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