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