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