1 /*
2 * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsOopClosures.inline.hpp"
33 #include "gc/cms/compactibleFreeListSpace.hpp"
34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc/cms/concurrentMarkSweepThread.hpp"
36 #include "gc/cms/parNewGeneration.hpp"
37 #include "gc/cms/vmCMSOperations.hpp"
38 #include "gc/serial/genMarkSweep.hpp"
39 #include "gc/serial/tenuredGeneration.hpp"
40 #include "gc/shared/adaptiveSizePolicy.hpp"
41 #include "gc/shared/cardGeneration.inline.hpp"
42 #include "gc/shared/cardTableRS.hpp"
43 #include "gc/shared/collectedHeap.inline.hpp"
44 #include "gc/shared/collectorCounters.hpp"
45 #include "gc/shared/collectorPolicy.hpp"
46 #include "gc/shared/gcLocker.inline.hpp"
47 #include "gc/shared/gcPolicyCounters.hpp"
48 #include "gc/shared/gcTimer.hpp"
49 #include "gc/shared/gcTrace.hpp"
50 #include "gc/shared/gcTraceTime.inline.hpp"
51 #include "gc/shared/genCollectedHeap.hpp"
52 #include "gc/shared/genOopClosures.inline.hpp"
53 #include "gc/shared/isGCActiveMark.hpp"
54 #include "gc/shared/referencePolicy.hpp"
55 #include "gc/shared/strongRootsScope.hpp"
56 #include "gc/shared/taskqueue.inline.hpp"
57 #include "logging/log.hpp"
58 #include "memory/allocation.hpp"
59 #include "memory/iterator.inline.hpp"
60 #include "memory/padded.hpp"
61 #include "memory/resourceArea.hpp"
62 #include "oops/oop.inline.hpp"
63 #include "prims/jvmtiExport.hpp"
64 #include "runtime/atomic.hpp"
65 #include "runtime/globals_extension.hpp"
66 #include "runtime/handles.inline.hpp"
67 #include "runtime/java.hpp"
68 #include "runtime/orderAccess.inline.hpp"
69 #include "runtime/timer.hpp"
70 #include "runtime/vmThread.hpp"
71 #include "services/memoryService.hpp"
72 #include "services/runtimeService.hpp"
73 #include "utilities/stack.inline.hpp"
74
75 // statics
76 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
77 bool CMSCollector::_full_gc_requested = false;
78 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
79
80 //////////////////////////////////////////////////////////////////
81 // In support of CMS/VM thread synchronization
82 //////////////////////////////////////////////////////////////////
83 // We split use of the CGC_lock into 2 "levels".
84 // The low-level locking is of the usual CGC_lock monitor. We introduce
85 // a higher level "token" (hereafter "CMS token") built on top of the
86 // low level monitor (hereafter "CGC lock").
87 // The token-passing protocol gives priority to the VM thread. The
88 // CMS-lock doesn't provide any fairness guarantees, but clients
89 // should ensure that it is only held for very short, bounded
90 // durations.
91 //
92 // When either of the CMS thread or the VM thread is involved in
93 // collection operations during which it does not want the other
94 // thread to interfere, it obtains the CMS token.
95 //
96 // If either thread tries to get the token while the other has
97 // it, that thread waits. However, if the VM thread and CMS thread
98 // both want the token, then the VM thread gets priority while the
99 // CMS thread waits. This ensures, for instance, that the "concurrent"
100 // phases of the CMS thread's work do not block out the VM thread
101 // for long periods of time as the CMS thread continues to hog
102 // the token. (See bug 4616232).
103 //
104 // The baton-passing functions are, however, controlled by the
105 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
106 // and here the low-level CMS lock, not the high level token,
107 // ensures mutual exclusion.
108 //
109 // Two important conditions that we have to satisfy:
110 // 1. if a thread does a low-level wait on the CMS lock, then it
111 // relinquishes the CMS token if it were holding that token
112 // when it acquired the low-level CMS lock.
113 // 2. any low-level notifications on the low-level lock
114 // should only be sent when a thread has relinquished the token.
115 //
116 // In the absence of either property, we'd have potential deadlock.
117 //
118 // We protect each of the CMS (concurrent and sequential) phases
119 // with the CMS _token_, not the CMS _lock_.
120 //
121 // The only code protected by CMS lock is the token acquisition code
122 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
123 // baton-passing code.
124 //
125 // Unfortunately, i couldn't come up with a good abstraction to factor and
126 // hide the naked CGC_lock manipulation in the baton-passing code
127 // further below. That's something we should try to do. Also, the proof
128 // of correctness of this 2-level locking scheme is far from obvious,
129 // and potentially quite slippery. We have an uneasy suspicion, for instance,
130 // that there may be a theoretical possibility of delay/starvation in the
131 // low-level lock/wait/notify scheme used for the baton-passing because of
132 // potential interference with the priority scheme embodied in the
133 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
134 // invocation further below and marked with "XXX 20011219YSR".
135 // Indeed, as we note elsewhere, this may become yet more slippery
136 // in the presence of multiple CMS and/or multiple VM threads. XXX
137
138 class CMSTokenSync: public StackObj {
139 private:
140 bool _is_cms_thread;
141 public:
142 CMSTokenSync(bool is_cms_thread):
143 _is_cms_thread(is_cms_thread) {
144 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
145 "Incorrect argument to constructor");
146 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
147 }
148
149 ~CMSTokenSync() {
150 assert(_is_cms_thread ?
151 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
152 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
153 "Incorrect state");
154 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
155 }
156 };
157
158 // Convenience class that does a CMSTokenSync, and then acquires
159 // upto three locks.
160 class CMSTokenSyncWithLocks: public CMSTokenSync {
161 private:
162 // Note: locks are acquired in textual declaration order
163 // and released in the opposite order
164 MutexLockerEx _locker1, _locker2, _locker3;
165 public:
166 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
167 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
168 CMSTokenSync(is_cms_thread),
169 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
170 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
171 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
172 { }
173 };
174
175
176 //////////////////////////////////////////////////////////////////
177 // Concurrent Mark-Sweep Generation /////////////////////////////
178 //////////////////////////////////////////////////////////////////
179
180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
181
182 // This struct contains per-thread things necessary to support parallel
183 // young-gen collection.
184 class CMSParGCThreadState: public CHeapObj<mtGC> {
185 public:
186 CompactibleFreeListSpaceLAB lab;
187 PromotionInfo promo;
188
189 // Constructor.
190 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
191 promo.setSpace(cfls);
192 }
193 };
194
195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
196 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
197 CardGeneration(rs, initial_byte_size, ct),
198 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
199 _did_compact(false)
200 {
201 HeapWord* bottom = (HeapWord*) _virtual_space.low();
202 HeapWord* end = (HeapWord*) _virtual_space.high();
203
204 _direct_allocated_words = 0;
205 NOT_PRODUCT(
206 _numObjectsPromoted = 0;
207 _numWordsPromoted = 0;
208 _numObjectsAllocated = 0;
209 _numWordsAllocated = 0;
210 )
211
212 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
213 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
214 _cmsSpace->_old_gen = this;
215
216 _gc_stats = new CMSGCStats();
217
218 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
219 // offsets match. The ability to tell free chunks from objects
220 // depends on this property.
221 debug_only(
222 FreeChunk* junk = NULL;
223 assert(UseCompressedClassPointers ||
224 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
225 "Offset of FreeChunk::_prev within FreeChunk must match"
226 " that of OopDesc::_klass within OopDesc");
227 )
228
229 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
230 for (uint i = 0; i < ParallelGCThreads; i++) {
231 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
232 }
233
234 _incremental_collection_failed = false;
235 // The "dilatation_factor" is the expansion that can occur on
236 // account of the fact that the minimum object size in the CMS
237 // generation may be larger than that in, say, a contiguous young
238 // generation.
239 // Ideally, in the calculation below, we'd compute the dilatation
240 // factor as: MinChunkSize/(promoting_gen's min object size)
241 // Since we do not have such a general query interface for the
242 // promoting generation, we'll instead just use the minimum
243 // object size (which today is a header's worth of space);
244 // note that all arithmetic is in units of HeapWords.
245 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
246 assert(_dilatation_factor >= 1.0, "from previous assert");
247 }
248
249
250 // The field "_initiating_occupancy" represents the occupancy percentage
251 // at which we trigger a new collection cycle. Unless explicitly specified
252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
253 // is calculated by:
254 //
255 // Let "f" be MinHeapFreeRatio in
256 //
257 // _initiating_occupancy = 100-f +
258 // f * (CMSTriggerRatio/100)
259 // where CMSTriggerRatio is the argument "tr" below.
260 //
261 // That is, if we assume the heap is at its desired maximum occupancy at the
262 // end of a collection, we let CMSTriggerRatio of the (purported) free
263 // space be allocated before initiating a new collection cycle.
264 //
265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
266 assert(io <= 100 && tr <= 100, "Check the arguments");
267 if (io >= 0) {
268 _initiating_occupancy = (double)io / 100.0;
269 } else {
270 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
271 (double)(tr * MinHeapFreeRatio) / 100.0)
272 / 100.0;
273 }
274 }
275
276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
277 assert(collector() != NULL, "no collector");
278 collector()->ref_processor_init();
279 }
280
281 void CMSCollector::ref_processor_init() {
282 if (_ref_processor == NULL) {
283 // Allocate and initialize a reference processor
284 _ref_processor =
285 new ReferenceProcessor(_span, // span
286 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
287 ParallelGCThreads, // mt processing degree
288 _cmsGen->refs_discovery_is_mt(), // mt discovery
289 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
290 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
291 &_is_alive_closure); // closure for liveness info
292 // Initialize the _ref_processor field of CMSGen
293 _cmsGen->set_ref_processor(_ref_processor);
294
295 }
296 }
297
298 AdaptiveSizePolicy* CMSCollector::size_policy() {
299 GenCollectedHeap* gch = GenCollectedHeap::heap();
300 return gch->gen_policy()->size_policy();
301 }
302
303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
304
305 const char* gen_name = "old";
306 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
307 // Generation Counters - generation 1, 1 subspace
308 _gen_counters = new GenerationCounters(gen_name, 1, 1,
309 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
310
311 _space_counters = new GSpaceCounters(gen_name, 0,
312 _virtual_space.reserved_size(),
313 this, _gen_counters);
314 }
315
316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
317 _cms_gen(cms_gen)
318 {
319 assert(alpha <= 100, "bad value");
320 _saved_alpha = alpha;
321
322 // Initialize the alphas to the bootstrap value of 100.
323 _gc0_alpha = _cms_alpha = 100;
324
325 _cms_begin_time.update();
326 _cms_end_time.update();
327
328 _gc0_duration = 0.0;
329 _gc0_period = 0.0;
330 _gc0_promoted = 0;
331
332 _cms_duration = 0.0;
333 _cms_period = 0.0;
334 _cms_allocated = 0;
335
336 _cms_used_at_gc0_begin = 0;
337 _cms_used_at_gc0_end = 0;
338 _allow_duty_cycle_reduction = false;
339 _valid_bits = 0;
340 }
341
342 double CMSStats::cms_free_adjustment_factor(size_t free) const {
343 // TBD: CR 6909490
344 return 1.0;
345 }
346
347 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
348 }
349
350 // If promotion failure handling is on use
351 // the padded average size of the promotion for each
352 // young generation collection.
353 double CMSStats::time_until_cms_gen_full() const {
354 size_t cms_free = _cms_gen->cmsSpace()->free();
355 GenCollectedHeap* gch = GenCollectedHeap::heap();
356 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
357 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
358 if (cms_free > expected_promotion) {
359 // Start a cms collection if there isn't enough space to promote
360 // for the next young collection. Use the padded average as
361 // a safety factor.
362 cms_free -= expected_promotion;
363
364 // Adjust by the safety factor.
365 double cms_free_dbl = (double)cms_free;
366 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
367 // Apply a further correction factor which tries to adjust
368 // for recent occurance of concurrent mode failures.
369 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
370 cms_free_dbl = cms_free_dbl * cms_adjustment;
371
372 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
373 cms_free, expected_promotion);
374 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
375 // Add 1 in case the consumption rate goes to zero.
376 return cms_free_dbl / (cms_consumption_rate() + 1.0);
377 }
378 return 0.0;
379 }
380
381 // Compare the duration of the cms collection to the
382 // time remaining before the cms generation is empty.
383 // Note that the time from the start of the cms collection
384 // to the start of the cms sweep (less than the total
385 // duration of the cms collection) can be used. This
386 // has been tried and some applications experienced
387 // promotion failures early in execution. This was
388 // possibly because the averages were not accurate
389 // enough at the beginning.
390 double CMSStats::time_until_cms_start() const {
391 // We add "gc0_period" to the "work" calculation
392 // below because this query is done (mostly) at the
393 // end of a scavenge, so we need to conservatively
394 // account for that much possible delay
395 // in the query so as to avoid concurrent mode failures
396 // due to starting the collection just a wee bit too
397 // late.
398 double work = cms_duration() + gc0_period();
399 double deadline = time_until_cms_gen_full();
400 // If a concurrent mode failure occurred recently, we want to be
401 // more conservative and halve our expected time_until_cms_gen_full()
402 if (work > deadline) {
403 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
404 cms_duration(), gc0_period(), time_until_cms_gen_full());
405 return 0.0;
406 }
407 return work - deadline;
408 }
409
410 #ifndef PRODUCT
411 void CMSStats::print_on(outputStream *st) const {
412 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
413 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
414 gc0_duration(), gc0_period(), gc0_promoted());
415 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
416 cms_duration(), cms_period(), cms_allocated());
417 st->print(",cms_since_beg=%g,cms_since_end=%g",
418 cms_time_since_begin(), cms_time_since_end());
419 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
420 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
421
422 if (valid()) {
423 st->print(",promo_rate=%g,cms_alloc_rate=%g",
424 promotion_rate(), cms_allocation_rate());
425 st->print(",cms_consumption_rate=%g,time_until_full=%g",
426 cms_consumption_rate(), time_until_cms_gen_full());
427 }
428 st->cr();
429 }
430 #endif // #ifndef PRODUCT
431
432 CMSCollector::CollectorState CMSCollector::_collectorState =
433 CMSCollector::Idling;
434 bool CMSCollector::_foregroundGCIsActive = false;
435 bool CMSCollector::_foregroundGCShouldWait = false;
436
437 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
438 CardTableRS* ct,
439 ConcurrentMarkSweepPolicy* cp):
440 _cmsGen(cmsGen),
441 _ct(ct),
442 _ref_processor(NULL), // will be set later
443 _conc_workers(NULL), // may be set later
444 _abort_preclean(false),
445 _start_sampling(false),
446 _between_prologue_and_epilogue(false),
447 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
448 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
449 -1 /* lock-free */, "No_lock" /* dummy */),
450 _modUnionClosurePar(&_modUnionTable),
451 // Adjust my span to cover old (cms) gen
452 _span(cmsGen->reserved()),
453 // Construct the is_alive_closure with _span & markBitMap
454 _is_alive_closure(_span, &_markBitMap),
455 _restart_addr(NULL),
456 _overflow_list(NULL),
457 _stats(cmsGen),
458 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
459 //verify that this lock should be acquired with safepoint check.
460 Monitor::_safepoint_check_sometimes)),
461 _eden_chunk_array(NULL), // may be set in ctor body
462 _eden_chunk_capacity(0), // -- ditto --
463 _eden_chunk_index(0), // -- ditto --
464 _survivor_plab_array(NULL), // -- ditto --
465 _survivor_chunk_array(NULL), // -- ditto --
466 _survivor_chunk_capacity(0), // -- ditto --
467 _survivor_chunk_index(0), // -- ditto --
468 _ser_pmc_preclean_ovflw(0),
469 _ser_kac_preclean_ovflw(0),
470 _ser_pmc_remark_ovflw(0),
471 _par_pmc_remark_ovflw(0),
472 _ser_kac_ovflw(0),
473 _par_kac_ovflw(0),
474 #ifndef PRODUCT
475 _num_par_pushes(0),
476 #endif
477 _collection_count_start(0),
478 _verifying(false),
479 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
480 _completed_initialization(false),
481 _collector_policy(cp),
482 _should_unload_classes(CMSClassUnloadingEnabled),
483 _concurrent_cycles_since_last_unload(0),
484 _roots_scanning_options(GenCollectedHeap::SO_None),
485 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
486 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
487 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
488 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
489 _cms_start_registered(false)
490 {
491 // Now expand the span and allocate the collection support structures
492 // (MUT, marking bit map etc.) to cover both generations subject to
493 // collection.
494
495 // For use by dirty card to oop closures.
496 _cmsGen->cmsSpace()->set_collector(this);
497
498 // Allocate MUT and marking bit map
499 {
500 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
501 if (!_markBitMap.allocate(_span)) {
502 log_warning(gc)("Failed to allocate CMS Bit Map");
503 return;
504 }
505 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
506 }
507 {
508 _modUnionTable.allocate(_span);
509 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
510 }
511
512 if (!_markStack.allocate(MarkStackSize)) {
513 log_warning(gc)("Failed to allocate CMS Marking Stack");
514 return;
515 }
516
517 // Support for multi-threaded concurrent phases
518 if (CMSConcurrentMTEnabled) {
519 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
520 // just for now
521 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
522 }
523 if (ConcGCThreads > 1) {
524 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
525 ConcGCThreads, true);
526 if (_conc_workers == NULL) {
527 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
528 CMSConcurrentMTEnabled = false;
529 } else {
530 _conc_workers->initialize_workers();
531 }
532 } else {
533 CMSConcurrentMTEnabled = false;
534 }
535 }
536 if (!CMSConcurrentMTEnabled) {
537 ConcGCThreads = 0;
538 } else {
539 // Turn off CMSCleanOnEnter optimization temporarily for
540 // the MT case where it's not fixed yet; see 6178663.
541 CMSCleanOnEnter = false;
542 }
543 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
544 "Inconsistency");
545 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
546 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
547
548 // Parallel task queues; these are shared for the
549 // concurrent and stop-world phases of CMS, but
550 // are not shared with parallel scavenge (ParNew).
551 {
552 uint i;
553 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
554
555 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
556 || ParallelRefProcEnabled)
557 && num_queues > 0) {
558 _task_queues = new OopTaskQueueSet(num_queues);
559 if (_task_queues == NULL) {
560 log_warning(gc)("task_queues allocation failure.");
561 return;
562 }
563 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
564 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
565 for (i = 0; i < num_queues; i++) {
566 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
567 if (q == NULL) {
568 log_warning(gc)("work_queue allocation failure.");
569 return;
570 }
571 _task_queues->register_queue(i, q);
572 }
573 for (i = 0; i < num_queues; i++) {
574 _task_queues->queue(i)->initialize();
575 _hash_seed[i] = 17; // copied from ParNew
576 }
577 }
578 }
579
580 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
581
582 // Clip CMSBootstrapOccupancy between 0 and 100.
583 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
584
585 // Now tell CMS generations the identity of their collector
586 ConcurrentMarkSweepGeneration::set_collector(this);
587
588 // Create & start a CMS thread for this CMS collector
589 _cmsThread = ConcurrentMarkSweepThread::start(this);
590 assert(cmsThread() != NULL, "CMS Thread should have been created");
591 assert(cmsThread()->collector() == this,
592 "CMS Thread should refer to this gen");
593 assert(CGC_lock != NULL, "Where's the CGC_lock?");
594
595 // Support for parallelizing young gen rescan
596 GenCollectedHeap* gch = GenCollectedHeap::heap();
597 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
598 _young_gen = (ParNewGeneration*)gch->young_gen();
599 if (gch->supports_inline_contig_alloc()) {
600 _top_addr = gch->top_addr();
601 _end_addr = gch->end_addr();
602 assert(_young_gen != NULL, "no _young_gen");
603 _eden_chunk_index = 0;
604 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
605 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
606 }
607
608 // Support for parallelizing survivor space rescan
609 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
610 const size_t max_plab_samples =
611 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
612
613 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
614 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
615 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
616 _survivor_chunk_capacity = max_plab_samples;
617 for (uint i = 0; i < ParallelGCThreads; i++) {
618 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
619 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
620 assert(cur->end() == 0, "Should be 0");
621 assert(cur->array() == vec, "Should be vec");
622 assert(cur->capacity() == max_plab_samples, "Error");
623 }
624 }
625
626 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
627 _gc_counters = new CollectorCounters("CMS", 1);
628 _completed_initialization = true;
629 _inter_sweep_timer.start(); // start of time
630 }
631
632 const char* ConcurrentMarkSweepGeneration::name() const {
633 return "concurrent mark-sweep generation";
634 }
635 void ConcurrentMarkSweepGeneration::update_counters() {
636 if (UsePerfData) {
637 _space_counters->update_all();
638 _gen_counters->update_all();
639 }
640 }
641
642 // this is an optimized version of update_counters(). it takes the
643 // used value as a parameter rather than computing it.
644 //
645 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
646 if (UsePerfData) {
647 _space_counters->update_used(used);
648 _space_counters->update_capacity();
649 _gen_counters->update_all();
650 }
651 }
652
653 void ConcurrentMarkSweepGeneration::print() const {
654 Generation::print();
655 cmsSpace()->print();
656 }
657
658 #ifndef PRODUCT
659 void ConcurrentMarkSweepGeneration::print_statistics() {
660 cmsSpace()->printFLCensus(0);
661 }
662 #endif
663
664 size_t
665 ConcurrentMarkSweepGeneration::contiguous_available() const {
666 // dld proposes an improvement in precision here. If the committed
667 // part of the space ends in a free block we should add that to
668 // uncommitted size in the calculation below. Will make this
669 // change later, staying with the approximation below for the
670 // time being. -- ysr.
671 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
672 }
673
674 size_t
675 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
676 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
677 }
678
679 size_t ConcurrentMarkSweepGeneration::max_available() const {
680 return free() + _virtual_space.uncommitted_size();
681 }
682
683 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
684 size_t available = max_available();
685 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
686 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
687 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
688 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
689 return res;
690 }
691
692 // At a promotion failure dump information on block layout in heap
693 // (cms old generation).
694 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
695 Log(gc, promotion) log;
696 if (log.is_trace()) {
697 ResourceMark rm;
698 cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
699 }
700 }
701
702 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
703 // Clear the promotion information. These pointers can be adjusted
704 // along with all the other pointers into the heap but
705 // compaction is expected to be a rare event with
706 // a heap using cms so don't do it without seeing the need.
707 for (uint i = 0; i < ParallelGCThreads; i++) {
708 _par_gc_thread_states[i]->promo.reset();
709 }
710 }
711
712 void ConcurrentMarkSweepGeneration::compute_new_size() {
713 assert_locked_or_safepoint(Heap_lock);
714
715 // If incremental collection failed, we just want to expand
716 // to the limit.
717 if (incremental_collection_failed()) {
718 clear_incremental_collection_failed();
719 grow_to_reserved();
720 return;
721 }
722
723 // The heap has been compacted but not reset yet.
724 // Any metric such as free() or used() will be incorrect.
725
726 CardGeneration::compute_new_size();
727
728 // Reset again after a possible resizing
729 if (did_compact()) {
730 cmsSpace()->reset_after_compaction();
731 }
732 }
733
734 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
735 assert_locked_or_safepoint(Heap_lock);
736
737 // If incremental collection failed, we just want to expand
738 // to the limit.
739 if (incremental_collection_failed()) {
740 clear_incremental_collection_failed();
741 grow_to_reserved();
742 return;
743 }
744
745 double free_percentage = ((double) free()) / capacity();
746 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
747 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
748
749 // compute expansion delta needed for reaching desired free percentage
750 if (free_percentage < desired_free_percentage) {
751 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
752 assert(desired_capacity >= capacity(), "invalid expansion size");
753 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
754 Log(gc) log;
755 if (log.is_trace()) {
756 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
757 log.trace("From compute_new_size: ");
758 log.trace(" Free fraction %f", free_percentage);
759 log.trace(" Desired free fraction %f", desired_free_percentage);
760 log.trace(" Maximum free fraction %f", maximum_free_percentage);
761 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
762 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
763 GenCollectedHeap* gch = GenCollectedHeap::heap();
764 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
765 size_t young_size = gch->young_gen()->capacity();
766 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
767 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
768 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
769 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
770 }
771 // safe if expansion fails
772 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
773 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
774 } else {
775 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
776 assert(desired_capacity <= capacity(), "invalid expansion size");
777 size_t shrink_bytes = capacity() - desired_capacity;
778 // Don't shrink unless the delta is greater than the minimum shrink we want
779 if (shrink_bytes >= MinHeapDeltaBytes) {
780 shrink_free_list_by(shrink_bytes);
781 }
782 }
783 }
784
785 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
786 return cmsSpace()->freelistLock();
787 }
788
789 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
790 CMSSynchronousYieldRequest yr;
791 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
792 return have_lock_and_allocate(size, tlab);
793 }
794
795 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
796 bool tlab /* ignored */) {
797 assert_lock_strong(freelistLock());
798 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
799 HeapWord* res = cmsSpace()->allocate(adjustedSize);
800 // Allocate the object live (grey) if the background collector has
801 // started marking. This is necessary because the marker may
802 // have passed this address and consequently this object will
803 // not otherwise be greyed and would be incorrectly swept up.
804 // Note that if this object contains references, the writing
805 // of those references will dirty the card containing this object
806 // allowing the object to be blackened (and its references scanned)
807 // either during a preclean phase or at the final checkpoint.
808 if (res != NULL) {
809 // We may block here with an uninitialized object with
810 // its mark-bit or P-bits not yet set. Such objects need
811 // to be safely navigable by block_start().
812 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
813 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
814 collector()->direct_allocated(res, adjustedSize);
815 _direct_allocated_words += adjustedSize;
816 // allocation counters
817 NOT_PRODUCT(
818 _numObjectsAllocated++;
819 _numWordsAllocated += (int)adjustedSize;
820 )
821 }
822 return res;
823 }
824
825 // In the case of direct allocation by mutators in a generation that
826 // is being concurrently collected, the object must be allocated
827 // live (grey) if the background collector has started marking.
828 // This is necessary because the marker may
829 // have passed this address and consequently this object will
830 // not otherwise be greyed and would be incorrectly swept up.
831 // Note that if this object contains references, the writing
832 // of those references will dirty the card containing this object
833 // allowing the object to be blackened (and its references scanned)
834 // either during a preclean phase or at the final checkpoint.
835 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
836 assert(_markBitMap.covers(start, size), "Out of bounds");
837 if (_collectorState >= Marking) {
838 MutexLockerEx y(_markBitMap.lock(),
839 Mutex::_no_safepoint_check_flag);
840 // [see comments preceding SweepClosure::do_blk() below for details]
841 //
842 // Can the P-bits be deleted now? JJJ
843 //
844 // 1. need to mark the object as live so it isn't collected
845 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
846 // 3. need to mark the end of the object so marking, precleaning or sweeping
847 // can skip over uninitialized or unparsable objects. An allocated
848 // object is considered uninitialized for our purposes as long as
849 // its klass word is NULL. All old gen objects are parsable
850 // as soon as they are initialized.)
851 _markBitMap.mark(start); // object is live
852 _markBitMap.mark(start + 1); // object is potentially uninitialized?
853 _markBitMap.mark(start + size - 1);
854 // mark end of object
855 }
856 // check that oop looks uninitialized
857 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
858 }
859
860 void CMSCollector::promoted(bool par, HeapWord* start,
861 bool is_obj_array, size_t obj_size) {
862 assert(_markBitMap.covers(start), "Out of bounds");
863 // See comment in direct_allocated() about when objects should
864 // be allocated live.
865 if (_collectorState >= Marking) {
866 // we already hold the marking bit map lock, taken in
867 // the prologue
868 if (par) {
869 _markBitMap.par_mark(start);
870 } else {
871 _markBitMap.mark(start);
872 }
873 // We don't need to mark the object as uninitialized (as
874 // in direct_allocated above) because this is being done with the
875 // world stopped and the object will be initialized by the
876 // time the marking, precleaning or sweeping get to look at it.
877 // But see the code for copying objects into the CMS generation,
878 // where we need to ensure that concurrent readers of the
879 // block offset table are able to safely navigate a block that
880 // is in flux from being free to being allocated (and in
881 // transition while being copied into) and subsequently
882 // becoming a bona-fide object when the copy/promotion is complete.
883 assert(SafepointSynchronize::is_at_safepoint(),
884 "expect promotion only at safepoints");
885
886 if (_collectorState < Sweeping) {
887 // Mark the appropriate cards in the modUnionTable, so that
888 // this object gets scanned before the sweep. If this is
889 // not done, CMS generation references in the object might
890 // not get marked.
891 // For the case of arrays, which are otherwise precisely
892 // marked, we need to dirty the entire array, not just its head.
893 if (is_obj_array) {
894 // The [par_]mark_range() method expects mr.end() below to
895 // be aligned to the granularity of a bit's representation
896 // in the heap. In the case of the MUT below, that's a
897 // card size.
898 MemRegion mr(start,
899 (HeapWord*)round_to((intptr_t)(start + obj_size),
900 CardTableModRefBS::card_size /* bytes */));
901 if (par) {
902 _modUnionTable.par_mark_range(mr);
903 } else {
904 _modUnionTable.mark_range(mr);
905 }
906 } else { // not an obj array; we can just mark the head
907 if (par) {
908 _modUnionTable.par_mark(start);
909 } else {
910 _modUnionTable.mark(start);
911 }
912 }
913 }
914 }
915 }
916
917 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
918 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
919 // allocate, copy and if necessary update promoinfo --
920 // delegate to underlying space.
921 assert_lock_strong(freelistLock());
922
923 #ifndef PRODUCT
924 if (GenCollectedHeap::heap()->promotion_should_fail()) {
925 return NULL;
926 }
927 #endif // #ifndef PRODUCT
928
929 oop res = _cmsSpace->promote(obj, obj_size);
930 if (res == NULL) {
931 // expand and retry
932 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
933 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
934 // Since this is the old generation, we don't try to promote
935 // into a more senior generation.
936 res = _cmsSpace->promote(obj, obj_size);
937 }
938 if (res != NULL) {
939 // See comment in allocate() about when objects should
940 // be allocated live.
941 assert(obj->is_oop(), "Will dereference klass pointer below");
942 collector()->promoted(false, // Not parallel
943 (HeapWord*)res, obj->is_objArray(), obj_size);
944 // promotion counters
945 NOT_PRODUCT(
946 _numObjectsPromoted++;
947 _numWordsPromoted +=
948 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
949 )
950 }
951 return res;
952 }
953
954
955 // IMPORTANT: Notes on object size recognition in CMS.
956 // ---------------------------------------------------
957 // A block of storage in the CMS generation is always in
958 // one of three states. A free block (FREE), an allocated
959 // object (OBJECT) whose size() method reports the correct size,
960 // and an intermediate state (TRANSIENT) in which its size cannot
961 // be accurately determined.
962 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
963 // -----------------------------------------------------
964 // FREE: klass_word & 1 == 1; mark_word holds block size
965 //
966 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
967 // obj->size() computes correct size
968 //
969 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
970 //
971 // STATE IDENTIFICATION: (64 bit+COOPS)
972 // ------------------------------------
973 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
974 //
975 // OBJECT: klass_word installed; klass_word != 0;
976 // obj->size() computes correct size
977 //
978 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
979 //
980 //
981 // STATE TRANSITION DIAGRAM
982 //
983 // mut / parnew mut / parnew
984 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
985 // ^ |
986 // |------------------------ DEAD <------------------------------------|
987 // sweep mut
988 //
989 // While a block is in TRANSIENT state its size cannot be determined
990 // so readers will either need to come back later or stall until
991 // the size can be determined. Note that for the case of direct
992 // allocation, P-bits, when available, may be used to determine the
993 // size of an object that may not yet have been initialized.
994
995 // Things to support parallel young-gen collection.
996 oop
997 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
998 oop old, markOop m,
999 size_t word_sz) {
1000 #ifndef PRODUCT
1001 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1002 return NULL;
1003 }
1004 #endif // #ifndef PRODUCT
1005
1006 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1007 PromotionInfo* promoInfo = &ps->promo;
1008 // if we are tracking promotions, then first ensure space for
1009 // promotion (including spooling space for saving header if necessary).
1010 // then allocate and copy, then track promoted info if needed.
1011 // When tracking (see PromotionInfo::track()), the mark word may
1012 // be displaced and in this case restoration of the mark word
1013 // occurs in the (oop_since_save_marks_)iterate phase.
1014 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1015 // Out of space for allocating spooling buffers;
1016 // try expanding and allocating spooling buffers.
1017 if (!expand_and_ensure_spooling_space(promoInfo)) {
1018 return NULL;
1019 }
1020 }
1021 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1022 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1023 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1024 if (obj_ptr == NULL) {
1025 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1026 if (obj_ptr == NULL) {
1027 return NULL;
1028 }
1029 }
1030 oop obj = oop(obj_ptr);
1031 OrderAccess::storestore();
1032 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1033 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1034 // IMPORTANT: See note on object initialization for CMS above.
1035 // Otherwise, copy the object. Here we must be careful to insert the
1036 // klass pointer last, since this marks the block as an allocated object.
1037 // Except with compressed oops it's the mark word.
1038 HeapWord* old_ptr = (HeapWord*)old;
1039 // Restore the mark word copied above.
1040 obj->set_mark(m);
1041 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1042 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1043 OrderAccess::storestore();
1044
1045 if (UseCompressedClassPointers) {
1046 // Copy gap missed by (aligned) header size calculation below
1047 obj->set_klass_gap(old->klass_gap());
1048 }
1049 if (word_sz > (size_t)oopDesc::header_size()) {
1050 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1051 obj_ptr + oopDesc::header_size(),
1052 word_sz - oopDesc::header_size());
1053 }
1054
1055 // Now we can track the promoted object, if necessary. We take care
1056 // to delay the transition from uninitialized to full object
1057 // (i.e., insertion of klass pointer) until after, so that it
1058 // atomically becomes a promoted object.
1059 if (promoInfo->tracking()) {
1060 promoInfo->track((PromotedObject*)obj, old->klass());
1061 }
1062 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1063 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1064 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1065
1066 // Finally, install the klass pointer (this should be volatile).
1067 OrderAccess::storestore();
1068 obj->set_klass(old->klass());
1069 // We should now be able to calculate the right size for this object
1070 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1071
1072 collector()->promoted(true, // parallel
1073 obj_ptr, old->is_objArray(), word_sz);
1074
1075 NOT_PRODUCT(
1076 Atomic::inc_ptr(&_numObjectsPromoted);
1077 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1078 )
1079
1080 return obj;
1081 }
1082
1083 void
1084 ConcurrentMarkSweepGeneration::
1085 par_promote_alloc_done(int thread_num) {
1086 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1087 ps->lab.retire(thread_num);
1088 }
1089
1090 void
1091 ConcurrentMarkSweepGeneration::
1092 par_oop_since_save_marks_iterate_done(int thread_num) {
1093 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1094 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1095 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1096
1097 // Because card-scanning has been completed, subsequent phases
1098 // (e.g., reference processing) will not need to recognize which
1099 // objects have been promoted during this GC. So, we can now disable
1100 // promotion tracking.
