsistency"); 1817 } 1818 break; 1819 case Precleaning: 1820 // marking from roots in markFromRoots has been completed 1821 preclean(); 1822 assert(_collectorState == AbortablePreclean || 1823 _collectorState == FinalMarking, 1824 "Collector state should have changed"); 1825 break; 1826 case AbortablePreclean: 1827 abortable_preclean(); 1828 assert(_collectorState == FinalMarking, "Collector state should " 1829 "have changed"); 1830 break; 1831 case FinalMarking: 1832 { 1833 ReleaseForegroundGC x(this); 1834 1835 VM_CMS_Final_Remark final_remark_op(this); 1836 VMThread::execute(&final_remark_op); 1837 } 1838 assert(_foregroundGCShouldWait, "block post-condition"); 1839 break; 1840 case Sweeping: 1841 // final marking in checkpointRootsFinal has been completed 1842 sweep(); 1843 assert(_collectorState == Resizing, "Collector state change " 1844 "to Resizing must be done under the free_list_lock"); 1845 1846 case Resizing: { 1847 // Sweeping has been completed... 1848 // At this point the background collection has completed. 1849 // Don't move the call to compute_new_size() down 1850 // into code that might be executed if the background 1851 // collection was preempted. 1852 { 1853 ReleaseForegroundGC x(this); // unblock FG collection 1854 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag); 1855 CMSTokenSync z(true); // not strictly needed. 1856 if (_collectorState == Resizing) { 1857 compute_new_size(); 1858 save_heap_summary(); 1859 _collectorState = Resetting; 1860 } else { 1861 assert(_collectorState == Idling, "The state should only change" 1862 " because the foreground collector has finished the collection"); 1863 } 1864 } 1865 break; 1866 } 1867 case Resetting: 1868 // CMS heap resizing has been completed 1869 reset_concurrent(); 1870 assert(_collectorState == Idling, "Collector state should " 1871 "have changed"); 1872 1873 MetaspaceGC::set_should_concurrent_collect(false); 1874 1875 stats().record_cms_end(); 1876 // Don't move the concurrent_phases_end() and compute_new_size() 1877 // calls to here because a preempted background collection 1878 // has it's state set to "Resetting". 1879 break; 1880 case Idling: 1881 default: 1882 ShouldNotReachHere(); 1883 break; 1884 } 1885 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d", 1886 p2i(Thread::current()), _collectorState); 1887 assert(_foregroundGCShouldWait, "block post-condition"); 1888 } 1889 1890 // Should this be in gc_epilogue? 1891 collector_policy()->counters()->update_counters(); 1892 1893 { 1894 // Clear _foregroundGCShouldWait and, in the event that the 1895 // foreground collector is waiting, notify it, before 1896 // returning. 1897 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1898 _foregroundGCShouldWait = false; 1899 if (_foregroundGCIsActive) { 1900 CGC_lock->notify(); 1901 } 1902 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 1903 "Possible deadlock"); 1904 } 1905 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d", 1906 p2i(Thread::current()), _collectorState); 1907 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)", 1908 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K); 1909 } 1910 1911 void CMSCollector::register_gc_start(GCCause::Cause cause) { 1912 _cms_start_registered = true; 1913 _gc_timer_cm->register_gc_start(); 1914 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start()); 1915 } 1916 1917 void CMSCollector::register_gc_end() { 1918 if (_cms_start_registered) { 1919 report_heap_summary(GCWhen::AfterGC); 1920 1921 _gc_timer_cm->register_gc_end(); 1922 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions()); 1923 _cms_start_registered = false; 1924 } 1925 } 1926 1927 void CMSCollector::save_heap_summary() { 1928 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1929 _last_heap_summary = gch->create_heap_summary(); 1930 _last_metaspace_summary = gch->create_metaspace_summary(); 1931 } 1932 1933 void CMSCollector::report_heap_summary(GCWhen::Type when) { 1934 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary); 1935 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary); 1936 } 1937 1938 bool CMSCollector::waitForForegroundGC() { 1939 bool res = false; 1940 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 1941 "CMS thread should have CMS token"); 1942 // Block the foreground collector until the 1943 // background collectors decides whether to 1944 // yield. 1945 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1946 _foregroundGCShouldWait = true; 1947 if (_foregroundGCIsActive) { 1948 // The background collector yields to the 1949 // foreground collector and returns a value 1950 // indicating that it has yielded. The foreground 1951 // collector can proceed. 1952 res = true; 1953 _foregroundGCShouldWait = false; 1954 ConcurrentMarkSweepThread::clear_CMS_flag( 1955 ConcurrentMarkSweepThread::CMS_cms_has_token); 1956 ConcurrentMarkSweepThread::set_CMS_flag( 1957 ConcurrentMarkSweepThread::CMS_cms_wants_token); 1958 // Get a possibly blocked foreground thread going 1959 CGC_lock->notify(); 1960 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", 1961 p2i(Thread::current()), _collectorState); 1962 while (_foregroundGCIsActive) { 1963 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 1964 } 1965 ConcurrentMarkSweepThread::set_CMS_flag( 1966 ConcurrentMarkSweepThread::CMS_cms_has_token); 1967 ConcurrentMarkSweepThread::clear_CMS_flag( 1968 ConcurrentMarkSweepThread::CMS_cms_wants_token); 1969 } 1970 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", 1971 p2i(Thread::current()), _collectorState); 1972 return res; 1973 } 1974 1975 // Because of the need to lock the free lists and other structures in 1976 // the collector, common to all the generations that the collector is 1977 // collecting, we need the gc_prologues of individual CMS generations 1978 // delegate to their collector. It may have been simpler had the 1979 // current infrastructure allowed one to call a prologue on a 1980 // collector. In the absence of that we have the generation's 1981 // prologue delegate to the collector, which delegates back 1982 // some "local" work to a worker method in the individual generations 1983 // that it's responsible for collecting, while itself doing any 1984 // work common to all generations it's responsible for. A similar 1985 // comment applies to the gc_epilogue()'s. 1986 // The role of the variable _between_prologue_and_epilogue is to 1987 // enforce the invocation protocol. 1988 void CMSCollector::gc_prologue(bool full) { 1989 // Call gc_prologue_work() for the CMSGen 1990 // we are responsible for. 1991 1992 // The following locking discipline assumes that we are only called 1993 // when the world is stopped. 1994 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); 1995 1996 // The CMSCollector prologue must call the gc_prologues for the 1997 // "generations" that it's responsible 1998 // for. 1999 2000 assert( Thread::current()->is_VM_thread() 2001 || ( CMSScavengeBeforeRemark 2002 && Thread::current()->is_ConcurrentGC_thread()), 2003 "Incorrect thread type for prologue execution"); 2004 2005 if (_between_prologue_and_epilogue) { 2006 // We have already been invoked; this is a gc_prologue delegation 2007 // from yet another CMS generation that we are responsible for, just 2008 // ignore it since all relevant work has already been done. 2009 return; 2010 } 2011 2012 // set a bit saying prologue has been called; cleared in epilogue 2013 _between_prologue_and_epilogue = true; 2014 // Claim locks for common data structures, then call gc_prologue_work() 2015 // for each CMSGen. 2016 2017 getFreelistLocks(); // gets free list locks on constituent spaces 2018 bitMapLock()->lock_without_safepoint_check(); 2019 2020 // Should call gc_prologue_work() for all cms gens we are responsible for 2021 bool duringMarking = _collectorState >= Marking 2022 && _collectorState < Sweeping; 2023 2024 // The young collections clear the modified oops state, which tells if 2025 // there are any modified oops in the class. The remark phase also needs 2026 // that information. Tell the young collection to save the union of all 2027 // modified klasses. 2028 if (duringMarking) { 2029 _ct->klass_rem_set()->set_accumulate_modified_oops(true); 2030 } 2031 2032 bool registerClosure = duringMarking; 2033 2034 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar); 2035 2036 if (!full) { 2037 stats().record_gc0_begin(); 2038 } 2039 } 2040 2041 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { 2042 2043 _capacity_at_prologue = capacity(); 2044 _used_at_prologue = used(); 2045 2046 // We enable promotion tracking so that card-scanning can recognize 2047 // which objects have been promoted during this GC and skip them. 2048 for (uint i = 0; i < ParallelGCThreads; i++) { 2049 _par_gc_thread_states[i]->promo.startTrackingPromotions(); 2050 } 2051 2052 // Delegate to CMScollector which knows how to coordinate between 2053 // this and any other CMS generations that it is responsible for 2054 // collecting. 2055 collector()->gc_prologue(full); 2056 } 2057 2058 // This is a "private" interface for use by this generation's CMSCollector. 2059 // Not to be called directly by any other entity (for instance, 2060 // GenCollectedHeap, which calls the "public" gc_prologue method above). 2061 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, 2062 bool registerClosure, ModUnionClosure* modUnionClosure) { 2063 assert(!incremental_collection_failed(), "Shouldn't be set yet"); 2064 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, 2065 "Should be NULL"); 2066 if (registerClosure) { 2067 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); 2068 } 2069 cmsSpace()->gc_prologue(); 2070 // Clear stat counters 2071 NOT_PRODUCT( 2072 assert(_numObjectsPromoted == 0, "check"); 2073 assert(_numWordsPromoted == 0, "check"); 2074 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently", 2075 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); 2076 _numObjectsAllocated = 0; 2077 _numWordsAllocated = 0; 2078 ) 2079 } 2080 2081 void CMSCollector::gc_epilogue(bool full) { 2082 // The following locking discipline assumes that we are only called 2083 // when the world is stopped. 2084 assert(SafepointSynchronize::is_at_safepoint(), 2085 "world is stopped assumption"); 2086 2087 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks 2088 // if linear allocation blocks need to be appropriately marked to allow the 2089 // the blocks to be parsable. We also check here whether we need to nudge the 2090 // CMS collector thread to start a new cycle (if it's not already active). 2091 assert( Thread::current()->is_VM_thread() 2092 || ( CMSScavengeBeforeRemark 2093 && Thread::current()->is_ConcurrentGC_thread()), 2094 "Incorrect thread type for epilogue execution"); 2095 2096 if (!_between_prologue_and_epilogue) { 2097 // We have already been invoked; this is a gc_epilogue delegation 2098 // from yet another CMS generation that we are responsible for, just 2099 // ignore it since all relevant work has already been done. 2100 return; 2101 } 2102 assert(haveFreelistLocks(), "must have freelist locks"); 2103 assert_lock_strong(bitMapLock()); 2104 2105 _ct->klass_rem_set()->set_accumulate_modified_oops(false); 2106 2107 _cmsGen->gc_epilogue_work(full); 2108 2109 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { 2110 // in case sampling was not already enabled, enable it 2111 _start_sampling = true; 2112 } 2113 // reset _eden_chunk_array so sampling starts afresh 2114 _eden_chunk_index = 0; 2115 2116 size_t cms_used = _cmsGen->cmsSpace()->used(); 2117 2118 // update performance counters - this uses a special version of 2119 // update_counters() that allows the utilization to be passed as a 2120 // parameter, avoiding multiple calls to used(). 2121 // 2122 _cmsGen->update_counters(cms_used); 2123 2124 bitMapLock()->unlock(); 2125 releaseFreelistLocks(); 2126 2127 if (!CleanChunkPoolAsync) { 2128 Chunk::clean_chunk_pool(); 2129 } 2130 2131 set_did_compact(false); 2132 _between_prologue_and_epilogue = false; // ready for next cycle 2133 } 2134 2135 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { 2136 collector()->gc_epilogue(full); 2137 2138 // When using ParNew, promotion tracking should have already been 2139 // disabled. However, the prologue (which enables promotion 2140 // tracking) and epilogue are called irrespective of the type of 2141 // GC. So they will also be called before and after Full GCs, during 2142 // which promotion tracking will not be explicitly disabled. So, 2143 // it's safer to also disable it here too (to be symmetric with 2144 // enabling it in the prologue). 2145 for (uint i = 0; i < ParallelGCThreads; i++) { 2146 _par_gc_thread_states[i]->promo.stopTrackingPromotions(); 2147 } 2148 } 2149 2150 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { 2151 assert(!incremental_collection_failed(), "Should have been cleared"); 2152 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); 2153 cmsSpace()->gc_epilogue(); 2154 // Print stat counters 2155 NOT_PRODUCT( 2156 assert(_numObjectsAllocated == 0, "check"); 2157 assert(_numWordsAllocated == 0, "check"); 2158 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", 2159 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); 2160 _numObjectsPromoted = 0; 2161 _numWordsPromoted = 0; 2162 ) 2163 2164 // Call down the chain in contiguous_available needs the freelistLock 2165 // so print this out before releasing the freeListLock. 2166 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available()); 2167 } 2168 2169 #ifndef PRODUCT 2170 bool CMSCollector::have_cms_token() { 2171 Thread* thr = Thread::current(); 2172 if (thr->is_VM_thread()) { 2173 return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); 2174 } else if (thr->is_ConcurrentGC_thread()) { 2175 return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); 2176 } else if (thr->is_GC_task_thread()) { 2177 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && 2178 ParGCRareEvent_lock->owned_by_self(); 2179 } 2180 return false; 2181 } 2182 2183 // Check reachability of the given heap address in CMS generation, 2184 // treating all other generations as roots. 2185 bool CMSCollector::is_cms_reachable(HeapWord* addr) { 2186 // We could "guarantee" below, rather than assert, but I'll 2187 // leave these as "asserts" so that an adventurous debugger 2188 // could try this in the product build provided some subset of 2189 // the conditions were met, provided they were interested in the 2190 // results and knew that the computation below wouldn't interfere 2191 // with other concurrent computations mutating the structures 2192 // being read or written. 2193 assert(SafepointSynchronize::is_at_safepoint(), 2194 "Else mutations in object graph will make answer suspect"); 2195 assert(have_cms_token(), "Should hold cms token"); 2196 assert(haveFreelistLocks(), "must hold free list locks"); 2197 assert_lock_strong(bitMapLock()); 2198 2199 // Clear the marking bit map array before starting, but, just 2200 // for kicks, first report if the given address is already marked 2201 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr), 2202 _markBitMap.isMarked(addr) ? "" : " not"); 2203 2204 if (verify_after_remark()) { 2205 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); 2206 bool result = verification_mark_bm()->isMarked(addr); 2207 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr), 2208 result ? "IS" : "is NOT"); 2209 return result; 2210 } else { 2211 tty->print_cr("Could not compute result"); 2212 return false; 2213 } 2214 } 2215 #endif 2216 2217 void 2218 CMSCollector::print_on_error(outputStream* st) { 2219 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector; 2220 if (collector != NULL) { 2221 CMSBitMap* bitmap = &collector->_markBitMap; 2222 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap)); 2223 bitmap->print_on_error(st, " Bits: "); 2224 2225 st->cr(); 2226 2227 CMSBitMap* mut_bitmap = &collector->_modUnionTable; 2228 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap)); 2229 mut_bitmap->print_on_error(st, " Bits: "); 2230 } 2231 } 2232 2233 //////////////////////////////////////////////////////// 2234 // CMS Verification Support 2235 //////////////////////////////////////////////////////// 2236 // Following the remark phase, the following invariant 2237 // should hold -- each object in the CMS heap which is 2238 // marked in markBitMap() should be marked in the verification_mark_bm(). 2239 2240 class VerifyMarkedClosure: public BitMapClosure { 2241 CMSBitMap* _marks; 2242 bool _failed; 2243 2244 public: 2245 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} 2246 2247 bool do_bit(size_t offset) { 2248 HeapWord* addr = _marks->offsetToHeapWord(offset); 2249 if (!_marks->isMarked(addr)) { 2250 Log(gc, verify) log; 2251 ResourceMark rm; 2252 oop(addr)->print_on(log.error_stream()); 2253 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); 2254 _failed = true; 2255 } 2256 return true; 2257 } 2258 2259 bool failed() { return _failed; } 2260 }; 2261 2262 bool CMSCollector::verify_after_remark() { 2263 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking."); 2264 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); 2265 static bool init = false; 2266 2267 assert(SafepointSynchronize::is_at_safepoint(), 2268 "Else mutations in object graph will make answer suspect"); 2269 assert(have_cms_token(), 2270 "Else there may be mutual interference in use of " 2271 " verification data structures"); 2272 assert(_collectorState > Marking && _collectorState <= Sweeping, 2273 "Else marking info checked here may be obsolete"); 2274 assert(haveFreelistLocks(), "must hold free list locks"); 2275 assert_lock_strong(bitMapLock()); 2276 2277 2278 // Allocate marking bit map if not already allocated 2279 if (!init) { // first time 2280 if (!verification_mark_bm()->allocate(_span)) { 2281 return false; 2282 } 2283 init = true; 2284 } 2285 2286 assert(verification_mark_stack()->isEmpty(), "Should be empty"); 2287 2288 // Turn off refs discovery -- so we will be tracing through refs. 2289 // This is as intended, because by this time 2290 // GC must already have cleared any refs that need to be cleared, 2291 // and traced those that need to be marked; moreover, 2292 // the marking done here is not going to interfere in any 2293 // way with the marking information used by GC. 2294 NoRefDiscovery no_discovery(ref_processor()); 2295 2296 #if defined(COMPILER2) || INCLUDE_JVMCI 2297 DerivedPointerTableDeactivate dpt_deact; 2298 #endif 2299 2300 // Clear any marks from a previous round 2301 verification_mark_bm()->clear_all(); 2302 assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); 2303 verify_work_stacks_empty(); 2304 2305 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2306 gch->ensure_parsability(false); // fill TLABs, but no need to retire them 2307 // Update the saved marks which may affect the root scans. 2308 gch->save_marks(); 2309 2310 if (CMSRemarkVerifyVariant == 1) { 2311 // In this first variant of verification, we complete 2312 // all marking, then check if the new marks-vector is 2313 // a subset of the CMS marks-vector. 2314 verify_after_remark_work_1(); 2315 } else { 2316 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2"); 2317 // In this second variant of verification, we flag an error 2318 // (i.e. an object reachable in the new marks-vector not reachable 2319 // in the CMS marks-vector) immediately, also indicating the 2320 // identify of an object (A) that references the unmarked object (B) -- 2321 // presumably, a mutation to A failed to be picked up by preclean/remark? 2322 verify_after_remark_work_2(); 2323 } 2324 2325 return true; 2326 } 2327 2328 void CMSCollector::verify_after_remark_work_1() { 2329 ResourceMark rm; 2330 HandleMark hm; 2331 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2332 2333 // Get a clear set of claim bits for the roots processing to work with. 2334 ClassLoaderDataGraph::clear_claimed_marks(); 2335 2336 // Mark from roots one level into CMS 2337 MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); 2338 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 2339 2340 { 2341 StrongRootsScope srs(1); 2342 2343 gch->gen_process_roots(&srs, 2344 GenCollectedHeap::OldGen, 2345 true, // young gen as roots 2346 GenCollectedHeap::ScanningOption(roots_scanning_options()), 2347 should_unload_classes(), 2348 ¬Older, 2349 NULL, 2350 NULL); 2351 } 2352 2353 // Now mark from the roots 2354 MarkFromRootsClosure markFromRootsClosure(this, _span, 2355 verification_mark_bm(), verification_mark_stack(), 2356 false /* don't yield */, true /* verifying */); 2357 assert(_restart_addr == NULL, "Expected pre-condition"); 2358 verification_mark_bm()->iterate(&markFromRootsClosure); 2359 while (_restart_addr != NULL) { 2360 // Deal with stack overflow: by restarting at the indicated 2361 // address. 2362 HeapWord* ra = _restart_addr; 2363 markFromRootsClosure.reset(ra); 2364 _restart_addr = NULL; 2365 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); 2366 } 2367 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); 2368 verify_work_stacks_empty(); 2369 2370 // Marking completed -- now verify that each bit marked in 2371 // verification_mark_bm() is also marked in markBitMap(); flag all 2372 // errors by printing corresponding objects. 2373 VerifyMarkedClosure vcl(markBitMap()); 2374 verification_mark_bm()->iterate(&vcl); 2375 if (vcl.failed()) { 2376 Log(gc, verify) log; 2377 log.error("Failed marking verification after remark"); 2378 ResourceMark rm; 2379 gch->print_on(log.error_stream()); 2380 fatal("CMS: failed marking verification after remark"); 2381 } 2382 } 2383 2384 class VerifyKlassOopsKlassClosure : public KlassClosure { 2385 class VerifyKlassOopsClosure : public OopClosure { 2386 CMSBitMap* _bitmap; 2387 public: 2388 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { } 2389 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); } 2390 void do_oop(narrowOop* p) { ShouldNotReachHere(); } 2391 } _oop_closure; 2392 public: 2393 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {} 2394 void do_klass(Klass* k) { 2395 k->oops_do(&_oop_closure); 2396 } 2397 }; 2398 2399 void CMSCollector::verify_after_remark_work_2() { 2400 ResourceMark rm; 2401 HandleMark hm; 2402 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2403 2404 // Get a clear set of claim bits for the roots processing to work with. 2405 ClassLoaderDataGraph::clear_claimed_marks(); 2406 2407 // Mark from roots one level into CMS 2408 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), 2409 markBitMap()); 2410 CLDToOopClosure cld_closure(¬Older, true); 2411 2412 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 2413 2414 { 2415 StrongRootsScope srs(1); 2416 2417 gch->gen_process_roots(&srs, 2418 GenCollectedHeap::OldGen, 2419 true, // young gen as roots 2420 GenCollectedHeap::ScanningOption(roots_scanning_options()), 2421 should_unload_classes(), 2422 ¬Older, 2423 NULL, 2424 &cld_closure); 2425 } 2426 2427 // Now mark from the roots 2428 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, 2429 verification_mark_bm(), markBitMap(), verification_mark_stack()); 2430 assert(_restart_addr == NULL, "Expected pre-condition"); 2431 verification_mark_bm()->iterate(&markFromRootsClosure); 2432 while (_restart_addr != NULL) { 2433 // Deal with stack overflow: by restarting at the indicated 2434 // address. 2435 HeapWord* ra = _restart_addr; 2436 markFromRootsClosure.reset(ra); 2437 _restart_addr = NULL; 2438 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); 2439 } 2440 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); 2441 verify_work_stacks_empty(); 2442 2443 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm()); 2444 ClassLoaderDataGraph::classes_do(&verify_klass_oops); 2445 2446 // Marking completed -- now verify that each bit marked in 2447 // verification_mark_bm() is also marked in markBitMap(); flag all 2448 // errors by printing corresponding objects. 2449 VerifyMarkedClosure vcl(markBitMap()); 2450 verification_mark_bm()->iterate(&vcl); 2451 assert(!vcl.failed(), "Else verification above should not have succeeded"); 2452 } 2453 2454 void ConcurrentMarkSweepGeneration::save_marks() { 2455 // delegate to CMS space 2456 cmsSpace()->save_marks(); 2457 } 2458 2459 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { 2460 return cmsSpace()->no_allocs_since_save_marks(); 2461 } 2462 2463 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \ 2464 \ 2465 void ConcurrentMarkSweepGeneration:: \ 2466 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ 2467 cl->set_generation(this); \ 2468 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \ 2469 cl->reset_generation(); \ 2470 save_marks(); \ 2471 } 2472 2473 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN) 2474 2475 void 2476 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) { 2477 if (freelistLock()->owned_by_self()) { 2478 Generation::oop_iterate(cl); 2479 } else { 2480 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2481 Generation::oop_iterate(cl); 2482 } 2483 } 2484 2485 void 2486 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { 2487 if (freelistLock()->owned_by_self()) { 2488 Generation::object_iterate(cl); 2489 } else { 2490 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2491 Generation::object_iterate(cl); 2492 } 2493 } 2494 2495 void 2496 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) { 2497 if (freelistLock()->owned_by_self()) { 2498 Generation::safe_object_iterate(cl); 2499 } else { 2500 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2501 Generation::safe_object_iterate(cl); 2502 } 2503 } 2504 2505 void 2506 ConcurrentMarkSweepGeneration::post_compact() { 2507 } 2508 2509 void 2510 ConcurrentMarkSweepGeneration::prepare_for_verify() { 2511 // Fix the linear allocation blocks to look like free blocks. 2512 2513 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those 2514 // are not called when the heap is verified during universe initialization and 2515 // at vm shutdown. 2516 if (freelistLock()->owned_by_self()) { 2517 cmsSpace()->prepare_for_verify(); 2518 } else { 2519 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); 2520 cmsSpace()->prepare_for_verify(); 2521 } 2522 } 2523 2524 void 2525 ConcurrentMarkSweepGeneration::verify() { 2526 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those 2527 // are not called when the heap is verified during universe initialization and 2528 // at vm shutdown. 2529 if (freelistLock()->owned_by_self()) { 2530 cmsSpace()->verify(); 2531 } else { 2532 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); 2533 cmsSpace()->verify(); 2534 } 2535 } 2536 2537 void CMSCollector::verify() { 2538 _cmsGen->verify(); 2539 } 2540 2541 #ifndef PRODUCT 2542 bool CMSCollector::overflow_list_is_empty() const { 2543 assert(_num_par_pushes >= 0, "Inconsistency"); 2544 if (_overflow_list == NULL) { 2545 assert(_num_par_pushes == 0, "Inconsistency"); 2546 } 2547 return _overflow_list == NULL; 2548 } 2549 2550 // The methods verify_work_stacks_empty() and verify_overflow_empty() 2551 // merely consolidate assertion checks that appear to occur together frequently. 2552 void CMSCollector::verify_work_stacks_empty() const { 2553 assert(_markStack.isEmpty(), "Marking stack should be empty"); 2554 assert(overflow_list_is_empty(), "Overflow list should be empty"); 2555 } 2556 2557 void CMSCollector::verify_overflow_empty() const { 2558 assert(overflow_list_is_empty(), "Overflow list should be empty"); 2559 assert(no_preserved_marks(), "No preserved marks"); 2560 } 2561 #endif // PRODUCT 2562 2563 // Decide if we want to enable class unloading as part of the 2564 // ensuing concurrent GC cycle. We will collect and 2565 // unload classes if it's the case that: 2566 // (1) an explicit gc request has been made and the flag 2567 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR 2568 // (2) (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 // Condition 1 above 2583 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) { 2584 _should_unload_classes = true; 2585 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above 2586 // Disjuncts 2.b.(i,ii,iii) above 2587 _should_unload_classes = (concurrent_cycles_since_last_unload() >= 2588 CMSClassUnloadingMaxInterval) 2589 || _cmsGen->is_too_full(); 2590 } 2591 } 2592 2593 bool ConcurrentMarkSweepGeneration::is_too_full() const { 2594 bool res = should_concurrent_collect(); 2595 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0); 2596 return res; 2597 } 2598 2599 void CMSCollector::setup_cms_unloading_and_verification_state() { 2600 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC 2601 || VerifyBeforeExit; 2602 const int rso = GenCollectedHeap::SO_AllCodeCache; 2603 2604 // We set the proper root for this CMS cycle here. 2605 if (should_unload_classes()) { // Should unload classes this cycle 2606 remove_root_scanning_option(rso); // Shrink the root set appropriately 2607 set_verifying(should_verify); // Set verification state for this cycle 2608 return; // Nothing else needs to be done at this time 2609 } 2610 2611 // Not unloading classes this cycle 2612 assert(!should_unload_classes(), "Inconsistency!"); 2613 2614 // If we are not unloading classes then add SO_AllCodeCache to root 2615 // scanning options. 2616 add_root_scanning_option(rso); 2617 2618 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { 2619 set_verifying(true); 2620 } else if (verifying() && !should_verify) { 2621 // We were verifying, but some verification flags got disabled. 2622 set_verifying(false); 2623 // Exclude symbols, strings and code cache elements from root scanning to 2624 // reduce IM and RM pauses. 2625 remove_root_scanning_option(rso); 2626 } 2627 } 2628 2629 2630 #ifndef PRODUCT 2631 HeapWord* CMSCollector::block_start(const void* p) const { 2632 const HeapWord* addr = (HeapWord*)p; 2633 if (_span.contains(p)) { 2634 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { 2635 return _cmsGen->cmsSpace()->block_start(p); 2636 } 2637 } 2638 return NULL; 2639 } 2640 #endif 2641 2642 HeapWord* 2643 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, 2644 bool tlab, 2645 bool parallel) { 2646 CMSSynchronousYieldRequest yr; 2647 assert(!tlab, "Can't deal with TLAB allocation"); 2648 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 2649 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation); 2650 if (GCExpandToAllocateDelayMillis > 0) { 2651 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 2652 } 2653 return have_lock_and_allocate(word_size, tlab); 2654 } 2655 2656 void ConcurrentMarkSweepGeneration::expand_for_gc_cause( 2657 size_t bytes, 2658 size_t expand_bytes, 2659 CMSExpansionCause::Cause cause) 2660 { 2661 2662 bool success = expand(bytes, expand_bytes); 2663 2664 // remember why we expanded; this information is used 2665 // by shouldConcurrentCollect() when making decisions on whether to start 2666 // a new CMS cycle. 