1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
190 ReservedSpace rs, size_t initial_byte_size, int level,
191 CardTableRS* ct, bool use_adaptive_freelists,
192 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
193 CardGeneration(rs, initial_byte_size, level, ct),
194 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
195 _debug_collection_type(Concurrent_collection_type),
196 _did_compact(false)
197 {
198 HeapWord* bottom = (HeapWord*) _virtual_space.low();
199 HeapWord* end = (HeapWord*) _virtual_space.high();
200
201 _direct_allocated_words = 0;
202 NOT_PRODUCT(
203 _numObjectsPromoted = 0;
204 _numWordsPromoted = 0;
205 _numObjectsAllocated = 0;
206 _numWordsAllocated = 0;
207 )
208
209 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
210 use_adaptive_freelists,
211 dictionaryChoice);
212 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
213 if (_cmsSpace == NULL) {
214 vm_exit_during_initialization(
215 "CompactibleFreeListSpace allocation failure");
216 }
217 _cmsSpace->_gen = this;
218
219 _gc_stats = new CMSGCStats();
220
221 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
222 // offsets match. The ability to tell free chunks from objects
223 // depends on this property.
224 debug_only(
225 FreeChunk* junk = NULL;
226 assert(UseCompressedClassPointers ||
227 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
228 "Offset of FreeChunk::_prev within FreeChunk must match"
229 " that of OopDesc::_klass within OopDesc");
230 )
231 if (CollectedHeap::use_parallel_gc_threads()) {
232 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
233 _par_gc_thread_states =
234 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
235 if (_par_gc_thread_states == NULL) {
236 vm_exit_during_initialization("Could not allocate par gc structs");
237 }
238 for (uint i = 0; i < ParallelGCThreads; i++) {
239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
240 if (_par_gc_thread_states[i] == NULL) {
241 vm_exit_during_initialization("Could not allocate par gc structs");
242 }
243 }
244 } else {
245 _par_gc_thread_states = NULL;
246 }
247 _incremental_collection_failed = false;
248 // The "dilatation_factor" is the expansion that can occur on
249 // account of the fact that the minimum object size in the CMS
250 // generation may be larger than that in, say, a contiguous young
251 // generation.
252 // Ideally, in the calculation below, we'd compute the dilatation
253 // factor as: MinChunkSize/(promoting_gen's min object size)
254 // Since we do not have such a general query interface for the
255 // promoting generation, we'll instead just use the minimum
256 // object size (which today is a header's worth of space);
257 // note that all arithmetic is in units of HeapWords.
258 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
259 assert(_dilatation_factor >= 1.0, "from previous assert");
260 }
261
262
263 // The field "_initiating_occupancy" represents the occupancy percentage
264 // at which we trigger a new collection cycle. Unless explicitly specified
265 // via CMSInitiatingOccupancyFraction (argument "io" below), it
266 // is calculated by:
267 //
268 // Let "f" be MinHeapFreeRatio in
269 //
270 // _initiating_occupancy = 100-f +
271 // f * (CMSTriggerRatio/100)
272 // where CMSTriggerRatio is the argument "tr" below.
273 //
274 // That is, if we assume the heap is at its desired maximum occupancy at the
275 // end of a collection, we let CMSTriggerRatio of the (purported) free
276 // space be allocated before initiating a new collection cycle.
277 //
278 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
279 assert(io <= 100 && tr <= 100, "Check the arguments");
280 if (io >= 0) {
281 _initiating_occupancy = (double)io / 100.0;
282 } else {
283 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
284 (double)(tr * MinHeapFreeRatio) / 100.0)
285 / 100.0;
286 }
287 }
288
289 void ConcurrentMarkSweepGeneration::ref_processor_init() {
290 assert(collector() != NULL, "no collector");
291 collector()->ref_processor_init();
292 }
293
294 void CMSCollector::ref_processor_init() {
295 if (_ref_processor == NULL) {
296 // Allocate and initialize a reference processor
297 _ref_processor =
298 new ReferenceProcessor(_span, // span
299 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
300 (int) ParallelGCThreads, // mt processing degree
301 _cmsGen->refs_discovery_is_mt(), // mt discovery
302 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
303 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
304 &_is_alive_closure); // closure for liveness info
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 AdaptiveSizePolicy* CMSCollector::size_policy() {
312 GenCollectedHeap* gch = GenCollectedHeap::heap();
313 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
314 "Wrong type of heap");
315 return gch->gen_policy()->size_policy();
316 }
317
318 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
319
320 const char* gen_name = "old";
321 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
322
323 // Generation Counters - generation 1, 1 subspace
324 _gen_counters = new GenerationCounters(gen_name, 1, 1,
325 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
326
327 _space_counters = new GSpaceCounters(gen_name, 0,
328 _virtual_space.reserved_size(),
329 this, _gen_counters);
330 }
331
332 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
333 _cms_gen(cms_gen)
334 {
335 assert(alpha <= 100, "bad value");
336 _saved_alpha = alpha;
337
338 // Initialize the alphas to the bootstrap value of 100.
339 _gc0_alpha = _cms_alpha = 100;
340
341 _cms_begin_time.update();
342 _cms_end_time.update();
343
344 _gc0_duration = 0.0;
345 _gc0_period = 0.0;
346 _gc0_promoted = 0;
347
348 _cms_duration = 0.0;
349 _cms_period = 0.0;
350 _cms_allocated = 0;
351
352 _cms_used_at_gc0_begin = 0;
353 _cms_used_at_gc0_end = 0;
354 _allow_duty_cycle_reduction = false;
355 _valid_bits = 0;
356 }
357
358 double CMSStats::cms_free_adjustment_factor(size_t free) const {
359 // TBD: CR 6909490
360 return 1.0;
361 }
362
363 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
364 }
365
366 // If promotion failure handling is on use
367 // the padded average size of the promotion for each
368 // young generation collection.
369 double CMSStats::time_until_cms_gen_full() const {
370 size_t cms_free = _cms_gen->cmsSpace()->free();
371 GenCollectedHeap* gch = GenCollectedHeap::heap();
372 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
373 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
374 if (cms_free > expected_promotion) {
375 // Start a cms collection if there isn't enough space to promote
376 // for the next minor collection. Use the padded average as
377 // a safety factor.
378 cms_free -= expected_promotion;
379
380 // Adjust by the safety factor.
381 double cms_free_dbl = (double)cms_free;
382 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
383 // Apply a further correction factor which tries to adjust
384 // for recent occurance of concurrent mode failures.
385 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
386 cms_free_dbl = cms_free_dbl * cms_adjustment;
387
388 if (PrintGCDetails && Verbose) {
389 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
390 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
391 cms_free, expected_promotion);
392 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
393 cms_free_dbl, cms_consumption_rate() + 1.0);
394 }
395 // Add 1 in case the consumption rate goes to zero.
396 return cms_free_dbl / (cms_consumption_rate() + 1.0);
397 }
398 return 0.0;
399 }
400
401 // Compare the duration of the cms collection to the
402 // time remaining before the cms generation is empty.
403 // Note that the time from the start of the cms collection
404 // to the start of the cms sweep (less than the total
405 // duration of the cms collection) can be used. This
406 // has been tried and some applications experienced
407 // promotion failures early in execution. This was
408 // possibly because the averages were not accurate
409 // enough at the beginning.
410 double CMSStats::time_until_cms_start() const {
411 // We add "gc0_period" to the "work" calculation
412 // below because this query is done (mostly) at the
413 // end of a scavenge, so we need to conservatively
414 // account for that much possible delay
415 // in the query so as to avoid concurrent mode failures
416 // due to starting the collection just a wee bit too
417 // late.
418 double work = cms_duration() + gc0_period();
419 double deadline = time_until_cms_gen_full();
420 // If a concurrent mode failure occurred recently, we want to be
421 // more conservative and halve our expected time_until_cms_gen_full()
422 if (work > deadline) {
423 if (Verbose && PrintGCDetails) {
424 gclog_or_tty->print(
425 " CMSCollector: collect because of anticipated promotion "
426 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
427 gc0_period(), time_until_cms_gen_full());
428 }
429 return 0.0;
430 }
431 return work - deadline;
432 }
433
434 #ifndef PRODUCT
435 void CMSStats::print_on(outputStream *st) const {
436 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
437 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
438 gc0_duration(), gc0_period(), gc0_promoted());
439 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
440 cms_duration(), cms_period(), cms_allocated());
441 st->print(",cms_since_beg=%g,cms_since_end=%g",
442 cms_time_since_begin(), cms_time_since_end());
443 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
444 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
445
446 if (valid()) {
447 st->print(",promo_rate=%g,cms_alloc_rate=%g",
448 promotion_rate(), cms_allocation_rate());
449 st->print(",cms_consumption_rate=%g,time_until_full=%g",
450 cms_consumption_rate(), time_until_cms_gen_full());
451 }
452 st->print(" ");
453 }
454 #endif // #ifndef PRODUCT
455
456 CMSCollector::CollectorState CMSCollector::_collectorState =
457 CMSCollector::Idling;
458 bool CMSCollector::_foregroundGCIsActive = false;
459 bool CMSCollector::_foregroundGCShouldWait = false;
460
461 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
462 CardTableRS* ct,
463 ConcurrentMarkSweepPolicy* cp):
464 _cmsGen(cmsGen),
465 _ct(ct),
466 _ref_processor(NULL), // will be set later
467 _conc_workers(NULL), // may be set later
468 _abort_preclean(false),
469 _start_sampling(false),
470 _between_prologue_and_epilogue(false),
471 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
472 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
473 -1 /* lock-free */, "No_lock" /* dummy */),
474 _modUnionClosure(&_modUnionTable),
475 _modUnionClosurePar(&_modUnionTable),
476 // Adjust my span to cover old (cms) gen
477 _span(cmsGen->reserved()),
478 // Construct the is_alive_closure with _span & markBitMap
479 _is_alive_closure(_span, &_markBitMap),
480 _restart_addr(NULL),
481 _overflow_list(NULL),
482 _stats(cmsGen),
483 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
484 _eden_chunk_array(NULL), // may be set in ctor body
485 _eden_chunk_capacity(0), // -- ditto --
486 _eden_chunk_index(0), // -- ditto --
487 _survivor_plab_array(NULL), // -- ditto --
488 _survivor_chunk_array(NULL), // -- ditto --
489 _survivor_chunk_capacity(0), // -- ditto --
490 _survivor_chunk_index(0), // -- ditto --
491 _ser_pmc_preclean_ovflw(0),
492 _ser_kac_preclean_ovflw(0),
493 _ser_pmc_remark_ovflw(0),
494 _par_pmc_remark_ovflw(0),
495 _ser_kac_ovflw(0),
496 _par_kac_ovflw(0),
497 #ifndef PRODUCT
498 _num_par_pushes(0),
499 #endif
500 _collection_count_start(0),
501 _verifying(false),
502 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
503 _completed_initialization(false),
504 _collector_policy(cp),
505 _should_unload_classes(CMSClassUnloadingEnabled),
506 _concurrent_cycles_since_last_unload(0),
507 _roots_scanning_options(SharedHeap::SO_None),
508 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
509 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
510 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
511 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
512 _cms_start_registered(false)
513 {
514 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
515 ExplicitGCInvokesConcurrent = true;
516 }
517 // Now expand the span and allocate the collection support structures
518 // (MUT, marking bit map etc.) to cover both generations subject to
519 // collection.
520
521 // For use by dirty card to oop closures.
522 _cmsGen->cmsSpace()->set_collector(this);
523
524 // Allocate MUT and marking bit map
525 {
526 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
527 if (!_markBitMap.allocate(_span)) {
528 warning("Failed to allocate CMS Bit Map");
529 return;
530 }
531 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
532 }
533 {
534 _modUnionTable.allocate(_span);
535 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
536 }
537
538 if (!_markStack.allocate(MarkStackSize)) {
539 warning("Failed to allocate CMS Marking Stack");
540 return;
541 }
542
543 // Support for multi-threaded concurrent phases
544 if (CMSConcurrentMTEnabled) {
545 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
546 // just for now
547 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
548 }
549 if (ConcGCThreads > 1) {
550 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
551 ConcGCThreads, true);
552 if (_conc_workers == NULL) {
553 warning("GC/CMS: _conc_workers allocation failure: "
554 "forcing -CMSConcurrentMTEnabled");
555 CMSConcurrentMTEnabled = false;
556 } else {
557 _conc_workers->initialize_workers();
558 }
559 } else {
560 CMSConcurrentMTEnabled = false;
561 }
562 }
563 if (!CMSConcurrentMTEnabled) {
564 ConcGCThreads = 0;
565 } else {
566 // Turn off CMSCleanOnEnter optimization temporarily for
567 // the MT case where it's not fixed yet; see 6178663.
568 CMSCleanOnEnter = false;
569 }
570 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
571 "Inconsistency");
572
573 // Parallel task queues; these are shared for the
574 // concurrent and stop-world phases of CMS, but
575 // are not shared with parallel scavenge (ParNew).
576 {
577 uint i;
578 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
579
580 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
581 || ParallelRefProcEnabled)
582 && num_queues > 0) {
583 _task_queues = new OopTaskQueueSet(num_queues);
584 if (_task_queues == NULL) {
585 warning("task_queues allocation failure.");
586 return;
587 }
588 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
589 if (_hash_seed == NULL) {
590 warning("_hash_seed array allocation failure");
591 return;
592 }
593
594 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
595 for (i = 0; i < num_queues; i++) {
596 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
597 if (q == NULL) {
598 warning("work_queue allocation failure.");
599 return;
600 }
601 _task_queues->register_queue(i, q);
602 }
603 for (i = 0; i < num_queues; i++) {
604 _task_queues->queue(i)->initialize();
605 _hash_seed[i] = 17; // copied from ParNew
606 }
607 }
608 }
609
610 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
611
612 // Clip CMSBootstrapOccupancy between 0 and 100.
613 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
614
615 _full_gcs_since_conc_gc = 0;
616
617 // Now tell CMS generations the identity of their collector
618 ConcurrentMarkSweepGeneration::set_collector(this);
619
620 // Create & start a CMS thread for this CMS collector
621 _cmsThread = ConcurrentMarkSweepThread::start(this);
622 assert(cmsThread() != NULL, "CMS Thread should have been created");
623 assert(cmsThread()->collector() == this,
624 "CMS Thread should refer to this gen");
625 assert(CGC_lock != NULL, "Where's the CGC_lock?");
626
627 // Support for parallelizing young gen rescan
628 GenCollectedHeap* gch = GenCollectedHeap::heap();
629 _young_gen = gch->prev_gen(_cmsGen);
630 if (gch->supports_inline_contig_alloc()) {
631 _top_addr = gch->top_addr();
632 _end_addr = gch->end_addr();
633 assert(_young_gen != NULL, "no _young_gen");
634 _eden_chunk_index = 0;
635 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
636 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
637 if (_eden_chunk_array == NULL) {
638 _eden_chunk_capacity = 0;
639 warning("GC/CMS: _eden_chunk_array allocation failure");
640 }
641 }
642 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
643
644 // Support for parallelizing survivor space rescan
645 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
646 const size_t max_plab_samples =
647 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
648
649 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
650 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
651 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
652 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
653 || _cursor == NULL) {
654 warning("Failed to allocate survivor plab/chunk array");
655 if (_survivor_plab_array != NULL) {
656 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
657 _survivor_plab_array = NULL;
658 }
659 if (_survivor_chunk_array != NULL) {
660 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
661 _survivor_chunk_array = NULL;
662 }
663 if (_cursor != NULL) {
664 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
665 _cursor = NULL;
666 }
667 } else {
668 _survivor_chunk_capacity = 2*max_plab_samples;
669 for (uint i = 0; i < ParallelGCThreads; i++) {
670 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
671 if (vec == NULL) {
672 warning("Failed to allocate survivor plab array");
673 for (int j = i; j > 0; j--) {
674 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
675 }
676 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
677 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
678 _survivor_plab_array = NULL;
679 _survivor_chunk_array = NULL;
680 _survivor_chunk_capacity = 0;
681 break;
682 } else {
683 ChunkArray* cur =
684 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
685 max_plab_samples);
686 assert(cur->end() == 0, "Should be 0");
687 assert(cur->array() == vec, "Should be vec");
688 assert(cur->capacity() == max_plab_samples, "Error");
689 }
690 }
691 }
692 }
693 assert( ( _survivor_plab_array != NULL
694 && _survivor_chunk_array != NULL)
695 || ( _survivor_chunk_capacity == 0
696 && _survivor_chunk_index == 0),
697 "Error");
698
699 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
700 _gc_counters = new CollectorCounters("CMS", 1);
701 _completed_initialization = true;
702 _inter_sweep_timer.start(); // start of time
703 }
704
705 const char* ConcurrentMarkSweepGeneration::name() const {
706 return "concurrent mark-sweep generation";
707 }
708 void ConcurrentMarkSweepGeneration::update_counters() {
709 if (UsePerfData) {
710 _space_counters->update_all();
711 _gen_counters->update_all();
712 }
713 }
714
715 // this is an optimized version of update_counters(). it takes the
716 // used value as a parameter rather than computing it.
717 //
718 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
719 if (UsePerfData) {
720 _space_counters->update_used(used);
721 _space_counters->update_capacity();
722 _gen_counters->update_all();
723 }
724 }
725
726 void ConcurrentMarkSweepGeneration::print() const {
727 Generation::print();
728 cmsSpace()->print();
729 }
730
731 #ifndef PRODUCT
732 void ConcurrentMarkSweepGeneration::print_statistics() {
733 cmsSpace()->printFLCensus(0);
734 }
735 #endif
736
737 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
738 GenCollectedHeap* gch = GenCollectedHeap::heap();
739 if (PrintGCDetails) {
740 if (Verbose) {
741 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
742 level(), short_name(), s, used(), capacity());
743 } else {
744 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
745 level(), short_name(), s, used() / K, capacity() / K);
746 }
747 }
748 if (Verbose) {
749 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
750 gch->used(), gch->capacity());
751 } else {
752 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
753 gch->used() / K, gch->capacity() / K);
754 }
755 }
756
757 size_t
758 ConcurrentMarkSweepGeneration::contiguous_available() const {
759 // dld proposes an improvement in precision here. If the committed
760 // part of the space ends in a free block we should add that to
761 // uncommitted size in the calculation below. Will make this
762 // change later, staying with the approximation below for the
763 // time being. -- ysr.
764 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
765 }
766
767 size_t
768 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
769 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
770 }
771
772 size_t ConcurrentMarkSweepGeneration::max_available() const {
773 return free() + _virtual_space.uncommitted_size();
774 }
775
776 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
777 size_t available = max_available();
778 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
779 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
780 if (Verbose && PrintGCDetails) {
781 gclog_or_tty->print_cr(
782 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
783 "max_promo("SIZE_FORMAT")",
784 res? "":" not", available, res? ">=":"<",
785 av_promo, max_promotion_in_bytes);
786 }
787 return res;
788 }
789
790 // At a promotion failure dump information on block layout in heap
791 // (cms old generation).
792 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
793 if (CMSDumpAtPromotionFailure) {
794 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
795 }
796 }
797
798 CompactibleSpace*
799 ConcurrentMarkSweepGeneration::first_compaction_space() const {
800 return _cmsSpace;
801 }
802
803 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
804 // Clear the promotion information. These pointers can be adjusted
805 // along with all the other pointers into the heap but
806 // compaction is expected to be a rare event with
807 // a heap using cms so don't do it without seeing the need.
808 if (CollectedHeap::use_parallel_gc_threads()) {
809 for (uint i = 0; i < ParallelGCThreads; i++) {
810 _par_gc_thread_states[i]->promo.reset();
811 }
812 }
813 }
814
815 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
816 blk->do_space(_cmsSpace);
817 }
818
819 void ConcurrentMarkSweepGeneration::compute_new_size() {
820 assert_locked_or_safepoint(Heap_lock);
821
822 // If incremental collection failed, we just want to expand
823 // to the limit.
824 if (incremental_collection_failed()) {
825 clear_incremental_collection_failed();
826 grow_to_reserved();
827 return;
828 }
829
830 // The heap has been compacted but not reset yet.
831 // Any metric such as free() or used() will be incorrect.
832
833 CardGeneration::compute_new_size();
834
835 // Reset again after a possible resizing
836 if (did_compact()) {
837 cmsSpace()->reset_after_compaction();
838 }
839 }
840
841 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
842 assert_locked_or_safepoint(Heap_lock);
843
844 // If incremental collection failed, we just want to expand
845 // to the limit.
846 if (incremental_collection_failed()) {
847 clear_incremental_collection_failed();
848 grow_to_reserved();
849 return;
850 }
851
852 double free_percentage = ((double) free()) / capacity();
853 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
854 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
855
856 // compute expansion delta needed for reaching desired free percentage
857 if (free_percentage < desired_free_percentage) {
858 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
859 assert(desired_capacity >= capacity(), "invalid expansion size");
860 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
861 if (PrintGCDetails && Verbose) {
862 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
863 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
864 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
865 gclog_or_tty->print_cr(" Desired free fraction %f",
866 desired_free_percentage);
867 gclog_or_tty->print_cr(" Maximum free fraction %f",
868 maximum_free_percentage);
869 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
870 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
871 desired_capacity/1000);
872 int prev_level = level() - 1;
873 if (prev_level >= 0) {
874 size_t prev_size = 0;
875 GenCollectedHeap* gch = GenCollectedHeap::heap();
876 Generation* prev_gen = gch->_gens[prev_level];
877 prev_size = prev_gen->capacity();
878 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
879 prev_size/1000);
880 }
881 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
882 unsafe_max_alloc_nogc()/1000);
883 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
884 contiguous_available()/1000);
885 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
886 expand_bytes);
887 }
888 // safe if expansion fails
889 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
890 if (PrintGCDetails && Verbose) {
891 gclog_or_tty->print_cr(" Expanded free fraction %f",
892 ((double) free()) / capacity());
893 }
894 } else {
895 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
896 assert(desired_capacity <= capacity(), "invalid expansion size");
897 size_t shrink_bytes = capacity() - desired_capacity;
898 // Don't shrink unless the delta is greater than the minimum shrink we want
899 if (shrink_bytes >= MinHeapDeltaBytes) {
900 shrink_free_list_by(shrink_bytes);
901 }
902 }
903 }
904
905 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
906 return cmsSpace()->freelistLock();
907 }
908
909 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
910 bool tlab) {
911 CMSSynchronousYieldRequest yr;
912 MutexLockerEx x(freelistLock(),
913 Mutex::_no_safepoint_check_flag);
914 return have_lock_and_allocate(size, tlab);
915 }
916
917 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
918 bool tlab /* ignored */) {
919 assert_lock_strong(freelistLock());
920 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
921 HeapWord* res = cmsSpace()->allocate(adjustedSize);
922 // Allocate the object live (grey) if the background collector has
923 // started marking. This is necessary because the marker may
924 // have passed this address and consequently this object will
925 // not otherwise be greyed and would be incorrectly swept up.
926 // Note that if this object contains references, the writing
927 // of those references will dirty the card containing this object
928 // allowing the object to be blackened (and its references scanned)
929 // either during a preclean phase or at the final checkpoint.
930 if (res != NULL) {
931 // We may block here with an uninitialized object with
932 // its mark-bit or P-bits not yet set. Such objects need
933 // to be safely navigable by block_start().
934 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
935 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
936 collector()->direct_allocated(res, adjustedSize);
937 _direct_allocated_words += adjustedSize;
938 // allocation counters
939 NOT_PRODUCT(
940 _numObjectsAllocated++;
941 _numWordsAllocated += (int)adjustedSize;
942 )
943 }
944 return res;
945 }
946
947 // In the case of direct allocation by mutators in a generation that
948 // is being concurrently collected, the object must be allocated
949 // live (grey) if the background collector has started marking.
950 // This is necessary because the marker may
951 // have passed this address and consequently this object will
952 // not otherwise be greyed and would be incorrectly swept up.
953 // Note that if this object contains references, the writing
954 // of those references will dirty the card containing this object
955 // allowing the object to be blackened (and its references scanned)
956 // either during a preclean phase or at the final checkpoint.
957 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
958 assert(_markBitMap.covers(start, size), "Out of bounds");
959 if (_collectorState >= Marking) {
960 MutexLockerEx y(_markBitMap.lock(),
961 Mutex::_no_safepoint_check_flag);
962 // [see comments preceding SweepClosure::do_blk() below for details]
963 //
964 // Can the P-bits be deleted now? JJJ
965 //
966 // 1. need to mark the object as live so it isn't collected
967 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
968 // 3. need to mark the end of the object so marking, precleaning or sweeping
969 // can skip over uninitialized or unparsable objects. An allocated
970 // object is considered uninitialized for our purposes as long as
971 // its klass word is NULL. All old gen objects are parsable
972 // as soon as they are initialized.)
973 _markBitMap.mark(start); // object is live
974 _markBitMap.mark(start + 1); // object is potentially uninitialized?
975 _markBitMap.mark(start + size - 1);
976 // mark end of object
977 }
978 // check that oop looks uninitialized
979 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
980 }
981
982 void CMSCollector::promoted(bool par, HeapWord* start,
983 bool is_obj_array, size_t obj_size) {
984 assert(_markBitMap.covers(start), "Out of bounds");
985 // See comment in direct_allocated() about when objects should
986 // be allocated live.
987 if (_collectorState >= Marking) {
988 // we already hold the marking bit map lock, taken in
989 // the prologue
990 if (par) {
991 _markBitMap.par_mark(start);
992 } else {
993 _markBitMap.mark(start);
994 }
995 // We don't need to mark the object as uninitialized (as
996 // in direct_allocated above) because this is being done with the
997 // world stopped and the object will be initialized by the
998 // time the marking, precleaning or sweeping get to look at it.
999 // But see the code for copying objects into the CMS generation,
1000 // where we need to ensure that concurrent readers of the
1001 // block offset table are able to safely navigate a block that
1002 // is in flux from being free to being allocated (and in
1003 // transition while being copied into) and subsequently
1004 // becoming a bona-fide object when the copy/promotion is complete.
1005 assert(SafepointSynchronize::is_at_safepoint(),
1006 "expect promotion only at safepoints");
1007
1008 if (_collectorState < Sweeping) {
1009 // Mark the appropriate cards in the modUnionTable, so that
1010 // this object gets scanned before the sweep. If this is
1011 // not done, CMS generation references in the object might
1012 // not get marked.
1013 // For the case of arrays, which are otherwise precisely
1014 // marked, we need to dirty the entire array, not just its head.
1015 if (is_obj_array) {
1016 // The [par_]mark_range() method expects mr.end() below to
1017 // be aligned to the granularity of a bit's representation
1018 // in the heap. In the case of the MUT below, that's a
1019 // card size.
1020 MemRegion mr(start,
1021 (HeapWord*)round_to((intptr_t)(start + obj_size),
1022 CardTableModRefBS::card_size /* bytes */));
1023 if (par) {
1024 _modUnionTable.par_mark_range(mr);
1025 } else {
1026 _modUnionTable.mark_range(mr);
1027 }
1028 } else { // not an obj array; we can just mark the head
1029 if (par) {
1030 _modUnionTable.par_mark(start);
1031 } else {
1032 _modUnionTable.mark(start);
1033 }
1034 }
1035 }
1036 }
1037 }
1038
1039 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1040 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1041 // allocate, copy and if necessary update promoinfo --
1042 // delegate to underlying space.
1043 assert_lock_strong(freelistLock());
1044
1045 #ifndef PRODUCT
1046 if (Universe::heap()->promotion_should_fail()) {
1047 return NULL;
1048 }
1049 #endif // #ifndef PRODUCT
1050
1051 oop res = _cmsSpace->promote(obj, obj_size);
1052 if (res == NULL) {
1053 // expand and retry
1054 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1055 expand(s*HeapWordSize, MinHeapDeltaBytes,
1056 CMSExpansionCause::_satisfy_promotion);
1057 // Since there's currently no next generation, we don't try to promote
1058 // into a more senior generation.
1059 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1060 "is made to pass on a possibly failing "
1061 "promotion to next generation");
1062 res = _cmsSpace->promote(obj, obj_size);
1063 }
1064 if (res != NULL) {
1065 // See comment in allocate() about when objects should
1066 // be allocated live.
1067 assert(obj->is_oop(), "Will dereference klass pointer below");
1068 collector()->promoted(false, // Not parallel
1069 (HeapWord*)res, obj->is_objArray(), obj_size);
1070 // promotion counters
1071 NOT_PRODUCT(
1072 _numObjectsPromoted++;
1073 _numWordsPromoted +=
1074 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1075 )
1076 }
1077 return res;
1078 }
1079
1080
1081 // IMPORTANT: Notes on object size recognition in CMS.
1082 // ---------------------------------------------------
1083 // A block of storage in the CMS generation is always in
1084 // one of three states. A free block (FREE), an allocated
1085 // object (OBJECT) whose size() method reports the correct size,
1086 // and an intermediate state (TRANSIENT) in which its size cannot
1087 // be accurately determined.
1088 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1089 // -----------------------------------------------------
1090 // FREE: klass_word & 1 == 1; mark_word holds block size
1091 //
1092 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1093 // obj->size() computes correct size
1094 //
1095 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1096 //
1097 // STATE IDENTIFICATION: (64 bit+COOPS)
1098 // ------------------------------------
1099 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1100 //
1101 // OBJECT: klass_word installed; klass_word != 0;
1102 // obj->size() computes correct size
1103 //
1104 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1105 //
1106 //
1107 // STATE TRANSITION DIAGRAM
1108 //
1109 // mut / parnew mut / parnew
1110 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1111 // ^ |
1112 // |------------------------ DEAD <------------------------------------|
1113 // sweep mut
1114 //
1115 // While a block is in TRANSIENT state its size cannot be determined
1116 // so readers will either need to come back later or stall until
1117 // the size can be determined. Note that for the case of direct
1118 // allocation, P-bits, when available, may be used to determine the
1119 // size of an object that may not yet have been initialized.
1120
1121 // Things to support parallel young-gen collection.
1122 oop
1123 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1124 oop old, markOop m,
1125 size_t word_sz) {
1126 #ifndef PRODUCT
1127 if (Universe::heap()->promotion_should_fail()) {
1128 return NULL;
1129 }
1130 #endif // #ifndef PRODUCT
1131
1132 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1133 PromotionInfo* promoInfo = &ps->promo;
1134 // if we are tracking promotions, then first ensure space for
1135 // promotion (including spooling space for saving header if necessary).
1136 // then allocate and copy, then track promoted info if needed.
1137 // When tracking (see PromotionInfo::track()), the mark word may
1138 // be displaced and in this case restoration of the mark word
1139 // occurs in the (oop_since_save_marks_)iterate phase.
1140 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1141 // Out of space for allocating spooling buffers;
1142 // try expanding and allocating spooling buffers.
1143 if (!expand_and_ensure_spooling_space(promoInfo)) {
1144 return NULL;
1145 }
1146 }
1147 assert(promoInfo->has_spooling_space(), "Control point invariant");
1148 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1149 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1150 if (obj_ptr == NULL) {
1151 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1152 if (obj_ptr == NULL) {
1153 return NULL;
1154 }
1155 }
1156 oop obj = oop(obj_ptr);
1157 OrderAccess::storestore();
1158 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1159 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1160 // IMPORTANT: See note on object initialization for CMS above.
1161 // Otherwise, copy the object. Here we must be careful to insert the
1162 // klass pointer last, since this marks the block as an allocated object.
1163 // Except with compressed oops it's the mark word.
1164 HeapWord* old_ptr = (HeapWord*)old;
1165 // Restore the mark word copied above.
1166 obj->set_mark(m);
1167 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1168 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1169 OrderAccess::storestore();
1170
1171 if (UseCompressedClassPointers) {
1172 // Copy gap missed by (aligned) header size calculation below
1173 obj->set_klass_gap(old->klass_gap());
1174 }
1175 if (word_sz > (size_t)oopDesc::header_size()) {
1176 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1177 obj_ptr + oopDesc::header_size(),
1178 word_sz - oopDesc::header_size());
1179 }
1180
1181 // Now we can track the promoted object, if necessary. We take care
1182 // to delay the transition from uninitialized to full object
1183 // (i.e., insertion of klass pointer) until after, so that it
1184 // atomically becomes a promoted object.
1185 if (promoInfo->tracking()) {
1186 promoInfo->track((PromotedObject*)obj, old->klass());
1187 }
1188 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1189 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1190 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1191
1192 // Finally, install the klass pointer (this should be volatile).
1193 OrderAccess::storestore();
1194 obj->set_klass(old->klass());
1195 // We should now be able to calculate the right size for this object
1196 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1197
1198 collector()->promoted(true, // parallel
1199 obj_ptr, old->is_objArray(), word_sz);
1200
1201 NOT_PRODUCT(
1202 Atomic::inc_ptr(&_numObjectsPromoted);
1203 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1204 )
1205
1206 return obj;
1207 }
1208
1209 void
1210 ConcurrentMarkSweepGeneration::
1211 par_promote_alloc_undo(int thread_num,
1212 HeapWord* obj, size_t word_sz) {
1213 // CMS does not support promotion undo.
1214 ShouldNotReachHere();
1215 }
1216
1217 void
1218 ConcurrentMarkSweepGeneration::
1219 par_promote_alloc_done(int thread_num) {
1220 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1221 ps->lab.retire(thread_num);
1222 }
1223
1224 void
1225 ConcurrentMarkSweepGeneration::
1226 par_oop_since_save_marks_iterate_done(int thread_num) {
1227 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1228 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1229 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1230 }
1231
1232 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1233 size_t size,
1234 bool tlab)
1235 {
1236 // We allow a STW collection only if a full
1237 // collection was requested.
1238 return full || should_allocate(size, tlab); // FIX ME !!!
1239 // This and promotion failure handling are connected at the
1240 // hip and should be fixed by untying them.
1241 }
1242
1243 bool CMSCollector::shouldConcurrentCollect() {
1244 if (_full_gc_requested) {
1245 if (Verbose && PrintGCDetails) {
1246 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1247 " gc request (or gc_locker)");
1248 }
1249 return true;
1250 }
1251
1252 // For debugging purposes, change the type of collection.
1253 // If the rotation is not on the concurrent collection
1254 // type, don't start a concurrent collection.
1255 NOT_PRODUCT(
1256 if (RotateCMSCollectionTypes &&
1257 (_cmsGen->debug_collection_type() !=
1258 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1259 assert(_cmsGen->debug_collection_type() !=
1260 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1261 "Bad cms collection type");
1262 return false;
1263 }
1264 )
1265
1266 FreelistLocker x(this);
1267 // ------------------------------------------------------------------
1268 // Print out lots of information which affects the initiation of
1269 // a collection.
1270 if (PrintCMSInitiationStatistics && stats().valid()) {
1271 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1272 gclog_or_tty->stamp();
1273 gclog_or_tty->cr();
1274 stats().print_on(gclog_or_tty);
1275 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1276 stats().time_until_cms_gen_full());
1277 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1278 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1279 _cmsGen->contiguous_available());
1280 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1281 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1282 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1283 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1284 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1285 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1286 gclog_or_tty->print_cr("metadata initialized %d",
1287 MetaspaceGC::should_concurrent_collect());
1288 }
1289 // ------------------------------------------------------------------
1290
1291 // If the estimated time to complete a cms collection (cms_duration())
1292 // is less than the estimated time remaining until the cms generation
1293 // is full, start a collection.
1294 if (!UseCMSInitiatingOccupancyOnly) {
1295 if (stats().valid()) {
1296 if (stats().time_until_cms_start() == 0.0) {
1297 return true;
1298 }
1299 } else {
1300 // We want to conservatively collect somewhat early in order
1301 // to try and "bootstrap" our CMS/promotion statistics;
1302 // this branch will not fire after the first successful CMS
1303 // collection because the stats should then be valid.
1304 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1305 if (Verbose && PrintGCDetails) {
1306 gclog_or_tty->print_cr(
1307 " CMSCollector: collect for bootstrapping statistics:"
1308 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1309 _bootstrap_occupancy);
1310 }
1311 return true;
1312 }
1313 }
1314 }
1315
1316 // Otherwise, we start a collection cycle if
1317 // old gen want a collection cycle started. Each may use
1318 // an appropriate criterion for making this decision.
1319 // XXX We need to make sure that the gen expansion
1320 // criterion dovetails well with this. XXX NEED TO FIX THIS
1321 if (_cmsGen->should_concurrent_collect()) {
1322 if (Verbose && PrintGCDetails) {
1323 gclog_or_tty->print_cr("CMS old gen initiated");
1324 }
1325 return true;
1326 }
1327
1328 // We start a collection if we believe an incremental collection may fail;
1329 // this is not likely to be productive in practice because it's probably too
1330 // late anyway.
1331 GenCollectedHeap* gch = GenCollectedHeap::heap();
1332 assert(gch->collector_policy()->is_generation_policy(),
1333 "You may want to check the correctness of the following");
1334 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1335 if (Verbose && PrintGCDetails) {
1336 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1337 }
1338 return true;
1339 }
1340
1341 if (MetaspaceGC::should_concurrent_collect()) {
1342 if (Verbose && PrintGCDetails) {
1343 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1344 }
1345 return true;
1346 }
1347
1348 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1349 if (CMSTriggerInterval >= 0) {
1350 if (CMSTriggerInterval == 0) {
1351 // Trigger always
1352 return true;
1353 }
1354
1355 // Check the CMS time since begin (we do not check the stats validity
1356 // as we want to be able to trigger the first CMS cycle as well)
1357 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1358 if (Verbose && PrintGCDetails) {
1359 if (stats().valid()) {
1360 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1361 stats().cms_time_since_begin());
1362 } else {
1363 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1364 }
1365 }
1366 return true;
1367 }
1368 }
1369
1370 return false;
1371 }
1372
1373 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1374
1375 // Clear _expansion_cause fields of constituent generations
1376 void CMSCollector::clear_expansion_cause() {
1377 _cmsGen->clear_expansion_cause();
1378 }
1379
1380 // We should be conservative in starting a collection cycle. To
1381 // start too eagerly runs the risk of collecting too often in the
1382 // extreme. To collect too rarely falls back on full collections,
1383 // which works, even if not optimum in terms of concurrent work.
