1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.inline.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "logging/log.hpp"
57 #include "memory/allocation.hpp"
58 #include "memory/iterator.inline.hpp"
59 #include "memory/padded.hpp"
60 #include "memory/resourceArea.hpp"
61 #include "oops/oop.inline.hpp"
62 #include "prims/jvmtiExport.hpp"
63 #include "runtime/atomic.inline.hpp"
64 #include "runtime/globals_extension.hpp"
65 #include "runtime/handles.inline.hpp"
66 #include "runtime/java.hpp"
67 #include "runtime/orderAccess.inline.hpp"
68 #include "runtime/timer.hpp"
69 #include "runtime/vmThread.hpp"
70 #include "services/memoryService.hpp"
71 #include "services/runtimeService.hpp"
72 #include "utilities/stack.inline.hpp"
73
74 // statics
75 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
76 bool CMSCollector::_full_gc_requested = false;
77 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
78
79 //////////////////////////////////////////////////////////////////
80 // In support of CMS/VM thread synchronization
81 //////////////////////////////////////////////////////////////////
82 // We split use of the CGC_lock into 2 "levels".
83 // The low-level locking is of the usual CGC_lock monitor. We introduce
84 // a higher level "token" (hereafter "CMS token") built on top of the
85 // low level monitor (hereafter "CGC lock").
86 // The token-passing protocol gives priority to the VM thread. The
87 // CMS-lock doesn't provide any fairness guarantees, but clients
88 // should ensure that it is only held for very short, bounded
89 // durations.
90 //
91 // When either of the CMS thread or the VM thread is involved in
92 // collection operations during which it does not want the other
93 // thread to interfere, it obtains the CMS token.
94 //
95 // If either thread tries to get the token while the other has
96 // it, that thread waits. However, if the VM thread and CMS thread
97 // both want the token, then the VM thread gets priority while the
98 // CMS thread waits. This ensures, for instance, that the "concurrent"
99 // phases of the CMS thread's work do not block out the VM thread
100 // for long periods of time as the CMS thread continues to hog
101 // the token. (See bug 4616232).
102 //
103 // The baton-passing functions are, however, controlled by the
104 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
105 // and here the low-level CMS lock, not the high level token,
106 // ensures mutual exclusion.
107 //
108 // Two important conditions that we have to satisfy:
109 // 1. if a thread does a low-level wait on the CMS lock, then it
110 // relinquishes the CMS token if it were holding that token
111 // when it acquired the low-level CMS lock.
112 // 2. any low-level notifications on the low-level lock
113 // should only be sent when a thread has relinquished the token.
114 //
115 // In the absence of either property, we'd have potential deadlock.
116 //
117 // We protect each of the CMS (concurrent and sequential) phases
118 // with the CMS _token_, not the CMS _lock_.
119 //
120 // The only code protected by CMS lock is the token acquisition code
121 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
122 // baton-passing code.
123 //
124 // Unfortunately, i couldn't come up with a good abstraction to factor and
125 // hide the naked CGC_lock manipulation in the baton-passing code
126 // further below. That's something we should try to do. Also, the proof
127 // of correctness of this 2-level locking scheme is far from obvious,
128 // and potentially quite slippery. We have an uneasy suspicion, for instance,
129 // that there may be a theoretical possibility of delay/starvation in the
130 // low-level lock/wait/notify scheme used for the baton-passing because of
131 // potential interference with the priority scheme embodied in the
132 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
133 // invocation further below and marked with "XXX 20011219YSR".
134 // Indeed, as we note elsewhere, this may become yet more slippery
135 // in the presence of multiple CMS and/or multiple VM threads. XXX
136
137 class CMSTokenSync: public StackObj {
138 private:
139 bool _is_cms_thread;
140 public:
141 CMSTokenSync(bool is_cms_thread):
142 _is_cms_thread(is_cms_thread) {
143 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
144 "Incorrect argument to constructor");
145 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
146 }
147
148 ~CMSTokenSync() {
149 assert(_is_cms_thread ?
150 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
151 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
152 "Incorrect state");
153 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
154 }
155 };
156
157 // Convenience class that does a CMSTokenSync, and then acquires
158 // upto three locks.
159 class CMSTokenSyncWithLocks: public CMSTokenSync {
160 private:
161 // Note: locks are acquired in textual declaration order
162 // and released in the opposite order
163 MutexLockerEx _locker1, _locker2, _locker3;
164 public:
165 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
166 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
167 CMSTokenSync(is_cms_thread),
168 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
169 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
170 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
171 { }
172 };
173
174
175 //////////////////////////////////////////////////////////////////
176 // Concurrent Mark-Sweep Generation /////////////////////////////
177 //////////////////////////////////////////////////////////////////
178
179 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
180
181 // This struct contains per-thread things necessary to support parallel
182 // young-gen collection.
183 class CMSParGCThreadState: public CHeapObj<mtGC> {
184 public:
185 CFLS_LAB lab;
186 PromotionInfo promo;
187
188 // Constructor.
189 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
190 promo.setSpace(cfls);
191 }
192 };
193
194 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
195 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
196 CardGeneration(rs, initial_byte_size, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
212 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
213 _cmsSpace->_old_gen = this;
214
215 _gc_stats = new CMSGCStats();
216
217 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
218 // offsets match. The ability to tell free chunks from objects
219 // depends on this property.
220 debug_only(
221 FreeChunk* junk = NULL;
222 assert(UseCompressedClassPointers ||
223 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
224 "Offset of FreeChunk::_prev within FreeChunk must match"
225 " that of OopDesc::_klass within OopDesc");
226 )
227
228 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
229 for (uint i = 0; i < ParallelGCThreads; i++) {
230 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
231 }
232
233 _incremental_collection_failed = false;
234 // The "dilatation_factor" is the expansion that can occur on
235 // account of the fact that the minimum object size in the CMS
236 // generation may be larger than that in, say, a contiguous young
237 // generation.
238 // Ideally, in the calculation below, we'd compute the dilatation
239 // factor as: MinChunkSize/(promoting_gen's min object size)
240 // Since we do not have such a general query interface for the
241 // promoting generation, we'll instead just use the minimum
242 // object size (which today is a header's worth of space);
243 // note that all arithmetic is in units of HeapWords.
244 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
245 assert(_dilatation_factor >= 1.0, "from previous assert");
246 }
247
248
249 // The field "_initiating_occupancy" represents the occupancy percentage
250 // at which we trigger a new collection cycle. Unless explicitly specified
251 // via CMSInitiatingOccupancyFraction (argument "io" below), it
252 // is calculated by:
253 //
254 // Let "f" be MinHeapFreeRatio in
255 //
256 // _initiating_occupancy = 100-f +
257 // f * (CMSTriggerRatio/100)
258 // where CMSTriggerRatio is the argument "tr" below.
259 //
260 // That is, if we assume the heap is at its desired maximum occupancy at the
261 // end of a collection, we let CMSTriggerRatio of the (purported) free
262 // space be allocated before initiating a new collection cycle.
263 //
264 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
265 assert(io <= 100 && tr <= 100, "Check the arguments");
266 if (io >= 0) {
267 _initiating_occupancy = (double)io / 100.0;
268 } else {
269 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
270 (double)(tr * MinHeapFreeRatio) / 100.0)
271 / 100.0;
272 }
273 }
274
275 void ConcurrentMarkSweepGeneration::ref_processor_init() {
276 assert(collector() != NULL, "no collector");
277 collector()->ref_processor_init();
278 }
279
280 void CMSCollector::ref_processor_init() {
281 if (_ref_processor == NULL) {
282 // Allocate and initialize a reference processor
283 _ref_processor =
284 new ReferenceProcessor(_span, // span
285 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
286 ParallelGCThreads, // mt processing degree
287 _cmsGen->refs_discovery_is_mt(), // mt discovery
288 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
289 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
290 &_is_alive_closure); // closure for liveness info
291 // Initialize the _ref_processor field of CMSGen
292 _cmsGen->set_ref_processor(_ref_processor);
293
294 }
295 }
296
297 AdaptiveSizePolicy* CMSCollector::size_policy() {
298 GenCollectedHeap* gch = GenCollectedHeap::heap();
299 return gch->gen_policy()->size_policy();
300 }
301
302 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
303
304 const char* gen_name = "old";
305 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
306 // Generation Counters - generation 1, 1 subspace
307 _gen_counters = new GenerationCounters(gen_name, 1, 1,
308 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
309
310 _space_counters = new GSpaceCounters(gen_name, 0,
311 _virtual_space.reserved_size(),
312 this, _gen_counters);
313 }
314
315 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
316 _cms_gen(cms_gen)
317 {
318 assert(alpha <= 100, "bad value");
319 _saved_alpha = alpha;
320
321 // Initialize the alphas to the bootstrap value of 100.
322 _gc0_alpha = _cms_alpha = 100;
323
324 _cms_begin_time.update();
325 _cms_end_time.update();
326
327 _gc0_duration = 0.0;
328 _gc0_period = 0.0;
329 _gc0_promoted = 0;
330
331 _cms_duration = 0.0;
332 _cms_period = 0.0;
333 _cms_allocated = 0;
334
335 _cms_used_at_gc0_begin = 0;
336 _cms_used_at_gc0_end = 0;
337 _allow_duty_cycle_reduction = false;
338 _valid_bits = 0;
339 }
340
341 double CMSStats::cms_free_adjustment_factor(size_t free) const {
342 // TBD: CR 6909490
343 return 1.0;
344 }
345
346 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
347 }
348
349 // If promotion failure handling is on use
350 // the padded average size of the promotion for each
351 // young generation collection.
352 double CMSStats::time_until_cms_gen_full() const {
353 size_t cms_free = _cms_gen->cmsSpace()->free();
354 GenCollectedHeap* gch = GenCollectedHeap::heap();
355 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
356 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
357 if (cms_free > expected_promotion) {
358 // Start a cms collection if there isn't enough space to promote
359 // for the next young collection. Use the padded average as
360 // a safety factor.
361 cms_free -= expected_promotion;
362
363 // Adjust by the safety factor.
364 double cms_free_dbl = (double)cms_free;
365 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
366 // Apply a further correction factor which tries to adjust
367 // for recent occurance of concurrent mode failures.
368 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
369 cms_free_dbl = cms_free_dbl * cms_adjustment;
370
371 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
372 cms_free, expected_promotion);
373 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
374 // Add 1 in case the consumption rate goes to zero.
375 return cms_free_dbl / (cms_consumption_rate() + 1.0);
376 }
377 return 0.0;
378 }
379
380 // Compare the duration of the cms collection to the
381 // time remaining before the cms generation is empty.
382 // Note that the time from the start of the cms collection
383 // to the start of the cms sweep (less than the total
384 // duration of the cms collection) can be used. This
385 // has been tried and some applications experienced
386 // promotion failures early in execution. This was
387 // possibly because the averages were not accurate
388 // enough at the beginning.
389 double CMSStats::time_until_cms_start() const {
390 // We add "gc0_period" to the "work" calculation
391 // below because this query is done (mostly) at the
392 // end of a scavenge, so we need to conservatively
393 // account for that much possible delay
394 // in the query so as to avoid concurrent mode failures
395 // due to starting the collection just a wee bit too
396 // late.
397 double work = cms_duration() + gc0_period();
398 double deadline = time_until_cms_gen_full();
399 // If a concurrent mode failure occurred recently, we want to be
400 // more conservative and halve our expected time_until_cms_gen_full()
401 if (work > deadline) {
402 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
403 cms_duration(), gc0_period(), time_until_cms_gen_full());
404 return 0.0;
405 }
406 return work - deadline;
407 }
408
409 #ifndef PRODUCT
410 void CMSStats::print_on(outputStream *st) const {
411 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
412 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
413 gc0_duration(), gc0_period(), gc0_promoted());
414 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
415 cms_duration(), cms_period(), cms_allocated());
416 st->print(",cms_since_beg=%g,cms_since_end=%g",
417 cms_time_since_begin(), cms_time_since_end());
418 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
419 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
420
421 if (valid()) {
422 st->print(",promo_rate=%g,cms_alloc_rate=%g",
423 promotion_rate(), cms_allocation_rate());
424 st->print(",cms_consumption_rate=%g,time_until_full=%g",
425 cms_consumption_rate(), time_until_cms_gen_full());
426 }
427 st->print(" ");
428 }
429 #endif // #ifndef PRODUCT
430
431 CMSCollector::CollectorState CMSCollector::_collectorState =
432 CMSCollector::Idling;
433 bool CMSCollector::_foregroundGCIsActive = false;
434 bool CMSCollector::_foregroundGCShouldWait = false;
435
436 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
437 CardTableRS* ct,
438 ConcurrentMarkSweepPolicy* cp):
439 _cmsGen(cmsGen),
440 _ct(ct),
441 _ref_processor(NULL), // will be set later
442 _conc_workers(NULL), // may be set later
443 _abort_preclean(false),
444 _start_sampling(false),
445 _between_prologue_and_epilogue(false),
446 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
447 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
448 -1 /* lock-free */, "No_lock" /* dummy */),
449 _modUnionClosurePar(&_modUnionTable),
450 // Adjust my span to cover old (cms) gen
451 _span(cmsGen->reserved()),
452 // Construct the is_alive_closure with _span & markBitMap
453 _is_alive_closure(_span, &_markBitMap),
454 _restart_addr(NULL),
455 _overflow_list(NULL),
456 _stats(cmsGen),
457 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
458 //verify that this lock should be acquired with safepoint check.
459 Monitor::_safepoint_check_sometimes)),
460 _eden_chunk_array(NULL), // may be set in ctor body
461 _eden_chunk_capacity(0), // -- ditto --
462 _eden_chunk_index(0), // -- ditto --
463 _survivor_plab_array(NULL), // -- ditto --
464 _survivor_chunk_array(NULL), // -- ditto --
465 _survivor_chunk_capacity(0), // -- ditto --
466 _survivor_chunk_index(0), // -- ditto --
467 _ser_pmc_preclean_ovflw(0),
468 _ser_kac_preclean_ovflw(0),
469 _ser_pmc_remark_ovflw(0),
470 _par_pmc_remark_ovflw(0),
471 _ser_kac_ovflw(0),
472 _par_kac_ovflw(0),
473 #ifndef PRODUCT
474 _num_par_pushes(0),
475 #endif
476 _collection_count_start(0),
477 _verifying(false),
478 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
479 _completed_initialization(false),
480 _collector_policy(cp),
481 _should_unload_classes(CMSClassUnloadingEnabled),
482 _concurrent_cycles_since_last_unload(0),
483 _roots_scanning_options(GenCollectedHeap::SO_None),
484 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
485 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
486 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
487 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
488 _cms_start_registered(false)
489 {
490 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
491 ExplicitGCInvokesConcurrent = true;
492 }
493 // Now expand the span and allocate the collection support structures
494 // (MUT, marking bit map etc.) to cover both generations subject to
495 // collection.
496
497 // For use by dirty card to oop closures.
498 _cmsGen->cmsSpace()->set_collector(this);
499
500 // Allocate MUT and marking bit map
501 {
502 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
503 if (!_markBitMap.allocate(_span)) {
504 warning("Failed to allocate CMS Bit Map");
505 return;
506 }
507 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
508 }
509 {
510 _modUnionTable.allocate(_span);
511 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
512 }
513
514 if (!_markStack.allocate(MarkStackSize)) {
515 warning("Failed to allocate CMS Marking Stack");
516 return;
517 }
518
519 // Support for multi-threaded concurrent phases
520 if (CMSConcurrentMTEnabled) {
521 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
522 // just for now
523 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
524 }
525 if (ConcGCThreads > 1) {
526 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
527 ConcGCThreads, true);
528 if (_conc_workers == NULL) {
529 warning("GC/CMS: _conc_workers allocation failure: "
530 "forcing -CMSConcurrentMTEnabled");
531 CMSConcurrentMTEnabled = false;
532 } else {
533 _conc_workers->initialize_workers();
534 }
535 } else {
536 CMSConcurrentMTEnabled = false;
537 }
538 }
539 if (!CMSConcurrentMTEnabled) {
540 ConcGCThreads = 0;
541 } else {
542 // Turn off CMSCleanOnEnter optimization temporarily for
543 // the MT case where it's not fixed yet; see 6178663.
544 CMSCleanOnEnter = false;
545 }
546 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
547 "Inconsistency");
548
549 // Parallel task queues; these are shared for the
550 // concurrent and stop-world phases of CMS, but
551 // are not shared with parallel scavenge (ParNew).
552 {
553 uint i;
554 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
555
556 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
557 || ParallelRefProcEnabled)
558 && num_queues > 0) {
559 _task_queues = new OopTaskQueueSet(num_queues);
560 if (_task_queues == NULL) {
561 warning("task_queues allocation failure.");
562 return;
563 }
564 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
565 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
566 for (i = 0; i < num_queues; i++) {
567 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
568 if (q == NULL) {
569 warning("work_queue allocation failure.");
570 return;
571 }
572 _task_queues->register_queue(i, q);
573 }
574 for (i = 0; i < num_queues; i++) {
575 _task_queues->queue(i)->initialize();
576 _hash_seed[i] = 17; // copied from ParNew
577 }
578 }
579 }
580
581 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
582
583 // Clip CMSBootstrapOccupancy between 0 and 100.
584 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
585
586 // Now tell CMS generations the identity of their collector
587 ConcurrentMarkSweepGeneration::set_collector(this);
588
589 // Create & start a CMS thread for this CMS collector
590 _cmsThread = ConcurrentMarkSweepThread::start(this);
591 assert(cmsThread() != NULL, "CMS Thread should have been created");
592 assert(cmsThread()->collector() == this,
593 "CMS Thread should refer to this gen");
594 assert(CGC_lock != NULL, "Where's the CGC_lock?");
595
596 // Support for parallelizing young gen rescan
597 GenCollectedHeap* gch = GenCollectedHeap::heap();
598 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
599 _young_gen = (ParNewGeneration*)gch->young_gen();
600 if (gch->supports_inline_contig_alloc()) {
601 _top_addr = gch->top_addr();
602 _end_addr = gch->end_addr();
603 assert(_young_gen != NULL, "no _young_gen");
604 _eden_chunk_index = 0;
605 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
606 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
607 }
608
609 // Support for parallelizing survivor space rescan
610 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
611 const size_t max_plab_samples =
612 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
613
614 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
615 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
616 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
617 _survivor_chunk_capacity = max_plab_samples;
618 for (uint i = 0; i < ParallelGCThreads; i++) {
619 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
620 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
621 assert(cur->end() == 0, "Should be 0");
622 assert(cur->array() == vec, "Should be vec");
623 assert(cur->capacity() == max_plab_samples, "Error");
624 }
625 }
626
627 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
628 _gc_counters = new CollectorCounters("CMS", 1);
629 _completed_initialization = true;
630 _inter_sweep_timer.start(); // start of time
631 }
632
633 const char* ConcurrentMarkSweepGeneration::name() const {
634 return "concurrent mark-sweep generation";
635 }
636 void ConcurrentMarkSweepGeneration::update_counters() {
637 if (UsePerfData) {
638 _space_counters->update_all();
639 _gen_counters->update_all();
640 }
641 }
642
643 // this is an optimized version of update_counters(). it takes the
644 // used value as a parameter rather than computing it.
645 //
646 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
647 if (UsePerfData) {
648 _space_counters->update_used(used);
649 _space_counters->update_capacity();
650 _gen_counters->update_all();
651 }
652 }
653
654 void ConcurrentMarkSweepGeneration::print() const {
655 Generation::print();
656 cmsSpace()->print();
657 }
658
659 #ifndef PRODUCT
660 void ConcurrentMarkSweepGeneration::print_statistics() {
661 cmsSpace()->printFLCensus(0);
662 }
663 #endif
664
665 size_t
666 ConcurrentMarkSweepGeneration::contiguous_available() const {
667 // dld proposes an improvement in precision here. If the committed
668 // part of the space ends in a free block we should add that to
669 // uncommitted size in the calculation below. Will make this
670 // change later, staying with the approximation below for the
671 // time being. -- ysr.
672 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
673 }
674
675 size_t
676 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
677 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
678 }
679
680 size_t ConcurrentMarkSweepGeneration::max_available() const {
681 return free() + _virtual_space.uncommitted_size();
682 }
683
684 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
685 size_t available = max_available();
686 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
687 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
688 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
689 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
690 return res;
691 }
692
693 // At a promotion failure dump information on block layout in heap
694 // (cms old generation).
695 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
696 LogHandle(gc, promotion) log;
697 if (log.is_trace()) {
698 ResourceMark rm;
699 cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
700 }
701 }
702
703 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
704 // Clear the promotion information. These pointers can be adjusted
705 // along with all the other pointers into the heap but
706 // compaction is expected to be a rare event with
707 // a heap using cms so don't do it without seeing the need.
708 for (uint i = 0; i < ParallelGCThreads; i++) {
709 _par_gc_thread_states[i]->promo.reset();
710 }
711 }
712
713 void ConcurrentMarkSweepGeneration::compute_new_size() {
714 assert_locked_or_safepoint(Heap_lock);
715
716 // If incremental collection failed, we just want to expand
717 // to the limit.
718 if (incremental_collection_failed()) {
719 clear_incremental_collection_failed();
720 grow_to_reserved();
721 return;
722 }
723
724 // The heap has been compacted but not reset yet.
725 // Any metric such as free() or used() will be incorrect.
726
727 CardGeneration::compute_new_size();
728
729 // Reset again after a possible resizing
730 if (did_compact()) {
731 cmsSpace()->reset_after_compaction();
732 }
733 }
734
735 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
736 assert_locked_or_safepoint(Heap_lock);
737
738 // If incremental collection failed, we just want to expand
739 // to the limit.
740 if (incremental_collection_failed()) {
741 clear_incremental_collection_failed();
742 grow_to_reserved();
743 return;
744 }
745
746 double free_percentage = ((double) free()) / capacity();
747 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
748 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
749
750 // compute expansion delta needed for reaching desired free percentage
751 if (free_percentage < desired_free_percentage) {
752 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
753 assert(desired_capacity >= capacity(), "invalid expansion size");
754 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
755 LogHandle(gc) log;
756 if (log.is_trace()) {
757 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
758 log.trace("From compute_new_size: ");
759 log.trace(" Free fraction %f", free_percentage);
760 log.trace(" Desired free fraction %f", desired_free_percentage);
761 log.trace(" Maximum free fraction %f", maximum_free_percentage);
762 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
763 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
764 GenCollectedHeap* gch = GenCollectedHeap::heap();
765 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
766 size_t young_size = gch->young_gen()->capacity();
767 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
768 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
769 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
770 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
771 }
772 // safe if expansion fails
773 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
774 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
775 } else {
776 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
777 assert(desired_capacity <= capacity(), "invalid expansion size");
778 size_t shrink_bytes = capacity() - desired_capacity;
779 // Don't shrink unless the delta is greater than the minimum shrink we want
780 if (shrink_bytes >= MinHeapDeltaBytes) {
781 shrink_free_list_by(shrink_bytes);
782 }
783 }
784 }
785
786 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
787 return cmsSpace()->freelistLock();
788 }
789
790 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
791 CMSSynchronousYieldRequest yr;
792 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
793 return have_lock_and_allocate(size, tlab);
794 }
795
796 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
797 bool tlab /* ignored */) {
798 assert_lock_strong(freelistLock());
799 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
800 HeapWord* res = cmsSpace()->allocate(adjustedSize);
801 // Allocate the object live (grey) if the background collector has
802 // started marking. This is necessary because the marker may
803 // have passed this address and consequently this object will
804 // not otherwise be greyed and would be incorrectly swept up.
805 // Note that if this object contains references, the writing
806 // of those references will dirty the card containing this object
807 // allowing the object to be blackened (and its references scanned)
808 // either during a preclean phase or at the final checkpoint.
809 if (res != NULL) {
810 // We may block here with an uninitialized object with
811 // its mark-bit or P-bits not yet set. Such objects need
812 // to be safely navigable by block_start().
813 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
814 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
815 collector()->direct_allocated(res, adjustedSize);
816 _direct_allocated_words += adjustedSize;
817 // allocation counters
818 NOT_PRODUCT(
819 _numObjectsAllocated++;
820 _numWordsAllocated += (int)adjustedSize;
821 )
822 }
823 return res;
824 }
825
826 // In the case of direct allocation by mutators in a generation that
827 // is being concurrently collected, the object must be allocated
828 // live (grey) if the background collector has started marking.
829 // This is necessary because the marker may
830 // have passed this address and consequently this object will
831 // not otherwise be greyed and would be incorrectly swept up.
832 // Note that if this object contains references, the writing
833 // of those references will dirty the card containing this object
834 // allowing the object to be blackened (and its references scanned)
835 // either during a preclean phase or at the final checkpoint.
836 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
837 assert(_markBitMap.covers(start, size), "Out of bounds");
838 if (_collectorState >= Marking) {
839 MutexLockerEx y(_markBitMap.lock(),
840 Mutex::_no_safepoint_check_flag);
841 // [see comments preceding SweepClosure::do_blk() below for details]
842 //
843 // Can the P-bits be deleted now? JJJ
844 //
845 // 1. need to mark the object as live so it isn't collected
846 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
847 // 3. need to mark the end of the object so marking, precleaning or sweeping
848 // can skip over uninitialized or unparsable objects. An allocated
849 // object is considered uninitialized for our purposes as long as
850 // its klass word is NULL. All old gen objects are parsable
851 // as soon as they are initialized.)
852 _markBitMap.mark(start); // object is live
853 _markBitMap.mark(start + 1); // object is potentially uninitialized?
854 _markBitMap.mark(start + size - 1);
855 // mark end of object
856 }
857 // check that oop looks uninitialized
858 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
859 }
860
861 void CMSCollector::promoted(bool par, HeapWord* start,
862 bool is_obj_array, size_t obj_size) {
863 assert(_markBitMap.covers(start), "Out of bounds");
864 // See comment in direct_allocated() about when objects should
865 // be allocated live.
866 if (_collectorState >= Marking) {
867 // we already hold the marking bit map lock, taken in
868 // the prologue
869 if (par) {
870 _markBitMap.par_mark(start);
871 } else {
872 _markBitMap.mark(start);
873 }
874 // We don't need to mark the object as uninitialized (as
875 // in direct_allocated above) because this is being done with the
876 // world stopped and the object will be initialized by the
877 // time the marking, precleaning or sweeping get to look at it.
878 // But see the code for copying objects into the CMS generation,
879 // where we need to ensure that concurrent readers of the
880 // block offset table are able to safely navigate a block that
881 // is in flux from being free to being allocated (and in
882 // transition while being copied into) and subsequently
883 // becoming a bona-fide object when the copy/promotion is complete.
884 assert(SafepointSynchronize::is_at_safepoint(),
885 "expect promotion only at safepoints");
886
887 if (_collectorState < Sweeping) {
888 // Mark the appropriate cards in the modUnionTable, so that
889 // this object gets scanned before the sweep. If this is
890 // not done, CMS generation references in the object might
891 // not get marked.
892 // For the case of arrays, which are otherwise precisely
893 // marked, we need to dirty the entire array, not just its head.
894 if (is_obj_array) {
895 // The [par_]mark_range() method expects mr.end() below to
896 // be aligned to the granularity of a bit's representation
897 // in the heap. In the case of the MUT below, that's a
898 // card size.
899 MemRegion mr(start,
900 (HeapWord*)round_to((intptr_t)(start + obj_size),
901 CardTableModRefBS::card_size /* bytes */));
902 if (par) {
903 _modUnionTable.par_mark_range(mr);
904 } else {
905 _modUnionTable.mark_range(mr);
906 }
907 } else { // not an obj array; we can just mark the head
908 if (par) {
909 _modUnionTable.par_mark(start);
910 } else {
911 _modUnionTable.mark(start);
912 }
913 }
914 }
915 }
916 }
917
918 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
919 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
920 // allocate, copy and if necessary update promoinfo --
921 // delegate to underlying space.
922 assert_lock_strong(freelistLock());
923
924 #ifndef PRODUCT
925 if (GenCollectedHeap::heap()->promotion_should_fail()) {
926 return NULL;
927 }
928 #endif // #ifndef PRODUCT
929
930 oop res = _cmsSpace->promote(obj, obj_size);
931 if (res == NULL) {
932 // expand and retry
933 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
934 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
935 // Since this is the old generation, we don't try to promote
936 // into a more senior generation.
937 res = _cmsSpace->promote(obj, obj_size);
938 }
939 if (res != NULL) {
940 // See comment in allocate() about when objects should
941 // be allocated live.
942 assert(obj->is_oop(), "Will dereference klass pointer below");
943 collector()->promoted(false, // Not parallel
944 (HeapWord*)res, obj->is_objArray(), obj_size);
945 // promotion counters
946 NOT_PRODUCT(
947 _numObjectsPromoted++;
948 _numWordsPromoted +=
949 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
950 )
951 }
952 return res;
953 }
954
955
956 // IMPORTANT: Notes on object size recognition in CMS.
957 // ---------------------------------------------------
958 // A block of storage in the CMS generation is always in
959 // one of three states. A free block (FREE), an allocated
960 // object (OBJECT) whose size() method reports the correct size,
961 // and an intermediate state (TRANSIENT) in which its size cannot
962 // be accurately determined.
963 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
964 // -----------------------------------------------------
965 // FREE: klass_word & 1 == 1; mark_word holds block size
966 //
967 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
968 // obj->size() computes correct size
969 //
970 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
971 //
972 // STATE IDENTIFICATION: (64 bit+COOPS)
973 // ------------------------------------
974 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
975 //
976 // OBJECT: klass_word installed; klass_word != 0;
977 // obj->size() computes correct size
978 //
979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
980 //
981 //
982 // STATE TRANSITION DIAGRAM
983 //
984 // mut / parnew mut / parnew
985 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
986 // ^ |
987 // |------------------------ DEAD <------------------------------------|
988 // sweep mut
989 //
990 // While a block is in TRANSIENT state its size cannot be determined
991 // so readers will either need to come back later or stall until
992 // the size can be determined. Note that for the case of direct
993 // allocation, P-bits, when available, may be used to determine the
994 // size of an object that may not yet have been initialized.
995
996 // Things to support parallel young-gen collection.
997 oop
998 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
999 oop old, markOop m,
1000 size_t word_sz) {
1001 #ifndef PRODUCT
1002 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1003 return NULL;
1004 }
1005 #endif // #ifndef PRODUCT
1006
1007 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1008 PromotionInfo* promoInfo = &ps->promo;
1009 // if we are tracking promotions, then first ensure space for
1010 // promotion (including spooling space for saving header if necessary).
1011 // then allocate and copy, then track promoted info if needed.
1012 // When tracking (see PromotionInfo::track()), the mark word may
1013 // be displaced and in this case restoration of the mark word
1014 // occurs in the (oop_since_save_marks_)iterate phase.
1015 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1016 // Out of space for allocating spooling buffers;
1017 // try expanding and allocating spooling buffers.
1018 if (!expand_and_ensure_spooling_space(promoInfo)) {
1019 return NULL;
1020 }
1021 }
1022 assert(promoInfo->has_spooling_space(), "Control point invariant");
1023 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1024 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1025 if (obj_ptr == NULL) {
1026 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1027 if (obj_ptr == NULL) {
1028 return NULL;
1029 }
1030 }
1031 oop obj = oop(obj_ptr);
1032 OrderAccess::storestore();
1033 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1034 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1035 // IMPORTANT: See note on object initialization for CMS above.
1036 // Otherwise, copy the object. Here we must be careful to insert the
1037 // klass pointer last, since this marks the block as an allocated object.
1038 // Except with compressed oops it's the mark word.
1039 HeapWord* old_ptr = (HeapWord*)old;
1040 // Restore the mark word copied above.
1041 obj->set_mark(m);
1042 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044 OrderAccess::storestore();
1045
1046 if (UseCompressedClassPointers) {
1047 // Copy gap missed by (aligned) header size calculation below
1048 obj->set_klass_gap(old->klass_gap());
1049 }
1050 if (word_sz > (size_t)oopDesc::header_size()) {
1051 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1052 obj_ptr + oopDesc::header_size(),
1053 word_sz - oopDesc::header_size());
1054 }
1055
1056 // Now we can track the promoted object, if necessary. We take care
1057 // to delay the transition from uninitialized to full object
1058 // (i.e., insertion of klass pointer) until after, so that it
1059 // atomically becomes a promoted object.
1060 if (promoInfo->tracking()) {
1061 promoInfo->track((PromotedObject*)obj, old->klass());
1062 }
1063 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1064 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1065 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1066
1067 // Finally, install the klass pointer (this should be volatile).
1068 OrderAccess::storestore();
1069 obj->set_klass(old->klass());
1070 // We should now be able to calculate the right size for this object
1071 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1072
1073 collector()->promoted(true, // parallel
1074 obj_ptr, old->is_objArray(), word_sz);
1075
1076 NOT_PRODUCT(
1077 Atomic::inc_ptr(&_numObjectsPromoted);
1078 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1079 )
1080
1081 return obj;
1082 }
1083
1084 void
1085 ConcurrentMarkSweepGeneration::
1086 par_promote_alloc_done(int thread_num) {
1087 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1088 ps->lab.retire(thread_num);
1089 }
1090
1091 void
1092 ConcurrentMarkSweepGeneration::
1093 par_oop_since_save_marks_iterate_done(int thread_num) {
1094 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1095 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1096 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1097 }
1098
1099 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1100 size_t size,
1101 bool tlab)
1102 {
1103 // We allow a STW collection only if a full
1104 // collection was requested.
1105 return full || should_allocate(size, tlab); // FIX ME !!!
1106 // This and promotion failure handling are connected at the
1107 // hip and should be fixed by untying them.
1108 }
1109
1110 bool CMSCollector::shouldConcurrentCollect() {
1111 if (_full_gc_requested) {
1112 log_trace(gc)("CMSCollector: collect because of explicit gc request (or gc_locker)");
1113 return true;
1114 }
1115
1116 FreelistLocker x(this);
1117 // ------------------------------------------------------------------
1118 // Print out lots of information which affects the initiation of
1119 // a collection.
1120 LogHandle(gc) log;
1121 if (log.is_trace() && stats().valid()) {
1122 log.trace("CMSCollector shouldConcurrentCollect: ");
1123 ResourceMark rm;
1124 stats().print_on(log.debug_stream());
1125 log.trace("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1126 log.trace("free=" SIZE_FORMAT, _cmsGen->free());
1127 log.trace("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1128 log.trace("promotion_rate=%g", stats().promotion_rate());
1129 log.trace("cms_allocation_rate=%g", stats().cms_allocation_rate());
1130 log.trace("occupancy=%3.7f", _cmsGen->occupancy());
1131 log.trace("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1132 log.trace("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1133 log.trace("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1134 log.trace("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1135 }
1136 // ------------------------------------------------------------------
1137
1138 // If the estimated time to complete a cms collection (cms_duration())
1139 // is less than the estimated time remaining until the cms generation
1140 // is full, start a collection.
