1 /*
2 * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsHeap.hpp"
33 #include "gc/cms/cmsOopClosures.inline.hpp"
34 #include "gc/cms/compactibleFreeListSpace.hpp"
35 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc/cms/concurrentMarkSweepThread.hpp"
37 #include "gc/cms/parNewGeneration.hpp"
38 #include "gc/cms/vmCMSOperations.hpp"
39 #include "gc/serial/genMarkSweep.hpp"
40 #include "gc/serial/tenuredGeneration.hpp"
41 #include "gc/shared/adaptiveSizePolicy.hpp"
42 #include "gc/shared/cardGeneration.inline.hpp"
43 #include "gc/shared/cardTableRS.hpp"
44 #include "gc/shared/collectedHeap.inline.hpp"
45 #include "gc/shared/collectorCounters.hpp"
46 #include "gc/shared/collectorPolicy.hpp"
47 #include "gc/shared/gcLocker.inline.hpp"
48 #include "gc/shared/gcPolicyCounters.hpp"
49 #include "gc/shared/gcTimer.hpp"
50 #include "gc/shared/gcTrace.hpp"
51 #include "gc/shared/gcTraceTime.inline.hpp"
52 #include "gc/shared/genCollectedHeap.hpp"
53 #include "gc/shared/genOopClosures.inline.hpp"
54 #include "gc/shared/isGCActiveMark.hpp"
55 #include "gc/shared/referencePolicy.hpp"
56 #include "gc/shared/strongRootsScope.hpp"
57 #include "gc/shared/taskqueue.inline.hpp"
58 #include "logging/log.hpp"
59 #include "memory/allocation.hpp"
60 #include "memory/iterator.inline.hpp"
61 #include "memory/padded.hpp"
62 #include "memory/resourceArea.hpp"
63 #include "oops/oop.inline.hpp"
64 #include "prims/jvmtiExport.hpp"
65 #include "runtime/atomic.hpp"
66 #include "runtime/globals_extension.hpp"
67 #include "runtime/handles.inline.hpp"
68 #include "runtime/java.hpp"
69 #include "runtime/orderAccess.inline.hpp"
70 #include "runtime/timer.hpp"
71 #include "runtime/vmThread.hpp"
72 #include "services/memoryService.hpp"
73 #include "services/runtimeService.hpp"
74 #include "utilities/stack.inline.hpp"
75
76 // statics
77 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
78 bool CMSCollector::_full_gc_requested = false;
79 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
80
81 //////////////////////////////////////////////////////////////////
82 // In support of CMS/VM thread synchronization
83 //////////////////////////////////////////////////////////////////
84 // We split use of the CGC_lock into 2 "levels".
85 // The low-level locking is of the usual CGC_lock monitor. We introduce
86 // a higher level "token" (hereafter "CMS token") built on top of the
87 // low level monitor (hereafter "CGC lock").
88 // The token-passing protocol gives priority to the VM thread. The
89 // CMS-lock doesn't provide any fairness guarantees, but clients
90 // should ensure that it is only held for very short, bounded
91 // durations.
92 //
93 // When either of the CMS thread or the VM thread is involved in
94 // collection operations during which it does not want the other
95 // thread to interfere, it obtains the CMS token.
96 //
97 // If either thread tries to get the token while the other has
98 // it, that thread waits. However, if the VM thread and CMS thread
99 // both want the token, then the VM thread gets priority while the
100 // CMS thread waits. This ensures, for instance, that the "concurrent"
101 // phases of the CMS thread's work do not block out the VM thread
102 // for long periods of time as the CMS thread continues to hog
103 // the token. (See bug 4616232).
104 //
105 // The baton-passing functions are, however, controlled by the
106 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
107 // and here the low-level CMS lock, not the high level token,
108 // ensures mutual exclusion.
109 //
110 // Two important conditions that we have to satisfy:
111 // 1. if a thread does a low-level wait on the CMS lock, then it
112 // relinquishes the CMS token if it were holding that token
113 // when it acquired the low-level CMS lock.
114 // 2. any low-level notifications on the low-level lock
115 // should only be sent when a thread has relinquished the token.
116 //
117 // In the absence of either property, we'd have potential deadlock.
118 //
119 // We protect each of the CMS (concurrent and sequential) phases
120 // with the CMS _token_, not the CMS _lock_.
121 //
122 // The only code protected by CMS lock is the token acquisition code
123 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
124 // baton-passing code.
125 //
126 // Unfortunately, i couldn't come up with a good abstraction to factor and
127 // hide the naked CGC_lock manipulation in the baton-passing code
128 // further below. That's something we should try to do. Also, the proof
129 // of correctness of this 2-level locking scheme is far from obvious,
130 // and potentially quite slippery. We have an uneasy suspicion, for instance,
131 // that there may be a theoretical possibility of delay/starvation in the
132 // low-level lock/wait/notify scheme used for the baton-passing because of
133 // potential interference with the priority scheme embodied in the
134 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
135 // invocation further below and marked with "XXX 20011219YSR".
136 // Indeed, as we note elsewhere, this may become yet more slippery
137 // in the presence of multiple CMS and/or multiple VM threads. XXX
138
139 class CMSTokenSync: public StackObj {
140 private:
141 bool _is_cms_thread;
142 public:
143 CMSTokenSync(bool is_cms_thread):
144 _is_cms_thread(is_cms_thread) {
145 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
146 "Incorrect argument to constructor");
147 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
148 }
149
150 ~CMSTokenSync() {
151 assert(_is_cms_thread ?
152 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
153 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
154 "Incorrect state");
155 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
156 }
157 };
158
159 // Convenience class that does a CMSTokenSync, and then acquires
160 // upto three locks.
161 class CMSTokenSyncWithLocks: public CMSTokenSync {
162 private:
163 // Note: locks are acquired in textual declaration order
164 // and released in the opposite order
165 MutexLockerEx _locker1, _locker2, _locker3;
166 public:
167 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
168 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
169 CMSTokenSync(is_cms_thread),
170 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
171 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
172 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
173 { }
174 };
175
176
177 //////////////////////////////////////////////////////////////////
178 // Concurrent Mark-Sweep Generation /////////////////////////////
179 //////////////////////////////////////////////////////////////////
180
181 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
182
183 // This struct contains per-thread things necessary to support parallel
184 // young-gen collection.
185 class CMSParGCThreadState: public CHeapObj<mtGC> {
186 public:
187 CompactibleFreeListSpaceLAB lab;
188 PromotionInfo promo;
189
190 // Constructor.
191 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
192 promo.setSpace(cfls);
193 }
194 };
195
196 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
197 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
198 CardGeneration(rs, initial_byte_size, ct),
199 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
200 _did_compact(false)
201 {
202 HeapWord* bottom = (HeapWord*) _virtual_space.low();
203 HeapWord* end = (HeapWord*) _virtual_space.high();
204
205 _direct_allocated_words = 0;
206 NOT_PRODUCT(
207 _numObjectsPromoted = 0;
208 _numWordsPromoted = 0;
209 _numObjectsAllocated = 0;
210 _numWordsAllocated = 0;
211 )
212
213 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_old_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1,
310 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
311
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
316
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
322
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
325
326 _cms_begin_time.update();
327 _cms_end_time.update();
328
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
332
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
336
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
358 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
359 if (cms_free > expected_promotion) {
360 // Start a cms collection if there isn't enough space to promote
361 // for the next young collection. Use the padded average as
362 // a safety factor.
363 cms_free -= expected_promotion;
364
365 // Adjust by the safety factor.
366 double cms_free_dbl = (double)cms_free;
367 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
368 // Apply a further correction factor which tries to adjust
369 // for recent occurance of concurrent mode failures.
370 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
371 cms_free_dbl = cms_free_dbl * cms_adjustment;
372
373 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
374 cms_free, expected_promotion);
375 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
376 // Add 1 in case the consumption rate goes to zero.
377 return cms_free_dbl / (cms_consumption_rate() + 1.0);
378 }
379 return 0.0;
380 }
381
382 // Compare the duration of the cms collection to the
383 // time remaining before the cms generation is empty.
384 // Note that the time from the start of the cms collection
385 // to the start of the cms sweep (less than the total
386 // duration of the cms collection) can be used. This
387 // has been tried and some applications experienced
388 // promotion failures early in execution. This was
389 // possibly because the averages were not accurate
390 // enough at the beginning.
391 double CMSStats::time_until_cms_start() const {
392 // We add "gc0_period" to the "work" calculation
393 // below because this query is done (mostly) at the
394 // end of a scavenge, so we need to conservatively
395 // account for that much possible delay
396 // in the query so as to avoid concurrent mode failures
397 // due to starting the collection just a wee bit too
398 // late.
399 double work = cms_duration() + gc0_period();
400 double deadline = time_until_cms_gen_full();
401 // If a concurrent mode failure occurred recently, we want to be
402 // more conservative and halve our expected time_until_cms_gen_full()
403 if (work > deadline) {
404 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
405 cms_duration(), gc0_period(), time_until_cms_gen_full());
406 return 0.0;
407 }
408 return work - deadline;
409 }
410
411 #ifndef PRODUCT
412 void CMSStats::print_on(outputStream *st) const {
413 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
414 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
415 gc0_duration(), gc0_period(), gc0_promoted());
416 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
417 cms_duration(), cms_period(), cms_allocated());
418 st->print(",cms_since_beg=%g,cms_since_end=%g",
419 cms_time_since_begin(), cms_time_since_end());
420 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
421 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
422
423 if (valid()) {
424 st->print(",promo_rate=%g,cms_alloc_rate=%g",
425 promotion_rate(), cms_allocation_rate());
426 st->print(",cms_consumption_rate=%g,time_until_full=%g",
427 cms_consumption_rate(), time_until_cms_gen_full());
428 }
429 st->cr();
430 }
431 #endif // #ifndef PRODUCT
432
433 CMSCollector::CollectorState CMSCollector::_collectorState =
434 CMSCollector::Idling;
435 bool CMSCollector::_foregroundGCIsActive = false;
436 bool CMSCollector::_foregroundGCShouldWait = false;
437
438 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
439 CardTableRS* ct,
440 ConcurrentMarkSweepPolicy* cp):
441 _cmsGen(cmsGen),
442 _ct(ct),
443 _ref_processor(NULL), // will be set later
444 _conc_workers(NULL), // may be set later
445 _abort_preclean(false),
446 _start_sampling(false),
447 _between_prologue_and_epilogue(false),
448 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
449 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
450 -1 /* lock-free */, "No_lock" /* dummy */),
451 _modUnionClosurePar(&_modUnionTable),
452 // Adjust my span to cover old (cms) gen
453 _span(cmsGen->reserved()),
454 // Construct the is_alive_closure with _span & markBitMap
455 _is_alive_closure(_span, &_markBitMap),
456 _restart_addr(NULL),
457 _overflow_list(NULL),
458 _stats(cmsGen),
459 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
460 //verify that this lock should be acquired with safepoint check.
461 Monitor::_safepoint_check_sometimes)),
462 _eden_chunk_array(NULL), // may be set in ctor body
463 _eden_chunk_capacity(0), // -- ditto --
464 _eden_chunk_index(0), // -- ditto --
465 _survivor_plab_array(NULL), // -- ditto --
466 _survivor_chunk_array(NULL), // -- ditto --
467 _survivor_chunk_capacity(0), // -- ditto --
468 _survivor_chunk_index(0), // -- ditto --
469 _ser_pmc_preclean_ovflw(0),
470 _ser_kac_preclean_ovflw(0),
471 _ser_pmc_remark_ovflw(0),
472 _par_pmc_remark_ovflw(0),
473 _ser_kac_ovflw(0),
474 _par_kac_ovflw(0),
475 #ifndef PRODUCT
476 _num_par_pushes(0),
477 #endif
478 _collection_count_start(0),
479 _verifying(false),
480 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
481 _completed_initialization(false),
482 _collector_policy(cp),
483 _should_unload_classes(CMSClassUnloadingEnabled),
484 _concurrent_cycles_since_last_unload(0),
485 _roots_scanning_options(GenCollectedHeap::SO_None),
486 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
487 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
488 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
489 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
490 _cms_start_registered(false)
491 {
492 // Now expand the span and allocate the collection support structures
493 // (MUT, marking bit map etc.) to cover both generations subject to
494 // collection.
495
496 // For use by dirty card to oop closures.
497 _cmsGen->cmsSpace()->set_collector(this);
498
499 // Allocate MUT and marking bit map
500 {
501 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
502 if (!_markBitMap.allocate(_span)) {
503 log_warning(gc)("Failed to allocate CMS Bit Map");
504 return;
505 }
506 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
507 }
508 {
509 _modUnionTable.allocate(_span);
510 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
511 }
512
513 if (!_markStack.allocate(MarkStackSize)) {
514 log_warning(gc)("Failed to allocate CMS Marking Stack");
515 return;
516 }
517
518 // Support for multi-threaded concurrent phases
519 if (CMSConcurrentMTEnabled) {
520 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
521 // just for now
522 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
523 }
524 if (ConcGCThreads > 1) {
525 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
526 ConcGCThreads, true);
527 if (_conc_workers == NULL) {
528 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
529 CMSConcurrentMTEnabled = false;
530 } else {
531 _conc_workers->initialize_workers();
532 }
533 } else {
534 CMSConcurrentMTEnabled = false;
535 }
536 }
537 if (!CMSConcurrentMTEnabled) {
538 ConcGCThreads = 0;
539 } else {
540 // Turn off CMSCleanOnEnter optimization temporarily for
541 // the MT case where it's not fixed yet; see 6178663.
542 CMSCleanOnEnter = false;
543 }
544 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
545 "Inconsistency");
546 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
547 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
548
549 // Parallel task queues; these are shared for the
550 // concurrent and stop-world phases of CMS, but
551 // are not shared with parallel scavenge (ParNew).
552 {
553 uint i;
554 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
555
556 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
557 || ParallelRefProcEnabled)
558 && num_queues > 0) {
559 _task_queues = new OopTaskQueueSet(num_queues);
560 if (_task_queues == NULL) {
561 log_warning(gc)("task_queues allocation failure.");
562 return;
563 }
564 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
565 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
566 for (i = 0; i < num_queues; i++) {
567 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
568 if (q == NULL) {
569 log_warning(gc)("work_queue allocation failure.");
570 return;
571 }
572 _task_queues->register_queue(i, q);
573 }
574 for (i = 0; i < num_queues; i++) {
575 _task_queues->queue(i)->initialize();
576 _hash_seed[i] = 17; // copied from ParNew
577 }
578 }
579 }
580
581 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
582
583 // Clip CMSBootstrapOccupancy between 0 and 100.
584 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
585
586 // Now tell CMS generations the identity of their collector
587 ConcurrentMarkSweepGeneration::set_collector(this);
588
589 // Create & start a CMS thread for this CMS collector
590 _cmsThread = ConcurrentMarkSweepThread::start(this);
591 assert(cmsThread() != NULL, "CMS Thread should have been created");
592 assert(cmsThread()->collector() == this,
593 "CMS Thread should refer to this gen");
594 assert(CGC_lock != NULL, "Where's the CGC_lock?");
595
596 // Support for parallelizing young gen rescan
597 GenCollectedHeap* gch = GenCollectedHeap::heap();
598 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
599 _young_gen = (ParNewGeneration*)gch->young_gen();
600 if (gch->supports_inline_contig_alloc()) {
601 _top_addr = gch->top_addr();
602 _end_addr = gch->end_addr();
603 assert(_young_gen != NULL, "no _young_gen");
604 _eden_chunk_index = 0;
605 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
606 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
607 }
608
609 // Support for parallelizing survivor space rescan
610 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
611 const size_t max_plab_samples =
612 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
613
614 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
615 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
616 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
617 _survivor_chunk_capacity = max_plab_samples;
618 for (uint i = 0; i < ParallelGCThreads; i++) {
619 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
620 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
621 assert(cur->end() == 0, "Should be 0");
622 assert(cur->array() == vec, "Should be vec");
623 assert(cur->capacity() == max_plab_samples, "Error");
624 }
625 }
626
627 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
628 _gc_counters = new CollectorCounters("CMS", 1);
629 _completed_initialization = true;
630 _inter_sweep_timer.start(); // start of time
631 }
632
633 const char* ConcurrentMarkSweepGeneration::name() const {
634 return "concurrent mark-sweep generation";
635 }
636 void ConcurrentMarkSweepGeneration::update_counters() {
637 if (UsePerfData) {
638 _space_counters->update_all();
639 _gen_counters->update_all();
640 }
641 }
642
643 // this is an optimized version of update_counters(). it takes the
644 // used value as a parameter rather than computing it.
645 //
646 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
647 if (UsePerfData) {
648 _space_counters->update_used(used);
649 _space_counters->update_capacity();
650 _gen_counters->update_all();
651 }
652 }
653
654 void ConcurrentMarkSweepGeneration::print() const {
655 Generation::print();
656 cmsSpace()->print();
657 }
658
659 #ifndef PRODUCT
660 void ConcurrentMarkSweepGeneration::print_statistics() {
661 cmsSpace()->printFLCensus(0);
662 }
663 #endif
664
665 size_t
666 ConcurrentMarkSweepGeneration::contiguous_available() const {
667 // dld proposes an improvement in precision here. If the committed
668 // part of the space ends in a free block we should add that to
669 // uncommitted size in the calculation below. Will make this
670 // change later, staying with the approximation below for the
671 // time being. -- ysr.
672 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
673 }
674
675 size_t
676 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
677 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
678 }
679
680 size_t ConcurrentMarkSweepGeneration::max_available() const {
681 return free() + _virtual_space.uncommitted_size();
682 }
683
684 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
685 size_t available = max_available();
686 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
687 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
688 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
689 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
690 return res;
691 }
692
693 // At a promotion failure dump information on block layout in heap
694 // (cms old generation).
695 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
696 Log(gc, promotion) log;
697 if (log.is_trace()) {
698 ResourceMark rm;
699 cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
700 }
701 }
702
703 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
704 // Clear the promotion information. These pointers can be adjusted
705 // along with all the other pointers into the heap but
706 // compaction is expected to be a rare event with
707 // a heap using cms so don't do it without seeing the need.
708 for (uint i = 0; i < ParallelGCThreads; i++) {
709 _par_gc_thread_states[i]->promo.reset();
710 }
711 }
712
713 void ConcurrentMarkSweepGeneration::compute_new_size() {
714 assert_locked_or_safepoint(Heap_lock);
715
716 // If incremental collection failed, we just want to expand
717 // to the limit.
718 if (incremental_collection_failed()) {
719 clear_incremental_collection_failed();
720 grow_to_reserved();
721 return;
722 }
723
724 // The heap has been compacted but not reset yet.
725 // Any metric such as free() or used() will be incorrect.
726
727 CardGeneration::compute_new_size();
728
729 // Reset again after a possible resizing
730 if (did_compact()) {
731 cmsSpace()->reset_after_compaction();
732 }
733 }
734
735 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
736 assert_locked_or_safepoint(Heap_lock);
737
738 // If incremental collection failed, we just want to expand
739 // to the limit.
740 if (incremental_collection_failed()) {
741 clear_incremental_collection_failed();
742 grow_to_reserved();
743 return;
744 }
745
746 double free_percentage = ((double) free()) / capacity();
747 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
748 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
749
750 // compute expansion delta needed for reaching desired free percentage
751 if (free_percentage < desired_free_percentage) {
752 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
753 assert(desired_capacity >= capacity(), "invalid expansion size");
754 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
755 Log(gc) log;
756 if (log.is_trace()) {
757 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
758 log.trace("From compute_new_size: ");
759 log.trace(" Free fraction %f", free_percentage);
760 log.trace(" Desired free fraction %f", desired_free_percentage);
761 log.trace(" Maximum free fraction %f", maximum_free_percentage);
762 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
763 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
764 GenCollectedHeap* gch = GenCollectedHeap::heap();
765 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
766 size_t young_size = gch->young_gen()->capacity();
767 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
768 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
769 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
770 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
771 }
772 // safe if expansion fails
773 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
774 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
775 } else {
776 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
777 assert(desired_capacity <= capacity(), "invalid expansion size");
778 size_t shrink_bytes = capacity() - desired_capacity;
779 // Don't shrink unless the delta is greater than the minimum shrink we want
780 if (shrink_bytes >= MinHeapDeltaBytes) {
781 shrink_free_list_by(shrink_bytes);
782 }
783 }
784 }
785
786 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
787 return cmsSpace()->freelistLock();
788 }
789
790 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
791 CMSSynchronousYieldRequest yr;
792 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
793 return have_lock_and_allocate(size, tlab);
794 }
795
796 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
797 bool tlab /* ignored */) {
798 assert_lock_strong(freelistLock());
799 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
800 HeapWord* res = cmsSpace()->allocate(adjustedSize);
801 // Allocate the object live (grey) if the background collector has
802 // started marking. This is necessary because the marker may
803 // have passed this address and consequently this object will
804 // not otherwise be greyed and would be incorrectly swept up.
805 // Note that if this object contains references, the writing
806 // of those references will dirty the card containing this object
807 // allowing the object to be blackened (and its references scanned)
808 // either during a preclean phase or at the final checkpoint.
809 if (res != NULL) {
810 // We may block here with an uninitialized object with
811 // its mark-bit or P-bits not yet set. Such objects need
812 // to be safely navigable by block_start().
813 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
814 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
815 collector()->direct_allocated(res, adjustedSize);
816 _direct_allocated_words += adjustedSize;
817 // allocation counters
818 NOT_PRODUCT(
819 _numObjectsAllocated++;
820 _numWordsAllocated += (int)adjustedSize;
821 )
822 }
823 return res;
824 }
825
826 // In the case of direct allocation by mutators in a generation that
827 // is being concurrently collected, the object must be allocated
828 // live (grey) if the background collector has started marking.
829 // This is necessary because the marker may
830 // have passed this address and consequently this object will
831 // not otherwise be greyed and would be incorrectly swept up.
832 // Note that if this object contains references, the writing
833 // of those references will dirty the card containing this object
834 // allowing the object to be blackened (and its references scanned)
835 // either during a preclean phase or at the final checkpoint.
836 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
837 assert(_markBitMap.covers(start, size), "Out of bounds");
838 if (_collectorState >= Marking) {
839 MutexLockerEx y(_markBitMap.lock(),
840 Mutex::_no_safepoint_check_flag);
841 // [see comments preceding SweepClosure::do_blk() below for details]
842 //
843 // Can the P-bits be deleted now? JJJ
844 //
845 // 1. need to mark the object as live so it isn't collected
846 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
847 // 3. need to mark the end of the object so marking, precleaning or sweeping
848 // can skip over uninitialized or unparsable objects. An allocated
849 // object is considered uninitialized for our purposes as long as
850 // its klass word is NULL. All old gen objects are parsable
851 // as soon as they are initialized.)
852 _markBitMap.mark(start); // object is live
853 _markBitMap.mark(start + 1); // object is potentially uninitialized?
854 _markBitMap.mark(start + size - 1);
855 // mark end of object
856 }
857 // check that oop looks uninitialized
858 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
859 }
860
861 void CMSCollector::promoted(bool par, HeapWord* start,
862 bool is_obj_array, size_t obj_size) {
863 assert(_markBitMap.covers(start), "Out of bounds");
864 // See comment in direct_allocated() about when objects should
865 // be allocated live.
866 if (_collectorState >= Marking) {
867 // we already hold the marking bit map lock, taken in
868 // the prologue
869 if (par) {
870 _markBitMap.par_mark(start);
871 } else {
872 _markBitMap.mark(start);
873 }
874 // We don't need to mark the object as uninitialized (as
875 // in direct_allocated above) because this is being done with the
876 // world stopped and the object will be initialized by the
877 // time the marking, precleaning or sweeping get to look at it.
878 // But see the code for copying objects into the CMS generation,
879 // where we need to ensure that concurrent readers of the
880 // block offset table are able to safely navigate a block that
881 // is in flux from being free to being allocated (and in
882 // transition while being copied into) and subsequently
883 // becoming a bona-fide object when the copy/promotion is complete.
884 assert(SafepointSynchronize::is_at_safepoint(),
885 "expect promotion only at safepoints");
886
887 if (_collectorState < Sweeping) {
888 // Mark the appropriate cards in the modUnionTable, so that
889 // this object gets scanned before the sweep. If this is
890 // not done, CMS generation references in the object might
891 // not get marked.
892 // For the case of arrays, which are otherwise precisely
893 // marked, we need to dirty the entire array, not just its head.
894 if (is_obj_array) {
895 // The [par_]mark_range() method expects mr.end() below to
896 // be aligned to the granularity of a bit's representation
897 // in the heap. In the case of the MUT below, that's a
898 // card size.
899 MemRegion mr(start,
900 (HeapWord*)round_to((intptr_t)(start + obj_size),
901 CardTableModRefBS::card_size /* bytes */));
902 if (par) {
903 _modUnionTable.par_mark_range(mr);
904 } else {
905 _modUnionTable.mark_range(mr);
906 }
907 } else { // not an obj array; we can just mark the head
908 if (par) {
909 _modUnionTable.par_mark(start);
910 } else {
911 _modUnionTable.mark(start);
912 }
913 }
914 }
915 }
916 }
917
918 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
919 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
920 // allocate, copy and if necessary update promoinfo --
921 // delegate to underlying space.
922 assert_lock_strong(freelistLock());
923
924 #ifndef PRODUCT
925 if (GenCollectedHeap::heap()->promotion_should_fail()) {
926 return NULL;
927 }
928 #endif // #ifndef PRODUCT
929
930 oop res = _cmsSpace->promote(obj, obj_size);
931 if (res == NULL) {
932 // expand and retry
933 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
934 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
935 // Since this is the old generation, we don't try to promote
936 // into a more senior generation.
937 res = _cmsSpace->promote(obj, obj_size);
938 }
939 if (res != NULL) {
940 // See comment in allocate() about when objects should
941 // be allocated live.
942 assert(obj->is_oop(), "Will dereference klass pointer below");
943 collector()->promoted(false, // Not parallel
944 (HeapWord*)res, obj->is_objArray(), obj_size);
945 // promotion counters
946 NOT_PRODUCT(
947 _numObjectsPromoted++;
948 _numWordsPromoted +=
949 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
950 )
951 }
952 return res;
953 }
954
955
956 // IMPORTANT: Notes on object size recognition in CMS.
957 // ---------------------------------------------------
958 // A block of storage in the CMS generation is always in
959 // one of three states. A free block (FREE), an allocated
960 // object (OBJECT) whose size() method reports the correct size,
961 // and an intermediate state (TRANSIENT) in which its size cannot
962 // be accurately determined.
963 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
964 // -----------------------------------------------------
965 // FREE: klass_word & 1 == 1; mark_word holds block size
966 //
967 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
968 // obj->size() computes correct size
969 //
970 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
971 //
972 // STATE IDENTIFICATION: (64 bit+COOPS)
973 // ------------------------------------
974 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
975 //
976 // OBJECT: klass_word installed; klass_word != 0;
977 // obj->size() computes correct size
978 //
979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
980 //
981 //
982 // STATE TRANSITION DIAGRAM
983 //
984 // mut / parnew mut / parnew
985 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
986 // ^ |
987 // |------------------------ DEAD <------------------------------------|
988 // sweep mut
989 //
990 // While a block is in TRANSIENT state its size cannot be determined
991 // so readers will either need to come back later or stall until
992 // the size can be determined. Note that for the case of direct
993 // allocation, P-bits, when available, may be used to determine the
994 // size of an object that may not yet have been initialized.
995
996 // Things to support parallel young-gen collection.
997 oop
998 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
999 oop old, markOop m,
1000 size_t word_sz) {
1001 #ifndef PRODUCT
1002 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1003 return NULL;
1004 }
1005 #endif // #ifndef PRODUCT
1006
1007 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1008 PromotionInfo* promoInfo = &ps->promo;
1009 // if we are tracking promotions, then first ensure space for
1010 // promotion (including spooling space for saving header if necessary).
1011 // then allocate and copy, then track promoted info if needed.
1012 // When tracking (see PromotionInfo::track()), the mark word may
1013 // be displaced and in this case restoration of the mark word
1014 // occurs in the (oop_since_save_marks_)iterate phase.
1015 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1016 // Out of space for allocating spooling buffers;
1017 // try expanding and allocating spooling buffers.
1018 if (!expand_and_ensure_spooling_space(promoInfo)) {
1019 return NULL;
1020 }
1021 }
1022 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1023 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1024 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1025 if (obj_ptr == NULL) {
1026 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1027 if (obj_ptr == NULL) {
1028 return NULL;
1029 }
1030 }
1031 oop obj = oop(obj_ptr);
1032 OrderAccess::storestore();
1033 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1034 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1035 // IMPORTANT: See note on object initialization for CMS above.
1036 // Otherwise, copy the object. Here we must be careful to insert the
1037 // klass pointer last, since this marks the block as an allocated object.
1038 // Except with compressed oops it's the mark word.
1039 HeapWord* old_ptr = (HeapWord*)old;
1040 // Restore the mark word copied above.
1041 obj->set_mark(m);
1042 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044 OrderAccess::storestore();
1045
1046 if (UseCompressedClassPointers) {
1047 // Copy gap missed by (aligned) header size calculation below
1048 obj->set_klass_gap(old->klass_gap());
1049 }
1050 if (word_sz > (size_t)oopDesc::header_size()) {
1051 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1052 obj_ptr + oopDesc::header_size(),
1053 word_sz - oopDesc::header_size());
1054 }
1055
1056 // Now we can track the promoted object, if necessary. We take care
1057 // to delay the transition from uninitialized to full object
1058 // (i.e., insertion of klass pointer) until after, so that it
1059 // atomically becomes a promoted object.
1060 if (promoInfo->tracking()) {
1061 promoInfo->track((PromotedObject*)obj, old->klass());
1062 }
1063 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1064 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1065 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1066
1067 // Finally, install the klass pointer (this should be volatile).
1068 OrderAccess::storestore();
1069 obj->set_klass(old->klass());
1070 // We should now be able to calculate the right size for this object
1071 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1072
1073 collector()->promoted(true, // parallel
1074 obj_ptr, old->is_objArray(), word_sz);
1075
1076 NOT_PRODUCT(
1077 Atomic::inc_ptr(&_numObjectsPromoted);
1078 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1079 )
1080
1081 return obj;
1082 }
1083
1084 void
1085 ConcurrentMarkSweepGeneration::
1086 par_promote_alloc_done(int thread_num) {
1087 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1088 ps->lab.retire(thread_num);
1089 }
1090
1091 void
1092 ConcurrentMarkSweepGeneration::
1093 par_oop_since_save_marks_iterate_done(int thread_num) {
1094 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1095 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1096 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1097
1098 // Because card-scanning has been completed, subsequent phases
1099 // (e.g., reference processing) will not need to recognize which
1100 // objects have been promoted during this GC. So, we can now disable
1101 // promotion tracking.
1102 ps->promo.stopTrackingPromotions();
1103 }
1104
1105 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1106 size_t size,
1107 bool tlab)
1108 {
1109 // We allow a STW collection only if a full
1110 // collection was requested.
1111 return full || should_allocate(size, tlab); // FIX ME !!!
1112 // This and promotion failure handling are connected at the
1113 // hip and should be fixed by untying them.
1114 }
1115
1116 bool CMSCollector::shouldConcurrentCollect() {
1117 LogTarget(Trace, gc) log;
1118
1119 if (_full_gc_requested) {
1120 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1121 return true;
1122 }
1123
1124 FreelistLocker x(this);
1125 // ------------------------------------------------------------------
1126 // Print out lots of information which affects the initiation of
1127 // a collection.
1128 if (log.is_enabled() && stats().valid()) {
1129 log.print("CMSCollector shouldConcurrentCollect: ");
1130
1131 LogStream out(log);
1132 stats().print_on(&out);
1133
1134 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1135 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1136 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1137 log.print("promotion_rate=%g", stats().promotion_rate());
1138 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1139 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1140 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1141 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1142 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1143 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1144 }
1145 // ------------------------------------------------------------------
1146
1147 // If the estimated time to complete a cms collection (cms_duration())
1148 // is less than the estimated time remaining until the cms generation
1149 // is full, start a collection.
1150 if (!UseCMSInitiatingOccupancyOnly) {
1151 if (stats().valid()) {
1152 if (stats().time_until_cms_start() == 0.0) {
1153 return true;
1154 }
1155 } else {
1156 // We want to conservatively collect somewhat early in order
1157 // to try and "bootstrap" our CMS/promotion statistics;
1158 // this branch will not fire after the first successful CMS
1159 // collection because the stats should then be valid.
1160 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1161 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1162 _cmsGen->occupancy(), _bootstrap_occupancy);
1163 return true;
1164 }
1165 }
1166 }
1167
1168 // Otherwise, we start a collection cycle if
1169 // old gen want a collection cycle started. Each may use
1170 // an appropriate criterion for making this decision.
1171 // XXX We need to make sure that the gen expansion
1172 // criterion dovetails well with this. XXX NEED TO FIX THIS
1173 if (_cmsGen->should_concurrent_collect()) {
1174 log.print("CMS old gen initiated");
1175 return true;
1176 }
1177
1178 // We start a collection if we believe an incremental collection may fail;
1179 // this is not likely to be productive in practice because it's probably too
1180 // late anyway.
1181 GenCollectedHeap* gch = GenCollectedHeap::heap();
1182 assert(gch->collector_policy()->is_generation_policy(),
1183 "You may want to check the correctness of the following");
1184 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1185 log.print("CMSCollector: collect because incremental collection will fail ");
1186 return true;
1187 }
1188
1189 if (MetaspaceGC::should_concurrent_collect()) {
1190 log.print("CMSCollector: collect for metadata allocation ");
1191 return true;
1192 }
1193
1194 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1195 if (CMSTriggerInterval >= 0) {
1196 if (CMSTriggerInterval == 0) {
1197 // Trigger always
1198 return true;
1199 }
1200
1201 // Check the CMS time since begin (we do not check the stats validity
1202 // as we want to be able to trigger the first CMS cycle as well)
1203 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1204 if (stats().valid()) {
1205 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1206 stats().cms_time_since_begin());
1207 } else {
1208 log.print("CMSCollector: collect because of trigger interval (first collection)");
1209 }
1210 return true;
1211 }
1212 }
1213
1214 return false;
1215 }
1216
1217 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1218
1219 // Clear _expansion_cause fields of constituent generations
1220 void CMSCollector::clear_expansion_cause() {
1221 _cmsGen->clear_expansion_cause();
1222 }
1223
1224 // We should be conservative in starting a collection cycle. To
1225 // start too eagerly runs the risk of collecting too often in the
1226 // extreme. To collect too rarely falls back on full collections,
1227 // which works, even if not optimum in terms of concurrent work.
