1 /*
2 * Copyright (c) 2001, 2012, 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/symbolTable.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "code/codeCache.hpp"
29 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.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/isGCActiveMark.hpp"
40 #include "gc_interface/collectedHeap.inline.hpp"
41 #include "memory/cardTableRS.hpp"
42 #include "memory/collectorPolicy.hpp"
43 #include "memory/gcLocker.inline.hpp"
44 #include "memory/genCollectedHeap.hpp"
45 #include "memory/genMarkSweep.hpp"
46 #include "memory/genOopClosures.inline.hpp"
47 #include "memory/iterator.hpp"
48 #include "memory/referencePolicy.hpp"
49 #include "memory/resourceArea.hpp"
50 #include "oops/oop.inline.hpp"
51 #include "prims/jvmtiExport.hpp"
52 #include "runtime/globals_extension.hpp"
53 #include "runtime/handles.inline.hpp"
54 #include "runtime/java.hpp"
55 #include "runtime/vmThread.hpp"
56 #include "services/memoryService.hpp"
57 #include "services/runtimeService.hpp"
58
59 // statics
60 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
61 bool CMSCollector::_full_gc_requested = false;
62
63 //////////////////////////////////////////////////////////////////
64 // In support of CMS/VM thread synchronization
65 //////////////////////////////////////////////////////////////////
66 // We split use of the CGC_lock into 2 "levels".
67 // The low-level locking is of the usual CGC_lock monitor. We introduce
68 // a higher level "token" (hereafter "CMS token") built on top of the
69 // low level monitor (hereafter "CGC lock").
70 // The token-passing protocol gives priority to the VM thread. The
71 // CMS-lock doesn't provide any fairness guarantees, but clients
72 // should ensure that it is only held for very short, bounded
73 // durations.
74 //
75 // When either of the CMS thread or the VM thread is involved in
76 // collection operations during which it does not want the other
77 // thread to interfere, it obtains the CMS token.
78 //
79 // If either thread tries to get the token while the other has
80 // it, that thread waits. However, if the VM thread and CMS thread
81 // both want the token, then the VM thread gets priority while the
82 // CMS thread waits. This ensures, for instance, that the "concurrent"
83 // phases of the CMS thread's work do not block out the VM thread
84 // for long periods of time as the CMS thread continues to hog
85 // the token. (See bug 4616232).
86 //
87 // The baton-passing functions are, however, controlled by the
88 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
89 // and here the low-level CMS lock, not the high level token,
90 // ensures mutual exclusion.
91 //
92 // Two important conditions that we have to satisfy:
93 // 1. if a thread does a low-level wait on the CMS lock, then it
94 // relinquishes the CMS token if it were holding that token
95 // when it acquired the low-level CMS lock.
96 // 2. any low-level notifications on the low-level lock
97 // should only be sent when a thread has relinquished the token.
98 //
99 // In the absence of either property, we'd have potential deadlock.
100 //
101 // We protect each of the CMS (concurrent and sequential) phases
102 // with the CMS _token_, not the CMS _lock_.
103 //
104 // The only code protected by CMS lock is the token acquisition code
105 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
106 // baton-passing code.
107 //
108 // Unfortunately, i couldn't come up with a good abstraction to factor and
109 // hide the naked CGC_lock manipulation in the baton-passing code
110 // further below. That's something we should try to do. Also, the proof
111 // of correctness of this 2-level locking scheme is far from obvious,
112 // and potentially quite slippery. We have an uneasy supsicion, for instance,
113 // that there may be a theoretical possibility of delay/starvation in the
114 // low-level lock/wait/notify scheme used for the baton-passing because of
115 // potential intereference with the priority scheme embodied in the
116 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
117 // invocation further below and marked with "XXX 20011219YSR".
118 // Indeed, as we note elsewhere, this may become yet more slippery
119 // in the presence of multiple CMS and/or multiple VM threads. XXX
120
121 class CMSTokenSync: public StackObj {
122 private:
123 bool _is_cms_thread;
124 public:
125 CMSTokenSync(bool is_cms_thread):
126 _is_cms_thread(is_cms_thread) {
127 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
128 "Incorrect argument to constructor");
129 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
130 }
131
132 ~CMSTokenSync() {
133 assert(_is_cms_thread ?
134 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
135 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
136 "Incorrect state");
137 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
138 }
139 };
140
141 // Convenience class that does a CMSTokenSync, and then acquires
142 // upto three locks.
143 class CMSTokenSyncWithLocks: public CMSTokenSync {
144 private:
145 // Note: locks are acquired in textual declaration order
146 // and released in the opposite order
147 MutexLockerEx _locker1, _locker2, _locker3;
148 public:
149 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
150 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
151 CMSTokenSync(is_cms_thread),
152 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
153 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
154 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
155 { }
156 };
157
158
159 // Wrapper class to temporarily disable icms during a foreground cms collection.
160 class ICMSDisabler: public StackObj {
161 public:
162 // The ctor disables icms and wakes up the thread so it notices the change;
163 // the dtor re-enables icms. Note that the CMSCollector methods will check
164 // CMSIncrementalMode.
165 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
166 ~ICMSDisabler() { CMSCollector::enable_icms(); }
167 };
168
169 //////////////////////////////////////////////////////////////////
170 // Concurrent Mark-Sweep Generation /////////////////////////////
171 //////////////////////////////////////////////////////////////////
172
173 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
174
175 // This struct contains per-thread things necessary to support parallel
176 // young-gen collection.
177 class CMSParGCThreadState: public CHeapObj {
178 public:
179 CFLS_LAB lab;
180 PromotionInfo promo;
181
182 // Constructor.
183 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
184 promo.setSpace(cfls);
185 }
186 };
187
188 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
189 ReservedSpace rs, size_t initial_byte_size, int level,
190 CardTableRS* ct, bool use_adaptive_freelists,
191 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
192 CardGeneration(rs, initial_byte_size, level, ct),
193 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
194 _debug_collection_type(Concurrent_collection_type)
195 {
196 HeapWord* bottom = (HeapWord*) _virtual_space.low();
197 HeapWord* end = (HeapWord*) _virtual_space.high();
198
199 _direct_allocated_words = 0;
200 NOT_PRODUCT(
201 _numObjectsPromoted = 0;
202 _numWordsPromoted = 0;
203 _numObjectsAllocated = 0;
204 _numWordsAllocated = 0;
205 )
206
207 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
208 use_adaptive_freelists,
209 dictionaryChoice);
210 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
211 if (_cmsSpace == NULL) {
212 vm_exit_during_initialization(
213 "CompactibleFreeListSpace allocation failure");
214 }
215 _cmsSpace->_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedOops ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229 if (CollectedHeap::use_parallel_gc_threads()) {
230 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
231 _par_gc_thread_states =
232 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
233 if (_par_gc_thread_states == NULL) {
234 vm_exit_during_initialization("Could not allocate par gc structs");
235 }
236 for (uint i = 0; i < ParallelGCThreads; i++) {
237 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
238 if (_par_gc_thread_states[i] == NULL) {
239 vm_exit_during_initialization("Could not allocate par gc structs");
240 }
241 }
242 } else {
243 _par_gc_thread_states = NULL;
244 }
245 _incremental_collection_failed = false;
246 // The "dilatation_factor" is the expansion that can occur on
247 // account of the fact that the minimum object size in the CMS
248 // generation may be larger than that in, say, a contiguous young
249 // generation.
250 // Ideally, in the calculation below, we'd compute the dilatation
251 // factor as: MinChunkSize/(promoting_gen's min object size)
252 // Since we do not have such a general query interface for the
253 // promoting generation, we'll instead just use the mimimum
254 // object size (which today is a header's worth of space);
255 // note that all arithmetic is in units of HeapWords.
256 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
257 assert(_dilatation_factor >= 1.0, "from previous assert");
258 }
259
260
261 // The field "_initiating_occupancy" represents the occupancy percentage
262 // at which we trigger a new collection cycle. Unless explicitly specified
263 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
264 // is calculated by:
265 //
266 // Let "f" be MinHeapFreeRatio in
267 //
268 // _intiating_occupancy = 100-f +
269 // f * (CMSTrigger[Perm]Ratio/100)
270 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
271 //
272 // That is, if we assume the heap is at its desired maximum occupancy at the
273 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
274 // space be allocated before initiating a new collection cycle.
275 //
276 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
277 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
278 if (io >= 0) {
279 _initiating_occupancy = (double)io / 100.0;
280 } else {
281 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
282 (double)(tr * MinHeapFreeRatio) / 100.0)
283 / 100.0;
284 }
285 }
286
287 void ConcurrentMarkSweepGeneration::ref_processor_init() {
288 assert(collector() != NULL, "no collector");
289 collector()->ref_processor_init();
290 }
291
292 void CMSCollector::ref_processor_init() {
293 if (_ref_processor == NULL) {
294 // Allocate and initialize a reference processor
295 _ref_processor =
296 new ReferenceProcessor(_span, // span
297 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
298 (int) ParallelGCThreads, // mt processing degree
299 _cmsGen->refs_discovery_is_mt(), // mt discovery
300 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
301 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
302 &_is_alive_closure, // closure for liveness info
303 false); // next field updates do not need write barrier
304 // Initialize the _ref_processor field of CMSGen
305 _cmsGen->set_ref_processor(_ref_processor);
306
307 // Allocate a dummy ref processor for perm gen.
308 ReferenceProcessor* rp2 = new ReferenceProcessor();
309 if (rp2 == NULL) {
310 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
311 }
312 _permGen->set_ref_processor(rp2);
313 }
314 }
315
316 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
317 GenCollectedHeap* gch = GenCollectedHeap::heap();
318 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
319 "Wrong type of heap");
320 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
321 gch->gen_policy()->size_policy();
322 assert(sp->is_gc_cms_adaptive_size_policy(),
323 "Wrong type of size policy");
324 return sp;
325 }
326
327 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
328 CMSGCAdaptivePolicyCounters* results =
329 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
330 assert(
331 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
332 "Wrong gc policy counter kind");
333 return results;
334 }
335
336
337 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
338
339 const char* gen_name = "old";
340
341 // Generation Counters - generation 1, 1 subspace
342 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
343
344 _space_counters = new GSpaceCounters(gen_name, 0,
345 _virtual_space.reserved_size(),
346 this, _gen_counters);
347 }
348
349 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
350 _cms_gen(cms_gen)
351 {
352 assert(alpha <= 100, "bad value");
353 _saved_alpha = alpha;
354
355 // Initialize the alphas to the bootstrap value of 100.
356 _gc0_alpha = _cms_alpha = 100;
357
358 _cms_begin_time.update();
359 _cms_end_time.update();
360
361 _gc0_duration = 0.0;
362 _gc0_period = 0.0;
363 _gc0_promoted = 0;
364
365 _cms_duration = 0.0;
366 _cms_period = 0.0;
367 _cms_allocated = 0;
368
369 _cms_used_at_gc0_begin = 0;
370 _cms_used_at_gc0_end = 0;
371 _allow_duty_cycle_reduction = false;
372 _valid_bits = 0;
373 _icms_duty_cycle = CMSIncrementalDutyCycle;
374 }
375
376 double CMSStats::cms_free_adjustment_factor(size_t free) const {
377 // TBD: CR 6909490
378 return 1.0;
379 }
380
381 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
382 }
383
384 // If promotion failure handling is on use
385 // the padded average size of the promotion for each
386 // young generation collection.
387 double CMSStats::time_until_cms_gen_full() const {
388 size_t cms_free = _cms_gen->cmsSpace()->free();
389 GenCollectedHeap* gch = GenCollectedHeap::heap();
390 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
391 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
392 if (cms_free > expected_promotion) {
393 // Start a cms collection if there isn't enough space to promote
394 // for the next minor collection. Use the padded average as
395 // a safety factor.
396 cms_free -= expected_promotion;
397
398 // Adjust by the safety factor.
399 double cms_free_dbl = (double)cms_free;
400 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
401 // Apply a further correction factor which tries to adjust
402 // for recent occurance of concurrent mode failures.
403 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
404 cms_free_dbl = cms_free_dbl * cms_adjustment;
405
406 if (PrintGCDetails && Verbose) {
407 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
408 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
409 cms_free, expected_promotion);
410 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
411 cms_free_dbl, cms_consumption_rate() + 1.0);
412 }
413 // Add 1 in case the consumption rate goes to zero.
414 return cms_free_dbl / (cms_consumption_rate() + 1.0);
415 }
416 return 0.0;
417 }
418
419 // Compare the duration of the cms collection to the
420 // time remaining before the cms generation is empty.
421 // Note that the time from the start of the cms collection
422 // to the start of the cms sweep (less than the total
423 // duration of the cms collection) can be used. This
424 // has been tried and some applications experienced
425 // promotion failures early in execution. This was
426 // possibly because the averages were not accurate
427 // enough at the beginning.
428 double CMSStats::time_until_cms_start() const {
429 // We add "gc0_period" to the "work" calculation
430 // below because this query is done (mostly) at the
431 // end of a scavenge, so we need to conservatively
432 // account for that much possible delay
433 // in the query so as to avoid concurrent mode failures
434 // due to starting the collection just a wee bit too
435 // late.
436 double work = cms_duration() + gc0_period();
437 double deadline = time_until_cms_gen_full();
438 // If a concurrent mode failure occurred recently, we want to be
439 // more conservative and halve our expected time_until_cms_gen_full()
440 if (work > deadline) {
441 if (Verbose && PrintGCDetails) {
442 gclog_or_tty->print(
443 " CMSCollector: collect because of anticipated promotion "
444 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
445 gc0_period(), time_until_cms_gen_full());
446 }
447 return 0.0;
448 }
449 return work - deadline;
450 }
451
452 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
453 // amount of change to prevent wild oscillation.
454 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
455 unsigned int new_duty_cycle) {
456 assert(old_duty_cycle <= 100, "bad input value");
457 assert(new_duty_cycle <= 100, "bad input value");
458
459 // Note: use subtraction with caution since it may underflow (values are
460 // unsigned). Addition is safe since we're in the range 0-100.
461 unsigned int damped_duty_cycle = new_duty_cycle;
462 if (new_duty_cycle < old_duty_cycle) {
463 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
464 if (new_duty_cycle + largest_delta < old_duty_cycle) {
465 damped_duty_cycle = old_duty_cycle - largest_delta;
466 }
467 } else if (new_duty_cycle > old_duty_cycle) {
468 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
469 if (new_duty_cycle > old_duty_cycle + largest_delta) {
470 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
471 }
472 }
473 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
474
475 if (CMSTraceIncrementalPacing) {
476 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
477 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
478 }
479 return damped_duty_cycle;
480 }
481
482 unsigned int CMSStats::icms_update_duty_cycle_impl() {
483 assert(CMSIncrementalPacing && valid(),
484 "should be handled in icms_update_duty_cycle()");
485
486 double cms_time_so_far = cms_timer().seconds();
487 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
488 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
489
490 // Avoid division by 0.
491 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
492 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
493
494 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
495 if (new_duty_cycle > _icms_duty_cycle) {
496 // Avoid very small duty cycles (1 or 2); 0 is allowed.
497 if (new_duty_cycle > 2) {
498 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
499 new_duty_cycle);
500 }
501 } else if (_allow_duty_cycle_reduction) {
502 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
503 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
504 // Respect the minimum duty cycle.
505 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
506 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
507 }
508
509 if (PrintGCDetails || CMSTraceIncrementalPacing) {
510 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
511 }
512
513 _allow_duty_cycle_reduction = false;
514 return _icms_duty_cycle;
515 }
516
517 #ifndef PRODUCT
518 void CMSStats::print_on(outputStream *st) const {
519 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
520 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
521 gc0_duration(), gc0_period(), gc0_promoted());
522 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
523 cms_duration(), cms_duration_per_mb(),
524 cms_period(), cms_allocated());
525 st->print(",cms_since_beg=%g,cms_since_end=%g",
526 cms_time_since_begin(), cms_time_since_end());
527 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
528 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
529 if (CMSIncrementalMode) {
530 st->print(",dc=%d", icms_duty_cycle());
531 }
532
533 if (valid()) {
534 st->print(",promo_rate=%g,cms_alloc_rate=%g",
535 promotion_rate(), cms_allocation_rate());
536 st->print(",cms_consumption_rate=%g,time_until_full=%g",
537 cms_consumption_rate(), time_until_cms_gen_full());
538 }
539 st->print(" ");
540 }
541 #endif // #ifndef PRODUCT
542
543 CMSCollector::CollectorState CMSCollector::_collectorState =
544 CMSCollector::Idling;
545 bool CMSCollector::_foregroundGCIsActive = false;
546 bool CMSCollector::_foregroundGCShouldWait = false;
547
548 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
549 ConcurrentMarkSweepGeneration* permGen,
550 CardTableRS* ct,
551 ConcurrentMarkSweepPolicy* cp):
552 _cmsGen(cmsGen),
553 _permGen(permGen),
554 _ct(ct),
555 _ref_processor(NULL), // will be set later
556 _conc_workers(NULL), // may be set later
557 _abort_preclean(false),
558 _start_sampling(false),
559 _between_prologue_and_epilogue(false),
560 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
561 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
562 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
563 -1 /* lock-free */, "No_lock" /* dummy */),
564 _modUnionClosure(&_modUnionTable),
565 _modUnionClosurePar(&_modUnionTable),
566 // Adjust my span to cover old (cms) gen and perm gen
567 _span(cmsGen->reserved()._union(permGen->reserved())),
568 // Construct the is_alive_closure with _span & markBitMap
569 _is_alive_closure(_span, &_markBitMap),
570 _restart_addr(NULL),
571 _overflow_list(NULL),
572 _stats(cmsGen),
573 _eden_chunk_array(NULL), // may be set in ctor body
574 _eden_chunk_capacity(0), // -- ditto --
575 _eden_chunk_index(0), // -- ditto --
576 _survivor_plab_array(NULL), // -- ditto --
577 _survivor_chunk_array(NULL), // -- ditto --
578 _survivor_chunk_capacity(0), // -- ditto --
579 _survivor_chunk_index(0), // -- ditto --
580 _ser_pmc_preclean_ovflw(0),
581 _ser_kac_preclean_ovflw(0),
582 _ser_pmc_remark_ovflw(0),
583 _par_pmc_remark_ovflw(0),
584 _ser_kac_ovflw(0),
585 _par_kac_ovflw(0),
586 #ifndef PRODUCT
587 _num_par_pushes(0),
588 #endif
589 _collection_count_start(0),
590 _verifying(false),
591 _icms_start_limit(NULL),
592 _icms_stop_limit(NULL),
593 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
594 _completed_initialization(false),
595 _collector_policy(cp),
596 _should_unload_classes(false),
597 _concurrent_cycles_since_last_unload(0),
598 _roots_scanning_options(0),
599 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
600 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
601 {
602 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
603 ExplicitGCInvokesConcurrent = true;
604 }
605 // Now expand the span and allocate the collection support structures
606 // (MUT, marking bit map etc.) to cover both generations subject to
607 // collection.
608
609 // First check that _permGen is adjacent to _cmsGen and above it.
610 assert( _cmsGen->reserved().word_size() > 0
611 && _permGen->reserved().word_size() > 0,
612 "generations should not be of zero size");
613 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
614 "_cmsGen and _permGen should not overlap");
615 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
616 "_cmsGen->end() different from _permGen->start()");
617
618 // For use by dirty card to oop closures.
619 _cmsGen->cmsSpace()->set_collector(this);
620 _permGen->cmsSpace()->set_collector(this);
621
622 // Allocate MUT and marking bit map
623 {
624 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
625 if (!_markBitMap.allocate(_span)) {
626 warning("Failed to allocate CMS Bit Map");
627 return;
628 }
629 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
630 }
631 {
632 _modUnionTable.allocate(_span);
633 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
634 }
635
636 if (!_markStack.allocate(MarkStackSize)) {
637 warning("Failed to allocate CMS Marking Stack");
638 return;
639 }
640 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
641 warning("Failed to allocate CMS Revisit Stack");
642 return;
643 }
644
645 // Support for multi-threaded concurrent phases
646 if (CMSConcurrentMTEnabled) {
647 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
648 // just for now
649 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
650 }
651 if (ConcGCThreads > 1) {
652 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
653 ConcGCThreads, true);
654 if (_conc_workers == NULL) {
655 warning("GC/CMS: _conc_workers allocation failure: "
656 "forcing -CMSConcurrentMTEnabled");
657 CMSConcurrentMTEnabled = false;
658 } else {
659 _conc_workers->initialize_workers();
660 }
661 } else {
662 CMSConcurrentMTEnabled = false;
663 }
664 }
665 if (!CMSConcurrentMTEnabled) {
666 ConcGCThreads = 0;
667 } else {
668 // Turn off CMSCleanOnEnter optimization temporarily for
669 // the MT case where it's not fixed yet; see 6178663.
670 CMSCleanOnEnter = false;
671 }
672 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
673 "Inconsistency");
674
675 // Parallel task queues; these are shared for the
676 // concurrent and stop-world phases of CMS, but
677 // are not shared with parallel scavenge (ParNew).
678 {
679 uint i;
680 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
681
682 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
683 || ParallelRefProcEnabled)
684 && num_queues > 0) {
685 _task_queues = new OopTaskQueueSet(num_queues);
686 if (_task_queues == NULL) {
687 warning("task_queues allocation failure.");
688 return;
689 }
690 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
691 if (_hash_seed == NULL) {
692 warning("_hash_seed array allocation failure");
693 return;
694 }
695
696 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
697 for (i = 0; i < num_queues; i++) {
698 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
699 if (q == NULL) {
700 warning("work_queue allocation failure.");
701 return;
702 }
703 _task_queues->register_queue(i, q);
704 }
705 for (i = 0; i < num_queues; i++) {
706 _task_queues->queue(i)->initialize();
707 _hash_seed[i] = 17; // copied from ParNew
708 }
709 }
710 }
711
712 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
713 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
714
715 // Clip CMSBootstrapOccupancy between 0 and 100.
716 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
717 /(double)100;
718
719 _full_gcs_since_conc_gc = 0;
720
721 // Now tell CMS generations the identity of their collector
722 ConcurrentMarkSweepGeneration::set_collector(this);
723
724 // Create & start a CMS thread for this CMS collector
725 _cmsThread = ConcurrentMarkSweepThread::start(this);
726 assert(cmsThread() != NULL, "CMS Thread should have been created");
727 assert(cmsThread()->collector() == this,
728 "CMS Thread should refer to this gen");
729 assert(CGC_lock != NULL, "Where's the CGC_lock?");
730
731 // Support for parallelizing young gen rescan
732 GenCollectedHeap* gch = GenCollectedHeap::heap();
733 _young_gen = gch->prev_gen(_cmsGen);
734 if (gch->supports_inline_contig_alloc()) {
735 _top_addr = gch->top_addr();
736 _end_addr = gch->end_addr();
737 assert(_young_gen != NULL, "no _young_gen");
738 _eden_chunk_index = 0;
739 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
740 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
741 if (_eden_chunk_array == NULL) {
742 _eden_chunk_capacity = 0;
743 warning("GC/CMS: _eden_chunk_array allocation failure");
744 }
745 }
746 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
747
748 // Support for parallelizing survivor space rescan
749 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
750 const size_t max_plab_samples =
751 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
752
753 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
754 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
755 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
756 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
757 || _cursor == NULL) {
758 warning("Failed to allocate survivor plab/chunk array");
759 if (_survivor_plab_array != NULL) {
760 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
761 _survivor_plab_array = NULL;
762 }
763 if (_survivor_chunk_array != NULL) {
764 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
765 _survivor_chunk_array = NULL;
766 }
767 if (_cursor != NULL) {
768 FREE_C_HEAP_ARRAY(size_t, _cursor);
769 _cursor = NULL;
770 }
771 } else {
772 _survivor_chunk_capacity = 2*max_plab_samples;
773 for (uint i = 0; i < ParallelGCThreads; i++) {
774 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
775 if (vec == NULL) {
776 warning("Failed to allocate survivor plab array");
777 for (int j = i; j > 0; j--) {
778 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
779 }
780 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
781 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
782 _survivor_plab_array = NULL;
783 _survivor_chunk_array = NULL;
784 _survivor_chunk_capacity = 0;
785 break;
786 } else {
787 ChunkArray* cur =
788 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
789 max_plab_samples);
790 assert(cur->end() == 0, "Should be 0");
791 assert(cur->array() == vec, "Should be vec");
792 assert(cur->capacity() == max_plab_samples, "Error");
793 }
794 }
795 }
796 }
797 assert( ( _survivor_plab_array != NULL
798 && _survivor_chunk_array != NULL)
799 || ( _survivor_chunk_capacity == 0
800 && _survivor_chunk_index == 0),
801 "Error");
802
803 // Choose what strong roots should be scanned depending on verification options
804 // and perm gen collection mode.
805 if (!CMSClassUnloadingEnabled) {
806 // If class unloading is disabled we want to include all classes into the root set.
807 add_root_scanning_option(SharedHeap::SO_AllClasses);
808 } else {
809 add_root_scanning_option(SharedHeap::SO_SystemClasses);
810 }
811
812 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
813 _gc_counters = new CollectorCounters("CMS", 1);
814 _completed_initialization = true;
815 _inter_sweep_timer.start(); // start of time
816 #ifdef SPARC
817 // Issue a stern warning, but allow use for experimentation and debugging.
818 if (VM_Version::is_sun4v() && UseMemSetInBOT) {
819 assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
820 warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
821 " on sun4v; please understand that you are using at your own risk!");
822 }
823 #endif
824 }
825
826 const char* ConcurrentMarkSweepGeneration::name() const {
827 return "concurrent mark-sweep generation";
828 }
829 void ConcurrentMarkSweepGeneration::update_counters() {
830 if (UsePerfData) {
831 _space_counters->update_all();
832 _gen_counters->update_all();
833 }
834 }
835
836 // this is an optimized version of update_counters(). it takes the
837 // used value as a parameter rather than computing it.
838 //
839 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
840 if (UsePerfData) {
841 _space_counters->update_used(used);
842 _space_counters->update_capacity();
843 _gen_counters->update_all();
844 }
845 }
846
847 void ConcurrentMarkSweepGeneration::print() const {
848 Generation::print();
849 cmsSpace()->print();
850 }
851
852 #ifndef PRODUCT
853 void ConcurrentMarkSweepGeneration::print_statistics() {
854 cmsSpace()->printFLCensus(0);
855 }
856 #endif
857
858 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
859 GenCollectedHeap* gch = GenCollectedHeap::heap();
860 if (PrintGCDetails) {
861 if (Verbose) {
862 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
863 level(), short_name(), s, used(), capacity());
864 } else {
865 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
866 level(), short_name(), s, used() / K, capacity() / K);
867 }
868 }
869 if (Verbose) {
870 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
871 gch->used(), gch->capacity());
872 } else {
873 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
874 gch->used() / K, gch->capacity() / K);
875 }
876 }
877
878 size_t
879 ConcurrentMarkSweepGeneration::contiguous_available() const {
880 // dld proposes an improvement in precision here. If the committed
881 // part of the space ends in a free block we should add that to
882 // uncommitted size in the calculation below. Will make this
883 // change later, staying with the approximation below for the
884 // time being. -- ysr.
885 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
886 }
887
888 size_t
889 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
890 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
891 }
892
893 size_t ConcurrentMarkSweepGeneration::max_available() const {
894 return free() + _virtual_space.uncommitted_size();
895 }
896
897 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
898 size_t available = max_available();
899 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
900 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
901 if (Verbose && PrintGCDetails) {
902 gclog_or_tty->print_cr(
903 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
904 "max_promo("SIZE_FORMAT")",
905 res? "":" not", available, res? ">=":"<",
906 av_promo, max_promotion_in_bytes);
907 }
908 return res;
909 }
910
911 // At a promotion failure dump information on block layout in heap
912 // (cms old generation).
913 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
914 if (CMSDumpAtPromotionFailure) {
915 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
916 }
917 }
918
919 CompactibleSpace*
920 ConcurrentMarkSweepGeneration::first_compaction_space() const {
921 return _cmsSpace;
922 }
923
924 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
925 // Clear the promotion information. These pointers can be adjusted
926 // along with all the other pointers into the heap but
927 // compaction is expected to be a rare event with
928 // a heap using cms so don't do it without seeing the need.
929 if (CollectedHeap::use_parallel_gc_threads()) {
930 for (uint i = 0; i < ParallelGCThreads; i++) {
931 _par_gc_thread_states[i]->promo.reset();
932 }
933 }
934 }
935
936 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
937 blk->do_space(_cmsSpace);
938 }
939
940 void ConcurrentMarkSweepGeneration::compute_new_size() {
941 assert_locked_or_safepoint(Heap_lock);
942
943 // If incremental collection failed, we just want to expand
944 // to the limit.
945 if (incremental_collection_failed()) {
946 clear_incremental_collection_failed();
947 grow_to_reserved();
948 return;
949 }
950
951 size_t expand_bytes = 0;
952 double free_percentage = ((double) free()) / capacity();
953 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
954 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
955
956 // compute expansion delta needed for reaching desired free percentage
957 if (free_percentage < desired_free_percentage) {
958 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
959 assert(desired_capacity >= capacity(), "invalid expansion size");
960 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
961 }
962 if (expand_bytes > 0) {
963 if (PrintGCDetails && Verbose) {
964 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
965 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
966 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
967 gclog_or_tty->print_cr(" Desired free fraction %f",
968 desired_free_percentage);
969 gclog_or_tty->print_cr(" Maximum free fraction %f",
970 maximum_free_percentage);
971 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
972 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
973 desired_capacity/1000);
974 int prev_level = level() - 1;
975 if (prev_level >= 0) {
976 size_t prev_size = 0;
977 GenCollectedHeap* gch = GenCollectedHeap::heap();
978 Generation* prev_gen = gch->_gens[prev_level];
979 prev_size = prev_gen->capacity();
980 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
981 prev_size/1000);
982 }
983 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
984 unsafe_max_alloc_nogc()/1000);
985 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
986 contiguous_available()/1000);
987 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
988 expand_bytes);
989 }
990 // safe if expansion fails
991 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
992 if (PrintGCDetails && Verbose) {
993 gclog_or_tty->print_cr(" Expanded free fraction %f",
994 ((double) free()) / capacity());
995 }
996 }
997 }
998
999 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1000 return cmsSpace()->freelistLock();
1001 }
1002
1003 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1004 bool tlab) {
1005 CMSSynchronousYieldRequest yr;
1006 MutexLockerEx x(freelistLock(),
1007 Mutex::_no_safepoint_check_flag);
1008 return have_lock_and_allocate(size, tlab);
1009 }
1010
1011 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1012 bool tlab /* ignored */) {
1013 assert_lock_strong(freelistLock());
1014 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1015 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1016 // Allocate the object live (grey) if the background collector has
1017 // started marking. This is necessary because the marker may
1018 // have passed this address and consequently this object will
1019 // not otherwise be greyed and would be incorrectly swept up.
1020 // Note that if this object contains references, the writing
1021 // of those references will dirty the card containing this object
1022 // allowing the object to be blackened (and its references scanned)
1023 // either during a preclean phase or at the final checkpoint.
1024 if (res != NULL) {
1025 // We may block here with an uninitialized object with
1026 // its mark-bit or P-bits not yet set. Such objects need
1027 // to be safely navigable by block_start().
1028 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1029 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1030 collector()->direct_allocated(res, adjustedSize);
1031 _direct_allocated_words += adjustedSize;
1032 // allocation counters
1033 NOT_PRODUCT(
1034 _numObjectsAllocated++;
1035 _numWordsAllocated += (int)adjustedSize;
1036 )
1037 }
1038 return res;
1039 }
1040
1041 // In the case of direct allocation by mutators in a generation that
1042 // is being concurrently collected, the object must be allocated
1043 // live (grey) if the background collector has started marking.
1044 // This is necessary because the marker may
1045 // have passed this address and consequently this object will
1046 // not otherwise be greyed and would be incorrectly swept up.
1047 // Note that if this object contains references, the writing
1048 // of those references will dirty the card containing this object
1049 // allowing the object to be blackened (and its references scanned)
1050 // either during a preclean phase or at the final checkpoint.
1051 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1052 assert(_markBitMap.covers(start, size), "Out of bounds");
1053 if (_collectorState >= Marking) {
1054 MutexLockerEx y(_markBitMap.lock(),
1055 Mutex::_no_safepoint_check_flag);
1056 // [see comments preceding SweepClosure::do_blk() below for details]
1057 // 1. need to mark the object as live so it isn't collected
1058 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1059 // 3. need to mark the end of the object so marking, precleaning or sweeping
1060 // can skip over uninitialized or unparsable objects. An allocated
1061 // object is considered uninitialized for our purposes as long as
1062 // its klass word is NULL. (Unparsable objects are those which are
1063 // initialized in the sense just described, but whose sizes can still
1064 // not be correctly determined. Note that the class of unparsable objects
1065 // can only occur in the perm gen. All old gen objects are parsable
1066 // as soon as they are initialized.)
1067 _markBitMap.mark(start); // object is live
1068 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1069 _markBitMap.mark(start + size - 1);
1070 // mark end of object
1071 }
1072 // check that oop looks uninitialized
1073 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1074 }
1075
1076 void CMSCollector::promoted(bool par, HeapWord* start,
1077 bool is_obj_array, size_t obj_size) {
1078 assert(_markBitMap.covers(start), "Out of bounds");
1079 // See comment in direct_allocated() about when objects should
1080 // be allocated live.
1081 if (_collectorState >= Marking) {
1082 // we already hold the marking bit map lock, taken in
1083 // the prologue
1084 if (par) {
1085 _markBitMap.par_mark(start);
1086 } else {
1087 _markBitMap.mark(start);
1088 }
1089 // We don't need to mark the object as uninitialized (as
1090 // in direct_allocated above) because this is being done with the
1091 // world stopped and the object will be initialized by the
1092 // time the marking, precleaning or sweeping get to look at it.
1093 // But see the code for copying objects into the CMS generation,
1094 // where we need to ensure that concurrent readers of the
1095 // block offset table are able to safely navigate a block that
1096 // is in flux from being free to being allocated (and in
1097 // transition while being copied into) and subsequently
1098 // becoming a bona-fide object when the copy/promotion is complete.
1099 assert(SafepointSynchronize::is_at_safepoint(),
1100 "expect promotion only at safepoints");
1101
1102 if (_collectorState < Sweeping) {
1103 // Mark the appropriate cards in the modUnionTable, so that
1104 // this object gets scanned before the sweep. If this is
1105 // not done, CMS generation references in the object might
1106 // not get marked.
1107 // For the case of arrays, which are otherwise precisely
1108 // marked, we need to dirty the entire array, not just its head.
1109 if (is_obj_array) {
1110 // The [par_]mark_range() method expects mr.end() below to
1111 // be aligned to the granularity of a bit's representation
1112 // in the heap. In the case of the MUT below, that's a
1113 // card size.
1114 MemRegion mr(start,
1115 (HeapWord*)round_to((intptr_t)(start + obj_size),
1116 CardTableModRefBS::card_size /* bytes */));
1117 if (par) {
1118 _modUnionTable.par_mark_range(mr);
1119 } else {
1120 _modUnionTable.mark_range(mr);
1121 }
1122 } else { // not an obj array; we can just mark the head
1123 if (par) {
1124 _modUnionTable.par_mark(start);
1125 } else {
1126 _modUnionTable.mark(start);
1127 }
1128 }
1129 }
1130 }
1131 }
1132
1133 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1134 {
1135 size_t delta = pointer_delta(addr, space->bottom());
1136 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1137 }
1138
1139 void CMSCollector::icms_update_allocation_limits()
1140 {
1141 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1142 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1143
1144 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1145 if (CMSTraceIncrementalPacing) {
1146 stats().print();
1147 }
1148
1149 assert(duty_cycle <= 100, "invalid duty cycle");
1150 if (duty_cycle != 0) {
1151 // The duty_cycle is a percentage between 0 and 100; convert to words and
1152 // then compute the offset from the endpoints of the space.
1153 size_t free_words = eden->free() / HeapWordSize;
1154 double free_words_dbl = (double)free_words;
1155 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1156 size_t offset_words = (free_words - duty_cycle_words) / 2;
1157
1158 _icms_start_limit = eden->top() + offset_words;
1159 _icms_stop_limit = eden->end() - offset_words;
1160
1161 // The limits may be adjusted (shifted to the right) by
1162 // CMSIncrementalOffset, to allow the application more mutator time after a
1163 // young gen gc (when all mutators were stopped) and before CMS starts and
1164 // takes away one or more cpus.
1165 if (CMSIncrementalOffset != 0) {
1166 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1167 size_t adjustment = (size_t)adjustment_dbl;
1168 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1169 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1170 _icms_start_limit += adjustment;
1171 _icms_stop_limit = tmp_stop;
1172 }
1173 }
1174 }
1175 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1176 _icms_start_limit = _icms_stop_limit = eden->end();
1177 }
1178
1179 // Install the new start limit.
1180 eden->set_soft_end(_icms_start_limit);
1181
1182 if (CMSTraceIncrementalMode) {
1183 gclog_or_tty->print(" icms alloc limits: "
1184 PTR_FORMAT "," PTR_FORMAT
1185 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1186 _icms_start_limit, _icms_stop_limit,
1187 percent_of_space(eden, _icms_start_limit),
1188 percent_of_space(eden, _icms_stop_limit));
1189 if (Verbose) {
1190 gclog_or_tty->print("eden: ");
1191 eden->print_on(gclog_or_tty);
1192 }
1193 }
1194 }
1195
1196 // Any changes here should try to maintain the invariant
1197 // that if this method is called with _icms_start_limit
1198 // and _icms_stop_limit both NULL, then it should return NULL
1199 // and not notify the icms thread.
1200 HeapWord*
1201 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1202 size_t word_size)
1203 {
1204 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1205 // nop.
1206 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1207 if (top <= _icms_start_limit) {
1208 if (CMSTraceIncrementalMode) {
1209 space->print_on(gclog_or_tty);
1210 gclog_or_tty->stamp();
1211 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1212 ", new limit=" PTR_FORMAT
1213 " (" SIZE_FORMAT "%%)",
1214 top, _icms_stop_limit,
1215 percent_of_space(space, _icms_stop_limit));
1216 }
1217 ConcurrentMarkSweepThread::start_icms();
1218 assert(top < _icms_stop_limit, "Tautology");
1219 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1220 return _icms_stop_limit;
1221 }
1222
1223 // The allocation will cross both the _start and _stop limits, so do the
1224 // stop notification also and return end().
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 top, space->end(),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1237
1238 if (top <= _icms_stop_limit) {
1239 if (CMSTraceIncrementalMode) {
1240 space->print_on(gclog_or_tty);
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1243 ", new limit=" PTR_FORMAT
1244 " (" SIZE_FORMAT "%%)",
1245 top, space->end(),
1246 percent_of_space(space, space->end()));
1247 }
1248 ConcurrentMarkSweepThread::stop_icms();
1249 return space->end();
1250 }
1251
1252 if (CMSTraceIncrementalMode) {
1253 space->print_on(gclog_or_tty);
1254 gclog_or_tty->stamp();
1255 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1256 ", new limit=" PTR_FORMAT,
1257 top, NULL);
1258 }
1259 }
1260
1261 return NULL;
1262 }
1263
1264 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1265 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1266 // allocate, copy and if necessary update promoinfo --
1267 // delegate to underlying space.
1268 assert_lock_strong(freelistLock());
1269
1270 #ifndef PRODUCT
1271 if (Universe::heap()->promotion_should_fail()) {
1272 return NULL;
1273 }
1274 #endif // #ifndef PRODUCT
1275
1276 oop res = _cmsSpace->promote(obj, obj_size);
1277 if (res == NULL) {
1278 // expand and retry
1279 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1280 expand(s*HeapWordSize, MinHeapDeltaBytes,
1281 CMSExpansionCause::_satisfy_promotion);
1282 // Since there's currently no next generation, we don't try to promote
1283 // into a more senior generation.
1284 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1285 "is made to pass on a possibly failing "
1286 "promotion to next generation");
1287 res = _cmsSpace->promote(obj, obj_size);
1288 }
1289 if (res != NULL) {
1290 // See comment in allocate() about when objects should
1291 // be allocated live.