1141 if (!UseCMSInitiatingOccupancyOnly) {
1142 if (stats().valid()) {
1143 if (stats().time_until_cms_start() == 0.0) {
1144 return true;
1145 }
1146 } else {
1147 // We want to conservatively collect somewhat early in order
1148 // to try and "bootstrap" our CMS/promotion statistics;
1149 // this branch will not fire after the first successful CMS
1150 // collection because the stats should then be valid.
1151 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1152 log_trace(gc)(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1153 _cmsGen->occupancy(), _bootstrap_occupancy);
1154 return true;
1155 }
1156 }
1157 }
1158
1159 // Otherwise, we start a collection cycle if
1160 // old gen want a collection cycle started. Each may use
1161 // an appropriate criterion for making this decision.
1162 // XXX We need to make sure that the gen expansion
1163 // criterion dovetails well with this. XXX NEED TO FIX THIS
1164 if (_cmsGen->should_concurrent_collect()) {
1165 log_trace(gc)("CMS old gen initiated");
1166 return true;
1167 }
1168
1169 // We start a collection if we believe an incremental collection may fail;
1170 // this is not likely to be productive in practice because it's probably too
1171 // late anyway.
1172 GenCollectedHeap* gch = GenCollectedHeap::heap();
1173 assert(gch->collector_policy()->is_generation_policy(),
1174 "You may want to check the correctness of the following");
1175 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1176 log_trace(gc)("CMSCollector: collect because incremental collection will fail ");
1177 return true;
1178 }
1179
1180 if (MetaspaceGC::should_concurrent_collect()) {
1181 log_trace(gc)("CMSCollector: collect for metadata allocation ");
1182 return true;
1183 }
1184
1185 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1186 if (CMSTriggerInterval >= 0) {
1187 if (CMSTriggerInterval == 0) {
1188 // Trigger always
1189 return true;
1190 }
1191
1192 // Check the CMS time since begin (we do not check the stats validity
1193 // as we want to be able to trigger the first CMS cycle as well)
1194 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1195 if (stats().valid()) {
1196 log_trace(gc)("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1197 stats().cms_time_since_begin());
1198 } else {
1199 log_trace(gc)("CMSCollector: collect because of trigger interval (first collection)");
1200 }
1201 return true;
1202 }
1203 }
1204
1205 return false;
1206 }
1207
1208 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1209
1210 // Clear _expansion_cause fields of constituent generations
1211 void CMSCollector::clear_expansion_cause() {
1212 _cmsGen->clear_expansion_cause();
1213 }
1214
1215 // We should be conservative in starting a collection cycle. To
1216 // start too eagerly runs the risk of collecting too often in the
1217 // extreme. To collect too rarely falls back on full collections,
1218 // which works, even if not optimum in terms of concurrent work.
1219 // As a work around for too eagerly collecting, use the flag
1220 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1221 // giving the user an easily understandable way of controlling the
1222 // collections.
1223 // We want to start a new collection cycle if any of the following
1224 // conditions hold:
1225 // . our current occupancy exceeds the configured initiating occupancy
1226 // for this generation, or
1227 // . we recently needed to expand this space and have not, since that
1228 // expansion, done a collection of this generation, or
1229 // . the underlying space believes that it may be a good idea to initiate
1230 // a concurrent collection (this may be based on criteria such as the
1231 // following: the space uses linear allocation and linear allocation is
1232 // going to fail, or there is believed to be excessive fragmentation in
1233 // the generation, etc... or ...
1234 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1235 // the case of the old generation; see CR 6543076):
1236 // we may be approaching a point at which allocation requests may fail because
1237 // we will be out of sufficient free space given allocation rate estimates.]
1238 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1239
1240 assert_lock_strong(freelistLock());
1241 if (occupancy() > initiating_occupancy()) {
1242 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1243 short_name(), occupancy(), initiating_occupancy());
1244 return true;
1245 }
1246 if (UseCMSInitiatingOccupancyOnly) {
1247 return false;
1248 }
1249 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1250 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1251 return true;
1252 }
1253 return false;
1254 }
1255
1256 void ConcurrentMarkSweepGeneration::collect(bool full,
1257 bool clear_all_soft_refs,
1258 size_t size,
1259 bool tlab)
1260 {
1261 collector()->collect(full, clear_all_soft_refs, size, tlab);
1262 }
1263
1264 void CMSCollector::collect(bool full,
1265 bool clear_all_soft_refs,
1266 size_t size,
1267 bool tlab)
1268 {
1269 // The following "if" branch is present for defensive reasons.
1270 // In the current uses of this interface, it can be replaced with:
1271 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1272 // But I am not placing that assert here to allow future
1273 // generality in invoking this interface.
1274 if (GC_locker::is_active()) {
1275 // A consistency test for GC_locker
1276 assert(GC_locker::needs_gc(), "Should have been set already");
1277 // Skip this foreground collection, instead
1278 // expanding the heap if necessary.
1279 // Need the free list locks for the call to free() in compute_new_size()
1280 compute_new_size();
1281 return;
1282 }
1283 acquire_control_and_collect(full, clear_all_soft_refs);
1284 }
1285
1286 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1287 GenCollectedHeap* gch = GenCollectedHeap::heap();
1288 unsigned int gc_count = gch->total_full_collections();
1289 if (gc_count == full_gc_count) {
1290 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1291 _full_gc_requested = true;
1292 _full_gc_cause = cause;
1293 CGC_lock->notify(); // nudge CMS thread
1294 } else {
1295 assert(gc_count > full_gc_count, "Error: causal loop");
1296 }
1297 }
1298
1299 bool CMSCollector::is_external_interruption() {
1300 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1301 return GCCause::is_user_requested_gc(cause) ||
1302 GCCause::is_serviceability_requested_gc(cause);
1303 }
1304
1305 void CMSCollector::report_concurrent_mode_interruption() {
1306 if (is_external_interruption()) {
1307 log_debug(gc)("Concurrent mode interrupted");
1308 } else {
1309 log_debug(gc)("Concurrent mode failure");
1310 _gc_tracer_cm->report_concurrent_mode_failure();
1311 }
1312 }
1313
1314
1315 // The foreground and background collectors need to coordinate in order
1316 // to make sure that they do not mutually interfere with CMS collections.
1317 // When a background collection is active,
1318 // the foreground collector may need to take over (preempt) and
1319 // synchronously complete an ongoing collection. Depending on the
1320 // frequency of the background collections and the heap usage
1321 // of the application, this preemption can be seldom or frequent.
1322 // There are only certain
1323 // points in the background collection that the "collection-baton"
1324 // can be passed to the foreground collector.
1325 //
1326 // The foreground collector will wait for the baton before
1327 // starting any part of the collection. The foreground collector
1328 // will only wait at one location.
1329 //
1330 // The background collector will yield the baton before starting a new
1331 // phase of the collection (e.g., before initial marking, marking from roots,
1332 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1333 // of the loop which switches the phases. The background collector does some
1334 // of the phases (initial mark, final re-mark) with the world stopped.
1335 // Because of locking involved in stopping the world,
1336 // the foreground collector should not block waiting for the background
1337 // collector when it is doing a stop-the-world phase. The background
1338 // collector will yield the baton at an additional point just before
1339 // it enters a stop-the-world phase. Once the world is stopped, the
1340 // background collector checks the phase of the collection. If the
1341 // phase has not changed, it proceeds with the collection. If the
1342 // phase has changed, it skips that phase of the collection. See
1343 // the comments on the use of the Heap_lock in collect_in_background().
1344 //
1345 // Variable used in baton passing.
1346 // _foregroundGCIsActive - Set to true by the foreground collector when
1347 // it wants the baton. The foreground clears it when it has finished
1348 // the collection.
1349 // _foregroundGCShouldWait - Set to true by the background collector
1350 // when it is running. The foreground collector waits while
1351 // _foregroundGCShouldWait is true.
1352 // CGC_lock - monitor used to protect access to the above variables
1353 // and to notify the foreground and background collectors.
1354 // _collectorState - current state of the CMS collection.
1355 //
1356 // The foreground collector
1357 // acquires the CGC_lock
1358 // sets _foregroundGCIsActive
1359 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1360 // various locks acquired in preparation for the collection
1361 // are released so as not to block the background collector
1362 // that is in the midst of a collection
1363 // proceeds with the collection
1364 // clears _foregroundGCIsActive
1365 // returns
1366 //
1367 // The background collector in a loop iterating on the phases of the
1368 // collection
1369 // acquires the CGC_lock
1370 // sets _foregroundGCShouldWait
1371 // if _foregroundGCIsActive is set
1372 // clears _foregroundGCShouldWait, notifies _CGC_lock
1373 // waits on _CGC_lock for _foregroundGCIsActive to become false
1374 // and exits the loop.
1375 // otherwise
1376 // proceed with that phase of the collection
1377 // if the phase is a stop-the-world phase,
1378 // yield the baton once more just before enqueueing
1379 // the stop-world CMS operation (executed by the VM thread).
1380 // returns after all phases of the collection are done
1381 //
1382
1383 void CMSCollector::acquire_control_and_collect(bool full,
1384 bool clear_all_soft_refs) {
1385 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1386 assert(!Thread::current()->is_ConcurrentGC_thread(),
1387 "shouldn't try to acquire control from self!");
1388
1389 // Start the protocol for acquiring control of the
1390 // collection from the background collector (aka CMS thread).
1391 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1392 "VM thread should have CMS token");
1393 // Remember the possibly interrupted state of an ongoing
1394 // concurrent collection
1395 CollectorState first_state = _collectorState;
1396
1397 // Signal to a possibly ongoing concurrent collection that
1398 // we want to do a foreground collection.
1399 _foregroundGCIsActive = true;
1400
1401 // release locks and wait for a notify from the background collector
1402 // releasing the locks in only necessary for phases which
1403 // do yields to improve the granularity of the collection.
1404 assert_lock_strong(bitMapLock());
1405 // We need to lock the Free list lock for the space that we are
1406 // currently collecting.
1407 assert(haveFreelistLocks(), "Must be holding free list locks");
1408 bitMapLock()->unlock();
1409 releaseFreelistLocks();
1410 {
1411 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1412 if (_foregroundGCShouldWait) {
1413 // We are going to be waiting for action for the CMS thread;
1414 // it had better not be gone (for instance at shutdown)!
1415 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1416 "CMS thread must be running");
1417 // Wait here until the background collector gives us the go-ahead
1418 ConcurrentMarkSweepThread::clear_CMS_flag(
1419 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1420 // Get a possibly blocked CMS thread going:
1421 // Note that we set _foregroundGCIsActive true above,
1422 // without protection of the CGC_lock.
1423 CGC_lock->notify();
1424 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1425 "Possible deadlock");
1426 while (_foregroundGCShouldWait) {
1427 // wait for notification
1428 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1429 // Possibility of delay/starvation here, since CMS token does
1430 // not know to give priority to VM thread? Actually, i think
1431 // there wouldn't be any delay/starvation, but the proof of
1432 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1433 }
1434 ConcurrentMarkSweepThread::set_CMS_flag(
1435 ConcurrentMarkSweepThread::CMS_vm_has_token);
1436 }
1437 }
1438 // The CMS_token is already held. Get back the other locks.
1439 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1440 "VM thread should have CMS token");
1441 getFreelistLocks();
1442 bitMapLock()->lock_without_safepoint_check();
1443 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1444 p2i(Thread::current()), first_state);
1445 log_debug(gc, state)(" gets control with state %d", _collectorState);
1446
1447 // Inform cms gen if this was due to partial collection failing.
1448 // The CMS gen may use this fact to determine its expansion policy.
1449 GenCollectedHeap* gch = GenCollectedHeap::heap();
1450 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1451 assert(!_cmsGen->incremental_collection_failed(),
1452 "Should have been noticed, reacted to and cleared");
1453 _cmsGen->set_incremental_collection_failed();
1454 }
1455
1456 if (first_state > Idling) {
1457 report_concurrent_mode_interruption();
1458 }
1459
1460 set_did_compact(true);
1461
1462 // If the collection is being acquired from the background
1463 // collector, there may be references on the discovered
1464 // references lists. Abandon those references, since some
1465 // of them may have become unreachable after concurrent
1466 // discovery; the STW compacting collector will redo discovery
1467 // more precisely, without being subject to floating garbage.
1468 // Leaving otherwise unreachable references in the discovered
1469 // lists would require special handling.
1470 ref_processor()->disable_discovery();
1471 ref_processor()->abandon_partial_discovery();
1472 ref_processor()->verify_no_references_recorded();
1473
1474 if (first_state > Idling) {
1475 save_heap_summary();
1476 }
1477
1478 do_compaction_work(clear_all_soft_refs);
1479
1480 // Has the GC time limit been exceeded?
1481 size_t max_eden_size = _young_gen->max_eden_size();
1482 GCCause::Cause gc_cause = gch->gc_cause();
1483 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1484 _young_gen->eden()->used(),
1485 _cmsGen->max_capacity(),
1486 max_eden_size,
1487 full,
1488 gc_cause,
1489 gch->collector_policy());
1490
1491 // Reset the expansion cause, now that we just completed
1492 // a collection cycle.
1493 clear_expansion_cause();
1494 _foregroundGCIsActive = false;
1495 return;
1496 }
1497
1498 // Resize the tenured generation
1499 // after obtaining the free list locks for the
1500 // two generations.
1501 void CMSCollector::compute_new_size() {
1502 assert_locked_or_safepoint(Heap_lock);
1503 FreelistLocker z(this);
1504 MetaspaceGC::compute_new_size();
1505 _cmsGen->compute_new_size_free_list();
1506 }
1507
1508 // A work method used by the foreground collector to do
1509 // a mark-sweep-compact.
1510 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1511 GenCollectedHeap* gch = GenCollectedHeap::heap();
1512
1513 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1514 gc_timer->register_gc_start();
1515
1516 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1517 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1518
1519 GCTraceTime(Trace, gc) t("CMS:MSC");
1520
1521 // Temporarily widen the span of the weak reference processing to
1522 // the entire heap.
1523 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1524 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1525 // Temporarily, clear the "is_alive_non_header" field of the
1526 // reference processor.
1527 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1528 // Temporarily make reference _processing_ single threaded (non-MT).
1529 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1530 // Temporarily make refs discovery atomic
1531 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1532 // Temporarily make reference _discovery_ single threaded (non-MT)
1533 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1534
1535 ref_processor()->set_enqueuing_is_done(false);
1536 ref_processor()->enable_discovery();
1537 ref_processor()->setup_policy(clear_all_soft_refs);
1538 // If an asynchronous collection finishes, the _modUnionTable is
1539 // all clear. If we are assuming the collection from an asynchronous
1540 // collection, clear the _modUnionTable.
1541 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1542 "_modUnionTable should be clear if the baton was not passed");
1543 _modUnionTable.clear_all();
1544 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1545 "mod union for klasses should be clear if the baton was passed");
1546 _ct->klass_rem_set()->clear_mod_union();
1547
1548 // We must adjust the allocation statistics being maintained
1549 // in the free list space. We do so by reading and clearing
1550 // the sweep timer and updating the block flux rate estimates below.
1551 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1552 if (_inter_sweep_timer.is_active()) {
1553 _inter_sweep_timer.stop();
1554 // Note that we do not use this sample to update the _inter_sweep_estimate.
1555 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1556 _inter_sweep_estimate.padded_average(),
1557 _intra_sweep_estimate.padded_average());
1558 }
1559
1560 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1561 #ifdef ASSERT
1562 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1563 size_t free_size = cms_space->free();
1564 assert(free_size ==
1565 pointer_delta(cms_space->end(), cms_space->compaction_top())
1566 * HeapWordSize,
1567 "All the free space should be compacted into one chunk at top");
1568 assert(cms_space->dictionary()->total_chunk_size(
1569 debug_only(cms_space->freelistLock())) == 0 ||
1570 cms_space->totalSizeInIndexedFreeLists() == 0,
1571 "All the free space should be in a single chunk");
1572 size_t num = cms_space->totalCount();
1573 assert((free_size == 0 && num == 0) ||
1574 (free_size > 0 && (num == 1 || num == 2)),
1575 "There should be at most 2 free chunks after compaction");
1576 #endif // ASSERT
1577 _collectorState = Resetting;
1578 assert(_restart_addr == NULL,
1579 "Should have been NULL'd before baton was passed");
1580 reset_stw();
1581 _cmsGen->reset_after_compaction();
1582 _concurrent_cycles_since_last_unload = 0;
1583
1584 // Clear any data recorded in the PLAB chunk arrays.
1585 if (_survivor_plab_array != NULL) {
1586 reset_survivor_plab_arrays();
1587 }
1588
1589 // Adjust the per-size allocation stats for the next epoch.
1590 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1591 // Restart the "inter sweep timer" for the next epoch.
1592 _inter_sweep_timer.reset();
1593 _inter_sweep_timer.start();
1594
1595 gc_timer->register_gc_end();
1596
1597 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1598
1599 // For a mark-sweep-compact, compute_new_size() will be called
1600 // in the heap's do_collection() method.
1601 }
1602
1603 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1604 LogHandle(gc, heap) log;
1605 if (!log.is_trace()) {
1606 return;
1607 }
1608
1609 ContiguousSpace* eden_space = _young_gen->eden();
1610 ContiguousSpace* from_space = _young_gen->from();
1611 ContiguousSpace* to_space = _young_gen->to();
1612 // Eden
1613 if (_eden_chunk_array != NULL) {
1614 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1615 p2i(eden_space->bottom()), p2i(eden_space->top()),
1616 p2i(eden_space->end()), eden_space->capacity());
1617 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1618 _eden_chunk_index, _eden_chunk_capacity);
1619 for (size_t i = 0; i < _eden_chunk_index; i++) {
1620 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1621 }
1622 }
1623 // Survivor
1624 if (_survivor_chunk_array != NULL) {
1625 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1626 p2i(from_space->bottom()), p2i(from_space->top()),
1627 p2i(from_space->end()), from_space->capacity());
1628 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1629 _survivor_chunk_index, _survivor_chunk_capacity);
1630 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1631 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1632 }
1633 }
1634 }
1635
1636 void CMSCollector::getFreelistLocks() const {
1637 // Get locks for all free lists in all generations that this
1638 // collector is responsible for
1639 _cmsGen->freelistLock()->lock_without_safepoint_check();
1640 }
1641
1642 void CMSCollector::releaseFreelistLocks() const {
1643 // Release locks for all free lists in all generations that this
1644 // collector is responsible for
1645 _cmsGen->freelistLock()->unlock();
1646 }
1647
1648 bool CMSCollector::haveFreelistLocks() const {
1649 // Check locks for all free lists in all generations that this
1650 // collector is responsible for
1651 assert_lock_strong(_cmsGen->freelistLock());
1652 PRODUCT_ONLY(ShouldNotReachHere());
1653 return true;
1654 }
1655
1656 // A utility class that is used by the CMS collector to
1657 // temporarily "release" the foreground collector from its
1658 // usual obligation to wait for the background collector to
1659 // complete an ongoing phase before proceeding.
1660 class ReleaseForegroundGC: public StackObj {
1661 private:
1662 CMSCollector* _c;
1663 public:
1664 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1665 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1666 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1667 // allow a potentially blocked foreground collector to proceed
1668 _c->_foregroundGCShouldWait = false;
1669 if (_c->_foregroundGCIsActive) {
1670 CGC_lock->notify();
1671 }
1672 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1673 "Possible deadlock");
1674 }
1675
1676 ~ReleaseForegroundGC() {
1677 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1678 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1679 _c->_foregroundGCShouldWait = true;
1680 }
1681 };
1682
1683 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1684 assert(Thread::current()->is_ConcurrentGC_thread(),
1685 "A CMS asynchronous collection is only allowed on a CMS thread.");
1686
1687 GenCollectedHeap* gch = GenCollectedHeap::heap();
1688 {
1689 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1690 MutexLockerEx hl(Heap_lock, safepoint_check);
1691 FreelistLocker fll(this);
1692 MutexLockerEx x(CGC_lock, safepoint_check);
1693 if (_foregroundGCIsActive) {
1694 // The foreground collector is. Skip this
1695 // background collection.
1696 assert(!_foregroundGCShouldWait, "Should be clear");
1697 return;
1698 } else {
1699 assert(_collectorState == Idling, "Should be idling before start.");
1700 _collectorState = InitialMarking;
1701 register_gc_start(cause);
1702 // Reset the expansion cause, now that we are about to begin
1703 // a new cycle.
1704 clear_expansion_cause();
1705
1706 // Clear the MetaspaceGC flag since a concurrent collection
1707 // is starting but also clear it after the collection.
1708 MetaspaceGC::set_should_concurrent_collect(false);
1709 }
1710 // Decide if we want to enable class unloading as part of the
1711 // ensuing concurrent GC cycle.
1712 update_should_unload_classes();
1713 _full_gc_requested = false; // acks all outstanding full gc requests
1714 _full_gc_cause = GCCause::_no_gc;
1715 // Signal that we are about to start a collection
1716 gch->increment_total_full_collections(); // ... starting a collection cycle
1717 _collection_count_start = gch->total_full_collections();
1718 }
1719
1720 size_t prev_used = _cmsGen->used();
1721
1722 // The change of the collection state is normally done at this level;
1723 // the exceptions are phases that are executed while the world is
1724 // stopped. For those phases the change of state is done while the
1725 // world is stopped. For baton passing purposes this allows the
1726 // background collector to finish the phase and change state atomically.
1727 // The foreground collector cannot wait on a phase that is done
1728 // while the world is stopped because the foreground collector already
1729 // has the world stopped and would deadlock.
1730 while (_collectorState != Idling) {
1731 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1732 p2i(Thread::current()), _collectorState);
1733 // The foreground collector
1734 // holds the Heap_lock throughout its collection.
1735 // holds the CMS token (but not the lock)
1736 // except while it is waiting for the background collector to yield.
1737 //
1738 // The foreground collector should be blocked (not for long)
1739 // if the background collector is about to start a phase
1740 // executed with world stopped. If the background
1741 // collector has already started such a phase, the
1742 // foreground collector is blocked waiting for the
1743 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1744 // are executed in the VM thread.
1745 //
1746 // The locking order is
1747 // PendingListLock (PLL) -- if applicable (FinalMarking)
1748 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1749 // CMS token (claimed in
1750 // stop_world_and_do() -->
1751 // safepoint_synchronize() -->
1752 // CMSThread::synchronize())
1753
1754 {
1755 // Check if the FG collector wants us to yield.
1756 CMSTokenSync x(true); // is cms thread
1757 if (waitForForegroundGC()) {
1758 // We yielded to a foreground GC, nothing more to be
1759 // done this round.
1760 assert(_foregroundGCShouldWait == false, "We set it to false in "
1761 "waitForForegroundGC()");
1762 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1763 p2i(Thread::current()), _collectorState);
1764 return;
1765 } else {
1766 // The background collector can run but check to see if the
1767 // foreground collector has done a collection while the
1768 // background collector was waiting to get the CGC_lock
1769 // above. If yes, break so that _foregroundGCShouldWait
1770 // is cleared before returning.
1771 if (_collectorState == Idling) {
1772 break;
1773 }
1774 }
1775 }
1776
1777 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1778 "should be waiting");
1779
1780 switch (_collectorState) {
1781 case InitialMarking:
1782 {
1783 ReleaseForegroundGC x(this);
1784 stats().record_cms_begin();
1785 VM_CMS_Initial_Mark initial_mark_op(this);
1786 VMThread::execute(&initial_mark_op);
1787 }
1788 // The collector state may be any legal state at this point
1789 // since the background collector may have yielded to the
1790 // foreground collector.
1791 break;
1792 case Marking:
1793 // initial marking in checkpointRootsInitialWork has been completed
1794 if (markFromRoots()) { // we were successful
1795 assert(_collectorState == Precleaning, "Collector state should "
1796 "have changed");
1797 } else {
1798 assert(_foregroundGCIsActive, "Internal state inconsistency");
1799 }
1800 break;
1801 case Precleaning:
1802 // marking from roots in markFromRoots has been completed
1803 preclean();
1804 assert(_collectorState == AbortablePreclean ||
1805 _collectorState == FinalMarking,
1806 "Collector state should have changed");
1807 break;
1808 case AbortablePreclean:
1809 abortable_preclean();
1810 assert(_collectorState == FinalMarking, "Collector state should "
1811 "have changed");
1812 break;
1813 case FinalMarking:
1814 {
1815 ReleaseForegroundGC x(this);
1816
1817 VM_CMS_Final_Remark final_remark_op(this);
1818 VMThread::execute(&final_remark_op);
1819 }
1820 assert(_foregroundGCShouldWait, "block post-condition");
1821 break;
1822 case Sweeping:
1823 // final marking in checkpointRootsFinal has been completed
1824 sweep();
1825 assert(_collectorState == Resizing, "Collector state change "
1826 "to Resizing must be done under the free_list_lock");
1827
1828 case Resizing: {
1829 // Sweeping has been completed...
1830 // At this point the background collection has completed.
1831 // Don't move the call to compute_new_size() down
1832 // into code that might be executed if the background
1833 // collection was preempted.
1834 {
1835 ReleaseForegroundGC x(this); // unblock FG collection
1836 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1837 CMSTokenSync z(true); // not strictly needed.
1838 if (_collectorState == Resizing) {
1839 compute_new_size();
1840 save_heap_summary();
1841 _collectorState = Resetting;
1842 } else {
1843 assert(_collectorState == Idling, "The state should only change"
1844 " because the foreground collector has finished the collection");
1845 }
1846 }
1847 break;
1848 }
1849 case Resetting:
1850 // CMS heap resizing has been completed
1851 reset_concurrent();
1852 assert(_collectorState == Idling, "Collector state should "
1853 "have changed");
1854
1855 MetaspaceGC::set_should_concurrent_collect(false);
1856
1857 stats().record_cms_end();
1858 // Don't move the concurrent_phases_end() and compute_new_size()
1859 // calls to here because a preempted background collection
1860 // has it's state set to "Resetting".
1861 break;
1862 case Idling:
1863 default:
1864 ShouldNotReachHere();
1865 break;
1866 }
1867 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1868 p2i(Thread::current()), _collectorState);
1869 assert(_foregroundGCShouldWait, "block post-condition");
1870 }
1871
1872 // Should this be in gc_epilogue?
1873 collector_policy()->counters()->update_counters();
1874
1875 {
1876 // Clear _foregroundGCShouldWait and, in the event that the
1877 // foreground collector is waiting, notify it, before
1878 // returning.
1879 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1880 _foregroundGCShouldWait = false;
1881 if (_foregroundGCIsActive) {
1882 CGC_lock->notify();
1883 }
1884 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1885 "Possible deadlock");
1886 }
1887 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1888 p2i(Thread::current()), _collectorState);
1889 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1890 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1891 }
1892
1893 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1894 _cms_start_registered = true;
1895 _gc_timer_cm->register_gc_start();
1896 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1897 }
1898
1899 void CMSCollector::register_gc_end() {
1900 if (_cms_start_registered) {
1901 report_heap_summary(GCWhen::AfterGC);
1902
1903 _gc_timer_cm->register_gc_end();
1904 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1905 _cms_start_registered = false;
1906 }
1907 }
1908
1909 void CMSCollector::save_heap_summary() {
1910 GenCollectedHeap* gch = GenCollectedHeap::heap();
1911 _last_heap_summary = gch->create_heap_summary();
1912 _last_metaspace_summary = gch->create_metaspace_summary();
1913 }
1914
1915 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1916 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1917 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1918 }
1919
1920 bool CMSCollector::waitForForegroundGC() {
1921 bool res = false;
1922 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1923 "CMS thread should have CMS token");
1924 // Block the foreground collector until the
1925 // background collectors decides whether to
1926 // yield.
1927 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1928 _foregroundGCShouldWait = true;
1929 if (_foregroundGCIsActive) {
1930 // The background collector yields to the
1931 // foreground collector and returns a value
1932 // indicating that it has yielded. The foreground
1933 // collector can proceed.
1934 res = true;
1935 _foregroundGCShouldWait = false;
1936 ConcurrentMarkSweepThread::clear_CMS_flag(
1937 ConcurrentMarkSweepThread::CMS_cms_has_token);
1938 ConcurrentMarkSweepThread::set_CMS_flag(
1939 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1940 // Get a possibly blocked foreground thread going
1941 CGC_lock->notify();
1942 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1943 p2i(Thread::current()), _collectorState);
1944 while (_foregroundGCIsActive) {
1945 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1946 }
1947 ConcurrentMarkSweepThread::set_CMS_flag(
1948 ConcurrentMarkSweepThread::CMS_cms_has_token);
1949 ConcurrentMarkSweepThread::clear_CMS_flag(
1950 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1951 }
1952 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1953 p2i(Thread::current()), _collectorState);
1954 return res;
1955 }
1956
1957 // Because of the need to lock the free lists and other structures in
1958 // the collector, common to all the generations that the collector is
1959 // collecting, we need the gc_prologues of individual CMS generations
1960 // delegate to their collector. It may have been simpler had the
1961 // current infrastructure allowed one to call a prologue on a
1962 // collector. In the absence of that we have the generation's
1963 // prologue delegate to the collector, which delegates back
1964 // some "local" work to a worker method in the individual generations
1965 // that it's responsible for collecting, while itself doing any
1966 // work common to all generations it's responsible for. A similar
1967 // comment applies to the gc_epilogue()'s.
1968 // The role of the variable _between_prologue_and_epilogue is to
1969 // enforce the invocation protocol.
1970 void CMSCollector::gc_prologue(bool full) {
1971 // Call gc_prologue_work() for the CMSGen
1972 // we are responsible for.
1973
1974 // The following locking discipline assumes that we are only called
1975 // when the world is stopped.
1976 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1977
1978 // The CMSCollector prologue must call the gc_prologues for the
1979 // "generations" that it's responsible
1980 // for.
1981
1982 assert( Thread::current()->is_VM_thread()
1983 || ( CMSScavengeBeforeRemark
1984 && Thread::current()->is_ConcurrentGC_thread()),
1985 "Incorrect thread type for prologue execution");
1986
1987 if (_between_prologue_and_epilogue) {
1988 // We have already been invoked; this is a gc_prologue delegation
1989 // from yet another CMS generation that we are responsible for, just
1990 // ignore it since all relevant work has already been done.
1991 return;
1992 }
1993
1994 // set a bit saying prologue has been called; cleared in epilogue
1995 _between_prologue_and_epilogue = true;
1996 // Claim locks for common data structures, then call gc_prologue_work()
1997 // for each CMSGen.
1998
1999 getFreelistLocks(); // gets free list locks on constituent spaces
2000 bitMapLock()->lock_without_safepoint_check();
2001
2002 // Should call gc_prologue_work() for all cms gens we are responsible for
2003 bool duringMarking = _collectorState >= Marking
2004 && _collectorState < Sweeping;
2005
2006 // The young collections clear the modified oops state, which tells if
2007 // there are any modified oops in the class. The remark phase also needs
2008 // that information. Tell the young collection to save the union of all
2009 // modified klasses.
2010 if (duringMarking) {
2011 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2012 }
2013
2014 bool registerClosure = duringMarking;
2015
2016 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2017
2018 if (!full) {
2019 stats().record_gc0_begin();
2020 }
2021 }
2022
2023 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2024
2025 _capacity_at_prologue = capacity();
2026 _used_at_prologue = used();
2027
2028 // Delegate to CMScollector which knows how to coordinate between
2029 // this and any other CMS generations that it is responsible for
2030 // collecting.
2031 collector()->gc_prologue(full);
2032 }
2033
2034 // This is a "private" interface for use by this generation's CMSCollector.
2035 // Not to be called directly by any other entity (for instance,
2036 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2037 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2038 bool registerClosure, ModUnionClosure* modUnionClosure) {
2039 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2040 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2041 "Should be NULL");
2042 if (registerClosure) {
2043 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2044 }
2045 cmsSpace()->gc_prologue();
2046 // Clear stat counters
2047 NOT_PRODUCT(
2048 assert(_numObjectsPromoted == 0, "check");
2049 assert(_numWordsPromoted == 0, "check");
2050 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2051 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2052 _numObjectsAllocated = 0;
2053 _numWordsAllocated = 0;
2054 )
2055 }
2056
2057 void CMSCollector::gc_epilogue(bool full) {
2058 // The following locking discipline assumes that we are only called
2059 // when the world is stopped.
2060 assert(SafepointSynchronize::is_at_safepoint(),
2061 "world is stopped assumption");
2062
2063 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2064 // if linear allocation blocks need to be appropriately marked to allow the
2065 // the blocks to be parsable. We also check here whether we need to nudge the
2066 // CMS collector thread to start a new cycle (if it's not already active).
2067 assert( Thread::current()->is_VM_thread()
2068 || ( CMSScavengeBeforeRemark
2069 && Thread::current()->is_ConcurrentGC_thread()),
2070 "Incorrect thread type for epilogue execution");
2071
2072 if (!_between_prologue_and_epilogue) {
2073 // We have already been invoked; this is a gc_epilogue delegation
2074 // from yet another CMS generation that we are responsible for, just
2075 // ignore it since all relevant work has already been done.
2076 return;
2077 }
2078 assert(haveFreelistLocks(), "must have freelist locks");
2079 assert_lock_strong(bitMapLock());
2080
2081 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2082
2083 _cmsGen->gc_epilogue_work(full);
2084
2085 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2086 // in case sampling was not already enabled, enable it
2087 _start_sampling = true;
2088 }
2089 // reset _eden_chunk_array so sampling starts afresh
2090 _eden_chunk_index = 0;
2091
2092 size_t cms_used = _cmsGen->cmsSpace()->used();
2093
2094 // update performance counters - this uses a special version of
2095 // update_counters() that allows the utilization to be passed as a
2096 // parameter, avoiding multiple calls to used().
2097 //
2098 _cmsGen->update_counters(cms_used);
2099
2100 bitMapLock()->unlock();
2101 releaseFreelistLocks();
2102
2103 if (!CleanChunkPoolAsync) {
2104 Chunk::clean_chunk_pool();
2105 }
2106
2107 set_did_compact(false);
2108 _between_prologue_and_epilogue = false; // ready for next cycle
2109 }
2110
2111 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2112 collector()->gc_epilogue(full);
2113
2114 // Also reset promotion tracking in par gc thread states.
2115 for (uint i = 0; i < ParallelGCThreads; i++) {
2116 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2117 }
2118 }
2119
2120 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2121 assert(!incremental_collection_failed(), "Should have been cleared");
2122 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2123 cmsSpace()->gc_epilogue();
2124 // Print stat counters
2125 NOT_PRODUCT(
2126 assert(_numObjectsAllocated == 0, "check");
2127 assert(_numWordsAllocated == 0, "check");
2128 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2129 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2130 _numObjectsPromoted = 0;
2131 _numWordsPromoted = 0;
2132 )
2133
2134 // Call down the chain in contiguous_available needs the freelistLock
2135 // so print this out before releasing the freeListLock.