1101 ps->promo.stopTrackingPromotions();
1102 }
1103
1104 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1105 size_t size,
1106 bool tlab)
1107 {
1108 // We allow a STW collection only if a full
1109 // collection was requested.
1110 return full || should_allocate(size, tlab); // FIX ME !!!
1111 // This and promotion failure handling are connected at the
1112 // hip and should be fixed by untying them.
1113 }
1114
1115 bool CMSCollector::shouldConcurrentCollect() {
1116 LogTarget(Trace, gc) log;
1117
1118 if (_full_gc_requested) {
1119 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1120 return true;
1121 }
1122
1123 FreelistLocker x(this);
1124 // ------------------------------------------------------------------
1125 // Print out lots of information which affects the initiation of
1126 // a collection.
1127 if (log.is_enabled() && stats().valid()) {
1128 log.print("CMSCollector shouldConcurrentCollect: ");
1129
1130 LogStream out(log);
1131 stats().print_on(&out);
1132
1133 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1134 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1135 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1136 log.print("promotion_rate=%g", stats().promotion_rate());
1137 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1138 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1139 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1140 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1141 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1142 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1143 }
1144 // ------------------------------------------------------------------
1145
1146 // If the estimated time to complete a cms collection (cms_duration())
1147 // is less than the estimated time remaining until the cms generation
1148 // is full, start a collection.
1149 if (!UseCMSInitiatingOccupancyOnly) {
1150 if (stats().valid()) {
1151 if (stats().time_until_cms_start() == 0.0) {
1152 return true;
1153 }
1154 } else {
1155 // We want to conservatively collect somewhat early in order
1156 // to try and "bootstrap" our CMS/promotion statistics;
1157 // this branch will not fire after the first successful CMS
1158 // collection because the stats should then be valid.
1159 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1160 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1161 _cmsGen->occupancy(), _bootstrap_occupancy);
1162 return true;
1163 }
1164 }
1165 }
1166
1167 // Otherwise, we start a collection cycle if
1168 // old gen want a collection cycle started. Each may use
1169 // an appropriate criterion for making this decision.
1170 // XXX We need to make sure that the gen expansion
1171 // criterion dovetails well with this. XXX NEED TO FIX THIS
1172 if (_cmsGen->should_concurrent_collect()) {
1173 log.print("CMS old gen initiated");
1174 return true;
1175 }
1176
1177 // We start a collection if we believe an incremental collection may fail;
1178 // this is not likely to be productive in practice because it's probably too
1179 // late anyway.
1180 GenCollectedHeap* gch = GenCollectedHeap::heap();
1181 assert(gch->collector_policy()->is_generation_policy(),
1182 "You may want to check the correctness of the following");
1183 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1184 log.print("CMSCollector: collect because incremental collection will fail ");
1185 return true;
1186 }
1187
1188 if (MetaspaceGC::should_concurrent_collect()) {
1189 log.print("CMSCollector: collect for metadata allocation ");
1190 return true;
1191 }
1192
1193 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1194 if (CMSTriggerInterval >= 0) {
1195 if (CMSTriggerInterval == 0) {
1196 // Trigger always
1197 return true;
1198 }
1199
1200 // Check the CMS time since begin (we do not check the stats validity
1201 // as we want to be able to trigger the first CMS cycle as well)
1202 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1203 if (stats().valid()) {
1204 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1205 stats().cms_time_since_begin());
1206 } else {
1207 log.print("CMSCollector: collect because of trigger interval (first collection)");
1208 }
1209 return true;
1210 }
1211 }
1212
1213 return false;
1214 }
1215
1216 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1217
1218 // Clear _expansion_cause fields of constituent generations
1219 void CMSCollector::clear_expansion_cause() {
1220 _cmsGen->clear_expansion_cause();
1221 }
1222
1223 // We should be conservative in starting a collection cycle. To
1224 // start too eagerly runs the risk of collecting too often in the
1225 // extreme. To collect too rarely falls back on full collections,
1226 // which works, even if not optimum in terms of concurrent work.
1227 // As a work around for too eagerly collecting, use the flag
1228 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1229 // giving the user an easily understandable way of controlling the
1230 // collections.
1231 // We want to start a new collection cycle if any of the following
1232 // conditions hold:
1233 // . our current occupancy exceeds the configured initiating occupancy
1234 // for this generation, or
1235 // . we recently needed to expand this space and have not, since that
1236 // expansion, done a collection of this generation, or
1237 // . the underlying space believes that it may be a good idea to initiate
1238 // a concurrent collection (this may be based on criteria such as the
1239 // following: the space uses linear allocation and linear allocation is
1240 // going to fail, or there is believed to be excessive fragmentation in
1241 // the generation, etc... or ...
1242 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1243 // the case of the old generation; see CR 6543076):
1244 // we may be approaching a point at which allocation requests may fail because
1245 // we will be out of sufficient free space given allocation rate estimates.]
1246 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1247
1248 assert_lock_strong(freelistLock());
1249 if (occupancy() > initiating_occupancy()) {
1250 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1251 short_name(), occupancy(), initiating_occupancy());
1252 return true;
1253 }
1254 if (UseCMSInitiatingOccupancyOnly) {
1255 return false;
1256 }
1257 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1258 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1259 return true;
1260 }
1261 return false;
1262 }
1263
1264 void ConcurrentMarkSweepGeneration::collect(bool full,
1265 bool clear_all_soft_refs,
1266 size_t size,
1267 bool tlab)
1268 {
1269 collector()->collect(full, clear_all_soft_refs, size, tlab);
1270 }
1271
1272 void CMSCollector::collect(bool full,
1273 bool clear_all_soft_refs,
1274 size_t size,
1275 bool tlab)
1276 {
1277 // The following "if" branch is present for defensive reasons.
1278 // In the current uses of this interface, it can be replaced with:
1279 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1280 // But I am not placing that assert here to allow future
1281 // generality in invoking this interface.
1282 if (GCLocker::is_active()) {
1283 // A consistency test for GCLocker
1284 assert(GCLocker::needs_gc(), "Should have been set already");
1285 // Skip this foreground collection, instead
1286 // expanding the heap if necessary.
1287 // Need the free list locks for the call to free() in compute_new_size()
1288 compute_new_size();
1289 return;
1290 }
1291 acquire_control_and_collect(full, clear_all_soft_refs);
1292 }
1293
1294 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1295 GenCollectedHeap* gch = GenCollectedHeap::heap();
1296 unsigned int gc_count = gch->total_full_collections();
1297 if (gc_count == full_gc_count) {
1298 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1299 _full_gc_requested = true;
1300 _full_gc_cause = cause;
1301 CGC_lock->notify(); // nudge CMS thread
1302 } else {
1303 assert(gc_count > full_gc_count, "Error: causal loop");
1304 }
1305 }
1306
1307 bool CMSCollector::is_external_interruption() {
1308 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1309 return GCCause::is_user_requested_gc(cause) ||
1310 GCCause::is_serviceability_requested_gc(cause);
1311 }
1312
1313 void CMSCollector::report_concurrent_mode_interruption() {
1314 if (is_external_interruption()) {
1315 log_debug(gc)("Concurrent mode interrupted");
1316 } else {
1317 log_debug(gc)("Concurrent mode failure");
1318 _gc_tracer_cm->report_concurrent_mode_failure();
1319 }
1320 }
1321
1322
1323 // The foreground and background collectors need to coordinate in order
1324 // to make sure that they do not mutually interfere with CMS collections.
1325 // When a background collection is active,
1326 // the foreground collector may need to take over (preempt) and
1327 // synchronously complete an ongoing collection. Depending on the
1328 // frequency of the background collections and the heap usage
1329 // of the application, this preemption can be seldom or frequent.
1330 // There are only certain
1331 // points in the background collection that the "collection-baton"
1332 // can be passed to the foreground collector.
1333 //
1334 // The foreground collector will wait for the baton before
1335 // starting any part of the collection. The foreground collector
1336 // will only wait at one location.
1337 //
1338 // The background collector will yield the baton before starting a new
1339 // phase of the collection (e.g., before initial marking, marking from roots,
1340 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1341 // of the loop which switches the phases. The background collector does some
1342 // of the phases (initial mark, final re-mark) with the world stopped.
1343 // Because of locking involved in stopping the world,
1344 // the foreground collector should not block waiting for the background
1345 // collector when it is doing a stop-the-world phase. The background
1346 // collector will yield the baton at an additional point just before
1347 // it enters a stop-the-world phase. Once the world is stopped, the
1348 // background collector checks the phase of the collection. If the
1349 // phase has not changed, it proceeds with the collection. If the
1350 // phase has changed, it skips that phase of the collection. See
1351 // the comments on the use of the Heap_lock in collect_in_background().
1352 //
1353 // Variable used in baton passing.
1354 // _foregroundGCIsActive - Set to true by the foreground collector when
1355 // it wants the baton. The foreground clears it when it has finished
1356 // the collection.
1357 // _foregroundGCShouldWait - Set to true by the background collector
1358 // when it is running. The foreground collector waits while
1359 // _foregroundGCShouldWait is true.
1360 // CGC_lock - monitor used to protect access to the above variables
1361 // and to notify the foreground and background collectors.
1362 // _collectorState - current state of the CMS collection.
1363 //
1364 // The foreground collector
1365 // acquires the CGC_lock
1366 // sets _foregroundGCIsActive
1367 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1368 // various locks acquired in preparation for the collection
1369 // are released so as not to block the background collector
1370 // that is in the midst of a collection
1371 // proceeds with the collection
1372 // clears _foregroundGCIsActive
1373 // returns
1374 //
1375 // The background collector in a loop iterating on the phases of the
1376 // collection
1377 // acquires the CGC_lock
1378 // sets _foregroundGCShouldWait
1379 // if _foregroundGCIsActive is set
1380 // clears _foregroundGCShouldWait, notifies _CGC_lock
1381 // waits on _CGC_lock for _foregroundGCIsActive to become false
1382 // and exits the loop.
1383 // otherwise
1384 // proceed with that phase of the collection
1385 // if the phase is a stop-the-world phase,
1386 // yield the baton once more just before enqueueing
1387 // the stop-world CMS operation (executed by the VM thread).
1388 // returns after all phases of the collection are done
1389 //
1390
1391 void CMSCollector::acquire_control_and_collect(bool full,
1392 bool clear_all_soft_refs) {
1393 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1394 assert(!Thread::current()->is_ConcurrentGC_thread(),
1395 "shouldn't try to acquire control from self!");
1396
1397 // Start the protocol for acquiring control of the
1398 // collection from the background collector (aka CMS thread).
1399 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1400 "VM thread should have CMS token");
1401 // Remember the possibly interrupted state of an ongoing
1402 // concurrent collection
1403 CollectorState first_state = _collectorState;
1404
1405 // Signal to a possibly ongoing concurrent collection that
1406 // we want to do a foreground collection.
1407 _foregroundGCIsActive = true;
1408
1409 // release locks and wait for a notify from the background collector
1410 // releasing the locks in only necessary for phases which
1411 // do yields to improve the granularity of the collection.
1412 assert_lock_strong(bitMapLock());
1413 // We need to lock the Free list lock for the space that we are
1414 // currently collecting.
1415 assert(haveFreelistLocks(), "Must be holding free list locks");
1416 bitMapLock()->unlock();
1417 releaseFreelistLocks();
1418 {
1419 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1420 if (_foregroundGCShouldWait) {
1421 // We are going to be waiting for action for the CMS thread;
1422 // it had better not be gone (for instance at shutdown)!
1423 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1424 "CMS thread must be running");
1425 // Wait here until the background collector gives us the go-ahead
1426 ConcurrentMarkSweepThread::clear_CMS_flag(
1427 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1428 // Get a possibly blocked CMS thread going:
1429 // Note that we set _foregroundGCIsActive true above,
1430 // without protection of the CGC_lock.
1431 CGC_lock->notify();
1432 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1433 "Possible deadlock");
1434 while (_foregroundGCShouldWait) {
1435 // wait for notification
1436 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1437 // Possibility of delay/starvation here, since CMS token does
1438 // not know to give priority to VM thread? Actually, i think
1439 // there wouldn't be any delay/starvation, but the proof of
1440 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1441 }
1442 ConcurrentMarkSweepThread::set_CMS_flag(
1443 ConcurrentMarkSweepThread::CMS_vm_has_token);
1444 }
1445 }
1446 // The CMS_token is already held. Get back the other locks.
1447 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1448 "VM thread should have CMS token");
1449 getFreelistLocks();
1450 bitMapLock()->lock_without_safepoint_check();
1451 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1452 p2i(Thread::current()), first_state);
1453 log_debug(gc, state)(" gets control with state %d", _collectorState);
1454
1455 // Inform cms gen if this was due to partial collection failing.
1456 // The CMS gen may use this fact to determine its expansion policy.
1457 GenCollectedHeap* gch = GenCollectedHeap::heap();
1458 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1459 assert(!_cmsGen->incremental_collection_failed(),
1460 "Should have been noticed, reacted to and cleared");
1461 _cmsGen->set_incremental_collection_failed();
1462 }
1463
1464 if (first_state > Idling) {
1465 report_concurrent_mode_interruption();
1466 }
1467
1468 set_did_compact(true);
1469
1470 // If the collection is being acquired from the background
1471 // collector, there may be references on the discovered
1472 // references lists. Abandon those references, since some
1473 // of them may have become unreachable after concurrent
1474 // discovery; the STW compacting collector will redo discovery
1475 // more precisely, without being subject to floating garbage.
1476 // Leaving otherwise unreachable references in the discovered
1477 // lists would require special handling.
1478 ref_processor()->disable_discovery();
1479 ref_processor()->abandon_partial_discovery();
1480 ref_processor()->verify_no_references_recorded();
1481
1482 if (first_state > Idling) {
1483 save_heap_summary();
1484 }
1485
1486 do_compaction_work(clear_all_soft_refs);
1487
1488 // Has the GC time limit been exceeded?
1489 size_t max_eden_size = _young_gen->max_eden_size();
1490 GCCause::Cause gc_cause = gch->gc_cause();
1491 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1492 _young_gen->eden()->used(),
1493 _cmsGen->max_capacity(),
1494 max_eden_size,
1495 full,
1496 gc_cause,
1497 gch->collector_policy());
1498
1499 // Reset the expansion cause, now that we just completed
1500 // a collection cycle.
1501 clear_expansion_cause();
1502 _foregroundGCIsActive = false;
1503 return;
1504 }
1505
1506 // Resize the tenured generation
1507 // after obtaining the free list locks for the
1508 // two generations.
1509 void CMSCollector::compute_new_size() {
1510 assert_locked_or_safepoint(Heap_lock);
1511 FreelistLocker z(this);
1512 MetaspaceGC::compute_new_size();
1513 _cmsGen->compute_new_size_free_list();
1514 }
1515
1516 // A work method used by the foreground collector to do
1517 // a mark-sweep-compact.
1518 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1519 GenCollectedHeap* gch = GenCollectedHeap::heap();
1520
1521 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1522 gc_timer->register_gc_start();
1523
1524 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1525 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1526
1527 gch->pre_full_gc_dump(gc_timer);
1528
1529 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1530
1531 // Temporarily widen the span of the weak reference processing to
1532 // the entire heap.
1533 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1534 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1535 // Temporarily, clear the "is_alive_non_header" field of the
1536 // reference processor.
1537 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1538 // Temporarily make reference _processing_ single threaded (non-MT).
1539 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1540 // Temporarily make refs discovery atomic
1541 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1542 // Temporarily make reference _discovery_ single threaded (non-MT)
1543 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1544
1545 ref_processor()->set_enqueuing_is_done(false);
1546 ref_processor()->enable_discovery();
1547 ref_processor()->setup_policy(clear_all_soft_refs);
1548 // If an asynchronous collection finishes, the _modUnionTable is
1549 // all clear. If we are assuming the collection from an asynchronous
1550 // collection, clear the _modUnionTable.
1551 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1552 "_modUnionTable should be clear if the baton was not passed");
1553 _modUnionTable.clear_all();
1554 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1555 "mod union for klasses should be clear if the baton was passed");
1556 _ct->klass_rem_set()->clear_mod_union();
1557
1558 // We must adjust the allocation statistics being maintained
1559 // in the free list space. We do so by reading and clearing
1560 // the sweep timer and updating the block flux rate estimates below.
1561 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1562 if (_inter_sweep_timer.is_active()) {
1563 _inter_sweep_timer.stop();
1564 // Note that we do not use this sample to update the _inter_sweep_estimate.
1565 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1566 _inter_sweep_estimate.padded_average(),
1567 _intra_sweep_estimate.padded_average());
1568 }
1569
1570 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1571 #ifdef ASSERT
1572 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1573 size_t free_size = cms_space->free();
1574 assert(free_size ==
1575 pointer_delta(cms_space->end(), cms_space->compaction_top())
1576 * HeapWordSize,
1577 "All the free space should be compacted into one chunk at top");
1578 assert(cms_space->dictionary()->total_chunk_size(
1579 debug_only(cms_space->freelistLock())) == 0 ||
1580 cms_space->totalSizeInIndexedFreeLists() == 0,
1581 "All the free space should be in a single chunk");
1582 size_t num = cms_space->totalCount();
1583 assert((free_size == 0 && num == 0) ||
1584 (free_size > 0 && (num == 1 || num == 2)),
1585 "There should be at most 2 free chunks after compaction");
1586 #endif // ASSERT
1587 _collectorState = Resetting;
1588 assert(_restart_addr == NULL,
1589 "Should have been NULL'd before baton was passed");
1590 reset_stw();
1591 _cmsGen->reset_after_compaction();
1592 _concurrent_cycles_since_last_unload = 0;
1593
1594 // Clear any data recorded in the PLAB chunk arrays.
1595 if (_survivor_plab_array != NULL) {
1596 reset_survivor_plab_arrays();
1597 }
1598
1599 // Adjust the per-size allocation stats for the next epoch.
1600 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1601 // Restart the "inter sweep timer" for the next epoch.
1602 _inter_sweep_timer.reset();
1603 _inter_sweep_timer.start();
1604
1605 // No longer a need to do a concurrent collection for Metaspace.
1606 MetaspaceGC::set_should_concurrent_collect(false);
1607
1608 gch->post_full_gc_dump(gc_timer);
1609
1610 gc_timer->register_gc_end();
1611
1612 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1613
1614 // For a mark-sweep-compact, compute_new_size() will be called
1615 // in the heap's do_collection() method.
1616 }
1617
1618 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1619 Log(gc, heap) log;
1620 if (!log.is_trace()) {
1621 return;
1622 }
1623
1624 ContiguousSpace* eden_space = _young_gen->eden();
1625 ContiguousSpace* from_space = _young_gen->from();
1626 ContiguousSpace* to_space = _young_gen->to();
1627 // Eden
1628 if (_eden_chunk_array != NULL) {
1629 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1630 p2i(eden_space->bottom()), p2i(eden_space->top()),
1631 p2i(eden_space->end()), eden_space->capacity());
1632 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1633 _eden_chunk_index, _eden_chunk_capacity);
1634 for (size_t i = 0; i < _eden_chunk_index; i++) {
1635 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1636 }
1637 }
1638 // Survivor
1639 if (_survivor_chunk_array != NULL) {
1640 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1641 p2i(from_space->bottom()), p2i(from_space->top()),
1642 p2i(from_space->end()), from_space->capacity());
1643 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1644 _survivor_chunk_index, _survivor_chunk_capacity);
1645 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1646 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1647 }
1648 }
1649 }
1650
1651 void CMSCollector::getFreelistLocks() const {
1652 // Get locks for all free lists in all generations that this
1653 // collector is responsible for
1654 _cmsGen->freelistLock()->lock_without_safepoint_check();
1655 }
1656
1657 void CMSCollector::releaseFreelistLocks() const {
1658 // Release locks for all free lists in all generations that this
1659 // collector is responsible for
1660 _cmsGen->freelistLock()->unlock();
1661 }
1662
1663 bool CMSCollector::haveFreelistLocks() const {
1664 // Check locks for all free lists in all generations that this
1665 // collector is responsible for
1666 assert_lock_strong(_cmsGen->freelistLock());
1667 PRODUCT_ONLY(ShouldNotReachHere());
1668 return true;
1669 }
1670
1671 // A utility class that is used by the CMS collector to
1672 // temporarily "release" the foreground collector from its
1673 // usual obligation to wait for the background collector to
1674 // complete an ongoing phase before proceeding.
1675 class ReleaseForegroundGC: public StackObj {
1676 private:
1677 CMSCollector* _c;
1678 public:
1679 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1680 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1681 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1682 // allow a potentially blocked foreground collector to proceed
1683 _c->_foregroundGCShouldWait = false;
1684 if (_c->_foregroundGCIsActive) {
1685 CGC_lock->notify();
1686 }
1687 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1688 "Possible deadlock");
1689 }
1690
1691 ~ReleaseForegroundGC() {
1692 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1693 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1694 _c->_foregroundGCShouldWait = true;
1695 }
1696 };
1697
1698 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1699 assert(Thread::current()->is_ConcurrentGC_thread(),
1700 "A CMS asynchronous collection is only allowed on a CMS thread.");
1701
1702 GenCollectedHeap* gch = GenCollectedHeap::heap();
1703 {
1704 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1705 MutexLockerEx hl(Heap_lock, safepoint_check);
1706 FreelistLocker fll(this);
1707 MutexLockerEx x(CGC_lock, safepoint_check);
1708 if (_foregroundGCIsActive) {
1709 // The foreground collector is. Skip this
1710 // background collection.
1711 assert(!_foregroundGCShouldWait, "Should be clear");
1712 return;
1713 } else {
1714 assert(_collectorState == Idling, "Should be idling before start.");
1715 _collectorState = InitialMarking;
1716 register_gc_start(cause);
1717 // Reset the expansion cause, now that we are about to begin
1718 // a new cycle.
1719 clear_expansion_cause();
1720
1721 // Clear the MetaspaceGC flag since a concurrent collection
1722 // is starting but also clear it after the collection.
1723 MetaspaceGC::set_should_concurrent_collect(false);
1724 }
1725 // Decide if we want to enable class unloading as part of the
1726 // ensuing concurrent GC cycle.
1727 update_should_unload_classes();
1728 _full_gc_requested = false; // acks all outstanding full gc requests
1729 _full_gc_cause = GCCause::_no_gc;
1730 // Signal that we are about to start a collection
1731 gch->increment_total_full_collections(); // ... starting a collection cycle
1732 _collection_count_start = gch->total_full_collections();
1733 }
1734
1735 size_t prev_used = _cmsGen->used();
1736
1737 // The change of the collection state is normally done at this level;
1738 // the exceptions are phases that are executed while the world is
1739 // stopped. For those phases the change of state is done while the
1740 // world is stopped. For baton passing purposes this allows the
1741 // background collector to finish the phase and change state atomically.
1742 // The foreground collector cannot wait on a phase that is done
1743 // while the world is stopped because the foreground collector already
1744 // has the world stopped and would deadlock.
1745 while (_collectorState != Idling) {
1746 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1747 p2i(Thread::current()), _collectorState);
1748 // The foreground collector
1749 // holds the Heap_lock throughout its collection.
1750 // holds the CMS token (but not the lock)
1751 // except while it is waiting for the background collector to yield.
1752 //
1753 // The foreground collector should be blocked (not for long)
1754 // if the background collector is about to start a phase
1755 // executed with world stopped. If the background
1756 // collector has already started such a phase, the
1757 // foreground collector is blocked waiting for the
1758 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1759 // are executed in the VM thread.
1760 //
1761 // The locking order is
1762 // PendingListLock (PLL) -- if applicable (FinalMarking)
1763 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1764 // CMS token (claimed in
1765 // stop_world_and_do() -->
1766 // safepoint_synchronize() -->
1767 // CMSThread::synchronize())
1768
1769 {
1770 // Check if the FG collector wants us to yield.
1771 CMSTokenSync x(true); // is cms thread
1772 if (waitForForegroundGC()) {
1773 // We yielded to a foreground GC, nothing more to be
1774 // done this round.
1775 assert(_foregroundGCShouldWait == false, "We set it to false in "
1776 "waitForForegroundGC()");
1777 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1778 p2i(Thread::current()), _collectorState);
1779 return;
1780 } else {
1781 // The background collector can run but check to see if the
1782 // foreground collector has done a collection while the
1783 // background collector was waiting to get the CGC_lock
1784 // above. If yes, break so that _foregroundGCShouldWait
1785 // is cleared before returning.
1786 if (_collectorState == Idling) {
1787 break;
1788 }
1789 }
1790 }
1791
1792 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1793 "should be waiting");
1794
1795 switch (_collectorState) {
1796 case InitialMarking:
1797 {
1798 ReleaseForegroundGC x(this);
1799 stats().record_cms_begin();
1800 VM_CMS_Initial_Mark initial_mark_op(this);
1801 VMThread::execute(&initial_mark_op);
1802 }
1803 // The collector state may be any legal state at this point
1804 // since the background collector may have yielded to the
1805 // foreground collector.
1806 break;
1807 case Marking:
1808 // initial marking in checkpointRootsInitialWork has been completed
1809 if (markFromRoots()) { // we were successful
1810 assert(_collectorState == Precleaning, "Collector state should "
1811 "have changed");
1812 } else {
1813 assert(_foregroundGCIsActive, "Internal state inconsistency");
1814 }
1815 break;
1816 case Precleaning:
1817 // marking from roots in markFromRoots has been completed
1818 preclean();
1819 assert(_collectorState == AbortablePreclean ||
1820 _collectorState == FinalMarking,
1821 "Collector state should have changed");
1822 break;
1823 case AbortablePreclean:
1824 abortable_preclean();
1825 assert(_collectorState == FinalMarking, "Collector state should "
1826 "have changed");
1827 break;
1828 case FinalMarking:
1829 {
1830 ReleaseForegroundGC x(this);
1831
1832 VM_CMS_Final_Remark final_remark_op(this);
1833 VMThread::execute(&final_remark_op);
1834 }
1835 assert(_foregroundGCShouldWait, "block post-condition");
1836 break;
1837 case Sweeping:
1838 // final marking in checkpointRootsFinal has been completed
1839 sweep();
1840 assert(_collectorState == Resizing, "Collector state change "
1841 "to Resizing must be done under the free_list_lock");
1842
1843 case Resizing: {
1844 // Sweeping has been completed...
1845 // At this point the background collection has completed.
1846 // Don't move the call to compute_new_size() down
1847 // into code that might be executed if the background
1848 // collection was preempted.
1849 {
1850 ReleaseForegroundGC x(this); // unblock FG collection
1851 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1852 CMSTokenSync z(true); // not strictly needed.
1853 if (_collectorState == Resizing) {
1854 compute_new_size();
1855 save_heap_summary();
1856 _collectorState = Resetting;
1857 } else {
1858 assert(_collectorState == Idling, "The state should only change"
1859 " because the foreground collector has finished the collection");
1860 }
1861 }
1862 break;
1863 }
1864 case Resetting:
1865 // CMS heap resizing has been completed
1866 reset_concurrent();
1867 assert(_collectorState == Idling, "Collector state should "
1868 "have changed");
1869
1870 MetaspaceGC::set_should_concurrent_collect(false);
1871
1872 stats().record_cms_end();
1873 // Don't move the concurrent_phases_end() and compute_new_size()
1874 // calls to here because a preempted background collection
1875 // has it's state set to "Resetting".
1876 break;
1877 case Idling:
1878 default:
1879 ShouldNotReachHere();
1880 break;
1881 }
1882 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1883 p2i(Thread::current()), _collectorState);
1884 assert(_foregroundGCShouldWait, "block post-condition");
1885 }
1886
1887 // Should this be in gc_epilogue?
1888 collector_policy()->counters()->update_counters();
1889
1890 {
1891 // Clear _foregroundGCShouldWait and, in the event that the
1892 // foreground collector is waiting, notify it, before
1893 // returning.
1894 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1895 _foregroundGCShouldWait = false;
1896 if (_foregroundGCIsActive) {
1897 CGC_lock->notify();
1898 }
1899 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1900 "Possible deadlock");
1901 }
1902 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1903 p2i(Thread::current()), _collectorState);
1904 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1905 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1906 }
1907
1908 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1909 _cms_start_registered = true;
1910 _gc_timer_cm->register_gc_start();
1911 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1912 }
1913
1914 void CMSCollector::register_gc_end() {
1915 if (_cms_start_registered) {
1916 report_heap_summary(GCWhen::AfterGC);
1917
1918 _gc_timer_cm->register_gc_end();
1919 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1920 _cms_start_registered = false;
1921 }
1922 }
1923
1924 void CMSCollector::save_heap_summary() {
1925 GenCollectedHeap* gch = GenCollectedHeap::heap();
1926 _last_heap_summary = gch->create_heap_summary();
1927 _last_metaspace_summary = gch->create_metaspace_summary();
1928 }
1929
1930 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1931 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1932 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1933 }
1934
1935 bool CMSCollector::waitForForegroundGC() {
1936 bool res = false;
1937 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1938 "CMS thread should have CMS token");
1939 // Block the foreground collector until the
1940 // background collectors decides whether to
1941 // yield.
1942 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1943 _foregroundGCShouldWait = true;
1944 if (_foregroundGCIsActive) {
1945 // The background collector yields to the
1946 // foreground collector and returns a value
1947 // indicating that it has yielded. The foreground
1948 // collector can proceed.
1949 res = true;
1950 _foregroundGCShouldWait = false;
1951 ConcurrentMarkSweepThread::clear_CMS_flag(
1952 ConcurrentMarkSweepThread::CMS_cms_has_token);
1953 ConcurrentMarkSweepThread::set_CMS_flag(
1954 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1955 // Get a possibly blocked foreground thread going
1956 CGC_lock->notify();
1957 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1958 p2i(Thread::current()), _collectorState);
1959 while (_foregroundGCIsActive) {
1960 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1961 }
1962 ConcurrentMarkSweepThread::set_CMS_flag(
1963 ConcurrentMarkSweepThread::CMS_cms_has_token);
1964 ConcurrentMarkSweepThread::clear_CMS_flag(
1965 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1966 }
1967 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1968 p2i(Thread::current()), _collectorState);
1969 return res;
1970 }
1971
1972 // Because of the need to lock the free lists and other structures in
1973 // the collector, common to all the generations that the collector is
1974 // collecting, we need the gc_prologues of individual CMS generations
1975 // delegate to their collector. It may have been simpler had the
1976 // current infrastructure allowed one to call a prologue on a
1977 // collector. In the absence of that we have the generation's
1978 // prologue delegate to the collector, which delegates back
1979 // some "local" work to a worker method in the individual generations
1980 // that it's responsible for collecting, while itself doing any
1981 // work common to all generations it's responsible for. A similar
1982 // comment applies to the gc_epilogue()'s.
1983 // The role of the variable _between_prologue_and_epilogue is to
1984 // enforce the invocation protocol.
1985 void CMSCollector::gc_prologue(bool full) {
1986 // Call gc_prologue_work() for the CMSGen
1987 // we are responsible for.
1988
1989 // The following locking discipline assumes that we are only called
1990 // when the world is stopped.
1991 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1992
1993 // The CMSCollector prologue must call the gc_prologues for the
1994 // "generations" that it's responsible
1995 // for.
1996
1997 assert( Thread::current()->is_VM_thread()
1998 || ( CMSScavengeBeforeRemark
1999 && Thread::current()->is_ConcurrentGC_thread()),
2000 "Incorrect thread type for prologue execution");
2001
2002 if (_between_prologue_and_epilogue) {
2003 // We have already been invoked; this is a gc_prologue delegation
2004 // from yet another CMS generation that we are responsible for, just
2005 // ignore it since all relevant work has already been done.
2006 return;
2007 }
2008
2009 // set a bit saying prologue has been called; cleared in epilogue
2010 _between_prologue_and_epilogue = true;
2011 // Claim locks for common data structures, then call gc_prologue_work()
2012 // for each CMSGen.
2013
2014 getFreelistLocks(); // gets free list locks on constituent spaces
2015 bitMapLock()->lock_without_safepoint_check();
2016
2017 // Should call gc_prologue_work() for all cms gens we are responsible for
2018 bool duringMarking = _collectorState >= Marking
2019 && _collectorState < Sweeping;
2020
2021 // The young collections clear the modified oops state, which tells if
2022 // there are any modified oops in the class. The remark phase also needs
2023 // that information. Tell the young collection to save the union of all
2024 // modified klasses.
2025 if (duringMarking) {
2026 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2027 }
2028
2029 bool registerClosure = duringMarking;
2030
2031 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2032
2033 if (!full) {
2034 stats().record_gc0_begin();
2035 }
2036 }
2037
2038 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2039
2040 _capacity_at_prologue = capacity();
2041 _used_at_prologue = used();
2042
2043 // We enable promotion tracking so that card-scanning can recognize
2044 // which objects have been promoted during this GC and skip them.
2045 for (uint i = 0; i < ParallelGCThreads; i++) {
2046 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2047 }
2048
2049 // Delegate to CMScollector which knows how to coordinate between
2050 // this and any other CMS generations that it is responsible for
2051 // collecting.
2052 collector()->gc_prologue(full);
2053 }
2054
2055 // This is a "private" interface for use by this generation's CMSCollector.
2056 // Not to be called directly by any other entity (for instance,
2057 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2058 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2059 bool registerClosure, ModUnionClosure* modUnionClosure) {
2060 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2061 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2062 "Should be NULL");
2063 if (registerClosure) {
2064 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2065 }
2066 cmsSpace()->gc_prologue();
2067 // Clear stat counters
2068 NOT_PRODUCT(
2069 assert(_numObjectsPromoted == 0, "check");
2070 assert(_numWordsPromoted == 0, "check");
2071 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2072 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2073 _numObjectsAllocated = 0;
2074 _numWordsAllocated = 0;
2075 )
2076 }
2077
2078 void CMSCollector::gc_epilogue(bool full) {
2079 // The following locking discipline assumes that we are only called
2080 // when the world is stopped.
2081 assert(SafepointSynchronize::is_at_safepoint(),
2082 "world is stopped assumption");
2083
2084 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2085 // if linear allocation blocks need to be appropriately marked to allow the
2086 // the blocks to be parsable. We also check here whether we need to nudge the
2087 // CMS collector thread to start a new cycle (if it's not already active).
2088 assert( Thread::current()->is_VM_thread()
2089 || ( CMSScavengeBeforeRemark
2090 && Thread::current()->is_ConcurrentGC_thread()),
2091 "Incorrect thread type for epilogue execution");
2092
2093 if (!_between_prologue_and_epilogue) {
2094 // We have already been invoked; this is a gc_epilogue delegation
2095 // from yet another CMS generation that we are responsible for, just
2096 // ignore it since all relevant work has already been done.