1292 assert(obj->is_oop(), "Will dereference klass pointer below");
1293 collector()->promoted(false, // Not parallel
1294 (HeapWord*)res, obj->is_objArray(), obj_size);
1295 // promotion counters
1296 NOT_PRODUCT(
1297 _numObjectsPromoted++;
1298 _numWordsPromoted +=
1299 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1300 )
1301 }
1302 return res;
1303 }
1304
1305
1306 HeapWord*
1307 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1308 HeapWord* top,
1309 size_t word_sz)
1310 {
1311 return collector()->allocation_limit_reached(space, top, word_sz);
1312 }
1313
1314 // IMPORTANT: Notes on object size recognition in CMS.
1315 // ---------------------------------------------------
1316 // A block of storage in the CMS generation is always in
1317 // one of three states. A free block (FREE), an allocated
1318 // object (OBJECT) whose size() method reports the correct size,
1319 // and an intermediate state (TRANSIENT) in which its size cannot
1320 // be accurately determined.
1321 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1322 // -----------------------------------------------------
1323 // FREE: klass_word & 1 == 1; mark_word holds block size
1324 //
1325 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1326 // obj->size() computes correct size
1327 // [Perm Gen objects needs to be "parsable" before they can be navigated]
1328 //
1329 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1330 //
1331 // STATE IDENTIFICATION: (64 bit+COOPS)
1332 // ------------------------------------
1333 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1334 //
1335 // OBJECT: klass_word installed; klass_word != 0;
1336 // obj->size() computes correct size
1337 // [Perm Gen comment above continues to hold]
1338 //
1339 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1340 //
1341 //
1342 // STATE TRANSITION DIAGRAM
1343 //
1344 // mut / parnew mut / parnew
1345 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1346 // ^ |
1347 // |------------------------ DEAD <------------------------------------|
1348 // sweep mut
1349 //
1350 // While a block is in TRANSIENT state its size cannot be determined
1351 // so readers will either need to come back later or stall until
1352 // the size can be determined. Note that for the case of direct
1353 // allocation, P-bits, when available, may be used to determine the
1354 // size of an object that may not yet have been initialized.
1355
1356 // Things to support parallel young-gen collection.
1357 oop
1358 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1359 oop old, markOop m,
1360 size_t word_sz) {
1361 #ifndef PRODUCT
1362 if (Universe::heap()->promotion_should_fail()) {
1363 return NULL;
1364 }
1365 #endif // #ifndef PRODUCT
1366
1367 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1368 PromotionInfo* promoInfo = &ps->promo;
1369 // if we are tracking promotions, then first ensure space for
1370 // promotion (including spooling space for saving header if necessary).
1371 // then allocate and copy, then track promoted info if needed.
1372 // When tracking (see PromotionInfo::track()), the mark word may
1373 // be displaced and in this case restoration of the mark word
1374 // occurs in the (oop_since_save_marks_)iterate phase.
1375 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1376 // Out of space for allocating spooling buffers;
1377 // try expanding and allocating spooling buffers.
1378 if (!expand_and_ensure_spooling_space(promoInfo)) {
1379 return NULL;
1380 }
1381 }
1382 assert(promoInfo->has_spooling_space(), "Control point invariant");
1383 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1384 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1385 if (obj_ptr == NULL) {
1386 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1387 if (obj_ptr == NULL) {
1388 return NULL;
1389 }
1390 }
1391 oop obj = oop(obj_ptr);
1392 OrderAccess::storestore();
1393 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1394 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1395 // IMPORTANT: See note on object initialization for CMS above.
1396 // Otherwise, copy the object. Here we must be careful to insert the
1397 // klass pointer last, since this marks the block as an allocated object.
1398 // Except with compressed oops it's the mark word.
1399 HeapWord* old_ptr = (HeapWord*)old;
1400 // Restore the mark word copied above.
1401 obj->set_mark(m);
1402 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1403 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1404 OrderAccess::storestore();
1405
1406 if (UseCompressedOops) {
1407 // Copy gap missed by (aligned) header size calculation below
1408 obj->set_klass_gap(old->klass_gap());
1409 }
1410 if (word_sz > (size_t)oopDesc::header_size()) {
1411 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1412 obj_ptr + oopDesc::header_size(),
1413 word_sz - oopDesc::header_size());
1414 }
1415
1416 // Now we can track the promoted object, if necessary. We take care
1417 // to delay the transition from uninitialized to full object
1418 // (i.e., insertion of klass pointer) until after, so that it
1419 // atomically becomes a promoted object.
1420 if (promoInfo->tracking()) {
1421 promoInfo->track((PromotedObject*)obj, old->klass());
1422 }
1423 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1424 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1425 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1426
1427 // Finally, install the klass pointer (this should be volatile).
1428 OrderAccess::storestore();
1429 obj->set_klass(old->klass());
1430 // We should now be able to calculate the right size for this object
1431 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1432
1433 collector()->promoted(true, // parallel
1434 obj_ptr, old->is_objArray(), word_sz);
1435
1436 NOT_PRODUCT(
1437 Atomic::inc_ptr(&_numObjectsPromoted);
1438 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1439 )
1440
1441 return obj;
1442 }
1443
1444 void
1445 ConcurrentMarkSweepGeneration::
1446 par_promote_alloc_undo(int thread_num,
1447 HeapWord* obj, size_t word_sz) {
1448 // CMS does not support promotion undo.
1449 ShouldNotReachHere();
1450 }
1451
1452 void
1453 ConcurrentMarkSweepGeneration::
1454 par_promote_alloc_done(int thread_num) {
1455 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1456 ps->lab.retire(thread_num);
1457 }
1458
1459 void
1460 ConcurrentMarkSweepGeneration::
1461 par_oop_since_save_marks_iterate_done(int thread_num) {
1462 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1463 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1464 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1465 }
1466
1467 // XXXPERM
1468 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1469 size_t size,
1470 bool tlab)
1471 {
1472 // We allow a STW collection only if a full
1473 // collection was requested.
1474 return full || should_allocate(size, tlab); // FIX ME !!!
1475 // This and promotion failure handling are connected at the
1476 // hip and should be fixed by untying them.
1477 }
1478
1479 bool CMSCollector::shouldConcurrentCollect() {
1480 if (_full_gc_requested) {
1481 if (Verbose && PrintGCDetails) {
1482 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1483 " gc request (or gc_locker)");
1484 }
1485 return true;
1486 }
1487
1488 // For debugging purposes, change the type of collection.
1489 // If the rotation is not on the concurrent collection
1490 // type, don't start a concurrent collection.
1491 NOT_PRODUCT(
1492 if (RotateCMSCollectionTypes &&
1493 (_cmsGen->debug_collection_type() !=
1494 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1495 assert(_cmsGen->debug_collection_type() !=
1496 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1497 "Bad cms collection type");
1498 return false;
1499 }
1500 )
1501
1502 FreelistLocker x(this);
1503 // ------------------------------------------------------------------
1504 // Print out lots of information which affects the initiation of
1505 // a collection.
1506 if (PrintCMSInitiationStatistics && stats().valid()) {
1507 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1508 gclog_or_tty->stamp();
1509 gclog_or_tty->print_cr("");
1510 stats().print_on(gclog_or_tty);
1511 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1512 stats().time_until_cms_gen_full());
1513 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1514 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1515 _cmsGen->contiguous_available());
1516 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1517 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1518 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1519 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1520 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1521 }
1522 // ------------------------------------------------------------------
1523
1524 // If the estimated time to complete a cms collection (cms_duration())
1525 // is less than the estimated time remaining until the cms generation
1526 // is full, start a collection.
1527 if (!UseCMSInitiatingOccupancyOnly) {
1528 if (stats().valid()) {
1529 if (stats().time_until_cms_start() == 0.0) {
1530 return true;
1531 }
1532 } else {
1533 // We want to conservatively collect somewhat early in order
1534 // to try and "bootstrap" our CMS/promotion statistics;
1535 // this branch will not fire after the first successful CMS
1536 // collection because the stats should then be valid.
1537 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1538 if (Verbose && PrintGCDetails) {
1539 gclog_or_tty->print_cr(
1540 " CMSCollector: collect for bootstrapping statistics:"
1541 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1542 _bootstrap_occupancy);
1543 }
1544 return true;
1545 }
1546 }
1547 }
1548
1549 // Otherwise, we start a collection cycle if either the perm gen or
1550 // old gen want a collection cycle started. Each may use
1551 // an appropriate criterion for making this decision.
1552 // XXX We need to make sure that the gen expansion
1553 // criterion dovetails well with this. XXX NEED TO FIX THIS
1554 if (_cmsGen->should_concurrent_collect()) {
1555 if (Verbose && PrintGCDetails) {
1556 gclog_or_tty->print_cr("CMS old gen initiated");
1557 }
1558 return true;
1559 }
1560
1561 // We start a collection if we believe an incremental collection may fail;
1562 // this is not likely to be productive in practice because it's probably too
1563 // late anyway.
1564 GenCollectedHeap* gch = GenCollectedHeap::heap();
1565 assert(gch->collector_policy()->is_two_generation_policy(),
1566 "You may want to check the correctness of the following");
1567 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1568 if (Verbose && PrintGCDetails) {
1569 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1570 }
1571 return true;
1572 }
1573
1574 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1575 bool res = update_should_unload_classes();
1576 if (res) {
1577 if (Verbose && PrintGCDetails) {
1578 gclog_or_tty->print_cr("CMS perm gen initiated");
1579 }
1580 return true;
1581 }
1582 }
1583 return false;
1584 }
1585
1586 // Clear _expansion_cause fields of constituent generations
1587 void CMSCollector::clear_expansion_cause() {
1588 _cmsGen->clear_expansion_cause();
1589 _permGen->clear_expansion_cause();
1590 }
1591
1592 // We should be conservative in starting a collection cycle. To
1593 // start too eagerly runs the risk of collecting too often in the
1594 // extreme. To collect too rarely falls back on full collections,
1595 // which works, even if not optimum in terms of concurrent work.
1596 // As a work around for too eagerly collecting, use the flag
1597 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1598 // giving the user an easily understandable way of controlling the
1599 // collections.
1600 // We want to start a new collection cycle if any of the following
1601 // conditions hold:
1602 // . our current occupancy exceeds the configured initiating occupancy
1603 // for this generation, or
1604 // . we recently needed to expand this space and have not, since that
1605 // expansion, done a collection of this generation, or
1606 // . the underlying space believes that it may be a good idea to initiate
1607 // a concurrent collection (this may be based on criteria such as the
1608 // following: the space uses linear allocation and linear allocation is
1609 // going to fail, or there is believed to be excessive fragmentation in
1610 // the generation, etc... or ...
1611 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1612 // the case of the old generation, not the perm generation; see CR 6543076):
1613 // we may be approaching a point at which allocation requests may fail because
1614 // we will be out of sufficient free space given allocation rate estimates.]
1615 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1616
1617 assert_lock_strong(freelistLock());
1618 if (occupancy() > initiating_occupancy()) {
1619 if (PrintGCDetails && Verbose) {
1620 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1621 short_name(), occupancy(), initiating_occupancy());
1622 }
1623 return true;
1624 }
1625 if (UseCMSInitiatingOccupancyOnly) {
1626 return false;
1627 }
1628 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1629 if (PrintGCDetails && Verbose) {
1630 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1631 short_name());
1632 }
1633 return true;
1634 }
1635 if (_cmsSpace->should_concurrent_collect()) {
1636 if (PrintGCDetails && Verbose) {
1637 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1638 short_name());
1639 }
1640 return true;
1641 }
1642 return false;
1643 }
1644
1645 void ConcurrentMarkSweepGeneration::collect(bool full,
1646 bool clear_all_soft_refs,
1647 size_t size,
1648 bool tlab)
1649 {
1650 collector()->collect(full, clear_all_soft_refs, size, tlab);
1651 }
1652
1653 void CMSCollector::collect(bool full,
1654 bool clear_all_soft_refs,
1655 size_t size,
1656 bool tlab)
1657 {
1658 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1659 // For debugging purposes skip the collection if the state
1660 // is not currently idle
1661 if (TraceCMSState) {
1662 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1663 Thread::current(), full, _collectorState);
1664 }
1665 return;
1666 }
1667
1668 // The following "if" branch is present for defensive reasons.
1669 // In the current uses of this interface, it can be replaced with:
1670 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1671 // But I am not placing that assert here to allow future
1672 // generality in invoking this interface.
1673 if (GC_locker::is_active()) {
1674 // A consistency test for GC_locker
1675 assert(GC_locker::needs_gc(), "Should have been set already");
1676 // Skip this foreground collection, instead
1677 // expanding the heap if necessary.
1678 // Need the free list locks for the call to free() in compute_new_size()
1679 compute_new_size();
1680 return;
1681 }
1682 acquire_control_and_collect(full, clear_all_soft_refs);
1683 _full_gcs_since_conc_gc++;
1684
1685 }
1686
1687 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1688 GenCollectedHeap* gch = GenCollectedHeap::heap();
1689 unsigned int gc_count = gch->total_full_collections();
1690 if (gc_count == full_gc_count) {
1691 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1692 _full_gc_requested = true;
1693 CGC_lock->notify(); // nudge CMS thread
1694 } else {
1695 assert(gc_count > full_gc_count, "Error: causal loop");
1696 }
1697 }
1698
1699
1700 // The foreground and background collectors need to coordinate in order
1701 // to make sure that they do not mutually interfere with CMS collections.
1702 // When a background collection is active,
1703 // the foreground collector may need to take over (preempt) and
1704 // synchronously complete an ongoing collection. Depending on the
1705 // frequency of the background collections and the heap usage
1706 // of the application, this preemption can be seldom or frequent.
1707 // There are only certain
1708 // points in the background collection that the "collection-baton"
1709 // can be passed to the foreground collector.
1710 //
1711 // The foreground collector will wait for the baton before
1712 // starting any part of the collection. The foreground collector
1713 // will only wait at one location.
1714 //
1715 // The background collector will yield the baton before starting a new
1716 // phase of the collection (e.g., before initial marking, marking from roots,
1717 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1718 // of the loop which switches the phases. The background collector does some
1719 // of the phases (initial mark, final re-mark) with the world stopped.
1720 // Because of locking involved in stopping the world,
1721 // the foreground collector should not block waiting for the background
1722 // collector when it is doing a stop-the-world phase. The background
1723 // collector will yield the baton at an additional point just before
1724 // it enters a stop-the-world phase. Once the world is stopped, the
1725 // background collector checks the phase of the collection. If the
1726 // phase has not changed, it proceeds with the collection. If the
1727 // phase has changed, it skips that phase of the collection. See
1728 // the comments on the use of the Heap_lock in collect_in_background().
1729 //
1730 // Variable used in baton passing.
1731 // _foregroundGCIsActive - Set to true by the foreground collector when
1732 // it wants the baton. The foreground clears it when it has finished
1733 // the collection.
1734 // _foregroundGCShouldWait - Set to true by the background collector
1735 // when it is running. The foreground collector waits while
1736 // _foregroundGCShouldWait is true.
1737 // CGC_lock - monitor used to protect access to the above variables
1738 // and to notify the foreground and background collectors.
1739 // _collectorState - current state of the CMS collection.
1740 //
1741 // The foreground collector
1742 // acquires the CGC_lock
1743 // sets _foregroundGCIsActive
1744 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1745 // various locks acquired in preparation for the collection
1746 // are released so as not to block the background collector
1747 // that is in the midst of a collection
1748 // proceeds with the collection
1749 // clears _foregroundGCIsActive
1750 // returns
1751 //
1752 // The background collector in a loop iterating on the phases of the
1753 // collection
1754 // acquires the CGC_lock
1755 // sets _foregroundGCShouldWait
1756 // if _foregroundGCIsActive is set
1757 // clears _foregroundGCShouldWait, notifies _CGC_lock
1758 // waits on _CGC_lock for _foregroundGCIsActive to become false
1759 // and exits the loop.
1760 // otherwise
1761 // proceed with that phase of the collection
1762 // if the phase is a stop-the-world phase,
1763 // yield the baton once more just before enqueueing
1764 // the stop-world CMS operation (executed by the VM thread).
1765 // returns after all phases of the collection are done
1766 //
1767
1768 void CMSCollector::acquire_control_and_collect(bool full,
1769 bool clear_all_soft_refs) {
1770 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1771 assert(!Thread::current()->is_ConcurrentGC_thread(),
1772 "shouldn't try to acquire control from self!");
1773
1774 // Start the protocol for acquiring control of the
1775 // collection from the background collector (aka CMS thread).
1776 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1777 "VM thread should have CMS token");
1778 // Remember the possibly interrupted state of an ongoing
1779 // concurrent collection
1780 CollectorState first_state = _collectorState;
1781
1782 // Signal to a possibly ongoing concurrent collection that
1783 // we want to do a foreground collection.
1784 _foregroundGCIsActive = true;
1785
1786 // Disable incremental mode during a foreground collection.
1787 ICMSDisabler icms_disabler;
1788
1789 // release locks and wait for a notify from the background collector
1790 // releasing the locks in only necessary for phases which
1791 // do yields to improve the granularity of the collection.
1792 assert_lock_strong(bitMapLock());
1793 // We need to lock the Free list lock for the space that we are
1794 // currently collecting.
1795 assert(haveFreelistLocks(), "Must be holding free list locks");
1796 bitMapLock()->unlock();
1797 releaseFreelistLocks();
1798 {
1799 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1800 if (_foregroundGCShouldWait) {
1801 // We are going to be waiting for action for the CMS thread;
1802 // it had better not be gone (for instance at shutdown)!
1803 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1804 "CMS thread must be running");
1805 // Wait here until the background collector gives us the go-ahead
1806 ConcurrentMarkSweepThread::clear_CMS_flag(
1807 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1808 // Get a possibly blocked CMS thread going:
1809 // Note that we set _foregroundGCIsActive true above,
1810 // without protection of the CGC_lock.
1811 CGC_lock->notify();
1812 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1813 "Possible deadlock");
1814 while (_foregroundGCShouldWait) {
1815 // wait for notification
1816 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1817 // Possibility of delay/starvation here, since CMS token does
1818 // not know to give priority to VM thread? Actually, i think
1819 // there wouldn't be any delay/starvation, but the proof of
1820 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1821 }
1822 ConcurrentMarkSweepThread::set_CMS_flag(
1823 ConcurrentMarkSweepThread::CMS_vm_has_token);
1824 }
1825 }
1826 // The CMS_token is already held. Get back the other locks.
1827 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1828 "VM thread should have CMS token");
1829 getFreelistLocks();
1830 bitMapLock()->lock_without_safepoint_check();
1831 if (TraceCMSState) {
1832 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1833 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1834 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1835 }
1836
1837 // Check if we need to do a compaction, or if not, whether
1838 // we need to start the mark-sweep from scratch.
1839 bool should_compact = false;
1840 bool should_start_over = false;
1841 decide_foreground_collection_type(clear_all_soft_refs,
1842 &should_compact, &should_start_over);
1843
1844 NOT_PRODUCT(
1845 if (RotateCMSCollectionTypes) {
1846 if (_cmsGen->debug_collection_type() ==
1847 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1848 should_compact = true;
1849 } else if (_cmsGen->debug_collection_type() ==
1850 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1851 should_compact = false;
1852 }
1853 }
1854 )
1855
1856 if (PrintGCDetails && first_state > Idling) {
1857 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1858 if (GCCause::is_user_requested_gc(cause) ||
1859 GCCause::is_serviceability_requested_gc(cause)) {
1860 gclog_or_tty->print(" (concurrent mode interrupted)");
1861 } else {
1862 gclog_or_tty->print(" (concurrent mode failure)");
1863 }
1864 }
1865
1866 if (should_compact) {
1867 // If the collection is being acquired from the background
1868 // collector, there may be references on the discovered
1869 // references lists that have NULL referents (being those
1870 // that were concurrently cleared by a mutator) or
1871 // that are no longer active (having been enqueued concurrently
1872 // by the mutator).
1873 // Scrub the list of those references because Mark-Sweep-Compact
1874 // code assumes referents are not NULL and that all discovered
1875 // Reference objects are active.
1876 ref_processor()->clean_up_discovered_references();
1877
1878 do_compaction_work(clear_all_soft_refs);
1879
1880 // Has the GC time limit been exceeded?
1881 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1882 size_t max_eden_size = young_gen->max_capacity() -
1883 young_gen->to()->capacity() -
1884 young_gen->from()->capacity();
1885 GenCollectedHeap* gch = GenCollectedHeap::heap();
1886 GCCause::Cause gc_cause = gch->gc_cause();
1887 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1888 young_gen->eden()->used(),
1889 _cmsGen->max_capacity(),
1890 max_eden_size,
1891 full,
1892 gc_cause,
1893 gch->collector_policy());
1894 } else {
1895 do_mark_sweep_work(clear_all_soft_refs, first_state,
1896 should_start_over);
1897 }
1898 // Reset the expansion cause, now that we just completed
1899 // a collection cycle.
1900 clear_expansion_cause();
1901 _foregroundGCIsActive = false;
1902 return;
1903 }
1904
1905 // Resize the perm generation and the tenured generation
1906 // after obtaining the free list locks for the
1907 // two generations.
1908 void CMSCollector::compute_new_size() {
1909 assert_locked_or_safepoint(Heap_lock);
1910 FreelistLocker z(this);
1911 _permGen->compute_new_size();
1912 _cmsGen->compute_new_size();
1913 }
1914
1915 // A work method used by foreground collection to determine
1916 // what type of collection (compacting or not, continuing or fresh)
1917 // it should do.
1918 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1919 // and CMSCompactWhenClearAllSoftRefs the default in the future
1920 // and do away with the flags after a suitable period.
1921 void CMSCollector::decide_foreground_collection_type(
1922 bool clear_all_soft_refs, bool* should_compact,
1923 bool* should_start_over) {
1924 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1925 // flag is set, and we have either requested a System.gc() or
1926 // the number of full gc's since the last concurrent cycle
1927 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1928 // or if an incremental collection has failed
1929 GenCollectedHeap* gch = GenCollectedHeap::heap();
1930 assert(gch->collector_policy()->is_two_generation_policy(),
1931 "You may want to check the correctness of the following");
1932 // Inform cms gen if this was due to partial collection failing.
1933 // The CMS gen may use this fact to determine its expansion policy.
1934 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1935 assert(!_cmsGen->incremental_collection_failed(),
1936 "Should have been noticed, reacted to and cleared");
1937 _cmsGen->set_incremental_collection_failed();
1938 }
1939 *should_compact =
1940 UseCMSCompactAtFullCollection &&
1941 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1942 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1943 gch->incremental_collection_will_fail(true /* consult_young */));
1944 *should_start_over = false;
1945 if (clear_all_soft_refs && !*should_compact) {
1946 // We are about to do a last ditch collection attempt
1947 // so it would normally make sense to do a compaction
1948 // to reclaim as much space as possible.
1949 if (CMSCompactWhenClearAllSoftRefs) {
1950 // Default: The rationale is that in this case either
1951 // we are past the final marking phase, in which case
1952 // we'd have to start over, or so little has been done
1953 // that there's little point in saving that work. Compaction
1954 // appears to be the sensible choice in either case.
1955 *should_compact = true;
1956 } else {
1957 // We have been asked to clear all soft refs, but not to
1958 // compact. Make sure that we aren't past the final checkpoint
1959 // phase, for that is where we process soft refs. If we are already
1960 // past that phase, we'll need to redo the refs discovery phase and
1961 // if necessary clear soft refs that weren't previously
1962 // cleared. We do so by remembering the phase in which
1963 // we came in, and if we are past the refs processing
1964 // phase, we'll choose to just redo the mark-sweep
1965 // collection from scratch.
1966 if (_collectorState > FinalMarking) {
1967 // We are past the refs processing phase;
1968 // start over and do a fresh synchronous CMS cycle
1969 _collectorState = Resetting; // skip to reset to start new cycle
1970 reset(false /* == !asynch */);
1971 *should_start_over = true;
1972 } // else we can continue a possibly ongoing current cycle
1973 }
1974 }
1975 }
1976
1977 // A work method used by the foreground collector to do
1978 // a mark-sweep-compact.
1979 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1980 GenCollectedHeap* gch = GenCollectedHeap::heap();
1981 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1982 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1983 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1984 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1985 }
1986
1987 // Sample collection interval time and reset for collection pause.
1988 if (UseAdaptiveSizePolicy) {
1989 size_policy()->msc_collection_begin();
1990 }
1991
1992 // Temporarily widen the span of the weak reference processing to
1993 // the entire heap.
1994 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1995 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1996 // Temporarily, clear the "is_alive_non_header" field of the
1997 // reference processor.
1998 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1999 // Temporarily make reference _processing_ single threaded (non-MT).
2000 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2001 // Temporarily make refs discovery atomic
2002 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2003 // Temporarily make reference _discovery_ single threaded (non-MT)
2004 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2005
2006 ref_processor()->set_enqueuing_is_done(false);
2007 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2008 ref_processor()->setup_policy(clear_all_soft_refs);
2009 // If an asynchronous collection finishes, the _modUnionTable is
2010 // all clear. If we are assuming the collection from an asynchronous
2011 // collection, clear the _modUnionTable.
2012 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2013 "_modUnionTable should be clear if the baton was not passed");
2014 _modUnionTable.clear_all();
2015
2016 // We must adjust the allocation statistics being maintained
2017 // in the free list space. We do so by reading and clearing
2018 // the sweep timer and updating the block flux rate estimates below.
2019 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2020 if (_inter_sweep_timer.is_active()) {
2021 _inter_sweep_timer.stop();
2022 // Note that we do not use this sample to update the _inter_sweep_estimate.
2023 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2024 _inter_sweep_estimate.padded_average(),
2025 _intra_sweep_estimate.padded_average());
2026 }
2027
2028 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2029 ref_processor(), clear_all_soft_refs);
2030 #ifdef ASSERT
2031 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2032 size_t free_size = cms_space->free();
2033 assert(free_size ==
2034 pointer_delta(cms_space->end(), cms_space->compaction_top())
2035 * HeapWordSize,
2036 "All the free space should be compacted into one chunk at top");
2037 assert(cms_space->dictionary()->total_chunk_size(
2038 debug_only(cms_space->freelistLock())) == 0 ||
2039 cms_space->totalSizeInIndexedFreeLists() == 0,
2040 "All the free space should be in a single chunk");
2041 size_t num = cms_space->totalCount();
2042 assert((free_size == 0 && num == 0) ||
2043 (free_size > 0 && (num == 1 || num == 2)),
2044 "There should be at most 2 free chunks after compaction");
2045 #endif // ASSERT
2046 _collectorState = Resetting;
2047 assert(_restart_addr == NULL,
2048 "Should have been NULL'd before baton was passed");
2049 reset(false /* == !asynch */);
2050 _cmsGen->reset_after_compaction();
2051 _concurrent_cycles_since_last_unload = 0;
2052
2053 if (verifying() && !should_unload_classes()) {
2054 perm_gen_verify_bit_map()->clear_all();
2055 }
2056
2057 // Clear any data recorded in the PLAB chunk arrays.
2058 if (_survivor_plab_array != NULL) {
2059 reset_survivor_plab_arrays();
2060 }
2061
2062 // Adjust the per-size allocation stats for the next epoch.
2063 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2064 // Restart the "inter sweep timer" for the next epoch.
2065 _inter_sweep_timer.reset();
2066 _inter_sweep_timer.start();
2067
2068 // Sample collection pause time and reset for collection interval.
2069 if (UseAdaptiveSizePolicy) {
2070 size_policy()->msc_collection_end(gch->gc_cause());
2071 }
2072
2073 // For a mark-sweep-compact, compute_new_size() will be called
2074 // in the heap's do_collection() method.
2075 }
2076
2077 // A work method used by the foreground collector to do
2078 // a mark-sweep, after taking over from a possibly on-going
2079 // concurrent mark-sweep collection.
2080 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2081 CollectorState first_state, bool should_start_over) {
2082 if (PrintGC && Verbose) {
2083 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2084 "collector with count %d",
2085 _full_gcs_since_conc_gc);
2086 }
2087 switch (_collectorState) {
2088 case Idling:
2089 if (first_state == Idling || should_start_over) {
2090 // The background GC was not active, or should
2091 // restarted from scratch; start the cycle.
2092 _collectorState = InitialMarking;
2093 }
2094 // If first_state was not Idling, then a background GC
2095 // was in progress and has now finished. No need to do it
2096 // again. Leave the state as Idling.
2097 break;
2098 case Precleaning:
2099 // In the foreground case don't do the precleaning since
2100 // it is not done concurrently and there is extra work
2101 // required.
2102 _collectorState = FinalMarking;
2103 }
2104 if (PrintGCDetails &&
2105 (_collectorState > Idling ||
2106 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2107 gclog_or_tty->print(" (concurrent mode failure)");
2108 }
2109 collect_in_foreground(clear_all_soft_refs);
2110
2111 // For a mark-sweep, compute_new_size() will be called
2112 // in the heap's do_collection() method.
2113 }
2114
2115
2116 void CMSCollector::getFreelistLocks() const {
2117 // Get locks for all free lists in all generations that this
2118 // collector is responsible for
2119 _cmsGen->freelistLock()->lock_without_safepoint_check();
2120 _permGen->freelistLock()->lock_without_safepoint_check();
2121 }
2122
2123 void CMSCollector::releaseFreelistLocks() const {
2124 // Release locks for all free lists in all generations that this
2125 // collector is responsible for
2126 _cmsGen->freelistLock()->unlock();
2127 _permGen->freelistLock()->unlock();
2128 }
2129
2130 bool CMSCollector::haveFreelistLocks() const {
2131 // Check locks for all free lists in all generations that this
2132 // collector is responsible for
2133 assert_lock_strong(_cmsGen->freelistLock());
2134 assert_lock_strong(_permGen->freelistLock());
2135 PRODUCT_ONLY(ShouldNotReachHere());
2136 return true;
2137 }
2138
2139 // A utility class that is used by the CMS collector to
2140 // temporarily "release" the foreground collector from its
2141 // usual obligation to wait for the background collector to
2142 // complete an ongoing phase before proceeding.
2143 class ReleaseForegroundGC: public StackObj {
2144 private:
2145 CMSCollector* _c;
2146 public:
2147 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2148 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2149 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2150 // allow a potentially blocked foreground collector to proceed
2151 _c->_foregroundGCShouldWait = false;
2152 if (_c->_foregroundGCIsActive) {
2153 CGC_lock->notify();
2154 }
2155 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2156 "Possible deadlock");
2157 }
2158
2159 ~ReleaseForegroundGC() {
2160 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2161 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2162 _c->_foregroundGCShouldWait = true;
2163 }
2164 };
2165
2166 // There are separate collect_in_background and collect_in_foreground because of
2167 // the different locking requirements of the background collector and the
2168 // foreground collector. There was originally an attempt to share
2169 // one "collect" method between the background collector and the foreground
2170 // collector but the if-then-else required made it cleaner to have
2171 // separate methods.
2172 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2173 assert(Thread::current()->is_ConcurrentGC_thread(),
2174 "A CMS asynchronous collection is only allowed on a CMS thread.");
2175
2176 GenCollectedHeap* gch = GenCollectedHeap::heap();
2177 {
2178 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2179 MutexLockerEx hl(Heap_lock, safepoint_check);
2180 FreelistLocker fll(this);
2181 MutexLockerEx x(CGC_lock, safepoint_check);
2182 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2183 // The foreground collector is active or we're
2184 // not using asynchronous collections. Skip this
2185 // background collection.
2186 assert(!_foregroundGCShouldWait, "Should be clear");
2187 return;
2188 } else {
2189 assert(_collectorState == Idling, "Should be idling before start.");
2190 _collectorState = InitialMarking;
2191 // Reset the expansion cause, now that we are about to begin
2192 // a new cycle.
2193 clear_expansion_cause();
2194 }
2195 // Decide if we want to enable class unloading as part of the
2196 // ensuing concurrent GC cycle.
2197 update_should_unload_classes();
2198 _full_gc_requested = false; // acks all outstanding full gc requests
2199 // Signal that we are about to start a collection
2200 gch->increment_total_full_collections(); // ... starting a collection cycle
2201 _collection_count_start = gch->total_full_collections();
2202 }
2203
2204 // Used for PrintGC
2205 size_t prev_used;
2206 if (PrintGC && Verbose) {
2207 prev_used = _cmsGen->used(); // XXXPERM
2208 }
2209
2210 // The change of the collection state is normally done at this level;
2211 // the exceptions are phases that are executed while the world is
2212 // stopped. For those phases the change of state is done while the
2213 // world is stopped. For baton passing purposes this allows the
2214 // background collector to finish the phase and change state atomically.
2215 // The foreground collector cannot wait on a phase that is done
2216 // while the world is stopped because the foreground collector already
2217 // has the world stopped and would deadlock.
2218 while (_collectorState != Idling) {
2219 if (TraceCMSState) {
2220 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2221 Thread::current(), _collectorState);
2222 }
2223 // The foreground collector
2224 // holds the Heap_lock throughout its collection.
2225 // holds the CMS token (but not the lock)
2226 // except while it is waiting for the background collector to yield.
2227 //
2228 // The foreground collector should be blocked (not for long)
2229 // if the background collector is about to start a phase
2230 // executed with world stopped. If the background
2231 // collector has already started such a phase, the
2232 // foreground collector is blocked waiting for the
2233 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2234 // are executed in the VM thread.
2235 //
2236 // The locking order is
2237 // PendingListLock (PLL) -- if applicable (FinalMarking)
2238 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2239 // CMS token (claimed in
2240 // stop_world_and_do() -->
2241 // safepoint_synchronize() -->
2242 // CMSThread::synchronize())
2243
2244 {
2245 // Check if the FG collector wants us to yield.
2246 CMSTokenSync x(true); // is cms thread
2247 if (waitForForegroundGC()) {
2248 // We yielded to a foreground GC, nothing more to be
2249 // done this round.
2250 assert(_foregroundGCShouldWait == false, "We set it to false in "
2251 "waitForForegroundGC()");
2252 if (TraceCMSState) {
2253 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2254 " exiting collection CMS state %d",
2255 Thread::current(), _collectorState);
2256 }
2257 return;
2258 } else {
2259 // The background collector can run but check to see if the
2260 // foreground collector has done a collection while the
2261 // background collector was waiting to get the CGC_lock
2262 // above. If yes, break so that _foregroundGCShouldWait
2263 // is cleared before returning.
2264 if (_collectorState == Idling) {
2265 break;
2266 }
2267 }
2268 }
2269
2270 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2271 "should be waiting");
2272
2273 switch (_collectorState) {
2274 case InitialMarking:
2275 {
2276 ReleaseForegroundGC x(this);
2277 stats().record_cms_begin();
2278
2279 VM_CMS_Initial_Mark initial_mark_op(this);
2280 VMThread::execute(&initial_mark_op);
2281 }
2282 // The collector state may be any legal state at this point
2283 // since the background collector may have yielded to the
2284 // foreground collector.
2285 break;
2286 case Marking:
2287 // initial marking in checkpointRootsInitialWork has been completed
2288 if (markFromRoots(true)) { // we were successful
2289 assert(_collectorState == Precleaning, "Collector state should "
2290 "have changed");
2291 } else {
2292 assert(_foregroundGCIsActive, "Internal state inconsistency");
2293 }
2294 break;
2295 case Precleaning:
2296 if (UseAdaptiveSizePolicy) {
2297 size_policy()->concurrent_precleaning_begin();
2298 }
2299 // marking from roots in markFromRoots has been completed
2300 preclean();
2301 if (UseAdaptiveSizePolicy) {
2302 size_policy()->concurrent_precleaning_end();
2303 }
2304 assert(_collectorState == AbortablePreclean ||
2305 _collectorState == FinalMarking,
2306 "Collector state should have changed");
2307 break;
2308 case AbortablePreclean:
2309 if (UseAdaptiveSizePolicy) {
2310 size_policy()->concurrent_phases_resume();
2311 }
2312 abortable_preclean();
2313 if (UseAdaptiveSizePolicy) {
2314 size_policy()->concurrent_precleaning_end();
2315 }
2316 assert(_collectorState == FinalMarking, "Collector state should "
2317 "have changed");
2318 break;
2319 case FinalMarking:
2320 {
2321 ReleaseForegroundGC x(this);
2322
2323 VM_CMS_Final_Remark final_remark_op(this);
2324 VMThread::execute(&final_remark_op);
2325 }
2326 assert(_foregroundGCShouldWait, "block post-condition");
2327 break;
2328 case Sweeping:
2329 if (UseAdaptiveSizePolicy) {
2330 size_policy()->concurrent_sweeping_begin();
2331 }
2332 // final marking in checkpointRootsFinal has been completed
2333 sweep(true);
2334 assert(_collectorState == Resizing, "Collector state change "
2335 "to Resizing must be done under the free_list_lock");
2336 _full_gcs_since_conc_gc = 0;
2337
2338 // Stop the timers for adaptive size policy for the concurrent phases
2339 if (UseAdaptiveSizePolicy) {
2340 size_policy()->concurrent_sweeping_end();
2341 size_policy()->concurrent_phases_end(gch->gc_cause(),
2342 gch->prev_gen(_cmsGen)->capacity(),
2343 _cmsGen->free());
2344 }
2345
2346 case Resizing: {
2347 // Sweeping has been completed...
2348 // At this point the background collection has completed.
2349 // Don't move the call to compute_new_size() down
2350 // into code that might be executed if the background
2351 // collection was preempted.
2352 {
2353 ReleaseForegroundGC x(this); // unblock FG collection
2354 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2355 CMSTokenSync z(true); // not strictly needed.
2356 if (_collectorState == Resizing) {
2357 compute_new_size();
2358 _collectorState = Resetting;
2359 } else {
2360 assert(_collectorState == Idling, "The state should only change"
2361 " because the foreground collector has finished the collection");
2362 }
2363 }
2364 break;
2365 }
2366 case Resetting:
2367 // CMS heap resizing has been completed
2368 reset(true);
2369 assert(_collectorState == Idling, "Collector state should "
2370 "have changed");
2371 stats().record_cms_end();
2372 // Don't move the concurrent_phases_end() and compute_new_size()
2373 // calls to here because a preempted background collection
2374 // has it's state set to "Resetting".
2375 break;
2376 case Idling:
2377 default:
2378 ShouldNotReachHere();
2379 break;
2380 }
2381 if (TraceCMSState) {
2382 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2383 Thread::current(), _collectorState);
2384 }
2385 assert(_foregroundGCShouldWait, "block post-condition");
2386 }
2387
2388 // Should this be in gc_epilogue?
2389 collector_policy()->counters()->update_counters();
2390
2391 {
2392 // Clear _foregroundGCShouldWait and, in the event that the
2393 // foreground collector is waiting, notify it, before
2394 // returning.
2395 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2396 _foregroundGCShouldWait = false;
2397 if (_foregroundGCIsActive) {
2398 CGC_lock->notify();
2399 }
2400 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2401 "Possible deadlock");
2402 }
2403 if (TraceCMSState) {
2404 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2405 " exiting collection CMS state %d",
2406 Thread::current(), _collectorState);
2407 }
2408 if (PrintGC && Verbose) {
2409 _cmsGen->print_heap_change(prev_used);
2410 }
2411 }
2412
2413 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2414 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2415 "Foreground collector should be waiting, not executing");
2416 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2417 "may only be done by the VM Thread with the world stopped");
2418 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2419 "VM thread should have CMS token");
2420
2421 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2422 true, gclog_or_tty);)
2423 if (UseAdaptiveSizePolicy) {
2424 size_policy()->ms_collection_begin();
2425 }
2426 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2427
2428 HandleMark hm; // Discard invalid handles created during verification
2429
2430 if (VerifyBeforeGC &&
2431 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2432 Universe::verify(true);
2433 }
2434
2435 // Snapshot the soft reference policy to be used in this collection cycle.