2136 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2137 }
2138
2139 #ifndef PRODUCT
2140 bool CMSCollector::have_cms_token() {
2141 Thread* thr = Thread::current();
2142 if (thr->is_VM_thread()) {
2143 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2144 } else if (thr->is_ConcurrentGC_thread()) {
2145 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2146 } else if (thr->is_GC_task_thread()) {
2147 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2148 ParGCRareEvent_lock->owned_by_self();
2149 }
2150 return false;
2151 }
2152
2153 // Check reachability of the given heap address in CMS generation,
2154 // treating all other generations as roots.
2155 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2156 // We could "guarantee" below, rather than assert, but I'll
2157 // leave these as "asserts" so that an adventurous debugger
2158 // could try this in the product build provided some subset of
2159 // the conditions were met, provided they were interested in the
2160 // results and knew that the computation below wouldn't interfere
2161 // with other concurrent computations mutating the structures
2162 // being read or written.
2163 assert(SafepointSynchronize::is_at_safepoint(),
2164 "Else mutations in object graph will make answer suspect");
2165 assert(have_cms_token(), "Should hold cms token");
2166 assert(haveFreelistLocks(), "must hold free list locks");
2167 assert_lock_strong(bitMapLock());
2168
2169 // Clear the marking bit map array before starting, but, just
2170 // for kicks, first report if the given address is already marked
2171 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2172 _markBitMap.isMarked(addr) ? "" : " not");
2173
2174 if (verify_after_remark()) {
2175 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2176 bool result = verification_mark_bm()->isMarked(addr);
2177 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2178 result ? "IS" : "is NOT");
2179 return result;
2180 } else {
2181 tty->print_cr("Could not compute result");
2182 return false;
2183 }
2184 }
2185 #endif
2186
2187 void
2188 CMSCollector::print_on_error(outputStream* st) {
2189 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2190 if (collector != NULL) {
2191 CMSBitMap* bitmap = &collector->_markBitMap;
2192 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2193 bitmap->print_on_error(st, " Bits: ");
2194
2195 st->cr();
2196
2197 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2198 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2199 mut_bitmap->print_on_error(st, " Bits: ");
2200 }
2201 }
2202
2203 ////////////////////////////////////////////////////////
2204 // CMS Verification Support
2205 ////////////////////////////////////////////////////////
2206 // Following the remark phase, the following invariant
2207 // should hold -- each object in the CMS heap which is
2208 // marked in markBitMap() should be marked in the verification_mark_bm().
2209
2210 class VerifyMarkedClosure: public BitMapClosure {
2211 CMSBitMap* _marks;
2212 bool _failed;
2213
2214 public:
2215 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2216
2217 bool do_bit(size_t offset) {
2218 HeapWord* addr = _marks->offsetToHeapWord(offset);
2219 if (!_marks->isMarked(addr)) {
2220 LogHandle(gc, verify) log;
2221 ResourceMark rm;
2222 oop(addr)->print_on(log.info_stream());
2223 log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2224 _failed = true;
2225 }
2226 return true;
2227 }
2228
2229 bool failed() { return _failed; }
2230 };
2231
2232 bool CMSCollector::verify_after_remark() {
2233 GCTraceTime(Info, gc, verify) tm("Verifying CMS Marking.");
2234 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2235 static bool init = false;
2236
2237 assert(SafepointSynchronize::is_at_safepoint(),
2238 "Else mutations in object graph will make answer suspect");
2239 assert(have_cms_token(),
2240 "Else there may be mutual interference in use of "
2241 " verification data structures");
2242 assert(_collectorState > Marking && _collectorState <= Sweeping,
2243 "Else marking info checked here may be obsolete");
2244 assert(haveFreelistLocks(), "must hold free list locks");
2245 assert_lock_strong(bitMapLock());
2246
2247
2248 // Allocate marking bit map if not already allocated
2249 if (!init) { // first time
2250 if (!verification_mark_bm()->allocate(_span)) {
2251 return false;
2252 }
2253 init = true;
2254 }
2255
2256 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2257
2258 // Turn off refs discovery -- so we will be tracing through refs.
2259 // This is as intended, because by this time
2260 // GC must already have cleared any refs that need to be cleared,
2261 // and traced those that need to be marked; moreover,
2262 // the marking done here is not going to interfere in any
2263 // way with the marking information used by GC.
2264 NoRefDiscovery no_discovery(ref_processor());
2265
2266 #if defined(COMPILER2) || INCLUDE_JVMCI
2267 DerivedPointerTableDeactivate dpt_deact;
2268 #endif
2269
2270 // Clear any marks from a previous round
2271 verification_mark_bm()->clear_all();
2272 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2273 verify_work_stacks_empty();
2274
2275 GenCollectedHeap* gch = GenCollectedHeap::heap();
2276 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2277 // Update the saved marks which may affect the root scans.
2278 gch->save_marks();
2279
2280 if (CMSRemarkVerifyVariant == 1) {
2281 // In this first variant of verification, we complete
2282 // all marking, then check if the new marks-vector is
2283 // a subset of the CMS marks-vector.
2284 verify_after_remark_work_1();
2285 } else if (CMSRemarkVerifyVariant == 2) {
2286 // In this second variant of verification, we flag an error
2287 // (i.e. an object reachable in the new marks-vector not reachable
2288 // in the CMS marks-vector) immediately, also indicating the
2289 // identify of an object (A) that references the unmarked object (B) --
2290 // presumably, a mutation to A failed to be picked up by preclean/remark?
2291 verify_after_remark_work_2();
2292 } else {
2293 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2294 CMSRemarkVerifyVariant);
2295 }
2296 return true;
2297 }
2298
2299 void CMSCollector::verify_after_remark_work_1() {
2300 ResourceMark rm;
2301 HandleMark hm;
2302 GenCollectedHeap* gch = GenCollectedHeap::heap();
2303
2304 // Get a clear set of claim bits for the roots processing to work with.
2305 ClassLoaderDataGraph::clear_claimed_marks();
2306
2307 // Mark from roots one level into CMS
2308 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2309 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2310
2311 {
2312 StrongRootsScope srs(1);
2313
2314 gch->gen_process_roots(&srs,
2315 GenCollectedHeap::OldGen,
2316 true, // young gen as roots
2317 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2318 should_unload_classes(),
2319 ¬Older,
2320 NULL,
2321 NULL);
2322 }
2323
2324 // Now mark from the roots
2325 MarkFromRootsClosure markFromRootsClosure(this, _span,
2326 verification_mark_bm(), verification_mark_stack(),
2327 false /* don't yield */, true /* verifying */);
2328 assert(_restart_addr == NULL, "Expected pre-condition");
2329 verification_mark_bm()->iterate(&markFromRootsClosure);
2330 while (_restart_addr != NULL) {
2331 // Deal with stack overflow: by restarting at the indicated
2332 // address.
2333 HeapWord* ra = _restart_addr;
2334 markFromRootsClosure.reset(ra);
2335 _restart_addr = NULL;
2336 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2337 }
2338 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2339 verify_work_stacks_empty();
2340
2341 // Marking completed -- now verify that each bit marked in
2342 // verification_mark_bm() is also marked in markBitMap(); flag all
2343 // errors by printing corresponding objects.
2344 VerifyMarkedClosure vcl(markBitMap());
2345 verification_mark_bm()->iterate(&vcl);
2346 if (vcl.failed()) {
2347 LogHandle(gc, verify) log;
2348 log.info("Verification failed");
2349 ResourceMark rm;
2350 gch->print_on(log.info_stream());
2351 fatal("CMS: failed marking verification after remark");
2352 }
2353 }
2354
2355 class VerifyKlassOopsKlassClosure : public KlassClosure {
2356 class VerifyKlassOopsClosure : public OopClosure {
2357 CMSBitMap* _bitmap;
2358 public:
2359 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2360 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2361 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2362 } _oop_closure;
2363 public:
2364 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2365 void do_klass(Klass* k) {
2366 k->oops_do(&_oop_closure);
2367 }
2368 };
2369
2370 void CMSCollector::verify_after_remark_work_2() {
2371 ResourceMark rm;
2372 HandleMark hm;
2373 GenCollectedHeap* gch = GenCollectedHeap::heap();
2374
2375 // Get a clear set of claim bits for the roots processing to work with.
2376 ClassLoaderDataGraph::clear_claimed_marks();
2377
2378 // Mark from roots one level into CMS
2379 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2380 markBitMap());
2381 CLDToOopClosure cld_closure(¬Older, true);
2382
2383 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2384
2385 {
2386 StrongRootsScope srs(1);
2387
2388 gch->gen_process_roots(&srs,
2389 GenCollectedHeap::OldGen,
2390 true, // young gen as roots
2391 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2392 should_unload_classes(),
2393 ¬Older,
2394 NULL,
2395 &cld_closure);
2396 }
2397
2398 // Now mark from the roots
2399 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2400 verification_mark_bm(), markBitMap(), verification_mark_stack());
2401 assert(_restart_addr == NULL, "Expected pre-condition");
2402 verification_mark_bm()->iterate(&markFromRootsClosure);
2403 while (_restart_addr != NULL) {
2404 // Deal with stack overflow: by restarting at the indicated
2405 // address.
2406 HeapWord* ra = _restart_addr;
2407 markFromRootsClosure.reset(ra);
2408 _restart_addr = NULL;
2409 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2410 }
2411 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2412 verify_work_stacks_empty();
2413
2414 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2415 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2416
2417 // Marking completed -- now verify that each bit marked in
2418 // verification_mark_bm() is also marked in markBitMap(); flag all
2419 // errors by printing corresponding objects.
2420 VerifyMarkedClosure vcl(markBitMap());
2421 verification_mark_bm()->iterate(&vcl);
2422 assert(!vcl.failed(), "Else verification above should not have succeeded");
2423 }
2424
2425 void ConcurrentMarkSweepGeneration::save_marks() {
2426 // delegate to CMS space
2427 cmsSpace()->save_marks();
2428 for (uint i = 0; i < ParallelGCThreads; i++) {
2429 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2430 }
2431 }
2432
2433 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2434 return cmsSpace()->no_allocs_since_save_marks();
2435 }
2436
2437 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2438 \
2439 void ConcurrentMarkSweepGeneration:: \
2440 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2441 cl->set_generation(this); \
2442 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2443 cl->reset_generation(); \
2444 save_marks(); \
2445 }
2446
2447 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2448
2449 void
2450 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2451 if (freelistLock()->owned_by_self()) {
2452 Generation::oop_iterate(cl);
2453 } else {
2454 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2455 Generation::oop_iterate(cl);
2456 }
2457 }
2458
2459 void
2460 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2461 if (freelistLock()->owned_by_self()) {
2462 Generation::object_iterate(cl);
2463 } else {
2464 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2465 Generation::object_iterate(cl);
2466 }
2467 }
2468
2469 void
2470 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2471 if (freelistLock()->owned_by_self()) {
2472 Generation::safe_object_iterate(cl);
2473 } else {
2474 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2475 Generation::safe_object_iterate(cl);
2476 }
2477 }
2478
2479 void
2480 ConcurrentMarkSweepGeneration::post_compact() {
2481 }
2482
2483 void
2484 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2485 // Fix the linear allocation blocks to look like free blocks.
2486
2487 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2488 // are not called when the heap is verified during universe initialization and
2489 // at vm shutdown.
2490 if (freelistLock()->owned_by_self()) {
2491 cmsSpace()->prepare_for_verify();
2492 } else {
2493 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2494 cmsSpace()->prepare_for_verify();
2495 }
2496 }
2497
2498 void
2499 ConcurrentMarkSweepGeneration::verify() {
2500 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2501 // are not called when the heap is verified during universe initialization and
2502 // at vm shutdown.
2503 if (freelistLock()->owned_by_self()) {
2504 cmsSpace()->verify();
2505 } else {
2506 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2507 cmsSpace()->verify();
2508 }
2509 }
2510
2511 void CMSCollector::verify() {
2512 _cmsGen->verify();
2513 }
2514
2515 #ifndef PRODUCT
2516 bool CMSCollector::overflow_list_is_empty() const {
2517 assert(_num_par_pushes >= 0, "Inconsistency");
2518 if (_overflow_list == NULL) {
2519 assert(_num_par_pushes == 0, "Inconsistency");
2520 }
2521 return _overflow_list == NULL;
2522 }
2523
2524 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2525 // merely consolidate assertion checks that appear to occur together frequently.
2526 void CMSCollector::verify_work_stacks_empty() const {
2527 assert(_markStack.isEmpty(), "Marking stack should be empty");
2528 assert(overflow_list_is_empty(), "Overflow list should be empty");
2529 }
2530
2531 void CMSCollector::verify_overflow_empty() const {
2532 assert(overflow_list_is_empty(), "Overflow list should be empty");
2533 assert(no_preserved_marks(), "No preserved marks");
2534 }
2535 #endif // PRODUCT
2536
2537 // Decide if we want to enable class unloading as part of the
2538 // ensuing concurrent GC cycle. We will collect and
2539 // unload classes if it's the case that:
2540 // (1) an explicit gc request has been made and the flag
2541 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2542 // (2) (a) class unloading is enabled at the command line, and
2543 // (b) old gen is getting really full
2544 // NOTE: Provided there is no change in the state of the heap between
2545 // calls to this method, it should have idempotent results. Moreover,
2546 // its results should be monotonically increasing (i.e. going from 0 to 1,
2547 // but not 1 to 0) between successive calls between which the heap was
2548 // not collected. For the implementation below, it must thus rely on
2549 // the property that concurrent_cycles_since_last_unload()
2550 // will not decrease unless a collection cycle happened and that
2551 // _cmsGen->is_too_full() are
2552 // themselves also monotonic in that sense. See check_monotonicity()
2553 // below.
2554 void CMSCollector::update_should_unload_classes() {
2555 _should_unload_classes = false;
2556 // Condition 1 above
2557 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2558 _should_unload_classes = true;
2559 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2560 // Disjuncts 2.b.(i,ii,iii) above
2561 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2562 CMSClassUnloadingMaxInterval)
2563 || _cmsGen->is_too_full();
2564 }
2565 }
2566
2567 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2568 bool res = should_concurrent_collect();
2569 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2570 return res;
2571 }
2572
2573 void CMSCollector::setup_cms_unloading_and_verification_state() {
2574 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2575 || VerifyBeforeExit;
2576 const int rso = GenCollectedHeap::SO_AllCodeCache;
2577
2578 // We set the proper root for this CMS cycle here.
2579 if (should_unload_classes()) { // Should unload classes this cycle
2580 remove_root_scanning_option(rso); // Shrink the root set appropriately
2581 set_verifying(should_verify); // Set verification state for this cycle
2582 return; // Nothing else needs to be done at this time
2583 }
2584
2585 // Not unloading classes this cycle
2586 assert(!should_unload_classes(), "Inconsistency!");
2587
2588 // If we are not unloading classes then add SO_AllCodeCache to root
2589 // scanning options.
2590 add_root_scanning_option(rso);
2591
2592 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2593 set_verifying(true);
2594 } else if (verifying() && !should_verify) {
2595 // We were verifying, but some verification flags got disabled.
2596 set_verifying(false);
2597 // Exclude symbols, strings and code cache elements from root scanning to
2598 // reduce IM and RM pauses.
2599 remove_root_scanning_option(rso);
2600 }
2601 }
2602
2603
2604 #ifndef PRODUCT
2605 HeapWord* CMSCollector::block_start(const void* p) const {
2606 const HeapWord* addr = (HeapWord*)p;
2607 if (_span.contains(p)) {
2608 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2609 return _cmsGen->cmsSpace()->block_start(p);
2610 }
2611 }
2612 return NULL;
2613 }
2614 #endif
2615
2616 HeapWord*
2617 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2618 bool tlab,
2619 bool parallel) {
2620 CMSSynchronousYieldRequest yr;
2621 assert(!tlab, "Can't deal with TLAB allocation");
2622 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2623 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2624 if (GCExpandToAllocateDelayMillis > 0) {
2625 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2626 }
2627 return have_lock_and_allocate(word_size, tlab);
2628 }
2629
2630 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2631 size_t bytes,
2632 size_t expand_bytes,
2633 CMSExpansionCause::Cause cause)
2634 {
2635
2636 bool success = expand(bytes, expand_bytes);
2637
2638 // remember why we expanded; this information is used
2639 // by shouldConcurrentCollect() when making decisions on whether to start
2640 // a new CMS cycle.
2641 if (success) {
2642 set_expansion_cause(cause);
2643 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2644 }
2645 }
2646
2647 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2648 HeapWord* res = NULL;
2649 MutexLocker x(ParGCRareEvent_lock);
2650 while (true) {
2651 // Expansion by some other thread might make alloc OK now:
2652 res = ps->lab.alloc(word_sz);
2653 if (res != NULL) return res;
2654 // If there's not enough expansion space available, give up.
2655 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2656 return NULL;
2657 }
2658 // Otherwise, we try expansion.
2659 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2660 // Now go around the loop and try alloc again;
2661 // A competing par_promote might beat us to the expansion space,
2662 // so we may go around the loop again if promotion fails again.
2663 if (GCExpandToAllocateDelayMillis > 0) {
2664 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2665 }
2666 }
2667 }
2668
2669
2670 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2671 PromotionInfo* promo) {
2672 MutexLocker x(ParGCRareEvent_lock);
2673 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2674 while (true) {
2675 // Expansion by some other thread might make alloc OK now:
2676 if (promo->ensure_spooling_space()) {
2677 assert(promo->has_spooling_space(),
2678 "Post-condition of successful ensure_spooling_space()");
2679 return true;
2680 }
2681 // If there's not enough expansion space available, give up.
2682 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2683 return false;
2684 }
2685 // Otherwise, we try expansion.
2686 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2687 // Now go around the loop and try alloc again;
2688 // A competing allocation might beat us to the expansion space,
2689 // so we may go around the loop again if allocation fails again.
2690 if (GCExpandToAllocateDelayMillis > 0) {
2691 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2692 }
2693 }
2694 }
2695
2696 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2697 // Only shrink if a compaction was done so that all the free space
2698 // in the generation is in a contiguous block at the end.
2699 if (did_compact()) {
2700 CardGeneration::shrink(bytes);
2701 }
2702 }
2703
2704 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2705 assert_locked_or_safepoint(Heap_lock);
2706 }
2707
2708 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2709 assert_locked_or_safepoint(Heap_lock);
2710 assert_lock_strong(freelistLock());
2711 log_trace(gc)("Shrinking of CMS not yet implemented");
2712 return;
2713 }
2714
2715
2716 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2717 // phases.
2718 class CMSPhaseAccounting: public StackObj {
2719 public:
2720 CMSPhaseAccounting(CMSCollector *collector,
2721 const char *title);
2722 ~CMSPhaseAccounting();
2723
2724 private:
2725 CMSCollector *_collector;
2726 const char *_title;
2727 GCTraceConcTime(Info, gc) _trace_time;
2728
2729 public:
2730 // Not MT-safe; so do not pass around these StackObj's
2731 // where they may be accessed by other threads.
2732 jlong wallclock_millis() {
2733 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2734 }
2735 };
2736
2737 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2738 const char *title) :
2739 _collector(collector), _title(title), _trace_time(title) {
2740
2741 _collector->resetYields();
2742 _collector->resetTimer();
2743 _collector->startTimer();
2744 }
2745
2746 CMSPhaseAccounting::~CMSPhaseAccounting() {
2747 _collector->stopTimer();
2748 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2749 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2750 }
2751
2752 // CMS work
2753
2754 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2755 class CMSParMarkTask : public AbstractGangTask {
2756 protected:
2757 CMSCollector* _collector;
2758 uint _n_workers;
2759 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2760 AbstractGangTask(name),
2761 _collector(collector),
2762 _n_workers(n_workers) {}
2763 // Work method in support of parallel rescan ... of young gen spaces
2764 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2765 ContiguousSpace* space,
2766 HeapWord** chunk_array, size_t chunk_top);
2767 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2768 };
2769
2770 // Parallel initial mark task
2771 class CMSParInitialMarkTask: public CMSParMarkTask {
2772 StrongRootsScope* _strong_roots_scope;
2773 public:
2774 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2775 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2776 _strong_roots_scope(strong_roots_scope) {}
2777 void work(uint worker_id);
2778 };
2779
2780 // Checkpoint the roots into this generation from outside
2781 // this generation. [Note this initial checkpoint need only
2782 // be approximate -- we'll do a catch up phase subsequently.]
2783 void CMSCollector::checkpointRootsInitial() {
2784 assert(_collectorState == InitialMarking, "Wrong collector state");
2785 check_correct_thread_executing();
2786 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2787
2788 save_heap_summary();
2789 report_heap_summary(GCWhen::BeforeGC);
2790
2791 ReferenceProcessor* rp = ref_processor();
2792 assert(_restart_addr == NULL, "Control point invariant");
2793 {
2794 // acquire locks for subsequent manipulations
2795 MutexLockerEx x(bitMapLock(),
2796 Mutex::_no_safepoint_check_flag);
2797 checkpointRootsInitialWork();
2798 // enable ("weak") refs discovery
2799 rp->enable_discovery();
2800 _collectorState = Marking;
2801 }
2802 }
2803
2804 void CMSCollector::checkpointRootsInitialWork() {
2805 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2806 assert(_collectorState == InitialMarking, "just checking");
2807
2808 // Already have locks.
2809 assert_lock_strong(bitMapLock());
2810 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2811
2812 // Setup the verification and class unloading state for this
2813 // CMS collection cycle.
2814 setup_cms_unloading_and_verification_state();
2815
2816 GCTraceTime(Trace, gc) ts("checkpointRootsInitialWork", _gc_timer_cm);
2817
2818 // Reset all the PLAB chunk arrays if necessary.
2819 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2820 reset_survivor_plab_arrays();
2821 }
2822
2823 ResourceMark rm;
2824 HandleMark hm;
2825
2826 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2827 GenCollectedHeap* gch = GenCollectedHeap::heap();
2828
2829 verify_work_stacks_empty();
2830 verify_overflow_empty();
2831
2832 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2833 // Update the saved marks which may affect the root scans.
2834 gch->save_marks();
2835
2836 // weak reference processing has not started yet.
2837 ref_processor()->set_enqueuing_is_done(false);
2838
2839 // Need to remember all newly created CLDs,
2840 // so that we can guarantee that the remark finds them.
2841 ClassLoaderDataGraph::remember_new_clds(true);
2842
2843 // Whenever a CLD is found, it will be claimed before proceeding to mark
2844 // the klasses. The claimed marks need to be cleared before marking starts.
2845 ClassLoaderDataGraph::clear_claimed_marks();
2846
2847 print_eden_and_survivor_chunk_arrays();
2848
2849 {
2850 #if defined(COMPILER2) || INCLUDE_JVMCI
2851 DerivedPointerTableDeactivate dpt_deact;
2852 #endif
2853 if (CMSParallelInitialMarkEnabled) {
2854 // The parallel version.
2855 WorkGang* workers = gch->workers();
2856 assert(workers != NULL, "Need parallel worker threads.");
2857 uint n_workers = workers->active_workers();
2858
2859 StrongRootsScope srs(n_workers);
2860
2861 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2862 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2863 if (n_workers > 1) {
2864 workers->run_task(&tsk);
2865 } else {
2866 tsk.work(0);
2867 }
2868 } else {
2869 // The serial version.
2870 CLDToOopClosure cld_closure(¬Older, true);
2871 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2872
2873 StrongRootsScope srs(1);
2874
2875 gch->gen_process_roots(&srs,
2876 GenCollectedHeap::OldGen,
2877 true, // young gen as roots
2878 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2879 should_unload_classes(),
2880 ¬Older,
2881 NULL,
2882 &cld_closure);
2883 }
2884 }
2885
2886 // Clear mod-union table; it will be dirtied in the prologue of
2887 // CMS generation per each young generation collection.
2888
2889 assert(_modUnionTable.isAllClear(),
2890 "Was cleared in most recent final checkpoint phase"
2891 " or no bits are set in the gc_prologue before the start of the next "
2892 "subsequent marking phase.");
2893
2894 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2895
2896 // Save the end of the used_region of the constituent generations
2897 // to be used to limit the extent of sweep in each generation.
2898 save_sweep_limits();
2899 verify_overflow_empty();
2900 }
2901
2902 bool CMSCollector::markFromRoots() {
2903 // we might be tempted to assert that:
2904 // assert(!SafepointSynchronize::is_at_safepoint(),
2905 // "inconsistent argument?");
2906 // However that wouldn't be right, because it's possible that
2907 // a safepoint is indeed in progress as a young generation
2908 // stop-the-world GC happens even as we mark in this generation.
2909 assert(_collectorState == Marking, "inconsistent state?");
2910 check_correct_thread_executing();
2911 verify_overflow_empty();
2912
2913 // Weak ref discovery note: We may be discovering weak
2914 // refs in this generation concurrent (but interleaved) with
2915 // weak ref discovery by the young generation collector.
2916
2917 CMSTokenSyncWithLocks ts(true, bitMapLock());
2918 GCTraceCPUTime tcpu;
2919 CMSPhaseAccounting pa(this, "Concrurrent Mark");
2920 bool res = markFromRootsWork();
2921 if (res) {
2922 _collectorState = Precleaning;
2923 } else { // We failed and a foreground collection wants to take over
2924 assert(_foregroundGCIsActive, "internal state inconsistency");
2925 assert(_restart_addr == NULL, "foreground will restart from scratch");
2926 log_debug(gc)("bailing out to foreground collection");
2927 }
2928 verify_overflow_empty();
2929 return res;
2930 }
2931
2932 bool CMSCollector::markFromRootsWork() {
2933 // iterate over marked bits in bit map, doing a full scan and mark
2934 // from these roots using the following algorithm:
2935 // . if oop is to the right of the current scan pointer,
2936 // mark corresponding bit (we'll process it later)
2937 // . else (oop is to left of current scan pointer)
2938 // push oop on marking stack
2939 // . drain the marking stack
2940
2941 // Note that when we do a marking step we need to hold the
2942 // bit map lock -- recall that direct allocation (by mutators)
2943 // and promotion (by the young generation collector) is also
2944 // marking the bit map. [the so-called allocate live policy.]
2945 // Because the implementation of bit map marking is not
2946 // robust wrt simultaneous marking of bits in the same word,
2947 // we need to make sure that there is no such interference
2948 // between concurrent such updates.
2949
2950 // already have locks
2951 assert_lock_strong(bitMapLock());
2952
2953 verify_work_stacks_empty();
2954 verify_overflow_empty();
2955 bool result = false;
2956 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2957 result = do_marking_mt();
2958 } else {
2959 result = do_marking_st();
2960 }
2961 return result;
2962 }
2963
2964 // Forward decl
2965 class CMSConcMarkingTask;
2966
2967 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2968 CMSCollector* _collector;
2969 CMSConcMarkingTask* _task;
2970 public:
2971 virtual void yield();
2972
2973 // "n_threads" is the number of threads to be terminated.
2974 // "queue_set" is a set of work queues of other threads.
2975 // "collector" is the CMS collector associated with this task terminator.
2976 // "yield" indicates whether we need the gang as a whole to yield.
2977 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2978 ParallelTaskTerminator(n_threads, queue_set),
2979 _collector(collector) { }
2980
2981 void set_task(CMSConcMarkingTask* task) {
2982 _task = task;
2983 }
2984 };
2985
2986 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
2987 CMSConcMarkingTask* _task;
2988 public:
2989 bool should_exit_termination();
2990 void set_task(CMSConcMarkingTask* task) {
2991 _task = task;
2992 }
2993 };
2994
2995 // MT Concurrent Marking Task
2996 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
2997 CMSCollector* _collector;
2998 uint _n_workers; // requested/desired # workers
2999 bool _result;
3000 CompactibleFreeListSpace* _cms_space;
3001 char _pad_front[64]; // padding to ...
3002 HeapWord* _global_finger; // ... avoid sharing cache line
3003 char _pad_back[64];
3004 HeapWord* _restart_addr;
3005
3006 // Exposed here for yielding support
3007 Mutex* const _bit_map_lock;
3008
3009 // The per thread work queues, available here for stealing
3010 OopTaskQueueSet* _task_queues;
3011
3012 // Termination (and yielding) support
3013 CMSConcMarkingTerminator _term;
3014 CMSConcMarkingTerminatorTerminator _term_term;
3015
3016 public:
3017 CMSConcMarkingTask(CMSCollector* collector,
3018 CompactibleFreeListSpace* cms_space,
3019 YieldingFlexibleWorkGang* workers,
3020 OopTaskQueueSet* task_queues):
3021 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3022 _collector(collector),
3023 _cms_space(cms_space),
3024 _n_workers(0), _result(true),
3025 _task_queues(task_queues),
3026 _term(_n_workers, task_queues, _collector),
3027 _bit_map_lock(collector->bitMapLock())
3028 {
3029 _requested_size = _n_workers;
3030 _term.set_task(this);
3031 _term_term.set_task(this);
3032 _restart_addr = _global_finger = _cms_space->bottom();
3033 }
3034
3035
3036 OopTaskQueueSet* task_queues() { return _task_queues; }
3037
3038 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3039
3040 HeapWord** global_finger_addr() { return &_global_finger; }
3041
3042 CMSConcMarkingTerminator* terminator() { return &_term; }
3043
3044 virtual void set_for_termination(uint active_workers) {
3045 terminator()->reset_for_reuse(active_workers);
3046 }
3047
3048 void work(uint worker_id);
3049 bool should_yield() {
3050 return ConcurrentMarkSweepThread::should_yield()
3051 && !_collector->foregroundGCIsActive();
3052 }
3053
3054 virtual void coordinator_yield(); // stuff done by coordinator
3055 bool result() { return _result; }
3056
3057 void reset(HeapWord* ra) {
3058 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3059 _restart_addr = _global_finger = ra;
3060 _term.reset_for_reuse();
3061 }
3062
3063 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3064 OopTaskQueue* work_q);
3065
3066 private:
3067 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3068 void do_work_steal(int i);
3069 void bump_global_finger(HeapWord* f);
3070 };
3071
3072 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3073 assert(_task != NULL, "Error");
3074 return _task->yielding();
3075 // Note that we do not need the disjunct || _task->should_yield() above
3076 // because we want terminating threads to yield only if the task
3077 // is already in the midst of yielding, which happens only after at least one
3078 // thread has yielded.
3079 }
3080
3081 void CMSConcMarkingTerminator::yield() {
3082 if (_task->should_yield()) {
3083 _task->yield();
3084 } else {
3085 ParallelTaskTerminator::yield();
3086 }
3087 }
3088
3089 ////////////////////////////////////////////////////////////////
3090 // Concurrent Marking Algorithm Sketch
3091 ////////////////////////////////////////////////////////////////
3092 // Until all tasks exhausted (both spaces):
3093 // -- claim next available chunk
3094 // -- bump global finger via CAS
3095 // -- find first object that starts in this chunk
3096 // and start scanning bitmap from that position
3097 // -- scan marked objects for oops
3098 // -- CAS-mark target, and if successful:
3099 // . if target oop is above global finger (volatile read)
3100 // nothing to do
3101 // . if target oop is in chunk and above local finger
3102 // then nothing to do
3103 // . else push on work-queue
3104 // -- Deal with possible overflow issues:
3105 // . local work-queue overflow causes stuff to be pushed on
3106 // global (common) overflow queue
3107 // . always first empty local work queue
3108 // . then get a batch of oops from global work queue if any
3109 // . then do work stealing
3110 // -- When all tasks claimed (both spaces)
3111 // and local work queue empty,
3112 // then in a loop do:
3113 // . check global overflow stack; steal a batch of oops and trace
3114 // . try to steal from other threads oif GOS is empty
3115 // . if neither is available, offer termination
3116 // -- Terminate and return result
3117 //
3118 void CMSConcMarkingTask::work(uint worker_id) {
3119 elapsedTimer _timer;
3120 ResourceMark rm;
3121 HandleMark hm;
3122
3123 DEBUG_ONLY(_collector->verify_overflow_empty();)
3124
3125 // Before we begin work, our work queue should be empty
3126 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3127 // Scan the bitmap covering _cms_space, tracing through grey objects.
3128 _timer.start();
3129 do_scan_and_mark(worker_id, _cms_space);
3130 _timer.stop();
3131 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3132
3133 // ... do work stealing
3134 _timer.reset();
3135 _timer.start();
3136 do_work_steal(worker_id);
3137 _timer.stop();
3138 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3139 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3140 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3141 // Note that under the current task protocol, the
3142 // following assertion is true even of the spaces
3143 // expanded since the completion of the concurrent
3144 // marking. XXX This will likely change under a strict
3145 // ABORT semantics.
3146 // After perm removal the comparison was changed to
3147 // greater than or equal to from strictly greater than.
3148 // Before perm removal the highest address sweep would
3149 // have been at the end of perm gen but now is at the
3150 // end of the tenured gen.
3151 assert(_global_finger >= _cms_space->end(),
3152 "All tasks have been completed");
3153 DEBUG_ONLY(_collector->verify_overflow_empty();)
3154 }
3155
3156 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3157 HeapWord* read = _global_finger;
3158 HeapWord* cur = read;
3159 while (f > read) {
3160 cur = read;
3161 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3162 if (cur == read) {
3163 // our cas succeeded
3164 assert(_global_finger >= f, "protocol consistency");
3165 break;
3166 }
3167 }
3168 }
3169
3170 // This is really inefficient, and should be redone by
3171 // using (not yet available) block-read and -write interfaces to the
3172 // stack and the work_queue. XXX FIX ME !!!
3173 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3174 OopTaskQueue* work_q) {
3175 // Fast lock-free check
3176 if (ovflw_stk->length() == 0) {
3177 return false;
3178 }
3179 assert(work_q->size() == 0, "Shouldn't steal");
3180 MutexLockerEx ml(ovflw_stk->par_lock(),
3181 Mutex::_no_safepoint_check_flag);
3182 // Grab up to 1/4 the size of the work queue
3183 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3184 (size_t)ParGCDesiredObjsFromOverflowList);
3185 num = MIN2(num, ovflw_stk->length());
3186 for (int i = (int) num; i > 0; i--) {
3187 oop cur = ovflw_stk->pop();
3188 assert(cur != NULL, "Counted wrong?");
3189 work_q->push(cur);
3190 }
3191 return num > 0;
3192 }
3193
3194 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3195 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3196 int n_tasks = pst->n_tasks();
3197 // We allow that there may be no tasks to do here because
3198 // we are restarting after a stack overflow.
3199 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3200 uint nth_task = 0;
3201
3202 HeapWord* aligned_start = sp->bottom();
3203 if (sp->used_region().contains(_restart_addr)) {
3204 // Align down to a card boundary for the start of 0th task
3205 // for this space.