1384 // As a work around for too eagerly collecting, use the flag
1385 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1386 // giving the user an easily understandable way of controlling the
1387 // collections.
1388 // We want to start a new collection cycle if any of the following
1389 // conditions hold:
1390 // . our current occupancy exceeds the configured initiating occupancy
1391 // for this generation, or
1392 // . we recently needed to expand this space and have not, since that
1393 // expansion, done a collection of this generation, or
1394 // . the underlying space believes that it may be a good idea to initiate
1395 // a concurrent collection (this may be based on criteria such as the
1396 // following: the space uses linear allocation and linear allocation is
1397 // going to fail, or there is believed to be excessive fragmentation in
1398 // the generation, etc... or ...
1399 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1400 // the case of the old generation; see CR 6543076):
1401 // we may be approaching a point at which allocation requests may fail because
1402 // we will be out of sufficient free space given allocation rate estimates.]
1403 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1404
1405 assert_lock_strong(freelistLock());
1406 if (occupancy() > initiating_occupancy()) {
1407 if (PrintGCDetails && Verbose) {
1408 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1409 short_name(), occupancy(), initiating_occupancy());
1410 }
1411 return true;
1412 }
1413 if (UseCMSInitiatingOccupancyOnly) {
1414 return false;
1415 }
1416 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1417 if (PrintGCDetails && Verbose) {
1418 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1419 short_name());
1420 }
1421 return true;
1422 }
1423 if (_cmsSpace->should_concurrent_collect()) {
1424 if (PrintGCDetails && Verbose) {
1425 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1426 short_name());
1427 }
1428 return true;
1429 }
1430 return false;
1431 }
1432
1433 void ConcurrentMarkSweepGeneration::collect(bool full,
1434 bool clear_all_soft_refs,
1435 size_t size,
1436 bool tlab)
1437 {
1438 collector()->collect(full, clear_all_soft_refs, size, tlab);
1439 }
1440
1441 void CMSCollector::collect(bool full,
1442 bool clear_all_soft_refs,
1443 size_t size,
1444 bool tlab)
1445 {
1446 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1447 // For debugging purposes skip the collection if the state
1448 // is not currently idle
1449 if (TraceCMSState) {
1450 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1451 Thread::current(), full, _collectorState);
1452 }
1453 return;
1454 }
1455
1456 // The following "if" branch is present for defensive reasons.
1457 // In the current uses of this interface, it can be replaced with:
1458 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1459 // But I am not placing that assert here to allow future
1460 // generality in invoking this interface.
1461 if (GC_locker::is_active()) {
1462 // A consistency test for GC_locker
1463 assert(GC_locker::needs_gc(), "Should have been set already");
1464 // Skip this foreground collection, instead
1465 // expanding the heap if necessary.
1466 // Need the free list locks for the call to free() in compute_new_size()
1467 compute_new_size();
1468 return;
1469 }
1470 acquire_control_and_collect(full, clear_all_soft_refs);
1471 _full_gcs_since_conc_gc++;
1472 }
1473
1474 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1475 GenCollectedHeap* gch = GenCollectedHeap::heap();
1476 unsigned int gc_count = gch->total_full_collections();
1477 if (gc_count == full_gc_count) {
1478 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1479 _full_gc_requested = true;
1480 _full_gc_cause = cause;
1481 CGC_lock->notify(); // nudge CMS thread
1482 } else {
1483 assert(gc_count > full_gc_count, "Error: causal loop");
1484 }
1485 }
1486
1487 bool CMSCollector::is_external_interruption() {
1488 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1489 return GCCause::is_user_requested_gc(cause) ||
1490 GCCause::is_serviceability_requested_gc(cause);
1491 }
1492
1493 void CMSCollector::report_concurrent_mode_interruption() {
1494 if (is_external_interruption()) {
1495 if (PrintGCDetails) {
1496 gclog_or_tty->print(" (concurrent mode interrupted)");
1497 }
1498 } else {
1499 if (PrintGCDetails) {
1500 gclog_or_tty->print(" (concurrent mode failure)");
1501 }
1502 _gc_tracer_cm->report_concurrent_mode_failure();
1503 }
1504 }
1505
1506
1507 // The foreground and background collectors need to coordinate in order
1508 // to make sure that they do not mutually interfere with CMS collections.
1509 // When a background collection is active,
1510 // the foreground collector may need to take over (preempt) and
1511 // synchronously complete an ongoing collection. Depending on the
1512 // frequency of the background collections and the heap usage
1513 // of the application, this preemption can be seldom or frequent.
1514 // There are only certain
1515 // points in the background collection that the "collection-baton"
1516 // can be passed to the foreground collector.
1517 //
1518 // The foreground collector will wait for the baton before
1519 // starting any part of the collection. The foreground collector
1520 // will only wait at one location.
1521 //
1522 // The background collector will yield the baton before starting a new
1523 // phase of the collection (e.g., before initial marking, marking from roots,
1524 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1525 // of the loop which switches the phases. The background collector does some
1526 // of the phases (initial mark, final re-mark) with the world stopped.
1527 // Because of locking involved in stopping the world,
1528 // the foreground collector should not block waiting for the background
1529 // collector when it is doing a stop-the-world phase. The background
1530 // collector will yield the baton at an additional point just before
1531 // it enters a stop-the-world phase. Once the world is stopped, the
1532 // background collector checks the phase of the collection. If the
1533 // phase has not changed, it proceeds with the collection. If the
1534 // phase has changed, it skips that phase of the collection. See
1535 // the comments on the use of the Heap_lock in collect_in_background().
1536 //
1537 // Variable used in baton passing.
1538 // _foregroundGCIsActive - Set to true by the foreground collector when
1539 // it wants the baton. The foreground clears it when it has finished
1540 // the collection.
1541 // _foregroundGCShouldWait - Set to true by the background collector
1542 // when it is running. The foreground collector waits while
1543 // _foregroundGCShouldWait is true.
1544 // CGC_lock - monitor used to protect access to the above variables
1545 // and to notify the foreground and background collectors.
1546 // _collectorState - current state of the CMS collection.
1547 //
1548 // The foreground collector
1549 // acquires the CGC_lock
1550 // sets _foregroundGCIsActive
1551 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1552 // various locks acquired in preparation for the collection
1553 // are released so as not to block the background collector
1554 // that is in the midst of a collection
1555 // proceeds with the collection
1556 // clears _foregroundGCIsActive
1557 // returns
1558 //
1559 // The background collector in a loop iterating on the phases of the
1560 // collection
1561 // acquires the CGC_lock
1562 // sets _foregroundGCShouldWait
1563 // if _foregroundGCIsActive is set
1564 // clears _foregroundGCShouldWait, notifies _CGC_lock
1565 // waits on _CGC_lock for _foregroundGCIsActive to become false
1566 // and exits the loop.
1567 // otherwise
1568 // proceed with that phase of the collection
1569 // if the phase is a stop-the-world phase,
1570 // yield the baton once more just before enqueueing
1571 // the stop-world CMS operation (executed by the VM thread).
1572 // returns after all phases of the collection are done
1573 //
1574
1575 void CMSCollector::acquire_control_and_collect(bool full,
1576 bool clear_all_soft_refs) {
1577 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1578 assert(!Thread::current()->is_ConcurrentGC_thread(),
1579 "shouldn't try to acquire control from self!");
1580
1581 // Start the protocol for acquiring control of the
1582 // collection from the background collector (aka CMS thread).
1583 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1584 "VM thread should have CMS token");
1585 // Remember the possibly interrupted state of an ongoing
1586 // concurrent collection
1587 CollectorState first_state = _collectorState;
1588
1589 // Signal to a possibly ongoing concurrent collection that
1590 // we want to do a foreground collection.
1591 _foregroundGCIsActive = true;
1592
1593 // release locks and wait for a notify from the background collector
1594 // releasing the locks in only necessary for phases which
1595 // do yields to improve the granularity of the collection.
1596 assert_lock_strong(bitMapLock());
1597 // We need to lock the Free list lock for the space that we are
1598 // currently collecting.
1599 assert(haveFreelistLocks(), "Must be holding free list locks");
1600 bitMapLock()->unlock();
1601 releaseFreelistLocks();
1602 {
1603 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1604 if (_foregroundGCShouldWait) {
1605 // We are going to be waiting for action for the CMS thread;
1606 // it had better not be gone (for instance at shutdown)!
1607 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1608 "CMS thread must be running");
1609 // Wait here until the background collector gives us the go-ahead
1610 ConcurrentMarkSweepThread::clear_CMS_flag(
1611 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1612 // Get a possibly blocked CMS thread going:
1613 // Note that we set _foregroundGCIsActive true above,
1614 // without protection of the CGC_lock.
1615 CGC_lock->notify();
1616 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1617 "Possible deadlock");
1618 while (_foregroundGCShouldWait) {
1619 // wait for notification
1620 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1621 // Possibility of delay/starvation here, since CMS token does
1622 // not know to give priority to VM thread? Actually, i think
1623 // there wouldn't be any delay/starvation, but the proof of
1624 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1625 }
1626 ConcurrentMarkSweepThread::set_CMS_flag(
1627 ConcurrentMarkSweepThread::CMS_vm_has_token);
1628 }
1629 }
1630 // The CMS_token is already held. Get back the other locks.
1631 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1632 "VM thread should have CMS token");
1633 getFreelistLocks();
1634 bitMapLock()->lock_without_safepoint_check();
1635 if (TraceCMSState) {
1636 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1637 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1638 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1639 }
1640
1641 // Check if we need to do a compaction, or if not, whether
1642 // we need to start the mark-sweep from scratch.
1643 bool should_compact = false;
1644 bool should_start_over = false;
1645 decide_foreground_collection_type(clear_all_soft_refs,
1646 &should_compact, &should_start_over);
1647
1648 NOT_PRODUCT(
1649 if (RotateCMSCollectionTypes) {
1650 if (_cmsGen->debug_collection_type() ==
1651 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1652 should_compact = true;
1653 } else if (_cmsGen->debug_collection_type() ==
1654 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1655 should_compact = false;
1656 }
1657 }
1658 )
1659
1660 if (first_state > Idling) {
1661 report_concurrent_mode_interruption();
1662 }
1663
1664 set_did_compact(should_compact);
1665 if (should_compact) {
1666 // If the collection is being acquired from the background
1667 // collector, there may be references on the discovered
1668 // references lists that have NULL referents (being those
1669 // that were concurrently cleared by a mutator) or
1670 // that are no longer active (having been enqueued concurrently
1671 // by the mutator).
1672 // Scrub the list of those references because Mark-Sweep-Compact
1673 // code assumes referents are not NULL and that all discovered
1674 // Reference objects are active.
1675 ref_processor()->clean_up_discovered_references();
1676
1677 if (first_state > Idling) {
1678 save_heap_summary();
1679 }
1680
1681 do_compaction_work(clear_all_soft_refs);
1682
1683 // Has the GC time limit been exceeded?
1684 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1685 size_t max_eden_size = young_gen->max_capacity() -
1686 young_gen->to()->capacity() -
1687 young_gen->from()->capacity();
1688 GenCollectedHeap* gch = GenCollectedHeap::heap();
1689 GCCause::Cause gc_cause = gch->gc_cause();
1690 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1691 young_gen->eden()->used(),
1692 _cmsGen->max_capacity(),
1693 max_eden_size,
1694 full,
1695 gc_cause,
1696 gch->collector_policy());
1697 } else {
1698 do_mark_sweep_work(clear_all_soft_refs, first_state,
1699 should_start_over);
1700 }
1701 // Reset the expansion cause, now that we just completed
1702 // a collection cycle.
1703 clear_expansion_cause();
1704 _foregroundGCIsActive = false;
1705 return;
1706 }
1707
1708 // Resize the tenured generation
1709 // after obtaining the free list locks for the
1710 // two generations.
1711 void CMSCollector::compute_new_size() {
1712 assert_locked_or_safepoint(Heap_lock);
1713 FreelistLocker z(this);
1714 MetaspaceGC::compute_new_size();
1715 _cmsGen->compute_new_size_free_list();
1716 }
1717
1718 // A work method used by foreground collection to determine
1719 // what type of collection (compacting or not, continuing or fresh)
1720 // it should do.
1721 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1722 // and CMSCompactWhenClearAllSoftRefs the default in the future
1723 // and do away with the flags after a suitable period.
1724 void CMSCollector::decide_foreground_collection_type(
1725 bool clear_all_soft_refs, bool* should_compact,
1726 bool* should_start_over) {
1727 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1728 // flag is set, and we have either requested a System.gc() or
1729 // the number of full gc's since the last concurrent cycle
1730 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1731 // or if an incremental collection has failed
1732 GenCollectedHeap* gch = GenCollectedHeap::heap();
1733 assert(gch->collector_policy()->is_generation_policy(),
1734 "You may want to check the correctness of the following");
1735 // Inform cms gen if this was due to partial collection failing.
1736 // The CMS gen may use this fact to determine its expansion policy.
1737 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1738 assert(!_cmsGen->incremental_collection_failed(),
1739 "Should have been noticed, reacted to and cleared");
1740 _cmsGen->set_incremental_collection_failed();
1741 }
1742 *should_compact =
1743 UseCMSCompactAtFullCollection &&
1744 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1745 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1746 gch->incremental_collection_will_fail(true /* consult_young */));
1747 *should_start_over = false;
1748 if (clear_all_soft_refs && !*should_compact) {
1749 // We are about to do a last ditch collection attempt
1750 // so it would normally make sense to do a compaction
1751 // to reclaim as much space as possible.
1752 if (CMSCompactWhenClearAllSoftRefs) {
1753 // Default: The rationale is that in this case either
1754 // we are past the final marking phase, in which case
1755 // we'd have to start over, or so little has been done
1756 // that there's little point in saving that work. Compaction
1757 // appears to be the sensible choice in either case.
1758 *should_compact = true;
1759 } else {
1760 // We have been asked to clear all soft refs, but not to
1761 // compact. Make sure that we aren't past the final checkpoint
1762 // phase, for that is where we process soft refs. If we are already
1763 // past that phase, we'll need to redo the refs discovery phase and
1764 // if necessary clear soft refs that weren't previously
1765 // cleared. We do so by remembering the phase in which
1766 // we came in, and if we are past the refs processing
1767 // phase, we'll choose to just redo the mark-sweep
1768 // collection from scratch.
1769 if (_collectorState > FinalMarking) {
1770 // We are past the refs processing phase;
1771 // start over and do a fresh synchronous CMS cycle
1772 _collectorState = Resetting; // skip to reset to start new cycle
1773 reset(false /* == !asynch */);
1774 *should_start_over = true;
1775 } // else we can continue a possibly ongoing current cycle
1776 }
1777 }
1778 }
1779
1780 // A work method used by the foreground collector to do
1781 // a mark-sweep-compact.
1782 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1783 GenCollectedHeap* gch = GenCollectedHeap::heap();
1784
1785 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1786 gc_timer->register_gc_start();
1787
1788 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1789 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1790
1791 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1792 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1793 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1794 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1795 }
1796
1797 // Temporarily widen the span of the weak reference processing to
1798 // the entire heap.
1799 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1800 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1801 // Temporarily, clear the "is_alive_non_header" field of the
1802 // reference processor.
1803 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1804 // Temporarily make reference _processing_ single threaded (non-MT).
1805 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1806 // Temporarily make refs discovery atomic
1807 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1808 // Temporarily make reference _discovery_ single threaded (non-MT)
1809 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1810
1811 ref_processor()->set_enqueuing_is_done(false);
1812 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1813 ref_processor()->setup_policy(clear_all_soft_refs);
1814 // If an asynchronous collection finishes, the _modUnionTable is
1815 // all clear. If we are assuming the collection from an asynchronous
1816 // collection, clear the _modUnionTable.
1817 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1818 "_modUnionTable should be clear if the baton was not passed");
1819 _modUnionTable.clear_all();
1820 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1821 "mod union for klasses should be clear if the baton was passed");
1822 _ct->klass_rem_set()->clear_mod_union();
1823
1824 // We must adjust the allocation statistics being maintained
1825 // in the free list space. We do so by reading and clearing
1826 // the sweep timer and updating the block flux rate estimates below.
1827 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1828 if (_inter_sweep_timer.is_active()) {
1829 _inter_sweep_timer.stop();
1830 // Note that we do not use this sample to update the _inter_sweep_estimate.
1831 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1832 _inter_sweep_estimate.padded_average(),
1833 _intra_sweep_estimate.padded_average());
1834 }
1835
1836 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1837 ref_processor(), clear_all_soft_refs);
1838 #ifdef ASSERT
1839 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1840 size_t free_size = cms_space->free();
1841 assert(free_size ==
1842 pointer_delta(cms_space->end(), cms_space->compaction_top())
1843 * HeapWordSize,
1844 "All the free space should be compacted into one chunk at top");
1845 assert(cms_space->dictionary()->total_chunk_size(
1846 debug_only(cms_space->freelistLock())) == 0 ||
1847 cms_space->totalSizeInIndexedFreeLists() == 0,
1848 "All the free space should be in a single chunk");
1849 size_t num = cms_space->totalCount();
1850 assert((free_size == 0 && num == 0) ||
1851 (free_size > 0 && (num == 1 || num == 2)),
1852 "There should be at most 2 free chunks after compaction");
1853 #endif // ASSERT
1854 _collectorState = Resetting;
1855 assert(_restart_addr == NULL,
1856 "Should have been NULL'd before baton was passed");
1857 reset(false /* == !asynch */);
1858 _cmsGen->reset_after_compaction();
1859 _concurrent_cycles_since_last_unload = 0;
1860
1861 // Clear any data recorded in the PLAB chunk arrays.
1862 if (_survivor_plab_array != NULL) {
1863 reset_survivor_plab_arrays();
1864 }
1865
1866 // Adjust the per-size allocation stats for the next epoch.
1867 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1868 // Restart the "inter sweep timer" for the next epoch.
1869 _inter_sweep_timer.reset();
1870 _inter_sweep_timer.start();
1871
1872 gc_timer->register_gc_end();
1873
1874 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1875
1876 // For a mark-sweep-compact, compute_new_size() will be called
1877 // in the heap's do_collection() method.
1878 }
1879
1880 // A work method used by the foreground collector to do
1881 // a mark-sweep, after taking over from a possibly on-going
1882 // concurrent mark-sweep collection.
1883 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
1884 CollectorState first_state, bool should_start_over) {
1885 if (PrintGC && Verbose) {
1886 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
1887 "collector with count %d",
1888 _full_gcs_since_conc_gc);
1889 }
1890 switch (_collectorState) {
1891 case Idling:
1892 if (first_state == Idling || should_start_over) {
1893 // The background GC was not active, or should
1894 // restarted from scratch; start the cycle.
1895 _collectorState = InitialMarking;
1896 }
1897 // If first_state was not Idling, then a background GC
1898 // was in progress and has now finished. No need to do it
1899 // again. Leave the state as Idling.
1900 break;
1901 case Precleaning:
1902 // In the foreground case don't do the precleaning since
1903 // it is not done concurrently and there is extra work
1904 // required.
1905 _collectorState = FinalMarking;
1906 }
1907 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
1908
1909 // For a mark-sweep, compute_new_size() will be called
1910 // in the heap's do_collection() method.
1911 }
1912
1913
1914 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1915 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
1916 ContiguousSpace* eden_space = dng->eden();
1917 ContiguousSpace* from_space = dng->from();
1918 ContiguousSpace* to_space = dng->to();
1919 // Eden
1920 if (_eden_chunk_array != NULL) {
1921 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1922 eden_space->bottom(), eden_space->top(),
1923 eden_space->end(), eden_space->capacity());
1924 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1925 "_eden_chunk_capacity=" SIZE_FORMAT,
1926 _eden_chunk_index, _eden_chunk_capacity);
1927 for (size_t i = 0; i < _eden_chunk_index; i++) {
1928 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1929 i, _eden_chunk_array[i]);
1930 }
1931 }
1932 // Survivor
1933 if (_survivor_chunk_array != NULL) {
1934 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1935 from_space->bottom(), from_space->top(),
1936 from_space->end(), from_space->capacity());
1937 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1938 "_survivor_chunk_capacity=" SIZE_FORMAT,
1939 _survivor_chunk_index, _survivor_chunk_capacity);
1940 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1941 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1942 i, _survivor_chunk_array[i]);
1943 }
1944 }
1945 }
1946
1947 void CMSCollector::getFreelistLocks() const {
1948 // Get locks for all free lists in all generations that this
1949 // collector is responsible for
1950 _cmsGen->freelistLock()->lock_without_safepoint_check();
1951 }
1952
1953 void CMSCollector::releaseFreelistLocks() const {
1954 // Release locks for all free lists in all generations that this
1955 // collector is responsible for
1956 _cmsGen->freelistLock()->unlock();
1957 }
1958
1959 bool CMSCollector::haveFreelistLocks() const {
1960 // Check locks for all free lists in all generations that this
1961 // collector is responsible for
1962 assert_lock_strong(_cmsGen->freelistLock());
1963 PRODUCT_ONLY(ShouldNotReachHere());
1964 return true;
1965 }
1966
1967 // A utility class that is used by the CMS collector to
1968 // temporarily "release" the foreground collector from its
1969 // usual obligation to wait for the background collector to
1970 // complete an ongoing phase before proceeding.
1971 class ReleaseForegroundGC: public StackObj {
1972 private:
1973 CMSCollector* _c;
1974 public:
1975 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1976 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1977 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1978 // allow a potentially blocked foreground collector to proceed
1979 _c->_foregroundGCShouldWait = false;
1980 if (_c->_foregroundGCIsActive) {
1981 CGC_lock->notify();
1982 }
1983 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1984 "Possible deadlock");
1985 }
1986
1987 ~ReleaseForegroundGC() {
1988 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1989 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1990 _c->_foregroundGCShouldWait = true;
1991 }
1992 };
1993
1994 // There are separate collect_in_background and collect_in_foreground because of
1995 // the different locking requirements of the background collector and the
1996 // foreground collector. There was originally an attempt to share
1997 // one "collect" method between the background collector and the foreground
1998 // collector but the if-then-else required made it cleaner to have
1999 // separate methods.
2000 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2001 assert(Thread::current()->is_ConcurrentGC_thread(),
2002 "A CMS asynchronous collection is only allowed on a CMS thread.");
2003
2004 GenCollectedHeap* gch = GenCollectedHeap::heap();
2005 {
2006 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2007 MutexLockerEx hl(Heap_lock, safepoint_check);
2008 FreelistLocker fll(this);
2009 MutexLockerEx x(CGC_lock, safepoint_check);
2010 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2011 // The foreground collector is active or we're
2012 // not using asynchronous collections. Skip this
2013 // background collection.
2014 assert(!_foregroundGCShouldWait, "Should be clear");
2015 return;
2016 } else {
2017 assert(_collectorState == Idling, "Should be idling before start.");
2018 _collectorState = InitialMarking;
2019 register_gc_start(cause);
2020 // Reset the expansion cause, now that we are about to begin
2021 // a new cycle.
2022 clear_expansion_cause();
2023
2024 // Clear the MetaspaceGC flag since a concurrent collection
2025 // is starting but also clear it after the collection.
2026 MetaspaceGC::set_should_concurrent_collect(false);
2027 }
2028 // Decide if we want to enable class unloading as part of the
2029 // ensuing concurrent GC cycle.
2030 update_should_unload_classes();
2031 _full_gc_requested = false; // acks all outstanding full gc requests
2032 _full_gc_cause = GCCause::_no_gc;
2033 // Signal that we are about to start a collection
2034 gch->increment_total_full_collections(); // ... starting a collection cycle
2035 _collection_count_start = gch->total_full_collections();
2036 }
2037
2038 // Used for PrintGC
2039 size_t prev_used;
2040 if (PrintGC && Verbose) {
2041 prev_used = _cmsGen->used(); // XXXPERM
2042 }
2043
2044 // The change of the collection state is normally done at this level;
2045 // the exceptions are phases that are executed while the world is
2046 // stopped. For those phases the change of state is done while the
2047 // world is stopped. For baton passing purposes this allows the
2048 // background collector to finish the phase and change state atomically.
2049 // The foreground collector cannot wait on a phase that is done
2050 // while the world is stopped because the foreground collector already
2051 // has the world stopped and would deadlock.
2052 while (_collectorState != Idling) {
2053 if (TraceCMSState) {
2054 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2055 Thread::current(), _collectorState);
2056 }
2057 // The foreground collector
2058 // holds the Heap_lock throughout its collection.
2059 // holds the CMS token (but not the lock)
2060 // except while it is waiting for the background collector to yield.
2061 //
2062 // The foreground collector should be blocked (not for long)
2063 // if the background collector is about to start a phase
2064 // executed with world stopped. If the background
2065 // collector has already started such a phase, the
2066 // foreground collector is blocked waiting for the
2067 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2068 // are executed in the VM thread.
2069 //
2070 // The locking order is
2071 // PendingListLock (PLL) -- if applicable (FinalMarking)
2072 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2073 // CMS token (claimed in
2074 // stop_world_and_do() -->
2075 // safepoint_synchronize() -->
2076 // CMSThread::synchronize())
2077
2078 {
2079 // Check if the FG collector wants us to yield.
2080 CMSTokenSync x(true); // is cms thread
2081 if (waitForForegroundGC()) {
2082 // We yielded to a foreground GC, nothing more to be
2083 // done this round.
2084 assert(_foregroundGCShouldWait == false, "We set it to false in "
2085 "waitForForegroundGC()");
2086 if (TraceCMSState) {
2087 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2088 " exiting collection CMS state %d",
2089 Thread::current(), _collectorState);
2090 }
2091 return;
2092 } else {
2093 // The background collector can run but check to see if the
2094 // foreground collector has done a collection while the
2095 // background collector was waiting to get the CGC_lock
2096 // above. If yes, break so that _foregroundGCShouldWait
2097 // is cleared before returning.
2098 if (_collectorState == Idling) {
2099 break;
2100 }
2101 }
2102 }
2103
2104 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2105 "should be waiting");
2106
2107 switch (_collectorState) {
2108 case InitialMarking:
2109 {
2110 ReleaseForegroundGC x(this);
2111 stats().record_cms_begin();
2112 VM_CMS_Initial_Mark initial_mark_op(this);
2113 VMThread::execute(&initial_mark_op);
2114 }
2115 // The collector state may be any legal state at this point
2116 // since the background collector may have yielded to the
2117 // foreground collector.
2118 break;
2119 case Marking:
2120 // initial marking in checkpointRootsInitialWork has been completed
2121 if (markFromRoots(true)) { // we were successful
2122 assert(_collectorState == Precleaning, "Collector state should "
2123 "have changed");
2124 } else {
2125 assert(_foregroundGCIsActive, "Internal state inconsistency");
2126 }
2127 break;
2128 case Precleaning:
2129 // marking from roots in markFromRoots has been completed
2130 preclean();
2131 assert(_collectorState == AbortablePreclean ||
2132 _collectorState == FinalMarking,
2133 "Collector state should have changed");
2134 break;
2135 case AbortablePreclean:
2136 abortable_preclean();
2137 assert(_collectorState == FinalMarking, "Collector state should "
2138 "have changed");
2139 break;
2140 case FinalMarking:
2141 {
2142 ReleaseForegroundGC x(this);
2143
2144 VM_CMS_Final_Remark final_remark_op(this);
2145 VMThread::execute(&final_remark_op);
2146 }
2147 assert(_foregroundGCShouldWait, "block post-condition");
2148 break;
2149 case Sweeping:
2150 // final marking in checkpointRootsFinal has been completed
2151 sweep(true);
2152 assert(_collectorState == Resizing, "Collector state change "
2153 "to Resizing must be done under the free_list_lock");
2154 _full_gcs_since_conc_gc = 0;
2155
2156 case Resizing: {
2157 // Sweeping has been completed...
2158 // At this point the background collection has completed.
2159 // Don't move the call to compute_new_size() down
2160 // into code that might be executed if the background
2161 // collection was preempted.
2162 {
2163 ReleaseForegroundGC x(this); // unblock FG collection
2164 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2165 CMSTokenSync z(true); // not strictly needed.
2166 if (_collectorState == Resizing) {
2167 compute_new_size();
2168 save_heap_summary();
2169 _collectorState = Resetting;
2170 } else {
2171 assert(_collectorState == Idling, "The state should only change"
2172 " because the foreground collector has finished the collection");
2173 }
2174 }
2175 break;
2176 }
2177 case Resetting:
2178 // CMS heap resizing has been completed
2179 reset(true);
2180 assert(_collectorState == Idling, "Collector state should "
2181 "have changed");
2182
2183 MetaspaceGC::set_should_concurrent_collect(false);
2184
2185 stats().record_cms_end();
2186 // Don't move the concurrent_phases_end() and compute_new_size()
2187 // calls to here because a preempted background collection
2188 // has it's state set to "Resetting".
2189 break;
2190 case Idling:
2191 default:
2192 ShouldNotReachHere();
2193 break;
2194 }
2195 if (TraceCMSState) {
2196 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2197 Thread::current(), _collectorState);
2198 }
2199 assert(_foregroundGCShouldWait, "block post-condition");
2200 }
2201
2202 // Should this be in gc_epilogue?
2203 collector_policy()->counters()->update_counters();
2204
2205 {
2206 // Clear _foregroundGCShouldWait and, in the event that the
2207 // foreground collector is waiting, notify it, before
2208 // returning.
2209 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2210 _foregroundGCShouldWait = false;
2211 if (_foregroundGCIsActive) {
2212 CGC_lock->notify();
2213 }
2214 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2215 "Possible deadlock");
2216 }
2217 if (TraceCMSState) {
2218 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2219 " exiting collection CMS state %d",
2220 Thread::current(), _collectorState);
2221 }
2222 if (PrintGC && Verbose) {
2223 _cmsGen->print_heap_change(prev_used);
2224 }
2225 }
2226
2227 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2228 if (!_cms_start_registered) {
2229 register_gc_start(cause);
2230 }
2231 }
2232
2233 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2234 _cms_start_registered = true;
2235 _gc_timer_cm->register_gc_start();
2236 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2237 }
2238
2239 void CMSCollector::register_gc_end() {
2240 if (_cms_start_registered) {
2241 report_heap_summary(GCWhen::AfterGC);
2242
2243 _gc_timer_cm->register_gc_end();
2244 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2245 _cms_start_registered = false;
2246 }
2247 }
2248
2249 void CMSCollector::save_heap_summary() {
2250 GenCollectedHeap* gch = GenCollectedHeap::heap();
2251 _last_heap_summary = gch->create_heap_summary();
2252 _last_metaspace_summary = gch->create_metaspace_summary();
2253 }
2254
2255 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2256 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2257 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2258 }
2259
2260 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2261 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2262 "Foreground collector should be waiting, not executing");
2263 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2264 "may only be done by the VM Thread with the world stopped");
2265 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2266 "VM thread should have CMS token");
2267
2268 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2269 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2270 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2271 true, NULL, gc_id);)
2272 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2273
2274 HandleMark hm; // Discard invalid handles created during verification
2275
2276 if (VerifyBeforeGC &&
2277 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2278 Universe::verify();
2279 }
2280
2281 // Snapshot the soft reference policy to be used in this collection cycle.
2282 ref_processor()->setup_policy(clear_all_soft_refs);
2283
2284 // Decide if class unloading should be done
2285 update_should_unload_classes();
2286
2287 bool init_mark_was_synchronous = false; // until proven otherwise
2288 while (_collectorState != Idling) {
2289 if (TraceCMSState) {
2290 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2291 Thread::current(), _collectorState);
2292 }
2293 switch (_collectorState) {
2294 case InitialMarking:
2295 register_foreground_gc_start(cause);
2296 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2297 checkpointRootsInitial(false);
2298 assert(_collectorState == Marking, "Collector state should have changed"
2299 " within checkpointRootsInitial()");
2300 break;
2301 case Marking:
2302 // initial marking in checkpointRootsInitialWork has been completed
2303 if (VerifyDuringGC &&
2304 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2305 Universe::verify("Verify before initial mark: ");
2306 }
2307 {
2308 bool res = markFromRoots(false);
2309 assert(res && _collectorState == FinalMarking, "Collector state should "
2310 "have changed");
2311 break;
2312 }
2313 case FinalMarking:
2314 if (VerifyDuringGC &&
2315 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2316 Universe::verify("Verify before re-mark: ");
2317 }
2318 checkpointRootsFinal(false, clear_all_soft_refs,
2319 init_mark_was_synchronous);
2320 assert(_collectorState == Sweeping, "Collector state should not "
2321 "have changed within checkpointRootsFinal()");
2322 break;
2323 case Sweeping:
2324 // final marking in checkpointRootsFinal has been completed
2325 if (VerifyDuringGC &&
2326 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2327 Universe::verify("Verify before sweep: ");
2328 }
2329 sweep(false);
2330 assert(_collectorState == Resizing, "Incorrect state");
2331 break;
2332 case Resizing: {
2333 // Sweeping has been completed; the actual resize in this case
2334 // is done separately; nothing to be done in this state.
2335 _collectorState = Resetting;
2336 break;
2337 }
2338 case Resetting:
2339 // The heap has been resized.
2340 if (VerifyDuringGC &&
2341 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2342 Universe::verify("Verify before reset: ");
2343 }
2344 save_heap_summary();
2345 reset(false);
2346 assert(_collectorState == Idling, "Collector state should "
2347 "have changed");
2348 break;
2349 case Precleaning:
2350 case AbortablePreclean:
2351 // Elide the preclean phase
2352 _collectorState = FinalMarking;
2353 break;
2354 default:
2355 ShouldNotReachHere();
2356 }
2357 if (TraceCMSState) {
2358 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2359 Thread::current(), _collectorState);
2360 }
2361 }
2362
2363 if (VerifyAfterGC &&
2364 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2365 Universe::verify();
2366 }
2367 if (TraceCMSState) {
2368 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2369 " exiting collection CMS state %d",
2370 Thread::current(), _collectorState);
2371 }
2372 }
2373
2374 bool CMSCollector::waitForForegroundGC() {
2375 bool res = false;
2376 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2377 "CMS thread should have CMS token");
2378 // Block the foreground collector until the
2379 // background collectors decides whether to
2380 // yield.
2381 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2382 _foregroundGCShouldWait = true;
2383 if (_foregroundGCIsActive) {
2384 // The background collector yields to the
2385 // foreground collector and returns a value
2386 // indicating that it has yielded. The foreground
2387 // collector can proceed.
2388 res = true;
2389 _foregroundGCShouldWait = false;
2390 ConcurrentMarkSweepThread::clear_CMS_flag(
2391 ConcurrentMarkSweepThread::CMS_cms_has_token);
2392 ConcurrentMarkSweepThread::set_CMS_flag(
2393 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2394 // Get a possibly blocked foreground thread going
2395 CGC_lock->notify();
2396 if (TraceCMSState) {
2397 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2398 Thread::current(), _collectorState);
2399 }
2400 while (_foregroundGCIsActive) {
2401 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2402 }
2403 ConcurrentMarkSweepThread::set_CMS_flag(
2404 ConcurrentMarkSweepThread::CMS_cms_has_token);
2405 ConcurrentMarkSweepThread::clear_CMS_flag(
2406 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2407 }
2408 if (TraceCMSState) {
2409 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2410 Thread::current(), _collectorState);
2411 }
2412 return res;
2413 }
2414
2415 // Because of the need to lock the free lists and other structures in
2416 // the collector, common to all the generations that the collector is
2417 // collecting, we need the gc_prologues of individual CMS generations
2418 // delegate to their collector. It may have been simpler had the
2419 // current infrastructure allowed one to call a prologue on a
2420 // collector. In the absence of that we have the generation's
2421 // prologue delegate to the collector, which delegates back
2422 // some "local" work to a worker method in the individual generations
2423 // that it's responsible for collecting, while itself doing any
2424 // work common to all generations it's responsible for. A similar
2425 // comment applies to the gc_epilogue()'s.
2426 // The role of the variable _between_prologue_and_epilogue is to
2427 // enforce the invocation protocol.
2428 void CMSCollector::gc_prologue(bool full) {
2429 // Call gc_prologue_work() for the CMSGen
2430 // we are responsible for.
2431
2432 // The following locking discipline assumes that we are only called
2433 // when the world is stopped.
2434 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2435
2436 // The CMSCollector prologue must call the gc_prologues for the
2437 // "generations" that it's responsible
2438 // for.
2439
2440 assert( Thread::current()->is_VM_thread()
2441 || ( CMSScavengeBeforeRemark
2442 && Thread::current()->is_ConcurrentGC_thread()),
2443 "Incorrect thread type for prologue execution");
2444
2445 if (_between_prologue_and_epilogue) {
2446 // We have already been invoked; this is a gc_prologue delegation
2447 // from yet another CMS generation that we are responsible for, just
2448 // ignore it since all relevant work has already been done.
2449 return;
2450 }
2451
2452 // set a bit saying prologue has been called; cleared in epilogue
2453 _between_prologue_and_epilogue = true;
2454 // Claim locks for common data structures, then call gc_prologue_work()
2455 // for each CMSGen.
2456
2457 getFreelistLocks(); // gets free list locks on constituent spaces
2458 bitMapLock()->lock_without_safepoint_check();
2459
2460 // Should call gc_prologue_work() for all cms gens we are responsible for
2461 bool duringMarking = _collectorState >= Marking
2462 && _collectorState < Sweeping;
2463
2464 // The young collections clear the modified oops state, which tells if
2465 // there are any modified oops in the class. The remark phase also needs
2466 // that information. Tell the young collection to save the union of all
2467 // modified klasses.
