1 /*
2 * Copyright (c) 2001, 2010, 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.
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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.
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23 */
24
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
27
28 // statics
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
30 bool CMSCollector::_full_gc_requested = false;
31
32 //////////////////////////////////////////////////////////////////
33 // In support of CMS/VM thread synchronization
34 //////////////////////////////////////////////////////////////////
35 // We split use of the CGC_lock into 2 "levels".
36 // The low-level locking is of the usual CGC_lock monitor. We introduce
37 // a higher level "token" (hereafter "CMS token") built on top of the
38 // low level monitor (hereafter "CGC lock").
39 // The token-passing protocol gives priority to the VM thread. The
40 // CMS-lock doesn't provide any fairness guarantees, but clients
41 // should ensure that it is only held for very short, bounded
42 // durations.
43 //
44 // When either of the CMS thread or the VM thread is involved in
45 // collection operations during which it does not want the other
46 // thread to interfere, it obtains the CMS token.
47 //
48 // If either thread tries to get the token while the other has
49 // it, that thread waits. However, if the VM thread and CMS thread
50 // both want the token, then the VM thread gets priority while the
51 // CMS thread waits. This ensures, for instance, that the "concurrent"
52 // phases of the CMS thread's work do not block out the VM thread
53 // for long periods of time as the CMS thread continues to hog
54 // the token. (See bug 4616232).
55 //
56 // The baton-passing functions are, however, controlled by the
57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
58 // and here the low-level CMS lock, not the high level token,
59 // ensures mutual exclusion.
60 //
61 // Two important conditions that we have to satisfy:
62 // 1. if a thread does a low-level wait on the CMS lock, then it
63 // relinquishes the CMS token if it were holding that token
64 // when it acquired the low-level CMS lock.
65 // 2. any low-level notifications on the low-level lock
66 // should only be sent when a thread has relinquished the token.
67 //
68 // In the absence of either property, we'd have potential deadlock.
69 //
70 // We protect each of the CMS (concurrent and sequential) phases
71 // with the CMS _token_, not the CMS _lock_.
72 //
73 // The only code protected by CMS lock is the token acquisition code
74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
75 // baton-passing code.
76 //
77 // Unfortunately, i couldn't come up with a good abstraction to factor and
78 // hide the naked CGC_lock manipulation in the baton-passing code
79 // further below. That's something we should try to do. Also, the proof
80 // of correctness of this 2-level locking scheme is far from obvious,
81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
82 // that there may be a theoretical possibility of delay/starvation in the
83 // low-level lock/wait/notify scheme used for the baton-passing because of
84 // potential intereference with the priority scheme embodied in the
85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
86 // invocation further below and marked with "XXX 20011219YSR".
87 // Indeed, as we note elsewhere, this may become yet more slippery
88 // in the presence of multiple CMS and/or multiple VM threads. XXX
89
90 class CMSTokenSync: public StackObj {
91 private:
92 bool _is_cms_thread;
93 public:
94 CMSTokenSync(bool is_cms_thread):
95 _is_cms_thread(is_cms_thread) {
96 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
97 "Incorrect argument to constructor");
98 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
99 }
100
101 ~CMSTokenSync() {
102 assert(_is_cms_thread ?
103 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
104 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
105 "Incorrect state");
106 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
107 }
108 };
109
110 // Convenience class that does a CMSTokenSync, and then acquires
111 // upto three locks.
112 class CMSTokenSyncWithLocks: public CMSTokenSync {
113 private:
114 // Note: locks are acquired in textual declaration order
115 // and released in the opposite order
116 MutexLockerEx _locker1, _locker2, _locker3;
117 public:
118 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
119 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
120 CMSTokenSync(is_cms_thread),
121 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
122 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
123 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
124 { }
125 };
126
127
128 // Wrapper class to temporarily disable icms during a foreground cms collection.
129 class ICMSDisabler: public StackObj {
130 public:
131 // The ctor disables icms and wakes up the thread so it notices the change;
132 // the dtor re-enables icms. Note that the CMSCollector methods will check
133 // CMSIncrementalMode.