2436 ref_processor()->setup_policy(clear_all_soft_refs);
2437
2438 bool init_mark_was_synchronous = false; // until proven otherwise
2439 while (_collectorState != Idling) {
2440 if (TraceCMSState) {
2441 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2442 Thread::current(), _collectorState);
2443 }
2444 switch (_collectorState) {
2445 case InitialMarking:
2446 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2447 checkpointRootsInitial(false);
2448 assert(_collectorState == Marking, "Collector state should have changed"
2449 " within checkpointRootsInitial()");
2450 break;
2451 case Marking:
2452 // initial marking in checkpointRootsInitialWork has been completed
2453 if (VerifyDuringGC &&
2454 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2455 gclog_or_tty->print("Verify before initial mark: ");
2456 Universe::verify(true);
2457 }
2458 {
2459 bool res = markFromRoots(false);
2460 assert(res && _collectorState == FinalMarking, "Collector state should "
2461 "have changed");
2462 break;
2463 }
2464 case FinalMarking:
2465 if (VerifyDuringGC &&
2466 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2467 gclog_or_tty->print("Verify before re-mark: ");
2468 Universe::verify(true);
2469 }
2470 checkpointRootsFinal(false, clear_all_soft_refs,
2471 init_mark_was_synchronous);
2472 assert(_collectorState == Sweeping, "Collector state should not "
2473 "have changed within checkpointRootsFinal()");
2474 break;
2475 case Sweeping:
2476 // final marking in checkpointRootsFinal has been completed
2477 if (VerifyDuringGC &&
2478 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2479 gclog_or_tty->print("Verify before sweep: ");
2480 Universe::verify(true);
2481 }
2482 sweep(false);
2483 assert(_collectorState == Resizing, "Incorrect state");
2484 break;
2485 case Resizing: {
2486 // Sweeping has been completed; the actual resize in this case
2487 // is done separately; nothing to be done in this state.
2488 _collectorState = Resetting;
2489 break;
2490 }
2491 case Resetting:
2492 // The heap has been resized.
2493 if (VerifyDuringGC &&
2494 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2495 gclog_or_tty->print("Verify before reset: ");
2496 Universe::verify(true);
2497 }
2498 reset(false);
2499 assert(_collectorState == Idling, "Collector state should "
2500 "have changed");
2501 break;
2502 case Precleaning:
2503 case AbortablePreclean:
2504 // Elide the preclean phase
2505 _collectorState = FinalMarking;
2506 break;
2507 default:
2508 ShouldNotReachHere();
2509 }
2510 if (TraceCMSState) {
2511 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2512 Thread::current(), _collectorState);
2513 }
2514 }
2515
2516 if (UseAdaptiveSizePolicy) {
2517 GenCollectedHeap* gch = GenCollectedHeap::heap();
2518 size_policy()->ms_collection_end(gch->gc_cause());
2519 }
2520
2521 if (VerifyAfterGC &&
2522 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2523 Universe::verify(true);
2524 }
2525 if (TraceCMSState) {
2526 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2527 " exiting collection CMS state %d",
2528 Thread::current(), _collectorState);
2529 }
2530 }
2531
2532 bool CMSCollector::waitForForegroundGC() {
2533 bool res = false;
2534 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2535 "CMS thread should have CMS token");
2536 // Block the foreground collector until the
2537 // background collectors decides whether to
2538 // yield.
2539 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2540 _foregroundGCShouldWait = true;
2541 if (_foregroundGCIsActive) {
2542 // The background collector yields to the
2543 // foreground collector and returns a value
2544 // indicating that it has yielded. The foreground
2545 // collector can proceed.
2546 res = true;
2547 _foregroundGCShouldWait = false;
2548 ConcurrentMarkSweepThread::clear_CMS_flag(
2549 ConcurrentMarkSweepThread::CMS_cms_has_token);
2550 ConcurrentMarkSweepThread::set_CMS_flag(
2551 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2552 // Get a possibly blocked foreground thread going
2553 CGC_lock->notify();
2554 if (TraceCMSState) {
2555 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2556 Thread::current(), _collectorState);
2557 }
2558 while (_foregroundGCIsActive) {
2559 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2560 }
2561 ConcurrentMarkSweepThread::set_CMS_flag(
2562 ConcurrentMarkSweepThread::CMS_cms_has_token);
2563 ConcurrentMarkSweepThread::clear_CMS_flag(
2564 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2565 }
2566 if (TraceCMSState) {
2567 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2568 Thread::current(), _collectorState);
2569 }
2570 return res;
2571 }
2572
2573 // Because of the need to lock the free lists and other structures in
2574 // the collector, common to all the generations that the collector is
2575 // collecting, we need the gc_prologues of individual CMS generations
2576 // delegate to their collector. It may have been simpler had the
2577 // current infrastructure allowed one to call a prologue on a
2578 // collector. In the absence of that we have the generation's
2579 // prologue delegate to the collector, which delegates back
2580 // some "local" work to a worker method in the individual generations
2581 // that it's responsible for collecting, while itself doing any
2582 // work common to all generations it's responsible for. A similar
2583 // comment applies to the gc_epilogue()'s.
2584 // The role of the varaible _between_prologue_and_epilogue is to
2585 // enforce the invocation protocol.
2586 void CMSCollector::gc_prologue(bool full) {
2587 // Call gc_prologue_work() for each CMSGen and PermGen that
2588 // we are responsible for.
2589
2590 // The following locking discipline assumes that we are only called
2591 // when the world is stopped.
2592 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2593
2594 // The CMSCollector prologue must call the gc_prologues for the
2595 // "generations" (including PermGen if any) that it's responsible
2596 // for.
2597
2598 assert( Thread::current()->is_VM_thread()
2599 || ( CMSScavengeBeforeRemark
2600 && Thread::current()->is_ConcurrentGC_thread()),
2601 "Incorrect thread type for prologue execution");
2602
2603 if (_between_prologue_and_epilogue) {
2604 // We have already been invoked; this is a gc_prologue delegation
2605 // from yet another CMS generation that we are responsible for, just
2606 // ignore it since all relevant work has already been done.
2607 return;
2608 }
2609
2610 // set a bit saying prologue has been called; cleared in epilogue
2611 _between_prologue_and_epilogue = true;
2612 // Claim locks for common data structures, then call gc_prologue_work()
2613 // for each CMSGen and PermGen that we are responsible for.
2614
2615 getFreelistLocks(); // gets free list locks on constituent spaces
2616 bitMapLock()->lock_without_safepoint_check();
2617
2618 // Should call gc_prologue_work() for all cms gens we are responsible for
2619 bool registerClosure = _collectorState >= Marking
2620 && _collectorState < Sweeping;
2621 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2622 &_modUnionClosurePar
2623 : &_modUnionClosure;
2624 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2625 _permGen->gc_prologue_work(full, registerClosure, muc);
2626
2627 if (!full) {
2628 stats().record_gc0_begin();
2629 }
2630 }
2631
2632 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2633 // Delegate to CMScollector which knows how to coordinate between
2634 // this and any other CMS generations that it is responsible for
2635 // collecting.
2636 collector()->gc_prologue(full);
2637 }
2638
2639 // This is a "private" interface for use by this generation's CMSCollector.
2640 // Not to be called directly by any other entity (for instance,
2641 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2642 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2643 bool registerClosure, ModUnionClosure* modUnionClosure) {
2644 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2645 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2646 "Should be NULL");
2647 if (registerClosure) {
2648 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2649 }
2650 cmsSpace()->gc_prologue();
2651 // Clear stat counters
2652 NOT_PRODUCT(
2653 assert(_numObjectsPromoted == 0, "check");
2654 assert(_numWordsPromoted == 0, "check");
2655 if (Verbose && PrintGC) {
2656 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2657 SIZE_FORMAT" bytes concurrently",
2658 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2659 }
2660 _numObjectsAllocated = 0;
2661 _numWordsAllocated = 0;
2662 )
2663 }
2664
2665 void CMSCollector::gc_epilogue(bool full) {
2666 // The following locking discipline assumes that we are only called
2667 // when the world is stopped.
2668 assert(SafepointSynchronize::is_at_safepoint(),
2669 "world is stopped assumption");
2670
2671 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2672 // if linear allocation blocks need to be appropriately marked to allow the
2673 // the blocks to be parsable. We also check here whether we need to nudge the
2674 // CMS collector thread to start a new cycle (if it's not already active).
2675 assert( Thread::current()->is_VM_thread()
2676 || ( CMSScavengeBeforeRemark
2677 && Thread::current()->is_ConcurrentGC_thread()),
2678 "Incorrect thread type for epilogue execution");
2679
2680 if (!_between_prologue_and_epilogue) {
2681 // We have already been invoked; this is a gc_epilogue delegation
2682 // from yet another CMS generation that we are responsible for, just
2683 // ignore it since all relevant work has already been done.
2684 return;
2685 }
2686 assert(haveFreelistLocks(), "must have freelist locks");
2687 assert_lock_strong(bitMapLock());
2688
2689 _cmsGen->gc_epilogue_work(full);
2690 _permGen->gc_epilogue_work(full);
2691
2692 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2693 // in case sampling was not already enabled, enable it
2694 _start_sampling = true;
2695 }
2696 // reset _eden_chunk_array so sampling starts afresh
2697 _eden_chunk_index = 0;
2698
2699 size_t cms_used = _cmsGen->cmsSpace()->used();
2700 size_t perm_used = _permGen->cmsSpace()->used();
2701
2702 // update performance counters - this uses a special version of
2703 // update_counters() that allows the utilization to be passed as a
2704 // parameter, avoiding multiple calls to used().
2705 //
2706 _cmsGen->update_counters(cms_used);
2707 _permGen->update_counters(perm_used);
2708
2709 if (CMSIncrementalMode) {
2710 icms_update_allocation_limits();
2711 }
2712
2713 bitMapLock()->unlock();
2714 releaseFreelistLocks();
2715
2716 if (!CleanChunkPoolAsync) {
2717 Chunk::clean_chunk_pool();
2718 }
2719
2720 _between_prologue_and_epilogue = false; // ready for next cycle
2721 }
2722
2723 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2724 collector()->gc_epilogue(full);
2725
2726 // Also reset promotion tracking in par gc thread states.
2727 if (CollectedHeap::use_parallel_gc_threads()) {
2728 for (uint i = 0; i < ParallelGCThreads; i++) {
2729 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2730 }
2731 }
2732 }
2733
2734 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2735 assert(!incremental_collection_failed(), "Should have been cleared");
2736 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2737 cmsSpace()->gc_epilogue();
2738 // Print stat counters
2739 NOT_PRODUCT(
2740 assert(_numObjectsAllocated == 0, "check");
2741 assert(_numWordsAllocated == 0, "check");
2742 if (Verbose && PrintGC) {
2743 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2744 SIZE_FORMAT" bytes",
2745 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2746 }
2747 _numObjectsPromoted = 0;
2748 _numWordsPromoted = 0;
2749 )
2750
2751 if (PrintGC && Verbose) {
2752 // Call down the chain in contiguous_available needs the freelistLock
2753 // so print this out before releasing the freeListLock.
2754 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2755 contiguous_available());
2756 }
2757 }
2758
2759 #ifndef PRODUCT
2760 bool CMSCollector::have_cms_token() {
2761 Thread* thr = Thread::current();
2762 if (thr->is_VM_thread()) {
2763 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2764 } else if (thr->is_ConcurrentGC_thread()) {
2765 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2766 } else if (thr->is_GC_task_thread()) {
2767 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2768 ParGCRareEvent_lock->owned_by_self();
2769 }
2770 return false;
2771 }
2772 #endif
2773
2774 // Check reachability of the given heap address in CMS generation,
2775 // treating all other generations as roots.
2776 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2777 // We could "guarantee" below, rather than assert, but i'll
2778 // leave these as "asserts" so that an adventurous debugger
2779 // could try this in the product build provided some subset of
2780 // the conditions were met, provided they were intersted in the
2781 // results and knew that the computation below wouldn't interfere
2782 // with other concurrent computations mutating the structures
2783 // being read or written.
2784 assert(SafepointSynchronize::is_at_safepoint(),
2785 "Else mutations in object graph will make answer suspect");
2786 assert(have_cms_token(), "Should hold cms token");
2787 assert(haveFreelistLocks(), "must hold free list locks");
2788 assert_lock_strong(bitMapLock());
2789
2790 // Clear the marking bit map array before starting, but, just
2791 // for kicks, first report if the given address is already marked
2792 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2793 _markBitMap.isMarked(addr) ? "" : " not");
2794
2795 if (verify_after_remark()) {
2796 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2797 bool result = verification_mark_bm()->isMarked(addr);
2798 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2799 result ? "IS" : "is NOT");
2800 return result;
2801 } else {
2802 gclog_or_tty->print_cr("Could not compute result");
2803 return false;
2804 }
2805 }
2806
2807 ////////////////////////////////////////////////////////
2808 // CMS Verification Support
2809 ////////////////////////////////////////////////////////
2810 // Following the remark phase, the following invariant
2811 // should hold -- each object in the CMS heap which is
2812 // marked in markBitMap() should be marked in the verification_mark_bm().
2813
2814 class VerifyMarkedClosure: public BitMapClosure {
2815 CMSBitMap* _marks;
2816 bool _failed;
2817
2818 public:
2819 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2820
2821 bool do_bit(size_t offset) {
2822 HeapWord* addr = _marks->offsetToHeapWord(offset);
2823 if (!_marks->isMarked(addr)) {
2824 oop(addr)->print_on(gclog_or_tty);
2825 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2826 _failed = true;
2827 }
2828 return true;
2829 }
2830
2831 bool failed() { return _failed; }
2832 };
2833
2834 bool CMSCollector::verify_after_remark() {
2835 gclog_or_tty->print(" [Verifying CMS Marking... ");
2836 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2837 static bool init = false;
2838
2839 assert(SafepointSynchronize::is_at_safepoint(),
2840 "Else mutations in object graph will make answer suspect");
2841 assert(have_cms_token(),
2842 "Else there may be mutual interference in use of "
2843 " verification data structures");
2844 assert(_collectorState > Marking && _collectorState <= Sweeping,
2845 "Else marking info checked here may be obsolete");
2846 assert(haveFreelistLocks(), "must hold free list locks");
2847 assert_lock_strong(bitMapLock());
2848
2849
2850 // Allocate marking bit map if not already allocated
2851 if (!init) { // first time
2852 if (!verification_mark_bm()->allocate(_span)) {
2853 return false;
2854 }
2855 init = true;
2856 }
2857
2858 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2859
2860 // Turn off refs discovery -- so we will be tracing through refs.
2861 // This is as intended, because by this time
2862 // GC must already have cleared any refs that need to be cleared,
2863 // and traced those that need to be marked; moreover,
2864 // the marking done here is not going to intefere in any
2865 // way with the marking information used by GC.
2866 NoRefDiscovery no_discovery(ref_processor());
2867
2868 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2869
2870 // Clear any marks from a previous round
2871 verification_mark_bm()->clear_all();
2872 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2873 verify_work_stacks_empty();
2874
2875 GenCollectedHeap* gch = GenCollectedHeap::heap();
2876 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2877 // Update the saved marks which may affect the root scans.
2878 gch->save_marks();
2879
2880 if (CMSRemarkVerifyVariant == 1) {
2881 // In this first variant of verification, we complete
2882 // all marking, then check if the new marks-verctor is
2883 // a subset of the CMS marks-vector.
2884 verify_after_remark_work_1();
2885 } else if (CMSRemarkVerifyVariant == 2) {
2886 // In this second variant of verification, we flag an error
2887 // (i.e. an object reachable in the new marks-vector not reachable
2888 // in the CMS marks-vector) immediately, also indicating the
2889 // identify of an object (A) that references the unmarked object (B) --
2890 // presumably, a mutation to A failed to be picked up by preclean/remark?
2891 verify_after_remark_work_2();
2892 } else {
2893 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2894 CMSRemarkVerifyVariant);
2895 }
2896 gclog_or_tty->print(" done] ");
2897 return true;
2898 }
2899
2900 void CMSCollector::verify_after_remark_work_1() {
2901 ResourceMark rm;
2902 HandleMark hm;
2903 GenCollectedHeap* gch = GenCollectedHeap::heap();
2904
2905 // Mark from roots one level into CMS
2906 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2907 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2908
2909 gch->gen_process_strong_roots(_cmsGen->level(),
2910 true, // younger gens are roots
2911 true, // activate StrongRootsScope
2912 true, // collecting perm gen
2913 SharedHeap::ScanningOption(roots_scanning_options()),
2914 ¬Older,
2915 true, // walk code active on stacks
2916 NULL);
2917
2918 // Now mark from the roots
2919 assert(_revisitStack.isEmpty(), "Should be empty");
2920 MarkFromRootsClosure markFromRootsClosure(this, _span,
2921 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2922 false /* don't yield */, true /* verifying */);
2923 assert(_restart_addr == NULL, "Expected pre-condition");
2924 verification_mark_bm()->iterate(&markFromRootsClosure);
2925 while (_restart_addr != NULL) {
2926 // Deal with stack overflow: by restarting at the indicated
2927 // address.
2928 HeapWord* ra = _restart_addr;
2929 markFromRootsClosure.reset(ra);
2930 _restart_addr = NULL;
2931 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2932 }
2933 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2934 verify_work_stacks_empty();
2935 // Should reset the revisit stack above, since no class tree
2936 // surgery is forthcoming.
2937 _revisitStack.reset(); // throwing away all contents
2938
2939 // Marking completed -- now verify that each bit marked in
2940 // verification_mark_bm() is also marked in markBitMap(); flag all
2941 // errors by printing corresponding objects.
2942 VerifyMarkedClosure vcl(markBitMap());
2943 verification_mark_bm()->iterate(&vcl);
2944 if (vcl.failed()) {
2945 gclog_or_tty->print("Verification failed");
2946 Universe::heap()->print_on(gclog_or_tty);
2947 fatal("CMS: failed marking verification after remark");
2948 }
2949 }
2950
2951 void CMSCollector::verify_after_remark_work_2() {
2952 ResourceMark rm;
2953 HandleMark hm;
2954 GenCollectedHeap* gch = GenCollectedHeap::heap();
2955
2956 // Mark from roots one level into CMS
2957 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2958 markBitMap());
2959 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2960 gch->gen_process_strong_roots(_cmsGen->level(),
2961 true, // younger gens are roots
2962 true, // activate StrongRootsScope
2963 true, // collecting perm gen
2964 SharedHeap::ScanningOption(roots_scanning_options()),
2965 ¬Older,
2966 true, // walk code active on stacks
2967 NULL);
2968
2969 // Now mark from the roots
2970 assert(_revisitStack.isEmpty(), "Should be empty");
2971 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2972 verification_mark_bm(), markBitMap(), verification_mark_stack());
2973 assert(_restart_addr == NULL, "Expected pre-condition");
2974 verification_mark_bm()->iterate(&markFromRootsClosure);
2975 while (_restart_addr != NULL) {
2976 // Deal with stack overflow: by restarting at the indicated
2977 // address.
2978 HeapWord* ra = _restart_addr;
2979 markFromRootsClosure.reset(ra);
2980 _restart_addr = NULL;
2981 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2982 }
2983 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2984 verify_work_stacks_empty();
2985 // Should reset the revisit stack above, since no class tree
2986 // surgery is forthcoming.
2987 _revisitStack.reset(); // throwing away all contents
2988
2989 // Marking completed -- now verify that each bit marked in
2990 // verification_mark_bm() is also marked in markBitMap(); flag all
2991 // errors by printing corresponding objects.
2992 VerifyMarkedClosure vcl(markBitMap());
2993 verification_mark_bm()->iterate(&vcl);
2994 assert(!vcl.failed(), "Else verification above should not have succeeded");
2995 }
2996
2997 void ConcurrentMarkSweepGeneration::save_marks() {
2998 // delegate to CMS space
2999 cmsSpace()->save_marks();
3000 for (uint i = 0; i < ParallelGCThreads; i++) {
3001 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3002 }
3003 }
3004
3005 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3006 return cmsSpace()->no_allocs_since_save_marks();
3007 }
3008
3009 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3010 \
3011 void ConcurrentMarkSweepGeneration:: \
3012 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3013 cl->set_generation(this); \
3014 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3015 cl->reset_generation(); \
3016 save_marks(); \
3017 }
3018
3019 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3020
3021 void
3022 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3023 {
3024 // Not currently implemented; need to do the following. -- ysr.
3025 // dld -- I think that is used for some sort of allocation profiler. So it
3026 // really means the objects allocated by the mutator since the last
3027 // GC. We could potentially implement this cheaply by recording only
3028 // the direct allocations in a side data structure.
3029 //
3030 // I think we probably ought not to be required to support these
3031 // iterations at any arbitrary point; I think there ought to be some
3032 // call to enable/disable allocation profiling in a generation/space,
3033 // and the iterator ought to return the objects allocated in the
3034 // gen/space since the enable call, or the last iterator call (which
3035 // will probably be at a GC.) That way, for gens like CM&S that would
3036 // require some extra data structure to support this, we only pay the
3037 // cost when it's in use...
3038 cmsSpace()->object_iterate_since_last_GC(blk);
3039 }
3040
3041 void
3042 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3043 cl->set_generation(this);
3044 younger_refs_in_space_iterate(_cmsSpace, cl);
3045 cl->reset_generation();
3046 }
3047
3048 void
3049 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3050 if (freelistLock()->owned_by_self()) {
3051 Generation::oop_iterate(mr, cl);
3052 } else {
3053 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3054 Generation::oop_iterate(mr, cl);
3055 }
3056 }
3057
3058 void
3059 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3060 if (freelistLock()->owned_by_self()) {
3061 Generation::oop_iterate(cl);
3062 } else {
3063 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3064 Generation::oop_iterate(cl);
3065 }
3066 }
3067
3068 void
3069 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3070 if (freelistLock()->owned_by_self()) {
3071 Generation::object_iterate(cl);
3072 } else {
3073 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3074 Generation::object_iterate(cl);
3075 }
3076 }
3077
3078 void
3079 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3080 if (freelistLock()->owned_by_self()) {
3081 Generation::safe_object_iterate(cl);
3082 } else {
3083 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3084 Generation::safe_object_iterate(cl);
3085 }
3086 }
3087
3088 void
3089 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3090 }
3091
3092 void
3093 ConcurrentMarkSweepGeneration::post_compact() {
3094 }
3095
3096 void
3097 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3098 // Fix the linear allocation blocks to look like free blocks.
3099
3100 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3101 // are not called when the heap is verified during universe initialization and
3102 // at vm shutdown.
3103 if (freelistLock()->owned_by_self()) {
3104 cmsSpace()->prepare_for_verify();
3105 } else {
3106 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3107 cmsSpace()->prepare_for_verify();
3108 }
3109 }
3110
3111 void
3112 ConcurrentMarkSweepGeneration::verify() {
3113 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3114 // are not called when the heap is verified during universe initialization and
3115 // at vm shutdown.
3116 if (freelistLock()->owned_by_self()) {
3117 cmsSpace()->verify();
3118 } else {
3119 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3120 cmsSpace()->verify();
3121 }
3122 }
3123
3124 void CMSCollector::verify() {
3125 _cmsGen->verify();
3126 _permGen->verify();
3127 }
3128
3129 #ifndef PRODUCT
3130 bool CMSCollector::overflow_list_is_empty() const {
3131 assert(_num_par_pushes >= 0, "Inconsistency");
3132 if (_overflow_list == NULL) {
3133 assert(_num_par_pushes == 0, "Inconsistency");
3134 }
3135 return _overflow_list == NULL;
3136 }
3137
3138 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3139 // merely consolidate assertion checks that appear to occur together frequently.
3140 void CMSCollector::verify_work_stacks_empty() const {
3141 assert(_markStack.isEmpty(), "Marking stack should be empty");
3142 assert(overflow_list_is_empty(), "Overflow list should be empty");
3143 }
3144
3145 void CMSCollector::verify_overflow_empty() const {
3146 assert(overflow_list_is_empty(), "Overflow list should be empty");
3147 assert(no_preserved_marks(), "No preserved marks");
3148 }
3149 #endif // PRODUCT
3150
3151 // Decide if we want to enable class unloading as part of the
3152 // ensuing concurrent GC cycle. We will collect the perm gen and
3153 // unload classes if it's the case that:
3154 // (1) an explicit gc request has been made and the flag
3155 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3156 // (2) (a) class unloading is enabled at the command line, and
3157 // (b) (i) perm gen threshold has been crossed, or
3158 // (ii) old gen is getting really full, or
3159 // (iii) the previous N CMS collections did not collect the
3160 // perm gen
3161 // NOTE: Provided there is no change in the state of the heap between
3162 // calls to this method, it should have idempotent results. Moreover,
3163 // its results should be monotonically increasing (i.e. going from 0 to 1,
3164 // but not 1 to 0) between successive calls between which the heap was
3165 // not collected. For the implementation below, it must thus rely on
3166 // the property that concurrent_cycles_since_last_unload()
3167 // will not decrease unless a collection cycle happened and that
3168 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3169 // themselves also monotonic in that sense. See check_monotonicity()
3170 // below.
3171 bool CMSCollector::update_should_unload_classes() {
3172 _should_unload_classes = false;
3173 // Condition 1 above
3174 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3175 _should_unload_classes = true;
3176 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3177 // Disjuncts 2.b.(i,ii,iii) above
3178 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3179 CMSClassUnloadingMaxInterval)
3180 || _permGen->should_concurrent_collect()
3181 || _cmsGen->is_too_full();
3182 }
3183 return _should_unload_classes;
3184 }
3185
3186 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3187 bool res = should_concurrent_collect();
3188 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3189 return res;
3190 }
3191
3192 void CMSCollector::setup_cms_unloading_and_verification_state() {
3193 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3194 || VerifyBeforeExit;
3195 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3196
3197 if (should_unload_classes()) { // Should unload classes this cycle
3198 remove_root_scanning_option(rso); // Shrink the root set appropriately
3199 set_verifying(should_verify); // Set verification state for this cycle
3200 return; // Nothing else needs to be done at this time
3201 }
3202
3203 // Not unloading classes this cycle
3204 assert(!should_unload_classes(), "Inconsitency!");
3205 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3206 // We were not verifying, or we _were_ unloading classes in the last cycle,
3207 // AND some verification options are enabled this cycle; in this case,
3208 // we must make sure that the deadness map is allocated if not already so,
3209 // and cleared (if already allocated previously --
3210 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3211 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3212 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3213 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3214 "permanent generation verification disabled");
3215 return; // Note that we leave verification disabled, so we'll retry this
3216 // allocation next cycle. We _could_ remember this failure
3217 // and skip further attempts and permanently disable verification
3218 // attempts if that is considered more desirable.
3219 }
3220 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3221 "_perm_gen_ver_bit_map inconsistency?");
3222 } else {
3223 perm_gen_verify_bit_map()->clear_all();
3224 }
3225 // Include symbols, strings and code cache elements to prevent their resurrection.
3226 add_root_scanning_option(rso);
3227 set_verifying(true);
3228 } else if (verifying() && !should_verify) {
3229 // We were verifying, but some verification flags got disabled.
3230 set_verifying(false);
3231 // Exclude symbols, strings and code cache elements from root scanning to
3232 // reduce IM and RM pauses.
3233 remove_root_scanning_option(rso);
3234 }
3235 }
3236
3237
3238 #ifndef PRODUCT
3239 HeapWord* CMSCollector::block_start(const void* p) const {
3240 const HeapWord* addr = (HeapWord*)p;
3241 if (_span.contains(p)) {
3242 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3243 return _cmsGen->cmsSpace()->block_start(p);
3244 } else {
3245 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3246 "Inconsistent _span?");
3247 return _permGen->cmsSpace()->block_start(p);
3248 }
3249 }
3250 return NULL;
3251 }
3252 #endif
3253
3254 HeapWord*
3255 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3256 bool tlab,
3257 bool parallel) {
3258 CMSSynchronousYieldRequest yr;
3259 assert(!tlab, "Can't deal with TLAB allocation");
3260 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3261 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3262 CMSExpansionCause::_satisfy_allocation);
3263 if (GCExpandToAllocateDelayMillis > 0) {
3264 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3265 }
3266 return have_lock_and_allocate(word_size, tlab);
3267 }
3268
3269 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3270 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3271 // to CardGeneration and share it...
3272 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3273 return CardGeneration::expand(bytes, expand_bytes);
3274 }
3275
3276 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3277 CMSExpansionCause::Cause cause)
3278 {
3279
3280 bool success = expand(bytes, expand_bytes);
3281
3282 // remember why we expanded; this information is used
3283 // by shouldConcurrentCollect() when making decisions on whether to start
3284 // a new CMS cycle.
3285 if (success) {
3286 set_expansion_cause(cause);
3287 if (PrintGCDetails && Verbose) {
3288 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3289 CMSExpansionCause::to_string(cause));
3290 }
3291 }
3292 }
3293
3294 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3295 HeapWord* res = NULL;
3296 MutexLocker x(ParGCRareEvent_lock);
3297 while (true) {
3298 // Expansion by some other thread might make alloc OK now:
3299 res = ps->lab.alloc(word_sz);
3300 if (res != NULL) return res;
3301 // If there's not enough expansion space available, give up.
3302 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3303 return NULL;
3304 }
3305 // Otherwise, we try expansion.
3306 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3307 CMSExpansionCause::_allocate_par_lab);
3308 // Now go around the loop and try alloc again;
3309 // A competing par_promote might beat us to the expansion space,
3310 // so we may go around the loop again if promotion fails agaion.
3311 if (GCExpandToAllocateDelayMillis > 0) {
3312 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3313 }
3314 }
3315 }
3316
3317
3318 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3319 PromotionInfo* promo) {
3320 MutexLocker x(ParGCRareEvent_lock);
3321 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3322 while (true) {
3323 // Expansion by some other thread might make alloc OK now:
3324 if (promo->ensure_spooling_space()) {
3325 assert(promo->has_spooling_space(),
3326 "Post-condition of successful ensure_spooling_space()");
3327 return true;
3328 }
3329 // If there's not enough expansion space available, give up.
3330 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3331 return false;
3332 }
3333 // Otherwise, we try expansion.
3334 expand(refill_size_bytes, MinHeapDeltaBytes,
3335 CMSExpansionCause::_allocate_par_spooling_space);
3336 // Now go around the loop and try alloc again;
3337 // A competing allocation might beat us to the expansion space,
3338 // so we may go around the loop again if allocation fails again.
3339 if (GCExpandToAllocateDelayMillis > 0) {
3340 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3341 }
3342 }
3343 }
3344
3345
3346
3347 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3348 assert_locked_or_safepoint(Heap_lock);
3349 size_t size = ReservedSpace::page_align_size_down(bytes);
3350 if (size > 0) {
3351 shrink_by(size);
3352 }
3353 }
3354
3355 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3356 assert_locked_or_safepoint(Heap_lock);
3357 bool result = _virtual_space.expand_by(bytes);
3358 if (result) {
3359 HeapWord* old_end = _cmsSpace->end();
3360 size_t new_word_size =
3361 heap_word_size(_virtual_space.committed_size());
3362 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3363 _bts->resize(new_word_size); // resize the block offset shared array
3364 Universe::heap()->barrier_set()->resize_covered_region(mr);
3365 // Hmmmm... why doesn't CFLS::set_end verify locking?
3366 // This is quite ugly; FIX ME XXX
3367 _cmsSpace->assert_locked(freelistLock());
3368 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3369
3370 // update the space and generation capacity counters
3371 if (UsePerfData) {
3372 _space_counters->update_capacity();
3373 _gen_counters->update_all();
3374 }
3375
3376 if (Verbose && PrintGC) {
3377 size_t new_mem_size = _virtual_space.committed_size();
3378 size_t old_mem_size = new_mem_size - bytes;
3379 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3380 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3381 }
3382 }
3383 return result;
3384 }
3385
3386 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3387 assert_locked_or_safepoint(Heap_lock);
3388 bool success = true;
3389 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3390 if (remaining_bytes > 0) {
3391 success = grow_by(remaining_bytes);
3392 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3393 }
3394 return success;
3395 }
3396
3397 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3398 assert_locked_or_safepoint(Heap_lock);
3399 assert_lock_strong(freelistLock());
3400 // XXX Fix when compaction is implemented.
3401 warning("Shrinking of CMS not yet implemented");
3402 return;
3403 }
3404
3405
3406 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3407 // phases.
3408 class CMSPhaseAccounting: public StackObj {
3409 public:
3410 CMSPhaseAccounting(CMSCollector *collector,
3411 const char *phase,
3412 bool print_cr = true);
3413 ~CMSPhaseAccounting();
3414
3415 private:
3416 CMSCollector *_collector;
3417 const char *_phase;
3418 elapsedTimer _wallclock;
3419 bool _print_cr;
3420
3421 public:
3422 // Not MT-safe; so do not pass around these StackObj's
3423 // where they may be accessed by other threads.
3424 jlong wallclock_millis() {
3425 assert(_wallclock.is_active(), "Wall clock should not stop");
3426 _wallclock.stop(); // to record time
3427 jlong ret = _wallclock.milliseconds();
3428 _wallclock.start(); // restart
3429 return ret;
3430 }
3431 };
3432
3433 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3434 const char *phase,
3435 bool print_cr) :
3436 _collector(collector), _phase(phase), _print_cr(print_cr) {
3437
3438 if (PrintCMSStatistics != 0) {
3439 _collector->resetYields();
3440 }
3441 if (PrintGCDetails && PrintGCTimeStamps) {
3442 gclog_or_tty->date_stamp(PrintGCDateStamps);
3443 gclog_or_tty->stamp();
3444 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3445 _collector->cmsGen()->short_name(), _phase);
3446 }
3447 _collector->resetTimer();
3448 _wallclock.start();
3449 _collector->startTimer();
3450 }
3451
3452 CMSPhaseAccounting::~CMSPhaseAccounting() {
3453 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3454 _collector->stopTimer();
3455 _wallclock.stop();
3456 if (PrintGCDetails) {
3457 gclog_or_tty->date_stamp(PrintGCDateStamps);
3458 if (PrintGCTimeStamps) {
3459 gclog_or_tty->stamp();
3460 gclog_or_tty->print(": ");
3461 }
3462 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3463 _collector->cmsGen()->short_name(),
3464 _phase, _collector->timerValue(), _wallclock.seconds());
3465 if (_print_cr) {
3466 gclog_or_tty->print_cr("");
3467 }
3468 if (PrintCMSStatistics != 0) {
3469 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3470 _collector->yields());
3471 }
3472 }
3473 }
3474
3475 // CMS work
3476
3477 // Checkpoint the roots into this generation from outside
3478 // this generation. [Note this initial checkpoint need only
3479 // be approximate -- we'll do a catch up phase subsequently.]
3480 void CMSCollector::checkpointRootsInitial(bool asynch) {
3481 assert(_collectorState == InitialMarking, "Wrong collector state");
3482 check_correct_thread_executing();
3483 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3484
3485 ReferenceProcessor* rp = ref_processor();
3486 SpecializationStats::clear();
3487 assert(_restart_addr == NULL, "Control point invariant");
3488 if (asynch) {
3489 // acquire locks for subsequent manipulations
3490 MutexLockerEx x(bitMapLock(),
3491 Mutex::_no_safepoint_check_flag);
3492 checkpointRootsInitialWork(asynch);
3493 // enable ("weak") refs discovery
3494 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3495 _collectorState = Marking;
3496 } else {
3497 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3498 // which recognizes if we are a CMS generation, and doesn't try to turn on
3499 // discovery; verify that they aren't meddling.
3500 assert(!rp->discovery_is_atomic(),
3501 "incorrect setting of discovery predicate");
3502 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3503 "ref discovery for this generation kind");
3504 // already have locks
3505 checkpointRootsInitialWork(asynch);
3506 // now enable ("weak") refs discovery
3507 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3508 _collectorState = Marking;
3509 }
3510 SpecializationStats::print();
3511 }
3512
3513 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3514 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3515 assert(_collectorState == InitialMarking, "just checking");
3516
3517 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3518 // precede our marking with a collection of all
3519 // younger generations to keep floating garbage to a minimum.
3520 // XXX: we won't do this for now -- it's an optimization to be done later.
3521
3522 // already have locks
3523 assert_lock_strong(bitMapLock());
3524 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3525
3526 // Setup the verification and class unloading state for this
3527 // CMS collection cycle.
3528 setup_cms_unloading_and_verification_state();
3529
3530 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3531 PrintGCDetails && Verbose, true, gclog_or_tty);)
3532 if (UseAdaptiveSizePolicy) {
3533 size_policy()->checkpoint_roots_initial_begin();
3534 }
3535
3536 // Reset all the PLAB chunk arrays if necessary.
3537 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3538 reset_survivor_plab_arrays();
3539 }
3540
3541 ResourceMark rm;
3542 HandleMark hm;
3543
3544 FalseClosure falseClosure;
3545 // In the case of a synchronous collection, we will elide the
3546 // remark step, so it's important to catch all the nmethod oops
3547 // in this step.
3548 // The final 'true' flag to gen_process_strong_roots will ensure this.
3549 // If 'async' is true, we can relax the nmethod tracing.
3550 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3551 GenCollectedHeap* gch = GenCollectedHeap::heap();
3552
3553 verify_work_stacks_empty();
3554 verify_overflow_empty();
3555
3556 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3557 // Update the saved marks which may affect the root scans.
3558 gch->save_marks();
3559
3560 // weak reference processing has not started yet.
3561 ref_processor()->set_enqueuing_is_done(false);
3562
3563 {
3564 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3565 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3566 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3567 gch->gen_process_strong_roots(_cmsGen->level(),
3568 true, // younger gens are roots
3569 true, // activate StrongRootsScope
3570 true, // collecting perm gen
3571 SharedHeap::ScanningOption(roots_scanning_options()),
3572 ¬Older,
3573 true, // walk all of code cache if (so & SO_CodeCache)
3574 NULL);
3575 }
3576
3577 // Clear mod-union table; it will be dirtied in the prologue of
3578 // CMS generation per each younger generation collection.
3579
3580 assert(_modUnionTable.isAllClear(),
3581 "Was cleared in most recent final checkpoint phase"
3582 " or no bits are set in the gc_prologue before the start of the next "
3583 "subsequent marking phase.");
3584
3585 // Save the end of the used_region of the constituent generations
3586 // to be used to limit the extent of sweep in each generation.
3587 save_sweep_limits();
3588 if (UseAdaptiveSizePolicy) {
3589 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3590 }
3591 verify_overflow_empty();
3592 }
3593
3594 bool CMSCollector::markFromRoots(bool asynch) {
3595 // we might be tempted to assert that:
3596 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3597 // "inconsistent argument?");
3598 // However that wouldn't be right, because it's possible that
3599 // a safepoint is indeed in progress as a younger generation
3600 // stop-the-world GC happens even as we mark in this generation.
3601 assert(_collectorState == Marking, "inconsistent state?");
3602 check_correct_thread_executing();
3603 verify_overflow_empty();
3604
3605 bool res;
3606 if (asynch) {
3607
3608 // Start the timers for adaptive size policy for the concurrent phases
3609 // Do it here so that the foreground MS can use the concurrent
3610 // timer since a foreground MS might has the sweep done concurrently
3611 // or STW.
3612 if (UseAdaptiveSizePolicy) {
3613 size_policy()->concurrent_marking_begin();
3614 }
3615
3616 // Weak ref discovery note: We may be discovering weak
3617 // refs in this generation concurrent (but interleaved) with
3618 // weak ref discovery by a younger generation collector.
3619
3620 CMSTokenSyncWithLocks ts(true, bitMapLock());
3621 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3622 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3623 res = markFromRootsWork(asynch);
3624 if (res) {
3625 _collectorState = Precleaning;
3626 } else { // We failed and a foreground collection wants to take over
3627 assert(_foregroundGCIsActive, "internal state inconsistency");
3628 assert(_restart_addr == NULL, "foreground will restart from scratch");
3629 if (PrintGCDetails) {
3630 gclog_or_tty->print_cr("bailing out to foreground collection");
3631 }
3632 }
3633 if (UseAdaptiveSizePolicy) {
3634 size_policy()->concurrent_marking_end();
3635 }
3636 } else {
3637 assert(SafepointSynchronize::is_at_safepoint(),
3638 "inconsistent with asynch == false");
3639 if (UseAdaptiveSizePolicy) {
3640 size_policy()->ms_collection_marking_begin();
3641 }
3642 // already have locks
3643 res = markFromRootsWork(asynch);
3644 _collectorState = FinalMarking;
3645 if (UseAdaptiveSizePolicy) {
3646 GenCollectedHeap* gch = GenCollectedHeap::heap();
3647 size_policy()->ms_collection_marking_end(gch->gc_cause());
3648 }
3649 }
3650 verify_overflow_empty();
3651 return res;
3652 }
3653
3654 bool CMSCollector::markFromRootsWork(bool asynch) {
3655 // iterate over marked bits in bit map, doing a full scan and mark
3656 // from these roots using the following algorithm:
3657 // . if oop is to the right of the current scan pointer,
3658 // mark corresponding bit (we'll process it later)
3659 // . else (oop is to left of current scan pointer)
3660 // push oop on marking stack
3661 // . drain the marking stack
3662
3663 // Note that when we do a marking step we need to hold the
3664 // bit map lock -- recall that direct allocation (by mutators)
3665 // and promotion (by younger generation collectors) is also
3666 // marking the bit map. [the so-called allocate live policy.]