2468 if (duringMarking) {
2469 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2470 }
2471
2472 bool registerClosure = duringMarking;
2473
2474 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2475 &_modUnionClosurePar
2476 : &_modUnionClosure;
2477 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2478
2479 if (!full) {
2480 stats().record_gc0_begin();
2481 }
2482 }
2483
2484 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2485
2486 _capacity_at_prologue = capacity();
2487 _used_at_prologue = used();
2488
2489 // Delegate to CMScollector which knows how to coordinate between
2490 // this and any other CMS generations that it is responsible for
2491 // collecting.
2492 collector()->gc_prologue(full);
2493 }
2494
2495 // This is a "private" interface for use by this generation's CMSCollector.
2496 // Not to be called directly by any other entity (for instance,
2497 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2498 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2499 bool registerClosure, ModUnionClosure* modUnionClosure) {
2500 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2501 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2502 "Should be NULL");
2503 if (registerClosure) {
2504 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2505 }
2506 cmsSpace()->gc_prologue();
2507 // Clear stat counters
2508 NOT_PRODUCT(
2509 assert(_numObjectsPromoted == 0, "check");
2510 assert(_numWordsPromoted == 0, "check");
2511 if (Verbose && PrintGC) {
2512 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2513 SIZE_FORMAT" bytes concurrently",
2514 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2515 }
2516 _numObjectsAllocated = 0;
2517 _numWordsAllocated = 0;
2518 )
2519 }
2520
2521 void CMSCollector::gc_epilogue(bool full) {
2522 // The following locking discipline assumes that we are only called
2523 // when the world is stopped.
2524 assert(SafepointSynchronize::is_at_safepoint(),
2525 "world is stopped assumption");
2526
2527 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2528 // if linear allocation blocks need to be appropriately marked to allow the
2529 // the blocks to be parsable. We also check here whether we need to nudge the
2530 // CMS collector thread to start a new cycle (if it's not already active).
2531 assert( Thread::current()->is_VM_thread()
2532 || ( CMSScavengeBeforeRemark
2533 && Thread::current()->is_ConcurrentGC_thread()),
2534 "Incorrect thread type for epilogue execution");
2535
2536 if (!_between_prologue_and_epilogue) {
2537 // We have already been invoked; this is a gc_epilogue delegation
2538 // from yet another CMS generation that we are responsible for, just
2539 // ignore it since all relevant work has already been done.
2540 return;
2541 }
2542 assert(haveFreelistLocks(), "must have freelist locks");
2543 assert_lock_strong(bitMapLock());
2544
2545 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2546
2547 _cmsGen->gc_epilogue_work(full);
2548
2549 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2550 // in case sampling was not already enabled, enable it
2551 _start_sampling = true;
2552 }
2553 // reset _eden_chunk_array so sampling starts afresh
2554 _eden_chunk_index = 0;
2555
2556 size_t cms_used = _cmsGen->cmsSpace()->used();
2557
2558 // update performance counters - this uses a special version of
2559 // update_counters() that allows the utilization to be passed as a
2560 // parameter, avoiding multiple calls to used().
2561 //
2562 _cmsGen->update_counters(cms_used);
2563
2564 bitMapLock()->unlock();
2565 releaseFreelistLocks();
2566
2567 if (!CleanChunkPoolAsync) {
2568 Chunk::clean_chunk_pool();
2569 }
2570
2571 set_did_compact(false);
2572 _between_prologue_and_epilogue = false; // ready for next cycle
2573 }
2574
2575 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2576 collector()->gc_epilogue(full);
2577
2578 // Also reset promotion tracking in par gc thread states.
2579 if (CollectedHeap::use_parallel_gc_threads()) {
2580 for (uint i = 0; i < ParallelGCThreads; i++) {
2581 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2582 }
2583 }
2584 }
2585
2586 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2587 assert(!incremental_collection_failed(), "Should have been cleared");
2588 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2589 cmsSpace()->gc_epilogue();
2590 // Print stat counters
2591 NOT_PRODUCT(
2592 assert(_numObjectsAllocated == 0, "check");
2593 assert(_numWordsAllocated == 0, "check");
2594 if (Verbose && PrintGC) {
2595 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2596 SIZE_FORMAT" bytes",
2597 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2598 }
2599 _numObjectsPromoted = 0;
2600 _numWordsPromoted = 0;
2601 )
2602
2603 if (PrintGC && Verbose) {
2604 // Call down the chain in contiguous_available needs the freelistLock
2605 // so print this out before releasing the freeListLock.
2606 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2607 contiguous_available());
2608 }
2609 }
2610
2611 #ifndef PRODUCT
2612 bool CMSCollector::have_cms_token() {
2613 Thread* thr = Thread::current();
2614 if (thr->is_VM_thread()) {
2615 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2616 } else if (thr->is_ConcurrentGC_thread()) {
2617 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2618 } else if (thr->is_GC_task_thread()) {
2619 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2620 ParGCRareEvent_lock->owned_by_self();
2621 }
2622 return false;
2623 }
2624 #endif
2625
2626 // Check reachability of the given heap address in CMS generation,
2627 // treating all other generations as roots.
2628 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2629 // We could "guarantee" below, rather than assert, but I'll
2630 // leave these as "asserts" so that an adventurous debugger
2631 // could try this in the product build provided some subset of
2632 // the conditions were met, provided they were interested in the
2633 // results and knew that the computation below wouldn't interfere
2634 // with other concurrent computations mutating the structures
2635 // being read or written.
2636 assert(SafepointSynchronize::is_at_safepoint(),
2637 "Else mutations in object graph will make answer suspect");
2638 assert(have_cms_token(), "Should hold cms token");
2639 assert(haveFreelistLocks(), "must hold free list locks");
2640 assert_lock_strong(bitMapLock());
2641
2642 // Clear the marking bit map array before starting, but, just
2643 // for kicks, first report if the given address is already marked
2644 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2645 _markBitMap.isMarked(addr) ? "" : " not");
2646
2647 if (verify_after_remark()) {
2648 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2649 bool result = verification_mark_bm()->isMarked(addr);
2650 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2651 result ? "IS" : "is NOT");
2652 return result;
2653 } else {
2654 gclog_or_tty->print_cr("Could not compute result");
2655 return false;
2656 }
2657 }
2658
2659
2660 void
2661 CMSCollector::print_on_error(outputStream* st) {
2662 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2663 if (collector != NULL) {
2664 CMSBitMap* bitmap = &collector->_markBitMap;
2665 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2666 bitmap->print_on_error(st, " Bits: ");
2667
2668 st->cr();
2669
2670 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2671 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2672 mut_bitmap->print_on_error(st, " Bits: ");
2673 }
2674 }
2675
2676 ////////////////////////////////////////////////////////
2677 // CMS Verification Support
2678 ////////////////////////////////////////////////////////
2679 // Following the remark phase, the following invariant
2680 // should hold -- each object in the CMS heap which is
2681 // marked in markBitMap() should be marked in the verification_mark_bm().
2682
2683 class VerifyMarkedClosure: public BitMapClosure {
2684 CMSBitMap* _marks;
2685 bool _failed;
2686
2687 public:
2688 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2689
2690 bool do_bit(size_t offset) {
2691 HeapWord* addr = _marks->offsetToHeapWord(offset);
2692 if (!_marks->isMarked(addr)) {
2693 oop(addr)->print_on(gclog_or_tty);
2694 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2695 _failed = true;
2696 }
2697 return true;
2698 }
2699
2700 bool failed() { return _failed; }
2701 };
2702
2703 bool CMSCollector::verify_after_remark(bool silent) {
2704 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2705 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2706 static bool init = false;
2707
2708 assert(SafepointSynchronize::is_at_safepoint(),
2709 "Else mutations in object graph will make answer suspect");
2710 assert(have_cms_token(),
2711 "Else there may be mutual interference in use of "
2712 " verification data structures");
2713 assert(_collectorState > Marking && _collectorState <= Sweeping,
2714 "Else marking info checked here may be obsolete");
2715 assert(haveFreelistLocks(), "must hold free list locks");
2716 assert_lock_strong(bitMapLock());
2717
2718
2719 // Allocate marking bit map if not already allocated
2720 if (!init) { // first time
2721 if (!verification_mark_bm()->allocate(_span)) {
2722 return false;
2723 }
2724 init = true;
2725 }
2726
2727 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2728
2729 // Turn off refs discovery -- so we will be tracing through refs.
2730 // This is as intended, because by this time
2731 // GC must already have cleared any refs that need to be cleared,
2732 // and traced those that need to be marked; moreover,
2733 // the marking done here is not going to interfere in any
2734 // way with the marking information used by GC.
2735 NoRefDiscovery no_discovery(ref_processor());
2736
2737 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2738
2739 // Clear any marks from a previous round
2740 verification_mark_bm()->clear_all();
2741 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2742 verify_work_stacks_empty();
2743
2744 GenCollectedHeap* gch = GenCollectedHeap::heap();
2745 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2746 // Update the saved marks which may affect the root scans.
2747 gch->save_marks();
2748
2749 if (CMSRemarkVerifyVariant == 1) {
2750 // In this first variant of verification, we complete
2751 // all marking, then check if the new marks-vector is
2752 // a subset of the CMS marks-vector.
2753 verify_after_remark_work_1();
2754 } else if (CMSRemarkVerifyVariant == 2) {
2755 // In this second variant of verification, we flag an error
2756 // (i.e. an object reachable in the new marks-vector not reachable
2757 // in the CMS marks-vector) immediately, also indicating the
2758 // identify of an object (A) that references the unmarked object (B) --
2759 // presumably, a mutation to A failed to be picked up by preclean/remark?
2760 verify_after_remark_work_2();
2761 } else {
2762 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2763 CMSRemarkVerifyVariant);
2764 }
2765 if (!silent) gclog_or_tty->print(" done] ");
2766 return true;
2767 }
2768
2769 void CMSCollector::verify_after_remark_work_1() {
2770 ResourceMark rm;
2771 HandleMark hm;
2772 GenCollectedHeap* gch = GenCollectedHeap::heap();
2773
2774 // Get a clear set of claim bits for the roots processing to work with.
2775 ClassLoaderDataGraph::clear_claimed_marks();
2776
2777 // Mark from roots one level into CMS
2778 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2779 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2780
2781 gch->gen_process_roots(_cmsGen->level(),
2782 true, // younger gens are roots
2783 true, // activate StrongRootsScope
2784 SharedHeap::ScanningOption(roots_scanning_options()),
2785 should_unload_classes(),
2786 ¬Older,
2787 NULL,
2788 NULL); // SSS: Provide correct closure
2789
2790 // Now mark from the roots
2791 MarkFromRootsClosure markFromRootsClosure(this, _span,
2792 verification_mark_bm(), verification_mark_stack(),
2793 false /* don't yield */, true /* verifying */);
2794 assert(_restart_addr == NULL, "Expected pre-condition");
2795 verification_mark_bm()->iterate(&markFromRootsClosure);
2796 while (_restart_addr != NULL) {
2797 // Deal with stack overflow: by restarting at the indicated
2798 // address.
2799 HeapWord* ra = _restart_addr;
2800 markFromRootsClosure.reset(ra);
2801 _restart_addr = NULL;
2802 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2803 }
2804 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2805 verify_work_stacks_empty();
2806
2807 // Marking completed -- now verify that each bit marked in
2808 // verification_mark_bm() is also marked in markBitMap(); flag all
2809 // errors by printing corresponding objects.
2810 VerifyMarkedClosure vcl(markBitMap());
2811 verification_mark_bm()->iterate(&vcl);
2812 if (vcl.failed()) {
2813 gclog_or_tty->print("Verification failed");
2814 Universe::heap()->print_on(gclog_or_tty);
2815 fatal("CMS: failed marking verification after remark");
2816 }
2817 }
2818
2819 class VerifyKlassOopsKlassClosure : public KlassClosure {
2820 class VerifyKlassOopsClosure : public OopClosure {
2821 CMSBitMap* _bitmap;
2822 public:
2823 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2824 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2825 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2826 } _oop_closure;
2827 public:
2828 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2829 void do_klass(Klass* k) {
2830 k->oops_do(&_oop_closure);
2831 }
2832 };
2833
2834 void CMSCollector::verify_after_remark_work_2() {
2835 ResourceMark rm;
2836 HandleMark hm;
2837 GenCollectedHeap* gch = GenCollectedHeap::heap();
2838
2839 // Get a clear set of claim bits for the roots processing to work with.
2840 ClassLoaderDataGraph::clear_claimed_marks();
2841
2842 // Mark from roots one level into CMS
2843 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2844 markBitMap());
2845 CLDToOopClosure cld_closure(¬Older, true);
2846
2847 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2848
2849 gch->gen_process_roots(_cmsGen->level(),
2850 true, // younger gens are roots
2851 true, // activate StrongRootsScope
2852 SharedHeap::ScanningOption(roots_scanning_options()),
2853 should_unload_classes(),
2854 ¬Older,
2855 NULL,
2856 &cld_closure);
2857
2858 // Now mark from the roots
2859 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2860 verification_mark_bm(), markBitMap(), verification_mark_stack());
2861 assert(_restart_addr == NULL, "Expected pre-condition");
2862 verification_mark_bm()->iterate(&markFromRootsClosure);
2863 while (_restart_addr != NULL) {
2864 // Deal with stack overflow: by restarting at the indicated
2865 // address.
2866 HeapWord* ra = _restart_addr;
2867 markFromRootsClosure.reset(ra);
2868 _restart_addr = NULL;
2869 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2870 }
2871 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2872 verify_work_stacks_empty();
2873
2874 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2875 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2876
2877 // Marking completed -- now verify that each bit marked in
2878 // verification_mark_bm() is also marked in markBitMap(); flag all
2879 // errors by printing corresponding objects.
2880 VerifyMarkedClosure vcl(markBitMap());
2881 verification_mark_bm()->iterate(&vcl);
2882 assert(!vcl.failed(), "Else verification above should not have succeeded");
2883 }
2884
2885 void ConcurrentMarkSweepGeneration::save_marks() {
2886 // delegate to CMS space
2887 cmsSpace()->save_marks();
2888 for (uint i = 0; i < ParallelGCThreads; i++) {
2889 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2890 }
2891 }
2892
2893 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2894 return cmsSpace()->no_allocs_since_save_marks();
2895 }
2896
2897 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2898 \
2899 void ConcurrentMarkSweepGeneration:: \
2900 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2901 cl->set_generation(this); \
2902 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2903 cl->reset_generation(); \
2904 save_marks(); \
2905 }
2906
2907 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2908
2909 void
2910 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2911 cl->set_generation(this);
2912 younger_refs_in_space_iterate(_cmsSpace, cl);
2913 cl->reset_generation();
2914 }
2915
2916 void
2917 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2918 if (freelistLock()->owned_by_self()) {
2919 Generation::oop_iterate(cl);
2920 } else {
2921 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2922 Generation::oop_iterate(cl);
2923 }
2924 }
2925
2926 void
2927 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2928 if (freelistLock()->owned_by_self()) {
2929 Generation::object_iterate(cl);
2930 } else {
2931 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2932 Generation::object_iterate(cl);
2933 }
2934 }
2935
2936 void
2937 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2938 if (freelistLock()->owned_by_self()) {
2939 Generation::safe_object_iterate(cl);
2940 } else {
2941 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2942 Generation::safe_object_iterate(cl);
2943 }
2944 }
2945
2946 void
2947 ConcurrentMarkSweepGeneration::post_compact() {
2948 }
2949
2950 void
2951 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2952 // Fix the linear allocation blocks to look like free blocks.
2953
2954 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2955 // are not called when the heap is verified during universe initialization and
2956 // at vm shutdown.
2957 if (freelistLock()->owned_by_self()) {
2958 cmsSpace()->prepare_for_verify();
2959 } else {
2960 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2961 cmsSpace()->prepare_for_verify();
2962 }
2963 }
2964
2965 void
2966 ConcurrentMarkSweepGeneration::verify() {
2967 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2968 // are not called when the heap is verified during universe initialization and
2969 // at vm shutdown.
2970 if (freelistLock()->owned_by_self()) {
2971 cmsSpace()->verify();
2972 } else {
2973 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2974 cmsSpace()->verify();
2975 }
2976 }
2977
2978 void CMSCollector::verify() {
2979 _cmsGen->verify();
2980 }
2981
2982 #ifndef PRODUCT
2983 bool CMSCollector::overflow_list_is_empty() const {
2984 assert(_num_par_pushes >= 0, "Inconsistency");
2985 if (_overflow_list == NULL) {
2986 assert(_num_par_pushes == 0, "Inconsistency");
2987 }
2988 return _overflow_list == NULL;
2989 }
2990
2991 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2992 // merely consolidate assertion checks that appear to occur together frequently.
2993 void CMSCollector::verify_work_stacks_empty() const {
2994 assert(_markStack.isEmpty(), "Marking stack should be empty");
2995 assert(overflow_list_is_empty(), "Overflow list should be empty");
2996 }
2997
2998 void CMSCollector::verify_overflow_empty() const {
2999 assert(overflow_list_is_empty(), "Overflow list should be empty");
3000 assert(no_preserved_marks(), "No preserved marks");
3001 }
3002 #endif // PRODUCT
3003
3004 // Decide if we want to enable class unloading as part of the
3005 // ensuing concurrent GC cycle. We will collect and
3006 // unload classes if it's the case that:
3007 // (1) an explicit gc request has been made and the flag
3008 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3009 // (2) (a) class unloading is enabled at the command line, and
3010 // (b) old gen is getting really full
3011 // NOTE: Provided there is no change in the state of the heap between
3012 // calls to this method, it should have idempotent results. Moreover,
3013 // its results should be monotonically increasing (i.e. going from 0 to 1,
3014 // but not 1 to 0) between successive calls between which the heap was
3015 // not collected. For the implementation below, it must thus rely on
3016 // the property that concurrent_cycles_since_last_unload()
3017 // will not decrease unless a collection cycle happened and that
3018 // _cmsGen->is_too_full() are
3019 // themselves also monotonic in that sense. See check_monotonicity()
3020 // below.
3021 void CMSCollector::update_should_unload_classes() {
3022 _should_unload_classes = false;
3023 // Condition 1 above
3024 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3025 _should_unload_classes = true;
3026 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3027 // Disjuncts 2.b.(i,ii,iii) above
3028 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3029 CMSClassUnloadingMaxInterval)
3030 || _cmsGen->is_too_full();
3031 }
3032 }
3033
3034 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3035 bool res = should_concurrent_collect();
3036 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3037 return res;
3038 }
3039
3040 void CMSCollector::setup_cms_unloading_and_verification_state() {
3041 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3042 || VerifyBeforeExit;
3043 const int rso = SharedHeap::SO_AllCodeCache;
3044
3045 // We set the proper root for this CMS cycle here.
3046 if (should_unload_classes()) { // Should unload classes this cycle
3047 remove_root_scanning_option(rso); // Shrink the root set appropriately
3048 set_verifying(should_verify); // Set verification state for this cycle
3049 return; // Nothing else needs to be done at this time
3050 }
3051
3052 // Not unloading classes this cycle
3053 assert(!should_unload_classes(), "Inconsistency!");
3054
3055 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3056 // Include symbols, strings and code cache elements to prevent their resurrection.
3057 add_root_scanning_option(rso);
3058 set_verifying(true);
3059 } else if (verifying() && !should_verify) {
3060 // We were verifying, but some verification flags got disabled.
3061 set_verifying(false);
3062 // Exclude symbols, strings and code cache elements from root scanning to
3063 // reduce IM and RM pauses.
3064 remove_root_scanning_option(rso);
3065 }
3066 }
3067
3068
3069 #ifndef PRODUCT
3070 HeapWord* CMSCollector::block_start(const void* p) const {
3071 const HeapWord* addr = (HeapWord*)p;
3072 if (_span.contains(p)) {
3073 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3074 return _cmsGen->cmsSpace()->block_start(p);
3075 }
3076 }
3077 return NULL;
3078 }
3079 #endif
3080
3081 HeapWord*
3082 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3083 bool tlab,
3084 bool parallel) {
3085 CMSSynchronousYieldRequest yr;
3086 assert(!tlab, "Can't deal with TLAB allocation");
3087 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3088 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3089 CMSExpansionCause::_satisfy_allocation);
3090 if (GCExpandToAllocateDelayMillis > 0) {
3091 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3092 }
3093 return have_lock_and_allocate(word_size, tlab);
3094 }
3095
3096 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3097 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3098 // to CardGeneration and share it...
3099 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3100 return CardGeneration::expand(bytes, expand_bytes);
3101 }
3102
3103 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3104 CMSExpansionCause::Cause cause)
3105 {
3106
3107 bool success = expand(bytes, expand_bytes);
3108
3109 // remember why we expanded; this information is used
3110 // by shouldConcurrentCollect() when making decisions on whether to start
3111 // a new CMS cycle.
3112 if (success) {
3113 set_expansion_cause(cause);
3114 if (PrintGCDetails && Verbose) {
3115 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3116 CMSExpansionCause::to_string(cause));
3117 }
3118 }
3119 }
3120
3121 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3122 HeapWord* res = NULL;
3123 MutexLocker x(ParGCRareEvent_lock);
3124 while (true) {
3125 // Expansion by some other thread might make alloc OK now:
3126 res = ps->lab.alloc(word_sz);
3127 if (res != NULL) return res;
3128 // If there's not enough expansion space available, give up.
3129 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3130 return NULL;
3131 }
3132 // Otherwise, we try expansion.
3133 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3134 CMSExpansionCause::_allocate_par_lab);
3135 // Now go around the loop and try alloc again;
3136 // A competing par_promote might beat us to the expansion space,
3137 // so we may go around the loop again if promotion fails again.
3138 if (GCExpandToAllocateDelayMillis > 0) {
3139 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3140 }
3141 }
3142 }
3143
3144
3145 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3146 PromotionInfo* promo) {
3147 MutexLocker x(ParGCRareEvent_lock);
3148 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3149 while (true) {
3150 // Expansion by some other thread might make alloc OK now:
3151 if (promo->ensure_spooling_space()) {
3152 assert(promo->has_spooling_space(),
3153 "Post-condition of successful ensure_spooling_space()");
3154 return true;
3155 }
3156 // If there's not enough expansion space available, give up.
3157 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3158 return false;
3159 }
3160 // Otherwise, we try expansion.
3161 expand(refill_size_bytes, MinHeapDeltaBytes,
3162 CMSExpansionCause::_allocate_par_spooling_space);
3163 // Now go around the loop and try alloc again;
3164 // A competing allocation might beat us to the expansion space,
3165 // so we may go around the loop again if allocation fails again.
3166 if (GCExpandToAllocateDelayMillis > 0) {
3167 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3168 }
3169 }
3170 }
3171
3172
3173 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3174 assert_locked_or_safepoint(ExpandHeap_lock);
3175 // Shrink committed space
3176 _virtual_space.shrink_by(bytes);
3177 // Shrink space; this also shrinks the space's BOT
3178 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3179 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3180 // Shrink the shared block offset array
3181 _bts->resize(new_word_size);
3182 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3183 // Shrink the card table
3184 Universe::heap()->barrier_set()->resize_covered_region(mr);
3185
3186 if (Verbose && PrintGC) {
3187 size_t new_mem_size = _virtual_space.committed_size();
3188 size_t old_mem_size = new_mem_size + bytes;
3189 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3190 name(), old_mem_size/K, new_mem_size/K);
3191 }
3192 }
3193
3194 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3195 assert_locked_or_safepoint(Heap_lock);
3196 size_t size = ReservedSpace::page_align_size_down(bytes);
3197 // Only shrink if a compaction was done so that all the free space
3198 // in the generation is in a contiguous block at the end.
3199 if (size > 0 && did_compact()) {
3200 shrink_by(size);
3201 }
3202 }
3203
3204 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3205 assert_locked_or_safepoint(Heap_lock);
3206 bool result = _virtual_space.expand_by(bytes);
3207 if (result) {
3208 size_t new_word_size =
3209 heap_word_size(_virtual_space.committed_size());
3210 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3211 _bts->resize(new_word_size); // resize the block offset shared array
3212 Universe::heap()->barrier_set()->resize_covered_region(mr);
3213 // Hmmmm... why doesn't CFLS::set_end verify locking?
3214 // This is quite ugly; FIX ME XXX
3215 _cmsSpace->assert_locked(freelistLock());
3216 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3217
3218 // update the space and generation capacity counters
3219 if (UsePerfData) {
3220 _space_counters->update_capacity();
3221 _gen_counters->update_all();
3222 }
3223
3224 if (Verbose && PrintGC) {
3225 size_t new_mem_size = _virtual_space.committed_size();
3226 size_t old_mem_size = new_mem_size - bytes;
3227 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3228 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3229 }
3230 }
3231 return result;
3232 }
3233
3234 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3235 assert_locked_or_safepoint(Heap_lock);
3236 bool success = true;
3237 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3238 if (remaining_bytes > 0) {
3239 success = grow_by(remaining_bytes);
3240 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3241 }
3242 return success;
3243 }
3244
3245 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3246 assert_locked_or_safepoint(Heap_lock);
3247 assert_lock_strong(freelistLock());
3248 if (PrintGCDetails && Verbose) {
3249 warning("Shrinking of CMS not yet implemented");
3250 }
3251 return;
3252 }
3253
3254
3255 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3256 // phases.
3257 class CMSPhaseAccounting: public StackObj {
3258 public:
3259 CMSPhaseAccounting(CMSCollector *collector,
3260 const char *phase,
3261 const GCId gc_id,
3262 bool print_cr = true);
3263 ~CMSPhaseAccounting();
3264
3265 private:
3266 CMSCollector *_collector;
3267 const char *_phase;
3268 elapsedTimer _wallclock;
3269 bool _print_cr;
3270 const GCId _gc_id;
3271
3272 public:
3273 // Not MT-safe; so do not pass around these StackObj's
3274 // where they may be accessed by other threads.
3275 jlong wallclock_millis() {
3276 assert(_wallclock.is_active(), "Wall clock should not stop");
3277 _wallclock.stop(); // to record time
3278 jlong ret = _wallclock.milliseconds();
3279 _wallclock.start(); // restart
3280 return ret;
3281 }
3282 };
3283
3284 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3285 const char *phase,
3286 const GCId gc_id,
3287 bool print_cr) :
3288 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3289
3290 if (PrintCMSStatistics != 0) {
3291 _collector->resetYields();
3292 }
3293 if (PrintGCDetails) {
3294 gclog_or_tty->gclog_stamp(_gc_id);
3295 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3296 _collector->cmsGen()->short_name(), _phase);
3297 }
3298 _collector->resetTimer();
3299 _wallclock.start();
3300 _collector->startTimer();
3301 }
3302
3303 CMSPhaseAccounting::~CMSPhaseAccounting() {
3304 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3305 _collector->stopTimer();
3306 _wallclock.stop();
3307 if (PrintGCDetails) {
3308 gclog_or_tty->gclog_stamp(_gc_id);
3309 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3310 _collector->cmsGen()->short_name(),
3311 _phase, _collector->timerValue(), _wallclock.seconds());
3312 if (_print_cr) {
3313 gclog_or_tty->cr();
3314 }
3315 if (PrintCMSStatistics != 0) {
3316 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3317 _collector->yields());
3318 }
3319 }
3320 }
3321
3322 // CMS work
3323
3324 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3325 class CMSParMarkTask : public AbstractGangTask {
3326 protected:
3327 CMSCollector* _collector;
3328 int _n_workers;
3329 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3330 AbstractGangTask(name),
3331 _collector(collector),
3332 _n_workers(n_workers) {}
3333 // Work method in support of parallel rescan ... of young gen spaces
3334 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3335 ContiguousSpace* space,
3336 HeapWord** chunk_array, size_t chunk_top);
3337 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3338 };
3339
3340 // Parallel initial mark task
3341 class CMSParInitialMarkTask: public CMSParMarkTask {
3342 public:
3343 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3344 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3345 collector, n_workers) {}
3346 void work(uint worker_id);
3347 };
3348
3349 // Checkpoint the roots into this generation from outside
3350 // this generation. [Note this initial checkpoint need only
3351 // be approximate -- we'll do a catch up phase subsequently.]
3352 void CMSCollector::checkpointRootsInitial(bool asynch) {
3353 assert(_collectorState == InitialMarking, "Wrong collector state");
3354 check_correct_thread_executing();
3355 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3356
3357 save_heap_summary();
3358 report_heap_summary(GCWhen::BeforeGC);
3359
3360 ReferenceProcessor* rp = ref_processor();
3361 SpecializationStats::clear();
3362 assert(_restart_addr == NULL, "Control point invariant");
3363 if (asynch) {
3364 // acquire locks for subsequent manipulations
3365 MutexLockerEx x(bitMapLock(),
3366 Mutex::_no_safepoint_check_flag);
3367 checkpointRootsInitialWork(asynch);
3368 // enable ("weak") refs discovery
3369 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3370 _collectorState = Marking;
3371 } else {
3372 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3373 // which recognizes if we are a CMS generation, and doesn't try to turn on
3374 // discovery; verify that they aren't meddling.
3375 assert(!rp->discovery_is_atomic(),
3376 "incorrect setting of discovery predicate");
3377 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3378 "ref discovery for this generation kind");
3379 // already have locks
3380 checkpointRootsInitialWork(asynch);
3381 // now enable ("weak") refs discovery
3382 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3383 _collectorState = Marking;
3384 }
3385 SpecializationStats::print();
3386 }
3387
3388 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3389 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3390 assert(_collectorState == InitialMarking, "just checking");
3391
3392 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3393 // precede our marking with a collection of all
3394 // younger generations to keep floating garbage to a minimum.
3395 // XXX: we won't do this for now -- it's an optimization to be done later.
3396
3397 // already have locks
3398 assert_lock_strong(bitMapLock());
3399 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3400
3401 // Setup the verification and class unloading state for this
3402 // CMS collection cycle.
3403 setup_cms_unloading_and_verification_state();
3404
3405 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3406 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3407
3408 // Reset all the PLAB chunk arrays if necessary.
3409 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3410 reset_survivor_plab_arrays();
3411 }
3412
3413 ResourceMark rm;
3414 HandleMark hm;
3415
3416 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3417 GenCollectedHeap* gch = GenCollectedHeap::heap();
3418
3419 verify_work_stacks_empty();
3420 verify_overflow_empty();
3421
3422 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3423 // Update the saved marks which may affect the root scans.
3424 gch->save_marks();
3425
3426 // weak reference processing has not started yet.
3427 ref_processor()->set_enqueuing_is_done(false);
3428
3429 // Need to remember all newly created CLDs,
3430 // so that we can guarantee that the remark finds them.
3431 ClassLoaderDataGraph::remember_new_clds(true);
3432
3433 // Whenever a CLD is found, it will be claimed before proceeding to mark
3434 // the klasses. The claimed marks need to be cleared before marking starts.
3435 ClassLoaderDataGraph::clear_claimed_marks();
3436
3437 if (CMSPrintEdenSurvivorChunks) {
3438 print_eden_and_survivor_chunk_arrays();
3439 }
3440
3441 {
3442 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3443 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3444 // The parallel version.
3445 FlexibleWorkGang* workers = gch->workers();
3446 assert(workers != NULL, "Need parallel worker threads.");
3447 int n_workers = workers->active_workers();
3448 CMSParInitialMarkTask tsk(this, n_workers);
3449 gch->set_par_threads(n_workers);
3450 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3451 if (n_workers > 1) {
3452 GenCollectedHeap::StrongRootsScope srs(gch);
3453 workers->run_task(&tsk);
3454 } else {
3455 GenCollectedHeap::StrongRootsScope srs(gch);
3456 tsk.work(0);
3457 }
3458 gch->set_par_threads(0);
3459 } else {
3460 // The serial version.
3461 CLDToOopClosure cld_closure(¬Older, true);
3462 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3463 gch->gen_process_roots(_cmsGen->level(),
3464 true, // younger gens are roots
3465 true, // activate StrongRootsScope
3466 SharedHeap::ScanningOption(roots_scanning_options()),
3467 should_unload_classes(),
3468 ¬Older,
3469 NULL,
3470 &cld_closure);
3471 }
3472 }
3473
3474 // Clear mod-union table; it will be dirtied in the prologue of
3475 // CMS generation per each younger generation collection.
3476
3477 assert(_modUnionTable.isAllClear(),
3478 "Was cleared in most recent final checkpoint phase"
3479 " or no bits are set in the gc_prologue before the start of the next "
3480 "subsequent marking phase.");
3481
3482 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3483
3484 // Save the end of the used_region of the constituent generations
3485 // to be used to limit the extent of sweep in each generation.
3486 save_sweep_limits();
3487 verify_overflow_empty();
3488 }
3489
3490 bool CMSCollector::markFromRoots(bool asynch) {
3491 // we might be tempted to assert that:
3492 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3493 // "inconsistent argument?");
3494 // However that wouldn't be right, because it's possible that
3495 // a safepoint is indeed in progress as a younger generation
3496 // stop-the-world GC happens even as we mark in this generation.
3497 assert(_collectorState == Marking, "inconsistent state?");
3498 check_correct_thread_executing();
3499 verify_overflow_empty();
3500
3501 bool res;
3502 if (asynch) {
3503 // Weak ref discovery note: We may be discovering weak
3504 // refs in this generation concurrent (but interleaved) with
3505 // weak ref discovery by a younger generation collector.
3506
3507 CMSTokenSyncWithLocks ts(true, bitMapLock());
3508 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3509 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3510 res = markFromRootsWork(asynch);
3511 if (res) {
3512 _collectorState = Precleaning;
3513 } else { // We failed and a foreground collection wants to take over
3514 assert(_foregroundGCIsActive, "internal state inconsistency");
3515 assert(_restart_addr == NULL, "foreground will restart from scratch");
3516 if (PrintGCDetails) {
3517 gclog_or_tty->print_cr("bailing out to foreground collection");
3518 }
3519 }
3520 } else {
3521 assert(SafepointSynchronize::is_at_safepoint(),
3522 "inconsistent with asynch == false");
3523 // already have locks
3524 res = markFromRootsWork(asynch);
3525 _collectorState = FinalMarking;
3526 }
3527 verify_overflow_empty();
3528 return res;
3529 }
3530
3531 bool CMSCollector::markFromRootsWork(bool asynch) {
3532 // iterate over marked bits in bit map, doing a full scan and mark
3533 // from these roots using the following algorithm:
3534 // . if oop is to the right of the current scan pointer,
3535 // mark corresponding bit (we'll process it later)
3536 // . else (oop is to left of current scan pointer)
3537 // push oop on marking stack
3538 // . drain the marking stack
3539
3540 // Note that when we do a marking step we need to hold the
3541 // bit map lock -- recall that direct allocation (by mutators)
3542 // and promotion (by younger generation collectors) is also
3543 // marking the bit map. [the so-called allocate live policy.]
3544 // Because the implementation of bit map marking is not
3545 // robust wrt simultaneous marking of bits in the same word,
3546 // we need to make sure that there is no such interference
3547 // between concurrent such updates.
3548
3549 // already have locks
3550 assert_lock_strong(bitMapLock());
3551
3552 verify_work_stacks_empty();
3553 verify_overflow_empty();
3554 bool result = false;
3555 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3556 result = do_marking_mt(asynch);
3557 } else {
3558 result = do_marking_st(asynch);
3559 }
3560 return result;
3561 }
3562
3563 // Forward decl
3564 class CMSConcMarkingTask;
3565
3566 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3567 CMSCollector* _collector;
3568 CMSConcMarkingTask* _task;
3569 public:
3570 virtual void yield();
3571
3572 // "n_threads" is the number of threads to be terminated.
3573 // "queue_set" is a set of work queues of other threads.
3574 // "collector" is the CMS collector associated with this task terminator.
3575 // "yield" indicates whether we need the gang as a whole to yield.
3576 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3577 ParallelTaskTerminator(n_threads, queue_set),
3578 _collector(collector) { }
3579
3580 void set_task(CMSConcMarkingTask* task) {
3581 _task = task;
3582 }
3583 };
3584
3585 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3586 CMSConcMarkingTask* _task;
3587 public:
3588 bool should_exit_termination();
3589 void set_task(CMSConcMarkingTask* task) {
3590 _task = task;
3591 }
3592 };
3593
3594 // MT Concurrent Marking Task
3595 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3596 CMSCollector* _collector;
3597 int _n_workers; // requested/desired # workers
3598 bool _asynch;
3599 bool _result;
3600 CompactibleFreeListSpace* _cms_space;
3601 char _pad_front[64]; // padding to ...
3602 HeapWord* _global_finger; // ... avoid sharing cache line
3603 char _pad_back[64];
3604 HeapWord* _restart_addr;
3605
3606 // Exposed here for yielding support
3607 Mutex* const _bit_map_lock;
3608
3609 // The per thread work queues, available here for stealing
3610 OopTaskQueueSet* _task_queues;
3611
3612 // Termination (and yielding) support
3613 CMSConcMarkingTerminator _term;
3614 CMSConcMarkingTerminatorTerminator _term_term;
3615
3616 public:
3617 CMSConcMarkingTask(CMSCollector* collector,
3618 CompactibleFreeListSpace* cms_space,
3619 bool asynch,
3620 YieldingFlexibleWorkGang* workers,
3621 OopTaskQueueSet* task_queues):
3622 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3623 _collector(collector),
3624 _cms_space(cms_space),
3625 _asynch(asynch), _n_workers(0), _result(true),
3626 _task_queues(task_queues),
3627 _term(_n_workers, task_queues, _collector),
3628 _bit_map_lock(collector->bitMapLock())
3629 {
3630 _requested_size = _n_workers;
3631 _term.set_task(this);
3632 _term_term.set_task(this);
3633 _restart_addr = _global_finger = _cms_space->bottom();
3634 }
3635
3636
3637 OopTaskQueueSet* task_queues() { return _task_queues; }
3638
3639 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3640
3641 HeapWord** global_finger_addr() { return &_global_finger; }
3642
3643 CMSConcMarkingTerminator* terminator() { return &_term; }
3644
3645 virtual void set_for_termination(int active_workers) {
3646 terminator()->reset_for_reuse(active_workers);
3647 }
3648
3649 void work(uint worker_id);
3650 bool should_yield() {
3651 return ConcurrentMarkSweepThread::should_yield()
3652 && !_collector->foregroundGCIsActive()
3653 && _asynch;
3654 }
3655
3656 virtual void coordinator_yield(); // stuff done by coordinator
3657 bool result() { return _result; }
3658
3659 void reset(HeapWord* ra) {
3660 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3661 _restart_addr = _global_finger = ra;
3662 _term.reset_for_reuse();
3663 }
3664
3665 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3666 OopTaskQueue* work_q);
3667
3668 private:
3669 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3670 void do_work_steal(int i);
3671 void bump_global_finger(HeapWord* f);
3672 };
3673
3674 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3675 assert(_task != NULL, "Error");
3676 return _task->yielding();
3677 // Note that we do not need the disjunct || _task->should_yield() above
3678 // because we want terminating threads to yield only if the task
3679 // is already in the midst of yielding, which happens only after at least one
3680 // thread has yielded.