134 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
135 ~ICMSDisabler() { CMSCollector::enable_icms(); }
136 };
137
138 //////////////////////////////////////////////////////////////////
139 // Concurrent Mark-Sweep Generation /////////////////////////////
140 //////////////////////////////////////////////////////////////////
141
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
143
144 // This struct contains per-thread things necessary to support parallel
145 // young-gen collection.
146 class CMSParGCThreadState: public CHeapObj {
147 public:
148 CFLS_LAB lab;
149 PromotionInfo promo;
150
151 // Constructor.
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
153 promo.setSpace(cfls);
154 }
155 };
156
157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
158 ReservedSpace rs, size_t initial_byte_size, int level,
159 CardTableRS* ct, bool use_adaptive_freelists,
160 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
161 CardGeneration(rs, initial_byte_size, level, ct),
162 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
163 _debug_collection_type(Concurrent_collection_type)
164 {
165 HeapWord* bottom = (HeapWord*) _virtual_space.low();
166 HeapWord* end = (HeapWord*) _virtual_space.high();
167
168 _direct_allocated_words = 0;
169 NOT_PRODUCT(
170 _numObjectsPromoted = 0;
171 _numWordsPromoted = 0;
172 _numObjectsAllocated = 0;
173 _numWordsAllocated = 0;
174 )
175
176 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
177 use_adaptive_freelists,
178 dictionaryChoice);
179 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
180 if (_cmsSpace == NULL) {
181 vm_exit_during_initialization(
182 "CompactibleFreeListSpace allocation failure");
183 }
184 _cmsSpace->_gen = this;
185
186 _gc_stats = new CMSGCStats();
187
188 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
189 // offsets match. The ability to tell free chunks from objects
190 // depends on this property.
191 debug_only(
192 FreeChunk* junk = NULL;
193 assert(UseCompressedOops ||
194 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
195 "Offset of FreeChunk::_prev within FreeChunk must match"
196 " that of OopDesc::_klass within OopDesc");
197 )
198 if (ParallelGCThreads > 0) {
199 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
200 _par_gc_thread_states =
201 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
202 if (_par_gc_thread_states == NULL) {
203 vm_exit_during_initialization("Could not allocate par gc structs");
204 }
205 for (uint i = 0; i < ParallelGCThreads; i++) {
206 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
207 if (_par_gc_thread_states[i] == NULL) {
208 vm_exit_during_initialization("Could not allocate par gc structs");
209 }
210 }
211 } else {
212 _par_gc_thread_states = NULL;
213 }
214 _incremental_collection_failed = false;
215 // The "dilatation_factor" is the expansion that can occur on
216 // account of the fact that the minimum object size in the CMS
217 // generation may be larger than that in, say, a contiguous young
218 // generation.
219 // Ideally, in the calculation below, we'd compute the dilatation
220 // factor as: MinChunkSize/(promoting_gen's min object size)
221 // Since we do not have such a general query interface for the
222 // promoting generation, we'll instead just use the mimimum
223 // object size (which today is a header's worth of space);
224 // note that all arithmetic is in units of HeapWords.
225 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
226 assert(_dilatation_factor >= 1.0, "from previous assert");
227 }
228
229
230 // The field "_initiating_occupancy" represents the occupancy percentage
231 // at which we trigger a new collection cycle. Unless explicitly specified
232 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
233 // is calculated by:
234 //
235 // Let "f" be MinHeapFreeRatio in
236 //
237 // _intiating_occupancy = 100-f +
238 // f * (CMSTrigger[Perm]Ratio/100)
239 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
240 //
241 // That is, if we assume the heap is at its desired maximum occupancy at the
242 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
243 // space be allocated before initiating a new collection cycle.