3206 aligned_start =
3207 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3208 CardTableModRefBS::card_size);
3209 }
3210
3211 size_t chunk_size = sp->marking_task_size();
3212 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3213 // Having claimed the nth task in this space,
3214 // compute the chunk that it corresponds to:
3215 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3216 aligned_start + (nth_task+1)*chunk_size);
3217 // Try and bump the global finger via a CAS;
3218 // note that we need to do the global finger bump
3219 // _before_ taking the intersection below, because
3220 // the task corresponding to that region will be
3221 // deemed done even if the used_region() expands
3222 // because of allocation -- as it almost certainly will
3223 // during start-up while the threads yield in the
3224 // closure below.
3225 HeapWord* finger = span.end();
3226 bump_global_finger(finger); // atomically
3227 // There are null tasks here corresponding to chunks
3228 // beyond the "top" address of the space.
3229 span = span.intersection(sp->used_region());
3230 if (!span.is_empty()) { // Non-null task
3231 HeapWord* prev_obj;
3232 assert(!span.contains(_restart_addr) || nth_task == 0,
3233 "Inconsistency");
3234 if (nth_task == 0) {
3235 // For the 0th task, we'll not need to compute a block_start.
3236 if (span.contains(_restart_addr)) {
3237 // In the case of a restart because of stack overflow,
3238 // we might additionally skip a chunk prefix.
3239 prev_obj = _restart_addr;
3240 } else {
3241 prev_obj = span.start();
3242 }
3243 } else {
3244 // We want to skip the first object because
3245 // the protocol is to scan any object in its entirety
3246 // that _starts_ in this span; a fortiori, any
3247 // object starting in an earlier span is scanned
3248 // as part of an earlier claimed task.
3249 // Below we use the "careful" version of block_start
3250 // so we do not try to navigate uninitialized objects.
3251 prev_obj = sp->block_start_careful(span.start());
3252 // Below we use a variant of block_size that uses the
3253 // Printezis bits to avoid waiting for allocated
3254 // objects to become initialized/parsable.
3255 while (prev_obj < span.start()) {
3256 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3257 if (sz > 0) {
3258 prev_obj += sz;
3259 } else {
3260 // In this case we may end up doing a bit of redundant
3261 // scanning, but that appears unavoidable, short of
3262 // locking the free list locks; see bug 6324141.
3263 break;
3264 }
3265 }
3266 }
3267 if (prev_obj < span.end()) {
3268 MemRegion my_span = MemRegion(prev_obj, span.end());
3269 // Do the marking work within a non-empty span --
3270 // the last argument to the constructor indicates whether the
3271 // iteration should be incremental with periodic yields.
3272 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3273 &_collector->_markBitMap,
3274 work_queue(i),
3275 &_collector->_markStack);
3276 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3277 } // else nothing to do for this task
3278 } // else nothing to do for this task
3279 }
3280 // We'd be tempted to assert here that since there are no
3281 // more tasks left to claim in this space, the global_finger
3282 // must exceed space->top() and a fortiori space->end(). However,
3283 // that would not quite be correct because the bumping of
3284 // global_finger occurs strictly after the claiming of a task,
3285 // so by the time we reach here the global finger may not yet
3286 // have been bumped up by the thread that claimed the last
3287 // task.
3288 pst->all_tasks_completed();
3289 }
3290
3291 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3292 private:
3293 CMSCollector* _collector;
3294 CMSConcMarkingTask* _task;
3295 MemRegion _span;
3296 CMSBitMap* _bit_map;
3297 CMSMarkStack* _overflow_stack;
3298 OopTaskQueue* _work_queue;
3299 protected:
3300 DO_OOP_WORK_DEFN
3301 public:
3302 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3303 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3304 MetadataAwareOopClosure(collector->ref_processor()),
3305 _collector(collector),
3306 _task(task),
3307 _span(collector->_span),
3308 _work_queue(work_queue),
3309 _bit_map(bit_map),
3310 _overflow_stack(overflow_stack)
3311 { }
3312 virtual void do_oop(oop* p);
3313 virtual void do_oop(narrowOop* p);
3314
3315 void trim_queue(size_t max);
3316 void handle_stack_overflow(HeapWord* lost);
3317 void do_yield_check() {
3318 if (_task->should_yield()) {
3319 _task->yield();
3320 }
3321 }
3322 };
3323
3324 // Grey object scanning during work stealing phase --
3325 // the salient assumption here is that any references
3326 // that are in these stolen objects being scanned must
3327 // already have been initialized (else they would not have
3328 // been published), so we do not need to check for
3329 // uninitialized objects before pushing here.
3330 void Par_ConcMarkingClosure::do_oop(oop obj) {
3331 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3332 HeapWord* addr = (HeapWord*)obj;
3333 // Check if oop points into the CMS generation
3334 // and is not marked
3335 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3336 // a white object ...
3337 // If we manage to "claim" the object, by being the
3338 // first thread to mark it, then we push it on our
3339 // marking stack
3340 if (_bit_map->par_mark(addr)) { // ... now grey
3341 // push on work queue (grey set)
3342 bool simulate_overflow = false;
3343 NOT_PRODUCT(
3344 if (CMSMarkStackOverflowALot &&
3345 _collector->simulate_overflow()) {
3346 // simulate a stack overflow
3347 simulate_overflow = true;
3348 }
3349 )
3350 if (simulate_overflow ||
3351 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3352 // stack overflow
3353 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3354 // We cannot assert that the overflow stack is full because
3355 // it may have been emptied since.
3356 assert(simulate_overflow ||
3357 _work_queue->size() == _work_queue->max_elems(),
3358 "Else push should have succeeded");
3359 handle_stack_overflow(addr);
3360 }
3361 } // Else, some other thread got there first
3362 do_yield_check();
3363 }
3364 }
3365
3366 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3367 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3368
3369 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3370 while (_work_queue->size() > max) {
3371 oop new_oop;
3372 if (_work_queue->pop_local(new_oop)) {
3373 assert(new_oop->is_oop(), "Should be an oop");
3374 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3375 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3376 new_oop->oop_iterate(this); // do_oop() above
3377 do_yield_check();
3378 }
3379 }
3380 }
3381
3382 // Upon stack overflow, we discard (part of) the stack,
3383 // remembering the least address amongst those discarded
3384 // in CMSCollector's _restart_address.
3385 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3386 // We need to do this under a mutex to prevent other
3387 // workers from interfering with the work done below.
3388 MutexLockerEx ml(_overflow_stack->par_lock(),
3389 Mutex::_no_safepoint_check_flag);
3390 // Remember the least grey address discarded
3391 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3392 _collector->lower_restart_addr(ra);
3393 _overflow_stack->reset(); // discard stack contents
3394 _overflow_stack->expand(); // expand the stack if possible
3395 }
3396
3397
3398 void CMSConcMarkingTask::do_work_steal(int i) {
3399 OopTaskQueue* work_q = work_queue(i);
3400 oop obj_to_scan;
3401 CMSBitMap* bm = &(_collector->_markBitMap);
3402 CMSMarkStack* ovflw = &(_collector->_markStack);
3403 int* seed = _collector->hash_seed(i);
3404 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3405 while (true) {
3406 cl.trim_queue(0);
3407 assert(work_q->size() == 0, "Should have been emptied above");
3408 if (get_work_from_overflow_stack(ovflw, work_q)) {
3409 // Can't assert below because the work obtained from the
3410 // overflow stack may already have been stolen from us.
3411 // assert(work_q->size() > 0, "Work from overflow stack");
3412 continue;
3413 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3414 assert(obj_to_scan->is_oop(), "Should be an oop");
3415 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3416 obj_to_scan->oop_iterate(&cl);
3417 } else if (terminator()->offer_termination(&_term_term)) {
3418 assert(work_q->size() == 0, "Impossible!");
3419 break;
3420 } else if (yielding() || should_yield()) {
3421 yield();
3422 }
3423 }
3424 }
3425
3426 // This is run by the CMS (coordinator) thread.
3427 void CMSConcMarkingTask::coordinator_yield() {
3428 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3429 "CMS thread should hold CMS token");
3430 // First give up the locks, then yield, then re-lock
3431 // We should probably use a constructor/destructor idiom to
3432 // do this unlock/lock or modify the MutexUnlocker class to
3433 // serve our purpose. XXX
3434 assert_lock_strong(_bit_map_lock);
3435 _bit_map_lock->unlock();
3436 ConcurrentMarkSweepThread::desynchronize(true);
3437 _collector->stopTimer();
3438 _collector->incrementYields();
3439
3440 // It is possible for whichever thread initiated the yield request
3441 // not to get a chance to wake up and take the bitmap lock between
3442 // this thread releasing it and reacquiring it. So, while the
3443 // should_yield() flag is on, let's sleep for a bit to give the
3444 // other thread a chance to wake up. The limit imposed on the number
3445 // of iterations is defensive, to avoid any unforseen circumstances
3446 // putting us into an infinite loop. Since it's always been this
3447 // (coordinator_yield()) method that was observed to cause the
3448 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3449 // which is by default non-zero. For the other seven methods that
3450 // also perform the yield operation, as are using a different
3451 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3452 // can enable the sleeping for those methods too, if necessary.
3453 // See 6442774.
3454 //
3455 // We really need to reconsider the synchronization between the GC
3456 // thread and the yield-requesting threads in the future and we
3457 // should really use wait/notify, which is the recommended
3458 // way of doing this type of interaction. Additionally, we should
3459 // consolidate the eight methods that do the yield operation and they
3460 // are almost identical into one for better maintainability and
3461 // readability. See 6445193.
3462 //
3463 // Tony 2006.06.29
3464 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3465 ConcurrentMarkSweepThread::should_yield() &&
3466 !CMSCollector::foregroundGCIsActive(); ++i) {
3467 os::sleep(Thread::current(), 1, false);
3468 }
3469
3470 ConcurrentMarkSweepThread::synchronize(true);
3471 _bit_map_lock->lock_without_safepoint_check();
3472 _collector->startTimer();
3473 }
3474
3475 bool CMSCollector::do_marking_mt() {
3476 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3477 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3478 conc_workers()->active_workers(),
3479 Threads::number_of_non_daemon_threads());
3480 conc_workers()->set_active_workers(num_workers);
3481
3482 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3483
3484 CMSConcMarkingTask tsk(this,
3485 cms_space,
3486 conc_workers(),
3487 task_queues());
3488
3489 // Since the actual number of workers we get may be different
3490 // from the number we requested above, do we need to do anything different
3491 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3492 // class?? XXX
3493 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3494
3495 // Refs discovery is already non-atomic.
3496 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3497 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3498 conc_workers()->start_task(&tsk);
3499 while (tsk.yielded()) {
3500 tsk.coordinator_yield();
3501 conc_workers()->continue_task(&tsk);
3502 }
3503 // If the task was aborted, _restart_addr will be non-NULL
3504 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3505 while (_restart_addr != NULL) {
3506 // XXX For now we do not make use of ABORTED state and have not
3507 // yet implemented the right abort semantics (even in the original
3508 // single-threaded CMS case). That needs some more investigation
3509 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3510 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3511 // If _restart_addr is non-NULL, a marking stack overflow
3512 // occurred; we need to do a fresh marking iteration from the
3513 // indicated restart address.
3514 if (_foregroundGCIsActive) {
3515 // We may be running into repeated stack overflows, having
3516 // reached the limit of the stack size, while making very
3517 // slow forward progress. It may be best to bail out and
3518 // let the foreground collector do its job.
3519 // Clear _restart_addr, so that foreground GC
3520 // works from scratch. This avoids the headache of
3521 // a "rescan" which would otherwise be needed because
3522 // of the dirty mod union table & card table.
3523 _restart_addr = NULL;
3524 return false;
3525 }
3526 // Adjust the task to restart from _restart_addr
3527 tsk.reset(_restart_addr);
3528 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3529 _restart_addr);
3530 _restart_addr = NULL;
3531 // Get the workers going again
3532 conc_workers()->start_task(&tsk);
3533 while (tsk.yielded()) {
3534 tsk.coordinator_yield();
3535 conc_workers()->continue_task(&tsk);
3536 }
3537 }
3538 assert(tsk.completed(), "Inconsistency");
3539 assert(tsk.result() == true, "Inconsistency");
3540 return true;
3541 }
3542
3543 bool CMSCollector::do_marking_st() {
3544 ResourceMark rm;
3545 HandleMark hm;
3546
3547 // Temporarily make refs discovery single threaded (non-MT)
3548 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3549 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3550 &_markStack, CMSYield);
3551 // the last argument to iterate indicates whether the iteration
3552 // should be incremental with periodic yields.
3553 _markBitMap.iterate(&markFromRootsClosure);
3554 // If _restart_addr is non-NULL, a marking stack overflow
3555 // occurred; we need to do a fresh iteration from the
3556 // indicated restart address.
3557 while (_restart_addr != NULL) {
3558 if (_foregroundGCIsActive) {
3559 // We may be running into repeated stack overflows, having
3560 // reached the limit of the stack size, while making very
3561 // slow forward progress. It may be best to bail out and
3562 // let the foreground collector do its job.
3563 // Clear _restart_addr, so that foreground GC
3564 // works from scratch. This avoids the headache of
3565 // a "rescan" which would otherwise be needed because
3566 // of the dirty mod union table & card table.
3567 _restart_addr = NULL;
3568 return false; // indicating failure to complete marking
3569 }
3570 // Deal with stack overflow:
3571 // we restart marking from _restart_addr
3572 HeapWord* ra = _restart_addr;
3573 markFromRootsClosure.reset(ra);
3574 _restart_addr = NULL;
3575 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3576 }
3577 return true;
3578 }
3579
3580 void CMSCollector::preclean() {
3581 check_correct_thread_executing();
3582 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3583 verify_work_stacks_empty();
3584 verify_overflow_empty();
3585 _abort_preclean = false;
3586 if (CMSPrecleaningEnabled) {
3587 if (!CMSEdenChunksRecordAlways) {
3588 _eden_chunk_index = 0;
3589 }
3590 size_t used = get_eden_used();
3591 size_t capacity = get_eden_capacity();
3592 // Don't start sampling unless we will get sufficiently
3593 // many samples.
3594 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3595 * CMSScheduleRemarkEdenPenetration)) {
3596 _start_sampling = true;
3597 } else {
3598 _start_sampling = false;
3599 }
3600 GCTraceCPUTime tcpu;
3601 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3602 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3603 }
3604 CMSTokenSync x(true); // is cms thread
3605 if (CMSPrecleaningEnabled) {
3606 sample_eden();
3607 _collectorState = AbortablePreclean;
3608 } else {
3609 _collectorState = FinalMarking;
3610 }
3611 verify_work_stacks_empty();
3612 verify_overflow_empty();
3613 }
3614
3615 // Try and schedule the remark such that young gen
3616 // occupancy is CMSScheduleRemarkEdenPenetration %.
3617 void CMSCollector::abortable_preclean() {
3618 check_correct_thread_executing();
3619 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3620 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3621
3622 // If Eden's current occupancy is below this threshold,
3623 // immediately schedule the remark; else preclean
3624 // past the next scavenge in an effort to
3625 // schedule the pause as described above. By choosing
3626 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3627 // we will never do an actual abortable preclean cycle.
3628 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3629 GCTraceCPUTime tcpu;
3630 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3631 // We need more smarts in the abortable preclean
3632 // loop below to deal with cases where allocation
3633 // in young gen is very very slow, and our precleaning
3634 // is running a losing race against a horde of
3635 // mutators intent on flooding us with CMS updates
3636 // (dirty cards).
3637 // One, admittedly dumb, strategy is to give up
3638 // after a certain number of abortable precleaning loops
3639 // or after a certain maximum time. We want to make
3640 // this smarter in the next iteration.
3641 // XXX FIX ME!!! YSR
3642 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3643 while (!(should_abort_preclean() ||
3644 ConcurrentMarkSweepThread::should_terminate())) {
3645 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3646 cumworkdone += workdone;
3647 loops++;
3648 // Voluntarily terminate abortable preclean phase if we have
3649 // been at it for too long.
3650 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3651 loops >= CMSMaxAbortablePrecleanLoops) {
3652 log_debug(gc)(" CMS: abort preclean due to loops ");
3653 break;
3654 }
3655 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3656 log_debug(gc)(" CMS: abort preclean due to time ");
3657 break;
3658 }
3659 // If we are doing little work each iteration, we should
3660 // take a short break.
3661 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3662 // Sleep for some time, waiting for work to accumulate
3663 stopTimer();
3664 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3665 startTimer();
3666 waited++;
3667 }
3668 }
3669 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3670 loops, waited, cumworkdone);
3671 }
3672 CMSTokenSync x(true); // is cms thread
3673 if (_collectorState != Idling) {
3674 assert(_collectorState == AbortablePreclean,
3675 "Spontaneous state transition?");
3676 _collectorState = FinalMarking;
3677 } // Else, a foreground collection completed this CMS cycle.
3678 return;
3679 }
3680
3681 // Respond to an Eden sampling opportunity
3682 void CMSCollector::sample_eden() {
3683 // Make sure a young gc cannot sneak in between our
3684 // reading and recording of a sample.
3685 assert(Thread::current()->is_ConcurrentGC_thread(),
3686 "Only the cms thread may collect Eden samples");
3687 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3688 "Should collect samples while holding CMS token");
3689 if (!_start_sampling) {
3690 return;
3691 }
3692 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3693 // is populated by the young generation.
3694 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3695 if (_eden_chunk_index < _eden_chunk_capacity) {
3696 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3697 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3698 "Unexpected state of Eden");
3699 // We'd like to check that what we just sampled is an oop-start address;
3700 // however, we cannot do that here since the object may not yet have been
3701 // initialized. So we'll instead do the check when we _use_ this sample
3702 // later.
3703 if (_eden_chunk_index == 0 ||
3704 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3705 _eden_chunk_array[_eden_chunk_index-1])
3706 >= CMSSamplingGrain)) {
3707 _eden_chunk_index++; // commit sample
3708 }
3709 }
3710 }
3711 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3712 size_t used = get_eden_used();
3713 size_t capacity = get_eden_capacity();
3714 assert(used <= capacity, "Unexpected state of Eden");
3715 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3716 _abort_preclean = true;
3717 }
3718 }
3719 }
3720
3721
3722 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3723 assert(_collectorState == Precleaning ||
3724 _collectorState == AbortablePreclean, "incorrect state");
3725 ResourceMark rm;
3726 HandleMark hm;
3727
3728 // Precleaning is currently not MT but the reference processor
3729 // may be set for MT. Disable it temporarily here.
3730 ReferenceProcessor* rp = ref_processor();
3731 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3732
3733 // Do one pass of scrubbing the discovered reference lists
3734 // to remove any reference objects with strongly-reachable
3735 // referents.
3736 if (clean_refs) {
3737 CMSPrecleanRefsYieldClosure yield_cl(this);
3738 assert(rp->span().equals(_span), "Spans should be equal");
3739 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3740 &_markStack, true /* preclean */);
3741 CMSDrainMarkingStackClosure complete_trace(this,
3742 _span, &_markBitMap, &_markStack,
3743 &keep_alive, true /* preclean */);
3744
3745 // We don't want this step to interfere with a young
3746 // collection because we don't want to take CPU
3747 // or memory bandwidth away from the young GC threads
3748 // (which may be as many as there are CPUs).
3749 // Note that we don't need to protect ourselves from
3750 // interference with mutators because they can't
3751 // manipulate the discovered reference lists nor affect
3752 // the computed reachability of the referents, the
3753 // only properties manipulated by the precleaning
3754 // of these reference lists.
3755 stopTimer();
3756 CMSTokenSyncWithLocks x(true /* is cms thread */,
3757 bitMapLock());
3758 startTimer();
3759 sample_eden();
3760
3761 // The following will yield to allow foreground
3762 // collection to proceed promptly. XXX YSR:
3763 // The code in this method may need further
3764 // tweaking for better performance and some restructuring
3765 // for cleaner interfaces.
3766 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3767 rp->preclean_discovered_references(
3768 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3769 gc_timer);
3770 }
3771
3772 if (clean_survivor) { // preclean the active survivor space(s)
3773 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3774 &_markBitMap, &_modUnionTable,
3775 &_markStack, true /* precleaning phase */);
3776 stopTimer();
3777 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3778 bitMapLock());
3779 startTimer();
3780 unsigned int before_count =
3781 GenCollectedHeap::heap()->total_collections();
3782 SurvivorSpacePrecleanClosure
3783 sss_cl(this, _span, &_markBitMap, &_markStack,
3784 &pam_cl, before_count, CMSYield);
3785 _young_gen->from()->object_iterate_careful(&sss_cl);
3786 _young_gen->to()->object_iterate_careful(&sss_cl);
3787 }
3788 MarkRefsIntoAndScanClosure
3789 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3790 &_markStack, this, CMSYield,
3791 true /* precleaning phase */);
3792 // CAUTION: The following closure has persistent state that may need to
3793 // be reset upon a decrease in the sequence of addresses it
3794 // processes.
3795 ScanMarkedObjectsAgainCarefullyClosure
3796 smoac_cl(this, _span,
3797 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3798
3799 // Preclean dirty cards in ModUnionTable and CardTable using
3800 // appropriate convergence criterion;
3801 // repeat CMSPrecleanIter times unless we find that
3802 // we are losing.
3803 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3804 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3805 "Bad convergence multiplier");
3806 assert(CMSPrecleanThreshold >= 100,
3807 "Unreasonably low CMSPrecleanThreshold");
3808
3809 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3810 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3811 numIter < CMSPrecleanIter;
3812 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3813 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3814 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3815 // Either there are very few dirty cards, so re-mark
3816 // pause will be small anyway, or our pre-cleaning isn't
3817 // that much faster than the rate at which cards are being
3818 // dirtied, so we might as well stop and re-mark since
3819 // precleaning won't improve our re-mark time by much.
3820 if (curNumCards <= CMSPrecleanThreshold ||
3821 (numIter > 0 &&
3822 (curNumCards * CMSPrecleanDenominator >
3823 lastNumCards * CMSPrecleanNumerator))) {
3824 numIter++;
3825 cumNumCards += curNumCards;
3826 break;
3827 }
3828 }
3829
3830 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3831
3832 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3833 cumNumCards += curNumCards;
3834 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3835 curNumCards, cumNumCards, numIter);
3836 return cumNumCards; // as a measure of useful work done
3837 }
3838
3839 // PRECLEANING NOTES:
3840 // Precleaning involves:
3841 // . reading the bits of the modUnionTable and clearing the set bits.
3842 // . For the cards corresponding to the set bits, we scan the
3843 // objects on those cards. This means we need the free_list_lock
3844 // so that we can safely iterate over the CMS space when scanning
3845 // for oops.
3846 // . When we scan the objects, we'll be both reading and setting
3847 // marks in the marking bit map, so we'll need the marking bit map.
3848 // . For protecting _collector_state transitions, we take the CGC_lock.
3849 // Note that any races in the reading of of card table entries by the
3850 // CMS thread on the one hand and the clearing of those entries by the
3851 // VM thread or the setting of those entries by the mutator threads on the
3852 // other are quite benign. However, for efficiency it makes sense to keep
3853 // the VM thread from racing with the CMS thread while the latter is
3854 // dirty card info to the modUnionTable. We therefore also use the
3855 // CGC_lock to protect the reading of the card table and the mod union
3856 // table by the CM thread.
3857 // . We run concurrently with mutator updates, so scanning
3858 // needs to be done carefully -- we should not try to scan
3859 // potentially uninitialized objects.
3860 //
3861 // Locking strategy: While holding the CGC_lock, we scan over and
3862 // reset a maximal dirty range of the mod union / card tables, then lock
3863 // the free_list_lock and bitmap lock to do a full marking, then
3864 // release these locks; and repeat the cycle. This allows for a
3865 // certain amount of fairness in the sharing of these locks between
3866 // the CMS collector on the one hand, and the VM thread and the
3867 // mutators on the other.
3868
3869 // NOTE: preclean_mod_union_table() and preclean_card_table()
3870 // further below are largely identical; if you need to modify
3871 // one of these methods, please check the other method too.
3872
3873 size_t CMSCollector::preclean_mod_union_table(
3874 ConcurrentMarkSweepGeneration* old_gen,
3875 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3876 verify_work_stacks_empty();
3877 verify_overflow_empty();
3878
3879 // strategy: starting with the first card, accumulate contiguous
3880 // ranges of dirty cards; clear these cards, then scan the region
3881 // covered by these cards.
3882
3883 // Since all of the MUT is committed ahead, we can just use
3884 // that, in case the generations expand while we are precleaning.
3885 // It might also be fine to just use the committed part of the
3886 // generation, but we might potentially miss cards when the
3887 // generation is rapidly expanding while we are in the midst
3888 // of precleaning.
3889 HeapWord* startAddr = old_gen->reserved().start();
3890 HeapWord* endAddr = old_gen->reserved().end();
3891
3892 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3893
3894 size_t numDirtyCards, cumNumDirtyCards;
3895 HeapWord *nextAddr, *lastAddr;
3896 for (cumNumDirtyCards = numDirtyCards = 0,
3897 nextAddr = lastAddr = startAddr;
3898 nextAddr < endAddr;
3899 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3900
3901 ResourceMark rm;
3902 HandleMark hm;
3903
3904 MemRegion dirtyRegion;
3905 {
3906 stopTimer();
3907 // Potential yield point
3908 CMSTokenSync ts(true);
3909 startTimer();
3910 sample_eden();
3911 // Get dirty region starting at nextOffset (inclusive),
3912 // simultaneously clearing it.
3913 dirtyRegion =
3914 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3915 assert(dirtyRegion.start() >= nextAddr,
3916 "returned region inconsistent?");
3917 }
3918 // Remember where the next search should begin.
3919 // The returned region (if non-empty) is a right open interval,
3920 // so lastOffset is obtained from the right end of that
3921 // interval.
3922 lastAddr = dirtyRegion.end();
3923 // Should do something more transparent and less hacky XXX
3924 numDirtyCards =
3925 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3926
3927 // We'll scan the cards in the dirty region (with periodic
3928 // yields for foreground GC as needed).
3929 if (!dirtyRegion.is_empty()) {
3930 assert(numDirtyCards > 0, "consistency check");
3931 HeapWord* stop_point = NULL;
3932 stopTimer();
3933 // Potential yield point
3934 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3935 bitMapLock());
3936 startTimer();
3937 {
3938 verify_work_stacks_empty();
3939 verify_overflow_empty();
3940 sample_eden();
3941 stop_point =
3942 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3943 }
3944 if (stop_point != NULL) {
3945 // The careful iteration stopped early either because it found an
3946 // uninitialized object, or because we were in the midst of an
3947 // "abortable preclean", which should now be aborted. Redirty
3948 // the bits corresponding to the partially-scanned or unscanned
3949 // cards. We'll either restart at the next block boundary or
3950 // abort the preclean.
3951 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3952 "Should only be AbortablePreclean.");
3953 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3954 if (should_abort_preclean()) {
3955 break; // out of preclean loop
3956 } else {
3957 // Compute the next address at which preclean should pick up;
3958 // might need bitMapLock in order to read P-bits.
3959 lastAddr = next_card_start_after_block(stop_point);
3960 }
3961 }
3962 } else {
3963 assert(lastAddr == endAddr, "consistency check");
3964 assert(numDirtyCards == 0, "consistency check");
3965 break;
3966 }
3967 }
3968 verify_work_stacks_empty();
3969 verify_overflow_empty();
3970 return cumNumDirtyCards;
3971 }
3972
3973 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3974 // below are largely identical; if you need to modify
3975 // one of these methods, please check the other method too.
3976
3977 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3978 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3979 // strategy: it's similar to precleamModUnionTable above, in that
3980 // we accumulate contiguous ranges of dirty cards, mark these cards
3981 // precleaned, then scan the region covered by these cards.
3982 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
3983 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3984
3985 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3986
3987 size_t numDirtyCards, cumNumDirtyCards;
3988 HeapWord *lastAddr, *nextAddr;
3989
3990 for (cumNumDirtyCards = numDirtyCards = 0,
3991 nextAddr = lastAddr = startAddr;
3992 nextAddr < endAddr;
3993 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3994
3995 ResourceMark rm;
3996 HandleMark hm;
3997
3998 MemRegion dirtyRegion;
3999 {
4000 // See comments in "Precleaning notes" above on why we
4001 // do this locking. XXX Could the locking overheads be
4002 // too high when dirty cards are sparse? [I don't think so.]
4003 stopTimer();
4004 CMSTokenSync x(true); // is cms thread
4005 startTimer();
4006 sample_eden();
4007 // Get and clear dirty region from card table
4008 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4009 MemRegion(nextAddr, endAddr),
4010 true,
4011 CardTableModRefBS::precleaned_card_val());
4012
4013 assert(dirtyRegion.start() >= nextAddr,
4014 "returned region inconsistent?");
4015 }
4016 lastAddr = dirtyRegion.end();
4017 numDirtyCards =
4018 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4019
4020 if (!dirtyRegion.is_empty()) {
4021 stopTimer();
4022 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4023 startTimer();
4024 sample_eden();
4025 verify_work_stacks_empty();
4026 verify_overflow_empty();
4027 HeapWord* stop_point =
4028 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4029 if (stop_point != NULL) {
4030 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4031 "Should only be AbortablePreclean.");
4032 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4033 if (should_abort_preclean()) {
4034 break; // out of preclean loop
4035 } else {
4036 // Compute the next address at which preclean should pick up.
4037 lastAddr = next_card_start_after_block(stop_point);
4038 }
4039 }
4040 } else {
4041 break;
4042 }
4043 }
4044 verify_work_stacks_empty();
4045 verify_overflow_empty();
4046 return cumNumDirtyCards;
4047 }
4048
4049 class PrecleanKlassClosure : public KlassClosure {
4050 KlassToOopClosure _cm_klass_closure;
4051 public:
4052 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4053 void do_klass(Klass* k) {
4054 if (k->has_accumulated_modified_oops()) {
4055 k->clear_accumulated_modified_oops();
4056
4057 _cm_klass_closure.do_klass(k);
4058 }
4059 }
4060 };
4061
4062 // The freelist lock is needed to prevent asserts, is it really needed?
4063 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4064
4065 cl->set_freelistLock(freelistLock);
4066
4067 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4068
4069 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4070 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4071 PrecleanKlassClosure preclean_klass_closure(cl);
4072 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4073
4074 verify_work_stacks_empty();
4075 verify_overflow_empty();
4076 }
4077
4078 void CMSCollector::checkpointRootsFinal() {
4079 assert(_collectorState == FinalMarking, "incorrect state transition?");
4080 check_correct_thread_executing();
4081 // world is stopped at this checkpoint
4082 assert(SafepointSynchronize::is_at_safepoint(),
4083 "world should be stopped");
4084 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4085
4086 verify_work_stacks_empty();
4087 verify_overflow_empty();
4088
4089 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4090 _young_gen->used() / K, _young_gen->capacity() / K);
4091 {
4092 if (CMSScavengeBeforeRemark) {
4093 GenCollectedHeap* gch = GenCollectedHeap::heap();
4094 // Temporarily set flag to false, GCH->do_collection will
4095 // expect it to be false and set to true
4096 FlagSetting fl(gch->_is_gc_active, false);
4097
4098 GCTraceTime(Trace, gc) tm("Pause Scavenge Before Remark", _gc_timer_cm);
4099
4100 gch->do_collection(true, // full (i.e. force, see below)
4101 false, // !clear_all_soft_refs
4102 0, // size
4103 false, // is_tlab
4104 GenCollectedHeap::YoungGen // type
4105 );
4106 }
4107 FreelistLocker x(this);
4108 MutexLockerEx y(bitMapLock(),
4109 Mutex::_no_safepoint_check_flag);
4110 checkpointRootsFinalWork();
4111 }
4112 verify_work_stacks_empty();
4113 verify_overflow_empty();
4114 }
4115
4116 void CMSCollector::checkpointRootsFinalWork() {
4117 GCTraceTime(Trace, gc) tm("checkpointRootsFinalWork", _gc_timer_cm);
4118
4119 assert(haveFreelistLocks(), "must have free list locks");
4120 assert_lock_strong(bitMapLock());
4121
4122 ResourceMark rm;
4123 HandleMark hm;
4124
4125 GenCollectedHeap* gch = GenCollectedHeap::heap();
4126
4127 if (should_unload_classes()) {
4128 CodeCache::gc_prologue();
4129 }
4130 assert(haveFreelistLocks(), "must have free list locks");
4131 assert_lock_strong(bitMapLock());
4132
4133 // We might assume that we need not fill TLAB's when
4134 // CMSScavengeBeforeRemark is set, because we may have just done
4135 // a scavenge which would have filled all TLAB's -- and besides
4136 // Eden would be empty. This however may not always be the case --
4137 // for instance although we asked for a scavenge, it may not have
4138 // happened because of a JNI critical section. We probably need
4139 // a policy for deciding whether we can in that case wait until
4140 // the critical section releases and then do the remark following
4141 // the scavenge, and skip it here. In the absence of that policy,
4142 // or of an indication of whether the scavenge did indeed occur,
4143 // we cannot rely on TLAB's having been filled and must do
4144 // so here just in case a scavenge did not happen.
4145 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4146 // Update the saved marks which may affect the root scans.
4147 gch->save_marks();
4148
4149 print_eden_and_survivor_chunk_arrays();
4150
4151 {
4152 #if defined(COMPILER2) || INCLUDE_JVMCI
4153 DerivedPointerTableDeactivate dpt_deact;
4154 #endif
4155
4156 // Note on the role of the mod union table:
4157 // Since the marker in "markFromRoots" marks concurrently with
4158 // mutators, it is possible for some reachable objects not to have been
4159 // scanned. For instance, an only reference to an object A was
4160 // placed in object B after the marker scanned B. Unless B is rescanned,
4161 // A would be collected. Such updates to references in marked objects
4162 // are detected via the mod union table which is the set of all cards
4163 // dirtied since the first checkpoint in this GC cycle and prior to
4164 // the most recent young generation GC, minus those cleaned up by the
4165 // concurrent precleaning.
4166 if (CMSParallelRemarkEnabled) {
4167 GCTraceTime(Debug, gc) t("Rescan (parallel)", _gc_timer_cm);
4168 do_remark_parallel();
4169 } else {
4170 GCTraceTime(Debug, gc) t("Rescan (non-parallel)", _gc_timer_cm);
4171 do_remark_non_parallel();
4172 }
4173 }
4174 verify_work_stacks_empty();
4175 verify_overflow_empty();
4176
4177 {
4178 GCTraceTime(Trace, gc) ts("refProcessingWork", _gc_timer_cm);
4179 refProcessingWork();
4180 }
4181 verify_work_stacks_empty();
4182 verify_overflow_empty();
4183
4184 if (should_unload_classes()) {
4185 CodeCache::gc_epilogue();
4186 }
4187 JvmtiExport::gc_epilogue();
4188
4189 // If we encountered any (marking stack / work queue) overflow
4190 // events during the current CMS cycle, take appropriate
4191 // remedial measures, where possible, so as to try and avoid
4192 // recurrence of that condition.