1228 // As a work around for too eagerly collecting, use the flag
1229 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1230 // giving the user an easily understandable way of controlling the
1231 // collections.
1232 // We want to start a new collection cycle if any of the following
1233 // conditions hold:
1234 // . our current occupancy exceeds the configured initiating occupancy
1235 // for this generation, or
1236 // . we recently needed to expand this space and have not, since that
1237 // expansion, done a collection of this generation, or
1238 // . the underlying space believes that it may be a good idea to initiate
1239 // a concurrent collection (this may be based on criteria such as the
1240 // following: the space uses linear allocation and linear allocation is
1241 // going to fail, or there is believed to be excessive fragmentation in
1242 // the generation, etc... or ...
1243 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1244 // the case of the old generation; see CR 6543076):
1245 // we may be approaching a point at which allocation requests may fail because
1246 // we will be out of sufficient free space given allocation rate estimates.]
1247 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1248
1249 assert_lock_strong(freelistLock());
1250 if (occupancy() > initiating_occupancy()) {
1251 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1252 short_name(), occupancy(), initiating_occupancy());
1253 return true;
1254 }
1255 if (UseCMSInitiatingOccupancyOnly) {
1256 return false;
1257 }
1258 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1259 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1260 return true;
1261 }
1262 return false;
1263 }
1264
1265 void ConcurrentMarkSweepGeneration::collect(bool full,
1266 bool clear_all_soft_refs,
1267 size_t size,
1268 bool tlab)
1269 {
1270 collector()->collect(full, clear_all_soft_refs, size, tlab);
1271 }
1272
1273 void CMSCollector::collect(bool full,
1274 bool clear_all_soft_refs,
1275 size_t size,
1276 bool tlab)
1277 {
1278 // The following "if" branch is present for defensive reasons.
1279 // In the current uses of this interface, it can be replaced with:
1280 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1281 // But I am not placing that assert here to allow future
1282 // generality in invoking this interface.
1283 if (GCLocker::is_active()) {
1284 // A consistency test for GCLocker
1285 assert(GCLocker::needs_gc(), "Should have been set already");
1286 // Skip this foreground collection, instead
1287 // expanding the heap if necessary.
1288 // Need the free list locks for the call to free() in compute_new_size()
1289 compute_new_size();
1290 return;
1291 }
1292 acquire_control_and_collect(full, clear_all_soft_refs);
1293 }
1294
1295 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1296 GenCollectedHeap* gch = GenCollectedHeap::heap();
1297 unsigned int gc_count = gch->total_full_collections();
1298 if (gc_count == full_gc_count) {
1299 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1300 _full_gc_requested = true;
1301 _full_gc_cause = cause;
1302 CGC_lock->notify(); // nudge CMS thread
1303 } else {
1304 assert(gc_count > full_gc_count, "Error: causal loop");
1305 }
1306 }
1307
1308 bool CMSCollector::is_external_interruption() {
1309 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1310 return GCCause::is_user_requested_gc(cause) ||
1311 GCCause::is_serviceability_requested_gc(cause);
1312 }
1313
1314 void CMSCollector::report_concurrent_mode_interruption() {
1315 if (is_external_interruption()) {
1316 log_debug(gc)("Concurrent mode interrupted");
1317 } else {
1318 log_debug(gc)("Concurrent mode failure");
1319 _gc_tracer_cm->report_concurrent_mode_failure();
1320 }
1321 }
1322
1323
1324 // The foreground and background collectors need to coordinate in order
1325 // to make sure that they do not mutually interfere with CMS collections.
1326 // When a background collection is active,
1327 // the foreground collector may need to take over (preempt) and
1328 // synchronously complete an ongoing collection. Depending on the
1329 // frequency of the background collections and the heap usage
1330 // of the application, this preemption can be seldom or frequent.
1331 // There are only certain
1332 // points in the background collection that the "collection-baton"
1333 // can be passed to the foreground collector.
1334 //
1335 // The foreground collector will wait for the baton before
1336 // starting any part of the collection. The foreground collector
1337 // will only wait at one location.
1338 //
1339 // The background collector will yield the baton before starting a new
1340 // phase of the collection (e.g., before initial marking, marking from roots,
1341 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1342 // of the loop which switches the phases. The background collector does some
1343 // of the phases (initial mark, final re-mark) with the world stopped.
1344 // Because of locking involved in stopping the world,
1345 // the foreground collector should not block waiting for the background
1346 // collector when it is doing a stop-the-world phase. The background
1347 // collector will yield the baton at an additional point just before
1348 // it enters a stop-the-world phase. Once the world is stopped, the
1349 // background collector checks the phase of the collection. If the
1350 // phase has not changed, it proceeds with the collection. If the
1351 // phase has changed, it skips that phase of the collection. See
1352 // the comments on the use of the Heap_lock in collect_in_background().
1353 //
1354 // Variable used in baton passing.
1355 // _foregroundGCIsActive - Set to true by the foreground collector when
1356 // it wants the baton. The foreground clears it when it has finished
1357 // the collection.
1358 // _foregroundGCShouldWait - Set to true by the background collector
1359 // when it is running. The foreground collector waits while
1360 // _foregroundGCShouldWait is true.
1361 // CGC_lock - monitor used to protect access to the above variables
1362 // and to notify the foreground and background collectors.
1363 // _collectorState - current state of the CMS collection.
1364 //
1365 // The foreground collector
1366 // acquires the CGC_lock
1367 // sets _foregroundGCIsActive
1368 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1369 // various locks acquired in preparation for the collection
1370 // are released so as not to block the background collector
1371 // that is in the midst of a collection
1372 // proceeds with the collection
1373 // clears _foregroundGCIsActive
1374 // returns
1375 //
1376 // The background collector in a loop iterating on the phases of the
1377 // collection
1378 // acquires the CGC_lock
1379 // sets _foregroundGCShouldWait
1380 // if _foregroundGCIsActive is set
1381 // clears _foregroundGCShouldWait, notifies _CGC_lock
1382 // waits on _CGC_lock for _foregroundGCIsActive to become false
1383 // and exits the loop.
1384 // otherwise
1385 // proceed with that phase of the collection
1386 // if the phase is a stop-the-world phase,
1387 // yield the baton once more just before enqueueing
1388 // the stop-world CMS operation (executed by the VM thread).
1389 // returns after all phases of the collection are done
1390 //
1391
1392 void CMSCollector::acquire_control_and_collect(bool full,
1393 bool clear_all_soft_refs) {
1394 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1395 assert(!Thread::current()->is_ConcurrentGC_thread(),
1396 "shouldn't try to acquire control from self!");
1397
1398 // Start the protocol for acquiring control of the
1399 // collection from the background collector (aka CMS thread).
1400 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1401 "VM thread should have CMS token");
1402 // Remember the possibly interrupted state of an ongoing
1403 // concurrent collection
1404 CollectorState first_state = _collectorState;
1405
1406 // Signal to a possibly ongoing concurrent collection that
1407 // we want to do a foreground collection.
1408 _foregroundGCIsActive = true;
1409
1410 // release locks and wait for a notify from the background collector
1411 // releasing the locks in only necessary for phases which
1412 // do yields to improve the granularity of the collection.
1413 assert_lock_strong(bitMapLock());
1414 // We need to lock the Free list lock for the space that we are
1415 // currently collecting.
1416 assert(haveFreelistLocks(), "Must be holding free list locks");
1417 bitMapLock()->unlock();
1418 releaseFreelistLocks();
1419 {
1420 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1421 if (_foregroundGCShouldWait) {
1422 // We are going to be waiting for action for the CMS thread;
1423 // it had better not be gone (for instance at shutdown)!
1424 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1425 "CMS thread must be running");
1426 // Wait here until the background collector gives us the go-ahead
1427 ConcurrentMarkSweepThread::clear_CMS_flag(
1428 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1429 // Get a possibly blocked CMS thread going:
1430 // Note that we set _foregroundGCIsActive true above,
1431 // without protection of the CGC_lock.
1432 CGC_lock->notify();
1433 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1434 "Possible deadlock");
1435 while (_foregroundGCShouldWait) {
1436 // wait for notification
1437 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1438 // Possibility of delay/starvation here, since CMS token does
1439 // not know to give priority to VM thread? Actually, i think
1440 // there wouldn't be any delay/starvation, but the proof of
1441 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1442 }
1443 ConcurrentMarkSweepThread::set_CMS_flag(
1444 ConcurrentMarkSweepThread::CMS_vm_has_token);
1445 }
1446 }
1447 // The CMS_token is already held. Get back the other locks.
1448 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1449 "VM thread should have CMS token");
1450 getFreelistLocks();
1451 bitMapLock()->lock_without_safepoint_check();
1452 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1453 p2i(Thread::current()), first_state);
1454 log_debug(gc, state)(" gets control with state %d", _collectorState);
1455
1456 // Inform cms gen if this was due to partial collection failing.
1457 // The CMS gen may use this fact to determine its expansion policy.
1458 GenCollectedHeap* gch = GenCollectedHeap::heap();
1459 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1460 assert(!_cmsGen->incremental_collection_failed(),
1461 "Should have been noticed, reacted to and cleared");
1462 _cmsGen->set_incremental_collection_failed();
1463 }
1464
1465 if (first_state > Idling) {
1466 report_concurrent_mode_interruption();
1467 }
1468
1469 set_did_compact(true);
1470
1471 // If the collection is being acquired from the background
1472 // collector, there may be references on the discovered
1473 // references lists. Abandon those references, since some
1474 // of them may have become unreachable after concurrent
1475 // discovery; the STW compacting collector will redo discovery
1476 // more precisely, without being subject to floating garbage.
1477 // Leaving otherwise unreachable references in the discovered
1478 // lists would require special handling.
1479 ref_processor()->disable_discovery();
1480 ref_processor()->abandon_partial_discovery();
1481 ref_processor()->verify_no_references_recorded();
1482
1483 if (first_state > Idling) {
1484 save_heap_summary();
1485 }
1486
1487 do_compaction_work(clear_all_soft_refs);
1488
1489 // Has the GC time limit been exceeded?
1490 size_t max_eden_size = _young_gen->max_eden_size();
1491 GCCause::Cause gc_cause = gch->gc_cause();
1492 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1493 _young_gen->eden()->used(),
1494 _cmsGen->max_capacity(),
1495 max_eden_size,
1496 full,
1497 gc_cause,
1498 gch->collector_policy());
1499
1500 // Reset the expansion cause, now that we just completed
1501 // a collection cycle.
1502 clear_expansion_cause();
1503 _foregroundGCIsActive = false;
1504 return;
1505 }
1506
1507 // Resize the tenured generation
1508 // after obtaining the free list locks for the
1509 // two generations.
1510 void CMSCollector::compute_new_size() {
1511 assert_locked_or_safepoint(Heap_lock);
1512 FreelistLocker z(this);
1513 MetaspaceGC::compute_new_size();
1514 _cmsGen->compute_new_size_free_list();
1515 }
1516
1517 // A work method used by the foreground collector to do
1518 // a mark-sweep-compact.
1519 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1520 GenCollectedHeap* gch = GenCollectedHeap::heap();
1521
1522 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1523 gc_timer->register_gc_start();
1524
1525 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1526 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1527
1528 gch->pre_full_gc_dump(gc_timer);
1529
1530 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1531
1532 // Temporarily widen the span of the weak reference processing to
1533 // the entire heap.
1534 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1535 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1536 // Temporarily, clear the "is_alive_non_header" field of the
1537 // reference processor.
1538 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1539 // Temporarily make reference _processing_ single threaded (non-MT).
1540 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1541 // Temporarily make refs discovery atomic
1542 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1543 // Temporarily make reference _discovery_ single threaded (non-MT)
1544 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1545
1546 ref_processor()->set_enqueuing_is_done(false);
1547 ref_processor()->enable_discovery();
1548 ref_processor()->setup_policy(clear_all_soft_refs);
1549 // If an asynchronous collection finishes, the _modUnionTable is
1550 // all clear. If we are assuming the collection from an asynchronous
1551 // collection, clear the _modUnionTable.
1552 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1553 "_modUnionTable should be clear if the baton was not passed");
1554 _modUnionTable.clear_all();
1555 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1556 "mod union for klasses should be clear if the baton was passed");
1557 _ct->klass_rem_set()->clear_mod_union();
1558
1559 // We must adjust the allocation statistics being maintained
1560 // in the free list space. We do so by reading and clearing
1561 // the sweep timer and updating the block flux rate estimates below.
1562 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1563 if (_inter_sweep_timer.is_active()) {
1564 _inter_sweep_timer.stop();
1565 // Note that we do not use this sample to update the _inter_sweep_estimate.
1566 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1567 _inter_sweep_estimate.padded_average(),
1568 _intra_sweep_estimate.padded_average());
1569 }
1570
1571 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1572 #ifdef ASSERT
1573 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1574 size_t free_size = cms_space->free();
1575 assert(free_size ==
1576 pointer_delta(cms_space->end(), cms_space->compaction_top())
1577 * HeapWordSize,
1578 "All the free space should be compacted into one chunk at top");
1579 assert(cms_space->dictionary()->total_chunk_size(
1580 debug_only(cms_space->freelistLock())) == 0 ||
1581 cms_space->totalSizeInIndexedFreeLists() == 0,
1582 "All the free space should be in a single chunk");
1583 size_t num = cms_space->totalCount();
1584 assert((free_size == 0 && num == 0) ||
1585 (free_size > 0 && (num == 1 || num == 2)),
1586 "There should be at most 2 free chunks after compaction");
1587 #endif // ASSERT
1588 _collectorState = Resetting;
1589 assert(_restart_addr == NULL,
1590 "Should have been NULL'd before baton was passed");
1591 reset_stw();
1592 _cmsGen->reset_after_compaction();
1593 _concurrent_cycles_since_last_unload = 0;
1594
1595 // Clear any data recorded in the PLAB chunk arrays.
1596 if (_survivor_plab_array != NULL) {
1597 reset_survivor_plab_arrays();
1598 }
1599
1600 // Adjust the per-size allocation stats for the next epoch.
1601 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1602 // Restart the "inter sweep timer" for the next epoch.
1603 _inter_sweep_timer.reset();
1604 _inter_sweep_timer.start();
1605
1606 // No longer a need to do a concurrent collection for Metaspace.
1607 MetaspaceGC::set_should_concurrent_collect(false);
1608
1609 gch->post_full_gc_dump(gc_timer);
1610
1611 gc_timer->register_gc_end();
1612
1613 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1614
1615 // For a mark-sweep-compact, compute_new_size() will be called
1616 // in the heap's do_collection() method.
1617 }
1618
1619 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1620 Log(gc, heap) log;
1621 if (!log.is_trace()) {
1622 return;
1623 }
1624
1625 ContiguousSpace* eden_space = _young_gen->eden();
1626 ContiguousSpace* from_space = _young_gen->from();
1627 ContiguousSpace* to_space = _young_gen->to();
1628 // Eden
1629 if (_eden_chunk_array != NULL) {
1630 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1631 p2i(eden_space->bottom()), p2i(eden_space->top()),
1632 p2i(eden_space->end()), eden_space->capacity());
1633 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1634 _eden_chunk_index, _eden_chunk_capacity);
1635 for (size_t i = 0; i < _eden_chunk_index; i++) {
1636 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1637 }
1638 }
1639 // Survivor
1640 if (_survivor_chunk_array != NULL) {
1641 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1642 p2i(from_space->bottom()), p2i(from_space->top()),
1643 p2i(from_space->end()), from_space->capacity());
1644 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1645 _survivor_chunk_index, _survivor_chunk_capacity);
1646 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1647 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1648 }
1649 }
1650 }
1651
1652 void CMSCollector::getFreelistLocks() const {
1653 // Get locks for all free lists in all generations that this
1654 // collector is responsible for
1655 _cmsGen->freelistLock()->lock_without_safepoint_check();
1656 }
1657
1658 void CMSCollector::releaseFreelistLocks() const {
1659 // Release locks for all free lists in all generations that this
1660 // collector is responsible for
1661 _cmsGen->freelistLock()->unlock();
1662 }
1663
1664 bool CMSCollector::haveFreelistLocks() const {
1665 // Check locks for all free lists in all generations that this
1666 // collector is responsible for
1667 assert_lock_strong(_cmsGen->freelistLock());
1668 PRODUCT_ONLY(ShouldNotReachHere());
1669 return true;
1670 }
1671
1672 // A utility class that is used by the CMS collector to
1673 // temporarily "release" the foreground collector from its
1674 // usual obligation to wait for the background collector to
1675 // complete an ongoing phase before proceeding.
1676 class ReleaseForegroundGC: public StackObj {
1677 private:
1678 CMSCollector* _c;
1679 public:
1680 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1681 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1682 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1683 // allow a potentially blocked foreground collector to proceed
1684 _c->_foregroundGCShouldWait = false;
1685 if (_c->_foregroundGCIsActive) {
1686 CGC_lock->notify();
1687 }
1688 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1689 "Possible deadlock");
1690 }
1691
1692 ~ReleaseForegroundGC() {
1693 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1694 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1695 _c->_foregroundGCShouldWait = true;
1696 }
1697 };
1698
1699 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1700 assert(Thread::current()->is_ConcurrentGC_thread(),
1701 "A CMS asynchronous collection is only allowed on a CMS thread.");
1702
1703 GenCollectedHeap* gch = GenCollectedHeap::heap();
1704 {
1705 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1706 MutexLockerEx hl(Heap_lock, safepoint_check);
1707 FreelistLocker fll(this);
1708 MutexLockerEx x(CGC_lock, safepoint_check);
1709 if (_foregroundGCIsActive) {
1710 // The foreground collector is. Skip this
1711 // background collection.
1712 assert(!_foregroundGCShouldWait, "Should be clear");
1713 return;
1714 } else {
1715 assert(_collectorState == Idling, "Should be idling before start.");
1716 _collectorState = InitialMarking;
1717 register_gc_start(cause);
1718 // Reset the expansion cause, now that we are about to begin
1719 // a new cycle.
1720 clear_expansion_cause();
1721
1722 // Clear the MetaspaceGC flag since a concurrent collection
1723 // is starting but also clear it after the collection.
1724 MetaspaceGC::set_should_concurrent_collect(false);
1725 }
1726 // Decide if we want to enable class unloading as part of the
1727 // ensuing concurrent GC cycle.
1728 update_should_unload_classes();
1729 _full_gc_requested = false; // acks all outstanding full gc requests
1730 _full_gc_cause = GCCause::_no_gc;
1731 // Signal that we are about to start a collection
1732 gch->increment_total_full_collections(); // ... starting a collection cycle
1733 _collection_count_start = gch->total_full_collections();
1734 }
1735
1736 size_t prev_used = _cmsGen->used();
1737
1738 // The change of the collection state is normally done at this level;
1739 // the exceptions are phases that are executed while the world is
1740 // stopped. For those phases the change of state is done while the
1741 // world is stopped. For baton passing purposes this allows the
1742 // background collector to finish the phase and change state atomically.
1743 // The foreground collector cannot wait on a phase that is done
1744 // while the world is stopped because the foreground collector already
1745 // has the world stopped and would deadlock.
1746 while (_collectorState != Idling) {
1747 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1748 p2i(Thread::current()), _collectorState);
1749 // The foreground collector
1750 // holds the Heap_lock throughout its collection.
1751 // holds the CMS token (but not the lock)
1752 // except while it is waiting for the background collector to yield.
1753 //
1754 // The foreground collector should be blocked (not for long)
1755 // if the background collector is about to start a phase
1756 // executed with world stopped. If the background
1757 // collector has already started such a phase, the
1758 // foreground collector is blocked waiting for the
1759 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1760 // are executed in the VM thread.
1761 //
1762 // The locking order is
1763 // PendingListLock (PLL) -- if applicable (FinalMarking)
1764 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1765 // CMS token (claimed in
1766 // stop_world_and_do() -->
1767 // safepoint_synchronize() -->
1768 // CMSThread::synchronize())
1769
1770 {
1771 // Check if the FG collector wants us to yield.
1772 CMSTokenSync x(true); // is cms thread
1773 if (waitForForegroundGC()) {
1774 // We yielded to a foreground GC, nothing more to be
1775 // done this round.
1776 assert(_foregroundGCShouldWait == false, "We set it to false in "
1777 "waitForForegroundGC()");
1778 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1779 p2i(Thread::current()), _collectorState);
1780 return;
1781 } else {
1782 // The background collector can run but check to see if the
1783 // foreground collector has done a collection while the
1784 // background collector was waiting to get the CGC_lock
1785 // above. If yes, break so that _foregroundGCShouldWait
1786 // is cleared before returning.
1787 if (_collectorState == Idling) {
1788 break;
1789 }
1790 }
1791 }
1792
1793 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1794 "should be waiting");
1795
1796 switch (_collectorState) {
1797 case InitialMarking:
1798 {
1799 ReleaseForegroundGC x(this);
1800 stats().record_cms_begin();
1801 VM_CMS_Initial_Mark initial_mark_op(this);
1802 VMThread::execute(&initial_mark_op);
1803 }
1804 // The collector state may be any legal state at this point
1805 // since the background collector may have yielded to the
1806 // foreground collector.
1807 break;
1808 case Marking:
1809 // initial marking in checkpointRootsInitialWork has been completed
1810 if (markFromRoots()) { // we were successful
1811 assert(_collectorState == Precleaning, "Collector state should "
1812 "have changed");
1813 } else {
1814 assert(_foregroundGCIsActive, "Internal state inconsistency");
1815 }
1816 break;
1817 case Precleaning:
1818 // marking from roots in markFromRoots has been completed
1819 preclean();
1820 assert(_collectorState == AbortablePreclean ||
1821 _collectorState == FinalMarking,
1822 "Collector state should have changed");
1823 break;
1824 case AbortablePreclean:
1825 abortable_preclean();
1826 assert(_collectorState == FinalMarking, "Collector state should "
1827 "have changed");
1828 break;
1829 case FinalMarking:
1830 {
1831 ReleaseForegroundGC x(this);
1832
1833 VM_CMS_Final_Remark final_remark_op(this);
1834 VMThread::execute(&final_remark_op);
1835 }
1836 assert(_foregroundGCShouldWait, "block post-condition");
1837 break;
1838 case Sweeping:
1839 // final marking in checkpointRootsFinal has been completed
1840 sweep();
1841 assert(_collectorState == Resizing, "Collector state change "
1842 "to Resizing must be done under the free_list_lock");
1843
1844 case Resizing: {
1845 // Sweeping has been completed...
1846 // At this point the background collection has completed.
1847 // Don't move the call to compute_new_size() down
1848 // into code that might be executed if the background
1849 // collection was preempted.
1850 {
1851 ReleaseForegroundGC x(this); // unblock FG collection
1852 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1853 CMSTokenSync z(true); // not strictly needed.
1854 if (_collectorState == Resizing) {
1855 compute_new_size();
1856 save_heap_summary();
1857 _collectorState = Resetting;
1858 } else {
1859 assert(_collectorState == Idling, "The state should only change"
1860 " because the foreground collector has finished the collection");
1861 }
1862 }
1863 break;
1864 }
1865 case Resetting:
1866 // CMS heap resizing has been completed
1867 reset_concurrent();
1868 assert(_collectorState == Idling, "Collector state should "
1869 "have changed");
1870
1871 MetaspaceGC::set_should_concurrent_collect(false);
1872
1873 stats().record_cms_end();
1874 // Don't move the concurrent_phases_end() and compute_new_size()
1875 // calls to here because a preempted background collection
1876 // has it's state set to "Resetting".
1877 break;
1878 case Idling:
1879 default:
1880 ShouldNotReachHere();
1881 break;
1882 }
1883 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1884 p2i(Thread::current()), _collectorState);
1885 assert(_foregroundGCShouldWait, "block post-condition");
1886 }
1887
1888 // Should this be in gc_epilogue?
1889 collector_policy()->counters()->update_counters();
1890
1891 {
1892 // Clear _foregroundGCShouldWait and, in the event that the
1893 // foreground collector is waiting, notify it, before
1894 // returning.
1895 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1896 _foregroundGCShouldWait = false;
1897 if (_foregroundGCIsActive) {
1898 CGC_lock->notify();
1899 }
1900 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1901 "Possible deadlock");
1902 }
1903 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1904 p2i(Thread::current()), _collectorState);
1905 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1906 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1907 }
1908
1909 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1910 _cms_start_registered = true;
1911 _gc_timer_cm->register_gc_start();
1912 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1913 }
1914
1915 void CMSCollector::register_gc_end() {
1916 if (_cms_start_registered) {
1917 report_heap_summary(GCWhen::AfterGC);
1918
1919 _gc_timer_cm->register_gc_end();
1920 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1921 _cms_start_registered = false;
1922 }
1923 }
1924
1925 void CMSCollector::save_heap_summary() {
1926 GenCollectedHeap* gch = GenCollectedHeap::heap();
1927 _last_heap_summary = gch->create_heap_summary();
1928 _last_metaspace_summary = gch->create_metaspace_summary();
1929 }
1930
1931 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1932 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1933 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1934 }
1935
1936 bool CMSCollector::waitForForegroundGC() {
1937 bool res = false;
1938 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1939 "CMS thread should have CMS token");
1940 // Block the foreground collector until the
1941 // background collectors decides whether to
1942 // yield.
1943 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1944 _foregroundGCShouldWait = true;
1945 if (_foregroundGCIsActive) {
1946 // The background collector yields to the
1947 // foreground collector and returns a value
1948 // indicating that it has yielded. The foreground
1949 // collector can proceed.
1950 res = true;
1951 _foregroundGCShouldWait = false;
1952 ConcurrentMarkSweepThread::clear_CMS_flag(
1953 ConcurrentMarkSweepThread::CMS_cms_has_token);
1954 ConcurrentMarkSweepThread::set_CMS_flag(
1955 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1956 // Get a possibly blocked foreground thread going
1957 CGC_lock->notify();
1958 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1959 p2i(Thread::current()), _collectorState);
1960 while (_foregroundGCIsActive) {
1961 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1962 }
1963 ConcurrentMarkSweepThread::set_CMS_flag(
1964 ConcurrentMarkSweepThread::CMS_cms_has_token);
1965 ConcurrentMarkSweepThread::clear_CMS_flag(
1966 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1967 }
1968 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1969 p2i(Thread::current()), _collectorState);
1970 return res;
1971 }
1972
1973 // Because of the need to lock the free lists and other structures in
1974 // the collector, common to all the generations that the collector is
1975 // collecting, we need the gc_prologues of individual CMS generations
1976 // delegate to their collector. It may have been simpler had the
1977 // current infrastructure allowed one to call a prologue on a
1978 // collector. In the absence of that we have the generation's
1979 // prologue delegate to the collector, which delegates back
1980 // some "local" work to a worker method in the individual generations
1981 // that it's responsible for collecting, while itself doing any
1982 // work common to all generations it's responsible for. A similar
1983 // comment applies to the gc_epilogue()'s.
1984 // The role of the variable _between_prologue_and_epilogue is to
1985 // enforce the invocation protocol.
1986 void CMSCollector::gc_prologue(bool full) {
1987 // Call gc_prologue_work() for the CMSGen
1988 // we are responsible for.
1989
1990 // The following locking discipline assumes that we are only called
1991 // when the world is stopped.
1992 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1993
1994 // The CMSCollector prologue must call the gc_prologues for the
1995 // "generations" that it's responsible
1996 // for.
1997
1998 assert( Thread::current()->is_VM_thread()
1999 || ( CMSScavengeBeforeRemark
2000 && Thread::current()->is_ConcurrentGC_thread()),
2001 "Incorrect thread type for prologue execution");
2002
2003 if (_between_prologue_and_epilogue) {
2004 // We have already been invoked; this is a gc_prologue delegation
2005 // from yet another CMS generation that we are responsible for, just
2006 // ignore it since all relevant work has already been done.
2007 return;
2008 }
2009
2010 // set a bit saying prologue has been called; cleared in epilogue
2011 _between_prologue_and_epilogue = true;
2012 // Claim locks for common data structures, then call gc_prologue_work()
2013 // for each CMSGen.
2014
2015 getFreelistLocks(); // gets free list locks on constituent spaces
2016 bitMapLock()->lock_without_safepoint_check();
2017
2018 // Should call gc_prologue_work() for all cms gens we are responsible for
2019 bool duringMarking = _collectorState >= Marking
2020 && _collectorState < Sweeping;
2021
2022 // The young collections clear the modified oops state, which tells if
2023 // there are any modified oops in the class. The remark phase also needs
2024 // that information. Tell the young collection to save the union of all
2025 // modified klasses.
2026 if (duringMarking) {
2027 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2028 }
2029
2030 bool registerClosure = duringMarking;
2031
2032 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2033
2034 if (!full) {
2035 stats().record_gc0_begin();
2036 }
2037 }
2038
2039 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2040
2041 _capacity_at_prologue = capacity();
2042 _used_at_prologue = used();
2043
2044 // We enable promotion tracking so that card-scanning can recognize
2045 // which objects have been promoted during this GC and skip them.
2046 for (uint i = 0; i < ParallelGCThreads; i++) {
2047 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2048 }
2049
2050 // Delegate to CMScollector which knows how to coordinate between
2051 // this and any other CMS generations that it is responsible for
2052 // collecting.
2053 collector()->gc_prologue(full);
2054 }
2055
2056 // This is a "private" interface for use by this generation's CMSCollector.
2057 // Not to be called directly by any other entity (for instance,
2058 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2059 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2060 bool registerClosure, ModUnionClosure* modUnionClosure) {
2061 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2062 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2063 "Should be NULL");
2064 if (registerClosure) {
2065 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2066 }
2067 cmsSpace()->gc_prologue();
2068 // Clear stat counters
2069 NOT_PRODUCT(
2070 assert(_numObjectsPromoted == 0, "check");
2071 assert(_numWordsPromoted == 0, "check");
2072 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2073 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2074 _numObjectsAllocated = 0;
2075 _numWordsAllocated = 0;
2076 )
2077 }
2078
2079 void CMSCollector::gc_epilogue(bool full) {
2080 // The following locking discipline assumes that we are only called
2081 // when the world is stopped.
2082 assert(SafepointSynchronize::is_at_safepoint(),
2083 "world is stopped assumption");
2084
2085 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2086 // if linear allocation blocks need to be appropriately marked to allow the
2087 // the blocks to be parsable. We also check here whether we need to nudge the
2088 // CMS collector thread to start a new cycle (if it's not already active).
2089 assert( Thread::current()->is_VM_thread()
2090 || ( CMSScavengeBeforeRemark
2091 && Thread::current()->is_ConcurrentGC_thread()),
2092 "Incorrect thread type for epilogue execution");
2093
2094 if (!_between_prologue_and_epilogue) {
2095 // We have already been invoked; this is a gc_epilogue delegation
2096 // from yet another CMS generation that we are responsible for, just
2097 // ignore it since all relevant work has already been done.
2098 return;
2099 }
2100 assert(haveFreelistLocks(), "must have freelist locks");
2101 assert_lock_strong(bitMapLock());
2102
2103 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2104
2105 _cmsGen->gc_epilogue_work(full);
2106
2107 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2108 // in case sampling was not already enabled, enable it
2109 _start_sampling = true;
2110 }
2111 // reset _eden_chunk_array so sampling starts afresh
2112 _eden_chunk_index = 0;
2113
2114 size_t cms_used = _cmsGen->cmsSpace()->used();
2115
2116 // update performance counters - this uses a special version of
2117 // update_counters() that allows the utilization to be passed as a
2118 // parameter, avoiding multiple calls to used().
2119 //
2120 _cmsGen->update_counters(cms_used);
2121
2122 bitMapLock()->unlock();
2123 releaseFreelistLocks();
2124
2125 if (!CleanChunkPoolAsync) {
2126 Chunk::clean_chunk_pool();
2127 }
2128
2129 set_did_compact(false);
2130 _between_prologue_and_epilogue = false; // ready for next cycle
2131 }
2132
2133 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2134 collector()->gc_epilogue(full);
2135
2136 // When using ParNew, promotion tracking should have already been
2137 // disabled. However, the prologue (which enables promotion
2138 // tracking) and epilogue are called irrespective of the type of
2139 // GC. So they will also be called before and after Full GCs, during
2140 // which promotion tracking will not be explicitly disabled. So,
2141 // it's safer to also disable it here too (to be symmetric with
2142 // enabling it in the prologue).
2143 for (uint i = 0; i < ParallelGCThreads; i++) {
2144 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2145 }
2146 }
2147
2148 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2149 assert(!incremental_collection_failed(), "Should have been cleared");
2150 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2151 cmsSpace()->gc_epilogue();
2152 // Print stat counters
2153 NOT_PRODUCT(
2154 assert(_numObjectsAllocated == 0, "check");
2155 assert(_numWordsAllocated == 0, "check");
2156 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2157 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2158 _numObjectsPromoted = 0;
2159 _numWordsPromoted = 0;
2160 )
2161
2162 // Call down the chain in contiguous_available needs the freelistLock
2163 // so print this out before releasing the freeListLock.
2164 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2165 }
2166
2167 #ifndef PRODUCT
2168 bool CMSCollector::have_cms_token() {
2169 Thread* thr = Thread::current();
2170 if (thr->is_VM_thread()) {
2171 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2172 } else if (thr->is_ConcurrentGC_thread()) {
2173 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2174 } else if (thr->is_GC_task_thread()) {
2175 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2176 ParGCRareEvent_lock->owned_by_self();
2177 }
2178 return false;
2179 }
2180
2181 // Check reachability of the given heap address in CMS generation,
2182 // treating all other generations as roots.
2183 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2184 // We could "guarantee" below, rather than assert, but I'll
2185 // leave these as "asserts" so that an adventurous debugger
2186 // could try this in the product build provided some subset of
2187 // the conditions were met, provided they were interested in the
2188 // results and knew that the computation below wouldn't interfere
2189 // with other concurrent computations mutating the structures
2190 // being read or written.