244 //
245 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
246 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
247 if (io >= 0) {
248 _initiating_occupancy = (double)io / 100.0;
249 } else {
250 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
251 (double)(tr * MinHeapFreeRatio) / 100.0)
252 / 100.0;
253 }
254 }
255
256 void ConcurrentMarkSweepGeneration::ref_processor_init() {
257 assert(collector() != NULL, "no collector");
258 collector()->ref_processor_init();
259 }
260
261 void CMSCollector::ref_processor_init() {
262 if (_ref_processor == NULL) {
263 // Allocate and initialize a reference processor
264 _ref_processor = ReferenceProcessor::create_ref_processor(
265 _span, // span
266 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
267 _cmsGen->refs_discovery_is_mt(), // mt_discovery
268 &_is_alive_closure,
269 ParallelGCThreads,
270 ParallelRefProcEnabled);
271 // Initialize the _ref_processor field of CMSGen
272 _cmsGen->set_ref_processor(_ref_processor);
273
274 // Allocate a dummy ref processor for perm gen.
275 ReferenceProcessor* rp2 = new ReferenceProcessor();
276 if (rp2 == NULL) {
277 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
278 }
279 _permGen->set_ref_processor(rp2);
280 }
281 }
282
283 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
284 GenCollectedHeap* gch = GenCollectedHeap::heap();
285 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
286 "Wrong type of heap");
287 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
288 gch->gen_policy()->size_policy();
289 assert(sp->is_gc_cms_adaptive_size_policy(),
290 "Wrong type of size policy");
291 return sp;
292 }
293
294 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
295 CMSGCAdaptivePolicyCounters* results =
296 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
297 assert(
298 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
299 "Wrong gc policy counter kind");
300 return results;
301 }
302
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
310
311 _space_counters = new GSpaceCounters(gen_name, 0,
312 _virtual_space.reserved_size(),
313 this, _gen_counters);
314 }
315
316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
317 _cms_gen(cms_gen)
318 {
319 assert(alpha <= 100, "bad value");
320 _saved_alpha = alpha;
321
322 // Initialize the alphas to the bootstrap value of 100.
323 _gc0_alpha = _cms_alpha = 100;
324
325 _cms_begin_time.update();
326 _cms_end_time.update();
327
328 _gc0_duration = 0.0;
329 _gc0_period = 0.0;
330 _gc0_promoted = 0;
331
332 _cms_duration = 0.0;
333 _cms_period = 0.0;
334 _cms_allocated = 0;
335
336 _cms_used_at_gc0_begin = 0;
337 _cms_used_at_gc0_end = 0;
338 _allow_duty_cycle_reduction = false;
339 _valid_bits = 0;
340 _icms_duty_cycle = CMSIncrementalDutyCycle;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = gch->get_gen(0)->capacity();
358 if (HandlePromotionFailure) {
359 expected_promotion = MIN2(
360 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
361 expected_promotion);
362 }
363 if (cms_free > expected_promotion) {
364 // Start a cms collection if there isn't enough space to promote
365 // for the next minor collection. Use the padded average as
366 // a safety factor.
367 cms_free -= expected_promotion;
368
369 // Adjust by the safety factor.
370 double cms_free_dbl = (double)cms_free;
371 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
372 // Apply a further correction factor which tries to adjust
373 // for recent occurance of concurrent mode failures.
374 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
375 cms_free_dbl = cms_free_dbl * cms_adjustment;
376
377 if (PrintGCDetails && Verbose) {
378 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
379 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
380 cms_free, expected_promotion);
381 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
382 cms_free_dbl, cms_consumption_rate() + 1.0);
383 }
384 // Add 1 in case the consumption rate goes to zero.
385 return cms_free_dbl / (cms_consumption_rate() + 1.0);
386 }
387 return 0.0;
388 }
389
390 // Compare the duration of the cms collection to the
391 // time remaining before the cms generation is empty.
392 // Note that the time from the start of the cms collection
393 // to the start of the cms sweep (less than the total
394 // duration of the cms collection) can be used. This
395 // has been tried and some applications experienced
396 // promotion failures early in execution. This was
397 // possibly because the averages were not accurate
398 // enough at the beginning.