3681 }
3682
3683 void CMSConcMarkingTerminator::yield() {
3684 if (_task->should_yield()) {
3685 _task->yield();
3686 } else {
3687 ParallelTaskTerminator::yield();
3688 }
3689 }
3690
3691 ////////////////////////////////////////////////////////////////
3692 // Concurrent Marking Algorithm Sketch
3693 ////////////////////////////////////////////////////////////////
3694 // Until all tasks exhausted (both spaces):
3695 // -- claim next available chunk
3696 // -- bump global finger via CAS
3697 // -- find first object that starts in this chunk
3698 // and start scanning bitmap from that position
3699 // -- scan marked objects for oops
3700 // -- CAS-mark target, and if successful:
3701 // . if target oop is above global finger (volatile read)
3702 // nothing to do
3703 // . if target oop is in chunk and above local finger
3704 // then nothing to do
3705 // . else push on work-queue
3706 // -- Deal with possible overflow issues:
3707 // . local work-queue overflow causes stuff to be pushed on
3708 // global (common) overflow queue
3709 // . always first empty local work queue
3710 // . then get a batch of oops from global work queue if any
3711 // . then do work stealing
3712 // -- When all tasks claimed (both spaces)
3713 // and local work queue empty,
3714 // then in a loop do:
3715 // . check global overflow stack; steal a batch of oops and trace
3716 // . try to steal from other threads oif GOS is empty
3717 // . if neither is available, offer termination
3718 // -- Terminate and return result
3719 //
3720 void CMSConcMarkingTask::work(uint worker_id) {
3721 elapsedTimer _timer;
3722 ResourceMark rm;
3723 HandleMark hm;
3724
3725 DEBUG_ONLY(_collector->verify_overflow_empty();)
3726
3727 // Before we begin work, our work queue should be empty
3728 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3729 // Scan the bitmap covering _cms_space, tracing through grey objects.
3730 _timer.start();
3731 do_scan_and_mark(worker_id, _cms_space);
3732 _timer.stop();
3733 if (PrintCMSStatistics != 0) {
3734 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3735 worker_id, _timer.seconds());
3736 // XXX: need xxx/xxx type of notation, two timers
3737 }
3738
3739 // ... do work stealing
3740 _timer.reset();
3741 _timer.start();
3742 do_work_steal(worker_id);
3743 _timer.stop();
3744 if (PrintCMSStatistics != 0) {
3745 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3746 worker_id, _timer.seconds());
3747 // XXX: need xxx/xxx type of notation, two timers
3748 }
3749 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3750 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3751 // Note that under the current task protocol, the
3752 // following assertion is true even of the spaces
3753 // expanded since the completion of the concurrent
3754 // marking. XXX This will likely change under a strict
3755 // ABORT semantics.
3756 // After perm removal the comparison was changed to
3757 // greater than or equal to from strictly greater than.
3758 // Before perm removal the highest address sweep would
3759 // have been at the end of perm gen but now is at the
3760 // end of the tenured gen.
3761 assert(_global_finger >= _cms_space->end(),
3762 "All tasks have been completed");
3763 DEBUG_ONLY(_collector->verify_overflow_empty();)
3764 }
3765
3766 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3767 HeapWord* read = _global_finger;
3768 HeapWord* cur = read;
3769 while (f > read) {
3770 cur = read;
3771 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3772 if (cur == read) {
3773 // our cas succeeded
3774 assert(_global_finger >= f, "protocol consistency");
3775 break;
3776 }
3777 }
3778 }
3779
3780 // This is really inefficient, and should be redone by
3781 // using (not yet available) block-read and -write interfaces to the
3782 // stack and the work_queue. XXX FIX ME !!!
3783 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3784 OopTaskQueue* work_q) {
3785 // Fast lock-free check
3786 if (ovflw_stk->length() == 0) {
3787 return false;
3788 }
3789 assert(work_q->size() == 0, "Shouldn't steal");
3790 MutexLockerEx ml(ovflw_stk->par_lock(),
3791 Mutex::_no_safepoint_check_flag);
3792 // Grab up to 1/4 the size of the work queue
3793 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3794 (size_t)ParGCDesiredObjsFromOverflowList);
3795 num = MIN2(num, ovflw_stk->length());
3796 for (int i = (int) num; i > 0; i--) {
3797 oop cur = ovflw_stk->pop();
3798 assert(cur != NULL, "Counted wrong?");
3799 work_q->push(cur);
3800 }
3801 return num > 0;
3802 }
3803
3804 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3805 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3806 int n_tasks = pst->n_tasks();
3807 // We allow that there may be no tasks to do here because
3808 // we are restarting after a stack overflow.
3809 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3810 uint nth_task = 0;
3811
3812 HeapWord* aligned_start = sp->bottom();
3813 if (sp->used_region().contains(_restart_addr)) {
3814 // Align down to a card boundary for the start of 0th task
3815 // for this space.
3816 aligned_start =
3817 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3818 CardTableModRefBS::card_size);
3819 }
3820
3821 size_t chunk_size = sp->marking_task_size();
3822 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3823 // Having claimed the nth task in this space,
3824 // compute the chunk that it corresponds to:
3825 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3826 aligned_start + (nth_task+1)*chunk_size);
3827 // Try and bump the global finger via a CAS;
3828 // note that we need to do the global finger bump
3829 // _before_ taking the intersection below, because
3830 // the task corresponding to that region will be
3831 // deemed done even if the used_region() expands
3832 // because of allocation -- as it almost certainly will
3833 // during start-up while the threads yield in the
3834 // closure below.
3835 HeapWord* finger = span.end();
3836 bump_global_finger(finger); // atomically
3837 // There are null tasks here corresponding to chunks
3838 // beyond the "top" address of the space.
3839 span = span.intersection(sp->used_region());
3840 if (!span.is_empty()) { // Non-null task
3841 HeapWord* prev_obj;
3842 assert(!span.contains(_restart_addr) || nth_task == 0,
3843 "Inconsistency");
3844 if (nth_task == 0) {
3845 // For the 0th task, we'll not need to compute a block_start.
3846 if (span.contains(_restart_addr)) {
3847 // In the case of a restart because of stack overflow,
3848 // we might additionally skip a chunk prefix.
3849 prev_obj = _restart_addr;
3850 } else {
3851 prev_obj = span.start();
3852 }
3853 } else {
3854 // We want to skip the first object because
3855 // the protocol is to scan any object in its entirety
3856 // that _starts_ in this span; a fortiori, any
3857 // object starting in an earlier span is scanned
3858 // as part of an earlier claimed task.
3859 // Below we use the "careful" version of block_start
3860 // so we do not try to navigate uninitialized objects.
3861 prev_obj = sp->block_start_careful(span.start());
3862 // Below we use a variant of block_size that uses the
3863 // Printezis bits to avoid waiting for allocated
3864 // objects to become initialized/parsable.
3865 while (prev_obj < span.start()) {
3866 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3867 if (sz > 0) {
3868 prev_obj += sz;
3869 } else {
3870 // In this case we may end up doing a bit of redundant
3871 // scanning, but that appears unavoidable, short of
3872 // locking the free list locks; see bug 6324141.
3873 break;
3874 }
3875 }
3876 }
3877 if (prev_obj < span.end()) {
3878 MemRegion my_span = MemRegion(prev_obj, span.end());
3879 // Do the marking work within a non-empty span --
3880 // the last argument to the constructor indicates whether the
3881 // iteration should be incremental with periodic yields.
3882 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3883 &_collector->_markBitMap,
3884 work_queue(i),
3885 &_collector->_markStack,
3886 _asynch);
3887 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3888 } // else nothing to do for this task
3889 } // else nothing to do for this task
3890 }
3891 // We'd be tempted to assert here that since there are no
3892 // more tasks left to claim in this space, the global_finger
3893 // must exceed space->top() and a fortiori space->end(). However,
3894 // that would not quite be correct because the bumping of
3895 // global_finger occurs strictly after the claiming of a task,
3896 // so by the time we reach here the global finger may not yet
3897 // have been bumped up by the thread that claimed the last
3898 // task.
3899 pst->all_tasks_completed();
3900 }
3901
3902 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3903 private:
3904 CMSCollector* _collector;
3905 CMSConcMarkingTask* _task;
3906 MemRegion _span;
3907 CMSBitMap* _bit_map;
3908 CMSMarkStack* _overflow_stack;
3909 OopTaskQueue* _work_queue;
3910 protected:
3911 DO_OOP_WORK_DEFN
3912 public:
3913 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3914 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3915 MetadataAwareOopClosure(collector->ref_processor()),
3916 _collector(collector),
3917 _task(task),
3918 _span(collector->_span),
3919 _work_queue(work_queue),
3920 _bit_map(bit_map),
3921 _overflow_stack(overflow_stack)
3922 { }
3923 virtual void do_oop(oop* p);
3924 virtual void do_oop(narrowOop* p);
3925
3926 void trim_queue(size_t max);
3927 void handle_stack_overflow(HeapWord* lost);
3928 void do_yield_check() {
3929 if (_task->should_yield()) {
3930 _task->yield();
3931 }
3932 }
3933 };
3934
3935 // Grey object scanning during work stealing phase --
3936 // the salient assumption here is that any references
3937 // that are in these stolen objects being scanned must
3938 // already have been initialized (else they would not have
3939 // been published), so we do not need to check for
3940 // uninitialized objects before pushing here.
3941 void Par_ConcMarkingClosure::do_oop(oop obj) {
3942 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3943 HeapWord* addr = (HeapWord*)obj;
3944 // Check if oop points into the CMS generation
3945 // and is not marked
3946 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3947 // a white object ...
3948 // If we manage to "claim" the object, by being the
3949 // first thread to mark it, then we push it on our
3950 // marking stack
3951 if (_bit_map->par_mark(addr)) { // ... now grey
3952 // push on work queue (grey set)
3953 bool simulate_overflow = false;
3954 NOT_PRODUCT(
3955 if (CMSMarkStackOverflowALot &&
3956 _collector->simulate_overflow()) {
3957 // simulate a stack overflow
3958 simulate_overflow = true;
3959 }
3960 )
3961 if (simulate_overflow ||
3962 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3963 // stack overflow
3964 if (PrintCMSStatistics != 0) {
3965 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3966 SIZE_FORMAT, _overflow_stack->capacity());
3967 }
3968 // We cannot assert that the overflow stack is full because
3969 // it may have been emptied since.
3970 assert(simulate_overflow ||
3971 _work_queue->size() == _work_queue->max_elems(),
3972 "Else push should have succeeded");
3973 handle_stack_overflow(addr);
3974 }
3975 } // Else, some other thread got there first
3976 do_yield_check();
3977 }
3978 }
3979
3980 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3981 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3982
3983 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3984 while (_work_queue->size() > max) {
3985 oop new_oop;
3986 if (_work_queue->pop_local(new_oop)) {
3987 assert(new_oop->is_oop(), "Should be an oop");
3988 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3989 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3990 new_oop->oop_iterate(this); // do_oop() above
3991 do_yield_check();
3992 }
3993 }
3994 }
3995
3996 // Upon stack overflow, we discard (part of) the stack,
3997 // remembering the least address amongst those discarded
3998 // in CMSCollector's _restart_address.
3999 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4000 // We need to do this under a mutex to prevent other
4001 // workers from interfering with the work done below.
4002 MutexLockerEx ml(_overflow_stack->par_lock(),
4003 Mutex::_no_safepoint_check_flag);
4004 // Remember the least grey address discarded
4005 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4006 _collector->lower_restart_addr(ra);
4007 _overflow_stack->reset(); // discard stack contents
4008 _overflow_stack->expand(); // expand the stack if possible
4009 }
4010
4011
4012 void CMSConcMarkingTask::do_work_steal(int i) {
4013 OopTaskQueue* work_q = work_queue(i);
4014 oop obj_to_scan;
4015 CMSBitMap* bm = &(_collector->_markBitMap);
4016 CMSMarkStack* ovflw = &(_collector->_markStack);
4017 int* seed = _collector->hash_seed(i);
4018 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4019 while (true) {
4020 cl.trim_queue(0);
4021 assert(work_q->size() == 0, "Should have been emptied above");
4022 if (get_work_from_overflow_stack(ovflw, work_q)) {
4023 // Can't assert below because the work obtained from the
4024 // overflow stack may already have been stolen from us.
4025 // assert(work_q->size() > 0, "Work from overflow stack");
4026 continue;
4027 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4028 assert(obj_to_scan->is_oop(), "Should be an oop");
4029 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4030 obj_to_scan->oop_iterate(&cl);
4031 } else if (terminator()->offer_termination(&_term_term)) {
4032 assert(work_q->size() == 0, "Impossible!");
4033 break;
4034 } else if (yielding() || should_yield()) {
4035 yield();
4036 }
4037 }
4038 }
4039
4040 // This is run by the CMS (coordinator) thread.
4041 void CMSConcMarkingTask::coordinator_yield() {
4042 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4043 "CMS thread should hold CMS token");
4044 // First give up the locks, then yield, then re-lock
4045 // We should probably use a constructor/destructor idiom to
4046 // do this unlock/lock or modify the MutexUnlocker class to
4047 // serve our purpose. XXX
4048 assert_lock_strong(_bit_map_lock);
4049 _bit_map_lock->unlock();
4050 ConcurrentMarkSweepThread::desynchronize(true);
4051 _collector->stopTimer();
4052 if (PrintCMSStatistics != 0) {
4053 _collector->incrementYields();
4054 }
4055
4056 // It is possible for whichever thread initiated the yield request
4057 // not to get a chance to wake up and take the bitmap lock between
4058 // this thread releasing it and reacquiring it. So, while the
4059 // should_yield() flag is on, let's sleep for a bit to give the
4060 // other thread a chance to wake up. The limit imposed on the number
4061 // of iterations is defensive, to avoid any unforseen circumstances
4062 // putting us into an infinite loop. Since it's always been this
4063 // (coordinator_yield()) method that was observed to cause the
4064 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4065 // which is by default non-zero. For the other seven methods that
4066 // also perform the yield operation, as are using a different
4067 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4068 // can enable the sleeping for those methods too, if necessary.
4069 // See 6442774.
4070 //
4071 // We really need to reconsider the synchronization between the GC
4072 // thread and the yield-requesting threads in the future and we
4073 // should really use wait/notify, which is the recommended
4074 // way of doing this type of interaction. Additionally, we should
4075 // consolidate the eight methods that do the yield operation and they
4076 // are almost identical into one for better maintainability and
4077 // readability. See 6445193.
4078 //
4079 // Tony 2006.06.29
4080 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4081 ConcurrentMarkSweepThread::should_yield() &&
4082 !CMSCollector::foregroundGCIsActive(); ++i) {
4083 os::sleep(Thread::current(), 1, false);
4084 }
4085
4086 ConcurrentMarkSweepThread::synchronize(true);
4087 _bit_map_lock->lock_without_safepoint_check();
4088 _collector->startTimer();
4089 }
4090
4091 bool CMSCollector::do_marking_mt(bool asynch) {
4092 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4093 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4094 conc_workers()->total_workers(),
4095 conc_workers()->active_workers(),
4096 Threads::number_of_non_daemon_threads());
4097 conc_workers()->set_active_workers(num_workers);
4098
4099 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4100
4101 CMSConcMarkingTask tsk(this,
4102 cms_space,
4103 asynch,
4104 conc_workers(),
4105 task_queues());
4106
4107 // Since the actual number of workers we get may be different
4108 // from the number we requested above, do we need to do anything different
4109 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4110 // class?? XXX
4111 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4112
4113 // Refs discovery is already non-atomic.
4114 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4115 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4116 conc_workers()->start_task(&tsk);
4117 while (tsk.yielded()) {
4118 tsk.coordinator_yield();
4119 conc_workers()->continue_task(&tsk);
4120 }
4121 // If the task was aborted, _restart_addr will be non-NULL
4122 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4123 while (_restart_addr != NULL) {
4124 // XXX For now we do not make use of ABORTED state and have not
4125 // yet implemented the right abort semantics (even in the original
4126 // single-threaded CMS case). That needs some more investigation
4127 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4128 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4129 // If _restart_addr is non-NULL, a marking stack overflow
4130 // occurred; we need to do a fresh marking iteration from the
4131 // indicated restart address.
4132 if (_foregroundGCIsActive && asynch) {
4133 // We may be running into repeated stack overflows, having
4134 // reached the limit of the stack size, while making very
4135 // slow forward progress. It may be best to bail out and
4136 // let the foreground collector do its job.
4137 // Clear _restart_addr, so that foreground GC
4138 // works from scratch. This avoids the headache of
4139 // a "rescan" which would otherwise be needed because
4140 // of the dirty mod union table & card table.
4141 _restart_addr = NULL;
4142 return false;
4143 }
4144 // Adjust the task to restart from _restart_addr
4145 tsk.reset(_restart_addr);
4146 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4147 _restart_addr);
4148 _restart_addr = NULL;
4149 // Get the workers going again
4150 conc_workers()->start_task(&tsk);
4151 while (tsk.yielded()) {
4152 tsk.coordinator_yield();
4153 conc_workers()->continue_task(&tsk);
4154 }
4155 }
4156 assert(tsk.completed(), "Inconsistency");
4157 assert(tsk.result() == true, "Inconsistency");
4158 return true;
4159 }
4160
4161 bool CMSCollector::do_marking_st(bool asynch) {
4162 ResourceMark rm;
4163 HandleMark hm;
4164
4165 // Temporarily make refs discovery single threaded (non-MT)
4166 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4167 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4168 &_markStack, CMSYield && asynch);
4169 // the last argument to iterate indicates whether the iteration
4170 // should be incremental with periodic yields.
4171 _markBitMap.iterate(&markFromRootsClosure);
4172 // If _restart_addr is non-NULL, a marking stack overflow
4173 // occurred; we need to do a fresh iteration from the
4174 // indicated restart address.
4175 while (_restart_addr != NULL) {
4176 if (_foregroundGCIsActive && asynch) {
4177 // We may be running into repeated stack overflows, having
4178 // reached the limit of the stack size, while making very
4179 // slow forward progress. It may be best to bail out and
4180 // let the foreground collector do its job.
4181 // Clear _restart_addr, so that foreground GC
4182 // works from scratch. This avoids the headache of
4183 // a "rescan" which would otherwise be needed because
4184 // of the dirty mod union table & card table.
4185 _restart_addr = NULL;
4186 return false; // indicating failure to complete marking
4187 }
4188 // Deal with stack overflow:
4189 // we restart marking from _restart_addr
4190 HeapWord* ra = _restart_addr;
4191 markFromRootsClosure.reset(ra);
4192 _restart_addr = NULL;
4193 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4194 }
4195 return true;
4196 }
4197
4198 void CMSCollector::preclean() {
4199 check_correct_thread_executing();
4200 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4201 verify_work_stacks_empty();
4202 verify_overflow_empty();
4203 _abort_preclean = false;
4204 if (CMSPrecleaningEnabled) {
4205 if (!CMSEdenChunksRecordAlways) {
4206 _eden_chunk_index = 0;
4207 }
4208 size_t used = get_eden_used();
4209 size_t capacity = get_eden_capacity();
4210 // Don't start sampling unless we will get sufficiently
4211 // many samples.
4212 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4213 * CMSScheduleRemarkEdenPenetration)) {
4214 _start_sampling = true;
4215 } else {
4216 _start_sampling = false;
4217 }
4218 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4219 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4220 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4221 }
4222 CMSTokenSync x(true); // is cms thread
4223 if (CMSPrecleaningEnabled) {
4224 sample_eden();
4225 _collectorState = AbortablePreclean;
4226 } else {
4227 _collectorState = FinalMarking;
4228 }
4229 verify_work_stacks_empty();
4230 verify_overflow_empty();
4231 }
4232
4233 // Try and schedule the remark such that young gen
4234 // occupancy is CMSScheduleRemarkEdenPenetration %.
4235 void CMSCollector::abortable_preclean() {
4236 check_correct_thread_executing();
4237 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4238 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4239
4240 // If Eden's current occupancy is below this threshold,
4241 // immediately schedule the remark; else preclean
4242 // past the next scavenge in an effort to
4243 // schedule the pause as described above. By choosing
4244 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4245 // we will never do an actual abortable preclean cycle.
4246 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4247 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4248 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4249 // We need more smarts in the abortable preclean
4250 // loop below to deal with cases where allocation
4251 // in young gen is very very slow, and our precleaning
4252 // is running a losing race against a horde of
4253 // mutators intent on flooding us with CMS updates
4254 // (dirty cards).
4255 // One, admittedly dumb, strategy is to give up
4256 // after a certain number of abortable precleaning loops
4257 // or after a certain maximum time. We want to make
4258 // this smarter in the next iteration.
4259 // XXX FIX ME!!! YSR
4260 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4261 while (!(should_abort_preclean() ||
4262 ConcurrentMarkSweepThread::should_terminate())) {
4263 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4264 cumworkdone += workdone;
4265 loops++;
4266 // Voluntarily terminate abortable preclean phase if we have
4267 // been at it for too long.
4268 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4269 loops >= CMSMaxAbortablePrecleanLoops) {
4270 if (PrintGCDetails) {
4271 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4272 }
4273 break;
4274 }
4275 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4276 if (PrintGCDetails) {
4277 gclog_or_tty->print(" CMS: abort preclean due to time ");
4278 }
4279 break;
4280 }
4281 // If we are doing little work each iteration, we should
4282 // take a short break.
4283 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4284 // Sleep for some time, waiting for work to accumulate
4285 stopTimer();
4286 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4287 startTimer();
4288 waited++;
4289 }
4290 }
4291 if (PrintCMSStatistics > 0) {
4292 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4293 loops, waited, cumworkdone);
4294 }
4295 }
4296 CMSTokenSync x(true); // is cms thread
4297 if (_collectorState != Idling) {
4298 assert(_collectorState == AbortablePreclean,
4299 "Spontaneous state transition?");
4300 _collectorState = FinalMarking;
4301 } // Else, a foreground collection completed this CMS cycle.
4302 return;
4303 }
4304
4305 // Respond to an Eden sampling opportunity
4306 void CMSCollector::sample_eden() {
4307 // Make sure a young gc cannot sneak in between our
4308 // reading and recording of a sample.
4309 assert(Thread::current()->is_ConcurrentGC_thread(),
4310 "Only the cms thread may collect Eden samples");
4311 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4312 "Should collect samples while holding CMS token");
4313 if (!_start_sampling) {
4314 return;
4315 }
4316 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4317 // is populated by the young generation.
4318 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4319 if (_eden_chunk_index < _eden_chunk_capacity) {
4320 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4321 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4322 "Unexpected state of Eden");
4323 // We'd like to check that what we just sampled is an oop-start address;
4324 // however, we cannot do that here since the object may not yet have been
4325 // initialized. So we'll instead do the check when we _use_ this sample
4326 // later.
4327 if (_eden_chunk_index == 0 ||
4328 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4329 _eden_chunk_array[_eden_chunk_index-1])
4330 >= CMSSamplingGrain)) {
4331 _eden_chunk_index++; // commit sample
4332 }
4333 }
4334 }
4335 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4336 size_t used = get_eden_used();
4337 size_t capacity = get_eden_capacity();
4338 assert(used <= capacity, "Unexpected state of Eden");
4339 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4340 _abort_preclean = true;
4341 }
4342 }
4343 }
4344
4345
4346 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4347 assert(_collectorState == Precleaning ||
4348 _collectorState == AbortablePreclean, "incorrect state");
4349 ResourceMark rm;
4350 HandleMark hm;
4351
4352 // Precleaning is currently not MT but the reference processor
4353 // may be set for MT. Disable it temporarily here.
4354 ReferenceProcessor* rp = ref_processor();
4355 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4356
4357 // Do one pass of scrubbing the discovered reference lists
4358 // to remove any reference objects with strongly-reachable
4359 // referents.
4360 if (clean_refs) {
4361 CMSPrecleanRefsYieldClosure yield_cl(this);
4362 assert(rp->span().equals(_span), "Spans should be equal");
4363 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4364 &_markStack, true /* preclean */);
4365 CMSDrainMarkingStackClosure complete_trace(this,
4366 _span, &_markBitMap, &_markStack,
4367 &keep_alive, true /* preclean */);
4368
4369 // We don't want this step to interfere with a young
4370 // collection because we don't want to take CPU
4371 // or memory bandwidth away from the young GC threads
4372 // (which may be as many as there are CPUs).
4373 // Note that we don't need to protect ourselves from
4374 // interference with mutators because they can't
4375 // manipulate the discovered reference lists nor affect
4376 // the computed reachability of the referents, the
4377 // only properties manipulated by the precleaning
4378 // of these reference lists.
4379 stopTimer();
4380 CMSTokenSyncWithLocks x(true /* is cms thread */,
4381 bitMapLock());
4382 startTimer();
4383 sample_eden();
4384
4385 // The following will yield to allow foreground
4386 // collection to proceed promptly. XXX YSR:
4387 // The code in this method may need further
4388 // tweaking for better performance and some restructuring
4389 // for cleaner interfaces.
4390 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4391 rp->preclean_discovered_references(
4392 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4393 gc_timer, _gc_tracer_cm->gc_id());
4394 }
4395
4396 if (clean_survivor) { // preclean the active survivor space(s)
4397 assert(_young_gen->kind() == Generation::DefNew ||
4398 _young_gen->kind() == Generation::ParNew,
4399 "incorrect type for cast");
4400 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4401 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4402 &_markBitMap, &_modUnionTable,
4403 &_markStack, true /* precleaning phase */);
4404 stopTimer();
4405 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4406 bitMapLock());
4407 startTimer();
4408 unsigned int before_count =
4409 GenCollectedHeap::heap()->total_collections();
4410 SurvivorSpacePrecleanClosure
4411 sss_cl(this, _span, &_markBitMap, &_markStack,
4412 &pam_cl, before_count, CMSYield);
4413 dng->from()->object_iterate_careful(&sss_cl);
4414 dng->to()->object_iterate_careful(&sss_cl);
4415 }
4416 MarkRefsIntoAndScanClosure
4417 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4418 &_markStack, this, CMSYield,
4419 true /* precleaning phase */);
4420 // CAUTION: The following closure has persistent state that may need to
4421 // be reset upon a decrease in the sequence of addresses it
4422 // processes.
4423 ScanMarkedObjectsAgainCarefullyClosure
4424 smoac_cl(this, _span,
4425 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4426
4427 // Preclean dirty cards in ModUnionTable and CardTable using
4428 // appropriate convergence criterion;
4429 // repeat CMSPrecleanIter times unless we find that
4430 // we are losing.
4431 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4432 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4433 "Bad convergence multiplier");
4434 assert(CMSPrecleanThreshold >= 100,
4435 "Unreasonably low CMSPrecleanThreshold");
4436
4437 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4438 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4439 numIter < CMSPrecleanIter;
4440 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4441 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4442 if (Verbose && PrintGCDetails) {
4443 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4444 }
4445 // Either there are very few dirty cards, so re-mark
4446 // pause will be small anyway, or our pre-cleaning isn't
4447 // that much faster than the rate at which cards are being
4448 // dirtied, so we might as well stop and re-mark since
4449 // precleaning won't improve our re-mark time by much.
4450 if (curNumCards <= CMSPrecleanThreshold ||
4451 (numIter > 0 &&
4452 (curNumCards * CMSPrecleanDenominator >
4453 lastNumCards * CMSPrecleanNumerator))) {
4454 numIter++;
4455 cumNumCards += curNumCards;
4456 break;
4457 }
4458 }
4459
4460 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4461
4462 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4463 cumNumCards += curNumCards;
4464 if (PrintGCDetails && PrintCMSStatistics != 0) {
4465 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4466 curNumCards, cumNumCards, numIter);
4467 }
4468 return cumNumCards; // as a measure of useful work done
4469 }
4470
4471 // PRECLEANING NOTES:
4472 // Precleaning involves:
4473 // . reading the bits of the modUnionTable and clearing the set bits.
4474 // . For the cards corresponding to the set bits, we scan the
4475 // objects on those cards. This means we need the free_list_lock
4476 // so that we can safely iterate over the CMS space when scanning
4477 // for oops.
4478 // . When we scan the objects, we'll be both reading and setting
4479 // marks in the marking bit map, so we'll need the marking bit map.
4480 // . For protecting _collector_state transitions, we take the CGC_lock.
4481 // Note that any races in the reading of of card table entries by the
4482 // CMS thread on the one hand and the clearing of those entries by the
4483 // VM thread or the setting of those entries by the mutator threads on the
4484 // other are quite benign. However, for efficiency it makes sense to keep
4485 // the VM thread from racing with the CMS thread while the latter is
4486 // dirty card info to the modUnionTable. We therefore also use the
4487 // CGC_lock to protect the reading of the card table and the mod union
4488 // table by the CM thread.
4489 // . We run concurrently with mutator updates, so scanning
4490 // needs to be done carefully -- we should not try to scan
4491 // potentially uninitialized objects.
4492 //
4493 // Locking strategy: While holding the CGC_lock, we scan over and
4494 // reset a maximal dirty range of the mod union / card tables, then lock
4495 // the free_list_lock and bitmap lock to do a full marking, then
4496 // release these locks; and repeat the cycle. This allows for a
4497 // certain amount of fairness in the sharing of these locks between
4498 // the CMS collector on the one hand, and the VM thread and the
4499 // mutators on the other.
4500
4501 // NOTE: preclean_mod_union_table() and preclean_card_table()
4502 // further below are largely identical; if you need to modify
4503 // one of these methods, please check the other method too.
4504
4505 size_t CMSCollector::preclean_mod_union_table(
4506 ConcurrentMarkSweepGeneration* gen,
4507 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4508 verify_work_stacks_empty();
4509 verify_overflow_empty();
4510
4511 // strategy: starting with the first card, accumulate contiguous
4512 // ranges of dirty cards; clear these cards, then scan the region
4513 // covered by these cards.
4514
4515 // Since all of the MUT is committed ahead, we can just use
4516 // that, in case the generations expand while we are precleaning.
4517 // It might also be fine to just use the committed part of the
4518 // generation, but we might potentially miss cards when the
4519 // generation is rapidly expanding while we are in the midst
4520 // of precleaning.
4521 HeapWord* startAddr = gen->reserved().start();
4522 HeapWord* endAddr = gen->reserved().end();
4523
4524 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4525
4526 size_t numDirtyCards, cumNumDirtyCards;
4527 HeapWord *nextAddr, *lastAddr;
4528 for (cumNumDirtyCards = numDirtyCards = 0,
4529 nextAddr = lastAddr = startAddr;
4530 nextAddr < endAddr;
4531 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4532
4533 ResourceMark rm;
4534 HandleMark hm;
4535
4536 MemRegion dirtyRegion;
4537 {
4538 stopTimer();
4539 // Potential yield point
4540 CMSTokenSync ts(true);
4541 startTimer();
4542 sample_eden();
4543 // Get dirty region starting at nextOffset (inclusive),
4544 // simultaneously clearing it.
4545 dirtyRegion =
4546 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4547 assert(dirtyRegion.start() >= nextAddr,
4548 "returned region inconsistent?");
4549 }
4550 // Remember where the next search should begin.
4551 // The returned region (if non-empty) is a right open interval,
4552 // so lastOffset is obtained from the right end of that
4553 // interval.
4554 lastAddr = dirtyRegion.end();
4555 // Should do something more transparent and less hacky XXX
4556 numDirtyCards =
4557 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4558
4559 // We'll scan the cards in the dirty region (with periodic
4560 // yields for foreground GC as needed).
4561 if (!dirtyRegion.is_empty()) {
4562 assert(numDirtyCards > 0, "consistency check");
4563 HeapWord* stop_point = NULL;
4564 stopTimer();
4565 // Potential yield point
4566 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4567 bitMapLock());
4568 startTimer();
4569 {
4570 verify_work_stacks_empty();
4571 verify_overflow_empty();
4572 sample_eden();
4573 stop_point =
4574 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4575 }
4576 if (stop_point != NULL) {
4577 // The careful iteration stopped early either because it found an
4578 // uninitialized object, or because we were in the midst of an
4579 // "abortable preclean", which should now be aborted. Redirty
4580 // the bits corresponding to the partially-scanned or unscanned
4581 // cards. We'll either restart at the next block boundary or
4582 // abort the preclean.
4583 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4584 "Should only be AbortablePreclean.");
4585 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4586 if (should_abort_preclean()) {
4587 break; // out of preclean loop
4588 } else {
4589 // Compute the next address at which preclean should pick up;
4590 // might need bitMapLock in order to read P-bits.
4591 lastAddr = next_card_start_after_block(stop_point);
4592 }
4593 }
4594 } else {
4595 assert(lastAddr == endAddr, "consistency check");
4596 assert(numDirtyCards == 0, "consistency check");
4597 break;
4598 }
4599 }
4600 verify_work_stacks_empty();
4601 verify_overflow_empty();
4602 return cumNumDirtyCards;
4603 }
4604
4605 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4606 // below are largely identical; if you need to modify
4607 // one of these methods, please check the other method too.
4608
4609 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4610 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4611 // strategy: it's similar to precleamModUnionTable above, in that
4612 // we accumulate contiguous ranges of dirty cards, mark these cards
4613 // precleaned, then scan the region covered by these cards.
4614 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4615 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4616
4617 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4618
4619 size_t numDirtyCards, cumNumDirtyCards;
4620 HeapWord *lastAddr, *nextAddr;
4621
4622 for (cumNumDirtyCards = numDirtyCards = 0,
4623 nextAddr = lastAddr = startAddr;
4624 nextAddr < endAddr;
4625 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4626
4627 ResourceMark rm;
4628 HandleMark hm;
4629
4630 MemRegion dirtyRegion;
4631 {
4632 // See comments in "Precleaning notes" above on why we
4633 // do this locking. XXX Could the locking overheads be
4634 // too high when dirty cards are sparse? [I don't think so.]
4635 stopTimer();
4636 CMSTokenSync x(true); // is cms thread
4637 startTimer();
4638 sample_eden();
4639 // Get and clear dirty region from card table
4640 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4641 MemRegion(nextAddr, endAddr),
4642 true,
4643 CardTableModRefBS::precleaned_card_val());
4644
4645 assert(dirtyRegion.start() >= nextAddr,
4646 "returned region inconsistent?");
4647 }
4648 lastAddr = dirtyRegion.end();
4649 numDirtyCards =
4650 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4651
4652 if (!dirtyRegion.is_empty()) {
4653 stopTimer();
4654 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4655 startTimer();
4656 sample_eden();
4657 verify_work_stacks_empty();
4658 verify_overflow_empty();
4659 HeapWord* stop_point =
4660 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4661 if (stop_point != NULL) {
4662 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4663 "Should only be AbortablePreclean.");
4664 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4665 if (should_abort_preclean()) {
4666 break; // out of preclean loop
4667 } else {
4668 // Compute the next address at which preclean should pick up.
4669 lastAddr = next_card_start_after_block(stop_point);
4670 }
4671 }
4672 } else {
4673 break;
4674 }
4675 }
4676 verify_work_stacks_empty();
4677 verify_overflow_empty();
4678 return cumNumDirtyCards;
4679 }
4680
4681 class PrecleanKlassClosure : public KlassClosure {
4682 KlassToOopClosure _cm_klass_closure;
4683 public:
4684 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4685 void do_klass(Klass* k) {
4686 if (k->has_accumulated_modified_oops()) {
4687 k->clear_accumulated_modified_oops();
4688
4689 _cm_klass_closure.do_klass(k);
4690 }
4691 }
4692 };
4693
4694 // The freelist lock is needed to prevent asserts, is it really needed?