2097 return;
2098 }
2099 assert(haveFreelistLocks(), "must have freelist locks");
2100 assert_lock_strong(bitMapLock());
2101
2102 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2103
2104 _cmsGen->gc_epilogue_work(full);
2105
2106 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2107 // in case sampling was not already enabled, enable it
2108 _start_sampling = true;
2109 }
2110 // reset _eden_chunk_array so sampling starts afresh
2111 _eden_chunk_index = 0;
2112
2113 size_t cms_used = _cmsGen->cmsSpace()->used();
2114
2115 // update performance counters - this uses a special version of
2116 // update_counters() that allows the utilization to be passed as a
2117 // parameter, avoiding multiple calls to used().
2118 //
2119 _cmsGen->update_counters(cms_used);
2120
2121 bitMapLock()->unlock();
2122 releaseFreelistLocks();
2123
2124 if (!CleanChunkPoolAsync) {
2125 Chunk::clean_chunk_pool();
2126 }
2127
2128 set_did_compact(false);
2129 _between_prologue_and_epilogue = false; // ready for next cycle
2130 }
2131
2132 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2133 collector()->gc_epilogue(full);
2134
2135 // When using ParNew, promotion tracking should have already been
2136 // disabled. However, the prologue (which enables promotion
2137 // tracking) and epilogue are called irrespective of the type of
2138 // GC. So they will also be called before and after Full GCs, during
2139 // which promotion tracking will not be explicitly disabled. So,
2140 // it's safer to also disable it here too (to be symmetric with
2141 // enabling it in the prologue).
2142 for (uint i = 0; i < ParallelGCThreads; i++) {
2143 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2144 }
2145 }
2146
2147 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2148 assert(!incremental_collection_failed(), "Should have been cleared");
2149 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2150 cmsSpace()->gc_epilogue();
2151 // Print stat counters
2152 NOT_PRODUCT(
2153 assert(_numObjectsAllocated == 0, "check");
2154 assert(_numWordsAllocated == 0, "check");
2155 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2156 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2157 _numObjectsPromoted = 0;
2158 _numWordsPromoted = 0;
2159 )
2160
2161 // Call down the chain in contiguous_available needs the freelistLock
2162 // so print this out before releasing the freeListLock.
2163 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2164 }
2165
2166 #ifndef PRODUCT
2167 bool CMSCollector::have_cms_token() {
2168 Thread* thr = Thread::current();
2169 if (thr->is_VM_thread()) {
2170 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2171 } else if (thr->is_ConcurrentGC_thread()) {
2172 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2173 } else if (thr->is_GC_task_thread()) {
2174 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2175 ParGCRareEvent_lock->owned_by_self();
2176 }
2177 return false;
2178 }
2179
2180 // Check reachability of the given heap address in CMS generation,
2181 // treating all other generations as roots.
2182 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2183 // We could "guarantee" below, rather than assert, but I'll
2184 // leave these as "asserts" so that an adventurous debugger
2185 // could try this in the product build provided some subset of
2186 // the conditions were met, provided they were interested in the
2187 // results and knew that the computation below wouldn't interfere
2188 // with other concurrent computations mutating the structures
2189 // being read or written.
2190 assert(SafepointSynchronize::is_at_safepoint(),
2191 "Else mutations in object graph will make answer suspect");
2192 assert(have_cms_token(), "Should hold cms token");
2193 assert(haveFreelistLocks(), "must hold free list locks");
2194 assert_lock_strong(bitMapLock());
2195
2196 // Clear the marking bit map array before starting, but, just
2197 // for kicks, first report if the given address is already marked
2198 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2199 _markBitMap.isMarked(addr) ? "" : " not");
2200
2201 if (verify_after_remark()) {
2202 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2203 bool result = verification_mark_bm()->isMarked(addr);
2204 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2205 result ? "IS" : "is NOT");
2206 return result;
2207 } else {
2208 tty->print_cr("Could not compute result");
2209 return false;
2210 }
2211 }
2212 #endif
2213
2214 void
2215 CMSCollector::print_on_error(outputStream* st) {
2216 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2217 if (collector != NULL) {
2218 CMSBitMap* bitmap = &collector->_markBitMap;
2219 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2220 bitmap->print_on_error(st, " Bits: ");
2221
2222 st->cr();
2223
2224 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2225 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2226 mut_bitmap->print_on_error(st, " Bits: ");
2227 }
2228 }
2229
2230 ////////////////////////////////////////////////////////
2231 // CMS Verification Support
2232 ////////////////////////////////////////////////////////
2233 // Following the remark phase, the following invariant
2234 // should hold -- each object in the CMS heap which is
2235 // marked in markBitMap() should be marked in the verification_mark_bm().
2236
2237 class VerifyMarkedClosure: public BitMapClosure {
2238 CMSBitMap* _marks;
2239 bool _failed;
2240
2241 public:
2242 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2243
2244 bool do_bit(size_t offset) {
2245 HeapWord* addr = _marks->offsetToHeapWord(offset);
2246 if (!_marks->isMarked(addr)) {
2247 Log(gc, verify) log;
2248 ResourceMark rm;
2249 oop(addr)->print_on(log.error_stream());
2250 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2251 _failed = true;
2252 }
2253 return true;
2254 }
2255
2256 bool failed() { return _failed; }
2257 };
2258
2259 bool CMSCollector::verify_after_remark() {
2260 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2261 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2262 static bool init = false;
2263
2264 assert(SafepointSynchronize::is_at_safepoint(),
2265 "Else mutations in object graph will make answer suspect");
2266 assert(have_cms_token(),
2267 "Else there may be mutual interference in use of "
2268 " verification data structures");
2269 assert(_collectorState > Marking && _collectorState <= Sweeping,
2270 "Else marking info checked here may be obsolete");
2271 assert(haveFreelistLocks(), "must hold free list locks");
2272 assert_lock_strong(bitMapLock());
2273
2274
2275 // Allocate marking bit map if not already allocated
2276 if (!init) { // first time
2277 if (!verification_mark_bm()->allocate(_span)) {
2278 return false;
2279 }
2280 init = true;
2281 }
2282
2283 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2284
2285 // Turn off refs discovery -- so we will be tracing through refs.
2286 // This is as intended, because by this time
2287 // GC must already have cleared any refs that need to be cleared,
2288 // and traced those that need to be marked; moreover,
2289 // the marking done here is not going to interfere in any
2290 // way with the marking information used by GC.
2291 NoRefDiscovery no_discovery(ref_processor());
2292
2293 #if defined(COMPILER2) || INCLUDE_JVMCI
2294 DerivedPointerTableDeactivate dpt_deact;
2295 #endif
2296
2297 // Clear any marks from a previous round
2298 verification_mark_bm()->clear_all();
2299 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2300 verify_work_stacks_empty();
2301
2302 GenCollectedHeap* gch = GenCollectedHeap::heap();
2303 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2304 // Update the saved marks which may affect the root scans.
2305 gch->save_marks();
2306
2307 if (CMSRemarkVerifyVariant == 1) {
2308 // In this first variant of verification, we complete
2309 // all marking, then check if the new marks-vector is
2310 // a subset of the CMS marks-vector.
2311 verify_after_remark_work_1();
2312 } else {
2313 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2314 // In this second variant of verification, we flag an error
2315 // (i.e. an object reachable in the new marks-vector not reachable
2316 // in the CMS marks-vector) immediately, also indicating the
2317 // identify of an object (A) that references the unmarked object (B) --
2318 // presumably, a mutation to A failed to be picked up by preclean/remark?
2319 verify_after_remark_work_2();
2320 }
2321
2322 return true;
2323 }
2324
2325 void CMSCollector::verify_after_remark_work_1() {
2326 ResourceMark rm;
2327 HandleMark hm;
2328 GenCollectedHeap* gch = GenCollectedHeap::heap();
2329
2330 // Get a clear set of claim bits for the roots processing to work with.
2331 ClassLoaderDataGraph::clear_claimed_marks();
2332
2333 // Mark from roots one level into CMS
2334 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2335 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2336
2337 {
2338 StrongRootsScope srs(1);
2339
2340 gch->cms_process_roots(&srs,
2341 true, // young gen as roots
2342 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2343 should_unload_classes(),
2344 ¬Older,
2345 NULL);
2346 }
2347
2348 // Now mark from the roots
2349 MarkFromRootsClosure markFromRootsClosure(this, _span,
2350 verification_mark_bm(), verification_mark_stack(),
2351 false /* don't yield */, true /* verifying */);
2352 assert(_restart_addr == NULL, "Expected pre-condition");
2353 verification_mark_bm()->iterate(&markFromRootsClosure);
2354 while (_restart_addr != NULL) {
2355 // Deal with stack overflow: by restarting at the indicated
2356 // address.
2357 HeapWord* ra = _restart_addr;
2358 markFromRootsClosure.reset(ra);
2359 _restart_addr = NULL;
2360 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2361 }
2362 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2363 verify_work_stacks_empty();
2364
2365 // Marking completed -- now verify that each bit marked in
2366 // verification_mark_bm() is also marked in markBitMap(); flag all
2367 // errors by printing corresponding objects.
2368 VerifyMarkedClosure vcl(markBitMap());
2369 verification_mark_bm()->iterate(&vcl);
2370 if (vcl.failed()) {
2371 Log(gc, verify) log;
2372 log.error("Failed marking verification after remark");
2373 ResourceMark rm;
2374 gch->print_on(log.error_stream());
2375 fatal("CMS: failed marking verification after remark");
2376 }
2377 }
2378
2379 class VerifyKlassOopsKlassClosure : public KlassClosure {
2380 class VerifyKlassOopsClosure : public OopClosure {
2381 CMSBitMap* _bitmap;
2382 public:
2383 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2384 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2385 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2386 } _oop_closure;
2387 public:
2388 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2389 void do_klass(Klass* k) {
2390 k->oops_do(&_oop_closure);
2391 }
2392 };
2393
2394 void CMSCollector::verify_after_remark_work_2() {
2395 ResourceMark rm;
2396 HandleMark hm;
2397 GenCollectedHeap* gch = GenCollectedHeap::heap();
2398
2399 // Get a clear set of claim bits for the roots processing to work with.
2400 ClassLoaderDataGraph::clear_claimed_marks();
2401
2402 // Mark from roots one level into CMS
2403 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2404 markBitMap());
2405 CLDToOopClosure cld_closure(¬Older, true);
2406
2407 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2408
2409 {
2410 StrongRootsScope srs(1);
2411
2412 gch->cms_process_roots(&srs,
2413 true, // young gen as roots
2414 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2415 should_unload_classes(),
2416 ¬Older,
2417 &cld_closure);
2418 }
2419
2420 // Now mark from the roots
2421 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2422 verification_mark_bm(), markBitMap(), verification_mark_stack());
2423 assert(_restart_addr == NULL, "Expected pre-condition");
2424 verification_mark_bm()->iterate(&markFromRootsClosure);
2425 while (_restart_addr != NULL) {
2426 // Deal with stack overflow: by restarting at the indicated
2427 // address.
2428 HeapWord* ra = _restart_addr;
2429 markFromRootsClosure.reset(ra);
2430 _restart_addr = NULL;
2431 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2432 }
2433 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2434 verify_work_stacks_empty();
2435
2436 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2437 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2438
2439 // Marking completed -- now verify that each bit marked in
2440 // verification_mark_bm() is also marked in markBitMap(); flag all
2441 // errors by printing corresponding objects.
2442 VerifyMarkedClosure vcl(markBitMap());
2443 verification_mark_bm()->iterate(&vcl);
2444 assert(!vcl.failed(), "Else verification above should not have succeeded");
2445 }
2446
2447 void ConcurrentMarkSweepGeneration::save_marks() {
2448 // delegate to CMS space
2449 cmsSpace()->save_marks();
2450 }
2451
2452 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2453 return cmsSpace()->no_allocs_since_save_marks();
2454 }
2455
2456 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2457 \
2458 void ConcurrentMarkSweepGeneration:: \
2459 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2460 cl->set_generation(this); \
2461 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2462 cl->reset_generation(); \
2463 save_marks(); \
2464 }
2465
2466 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2467
2468 void
2469 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2470 if (freelistLock()->owned_by_self()) {
2471 Generation::oop_iterate(cl);
2472 } else {
2473 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2474 Generation::oop_iterate(cl);
2475 }
2476 }
2477
2478 void
2479 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2480 if (freelistLock()->owned_by_self()) {
2481 Generation::object_iterate(cl);
2482 } else {
2483 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2484 Generation::object_iterate(cl);
2485 }
2486 }
2487
2488 void
2489 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2490 if (freelistLock()->owned_by_self()) {
2491 Generation::safe_object_iterate(cl);
2492 } else {
2493 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2494 Generation::safe_object_iterate(cl);
2495 }
2496 }
2497
2498 void
2499 ConcurrentMarkSweepGeneration::post_compact() {
2500 }
2501
2502 void
2503 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2504 // Fix the linear allocation blocks to look like free blocks.
2505
2506 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2507 // are not called when the heap is verified during universe initialization and
2508 // at vm shutdown.
2509 if (freelistLock()->owned_by_self()) {
2510 cmsSpace()->prepare_for_verify();
2511 } else {
2512 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2513 cmsSpace()->prepare_for_verify();
2514 }
2515 }
2516
2517 void
2518 ConcurrentMarkSweepGeneration::verify() {
2519 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2520 // are not called when the heap is verified during universe initialization and
2521 // at vm shutdown.
2522 if (freelistLock()->owned_by_self()) {
2523 cmsSpace()->verify();
2524 } else {
2525 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2526 cmsSpace()->verify();
2527 }
2528 }
2529
2530 void CMSCollector::verify() {
2531 _cmsGen->verify();
2532 }
2533
2534 #ifndef PRODUCT
2535 bool CMSCollector::overflow_list_is_empty() const {
2536 assert(_num_par_pushes >= 0, "Inconsistency");
2537 if (_overflow_list == NULL) {
2538 assert(_num_par_pushes == 0, "Inconsistency");
2539 }
2540 return _overflow_list == NULL;
2541 }
2542
2543 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2544 // merely consolidate assertion checks that appear to occur together frequently.
2545 void CMSCollector::verify_work_stacks_empty() const {
2546 assert(_markStack.isEmpty(), "Marking stack should be empty");
2547 assert(overflow_list_is_empty(), "Overflow list should be empty");
2548 }
2549
2550 void CMSCollector::verify_overflow_empty() const {
2551 assert(overflow_list_is_empty(), "Overflow list should be empty");
2552 assert(no_preserved_marks(), "No preserved marks");
2553 }
2554 #endif // PRODUCT
2555
2556 // Decide if we want to enable class unloading as part of the
2557 // ensuing concurrent GC cycle. We will collect and
2558 // unload classes if it's the case that:
2559 // (a) class unloading is enabled at the command line, and
2560 // (b) old gen is getting really full
2561 // NOTE: Provided there is no change in the state of the heap between
2562 // calls to this method, it should have idempotent results. Moreover,
2563 // its results should be monotonically increasing (i.e. going from 0 to 1,
2564 // but not 1 to 0) between successive calls between which the heap was
2565 // not collected. For the implementation below, it must thus rely on
2566 // the property that concurrent_cycles_since_last_unload()
2567 // will not decrease unless a collection cycle happened and that
2568 // _cmsGen->is_too_full() are
2569 // themselves also monotonic in that sense. See check_monotonicity()
2570 // below.
2571 void CMSCollector::update_should_unload_classes() {
2572 _should_unload_classes = false;
2573 if (CMSClassUnloadingEnabled) {
2574 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2575 CMSClassUnloadingMaxInterval)
2576 || _cmsGen->is_too_full();
2577 }
2578 }
2579
2580 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2581 bool res = should_concurrent_collect();
2582 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2583 return res;
2584 }
2585
2586 void CMSCollector::setup_cms_unloading_and_verification_state() {
2587 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2588 || VerifyBeforeExit;
2589 const int rso = GenCollectedHeap::SO_AllCodeCache;
2590
2591 // We set the proper root for this CMS cycle here.
2592 if (should_unload_classes()) { // Should unload classes this cycle
2593 remove_root_scanning_option(rso); // Shrink the root set appropriately
2594 set_verifying(should_verify); // Set verification state for this cycle
2595 return; // Nothing else needs to be done at this time
2596 }
2597
2598 // Not unloading classes this cycle
2599 assert(!should_unload_classes(), "Inconsistency!");
2600
2601 // If we are not unloading classes then add SO_AllCodeCache to root
2602 // scanning options.
2603 add_root_scanning_option(rso);
2604
2605 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2606 set_verifying(true);
2607 } else if (verifying() && !should_verify) {
2608 // We were verifying, but some verification flags got disabled.
2609 set_verifying(false);
2610 // Exclude symbols, strings and code cache elements from root scanning to
2611 // reduce IM and RM pauses.
2612 remove_root_scanning_option(rso);
2613 }
2614 }
2615
2616
2617 #ifndef PRODUCT
2618 HeapWord* CMSCollector::block_start(const void* p) const {
2619 const HeapWord* addr = (HeapWord*)p;
2620 if (_span.contains(p)) {
2621 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2622 return _cmsGen->cmsSpace()->block_start(p);
2623 }
2624 }
2625 return NULL;
2626 }
2627 #endif
2628
2629 HeapWord*
2630 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2631 bool tlab,
2632 bool parallel) {
2633 CMSSynchronousYieldRequest yr;
2634 assert(!tlab, "Can't deal with TLAB allocation");
2635 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2636 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2637 if (GCExpandToAllocateDelayMillis > 0) {
2638 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2639 }
2640 return have_lock_and_allocate(word_size, tlab);
2641 }
2642
2643 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2644 size_t bytes,
2645 size_t expand_bytes,
2646 CMSExpansionCause::Cause cause)
2647 {
2648
2649 bool success = expand(bytes, expand_bytes);
2650
2651 // remember why we expanded; this information is used
2652 // by shouldConcurrentCollect() when making decisions on whether to start
2653 // a new CMS cycle.
2654 if (success) {
2655 set_expansion_cause(cause);
2656 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2657 }
2658 }
2659
2660 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2661 HeapWord* res = NULL;
2662 MutexLocker x(ParGCRareEvent_lock);
2663 while (true) {
2664 // Expansion by some other thread might make alloc OK now:
2665 res = ps->lab.alloc(word_sz);
2666 if (res != NULL) return res;
2667 // If there's not enough expansion space available, give up.
2668 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2669 return NULL;
2670 }
2671 // Otherwise, we try expansion.
2672 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2673 // Now go around the loop and try alloc again;
2674 // A competing par_promote might beat us to the expansion space,
2675 // so we may go around the loop again if promotion fails again.
2676 if (GCExpandToAllocateDelayMillis > 0) {
2677 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2678 }
2679 }
2680 }
2681
2682
2683 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2684 PromotionInfo* promo) {
2685 MutexLocker x(ParGCRareEvent_lock);
2686 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2687 while (true) {
2688 // Expansion by some other thread might make alloc OK now:
2689 if (promo->ensure_spooling_space()) {
2690 assert(promo->has_spooling_space(),
2691 "Post-condition of successful ensure_spooling_space()");
2692 return true;
2693 }
2694 // If there's not enough expansion space available, give up.
2695 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2696 return false;
2697 }
2698 // Otherwise, we try expansion.
2699 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2700 // Now go around the loop and try alloc again;
2701 // A competing allocation might beat us to the expansion space,
2702 // so we may go around the loop again if allocation fails again.
2703 if (GCExpandToAllocateDelayMillis > 0) {
2704 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2705 }
2706 }
2707 }
2708
2709 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2710 // Only shrink if a compaction was done so that all the free space
2711 // in the generation is in a contiguous block at the end.
2712 if (did_compact()) {
2713 CardGeneration::shrink(bytes);
2714 }
2715 }
2716
2717 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2718 assert_locked_or_safepoint(Heap_lock);
2719 }
2720
2721 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2722 assert_locked_or_safepoint(Heap_lock);
2723 assert_lock_strong(freelistLock());
2724 log_trace(gc)("Shrinking of CMS not yet implemented");
2725 return;
2726 }
2727
2728
2729 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2730 // phases.
2731 class CMSPhaseAccounting: public StackObj {
2732 public:
2733 CMSPhaseAccounting(CMSCollector *collector,
2734 const char *title);
2735 ~CMSPhaseAccounting();
2736
2737 private:
2738 CMSCollector *_collector;
2739 const char *_title;
2740 GCTraceConcTime(Info, gc) _trace_time;
2741
2742 public:
2743 // Not MT-safe; so do not pass around these StackObj's
2744 // where they may be accessed by other threads.
2745 double wallclock_millis() {
2746 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2747 }
2748 };
2749
2750 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2751 const char *title) :
2752 _collector(collector), _title(title), _trace_time(title) {
2753
2754 _collector->resetYields();
2755 _collector->resetTimer();
2756 _collector->startTimer();
2757 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2758 }
2759
2760 CMSPhaseAccounting::~CMSPhaseAccounting() {
2761 _collector->gc_timer_cm()->register_gc_concurrent_end();
2762 _collector->stopTimer();
2763 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2764 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2765 }
2766
2767 // CMS work
2768
2769 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2770 class CMSParMarkTask : public AbstractGangTask {
2771 protected:
2772 CMSCollector* _collector;
2773 uint _n_workers;
2774 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2775 AbstractGangTask(name),
2776 _collector(collector),
2777 _n_workers(n_workers) {}
2778 // Work method in support of parallel rescan ... of young gen spaces
2779 void do_young_space_rescan(OopsInGenClosure* cl,
2780 ContiguousSpace* space,
2781 HeapWord** chunk_array, size_t chunk_top);
2782 void work_on_young_gen_roots(OopsInGenClosure* cl);
2783 };
2784
2785 // Parallel initial mark task
2786 class CMSParInitialMarkTask: public CMSParMarkTask {
2787 StrongRootsScope* _strong_roots_scope;
2788 public:
2789 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2790 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2791 _strong_roots_scope(strong_roots_scope) {}
2792 void work(uint worker_id);
2793 };
2794
2795 // Checkpoint the roots into this generation from outside
2796 // this generation. [Note this initial checkpoint need only
2797 // be approximate -- we'll do a catch up phase subsequently.]
2798 void CMSCollector::checkpointRootsInitial() {
2799 assert(_collectorState == InitialMarking, "Wrong collector state");
2800 check_correct_thread_executing();
2801 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2802
2803 save_heap_summary();
2804 report_heap_summary(GCWhen::BeforeGC);
2805
2806 ReferenceProcessor* rp = ref_processor();
2807 assert(_restart_addr == NULL, "Control point invariant");
2808 {
2809 // acquire locks for subsequent manipulations
2810 MutexLockerEx x(bitMapLock(),
2811 Mutex::_no_safepoint_check_flag);
2812 checkpointRootsInitialWork();
2813 // enable ("weak") refs discovery
2814 rp->enable_discovery();
2815 _collectorState = Marking;
2816 }
2817 }
2818
2819 void CMSCollector::checkpointRootsInitialWork() {
2820 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2821 assert(_collectorState == InitialMarking, "just checking");
2822
2823 // Already have locks.
2824 assert_lock_strong(bitMapLock());
2825 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2826
2827 // Setup the verification and class unloading state for this
2828 // CMS collection cycle.
2829 setup_cms_unloading_and_verification_state();
2830
2831 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2832
2833 // Reset all the PLAB chunk arrays if necessary.
2834 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2835 reset_survivor_plab_arrays();
2836 }
2837
2838 ResourceMark rm;
2839 HandleMark hm;
2840
2841 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2842 GenCollectedHeap* gch = GenCollectedHeap::heap();
2843
2844 verify_work_stacks_empty();
2845 verify_overflow_empty();
2846
2847 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2848 // Update the saved marks which may affect the root scans.
2849 gch->save_marks();
2850
2851 // weak reference processing has not started yet.
2852 ref_processor()->set_enqueuing_is_done(false);
2853
2854 // Need to remember all newly created CLDs,
2855 // so that we can guarantee that the remark finds them.
2856 ClassLoaderDataGraph::remember_new_clds(true);
2857
2858 // Whenever a CLD is found, it will be claimed before proceeding to mark
2859 // the klasses. The claimed marks need to be cleared before marking starts.
2860 ClassLoaderDataGraph::clear_claimed_marks();
2861
2862 print_eden_and_survivor_chunk_arrays();
2863
2864 {
2865 #if defined(COMPILER2) || INCLUDE_JVMCI
2866 DerivedPointerTableDeactivate dpt_deact;
2867 #endif
2868 if (CMSParallelInitialMarkEnabled) {
2869 // The parallel version.
2870 WorkGang* workers = gch->workers();
2871 assert(workers != NULL, "Need parallel worker threads.");
2872 uint n_workers = workers->active_workers();
2873
2874 StrongRootsScope srs(n_workers);
2875
2876 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2877 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2878 // If the total workers is greater than 1, then multiple workers
2879 // may be used at some time and the initialization has been set
2880 // such that the single threaded path cannot be used.
2881 if (workers->total_workers() > 1) {
2882 workers->run_task(&tsk);
2883 } else {
2884 tsk.work(0);
2885 }
2886 } else {
2887 // The serial version.
2888 CLDToOopClosure cld_closure(¬Older, true);
2889 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2890
2891 StrongRootsScope srs(1);
2892
2893 gch->cms_process_roots(&srs,
2894 true, // young gen as roots
2895 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2896 should_unload_classes(),
2897 ¬Older,
2898 &cld_closure);
2899 }
2900 }
2901
2902 // Clear mod-union table; it will be dirtied in the prologue of
2903 // CMS generation per each young generation collection.
2904
2905 assert(_modUnionTable.isAllClear(),
2906 "Was cleared in most recent final checkpoint phase"
2907 " or no bits are set in the gc_prologue before the start of the next "
2908 "subsequent marking phase.");
2909
2910 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2911
2912 // Save the end of the used_region of the constituent generations
2913 // to be used to limit the extent of sweep in each generation.
2914 save_sweep_limits();
2915 verify_overflow_empty();
2916 }
2917
2918 bool CMSCollector::markFromRoots() {
2919 // we might be tempted to assert that:
2920 // assert(!SafepointSynchronize::is_at_safepoint(),
2921 // "inconsistent argument?");
2922 // However that wouldn't be right, because it's possible that
2923 // a safepoint is indeed in progress as a young generation
2924 // stop-the-world GC happens even as we mark in this generation.
2925 assert(_collectorState == Marking, "inconsistent state?");
2926 check_correct_thread_executing();
2927 verify_overflow_empty();
2928
2929 // Weak ref discovery note: We may be discovering weak
2930 // refs in this generation concurrent (but interleaved) with
2931 // weak ref discovery by the young generation collector.
2932
2933 CMSTokenSyncWithLocks ts(true, bitMapLock());
2934 GCTraceCPUTime tcpu;
2935 CMSPhaseAccounting pa(this, "Concurrent Mark");
2936 bool res = markFromRootsWork();
2937 if (res) {
2938 _collectorState = Precleaning;
2939 } else { // We failed and a foreground collection wants to take over
2940 assert(_foregroundGCIsActive, "internal state inconsistency");
2941 assert(_restart_addr == NULL, "foreground will restart from scratch");
2942 log_debug(gc)("bailing out to foreground collection");
2943 }
2944 verify_overflow_empty();
2945 return res;
2946 }
2947
2948 bool CMSCollector::markFromRootsWork() {
2949 // iterate over marked bits in bit map, doing a full scan and mark
2950 // from these roots using the following algorithm:
2951 // . if oop is to the right of the current scan pointer,
2952 // mark corresponding bit (we'll process it later)
2953 // . else (oop is to left of current scan pointer)
2954 // push oop on marking stack
2955 // . drain the marking stack
2956
2957 // Note that when we do a marking step we need to hold the
2958 // bit map lock -- recall that direct allocation (by mutators)
2959 // and promotion (by the young generation collector) is also
2960 // marking the bit map. [the so-called allocate live policy.]
2961 // Because the implementation of bit map marking is not
2962 // robust wrt simultaneous marking of bits in the same word,
2963 // we need to make sure that there is no such interference
2964 // between concurrent such updates.
2965
2966 // already have locks
2967 assert_lock_strong(bitMapLock());
2968
2969 verify_work_stacks_empty();
2970 verify_overflow_empty();
2971 bool result = false;
2972 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2973 result = do_marking_mt();
2974 } else {
2975 result = do_marking_st();
2976 }
2977 return result;
2978 }
2979
2980 // Forward decl
2981 class CMSConcMarkingTask;
2982
2983 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2984 CMSCollector* _collector;
2985 CMSConcMarkingTask* _task;
2986 public:
2987 virtual void yield();
2988
2989 // "n_threads" is the number of threads to be terminated.
2990 // "queue_set" is a set of work queues of other threads.
2991 // "collector" is the CMS collector associated with this task terminator.
2992 // "yield" indicates whether we need the gang as a whole to yield.
2993 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2994 ParallelTaskTerminator(n_threads, queue_set),
2995 _collector(collector) { }
2996
2997 void set_task(CMSConcMarkingTask* task) {
2998 _task = task;
2999 }
3000 };
3001
3002 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3003 CMSConcMarkingTask* _task;
3004 public:
3005 bool should_exit_termination();
3006 void set_task(CMSConcMarkingTask* task) {
3007 _task = task;
3008 }
3009 };
3010
3011 // MT Concurrent Marking Task
3012 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3013 CMSCollector* _collector;
3014 uint _n_workers; // requested/desired # workers
3015 bool _result;
3016 CompactibleFreeListSpace* _cms_space;
3017 char _pad_front[64]; // padding to ...
3018 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3019 char _pad_back[64];
3020 HeapWord* _restart_addr;
3021
3022 // Exposed here for yielding support
3023 Mutex* const _bit_map_lock;
3024
3025 // The per thread work queues, available here for stealing
3026 OopTaskQueueSet* _task_queues;
3027
3028 // Termination (and yielding) support
3029 CMSConcMarkingTerminator _term;
3030 CMSConcMarkingTerminatorTerminator _term_term;
3031
3032 public:
3033 CMSConcMarkingTask(CMSCollector* collector,
3034 CompactibleFreeListSpace* cms_space,
3035 YieldingFlexibleWorkGang* workers,
3036 OopTaskQueueSet* task_queues):
3037 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3038 _collector(collector),
3039 _cms_space(cms_space),
3040 _n_workers(0), _result(true),
3041 _task_queues(task_queues),
3042 _term(_n_workers, task_queues, _collector),
3043 _bit_map_lock(collector->bitMapLock())
3044 {
3045 _requested_size = _n_workers;
3046 _term.set_task(this);
3047 _term_term.set_task(this);
3048 _restart_addr = _global_finger = _cms_space->bottom();
3049 }
3050
3051
3052 OopTaskQueueSet* task_queues() { return _task_queues; }
3053
3054 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3055
3056 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3057
3058 CMSConcMarkingTerminator* terminator() { return &_term; }
3059
3060 virtual void set_for_termination(uint active_workers) {
3061 terminator()->reset_for_reuse(active_workers);
3062 }
3063
3064 void work(uint worker_id);
3065 bool should_yield() {
3066 return ConcurrentMarkSweepThread::should_yield()
3067 && !_collector->foregroundGCIsActive();
3068 }
3069
3070 virtual void coordinator_yield(); // stuff done by coordinator
3071 bool result() { return _result; }
3072
3073 void reset(HeapWord* ra) {
3074 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3075 _restart_addr = _global_finger = ra;
3076 _term.reset_for_reuse();
3077 }
3078
3079 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3080 OopTaskQueue* work_q);
3081
3082 private:
3083 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3084 void do_work_steal(int i);
3085 void bump_global_finger(HeapWord* f);
3086 };
3087
3088 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3089 assert(_task != NULL, "Error");
3090 return _task->yielding();
3091 // Note that we do not need the disjunct || _task->should_yield() above
3092 // because we want terminating threads to yield only if the task
3093 // is already in the midst of yielding, which happens only after at least one
3094 // thread has yielded.
3095 }
3096
3097 void CMSConcMarkingTerminator::yield() {
3098 if (_task->should_yield()) {
3099 _task->yield();
3100 } else {
3101 ParallelTaskTerminator::yield();
3102 }
3103 }
3104
3105 ////////////////////////////////////////////////////////////////
3106 // Concurrent Marking Algorithm Sketch
3107 ////////////////////////////////////////////////////////////////
3108 // Until all tasks exhausted (both spaces):
3109 // -- claim next available chunk
3110 // -- bump global finger via CAS
3111 // -- find first object that starts in this chunk
3112 // and start scanning bitmap from that position
3113 // -- scan marked objects for oops
3114 // -- CAS-mark target, and if successful:
3115 // . if target oop is above global finger (volatile read)
3116 // nothing to do
3117 // . if target oop is in chunk and above local finger
3118 // then nothing to do
3119 // . else push on work-queue
3120 // -- Deal with possible overflow issues:
3121 // . local work-queue overflow causes stuff to be pushed on
3122 // global (common) overflow queue
3123 // . always first empty local work queue
3124 // . then get a batch of oops from global work queue if any
3125 // . then do work stealing
3126 // -- When all tasks claimed (both spaces)
3127 // and local work queue empty,
3128 // then in a loop do:
3129 // . check global overflow stack; steal a batch of oops and trace
3130 // . try to steal from other threads oif GOS is empty
3131 // . if neither is available, offer termination
3132 // -- Terminate and return result
3133 //
3134 void CMSConcMarkingTask::work(uint worker_id) {
3135 elapsedTimer _timer;
3136 ResourceMark rm;
3137 HandleMark hm;
3138
3139 DEBUG_ONLY(_collector->verify_overflow_empty();)
3140
3141 // Before we begin work, our work queue should be empty
3142 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3143 // Scan the bitmap covering _cms_space, tracing through grey objects.
3144 _timer.start();
3145 do_scan_and_mark(worker_id, _cms_space);
3146 _timer.stop();
3147 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3148
3149 // ... do work stealing
3150 _timer.reset();
3151 _timer.start();
3152 do_work_steal(worker_id);
3153 _timer.stop();
3154 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3155 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3156 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3157 // Note that under the current task protocol, the
3158 // following assertion is true even of the spaces
3159 // expanded since the completion of the concurrent
3160 // marking. XXX This will likely change under a strict
3161 // ABORT semantics.
3162 // After perm removal the comparison was changed to
3163 // greater than or equal to from strictly greater than.
3164 // Before perm removal the highest address sweep would
3165 // have been at the end of perm gen but now is at the
3166 // end of the tenured gen.
3167 assert(_global_finger >= _cms_space->end(),
3168 "All tasks have been completed");
3169 DEBUG_ONLY(_collector->verify_overflow_empty();)
3170 }
3171
3172 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3173 HeapWord* read = _global_finger;
3174 HeapWord* cur = read;
3175 while (f > read) {
3176 cur = read;
3177 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3178 if (cur == read) {
3179 // our cas succeeded
3180 assert(_global_finger >= f, "protocol consistency");
3181 break;
3182 }
3183 }
3184 }
3185
3186 // This is really inefficient, and should be redone by
3187 // using (not yet available) block-read and -write interfaces to the
3188 // stack and the work_queue. XXX FIX ME !!!