3667 // Because the implementation of bit map marking is not
3668 // robust wrt simultaneous marking of bits in the same word,
3669 // we need to make sure that there is no such interference
3670 // between concurrent such updates.
3671
3672 // already have locks
3673 assert_lock_strong(bitMapLock());
3674
3675 // Clear the revisit stack, just in case there are any
3676 // obsolete contents from a short-circuited previous CMS cycle.
3677 _revisitStack.reset();
3678 verify_work_stacks_empty();
3679 verify_overflow_empty();
3680 assert(_revisitStack.isEmpty(), "tabula rasa");
3681 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3682 bool result = false;
3683 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3684 result = do_marking_mt(asynch);
3685 } else {
3686 result = do_marking_st(asynch);
3687 }
3688 return result;
3689 }
3690
3691 // Forward decl
3692 class CMSConcMarkingTask;
3693
3694 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3695 CMSCollector* _collector;
3696 CMSConcMarkingTask* _task;
3697 public:
3698 virtual void yield();
3699
3700 // "n_threads" is the number of threads to be terminated.
3701 // "queue_set" is a set of work queues of other threads.
3702 // "collector" is the CMS collector associated with this task terminator.
3703 // "yield" indicates whether we need the gang as a whole to yield.
3704 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3705 ParallelTaskTerminator(n_threads, queue_set),
3706 _collector(collector) { }
3707
3708 void set_task(CMSConcMarkingTask* task) {
3709 _task = task;
3710 }
3711 };
3712
3713 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3714 CMSConcMarkingTask* _task;
3715 public:
3716 bool should_exit_termination();
3717 void set_task(CMSConcMarkingTask* task) {
3718 _task = task;
3719 }
3720 };
3721
3722 // MT Concurrent Marking Task
3723 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3724 CMSCollector* _collector;
3725 int _n_workers; // requested/desired # workers
3726 bool _asynch;
3727 bool _result;
3728 CompactibleFreeListSpace* _cms_space;
3729 CompactibleFreeListSpace* _perm_space;
3730 char _pad_front[64]; // padding to ...
3731 HeapWord* _global_finger; // ... avoid sharing cache line
3732 char _pad_back[64];
3733 HeapWord* _restart_addr;
3734
3735 // Exposed here for yielding support
3736 Mutex* const _bit_map_lock;
3737
3738 // The per thread work queues, available here for stealing
3739 OopTaskQueueSet* _task_queues;
3740
3741 // Termination (and yielding) support
3742 CMSConcMarkingTerminator _term;
3743 CMSConcMarkingTerminatorTerminator _term_term;
3744
3745 public:
3746 CMSConcMarkingTask(CMSCollector* collector,
3747 CompactibleFreeListSpace* cms_space,
3748 CompactibleFreeListSpace* perm_space,
3749 bool asynch,
3750 YieldingFlexibleWorkGang* workers,
3751 OopTaskQueueSet* task_queues):
3752 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3753 _collector(collector),
3754 _cms_space(cms_space),
3755 _perm_space(perm_space),
3756 _asynch(asynch), _n_workers(0), _result(true),
3757 _task_queues(task_queues),
3758 _term(_n_workers, task_queues, _collector),
3759 _bit_map_lock(collector->bitMapLock())
3760 {
3761 _requested_size = _n_workers;
3762 _term.set_task(this);
3763 _term_term.set_task(this);
3764 assert(_cms_space->bottom() < _perm_space->bottom(),
3765 "Finger incorrectly initialized below");
3766 _restart_addr = _global_finger = _cms_space->bottom();
3767 }
3768
3769
3770 OopTaskQueueSet* task_queues() { return _task_queues; }
3771
3772 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3773
3774 HeapWord** global_finger_addr() { return &_global_finger; }
3775
3776 CMSConcMarkingTerminator* terminator() { return &_term; }
3777
3778 virtual void set_for_termination(int active_workers) {
3779 terminator()->reset_for_reuse(active_workers);
3780 }
3781
3782 void work(uint worker_id);
3783 bool should_yield() {
3784 return ConcurrentMarkSweepThread::should_yield()
3785 && !_collector->foregroundGCIsActive()
3786 && _asynch;
3787 }
3788
3789 virtual void coordinator_yield(); // stuff done by coordinator
3790 bool result() { return _result; }
3791
3792 void reset(HeapWord* ra) {
3793 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3794 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3795 assert(ra < _perm_space->end(), "ra too large");
3796 _restart_addr = _global_finger = ra;
3797 _term.reset_for_reuse();
3798 }
3799
3800 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3801 OopTaskQueue* work_q);
3802
3803 private:
3804 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3805 void do_work_steal(int i);
3806 void bump_global_finger(HeapWord* f);
3807 };
3808
3809 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3810 assert(_task != NULL, "Error");
3811 return _task->yielding();
3812 // Note that we do not need the disjunct || _task->should_yield() above
3813 // because we want terminating threads to yield only if the task
3814 // is already in the midst of yielding, which happens only after at least one
3815 // thread has yielded.
3816 }
3817
3818 void CMSConcMarkingTerminator::yield() {
3819 if (_task->should_yield()) {
3820 _task->yield();
3821 } else {
3822 ParallelTaskTerminator::yield();
3823 }
3824 }
3825
3826 ////////////////////////////////////////////////////////////////
3827 // Concurrent Marking Algorithm Sketch
3828 ////////////////////////////////////////////////////////////////
3829 // Until all tasks exhausted (both spaces):
3830 // -- claim next available chunk
3831 // -- bump global finger via CAS
3832 // -- find first object that starts in this chunk
3833 // and start scanning bitmap from that position
3834 // -- scan marked objects for oops
3835 // -- CAS-mark target, and if successful:
3836 // . if target oop is above global finger (volatile read)
3837 // nothing to do
3838 // . if target oop is in chunk and above local finger
3839 // then nothing to do
3840 // . else push on work-queue
3841 // -- Deal with possible overflow issues:
3842 // . local work-queue overflow causes stuff to be pushed on
3843 // global (common) overflow queue
3844 // . always first empty local work queue
3845 // . then get a batch of oops from global work queue if any
3846 // . then do work stealing
3847 // -- When all tasks claimed (both spaces)
3848 // and local work queue empty,
3849 // then in a loop do:
3850 // . check global overflow stack; steal a batch of oops and trace
3851 // . try to steal from other threads oif GOS is empty
3852 // . if neither is available, offer termination
3853 // -- Terminate and return result
3854 //
3855 void CMSConcMarkingTask::work(uint worker_id) {
3856 elapsedTimer _timer;
3857 ResourceMark rm;
3858 HandleMark hm;
3859
3860 DEBUG_ONLY(_collector->verify_overflow_empty();)
3861
3862 // Before we begin work, our work queue should be empty
3863 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3864 // Scan the bitmap covering _cms_space, tracing through grey objects.
3865 _timer.start();
3866 do_scan_and_mark(worker_id, _cms_space);
3867 _timer.stop();
3868 if (PrintCMSStatistics != 0) {
3869 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3870 worker_id, _timer.seconds());
3871 // XXX: need xxx/xxx type of notation, two timers
3872 }
3873
3874 // ... do the same for the _perm_space
3875 _timer.reset();
3876 _timer.start();
3877 do_scan_and_mark(worker_id, _perm_space);
3878 _timer.stop();
3879 if (PrintCMSStatistics != 0) {
3880 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3881 worker_id, _timer.seconds());
3882 // XXX: need xxx/xxx type of notation, two timers
3883 }
3884
3885 // ... do work stealing
3886 _timer.reset();
3887 _timer.start();
3888 do_work_steal(worker_id);
3889 _timer.stop();
3890 if (PrintCMSStatistics != 0) {
3891 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3892 worker_id, _timer.seconds());
3893 // XXX: need xxx/xxx type of notation, two timers
3894 }
3895 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3896 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3897 // Note that under the current task protocol, the
3898 // following assertion is true even of the spaces
3899 // expanded since the completion of the concurrent
3900 // marking. XXX This will likely change under a strict
3901 // ABORT semantics.
3902 assert(_global_finger > _cms_space->end() &&
3903 _global_finger >= _perm_space->end(),
3904 "All tasks have been completed");
3905 DEBUG_ONLY(_collector->verify_overflow_empty();)
3906 }
3907
3908 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3909 HeapWord* read = _global_finger;
3910 HeapWord* cur = read;
3911 while (f > read) {
3912 cur = read;
3913 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3914 if (cur == read) {
3915 // our cas succeeded
3916 assert(_global_finger >= f, "protocol consistency");
3917 break;
3918 }
3919 }
3920 }
3921
3922 // This is really inefficient, and should be redone by
3923 // using (not yet available) block-read and -write interfaces to the
3924 // stack and the work_queue. XXX FIX ME !!!
3925 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3926 OopTaskQueue* work_q) {
3927 // Fast lock-free check
3928 if (ovflw_stk->length() == 0) {
3929 return false;
3930 }
3931 assert(work_q->size() == 0, "Shouldn't steal");
3932 MutexLockerEx ml(ovflw_stk->par_lock(),
3933 Mutex::_no_safepoint_check_flag);
3934 // Grab up to 1/4 the size of the work queue
3935 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3936 (size_t)ParGCDesiredObjsFromOverflowList);
3937 num = MIN2(num, ovflw_stk->length());
3938 for (int i = (int) num; i > 0; i--) {
3939 oop cur = ovflw_stk->pop();
3940 assert(cur != NULL, "Counted wrong?");
3941 work_q->push(cur);
3942 }
3943 return num > 0;
3944 }
3945
3946 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3947 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3948 int n_tasks = pst->n_tasks();
3949 // We allow that there may be no tasks to do here because
3950 // we are restarting after a stack overflow.
3951 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3952 uint nth_task = 0;
3953
3954 HeapWord* aligned_start = sp->bottom();
3955 if (sp->used_region().contains(_restart_addr)) {
3956 // Align down to a card boundary for the start of 0th task
3957 // for this space.
3958 aligned_start =
3959 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3960 CardTableModRefBS::card_size);
3961 }
3962
3963 size_t chunk_size = sp->marking_task_size();
3964 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3965 // Having claimed the nth task in this space,
3966 // compute the chunk that it corresponds to:
3967 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3968 aligned_start + (nth_task+1)*chunk_size);
3969 // Try and bump the global finger via a CAS;
3970 // note that we need to do the global finger bump
3971 // _before_ taking the intersection below, because
3972 // the task corresponding to that region will be
3973 // deemed done even if the used_region() expands
3974 // because of allocation -- as it almost certainly will
3975 // during start-up while the threads yield in the
3976 // closure below.
3977 HeapWord* finger = span.end();
3978 bump_global_finger(finger); // atomically
3979 // There are null tasks here corresponding to chunks
3980 // beyond the "top" address of the space.
3981 span = span.intersection(sp->used_region());
3982 if (!span.is_empty()) { // Non-null task
3983 HeapWord* prev_obj;
3984 assert(!span.contains(_restart_addr) || nth_task == 0,
3985 "Inconsistency");
3986 if (nth_task == 0) {
3987 // For the 0th task, we'll not need to compute a block_start.
3988 if (span.contains(_restart_addr)) {
3989 // In the case of a restart because of stack overflow,
3990 // we might additionally skip a chunk prefix.
3991 prev_obj = _restart_addr;
3992 } else {
3993 prev_obj = span.start();
3994 }
3995 } else {
3996 // We want to skip the first object because
3997 // the protocol is to scan any object in its entirety
3998 // that _starts_ in this span; a fortiori, any
3999 // object starting in an earlier span is scanned
4000 // as part of an earlier claimed task.
4001 // Below we use the "careful" version of block_start
4002 // so we do not try to navigate uninitialized objects.
4003 prev_obj = sp->block_start_careful(span.start());
4004 // Below we use a variant of block_size that uses the
4005 // Printezis bits to avoid waiting for allocated
4006 // objects to become initialized/parsable.
4007 while (prev_obj < span.start()) {
4008 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4009 if (sz > 0) {
4010 prev_obj += sz;
4011 } else {
4012 // In this case we may end up doing a bit of redundant
4013 // scanning, but that appears unavoidable, short of
4014 // locking the free list locks; see bug 6324141.
4015 break;
4016 }
4017 }
4018 }
4019 if (prev_obj < span.end()) {
4020 MemRegion my_span = MemRegion(prev_obj, span.end());
4021 // Do the marking work within a non-empty span --
4022 // the last argument to the constructor indicates whether the
4023 // iteration should be incremental with periodic yields.
4024 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4025 &_collector->_markBitMap,
4026 work_queue(i),
4027 &_collector->_markStack,
4028 &_collector->_revisitStack,
4029 _asynch);
4030 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4031 } // else nothing to do for this task
4032 } // else nothing to do for this task
4033 }
4034 // We'd be tempted to assert here that since there are no
4035 // more tasks left to claim in this space, the global_finger
4036 // must exceed space->top() and a fortiori space->end(). However,
4037 // that would not quite be correct because the bumping of
4038 // global_finger occurs strictly after the claiming of a task,
4039 // so by the time we reach here the global finger may not yet
4040 // have been bumped up by the thread that claimed the last
4041 // task.
4042 pst->all_tasks_completed();
4043 }
4044
4045 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4046 private:
4047 CMSConcMarkingTask* _task;
4048 MemRegion _span;
4049 CMSBitMap* _bit_map;
4050 CMSMarkStack* _overflow_stack;
4051 OopTaskQueue* _work_queue;
4052 protected:
4053 DO_OOP_WORK_DEFN
4054 public:
4055 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4056 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4057 CMSMarkStack* revisit_stack):
4058 Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4059 _task(task),
4060 _span(collector->_span),
4061 _work_queue(work_queue),
4062 _bit_map(bit_map),
4063 _overflow_stack(overflow_stack)
4064 { }
4065 virtual void do_oop(oop* p);
4066 virtual void do_oop(narrowOop* p);
4067 void trim_queue(size_t max);
4068 void handle_stack_overflow(HeapWord* lost);
4069 void do_yield_check() {
4070 if (_task->should_yield()) {
4071 _task->yield();
4072 }
4073 }
4074 };
4075
4076 // Grey object scanning during work stealing phase --
4077 // the salient assumption here is that any references
4078 // that are in these stolen objects being scanned must
4079 // already have been initialized (else they would not have
4080 // been published), so we do not need to check for
4081 // uninitialized objects before pushing here.
4082 void Par_ConcMarkingClosure::do_oop(oop obj) {
4083 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4084 HeapWord* addr = (HeapWord*)obj;
4085 // Check if oop points into the CMS generation
4086 // and is not marked
4087 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4088 // a white object ...
4089 // If we manage to "claim" the object, by being the
4090 // first thread to mark it, then we push it on our
4091 // marking stack
4092 if (_bit_map->par_mark(addr)) { // ... now grey
4093 // push on work queue (grey set)
4094 bool simulate_overflow = false;
4095 NOT_PRODUCT(
4096 if (CMSMarkStackOverflowALot &&
4097 _collector->simulate_overflow()) {
4098 // simulate a stack overflow
4099 simulate_overflow = true;
4100 }
4101 )
4102 if (simulate_overflow ||
4103 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4104 // stack overflow
4105 if (PrintCMSStatistics != 0) {
4106 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4107 SIZE_FORMAT, _overflow_stack->capacity());
4108 }
4109 // We cannot assert that the overflow stack is full because
4110 // it may have been emptied since.
4111 assert(simulate_overflow ||
4112 _work_queue->size() == _work_queue->max_elems(),
4113 "Else push should have succeeded");
4114 handle_stack_overflow(addr);
4115 }
4116 } // Else, some other thread got there first
4117 do_yield_check();
4118 }
4119 }
4120
4121 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4122 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4123
4124 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4125 while (_work_queue->size() > max) {
4126 oop new_oop;
4127 if (_work_queue->pop_local(new_oop)) {
4128 assert(new_oop->is_oop(), "Should be an oop");
4129 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4130 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4131 assert(new_oop->is_parsable(), "Should be parsable");
4132 new_oop->oop_iterate(this); // do_oop() above
4133 do_yield_check();
4134 }
4135 }
4136 }
4137
4138 // Upon stack overflow, we discard (part of) the stack,
4139 // remembering the least address amongst those discarded
4140 // in CMSCollector's _restart_address.
4141 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4142 // We need to do this under a mutex to prevent other
4143 // workers from interfering with the work done below.
4144 MutexLockerEx ml(_overflow_stack->par_lock(),
4145 Mutex::_no_safepoint_check_flag);
4146 // Remember the least grey address discarded
4147 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4148 _collector->lower_restart_addr(ra);
4149 _overflow_stack->reset(); // discard stack contents
4150 _overflow_stack->expand(); // expand the stack if possible
4151 }
4152
4153
4154 void CMSConcMarkingTask::do_work_steal(int i) {
4155 OopTaskQueue* work_q = work_queue(i);
4156 oop obj_to_scan;
4157 CMSBitMap* bm = &(_collector->_markBitMap);
4158 CMSMarkStack* ovflw = &(_collector->_markStack);
4159 CMSMarkStack* revisit = &(_collector->_revisitStack);
4160 int* seed = _collector->hash_seed(i);
4161 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4162 while (true) {
4163 cl.trim_queue(0);
4164 assert(work_q->size() == 0, "Should have been emptied above");
4165 if (get_work_from_overflow_stack(ovflw, work_q)) {
4166 // Can't assert below because the work obtained from the
4167 // overflow stack may already have been stolen from us.
4168 // assert(work_q->size() > 0, "Work from overflow stack");
4169 continue;
4170 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4171 assert(obj_to_scan->is_oop(), "Should be an oop");
4172 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4173 obj_to_scan->oop_iterate(&cl);
4174 } else if (terminator()->offer_termination(&_term_term)) {
4175 assert(work_q->size() == 0, "Impossible!");
4176 break;
4177 } else if (yielding() || should_yield()) {
4178 yield();
4179 }
4180 }
4181 }
4182
4183 // This is run by the CMS (coordinator) thread.
4184 void CMSConcMarkingTask::coordinator_yield() {
4185 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4186 "CMS thread should hold CMS token");
4187 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4188 // First give up the locks, then yield, then re-lock
4189 // We should probably use a constructor/destructor idiom to
4190 // do this unlock/lock or modify the MutexUnlocker class to
4191 // serve our purpose. XXX
4192 assert_lock_strong(_bit_map_lock);
4193 _bit_map_lock->unlock();
4194 ConcurrentMarkSweepThread::desynchronize(true);
4195 ConcurrentMarkSweepThread::acknowledge_yield_request();
4196 _collector->stopTimer();
4197 if (PrintCMSStatistics != 0) {
4198 _collector->incrementYields();
4199 }
4200 _collector->icms_wait();
4201
4202 // It is possible for whichever thread initiated the yield request
4203 // not to get a chance to wake up and take the bitmap lock between
4204 // this thread releasing it and reacquiring it. So, while the
4205 // should_yield() flag is on, let's sleep for a bit to give the
4206 // other thread a chance to wake up. The limit imposed on the number
4207 // of iterations is defensive, to avoid any unforseen circumstances
4208 // putting us into an infinite loop. Since it's always been this
4209 // (coordinator_yield()) method that was observed to cause the
4210 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4211 // which is by default non-zero. For the other seven methods that
4212 // also perform the yield operation, as are using a different
4213 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4214 // can enable the sleeping for those methods too, if necessary.
4215 // See 6442774.
4216 //
4217 // We really need to reconsider the synchronization between the GC
4218 // thread and the yield-requesting threads in the future and we
4219 // should really use wait/notify, which is the recommended
4220 // way of doing this type of interaction. Additionally, we should
4221 // consolidate the eight methods that do the yield operation and they
4222 // are almost identical into one for better maintenability and
4223 // readability. See 6445193.
4224 //
4225 // Tony 2006.06.29
4226 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4227 ConcurrentMarkSweepThread::should_yield() &&
4228 !CMSCollector::foregroundGCIsActive(); ++i) {
4229 os::sleep(Thread::current(), 1, false);
4230 ConcurrentMarkSweepThread::acknowledge_yield_request();
4231 }
4232
4233 ConcurrentMarkSweepThread::synchronize(true);
4234 _bit_map_lock->lock_without_safepoint_check();
4235 _collector->startTimer();
4236 }
4237
4238 bool CMSCollector::do_marking_mt(bool asynch) {
4239 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4240 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4241 conc_workers()->total_workers(),
4242 conc_workers()->active_workers(),
4243 Threads::number_of_non_daemon_threads());
4244 conc_workers()->set_active_workers(num_workers);
4245
4246 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4247 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4248
4249 CMSConcMarkingTask tsk(this,
4250 cms_space,
4251 perm_space,
4252 asynch,
4253 conc_workers(),
4254 task_queues());
4255
4256 // Since the actual number of workers we get may be different
4257 // from the number we requested above, do we need to do anything different
4258 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4259 // class?? XXX
4260 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4261 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4262
4263 // Refs discovery is already non-atomic.
4264 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4265 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4266 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4267 conc_workers()->start_task(&tsk);
4268 while (tsk.yielded()) {
4269 tsk.coordinator_yield();
4270 conc_workers()->continue_task(&tsk);
4271 }
4272 // If the task was aborted, _restart_addr will be non-NULL
4273 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4274 while (_restart_addr != NULL) {
4275 // XXX For now we do not make use of ABORTED state and have not
4276 // yet implemented the right abort semantics (even in the original
4277 // single-threaded CMS case). That needs some more investigation
4278 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4279 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4280 // If _restart_addr is non-NULL, a marking stack overflow
4281 // occurred; we need to do a fresh marking iteration from the
4282 // indicated restart address.
4283 if (_foregroundGCIsActive && asynch) {
4284 // We may be running into repeated stack overflows, having
4285 // reached the limit of the stack size, while making very
4286 // slow forward progress. It may be best to bail out and
4287 // let the foreground collector do its job.
4288 // Clear _restart_addr, so that foreground GC
4289 // works from scratch. This avoids the headache of
4290 // a "rescan" which would otherwise be needed because
4291 // of the dirty mod union table & card table.
4292 _restart_addr = NULL;
4293 return false;
4294 }
4295 // Adjust the task to restart from _restart_addr
4296 tsk.reset(_restart_addr);
4297 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4298 _restart_addr);
4299 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4300 _restart_addr);
4301 _restart_addr = NULL;
4302 // Get the workers going again
4303 conc_workers()->start_task(&tsk);
4304 while (tsk.yielded()) {
4305 tsk.coordinator_yield();
4306 conc_workers()->continue_task(&tsk);
4307 }
4308 }
4309 assert(tsk.completed(), "Inconsistency");
4310 assert(tsk.result() == true, "Inconsistency");
4311 return true;
4312 }
4313
4314 bool CMSCollector::do_marking_st(bool asynch) {
4315 ResourceMark rm;
4316 HandleMark hm;
4317
4318 // Temporarily make refs discovery single threaded (non-MT)
4319 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4320 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4321 &_markStack, &_revisitStack, CMSYield && asynch);
4322 // the last argument to iterate indicates whether the iteration
4323 // should be incremental with periodic yields.
4324 _markBitMap.iterate(&markFromRootsClosure);
4325 // If _restart_addr is non-NULL, a marking stack overflow
4326 // occurred; we need to do a fresh iteration from the
4327 // indicated restart address.
4328 while (_restart_addr != NULL) {
4329 if (_foregroundGCIsActive && asynch) {
4330 // We may be running into repeated stack overflows, having
4331 // reached the limit of the stack size, while making very
4332 // slow forward progress. It may be best to bail out and
4333 // let the foreground collector do its job.
4334 // Clear _restart_addr, so that foreground GC
4335 // works from scratch. This avoids the headache of
4336 // a "rescan" which would otherwise be needed because
4337 // of the dirty mod union table & card table.
4338 _restart_addr = NULL;
4339 return false; // indicating failure to complete marking
4340 }
4341 // Deal with stack overflow:
4342 // we restart marking from _restart_addr
4343 HeapWord* ra = _restart_addr;
4344 markFromRootsClosure.reset(ra);
4345 _restart_addr = NULL;
4346 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4347 }
4348 return true;
4349 }
4350
4351 void CMSCollector::preclean() {
4352 check_correct_thread_executing();
4353 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4354 verify_work_stacks_empty();
4355 verify_overflow_empty();
4356 _abort_preclean = false;
4357 if (CMSPrecleaningEnabled) {
4358 _eden_chunk_index = 0;
4359 size_t used = get_eden_used();
4360 size_t capacity = get_eden_capacity();
4361 // Don't start sampling unless we will get sufficiently
4362 // many samples.
4363 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4364 * CMSScheduleRemarkEdenPenetration)) {
4365 _start_sampling = true;
4366 } else {
4367 _start_sampling = false;
4368 }
4369 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4370 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4371 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4372 }
4373 CMSTokenSync x(true); // is cms thread
4374 if (CMSPrecleaningEnabled) {
4375 sample_eden();
4376 _collectorState = AbortablePreclean;
4377 } else {
4378 _collectorState = FinalMarking;
4379 }
4380 verify_work_stacks_empty();
4381 verify_overflow_empty();
4382 }
4383
4384 // Try and schedule the remark such that young gen
4385 // occupancy is CMSScheduleRemarkEdenPenetration %.
4386 void CMSCollector::abortable_preclean() {
4387 check_correct_thread_executing();
4388 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4389 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4390
4391 // If Eden's current occupancy is below this threshold,
4392 // immediately schedule the remark; else preclean
4393 // past the next scavenge in an effort to
4394 // schedule the pause as described avove. By choosing
4395 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4396 // we will never do an actual abortable preclean cycle.
4397 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4398 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4399 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4400 // We need more smarts in the abortable preclean
4401 // loop below to deal with cases where allocation
4402 // in young gen is very very slow, and our precleaning
4403 // is running a losing race against a horde of
4404 // mutators intent on flooding us with CMS updates
4405 // (dirty cards).
4406 // One, admittedly dumb, strategy is to give up
4407 // after a certain number of abortable precleaning loops
4408 // or after a certain maximum time. We want to make
4409 // this smarter in the next iteration.
4410 // XXX FIX ME!!! YSR
4411 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4412 while (!(should_abort_preclean() ||
4413 ConcurrentMarkSweepThread::should_terminate())) {
4414 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4415 cumworkdone += workdone;
4416 loops++;
4417 // Voluntarily terminate abortable preclean phase if we have
4418 // been at it for too long.
4419 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4420 loops >= CMSMaxAbortablePrecleanLoops) {
4421 if (PrintGCDetails) {
4422 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4423 }
4424 break;
4425 }
4426 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4427 if (PrintGCDetails) {
4428 gclog_or_tty->print(" CMS: abort preclean due to time ");
4429 }
4430 break;
4431 }
4432 // If we are doing little work each iteration, we should
4433 // take a short break.
4434 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4435 // Sleep for some time, waiting for work to accumulate
4436 stopTimer();
4437 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4438 startTimer();
4439 waited++;
4440 }
4441 }
4442 if (PrintCMSStatistics > 0) {
4443 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4444 loops, waited, cumworkdone);
4445 }
4446 }
4447 CMSTokenSync x(true); // is cms thread
4448 if (_collectorState != Idling) {
4449 assert(_collectorState == AbortablePreclean,
4450 "Spontaneous state transition?");
4451 _collectorState = FinalMarking;
4452 } // Else, a foreground collection completed this CMS cycle.
4453 return;
4454 }
4455
4456 // Respond to an Eden sampling opportunity
4457 void CMSCollector::sample_eden() {
4458 // Make sure a young gc cannot sneak in between our
4459 // reading and recording of a sample.
4460 assert(Thread::current()->is_ConcurrentGC_thread(),
4461 "Only the cms thread may collect Eden samples");
4462 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4463 "Should collect samples while holding CMS token");
4464 if (!_start_sampling) {
4465 return;
4466 }
4467 if (_eden_chunk_array) {
4468 if (_eden_chunk_index < _eden_chunk_capacity) {
4469 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4470 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4471 "Unexpected state of Eden");
4472 // We'd like to check that what we just sampled is an oop-start address;
4473 // however, we cannot do that here since the object may not yet have been
4474 // initialized. So we'll instead do the check when we _use_ this sample
4475 // later.
4476 if (_eden_chunk_index == 0 ||
4477 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4478 _eden_chunk_array[_eden_chunk_index-1])
4479 >= CMSSamplingGrain)) {
4480 _eden_chunk_index++; // commit sample
4481 }
4482 }
4483 }
4484 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4485 size_t used = get_eden_used();
4486 size_t capacity = get_eden_capacity();
4487 assert(used <= capacity, "Unexpected state of Eden");
4488 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4489 _abort_preclean = true;
4490 }
4491 }
4492 }
4493
4494
4495 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4496 assert(_collectorState == Precleaning ||
4497 _collectorState == AbortablePreclean, "incorrect state");
4498 ResourceMark rm;
4499 HandleMark hm;
4500
4501 // Precleaning is currently not MT but the reference processor
4502 // may be set for MT. Disable it temporarily here.
4503 ReferenceProcessor* rp = ref_processor();
4504 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4505
4506 // Do one pass of scrubbing the discovered reference lists
4507 // to remove any reference objects with strongly-reachable
4508 // referents.
4509 if (clean_refs) {
4510 CMSPrecleanRefsYieldClosure yield_cl(this);
4511 assert(rp->span().equals(_span), "Spans should be equal");
4512 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4513 &_markStack, &_revisitStack,
4514 true /* preclean */);
4515 CMSDrainMarkingStackClosure complete_trace(this,
4516 _span, &_markBitMap, &_markStack,
4517 &keep_alive, true /* preclean */);
4518
4519 // We don't want this step to interfere with a young
4520 // collection because we don't want to take CPU
4521 // or memory bandwidth away from the young GC threads
4522 // (which may be as many as there are CPUs).
4523 // Note that we don't need to protect ourselves from
4524 // interference with mutators because they can't
4525 // manipulate the discovered reference lists nor affect
4526 // the computed reachability of the referents, the
4527 // only properties manipulated by the precleaning
4528 // of these reference lists.
4529 stopTimer();
4530 CMSTokenSyncWithLocks x(true /* is cms thread */,
4531 bitMapLock());
4532 startTimer();
4533 sample_eden();
4534
4535 // The following will yield to allow foreground
4536 // collection to proceed promptly. XXX YSR:
4537 // The code in this method may need further
4538 // tweaking for better performance and some restructuring
4539 // for cleaner interfaces.
4540 rp->preclean_discovered_references(
4541 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4542 &yield_cl, should_unload_classes());
4543 }
4544
4545 if (clean_survivor) { // preclean the active survivor space(s)
4546 assert(_young_gen->kind() == Generation::DefNew ||
4547 _young_gen->kind() == Generation::ParNew ||
4548 _young_gen->kind() == Generation::ASParNew,
4549 "incorrect type for cast");
4550 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4551 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4552 &_markBitMap, &_modUnionTable,
4553 &_markStack, &_revisitStack,
4554 true /* precleaning phase */);
4555 stopTimer();
4556 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4557 bitMapLock());
4558 startTimer();
4559 unsigned int before_count =
4560 GenCollectedHeap::heap()->total_collections();
4561 SurvivorSpacePrecleanClosure
4562 sss_cl(this, _span, &_markBitMap, &_markStack,
4563 &pam_cl, before_count, CMSYield);
4564 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4565 dng->from()->object_iterate_careful(&sss_cl);
4566 dng->to()->object_iterate_careful(&sss_cl);
4567 }
4568 MarkRefsIntoAndScanClosure
4569 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4570 &_markStack, &_revisitStack, this, CMSYield,
4571 true /* precleaning phase */);
4572 // CAUTION: The following closure has persistent state that may need to
4573 // be reset upon a decrease in the sequence of addresses it
4574 // processes.
4575 ScanMarkedObjectsAgainCarefullyClosure
4576 smoac_cl(this, _span,
4577 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4578
4579 // Preclean dirty cards in ModUnionTable and CardTable using
4580 // appropriate convergence criterion;
4581 // repeat CMSPrecleanIter times unless we find that
4582 // we are losing.
4583 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4584 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4585 "Bad convergence multiplier");
4586 assert(CMSPrecleanThreshold >= 100,
4587 "Unreasonably low CMSPrecleanThreshold");
4588
4589 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4590 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4591 numIter < CMSPrecleanIter;
4592 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4593 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4594 if (CMSPermGenPrecleaningEnabled) {
4595 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4596 }
4597 if (Verbose && PrintGCDetails) {
4598 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4599 }
4600 // Either there are very few dirty cards, so re-mark
4601 // pause will be small anyway, or our pre-cleaning isn't
4602 // that much faster than the rate at which cards are being
4603 // dirtied, so we might as well stop and re-mark since
4604 // precleaning won't improve our re-mark time by much.
4605 if (curNumCards <= CMSPrecleanThreshold ||
4606 (numIter > 0 &&
4607 (curNumCards * CMSPrecleanDenominator >
4608 lastNumCards * CMSPrecleanNumerator))) {
4609 numIter++;
4610 cumNumCards += curNumCards;
4611 break;
4612 }
4613 }
4614 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4615 if (CMSPermGenPrecleaningEnabled) {
4616 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4617 }
4618 cumNumCards += curNumCards;
4619 if (PrintGCDetails && PrintCMSStatistics != 0) {
4620 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4621 curNumCards, cumNumCards, numIter);
4622 }
4623 return cumNumCards; // as a measure of useful work done
4624 }
4625
4626 // PRECLEANING NOTES:
4627 // Precleaning involves:
4628 // . reading the bits of the modUnionTable and clearing the set bits.
4629 // . For the cards corresponding to the set bits, we scan the
4630 // objects on those cards. This means we need the free_list_lock
4631 // so that we can safely iterate over the CMS space when scanning
4632 // for oops.
4633 // . When we scan the objects, we'll be both reading and setting
4634 // marks in the marking bit map, so we'll need the marking bit map.
4635 // . For protecting _collector_state transitions, we take the CGC_lock.
4636 // Note that any races in the reading of of card table entries by the
4637 // CMS thread on the one hand and the clearing of those entries by the
4638 // VM thread or the setting of those entries by the mutator threads on the
4639 // other are quite benign. However, for efficiency it makes sense to keep
4640 // the VM thread from racing with the CMS thread while the latter is
4641 // dirty card info to the modUnionTable. We therefore also use the
4642 // CGC_lock to protect the reading of the card table and the mod union
4643 // table by the CM thread.
4644 // . We run concurrently with mutator updates, so scanning
4645 // needs to be done carefully -- we should not try to scan
4646 // potentially uninitialized objects.
4647 //
4648 // Locking strategy: While holding the CGC_lock, we scan over and
4649 // reset a maximal dirty range of the mod union / card tables, then lock
4650 // the free_list_lock and bitmap lock to do a full marking, then
4651 // release these locks; and repeat the cycle. This allows for a
4652 // certain amount of fairness in the sharing of these locks between
4653 // the CMS collector on the one hand, and the VM thread and the
4654 // mutators on the other.
4655
4656 // NOTE: preclean_mod_union_table() and preclean_card_table()
4657 // further below are largely identical; if you need to modify
4658 // one of these methods, please check the other method too.
4659
4660 size_t CMSCollector::preclean_mod_union_table(
4661 ConcurrentMarkSweepGeneration* gen,
4662 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4663 verify_work_stacks_empty();
4664 verify_overflow_empty();
4665
4666 // Turn off checking for this method but turn it back on
4667 // selectively. There are yield points in this method
4668 // but it is difficult to turn the checking off just around
4669 // the yield points. It is simpler to selectively turn
4670 // it on.
4671 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4672
4673 // strategy: starting with the first card, accumulate contiguous
4674 // ranges of dirty cards; clear these cards, then scan the region
4675 // covered by these cards.
4676
4677 // Since all of the MUT is committed ahead, we can just use
4678 // that, in case the generations expand while we are precleaning.
4679 // It might also be fine to just use the committed part of the
4680 // generation, but we might potentially miss cards when the
4681 // generation is rapidly expanding while we are in the midst
4682 // of precleaning.
4683 HeapWord* startAddr = gen->reserved().start();
4684 HeapWord* endAddr = gen->reserved().end();
4685
4686 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4687
4688 size_t numDirtyCards, cumNumDirtyCards;
4689 HeapWord *nextAddr, *lastAddr;
4690 for (cumNumDirtyCards = numDirtyCards = 0,
4691 nextAddr = lastAddr = startAddr;
4692 nextAddr < endAddr;
4693 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4694
4695 ResourceMark rm;
4696 HandleMark hm;
4697
4698 MemRegion dirtyRegion;
4699 {
4700 stopTimer();
4701 // Potential yield point
4702 CMSTokenSync ts(true);
4703 startTimer();
4704 sample_eden();
4705 // Get dirty region starting at nextOffset (inclusive),
4706 // simultaneously clearing it.
4707 dirtyRegion =
4708 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4709 assert(dirtyRegion.start() >= nextAddr,
4710 "returned region inconsistent?");
4711 }
4712 // Remember where the next search should begin.
4713 // The returned region (if non-empty) is a right open interval,
4714 // so lastOffset is obtained from the right end of that
4715 // interval.
4716 lastAddr = dirtyRegion.end();
4717 // Should do something more transparent and less hacky XXX
4718 numDirtyCards =
4719 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4720
4721 // We'll scan the cards in the dirty region (with periodic
4722 // yields for foreground GC as needed).
4723 if (!dirtyRegion.is_empty()) {
4724 assert(numDirtyCards > 0, "consistency check");
4725 HeapWord* stop_point = NULL;
4726 stopTimer();
4727 // Potential yield point
4728 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4729 bitMapLock());
4730 startTimer();
4731 {
4732 verify_work_stacks_empty();
4733 verify_overflow_empty();
4734 sample_eden();
4735 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4736 stop_point =
4737 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4738 }
4739 if (stop_point != NULL) {
4740 // The careful iteration stopped early either because it found an
4741 // uninitialized object, or because we were in the midst of an
4742 // "abortable preclean", which should now be aborted. Redirty
4743 // the bits corresponding to the partially-scanned or unscanned
4744 // cards. We'll either restart at the next block boundary or
4745 // abort the preclean.
4746 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4747 (_collectorState == AbortablePreclean && should_abort_preclean()),
4748 "Unparsable objects should only be in perm gen.");
4749 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4750 if (should_abort_preclean()) {
4751 break; // out of preclean loop
4752 } else {
4753 // Compute the next address at which preclean should pick up;
4754 // might need bitMapLock in order to read P-bits.
4755 lastAddr = next_card_start_after_block(stop_point);
4756 }
4757 }
4758 } else {
4759 assert(lastAddr == endAddr, "consistency check");
4760 assert(numDirtyCards == 0, "consistency check");
4761 break;
4762 }
4763 }
4764 verify_work_stacks_empty();
4765 verify_overflow_empty();
4766 return cumNumDirtyCards;
4767 }
4768
4769 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4770 // below are largely identical; if you need to modify
4771 // one of these methods, please check the other method too.
4772
4773 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4774 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4775 // strategy: it's similar to precleamModUnionTable above, in that
4776 // we accumulate contiguous ranges of dirty cards, mark these cards
4777 // precleaned, then scan the region covered by these cards.
4778 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4779 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4780
4781 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4782
4783 size_t numDirtyCards, cumNumDirtyCards;
4784 HeapWord *lastAddr, *nextAddr;
4785
4786 for (cumNumDirtyCards = numDirtyCards = 0,
4787 nextAddr = lastAddr = startAddr;
4788 nextAddr < endAddr;
4789 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4790
4791 ResourceMark rm;
4792 HandleMark hm;
4793
4794 MemRegion dirtyRegion;
4795 {
4796 // See comments in "Precleaning notes" above on why we
4797 // do this locking. XXX Could the locking overheads be
4798 // too high when dirty cards are sparse? [I don't think so.]