399 double CMSStats::time_until_cms_start() const {
400 // We add "gc0_period" to the "work" calculation
401 // below because this query is done (mostly) at the
402 // end of a scavenge, so we need to conservatively
403 // account for that much possible delay
404 // in the query so as to avoid concurrent mode failures
405 // due to starting the collection just a wee bit too
406 // late.
407 double work = cms_duration() + gc0_period();
408 double deadline = time_until_cms_gen_full();
409 // If a concurrent mode failure occurred recently, we want to be
410 // more conservative and halve our expected time_until_cms_gen_full()
411 if (work > deadline) {
412 if (Verbose && PrintGCDetails) {
413 gclog_or_tty->print(
414 " CMSCollector: collect because of anticipated promotion "
415 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
416 gc0_period(), time_until_cms_gen_full());
417 }
418 return 0.0;
419 }
420 return work - deadline;
421 }
422
423 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
424 // amount of change to prevent wild oscillation.
425 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
426 unsigned int new_duty_cycle) {
427 assert(old_duty_cycle <= 100, "bad input value");
428 assert(new_duty_cycle <= 100, "bad input value");
429
430 // Note: use subtraction with caution since it may underflow (values are
431 // unsigned). Addition is safe since we're in the range 0-100.
432 unsigned int damped_duty_cycle = new_duty_cycle;
433 if (new_duty_cycle < old_duty_cycle) {
434 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
435 if (new_duty_cycle + largest_delta < old_duty_cycle) {
436 damped_duty_cycle = old_duty_cycle - largest_delta;
437 }
438 } else if (new_duty_cycle > old_duty_cycle) {
439 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
440 if (new_duty_cycle > old_duty_cycle + largest_delta) {
441 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
442 }
443 }
444 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
445
446 if (CMSTraceIncrementalPacing) {
447 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
448 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
449 }
450 return damped_duty_cycle;
451 }
452
453 unsigned int CMSStats::icms_update_duty_cycle_impl() {
454 assert(CMSIncrementalPacing && valid(),
455 "should be handled in icms_update_duty_cycle()");
456
457 double cms_time_so_far = cms_timer().seconds();
458 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
459 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
460
461 // Avoid division by 0.
462 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
463 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
464
465 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
466 if (new_duty_cycle > _icms_duty_cycle) {
467 // Avoid very small duty cycles (1 or 2); 0 is allowed.
468 if (new_duty_cycle > 2) {
469 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
470 new_duty_cycle);
471 }
472 } else if (_allow_duty_cycle_reduction) {
473 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
474 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
475 // Respect the minimum duty cycle.
476 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
477 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
478 }
479
480 if (PrintGCDetails || CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
482 }
483
484 _allow_duty_cycle_reduction = false;
485 return _icms_duty_cycle;
486 }
487
488 #ifndef PRODUCT
489 void CMSStats::print_on(outputStream *st) const {
490 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
491 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
492 gc0_duration(), gc0_period(), gc0_promoted());
493 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
494 cms_duration(), cms_duration_per_mb(),
495 cms_period(), cms_allocated());
496 st->print(",cms_since_beg=%g,cms_since_end=%g",
497 cms_time_since_begin(), cms_time_since_end());
498 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
499 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
500 if (CMSIncrementalMode) {
501 st->print(",dc=%d", icms_duty_cycle());
502 }
503
504 if (valid()) {
505 st->print(",promo_rate=%g,cms_alloc_rate=%g",
506 promotion_rate(), cms_allocation_rate());
507 st->print(",cms_consumption_rate=%g,time_until_full=%g",
508 cms_consumption_rate(), time_until_cms_gen_full());
509 }
510 st->print(" ");
511 }
512 #endif // #ifndef PRODUCT
513
514 CMSCollector::CollectorState CMSCollector::_collectorState =