3189 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3190 OopTaskQueue* work_q) {
3191 // Fast lock-free check
3192 if (ovflw_stk->length() == 0) {
3193 return false;
3194 }
3195 assert(work_q->size() == 0, "Shouldn't steal");
3196 MutexLockerEx ml(ovflw_stk->par_lock(),
3197 Mutex::_no_safepoint_check_flag);
3198 // Grab up to 1/4 the size of the work queue
3199 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3200 (size_t)ParGCDesiredObjsFromOverflowList);
3201 num = MIN2(num, ovflw_stk->length());
3202 for (int i = (int) num; i > 0; i--) {
3203 oop cur = ovflw_stk->pop();
3204 assert(cur != NULL, "Counted wrong?");
3205 work_q->push(cur);
3206 }
3207 return num > 0;
3208 }
3209
3210 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3211 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3212 int n_tasks = pst->n_tasks();
3213 // We allow that there may be no tasks to do here because
3214 // we are restarting after a stack overflow.
3215 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3216 uint nth_task = 0;
3217
3218 HeapWord* aligned_start = sp->bottom();
3219 if (sp->used_region().contains(_restart_addr)) {
3220 // Align down to a card boundary for the start of 0th task
3221 // for this space.
3222 aligned_start =
3223 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3224 CardTableModRefBS::card_size);
3225 }
3226
3227 size_t chunk_size = sp->marking_task_size();
3228 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3229 // Having claimed the nth task in this space,
3230 // compute the chunk that it corresponds to:
3231 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3232 aligned_start + (nth_task+1)*chunk_size);
3233 // Try and bump the global finger via a CAS;
3234 // note that we need to do the global finger bump
3235 // _before_ taking the intersection below, because
3236 // the task corresponding to that region will be
3237 // deemed done even if the used_region() expands
3238 // because of allocation -- as it almost certainly will
3239 // during start-up while the threads yield in the
3240 // closure below.
3241 HeapWord* finger = span.end();
3242 bump_global_finger(finger); // atomically
3243 // There are null tasks here corresponding to chunks
3244 // beyond the "top" address of the space.
3245 span = span.intersection(sp->used_region());
3246 if (!span.is_empty()) { // Non-null task
3247 HeapWord* prev_obj;
3248 assert(!span.contains(_restart_addr) || nth_task == 0,
3249 "Inconsistency");
3250 if (nth_task == 0) {
3251 // For the 0th task, we'll not need to compute a block_start.
3252 if (span.contains(_restart_addr)) {
3253 // In the case of a restart because of stack overflow,
3254 // we might additionally skip a chunk prefix.
3255 prev_obj = _restart_addr;
3256 } else {
3257 prev_obj = span.start();
3258 }
3259 } else {
3260 // We want to skip the first object because
3261 // the protocol is to scan any object in its entirety
3262 // that _starts_ in this span; a fortiori, any
3263 // object starting in an earlier span is scanned
3264 // as part of an earlier claimed task.
3265 // Below we use the "careful" version of block_start
3266 // so we do not try to navigate uninitialized objects.
3267 prev_obj = sp->block_start_careful(span.start());
3268 // Below we use a variant of block_size that uses the
3269 // Printezis bits to avoid waiting for allocated
3270 // objects to become initialized/parsable.
3271 while (prev_obj < span.start()) {
3272 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3273 if (sz > 0) {
3274 prev_obj += sz;
3275 } else {
3276 // In this case we may end up doing a bit of redundant
3277 // scanning, but that appears unavoidable, short of
3278 // locking the free list locks; see bug 6324141.
3279 break;
3280 }
3281 }
3282 }
3283 if (prev_obj < span.end()) {
3284 MemRegion my_span = MemRegion(prev_obj, span.end());
3285 // Do the marking work within a non-empty span --
3286 // the last argument to the constructor indicates whether the
3287 // iteration should be incremental with periodic yields.
3288 ParMarkFromRootsClosure cl(this, _collector, my_span,
3289 &_collector->_markBitMap,
3290 work_queue(i),
3291 &_collector->_markStack);
3292 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3293 } // else nothing to do for this task
3294 } // else nothing to do for this task
3295 }
3296 // We'd be tempted to assert here that since there are no
3297 // more tasks left to claim in this space, the global_finger
3298 // must exceed space->top() and a fortiori space->end(). However,
3299 // that would not quite be correct because the bumping of
3300 // global_finger occurs strictly after the claiming of a task,
3301 // so by the time we reach here the global finger may not yet
3302 // have been bumped up by the thread that claimed the last
3303 // task.
3304 pst->all_tasks_completed();
3305 }
3306
3307 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3308 private:
3309 CMSCollector* _collector;
3310 CMSConcMarkingTask* _task;
3311 MemRegion _span;
3312 CMSBitMap* _bit_map;
3313 CMSMarkStack* _overflow_stack;
3314 OopTaskQueue* _work_queue;
3315 protected:
3316 DO_OOP_WORK_DEFN
3317 public:
3318 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3319 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3320 MetadataAwareOopClosure(collector->ref_processor()),
3321 _collector(collector),
3322 _task(task),
3323 _span(collector->_span),
3324 _work_queue(work_queue),
3325 _bit_map(bit_map),
3326 _overflow_stack(overflow_stack)
3327 { }
3328 virtual void do_oop(oop* p);
3329 virtual void do_oop(narrowOop* p);
3330
3331 void trim_queue(size_t max);
3332 void handle_stack_overflow(HeapWord* lost);
3333 void do_yield_check() {
3334 if (_task->should_yield()) {
3335 _task->yield();
3336 }
3337 }
3338 };
3339
3340 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3341
3342 // Grey object scanning during work stealing phase --
3343 // the salient assumption here is that any references
3344 // that are in these stolen objects being scanned must
3345 // already have been initialized (else they would not have
3346 // been published), so we do not need to check for
3347 // uninitialized objects before pushing here.
3348 void ParConcMarkingClosure::do_oop(oop obj) {
3349 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3350 HeapWord* addr = (HeapWord*)obj;
3351 // Check if oop points into the CMS generation
3352 // and is not marked
3353 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3354 // a white object ...
3355 // If we manage to "claim" the object, by being the
3356 // first thread to mark it, then we push it on our
3357 // marking stack
3358 if (_bit_map->par_mark(addr)) { // ... now grey
3359 // push on work queue (grey set)
3360 bool simulate_overflow = false;
3361 NOT_PRODUCT(
3362 if (CMSMarkStackOverflowALot &&
3363 _collector->simulate_overflow()) {
3364 // simulate a stack overflow
3365 simulate_overflow = true;
3366 }
3367 )
3368 if (simulate_overflow ||
3369 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3370 // stack overflow
3371 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3372 // We cannot assert that the overflow stack is full because
3373 // it may have been emptied since.
3374 assert(simulate_overflow ||
3375 _work_queue->size() == _work_queue->max_elems(),
3376 "Else push should have succeeded");
3377 handle_stack_overflow(addr);
3378 }
3379 } // Else, some other thread got there first
3380 do_yield_check();
3381 }
3382 }
3383
3384 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); }
3385 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3386
3387 void ParConcMarkingClosure::trim_queue(size_t max) {
3388 while (_work_queue->size() > max) {
3389 oop new_oop;
3390 if (_work_queue->pop_local(new_oop)) {
3391 assert(new_oop->is_oop(), "Should be an oop");
3392 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3393 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3394 new_oop->oop_iterate(this); // do_oop() above
3395 do_yield_check();
3396 }
3397 }
3398 }
3399
3400 // Upon stack overflow, we discard (part of) the stack,
3401 // remembering the least address amongst those discarded
3402 // in CMSCollector's _restart_address.
3403 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3404 // We need to do this under a mutex to prevent other
3405 // workers from interfering with the work done below.
3406 MutexLockerEx ml(_overflow_stack->par_lock(),
3407 Mutex::_no_safepoint_check_flag);
3408 // Remember the least grey address discarded
3409 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3410 _collector->lower_restart_addr(ra);
3411 _overflow_stack->reset(); // discard stack contents
3412 _overflow_stack->expand(); // expand the stack if possible
3413 }
3414
3415
3416 void CMSConcMarkingTask::do_work_steal(int i) {
3417 OopTaskQueue* work_q = work_queue(i);
3418 oop obj_to_scan;
3419 CMSBitMap* bm = &(_collector->_markBitMap);
3420 CMSMarkStack* ovflw = &(_collector->_markStack);
3421 int* seed = _collector->hash_seed(i);
3422 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3423 while (true) {
3424 cl.trim_queue(0);
3425 assert(work_q->size() == 0, "Should have been emptied above");
3426 if (get_work_from_overflow_stack(ovflw, work_q)) {
3427 // Can't assert below because the work obtained from the
3428 // overflow stack may already have been stolen from us.
3429 // assert(work_q->size() > 0, "Work from overflow stack");
3430 continue;
3431 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3432 assert(obj_to_scan->is_oop(), "Should be an oop");
3433 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3434 obj_to_scan->oop_iterate(&cl);
3435 } else if (terminator()->offer_termination(&_term_term)) {
3436 assert(work_q->size() == 0, "Impossible!");
3437 break;
3438 } else if (yielding() || should_yield()) {
3439 yield();
3440 }
3441 }
3442 }
3443
3444 // This is run by the CMS (coordinator) thread.
3445 void CMSConcMarkingTask::coordinator_yield() {
3446 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3447 "CMS thread should hold CMS token");
3448 // First give up the locks, then yield, then re-lock
3449 // We should probably use a constructor/destructor idiom to
3450 // do this unlock/lock or modify the MutexUnlocker class to
3451 // serve our purpose. XXX
3452 assert_lock_strong(_bit_map_lock);
3453 _bit_map_lock->unlock();
3454 ConcurrentMarkSweepThread::desynchronize(true);
3455 _collector->stopTimer();
3456 _collector->incrementYields();
3457
3458 // It is possible for whichever thread initiated the yield request
3459 // not to get a chance to wake up and take the bitmap lock between
3460 // this thread releasing it and reacquiring it. So, while the
3461 // should_yield() flag is on, let's sleep for a bit to give the
3462 // other thread a chance to wake up. The limit imposed on the number
3463 // of iterations is defensive, to avoid any unforseen circumstances
3464 // putting us into an infinite loop. Since it's always been this
3465 // (coordinator_yield()) method that was observed to cause the
3466 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3467 // which is by default non-zero. For the other seven methods that
3468 // also perform the yield operation, as are using a different
3469 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3470 // can enable the sleeping for those methods too, if necessary.
3471 // See 6442774.
3472 //
3473 // We really need to reconsider the synchronization between the GC
3474 // thread and the yield-requesting threads in the future and we
3475 // should really use wait/notify, which is the recommended
3476 // way of doing this type of interaction. Additionally, we should
3477 // consolidate the eight methods that do the yield operation and they
3478 // are almost identical into one for better maintainability and
3479 // readability. See 6445193.
3480 //
3481 // Tony 2006.06.29
3482 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3483 ConcurrentMarkSweepThread::should_yield() &&
3484 !CMSCollector::foregroundGCIsActive(); ++i) {
3485 os::sleep(Thread::current(), 1, false);
3486 }
3487
3488 ConcurrentMarkSweepThread::synchronize(true);
3489 _bit_map_lock->lock_without_safepoint_check();
3490 _collector->startTimer();
3491 }
3492
3493 bool CMSCollector::do_marking_mt() {
3494 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3495 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3496 conc_workers()->active_workers(),
3497 Threads::number_of_non_daemon_threads());
3498 num_workers = conc_workers()->update_active_workers(num_workers);
3499 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3500
3501 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3502
3503 CMSConcMarkingTask tsk(this,
3504 cms_space,
3505 conc_workers(),
3506 task_queues());
3507
3508 // Since the actual number of workers we get may be different
3509 // from the number we requested above, do we need to do anything different
3510 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3511 // class?? XXX
3512 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3513
3514 // Refs discovery is already non-atomic.
3515 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3516 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3517 conc_workers()->start_task(&tsk);
3518 while (tsk.yielded()) {
3519 tsk.coordinator_yield();
3520 conc_workers()->continue_task(&tsk);
3521 }
3522 // If the task was aborted, _restart_addr will be non-NULL
3523 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3524 while (_restart_addr != NULL) {
3525 // XXX For now we do not make use of ABORTED state and have not
3526 // yet implemented the right abort semantics (even in the original
3527 // single-threaded CMS case). That needs some more investigation
3528 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3529 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3530 // If _restart_addr is non-NULL, a marking stack overflow
3531 // occurred; we need to do a fresh marking iteration from the
3532 // indicated restart address.
3533 if (_foregroundGCIsActive) {
3534 // We may be running into repeated stack overflows, having
3535 // reached the limit of the stack size, while making very
3536 // slow forward progress. It may be best to bail out and
3537 // let the foreground collector do its job.
3538 // Clear _restart_addr, so that foreground GC
3539 // works from scratch. This avoids the headache of
3540 // a "rescan" which would otherwise be needed because
3541 // of the dirty mod union table & card table.
3542 _restart_addr = NULL;
3543 return false;
3544 }
3545 // Adjust the task to restart from _restart_addr
3546 tsk.reset(_restart_addr);
3547 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3548 _restart_addr);
3549 _restart_addr = NULL;
3550 // Get the workers going again
3551 conc_workers()->start_task(&tsk);
3552 while (tsk.yielded()) {
3553 tsk.coordinator_yield();
3554 conc_workers()->continue_task(&tsk);
3555 }
3556 }
3557 assert(tsk.completed(), "Inconsistency");
3558 assert(tsk.result() == true, "Inconsistency");
3559 return true;
3560 }
3561
3562 bool CMSCollector::do_marking_st() {
3563 ResourceMark rm;
3564 HandleMark hm;
3565
3566 // Temporarily make refs discovery single threaded (non-MT)
3567 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3568 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3569 &_markStack, CMSYield);
3570 // the last argument to iterate indicates whether the iteration
3571 // should be incremental with periodic yields.
3572 _markBitMap.iterate(&markFromRootsClosure);
3573 // If _restart_addr is non-NULL, a marking stack overflow
3574 // occurred; we need to do a fresh iteration from the
3575 // indicated restart address.
3576 while (_restart_addr != NULL) {
3577 if (_foregroundGCIsActive) {
3578 // We may be running into repeated stack overflows, having
3579 // reached the limit of the stack size, while making very
3580 // slow forward progress. It may be best to bail out and
3581 // let the foreground collector do its job.
3582 // Clear _restart_addr, so that foreground GC
3583 // works from scratch. This avoids the headache of
3584 // a "rescan" which would otherwise be needed because
3585 // of the dirty mod union table & card table.
3586 _restart_addr = NULL;
3587 return false; // indicating failure to complete marking
3588 }
3589 // Deal with stack overflow:
3590 // we restart marking from _restart_addr
3591 HeapWord* ra = _restart_addr;
3592 markFromRootsClosure.reset(ra);
3593 _restart_addr = NULL;
3594 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3595 }
3596 return true;
3597 }
3598
3599 void CMSCollector::preclean() {
3600 check_correct_thread_executing();
3601 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3602 verify_work_stacks_empty();
3603 verify_overflow_empty();
3604 _abort_preclean = false;
3605 if (CMSPrecleaningEnabled) {
3606 if (!CMSEdenChunksRecordAlways) {
3607 _eden_chunk_index = 0;
3608 }
3609 size_t used = get_eden_used();
3610 size_t capacity = get_eden_capacity();
3611 // Don't start sampling unless we will get sufficiently
3612 // many samples.
3613 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3614 * CMSScheduleRemarkEdenPenetration)) {
3615 _start_sampling = true;
3616 } else {
3617 _start_sampling = false;
3618 }
3619 GCTraceCPUTime tcpu;
3620 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3621 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3622 }
3623 CMSTokenSync x(true); // is cms thread
3624 if (CMSPrecleaningEnabled) {
3625 sample_eden();
3626 _collectorState = AbortablePreclean;
3627 } else {
3628 _collectorState = FinalMarking;
3629 }
3630 verify_work_stacks_empty();
3631 verify_overflow_empty();
3632 }
3633
3634 // Try and schedule the remark such that young gen
3635 // occupancy is CMSScheduleRemarkEdenPenetration %.
3636 void CMSCollector::abortable_preclean() {
3637 check_correct_thread_executing();
3638 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3639 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3640
3641 // If Eden's current occupancy is below this threshold,
3642 // immediately schedule the remark; else preclean
3643 // past the next scavenge in an effort to
3644 // schedule the pause as described above. By choosing
3645 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3646 // we will never do an actual abortable preclean cycle.
3647 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3648 GCTraceCPUTime tcpu;
3649 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3650 // We need more smarts in the abortable preclean
3651 // loop below to deal with cases where allocation
3652 // in young gen is very very slow, and our precleaning
3653 // is running a losing race against a horde of
3654 // mutators intent on flooding us with CMS updates
3655 // (dirty cards).
3656 // One, admittedly dumb, strategy is to give up
3657 // after a certain number of abortable precleaning loops
3658 // or after a certain maximum time. We want to make
3659 // this smarter in the next iteration.
3660 // XXX FIX ME!!! YSR
3661 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3662 while (!(should_abort_preclean() ||
3663 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3664 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3665 cumworkdone += workdone;
3666 loops++;
3667 // Voluntarily terminate abortable preclean phase if we have
3668 // been at it for too long.
3669 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3670 loops >= CMSMaxAbortablePrecleanLoops) {
3671 log_debug(gc)(" CMS: abort preclean due to loops ");
3672 break;
3673 }
3674 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3675 log_debug(gc)(" CMS: abort preclean due to time ");
3676 break;
3677 }
3678 // If we are doing little work each iteration, we should
3679 // take a short break.
3680 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3681 // Sleep for some time, waiting for work to accumulate
3682 stopTimer();
3683 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3684 startTimer();
3685 waited++;
3686 }
3687 }
3688 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3689 loops, waited, cumworkdone);
3690 }
3691 CMSTokenSync x(true); // is cms thread
3692 if (_collectorState != Idling) {
3693 assert(_collectorState == AbortablePreclean,
3694 "Spontaneous state transition?");
3695 _collectorState = FinalMarking;
3696 } // Else, a foreground collection completed this CMS cycle.
3697 return;
3698 }
3699
3700 // Respond to an Eden sampling opportunity
3701 void CMSCollector::sample_eden() {
3702 // Make sure a young gc cannot sneak in between our
3703 // reading and recording of a sample.
3704 assert(Thread::current()->is_ConcurrentGC_thread(),
3705 "Only the cms thread may collect Eden samples");
3706 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3707 "Should collect samples while holding CMS token");
3708 if (!_start_sampling) {
3709 return;
3710 }
3711 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3712 // is populated by the young generation.
3713 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3714 if (_eden_chunk_index < _eden_chunk_capacity) {
3715 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3716 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3717 "Unexpected state of Eden");
3718 // We'd like to check that what we just sampled is an oop-start address;
3719 // however, we cannot do that here since the object may not yet have been
3720 // initialized. So we'll instead do the check when we _use_ this sample
3721 // later.
3722 if (_eden_chunk_index == 0 ||
3723 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3724 _eden_chunk_array[_eden_chunk_index-1])
3725 >= CMSSamplingGrain)) {
3726 _eden_chunk_index++; // commit sample
3727 }
3728 }
3729 }
3730 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3731 size_t used = get_eden_used();
3732 size_t capacity = get_eden_capacity();
3733 assert(used <= capacity, "Unexpected state of Eden");
3734 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3735 _abort_preclean = true;
3736 }
3737 }
3738 }
3739
3740
3741 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3742 assert(_collectorState == Precleaning ||
3743 _collectorState == AbortablePreclean, "incorrect state");
3744 ResourceMark rm;
3745 HandleMark hm;
3746
3747 // Precleaning is currently not MT but the reference processor
3748 // may be set for MT. Disable it temporarily here.
3749 ReferenceProcessor* rp = ref_processor();
3750 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3751
3752 // Do one pass of scrubbing the discovered reference lists
3753 // to remove any reference objects with strongly-reachable
3754 // referents.
3755 if (clean_refs) {
3756 CMSPrecleanRefsYieldClosure yield_cl(this);
3757 assert(rp->span().equals(_span), "Spans should be equal");
3758 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3759 &_markStack, true /* preclean */);
3760 CMSDrainMarkingStackClosure complete_trace(this,
3761 _span, &_markBitMap, &_markStack,
3762 &keep_alive, true /* preclean */);
3763
3764 // We don't want this step to interfere with a young
3765 // collection because we don't want to take CPU
3766 // or memory bandwidth away from the young GC threads
3767 // (which may be as many as there are CPUs).
3768 // Note that we don't need to protect ourselves from
3769 // interference with mutators because they can't
3770 // manipulate the discovered reference lists nor affect
3771 // the computed reachability of the referents, the
3772 // only properties manipulated by the precleaning
3773 // of these reference lists.
3774 stopTimer();
3775 CMSTokenSyncWithLocks x(true /* is cms thread */,
3776 bitMapLock());
3777 startTimer();
3778 sample_eden();
3779
3780 // The following will yield to allow foreground
3781 // collection to proceed promptly. XXX YSR:
3782 // The code in this method may need further
3783 // tweaking for better performance and some restructuring
3784 // for cleaner interfaces.
3785 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3786 rp->preclean_discovered_references(
3787 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3788 gc_timer);
3789 }
3790
3791 if (clean_survivor) { // preclean the active survivor space(s)
3792 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3793 &_markBitMap, &_modUnionTable,
3794 &_markStack, true /* precleaning phase */);
3795 stopTimer();
3796 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3797 bitMapLock());
3798 startTimer();
3799 unsigned int before_count =
3800 GenCollectedHeap::heap()->total_collections();
3801 SurvivorSpacePrecleanClosure
3802 sss_cl(this, _span, &_markBitMap, &_markStack,
3803 &pam_cl, before_count, CMSYield);
3804 _young_gen->from()->object_iterate_careful(&sss_cl);
3805 _young_gen->to()->object_iterate_careful(&sss_cl);
3806 }
3807 MarkRefsIntoAndScanClosure
3808 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3809 &_markStack, this, CMSYield,
3810 true /* precleaning phase */);
3811 // CAUTION: The following closure has persistent state that may need to
3812 // be reset upon a decrease in the sequence of addresses it
3813 // processes.
3814 ScanMarkedObjectsAgainCarefullyClosure
3815 smoac_cl(this, _span,
3816 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3817
3818 // Preclean dirty cards in ModUnionTable and CardTable using
3819 // appropriate convergence criterion;
3820 // repeat CMSPrecleanIter times unless we find that
3821 // we are losing.
3822 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3823 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3824 "Bad convergence multiplier");
3825 assert(CMSPrecleanThreshold >= 100,
3826 "Unreasonably low CMSPrecleanThreshold");
3827
3828 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3829 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3830 numIter < CMSPrecleanIter;
3831 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3832 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3833 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3834 // Either there are very few dirty cards, so re-mark
3835 // pause will be small anyway, or our pre-cleaning isn't
3836 // that much faster than the rate at which cards are being
3837 // dirtied, so we might as well stop and re-mark since
3838 // precleaning won't improve our re-mark time by much.
3839 if (curNumCards <= CMSPrecleanThreshold ||
3840 (numIter > 0 &&
3841 (curNumCards * CMSPrecleanDenominator >
3842 lastNumCards * CMSPrecleanNumerator))) {
3843 numIter++;
3844 cumNumCards += curNumCards;
3845 break;
3846 }
3847 }
3848
3849 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3850
3851 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3852 cumNumCards += curNumCards;
3853 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3854 curNumCards, cumNumCards, numIter);
3855 return cumNumCards; // as a measure of useful work done
3856 }
3857
3858 // PRECLEANING NOTES:
3859 // Precleaning involves:
3860 // . reading the bits of the modUnionTable and clearing the set bits.
3861 // . For the cards corresponding to the set bits, we scan the
3862 // objects on those cards. This means we need the free_list_lock
3863 // so that we can safely iterate over the CMS space when scanning
3864 // for oops.
3865 // . When we scan the objects, we'll be both reading and setting
3866 // marks in the marking bit map, so we'll need the marking bit map.
3867 // . For protecting _collector_state transitions, we take the CGC_lock.
3868 // Note that any races in the reading of of card table entries by the
3869 // CMS thread on the one hand and the clearing of those entries by the
3870 // VM thread or the setting of those entries by the mutator threads on the
3871 // other are quite benign. However, for efficiency it makes sense to keep
3872 // the VM thread from racing with the CMS thread while the latter is
3873 // dirty card info to the modUnionTable. We therefore also use the
3874 // CGC_lock to protect the reading of the card table and the mod union
3875 // table by the CM thread.
3876 // . We run concurrently with mutator updates, so scanning
3877 // needs to be done carefully -- we should not try to scan
3878 // potentially uninitialized objects.
3879 //
3880 // Locking strategy: While holding the CGC_lock, we scan over and
3881 // reset a maximal dirty range of the mod union / card tables, then lock
3882 // the free_list_lock and bitmap lock to do a full marking, then
3883 // release these locks; and repeat the cycle. This allows for a
3884 // certain amount of fairness in the sharing of these locks between
3885 // the CMS collector on the one hand, and the VM thread and the
3886 // mutators on the other.
3887
3888 // NOTE: preclean_mod_union_table() and preclean_card_table()
3889 // further below are largely identical; if you need to modify
3890 // one of these methods, please check the other method too.
3891
3892 size_t CMSCollector::preclean_mod_union_table(
3893 ConcurrentMarkSweepGeneration* old_gen,
3894 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3895 verify_work_stacks_empty();
3896 verify_overflow_empty();
3897
3898 // strategy: starting with the first card, accumulate contiguous
3899 // ranges of dirty cards; clear these cards, then scan the region
3900 // covered by these cards.
3901
3902 // Since all of the MUT is committed ahead, we can just use
3903 // that, in case the generations expand while we are precleaning.
3904 // It might also be fine to just use the committed part of the
3905 // generation, but we might potentially miss cards when the
3906 // generation is rapidly expanding while we are in the midst
3907 // of precleaning.
3908 HeapWord* startAddr = old_gen->reserved().start();
3909 HeapWord* endAddr = old_gen->reserved().end();
3910
3911 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3912
3913 size_t numDirtyCards, cumNumDirtyCards;
3914 HeapWord *nextAddr, *lastAddr;
3915 for (cumNumDirtyCards = numDirtyCards = 0,
3916 nextAddr = lastAddr = startAddr;
3917 nextAddr < endAddr;
3918 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3919
3920 ResourceMark rm;
3921 HandleMark hm;
3922
3923 MemRegion dirtyRegion;
3924 {
3925 stopTimer();
3926 // Potential yield point
3927 CMSTokenSync ts(true);
3928 startTimer();
3929 sample_eden();
3930 // Get dirty region starting at nextOffset (inclusive),
3931 // simultaneously clearing it.
3932 dirtyRegion =
3933 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3934 assert(dirtyRegion.start() >= nextAddr,
3935 "returned region inconsistent?");
3936 }
3937 // Remember where the next search should begin.
3938 // The returned region (if non-empty) is a right open interval,
3939 // so lastOffset is obtained from the right end of that
3940 // interval.
3941 lastAddr = dirtyRegion.end();
3942 // Should do something more transparent and less hacky XXX
3943 numDirtyCards =
3944 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3945
3946 // We'll scan the cards in the dirty region (with periodic
3947 // yields for foreground GC as needed).
3948 if (!dirtyRegion.is_empty()) {
3949 assert(numDirtyCards > 0, "consistency check");
3950 HeapWord* stop_point = NULL;
3951 stopTimer();
3952 // Potential yield point
3953 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3954 bitMapLock());
3955 startTimer();
3956 {
3957 verify_work_stacks_empty();
3958 verify_overflow_empty();
3959 sample_eden();
3960 stop_point =
3961 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3962 }
3963 if (stop_point != NULL) {
3964 // The careful iteration stopped early either because it found an
3965 // uninitialized object, or because we were in the midst of an
3966 // "abortable preclean", which should now be aborted. Redirty
3967 // the bits corresponding to the partially-scanned or unscanned
3968 // cards. We'll either restart at the next block boundary or
3969 // abort the preclean.
3970 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3971 "Should only be AbortablePreclean.");
3972 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3973 if (should_abort_preclean()) {
3974 break; // out of preclean loop
3975 } else {
3976 // Compute the next address at which preclean should pick up;
3977 // might need bitMapLock in order to read P-bits.
3978 lastAddr = next_card_start_after_block(stop_point);
3979 }
3980 }
3981 } else {
3982 assert(lastAddr == endAddr, "consistency check");
3983 assert(numDirtyCards == 0, "consistency check");
3984 break;
3985 }
3986 }
3987 verify_work_stacks_empty();
3988 verify_overflow_empty();
3989 return cumNumDirtyCards;
3990 }
3991
3992 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3993 // below are largely identical; if you need to modify
3994 // one of these methods, please check the other method too.
3995
3996 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3997 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3998 // strategy: it's similar to precleamModUnionTable above, in that
3999 // we accumulate contiguous ranges of dirty cards, mark these cards
4000 // precleaned, then scan the region covered by these cards.
4001 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4002 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4003
4004 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4005
4006 size_t numDirtyCards, cumNumDirtyCards;
4007 HeapWord *lastAddr, *nextAddr;
4008
4009 for (cumNumDirtyCards = numDirtyCards = 0,
4010 nextAddr = lastAddr = startAddr;
4011 nextAddr < endAddr;
4012 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4013
4014 ResourceMark rm;
4015 HandleMark hm;
4016
4017 MemRegion dirtyRegion;
4018 {
4019 // See comments in "Precleaning notes" above on why we
4020 // do this locking. XXX Could the locking overheads be
4021 // too high when dirty cards are sparse? [I don't think so.]
4022 stopTimer();
4023 CMSTokenSync x(true); // is cms thread
4024 startTimer();
4025 sample_eden();
4026 // Get and clear dirty region from card table
4027 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4028 MemRegion(nextAddr, endAddr),
4029 true,
4030 CardTableModRefBS::precleaned_card_val());
4031
4032 assert(dirtyRegion.start() >= nextAddr,
4033 "returned region inconsistent?");
4034 }
4035 lastAddr = dirtyRegion.end();
4036 numDirtyCards =
4037 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4038
4039 if (!dirtyRegion.is_empty()) {
4040 stopTimer();
4041 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4042 startTimer();
4043 sample_eden();
4044 verify_work_stacks_empty();
4045 verify_overflow_empty();
4046 HeapWord* stop_point =
4047 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4048 if (stop_point != NULL) {
4049 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4050 "Should only be AbortablePreclean.");
4051 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4052 if (should_abort_preclean()) {
4053 break; // out of preclean loop
4054 } else {
4055 // Compute the next address at which preclean should pick up.
4056 lastAddr = next_card_start_after_block(stop_point);
4057 }
4058 }
4059 } else {
4060 break;
4061 }
4062 }
4063 verify_work_stacks_empty();
4064 verify_overflow_empty();
4065 return cumNumDirtyCards;
4066 }
4067
4068 class PrecleanKlassClosure : public KlassClosure {
4069 KlassToOopClosure _cm_klass_closure;
4070 public:
4071 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4072 void do_klass(Klass* k) {
4073 if (k->has_accumulated_modified_oops()) {
4074 k->clear_accumulated_modified_oops();
4075
4076 _cm_klass_closure.do_klass(k);
4077 }
4078 }
4079 };
4080
4081 // The freelist lock is needed to prevent asserts, is it really needed?
4082 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4083
4084 cl->set_freelistLock(freelistLock);
4085
4086 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4087
4088 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4089 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4090 PrecleanKlassClosure preclean_klass_closure(cl);
4091 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4092
4093 verify_work_stacks_empty();
4094 verify_overflow_empty();
4095 }
4096
4097 void CMSCollector::checkpointRootsFinal() {
4098 assert(_collectorState == FinalMarking, "incorrect state transition?");
4099 check_correct_thread_executing();
4100 // world is stopped at this checkpoint
4101 assert(SafepointSynchronize::is_at_safepoint(),
4102 "world should be stopped");
4103 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4104
4105 verify_work_stacks_empty();
4106 verify_overflow_empty();
4107
4108 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4109 _young_gen->used() / K, _young_gen->capacity() / K);
4110 {
4111 if (CMSScavengeBeforeRemark) {
4112 GenCollectedHeap* gch = GenCollectedHeap::heap();
4113 // Temporarily set flag to false, GCH->do_collection will
4114 // expect it to be false and set to true
4115 FlagSetting fl(gch->_is_gc_active, false);
4116
4117 gch->do_collection(true, // full (i.e. force, see below)
4118 false, // !clear_all_soft_refs
4119 0, // size
4120 false, // is_tlab
4121 GenCollectedHeap::YoungGen // type
4122 );
4123 }
4124 FreelistLocker x(this);
4125 MutexLockerEx y(bitMapLock(),
4126 Mutex::_no_safepoint_check_flag);
4127 checkpointRootsFinalWork();
4128 }
4129 verify_work_stacks_empty();
4130 verify_overflow_empty();
4131 }
4132
4133 void CMSCollector::checkpointRootsFinalWork() {
4134 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4135
4136 assert(haveFreelistLocks(), "must have free list locks");
4137 assert_lock_strong(bitMapLock());
4138
4139 ResourceMark rm;
4140 HandleMark hm;
4141
4142 GenCollectedHeap* gch = GenCollectedHeap::heap();
4143
4144 if (should_unload_classes()) {
4145 CodeCache::gc_prologue();
4146 }
4147 assert(haveFreelistLocks(), "must have free list locks");
4148 assert_lock_strong(bitMapLock());
4149
4150 // We might assume that we need not fill TLAB's when
4151 // CMSScavengeBeforeRemark is set, because we may have just done
4152 // a scavenge which would have filled all TLAB's -- and besides
4153 // Eden would be empty. This however may not always be the case --
4154 // for instance although we asked for a scavenge, it may not have
4155 // happened because of a JNI critical section. We probably need
4156 // a policy for deciding whether we can in that case wait until
4157 // the critical section releases and then do the remark following
4158 // the scavenge, and skip it here. In the absence of that policy,
4159 // or of an indication of whether the scavenge did indeed occur,
4160 // we cannot rely on TLAB's having been filled and must do
4161 // so here just in case a scavenge did not happen.
4162 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4163 // Update the saved marks which may affect the root scans.
4164 gch->save_marks();
4165
4166 print_eden_and_survivor_chunk_arrays();
4167
4168 {
4169 #if defined(COMPILER2) || INCLUDE_JVMCI
4170 DerivedPointerTableDeactivate dpt_deact;
4171 #endif
4172
4173 // Note on the role of the mod union table:
4174 // Since the marker in "markFromRoots" marks concurrently with
4175 // mutators, it is possible for some reachable objects not to have been
4176 // scanned. For instance, an only reference to an object A was
4177 // placed in object B after the marker scanned B. Unless B is rescanned,
4178 // A would be collected. Such updates to references in marked objects
4179 // are detected via the mod union table which is the set of all cards
4180 // dirtied since the first checkpoint in this GC cycle and prior to
4181 // the most recent young generation GC, minus those cleaned up by the
4182 // concurrent precleaning.