2667 if (success) { 2668 set_expansion_cause(cause); 2669 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause)); 2670 } 2671 } 2672 2673 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { 2674 HeapWord* res = NULL; 2675 MutexLocker x(ParGCRareEvent_lock); 2676 while (true) { 2677 // Expansion by some other thread might make alloc OK now: 2678 res = ps->lab.alloc(word_sz); 2679 if (res != NULL) return res; 2680 // If there's not enough expansion space available, give up. 2681 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { 2682 return NULL; 2683 } 2684 // Otherwise, we try expansion. 2685 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab); 2686 // Now go around the loop and try alloc again; 2687 // A competing par_promote might beat us to the expansion space, 2688 // so we may go around the loop again if promotion fails again. 2689 if (GCExpandToAllocateDelayMillis > 0) { 2690 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 2691 } 2692 } 2693 } 2694 2695 2696 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( 2697 PromotionInfo* promo) { 2698 MutexLocker x(ParGCRareEvent_lock); 2699 size_t refill_size_bytes = promo->refillSize() * HeapWordSize; 2700 while (true) { 2701 // Expansion by some other thread might make alloc OK now: 2702 if (promo->ensure_spooling_space()) { 2703 assert(promo->has_spooling_space(), 2704 "Post-condition of successful ensure_spooling_space()"); 2705 return true; 2706 } 2707 // If there's not enough expansion space available, give up. 2708 if (_virtual_space.uncommitted_size() < refill_size_bytes) { 2709 return false; 2710 } 2711 // Otherwise, we try expansion. 2712 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space); 2713 // Now go around the loop and try alloc again; 2714 // A competing allocation might beat us to the expansion space, 2715 // so we may go around the loop again if allocation fails again. 2716 if (GCExpandToAllocateDelayMillis > 0) { 2717 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 2718 } 2719 } 2720 } 2721 2722 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { 2723 // Only shrink if a compaction was done so that all the free space 2724 // in the generation is in a contiguous block at the end. 2725 if (did_compact()) { 2726 CardGeneration::shrink(bytes); 2727 } 2728 } 2729 2730 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() { 2731 assert_locked_or_safepoint(Heap_lock); 2732 } 2733 2734 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) { 2735 assert_locked_or_safepoint(Heap_lock); 2736 assert_lock_strong(freelistLock()); 2737 log_trace(gc)("Shrinking of CMS not yet implemented"); 2738 return; 2739 } 2740 2741 2742 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent 2743 // phases. 2744 class CMSPhaseAccounting: public StackObj { 2745 public: 2746 CMSPhaseAccounting(CMSCollector *collector, 2747 const char *title); 2748 ~CMSPhaseAccounting(); 2749 2750 private: 2751 CMSCollector *_collector; 2752 const char *_title; 2753 GCTraceConcTime(Info, gc) _trace_time; 2754 2755 public: 2756 // Not MT-safe; so do not pass around these StackObj's 2757 // where they may be accessed by other threads. 2758 double wallclock_millis() { 2759 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time()); 2760 } 2761 }; 2762 2763 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, 2764 const char *title) : 2765 _collector(collector), _title(title), _trace_time(title) { 2766 2767 _collector->resetYields(); 2768 _collector->resetTimer(); 2769 _collector->startTimer(); 2770 _collector->gc_timer_cm()->register_gc_concurrent_start(title); 2771 } 2772 2773 CMSPhaseAccounting::~CMSPhaseAccounting() { 2774 _collector->gc_timer_cm()->register_gc_concurrent_end(); 2775 _collector->stopTimer(); 2776 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks())); 2777 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields()); 2778 } 2779 2780 // CMS work 2781 2782 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask. 2783 class CMSParMarkTask : public AbstractGangTask { 2784 protected: 2785 CMSCollector* _collector; 2786 uint _n_workers; 2787 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) : 2788 AbstractGangTask(name), 2789 _collector(collector), 2790 _n_workers(n_workers) {} 2791 // Work method in support of parallel rescan ... of young gen spaces 2792 void do_young_space_rescan(OopsInGenClosure* cl, 2793 ContiguousSpace* space, 2794 HeapWord** chunk_array, size_t chunk_top); 2795 void work_on_young_gen_roots(OopsInGenClosure* cl); 2796 }; 2797 2798 // Parallel initial mark task 2799 class CMSParInitialMarkTask: public CMSParMarkTask { 2800 StrongRootsScope* _strong_roots_scope; 2801 public: 2802 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) : 2803 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers), 2804 _strong_roots_scope(strong_roots_scope) {} 2805 void work(uint worker_id); 2806 }; 2807 2808 // Checkpoint the roots into this generation from outside 2809 // this generation. [Note this initial checkpoint need only 2810 // be approximate -- we'll do a catch up phase subsequently.] 2811 void CMSCollector::checkpointRootsInitial() { 2812 assert(_collectorState == InitialMarking, "Wrong collector state"); 2813 check_correct_thread_executing(); 2814 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); 2815 2816 save_heap_summary(); 2817 report_heap_summary(GCWhen::BeforeGC); 2818 2819 ReferenceProcessor* rp = ref_processor(); 2820 assert(_restart_addr == NULL, "Control point invariant"); 2821 { 2822 // acquire locks for subsequent manipulations 2823 MutexLockerEx x(bitMapLock(), 2824 Mutex::_no_safepoint_check_flag); 2825 checkpointRootsInitialWork(); 2826 // enable ("weak") refs discovery 2827 rp->enable_discovery(); 2828 _collectorState = Marking; 2829 } 2830 } 2831 2832 void CMSCollector::checkpointRootsInitialWork() { 2833 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); 2834 assert(_collectorState == InitialMarking, "just checking"); 2835 2836 // Already have locks. 2837 assert_lock_strong(bitMapLock()); 2838 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); 2839 2840 // Setup the verification and class unloading state for this 2841 // CMS collection cycle. 2842 setup_cms_unloading_and_verification_state(); 2843 2844 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm); 2845 2846 // Reset all the PLAB chunk arrays if necessary. 2847 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { 2848 reset_survivor_plab_arrays(); 2849 } 2850 2851 ResourceMark rm; 2852 HandleMark hm; 2853 2854 MarkRefsIntoClosure notOlder(_span, &_markBitMap); 2855 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2856 2857 verify_work_stacks_empty(); 2858 verify_overflow_empty(); 2859 2860 gch->ensure_parsability(false); // fill TLABs, but no need to retire them 2861 // Update the saved marks which may affect the root scans. 2862 gch->save_marks(); 2863 2864 // weak reference processing has not started yet. 2865 ref_processor()->set_enqueuing_is_done(false); 2866 2867 // Need to remember all newly created CLDs, 2868 // so that we can guarantee that the remark finds them. 2869 ClassLoaderDataGraph::remember_new_clds(true); 2870 2871 // Whenever a CLD is found, it will be claimed before proceeding to mark 2872 // the klasses. The claimed marks need to be cleared before marking starts. 2873 ClassLoaderDataGraph::clear_claimed_marks(); 2874 2875 print_eden_and_survivor_chunk_arrays(); 2876 2877 { 2878 #if defined(COMPILER2) || INCLUDE_JVMCI 2879 DerivedPointerTableDeactivate dpt_deact; 2880 #endif 2881 if (CMSParallelInitialMarkEnabled) { 2882 // The parallel version. 2883 WorkGang* workers = gch->workers(); 2884 assert(workers != NULL, "Need parallel worker threads."); 2885 uint n_workers = workers->active_workers(); 2886 2887 StrongRootsScope srs(n_workers); 2888 2889 CMSParInitialMarkTask tsk(this, &srs, n_workers); 2890 initialize_sequential_subtasks_for_young_gen_rescan(n_workers); 2891 if (n_workers > 1) { 2892 workers->run_task(&tsk); 2893 } else { 2894 tsk.work(0); 2895 } 2896 } else { 2897 // The serial version. 2898 CLDToOopClosure cld_closure(¬Older, true); 2899 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 2900 2901 StrongRootsScope srs(1); 2902 2903 gch->gen_process_roots(&srs, 2904 GenCollectedHeap::OldGen, 2905 true, // young gen as roots 2906 GenCollectedHeap::ScanningOption(roots_scanning_options()), 2907 should_unload_classes(), 2908 ¬Older, 2909 NULL, 2910 &cld_closure); 2911 } 2912 } 2913 2914 // Clear mod-union table; it will be dirtied in the prologue of 2915 // CMS generation per each young generation collection. 2916 2917 assert(_modUnionTable.isAllClear(), 2918 "Was cleared in most recent final checkpoint phase" 2919 " or no bits are set in the gc_prologue before the start of the next " 2920 "subsequent marking phase."); 2921 2922 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be"); 2923 2924 // Save the end of the used_region of the constituent generations 2925 // to be used to limit the extent of sweep in each generation. 2926 save_sweep_limits(); 2927 verify_overflow_empty(); 2928 } 2929 2930 bool CMSCollector::markFromRoots() { 2931 // we might be tempted to assert that: 2932 // assert(!SafepointSynchronize::is_at_safepoint(), 2933 // "inconsistent argument?"); 2934 // However that wouldn't be right, because it's possible that 2935 // a safepoint is indeed in progress as a young generation 2936 // stop-the-world GC happens even as we mark in this generation. 2937 assert(_collectorState == Marking, "inconsistent state?"); 2938 check_correct_thread_executing(); 2939 verify_overflow_empty(); 2940 2941 // Weak ref discovery note: We may be discovering weak 2942 // refs in this generation concurrent (but interleaved) with 2943 // weak ref discovery by the young generation collector. 2944 2945 CMSTokenSyncWithLocks ts(true, bitMapLock()); 2946 GCTraceCPUTime tcpu; 2947 CMSPhaseAccounting pa(this, "Concurrent Mark"); 2948 bool res = markFromRootsWork(); 2949 if (res) { 2950 _collectorState = Precleaning; 2951 } else { // We failed and a foreground collection wants to take over 2952 assert(_foregroundGCIsActive, "internal state inconsistency"); 2953 assert(_restart_addr == NULL, "foreground will restart from scratch"); 2954 log_debug(gc)("bailing out to foreground collection"); 2955 } 2956 verify_overflow_empty(); 2957 return res; 2958 } 2959 2960 bool CMSCollector::markFromRootsWork() { 2961 // iterate over marked bits in bit map, doing a full scan and mark 2962 // from these roots using the following algorithm: 2963 // . if oop is to the right of the current scan pointer, 2964 // mark corresponding bit (we'll process it later) 2965 // . else (oop is to left of current scan pointer) 2966 // push oop on marking stack 2967 // . drain the marking stack 2968 2969 // Note that when we do a marking step we need to hold the 2970 // bit map lock -- recall that direct allocation (by mutators) 2971 // and promotion (by the young generation collector) is also 2972 // marking the bit map. [the so-called allocate live policy.] 2973 // Because the implementation of bit map marking is not 2974 // robust wrt simultaneous marking of bits in the same word, 2975 // we need to make sure that there is no such interference 2976 // between concurrent such updates. 2977 2978 // already have locks 2979 assert_lock_strong(bitMapLock()); 2980 2981 verify_work_stacks_empty(); 2982 verify_overflow_empty(); 2983 bool result = false; 2984 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) { 2985 result = do_marking_mt(); 2986 } else { 2987 result = do_marking_st(); 2988 } 2989 return result; 2990 } 2991 2992 // Forward decl 2993 class CMSConcMarkingTask; 2994 2995 class CMSConcMarkingTerminator: public ParallelTaskTerminator { 2996 CMSCollector* _collector; 2997 CMSConcMarkingTask* _task; 2998 public: 2999 virtual void yield(); 3000 3001 // "n_threads" is the number of threads to be terminated. 3002 // "queue_set" is a set of work queues of other threads. 3003 // "collector" is the CMS collector associated with this task terminator. 3004 // "yield" indicates whether we need the gang as a whole to yield. 3005 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : 3006 ParallelTaskTerminator(n_threads, queue_set), 3007 _collector(collector) { } 3008 3009 void set_task(CMSConcMarkingTask* task) { 3010 _task = task; 3011 } 3012 }; 3013 3014 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator { 3015 CMSConcMarkingTask* _task; 3016 public: 3017 bool should_exit_termination(); 3018 void set_task(CMSConcMarkingTask* task) { 3019 _task = task; 3020 } 3021 }; 3022 3023 // MT Concurrent Marking Task 3024 class CMSConcMarkingTask: public YieldingFlexibleGangTask { 3025 CMSCollector* _collector; 3026 uint _n_workers; // requested/desired # workers 3027 bool _result; 3028 CompactibleFreeListSpace* _cms_space; 3029 char _pad_front[64]; // padding to ... 3030 HeapWord* _global_finger; // ... avoid sharing cache line 3031 char _pad_back[64]; 3032 HeapWord* _restart_addr; 3033 3034 // Exposed here for yielding support 3035 Mutex* const _bit_map_lock; 3036 3037 // The per thread work queues, available here for stealing 3038 OopTaskQueueSet* _task_queues; 3039 3040 // Termination (and yielding) support 3041 CMSConcMarkingTerminator _term; 3042 CMSConcMarkingTerminatorTerminator _term_term; 3043 3044 public: 3045 CMSConcMarkingTask(CMSCollector* collector, 3046 CompactibleFreeListSpace* cms_space, 3047 YieldingFlexibleWorkGang* workers, 3048 OopTaskQueueSet* task_queues): 3049 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), 3050 _collector(collector), 3051 _cms_space(cms_space), 3052 _n_workers(0), _result(true), 3053 _task_queues(task_queues), 3054 _term(_n_workers, task_queues, _collector), 3055 _bit_map_lock(collector->bitMapLock()) 3056 { 3057 _requested_size = _n_workers; 3058 _term.set_task(this); 3059 _term_term.set_task(this); 3060 _restart_addr = _global_finger = _cms_space->bottom(); 3061 } 3062 3063 3064 OopTaskQueueSet* task_queues() { return _task_queues; } 3065 3066 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 3067 3068 HeapWord** global_finger_addr() { return &_global_finger; } 3069 3070 CMSConcMarkingTerminator* terminator() { return &_term; } 3071 3072 virtual void set_for_termination(uint active_workers) { 3073 terminator()->reset_for_reuse(active_workers); 3074 } 3075 3076 void work(uint worker_id); 3077 bool should_yield() { 3078 return ConcurrentMarkSweepThread::should_yield() 3079 && !_collector->foregroundGCIsActive(); 3080 } 3081 3082 virtual void coordinator_yield(); // stuff done by coordinator 3083 bool result() { return _result; } 3084 3085 void reset(HeapWord* ra) { 3086 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)"); 3087 _restart_addr = _global_finger = ra; 3088 _term.reset_for_reuse(); 3089 } 3090 3091 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, 3092 OopTaskQueue* work_q); 3093 3094 private: 3095 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); 3096 void do_work_steal(int i); 3097 void bump_global_finger(HeapWord* f); 3098 }; 3099 3100 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() { 3101 assert(_task != NULL, "Error"); 3102 return _task->yielding(); 3103 // Note that we do not need the disjunct || _task->should_yield() above 3104 // because we want terminating threads to yield only if the task 3105 // is already in the midst of yielding, which happens only after at least one 3106 // thread has yielded. 3107 } 3108 3109 void CMSConcMarkingTerminator::yield() { 3110 if (_task->should_yield()) { 3111 _task->yield(); 3112 } else { 3113 ParallelTaskTerminator::yield(); 3114 } 3115 } 3116 3117 //////////////////////////////////////////////////////////////// 3118 // Concurrent Marking Algorithm Sketch 3119 //////////////////////////////////////////////////////////////// 3120 // Until all tasks exhausted (both spaces): 3121 // -- claim next available chunk 3122 // -- bump global finger via CAS 3123 // -- find first object that starts in this chunk 3124 // and start scanning bitmap from that position 3125 // -- scan marked objects for oops 3126 // -- CAS-mark target, and if successful: 3127 // . if target oop is above global finger (volatile read) 3128 // nothing to do 3129 // . if target oop is in chunk and above local finger 3130 // then nothing to do 3131 // . else push on work-queue 3132 // -- Deal with possible overflow issues: 3133 // . local work-queue overflow causes stuff to be pushed on 3134 // global (common) overflow queue 3135 // . always first empty local work queue 3136 // . then get a batch of oops from global work queue if any 3137 // . then do work stealing 3138 // -- When all tasks claimed (both spaces) 3139 // and local work queue empty, 3140 // then in a loop do: 3141 // . check global overflow stack; steal a batch of oops and trace 3142 // . try to steal from other threads oif GOS is empty 3143 // . if neither is available, offer termination 3144 // -- Terminate and return result 3145 // 3146 void CMSConcMarkingTask::work(uint worker_id) { 3147 elapsedTimer _timer; 3148 ResourceMark rm; 3149 HandleMark hm; 3150 3151 DEBUG_ONLY(_collector->verify_overflow_empty();) 3152 3153 // Before we begin work, our work queue should be empty 3154 assert(work_queue(worker_id)->size() == 0, "Expected to be empty"); 3155 // Scan the bitmap covering _cms_space, tracing through grey objects. 3156 _timer.start(); 3157 do_scan_and_mark(worker_id, _cms_space); 3158 _timer.stop(); 3159 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 3160 3161 // ... do work stealing 3162 _timer.reset(); 3163 _timer.start(); 3164 do_work_steal(worker_id); 3165 _timer.stop(); 3166 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 3167 assert(_collector->_markStack.isEmpty(), "Should have been emptied"); 3168 assert(work_queue(worker_id)->size() == 0, "Should have been emptied"); 3169 // Note that under the current task protocol, the 3170 // following assertion is true even of the spaces 3171 // expanded since the completion of the concurrent 3172 // marking. XXX This will likely change under a strict 3173 // ABORT semantics. 3174 // After perm removal the comparison was changed to 3175 // greater than or equal to from strictly greater than. 3176 // Before perm removal the highest address sweep would 3177 // have been at the end of perm gen but now is at the 3178 // end of the tenured gen. 3179 assert(_global_finger >= _cms_space->end(), 3180 "All tasks have been completed"); 3181 DEBUG_ONLY(_collector->verify_overflow_empty();) 3182 } 3183 3184 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { 3185 HeapWord* read = _global_finger; 3186 HeapWord* cur = read; 3187 while (f > read) { 3188 cur = read; 3189 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur); 3190 if (cur == read) { 3191 // our cas succeeded 3192 assert(_global_finger >= f, "protocol consistency"); 3193 break; 3194 } 3195 } 3196 } 3197 3198 // This is really inefficient, and should be redone by 3199 // using (not yet available) block-read and -write interfaces to the 3200 // stack and the work_queue. XXX FIX ME !!! 3201 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, 3202 OopTaskQueue* work_q) { 3203 // Fast lock-free check 3204 if (ovflw_stk->length() == 0) { 3205 return false; 3206 } 3207 assert(work_q->size() == 0, "Shouldn't steal"); 3208 MutexLockerEx ml(ovflw_stk->par_lock(), 3209 Mutex::_no_safepoint_check_flag); 3210 // Grab up to 1/4 the size of the work queue 3211 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 3212 (size_t)ParGCDesiredObjsFromOverflowList); 3213 num = MIN2(num, ovflw_stk->length()); 3214 for (int i = (int) num; i > 0; i--) { 3215 oop cur = ovflw_stk->pop(); 3216 assert(cur != NULL, "Counted wrong?"); 3217 work_q->push(cur); 3218 } 3219 return num > 0; 3220 } 3221 3222 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { 3223 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); 3224 int n_tasks = pst->n_tasks(); 3225 // We allow that there may be no tasks to do here because 3226 // we are restarting after a stack overflow. 3227 assert(pst->valid() || n_tasks == 0, "Uninitialized use?"); 3228 uint nth_task = 0; 3229 3230 HeapWord* aligned_start = sp->bottom(); 3231 if (sp->used_region().contains(_restart_addr)) { 3232 // Align down to a card boundary for the start of 0th task 3233 // for this space. 3234 aligned_start = 3235 (HeapWord*)align_size_down((uintptr_t)_restart_addr, 3236 CardTableModRefBS::card_size); 3237 } 3238 3239 size_t chunk_size = sp->marking_task_size(); 3240 while (!pst->is_task_claimed(/* reference */ nth_task)) { 3241 // Having claimed the nth task in this space, 3242 // compute the chunk that it corresponds to: 3243 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size, 3244 aligned_start + (nth_task+1)*chunk_size); 3245 // Try and bump the global finger via a CAS; 3246 // note that we need to do the global finger bump 3247 // _before_ taking the intersection below, because 3248 // the task corresponding to that region will be 3249 // deemed done even if the used_region() expands 3250 // because of allocation -- as it almost certainly will 3251 // during start-up while the threads yield in the 3252 // closure below. 3253 HeapWord* finger = span.end(); 3254 bump_global_finger(finger); // atomically 3255 // There are null tasks here corresponding to chunks 3256 // beyond the "top" address of the space. 3257 span = span.intersection(sp->used_region()); 3258 if (!span.is_empty()) { // Non-null task 3259 HeapWord* prev_obj; 3260 assert(!span.contains(_restart_addr) || nth_task == 0, 3261 "Inconsistency"); 3262 if (nth_task == 0) { 3263 // For the 0th task, we'll not need to compute a block_start. 3264 if (span.contains(_restart_addr)) { 3265 // In the case of a restart because of stack overflow, 3266 // we might additionally skip a chunk prefix. 3267 prev_obj = _restart_addr; 3268 } else { 3269 prev_obj = span.start(); 3270 } 3271 } else { 3272 // We want to skip the first object because 3273 // the protocol is to scan any object in its entirety 3274 // that _starts_ in this span; a fortiori, any 3275 // object starting in an earlier span is scanned 3276 // as part of an earlier claimed task. 3277 // Below we use the "careful" version of block_start 3278 // so we do not try to navigate uninitialized objects. 3279 prev_obj = sp->block_start_careful(span.start()); 3280 // Below we use a variant of block_size that uses the 3281 // Printezis bits to avoid waiting for allocated 3282 // objects to become initialized/parsable. 3283 while (prev_obj < span.start()) { 3284 size_t sz = sp->block_size_no_stall(prev_obj, _collector); 3285 if (sz > 0) { 3286 prev_obj += sz; 3287 } else { 3288 // In this case we may end up doing a bit of redundant 3289 // scanning, but that appears unavoidable, short of 3290 // locking the free list locks; see bug 6324141. 3291 break; 3292 } 3293 } 3294 } 3295 if (prev_obj < span.end()) { 3296 MemRegion my_span = MemRegion(prev_obj, span.end()); 3297 // Do the marking work within a non-empty span -- 3298 // the last argument to the constructor indicates whether the 3299 // iteration should be incremental with periodic yields. 3300 ParMarkFromRootsClosure cl(this, _collector, my_span, 3301 &_collector->_markBitMap, 3302 work_queue(i), 3303 &_collector->_markStack); 3304 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); 3305 } // else nothing to do for this task 3306 } // else nothing to do for this task 3307 } 3308 // We'd be tempted to assert here that since there are no 3309 // more tasks left to claim in this space, the global_finger 3310 // must exceed space->top() and a fortiori space->end(). However, 3311 // that would not quite be correct because the bumping of 3312 // global_finger occurs strictly after the claiming of a task, 3313 // so by the time we reach here the global finger may not yet 3314 // have been bumped up by the thread that claimed the last 3315 // task. 3316 pst->all_tasks_completed(); 3317 } 3318 3319 class ParConcMarkingClosure: public MetadataAwareOopClosure { 3320 private: 3321 CMSCollector* _collector; 3322 CMSConcMarkingTask* _task; 3323 MemRegion _span; 3324 CMSBitMap* _bit_map; 3325 CMSMarkStack* _overflow_stack; 3326 OopTaskQueue* _work_queue; 3327 protected: 3328 DO_OOP_WORK_DEFN 3329 public: 3330 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, 3331 CMSBitMap* bit_map, CMSMarkStack* overflow_stack): 3332 MetadataAwareOopClosure(collector->ref_processor()), 3333 _collector(collector), 3334 _task(task), 3335 _span(collector->_span), 3336 _work_queue(work_queue), 3337 _bit_map(bit_map), 3338 _overflow_stack(overflow_stack) 3339 { } 3340 virtual void do_oop(oop* p); 3341 virtual void do_oop(narrowOop* p); 3342 3343 void trim_queue(size_t max); 3344 void handle_stack_overflow(HeapWord* lost); 3345 void do_yield_check() { 3346 if (_task->should_yield()) { 3347 _task->yield(); 3348 } 3349 } 3350 }; 3351 3352 DO_OOP_WORK_IMPL(ParConcMarkingClosure) 3353 3354 // Grey object scanning during work stealing phase -- 3355 // the salient assumption here is that any references 3356 // that are in these stolen objects being scanned must 3357 // already have been initialized (else they would not have 3358 // been published), so we do not need to check for 3359 // uninitialized objects before pushing here. 3360 void ParConcMarkingClosure::do_oop(oop obj) { 3361 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 3362 HeapWord* addr = (HeapWord*)obj; 3363 // Check if oop points into the CMS generation 3364 // and is not marked 3365 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 3366 // a white object ... 3367 // If we manage to "claim" the object, by being the 3368 // first thread to mark it, then we push it on our 3369 // marking stack 3370 if (_bit_map->par_mark(addr)) { // ... now grey 3371 // push on work queue (grey set) 3372 bool simulate_overflow = false; 3373 NOT_PRODUCT( 3374 if (CMSMarkStackOverflowALot && 3375 _collector->simulate_overflow()) { 3376 // simulate a stack overflow 3377 simulate_overflow = true; 3378 } 3379 ) 3380 if (simulate_overflow || 3381 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { 3382 // stack overflow 3383 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity()); 3384 // We cannot assert that the overflow stack is full because 3385 // it may have been emptied since. 3386 assert(simulate_overflow || 3387 _work_queue->size() == _work_queue->max_elems(), 3388 "Else push should have succeeded"); 3389 handle_stack_overflow(addr); 3390 } 3391 } // Else, some other thread got there first 3392 do_yield_check(); 3393 } 3394 } 3395 3396 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); } 3397 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); } 3398 3399 void ParConcMarkingClosure::trim_queue(size_t max) { 3400 while (_work_queue->size() > max) { 3401 oop new_oop; 3402 if (_work_queue->pop_local(new_oop)) { 3403 assert(new_oop->is_oop(), "Should be an oop"); 3404 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); 3405 assert(_span.contains((HeapWord*)new_oop), "Not in span"); 3406 new_oop->oop_iterate(this); // do_oop() above 3407 do_yield_check(); 3408 } 3409 } 3410 } 3411 3412 // Upon stack overflow, we discard (part of) the stack, 3413 // remembering the least address amongst those discarded 3414 // in CMSCollector's _restart_address. 3415 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { 3416 // We need to do this under a mutex to prevent other 3417 // workers from interfering with the work done below. 3418 MutexLockerEx ml(_overflow_stack->par_lock(), 3419 Mutex::_no_safepoint_check_flag); 3420 // Remember the least grey address discarded 3421 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); 3422 _collector->lower_restart_addr(ra); 3423 _overflow_stack->reset(); // discard stack contents 3424 _overflow_stack->expand(); // expand the stack if possible 3425 } 3426 3427 3428 void CMSConcMarkingTask::do_work_steal(int i) { 3429 OopTaskQueue* work_q = work_queue(i); 3430 oop obj_to_scan; 3431 CMSBitMap* bm = &(_collector->_markBitMap); 3432 CMSMarkStack* ovflw = &(_collector->_markStack); 3433 int* seed = _collector->hash_seed(i); 3434 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw); 3435 while (true) { 3436 cl.trim_queue(0); 3437 assert(work_q->size() == 0, "Should have been emptied above"); 3438 if (get_work_from_overflow_stack(ovflw, work_q)) { 3439 // Can't assert below because the work obtained from the 3440 // overflow stack may already have been stolen from us. 3441 // assert(work_q->size() > 0, "Work from overflow stack"); 3442 continue; 3443 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 3444 assert(obj_to_scan->is_oop(), "Should be an oop"); 3445 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); 3446 obj_to_scan->oop_iterate(&cl); 3447 } else if (terminator()->offer_termination(&_term_term)) { 3448 assert(work_q->size() == 0, "Impossible!"); 3449 break; 3450 } else if (yielding() || should_yield()) { 3451 yield(); 3452 } 3453 } 3454 } 3455 3456 // This is run by the CMS (coordinator) thread. 3457 void CMSConcMarkingTask::coordinator_yield() { 3458 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 3459 "CMS thread should hold CMS token"); 3460 // First give up the locks, then yield, then re-lock 3461 // We should probably use a constructor/destructor idiom to 3462 // do this unlock/lock or modify the MutexUnlocker class to 3463 // serve our purpose. XXX 3464 assert_lock_strong(_bit_map_lock); 3465 _bit_map_lock->unlock(); 3466 ConcurrentMarkSweepThread::desynchronize(true); 3467 _collector->stopTimer(); 3468 _collector->incrementYields(); 3469 3470 // It is possible for whichever thread initiated the yield request 3471 // not to get a chance to wake up and take the bitmap lock between 3472 // this thread releasing it and reacquiring it. So, while the 3473 // should_yield() flag is on, let's sleep for a bit to give the 3474 // other thread a chance to wake up. The limit imposed on the number 3475 // of iterations is defensive, to avoid any unforseen circumstances 3476 // putting us into an infinite loop. Since it's always been this 3477 // (coordinator_yield()) method that was observed to cause the 3478 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) 3479 // which is by default non-zero. For the other seven methods that 3480 // also perform the yield operation, as are using a different 3481 // parameter (CMSYieldSleepCount) which is by default zero. This way we 3482 // can enable the sleeping for those methods too, if necessary. 3483 // See 6442774. 3484 // 3485 // We really need to reconsider the synchronization between the GC 3486 // thread and the yield-requesting threads in the future and we 3487 // should really use wait/notify, which is the recommended 3488 // way of doing this type of interaction. Additionally, we should 3489 // consolidate the eight methods that do the yield operation and they 3490 // are almost identical into one for better maintainability and 3491 // readability. See 6445193. 