515 CMSCollector::Idling;
516 bool CMSCollector::_foregroundGCIsActive = false;
517 bool CMSCollector::_foregroundGCShouldWait = false;
518
519 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
520 ConcurrentMarkSweepGeneration* permGen,
521 CardTableRS* ct,
522 ConcurrentMarkSweepPolicy* cp):
523 _cmsGen(cmsGen),
524 _permGen(permGen),
525 _ct(ct),
526 _ref_processor(NULL), // will be set later
527 _conc_workers(NULL), // may be set later
528 _abort_preclean(false),
529 _start_sampling(false),
530 _between_prologue_and_epilogue(false),
531 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
532 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
533 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
534 -1 /* lock-free */, "No_lock" /* dummy */),
535 _modUnionClosure(&_modUnionTable),
536 _modUnionClosurePar(&_modUnionTable),
537 // Adjust my span to cover old (cms) gen and perm gen
538 _span(cmsGen->reserved()._union(permGen->reserved())),
539 // Construct the is_alive_closure with _span & markBitMap
540 _is_alive_closure(_span, &_markBitMap),
541 _restart_addr(NULL),
542 _overflow_list(NULL),
543 _preserved_oop_stack(NULL),
544 _preserved_mark_stack(NULL),
545 _stats(cmsGen),
546 _eden_chunk_array(NULL), // may be set in ctor body
547 _eden_chunk_capacity(0), // -- ditto --
548 _eden_chunk_index(0), // -- ditto --
549 _survivor_plab_array(NULL), // -- ditto --
550 _survivor_chunk_array(NULL), // -- ditto --
551 _survivor_chunk_capacity(0), // -- ditto --
552 _survivor_chunk_index(0), // -- ditto --
553 _ser_pmc_preclean_ovflw(0),
554 _ser_kac_preclean_ovflw(0),
555 _ser_pmc_remark_ovflw(0),
556 _par_pmc_remark_ovflw(0),
557 _ser_kac_ovflw(0),
558 _par_kac_ovflw(0),
559 #ifndef PRODUCT
560 _num_par_pushes(0),
561 #endif
562 _collection_count_start(0),
563 _verifying(false),
564 _icms_start_limit(NULL),
565 _icms_stop_limit(NULL),
566 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
567 _completed_initialization(false),
568 _collector_policy(cp),
569 _should_unload_classes(false),
570 _concurrent_cycles_since_last_unload(0),
571 _roots_scanning_options(0),
572 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
573 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
574 {
575 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
576 ExplicitGCInvokesConcurrent = true;
577 }
578 // Now expand the span and allocate the collection support structures
579 // (MUT, marking bit map etc.) to cover both generations subject to
580 // collection.
581
582 // First check that _permGen is adjacent to _cmsGen and above it.
583 assert( _cmsGen->reserved().word_size() > 0
584 && _permGen->reserved().word_size() > 0,
585 "generations should not be of zero size");
586 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
587 "_cmsGen and _permGen should not overlap");
588 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
589 "_cmsGen->end() different from _permGen->start()");
590
591 // For use by dirty card to oop closures.
592 _cmsGen->cmsSpace()->set_collector(this);
593 _permGen->cmsSpace()->set_collector(this);
594
595 // Allocate MUT and marking bit map
596 {
597 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
598 if (!_markBitMap.allocate(_span)) {
599 warning("Failed to allocate CMS Bit Map");
600 return;
601 }
602 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
603 }
604 {
605 _modUnionTable.allocate(_span);
606 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
607 }
608
609 if (!_markStack.allocate(MarkStackSize)) {
610 warning("Failed to allocate CMS Marking Stack");
611 return;
612 }
613 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
614 warning("Failed to allocate CMS Revisit Stack");
615 return;
616 }
617
618 // Support for multi-threaded concurrent phases
619 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
620 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
621 // just for now
622 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
623 }
624 if (ConcGCThreads > 1) {
625 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
626 ConcGCThreads, true);
627 if (_conc_workers == NULL) {
628 warning("GC/CMS: _conc_workers allocation failure: "
629 "forcing -CMSConcurrentMTEnabled");
630 CMSConcurrentMTEnabled = false;
631 }
632 } else {
633 CMSConcurrentMTEnabled = false;
634 }
635 }
636 if (!CMSConcurrentMTEnabled) {
637 ConcGCThreads = 0;
638 } else {
639 // Turn off CMSCleanOnEnter optimization temporarily for
640 // the MT case where it's not fixed yet; see 6178663.