2191 assert(SafepointSynchronize::is_at_safepoint(),
2192 "Else mutations in object graph will make answer suspect");
2193 assert(have_cms_token(), "Should hold cms token");
2194 assert(haveFreelistLocks(), "must hold free list locks");
2195 assert_lock_strong(bitMapLock());
2196
2197 // Clear the marking bit map array before starting, but, just
2198 // for kicks, first report if the given address is already marked
2199 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2200 _markBitMap.isMarked(addr) ? "" : " not");
2201
2202 if (verify_after_remark()) {
2203 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2204 bool result = verification_mark_bm()->isMarked(addr);
2205 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2206 result ? "IS" : "is NOT");
2207 return result;
2208 } else {
2209 tty->print_cr("Could not compute result");
2210 return false;
2211 }
2212 }
2213 #endif
2214
2215 void
2216 CMSCollector::print_on_error(outputStream* st) {
2217 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2218 if (collector != NULL) {
2219 CMSBitMap* bitmap = &collector->_markBitMap;
2220 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2221 bitmap->print_on_error(st, " Bits: ");
2222
2223 st->cr();
2224
2225 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2226 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2227 mut_bitmap->print_on_error(st, " Bits: ");
2228 }
2229 }
2230
2231 ////////////////////////////////////////////////////////
2232 // CMS Verification Support
2233 ////////////////////////////////////////////////////////
2234 // Following the remark phase, the following invariant
2235 // should hold -- each object in the CMS heap which is
2236 // marked in markBitMap() should be marked in the verification_mark_bm().
2237
2238 class VerifyMarkedClosure: public BitMapClosure {
2239 CMSBitMap* _marks;
2240 bool _failed;
2241
2242 public:
2243 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2244
2245 bool do_bit(size_t offset) {
2246 HeapWord* addr = _marks->offsetToHeapWord(offset);
2247 if (!_marks->isMarked(addr)) {
2248 Log(gc, verify) log;
2249 ResourceMark rm;
2250 oop(addr)->print_on(log.error_stream());
2251 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2252 _failed = true;
2253 }
2254 return true;
2255 }
2256
2257 bool failed() { return _failed; }
2258 };
2259
2260 bool CMSCollector::verify_after_remark() {
2261 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2262 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2263 static bool init = false;
2264
2265 assert(SafepointSynchronize::is_at_safepoint(),
2266 "Else mutations in object graph will make answer suspect");
2267 assert(have_cms_token(),
2268 "Else there may be mutual interference in use of "
2269 " verification data structures");
2270 assert(_collectorState > Marking && _collectorState <= Sweeping,
2271 "Else marking info checked here may be obsolete");
2272 assert(haveFreelistLocks(), "must hold free list locks");
2273 assert_lock_strong(bitMapLock());
2274
2275
2276 // Allocate marking bit map if not already allocated
2277 if (!init) { // first time
2278 if (!verification_mark_bm()->allocate(_span)) {
2279 return false;
2280 }
2281 init = true;
2282 }
2283
2284 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2285
2286 // Turn off refs discovery -- so we will be tracing through refs.
2287 // This is as intended, because by this time
2288 // GC must already have cleared any refs that need to be cleared,
2289 // and traced those that need to be marked; moreover,
2290 // the marking done here is not going to interfere in any
2291 // way with the marking information used by GC.
2292 NoRefDiscovery no_discovery(ref_processor());
2293
2294 #if defined(COMPILER2) || INCLUDE_JVMCI
2295 DerivedPointerTableDeactivate dpt_deact;
2296 #endif
2297
2298 // Clear any marks from a previous round
2299 verification_mark_bm()->clear_all();
2300 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2301 verify_work_stacks_empty();
2302
2303 GenCollectedHeap* gch = GenCollectedHeap::heap();
2304 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2305 // Update the saved marks which may affect the root scans.
2306 gch->save_marks();
2307
2308 if (CMSRemarkVerifyVariant == 1) {
2309 // In this first variant of verification, we complete
2310 // all marking, then check if the new marks-vector is
2311 // a subset of the CMS marks-vector.
2312 verify_after_remark_work_1();
2313 } else {
2314 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2315 // In this second variant of verification, we flag an error
2316 // (i.e. an object reachable in the new marks-vector not reachable
2317 // in the CMS marks-vector) immediately, also indicating the
2318 // identify of an object (A) that references the unmarked object (B) --
2319 // presumably, a mutation to A failed to be picked up by preclean/remark?
2320 verify_after_remark_work_2();
2321 }
2322
2323 return true;
2324 }
2325
2326 void CMSCollector::verify_after_remark_work_1() {
2327 ResourceMark rm;
2328 HandleMark hm;
2329 CMSHeap* gch = CMSHeap::heap();
2330
2331 // Get a clear set of claim bits for the roots processing to work with.
2332 ClassLoaderDataGraph::clear_claimed_marks();
2333
2334 // Mark from roots one level into CMS
2335 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2336 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2337
2338 {
2339 StrongRootsScope srs(1);
2340
2341 gch->cms_process_roots(&srs,
2342 true, // young gen as roots
2343 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2344 should_unload_classes(),
2345 ¬Older,
2346 NULL);
2347 }
2348
2349 // Now mark from the roots
2350 MarkFromRootsClosure markFromRootsClosure(this, _span,
2351 verification_mark_bm(), verification_mark_stack(),
2352 false /* don't yield */, true /* verifying */);
2353 assert(_restart_addr == NULL, "Expected pre-condition");
2354 verification_mark_bm()->iterate(&markFromRootsClosure);
2355 while (_restart_addr != NULL) {
2356 // Deal with stack overflow: by restarting at the indicated
2357 // address.
2358 HeapWord* ra = _restart_addr;
2359 markFromRootsClosure.reset(ra);
2360 _restart_addr = NULL;
2361 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2362 }
2363 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2364 verify_work_stacks_empty();
2365
2366 // Marking completed -- now verify that each bit marked in
2367 // verification_mark_bm() is also marked in markBitMap(); flag all
2368 // errors by printing corresponding objects.
2369 VerifyMarkedClosure vcl(markBitMap());
2370 verification_mark_bm()->iterate(&vcl);
2371 if (vcl.failed()) {
2372 Log(gc, verify) log;
2373 log.error("Failed marking verification after remark");
2374 ResourceMark rm;
2375 gch->print_on(log.error_stream());
2376 fatal("CMS: failed marking verification after remark");
2377 }
2378 }
2379
2380 class VerifyKlassOopsKlassClosure : public KlassClosure {
2381 class VerifyKlassOopsClosure : public OopClosure {
2382 CMSBitMap* _bitmap;
2383 public:
2384 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2385 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2386 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2387 } _oop_closure;
2388 public:
2389 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2390 void do_klass(Klass* k) {
2391 k->oops_do(&_oop_closure);
2392 }
2393 };
2394
2395 void CMSCollector::verify_after_remark_work_2() {
2396 ResourceMark rm;
2397 HandleMark hm;
2398 CMSHeap* gch = CMSHeap::heap();
2399
2400 // Get a clear set of claim bits for the roots processing to work with.
2401 ClassLoaderDataGraph::clear_claimed_marks();
2402
2403 // Mark from roots one level into CMS
2404 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2405 markBitMap());
2406 CLDToOopClosure cld_closure(¬Older, true);
2407
2408 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2409
2410 {
2411 StrongRootsScope srs(1);
2412
2413 gch->cms_process_roots(&srs,
2414 true, // young gen as roots
2415 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2416 should_unload_classes(),
2417 ¬Older,
2418 &cld_closure);
2419 }
2420
2421 // Now mark from the roots
2422 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2423 verification_mark_bm(), markBitMap(), verification_mark_stack());
2424 assert(_restart_addr == NULL, "Expected pre-condition");
2425 verification_mark_bm()->iterate(&markFromRootsClosure);
2426 while (_restart_addr != NULL) {
2427 // Deal with stack overflow: by restarting at the indicated
2428 // address.
2429 HeapWord* ra = _restart_addr;
2430 markFromRootsClosure.reset(ra);
2431 _restart_addr = NULL;
2432 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2433 }
2434 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2435 verify_work_stacks_empty();
2436
2437 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2438 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2439
2440 // Marking completed -- now verify that each bit marked in
2441 // verification_mark_bm() is also marked in markBitMap(); flag all
2442 // errors by printing corresponding objects.
2443 VerifyMarkedClosure vcl(markBitMap());
2444 verification_mark_bm()->iterate(&vcl);
2445 assert(!vcl.failed(), "Else verification above should not have succeeded");
2446 }
2447
2448 void ConcurrentMarkSweepGeneration::save_marks() {
2449 // delegate to CMS space
2450 cmsSpace()->save_marks();
2451 }
2452
2453 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2454 return cmsSpace()->no_allocs_since_save_marks();
2455 }
2456
2457 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2458 \
2459 void ConcurrentMarkSweepGeneration:: \
2460 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2461 cl->set_generation(this); \
2462 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2463 cl->reset_generation(); \
2464 save_marks(); \
2465 }
2466
2467 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2468
2469 void
2470 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2471 if (freelistLock()->owned_by_self()) {
2472 Generation::oop_iterate(cl);
2473 } else {
2474 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2475 Generation::oop_iterate(cl);
2476 }
2477 }
2478
2479 void
2480 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2481 if (freelistLock()->owned_by_self()) {
2482 Generation::object_iterate(cl);
2483 } else {
2484 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2485 Generation::object_iterate(cl);
2486 }
2487 }
2488
2489 void
2490 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2491 if (freelistLock()->owned_by_self()) {
2492 Generation::safe_object_iterate(cl);
2493 } else {
2494 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2495 Generation::safe_object_iterate(cl);
2496 }
2497 }
2498
2499 void
2500 ConcurrentMarkSweepGeneration::post_compact() {
2501 }
2502
2503 void
2504 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2505 // Fix the linear allocation blocks to look like free blocks.
2506
2507 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2508 // are not called when the heap is verified during universe initialization and
2509 // at vm shutdown.
2510 if (freelistLock()->owned_by_self()) {
2511 cmsSpace()->prepare_for_verify();
2512 } else {
2513 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2514 cmsSpace()->prepare_for_verify();
2515 }
2516 }
2517
2518 void
2519 ConcurrentMarkSweepGeneration::verify() {
2520 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2521 // are not called when the heap is verified during universe initialization and
2522 // at vm shutdown.
2523 if (freelistLock()->owned_by_self()) {
2524 cmsSpace()->verify();
2525 } else {
2526 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2527 cmsSpace()->verify();
2528 }
2529 }
2530
2531 void CMSCollector::verify() {
2532 _cmsGen->verify();
2533 }
2534
2535 #ifndef PRODUCT
2536 bool CMSCollector::overflow_list_is_empty() const {
2537 assert(_num_par_pushes >= 0, "Inconsistency");
2538 if (_overflow_list == NULL) {
2539 assert(_num_par_pushes == 0, "Inconsistency");
2540 }
2541 return _overflow_list == NULL;
2542 }
2543
2544 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2545 // merely consolidate assertion checks that appear to occur together frequently.
2546 void CMSCollector::verify_work_stacks_empty() const {
2547 assert(_markStack.isEmpty(), "Marking stack should be empty");
2548 assert(overflow_list_is_empty(), "Overflow list should be empty");
2549 }
2550
2551 void CMSCollector::verify_overflow_empty() const {
2552 assert(overflow_list_is_empty(), "Overflow list should be empty");
2553 assert(no_preserved_marks(), "No preserved marks");
2554 }
2555 #endif // PRODUCT
2556
2557 // Decide if we want to enable class unloading as part of the
2558 // ensuing concurrent GC cycle. We will collect and
2559 // unload classes if it's the case that:
2560 // (a) class unloading is enabled at the command line, and
2561 // (b) old gen is getting really full
2562 // NOTE: Provided there is no change in the state of the heap between
2563 // calls to this method, it should have idempotent results. Moreover,
2564 // its results should be monotonically increasing (i.e. going from 0 to 1,
2565 // but not 1 to 0) between successive calls between which the heap was
2566 // not collected. For the implementation below, it must thus rely on
2567 // the property that concurrent_cycles_since_last_unload()
2568 // will not decrease unless a collection cycle happened and that
2569 // _cmsGen->is_too_full() are
2570 // themselves also monotonic in that sense. See check_monotonicity()
2571 // below.
2572 void CMSCollector::update_should_unload_classes() {
2573 _should_unload_classes = false;
2574 if (CMSClassUnloadingEnabled) {
2575 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2576 CMSClassUnloadingMaxInterval)
2577 || _cmsGen->is_too_full();
2578 }
2579 }
2580
2581 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2582 bool res = should_concurrent_collect();
2583 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2584 return res;
2585 }
2586
2587 void CMSCollector::setup_cms_unloading_and_verification_state() {
2588 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2589 || VerifyBeforeExit;
2590 const int rso = GenCollectedHeap::SO_AllCodeCache;
2591
2592 // We set the proper root for this CMS cycle here.
2593 if (should_unload_classes()) { // Should unload classes this cycle
2594 remove_root_scanning_option(rso); // Shrink the root set appropriately
2595 set_verifying(should_verify); // Set verification state for this cycle
2596 return; // Nothing else needs to be done at this time
2597 }
2598
2599 // Not unloading classes this cycle
2600 assert(!should_unload_classes(), "Inconsistency!");
2601
2602 // If we are not unloading classes then add SO_AllCodeCache to root
2603 // scanning options.
2604 add_root_scanning_option(rso);
2605
2606 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2607 set_verifying(true);
2608 } else if (verifying() && !should_verify) {
2609 // We were verifying, but some verification flags got disabled.
2610 set_verifying(false);
2611 // Exclude symbols, strings and code cache elements from root scanning to
2612 // reduce IM and RM pauses.
2613 remove_root_scanning_option(rso);
2614 }
2615 }
2616
2617
2618 #ifndef PRODUCT
2619 HeapWord* CMSCollector::block_start(const void* p) const {
2620 const HeapWord* addr = (HeapWord*)p;
2621 if (_span.contains(p)) {
2622 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2623 return _cmsGen->cmsSpace()->block_start(p);
2624 }
2625 }
2626 return NULL;
2627 }
2628 #endif
2629
2630 HeapWord*
2631 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2632 bool tlab,
2633 bool parallel) {
2634 CMSSynchronousYieldRequest yr;
2635 assert(!tlab, "Can't deal with TLAB allocation");
2636 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2637 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2638 if (GCExpandToAllocateDelayMillis > 0) {
2639 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2640 }
2641 return have_lock_and_allocate(word_size, tlab);
2642 }
2643
2644 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2645 size_t bytes,
2646 size_t expand_bytes,
2647 CMSExpansionCause::Cause cause)
2648 {
2649
2650 bool success = expand(bytes, expand_bytes);
2651
2652 // remember why we expanded; this information is used
2653 // by shouldConcurrentCollect() when making decisions on whether to start
2654 // a new CMS cycle.
2655 if (success) {
2656 set_expansion_cause(cause);
2657 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2658 }
2659 }
2660
2661 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2662 HeapWord* res = NULL;
2663 MutexLocker x(ParGCRareEvent_lock);
2664 while (true) {
2665 // Expansion by some other thread might make alloc OK now:
2666 res = ps->lab.alloc(word_sz);
2667 if (res != NULL) return res;
2668 // If there's not enough expansion space available, give up.
2669 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2670 return NULL;
2671 }
2672 // Otherwise, we try expansion.
2673 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2674 // Now go around the loop and try alloc again;
2675 // A competing par_promote might beat us to the expansion space,
2676 // so we may go around the loop again if promotion fails again.
2677 if (GCExpandToAllocateDelayMillis > 0) {
2678 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2679 }
2680 }
2681 }
2682
2683
2684 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2685 PromotionInfo* promo) {
2686 MutexLocker x(ParGCRareEvent_lock);
2687 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2688 while (true) {
2689 // Expansion by some other thread might make alloc OK now:
2690 if (promo->ensure_spooling_space()) {
2691 assert(promo->has_spooling_space(),
2692 "Post-condition of successful ensure_spooling_space()");
2693 return true;
2694 }
2695 // If there's not enough expansion space available, give up.
2696 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2697 return false;
2698 }
2699 // Otherwise, we try expansion.
2700 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2701 // Now go around the loop and try alloc again;
2702 // A competing allocation might beat us to the expansion space,
2703 // so we may go around the loop again if allocation fails again.
2704 if (GCExpandToAllocateDelayMillis > 0) {
2705 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2706 }
2707 }
2708 }
2709
2710 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2711 // Only shrink if a compaction was done so that all the free space
2712 // in the generation is in a contiguous block at the end.
2713 if (did_compact()) {
2714 CardGeneration::shrink(bytes);
2715 }
2716 }
2717
2718 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2719 assert_locked_or_safepoint(Heap_lock);
2720 }
2721
2722 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2723 assert_locked_or_safepoint(Heap_lock);
2724 assert_lock_strong(freelistLock());
2725 log_trace(gc)("Shrinking of CMS not yet implemented");
2726 return;
2727 }
2728
2729
2730 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2731 // phases.
2732 class CMSPhaseAccounting: public StackObj {
2733 public:
2734 CMSPhaseAccounting(CMSCollector *collector,
2735 const char *title);
2736 ~CMSPhaseAccounting();
2737
2738 private:
2739 CMSCollector *_collector;
2740 const char *_title;
2741 GCTraceConcTime(Info, gc) _trace_time;
2742
2743 public:
2744 // Not MT-safe; so do not pass around these StackObj's
2745 // where they may be accessed by other threads.
2746 double wallclock_millis() {
2747 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2748 }
2749 };
2750
2751 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2752 const char *title) :
2753 _collector(collector), _title(title), _trace_time(title) {
2754
2755 _collector->resetYields();
2756 _collector->resetTimer();
2757 _collector->startTimer();
2758 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2759 }
2760
2761 CMSPhaseAccounting::~CMSPhaseAccounting() {
2762 _collector->gc_timer_cm()->register_gc_concurrent_end();
2763 _collector->stopTimer();
2764 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2765 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2766 }
2767
2768 // CMS work
2769
2770 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2771 class CMSParMarkTask : public AbstractGangTask {
2772 protected:
2773 CMSCollector* _collector;
2774 uint _n_workers;
2775 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2776 AbstractGangTask(name),
2777 _collector(collector),
2778 _n_workers(n_workers) {}
2779 // Work method in support of parallel rescan ... of young gen spaces
2780 void do_young_space_rescan(OopsInGenClosure* cl,
2781 ContiguousSpace* space,
2782 HeapWord** chunk_array, size_t chunk_top);
2783 void work_on_young_gen_roots(OopsInGenClosure* cl);
2784 };
2785
2786 // Parallel initial mark task
2787 class CMSParInitialMarkTask: public CMSParMarkTask {
2788 StrongRootsScope* _strong_roots_scope;
2789 public:
2790 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2791 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2792 _strong_roots_scope(strong_roots_scope) {}
2793 void work(uint worker_id);
2794 };
2795
2796 // Checkpoint the roots into this generation from outside
2797 // this generation. [Note this initial checkpoint need only
2798 // be approximate -- we'll do a catch up phase subsequently.]
2799 void CMSCollector::checkpointRootsInitial() {
2800 assert(_collectorState == InitialMarking, "Wrong collector state");
2801 check_correct_thread_executing();
2802 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2803
2804 save_heap_summary();
2805 report_heap_summary(GCWhen::BeforeGC);
2806
2807 ReferenceProcessor* rp = ref_processor();
2808 assert(_restart_addr == NULL, "Control point invariant");
2809 {
2810 // acquire locks for subsequent manipulations
2811 MutexLockerEx x(bitMapLock(),
2812 Mutex::_no_safepoint_check_flag);
2813 checkpointRootsInitialWork();
2814 // enable ("weak") refs discovery
2815 rp->enable_discovery();
2816 _collectorState = Marking;
2817 }
2818 }
2819
2820 void CMSCollector::checkpointRootsInitialWork() {
2821 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2822 assert(_collectorState == InitialMarking, "just checking");
2823
2824 // Already have locks.
2825 assert_lock_strong(bitMapLock());
2826 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2827
2828 // Setup the verification and class unloading state for this
2829 // CMS collection cycle.
2830 setup_cms_unloading_and_verification_state();
2831
2832 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2833
2834 // Reset all the PLAB chunk arrays if necessary.
2835 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2836 reset_survivor_plab_arrays();
2837 }
2838
2839 ResourceMark rm;
2840 HandleMark hm;
2841
2842 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2843 CMSHeap* gch = CMSHeap::heap();
2844
2845 verify_work_stacks_empty();
2846 verify_overflow_empty();
2847
2848 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2849 // Update the saved marks which may affect the root scans.
2850 gch->save_marks();
2851
2852 // weak reference processing has not started yet.
2853 ref_processor()->set_enqueuing_is_done(false);
2854
2855 // Need to remember all newly created CLDs,
2856 // so that we can guarantee that the remark finds them.
2857 ClassLoaderDataGraph::remember_new_clds(true);
2858
2859 // Whenever a CLD is found, it will be claimed before proceeding to mark
2860 // the klasses. The claimed marks need to be cleared before marking starts.
2861 ClassLoaderDataGraph::clear_claimed_marks();
2862
2863 print_eden_and_survivor_chunk_arrays();
2864
2865 {
2866 #if defined(COMPILER2) || INCLUDE_JVMCI
2867 DerivedPointerTableDeactivate dpt_deact;
2868 #endif
2869 if (CMSParallelInitialMarkEnabled) {
2870 // The parallel version.
2871 WorkGang* workers = gch->workers();
2872 assert(workers != NULL, "Need parallel worker threads.");
2873 uint n_workers = workers->active_workers();
2874
2875 StrongRootsScope srs(n_workers);
2876
2877 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2878 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2879 // If the total workers is greater than 1, then multiple workers
2880 // may be used at some time and the initialization has been set
2881 // such that the single threaded path cannot be used.
2882 if (workers->total_workers() > 1) {
2883 workers->run_task(&tsk);
2884 } else {
2885 tsk.work(0);
2886 }
2887 } else {
2888 // The serial version.
2889 CLDToOopClosure cld_closure(¬Older, true);
2890 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2891
2892 StrongRootsScope srs(1);
2893
2894 gch->cms_process_roots(&srs,
2895 true, // young gen as roots
2896 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2897 should_unload_classes(),
2898 ¬Older,
2899 &cld_closure);
2900 }
2901 }
2902
2903 // Clear mod-union table; it will be dirtied in the prologue of
2904 // CMS generation per each young generation collection.
2905
2906 assert(_modUnionTable.isAllClear(),
2907 "Was cleared in most recent final checkpoint phase"
2908 " or no bits are set in the gc_prologue before the start of the next "
2909 "subsequent marking phase.");
2910
2911 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2912
2913 // Save the end of the used_region of the constituent generations
2914 // to be used to limit the extent of sweep in each generation.
2915 save_sweep_limits();
2916 verify_overflow_empty();
2917 }
2918
2919 bool CMSCollector::markFromRoots() {
2920 // we might be tempted to assert that:
2921 // assert(!SafepointSynchronize::is_at_safepoint(),
2922 // "inconsistent argument?");
2923 // However that wouldn't be right, because it's possible that
2924 // a safepoint is indeed in progress as a young generation
2925 // stop-the-world GC happens even as we mark in this generation.
2926 assert(_collectorState == Marking, "inconsistent state?");
2927 check_correct_thread_executing();
2928 verify_overflow_empty();
2929
2930 // Weak ref discovery note: We may be discovering weak
2931 // refs in this generation concurrent (but interleaved) with
2932 // weak ref discovery by the young generation collector.
2933
2934 CMSTokenSyncWithLocks ts(true, bitMapLock());
2935 GCTraceCPUTime tcpu;
2936 CMSPhaseAccounting pa(this, "Concurrent Mark");
2937 bool res = markFromRootsWork();
2938 if (res) {
2939 _collectorState = Precleaning;
2940 } else { // We failed and a foreground collection wants to take over
2941 assert(_foregroundGCIsActive, "internal state inconsistency");
2942 assert(_restart_addr == NULL, "foreground will restart from scratch");
2943 log_debug(gc)("bailing out to foreground collection");
2944 }
2945 verify_overflow_empty();
2946 return res;
2947 }
2948
2949 bool CMSCollector::markFromRootsWork() {
2950 // iterate over marked bits in bit map, doing a full scan and mark
2951 // from these roots using the following algorithm:
2952 // . if oop is to the right of the current scan pointer,
2953 // mark corresponding bit (we'll process it later)
2954 // . else (oop is to left of current scan pointer)
2955 // push oop on marking stack
2956 // . drain the marking stack
2957
2958 // Note that when we do a marking step we need to hold the
2959 // bit map lock -- recall that direct allocation (by mutators)
2960 // and promotion (by the young generation collector) is also
2961 // marking the bit map. [the so-called allocate live policy.]
2962 // Because the implementation of bit map marking is not
2963 // robust wrt simultaneous marking of bits in the same word,
2964 // we need to make sure that there is no such interference
2965 // between concurrent such updates.
2966
2967 // already have locks
2968 assert_lock_strong(bitMapLock());
2969
2970 verify_work_stacks_empty();
2971 verify_overflow_empty();
2972 bool result = false;
2973 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2974 result = do_marking_mt();
2975 } else {
2976 result = do_marking_st();
2977 }
2978 return result;
2979 }
2980
2981 // Forward decl
2982 class CMSConcMarkingTask;
2983
2984 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2985 CMSCollector* _collector;
2986 CMSConcMarkingTask* _task;
2987 public:
2988 virtual void yield();
2989
2990 // "n_threads" is the number of threads to be terminated.
2991 // "queue_set" is a set of work queues of other threads.
2992 // "collector" is the CMS collector associated with this task terminator.
2993 // "yield" indicates whether we need the gang as a whole to yield.
2994 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2995 ParallelTaskTerminator(n_threads, queue_set),
2996 _collector(collector) { }
2997
2998 void set_task(CMSConcMarkingTask* task) {
2999 _task = task;
3000 }
3001 };
3002
3003 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3004 CMSConcMarkingTask* _task;
3005 public:
3006 bool should_exit_termination();
3007 void set_task(CMSConcMarkingTask* task) {
3008 _task = task;
3009 }
3010 };
3011
3012 // MT Concurrent Marking Task
3013 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3014 CMSCollector* _collector;
3015 uint _n_workers; // requested/desired # workers
3016 bool _result;
3017 CompactibleFreeListSpace* _cms_space;
3018 char _pad_front[64]; // padding to ...
3019 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3020 char _pad_back[64];
3021 HeapWord* _restart_addr;
3022
3023 // Exposed here for yielding support
3024 Mutex* const _bit_map_lock;
3025
3026 // The per thread work queues, available here for stealing
3027 OopTaskQueueSet* _task_queues;
3028
3029 // Termination (and yielding) support
3030 CMSConcMarkingTerminator _term;
3031 CMSConcMarkingTerminatorTerminator _term_term;
3032
3033 public:
3034 CMSConcMarkingTask(CMSCollector* collector,
3035 CompactibleFreeListSpace* cms_space,
3036 YieldingFlexibleWorkGang* workers,
3037 OopTaskQueueSet* task_queues):
3038 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3039 _collector(collector),
3040 _cms_space(cms_space),
3041 _n_workers(0), _result(true),
3042 _task_queues(task_queues),
3043 _term(_n_workers, task_queues, _collector),
3044 _bit_map_lock(collector->bitMapLock())
3045 {
3046 _requested_size = _n_workers;
3047 _term.set_task(this);
3048 _term_term.set_task(this);
3049 _restart_addr = _global_finger = _cms_space->bottom();
3050 }
3051
3052
3053 OopTaskQueueSet* task_queues() { return _task_queues; }
3054
3055 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3056
3057 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3058
3059 CMSConcMarkingTerminator* terminator() { return &_term; }
3060
3061 virtual void set_for_termination(uint active_workers) {
3062 terminator()->reset_for_reuse(active_workers);
3063 }
3064
3065 void work(uint worker_id);
3066 bool should_yield() {
3067 return ConcurrentMarkSweepThread::should_yield()
3068 && !_collector->foregroundGCIsActive();
3069 }
3070
3071 virtual void coordinator_yield(); // stuff done by coordinator
3072 bool result() { return _result; }
3073
3074 void reset(HeapWord* ra) {
3075 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3076 _restart_addr = _global_finger = ra;
3077 _term.reset_for_reuse();
3078 }
3079
3080 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3081 OopTaskQueue* work_q);
3082
3083 private:
3084 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3085 void do_work_steal(int i);
3086 void bump_global_finger(HeapWord* f);
3087 };
3088
3089 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3090 assert(_task != NULL, "Error");
3091 return _task->yielding();
3092 // Note that we do not need the disjunct || _task->should_yield() above
3093 // because we want terminating threads to yield only if the task
3094 // is already in the midst of yielding, which happens only after at least one
3095 // thread has yielded.
3096 }
3097
3098 void CMSConcMarkingTerminator::yield() {
3099 if (_task->should_yield()) {
3100 _task->yield();
3101 } else {
3102 ParallelTaskTerminator::yield();
3103 }
3104 }
3105
3106 ////////////////////////////////////////////////////////////////
3107 // Concurrent Marking Algorithm Sketch
3108 ////////////////////////////////////////////////////////////////
3109 // Until all tasks exhausted (both spaces):
3110 // -- claim next available chunk
3111 // -- bump global finger via CAS
3112 // -- find first object that starts in this chunk
3113 // and start scanning bitmap from that position
3114 // -- scan marked objects for oops
3115 // -- CAS-mark target, and if successful:
3116 // . if target oop is above global finger (volatile read)
3117 // nothing to do
3118 // . if target oop is in chunk and above local finger
3119 // then nothing to do
3120 // . else push on work-queue
3121 // -- Deal with possible overflow issues:
3122 // . local work-queue overflow causes stuff to be pushed on
3123 // global (common) overflow queue
3124 // . always first empty local work queue
3125 // . then get a batch of oops from global work queue if any
3126 // . then do work stealing
3127 // -- When all tasks claimed (both spaces)
3128 // and local work queue empty,
3129 // then in a loop do:
3130 // . check global overflow stack; steal a batch of oops and trace
3131 // . try to steal from other threads oif GOS is empty
3132 // . if neither is available, offer termination
3133 // -- Terminate and return result
3134 //
3135 void CMSConcMarkingTask::work(uint worker_id) {
3136 elapsedTimer _timer;
3137 ResourceMark rm;
3138 HandleMark hm;
3139
3140 DEBUG_ONLY(_collector->verify_overflow_empty();)
3141
3142 // Before we begin work, our work queue should be empty
3143 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3144 // Scan the bitmap covering _cms_space, tracing through grey objects.
3145 _timer.start();
3146 do_scan_and_mark(worker_id, _cms_space);
3147 _timer.stop();
3148 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3149
3150 // ... do work stealing
3151 _timer.reset();
3152 _timer.start();
3153 do_work_steal(worker_id);
3154 _timer.stop();
3155 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3156 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3157 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3158 // Note that under the current task protocol, the
3159 // following assertion is true even of the spaces
3160 // expanded since the completion of the concurrent
3161 // marking. XXX This will likely change under a strict
3162 // ABORT semantics.
3163 // After perm removal the comparison was changed to
3164 // greater than or equal to from strictly greater than.
3165 // Before perm removal the highest address sweep would
3166 // have been at the end of perm gen but now is at the
3167 // end of the tenured gen.
3168 assert(_global_finger >= _cms_space->end(),
3169 "All tasks have been completed");
3170 DEBUG_ONLY(_collector->verify_overflow_empty();)
3171 }
3172
3173 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3174 HeapWord* read = _global_finger;
3175 HeapWord* cur = read;
3176 while (f > read) {
3177 cur = read;
3178 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3179 if (cur == read) {
3180 // our cas succeeded
3181 assert(_global_finger >= f, "protocol consistency");
3182 break;
3183 }
3184 }
3185 }
3186
3187 // This is really inefficient, and should be redone by
3188 // using (not yet available) block-read and -write interfaces to the
3189 // stack and the work_queue. XXX FIX ME !!!
3190 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3191 OopTaskQueue* work_q) {
3192 // Fast lock-free check
3193 if (ovflw_stk->length() == 0) {
3194 return false;
3195 }
3196 assert(work_q->size() == 0, "Shouldn't steal");
3197 MutexLockerEx ml(ovflw_stk->par_lock(),
3198 Mutex::_no_safepoint_check_flag);
3199 // Grab up to 1/4 the size of the work queue
3200 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3201 (size_t)ParGCDesiredObjsFromOverflowList);
3202 num = MIN2(num, ovflw_stk->length());
3203 for (int i = (int) num; i > 0; i--) {
3204 oop cur = ovflw_stk->pop();
3205 assert(cur != NULL, "Counted wrong?");
3206 work_q->push(cur);
3207 }
3208 return num > 0;
3209 }
3210
3211 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3212 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3213 int n_tasks = pst->n_tasks();
3214 // We allow that there may be no tasks to do here because
3215 // we are restarting after a stack overflow.
3216 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3217 uint nth_task = 0;
3218
3219 HeapWord* aligned_start = sp->bottom();
3220 if (sp->used_region().contains(_restart_addr)) {
3221 // Align down to a card boundary for the start of 0th task
3222 // for this space.
3223 aligned_start =
3224 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3225 CardTableModRefBS::card_size);
3226 }
3227
3228 size_t chunk_size = sp->marking_task_size();
3229 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3230 // Having claimed the nth task in this space,
3231 // compute the chunk that it corresponds to:
3232 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3233 aligned_start + (nth_task+1)*chunk_size);
3234 // Try and bump the global finger via a CAS;
3235 // note that we need to do the global finger bump
3236 // _before_ taking the intersection below, because
3237 // the task corresponding to that region will be
3238 // deemed done even if the used_region() expands
3239 // because of allocation -- as it almost certainly will
3240 // during start-up while the threads yield in the
3241 // closure below.
3242 HeapWord* finger = span.end();
3243 bump_global_finger(finger); // atomically
3244 // There are null tasks here corresponding to chunks
3245 // beyond the "top" address of the space.
3246 span = span.intersection(sp->used_region());
3247 if (!span.is_empty()) { // Non-null task
3248 HeapWord* prev_obj;
3249 assert(!span.contains(_restart_addr) || nth_task == 0,
3250 "Inconsistency");
3251 if (nth_task == 0) {
3252 // For the 0th task, we'll not need to compute a block_start.
3253 if (span.contains(_restart_addr)) {
3254 // In the case of a restart because of stack overflow,
3255 // we might additionally skip a chunk prefix.
3256 prev_obj = _restart_addr;
3257 } else {
3258 prev_obj = span.start();
3259 }
3260 } else {
3261 // We want to skip the first object because
3262 // the protocol is to scan any object in its entirety
3263 // that _starts_ in this span; a fortiori, any
3264 // object starting in an earlier span is scanned
3265 // as part of an earlier claimed task.