3492 // 3493 // Tony 2006.06.29 3494 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && 3495 ConcurrentMarkSweepThread::should_yield() && 3496 !CMSCollector::foregroundGCIsActive(); ++i) { 3497 os::sleep(Thread::current(), 1, false); 3498 } 3499 3500 ConcurrentMarkSweepThread::synchronize(true); 3501 _bit_map_lock->lock_without_safepoint_check(); 3502 _collector->startTimer(); 3503 } 3504 3505 bool CMSCollector::do_marking_mt() { 3506 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); 3507 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(), 3508 conc_workers()->active_workers(), 3509 Threads::number_of_non_daemon_threads()); 3510 conc_workers()->set_active_workers(num_workers); 3511 3512 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 3513 3514 CMSConcMarkingTask tsk(this, 3515 cms_space, 3516 conc_workers(), 3517 task_queues()); 3518 3519 // Since the actual number of workers we get may be different 3520 // from the number we requested above, do we need to do anything different 3521 // below? In particular, may be we need to subclass the SequantialSubTasksDone 3522 // class?? XXX 3523 cms_space ->initialize_sequential_subtasks_for_marking(num_workers); 3524 3525 // Refs discovery is already non-atomic. 3526 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); 3527 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT"); 3528 conc_workers()->start_task(&tsk); 3529 while (tsk.yielded()) { 3530 tsk.coordinator_yield(); 3531 conc_workers()->continue_task(&tsk); 3532 } 3533 // If the task was aborted, _restart_addr will be non-NULL 3534 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); 3535 while (_restart_addr != NULL) { 3536 // XXX For now we do not make use of ABORTED state and have not 3537 // yet implemented the right abort semantics (even in the original 3538 // single-threaded CMS case). That needs some more investigation 3539 // and is deferred for now; see CR# TBF. 07252005YSR. XXX 3540 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); 3541 // If _restart_addr is non-NULL, a marking stack overflow 3542 // occurred; we need to do a fresh marking iteration from the 3543 // indicated restart address. 3544 if (_foregroundGCIsActive) { 3545 // We may be running into repeated stack overflows, having 3546 // reached the limit of the stack size, while making very 3547 // slow forward progress. It may be best to bail out and 3548 // let the foreground collector do its job. 3549 // Clear _restart_addr, so that foreground GC 3550 // works from scratch. This avoids the headache of 3551 // a "rescan" which would otherwise be needed because 3552 // of the dirty mod union table & card table. 3553 _restart_addr = NULL; 3554 return false; 3555 } 3556 // Adjust the task to restart from _restart_addr 3557 tsk.reset(_restart_addr); 3558 cms_space ->initialize_sequential_subtasks_for_marking(num_workers, 3559 _restart_addr); 3560 _restart_addr = NULL; 3561 // Get the workers going again 3562 conc_workers()->start_task(&tsk); 3563 while (tsk.yielded()) { 3564 tsk.coordinator_yield(); 3565 conc_workers()->continue_task(&tsk); 3566 } 3567 } 3568 assert(tsk.completed(), "Inconsistency"); 3569 assert(tsk.result() == true, "Inconsistency"); 3570 return true; 3571 } 3572 3573 bool CMSCollector::do_marking_st() { 3574 ResourceMark rm; 3575 HandleMark hm; 3576 3577 // Temporarily make refs discovery single threaded (non-MT) 3578 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); 3579 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, 3580 &_markStack, CMSYield); 3581 // the last argument to iterate indicates whether the iteration 3582 // should be incremental with periodic yields. 3583 _markBitMap.iterate(&markFromRootsClosure); 3584 // If _restart_addr is non-NULL, a marking stack overflow 3585 // occurred; we need to do a fresh iteration from the 3586 // indicated restart address. 3587 while (_restart_addr != NULL) { 3588 if (_foregroundGCIsActive) { 3589 // We may be running into repeated stack overflows, having 3590 // reached the limit of the stack size, while making very 3591 // slow forward progress. It may be best to bail out and 3592 // let the foreground collector do its job. 3593 // Clear _restart_addr, so that foreground GC 3594 // works from scratch. This avoids the headache of 3595 // a "rescan" which would otherwise be needed because 3596 // of the dirty mod union table & card table. 3597 _restart_addr = NULL; 3598 return false; // indicating failure to complete marking 3599 } 3600 // Deal with stack overflow: 3601 // we restart marking from _restart_addr 3602 HeapWord* ra = _restart_addr; 3603 markFromRootsClosure.reset(ra); 3604 _restart_addr = NULL; 3605 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); 3606 } 3607 return true; 3608 } 3609 3610 void CMSCollector::preclean() { 3611 check_correct_thread_executing(); 3612 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); 3613 verify_work_stacks_empty(); 3614 verify_overflow_empty(); 3615 _abort_preclean = false; 3616 if (CMSPrecleaningEnabled) { 3617 if (!CMSEdenChunksRecordAlways) { 3618 _eden_chunk_index = 0; 3619 } 3620 size_t used = get_eden_used(); 3621 size_t capacity = get_eden_capacity(); 3622 // Don't start sampling unless we will get sufficiently 3623 // many samples. 3624 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100) 3625 * CMSScheduleRemarkEdenPenetration)) { 3626 _start_sampling = true; 3627 } else { 3628 _start_sampling = false; 3629 } 3630 GCTraceCPUTime tcpu; 3631 CMSPhaseAccounting pa(this, "Concurrent Preclean"); 3632 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); 3633 } 3634 CMSTokenSync x(true); // is cms thread 3635 if (CMSPrecleaningEnabled) { 3636 sample_eden(); 3637 _collectorState = AbortablePreclean; 3638 } else { 3639 _collectorState = FinalMarking; 3640 } 3641 verify_work_stacks_empty(); 3642 verify_overflow_empty(); 3643 } 3644 3645 // Try and schedule the remark such that young gen 3646 // occupancy is CMSScheduleRemarkEdenPenetration %. 3647 void CMSCollector::abortable_preclean() { 3648 check_correct_thread_executing(); 3649 assert(CMSPrecleaningEnabled, "Inconsistent control state"); 3650 assert(_collectorState == AbortablePreclean, "Inconsistent control state"); 3651 3652 // If Eden's current occupancy is below this threshold, 3653 // immediately schedule the remark; else preclean 3654 // past the next scavenge in an effort to 3655 // schedule the pause as described above. By choosing 3656 // CMSScheduleRemarkEdenSizeThreshold >= max eden size 3657 // we will never do an actual abortable preclean cycle. 3658 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { 3659 GCTraceCPUTime tcpu; 3660 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean"); 3661 // We need more smarts in the abortable preclean 3662 // loop below to deal with cases where allocation 3663 // in young gen is very very slow, and our precleaning 3664 // is running a losing race against a horde of 3665 // mutators intent on flooding us with CMS updates 3666 // (dirty cards). 3667 // One, admittedly dumb, strategy is to give up 3668 // after a certain number of abortable precleaning loops 3669 // or after a certain maximum time. We want to make 3670 // this smarter in the next iteration. 3671 // XXX FIX ME!!! YSR 3672 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; 3673 while (!(should_abort_preclean() || 3674 ConcurrentMarkSweepThread::cmst()->should_terminate())) { 3675 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); 3676 cumworkdone += workdone; 3677 loops++; 3678 // Voluntarily terminate abortable preclean phase if we have 3679 // been at it for too long. 3680 if ((CMSMaxAbortablePrecleanLoops != 0) && 3681 loops >= CMSMaxAbortablePrecleanLoops) { 3682 log_debug(gc)(" CMS: abort preclean due to loops "); 3683 break; 3684 } 3685 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { 3686 log_debug(gc)(" CMS: abort preclean due to time "); 3687 break; 3688 } 3689 // If we are doing little work each iteration, we should 3690 // take a short break. 3691 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { 3692 // Sleep for some time, waiting for work to accumulate 3693 stopTimer(); 3694 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); 3695 startTimer(); 3696 waited++; 3697 } 3698 } 3699 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ", 3700 loops, waited, cumworkdone); 3701 } 3702 CMSTokenSync x(true); // is cms thread 3703 if (_collectorState != Idling) { 3704 assert(_collectorState == AbortablePreclean, 3705 "Spontaneous state transition?"); 3706 _collectorState = FinalMarking; 3707 } // Else, a foreground collection completed this CMS cycle. 3708 return; 3709 } 3710 3711 // Respond to an Eden sampling opportunity 3712 void CMSCollector::sample_eden() { 3713 // Make sure a young gc cannot sneak in between our 3714 // reading and recording of a sample. 3715 assert(Thread::current()->is_ConcurrentGC_thread(), 3716 "Only the cms thread may collect Eden samples"); 3717 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 3718 "Should collect samples while holding CMS token"); 3719 if (!_start_sampling) { 3720 return; 3721 } 3722 // When CMSEdenChunksRecordAlways is true, the eden chunk array 3723 // is populated by the young generation. 3724 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) { 3725 if (_eden_chunk_index < _eden_chunk_capacity) { 3726 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample 3727 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, 3728 "Unexpected state of Eden"); 3729 // We'd like to check that what we just sampled is an oop-start address; 3730 // however, we cannot do that here since the object may not yet have been 3731 // initialized. So we'll instead do the check when we _use_ this sample 3732 // later. 3733 if (_eden_chunk_index == 0 || 3734 (pointer_delta(_eden_chunk_array[_eden_chunk_index], 3735 _eden_chunk_array[_eden_chunk_index-1]) 3736 >= CMSSamplingGrain)) { 3737 _eden_chunk_index++; // commit sample 3738 } 3739 } 3740 } 3741 if ((_collectorState == AbortablePreclean) && !_abort_preclean) { 3742 size_t used = get_eden_used(); 3743 size_t capacity = get_eden_capacity(); 3744 assert(used <= capacity, "Unexpected state of Eden"); 3745 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { 3746 _abort_preclean = true; 3747 } 3748 } 3749 } 3750 3751 3752 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { 3753 assert(_collectorState == Precleaning || 3754 _collectorState == AbortablePreclean, "incorrect state"); 3755 ResourceMark rm; 3756 HandleMark hm; 3757 3758 // Precleaning is currently not MT but the reference processor 3759 // may be set for MT. Disable it temporarily here. 3760 ReferenceProcessor* rp = ref_processor(); 3761 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false); 3762 3763 // Do one pass of scrubbing the discovered reference lists 3764 // to remove any reference objects with strongly-reachable 3765 // referents. 3766 if (clean_refs) { 3767 CMSPrecleanRefsYieldClosure yield_cl(this); 3768 assert(rp->span().equals(_span), "Spans should be equal"); 3769 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, 3770 &_markStack, true /* preclean */); 3771 CMSDrainMarkingStackClosure complete_trace(this, 3772 _span, &_markBitMap, &_markStack, 3773 &keep_alive, true /* preclean */); 3774 3775 // We don't want this step to interfere with a young 3776 // collection because we don't want to take CPU 3777 // or memory bandwidth away from the young GC threads 3778 // (which may be as many as there are CPUs). 3779 // Note that we don't need to protect ourselves from 3780 // interference with mutators because they can't 3781 // manipulate the discovered reference lists nor affect 3782 // the computed reachability of the referents, the 3783 // only properties manipulated by the precleaning 3784 // of these reference lists. 3785 stopTimer(); 3786 CMSTokenSyncWithLocks x(true /* is cms thread */, 3787 bitMapLock()); 3788 startTimer(); 3789 sample_eden(); 3790 3791 // The following will yield to allow foreground 3792 // collection to proceed promptly. XXX YSR: 3793 // The code in this method may need further 3794 // tweaking for better performance and some restructuring 3795 // for cleaner interfaces. 3796 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases 3797 rp->preclean_discovered_references( 3798 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl, 3799 gc_timer); 3800 } 3801 3802 if (clean_survivor) { // preclean the active survivor space(s) 3803 PushAndMarkClosure pam_cl(this, _span, ref_processor(), 3804 &_markBitMap, &_modUnionTable, 3805 &_markStack, true /* precleaning phase */); 3806 stopTimer(); 3807 CMSTokenSyncWithLocks ts(true /* is cms thread */, 3808 bitMapLock()); 3809 startTimer(); 3810 unsigned int before_count = 3811 GenCollectedHeap::heap()->total_collections(); 3812 SurvivorSpacePrecleanClosure 3813 sss_cl(this, _span, &_markBitMap, &_markStack, 3814 &pam_cl, before_count, CMSYield); 3815 _young_gen->from()->object_iterate_careful(&sss_cl); 3816 _young_gen->to()->object_iterate_careful(&sss_cl); 3817 } 3818 MarkRefsIntoAndScanClosure 3819 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, 3820 &_markStack, this, CMSYield, 3821 true /* precleaning phase */); 3822 // CAUTION: The following closure has persistent state that may need to 3823 // be reset upon a decrease in the sequence of addresses it 3824 // processes. 3825 ScanMarkedObjectsAgainCarefullyClosure 3826 smoac_cl(this, _span, 3827 &_markBitMap, &_markStack, &mrias_cl, CMSYield); 3828 3829 // Preclean dirty cards in ModUnionTable and CardTable using 3830 // appropriate convergence criterion; 3831 // repeat CMSPrecleanIter times unless we find that 3832 // we are losing. 3833 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); 3834 assert(CMSPrecleanNumerator < CMSPrecleanDenominator, 3835 "Bad convergence multiplier"); 3836 assert(CMSPrecleanThreshold >= 100, 3837 "Unreasonably low CMSPrecleanThreshold"); 3838 3839 size_t numIter, cumNumCards, lastNumCards, curNumCards; 3840 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; 3841 numIter < CMSPrecleanIter; 3842 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { 3843 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); 3844 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards); 3845 // Either there are very few dirty cards, so re-mark 3846 // pause will be small anyway, or our pre-cleaning isn't 3847 // that much faster than the rate at which cards are being 3848 // dirtied, so we might as well stop and re-mark since 3849 // precleaning won't improve our re-mark time by much. 3850 if (curNumCards <= CMSPrecleanThreshold || 3851 (numIter > 0 && 3852 (curNumCards * CMSPrecleanDenominator > 3853 lastNumCards * CMSPrecleanNumerator))) { 3854 numIter++; 3855 cumNumCards += curNumCards; 3856 break; 3857 } 3858 } 3859 3860 preclean_klasses(&mrias_cl, _cmsGen->freelistLock()); 3861 3862 curNumCards = preclean_card_table(_cmsGen, &smoac_cl); 3863 cumNumCards += curNumCards; 3864 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)", 3865 curNumCards, cumNumCards, numIter); 3866 return cumNumCards; // as a measure of useful work done 3867 } 3868 3869 // PRECLEANING NOTES: 3870 // Precleaning involves: 3871 // . reading the bits of the modUnionTable and clearing the set bits. 3872 // . For the cards corresponding to the set bits, we scan the 3873 // objects on those cards. This means we need the free_list_lock 3874 // so that we can safely iterate over the CMS space when scanning 3875 // for oops. 3876 // . When we scan the objects, we'll be both reading and setting 3877 // marks in the marking bit map, so we'll need the marking bit map. 3878 // . For protecting _collector_state transitions, we take the CGC_lock. 3879 // Note that any races in the reading of of card table entries by the 3880 // CMS thread on the one hand and the clearing of those entries by the 3881 // VM thread or the setting of those entries by the mutator threads on the 3882 // other are quite benign. However, for efficiency it makes sense to keep 3883 // the VM thread from racing with the CMS thread while the latter is 3884 // dirty card info to the modUnionTable. We therefore also use the 3885 // CGC_lock to protect the reading of the card table and the mod union 3886 // table by the CM thread. 3887 // . We run concurrently with mutator updates, so scanning 3888 // needs to be done carefully -- we should not try to scan 3889 // potentially uninitialized objects. 3890 // 3891 // Locking strategy: While holding the CGC_lock, we scan over and 3892 // reset a maximal dirty range of the mod union / card tables, then lock 3893 // the free_list_lock and bitmap lock to do a full marking, then 3894 // release these locks; and repeat the cycle. This allows for a 3895 // certain amount of fairness in the sharing of these locks between 3896 // the CMS collector on the one hand, and the VM thread and the 3897 // mutators on the other. 3898 3899 // NOTE: preclean_mod_union_table() and preclean_card_table() 3900 // further below are largely identical; if you need to modify 3901 // one of these methods, please check the other method too. 3902 3903 size_t CMSCollector::preclean_mod_union_table( 3904 ConcurrentMarkSweepGeneration* old_gen, 3905 ScanMarkedObjectsAgainCarefullyClosure* cl) { 3906 verify_work_stacks_empty(); 3907 verify_overflow_empty(); 3908 3909 // strategy: starting with the first card, accumulate contiguous 3910 // ranges of dirty cards; clear these cards, then scan the region 3911 // covered by these cards. 3912 3913 // Since all of the MUT is committed ahead, we can just use 3914 // that, in case the generations expand while we are precleaning. 3915 // It might also be fine to just use the committed part of the 3916 // generation, but we might potentially miss cards when the 3917 // generation is rapidly expanding while we are in the midst 3918 // of precleaning. 3919 HeapWord* startAddr = old_gen->reserved().start(); 3920 HeapWord* endAddr = old_gen->reserved().end(); 3921 3922 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding 3923 3924 size_t numDirtyCards, cumNumDirtyCards; 3925 HeapWord *nextAddr, *lastAddr; 3926 for (cumNumDirtyCards = numDirtyCards = 0, 3927 nextAddr = lastAddr = startAddr; 3928 nextAddr < endAddr; 3929 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { 3930 3931 ResourceMark rm; 3932 HandleMark hm; 3933 3934 MemRegion dirtyRegion; 3935 { 3936 stopTimer(); 3937 // Potential yield point 3938 CMSTokenSync ts(true); 3939 startTimer(); 3940 sample_eden(); 3941 // Get dirty region starting at nextOffset (inclusive), 3942 // simultaneously clearing it. 3943 dirtyRegion = 3944 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); 3945 assert(dirtyRegion.start() >= nextAddr, 3946 "returned region inconsistent?"); 3947 } 3948 // Remember where the next search should begin. 3949 // The returned region (if non-empty) is a right open interval, 3950 // so lastOffset is obtained from the right end of that 3951 // interval. 3952 lastAddr = dirtyRegion.end(); 3953 // Should do something more transparent and less hacky XXX 3954 numDirtyCards = 3955 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); 3956 3957 // We'll scan the cards in the dirty region (with periodic 3958 // yields for foreground GC as needed). 3959 if (!dirtyRegion.is_empty()) { 3960 assert(numDirtyCards > 0, "consistency check"); 3961 HeapWord* stop_point = NULL; 3962 stopTimer(); 3963 // Potential yield point 3964 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), 3965 bitMapLock()); 3966 startTimer(); 3967 { 3968 verify_work_stacks_empty(); 3969 verify_overflow_empty(); 3970 sample_eden(); 3971 stop_point = 3972 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); 3973 } 3974 if (stop_point != NULL) { 3975 // The careful iteration stopped early either because it found an 3976 // uninitialized object, or because we were in the midst of an 3977 // "abortable preclean", which should now be aborted. Redirty 3978 // the bits corresponding to the partially-scanned or unscanned 3979 // cards. We'll either restart at the next block boundary or 3980 // abort the preclean. 3981 assert((_collectorState == AbortablePreclean && should_abort_preclean()), 3982 "Should only be AbortablePreclean."); 3983 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); 3984 if (should_abort_preclean()) { 3985 break; // out of preclean loop 3986 } else { 3987 // Compute the next address at which preclean should pick up; 3988 // might need bitMapLock in order to read P-bits. 3989 lastAddr = next_card_start_after_block(stop_point); 3990 } 3991 } 3992 } else { 3993 assert(lastAddr == endAddr, "consistency check"); 3994 assert(numDirtyCards == 0, "consistency check"); 3995 break; 3996 } 3997 } 3998 verify_work_stacks_empty(); 3999 verify_overflow_empty(); 4000 return cumNumDirtyCards; 4001 } 4002 4003 // NOTE: preclean_mod_union_table() above and preclean_card_table() 4004 // below are largely identical; if you need to modify 4005 // one of these methods, please check the other method too. 4006 4007 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen, 4008 ScanMarkedObjectsAgainCarefullyClosure* cl) { 4009 // strategy: it's similar to precleamModUnionTable above, in that 4010 // we accumulate contiguous ranges of dirty cards, mark these cards 4011 // precleaned, then scan the region covered by these cards. 4012 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high()); 4013 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low()); 4014 4015 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding 4016 4017 size_t numDirtyCards, cumNumDirtyCards; 4018 HeapWord *lastAddr, *nextAddr; 4019 4020 for (cumNumDirtyCards = numDirtyCards = 0, 4021 nextAddr = lastAddr = startAddr; 4022 nextAddr < endAddr; 4023 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { 4024 4025 ResourceMark rm; 4026 HandleMark hm; 4027 4028 MemRegion dirtyRegion; 4029 { 4030 // See comments in "Precleaning notes" above on why we 4031 // do this locking. XXX Could the locking overheads be 4032 // too high when dirty cards are sparse? [I don't think so.] 4033 stopTimer(); 4034 CMSTokenSync x(true); // is cms thread 4035 startTimer(); 4036 sample_eden(); 4037 // Get and clear dirty region from card table 4038 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset( 4039 MemRegion(nextAddr, endAddr), 4040 true, 4041 CardTableModRefBS::precleaned_card_val()); 4042 4043 assert(dirtyRegion.start() >= nextAddr, 4044 "returned region inconsistent?"); 4045 } 4046 lastAddr = dirtyRegion.end(); 4047 numDirtyCards = 4048 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words; 4049 4050 if (!dirtyRegion.is_empty()) { 4051 stopTimer(); 4052 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock()); 4053 startTimer(); 4054 sample_eden(); 4055 verify_work_stacks_empty(); 4056 verify_overflow_empty(); 4057 HeapWord* stop_point = 4058 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); 4059 if (stop_point != NULL) { 4060 assert((_collectorState == AbortablePreclean && should_abort_preclean()), 4061 "Should only be AbortablePreclean."); 4062 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end())); 4063 if (should_abort_preclean()) { 4064 break; // out of preclean loop 4065 } else { 4066 // Compute the next address at which preclean should pick up. 4067 lastAddr = next_card_start_after_block(stop_point); 4068 } 4069 } 4070 } else { 4071 break; 4072 } 4073 } 4074 verify_work_stacks_empty(); 4075 verify_overflow_empty(); 4076 return cumNumDirtyCards; 4077 } 4078 4079 class PrecleanKlassClosure : public KlassClosure { 4080 KlassToOopClosure _cm_klass_closure; 4081 public: 4082 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {} 4083 void do_klass(Klass* k) { 4084 if (k->has_accumulated_modified_oops()) { 4085 k->clear_accumulated_modified_oops(); 4086 4087 _cm_klass_closure.do_klass(k); 4088 } 4089 } 4090 }; 4091 4092 // The freelist lock is needed to prevent asserts, is it really needed? 4093 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) { 4094 4095 cl->set_freelistLock(freelistLock); 4096 4097 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock()); 4098 4099 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean? 4100 // SSS: We should probably check if precleaning should be aborted, at suitable intervals? 4101 PrecleanKlassClosure preclean_klass_closure(cl); 4102 ClassLoaderDataGraph::classes_do(&preclean_klass_closure); 4103 4104 verify_work_stacks_empty(); 4105 verify_overflow_empty(); 4106 } 4107 4108 void CMSCollector::checkpointRootsFinal() { 4109 assert(_collectorState == FinalMarking, "incorrect state transition?"); 4110 check_correct_thread_executing(); 4111 // world is stopped at this checkpoint 4112 assert(SafepointSynchronize::is_at_safepoint(), 4113 "world should be stopped"); 4114 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); 4115 4116 verify_work_stacks_empty(); 4117 verify_overflow_empty(); 4118 4119 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)", 4120 _young_gen->used() / K, _young_gen->capacity() / K); 4121 { 4122 if (CMSScavengeBeforeRemark) { 4123 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4124 // Temporarily set flag to false, GCH->do_collection will 4125 // expect it to be false and set to true 4126 FlagSetting fl(gch->_is_gc_active, false); 4127 4128 gch->do_collection(true, // full (i.e. force, see below) 4129 false, // !clear_all_soft_refs 4130 0, // size 4131 false, // is_tlab 4132 GenCollectedHeap::YoungGen // type 4133 ); 4134 } 4135 FreelistLocker x(this); 4136 MutexLockerEx y(bitMapLock(), 4137 Mutex::_no_safepoint_check_flag); 4138 checkpointRootsFinalWork(); 4139 } 4140 verify_work_stacks_empty(); 4141 verify_overflow_empty(); 4142 } 4143 4144 void CMSCollector::checkpointRootsFinalWork() { 4145 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm); 4146 4147 assert(haveFreelistLocks(), "must have free list locks"); 4148 assert_lock_strong(bitMapLock()); 4149 4150 ResourceMark rm; 4151 HandleMark hm; 4152 4153 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4154 4155 if (should_unload_classes()) { 4156 CodeCache::gc_prologue(); 4157 } 4158 assert(haveFreelistLocks(), "must have free list locks"); 4159 assert_lock_strong(bitMapLock()); 4160 4161 // We might assume that we need not fill TLAB's when 4162 // CMSScavengeBeforeRemark is set, because we may have just done 4163 // a scavenge which would have filled all TLAB's -- and besides 4164 // Eden would be empty. This however may not always be the case -- 4165 // for instance although we asked for a scavenge, it may not have 4166 // happened because of a JNI critical section. We probably need 4167 // a policy for deciding whether we can in that case wait until 4168 // the critical section releases and then do the remark following 4169 // the scavenge, and skip it here. In the absence of that policy, 4170 // or of an indication of whether the scavenge did indeed occur, 4171 // we cannot rely on TLAB's having been filled and must do 4172 // so here just in case a scavenge did not happen. 4173 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them 4174 // Update the saved marks which may affect the root scans. 4175 gch->save_marks(); 4176 4177 print_eden_and_survivor_chunk_arrays(); 4178 4179 { 4180 #if defined(COMPILER2) || INCLUDE_JVMCI 4181 DerivedPointerTableDeactivate dpt_deact; 4182 #endif 4183 4184 // Note on the role of the mod union table: 4185 // Since the marker in "markFromRoots" marks concurrently with 4186 // mutators, it is possible for some reachable objects not to have been 4187 // scanned. For instance, an only reference to an object A was 4188 // placed in object B after the marker scanned B. Unless B is rescanned, 4189 // A would be collected. Such updates to references in marked objects 4190 // are detected via the mod union table which is the set of all cards 4191 // dirtied since the first checkpoint in this GC cycle and prior to 4192 // the most recent young generation GC, minus those cleaned up by the 4193 // concurrent precleaning. 4194 if (CMSParallelRemarkEnabled) { 4195 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm); 4196 do_remark_parallel(); 4197 } else { 4198 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm); 4199 do_remark_non_parallel(); 4200 } 4201 } 4202 verify_work_stacks_empty(); 4203 verify_overflow_empty(); 4204 4205 { 4206 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm); 4207 refProcessingWork(); 4208 } 4209 verify_work_stacks_empty(); 4210 verify_overflow_empty(); 4211 4212 if (should_unload_classes()) { 4213 CodeCache::gc_epilogue(); 4214 } 4215 JvmtiExport::gc_epilogue(); 4216 4217 // If we encountered any (marking stack / work queue) overflow 4218 // events during the current CMS cycle, take appropriate 4219 // remedial measures, where possible, so as to try and avoid 4220 // recurrence of that condition. 4221 assert(_markStack.isEmpty(), "No grey objects"); 4222 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + 4223 _ser_kac_ovflw + _ser_kac_preclean_ovflw; 4224 if (ser_ovflw > 0) { 4225 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")", 4226 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw); 4227 _markStack.expand(); 4228 _ser_pmc_remark_ovflw = 0; 4229 _ser_pmc_preclean_ovflw = 0; 4230 _ser_kac_preclean_ovflw = 0; 4231 _ser_kac_ovflw = 0; 4232 } 4233 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { 4234 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")", 4235 _par_pmc_remark_ovflw, _par_kac_ovflw); 4236 _par_pmc_remark_ovflw = 0; 4237 _par_kac_ovflw = 0; 4238 } 4239 if (_markStack._hit_limit > 0) { 4240 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")", 4241 _markStack._hit_limit); 4242 } 4243 if (_markStack._failed_double > 0) { 4244 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT, 4245 _markStack._failed_double, _markStack.capacity()); 4246 } 4247 _markStack._hit_limit = 0; 4248 _markStack._failed_double = 0; 4249 4250 if ((VerifyAfterGC || VerifyDuringGC) && 4251 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 4252 verify_after_remark(); 4253 } 4254 4255 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure); 4256 4257 // Change under the freelistLocks. 