4183 if (CMSParallelRemarkEnabled) {
4184 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4185 do_remark_parallel();
4186 } else {
4187 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4188 do_remark_non_parallel();
4189 }
4190 }
4191 verify_work_stacks_empty();
4192 verify_overflow_empty();
4193
4194 {
4195 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4196 refProcessingWork();
4197 }
4198 verify_work_stacks_empty();
4199 verify_overflow_empty();
4200
4201 if (should_unload_classes()) {
4202 CodeCache::gc_epilogue();
4203 }
4204 JvmtiExport::gc_epilogue();
4205
4206 // If we encountered any (marking stack / work queue) overflow
4207 // events during the current CMS cycle, take appropriate
4208 // remedial measures, where possible, so as to try and avoid
4209 // recurrence of that condition.
4210 assert(_markStack.isEmpty(), "No grey objects");
4211 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4212 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4213 if (ser_ovflw > 0) {
4214 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4215 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4216 _markStack.expand();
4217 _ser_pmc_remark_ovflw = 0;
4218 _ser_pmc_preclean_ovflw = 0;
4219 _ser_kac_preclean_ovflw = 0;
4220 _ser_kac_ovflw = 0;
4221 }
4222 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4223 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4224 _par_pmc_remark_ovflw, _par_kac_ovflw);
4225 _par_pmc_remark_ovflw = 0;
4226 _par_kac_ovflw = 0;
4227 }
4228 if (_markStack._hit_limit > 0) {
4229 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4230 _markStack._hit_limit);
4231 }
4232 if (_markStack._failed_double > 0) {
4233 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4234 _markStack._failed_double, _markStack.capacity());
4235 }
4236 _markStack._hit_limit = 0;
4237 _markStack._failed_double = 0;
4238
4239 if ((VerifyAfterGC || VerifyDuringGC) &&
4240 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4241 verify_after_remark();
4242 }
4243
4244 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4245
4246 // Change under the freelistLocks.
4247 _collectorState = Sweeping;
4248 // Call isAllClear() under bitMapLock
4249 assert(_modUnionTable.isAllClear(),
4250 "Should be clear by end of the final marking");
4251 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4252 "Should be clear by end of the final marking");
4253 }
4254
4255 void CMSParInitialMarkTask::work(uint worker_id) {
4256 elapsedTimer _timer;
4257 ResourceMark rm;
4258 HandleMark hm;
4259
4260 // ---------- scan from roots --------------
4261 _timer.start();
4262 GenCollectedHeap* gch = GenCollectedHeap::heap();
4263 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4264
4265 // ---------- young gen roots --------------
4266 {
4267 work_on_young_gen_roots(&par_mri_cl);
4268 _timer.stop();
4269 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4270 }
4271
4272 // ---------- remaining roots --------------
4273 _timer.reset();
4274 _timer.start();
4275
4276 CLDToOopClosure cld_closure(&par_mri_cl, true);
4277
4278 gch->cms_process_roots(_strong_roots_scope,
4279 false, // yg was scanned above
4280 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4281 _collector->should_unload_classes(),
4282 &par_mri_cl,
4283 &cld_closure);
4284 assert(_collector->should_unload_classes()
4285 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4286 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4287 _timer.stop();
4288 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4289 }
4290
4291 // Parallel remark task
4292 class CMSParRemarkTask: public CMSParMarkTask {
4293 CompactibleFreeListSpace* _cms_space;
4294
4295 // The per-thread work queues, available here for stealing.
4296 OopTaskQueueSet* _task_queues;
4297 ParallelTaskTerminator _term;
4298 StrongRootsScope* _strong_roots_scope;
4299
4300 public:
4301 // A value of 0 passed to n_workers will cause the number of
4302 // workers to be taken from the active workers in the work gang.
4303 CMSParRemarkTask(CMSCollector* collector,
4304 CompactibleFreeListSpace* cms_space,
4305 uint n_workers, WorkGang* workers,
4306 OopTaskQueueSet* task_queues,
4307 StrongRootsScope* strong_roots_scope):
4308 CMSParMarkTask("Rescan roots and grey objects in parallel",
4309 collector, n_workers),
4310 _cms_space(cms_space),
4311 _task_queues(task_queues),
4312 _term(n_workers, task_queues),
4313 _strong_roots_scope(strong_roots_scope) { }
4314
4315 OopTaskQueueSet* task_queues() { return _task_queues; }
4316
4317 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4318
4319 ParallelTaskTerminator* terminator() { return &_term; }
4320 uint n_workers() { return _n_workers; }
4321
4322 void work(uint worker_id);
4323
4324 private:
4325 // ... of dirty cards in old space
4326 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4327 ParMarkRefsIntoAndScanClosure* cl);
4328
4329 // ... work stealing for the above
4330 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4331 };
4332
4333 class RemarkKlassClosure : public KlassClosure {
4334 KlassToOopClosure _cm_klass_closure;
4335 public:
4336 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4337 void do_klass(Klass* k) {
4338 // Check if we have modified any oops in the Klass during the concurrent marking.
4339 if (k->has_accumulated_modified_oops()) {
4340 k->clear_accumulated_modified_oops();
4341
4342 // We could have transfered the current modified marks to the accumulated marks,
4343 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4344 } else if (k->has_modified_oops()) {
4345 // Don't clear anything, this info is needed by the next young collection.
4346 } else {
4347 // No modified oops in the Klass.
4348 return;
4349 }
4350
4351 // The klass has modified fields, need to scan the klass.
4352 _cm_klass_closure.do_klass(k);
4353 }
4354 };
4355
4356 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4357 ParNewGeneration* young_gen = _collector->_young_gen;
4358 ContiguousSpace* eden_space = young_gen->eden();
4359 ContiguousSpace* from_space = young_gen->from();
4360 ContiguousSpace* to_space = young_gen->to();
4361
4362 HeapWord** eca = _collector->_eden_chunk_array;
4363 size_t ect = _collector->_eden_chunk_index;
4364 HeapWord** sca = _collector->_survivor_chunk_array;
4365 size_t sct = _collector->_survivor_chunk_index;
4366
4367 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4368 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4369
4370 do_young_space_rescan(cl, to_space, NULL, 0);
4371 do_young_space_rescan(cl, from_space, sca, sct);
4372 do_young_space_rescan(cl, eden_space, eca, ect);
4373 }
4374
4375 // work_queue(i) is passed to the closure
4376 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4377 // also is passed to do_dirty_card_rescan_tasks() and to
4378 // do_work_steal() to select the i-th task_queue.
4379
4380 void CMSParRemarkTask::work(uint worker_id) {
4381 elapsedTimer _timer;
4382 ResourceMark rm;
4383 HandleMark hm;
4384
4385 // ---------- rescan from roots --------------
4386 _timer.start();
4387 GenCollectedHeap* gch = GenCollectedHeap::heap();
4388 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4389 _collector->_span, _collector->ref_processor(),
4390 &(_collector->_markBitMap),
4391 work_queue(worker_id));
4392
4393 // Rescan young gen roots first since these are likely
4394 // coarsely partitioned and may, on that account, constitute
4395 // the critical path; thus, it's best to start off that
4396 // work first.
4397 // ---------- young gen roots --------------
4398 {
4399 work_on_young_gen_roots(&par_mrias_cl);
4400 _timer.stop();
4401 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4402 }
4403
4404 // ---------- remaining roots --------------
4405 _timer.reset();
4406 _timer.start();
4407 gch->cms_process_roots(_strong_roots_scope,
4408 false, // yg was scanned above
4409 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4410 _collector->should_unload_classes(),
4411 &par_mrias_cl,
4412 NULL); // The dirty klasses will be handled below
4413
4414 assert(_collector->should_unload_classes()
4415 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4416 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4417 _timer.stop();
4418 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4419
4420 // ---------- unhandled CLD scanning ----------
4421 if (worker_id == 0) { // Single threaded at the moment.
4422 _timer.reset();
4423 _timer.start();
4424
4425 // Scan all new class loader data objects and new dependencies that were
4426 // introduced during concurrent marking.
4427 ResourceMark rm;
4428 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4429 for (int i = 0; i < array->length(); i++) {
4430 par_mrias_cl.do_cld_nv(array->at(i));
4431 }
4432
4433 // We don't need to keep track of new CLDs anymore.
4434 ClassLoaderDataGraph::remember_new_clds(false);
4435
4436 _timer.stop();
4437 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4438 }
4439
4440 // ---------- dirty klass scanning ----------
4441 if (worker_id == 0) { // Single threaded at the moment.
4442 _timer.reset();
4443 _timer.start();
4444
4445 // Scan all classes that was dirtied during the concurrent marking phase.
4446 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4447 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4448
4449 _timer.stop();
4450 log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4451 }
4452
4453 // We might have added oops to ClassLoaderData::_handles during the
4454 // concurrent marking phase. These oops point to newly allocated objects
4455 // that are guaranteed to be kept alive. Either by the direct allocation
4456 // code, or when the young collector processes the roots. Hence,
4457 // we don't have to revisit the _handles block during the remark phase.
4458
4459 // ---------- rescan dirty cards ------------
4460 _timer.reset();
4461 _timer.start();
4462
4463 // Do the rescan tasks for each of the two spaces
4464 // (cms_space) in turn.
4465 // "worker_id" is passed to select the task_queue for "worker_id"
4466 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4467 _timer.stop();
4468 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4469
4470 // ---------- steal work from other threads ...
4471 // ---------- ... and drain overflow list.
4472 _timer.reset();
4473 _timer.start();
4474 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4475 _timer.stop();
4476 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4477 }
4478
4479 void
4480 CMSParMarkTask::do_young_space_rescan(
4481 OopsInGenClosure* cl, ContiguousSpace* space,
4482 HeapWord** chunk_array, size_t chunk_top) {
4483 // Until all tasks completed:
4484 // . claim an unclaimed task
4485 // . compute region boundaries corresponding to task claimed
4486 // using chunk_array
4487 // . par_oop_iterate(cl) over that region
4488
4489 ResourceMark rm;
4490 HandleMark hm;
4491
4492 SequentialSubTasksDone* pst = space->par_seq_tasks();
4493
4494 uint nth_task = 0;
4495 uint n_tasks = pst->n_tasks();
4496
4497 if (n_tasks > 0) {
4498 assert(pst->valid(), "Uninitialized use?");
4499 HeapWord *start, *end;
4500 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4501 // We claimed task # nth_task; compute its boundaries.
4502 if (chunk_top == 0) { // no samples were taken
4503 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4504 start = space->bottom();
4505 end = space->top();
4506 } else if (nth_task == 0) {
4507 start = space->bottom();
4508 end = chunk_array[nth_task];
4509 } else if (nth_task < (uint)chunk_top) {
4510 assert(nth_task >= 1, "Control point invariant");
4511 start = chunk_array[nth_task - 1];
4512 end = chunk_array[nth_task];
4513 } else {
4514 assert(nth_task == (uint)chunk_top, "Control point invariant");
4515 start = chunk_array[chunk_top - 1];
4516 end = space->top();
4517 }
4518 MemRegion mr(start, end);
4519 // Verify that mr is in space
4520 assert(mr.is_empty() || space->used_region().contains(mr),
4521 "Should be in space");
4522 // Verify that "start" is an object boundary
4523 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4524 "Should be an oop");
4525 space->par_oop_iterate(mr, cl);
4526 }
4527 pst->all_tasks_completed();
4528 }
4529 }
4530
4531 void
4532 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4533 CompactibleFreeListSpace* sp, int i,
4534 ParMarkRefsIntoAndScanClosure* cl) {
4535 // Until all tasks completed:
4536 // . claim an unclaimed task
4537 // . compute region boundaries corresponding to task claimed
4538 // . transfer dirty bits ct->mut for that region
4539 // . apply rescanclosure to dirty mut bits for that region
4540
4541 ResourceMark rm;
4542 HandleMark hm;
4543
4544 OopTaskQueue* work_q = work_queue(i);
4545 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4546 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4547 // CAUTION: This closure has state that persists across calls to
4548 // the work method dirty_range_iterate_clear() in that it has
4549 // embedded in it a (subtype of) UpwardsObjectClosure. The
4550 // use of that state in the embedded UpwardsObjectClosure instance
4551 // assumes that the cards are always iterated (even if in parallel
4552 // by several threads) in monotonically increasing order per each
4553 // thread. This is true of the implementation below which picks
4554 // card ranges (chunks) in monotonically increasing order globally
4555 // and, a-fortiori, in monotonically increasing order per thread
4556 // (the latter order being a subsequence of the former).
4557 // If the work code below is ever reorganized into a more chaotic
4558 // work-partitioning form than the current "sequential tasks"
4559 // paradigm, the use of that persistent state will have to be
4560 // revisited and modified appropriately. See also related
4561 // bug 4756801 work on which should examine this code to make
4562 // sure that the changes there do not run counter to the
4563 // assumptions made here and necessary for correctness and
4564 // efficiency. Note also that this code might yield inefficient
4565 // behavior in the case of very large objects that span one or
4566 // more work chunks. Such objects would potentially be scanned
4567 // several times redundantly. Work on 4756801 should try and
4568 // address that performance anomaly if at all possible. XXX
4569 MemRegion full_span = _collector->_span;
4570 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4571 MarkFromDirtyCardsClosure
4572 greyRescanClosure(_collector, full_span, // entire span of interest
4573 sp, bm, work_q, cl);
4574
4575 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4576 assert(pst->valid(), "Uninitialized use?");
4577 uint nth_task = 0;
4578 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4579 MemRegion span = sp->used_region();
4580 HeapWord* start_addr = span.start();
4581 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4582 alignment);
4583 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4584 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4585 start_addr, "Check alignment");
4586 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4587 chunk_size, "Check alignment");
4588
4589 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4590 // Having claimed the nth_task, compute corresponding mem-region,
4591 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4592 // The alignment restriction ensures that we do not need any
4593 // synchronization with other gang-workers while setting or
4594 // clearing bits in thus chunk of the MUT.
4595 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4596 start_addr + (nth_task+1)*chunk_size);
4597 // The last chunk's end might be way beyond end of the
4598 // used region. In that case pull back appropriately.
4599 if (this_span.end() > end_addr) {
4600 this_span.set_end(end_addr);
4601 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4602 }
4603 // Iterate over the dirty cards covering this chunk, marking them
4604 // precleaned, and setting the corresponding bits in the mod union
4605 // table. Since we have been careful to partition at Card and MUT-word
4606 // boundaries no synchronization is needed between parallel threads.
4607 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4608 &modUnionClosure);
4609
4610 // Having transferred these marks into the modUnionTable,
4611 // rescan the marked objects on the dirty cards in the modUnionTable.
4612 // Even if this is at a synchronous collection, the initial marking
4613 // may have been done during an asynchronous collection so there
4614 // may be dirty bits in the mod-union table.
4615 _collector->_modUnionTable.dirty_range_iterate_clear(
4616 this_span, &greyRescanClosure);
4617 _collector->_modUnionTable.verifyNoOneBitsInRange(
4618 this_span.start(),
4619 this_span.end());
4620 }
4621 pst->all_tasks_completed(); // declare that i am done
4622 }
4623
4624 // . see if we can share work_queues with ParNew? XXX
4625 void
4626 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4627 int* seed) {
4628 OopTaskQueue* work_q = work_queue(i);
4629 NOT_PRODUCT(int num_steals = 0;)
4630 oop obj_to_scan;
4631 CMSBitMap* bm = &(_collector->_markBitMap);
4632
4633 while (true) {
4634 // Completely finish any left over work from (an) earlier round(s)
4635 cl->trim_queue(0);
4636 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4637 (size_t)ParGCDesiredObjsFromOverflowList);
4638 // Now check if there's any work in the overflow list
4639 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4640 // only affects the number of attempts made to get work from the
4641 // overflow list and does not affect the number of workers. Just
4642 // pass ParallelGCThreads so this behavior is unchanged.
4643 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4644 work_q,
4645 ParallelGCThreads)) {
4646 // found something in global overflow list;
4647 // not yet ready to go stealing work from others.
4648 // We'd like to assert(work_q->size() != 0, ...)
4649 // because we just took work from the overflow list,
4650 // but of course we can't since all of that could have
4651 // been already stolen from us.
4652 // "He giveth and He taketh away."
4653 continue;
4654 }
4655 // Verify that we have no work before we resort to stealing
4656 assert(work_q->size() == 0, "Have work, shouldn't steal");
4657 // Try to steal from other queues that have work
4658 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4659 NOT_PRODUCT(num_steals++;)
4660 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4661 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4662 // Do scanning work
4663 obj_to_scan->oop_iterate(cl);
4664 // Loop around, finish this work, and try to steal some more
4665 } else if (terminator()->offer_termination()) {
4666 break; // nirvana from the infinite cycle
4667 }
4668 }
4669 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4670 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4671 "Else our work is not yet done");
4672 }
4673
4674 // Record object boundaries in _eden_chunk_array by sampling the eden
4675 // top in the slow-path eden object allocation code path and record
4676 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4677 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4678 // sampling in sample_eden() that activates during the part of the
4679 // preclean phase.
4680 void CMSCollector::sample_eden_chunk() {
4681 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4682 if (_eden_chunk_lock->try_lock()) {
4683 // Record a sample. This is the critical section. The contents
4684 // of the _eden_chunk_array have to be non-decreasing in the
4685 // address order.
4686 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4687 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4688 "Unexpected state of Eden");
4689 if (_eden_chunk_index == 0 ||
4690 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4691 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4692 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4693 _eden_chunk_index++; // commit sample
4694 }
4695 _eden_chunk_lock->unlock();
4696 }
4697 }
4698 }
4699
4700 // Return a thread-local PLAB recording array, as appropriate.
4701 void* CMSCollector::get_data_recorder(int thr_num) {
4702 if (_survivor_plab_array != NULL &&
4703 (CMSPLABRecordAlways ||
4704 (_collectorState > Marking && _collectorState < FinalMarking))) {
4705 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4706 ChunkArray* ca = &_survivor_plab_array[thr_num];
4707 ca->reset(); // clear it so that fresh data is recorded
4708 return (void*) ca;
4709 } else {
4710 return NULL;
4711 }
4712 }
4713
4714 // Reset all the thread-local PLAB recording arrays
4715 void CMSCollector::reset_survivor_plab_arrays() {
4716 for (uint i = 0; i < ParallelGCThreads; i++) {
4717 _survivor_plab_array[i].reset();
4718 }
4719 }
4720
4721 // Merge the per-thread plab arrays into the global survivor chunk
4722 // array which will provide the partitioning of the survivor space
4723 // for CMS initial scan and rescan.
4724 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4725 int no_of_gc_threads) {
4726 assert(_survivor_plab_array != NULL, "Error");
4727 assert(_survivor_chunk_array != NULL, "Error");
4728 assert(_collectorState == FinalMarking ||
4729 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4730 for (int j = 0; j < no_of_gc_threads; j++) {
4731 _cursor[j] = 0;
4732 }
4733 HeapWord* top = surv->top();
4734 size_t i;
4735 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4736 HeapWord* min_val = top; // Higher than any PLAB address
4737 uint min_tid = 0; // position of min_val this round
4738 for (int j = 0; j < no_of_gc_threads; j++) {
4739 ChunkArray* cur_sca = &_survivor_plab_array[j];
4740 if (_cursor[j] == cur_sca->end()) {
4741 continue;
4742 }
4743 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4744 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4745 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4746 if (cur_val < min_val) {
4747 min_tid = j;
4748 min_val = cur_val;
4749 } else {
4750 assert(cur_val < top, "All recorded addresses should be less");
4751 }
4752 }
4753 // At this point min_val and min_tid are respectively
4754 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4755 // and the thread (j) that witnesses that address.
4756 // We record this address in the _survivor_chunk_array[i]
4757 // and increment _cursor[min_tid] prior to the next round i.
4758 if (min_val == top) {
4759 break;
4760 }
4761 _survivor_chunk_array[i] = min_val;
4762 _cursor[min_tid]++;
4763 }
4764 // We are all done; record the size of the _survivor_chunk_array
4765 _survivor_chunk_index = i; // exclusive: [0, i)
4766 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4767 // Verify that we used up all the recorded entries
4768 #ifdef ASSERT
4769 size_t total = 0;
4770 for (int j = 0; j < no_of_gc_threads; j++) {
4771 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4772 total += _cursor[j];
4773 }
4774 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4775 // Check that the merged array is in sorted order
4776 if (total > 0) {
4777 for (size_t i = 0; i < total - 1; i++) {
4778 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4779 i, p2i(_survivor_chunk_array[i]));
4780 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4781 "Not sorted");
4782 }
4783 }
4784 #endif // ASSERT
4785 }
4786
4787 // Set up the space's par_seq_tasks structure for work claiming
4788 // for parallel initial scan and rescan of young gen.
4789 // See ParRescanTask where this is currently used.
4790 void
4791 CMSCollector::
4792 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4793 assert(n_threads > 0, "Unexpected n_threads argument");
4794
4795 // Eden space
4796 if (!_young_gen->eden()->is_empty()) {
4797 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4798 assert(!pst->valid(), "Clobbering existing data?");
4799 // Each valid entry in [0, _eden_chunk_index) represents a task.
4800 size_t n_tasks = _eden_chunk_index + 1;
4801 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4802 // Sets the condition for completion of the subtask (how many threads
4803 // need to finish in order to be done).
4804 pst->set_n_threads(n_threads);
4805 pst->set_n_tasks((int)n_tasks);
4806 }
4807
4808 // Merge the survivor plab arrays into _survivor_chunk_array
4809 if (_survivor_plab_array != NULL) {
4810 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4811 } else {
4812 assert(_survivor_chunk_index == 0, "Error");
4813 }
4814
4815 // To space
4816 {
4817 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4818 assert(!pst->valid(), "Clobbering existing data?");
4819 // Sets the condition for completion of the subtask (how many threads
4820 // need to finish in order to be done).
4821 pst->set_n_threads(n_threads);
4822 pst->set_n_tasks(1);
4823 assert(pst->valid(), "Error");
4824 }
4825
4826 // From space
4827 {
4828 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4829 assert(!pst->valid(), "Clobbering existing data?");
4830 size_t n_tasks = _survivor_chunk_index + 1;
4831 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4832 // Sets the condition for completion of the subtask (how many threads
4833 // need to finish in order to be done).
4834 pst->set_n_threads(n_threads);
4835 pst->set_n_tasks((int)n_tasks);
4836 assert(pst->valid(), "Error");
4837 }
4838 }
4839
4840 // Parallel version of remark
4841 void CMSCollector::do_remark_parallel() {
4842 GenCollectedHeap* gch = GenCollectedHeap::heap();
4843 WorkGang* workers = gch->workers();
4844 assert(workers != NULL, "Need parallel worker threads.");
4845 // Choose to use the number of GC workers most recently set
4846 // into "active_workers".
4847 uint n_workers = workers->active_workers();
4848
4849 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4850
4851 StrongRootsScope srs(n_workers);
4852
4853 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4854
4855 // We won't be iterating over the cards in the card table updating
4856 // the younger_gen cards, so we shouldn't call the following else
4857 // the verification code as well as subsequent younger_refs_iterate
4858 // code would get confused. XXX
4859 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4860
4861 // The young gen rescan work will not be done as part of
4862 // process_roots (which currently doesn't know how to
4863 // parallelize such a scan), but rather will be broken up into
4864 // a set of parallel tasks (via the sampling that the [abortable]
4865 // preclean phase did of eden, plus the [two] tasks of
4866 // scanning the [two] survivor spaces. Further fine-grain
4867 // parallelization of the scanning of the survivor spaces
4868 // themselves, and of precleaning of the young gen itself
4869 // is deferred to the future.
4870 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4871
4872 // The dirty card rescan work is broken up into a "sequence"
4873 // of parallel tasks (per constituent space) that are dynamically
4874 // claimed by the parallel threads.
4875 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4876
4877 // It turns out that even when we're using 1 thread, doing the work in a
4878 // separate thread causes wide variance in run times. We can't help this
4879 // in the multi-threaded case, but we special-case n=1 here to get
4880 // repeatable measurements of the 1-thread overhead of the parallel code.
4881 if (n_workers > 1) {
4882 // Make refs discovery MT-safe, if it isn't already: it may not
4883 // necessarily be so, since it's possible that we are doing
4884 // ST marking.
4885 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4886 workers->run_task(&tsk);
4887 } else {
4888 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4889 tsk.work(0);
4890 }
4891
4892 // restore, single-threaded for now, any preserved marks
4893 // as a result of work_q overflow
4894 restore_preserved_marks_if_any();
4895 }
4896
4897 // Non-parallel version of remark
4898 void CMSCollector::do_remark_non_parallel() {
4899 ResourceMark rm;
4900 HandleMark hm;
4901 GenCollectedHeap* gch = GenCollectedHeap::heap();
4902 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4903
4904 MarkRefsIntoAndScanClosure
4905 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4906 &_markStack, this,
4907 false /* should_yield */, false /* not precleaning */);
4908 MarkFromDirtyCardsClosure
4909 markFromDirtyCardsClosure(this, _span,
4910 NULL, // space is set further below
4911 &_markBitMap, &_markStack, &mrias_cl);
4912 {
4913 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4914 // Iterate over the dirty cards, setting the corresponding bits in the
4915 // mod union table.
4916 {
4917 ModUnionClosure modUnionClosure(&_modUnionTable);
4918 _ct->ct_bs()->dirty_card_iterate(
4919 _cmsGen->used_region(),
4920 &modUnionClosure);
4921 }
4922 // Having transferred these marks into the modUnionTable, we just need
4923 // to rescan the marked objects on the dirty cards in the modUnionTable.
4924 // The initial marking may have been done during an asynchronous
4925 // collection so there may be dirty bits in the mod-union table.
4926 const int alignment =
4927 CardTableModRefBS::card_size * BitsPerWord;
4928 {
4929 // ... First handle dirty cards in CMS gen
4930 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4931 MemRegion ur = _cmsGen->used_region();
4932 HeapWord* lb = ur.start();
4933 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4934 MemRegion cms_span(lb, ub);
4935 _modUnionTable.dirty_range_iterate_clear(cms_span,
4936 &markFromDirtyCardsClosure);
4937 verify_work_stacks_empty();
4938 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4939 }
4940 }
4941 if (VerifyDuringGC &&
4942 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4943 HandleMark hm; // Discard invalid handles created during verification
4944 Universe::verify();
4945 }
4946 {
4947 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4948
4949 verify_work_stacks_empty();
4950
4951 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4952 StrongRootsScope srs(1);
4953
4954 gch->cms_process_roots(&srs,
4955 true, // young gen as roots
4956 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4957 should_unload_classes(),
4958 &mrias_cl,
4959 NULL); // The dirty klasses will be handled below
4960
4961 assert(should_unload_classes()
4962 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4963 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4964 }
4965
4966 {
4967 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4968
4969 verify_work_stacks_empty();
4970
4971 // Scan all class loader data objects that might have been introduced
4972 // during concurrent marking.
4973 ResourceMark rm;
4974 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4975 for (int i = 0; i < array->length(); i++) {
4976 mrias_cl.do_cld_nv(array->at(i));
4977 }
4978
4979 // We don't need to keep track of new CLDs anymore.
4980 ClassLoaderDataGraph::remember_new_clds(false);
4981
4982 verify_work_stacks_empty();
4983 }
4984
4985 {
4986 GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
4987
4988 verify_work_stacks_empty();
4989
4990 RemarkKlassClosure remark_klass_closure(&mrias_cl);
4991 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4992
4993 verify_work_stacks_empty();
4994 }
4995
4996 // We might have added oops to ClassLoaderData::_handles during the
4997 // concurrent marking phase. These oops point to newly allocated objects
4998 // that are guaranteed to be kept alive. Either by the direct allocation
4999 // code, or when the young collector processes the roots. Hence,
5000 // we don't have to revisit the _handles block during the remark phase.
5001
5002 verify_work_stacks_empty();
5003 // Restore evacuated mark words, if any, used for overflow list links
5004 restore_preserved_marks_if_any();
5005
5006 verify_overflow_empty();
5007 }
5008
5009 ////////////////////////////////////////////////////////
5010 // Parallel Reference Processing Task Proxy Class
5011 ////////////////////////////////////////////////////////
5012 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5013 OopTaskQueueSet* _queues;
5014 ParallelTaskTerminator _terminator;
5015 public:
5016 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5017 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5018 ParallelTaskTerminator* terminator() { return &_terminator; }
5019 OopTaskQueueSet* queues() { return _queues; }
5020 };
5021
5022 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5023 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5024 CMSCollector* _collector;
5025 CMSBitMap* _mark_bit_map;
5026 const MemRegion _span;
5027 ProcessTask& _task;
5028
5029 public:
5030 CMSRefProcTaskProxy(ProcessTask& task,
5031 CMSCollector* collector,
5032 const MemRegion& span,
5033 CMSBitMap* mark_bit_map,
5034 AbstractWorkGang* workers,
5035 OopTaskQueueSet* task_queues):
5036 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5037 task_queues,
5038 workers->active_workers()),
5039 _task(task),
5040 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5041 {
5042 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5043 "Inconsistency in _span");
5044 }
5045
5046 OopTaskQueueSet* task_queues() { return queues(); }
5047
5048 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5049
5050 void do_work_steal(int i,
5051 CMSParDrainMarkingStackClosure* drain,
5052 CMSParKeepAliveClosure* keep_alive,
5053 int* seed);
5054
5055 virtual void work(uint worker_id);
5056 };
5057
5058 void CMSRefProcTaskProxy::work(uint worker_id) {
5059 ResourceMark rm;
5060 HandleMark hm;
5061 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5062 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5063 _mark_bit_map,
5064 work_queue(worker_id));
5065 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5066 _mark_bit_map,
5067 work_queue(worker_id));
5068 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5069 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5070 if (_task.marks_oops_alive()) {
5071 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5072 _collector->hash_seed(worker_id));
5073 }
5074 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5075 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5076 }
5077
5078 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5079 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5080 EnqueueTask& _task;
5081
5082 public:
5083 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5084 : AbstractGangTask("Enqueue reference objects in parallel"),
5085 _task(task)
5086 { }
5087
5088 virtual void work(uint worker_id)
5089 {
5090 _task.work(worker_id);
5091 }
5092 };
5093
5094 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5095 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5096 _span(span),
5097 _bit_map(bit_map),
5098 _work_queue(work_queue),
5099 _mark_and_push(collector, span, bit_map, work_queue),
5100 _low_water_mark(MIN2((work_queue->max_elems()/4),
5101 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5102 { }
5103
5104 // . see if we can share work_queues with ParNew? XXX
5105 void CMSRefProcTaskProxy::do_work_steal(int i,
5106 CMSParDrainMarkingStackClosure* drain,
5107 CMSParKeepAliveClosure* keep_alive,
5108 int* seed) {
5109 OopTaskQueue* work_q = work_queue(i);
5110 NOT_PRODUCT(int num_steals = 0;)
5111 oop obj_to_scan;
5112
5113 while (true) {
5114 // Completely finish any left over work from (an) earlier round(s)
5115 drain->trim_queue(0);
5116 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5117 (size_t)ParGCDesiredObjsFromOverflowList);
5118 // Now check if there's any work in the overflow list
5119 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5120 // only affects the number of attempts made to get work from the
5121 // overflow list and does not affect the number of workers. Just
5122 // pass ParallelGCThreads so this behavior is unchanged.
5123 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5124 work_q,
5125 ParallelGCThreads)) {
5126 // Found something in global overflow list;
5127 // not yet ready to go stealing work from others.
5128 // We'd like to assert(work_q->size() != 0, ...)
5129 // because we just took work from the overflow list,
5130 // but of course we can't, since all of that might have
5131 // been already stolen from us.
5132 continue;
5133 }
5134 // Verify that we have no work before we resort to stealing
5135 assert(work_q->size() == 0, "Have work, shouldn't steal");
5136 // Try to steal from other queues that have work
5137 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5138 NOT_PRODUCT(num_steals++;)
5139 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5140 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5141 // Do scanning work
5142 obj_to_scan->oop_iterate(keep_alive);
5143 // Loop around, finish this work, and try to steal some more
5144 } else if (terminator()->offer_termination()) {
5145 break; // nirvana from the infinite cycle
5146 }
5147 }
5148 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5149 }
5150
5151 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5152 {
5153 GenCollectedHeap* gch = GenCollectedHeap::heap();
5154 WorkGang* workers = gch->workers();
5155 assert(workers != NULL, "Need parallel worker threads.");
5156 CMSRefProcTaskProxy rp_task(task, &_collector,
5157 _collector.ref_processor()->span(),
5158 _collector.markBitMap(),
5159 workers, _collector.task_queues());
5160 workers->run_task(&rp_task);
5161 }
5162
5163 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5164 {
5165
5166 GenCollectedHeap* gch = GenCollectedHeap::heap();
5167 WorkGang* workers = gch->workers();
5168 assert(workers != NULL, "Need parallel worker threads.");
5169 CMSRefEnqueueTaskProxy enq_task(task);
5170 workers->run_task(&enq_task);
5171 }
5172
5173 void CMSCollector::refProcessingWork() {
5174 ResourceMark rm;
5175 HandleMark hm;
5176
5177 ReferenceProcessor* rp = ref_processor();
5178 assert(rp->span().equals(_span), "Spans should be equal");
5179 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5180 // Process weak references.
5181 rp->setup_policy(false);
5182 verify_work_stacks_empty();
5183
5184 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5185 &_markStack, false /* !preclean */);
5186 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5187 _span, &_markBitMap, &_markStack,
5188 &cmsKeepAliveClosure, false /* !preclean */);
5189 {
5190 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5191
5192 ReferenceProcessorStats stats;
5193 if (rp->processing_is_mt()) {
5194 // Set the degree of MT here. If the discovery is done MT, there
5195 // may have been a different number of threads doing the discovery
5196 // and a different number of discovered lists may have Ref objects.
5197 // That is OK as long as the Reference lists are balanced (see
5198 // balance_all_queues() and balance_queues()).
5199 GenCollectedHeap* gch = GenCollectedHeap::heap();
5200 uint active_workers = ParallelGCThreads;
5201 WorkGang* workers = gch->workers();
5202 if (workers != NULL) {
5203 active_workers = workers->active_workers();
5204 // The expectation is that active_workers will have already
5205 // been set to a reasonable value. If it has not been set,
5206 // investigate.
5207 assert(active_workers > 0, "Should have been set during scavenge");
5208 }
5209 rp->set_active_mt_degree(active_workers);
5210 CMSRefProcTaskExecutor task_executor(*this);
5211 stats = rp->process_discovered_references(&_is_alive_closure,
5212 &cmsKeepAliveClosure,
5213 &cmsDrainMarkingStackClosure,
5214 &task_executor,
5215 _gc_timer_cm);
5216 } else {
5217 stats = rp->process_discovered_references(&_is_alive_closure,
5218 &cmsKeepAliveClosure,
5219 &cmsDrainMarkingStackClosure,
5220 NULL,
5221 _gc_timer_cm);
5222 }
5223 _gc_tracer_cm->report_gc_reference_stats(stats);
5224
5225 }
5226
5227 // This is the point where the entire marking should have completed.