641 CMSCleanOnEnter = false;
642 }
643 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
644 "Inconsistency");
645
646 // Parallel task queues; these are shared for the
647 // concurrent and stop-world phases of CMS, but
648 // are not shared with parallel scavenge (ParNew).
649 {
650 uint i;
651 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
652
653 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
654 || ParallelRefProcEnabled)
655 && num_queues > 0) {
656 _task_queues = new OopTaskQueueSet(num_queues);
657 if (_task_queues == NULL) {
658 warning("task_queues allocation failure.");
659 return;
660 }
661 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
662 if (_hash_seed == NULL) {
663 warning("_hash_seed array allocation failure");
664 return;
665 }
666
667 // XXX use a global constant instead of 64!
668 typedef struct OopTaskQueuePadded {
669 OopTaskQueue work_queue;
670 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing
671 } OopTaskQueuePadded;
672
673 for (i = 0; i < num_queues; i++) {
674 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
675 if (q_padded == NULL) {
676 warning("work_queue allocation failure.");
677 return;
678 }
679 _task_queues->register_queue(i, &q_padded->work_queue);
680 }
681 for (i = 0; i < num_queues; i++) {
682 _task_queues->queue(i)->initialize();
683 _hash_seed[i] = 17; // copied from ParNew
684 }
685 }
686 }
687
688 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
689 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
690
691 // Clip CMSBootstrapOccupancy between 0 and 100.
692 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
693 /(double)100;
694
695 _full_gcs_since_conc_gc = 0;
696
697 // Now tell CMS generations the identity of their collector
698 ConcurrentMarkSweepGeneration::set_collector(this);
699
700 // Create & start a CMS thread for this CMS collector
701 _cmsThread = ConcurrentMarkSweepThread::start(this);
702 assert(cmsThread() != NULL, "CMS Thread should have been created");
703 assert(cmsThread()->collector() == this,
704 "CMS Thread should refer to this gen");
705 assert(CGC_lock != NULL, "Where's the CGC_lock?");
706
707 // Support for parallelizing young gen rescan
708 GenCollectedHeap* gch = GenCollectedHeap::heap();
709 _young_gen = gch->prev_gen(_cmsGen);
710 if (gch->supports_inline_contig_alloc()) {
711 _top_addr = gch->top_addr();
712 _end_addr = gch->end_addr();
713 assert(_young_gen != NULL, "no _young_gen");
714 _eden_chunk_index = 0;
715 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
716 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
717 if (_eden_chunk_array == NULL) {
718 _eden_chunk_capacity = 0;
719 warning("GC/CMS: _eden_chunk_array allocation failure");
720 }
721 }
722 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
723
724 // Support for parallelizing survivor space rescan
725 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
726 const size_t max_plab_samples =
727 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
728
729 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
730 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
731 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
732 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
733 || _cursor == NULL) {
734 warning("Failed to allocate survivor plab/chunk array");
735 if (_survivor_plab_array != NULL) {
736 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
737 _survivor_plab_array = NULL;
738 }
739 if (_survivor_chunk_array != NULL) {
740 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
741 _survivor_chunk_array = NULL;
742 }
743 if (_cursor != NULL) {
744 FREE_C_HEAP_ARRAY(size_t, _cursor);
745 _cursor = NULL;
746 }
747 } else {
748 _survivor_chunk_capacity = 2*max_plab_samples;
749 for (uint i = 0; i < ParallelGCThreads; i++) {
750 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
751 if (vec == NULL) {
752 warning("Failed to allocate survivor plab array");
753 for (int j = i; j > 0; j--) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
755 }
756 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
757 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
758 _survivor_plab_array = NULL;
759 _survivor_chunk_array = NULL;
760 _survivor_chunk_capacity = 0;
761 break;
762 } else {
763 ChunkArray* cur =
764 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
765 max_plab_samples);
766 assert(cur->end() == 0, "Should be 0");
767 assert(cur->array() == vec, "Should be vec");
768 assert(cur->capacity() == max_plab_samples, "Error");
769 }
770 }
771 }
772 }
773 assert( ( _survivor_plab_array != NULL
774 && _survivor_chunk_array != NULL)
775 || ( _survivor_chunk_capacity == 0
776 && _survivor_chunk_index == 0),
777 "Error");
778
779 // Choose what strong roots should be scanned depending on verification options
780 // and perm gen collection mode.