4258 _collectorState = Sweeping; 4259 // Call isAllClear() under bitMapLock 4260 assert(_modUnionTable.isAllClear(), 4261 "Should be clear by end of the final marking"); 4262 assert(_ct->klass_rem_set()->mod_union_is_clear(), 4263 "Should be clear by end of the final marking"); 4264 } 4265 4266 void CMSParInitialMarkTask::work(uint worker_id) { 4267 elapsedTimer _timer; 4268 ResourceMark rm; 4269 HandleMark hm; 4270 4271 // ---------- scan from roots -------------- 4272 _timer.start(); 4273 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4274 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap)); 4275 4276 // ---------- young gen roots -------------- 4277 { 4278 work_on_young_gen_roots(&par_mri_cl); 4279 _timer.stop(); 4280 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4281 } 4282 4283 // ---------- remaining roots -------------- 4284 _timer.reset(); 4285 _timer.start(); 4286 4287 CLDToOopClosure cld_closure(&par_mri_cl, true); 4288 4289 gch->gen_process_roots(_strong_roots_scope, 4290 GenCollectedHeap::OldGen, 4291 false, // yg was scanned above 4292 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), 4293 _collector->should_unload_classes(), 4294 &par_mri_cl, 4295 NULL, 4296 &cld_closure); 4297 assert(_collector->should_unload_classes() 4298 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), 4299 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 4300 _timer.stop(); 4301 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4302 } 4303 4304 // Parallel remark task 4305 class CMSParRemarkTask: public CMSParMarkTask { 4306 CompactibleFreeListSpace* _cms_space; 4307 4308 // The per-thread work queues, available here for stealing. 4309 OopTaskQueueSet* _task_queues; 4310 ParallelTaskTerminator _term; 4311 StrongRootsScope* _strong_roots_scope; 4312 4313 public: 4314 // A value of 0 passed to n_workers will cause the number of 4315 // workers to be taken from the active workers in the work gang. 4316 CMSParRemarkTask(CMSCollector* collector, 4317 CompactibleFreeListSpace* cms_space, 4318 uint n_workers, WorkGang* workers, 4319 OopTaskQueueSet* task_queues, 4320 StrongRootsScope* strong_roots_scope): 4321 CMSParMarkTask("Rescan roots and grey objects in parallel", 4322 collector, n_workers), 4323 _cms_space(cms_space), 4324 _task_queues(task_queues), 4325 _term(n_workers, task_queues), 4326 _strong_roots_scope(strong_roots_scope) { } 4327 4328 OopTaskQueueSet* task_queues() { return _task_queues; } 4329 4330 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 4331 4332 ParallelTaskTerminator* terminator() { return &_term; } 4333 uint n_workers() { return _n_workers; } 4334 4335 void work(uint worker_id); 4336 4337 private: 4338 // ... of dirty cards in old space 4339 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, 4340 ParMarkRefsIntoAndScanClosure* cl); 4341 4342 // ... work stealing for the above 4343 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed); 4344 }; 4345 4346 class RemarkKlassClosure : public KlassClosure { 4347 KlassToOopClosure _cm_klass_closure; 4348 public: 4349 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {} 4350 void do_klass(Klass* k) { 4351 // Check if we have modified any oops in the Klass during the concurrent marking. 4352 if (k->has_accumulated_modified_oops()) { 4353 k->clear_accumulated_modified_oops(); 4354 4355 // We could have transfered the current modified marks to the accumulated marks, 4356 // like we do with the Card Table to Mod Union Table. But it's not really necessary. 4357 } else if (k->has_modified_oops()) { 4358 // Don't clear anything, this info is needed by the next young collection. 4359 } else { 4360 // No modified oops in the Klass. 4361 return; 4362 } 4363 4364 // The klass has modified fields, need to scan the klass. 4365 _cm_klass_closure.do_klass(k); 4366 } 4367 }; 4368 4369 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) { 4370 ParNewGeneration* young_gen = _collector->_young_gen; 4371 ContiguousSpace* eden_space = young_gen->eden(); 4372 ContiguousSpace* from_space = young_gen->from(); 4373 ContiguousSpace* to_space = young_gen->to(); 4374 4375 HeapWord** eca = _collector->_eden_chunk_array; 4376 size_t ect = _collector->_eden_chunk_index; 4377 HeapWord** sca = _collector->_survivor_chunk_array; 4378 size_t sct = _collector->_survivor_chunk_index; 4379 4380 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); 4381 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); 4382 4383 do_young_space_rescan(cl, to_space, NULL, 0); 4384 do_young_space_rescan(cl, from_space, sca, sct); 4385 do_young_space_rescan(cl, eden_space, eca, ect); 4386 } 4387 4388 // work_queue(i) is passed to the closure 4389 // ParMarkRefsIntoAndScanClosure. The "i" parameter 4390 // also is passed to do_dirty_card_rescan_tasks() and to 4391 // do_work_steal() to select the i-th task_queue. 4392 4393 void CMSParRemarkTask::work(uint worker_id) { 4394 elapsedTimer _timer; 4395 ResourceMark rm; 4396 HandleMark hm; 4397 4398 // ---------- rescan from roots -------------- 4399 _timer.start(); 4400 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4401 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector, 4402 _collector->_span, _collector->ref_processor(), 4403 &(_collector->_markBitMap), 4404 work_queue(worker_id)); 4405 4406 // Rescan young gen roots first since these are likely 4407 // coarsely partitioned and may, on that account, constitute 4408 // the critical path; thus, it's best to start off that 4409 // work first. 4410 // ---------- young gen roots -------------- 4411 { 4412 work_on_young_gen_roots(&par_mrias_cl); 4413 _timer.stop(); 4414 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4415 } 4416 4417 // ---------- remaining roots -------------- 4418 _timer.reset(); 4419 _timer.start(); 4420 gch->gen_process_roots(_strong_roots_scope, 4421 GenCollectedHeap::OldGen, 4422 false, // yg was scanned above 4423 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), 4424 _collector->should_unload_classes(), 4425 &par_mrias_cl, 4426 NULL, 4427 NULL); // The dirty klasses will be handled below 4428 4429 assert(_collector->should_unload_classes() 4430 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), 4431 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 4432 _timer.stop(); 4433 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4434 4435 // ---------- unhandled CLD scanning ---------- 4436 if (worker_id == 0) { // Single threaded at the moment. 4437 _timer.reset(); 4438 _timer.start(); 4439 4440 // Scan all new class loader data objects and new dependencies that were 4441 // introduced during concurrent marking. 4442 ResourceMark rm; 4443 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); 4444 for (int i = 0; i < array->length(); i++) { 4445 par_mrias_cl.do_cld_nv(array->at(i)); 4446 } 4447 4448 // We don't need to keep track of new CLDs anymore. 4449 ClassLoaderDataGraph::remember_new_clds(false); 4450 4451 _timer.stop(); 4452 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4453 } 4454 4455 // ---------- dirty klass scanning ---------- 4456 if (worker_id == 0) { // Single threaded at the moment. 4457 _timer.reset(); 4458 _timer.start(); 4459 4460 // Scan all classes that was dirtied during the concurrent marking phase. 4461 RemarkKlassClosure remark_klass_closure(&par_mrias_cl); 4462 ClassLoaderDataGraph::classes_do(&remark_klass_closure); 4463 4464 _timer.stop(); 4465 log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4466 } 4467 4468 // We might have added oops to ClassLoaderData::_handles during the 4469 // concurrent marking phase. These oops point to newly allocated objects 4470 // that are guaranteed to be kept alive. Either by the direct allocation 4471 // code, or when the young collector processes the roots. Hence, 4472 // we don't have to revisit the _handles block during the remark phase. 4473 4474 // ---------- rescan dirty cards ------------ 4475 _timer.reset(); 4476 _timer.start(); 4477 4478 // Do the rescan tasks for each of the two spaces 4479 // (cms_space) in turn. 4480 // "worker_id" is passed to select the task_queue for "worker_id" 4481 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl); 4482 _timer.stop(); 4483 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4484 4485 // ---------- steal work from other threads ... 4486 // ---------- ... and drain overflow list. 4487 _timer.reset(); 4488 _timer.start(); 4489 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id)); 4490 _timer.stop(); 4491 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); 4492 } 4493 4494 void 4495 CMSParMarkTask::do_young_space_rescan( 4496 OopsInGenClosure* cl, ContiguousSpace* space, 4497 HeapWord** chunk_array, size_t chunk_top) { 4498 // Until all tasks completed: 4499 // . claim an unclaimed task 4500 // . compute region boundaries corresponding to task claimed 4501 // using chunk_array 4502 // . par_oop_iterate(cl) over that region 4503 4504 ResourceMark rm; 4505 HandleMark hm; 4506 4507 SequentialSubTasksDone* pst = space->par_seq_tasks(); 4508 4509 uint nth_task = 0; 4510 uint n_tasks = pst->n_tasks(); 4511 4512 if (n_tasks > 0) { 4513 assert(pst->valid(), "Uninitialized use?"); 4514 HeapWord *start, *end; 4515 while (!pst->is_task_claimed(/* reference */ nth_task)) { 4516 // We claimed task # nth_task; compute its boundaries. 4517 if (chunk_top == 0) { // no samples were taken 4518 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task"); 4519 start = space->bottom(); 4520 end = space->top(); 4521 } else if (nth_task == 0) { 4522 start = space->bottom(); 4523 end = chunk_array[nth_task]; 4524 } else if (nth_task < (uint)chunk_top) { 4525 assert(nth_task >= 1, "Control point invariant"); 4526 start = chunk_array[nth_task - 1]; 4527 end = chunk_array[nth_task]; 4528 } else { 4529 assert(nth_task == (uint)chunk_top, "Control point invariant"); 4530 start = chunk_array[chunk_top - 1]; 4531 end = space->top(); 4532 } 4533 MemRegion mr(start, end); 4534 // Verify that mr is in space 4535 assert(mr.is_empty() || space->used_region().contains(mr), 4536 "Should be in space"); 4537 // Verify that "start" is an object boundary 4538 assert(mr.is_empty() || oop(mr.start())->is_oop(), 4539 "Should be an oop"); 4540 space->par_oop_iterate(mr, cl); 4541 } 4542 pst->all_tasks_completed(); 4543 } 4544 } 4545 4546 void 4547 CMSParRemarkTask::do_dirty_card_rescan_tasks( 4548 CompactibleFreeListSpace* sp, int i, 4549 ParMarkRefsIntoAndScanClosure* cl) { 4550 // Until all tasks completed: 4551 // . claim an unclaimed task 4552 // . compute region boundaries corresponding to task claimed 4553 // . transfer dirty bits ct->mut for that region 4554 // . apply rescanclosure to dirty mut bits for that region 4555 4556 ResourceMark rm; 4557 HandleMark hm; 4558 4559 OopTaskQueue* work_q = work_queue(i); 4560 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); 4561 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! 4562 // CAUTION: This closure has state that persists across calls to 4563 // the work method dirty_range_iterate_clear() in that it has 4564 // embedded in it a (subtype of) UpwardsObjectClosure. The 4565 // use of that state in the embedded UpwardsObjectClosure instance 4566 // assumes that the cards are always iterated (even if in parallel 4567 // by several threads) in monotonically increasing order per each 4568 // thread. This is true of the implementation below which picks 4569 // card ranges (chunks) in monotonically increasing order globally 4570 // and, a-fortiori, in monotonically increasing order per thread 4571 // (the latter order being a subsequence of the former). 4572 // If the work code below is ever reorganized into a more chaotic 4573 // work-partitioning form than the current "sequential tasks" 4574 // paradigm, the use of that persistent state will have to be 4575 // revisited and modified appropriately. See also related 4576 // bug 4756801 work on which should examine this code to make 4577 // sure that the changes there do not run counter to the 4578 // assumptions made here and necessary for correctness and 4579 // efficiency. Note also that this code might yield inefficient 4580 // behavior in the case of very large objects that span one or 4581 // more work chunks. Such objects would potentially be scanned 4582 // several times redundantly. Work on 4756801 should try and 4583 // address that performance anomaly if at all possible. XXX 4584 MemRegion full_span = _collector->_span; 4585 CMSBitMap* bm = &(_collector->_markBitMap); // shared 4586 MarkFromDirtyCardsClosure 4587 greyRescanClosure(_collector, full_span, // entire span of interest 4588 sp, bm, work_q, cl); 4589 4590 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); 4591 assert(pst->valid(), "Uninitialized use?"); 4592 uint nth_task = 0; 4593 const int alignment = CardTableModRefBS::card_size * BitsPerWord; 4594 MemRegion span = sp->used_region(); 4595 HeapWord* start_addr = span.start(); 4596 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(), 4597 alignment); 4598 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units 4599 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) == 4600 start_addr, "Check alignment"); 4601 assert((size_t)round_to((intptr_t)chunk_size, alignment) == 4602 chunk_size, "Check alignment"); 4603 4604 while (!pst->is_task_claimed(/* reference */ nth_task)) { 4605 // Having claimed the nth_task, compute corresponding mem-region, 4606 // which is a-fortiori aligned correctly (i.e. at a MUT boundary). 4607 // The alignment restriction ensures that we do not need any 4608 // synchronization with other gang-workers while setting or 4609 // clearing bits in thus chunk of the MUT. 4610 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, 4611 start_addr + (nth_task+1)*chunk_size); 4612 // The last chunk's end might be way beyond end of the 4613 // used region. In that case pull back appropriately. 4614 if (this_span.end() > end_addr) { 4615 this_span.set_end(end_addr); 4616 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); 4617 } 4618 // Iterate over the dirty cards covering this chunk, marking them 4619 // precleaned, and setting the corresponding bits in the mod union 4620 // table. Since we have been careful to partition at Card and MUT-word 4621 // boundaries no synchronization is needed between parallel threads. 4622 _collector->_ct->ct_bs()->dirty_card_iterate(this_span, 4623 &modUnionClosure); 4624 4625 // Having transferred these marks into the modUnionTable, 4626 // rescan the marked objects on the dirty cards in the modUnionTable. 4627 // Even if this is at a synchronous collection, the initial marking 4628 // may have been done during an asynchronous collection so there 4629 // may be dirty bits in the mod-union table. 4630 _collector->_modUnionTable.dirty_range_iterate_clear( 4631 this_span, &greyRescanClosure); 4632 _collector->_modUnionTable.verifyNoOneBitsInRange( 4633 this_span.start(), 4634 this_span.end()); 4635 } 4636 pst->all_tasks_completed(); // declare that i am done 4637 } 4638 4639 // . see if we can share work_queues with ParNew? XXX 4640 void 4641 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, 4642 int* seed) { 4643 OopTaskQueue* work_q = work_queue(i); 4644 NOT_PRODUCT(int num_steals = 0;) 4645 oop obj_to_scan; 4646 CMSBitMap* bm = &(_collector->_markBitMap); 4647 4648 while (true) { 4649 // Completely finish any left over work from (an) earlier round(s) 4650 cl->trim_queue(0); 4651 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 4652 (size_t)ParGCDesiredObjsFromOverflowList); 4653 // Now check if there's any work in the overflow list 4654 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, 4655 // only affects the number of attempts made to get work from the 4656 // overflow list and does not affect the number of workers. Just 4657 // pass ParallelGCThreads so this behavior is unchanged. 4658 if (_collector->par_take_from_overflow_list(num_from_overflow_list, 4659 work_q, 4660 ParallelGCThreads)) { 4661 // found something in global overflow list; 4662 // not yet ready to go stealing work from others. 4663 // We'd like to assert(work_q->size() != 0, ...) 4664 // because we just took work from the overflow list, 4665 // but of course we can't since all of that could have 4666 // been already stolen from us. 4667 // "He giveth and He taketh away." 4668 continue; 4669 } 4670 // Verify that we have no work before we resort to stealing 4671 assert(work_q->size() == 0, "Have work, shouldn't steal"); 4672 // Try to steal from other queues that have work 4673 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 4674 NOT_PRODUCT(num_steals++;) 4675 assert(obj_to_scan->is_oop(), "Oops, not an oop!"); 4676 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); 4677 // Do scanning work 4678 obj_to_scan->oop_iterate(cl); 4679 // Loop around, finish this work, and try to steal some more 4680 } else if (terminator()->offer_termination()) { 4681 break; // nirvana from the infinite cycle 4682 } 4683 } 4684 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); 4685 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), 4686 "Else our work is not yet done"); 4687 } 4688 4689 // Record object boundaries in _eden_chunk_array by sampling the eden 4690 // top in the slow-path eden object allocation code path and record 4691 // the boundaries, if CMSEdenChunksRecordAlways is true. If 4692 // CMSEdenChunksRecordAlways is false, we use the other asynchronous 4693 // sampling in sample_eden() that activates during the part of the 4694 // preclean phase. 4695 void CMSCollector::sample_eden_chunk() { 4696 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) { 4697 if (_eden_chunk_lock->try_lock()) { 4698 // Record a sample. This is the critical section. The contents 4699 // of the _eden_chunk_array have to be non-decreasing in the 4700 // address order. 4701 _eden_chunk_array[_eden_chunk_index] = *_top_addr; 4702 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, 4703 "Unexpected state of Eden"); 4704 if (_eden_chunk_index == 0 || 4705 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) && 4706 (pointer_delta(_eden_chunk_array[_eden_chunk_index], 4707 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) { 4708 _eden_chunk_index++; // commit sample 4709 } 4710 _eden_chunk_lock->unlock(); 4711 } 4712 } 4713 } 4714 4715 // Return a thread-local PLAB recording array, as appropriate. 4716 void* CMSCollector::get_data_recorder(int thr_num) { 4717 if (_survivor_plab_array != NULL && 4718 (CMSPLABRecordAlways || 4719 (_collectorState > Marking && _collectorState < FinalMarking))) { 4720 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); 4721 ChunkArray* ca = &_survivor_plab_array[thr_num]; 4722 ca->reset(); // clear it so that fresh data is recorded 4723 return (void*) ca; 4724 } else { 4725 return NULL; 4726 } 4727 } 4728 4729 // Reset all the thread-local PLAB recording arrays 4730 void CMSCollector::reset_survivor_plab_arrays() { 4731 for (uint i = 0; i < ParallelGCThreads; i++) { 4732 _survivor_plab_array[i].reset(); 4733 } 4734 } 4735 4736 // Merge the per-thread plab arrays into the global survivor chunk 4737 // array which will provide the partitioning of the survivor space 4738 // for CMS initial scan and rescan. 4739 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv, 4740 int no_of_gc_threads) { 4741 assert(_survivor_plab_array != NULL, "Error"); 4742 assert(_survivor_chunk_array != NULL, "Error"); 4743 assert(_collectorState == FinalMarking || 4744 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error"); 4745 for (int j = 0; j < no_of_gc_threads; j++) { 4746 _cursor[j] = 0; 4747 } 4748 HeapWord* top = surv->top(); 4749 size_t i; 4750 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries 4751 HeapWord* min_val = top; // Higher than any PLAB address 4752 uint min_tid = 0; // position of min_val this round 4753 for (int j = 0; j < no_of_gc_threads; j++) { 4754 ChunkArray* cur_sca = &_survivor_plab_array[j]; 4755 if (_cursor[j] == cur_sca->end()) { 4756 continue; 4757 } 4758 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); 4759 HeapWord* cur_val = cur_sca->nth(_cursor[j]); 4760 assert(surv->used_region().contains(cur_val), "Out of bounds value"); 4761 if (cur_val < min_val) { 4762 min_tid = j; 4763 min_val = cur_val; 4764 } else { 4765 assert(cur_val < top, "All recorded addresses should be less"); 4766 } 4767 } 4768 // At this point min_val and min_tid are respectively 4769 // the least address in _survivor_plab_array[j]->nth(_cursor[j]) 4770 // and the thread (j) that witnesses that address. 4771 // We record this address in the _survivor_chunk_array[i] 4772 // and increment _cursor[min_tid] prior to the next round i. 4773 if (min_val == top) { 4774 break; 4775 } 4776 _survivor_chunk_array[i] = min_val; 4777 _cursor[min_tid]++; 4778 } 4779 // We are all done; record the size of the _survivor_chunk_array 4780 _survivor_chunk_index = i; // exclusive: [0, i) 4781 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i); 4782 // Verify that we used up all the recorded entries 4783 #ifdef ASSERT 4784 size_t total = 0; 4785 for (int j = 0; j < no_of_gc_threads; j++) { 4786 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); 4787 total += _cursor[j]; 4788 } 4789 assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); 4790 // Check that the merged array is in sorted order 4791 if (total > 0) { 4792 for (size_t i = 0; i < total - 1; i++) { 4793 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", 4794 i, p2i(_survivor_chunk_array[i])); 4795 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], 4796 "Not sorted"); 4797 } 4798 } 4799 #endif // ASSERT 4800 } 4801 4802 // Set up the space's par_seq_tasks structure for work claiming 4803 // for parallel initial scan and rescan of young gen. 4804 // See ParRescanTask where this is currently used. 4805 void 4806 CMSCollector:: 4807 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { 4808 assert(n_threads > 0, "Unexpected n_threads argument"); 4809 4810 // Eden space 4811 if (!_young_gen->eden()->is_empty()) { 4812 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks(); 4813 assert(!pst->valid(), "Clobbering existing data?"); 4814 // Each valid entry in [0, _eden_chunk_index) represents a task. 4815 size_t n_tasks = _eden_chunk_index + 1; 4816 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); 4817 // Sets the condition for completion of the subtask (how many threads 4818 // need to finish in order to be done). 4819 pst->set_n_threads(n_threads); 4820 pst->set_n_tasks((int)n_tasks); 4821 } 4822 4823 // Merge the survivor plab arrays into _survivor_chunk_array 4824 if (_survivor_plab_array != NULL) { 4825 merge_survivor_plab_arrays(_young_gen->from(), n_threads); 4826 } else { 4827 assert(_survivor_chunk_index == 0, "Error"); 4828 } 4829 4830 // To space 4831 { 4832 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks(); 4833 assert(!pst->valid(), "Clobbering existing data?"); 4834 // Sets the condition for completion of the subtask (how many threads 4835 // need to finish in order to be done). 4836 pst->set_n_threads(n_threads); 4837 pst->set_n_tasks(1); 4838 assert(pst->valid(), "Error"); 4839 } 4840 4841 // From space 4842 { 4843 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks(); 4844 assert(!pst->valid(), "Clobbering existing data?"); 4845 size_t n_tasks = _survivor_chunk_index + 1; 4846 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); 4847 // Sets the condition for completion of the subtask (how many threads 4848 // need to finish in order to be done). 4849 pst->set_n_threads(n_threads); 4850 pst->set_n_tasks((int)n_tasks); 4851 assert(pst->valid(), "Error"); 4852 } 4853 } 4854 4855 // Parallel version of remark 4856 void CMSCollector::do_remark_parallel() { 4857 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4858 WorkGang* workers = gch->workers(); 4859 assert(workers != NULL, "Need parallel worker threads."); 4860 // Choose to use the number of GC workers most recently set 4861 // into "active_workers". 4862 uint n_workers = workers->active_workers(); 4863 4864 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 4865 4866 StrongRootsScope srs(n_workers); 4867 4868 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs); 4869 4870 // We won't be iterating over the cards in the card table updating 4871 // the younger_gen cards, so we shouldn't call the following else 4872 // the verification code as well as subsequent younger_refs_iterate 4873 // code would get confused. XXX 4874 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel 4875 4876 // The young gen rescan work will not be done as part of 4877 // process_roots (which currently doesn't know how to 4878 // parallelize such a scan), but rather will be broken up into 4879 // a set of parallel tasks (via the sampling that the [abortable] 4880 // preclean phase did of eden, plus the [two] tasks of 4881 // scanning the [two] survivor spaces. Further fine-grain 4882 // parallelization of the scanning of the survivor spaces 4883 // themselves, and of precleaning of the young gen itself 4884 // is deferred to the future. 4885 initialize_sequential_subtasks_for_young_gen_rescan(n_workers); 4886 4887 // The dirty card rescan work is broken up into a "sequence" 4888 // of parallel tasks (per constituent space) that are dynamically 4889 // claimed by the parallel threads. 4890 cms_space->initialize_sequential_subtasks_for_rescan(n_workers); 4891 4892 // It turns out that even when we're using 1 thread, doing the work in a 4893 // separate thread causes wide variance in run times. We can't help this 4894 // in the multi-threaded case, but we special-case n=1 here to get 4895 // repeatable measurements of the 1-thread overhead of the parallel code. 4896 if (n_workers > 1) { 4897 // Make refs discovery MT-safe, if it isn't already: it may not 4898 // necessarily be so, since it's possible that we are doing 4899 // ST marking. 4900 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true); 4901 workers->run_task(&tsk); 4902 } else { 4903 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); 4904 tsk.work(0); 4905 } 4906 4907 // restore, single-threaded for now, any preserved marks 4908 // as a result of work_q overflow 4909 restore_preserved_marks_if_any(); 4910 } 4911 4912 // Non-parallel version of remark 4913 void CMSCollector::do_remark_non_parallel() { 4914 ResourceMark rm; 4915 HandleMark hm; 4916 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4917 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); 4918 4919 MarkRefsIntoAndScanClosure 4920 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */, 4921 &_markStack, this, 4922 false /* should_yield */, false /* not precleaning */); 4923 MarkFromDirtyCardsClosure 4924 markFromDirtyCardsClosure(this, _span, 4925 NULL, // space is set further below 4926 &_markBitMap, &_markStack, &mrias_cl); 4927 { 4928 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm); 4929 // Iterate over the dirty cards, setting the corresponding bits in the 4930 // mod union table. 4931 { 4932 ModUnionClosure modUnionClosure(&_modUnionTable); 4933 _ct->ct_bs()->dirty_card_iterate( 4934 _cmsGen->used_region(), 4935 &modUnionClosure); 4936 } 4937 // Having transferred these marks into the modUnionTable, we just need 4938 // to rescan the marked objects on the dirty cards in the modUnionTable. 4939 // The initial marking may have been done during an asynchronous 4940 // collection so there may be dirty bits in the mod-union table. 4941 const int alignment = 4942 CardTableModRefBS::card_size * BitsPerWord; 4943 { 4944 // ... First handle dirty cards in CMS gen 4945 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); 4946 MemRegion ur = _cmsGen->used_region(); 4947 HeapWord* lb = ur.start(); 4948 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); 4949 MemRegion cms_span(lb, ub); 4950 _modUnionTable.dirty_range_iterate_clear(cms_span, 4951 &markFromDirtyCardsClosure); 4952 verify_work_stacks_empty(); 4953 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards()); 4954 } 4955 } 4956 if (VerifyDuringGC && 4957 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 4958 HandleMark hm; // Discard invalid handles created during verification 4959 Universe::verify(); 4960 } 4961 { 4962 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm); 4963 4964 verify_work_stacks_empty(); 4965 4966 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 4967 StrongRootsScope srs(1); 4968 4969 gch->gen_process_roots(&srs, 4970 GenCollectedHeap::OldGen, 4971 true, // young gen as roots 4972 GenCollectedHeap::ScanningOption(roots_scanning_options()), 4973 should_unload_classes(), 4974 &mrias_cl, 4975 NULL, 4976 NULL); // The dirty klasses will be handled below 4977 4978 assert(should_unload_classes() 4979 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), 4980 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 4981 } 4982 4983 { 4984 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm); 4985 4986 verify_work_stacks_empty(); 4987 4988 // Scan all class loader data objects that might have been introduced 4989 // during concurrent marking. 4990 ResourceMark rm; 4991 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); 4992 for (int i = 0; i < array->length(); i++) { 4993 mrias_cl.do_cld_nv(array->at(i)); 4994 } 4995 4996 // We don't need to keep track of new CLDs anymore. 4997 ClassLoaderDataGraph::remember_new_clds(false); 4998 4999 verify_work_stacks_empty(); 5000 } 5001 5002 { 5003 GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm); 5004 5005 verify_work_stacks_empty(); 5006 5007 RemarkKlassClosure remark_klass_closure(&mrias_cl); 5008 ClassLoaderDataGraph::classes_do(&remark_klass_closure); 5009 5010 verify_work_stacks_empty(); 5011 } 5012 5013 // We might have added oops to ClassLoaderData::_handles during the 5014 // concurrent marking phase. These oops point to newly allocated objects 5015 // that are guaranteed to be kept alive. Either by the direct allocation 5016 // code, or when the young collector processes the roots. Hence, 5017 // we don't have to revisit the _handles block during the remark phase. 5018 5019 verify_work_stacks_empty(); 5020 // Restore evacuated mark words, if any, used for overflow list links 5021 restore_preserved_marks_if_any(); 5022 5023 verify_overflow_empty(); 5024 } 5025 5026 //////////////////////////////////////////////////////// 5027 // Parallel Reference Processing Task Proxy Class 5028 //////////////////////////////////////////////////////// 5029 class AbstractGangTaskWOopQueues : public AbstractGangTask { 5030 OopTaskQueueSet* _queues; 5031 ParallelTaskTerminator _terminator; 5032 public: 5033 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) : 5034 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {} 5035 ParallelTaskTerminator* terminator() { return &_terminator; } 5036 OopTaskQueueSet* queues() { return _queues; } 5037 }; 5038 5039 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues { 5040 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 5041 CMSCollector* _collector; 5042 CMSBitMap* _mark_bit_map; 5043 const MemRegion _span; 5044 ProcessTask& _task; 5045 5046 public: 5047 CMSRefProcTaskProxy(ProcessTask& task, 5048 CMSCollector* collector, 5049 const MemRegion& span, 5050 CMSBitMap* mark_bit_map, 5051 AbstractWorkGang* workers, 5052 OopTaskQueueSet* task_queues): 5053 AbstractGangTaskWOopQueues("Process referents by policy in parallel", 5054 task_queues, 5055 workers->active_workers()), 5056 _task(task), 5057 _collector(collector), _span(span), _mark_bit_map(mark_bit_map) 5058 { 5059 assert(_collector->_span.equals(_span) && !