5228 verify_work_stacks_empty();
5229
5230 if (should_unload_classes()) {
5231 {
5232 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5233
5234 // Unload classes and purge the SystemDictionary.
5235 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5236
5237 // Unload nmethods.
5238 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5239
5240 // Prune dead klasses from subklass/sibling/implementor lists.
5241 Klass::clean_weak_klass_links(&_is_alive_closure);
5242 }
5243
5244 {
5245 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5246 // Clean up unreferenced symbols in symbol table.
5247 SymbolTable::unlink();
5248 }
5249
5250 {
5251 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5252 // Delete entries for dead interned strings.
5253 StringTable::unlink(&_is_alive_closure);
5254 }
5255 }
5256
5257 // Restore any preserved marks as a result of mark stack or
5258 // work queue overflow
5259 restore_preserved_marks_if_any(); // done single-threaded for now
5260
5261 rp->set_enqueuing_is_done(true);
5262 if (rp->processing_is_mt()) {
5263 rp->balance_all_queues();
5264 CMSRefProcTaskExecutor task_executor(*this);
5265 rp->enqueue_discovered_references(&task_executor, _gc_timer_cm);
5266 } else {
5267 rp->enqueue_discovered_references(NULL, _gc_timer_cm);
5268 }
5269 rp->verify_no_references_recorded();
5270 assert(!rp->discovery_enabled(), "should have been disabled");
5271 }
5272
5273 #ifndef PRODUCT
5274 void CMSCollector::check_correct_thread_executing() {
5275 Thread* t = Thread::current();
5276 // Only the VM thread or the CMS thread should be here.
5277 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5278 "Unexpected thread type");
5279 // If this is the vm thread, the foreground process
5280 // should not be waiting. Note that _foregroundGCIsActive is
5281 // true while the foreground collector is waiting.
5282 if (_foregroundGCShouldWait) {
5283 // We cannot be the VM thread
5284 assert(t->is_ConcurrentGC_thread(),
5285 "Should be CMS thread");
5286 } else {
5287 // We can be the CMS thread only if we are in a stop-world
5288 // phase of CMS collection.
5289 if (t->is_ConcurrentGC_thread()) {
5290 assert(_collectorState == InitialMarking ||
5291 _collectorState == FinalMarking,
5292 "Should be a stop-world phase");
5293 // The CMS thread should be holding the CMS_token.
5294 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5295 "Potential interference with concurrently "
5296 "executing VM thread");
5297 }
5298 }
5299 }
5300 #endif
5301
5302 void CMSCollector::sweep() {
5303 assert(_collectorState == Sweeping, "just checking");
5304 check_correct_thread_executing();
5305 verify_work_stacks_empty();
5306 verify_overflow_empty();
5307 increment_sweep_count();
5308 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5309
5310 _inter_sweep_timer.stop();
5311 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5312
5313 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5314 _intra_sweep_timer.reset();
5315 _intra_sweep_timer.start();
5316 {
5317 GCTraceCPUTime tcpu;
5318 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5319 // First sweep the old gen
5320 {
5321 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5322 bitMapLock());
5323 sweepWork(_cmsGen);
5324 }
5325
5326 // Update Universe::_heap_*_at_gc figures.
5327 // We need all the free list locks to make the abstract state
5328 // transition from Sweeping to Resetting. See detailed note
5329 // further below.
5330 {
5331 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5332 // Update heap occupancy information which is used as
5333 // input to soft ref clearing policy at the next gc.
5334 Universe::update_heap_info_at_gc();
5335 _collectorState = Resizing;
5336 }
5337 }
5338 verify_work_stacks_empty();
5339 verify_overflow_empty();
5340
5341 if (should_unload_classes()) {
5342 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5343 // requires that the virtual spaces are stable and not deleted.
5344 ClassLoaderDataGraph::set_should_purge(true);
5345 }
5346
5347 _intra_sweep_timer.stop();
5348 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5349
5350 _inter_sweep_timer.reset();
5351 _inter_sweep_timer.start();
5352
5353 // We need to use a monotonically non-decreasing time in ms
5354 // or we will see time-warp warnings and os::javaTimeMillis()
5355 // does not guarantee monotonicity.
5356 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5357 update_time_of_last_gc(now);
5358
5359 // NOTE on abstract state transitions:
5360 // Mutators allocate-live and/or mark the mod-union table dirty
5361 // based on the state of the collection. The former is done in
5362 // the interval [Marking, Sweeping] and the latter in the interval
5363 // [Marking, Sweeping). Thus the transitions into the Marking state
5364 // and out of the Sweeping state must be synchronously visible
5365 // globally to the mutators.
5366 // The transition into the Marking state happens with the world
5367 // stopped so the mutators will globally see it. Sweeping is
5368 // done asynchronously by the background collector so the transition
5369 // from the Sweeping state to the Resizing state must be done
5370 // under the freelistLock (as is the check for whether to
5371 // allocate-live and whether to dirty the mod-union table).
5372 assert(_collectorState == Resizing, "Change of collector state to"
5373 " Resizing must be done under the freelistLocks (plural)");
5374
5375 // Now that sweeping has been completed, we clear
5376 // the incremental_collection_failed flag,
5377 // thus inviting a younger gen collection to promote into
5378 // this generation. If such a promotion may still fail,
5379 // the flag will be set again when a young collection is
5380 // attempted.
5381 GenCollectedHeap* gch = GenCollectedHeap::heap();
5382 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5383 gch->update_full_collections_completed(_collection_count_start);
5384 }
5385
5386 // FIX ME!!! Looks like this belongs in CFLSpace, with
5387 // CMSGen merely delegating to it.
5388 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5389 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5390 HeapWord* minAddr = _cmsSpace->bottom();
5391 HeapWord* largestAddr =
5392 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5393 if (largestAddr == NULL) {
5394 // The dictionary appears to be empty. In this case
5395 // try to coalesce at the end of the heap.
5396 largestAddr = _cmsSpace->end();
5397 }
5398 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5399 size_t nearLargestOffset =
5400 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5401 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5402 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5403 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5404 }
5405
5406 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5407 return addr >= _cmsSpace->nearLargestChunk();
5408 }
5409
5410 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5411 return _cmsSpace->find_chunk_at_end();
5412 }
5413
5414 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5415 bool full) {
5416 // If the young generation has been collected, gather any statistics
5417 // that are of interest at this point.
5418 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5419 if (!full && current_is_young) {
5420 // Gather statistics on the young generation collection.
5421 collector()->stats().record_gc0_end(used());
5422 }
5423 }
5424
5425 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5426 // We iterate over the space(s) underlying this generation,
5427 // checking the mark bit map to see if the bits corresponding
5428 // to specific blocks are marked or not. Blocks that are
5429 // marked are live and are not swept up. All remaining blocks
5430 // are swept up, with coalescing on-the-fly as we sweep up
5431 // contiguous free and/or garbage blocks:
5432 // We need to ensure that the sweeper synchronizes with allocators
5433 // and stop-the-world collectors. In particular, the following
5434 // locks are used:
5435 // . CMS token: if this is held, a stop the world collection cannot occur
5436 // . freelistLock: if this is held no allocation can occur from this
5437 // generation by another thread
5438 // . bitMapLock: if this is held, no other thread can access or update
5439 //
5440
5441 // Note that we need to hold the freelistLock if we use
5442 // block iterate below; else the iterator might go awry if
5443 // a mutator (or promotion) causes block contents to change
5444 // (for instance if the allocator divvies up a block).
5445 // If we hold the free list lock, for all practical purposes
5446 // young generation GC's can't occur (they'll usually need to
5447 // promote), so we might as well prevent all young generation
5448 // GC's while we do a sweeping step. For the same reason, we might
5449 // as well take the bit map lock for the entire duration
5450
5451 // check that we hold the requisite locks
5452 assert(have_cms_token(), "Should hold cms token");
5453 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5454 assert_lock_strong(old_gen->freelistLock());
5455 assert_lock_strong(bitMapLock());
5456
5457 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5458 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5459 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5460 _inter_sweep_estimate.padded_average(),
5461 _intra_sweep_estimate.padded_average());
5462 old_gen->setNearLargestChunk();
5463
5464 {
5465 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5466 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5467 // We need to free-up/coalesce garbage/blocks from a
5468 // co-terminal free run. This is done in the SweepClosure
5469 // destructor; so, do not remove this scope, else the
5470 // end-of-sweep-census below will be off by a little bit.
5471 }
5472 old_gen->cmsSpace()->sweep_completed();
5473 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5474 if (should_unload_classes()) { // unloaded classes this cycle,
5475 _concurrent_cycles_since_last_unload = 0; // ... reset count
5476 } else { // did not unload classes,
5477 _concurrent_cycles_since_last_unload++; // ... increment count
5478 }
5479 }
5480
5481 // Reset CMS data structures (for now just the marking bit map)
5482 // preparatory for the next cycle.
5483 void CMSCollector::reset_concurrent() {
5484 CMSTokenSyncWithLocks ts(true, bitMapLock());
5485
5486 // If the state is not "Resetting", the foreground thread
5487 // has done a collection and the resetting.
5488 if (_collectorState != Resetting) {
5489 assert(_collectorState == Idling, "The state should only change"
5490 " because the foreground collector has finished the collection");
5491 return;
5492 }
5493
5494 {
5495 // Clear the mark bitmap (no grey objects to start with)
5496 // for the next cycle.
5497 GCTraceCPUTime tcpu;
5498 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5499
5500 HeapWord* curAddr = _markBitMap.startWord();
5501 while (curAddr < _markBitMap.endWord()) {
5502 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5503 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5504 _markBitMap.clear_large_range(chunk);
5505 if (ConcurrentMarkSweepThread::should_yield() &&
5506 !foregroundGCIsActive() &&
5507 CMSYield) {
5508 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5509 "CMS thread should hold CMS token");
5510 assert_lock_strong(bitMapLock());
5511 bitMapLock()->unlock();
5512 ConcurrentMarkSweepThread::desynchronize(true);
5513 stopTimer();
5514 incrementYields();
5515
5516 // See the comment in coordinator_yield()
5517 for (unsigned i = 0; i < CMSYieldSleepCount &&
5518 ConcurrentMarkSweepThread::should_yield() &&
5519 !CMSCollector::foregroundGCIsActive(); ++i) {
5520 os::sleep(Thread::current(), 1, false);
5521 }
5522
5523 ConcurrentMarkSweepThread::synchronize(true);
5524 bitMapLock()->lock_without_safepoint_check();
5525 startTimer();
5526 }
5527 curAddr = chunk.end();
5528 }
5529 // A successful mostly concurrent collection has been done.
5530 // Because only the full (i.e., concurrent mode failure) collections
5531 // are being measured for gc overhead limits, clean the "near" flag
5532 // and count.
5533 size_policy()->reset_gc_overhead_limit_count();
5534 _collectorState = Idling;
5535 }
5536
5537 register_gc_end();
5538 }
5539
5540 // Same as above but for STW paths
5541 void CMSCollector::reset_stw() {
5542 // already have the lock
5543 assert(_collectorState == Resetting, "just checking");
5544 assert_lock_strong(bitMapLock());
5545 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5546 _markBitMap.clear_all();
5547 _collectorState = Idling;
5548 register_gc_end();
5549 }
5550
5551 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5552 GCTraceCPUTime tcpu;
5553 TraceCollectorStats tcs(counters());
5554
5555 switch (op) {
5556 case CMS_op_checkpointRootsInitial: {
5557 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5558 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5559 checkpointRootsInitial();
5560 break;
5561 }
5562 case CMS_op_checkpointRootsFinal: {
5563 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5564 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5565 checkpointRootsFinal();
5566 break;
5567 }
5568 default:
5569 fatal("No such CMS_op");
5570 }
5571 }
5572
5573 #ifndef PRODUCT
5574 size_t const CMSCollector::skip_header_HeapWords() {
5575 return FreeChunk::header_size();
5576 }
5577
5578 // Try and collect here conditions that should hold when
5579 // CMS thread is exiting. The idea is that the foreground GC
5580 // thread should not be blocked if it wants to terminate
5581 // the CMS thread and yet continue to run the VM for a while
5582 // after that.
5583 void CMSCollector::verify_ok_to_terminate() const {
5584 assert(Thread::current()->is_ConcurrentGC_thread(),
5585 "should be called by CMS thread");
5586 assert(!_foregroundGCShouldWait, "should be false");
5587 // We could check here that all the various low-level locks
5588 // are not held by the CMS thread, but that is overkill; see
5589 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5590 // is checked.
5591 }
5592 #endif
5593
5594 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5595 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5596 "missing Printezis mark?");
5597 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5598 size_t size = pointer_delta(nextOneAddr + 1, addr);
5599 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5600 "alignment problem");
5601 assert(size >= 3, "Necessary for Printezis marks to work");
5602 return size;
5603 }
5604
5605 // A variant of the above (block_size_using_printezis_bits()) except
5606 // that we return 0 if the P-bits are not yet set.
5607 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5608 if (_markBitMap.isMarked(addr + 1)) {
5609 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5610 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5611 size_t size = pointer_delta(nextOneAddr + 1, addr);
5612 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5613 "alignment problem");
5614 assert(size >= 3, "Necessary for Printezis marks to work");
5615 return size;
5616 }
5617 return 0;
5618 }
5619
5620 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5621 size_t sz = 0;
5622 oop p = (oop)addr;
5623 if (p->klass_or_null_acquire() != NULL) {
5624 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5625 } else {
5626 sz = block_size_using_printezis_bits(addr);
5627 }
5628 assert(sz > 0, "size must be nonzero");
5629 HeapWord* next_block = addr + sz;
5630 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5631 CardTableModRefBS::card_size);
5632 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5633 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5634 "must be different cards");
5635 return next_card;
5636 }
5637
5638
5639 // CMS Bit Map Wrapper /////////////////////////////////////////
5640
5641 // Construct a CMS bit map infrastructure, but don't create the
5642 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5643 // further below.
5644 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5645 _bm(),
5646 _shifter(shifter),
5647 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5648 Monitor::_safepoint_check_sometimes) : NULL)
5649 {
5650 _bmStartWord = 0;
5651 _bmWordSize = 0;
5652 }
5653
5654 bool CMSBitMap::allocate(MemRegion mr) {
5655 _bmStartWord = mr.start();
5656 _bmWordSize = mr.word_size();
5657 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5658 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5659 if (!brs.is_reserved()) {
5660 log_warning(gc)("CMS bit map allocation failure");
5661 return false;
5662 }
5663 // For now we'll just commit all of the bit map up front.
5664 // Later on we'll try to be more parsimonious with swap.
5665 if (!_virtual_space.initialize(brs, brs.size())) {
5666 log_warning(gc)("CMS bit map backing store failure");
5667 return false;
5668 }
5669 assert(_virtual_space.committed_size() == brs.size(),
5670 "didn't reserve backing store for all of CMS bit map?");
5671 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5672 _bmWordSize, "inconsistency in bit map sizing");
5673 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5674
5675 // bm.clear(); // can we rely on getting zero'd memory? verify below
5676 assert(isAllClear(),
5677 "Expected zero'd memory from ReservedSpace constructor");
5678 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5679 "consistency check");
5680 return true;
5681 }
5682
5683 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5684 HeapWord *next_addr, *end_addr, *last_addr;
5685 assert_locked();
5686 assert(covers(mr), "out-of-range error");
5687 // XXX assert that start and end are appropriately aligned
5688 for (next_addr = mr.start(), end_addr = mr.end();
5689 next_addr < end_addr; next_addr = last_addr) {
5690 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5691 last_addr = dirty_region.end();
5692 if (!dirty_region.is_empty()) {
5693 cl->do_MemRegion(dirty_region);
5694 } else {
5695 assert(last_addr == end_addr, "program logic");
5696 return;
5697 }
5698 }
5699 }
5700
5701 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5702 _bm.print_on_error(st, prefix);
5703 }
5704
5705 #ifndef PRODUCT
5706 void CMSBitMap::assert_locked() const {
5707 CMSLockVerifier::assert_locked(lock());
5708 }
5709
5710 bool CMSBitMap::covers(MemRegion mr) const {
5711 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5712 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5713 "size inconsistency");
5714 return (mr.start() >= _bmStartWord) &&
5715 (mr.end() <= endWord());
5716 }
5717
5718 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5719 return (start >= _bmStartWord && (start + size) <= endWord());
5720 }
5721
5722 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5723 // verify that there are no 1 bits in the interval [left, right)
5724 FalseBitMapClosure falseBitMapClosure;
5725 iterate(&falseBitMapClosure, left, right);
5726 }
5727
5728 void CMSBitMap::region_invariant(MemRegion mr)
5729 {
5730 assert_locked();
5731 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5732 assert(!mr.is_empty(), "unexpected empty region");
5733 assert(covers(mr), "mr should be covered by bit map");
5734 // convert address range into offset range
5735 size_t start_ofs = heapWordToOffset(mr.start());
5736 // Make sure that end() is appropriately aligned
5737 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5738 (1 << (_shifter+LogHeapWordSize))),
5739 "Misaligned mr.end()");
5740 size_t end_ofs = heapWordToOffset(mr.end());
5741 assert(end_ofs > start_ofs, "Should mark at least one bit");
5742 }
5743
5744 #endif
5745
5746 bool CMSMarkStack::allocate(size_t size) {
5747 // allocate a stack of the requisite depth
5748 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5749 size * sizeof(oop)));
5750 if (!rs.is_reserved()) {
5751 log_warning(gc)("CMSMarkStack allocation failure");
5752 return false;
5753 }
5754 if (!_virtual_space.initialize(rs, rs.size())) {
5755 log_warning(gc)("CMSMarkStack backing store failure");
5756 return false;
5757 }
5758 assert(_virtual_space.committed_size() == rs.size(),
5759 "didn't reserve backing store for all of CMS stack?");
5760 _base = (oop*)(_virtual_space.low());
5761 _index = 0;
5762 _capacity = size;
5763 NOT_PRODUCT(_max_depth = 0);
5764 return true;
5765 }
5766
5767 // XXX FIX ME !!! In the MT case we come in here holding a
5768 // leaf lock. For printing we need to take a further lock
5769 // which has lower rank. We need to recalibrate the two
5770 // lock-ranks involved in order to be able to print the
5771 // messages below. (Or defer the printing to the caller.
5772 // For now we take the expedient path of just disabling the
5773 // messages for the problematic case.)
5774 void CMSMarkStack::expand() {
5775 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5776 if (_capacity == MarkStackSizeMax) {
5777 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5778 // We print a warning message only once per CMS cycle.
5779 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5780 }
5781 return;
5782 }
5783 // Double capacity if possible
5784 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5785 // Do not give up existing stack until we have managed to
5786 // get the double capacity that we desired.
5787 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5788 new_capacity * sizeof(oop)));
5789 if (rs.is_reserved()) {
5790 // Release the backing store associated with old stack
5791 _virtual_space.release();
5792 // Reinitialize virtual space for new stack
5793 if (!_virtual_space.initialize(rs, rs.size())) {
5794 fatal("Not enough swap for expanded marking stack");
5795 }
5796 _base = (oop*)(_virtual_space.low());
5797 _index = 0;
5798 _capacity = new_capacity;
5799 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5800 // Failed to double capacity, continue;
5801 // we print a detail message only once per CMS cycle.
5802 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5803 _capacity / K, new_capacity / K);
5804 }
5805 }
5806
5807
5808 // Closures
5809 // XXX: there seems to be a lot of code duplication here;
5810 // should refactor and consolidate common code.
5811
5812 // This closure is used to mark refs into the CMS generation in
5813 // the CMS bit map. Called at the first checkpoint. This closure
5814 // assumes that we do not need to re-mark dirty cards; if the CMS
5815 // generation on which this is used is not an oldest
5816 // generation then this will lose younger_gen cards!
5817
5818 MarkRefsIntoClosure::MarkRefsIntoClosure(
5819 MemRegion span, CMSBitMap* bitMap):
5820 _span(span),
5821 _bitMap(bitMap)
5822 {
5823 assert(ref_processor() == NULL, "deliberately left NULL");
5824 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5825 }
5826
5827 void MarkRefsIntoClosure::do_oop(oop obj) {
5828 // if p points into _span, then mark corresponding bit in _markBitMap
5829 assert(obj->is_oop(), "expected an oop");
5830 HeapWord* addr = (HeapWord*)obj;
5831 if (_span.contains(addr)) {
5832 // this should be made more efficient
5833 _bitMap->mark(addr);
5834 }
5835 }
5836
5837 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5838 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5839
5840 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5841 MemRegion span, CMSBitMap* bitMap):
5842 _span(span),
5843 _bitMap(bitMap)
5844 {
5845 assert(ref_processor() == NULL, "deliberately left NULL");
5846 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5847 }
5848
5849 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5850 // if p points into _span, then mark corresponding bit in _markBitMap
5851 assert(obj->is_oop(), "expected an oop");
5852 HeapWord* addr = (HeapWord*)obj;
5853 if (_span.contains(addr)) {
5854 // this should be made more efficient
5855 _bitMap->par_mark(addr);
5856 }
5857 }
5858
5859 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5860 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5861
5862 // A variant of the above, used for CMS marking verification.
5863 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5864 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5865 _span(span),
5866 _verification_bm(verification_bm),
5867 _cms_bm(cms_bm)
5868 {
5869 assert(ref_processor() == NULL, "deliberately left NULL");
5870 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5871 }
5872
5873 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5874 // if p points into _span, then mark corresponding bit in _markBitMap
5875 assert(obj->is_oop(), "expected an oop");
5876 HeapWord* addr = (HeapWord*)obj;
5877 if (_span.contains(addr)) {
5878 _verification_bm->mark(addr);
5879 if (!_cms_bm->isMarked(addr)) {
5880 Log(gc, verify) log;
5881 ResourceMark rm;
5882 oop(addr)->print_on(log.error_stream());
5883 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5884 fatal("... aborting");
5885 }
5886 }
5887 }
5888
5889 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5890 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5891
5892 //////////////////////////////////////////////////
5893 // MarkRefsIntoAndScanClosure
5894 //////////////////////////////////////////////////
5895
5896 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5897 ReferenceProcessor* rp,
5898 CMSBitMap* bit_map,
5899 CMSBitMap* mod_union_table,
5900 CMSMarkStack* mark_stack,
5901 CMSCollector* collector,
5902 bool should_yield,
5903 bool concurrent_precleaning):
5904 _collector(collector),
5905 _span(span),
5906 _bit_map(bit_map),
5907 _mark_stack(mark_stack),
5908 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5909 mark_stack, concurrent_precleaning),
5910 _yield(should_yield),
5911 _concurrent_precleaning(concurrent_precleaning),
5912 _freelistLock(NULL)
5913 {
5914 // FIXME: Should initialize in base class constructor.
5915 assert(rp != NULL, "ref_processor shouldn't be NULL");
5916 set_ref_processor_internal(rp);
5917 }
5918
5919 // This closure is used to mark refs into the CMS generation at the
5920 // second (final) checkpoint, and to scan and transitively follow
5921 // the unmarked oops. It is also used during the concurrent precleaning
5922 // phase while scanning objects on dirty cards in the CMS generation.
5923 // The marks are made in the marking bit map and the marking stack is
5924 // used for keeping the (newly) grey objects during the scan.
5925 // The parallel version (Par_...) appears further below.
5926 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5927 if (obj != NULL) {
5928 assert(obj->is_oop(), "expected an oop");
5929 HeapWord* addr = (HeapWord*)obj;
5930 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5931 assert(_collector->overflow_list_is_empty(),
5932 "overflow list should be empty");
5933 if (_span.contains(addr) &&
5934 !_bit_map->isMarked(addr)) {
5935 // mark bit map (object is now grey)
5936 _bit_map->mark(addr);
5937 // push on marking stack (stack should be empty), and drain the
5938 // stack by applying this closure to the oops in the oops popped
5939 // from the stack (i.e. blacken the grey objects)
5940 bool res = _mark_stack->push(obj);
5941 assert(res, "Should have space to push on empty stack");
5942 do {
5943 oop new_oop = _mark_stack->pop();
5944 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5945 assert(_bit_map->isMarked((HeapWord*)new_oop),
5946 "only grey objects on this stack");
5947 // iterate over the oops in this oop, marking and pushing
5948 // the ones in CMS heap (i.e. in _span).
5949 new_oop->oop_iterate(&_pushAndMarkClosure);
5950 // check if it's time to yield
5951 do_yield_check();
5952 } while (!_mark_stack->isEmpty() ||
5953 (!_concurrent_precleaning && take_from_overflow_list()));
5954 // if marking stack is empty, and we are not doing this
5955 // during precleaning, then check the overflow list
5956 }
5957 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5958 assert(_collector->overflow_list_is_empty(),
5959 "overflow list was drained above");
5960
5961 assert(_collector->no_preserved_marks(),
5962 "All preserved marks should have been restored above");
5963 }
5964 }
5965
5966 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5967 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5968
5969 void MarkRefsIntoAndScanClosure::do_yield_work() {
5970 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5971 "CMS thread should hold CMS token");
5972 assert_lock_strong(_freelistLock);
5973 assert_lock_strong(_bit_map->lock());
5974 // relinquish the free_list_lock and bitMaplock()
5975 _bit_map->lock()->unlock();
5976 _freelistLock->unlock();
5977 ConcurrentMarkSweepThread::desynchronize(true);
5978 _collector->stopTimer();
5979 _collector->incrementYields();
5980
5981 // See the comment in coordinator_yield()
5982 for (unsigned i = 0;
5983 i < CMSYieldSleepCount &&
5984 ConcurrentMarkSweepThread::should_yield() &&
5985 !CMSCollector::foregroundGCIsActive();
5986 ++i) {
5987 os::sleep(Thread::current(), 1, false);
5988 }
5989
5990 ConcurrentMarkSweepThread::synchronize(true);
5991 _freelistLock->lock_without_safepoint_check();
5992 _bit_map->lock()->lock_without_safepoint_check();
5993 _collector->startTimer();
5994 }
5995
5996 ///////////////////////////////////////////////////////////
5997 // ParMarkRefsIntoAndScanClosure: a parallel version of
5998 // MarkRefsIntoAndScanClosure
5999 ///////////////////////////////////////////////////////////
6000 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6001 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6002 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6003 _span(span),
6004 _bit_map(bit_map),
6005 _work_queue(work_queue),
6006 _low_water_mark(MIN2((work_queue->max_elems()/4),
6007 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6008 _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6009 {
6010 // FIXME: Should initialize in base class constructor.
6011 assert(rp != NULL, "ref_processor shouldn't be NULL");
6012 set_ref_processor_internal(rp);
6013 }
6014
6015 // This closure is used to mark refs into the CMS generation at the
6016 // second (final) checkpoint, and to scan and transitively follow
6017 // the unmarked oops. The marks are made in the marking bit map and
6018 // the work_queue is used for keeping the (newly) grey objects during
6019 // the scan phase whence they are also available for stealing by parallel
6020 // threads. Since the marking bit map is shared, updates are
6021 // synchronized (via CAS).
6022 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6023 if (obj != NULL) {
6024 // Ignore mark word because this could be an already marked oop
6025 // that may be chained at the end of the overflow list.
6026 assert(obj->is_oop(true), "expected an oop");
6027 HeapWord* addr = (HeapWord*)obj;
6028 if (_span.contains(addr) &&
6029 !_bit_map->isMarked(addr)) {
6030 // mark bit map (object will become grey):
6031 // It is possible for several threads to be
6032 // trying to "claim" this object concurrently;
6033 // the unique thread that succeeds in marking the
6034 // object first will do the subsequent push on
6035 // to the work queue (or overflow list).
6036 if (_bit_map->par_mark(addr)) {
6037 // push on work_queue (which may not be empty), and trim the
6038 // queue to an appropriate length by applying this closure to
6039 // the oops in the oops popped from the stack (i.e. blacken the
6040 // grey objects)
6041 bool res = _work_queue->push(obj);
6042 assert(res, "Low water mark should be less than capacity?");
6043 trim_queue(_low_water_mark);
6044 } // Else, another thread claimed the object
6045 }
6046 }
6047 }
6048
6049 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6050 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6051
6052 // This closure is used to rescan the marked objects on the dirty cards
6053 // in the mod union table and the card table proper.
6054 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6055 oop p, MemRegion mr) {
6056
6057 size_t size = 0;
6058 HeapWord* addr = (HeapWord*)p;
6059 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6060 assert(_span.contains(addr), "we are scanning the CMS generation");
6061 // check if it's time to yield
6062 if (do_yield_check()) {
6063 // We yielded for some foreground stop-world work,
6064 // and we have been asked to abort this ongoing preclean cycle.
6065 return 0;
6066 }
6067 if (_bitMap->isMarked(addr)) {
6068 // it's marked; is it potentially uninitialized?
6069 if (p->klass_or_null_acquire() != NULL) {
6070 // an initialized object; ignore mark word in verification below
6071 // since we are running concurrent with mutators
6072 assert(p->is_oop(true), "should be an oop");
6073 if (p->is_objArray()) {
6074 // objArrays are precisely marked; restrict scanning
6075 // to dirty cards only.
6076 size = CompactibleFreeListSpace::adjustObjectSize(
6077 p->oop_iterate_size(_scanningClosure, mr));
6078 } else {
6079 // A non-array may have been imprecisely marked; we need
6080 // to scan object in its entirety.
6081 size = CompactibleFreeListSpace::adjustObjectSize(
6082 p->oop_iterate_size(_scanningClosure));
6083 }
6084 #ifdef ASSERT
6085 size_t direct_size =
6086 CompactibleFreeListSpace::adjustObjectSize(p->size());
6087 assert(size == direct_size, "Inconsistency in size");
6088 assert(size >= 3, "Necessary for Printezis marks to work");
6089 HeapWord* start_pbit = addr + 1;
6090 HeapWord* end_pbit = addr + size - 1;
6091 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6092 "inconsistent Printezis mark");
6093 // Verify inner mark bits (between Printezis bits) are clear,
6094 // but don't repeat if there are multiple dirty regions for
6095 // the same object, to avoid potential O(N^2) performance.
6096 if (addr != _last_scanned_object) {
6097 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6098 _last_scanned_object = addr;
6099 }
6100 #endif // ASSERT
6101 } else {
6102 // An uninitialized object.
6103 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6104 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6105 size = pointer_delta(nextOneAddr + 1, addr);
6106 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6107 "alignment problem");
6108 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6109 // will dirty the card when the klass pointer is installed in the
6110 // object (signaling the completion of initialization).
6111 }
6112 } else {
6113 // Either a not yet marked object or an uninitialized object
6114 if (p->klass_or_null_acquire() == NULL) {
6115 // An uninitialized object, skip to the next card, since
6116 // we may not be able to read its P-bits yet.
6117 assert(size == 0, "Initial value");
6118 } else {
6119 // An object not (yet) reached by marking: we merely need to
6120 // compute its size so as to go look at the next block.
6121 assert(p->is_oop(true), "should be an oop");
6122 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6123 }
6124 }
6125 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6126 return size;
6127 }
6128
6129 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6130 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6131 "CMS thread should hold CMS token");
6132 assert_lock_strong(_freelistLock);
6133 assert_lock_strong(_bitMap->lock());
6134 // relinquish the free_list_lock and bitMaplock()
6135 _bitMap->lock()->unlock();
6136 _freelistLock->unlock();
6137 ConcurrentMarkSweepThread::desynchronize(true);
6138 _collector->stopTimer();
6139 _collector->incrementYields();
6140
6141 // See the comment in coordinator_yield()
6142 for (unsigned i = 0; i < CMSYieldSleepCount &&
6143 ConcurrentMarkSweepThread::should_yield() &&
6144 !CMSCollector::foregroundGCIsActive(); ++i) {
6145 os::sleep(Thread::current(), 1, false);
6146 }
6147
6148 ConcurrentMarkSweepThread::synchronize(true);
6149 _freelistLock->lock_without_safepoint_check();
6150 _bitMap->lock()->lock_without_safepoint_check();
6151 _collector->startTimer();
6152 }
6153
6154
6155 //////////////////////////////////////////////////////////////////
6156 // SurvivorSpacePrecleanClosure
6157 //////////////////////////////////////////////////////////////////
6158 // This (single-threaded) closure is used to preclean the oops in
6159 // the survivor spaces.
6160 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6161
6162 HeapWord* addr = (HeapWord*)p;
6163 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6164 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6165 assert(p->klass_or_null() != NULL, "object should be initialized");
6166 // an initialized object; ignore mark word in verification below
6167 // since we are running concurrent with mutators
6168 assert(p->is_oop(true), "should be an oop");
6169 // Note that we do not yield while we iterate over
6170 // the interior oops of p, pushing the relevant ones
6171 // on our marking stack.
6172 size_t size = p->oop_iterate_size(_scanning_closure);
6173 do_yield_check();
6174 // Observe that below, we do not abandon the preclean
6175 // phase as soon as we should; rather we empty the
6176 // marking stack before returning. This is to satisfy
6177 // some existing assertions. In general, it may be a
6178 // good idea to abort immediately and complete the marking
6179 // from the grey objects at a later time.
6180 while (!_mark_stack->isEmpty()) {
6181 oop new_oop = _mark_stack->pop();
6182 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6183 assert(_bit_map->isMarked((HeapWord*)new_oop),
6184 "only grey objects on this stack");
6185 // iterate over the oops in this oop, marking and pushing
6186 // the ones in CMS heap (i.e. in _span).
6187 new_oop->oop_iterate(_scanning_closure);
6188 // check if it's time to yield
6189 do_yield_check();
6190 }
6191 unsigned int after_count =
6192 GenCollectedHeap::heap()->total_collections();
6193 bool abort = (_before_count != after_count) ||
6194 _collector->should_abort_preclean();
6195 return abort ? 0 : size;
6196 }
6197
6198 void SurvivorSpacePrecleanClosure::do_yield_work() {
6199 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6200 "CMS thread should hold CMS token");
6201 assert_lock_strong(_bit_map->lock());
6202 // Relinquish the bit map lock
6203 _bit_map->lock()->unlock();
6204 ConcurrentMarkSweepThread::desynchronize(true);
6205 _collector->stopTimer();
6206 _collector->incrementYields();
6207
6208 // See the comment in coordinator_yield()
6209 for (unsigned i = 0; i < CMSYieldSleepCount &&
6210 ConcurrentMarkSweepThread::should_yield() &&
6211 !CMSCollector::foregroundGCIsActive(); ++i) {
6212 os::sleep(Thread::current(), 1, false);
6213 }
6214
6215 ConcurrentMarkSweepThread::synchronize(true);
6216 _bit_map->lock()->lock_without_safepoint_check();
6217 _collector->startTimer();
6218 }
6219
6220 // This closure is used to rescan the marked objects on the dirty cards
6221 // in the mod union table and the card table proper. In the parallel
6222 // case, although the bitMap is shared, we do a single read so the
6223 // isMarked() query is "safe".