4799 stopTimer();
4800 CMSTokenSync x(true); // is cms thread
4801 startTimer();
4802 sample_eden();
4803 // Get and clear dirty region from card table
4804 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4805 MemRegion(nextAddr, endAddr),
4806 true,
4807 CardTableModRefBS::precleaned_card_val());
4808
4809 assert(dirtyRegion.start() >= nextAddr,
4810 "returned region inconsistent?");
4811 }
4812 lastAddr = dirtyRegion.end();
4813 numDirtyCards =
4814 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4815
4816 if (!dirtyRegion.is_empty()) {
4817 stopTimer();
4818 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4819 startTimer();
4820 sample_eden();
4821 verify_work_stacks_empty();
4822 verify_overflow_empty();
4823 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4824 HeapWord* stop_point =
4825 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4826 if (stop_point != NULL) {
4827 // The careful iteration stopped early because it found an
4828 // uninitialized object. Redirty the bits corresponding to the
4829 // partially-scanned or unscanned cards, and start again at the
4830 // next block boundary.
4831 assert(CMSPermGenPrecleaningEnabled ||
4832 (_collectorState == AbortablePreclean && should_abort_preclean()),
4833 "Unparsable objects should only be in perm gen.");
4834 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4835 if (should_abort_preclean()) {
4836 break; // out of preclean loop
4837 } else {
4838 // Compute the next address at which preclean should pick up.
4839 lastAddr = next_card_start_after_block(stop_point);
4840 }
4841 }
4842 } else {
4843 break;
4844 }
4845 }
4846 verify_work_stacks_empty();
4847 verify_overflow_empty();
4848 return cumNumDirtyCards;
4849 }
4850
4851 void CMSCollector::checkpointRootsFinal(bool asynch,
4852 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4853 assert(_collectorState == FinalMarking, "incorrect state transition?");
4854 check_correct_thread_executing();
4855 // world is stopped at this checkpoint
4856 assert(SafepointSynchronize::is_at_safepoint(),
4857 "world should be stopped");
4858 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4859
4860 verify_work_stacks_empty();
4861 verify_overflow_empty();
4862
4863 SpecializationStats::clear();
4864 if (PrintGCDetails) {
4865 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4866 _young_gen->used() / K,
4867 _young_gen->capacity() / K);
4868 }
4869 if (asynch) {
4870 if (CMSScavengeBeforeRemark) {
4871 GenCollectedHeap* gch = GenCollectedHeap::heap();
4872 // Temporarily set flag to false, GCH->do_collection will
4873 // expect it to be false and set to true
4874 FlagSetting fl(gch->_is_gc_active, false);
4875 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4876 PrintGCDetails && Verbose, true, gclog_or_tty);)
4877 int level = _cmsGen->level() - 1;
4878 if (level >= 0) {
4879 gch->do_collection(true, // full (i.e. force, see below)
4880 false, // !clear_all_soft_refs
4881 0, // size
4882 false, // is_tlab
4883 level // max_level
4884 );
4885 }
4886 }
4887 FreelistLocker x(this);
4888 MutexLockerEx y(bitMapLock(),
4889 Mutex::_no_safepoint_check_flag);
4890 assert(!init_mark_was_synchronous, "but that's impossible!");
4891 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4892 } else {
4893 // already have all the locks
4894 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4895 init_mark_was_synchronous);
4896 }
4897 verify_work_stacks_empty();
4898 verify_overflow_empty();
4899 SpecializationStats::print();
4900 }
4901
4902 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4903 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4904
4905 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4906
4907 assert(haveFreelistLocks(), "must have free list locks");
4908 assert_lock_strong(bitMapLock());
4909
4910 if (UseAdaptiveSizePolicy) {
4911 size_policy()->checkpoint_roots_final_begin();
4912 }
4913
4914 ResourceMark rm;
4915 HandleMark hm;
4916
4917 GenCollectedHeap* gch = GenCollectedHeap::heap();
4918
4919 if (should_unload_classes()) {
4920 CodeCache::gc_prologue();
4921 }
4922 assert(haveFreelistLocks(), "must have free list locks");
4923 assert_lock_strong(bitMapLock());
4924
4925 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4926 if (!init_mark_was_synchronous) {
4927 // We might assume that we need not fill TLAB's when
4928 // CMSScavengeBeforeRemark is set, because we may have just done
4929 // a scavenge which would have filled all TLAB's -- and besides
4930 // Eden would be empty. This however may not always be the case --
4931 // for instance although we asked for a scavenge, it may not have
4932 // happened because of a JNI critical section. We probably need
4933 // a policy for deciding whether we can in that case wait until
4934 // the critical section releases and then do the remark following
4935 // the scavenge, and skip it here. In the absence of that policy,
4936 // or of an indication of whether the scavenge did indeed occur,
4937 // we cannot rely on TLAB's having been filled and must do
4938 // so here just in case a scavenge did not happen.
4939 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4940 // Update the saved marks which may affect the root scans.
4941 gch->save_marks();
4942
4943 {
4944 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4945
4946 // Note on the role of the mod union table:
4947 // Since the marker in "markFromRoots" marks concurrently with
4948 // mutators, it is possible for some reachable objects not to have been
4949 // scanned. For instance, an only reference to an object A was
4950 // placed in object B after the marker scanned B. Unless B is rescanned,
4951 // A would be collected. Such updates to references in marked objects
4952 // are detected via the mod union table which is the set of all cards
4953 // dirtied since the first checkpoint in this GC cycle and prior to
4954 // the most recent young generation GC, minus those cleaned up by the
4955 // concurrent precleaning.
4956 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4957 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4958 do_remark_parallel();
4959 } else {
4960 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4961 gclog_or_tty);
4962 do_remark_non_parallel();
4963 }
4964 }
4965 } else {
4966 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4967 // The initial mark was stop-world, so there's no rescanning to
4968 // do; go straight on to the next step below.
4969 }
4970 verify_work_stacks_empty();
4971 verify_overflow_empty();
4972
4973 {
4974 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4975 refProcessingWork(asynch, clear_all_soft_refs);
4976 }
4977 verify_work_stacks_empty();
4978 verify_overflow_empty();
4979
4980 if (should_unload_classes()) {
4981 CodeCache::gc_epilogue();
4982 }
4983 JvmtiExport::gc_epilogue();
4984
4985 // If we encountered any (marking stack / work queue) overflow
4986 // events during the current CMS cycle, take appropriate
4987 // remedial measures, where possible, so as to try and avoid
4988 // recurrence of that condition.
4989 assert(_markStack.isEmpty(), "No grey objects");
4990 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4991 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4992 if (ser_ovflw > 0) {
4993 if (PrintCMSStatistics != 0) {
4994 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4995 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4996 ", kac_preclean="SIZE_FORMAT")",
4997 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4998 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4999 }
5000 _markStack.expand();
5001 _ser_pmc_remark_ovflw = 0;
5002 _ser_pmc_preclean_ovflw = 0;
5003 _ser_kac_preclean_ovflw = 0;
5004 _ser_kac_ovflw = 0;
5005 }
5006 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5007 if (PrintCMSStatistics != 0) {
5008 gclog_or_tty->print_cr("Work queue overflow (benign) "
5009 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5010 _par_pmc_remark_ovflw, _par_kac_ovflw);
5011 }
5012 _par_pmc_remark_ovflw = 0;
5013 _par_kac_ovflw = 0;
5014 }
5015 if (PrintCMSStatistics != 0) {
5016 if (_markStack._hit_limit > 0) {
5017 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5018 _markStack._hit_limit);
5019 }
5020 if (_markStack._failed_double > 0) {
5021 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5022 " current capacity "SIZE_FORMAT,
5023 _markStack._failed_double,
5024 _markStack.capacity());
5025 }
5026 }
5027 _markStack._hit_limit = 0;
5028 _markStack._failed_double = 0;
5029
5030 // Check that all the klasses have been checked
5031 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5032
5033 if ((VerifyAfterGC || VerifyDuringGC) &&
5034 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5035 verify_after_remark();
5036 }
5037
5038 // Change under the freelistLocks.
5039 _collectorState = Sweeping;
5040 // Call isAllClear() under bitMapLock
5041 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5042 " final marking");
5043 if (UseAdaptiveSizePolicy) {
5044 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5045 }
5046 }
5047
5048 // Parallel remark task
5049 class CMSParRemarkTask: public AbstractGangTask {
5050 CMSCollector* _collector;
5051 int _n_workers;
5052 CompactibleFreeListSpace* _cms_space;
5053 CompactibleFreeListSpace* _perm_space;
5054
5055 // The per-thread work queues, available here for stealing.
5056 OopTaskQueueSet* _task_queues;
5057 ParallelTaskTerminator _term;
5058
5059 public:
5060 // A value of 0 passed to n_workers will cause the number of
5061 // workers to be taken from the active workers in the work gang.
5062 CMSParRemarkTask(CMSCollector* collector,
5063 CompactibleFreeListSpace* cms_space,
5064 CompactibleFreeListSpace* perm_space,
5065 int n_workers, FlexibleWorkGang* workers,
5066 OopTaskQueueSet* task_queues):
5067 AbstractGangTask("Rescan roots and grey objects in parallel"),
5068 _collector(collector),
5069 _cms_space(cms_space), _perm_space(perm_space),
5070 _n_workers(n_workers),
5071 _task_queues(task_queues),
5072 _term(n_workers, task_queues) { }
5073
5074 OopTaskQueueSet* task_queues() { return _task_queues; }
5075
5076 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5077
5078 ParallelTaskTerminator* terminator() { return &_term; }
5079 int n_workers() { return _n_workers; }
5080
5081 void work(uint worker_id);
5082
5083 private:
5084 // Work method in support of parallel rescan ... of young gen spaces
5085 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5086 ContiguousSpace* space,
5087 HeapWord** chunk_array, size_t chunk_top);
5088
5089 // ... of dirty cards in old space
5090 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5091 Par_MarkRefsIntoAndScanClosure* cl);
5092
5093 // ... work stealing for the above
5094 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5095 };
5096
5097 // work_queue(i) is passed to the closure
5098 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5099 // also is passed to do_dirty_card_rescan_tasks() and to
5100 // do_work_steal() to select the i-th task_queue.
5101
5102 void CMSParRemarkTask::work(uint worker_id) {
5103 elapsedTimer _timer;
5104 ResourceMark rm;
5105 HandleMark hm;
5106
5107 // ---------- rescan from roots --------------
5108 _timer.start();
5109 GenCollectedHeap* gch = GenCollectedHeap::heap();
5110 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5111 _collector->_span, _collector->ref_processor(),
5112 &(_collector->_markBitMap),
5113 work_queue(worker_id), &(_collector->_revisitStack));
5114
5115 // Rescan young gen roots first since these are likely
5116 // coarsely partitioned and may, on that account, constitute
5117 // the critical path; thus, it's best to start off that
5118 // work first.
5119 // ---------- young gen roots --------------
5120 {
5121 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5122 EdenSpace* eden_space = dng->eden();
5123 ContiguousSpace* from_space = dng->from();
5124 ContiguousSpace* to_space = dng->to();
5125
5126 HeapWord** eca = _collector->_eden_chunk_array;
5127 size_t ect = _collector->_eden_chunk_index;
5128 HeapWord** sca = _collector->_survivor_chunk_array;
5129 size_t sct = _collector->_survivor_chunk_index;
5130
5131 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5132 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5133
5134 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5135 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5136 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5137
5138 _timer.stop();
5139 if (PrintCMSStatistics != 0) {
5140 gclog_or_tty->print_cr(
5141 "Finished young gen rescan work in %dth thread: %3.3f sec",
5142 worker_id, _timer.seconds());
5143 }
5144 }
5145
5146 // ---------- remaining roots --------------
5147 _timer.reset();
5148 _timer.start();
5149 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5150 false, // yg was scanned above
5151 false, // this is parallel code
5152 true, // collecting perm gen
5153 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5154 &par_mrias_cl,
5155 true, // walk all of code cache if (so & SO_CodeCache)
5156 NULL);
5157 assert(_collector->should_unload_classes()
5158 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5159 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5160 _timer.stop();
5161 if (PrintCMSStatistics != 0) {
5162 gclog_or_tty->print_cr(
5163 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5164 worker_id, _timer.seconds());
5165 }
5166
5167 // ---------- rescan dirty cards ------------
5168 _timer.reset();
5169 _timer.start();
5170
5171 // Do the rescan tasks for each of the two spaces
5172 // (cms_space and perm_space) in turn.
5173 // "worker_id" is passed to select the task_queue for "worker_id"
5174 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5175 do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5176 _timer.stop();
5177 if (PrintCMSStatistics != 0) {
5178 gclog_or_tty->print_cr(
5179 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5180 worker_id, _timer.seconds());
5181 }
5182
5183 // ---------- steal work from other threads ...
5184 // ---------- ... and drain overflow list.
5185 _timer.reset();
5186 _timer.start();
5187 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5188 _timer.stop();
5189 if (PrintCMSStatistics != 0) {
5190 gclog_or_tty->print_cr(
5191 "Finished work stealing in %dth thread: %3.3f sec",
5192 worker_id, _timer.seconds());
5193 }
5194 }
5195
5196 // Note that parameter "i" is not used.
5197 void
5198 CMSParRemarkTask::do_young_space_rescan(int i,
5199 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5200 HeapWord** chunk_array, size_t chunk_top) {
5201 // Until all tasks completed:
5202 // . claim an unclaimed task
5203 // . compute region boundaries corresponding to task claimed
5204 // using chunk_array
5205 // . par_oop_iterate(cl) over that region
5206
5207 ResourceMark rm;
5208 HandleMark hm;
5209
5210 SequentialSubTasksDone* pst = space->par_seq_tasks();
5211 assert(pst->valid(), "Uninitialized use?");
5212
5213 uint nth_task = 0;
5214 uint n_tasks = pst->n_tasks();
5215
5216 HeapWord *start, *end;
5217 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5218 // We claimed task # nth_task; compute its boundaries.
5219 if (chunk_top == 0) { // no samples were taken
5220 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5221 start = space->bottom();
5222 end = space->top();
5223 } else if (nth_task == 0) {
5224 start = space->bottom();
5225 end = chunk_array[nth_task];
5226 } else if (nth_task < (uint)chunk_top) {
5227 assert(nth_task >= 1, "Control point invariant");
5228 start = chunk_array[nth_task - 1];
5229 end = chunk_array[nth_task];
5230 } else {
5231 assert(nth_task == (uint)chunk_top, "Control point invariant");
5232 start = chunk_array[chunk_top - 1];
5233 end = space->top();
5234 }
5235 MemRegion mr(start, end);
5236 // Verify that mr is in space
5237 assert(mr.is_empty() || space->used_region().contains(mr),
5238 "Should be in space");
5239 // Verify that "start" is an object boundary
5240 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5241 "Should be an oop");
5242 space->par_oop_iterate(mr, cl);
5243 }
5244 pst->all_tasks_completed();
5245 }
5246
5247 void
5248 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5249 CompactibleFreeListSpace* sp, int i,
5250 Par_MarkRefsIntoAndScanClosure* cl) {
5251 // Until all tasks completed:
5252 // . claim an unclaimed task
5253 // . compute region boundaries corresponding to task claimed
5254 // . transfer dirty bits ct->mut for that region
5255 // . apply rescanclosure to dirty mut bits for that region
5256
5257 ResourceMark rm;
5258 HandleMark hm;
5259
5260 OopTaskQueue* work_q = work_queue(i);
5261 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5262 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5263 // CAUTION: This closure has state that persists across calls to
5264 // the work method dirty_range_iterate_clear() in that it has
5265 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5266 // use of that state in the imbedded UpwardsObjectClosure instance
5267 // assumes that the cards are always iterated (even if in parallel
5268 // by several threads) in monotonically increasing order per each
5269 // thread. This is true of the implementation below which picks
5270 // card ranges (chunks) in monotonically increasing order globally
5271 // and, a-fortiori, in monotonically increasing order per thread
5272 // (the latter order being a subsequence of the former).
5273 // If the work code below is ever reorganized into a more chaotic
5274 // work-partitioning form than the current "sequential tasks"
5275 // paradigm, the use of that persistent state will have to be
5276 // revisited and modified appropriately. See also related
5277 // bug 4756801 work on which should examine this code to make
5278 // sure that the changes there do not run counter to the
5279 // assumptions made here and necessary for correctness and
5280 // efficiency. Note also that this code might yield inefficient
5281 // behaviour in the case of very large objects that span one or
5282 // more work chunks. Such objects would potentially be scanned
5283 // several times redundantly. Work on 4756801 should try and
5284 // address that performance anomaly if at all possible. XXX
5285 MemRegion full_span = _collector->_span;
5286 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5287 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5288 MarkFromDirtyCardsClosure
5289 greyRescanClosure(_collector, full_span, // entire span of interest
5290 sp, bm, work_q, rs, cl);
5291
5292 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5293 assert(pst->valid(), "Uninitialized use?");
5294 uint nth_task = 0;
5295 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5296 MemRegion span = sp->used_region();
5297 HeapWord* start_addr = span.start();
5298 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5299 alignment);
5300 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5301 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5302 start_addr, "Check alignment");
5303 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5304 chunk_size, "Check alignment");
5305
5306 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5307 // Having claimed the nth_task, compute corresponding mem-region,
5308 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5309 // The alignment restriction ensures that we do not need any
5310 // synchronization with other gang-workers while setting or
5311 // clearing bits in thus chunk of the MUT.
5312 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5313 start_addr + (nth_task+1)*chunk_size);
5314 // The last chunk's end might be way beyond end of the
5315 // used region. In that case pull back appropriately.
5316 if (this_span.end() > end_addr) {
5317 this_span.set_end(end_addr);
5318 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5319 }
5320 // Iterate over the dirty cards covering this chunk, marking them
5321 // precleaned, and setting the corresponding bits in the mod union
5322 // table. Since we have been careful to partition at Card and MUT-word
5323 // boundaries no synchronization is needed between parallel threads.
5324 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5325 &modUnionClosure);
5326
5327 // Having transferred these marks into the modUnionTable,
5328 // rescan the marked objects on the dirty cards in the modUnionTable.
5329 // Even if this is at a synchronous collection, the initial marking
5330 // may have been done during an asynchronous collection so there
5331 // may be dirty bits in the mod-union table.
5332 _collector->_modUnionTable.dirty_range_iterate_clear(
5333 this_span, &greyRescanClosure);
5334 _collector->_modUnionTable.verifyNoOneBitsInRange(
5335 this_span.start(),
5336 this_span.end());
5337 }
5338 pst->all_tasks_completed(); // declare that i am done
5339 }
5340
5341 // . see if we can share work_queues with ParNew? XXX
5342 void
5343 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5344 int* seed) {
5345 OopTaskQueue* work_q = work_queue(i);
5346 NOT_PRODUCT(int num_steals = 0;)
5347 oop obj_to_scan;
5348 CMSBitMap* bm = &(_collector->_markBitMap);
5349
5350 while (true) {
5351 // Completely finish any left over work from (an) earlier round(s)
5352 cl->trim_queue(0);
5353 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5354 (size_t)ParGCDesiredObjsFromOverflowList);
5355 // Now check if there's any work in the overflow list
5356 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5357 // only affects the number of attempts made to get work from the
5358 // overflow list and does not affect the number of workers. Just
5359 // pass ParallelGCThreads so this behavior is unchanged.
5360 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5361 work_q,
5362 ParallelGCThreads)) {
5363 // found something in global overflow list;
5364 // not yet ready to go stealing work from others.
5365 // We'd like to assert(work_q->size() != 0, ...)
5366 // because we just took work from the overflow list,
5367 // but of course we can't since all of that could have
5368 // been already stolen from us.
5369 // "He giveth and He taketh away."
5370 continue;
5371 }
5372 // Verify that we have no work before we resort to stealing
5373 assert(work_q->size() == 0, "Have work, shouldn't steal");
5374 // Try to steal from other queues that have work
5375 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5376 NOT_PRODUCT(num_steals++;)
5377 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5378 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5379 // Do scanning work
5380 obj_to_scan->oop_iterate(cl);
5381 // Loop around, finish this work, and try to steal some more
5382 } else if (terminator()->offer_termination()) {
5383 break; // nirvana from the infinite cycle
5384 }
5385 }
5386 NOT_PRODUCT(
5387 if (PrintCMSStatistics != 0) {
5388 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5389 }
5390 )
5391 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5392 "Else our work is not yet done");
5393 }
5394
5395 // Return a thread-local PLAB recording array, as appropriate.
5396 void* CMSCollector::get_data_recorder(int thr_num) {
5397 if (_survivor_plab_array != NULL &&
5398 (CMSPLABRecordAlways ||
5399 (_collectorState > Marking && _collectorState < FinalMarking))) {
5400 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5401 ChunkArray* ca = &_survivor_plab_array[thr_num];
5402 ca->reset(); // clear it so that fresh data is recorded
5403 return (void*) ca;
5404 } else {
5405 return NULL;
5406 }
5407 }
5408
5409 // Reset all the thread-local PLAB recording arrays
5410 void CMSCollector::reset_survivor_plab_arrays() {
5411 for (uint i = 0; i < ParallelGCThreads; i++) {
5412 _survivor_plab_array[i].reset();
5413 }
5414 }
5415
5416 // Merge the per-thread plab arrays into the global survivor chunk
5417 // array which will provide the partitioning of the survivor space
5418 // for CMS rescan.
5419 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5420 int no_of_gc_threads) {
5421 assert(_survivor_plab_array != NULL, "Error");
5422 assert(_survivor_chunk_array != NULL, "Error");
5423 assert(_collectorState == FinalMarking, "Error");
5424 for (int j = 0; j < no_of_gc_threads; j++) {
5425 _cursor[j] = 0;
5426 }
5427 HeapWord* top = surv->top();
5428 size_t i;
5429 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5430 HeapWord* min_val = top; // Higher than any PLAB address
5431 uint min_tid = 0; // position of min_val this round
5432 for (int j = 0; j < no_of_gc_threads; j++) {
5433 ChunkArray* cur_sca = &_survivor_plab_array[j];
5434 if (_cursor[j] == cur_sca->end()) {
5435 continue;
5436 }
5437 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5438 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5439 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5440 if (cur_val < min_val) {
5441 min_tid = j;
5442 min_val = cur_val;
5443 } else {
5444 assert(cur_val < top, "All recorded addresses should be less");
5445 }
5446 }
5447 // At this point min_val and min_tid are respectively
5448 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5449 // and the thread (j) that witnesses that address.
5450 // We record this address in the _survivor_chunk_array[i]
5451 // and increment _cursor[min_tid] prior to the next round i.
5452 if (min_val == top) {
5453 break;
5454 }
5455 _survivor_chunk_array[i] = min_val;
5456 _cursor[min_tid]++;
5457 }
5458 // We are all done; record the size of the _survivor_chunk_array
5459 _survivor_chunk_index = i; // exclusive: [0, i)
5460 if (PrintCMSStatistics > 0) {
5461 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5462 }
5463 // Verify that we used up all the recorded entries
5464 #ifdef ASSERT
5465 size_t total = 0;
5466 for (int j = 0; j < no_of_gc_threads; j++) {
5467 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5468 total += _cursor[j];
5469 }
5470 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5471 // Check that the merged array is in sorted order
5472 if (total > 0) {
5473 for (size_t i = 0; i < total - 1; i++) {
5474 if (PrintCMSStatistics > 0) {
5475 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5476 i, _survivor_chunk_array[i]);
5477 }
5478 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5479 "Not sorted");
5480 }
5481 }
5482 #endif // ASSERT
5483 }
5484
5485 // Set up the space's par_seq_tasks structure for work claiming
5486 // for parallel rescan of young gen.
5487 // See ParRescanTask where this is currently used.
5488 void
5489 CMSCollector::
5490 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5491 assert(n_threads > 0, "Unexpected n_threads argument");
5492 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5493
5494 // Eden space
5495 {
5496 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5497 assert(!pst->valid(), "Clobbering existing data?");
5498 // Each valid entry in [0, _eden_chunk_index) represents a task.
5499 size_t n_tasks = _eden_chunk_index + 1;
5500 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5501 // Sets the condition for completion of the subtask (how many threads
5502 // need to finish in order to be done).
5503 pst->set_n_threads(n_threads);
5504 pst->set_n_tasks((int)n_tasks);
5505 }
5506
5507 // Merge the survivor plab arrays into _survivor_chunk_array
5508 if (_survivor_plab_array != NULL) {
5509 merge_survivor_plab_arrays(dng->from(), n_threads);
5510 } else {
5511 assert(_survivor_chunk_index == 0, "Error");
5512 }
5513
5514 // To space
5515 {
5516 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5517 assert(!pst->valid(), "Clobbering existing data?");
5518 // Sets the condition for completion of the subtask (how many threads
5519 // need to finish in order to be done).
5520 pst->set_n_threads(n_threads);
5521 pst->set_n_tasks(1);
5522 assert(pst->valid(), "Error");
5523 }
5524
5525 // From space
5526 {
5527 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5528 assert(!pst->valid(), "Clobbering existing data?");
5529 size_t n_tasks = _survivor_chunk_index + 1;
5530 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5531 // Sets the condition for completion of the subtask (how many threads
5532 // need to finish in order to be done).
5533 pst->set_n_threads(n_threads);
5534 pst->set_n_tasks((int)n_tasks);
5535 assert(pst->valid(), "Error");
5536 }
5537 }
5538
5539 // Parallel version of remark
5540 void CMSCollector::do_remark_parallel() {
5541 GenCollectedHeap* gch = GenCollectedHeap::heap();
5542 FlexibleWorkGang* workers = gch->workers();
5543 assert(workers != NULL, "Need parallel worker threads.");
5544 // Choose to use the number of GC workers most recently set
5545 // into "active_workers". If active_workers is not set, set it
5546 // to ParallelGCThreads.
5547 int n_workers = workers->active_workers();
5548 if (n_workers == 0) {
5549 assert(n_workers > 0, "Should have been set during scavenge");
5550 n_workers = ParallelGCThreads;
5551 workers->set_active_workers(n_workers);
5552 }
5553 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5554 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5555
5556 CMSParRemarkTask tsk(this,
5557 cms_space, perm_space,
5558 n_workers, workers, task_queues());
5559
5560 // Set up for parallel process_strong_roots work.
5561 gch->set_par_threads(n_workers);
5562 // We won't be iterating over the cards in the card table updating
5563 // the younger_gen cards, so we shouldn't call the following else
5564 // the verification code as well as subsequent younger_refs_iterate
5565 // code would get confused. XXX
5566 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5567
5568 // The young gen rescan work will not be done as part of
5569 // process_strong_roots (which currently doesn't knw how to
5570 // parallelize such a scan), but rather will be broken up into
5571 // a set of parallel tasks (via the sampling that the [abortable]
5572 // preclean phase did of EdenSpace, plus the [two] tasks of
5573 // scanning the [two] survivor spaces. Further fine-grain
5574 // parallelization of the scanning of the survivor spaces
5575 // themselves, and of precleaning of the younger gen itself
5576 // is deferred to the future.
5577 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5578
5579 // The dirty card rescan work is broken up into a "sequence"
5580 // of parallel tasks (per constituent space) that are dynamically
5581 // claimed by the parallel threads.
5582 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5583 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5584
5585 // It turns out that even when we're using 1 thread, doing the work in a
5586 // separate thread causes wide variance in run times. We can't help this
5587 // in the multi-threaded case, but we special-case n=1 here to get
5588 // repeatable measurements of the 1-thread overhead of the parallel code.
5589 if (n_workers > 1) {
5590 // Make refs discovery MT-safe, if it isn't already: it may not
5591 // necessarily be so, since it's possible that we are doing
5592 // ST marking.
5593 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5594 GenCollectedHeap::StrongRootsScope srs(gch);
5595 workers->run_task(&tsk);
5596 } else {
5597 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5598 GenCollectedHeap::StrongRootsScope srs(gch);
5599 tsk.work(0);
5600 }
5601 gch->set_par_threads(0); // 0 ==> non-parallel.
5602 // restore, single-threaded for now, any preserved marks
5603 // as a result of work_q overflow
5604 restore_preserved_marks_if_any();
5605 }
5606
5607 // Non-parallel version of remark
5608 void CMSCollector::do_remark_non_parallel() {
5609 ResourceMark rm;
5610 HandleMark hm;
5611 GenCollectedHeap* gch = GenCollectedHeap::heap();
5612 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5613
5614 MarkRefsIntoAndScanClosure
5615 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5616 &_markStack, &_revisitStack, this,
5617 false /* should_yield */, false /* not precleaning */);
5618 MarkFromDirtyCardsClosure
5619 markFromDirtyCardsClosure(this, _span,
5620 NULL, // space is set further below
5621 &_markBitMap, &_markStack, &_revisitStack,
5622 &mrias_cl);
5623 {
5624 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5625 // Iterate over the dirty cards, setting the corresponding bits in the
5626 // mod union table.
5627 {
5628 ModUnionClosure modUnionClosure(&_modUnionTable);
5629 _ct->ct_bs()->dirty_card_iterate(
5630 _cmsGen->used_region(),
5631 &modUnionClosure);
5632 _ct->ct_bs()->dirty_card_iterate(
5633 _permGen->used_region(),
5634 &modUnionClosure);
5635 }
5636 // Having transferred these marks into the modUnionTable, we just need
5637 // to rescan the marked objects on the dirty cards in the modUnionTable.
5638 // The initial marking may have been done during an asynchronous
5639 // collection so there may be dirty bits in the mod-union table.
5640 const int alignment =
5641 CardTableModRefBS::card_size * BitsPerWord;
5642 {
5643 // ... First handle dirty cards in CMS gen
5644 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5645 MemRegion ur = _cmsGen->used_region();
5646 HeapWord* lb = ur.start();
5647 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5648 MemRegion cms_span(lb, ub);
5649 _modUnionTable.dirty_range_iterate_clear(cms_span,
5650 &markFromDirtyCardsClosure);
5651 verify_work_stacks_empty();
5652 if (PrintCMSStatistics != 0) {
5653 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5654 markFromDirtyCardsClosure.num_dirty_cards());
5655 }
5656 }
5657 {
5658 // .. and then repeat for dirty cards in perm gen
5659 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5660 MemRegion ur = _permGen->used_region();
5661 HeapWord* lb = ur.start();
5662 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5663 MemRegion perm_span(lb, ub);
5664 _modUnionTable.dirty_range_iterate_clear(perm_span,
5665 &markFromDirtyCardsClosure);
5666 verify_work_stacks_empty();
5667 if (PrintCMSStatistics != 0) {
5668 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5669 markFromDirtyCardsClosure.num_dirty_cards());
5670 }
5671 }
5672 }
5673 if (VerifyDuringGC &&
5674 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5675 HandleMark hm; // Discard invalid handles created during verification
5676 Universe::verify(true);
5677 }
5678 {
5679 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5680
5681 verify_work_stacks_empty();
5682
5683 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5684 GenCollectedHeap::StrongRootsScope srs(gch);
5685 gch->gen_process_strong_roots(_cmsGen->level(),
5686 true, // younger gens as roots
5687 false, // use the local StrongRootsScope
5688 true, // collecting perm gen
5689 SharedHeap::ScanningOption(roots_scanning_options()),
5690 &mrias_cl,
5691 true, // walk code active on stacks
5692 NULL);
5693 assert(should_unload_classes()
5694 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5695 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5696 }
5697 verify_work_stacks_empty();
5698 // Restore evacuated mark words, if any, used for overflow list links
5699 if (!CMSOverflowEarlyRestoration) {
5700 restore_preserved_marks_if_any();
5701 }
5702 verify_overflow_empty();
5703 }
5704
5705 ////////////////////////////////////////////////////////
5706 // Parallel Reference Processing Task Proxy Class
5707 ////////////////////////////////////////////////////////
5708 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5709 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5710 CMSCollector* _collector;
5711 CMSBitMap* _mark_bit_map;
5712 const MemRegion _span;
5713 ProcessTask& _task;
5714
5715 public:
5716 CMSRefProcTaskProxy(ProcessTask& task,
5717 CMSCollector* collector,
5718 const MemRegion& span,
5719 CMSBitMap* mark_bit_map,
5720 AbstractWorkGang* workers,
5721 OopTaskQueueSet* task_queues):
5722 // XXX Should superclass AGTWOQ also know about AWG since it knows
5723 // about the task_queues used by the AWG? Then it could initialize
5724 // the terminator() object. See 6984287. The set_for_termination()
5725 // below is a temporary band-aid for the regression in 6984287.
5726 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5727 task_queues),
5728 _task(task),
5729 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5730 {
5731 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5732 "Inconsistency in _span");
5733 set_for_termination(workers->active_workers());
5734 }
5735
5736 OopTaskQueueSet* task_queues() { return queues(); }
5737
5738 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5739
5740 void do_work_steal(int i,
5741 CMSParDrainMarkingStackClosure* drain,
5742 CMSParKeepAliveClosure* keep_alive,
5743 int* seed);
5744
5745 virtual void work(uint worker_id);
5746 };
5747
5748 void CMSRefProcTaskProxy::work(uint worker_id) {
5749 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5750 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5751 _mark_bit_map,
5752 &_collector->_revisitStack,
5753 work_queue(worker_id));
5754 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5755 _mark_bit_map,
5756 &_collector->_revisitStack,
5757 work_queue(worker_id));
5758 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5759 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5760 if (_task.marks_oops_alive()) {
5761 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5762 _collector->hash_seed(worker_id));
5763 }
5764 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5765 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5766 }
5767
5768 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5769 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5770 EnqueueTask& _task;
5771
5772 public:
5773 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5774 : AbstractGangTask("Enqueue reference objects in parallel"),
5775 _task(task)
5776 { }
5777
5778 virtual void work(uint worker_id)
5779 {
5780 _task.work(worker_id);
5781 }
5782 };
5783
5784 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5785 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5786 OopTaskQueue* work_queue):
5787 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5788 _span(span),
5789 _bit_map(bit_map),
5790 _work_queue(work_queue),
5791 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5792 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5793 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5794 { }
5795
5796 // . see if we can share work_queues with ParNew? XXX
5797 void CMSRefProcTaskProxy::do_work_steal(int i,
5798 CMSParDrainMarkingStackClosure* drain,
5799 CMSParKeepAliveClosure* keep_alive,
5800 int* seed) {
5801 OopTaskQueue* work_q = work_queue(i);
5802 NOT_PRODUCT(int num_steals = 0;)
5803 oop obj_to_scan;
5804
5805 while (true) {
5806 // Completely finish any left over work from (an) earlier round(s)
5807 drain->trim_queue(0);
5808 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5809 (size_t)ParGCDesiredObjsFromOverflowList);
5810 // Now check if there's any work in the overflow list
5811 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5812 // only affects the number of attempts made to get work from the
5813 // overflow list and does not affect the number of workers. Just
5814 // pass ParallelGCThreads so this behavior is unchanged.
5815 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5816 work_q,
5817 ParallelGCThreads)) {
5818 // Found something in global overflow list;
5819 // not yet ready to go stealing work from others.
5820 // We'd like to assert(work_q->size() != 0, ...)
5821 // because we just took work from the overflow list,
5822 // but of course we can't, since all of that might have
5823 // been already stolen from us.
5824 continue;
5825 }
5826 // Verify that we have no work before we resort to stealing
5827 assert(work_q->size() == 0, "Have work, shouldn't steal");
5828 // Try to steal from other queues that have work
5829 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5830 NOT_PRODUCT(num_steals++;)
5831 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5832 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5833 // Do scanning work
5834 obj_to_scan->oop_iterate(keep_alive);
5835 // Loop around, finish this work, and try to steal some more
5836 } else if (terminator()->offer_termination()) {
5837 break; // nirvana from the infinite cycle
5838 }
5839 }
5840 NOT_PRODUCT(
5841 if (PrintCMSStatistics != 0) {
5842 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5843 }
5844 )
5845 }
5846
5847 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5848 {
5849 GenCollectedHeap* gch = GenCollectedHeap::heap();
5850 FlexibleWorkGang* workers = gch->workers();
5851 assert(workers != NULL, "Need parallel worker threads.");
5852 CMSRefProcTaskProxy rp_task(task, &_collector,
5853 _collector.ref_processor()->span(),
5854 _collector.markBitMap(),
5855 workers, _collector.task_queues());
5856 workers->run_task(&rp_task);
5857 }
5858
5859 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5860 {
5861
5862 GenCollectedHeap* gch = GenCollectedHeap::heap();
5863 FlexibleWorkGang* workers = gch->workers();
5864 assert(workers != NULL, "Need parallel worker threads.");
5865 CMSRefEnqueueTaskProxy enq_task(task);
5866 workers->run_task(&enq_task);
5867 }
5868
5869 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5870
5871 ResourceMark rm;
5872 HandleMark hm;
5873
5874 ReferenceProcessor* rp = ref_processor();
5875 assert(rp->span().equals(_span), "Spans should be equal");
5876 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5877 // Process weak references.
5878 rp->setup_policy(clear_all_soft_refs);
5879 verify_work_stacks_empty();
5880
5881 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5882 &_markStack, &_revisitStack,
5883 false /* !preclean */);
5884 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5885 _span, &_markBitMap, &_markStack,
5886 &cmsKeepAliveClosure, false /* !preclean */);
5887 {
5888 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5889 if (rp->processing_is_mt()) {
5890 // Set the degree of MT here. If the discovery is done MT, there
5891 // may have been a different number of threads doing the discovery
5892 // and a different number of discovered lists may have Ref objects.
5893 // That is OK as long as the Reference lists are balanced (see
5894 // balance_all_queues() and balance_queues()).
5895 GenCollectedHeap* gch = GenCollectedHeap::heap();
5896 int active_workers = ParallelGCThreads;
5897 FlexibleWorkGang* workers = gch->workers();
5898 if (workers != NULL) {
5899 active_workers = workers->active_workers();
5900 // The expectation is that active_workers will have already
5901 // been set to a reasonable value. If it has not been set,
5902 // investigate.
5903 assert(active_workers > 0, "Should have been set during scavenge");
5904 }
5905 rp->set_active_mt_degree(active_workers);
5906 CMSRefProcTaskExecutor task_executor(*this);
5907 rp->process_discovered_references(&_is_alive_closure,
5908 &cmsKeepAliveClosure,
5909 &cmsDrainMarkingStackClosure,
5910 &task_executor);
5911 } else {
5912 rp->process_discovered_references(&_is_alive_closure,
5913 &cmsKeepAliveClosure,
5914 &cmsDrainMarkingStackClosure,
5915 NULL);
5916 }
5917 verify_work_stacks_empty();
5918 }
5919
5920 if (should_unload_classes()) {
5921 {
5922 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5923
5924 // Follow SystemDictionary roots and unload classes
5925 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5926
5927 // Follow CodeCache roots and unload any methods marked for unloading
5928 CodeCache::do_unloading(&_is_alive_closure,
5929 &cmsKeepAliveClosure,
5930 purged_class);
5931
5932 cmsDrainMarkingStackClosure.do_void();
5933 verify_work_stacks_empty();
5934
5935 // Update subklass/sibling/implementor links in KlassKlass descendants
5936 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5937 oop k;
5938 while ((k = _revisitStack.pop()) != NULL) {
5939 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5940 &_is_alive_closure,
5941 &cmsKeepAliveClosure);
5942 }
5943 assert(!ClassUnloading ||
5944 (_markStack.isEmpty() && overflow_list_is_empty()),
5945 "Should not have found new reachable objects");
5946 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5947 cmsDrainMarkingStackClosure.do_void();
5948 verify_work_stacks_empty();
5949 }
5950
5951 {
5952 TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
5953 // Clean up unreferenced symbols in symbol table.
5954 SymbolTable::unlink();
5955 }
5956 }
5957
5958 if (should_unload_classes() || !JavaObjectsInPerm) {
5959 TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
5960 // Now clean up stale oops in StringTable
5961 StringTable::unlink(&_is_alive_closure);
5962 }
5963
5964 verify_work_stacks_empty();
5965 // Restore any preserved marks as a result of mark stack or
5966 // work queue overflow
5967 restore_preserved_marks_if_any(); // done single-threaded for now
5968
5969 rp->set_enqueuing_is_done(true);
5970 if (rp->processing_is_mt()) {
5971 rp->balance_all_queues();
5972 CMSRefProcTaskExecutor task_executor(*this);
5973 rp->enqueue_discovered_references(&task_executor);
5974 } else {
5975 rp->enqueue_discovered_references(NULL);
5976 }
5977 rp->verify_no_references_recorded();
5978 assert(!rp->discovery_enabled(), "should have been disabled");
5979 }
5980
5981 #ifndef PRODUCT
5982 void CMSCollector::check_correct_thread_executing() {
5983 Thread* t = Thread::current();
5984 // Only the VM thread or the CMS thread should be here.