3266 // Below we use the "careful" version of block_start
3267 // so we do not try to navigate uninitialized objects.
3268 prev_obj = sp->block_start_careful(span.start());
3269 // Below we use a variant of block_size that uses the
3270 // Printezis bits to avoid waiting for allocated
3271 // objects to become initialized/parsable.
3272 while (prev_obj < span.start()) {
3273 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3274 if (sz > 0) {
3275 prev_obj += sz;
3276 } else {
3277 // In this case we may end up doing a bit of redundant
3278 // scanning, but that appears unavoidable, short of
3279 // locking the free list locks; see bug 6324141.
3280 break;
3281 }
3282 }
3283 }
3284 if (prev_obj < span.end()) {
3285 MemRegion my_span = MemRegion(prev_obj, span.end());
3286 // Do the marking work within a non-empty span --
3287 // the last argument to the constructor indicates whether the
3288 // iteration should be incremental with periodic yields.
3289 ParMarkFromRootsClosure cl(this, _collector, my_span,
3290 &_collector->_markBitMap,
3291 work_queue(i),
3292 &_collector->_markStack);
3293 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3294 } // else nothing to do for this task
3295 } // else nothing to do for this task
3296 }
3297 // We'd be tempted to assert here that since there are no
3298 // more tasks left to claim in this space, the global_finger
3299 // must exceed space->top() and a fortiori space->end(). However,
3300 // that would not quite be correct because the bumping of
3301 // global_finger occurs strictly after the claiming of a task,
3302 // so by the time we reach here the global finger may not yet
3303 // have been bumped up by the thread that claimed the last
3304 // task.
3305 pst->all_tasks_completed();
3306 }
3307
3308 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3309 private:
3310 CMSCollector* _collector;
3311 CMSConcMarkingTask* _task;
3312 MemRegion _span;
3313 CMSBitMap* _bit_map;
3314 CMSMarkStack* _overflow_stack;
3315 OopTaskQueue* _work_queue;
3316 protected:
3317 DO_OOP_WORK_DEFN
3318 public:
3319 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3320 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3321 MetadataAwareOopClosure(collector->ref_processor()),
3322 _collector(collector),
3323 _task(task),
3324 _span(collector->_span),
3325 _work_queue(work_queue),
3326 _bit_map(bit_map),
3327 _overflow_stack(overflow_stack)
3328 { }
3329 virtual void do_oop(oop* p);
3330 virtual void do_oop(narrowOop* p);
3331
3332 void trim_queue(size_t max);
3333 void handle_stack_overflow(HeapWord* lost);
3334 void do_yield_check() {
3335 if (_task->should_yield()) {
3336 _task->yield();
3337 }
3338 }
3339 };
3340
3341 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3342
3343 // Grey object scanning during work stealing phase --
3344 // the salient assumption here is that any references
3345 // that are in these stolen objects being scanned must
3346 // already have been initialized (else they would not have
3347 // been published), so we do not need to check for
3348 // uninitialized objects before pushing here.
3349 void ParConcMarkingClosure::do_oop(oop obj) {
3350 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3351 HeapWord* addr = (HeapWord*)obj;
3352 // Check if oop points into the CMS generation
3353 // and is not marked
3354 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3355 // a white object ...
3356 // If we manage to "claim" the object, by being the
3357 // first thread to mark it, then we push it on our
3358 // marking stack
3359 if (_bit_map->par_mark(addr)) { // ... now grey
3360 // push on work queue (grey set)
3361 bool simulate_overflow = false;
3362 NOT_PRODUCT(
3363 if (CMSMarkStackOverflowALot &&
3364 _collector->simulate_overflow()) {
3365 // simulate a stack overflow
3366 simulate_overflow = true;
3367 }
3368 )
3369 if (simulate_overflow ||
3370 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3371 // stack overflow
3372 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3373 // We cannot assert that the overflow stack is full because
3374 // it may have been emptied since.
3375 assert(simulate_overflow ||
3376 _work_queue->size() == _work_queue->max_elems(),
3377 "Else push should have succeeded");
3378 handle_stack_overflow(addr);
3379 }
3380 } // Else, some other thread got there first
3381 do_yield_check();
3382 }
3383 }
3384
3385 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); }
3386 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3387
3388 void ParConcMarkingClosure::trim_queue(size_t max) {
3389 while (_work_queue->size() > max) {
3390 oop new_oop;
3391 if (_work_queue->pop_local(new_oop)) {
3392 assert(new_oop->is_oop(), "Should be an oop");
3393 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3394 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3395 new_oop->oop_iterate(this); // do_oop() above
3396 do_yield_check();
3397 }
3398 }
3399 }
3400
3401 // Upon stack overflow, we discard (part of) the stack,
3402 // remembering the least address amongst those discarded
3403 // in CMSCollector's _restart_address.
3404 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3405 // We need to do this under a mutex to prevent other
3406 // workers from interfering with the work done below.
3407 MutexLockerEx ml(_overflow_stack->par_lock(),
3408 Mutex::_no_safepoint_check_flag);
3409 // Remember the least grey address discarded
3410 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3411 _collector->lower_restart_addr(ra);
3412 _overflow_stack->reset(); // discard stack contents
3413 _overflow_stack->expand(); // expand the stack if possible
3414 }
3415
3416
3417 void CMSConcMarkingTask::do_work_steal(int i) {
3418 OopTaskQueue* work_q = work_queue(i);
3419 oop obj_to_scan;
3420 CMSBitMap* bm = &(_collector->_markBitMap);
3421 CMSMarkStack* ovflw = &(_collector->_markStack);
3422 int* seed = _collector->hash_seed(i);
3423 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3424 while (true) {
3425 cl.trim_queue(0);
3426 assert(work_q->size() == 0, "Should have been emptied above");
3427 if (get_work_from_overflow_stack(ovflw, work_q)) {
3428 // Can't assert below because the work obtained from the
3429 // overflow stack may already have been stolen from us.
3430 // assert(work_q->size() > 0, "Work from overflow stack");
3431 continue;
3432 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3433 assert(obj_to_scan->is_oop(), "Should be an oop");
3434 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3435 obj_to_scan->oop_iterate(&cl);
3436 } else if (terminator()->offer_termination(&_term_term)) {
3437 assert(work_q->size() == 0, "Impossible!");
3438 break;
3439 } else if (yielding() || should_yield()) {
3440 yield();
3441 }
3442 }
3443 }
3444
3445 // This is run by the CMS (coordinator) thread.
3446 void CMSConcMarkingTask::coordinator_yield() {
3447 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3448 "CMS thread should hold CMS token");
3449 // First give up the locks, then yield, then re-lock
3450 // We should probably use a constructor/destructor idiom to
3451 // do this unlock/lock or modify the MutexUnlocker class to
3452 // serve our purpose. XXX
3453 assert_lock_strong(_bit_map_lock);
3454 _bit_map_lock->unlock();
3455 ConcurrentMarkSweepThread::desynchronize(true);
3456 _collector->stopTimer();
3457 _collector->incrementYields();
3458
3459 // It is possible for whichever thread initiated the yield request
3460 // not to get a chance to wake up and take the bitmap lock between
3461 // this thread releasing it and reacquiring it. So, while the
3462 // should_yield() flag is on, let's sleep for a bit to give the
3463 // other thread a chance to wake up. The limit imposed on the number
3464 // of iterations is defensive, to avoid any unforseen circumstances
3465 // putting us into an infinite loop. Since it's always been this
3466 // (coordinator_yield()) method that was observed to cause the
3467 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3468 // which is by default non-zero. For the other seven methods that
3469 // also perform the yield operation, as are using a different
3470 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3471 // can enable the sleeping for those methods too, if necessary.
3472 // See 6442774.
3473 //
3474 // We really need to reconsider the synchronization between the GC
3475 // thread and the yield-requesting threads in the future and we
3476 // should really use wait/notify, which is the recommended
3477 // way of doing this type of interaction. Additionally, we should
3478 // consolidate the eight methods that do the yield operation and they
3479 // are almost identical into one for better maintainability and
3480 // readability. See 6445193.
3481 //
3482 // Tony 2006.06.29
3483 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3484 ConcurrentMarkSweepThread::should_yield() &&
3485 !CMSCollector::foregroundGCIsActive(); ++i) {
3486 os::sleep(Thread::current(), 1, false);
3487 }
3488
3489 ConcurrentMarkSweepThread::synchronize(true);
3490 _bit_map_lock->lock_without_safepoint_check();
3491 _collector->startTimer();
3492 }
3493
3494 bool CMSCollector::do_marking_mt() {
3495 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3496 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3497 conc_workers()->active_workers(),
3498 Threads::number_of_non_daemon_threads());
3499 num_workers = conc_workers()->update_active_workers(num_workers);
3500 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3501
3502 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3503
3504 CMSConcMarkingTask tsk(this,
3505 cms_space,
3506 conc_workers(),
3507 task_queues());
3508
3509 // Since the actual number of workers we get may be different
3510 // from the number we requested above, do we need to do anything different
3511 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3512 // class?? XXX
3513 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3514
3515 // Refs discovery is already non-atomic.
3516 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3517 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3518 conc_workers()->start_task(&tsk);
3519 while (tsk.yielded()) {
3520 tsk.coordinator_yield();
3521 conc_workers()->continue_task(&tsk);
3522 }
3523 // If the task was aborted, _restart_addr will be non-NULL
3524 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3525 while (_restart_addr != NULL) {
3526 // XXX For now we do not make use of ABORTED state and have not
3527 // yet implemented the right abort semantics (even in the original
3528 // single-threaded CMS case). That needs some more investigation
3529 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3530 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3531 // If _restart_addr is non-NULL, a marking stack overflow
3532 // occurred; we need to do a fresh marking iteration from the
3533 // indicated restart address.
3534 if (_foregroundGCIsActive) {
3535 // We may be running into repeated stack overflows, having
3536 // reached the limit of the stack size, while making very
3537 // slow forward progress. It may be best to bail out and
3538 // let the foreground collector do its job.
3539 // Clear _restart_addr, so that foreground GC
3540 // works from scratch. This avoids the headache of
3541 // a "rescan" which would otherwise be needed because
3542 // of the dirty mod union table & card table.
3543 _restart_addr = NULL;
3544 return false;
3545 }
3546 // Adjust the task to restart from _restart_addr
3547 tsk.reset(_restart_addr);
3548 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3549 _restart_addr);
3550 _restart_addr = NULL;
3551 // Get the workers going again
3552 conc_workers()->start_task(&tsk);
3553 while (tsk.yielded()) {
3554 tsk.coordinator_yield();
3555 conc_workers()->continue_task(&tsk);
3556 }
3557 }
3558 assert(tsk.completed(), "Inconsistency");
3559 assert(tsk.result() == true, "Inconsistency");
3560 return true;
3561 }
3562
3563 bool CMSCollector::do_marking_st() {
3564 ResourceMark rm;
3565 HandleMark hm;
3566
3567 // Temporarily make refs discovery single threaded (non-MT)
3568 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3569 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3570 &_markStack, CMSYield);
3571 // the last argument to iterate indicates whether the iteration
3572 // should be incremental with periodic yields.
3573 _markBitMap.iterate(&markFromRootsClosure);
3574 // If _restart_addr is non-NULL, a marking stack overflow
3575 // occurred; we need to do a fresh iteration from the
3576 // indicated restart address.
3577 while (_restart_addr != NULL) {
3578 if (_foregroundGCIsActive) {
3579 // We may be running into repeated stack overflows, having
3580 // reached the limit of the stack size, while making very
3581 // slow forward progress. It may be best to bail out and
3582 // let the foreground collector do its job.
3583 // Clear _restart_addr, so that foreground GC
3584 // works from scratch. This avoids the headache of
3585 // a "rescan" which would otherwise be needed because
3586 // of the dirty mod union table & card table.
3587 _restart_addr = NULL;
3588 return false; // indicating failure to complete marking
3589 }
3590 // Deal with stack overflow:
3591 // we restart marking from _restart_addr
3592 HeapWord* ra = _restart_addr;
3593 markFromRootsClosure.reset(ra);
3594 _restart_addr = NULL;
3595 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3596 }
3597 return true;
3598 }
3599
3600 void CMSCollector::preclean() {
3601 check_correct_thread_executing();
3602 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3603 verify_work_stacks_empty();
3604 verify_overflow_empty();
3605 _abort_preclean = false;
3606 if (CMSPrecleaningEnabled) {
3607 if (!CMSEdenChunksRecordAlways) {
3608 _eden_chunk_index = 0;
3609 }
3610 size_t used = get_eden_used();
3611 size_t capacity = get_eden_capacity();
3612 // Don't start sampling unless we will get sufficiently
3613 // many samples.
3614 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3615 * CMSScheduleRemarkEdenPenetration)) {
3616 _start_sampling = true;
3617 } else {
3618 _start_sampling = false;
3619 }
3620 GCTraceCPUTime tcpu;
3621 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3622 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3623 }
3624 CMSTokenSync x(true); // is cms thread
3625 if (CMSPrecleaningEnabled) {
3626 sample_eden();
3627 _collectorState = AbortablePreclean;
3628 } else {
3629 _collectorState = FinalMarking;
3630 }
3631 verify_work_stacks_empty();
3632 verify_overflow_empty();
3633 }
3634
3635 // Try and schedule the remark such that young gen
3636 // occupancy is CMSScheduleRemarkEdenPenetration %.
3637 void CMSCollector::abortable_preclean() {
3638 check_correct_thread_executing();
3639 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3640 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3641
3642 // If Eden's current occupancy is below this threshold,
3643 // immediately schedule the remark; else preclean
3644 // past the next scavenge in an effort to
3645 // schedule the pause as described above. By choosing
3646 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3647 // we will never do an actual abortable preclean cycle.
3648 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3649 GCTraceCPUTime tcpu;
3650 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3651 // We need more smarts in the abortable preclean
3652 // loop below to deal with cases where allocation
3653 // in young gen is very very slow, and our precleaning
3654 // is running a losing race against a horde of
3655 // mutators intent on flooding us with CMS updates
3656 // (dirty cards).
3657 // One, admittedly dumb, strategy is to give up
3658 // after a certain number of abortable precleaning loops
3659 // or after a certain maximum time. We want to make
3660 // this smarter in the next iteration.
3661 // XXX FIX ME!!! YSR
3662 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3663 while (!(should_abort_preclean() ||
3664 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3665 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3666 cumworkdone += workdone;
3667 loops++;
3668 // Voluntarily terminate abortable preclean phase if we have
3669 // been at it for too long.
3670 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3671 loops >= CMSMaxAbortablePrecleanLoops) {
3672 log_debug(gc)(" CMS: abort preclean due to loops ");
3673 break;
3674 }
3675 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3676 log_debug(gc)(" CMS: abort preclean due to time ");
3677 break;
3678 }
3679 // If we are doing little work each iteration, we should
3680 // take a short break.
3681 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3682 // Sleep for some time, waiting for work to accumulate
3683 stopTimer();
3684 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3685 startTimer();
3686 waited++;
3687 }
3688 }
3689 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3690 loops, waited, cumworkdone);
3691 }
3692 CMSTokenSync x(true); // is cms thread
3693 if (_collectorState != Idling) {
3694 assert(_collectorState == AbortablePreclean,
3695 "Spontaneous state transition?");
3696 _collectorState = FinalMarking;
3697 } // Else, a foreground collection completed this CMS cycle.
3698 return;
3699 }
3700
3701 // Respond to an Eden sampling opportunity
3702 void CMSCollector::sample_eden() {
3703 // Make sure a young gc cannot sneak in between our
3704 // reading and recording of a sample.
3705 assert(Thread::current()->is_ConcurrentGC_thread(),
3706 "Only the cms thread may collect Eden samples");
3707 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3708 "Should collect samples while holding CMS token");
3709 if (!_start_sampling) {
3710 return;
3711 }
3712 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3713 // is populated by the young generation.
3714 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3715 if (_eden_chunk_index < _eden_chunk_capacity) {
3716 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3717 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3718 "Unexpected state of Eden");
3719 // We'd like to check that what we just sampled is an oop-start address;
3720 // however, we cannot do that here since the object may not yet have been
3721 // initialized. So we'll instead do the check when we _use_ this sample
3722 // later.
3723 if (_eden_chunk_index == 0 ||
3724 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3725 _eden_chunk_array[_eden_chunk_index-1])
3726 >= CMSSamplingGrain)) {
3727 _eden_chunk_index++; // commit sample
3728 }
3729 }
3730 }
3731 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3732 size_t used = get_eden_used();
3733 size_t capacity = get_eden_capacity();
3734 assert(used <= capacity, "Unexpected state of Eden");
3735 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3736 _abort_preclean = true;
3737 }
3738 }
3739 }
3740
3741
3742 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3743 assert(_collectorState == Precleaning ||
3744 _collectorState == AbortablePreclean, "incorrect state");
3745 ResourceMark rm;
3746 HandleMark hm;
3747
3748 // Precleaning is currently not MT but the reference processor
3749 // may be set for MT. Disable it temporarily here.
3750 ReferenceProcessor* rp = ref_processor();
3751 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3752
3753 // Do one pass of scrubbing the discovered reference lists
3754 // to remove any reference objects with strongly-reachable
3755 // referents.
3756 if (clean_refs) {
3757 CMSPrecleanRefsYieldClosure yield_cl(this);
3758 assert(rp->span().equals(_span), "Spans should be equal");
3759 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3760 &_markStack, true /* preclean */);
3761 CMSDrainMarkingStackClosure complete_trace(this,
3762 _span, &_markBitMap, &_markStack,
3763 &keep_alive, true /* preclean */);
3764
3765 // We don't want this step to interfere with a young
3766 // collection because we don't want to take CPU
3767 // or memory bandwidth away from the young GC threads
3768 // (which may be as many as there are CPUs).
3769 // Note that we don't need to protect ourselves from
3770 // interference with mutators because they can't
3771 // manipulate the discovered reference lists nor affect
3772 // the computed reachability of the referents, the
3773 // only properties manipulated by the precleaning
3774 // of these reference lists.
3775 stopTimer();
3776 CMSTokenSyncWithLocks x(true /* is cms thread */,
3777 bitMapLock());
3778 startTimer();
3779 sample_eden();
3780
3781 // The following will yield to allow foreground
3782 // collection to proceed promptly. XXX YSR:
3783 // The code in this method may need further
3784 // tweaking for better performance and some restructuring
3785 // for cleaner interfaces.
3786 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3787 rp->preclean_discovered_references(
3788 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3789 gc_timer);
3790 }
3791
3792 if (clean_survivor) { // preclean the active survivor space(s)
3793 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3794 &_markBitMap, &_modUnionTable,
3795 &_markStack, true /* precleaning phase */);
3796 stopTimer();
3797 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3798 bitMapLock());
3799 startTimer();
3800 unsigned int before_count =
3801 GenCollectedHeap::heap()->total_collections();
3802 SurvivorSpacePrecleanClosure
3803 sss_cl(this, _span, &_markBitMap, &_markStack,
3804 &pam_cl, before_count, CMSYield);
3805 _young_gen->from()->object_iterate_careful(&sss_cl);
3806 _young_gen->to()->object_iterate_careful(&sss_cl);
3807 }
3808 MarkRefsIntoAndScanClosure
3809 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3810 &_markStack, this, CMSYield,
3811 true /* precleaning phase */);
3812 // CAUTION: The following closure has persistent state that may need to
3813 // be reset upon a decrease in the sequence of addresses it
3814 // processes.
3815 ScanMarkedObjectsAgainCarefullyClosure
3816 smoac_cl(this, _span,
3817 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3818
3819 // Preclean dirty cards in ModUnionTable and CardTable using
3820 // appropriate convergence criterion;
3821 // repeat CMSPrecleanIter times unless we find that
3822 // we are losing.
3823 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3824 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3825 "Bad convergence multiplier");
3826 assert(CMSPrecleanThreshold >= 100,
3827 "Unreasonably low CMSPrecleanThreshold");
3828
3829 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3830 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3831 numIter < CMSPrecleanIter;
3832 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3833 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3834 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3835 // Either there are very few dirty cards, so re-mark
3836 // pause will be small anyway, or our pre-cleaning isn't
3837 // that much faster than the rate at which cards are being
3838 // dirtied, so we might as well stop and re-mark since
3839 // precleaning won't improve our re-mark time by much.
3840 if (curNumCards <= CMSPrecleanThreshold ||
3841 (numIter > 0 &&
3842 (curNumCards * CMSPrecleanDenominator >
3843 lastNumCards * CMSPrecleanNumerator))) {
3844 numIter++;
3845 cumNumCards += curNumCards;
3846 break;
3847 }
3848 }
3849
3850 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3851
3852 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3853 cumNumCards += curNumCards;
3854 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3855 curNumCards, cumNumCards, numIter);
3856 return cumNumCards; // as a measure of useful work done
3857 }
3858
3859 // PRECLEANING NOTES:
3860 // Precleaning involves:
3861 // . reading the bits of the modUnionTable and clearing the set bits.
3862 // . For the cards corresponding to the set bits, we scan the
3863 // objects on those cards. This means we need the free_list_lock
3864 // so that we can safely iterate over the CMS space when scanning
3865 // for oops.
3866 // . When we scan the objects, we'll be both reading and setting
3867 // marks in the marking bit map, so we'll need the marking bit map.
3868 // . For protecting _collector_state transitions, we take the CGC_lock.
3869 // Note that any races in the reading of of card table entries by the
3870 // CMS thread on the one hand and the clearing of those entries by the
3871 // VM thread or the setting of those entries by the mutator threads on the
3872 // other are quite benign. However, for efficiency it makes sense to keep
3873 // the VM thread from racing with the CMS thread while the latter is
3874 // dirty card info to the modUnionTable. We therefore also use the
3875 // CGC_lock to protect the reading of the card table and the mod union
3876 // table by the CM thread.
3877 // . We run concurrently with mutator updates, so scanning
3878 // needs to be done carefully -- we should not try to scan
3879 // potentially uninitialized objects.
3880 //
3881 // Locking strategy: While holding the CGC_lock, we scan over and
3882 // reset a maximal dirty range of the mod union / card tables, then lock
3883 // the free_list_lock and bitmap lock to do a full marking, then
3884 // release these locks; and repeat the cycle. This allows for a
3885 // certain amount of fairness in the sharing of these locks between
3886 // the CMS collector on the one hand, and the VM thread and the
3887 // mutators on the other.
3888
3889 // NOTE: preclean_mod_union_table() and preclean_card_table()
3890 // further below are largely identical; if you need to modify
3891 // one of these methods, please check the other method too.
3892
3893 size_t CMSCollector::preclean_mod_union_table(
3894 ConcurrentMarkSweepGeneration* old_gen,
3895 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3896 verify_work_stacks_empty();
3897 verify_overflow_empty();
3898
3899 // strategy: starting with the first card, accumulate contiguous
3900 // ranges of dirty cards; clear these cards, then scan the region
3901 // covered by these cards.
3902
3903 // Since all of the MUT is committed ahead, we can just use
3904 // that, in case the generations expand while we are precleaning.
3905 // It might also be fine to just use the committed part of the
3906 // generation, but we might potentially miss cards when the
3907 // generation is rapidly expanding while we are in the midst
3908 // of precleaning.
3909 HeapWord* startAddr = old_gen->reserved().start();
3910 HeapWord* endAddr = old_gen->reserved().end();
3911
3912 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3913
3914 size_t numDirtyCards, cumNumDirtyCards;
3915 HeapWord *nextAddr, *lastAddr;
3916 for (cumNumDirtyCards = numDirtyCards = 0,
3917 nextAddr = lastAddr = startAddr;
3918 nextAddr < endAddr;
3919 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3920
3921 ResourceMark rm;
3922 HandleMark hm;
3923
3924 MemRegion dirtyRegion;
3925 {
3926 stopTimer();
3927 // Potential yield point
3928 CMSTokenSync ts(true);
3929 startTimer();
3930 sample_eden();
3931 // Get dirty region starting at nextOffset (inclusive),
3932 // simultaneously clearing it.
3933 dirtyRegion =
3934 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3935 assert(dirtyRegion.start() >= nextAddr,
3936 "returned region inconsistent?");
3937 }
3938 // Remember where the next search should begin.
3939 // The returned region (if non-empty) is a right open interval,
3940 // so lastOffset is obtained from the right end of that
3941 // interval.
3942 lastAddr = dirtyRegion.end();
3943 // Should do something more transparent and less hacky XXX
3944 numDirtyCards =
3945 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3946
3947 // We'll scan the cards in the dirty region (with periodic
3948 // yields for foreground GC as needed).
3949 if (!dirtyRegion.is_empty()) {
3950 assert(numDirtyCards > 0, "consistency check");
3951 HeapWord* stop_point = NULL;
3952 stopTimer();
3953 // Potential yield point
3954 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3955 bitMapLock());
3956 startTimer();
3957 {
3958 verify_work_stacks_empty();
3959 verify_overflow_empty();
3960 sample_eden();
3961 stop_point =
3962 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3963 }
3964 if (stop_point != NULL) {
3965 // The careful iteration stopped early either because it found an
3966 // uninitialized object, or because we were in the midst of an
3967 // "abortable preclean", which should now be aborted. Redirty
3968 // the bits corresponding to the partially-scanned or unscanned
3969 // cards. We'll either restart at the next block boundary or
3970 // abort the preclean.
3971 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3972 "Should only be AbortablePreclean.");
3973 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3974 if (should_abort_preclean()) {
3975 break; // out of preclean loop
3976 } else {
3977 // Compute the next address at which preclean should pick up;
3978 // might need bitMapLock in order to read P-bits.
3979 lastAddr = next_card_start_after_block(stop_point);
3980 }
3981 }
3982 } else {
3983 assert(lastAddr == endAddr, "consistency check");
3984 assert(numDirtyCards == 0, "consistency check");
3985 break;
3986 }
3987 }
3988 verify_work_stacks_empty();
3989 verify_overflow_empty();
3990 return cumNumDirtyCards;
3991 }
3992
3993 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3994 // below are largely identical; if you need to modify
3995 // one of these methods, please check the other method too.
3996
3997 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3998 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3999 // strategy: it's similar to precleamModUnionTable above, in that
4000 // we accumulate contiguous ranges of dirty cards, mark these cards
4001 // precleaned, then scan the region covered by these cards.
4002 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4003 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4004
4005 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4006
4007 size_t numDirtyCards, cumNumDirtyCards;
4008 HeapWord *lastAddr, *nextAddr;
4009
4010 for (cumNumDirtyCards = numDirtyCards = 0,
4011 nextAddr = lastAddr = startAddr;
4012 nextAddr < endAddr;
4013 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4014
4015 ResourceMark rm;
4016 HandleMark hm;
4017
4018 MemRegion dirtyRegion;
4019 {
4020 // See comments in "Precleaning notes" above on why we
4021 // do this locking. XXX Could the locking overheads be
4022 // too high when dirty cards are sparse? [I don't think so.]
4023 stopTimer();
4024 CMSTokenSync x(true); // is cms thread
4025 startTimer();
4026 sample_eden();
4027 // Get and clear dirty region from card table
4028 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4029 MemRegion(nextAddr, endAddr),
4030 true,
4031 CardTableModRefBS::precleaned_card_val());
4032
4033 assert(dirtyRegion.start() >= nextAddr,
4034 "returned region inconsistent?");
4035 }
4036 lastAddr = dirtyRegion.end();
4037 numDirtyCards =
4038 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4039
4040 if (!dirtyRegion.is_empty()) {
4041 stopTimer();
4042 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4043 startTimer();
4044 sample_eden();
4045 verify_work_stacks_empty();
4046 verify_overflow_empty();
4047 HeapWord* stop_point =
4048 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4049 if (stop_point != NULL) {
4050 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4051 "Should only be AbortablePreclean.");
4052 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4053 if (should_abort_preclean()) {
4054 break; // out of preclean loop
4055 } else {
4056 // Compute the next address at which preclean should pick up.
4057 lastAddr = next_card_start_after_block(stop_point);
4058 }
4059 }
4060 } else {
4061 break;
4062 }
4063 }
4064 verify_work_stacks_empty();
4065 verify_overflow_empty();
4066 return cumNumDirtyCards;
4067 }
4068
4069 class PrecleanKlassClosure : public KlassClosure {
4070 KlassToOopClosure _cm_klass_closure;
4071 public:
4072 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4073 void do_klass(Klass* k) {
4074 if (k->has_accumulated_modified_oops()) {
4075 k->clear_accumulated_modified_oops();
4076
4077 _cm_klass_closure.do_klass(k);
4078 }
4079 }
4080 };
4081
4082 // The freelist lock is needed to prevent asserts, is it really needed?
4083 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4084
4085 cl->set_freelistLock(freelistLock);
4086
4087 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4088
4089 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4090 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4091 PrecleanKlassClosure preclean_klass_closure(cl);
4092 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4093
4094 verify_work_stacks_empty();
4095 verify_overflow_empty();
4096 }
4097
4098 void CMSCollector::checkpointRootsFinal() {
4099 assert(_collectorState == FinalMarking, "incorrect state transition?");
4100 check_correct_thread_executing();
4101 // world is stopped at this checkpoint
4102 assert(SafepointSynchronize::is_at_safepoint(),
4103 "world should be stopped");
4104 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4105
4106 verify_work_stacks_empty();
4107 verify_overflow_empty();
4108
4109 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4110 _young_gen->used() / K, _young_gen->capacity() / K);
4111 {
4112 if (CMSScavengeBeforeRemark) {
4113 GenCollectedHeap* gch = GenCollectedHeap::heap();
4114 // Temporarily set flag to false, GCH->do_collection will
4115 // expect it to be false and set to true
4116 FlagSetting fl(gch->_is_gc_active, false);
4117
4118 gch->do_collection(true, // full (i.e. force, see below)
4119 false, // !clear_all_soft_refs
4120 0, // size
4121 false, // is_tlab
4122 GenCollectedHeap::YoungGen // type
4123 );
4124 }
4125 FreelistLocker x(this);
4126 MutexLockerEx y(bitMapLock(),
4127 Mutex::_no_safepoint_check_flag);
4128 checkpointRootsFinalWork();
4129 }
4130 verify_work_stacks_empty();
4131 verify_overflow_empty();
4132 }
4133
4134 void CMSCollector::checkpointRootsFinalWork() {
4135 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4136
4137 assert(haveFreelistLocks(), "must have free list locks");
4138 assert_lock_strong(bitMapLock());
4139
4140 ResourceMark rm;
4141 HandleMark hm;
4142
4143 GenCollectedHeap* gch = GenCollectedHeap::heap();
4144
4145 if (should_unload_classes()) {
4146 CodeCache::gc_prologue();
4147 }
4148 assert(haveFreelistLocks(), "must have free list locks");
4149 assert_lock_strong(bitMapLock());
4150
4151 // We might assume that we need not fill TLAB's when
4152 // CMSScavengeBeforeRemark is set, because we may have just done
4153 // a scavenge which would have filled all TLAB's -- and besides
4154 // Eden would be empty. This however may not always be the case --
4155 // for instance although we asked for a scavenge, it may not have
4156 // happened because of a JNI critical section. We probably need
4157 // a policy for deciding whether we can in that case wait until
4158 // the critical section releases and then do the remark following
4159 // the scavenge, and skip it here. In the absence of that policy,
4160 // or of an indication of whether the scavenge did indeed occur,
4161 // we cannot rely on TLAB's having been filled and must do
4162 // so here just in case a scavenge did not happen.
4163 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4164 // Update the saved marks which may affect the root scans.
4165 gch->save_marks();
4166
4167 print_eden_and_survivor_chunk_arrays();
4168
4169 {
4170 #if defined(COMPILER2) || INCLUDE_JVMCI
4171 DerivedPointerTableDeactivate dpt_deact;
4172 #endif
4173
4174 // Note on the role of the mod union table:
4175 // Since the marker in "markFromRoots" marks concurrently with
4176 // mutators, it is possible for some reachable objects not to have been
4177 // scanned. For instance, an only reference to an object A was
4178 // placed in object B after the marker scanned B. Unless B is rescanned,
4179 // A would be collected. Such updates to references in marked objects
4180 // are detected via the mod union table which is the set of all cards
4181 // dirtied since the first checkpoint in this GC cycle and prior to
4182 // the most recent young generation GC, minus those cleaned up by the
4183 // concurrent precleaning.
4184 if (CMSParallelRemarkEnabled) {
4185 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4186 do_remark_parallel();
4187 } else {
4188 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4189 do_remark_non_parallel();
4190 }
4191 }
4192 verify_work_stacks_empty();
4193 verify_overflow_empty();
4194
4195 {
4196 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4197 refProcessingWork();
4198 }
4199 verify_work_stacks_empty();
4200 verify_overflow_empty();
4201
4202 if (should_unload_classes()) {
4203 CodeCache::gc_epilogue();
4204 }
4205 JvmtiExport::gc_epilogue();
4206
4207 // If we encountered any (marking stack / work queue) overflow
4208 // events during the current CMS cycle, take appropriate
4209 // remedial measures, where possible, so as to try and avoid
4210 // recurrence of that condition.
4211 assert(_markStack.isEmpty(), "No grey objects");
4212 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4213 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4214 if (ser_ovflw > 0) {
4215 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4216 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4217 _markStack.expand();
4218 _ser_pmc_remark_ovflw = 0;
4219 _ser_pmc_preclean_ovflw = 0;
4220 _ser_kac_preclean_ovflw = 0;
4221 _ser_kac_ovflw = 0;
4222 }
4223 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4224 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4225 _par_pmc_remark_ovflw, _par_kac_ovflw);
4226 _par_pmc_remark_ovflw = 0;
4227 _par_kac_ovflw = 0;
4228 }
4229 if (_markStack._hit_limit > 0) {
4230 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4231 _markStack._hit_limit);
4232 }
4233 if (_markStack._failed_double > 0) {
4234 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4235 _markStack._failed_double, _markStack.capacity());
4236 }
4237 _markStack._hit_limit = 0;
4238 _markStack._failed_double = 0;
4239
4240 if ((VerifyAfterGC || VerifyDuringGC) &&
4241 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4242 verify_after_remark();
4243 }
4244
4245 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4246
4247 // Change under the freelistLocks.