4193 assert(_markStack.isEmpty(), "No grey objects");
4194 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4195 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4196 if (ser_ovflw > 0) {
4197 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4198 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4199 _markStack.expand();
4200 _ser_pmc_remark_ovflw = 0;
4201 _ser_pmc_preclean_ovflw = 0;
4202 _ser_kac_preclean_ovflw = 0;
4203 _ser_kac_ovflw = 0;
4204 }
4205 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4206 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4207 _par_pmc_remark_ovflw, _par_kac_ovflw);
4208 _par_pmc_remark_ovflw = 0;
4209 _par_kac_ovflw = 0;
4210 }
4211 if (_markStack._hit_limit > 0) {
4212 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4213 _markStack._hit_limit);
4214 }
4215 if (_markStack._failed_double > 0) {
4216 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4217 _markStack._failed_double, _markStack.capacity());
4218 }
4219 _markStack._hit_limit = 0;
4220 _markStack._failed_double = 0;
4221
4222 if ((VerifyAfterGC || VerifyDuringGC) &&
4223 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4224 verify_after_remark();
4225 }
4226
4227 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4228
4229 // Change under the freelistLocks.
4230 _collectorState = Sweeping;
4231 // Call isAllClear() under bitMapLock
4232 assert(_modUnionTable.isAllClear(),
4233 "Should be clear by end of the final marking");
4234 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4235 "Should be clear by end of the final marking");
4236 }
4237
4238 void CMSParInitialMarkTask::work(uint worker_id) {
4239 elapsedTimer _timer;
4240 ResourceMark rm;
4241 HandleMark hm;
4242
4243 // ---------- scan from roots --------------
4244 _timer.start();
4245 GenCollectedHeap* gch = GenCollectedHeap::heap();
4246 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4247
4248 // ---------- young gen roots --------------
4249 {
4250 work_on_young_gen_roots(worker_id, &par_mri_cl);
4251 _timer.stop();
4252 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4253 }
4254
4255 // ---------- remaining roots --------------
4256 _timer.reset();
4257 _timer.start();
4258
4259 CLDToOopClosure cld_closure(&par_mri_cl, true);
4260
4261 gch->gen_process_roots(_strong_roots_scope,
4262 GenCollectedHeap::OldGen,
4263 false, // yg was scanned above
4264 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4265 _collector->should_unload_classes(),
4266 &par_mri_cl,
4267 NULL,
4268 &cld_closure);
4269 assert(_collector->should_unload_classes()
4270 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4271 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4272 _timer.stop();
4273 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4274 }
4275
4276 // Parallel remark task
4277 class CMSParRemarkTask: public CMSParMarkTask {
4278 CompactibleFreeListSpace* _cms_space;
4279
4280 // The per-thread work queues, available here for stealing.
4281 OopTaskQueueSet* _task_queues;
4282 ParallelTaskTerminator _term;
4283 StrongRootsScope* _strong_roots_scope;
4284
4285 public:
4286 // A value of 0 passed to n_workers will cause the number of
4287 // workers to be taken from the active workers in the work gang.
4288 CMSParRemarkTask(CMSCollector* collector,
4289 CompactibleFreeListSpace* cms_space,
4290 uint n_workers, WorkGang* workers,
4291 OopTaskQueueSet* task_queues,
4292 StrongRootsScope* strong_roots_scope):
4293 CMSParMarkTask("Rescan roots and grey objects in parallel",
4294 collector, n_workers),
4295 _cms_space(cms_space),
4296 _task_queues(task_queues),
4297 _term(n_workers, task_queues),
4298 _strong_roots_scope(strong_roots_scope) { }
4299
4300 OopTaskQueueSet* task_queues() { return _task_queues; }
4301
4302 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4303
4304 ParallelTaskTerminator* terminator() { return &_term; }
4305 uint n_workers() { return _n_workers; }
4306
4307 void work(uint worker_id);
4308
4309 private:
4310 // ... of dirty cards in old space
4311 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4312 Par_MarkRefsIntoAndScanClosure* cl);
4313
4314 // ... work stealing for the above
4315 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4316 };
4317
4318 class RemarkKlassClosure : public KlassClosure {
4319 KlassToOopClosure _cm_klass_closure;
4320 public:
4321 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4322 void do_klass(Klass* k) {
4323 // Check if we have modified any oops in the Klass during the concurrent marking.
4324 if (k->has_accumulated_modified_oops()) {
4325 k->clear_accumulated_modified_oops();
4326
4327 // We could have transfered the current modified marks to the accumulated marks,
4328 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4329 } else if (k->has_modified_oops()) {
4330 // Don't clear anything, this info is needed by the next young collection.
4331 } else {
4332 // No modified oops in the Klass.
4333 return;
4334 }
4335
4336 // The klass has modified fields, need to scan the klass.
4337 _cm_klass_closure.do_klass(k);
4338 }
4339 };
4340
4341 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4342 ParNewGeneration* young_gen = _collector->_young_gen;
4343 ContiguousSpace* eden_space = young_gen->eden();
4344 ContiguousSpace* from_space = young_gen->from();
4345 ContiguousSpace* to_space = young_gen->to();
4346
4347 HeapWord** eca = _collector->_eden_chunk_array;
4348 size_t ect = _collector->_eden_chunk_index;
4349 HeapWord** sca = _collector->_survivor_chunk_array;
4350 size_t sct = _collector->_survivor_chunk_index;
4351
4352 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4353 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4354
4355 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4356 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4357 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4358 }
4359
4360 // work_queue(i) is passed to the closure
4361 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4362 // also is passed to do_dirty_card_rescan_tasks() and to
4363 // do_work_steal() to select the i-th task_queue.
4364
4365 void CMSParRemarkTask::work(uint worker_id) {
4366 elapsedTimer _timer;
4367 ResourceMark rm;
4368 HandleMark hm;
4369
4370 // ---------- rescan from roots --------------
4371 _timer.start();
4372 GenCollectedHeap* gch = GenCollectedHeap::heap();
4373 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4374 _collector->_span, _collector->ref_processor(),
4375 &(_collector->_markBitMap),
4376 work_queue(worker_id));
4377
4378 // Rescan young gen roots first since these are likely
4379 // coarsely partitioned and may, on that account, constitute
4380 // the critical path; thus, it's best to start off that
4381 // work first.
4382 // ---------- young gen roots --------------
4383 {
4384 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4385 _timer.stop();
4386 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4387 }
4388
4389 // ---------- remaining roots --------------
4390 _timer.reset();
4391 _timer.start();
4392 gch->gen_process_roots(_strong_roots_scope,
4393 GenCollectedHeap::OldGen,
4394 false, // yg was scanned above
4395 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4396 _collector->should_unload_classes(),
4397 &par_mrias_cl,
4398 NULL,
4399 NULL); // The dirty klasses will be handled below
4400
4401 assert(_collector->should_unload_classes()
4402 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4403 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4404 _timer.stop();
4405 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4406
4407 // ---------- unhandled CLD scanning ----------
4408 if (worker_id == 0) { // Single threaded at the moment.
4409 _timer.reset();
4410 _timer.start();
4411
4412 // Scan all new class loader data objects and new dependencies that were
4413 // introduced during concurrent marking.
4414 ResourceMark rm;
4415 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4416 for (int i = 0; i < array->length(); i++) {
4417 par_mrias_cl.do_cld_nv(array->at(i));
4418 }
4419
4420 // We don't need to keep track of new CLDs anymore.
4421 ClassLoaderDataGraph::remember_new_clds(false);
4422
4423 _timer.stop();
4424 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4425 }
4426
4427 // ---------- dirty klass scanning ----------
4428 if (worker_id == 0) { // Single threaded at the moment.
4429 _timer.reset();
4430 _timer.start();
4431
4432 // Scan all classes that was dirtied during the concurrent marking phase.
4433 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4434 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4435
4436 _timer.stop();
4437 log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4438 }
4439
4440 // We might have added oops to ClassLoaderData::_handles during the
4441 // concurrent marking phase. These oops point to newly allocated objects
4442 // that are guaranteed to be kept alive. Either by the direct allocation
4443 // code, or when the young collector processes the roots. Hence,
4444 // we don't have to revisit the _handles block during the remark phase.
4445
4446 // ---------- rescan dirty cards ------------
4447 _timer.reset();
4448 _timer.start();
4449
4450 // Do the rescan tasks for each of the two spaces
4451 // (cms_space) in turn.
4452 // "worker_id" is passed to select the task_queue for "worker_id"
4453 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4454 _timer.stop();
4455 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4456
4457 // ---------- steal work from other threads ...
4458 // ---------- ... and drain overflow list.
4459 _timer.reset();
4460 _timer.start();
4461 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4462 _timer.stop();
4463 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4464 }
4465
4466 // Note that parameter "i" is not used.
4467 void
4468 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4469 OopsInGenClosure* cl, ContiguousSpace* space,
4470 HeapWord** chunk_array, size_t chunk_top) {
4471 // Until all tasks completed:
4472 // . claim an unclaimed task
4473 // . compute region boundaries corresponding to task claimed
4474 // using chunk_array
4475 // . par_oop_iterate(cl) over that region
4476
4477 ResourceMark rm;
4478 HandleMark hm;
4479
4480 SequentialSubTasksDone* pst = space->par_seq_tasks();
4481
4482 uint nth_task = 0;
4483 uint n_tasks = pst->n_tasks();
4484
4485 if (n_tasks > 0) {
4486 assert(pst->valid(), "Uninitialized use?");
4487 HeapWord *start, *end;
4488 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4489 // We claimed task # nth_task; compute its boundaries.
4490 if (chunk_top == 0) { // no samples were taken
4491 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4492 start = space->bottom();
4493 end = space->top();
4494 } else if (nth_task == 0) {
4495 start = space->bottom();
4496 end = chunk_array[nth_task];
4497 } else if (nth_task < (uint)chunk_top) {
4498 assert(nth_task >= 1, "Control point invariant");
4499 start = chunk_array[nth_task - 1];
4500 end = chunk_array[nth_task];
4501 } else {
4502 assert(nth_task == (uint)chunk_top, "Control point invariant");
4503 start = chunk_array[chunk_top - 1];
4504 end = space->top();
4505 }
4506 MemRegion mr(start, end);
4507 // Verify that mr is in space
4508 assert(mr.is_empty() || space->used_region().contains(mr),
4509 "Should be in space");
4510 // Verify that "start" is an object boundary
4511 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4512 "Should be an oop");
4513 space->par_oop_iterate(mr, cl);
4514 }
4515 pst->all_tasks_completed();
4516 }
4517 }
4518
4519 void
4520 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4521 CompactibleFreeListSpace* sp, int i,
4522 Par_MarkRefsIntoAndScanClosure* cl) {
4523 // Until all tasks completed:
4524 // . claim an unclaimed task
4525 // . compute region boundaries corresponding to task claimed
4526 // . transfer dirty bits ct->mut for that region
4527 // . apply rescanclosure to dirty mut bits for that region
4528
4529 ResourceMark rm;
4530 HandleMark hm;
4531
4532 OopTaskQueue* work_q = work_queue(i);
4533 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4534 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4535 // CAUTION: This closure has state that persists across calls to
4536 // the work method dirty_range_iterate_clear() in that it has
4537 // embedded in it a (subtype of) UpwardsObjectClosure. The
4538 // use of that state in the embedded UpwardsObjectClosure instance
4539 // assumes that the cards are always iterated (even if in parallel
4540 // by several threads) in monotonically increasing order per each
4541 // thread. This is true of the implementation below which picks
4542 // card ranges (chunks) in monotonically increasing order globally
4543 // and, a-fortiori, in monotonically increasing order per thread
4544 // (the latter order being a subsequence of the former).
4545 // If the work code below is ever reorganized into a more chaotic
4546 // work-partitioning form than the current "sequential tasks"
4547 // paradigm, the use of that persistent state will have to be
4548 // revisited and modified appropriately. See also related
4549 // bug 4756801 work on which should examine this code to make
4550 // sure that the changes there do not run counter to the
4551 // assumptions made here and necessary for correctness and
4552 // efficiency. Note also that this code might yield inefficient
4553 // behavior in the case of very large objects that span one or
4554 // more work chunks. Such objects would potentially be scanned
4555 // several times redundantly. Work on 4756801 should try and
4556 // address that performance anomaly if at all possible. XXX
4557 MemRegion full_span = _collector->_span;
4558 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4559 MarkFromDirtyCardsClosure
4560 greyRescanClosure(_collector, full_span, // entire span of interest
4561 sp, bm, work_q, cl);
4562
4563 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4564 assert(pst->valid(), "Uninitialized use?");
4565 uint nth_task = 0;
4566 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4567 MemRegion span = sp->used_region();
4568 HeapWord* start_addr = span.start();
4569 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4570 alignment);
4571 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4572 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4573 start_addr, "Check alignment");
4574 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4575 chunk_size, "Check alignment");
4576
4577 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4578 // Having claimed the nth_task, compute corresponding mem-region,
4579 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4580 // The alignment restriction ensures that we do not need any
4581 // synchronization with other gang-workers while setting or
4582 // clearing bits in thus chunk of the MUT.
4583 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4584 start_addr + (nth_task+1)*chunk_size);
4585 // The last chunk's end might be way beyond end of the
4586 // used region. In that case pull back appropriately.
4587 if (this_span.end() > end_addr) {
4588 this_span.set_end(end_addr);
4589 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4590 }
4591 // Iterate over the dirty cards covering this chunk, marking them
4592 // precleaned, and setting the corresponding bits in the mod union
4593 // table. Since we have been careful to partition at Card and MUT-word
4594 // boundaries no synchronization is needed between parallel threads.
4595 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4596 &modUnionClosure);
4597
4598 // Having transferred these marks into the modUnionTable,
4599 // rescan the marked objects on the dirty cards in the modUnionTable.
4600 // Even if this is at a synchronous collection, the initial marking
4601 // may have been done during an asynchronous collection so there
4602 // may be dirty bits in the mod-union table.
4603 _collector->_modUnionTable.dirty_range_iterate_clear(
4604 this_span, &greyRescanClosure);
4605 _collector->_modUnionTable.verifyNoOneBitsInRange(
4606 this_span.start(),
4607 this_span.end());
4608 }
4609 pst->all_tasks_completed(); // declare that i am done
4610 }
4611
4612 // . see if we can share work_queues with ParNew? XXX
4613 void
4614 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4615 int* seed) {
4616 OopTaskQueue* work_q = work_queue(i);
4617 NOT_PRODUCT(int num_steals = 0;)
4618 oop obj_to_scan;
4619 CMSBitMap* bm = &(_collector->_markBitMap);
4620
4621 while (true) {
4622 // Completely finish any left over work from (an) earlier round(s)
4623 cl->trim_queue(0);
4624 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4625 (size_t)ParGCDesiredObjsFromOverflowList);
4626 // Now check if there's any work in the overflow list
4627 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4628 // only affects the number of attempts made to get work from the
4629 // overflow list and does not affect the number of workers. Just
4630 // pass ParallelGCThreads so this behavior is unchanged.
4631 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4632 work_q,
4633 ParallelGCThreads)) {
4634 // found something in global overflow list;
4635 // not yet ready to go stealing work from others.
4636 // We'd like to assert(work_q->size() != 0, ...)
4637 // because we just took work from the overflow list,
4638 // but of course we can't since all of that could have
4639 // been already stolen from us.
4640 // "He giveth and He taketh away."
4641 continue;
4642 }
4643 // Verify that we have no work before we resort to stealing
4644 assert(work_q->size() == 0, "Have work, shouldn't steal");
4645 // Try to steal from other queues that have work
4646 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4647 NOT_PRODUCT(num_steals++;)
4648 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4649 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4650 // Do scanning work
4651 obj_to_scan->oop_iterate(cl);
4652 // Loop around, finish this work, and try to steal some more
4653 } else if (terminator()->offer_termination()) {
4654 break; // nirvana from the infinite cycle
4655 }
4656 }
4657 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4658 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4659 "Else our work is not yet done");
4660 }
4661
4662 // Record object boundaries in _eden_chunk_array by sampling the eden
4663 // top in the slow-path eden object allocation code path and record
4664 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4665 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4666 // sampling in sample_eden() that activates during the part of the
4667 // preclean phase.
4668 void CMSCollector::sample_eden_chunk() {
4669 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4670 if (_eden_chunk_lock->try_lock()) {
4671 // Record a sample. This is the critical section. The contents
4672 // of the _eden_chunk_array have to be non-decreasing in the
4673 // address order.
4674 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4675 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4676 "Unexpected state of Eden");
4677 if (_eden_chunk_index == 0 ||
4678 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4679 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4680 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4681 _eden_chunk_index++; // commit sample
4682 }
4683 _eden_chunk_lock->unlock();
4684 }
4685 }
4686 }
4687
4688 // Return a thread-local PLAB recording array, as appropriate.
4689 void* CMSCollector::get_data_recorder(int thr_num) {
4690 if (_survivor_plab_array != NULL &&
4691 (CMSPLABRecordAlways ||
4692 (_collectorState > Marking && _collectorState < FinalMarking))) {
4693 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4694 ChunkArray* ca = &_survivor_plab_array[thr_num];
4695 ca->reset(); // clear it so that fresh data is recorded
4696 return (void*) ca;
4697 } else {
4698 return NULL;
4699 }
4700 }
4701
4702 // Reset all the thread-local PLAB recording arrays
4703 void CMSCollector::reset_survivor_plab_arrays() {
4704 for (uint i = 0; i < ParallelGCThreads; i++) {
4705 _survivor_plab_array[i].reset();
4706 }
4707 }
4708
4709 // Merge the per-thread plab arrays into the global survivor chunk
4710 // array which will provide the partitioning of the survivor space
4711 // for CMS initial scan and rescan.
4712 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4713 int no_of_gc_threads) {
4714 assert(_survivor_plab_array != NULL, "Error");
4715 assert(_survivor_chunk_array != NULL, "Error");
4716 assert(_collectorState == FinalMarking ||
4717 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4718 for (int j = 0; j < no_of_gc_threads; j++) {
4719 _cursor[j] = 0;
4720 }
4721 HeapWord* top = surv->top();
4722 size_t i;
4723 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4724 HeapWord* min_val = top; // Higher than any PLAB address
4725 uint min_tid = 0; // position of min_val this round
4726 for (int j = 0; j < no_of_gc_threads; j++) {
4727 ChunkArray* cur_sca = &_survivor_plab_array[j];
4728 if (_cursor[j] == cur_sca->end()) {
4729 continue;
4730 }
4731 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4732 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4733 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4734 if (cur_val < min_val) {
4735 min_tid = j;
4736 min_val = cur_val;
4737 } else {
4738 assert(cur_val < top, "All recorded addresses should be less");
4739 }
4740 }
4741 // At this point min_val and min_tid are respectively
4742 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4743 // and the thread (j) that witnesses that address.
4744 // We record this address in the _survivor_chunk_array[i]
4745 // and increment _cursor[min_tid] prior to the next round i.
4746 if (min_val == top) {
4747 break;
4748 }
4749 _survivor_chunk_array[i] = min_val;
4750 _cursor[min_tid]++;
4751 }
4752 // We are all done; record the size of the _survivor_chunk_array
4753 _survivor_chunk_index = i; // exclusive: [0, i)
4754 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4755 // Verify that we used up all the recorded entries
4756 #ifdef ASSERT
4757 size_t total = 0;
4758 for (int j = 0; j < no_of_gc_threads; j++) {
4759 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4760 total += _cursor[j];
4761 }
4762 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4763 // Check that the merged array is in sorted order
4764 if (total > 0) {
4765 for (size_t i = 0; i < total - 1; i++) {
4766 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4767 i, p2i(_survivor_chunk_array[i]));
4768 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4769 "Not sorted");
4770 }
4771 }
4772 #endif // ASSERT
4773 }
4774
4775 // Set up the space's par_seq_tasks structure for work claiming
4776 // for parallel initial scan and rescan of young gen.
4777 // See ParRescanTask where this is currently used.
4778 void
4779 CMSCollector::
4780 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4781 assert(n_threads > 0, "Unexpected n_threads argument");
4782
4783 // Eden space
4784 if (!_young_gen->eden()->is_empty()) {
4785 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4786 assert(!pst->valid(), "Clobbering existing data?");
4787 // Each valid entry in [0, _eden_chunk_index) represents a task.
4788 size_t n_tasks = _eden_chunk_index + 1;
4789 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4790 // Sets the condition for completion of the subtask (how many threads
4791 // need to finish in order to be done).
4792 pst->set_n_threads(n_threads);
4793 pst->set_n_tasks((int)n_tasks);
4794 }
4795
4796 // Merge the survivor plab arrays into _survivor_chunk_array
4797 if (_survivor_plab_array != NULL) {
4798 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4799 } else {
4800 assert(_survivor_chunk_index == 0, "Error");
4801 }
4802
4803 // To space
4804 {
4805 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4806 assert(!pst->valid(), "Clobbering existing data?");
4807 // Sets the condition for completion of the subtask (how many threads
4808 // need to finish in order to be done).
4809 pst->set_n_threads(n_threads);
4810 pst->set_n_tasks(1);
4811 assert(pst->valid(), "Error");
4812 }
4813
4814 // From space
4815 {
4816 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4817 assert(!pst->valid(), "Clobbering existing data?");
4818 size_t n_tasks = _survivor_chunk_index + 1;
4819 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
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((int)n_tasks);
4824 assert(pst->valid(), "Error");
4825 }
4826 }
4827
4828 // Parallel version of remark
4829 void CMSCollector::do_remark_parallel() {
4830 GenCollectedHeap* gch = GenCollectedHeap::heap();
4831 WorkGang* workers = gch->workers();
4832 assert(workers != NULL, "Need parallel worker threads.");
4833 // Choose to use the number of GC workers most recently set
4834 // into "active_workers".
4835 uint n_workers = workers->active_workers();
4836
4837 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4838
4839 StrongRootsScope srs(n_workers);
4840
4841 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4842
4843 // We won't be iterating over the cards in the card table updating
4844 // the younger_gen cards, so we shouldn't call the following else
4845 // the verification code as well as subsequent younger_refs_iterate
4846 // code would get confused. XXX
4847 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4848
4849 // The young gen rescan work will not be done as part of
4850 // process_roots (which currently doesn't know how to
4851 // parallelize such a scan), but rather will be broken up into
4852 // a set of parallel tasks (via the sampling that the [abortable]
4853 // preclean phase did of eden, plus the [two] tasks of
4854 // scanning the [two] survivor spaces. Further fine-grain
4855 // parallelization of the scanning of the survivor spaces
4856 // themselves, and of precleaning of the young gen itself
4857 // is deferred to the future.
4858 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4859
4860 // The dirty card rescan work is broken up into a "sequence"
4861 // of parallel tasks (per constituent space) that are dynamically
4862 // claimed by the parallel threads.
4863 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4864
4865 // It turns out that even when we're using 1 thread, doing the work in a
4866 // separate thread causes wide variance in run times. We can't help this
4867 // in the multi-threaded case, but we special-case n=1 here to get
4868 // repeatable measurements of the 1-thread overhead of the parallel code.
4869 if (n_workers > 1) {
4870 // Make refs discovery MT-safe, if it isn't already: it may not
4871 // necessarily be so, since it's possible that we are doing
4872 // ST marking.
4873 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4874 workers->run_task(&tsk);
4875 } else {
4876 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4877 tsk.work(0);
4878 }
4879
4880 // restore, single-threaded for now, any preserved marks
4881 // as a result of work_q overflow
4882 restore_preserved_marks_if_any();
4883 }
4884
4885 // Non-parallel version of remark
4886 void CMSCollector::do_remark_non_parallel() {
4887 ResourceMark rm;
4888 HandleMark hm;
4889 GenCollectedHeap* gch = GenCollectedHeap::heap();
4890 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4891
4892 MarkRefsIntoAndScanClosure
4893 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4894 &_markStack, this,
4895 false /* should_yield */, false /* not precleaning */);
4896 MarkFromDirtyCardsClosure
4897 markFromDirtyCardsClosure(this, _span,
4898 NULL, // space is set further below
4899 &_markBitMap, &_markStack, &mrias_cl);
4900 {
4901 GCTraceTime(Trace, gc) t("Grey Object Rescan", _gc_timer_cm);
4902 // Iterate over the dirty cards, setting the corresponding bits in the
4903 // mod union table.
4904 {
4905 ModUnionClosure modUnionClosure(&_modUnionTable);
4906 _ct->ct_bs()->dirty_card_iterate(
4907 _cmsGen->used_region(),
4908 &modUnionClosure);
4909 }
4910 // Having transferred these marks into the modUnionTable, we just need
4911 // to rescan the marked objects on the dirty cards in the modUnionTable.
4912 // The initial marking may have been done during an asynchronous
4913 // collection so there may be dirty bits in the mod-union table.
4914 const int alignment =
4915 CardTableModRefBS::card_size * BitsPerWord;
4916 {
4917 // ... First handle dirty cards in CMS gen
4918 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4919 MemRegion ur = _cmsGen->used_region();
4920 HeapWord* lb = ur.start();
4921 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4922 MemRegion cms_span(lb, ub);
4923 _modUnionTable.dirty_range_iterate_clear(cms_span,
4924 &markFromDirtyCardsClosure);
4925 verify_work_stacks_empty();
4926 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4927 }
4928 }
4929 if (VerifyDuringGC &&
4930 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4931 HandleMark hm; // Discard invalid handles created during verification
4932 Universe::verify();
4933 }
4934 {
4935 GCTraceTime(Trace, gc) t("Root Rescan", _gc_timer_cm);
4936
4937 verify_work_stacks_empty();
4938
4939 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4940 StrongRootsScope srs(1);
4941
4942 gch->gen_process_roots(&srs,
4943 GenCollectedHeap::OldGen,
4944 true, // young gen as roots
4945 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4946 should_unload_classes(),
4947 &mrias_cl,
4948 NULL,
4949 NULL); // The dirty klasses will be handled below
4950
4951 assert(should_unload_classes()
4952 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4953 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4954 }
4955
4956 {
4957 GCTraceTime(Trace, gc) t("Visit Unhandled CLDs", _gc_timer_cm);
4958
4959 verify_work_stacks_empty();
4960
4961 // Scan all class loader data objects that might have been introduced
4962 // during concurrent marking.
4963 ResourceMark rm;
4964 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4965 for (int i = 0; i < array->length(); i++) {
4966 mrias_cl.do_cld_nv(array->at(i));
4967 }
4968
4969 // We don't need to keep track of new CLDs anymore.
4970 ClassLoaderDataGraph::remember_new_clds(false);
4971
4972 verify_work_stacks_empty();
4973 }
4974
4975 {
4976 GCTraceTime(Trace, gc) t("Dirty Klass Scan", _gc_timer_cm);
4977
4978 verify_work_stacks_empty();
4979
4980 RemarkKlassClosure remark_klass_closure(&mrias_cl);
4981 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4982
4983 verify_work_stacks_empty();
4984 }
4985
4986 // We might have added oops to ClassLoaderData::_handles during the
4987 // concurrent marking phase. These oops point to newly allocated objects
4988 // that are guaranteed to be kept alive. Either by the direct allocation
4989 // code, or when the young collector processes the roots. Hence,
4990 // we don't have to revisit the _handles block during the remark phase.
4991
4992 verify_work_stacks_empty();
4993 // Restore evacuated mark words, if any, used for overflow list links
4994 restore_preserved_marks_if_any();
4995
4996 verify_overflow_empty();
4997 }
4998
4999 ////////////////////////////////////////////////////////
5000 // Parallel Reference Processing Task Proxy Class
5001 ////////////////////////////////////////////////////////
5002 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5003 OopTaskQueueSet* _queues;
5004 ParallelTaskTerminator _terminator;
5005 public:
5006 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5007 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5008 ParallelTaskTerminator* terminator() { return &_terminator; }
5009 OopTaskQueueSet* queues() { return _queues; }
5010 };
5011
5012 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5013 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5014 CMSCollector* _collector;
5015 CMSBitMap* _mark_bit_map;
5016 const MemRegion _span;
5017 ProcessTask& _task;
5018
5019 public:
5020 CMSRefProcTaskProxy(ProcessTask& task,
5021 CMSCollector* collector,
5022 const MemRegion& span,
5023 CMSBitMap* mark_bit_map,
5024 AbstractWorkGang* workers,
5025 OopTaskQueueSet* task_queues):
5026 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5027 task_queues,
5028 workers->active_workers()),
5029 _task(task),
5030 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5031 {
5032 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5033 "Inconsistency in _span");
5034 }
5035
5036 OopTaskQueueSet* task_queues() { return queues(); }
5037
5038 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5039
5040 void do_work_steal(int i,
5041 CMSParDrainMarkingStackClosure* drain,
5042 CMSParKeepAliveClosure* keep_alive,
5043 int* seed);
5044
5045 virtual void work(uint worker_id);
5046 };
5047
5048 void CMSRefProcTaskProxy::work(uint worker_id) {
5049 ResourceMark rm;
5050 HandleMark hm;
5051 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5052 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5053 _mark_bit_map,
5054 work_queue(worker_id));
5055 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5056 _mark_bit_map,
5057 work_queue(worker_id));
5058 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5059 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5060 if (_task.marks_oops_alive()) {
5061 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5062 _collector->hash_seed(worker_id));
5063 }
5064 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5065 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5066 }
5067
5068 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5069 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5070 EnqueueTask& _task;
5071
5072 public:
5073 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5074 : AbstractGangTask("Enqueue reference objects in parallel"),
5075 _task(task)
5076 { }
5077
5078 virtual void work(uint worker_id)
5079 {
5080 _task.work(worker_id);
5081 }
5082 };
5083
5084 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5085 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5086 _span(span),
5087 _bit_map(bit_map),
5088 _work_queue(work_queue),
5089 _mark_and_push(collector, span, bit_map, work_queue),
5090 _low_water_mark(MIN2((work_queue->max_elems()/4),
5091 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5092 { }
5093
5094 // . see if we can share work_queues with ParNew? XXX
5095 void CMSRefProcTaskProxy::do_work_steal(int i,
5096 CMSParDrainMarkingStackClosure* drain,
5097 CMSParKeepAliveClosure* keep_alive,
5098 int* seed) {
5099 OopTaskQueue* work_q = work_queue(i);
5100 NOT_PRODUCT(int num_steals = 0;)
5101 oop obj_to_scan;
5102
5103 while (true) {
5104 // Completely finish any left over work from (an) earlier round(s)
5105 drain->trim_queue(0);
5106 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5107 (size_t)ParGCDesiredObjsFromOverflowList);
5108 // Now check if there's any work in the overflow list
5109 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5110 // only affects the number of attempts made to get work from the
5111 // overflow list and does not affect the number of workers. Just
5112 // pass ParallelGCThreads so this behavior is unchanged.
5113 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5114 work_q,
5115 ParallelGCThreads)) {
5116 // Found something in global overflow list;
5117 // not yet ready to go stealing work from others.
5118 // We'd like to assert(work_q->size() != 0, ...)
5119 // because we just took work from the overflow list,
5120 // but of course we can't, since all of that might have
5121 // been already stolen from us.
5122 continue;
5123 }
5124 // Verify that we have no work before we resort to stealing
5125 assert(work_q->size() == 0, "Have work, shouldn't steal");
5126 // Try to steal from other queues that have work
5127 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5128 NOT_PRODUCT(num_steals++;)
5129 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5130 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5131 // Do scanning work
5132 obj_to_scan->oop_iterate(keep_alive);
5133 // Loop around, finish this work, and try to steal some more
5134 } else if (terminator()->offer_termination()) {
5135 break; // nirvana from the infinite cycle
5136 }
5137 }
5138 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5139 }
5140
5141 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5142 {
5143 GenCollectedHeap* gch = GenCollectedHeap::heap();
5144 WorkGang* workers = gch->workers();
5145 assert(workers != NULL, "Need parallel worker threads.");
5146 CMSRefProcTaskProxy rp_task(task, &_collector,
5147 _collector.ref_processor()->span(),
5148 _collector.markBitMap(),
5149 workers, _collector.task_queues());
5150 workers->run_task(&rp_task);
5151 }
5152
5153 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5154 {
5155
5156 GenCollectedHeap* gch = GenCollectedHeap::heap();
5157 WorkGang* workers = gch->workers();
5158 assert(workers != NULL, "Need parallel worker threads.");
5159 CMSRefEnqueueTaskProxy enq_task(task);
5160 workers->run_task(&enq_task);
5161 }
5162
5163 void CMSCollector::refProcessingWork() {
5164 ResourceMark rm;
5165 HandleMark hm;
5166
5167 ReferenceProcessor* rp = ref_processor();
5168 assert(rp->span().equals(_span), "Spans should be equal");
5169 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5170 // Process weak references.
5171 rp->setup_policy(false);
5172 verify_work_stacks_empty();
5173
5174 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5175 &_markStack, false /* !preclean */);
5176 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5177 _span, &_markBitMap, &_markStack,
5178 &cmsKeepAliveClosure, false /* !preclean */);
5179 {
5180 GCTraceTime(Debug, gc) t("Weak Refs Processing", _gc_timer_cm);
5181
5182 ReferenceProcessorStats stats;
5183 if (rp->processing_is_mt()) {
5184 // Set the degree of MT here. If the discovery is done MT, there
5185 // may have been a different number of threads doing the discovery
5186 // and a different number of discovered lists may have Ref objects.
5187 // That is OK as long as the Reference lists are balanced (see
5188 // balance_all_queues() and balance_queues()).
5189 GenCollectedHeap* gch = GenCollectedHeap::heap();
5190 uint active_workers = ParallelGCThreads;
5191 WorkGang* workers = gch->workers();
5192 if (workers != NULL) {
5193 active_workers = workers->active_workers();
5194 // The expectation is that active_workers will have already
5195 // been set to a reasonable value. If it has not been set,
5196 // investigate.
5197 assert(active_workers > 0, "Should have been set during scavenge");
5198 }
5199 rp->set_active_mt_degree(active_workers);
5200 CMSRefProcTaskExecutor task_executor(*this);
5201 stats = rp->process_discovered_references(&_is_alive_closure,
5202 &cmsKeepAliveClosure,
5203 &cmsDrainMarkingStackClosure,
5204 &task_executor,
5205 _gc_timer_cm);
5206 } else {
5207 stats = rp->process_discovered_references(&_is_alive_closure,
5208 &cmsKeepAliveClosure,
5209 &cmsDrainMarkingStackClosure,
5210 NULL,
5211 _gc_timer_cm);
5212 }
5213 _gc_tracer_cm->report_gc_reference_stats(stats);
5214
5215 }
5216
5217 // This is the point where the entire marking should have completed.
5218 verify_work_stacks_empty();
5219
5220 if (should_unload_classes()) {
5221 {
5222 GCTraceTime(Debug, gc) t("Class Unloading", _gc_timer_cm);
5223
5224 // Unload classes and purge the SystemDictionary.