5985 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5986 "Unexpected thread type");
5987 // If this is the vm thread, the foreground process
5988 // should not be waiting. Note that _foregroundGCIsActive is
5989 // true while the foreground collector is waiting.
5990 if (_foregroundGCShouldWait) {
5991 // We cannot be the VM thread
5992 assert(t->is_ConcurrentGC_thread(),
5993 "Should be CMS thread");
5994 } else {
5995 // We can be the CMS thread only if we are in a stop-world
5996 // phase of CMS collection.
5997 if (t->is_ConcurrentGC_thread()) {
5998 assert(_collectorState == InitialMarking ||
5999 _collectorState == FinalMarking,
6000 "Should be a stop-world phase");
6001 // The CMS thread should be holding the CMS_token.
6002 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6003 "Potential interference with concurrently "
6004 "executing VM thread");
6005 }
6006 }
6007 }
6008 #endif
6009
6010 void CMSCollector::sweep(bool asynch) {
6011 assert(_collectorState == Sweeping, "just checking");
6012 check_correct_thread_executing();
6013 verify_work_stacks_empty();
6014 verify_overflow_empty();
6015 increment_sweep_count();
6016 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6017
6018 _inter_sweep_timer.stop();
6019 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6020 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6021
6022 // PermGen verification support: If perm gen sweeping is disabled in
6023 // this cycle, we preserve the perm gen object "deadness" information
6024 // in the perm_gen_verify_bit_map. In order to do that we traverse
6025 // all blocks in perm gen and mark all dead objects.
6026 if (verifying() && !should_unload_classes()) {
6027 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6028 "Should have already been allocated");
6029 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6030 markBitMap(), perm_gen_verify_bit_map());
6031 if (asynch) {
6032 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6033 bitMapLock());
6034 _permGen->cmsSpace()->blk_iterate(&mdo);
6035 } else {
6036 // In the case of synchronous sweep, we already have
6037 // the requisite locks/tokens.
6038 _permGen->cmsSpace()->blk_iterate(&mdo);
6039 }
6040 }
6041
6042 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6043 _intra_sweep_timer.reset();
6044 _intra_sweep_timer.start();
6045 if (asynch) {
6046 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6047 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6048 // First sweep the old gen then the perm gen
6049 {
6050 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6051 bitMapLock());
6052 sweepWork(_cmsGen, asynch);
6053 }
6054
6055 // Now repeat for perm gen
6056 if (should_unload_classes()) {
6057 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6058 bitMapLock());
6059 sweepWork(_permGen, asynch);
6060 }
6061
6062 // Update Universe::_heap_*_at_gc figures.
6063 // We need all the free list locks to make the abstract state
6064 // transition from Sweeping to Resetting. See detailed note
6065 // further below.
6066 {
6067 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6068 _permGen->freelistLock());
6069 // Update heap occupancy information which is used as
6070 // input to soft ref clearing policy at the next gc.
6071 Universe::update_heap_info_at_gc();
6072 _collectorState = Resizing;
6073 }
6074 } else {
6075 // already have needed locks
6076 sweepWork(_cmsGen, asynch);
6077
6078 if (should_unload_classes()) {
6079 sweepWork(_permGen, asynch);
6080 }
6081 // Update heap occupancy information which is used as
6082 // input to soft ref clearing policy at the next gc.
6083 Universe::update_heap_info_at_gc();
6084 _collectorState = Resizing;
6085 }
6086 verify_work_stacks_empty();
6087 verify_overflow_empty();
6088
6089 _intra_sweep_timer.stop();
6090 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6091
6092 _inter_sweep_timer.reset();
6093 _inter_sweep_timer.start();
6094
6095 // We need to use a monotonically non-deccreasing time in ms
6096 // or we will see time-warp warnings and os::javaTimeMillis()
6097 // does not guarantee monotonicity.
6098 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6099 update_time_of_last_gc(now);
6100
6101 // NOTE on abstract state transitions:
6102 // Mutators allocate-live and/or mark the mod-union table dirty
6103 // based on the state of the collection. The former is done in
6104 // the interval [Marking, Sweeping] and the latter in the interval
6105 // [Marking, Sweeping). Thus the transitions into the Marking state
6106 // and out of the Sweeping state must be synchronously visible
6107 // globally to the mutators.
6108 // The transition into the Marking state happens with the world
6109 // stopped so the mutators will globally see it. Sweeping is
6110 // done asynchronously by the background collector so the transition
6111 // from the Sweeping state to the Resizing state must be done
6112 // under the freelistLock (as is the check for whether to
6113 // allocate-live and whether to dirty the mod-union table).
6114 assert(_collectorState == Resizing, "Change of collector state to"
6115 " Resizing must be done under the freelistLocks (plural)");
6116
6117 // Now that sweeping has been completed, we clear
6118 // the incremental_collection_failed flag,
6119 // thus inviting a younger gen collection to promote into
6120 // this generation. If such a promotion may still fail,
6121 // the flag will be set again when a young collection is
6122 // attempted.
6123 GenCollectedHeap* gch = GenCollectedHeap::heap();
6124 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6125 gch->update_full_collections_completed(_collection_count_start);
6126 }
6127
6128 // FIX ME!!! Looks like this belongs in CFLSpace, with
6129 // CMSGen merely delegating to it.
6130 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6131 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6132 HeapWord* minAddr = _cmsSpace->bottom();
6133 HeapWord* largestAddr =
6134 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6135 if (largestAddr == NULL) {
6136 // The dictionary appears to be empty. In this case
6137 // try to coalesce at the end of the heap.
6138 largestAddr = _cmsSpace->end();
6139 }
6140 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6141 size_t nearLargestOffset =
6142 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6143 if (PrintFLSStatistics != 0) {
6144 gclog_or_tty->print_cr(
6145 "CMS: Large Block: " PTR_FORMAT ";"
6146 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6147 largestAddr,
6148 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6149 }
6150 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6151 }
6152
6153 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6154 return addr >= _cmsSpace->nearLargestChunk();
6155 }
6156
6157 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6158 return _cmsSpace->find_chunk_at_end();
6159 }
6160
6161 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6162 bool full) {
6163 // The next lower level has been collected. Gather any statistics
6164 // that are of interest at this point.
6165 if (!full && (current_level + 1) == level()) {
6166 // Gather statistics on the young generation collection.
6167 collector()->stats().record_gc0_end(used());
6168 }
6169 }
6170
6171 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6172 GenCollectedHeap* gch = GenCollectedHeap::heap();
6173 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6174 "Wrong type of heap");
6175 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6176 gch->gen_policy()->size_policy();
6177 assert(sp->is_gc_cms_adaptive_size_policy(),
6178 "Wrong type of size policy");
6179 return sp;
6180 }
6181
6182 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6183 if (PrintGCDetails && Verbose) {
6184 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6185 }
6186 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6187 _debug_collection_type =
6188 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6189 if (PrintGCDetails && Verbose) {
6190 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6191 }
6192 }
6193
6194 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6195 bool asynch) {
6196 // We iterate over the space(s) underlying this generation,
6197 // checking the mark bit map to see if the bits corresponding
6198 // to specific blocks are marked or not. Blocks that are
6199 // marked are live and are not swept up. All remaining blocks
6200 // are swept up, with coalescing on-the-fly as we sweep up
6201 // contiguous free and/or garbage blocks:
6202 // We need to ensure that the sweeper synchronizes with allocators
6203 // and stop-the-world collectors. In particular, the following
6204 // locks are used:
6205 // . CMS token: if this is held, a stop the world collection cannot occur
6206 // . freelistLock: if this is held no allocation can occur from this
6207 // generation by another thread
6208 // . bitMapLock: if this is held, no other thread can access or update
6209 //
6210
6211 // Note that we need to hold the freelistLock if we use
6212 // block iterate below; else the iterator might go awry if
6213 // a mutator (or promotion) causes block contents to change
6214 // (for instance if the allocator divvies up a block).
6215 // If we hold the free list lock, for all practical purposes
6216 // young generation GC's can't occur (they'll usually need to
6217 // promote), so we might as well prevent all young generation
6218 // GC's while we do a sweeping step. For the same reason, we might
6219 // as well take the bit map lock for the entire duration
6220
6221 // check that we hold the requisite locks
6222 assert(have_cms_token(), "Should hold cms token");
6223 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6224 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6225 "Should possess CMS token to sweep");
6226 assert_lock_strong(gen->freelistLock());
6227 assert_lock_strong(bitMapLock());
6228
6229 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6230 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6231 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6232 _inter_sweep_estimate.padded_average(),
6233 _intra_sweep_estimate.padded_average());
6234 gen->setNearLargestChunk();
6235
6236 {
6237 SweepClosure sweepClosure(this, gen, &_markBitMap,
6238 CMSYield && asynch);
6239 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6240 // We need to free-up/coalesce garbage/blocks from a
6241 // co-terminal free run. This is done in the SweepClosure
6242 // destructor; so, do not remove this scope, else the
6243 // end-of-sweep-census below will be off by a little bit.
6244 }
6245 gen->cmsSpace()->sweep_completed();
6246 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6247 if (should_unload_classes()) { // unloaded classes this cycle,
6248 _concurrent_cycles_since_last_unload = 0; // ... reset count
6249 } else { // did not unload classes,
6250 _concurrent_cycles_since_last_unload++; // ... increment count
6251 }
6252 }
6253
6254 // Reset CMS data structures (for now just the marking bit map)
6255 // preparatory for the next cycle.
6256 void CMSCollector::reset(bool asynch) {
6257 GenCollectedHeap* gch = GenCollectedHeap::heap();
6258 CMSAdaptiveSizePolicy* sp = size_policy();
6259 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6260 if (asynch) {
6261 CMSTokenSyncWithLocks ts(true, bitMapLock());
6262
6263 // If the state is not "Resetting", the foreground thread
6264 // has done a collection and the resetting.
6265 if (_collectorState != Resetting) {
6266 assert(_collectorState == Idling, "The state should only change"
6267 " because the foreground collector has finished the collection");
6268 return;
6269 }
6270
6271 // Clear the mark bitmap (no grey objects to start with)
6272 // for the next cycle.
6273 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6274 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6275
6276 HeapWord* curAddr = _markBitMap.startWord();
6277 while (curAddr < _markBitMap.endWord()) {
6278 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6279 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6280 _markBitMap.clear_large_range(chunk);
6281 if (ConcurrentMarkSweepThread::should_yield() &&
6282 !foregroundGCIsActive() &&
6283 CMSYield) {
6284 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6285 "CMS thread should hold CMS token");
6286 assert_lock_strong(bitMapLock());
6287 bitMapLock()->unlock();
6288 ConcurrentMarkSweepThread::desynchronize(true);
6289 ConcurrentMarkSweepThread::acknowledge_yield_request();
6290 stopTimer();
6291 if (PrintCMSStatistics != 0) {
6292 incrementYields();
6293 }
6294 icms_wait();
6295
6296 // See the comment in coordinator_yield()
6297 for (unsigned i = 0; i < CMSYieldSleepCount &&
6298 ConcurrentMarkSweepThread::should_yield() &&
6299 !CMSCollector::foregroundGCIsActive(); ++i) {
6300 os::sleep(Thread::current(), 1, false);
6301 ConcurrentMarkSweepThread::acknowledge_yield_request();
6302 }
6303
6304 ConcurrentMarkSweepThread::synchronize(true);
6305 bitMapLock()->lock_without_safepoint_check();
6306 startTimer();
6307 }
6308 curAddr = chunk.end();
6309 }
6310 // A successful mostly concurrent collection has been done.
6311 // Because only the full (i.e., concurrent mode failure) collections
6312 // are being measured for gc overhead limits, clean the "near" flag
6313 // and count.
6314 sp->reset_gc_overhead_limit_count();
6315 _collectorState = Idling;
6316 } else {
6317 // already have the lock
6318 assert(_collectorState == Resetting, "just checking");
6319 assert_lock_strong(bitMapLock());
6320 _markBitMap.clear_all();
6321 _collectorState = Idling;
6322 }
6323
6324 // Stop incremental mode after a cycle completes, so that any future cycles
6325 // are triggered by allocation.
6326 stop_icms();
6327
6328 NOT_PRODUCT(
6329 if (RotateCMSCollectionTypes) {
6330 _cmsGen->rotate_debug_collection_type();
6331 }
6332 )
6333 }
6334
6335 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6336 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6337 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6338 TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6339 TraceCollectorStats tcs(counters());
6340
6341 switch (op) {
6342 case CMS_op_checkpointRootsInitial: {
6343 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6344 checkpointRootsInitial(true); // asynch
6345 if (PrintGC) {
6346 _cmsGen->printOccupancy("initial-mark");
6347 }
6348 break;
6349 }
6350 case CMS_op_checkpointRootsFinal: {
6351 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6352 checkpointRootsFinal(true, // asynch
6353 false, // !clear_all_soft_refs
6354 false); // !init_mark_was_synchronous
6355 if (PrintGC) {
6356 _cmsGen->printOccupancy("remark");
6357 }
6358 break;
6359 }
6360 default:
6361 fatal("No such CMS_op");
6362 }
6363 }
6364
6365 #ifndef PRODUCT
6366 size_t const CMSCollector::skip_header_HeapWords() {
6367 return FreeChunk::header_size();
6368 }
6369
6370 // Try and collect here conditions that should hold when
6371 // CMS thread is exiting. The idea is that the foreground GC
6372 // thread should not be blocked if it wants to terminate
6373 // the CMS thread and yet continue to run the VM for a while
6374 // after that.
6375 void CMSCollector::verify_ok_to_terminate() const {
6376 assert(Thread::current()->is_ConcurrentGC_thread(),
6377 "should be called by CMS thread");
6378 assert(!_foregroundGCShouldWait, "should be false");
6379 // We could check here that all the various low-level locks
6380 // are not held by the CMS thread, but that is overkill; see
6381 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6382 // is checked.
6383 }
6384 #endif
6385
6386 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6387 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6388 "missing Printezis mark?");
6389 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6390 size_t size = pointer_delta(nextOneAddr + 1, addr);
6391 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6392 "alignment problem");
6393 assert(size >= 3, "Necessary for Printezis marks to work");
6394 return size;
6395 }
6396
6397 // A variant of the above (block_size_using_printezis_bits()) except
6398 // that we return 0 if the P-bits are not yet set.
6399 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6400 if (_markBitMap.isMarked(addr + 1)) {
6401 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6402 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6403 size_t size = pointer_delta(nextOneAddr + 1, addr);
6404 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6405 "alignment problem");
6406 assert(size >= 3, "Necessary for Printezis marks to work");
6407 return size;
6408 }
6409 return 0;
6410 }
6411
6412 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6413 size_t sz = 0;
6414 oop p = (oop)addr;
6415 if (p->klass_or_null() != NULL && p->is_parsable()) {
6416 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6417 } else {
6418 sz = block_size_using_printezis_bits(addr);
6419 }
6420 assert(sz > 0, "size must be nonzero");
6421 HeapWord* next_block = addr + sz;
6422 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6423 CardTableModRefBS::card_size);
6424 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6425 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6426 "must be different cards");
6427 return next_card;
6428 }
6429
6430
6431 // CMS Bit Map Wrapper /////////////////////////////////////////
6432
6433 // Construct a CMS bit map infrastructure, but don't create the
6434 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6435 // further below.
6436 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6437 _bm(),
6438 _shifter(shifter),
6439 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6440 {
6441 _bmStartWord = 0;
6442 _bmWordSize = 0;
6443 }
6444
6445 bool CMSBitMap::allocate(MemRegion mr) {
6446 _bmStartWord = mr.start();
6447 _bmWordSize = mr.word_size();
6448 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6449 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6450 if (!brs.is_reserved()) {
6451 warning("CMS bit map allocation failure");
6452 return false;
6453 }
6454 // For now we'll just commit all of the bit map up fromt.
6455 // Later on we'll try to be more parsimonious with swap.
6456 if (!_virtual_space.initialize(brs, brs.size())) {
6457 warning("CMS bit map backing store failure");
6458 return false;
6459 }
6460 assert(_virtual_space.committed_size() == brs.size(),
6461 "didn't reserve backing store for all of CMS bit map?");
6462 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6463 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6464 _bmWordSize, "inconsistency in bit map sizing");
6465 _bm.set_size(_bmWordSize >> _shifter);
6466
6467 // bm.clear(); // can we rely on getting zero'd memory? verify below
6468 assert(isAllClear(),
6469 "Expected zero'd memory from ReservedSpace constructor");
6470 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6471 "consistency check");
6472 return true;
6473 }
6474
6475 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6476 HeapWord *next_addr, *end_addr, *last_addr;
6477 assert_locked();
6478 assert(covers(mr), "out-of-range error");
6479 // XXX assert that start and end are appropriately aligned
6480 for (next_addr = mr.start(), end_addr = mr.end();
6481 next_addr < end_addr; next_addr = last_addr) {
6482 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6483 last_addr = dirty_region.end();
6484 if (!dirty_region.is_empty()) {
6485 cl->do_MemRegion(dirty_region);
6486 } else {
6487 assert(last_addr == end_addr, "program logic");
6488 return;
6489 }
6490 }
6491 }
6492
6493 #ifndef PRODUCT
6494 void CMSBitMap::assert_locked() const {
6495 CMSLockVerifier::assert_locked(lock());
6496 }
6497
6498 bool CMSBitMap::covers(MemRegion mr) const {
6499 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6500 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6501 "size inconsistency");
6502 return (mr.start() >= _bmStartWord) &&
6503 (mr.end() <= endWord());
6504 }
6505
6506 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6507 return (start >= _bmStartWord && (start + size) <= endWord());
6508 }
6509
6510 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6511 // verify that there are no 1 bits in the interval [left, right)
6512 FalseBitMapClosure falseBitMapClosure;
6513 iterate(&falseBitMapClosure, left, right);
6514 }
6515
6516 void CMSBitMap::region_invariant(MemRegion mr)
6517 {
6518 assert_locked();
6519 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6520 assert(!mr.is_empty(), "unexpected empty region");
6521 assert(covers(mr), "mr should be covered by bit map");
6522 // convert address range into offset range
6523 size_t start_ofs = heapWordToOffset(mr.start());
6524 // Make sure that end() is appropriately aligned
6525 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6526 (1 << (_shifter+LogHeapWordSize))),
6527 "Misaligned mr.end()");
6528 size_t end_ofs = heapWordToOffset(mr.end());
6529 assert(end_ofs > start_ofs, "Should mark at least one bit");
6530 }
6531
6532 #endif
6533
6534 bool CMSMarkStack::allocate(size_t size) {
6535 // allocate a stack of the requisite depth
6536 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6537 size * sizeof(oop)));
6538 if (!rs.is_reserved()) {
6539 warning("CMSMarkStack allocation failure");
6540 return false;
6541 }
6542 if (!_virtual_space.initialize(rs, rs.size())) {
6543 warning("CMSMarkStack backing store failure");
6544 return false;
6545 }
6546 assert(_virtual_space.committed_size() == rs.size(),
6547 "didn't reserve backing store for all of CMS stack?");
6548 _base = (oop*)(_virtual_space.low());
6549 _index = 0;
6550 _capacity = size;
6551 NOT_PRODUCT(_max_depth = 0);
6552 return true;
6553 }
6554
6555 // XXX FIX ME !!! In the MT case we come in here holding a
6556 // leaf lock. For printing we need to take a further lock
6557 // which has lower rank. We need to recallibrate the two
6558 // lock-ranks involved in order to be able to rpint the
6559 // messages below. (Or defer the printing to the caller.
6560 // For now we take the expedient path of just disabling the
6561 // messages for the problematic case.)
6562 void CMSMarkStack::expand() {
6563 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6564 if (_capacity == MarkStackSizeMax) {
6565 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6566 // We print a warning message only once per CMS cycle.
6567 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6568 }
6569 return;
6570 }
6571 // Double capacity if possible
6572 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6573 // Do not give up existing stack until we have managed to
6574 // get the double capacity that we desired.
6575 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6576 new_capacity * sizeof(oop)));
6577 if (rs.is_reserved()) {
6578 // Release the backing store associated with old stack
6579 _virtual_space.release();
6580 // Reinitialize virtual space for new stack
6581 if (!_virtual_space.initialize(rs, rs.size())) {
6582 fatal("Not enough swap for expanded marking stack");
6583 }
6584 _base = (oop*)(_virtual_space.low());
6585 _index = 0;
6586 _capacity = new_capacity;
6587 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6588 // Failed to double capacity, continue;
6589 // we print a detail message only once per CMS cycle.
6590 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6591 SIZE_FORMAT"K",
6592 _capacity / K, new_capacity / K);
6593 }
6594 }
6595
6596
6597 // Closures
6598 // XXX: there seems to be a lot of code duplication here;
6599 // should refactor and consolidate common code.
6600
6601 // This closure is used to mark refs into the CMS generation in
6602 // the CMS bit map. Called at the first checkpoint. This closure
6603 // assumes that we do not need to re-mark dirty cards; if the CMS
6604 // generation on which this is used is not an oldest (modulo perm gen)
6605 // generation then this will lose younger_gen cards!
6606
6607 MarkRefsIntoClosure::MarkRefsIntoClosure(
6608 MemRegion span, CMSBitMap* bitMap):
6609 _span(span),
6610 _bitMap(bitMap)
6611 {
6612 assert(_ref_processor == NULL, "deliberately left NULL");
6613 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6614 }
6615
6616 void MarkRefsIntoClosure::do_oop(oop obj) {
6617 // if p points into _span, then mark corresponding bit in _markBitMap
6618 assert(obj->is_oop(), "expected an oop");
6619 HeapWord* addr = (HeapWord*)obj;
6620 if (_span.contains(addr)) {
6621 // this should be made more efficient
6622 _bitMap->mark(addr);
6623 }
6624 }
6625
6626 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6627 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6628
6629 // A variant of the above, used for CMS marking verification.
6630 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6631 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6632 _span(span),
6633 _verification_bm(verification_bm),
6634 _cms_bm(cms_bm)
6635 {
6636 assert(_ref_processor == NULL, "deliberately left NULL");
6637 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6638 }
6639
6640 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6641 // if p points into _span, then mark corresponding bit in _markBitMap
6642 assert(obj->is_oop(), "expected an oop");
6643 HeapWord* addr = (HeapWord*)obj;
6644 if (_span.contains(addr)) {
6645 _verification_bm->mark(addr);
6646 if (!_cms_bm->isMarked(addr)) {
6647 oop(addr)->print();
6648 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6649 fatal("... aborting");
6650 }
6651 }
6652 }
6653
6654 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6655 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6656
6657 //////////////////////////////////////////////////
6658 // MarkRefsIntoAndScanClosure
6659 //////////////////////////////////////////////////
6660
6661 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6662 ReferenceProcessor* rp,
6663 CMSBitMap* bit_map,
6664 CMSBitMap* mod_union_table,
6665 CMSMarkStack* mark_stack,
6666 CMSMarkStack* revisit_stack,
6667 CMSCollector* collector,
6668 bool should_yield,
6669 bool concurrent_precleaning):
6670 _collector(collector),
6671 _span(span),
6672 _bit_map(bit_map),
6673 _mark_stack(mark_stack),
6674 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6675 mark_stack, revisit_stack, concurrent_precleaning),
6676 _yield(should_yield),
6677 _concurrent_precleaning(concurrent_precleaning),
6678 _freelistLock(NULL)
6679 {
6680 _ref_processor = rp;
6681 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6682 }
6683
6684 // This closure is used to mark refs into the CMS generation at the
6685 // second (final) checkpoint, and to scan and transitively follow
6686 // the unmarked oops. It is also used during the concurrent precleaning
6687 // phase while scanning objects on dirty cards in the CMS generation.
6688 // The marks are made in the marking bit map and the marking stack is
6689 // used for keeping the (newly) grey objects during the scan.
6690 // The parallel version (Par_...) appears further below.
6691 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6692 if (obj != NULL) {
6693 assert(obj->is_oop(), "expected an oop");
6694 HeapWord* addr = (HeapWord*)obj;
6695 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6696 assert(_collector->overflow_list_is_empty(),
6697 "overflow list should be empty");
6698 if (_span.contains(addr) &&
6699 !_bit_map->isMarked(addr)) {
6700 // mark bit map (object is now grey)
6701 _bit_map->mark(addr);
6702 // push on marking stack (stack should be empty), and drain the
6703 // stack by applying this closure to the oops in the oops popped
6704 // from the stack (i.e. blacken the grey objects)
6705 bool res = _mark_stack->push(obj);
6706 assert(res, "Should have space to push on empty stack");
6707 do {
6708 oop new_oop = _mark_stack->pop();
6709 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6710 assert(new_oop->is_parsable(), "Found unparsable oop");
6711 assert(_bit_map->isMarked((HeapWord*)new_oop),
6712 "only grey objects on this stack");
6713 // iterate over the oops in this oop, marking and pushing
6714 // the ones in CMS heap (i.e. in _span).
6715 new_oop->oop_iterate(&_pushAndMarkClosure);
6716 // check if it's time to yield
6717 do_yield_check();
6718 } while (!_mark_stack->isEmpty() ||
6719 (!_concurrent_precleaning && take_from_overflow_list()));
6720 // if marking stack is empty, and we are not doing this
6721 // during precleaning, then check the overflow list
6722 }
6723 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6724 assert(_collector->overflow_list_is_empty(),
6725 "overflow list was drained above");
6726 // We could restore evacuated mark words, if any, used for
6727 // overflow list links here because the overflow list is
6728 // provably empty here. That would reduce the maximum
6729 // size requirements for preserved_{oop,mark}_stack.
6730 // But we'll just postpone it until we are all done
6731 // so we can just stream through.
6732 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6733 _collector->restore_preserved_marks_if_any();
6734 assert(_collector->no_preserved_marks(), "No preserved marks");
6735 }
6736 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6737 "All preserved marks should have been restored above");
6738 }
6739 }
6740
6741 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6742 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6743
6744 void MarkRefsIntoAndScanClosure::do_yield_work() {
6745 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6746 "CMS thread should hold CMS token");
6747 assert_lock_strong(_freelistLock);
6748 assert_lock_strong(_bit_map->lock());
6749 // relinquish the free_list_lock and bitMaplock()
6750 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6751 _bit_map->lock()->unlock();
6752 _freelistLock->unlock();
6753 ConcurrentMarkSweepThread::desynchronize(true);
6754 ConcurrentMarkSweepThread::acknowledge_yield_request();
6755 _collector->stopTimer();
6756 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6757 if (PrintCMSStatistics != 0) {
6758 _collector->incrementYields();
6759 }
6760 _collector->icms_wait();
6761
6762 // See the comment in coordinator_yield()
6763 for (unsigned i = 0;
6764 i < CMSYieldSleepCount &&
6765 ConcurrentMarkSweepThread::should_yield() &&
6766 !CMSCollector::foregroundGCIsActive();
6767 ++i) {
6768 os::sleep(Thread::current(), 1, false);
6769 ConcurrentMarkSweepThread::acknowledge_yield_request();
6770 }
6771
6772 ConcurrentMarkSweepThread::synchronize(true);
6773 _freelistLock->lock_without_safepoint_check();
6774 _bit_map->lock()->lock_without_safepoint_check();
6775 _collector->startTimer();
6776 }
6777
6778 ///////////////////////////////////////////////////////////
6779 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6780 // MarkRefsIntoAndScanClosure
6781 ///////////////////////////////////////////////////////////
6782 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6783 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6784 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6785 _span(span),
6786 _bit_map(bit_map),
6787 _work_queue(work_queue),
6788 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6789 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6790 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6791 revisit_stack)
6792 {
6793 _ref_processor = rp;
6794 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6795 }
6796
6797 // This closure is used to mark refs into the CMS generation at the
6798 // second (final) checkpoint, and to scan and transitively follow
6799 // the unmarked oops. The marks are made in the marking bit map and
6800 // the work_queue is used for keeping the (newly) grey objects during
6801 // the scan phase whence they are also available for stealing by parallel
6802 // threads. Since the marking bit map is shared, updates are
6803 // synchronized (via CAS).
6804 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6805 if (obj != NULL) {
6806 // Ignore mark word because this could be an already marked oop
6807 // that may be chained at the end of the overflow list.
6808 assert(obj->is_oop(true), "expected an oop");
6809 HeapWord* addr = (HeapWord*)obj;
6810 if (_span.contains(addr) &&
6811 !_bit_map->isMarked(addr)) {
6812 // mark bit map (object will become grey):
6813 // It is possible for several threads to be
6814 // trying to "claim" this object concurrently;
6815 // the unique thread that succeeds in marking the
6816 // object first will do the subsequent push on
6817 // to the work queue (or overflow list).
6818 if (_bit_map->par_mark(addr)) {
6819 // push on work_queue (which may not be empty), and trim the
6820 // queue to an appropriate length by applying this closure to
6821 // the oops in the oops popped from the stack (i.e. blacken the
6822 // grey objects)
6823 bool res = _work_queue->push(obj);
6824 assert(res, "Low water mark should be less than capacity?");
6825 trim_queue(_low_water_mark);
6826 } // Else, another thread claimed the object
6827 }
6828 }
6829 }
6830
6831 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6832 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6833
6834 // This closure is used to rescan the marked objects on the dirty cards
6835 // in the mod union table and the card table proper.
6836 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6837 oop p, MemRegion mr) {
6838
6839 size_t size = 0;
6840 HeapWord* addr = (HeapWord*)p;
6841 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6842 assert(_span.contains(addr), "we are scanning the CMS generation");
6843 // check if it's time to yield
6844 if (do_yield_check()) {
6845 // We yielded for some foreground stop-world work,
6846 // and we have been asked to abort this ongoing preclean cycle.
6847 return 0;
6848 }
6849 if (_bitMap->isMarked(addr)) {
6850 // it's marked; is it potentially uninitialized?
6851 if (p->klass_or_null() != NULL) {
6852 // If is_conc_safe is false, the object may be undergoing
6853 // change by the VM outside a safepoint. Don't try to
6854 // scan it, but rather leave it for the remark phase.
6855 if (CMSPermGenPrecleaningEnabled &&
6856 (!p->is_conc_safe() || !p->is_parsable())) {
6857 // Signal precleaning to redirty the card since
6858 // the klass pointer is already installed.
6859 assert(size == 0, "Initial value");
6860 } else {
6861 assert(p->is_parsable(), "must be parsable.");
6862 // an initialized object; ignore mark word in verification below
6863 // since we are running concurrent with mutators
6864 assert(p->is_oop(true), "should be an oop");
6865 if (p->is_objArray()) {
6866 // objArrays are precisely marked; restrict scanning
6867 // to dirty cards only.
6868 size = CompactibleFreeListSpace::adjustObjectSize(
6869 p->oop_iterate(_scanningClosure, mr));
6870 } else {
6871 // A non-array may have been imprecisely marked; we need
6872 // to scan object in its entirety.
6873 size = CompactibleFreeListSpace::adjustObjectSize(
6874 p->oop_iterate(_scanningClosure));
6875 }
6876 #ifdef DEBUG
6877 size_t direct_size =
6878 CompactibleFreeListSpace::adjustObjectSize(p->size());
6879 assert(size == direct_size, "Inconsistency in size");
6880 assert(size >= 3, "Necessary for Printezis marks to work");
6881 if (!_bitMap->isMarked(addr+1)) {
6882 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6883 } else {
6884 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6885 assert(_bitMap->isMarked(addr+size-1),
6886 "inconsistent Printezis mark");
6887 }
6888 #endif // DEBUG
6889 }
6890 } else {
6891 // an unitialized object
6892 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6893 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6894 size = pointer_delta(nextOneAddr + 1, addr);
6895 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6896 "alignment problem");
6897 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6898 // will dirty the card when the klass pointer is installed in the
6899 // object (signalling the completion of initialization).
6900 }
6901 } else {
6902 // Either a not yet marked object or an uninitialized object
6903 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6904 // An uninitialized object, skip to the next card, since
6905 // we may not be able to read its P-bits yet.
6906 assert(size == 0, "Initial value");
6907 } else {
6908 // An object not (yet) reached by marking: we merely need to
6909 // compute its size so as to go look at the next block.
6910 assert(p->is_oop(true), "should be an oop");
6911 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6912 }
6913 }
6914 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6915 return size;
6916 }
6917
6918 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6919 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6920 "CMS thread should hold CMS token");
6921 assert_lock_strong(_freelistLock);
6922 assert_lock_strong(_bitMap->lock());
6923 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6924 // relinquish the free_list_lock and bitMaplock()
6925 _bitMap->lock()->unlock();
6926 _freelistLock->unlock();
6927 ConcurrentMarkSweepThread::desynchronize(true);
6928 ConcurrentMarkSweepThread::acknowledge_yield_request();
6929 _collector->stopTimer();
6930 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6931 if (PrintCMSStatistics != 0) {
6932 _collector->incrementYields();
6933 }
6934 _collector->icms_wait();
6935
6936 // See the comment in coordinator_yield()
6937 for (unsigned i = 0; i < CMSYieldSleepCount &&
6938 ConcurrentMarkSweepThread::should_yield() &&
6939 !CMSCollector::foregroundGCIsActive(); ++i) {
6940 os::sleep(Thread::current(), 1, false);
6941 ConcurrentMarkSweepThread::acknowledge_yield_request();
6942 }
6943
6944 ConcurrentMarkSweepThread::synchronize(true);
6945 _freelistLock->lock_without_safepoint_check();
6946 _bitMap->lock()->lock_without_safepoint_check();
6947 _collector->startTimer();
6948 }
6949
6950
6951 //////////////////////////////////////////////////////////////////
6952 // SurvivorSpacePrecleanClosure
6953 //////////////////////////////////////////////////////////////////
6954 // This (single-threaded) closure is used to preclean the oops in
6955 // the survivor spaces.
6956 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6957
6958 HeapWord* addr = (HeapWord*)p;
6959 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6960 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6961 assert(p->klass_or_null() != NULL, "object should be initializd");
6962 assert(p->is_parsable(), "must be parsable.");
6963 // an initialized object; ignore mark word in verification below
6964 // since we are running concurrent with mutators
6965 assert(p->is_oop(true), "should be an oop");
6966 // Note that we do not yield while we iterate over
6967 // the interior oops of p, pushing the relevant ones
6968 // on our marking stack.
6969 size_t size = p->oop_iterate(_scanning_closure);
6970 do_yield_check();
6971 // Observe that below, we do not abandon the preclean
6972 // phase as soon as we should; rather we empty the
6973 // marking stack before returning. This is to satisfy
6974 // some existing assertions. In general, it may be a
6975 // good idea to abort immediately and complete the marking
6976 // from the grey objects at a later time.
6977 while (!_mark_stack->isEmpty()) {
6978 oop new_oop = _mark_stack->pop();
6979 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6980 assert(new_oop->is_parsable(), "Found unparsable oop");
6981 assert(_bit_map->isMarked((HeapWord*)new_oop),
6982 "only grey objects on this stack");
6983 // iterate over the oops in this oop, marking and pushing
6984 // the ones in CMS heap (i.e. in _span).
6985 new_oop->oop_iterate(_scanning_closure);
6986 // check if it's time to yield
6987 do_yield_check();
6988 }
6989 unsigned int after_count =
6990 GenCollectedHeap::heap()->total_collections();
6991 bool abort = (_before_count != after_count) ||
6992 _collector->should_abort_preclean();
6993 return abort ? 0 : size;
6994 }
6995
6996 void SurvivorSpacePrecleanClosure::do_yield_work() {
6997 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6998 "CMS thread should hold CMS token");
6999 assert_lock_strong(_bit_map->lock());
7000 DEBUG_ONLY(RememberKlassesChecker smx(false);)
7001 // Relinquish the bit map lock
7002 _bit_map->lock()->unlock();
7003 ConcurrentMarkSweepThread::desynchronize(true);
7004 ConcurrentMarkSweepThread::acknowledge_yield_request();
7005 _collector->stopTimer();
7006 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7007 if (PrintCMSStatistics != 0) {
7008 _collector->incrementYields();
7009 }
7010 _collector->icms_wait();
7011
7012 // See the comment in coordinator_yield()
7013 for (unsigned i = 0; i < CMSYieldSleepCount &&
7014 ConcurrentMarkSweepThread::should_yield() &&
7015 !CMSCollector::foregroundGCIsActive(); ++i) {
7016 os::sleep(Thread::current(), 1, false);
7017 ConcurrentMarkSweepThread::acknowledge_yield_request();
7018 }
7019
7020 ConcurrentMarkSweepThread::synchronize(true);
7021 _bit_map->lock()->lock_without_safepoint_check();
7022 _collector->startTimer();
7023 }
7024
7025 // This closure is used to rescan the marked objects on the dirty cards
7026 // in the mod union table and the card table proper. In the parallel
7027 // case, although the bitMap is shared, we do a single read so the
7028 // isMarked() query is "safe".
7029 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7030 // Ignore mark word because we are running concurrent with mutators
7031 assert(p->is_oop_or_null(true), "expected an oop or null");
7032 HeapWord* addr = (HeapWord*)p;
7033 assert(_span.contains(addr), "we are scanning the CMS generation");
7034 bool is_obj_array = false;
7035 #ifdef DEBUG
7036 if (!_parallel) {
7037 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7038 assert(_collector->overflow_list_is_empty(),
7039 "overflow list should be empty");
7040
7041 }
7042 #endif // DEBUG
7043 if (_bit_map->isMarked(addr)) {
7044 // Obj arrays are precisely marked, non-arrays are not;
7045 // so we scan objArrays precisely and non-arrays in their
7046 // entirety.
7047 if (p->is_objArray()) {
7048 is_obj_array = true;
7049 if (_parallel) {
7050 p->oop_iterate(_par_scan_closure, mr);
7051 } else {
7052 p->oop_iterate(_scan_closure, mr);
7053 }
7054 } else {
7055 if (_parallel) {
7056 p->oop_iterate(_par_scan_closure);
7057 } else {
7058 p->oop_iterate(_scan_closure);
7059 }
7060 }
7061 }
7062 #ifdef DEBUG
7063 if (!_parallel) {
7064 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7065 assert(_collector->overflow_list_is_empty(),
7066 "overflow list should be empty");
7067
7068 }
7069 #endif // DEBUG
7070 return is_obj_array;
7071 }
7072
7073 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7074 MemRegion span,
7075 CMSBitMap* bitMap, CMSMarkStack* markStack,
7076 CMSMarkStack* revisitStack,
7077 bool should_yield, bool verifying):
7078 _collector(collector),
7079 _span(span),
7080 _bitMap(bitMap),
7081 _mut(&collector->_modUnionTable),
7082 _markStack(markStack),
7083 _revisitStack(revisitStack),
7084 _yield(should_yield),
7085 _skipBits(0)
7086 {
7087 assert(_markStack->isEmpty(), "stack should be empty");
7088 _finger = _bitMap->startWord();
7089 _threshold = _finger;
7090 assert(_collector->_restart_addr == NULL, "Sanity check");
7091 assert(_span.contains(_finger), "Out of bounds _finger?");
7092 DEBUG_ONLY(_verifying = verifying;)
7093 }
7094
7095 void MarkFromRootsClosure::reset(HeapWord* addr) {
7096 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7097 assert(_span.contains(addr), "Out of bounds _finger?");
7098 _finger = addr;
7099 _threshold = (HeapWord*)round_to(
7100 (intptr_t)_finger, CardTableModRefBS::card_size);
7101 }
7102
7103 // Should revisit to see if this should be restructured for
7104 // greater efficiency.