4248 _collectorState = Sweeping;
4249 // Call isAllClear() under bitMapLock
4250 assert(_modUnionTable.isAllClear(),
4251 "Should be clear by end of the final marking");
4252 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4253 "Should be clear by end of the final marking");
4254 }
4255
4256 void CMSParInitialMarkTask::work(uint worker_id) {
4257 elapsedTimer _timer;
4258 ResourceMark rm;
4259 HandleMark hm;
4260
4261 // ---------- scan from roots --------------
4262 _timer.start();
4263 CMSHeap* gch = CMSHeap::heap();
4264 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4265
4266 // ---------- young gen roots --------------
4267 {
4268 work_on_young_gen_roots(&par_mri_cl);
4269 _timer.stop();
4270 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4271 }
4272
4273 // ---------- remaining roots --------------
4274 _timer.reset();
4275 _timer.start();
4276
4277 CLDToOopClosure cld_closure(&par_mri_cl, true);
4278
4279 gch->cms_process_roots(_strong_roots_scope,
4280 false, // yg was scanned above
4281 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4282 _collector->should_unload_classes(),
4283 &par_mri_cl,
4284 &cld_closure);
4285 assert(_collector->should_unload_classes()
4286 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4287 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4288 _timer.stop();
4289 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4290 }
4291
4292 // Parallel remark task
4293 class CMSParRemarkTask: public CMSParMarkTask {
4294 CompactibleFreeListSpace* _cms_space;
4295
4296 // The per-thread work queues, available here for stealing.
4297 OopTaskQueueSet* _task_queues;
4298 ParallelTaskTerminator _term;
4299 StrongRootsScope* _strong_roots_scope;
4300
4301 public:
4302 // A value of 0 passed to n_workers will cause the number of
4303 // workers to be taken from the active workers in the work gang.
4304 CMSParRemarkTask(CMSCollector* collector,
4305 CompactibleFreeListSpace* cms_space,
4306 uint n_workers, WorkGang* workers,
4307 OopTaskQueueSet* task_queues,
4308 StrongRootsScope* strong_roots_scope):
4309 CMSParMarkTask("Rescan roots and grey objects in parallel",
4310 collector, n_workers),
4311 _cms_space(cms_space),
4312 _task_queues(task_queues),
4313 _term(n_workers, task_queues),
4314 _strong_roots_scope(strong_roots_scope) { }
4315
4316 OopTaskQueueSet* task_queues() { return _task_queues; }
4317
4318 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4319
4320 ParallelTaskTerminator* terminator() { return &_term; }
4321 uint n_workers() { return _n_workers; }
4322
4323 void work(uint worker_id);
4324
4325 private:
4326 // ... of dirty cards in old space
4327 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4328 ParMarkRefsIntoAndScanClosure* cl);
4329
4330 // ... work stealing for the above
4331 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4332 };
4333
4334 class RemarkKlassClosure : public KlassClosure {
4335 KlassToOopClosure _cm_klass_closure;
4336 public:
4337 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4338 void do_klass(Klass* k) {
4339 // Check if we have modified any oops in the Klass during the concurrent marking.
4340 if (k->has_accumulated_modified_oops()) {
4341 k->clear_accumulated_modified_oops();
4342
4343 // We could have transfered the current modified marks to the accumulated marks,
4344 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4345 } else if (k->has_modified_oops()) {
4346 // Don't clear anything, this info is needed by the next young collection.
4347 } else {
4348 // No modified oops in the Klass.
4349 return;
4350 }
4351
4352 // The klass has modified fields, need to scan the klass.
4353 _cm_klass_closure.do_klass(k);
4354 }
4355 };
4356
4357 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4358 ParNewGeneration* young_gen = _collector->_young_gen;
4359 ContiguousSpace* eden_space = young_gen->eden();
4360 ContiguousSpace* from_space = young_gen->from();
4361 ContiguousSpace* to_space = young_gen->to();
4362
4363 HeapWord** eca = _collector->_eden_chunk_array;
4364 size_t ect = _collector->_eden_chunk_index;
4365 HeapWord** sca = _collector->_survivor_chunk_array;
4366 size_t sct = _collector->_survivor_chunk_index;
4367
4368 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4369 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4370
4371 do_young_space_rescan(cl, to_space, NULL, 0);
4372 do_young_space_rescan(cl, from_space, sca, sct);
4373 do_young_space_rescan(cl, eden_space, eca, ect);
4374 }
4375
4376 // work_queue(i) is passed to the closure
4377 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4378 // also is passed to do_dirty_card_rescan_tasks() and to
4379 // do_work_steal() to select the i-th task_queue.
4380
4381 void CMSParRemarkTask::work(uint worker_id) {
4382 elapsedTimer _timer;
4383 ResourceMark rm;
4384 HandleMark hm;
4385
4386 // ---------- rescan from roots --------------
4387 _timer.start();
4388 CMSHeap* gch = CMSHeap::heap();
4389 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4390 _collector->_span, _collector->ref_processor(),
4391 &(_collector->_markBitMap),
4392 work_queue(worker_id));
4393
4394 // Rescan young gen roots first since these are likely
4395 // coarsely partitioned and may, on that account, constitute
4396 // the critical path; thus, it's best to start off that
4397 // work first.
4398 // ---------- young gen roots --------------
4399 {
4400 work_on_young_gen_roots(&par_mrias_cl);
4401 _timer.stop();
4402 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4403 }
4404
4405 // ---------- remaining roots --------------
4406 _timer.reset();
4407 _timer.start();
4408 gch->cms_process_roots(_strong_roots_scope,
4409 false, // yg was scanned above
4410 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4411 _collector->should_unload_classes(),
4412 &par_mrias_cl,
4413 NULL); // The dirty klasses will be handled below
4414
4415 assert(_collector->should_unload_classes()
4416 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4417 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4418 _timer.stop();
4419 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4420
4421 // ---------- unhandled CLD scanning ----------
4422 if (worker_id == 0) { // Single threaded at the moment.
4423 _timer.reset();
4424 _timer.start();
4425
4426 // Scan all new class loader data objects and new dependencies that were
4427 // introduced during concurrent marking.
4428 ResourceMark rm;
4429 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4430 for (int i = 0; i < array->length(); i++) {
4431 par_mrias_cl.do_cld_nv(array->at(i));
4432 }
4433
4434 // We don't need to keep track of new CLDs anymore.
4435 ClassLoaderDataGraph::remember_new_clds(false);
4436
4437 _timer.stop();
4438 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4439 }
4440
4441 // ---------- dirty klass scanning ----------
4442 if (worker_id == 0) { // Single threaded at the moment.
4443 _timer.reset();
4444 _timer.start();
4445
4446 // Scan all classes that was dirtied during the concurrent marking phase.
4447 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4448 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4449
4450 _timer.stop();
4451 log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4452 }
4453
4454 // We might have added oops to ClassLoaderData::_handles during the
4455 // concurrent marking phase. These oops point to newly allocated objects
4456 // that are guaranteed to be kept alive. Either by the direct allocation
4457 // code, or when the young collector processes the roots. Hence,
4458 // we don't have to revisit the _handles block during the remark phase.
4459
4460 // ---------- rescan dirty cards ------------
4461 _timer.reset();
4462 _timer.start();
4463
4464 // Do the rescan tasks for each of the two spaces
4465 // (cms_space) in turn.
4466 // "worker_id" is passed to select the task_queue for "worker_id"
4467 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4468 _timer.stop();
4469 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4470
4471 // ---------- steal work from other threads ...
4472 // ---------- ... and drain overflow list.
4473 _timer.reset();
4474 _timer.start();
4475 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4476 _timer.stop();
4477 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4478 }
4479
4480 void
4481 CMSParMarkTask::do_young_space_rescan(
4482 OopsInGenClosure* cl, ContiguousSpace* space,
4483 HeapWord** chunk_array, size_t chunk_top) {
4484 // Until all tasks completed:
4485 // . claim an unclaimed task
4486 // . compute region boundaries corresponding to task claimed
4487 // using chunk_array
4488 // . par_oop_iterate(cl) over that region
4489
4490 ResourceMark rm;
4491 HandleMark hm;
4492
4493 SequentialSubTasksDone* pst = space->par_seq_tasks();
4494
4495 uint nth_task = 0;
4496 uint n_tasks = pst->n_tasks();
4497
4498 if (n_tasks > 0) {
4499 assert(pst->valid(), "Uninitialized use?");
4500 HeapWord *start, *end;
4501 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4502 // We claimed task # nth_task; compute its boundaries.
4503 if (chunk_top == 0) { // no samples were taken
4504 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4505 start = space->bottom();
4506 end = space->top();
4507 } else if (nth_task == 0) {
4508 start = space->bottom();
4509 end = chunk_array[nth_task];
4510 } else if (nth_task < (uint)chunk_top) {
4511 assert(nth_task >= 1, "Control point invariant");
4512 start = chunk_array[nth_task - 1];
4513 end = chunk_array[nth_task];
4514 } else {
4515 assert(nth_task == (uint)chunk_top, "Control point invariant");
4516 start = chunk_array[chunk_top - 1];
4517 end = space->top();
4518 }
4519 MemRegion mr(start, end);
4520 // Verify that mr is in space
4521 assert(mr.is_empty() || space->used_region().contains(mr),
4522 "Should be in space");
4523 // Verify that "start" is an object boundary
4524 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4525 "Should be an oop");
4526 space->par_oop_iterate(mr, cl);
4527 }
4528 pst->all_tasks_completed();
4529 }
4530 }
4531
4532 void
4533 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4534 CompactibleFreeListSpace* sp, int i,
4535 ParMarkRefsIntoAndScanClosure* cl) {
4536 // Until all tasks completed:
4537 // . claim an unclaimed task
4538 // . compute region boundaries corresponding to task claimed
4539 // . transfer dirty bits ct->mut for that region
4540 // . apply rescanclosure to dirty mut bits for that region
4541
4542 ResourceMark rm;
4543 HandleMark hm;
4544
4545 OopTaskQueue* work_q = work_queue(i);
4546 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4547 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4548 // CAUTION: This closure has state that persists across calls to
4549 // the work method dirty_range_iterate_clear() in that it has
4550 // embedded in it a (subtype of) UpwardsObjectClosure. The
4551 // use of that state in the embedded UpwardsObjectClosure instance
4552 // assumes that the cards are always iterated (even if in parallel
4553 // by several threads) in monotonically increasing order per each
4554 // thread. This is true of the implementation below which picks
4555 // card ranges (chunks) in monotonically increasing order globally
4556 // and, a-fortiori, in monotonically increasing order per thread
4557 // (the latter order being a subsequence of the former).
4558 // If the work code below is ever reorganized into a more chaotic
4559 // work-partitioning form than the current "sequential tasks"
4560 // paradigm, the use of that persistent state will have to be
4561 // revisited and modified appropriately. See also related
4562 // bug 4756801 work on which should examine this code to make
4563 // sure that the changes there do not run counter to the
4564 // assumptions made here and necessary for correctness and
4565 // efficiency. Note also that this code might yield inefficient
4566 // behavior in the case of very large objects that span one or
4567 // more work chunks. Such objects would potentially be scanned
4568 // several times redundantly. Work on 4756801 should try and
4569 // address that performance anomaly if at all possible. XXX
4570 MemRegion full_span = _collector->_span;
4571 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4572 MarkFromDirtyCardsClosure
4573 greyRescanClosure(_collector, full_span, // entire span of interest
4574 sp, bm, work_q, cl);
4575
4576 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4577 assert(pst->valid(), "Uninitialized use?");
4578 uint nth_task = 0;
4579 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4580 MemRegion span = sp->used_region();
4581 HeapWord* start_addr = span.start();
4582 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4583 alignment);
4584 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4585 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4586 start_addr, "Check alignment");
4587 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4588 chunk_size, "Check alignment");
4589
4590 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4591 // Having claimed the nth_task, compute corresponding mem-region,
4592 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4593 // The alignment restriction ensures that we do not need any
4594 // synchronization with other gang-workers while setting or
4595 // clearing bits in thus chunk of the MUT.
4596 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4597 start_addr + (nth_task+1)*chunk_size);
4598 // The last chunk's end might be way beyond end of the
4599 // used region. In that case pull back appropriately.
4600 if (this_span.end() > end_addr) {
4601 this_span.set_end(end_addr);
4602 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4603 }
4604 // Iterate over the dirty cards covering this chunk, marking them
4605 // precleaned, and setting the corresponding bits in the mod union
4606 // table. Since we have been careful to partition at Card and MUT-word
4607 // boundaries no synchronization is needed between parallel threads.
4608 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4609 &modUnionClosure);
4610
4611 // Having transferred these marks into the modUnionTable,
4612 // rescan the marked objects on the dirty cards in the modUnionTable.
4613 // Even if this is at a synchronous collection, the initial marking
4614 // may have been done during an asynchronous collection so there
4615 // may be dirty bits in the mod-union table.
4616 _collector->_modUnionTable.dirty_range_iterate_clear(
4617 this_span, &greyRescanClosure);
4618 _collector->_modUnionTable.verifyNoOneBitsInRange(
4619 this_span.start(),
4620 this_span.end());
4621 }
4622 pst->all_tasks_completed(); // declare that i am done
4623 }
4624
4625 // . see if we can share work_queues with ParNew? XXX
4626 void
4627 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4628 int* seed) {
4629 OopTaskQueue* work_q = work_queue(i);
4630 NOT_PRODUCT(int num_steals = 0;)
4631 oop obj_to_scan;
4632 CMSBitMap* bm = &(_collector->_markBitMap);
4633
4634 while (true) {
4635 // Completely finish any left over work from (an) earlier round(s)
4636 cl->trim_queue(0);
4637 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4638 (size_t)ParGCDesiredObjsFromOverflowList);
4639 // Now check if there's any work in the overflow list
4640 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4641 // only affects the number of attempts made to get work from the
4642 // overflow list and does not affect the number of workers. Just
4643 // pass ParallelGCThreads so this behavior is unchanged.
4644 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4645 work_q,
4646 ParallelGCThreads)) {
4647 // found something in global overflow list;
4648 // not yet ready to go stealing work from others.
4649 // We'd like to assert(work_q->size() != 0, ...)
4650 // because we just took work from the overflow list,
4651 // but of course we can't since all of that could have
4652 // been already stolen from us.
4653 // "He giveth and He taketh away."
4654 continue;
4655 }
4656 // Verify that we have no work before we resort to stealing
4657 assert(work_q->size() == 0, "Have work, shouldn't steal");
4658 // Try to steal from other queues that have work
4659 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4660 NOT_PRODUCT(num_steals++;)
4661 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4662 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4663 // Do scanning work
4664 obj_to_scan->oop_iterate(cl);
4665 // Loop around, finish this work, and try to steal some more
4666 } else if (terminator()->offer_termination()) {
4667 break; // nirvana from the infinite cycle
4668 }
4669 }
4670 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4671 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4672 "Else our work is not yet done");
4673 }
4674
4675 // Record object boundaries in _eden_chunk_array by sampling the eden
4676 // top in the slow-path eden object allocation code path and record
4677 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4678 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4679 // sampling in sample_eden() that activates during the part of the
4680 // preclean phase.
4681 void CMSCollector::sample_eden_chunk() {
4682 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4683 if (_eden_chunk_lock->try_lock()) {
4684 // Record a sample. This is the critical section. The contents
4685 // of the _eden_chunk_array have to be non-decreasing in the
4686 // address order.
4687 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4688 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4689 "Unexpected state of Eden");
4690 if (_eden_chunk_index == 0 ||
4691 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4692 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4693 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4694 _eden_chunk_index++; // commit sample
4695 }
4696 _eden_chunk_lock->unlock();
4697 }
4698 }
4699 }
4700
4701 // Return a thread-local PLAB recording array, as appropriate.
4702 void* CMSCollector::get_data_recorder(int thr_num) {
4703 if (_survivor_plab_array != NULL &&
4704 (CMSPLABRecordAlways ||
4705 (_collectorState > Marking && _collectorState < FinalMarking))) {
4706 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4707 ChunkArray* ca = &_survivor_plab_array[thr_num];
4708 ca->reset(); // clear it so that fresh data is recorded
4709 return (void*) ca;
4710 } else {
4711 return NULL;
4712 }
4713 }
4714
4715 // Reset all the thread-local PLAB recording arrays
4716 void CMSCollector::reset_survivor_plab_arrays() {
4717 for (uint i = 0; i < ParallelGCThreads; i++) {
4718 _survivor_plab_array[i].reset();
4719 }
4720 }
4721
4722 // Merge the per-thread plab arrays into the global survivor chunk
4723 // array which will provide the partitioning of the survivor space
4724 // for CMS initial scan and rescan.
4725 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4726 int no_of_gc_threads) {
4727 assert(_survivor_plab_array != NULL, "Error");
4728 assert(_survivor_chunk_array != NULL, "Error");
4729 assert(_collectorState == FinalMarking ||
4730 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4731 for (int j = 0; j < no_of_gc_threads; j++) {
4732 _cursor[j] = 0;
4733 }
4734 HeapWord* top = surv->top();
4735 size_t i;
4736 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4737 HeapWord* min_val = top; // Higher than any PLAB address
4738 uint min_tid = 0; // position of min_val this round
4739 for (int j = 0; j < no_of_gc_threads; j++) {
4740 ChunkArray* cur_sca = &_survivor_plab_array[j];
4741 if (_cursor[j] == cur_sca->end()) {
4742 continue;
4743 }
4744 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4745 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4746 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4747 if (cur_val < min_val) {
4748 min_tid = j;
4749 min_val = cur_val;
4750 } else {
4751 assert(cur_val < top, "All recorded addresses should be less");
4752 }
4753 }
4754 // At this point min_val and min_tid are respectively
4755 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4756 // and the thread (j) that witnesses that address.
4757 // We record this address in the _survivor_chunk_array[i]
4758 // and increment _cursor[min_tid] prior to the next round i.
4759 if (min_val == top) {
4760 break;
4761 }
4762 _survivor_chunk_array[i] = min_val;
4763 _cursor[min_tid]++;
4764 }
4765 // We are all done; record the size of the _survivor_chunk_array
4766 _survivor_chunk_index = i; // exclusive: [0, i)
4767 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4768 // Verify that we used up all the recorded entries
4769 #ifdef ASSERT
4770 size_t total = 0;
4771 for (int j = 0; j < no_of_gc_threads; j++) {
4772 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4773 total += _cursor[j];
4774 }
4775 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4776 // Check that the merged array is in sorted order
4777 if (total > 0) {
4778 for (size_t i = 0; i < total - 1; i++) {
4779 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4780 i, p2i(_survivor_chunk_array[i]));
4781 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4782 "Not sorted");
4783 }
4784 }
4785 #endif // ASSERT
4786 }
4787
4788 // Set up the space's par_seq_tasks structure for work claiming
4789 // for parallel initial scan and rescan of young gen.
4790 // See ParRescanTask where this is currently used.
4791 void
4792 CMSCollector::
4793 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4794 assert(n_threads > 0, "Unexpected n_threads argument");
4795
4796 // Eden space
4797 if (!_young_gen->eden()->is_empty()) {
4798 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4799 assert(!pst->valid(), "Clobbering existing data?");
4800 // Each valid entry in [0, _eden_chunk_index) represents a task.
4801 size_t n_tasks = _eden_chunk_index + 1;
4802 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4803 // Sets the condition for completion of the subtask (how many threads
4804 // need to finish in order to be done).
4805 pst->set_n_threads(n_threads);
4806 pst->set_n_tasks((int)n_tasks);
4807 }
4808
4809 // Merge the survivor plab arrays into _survivor_chunk_array
4810 if (_survivor_plab_array != NULL) {
4811 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4812 } else {
4813 assert(_survivor_chunk_index == 0, "Error");
4814 }
4815
4816 // To space
4817 {
4818 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4819 assert(!pst->valid(), "Clobbering existing data?");
4820 // Sets the condition for completion of the subtask (how many threads
4821 // need to finish in order to be done).
4822 pst->set_n_threads(n_threads);
4823 pst->set_n_tasks(1);
4824 assert(pst->valid(), "Error");
4825 }
4826
4827 // From space
4828 {
4829 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4830 assert(!pst->valid(), "Clobbering existing data?");
4831 size_t n_tasks = _survivor_chunk_index + 1;
4832 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4833 // Sets the condition for completion of the subtask (how many threads
4834 // need to finish in order to be done).
4835 pst->set_n_threads(n_threads);
4836 pst->set_n_tasks((int)n_tasks);
4837 assert(pst->valid(), "Error");
4838 }
4839 }
4840
4841 // Parallel version of remark
4842 void CMSCollector::do_remark_parallel() {
4843 CMSHeap* gch = CMSHeap::heap();
4844 WorkGang* workers = gch->workers();
4845 assert(workers != NULL, "Need parallel worker threads.");
4846 // Choose to use the number of GC workers most recently set
4847 // into "active_workers".
4848 uint n_workers = workers->active_workers();
4849
4850 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4851
4852 StrongRootsScope srs(n_workers);
4853
4854 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4855
4856 // We won't be iterating over the cards in the card table updating
4857 // the younger_gen cards, so we shouldn't call the following else
4858 // the verification code as well as subsequent younger_refs_iterate
4859 // code would get confused. XXX
4860 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4861
4862 // The young gen rescan work will not be done as part of
4863 // process_roots (which currently doesn't know how to
4864 // parallelize such a scan), but rather will be broken up into
4865 // a set of parallel tasks (via the sampling that the [abortable]
4866 // preclean phase did of eden, plus the [two] tasks of
4867 // scanning the [two] survivor spaces. Further fine-grain
4868 // parallelization of the scanning of the survivor spaces
4869 // themselves, and of precleaning of the young gen itself
4870 // is deferred to the future.
4871 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4872
4873 // The dirty card rescan work is broken up into a "sequence"
4874 // of parallel tasks (per constituent space) that are dynamically
4875 // claimed by the parallel threads.
4876 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4877
4878 // It turns out that even when we're using 1 thread, doing the work in a
4879 // separate thread causes wide variance in run times. We can't help this
4880 // in the multi-threaded case, but we special-case n=1 here to get
4881 // repeatable measurements of the 1-thread overhead of the parallel code.
4882 if (n_workers > 1) {
4883 // Make refs discovery MT-safe, if it isn't already: it may not
4884 // necessarily be so, since it's possible that we are doing
4885 // ST marking.
4886 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4887 workers->run_task(&tsk);
4888 } else {
4889 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4890 tsk.work(0);
4891 }
4892
4893 // restore, single-threaded for now, any preserved marks
4894 // as a result of work_q overflow
4895 restore_preserved_marks_if_any();
4896 }
4897
4898 // Non-parallel version of remark
4899 void CMSCollector::do_remark_non_parallel() {
4900 ResourceMark rm;
4901 HandleMark hm;
4902 CMSHeap* gch = CMSHeap::heap();
4903 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4904
4905 MarkRefsIntoAndScanClosure
4906 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4907 &_markStack, this,
4908 false /* should_yield */, false /* not precleaning */);
4909 MarkFromDirtyCardsClosure
4910 markFromDirtyCardsClosure(this, _span,
4911 NULL, // space is set further below
4912 &_markBitMap, &_markStack, &mrias_cl);
4913 {
4914 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4915 // Iterate over the dirty cards, setting the corresponding bits in the
4916 // mod union table.
4917 {
4918 ModUnionClosure modUnionClosure(&_modUnionTable);
4919 _ct->ct_bs()->dirty_card_iterate(
4920 _cmsGen->used_region(),
4921 &modUnionClosure);
4922 }
4923 // Having transferred these marks into the modUnionTable, we just need
4924 // to rescan the marked objects on the dirty cards in the modUnionTable.
4925 // The initial marking may have been done during an asynchronous
4926 // collection so there may be dirty bits in the mod-union table.
4927 const int alignment =
4928 CardTableModRefBS::card_size * BitsPerWord;
4929 {
4930 // ... First handle dirty cards in CMS gen
4931 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4932 MemRegion ur = _cmsGen->used_region();
4933 HeapWord* lb = ur.start();
4934 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4935 MemRegion cms_span(lb, ub);
4936 _modUnionTable.dirty_range_iterate_clear(cms_span,
4937 &markFromDirtyCardsClosure);
4938 verify_work_stacks_empty();
4939 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4940 }
4941 }
4942 if (VerifyDuringGC &&
4943 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4944 HandleMark hm; // Discard invalid handles created during verification
4945 Universe::verify();
4946 }
4947 {
4948 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4949
4950 verify_work_stacks_empty();
4951
4952 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4953 StrongRootsScope srs(1);
4954
4955 gch->cms_process_roots(&srs,
4956 true, // young gen as roots
4957 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4958 should_unload_classes(),
4959 &mrias_cl,
4960 NULL); // The dirty klasses will be handled below
4961
4962 assert(should_unload_classes()
4963 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4964 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4965 }
4966
4967 {
4968 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4969
4970 verify_work_stacks_empty();
4971
4972 // Scan all class loader data objects that might have been introduced
4973 // during concurrent marking.
4974 ResourceMark rm;
4975 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4976 for (int i = 0; i < array->length(); i++) {
4977 mrias_cl.do_cld_nv(array->at(i));
4978 }
4979
4980 // We don't need to keep track of new CLDs anymore.
4981 ClassLoaderDataGraph::remember_new_clds(false);
4982
4983 verify_work_stacks_empty();
4984 }
4985
4986 {
4987 GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
4988
4989 verify_work_stacks_empty();
4990
4991 RemarkKlassClosure remark_klass_closure(&mrias_cl);
4992 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4993
4994 verify_work_stacks_empty();
4995 }
4996
4997 // We might have added oops to ClassLoaderData::_handles during the
4998 // concurrent marking phase. These oops point to newly allocated objects
4999 // that are guaranteed to be kept alive. Either by the direct allocation
5000 // code, or when the young collector processes the roots. Hence,
5001 // we don't have to revisit the _handles block during the remark phase.
5002
5003 verify_work_stacks_empty();
5004 // Restore evacuated mark words, if any, used for overflow list links
5005 restore_preserved_marks_if_any();
5006
5007 verify_overflow_empty();
5008 }
5009
5010 ////////////////////////////////////////////////////////
5011 // Parallel Reference Processing Task Proxy Class
5012 ////////////////////////////////////////////////////////
5013 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5014 OopTaskQueueSet* _queues;
5015 ParallelTaskTerminator _terminator;
5016 public:
5017 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5018 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5019 ParallelTaskTerminator* terminator() { return &_terminator; }
5020 OopTaskQueueSet* queues() { return _queues; }
5021 };
5022
5023 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5024 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5025 CMSCollector* _collector;
5026 CMSBitMap* _mark_bit_map;
5027 const MemRegion _span;
5028 ProcessTask& _task;
5029
5030 public:
5031 CMSRefProcTaskProxy(ProcessTask& task,
5032 CMSCollector* collector,
5033 const MemRegion& span,
5034 CMSBitMap* mark_bit_map,
5035 AbstractWorkGang* workers,
5036 OopTaskQueueSet* task_queues):
5037 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5038 task_queues,
5039 workers->active_workers()),
5040 _task(task),
5041 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5042 {
5043 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5044 "Inconsistency in _span");
5045 }
5046
5047 OopTaskQueueSet* task_queues() { return queues(); }
5048
5049 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5050
5051 void do_work_steal(int i,
5052 CMSParDrainMarkingStackClosure* drain,
5053 CMSParKeepAliveClosure* keep_alive,
5054 int* seed);
5055
5056 virtual void work(uint worker_id);
5057 };
5058
5059 void CMSRefProcTaskProxy::work(uint worker_id) {
5060 ResourceMark rm;
5061 HandleMark hm;
5062 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5063 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5064 _mark_bit_map,
5065 work_queue(worker_id));
5066 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5067 _mark_bit_map,
5068 work_queue(worker_id));
5069 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5070 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5071 if (_task.marks_oops_alive()) {
5072 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5073 _collector->hash_seed(worker_id));
5074 }
5075 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5076 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5077 }
5078
5079 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5080 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5081 EnqueueTask& _task;
5082
5083 public:
5084 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5085 : AbstractGangTask("Enqueue reference objects in parallel"),
5086 _task(task)
5087 { }
5088
5089 virtual void work(uint worker_id)
5090 {
5091 _task.work(worker_id);
5092 }
5093 };
5094
5095 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5096 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5097 _span(span),
5098 _bit_map(bit_map),
5099 _work_queue(work_queue),
5100 _mark_and_push(collector, span, bit_map, work_queue),
5101 _low_water_mark(MIN2((work_queue->max_elems()/4),
5102 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5103 { }
5104
5105 // . see if we can share work_queues with ParNew? XXX
5106 void CMSRefProcTaskProxy::do_work_steal(int i,
5107 CMSParDrainMarkingStackClosure* drain,
5108 CMSParKeepAliveClosure* keep_alive,
5109 int* seed) {
5110 OopTaskQueue* work_q = work_queue(i);
5111 NOT_PRODUCT(int num_steals = 0;)
5112 oop obj_to_scan;
5113
5114 while (true) {
5115 // Completely finish any left over work from (an) earlier round(s)
5116 drain->trim_queue(0);
5117 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5118 (size_t)ParGCDesiredObjsFromOverflowList);
5119 // Now check if there's any work in the overflow list
5120 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5121 // only affects the number of attempts made to get work from the
5122 // overflow list and does not affect the number of workers. Just
5123 // pass ParallelGCThreads so this behavior is unchanged.
5124 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5125 work_q,
5126 ParallelGCThreads)) {
5127 // Found something in global overflow list;
5128 // not yet ready to go stealing work from others.
5129 // We'd like to assert(work_q->size() != 0, ...)
5130 // because we just took work from the overflow list,
5131 // but of course we can't, since all of that might have
5132 // been already stolen from us.
5133 continue;
5134 }
5135 // Verify that we have no work before we resort to stealing
5136 assert(work_q->size() == 0, "Have work, shouldn't steal");
5137 // Try to steal from other queues that have work
5138 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5139 NOT_PRODUCT(num_steals++;)
5140 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5141 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5142 // Do scanning work
5143 obj_to_scan->oop_iterate(keep_alive);
5144 // Loop around, finish this work, and try to steal some more
5145 } else if (terminator()->offer_termination()) {
5146 break; // nirvana from the infinite cycle
5147 }
5148 }
5149 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5150 }
5151
5152 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5153 {
5154 CMSHeap* gch = CMSHeap::heap();
5155 WorkGang* workers = gch->workers();
5156 assert(workers != NULL, "Need parallel worker threads.");
5157 CMSRefProcTaskProxy rp_task(task, &_collector,
5158 _collector.ref_processor()->span(),
5159 _collector.markBitMap(),
5160 workers, _collector.task_queues());
5161 workers->run_task(&rp_task);
5162 }
5163
5164 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5165 {
5166
5167 CMSHeap* gch = CMSHeap::heap();
5168 WorkGang* workers = gch->workers();
5169 assert(workers != NULL, "Need parallel worker threads.");
5170 CMSRefEnqueueTaskProxy enq_task(task);
5171 workers->run_task(&enq_task);
5172 }
5173
5174 void CMSCollector::refProcessingWork() {
5175 ResourceMark rm;
5176 HandleMark hm;
5177
5178 ReferenceProcessor* rp = ref_processor();
5179 assert(rp->span().equals(_span), "Spans should be equal");
5180 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5181 // Process weak references.
5182 rp->setup_policy(false);
5183 verify_work_stacks_empty();
5184
5185 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5186 &_markStack, false /* !preclean */);
5187 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5188 _span, &_markBitMap, &_markStack,
5189 &cmsKeepAliveClosure, false /* !preclean */);
5190 {
5191 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5192
5193 ReferenceProcessorStats stats;
5194 if (rp->processing_is_mt()) {
5195 // Set the degree of MT here. If the discovery is done MT, there
5196 // may have been a different number of threads doing the discovery
5197 // and a different number of discovered lists may have Ref objects.
5198 // That is OK as long as the Reference lists are balanced (see
5199 // balance_all_queues() and balance_queues()).
5200 CMSHeap* gch = CMSHeap::heap();
5201 uint active_workers = ParallelGCThreads;
5202 WorkGang* workers = gch->workers();
5203 if (workers != NULL) {
5204 active_workers = workers->active_workers();
5205 // The expectation is that active_workers will have already
5206 // been set to a reasonable value. If it has not been set,
5207 // investigate.
5208 assert(active_workers > 0, "Should have been set during scavenge");
5209 }
5210 rp->set_active_mt_degree(active_workers);
5211 CMSRefProcTaskExecutor task_executor(*this);
5212 stats = rp->process_discovered_references(&_is_alive_closure,
5213 &cmsKeepAliveClosure,
5214 &cmsDrainMarkingStackClosure,
5215 &task_executor,
5216 _gc_timer_cm);
5217 } else {
5218 stats = rp->process_discovered_references(&_is_alive_closure,
5219 &cmsKeepAliveClosure,
5220 &cmsDrainMarkingStackClosure,
5221 NULL,
5222 _gc_timer_cm);
5223 }
5224 _gc_tracer_cm->report_gc_reference_stats(stats);
5225
5226 }
5227
5228 // This is the point where the entire marking should have completed.
5229 verify_work_stacks_empty();
5230
5231 if (should_unload_classes()) {
5232 {
5233 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5234
5235 // Unload classes and purge the SystemDictionary.
5236 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5237
5238 // Unload nmethods.
5239 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5240
5241 // Prune dead klasses from subklass/sibling/implementor lists.
5242 Klass::clean_weak_klass_links(&_is_alive_closure);
5243 }
5244
5245 {
5246 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5247 // Clean up unreferenced symbols in symbol table.
5248 SymbolTable::unlink();
5249 }
5250
5251 {
5252 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5253 // Delete entries for dead interned strings.
5254 StringTable::unlink(&_is_alive_closure);
5255 }
5256 }
5257
5258 // Restore any preserved marks as a result of mark stack or
5259 // work queue overflow
5260 restore_preserved_marks_if_any(); // done single-threaded for now
5261
5262 rp->set_enqueuing_is_done(true);
5263 if (rp->processing_is_mt()) {
5264 rp->balance_all_queues();
5265 CMSRefProcTaskExecutor task_executor(*this);
5266 rp->enqueue_discovered_references(&task_executor);
5267 } else {
5268 rp->enqueue_discovered_references(NULL);
5269 }
5270 rp->verify_no_references_recorded();
5271 assert(!rp->discovery_enabled(), "should have been disabled");
5272 }
5273
5274 #ifndef PRODUCT
5275 void CMSCollector::check_correct_thread_executing() {
5276 Thread* t = Thread::current();
5277 // Only the VM thread or the CMS thread should be here.