_span.is_empty(), 5060 "Inconsistency in _span"); 5061 } 5062 5063 OopTaskQueueSet* task_queues() { return queues(); } 5064 5065 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 5066 5067 void do_work_steal(int i, 5068 CMSParDrainMarkingStackClosure* drain, 5069 CMSParKeepAliveClosure* keep_alive, 5070 int* seed); 5071 5072 virtual void work(uint worker_id); 5073 }; 5074 5075 void CMSRefProcTaskProxy::work(uint worker_id) { 5076 ResourceMark rm; 5077 HandleMark hm; 5078 assert(_collector->_span.equals(_span), "Inconsistency in _span"); 5079 CMSParKeepAliveClosure par_keep_alive(_collector, _span, 5080 _mark_bit_map, 5081 work_queue(worker_id)); 5082 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, 5083 _mark_bit_map, 5084 work_queue(worker_id)); 5085 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map); 5086 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack); 5087 if (_task.marks_oops_alive()) { 5088 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive, 5089 _collector->hash_seed(worker_id)); 5090 } 5091 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); 5092 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); 5093 } 5094 5095 class CMSRefEnqueueTaskProxy: public AbstractGangTask { 5096 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 5097 EnqueueTask& _task; 5098 5099 public: 5100 CMSRefEnqueueTaskProxy(EnqueueTask& task) 5101 : AbstractGangTask("Enqueue reference objects in parallel"), 5102 _task(task) 5103 { } 5104 5105 virtual void work(uint worker_id) 5106 { 5107 _task.work(worker_id); 5108 } 5109 }; 5110 5111 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, 5112 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): 5113 _span(span), 5114 _bit_map(bit_map), 5115 _work_queue(work_queue), 5116 _mark_and_push(collector, span, bit_map, work_queue), 5117 _low_water_mark(MIN2((work_queue->max_elems()/4), 5118 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))) 5119 { } 5120 5121 // . see if we can share work_queues with ParNew? XXX 5122 void CMSRefProcTaskProxy::do_work_steal(int i, 5123 CMSParDrainMarkingStackClosure* drain, 5124 CMSParKeepAliveClosure* keep_alive, 5125 int* seed) { 5126 OopTaskQueue* work_q = work_queue(i); 5127 NOT_PRODUCT(int num_steals = 0;) 5128 oop obj_to_scan; 5129 5130 while (true) { 5131 // Completely finish any left over work from (an) earlier round(s) 5132 drain->trim_queue(0); 5133 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 5134 (size_t)ParGCDesiredObjsFromOverflowList); 5135 // Now check if there's any work in the overflow list 5136 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, 5137 // only affects the number of attempts made to get work from the 5138 // overflow list and does not affect the number of workers. Just 5139 // pass ParallelGCThreads so this behavior is unchanged. 5140 if (_collector->par_take_from_overflow_list(num_from_overflow_list, 5141 work_q, 5142 ParallelGCThreads)) { 5143 // Found something in global overflow list; 5144 // not yet ready to go stealing work from others. 5145 // We'd like to assert(work_q->size() != 0, ...) 5146 // because we just took work from the overflow list, 5147 // but of course we can't, since all of that might have 5148 // been already stolen from us. 5149 continue; 5150 } 5151 // Verify that we have no work before we resort to stealing 5152 assert(work_q->size() == 0, "Have work, shouldn't steal"); 5153 // Try to steal from other queues that have work 5154 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 5155 NOT_PRODUCT(num_steals++;) 5156 assert(obj_to_scan->is_oop(), "Oops, not an oop!"); 5157 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); 5158 // Do scanning work 5159 obj_to_scan->oop_iterate(keep_alive); 5160 // Loop around, finish this work, and try to steal some more 5161 } else if (terminator()->offer_termination()) { 5162 break; // nirvana from the infinite cycle 5163 } 5164 } 5165 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); 5166 } 5167 5168 void CMSRefProcTaskExecutor::execute(ProcessTask& task) 5169 { 5170 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5171 WorkGang* workers = gch->workers(); 5172 assert(workers != NULL, "Need parallel worker threads."); 5173 CMSRefProcTaskProxy rp_task(task, &_collector, 5174 _collector.ref_processor()->span(), 5175 _collector.markBitMap(), 5176 workers, _collector.task_queues()); 5177 workers->run_task(&rp_task); 5178 } 5179 5180 void CMSRefProcTaskExecutor::execute(EnqueueTask& task) 5181 { 5182 5183 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5184 WorkGang* workers = gch->workers(); 5185 assert(workers != NULL, "Need parallel worker threads."); 5186 CMSRefEnqueueTaskProxy enq_task(task); 5187 workers->run_task(&enq_task); 5188 } 5189 5190 void CMSCollector::refProcessingWork() { 5191 ResourceMark rm; 5192 HandleMark hm; 5193 5194 ReferenceProcessor* rp = ref_processor(); 5195 assert(rp->span().equals(_span), "Spans should be equal"); 5196 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); 5197 // Process weak references. 5198 rp->setup_policy(false); 5199 verify_work_stacks_empty(); 5200 5201 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, 5202 &_markStack, false /* !preclean */); 5203 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, 5204 _span, &_markBitMap, &_markStack, 5205 &cmsKeepAliveClosure, false /* !preclean */); 5206 { 5207 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm); 5208 5209 ReferenceProcessorStats stats; 5210 if (rp->processing_is_mt()) { 5211 // Set the degree of MT here. If the discovery is done MT, there 5212 // may have been a different number of threads doing the discovery 5213 // and a different number of discovered lists may have Ref objects. 5214 // That is OK as long as the Reference lists are balanced (see 5215 // balance_all_queues() and balance_queues()). 5216 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5217 uint active_workers = ParallelGCThreads; 5218 WorkGang* workers = gch->workers(); 5219 if (workers != NULL) { 5220 active_workers = workers->active_workers(); 5221 // The expectation is that active_workers will have already 5222 // been set to a reasonable value. If it has not been set, 5223 // investigate. 5224 assert(active_workers > 0, "Should have been set during scavenge"); 5225 } 5226 rp->set_active_mt_degree(active_workers); 5227 CMSRefProcTaskExecutor task_executor(*this); 5228 stats = rp->process_discovered_references(&_is_alive_closure, 5229 &cmsKeepAliveClosure, 5230 &cmsDrainMarkingStackClosure, 5231 &task_executor, 5232 _gc_timer_cm); 5233 } else { 5234 stats = rp->process_discovered_references(&_is_alive_closure, 5235 &cmsKeepAliveClosure, 5236 &cmsDrainMarkingStackClosure, 5237 NULL, 5238 _gc_timer_cm); 5239 } 5240 _gc_tracer_cm->report_gc_reference_stats(stats); 5241 5242 } 5243 5244 // This is the point where the entire marking should have completed. 5245 verify_work_stacks_empty(); 5246 5247 if (should_unload_classes()) { 5248 { 5249 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm); 5250 5251 // Unload classes and purge the SystemDictionary. 5252 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure); 5253 5254 // Unload nmethods. 5255 CodeCache::do_unloading(&_is_alive_closure, purged_class); 5256 5257 // Prune dead klasses from subklass/sibling/implementor lists. 5258 Klass::clean_weak_klass_links(&_is_alive_closure); 5259 } 5260 5261 { 5262 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm); 5263 // Clean up unreferenced symbols in symbol table. 5264 SymbolTable::unlink(); 5265 } 5266 5267 { 5268 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm); 5269 // Delete entries for dead interned strings. 5270 StringTable::unlink(&_is_alive_closure); 5271 } 5272 } 5273 5274 5275 // Restore any preserved marks as a result of mark stack or 5276 // work queue overflow 5277 restore_preserved_marks_if_any(); // done single-threaded for now 5278 5279 rp->set_enqueuing_is_done(true); 5280 if (rp->processing_is_mt()) { 5281 rp->balance_all_queues(); 5282 CMSRefProcTaskExecutor task_executor(*this); 5283 rp->enqueue_discovered_references(&task_executor); 5284 } else { 5285 rp->enqueue_discovered_references(NULL); 5286 } 5287 rp->verify_no_references_recorded(); 5288 assert(!rp->discovery_enabled(), "should have been disabled"); 5289 } 5290 5291 #ifndef PRODUCT 5292 void CMSCollector::check_correct_thread_executing() { 5293 Thread* t = Thread::current(); 5294 // Only the VM thread or the CMS thread should be here. 5295 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), 5296 "Unexpected thread type"); 5297 // If this is the vm thread, the foreground process 5298 // should not be waiting. Note that _foregroundGCIsActive is 5299 // true while the foreground collector is waiting. 5300 if (_foregroundGCShouldWait) { 5301 // We cannot be the VM thread 5302 assert(t->is_ConcurrentGC_thread(), 5303 "Should be CMS thread"); 5304 } else { 5305 // We can be the CMS thread only if we are in a stop-world 5306 // phase of CMS collection. 5307 if (t->is_ConcurrentGC_thread()) { 5308 assert(_collectorState == InitialMarking || 5309 _collectorState == FinalMarking, 5310 "Should be a stop-world phase"); 5311 // The CMS thread should be holding the CMS_token. 5312 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 5313 "Potential interference with concurrently " 5314 "executing VM thread"); 5315 } 5316 } 5317 } 5318 #endif 5319 5320 void CMSCollector::sweep() { 5321 assert(_collectorState == Sweeping, "just checking"); 5322 check_correct_thread_executing(); 5323 verify_work_stacks_empty(); 5324 verify_overflow_empty(); 5325 increment_sweep_count(); 5326 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); 5327 5328 _inter_sweep_timer.stop(); 5329 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); 5330 5331 assert(!_intra_sweep_timer.is_active(), "Should not be active"); 5332 _intra_sweep_timer.reset(); 5333 _intra_sweep_timer.start(); 5334 { 5335 GCTraceCPUTime tcpu; 5336 CMSPhaseAccounting pa(this, "Concurrent Sweep"); 5337 // First sweep the old gen 5338 { 5339 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), 5340 bitMapLock()); 5341 sweepWork(_cmsGen); 5342 } 5343 5344 // Update Universe::_heap_*_at_gc figures. 5345 // We need all the free list locks to make the abstract state 5346 // transition from Sweeping to Resetting. See detailed note 5347 // further below. 5348 { 5349 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock()); 5350 // Update heap occupancy information which is used as 5351 // input to soft ref clearing policy at the next gc. 5352 Universe::update_heap_info_at_gc(); 5353 _collectorState = Resizing; 5354 } 5355 } 5356 verify_work_stacks_empty(); 5357 verify_overflow_empty(); 5358 5359 if (should_unload_classes()) { 5360 // Delay purge to the beginning of the next safepoint. Metaspace::contains 5361 // requires that the virtual spaces are stable and not deleted. 5362 ClassLoaderDataGraph::set_should_purge(true); 5363 } 5364 5365 _intra_sweep_timer.stop(); 5366 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds()); 5367 5368 _inter_sweep_timer.reset(); 5369 _inter_sweep_timer.start(); 5370 5371 // We need to use a monotonically non-decreasing time in ms 5372 // or we will see time-warp warnings and os::javaTimeMillis() 5373 // does not guarantee monotonicity. 5374 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 5375 update_time_of_last_gc(now); 5376 5377 // NOTE on abstract state transitions: 5378 // Mutators allocate-live and/or mark the mod-union table dirty 5379 // based on the state of the collection. The former is done in 5380 // the interval [Marking, Sweeping] and the latter in the interval 5381 // [Marking, Sweeping). Thus the transitions into the Marking state 5382 // and out of the Sweeping state must be synchronously visible 5383 // globally to the mutators. 5384 // The transition into the Marking state happens with the world 5385 // stopped so the mutators will globally see it. Sweeping is 5386 // done asynchronously by the background collector so the transition 5387 // from the Sweeping state to the Resizing state must be done 5388 // under the freelistLock (as is the check for whether to 5389 // allocate-live and whether to dirty the mod-union table). 5390 assert(_collectorState == Resizing, "Change of collector state to" 5391 " Resizing must be done under the freelistLocks (plural)"); 5392 5393 // Now that sweeping has been completed, we clear 5394 // the incremental_collection_failed flag, 5395 // thus inviting a younger gen collection to promote into 5396 // this generation. If such a promotion may still fail, 5397 // the flag will be set again when a young collection is 5398 // attempted. 5399 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5400 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up 5401 gch->update_full_collections_completed(_collection_count_start); 5402 } 5403 5404 // FIX ME!!! Looks like this belongs in CFLSpace, with 5405 // CMSGen merely delegating to it. 5406 void ConcurrentMarkSweepGeneration::setNearLargestChunk() { 5407 double nearLargestPercent = FLSLargestBlockCoalesceProximity; 5408 HeapWord* minAddr = _cmsSpace->bottom(); 5409 HeapWord* largestAddr = 5410 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict(); 5411 if (largestAddr == NULL) { 5412 // The dictionary appears to be empty. In this case 5413 // try to coalesce at the end of the heap. 5414 largestAddr = _cmsSpace->end(); 5415 } 5416 size_t largestOffset = pointer_delta(largestAddr, minAddr); 5417 size_t nearLargestOffset = 5418 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; 5419 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT, 5420 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset)); 5421 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); 5422 } 5423 5424 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { 5425 return addr >= _cmsSpace->nearLargestChunk(); 5426 } 5427 5428 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { 5429 return _cmsSpace->find_chunk_at_end(); 5430 } 5431 5432 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation, 5433 bool full) { 5434 // If the young generation has been collected, gather any statistics 5435 // that are of interest at this point. 5436 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation); 5437 if (!full && current_is_young) { 5438 // Gather statistics on the young generation collection. 5439 collector()->stats().record_gc0_end(used()); 5440 } 5441 } 5442 5443 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) { 5444 // We iterate over the space(s) underlying this generation, 5445 // checking the mark bit map to see if the bits corresponding 5446 // to specific blocks are marked or not. Blocks that are 5447 // marked are live and are not swept up. All remaining blocks 5448 // are swept up, with coalescing on-the-fly as we sweep up 5449 // contiguous free and/or garbage blocks: 5450 // We need to ensure that the sweeper synchronizes with allocators 5451 // and stop-the-world collectors. In particular, the following 5452 // locks are used: 5453 // . CMS token: if this is held, a stop the world collection cannot occur 5454 // . freelistLock: if this is held no allocation can occur from this 5455 // generation by another thread 5456 // . bitMapLock: if this is held, no other thread can access or update 5457 // 5458 5459 // Note that we need to hold the freelistLock if we use 5460 // block iterate below; else the iterator might go awry if 5461 // a mutator (or promotion) causes block contents to change 5462 // (for instance if the allocator divvies up a block). 5463 // If we hold the free list lock, for all practical purposes 5464 // young generation GC's can't occur (they'll usually need to 5465 // promote), so we might as well prevent all young generation 5466 // GC's while we do a sweeping step. For the same reason, we might 5467 // as well take the bit map lock for the entire duration 5468 5469 // check that we hold the requisite locks 5470 assert(have_cms_token(), "Should hold cms token"); 5471 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep"); 5472 assert_lock_strong(old_gen->freelistLock()); 5473 assert_lock_strong(bitMapLock()); 5474 5475 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context"); 5476 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context"); 5477 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), 5478 _inter_sweep_estimate.padded_average(), 5479 _intra_sweep_estimate.padded_average()); 5480 old_gen->setNearLargestChunk(); 5481 5482 { 5483 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield); 5484 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure); 5485 // We need to free-up/coalesce garbage/blocks from a 5486 // co-terminal free run. This is done in the SweepClosure 5487 // destructor; so, do not remove this scope, else the 5488 // end-of-sweep-census below will be off by a little bit. 5489 } 5490 old_gen->cmsSpace()->sweep_completed(); 5491 old_gen->cmsSpace()->endSweepFLCensus(sweep_count()); 5492 if (should_unload_classes()) { // unloaded classes this cycle, 5493 _concurrent_cycles_since_last_unload = 0; // ... reset count 5494 } else { // did not unload classes, 5495 _concurrent_cycles_since_last_unload++; // ... increment count 5496 } 5497 } 5498 5499 // Reset CMS data structures (for now just the marking bit map) 5500 // preparatory for the next cycle. 5501 void CMSCollector::reset_concurrent() { 5502 CMSTokenSyncWithLocks ts(true, bitMapLock()); 5503 5504 // If the state is not "Resetting", the foreground thread 5505 // has done a collection and the resetting. 5506 if (_collectorState != Resetting) { 5507 assert(_collectorState == Idling, "The state should only change" 5508 " because the foreground collector has finished the collection"); 5509 return; 5510 } 5511 5512 { 5513 // Clear the mark bitmap (no grey objects to start with) 5514 // for the next cycle. 5515 GCTraceCPUTime tcpu; 5516 CMSPhaseAccounting cmspa(this, "Concurrent Reset"); 5517 5518 HeapWord* curAddr = _markBitMap.startWord(); 5519 while (curAddr < _markBitMap.endWord()) { 5520 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); 5521 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); 5522 _markBitMap.clear_large_range(chunk); 5523 if (ConcurrentMarkSweepThread::should_yield() && 5524 !foregroundGCIsActive() && 5525 CMSYield) { 5526 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 5527 "CMS thread should hold CMS token"); 5528 assert_lock_strong(bitMapLock()); 5529 bitMapLock()->unlock(); 5530 ConcurrentMarkSweepThread::desynchronize(true); 5531 stopTimer(); 5532 incrementYields(); 5533 5534 // See the comment in coordinator_yield() 5535 for (unsigned i = 0; i < CMSYieldSleepCount && 5536 ConcurrentMarkSweepThread::should_yield() && 5537 !CMSCollector::foregroundGCIsActive(); ++i) { 5538 os::sleep(Thread::current(), 1, false); 5539 } 5540 5541 ConcurrentMarkSweepThread::synchronize(true); 5542 bitMapLock()->lock_without_safepoint_check(); 5543 startTimer(); 5544 } 5545 curAddr = chunk.end(); 5546 } 5547 // A successful mostly concurrent collection has been done. 5548 // Because only the full (i.e., concurrent mode failure) collections 5549 // are being measured for gc overhead limits, clean the "near" flag 5550 // and count. 5551 size_policy()->reset_gc_overhead_limit_count(); 5552 _collectorState = Idling; 5553 } 5554 5555 register_gc_end(); 5556 } 5557 5558 // Same as above but for STW paths 5559 void CMSCollector::reset_stw() { 5560 // already have the lock 5561 assert(_collectorState == Resetting, "just checking"); 5562 assert_lock_strong(bitMapLock()); 5563 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id()); 5564 _markBitMap.clear_all(); 5565 _collectorState = Idling; 5566 register_gc_end(); 5567 } 5568 5569 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) { 5570 GCTraceCPUTime tcpu; 5571 TraceCollectorStats tcs(counters()); 5572 5573 switch (op) { 5574 case CMS_op_checkpointRootsInitial: { 5575 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true); 5576 SvcGCMarker sgcm(SvcGCMarker::OTHER); 5577 checkpointRootsInitial(); 5578 break; 5579 } 5580 case CMS_op_checkpointRootsFinal: { 5581 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true); 5582 SvcGCMarker sgcm(SvcGCMarker::OTHER); 5583 checkpointRootsFinal(); 5584 break; 5585 } 5586 default: 5587 fatal("No such CMS_op"); 5588 } 5589 } 5590 5591 #ifndef PRODUCT 5592 size_t const CMSCollector::skip_header_HeapWords() { 5593 return FreeChunk::header_size(); 5594 } 5595 5596 // Try and collect here conditions that should hold when 5597 // CMS thread is exiting. The idea is that the foreground GC 5598 // thread should not be blocked if it wants to terminate 5599 // the CMS thread and yet continue to run the VM for a while 5600 // after that. 5601 void CMSCollector::verify_ok_to_terminate() const { 5602 assert(Thread::current()->is_ConcurrentGC_thread(), 5603 "should be called by CMS thread"); 5604 assert(!_foregroundGCShouldWait, "should be false"); 5605 // We could check here that all the various low-level locks 5606 // are not held by the CMS thread, but that is overkill; see 5607 // also CMSThread::verify_ok_to_terminate() where the CGC_lock 5608 // is checked. 5609 } 5610 #endif 5611 5612 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { 5613 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), 5614 "missing Printezis mark?"); 5615 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); 5616 size_t size = pointer_delta(nextOneAddr + 1, addr); 5617 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 5618 "alignment problem"); 5619 assert(size >= 3, "Necessary for Printezis marks to work"); 5620 return size; 5621 } 5622 5623 // A variant of the above (block_size_using_printezis_bits()) except 5624 // that we return 0 if the P-bits are not yet set. 5625 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { 5626 if (_markBitMap.isMarked(addr + 1)) { 5627 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects"); 5628 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); 5629 size_t size = pointer_delta(nextOneAddr + 1, addr); 5630 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 5631 "alignment problem"); 5632 assert(size >= 3, "Necessary for Printezis marks to work"); 5633 return size; 5634 } 5635 return 0; 5636 } 5637 5638 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { 5639 size_t sz = 0; 5640 oop p = (oop)addr; 5641 if (p->klass_or_null() != NULL) { 5642 sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); 5643 } else { 5644 sz = block_size_using_printezis_bits(addr); 5645 } 5646 assert(sz > 0, "size must be nonzero"); 5647 HeapWord* next_block = addr + sz; 5648 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block, 5649 CardTableModRefBS::card_size); 5650 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) < 5651 round_down((uintptr_t)next_card, CardTableModRefBS::card_size), 5652 "must be different cards"); 5653 return next_card; 5654 } 5655 5656 5657 // CMS Bit Map Wrapper ///////////////////////////////////////// 5658 5659 // Construct a CMS bit map infrastructure, but don't create the 5660 // bit vector itself. That is done by a separate call CMSBitMap::allocate() 5661 // further below. 5662 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): 5663 _bm(), 5664 _shifter(shifter), 5665 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true, 5666 Monitor::_safepoint_check_sometimes) : NULL) 5667 { 5668 _bmStartWord = 0; 5669 _bmWordSize = 0; 5670 } 5671 5672 bool CMSBitMap::allocate(MemRegion mr) { 5673 _bmStartWord = mr.start(); 5674 _bmWordSize = mr.word_size(); 5675 ReservedSpace brs(ReservedSpace::allocation_align_size_up( 5676 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); 5677 if (!brs.is_reserved()) { 5678 log_warning(gc)("CMS bit map allocation failure"); 5679 return false; 5680 } 5681 // For now we'll just commit all of the bit map up front. 5682 // Later on we'll try to be more parsimonious with swap. 5683 if (!_virtual_space.initialize(brs, brs.size())) { 5684 log_warning(gc)("CMS bit map backing store failure"); 5685 return false; 5686 } 5687 assert(_virtual_space.committed_size() == brs.size(), 5688 "didn't reserve backing store for all of CMS bit map?"); 5689 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= 5690 _bmWordSize, "inconsistency in bit map sizing"); 5691 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter); 5692 5693 // bm.clear(); // can we rely on getting zero'd memory? verify below 5694 assert(isAllClear(), 5695 "Expected zero'd memory from ReservedSpace constructor"); 5696 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), 5697 "consistency check"); 5698 return true; 5699 } 5700 5701 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { 5702 HeapWord *next_addr, *end_addr, *last_addr; 5703 assert_locked(); 5704 assert(covers(mr), "out-of-range error"); 5705 // XXX assert that start and end are appropriately aligned 5706 for (next_addr = mr.start(), end_addr = mr.end(); 5707 next_addr < end_addr; next_addr = last_addr) { 5708 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); 5709 last_addr = dirty_region.end(); 5710 if (!dirty_region.is_empty()) { 5711 cl->do_MemRegion(dirty_region); 5712 } else { 5713 assert(last_addr == end_addr, "program logic"); 5714 return; 5715 } 5716 } 5717 } 5718 5719 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const { 5720 _bm.print_on_error(st, prefix); 5721 } 5722 5723 #ifndef PRODUCT 5724 void CMSBitMap::assert_locked() const { 5725 CMSLockVerifier::assert_locked(lock()); 5726 } 5727 5728 bool CMSBitMap::covers(MemRegion mr) const { 5729 // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); 5730 assert((size_t)_bm.size() == (_bmWordSize >> _shifter), 5731 "size inconsistency"); 5732 return (mr.start() >= _bmStartWord) && 5733 (mr.end() <= endWord()); 5734 } 5735 5736 bool CMSBitMap::covers(HeapWord* start, size_t size) const { 5737 return (start >= _bmStartWord && (start + size) <= endWord()); 5738 } 5739 5740 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { 5741 // verify that there are no 1 bits in the interval [left, right) 5742 FalseBitMapClosure falseBitMapClosure; 5743 iterate(&falseBitMapClosure, left, right); 5744 } 5745 5746 void CMSBitMap::region_invariant(MemRegion mr) 5747 { 5748 assert_locked(); 5749 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); 5750 assert(!mr.is_empty(), "unexpected empty region"); 5751 assert(covers(mr), "mr should be covered by bit map"); 5752 // convert address range into offset range 5753 size_t start_ofs = heapWordToOffset(mr.start()); 5754 // Make sure that end() is appropriately aligned 5755 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(), 5756 (1 << (_shifter+LogHeapWordSize))), 5757 "Misaligned mr.end()"); 5758 size_t end_ofs = heapWordToOffset(mr.end()); 5759 assert(end_ofs > start_ofs, "Should mark at least one bit"); 5760 } 5761 5762 #endif 5763 5764 bool CMSMarkStack::allocate(size_t size) { 5765 // allocate a stack of the requisite depth 5766 ReservedSpace rs(ReservedSpace::allocation_align_size_up( 5767 size * sizeof(oop))); 5768 if (!rs.is_reserved()) { 5769 log_warning(gc)("CMSMarkStack allocation failure"); 5770 return false; 5771 } 5772 if (!_virtual_space.initialize(rs, rs.size())) { 5773 log_warning(gc)("CMSMarkStack backing store failure"); 5774 return false; 5775 } 5776 assert(_virtual_space.committed_size() == rs.size(), 5777 "didn't reserve backing store for all of CMS stack?"); 5778 _base = (oop*)(_virtual_space.low()); 5779 _index = 0; 5780 _capacity = size; 5781 NOT_PRODUCT(_max_depth = 0); 5782 return true; 5783 } 5784 5785 // XXX FIX ME !!! In the MT case we come in here holding a 5786 // leaf lock. For printing we need to take a further lock 5787 // which has lower rank. We need to recalibrate the two 5788 // lock-ranks involved in order to be able to print the 5789 // messages below. (Or defer the printing to the caller. 5790 // For now we take the expedient path of just disabling the 5791 // messages for the problematic case.) 5792 void CMSMarkStack::expand() { 5793 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted"); 5794 if (_capacity == MarkStackSizeMax) { 5795 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) { 5796 // We print a warning message only once per CMS cycle. 5797 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit"); 5798 } 5799 return; 5800 } 5801 // Double capacity if possible 5802 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax); 5803 // Do not give up existing stack until we have managed to 5804 // get the double capacity that we desired. 5805 ReservedSpace rs(ReservedSpace::allocation_align_size_up( 5806 new_capacity * sizeof(oop))); 5807 if (rs.is_reserved()) { 5808 // Release the backing store associated with old stack 5809 _virtual_space.release(); 5810 // Reinitialize virtual space for new stack 5811 if (!_virtual_space.initialize(rs, rs.size())) { 5812 fatal("Not enough swap for expanded marking stack"); 5813 } 5814 _base = (oop*)(_virtual_space.low()); 5815 _index = 0; 5816 _capacity = new_capacity; 5817 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) { 5818 // Failed to double capacity, continue; 5819 // we print a detail message only once per CMS cycle. 5820 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K", 5821 _capacity / K, new_capacity / K); 5822 } 5823 } 5824 5825 5826 // Closures 5827 // XXX: there seems to be a lot of code duplication here; 5828 // should refactor and consolidate common code. 5829 5830 // This closure is used to mark refs into the CMS generation in 5831 // the CMS bit map. Called at the first checkpoint. This closure 5832 // assumes that we do not need to re-mark dirty cards; if the CMS 5833 // generation on which this is used is not an oldest 5834 // generation then this will lose younger_gen cards! 5835 5836 MarkRefsIntoClosure::MarkRefsIntoClosure( 5837 MemRegion span, CMSBitMap* bitMap): 5838 _span(span), 5839 _bitMap(bitMap) 5840 { 5841 assert(ref_processor() == NULL, "deliberately left NULL"); 5842 assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); 5843 } 5844 5845 void MarkRefsIntoClosure::do_oop(oop obj) { 5846 // if p points into _span, then mark corresponding bit in _markBitMap 5847 assert(obj->is_oop(), "expected an oop"); 5848 HeapWord* addr = (HeapWord*)obj; 5849 if (_span.contains(addr)) { 5850 // this should be made more efficient 5851 _bitMap->mark(addr); 5852 } 5853 } 5854 5855 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); } 5856 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); } 5857 5858 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure( 5859 MemRegion span, CMSBitMap* bitMap): 5860 _span(span), 5861 _bitMap(bitMap) 5862 { 5863 assert(ref_processor() == NULL, "deliberately left NULL"); 5864 assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); 5865 } 5866 5867 void ParMarkRefsIntoClosure::do_oop(oop obj) { 5868 // if p points into _span, then mark corresponding bit in _markBitMap 5869 assert(obj->is_oop(), "expected an oop"); 5870 HeapWord* addr = (HeapWord*)obj; 5871 if (_span.contains(addr)) { 5872 // this should be made more efficient 5873 _bitMap->par_mark(addr); 5874 } 5875 } 5876 5877 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); } 5878 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); } 5879 5880 // A variant of the above, used for CMS marking verification. 