7105 bool MarkFromRootsClosure::do_bit(size_t offset) {
7106 if (_skipBits > 0) {
7107 _skipBits--;
7108 return true;
7109 }
7110 // convert offset into a HeapWord*
7111 HeapWord* addr = _bitMap->startWord() + offset;
7112 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7113 "address out of range");
7114 assert(_bitMap->isMarked(addr), "tautology");
7115 if (_bitMap->isMarked(addr+1)) {
7116 // this is an allocated but not yet initialized object
7117 assert(_skipBits == 0, "tautology");
7118 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7119 oop p = oop(addr);
7120 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7121 DEBUG_ONLY(if (!_verifying) {)
7122 // We re-dirty the cards on which this object lies and increase
7123 // the _threshold so that we'll come back to scan this object
7124 // during the preclean or remark phase. (CMSCleanOnEnter)
7125 if (CMSCleanOnEnter) {
7126 size_t sz = _collector->block_size_using_printezis_bits(addr);
7127 HeapWord* end_card_addr = (HeapWord*)round_to(
7128 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7129 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7130 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7131 // Bump _threshold to end_card_addr; note that
7132 // _threshold cannot possibly exceed end_card_addr, anyhow.
7133 // This prevents future clearing of the card as the scan proceeds
7134 // to the right.
7135 assert(_threshold <= end_card_addr,
7136 "Because we are just scanning into this object");
7137 if (_threshold < end_card_addr) {
7138 _threshold = end_card_addr;
7139 }
7140 if (p->klass_or_null() != NULL) {
7141 // Redirty the range of cards...
7142 _mut->mark_range(redirty_range);
7143 } // ...else the setting of klass will dirty the card anyway.
7144 }
7145 DEBUG_ONLY(})
7146 return true;
7147 }
7148 }
7149 scanOopsInOop(addr);
7150 return true;
7151 }
7152
7153 // We take a break if we've been at this for a while,
7154 // so as to avoid monopolizing the locks involved.
7155 void MarkFromRootsClosure::do_yield_work() {
7156 // First give up the locks, then yield, then re-lock
7157 // We should probably use a constructor/destructor idiom to
7158 // do this unlock/lock or modify the MutexUnlocker class to
7159 // serve our purpose. XXX
7160 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7161 "CMS thread should hold CMS token");
7162 assert_lock_strong(_bitMap->lock());
7163 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7164 _bitMap->lock()->unlock();
7165 ConcurrentMarkSweepThread::desynchronize(true);
7166 ConcurrentMarkSweepThread::acknowledge_yield_request();
7167 _collector->stopTimer();
7168 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7169 if (PrintCMSStatistics != 0) {
7170 _collector->incrementYields();
7171 }
7172 _collector->icms_wait();
7173
7174 // See the comment in coordinator_yield()
7175 for (unsigned i = 0; i < CMSYieldSleepCount &&
7176 ConcurrentMarkSweepThread::should_yield() &&
7177 !CMSCollector::foregroundGCIsActive(); ++i) {
7178 os::sleep(Thread::current(), 1, false);
7179 ConcurrentMarkSweepThread::acknowledge_yield_request();
7180 }
7181
7182 ConcurrentMarkSweepThread::synchronize(true);
7183 _bitMap->lock()->lock_without_safepoint_check();
7184 _collector->startTimer();
7185 }
7186
7187 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7188 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7189 assert(_markStack->isEmpty(),
7190 "should drain stack to limit stack usage");
7191 // convert ptr to an oop preparatory to scanning
7192 oop obj = oop(ptr);
7193 // Ignore mark word in verification below, since we
7194 // may be running concurrent with mutators.
7195 assert(obj->is_oop(true), "should be an oop");
7196 assert(_finger <= ptr, "_finger runneth ahead");
7197 // advance the finger to right end of this object
7198 _finger = ptr + obj->size();
7199 assert(_finger > ptr, "we just incremented it above");
7200 // On large heaps, it may take us some time to get through
7201 // the marking phase (especially if running iCMS). During
7202 // this time it's possible that a lot of mutations have
7203 // accumulated in the card table and the mod union table --
7204 // these mutation records are redundant until we have
7205 // actually traced into the corresponding card.
7206 // Here, we check whether advancing the finger would make
7207 // us cross into a new card, and if so clear corresponding
7208 // cards in the MUT (preclean them in the card-table in the
7209 // future).
7210
7211 DEBUG_ONLY(if (!_verifying) {)
7212 // The clean-on-enter optimization is disabled by default,
7213 // until we fix 6178663.
7214 if (CMSCleanOnEnter && (_finger > _threshold)) {
7215 // [_threshold, _finger) represents the interval
7216 // of cards to be cleared in MUT (or precleaned in card table).
7217 // The set of cards to be cleared is all those that overlap
7218 // with the interval [_threshold, _finger); note that
7219 // _threshold is always kept card-aligned but _finger isn't
7220 // always card-aligned.
7221 HeapWord* old_threshold = _threshold;
7222 assert(old_threshold == (HeapWord*)round_to(
7223 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7224 "_threshold should always be card-aligned");
7225 _threshold = (HeapWord*)round_to(
7226 (intptr_t)_finger, CardTableModRefBS::card_size);
7227 MemRegion mr(old_threshold, _threshold);
7228 assert(!mr.is_empty(), "Control point invariant");
7229 assert(_span.contains(mr), "Should clear within span");
7230 // XXX When _finger crosses from old gen into perm gen
7231 // we may be doing unnecessary cleaning; do better in the
7232 // future by detecting that condition and clearing fewer
7233 // MUT/CT entries.
7234 _mut->clear_range(mr);
7235 }
7236 DEBUG_ONLY(})
7237 // Note: the finger doesn't advance while we drain
7238 // the stack below.
7239 PushOrMarkClosure pushOrMarkClosure(_collector,
7240 _span, _bitMap, _markStack,
7241 _revisitStack,
7242 _finger, this);
7243 bool res = _markStack->push(obj);
7244 assert(res, "Empty non-zero size stack should have space for single push");
7245 while (!_markStack->isEmpty()) {
7246 oop new_oop = _markStack->pop();
7247 // Skip verifying header mark word below because we are
7248 // running concurrent with mutators.
7249 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7250 // now scan this oop's oops
7251 new_oop->oop_iterate(&pushOrMarkClosure);
7252 do_yield_check();
7253 }
7254 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7255 }
7256
7257 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7258 CMSCollector* collector, MemRegion span,
7259 CMSBitMap* bit_map,
7260 OopTaskQueue* work_queue,
7261 CMSMarkStack* overflow_stack,
7262 CMSMarkStack* revisit_stack,
7263 bool should_yield):
7264 _collector(collector),
7265 _whole_span(collector->_span),
7266 _span(span),
7267 _bit_map(bit_map),
7268 _mut(&collector->_modUnionTable),
7269 _work_queue(work_queue),
7270 _overflow_stack(overflow_stack),
7271 _revisit_stack(revisit_stack),
7272 _yield(should_yield),
7273 _skip_bits(0),
7274 _task(task)
7275 {
7276 assert(_work_queue->size() == 0, "work_queue should be empty");
7277 _finger = span.start();
7278 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7279 assert(_span.contains(_finger), "Out of bounds _finger?");
7280 }
7281
7282 // Should revisit to see if this should be restructured for
7283 // greater efficiency.
7284 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7285 if (_skip_bits > 0) {
7286 _skip_bits--;
7287 return true;
7288 }
7289 // convert offset into a HeapWord*
7290 HeapWord* addr = _bit_map->startWord() + offset;
7291 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7292 "address out of range");
7293 assert(_bit_map->isMarked(addr), "tautology");
7294 if (_bit_map->isMarked(addr+1)) {
7295 // this is an allocated object that might not yet be initialized
7296 assert(_skip_bits == 0, "tautology");
7297 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7298 oop p = oop(addr);
7299 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7300 // in the case of Clean-on-Enter optimization, redirty card
7301 // and avoid clearing card by increasing the threshold.
7302 return true;
7303 }
7304 }
7305 scan_oops_in_oop(addr);
7306 return true;
7307 }
7308
7309 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7310 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7311 // Should we assert that our work queue is empty or
7312 // below some drain limit?
7313 assert(_work_queue->size() == 0,
7314 "should drain stack to limit stack usage");
7315 // convert ptr to an oop preparatory to scanning
7316 oop obj = oop(ptr);
7317 // Ignore mark word in verification below, since we
7318 // may be running concurrent with mutators.
7319 assert(obj->is_oop(true), "should be an oop");
7320 assert(_finger <= ptr, "_finger runneth ahead");
7321 // advance the finger to right end of this object
7322 _finger = ptr + obj->size();
7323 assert(_finger > ptr, "we just incremented it above");
7324 // On large heaps, it may take us some time to get through
7325 // the marking phase (especially if running iCMS). During
7326 // this time it's possible that a lot of mutations have
7327 // accumulated in the card table and the mod union table --
7328 // these mutation records are redundant until we have
7329 // actually traced into the corresponding card.
7330 // Here, we check whether advancing the finger would make
7331 // us cross into a new card, and if so clear corresponding
7332 // cards in the MUT (preclean them in the card-table in the
7333 // future).
7334
7335 // The clean-on-enter optimization is disabled by default,
7336 // until we fix 6178663.
7337 if (CMSCleanOnEnter && (_finger > _threshold)) {
7338 // [_threshold, _finger) represents the interval
7339 // of cards to be cleared in MUT (or precleaned in card table).
7340 // The set of cards to be cleared is all those that overlap
7341 // with the interval [_threshold, _finger); note that
7342 // _threshold is always kept card-aligned but _finger isn't
7343 // always card-aligned.
7344 HeapWord* old_threshold = _threshold;
7345 assert(old_threshold == (HeapWord*)round_to(
7346 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7347 "_threshold should always be card-aligned");
7348 _threshold = (HeapWord*)round_to(
7349 (intptr_t)_finger, CardTableModRefBS::card_size);
7350 MemRegion mr(old_threshold, _threshold);
7351 assert(!mr.is_empty(), "Control point invariant");
7352 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7353 // XXX When _finger crosses from old gen into perm gen
7354 // we may be doing unnecessary cleaning; do better in the
7355 // future by detecting that condition and clearing fewer
7356 // MUT/CT entries.
7357 _mut->clear_range(mr);
7358 }
7359
7360 // Note: the local finger doesn't advance while we drain
7361 // the stack below, but the global finger sure can and will.
7362 HeapWord** gfa = _task->global_finger_addr();
7363 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7364 _span, _bit_map,
7365 _work_queue,
7366 _overflow_stack,
7367 _revisit_stack,
7368 _finger,
7369 gfa, this);
7370 bool res = _work_queue->push(obj); // overflow could occur here
7371 assert(res, "Will hold once we use workqueues");
7372 while (true) {
7373 oop new_oop;
7374 if (!_work_queue->pop_local(new_oop)) {
7375 // We emptied our work_queue; check if there's stuff that can
7376 // be gotten from the overflow stack.
7377 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7378 _overflow_stack, _work_queue)) {
7379 do_yield_check();
7380 continue;
7381 } else { // done
7382 break;
7383 }
7384 }
7385 // Skip verifying header mark word below because we are
7386 // running concurrent with mutators.
7387 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7388 // now scan this oop's oops
7389 new_oop->oop_iterate(&pushOrMarkClosure);
7390 do_yield_check();
7391 }
7392 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7393 }
7394
7395 // Yield in response to a request from VM Thread or
7396 // from mutators.
7397 void Par_MarkFromRootsClosure::do_yield_work() {
7398 assert(_task != NULL, "sanity");
7399 _task->yield();
7400 }
7401
7402 // A variant of the above used for verifying CMS marking work.
7403 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7404 MemRegion span,
7405 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7406 CMSMarkStack* mark_stack):
7407 _collector(collector),
7408 _span(span),
7409 _verification_bm(verification_bm),
7410 _cms_bm(cms_bm),
7411 _mark_stack(mark_stack),
7412 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7413 mark_stack)
7414 {
7415 assert(_mark_stack->isEmpty(), "stack should be empty");
7416 _finger = _verification_bm->startWord();
7417 assert(_collector->_restart_addr == NULL, "Sanity check");
7418 assert(_span.contains(_finger), "Out of bounds _finger?");
7419 }
7420
7421 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7422 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7423 assert(_span.contains(addr), "Out of bounds _finger?");
7424 _finger = addr;
7425 }
7426
7427 // Should revisit to see if this should be restructured for
7428 // greater efficiency.
7429 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7430 // convert offset into a HeapWord*
7431 HeapWord* addr = _verification_bm->startWord() + offset;
7432 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7433 "address out of range");
7434 assert(_verification_bm->isMarked(addr), "tautology");
7435 assert(_cms_bm->isMarked(addr), "tautology");
7436
7437 assert(_mark_stack->isEmpty(),
7438 "should drain stack to limit stack usage");
7439 // convert addr to an oop preparatory to scanning
7440 oop obj = oop(addr);
7441 assert(obj->is_oop(), "should be an oop");
7442 assert(_finger <= addr, "_finger runneth ahead");
7443 // advance the finger to right end of this object
7444 _finger = addr + obj->size();
7445 assert(_finger > addr, "we just incremented it above");
7446 // Note: the finger doesn't advance while we drain
7447 // the stack below.
7448 bool res = _mark_stack->push(obj);
7449 assert(res, "Empty non-zero size stack should have space for single push");
7450 while (!_mark_stack->isEmpty()) {
7451 oop new_oop = _mark_stack->pop();
7452 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7453 // now scan this oop's oops
7454 new_oop->oop_iterate(&_pam_verify_closure);
7455 }
7456 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7457 return true;
7458 }
7459
7460 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7461 CMSCollector* collector, MemRegion span,
7462 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7463 CMSMarkStack* mark_stack):
7464 OopClosure(collector->ref_processor()),
7465 _collector(collector),
7466 _span(span),
7467 _verification_bm(verification_bm),
7468 _cms_bm(cms_bm),
7469 _mark_stack(mark_stack)
7470 { }
7471
7472 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7473 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7474
7475 // Upon stack overflow, we discard (part of) the stack,
7476 // remembering the least address amongst those discarded
7477 // in CMSCollector's _restart_address.
7478 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7479 // Remember the least grey address discarded
7480 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7481 _collector->lower_restart_addr(ra);
7482 _mark_stack->reset(); // discard stack contents
7483 _mark_stack->expand(); // expand the stack if possible
7484 }
7485
7486 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7487 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7488 HeapWord* addr = (HeapWord*)obj;
7489 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7490 // Oop lies in _span and isn't yet grey or black
7491 _verification_bm->mark(addr); // now grey
7492 if (!_cms_bm->isMarked(addr)) {
7493 oop(addr)->print();
7494 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7495 addr);
7496 fatal("... aborting");
7497 }
7498
7499 if (!_mark_stack->push(obj)) { // stack overflow
7500 if (PrintCMSStatistics != 0) {
7501 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7502 SIZE_FORMAT, _mark_stack->capacity());
7503 }
7504 assert(_mark_stack->isFull(), "Else push should have succeeded");
7505 handle_stack_overflow(addr);
7506 }
7507 // anything including and to the right of _finger
7508 // will be scanned as we iterate over the remainder of the
7509 // bit map
7510 }
7511 }
7512
7513 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7514 MemRegion span,
7515 CMSBitMap* bitMap, CMSMarkStack* markStack,
7516 CMSMarkStack* revisitStack,
7517 HeapWord* finger, MarkFromRootsClosure* parent) :
7518 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7519 _span(span),
7520 _bitMap(bitMap),
7521 _markStack(markStack),
7522 _finger(finger),
7523 _parent(parent)
7524 { }
7525
7526 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7527 MemRegion span,
7528 CMSBitMap* bit_map,
7529 OopTaskQueue* work_queue,
7530 CMSMarkStack* overflow_stack,
7531 CMSMarkStack* revisit_stack,
7532 HeapWord* finger,
7533 HeapWord** global_finger_addr,
7534 Par_MarkFromRootsClosure* parent) :
7535 Par_KlassRememberingOopClosure(collector,
7536 collector->ref_processor(),
7537 revisit_stack),
7538 _whole_span(collector->_span),
7539 _span(span),
7540 _bit_map(bit_map),
7541 _work_queue(work_queue),
7542 _overflow_stack(overflow_stack),
7543 _finger(finger),
7544 _global_finger_addr(global_finger_addr),
7545 _parent(parent)
7546 { }
7547
7548 // Assumes thread-safe access by callers, who are
7549 // responsible for mutual exclusion.
7550 void CMSCollector::lower_restart_addr(HeapWord* low) {
7551 assert(_span.contains(low), "Out of bounds addr");
7552 if (_restart_addr == NULL) {
7553 _restart_addr = low;
7554 } else {
7555 _restart_addr = MIN2(_restart_addr, low);
7556 }
7557 }
7558
7559 // Upon stack overflow, we discard (part of) the stack,
7560 // remembering the least address amongst those discarded
7561 // in CMSCollector's _restart_address.
7562 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7563 // Remember the least grey address discarded
7564 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7565 _collector->lower_restart_addr(ra);
7566 _markStack->reset(); // discard stack contents
7567 _markStack->expand(); // expand the stack if possible
7568 }
7569
7570 // Upon stack overflow, we discard (part of) the stack,
7571 // remembering the least address amongst those discarded
7572 // in CMSCollector's _restart_address.
7573 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7574 // We need to do this under a mutex to prevent other
7575 // workers from interfering with the work done below.
7576 MutexLockerEx ml(_overflow_stack->par_lock(),
7577 Mutex::_no_safepoint_check_flag);
7578 // Remember the least grey address discarded
7579 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7580 _collector->lower_restart_addr(ra);
7581 _overflow_stack->reset(); // discard stack contents
7582 _overflow_stack->expand(); // expand the stack if possible
7583 }
7584
7585 void PushOrMarkClosure::do_oop(oop obj) {
7586 // Ignore mark word because we are running concurrent with mutators.
7587 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7588 HeapWord* addr = (HeapWord*)obj;
7589 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7590 // Oop lies in _span and isn't yet grey or black
7591 _bitMap->mark(addr); // now grey
7592 if (addr < _finger) {
7593 // the bit map iteration has already either passed, or
7594 // sampled, this bit in the bit map; we'll need to
7595 // use the marking stack to scan this oop's oops.
7596 bool simulate_overflow = false;
7597 NOT_PRODUCT(
7598 if (CMSMarkStackOverflowALot &&
7599 _collector->simulate_overflow()) {
7600 // simulate a stack overflow
7601 simulate_overflow = true;
7602 }
7603 )
7604 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7605 if (PrintCMSStatistics != 0) {
7606 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7607 SIZE_FORMAT, _markStack->capacity());
7608 }
7609 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7610 handle_stack_overflow(addr);
7611 }
7612 }
7613 // anything including and to the right of _finger
7614 // will be scanned as we iterate over the remainder of the
7615 // bit map
7616 do_yield_check();
7617 }
7618 }
7619
7620 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7621 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7622
7623 void Par_PushOrMarkClosure::do_oop(oop obj) {
7624 // Ignore mark word because we are running concurrent with mutators.
7625 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7626 HeapWord* addr = (HeapWord*)obj;
7627 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7628 // Oop lies in _span and isn't yet grey or black
7629 // We read the global_finger (volatile read) strictly after marking oop
7630 bool res = _bit_map->par_mark(addr); // now grey
7631 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7632 // Should we push this marked oop on our stack?
7633 // -- if someone else marked it, nothing to do
7634 // -- if target oop is above global finger nothing to do
7635 // -- if target oop is in chunk and above local finger
7636 // then nothing to do
7637 // -- else push on work queue
7638 if ( !res // someone else marked it, they will deal with it
7639 || (addr >= *gfa) // will be scanned in a later task
7640 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7641 return;
7642 }
7643 // the bit map iteration has already either passed, or
7644 // sampled, this bit in the bit map; we'll need to
7645 // use the marking stack to scan this oop's oops.
7646 bool simulate_overflow = false;
7647 NOT_PRODUCT(
7648 if (CMSMarkStackOverflowALot &&
7649 _collector->simulate_overflow()) {
7650 // simulate a stack overflow
7651 simulate_overflow = true;
7652 }
7653 )
7654 if (simulate_overflow ||
7655 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7656 // stack overflow
7657 if (PrintCMSStatistics != 0) {
7658 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7659 SIZE_FORMAT, _overflow_stack->capacity());
7660 }
7661 // We cannot assert that the overflow stack is full because
7662 // it may have been emptied since.
7663 assert(simulate_overflow ||
7664 _work_queue->size() == _work_queue->max_elems(),
7665 "Else push should have succeeded");
7666 handle_stack_overflow(addr);
7667 }
7668 do_yield_check();
7669 }
7670 }
7671
7672 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7673 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7674
7675 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7676 ReferenceProcessor* rp,
7677 CMSMarkStack* revisit_stack) :
7678 OopClosure(rp),
7679 _collector(collector),
7680 _revisit_stack(revisit_stack),
7681 _should_remember_klasses(collector->should_unload_classes()) {}
7682
7683 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7684 MemRegion span,
7685 ReferenceProcessor* rp,
7686 CMSBitMap* bit_map,
7687 CMSBitMap* mod_union_table,
7688 CMSMarkStack* mark_stack,
7689 CMSMarkStack* revisit_stack,
7690 bool concurrent_precleaning):
7691 KlassRememberingOopClosure(collector, rp, revisit_stack),
7692 _span(span),
7693 _bit_map(bit_map),
7694 _mod_union_table(mod_union_table),
7695 _mark_stack(mark_stack),
7696 _concurrent_precleaning(concurrent_precleaning)
7697 {
7698 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7699 }
7700
7701 // Grey object rescan during pre-cleaning and second checkpoint phases --
7702 // the non-parallel version (the parallel version appears further below.)
7703 void PushAndMarkClosure::do_oop(oop obj) {
7704 // Ignore mark word verification. If during concurrent precleaning,
7705 // the object monitor may be locked. If during the checkpoint
7706 // phases, the object may already have been reached by a different
7707 // path and may be at the end of the global overflow list (so
7708 // the mark word may be NULL).
7709 assert(obj->is_oop_or_null(true /* ignore mark word */),
7710 "expected an oop or NULL");
7711 HeapWord* addr = (HeapWord*)obj;
7712 // Check if oop points into the CMS generation
7713 // and is not marked
7714 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7715 // a white object ...
7716 _bit_map->mark(addr); // ... now grey
7717 // push on the marking stack (grey set)
7718 bool simulate_overflow = false;
7719 NOT_PRODUCT(
7720 if (CMSMarkStackOverflowALot &&
7721 _collector->simulate_overflow()) {
7722 // simulate a stack overflow
7723 simulate_overflow = true;
7724 }
7725 )
7726 if (simulate_overflow || !_mark_stack->push(obj)) {
7727 if (_concurrent_precleaning) {
7728 // During precleaning we can just dirty the appropriate card(s)
7729 // in the mod union table, thus ensuring that the object remains
7730 // in the grey set and continue. In the case of object arrays
7731 // we need to dirty all of the cards that the object spans,
7732 // since the rescan of object arrays will be limited to the
7733 // dirty cards.
7734 // Note that no one can be intefering with us in this action
7735 // of dirtying the mod union table, so no locking or atomics
7736 // are required.
7737 if (obj->is_objArray()) {
7738 size_t sz = obj->size();
7739 HeapWord* end_card_addr = (HeapWord*)round_to(
7740 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7741 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7742 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7743 _mod_union_table->mark_range(redirty_range);
7744 } else {
7745 _mod_union_table->mark(addr);
7746 }
7747 _collector->_ser_pmc_preclean_ovflw++;
7748 } else {
7749 // During the remark phase, we need to remember this oop
7750 // in the overflow list.
7751 _collector->push_on_overflow_list(obj);
7752 _collector->_ser_pmc_remark_ovflw++;
7753 }
7754 }
7755 }
7756 }
7757
7758 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7759 MemRegion span,
7760 ReferenceProcessor* rp,
7761 CMSBitMap* bit_map,
7762 OopTaskQueue* work_queue,
7763 CMSMarkStack* revisit_stack):
7764 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7765 _span(span),
7766 _bit_map(bit_map),
7767 _work_queue(work_queue)
7768 {
7769 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7770 }
7771
7772 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7773 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7774
7775 // Grey object rescan during second checkpoint phase --
7776 // the parallel version.
7777 void Par_PushAndMarkClosure::do_oop(oop obj) {
7778 // In the assert below, we ignore the mark word because
7779 // this oop may point to an already visited object that is
7780 // on the overflow stack (in which case the mark word has
7781 // been hijacked for chaining into the overflow stack --
7782 // if this is the last object in the overflow stack then
7783 // its mark word will be NULL). Because this object may
7784 // have been subsequently popped off the global overflow
7785 // stack, and the mark word possibly restored to the prototypical
7786 // value, by the time we get to examined this failing assert in
7787 // the debugger, is_oop_or_null(false) may subsequently start
7788 // to hold.
7789 assert(obj->is_oop_or_null(true),
7790 "expected an oop or NULL");
7791 HeapWord* addr = (HeapWord*)obj;
7792 // Check if oop points into the CMS generation
7793 // and is not marked
7794 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7795 // a white object ...
7796 // If we manage to "claim" the object, by being the
7797 // first thread to mark it, then we push it on our
7798 // marking stack
7799 if (_bit_map->par_mark(addr)) { // ... now grey
7800 // push on work queue (grey set)
7801 bool simulate_overflow = false;
7802 NOT_PRODUCT(
7803 if (CMSMarkStackOverflowALot &&
7804 _collector->par_simulate_overflow()) {
7805 // simulate a stack overflow
7806 simulate_overflow = true;
7807 }
7808 )
7809 if (simulate_overflow || !_work_queue->push(obj)) {
7810 _collector->par_push_on_overflow_list(obj);
7811 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7812 }
7813 } // Else, some other thread got there first
7814 }
7815 }
7816
7817 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7818 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7819
7820 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7821 // TBD
7822 }
7823
7824 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7825 // TBD
7826 }
7827
7828 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7829 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7830 Mutex* bml = _collector->bitMapLock();
7831 assert_lock_strong(bml);
7832 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7833 "CMS thread should hold CMS token");
7834
7835 bml->unlock();
7836 ConcurrentMarkSweepThread::desynchronize(true);
7837
7838 ConcurrentMarkSweepThread::acknowledge_yield_request();
7839
7840 _collector->stopTimer();
7841 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7842 if (PrintCMSStatistics != 0) {
7843 _collector->incrementYields();
7844 }
7845 _collector->icms_wait();
7846
7847 // See the comment in coordinator_yield()
7848 for (unsigned i = 0; i < CMSYieldSleepCount &&
7849 ConcurrentMarkSweepThread::should_yield() &&
7850 !CMSCollector::foregroundGCIsActive(); ++i) {
7851 os::sleep(Thread::current(), 1, false);
7852 ConcurrentMarkSweepThread::acknowledge_yield_request();
7853 }
7854
7855 ConcurrentMarkSweepThread::synchronize(true);
7856 bml->lock();
7857
7858 _collector->startTimer();
7859 }
7860
7861 bool CMSPrecleanRefsYieldClosure::should_return() {
7862 if (ConcurrentMarkSweepThread::should_yield()) {
7863 do_yield_work();
7864 }
7865 return _collector->foregroundGCIsActive();
7866 }
7867
7868 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7869 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7870 "mr should be aligned to start at a card boundary");
7871 // We'd like to assert:
7872 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7873 // "mr should be a range of cards");
7874 // However, that would be too strong in one case -- the last
7875 // partition ends at _unallocated_block which, in general, can be
7876 // an arbitrary boundary, not necessarily card aligned.
7877 if (PrintCMSStatistics != 0) {
7878 _num_dirty_cards +=
7879 mr.word_size()/CardTableModRefBS::card_size_in_words;
7880 }
7881 _space->object_iterate_mem(mr, &_scan_cl);
7882 }
7883
7884 SweepClosure::SweepClosure(CMSCollector* collector,
7885 ConcurrentMarkSweepGeneration* g,
7886 CMSBitMap* bitMap, bool should_yield) :
7887 _collector(collector),
7888 _g(g),
7889 _sp(g->cmsSpace()),
7890 _limit(_sp->sweep_limit()),
7891 _freelistLock(_sp->freelistLock()),
7892 _bitMap(bitMap),
7893 _yield(should_yield),
7894 _inFreeRange(false), // No free range at beginning of sweep
7895 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7896 _lastFreeRangeCoalesced(false),
7897 _freeFinger(g->used_region().start())
7898 {
7899 NOT_PRODUCT(
7900 _numObjectsFreed = 0;
7901 _numWordsFreed = 0;
7902 _numObjectsLive = 0;
7903 _numWordsLive = 0;
7904 _numObjectsAlreadyFree = 0;
7905 _numWordsAlreadyFree = 0;
7906 _last_fc = NULL;
7907
7908 _sp->initializeIndexedFreeListArrayReturnedBytes();
7909 _sp->dictionary()->initialize_dict_returned_bytes();
7910 )
7911 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7912 "sweep _limit out of bounds");
7913 if (CMSTraceSweeper) {
7914 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7915 _limit);
7916 }
7917 }
7918
7919 void SweepClosure::print_on(outputStream* st) const {
7920 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7921 _sp->bottom(), _sp->end());
7922 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7923 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7924 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7925 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7926 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7927 }
7928
7929 #ifndef PRODUCT
7930 // Assertion checking only: no useful work in product mode --
7931 // however, if any of the flags below become product flags,
7932 // you may need to review this code to see if it needs to be
7933 // enabled in product mode.
7934 SweepClosure::~SweepClosure() {
7935 assert_lock_strong(_freelistLock);
7936 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7937 "sweep _limit out of bounds");
7938 if (inFreeRange()) {
7939 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7940 print();
7941 ShouldNotReachHere();
7942 }
7943 if (Verbose && PrintGC) {
7944 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7945 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7946 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7947 SIZE_FORMAT" bytes "
7948 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7949 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7950 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7951 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7952 * sizeof(HeapWord);
7953 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7954
7955 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7956 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7957 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7958 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7959 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7960 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7961 indexListReturnedBytes);
7962 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7963 dict_returned_bytes);
7964 }
7965 }
7966 if (CMSTraceSweeper) {
7967 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7968 _limit);
7969 }
7970 }
7971 #endif // PRODUCT
7972
7973 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7974 bool freeRangeInFreeLists) {
7975 if (CMSTraceSweeper) {
7976 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7977 freeFinger, freeRangeInFreeLists);
7978 }
7979 assert(!inFreeRange(), "Trampling existing free range");
7980 set_inFreeRange(true);
7981 set_lastFreeRangeCoalesced(false);
7982
7983 set_freeFinger(freeFinger);
7984 set_freeRangeInFreeLists(freeRangeInFreeLists);
7985 if (CMSTestInFreeList) {
7986 if (freeRangeInFreeLists) {
7987 FreeChunk* fc = (FreeChunk*) freeFinger;
7988 assert(fc->is_free(), "A chunk on the free list should be free.");
7989 assert(fc->size() > 0, "Free range should have a size");
7990 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7991 }
7992 }
7993 }
7994
7995 // Note that the sweeper runs concurrently with mutators. Thus,
7996 // it is possible for direct allocation in this generation to happen
7997 // in the middle of the sweep. Note that the sweeper also coalesces
7998 // contiguous free blocks. Thus, unless the sweeper and the allocator
7999 // synchronize appropriately freshly allocated blocks may get swept up.
8000 // This is accomplished by the sweeper locking the free lists while
8001 // it is sweeping. Thus blocks that are determined to be free are
8002 // indeed free. There is however one additional complication:
8003 // blocks that have been allocated since the final checkpoint and
8004 // mark, will not have been marked and so would be treated as
8005 // unreachable and swept up. To prevent this, the allocator marks
8006 // the bit map when allocating during the sweep phase. This leads,
8007 // however, to a further complication -- objects may have been allocated
8008 // but not yet initialized -- in the sense that the header isn't yet
8009 // installed. The sweeper can not then determine the size of the block
8010 // in order to skip over it. To deal with this case, we use a technique
8011 // (due to Printezis) to encode such uninitialized block sizes in the
8012 // bit map. Since the bit map uses a bit per every HeapWord, but the
8013 // CMS generation has a minimum object size of 3 HeapWords, it follows
8014 // that "normal marks" won't be adjacent in the bit map (there will
8015 // always be at least two 0 bits between successive 1 bits). We make use
8016 // of these "unused" bits to represent uninitialized blocks -- the bit
8017 // corresponding to the start of the uninitialized object and the next
8018 // bit are both set. Finally, a 1 bit marks the end of the object that
8019 // started with the two consecutive 1 bits to indicate its potentially
8020 // uninitialized state.
8021
8022 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8023 FreeChunk* fc = (FreeChunk*)addr;
8024 size_t res;
8025
8026 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8027 // than "addr == _limit" because although _limit was a block boundary when
8028 // we started the sweep, it may no longer be one because heap expansion
8029 // may have caused us to coalesce the block ending at the address _limit
8030 // with a newly expanded chunk (this happens when _limit was set to the
8031 // previous _end of the space), so we may have stepped past _limit:
8032 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8033 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8034 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8035 "sweep _limit out of bounds");
8036 assert(addr < _sp->end(), "addr out of bounds");
8037 // Flush any free range we might be holding as a single
8038 // coalesced chunk to the appropriate free list.
8039 if (inFreeRange()) {
8040 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8041 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8042 flush_cur_free_chunk(freeFinger(),
8043 pointer_delta(addr, freeFinger()));
8044 if (CMSTraceSweeper) {
8045 gclog_or_tty->print("Sweep: last chunk: ");
8046 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8047 "[coalesced:"SIZE_FORMAT"]\n",
8048 freeFinger(), pointer_delta(addr, freeFinger()),
8049 lastFreeRangeCoalesced());
8050 }
8051 }
8052
8053 // help the iterator loop finish
8054 return pointer_delta(_sp->end(), addr);
8055 }
8056
8057 assert(addr < _limit, "sweep invariant");
8058 // check if we should yield
8059 do_yield_check(addr);
8060 if (fc->is_free()) {
8061 // Chunk that is already free
8062 res = fc->size();
8063 do_already_free_chunk(fc);
8064 debug_only(_sp->verifyFreeLists());
8065 // If we flush the chunk at hand in lookahead_and_flush()
8066 // and it's coalesced with a preceding chunk, then the
8067 // process of "mangling" the payload of the coalesced block
8068 // will cause erasure of the size information from the
8069 // (erstwhile) header of all the coalesced blocks but the
8070 // first, so the first disjunct in the assert will not hold
8071 // in that specific case (in which case the second disjunct
8072 // will hold).
8073 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8074 "Otherwise the size info doesn't change at this step");
8075 NOT_PRODUCT(
8076 _numObjectsAlreadyFree++;
8077 _numWordsAlreadyFree += res;
8078 )
8079 NOT_PRODUCT(_last_fc = fc;)
8080 } else if (!_bitMap->isMarked(addr)) {
8081 // Chunk is fresh garbage
8082 res = do_garbage_chunk(fc);
8083 debug_only(_sp->verifyFreeLists());
8084 NOT_PRODUCT(
8085 _numObjectsFreed++;
8086 _numWordsFreed += res;
8087 )
8088 } else {
8089 // Chunk that is alive.
8090 res = do_live_chunk(fc);
8091 debug_only(_sp->verifyFreeLists());
8092 NOT_PRODUCT(
8093 _numObjectsLive++;
8094 _numWordsLive += res;
8095 )
8096 }
8097 return res;
8098 }
8099
8100 // For the smart allocation, record following
8101 // split deaths - a free chunk is removed from its free list because
8102 // it is being split into two or more chunks.
8103 // split birth - a free chunk is being added to its free list because
8104 // a larger free chunk has been split and resulted in this free chunk.
8105 // coal death - a free chunk is being removed from its free list because
8106 // it is being coalesced into a large free chunk.
8107 // coal birth - a free chunk is being added to its free list because
8108 // it was created when two or more free chunks where coalesced into
8109 // this free chunk.
8110 //
8111 // These statistics are used to determine the desired number of free
8112 // chunks of a given size. The desired number is chosen to be relative
8113 // to the end of a CMS sweep. The desired number at the end of a sweep
8114 // is the
8115 // count-at-end-of-previous-sweep (an amount that was enough)
8116 // - count-at-beginning-of-current-sweep (the excess)
8117 // + split-births (gains in this size during interval)
8118 // - split-deaths (demands on this size during interval)
8119 // where the interval is from the end of one sweep to the end of the
8120 // next.
8121 //
8122 // When sweeping the sweeper maintains an accumulated chunk which is
8123 // the chunk that is made up of chunks that have been coalesced. That
8124 // will be termed the left-hand chunk. A new chunk of garbage that
8125 // is being considered for coalescing will be referred to as the
8126 // right-hand chunk.
8127 //
8128 // When making a decision on whether to coalesce a right-hand chunk with
8129 // the current left-hand chunk, the current count vs. the desired count
8130 // of the left-hand chunk is considered. Also if the right-hand chunk
8131 // is near the large chunk at the end of the heap (see
8132 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8133 // left-hand chunk is coalesced.
8134 //
8135 // When making a decision about whether to split a chunk, the desired count
8136 // vs. the current count of the candidate to be split is also considered.
8137 // If the candidate is underpopulated (currently fewer chunks than desired)
8138 // a chunk of an overpopulated (currently more chunks than desired) size may
8139 // be chosen. The "hint" associated with a free list, if non-null, points
8140 // to a free list which may be overpopulated.
8141 //
8142
8143 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8144 const size_t size = fc->size();
8145 // Chunks that cannot be coalesced are not in the
8146 // free lists.
8147 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8148 assert(_sp->verify_chunk_in_free_list(fc),
8149 "free chunk should be in free lists");
8150 }
8151 // a chunk that is already free, should not have been
8152 // marked in the bit map
8153 HeapWord* const addr = (HeapWord*) fc;
8154 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8155 // Verify that the bit map has no bits marked between
8156 // addr and purported end of this block.
8157 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8158
8159 // Some chunks cannot be coalesced under any circumstances.
8160 // See the definition of cantCoalesce().
8161 if (!fc->cantCoalesce()) {
8162 // This chunk can potentially be coalesced.
8163 if (_sp->adaptive_freelists()) {
8164 // All the work is done in
8165 do_post_free_or_garbage_chunk(fc, size);
8166 } else { // Not adaptive free lists
8167 // this is a free chunk that can potentially be coalesced by the sweeper;
8168 if (!inFreeRange()) {
8169 // if the next chunk is a free block that can't be coalesced
8170 // it doesn't make sense to remove this chunk from the free lists
8171 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8172 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8173 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8174 nextChunk->is_free() && // ... which is free...
8175 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8176 // nothing to do
8177 } else {
8178 // Potentially the start of a new free range:
8179 // Don't eagerly remove it from the free lists.
8180 // No need to remove it if it will just be put
8181 // back again. (Also from a pragmatic point of view
8182 // if it is a free block in a region that is beyond
8183 // any allocated blocks, an assertion will fail)
8184 // Remember the start of a free run.
8185 initialize_free_range(addr, true);
8186 // end - can coalesce with next chunk
8187 }
8188 } else {
8189 // the midst of a free range, we are coalescing
8190 print_free_block_coalesced(fc);
8191 if (CMSTraceSweeper) {
8192 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8193 }
8194 // remove it from the free lists
8195 _sp->removeFreeChunkFromFreeLists(fc);
8196 set_lastFreeRangeCoalesced(true);
8197 // If the chunk is being coalesced and the current free range is
8198 // in the free lists, remove the current free range so that it
8199 // will be returned to the free lists in its entirety - all
8200 // the coalesced pieces included.
8201 if (freeRangeInFreeLists()) {
8202 FreeChunk* ffc = (FreeChunk*) freeFinger();
8203 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8204 "Size of free range is inconsistent with chunk size.");
8205 if (CMSTestInFreeList) {
8206 assert(_sp->verify_chunk_in_free_list(ffc),
8207 "free range is not in free lists");
8208 }
8209 _sp->removeFreeChunkFromFreeLists(ffc);
8210 set_freeRangeInFreeLists(false);
8211 }
8212 }
8213 }
8214 // Note that if the chunk is not coalescable (the else arm
8215 // below), we unconditionally flush, without needing to do
8216 // a "lookahead," as we do below.
8217 if (inFreeRange()) lookahead_and_flush(fc, size);
8218 } else {
8219 // Code path common to both original and adaptive free lists.
8220
8221 // cant coalesce with previous block; this should be treated
8222 // as the end of a free run if any
8223 if (inFreeRange()) {
8224 // we kicked some butt; time to pick up the garbage
8225 assert(freeFinger() < addr, "freeFinger points too high");
8226 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8227 }
8228 // else, nothing to do, just continue
8229 }
8230 }
8231
8232 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8233 // This is a chunk of garbage. It is not in any free list.