4695 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4696
4697 cl->set_freelistLock(freelistLock);
4698
4699 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4700
4701 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4702 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4703 PrecleanKlassClosure preclean_klass_closure(cl);
4704 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4705
4706 verify_work_stacks_empty();
4707 verify_overflow_empty();
4708 }
4709
4710 void CMSCollector::checkpointRootsFinal(bool asynch,
4711 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4712 assert(_collectorState == FinalMarking, "incorrect state transition?");
4713 check_correct_thread_executing();
4714 // world is stopped at this checkpoint
4715 assert(SafepointSynchronize::is_at_safepoint(),
4716 "world should be stopped");
4717 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4718
4719 verify_work_stacks_empty();
4720 verify_overflow_empty();
4721
4722 SpecializationStats::clear();
4723 if (PrintGCDetails) {
4724 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4725 _young_gen->used() / K,
4726 _young_gen->capacity() / K);
4727 }
4728 if (asynch) {
4729 if (CMSScavengeBeforeRemark) {
4730 GenCollectedHeap* gch = GenCollectedHeap::heap();
4731 // Temporarily set flag to false, GCH->do_collection will
4732 // expect it to be false and set to true
4733 FlagSetting fl(gch->_is_gc_active, false);
4734 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4735 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4736 int level = _cmsGen->level() - 1;
4737 if (level >= 0) {
4738 gch->do_collection(true, // full (i.e. force, see below)
4739 false, // !clear_all_soft_refs
4740 0, // size
4741 false, // is_tlab
4742 level // max_level
4743 );
4744 }
4745 }
4746 FreelistLocker x(this);
4747 MutexLockerEx y(bitMapLock(),
4748 Mutex::_no_safepoint_check_flag);
4749 assert(!init_mark_was_synchronous, "but that's impossible!");
4750 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4751 } else {
4752 // already have all the locks
4753 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4754 init_mark_was_synchronous);
4755 }
4756 verify_work_stacks_empty();
4757 verify_overflow_empty();
4758 SpecializationStats::print();
4759 }
4760
4761 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4762 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4763
4764 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4765
4766 assert(haveFreelistLocks(), "must have free list locks");
4767 assert_lock_strong(bitMapLock());
4768
4769 ResourceMark rm;
4770 HandleMark hm;
4771
4772 GenCollectedHeap* gch = GenCollectedHeap::heap();
4773
4774 if (should_unload_classes()) {
4775 CodeCache::gc_prologue();
4776 }
4777 assert(haveFreelistLocks(), "must have free list locks");
4778 assert_lock_strong(bitMapLock());
4779
4780 if (!init_mark_was_synchronous) {
4781 // We might assume that we need not fill TLAB's when
4782 // CMSScavengeBeforeRemark is set, because we may have just done
4783 // a scavenge which would have filled all TLAB's -- and besides
4784 // Eden would be empty. This however may not always be the case --
4785 // for instance although we asked for a scavenge, it may not have
4786 // happened because of a JNI critical section. We probably need
4787 // a policy for deciding whether we can in that case wait until
4788 // the critical section releases and then do the remark following
4789 // the scavenge, and skip it here. In the absence of that policy,
4790 // or of an indication of whether the scavenge did indeed occur,
4791 // we cannot rely on TLAB's having been filled and must do
4792 // so here just in case a scavenge did not happen.
4793 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4794 // Update the saved marks which may affect the root scans.
4795 gch->save_marks();
4796
4797 if (CMSPrintEdenSurvivorChunks) {
4798 print_eden_and_survivor_chunk_arrays();
4799 }
4800
4801 {
4802 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4803
4804 // Note on the role of the mod union table:
4805 // Since the marker in "markFromRoots" marks concurrently with
4806 // mutators, it is possible for some reachable objects not to have been
4807 // scanned. For instance, an only reference to an object A was
4808 // placed in object B after the marker scanned B. Unless B is rescanned,
4809 // A would be collected. Such updates to references in marked objects
4810 // are detected via the mod union table which is the set of all cards
4811 // dirtied since the first checkpoint in this GC cycle and prior to
4812 // the most recent young generation GC, minus those cleaned up by the
4813 // concurrent precleaning.
4814 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4815 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4816 do_remark_parallel();
4817 } else {
4818 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4819 _gc_timer_cm, _gc_tracer_cm->gc_id());
4820 do_remark_non_parallel();
4821 }
4822 }
4823 } else {
4824 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4825 // The initial mark was stop-world, so there's no rescanning to
4826 // do; go straight on to the next step below.
4827 }
4828 verify_work_stacks_empty();
4829 verify_overflow_empty();
4830
4831 {
4832 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4833 refProcessingWork(asynch, clear_all_soft_refs);
4834 }
4835 verify_work_stacks_empty();
4836 verify_overflow_empty();
4837
4838 if (should_unload_classes()) {
4839 CodeCache::gc_epilogue();
4840 }
4841 JvmtiExport::gc_epilogue();
4842
4843 // If we encountered any (marking stack / work queue) overflow
4844 // events during the current CMS cycle, take appropriate
4845 // remedial measures, where possible, so as to try and avoid
4846 // recurrence of that condition.
4847 assert(_markStack.isEmpty(), "No grey objects");
4848 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4849 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4850 if (ser_ovflw > 0) {
4851 if (PrintCMSStatistics != 0) {
4852 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4853 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4854 ", kac_preclean="SIZE_FORMAT")",
4855 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4856 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4857 }
4858 _markStack.expand();
4859 _ser_pmc_remark_ovflw = 0;
4860 _ser_pmc_preclean_ovflw = 0;
4861 _ser_kac_preclean_ovflw = 0;
4862 _ser_kac_ovflw = 0;
4863 }
4864 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4865 if (PrintCMSStatistics != 0) {
4866 gclog_or_tty->print_cr("Work queue overflow (benign) "
4867 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4868 _par_pmc_remark_ovflw, _par_kac_ovflw);
4869 }
4870 _par_pmc_remark_ovflw = 0;
4871 _par_kac_ovflw = 0;
4872 }
4873 if (PrintCMSStatistics != 0) {
4874 if (_markStack._hit_limit > 0) {
4875 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4876 _markStack._hit_limit);
4877 }
4878 if (_markStack._failed_double > 0) {
4879 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4880 " current capacity "SIZE_FORMAT,
4881 _markStack._failed_double,
4882 _markStack.capacity());
4883 }
4884 }
4885 _markStack._hit_limit = 0;
4886 _markStack._failed_double = 0;
4887
4888 if ((VerifyAfterGC || VerifyDuringGC) &&
4889 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4890 verify_after_remark();
4891 }
4892
4893 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4894
4895 // Change under the freelistLocks.
4896 _collectorState = Sweeping;
4897 // Call isAllClear() under bitMapLock
4898 assert(_modUnionTable.isAllClear(),
4899 "Should be clear by end of the final marking");
4900 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4901 "Should be clear by end of the final marking");
4902 }
4903
4904 void CMSParInitialMarkTask::work(uint worker_id) {
4905 elapsedTimer _timer;
4906 ResourceMark rm;
4907 HandleMark hm;
4908
4909 // ---------- scan from roots --------------
4910 _timer.start();
4911 GenCollectedHeap* gch = GenCollectedHeap::heap();
4912 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4913
4914 // ---------- young gen roots --------------
4915 {
4916 work_on_young_gen_roots(worker_id, &par_mri_cl);
4917 _timer.stop();
4918 if (PrintCMSStatistics != 0) {
4919 gclog_or_tty->print_cr(
4920 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4921 worker_id, _timer.seconds());
4922 }
4923 }
4924
4925 // ---------- remaining roots --------------
4926 _timer.reset();
4927 _timer.start();
4928
4929 CLDToOopClosure cld_closure(&par_mri_cl, true);
4930
4931 gch->gen_process_roots(_collector->_cmsGen->level(),
4932 false, // yg was scanned above
4933 false, // this is parallel code
4934 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4935 _collector->should_unload_classes(),
4936 &par_mri_cl,
4937 NULL,
4938 &cld_closure);
4939 assert(_collector->should_unload_classes()
4940 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4941 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4942 _timer.stop();
4943 if (PrintCMSStatistics != 0) {
4944 gclog_or_tty->print_cr(
4945 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4946 worker_id, _timer.seconds());
4947 }
4948 }
4949
4950 // Parallel remark task
4951 class CMSParRemarkTask: public CMSParMarkTask {
4952 CompactibleFreeListSpace* _cms_space;
4953
4954 // The per-thread work queues, available here for stealing.
4955 OopTaskQueueSet* _task_queues;
4956 ParallelTaskTerminator _term;
4957
4958 public:
4959 // A value of 0 passed to n_workers will cause the number of
4960 // workers to be taken from the active workers in the work gang.
4961 CMSParRemarkTask(CMSCollector* collector,
4962 CompactibleFreeListSpace* cms_space,
4963 int n_workers, FlexibleWorkGang* workers,
4964 OopTaskQueueSet* task_queues):
4965 CMSParMarkTask("Rescan roots and grey objects in parallel",
4966 collector, n_workers),
4967 _cms_space(cms_space),
4968 _task_queues(task_queues),
4969 _term(n_workers, task_queues) { }
4970
4971 OopTaskQueueSet* task_queues() { return _task_queues; }
4972
4973 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4974
4975 ParallelTaskTerminator* terminator() { return &_term; }
4976 int n_workers() { return _n_workers; }
4977
4978 void work(uint worker_id);
4979
4980 private:
4981 // ... of dirty cards in old space
4982 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4983 Par_MarkRefsIntoAndScanClosure* cl);
4984
4985 // ... work stealing for the above
4986 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4987 };
4988
4989 class RemarkKlassClosure : public KlassClosure {
4990 KlassToOopClosure _cm_klass_closure;
4991 public:
4992 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4993 void do_klass(Klass* k) {
4994 // Check if we have modified any oops in the Klass during the concurrent marking.
4995 if (k->has_accumulated_modified_oops()) {
4996 k->clear_accumulated_modified_oops();
4997
4998 // We could have transfered the current modified marks to the accumulated marks,
4999 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5000 } else if (k->has_modified_oops()) {
5001 // Don't clear anything, this info is needed by the next young collection.
5002 } else {
5003 // No modified oops in the Klass.
5004 return;
5005 }
5006
5007 // The klass has modified fields, need to scan the klass.
5008 _cm_klass_closure.do_klass(k);
5009 }
5010 };
5011
5012 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5013 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5014 ContiguousSpace* eden_space = dng->eden();
5015 ContiguousSpace* from_space = dng->from();
5016 ContiguousSpace* to_space = dng->to();
5017
5018 HeapWord** eca = _collector->_eden_chunk_array;
5019 size_t ect = _collector->_eden_chunk_index;
5020 HeapWord** sca = _collector->_survivor_chunk_array;
5021 size_t sct = _collector->_survivor_chunk_index;
5022
5023 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5024 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5025
5026 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5027 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5028 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5029 }
5030
5031 // work_queue(i) is passed to the closure
5032 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5033 // also is passed to do_dirty_card_rescan_tasks() and to
5034 // do_work_steal() to select the i-th task_queue.
5035
5036 void CMSParRemarkTask::work(uint worker_id) {
5037 elapsedTimer _timer;
5038 ResourceMark rm;
5039 HandleMark hm;
5040
5041 // ---------- rescan from roots --------------
5042 _timer.start();
5043 GenCollectedHeap* gch = GenCollectedHeap::heap();
5044 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5045 _collector->_span, _collector->ref_processor(),
5046 &(_collector->_markBitMap),
5047 work_queue(worker_id));
5048
5049 // Rescan young gen roots first since these are likely
5050 // coarsely partitioned and may, on that account, constitute
5051 // the critical path; thus, it's best to start off that
5052 // work first.
5053 // ---------- young gen roots --------------
5054 {
5055 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5056 _timer.stop();
5057 if (PrintCMSStatistics != 0) {
5058 gclog_or_tty->print_cr(
5059 "Finished young gen rescan work in %dth thread: %3.3f sec",
5060 worker_id, _timer.seconds());
5061 }
5062 }
5063
5064 // ---------- remaining roots --------------
5065 _timer.reset();
5066 _timer.start();
5067 gch->gen_process_roots(_collector->_cmsGen->level(),
5068 false, // yg was scanned above
5069 false, // this is parallel code
5070 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5071 _collector->should_unload_classes(),
5072 &par_mrias_cl,
5073 NULL,
5074 NULL); // The dirty klasses will be handled below
5075
5076 assert(_collector->should_unload_classes()
5077 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5078 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5079 _timer.stop();
5080 if (PrintCMSStatistics != 0) {
5081 gclog_or_tty->print_cr(
5082 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5083 worker_id, _timer.seconds());
5084 }
5085
5086 // ---------- unhandled CLD scanning ----------
5087 if (worker_id == 0) { // Single threaded at the moment.
5088 _timer.reset();
5089 _timer.start();
5090
5091 // Scan all new class loader data objects and new dependencies that were
5092 // introduced during concurrent marking.
5093 ResourceMark rm;
5094 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5095 for (int i = 0; i < array->length(); i++) {
5096 par_mrias_cl.do_class_loader_data(array->at(i));
5097 }
5098
5099 // We don't need to keep track of new CLDs anymore.
5100 ClassLoaderDataGraph::remember_new_clds(false);
5101
5102 _timer.stop();
5103 if (PrintCMSStatistics != 0) {
5104 gclog_or_tty->print_cr(
5105 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5106 worker_id, _timer.seconds());
5107 }
5108 }
5109
5110 // ---------- dirty klass scanning ----------
5111 if (worker_id == 0) { // Single threaded at the moment.
5112 _timer.reset();
5113 _timer.start();
5114
5115 // Scan all classes that was dirtied during the concurrent marking phase.
5116 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5117 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5118
5119 _timer.stop();
5120 if (PrintCMSStatistics != 0) {
5121 gclog_or_tty->print_cr(
5122 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5123 worker_id, _timer.seconds());
5124 }
5125 }
5126
5127 // We might have added oops to ClassLoaderData::_handles during the
5128 // concurrent marking phase. These oops point to newly allocated objects
5129 // that are guaranteed to be kept alive. Either by the direct allocation
5130 // code, or when the young collector processes the roots. Hence,
5131 // we don't have to revisit the _handles block during the remark phase.
5132
5133 // ---------- rescan dirty cards ------------
5134 _timer.reset();
5135 _timer.start();
5136
5137 // Do the rescan tasks for each of the two spaces
5138 // (cms_space) in turn.
5139 // "worker_id" is passed to select the task_queue for "worker_id"
5140 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5141 _timer.stop();
5142 if (PrintCMSStatistics != 0) {
5143 gclog_or_tty->print_cr(
5144 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5145 worker_id, _timer.seconds());
5146 }
5147
5148 // ---------- steal work from other threads ...
5149 // ---------- ... and drain overflow list.
5150 _timer.reset();
5151 _timer.start();
5152 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5153 _timer.stop();
5154 if (PrintCMSStatistics != 0) {
5155 gclog_or_tty->print_cr(
5156 "Finished work stealing in %dth thread: %3.3f sec",
5157 worker_id, _timer.seconds());
5158 }
5159 }
5160
5161 // Note that parameter "i" is not used.
5162 void
5163 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5164 OopsInGenClosure* cl, ContiguousSpace* space,
5165 HeapWord** chunk_array, size_t chunk_top) {
5166 // Until all tasks completed:
5167 // . claim an unclaimed task
5168 // . compute region boundaries corresponding to task claimed
5169 // using chunk_array
5170 // . par_oop_iterate(cl) over that region
5171
5172 ResourceMark rm;
5173 HandleMark hm;
5174
5175 SequentialSubTasksDone* pst = space->par_seq_tasks();
5176
5177 uint nth_task = 0;
5178 uint n_tasks = pst->n_tasks();
5179
5180 if (n_tasks > 0) {
5181 assert(pst->valid(), "Uninitialized use?");
5182 HeapWord *start, *end;
5183 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5184 // We claimed task # nth_task; compute its boundaries.
5185 if (chunk_top == 0) { // no samples were taken
5186 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
5187 start = space->bottom();
5188 end = space->top();
5189 } else if (nth_task == 0) {
5190 start = space->bottom();
5191 end = chunk_array[nth_task];
5192 } else if (nth_task < (uint)chunk_top) {
5193 assert(nth_task >= 1, "Control point invariant");
5194 start = chunk_array[nth_task - 1];
5195 end = chunk_array[nth_task];
5196 } else {
5197 assert(nth_task == (uint)chunk_top, "Control point invariant");
5198 start = chunk_array[chunk_top - 1];
5199 end = space->top();
5200 }
5201 MemRegion mr(start, end);
5202 // Verify that mr is in space
5203 assert(mr.is_empty() || space->used_region().contains(mr),
5204 "Should be in space");
5205 // Verify that "start" is an object boundary
5206 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5207 "Should be an oop");
5208 space->par_oop_iterate(mr, cl);
5209 }
5210 pst->all_tasks_completed();
5211 }
5212 }
5213
5214 void
5215 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5216 CompactibleFreeListSpace* sp, int i,
5217 Par_MarkRefsIntoAndScanClosure* cl) {
5218 // Until all tasks completed:
5219 // . claim an unclaimed task
5220 // . compute region boundaries corresponding to task claimed
5221 // . transfer dirty bits ct->mut for that region
5222 // . apply rescanclosure to dirty mut bits for that region
5223
5224 ResourceMark rm;
5225 HandleMark hm;
5226
5227 OopTaskQueue* work_q = work_queue(i);
5228 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5229 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5230 // CAUTION: This closure has state that persists across calls to
5231 // the work method dirty_range_iterate_clear() in that it has
5232 // embedded in it a (subtype of) UpwardsObjectClosure. The
5233 // use of that state in the embedded UpwardsObjectClosure instance
5234 // assumes that the cards are always iterated (even if in parallel
5235 // by several threads) in monotonically increasing order per each
5236 // thread. This is true of the implementation below which picks
5237 // card ranges (chunks) in monotonically increasing order globally
5238 // and, a-fortiori, in monotonically increasing order per thread
5239 // (the latter order being a subsequence of the former).
5240 // If the work code below is ever reorganized into a more chaotic
5241 // work-partitioning form than the current "sequential tasks"
5242 // paradigm, the use of that persistent state will have to be
5243 // revisited and modified appropriately. See also related
5244 // bug 4756801 work on which should examine this code to make
5245 // sure that the changes there do not run counter to the
5246 // assumptions made here and necessary for correctness and
5247 // efficiency. Note also that this code might yield inefficient
5248 // behavior in the case of very large objects that span one or
5249 // more work chunks. Such objects would potentially be scanned
5250 // several times redundantly. Work on 4756801 should try and
5251 // address that performance anomaly if at all possible. XXX
5252 MemRegion full_span = _collector->_span;
5253 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5254 MarkFromDirtyCardsClosure
5255 greyRescanClosure(_collector, full_span, // entire span of interest
5256 sp, bm, work_q, cl);
5257
5258 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5259 assert(pst->valid(), "Uninitialized use?");
5260 uint nth_task = 0;
5261 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5262 MemRegion span = sp->used_region();
5263 HeapWord* start_addr = span.start();
5264 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5265 alignment);
5266 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5267 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5268 start_addr, "Check alignment");
5269 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5270 chunk_size, "Check alignment");
5271
5272 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5273 // Having claimed the nth_task, compute corresponding mem-region,
5274 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5275 // The alignment restriction ensures that we do not need any
5276 // synchronization with other gang-workers while setting or
5277 // clearing bits in thus chunk of the MUT.
5278 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5279 start_addr + (nth_task+1)*chunk_size);
5280 // The last chunk's end might be way beyond end of the
5281 // used region. In that case pull back appropriately.
5282 if (this_span.end() > end_addr) {
5283 this_span.set_end(end_addr);
5284 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5285 }
5286 // Iterate over the dirty cards covering this chunk, marking them
5287 // precleaned, and setting the corresponding bits in the mod union
5288 // table. Since we have been careful to partition at Card and MUT-word
5289 // boundaries no synchronization is needed between parallel threads.
5290 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5291 &modUnionClosure);
5292
5293 // Having transferred these marks into the modUnionTable,
5294 // rescan the marked objects on the dirty cards in the modUnionTable.
5295 // Even if this is at a synchronous collection, the initial marking
5296 // may have been done during an asynchronous collection so there
5297 // may be dirty bits in the mod-union table.
5298 _collector->_modUnionTable.dirty_range_iterate_clear(
5299 this_span, &greyRescanClosure);
5300 _collector->_modUnionTable.verifyNoOneBitsInRange(
5301 this_span.start(),
5302 this_span.end());
5303 }
5304 pst->all_tasks_completed(); // declare that i am done
5305 }
5306
5307 // . see if we can share work_queues with ParNew? XXX
5308 void
5309 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5310 int* seed) {
5311 OopTaskQueue* work_q = work_queue(i);
5312 NOT_PRODUCT(int num_steals = 0;)
5313 oop obj_to_scan;
5314 CMSBitMap* bm = &(_collector->_markBitMap);
5315
5316 while (true) {
5317 // Completely finish any left over work from (an) earlier round(s)
5318 cl->trim_queue(0);
5319 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5320 (size_t)ParGCDesiredObjsFromOverflowList);
5321 // Now check if there's any work in the overflow list
5322 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5323 // only affects the number of attempts made to get work from the
5324 // overflow list and does not affect the number of workers. Just
5325 // pass ParallelGCThreads so this behavior is unchanged.
5326 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5327 work_q,
5328 ParallelGCThreads)) {
5329 // found something in global overflow list;
5330 // not yet ready to go stealing work from others.
5331 // We'd like to assert(work_q->size() != 0, ...)
5332 // because we just took work from the overflow list,
5333 // but of course we can't since all of that could have
5334 // been already stolen from us.
5335 // "He giveth and He taketh away."
5336 continue;
5337 }
5338 // Verify that we have no work before we resort to stealing
5339 assert(work_q->size() == 0, "Have work, shouldn't steal");
5340 // Try to steal from other queues that have work
5341 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5342 NOT_PRODUCT(num_steals++;)
5343 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5344 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5345 // Do scanning work
5346 obj_to_scan->oop_iterate(cl);
5347 // Loop around, finish this work, and try to steal some more
5348 } else if (terminator()->offer_termination()) {
5349 break; // nirvana from the infinite cycle
5350 }
5351 }
5352 NOT_PRODUCT(
5353 if (PrintCMSStatistics != 0) {
5354 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5355 }
5356 )
5357 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5358 "Else our work is not yet done");
5359 }
5360
5361 // Record object boundaries in _eden_chunk_array by sampling the eden
5362 // top in the slow-path eden object allocation code path and record
5363 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5364 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5365 // sampling in sample_eden() that activates during the part of the
5366 // preclean phase.
5367 void CMSCollector::sample_eden_chunk() {
5368 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5369 if (_eden_chunk_lock->try_lock()) {
5370 // Record a sample. This is the critical section. The contents
5371 // of the _eden_chunk_array have to be non-decreasing in the
5372 // address order.
5373 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5374 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5375 "Unexpected state of Eden");
5376 if (_eden_chunk_index == 0 ||
5377 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5378 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5379 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5380 _eden_chunk_index++; // commit sample
5381 }
5382 _eden_chunk_lock->unlock();
5383 }
5384 }
5385 }
5386
5387 // Return a thread-local PLAB recording array, as appropriate.
5388 void* CMSCollector::get_data_recorder(int thr_num) {
5389 if (_survivor_plab_array != NULL &&
5390 (CMSPLABRecordAlways ||
5391 (_collectorState > Marking && _collectorState < FinalMarking))) {
5392 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5393 ChunkArray* ca = &_survivor_plab_array[thr_num];
5394 ca->reset(); // clear it so that fresh data is recorded
5395 return (void*) ca;
5396 } else {
5397 return NULL;
5398 }
5399 }
5400
5401 // Reset all the thread-local PLAB recording arrays
5402 void CMSCollector::reset_survivor_plab_arrays() {
5403 for (uint i = 0; i < ParallelGCThreads; i++) {
5404 _survivor_plab_array[i].reset();
5405 }
5406 }
5407
5408 // Merge the per-thread plab arrays into the global survivor chunk
5409 // array which will provide the partitioning of the survivor space
5410 // for CMS initial scan and rescan.
5411 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5412 int no_of_gc_threads) {
5413 assert(_survivor_plab_array != NULL, "Error");
5414 assert(_survivor_chunk_array != NULL, "Error");
5415 assert(_collectorState == FinalMarking ||
5416 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5417 for (int j = 0; j < no_of_gc_threads; j++) {
5418 _cursor[j] = 0;
5419 }
5420 HeapWord* top = surv->top();
5421 size_t i;
5422 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5423 HeapWord* min_val = top; // Higher than any PLAB address
5424 uint min_tid = 0; // position of min_val this round
5425 for (int j = 0; j < no_of_gc_threads; j++) {
5426 ChunkArray* cur_sca = &_survivor_plab_array[j];
5427 if (_cursor[j] == cur_sca->end()) {
5428 continue;
5429 }
5430 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5431 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5432 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5433 if (cur_val < min_val) {
5434 min_tid = j;
5435 min_val = cur_val;
5436 } else {
5437 assert(cur_val < top, "All recorded addresses should be less");
5438 }
5439 }
5440 // At this point min_val and min_tid are respectively
5441 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5442 // and the thread (j) that witnesses that address.
5443 // We record this address in the _survivor_chunk_array[i]
5444 // and increment _cursor[min_tid] prior to the next round i.
5445 if (min_val == top) {
5446 break;
5447 }
5448 _survivor_chunk_array[i] = min_val;
5449 _cursor[min_tid]++;
5450 }
5451 // We are all done; record the size of the _survivor_chunk_array
5452 _survivor_chunk_index = i; // exclusive: [0, i)
5453 if (PrintCMSStatistics > 0) {
5454 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5455 }
5456 // Verify that we used up all the recorded entries
5457 #ifdef ASSERT
5458 size_t total = 0;
5459 for (int j = 0; j < no_of_gc_threads; j++) {
5460 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5461 total += _cursor[j];
5462 }
5463 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5464 // Check that the merged array is in sorted order
5465 if (total > 0) {
5466 for (size_t i = 0; i < total - 1; i++) {
5467 if (PrintCMSStatistics > 0) {
5468 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5469 i, _survivor_chunk_array[i]);
5470 }
5471 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5472 "Not sorted");
5473 }
5474 }
5475 #endif // ASSERT
5476 }
5477
5478 // Set up the space's par_seq_tasks structure for work claiming
5479 // for parallel initial scan and rescan of young gen.
5480 // See ParRescanTask where this is currently used.
5481 void
5482 CMSCollector::
5483 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5484 assert(n_threads > 0, "Unexpected n_threads argument");
5485 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5486
5487 // Eden space
5488 if (!dng->eden()->is_empty()) {
5489 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5490 assert(!pst->valid(), "Clobbering existing data?");
5491 // Each valid entry in [0, _eden_chunk_index) represents a task.
5492 size_t n_tasks = _eden_chunk_index + 1;
5493 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5494 // Sets the condition for completion of the subtask (how many threads
5495 // need to finish in order to be done).
5496 pst->set_n_threads(n_threads);
5497 pst->set_n_tasks((int)n_tasks);
5498 }
5499
5500 // Merge the survivor plab arrays into _survivor_chunk_array
5501 if (_survivor_plab_array != NULL) {
5502 merge_survivor_plab_arrays(dng->from(), n_threads);
5503 } else {
5504 assert(_survivor_chunk_index == 0, "Error");
5505 }
5506
5507 // To space
5508 {
5509 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5510 assert(!pst->valid(), "Clobbering existing data?");
5511 // Sets the condition for completion of the subtask (how many threads
5512 // need to finish in order to be done).
5513 pst->set_n_threads(n_threads);
5514 pst->set_n_tasks(1);
5515 assert(pst->valid(), "Error");
5516 }
5517
5518 // From space
5519 {
5520 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5521 assert(!pst->valid(), "Clobbering existing data?");
5522 size_t n_tasks = _survivor_chunk_index + 1;
5523 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5524 // Sets the condition for completion of the subtask (how many threads
5525 // need to finish in order to be done).
5526 pst->set_n_threads(n_threads);
5527 pst->set_n_tasks((int)n_tasks);
5528 assert(pst->valid(), "Error");
5529 }
5530 }
5531
5532 // Parallel version of remark
5533 void CMSCollector::do_remark_parallel() {
5534 GenCollectedHeap* gch = GenCollectedHeap::heap();
5535 FlexibleWorkGang* workers = gch->workers();
5536 assert(workers != NULL, "Need parallel worker threads.");
5537 // Choose to use the number of GC workers most recently set
5538 // into "active_workers". If active_workers is not set, set it
5539 // to ParallelGCThreads.
5540 int n_workers = workers->active_workers();
5541 if (n_workers == 0) {
5542 assert(n_workers > 0, "Should have been set during scavenge");
5543 n_workers = ParallelGCThreads;
5544 workers->set_active_workers(n_workers);
5545 }
5546 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5547
5548 CMSParRemarkTask tsk(this,
5549 cms_space,
5550 n_workers, workers, task_queues());
5551
5552 // Set up for parallel process_roots work.
5553 gch->set_par_threads(n_workers);
5554 // We won't be iterating over the cards in the card table updating
5555 // the younger_gen cards, so we shouldn't call the following else
5556 // the verification code as well as subsequent younger_refs_iterate
5557 // code would get confused. XXX
5558 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5559
5560 // The young gen rescan work will not be done as part of
5561 // process_roots (which currently doesn't know how to
5562 // parallelize such a scan), but rather will be broken up into
5563 // a set of parallel tasks (via the sampling that the [abortable]
5564 // preclean phase did of eden, plus the [two] tasks of
5565 // scanning the [two] survivor spaces. Further fine-grain
5566 // parallelization of the scanning of the survivor spaces
5567 // themselves, and of precleaning of the younger gen itself
5568 // is deferred to the future.
5569 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5570
5571 // The dirty card rescan work is broken up into a "sequence"
5572 // of parallel tasks (per constituent space) that are dynamically
5573 // claimed by the parallel threads.
5574 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5575
5576 // It turns out that even when we're using 1 thread, doing the work in a
5577 // separate thread causes wide variance in run times. We can't help this
5578 // in the multi-threaded case, but we special-case n=1 here to get
5579 // repeatable measurements of the 1-thread overhead of the parallel code.
5580 if (n_workers > 1) {
5581 // Make refs discovery MT-safe, if it isn't already: it may not
5582 // necessarily be so, since it's possible that we are doing
5583 // ST marking.
5584 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5585 GenCollectedHeap::StrongRootsScope srs(gch);
5586 workers->run_task(&tsk);
5587 } else {
5588 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5589 GenCollectedHeap::StrongRootsScope srs(gch);
5590 tsk.work(0);
5591 }
5592
5593 gch->set_par_threads(0); // 0 ==> non-parallel.
5594 // restore, single-threaded for now, any preserved marks
5595 // as a result of work_q overflow
5596 restore_preserved_marks_if_any();
5597 }
5598
5599 // Non-parallel version of remark
5600 void CMSCollector::do_remark_non_parallel() {
5601 ResourceMark rm;
5602 HandleMark hm;
5603 GenCollectedHeap* gch = GenCollectedHeap::heap();
5604 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5605
5606 MarkRefsIntoAndScanClosure
5607 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5608 &_markStack, this,
5609 false /* should_yield */, false /* not precleaning */);
5610 MarkFromDirtyCardsClosure
5611 markFromDirtyCardsClosure(this, _span,
5612 NULL, // space is set further below
5613 &_markBitMap, &_markStack, &mrias_cl);
5614 {
5615 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5616 // Iterate over the dirty cards, setting the corresponding bits in the
5617 // mod union table.
5618 {
5619 ModUnionClosure modUnionClosure(&_modUnionTable);
5620 _ct->ct_bs()->dirty_card_iterate(
5621 _cmsGen->used_region(),
5622 &modUnionClosure);
5623 }
5624 // Having transferred these marks into the modUnionTable, we just need
5625 // to rescan the marked objects on the dirty cards in the modUnionTable.
5626 // The initial marking may have been done during an asynchronous
5627 // collection so there may be dirty bits in the mod-union table.
5628 const int alignment =
5629 CardTableModRefBS::card_size * BitsPerWord;
5630 {
5631 // ... First handle dirty cards in CMS gen
5632 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5633 MemRegion ur = _cmsGen->used_region();
5634 HeapWord* lb = ur.start();
5635 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5636 MemRegion cms_span(lb, ub);
5637 _modUnionTable.dirty_range_iterate_clear(cms_span,
5638 &markFromDirtyCardsClosure);
5639 verify_work_stacks_empty();
5640 if (PrintCMSStatistics != 0) {
5641 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5642 markFromDirtyCardsClosure.num_dirty_cards());
5643 }
5644 }
5645 }
5646 if (VerifyDuringGC &&
5647 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5648 HandleMark hm; // Discard invalid handles created during verification
5649 Universe::verify();
5650 }
5651 {
5652 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5653
5654 verify_work_stacks_empty();
5655
5656 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5657 GenCollectedHeap::StrongRootsScope srs(gch);
5658
5659 gch->gen_process_roots(_cmsGen->level(),
5660 true, // younger gens as roots
5661 false, // use the local StrongRootsScope
5662 SharedHeap::ScanningOption(roots_scanning_options()),
5663 should_unload_classes(),
5664 &mrias_cl,
5665 NULL,
5666 NULL); // The dirty klasses will be handled below
5667
5668 assert(should_unload_classes()
5669 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5670 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5671 }
5672
5673 {
5674 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5675
5676 verify_work_stacks_empty();
5677
5678 // Scan all class loader data objects that might have been introduced
5679 // during concurrent marking.
5680 ResourceMark rm;
5681 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5682 for (int i = 0; i < array->length(); i++) {
5683 mrias_cl.do_class_loader_data(array->at(i));
5684 }
5685
5686 // We don't need to keep track of new CLDs anymore.
5687 ClassLoaderDataGraph::remember_new_clds(false);
5688
5689 verify_work_stacks_empty();
5690 }
5691
5692 {
5693 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5694
5695 verify_work_stacks_empty();
5696
5697 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5698 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5699
5700 verify_work_stacks_empty();
5701 }
5702
5703 // We might have added oops to ClassLoaderData::_handles during the
5704 // concurrent marking phase. These oops point to newly allocated objects
5705 // that are guaranteed to be kept alive. Either by the direct allocation
5706 // code, or when the young collector processes the roots. Hence,
5707 // we don't have to revisit the _handles block during the remark phase.
5708
5709 verify_work_stacks_empty();
5710 // Restore evacuated mark words, if any, used for overflow list links
5711 if (!CMSOverflowEarlyRestoration) {
5712 restore_preserved_marks_if_any();
5713 }
5714 verify_overflow_empty();
5715 }
5716
5717 ////////////////////////////////////////////////////////
5718 // Parallel Reference Processing Task Proxy Class
5719 ////////////////////////////////////////////////////////
5720 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5721 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5722 CMSCollector* _collector;
5723 CMSBitMap* _mark_bit_map;
5724 const MemRegion _span;
5725 ProcessTask& _task;
5726
5727 public:
5728 CMSRefProcTaskProxy(ProcessTask& task,
5729 CMSCollector* collector,
5730 const MemRegion& span,
5731 CMSBitMap* mark_bit_map,
5732 AbstractWorkGang* workers,
5733 OopTaskQueueSet* task_queues):
5734 // XXX Should superclass AGTWOQ also know about AWG since it knows
5735 // about the task_queues used by the AWG? Then it could initialize
5736 // the terminator() object. See 6984287. The set_for_termination()
5737 // below is a temporary band-aid for the regression in 6984287.
5738 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5739 task_queues),
5740 _task(task),
5741 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5742 {
5743 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5744 "Inconsistency in _span");
5745 set_for_termination(workers->active_workers());
5746 }
5747
5748 OopTaskQueueSet* task_queues() { return queues(); }
5749
5750 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5751
5752 void do_work_steal(int i,
5753 CMSParDrainMarkingStackClosure* drain,
5754 CMSParKeepAliveClosure* keep_alive,
5755 int* seed);
5756
5757 virtual void work(uint worker_id);
5758 };
5759
5760 void CMSRefProcTaskProxy::work(uint worker_id) {
5761 ResourceMark rm;
5762 HandleMark hm;
5763 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5764 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5765 _mark_bit_map,
5766 work_queue(worker_id));
5767 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5768 _mark_bit_map,
5769 work_queue(worker_id));
5770 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5771 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5772 if (_task.marks_oops_alive()) {
5773 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5774 _collector->hash_seed(worker_id));
5775 }
5776 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5777 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5778 }
5779
5780 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5781 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5782 EnqueueTask& _task;
5783
5784 public:
5785 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5786 : AbstractGangTask("Enqueue reference objects in parallel"),
5787 _task(task)
5788 { }
5789
5790 virtual void work(uint worker_id)
5791 {
5792 _task.work(worker_id);
5793 }
5794 };
5795
5796 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5797 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5798 _span(span),
5799 _bit_map(bit_map),
5800 _work_queue(work_queue),
5801 _mark_and_push(collector, span, bit_map, work_queue),
5802 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5803 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5804 { }
5805
5806 // . see if we can share work_queues with ParNew? XXX
5807 void CMSRefProcTaskProxy::do_work_steal(int i,
5808 CMSParDrainMarkingStackClosure* drain,
5809 CMSParKeepAliveClosure* keep_alive,
5810 int* seed) {
5811 OopTaskQueue* work_q = work_queue(i);
5812 NOT_PRODUCT(int num_steals = 0;)
5813 oop obj_to_scan;
5814
5815 while (true) {
5816 // Completely finish any left over work from (an) earlier round(s)
5817 drain->trim_queue(0);
5818 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5819 (size_t)ParGCDesiredObjsFromOverflowList);
5820 // Now check if there's any work in the overflow list
5821 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5822 // only affects the number of attempts made to get work from the
5823 // overflow list and does not affect the number of workers. Just
5824 // pass ParallelGCThreads so this behavior is unchanged.
5825 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5826 work_q,
5827 ParallelGCThreads)) {
5828 // Found something in global overflow list;
5829 // not yet ready to go stealing work from others.
5830 // We'd like to assert(work_q->size() != 0, ...)
5831 // because we just took work from the overflow list,
5832 // but of course we can't, since all of that might have
5833 // been already stolen from us.