5225 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5226
5227 // Unload nmethods.
5228 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5229
5230 // Prune dead klasses from subklass/sibling/implementor lists.
5231 Klass::clean_weak_klass_links(&_is_alive_closure);
5232 }
5233
5234 {
5235 GCTraceTime(Debug, gc) t("Scrub Symbol Table", _gc_timer_cm);
5236 // Clean up unreferenced symbols in symbol table.
5237 SymbolTable::unlink();
5238 }
5239
5240 {
5241 GCTraceTime(Debug, gc) t("Scrub String Table", _gc_timer_cm);
5242 // Delete entries for dead interned strings.
5243 StringTable::unlink(&_is_alive_closure);
5244 }
5245 }
5246
5247
5248 // Restore any preserved marks as a result of mark stack or
5249 // work queue overflow
5250 restore_preserved_marks_if_any(); // done single-threaded for now
5251
5252 rp->set_enqueuing_is_done(true);
5253 if (rp->processing_is_mt()) {
5254 rp->balance_all_queues();
5255 CMSRefProcTaskExecutor task_executor(*this);
5256 rp->enqueue_discovered_references(&task_executor);
5257 } else {
5258 rp->enqueue_discovered_references(NULL);
5259 }
5260 rp->verify_no_references_recorded();
5261 assert(!rp->discovery_enabled(), "should have been disabled");
5262 }
5263
5264 #ifndef PRODUCT
5265 void CMSCollector::check_correct_thread_executing() {
5266 Thread* t = Thread::current();
5267 // Only the VM thread or the CMS thread should be here.
5268 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5269 "Unexpected thread type");
5270 // If this is the vm thread, the foreground process
5271 // should not be waiting. Note that _foregroundGCIsActive is
5272 // true while the foreground collector is waiting.
5273 if (_foregroundGCShouldWait) {
5274 // We cannot be the VM thread
5275 assert(t->is_ConcurrentGC_thread(),
5276 "Should be CMS thread");
5277 } else {
5278 // We can be the CMS thread only if we are in a stop-world
5279 // phase of CMS collection.
5280 if (t->is_ConcurrentGC_thread()) {
5281 assert(_collectorState == InitialMarking ||
5282 _collectorState == FinalMarking,
5283 "Should be a stop-world phase");
5284 // The CMS thread should be holding the CMS_token.
5285 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5286 "Potential interference with concurrently "
5287 "executing VM thread");
5288 }
5289 }
5290 }
5291 #endif
5292
5293 void CMSCollector::sweep() {
5294 assert(_collectorState == Sweeping, "just checking");
5295 check_correct_thread_executing();
5296 verify_work_stacks_empty();
5297 verify_overflow_empty();
5298 increment_sweep_count();
5299 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5300
5301 _inter_sweep_timer.stop();
5302 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5303
5304 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5305 _intra_sweep_timer.reset();
5306 _intra_sweep_timer.start();
5307 {
5308 GCTraceCPUTime tcpu;
5309 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5310 // First sweep the old gen
5311 {
5312 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5313 bitMapLock());
5314 sweepWork(_cmsGen);
5315 }
5316
5317 // Update Universe::_heap_*_at_gc figures.
5318 // We need all the free list locks to make the abstract state
5319 // transition from Sweeping to Resetting. See detailed note
5320 // further below.
5321 {
5322 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5323 // Update heap occupancy information which is used as
5324 // input to soft ref clearing policy at the next gc.
5325 Universe::update_heap_info_at_gc();
5326 _collectorState = Resizing;
5327 }
5328 }
5329 verify_work_stacks_empty();
5330 verify_overflow_empty();
5331
5332 if (should_unload_classes()) {
5333 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5334 // requires that the virtual spaces are stable and not deleted.
5335 ClassLoaderDataGraph::set_should_purge(true);
5336 }
5337
5338 _intra_sweep_timer.stop();
5339 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5340
5341 _inter_sweep_timer.reset();
5342 _inter_sweep_timer.start();
5343
5344 // We need to use a monotonically non-decreasing time in ms
5345 // or we will see time-warp warnings and os::javaTimeMillis()
5346 // does not guarantee monotonicity.
5347 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5348 update_time_of_last_gc(now);
5349
5350 // NOTE on abstract state transitions:
5351 // Mutators allocate-live and/or mark the mod-union table dirty
5352 // based on the state of the collection. The former is done in
5353 // the interval [Marking, Sweeping] and the latter in the interval
5354 // [Marking, Sweeping). Thus the transitions into the Marking state
5355 // and out of the Sweeping state must be synchronously visible
5356 // globally to the mutators.
5357 // The transition into the Marking state happens with the world
5358 // stopped so the mutators will globally see it. Sweeping is
5359 // done asynchronously by the background collector so the transition
5360 // from the Sweeping state to the Resizing state must be done
5361 // under the freelistLock (as is the check for whether to
5362 // allocate-live and whether to dirty the mod-union table).
5363 assert(_collectorState == Resizing, "Change of collector state to"
5364 " Resizing must be done under the freelistLocks (plural)");
5365
5366 // Now that sweeping has been completed, we clear
5367 // the incremental_collection_failed flag,
5368 // thus inviting a younger gen collection to promote into
5369 // this generation. If such a promotion may still fail,
5370 // the flag will be set again when a young collection is
5371 // attempted.
5372 GenCollectedHeap* gch = GenCollectedHeap::heap();
5373 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5374 gch->update_full_collections_completed(_collection_count_start);
5375 }
5376
5377 // FIX ME!!! Looks like this belongs in CFLSpace, with
5378 // CMSGen merely delegating to it.
5379 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5380 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5381 HeapWord* minAddr = _cmsSpace->bottom();
5382 HeapWord* largestAddr =
5383 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5384 if (largestAddr == NULL) {
5385 // The dictionary appears to be empty. In this case
5386 // try to coalesce at the end of the heap.
5387 largestAddr = _cmsSpace->end();
5388 }
5389 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5390 size_t nearLargestOffset =
5391 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5392 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5393 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5394 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5395 }
5396
5397 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5398 return addr >= _cmsSpace->nearLargestChunk();
5399 }
5400
5401 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5402 return _cmsSpace->find_chunk_at_end();
5403 }
5404
5405 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5406 bool full) {
5407 // If the young generation has been collected, gather any statistics
5408 // that are of interest at this point.
5409 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5410 if (!full && current_is_young) {
5411 // Gather statistics on the young generation collection.
5412 collector()->stats().record_gc0_end(used());
5413 }
5414 }
5415
5416 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5417 // We iterate over the space(s) underlying this generation,
5418 // checking the mark bit map to see if the bits corresponding
5419 // to specific blocks are marked or not. Blocks that are
5420 // marked are live and are not swept up. All remaining blocks
5421 // are swept up, with coalescing on-the-fly as we sweep up
5422 // contiguous free and/or garbage blocks:
5423 // We need to ensure that the sweeper synchronizes with allocators
5424 // and stop-the-world collectors. In particular, the following
5425 // locks are used:
5426 // . CMS token: if this is held, a stop the world collection cannot occur
5427 // . freelistLock: if this is held no allocation can occur from this
5428 // generation by another thread
5429 // . bitMapLock: if this is held, no other thread can access or update
5430 //
5431
5432 // Note that we need to hold the freelistLock if we use
5433 // block iterate below; else the iterator might go awry if
5434 // a mutator (or promotion) causes block contents to change
5435 // (for instance if the allocator divvies up a block).
5436 // If we hold the free list lock, for all practical purposes
5437 // young generation GC's can't occur (they'll usually need to
5438 // promote), so we might as well prevent all young generation
5439 // GC's while we do a sweeping step. For the same reason, we might
5440 // as well take the bit map lock for the entire duration
5441
5442 // check that we hold the requisite locks
5443 assert(have_cms_token(), "Should hold cms token");
5444 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5445 assert_lock_strong(old_gen->freelistLock());
5446 assert_lock_strong(bitMapLock());
5447
5448 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5449 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5450 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5451 _inter_sweep_estimate.padded_average(),
5452 _intra_sweep_estimate.padded_average());
5453 old_gen->setNearLargestChunk();
5454
5455 {
5456 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5457 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5458 // We need to free-up/coalesce garbage/blocks from a
5459 // co-terminal free run. This is done in the SweepClosure
5460 // destructor; so, do not remove this scope, else the
5461 // end-of-sweep-census below will be off by a little bit.
5462 }
5463 old_gen->cmsSpace()->sweep_completed();
5464 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5465 if (should_unload_classes()) { // unloaded classes this cycle,
5466 _concurrent_cycles_since_last_unload = 0; // ... reset count
5467 } else { // did not unload classes,
5468 _concurrent_cycles_since_last_unload++; // ... increment count
5469 }
5470 }
5471
5472 // Reset CMS data structures (for now just the marking bit map)
5473 // preparatory for the next cycle.
5474 void CMSCollector::reset_concurrent() {
5475 CMSTokenSyncWithLocks ts(true, bitMapLock());
5476
5477 // If the state is not "Resetting", the foreground thread
5478 // has done a collection and the resetting.
5479 if (_collectorState != Resetting) {
5480 assert(_collectorState == Idling, "The state should only change"
5481 " because the foreground collector has finished the collection");
5482 return;
5483 }
5484
5485 // Clear the mark bitmap (no grey objects to start with)
5486 // for the next cycle.
5487 GCTraceCPUTime tcpu;
5488 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5489
5490 HeapWord* curAddr = _markBitMap.startWord();
5491 while (curAddr < _markBitMap.endWord()) {
5492 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5493 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5494 _markBitMap.clear_large_range(chunk);
5495 if (ConcurrentMarkSweepThread::should_yield() &&
5496 !foregroundGCIsActive() &&
5497 CMSYield) {
5498 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5499 "CMS thread should hold CMS token");
5500 assert_lock_strong(bitMapLock());
5501 bitMapLock()->unlock();
5502 ConcurrentMarkSweepThread::desynchronize(true);
5503 stopTimer();
5504 incrementYields();
5505
5506 // See the comment in coordinator_yield()
5507 for (unsigned i = 0; i < CMSYieldSleepCount &&
5508 ConcurrentMarkSweepThread::should_yield() &&
5509 !CMSCollector::foregroundGCIsActive(); ++i) {
5510 os::sleep(Thread::current(), 1, false);
5511 }
5512
5513 ConcurrentMarkSweepThread::synchronize(true);
5514 bitMapLock()->lock_without_safepoint_check();
5515 startTimer();
5516 }
5517 curAddr = chunk.end();
5518 }
5519 // A successful mostly concurrent collection has been done.
5520 // Because only the full (i.e., concurrent mode failure) collections
5521 // are being measured for gc overhead limits, clean the "near" flag
5522 // and count.
5523 size_policy()->reset_gc_overhead_limit_count();
5524 _collectorState = Idling;
5525
5526 register_gc_end();
5527 }
5528
5529 // Same as above but for STW paths
5530 void CMSCollector::reset_stw() {
5531 // already have the lock
5532 assert(_collectorState == Resetting, "just checking");
5533 assert_lock_strong(bitMapLock());
5534 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5535 _markBitMap.clear_all();
5536 _collectorState = Idling;
5537 register_gc_end();
5538 }
5539
5540 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5541 GCTraceCPUTime tcpu;
5542 TraceCollectorStats tcs(counters());
5543
5544 switch (op) {
5545 case CMS_op_checkpointRootsInitial: {
5546 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5547 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5548 checkpointRootsInitial();
5549 break;
5550 }
5551 case CMS_op_checkpointRootsFinal: {
5552 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5553 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5554 checkpointRootsFinal();
5555 break;
5556 }
5557 default:
5558 fatal("No such CMS_op");
5559 }
5560 }
5561
5562 #ifndef PRODUCT
5563 size_t const CMSCollector::skip_header_HeapWords() {
5564 return FreeChunk::header_size();
5565 }
5566
5567 // Try and collect here conditions that should hold when
5568 // CMS thread is exiting. The idea is that the foreground GC
5569 // thread should not be blocked if it wants to terminate
5570 // the CMS thread and yet continue to run the VM for a while
5571 // after that.
5572 void CMSCollector::verify_ok_to_terminate() const {
5573 assert(Thread::current()->is_ConcurrentGC_thread(),
5574 "should be called by CMS thread");
5575 assert(!_foregroundGCShouldWait, "should be false");
5576 // We could check here that all the various low-level locks
5577 // are not held by the CMS thread, but that is overkill; see
5578 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5579 // is checked.
5580 }
5581 #endif
5582
5583 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5584 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5585 "missing Printezis mark?");
5586 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5587 size_t size = pointer_delta(nextOneAddr + 1, addr);
5588 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5589 "alignment problem");
5590 assert(size >= 3, "Necessary for Printezis marks to work");
5591 return size;
5592 }
5593
5594 // A variant of the above (block_size_using_printezis_bits()) except
5595 // that we return 0 if the P-bits are not yet set.
5596 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5597 if (_markBitMap.isMarked(addr + 1)) {
5598 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5599 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5600 size_t size = pointer_delta(nextOneAddr + 1, addr);
5601 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5602 "alignment problem");
5603 assert(size >= 3, "Necessary for Printezis marks to work");
5604 return size;
5605 }
5606 return 0;
5607 }
5608
5609 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5610 size_t sz = 0;
5611 oop p = (oop)addr;
5612 if (p->klass_or_null() != NULL) {
5613 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5614 } else {
5615 sz = block_size_using_printezis_bits(addr);
5616 }
5617 assert(sz > 0, "size must be nonzero");
5618 HeapWord* next_block = addr + sz;
5619 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5620 CardTableModRefBS::card_size);
5621 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5622 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5623 "must be different cards");
5624 return next_card;
5625 }
5626
5627
5628 // CMS Bit Map Wrapper /////////////////////////////////////////
5629
5630 // Construct a CMS bit map infrastructure, but don't create the
5631 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5632 // further below.
5633 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5634 _bm(),
5635 _shifter(shifter),
5636 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5637 Monitor::_safepoint_check_sometimes) : NULL)
5638 {
5639 _bmStartWord = 0;
5640 _bmWordSize = 0;
5641 }
5642
5643 bool CMSBitMap::allocate(MemRegion mr) {
5644 _bmStartWord = mr.start();
5645 _bmWordSize = mr.word_size();
5646 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5647 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5648 if (!brs.is_reserved()) {
5649 warning("CMS bit map allocation failure");
5650 return false;
5651 }
5652 // For now we'll just commit all of the bit map up front.
5653 // Later on we'll try to be more parsimonious with swap.
5654 if (!_virtual_space.initialize(brs, brs.size())) {
5655 warning("CMS bit map backing store failure");
5656 return false;
5657 }
5658 assert(_virtual_space.committed_size() == brs.size(),
5659 "didn't reserve backing store for all of CMS bit map?");
5660 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5661 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5662 _bmWordSize, "inconsistency in bit map sizing");
5663 _bm.set_size(_bmWordSize >> _shifter);
5664
5665 // bm.clear(); // can we rely on getting zero'd memory? verify below
5666 assert(isAllClear(),
5667 "Expected zero'd memory from ReservedSpace constructor");
5668 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5669 "consistency check");
5670 return true;
5671 }
5672
5673 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5674 HeapWord *next_addr, *end_addr, *last_addr;
5675 assert_locked();
5676 assert(covers(mr), "out-of-range error");
5677 // XXX assert that start and end are appropriately aligned
5678 for (next_addr = mr.start(), end_addr = mr.end();
5679 next_addr < end_addr; next_addr = last_addr) {
5680 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5681 last_addr = dirty_region.end();
5682 if (!dirty_region.is_empty()) {
5683 cl->do_MemRegion(dirty_region);
5684 } else {
5685 assert(last_addr == end_addr, "program logic");
5686 return;
5687 }
5688 }
5689 }
5690
5691 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5692 _bm.print_on_error(st, prefix);
5693 }
5694
5695 #ifndef PRODUCT
5696 void CMSBitMap::assert_locked() const {
5697 CMSLockVerifier::assert_locked(lock());
5698 }
5699
5700 bool CMSBitMap::covers(MemRegion mr) const {
5701 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5702 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5703 "size inconsistency");
5704 return (mr.start() >= _bmStartWord) &&
5705 (mr.end() <= endWord());
5706 }
5707
5708 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5709 return (start >= _bmStartWord && (start + size) <= endWord());
5710 }
5711
5712 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5713 // verify that there are no 1 bits in the interval [left, right)
5714 FalseBitMapClosure falseBitMapClosure;
5715 iterate(&falseBitMapClosure, left, right);
5716 }
5717
5718 void CMSBitMap::region_invariant(MemRegion mr)
5719 {
5720 assert_locked();
5721 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5722 assert(!mr.is_empty(), "unexpected empty region");
5723 assert(covers(mr), "mr should be covered by bit map");
5724 // convert address range into offset range
5725 size_t start_ofs = heapWordToOffset(mr.start());
5726 // Make sure that end() is appropriately aligned
5727 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5728 (1 << (_shifter+LogHeapWordSize))),
5729 "Misaligned mr.end()");
5730 size_t end_ofs = heapWordToOffset(mr.end());
5731 assert(end_ofs > start_ofs, "Should mark at least one bit");
5732 }
5733
5734 #endif
5735
5736 bool CMSMarkStack::allocate(size_t size) {
5737 // allocate a stack of the requisite depth
5738 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5739 size * sizeof(oop)));
5740 if (!rs.is_reserved()) {
5741 warning("CMSMarkStack allocation failure");
5742 return false;
5743 }
5744 if (!_virtual_space.initialize(rs, rs.size())) {
5745 warning("CMSMarkStack backing store failure");
5746 return false;
5747 }
5748 assert(_virtual_space.committed_size() == rs.size(),
5749 "didn't reserve backing store for all of CMS stack?");
5750 _base = (oop*)(_virtual_space.low());
5751 _index = 0;
5752 _capacity = size;
5753 NOT_PRODUCT(_max_depth = 0);
5754 return true;
5755 }
5756
5757 // XXX FIX ME !!! In the MT case we come in here holding a
5758 // leaf lock. For printing we need to take a further lock
5759 // which has lower rank. We need to recalibrate the two
5760 // lock-ranks involved in order to be able to print the
5761 // messages below. (Or defer the printing to the caller.
5762 // For now we take the expedient path of just disabling the
5763 // messages for the problematic case.)
5764 void CMSMarkStack::expand() {
5765 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5766 if (_capacity == MarkStackSizeMax) {
5767 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5768 // We print a warning message only once per CMS cycle.
5769 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5770 }
5771 return;
5772 }
5773 // Double capacity if possible
5774 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5775 // Do not give up existing stack until we have managed to
5776 // get the double capacity that we desired.
5777 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5778 new_capacity * sizeof(oop)));
5779 if (rs.is_reserved()) {
5780 // Release the backing store associated with old stack
5781 _virtual_space.release();
5782 // Reinitialize virtual space for new stack
5783 if (!_virtual_space.initialize(rs, rs.size())) {
5784 fatal("Not enough swap for expanded marking stack");
5785 }
5786 _base = (oop*)(_virtual_space.low());
5787 _index = 0;
5788 _capacity = new_capacity;
5789 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5790 // Failed to double capacity, continue;
5791 // we print a detail message only once per CMS cycle.
5792 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5793 _capacity / K, new_capacity / K);
5794 }
5795 }
5796
5797
5798 // Closures
5799 // XXX: there seems to be a lot of code duplication here;
5800 // should refactor and consolidate common code.
5801
5802 // This closure is used to mark refs into the CMS generation in
5803 // the CMS bit map. Called at the first checkpoint. This closure
5804 // assumes that we do not need to re-mark dirty cards; if the CMS
5805 // generation on which this is used is not an oldest
5806 // generation then this will lose younger_gen cards!
5807
5808 MarkRefsIntoClosure::MarkRefsIntoClosure(
5809 MemRegion span, CMSBitMap* bitMap):
5810 _span(span),
5811 _bitMap(bitMap)
5812 {
5813 assert(ref_processor() == NULL, "deliberately left NULL");
5814 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5815 }
5816
5817 void MarkRefsIntoClosure::do_oop(oop obj) {
5818 // if p points into _span, then mark corresponding bit in _markBitMap
5819 assert(obj->is_oop(), "expected an oop");
5820 HeapWord* addr = (HeapWord*)obj;
5821 if (_span.contains(addr)) {
5822 // this should be made more efficient
5823 _bitMap->mark(addr);
5824 }
5825 }
5826
5827 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5828 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5829
5830 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
5831 MemRegion span, CMSBitMap* bitMap):
5832 _span(span),
5833 _bitMap(bitMap)
5834 {
5835 assert(ref_processor() == NULL, "deliberately left NULL");
5836 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5837 }
5838
5839 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
5840 // if p points into _span, then mark corresponding bit in _markBitMap
5841 assert(obj->is_oop(), "expected an oop");
5842 HeapWord* addr = (HeapWord*)obj;
5843 if (_span.contains(addr)) {
5844 // this should be made more efficient
5845 _bitMap->par_mark(addr);
5846 }
5847 }
5848
5849 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
5850 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
5851
5852 // A variant of the above, used for CMS marking verification.
5853 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5854 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5855 _span(span),
5856 _verification_bm(verification_bm),
5857 _cms_bm(cms_bm)
5858 {
5859 assert(ref_processor() == NULL, "deliberately left NULL");
5860 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5861 }
5862
5863 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5864 // if p points into _span, then mark corresponding bit in _markBitMap
5865 assert(obj->is_oop(), "expected an oop");
5866 HeapWord* addr = (HeapWord*)obj;
5867 if (_span.contains(addr)) {
5868 _verification_bm->mark(addr);
5869 if (!_cms_bm->isMarked(addr)) {
5870 LogHandle(gc, verify) log;
5871 ResourceMark rm;
5872 oop(addr)->print_on(log.info_stream());
5873 log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5874 fatal("... aborting");
5875 }
5876 }
5877 }
5878
5879 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5880 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5881
5882 //////////////////////////////////////////////////
5883 // MarkRefsIntoAndScanClosure
5884 //////////////////////////////////////////////////
5885
5886 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5887 ReferenceProcessor* rp,
5888 CMSBitMap* bit_map,
5889 CMSBitMap* mod_union_table,
5890 CMSMarkStack* mark_stack,
5891 CMSCollector* collector,
5892 bool should_yield,
5893 bool concurrent_precleaning):
5894 _collector(collector),
5895 _span(span),
5896 _bit_map(bit_map),
5897 _mark_stack(mark_stack),
5898 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5899 mark_stack, concurrent_precleaning),
5900 _yield(should_yield),
5901 _concurrent_precleaning(concurrent_precleaning),
5902 _freelistLock(NULL)
5903 {
5904 // FIXME: Should initialize in base class constructor.
5905 assert(rp != NULL, "ref_processor shouldn't be NULL");
5906 set_ref_processor_internal(rp);
5907 }
5908
5909 // This closure is used to mark refs into the CMS generation at the
5910 // second (final) checkpoint, and to scan and transitively follow
5911 // the unmarked oops. It is also used during the concurrent precleaning
5912 // phase while scanning objects on dirty cards in the CMS generation.
5913 // The marks are made in the marking bit map and the marking stack is
5914 // used for keeping the (newly) grey objects during the scan.
5915 // The parallel version (Par_...) appears further below.
5916 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5917 if (obj != NULL) {
5918 assert(obj->is_oop(), "expected an oop");
5919 HeapWord* addr = (HeapWord*)obj;
5920 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5921 assert(_collector->overflow_list_is_empty(),
5922 "overflow list should be empty");
5923 if (_span.contains(addr) &&
5924 !_bit_map->isMarked(addr)) {
5925 // mark bit map (object is now grey)
5926 _bit_map->mark(addr);
5927 // push on marking stack (stack should be empty), and drain the
5928 // stack by applying this closure to the oops in the oops popped
5929 // from the stack (i.e. blacken the grey objects)
5930 bool res = _mark_stack->push(obj);
5931 assert(res, "Should have space to push on empty stack");
5932 do {
5933 oop new_oop = _mark_stack->pop();
5934 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5935 assert(_bit_map->isMarked((HeapWord*)new_oop),
5936 "only grey objects on this stack");
5937 // iterate over the oops in this oop, marking and pushing
5938 // the ones in CMS heap (i.e. in _span).
5939 new_oop->oop_iterate(&_pushAndMarkClosure);
5940 // check if it's time to yield
5941 do_yield_check();
5942 } while (!_mark_stack->isEmpty() ||
5943 (!_concurrent_precleaning && take_from_overflow_list()));
5944 // if marking stack is empty, and we are not doing this
5945 // during precleaning, then check the overflow list
5946 }
5947 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5948 assert(_collector->overflow_list_is_empty(),
5949 "overflow list was drained above");
5950
5951 assert(_collector->no_preserved_marks(),
5952 "All preserved marks should have been restored above");
5953 }
5954 }
5955
5956 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5957 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5958
5959 void MarkRefsIntoAndScanClosure::do_yield_work() {
5960 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5961 "CMS thread should hold CMS token");
5962 assert_lock_strong(_freelistLock);
5963 assert_lock_strong(_bit_map->lock());
5964 // relinquish the free_list_lock and bitMaplock()
5965 _bit_map->lock()->unlock();
5966 _freelistLock->unlock();
5967 ConcurrentMarkSweepThread::desynchronize(true);
5968 _collector->stopTimer();
5969 _collector->incrementYields();
5970
5971 // See the comment in coordinator_yield()
5972 for (unsigned i = 0;
5973 i < CMSYieldSleepCount &&
5974 ConcurrentMarkSweepThread::should_yield() &&
5975 !CMSCollector::foregroundGCIsActive();
5976 ++i) {
5977 os::sleep(Thread::current(), 1, false);
5978 }
5979
5980 ConcurrentMarkSweepThread::synchronize(true);
5981 _freelistLock->lock_without_safepoint_check();
5982 _bit_map->lock()->lock_without_safepoint_check();
5983 _collector->startTimer();
5984 }
5985
5986 ///////////////////////////////////////////////////////////
5987 // Par_MarkRefsIntoAndScanClosure: a parallel version of
5988 // MarkRefsIntoAndScanClosure
5989 ///////////////////////////////////////////////////////////
5990 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
5991 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
5992 CMSBitMap* bit_map, OopTaskQueue* work_queue):
5993 _span(span),
5994 _bit_map(bit_map),
5995 _work_queue(work_queue),
5996 _low_water_mark(MIN2((work_queue->max_elems()/4),
5997 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5998 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
5999 {
6000 // FIXME: Should initialize in base class constructor.
6001 assert(rp != NULL, "ref_processor shouldn't be NULL");
6002 set_ref_processor_internal(rp);
6003 }
6004
6005 // This closure is used to mark refs into the CMS generation at the
6006 // second (final) checkpoint, and to scan and transitively follow
6007 // the unmarked oops. The marks are made in the marking bit map and
6008 // the work_queue is used for keeping the (newly) grey objects during
6009 // the scan phase whence they are also available for stealing by parallel
6010 // threads. Since the marking bit map is shared, updates are
6011 // synchronized (via CAS).
6012 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6013 if (obj != NULL) {
6014 // Ignore mark word because this could be an already marked oop
6015 // that may be chained at the end of the overflow list.
6016 assert(obj->is_oop(true), "expected an oop");
6017 HeapWord* addr = (HeapWord*)obj;
6018 if (_span.contains(addr) &&
6019 !_bit_map->isMarked(addr)) {
6020 // mark bit map (object will become grey):
6021 // It is possible for several threads to be
6022 // trying to "claim" this object concurrently;
6023 // the unique thread that succeeds in marking the
6024 // object first will do the subsequent push on
6025 // to the work queue (or overflow list).
6026 if (_bit_map->par_mark(addr)) {
6027 // push on work_queue (which may not be empty), and trim the
6028 // queue to an appropriate length by applying this closure to
6029 // the oops in the oops popped from the stack (i.e. blacken the
6030 // grey objects)
6031 bool res = _work_queue->push(obj);
6032 assert(res, "Low water mark should be less than capacity?");
6033 trim_queue(_low_water_mark);
6034 } // Else, another thread claimed the object
6035 }
6036 }
6037 }
6038
6039 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6040 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6041
6042 // This closure is used to rescan the marked objects on the dirty cards
6043 // in the mod union table and the card table proper.
6044 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6045 oop p, MemRegion mr) {
6046
6047 size_t size = 0;
6048 HeapWord* addr = (HeapWord*)p;
6049 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6050 assert(_span.contains(addr), "we are scanning the CMS generation");
6051 // check if it's time to yield
6052 if (do_yield_check()) {
6053 // We yielded for some foreground stop-world work,
6054 // and we have been asked to abort this ongoing preclean cycle.
6055 return 0;
6056 }
6057 if (_bitMap->isMarked(addr)) {
6058 // it's marked; is it potentially uninitialized?
6059 if (p->klass_or_null() != NULL) {
6060 // an initialized object; ignore mark word in verification below
6061 // since we are running concurrent with mutators
6062 assert(p->is_oop(true), "should be an oop");
6063 if (p->is_objArray()) {
6064 // objArrays are precisely marked; restrict scanning
6065 // to dirty cards only.
6066 size = CompactibleFreeListSpace::adjustObjectSize(
6067 p->oop_iterate_size(_scanningClosure, mr));
6068 } else {
6069 // A non-array may have been imprecisely marked; we need
6070 // to scan object in its entirety.
6071 size = CompactibleFreeListSpace::adjustObjectSize(
6072 p->oop_iterate_size(_scanningClosure));
6073 }
6074 #ifdef ASSERT
6075 size_t direct_size =
6076 CompactibleFreeListSpace::adjustObjectSize(p->size());
6077 assert(size == direct_size, "Inconsistency in size");
6078 assert(size >= 3, "Necessary for Printezis marks to work");
6079 if (!_bitMap->isMarked(addr+1)) {
6080 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6081 } else {
6082 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6083 assert(_bitMap->isMarked(addr+size-1),
6084 "inconsistent Printezis mark");
6085 }
6086 #endif // ASSERT
6087 } else {
6088 // An uninitialized object.
6089 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6090 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6091 size = pointer_delta(nextOneAddr + 1, addr);
6092 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6093 "alignment problem");
6094 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6095 // will dirty the card when the klass pointer is installed in the
6096 // object (signaling the completion of initialization).
6097 }
6098 } else {
6099 // Either a not yet marked object or an uninitialized object
6100 if (p->klass_or_null() == NULL) {
6101 // An uninitialized object, skip to the next card, since
6102 // we may not be able to read its P-bits yet.
6103 assert(size == 0, "Initial value");
6104 } else {
6105 // An object not (yet) reached by marking: we merely need to
6106 // compute its size so as to go look at the next block.
6107 assert(p->is_oop(true), "should be an oop");
6108 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6109 }
6110 }
6111 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6112 return size;
6113 }
6114
6115 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6116 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6117 "CMS thread should hold CMS token");
6118 assert_lock_strong(_freelistLock);
6119 assert_lock_strong(_bitMap->lock());
6120 // relinquish the free_list_lock and bitMaplock()
6121 _bitMap->lock()->unlock();
6122 _freelistLock->unlock();
6123 ConcurrentMarkSweepThread::desynchronize(true);
6124 _collector->stopTimer();
6125 _collector->incrementYields();
6126
6127 // See the comment in coordinator_yield()
6128 for (unsigned i = 0; i < CMSYieldSleepCount &&
6129 ConcurrentMarkSweepThread::should_yield() &&
6130 !CMSCollector::foregroundGCIsActive(); ++i) {
6131 os::sleep(Thread::current(), 1, false);
6132 }
6133
6134 ConcurrentMarkSweepThread::synchronize(true);
6135 _freelistLock->lock_without_safepoint_check();
6136 _bitMap->lock()->lock_without_safepoint_check();
6137 _collector->startTimer();
6138 }
6139
6140
6141 //////////////////////////////////////////////////////////////////
6142 // SurvivorSpacePrecleanClosure
6143 //////////////////////////////////////////////////////////////////
6144 // This (single-threaded) closure is used to preclean the oops in
6145 // the survivor spaces.
6146 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6147
6148 HeapWord* addr = (HeapWord*)p;
6149 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6150 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6151 assert(p->klass_or_null() != NULL, "object should be initialized");
6152 // an initialized object; ignore mark word in verification below
6153 // since we are running concurrent with mutators
6154 assert(p->is_oop(true), "should be an oop");
6155 // Note that we do not yield while we iterate over
6156 // the interior oops of p, pushing the relevant ones
6157 // on our marking stack.
6158 size_t size = p->oop_iterate_size(_scanning_closure);
6159 do_yield_check();
6160 // Observe that below, we do not abandon the preclean
6161 // phase as soon as we should; rather we empty the
6162 // marking stack before returning. This is to satisfy
6163 // some existing assertions. In general, it may be a
6164 // good idea to abort immediately and complete the marking
6165 // from the grey objects at a later time.
6166 while (!_mark_stack->isEmpty()) {
6167 oop new_oop = _mark_stack->pop();
6168 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6169 assert(_bit_map->isMarked((HeapWord*)new_oop),
6170 "only grey objects on this stack");
6171 // iterate over the oops in this oop, marking and pushing
6172 // the ones in CMS heap (i.e. in _span).
6173 new_oop->oop_iterate(_scanning_closure);
6174 // check if it's time to yield
6175 do_yield_check();
6176 }
6177 unsigned int after_count =
6178 GenCollectedHeap::heap()->total_collections();
6179 bool abort = (_before_count != after_count) ||
6180 _collector->should_abort_preclean();
6181 return abort ? 0 : size;
6182 }
6183
6184 void SurvivorSpacePrecleanClosure::do_yield_work() {
6185 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6186 "CMS thread should hold CMS token");
6187 assert_lock_strong(_bit_map->lock());
6188 // Relinquish the bit map lock
6189 _bit_map->lock()->unlock();
6190 ConcurrentMarkSweepThread::desynchronize(true);
6191 _collector->stopTimer();
6192 _collector->incrementYields();
6193
6194 // See the comment in coordinator_yield()
6195 for (unsigned i = 0; i < CMSYieldSleepCount &&
6196 ConcurrentMarkSweepThread::should_yield() &&
6197 !CMSCollector::foregroundGCIsActive(); ++i) {
6198 os::sleep(Thread::current(), 1, false);
6199 }
6200
6201 ConcurrentMarkSweepThread::synchronize(true);
6202 _bit_map->lock()->lock_without_safepoint_check();
6203 _collector->startTimer();
6204 }
6205
6206 // This closure is used to rescan the marked objects on the dirty cards
6207 // in the mod union table and the card table proper. In the parallel
6208 // case, although the bitMap is shared, we do a single read so the
6209 // isMarked() query is "safe".