5278 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5279 "Unexpected thread type");
5280 // If this is the vm thread, the foreground process
5281 // should not be waiting. Note that _foregroundGCIsActive is
5282 // true while the foreground collector is waiting.
5283 if (_foregroundGCShouldWait) {
5284 // We cannot be the VM thread
5285 assert(t->is_ConcurrentGC_thread(),
5286 "Should be CMS thread");
5287 } else {
5288 // We can be the CMS thread only if we are in a stop-world
5289 // phase of CMS collection.
5290 if (t->is_ConcurrentGC_thread()) {
5291 assert(_collectorState == InitialMarking ||
5292 _collectorState == FinalMarking,
5293 "Should be a stop-world phase");
5294 // The CMS thread should be holding the CMS_token.
5295 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5296 "Potential interference with concurrently "
5297 "executing VM thread");
5298 }
5299 }
5300 }
5301 #endif
5302
5303 void CMSCollector::sweep() {
5304 assert(_collectorState == Sweeping, "just checking");
5305 check_correct_thread_executing();
5306 verify_work_stacks_empty();
5307 verify_overflow_empty();
5308 increment_sweep_count();
5309 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5310
5311 _inter_sweep_timer.stop();
5312 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5313
5314 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5315 _intra_sweep_timer.reset();
5316 _intra_sweep_timer.start();
5317 {
5318 GCTraceCPUTime tcpu;
5319 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5320 // First sweep the old gen
5321 {
5322 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5323 bitMapLock());
5324 sweepWork(_cmsGen);
5325 }
5326
5327 // Update Universe::_heap_*_at_gc figures.
5328 // We need all the free list locks to make the abstract state
5329 // transition from Sweeping to Resetting. See detailed note
5330 // further below.
5331 {
5332 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5333 // Update heap occupancy information which is used as
5334 // input to soft ref clearing policy at the next gc.
5335 Universe::update_heap_info_at_gc();
5336 _collectorState = Resizing;
5337 }
5338 }
5339 verify_work_stacks_empty();
5340 verify_overflow_empty();
5341
5342 if (should_unload_classes()) {
5343 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5344 // requires that the virtual spaces are stable and not deleted.
5345 ClassLoaderDataGraph::set_should_purge(true);
5346 }
5347
5348 _intra_sweep_timer.stop();
5349 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5350
5351 _inter_sweep_timer.reset();
5352 _inter_sweep_timer.start();
5353
5354 // We need to use a monotonically non-decreasing time in ms
5355 // or we will see time-warp warnings and os::javaTimeMillis()
5356 // does not guarantee monotonicity.
5357 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5358 update_time_of_last_gc(now);
5359
5360 // NOTE on abstract state transitions:
5361 // Mutators allocate-live and/or mark the mod-union table dirty
5362 // based on the state of the collection. The former is done in
5363 // the interval [Marking, Sweeping] and the latter in the interval
5364 // [Marking, Sweeping). Thus the transitions into the Marking state
5365 // and out of the Sweeping state must be synchronously visible
5366 // globally to the mutators.
5367 // The transition into the Marking state happens with the world
5368 // stopped so the mutators will globally see it. Sweeping is
5369 // done asynchronously by the background collector so the transition
5370 // from the Sweeping state to the Resizing state must be done
5371 // under the freelistLock (as is the check for whether to
5372 // allocate-live and whether to dirty the mod-union table).
5373 assert(_collectorState == Resizing, "Change of collector state to"
5374 " Resizing must be done under the freelistLocks (plural)");
5375
5376 // Now that sweeping has been completed, we clear
5377 // the incremental_collection_failed flag,
5378 // thus inviting a younger gen collection to promote into
5379 // this generation. If such a promotion may still fail,
5380 // the flag will be set again when a young collection is
5381 // attempted.
5382 GenCollectedHeap* gch = GenCollectedHeap::heap();
5383 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5384 gch->update_full_collections_completed(_collection_count_start);
5385 }
5386
5387 // FIX ME!!! Looks like this belongs in CFLSpace, with
5388 // CMSGen merely delegating to it.
5389 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5390 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5391 HeapWord* minAddr = _cmsSpace->bottom();
5392 HeapWord* largestAddr =
5393 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5394 if (largestAddr == NULL) {
5395 // The dictionary appears to be empty. In this case
5396 // try to coalesce at the end of the heap.
5397 largestAddr = _cmsSpace->end();
5398 }
5399 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5400 size_t nearLargestOffset =
5401 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5402 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5403 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5404 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5405 }
5406
5407 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5408 return addr >= _cmsSpace->nearLargestChunk();
5409 }
5410
5411 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5412 return _cmsSpace->find_chunk_at_end();
5413 }
5414
5415 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5416 bool full) {
5417 // If the young generation has been collected, gather any statistics
5418 // that are of interest at this point.
5419 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5420 if (!full && current_is_young) {
5421 // Gather statistics on the young generation collection.
5422 collector()->stats().record_gc0_end(used());
5423 }
5424 }
5425
5426 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5427 // We iterate over the space(s) underlying this generation,
5428 // checking the mark bit map to see if the bits corresponding
5429 // to specific blocks are marked or not. Blocks that are
5430 // marked are live and are not swept up. All remaining blocks
5431 // are swept up, with coalescing on-the-fly as we sweep up
5432 // contiguous free and/or garbage blocks:
5433 // We need to ensure that the sweeper synchronizes with allocators
5434 // and stop-the-world collectors. In particular, the following
5435 // locks are used:
5436 // . CMS token: if this is held, a stop the world collection cannot occur
5437 // . freelistLock: if this is held no allocation can occur from this
5438 // generation by another thread
5439 // . bitMapLock: if this is held, no other thread can access or update
5440 //
5441
5442 // Note that we need to hold the freelistLock if we use
5443 // block iterate below; else the iterator might go awry if
5444 // a mutator (or promotion) causes block contents to change
5445 // (for instance if the allocator divvies up a block).
5446 // If we hold the free list lock, for all practical purposes
5447 // young generation GC's can't occur (they'll usually need to
5448 // promote), so we might as well prevent all young generation
5449 // GC's while we do a sweeping step. For the same reason, we might
5450 // as well take the bit map lock for the entire duration
5451
5452 // check that we hold the requisite locks
5453 assert(have_cms_token(), "Should hold cms token");
5454 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5455 assert_lock_strong(old_gen->freelistLock());
5456 assert_lock_strong(bitMapLock());
5457
5458 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5459 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5460 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5461 _inter_sweep_estimate.padded_average(),
5462 _intra_sweep_estimate.padded_average());
5463 old_gen->setNearLargestChunk();
5464
5465 {
5466 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5467 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5468 // We need to free-up/coalesce garbage/blocks from a
5469 // co-terminal free run. This is done in the SweepClosure
5470 // destructor; so, do not remove this scope, else the
5471 // end-of-sweep-census below will be off by a little bit.
5472 }
5473 old_gen->cmsSpace()->sweep_completed();
5474 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5475 if (should_unload_classes()) { // unloaded classes this cycle,
5476 _concurrent_cycles_since_last_unload = 0; // ... reset count
5477 } else { // did not unload classes,
5478 _concurrent_cycles_since_last_unload++; // ... increment count
5479 }
5480 }
5481
5482 // Reset CMS data structures (for now just the marking bit map)
5483 // preparatory for the next cycle.
5484 void CMSCollector::reset_concurrent() {
5485 CMSTokenSyncWithLocks ts(true, bitMapLock());
5486
5487 // If the state is not "Resetting", the foreground thread
5488 // has done a collection and the resetting.
5489 if (_collectorState != Resetting) {
5490 assert(_collectorState == Idling, "The state should only change"
5491 " because the foreground collector has finished the collection");
5492 return;
5493 }
5494
5495 {
5496 // Clear the mark bitmap (no grey objects to start with)
5497 // for the next cycle.
5498 GCTraceCPUTime tcpu;
5499 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5500
5501 HeapWord* curAddr = _markBitMap.startWord();
5502 while (curAddr < _markBitMap.endWord()) {
5503 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5504 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5505 _markBitMap.clear_large_range(chunk);
5506 if (ConcurrentMarkSweepThread::should_yield() &&
5507 !foregroundGCIsActive() &&
5508 CMSYield) {
5509 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5510 "CMS thread should hold CMS token");
5511 assert_lock_strong(bitMapLock());
5512 bitMapLock()->unlock();
5513 ConcurrentMarkSweepThread::desynchronize(true);
5514 stopTimer();
5515 incrementYields();
5516
5517 // See the comment in coordinator_yield()
5518 for (unsigned i = 0; i < CMSYieldSleepCount &&
5519 ConcurrentMarkSweepThread::should_yield() &&
5520 !CMSCollector::foregroundGCIsActive(); ++i) {
5521 os::sleep(Thread::current(), 1, false);
5522 }
5523
5524 ConcurrentMarkSweepThread::synchronize(true);
5525 bitMapLock()->lock_without_safepoint_check();
5526 startTimer();
5527 }
5528 curAddr = chunk.end();
5529 }
5530 // A successful mostly concurrent collection has been done.
5531 // Because only the full (i.e., concurrent mode failure) collections
5532 // are being measured for gc overhead limits, clean the "near" flag
5533 // and count.
5534 size_policy()->reset_gc_overhead_limit_count();
5535 _collectorState = Idling;
5536 }
5537
5538 register_gc_end();
5539 }
5540
5541 // Same as above but for STW paths
5542 void CMSCollector::reset_stw() {
5543 // already have the lock
5544 assert(_collectorState == Resetting, "just checking");
5545 assert_lock_strong(bitMapLock());
5546 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5547 _markBitMap.clear_all();
5548 _collectorState = Idling;
5549 register_gc_end();
5550 }
5551
5552 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5553 GCTraceCPUTime tcpu;
5554 TraceCollectorStats tcs(counters());
5555
5556 switch (op) {
5557 case CMS_op_checkpointRootsInitial: {
5558 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5559 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5560 checkpointRootsInitial();
5561 break;
5562 }
5563 case CMS_op_checkpointRootsFinal: {
5564 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5565 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5566 checkpointRootsFinal();
5567 break;
5568 }
5569 default:
5570 fatal("No such CMS_op");
5571 }
5572 }
5573
5574 #ifndef PRODUCT
5575 size_t const CMSCollector::skip_header_HeapWords() {
5576 return FreeChunk::header_size();
5577 }
5578
5579 // Try and collect here conditions that should hold when
5580 // CMS thread is exiting. The idea is that the foreground GC
5581 // thread should not be blocked if it wants to terminate
5582 // the CMS thread and yet continue to run the VM for a while
5583 // after that.
5584 void CMSCollector::verify_ok_to_terminate() const {
5585 assert(Thread::current()->is_ConcurrentGC_thread(),
5586 "should be called by CMS thread");
5587 assert(!_foregroundGCShouldWait, "should be false");
5588 // We could check here that all the various low-level locks
5589 // are not held by the CMS thread, but that is overkill; see
5590 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5591 // is checked.
5592 }
5593 #endif
5594
5595 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5596 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5597 "missing Printezis mark?");
5598 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5599 size_t size = pointer_delta(nextOneAddr + 1, addr);
5600 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5601 "alignment problem");
5602 assert(size >= 3, "Necessary for Printezis marks to work");
5603 return size;
5604 }
5605
5606 // A variant of the above (block_size_using_printezis_bits()) except
5607 // that we return 0 if the P-bits are not yet set.
5608 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5609 if (_markBitMap.isMarked(addr + 1)) {
5610 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5611 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5612 size_t size = pointer_delta(nextOneAddr + 1, addr);
5613 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5614 "alignment problem");
5615 assert(size >= 3, "Necessary for Printezis marks to work");
5616 return size;
5617 }
5618 return 0;
5619 }
5620
5621 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5622 size_t sz = 0;
5623 oop p = (oop)addr;
5624 if (p->klass_or_null_acquire() != NULL) {
5625 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5626 } else {
5627 sz = block_size_using_printezis_bits(addr);
5628 }
5629 assert(sz > 0, "size must be nonzero");
5630 HeapWord* next_block = addr + sz;
5631 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5632 CardTableModRefBS::card_size);
5633 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5634 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5635 "must be different cards");
5636 return next_card;
5637 }
5638
5639
5640 // CMS Bit Map Wrapper /////////////////////////////////////////
5641
5642 // Construct a CMS bit map infrastructure, but don't create the
5643 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5644 // further below.
5645 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5646 _bm(),
5647 _shifter(shifter),
5648 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5649 Monitor::_safepoint_check_sometimes) : NULL)
5650 {
5651 _bmStartWord = 0;
5652 _bmWordSize = 0;
5653 }
5654
5655 bool CMSBitMap::allocate(MemRegion mr) {
5656 _bmStartWord = mr.start();
5657 _bmWordSize = mr.word_size();
5658 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5659 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5660 if (!brs.is_reserved()) {
5661 log_warning(gc)("CMS bit map allocation failure");
5662 return false;
5663 }
5664 // For now we'll just commit all of the bit map up front.
5665 // Later on we'll try to be more parsimonious with swap.
5666 if (!_virtual_space.initialize(brs, brs.size())) {
5667 log_warning(gc)("CMS bit map backing store failure");
5668 return false;
5669 }
5670 assert(_virtual_space.committed_size() == brs.size(),
5671 "didn't reserve backing store for all of CMS bit map?");
5672 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5673 _bmWordSize, "inconsistency in bit map sizing");
5674 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5675
5676 // bm.clear(); // can we rely on getting zero'd memory? verify below
5677 assert(isAllClear(),
5678 "Expected zero'd memory from ReservedSpace constructor");
5679 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5680 "consistency check");
5681 return true;
5682 }
5683
5684 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5685 HeapWord *next_addr, *end_addr, *last_addr;
5686 assert_locked();
5687 assert(covers(mr), "out-of-range error");
5688 // XXX assert that start and end are appropriately aligned
5689 for (next_addr = mr.start(), end_addr = mr.end();
5690 next_addr < end_addr; next_addr = last_addr) {
5691 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5692 last_addr = dirty_region.end();
5693 if (!dirty_region.is_empty()) {
5694 cl->do_MemRegion(dirty_region);
5695 } else {
5696 assert(last_addr == end_addr, "program logic");
5697 return;
5698 }
5699 }
5700 }
5701
5702 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5703 _bm.print_on_error(st, prefix);
5704 }
5705
5706 #ifndef PRODUCT
5707 void CMSBitMap::assert_locked() const {
5708 CMSLockVerifier::assert_locked(lock());
5709 }
5710
5711 bool CMSBitMap::covers(MemRegion mr) const {
5712 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5713 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5714 "size inconsistency");
5715 return (mr.start() >= _bmStartWord) &&
5716 (mr.end() <= endWord());
5717 }
5718
5719 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5720 return (start >= _bmStartWord && (start + size) <= endWord());
5721 }
5722
5723 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5724 // verify that there are no 1 bits in the interval [left, right)
5725 FalseBitMapClosure falseBitMapClosure;
5726 iterate(&falseBitMapClosure, left, right);
5727 }
5728
5729 void CMSBitMap::region_invariant(MemRegion mr)
5730 {
5731 assert_locked();
5732 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5733 assert(!mr.is_empty(), "unexpected empty region");
5734 assert(covers(mr), "mr should be covered by bit map");
5735 // convert address range into offset range
5736 size_t start_ofs = heapWordToOffset(mr.start());
5737 // Make sure that end() is appropriately aligned
5738 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5739 (1 << (_shifter+LogHeapWordSize))),
5740 "Misaligned mr.end()");
5741 size_t end_ofs = heapWordToOffset(mr.end());
5742 assert(end_ofs > start_ofs, "Should mark at least one bit");
5743 }
5744
5745 #endif
5746
5747 bool CMSMarkStack::allocate(size_t size) {
5748 // allocate a stack of the requisite depth
5749 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5750 size * sizeof(oop)));
5751 if (!rs.is_reserved()) {
5752 log_warning(gc)("CMSMarkStack allocation failure");
5753 return false;
5754 }
5755 if (!_virtual_space.initialize(rs, rs.size())) {
5756 log_warning(gc)("CMSMarkStack backing store failure");
5757 return false;
5758 }
5759 assert(_virtual_space.committed_size() == rs.size(),
5760 "didn't reserve backing store for all of CMS stack?");
5761 _base = (oop*)(_virtual_space.low());
5762 _index = 0;
5763 _capacity = size;
5764 NOT_PRODUCT(_max_depth = 0);
5765 return true;
5766 }
5767
5768 // XXX FIX ME !!! In the MT case we come in here holding a
5769 // leaf lock. For printing we need to take a further lock
5770 // which has lower rank. We need to recalibrate the two
5771 // lock-ranks involved in order to be able to print the
5772 // messages below. (Or defer the printing to the caller.
5773 // For now we take the expedient path of just disabling the
5774 // messages for the problematic case.)
5775 void CMSMarkStack::expand() {
5776 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5777 if (_capacity == MarkStackSizeMax) {
5778 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5779 // We print a warning message only once per CMS cycle.
5780 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5781 }
5782 return;
5783 }
5784 // Double capacity if possible
5785 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5786 // Do not give up existing stack until we have managed to
5787 // get the double capacity that we desired.
5788 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5789 new_capacity * sizeof(oop)));
5790 if (rs.is_reserved()) {
5791 // Release the backing store associated with old stack
5792 _virtual_space.release();
5793 // Reinitialize virtual space for new stack
5794 if (!_virtual_space.initialize(rs, rs.size())) {
5795 fatal("Not enough swap for expanded marking stack");
5796 }
5797 _base = (oop*)(_virtual_space.low());
5798 _index = 0;
5799 _capacity = new_capacity;
5800 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5801 // Failed to double capacity, continue;
5802 // we print a detail message only once per CMS cycle.
5803 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5804 _capacity / K, new_capacity / K);
5805 }
5806 }
5807
5808
5809 // Closures
5810 // XXX: there seems to be a lot of code duplication here;
5811 // should refactor and consolidate common code.
5812
5813 // This closure is used to mark refs into the CMS generation in
5814 // the CMS bit map. Called at the first checkpoint. This closure
5815 // assumes that we do not need to re-mark dirty cards; if the CMS
5816 // generation on which this is used is not an oldest
5817 // generation then this will lose younger_gen cards!
5818
5819 MarkRefsIntoClosure::MarkRefsIntoClosure(
5820 MemRegion span, CMSBitMap* bitMap):
5821 _span(span),
5822 _bitMap(bitMap)
5823 {
5824 assert(ref_processor() == NULL, "deliberately left NULL");
5825 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5826 }
5827
5828 void MarkRefsIntoClosure::do_oop(oop obj) {
5829 // if p points into _span, then mark corresponding bit in _markBitMap
5830 assert(obj->is_oop(), "expected an oop");
5831 HeapWord* addr = (HeapWord*)obj;
5832 if (_span.contains(addr)) {
5833 // this should be made more efficient
5834 _bitMap->mark(addr);
5835 }
5836 }
5837
5838 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5839 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5840
5841 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5842 MemRegion span, CMSBitMap* bitMap):
5843 _span(span),
5844 _bitMap(bitMap)
5845 {
5846 assert(ref_processor() == NULL, "deliberately left NULL");
5847 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5848 }
5849
5850 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5851 // if p points into _span, then mark corresponding bit in _markBitMap
5852 assert(obj->is_oop(), "expected an oop");
5853 HeapWord* addr = (HeapWord*)obj;
5854 if (_span.contains(addr)) {
5855 // this should be made more efficient
5856 _bitMap->par_mark(addr);
5857 }
5858 }
5859
5860 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5861 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5862
5863 // A variant of the above, used for CMS marking verification.
5864 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5865 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5866 _span(span),
5867 _verification_bm(verification_bm),
5868 _cms_bm(cms_bm)
5869 {
5870 assert(ref_processor() == NULL, "deliberately left NULL");
5871 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5872 }
5873
5874 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5875 // if p points into _span, then mark corresponding bit in _markBitMap
5876 assert(obj->is_oop(), "expected an oop");
5877 HeapWord* addr = (HeapWord*)obj;
5878 if (_span.contains(addr)) {
5879 _verification_bm->mark(addr);
5880 if (!_cms_bm->isMarked(addr)) {
5881 Log(gc, verify) log;
5882 ResourceMark rm;
5883 oop(addr)->print_on(log.error_stream());
5884 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5885 fatal("... aborting");
5886 }
5887 }
5888 }
5889
5890 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5891 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5892
5893 //////////////////////////////////////////////////
5894 // MarkRefsIntoAndScanClosure
5895 //////////////////////////////////////////////////
5896
5897 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5898 ReferenceProcessor* rp,
5899 CMSBitMap* bit_map,
5900 CMSBitMap* mod_union_table,
5901 CMSMarkStack* mark_stack,
5902 CMSCollector* collector,
5903 bool should_yield,
5904 bool concurrent_precleaning):
5905 _collector(collector),
5906 _span(span),
5907 _bit_map(bit_map),
5908 _mark_stack(mark_stack),
5909 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5910 mark_stack, concurrent_precleaning),
5911 _yield(should_yield),
5912 _concurrent_precleaning(concurrent_precleaning),
5913 _freelistLock(NULL)
5914 {
5915 // FIXME: Should initialize in base class constructor.
5916 assert(rp != NULL, "ref_processor shouldn't be NULL");
5917 set_ref_processor_internal(rp);
5918 }
5919
5920 // This closure is used to mark refs into the CMS generation at the
5921 // second (final) checkpoint, and to scan and transitively follow
5922 // the unmarked oops. It is also used during the concurrent precleaning
5923 // phase while scanning objects on dirty cards in the CMS generation.
5924 // The marks are made in the marking bit map and the marking stack is
5925 // used for keeping the (newly) grey objects during the scan.
5926 // The parallel version (Par_...) appears further below.
5927 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5928 if (obj != NULL) {
5929 assert(obj->is_oop(), "expected an oop");
5930 HeapWord* addr = (HeapWord*)obj;
5931 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5932 assert(_collector->overflow_list_is_empty(),
5933 "overflow list should be empty");
5934 if (_span.contains(addr) &&
5935 !_bit_map->isMarked(addr)) {
5936 // mark bit map (object is now grey)
5937 _bit_map->mark(addr);
5938 // push on marking stack (stack should be empty), and drain the
5939 // stack by applying this closure to the oops in the oops popped
5940 // from the stack (i.e. blacken the grey objects)
5941 bool res = _mark_stack->push(obj);
5942 assert(res, "Should have space to push on empty stack");
5943 do {
5944 oop new_oop = _mark_stack->pop();
5945 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5946 assert(_bit_map->isMarked((HeapWord*)new_oop),
5947 "only grey objects on this stack");
5948 // iterate over the oops in this oop, marking and pushing
5949 // the ones in CMS heap (i.e. in _span).
5950 new_oop->oop_iterate(&_pushAndMarkClosure);
5951 // check if it's time to yield
5952 do_yield_check();
5953 } while (!_mark_stack->isEmpty() ||
5954 (!_concurrent_precleaning && take_from_overflow_list()));
5955 // if marking stack is empty, and we are not doing this
5956 // during precleaning, then check the overflow list
5957 }
5958 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5959 assert(_collector->overflow_list_is_empty(),
5960 "overflow list was drained above");
5961
5962 assert(_collector->no_preserved_marks(),
5963 "All preserved marks should have been restored above");
5964 }
5965 }
5966
5967 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5968 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5969
5970 void MarkRefsIntoAndScanClosure::do_yield_work() {
5971 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5972 "CMS thread should hold CMS token");
5973 assert_lock_strong(_freelistLock);
5974 assert_lock_strong(_bit_map->lock());
5975 // relinquish the free_list_lock and bitMaplock()
5976 _bit_map->lock()->unlock();
5977 _freelistLock->unlock();
5978 ConcurrentMarkSweepThread::desynchronize(true);
5979 _collector->stopTimer();
5980 _collector->incrementYields();
5981
5982 // See the comment in coordinator_yield()
5983 for (unsigned i = 0;
5984 i < CMSYieldSleepCount &&
5985 ConcurrentMarkSweepThread::should_yield() &&
5986 !CMSCollector::foregroundGCIsActive();
5987 ++i) {
5988 os::sleep(Thread::current(), 1, false);
5989 }
5990
5991 ConcurrentMarkSweepThread::synchronize(true);
5992 _freelistLock->lock_without_safepoint_check();
5993 _bit_map->lock()->lock_without_safepoint_check();
5994 _collector->startTimer();
5995 }
5996
5997 ///////////////////////////////////////////////////////////
5998 // ParMarkRefsIntoAndScanClosure: a parallel version of
5999 // MarkRefsIntoAndScanClosure
6000 ///////////////////////////////////////////////////////////
6001 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6002 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6003 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6004 _span(span),
6005 _bit_map(bit_map),
6006 _work_queue(work_queue),
6007 _low_water_mark(MIN2((work_queue->max_elems()/4),
6008 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6009 _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6010 {
6011 // FIXME: Should initialize in base class constructor.
6012 assert(rp != NULL, "ref_processor shouldn't be NULL");
6013 set_ref_processor_internal(rp);
6014 }
6015
6016 // This closure is used to mark refs into the CMS generation at the
6017 // second (final) checkpoint, and to scan and transitively follow
6018 // the unmarked oops. The marks are made in the marking bit map and
6019 // the work_queue is used for keeping the (newly) grey objects during
6020 // the scan phase whence they are also available for stealing by parallel
6021 // threads. Since the marking bit map is shared, updates are
6022 // synchronized (via CAS).
6023 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6024 if (obj != NULL) {
6025 // Ignore mark word because this could be an already marked oop
6026 // that may be chained at the end of the overflow list.
6027 assert(obj->is_oop(true), "expected an oop");
6028 HeapWord* addr = (HeapWord*)obj;
6029 if (_span.contains(addr) &&
6030 !_bit_map->isMarked(addr)) {
6031 // mark bit map (object will become grey):
6032 // It is possible for several threads to be
6033 // trying to "claim" this object concurrently;
6034 // the unique thread that succeeds in marking the
6035 // object first will do the subsequent push on
6036 // to the work queue (or overflow list).
6037 if (_bit_map->par_mark(addr)) {
6038 // push on work_queue (which may not be empty), and trim the
6039 // queue to an appropriate length by applying this closure to
6040 // the oops in the oops popped from the stack (i.e. blacken the
6041 // grey objects)
6042 bool res = _work_queue->push(obj);
6043 assert(res, "Low water mark should be less than capacity?");
6044 trim_queue(_low_water_mark);
6045 } // Else, another thread claimed the object
6046 }
6047 }
6048 }
6049
6050 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6051 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6052
6053 // This closure is used to rescan the marked objects on the dirty cards
6054 // in the mod union table and the card table proper.
6055 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6056 oop p, MemRegion mr) {
6057
6058 size_t size = 0;
6059 HeapWord* addr = (HeapWord*)p;
6060 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6061 assert(_span.contains(addr), "we are scanning the CMS generation");
6062 // check if it's time to yield
6063 if (do_yield_check()) {
6064 // We yielded for some foreground stop-world work,
6065 // and we have been asked to abort this ongoing preclean cycle.
6066 return 0;
6067 }
6068 if (_bitMap->isMarked(addr)) {
6069 // it's marked; is it potentially uninitialized?
6070 if (p->klass_or_null_acquire() != NULL) {
6071 // an initialized object; ignore mark word in verification below
6072 // since we are running concurrent with mutators
6073 assert(p->is_oop(true), "should be an oop");
6074 if (p->is_objArray()) {
6075 // objArrays are precisely marked; restrict scanning
6076 // to dirty cards only.
6077 size = CompactibleFreeListSpace::adjustObjectSize(
6078 p->oop_iterate_size(_scanningClosure, mr));
6079 } else {
6080 // A non-array may have been imprecisely marked; we need
6081 // to scan object in its entirety.
6082 size = CompactibleFreeListSpace::adjustObjectSize(
6083 p->oop_iterate_size(_scanningClosure));
6084 }
6085 #ifdef ASSERT
6086 size_t direct_size =
6087 CompactibleFreeListSpace::adjustObjectSize(p->size());
6088 assert(size == direct_size, "Inconsistency in size");
6089 assert(size >= 3, "Necessary for Printezis marks to work");
6090 HeapWord* start_pbit = addr + 1;
6091 HeapWord* end_pbit = addr + size - 1;
6092 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6093 "inconsistent Printezis mark");
6094 // Verify inner mark bits (between Printezis bits) are clear,
6095 // but don't repeat if there are multiple dirty regions for
6096 // the same object, to avoid potential O(N^2) performance.
6097 if (addr != _last_scanned_object) {
6098 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6099 _last_scanned_object = addr;
6100 }
6101 #endif // ASSERT
6102 } else {
6103 // An uninitialized object.
6104 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6105 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6106 size = pointer_delta(nextOneAddr + 1, addr);
6107 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6108 "alignment problem");
6109 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6110 // will dirty the card when the klass pointer is installed in the
6111 // object (signaling the completion of initialization).
6112 }
6113 } else {
6114 // Either a not yet marked object or an uninitialized object
6115 if (p->klass_or_null_acquire() == NULL) {
6116 // An uninitialized object, skip to the next card, since
6117 // we may not be able to read its P-bits yet.
6118 assert(size == 0, "Initial value");
6119 } else {
6120 // An object not (yet) reached by marking: we merely need to
6121 // compute its size so as to go look at the next block.
6122 assert(p->is_oop(true), "should be an oop");
6123 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6124 }
6125 }
6126 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6127 return size;
6128 }
6129
6130 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6131 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6132 "CMS thread should hold CMS token");
6133 assert_lock_strong(_freelistLock);
6134 assert_lock_strong(_bitMap->lock());
6135 // relinquish the free_list_lock and bitMaplock()
6136 _bitMap->lock()->unlock();
6137 _freelistLock->unlock();
6138 ConcurrentMarkSweepThread::desynchronize(true);
6139 _collector->stopTimer();
6140 _collector->incrementYields();
6141
6142 // See the comment in coordinator_yield()
6143 for (unsigned i = 0; i < CMSYieldSleepCount &&
6144 ConcurrentMarkSweepThread::should_yield() &&
6145 !CMSCollector::foregroundGCIsActive(); ++i) {
6146 os::sleep(Thread::current(), 1, false);
6147 }
6148
6149 ConcurrentMarkSweepThread::synchronize(true);
6150 _freelistLock->lock_without_safepoint_check();
6151 _bitMap->lock()->lock_without_safepoint_check();
6152 _collector->startTimer();
6153 }
6154
6155
6156 //////////////////////////////////////////////////////////////////
6157 // SurvivorSpacePrecleanClosure
6158 //////////////////////////////////////////////////////////////////
6159 // This (single-threaded) closure is used to preclean the oops in
6160 // the survivor spaces.
6161 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6162
6163 HeapWord* addr = (HeapWord*)p;
6164 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6165 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6166 assert(p->klass_or_null() != NULL, "object should be initialized");
6167 // an initialized object; ignore mark word in verification below
6168 // since we are running concurrent with mutators
6169 assert(p->is_oop(true), "should be an oop");
6170 // Note that we do not yield while we iterate over
6171 // the interior oops of p, pushing the relevant ones
6172 // on our marking stack.
6173 size_t size = p->oop_iterate_size(_scanning_closure);
6174 do_yield_check();
6175 // Observe that below, we do not abandon the preclean
6176 // phase as soon as we should; rather we empty the
6177 // marking stack before returning. This is to satisfy
6178 // some existing assertions. In general, it may be a
6179 // good idea to abort immediately and complete the marking
6180 // from the grey objects at a later time.
6181 while (!_mark_stack->isEmpty()) {
6182 oop new_oop = _mark_stack->pop();
6183 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6184 assert(_bit_map->isMarked((HeapWord*)new_oop),
6185 "only grey objects on this stack");
6186 // iterate over the oops in this oop, marking and pushing
6187 // the ones in CMS heap (i.e. in _span).
6188 new_oop->oop_iterate(_scanning_closure);
6189 // check if it's time to yield
6190 do_yield_check();
6191 }
6192 unsigned int after_count =
6193 GenCollectedHeap::heap()->total_collections();
6194 bool abort = (_before_count != after_count) ||
6195 _collector->should_abort_preclean();
6196 return abort ? 0 : size;
6197 }
6198
6199 void SurvivorSpacePrecleanClosure::do_yield_work() {
6200 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6201 "CMS thread should hold CMS token");
6202 assert_lock_strong(_bit_map->lock());
6203 // Relinquish the bit map lock
6204 _bit_map->lock()->unlock();
6205 ConcurrentMarkSweepThread::desynchronize(true);
6206 _collector->stopTimer();
6207 _collector->incrementYields();
6208
6209 // See the comment in coordinator_yield()
6210 for (unsigned i = 0; i < CMSYieldSleepCount &&
6211 ConcurrentMarkSweepThread::should_yield() &&
6212 !CMSCollector::foregroundGCIsActive(); ++i) {
6213 os::sleep(Thread::current(), 1, false);
6214 }
6215
6216 ConcurrentMarkSweepThread::synchronize(true);
6217 _bit_map->lock()->lock_without_safepoint_check();
6218 _collector->startTimer();
6219 }
6220
6221 // This closure is used to rescan the marked objects on the dirty cards
6222 // in the mod union table and the card table proper. In the parallel
6223 // case, although the bitMap is shared, we do a single read so the
6224 // isMarked() query is "safe".
6225 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6226 // Ignore mark word because we are running concurrent with mutators
6227 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6228 HeapWord* addr = (HeapWord*)p;
6229 assert(_span.contains(addr), "we are scanning the CMS generation");
6230 bool is_obj_array = false;
6231 #ifdef ASSERT
6232 if (!_parallel) {
6233 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6234 assert(_collector->overflow_list_is_empty(),
6235 "overflow list should be empty");
6236
6237 }
6238 #endif // ASSERT
6239 if (_bit_map->isMarked(addr)) {
6240 // Obj arrays are precisely marked, non-arrays are not;
6241 // so we scan objArrays precisely and non-arrays in their
6242 // entirety.