8234 // Add it to a free list or let it possibly be coalesced into
8235 // a larger chunk.
8236 HeapWord* const addr = (HeapWord*) fc;
8237 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8238
8239 if (_sp->adaptive_freelists()) {
8240 // Verify that the bit map has no bits marked between
8241 // addr and purported end of just dead object.
8242 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8243
8244 do_post_free_or_garbage_chunk(fc, size);
8245 } else {
8246 if (!inFreeRange()) {
8247 // start of a new free range
8248 assert(size > 0, "A free range should have a size");
8249 initialize_free_range(addr, false);
8250 } else {
8251 // this will be swept up when we hit the end of the
8252 // free range
8253 if (CMSTraceSweeper) {
8254 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8255 }
8256 // If the chunk is being coalesced and the current free range is
8257 // in the free lists, remove the current free range so that it
8258 // will be returned to the free lists in its entirety - all
8259 // the coalesced pieces included.
8260 if (freeRangeInFreeLists()) {
8261 FreeChunk* ffc = (FreeChunk*)freeFinger();
8262 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8263 "Size of free range is inconsistent with chunk size.");
8264 if (CMSTestInFreeList) {
8265 assert(_sp->verify_chunk_in_free_list(ffc),
8266 "free range is not in free lists");
8267 }
8268 _sp->removeFreeChunkFromFreeLists(ffc);
8269 set_freeRangeInFreeLists(false);
8270 }
8271 set_lastFreeRangeCoalesced(true);
8272 }
8273 // this will be swept up when we hit the end of the free range
8274
8275 // Verify that the bit map has no bits marked between
8276 // addr and purported end of just dead object.
8277 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8278 }
8279 assert(_limit >= addr + size,
8280 "A freshly garbage chunk can't possibly straddle over _limit");
8281 if (inFreeRange()) lookahead_and_flush(fc, size);
8282 return size;
8283 }
8284
8285 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8286 HeapWord* addr = (HeapWord*) fc;
8287 // The sweeper has just found a live object. Return any accumulated
8288 // left hand chunk to the free lists.
8289 if (inFreeRange()) {
8290 assert(freeFinger() < addr, "freeFinger points too high");
8291 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8292 }
8293
8294 // This object is live: we'd normally expect this to be
8295 // an oop, and like to assert the following:
8296 // assert(oop(addr)->is_oop(), "live block should be an oop");
8297 // However, as we commented above, this may be an object whose
8298 // header hasn't yet been initialized.
8299 size_t size;
8300 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8301 if (_bitMap->isMarked(addr + 1)) {
8302 // Determine the size from the bit map, rather than trying to
8303 // compute it from the object header.
8304 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8305 size = pointer_delta(nextOneAddr + 1, addr);
8306 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8307 "alignment problem");
8308
8309 #ifdef DEBUG
8310 if (oop(addr)->klass_or_null() != NULL &&
8311 ( !_collector->should_unload_classes()
8312 || (oop(addr)->is_parsable()) &&
8313 oop(addr)->is_conc_safe())) {
8314 // Ignore mark word because we are running concurrent with mutators
8315 assert(oop(addr)->is_oop(true), "live block should be an oop");
8316 // is_conc_safe is checked before performing this assertion
8317 // because an object that is not is_conc_safe may yet have
8318 // the return from size() correct.
8319 assert(size ==
8320 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8321 "P-mark and computed size do not agree");
8322 }
8323 #endif
8324
8325 } else {
8326 // This should be an initialized object that's alive.
8327 assert(oop(addr)->klass_or_null() != NULL &&
8328 (!_collector->should_unload_classes()
8329 || oop(addr)->is_parsable()),
8330 "Should be an initialized object");
8331 // Note that there are objects used during class redefinition,
8332 // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8333 // which are discarded with their is_conc_safe state still
8334 // false. These object may be floating garbage so may be
8335 // seen here. If they are floating garbage their size
8336 // should be attainable from their klass. Do not that
8337 // is_conc_safe() is true for oop(addr).
8338 // Ignore mark word because we are running concurrent with mutators
8339 assert(oop(addr)->is_oop(true), "live block should be an oop");
8340 // Verify that the bit map has no bits marked between
8341 // addr and purported end of this block.
8342 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8343 assert(size >= 3, "Necessary for Printezis marks to work");
8344 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8345 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8346 }
8347 return size;
8348 }
8349
8350 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8351 size_t chunkSize) {
8352 // do_post_free_or_garbage_chunk() should only be called in the case
8353 // of the adaptive free list allocator.
8354 const bool fcInFreeLists = fc->is_free();
8355 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8356 assert((HeapWord*)fc <= _limit, "sweep invariant");
8357 if (CMSTestInFreeList && fcInFreeLists) {
8358 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8359 }
8360
8361 if (CMSTraceSweeper) {
8362 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8363 }
8364
8365 HeapWord* const fc_addr = (HeapWord*) fc;
8366
8367 bool coalesce;
8368 const size_t left = pointer_delta(fc_addr, freeFinger());
8369 const size_t right = chunkSize;
8370 switch (FLSCoalescePolicy) {
8371 // numeric value forms a coalition aggressiveness metric
8372 case 0: { // never coalesce
8373 coalesce = false;
8374 break;
8375 }
8376 case 1: { // coalesce if left & right chunks on overpopulated lists
8377 coalesce = _sp->coalOverPopulated(left) &&
8378 _sp->coalOverPopulated(right);
8379 break;
8380 }
8381 case 2: { // coalesce if left chunk on overpopulated list (default)
8382 coalesce = _sp->coalOverPopulated(left);
8383 break;
8384 }
8385 case 3: { // coalesce if left OR right chunk on overpopulated list
8386 coalesce = _sp->coalOverPopulated(left) ||
8387 _sp->coalOverPopulated(right);
8388 break;
8389 }
8390 case 4: { // always coalesce
8391 coalesce = true;
8392 break;
8393 }
8394 default:
8395 ShouldNotReachHere();
8396 }
8397
8398 // Should the current free range be coalesced?
8399 // If the chunk is in a free range and either we decided to coalesce above
8400 // or the chunk is near the large block at the end of the heap
8401 // (isNearLargestChunk() returns true), then coalesce this chunk.
8402 const bool doCoalesce = inFreeRange()
8403 && (coalesce || _g->isNearLargestChunk(fc_addr));
8404 if (doCoalesce) {
8405 // Coalesce the current free range on the left with the new
8406 // chunk on the right. If either is on a free list,
8407 // it must be removed from the list and stashed in the closure.
8408 if (freeRangeInFreeLists()) {
8409 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8410 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8411 "Size of free range is inconsistent with chunk size.");
8412 if (CMSTestInFreeList) {
8413 assert(_sp->verify_chunk_in_free_list(ffc),
8414 "Chunk is not in free lists");
8415 }
8416 _sp->coalDeath(ffc->size());
8417 _sp->removeFreeChunkFromFreeLists(ffc);
8418 set_freeRangeInFreeLists(false);
8419 }
8420 if (fcInFreeLists) {
8421 _sp->coalDeath(chunkSize);
8422 assert(fc->size() == chunkSize,
8423 "The chunk has the wrong size or is not in the free lists");
8424 _sp->removeFreeChunkFromFreeLists(fc);
8425 }
8426 set_lastFreeRangeCoalesced(true);
8427 print_free_block_coalesced(fc);
8428 } else { // not in a free range and/or should not coalesce
8429 // Return the current free range and start a new one.
8430 if (inFreeRange()) {
8431 // In a free range but cannot coalesce with the right hand chunk.
8432 // Put the current free range into the free lists.
8433 flush_cur_free_chunk(freeFinger(),
8434 pointer_delta(fc_addr, freeFinger()));
8435 }
8436 // Set up for new free range. Pass along whether the right hand
8437 // chunk is in the free lists.
8438 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8439 }
8440 }
8441
8442 // Lookahead flush:
8443 // If we are tracking a free range, and this is the last chunk that
8444 // we'll look at because its end crosses past _limit, we'll preemptively
8445 // flush it along with any free range we may be holding on to. Note that
8446 // this can be the case only for an already free or freshly garbage
8447 // chunk. If this block is an object, it can never straddle
8448 // over _limit. The "straddling" occurs when _limit is set at
8449 // the previous end of the space when this cycle started, and
8450 // a subsequent heap expansion caused the previously co-terminal
8451 // free block to be coalesced with the newly expanded portion,
8452 // thus rendering _limit a non-block-boundary making it dangerous
8453 // for the sweeper to step over and examine.
8454 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8455 assert(inFreeRange(), "Should only be called if currently in a free range.");
8456 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8457 assert(_sp->used_region().contains(eob - 1),
8458 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8459 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8460 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8461 if (eob >= _limit) {
8462 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8463 if (CMSTraceSweeper) {
8464 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8465 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8466 "[" PTR_FORMAT "," PTR_FORMAT ")",
8467 _limit, fc, eob, _sp->bottom(), _sp->end());
8468 }
8469 // Return the storage we are tracking back into the free lists.
8470 if (CMSTraceSweeper) {
8471 gclog_or_tty->print_cr("Flushing ... ");
8472 }
8473 assert(freeFinger() < eob, "Error");
8474 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8475 }
8476 }
8477
8478 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8479 assert(inFreeRange(), "Should only be called if currently in a free range.");
8480 assert(size > 0,
8481 "A zero sized chunk cannot be added to the free lists.");
8482 if (!freeRangeInFreeLists()) {
8483 if (CMSTestInFreeList) {
8484 FreeChunk* fc = (FreeChunk*) chunk;
8485 fc->set_size(size);
8486 assert(!_sp->verify_chunk_in_free_list(fc),
8487 "chunk should not be in free lists yet");
8488 }
8489 if (CMSTraceSweeper) {
8490 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8491 chunk, size);
8492 }
8493 // A new free range is going to be starting. The current
8494 // free range has not been added to the free lists yet or
8495 // was removed so add it back.
8496 // If the current free range was coalesced, then the death
8497 // of the free range was recorded. Record a birth now.
8498 if (lastFreeRangeCoalesced()) {
8499 _sp->coalBirth(size);
8500 }
8501 _sp->addChunkAndRepairOffsetTable(chunk, size,
8502 lastFreeRangeCoalesced());
8503 } else if (CMSTraceSweeper) {
8504 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8505 }
8506 set_inFreeRange(false);
8507 set_freeRangeInFreeLists(false);
8508 }
8509
8510 // We take a break if we've been at this for a while,
8511 // so as to avoid monopolizing the locks involved.
8512 void SweepClosure::do_yield_work(HeapWord* addr) {
8513 // Return current free chunk being used for coalescing (if any)
8514 // to the appropriate freelist. After yielding, the next
8515 // free block encountered will start a coalescing range of
8516 // free blocks. If the next free block is adjacent to the
8517 // chunk just flushed, they will need to wait for the next
8518 // sweep to be coalesced.
8519 if (inFreeRange()) {
8520 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8521 }
8522
8523 // First give up the locks, then yield, then re-lock.
8524 // We should probably use a constructor/destructor idiom to
8525 // do this unlock/lock or modify the MutexUnlocker class to
8526 // serve our purpose. XXX
8527 assert_lock_strong(_bitMap->lock());
8528 assert_lock_strong(_freelistLock);
8529 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8530 "CMS thread should hold CMS token");
8531 _bitMap->lock()->unlock();
8532 _freelistLock->unlock();
8533 ConcurrentMarkSweepThread::desynchronize(true);
8534 ConcurrentMarkSweepThread::acknowledge_yield_request();
8535 _collector->stopTimer();
8536 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8537 if (PrintCMSStatistics != 0) {
8538 _collector->incrementYields();
8539 }
8540 _collector->icms_wait();
8541
8542 // See the comment in coordinator_yield()
8543 for (unsigned i = 0; i < CMSYieldSleepCount &&
8544 ConcurrentMarkSweepThread::should_yield() &&
8545 !CMSCollector::foregroundGCIsActive(); ++i) {
8546 os::sleep(Thread::current(), 1, false);
8547 ConcurrentMarkSweepThread::acknowledge_yield_request();
8548 }
8549
8550 ConcurrentMarkSweepThread::synchronize(true);
8551 _freelistLock->lock();
8552 _bitMap->lock()->lock_without_safepoint_check();
8553 _collector->startTimer();
8554 }
8555
8556 #ifndef PRODUCT
8557 // This is actually very useful in a product build if it can
8558 // be called from the debugger. Compile it into the product
8559 // as needed.
8560 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8561 return debug_cms_space->verify_chunk_in_free_list(fc);
8562 }
8563 #endif
8564
8565 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8566 if (CMSTraceSweeper) {
8567 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8568 fc, fc->size());
8569 }
8570 }
8571
8572 // CMSIsAliveClosure
8573 bool CMSIsAliveClosure::do_object_b(oop obj) {
8574 HeapWord* addr = (HeapWord*)obj;
8575 return addr != NULL &&
8576 (!_span.contains(addr) || _bit_map->isMarked(addr));
8577 }
8578
8579 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8580 MemRegion span,
8581 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8582 CMSMarkStack* revisit_stack, bool cpc):
8583 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8584 _span(span),
8585 _bit_map(bit_map),
8586 _mark_stack(mark_stack),
8587 _concurrent_precleaning(cpc) {
8588 assert(!_span.is_empty(), "Empty span could spell trouble");
8589 }
8590
8591
8592 // CMSKeepAliveClosure: the serial version
8593 void CMSKeepAliveClosure::do_oop(oop obj) {
8594 HeapWord* addr = (HeapWord*)obj;
8595 if (_span.contains(addr) &&
8596 !_bit_map->isMarked(addr)) {
8597 _bit_map->mark(addr);
8598 bool simulate_overflow = false;
8599 NOT_PRODUCT(
8600 if (CMSMarkStackOverflowALot &&
8601 _collector->simulate_overflow()) {
8602 // simulate a stack overflow
8603 simulate_overflow = true;
8604 }
8605 )
8606 if (simulate_overflow || !_mark_stack->push(obj)) {
8607 if (_concurrent_precleaning) {
8608 // We dirty the overflown object and let the remark
8609 // phase deal with it.
8610 assert(_collector->overflow_list_is_empty(), "Error");
8611 // In the case of object arrays, we need to dirty all of
8612 // the cards that the object spans. No locking or atomics
8613 // are needed since no one else can be mutating the mod union
8614 // table.
8615 if (obj->is_objArray()) {
8616 size_t sz = obj->size();
8617 HeapWord* end_card_addr =
8618 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8619 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8620 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8621 _collector->_modUnionTable.mark_range(redirty_range);
8622 } else {
8623 _collector->_modUnionTable.mark(addr);
8624 }
8625 _collector->_ser_kac_preclean_ovflw++;
8626 } else {
8627 _collector->push_on_overflow_list(obj);
8628 _collector->_ser_kac_ovflw++;
8629 }
8630 }
8631 }
8632 }
8633
8634 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8635 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8636
8637 // CMSParKeepAliveClosure: a parallel version of the above.
8638 // The work queues are private to each closure (thread),
8639 // but (may be) available for stealing by other threads.
8640 void CMSParKeepAliveClosure::do_oop(oop obj) {
8641 HeapWord* addr = (HeapWord*)obj;
8642 if (_span.contains(addr) &&
8643 !_bit_map->isMarked(addr)) {
8644 // In general, during recursive tracing, several threads
8645 // may be concurrently getting here; the first one to
8646 // "tag" it, claims it.
8647 if (_bit_map->par_mark(addr)) {
8648 bool res = _work_queue->push(obj);
8649 assert(res, "Low water mark should be much less than capacity");
8650 // Do a recursive trim in the hope that this will keep
8651 // stack usage lower, but leave some oops for potential stealers
8652 trim_queue(_low_water_mark);
8653 } // Else, another thread got there first
8654 }
8655 }
8656
8657 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8658 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8659
8660 void CMSParKeepAliveClosure::trim_queue(uint max) {
8661 while (_work_queue->size() > max) {
8662 oop new_oop;
8663 if (_work_queue->pop_local(new_oop)) {
8664 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8665 assert(_bit_map->isMarked((HeapWord*)new_oop),
8666 "no white objects on this stack!");
8667 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8668 // iterate over the oops in this oop, marking and pushing
8669 // the ones in CMS heap (i.e. in _span).
8670 new_oop->oop_iterate(&_mark_and_push);
8671 }
8672 }
8673 }
8674
8675 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8676 CMSCollector* collector,
8677 MemRegion span, CMSBitMap* bit_map,
8678 CMSMarkStack* revisit_stack,
8679 OopTaskQueue* work_queue):
8680 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8681 _span(span),
8682 _bit_map(bit_map),
8683 _work_queue(work_queue) { }
8684
8685 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8686 HeapWord* addr = (HeapWord*)obj;
8687 if (_span.contains(addr) &&
8688 !_bit_map->isMarked(addr)) {
8689 if (_bit_map->par_mark(addr)) {
8690 bool simulate_overflow = false;
8691 NOT_PRODUCT(
8692 if (CMSMarkStackOverflowALot &&
8693 _collector->par_simulate_overflow()) {
8694 // simulate a stack overflow
8695 simulate_overflow = true;
8696 }
8697 )
8698 if (simulate_overflow || !_work_queue->push(obj)) {
8699 _collector->par_push_on_overflow_list(obj);
8700 _collector->_par_kac_ovflw++;
8701 }
8702 } // Else another thread got there already
8703 }
8704 }
8705
8706 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8707 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8708
8709 //////////////////////////////////////////////////////////////////
8710 // CMSExpansionCause /////////////////////////////
8711 //////////////////////////////////////////////////////////////////
8712 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8713 switch (cause) {
8714 case _no_expansion:
8715 return "No expansion";
8716 case _satisfy_free_ratio:
8717 return "Free ratio";
8718 case _satisfy_promotion:
8719 return "Satisfy promotion";
8720 case _satisfy_allocation:
8721 return "allocation";
8722 case _allocate_par_lab:
8723 return "Par LAB";
8724 case _allocate_par_spooling_space:
8725 return "Par Spooling Space";
8726 case _adaptive_size_policy:
8727 return "Ergonomics";
8728 default:
8729 return "unknown";
8730 }
8731 }
8732
8733 void CMSDrainMarkingStackClosure::do_void() {
8734 // the max number to take from overflow list at a time
8735 const size_t num = _mark_stack->capacity()/4;
8736 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8737 "Overflow list should be NULL during concurrent phases");
8738 while (!_mark_stack->isEmpty() ||
8739 // if stack is empty, check the overflow list
8740 _collector->take_from_overflow_list(num, _mark_stack)) {
8741 oop obj = _mark_stack->pop();
8742 HeapWord* addr = (HeapWord*)obj;
8743 assert(_span.contains(addr), "Should be within span");
8744 assert(_bit_map->isMarked(addr), "Should be marked");
8745 assert(obj->is_oop(), "Should be an oop");
8746 obj->oop_iterate(_keep_alive);
8747 }
8748 }
8749
8750 void CMSParDrainMarkingStackClosure::do_void() {
8751 // drain queue
8752 trim_queue(0);
8753 }
8754
8755 // Trim our work_queue so its length is below max at return
8756 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8757 while (_work_queue->size() > max) {
8758 oop new_oop;
8759 if (_work_queue->pop_local(new_oop)) {
8760 assert(new_oop->is_oop(), "Expected an oop");
8761 assert(_bit_map->isMarked((HeapWord*)new_oop),
8762 "no white objects on this stack!");
8763 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8764 // iterate over the oops in this oop, marking and pushing
8765 // the ones in CMS heap (i.e. in _span).
8766 new_oop->oop_iterate(&_mark_and_push);
8767 }
8768 }
8769 }
8770
8771 ////////////////////////////////////////////////////////////////////
8772 // Support for Marking Stack Overflow list handling and related code
8773 ////////////////////////////////////////////////////////////////////
8774 // Much of the following code is similar in shape and spirit to the
8775 // code used in ParNewGC. We should try and share that code
8776 // as much as possible in the future.
8777
8778 #ifndef PRODUCT
8779 // Debugging support for CMSStackOverflowALot
8780
8781 // It's OK to call this multi-threaded; the worst thing
8782 // that can happen is that we'll get a bunch of closely
8783 // spaced simulated oveflows, but that's OK, in fact
8784 // probably good as it would exercise the overflow code
8785 // under contention.
8786 bool CMSCollector::simulate_overflow() {
8787 if (_overflow_counter-- <= 0) { // just being defensive
8788 _overflow_counter = CMSMarkStackOverflowInterval;
8789 return true;
8790 } else {
8791 return false;
8792 }
8793 }
8794
8795 bool CMSCollector::par_simulate_overflow() {
8796 return simulate_overflow();
8797 }
8798 #endif
8799
8800 // Single-threaded
8801 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8802 assert(stack->isEmpty(), "Expected precondition");
8803 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8804 size_t i = num;
8805 oop cur = _overflow_list;
8806 const markOop proto = markOopDesc::prototype();
8807 NOT_PRODUCT(ssize_t n = 0;)
8808 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8809 next = oop(cur->mark());
8810 cur->set_mark(proto); // until proven otherwise
8811 assert(cur->is_oop(), "Should be an oop");
8812 bool res = stack->push(cur);
8813 assert(res, "Bit off more than can chew?");
8814 NOT_PRODUCT(n++;)
8815 }
8816 _overflow_list = cur;
8817 #ifndef PRODUCT
8818 assert(_num_par_pushes >= n, "Too many pops?");
8819 _num_par_pushes -=n;
8820 #endif
8821 return !stack->isEmpty();
8822 }
8823
8824 #define BUSY (oop(0x1aff1aff))
8825 // (MT-safe) Get a prefix of at most "num" from the list.
8826 // The overflow list is chained through the mark word of
8827 // each object in the list. We fetch the entire list,
8828 // break off a prefix of the right size and return the
8829 // remainder. If other threads try to take objects from
8830 // the overflow list at that time, they will wait for
8831 // some time to see if data becomes available. If (and
8832 // only if) another thread places one or more object(s)
8833 // on the global list before we have returned the suffix
8834 // to the global list, we will walk down our local list
8835 // to find its end and append the global list to
8836 // our suffix before returning it. This suffix walk can
8837 // prove to be expensive (quadratic in the amount of traffic)
8838 // when there are many objects in the overflow list and
8839 // there is much producer-consumer contention on the list.
8840 // *NOTE*: The overflow list manipulation code here and
8841 // in ParNewGeneration:: are very similar in shape,
8842 // except that in the ParNew case we use the old (from/eden)
8843 // copy of the object to thread the list via its klass word.
8844 // Because of the common code, if you make any changes in
8845 // the code below, please check the ParNew version to see if
8846 // similar changes might be needed.
8847 // CR 6797058 has been filed to consolidate the common code.
8848 bool CMSCollector::par_take_from_overflow_list(size_t num,
8849 OopTaskQueue* work_q,
8850 int no_of_gc_threads) {
8851 assert(work_q->size() == 0, "First empty local work queue");
8852 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8853 if (_overflow_list == NULL) {
8854 return false;
8855 }
8856 // Grab the entire list; we'll put back a suffix
8857 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8858 Thread* tid = Thread::current();
8859 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8860 // set to ParallelGCThreads.
8861 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8862 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8863 // If the list is busy, we spin for a short while,
8864 // sleeping between attempts to get the list.
8865 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8866 os::sleep(tid, sleep_time_millis, false);
8867 if (_overflow_list == NULL) {
8868 // Nothing left to take
8869 return false;
8870 } else if (_overflow_list != BUSY) {
8871 // Try and grab the prefix
8872 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8873 }
8874 }
8875 // If the list was found to be empty, or we spun long
8876 // enough, we give up and return empty-handed. If we leave
8877 // the list in the BUSY state below, it must be the case that
8878 // some other thread holds the overflow list and will set it
8879 // to a non-BUSY state in the future.
8880 if (prefix == NULL || prefix == BUSY) {
8881 // Nothing to take or waited long enough
8882 if (prefix == NULL) {
8883 // Write back the NULL in case we overwrote it with BUSY above
8884 // and it is still the same value.
8885 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8886 }
8887 return false;
8888 }
8889 assert(prefix != NULL && prefix != BUSY, "Error");
8890 size_t i = num;
8891 oop cur = prefix;
8892 // Walk down the first "num" objects, unless we reach the end.
8893 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8894 if (cur->mark() == NULL) {
8895 // We have "num" or fewer elements in the list, so there
8896 // is nothing to return to the global list.
8897 // Write back the NULL in lieu of the BUSY we wrote
8898 // above, if it is still the same value.
8899 if (_overflow_list == BUSY) {
8900 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8901 }
8902 } else {
8903 // Chop off the suffix and rerturn it to the global list.
8904 assert(cur->mark() != BUSY, "Error");
8905 oop suffix_head = cur->mark(); // suffix will be put back on global list
8906 cur->set_mark(NULL); // break off suffix
8907 // It's possible that the list is still in the empty(busy) state
8908 // we left it in a short while ago; in that case we may be
8909 // able to place back the suffix without incurring the cost
8910 // of a walk down the list.
8911 oop observed_overflow_list = _overflow_list;
8912 oop cur_overflow_list = observed_overflow_list;
8913 bool attached = false;
8914 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8915 observed_overflow_list =
8916 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8917 if (cur_overflow_list == observed_overflow_list) {
8918 attached = true;
8919 break;
8920 } else cur_overflow_list = observed_overflow_list;
8921 }
8922 if (!attached) {
8923 // Too bad, someone else sneaked in (at least) an element; we'll need
8924 // to do a splice. Find tail of suffix so we can prepend suffix to global
8925 // list.
8926 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8927 oop suffix_tail = cur;
8928 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8929 "Tautology");
8930 observed_overflow_list = _overflow_list;
8931 do {
8932 cur_overflow_list = observed_overflow_list;
8933 if (cur_overflow_list != BUSY) {
8934 // Do the splice ...
8935 suffix_tail->set_mark(markOop(cur_overflow_list));
8936 } else { // cur_overflow_list == BUSY
8937 suffix_tail->set_mark(NULL);
8938 }
8939 // ... and try to place spliced list back on overflow_list ...
8940 observed_overflow_list =
8941 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8942 } while (cur_overflow_list != observed_overflow_list);
8943 // ... until we have succeeded in doing so.
8944 }
8945 }
8946
8947 // Push the prefix elements on work_q
8948 assert(prefix != NULL, "control point invariant");
8949 const markOop proto = markOopDesc::prototype();
8950 oop next;
8951 NOT_PRODUCT(ssize_t n = 0;)
8952 for (cur = prefix; cur != NULL; cur = next) {
8953 next = oop(cur->mark());
8954 cur->set_mark(proto); // until proven otherwise
8955 assert(cur->is_oop(), "Should be an oop");
8956 bool res = work_q->push(cur);
8957 assert(res, "Bit off more than we can chew?");
8958 NOT_PRODUCT(n++;)
8959 }
8960 #ifndef PRODUCT
8961 assert(_num_par_pushes >= n, "Too many pops?");
8962 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8963 #endif
8964 return true;
8965 }
8966
8967 // Single-threaded
8968 void CMSCollector::push_on_overflow_list(oop p) {
8969 NOT_PRODUCT(_num_par_pushes++;)
8970 assert(p->is_oop(), "Not an oop");
8971 preserve_mark_if_necessary(p);
8972 p->set_mark((markOop)_overflow_list);
8973 _overflow_list = p;
8974 }
8975
8976 // Multi-threaded; use CAS to prepend to overflow list
8977 void CMSCollector::par_push_on_overflow_list(oop p) {
8978 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8979 assert(p->is_oop(), "Not an oop");
8980 par_preserve_mark_if_necessary(p);
8981 oop observed_overflow_list = _overflow_list;
8982 oop cur_overflow_list;
8983 do {
8984 cur_overflow_list = observed_overflow_list;
8985 if (cur_overflow_list != BUSY) {
8986 p->set_mark(markOop(cur_overflow_list));
8987 } else {
8988 p->set_mark(NULL);
8989 }
8990 observed_overflow_list =
8991 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8992 } while (cur_overflow_list != observed_overflow_list);
8993 }
8994 #undef BUSY
8995
8996 // Single threaded
8997 // General Note on GrowableArray: pushes may silently fail
8998 // because we are (temporarily) out of C-heap for expanding
8999 // the stack. The problem is quite ubiquitous and affects
9000 // a lot of code in the JVM. The prudent thing for GrowableArray
9001 // to do (for now) is to exit with an error. However, that may
9002 // be too draconian in some cases because the caller may be
9003 // able to recover without much harm. For such cases, we
9004 // should probably introduce a "soft_push" method which returns
9005 // an indication of success or failure with the assumption that
9006 // the caller may be able to recover from a failure; code in
9007 // the VM can then be changed, incrementally, to deal with such
9008 // failures where possible, thus, incrementally hardening the VM
9009 // in such low resource situations.
9010 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9011 _preserved_oop_stack.push(p);
9012 _preserved_mark_stack.push(m);
9013 assert(m == p->mark(), "Mark word changed");
9014 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9015 "bijection");
9016 }
9017
9018 // Single threaded
9019 void CMSCollector::preserve_mark_if_necessary(oop p) {
9020 markOop m = p->mark();
9021 if (m->must_be_preserved(p)) {
9022 preserve_mark_work(p, m);
9023 }
9024 }
9025
9026 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9027 markOop m = p->mark();
9028 if (m->must_be_preserved(p)) {
9029 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9030 // Even though we read the mark word without holding
9031 // the lock, we are assured that it will not change
9032 // because we "own" this oop, so no other thread can
9033 // be trying to push it on the overflow list; see
9034 // the assertion in preserve_mark_work() that checks
9035 // that m == p->mark().
9036 preserve_mark_work(p, m);
9037 }
9038 }
9039
9040 // We should be able to do this multi-threaded,
9041 // a chunk of stack being a task (this is
9042 // correct because each oop only ever appears
9043 // once in the overflow list. However, it's
9044 // not very easy to completely overlap this with
9045 // other operations, so will generally not be done
9046 // until all work's been completed. Because we
9047 // expect the preserved oop stack (set) to be small,
9048 // it's probably fine to do this single-threaded.
9049 // We can explore cleverer concurrent/overlapped/parallel
9050 // processing of preserved marks if we feel the
9051 // need for this in the future. Stack overflow should
9052 // be so rare in practice and, when it happens, its
9053 // effect on performance so great that this will
9054 // likely just be in the noise anyway.
9055 void CMSCollector::restore_preserved_marks_if_any() {
9056 assert(SafepointSynchronize::is_at_safepoint(),
9057 "world should be stopped");
9058 assert(Thread::current()->is_ConcurrentGC_thread() ||
9059 Thread::current()->is_VM_thread(),
9060 "should be single-threaded");
9061 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9062 "bijection");
9063
9064 while (!_preserved_oop_stack.is_empty()) {
9065 oop p = _preserved_oop_stack.pop();
9066 assert(p->is_oop(), "Should be an oop");
9067 assert(_span.contains(p), "oop should be in _span");
9068 assert(p->mark() == markOopDesc::prototype(),
9069 "Set when taken from overflow list");
9070 markOop m = _preserved_mark_stack.pop();
9071 p->set_mark(m);
9072 }
9073 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9074 "stacks were cleared above");
9075 }
9076
9077 #ifndef PRODUCT
9078 bool CMSCollector::no_preserved_marks() const {
9079 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9080 }
9081 #endif
9082
9083 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9084 {
9085 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9086 CMSAdaptiveSizePolicy* size_policy =
9087 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9088 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9089 "Wrong type for size policy");
9090 return size_policy;
9091 }
9092
9093 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9094 size_t desired_promo_size) {
9095 if (cur_promo_size < desired_promo_size) {
9096 size_t expand_bytes = desired_promo_size - cur_promo_size;
9097 if (PrintAdaptiveSizePolicy && Verbose) {
9098 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9099 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9100 expand_bytes);
9101 }
9102 expand(expand_bytes,
9103 MinHeapDeltaBytes,
9104 CMSExpansionCause::_adaptive_size_policy);
9105 } else if (desired_promo_size < cur_promo_size) {
9106 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9107 if (PrintAdaptiveSizePolicy && Verbose) {
9108 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9109 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9110 shrink_bytes);
9111 }
9112 shrink(shrink_bytes);
9113 }
9114 }
9115
9116 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9117 GenCollectedHeap* gch = GenCollectedHeap::heap();
9118 CMSGCAdaptivePolicyCounters* counters =
9119 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9120 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9121 "Wrong kind of counters");
9122 return counters;
9123 }
9124
9125
9126 void ASConcurrentMarkSweepGeneration::update_counters() {
9127 if (UsePerfData) {
9128 _space_counters->update_all();
9129 _gen_counters->update_all();
9130 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9131 GenCollectedHeap* gch = GenCollectedHeap::heap();
9132 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9133 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9134 "Wrong gc statistics type");
9135 counters->update_counters(gc_stats_l);
9136 }
9137 }
9138
9139 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9140 if (UsePerfData) {
9141 _space_counters->update_used(used);
9142 _space_counters->update_capacity();
9143 _gen_counters->update_all();
9144
9145 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9146 GenCollectedHeap* gch = GenCollectedHeap::heap();
9147 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9148 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9149 "Wrong gc statistics type");
9150 counters->update_counters(gc_stats_l);
9151 }
9152 }
9153
9154 // The desired expansion delta is computed so that:
9155 // . desired free percentage or greater is used
9156 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9157 assert_locked_or_safepoint(Heap_lock);
9158
9159 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9160
9161 // If incremental collection failed, we just want to expand
9162 // to the limit.
9163 if (incremental_collection_failed()) {
9164 clear_incremental_collection_failed();
9165 grow_to_reserved();
9166 return;
9167 }
9168
9169 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9170
9171 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9172 "Wrong type of heap");
9173 int prev_level = level() - 1;
9174 assert(prev_level >= 0, "The cms generation is the lowest generation");
9175 Generation* prev_gen = gch->get_gen(prev_level);
9176 assert(prev_gen->kind() == Generation::ASParNew,
9177 "Wrong type of young generation");
9178 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9179 size_t cur_eden = younger_gen->eden()->capacity();
9180 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9181 size_t cur_promo = free();
9182 size_policy->compute_tenured_generation_free_space(cur_promo,
9183 max_available(),
9184 cur_eden);
9185 resize(cur_promo, size_policy->promo_size());
9186
9187 // Record the new size of the space in the cms generation
9188 // that is available for promotions. This is temporary.
9189 // It should be the desired promo size.
9190 size_policy->avg_cms_promo()->sample(free());
9191 size_policy->avg_old_live()->sample(used());
9192
9193 if (UsePerfData) {
9194 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9195 counters->update_cms_capacity_counter(capacity());
9196 }
9197 }
9198
9199 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9200 assert_locked_or_safepoint(Heap_lock);
9201 assert_lock_strong(freelistLock());
9202 HeapWord* old_end = _cmsSpace->end();
9203 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9204 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9205 FreeChunk* chunk_at_end = find_chunk_at_end();
9206 if (chunk_at_end == NULL) {
9207 // No room to shrink
9208 if (PrintGCDetails && Verbose) {
9209 gclog_or_tty->print_cr("No room to shrink: old_end "
9210 PTR_FORMAT " unallocated_start " PTR_FORMAT
9211 " chunk_at_end " PTR_FORMAT,
9212 old_end, unallocated_start, chunk_at_end);
9213 }
9214 return;
9215 } else {
9216
9217 // Find the chunk at the end of the space and determine
9218 // how much it can be shrunk.
9219 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9220 size_t aligned_shrinkable_size_in_bytes =
9221 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9222 assert(unallocated_start <= chunk_at_end->end(),
9223 "Inconsistent chunk at end of space");
9224 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9225 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9226
9227 // Shrink the underlying space
9228 _virtual_space.shrink_by(bytes);
9229 if (PrintGCDetails && Verbose) {
9230 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9231 " desired_bytes " SIZE_FORMAT
9232 " shrinkable_size_in_bytes " SIZE_FORMAT
9233 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9234 " bytes " SIZE_FORMAT,
9235 desired_bytes, shrinkable_size_in_bytes,
9236 aligned_shrinkable_size_in_bytes, bytes);
9237 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9238 " unallocated_start " SIZE_FORMAT,
9239 old_end, unallocated_start);
9240 }
9241
9242 // If the space did shrink (shrinking is not guaranteed),
9243 // shrink the chunk at the end by the appropriate amount.
9244 if (((HeapWord*)_virtual_space.high()) < old_end) {
9245 size_t new_word_size =
9246 heap_word_size(_virtual_space.committed_size());
9247
9248 // Have to remove the chunk from the dictionary because it is changing
9249 // size and might be someplace elsewhere in the dictionary.
9250
9251 // Get the chunk at end, shrink it, and put it
9252 // back.
9253 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9254 size_t word_size_change = word_size_before - new_word_size;
9255 size_t chunk_at_end_old_size = chunk_at_end->size();
9256 assert(chunk_at_end_old_size >= word_size_change,
9257 "Shrink is too large");
9258 chunk_at_end->set_size(chunk_at_end_old_size -
9259 word_size_change);
9260 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9261 word_size_change);
9262
9263 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9264
9265 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9266 _bts->resize(new_word_size); // resize the block offset shared array
9267 Universe::heap()->barrier_set()->resize_covered_region(mr);
9268 _cmsSpace->assert_locked();
9269 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9270
9271 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9272
9273 // update the space and generation capacity counters
9274 if (UsePerfData) {
9275 _space_counters->update_capacity();
9276 _gen_counters->update_all();
9277 }
9278
9279 if (Verbose && PrintGCDetails) {
9280 size_t new_mem_size = _virtual_space.committed_size();
9281 size_t old_mem_size = new_mem_size + bytes;
9282 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9283 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9284 }
9285 }
9286
9287 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9288 "Inconsistency at end of space");
9289 assert(chunk_at_end->end() == _cmsSpace->end(),
9290 "Shrinking is inconsistent");
9291 return;
9292 }
9293 }
9294
9295 // Transfer some number of overflown objects to usual marking
9296 // stack. Return true if some objects were transferred.
9297 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9298 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9299 (size_t)ParGCDesiredObjsFromOverflowList);
9300
9301 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9302 assert(_collector->overflow_list_is_empty() || res,
9303 "If list is not empty, we should have taken something");
9304 assert(!res || !_mark_stack->isEmpty(),
9305 "If we took something, it should now be on our stack");
9306 return res;
9307 }
9308
9309 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9310 size_t res = _sp->block_size_no_stall(addr, _collector);
9311 if (_sp->block_is_obj(addr)) {
9312 if (_live_bit_map->isMarked(addr)) {
9313 // It can't have been dead in a previous cycle
9314 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9315 } else {
9316 _dead_bit_map->mark(addr); // mark the dead object
9317 }
9318 }
9319 // Could be 0, if the block size could not be computed without stalling.
9320 return res;
9321 }
9322
9323 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9324
9325 switch (phase) {
9326 case CMSCollector::InitialMarking:
9327 initialize(true /* fullGC */ ,
9328 cause /* cause of the GC */,
9329 true /* recordGCBeginTime */,
9330 true /* recordPreGCUsage */,
9331 false /* recordPeakUsage */,
9332 false /* recordPostGCusage */,
9333 true /* recordAccumulatedGCTime */,
9334 false /* recordGCEndTime */,
9335 false /* countCollection */ );
9336 break;
9337
9338 case CMSCollector::FinalMarking:
9339 initialize(true /* fullGC */ ,
9340 cause /* cause of the GC */,
9341 false /* recordGCBeginTime */,
9342 false /* recordPreGCUsage */,
9343 false /* recordPeakUsage */,
9344 false /* recordPostGCusage */,
9345 true /* recordAccumulatedGCTime */,
9346 false /* recordGCEndTime */,
9347 false /* countCollection */ );
9348 break;
9349
9350 case CMSCollector::Sweeping:
9351 initialize(true /* fullGC */ ,
9352 cause /* cause of the GC */,
9353 false /* recordGCBeginTime */,
9354 false /* recordPreGCUsage */,
9355 true /* recordPeakUsage */,
9356 true /* recordPostGCusage */,
9357 false /* recordAccumulatedGCTime */,
9358 true /* recordGCEndTime */,
9359 true /* countCollection */ );
9360 break;
9361
9362 default:
9363 ShouldNotReachHere();
9364 }
9365 }
9366