6210 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6211 // Ignore mark word because we are running concurrent with mutators
6212 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6213 HeapWord* addr = (HeapWord*)p;
6214 assert(_span.contains(addr), "we are scanning the CMS generation");
6215 bool is_obj_array = false;
6216 #ifdef ASSERT
6217 if (!_parallel) {
6218 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6219 assert(_collector->overflow_list_is_empty(),
6220 "overflow list should be empty");
6221
6222 }
6223 #endif // ASSERT
6224 if (_bit_map->isMarked(addr)) {
6225 // Obj arrays are precisely marked, non-arrays are not;
6226 // so we scan objArrays precisely and non-arrays in their
6227 // entirety.
6228 if (p->is_objArray()) {
6229 is_obj_array = true;
6230 if (_parallel) {
6231 p->oop_iterate(_par_scan_closure, mr);
6232 } else {
6233 p->oop_iterate(_scan_closure, mr);
6234 }
6235 } else {
6236 if (_parallel) {
6237 p->oop_iterate(_par_scan_closure);
6238 } else {
6239 p->oop_iterate(_scan_closure);
6240 }
6241 }
6242 }
6243 #ifdef ASSERT
6244 if (!_parallel) {
6245 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6246 assert(_collector->overflow_list_is_empty(),
6247 "overflow list should be empty");
6248
6249 }
6250 #endif // ASSERT
6251 return is_obj_array;
6252 }
6253
6254 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6255 MemRegion span,
6256 CMSBitMap* bitMap, CMSMarkStack* markStack,
6257 bool should_yield, bool verifying):
6258 _collector(collector),
6259 _span(span),
6260 _bitMap(bitMap),
6261 _mut(&collector->_modUnionTable),
6262 _markStack(markStack),
6263 _yield(should_yield),
6264 _skipBits(0)
6265 {
6266 assert(_markStack->isEmpty(), "stack should be empty");
6267 _finger = _bitMap->startWord();
6268 _threshold = _finger;
6269 assert(_collector->_restart_addr == NULL, "Sanity check");
6270 assert(_span.contains(_finger), "Out of bounds _finger?");
6271 DEBUG_ONLY(_verifying = verifying;)
6272 }
6273
6274 void MarkFromRootsClosure::reset(HeapWord* addr) {
6275 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6276 assert(_span.contains(addr), "Out of bounds _finger?");
6277 _finger = addr;
6278 _threshold = (HeapWord*)round_to(
6279 (intptr_t)_finger, CardTableModRefBS::card_size);
6280 }
6281
6282 // Should revisit to see if this should be restructured for
6283 // greater efficiency.
6284 bool MarkFromRootsClosure::do_bit(size_t offset) {
6285 if (_skipBits > 0) {
6286 _skipBits--;
6287 return true;
6288 }
6289 // convert offset into a HeapWord*
6290 HeapWord* addr = _bitMap->startWord() + offset;
6291 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6292 "address out of range");
6293 assert(_bitMap->isMarked(addr), "tautology");
6294 if (_bitMap->isMarked(addr+1)) {
6295 // this is an allocated but not yet initialized object
6296 assert(_skipBits == 0, "tautology");
6297 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6298 oop p = oop(addr);
6299 if (p->klass_or_null() == NULL) {
6300 DEBUG_ONLY(if (!_verifying) {)
6301 // We re-dirty the cards on which this object lies and increase
6302 // the _threshold so that we'll come back to scan this object
6303 // during the preclean or remark phase. (CMSCleanOnEnter)
6304 if (CMSCleanOnEnter) {
6305 size_t sz = _collector->block_size_using_printezis_bits(addr);
6306 HeapWord* end_card_addr = (HeapWord*)round_to(
6307 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6308 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6309 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6310 // Bump _threshold to end_card_addr; note that
6311 // _threshold cannot possibly exceed end_card_addr, anyhow.
6312 // This prevents future clearing of the card as the scan proceeds
6313 // to the right.
6314 assert(_threshold <= end_card_addr,
6315 "Because we are just scanning into this object");
6316 if (_threshold < end_card_addr) {
6317 _threshold = end_card_addr;
6318 }
6319 if (p->klass_or_null() != NULL) {
6320 // Redirty the range of cards...
6321 _mut->mark_range(redirty_range);
6322 } // ...else the setting of klass will dirty the card anyway.
6323 }
6324 DEBUG_ONLY(})
6325 return true;
6326 }
6327 }
6328 scanOopsInOop(addr);
6329 return true;
6330 }
6331
6332 // We take a break if we've been at this for a while,
6333 // so as to avoid monopolizing the locks involved.
6334 void MarkFromRootsClosure::do_yield_work() {
6335 // First give up the locks, then yield, then re-lock
6336 // We should probably use a constructor/destructor idiom to
6337 // do this unlock/lock or modify the MutexUnlocker class to
6338 // serve our purpose. XXX
6339 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6340 "CMS thread should hold CMS token");
6341 assert_lock_strong(_bitMap->lock());
6342 _bitMap->lock()->unlock();
6343 ConcurrentMarkSweepThread::desynchronize(true);
6344 _collector->stopTimer();
6345 _collector->incrementYields();
6346
6347 // See the comment in coordinator_yield()
6348 for (unsigned i = 0; i < CMSYieldSleepCount &&
6349 ConcurrentMarkSweepThread::should_yield() &&
6350 !CMSCollector::foregroundGCIsActive(); ++i) {
6351 os::sleep(Thread::current(), 1, false);
6352 }
6353
6354 ConcurrentMarkSweepThread::synchronize(true);
6355 _bitMap->lock()->lock_without_safepoint_check();
6356 _collector->startTimer();
6357 }
6358
6359 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6360 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6361 assert(_markStack->isEmpty(),
6362 "should drain stack to limit stack usage");
6363 // convert ptr to an oop preparatory to scanning
6364 oop obj = oop(ptr);
6365 // Ignore mark word in verification below, since we
6366 // may be running concurrent with mutators.
6367 assert(obj->is_oop(true), "should be an oop");
6368 assert(_finger <= ptr, "_finger runneth ahead");
6369 // advance the finger to right end of this object
6370 _finger = ptr + obj->size();
6371 assert(_finger > ptr, "we just incremented it above");
6372 // On large heaps, it may take us some time to get through
6373 // the marking phase. During
6374 // this time it's possible that a lot of mutations have
6375 // accumulated in the card table and the mod union table --
6376 // these mutation records are redundant until we have
6377 // actually traced into the corresponding card.
6378 // Here, we check whether advancing the finger would make
6379 // us cross into a new card, and if so clear corresponding
6380 // cards in the MUT (preclean them in the card-table in the
6381 // future).
6382
6383 DEBUG_ONLY(if (!_verifying) {)
6384 // The clean-on-enter optimization is disabled by default,
6385 // until we fix 6178663.
6386 if (CMSCleanOnEnter && (_finger > _threshold)) {
6387 // [_threshold, _finger) represents the interval
6388 // of cards to be cleared in MUT (or precleaned in card table).
6389 // The set of cards to be cleared is all those that overlap
6390 // with the interval [_threshold, _finger); note that
6391 // _threshold is always kept card-aligned but _finger isn't
6392 // always card-aligned.
6393 HeapWord* old_threshold = _threshold;
6394 assert(old_threshold == (HeapWord*)round_to(
6395 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6396 "_threshold should always be card-aligned");
6397 _threshold = (HeapWord*)round_to(
6398 (intptr_t)_finger, CardTableModRefBS::card_size);
6399 MemRegion mr(old_threshold, _threshold);
6400 assert(!mr.is_empty(), "Control point invariant");
6401 assert(_span.contains(mr), "Should clear within span");
6402 _mut->clear_range(mr);
6403 }
6404 DEBUG_ONLY(})
6405 // Note: the finger doesn't advance while we drain
6406 // the stack below.
6407 PushOrMarkClosure pushOrMarkClosure(_collector,
6408 _span, _bitMap, _markStack,
6409 _finger, this);
6410 bool res = _markStack->push(obj);
6411 assert(res, "Empty non-zero size stack should have space for single push");
6412 while (!_markStack->isEmpty()) {
6413 oop new_oop = _markStack->pop();
6414 // Skip verifying header mark word below because we are
6415 // running concurrent with mutators.
6416 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6417 // now scan this oop's oops
6418 new_oop->oop_iterate(&pushOrMarkClosure);
6419 do_yield_check();
6420 }
6421 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6422 }
6423
6424 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6425 CMSCollector* collector, MemRegion span,
6426 CMSBitMap* bit_map,
6427 OopTaskQueue* work_queue,
6428 CMSMarkStack* overflow_stack):
6429 _collector(collector),
6430 _whole_span(collector->_span),
6431 _span(span),
6432 _bit_map(bit_map),
6433 _mut(&collector->_modUnionTable),
6434 _work_queue(work_queue),
6435 _overflow_stack(overflow_stack),
6436 _skip_bits(0),
6437 _task(task)
6438 {
6439 assert(_work_queue->size() == 0, "work_queue should be empty");
6440 _finger = span.start();
6441 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6442 assert(_span.contains(_finger), "Out of bounds _finger?");
6443 }
6444
6445 // Should revisit to see if this should be restructured for
6446 // greater efficiency.
6447 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6448 if (_skip_bits > 0) {
6449 _skip_bits--;
6450 return true;
6451 }
6452 // convert offset into a HeapWord*
6453 HeapWord* addr = _bit_map->startWord() + offset;
6454 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6455 "address out of range");
6456 assert(_bit_map->isMarked(addr), "tautology");
6457 if (_bit_map->isMarked(addr+1)) {
6458 // this is an allocated object that might not yet be initialized
6459 assert(_skip_bits == 0, "tautology");
6460 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6461 oop p = oop(addr);
6462 if (p->klass_or_null() == NULL) {
6463 // in the case of Clean-on-Enter optimization, redirty card
6464 // and avoid clearing card by increasing the threshold.
6465 return true;
6466 }
6467 }
6468 scan_oops_in_oop(addr);
6469 return true;
6470 }
6471
6472 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6473 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6474 // Should we assert that our work queue is empty or
6475 // below some drain limit?
6476 assert(_work_queue->size() == 0,
6477 "should drain stack to limit stack usage");
6478 // convert ptr to an oop preparatory to scanning
6479 oop obj = oop(ptr);
6480 // Ignore mark word in verification below, since we
6481 // may be running concurrent with mutators.
6482 assert(obj->is_oop(true), "should be an oop");
6483 assert(_finger <= ptr, "_finger runneth ahead");
6484 // advance the finger to right end of this object
6485 _finger = ptr + obj->size();
6486 assert(_finger > ptr, "we just incremented it above");
6487 // On large heaps, it may take us some time to get through
6488 // the marking phase. During
6489 // this time it's possible that a lot of mutations have
6490 // accumulated in the card table and the mod union table --
6491 // these mutation records are redundant until we have
6492 // actually traced into the corresponding card.
6493 // Here, we check whether advancing the finger would make
6494 // us cross into a new card, and if so clear corresponding
6495 // cards in the MUT (preclean them in the card-table in the
6496 // future).
6497
6498 // The clean-on-enter optimization is disabled by default,
6499 // until we fix 6178663.
6500 if (CMSCleanOnEnter && (_finger > _threshold)) {
6501 // [_threshold, _finger) represents the interval
6502 // of cards to be cleared in MUT (or precleaned in card table).
6503 // The set of cards to be cleared is all those that overlap
6504 // with the interval [_threshold, _finger); note that
6505 // _threshold is always kept card-aligned but _finger isn't
6506 // always card-aligned.
6507 HeapWord* old_threshold = _threshold;
6508 assert(old_threshold == (HeapWord*)round_to(
6509 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6510 "_threshold should always be card-aligned");
6511 _threshold = (HeapWord*)round_to(
6512 (intptr_t)_finger, CardTableModRefBS::card_size);
6513 MemRegion mr(old_threshold, _threshold);
6514 assert(!mr.is_empty(), "Control point invariant");
6515 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6516 _mut->clear_range(mr);
6517 }
6518
6519 // Note: the local finger doesn't advance while we drain
6520 // the stack below, but the global finger sure can and will.
6521 HeapWord** gfa = _task->global_finger_addr();
6522 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6523 _span, _bit_map,
6524 _work_queue,
6525 _overflow_stack,
6526 _finger,
6527 gfa, this);
6528 bool res = _work_queue->push(obj); // overflow could occur here
6529 assert(res, "Will hold once we use workqueues");
6530 while (true) {
6531 oop new_oop;
6532 if (!_work_queue->pop_local(new_oop)) {
6533 // We emptied our work_queue; check if there's stuff that can
6534 // be gotten from the overflow stack.
6535 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6536 _overflow_stack, _work_queue)) {
6537 do_yield_check();
6538 continue;
6539 } else { // done
6540 break;
6541 }
6542 }
6543 // Skip verifying header mark word below because we are
6544 // running concurrent with mutators.
6545 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6546 // now scan this oop's oops
6547 new_oop->oop_iterate(&pushOrMarkClosure);
6548 do_yield_check();
6549 }
6550 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6551 }
6552
6553 // Yield in response to a request from VM Thread or
6554 // from mutators.
6555 void Par_MarkFromRootsClosure::do_yield_work() {
6556 assert(_task != NULL, "sanity");
6557 _task->yield();
6558 }
6559
6560 // A variant of the above used for verifying CMS marking work.
6561 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6562 MemRegion span,
6563 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6564 CMSMarkStack* mark_stack):
6565 _collector(collector),
6566 _span(span),
6567 _verification_bm(verification_bm),
6568 _cms_bm(cms_bm),
6569 _mark_stack(mark_stack),
6570 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6571 mark_stack)
6572 {
6573 assert(_mark_stack->isEmpty(), "stack should be empty");
6574 _finger = _verification_bm->startWord();
6575 assert(_collector->_restart_addr == NULL, "Sanity check");
6576 assert(_span.contains(_finger), "Out of bounds _finger?");
6577 }
6578
6579 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6580 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6581 assert(_span.contains(addr), "Out of bounds _finger?");
6582 _finger = addr;
6583 }
6584
6585 // Should revisit to see if this should be restructured for
6586 // greater efficiency.
6587 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6588 // convert offset into a HeapWord*
6589 HeapWord* addr = _verification_bm->startWord() + offset;
6590 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6591 "address out of range");
6592 assert(_verification_bm->isMarked(addr), "tautology");
6593 assert(_cms_bm->isMarked(addr), "tautology");
6594
6595 assert(_mark_stack->isEmpty(),
6596 "should drain stack to limit stack usage");
6597 // convert addr to an oop preparatory to scanning
6598 oop obj = oop(addr);
6599 assert(obj->is_oop(), "should be an oop");
6600 assert(_finger <= addr, "_finger runneth ahead");
6601 // advance the finger to right end of this object
6602 _finger = addr + obj->size();
6603 assert(_finger > addr, "we just incremented it above");
6604 // Note: the finger doesn't advance while we drain
6605 // the stack below.
6606 bool res = _mark_stack->push(obj);
6607 assert(res, "Empty non-zero size stack should have space for single push");
6608 while (!_mark_stack->isEmpty()) {
6609 oop new_oop = _mark_stack->pop();
6610 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6611 // now scan this oop's oops
6612 new_oop->oop_iterate(&_pam_verify_closure);
6613 }
6614 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6615 return true;
6616 }
6617
6618 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6619 CMSCollector* collector, MemRegion span,
6620 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6621 CMSMarkStack* mark_stack):
6622 MetadataAwareOopClosure(collector->ref_processor()),
6623 _collector(collector),
6624 _span(span),
6625 _verification_bm(verification_bm),
6626 _cms_bm(cms_bm),
6627 _mark_stack(mark_stack)
6628 { }
6629
6630 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6631 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6632
6633 // Upon stack overflow, we discard (part of) the stack,
6634 // remembering the least address amongst those discarded
6635 // in CMSCollector's _restart_address.
6636 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6637 // Remember the least grey address discarded
6638 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6639 _collector->lower_restart_addr(ra);
6640 _mark_stack->reset(); // discard stack contents
6641 _mark_stack->expand(); // expand the stack if possible
6642 }
6643
6644 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6645 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6646 HeapWord* addr = (HeapWord*)obj;
6647 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6648 // Oop lies in _span and isn't yet grey or black
6649 _verification_bm->mark(addr); // now grey
6650 if (!_cms_bm->isMarked(addr)) {
6651 LogHandle(gc, verify) log;
6652 ResourceMark rm;
6653 oop(addr)->print_on(log.info_stream());
6654 log.info(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6655 fatal("... aborting");
6656 }
6657
6658 if (!_mark_stack->push(obj)) { // stack overflow
6659 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6660 assert(_mark_stack->isFull(), "Else push should have succeeded");
6661 handle_stack_overflow(addr);
6662 }
6663 // anything including and to the right of _finger
6664 // will be scanned as we iterate over the remainder of the
6665 // bit map
6666 }
6667 }
6668
6669 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6670 MemRegion span,
6671 CMSBitMap* bitMap, CMSMarkStack* markStack,
6672 HeapWord* finger, MarkFromRootsClosure* parent) :
6673 MetadataAwareOopClosure(collector->ref_processor()),
6674 _collector(collector),
6675 _span(span),
6676 _bitMap(bitMap),
6677 _markStack(markStack),
6678 _finger(finger),
6679 _parent(parent)
6680 { }
6681
6682 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6683 MemRegion span,
6684 CMSBitMap* bit_map,
6685 OopTaskQueue* work_queue,
6686 CMSMarkStack* overflow_stack,
6687 HeapWord* finger,
6688 HeapWord** global_finger_addr,
6689 Par_MarkFromRootsClosure* parent) :
6690 MetadataAwareOopClosure(collector->ref_processor()),
6691 _collector(collector),
6692 _whole_span(collector->_span),
6693 _span(span),
6694 _bit_map(bit_map),
6695 _work_queue(work_queue),
6696 _overflow_stack(overflow_stack),
6697 _finger(finger),
6698 _global_finger_addr(global_finger_addr),
6699 _parent(parent)
6700 { }
6701
6702 // Assumes thread-safe access by callers, who are
6703 // responsible for mutual exclusion.
6704 void CMSCollector::lower_restart_addr(HeapWord* low) {
6705 assert(_span.contains(low), "Out of bounds addr");
6706 if (_restart_addr == NULL) {
6707 _restart_addr = low;
6708 } else {
6709 _restart_addr = MIN2(_restart_addr, low);
6710 }
6711 }
6712
6713 // Upon stack overflow, we discard (part of) the stack,
6714 // remembering the least address amongst those discarded
6715 // in CMSCollector's _restart_address.
6716 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6717 // Remember the least grey address discarded
6718 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6719 _collector->lower_restart_addr(ra);
6720 _markStack->reset(); // discard stack contents
6721 _markStack->expand(); // expand the stack if possible
6722 }
6723
6724 // Upon stack overflow, we discard (part of) the stack,
6725 // remembering the least address amongst those discarded
6726 // in CMSCollector's _restart_address.
6727 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6728 // We need to do this under a mutex to prevent other
6729 // workers from interfering with the work done below.
6730 MutexLockerEx ml(_overflow_stack->par_lock(),
6731 Mutex::_no_safepoint_check_flag);
6732 // Remember the least grey address discarded
6733 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6734 _collector->lower_restart_addr(ra);
6735 _overflow_stack->reset(); // discard stack contents
6736 _overflow_stack->expand(); // expand the stack if possible
6737 }
6738
6739 void PushOrMarkClosure::do_oop(oop obj) {
6740 // Ignore mark word because we are running concurrent with mutators.
6741 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6742 HeapWord* addr = (HeapWord*)obj;
6743 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6744 // Oop lies in _span and isn't yet grey or black
6745 _bitMap->mark(addr); // now grey
6746 if (addr < _finger) {
6747 // the bit map iteration has already either passed, or
6748 // sampled, this bit in the bit map; we'll need to
6749 // use the marking stack to scan this oop's oops.
6750 bool simulate_overflow = false;
6751 NOT_PRODUCT(
6752 if (CMSMarkStackOverflowALot &&
6753 _collector->simulate_overflow()) {
6754 // simulate a stack overflow
6755 simulate_overflow = true;
6756 }
6757 )
6758 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6759 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6760 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6761 handle_stack_overflow(addr);
6762 }
6763 }
6764 // anything including and to the right of _finger
6765 // will be scanned as we iterate over the remainder of the
6766 // bit map
6767 do_yield_check();
6768 }
6769 }
6770
6771 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6772 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6773
6774 void Par_PushOrMarkClosure::do_oop(oop obj) {
6775 // Ignore mark word because we are running concurrent with mutators.
6776 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6777 HeapWord* addr = (HeapWord*)obj;
6778 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6779 // Oop lies in _span and isn't yet grey or black
6780 // We read the global_finger (volatile read) strictly after marking oop
6781 bool res = _bit_map->par_mark(addr); // now grey
6782 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6783 // Should we push this marked oop on our stack?
6784 // -- if someone else marked it, nothing to do
6785 // -- if target oop is above global finger nothing to do
6786 // -- if target oop is in chunk and above local finger
6787 // then nothing to do
6788 // -- else push on work queue
6789 if ( !res // someone else marked it, they will deal with it
6790 || (addr >= *gfa) // will be scanned in a later task
6791 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6792 return;
6793 }
6794 // the bit map iteration has already either passed, or
6795 // sampled, this bit in the bit map; we'll need to
6796 // use the marking stack to scan this oop's oops.
6797 bool simulate_overflow = false;
6798 NOT_PRODUCT(
6799 if (CMSMarkStackOverflowALot &&
6800 _collector->simulate_overflow()) {
6801 // simulate a stack overflow
6802 simulate_overflow = true;
6803 }
6804 )
6805 if (simulate_overflow ||
6806 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6807 // stack overflow
6808 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6809 // We cannot assert that the overflow stack is full because
6810 // it may have been emptied since.
6811 assert(simulate_overflow ||
6812 _work_queue->size() == _work_queue->max_elems(),
6813 "Else push should have succeeded");
6814 handle_stack_overflow(addr);
6815 }
6816 do_yield_check();
6817 }
6818 }
6819
6820 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
6821 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
6822
6823 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6824 MemRegion span,
6825 ReferenceProcessor* rp,
6826 CMSBitMap* bit_map,
6827 CMSBitMap* mod_union_table,
6828 CMSMarkStack* mark_stack,
6829 bool concurrent_precleaning):
6830 MetadataAwareOopClosure(rp),
6831 _collector(collector),
6832 _span(span),
6833 _bit_map(bit_map),
6834 _mod_union_table(mod_union_table),
6835 _mark_stack(mark_stack),
6836 _concurrent_precleaning(concurrent_precleaning)
6837 {
6838 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6839 }
6840
6841 // Grey object rescan during pre-cleaning and second checkpoint phases --
6842 // the non-parallel version (the parallel version appears further below.)
6843 void PushAndMarkClosure::do_oop(oop obj) {
6844 // Ignore mark word verification. If during concurrent precleaning,
6845 // the object monitor may be locked. If during the checkpoint
6846 // phases, the object may already have been reached by a different
6847 // path and may be at the end of the global overflow list (so
6848 // the mark word may be NULL).
6849 assert(obj->is_oop_or_null(true /* ignore mark word */),
6850 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6851 HeapWord* addr = (HeapWord*)obj;
6852 // Check if oop points into the CMS generation
6853 // and is not marked
6854 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6855 // a white object ...
6856 _bit_map->mark(addr); // ... now grey
6857 // push on the marking stack (grey set)
6858 bool simulate_overflow = false;
6859 NOT_PRODUCT(
6860 if (CMSMarkStackOverflowALot &&
6861 _collector->simulate_overflow()) {
6862 // simulate a stack overflow
6863 simulate_overflow = true;
6864 }
6865 )
6866 if (simulate_overflow || !_mark_stack->push(obj)) {
6867 if (_concurrent_precleaning) {
6868 // During precleaning we can just dirty the appropriate card(s)
6869 // in the mod union table, thus ensuring that the object remains
6870 // in the grey set and continue. In the case of object arrays
6871 // we need to dirty all of the cards that the object spans,
6872 // since the rescan of object arrays will be limited to the
6873 // dirty cards.
6874 // Note that no one can be interfering with us in this action
6875 // of dirtying the mod union table, so no locking or atomics
6876 // are required.
6877 if (obj->is_objArray()) {
6878 size_t sz = obj->size();
6879 HeapWord* end_card_addr = (HeapWord*)round_to(
6880 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6881 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6882 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6883 _mod_union_table->mark_range(redirty_range);
6884 } else {
6885 _mod_union_table->mark(addr);
6886 }
6887 _collector->_ser_pmc_preclean_ovflw++;
6888 } else {
6889 // During the remark phase, we need to remember this oop
6890 // in the overflow list.
6891 _collector->push_on_overflow_list(obj);
6892 _collector->_ser_pmc_remark_ovflw++;
6893 }
6894 }
6895 }
6896 }
6897
6898 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
6899 MemRegion span,
6900 ReferenceProcessor* rp,
6901 CMSBitMap* bit_map,
6902 OopTaskQueue* work_queue):
6903 MetadataAwareOopClosure(rp),
6904 _collector(collector),
6905 _span(span),
6906 _bit_map(bit_map),
6907 _work_queue(work_queue)
6908 {
6909 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6910 }
6911
6912 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6913 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6914
6915 // Grey object rescan during second checkpoint phase --
6916 // the parallel version.
6917 void Par_PushAndMarkClosure::do_oop(oop obj) {
6918 // In the assert below, we ignore the mark word because
6919 // this oop may point to an already visited object that is
6920 // on the overflow stack (in which case the mark word has
6921 // been hijacked for chaining into the overflow stack --
6922 // if this is the last object in the overflow stack then
6923 // its mark word will be NULL). Because this object may
6924 // have been subsequently popped off the global overflow
6925 // stack, and the mark word possibly restored to the prototypical
6926 // value, by the time we get to examined this failing assert in
6927 // the debugger, is_oop_or_null(false) may subsequently start
6928 // to hold.
6929 assert(obj->is_oop_or_null(true),
6930 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6931 HeapWord* addr = (HeapWord*)obj;
6932 // Check if oop points into the CMS generation
6933 // and is not marked
6934 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6935 // a white object ...
6936 // If we manage to "claim" the object, by being the
6937 // first thread to mark it, then we push it on our
6938 // marking stack
6939 if (_bit_map->par_mark(addr)) { // ... now grey
6940 // push on work queue (grey set)
6941 bool simulate_overflow = false;
6942 NOT_PRODUCT(
6943 if (CMSMarkStackOverflowALot &&
6944 _collector->par_simulate_overflow()) {
6945 // simulate a stack overflow
6946 simulate_overflow = true;
6947 }
6948 )
6949 if (simulate_overflow || !_work_queue->push(obj)) {
6950 _collector->par_push_on_overflow_list(obj);
6951 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6952 }
6953 } // Else, some other thread got there first
6954 }
6955 }
6956
6957 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
6958 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
6959
6960 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6961 Mutex* bml = _collector->bitMapLock();
6962 assert_lock_strong(bml);
6963 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6964 "CMS thread should hold CMS token");
6965
6966 bml->unlock();
6967 ConcurrentMarkSweepThread::desynchronize(true);
6968
6969 _collector->stopTimer();
6970 _collector->incrementYields();
6971
6972 // See the comment in coordinator_yield()
6973 for (unsigned i = 0; i < CMSYieldSleepCount &&
6974 ConcurrentMarkSweepThread::should_yield() &&
6975 !CMSCollector::foregroundGCIsActive(); ++i) {
6976 os::sleep(Thread::current(), 1, false);
6977 }
6978
6979 ConcurrentMarkSweepThread::synchronize(true);
6980 bml->lock();
6981
6982 _collector->startTimer();
6983 }
6984
6985 bool CMSPrecleanRefsYieldClosure::should_return() {
6986 if (ConcurrentMarkSweepThread::should_yield()) {
6987 do_yield_work();
6988 }
6989 return _collector->foregroundGCIsActive();
6990 }
6991
6992 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6993 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
6994 "mr should be aligned to start at a card boundary");
6995 // We'd like to assert:
6996 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
6997 // "mr should be a range of cards");
6998 // However, that would be too strong in one case -- the last
6999 // partition ends at _unallocated_block which, in general, can be
7000 // an arbitrary boundary, not necessarily card aligned.
7001 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7002 _space->object_iterate_mem(mr, &_scan_cl);
7003 }
7004
7005 SweepClosure::SweepClosure(CMSCollector* collector,
7006 ConcurrentMarkSweepGeneration* g,
7007 CMSBitMap* bitMap, bool should_yield) :
7008 _collector(collector),
7009 _g(g),
7010 _sp(g->cmsSpace()),
7011 _limit(_sp->sweep_limit()),
7012 _freelistLock(_sp->freelistLock()),
7013 _bitMap(bitMap),
7014 _yield(should_yield),
7015 _inFreeRange(false), // No free range at beginning of sweep
7016 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7017 _lastFreeRangeCoalesced(false),
7018 _freeFinger(g->used_region().start())
7019 {
7020 NOT_PRODUCT(
7021 _numObjectsFreed = 0;
7022 _numWordsFreed = 0;
7023 _numObjectsLive = 0;
7024 _numWordsLive = 0;
7025 _numObjectsAlreadyFree = 0;
7026 _numWordsAlreadyFree = 0;
7027 _last_fc = NULL;
7028
7029 _sp->initializeIndexedFreeListArrayReturnedBytes();
7030 _sp->dictionary()->initialize_dict_returned_bytes();
7031 )
7032 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7033 "sweep _limit out of bounds");
7034 log_develop_trace(gc, sweep)("====================");
7035 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7036 }
7037
7038 void SweepClosure::print_on(outputStream* st) const {
7039 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7040 p2i(_sp->bottom()), p2i(_sp->end()));
7041 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7042 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7043 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7044 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7045 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7046 }
7047
7048 #ifndef PRODUCT
7049 // Assertion checking only: no useful work in product mode --
7050 // however, if any of the flags below become product flags,
7051 // you may need to review this code to see if it needs to be
7052 // enabled in product mode.
7053 SweepClosure::~SweepClosure() {
7054 assert_lock_strong(_freelistLock);
7055 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7056 "sweep _limit out of bounds");
7057 if (inFreeRange()) {
7058 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7059 print();
7060 ShouldNotReachHere();
7061 }
7062
7063 if (log_is_enabled(Debug, gc, sweep)) {
7064 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7065 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7066 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7067 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7068 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7069 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7070 }
7071
7072 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7073 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7074 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7075 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7076 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7077 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7078 }
7079 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7080 log_develop_trace(gc, sweep)("================");
7081 }
7082 #endif // PRODUCT
7083
7084 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7085 bool freeRangeInFreeLists) {
7086 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7087 p2i(freeFinger), freeRangeInFreeLists);
7088 assert(!inFreeRange(), "Trampling existing free range");
7089 set_inFreeRange(true);
7090 set_lastFreeRangeCoalesced(false);
7091
7092 set_freeFinger(freeFinger);
7093 set_freeRangeInFreeLists(freeRangeInFreeLists);
7094 if (CMSTestInFreeList) {
7095 if (freeRangeInFreeLists) {
7096 FreeChunk* fc = (FreeChunk*) freeFinger;
7097 assert(fc->is_free(), "A chunk on the free list should be free.");
7098 assert(fc->size() > 0, "Free range should have a size");
7099 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7100 }
7101 }
7102 }
7103
7104 // Note that the sweeper runs concurrently with mutators. Thus,
7105 // it is possible for direct allocation in this generation to happen
7106 // in the middle of the sweep. Note that the sweeper also coalesces
7107 // contiguous free blocks. Thus, unless the sweeper and the allocator
7108 // synchronize appropriately freshly allocated blocks may get swept up.
7109 // This is accomplished by the sweeper locking the free lists while
7110 // it is sweeping. Thus blocks that are determined to be free are
7111 // indeed free. There is however one additional complication:
7112 // blocks that have been allocated since the final checkpoint and
7113 // mark, will not have been marked and so would be treated as
7114 // unreachable and swept up. To prevent this, the allocator marks
7115 // the bit map when allocating during the sweep phase. This leads,
7116 // however, to a further complication -- objects may have been allocated
7117 // but not yet initialized -- in the sense that the header isn't yet
7118 // installed. The sweeper can not then determine the size of the block
7119 // in order to skip over it. To deal with this case, we use a technique
7120 // (due to Printezis) to encode such uninitialized block sizes in the
7121 // bit map. Since the bit map uses a bit per every HeapWord, but the
7122 // CMS generation has a minimum object size of 3 HeapWords, it follows
7123 // that "normal marks" won't be adjacent in the bit map (there will
7124 // always be at least two 0 bits between successive 1 bits). We make use
7125 // of these "unused" bits to represent uninitialized blocks -- the bit
7126 // corresponding to the start of the uninitialized object and the next
7127 // bit are both set. Finally, a 1 bit marks the end of the object that
7128 // started with the two consecutive 1 bits to indicate its potentially
7129 // uninitialized state.
7130
7131 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7132 FreeChunk* fc = (FreeChunk*)addr;
7133 size_t res;
7134
7135 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7136 // than "addr == _limit" because although _limit was a block boundary when
7137 // we started the sweep, it may no longer be one because heap expansion
7138 // may have caused us to coalesce the block ending at the address _limit
7139 // with a newly expanded chunk (this happens when _limit was set to the
7140 // previous _end of the space), so we may have stepped past _limit:
7141 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7142 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7143 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7144 "sweep _limit out of bounds");
7145 assert(addr < _sp->end(), "addr out of bounds");
7146 // Flush any free range we might be holding as a single
7147 // coalesced chunk to the appropriate free list.
7148 if (inFreeRange()) {
7149 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7150 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7151 flush_cur_free_chunk(freeFinger(),
7152 pointer_delta(addr, freeFinger()));
7153 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7154 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7155 lastFreeRangeCoalesced() ? 1 : 0);
7156 }
7157
7158 // help the iterator loop finish
7159 return pointer_delta(_sp->end(), addr);
7160 }
7161
7162 assert(addr < _limit, "sweep invariant");
7163 // check if we should yield
7164 do_yield_check(addr);
7165 if (fc->is_free()) {
7166 // Chunk that is already free
7167 res = fc->size();
7168 do_already_free_chunk(fc);
7169 debug_only(_sp->verifyFreeLists());
7170 // If we flush the chunk at hand in lookahead_and_flush()
7171 // and it's coalesced with a preceding chunk, then the
7172 // process of "mangling" the payload of the coalesced block
7173 // will cause erasure of the size information from the
7174 // (erstwhile) header of all the coalesced blocks but the
7175 // first, so the first disjunct in the assert will not hold
7176 // in that specific case (in which case the second disjunct
7177 // will hold).
7178 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7179 "Otherwise the size info doesn't change at this step");
7180 NOT_PRODUCT(
7181 _numObjectsAlreadyFree++;
7182 _numWordsAlreadyFree += res;
7183 )
7184 NOT_PRODUCT(_last_fc = fc;)
7185 } else if (!_bitMap->isMarked(addr)) {
7186 // Chunk is fresh garbage
7187 res = do_garbage_chunk(fc);
7188 debug_only(_sp->verifyFreeLists());
7189 NOT_PRODUCT(
7190 _numObjectsFreed++;
7191 _numWordsFreed += res;
7192 )
7193 } else {
7194 // Chunk that is alive.