6224 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6225 // Ignore mark word because we are running concurrent with mutators
6226 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6227 HeapWord* addr = (HeapWord*)p;
6228 assert(_span.contains(addr), "we are scanning the CMS generation");
6229 bool is_obj_array = false;
6230 #ifdef ASSERT
6231 if (!_parallel) {
6232 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6233 assert(_collector->overflow_list_is_empty(),
6234 "overflow list should be empty");
6235
6236 }
6237 #endif // ASSERT
6238 if (_bit_map->isMarked(addr)) {
6239 // Obj arrays are precisely marked, non-arrays are not;
6240 // so we scan objArrays precisely and non-arrays in their
6241 // entirety.
6242 if (p->is_objArray()) {
6243 is_obj_array = true;
6244 if (_parallel) {
6245 p->oop_iterate(_par_scan_closure, mr);
6246 } else {
6247 p->oop_iterate(_scan_closure, mr);
6248 }
6249 } else {
6250 if (_parallel) {
6251 p->oop_iterate(_par_scan_closure);
6252 } else {
6253 p->oop_iterate(_scan_closure);
6254 }
6255 }
6256 }
6257 #ifdef ASSERT
6258 if (!_parallel) {
6259 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6260 assert(_collector->overflow_list_is_empty(),
6261 "overflow list should be empty");
6262
6263 }
6264 #endif // ASSERT
6265 return is_obj_array;
6266 }
6267
6268 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6269 MemRegion span,
6270 CMSBitMap* bitMap, CMSMarkStack* markStack,
6271 bool should_yield, bool verifying):
6272 _collector(collector),
6273 _span(span),
6274 _bitMap(bitMap),
6275 _mut(&collector->_modUnionTable),
6276 _markStack(markStack),
6277 _yield(should_yield),
6278 _skipBits(0)
6279 {
6280 assert(_markStack->isEmpty(), "stack should be empty");
6281 _finger = _bitMap->startWord();
6282 _threshold = _finger;
6283 assert(_collector->_restart_addr == NULL, "Sanity check");
6284 assert(_span.contains(_finger), "Out of bounds _finger?");
6285 DEBUG_ONLY(_verifying = verifying;)
6286 }
6287
6288 void MarkFromRootsClosure::reset(HeapWord* addr) {
6289 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6290 assert(_span.contains(addr), "Out of bounds _finger?");
6291 _finger = addr;
6292 _threshold = (HeapWord*)round_to(
6293 (intptr_t)_finger, CardTableModRefBS::card_size);
6294 }
6295
6296 // Should revisit to see if this should be restructured for
6297 // greater efficiency.
6298 bool MarkFromRootsClosure::do_bit(size_t offset) {
6299 if (_skipBits > 0) {
6300 _skipBits--;
6301 return true;
6302 }
6303 // convert offset into a HeapWord*
6304 HeapWord* addr = _bitMap->startWord() + offset;
6305 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6306 "address out of range");
6307 assert(_bitMap->isMarked(addr), "tautology");
6308 if (_bitMap->isMarked(addr+1)) {
6309 // this is an allocated but not yet initialized object
6310 assert(_skipBits == 0, "tautology");
6311 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6312 oop p = oop(addr);
6313 if (p->klass_or_null_acquire() == NULL) {
6314 DEBUG_ONLY(if (!_verifying) {)
6315 // We re-dirty the cards on which this object lies and increase
6316 // the _threshold so that we'll come back to scan this object
6317 // during the preclean or remark phase. (CMSCleanOnEnter)
6318 if (CMSCleanOnEnter) {
6319 size_t sz = _collector->block_size_using_printezis_bits(addr);
6320 HeapWord* end_card_addr = (HeapWord*)round_to(
6321 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6322 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6323 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6324 // Bump _threshold to end_card_addr; note that
6325 // _threshold cannot possibly exceed end_card_addr, anyhow.
6326 // This prevents future clearing of the card as the scan proceeds
6327 // to the right.
6328 assert(_threshold <= end_card_addr,
6329 "Because we are just scanning into this object");
6330 if (_threshold < end_card_addr) {
6331 _threshold = end_card_addr;
6332 }
6333 if (p->klass_or_null_acquire() != NULL) {
6334 // Redirty the range of cards...
6335 _mut->mark_range(redirty_range);
6336 } // ...else the setting of klass will dirty the card anyway.
6337 }
6338 DEBUG_ONLY(})
6339 return true;
6340 }
6341 }
6342 scanOopsInOop(addr);
6343 return true;
6344 }
6345
6346 // We take a break if we've been at this for a while,
6347 // so as to avoid monopolizing the locks involved.
6348 void MarkFromRootsClosure::do_yield_work() {
6349 // First give up the locks, then yield, then re-lock
6350 // We should probably use a constructor/destructor idiom to
6351 // do this unlock/lock or modify the MutexUnlocker class to
6352 // serve our purpose. XXX
6353 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6354 "CMS thread should hold CMS token");
6355 assert_lock_strong(_bitMap->lock());
6356 _bitMap->lock()->unlock();
6357 ConcurrentMarkSweepThread::desynchronize(true);
6358 _collector->stopTimer();
6359 _collector->incrementYields();
6360
6361 // See the comment in coordinator_yield()
6362 for (unsigned i = 0; i < CMSYieldSleepCount &&
6363 ConcurrentMarkSweepThread::should_yield() &&
6364 !CMSCollector::foregroundGCIsActive(); ++i) {
6365 os::sleep(Thread::current(), 1, false);
6366 }
6367
6368 ConcurrentMarkSweepThread::synchronize(true);
6369 _bitMap->lock()->lock_without_safepoint_check();
6370 _collector->startTimer();
6371 }
6372
6373 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6374 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6375 assert(_markStack->isEmpty(),
6376 "should drain stack to limit stack usage");
6377 // convert ptr to an oop preparatory to scanning
6378 oop obj = oop(ptr);
6379 // Ignore mark word in verification below, since we
6380 // may be running concurrent with mutators.
6381 assert(obj->is_oop(true), "should be an oop");
6382 assert(_finger <= ptr, "_finger runneth ahead");
6383 // advance the finger to right end of this object
6384 _finger = ptr + obj->size();
6385 assert(_finger > ptr, "we just incremented it above");
6386 // On large heaps, it may take us some time to get through
6387 // the marking phase. During
6388 // this time it's possible that a lot of mutations have
6389 // accumulated in the card table and the mod union table --
6390 // these mutation records are redundant until we have
6391 // actually traced into the corresponding card.
6392 // Here, we check whether advancing the finger would make
6393 // us cross into a new card, and if so clear corresponding
6394 // cards in the MUT (preclean them in the card-table in the
6395 // future).
6396
6397 DEBUG_ONLY(if (!_verifying) {)
6398 // The clean-on-enter optimization is disabled by default,
6399 // until we fix 6178663.
6400 if (CMSCleanOnEnter && (_finger > _threshold)) {
6401 // [_threshold, _finger) represents the interval
6402 // of cards to be cleared in MUT (or precleaned in card table).
6403 // The set of cards to be cleared is all those that overlap
6404 // with the interval [_threshold, _finger); note that
6405 // _threshold is always kept card-aligned but _finger isn't
6406 // always card-aligned.
6407 HeapWord* old_threshold = _threshold;
6408 assert(old_threshold == (HeapWord*)round_to(
6409 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6410 "_threshold should always be card-aligned");
6411 _threshold = (HeapWord*)round_to(
6412 (intptr_t)_finger, CardTableModRefBS::card_size);
6413 MemRegion mr(old_threshold, _threshold);
6414 assert(!mr.is_empty(), "Control point invariant");
6415 assert(_span.contains(mr), "Should clear within span");
6416 _mut->clear_range(mr);
6417 }
6418 DEBUG_ONLY(})
6419 // Note: the finger doesn't advance while we drain
6420 // the stack below.
6421 PushOrMarkClosure pushOrMarkClosure(_collector,
6422 _span, _bitMap, _markStack,
6423 _finger, this);
6424 bool res = _markStack->push(obj);
6425 assert(res, "Empty non-zero size stack should have space for single push");
6426 while (!_markStack->isEmpty()) {
6427 oop new_oop = _markStack->pop();
6428 // Skip verifying header mark word below because we are
6429 // running concurrent with mutators.
6430 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6431 // now scan this oop's oops
6432 new_oop->oop_iterate(&pushOrMarkClosure);
6433 do_yield_check();
6434 }
6435 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6436 }
6437
6438 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6439 CMSCollector* collector, MemRegion span,
6440 CMSBitMap* bit_map,
6441 OopTaskQueue* work_queue,
6442 CMSMarkStack* overflow_stack):
6443 _collector(collector),
6444 _whole_span(collector->_span),
6445 _span(span),
6446 _bit_map(bit_map),
6447 _mut(&collector->_modUnionTable),
6448 _work_queue(work_queue),
6449 _overflow_stack(overflow_stack),
6450 _skip_bits(0),
6451 _task(task)
6452 {
6453 assert(_work_queue->size() == 0, "work_queue should be empty");
6454 _finger = span.start();
6455 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6456 assert(_span.contains(_finger), "Out of bounds _finger?");
6457 }
6458
6459 // Should revisit to see if this should be restructured for
6460 // greater efficiency.
6461 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6462 if (_skip_bits > 0) {
6463 _skip_bits--;
6464 return true;
6465 }
6466 // convert offset into a HeapWord*
6467 HeapWord* addr = _bit_map->startWord() + offset;
6468 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6469 "address out of range");
6470 assert(_bit_map->isMarked(addr), "tautology");
6471 if (_bit_map->isMarked(addr+1)) {
6472 // this is an allocated object that might not yet be initialized
6473 assert(_skip_bits == 0, "tautology");
6474 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6475 oop p = oop(addr);
6476 if (p->klass_or_null_acquire() == NULL) {
6477 // in the case of Clean-on-Enter optimization, redirty card
6478 // and avoid clearing card by increasing the threshold.
6479 return true;
6480 }
6481 }
6482 scan_oops_in_oop(addr);
6483 return true;
6484 }
6485
6486 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6487 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6488 // Should we assert that our work queue is empty or
6489 // below some drain limit?
6490 assert(_work_queue->size() == 0,
6491 "should drain stack to limit stack usage");
6492 // convert ptr to an oop preparatory to scanning
6493 oop obj = oop(ptr);
6494 // Ignore mark word in verification below, since we
6495 // may be running concurrent with mutators.
6496 assert(obj->is_oop(true), "should be an oop");
6497 assert(_finger <= ptr, "_finger runneth ahead");
6498 // advance the finger to right end of this object
6499 _finger = ptr + obj->size();
6500 assert(_finger > ptr, "we just incremented it above");
6501 // On large heaps, it may take us some time to get through
6502 // the marking phase. During
6503 // this time it's possible that a lot of mutations have
6504 // accumulated in the card table and the mod union table --
6505 // these mutation records are redundant until we have
6506 // actually traced into the corresponding card.
6507 // Here, we check whether advancing the finger would make
6508 // us cross into a new card, and if so clear corresponding
6509 // cards in the MUT (preclean them in the card-table in the
6510 // future).
6511
6512 // The clean-on-enter optimization is disabled by default,
6513 // until we fix 6178663.
6514 if (CMSCleanOnEnter && (_finger > _threshold)) {
6515 // [_threshold, _finger) represents the interval
6516 // of cards to be cleared in MUT (or precleaned in card table).
6517 // The set of cards to be cleared is all those that overlap
6518 // with the interval [_threshold, _finger); note that
6519 // _threshold is always kept card-aligned but _finger isn't
6520 // always card-aligned.
6521 HeapWord* old_threshold = _threshold;
6522 assert(old_threshold == (HeapWord*)round_to(
6523 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6524 "_threshold should always be card-aligned");
6525 _threshold = (HeapWord*)round_to(
6526 (intptr_t)_finger, CardTableModRefBS::card_size);
6527 MemRegion mr(old_threshold, _threshold);
6528 assert(!mr.is_empty(), "Control point invariant");
6529 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6530 _mut->clear_range(mr);
6531 }
6532
6533 // Note: the local finger doesn't advance while we drain
6534 // the stack below, but the global finger sure can and will.
6535 HeapWord* volatile* gfa = _task->global_finger_addr();
6536 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6537 _span, _bit_map,
6538 _work_queue,
6539 _overflow_stack,
6540 _finger,
6541 gfa, this);
6542 bool res = _work_queue->push(obj); // overflow could occur here
6543 assert(res, "Will hold once we use workqueues");
6544 while (true) {
6545 oop new_oop;
6546 if (!_work_queue->pop_local(new_oop)) {
6547 // We emptied our work_queue; check if there's stuff that can
6548 // be gotten from the overflow stack.
6549 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6550 _overflow_stack, _work_queue)) {
6551 do_yield_check();
6552 continue;
6553 } else { // done
6554 break;
6555 }
6556 }
6557 // Skip verifying header mark word below because we are
6558 // running concurrent with mutators.
6559 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6560 // now scan this oop's oops
6561 new_oop->oop_iterate(&pushOrMarkClosure);
6562 do_yield_check();
6563 }
6564 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6565 }
6566
6567 // Yield in response to a request from VM Thread or
6568 // from mutators.
6569 void ParMarkFromRootsClosure::do_yield_work() {
6570 assert(_task != NULL, "sanity");
6571 _task->yield();
6572 }
6573
6574 // A variant of the above used for verifying CMS marking work.
6575 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6576 MemRegion span,
6577 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6578 CMSMarkStack* mark_stack):
6579 _collector(collector),
6580 _span(span),
6581 _verification_bm(verification_bm),
6582 _cms_bm(cms_bm),
6583 _mark_stack(mark_stack),
6584 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6585 mark_stack)
6586 {
6587 assert(_mark_stack->isEmpty(), "stack should be empty");
6588 _finger = _verification_bm->startWord();
6589 assert(_collector->_restart_addr == NULL, "Sanity check");
6590 assert(_span.contains(_finger), "Out of bounds _finger?");
6591 }
6592
6593 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6594 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6595 assert(_span.contains(addr), "Out of bounds _finger?");
6596 _finger = addr;
6597 }
6598
6599 // Should revisit to see if this should be restructured for
6600 // greater efficiency.
6601 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6602 // convert offset into a HeapWord*
6603 HeapWord* addr = _verification_bm->startWord() + offset;
6604 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6605 "address out of range");
6606 assert(_verification_bm->isMarked(addr), "tautology");
6607 assert(_cms_bm->isMarked(addr), "tautology");
6608
6609 assert(_mark_stack->isEmpty(),
6610 "should drain stack to limit stack usage");
6611 // convert addr to an oop preparatory to scanning
6612 oop obj = oop(addr);
6613 assert(obj->is_oop(), "should be an oop");
6614 assert(_finger <= addr, "_finger runneth ahead");
6615 // advance the finger to right end of this object
6616 _finger = addr + obj->size();
6617 assert(_finger > addr, "we just incremented it above");
6618 // Note: the finger doesn't advance while we drain
6619 // the stack below.
6620 bool res = _mark_stack->push(obj);
6621 assert(res, "Empty non-zero size stack should have space for single push");
6622 while (!_mark_stack->isEmpty()) {
6623 oop new_oop = _mark_stack->pop();
6624 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6625 // now scan this oop's oops
6626 new_oop->oop_iterate(&_pam_verify_closure);
6627 }
6628 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6629 return true;
6630 }
6631
6632 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6633 CMSCollector* collector, MemRegion span,
6634 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6635 CMSMarkStack* mark_stack):
6636 MetadataAwareOopClosure(collector->ref_processor()),
6637 _collector(collector),
6638 _span(span),
6639 _verification_bm(verification_bm),
6640 _cms_bm(cms_bm),
6641 _mark_stack(mark_stack)
6642 { }
6643
6644 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6645 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6646
6647 // Upon stack overflow, we discard (part of) the stack,
6648 // remembering the least address amongst those discarded
6649 // in CMSCollector's _restart_address.
6650 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6651 // Remember the least grey address discarded
6652 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6653 _collector->lower_restart_addr(ra);
6654 _mark_stack->reset(); // discard stack contents
6655 _mark_stack->expand(); // expand the stack if possible
6656 }
6657
6658 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6659 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6660 HeapWord* addr = (HeapWord*)obj;
6661 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6662 // Oop lies in _span and isn't yet grey or black
6663 _verification_bm->mark(addr); // now grey
6664 if (!_cms_bm->isMarked(addr)) {
6665 Log(gc, verify) log;
6666 ResourceMark rm;
6667 oop(addr)->print_on(log.error_stream());
6668 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6669 fatal("... aborting");
6670 }
6671
6672 if (!_mark_stack->push(obj)) { // stack overflow
6673 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6674 assert(_mark_stack->isFull(), "Else push should have succeeded");
6675 handle_stack_overflow(addr);
6676 }
6677 // anything including and to the right of _finger
6678 // will be scanned as we iterate over the remainder of the
6679 // bit map
6680 }
6681 }
6682
6683 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6684 MemRegion span,
6685 CMSBitMap* bitMap, CMSMarkStack* markStack,
6686 HeapWord* finger, MarkFromRootsClosure* parent) :
6687 MetadataAwareOopClosure(collector->ref_processor()),
6688 _collector(collector),
6689 _span(span),
6690 _bitMap(bitMap),
6691 _markStack(markStack),
6692 _finger(finger),
6693 _parent(parent)
6694 { }
6695
6696 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6697 MemRegion span,
6698 CMSBitMap* bit_map,
6699 OopTaskQueue* work_queue,
6700 CMSMarkStack* overflow_stack,
6701 HeapWord* finger,
6702 HeapWord* volatile* global_finger_addr,
6703 ParMarkFromRootsClosure* parent) :
6704 MetadataAwareOopClosure(collector->ref_processor()),
6705 _collector(collector),
6706 _whole_span(collector->_span),
6707 _span(span),
6708 _bit_map(bit_map),
6709 _work_queue(work_queue),
6710 _overflow_stack(overflow_stack),
6711 _finger(finger),
6712 _global_finger_addr(global_finger_addr),
6713 _parent(parent)
6714 { }
6715
6716 // Assumes thread-safe access by callers, who are
6717 // responsible for mutual exclusion.
6718 void CMSCollector::lower_restart_addr(HeapWord* low) {
6719 assert(_span.contains(low), "Out of bounds addr");
6720 if (_restart_addr == NULL) {
6721 _restart_addr = low;
6722 } else {
6723 _restart_addr = MIN2(_restart_addr, low);
6724 }
6725 }
6726
6727 // Upon stack overflow, we discard (part of) the stack,
6728 // remembering the least address amongst those discarded
6729 // in CMSCollector's _restart_address.
6730 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6731 // Remember the least grey address discarded
6732 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6733 _collector->lower_restart_addr(ra);
6734 _markStack->reset(); // discard stack contents
6735 _markStack->expand(); // expand the stack if possible
6736 }
6737
6738 // Upon stack overflow, we discard (part of) the stack,
6739 // remembering the least address amongst those discarded
6740 // in CMSCollector's _restart_address.
6741 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6742 // We need to do this under a mutex to prevent other
6743 // workers from interfering with the work done below.
6744 MutexLockerEx ml(_overflow_stack->par_lock(),
6745 Mutex::_no_safepoint_check_flag);
6746 // Remember the least grey address discarded
6747 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6748 _collector->lower_restart_addr(ra);
6749 _overflow_stack->reset(); // discard stack contents
6750 _overflow_stack->expand(); // expand the stack if possible
6751 }
6752
6753 void PushOrMarkClosure::do_oop(oop obj) {
6754 // Ignore mark word because we are running concurrent with mutators.
6755 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6756 HeapWord* addr = (HeapWord*)obj;
6757 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6758 // Oop lies in _span and isn't yet grey or black
6759 _bitMap->mark(addr); // now grey
6760 if (addr < _finger) {
6761 // the bit map iteration has already either passed, or
6762 // sampled, this bit in the bit map; we'll need to
6763 // use the marking stack to scan this oop's oops.
6764 bool simulate_overflow = false;
6765 NOT_PRODUCT(
6766 if (CMSMarkStackOverflowALot &&
6767 _collector->simulate_overflow()) {
6768 // simulate a stack overflow
6769 simulate_overflow = true;
6770 }
6771 )
6772 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6773 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6774 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6775 handle_stack_overflow(addr);
6776 }
6777 }
6778 // anything including and to the right of _finger
6779 // will be scanned as we iterate over the remainder of the
6780 // bit map
6781 do_yield_check();
6782 }
6783 }
6784
6785 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6786 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6787
6788 void ParPushOrMarkClosure::do_oop(oop obj) {
6789 // Ignore mark word because we are running concurrent with mutators.
6790 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6791 HeapWord* addr = (HeapWord*)obj;
6792 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6793 // Oop lies in _span and isn't yet grey or black
6794 // We read the global_finger (volatile read) strictly after marking oop
6795 bool res = _bit_map->par_mark(addr); // now grey
6796 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6797 // Should we push this marked oop on our stack?
6798 // -- if someone else marked it, nothing to do
6799 // -- if target oop is above global finger nothing to do
6800 // -- if target oop is in chunk and above local finger
6801 // then nothing to do
6802 // -- else push on work queue
6803 if ( !res // someone else marked it, they will deal with it
6804 || (addr >= *gfa) // will be scanned in a later task
6805 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6806 return;
6807 }
6808 // the bit map iteration has already either passed, or
6809 // sampled, this bit in the bit map; we'll need to
6810 // use the marking stack to scan this oop's oops.
6811 bool simulate_overflow = false;
6812 NOT_PRODUCT(
6813 if (CMSMarkStackOverflowALot &&
6814 _collector->simulate_overflow()) {
6815 // simulate a stack overflow
6816 simulate_overflow = true;
6817 }
6818 )
6819 if (simulate_overflow ||
6820 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6821 // stack overflow
6822 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6823 // We cannot assert that the overflow stack is full because
6824 // it may have been emptied since.
6825 assert(simulate_overflow ||
6826 _work_queue->size() == _work_queue->max_elems(),
6827 "Else push should have succeeded");
6828 handle_stack_overflow(addr);
6829 }
6830 do_yield_check();
6831 }
6832 }
6833
6834 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6835 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6836
6837 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6838 MemRegion span,
6839 ReferenceProcessor* rp,
6840 CMSBitMap* bit_map,
6841 CMSBitMap* mod_union_table,
6842 CMSMarkStack* mark_stack,
6843 bool concurrent_precleaning):
6844 MetadataAwareOopClosure(rp),
6845 _collector(collector),
6846 _span(span),
6847 _bit_map(bit_map),
6848 _mod_union_table(mod_union_table),
6849 _mark_stack(mark_stack),
6850 _concurrent_precleaning(concurrent_precleaning)
6851 {
6852 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6853 }
6854
6855 // Grey object rescan during pre-cleaning and second checkpoint phases --
6856 // the non-parallel version (the parallel version appears further below.)
6857 void PushAndMarkClosure::do_oop(oop obj) {
6858 // Ignore mark word verification. If during concurrent precleaning,
6859 // the object monitor may be locked. If during the checkpoint
6860 // phases, the object may already have been reached by a different
6861 // path and may be at the end of the global overflow list (so
6862 // the mark word may be NULL).
6863 assert(obj->is_oop_or_null(true /* ignore mark word */),
6864 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6865 HeapWord* addr = (HeapWord*)obj;
6866 // Check if oop points into the CMS generation
6867 // and is not marked
6868 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6869 // a white object ...
6870 _bit_map->mark(addr); // ... now grey
6871 // push on the marking stack (grey set)
6872 bool simulate_overflow = false;
6873 NOT_PRODUCT(
6874 if (CMSMarkStackOverflowALot &&
6875 _collector->simulate_overflow()) {
6876 // simulate a stack overflow
6877 simulate_overflow = true;
6878 }
6879 )
6880 if (simulate_overflow || !_mark_stack->push(obj)) {
6881 if (_concurrent_precleaning) {
6882 // During precleaning we can just dirty the appropriate card(s)
6883 // in the mod union table, thus ensuring that the object remains
6884 // in the grey set and continue. In the case of object arrays
6885 // we need to dirty all of the cards that the object spans,
6886 // since the rescan of object arrays will be limited to the
6887 // dirty cards.
6888 // Note that no one can be interfering with us in this action
6889 // of dirtying the mod union table, so no locking or atomics
6890 // are required.
6891 if (obj->is_objArray()) {
6892 size_t sz = obj->size();
6893 HeapWord* end_card_addr = (HeapWord*)round_to(
6894 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6895 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6896 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6897 _mod_union_table->mark_range(redirty_range);
6898 } else {
6899 _mod_union_table->mark(addr);
6900 }
6901 _collector->_ser_pmc_preclean_ovflw++;
6902 } else {
6903 // During the remark phase, we need to remember this oop
6904 // in the overflow list.
6905 _collector->push_on_overflow_list(obj);
6906 _collector->_ser_pmc_remark_ovflw++;
6907 }
6908 }
6909 }
6910 }
6911
6912 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6913 MemRegion span,
6914 ReferenceProcessor* rp,
6915 CMSBitMap* bit_map,
6916 OopTaskQueue* work_queue):
6917 MetadataAwareOopClosure(rp),
6918 _collector(collector),
6919 _span(span),
6920 _bit_map(bit_map),
6921 _work_queue(work_queue)
6922 {
6923 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6924 }
6925
6926 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6927 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6928
6929 // Grey object rescan during second checkpoint phase --
6930 // the parallel version.
6931 void ParPushAndMarkClosure::do_oop(oop obj) {
6932 // In the assert below, we ignore the mark word because
6933 // this oop may point to an already visited object that is
6934 // on the overflow stack (in which case the mark word has
6935 // been hijacked for chaining into the overflow stack --
6936 // if this is the last object in the overflow stack then
6937 // its mark word will be NULL). Because this object may
6938 // have been subsequently popped off the global overflow
6939 // stack, and the mark word possibly restored to the prototypical
6940 // value, by the time we get to examined this failing assert in
6941 // the debugger, is_oop_or_null(false) may subsequently start
6942 // to hold.
6943 assert(obj->is_oop_or_null(true),
6944 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6945 HeapWord* addr = (HeapWord*)obj;
6946 // Check if oop points into the CMS generation
6947 // and is not marked
6948 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6949 // a white object ...
6950 // If we manage to "claim" the object, by being the
6951 // first thread to mark it, then we push it on our
6952 // marking stack
6953 if (_bit_map->par_mark(addr)) { // ... now grey
6954 // push on work queue (grey set)
6955 bool simulate_overflow = false;
6956 NOT_PRODUCT(
6957 if (CMSMarkStackOverflowALot &&
6958 _collector->par_simulate_overflow()) {
6959 // simulate a stack overflow
6960 simulate_overflow = true;
6961 }
6962 )
6963 if (simulate_overflow || !_work_queue->push(obj)) {
6964 _collector->par_push_on_overflow_list(obj);
6965 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6966 }
6967 } // Else, some other thread got there first
6968 }
6969 }
6970
6971 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6972 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6973
6974 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6975 Mutex* bml = _collector->bitMapLock();
6976 assert_lock_strong(bml);
6977 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6978 "CMS thread should hold CMS token");
6979
6980 bml->unlock();
6981 ConcurrentMarkSweepThread::desynchronize(true);
6982
6983 _collector->stopTimer();
6984 _collector->incrementYields();
6985
6986 // See the comment in coordinator_yield()
6987 for (unsigned i = 0; i < CMSYieldSleepCount &&
6988 ConcurrentMarkSweepThread::should_yield() &&
6989 !CMSCollector::foregroundGCIsActive(); ++i) {
6990 os::sleep(Thread::current(), 1, false);
6991 }
6992
6993 ConcurrentMarkSweepThread::synchronize(true);
6994 bml->lock();
6995
6996 _collector->startTimer();
6997 }
6998
6999 bool CMSPrecleanRefsYieldClosure::should_return() {
7000 if (ConcurrentMarkSweepThread::should_yield()) {
7001 do_yield_work();
7002 }
7003 return _collector->foregroundGCIsActive();
7004 }
7005
7006 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7007 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7008 "mr should be aligned to start at a card boundary");
7009 // We'd like to assert:
7010 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7011 // "mr should be a range of cards");
7012 // However, that would be too strong in one case -- the last
7013 // partition ends at _unallocated_block which, in general, can be
7014 // an arbitrary boundary, not necessarily card aligned.
7015 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7016 _space->object_iterate_mem(mr, &_scan_cl);
7017 }
7018
7019 SweepClosure::SweepClosure(CMSCollector* collector,
7020 ConcurrentMarkSweepGeneration* g,
7021 CMSBitMap* bitMap, bool should_yield) :
7022 _collector(collector),
7023 _g(g),
7024 _sp(g->cmsSpace()),
7025 _limit(_sp->sweep_limit()),
7026 _freelistLock(_sp->freelistLock()),
7027 _bitMap(bitMap),
7028 _yield(should_yield),
7029 _inFreeRange(false), // No free range at beginning of sweep
7030 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7031 _lastFreeRangeCoalesced(false),
7032 _freeFinger(g->used_region().start())
7033 {
7034 NOT_PRODUCT(
7035 _numObjectsFreed = 0;
7036 _numWordsFreed = 0;
7037 _numObjectsLive = 0;
7038 _numWordsLive = 0;
7039 _numObjectsAlreadyFree = 0;
7040 _numWordsAlreadyFree = 0;
7041 _last_fc = NULL;
7042
7043 _sp->initializeIndexedFreeListArrayReturnedBytes();
7044 _sp->dictionary()->initialize_dict_returned_bytes();
7045 )
7046 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7047 "sweep _limit out of bounds");
7048 log_develop_trace(gc, sweep)("====================");
7049 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7050 }
7051
7052 void SweepClosure::print_on(outputStream* st) const {
7053 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7054 p2i(_sp->bottom()), p2i(_sp->end()));
7055 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7056 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7057 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7058 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7059 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7060 }
7061
7062 #ifndef PRODUCT
7063 // Assertion checking only: no useful work in product mode --
7064 // however, if any of the flags below become product flags,
7065 // you may need to review this code to see if it needs to be
7066 // enabled in product mode.
7067 SweepClosure::~SweepClosure() {
7068 assert_lock_strong(_freelistLock);
7069 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7070 "sweep _limit out of bounds");
7071 if (inFreeRange()) {
7072 Log(gc, sweep) log;
7073 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7074 ResourceMark rm;
7075 print_on(log.error_stream());
7076 ShouldNotReachHere();
7077 }
7078
7079 if (log_is_enabled(Debug, gc, sweep)) {
7080 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7081 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7082 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7083 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7084 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7085 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7086 }
7087
7088 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7089 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7090 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7091 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7092 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7093 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7094 }
7095 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7096 log_develop_trace(gc, sweep)("================");
7097 }
7098 #endif // PRODUCT
7099
7100 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7101 bool freeRangeInFreeLists) {
7102 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7103 p2i(freeFinger), freeRangeInFreeLists);
7104 assert(!inFreeRange(), "Trampling existing free range");
7105 set_inFreeRange(true);
7106 set_lastFreeRangeCoalesced(false);
7107
7108 set_freeFinger(freeFinger);
7109 set_freeRangeInFreeLists(freeRangeInFreeLists);
7110 if (CMSTestInFreeList) {
7111 if (freeRangeInFreeLists) {
7112 FreeChunk* fc = (FreeChunk*) freeFinger;
7113 assert(fc->is_free(), "A chunk on the free list should be free.");
7114 assert(fc->size() > 0, "Free range should have a size");
7115 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7116 }
7117 }
7118 }
7119
7120 // Note that the sweeper runs concurrently with mutators. Thus,
7121 // it is possible for direct allocation in this generation to happen
7122 // in the middle of the sweep. Note that the sweeper also coalesces
7123 // contiguous free blocks. Thus, unless the sweeper and the allocator
7124 // synchronize appropriately freshly allocated blocks may get swept up.
7125 // This is accomplished by the sweeper locking the free lists while
7126 // it is sweeping. Thus blocks that are determined to be free are
7127 // indeed free. There is however one additional complication:
7128 // blocks that have been allocated since the final checkpoint and
7129 // mark, will not have been marked and so would be treated as
7130 // unreachable and swept up. To prevent this, the allocator marks
7131 // the bit map when allocating during the sweep phase. This leads,
7132 // however, to a further complication -- objects may have been allocated
7133 // but not yet initialized -- in the sense that the header isn't yet
7134 // installed. The sweeper can not then determine the size of the block
7135 // in order to skip over it. To deal with this case, we use a technique
7136 // (due to Printezis) to encode such uninitialized block sizes in the
7137 // bit map. Since the bit map uses a bit per every HeapWord, but the
7138 // CMS generation has a minimum object size of 3 HeapWords, it follows
7139 // that "normal marks" won't be adjacent in the bit map (there will
7140 // always be at least two 0 bits between successive 1 bits). We make use
7141 // of these "unused" bits to represent uninitialized blocks -- the bit
7142 // corresponding to the start of the uninitialized object and the next
7143 // bit are both set. Finally, a 1 bit marks the end of the object that
7144 // started with the two consecutive 1 bits to indicate its potentially
7145 // uninitialized state.
7146
7147 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7148 FreeChunk* fc = (FreeChunk*)addr;
7149 size_t res;
7150
7151 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7152 // than "addr == _limit" because although _limit was a block boundary when
7153 // we started the sweep, it may no longer be one because heap expansion
7154 // may have caused us to coalesce the block ending at the address _limit
7155 // with a newly expanded chunk (this happens when _limit was set to the
7156 // previous _end of the space), so we may have stepped past _limit:
7157 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7158 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7159 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7160 "sweep _limit out of bounds");
7161 assert(addr < _sp->end(), "addr out of bounds");
7162 // Flush any free range we might be holding as a single
7163 // coalesced chunk to the appropriate free list.
7164 if (inFreeRange()) {
7165 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7166 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7167 flush_cur_free_chunk(freeFinger(),
7168 pointer_delta(addr, freeFinger()));
7169 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7170 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7171 lastFreeRangeCoalesced() ? 1 : 0);
7172 }
7173
7174 // help the iterator loop finish
7175 return pointer_delta(_sp->end(), addr);
7176 }
7177
7178 assert(addr < _limit, "sweep invariant");
7179 // check if we should yield
7180 do_yield_check(addr);
7181 if (fc->is_free()) {
7182 // Chunk that is already free
7183 res = fc->size();
7184 do_already_free_chunk(fc);
7185 debug_only(_sp->verifyFreeLists());
7186 // If we flush the chunk at hand in lookahead_and_flush()
7187 // and it's coalesced with a preceding chunk, then the
7188 // process of "mangling" the payload of the coalesced block
7189 // will cause erasure of the size information from the
7190 // (erstwhile) header of all the coalesced blocks but the
7191 // first, so the first disjunct in the assert will not hold
7192 // in that specific case (in which case the second disjunct
7193 // will hold).
7194 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7195 "Otherwise the size info doesn't change at this step");
7196 NOT_PRODUCT(
7197 _numObjectsAlreadyFree++;
7198 _numWordsAlreadyFree += res;
7199 )
7200 NOT_PRODUCT(_last_fc = fc;)
7201 } else if (!_bitMap->isMarked(addr)) {
7202 // Chunk is fresh garbage
7203 res = do_garbage_chunk(fc);
7204 debug_only(_sp->verifyFreeLists());
7205 NOT_PRODUCT(
7206 _numObjectsFreed++;
7207 _numWordsFreed += res;
7208 )
7209 } else {
7210 // Chunk that is alive.