5834 continue;
5835 }
5836 // Verify that we have no work before we resort to stealing
5837 assert(work_q->size() == 0, "Have work, shouldn't steal");
5838 // Try to steal from other queues that have work
5839 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5840 NOT_PRODUCT(num_steals++;)
5841 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5842 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5843 // Do scanning work
5844 obj_to_scan->oop_iterate(keep_alive);
5845 // Loop around, finish this work, and try to steal some more
5846 } else if (terminator()->offer_termination()) {
5847 break; // nirvana from the infinite cycle
5848 }
5849 }
5850 NOT_PRODUCT(
5851 if (PrintCMSStatistics != 0) {
5852 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5853 }
5854 )
5855 }
5856
5857 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5858 {
5859 GenCollectedHeap* gch = GenCollectedHeap::heap();
5860 FlexibleWorkGang* workers = gch->workers();
5861 assert(workers != NULL, "Need parallel worker threads.");
5862 CMSRefProcTaskProxy rp_task(task, &_collector,
5863 _collector.ref_processor()->span(),
5864 _collector.markBitMap(),
5865 workers, _collector.task_queues());
5866 workers->run_task(&rp_task);
5867 }
5868
5869 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5870 {
5871
5872 GenCollectedHeap* gch = GenCollectedHeap::heap();
5873 FlexibleWorkGang* workers = gch->workers();
5874 assert(workers != NULL, "Need parallel worker threads.");
5875 CMSRefEnqueueTaskProxy enq_task(task);
5876 workers->run_task(&enq_task);
5877 }
5878
5879 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5880
5881 ResourceMark rm;
5882 HandleMark hm;
5883
5884 ReferenceProcessor* rp = ref_processor();
5885 assert(rp->span().equals(_span), "Spans should be equal");
5886 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5887 // Process weak references.
5888 rp->setup_policy(clear_all_soft_refs);
5889 verify_work_stacks_empty();
5890
5891 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5892 &_markStack, false /* !preclean */);
5893 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5894 _span, &_markBitMap, &_markStack,
5895 &cmsKeepAliveClosure, false /* !preclean */);
5896 {
5897 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5898
5899 ReferenceProcessorStats stats;
5900 if (rp->processing_is_mt()) {
5901 // Set the degree of MT here. If the discovery is done MT, there
5902 // may have been a different number of threads doing the discovery
5903 // and a different number of discovered lists may have Ref objects.
5904 // That is OK as long as the Reference lists are balanced (see
5905 // balance_all_queues() and balance_queues()).
5906 GenCollectedHeap* gch = GenCollectedHeap::heap();
5907 int active_workers = ParallelGCThreads;
5908 FlexibleWorkGang* workers = gch->workers();
5909 if (workers != NULL) {
5910 active_workers = workers->active_workers();
5911 // The expectation is that active_workers will have already
5912 // been set to a reasonable value. If it has not been set,
5913 // investigate.
5914 assert(active_workers > 0, "Should have been set during scavenge");
5915 }
5916 rp->set_active_mt_degree(active_workers);
5917 CMSRefProcTaskExecutor task_executor(*this);
5918 stats = rp->process_discovered_references(&_is_alive_closure,
5919 &cmsKeepAliveClosure,
5920 &cmsDrainMarkingStackClosure,
5921 &task_executor,
5922 _gc_timer_cm,
5923 _gc_tracer_cm->gc_id());
5924 } else {
5925 stats = rp->process_discovered_references(&_is_alive_closure,
5926 &cmsKeepAliveClosure,
5927 &cmsDrainMarkingStackClosure,
5928 NULL,
5929 _gc_timer_cm,
5930 _gc_tracer_cm->gc_id());
5931 }
5932 _gc_tracer_cm->report_gc_reference_stats(stats);
5933
5934 }
5935
5936 // This is the point where the entire marking should have completed.
5937 verify_work_stacks_empty();
5938
5939 if (should_unload_classes()) {
5940 {
5941 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5942
5943 // Unload classes and purge the SystemDictionary.
5944 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5945
5946 // Unload nmethods.
5947 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5948
5949 // Prune dead klasses from subklass/sibling/implementor lists.
5950 Klass::clean_weak_klass_links(&_is_alive_closure);
5951 }
5952
5953 {
5954 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5955 // Clean up unreferenced symbols in symbol table.
5956 SymbolTable::unlink();
5957 }
5958
5959 {
5960 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5961 // Delete entries for dead interned strings.
5962 StringTable::unlink(&_is_alive_closure);
5963 }
5964 }
5965
5966
5967 // Restore any preserved marks as a result of mark stack or
5968 // work queue overflow
5969 restore_preserved_marks_if_any(); // done single-threaded for now
5970
5971 rp->set_enqueuing_is_done(true);
5972 if (rp->processing_is_mt()) {
5973 rp->balance_all_queues();
5974 CMSRefProcTaskExecutor task_executor(*this);
5975 rp->enqueue_discovered_references(&task_executor);
5976 } else {
5977 rp->enqueue_discovered_references(NULL);
5978 }
5979 rp->verify_no_references_recorded();
5980 assert(!rp->discovery_enabled(), "should have been disabled");
5981 }
5982
5983 #ifndef PRODUCT
5984 void CMSCollector::check_correct_thread_executing() {
5985 Thread* t = Thread::current();
5986 // Only the VM thread or the CMS thread should be here.
5987 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5988 "Unexpected thread type");
5989 // If this is the vm thread, the foreground process
5990 // should not be waiting. Note that _foregroundGCIsActive is
5991 // true while the foreground collector is waiting.
5992 if (_foregroundGCShouldWait) {
5993 // We cannot be the VM thread
5994 assert(t->is_ConcurrentGC_thread(),
5995 "Should be CMS thread");
5996 } else {
5997 // We can be the CMS thread only if we are in a stop-world
5998 // phase of CMS collection.
5999 if (t->is_ConcurrentGC_thread()) {
6000 assert(_collectorState == InitialMarking ||
6001 _collectorState == FinalMarking,
6002 "Should be a stop-world phase");
6003 // The CMS thread should be holding the CMS_token.
6004 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6005 "Potential interference with concurrently "
6006 "executing VM thread");
6007 }
6008 }
6009 }
6010 #endif
6011
6012 void CMSCollector::sweep(bool asynch) {
6013 assert(_collectorState == Sweeping, "just checking");
6014 check_correct_thread_executing();
6015 verify_work_stacks_empty();
6016 verify_overflow_empty();
6017 increment_sweep_count();
6018 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6019
6020 _inter_sweep_timer.stop();
6021 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6022
6023 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6024 _intra_sweep_timer.reset();
6025 _intra_sweep_timer.start();
6026 if (asynch) {
6027 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6028 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6029 // First sweep the old gen
6030 {
6031 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6032 bitMapLock());
6033 sweepWork(_cmsGen, asynch);
6034 }
6035
6036 // Update Universe::_heap_*_at_gc figures.
6037 // We need all the free list locks to make the abstract state
6038 // transition from Sweeping to Resetting. See detailed note
6039 // further below.
6040 {
6041 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6042 // Update heap occupancy information which is used as
6043 // input to soft ref clearing policy at the next gc.
6044 Universe::update_heap_info_at_gc();
6045 _collectorState = Resizing;
6046 }
6047 } else {
6048 // already have needed locks
6049 sweepWork(_cmsGen, asynch);
6050 // Update heap occupancy information which is used as
6051 // input to soft ref clearing policy at the next gc.
6052 Universe::update_heap_info_at_gc();
6053 _collectorState = Resizing;
6054 }
6055 verify_work_stacks_empty();
6056 verify_overflow_empty();
6057
6058 if (should_unload_classes()) {
6059 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6060 // requires that the virtual spaces are stable and not deleted.
6061 ClassLoaderDataGraph::set_should_purge(true);
6062 }
6063
6064 _intra_sweep_timer.stop();
6065 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6066
6067 _inter_sweep_timer.reset();
6068 _inter_sweep_timer.start();
6069
6070 // We need to use a monotonically non-decreasing time in ms
6071 // or we will see time-warp warnings and os::javaTimeMillis()
6072 // does not guarantee monotonicity.
6073 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6074 update_time_of_last_gc(now);
6075
6076 // NOTE on abstract state transitions:
6077 // Mutators allocate-live and/or mark the mod-union table dirty
6078 // based on the state of the collection. The former is done in
6079 // the interval [Marking, Sweeping] and the latter in the interval
6080 // [Marking, Sweeping). Thus the transitions into the Marking state
6081 // and out of the Sweeping state must be synchronously visible
6082 // globally to the mutators.
6083 // The transition into the Marking state happens with the world
6084 // stopped so the mutators will globally see it. Sweeping is
6085 // done asynchronously by the background collector so the transition
6086 // from the Sweeping state to the Resizing state must be done
6087 // under the freelistLock (as is the check for whether to
6088 // allocate-live and whether to dirty the mod-union table).
6089 assert(_collectorState == Resizing, "Change of collector state to"
6090 " Resizing must be done under the freelistLocks (plural)");
6091
6092 // Now that sweeping has been completed, we clear
6093 // the incremental_collection_failed flag,
6094 // thus inviting a younger gen collection to promote into
6095 // this generation. If such a promotion may still fail,
6096 // the flag will be set again when a young collection is
6097 // attempted.
6098 GenCollectedHeap* gch = GenCollectedHeap::heap();
6099 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6100 gch->update_full_collections_completed(_collection_count_start);
6101 }
6102
6103 // FIX ME!!! Looks like this belongs in CFLSpace, with
6104 // CMSGen merely delegating to it.
6105 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6106 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6107 HeapWord* minAddr = _cmsSpace->bottom();
6108 HeapWord* largestAddr =
6109 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6110 if (largestAddr == NULL) {
6111 // The dictionary appears to be empty. In this case
6112 // try to coalesce at the end of the heap.
6113 largestAddr = _cmsSpace->end();
6114 }
6115 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6116 size_t nearLargestOffset =
6117 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6118 if (PrintFLSStatistics != 0) {
6119 gclog_or_tty->print_cr(
6120 "CMS: Large Block: " PTR_FORMAT ";"
6121 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6122 largestAddr,
6123 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6124 }
6125 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6126 }
6127
6128 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6129 return addr >= _cmsSpace->nearLargestChunk();
6130 }
6131
6132 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6133 return _cmsSpace->find_chunk_at_end();
6134 }
6135
6136 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6137 bool full) {
6138 // The next lower level has been collected. Gather any statistics
6139 // that are of interest at this point.
6140 if (!full && (current_level + 1) == level()) {
6141 // Gather statistics on the young generation collection.
6142 collector()->stats().record_gc0_end(used());
6143 }
6144 }
6145
6146 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6147 if (PrintGCDetails && Verbose) {
6148 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6149 }
6150 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6151 _debug_collection_type =
6152 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6153 if (PrintGCDetails && Verbose) {
6154 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6155 }
6156 }
6157
6158 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6159 bool asynch) {
6160 // We iterate over the space(s) underlying this generation,
6161 // checking the mark bit map to see if the bits corresponding
6162 // to specific blocks are marked or not. Blocks that are
6163 // marked are live and are not swept up. All remaining blocks
6164 // are swept up, with coalescing on-the-fly as we sweep up
6165 // contiguous free and/or garbage blocks:
6166 // We need to ensure that the sweeper synchronizes with allocators
6167 // and stop-the-world collectors. In particular, the following
6168 // locks are used:
6169 // . CMS token: if this is held, a stop the world collection cannot occur
6170 // . freelistLock: if this is held no allocation can occur from this
6171 // generation by another thread
6172 // . bitMapLock: if this is held, no other thread can access or update
6173 //
6174
6175 // Note that we need to hold the freelistLock if we use
6176 // block iterate below; else the iterator might go awry if
6177 // a mutator (or promotion) causes block contents to change
6178 // (for instance if the allocator divvies up a block).
6179 // If we hold the free list lock, for all practical purposes
6180 // young generation GC's can't occur (they'll usually need to
6181 // promote), so we might as well prevent all young generation
6182 // GC's while we do a sweeping step. For the same reason, we might
6183 // as well take the bit map lock for the entire duration
6184
6185 // check that we hold the requisite locks
6186 assert(have_cms_token(), "Should hold cms token");
6187 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6188 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6189 "Should possess CMS token to sweep");
6190 assert_lock_strong(gen->freelistLock());
6191 assert_lock_strong(bitMapLock());
6192
6193 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6194 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6195 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6196 _inter_sweep_estimate.padded_average(),
6197 _intra_sweep_estimate.padded_average());
6198 gen->setNearLargestChunk();
6199
6200 {
6201 SweepClosure sweepClosure(this, gen, &_markBitMap,
6202 CMSYield && asynch);
6203 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6204 // We need to free-up/coalesce garbage/blocks from a
6205 // co-terminal free run. This is done in the SweepClosure
6206 // destructor; so, do not remove this scope, else the
6207 // end-of-sweep-census below will be off by a little bit.
6208 }
6209 gen->cmsSpace()->sweep_completed();
6210 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6211 if (should_unload_classes()) { // unloaded classes this cycle,
6212 _concurrent_cycles_since_last_unload = 0; // ... reset count
6213 } else { // did not unload classes,
6214 _concurrent_cycles_since_last_unload++; // ... increment count
6215 }
6216 }
6217
6218 // Reset CMS data structures (for now just the marking bit map)
6219 // preparatory for the next cycle.
6220 void CMSCollector::reset(bool asynch) {
6221 if (asynch) {
6222 CMSTokenSyncWithLocks ts(true, bitMapLock());
6223
6224 // If the state is not "Resetting", the foreground thread
6225 // has done a collection and the resetting.
6226 if (_collectorState != Resetting) {
6227 assert(_collectorState == Idling, "The state should only change"
6228 " because the foreground collector has finished the collection");
6229 return;
6230 }
6231
6232 // Clear the mark bitmap (no grey objects to start with)
6233 // for the next cycle.
6234 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6235 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6236
6237 HeapWord* curAddr = _markBitMap.startWord();
6238 while (curAddr < _markBitMap.endWord()) {
6239 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6240 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6241 _markBitMap.clear_large_range(chunk);
6242 if (ConcurrentMarkSweepThread::should_yield() &&
6243 !foregroundGCIsActive() &&
6244 CMSYield) {
6245 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6246 "CMS thread should hold CMS token");
6247 assert_lock_strong(bitMapLock());
6248 bitMapLock()->unlock();
6249 ConcurrentMarkSweepThread::desynchronize(true);
6250 stopTimer();
6251 if (PrintCMSStatistics != 0) {
6252 incrementYields();
6253 }
6254
6255 // See the comment in coordinator_yield()
6256 for (unsigned i = 0; i < CMSYieldSleepCount &&
6257 ConcurrentMarkSweepThread::should_yield() &&
6258 !CMSCollector::foregroundGCIsActive(); ++i) {
6259 os::sleep(Thread::current(), 1, false);
6260 }
6261
6262 ConcurrentMarkSweepThread::synchronize(true);
6263 bitMapLock()->lock_without_safepoint_check();
6264 startTimer();
6265 }
6266 curAddr = chunk.end();
6267 }
6268 // A successful mostly concurrent collection has been done.
6269 // Because only the full (i.e., concurrent mode failure) collections
6270 // are being measured for gc overhead limits, clean the "near" flag
6271 // and count.
6272 size_policy()->reset_gc_overhead_limit_count();
6273 _collectorState = Idling;
6274 } else {
6275 // already have the lock
6276 assert(_collectorState == Resetting, "just checking");
6277 assert_lock_strong(bitMapLock());
6278 _markBitMap.clear_all();
6279 _collectorState = Idling;
6280 }
6281
6282 NOT_PRODUCT(
6283 if (RotateCMSCollectionTypes) {
6284 _cmsGen->rotate_debug_collection_type();
6285 }
6286 )
6287
6288 register_gc_end();
6289 }
6290
6291 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6292 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6293 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6294 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6295 TraceCollectorStats tcs(counters());
6296
6297 switch (op) {
6298 case CMS_op_checkpointRootsInitial: {
6299 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6300 checkpointRootsInitial(true); // asynch
6301 if (PrintGC) {
6302 _cmsGen->printOccupancy("initial-mark");
6303 }
6304 break;
6305 }
6306 case CMS_op_checkpointRootsFinal: {
6307 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6308 checkpointRootsFinal(true, // asynch
6309 false, // !clear_all_soft_refs
6310 false); // !init_mark_was_synchronous
6311 if (PrintGC) {
6312 _cmsGen->printOccupancy("remark");
6313 }
6314 break;
6315 }
6316 default:
6317 fatal("No such CMS_op");
6318 }
6319 }
6320
6321 #ifndef PRODUCT
6322 size_t const CMSCollector::skip_header_HeapWords() {
6323 return FreeChunk::header_size();
6324 }
6325
6326 // Try and collect here conditions that should hold when
6327 // CMS thread is exiting. The idea is that the foreground GC
6328 // thread should not be blocked if it wants to terminate
6329 // the CMS thread and yet continue to run the VM for a while
6330 // after that.
6331 void CMSCollector::verify_ok_to_terminate() const {
6332 assert(Thread::current()->is_ConcurrentGC_thread(),
6333 "should be called by CMS thread");
6334 assert(!_foregroundGCShouldWait, "should be false");
6335 // We could check here that all the various low-level locks
6336 // are not held by the CMS thread, but that is overkill; see
6337 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6338 // is checked.
6339 }
6340 #endif
6341
6342 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6343 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6344 "missing Printezis mark?");
6345 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6346 size_t size = pointer_delta(nextOneAddr + 1, addr);
6347 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6348 "alignment problem");
6349 assert(size >= 3, "Necessary for Printezis marks to work");
6350 return size;
6351 }
6352
6353 // A variant of the above (block_size_using_printezis_bits()) except
6354 // that we return 0 if the P-bits are not yet set.
6355 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6356 if (_markBitMap.isMarked(addr + 1)) {
6357 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6358 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6359 size_t size = pointer_delta(nextOneAddr + 1, addr);
6360 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6361 "alignment problem");
6362 assert(size >= 3, "Necessary for Printezis marks to work");
6363 return size;
6364 }
6365 return 0;
6366 }
6367
6368 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6369 size_t sz = 0;
6370 oop p = (oop)addr;
6371 if (p->klass_or_null() != NULL) {
6372 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6373 } else {
6374 sz = block_size_using_printezis_bits(addr);
6375 }
6376 assert(sz > 0, "size must be nonzero");
6377 HeapWord* next_block = addr + sz;
6378 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6379 CardTableModRefBS::card_size);
6380 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6381 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6382 "must be different cards");
6383 return next_card;
6384 }
6385
6386
6387 // CMS Bit Map Wrapper /////////////////////////////////////////
6388
6389 // Construct a CMS bit map infrastructure, but don't create the
6390 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6391 // further below.
6392 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6393 _bm(),
6394 _shifter(shifter),
6395 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6396 {
6397 _bmStartWord = 0;
6398 _bmWordSize = 0;
6399 }
6400
6401 bool CMSBitMap::allocate(MemRegion mr) {
6402 _bmStartWord = mr.start();
6403 _bmWordSize = mr.word_size();
6404 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6405 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6406 if (!brs.is_reserved()) {
6407 warning("CMS bit map allocation failure");
6408 return false;
6409 }
6410 // For now we'll just commit all of the bit map up front.
6411 // Later on we'll try to be more parsimonious with swap.
6412 if (!_virtual_space.initialize(brs, brs.size())) {
6413 warning("CMS bit map backing store failure");
6414 return false;
6415 }
6416 assert(_virtual_space.committed_size() == brs.size(),
6417 "didn't reserve backing store for all of CMS bit map?");
6418 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6419 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6420 _bmWordSize, "inconsistency in bit map sizing");
6421 _bm.set_size(_bmWordSize >> _shifter);
6422
6423 // bm.clear(); // can we rely on getting zero'd memory? verify below
6424 assert(isAllClear(),
6425 "Expected zero'd memory from ReservedSpace constructor");
6426 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6427 "consistency check");
6428 return true;
6429 }
6430
6431 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6432 HeapWord *next_addr, *end_addr, *last_addr;
6433 assert_locked();
6434 assert(covers(mr), "out-of-range error");
6435 // XXX assert that start and end are appropriately aligned
6436 for (next_addr = mr.start(), end_addr = mr.end();
6437 next_addr < end_addr; next_addr = last_addr) {
6438 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6439 last_addr = dirty_region.end();
6440 if (!dirty_region.is_empty()) {
6441 cl->do_MemRegion(dirty_region);
6442 } else {
6443 assert(last_addr == end_addr, "program logic");
6444 return;
6445 }
6446 }
6447 }
6448
6449 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6450 _bm.print_on_error(st, prefix);
6451 }
6452
6453 #ifndef PRODUCT
6454 void CMSBitMap::assert_locked() const {
6455 CMSLockVerifier::assert_locked(lock());
6456 }
6457
6458 bool CMSBitMap::covers(MemRegion mr) const {
6459 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6460 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6461 "size inconsistency");
6462 return (mr.start() >= _bmStartWord) &&
6463 (mr.end() <= endWord());
6464 }
6465
6466 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6467 return (start >= _bmStartWord && (start + size) <= endWord());
6468 }
6469
6470 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6471 // verify that there are no 1 bits in the interval [left, right)
6472 FalseBitMapClosure falseBitMapClosure;
6473 iterate(&falseBitMapClosure, left, right);
6474 }
6475
6476 void CMSBitMap::region_invariant(MemRegion mr)
6477 {
6478 assert_locked();
6479 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6480 assert(!mr.is_empty(), "unexpected empty region");
6481 assert(covers(mr), "mr should be covered by bit map");
6482 // convert address range into offset range
6483 size_t start_ofs = heapWordToOffset(mr.start());
6484 // Make sure that end() is appropriately aligned
6485 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6486 (1 << (_shifter+LogHeapWordSize))),
6487 "Misaligned mr.end()");
6488 size_t end_ofs = heapWordToOffset(mr.end());
6489 assert(end_ofs > start_ofs, "Should mark at least one bit");
6490 }
6491
6492 #endif
6493
6494 bool CMSMarkStack::allocate(size_t size) {
6495 // allocate a stack of the requisite depth
6496 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6497 size * sizeof(oop)));
6498 if (!rs.is_reserved()) {
6499 warning("CMSMarkStack allocation failure");
6500 return false;
6501 }
6502 if (!_virtual_space.initialize(rs, rs.size())) {
6503 warning("CMSMarkStack backing store failure");
6504 return false;
6505 }
6506 assert(_virtual_space.committed_size() == rs.size(),
6507 "didn't reserve backing store for all of CMS stack?");
6508 _base = (oop*)(_virtual_space.low());
6509 _index = 0;
6510 _capacity = size;
6511 NOT_PRODUCT(_max_depth = 0);
6512 return true;
6513 }
6514
6515 // XXX FIX ME !!! In the MT case we come in here holding a
6516 // leaf lock. For printing we need to take a further lock
6517 // which has lower rank. We need to recalibrate the two
6518 // lock-ranks involved in order to be able to print the
6519 // messages below. (Or defer the printing to the caller.
6520 // For now we take the expedient path of just disabling the
6521 // messages for the problematic case.)
6522 void CMSMarkStack::expand() {
6523 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6524 if (_capacity == MarkStackSizeMax) {
6525 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6526 // We print a warning message only once per CMS cycle.
6527 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6528 }
6529 return;
6530 }
6531 // Double capacity if possible
6532 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6533 // Do not give up existing stack until we have managed to
6534 // get the double capacity that we desired.
6535 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6536 new_capacity * sizeof(oop)));
6537 if (rs.is_reserved()) {
6538 // Release the backing store associated with old stack
6539 _virtual_space.release();
6540 // Reinitialize virtual space for new stack
6541 if (!_virtual_space.initialize(rs, rs.size())) {
6542 fatal("Not enough swap for expanded marking stack");
6543 }
6544 _base = (oop*)(_virtual_space.low());
6545 _index = 0;
6546 _capacity = new_capacity;
6547 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6548 // Failed to double capacity, continue;
6549 // we print a detail message only once per CMS cycle.
6550 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6551 SIZE_FORMAT"K",
6552 _capacity / K, new_capacity / K);
6553 }
6554 }
6555
6556
6557 // Closures
6558 // XXX: there seems to be a lot of code duplication here;
6559 // should refactor and consolidate common code.
6560
6561 // This closure is used to mark refs into the CMS generation in
6562 // the CMS bit map. Called at the first checkpoint. This closure
6563 // assumes that we do not need to re-mark dirty cards; if the CMS
6564 // generation on which this is used is not an oldest
6565 // generation then this will lose younger_gen cards!
6566
6567 MarkRefsIntoClosure::MarkRefsIntoClosure(
6568 MemRegion span, CMSBitMap* bitMap):
6569 _span(span),
6570 _bitMap(bitMap)
6571 {
6572 assert(_ref_processor == NULL, "deliberately left NULL");
6573 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6574 }
6575
6576 void MarkRefsIntoClosure::do_oop(oop obj) {
6577 // if p points into _span, then mark corresponding bit in _markBitMap
6578 assert(obj->is_oop(), "expected an oop");
6579 HeapWord* addr = (HeapWord*)obj;
6580 if (_span.contains(addr)) {
6581 // this should be made more efficient
6582 _bitMap->mark(addr);
6583 }
6584 }
6585
6586 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6587 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6588
6589 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6590 MemRegion span, CMSBitMap* bitMap):
6591 _span(span),
6592 _bitMap(bitMap)
6593 {
6594 assert(_ref_processor == NULL, "deliberately left NULL");
6595 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6596 }
6597
6598 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6599 // if p points into _span, then mark corresponding bit in _markBitMap
6600 assert(obj->is_oop(), "expected an oop");
6601 HeapWord* addr = (HeapWord*)obj;
6602 if (_span.contains(addr)) {
6603 // this should be made more efficient
6604 _bitMap->par_mark(addr);
6605 }
6606 }
6607
6608 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6609 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6610
6611 // A variant of the above, used for CMS marking verification.
6612 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6613 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6614 _span(span),
6615 _verification_bm(verification_bm),
6616 _cms_bm(cms_bm)
6617 {
6618 assert(_ref_processor == NULL, "deliberately left NULL");
6619 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6620 }
6621
6622 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6623 // if p points into _span, then mark corresponding bit in _markBitMap
6624 assert(obj->is_oop(), "expected an oop");
6625 HeapWord* addr = (HeapWord*)obj;
6626 if (_span.contains(addr)) {
6627 _verification_bm->mark(addr);
6628 if (!_cms_bm->isMarked(addr)) {
6629 oop(addr)->print();
6630 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6631 fatal("... aborting");
6632 }
6633 }
6634 }
6635
6636 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6637 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6638
6639 //////////////////////////////////////////////////
6640 // MarkRefsIntoAndScanClosure
6641 //////////////////////////////////////////////////
6642
6643 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6644 ReferenceProcessor* rp,
6645 CMSBitMap* bit_map,
6646 CMSBitMap* mod_union_table,
6647 CMSMarkStack* mark_stack,
6648 CMSCollector* collector,
6649 bool should_yield,
6650 bool concurrent_precleaning):
6651 _collector(collector),
6652 _span(span),
6653 _bit_map(bit_map),
6654 _mark_stack(mark_stack),
6655 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6656 mark_stack, concurrent_precleaning),
6657 _yield(should_yield),
6658 _concurrent_precleaning(concurrent_precleaning),
6659 _freelistLock(NULL)
6660 {
6661 _ref_processor = rp;
6662 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6663 }
6664
6665 // This closure is used to mark refs into the CMS generation at the
6666 // second (final) checkpoint, and to scan and transitively follow
6667 // the unmarked oops. It is also used during the concurrent precleaning
6668 // phase while scanning objects on dirty cards in the CMS generation.
6669 // The marks are made in the marking bit map and the marking stack is
6670 // used for keeping the (newly) grey objects during the scan.
6671 // The parallel version (Par_...) appears further below.
6672 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6673 if (obj != NULL) {
6674 assert(obj->is_oop(), "expected an oop");
6675 HeapWord* addr = (HeapWord*)obj;
6676 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6677 assert(_collector->overflow_list_is_empty(),
6678 "overflow list should be empty");
6679 if (_span.contains(addr) &&
6680 !_bit_map->isMarked(addr)) {
6681 // mark bit map (object is now grey)
6682 _bit_map->mark(addr);
6683 // push on marking stack (stack should be empty), and drain the
6684 // stack by applying this closure to the oops in the oops popped
6685 // from the stack (i.e. blacken the grey objects)
6686 bool res = _mark_stack->push(obj);
6687 assert(res, "Should have space to push on empty stack");
6688 do {
6689 oop new_oop = _mark_stack->pop();
6690 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6691 assert(_bit_map->isMarked((HeapWord*)new_oop),
6692 "only grey objects on this stack");
6693 // iterate over the oops in this oop, marking and pushing
6694 // the ones in CMS heap (i.e. in _span).
6695 new_oop->oop_iterate(&_pushAndMarkClosure);
6696 // check if it's time to yield
6697 do_yield_check();
6698 } while (!_mark_stack->isEmpty() ||
6699 (!_concurrent_precleaning && take_from_overflow_list()));
6700 // if marking stack is empty, and we are not doing this
6701 // during precleaning, then check the overflow list
6702 }
6703 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6704 assert(_collector->overflow_list_is_empty(),
6705 "overflow list was drained above");
6706 // We could restore evacuated mark words, if any, used for
6707 // overflow list links here because the overflow list is
6708 // provably empty here. That would reduce the maximum
6709 // size requirements for preserved_{oop,mark}_stack.
6710 // But we'll just postpone it until we are all done
6711 // so we can just stream through.
6712 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6713 _collector->restore_preserved_marks_if_any();
6714 assert(_collector->no_preserved_marks(), "No preserved marks");
6715 }
6716 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6717 "All preserved marks should have been restored above");
6718 }
6719 }
6720
6721 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6722 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6723
6724 void MarkRefsIntoAndScanClosure::do_yield_work() {
6725 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6726 "CMS thread should hold CMS token");
6727 assert_lock_strong(_freelistLock);
6728 assert_lock_strong(_bit_map->lock());
6729 // relinquish the free_list_lock and bitMaplock()
6730 _bit_map->lock()->unlock();
6731 _freelistLock->unlock();
6732 ConcurrentMarkSweepThread::desynchronize(true);
6733 _collector->stopTimer();
6734 if (PrintCMSStatistics != 0) {
6735 _collector->incrementYields();
6736 }
6737
6738 // See the comment in coordinator_yield()
6739 for (unsigned i = 0;
6740 i < CMSYieldSleepCount &&
6741 ConcurrentMarkSweepThread::should_yield() &&
6742 !CMSCollector::foregroundGCIsActive();
6743 ++i) {
6744 os::sleep(Thread::current(), 1, false);
6745 }
6746
6747 ConcurrentMarkSweepThread::synchronize(true);
6748 _freelistLock->lock_without_safepoint_check();
6749 _bit_map->lock()->lock_without_safepoint_check();
6750 _collector->startTimer();
6751 }
6752
6753 ///////////////////////////////////////////////////////////
6754 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6755 // MarkRefsIntoAndScanClosure
6756 ///////////////////////////////////////////////////////////
6757 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6758 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6759 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6760 _span(span),
6761 _bit_map(bit_map),
6762 _work_queue(work_queue),
6763 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6764 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6765 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6766 {
6767 _ref_processor = rp;
6768 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6769 }
6770
6771 // This closure is used to mark refs into the CMS generation at the
6772 // second (final) checkpoint, and to scan and transitively follow
6773 // the unmarked oops. The marks are made in the marking bit map and
6774 // the work_queue is used for keeping the (newly) grey objects during
6775 // the scan phase whence they are also available for stealing by parallel
6776 // threads. Since the marking bit map is shared, updates are
6777 // synchronized (via CAS).
6778 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6779 if (obj != NULL) {
6780 // Ignore mark word because this could be an already marked oop
6781 // that may be chained at the end of the overflow list.
6782 assert(obj->is_oop(true), "expected an oop");
6783 HeapWord* addr = (HeapWord*)obj;
6784 if (_span.contains(addr) &&
6785 !_bit_map->isMarked(addr)) {
6786 // mark bit map (object will become grey):
6787 // It is possible for several threads to be
6788 // trying to "claim" this object concurrently;
6789 // the unique thread that succeeds in marking the
6790 // object first will do the subsequent push on
6791 // to the work queue (or overflow list).
6792 if (_bit_map->par_mark(addr)) {
6793 // push on work_queue (which may not be empty), and trim the
6794 // queue to an appropriate length by applying this closure to
6795 // the oops in the oops popped from the stack (i.e. blacken the
6796 // grey objects)
6797 bool res = _work_queue->push(obj);
6798 assert(res, "Low water mark should be less than capacity?");
6799 trim_queue(_low_water_mark);
6800 } // Else, another thread claimed the object
6801 }
6802 }
6803 }
6804
6805 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6806 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6807
6808 // This closure is used to rescan the marked objects on the dirty cards
6809 // in the mod union table and the card table proper.
6810 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6811 oop p, MemRegion mr) {
6812
6813 size_t size = 0;
6814 HeapWord* addr = (HeapWord*)p;
6815 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6816 assert(_span.contains(addr), "we are scanning the CMS generation");
6817 // check if it's time to yield
6818 if (do_yield_check()) {
6819 // We yielded for some foreground stop-world work,
6820 // and we have been asked to abort this ongoing preclean cycle.
6821 return 0;
6822 }
6823 if (_bitMap->isMarked(addr)) {
6824 // it's marked; is it potentially uninitialized?
6825 if (p->klass_or_null() != NULL) {
6826 // an initialized object; ignore mark word in verification below
6827 // since we are running concurrent with mutators
6828 assert(p->is_oop(true), "should be an oop");
6829 if (p->is_objArray()) {
6830 // objArrays are precisely marked; restrict scanning
6831 // to dirty cards only.
6832 size = CompactibleFreeListSpace::adjustObjectSize(
6833 p->oop_iterate(_scanningClosure, mr));
6834 } else {
6835 // A non-array may have been imprecisely marked; we need
6836 // to scan object in its entirety.
6837 size = CompactibleFreeListSpace::adjustObjectSize(
6838 p->oop_iterate(_scanningClosure));
6839 }
6840 #ifdef ASSERT
6841 size_t direct_size =
6842 CompactibleFreeListSpace::adjustObjectSize(p->size());
6843 assert(size == direct_size, "Inconsistency in size");
6844 assert(size >= 3, "Necessary for Printezis marks to work");
6845 if (!_bitMap->isMarked(addr+1)) {
6846 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6847 } else {
6848 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6849 assert(_bitMap->isMarked(addr+size-1),
6850 "inconsistent Printezis mark");
6851 }
6852 #endif // ASSERT
6853 } else {
6854 // An uninitialized object.
6855 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6856 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6857 size = pointer_delta(nextOneAddr + 1, addr);
6858 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6859 "alignment problem");
6860 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6861 // will dirty the card when the klass pointer is installed in the
6862 // object (signaling the completion of initialization).
6863 }
6864 } else {
6865 // Either a not yet marked object or an uninitialized object
6866 if (p->klass_or_null() == NULL) {
6867 // An uninitialized object, skip to the next card, since
6868 // we may not be able to read its P-bits yet.
6869 assert(size == 0, "Initial value");
6870 } else {
6871 // An object not (yet) reached by marking: we merely need to
6872 // compute its size so as to go look at the next block.
6873 assert(p->is_oop(true), "should be an oop");
6874 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6875 }
6876 }
6877 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6878 return size;
6879 }
6880
6881 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6882 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6883 "CMS thread should hold CMS token");
6884 assert_lock_strong(_freelistLock);
6885 assert_lock_strong(_bitMap->lock());
6886 // relinquish the free_list_lock and bitMaplock()
6887 _bitMap->lock()->unlock();
6888 _freelistLock->unlock();
6889 ConcurrentMarkSweepThread::desynchronize(true);
6890 _collector->stopTimer();
6891 if (PrintCMSStatistics != 0) {
6892 _collector->incrementYields();
6893 }
6894
6895 // See the comment in coordinator_yield()
6896 for (unsigned i = 0; i < CMSYieldSleepCount &&
6897 ConcurrentMarkSweepThread::should_yield() &&
6898 !CMSCollector::foregroundGCIsActive(); ++i) {
6899 os::sleep(Thread::current(), 1, false);
6900 }
6901
6902 ConcurrentMarkSweepThread::synchronize(true);
6903 _freelistLock->lock_without_safepoint_check();
6904 _bitMap->lock()->lock_without_safepoint_check();
6905 _collector->startTimer();
6906 }
6907
6908
6909 //////////////////////////////////////////////////////////////////
6910 // SurvivorSpacePrecleanClosure
6911 //////////////////////////////////////////////////////////////////
6912 // This (single-threaded) closure is used to preclean the oops in
6913 // the survivor spaces.
6914 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6915
6916 HeapWord* addr = (HeapWord*)p;
6917 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6918 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6919 assert(p->klass_or_null() != NULL, "object should be initialized");
6920 // an initialized object; ignore mark word in verification below
6921 // since we are running concurrent with mutators
6922 assert(p->is_oop(true), "should be an oop");
6923 // Note that we do not yield while we iterate over
6924 // the interior oops of p, pushing the relevant ones
6925 // on our marking stack.
6926 size_t size = p->oop_iterate(_scanning_closure);
6927 do_yield_check();
6928 // Observe that below, we do not abandon the preclean
6929 // phase as soon as we should; rather we empty the
6930 // marking stack before returning. This is to satisfy
6931 // some existing assertions. In general, it may be a
6932 // good idea to abort immediately and complete the marking
6933 // from the grey objects at a later time.
6934 while (!_mark_stack->isEmpty()) {
6935 oop new_oop = _mark_stack->pop();
6936 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6937 assert(_bit_map->isMarked((HeapWord*)new_oop),
6938 "only grey objects on this stack");
6939 // iterate over the oops in this oop, marking and pushing
6940 // the ones in CMS heap (i.e. in _span).