7195 res = do_live_chunk(fc);
7196 debug_only(_sp->verifyFreeLists());
7197 NOT_PRODUCT(
7198 _numObjectsLive++;
7199 _numWordsLive += res;
7200 )
7201 }
7202 return res;
7203 }
7204
7205 // For the smart allocation, record following
7206 // split deaths - a free chunk is removed from its free list because
7207 // it is being split into two or more chunks.
7208 // split birth - a free chunk is being added to its free list because
7209 // a larger free chunk has been split and resulted in this free chunk.
7210 // coal death - a free chunk is being removed from its free list because
7211 // it is being coalesced into a large free chunk.
7212 // coal birth - a free chunk is being added to its free list because
7213 // it was created when two or more free chunks where coalesced into
7214 // this free chunk.
7215 //
7216 // These statistics are used to determine the desired number of free
7217 // chunks of a given size. The desired number is chosen to be relative
7218 // to the end of a CMS sweep. The desired number at the end of a sweep
7219 // is the
7220 // count-at-end-of-previous-sweep (an amount that was enough)
7221 // - count-at-beginning-of-current-sweep (the excess)
7222 // + split-births (gains in this size during interval)
7223 // - split-deaths (demands on this size during interval)
7224 // where the interval is from the end of one sweep to the end of the
7225 // next.
7226 //
7227 // When sweeping the sweeper maintains an accumulated chunk which is
7228 // the chunk that is made up of chunks that have been coalesced. That
7229 // will be termed the left-hand chunk. A new chunk of garbage that
7230 // is being considered for coalescing will be referred to as the
7231 // right-hand chunk.
7232 //
7233 // When making a decision on whether to coalesce a right-hand chunk with
7234 // the current left-hand chunk, the current count vs. the desired count
7235 // of the left-hand chunk is considered. Also if the right-hand chunk
7236 // is near the large chunk at the end of the heap (see
7237 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7238 // left-hand chunk is coalesced.
7239 //
7240 // When making a decision about whether to split a chunk, the desired count
7241 // vs. the current count of the candidate to be split is also considered.
7242 // If the candidate is underpopulated (currently fewer chunks than desired)
7243 // a chunk of an overpopulated (currently more chunks than desired) size may
7244 // be chosen. The "hint" associated with a free list, if non-null, points
7245 // to a free list which may be overpopulated.
7246 //
7247
7248 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7249 const size_t size = fc->size();
7250 // Chunks that cannot be coalesced are not in the
7251 // free lists.
7252 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7253 assert(_sp->verify_chunk_in_free_list(fc),
7254 "free chunk should be in free lists");
7255 }
7256 // a chunk that is already free, should not have been
7257 // marked in the bit map
7258 HeapWord* const addr = (HeapWord*) fc;
7259 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7260 // Verify that the bit map has no bits marked between
7261 // addr and purported end of this block.
7262 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7263
7264 // Some chunks cannot be coalesced under any circumstances.
7265 // See the definition of cantCoalesce().
7266 if (!fc->cantCoalesce()) {
7267 // This chunk can potentially be coalesced.
7268 // All the work is done in
7269 do_post_free_or_garbage_chunk(fc, size);
7270 // Note that if the chunk is not coalescable (the else arm
7271 // below), we unconditionally flush, without needing to do
7272 // a "lookahead," as we do below.
7273 if (inFreeRange()) lookahead_and_flush(fc, size);
7274 } else {
7275 // Code path common to both original and adaptive free lists.
7276
7277 // cant coalesce with previous block; this should be treated
7278 // as the end of a free run if any
7279 if (inFreeRange()) {
7280 // we kicked some butt; time to pick up the garbage
7281 assert(freeFinger() < addr, "freeFinger points too high");
7282 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7283 }
7284 // else, nothing to do, just continue
7285 }
7286 }
7287
7288 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7289 // This is a chunk of garbage. It is not in any free list.
7290 // Add it to a free list or let it possibly be coalesced into
7291 // a larger chunk.
7292 HeapWord* const addr = (HeapWord*) fc;
7293 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7294
7295 // Verify that the bit map has no bits marked between
7296 // addr and purported end of just dead object.
7297 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7298 do_post_free_or_garbage_chunk(fc, size);
7299
7300 assert(_limit >= addr + size,
7301 "A freshly garbage chunk can't possibly straddle over _limit");
7302 if (inFreeRange()) lookahead_and_flush(fc, size);
7303 return size;
7304 }
7305
7306 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7307 HeapWord* addr = (HeapWord*) fc;
7308 // The sweeper has just found a live object. Return any accumulated
7309 // left hand chunk to the free lists.
7310 if (inFreeRange()) {
7311 assert(freeFinger() < addr, "freeFinger points too high");
7312 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7313 }
7314
7315 // This object is live: we'd normally expect this to be
7316 // an oop, and like to assert the following:
7317 // assert(oop(addr)->is_oop(), "live block should be an oop");
7318 // However, as we commented above, this may be an object whose
7319 // header hasn't yet been initialized.
7320 size_t size;
7321 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7322 if (_bitMap->isMarked(addr + 1)) {
7323 // Determine the size from the bit map, rather than trying to
7324 // compute it from the object header.
7325 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7326 size = pointer_delta(nextOneAddr + 1, addr);
7327 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7328 "alignment problem");
7329
7330 #ifdef ASSERT
7331 if (oop(addr)->klass_or_null() != NULL) {
7332 // Ignore mark word because we are running concurrent with mutators
7333 assert(oop(addr)->is_oop(true), "live block should be an oop");
7334 assert(size ==
7335 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7336 "P-mark and computed size do not agree");
7337 }
7338 #endif
7339
7340 } else {
7341 // This should be an initialized object that's alive.
7342 assert(oop(addr)->klass_or_null() != NULL,
7343 "Should be an initialized object");
7344 // Ignore mark word because we are running concurrent with mutators
7345 assert(oop(addr)->is_oop(true), "live block should be an oop");
7346 // Verify that the bit map has no bits marked between
7347 // addr and purported end of this block.
7348 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7349 assert(size >= 3, "Necessary for Printezis marks to work");
7350 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7351 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7352 }
7353 return size;
7354 }
7355
7356 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7357 size_t chunkSize) {
7358 // do_post_free_or_garbage_chunk() should only be called in the case
7359 // of the adaptive free list allocator.
7360 const bool fcInFreeLists = fc->is_free();
7361 assert((HeapWord*)fc <= _limit, "sweep invariant");
7362 if (CMSTestInFreeList && fcInFreeLists) {
7363 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7364 }
7365
7366 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7367
7368 HeapWord* const fc_addr = (HeapWord*) fc;
7369
7370 bool coalesce = false;
7371 const size_t left = pointer_delta(fc_addr, freeFinger());
7372 const size_t right = chunkSize;
7373 switch (FLSCoalescePolicy) {
7374 // numeric value forms a coalition aggressiveness metric
7375 case 0: { // never coalesce
7376 coalesce = false;
7377 break;
7378 }
7379 case 1: { // coalesce if left & right chunks on overpopulated lists
7380 coalesce = _sp->coalOverPopulated(left) &&
7381 _sp->coalOverPopulated(right);
7382 break;
7383 }
7384 case 2: { // coalesce if left chunk on overpopulated list (default)
7385 coalesce = _sp->coalOverPopulated(left);
7386 break;
7387 }
7388 case 3: { // coalesce if left OR right chunk on overpopulated list
7389 coalesce = _sp->coalOverPopulated(left) ||
7390 _sp->coalOverPopulated(right);
7391 break;
7392 }
7393 case 4: { // always coalesce
7394 coalesce = true;
7395 break;
7396 }
7397 default:
7398 ShouldNotReachHere();
7399 }
7400
7401 // Should the current free range be coalesced?
7402 // If the chunk is in a free range and either we decided to coalesce above
7403 // or the chunk is near the large block at the end of the heap
7404 // (isNearLargestChunk() returns true), then coalesce this chunk.
7405 const bool doCoalesce = inFreeRange()
7406 && (coalesce || _g->isNearLargestChunk(fc_addr));
7407 if (doCoalesce) {
7408 // Coalesce the current free range on the left with the new
7409 // chunk on the right. If either is on a free list,
7410 // it must be removed from the list and stashed in the closure.
7411 if (freeRangeInFreeLists()) {
7412 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7413 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7414 "Size of free range is inconsistent with chunk size.");
7415 if (CMSTestInFreeList) {
7416 assert(_sp->verify_chunk_in_free_list(ffc),
7417 "Chunk is not in free lists");
7418 }
7419 _sp->coalDeath(ffc->size());
7420 _sp->removeFreeChunkFromFreeLists(ffc);
7421 set_freeRangeInFreeLists(false);
7422 }
7423 if (fcInFreeLists) {
7424 _sp->coalDeath(chunkSize);
7425 assert(fc->size() == chunkSize,
7426 "The chunk has the wrong size or is not in the free lists");
7427 _sp->removeFreeChunkFromFreeLists(fc);
7428 }
7429 set_lastFreeRangeCoalesced(true);
7430 print_free_block_coalesced(fc);
7431 } else { // not in a free range and/or should not coalesce
7432 // Return the current free range and start a new one.
7433 if (inFreeRange()) {
7434 // In a free range but cannot coalesce with the right hand chunk.
7435 // Put the current free range into the free lists.
7436 flush_cur_free_chunk(freeFinger(),
7437 pointer_delta(fc_addr, freeFinger()));
7438 }
7439 // Set up for new free range. Pass along whether the right hand
7440 // chunk is in the free lists.
7441 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7442 }
7443 }
7444
7445 // Lookahead flush:
7446 // If we are tracking a free range, and this is the last chunk that
7447 // we'll look at because its end crosses past _limit, we'll preemptively
7448 // flush it along with any free range we may be holding on to. Note that
7449 // this can be the case only for an already free or freshly garbage
7450 // chunk. If this block is an object, it can never straddle
7451 // over _limit. The "straddling" occurs when _limit is set at
7452 // the previous end of the space when this cycle started, and
7453 // a subsequent heap expansion caused the previously co-terminal
7454 // free block to be coalesced with the newly expanded portion,
7455 // thus rendering _limit a non-block-boundary making it dangerous
7456 // for the sweeper to step over and examine.
7457 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7458 assert(inFreeRange(), "Should only be called if currently in a free range.");
7459 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7460 assert(_sp->used_region().contains(eob - 1),
7461 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7462 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7463 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7464 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7465 if (eob >= _limit) {
7466 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7467 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7468 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7469 "[" PTR_FORMAT "," PTR_FORMAT ")",
7470 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7471 // Return the storage we are tracking back into the free lists.
7472 log_develop_trace(gc, sweep)("Flushing ... ");
7473 assert(freeFinger() < eob, "Error");
7474 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7475 }
7476 }
7477
7478 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7479 assert(inFreeRange(), "Should only be called if currently in a free range.");
7480 assert(size > 0,
7481 "A zero sized chunk cannot be added to the free lists.");
7482 if (!freeRangeInFreeLists()) {
7483 if (CMSTestInFreeList) {
7484 FreeChunk* fc = (FreeChunk*) chunk;
7485 fc->set_size(size);
7486 assert(!_sp->verify_chunk_in_free_list(fc),
7487 "chunk should not be in free lists yet");
7488 }
7489 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7490 // A new free range is going to be starting. The current
7491 // free range has not been added to the free lists yet or
7492 // was removed so add it back.
7493 // If the current free range was coalesced, then the death
7494 // of the free range was recorded. Record a birth now.
7495 if (lastFreeRangeCoalesced()) {
7496 _sp->coalBirth(size);
7497 }
7498 _sp->addChunkAndRepairOffsetTable(chunk, size,
7499 lastFreeRangeCoalesced());
7500 } else {
7501 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7502 }
7503 set_inFreeRange(false);
7504 set_freeRangeInFreeLists(false);
7505 }
7506
7507 // We take a break if we've been at this for a while,
7508 // so as to avoid monopolizing the locks involved.
7509 void SweepClosure::do_yield_work(HeapWord* addr) {
7510 // Return current free chunk being used for coalescing (if any)
7511 // to the appropriate freelist. After yielding, the next
7512 // free block encountered will start a coalescing range of
7513 // free blocks. If the next free block is adjacent to the
7514 // chunk just flushed, they will need to wait for the next
7515 // sweep to be coalesced.
7516 if (inFreeRange()) {
7517 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7518 }
7519
7520 // First give up the locks, then yield, then re-lock.
7521 // We should probably use a constructor/destructor idiom to
7522 // do this unlock/lock or modify the MutexUnlocker class to
7523 // serve our purpose. XXX
7524 assert_lock_strong(_bitMap->lock());
7525 assert_lock_strong(_freelistLock);
7526 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7527 "CMS thread should hold CMS token");
7528 _bitMap->lock()->unlock();
7529 _freelistLock->unlock();
7530 ConcurrentMarkSweepThread::desynchronize(true);
7531 _collector->stopTimer();
7532 _collector->incrementYields();
7533
7534 // See the comment in coordinator_yield()
7535 for (unsigned i = 0; i < CMSYieldSleepCount &&
7536 ConcurrentMarkSweepThread::should_yield() &&
7537 !CMSCollector::foregroundGCIsActive(); ++i) {
7538 os::sleep(Thread::current(), 1, false);
7539 }
7540
7541 ConcurrentMarkSweepThread::synchronize(true);
7542 _freelistLock->lock();
7543 _bitMap->lock()->lock_without_safepoint_check();
7544 _collector->startTimer();
7545 }
7546
7547 #ifndef PRODUCT
7548 // This is actually very useful in a product build if it can
7549 // be called from the debugger. Compile it into the product
7550 // as needed.
7551 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7552 return debug_cms_space->verify_chunk_in_free_list(fc);
7553 }
7554 #endif
7555
7556 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7557 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7558 p2i(fc), fc->size());
7559 }
7560
7561 // CMSIsAliveClosure
7562 bool CMSIsAliveClosure::do_object_b(oop obj) {
7563 HeapWord* addr = (HeapWord*)obj;
7564 return addr != NULL &&
7565 (!_span.contains(addr) || _bit_map->isMarked(addr));
7566 }
7567
7568
7569 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7570 MemRegion span,
7571 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7572 bool cpc):
7573 _collector(collector),
7574 _span(span),
7575 _bit_map(bit_map),
7576 _mark_stack(mark_stack),
7577 _concurrent_precleaning(cpc) {
7578 assert(!_span.is_empty(), "Empty span could spell trouble");
7579 }
7580
7581
7582 // CMSKeepAliveClosure: the serial version
7583 void CMSKeepAliveClosure::do_oop(oop obj) {
7584 HeapWord* addr = (HeapWord*)obj;
7585 if (_span.contains(addr) &&
7586 !_bit_map->isMarked(addr)) {
7587 _bit_map->mark(addr);
7588 bool simulate_overflow = false;
7589 NOT_PRODUCT(
7590 if (CMSMarkStackOverflowALot &&
7591 _collector->simulate_overflow()) {
7592 // simulate a stack overflow
7593 simulate_overflow = true;
7594 }
7595 )
7596 if (simulate_overflow || !_mark_stack->push(obj)) {
7597 if (_concurrent_precleaning) {
7598 // We dirty the overflown object and let the remark
7599 // phase deal with it.
7600 assert(_collector->overflow_list_is_empty(), "Error");
7601 // In the case of object arrays, we need to dirty all of
7602 // the cards that the object spans. No locking or atomics
7603 // are needed since no one else can be mutating the mod union
7604 // table.
7605 if (obj->is_objArray()) {
7606 size_t sz = obj->size();
7607 HeapWord* end_card_addr =
7608 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7609 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7610 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7611 _collector->_modUnionTable.mark_range(redirty_range);
7612 } else {
7613 _collector->_modUnionTable.mark(addr);
7614 }
7615 _collector->_ser_kac_preclean_ovflw++;
7616 } else {
7617 _collector->push_on_overflow_list(obj);
7618 _collector->_ser_kac_ovflw++;
7619 }
7620 }
7621 }
7622 }
7623
7624 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7625 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7626
7627 // CMSParKeepAliveClosure: a parallel version of the above.
7628 // The work queues are private to each closure (thread),
7629 // but (may be) available for stealing by other threads.
7630 void CMSParKeepAliveClosure::do_oop(oop obj) {
7631 HeapWord* addr = (HeapWord*)obj;
7632 if (_span.contains(addr) &&
7633 !_bit_map->isMarked(addr)) {
7634 // In general, during recursive tracing, several threads
7635 // may be concurrently getting here; the first one to
7636 // "tag" it, claims it.
7637 if (_bit_map->par_mark(addr)) {
7638 bool res = _work_queue->push(obj);
7639 assert(res, "Low water mark should be much less than capacity");
7640 // Do a recursive trim in the hope that this will keep
7641 // stack usage lower, but leave some oops for potential stealers
7642 trim_queue(_low_water_mark);
7643 } // Else, another thread got there first
7644 }
7645 }
7646
7647 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7648 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7649
7650 void CMSParKeepAliveClosure::trim_queue(uint max) {
7651 while (_work_queue->size() > max) {
7652 oop new_oop;
7653 if (_work_queue->pop_local(new_oop)) {
7654 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7655 assert(_bit_map->isMarked((HeapWord*)new_oop),
7656 "no white objects on this stack!");
7657 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7658 // iterate over the oops in this oop, marking and pushing
7659 // the ones in CMS heap (i.e. in _span).
7660 new_oop->oop_iterate(&_mark_and_push);
7661 }
7662 }
7663 }
7664
7665 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7666 CMSCollector* collector,
7667 MemRegion span, CMSBitMap* bit_map,
7668 OopTaskQueue* work_queue):
7669 _collector(collector),
7670 _span(span),
7671 _bit_map(bit_map),
7672 _work_queue(work_queue) { }
7673
7674 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7675 HeapWord* addr = (HeapWord*)obj;
7676 if (_span.contains(addr) &&
7677 !_bit_map->isMarked(addr)) {
7678 if (_bit_map->par_mark(addr)) {
7679 bool simulate_overflow = false;
7680 NOT_PRODUCT(
7681 if (CMSMarkStackOverflowALot &&
7682 _collector->par_simulate_overflow()) {
7683 // simulate a stack overflow
7684 simulate_overflow = true;
7685 }
7686 )
7687 if (simulate_overflow || !_work_queue->push(obj)) {
7688 _collector->par_push_on_overflow_list(obj);
7689 _collector->_par_kac_ovflw++;
7690 }
7691 } // Else another thread got there already
7692 }
7693 }
7694
7695 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7696 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7697
7698 //////////////////////////////////////////////////////////////////
7699 // CMSExpansionCause /////////////////////////////
7700 //////////////////////////////////////////////////////////////////
7701 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7702 switch (cause) {
7703 case _no_expansion:
7704 return "No expansion";
7705 case _satisfy_free_ratio:
7706 return "Free ratio";
7707 case _satisfy_promotion:
7708 return "Satisfy promotion";
7709 case _satisfy_allocation:
7710 return "allocation";
7711 case _allocate_par_lab:
7712 return "Par LAB";
7713 case _allocate_par_spooling_space:
7714 return "Par Spooling Space";
7715 case _adaptive_size_policy:
7716 return "Ergonomics";
7717 default:
7718 return "unknown";
7719 }
7720 }
7721
7722 void CMSDrainMarkingStackClosure::do_void() {
7723 // the max number to take from overflow list at a time
7724 const size_t num = _mark_stack->capacity()/4;
7725 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7726 "Overflow list should be NULL during concurrent phases");
7727 while (!_mark_stack->isEmpty() ||
7728 // if stack is empty, check the overflow list
7729 _collector->take_from_overflow_list(num, _mark_stack)) {
7730 oop obj = _mark_stack->pop();
7731 HeapWord* addr = (HeapWord*)obj;
7732 assert(_span.contains(addr), "Should be within span");
7733 assert(_bit_map->isMarked(addr), "Should be marked");
7734 assert(obj->is_oop(), "Should be an oop");
7735 obj->oop_iterate(_keep_alive);
7736 }
7737 }
7738
7739 void CMSParDrainMarkingStackClosure::do_void() {
7740 // drain queue
7741 trim_queue(0);
7742 }
7743
7744 // Trim our work_queue so its length is below max at return
7745 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7746 while (_work_queue->size() > max) {
7747 oop new_oop;
7748 if (_work_queue->pop_local(new_oop)) {
7749 assert(new_oop->is_oop(), "Expected an oop");
7750 assert(_bit_map->isMarked((HeapWord*)new_oop),
7751 "no white objects on this stack!");
7752 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7753 // iterate over the oops in this oop, marking and pushing
7754 // the ones in CMS heap (i.e. in _span).
7755 new_oop->oop_iterate(&_mark_and_push);
7756 }
7757 }
7758 }
7759
7760 ////////////////////////////////////////////////////////////////////
7761 // Support for Marking Stack Overflow list handling and related code
7762 ////////////////////////////////////////////////////////////////////
7763 // Much of the following code is similar in shape and spirit to the
7764 // code used in ParNewGC. We should try and share that code
7765 // as much as possible in the future.
7766
7767 #ifndef PRODUCT
7768 // Debugging support for CMSStackOverflowALot
7769
7770 // It's OK to call this multi-threaded; the worst thing
7771 // that can happen is that we'll get a bunch of closely
7772 // spaced simulated overflows, but that's OK, in fact
7773 // probably good as it would exercise the overflow code
7774 // under contention.
7775 bool CMSCollector::simulate_overflow() {
7776 if (_overflow_counter-- <= 0) { // just being defensive
7777 _overflow_counter = CMSMarkStackOverflowInterval;
7778 return true;
7779 } else {
7780 return false;
7781 }
7782 }
7783
7784 bool CMSCollector::par_simulate_overflow() {
7785 return simulate_overflow();
7786 }
7787 #endif
7788
7789 // Single-threaded
7790 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7791 assert(stack->isEmpty(), "Expected precondition");
7792 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7793 size_t i = num;
7794 oop cur = _overflow_list;
7795 const markOop proto = markOopDesc::prototype();
7796 NOT_PRODUCT(ssize_t n = 0;)
7797 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7798 next = oop(cur->mark());
7799 cur->set_mark(proto); // until proven otherwise
7800 assert(cur->is_oop(), "Should be an oop");
7801 bool res = stack->push(cur);
7802 assert(res, "Bit off more than can chew?");
7803 NOT_PRODUCT(n++;)
7804 }
7805 _overflow_list = cur;
7806 #ifndef PRODUCT
7807 assert(_num_par_pushes >= n, "Too many pops?");
7808 _num_par_pushes -=n;
7809 #endif
7810 return !stack->isEmpty();
7811 }
7812
7813 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7814 // (MT-safe) Get a prefix of at most "num" from the list.
7815 // The overflow list is chained through the mark word of
7816 // each object in the list. We fetch the entire list,
7817 // break off a prefix of the right size and return the
7818 // remainder. If other threads try to take objects from
7819 // the overflow list at that time, they will wait for
7820 // some time to see if data becomes available. If (and
7821 // only if) another thread places one or more object(s)
7822 // on the global list before we have returned the suffix
7823 // to the global list, we will walk down our local list
7824 // to find its end and append the global list to
7825 // our suffix before returning it. This suffix walk can
7826 // prove to be expensive (quadratic in the amount of traffic)
7827 // when there are many objects in the overflow list and
7828 // there is much producer-consumer contention on the list.
7829 // *NOTE*: The overflow list manipulation code here and
7830 // in ParNewGeneration:: are very similar in shape,
7831 // except that in the ParNew case we use the old (from/eden)
7832 // copy of the object to thread the list via its klass word.
7833 // Because of the common code, if you make any changes in
7834 // the code below, please check the ParNew version to see if
7835 // similar changes might be needed.
7836 // CR 6797058 has been filed to consolidate the common code.
7837 bool CMSCollector::par_take_from_overflow_list(size_t num,
7838 OopTaskQueue* work_q,
7839 int no_of_gc_threads) {
7840 assert(work_q->size() == 0, "First empty local work queue");
7841 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7842 if (_overflow_list == NULL) {
7843 return false;
7844 }
7845 // Grab the entire list; we'll put back a suffix
7846 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7847 Thread* tid = Thread::current();
7848 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7849 // set to ParallelGCThreads.
7850 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7851 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7852 // If the list is busy, we spin for a short while,
7853 // sleeping between attempts to get the list.
7854 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7855 os::sleep(tid, sleep_time_millis, false);
7856 if (_overflow_list == NULL) {
7857 // Nothing left to take
7858 return false;
7859 } else if (_overflow_list != BUSY) {
7860 // Try and grab the prefix
7861 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7862 }
7863 }
7864 // If the list was found to be empty, or we spun long
7865 // enough, we give up and return empty-handed. If we leave
7866 // the list in the BUSY state below, it must be the case that
7867 // some other thread holds the overflow list and will set it
7868 // to a non-BUSY state in the future.
7869 if (prefix == NULL || prefix == BUSY) {
7870 // Nothing to take or waited long enough
7871 if (prefix == NULL) {
7872 // Write back the NULL in case we overwrote it with BUSY above
7873 // and it is still the same value.
7874 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7875 }
7876 return false;
7877 }
7878 assert(prefix != NULL && prefix != BUSY, "Error");
7879 size_t i = num;
7880 oop cur = prefix;
7881 // Walk down the first "num" objects, unless we reach the end.
7882 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7883 if (cur->mark() == NULL) {
7884 // We have "num" or fewer elements in the list, so there
7885 // is nothing to return to the global list.
7886 // Write back the NULL in lieu of the BUSY we wrote
7887 // above, if it is still the same value.
7888 if (_overflow_list == BUSY) {
7889 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7890 }
7891 } else {
7892 // Chop off the suffix and return it to the global list.
7893 assert(cur->mark() != BUSY, "Error");
7894 oop suffix_head = cur->mark(); // suffix will be put back on global list
7895 cur->set_mark(NULL); // break off suffix
7896 // It's possible that the list is still in the empty(busy) state
7897 // we left it in a short while ago; in that case we may be
7898 // able to place back the suffix without incurring the cost
7899 // of a walk down the list.
7900 oop observed_overflow_list = _overflow_list;
7901 oop cur_overflow_list = observed_overflow_list;
7902 bool attached = false;
7903 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7904 observed_overflow_list =
7905 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7906 if (cur_overflow_list == observed_overflow_list) {
7907 attached = true;
7908 break;
7909 } else cur_overflow_list = observed_overflow_list;
7910 }
7911 if (!attached) {
7912 // Too bad, someone else sneaked in (at least) an element; we'll need
7913 // to do a splice. Find tail of suffix so we can prepend suffix to global
7914 // list.
7915 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7916 oop suffix_tail = cur;
7917 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7918 "Tautology");
7919 observed_overflow_list = _overflow_list;
7920 do {
7921 cur_overflow_list = observed_overflow_list;
7922 if (cur_overflow_list != BUSY) {
7923 // Do the splice ...
7924 suffix_tail->set_mark(markOop(cur_overflow_list));
7925 } else { // cur_overflow_list == BUSY
7926 suffix_tail->set_mark(NULL);
7927 }
7928 // ... and try to place spliced list back on overflow_list ...
7929 observed_overflow_list =
7930 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7931 } while (cur_overflow_list != observed_overflow_list);
7932 // ... until we have succeeded in doing so.
7933 }
7934 }
7935
7936 // Push the prefix elements on work_q
7937 assert(prefix != NULL, "control point invariant");
7938 const markOop proto = markOopDesc::prototype();
7939 oop next;
7940 NOT_PRODUCT(ssize_t n = 0;)
7941 for (cur = prefix; cur != NULL; cur = next) {
7942 next = oop(cur->mark());
7943 cur->set_mark(proto); // until proven otherwise
7944 assert(cur->is_oop(), "Should be an oop");
7945 bool res = work_q->push(cur);
7946 assert(res, "Bit off more than we can chew?");
7947 NOT_PRODUCT(n++;)
7948 }
7949 #ifndef PRODUCT
7950 assert(_num_par_pushes >= n, "Too many pops?");
7951 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7952 #endif
7953 return true;
7954 }
7955
7956 // Single-threaded
7957 void CMSCollector::push_on_overflow_list(oop p) {
7958 NOT_PRODUCT(_num_par_pushes++;)
7959 assert(p->is_oop(), "Not an oop");
7960 preserve_mark_if_necessary(p);
7961 p->set_mark((markOop)_overflow_list);
7962 _overflow_list = p;
7963 }
7964
7965 // Multi-threaded; use CAS to prepend to overflow list
7966 void CMSCollector::par_push_on_overflow_list(oop p) {
7967 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7968 assert(p->is_oop(), "Not an oop");
7969 par_preserve_mark_if_necessary(p);
7970 oop observed_overflow_list = _overflow_list;
7971 oop cur_overflow_list;
7972 do {
7973 cur_overflow_list = observed_overflow_list;
7974 if (cur_overflow_list != BUSY) {
7975 p->set_mark(markOop(cur_overflow_list));
7976 } else {
7977 p->set_mark(NULL);
7978 }
7979 observed_overflow_list =
7980 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7981 } while (cur_overflow_list != observed_overflow_list);
7982 }
7983 #undef BUSY
7984
7985 // Single threaded
7986 // General Note on GrowableArray: pushes may silently fail
7987 // because we are (temporarily) out of C-heap for expanding
7988 // the stack. The problem is quite ubiquitous and affects
7989 // a lot of code in the JVM. The prudent thing for GrowableArray
7990 // to do (for now) is to exit with an error. However, that may
7991 // be too draconian in some cases because the caller may be
7992 // able to recover without much harm. For such cases, we
7993 // should probably introduce a "soft_push" method which returns
7994 // an indication of success or failure with the assumption that
7995 // the caller may be able to recover from a failure; code in
7996 // the VM can then be changed, incrementally, to deal with such
7997 // failures where possible, thus, incrementally hardening the VM
7998 // in such low resource situations.
7999 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8000 _preserved_oop_stack.push(p);
8001 _preserved_mark_stack.push(m);
8002 assert(m == p->mark(), "Mark word changed");
8003 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8004 "bijection");
8005 }
8006
8007 // Single threaded
8008 void CMSCollector::preserve_mark_if_necessary(oop p) {
8009 markOop m = p->mark();
8010 if (m->must_be_preserved(p)) {
8011 preserve_mark_work(p, m);
8012 }
8013 }
8014
8015 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8016 markOop m = p->mark();
8017 if (m->must_be_preserved(p)) {
8018 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8019 // Even though we read the mark word without holding
8020 // the lock, we are assured that it will not change
8021 // because we "own" this oop, so no other thread can
8022 // be trying to push it on the overflow list; see
8023 // the assertion in preserve_mark_work() that checks
8024 // that m == p->mark().
8025 preserve_mark_work(p, m);
8026 }
8027 }
8028
8029 // We should be able to do this multi-threaded,
8030 // a chunk of stack being a task (this is
8031 // correct because each oop only ever appears
8032 // once in the overflow list. However, it's
8033 // not very easy to completely overlap this with
8034 // other operations, so will generally not be done
8035 // until all work's been completed. Because we
8036 // expect the preserved oop stack (set) to be small,
8037 // it's probably fine to do this single-threaded.
8038 // We can explore cleverer concurrent/overlapped/parallel
8039 // processing of preserved marks if we feel the
8040 // need for this in the future. Stack overflow should
8041 // be so rare in practice and, when it happens, its
8042 // effect on performance so great that this will
8043 // likely just be in the noise anyway.
8044 void CMSCollector::restore_preserved_marks_if_any() {
8045 assert(SafepointSynchronize::is_at_safepoint(),
8046 "world should be stopped");
8047 assert(Thread::current()->is_ConcurrentGC_thread() ||
8048 Thread::current()->is_VM_thread(),
8049 "should be single-threaded");
8050 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8051 "bijection");
8052
8053 while (!_preserved_oop_stack.is_empty()) {
8054 oop p = _preserved_oop_stack.pop();
8055 assert(p->is_oop(), "Should be an oop");
8056 assert(_span.contains(p), "oop should be in _span");
8057 assert(p->mark() == markOopDesc::prototype(),
8058 "Set when taken from overflow list");
8059 markOop m = _preserved_mark_stack.pop();
8060 p->set_mark(m);
8061 }
8062 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8063 "stacks were cleared above");
8064 }
8065
8066 #ifndef PRODUCT
8067 bool CMSCollector::no_preserved_marks() const {
8068 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8069 }
8070 #endif
8071
8072 // Transfer some number of overflown objects to usual marking
8073 // stack. Return true if some objects were transferred.
8074 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8075 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8076 (size_t)ParGCDesiredObjsFromOverflowList);
8077
8078 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8079 assert(_collector->overflow_list_is_empty() || res,
8080 "If list is not empty, we should have taken something");
8081 assert(!res || !_mark_stack->isEmpty(),
8082 "If we took something, it should now be on our stack");
8083 return res;
8084 }
8085
8086 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8087 size_t res = _sp->block_size_no_stall(addr, _collector);
8088 if (_sp->block_is_obj(addr)) {
8089 if (_live_bit_map->isMarked(addr)) {
8090 // It can't have been dead in a previous cycle
8091 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8092 } else {
8093 _dead_bit_map->mark(addr); // mark the dead object
8094 }
8095 }
8096 // Could be 0, if the block size could not be computed without stalling.
8097 return res;
8098 }
8099
8100 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8101
8102 switch (phase) {
8103 case CMSCollector::InitialMarking:
8104 initialize(true /* fullGC */ ,
8105 cause /* cause of the GC */,
8106 true /* recordGCBeginTime */,
8107 true /* recordPreGCUsage */,
8108 false /* recordPeakUsage */,
8109 false /* recordPostGCusage */,
8110 true /* recordAccumulatedGCTime */,
8111 false /* recordGCEndTime */,
8112 false /* countCollection */ );
8113 break;
8114
8115 case CMSCollector::FinalMarking:
8116 initialize(true /* fullGC */ ,
8117 cause /* cause of the GC */,
8118 false /* recordGCBeginTime */,
8119 false /* recordPreGCUsage */,
8120 false /* recordPeakUsage */,
8121 false /* recordPostGCusage */,
8122 true /* recordAccumulatedGCTime */,
8123 false /* recordGCEndTime */,
8124 false /* countCollection */ );
8125 break;
8126
8127 case CMSCollector::Sweeping:
8128 initialize(true /* fullGC */ ,
8129 cause /* cause of the GC */,
8130 false /* recordGCBeginTime */,
8131 false /* recordPreGCUsage */,
8132 true /* recordPeakUsage */,
8133 true /* recordPostGCusage */,
8134 false /* recordAccumulatedGCTime */,
8135 true /* recordGCEndTime */,
8136 true /* countCollection */ );
8137 break;
8138
8139 default:
8140 ShouldNotReachHere();
8141 }
8142 }