5881 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( 5882 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm): 5883 _span(span), 5884 _verification_bm(verification_bm), 5885 _cms_bm(cms_bm) 5886 { 5887 assert(ref_processor() == NULL, "deliberately left NULL"); 5888 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); 5889 } 5890 5891 void MarkRefsIntoVerifyClosure::do_oop(oop obj) { 5892 // if p points into _span, then mark corresponding bit in _markBitMap 5893 assert(obj->is_oop(), "expected an oop"); 5894 HeapWord* addr = (HeapWord*)obj; 5895 if (_span.contains(addr)) { 5896 _verification_bm->mark(addr); 5897 if (!_cms_bm->isMarked(addr)) { 5898 Log(gc, verify) log; 5899 ResourceMark rm; 5900 oop(addr)->print_on(log.error_stream()); 5901 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); 5902 fatal("... aborting"); 5903 } 5904 } 5905 } 5906 5907 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } 5908 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } 5909 5910 ////////////////////////////////////////////////// 5911 // MarkRefsIntoAndScanClosure 5912 ////////////////////////////////////////////////// 5913 5914 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, 5915 ReferenceProcessor* rp, 5916 CMSBitMap* bit_map, 5917 CMSBitMap* mod_union_table, 5918 CMSMarkStack* mark_stack, 5919 CMSCollector* collector, 5920 bool should_yield, 5921 bool concurrent_precleaning): 5922 _collector(collector), 5923 _span(span), 5924 _bit_map(bit_map), 5925 _mark_stack(mark_stack), 5926 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table, 5927 mark_stack, concurrent_precleaning), 5928 _yield(should_yield), 5929 _concurrent_precleaning(concurrent_precleaning), 5930 _freelistLock(NULL) 5931 { 5932 // FIXME: Should initialize in base class constructor. 5933 assert(rp != NULL, "ref_processor shouldn't be NULL"); 5934 set_ref_processor_internal(rp); 5935 } 5936 5937 // This closure is used to mark refs into the CMS generation at the 5938 // second (final) checkpoint, and to scan and transitively follow 5939 // the unmarked oops. It is also used during the concurrent precleaning 5940 // phase while scanning objects on dirty cards in the CMS generation. 5941 // The marks are made in the marking bit map and the marking stack is 5942 // used for keeping the (newly) grey objects during the scan. 5943 // The parallel version (Par_...) appears further below. 5944 void MarkRefsIntoAndScanClosure::do_oop(oop obj) { 5945 if (obj != NULL) { 5946 assert(obj->is_oop(), "expected an oop"); 5947 HeapWord* addr = (HeapWord*)obj; 5948 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); 5949 assert(_collector->overflow_list_is_empty(), 5950 "overflow list should be empty"); 5951 if (_span.contains(addr) && 5952 !_bit_map->isMarked(addr)) { 5953 // mark bit map (object is now grey) 5954 _bit_map->mark(addr); 5955 // push on marking stack (stack should be empty), and drain the 5956 // stack by applying this closure to the oops in the oops popped 5957 // from the stack (i.e. blacken the grey objects) 5958 bool res = _mark_stack->push(obj); 5959 assert(res, "Should have space to push on empty stack"); 5960 do { 5961 oop new_oop = _mark_stack->pop(); 5962 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); 5963 assert(_bit_map->isMarked((HeapWord*)new_oop), 5964 "only grey objects on this stack"); 5965 // iterate over the oops in this oop, marking and pushing 5966 // the ones in CMS heap (i.e. in _span). 5967 new_oop->oop_iterate(&_pushAndMarkClosure); 5968 // check if it's time to yield 5969 do_yield_check(); 5970 } while (!_mark_stack->isEmpty() || 5971 (!_concurrent_precleaning && take_from_overflow_list())); 5972 // if marking stack is empty, and we are not doing this 5973 // during precleaning, then check the overflow list 5974 } 5975 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); 5976 assert(_collector->overflow_list_is_empty(), 5977 "overflow list was drained above"); 5978 5979 assert(_collector->no_preserved_marks(), 5980 "All preserved marks should have been restored above"); 5981 } 5982 } 5983 5984 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } 5985 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } 5986 5987 void MarkRefsIntoAndScanClosure::do_yield_work() { 5988 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 5989 "CMS thread should hold CMS token"); 5990 assert_lock_strong(_freelistLock); 5991 assert_lock_strong(_bit_map->lock()); 5992 // relinquish the free_list_lock and bitMaplock() 5993 _bit_map->lock()->unlock(); 5994 _freelistLock->unlock(); 5995 ConcurrentMarkSweepThread::desynchronize(true); 5996 _collector->stopTimer(); 5997 _collector->incrementYields(); 5998 5999 // See the comment in coordinator_yield() 6000 for (unsigned i = 0; 6001 i < CMSYieldSleepCount && 6002 ConcurrentMarkSweepThread::should_yield() && 6003 !CMSCollector::foregroundGCIsActive(); 6004 ++i) { 6005 os::sleep(Thread::current(), 1, false); 6006 } 6007 6008 ConcurrentMarkSweepThread::synchronize(true); 6009 _freelistLock->lock_without_safepoint_check(); 6010 _bit_map->lock()->lock_without_safepoint_check(); 6011 _collector->startTimer(); 6012 } 6013 6014 /////////////////////////////////////////////////////////// 6015 // ParMarkRefsIntoAndScanClosure: a parallel version of 6016 // MarkRefsIntoAndScanClosure 6017 /////////////////////////////////////////////////////////// 6018 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure( 6019 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp, 6020 CMSBitMap* bit_map, OopTaskQueue* work_queue): 6021 _span(span), 6022 _bit_map(bit_map), 6023 _work_queue(work_queue), 6024 _low_water_mark(MIN2((work_queue->max_elems()/4), 6025 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))), 6026 _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue) 6027 { 6028 // FIXME: Should initialize in base class constructor. 6029 assert(rp != NULL, "ref_processor shouldn't be NULL"); 6030 set_ref_processor_internal(rp); 6031 } 6032 6033 // This closure is used to mark refs into the CMS generation at the 6034 // second (final) checkpoint, and to scan and transitively follow 6035 // the unmarked oops. The marks are made in the marking bit map and 6036 // the work_queue is used for keeping the (newly) grey objects during 6037 // the scan phase whence they are also available for stealing by parallel 6038 // threads. Since the marking bit map is shared, updates are 6039 // synchronized (via CAS). 6040 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) { 6041 if (obj != NULL) { 6042 // Ignore mark word because this could be an already marked oop 6043 // that may be chained at the end of the overflow list. 6044 assert(obj->is_oop(true), "expected an oop"); 6045 HeapWord* addr = (HeapWord*)obj; 6046 if (_span.contains(addr) && 6047 !_bit_map->isMarked(addr)) { 6048 // mark bit map (object will become grey): 6049 // It is possible for several threads to be 6050 // trying to "claim" this object concurrently; 6051 // the unique thread that succeeds in marking the 6052 // object first will do the subsequent push on 6053 // to the work queue (or overflow list). 6054 if (_bit_map->par_mark(addr)) { 6055 // push on work_queue (which may not be empty), and trim the 6056 // queue to an appropriate length by applying this closure to 6057 // the oops in the oops popped from the stack (i.e. blacken the 6058 // grey objects) 6059 bool res = _work_queue->push(obj); 6060 assert(res, "Low water mark should be less than capacity?"); 6061 trim_queue(_low_water_mark); 6062 } // Else, another thread claimed the object 6063 } 6064 } 6065 } 6066 6067 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); } 6068 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); } 6069 6070 // This closure is used to rescan the marked objects on the dirty cards 6071 // in the mod union table and the card table proper. 6072 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( 6073 oop p, MemRegion mr) { 6074 6075 size_t size = 0; 6076 HeapWord* addr = (HeapWord*)p; 6077 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6078 assert(_span.contains(addr), "we are scanning the CMS generation"); 6079 // check if it's time to yield 6080 if (do_yield_check()) { 6081 // We yielded for some foreground stop-world work, 6082 // and we have been asked to abort this ongoing preclean cycle. 6083 return 0; 6084 } 6085 if (_bitMap->isMarked(addr)) { 6086 // it's marked; is it potentially uninitialized? 6087 if (p->klass_or_null() != NULL) { 6088 // an initialized object; ignore mark word in verification below 6089 // since we are running concurrent with mutators 6090 assert(p->is_oop(true), "should be an oop"); 6091 if (p->is_objArray()) { 6092 // objArrays are precisely marked; restrict scanning 6093 // to dirty cards only. 6094 size = CompactibleFreeListSpace::adjustObjectSize( 6095 p->oop_iterate_size(_scanningClosure, mr)); 6096 } else { 6097 // A non-array may have been imprecisely marked; we need 6098 // to scan object in its entirety. 6099 size = CompactibleFreeListSpace::adjustObjectSize( 6100 p->oop_iterate_size(_scanningClosure)); 6101 } 6102 #ifdef ASSERT 6103 size_t direct_size = 6104 CompactibleFreeListSpace::adjustObjectSize(p->size()); 6105 assert(size == direct_size, "Inconsistency in size"); 6106 assert(size >= 3, "Necessary for Printezis marks to work"); 6107 HeapWord* start_pbit = addr + 1; 6108 HeapWord* end_pbit = addr + size - 1; 6109 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit), 6110 "inconsistent Printezis mark"); 6111 // Verify inner mark bits (between Printezis bits) are clear, 6112 // but don't repeat if there are multiple dirty regions for 6113 // the same object, to avoid potential O(N^2) performance. 6114 if (addr != _last_scanned_object) { 6115 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit); 6116 _last_scanned_object = addr; 6117 } 6118 #endif // ASSERT 6119 } else { 6120 // An uninitialized object. 6121 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); 6122 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); 6123 size = pointer_delta(nextOneAddr + 1, addr); 6124 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 6125 "alignment problem"); 6126 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() 6127 // will dirty the card when the klass pointer is installed in the 6128 // object (signaling the completion of initialization). 6129 } 6130 } else { 6131 // Either a not yet marked object or an uninitialized object 6132 if (p->klass_or_null() == NULL) { 6133 // An uninitialized object, skip to the next card, since 6134 // we may not be able to read its P-bits yet. 6135 assert(size == 0, "Initial value"); 6136 } else { 6137 // An object not (yet) reached by marking: we merely need to 6138 // compute its size so as to go look at the next block. 6139 assert(p->is_oop(true), "should be an oop"); 6140 size = CompactibleFreeListSpace::adjustObjectSize(p->size()); 6141 } 6142 } 6143 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6144 return size; 6145 } 6146 6147 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { 6148 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6149 "CMS thread should hold CMS token"); 6150 assert_lock_strong(_freelistLock); 6151 assert_lock_strong(_bitMap->lock()); 6152 // relinquish the free_list_lock and bitMaplock() 6153 _bitMap->lock()->unlock(); 6154 _freelistLock->unlock(); 6155 ConcurrentMarkSweepThread::desynchronize(true); 6156 _collector->stopTimer(); 6157 _collector->incrementYields(); 6158 6159 // See the comment in coordinator_yield() 6160 for (unsigned i = 0; i < CMSYieldSleepCount && 6161 ConcurrentMarkSweepThread::should_yield() && 6162 !CMSCollector::foregroundGCIsActive(); ++i) { 6163 os::sleep(Thread::current(), 1, false); 6164 } 6165 6166 ConcurrentMarkSweepThread::synchronize(true); 6167 _freelistLock->lock_without_safepoint_check(); 6168 _bitMap->lock()->lock_without_safepoint_check(); 6169 _collector->startTimer(); 6170 } 6171 6172 6173 ////////////////////////////////////////////////////////////////// 6174 // SurvivorSpacePrecleanClosure 6175 ////////////////////////////////////////////////////////////////// 6176 // This (single-threaded) closure is used to preclean the oops in 6177 // the survivor spaces. 6178 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { 6179 6180 HeapWord* addr = (HeapWord*)p; 6181 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6182 assert(!_span.contains(addr), "we are scanning the survivor spaces"); 6183 assert(p->klass_or_null() != NULL, "object should be initialized"); 6184 // an initialized object; ignore mark word in verification below 6185 // since we are running concurrent with mutators 6186 assert(p->is_oop(true), "should be an oop"); 6187 // Note that we do not yield while we iterate over 6188 // the interior oops of p, pushing the relevant ones 6189 // on our marking stack. 6190 size_t size = p->oop_iterate_size(_scanning_closure); 6191 do_yield_check(); 6192 // Observe that below, we do not abandon the preclean 6193 // phase as soon as we should; rather we empty the 6194 // marking stack before returning. This is to satisfy 6195 // some existing assertions. In general, it may be a 6196 // good idea to abort immediately and complete the marking 6197 // from the grey objects at a later time. 6198 while (!_mark_stack->isEmpty()) { 6199 oop new_oop = _mark_stack->pop(); 6200 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); 6201 assert(_bit_map->isMarked((HeapWord*)new_oop), 6202 "only grey objects on this stack"); 6203 // iterate over the oops in this oop, marking and pushing 6204 // the ones in CMS heap (i.e. in _span). 6205 new_oop->oop_iterate(_scanning_closure); 6206 // check if it's time to yield 6207 do_yield_check(); 6208 } 6209 unsigned int after_count = 6210 GenCollectedHeap::heap()->total_collections(); 6211 bool abort = (_before_count != after_count) || 6212 _collector->should_abort_preclean(); 6213 return abort ? 0 : size; 6214 } 6215 6216 void SurvivorSpacePrecleanClosure::do_yield_work() { 6217 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6218 "CMS thread should hold CMS token"); 6219 assert_lock_strong(_bit_map->lock()); 6220 // Relinquish the bit map lock 6221 _bit_map->lock()->unlock(); 6222 ConcurrentMarkSweepThread::desynchronize(true); 6223 _collector->stopTimer(); 6224 _collector->incrementYields(); 6225 6226 // See the comment in coordinator_yield() 6227 for (unsigned i = 0; i < CMSYieldSleepCount && 6228 ConcurrentMarkSweepThread::should_yield() && 6229 !CMSCollector::foregroundGCIsActive(); ++i) { 6230 os::sleep(Thread::current(), 1, false); 6231 } 6232 6233 ConcurrentMarkSweepThread::synchronize(true); 6234 _bit_map->lock()->lock_without_safepoint_check(); 6235 _collector->startTimer(); 6236 } 6237 6238 // This closure is used to rescan the marked objects on the dirty cards 6239 // in the mod union table and the card table proper. In the parallel 6240 // case, although the bitMap is shared, we do a single read so the 6241 // isMarked() query is "safe". 6242 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { 6243 // Ignore mark word because we are running concurrent with mutators 6244 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p)); 6245 HeapWord* addr = (HeapWord*)p; 6246 assert(_span.contains(addr), "we are scanning the CMS generation"); 6247 bool is_obj_array = false; 6248 #ifdef ASSERT 6249 if (!_parallel) { 6250 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); 6251 assert(_collector->overflow_list_is_empty(), 6252 "overflow list should be empty"); 6253 6254 } 6255 #endif // ASSERT 6256 if (_bit_map->isMarked(addr)) { 6257 // Obj arrays are precisely marked, non-arrays are not; 6258 // so we scan objArrays precisely and non-arrays in their 6259 // entirety. 6260 if (p->is_objArray()) { 6261 is_obj_array = true; 6262 if (_parallel) { 6263 p->oop_iterate(_par_scan_closure, mr); 6264 } else { 6265 p->oop_iterate(_scan_closure, mr); 6266 } 6267 } else { 6268 if (_parallel) { 6269 p->oop_iterate(_par_scan_closure); 6270 } else { 6271 p->oop_iterate(_scan_closure); 6272 } 6273 } 6274 } 6275 #ifdef ASSERT 6276 if (!_parallel) { 6277 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); 6278 assert(_collector->overflow_list_is_empty(), 6279 "overflow list should be empty"); 6280 6281 } 6282 #endif // ASSERT 6283 return is_obj_array; 6284 } 6285 6286 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, 6287 MemRegion span, 6288 CMSBitMap* bitMap, CMSMarkStack* markStack, 6289 bool should_yield, bool verifying): 6290 _collector(collector), 6291 _span(span), 6292 _bitMap(bitMap), 6293 _mut(&collector->_modUnionTable), 6294 _markStack(markStack), 6295 _yield(should_yield), 6296 _skipBits(0) 6297 { 6298 assert(_markStack->isEmpty(), "stack should be empty"); 6299 _finger = _bitMap->startWord(); 6300 _threshold = _finger; 6301 assert(_collector->_restart_addr == NULL, "Sanity check"); 6302 assert(_span.contains(_finger), "Out of bounds _finger?"); 6303 DEBUG_ONLY(_verifying = verifying;) 6304 } 6305 6306 void MarkFromRootsClosure::reset(HeapWord* addr) { 6307 assert(_markStack->isEmpty(), "would cause duplicates on stack"); 6308 assert(_span.contains(addr), "Out of bounds _finger?"); 6309 _finger = addr; 6310 _threshold = (HeapWord*)round_to( 6311 (intptr_t)_finger, CardTableModRefBS::card_size); 6312 } 6313 6314 // Should revisit to see if this should be restructured for 6315 // greater efficiency. 6316 bool MarkFromRootsClosure::do_bit(size_t offset) { 6317 if (_skipBits > 0) { 6318 _skipBits--; 6319 return true; 6320 } 6321 // convert offset into a HeapWord* 6322 HeapWord* addr = _bitMap->startWord() + offset; 6323 assert(_bitMap->endWord() && addr < _bitMap->endWord(), 6324 "address out of range"); 6325 assert(_bitMap->isMarked(addr), "tautology"); 6326 if (_bitMap->isMarked(addr+1)) { 6327 // this is an allocated but not yet initialized object 6328 assert(_skipBits == 0, "tautology"); 6329 _skipBits = 2; // skip next two marked bits ("Printezis-marks") 6330 oop p = oop(addr); 6331 if (p->klass_or_null() == NULL) { 6332 DEBUG_ONLY(if (!_verifying) {) 6333 // We re-dirty the cards on which this object lies and increase 6334 // the _threshold so that we'll come back to scan this object 6335 // during the preclean or remark phase. (CMSCleanOnEnter) 6336 if (CMSCleanOnEnter) { 6337 size_t sz = _collector->block_size_using_printezis_bits(addr); 6338 HeapWord* end_card_addr = (HeapWord*)round_to( 6339 (intptr_t)(addr+sz), CardTableModRefBS::card_size); 6340 MemRegion redirty_range = MemRegion(addr, end_card_addr); 6341 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 6342 // Bump _threshold to end_card_addr; note that 6343 // _threshold cannot possibly exceed end_card_addr, anyhow. 6344 // This prevents future clearing of the card as the scan proceeds 6345 // to the right. 6346 assert(_threshold <= end_card_addr, 6347 "Because we are just scanning into this object"); 6348 if (_threshold < end_card_addr) { 6349 _threshold = end_card_addr; 6350 } 6351 if (p->klass_or_null() != NULL) { 6352 // Redirty the range of cards... 6353 _mut->mark_range(redirty_range); 6354 } // ...else the setting of klass will dirty the card anyway. 6355 } 6356 DEBUG_ONLY(}) 6357 return true; 6358 } 6359 } 6360 scanOopsInOop(addr); 6361 return true; 6362 } 6363 6364 // We take a break if we've been at this for a while, 6365 // so as to avoid monopolizing the locks involved. 6366 void MarkFromRootsClosure::do_yield_work() { 6367 // First give up the locks, then yield, then re-lock 6368 // We should probably use a constructor/destructor idiom to 6369 // do this unlock/lock or modify the MutexUnlocker class to 6370 // serve our purpose. XXX 6371 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6372 "CMS thread should hold CMS token"); 6373 assert_lock_strong(_bitMap->lock()); 6374 _bitMap->lock()->unlock(); 6375 ConcurrentMarkSweepThread::desynchronize(true); 6376 _collector->stopTimer(); 6377 _collector->incrementYields(); 6378 6379 // See the comment in coordinator_yield() 6380 for (unsigned i = 0; i < CMSYieldSleepCount && 6381 ConcurrentMarkSweepThread::should_yield() && 6382 !CMSCollector::foregroundGCIsActive(); ++i) { 6383 os::sleep(Thread::current(), 1, false); 6384 } 6385 6386 ConcurrentMarkSweepThread::synchronize(true); 6387 _bitMap->lock()->lock_without_safepoint_check(); 6388 _collector->startTimer(); 6389 } 6390 6391 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { 6392 assert(_bitMap->isMarked(ptr), "expected bit to be set"); 6393 assert(_markStack->isEmpty(), 6394 "should drain stack to limit stack usage"); 6395 // convert ptr to an oop preparatory to scanning 6396 oop obj = oop(ptr); 6397 // Ignore mark word in verification below, since we 6398 // may be running concurrent with mutators. 6399 assert(obj->is_oop(true), "should be an oop"); 6400 assert(_finger <= ptr, "_finger runneth ahead"); 6401 // advance the finger to right end of this object 6402 _finger = ptr + obj->size(); 6403 assert(_finger > ptr, "we just incremented it above"); 6404 // On large heaps, it may take us some time to get through 6405 // the marking phase. During 6406 // this time it's possible that a lot of mutations have 6407 // accumulated in the card table and the mod union table -- 6408 // these mutation records are redundant until we have 6409 // actually traced into the corresponding card. 6410 // Here, we check whether advancing the finger would make 6411 // us cross into a new card, and if so clear corresponding 6412 // cards in the MUT (preclean them in the card-table in the 6413 // future). 6414 6415 DEBUG_ONLY(if (!_verifying) {) 6416 // The clean-on-enter optimization is disabled by default, 6417 // until we fix 6178663. 6418 if (CMSCleanOnEnter && (_finger > _threshold)) { 6419 // [_threshold, _finger) represents the interval 6420 // of cards to be cleared in MUT (or precleaned in card table). 6421 // The set of cards to be cleared is all those that overlap 6422 // with the interval [_threshold, _finger); note that 6423 // _threshold is always kept card-aligned but _finger isn't 6424 // always card-aligned. 6425 HeapWord* old_threshold = _threshold; 6426 assert(old_threshold == (HeapWord*)round_to( 6427 (intptr_t)old_threshold, CardTableModRefBS::card_size), 6428 "_threshold should always be card-aligned"); 6429 _threshold = (HeapWord*)round_to( 6430 (intptr_t)_finger, CardTableModRefBS::card_size); 6431 MemRegion mr(old_threshold, _threshold); 6432 assert(!mr.is_empty(), "Control point invariant"); 6433 assert(_span.contains(mr), "Should clear within span"); 6434 _mut->clear_range(mr); 6435 } 6436 DEBUG_ONLY(}) 6437 // Note: the finger doesn't advance while we drain 6438 // the stack below. 6439 PushOrMarkClosure pushOrMarkClosure(_collector, 6440 _span, _bitMap, _markStack, 6441 _finger, this); 6442 bool res = _markStack->push(obj); 6443 assert(res, "Empty non-zero size stack should have space for single push"); 6444 while (!_markStack->isEmpty()) { 6445 oop new_oop = _markStack->pop(); 6446 // Skip verifying header mark word below because we are 6447 // running concurrent with mutators. 6448 assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); 6449 // now scan this oop's oops 6450 new_oop->oop_iterate(&pushOrMarkClosure); 6451 do_yield_check(); 6452 } 6453 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); 6454 } 6455 6456 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task, 6457 CMSCollector* collector, MemRegion span, 6458 CMSBitMap* bit_map, 6459 OopTaskQueue* work_queue, 6460 CMSMarkStack* overflow_stack): 6461 _collector(collector), 6462 _whole_span(collector->_span), 6463 _span(span), 6464 _bit_map(bit_map), 6465 _mut(&collector->_modUnionTable), 6466 _work_queue(work_queue), 6467 _overflow_stack(overflow_stack), 6468 _skip_bits(0), 6469 _task(task) 6470 { 6471 assert(_work_queue->size() == 0, "work_queue should be empty"); 6472 _finger = span.start(); 6473 _threshold = _finger; // XXX Defer clear-on-enter optimization for now 6474 assert(_span.contains(_finger), "Out of bounds _finger?"); 6475 } 6476 6477 // Should revisit to see if this should be restructured for 6478 // greater efficiency. 6479 bool ParMarkFromRootsClosure::do_bit(size_t offset) { 6480 if (_skip_bits > 0) { 6481 _skip_bits--; 6482 return true; 6483 } 6484 // convert offset into a HeapWord* 6485 HeapWord* addr = _bit_map->startWord() + offset; 6486 assert(_bit_map->endWord() && addr < _bit_map->endWord(), 6487 "address out of range"); 6488 assert(_bit_map->isMarked(addr), "tautology"); 6489 if (_bit_map->isMarked(addr+1)) { 6490 // this is an allocated object that might not yet be initialized 6491 assert(_skip_bits == 0, "tautology"); 6492 _skip_bits = 2; // skip next two marked bits ("Printezis-marks") 6493 oop p = oop(addr); 6494 if (p->klass_or_null() == NULL) { 6495 // in the case of Clean-on-Enter optimization, redirty card 6496 // and avoid clearing card by increasing the threshold. 6497 return true; 6498 } 6499 } 6500 scan_oops_in_oop(addr); 6501 return true; 6502 } 6503 6504 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { 6505 assert(_bit_map->isMarked(ptr), "expected bit to be set"); 6506 // Should we assert that our work queue is empty or 6507 // below some drain limit? 6508 assert(_work_queue->size() == 0, 6509 "should drain stack to limit stack usage"); 6510 // convert ptr to an oop preparatory to scanning 6511 oop obj = oop(ptr); 6512 // Ignore mark word in verification below, since we 6513 // may be running concurrent with mutators. 6514 assert(obj->is_oop(true), "should be an oop"); 6515 assert(_finger <= ptr, "_finger runneth ahead"); 6516 // advance the finger to right end of this object 6517 _finger = ptr + obj->size(); 6518 assert(_finger > ptr, "we just incremented it above"); 6519 // On large heaps, it may take us some time to get through 6520 // the marking phase. During 6521 // this time it's possible that a lot of mutations have 6522 // accumulated in the card table and the mod union table -- 6523 // these mutation records are redundant until we have 6524 // actually traced into the corresponding card. 6525 // Here, we check whether advancing the finger would make 6526 // us cross into a new card, and if so clear corresponding 6527 // cards in the MUT (preclean them in the card-table in the 6528 // future). 6529 6530 // The clean-on-enter optimization is disabled by default, 6531 // until we fix 6178663. 6532 if (CMSCleanOnEnter && (_finger > _threshold)) { 6533 // [_threshold, _finger) represents the interval 6534 // of cards to be cleared in MUT (or precleaned in card table). 6535 // The set of cards to be cleared is all those that overlap 6536 // with the interval [_threshold, _finger); note that 6537 // _threshold is always kept card-aligned but _finger isn't 6538 // always card-aligned. 6539 HeapWord* old_threshold = _threshold; 6540 assert(old_threshold == (HeapWord*)round_to( 6541 (intptr_t)old_threshold, CardTableModRefBS::card_size), 6542 "_threshold should always be card-aligned"); 6543 _threshold = (HeapWord*)round_to( 6544 (intptr_t)_finger, CardTableModRefBS::card_size); 6545 MemRegion mr(old_threshold, _threshold); 6546 assert(!mr.is_empty(), "Control point invariant"); 6547 assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? 6548 _mut->clear_range(mr); 6549 } 6550 6551 // Note: the local finger doesn't advance while we drain 6552 // the stack below, but the global finger sure can and will. 6553 HeapWord** gfa = _task->global_finger_addr(); 6554 ParPushOrMarkClosure pushOrMarkClosure(_collector, 6555 _span, _bit_map, 6556 _work_queue, 6557 _overflow_stack, 6558 _finger, 6559 gfa, this); 6560 bool res = _work_queue->push(obj); // overflow could occur here 6561 assert(res, "Will hold once we use workqueues"); 6562 while (true) { 6563 oop new_oop; 6564 if (!_work_queue->pop_local(new_oop)) { 6565 // We emptied our work_queue; check if there's stuff that can 6566 // be gotten from the overflow stack. 6567 if (CMSConcMarkingTask::get_work_from_overflow_stack( 6568 _overflow_stack, _work_queue)) { 6569 do_yield_check(); 6570 continue; 6571 } else { // done 6572 break; 6573 } 6574 } 6575 // Skip verifying header mark word below because we are 6576 // running concurrent with mutators. 6577 assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); 6578 // now scan this oop's oops 6579 new_oop->oop_iterate(&pushOrMarkClosure); 6580 do_yield_check(); 6581 } 6582 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); 6583 } 6584 6585 // Yield in response to a request from VM Thread or 6586 // from mutators. 6587 void ParMarkFromRootsClosure::do_yield_work() { 6588 assert(_task != NULL, "sanity"); 6589 _task->yield(); 6590 } 6591 6592 // A variant of the above used for verifying CMS marking work. 6593 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, 6594 MemRegion span, 6595 CMSBitMap* verification_bm, CMSBitMap* cms_bm, 6596 CMSMarkStack* mark_stack): 6597 _collector(collector), 6598 _span(span), 6599 _verification_bm(verification_bm), 6600 _cms_bm(cms_bm), 6601 _mark_stack(mark_stack), 6602 _pam_verify_closure(collector, span, verification_bm, cms_bm, 6603 mark_stack) 6604 { 6605 assert(_mark_stack->isEmpty(), "stack should be empty"); 6606 _finger = _verification_bm->startWord(); 6607 assert(_collector->_restart_addr == NULL, "Sanity check"); 6608 assert(_span.contains(_finger), "Out of bounds _finger?"); 6609 } 6610 6611 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { 6612 assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); 6613 assert(_span.contains(addr), "Out of bounds _finger?"); 6614 _finger = addr; 6615 } 6616 6617 // Should revisit to see if this should be restructured for 6618 // greater efficiency. 6619 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) { 6620 // convert offset into a HeapWord* 6621 HeapWord* addr = _verification_bm->startWord() + offset; 6622 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), 6623 "address out of range"); 6624 assert(_verification_bm->isMarked(addr), "tautology"); 6625 assert(_cms_bm->isMarked(addr), "tautology"); 6626 6627 assert(_mark_stack->isEmpty(), 6628 "should drain stack to limit stack usage"); 6629 // convert addr to an oop preparatory to scanning 6630 oop obj = oop(addr); 6631 assert(obj->is_oop(), "should be an oop"); 6632 assert(_finger <= addr, "_finger runneth ahead"); 6633 // advance the finger to right end of this object 6634 _finger = addr + obj->size(); 6635 assert(_finger > addr, "we just incremented it above"); 6636 // Note: the finger doesn't advance while we drain 6637 // the stack below. 