6941 new_oop->oop_iterate(_scanning_closure);
6942 // check if it's time to yield
6943 do_yield_check();
6944 }
6945 unsigned int after_count =
6946 GenCollectedHeap::heap()->total_collections();
6947 bool abort = (_before_count != after_count) ||
6948 _collector->should_abort_preclean();
6949 return abort ? 0 : size;
6950 }
6951
6952 void SurvivorSpacePrecleanClosure::do_yield_work() {
6953 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6954 "CMS thread should hold CMS token");
6955 assert_lock_strong(_bit_map->lock());
6956 // Relinquish the bit map lock
6957 _bit_map->lock()->unlock();
6958 ConcurrentMarkSweepThread::desynchronize(true);
6959 _collector->stopTimer();
6960 if (PrintCMSStatistics != 0) {
6961 _collector->incrementYields();
6962 }
6963
6964 // See the comment in coordinator_yield()
6965 for (unsigned i = 0; i < CMSYieldSleepCount &&
6966 ConcurrentMarkSweepThread::should_yield() &&
6967 !CMSCollector::foregroundGCIsActive(); ++i) {
6968 os::sleep(Thread::current(), 1, false);
6969 }
6970
6971 ConcurrentMarkSweepThread::synchronize(true);
6972 _bit_map->lock()->lock_without_safepoint_check();
6973 _collector->startTimer();
6974 }
6975
6976 // This closure is used to rescan the marked objects on the dirty cards
6977 // in the mod union table and the card table proper. In the parallel
6978 // case, although the bitMap is shared, we do a single read so the
6979 // isMarked() query is "safe".
6980 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6981 // Ignore mark word because we are running concurrent with mutators
6982 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6983 HeapWord* addr = (HeapWord*)p;
6984 assert(_span.contains(addr), "we are scanning the CMS generation");
6985 bool is_obj_array = false;
6986 #ifdef ASSERT
6987 if (!_parallel) {
6988 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6989 assert(_collector->overflow_list_is_empty(),
6990 "overflow list should be empty");
6991
6992 }
6993 #endif // ASSERT
6994 if (_bit_map->isMarked(addr)) {
6995 // Obj arrays are precisely marked, non-arrays are not;
6996 // so we scan objArrays precisely and non-arrays in their
6997 // entirety.
6998 if (p->is_objArray()) {
6999 is_obj_array = true;
7000 if (_parallel) {
7001 p->oop_iterate(_par_scan_closure, mr);
7002 } else {
7003 p->oop_iterate(_scan_closure, mr);
7004 }
7005 } else {
7006 if (_parallel) {
7007 p->oop_iterate(_par_scan_closure);
7008 } else {
7009 p->oop_iterate(_scan_closure);
7010 }
7011 }
7012 }
7013 #ifdef ASSERT
7014 if (!_parallel) {
7015 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7016 assert(_collector->overflow_list_is_empty(),
7017 "overflow list should be empty");
7018
7019 }
7020 #endif // ASSERT
7021 return is_obj_array;
7022 }
7023
7024 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7025 MemRegion span,
7026 CMSBitMap* bitMap, CMSMarkStack* markStack,
7027 bool should_yield, bool verifying):
7028 _collector(collector),
7029 _span(span),
7030 _bitMap(bitMap),
7031 _mut(&collector->_modUnionTable),
7032 _markStack(markStack),
7033 _yield(should_yield),
7034 _skipBits(0)
7035 {
7036 assert(_markStack->isEmpty(), "stack should be empty");
7037 _finger = _bitMap->startWord();
7038 _threshold = _finger;
7039 assert(_collector->_restart_addr == NULL, "Sanity check");
7040 assert(_span.contains(_finger), "Out of bounds _finger?");
7041 DEBUG_ONLY(_verifying = verifying;)
7042 }
7043
7044 void MarkFromRootsClosure::reset(HeapWord* addr) {
7045 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7046 assert(_span.contains(addr), "Out of bounds _finger?");
7047 _finger = addr;
7048 _threshold = (HeapWord*)round_to(
7049 (intptr_t)_finger, CardTableModRefBS::card_size);
7050 }
7051
7052 // Should revisit to see if this should be restructured for
7053 // greater efficiency.
7054 bool MarkFromRootsClosure::do_bit(size_t offset) {
7055 if (_skipBits > 0) {
7056 _skipBits--;
7057 return true;
7058 }
7059 // convert offset into a HeapWord*
7060 HeapWord* addr = _bitMap->startWord() + offset;
7061 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7062 "address out of range");
7063 assert(_bitMap->isMarked(addr), "tautology");
7064 if (_bitMap->isMarked(addr+1)) {
7065 // this is an allocated but not yet initialized object
7066 assert(_skipBits == 0, "tautology");
7067 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7068 oop p = oop(addr);
7069 if (p->klass_or_null() == NULL) {
7070 DEBUG_ONLY(if (!_verifying) {)
7071 // We re-dirty the cards on which this object lies and increase
7072 // the _threshold so that we'll come back to scan this object
7073 // during the preclean or remark phase. (CMSCleanOnEnter)
7074 if (CMSCleanOnEnter) {
7075 size_t sz = _collector->block_size_using_printezis_bits(addr);
7076 HeapWord* end_card_addr = (HeapWord*)round_to(
7077 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7078 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7079 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7080 // Bump _threshold to end_card_addr; note that
7081 // _threshold cannot possibly exceed end_card_addr, anyhow.
7082 // This prevents future clearing of the card as the scan proceeds
7083 // to the right.
7084 assert(_threshold <= end_card_addr,
7085 "Because we are just scanning into this object");
7086 if (_threshold < end_card_addr) {
7087 _threshold = end_card_addr;
7088 }
7089 if (p->klass_or_null() != NULL) {
7090 // Redirty the range of cards...
7091 _mut->mark_range(redirty_range);
7092 } // ...else the setting of klass will dirty the card anyway.
7093 }
7094 DEBUG_ONLY(})
7095 return true;
7096 }
7097 }
7098 scanOopsInOop(addr);
7099 return true;
7100 }
7101
7102 // We take a break if we've been at this for a while,
7103 // so as to avoid monopolizing the locks involved.
7104 void MarkFromRootsClosure::do_yield_work() {
7105 // First give up the locks, then yield, then re-lock
7106 // We should probably use a constructor/destructor idiom to
7107 // do this unlock/lock or modify the MutexUnlocker class to
7108 // serve our purpose. XXX
7109 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7110 "CMS thread should hold CMS token");
7111 assert_lock_strong(_bitMap->lock());
7112 _bitMap->lock()->unlock();
7113 ConcurrentMarkSweepThread::desynchronize(true);
7114 _collector->stopTimer();
7115 if (PrintCMSStatistics != 0) {
7116 _collector->incrementYields();
7117 }
7118
7119 // See the comment in coordinator_yield()
7120 for (unsigned i = 0; i < CMSYieldSleepCount &&
7121 ConcurrentMarkSweepThread::should_yield() &&
7122 !CMSCollector::foregroundGCIsActive(); ++i) {
7123 os::sleep(Thread::current(), 1, false);
7124 }
7125
7126 ConcurrentMarkSweepThread::synchronize(true);
7127 _bitMap->lock()->lock_without_safepoint_check();
7128 _collector->startTimer();
7129 }
7130
7131 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7132 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7133 assert(_markStack->isEmpty(),
7134 "should drain stack to limit stack usage");
7135 // convert ptr to an oop preparatory to scanning
7136 oop obj = oop(ptr);
7137 // Ignore mark word in verification below, since we
7138 // may be running concurrent with mutators.
7139 assert(obj->is_oop(true), "should be an oop");
7140 assert(_finger <= ptr, "_finger runneth ahead");
7141 // advance the finger to right end of this object
7142 _finger = ptr + obj->size();
7143 assert(_finger > ptr, "we just incremented it above");
7144 // On large heaps, it may take us some time to get through
7145 // the marking phase. During
7146 // this time it's possible that a lot of mutations have
7147 // accumulated in the card table and the mod union table --
7148 // these mutation records are redundant until we have
7149 // actually traced into the corresponding card.
7150 // Here, we check whether advancing the finger would make
7151 // us cross into a new card, and if so clear corresponding
7152 // cards in the MUT (preclean them in the card-table in the
7153 // future).
7154
7155 DEBUG_ONLY(if (!_verifying) {)
7156 // The clean-on-enter optimization is disabled by default,
7157 // until we fix 6178663.
7158 if (CMSCleanOnEnter && (_finger > _threshold)) {
7159 // [_threshold, _finger) represents the interval
7160 // of cards to be cleared in MUT (or precleaned in card table).
7161 // The set of cards to be cleared is all those that overlap
7162 // with the interval [_threshold, _finger); note that
7163 // _threshold is always kept card-aligned but _finger isn't
7164 // always card-aligned.
7165 HeapWord* old_threshold = _threshold;
7166 assert(old_threshold == (HeapWord*)round_to(
7167 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7168 "_threshold should always be card-aligned");
7169 _threshold = (HeapWord*)round_to(
7170 (intptr_t)_finger, CardTableModRefBS::card_size);
7171 MemRegion mr(old_threshold, _threshold);
7172 assert(!mr.is_empty(), "Control point invariant");
7173 assert(_span.contains(mr), "Should clear within span");
7174 _mut->clear_range(mr);
7175 }
7176 DEBUG_ONLY(})
7177 // Note: the finger doesn't advance while we drain
7178 // the stack below.
7179 PushOrMarkClosure pushOrMarkClosure(_collector,
7180 _span, _bitMap, _markStack,
7181 _finger, this);
7182 bool res = _markStack->push(obj);
7183 assert(res, "Empty non-zero size stack should have space for single push");
7184 while (!_markStack->isEmpty()) {
7185 oop new_oop = _markStack->pop();
7186 // Skip verifying header mark word below because we are
7187 // running concurrent with mutators.
7188 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7189 // now scan this oop's oops
7190 new_oop->oop_iterate(&pushOrMarkClosure);
7191 do_yield_check();
7192 }
7193 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7194 }
7195
7196 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7197 CMSCollector* collector, MemRegion span,
7198 CMSBitMap* bit_map,
7199 OopTaskQueue* work_queue,
7200 CMSMarkStack* overflow_stack,
7201 bool should_yield):
7202 _collector(collector),
7203 _whole_span(collector->_span),
7204 _span(span),
7205 _bit_map(bit_map),
7206 _mut(&collector->_modUnionTable),
7207 _work_queue(work_queue),
7208 _overflow_stack(overflow_stack),
7209 _yield(should_yield),
7210 _skip_bits(0),
7211 _task(task)
7212 {
7213 assert(_work_queue->size() == 0, "work_queue should be empty");
7214 _finger = span.start();
7215 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7216 assert(_span.contains(_finger), "Out of bounds _finger?");
7217 }
7218
7219 // Should revisit to see if this should be restructured for
7220 // greater efficiency.
7221 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7222 if (_skip_bits > 0) {
7223 _skip_bits--;
7224 return true;
7225 }
7226 // convert offset into a HeapWord*
7227 HeapWord* addr = _bit_map->startWord() + offset;
7228 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7229 "address out of range");
7230 assert(_bit_map->isMarked(addr), "tautology");
7231 if (_bit_map->isMarked(addr+1)) {
7232 // this is an allocated object that might not yet be initialized
7233 assert(_skip_bits == 0, "tautology");
7234 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7235 oop p = oop(addr);
7236 if (p->klass_or_null() == NULL) {
7237 // in the case of Clean-on-Enter optimization, redirty card
7238 // and avoid clearing card by increasing the threshold.
7239 return true;
7240 }
7241 }
7242 scan_oops_in_oop(addr);
7243 return true;
7244 }
7245
7246 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7247 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7248 // Should we assert that our work queue is empty or
7249 // below some drain limit?
7250 assert(_work_queue->size() == 0,
7251 "should drain stack to limit stack usage");
7252 // convert ptr to an oop preparatory to scanning
7253 oop obj = oop(ptr);
7254 // Ignore mark word in verification below, since we
7255 // may be running concurrent with mutators.
7256 assert(obj->is_oop(true), "should be an oop");
7257 assert(_finger <= ptr, "_finger runneth ahead");
7258 // advance the finger to right end of this object
7259 _finger = ptr + obj->size();
7260 assert(_finger > ptr, "we just incremented it above");
7261 // On large heaps, it may take us some time to get through
7262 // the marking phase. During
7263 // this time it's possible that a lot of mutations have
7264 // accumulated in the card table and the mod union table --
7265 // these mutation records are redundant until we have
7266 // actually traced into the corresponding card.
7267 // Here, we check whether advancing the finger would make
7268 // us cross into a new card, and if so clear corresponding
7269 // cards in the MUT (preclean them in the card-table in the
7270 // future).
7271
7272 // The clean-on-enter optimization is disabled by default,
7273 // until we fix 6178663.
7274 if (CMSCleanOnEnter && (_finger > _threshold)) {
7275 // [_threshold, _finger) represents the interval
7276 // of cards to be cleared in MUT (or precleaned in card table).
7277 // The set of cards to be cleared is all those that overlap
7278 // with the interval [_threshold, _finger); note that
7279 // _threshold is always kept card-aligned but _finger isn't
7280 // always card-aligned.
7281 HeapWord* old_threshold = _threshold;
7282 assert(old_threshold == (HeapWord*)round_to(
7283 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7284 "_threshold should always be card-aligned");
7285 _threshold = (HeapWord*)round_to(
7286 (intptr_t)_finger, CardTableModRefBS::card_size);
7287 MemRegion mr(old_threshold, _threshold);
7288 assert(!mr.is_empty(), "Control point invariant");
7289 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7290 _mut->clear_range(mr);
7291 }
7292
7293 // Note: the local finger doesn't advance while we drain
7294 // the stack below, but the global finger sure can and will.
7295 HeapWord** gfa = _task->global_finger_addr();
7296 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7297 _span, _bit_map,
7298 _work_queue,
7299 _overflow_stack,
7300 _finger,
7301 gfa, this);
7302 bool res = _work_queue->push(obj); // overflow could occur here
7303 assert(res, "Will hold once we use workqueues");
7304 while (true) {
7305 oop new_oop;
7306 if (!_work_queue->pop_local(new_oop)) {
7307 // We emptied our work_queue; check if there's stuff that can
7308 // be gotten from the overflow stack.
7309 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7310 _overflow_stack, _work_queue)) {
7311 do_yield_check();
7312 continue;
7313 } else { // done
7314 break;
7315 }
7316 }
7317 // Skip verifying header mark word below because we are
7318 // running concurrent with mutators.
7319 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7320 // now scan this oop's oops
7321 new_oop->oop_iterate(&pushOrMarkClosure);
7322 do_yield_check();
7323 }
7324 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7325 }
7326
7327 // Yield in response to a request from VM Thread or
7328 // from mutators.
7329 void Par_MarkFromRootsClosure::do_yield_work() {
7330 assert(_task != NULL, "sanity");
7331 _task->yield();
7332 }
7333
7334 // A variant of the above used for verifying CMS marking work.
7335 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7336 MemRegion span,
7337 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7338 CMSMarkStack* mark_stack):
7339 _collector(collector),
7340 _span(span),
7341 _verification_bm(verification_bm),
7342 _cms_bm(cms_bm),
7343 _mark_stack(mark_stack),
7344 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7345 mark_stack)
7346 {
7347 assert(_mark_stack->isEmpty(), "stack should be empty");
7348 _finger = _verification_bm->startWord();
7349 assert(_collector->_restart_addr == NULL, "Sanity check");
7350 assert(_span.contains(_finger), "Out of bounds _finger?");
7351 }
7352
7353 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7354 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7355 assert(_span.contains(addr), "Out of bounds _finger?");
7356 _finger = addr;
7357 }
7358
7359 // Should revisit to see if this should be restructured for
7360 // greater efficiency.
7361 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7362 // convert offset into a HeapWord*
7363 HeapWord* addr = _verification_bm->startWord() + offset;
7364 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7365 "address out of range");
7366 assert(_verification_bm->isMarked(addr), "tautology");
7367 assert(_cms_bm->isMarked(addr), "tautology");
7368
7369 assert(_mark_stack->isEmpty(),
7370 "should drain stack to limit stack usage");
7371 // convert addr to an oop preparatory to scanning
7372 oop obj = oop(addr);
7373 assert(obj->is_oop(), "should be an oop");
7374 assert(_finger <= addr, "_finger runneth ahead");
7375 // advance the finger to right end of this object
7376 _finger = addr + obj->size();
7377 assert(_finger > addr, "we just incremented it above");
7378 // Note: the finger doesn't advance while we drain
7379 // the stack below.
7380 bool res = _mark_stack->push(obj);
7381 assert(res, "Empty non-zero size stack should have space for single push");
7382 while (!_mark_stack->isEmpty()) {
7383 oop new_oop = _mark_stack->pop();
7384 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7385 // now scan this oop's oops
7386 new_oop->oop_iterate(&_pam_verify_closure);
7387 }
7388 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7389 return true;
7390 }
7391
7392 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7393 CMSCollector* collector, MemRegion span,
7394 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7395 CMSMarkStack* mark_stack):
7396 MetadataAwareOopClosure(collector->ref_processor()),
7397 _collector(collector),
7398 _span(span),
7399 _verification_bm(verification_bm),
7400 _cms_bm(cms_bm),
7401 _mark_stack(mark_stack)
7402 { }
7403
7404 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7405 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7406
7407 // Upon stack overflow, we discard (part of) the stack,
7408 // remembering the least address amongst those discarded
7409 // in CMSCollector's _restart_address.
7410 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7411 // Remember the least grey address discarded
7412 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7413 _collector->lower_restart_addr(ra);
7414 _mark_stack->reset(); // discard stack contents
7415 _mark_stack->expand(); // expand the stack if possible
7416 }
7417
7418 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7419 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7420 HeapWord* addr = (HeapWord*)obj;
7421 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7422 // Oop lies in _span and isn't yet grey or black
7423 _verification_bm->mark(addr); // now grey
7424 if (!_cms_bm->isMarked(addr)) {
7425 oop(addr)->print();
7426 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7427 addr);
7428 fatal("... aborting");
7429 }
7430
7431 if (!_mark_stack->push(obj)) { // stack overflow
7432 if (PrintCMSStatistics != 0) {
7433 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7434 SIZE_FORMAT, _mark_stack->capacity());
7435 }
7436 assert(_mark_stack->isFull(), "Else push should have succeeded");
7437 handle_stack_overflow(addr);
7438 }
7439 // anything including and to the right of _finger
7440 // will be scanned as we iterate over the remainder of the
7441 // bit map
7442 }
7443 }
7444
7445 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7446 MemRegion span,
7447 CMSBitMap* bitMap, CMSMarkStack* markStack,
7448 HeapWord* finger, MarkFromRootsClosure* parent) :
7449 MetadataAwareOopClosure(collector->ref_processor()),
7450 _collector(collector),
7451 _span(span),
7452 _bitMap(bitMap),
7453 _markStack(markStack),
7454 _finger(finger),
7455 _parent(parent)
7456 { }
7457
7458 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7459 MemRegion span,
7460 CMSBitMap* bit_map,
7461 OopTaskQueue* work_queue,
7462 CMSMarkStack* overflow_stack,
7463 HeapWord* finger,
7464 HeapWord** global_finger_addr,
7465 Par_MarkFromRootsClosure* parent) :
7466 MetadataAwareOopClosure(collector->ref_processor()),
7467 _collector(collector),
7468 _whole_span(collector->_span),
7469 _span(span),
7470 _bit_map(bit_map),
7471 _work_queue(work_queue),
7472 _overflow_stack(overflow_stack),
7473 _finger(finger),
7474 _global_finger_addr(global_finger_addr),
7475 _parent(parent)
7476 { }
7477
7478 // Assumes thread-safe access by callers, who are
7479 // responsible for mutual exclusion.
7480 void CMSCollector::lower_restart_addr(HeapWord* low) {
7481 assert(_span.contains(low), "Out of bounds addr");
7482 if (_restart_addr == NULL) {
7483 _restart_addr = low;
7484 } else {
7485 _restart_addr = MIN2(_restart_addr, low);
7486 }
7487 }
7488
7489 // Upon stack overflow, we discard (part of) the stack,
7490 // remembering the least address amongst those discarded
7491 // in CMSCollector's _restart_address.
7492 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7493 // Remember the least grey address discarded
7494 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7495 _collector->lower_restart_addr(ra);
7496 _markStack->reset(); // discard stack contents
7497 _markStack->expand(); // expand the stack if possible
7498 }
7499
7500 // Upon stack overflow, we discard (part of) the stack,
7501 // remembering the least address amongst those discarded
7502 // in CMSCollector's _restart_address.
7503 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7504 // We need to do this under a mutex to prevent other
7505 // workers from interfering with the work done below.
7506 MutexLockerEx ml(_overflow_stack->par_lock(),
7507 Mutex::_no_safepoint_check_flag);
7508 // Remember the least grey address discarded
7509 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7510 _collector->lower_restart_addr(ra);
7511 _overflow_stack->reset(); // discard stack contents
7512 _overflow_stack->expand(); // expand the stack if possible
7513 }
7514
7515 void PushOrMarkClosure::do_oop(oop obj) {
7516 // Ignore mark word because we are running concurrent with mutators.
7517 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7518 HeapWord* addr = (HeapWord*)obj;
7519 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7520 // Oop lies in _span and isn't yet grey or black
7521 _bitMap->mark(addr); // now grey
7522 if (addr < _finger) {
7523 // the bit map iteration has already either passed, or
7524 // sampled, this bit in the bit map; we'll need to
7525 // use the marking stack to scan this oop's oops.
7526 bool simulate_overflow = false;
7527 NOT_PRODUCT(
7528 if (CMSMarkStackOverflowALot &&
7529 _collector->simulate_overflow()) {
7530 // simulate a stack overflow
7531 simulate_overflow = true;
7532 }
7533 )
7534 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7535 if (PrintCMSStatistics != 0) {
7536 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7537 SIZE_FORMAT, _markStack->capacity());
7538 }
7539 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7540 handle_stack_overflow(addr);
7541 }
7542 }
7543 // anything including and to the right of _finger
7544 // will be scanned as we iterate over the remainder of the
7545 // bit map
7546 do_yield_check();
7547 }
7548 }
7549
7550 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7551 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7552
7553 void Par_PushOrMarkClosure::do_oop(oop obj) {
7554 // Ignore mark word because we are running concurrent with mutators.
7555 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7556 HeapWord* addr = (HeapWord*)obj;
7557 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7558 // Oop lies in _span and isn't yet grey or black
7559 // We read the global_finger (volatile read) strictly after marking oop
7560 bool res = _bit_map->par_mark(addr); // now grey
7561 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7562 // Should we push this marked oop on our stack?
7563 // -- if someone else marked it, nothing to do
7564 // -- if target oop is above global finger nothing to do
7565 // -- if target oop is in chunk and above local finger
7566 // then nothing to do
7567 // -- else push on work queue
7568 if ( !res // someone else marked it, they will deal with it
7569 || (addr >= *gfa) // will be scanned in a later task
7570 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7571 return;
7572 }
7573 // the bit map iteration has already either passed, or
7574 // sampled, this bit in the bit map; we'll need to
7575 // use the marking stack to scan this oop's oops.
7576 bool simulate_overflow = false;
7577 NOT_PRODUCT(
7578 if (CMSMarkStackOverflowALot &&
7579 _collector->simulate_overflow()) {
7580 // simulate a stack overflow
7581 simulate_overflow = true;
7582 }
7583 )
7584 if (simulate_overflow ||
7585 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7586 // stack overflow
7587 if (PrintCMSStatistics != 0) {
7588 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7589 SIZE_FORMAT, _overflow_stack->capacity());
7590 }
7591 // We cannot assert that the overflow stack is full because
7592 // it may have been emptied since.
7593 assert(simulate_overflow ||
7594 _work_queue->size() == _work_queue->max_elems(),
7595 "Else push should have succeeded");
7596 handle_stack_overflow(addr);
7597 }
7598 do_yield_check();
7599 }
7600 }
7601
7602 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7603 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7604
7605 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7606 MemRegion span,
7607 ReferenceProcessor* rp,
7608 CMSBitMap* bit_map,
7609 CMSBitMap* mod_union_table,
7610 CMSMarkStack* mark_stack,
7611 bool concurrent_precleaning):
7612 MetadataAwareOopClosure(rp),
7613 _collector(collector),
7614 _span(span),
7615 _bit_map(bit_map),
7616 _mod_union_table(mod_union_table),
7617 _mark_stack(mark_stack),
7618 _concurrent_precleaning(concurrent_precleaning)
7619 {
7620 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7621 }
7622
7623 // Grey object rescan during pre-cleaning and second checkpoint phases --
7624 // the non-parallel version (the parallel version appears further below.)
7625 void PushAndMarkClosure::do_oop(oop obj) {
7626 // Ignore mark word verification. If during concurrent precleaning,
7627 // the object monitor may be locked. If during the checkpoint
7628 // phases, the object may already have been reached by a different
7629 // path and may be at the end of the global overflow list (so
7630 // the mark word may be NULL).
7631 assert(obj->is_oop_or_null(true /* ignore mark word */),
7632 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7633 HeapWord* addr = (HeapWord*)obj;
7634 // Check if oop points into the CMS generation
7635 // and is not marked
7636 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7637 // a white object ...
7638 _bit_map->mark(addr); // ... now grey
7639 // push on the marking stack (grey set)
7640 bool simulate_overflow = false;
7641 NOT_PRODUCT(
7642 if (CMSMarkStackOverflowALot &&
7643 _collector->simulate_overflow()) {
7644 // simulate a stack overflow
7645 simulate_overflow = true;
7646 }
7647 )
7648 if (simulate_overflow || !_mark_stack->push(obj)) {
7649 if (_concurrent_precleaning) {
7650 // During precleaning we can just dirty the appropriate card(s)
7651 // in the mod union table, thus ensuring that the object remains
7652 // in the grey set and continue. In the case of object arrays
7653 // we need to dirty all of the cards that the object spans,
7654 // since the rescan of object arrays will be limited to the
7655 // dirty cards.
7656 // Note that no one can be interfering with us in this action
7657 // of dirtying the mod union table, so no locking or atomics
7658 // are required.
7659 if (obj->is_objArray()) {
7660 size_t sz = obj->size();
7661 HeapWord* end_card_addr = (HeapWord*)round_to(
7662 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7663 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7664 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7665 _mod_union_table->mark_range(redirty_range);
7666 } else {
7667 _mod_union_table->mark(addr);
7668 }
7669 _collector->_ser_pmc_preclean_ovflw++;
7670 } else {
7671 // During the remark phase, we need to remember this oop
7672 // in the overflow list.
7673 _collector->push_on_overflow_list(obj);
7674 _collector->_ser_pmc_remark_ovflw++;
7675 }
7676 }
7677 }
7678 }
7679
7680 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7681 MemRegion span,
7682 ReferenceProcessor* rp,
7683 CMSBitMap* bit_map,
7684 OopTaskQueue* work_queue):
7685 MetadataAwareOopClosure(rp),
7686 _collector(collector),
7687 _span(span),
7688 _bit_map(bit_map),
7689 _work_queue(work_queue)
7690 {
7691 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7692 }
7693
7694 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7695 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7696
7697 // Grey object rescan during second checkpoint phase --
7698 // the parallel version.
7699 void Par_PushAndMarkClosure::do_oop(oop obj) {
7700 // In the assert below, we ignore the mark word because
7701 // this oop may point to an already visited object that is
7702 // on the overflow stack (in which case the mark word has
7703 // been hijacked for chaining into the overflow stack --
7704 // if this is the last object in the overflow stack then
7705 // its mark word will be NULL). Because this object may
7706 // have been subsequently popped off the global overflow
7707 // stack, and the mark word possibly restored to the prototypical
7708 // value, by the time we get to examined this failing assert in
7709 // the debugger, is_oop_or_null(false) may subsequently start
7710 // to hold.
7711 assert(obj->is_oop_or_null(true),
7712 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7713 HeapWord* addr = (HeapWord*)obj;
7714 // Check if oop points into the CMS generation
7715 // and is not marked
7716 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7717 // a white object ...
7718 // If we manage to "claim" the object, by being the
7719 // first thread to mark it, then we push it on our
7720 // marking stack
7721 if (_bit_map->par_mark(addr)) { // ... now grey
7722 // push on work queue (grey set)
7723 bool simulate_overflow = false;
7724 NOT_PRODUCT(
7725 if (CMSMarkStackOverflowALot &&
7726 _collector->par_simulate_overflow()) {
7727 // simulate a stack overflow
7728 simulate_overflow = true;
7729 }
7730 )
7731 if (simulate_overflow || !_work_queue->push(obj)) {
7732 _collector->par_push_on_overflow_list(obj);
7733 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7734 }
7735 } // Else, some other thread got there first
7736 }
7737 }
7738
7739 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7740 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7741
7742 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7743 Mutex* bml = _collector->bitMapLock();
7744 assert_lock_strong(bml);
7745 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7746 "CMS thread should hold CMS token");
7747
7748 bml->unlock();
7749 ConcurrentMarkSweepThread::desynchronize(true);
7750
7751 _collector->stopTimer();
7752 if (PrintCMSStatistics != 0) {
7753 _collector->incrementYields();
7754 }
7755
7756 // See the comment in coordinator_yield()
7757 for (unsigned i = 0; i < CMSYieldSleepCount &&
7758 ConcurrentMarkSweepThread::should_yield() &&
7759 !CMSCollector::foregroundGCIsActive(); ++i) {
7760 os::sleep(Thread::current(), 1, false);
7761 }
7762
7763 ConcurrentMarkSweepThread::synchronize(true);
7764 bml->lock();
7765
7766 _collector->startTimer();
7767 }
7768
7769 bool CMSPrecleanRefsYieldClosure::should_return() {
7770 if (ConcurrentMarkSweepThread::should_yield()) {
7771 do_yield_work();
7772 }
7773 return _collector->foregroundGCIsActive();
7774 }
7775
7776 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7777 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7778 "mr should be aligned to start at a card boundary");
7779 // We'd like to assert:
7780 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7781 // "mr should be a range of cards");
7782 // However, that would be too strong in one case -- the last
7783 // partition ends at _unallocated_block which, in general, can be
7784 // an arbitrary boundary, not necessarily card aligned.
7785 if (PrintCMSStatistics != 0) {
7786 _num_dirty_cards +=
7787 mr.word_size()/CardTableModRefBS::card_size_in_words;
7788 }
7789 _space->object_iterate_mem(mr, &_scan_cl);
7790 }
7791
7792 SweepClosure::SweepClosure(CMSCollector* collector,
7793 ConcurrentMarkSweepGeneration* g,
7794 CMSBitMap* bitMap, bool should_yield) :
7795 _collector(collector),
7796 _g(g),
7797 _sp(g->cmsSpace()),
7798 _limit(_sp->sweep_limit()),
7799 _freelistLock(_sp->freelistLock()),
7800 _bitMap(bitMap),
7801 _yield(should_yield),
7802 _inFreeRange(false), // No free range at beginning of sweep
7803 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7804 _lastFreeRangeCoalesced(false),
7805 _freeFinger(g->used_region().start())
7806 {
7807 NOT_PRODUCT(
7808 _numObjectsFreed = 0;
7809 _numWordsFreed = 0;
7810 _numObjectsLive = 0;
7811 _numWordsLive = 0;
7812 _numObjectsAlreadyFree = 0;
7813 _numWordsAlreadyFree = 0;
7814 _last_fc = NULL;
7815
7816 _sp->initializeIndexedFreeListArrayReturnedBytes();
7817 _sp->dictionary()->initialize_dict_returned_bytes();
7818 )
7819 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7820 "sweep _limit out of bounds");
7821 if (CMSTraceSweeper) {
7822 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7823 _limit);
7824 }
7825 }
7826
7827 void SweepClosure::print_on(outputStream* st) const {
7828 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7829 _sp->bottom(), _sp->end());
7830 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7831 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7832 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7833 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7834 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7835 }
7836
7837 #ifndef PRODUCT
7838 // Assertion checking only: no useful work in product mode --
7839 // however, if any of the flags below become product flags,
7840 // you may need to review this code to see if it needs to be
7841 // enabled in product mode.
7842 SweepClosure::~SweepClosure() {
7843 assert_lock_strong(_freelistLock);
7844 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7845 "sweep _limit out of bounds");
7846 if (inFreeRange()) {
7847 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7848 print();
7849 ShouldNotReachHere();
7850 }
7851 if (Verbose && PrintGC) {
7852 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7853 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7854 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7855 SIZE_FORMAT" bytes "
7856 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7857 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7858 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7859 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7860 * sizeof(HeapWord);
7861 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7862
7863 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7864 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7865 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7866 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7867 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7868 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7869 indexListReturnedBytes);
7870 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7871 dict_returned_bytes);
7872 }
7873 }
7874 if (CMSTraceSweeper) {
7875 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7876 _limit);
7877 }
7878 }
7879 #endif // PRODUCT
7880
7881 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7882 bool freeRangeInFreeLists) {
7883 if (CMSTraceSweeper) {
7884 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7885 freeFinger, freeRangeInFreeLists);
7886 }
7887 assert(!inFreeRange(), "Trampling existing free range");
7888 set_inFreeRange(true);
7889 set_lastFreeRangeCoalesced(false);
7890
7891 set_freeFinger(freeFinger);
7892 set_freeRangeInFreeLists(freeRangeInFreeLists);
7893 if (CMSTestInFreeList) {
7894 if (freeRangeInFreeLists) {
7895 FreeChunk* fc = (FreeChunk*) freeFinger;
7896 assert(fc->is_free(), "A chunk on the free list should be free.");
7897 assert(fc->size() > 0, "Free range should have a size");
7898 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7899 }
7900 }
7901 }
7902
7903 // Note that the sweeper runs concurrently with mutators. Thus,
7904 // it is possible for direct allocation in this generation to happen
7905 // in the middle of the sweep. Note that the sweeper also coalesces
7906 // contiguous free blocks. Thus, unless the sweeper and the allocator
7907 // synchronize appropriately freshly allocated blocks may get swept up.
7908 // This is accomplished by the sweeper locking the free lists while
7909 // it is sweeping. Thus blocks that are determined to be free are
7910 // indeed free. There is however one additional complication:
7911 // blocks that have been allocated since the final checkpoint and
7912 // mark, will not have been marked and so would be treated as
7913 // unreachable and swept up. To prevent this, the allocator marks
7914 // the bit map when allocating during the sweep phase. This leads,
7915 // however, to a further complication -- objects may have been allocated
7916 // but not yet initialized -- in the sense that the header isn't yet
7917 // installed. The sweeper can not then determine the size of the block
7918 // in order to skip over it. To deal with this case, we use a technique
7919 // (due to Printezis) to encode such uninitialized block sizes in the
7920 // bit map. Since the bit map uses a bit per every HeapWord, but the
7921 // CMS generation has a minimum object size of 3 HeapWords, it follows
7922 // that "normal marks" won't be adjacent in the bit map (there will
7923 // always be at least two 0 bits between successive 1 bits). We make use
7924 // of these "unused" bits to represent uninitialized blocks -- the bit
7925 // corresponding to the start of the uninitialized object and the next
7926 // bit are both set. Finally, a 1 bit marks the end of the object that
7927 // started with the two consecutive 1 bits to indicate its potentially
7928 // uninitialized state.
7929
7930 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7931 FreeChunk* fc = (FreeChunk*)addr;
7932 size_t res;
7933
7934 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7935 // than "addr == _limit" because although _limit was a block boundary when
7936 // we started the sweep, it may no longer be one because heap expansion
7937 // may have caused us to coalesce the block ending at the address _limit
7938 // with a newly expanded chunk (this happens when _limit was set to the
7939 // previous _end of the space), so we may have stepped past _limit:
7940 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7941 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7942 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7943 "sweep _limit out of bounds");
7944 assert(addr < _sp->end(), "addr out of bounds");
7945 // Flush any free range we might be holding as a single
7946 // coalesced chunk to the appropriate free list.
7947 if (inFreeRange()) {
7948 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7949 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7950 flush_cur_free_chunk(freeFinger(),
7951 pointer_delta(addr, freeFinger()));
7952 if (CMSTraceSweeper) {
7953 gclog_or_tty->print("Sweep: last chunk: ");
7954 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7955 "[coalesced:%d]\n",
7956 freeFinger(), pointer_delta(addr, freeFinger()),
7957 lastFreeRangeCoalesced() ? 1 : 0);
7958 }
7959 }
7960
7961 // help the iterator loop finish
7962 return pointer_delta(_sp->end(), addr);
7963 }
7964
7965 assert(addr < _limit, "sweep invariant");
7966 // check if we should yield
7967 do_yield_check(addr);
7968 if (fc->is_free()) {
7969 // Chunk that is already free
7970 res = fc->size();
7971 do_already_free_chunk(fc);
7972 debug_only(_sp->verifyFreeLists());
7973 // If we flush the chunk at hand in lookahead_and_flush()
7974 // and it's coalesced with a preceding chunk, then the
7975 // process of "mangling" the payload of the coalesced block
7976 // will cause erasure of the size information from the
7977 // (erstwhile) header of all the coalesced blocks but the
7978 // first, so the first disjunct in the assert will not hold
7979 // in that specific case (in which case the second disjunct
7980 // will hold).
7981 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7982 "Otherwise the size info doesn't change at this step");
7983 NOT_PRODUCT(
7984 _numObjectsAlreadyFree++;
7985 _numWordsAlreadyFree += res;
7986 )
7987 NOT_PRODUCT(_last_fc = fc;)
7988 } else if (!_bitMap->isMarked(addr)) {
7989 // Chunk is fresh garbage
7990 res = do_garbage_chunk(fc);
7991 debug_only(_sp->verifyFreeLists());
7992 NOT_PRODUCT(
7993 _numObjectsFreed++;
7994 _numWordsFreed += res;
7995 )
7996 } else {
7997 // Chunk that is alive.
7998 res = do_live_chunk(fc);
7999 debug_only(_sp->verifyFreeLists());
8000 NOT_PRODUCT(
8001 _numObjectsLive++;
8002 _numWordsLive += res;
8003 )
8004 }
8005 return res;
8006 }
8007
8008 // For the smart allocation, record following
8009 // split deaths - a free chunk is removed from its free list because
8010 // it is being split into two or more chunks.