7211 res = do_live_chunk(fc);
7212 debug_only(_sp->verifyFreeLists());
7213 NOT_PRODUCT(
7214 _numObjectsLive++;
7215 _numWordsLive += res;
7216 )
7217 }
7218 return res;
7219 }
7220
7221 // For the smart allocation, record following
7222 // split deaths - a free chunk is removed from its free list because
7223 // it is being split into two or more chunks.
7224 // split birth - a free chunk is being added to its free list because
7225 // a larger free chunk has been split and resulted in this free chunk.
7226 // coal death - a free chunk is being removed from its free list because
7227 // it is being coalesced into a large free chunk.
7228 // coal birth - a free chunk is being added to its free list because
7229 // it was created when two or more free chunks where coalesced into
7230 // this free chunk.
7231 //
7232 // These statistics are used to determine the desired number of free
7233 // chunks of a given size. The desired number is chosen to be relative
7234 // to the end of a CMS sweep. The desired number at the end of a sweep
7235 // is the
7236 // count-at-end-of-previous-sweep (an amount that was enough)
7237 // - count-at-beginning-of-current-sweep (the excess)
7238 // + split-births (gains in this size during interval)
7239 // - split-deaths (demands on this size during interval)
7240 // where the interval is from the end of one sweep to the end of the
7241 // next.
7242 //
7243 // When sweeping the sweeper maintains an accumulated chunk which is
7244 // the chunk that is made up of chunks that have been coalesced. That
7245 // will be termed the left-hand chunk. A new chunk of garbage that
7246 // is being considered for coalescing will be referred to as the
7247 // right-hand chunk.
7248 //
7249 // When making a decision on whether to coalesce a right-hand chunk with
7250 // the current left-hand chunk, the current count vs. the desired count
7251 // of the left-hand chunk is considered. Also if the right-hand chunk
7252 // is near the large chunk at the end of the heap (see
7253 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7254 // left-hand chunk is coalesced.
7255 //
7256 // When making a decision about whether to split a chunk, the desired count
7257 // vs. the current count of the candidate to be split is also considered.
7258 // If the candidate is underpopulated (currently fewer chunks than desired)
7259 // a chunk of an overpopulated (currently more chunks than desired) size may
7260 // be chosen. The "hint" associated with a free list, if non-null, points
7261 // to a free list which may be overpopulated.
7262 //
7263
7264 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7265 const size_t size = fc->size();
7266 // Chunks that cannot be coalesced are not in the
7267 // free lists.
7268 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7269 assert(_sp->verify_chunk_in_free_list(fc),
7270 "free chunk should be in free lists");
7271 }
7272 // a chunk that is already free, should not have been
7273 // marked in the bit map
7274 HeapWord* const addr = (HeapWord*) fc;
7275 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7276 // Verify that the bit map has no bits marked between
7277 // addr and purported end of this block.
7278 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7279
7280 // Some chunks cannot be coalesced under any circumstances.
7281 // See the definition of cantCoalesce().
7282 if (!fc->cantCoalesce()) {
7283 // This chunk can potentially be coalesced.
7284 // All the work is done in
7285 do_post_free_or_garbage_chunk(fc, size);
7286 // Note that if the chunk is not coalescable (the else arm
7287 // below), we unconditionally flush, without needing to do
7288 // a "lookahead," as we do below.
7289 if (inFreeRange()) lookahead_and_flush(fc, size);
7290 } else {
7291 // Code path common to both original and adaptive free lists.
7292
7293 // cant coalesce with previous block; this should be treated
7294 // as the end of a free run if any
7295 if (inFreeRange()) {
7296 // we kicked some butt; time to pick up the garbage
7297 assert(freeFinger() < addr, "freeFinger points too high");
7298 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7299 }
7300 // else, nothing to do, just continue
7301 }
7302 }
7303
7304 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7305 // This is a chunk of garbage. It is not in any free list.
7306 // Add it to a free list or let it possibly be coalesced into
7307 // a larger chunk.
7308 HeapWord* const addr = (HeapWord*) fc;
7309 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7310
7311 // Verify that the bit map has no bits marked between
7312 // addr and purported end of just dead object.
7313 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7314 do_post_free_or_garbage_chunk(fc, size);
7315
7316 assert(_limit >= addr + size,
7317 "A freshly garbage chunk can't possibly straddle over _limit");
7318 if (inFreeRange()) lookahead_and_flush(fc, size);
7319 return size;
7320 }
7321
7322 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7323 HeapWord* addr = (HeapWord*) fc;
7324 // The sweeper has just found a live object. Return any accumulated
7325 // left hand chunk to the free lists.
7326 if (inFreeRange()) {
7327 assert(freeFinger() < addr, "freeFinger points too high");
7328 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7329 }
7330
7331 // This object is live: we'd normally expect this to be
7332 // an oop, and like to assert the following:
7333 // assert(oop(addr)->is_oop(), "live block should be an oop");
7334 // However, as we commented above, this may be an object whose
7335 // header hasn't yet been initialized.
7336 size_t size;
7337 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7338 if (_bitMap->isMarked(addr + 1)) {
7339 // Determine the size from the bit map, rather than trying to
7340 // compute it from the object header.
7341 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7342 size = pointer_delta(nextOneAddr + 1, addr);
7343 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7344 "alignment problem");
7345
7346 #ifdef ASSERT
7347 if (oop(addr)->klass_or_null_acquire() != NULL) {
7348 // Ignore mark word because we are running concurrent with mutators
7349 assert(oop(addr)->is_oop(true), "live block should be an oop");
7350 assert(size ==
7351 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7352 "P-mark and computed size do not agree");
7353 }
7354 #endif
7355
7356 } else {
7357 // This should be an initialized object that's alive.
7358 assert(oop(addr)->klass_or_null_acquire() != NULL,
7359 "Should be an initialized object");
7360 // Ignore mark word because we are running concurrent with mutators
7361 assert(oop(addr)->is_oop(true), "live block should be an oop");
7362 // Verify that the bit map has no bits marked between
7363 // addr and purported end of this block.
7364 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7365 assert(size >= 3, "Necessary for Printezis marks to work");
7366 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7367 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7368 }
7369 return size;
7370 }
7371
7372 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7373 size_t chunkSize) {
7374 // do_post_free_or_garbage_chunk() should only be called in the case
7375 // of the adaptive free list allocator.
7376 const bool fcInFreeLists = fc->is_free();
7377 assert((HeapWord*)fc <= _limit, "sweep invariant");
7378 if (CMSTestInFreeList && fcInFreeLists) {
7379 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7380 }
7381
7382 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7383
7384 HeapWord* const fc_addr = (HeapWord*) fc;
7385
7386 bool coalesce = false;
7387 const size_t left = pointer_delta(fc_addr, freeFinger());
7388 const size_t right = chunkSize;
7389 switch (FLSCoalescePolicy) {
7390 // numeric value forms a coalition aggressiveness metric
7391 case 0: { // never coalesce
7392 coalesce = false;
7393 break;
7394 }
7395 case 1: { // coalesce if left & right chunks on overpopulated lists
7396 coalesce = _sp->coalOverPopulated(left) &&
7397 _sp->coalOverPopulated(right);
7398 break;
7399 }
7400 case 2: { // coalesce if left chunk on overpopulated list (default)
7401 coalesce = _sp->coalOverPopulated(left);
7402 break;
7403 }
7404 case 3: { // coalesce if left OR right chunk on overpopulated list
7405 coalesce = _sp->coalOverPopulated(left) ||
7406 _sp->coalOverPopulated(right);
7407 break;
7408 }
7409 case 4: { // always coalesce
7410 coalesce = true;
7411 break;
7412 }
7413 default:
7414 ShouldNotReachHere();
7415 }
7416
7417 // Should the current free range be coalesced?
7418 // If the chunk is in a free range and either we decided to coalesce above
7419 // or the chunk is near the large block at the end of the heap
7420 // (isNearLargestChunk() returns true), then coalesce this chunk.
7421 const bool doCoalesce = inFreeRange()
7422 && (coalesce || _g->isNearLargestChunk(fc_addr));
7423 if (doCoalesce) {
7424 // Coalesce the current free range on the left with the new
7425 // chunk on the right. If either is on a free list,
7426 // it must be removed from the list and stashed in the closure.
7427 if (freeRangeInFreeLists()) {
7428 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7429 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7430 "Size of free range is inconsistent with chunk size.");
7431 if (CMSTestInFreeList) {
7432 assert(_sp->verify_chunk_in_free_list(ffc),
7433 "Chunk is not in free lists");
7434 }
7435 _sp->coalDeath(ffc->size());
7436 _sp->removeFreeChunkFromFreeLists(ffc);
7437 set_freeRangeInFreeLists(false);
7438 }
7439 if (fcInFreeLists) {
7440 _sp->coalDeath(chunkSize);
7441 assert(fc->size() == chunkSize,
7442 "The chunk has the wrong size or is not in the free lists");
7443 _sp->removeFreeChunkFromFreeLists(fc);
7444 }
7445 set_lastFreeRangeCoalesced(true);
7446 print_free_block_coalesced(fc);
7447 } else { // not in a free range and/or should not coalesce
7448 // Return the current free range and start a new one.
7449 if (inFreeRange()) {
7450 // In a free range but cannot coalesce with the right hand chunk.
7451 // Put the current free range into the free lists.
7452 flush_cur_free_chunk(freeFinger(),
7453 pointer_delta(fc_addr, freeFinger()));
7454 }
7455 // Set up for new free range. Pass along whether the right hand
7456 // chunk is in the free lists.
7457 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7458 }
7459 }
7460
7461 // Lookahead flush:
7462 // If we are tracking a free range, and this is the last chunk that
7463 // we'll look at because its end crosses past _limit, we'll preemptively
7464 // flush it along with any free range we may be holding on to. Note that
7465 // this can be the case only for an already free or freshly garbage
7466 // chunk. If this block is an object, it can never straddle
7467 // over _limit. The "straddling" occurs when _limit is set at
7468 // the previous end of the space when this cycle started, and
7469 // a subsequent heap expansion caused the previously co-terminal
7470 // free block to be coalesced with the newly expanded portion,
7471 // thus rendering _limit a non-block-boundary making it dangerous
7472 // for the sweeper to step over and examine.
7473 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7474 assert(inFreeRange(), "Should only be called if currently in a free range.");
7475 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7476 assert(_sp->used_region().contains(eob - 1),
7477 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7478 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7479 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7480 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7481 if (eob >= _limit) {
7482 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7483 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7484 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7485 "[" PTR_FORMAT "," PTR_FORMAT ")",
7486 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7487 // Return the storage we are tracking back into the free lists.
7488 log_develop_trace(gc, sweep)("Flushing ... ");
7489 assert(freeFinger() < eob, "Error");
7490 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7491 }
7492 }
7493
7494 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7495 assert(inFreeRange(), "Should only be called if currently in a free range.");
7496 assert(size > 0,
7497 "A zero sized chunk cannot be added to the free lists.");
7498 if (!freeRangeInFreeLists()) {
7499 if (CMSTestInFreeList) {
7500 FreeChunk* fc = (FreeChunk*) chunk;
7501 fc->set_size(size);
7502 assert(!_sp->verify_chunk_in_free_list(fc),
7503 "chunk should not be in free lists yet");
7504 }
7505 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7506 // A new free range is going to be starting. The current
7507 // free range has not been added to the free lists yet or
7508 // was removed so add it back.
7509 // If the current free range was coalesced, then the death
7510 // of the free range was recorded. Record a birth now.
7511 if (lastFreeRangeCoalesced()) {
7512 _sp->coalBirth(size);
7513 }
7514 _sp->addChunkAndRepairOffsetTable(chunk, size,
7515 lastFreeRangeCoalesced());
7516 } else {
7517 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7518 }
7519 set_inFreeRange(false);
7520 set_freeRangeInFreeLists(false);
7521 }
7522
7523 // We take a break if we've been at this for a while,
7524 // so as to avoid monopolizing the locks involved.
7525 void SweepClosure::do_yield_work(HeapWord* addr) {
7526 // Return current free chunk being used for coalescing (if any)
7527 // to the appropriate freelist. After yielding, the next
7528 // free block encountered will start a coalescing range of
7529 // free blocks. If the next free block is adjacent to the
7530 // chunk just flushed, they will need to wait for the next
7531 // sweep to be coalesced.
7532 if (inFreeRange()) {
7533 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7534 }
7535
7536 // First give up the locks, then yield, then re-lock.
7537 // We should probably use a constructor/destructor idiom to
7538 // do this unlock/lock or modify the MutexUnlocker class to
7539 // serve our purpose. XXX
7540 assert_lock_strong(_bitMap->lock());
7541 assert_lock_strong(_freelistLock);
7542 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7543 "CMS thread should hold CMS token");
7544 _bitMap->lock()->unlock();
7545 _freelistLock->unlock();
7546 ConcurrentMarkSweepThread::desynchronize(true);
7547 _collector->stopTimer();
7548 _collector->incrementYields();
7549
7550 // See the comment in coordinator_yield()
7551 for (unsigned i = 0; i < CMSYieldSleepCount &&
7552 ConcurrentMarkSweepThread::should_yield() &&
7553 !CMSCollector::foregroundGCIsActive(); ++i) {
7554 os::sleep(Thread::current(), 1, false);
7555 }
7556
7557 ConcurrentMarkSweepThread::synchronize(true);
7558 _freelistLock->lock();
7559 _bitMap->lock()->lock_without_safepoint_check();
7560 _collector->startTimer();
7561 }
7562
7563 #ifndef PRODUCT
7564 // This is actually very useful in a product build if it can
7565 // be called from the debugger. Compile it into the product
7566 // as needed.
7567 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7568 return debug_cms_space->verify_chunk_in_free_list(fc);
7569 }
7570 #endif
7571
7572 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7573 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7574 p2i(fc), fc->size());
7575 }
7576
7577 // CMSIsAliveClosure
7578 bool CMSIsAliveClosure::do_object_b(oop obj) {
7579 HeapWord* addr = (HeapWord*)obj;
7580 return addr != NULL &&
7581 (!_span.contains(addr) || _bit_map->isMarked(addr));
7582 }
7583
7584
7585 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7586 MemRegion span,
7587 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7588 bool cpc):
7589 _collector(collector),
7590 _span(span),
7591 _bit_map(bit_map),
7592 _mark_stack(mark_stack),
7593 _concurrent_precleaning(cpc) {
7594 assert(!_span.is_empty(), "Empty span could spell trouble");
7595 }
7596
7597
7598 // CMSKeepAliveClosure: the serial version
7599 void CMSKeepAliveClosure::do_oop(oop obj) {
7600 HeapWord* addr = (HeapWord*)obj;
7601 if (_span.contains(addr) &&
7602 !_bit_map->isMarked(addr)) {
7603 _bit_map->mark(addr);
7604 bool simulate_overflow = false;
7605 NOT_PRODUCT(
7606 if (CMSMarkStackOverflowALot &&
7607 _collector->simulate_overflow()) {
7608 // simulate a stack overflow
7609 simulate_overflow = true;
7610 }
7611 )
7612 if (simulate_overflow || !_mark_stack->push(obj)) {
7613 if (_concurrent_precleaning) {
7614 // We dirty the overflown object and let the remark
7615 // phase deal with it.
7616 assert(_collector->overflow_list_is_empty(), "Error");
7617 // In the case of object arrays, we need to dirty all of
7618 // the cards that the object spans. No locking or atomics
7619 // are needed since no one else can be mutating the mod union
7620 // table.
7621 if (obj->is_objArray()) {
7622 size_t sz = obj->size();
7623 HeapWord* end_card_addr =
7624 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7625 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7626 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7627 _collector->_modUnionTable.mark_range(redirty_range);
7628 } else {
7629 _collector->_modUnionTable.mark(addr);
7630 }
7631 _collector->_ser_kac_preclean_ovflw++;
7632 } else {
7633 _collector->push_on_overflow_list(obj);
7634 _collector->_ser_kac_ovflw++;
7635 }
7636 }
7637 }
7638 }
7639
7640 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7641 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7642
7643 // CMSParKeepAliveClosure: a parallel version of the above.
7644 // The work queues are private to each closure (thread),
7645 // but (may be) available for stealing by other threads.
7646 void CMSParKeepAliveClosure::do_oop(oop obj) {
7647 HeapWord* addr = (HeapWord*)obj;
7648 if (_span.contains(addr) &&
7649 !_bit_map->isMarked(addr)) {
7650 // In general, during recursive tracing, several threads
7651 // may be concurrently getting here; the first one to
7652 // "tag" it, claims it.
7653 if (_bit_map->par_mark(addr)) {
7654 bool res = _work_queue->push(obj);
7655 assert(res, "Low water mark should be much less than capacity");
7656 // Do a recursive trim in the hope that this will keep
7657 // stack usage lower, but leave some oops for potential stealers
7658 trim_queue(_low_water_mark);
7659 } // Else, another thread got there first
7660 }
7661 }
7662
7663 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7664 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7665
7666 void CMSParKeepAliveClosure::trim_queue(uint max) {
7667 while (_work_queue->size() > max) {
7668 oop new_oop;
7669 if (_work_queue->pop_local(new_oop)) {
7670 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7671 assert(_bit_map->isMarked((HeapWord*)new_oop),
7672 "no white objects on this stack!");
7673 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7674 // iterate over the oops in this oop, marking and pushing
7675 // the ones in CMS heap (i.e. in _span).
7676 new_oop->oop_iterate(&_mark_and_push);
7677 }
7678 }
7679 }
7680
7681 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7682 CMSCollector* collector,
7683 MemRegion span, CMSBitMap* bit_map,
7684 OopTaskQueue* work_queue):
7685 _collector(collector),
7686 _span(span),
7687 _bit_map(bit_map),
7688 _work_queue(work_queue) { }
7689
7690 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7691 HeapWord* addr = (HeapWord*)obj;
7692 if (_span.contains(addr) &&
7693 !_bit_map->isMarked(addr)) {
7694 if (_bit_map->par_mark(addr)) {
7695 bool simulate_overflow = false;
7696 NOT_PRODUCT(
7697 if (CMSMarkStackOverflowALot &&
7698 _collector->par_simulate_overflow()) {
7699 // simulate a stack overflow
7700 simulate_overflow = true;
7701 }
7702 )
7703 if (simulate_overflow || !_work_queue->push(obj)) {
7704 _collector->par_push_on_overflow_list(obj);
7705 _collector->_par_kac_ovflw++;
7706 }
7707 } // Else another thread got there already
7708 }
7709 }
7710
7711 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7712 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7713
7714 //////////////////////////////////////////////////////////////////
7715 // CMSExpansionCause /////////////////////////////
7716 //////////////////////////////////////////////////////////////////
7717 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7718 switch (cause) {
7719 case _no_expansion:
7720 return "No expansion";
7721 case _satisfy_free_ratio:
7722 return "Free ratio";
7723 case _satisfy_promotion:
7724 return "Satisfy promotion";
7725 case _satisfy_allocation:
7726 return "allocation";
7727 case _allocate_par_lab:
7728 return "Par LAB";
7729 case _allocate_par_spooling_space:
7730 return "Par Spooling Space";
7731 case _adaptive_size_policy:
7732 return "Ergonomics";
7733 default:
7734 return "unknown";
7735 }
7736 }
7737
7738 void CMSDrainMarkingStackClosure::do_void() {
7739 // the max number to take from overflow list at a time
7740 const size_t num = _mark_stack->capacity()/4;
7741 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7742 "Overflow list should be NULL during concurrent phases");
7743 while (!_mark_stack->isEmpty() ||
7744 // if stack is empty, check the overflow list
7745 _collector->take_from_overflow_list(num, _mark_stack)) {
7746 oop obj = _mark_stack->pop();
7747 HeapWord* addr = (HeapWord*)obj;
7748 assert(_span.contains(addr), "Should be within span");
7749 assert(_bit_map->isMarked(addr), "Should be marked");
7750 assert(obj->is_oop(), "Should be an oop");
7751 obj->oop_iterate(_keep_alive);
7752 }
7753 }
7754
7755 void CMSParDrainMarkingStackClosure::do_void() {
7756 // drain queue
7757 trim_queue(0);
7758 }
7759
7760 // Trim our work_queue so its length is below max at return
7761 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7762 while (_work_queue->size() > max) {
7763 oop new_oop;
7764 if (_work_queue->pop_local(new_oop)) {
7765 assert(new_oop->is_oop(), "Expected an oop");
7766 assert(_bit_map->isMarked((HeapWord*)new_oop),
7767 "no white objects on this stack!");
7768 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7769 // iterate over the oops in this oop, marking and pushing
7770 // the ones in CMS heap (i.e. in _span).
7771 new_oop->oop_iterate(&_mark_and_push);
7772 }
7773 }
7774 }
7775
7776 ////////////////////////////////////////////////////////////////////
7777 // Support for Marking Stack Overflow list handling and related code
7778 ////////////////////////////////////////////////////////////////////
7779 // Much of the following code is similar in shape and spirit to the
7780 // code used in ParNewGC. We should try and share that code
7781 // as much as possible in the future.
7782
7783 #ifndef PRODUCT
7784 // Debugging support for CMSStackOverflowALot
7785
7786 // It's OK to call this multi-threaded; the worst thing
7787 // that can happen is that we'll get a bunch of closely
7788 // spaced simulated overflows, but that's OK, in fact
7789 // probably good as it would exercise the overflow code
7790 // under contention.
7791 bool CMSCollector::simulate_overflow() {
7792 if (_overflow_counter-- <= 0) { // just being defensive
7793 _overflow_counter = CMSMarkStackOverflowInterval;
7794 return true;
7795 } else {
7796 return false;
7797 }
7798 }
7799
7800 bool CMSCollector::par_simulate_overflow() {
7801 return simulate_overflow();
7802 }
7803 #endif
7804
7805 // Single-threaded
7806 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7807 assert(stack->isEmpty(), "Expected precondition");
7808 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7809 size_t i = num;
7810 oop cur = _overflow_list;
7811 const markOop proto = markOopDesc::prototype();
7812 NOT_PRODUCT(ssize_t n = 0;)
7813 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7814 next = oop(cur->mark());
7815 cur->set_mark(proto); // until proven otherwise
7816 assert(cur->is_oop(), "Should be an oop");
7817 bool res = stack->push(cur);
7818 assert(res, "Bit off more than can chew?");
7819 NOT_PRODUCT(n++;)
7820 }
7821 _overflow_list = cur;
7822 #ifndef PRODUCT
7823 assert(_num_par_pushes >= n, "Too many pops?");
7824 _num_par_pushes -=n;
7825 #endif
7826 return !stack->isEmpty();
7827 }
7828
7829 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7830 // (MT-safe) Get a prefix of at most "num" from the list.
7831 // The overflow list is chained through the mark word of
7832 // each object in the list. We fetch the entire list,
7833 // break off a prefix of the right size and return the
7834 // remainder. If other threads try to take objects from
7835 // the overflow list at that time, they will wait for
7836 // some time to see if data becomes available. If (and
7837 // only if) another thread places one or more object(s)
7838 // on the global list before we have returned the suffix
7839 // to the global list, we will walk down our local list
7840 // to find its end and append the global list to
7841 // our suffix before returning it. This suffix walk can
7842 // prove to be expensive (quadratic in the amount of traffic)
7843 // when there are many objects in the overflow list and
7844 // there is much producer-consumer contention on the list.
7845 // *NOTE*: The overflow list manipulation code here and
7846 // in ParNewGeneration:: are very similar in shape,
7847 // except that in the ParNew case we use the old (from/eden)
7848 // copy of the object to thread the list via its klass word.
7849 // Because of the common code, if you make any changes in
7850 // the code below, please check the ParNew version to see if
7851 // similar changes might be needed.
7852 // CR 6797058 has been filed to consolidate the common code.
7853 bool CMSCollector::par_take_from_overflow_list(size_t num,
7854 OopTaskQueue* work_q,
7855 int no_of_gc_threads) {
7856 assert(work_q->size() == 0, "First empty local work queue");
7857 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7858 if (_overflow_list == NULL) {
7859 return false;
7860 }
7861 // Grab the entire list; we'll put back a suffix
7862 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7863 Thread* tid = Thread::current();
7864 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7865 // set to ParallelGCThreads.
7866 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7867 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7868 // If the list is busy, we spin for a short while,
7869 // sleeping between attempts to get the list.
7870 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7871 os::sleep(tid, sleep_time_millis, false);
7872 if (_overflow_list == NULL) {
7873 // Nothing left to take
7874 return false;
7875 } else if (_overflow_list != BUSY) {
7876 // Try and grab the prefix
7877 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7878 }
7879 }
7880 // If the list was found to be empty, or we spun long
7881 // enough, we give up and return empty-handed. If we leave
7882 // the list in the BUSY state below, it must be the case that
7883 // some other thread holds the overflow list and will set it
7884 // to a non-BUSY state in the future.
7885 if (prefix == NULL || prefix == BUSY) {
7886 // Nothing to take or waited long enough
7887 if (prefix == NULL) {
7888 // Write back the NULL in case we overwrote it with BUSY above
7889 // and it is still the same value.
7890 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7891 }
7892 return false;
7893 }
7894 assert(prefix != NULL && prefix != BUSY, "Error");
7895 size_t i = num;
7896 oop cur = prefix;
7897 // Walk down the first "num" objects, unless we reach the end.
7898 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7899 if (cur->mark() == NULL) {
7900 // We have "num" or fewer elements in the list, so there
7901 // is nothing to return to the global list.
7902 // Write back the NULL in lieu of the BUSY we wrote
7903 // above, if it is still the same value.
7904 if (_overflow_list == BUSY) {
7905 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7906 }
7907 } else {
7908 // Chop off the suffix and return it to the global list.
7909 assert(cur->mark() != BUSY, "Error");
7910 oop suffix_head = cur->mark(); // suffix will be put back on global list
7911 cur->set_mark(NULL); // break off suffix
7912 // It's possible that the list is still in the empty(busy) state
7913 // we left it in a short while ago; in that case we may be
7914 // able to place back the suffix without incurring the cost
7915 // of a walk down the list.
7916 oop observed_overflow_list = _overflow_list;
7917 oop cur_overflow_list = observed_overflow_list;
7918 bool attached = false;
7919 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7920 observed_overflow_list =
7921 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7922 if (cur_overflow_list == observed_overflow_list) {
7923 attached = true;
7924 break;
7925 } else cur_overflow_list = observed_overflow_list;
7926 }
7927 if (!attached) {
7928 // Too bad, someone else sneaked in (at least) an element; we'll need
7929 // to do a splice. Find tail of suffix so we can prepend suffix to global
7930 // list.
7931 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7932 oop suffix_tail = cur;
7933 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7934 "Tautology");
7935 observed_overflow_list = _overflow_list;
7936 do {
7937 cur_overflow_list = observed_overflow_list;
7938 if (cur_overflow_list != BUSY) {
7939 // Do the splice ...
7940 suffix_tail->set_mark(markOop(cur_overflow_list));
7941 } else { // cur_overflow_list == BUSY
7942 suffix_tail->set_mark(NULL);
7943 }
7944 // ... and try to place spliced list back on overflow_list ...
7945 observed_overflow_list =
7946 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7947 } while (cur_overflow_list != observed_overflow_list);
7948 // ... until we have succeeded in doing so.
7949 }
7950 }
7951
7952 // Push the prefix elements on work_q
7953 assert(prefix != NULL, "control point invariant");
7954 const markOop proto = markOopDesc::prototype();
7955 oop next;
7956 NOT_PRODUCT(ssize_t n = 0;)
7957 for (cur = prefix; cur != NULL; cur = next) {
7958 next = oop(cur->mark());
7959 cur->set_mark(proto); // until proven otherwise
7960 assert(cur->is_oop(), "Should be an oop");
7961 bool res = work_q->push(cur);
7962 assert(res, "Bit off more than we can chew?");
7963 NOT_PRODUCT(n++;)
7964 }
7965 #ifndef PRODUCT
7966 assert(_num_par_pushes >= n, "Too many pops?");
7967 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7968 #endif
7969 return true;
7970 }
7971
7972 // Single-threaded
7973 void CMSCollector::push_on_overflow_list(oop p) {
7974 NOT_PRODUCT(_num_par_pushes++;)
7975 assert(p->is_oop(), "Not an oop");
7976 preserve_mark_if_necessary(p);
7977 p->set_mark((markOop)_overflow_list);
7978 _overflow_list = p;
7979 }
7980
7981 // Multi-threaded; use CAS to prepend to overflow list
7982 void CMSCollector::par_push_on_overflow_list(oop p) {
7983 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7984 assert(p->is_oop(), "Not an oop");
7985 par_preserve_mark_if_necessary(p);
7986 oop observed_overflow_list = _overflow_list;
7987 oop cur_overflow_list;
7988 do {
7989 cur_overflow_list = observed_overflow_list;
7990 if (cur_overflow_list != BUSY) {
7991 p->set_mark(markOop(cur_overflow_list));
7992 } else {
7993 p->set_mark(NULL);
7994 }
7995 observed_overflow_list =
7996 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7997 } while (cur_overflow_list != observed_overflow_list);
7998 }
7999 #undef BUSY
8000
8001 // Single threaded
8002 // General Note on GrowableArray: pushes may silently fail
8003 // because we are (temporarily) out of C-heap for expanding
8004 // the stack. The problem is quite ubiquitous and affects
8005 // a lot of code in the JVM. The prudent thing for GrowableArray
8006 // to do (for now) is to exit with an error. However, that may
8007 // be too draconian in some cases because the caller may be
8008 // able to recover without much harm. For such cases, we
8009 // should probably introduce a "soft_push" method which returns
8010 // an indication of success or failure with the assumption that
8011 // the caller may be able to recover from a failure; code in
8012 // the VM can then be changed, incrementally, to deal with such
8013 // failures where possible, thus, incrementally hardening the VM
8014 // in such low resource situations.
8015 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8016 _preserved_oop_stack.push(p);
8017 _preserved_mark_stack.push(m);
8018 assert(m == p->mark(), "Mark word changed");
8019 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8020 "bijection");
8021 }
8022
8023 // Single threaded
8024 void CMSCollector::preserve_mark_if_necessary(oop p) {
8025 markOop m = p->mark();
8026 if (m->must_be_preserved(p)) {
8027 preserve_mark_work(p, m);
8028 }
8029 }
8030
8031 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8032 markOop m = p->mark();
8033 if (m->must_be_preserved(p)) {
8034 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8035 // Even though we read the mark word without holding
8036 // the lock, we are assured that it will not change
8037 // because we "own" this oop, so no other thread can
8038 // be trying to push it on the overflow list; see
8039 // the assertion in preserve_mark_work() that checks
8040 // that m == p->mark().
8041 preserve_mark_work(p, m);
8042 }
8043 }
8044
8045 // We should be able to do this multi-threaded,
8046 // a chunk of stack being a task (this is
8047 // correct because each oop only ever appears
8048 // once in the overflow list. However, it's
8049 // not very easy to completely overlap this with
8050 // other operations, so will generally not be done
8051 // until all work's been completed. Because we
8052 // expect the preserved oop stack (set) to be small,
8053 // it's probably fine to do this single-threaded.
8054 // We can explore cleverer concurrent/overlapped/parallel
8055 // processing of preserved marks if we feel the
8056 // need for this in the future. Stack overflow should
8057 // be so rare in practice and, when it happens, its
8058 // effect on performance so great that this will
8059 // likely just be in the noise anyway.
8060 void CMSCollector::restore_preserved_marks_if_any() {
8061 assert(SafepointSynchronize::is_at_safepoint(),
8062 "world should be stopped");
8063 assert(Thread::current()->is_ConcurrentGC_thread() ||
8064 Thread::current()->is_VM_thread(),
8065 "should be single-threaded");
8066 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8067 "bijection");
8068
8069 while (!_preserved_oop_stack.is_empty()) {
8070 oop p = _preserved_oop_stack.pop();
8071 assert(p->is_oop(), "Should be an oop");
8072 assert(_span.contains(p), "oop should be in _span");
8073 assert(p->mark() == markOopDesc::prototype(),
8074 "Set when taken from overflow list");
8075 markOop m = _preserved_mark_stack.pop();
8076 p->set_mark(m);
8077 }
8078 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8079 "stacks were cleared above");
8080 }
8081
8082 #ifndef PRODUCT
8083 bool CMSCollector::no_preserved_marks() const {
8084 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8085 }
8086 #endif
8087
8088 // Transfer some number of overflown objects to usual marking
8089 // stack. Return true if some objects were transferred.
8090 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8091 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8092 (size_t)ParGCDesiredObjsFromOverflowList);
8093
8094 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8095 assert(_collector->overflow_list_is_empty() || res,
8096 "If list is not empty, we should have taken something");
8097 assert(!res || !_mark_stack->isEmpty(),
8098 "If we took something, it should now be on our stack");
8099 return res;
8100 }
8101
8102 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8103 size_t res = _sp->block_size_no_stall(addr, _collector);
8104 if (_sp->block_is_obj(addr)) {
8105 if (_live_bit_map->isMarked(addr)) {
8106 // It can't have been dead in a previous cycle
8107 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8108 } else {
8109 _dead_bit_map->mark(addr); // mark the dead object
8110 }
8111 }
8112 // Could be 0, if the block size could not be computed without stalling.
8113 return res;
8114 }
8115
8116 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8117
8118 switch (phase) {
8119 case CMSCollector::InitialMarking:
8120 initialize(true /* fullGC */ ,
8121 cause /* cause of the GC */,
8122 true /* recordGCBeginTime */,
8123 true /* recordPreGCUsage */,
8124 false /* recordPeakUsage */,
8125 false /* recordPostGCusage */,
8126 true /* recordAccumulatedGCTime */,
8127 false /* recordGCEndTime */,
8128 false /* countCollection */ );
8129 break;
8130
8131 case CMSCollector::FinalMarking:
8132 initialize(true /* fullGC */ ,
8133 cause /* cause of the GC */,
8134 false /* recordGCBeginTime */,
8135 false /* recordPreGCUsage */,
8136 false /* recordPeakUsage */,
8137 false /* recordPostGCusage */,
8138 true /* recordAccumulatedGCTime */,
8139 false /* recordGCEndTime */,
8140 false /* countCollection */ );
8141 break;
8142
8143 case CMSCollector::Sweeping:
8144 initialize(true /* fullGC */ ,
8145 cause /* cause of the GC */,
8146 false /* recordGCBeginTime */,
8147 false /* recordPreGCUsage */,
8148 true /* recordPeakUsage */,
8149 true /* recordPostGCusage */,
8150 false /* recordAccumulatedGCTime */,
8151 true /* recordGCEndTime */,
8152 true /* countCollection */ );
8153 break;
8154
8155 default:
8156 ShouldNotReachHere();
8157 }
8158 }