6638 bool res = _mark_stack->push(obj); 6639 assert(res, "Empty non-zero size stack should have space for single push"); 6640 while (!_mark_stack->isEmpty()) { 6641 oop new_oop = _mark_stack->pop(); 6642 assert(new_oop->is_oop(), "Oops! expected to pop an oop"); 6643 // now scan this oop's oops 6644 new_oop->oop_iterate(&_pam_verify_closure); 6645 } 6646 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); 6647 return true; 6648 } 6649 6650 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( 6651 CMSCollector* collector, MemRegion span, 6652 CMSBitMap* verification_bm, CMSBitMap* cms_bm, 6653 CMSMarkStack* mark_stack): 6654 MetadataAwareOopClosure(collector->ref_processor()), 6655 _collector(collector), 6656 _span(span), 6657 _verification_bm(verification_bm), 6658 _cms_bm(cms_bm), 6659 _mark_stack(mark_stack) 6660 { } 6661 6662 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } 6663 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } 6664 6665 // Upon stack overflow, we discard (part of) the stack, 6666 // remembering the least address amongst those discarded 6667 // in CMSCollector's _restart_address. 6668 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { 6669 // Remember the least grey address discarded 6670 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); 6671 _collector->lower_restart_addr(ra); 6672 _mark_stack->reset(); // discard stack contents 6673 _mark_stack->expand(); // expand the stack if possible 6674 } 6675 6676 void PushAndMarkVerifyClosure::do_oop(oop obj) { 6677 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6678 HeapWord* addr = (HeapWord*)obj; 6679 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { 6680 // Oop lies in _span and isn't yet grey or black 6681 _verification_bm->mark(addr); // now grey 6682 if (!_cms_bm->isMarked(addr)) { 6683 Log(gc, verify) log; 6684 ResourceMark rm; 6685 oop(addr)->print_on(log.error_stream()); 6686 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); 6687 fatal("... aborting"); 6688 } 6689 6690 if (!_mark_stack->push(obj)) { // stack overflow 6691 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity()); 6692 assert(_mark_stack->isFull(), "Else push should have succeeded"); 6693 handle_stack_overflow(addr); 6694 } 6695 // anything including and to the right of _finger 6696 // will be scanned as we iterate over the remainder of the 6697 // bit map 6698 } 6699 } 6700 6701 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, 6702 MemRegion span, 6703 CMSBitMap* bitMap, CMSMarkStack* markStack, 6704 HeapWord* finger, MarkFromRootsClosure* parent) : 6705 MetadataAwareOopClosure(collector->ref_processor()), 6706 _collector(collector), 6707 _span(span), 6708 _bitMap(bitMap), 6709 _markStack(markStack), 6710 _finger(finger), 6711 _parent(parent) 6712 { } 6713 6714 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector, 6715 MemRegion span, 6716 CMSBitMap* bit_map, 6717 OopTaskQueue* work_queue, 6718 CMSMarkStack* overflow_stack, 6719 HeapWord* finger, 6720 HeapWord** global_finger_addr, 6721 ParMarkFromRootsClosure* parent) : 6722 MetadataAwareOopClosure(collector->ref_processor()), 6723 _collector(collector), 6724 _whole_span(collector->_span), 6725 _span(span), 6726 _bit_map(bit_map), 6727 _work_queue(work_queue), 6728 _overflow_stack(overflow_stack), 6729 _finger(finger), 6730 _global_finger_addr(global_finger_addr), 6731 _parent(parent) 6732 { } 6733 6734 // Assumes thread-safe access by callers, who are 6735 // responsible for mutual exclusion. 6736 void CMSCollector::lower_restart_addr(HeapWord* low) { 6737 assert(_span.contains(low), "Out of bounds addr"); 6738 if (_restart_addr == NULL) { 6739 _restart_addr = low; 6740 } else { 6741 _restart_addr = MIN2(_restart_addr, low); 6742 } 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 PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { 6749 // Remember the least grey address discarded 6750 HeapWord* ra = (HeapWord*)_markStack->least_value(lost); 6751 _collector->lower_restart_addr(ra); 6752 _markStack->reset(); // discard stack contents 6753 _markStack->expand(); // expand the stack if possible 6754 } 6755 6756 // Upon stack overflow, we discard (part of) the stack, 6757 // remembering the least address amongst those discarded 6758 // in CMSCollector's _restart_address. 6759 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { 6760 // We need to do this under a mutex to prevent other 6761 // workers from interfering with the work done below. 6762 MutexLockerEx ml(_overflow_stack->par_lock(), 6763 Mutex::_no_safepoint_check_flag); 6764 // Remember the least grey address discarded 6765 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); 6766 _collector->lower_restart_addr(ra); 6767 _overflow_stack->reset(); // discard stack contents 6768 _overflow_stack->expand(); // expand the stack if possible 6769 } 6770 6771 void PushOrMarkClosure::do_oop(oop obj) { 6772 // Ignore mark word because we are running concurrent with mutators. 6773 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6774 HeapWord* addr = (HeapWord*)obj; 6775 if (_span.contains(addr) && !_bitMap->isMarked(addr)) { 6776 // Oop lies in _span and isn't yet grey or black 6777 _bitMap->mark(addr); // now grey 6778 if (addr < _finger) { 6779 // the bit map iteration has already either passed, or 6780 // sampled, this bit in the bit map; we'll need to 6781 // use the marking stack to scan this oop's oops. 6782 bool simulate_overflow = false; 6783 NOT_PRODUCT( 6784 if (CMSMarkStackOverflowALot && 6785 _collector->simulate_overflow()) { 6786 // simulate a stack overflow 6787 simulate_overflow = true; 6788 } 6789 ) 6790 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow 6791 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity()); 6792 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); 6793 handle_stack_overflow(addr); 6794 } 6795 } 6796 // anything including and to the right of _finger 6797 // will be scanned as we iterate over the remainder of the 6798 // bit map 6799 do_yield_check(); 6800 } 6801 } 6802 6803 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); } 6804 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); } 6805 6806 void ParPushOrMarkClosure::do_oop(oop obj) { 6807 // Ignore mark word because we are running concurrent with mutators. 6808 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6809 HeapWord* addr = (HeapWord*)obj; 6810 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { 6811 // Oop lies in _span and isn't yet grey or black 6812 // We read the global_finger (volatile read) strictly after marking oop 6813 bool res = _bit_map->par_mark(addr); // now grey 6814 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; 6815 // Should we push this marked oop on our stack? 6816 // -- if someone else marked it, nothing to do 6817 // -- if target oop is above global finger nothing to do 6818 // -- if target oop is in chunk and above local finger 6819 // then nothing to do 6820 // -- else push on work queue 6821 if ( !res // someone else marked it, they will deal with it 6822 || (addr >= *gfa) // will be scanned in a later task 6823 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk 6824 return; 6825 } 6826 // the bit map iteration has already either passed, or 6827 // sampled, this bit in the bit map; we'll need to 6828 // use the marking stack to scan this oop's oops. 6829 bool simulate_overflow = false; 6830 NOT_PRODUCT( 6831 if (CMSMarkStackOverflowALot && 6832 _collector->simulate_overflow()) { 6833 // simulate a stack overflow 6834 simulate_overflow = true; 6835 } 6836 ) 6837 if (simulate_overflow || 6838 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { 6839 // stack overflow 6840 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity()); 6841 // We cannot assert that the overflow stack is full because 6842 // it may have been emptied since. 6843 assert(simulate_overflow || 6844 _work_queue->size() == _work_queue->max_elems(), 6845 "Else push should have succeeded"); 6846 handle_stack_overflow(addr); 6847 } 6848 do_yield_check(); 6849 } 6850 } 6851 6852 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); } 6853 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); } 6854 6855 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, 6856 MemRegion span, 6857 ReferenceProcessor* rp, 6858 CMSBitMap* bit_map, 6859 CMSBitMap* mod_union_table, 6860 CMSMarkStack* mark_stack, 6861 bool concurrent_precleaning): 6862 MetadataAwareOopClosure(rp), 6863 _collector(collector), 6864 _span(span), 6865 _bit_map(bit_map), 6866 _mod_union_table(mod_union_table), 6867 _mark_stack(mark_stack), 6868 _concurrent_precleaning(concurrent_precleaning) 6869 { 6870 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL"); 6871 } 6872 6873 // Grey object rescan during pre-cleaning and second checkpoint phases -- 6874 // the non-parallel version (the parallel version appears further below.) 6875 void PushAndMarkClosure::do_oop(oop obj) { 6876 // Ignore mark word verification. If during concurrent precleaning, 6877 // the object monitor may be locked. If during the checkpoint 6878 // phases, the object may already have been reached by a different 6879 // path and may be at the end of the global overflow list (so 6880 // the mark word may be NULL). 6881 assert(obj->is_oop_or_null(true /* ignore mark word */), 6882 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6883 HeapWord* addr = (HeapWord*)obj; 6884 // Check if oop points into the CMS generation 6885 // and is not marked 6886 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 6887 // a white object ... 6888 _bit_map->mark(addr); // ... now grey 6889 // push on the marking stack (grey set) 6890 bool simulate_overflow = false; 6891 NOT_PRODUCT( 6892 if (CMSMarkStackOverflowALot && 6893 _collector->simulate_overflow()) { 6894 // simulate a stack overflow 6895 simulate_overflow = true; 6896 } 6897 ) 6898 if (simulate_overflow || !_mark_stack->push(obj)) { 6899 if (_concurrent_precleaning) { 6900 // During precleaning we can just dirty the appropriate card(s) 6901 // in the mod union table, thus ensuring that the object remains 6902 // in the grey set and continue. In the case of object arrays 6903 // we need to dirty all of the cards that the object spans, 6904 // since the rescan of object arrays will be limited to the 6905 // dirty cards. 6906 // Note that no one can be interfering with us in this action 6907 // of dirtying the mod union table, so no locking or atomics 6908 // are required. 6909 if (obj->is_objArray()) { 6910 size_t sz = obj->size(); 6911 HeapWord* end_card_addr = (HeapWord*)round_to( 6912 (intptr_t)(addr+sz), CardTableModRefBS::card_size); 6913 MemRegion redirty_range = MemRegion(addr, end_card_addr); 6914 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 6915 _mod_union_table->mark_range(redirty_range); 6916 } else { 6917 _mod_union_table->mark(addr); 6918 } 6919 _collector->_ser_pmc_preclean_ovflw++; 6920 } else { 6921 // During the remark phase, we need to remember this oop 6922 // in the overflow list. 6923 _collector->push_on_overflow_list(obj); 6924 _collector->_ser_pmc_remark_ovflw++; 6925 } 6926 } 6927 } 6928 } 6929 6930 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector, 6931 MemRegion span, 6932 ReferenceProcessor* rp, 6933 CMSBitMap* bit_map, 6934 OopTaskQueue* work_queue): 6935 MetadataAwareOopClosure(rp), 6936 _collector(collector), 6937 _span(span), 6938 _bit_map(bit_map), 6939 _work_queue(work_queue) 6940 { 6941 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL"); 6942 } 6943 6944 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); } 6945 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); } 6946 6947 // Grey object rescan during second checkpoint phase -- 6948 // the parallel version. 6949 void ParPushAndMarkClosure::do_oop(oop obj) { 6950 // In the assert below, we ignore the mark word because 6951 // this oop may point to an already visited object that is 6952 // on the overflow stack (in which case the mark word has 6953 // been hijacked for chaining into the overflow stack -- 6954 // if this is the last object in the overflow stack then 6955 // its mark word will be NULL). Because this object may 6956 // have been subsequently popped off the global overflow 6957 // stack, and the mark word possibly restored to the prototypical 6958 // value, by the time we get to examined this failing assert in 6959 // the debugger, is_oop_or_null(false) may subsequently start 6960 // to hold. 6961 assert(obj->is_oop_or_null(true), 6962 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); 6963 HeapWord* addr = (HeapWord*)obj; 6964 // Check if oop points into the CMS generation 6965 // and is not marked 6966 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 6967 // a white object ... 6968 // If we manage to "claim" the object, by being the 6969 // first thread to mark it, then we push it on our 6970 // marking stack 6971 if (_bit_map->par_mark(addr)) { // ... now grey 6972 // push on work queue (grey set) 6973 bool simulate_overflow = false; 6974 NOT_PRODUCT( 6975 if (CMSMarkStackOverflowALot && 6976 _collector->par_simulate_overflow()) { 6977 // simulate a stack overflow 6978 simulate_overflow = true; 6979 } 6980 ) 6981 if (simulate_overflow || !_work_queue->push(obj)) { 6982 _collector->par_push_on_overflow_list(obj); 6983 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS 6984 } 6985 } // Else, some other thread got there first 6986 } 6987 } 6988 6989 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); } 6990 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); } 6991 6992 void CMSPrecleanRefsYieldClosure::do_yield_work() { 6993 Mutex* bml = _collector->bitMapLock(); 6994 assert_lock_strong(bml); 6995 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6996 "CMS thread should hold CMS token"); 6997 6998 bml->unlock(); 6999 ConcurrentMarkSweepThread::desynchronize(true); 7000 7001 _collector->stopTimer(); 7002 _collector->incrementYields(); 7003 7004 // See the comment in coordinator_yield() 7005 for (unsigned i = 0; i < CMSYieldSleepCount && 7006 ConcurrentMarkSweepThread::should_yield() && 7007 !CMSCollector::foregroundGCIsActive(); ++i) { 7008 os::sleep(Thread::current(), 1, false); 7009 } 7010 7011 ConcurrentMarkSweepThread::synchronize(true); 7012 bml->lock(); 7013 7014 _collector->startTimer(); 7015 } 7016 7017 bool CMSPrecleanRefsYieldClosure::should_return() { 7018 if (ConcurrentMarkSweepThread::should_yield()) { 7019 do_yield_work(); 7020 } 7021 return _collector->foregroundGCIsActive(); 7022 } 7023 7024 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { 7025 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0, 7026 "mr should be aligned to start at a card boundary"); 7027 // We'd like to assert: 7028 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0, 7029 // "mr should be a range of cards"); 7030 // However, that would be too strong in one case -- the last 7031 // partition ends at _unallocated_block which, in general, can be 7032 // an arbitrary boundary, not necessarily card aligned. 7033 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words; 7034 _space->object_iterate_mem(mr, &_scan_cl); 7035 } 7036 7037 SweepClosure::SweepClosure(CMSCollector* collector, 7038 ConcurrentMarkSweepGeneration* g, 7039 CMSBitMap* bitMap, bool should_yield) : 7040 _collector(collector), 7041 _g(g), 7042 _sp(g->cmsSpace()), 7043 _limit(_sp->sweep_limit()), 7044 _freelistLock(_sp->freelistLock()), 7045 _bitMap(bitMap), 7046 _yield(should_yield), 7047 _inFreeRange(false), // No free range at beginning of sweep 7048 _freeRangeInFreeLists(false), // No free range at beginning of sweep 7049 _lastFreeRangeCoalesced(false), 7050 _freeFinger(g->used_region().start()) 7051 { 7052 NOT_PRODUCT( 7053 _numObjectsFreed = 0; 7054 _numWordsFreed = 0; 7055 _numObjectsLive = 0; 7056 _numWordsLive = 0; 7057 _numObjectsAlreadyFree = 0; 7058 _numWordsAlreadyFree = 0; 7059 _last_fc = NULL; 7060 7061 _sp->initializeIndexedFreeListArrayReturnedBytes(); 7062 _sp->dictionary()->initialize_dict_returned_bytes(); 7063 ) 7064 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 7065 "sweep _limit out of bounds"); 7066 log_develop_trace(gc, sweep)("===================="); 7067 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit)); 7068 } 7069 7070 void SweepClosure::print_on(outputStream* st) const { 7071 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")", 7072 p2i(_sp->bottom()), p2i(_sp->end())); 7073 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit)); 7074 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger)); 7075 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));) 7076 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d", 7077 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced); 7078 } 7079 7080 #ifndef PRODUCT 7081 // Assertion checking only: no useful work in product mode -- 7082 // however, if any of the flags below become product flags, 7083 // you may need to review this code to see if it needs to be 7084 // enabled in product mode. 7085 SweepClosure::~SweepClosure() { 7086 assert_lock_strong(_freelistLock); 7087 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 7088 "sweep _limit out of bounds"); 7089 if (inFreeRange()) { 7090 Log(gc, sweep) log; 7091 log.error("inFreeRange() should have been reset; dumping state of SweepClosure"); 7092 ResourceMark rm; 7093 print_on(log.error_stream()); 7094 ShouldNotReachHere(); 7095 } 7096 7097 if (log_is_enabled(Debug, gc, sweep)) { 7098 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", 7099 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); 7100 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", 7101 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); 7102 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord); 7103 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes); 7104 } 7105 7106 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) { 7107 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); 7108 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes(); 7109 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes; 7110 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes", 7111 returned_bytes, indexListReturnedBytes, dict_returned_bytes); 7112 } 7113 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit)); 7114 log_develop_trace(gc, sweep)("================"); 7115 } 7116 #endif // PRODUCT 7117 7118 void SweepClosure::initialize_free_range(HeapWord* freeFinger, 7119 bool freeRangeInFreeLists) { 7120 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)", 7121 p2i(freeFinger), freeRangeInFreeLists); 7122 assert(!inFreeRange(), "Trampling existing free range"); 7123 set_inFreeRange(true); 7124 set_lastFreeRangeCoalesced(false); 7125 7126 set_freeFinger(freeFinger); 7127 set_freeRangeInFreeLists(freeRangeInFreeLists); 7128 if (CMSTestInFreeList) { 7129 if (freeRangeInFreeLists) { 7130 FreeChunk* fc = (FreeChunk*) freeFinger; 7131 assert(fc->is_free(), "A chunk on the free list should be free."); 7132 assert(fc->size() > 0, "Free range should have a size"); 7133 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists"); 7134 } 7135 } 7136 } 7137 7138 // Note that the sweeper runs concurrently with mutators. Thus, 7139 // it is possible for direct allocation in this generation to happen 7140 // in the middle of the sweep. Note that the sweeper also coalesces 7141 // contiguous free blocks. Thus, unless the sweeper and the allocator 7142 // synchronize appropriately freshly allocated blocks may get swept up. 7143 // This is accomplished by the sweeper locking the free lists while 7144 // it is sweeping. Thus blocks that are determined to be free are 7145 // indeed free. There is however one additional complication: 7146 // blocks that have been allocated since the final checkpoint and 7147 // mark, will not have been marked and so would be treated as 7148 // unreachable and swept up. To prevent this, the allocator marks 7149 // the bit map when allocating during the sweep phase. This leads, 7150 // however, to a further complication -- objects may have been allocated 7151 // but not yet initialized -- in the sense that the header isn't yet 7152 // installed. The sweeper can not then determine the size of the block 7153 // in order to skip over it. To deal with this case, we use a technique 7154 // (due to Printezis) to encode such uninitialized block sizes in the 7155 // bit map. Since the bit map uses a bit per every HeapWord, but the 7156 // CMS generation has a minimum object size of 3 HeapWords, it follows 7157 // that "normal marks" won't be adjacent in the bit map (there will 7158 // always be at least two 0 bits between successive 1 bits). We make use 7159 // of these "unused" bits to represent uninitialized blocks -- the bit 7160 // corresponding to the start of the uninitialized object and the next 7161 // bit are both set. Finally, a 1 bit marks the end of the object that 7162 // started with the two consecutive 1 bits to indicate its potentially 7163 // uninitialized state. 7164 7165 size_t SweepClosure::do_blk_careful(HeapWord* addr) { 7166 FreeChunk* fc = (FreeChunk*)addr; 7167 size_t res; 7168 7169 // Check if we are done sweeping. Below we check "addr >= _limit" rather 7170 // than "addr == _limit" because although _limit was a block boundary when 7171 // we started the sweep, it may no longer be one because heap expansion 7172 // may have caused us to coalesce the block ending at the address _limit 7173 // with a newly expanded chunk (this happens when _limit was set to the 7174 // previous _end of the space), so we may have stepped past _limit: 7175 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740. 7176 if (addr >= _limit) { // we have swept up to or past the limit: finish up 7177 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 7178 "sweep _limit out of bounds"); 7179 assert(addr < _sp->end(), "addr out of bounds"); 7180 // Flush any free range we might be holding as a single 7181 // coalesced chunk to the appropriate free list. 7182 if (inFreeRange()) { 7183 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit, 7184 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger())); 7185 flush_cur_free_chunk(freeFinger(), 7186 pointer_delta(addr, freeFinger())); 7187 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]", 7188 p2i(freeFinger()), pointer_delta(addr, freeFinger()), 7189 lastFreeRangeCoalesced() ? 1 : 0); 7190 } 7191 7192 // help the iterator loop finish 7193 return pointer_delta(_sp->end(), addr); 7194 } 7195 7196 assert(addr < _limit, "sweep invariant"); 7197 // check if we should yield 7198 do_yield_check(addr); 7199 if (fc->is_free()) { 7200 // Chunk that is already free 7201 res = fc->size(); 7202 do_already_free_chunk(fc); 7203 debug_only(_sp->verifyFreeLists()); 7204 // If we flush the chunk at hand in lookahead_and_flush() 7205 // and it's coalesced with a preceding chunk, then the 7206 // process of "mangling" the payload of the coalesced block 7207 // will cause erasure of the size information from the 7208 // (erstwhile) header of all the coalesced blocks but the 7209 // first, so the first disjunct in the assert will not hold 7210 // in that specific case (in which case the second disjunct 7211 // will hold). 7212 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit, 7213 "Otherwise the size info doesn't change at this step"); 7214 NOT_PRODUCT( 7215 _numObjectsAlreadyFree++; 7216 _numWordsAlreadyFree += res; 7217 ) 7218 NOT_PRODUCT(_last_fc = fc;) 7219 } else if (!_bitMap->isMarked(addr)) { 7220 // Chunk is fresh garbage 7221 res = do_garbage_chunk(fc); 7222 debug_only(_sp->verifyFreeLists()); 7223 NOT_PRODUCT( 7224 _numObjectsFreed++; 7225 _numWordsFreed += res; 7226 ) 7227 } else { 7228 // Chunk that is alive. 7229 res = do_live_chunk(fc); 7230 debug_only(_sp->verifyFreeLists()); 7231 NOT_PRODUCT( 7232 _numObjectsLive++; 7233 _numWordsLive += res; 7234 ) 7235 } 7236 return res; 7237 } 7238 7239 // For the smart allocation, record following 7240 // split deaths - a free chunk is removed from its free list because 7241 // it is being split into two or more chunks. 7242 // split birth - a free chunk is being added to its free list because 7243 // a larger free chunk has been split and resulted in this free chunk. 7244 // coal death - a free chunk is being removed from its free list because 7245 // it is being coalesced into a large free chunk. 7246 // coal birth - a free chunk is being added to its free list because 7247 // it was created when two or more free chunks where coalesced into 7248 // this free chunk. 7249 // 7250 // These statistics are used to determine the desired number of free 7251 // chunks of a given size. The desired number is chosen to be relative 7252 // to the end of a CMS sweep. The desired number at the end of a sweep 7253 // is the 7254 // count-at-end-of-previous-sweep (an amount that was enough) 7255 // - count-at-beginning-of-current-sweep (the excess) 7256 // + split-births (gains in this size during interval) 7257 // - split-deaths (demands on this size during interval) 7258 // where the interval is from the end of one sweep to the end of the 7259 // next. 7260 // 7261 // When sweeping the sweeper maintains an accumulated chunk which is 7262 // the chunk that is made up of chunks that have been coalesced. That 7263 // will be termed the left-hand chunk. A new chunk of garbage that 7264 // is being considered for coalescing will be referred to as the 7265 // right-hand chunk. 7266 // 7267 // When making a decision on whether to coalesce a right-hand chunk with 7268 // the current left-hand chunk, the current count vs. the desired count 7269 // of the left-hand chunk is considered. Also if the right-hand chunk 7270 // is near the large chunk at the end of the heap (see 7271 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the 7272 // left-hand chunk is coalesced. 7273 // 7274 // When making a decision about whether to split a chunk, the desired count 7275 // vs. the current count of the candidate to be split is also considered. 7276 // If the candidate is underpopulated (currently fewer chunks than desired) 7277 // a chunk of an overpopulated (currently more chunks than desired) size may 7278 // be chosen. The "hint" associated with a free list, if non-null, points 7279 // to a free list which may be overpopulated. 7280 // 7281 7282 void SweepClosure::do_already_free_chunk(FreeChunk* fc) { 7283 const size_t size = fc->size(); 7284 // Chunks that cannot be coalesced are not in the 7285 // free lists. 7286 if (CMSTestInFreeList && !fc->cantCoalesce()) { 7287 assert(_sp->verify_chunk_in_free_list(fc), 7288 "free chunk should be in free lists"); 7289 } 7290 // a chunk that is already free, should not have been 7291 // marked in the bit map 7292 HeapWord* const addr = (HeapWord*) fc; 7293 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); 7294 // Verify that the bit map has no bits marked between 7295 // addr and purported end of this block. 7296 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 7297 7298 // Some chunks cannot be coalesced under any circumstances. 7299 // See the definition of cantCoalesce(). 7300 if (!fc->cantCoalesce()) { 7301 // This chunk can potentially be coalesced. 7302 // All the work is done in 7303 do_post_free_or_garbage_chunk(fc, size); 7304 // Note that if the chunk is not coalescable (the else arm 7305 // below), we unconditionally flush, without needing to do 7306 // a "lookahead," as we do below. 7307 if (inFreeRange()) lookahead_and_flush(fc, size); 7308 } else { 7309 // Code path common to both original and adaptive free lists. 7310 7311 // cant coalesce with previous block; this should be treated 7312 // as the end of a free run if any 7313 if (inFreeRange()) { 7314 // we kicked some butt; time to pick up the garbage 7315 assert(freeFinger() < addr, "freeFinger points too high"); 7316 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 7317 } 7318 // else, nothing to do, just continue 7319 } 7320 } 7321 7322 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) { 7323 // This is a chunk of garbage. It is not in any free list. 7324 // Add it to a free list or let it possibly be coalesced into 7325 // a larger chunk. 7326 HeapWord* const addr = (HeapWord*) fc; 7327 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); 7328 7329 // Verify that the bit map has no bits marked between 7330 // addr and purported end of just dead object. 7331 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 7332 do_post_free_or_garbage_chunk(fc, size); 7333 7334 assert(_limit >= addr + size, 7335 "A freshly garbage chunk can't possibly straddle over _limit"); 7336 if (inFreeRange()) lookahead_and_flush(fc, size); 7337 return size; 7338 } 7339 7340 size_t SweepClosure::do_live_chunk(FreeChunk* fc) { 7341 HeapWord* addr = (HeapWord*) fc; 7342 // The sweeper has just found a live object. Return any accumulated 7343 // left hand chunk to the free lists. 7344 if (inFreeRange()) { 7345 assert(freeFinger() < addr, "freeFinger points too high"); 7346 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 7347 } 7348 7349 // This object is live: we'd normally expect this to be 7350 // an oop, and like to assert the following: 7351 // assert(oop(addr)->is_oop(), "live block should be an oop"); 7352 // However, as we commented above, this may be an object whose 7353 // header hasn't yet been initialized. 7354 size_t size; 7355 assert(_bitMap->isMarked(addr), "Tautology for this control point"); 7356 if (_bitMap->isMarked(addr + 1)) { 7357 // Determine the size from the bit map, rather than trying to 7358 // compute it from the object header. 7359 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); 7360 size = pointer_delta(nextOneAddr + 1, addr); 7361 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 7362 "alignment problem"); 7363 7364 #ifdef ASSERT 7365 if (oop(addr)->klass_or_null() != NULL) { 7366 // Ignore mark word because we are running concurrent with mutators 7367 assert(oop(addr)->is_oop(true), "live block should be an oop"); 7368 assert(size == 7369 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), 7370 "P-mark and computed size do not agree"); 7371 } 7372 #endif 7373 7374 } else { 7375 // This should be an initialized object that's alive. 7376 assert(oop(addr)->klass_or_null() != NULL, 7377 "Should be an initialized object"); 7378 // Ignore mark word because we are running concurrent with mutators 7379 assert(oop(addr)->is_oop(true), "live block should be an oop"); 7380 // Verify that the bit map has no bits marked between 7381 // addr and purported end of this block. 