6243 if (p->is_objArray()) {
6244 is_obj_array = true;
6245 if (_parallel) {
6246 p->oop_iterate(_par_scan_closure, mr);
6247 } else {
6248 p->oop_iterate(_scan_closure, mr);
6249 }
6250 } else {
6251 if (_parallel) {
6252 p->oop_iterate(_par_scan_closure);
6253 } else {
6254 p->oop_iterate(_scan_closure);
6255 }
6256 }
6257 }
6258 #ifdef ASSERT
6259 if (!_parallel) {
6260 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6261 assert(_collector->overflow_list_is_empty(),
6262 "overflow list should be empty");
6263
6264 }
6265 #endif // ASSERT
6266 return is_obj_array;
6267 }
6268
6269 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6270 MemRegion span,
6271 CMSBitMap* bitMap, CMSMarkStack* markStack,
6272 bool should_yield, bool verifying):
6273 _collector(collector),
6274 _span(span),
6275 _bitMap(bitMap),
6276 _mut(&collector->_modUnionTable),
6277 _markStack(markStack),
6278 _yield(should_yield),
6279 _skipBits(0)
6280 {
6281 assert(_markStack->isEmpty(), "stack should be empty");
6282 _finger = _bitMap->startWord();
6283 _threshold = _finger;
6284 assert(_collector->_restart_addr == NULL, "Sanity check");
6285 assert(_span.contains(_finger), "Out of bounds _finger?");
6286 DEBUG_ONLY(_verifying = verifying;)
6287 }
6288
6289 void MarkFromRootsClosure::reset(HeapWord* addr) {
6290 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6291 assert(_span.contains(addr), "Out of bounds _finger?");
6292 _finger = addr;
6293 _threshold = (HeapWord*)round_to(
6294 (intptr_t)_finger, CardTableModRefBS::card_size);
6295 }
6296
6297 // Should revisit to see if this should be restructured for
6298 // greater efficiency.
6299 bool MarkFromRootsClosure::do_bit(size_t offset) {
6300 if (_skipBits > 0) {
6301 _skipBits--;
6302 return true;
6303 }
6304 // convert offset into a HeapWord*
6305 HeapWord* addr = _bitMap->startWord() + offset;
6306 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6307 "address out of range");
6308 assert(_bitMap->isMarked(addr), "tautology");
6309 if (_bitMap->isMarked(addr+1)) {
6310 // this is an allocated but not yet initialized object
6311 assert(_skipBits == 0, "tautology");
6312 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6313 oop p = oop(addr);
6314 if (p->klass_or_null_acquire() == NULL) {
6315 DEBUG_ONLY(if (!_verifying) {)
6316 // We re-dirty the cards on which this object lies and increase
6317 // the _threshold so that we'll come back to scan this object
6318 // during the preclean or remark phase. (CMSCleanOnEnter)
6319 if (CMSCleanOnEnter) {
6320 size_t sz = _collector->block_size_using_printezis_bits(addr);
6321 HeapWord* end_card_addr = (HeapWord*)round_to(
6322 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6323 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6324 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6325 // Bump _threshold to end_card_addr; note that
6326 // _threshold cannot possibly exceed end_card_addr, anyhow.
6327 // This prevents future clearing of the card as the scan proceeds
6328 // to the right.
6329 assert(_threshold <= end_card_addr,
6330 "Because we are just scanning into this object");
6331 if (_threshold < end_card_addr) {
6332 _threshold = end_card_addr;
6333 }
6334 if (p->klass_or_null_acquire() != NULL) {
6335 // Redirty the range of cards...
6336 _mut->mark_range(redirty_range);
6337 } // ...else the setting of klass will dirty the card anyway.
6338 }
6339 DEBUG_ONLY(})
6340 return true;
6341 }
6342 }
6343 scanOopsInOop(addr);
6344 return true;
6345 }
6346
6347 // We take a break if we've been at this for a while,
6348 // so as to avoid monopolizing the locks involved.
6349 void MarkFromRootsClosure::do_yield_work() {
6350 // First give up the locks, then yield, then re-lock
6351 // We should probably use a constructor/destructor idiom to
6352 // do this unlock/lock or modify the MutexUnlocker class to
6353 // serve our purpose. XXX
6354 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6355 "CMS thread should hold CMS token");
6356 assert_lock_strong(_bitMap->lock());
6357 _bitMap->lock()->unlock();
6358 ConcurrentMarkSweepThread::desynchronize(true);
6359 _collector->stopTimer();
6360 _collector->incrementYields();
6361
6362 // See the comment in coordinator_yield()
6363 for (unsigned i = 0; i < CMSYieldSleepCount &&
6364 ConcurrentMarkSweepThread::should_yield() &&
6365 !CMSCollector::foregroundGCIsActive(); ++i) {
6366 os::sleep(Thread::current(), 1, false);
6367 }
6368
6369 ConcurrentMarkSweepThread::synchronize(true);
6370 _bitMap->lock()->lock_without_safepoint_check();
6371 _collector->startTimer();
6372 }
6373
6374 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6375 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6376 assert(_markStack->isEmpty(),
6377 "should drain stack to limit stack usage");
6378 // convert ptr to an oop preparatory to scanning
6379 oop obj = oop(ptr);
6380 // Ignore mark word in verification below, since we
6381 // may be running concurrent with mutators.
6382 assert(obj->is_oop(true), "should be an oop");
6383 assert(_finger <= ptr, "_finger runneth ahead");
6384 // advance the finger to right end of this object
6385 _finger = ptr + obj->size();
6386 assert(_finger > ptr, "we just incremented it above");
6387 // On large heaps, it may take us some time to get through
6388 // the marking phase. During
6389 // this time it's possible that a lot of mutations have
6390 // accumulated in the card table and the mod union table --
6391 // these mutation records are redundant until we have
6392 // actually traced into the corresponding card.
6393 // Here, we check whether advancing the finger would make
6394 // us cross into a new card, and if so clear corresponding
6395 // cards in the MUT (preclean them in the card-table in the
6396 // future).
6397
6398 DEBUG_ONLY(if (!_verifying) {)
6399 // The clean-on-enter optimization is disabled by default,
6400 // until we fix 6178663.
6401 if (CMSCleanOnEnter && (_finger > _threshold)) {
6402 // [_threshold, _finger) represents the interval
6403 // of cards to be cleared in MUT (or precleaned in card table).
6404 // The set of cards to be cleared is all those that overlap
6405 // with the interval [_threshold, _finger); note that
6406 // _threshold is always kept card-aligned but _finger isn't
6407 // always card-aligned.
6408 HeapWord* old_threshold = _threshold;
6409 assert(old_threshold == (HeapWord*)round_to(
6410 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6411 "_threshold should always be card-aligned");
6412 _threshold = (HeapWord*)round_to(
6413 (intptr_t)_finger, CardTableModRefBS::card_size);
6414 MemRegion mr(old_threshold, _threshold);
6415 assert(!mr.is_empty(), "Control point invariant");
6416 assert(_span.contains(mr), "Should clear within span");
6417 _mut->clear_range(mr);
6418 }
6419 DEBUG_ONLY(})
6420 // Note: the finger doesn't advance while we drain
6421 // the stack below.
6422 PushOrMarkClosure pushOrMarkClosure(_collector,
6423 _span, _bitMap, _markStack,
6424 _finger, this);
6425 bool res = _markStack->push(obj);
6426 assert(res, "Empty non-zero size stack should have space for single push");
6427 while (!_markStack->isEmpty()) {
6428 oop new_oop = _markStack->pop();
6429 // Skip verifying header mark word below because we are
6430 // running concurrent with mutators.
6431 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6432 // now scan this oop's oops
6433 new_oop->oop_iterate(&pushOrMarkClosure);
6434 do_yield_check();
6435 }
6436 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6437 }
6438
6439 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6440 CMSCollector* collector, MemRegion span,
6441 CMSBitMap* bit_map,
6442 OopTaskQueue* work_queue,
6443 CMSMarkStack* overflow_stack):
6444 _collector(collector),
6445 _whole_span(collector->_span),
6446 _span(span),
6447 _bit_map(bit_map),
6448 _mut(&collector->_modUnionTable),
6449 _work_queue(work_queue),
6450 _overflow_stack(overflow_stack),
6451 _skip_bits(0),
6452 _task(task)
6453 {
6454 assert(_work_queue->size() == 0, "work_queue should be empty");
6455 _finger = span.start();
6456 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6457 assert(_span.contains(_finger), "Out of bounds _finger?");
6458 }
6459
6460 // Should revisit to see if this should be restructured for
6461 // greater efficiency.
6462 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6463 if (_skip_bits > 0) {
6464 _skip_bits--;
6465 return true;
6466 }
6467 // convert offset into a HeapWord*
6468 HeapWord* addr = _bit_map->startWord() + offset;
6469 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6470 "address out of range");
6471 assert(_bit_map->isMarked(addr), "tautology");
6472 if (_bit_map->isMarked(addr+1)) {
6473 // this is an allocated object that might not yet be initialized
6474 assert(_skip_bits == 0, "tautology");
6475 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6476 oop p = oop(addr);
6477 if (p->klass_or_null_acquire() == NULL) {
6478 // in the case of Clean-on-Enter optimization, redirty card
6479 // and avoid clearing card by increasing the threshold.
6480 return true;
6481 }
6482 }
6483 scan_oops_in_oop(addr);
6484 return true;
6485 }
6486
6487 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6488 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6489 // Should we assert that our work queue is empty or
6490 // below some drain limit?
6491 assert(_work_queue->size() == 0,
6492 "should drain stack to limit stack usage");
6493 // convert ptr to an oop preparatory to scanning
6494 oop obj = oop(ptr);
6495 // Ignore mark word in verification below, since we
6496 // may be running concurrent with mutators.
6497 assert(obj->is_oop(true), "should be an oop");
6498 assert(_finger <= ptr, "_finger runneth ahead");
6499 // advance the finger to right end of this object
6500 _finger = ptr + obj->size();
6501 assert(_finger > ptr, "we just incremented it above");
6502 // On large heaps, it may take us some time to get through
6503 // the marking phase. During
6504 // this time it's possible that a lot of mutations have
6505 // accumulated in the card table and the mod union table --
6506 // these mutation records are redundant until we have
6507 // actually traced into the corresponding card.
6508 // Here, we check whether advancing the finger would make
6509 // us cross into a new card, and if so clear corresponding
6510 // cards in the MUT (preclean them in the card-table in the
6511 // future).
6512
6513 // The clean-on-enter optimization is disabled by default,
6514 // until we fix 6178663.
6515 if (CMSCleanOnEnter && (_finger > _threshold)) {
6516 // [_threshold, _finger) represents the interval
6517 // of cards to be cleared in MUT (or precleaned in card table).
6518 // The set of cards to be cleared is all those that overlap
6519 // with the interval [_threshold, _finger); note that
6520 // _threshold is always kept card-aligned but _finger isn't
6521 // always card-aligned.
6522 HeapWord* old_threshold = _threshold;
6523 assert(old_threshold == (HeapWord*)round_to(
6524 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6525 "_threshold should always be card-aligned");
6526 _threshold = (HeapWord*)round_to(
6527 (intptr_t)_finger, CardTableModRefBS::card_size);
6528 MemRegion mr(old_threshold, _threshold);
6529 assert(!mr.is_empty(), "Control point invariant");
6530 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6531 _mut->clear_range(mr);
6532 }
6533
6534 // Note: the local finger doesn't advance while we drain
6535 // the stack below, but the global finger sure can and will.
6536 HeapWord* volatile* gfa = _task->global_finger_addr();
6537 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6538 _span, _bit_map,
6539 _work_queue,
6540 _overflow_stack,
6541 _finger,
6542 gfa, this);
6543 bool res = _work_queue->push(obj); // overflow could occur here
6544 assert(res, "Will hold once we use workqueues");
6545 while (true) {
6546 oop new_oop;
6547 if (!_work_queue->pop_local(new_oop)) {
6548 // We emptied our work_queue; check if there's stuff that can
6549 // be gotten from the overflow stack.
6550 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6551 _overflow_stack, _work_queue)) {
6552 do_yield_check();
6553 continue;
6554 } else { // done
6555 break;
6556 }
6557 }
6558 // Skip verifying header mark word below because we are
6559 // running concurrent with mutators.
6560 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6561 // now scan this oop's oops
6562 new_oop->oop_iterate(&pushOrMarkClosure);
6563 do_yield_check();
6564 }
6565 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6566 }
6567
6568 // Yield in response to a request from VM Thread or
6569 // from mutators.
6570 void ParMarkFromRootsClosure::do_yield_work() {
6571 assert(_task != NULL, "sanity");
6572 _task->yield();
6573 }
6574
6575 // A variant of the above used for verifying CMS marking work.
6576 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6577 MemRegion span,
6578 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6579 CMSMarkStack* mark_stack):
6580 _collector(collector),
6581 _span(span),
6582 _verification_bm(verification_bm),
6583 _cms_bm(cms_bm),
6584 _mark_stack(mark_stack),
6585 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6586 mark_stack)
6587 {
6588 assert(_mark_stack->isEmpty(), "stack should be empty");
6589 _finger = _verification_bm->startWord();
6590 assert(_collector->_restart_addr == NULL, "Sanity check");
6591 assert(_span.contains(_finger), "Out of bounds _finger?");
6592 }
6593
6594 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6595 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6596 assert(_span.contains(addr), "Out of bounds _finger?");
6597 _finger = addr;
6598 }
6599
6600 // Should revisit to see if this should be restructured for
6601 // greater efficiency.
6602 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6603 // convert offset into a HeapWord*
6604 HeapWord* addr = _verification_bm->startWord() + offset;
6605 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6606 "address out of range");
6607 assert(_verification_bm->isMarked(addr), "tautology");
6608 assert(_cms_bm->isMarked(addr), "tautology");
6609
6610 assert(_mark_stack->isEmpty(),
6611 "should drain stack to limit stack usage");
6612 // convert addr to an oop preparatory to scanning
6613 oop obj = oop(addr);
6614 assert(obj->is_oop(), "should be an oop");
6615 assert(_finger <= addr, "_finger runneth ahead");
6616 // advance the finger to right end of this object
6617 _finger = addr + obj->size();
6618 assert(_finger > addr, "we just incremented it above");
6619 // Note: the finger doesn't advance while we drain
6620 // the stack below.
6621 bool res = _mark_stack->push(obj);
6622 assert(res, "Empty non-zero size stack should have space for single push");
6623 while (!_mark_stack->isEmpty()) {
6624 oop new_oop = _mark_stack->pop();
6625 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6626 // now scan this oop's oops
6627 new_oop->oop_iterate(&_pam_verify_closure);
6628 }
6629 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6630 return true;
6631 }
6632
6633 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6634 CMSCollector* collector, MemRegion span,
6635 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6636 CMSMarkStack* mark_stack):
6637 MetadataAwareOopClosure(collector->ref_processor()),
6638 _collector(collector),
6639 _span(span),
6640 _verification_bm(verification_bm),
6641 _cms_bm(cms_bm),
6642 _mark_stack(mark_stack)
6643 { }
6644
6645 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6646 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6647
6648 // Upon stack overflow, we discard (part of) the stack,
6649 // remembering the least address amongst those discarded
6650 // in CMSCollector's _restart_address.
6651 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6652 // Remember the least grey address discarded
6653 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6654 _collector->lower_restart_addr(ra);
6655 _mark_stack->reset(); // discard stack contents
6656 _mark_stack->expand(); // expand the stack if possible
6657 }
6658
6659 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6660 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6661 HeapWord* addr = (HeapWord*)obj;
6662 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6663 // Oop lies in _span and isn't yet grey or black
6664 _verification_bm->mark(addr); // now grey
6665 if (!_cms_bm->isMarked(addr)) {
6666 Log(gc, verify) log;
6667 ResourceMark rm;
6668 oop(addr)->print_on(log.error_stream());
6669 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6670 fatal("... aborting");
6671 }
6672
6673 if (!_mark_stack->push(obj)) { // stack overflow
6674 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6675 assert(_mark_stack->isFull(), "Else push should have succeeded");
6676 handle_stack_overflow(addr);
6677 }
6678 // anything including and to the right of _finger
6679 // will be scanned as we iterate over the remainder of the
6680 // bit map
6681 }
6682 }
6683
6684 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6685 MemRegion span,
6686 CMSBitMap* bitMap, CMSMarkStack* markStack,
6687 HeapWord* finger, MarkFromRootsClosure* parent) :
6688 MetadataAwareOopClosure(collector->ref_processor()),
6689 _collector(collector),
6690 _span(span),
6691 _bitMap(bitMap),
6692 _markStack(markStack),
6693 _finger(finger),
6694 _parent(parent)
6695 { }
6696
6697 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6698 MemRegion span,
6699 CMSBitMap* bit_map,
6700 OopTaskQueue* work_queue,
6701 CMSMarkStack* overflow_stack,
6702 HeapWord* finger,
6703 HeapWord* volatile* global_finger_addr,
6704 ParMarkFromRootsClosure* parent) :
6705 MetadataAwareOopClosure(collector->ref_processor()),
6706 _collector(collector),
6707 _whole_span(collector->_span),
6708 _span(span),
6709 _bit_map(bit_map),
6710 _work_queue(work_queue),
6711 _overflow_stack(overflow_stack),
6712 _finger(finger),
6713 _global_finger_addr(global_finger_addr),
6714 _parent(parent)
6715 { }
6716
6717 // Assumes thread-safe access by callers, who are
6718 // responsible for mutual exclusion.
6719 void CMSCollector::lower_restart_addr(HeapWord* low) {
6720 assert(_span.contains(low), "Out of bounds addr");
6721 if (_restart_addr == NULL) {
6722 _restart_addr = low;
6723 } else {
6724 _restart_addr = MIN2(_restart_addr, low);
6725 }
6726 }
6727
6728 // Upon stack overflow, we discard (part of) the stack,
6729 // remembering the least address amongst those discarded
6730 // in CMSCollector's _restart_address.
6731 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6732 // Remember the least grey address discarded
6733 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6734 _collector->lower_restart_addr(ra);
6735 _markStack->reset(); // discard stack contents
6736 _markStack->expand(); // expand the stack if possible
6737 }
6738
6739 // Upon stack overflow, we discard (part of) the stack,
6740 // remembering the least address amongst those discarded
6741 // in CMSCollector's _restart_address.
6742 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6743 // We need to do this under a mutex to prevent other
6744 // workers from interfering with the work done below.
6745 MutexLockerEx ml(_overflow_stack->par_lock(),
6746 Mutex::_no_safepoint_check_flag);
6747 // Remember the least grey address discarded
6748 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6749 _collector->lower_restart_addr(ra);
6750 _overflow_stack->reset(); // discard stack contents
6751 _overflow_stack->expand(); // expand the stack if possible
6752 }
6753
6754 void PushOrMarkClosure::do_oop(oop obj) {
6755 // Ignore mark word because we are running concurrent with mutators.
6756 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6757 HeapWord* addr = (HeapWord*)obj;
6758 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6759 // Oop lies in _span and isn't yet grey or black
6760 _bitMap->mark(addr); // now grey
6761 if (addr < _finger) {
6762 // the bit map iteration has already either passed, or
6763 // sampled, this bit in the bit map; we'll need to
6764 // use the marking stack to scan this oop's oops.
6765 bool simulate_overflow = false;
6766 NOT_PRODUCT(
6767 if (CMSMarkStackOverflowALot &&
6768 _collector->simulate_overflow()) {
6769 // simulate a stack overflow
6770 simulate_overflow = true;
6771 }
6772 )
6773 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6774 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6775 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6776 handle_stack_overflow(addr);
6777 }
6778 }
6779 // anything including and to the right of _finger
6780 // will be scanned as we iterate over the remainder of the
6781 // bit map
6782 do_yield_check();
6783 }
6784 }
6785
6786 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6787 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6788
6789 void ParPushOrMarkClosure::do_oop(oop obj) {
6790 // Ignore mark word because we are running concurrent with mutators.
6791 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6792 HeapWord* addr = (HeapWord*)obj;
6793 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6794 // Oop lies in _span and isn't yet grey or black
6795 // We read the global_finger (volatile read) strictly after marking oop
6796 bool res = _bit_map->par_mark(addr); // now grey
6797 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6798 // Should we push this marked oop on our stack?
6799 // -- if someone else marked it, nothing to do
6800 // -- if target oop is above global finger nothing to do
6801 // -- if target oop is in chunk and above local finger
6802 // then nothing to do
6803 // -- else push on work queue
6804 if ( !res // someone else marked it, they will deal with it
6805 || (addr >= *gfa) // will be scanned in a later task
6806 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6807 return;
6808 }
6809 // the bit map iteration has already either passed, or
6810 // sampled, this bit in the bit map; we'll need to
6811 // use the marking stack to scan this oop's oops.
6812 bool simulate_overflow = false;
6813 NOT_PRODUCT(
6814 if (CMSMarkStackOverflowALot &&
6815 _collector->simulate_overflow()) {
6816 // simulate a stack overflow
6817 simulate_overflow = true;
6818 }
6819 )
6820 if (simulate_overflow ||
6821 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6822 // stack overflow
6823 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6824 // We cannot assert that the overflow stack is full because
6825 // it may have been emptied since.
6826 assert(simulate_overflow ||
6827 _work_queue->size() == _work_queue->max_elems(),
6828 "Else push should have succeeded");
6829 handle_stack_overflow(addr);
6830 }
6831 do_yield_check();
6832 }
6833 }
6834
6835 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6836 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6837
6838 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6839 MemRegion span,
6840 ReferenceProcessor* rp,
6841 CMSBitMap* bit_map,
6842 CMSBitMap* mod_union_table,
6843 CMSMarkStack* mark_stack,
6844 bool concurrent_precleaning):
6845 MetadataAwareOopClosure(rp),
6846 _collector(collector),
6847 _span(span),
6848 _bit_map(bit_map),
6849 _mod_union_table(mod_union_table),
6850 _mark_stack(mark_stack),
6851 _concurrent_precleaning(concurrent_precleaning)
6852 {
6853 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6854 }
6855
6856 // Grey object rescan during pre-cleaning and second checkpoint phases --
6857 // the non-parallel version (the parallel version appears further below.)
6858 void PushAndMarkClosure::do_oop(oop obj) {
6859 // Ignore mark word verification. If during concurrent precleaning,
6860 // the object monitor may be locked. If during the checkpoint
6861 // phases, the object may already have been reached by a different
6862 // path and may be at the end of the global overflow list (so
6863 // the mark word may be NULL).
6864 assert(obj->is_oop_or_null(true /* ignore mark word */),
6865 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6866 HeapWord* addr = (HeapWord*)obj;
6867 // Check if oop points into the CMS generation
6868 // and is not marked
6869 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6870 // a white object ...
6871 _bit_map->mark(addr); // ... now grey
6872 // push on the marking stack (grey set)
6873 bool simulate_overflow = false;
6874 NOT_PRODUCT(
6875 if (CMSMarkStackOverflowALot &&
6876 _collector->simulate_overflow()) {
6877 // simulate a stack overflow
6878 simulate_overflow = true;
6879 }
6880 )
6881 if (simulate_overflow || !_mark_stack->push(obj)) {
6882 if (_concurrent_precleaning) {
6883 // During precleaning we can just dirty the appropriate card(s)
6884 // in the mod union table, thus ensuring that the object remains
6885 // in the grey set and continue. In the case of object arrays
6886 // we need to dirty all of the cards that the object spans,
6887 // since the rescan of object arrays will be limited to the
6888 // dirty cards.
6889 // Note that no one can be interfering with us in this action
6890 // of dirtying the mod union table, so no locking or atomics
6891 // are required.
6892 if (obj->is_objArray()) {
6893 size_t sz = obj->size();
6894 HeapWord* end_card_addr = (HeapWord*)round_to(
6895 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6896 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6897 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6898 _mod_union_table->mark_range(redirty_range);
6899 } else {
6900 _mod_union_table->mark(addr);
6901 }
6902 _collector->_ser_pmc_preclean_ovflw++;
6903 } else {
6904 // During the remark phase, we need to remember this oop
6905 // in the overflow list.
6906 _collector->push_on_overflow_list(obj);
6907 _collector->_ser_pmc_remark_ovflw++;
6908 }
6909 }
6910 }
6911 }
6912
6913 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6914 MemRegion span,
6915 ReferenceProcessor* rp,
6916 CMSBitMap* bit_map,
6917 OopTaskQueue* work_queue):
6918 MetadataAwareOopClosure(rp),
6919 _collector(collector),
6920 _span(span),
6921 _bit_map(bit_map),
6922 _work_queue(work_queue)
6923 {
6924 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6925 }
6926
6927 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6928 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6929
6930 // Grey object rescan during second checkpoint phase --
6931 // the parallel version.
6932 void ParPushAndMarkClosure::do_oop(oop obj) {
6933 // In the assert below, we ignore the mark word because
6934 // this oop may point to an already visited object that is
6935 // on the overflow stack (in which case the mark word has
6936 // been hijacked for chaining into the overflow stack --
6937 // if this is the last object in the overflow stack then
6938 // its mark word will be NULL). Because this object may
6939 // have been subsequently popped off the global overflow
6940 // stack, and the mark word possibly restored to the prototypical
6941 // value, by the time we get to examined this failing assert in
6942 // the debugger, is_oop_or_null(false) may subsequently start
6943 // to hold.
6944 assert(obj->is_oop_or_null(true),
6945 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6946 HeapWord* addr = (HeapWord*)obj;
6947 // Check if oop points into the CMS generation
6948 // and is not marked
6949 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6950 // a white object ...
6951 // If we manage to "claim" the object, by being the
6952 // first thread to mark it, then we push it on our
6953 // marking stack
6954 if (_bit_map->par_mark(addr)) { // ... now grey
6955 // push on work queue (grey set)
6956 bool simulate_overflow = false;
6957 NOT_PRODUCT(
6958 if (CMSMarkStackOverflowALot &&
6959 _collector->par_simulate_overflow()) {
6960 // simulate a stack overflow
6961 simulate_overflow = true;
6962 }
6963 )
6964 if (simulate_overflow || !_work_queue->push(obj)) {
6965 _collector->par_push_on_overflow_list(obj);
6966 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6967 }
6968 } // Else, some other thread got there first
6969 }
6970 }
6971
6972 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6973 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6974
6975 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6976 Mutex* bml = _collector->bitMapLock();
6977 assert_lock_strong(bml);
6978 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6979 "CMS thread should hold CMS token");
6980
6981 bml->unlock();
6982 ConcurrentMarkSweepThread::desynchronize(true);
6983
6984 _collector->stopTimer();
6985 _collector->incrementYields();
6986
6987 // See the comment in coordinator_yield()
6988 for (unsigned i = 0; i < CMSYieldSleepCount &&
6989 ConcurrentMarkSweepThread::should_yield() &&
6990 !CMSCollector::foregroundGCIsActive(); ++i) {
6991 os::sleep(Thread::current(), 1, false);
6992 }
6993
6994 ConcurrentMarkSweepThread::synchronize(true);
6995 bml->lock();
6996
6997 _collector->startTimer();
6998 }
6999
7000 bool CMSPrecleanRefsYieldClosure::should_return() {
7001 if (ConcurrentMarkSweepThread::should_yield()) {
7002 do_yield_work();
7003 }
7004 return _collector->foregroundGCIsActive();
7005 }
7006
7007 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7008 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7009 "mr should be aligned to start at a card boundary");
7010 // We'd like to assert:
7011 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7012 // "mr should be a range of cards");
7013 // However, that would be too strong in one case -- the last
7014 // partition ends at _unallocated_block which, in general, can be
7015 // an arbitrary boundary, not necessarily card aligned.
7016 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7017 _space->object_iterate_mem(mr, &_scan_cl);
7018 }
7019
7020 SweepClosure::SweepClosure(CMSCollector* collector,
7021 ConcurrentMarkSweepGeneration* g,
7022 CMSBitMap* bitMap, bool should_yield) :
7023 _collector(collector),
7024 _g(g),
7025 _sp(g->cmsSpace()),
7026 _limit(_sp->sweep_limit()),
7027 _freelistLock(_sp->freelistLock()),
7028 _bitMap(bitMap),
7029 _yield(should_yield),
7030 _inFreeRange(false), // No free range at beginning of sweep
7031 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7032 _lastFreeRangeCoalesced(false),
7033 _freeFinger(g->used_region().start())
7034 {
7035 NOT_PRODUCT(
7036 _numObjectsFreed = 0;
7037 _numWordsFreed = 0;
7038 _numObjectsLive = 0;
7039 _numWordsLive = 0;
7040 _numObjectsAlreadyFree = 0;
7041 _numWordsAlreadyFree = 0;
7042 _last_fc = NULL;
7043
7044 _sp->initializeIndexedFreeListArrayReturnedBytes();
7045 _sp->dictionary()->initialize_dict_returned_bytes();
7046 )
7047 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7048 "sweep _limit out of bounds");
7049 log_develop_trace(gc, sweep)("====================");
7050 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7051 }
7052
7053 void SweepClosure::print_on(outputStream* st) const {
7054 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7055 p2i(_sp->bottom()), p2i(_sp->end()));
7056 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7057 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7058 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7059 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7060 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7061 }
7062
7063 #ifndef PRODUCT
7064 // Assertion checking only: no useful work in product mode --
7065 // however, if any of the flags below become product flags,
7066 // you may need to review this code to see if it needs to be
7067 // enabled in product mode.
7068 SweepClosure::~SweepClosure() {
7069 assert_lock_strong(_freelistLock);
7070 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7071 "sweep _limit out of bounds");
7072 if (inFreeRange()) {
7073 Log(gc, sweep) log;
7074 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7075 ResourceMark rm;
7076 print_on(log.error_stream());
7077 ShouldNotReachHere();
7078 }
7079
7080 if (log_is_enabled(Debug, gc, sweep)) {
7081 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7082 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7083 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7084 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7085 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7086 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7087 }
7088
7089 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7090 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7091 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7092 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7093 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7094 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7095 }
7096 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7097 log_develop_trace(gc, sweep)("================");
7098 }
7099 #endif // PRODUCT
7100
7101 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7102 bool freeRangeInFreeLists) {
7103 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7104 p2i(freeFinger), freeRangeInFreeLists);
7105 assert(!inFreeRange(), "Trampling existing free range");
7106 set_inFreeRange(true);
7107 set_lastFreeRangeCoalesced(false);
7108
7109 set_freeFinger(freeFinger);
7110 set_freeRangeInFreeLists(freeRangeInFreeLists);
7111 if (CMSTestInFreeList) {
7112 if (freeRangeInFreeLists) {
7113 FreeChunk* fc = (FreeChunk*) freeFinger;
7114 assert(fc->is_free(), "A chunk on the free list should be free.");
7115 assert(fc->size() > 0, "Free range should have a size");
7116 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7117 }
7118 }
7119 }
7120
7121 // Note that the sweeper runs concurrently with mutators. Thus,
7122 // it is possible for direct allocation in this generation to happen
7123 // in the middle of the sweep. Note that the sweeper also coalesces
7124 // contiguous free blocks. Thus, unless the sweeper and the allocator
7125 // synchronize appropriately freshly allocated blocks may get swept up.
7126 // This is accomplished by the sweeper locking the free lists while
7127 // it is sweeping. Thus blocks that are determined to be free are
7128 // indeed free. There is however one additional complication:
7129 // blocks that have been allocated since the final checkpoint and
7130 // mark, will not have been marked and so would be treated as
7131 // unreachable and swept up. To prevent this, the allocator marks
7132 // the bit map when allocating during the sweep phase. This leads,
7133 // however, to a further complication -- objects may have been allocated
7134 // but not yet initialized -- in the sense that the header isn't yet
7135 // installed. The sweeper can not then determine the size of the block
7136 // in order to skip over it. To deal with this case, we use a technique
7137 // (due to Printezis) to encode such uninitialized block sizes in the
7138 // bit map. Since the bit map uses a bit per every HeapWord, but the
7139 // CMS generation has a minimum object size of 3 HeapWords, it follows
7140 // that "normal marks" won't be adjacent in the bit map (there will
7141 // always be at least two 0 bits between successive 1 bits). We make use
7142 // of these "unused" bits to represent uninitialized blocks -- the bit
7143 // corresponding to the start of the uninitialized object and the next
7144 // bit are both set. Finally, a 1 bit marks the end of the object that
7145 // started with the two consecutive 1 bits to indicate its potentially
7146 // uninitialized state.
7147
7148 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7149 FreeChunk* fc = (FreeChunk*)addr;
7150 size_t res;
7151
7152 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7153 // than "addr == _limit" because although _limit was a block boundary when
7154 // we started the sweep, it may no longer be one because heap expansion
7155 // may have caused us to coalesce the block ending at the address _limit
7156 // with a newly expanded chunk (this happens when _limit was set to the
7157 // previous _end of the space), so we may have stepped past _limit:
7158 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7159 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7160 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7161 "sweep _limit out of bounds");
7162 assert(addr < _sp->end(), "addr out of bounds");
7163 // Flush any free range we might be holding as a single
7164 // coalesced chunk to the appropriate free list.
7165 if (inFreeRange()) {
7166 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7167 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7168 flush_cur_free_chunk(freeFinger(),
7169 pointer_delta(addr, freeFinger()));
7170 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7171 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7172 lastFreeRangeCoalesced() ? 1 : 0);
7173 }
7174
7175 // help the iterator loop finish
7176 return pointer_delta(_sp->end(), addr);
7177 }
7178
7179 assert(addr < _limit, "sweep invariant");
7180 // check if we should yield
7181 do_yield_check(addr);
7182 if (fc->is_free()) {
7183 // Chunk that is already free
7184 res = fc->size();
7185 do_already_free_chunk(fc);
7186 debug_only(_sp->verifyFreeLists());
7187 // If we flush the chunk at hand in lookahead_and_flush()
7188 // and it's coalesced with a preceding chunk, then the
7189 // process of "mangling" the payload of the coalesced block
7190 // will cause erasure of the size information from the
7191 // (erstwhile) header of all the coalesced blocks but the
7192 // first, so the first disjunct in the assert will not hold
7193 // in that specific case (in which case the second disjunct
7194 // will hold).
7195 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7196 "Otherwise the size info doesn't change at this step");
7197 NOT_PRODUCT(
7198 _numObjectsAlreadyFree++;
7199 _numWordsAlreadyFree += res;
7200 )
7201 NOT_PRODUCT(_last_fc = fc;)
7202 } else if (!_bitMap->isMarked(addr)) {
7203 // Chunk is fresh garbage
7204 res = do_garbage_chunk(fc);
7205 debug_only(_sp->verifyFreeLists());
7206 NOT_PRODUCT(
7207 _numObjectsFreed++;
7208 _numWordsFreed += res;
7209 )
7210 } else {
7211 // Chunk that is alive.
7212 res = do_live_chunk(fc);
7213 debug_only(_sp->verifyFreeLists());
7214 NOT_PRODUCT(
7215 _numObjectsLive++;
7216 _numWordsLive += res;
7217 )
7218 }
7219 return res;
7220 }
7221
7222 // For the smart allocation, record following
7223 // split deaths - a free chunk is removed from its free list because
7224 // it is being split into two or more chunks.