8011 // split birth - a free chunk is being added to its free list because
8012 // a larger free chunk has been split and resulted in this free chunk.
8013 // coal death - a free chunk is being removed from its free list because
8014 // it is being coalesced into a large free chunk.
8015 // coal birth - a free chunk is being added to its free list because
8016 // it was created when two or more free chunks where coalesced into
8017 // this free chunk.
8018 //
8019 // These statistics are used to determine the desired number of free
8020 // chunks of a given size. The desired number is chosen to be relative
8021 // to the end of a CMS sweep. The desired number at the end of a sweep
8022 // is the
8023 // count-at-end-of-previous-sweep (an amount that was enough)
8024 // - count-at-beginning-of-current-sweep (the excess)
8025 // + split-births (gains in this size during interval)
8026 // - split-deaths (demands on this size during interval)
8027 // where the interval is from the end of one sweep to the end of the
8028 // next.
8029 //
8030 // When sweeping the sweeper maintains an accumulated chunk which is
8031 // the chunk that is made up of chunks that have been coalesced. That
8032 // will be termed the left-hand chunk. A new chunk of garbage that
8033 // is being considered for coalescing will be referred to as the
8034 // right-hand chunk.
8035 //
8036 // When making a decision on whether to coalesce a right-hand chunk with
8037 // the current left-hand chunk, the current count vs. the desired count
8038 // of the left-hand chunk is considered. Also if the right-hand chunk
8039 // is near the large chunk at the end of the heap (see
8040 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8041 // left-hand chunk is coalesced.
8042 //
8043 // When making a decision about whether to split a chunk, the desired count
8044 // vs. the current count of the candidate to be split is also considered.
8045 // If the candidate is underpopulated (currently fewer chunks than desired)
8046 // a chunk of an overpopulated (currently more chunks than desired) size may
8047 // be chosen. The "hint" associated with a free list, if non-null, points
8048 // to a free list which may be overpopulated.
8049 //
8050
8051 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8052 const size_t size = fc->size();
8053 // Chunks that cannot be coalesced are not in the
8054 // free lists.
8055 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8056 assert(_sp->verify_chunk_in_free_list(fc),
8057 "free chunk should be in free lists");
8058 }
8059 // a chunk that is already free, should not have been
8060 // marked in the bit map
8061 HeapWord* const addr = (HeapWord*) fc;
8062 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8063 // Verify that the bit map has no bits marked between
8064 // addr and purported end of this block.
8065 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8066
8067 // Some chunks cannot be coalesced under any circumstances.
8068 // See the definition of cantCoalesce().
8069 if (!fc->cantCoalesce()) {
8070 // This chunk can potentially be coalesced.
8071 if (_sp->adaptive_freelists()) {
8072 // All the work is done in
8073 do_post_free_or_garbage_chunk(fc, size);
8074 } else { // Not adaptive free lists
8075 // this is a free chunk that can potentially be coalesced by the sweeper;
8076 if (!inFreeRange()) {
8077 // if the next chunk is a free block that can't be coalesced
8078 // it doesn't make sense to remove this chunk from the free lists
8079 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8080 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8081 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8082 nextChunk->is_free() && // ... which is free...
8083 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8084 // nothing to do
8085 } else {
8086 // Potentially the start of a new free range:
8087 // Don't eagerly remove it from the free lists.
8088 // No need to remove it if it will just be put
8089 // back again. (Also from a pragmatic point of view
8090 // if it is a free block in a region that is beyond
8091 // any allocated blocks, an assertion will fail)
8092 // Remember the start of a free run.
8093 initialize_free_range(addr, true);
8094 // end - can coalesce with next chunk
8095 }
8096 } else {
8097 // the midst of a free range, we are coalescing
8098 print_free_block_coalesced(fc);
8099 if (CMSTraceSweeper) {
8100 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8101 }
8102 // remove it from the free lists
8103 _sp->removeFreeChunkFromFreeLists(fc);
8104 set_lastFreeRangeCoalesced(true);
8105 // If the chunk is being coalesced and the current free range is
8106 // in the free lists, remove the current free range so that it
8107 // will be returned to the free lists in its entirety - all
8108 // the coalesced pieces included.
8109 if (freeRangeInFreeLists()) {
8110 FreeChunk* ffc = (FreeChunk*) freeFinger();
8111 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8112 "Size of free range is inconsistent with chunk size.");
8113 if (CMSTestInFreeList) {
8114 assert(_sp->verify_chunk_in_free_list(ffc),
8115 "free range is not in free lists");
8116 }
8117 _sp->removeFreeChunkFromFreeLists(ffc);
8118 set_freeRangeInFreeLists(false);
8119 }
8120 }
8121 }
8122 // Note that if the chunk is not coalescable (the else arm
8123 // below), we unconditionally flush, without needing to do
8124 // a "lookahead," as we do below.
8125 if (inFreeRange()) lookahead_and_flush(fc, size);
8126 } else {
8127 // Code path common to both original and adaptive free lists.
8128
8129 // cant coalesce with previous block; this should be treated
8130 // as the end of a free run if any
8131 if (inFreeRange()) {
8132 // we kicked some butt; time to pick up the garbage
8133 assert(freeFinger() < addr, "freeFinger points too high");
8134 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8135 }
8136 // else, nothing to do, just continue
8137 }
8138 }
8139
8140 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8141 // This is a chunk of garbage. It is not in any free list.
8142 // Add it to a free list or let it possibly be coalesced into
8143 // a larger chunk.
8144 HeapWord* const addr = (HeapWord*) fc;
8145 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8146
8147 if (_sp->adaptive_freelists()) {
8148 // Verify that the bit map has no bits marked between
8149 // addr and purported end of just dead object.
8150 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8151
8152 do_post_free_or_garbage_chunk(fc, size);
8153 } else {
8154 if (!inFreeRange()) {
8155 // start of a new free range
8156 assert(size > 0, "A free range should have a size");
8157 initialize_free_range(addr, false);
8158 } else {
8159 // this will be swept up when we hit the end of the
8160 // free range
8161 if (CMSTraceSweeper) {
8162 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8163 }
8164 // If the chunk is being coalesced and the current free range is
8165 // in the free lists, remove the current free range so that it
8166 // will be returned to the free lists in its entirety - all
8167 // the coalesced pieces included.
8168 if (freeRangeInFreeLists()) {
8169 FreeChunk* ffc = (FreeChunk*)freeFinger();
8170 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8171 "Size of free range is inconsistent with chunk size.");
8172 if (CMSTestInFreeList) {
8173 assert(_sp->verify_chunk_in_free_list(ffc),
8174 "free range is not in free lists");
8175 }
8176 _sp->removeFreeChunkFromFreeLists(ffc);
8177 set_freeRangeInFreeLists(false);
8178 }
8179 set_lastFreeRangeCoalesced(true);
8180 }
8181 // this will be swept up when we hit the end of the free range
8182
8183 // Verify that the bit map has no bits marked between
8184 // addr and purported end of just dead object.
8185 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8186 }
8187 assert(_limit >= addr + size,
8188 "A freshly garbage chunk can't possibly straddle over _limit");
8189 if (inFreeRange()) lookahead_and_flush(fc, size);
8190 return size;
8191 }
8192
8193 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8194 HeapWord* addr = (HeapWord*) fc;
8195 // The sweeper has just found a live object. Return any accumulated
8196 // left hand chunk to the free lists.
8197 if (inFreeRange()) {
8198 assert(freeFinger() < addr, "freeFinger points too high");
8199 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8200 }
8201
8202 // This object is live: we'd normally expect this to be
8203 // an oop, and like to assert the following:
8204 // assert(oop(addr)->is_oop(), "live block should be an oop");
8205 // However, as we commented above, this may be an object whose
8206 // header hasn't yet been initialized.
8207 size_t size;
8208 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8209 if (_bitMap->isMarked(addr + 1)) {
8210 // Determine the size from the bit map, rather than trying to
8211 // compute it from the object header.
8212 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8213 size = pointer_delta(nextOneAddr + 1, addr);
8214 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8215 "alignment problem");
8216
8217 #ifdef ASSERT
8218 if (oop(addr)->klass_or_null() != NULL) {
8219 // Ignore mark word because we are running concurrent with mutators
8220 assert(oop(addr)->is_oop(true), "live block should be an oop");
8221 assert(size ==
8222 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8223 "P-mark and computed size do not agree");
8224 }
8225 #endif
8226
8227 } else {
8228 // This should be an initialized object that's alive.
8229 assert(oop(addr)->klass_or_null() != NULL,
8230 "Should be an initialized object");
8231 // Ignore mark word because we are running concurrent with mutators
8232 assert(oop(addr)->is_oop(true), "live block should be an oop");
8233 // Verify that the bit map has no bits marked between
8234 // addr and purported end of this block.
8235 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8236 assert(size >= 3, "Necessary for Printezis marks to work");
8237 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8238 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8239 }
8240 return size;
8241 }
8242
8243 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8244 size_t chunkSize) {
8245 // do_post_free_or_garbage_chunk() should only be called in the case
8246 // of the adaptive free list allocator.
8247 const bool fcInFreeLists = fc->is_free();
8248 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8249 assert((HeapWord*)fc <= _limit, "sweep invariant");
8250 if (CMSTestInFreeList && fcInFreeLists) {
8251 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8252 }
8253
8254 if (CMSTraceSweeper) {
8255 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8256 }
8257
8258 HeapWord* const fc_addr = (HeapWord*) fc;
8259
8260 bool coalesce;
8261 const size_t left = pointer_delta(fc_addr, freeFinger());
8262 const size_t right = chunkSize;
8263 switch (FLSCoalescePolicy) {
8264 // numeric value forms a coalition aggressiveness metric
8265 case 0: { // never coalesce
8266 coalesce = false;
8267 break;
8268 }
8269 case 1: { // coalesce if left & right chunks on overpopulated lists
8270 coalesce = _sp->coalOverPopulated(left) &&
8271 _sp->coalOverPopulated(right);
8272 break;
8273 }
8274 case 2: { // coalesce if left chunk on overpopulated list (default)
8275 coalesce = _sp->coalOverPopulated(left);
8276 break;
8277 }
8278 case 3: { // coalesce if left OR right chunk on overpopulated list
8279 coalesce = _sp->coalOverPopulated(left) ||
8280 _sp->coalOverPopulated(right);
8281 break;
8282 }
8283 case 4: { // always coalesce
8284 coalesce = true;
8285 break;
8286 }
8287 default:
8288 ShouldNotReachHere();
8289 }
8290
8291 // Should the current free range be coalesced?
8292 // If the chunk is in a free range and either we decided to coalesce above
8293 // or the chunk is near the large block at the end of the heap
8294 // (isNearLargestChunk() returns true), then coalesce this chunk.
8295 const bool doCoalesce = inFreeRange()
8296 && (coalesce || _g->isNearLargestChunk(fc_addr));
8297 if (doCoalesce) {
8298 // Coalesce the current free range on the left with the new
8299 // chunk on the right. If either is on a free list,
8300 // it must be removed from the list and stashed in the closure.
8301 if (freeRangeInFreeLists()) {
8302 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8303 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8304 "Size of free range is inconsistent with chunk size.");
8305 if (CMSTestInFreeList) {
8306 assert(_sp->verify_chunk_in_free_list(ffc),
8307 "Chunk is not in free lists");
8308 }
8309 _sp->coalDeath(ffc->size());
8310 _sp->removeFreeChunkFromFreeLists(ffc);
8311 set_freeRangeInFreeLists(false);
8312 }
8313 if (fcInFreeLists) {
8314 _sp->coalDeath(chunkSize);
8315 assert(fc->size() == chunkSize,
8316 "The chunk has the wrong size or is not in the free lists");
8317 _sp->removeFreeChunkFromFreeLists(fc);
8318 }
8319 set_lastFreeRangeCoalesced(true);
8320 print_free_block_coalesced(fc);
8321 } else { // not in a free range and/or should not coalesce
8322 // Return the current free range and start a new one.
8323 if (inFreeRange()) {
8324 // In a free range but cannot coalesce with the right hand chunk.
8325 // Put the current free range into the free lists.
8326 flush_cur_free_chunk(freeFinger(),
8327 pointer_delta(fc_addr, freeFinger()));
8328 }
8329 // Set up for new free range. Pass along whether the right hand
8330 // chunk is in the free lists.
8331 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8332 }
8333 }
8334
8335 // Lookahead flush:
8336 // If we are tracking a free range, and this is the last chunk that
8337 // we'll look at because its end crosses past _limit, we'll preemptively
8338 // flush it along with any free range we may be holding on to. Note that
8339 // this can be the case only for an already free or freshly garbage
8340 // chunk. If this block is an object, it can never straddle
8341 // over _limit. The "straddling" occurs when _limit is set at
8342 // the previous end of the space when this cycle started, and
8343 // a subsequent heap expansion caused the previously co-terminal
8344 // free block to be coalesced with the newly expanded portion,
8345 // thus rendering _limit a non-block-boundary making it dangerous
8346 // for the sweeper to step over and examine.
8347 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8348 assert(inFreeRange(), "Should only be called if currently in a free range.");
8349 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8350 assert(_sp->used_region().contains(eob - 1),
8351 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8352 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8353 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8354 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8355 if (eob >= _limit) {
8356 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8357 if (CMSTraceSweeper) {
8358 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8359 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8360 "[" PTR_FORMAT "," PTR_FORMAT ")",
8361 _limit, fc, eob, _sp->bottom(), _sp->end());
8362 }
8363 // Return the storage we are tracking back into the free lists.
8364 if (CMSTraceSweeper) {
8365 gclog_or_tty->print_cr("Flushing ... ");
8366 }
8367 assert(freeFinger() < eob, "Error");
8368 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8369 }
8370 }
8371
8372 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8373 assert(inFreeRange(), "Should only be called if currently in a free range.");
8374 assert(size > 0,
8375 "A zero sized chunk cannot be added to the free lists.");
8376 if (!freeRangeInFreeLists()) {
8377 if (CMSTestInFreeList) {
8378 FreeChunk* fc = (FreeChunk*) chunk;
8379 fc->set_size(size);
8380 assert(!_sp->verify_chunk_in_free_list(fc),
8381 "chunk should not be in free lists yet");
8382 }
8383 if (CMSTraceSweeper) {
8384 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8385 chunk, size);
8386 }
8387 // A new free range is going to be starting. The current
8388 // free range has not been added to the free lists yet or
8389 // was removed so add it back.
8390 // If the current free range was coalesced, then the death
8391 // of the free range was recorded. Record a birth now.
8392 if (lastFreeRangeCoalesced()) {
8393 _sp->coalBirth(size);
8394 }
8395 _sp->addChunkAndRepairOffsetTable(chunk, size,
8396 lastFreeRangeCoalesced());
8397 } else if (CMSTraceSweeper) {
8398 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8399 }
8400 set_inFreeRange(false);
8401 set_freeRangeInFreeLists(false);
8402 }
8403
8404 // We take a break if we've been at this for a while,
8405 // so as to avoid monopolizing the locks involved.
8406 void SweepClosure::do_yield_work(HeapWord* addr) {
8407 // Return current free chunk being used for coalescing (if any)
8408 // to the appropriate freelist. After yielding, the next
8409 // free block encountered will start a coalescing range of
8410 // free blocks. If the next free block is adjacent to the
8411 // chunk just flushed, they will need to wait for the next
8412 // sweep to be coalesced.
8413 if (inFreeRange()) {
8414 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8415 }
8416
8417 // First give up the locks, then yield, then re-lock.
8418 // We should probably use a constructor/destructor idiom to
8419 // do this unlock/lock or modify the MutexUnlocker class to
8420 // serve our purpose. XXX
8421 assert_lock_strong(_bitMap->lock());
8422 assert_lock_strong(_freelistLock);
8423 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8424 "CMS thread should hold CMS token");
8425 _bitMap->lock()->unlock();
8426 _freelistLock->unlock();
8427 ConcurrentMarkSweepThread::desynchronize(true);
8428 _collector->stopTimer();
8429 if (PrintCMSStatistics != 0) {
8430 _collector->incrementYields();
8431 }
8432
8433 // See the comment in coordinator_yield()
8434 for (unsigned i = 0; i < CMSYieldSleepCount &&
8435 ConcurrentMarkSweepThread::should_yield() &&
8436 !CMSCollector::foregroundGCIsActive(); ++i) {
8437 os::sleep(Thread::current(), 1, false);
8438 }
8439
8440 ConcurrentMarkSweepThread::synchronize(true);
8441 _freelistLock->lock();
8442 _bitMap->lock()->lock_without_safepoint_check();
8443 _collector->startTimer();
8444 }
8445
8446 #ifndef PRODUCT
8447 // This is actually very useful in a product build if it can
8448 // be called from the debugger. Compile it into the product
8449 // as needed.
8450 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8451 return debug_cms_space->verify_chunk_in_free_list(fc);
8452 }
8453 #endif
8454
8455 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8456 if (CMSTraceSweeper) {
8457 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8458 fc, fc->size());
8459 }
8460 }
8461
8462 // CMSIsAliveClosure
8463 bool CMSIsAliveClosure::do_object_b(oop obj) {
8464 HeapWord* addr = (HeapWord*)obj;
8465 return addr != NULL &&
8466 (!_span.contains(addr) || _bit_map->isMarked(addr));
8467 }
8468
8469
8470 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8471 MemRegion span,
8472 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8473 bool cpc):
8474 _collector(collector),
8475 _span(span),
8476 _bit_map(bit_map),
8477 _mark_stack(mark_stack),
8478 _concurrent_precleaning(cpc) {
8479 assert(!_span.is_empty(), "Empty span could spell trouble");
8480 }
8481
8482
8483 // CMSKeepAliveClosure: the serial version
8484 void CMSKeepAliveClosure::do_oop(oop obj) {
8485 HeapWord* addr = (HeapWord*)obj;
8486 if (_span.contains(addr) &&
8487 !_bit_map->isMarked(addr)) {
8488 _bit_map->mark(addr);
8489 bool simulate_overflow = false;
8490 NOT_PRODUCT(
8491 if (CMSMarkStackOverflowALot &&
8492 _collector->simulate_overflow()) {
8493 // simulate a stack overflow
8494 simulate_overflow = true;
8495 }
8496 )
8497 if (simulate_overflow || !_mark_stack->push(obj)) {
8498 if (_concurrent_precleaning) {
8499 // We dirty the overflown object and let the remark
8500 // phase deal with it.
8501 assert(_collector->overflow_list_is_empty(), "Error");
8502 // In the case of object arrays, we need to dirty all of
8503 // the cards that the object spans. No locking or atomics
8504 // are needed since no one else can be mutating the mod union
8505 // table.
8506 if (obj->is_objArray()) {
8507 size_t sz = obj->size();
8508 HeapWord* end_card_addr =
8509 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8510 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8511 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8512 _collector->_modUnionTable.mark_range(redirty_range);
8513 } else {
8514 _collector->_modUnionTable.mark(addr);
8515 }
8516 _collector->_ser_kac_preclean_ovflw++;
8517 } else {
8518 _collector->push_on_overflow_list(obj);
8519 _collector->_ser_kac_ovflw++;
8520 }
8521 }
8522 }
8523 }
8524
8525 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8526 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8527
8528 // CMSParKeepAliveClosure: a parallel version of the above.
8529 // The work queues are private to each closure (thread),
8530 // but (may be) available for stealing by other threads.
8531 void CMSParKeepAliveClosure::do_oop(oop obj) {
8532 HeapWord* addr = (HeapWord*)obj;
8533 if (_span.contains(addr) &&
8534 !_bit_map->isMarked(addr)) {
8535 // In general, during recursive tracing, several threads
8536 // may be concurrently getting here; the first one to
8537 // "tag" it, claims it.
8538 if (_bit_map->par_mark(addr)) {
8539 bool res = _work_queue->push(obj);
8540 assert(res, "Low water mark should be much less than capacity");
8541 // Do a recursive trim in the hope that this will keep
8542 // stack usage lower, but leave some oops for potential stealers
8543 trim_queue(_low_water_mark);
8544 } // Else, another thread got there first
8545 }
8546 }
8547
8548 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8549 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8550
8551 void CMSParKeepAliveClosure::trim_queue(uint max) {
8552 while (_work_queue->size() > max) {
8553 oop new_oop;
8554 if (_work_queue->pop_local(new_oop)) {
8555 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8556 assert(_bit_map->isMarked((HeapWord*)new_oop),
8557 "no white objects on this stack!");
8558 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8559 // iterate over the oops in this oop, marking and pushing
8560 // the ones in CMS heap (i.e. in _span).
8561 new_oop->oop_iterate(&_mark_and_push);
8562 }
8563 }
8564 }
8565
8566 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8567 CMSCollector* collector,
8568 MemRegion span, CMSBitMap* bit_map,
8569 OopTaskQueue* work_queue):
8570 _collector(collector),
8571 _span(span),
8572 _bit_map(bit_map),
8573 _work_queue(work_queue) { }
8574
8575 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8576 HeapWord* addr = (HeapWord*)obj;
8577 if (_span.contains(addr) &&
8578 !_bit_map->isMarked(addr)) {
8579 if (_bit_map->par_mark(addr)) {
8580 bool simulate_overflow = false;
8581 NOT_PRODUCT(
8582 if (CMSMarkStackOverflowALot &&
8583 _collector->par_simulate_overflow()) {
8584 // simulate a stack overflow
8585 simulate_overflow = true;
8586 }
8587 )
8588 if (simulate_overflow || !_work_queue->push(obj)) {
8589 _collector->par_push_on_overflow_list(obj);
8590 _collector->_par_kac_ovflw++;
8591 }
8592 } // Else another thread got there already
8593 }
8594 }
8595
8596 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8597 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8598
8599 //////////////////////////////////////////////////////////////////
8600 // CMSExpansionCause /////////////////////////////
8601 //////////////////////////////////////////////////////////////////
8602 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8603 switch (cause) {
8604 case _no_expansion:
8605 return "No expansion";
8606 case _satisfy_free_ratio:
8607 return "Free ratio";
8608 case _satisfy_promotion:
8609 return "Satisfy promotion";
8610 case _satisfy_allocation:
8611 return "allocation";
8612 case _allocate_par_lab:
8613 return "Par LAB";
8614 case _allocate_par_spooling_space:
8615 return "Par Spooling Space";
8616 case _adaptive_size_policy:
8617 return "Ergonomics";
8618 default:
8619 return "unknown";
8620 }
8621 }
8622
8623 void CMSDrainMarkingStackClosure::do_void() {
8624 // the max number to take from overflow list at a time
8625 const size_t num = _mark_stack->capacity()/4;
8626 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8627 "Overflow list should be NULL during concurrent phases");
8628 while (!_mark_stack->isEmpty() ||
8629 // if stack is empty, check the overflow list
8630 _collector->take_from_overflow_list(num, _mark_stack)) {
8631 oop obj = _mark_stack->pop();
8632 HeapWord* addr = (HeapWord*)obj;
8633 assert(_span.contains(addr), "Should be within span");
8634 assert(_bit_map->isMarked(addr), "Should be marked");
8635 assert(obj->is_oop(), "Should be an oop");
8636 obj->oop_iterate(_keep_alive);
8637 }
8638 }
8639
8640 void CMSParDrainMarkingStackClosure::do_void() {
8641 // drain queue
8642 trim_queue(0);
8643 }
8644
8645 // Trim our work_queue so its length is below max at return
8646 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8647 while (_work_queue->size() > max) {
8648 oop new_oop;
8649 if (_work_queue->pop_local(new_oop)) {
8650 assert(new_oop->is_oop(), "Expected an oop");
8651 assert(_bit_map->isMarked((HeapWord*)new_oop),
8652 "no white objects on this stack!");
8653 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8654 // iterate over the oops in this oop, marking and pushing
8655 // the ones in CMS heap (i.e. in _span).
8656 new_oop->oop_iterate(&_mark_and_push);
8657 }
8658 }
8659 }
8660
8661 ////////////////////////////////////////////////////////////////////
8662 // Support for Marking Stack Overflow list handling and related code
8663 ////////////////////////////////////////////////////////////////////
8664 // Much of the following code is similar in shape and spirit to the
8665 // code used in ParNewGC. We should try and share that code
8666 // as much as possible in the future.
8667
8668 #ifndef PRODUCT
8669 // Debugging support for CMSStackOverflowALot
8670
8671 // It's OK to call this multi-threaded; the worst thing
8672 // that can happen is that we'll get a bunch of closely
8673 // spaced simulated overflows, but that's OK, in fact
8674 // probably good as it would exercise the overflow code
8675 // under contention.
8676 bool CMSCollector::simulate_overflow() {
8677 if (_overflow_counter-- <= 0) { // just being defensive
8678 _overflow_counter = CMSMarkStackOverflowInterval;
8679 return true;
8680 } else {
8681 return false;
8682 }
8683 }
8684
8685 bool CMSCollector::par_simulate_overflow() {
8686 return simulate_overflow();
8687 }
8688 #endif
8689
8690 // Single-threaded
8691 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8692 assert(stack->isEmpty(), "Expected precondition");
8693 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8694 size_t i = num;
8695 oop cur = _overflow_list;
8696 const markOop proto = markOopDesc::prototype();
8697 NOT_PRODUCT(ssize_t n = 0;)
8698 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8699 next = oop(cur->mark());
8700 cur->set_mark(proto); // until proven otherwise
8701 assert(cur->is_oop(), "Should be an oop");
8702 bool res = stack->push(cur);
8703 assert(res, "Bit off more than can chew?");
8704 NOT_PRODUCT(n++;)
8705 }
8706 _overflow_list = cur;
8707 #ifndef PRODUCT
8708 assert(_num_par_pushes >= n, "Too many pops?");
8709 _num_par_pushes -=n;
8710 #endif
8711 return !stack->isEmpty();
8712 }
8713
8714 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8715 // (MT-safe) Get a prefix of at most "num" from the list.
8716 // The overflow list is chained through the mark word of
8717 // each object in the list. We fetch the entire list,
8718 // break off a prefix of the right size and return the
8719 // remainder. If other threads try to take objects from
8720 // the overflow list at that time, they will wait for
8721 // some time to see if data becomes available. If (and
8722 // only if) another thread places one or more object(s)
8723 // on the global list before we have returned the suffix
8724 // to the global list, we will walk down our local list
8725 // to find its end and append the global list to
8726 // our suffix before returning it. This suffix walk can
8727 // prove to be expensive (quadratic in the amount of traffic)
8728 // when there are many objects in the overflow list and
8729 // there is much producer-consumer contention on the list.
8730 // *NOTE*: The overflow list manipulation code here and
8731 // in ParNewGeneration:: are very similar in shape,
8732 // except that in the ParNew case we use the old (from/eden)
8733 // copy of the object to thread the list via its klass word.
8734 // Because of the common code, if you make any changes in
8735 // the code below, please check the ParNew version to see if
8736 // similar changes might be needed.
8737 // CR 6797058 has been filed to consolidate the common code.
8738 bool CMSCollector::par_take_from_overflow_list(size_t num,
8739 OopTaskQueue* work_q,
8740 int no_of_gc_threads) {
8741 assert(work_q->size() == 0, "First empty local work queue");
8742 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8743 if (_overflow_list == NULL) {
8744 return false;
8745 }
8746 // Grab the entire list; we'll put back a suffix
8747 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8748 Thread* tid = Thread::current();
8749 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8750 // set to ParallelGCThreads.
8751 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8752 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8753 // If the list is busy, we spin for a short while,
8754 // sleeping between attempts to get the list.
8755 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8756 os::sleep(tid, sleep_time_millis, false);
8757 if (_overflow_list == NULL) {
8758 // Nothing left to take
8759 return false;
8760 } else if (_overflow_list != BUSY) {
8761 // Try and grab the prefix
8762 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8763 }
8764 }
8765 // If the list was found to be empty, or we spun long
8766 // enough, we give up and return empty-handed. If we leave
8767 // the list in the BUSY state below, it must be the case that
8768 // some other thread holds the overflow list and will set it
8769 // to a non-BUSY state in the future.
8770 if (prefix == NULL || prefix == BUSY) {
8771 // Nothing to take or waited long enough
8772 if (prefix == NULL) {
8773 // Write back the NULL in case we overwrote it with BUSY above
8774 // and it is still the same value.
8775 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8776 }
8777 return false;
8778 }
8779 assert(prefix != NULL && prefix != BUSY, "Error");
8780 size_t i = num;
8781 oop cur = prefix;
8782 // Walk down the first "num" objects, unless we reach the end.
8783 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8784 if (cur->mark() == NULL) {
8785 // We have "num" or fewer elements in the list, so there
8786 // is nothing to return to the global list.
8787 // Write back the NULL in lieu of the BUSY we wrote
8788 // above, if it is still the same value.
8789 if (_overflow_list == BUSY) {
8790 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8791 }
8792 } else {
8793 // Chop off the suffix and return it to the global list.
8794 assert(cur->mark() != BUSY, "Error");
8795 oop suffix_head = cur->mark(); // suffix will be put back on global list
8796 cur->set_mark(NULL); // break off suffix
8797 // It's possible that the list is still in the empty(busy) state
8798 // we left it in a short while ago; in that case we may be
8799 // able to place back the suffix without incurring the cost
8800 // of a walk down the list.
8801 oop observed_overflow_list = _overflow_list;
8802 oop cur_overflow_list = observed_overflow_list;
8803 bool attached = false;
8804 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8805 observed_overflow_list =
8806 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8807 if (cur_overflow_list == observed_overflow_list) {
8808 attached = true;
8809 break;
8810 } else cur_overflow_list = observed_overflow_list;
8811 }
8812 if (!attached) {
8813 // Too bad, someone else sneaked in (at least) an element; we'll need
8814 // to do a splice. Find tail of suffix so we can prepend suffix to global
8815 // list.
8816 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8817 oop suffix_tail = cur;
8818 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8819 "Tautology");
8820 observed_overflow_list = _overflow_list;
8821 do {
8822 cur_overflow_list = observed_overflow_list;
8823 if (cur_overflow_list != BUSY) {
8824 // Do the splice ...
8825 suffix_tail->set_mark(markOop(cur_overflow_list));
8826 } else { // cur_overflow_list == BUSY
8827 suffix_tail->set_mark(NULL);
8828 }
8829 // ... and try to place spliced list back on overflow_list ...
8830 observed_overflow_list =
8831 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8832 } while (cur_overflow_list != observed_overflow_list);
8833 // ... until we have succeeded in doing so.
8834 }
8835 }
8836
8837 // Push the prefix elements on work_q
8838 assert(prefix != NULL, "control point invariant");
8839 const markOop proto = markOopDesc::prototype();
8840 oop next;
8841 NOT_PRODUCT(ssize_t n = 0;)
8842 for (cur = prefix; cur != NULL; cur = next) {
8843 next = oop(cur->mark());
8844 cur->set_mark(proto); // until proven otherwise
8845 assert(cur->is_oop(), "Should be an oop");
8846 bool res = work_q->push(cur);
8847 assert(res, "Bit off more than we can chew?");
8848 NOT_PRODUCT(n++;)
8849 }
8850 #ifndef PRODUCT
8851 assert(_num_par_pushes >= n, "Too many pops?");
8852 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8853 #endif
8854 return true;
8855 }
8856
8857 // Single-threaded
8858 void CMSCollector::push_on_overflow_list(oop p) {
8859 NOT_PRODUCT(_num_par_pushes++;)
8860 assert(p->is_oop(), "Not an oop");
8861 preserve_mark_if_necessary(p);
8862 p->set_mark((markOop)_overflow_list);
8863 _overflow_list = p;
8864 }
8865
8866 // Multi-threaded; use CAS to prepend to overflow list
8867 void CMSCollector::par_push_on_overflow_list(oop p) {
8868 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8869 assert(p->is_oop(), "Not an oop");
8870 par_preserve_mark_if_necessary(p);
8871 oop observed_overflow_list = _overflow_list;
8872 oop cur_overflow_list;
8873 do {
8874 cur_overflow_list = observed_overflow_list;
8875 if (cur_overflow_list != BUSY) {
8876 p->set_mark(markOop(cur_overflow_list));
8877 } else {
8878 p->set_mark(NULL);
8879 }
8880 observed_overflow_list =
8881 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8882 } while (cur_overflow_list != observed_overflow_list);
8883 }
8884 #undef BUSY
8885
8886 // Single threaded
8887 // General Note on GrowableArray: pushes may silently fail
8888 // because we are (temporarily) out of C-heap for expanding
8889 // the stack. The problem is quite ubiquitous and affects
8890 // a lot of code in the JVM. The prudent thing for GrowableArray
8891 // to do (for now) is to exit with an error. However, that may
8892 // be too draconian in some cases because the caller may be
8893 // able to recover without much harm. For such cases, we
8894 // should probably introduce a "soft_push" method which returns
8895 // an indication of success or failure with the assumption that
8896 // the caller may be able to recover from a failure; code in
8897 // the VM can then be changed, incrementally, to deal with such
8898 // failures where possible, thus, incrementally hardening the VM
8899 // in such low resource situations.
8900 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8901 _preserved_oop_stack.push(p);
8902 _preserved_mark_stack.push(m);
8903 assert(m == p->mark(), "Mark word changed");
8904 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8905 "bijection");
8906 }
8907
8908 // Single threaded
8909 void CMSCollector::preserve_mark_if_necessary(oop p) {
8910 markOop m = p->mark();
8911 if (m->must_be_preserved(p)) {
8912 preserve_mark_work(p, m);
8913 }
8914 }
8915
8916 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8917 markOop m = p->mark();
8918 if (m->must_be_preserved(p)) {
8919 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8920 // Even though we read the mark word without holding
8921 // the lock, we are assured that it will not change
8922 // because we "own" this oop, so no other thread can
8923 // be trying to push it on the overflow list; see
8924 // the assertion in preserve_mark_work() that checks
8925 // that m == p->mark().
8926 preserve_mark_work(p, m);
8927 }
8928 }
8929
8930 // We should be able to do this multi-threaded,
8931 // a chunk of stack being a task (this is
8932 // correct because each oop only ever appears
8933 // once in the overflow list. However, it's
8934 // not very easy to completely overlap this with
8935 // other operations, so will generally not be done
8936 // until all work's been completed. Because we
8937 // expect the preserved oop stack (set) to be small,
8938 // it's probably fine to do this single-threaded.
8939 // We can explore cleverer concurrent/overlapped/parallel
8940 // processing of preserved marks if we feel the
8941 // need for this in the future. Stack overflow should
8942 // be so rare in practice and, when it happens, its
8943 // effect on performance so great that this will
8944 // likely just be in the noise anyway.
8945 void CMSCollector::restore_preserved_marks_if_any() {
8946 assert(SafepointSynchronize::is_at_safepoint(),
8947 "world should be stopped");
8948 assert(Thread::current()->is_ConcurrentGC_thread() ||
8949 Thread::current()->is_VM_thread(),
8950 "should be single-threaded");
8951 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8952 "bijection");
8953
8954 while (!_preserved_oop_stack.is_empty()) {
8955 oop p = _preserved_oop_stack.pop();
8956 assert(p->is_oop(), "Should be an oop");
8957 assert(_span.contains(p), "oop should be in _span");
8958 assert(p->mark() == markOopDesc::prototype(),
8959 "Set when taken from overflow list");
8960 markOop m = _preserved_mark_stack.pop();
8961 p->set_mark(m);
8962 }
8963 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8964 "stacks were cleared above");
8965 }
8966
8967 #ifndef PRODUCT
8968 bool CMSCollector::no_preserved_marks() const {
8969 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8970 }
8971 #endif
8972
8973 // Transfer some number of overflown objects to usual marking
8974 // stack. Return true if some objects were transferred.
8975 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8976 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8977 (size_t)ParGCDesiredObjsFromOverflowList);
8978
8979 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8980 assert(_collector->overflow_list_is_empty() || res,
8981 "If list is not empty, we should have taken something");
8982 assert(!res || !_mark_stack->isEmpty(),
8983 "If we took something, it should now be on our stack");
8984 return res;
8985 }
8986
8987 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8988 size_t res = _sp->block_size_no_stall(addr, _collector);
8989 if (_sp->block_is_obj(addr)) {
8990 if (_live_bit_map->isMarked(addr)) {
8991 // It can't have been dead in a previous cycle
8992 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8993 } else {
8994 _dead_bit_map->mark(addr); // mark the dead object
8995 }
8996 }
8997 // Could be 0, if the block size could not be computed without stalling.
8998 return res;
8999 }
9000
9001 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9002
9003 switch (phase) {
9004 case CMSCollector::InitialMarking:
9005 initialize(true /* fullGC */ ,
9006 cause /* cause of the GC */,
9007 true /* recordGCBeginTime */,
9008 true /* recordPreGCUsage */,
9009 false /* recordPeakUsage */,
9010 false /* recordPostGCusage */,
9011 true /* recordAccumulatedGCTime */,
9012 false /* recordGCEndTime */,
9013 false /* countCollection */ );
9014 break;
9015
9016 case CMSCollector::FinalMarking:
9017 initialize(true /* fullGC */ ,
9018 cause /* cause of the GC */,
9019 false /* recordGCBeginTime */,
9020 false /* recordPreGCUsage */,
9021 false /* recordPeakUsage */,
9022 false /* recordPostGCusage */,
9023 true /* recordAccumulatedGCTime */,
9024 false /* recordGCEndTime */,
9025 false /* countCollection */ );
9026 break;
9027
9028 case CMSCollector::Sweeping:
9029 initialize(true /* fullGC */ ,
9030 cause /* cause of the GC */,
9031 false /* recordGCBeginTime */,
9032 false /* recordPreGCUsage */,
9033 true /* recordPeakUsage */,
9034 true /* recordPostGCusage */,
9035 false /* recordAccumulatedGCTime */,
9036 true /* recordGCEndTime */,
9037 true /* countCollection */ );
9038 break;
9039
9040 default:
9041 ShouldNotReachHere();
9042 }
9043 }