7382 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); 7383 assert(size >= 3, "Necessary for Printezis marks to work"); 7384 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); 7385 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) 7386 } 7387 return size; 7388 } 7389 7390 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc, 7391 size_t chunkSize) { 7392 // do_post_free_or_garbage_chunk() should only be called in the case 7393 // of the adaptive free list allocator. 7394 const bool fcInFreeLists = fc->is_free(); 7395 assert((HeapWord*)fc <= _limit, "sweep invariant"); 7396 if (CMSTestInFreeList && fcInFreeLists) { 7397 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); 7398 } 7399 7400 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize); 7401 7402 HeapWord* const fc_addr = (HeapWord*) fc; 7403 7404 bool coalesce = false; 7405 const size_t left = pointer_delta(fc_addr, freeFinger()); 7406 const size_t right = chunkSize; 7407 switch (FLSCoalescePolicy) { 7408 // numeric value forms a coalition aggressiveness metric 7409 case 0: { // never coalesce 7410 coalesce = false; 7411 break; 7412 } 7413 case 1: { // coalesce if left & right chunks on overpopulated lists 7414 coalesce = _sp->coalOverPopulated(left) && 7415 _sp->coalOverPopulated(right); 7416 break; 7417 } 7418 case 2: { // coalesce if left chunk on overpopulated list (default) 7419 coalesce = _sp->coalOverPopulated(left); 7420 break; 7421 } 7422 case 3: { // coalesce if left OR right chunk on overpopulated list 7423 coalesce = _sp->coalOverPopulated(left) || 7424 _sp->coalOverPopulated(right); 7425 break; 7426 } 7427 case 4: { // always coalesce 7428 coalesce = true; 7429 break; 7430 } 7431 default: 7432 ShouldNotReachHere(); 7433 } 7434 7435 // Should the current free range be coalesced? 7436 // If the chunk is in a free range and either we decided to coalesce above 7437 // or the chunk is near the large block at the end of the heap 7438 // (isNearLargestChunk() returns true), then coalesce this chunk. 7439 const bool doCoalesce = inFreeRange() 7440 && (coalesce || _g->isNearLargestChunk(fc_addr)); 7441 if (doCoalesce) { 7442 // Coalesce the current free range on the left with the new 7443 // chunk on the right. If either is on a free list, 7444 // it must be removed from the list and stashed in the closure. 7445 if (freeRangeInFreeLists()) { 7446 FreeChunk* const ffc = (FreeChunk*)freeFinger(); 7447 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()), 7448 "Size of free range is inconsistent with chunk size."); 7449 if (CMSTestInFreeList) { 7450 assert(_sp->verify_chunk_in_free_list(ffc), 7451 "Chunk is not in free lists"); 7452 } 7453 _sp->coalDeath(ffc->size()); 7454 _sp->removeFreeChunkFromFreeLists(ffc); 7455 set_freeRangeInFreeLists(false); 7456 } 7457 if (fcInFreeLists) { 7458 _sp->coalDeath(chunkSize); 7459 assert(fc->size() == chunkSize, 7460 "The chunk has the wrong size or is not in the free lists"); 7461 _sp->removeFreeChunkFromFreeLists(fc); 7462 } 7463 set_lastFreeRangeCoalesced(true); 7464 print_free_block_coalesced(fc); 7465 } else { // not in a free range and/or should not coalesce 7466 // Return the current free range and start a new one. 7467 if (inFreeRange()) { 7468 // In a free range but cannot coalesce with the right hand chunk. 7469 // Put the current free range into the free lists. 7470 flush_cur_free_chunk(freeFinger(), 7471 pointer_delta(fc_addr, freeFinger())); 7472 } 7473 // Set up for new free range. Pass along whether the right hand 7474 // chunk is in the free lists. 7475 initialize_free_range((HeapWord*)fc, fcInFreeLists); 7476 } 7477 } 7478 7479 // Lookahead flush: 7480 // If we are tracking a free range, and this is the last chunk that 7481 // we'll look at because its end crosses past _limit, we'll preemptively 7482 // flush it along with any free range we may be holding on to. Note that 7483 // this can be the case only for an already free or freshly garbage 7484 // chunk. If this block is an object, it can never straddle 7485 // over _limit. The "straddling" occurs when _limit is set at 7486 // the previous end of the space when this cycle started, and 7487 // a subsequent heap expansion caused the previously co-terminal 7488 // free block to be coalesced with the newly expanded portion, 7489 // thus rendering _limit a non-block-boundary making it dangerous 7490 // for the sweeper to step over and examine. 7491 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) { 7492 assert(inFreeRange(), "Should only be called if currently in a free range."); 7493 HeapWord* const eob = ((HeapWord*)fc) + chunk_size; 7494 assert(_sp->used_region().contains(eob - 1), 7495 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT 7496 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")" 7497 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")", 7498 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size); 7499 if (eob >= _limit) { 7500 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); 7501 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block " 7502 "[" PTR_FORMAT "," PTR_FORMAT ") in space " 7503 "[" PTR_FORMAT "," PTR_FORMAT ")", 7504 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end())); 7505 // Return the storage we are tracking back into the free lists. 7506 log_develop_trace(gc, sweep)("Flushing ... "); 7507 assert(freeFinger() < eob, "Error"); 7508 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger())); 7509 } 7510 } 7511 7512 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) { 7513 assert(inFreeRange(), "Should only be called if currently in a free range."); 7514 assert(size > 0, 7515 "A zero sized chunk cannot be added to the free lists."); 7516 if (!freeRangeInFreeLists()) { 7517 if (CMSTestInFreeList) { 7518 FreeChunk* fc = (FreeChunk*) chunk; 7519 fc->set_size(size); 7520 assert(!_sp->verify_chunk_in_free_list(fc), 7521 "chunk should not be in free lists yet"); 7522 } 7523 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size); 7524 // A new free range is going to be starting. The current 7525 // free range has not been added to the free lists yet or 7526 // was removed so add it back. 7527 // If the current free range was coalesced, then the death 7528 // of the free range was recorded. Record a birth now. 7529 if (lastFreeRangeCoalesced()) { 7530 _sp->coalBirth(size); 7531 } 7532 _sp->addChunkAndRepairOffsetTable(chunk, size, 7533 lastFreeRangeCoalesced()); 7534 } else { 7535 log_develop_trace(gc, sweep)("Already in free list: nothing to flush"); 7536 } 7537 set_inFreeRange(false); 7538 set_freeRangeInFreeLists(false); 7539 } 7540 7541 // We take a break if we've been at this for a while, 7542 // so as to avoid monopolizing the locks involved. 7543 void SweepClosure::do_yield_work(HeapWord* addr) { 7544 // Return current free chunk being used for coalescing (if any) 7545 // to the appropriate freelist. After yielding, the next 7546 // free block encountered will start a coalescing range of 7547 // free blocks. If the next free block is adjacent to the 7548 // chunk just flushed, they will need to wait for the next 7549 // sweep to be coalesced. 7550 if (inFreeRange()) { 7551 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 7552 } 7553 7554 // First give up the locks, then yield, then re-lock. 7555 // We should probably use a constructor/destructor idiom to 7556 // do this unlock/lock or modify the MutexUnlocker class to 7557 // serve our purpose. XXX 7558 assert_lock_strong(_bitMap->lock()); 7559 assert_lock_strong(_freelistLock); 7560 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 7561 "CMS thread should hold CMS token"); 7562 _bitMap->lock()->unlock(); 7563 _freelistLock->unlock(); 7564 ConcurrentMarkSweepThread::desynchronize(true); 7565 _collector->stopTimer(); 7566 _collector->incrementYields(); 7567 7568 // See the comment in coordinator_yield() 7569 for (unsigned i = 0; i < CMSYieldSleepCount && 7570 ConcurrentMarkSweepThread::should_yield() && 7571 !CMSCollector::foregroundGCIsActive(); ++i) { 7572 os::sleep(Thread::current(), 1, false); 7573 } 7574 7575 ConcurrentMarkSweepThread::synchronize(true); 7576 _freelistLock->lock(); 7577 _bitMap->lock()->lock_without_safepoint_check(); 7578 _collector->startTimer(); 7579 } 7580 7581 #ifndef PRODUCT 7582 // This is actually very useful in a product build if it can 7583 // be called from the debugger. Compile it into the product 7584 // as needed. 7585 bool debug_verify_chunk_in_free_list(FreeChunk* fc) { 7586 return debug_cms_space->verify_chunk_in_free_list(fc); 7587 } 7588 #endif 7589 7590 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const { 7591 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")", 7592 p2i(fc), fc->size()); 7593 } 7594 7595 // CMSIsAliveClosure 7596 bool CMSIsAliveClosure::do_object_b(oop obj) { 7597 HeapWord* addr = (HeapWord*)obj; 7598 return addr != NULL && 7599 (!_span.contains(addr) || _bit_map->isMarked(addr)); 7600 } 7601 7602 7603 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector, 7604 MemRegion span, 7605 CMSBitMap* bit_map, CMSMarkStack* mark_stack, 7606 bool cpc): 7607 _collector(collector), 7608 _span(span), 7609 _bit_map(bit_map), 7610 _mark_stack(mark_stack), 7611 _concurrent_precleaning(cpc) { 7612 assert(!_span.is_empty(), "Empty span could spell trouble"); 7613 } 7614 7615 7616 // CMSKeepAliveClosure: the serial version 7617 void CMSKeepAliveClosure::do_oop(oop obj) { 7618 HeapWord* addr = (HeapWord*)obj; 7619 if (_span.contains(addr) && 7620 !_bit_map->isMarked(addr)) { 7621 _bit_map->mark(addr); 7622 bool simulate_overflow = false; 7623 NOT_PRODUCT( 7624 if (CMSMarkStackOverflowALot && 7625 _collector->simulate_overflow()) { 7626 // simulate a stack overflow 7627 simulate_overflow = true; 7628 } 7629 ) 7630 if (simulate_overflow || !_mark_stack->push(obj)) { 7631 if (_concurrent_precleaning) { 7632 // We dirty the overflown object and let the remark 7633 // phase deal with it. 7634 assert(_collector->overflow_list_is_empty(), "Error"); 7635 // In the case of object arrays, we need to dirty all of 7636 // the cards that the object spans. No locking or atomics 7637 // are needed since no one else can be mutating the mod union 7638 // table. 7639 if (obj->is_objArray()) { 7640 size_t sz = obj->size(); 7641 HeapWord* end_card_addr = 7642 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size); 7643 MemRegion redirty_range = MemRegion(addr, end_card_addr); 7644 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 7645 _collector->_modUnionTable.mark_range(redirty_range); 7646 } else { 7647 _collector->_modUnionTable.mark(addr); 7648 } 7649 _collector->_ser_kac_preclean_ovflw++; 7650 } else { 7651 _collector->push_on_overflow_list(obj); 7652 _collector->_ser_kac_ovflw++; 7653 } 7654 } 7655 } 7656 } 7657 7658 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); } 7659 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); } 7660 7661 // CMSParKeepAliveClosure: a parallel version of the above. 7662 // The work queues are private to each closure (thread), 7663 // but (may be) available for stealing by other threads. 7664 void CMSParKeepAliveClosure::do_oop(oop obj) { 7665 HeapWord* addr = (HeapWord*)obj; 7666 if (_span.contains(addr) && 7667 !_bit_map->isMarked(addr)) { 7668 // In general, during recursive tracing, several threads 7669 // may be concurrently getting here; the first one to 7670 // "tag" it, claims it. 7671 if (_bit_map->par_mark(addr)) { 7672 bool res = _work_queue->push(obj); 7673 assert(res, "Low water mark should be much less than capacity"); 7674 // Do a recursive trim in the hope that this will keep 7675 // stack usage lower, but leave some oops for potential stealers 7676 trim_queue(_low_water_mark); 7677 } // Else, another thread got there first 7678 } 7679 } 7680 7681 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); } 7682 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); } 7683 7684 void CMSParKeepAliveClosure::trim_queue(uint max) { 7685 while (_work_queue->size() > max) { 7686 oop new_oop; 7687 if (_work_queue->pop_local(new_oop)) { 7688 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); 7689 assert(_bit_map->isMarked((HeapWord*)new_oop), 7690 "no white objects on this stack!"); 7691 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); 7692 // iterate over the oops in this oop, marking and pushing 7693 // the ones in CMS heap (i.e. in _span). 7694 new_oop->oop_iterate(&_mark_and_push); 7695 } 7696 } 7697 } 7698 7699 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure( 7700 CMSCollector* collector, 7701 MemRegion span, CMSBitMap* bit_map, 7702 OopTaskQueue* work_queue): 7703 _collector(collector), 7704 _span(span), 7705 _bit_map(bit_map), 7706 _work_queue(work_queue) { } 7707 7708 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) { 7709 HeapWord* addr = (HeapWord*)obj; 7710 if (_span.contains(addr) && 7711 !_bit_map->isMarked(addr)) { 7712 if (_bit_map->par_mark(addr)) { 7713 bool simulate_overflow = false; 7714 NOT_PRODUCT( 7715 if (CMSMarkStackOverflowALot && 7716 _collector->par_simulate_overflow()) { 7717 // simulate a stack overflow 7718 simulate_overflow = true; 7719 } 7720 ) 7721 if (simulate_overflow || !_work_queue->push(obj)) { 7722 _collector->par_push_on_overflow_list(obj); 7723 _collector->_par_kac_ovflw++; 7724 } 7725 } // Else another thread got there already 7726 } 7727 } 7728 7729 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } 7730 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } 7731 7732 ////////////////////////////////////////////////////////////////// 7733 // CMSExpansionCause ///////////////////////////// 7734 ////////////////////////////////////////////////////////////////// 7735 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { 7736 switch (cause) { 7737 case _no_expansion: 7738 return "No expansion"; 7739 case _satisfy_free_ratio: 7740 return "Free ratio"; 7741 case _satisfy_promotion: 7742 return "Satisfy promotion"; 7743 case _satisfy_allocation: 7744 return "allocation"; 7745 case _allocate_par_lab: 7746 return "Par LAB"; 7747 case _allocate_par_spooling_space: 7748 return "Par Spooling Space"; 7749 case _adaptive_size_policy: 7750 return "Ergonomics"; 7751 default: 7752 return "unknown"; 7753 } 7754 } 7755 7756 void CMSDrainMarkingStackClosure::do_void() { 7757 // the max number to take from overflow list at a time 7758 const size_t num = _mark_stack->capacity()/4; 7759 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(), 7760 "Overflow list should be NULL during concurrent phases"); 7761 while (!_mark_stack->isEmpty() || 7762 // if stack is empty, check the overflow list 7763 _collector->take_from_overflow_list(num, _mark_stack)) { 7764 oop obj = _mark_stack->pop(); 7765 HeapWord* addr = (HeapWord*)obj; 7766 assert(_span.contains(addr), "Should be within span"); 7767 assert(_bit_map->isMarked(addr), "Should be marked"); 7768 assert(obj->is_oop(), "Should be an oop"); 7769 obj->oop_iterate(_keep_alive); 7770 } 7771 } 7772 7773 void CMSParDrainMarkingStackClosure::do_void() { 7774 // drain queue 7775 trim_queue(0); 7776 } 7777 7778 // Trim our work_queue so its length is below max at return 7779 void CMSParDrainMarkingStackClosure::trim_queue(uint max) { 7780 while (_work_queue->size() > max) { 7781 oop new_oop; 7782 if (_work_queue->pop_local(new_oop)) { 7783 assert(new_oop->is_oop(), "Expected an oop"); 7784 assert(_bit_map->isMarked((HeapWord*)new_oop), 7785 "no white objects on this stack!"); 7786 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); 7787 // iterate over the oops in this oop, marking and pushing 7788 // the ones in CMS heap (i.e. in _span). 7789 new_oop->oop_iterate(&_mark_and_push); 7790 } 7791 } 7792 } 7793 7794 //////////////////////////////////////////////////////////////////// 7795 // Support for Marking Stack Overflow list handling and related code 7796 //////////////////////////////////////////////////////////////////// 7797 // Much of the following code is similar in shape and spirit to the 7798 // code used in ParNewGC. We should try and share that code 7799 // as much as possible in the future. 7800 7801 #ifndef PRODUCT 7802 // Debugging support for CMSStackOverflowALot 7803 7804 // It's OK to call this multi-threaded; the worst thing 7805 // that can happen is that we'll get a bunch of closely 7806 // spaced simulated overflows, but that's OK, in fact 7807 // probably good as it would exercise the overflow code 7808 // under contention. 7809 bool CMSCollector::simulate_overflow() { 7810 if (_overflow_counter-- <= 0) { // just being defensive 7811 _overflow_counter = CMSMarkStackOverflowInterval; 7812 return true; 7813 } else { 7814 return false; 7815 } 7816 } 7817 7818 bool CMSCollector::par_simulate_overflow() { 7819 return simulate_overflow(); 7820 } 7821 #endif 7822 7823 // Single-threaded 7824 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { 7825 assert(stack->isEmpty(), "Expected precondition"); 7826 assert(stack->capacity() > num, "Shouldn't bite more than can chew"); 7827 size_t i = num; 7828 oop cur = _overflow_list; 7829 const markOop proto = markOopDesc::prototype(); 7830 NOT_PRODUCT(ssize_t n = 0;) 7831 for (oop next; i > 0 && cur != NULL; cur = next, i--) { 7832 next = oop(cur->mark()); 7833 cur->set_mark(proto); // until proven otherwise 7834 assert(cur->is_oop(), "Should be an oop"); 7835 bool res = stack->push(cur); 7836 assert(res, "Bit off more than can chew?"); 7837 NOT_PRODUCT(n++;) 7838 } 7839 _overflow_list = cur; 7840 #ifndef PRODUCT 7841 assert(_num_par_pushes >= n, "Too many pops?"); 7842 _num_par_pushes -=n; 7843 #endif 7844 return !stack->isEmpty(); 7845 } 7846 7847 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 7848 // (MT-safe) Get a prefix of at most "num" from the list. 7849 // The overflow list is chained through the mark word of 7850 // each object in the list. We fetch the entire list, 7851 // break off a prefix of the right size and return the 7852 // remainder. If other threads try to take objects from 7853 // the overflow list at that time, they will wait for 7854 // some time to see if data becomes available. If (and 7855 // only if) another thread places one or more object(s) 7856 // on the global list before we have returned the suffix 7857 // to the global list, we will walk down our local list 7858 // to find its end and append the global list to 7859 // our suffix before returning it. This suffix walk can 7860 // prove to be expensive (quadratic in the amount of traffic) 7861 // when there are many objects in the overflow list and 7862 // there is much producer-consumer contention on the list. 7863 // *NOTE*: The overflow list manipulation code here and 7864 // in ParNewGeneration:: are very similar in shape, 7865 // except that in the ParNew case we use the old (from/eden) 7866 // copy of the object to thread the list via its klass word. 7867 // Because of the common code, if you make any changes in 7868 // the code below, please check the ParNew version to see if 7869 // similar changes might be needed. 7870 // CR 6797058 has been filed to consolidate the common code. 7871 bool CMSCollector::par_take_from_overflow_list(size_t num, 7872 OopTaskQueue* work_q, 7873 int no_of_gc_threads) { 7874 assert(work_q->size() == 0, "First empty local work queue"); 7875 assert(num < work_q->max_elems(), "Can't bite more than we can chew"); 7876 if (_overflow_list == NULL) { 7877 return false; 7878 } 7879 // Grab the entire list; we'll put back a suffix 7880 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 7881 Thread* tid = Thread::current(); 7882 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was 7883 // set to ParallelGCThreads. 7884 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads; 7885 size_t sleep_time_millis = MAX2((size_t)1, num/100); 7886 // If the list is busy, we spin for a short while, 7887 // sleeping between attempts to get the list. 7888 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) { 7889 os::sleep(tid, sleep_time_millis, false); 7890 if (_overflow_list == NULL) { 7891 // Nothing left to take 7892 return false; 7893 } else if (_overflow_list != BUSY) { 7894 // Try and grab the prefix 7895 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 7896 } 7897 } 7898 // If the list was found to be empty, or we spun long 7899 // enough, we give up and return empty-handed. If we leave 7900 // the list in the BUSY state below, it must be the case that 7901 // some other thread holds the overflow list and will set it 7902 // to a non-BUSY state in the future. 7903 if (prefix == NULL || prefix == BUSY) { 7904 // Nothing to take or waited long enough 7905 if (prefix == NULL) { 7906 // Write back the NULL in case we overwrote it with BUSY above 7907 // and it is still the same value. 7908 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 7909 } 7910 return false; 7911 } 7912 assert(prefix != NULL && prefix != BUSY, "Error"); 7913 size_t i = num; 7914 oop cur = prefix; 7915 // Walk down the first "num" objects, unless we reach the end. 7916 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--); 7917 if (cur->mark() == NULL) { 7918 // We have "num" or fewer elements in the list, so there 7919 // is nothing to return to the global list. 7920 // Write back the NULL in lieu of the BUSY we wrote 7921 // above, if it is still the same value. 7922 if (_overflow_list == BUSY) { 7923 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 7924 } 7925 } else { 7926 // Chop off the suffix and return it to the global list. 7927 assert(cur->mark() != BUSY, "Error"); 7928 oop suffix_head = cur->mark(); // suffix will be put back on global list 7929 cur->set_mark(NULL); // break off suffix 7930 // It's possible that the list is still in the empty(busy) state 7931 // we left it in a short while ago; in that case we may be 7932 // able to place back the suffix without incurring the cost 7933 // of a walk down the list. 7934 oop observed_overflow_list = _overflow_list; 7935 oop cur_overflow_list = observed_overflow_list; 7936 bool attached = false; 7937 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 7938 observed_overflow_list = 7939 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list); 7940 if (cur_overflow_list == observed_overflow_list) { 7941 attached = true; 7942 break; 7943 } else cur_overflow_list = observed_overflow_list; 7944 } 7945 if (!attached) { 7946 // Too bad, someone else sneaked in (at least) an element; we'll need 7947 // to do a splice. Find tail of suffix so we can prepend suffix to global 7948 // list. 7949 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark())); 7950 oop suffix_tail = cur; 7951 assert(suffix_tail != NULL && suffix_tail->mark() == NULL, 7952 "Tautology"); 7953 observed_overflow_list = _overflow_list; 7954 do { 7955 cur_overflow_list = observed_overflow_list; 7956 if (cur_overflow_list != BUSY) { 7957 // Do the splice ... 7958 suffix_tail->set_mark(markOop(cur_overflow_list)); 7959 } else { // cur_overflow_list == BUSY 7960 suffix_tail->set_mark(NULL); 7961 } 7962 // ... and try to place spliced list back on overflow_list ... 7963 observed_overflow_list = 7964 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list); 7965 } while (cur_overflow_list != observed_overflow_list); 7966 // ... until we have succeeded in doing so. 7967 } 7968 } 7969 7970 // Push the prefix elements on work_q 7971 assert(prefix != NULL, "control point invariant"); 7972 const markOop proto = markOopDesc::prototype(); 7973 oop next; 7974 NOT_PRODUCT(ssize_t n = 0;) 7975 for (cur = prefix; cur != NULL; cur = next) { 7976 next = oop(cur->mark()); 7977 cur->set_mark(proto); // until proven otherwise 7978 assert(cur->is_oop(), "Should be an oop"); 7979 bool res = work_q->push(cur); 7980 assert(res, "Bit off more than we can chew?"); 7981 NOT_PRODUCT(n++;) 7982 } 7983 #ifndef PRODUCT 7984 assert(_num_par_pushes >= n, "Too many pops?"); 7985 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 7986 #endif 7987 return true; 7988 } 7989 7990 // Single-threaded 7991 void CMSCollector::push_on_overflow_list(oop p) { 7992 NOT_PRODUCT(_num_par_pushes++;) 7993 assert(p->is_oop(), "Not an oop"); 7994 preserve_mark_if_necessary(p); 7995 p->set_mark((markOop)_overflow_list); 7996 _overflow_list = p; 7997 } 7998 7999 // Multi-threaded; use CAS to prepend to overflow list 8000 void CMSCollector::par_push_on_overflow_list(oop p) { 8001 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);) 8002 assert(p->is_oop(), "Not an oop"); 8003 par_preserve_mark_if_necessary(p); 8004 oop observed_overflow_list = _overflow_list; 8005 oop cur_overflow_list; 8006 do { 8007 cur_overflow_list = observed_overflow_list; 8008 if (cur_overflow_list != BUSY) { 8009 p->set_mark(markOop(cur_overflow_list)); 8010 } else { 8011 p->set_mark(NULL); 8012 } 8013 observed_overflow_list = 8014 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list); 8015 } while (cur_overflow_list != observed_overflow_list); 8016 } 8017 #undef BUSY 8018 8019 // Single threaded 8020 // General Note on GrowableArray: pushes may silently fail 8021 // because we are (temporarily) out of C-heap for expanding 8022 // the stack. The problem is quite ubiquitous and affects 8023 // a lot of code in the JVM. The prudent thing for GrowableArray 8024 // to do (for now) is to exit with an error. However, that may 8025 // be too draconian in some cases because the caller may be 8026 // able to recover without much harm. For such cases, we 8027 // should probably introduce a "soft_push" method which returns 8028 // an indication of success or failure with the assumption that 8029 // the caller may be able to recover from a failure; code in 8030 // the VM can then be changed, incrementally, to deal with such 8031 // failures where possible, thus, incrementally hardening the VM 8032 // in such low resource situations. 8033 void CMSCollector::preserve_mark_work(oop p, markOop m) { 8034 _preserved_oop_stack.push(p); 8035 _preserved_mark_stack.push(m); 8036 assert(m == p->mark(), "Mark word changed"); 8037 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), 8038 "bijection"); 8039 } 8040 8041 // Single threaded 8042 void CMSCollector::preserve_mark_if_necessary(oop p) { 8043 markOop m = p->mark(); 8044 if (m->must_be_preserved(p)) { 8045 preserve_mark_work(p, m); 8046 } 8047 } 8048 8049 void CMSCollector::par_preserve_mark_if_necessary(oop p) { 8050 markOop m = p->mark(); 8051 if (m->must_be_preserved(p)) { 8052 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); 8053 // Even though we read the mark word without holding 8054 // the lock, we are assured that it will not change 8055 // because we "own" this oop, so no other thread can 8056 // be trying to push it on the overflow list; see 8057 // the assertion in preserve_mark_work() that checks 8058 // that m == p->mark(). 8059 preserve_mark_work(p, m); 8060 } 8061 } 8062 8063 // We should be able to do this multi-threaded, 8064 // a chunk of stack being a task (this is 8065 // correct because each oop only ever appears 8066 // once in the overflow list. However, it's 8067 // not very easy to completely overlap this with 8068 // other operations, so will generally not be done 8069 // until all work's been completed. Because we 8070 // expect the preserved oop stack (set) to be small, 8071 // it's probably fine to do this single-threaded. 8072 // We can explore cleverer concurrent/overlapped/parallel 8073 // processing of preserved marks if we feel the 8074 // need for this in the future. Stack overflow should 8075 // be so rare in practice and, when it happens, its 8076 // effect on performance so great that this will 8077 // likely just be in the noise anyway. 8078 void CMSCollector::restore_preserved_marks_if_any() { 8079 assert(SafepointSynchronize::is_at_safepoint(), 8080 "world should be stopped"); 8081 assert(Thread::current()->is_ConcurrentGC_thread() || 8082 Thread::current()->is_VM_thread(), 8083 "should be single-threaded"); 8084 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), 8085 "bijection"); 8086 8087 while (!_preserved_oop_stack.is_empty()) { 8088 oop p = _preserved_oop_stack.pop(); 8089 assert(p->is_oop(), "Should be an oop"); 8090 assert(_span.contains(p), "oop should be in _span"); 8091 assert(p->mark() == markOopDesc::prototype(), 8092 "Set when taken from overflow list"); 8093 markOop m = _preserved_mark_stack.pop(); 8094 p->set_mark(m); 8095 } 8096 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(), 8097 "stacks were cleared above"); 8098 } 8099 8100 #ifndef PRODUCT 8101 bool CMSCollector::no_preserved_marks() const { 8102 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(); 8103 } 8104 #endif 8105 8106 // Transfer some number of overflown objects to usual marking 8107 // stack. Return true if some objects were transferred. 8108 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { 8109 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4, 8110 (size_t)ParGCDesiredObjsFromOverflowList); 8111 8112 bool res = _collector->take_from_overflow_list(num, _mark_stack); 8113 assert(_collector->overflow_list_is_empty() || res, 8114 "If list is not empty, we should have taken something"); 8115 assert(!res || !_mark_stack->isEmpty(), 8116 "If we took something, it should now be on our stack"); 8117 return res; 8118 } 8119 8120 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { 8121 size_t res = _sp->block_size_no_stall(addr, _collector); 8122 if (_sp->block_is_obj(addr)) { 8123 if (_live_bit_map->isMarked(addr)) { 8124 // It can't have been dead in a previous cycle 8125 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); 8126 } else { 8127 _dead_bit_map->mark(addr); // mark the dead object 8128 } 8129 } 8130 // Could be 0, if the block size could not be computed without stalling. 8131 return res; 8132 } 8133 8134 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() { 8135 8136 switch (phase) { 8137 case CMSCollector::InitialMarking: 8138 initialize(true /* fullGC */ , 8139 cause /* cause of the GC */, 8140 true /* recordGCBeginTime */, 8141 true /* recordPreGCUsage */, 8142 false /* recordPeakUsage */, 8143 false /* recordPostGCusage */, 8144 true /* recordAccumulatedGCTime */, 8145 false /* recordGCEndTime */, 8146 false /* countCollection */ ); 8147 break; 8148 8149 case CMSCollector::FinalMarking: 8150 initialize(true /* fullGC */ , 8151 cause /* cause of the GC */, 8152 false /* recordGCBeginTime */, 8153 false /* recordPreGCUsage */, 8154 false /* recordPeakUsage */, 8155 false /* recordPostGCusage */, 8156 true /* recordAccumulatedGCTime */, 8157 false /* recordGCEndTime */, 8158 false /* countCollection */ ); 8159 break; 8160 8161 case CMSCollector::Sweeping: 8162 initialize(true /* fullGC */ , 8163 cause /* cause of the GC */, 8164 false /* recordGCBeginTime */, 8165 false /* recordPreGCUsage */, 8166 true /* recordPeakUsage */, 8167 true /* recordPostGCusage */, 8168 false /* recordAccumulatedGCTime */, 8169 true /* recordGCEndTime */, 8170 true /* countCollection */ ); 8171 break; 8172 8173 default: 8174 ShouldNotReachHere(); 8175 } 8176 }