7225 // split birth - a free chunk is being added to its free list because
7226 // a larger free chunk has been split and resulted in this free chunk.
7227 // coal death - a free chunk is being removed from its free list because
7228 // it is being coalesced into a large free chunk.
7229 // coal birth - a free chunk is being added to its free list because
7230 // it was created when two or more free chunks where coalesced into
7231 // this free chunk.
7232 //
7233 // These statistics are used to determine the desired number of free
7234 // chunks of a given size. The desired number is chosen to be relative
7235 // to the end of a CMS sweep. The desired number at the end of a sweep
7236 // is the
7237 // count-at-end-of-previous-sweep (an amount that was enough)
7238 // - count-at-beginning-of-current-sweep (the excess)
7239 // + split-births (gains in this size during interval)
7240 // - split-deaths (demands on this size during interval)
7241 // where the interval is from the end of one sweep to the end of the
7242 // next.
7243 //
7244 // When sweeping the sweeper maintains an accumulated chunk which is
7245 // the chunk that is made up of chunks that have been coalesced. That
7246 // will be termed the left-hand chunk. A new chunk of garbage that
7247 // is being considered for coalescing will be referred to as the
7248 // right-hand chunk.
7249 //
7250 // When making a decision on whether to coalesce a right-hand chunk with
7251 // the current left-hand chunk, the current count vs. the desired count
7252 // of the left-hand chunk is considered. Also if the right-hand chunk
7253 // is near the large chunk at the end of the heap (see
7254 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7255 // left-hand chunk is coalesced.
7256 //
7257 // When making a decision about whether to split a chunk, the desired count
7258 // vs. the current count of the candidate to be split is also considered.
7259 // If the candidate is underpopulated (currently fewer chunks than desired)
7260 // a chunk of an overpopulated (currently more chunks than desired) size may
7261 // be chosen. The "hint" associated with a free list, if non-null, points
7262 // to a free list which may be overpopulated.
7263 //
7264
7265 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7266 const size_t size = fc->size();
7267 // Chunks that cannot be coalesced are not in the
7268 // free lists.
7269 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7270 assert(_sp->verify_chunk_in_free_list(fc),
7271 "free chunk should be in free lists");
7272 }
7273 // a chunk that is already free, should not have been
7274 // marked in the bit map
7275 HeapWord* const addr = (HeapWord*) fc;
7276 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7277 // Verify that the bit map has no bits marked between
7278 // addr and purported end of this block.
7279 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7280
7281 // Some chunks cannot be coalesced under any circumstances.
7282 // See the definition of cantCoalesce().
7283 if (!fc->cantCoalesce()) {
7284 // This chunk can potentially be coalesced.
7285 // All the work is done in
7286 do_post_free_or_garbage_chunk(fc, size);
7287 // Note that if the chunk is not coalescable (the else arm
7288 // below), we unconditionally flush, without needing to do
7289 // a "lookahead," as we do below.
7290 if (inFreeRange()) lookahead_and_flush(fc, size);
7291 } else {
7292 // Code path common to both original and adaptive free lists.
7293
7294 // cant coalesce with previous block; this should be treated
7295 // as the end of a free run if any
7296 if (inFreeRange()) {
7297 // we kicked some butt; time to pick up the garbage
7298 assert(freeFinger() < addr, "freeFinger points too high");
7299 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7300 }
7301 // else, nothing to do, just continue
7302 }
7303 }
7304
7305 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7306 // This is a chunk of garbage. It is not in any free list.
7307 // Add it to a free list or let it possibly be coalesced into
7308 // a larger chunk.
7309 HeapWord* const addr = (HeapWord*) fc;
7310 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7311
7312 // Verify that the bit map has no bits marked between
7313 // addr and purported end of just dead object.
7314 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7315 do_post_free_or_garbage_chunk(fc, size);
7316
7317 assert(_limit >= addr + size,
7318 "A freshly garbage chunk can't possibly straddle over _limit");
7319 if (inFreeRange()) lookahead_and_flush(fc, size);
7320 return size;
7321 }
7322
7323 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7324 HeapWord* addr = (HeapWord*) fc;
7325 // The sweeper has just found a live object. Return any accumulated
7326 // left hand chunk to the free lists.
7327 if (inFreeRange()) {
7328 assert(freeFinger() < addr, "freeFinger points too high");
7329 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7330 }
7331
7332 // This object is live: we'd normally expect this to be
7333 // an oop, and like to assert the following:
7334 // assert(oop(addr)->is_oop(), "live block should be an oop");
7335 // However, as we commented above, this may be an object whose
7336 // header hasn't yet been initialized.
7337 size_t size;
7338 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7339 if (_bitMap->isMarked(addr + 1)) {
7340 // Determine the size from the bit map, rather than trying to
7341 // compute it from the object header.
7342 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7343 size = pointer_delta(nextOneAddr + 1, addr);
7344 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7345 "alignment problem");
7346
7347 #ifdef ASSERT
7348 if (oop(addr)->klass_or_null_acquire() != NULL) {
7349 // Ignore mark word because we are running concurrent with mutators
7350 assert(oop(addr)->is_oop(true), "live block should be an oop");
7351 assert(size ==
7352 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7353 "P-mark and computed size do not agree");
7354 }
7355 #endif
7356
7357 } else {
7358 // This should be an initialized object that's alive.
7359 assert(oop(addr)->klass_or_null_acquire() != NULL,
7360 "Should be an initialized object");
7361 // Ignore mark word because we are running concurrent with mutators
7362 assert(oop(addr)->is_oop(true), "live block should be an oop");
7363 // Verify that the bit map has no bits marked between
7364 // addr and purported end of this block.
7365 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7366 assert(size >= 3, "Necessary for Printezis marks to work");
7367 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7368 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7369 }
7370 return size;
7371 }
7372
7373 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7374 size_t chunkSize) {
7375 // do_post_free_or_garbage_chunk() should only be called in the case
7376 // of the adaptive free list allocator.
7377 const bool fcInFreeLists = fc->is_free();
7378 assert((HeapWord*)fc <= _limit, "sweep invariant");
7379 if (CMSTestInFreeList && fcInFreeLists) {
7380 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7381 }
7382
7383 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7384
7385 HeapWord* const fc_addr = (HeapWord*) fc;
7386
7387 bool coalesce = false;
7388 const size_t left = pointer_delta(fc_addr, freeFinger());
7389 const size_t right = chunkSize;
7390 switch (FLSCoalescePolicy) {
7391 // numeric value forms a coalition aggressiveness metric
7392 case 0: { // never coalesce
7393 coalesce = false;
7394 break;
7395 }
7396 case 1: { // coalesce if left & right chunks on overpopulated lists
7397 coalesce = _sp->coalOverPopulated(left) &&
7398 _sp->coalOverPopulated(right);
7399 break;
7400 }
7401 case 2: { // coalesce if left chunk on overpopulated list (default)
7402 coalesce = _sp->coalOverPopulated(left);
7403 break;
7404 }
7405 case 3: { // coalesce if left OR right chunk on overpopulated list
7406 coalesce = _sp->coalOverPopulated(left) ||
7407 _sp->coalOverPopulated(right);
7408 break;
7409 }
7410 case 4: { // always coalesce
7411 coalesce = true;
7412 break;
7413 }
7414 default:
7415 ShouldNotReachHere();
7416 }
7417
7418 // Should the current free range be coalesced?
7419 // If the chunk is in a free range and either we decided to coalesce above
7420 // or the chunk is near the large block at the end of the heap
7421 // (isNearLargestChunk() returns true), then coalesce this chunk.
7422 const bool doCoalesce = inFreeRange()
7423 && (coalesce || _g->isNearLargestChunk(fc_addr));
7424 if (doCoalesce) {
7425 // Coalesce the current free range on the left with the new
7426 // chunk on the right. If either is on a free list,
7427 // it must be removed from the list and stashed in the closure.
7428 if (freeRangeInFreeLists()) {
7429 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7430 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7431 "Size of free range is inconsistent with chunk size.");
7432 if (CMSTestInFreeList) {
7433 assert(_sp->verify_chunk_in_free_list(ffc),
7434 "Chunk is not in free lists");
7435 }
7436 _sp->coalDeath(ffc->size());
7437 _sp->removeFreeChunkFromFreeLists(ffc);
7438 set_freeRangeInFreeLists(false);
7439 }
7440 if (fcInFreeLists) {
7441 _sp->coalDeath(chunkSize);
7442 assert(fc->size() == chunkSize,
7443 "The chunk has the wrong size or is not in the free lists");
7444 _sp->removeFreeChunkFromFreeLists(fc);
7445 }
7446 set_lastFreeRangeCoalesced(true);
7447 print_free_block_coalesced(fc);
7448 } else { // not in a free range and/or should not coalesce
7449 // Return the current free range and start a new one.
7450 if (inFreeRange()) {
7451 // In a free range but cannot coalesce with the right hand chunk.
7452 // Put the current free range into the free lists.
7453 flush_cur_free_chunk(freeFinger(),
7454 pointer_delta(fc_addr, freeFinger()));
7455 }
7456 // Set up for new free range. Pass along whether the right hand
7457 // chunk is in the free lists.
7458 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7459 }
7460 }
7461
7462 // Lookahead flush:
7463 // If we are tracking a free range, and this is the last chunk that
7464 // we'll look at because its end crosses past _limit, we'll preemptively
7465 // flush it along with any free range we may be holding on to. Note that
7466 // this can be the case only for an already free or freshly garbage
7467 // chunk. If this block is an object, it can never straddle
7468 // over _limit. The "straddling" occurs when _limit is set at
7469 // the previous end of the space when this cycle started, and
7470 // a subsequent heap expansion caused the previously co-terminal
7471 // free block to be coalesced with the newly expanded portion,
7472 // thus rendering _limit a non-block-boundary making it dangerous
7473 // for the sweeper to step over and examine.
7474 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7475 assert(inFreeRange(), "Should only be called if currently in a free range.");
7476 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7477 assert(_sp->used_region().contains(eob - 1),
7478 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7479 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7480 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7481 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7482 if (eob >= _limit) {
7483 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7484 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7485 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7486 "[" PTR_FORMAT "," PTR_FORMAT ")",
7487 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7488 // Return the storage we are tracking back into the free lists.
7489 log_develop_trace(gc, sweep)("Flushing ... ");
7490 assert(freeFinger() < eob, "Error");
7491 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7492 }
7493 }
7494
7495 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7496 assert(inFreeRange(), "Should only be called if currently in a free range.");
7497 assert(size > 0,
7498 "A zero sized chunk cannot be added to the free lists.");
7499 if (!freeRangeInFreeLists()) {
7500 if (CMSTestInFreeList) {
7501 FreeChunk* fc = (FreeChunk*) chunk;
7502 fc->set_size(size);
7503 assert(!_sp->verify_chunk_in_free_list(fc),
7504 "chunk should not be in free lists yet");
7505 }
7506 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7507 // A new free range is going to be starting. The current
7508 // free range has not been added to the free lists yet or
7509 // was removed so add it back.
7510 // If the current free range was coalesced, then the death
7511 // of the free range was recorded. Record a birth now.
7512 if (lastFreeRangeCoalesced()) {
7513 _sp->coalBirth(size);
7514 }
7515 _sp->addChunkAndRepairOffsetTable(chunk, size,
7516 lastFreeRangeCoalesced());
7517 } else {
7518 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7519 }
7520 set_inFreeRange(false);
7521 set_freeRangeInFreeLists(false);
7522 }
7523
7524 // We take a break if we've been at this for a while,
7525 // so as to avoid monopolizing the locks involved.
7526 void SweepClosure::do_yield_work(HeapWord* addr) {
7527 // Return current free chunk being used for coalescing (if any)
7528 // to the appropriate freelist. After yielding, the next
7529 // free block encountered will start a coalescing range of
7530 // free blocks. If the next free block is adjacent to the
7531 // chunk just flushed, they will need to wait for the next
7532 // sweep to be coalesced.
7533 if (inFreeRange()) {
7534 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7535 }
7536
7537 // First give up the locks, then yield, then re-lock.
7538 // We should probably use a constructor/destructor idiom to
7539 // do this unlock/lock or modify the MutexUnlocker class to
7540 // serve our purpose. XXX
7541 assert_lock_strong(_bitMap->lock());
7542 assert_lock_strong(_freelistLock);
7543 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7544 "CMS thread should hold CMS token");
7545 _bitMap->lock()->unlock();
7546 _freelistLock->unlock();
7547 ConcurrentMarkSweepThread::desynchronize(true);
7548 _collector->stopTimer();
7549 _collector->incrementYields();
7550
7551 // See the comment in coordinator_yield()
7552 for (unsigned i = 0; i < CMSYieldSleepCount &&
7553 ConcurrentMarkSweepThread::should_yield() &&
7554 !CMSCollector::foregroundGCIsActive(); ++i) {
7555 os::sleep(Thread::current(), 1, false);
7556 }
7557
7558 ConcurrentMarkSweepThread::synchronize(true);
7559 _freelistLock->lock();
7560 _bitMap->lock()->lock_without_safepoint_check();
7561 _collector->startTimer();
7562 }
7563
7564 #ifndef PRODUCT
7565 // This is actually very useful in a product build if it can
7566 // be called from the debugger. Compile it into the product
7567 // as needed.
7568 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7569 return debug_cms_space->verify_chunk_in_free_list(fc);
7570 }
7571 #endif
7572
7573 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7574 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7575 p2i(fc), fc->size());
7576 }
7577
7578 // CMSIsAliveClosure
7579 bool CMSIsAliveClosure::do_object_b(oop obj) {
7580 HeapWord* addr = (HeapWord*)obj;
7581 return addr != NULL &&
7582 (!_span.contains(addr) || _bit_map->isMarked(addr));
7583 }
7584
7585
7586 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7587 MemRegion span,
7588 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7589 bool cpc):
7590 _collector(collector),
7591 _span(span),
7592 _bit_map(bit_map),
7593 _mark_stack(mark_stack),
7594 _concurrent_precleaning(cpc) {
7595 assert(!_span.is_empty(), "Empty span could spell trouble");
7596 }
7597
7598
7599 // CMSKeepAliveClosure: the serial version
7600 void CMSKeepAliveClosure::do_oop(oop obj) {
7601 HeapWord* addr = (HeapWord*)obj;
7602 if (_span.contains(addr) &&
7603 !_bit_map->isMarked(addr)) {
7604 _bit_map->mark(addr);
7605 bool simulate_overflow = false;
7606 NOT_PRODUCT(
7607 if (CMSMarkStackOverflowALot &&
7608 _collector->simulate_overflow()) {
7609 // simulate a stack overflow
7610 simulate_overflow = true;
7611 }
7612 )
7613 if (simulate_overflow || !_mark_stack->push(obj)) {
7614 if (_concurrent_precleaning) {
7615 // We dirty the overflown object and let the remark
7616 // phase deal with it.
7617 assert(_collector->overflow_list_is_empty(), "Error");
7618 // In the case of object arrays, we need to dirty all of
7619 // the cards that the object spans. No locking or atomics
7620 // are needed since no one else can be mutating the mod union
7621 // table.
7622 if (obj->is_objArray()) {
7623 size_t sz = obj->size();
7624 HeapWord* end_card_addr =
7625 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7626 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7627 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7628 _collector->_modUnionTable.mark_range(redirty_range);
7629 } else {
7630 _collector->_modUnionTable.mark(addr);
7631 }
7632 _collector->_ser_kac_preclean_ovflw++;
7633 } else {
7634 _collector->push_on_overflow_list(obj);
7635 _collector->_ser_kac_ovflw++;
7636 }
7637 }
7638 }
7639 }
7640
7641 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7642 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7643
7644 // CMSParKeepAliveClosure: a parallel version of the above.
7645 // The work queues are private to each closure (thread),
7646 // but (may be) available for stealing by other threads.
7647 void CMSParKeepAliveClosure::do_oop(oop obj) {
7648 HeapWord* addr = (HeapWord*)obj;
7649 if (_span.contains(addr) &&
7650 !_bit_map->isMarked(addr)) {
7651 // In general, during recursive tracing, several threads
7652 // may be concurrently getting here; the first one to
7653 // "tag" it, claims it.
7654 if (_bit_map->par_mark(addr)) {
7655 bool res = _work_queue->push(obj);
7656 assert(res, "Low water mark should be much less than capacity");
7657 // Do a recursive trim in the hope that this will keep
7658 // stack usage lower, but leave some oops for potential stealers
7659 trim_queue(_low_water_mark);
7660 } // Else, another thread got there first
7661 }
7662 }
7663
7664 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7665 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7666
7667 void CMSParKeepAliveClosure::trim_queue(uint max) {
7668 while (_work_queue->size() > max) {
7669 oop new_oop;
7670 if (_work_queue->pop_local(new_oop)) {
7671 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7672 assert(_bit_map->isMarked((HeapWord*)new_oop),
7673 "no white objects on this stack!");
7674 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7675 // iterate over the oops in this oop, marking and pushing
7676 // the ones in CMS heap (i.e. in _span).
7677 new_oop->oop_iterate(&_mark_and_push);
7678 }
7679 }
7680 }
7681
7682 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7683 CMSCollector* collector,
7684 MemRegion span, CMSBitMap* bit_map,
7685 OopTaskQueue* work_queue):
7686 _collector(collector),
7687 _span(span),
7688 _bit_map(bit_map),
7689 _work_queue(work_queue) { }
7690
7691 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7692 HeapWord* addr = (HeapWord*)obj;
7693 if (_span.contains(addr) &&
7694 !_bit_map->isMarked(addr)) {
7695 if (_bit_map->par_mark(addr)) {
7696 bool simulate_overflow = false;
7697 NOT_PRODUCT(
7698 if (CMSMarkStackOverflowALot &&
7699 _collector->par_simulate_overflow()) {
7700 // simulate a stack overflow
7701 simulate_overflow = true;
7702 }
7703 )
7704 if (simulate_overflow || !_work_queue->push(obj)) {
7705 _collector->par_push_on_overflow_list(obj);
7706 _collector->_par_kac_ovflw++;
7707 }
7708 } // Else another thread got there already
7709 }
7710 }
7711
7712 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7713 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7714
7715 //////////////////////////////////////////////////////////////////
7716 // CMSExpansionCause /////////////////////////////
7717 //////////////////////////////////////////////////////////////////
7718 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7719 switch (cause) {
7720 case _no_expansion:
7721 return "No expansion";
7722 case _satisfy_free_ratio:
7723 return "Free ratio";
7724 case _satisfy_promotion:
7725 return "Satisfy promotion";
7726 case _satisfy_allocation:
7727 return "allocation";
7728 case _allocate_par_lab:
7729 return "Par LAB";
7730 case _allocate_par_spooling_space:
7731 return "Par Spooling Space";
7732 case _adaptive_size_policy:
7733 return "Ergonomics";
7734 default:
7735 return "unknown";
7736 }
7737 }
7738
7739 void CMSDrainMarkingStackClosure::do_void() {
7740 // the max number to take from overflow list at a time
7741 const size_t num = _mark_stack->capacity()/4;
7742 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7743 "Overflow list should be NULL during concurrent phases");
7744 while (!_mark_stack->isEmpty() ||
7745 // if stack is empty, check the overflow list
7746 _collector->take_from_overflow_list(num, _mark_stack)) {
7747 oop obj = _mark_stack->pop();
7748 HeapWord* addr = (HeapWord*)obj;
7749 assert(_span.contains(addr), "Should be within span");
7750 assert(_bit_map->isMarked(addr), "Should be marked");
7751 assert(obj->is_oop(), "Should be an oop");
7752 obj->oop_iterate(_keep_alive);
7753 }
7754 }
7755
7756 void CMSParDrainMarkingStackClosure::do_void() {
7757 // drain queue
7758 trim_queue(0);
7759 }
7760
7761 // Trim our work_queue so its length is below max at return
7762 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7763 while (_work_queue->size() > max) {
7764 oop new_oop;
7765 if (_work_queue->pop_local(new_oop)) {
7766 assert(new_oop->is_oop(), "Expected an oop");
7767 assert(_bit_map->isMarked((HeapWord*)new_oop),
7768 "no white objects on this stack!");
7769 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7770 // iterate over the oops in this oop, marking and pushing
7771 // the ones in CMS heap (i.e. in _span).
7772 new_oop->oop_iterate(&_mark_and_push);
7773 }
7774 }
7775 }
7776
7777 ////////////////////////////////////////////////////////////////////
7778 // Support for Marking Stack Overflow list handling and related code
7779 ////////////////////////////////////////////////////////////////////
7780 // Much of the following code is similar in shape and spirit to the
7781 // code used in ParNewGC. We should try and share that code
7782 // as much as possible in the future.
7783
7784 #ifndef PRODUCT
7785 // Debugging support for CMSStackOverflowALot
7786
7787 // It's OK to call this multi-threaded; the worst thing
7788 // that can happen is that we'll get a bunch of closely
7789 // spaced simulated overflows, but that's OK, in fact
7790 // probably good as it would exercise the overflow code
7791 // under contention.
7792 bool CMSCollector::simulate_overflow() {
7793 if (_overflow_counter-- <= 0) { // just being defensive
7794 _overflow_counter = CMSMarkStackOverflowInterval;
7795 return true;
7796 } else {
7797 return false;
7798 }
7799 }
7800
7801 bool CMSCollector::par_simulate_overflow() {
7802 return simulate_overflow();
7803 }
7804 #endif
7805
7806 // Single-threaded
7807 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7808 assert(stack->isEmpty(), "Expected precondition");
7809 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7810 size_t i = num;
7811 oop cur = _overflow_list;
7812 const markOop proto = markOopDesc::prototype();
7813 NOT_PRODUCT(ssize_t n = 0;)
7814 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7815 next = oop(cur->mark());
7816 cur->set_mark(proto); // until proven otherwise
7817 assert(cur->is_oop(), "Should be an oop");
7818 bool res = stack->push(cur);
7819 assert(res, "Bit off more than can chew?");
7820 NOT_PRODUCT(n++;)
7821 }
7822 _overflow_list = cur;
7823 #ifndef PRODUCT
7824 assert(_num_par_pushes >= n, "Too many pops?");
7825 _num_par_pushes -=n;
7826 #endif
7827 return !stack->isEmpty();
7828 }
7829
7830 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7831 // (MT-safe) Get a prefix of at most "num" from the list.
7832 // The overflow list is chained through the mark word of
7833 // each object in the list. We fetch the entire list,
7834 // break off a prefix of the right size and return the
7835 // remainder. If other threads try to take objects from
7836 // the overflow list at that time, they will wait for
7837 // some time to see if data becomes available. If (and
7838 // only if) another thread places one or more object(s)
7839 // on the global list before we have returned the suffix
7840 // to the global list, we will walk down our local list
7841 // to find its end and append the global list to
7842 // our suffix before returning it. This suffix walk can
7843 // prove to be expensive (quadratic in the amount of traffic)
7844 // when there are many objects in the overflow list and
7845 // there is much producer-consumer contention on the list.
7846 // *NOTE*: The overflow list manipulation code here and
7847 // in ParNewGeneration:: are very similar in shape,
7848 // except that in the ParNew case we use the old (from/eden)
7849 // copy of the object to thread the list via its klass word.
7850 // Because of the common code, if you make any changes in
7851 // the code below, please check the ParNew version to see if
7852 // similar changes might be needed.
7853 // CR 6797058 has been filed to consolidate the common code.
7854 bool CMSCollector::par_take_from_overflow_list(size_t num,
7855 OopTaskQueue* work_q,
7856 int no_of_gc_threads) {
7857 assert(work_q->size() == 0, "First empty local work queue");
7858 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7859 if (_overflow_list == NULL) {
7860 return false;
7861 }
7862 // Grab the entire list; we'll put back a suffix
7863 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7864 Thread* tid = Thread::current();
7865 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7866 // set to ParallelGCThreads.
7867 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7868 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7869 // If the list is busy, we spin for a short while,
7870 // sleeping between attempts to get the list.
7871 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7872 os::sleep(tid, sleep_time_millis, false);
7873 if (_overflow_list == NULL) {
7874 // Nothing left to take
7875 return false;
7876 } else if (_overflow_list != BUSY) {
7877 // Try and grab the prefix
7878 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7879 }
7880 }
7881 // If the list was found to be empty, or we spun long
7882 // enough, we give up and return empty-handed. If we leave
7883 // the list in the BUSY state below, it must be the case that
7884 // some other thread holds the overflow list and will set it
7885 // to a non-BUSY state in the future.
7886 if (prefix == NULL || prefix == BUSY) {
7887 // Nothing to take or waited long enough
7888 if (prefix == NULL) {
7889 // Write back the NULL in case we overwrote it with BUSY above
7890 // and it is still the same value.
7891 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7892 }
7893 return false;
7894 }
7895 assert(prefix != NULL && prefix != BUSY, "Error");
7896 size_t i = num;
7897 oop cur = prefix;
7898 // Walk down the first "num" objects, unless we reach the end.
7899 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7900 if (cur->mark() == NULL) {
7901 // We have "num" or fewer elements in the list, so there
7902 // is nothing to return to the global list.
7903 // Write back the NULL in lieu of the BUSY we wrote
7904 // above, if it is still the same value.
7905 if (_overflow_list == BUSY) {
7906 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7907 }
7908 } else {
7909 // Chop off the suffix and return it to the global list.
7910 assert(cur->mark() != BUSY, "Error");
7911 oop suffix_head = cur->mark(); // suffix will be put back on global list
7912 cur->set_mark(NULL); // break off suffix
7913 // It's possible that the list is still in the empty(busy) state
7914 // we left it in a short while ago; in that case we may be
7915 // able to place back the suffix without incurring the cost
7916 // of a walk down the list.
7917 oop observed_overflow_list = _overflow_list;
7918 oop cur_overflow_list = observed_overflow_list;
7919 bool attached = false;
7920 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7921 observed_overflow_list =
7922 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7923 if (cur_overflow_list == observed_overflow_list) {
7924 attached = true;
7925 break;
7926 } else cur_overflow_list = observed_overflow_list;
7927 }
7928 if (!attached) {
7929 // Too bad, someone else sneaked in (at least) an element; we'll need
7930 // to do a splice. Find tail of suffix so we can prepend suffix to global
7931 // list.
7932 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7933 oop suffix_tail = cur;
7934 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7935 "Tautology");
7936 observed_overflow_list = _overflow_list;
7937 do {
7938 cur_overflow_list = observed_overflow_list;
7939 if (cur_overflow_list != BUSY) {
7940 // Do the splice ...
7941 suffix_tail->set_mark(markOop(cur_overflow_list));
7942 } else { // cur_overflow_list == BUSY
7943 suffix_tail->set_mark(NULL);
7944 }
7945 // ... and try to place spliced list back on overflow_list ...
7946 observed_overflow_list =
7947 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7948 } while (cur_overflow_list != observed_overflow_list);
7949 // ... until we have succeeded in doing so.
7950 }
7951 }
7952
7953 // Push the prefix elements on work_q
7954 assert(prefix != NULL, "control point invariant");
7955 const markOop proto = markOopDesc::prototype();
7956 oop next;
7957 NOT_PRODUCT(ssize_t n = 0;)
7958 for (cur = prefix; cur != NULL; cur = next) {
7959 next = oop(cur->mark());
7960 cur->set_mark(proto); // until proven otherwise
7961 assert(cur->is_oop(), "Should be an oop");
7962 bool res = work_q->push(cur);
7963 assert(res, "Bit off more than we can chew?");
7964 NOT_PRODUCT(n++;)
7965 }
7966 #ifndef PRODUCT
7967 assert(_num_par_pushes >= n, "Too many pops?");
7968 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7969 #endif
7970 return true;
7971 }
7972
7973 // Single-threaded
7974 void CMSCollector::push_on_overflow_list(oop p) {
7975 NOT_PRODUCT(_num_par_pushes++;)
7976 assert(p->is_oop(), "Not an oop");
7977 preserve_mark_if_necessary(p);
7978 p->set_mark((markOop)_overflow_list);
7979 _overflow_list = p;
7980 }
7981
7982 // Multi-threaded; use CAS to prepend to overflow list
7983 void CMSCollector::par_push_on_overflow_list(oop p) {
7984 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7985 assert(p->is_oop(), "Not an oop");
7986 par_preserve_mark_if_necessary(p);
7987 oop observed_overflow_list = _overflow_list;
7988 oop cur_overflow_list;
7989 do {
7990 cur_overflow_list = observed_overflow_list;
7991 if (cur_overflow_list != BUSY) {
7992 p->set_mark(markOop(cur_overflow_list));
7993 } else {
7994 p->set_mark(NULL);
7995 }
7996 observed_overflow_list =
7997 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7998 } while (cur_overflow_list != observed_overflow_list);
7999 }
8000 #undef BUSY
8001
8002 // Single threaded
8003 // General Note on GrowableArray: pushes may silently fail
8004 // because we are (temporarily) out of C-heap for expanding
8005 // the stack. The problem is quite ubiquitous and affects
8006 // a lot of code in the JVM. The prudent thing for GrowableArray
8007 // to do (for now) is to exit with an error. However, that may
8008 // be too draconian in some cases because the caller may be
8009 // able to recover without much harm. For such cases, we
8010 // should probably introduce a "soft_push" method which returns
8011 // an indication of success or failure with the assumption that
8012 // the caller may be able to recover from a failure; code in
8013 // the VM can then be changed, incrementally, to deal with such
8014 // failures where possible, thus, incrementally hardening the VM
8015 // in such low resource situations.
8016 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8017 _preserved_oop_stack.push(p);
8018 _preserved_mark_stack.push(m);
8019 assert(m == p->mark(), "Mark word changed");
8020 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8021 "bijection");
8022 }
8023
8024 // Single threaded
8025 void CMSCollector::preserve_mark_if_necessary(oop p) {
8026 markOop m = p->mark();
8027 if (m->must_be_preserved(p)) {
8028 preserve_mark_work(p, m);
8029 }
8030 }
8031
8032 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8033 markOop m = p->mark();
8034 if (m->must_be_preserved(p)) {
8035 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8036 // Even though we read the mark word without holding
8037 // the lock, we are assured that it will not change
8038 // because we "own" this oop, so no other thread can
8039 // be trying to push it on the overflow list; see
8040 // the assertion in preserve_mark_work() that checks
8041 // that m == p->mark().
8042 preserve_mark_work(p, m);
8043 }
8044 }
8045
8046 // We should be able to do this multi-threaded,
8047 // a chunk of stack being a task (this is
8048 // correct because each oop only ever appears
8049 // once in the overflow list. However, it's
8050 // not very easy to completely overlap this with
8051 // other operations, so will generally not be done
8052 // until all work's been completed. Because we
8053 // expect the preserved oop stack (set) to be small,
8054 // it's probably fine to do this single-threaded.
8055 // We can explore cleverer concurrent/overlapped/parallel
8056 // processing of preserved marks if we feel the
8057 // need for this in the future. Stack overflow should
8058 // be so rare in practice and, when it happens, its
8059 // effect on performance so great that this will
8060 // likely just be in the noise anyway.
8061 void CMSCollector::restore_preserved_marks_if_any() {
8062 assert(SafepointSynchronize::is_at_safepoint(),
8063 "world should be stopped");
8064 assert(Thread::current()->is_ConcurrentGC_thread() ||
8065 Thread::current()->is_VM_thread(),
8066 "should be single-threaded");
8067 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8068 "bijection");
8069
8070 while (!_preserved_oop_stack.is_empty()) {
8071 oop p = _preserved_oop_stack.pop();
8072 assert(p->is_oop(), "Should be an oop");
8073 assert(_span.contains(p), "oop should be in _span");
8074 assert(p->mark() == markOopDesc::prototype(),
8075 "Set when taken from overflow list");
8076 markOop m = _preserved_mark_stack.pop();
8077 p->set_mark(m);
8078 }
8079 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8080 "stacks were cleared above");
8081 }
8082
8083 #ifndef PRODUCT
8084 bool CMSCollector::no_preserved_marks() const {
8085 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8086 }
8087 #endif
8088
8089 // Transfer some number of overflown objects to usual marking
8090 // stack. Return true if some objects were transferred.
8091 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8092 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8093 (size_t)ParGCDesiredObjsFromOverflowList);
8094
8095 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8096 assert(_collector->overflow_list_is_empty() || res,
8097 "If list is not empty, we should have taken something");
8098 assert(!res || !_mark_stack->isEmpty(),
8099 "If we took something, it should now be on our stack");
8100 return res;
8101 }
8102
8103 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8104 size_t res = _sp->block_size_no_stall(addr, _collector);
8105 if (_sp->block_is_obj(addr)) {
8106 if (_live_bit_map->isMarked(addr)) {
8107 // It can't have been dead in a previous cycle
8108 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8109 } else {
8110 _dead_bit_map->mark(addr); // mark the dead object
8111 }
8112 }
8113 // Could be 0, if the block size could not be computed without stalling.
8114 return res;
8115 }
8116
8117 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8118
8119 switch (phase) {
8120 case CMSCollector::InitialMarking:
8121 initialize(true /* fullGC */ ,
8122 cause /* cause of the GC */,
8123 true /* recordGCBeginTime */,
8124 true /* recordPreGCUsage */,
8125 false /* recordPeakUsage */,
8126 false /* recordPostGCusage */,
8127 true /* recordAccumulatedGCTime */,
8128 false /* recordGCEndTime */,
8129 false /* countCollection */ );
8130 break;
8131
8132 case CMSCollector::FinalMarking:
8133 initialize(true /* fullGC */ ,
8134 cause /* cause of the GC */,
8135 false /* recordGCBeginTime */,
8136 false /* recordPreGCUsage */,
8137 false /* recordPeakUsage */,
8138 false /* recordPostGCusage */,
8139 true /* recordAccumulatedGCTime */,
8140 false /* recordGCEndTime */,
8141 false /* countCollection */ );
8142 break;
8143
8144 case CMSCollector::Sweeping:
8145 initialize(true /* fullGC */ ,
8146 cause /* cause of the GC */,
8147 false /* recordGCBeginTime */,
8148 false /* recordPreGCUsage */,
8149 true /* recordPeakUsage */,
8150 true /* recordPostGCusage */,
8151 false /* recordAccumulatedGCTime */,
8152 true /* recordGCEndTime */,
8153 true /* countCollection */ );
8154 break;
8155
8156 default:
8157 ShouldNotReachHere();
8158 }
8159 }