781 if (!CMSClassUnloadingEnabled) {
782 // If class unloading is disabled we want to include all classes into the root set.
783 add_root_scanning_option(SharedHeap::SO_AllClasses);
784 } else {
785 add_root_scanning_option(SharedHeap::SO_SystemClasses);
786 }
787
788 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
789 _gc_counters = new CollectorCounters("CMS", 1);
790 _completed_initialization = true;
791 _inter_sweep_timer.start(); // start of time
792 #ifdef SPARC
793 // Issue a stern warning, but allow use for experimentation and debugging.
794 if (VM_Version::is_sun4v() && UseMemSetInBOT) {
795 assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
796 warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
797 " on sun4v; please understand that you are using at your own risk!");
798 }
799 #endif
800 }
801
802 const char* ConcurrentMarkSweepGeneration::name() const {
803 return "concurrent mark-sweep generation";
804 }
805 void ConcurrentMarkSweepGeneration::update_counters() {
806 if (UsePerfData) {
807 _space_counters->update_all();
808 _gen_counters->update_all();
809 }
810 }
811
812 // this is an optimized version of update_counters(). it takes the
813 // used value as a parameter rather than computing it.
814 //
815 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
816 if (UsePerfData) {
817 _space_counters->update_used(used);
818 _space_counters->update_capacity();
819 _gen_counters->update_all();
820 }
821 }
822
823 void ConcurrentMarkSweepGeneration::print() const {
824 Generation::print();
825 cmsSpace()->print();
826 }
827
828 #ifndef PRODUCT
829 void ConcurrentMarkSweepGeneration::print_statistics() {
830 cmsSpace()->printFLCensus(0);
831 }
832 #endif
833
834 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
835 GenCollectedHeap* gch = GenCollectedHeap::heap();
836 if (PrintGCDetails) {
837 if (Verbose) {
838 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
839 level(), short_name(), s, used(), capacity());
840 } else {
841 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
842 level(), short_name(), s, used() / K, capacity() / K);
843 }
844 }
845 if (Verbose) {
846 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
847 gch->used(), gch->capacity());
848 } else {
849 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
850 gch->used() / K, gch->capacity() / K);
851 }
852 }
853
854 size_t
855 ConcurrentMarkSweepGeneration::contiguous_available() const {
856 // dld proposes an improvement in precision here. If the committed
857 // part of the space ends in a free block we should add that to
858 // uncommitted size in the calculation below. Will make this
859 // change later, staying with the approximation below for the
860 // time being. -- ysr.
861 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
862 }
863
864 size_t
865 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
866 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
867 }
868
869 size_t ConcurrentMarkSweepGeneration::max_available() const {
870 return free() + _virtual_space.uncommitted_size();
871 }
872
873 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
874 size_t max_promotion_in_bytes,
875 bool younger_handles_promotion_failure) const {
876
877 // This is the most conservative test. Full promotion is
878 // guaranteed if this is used. The multiplicative factor is to
879 // account for the worst case "dilatation".
880 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
881 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
882 adjusted_max_promo_bytes = (double)max_uintx;
883 }
884 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
885
886 if (younger_handles_promotion_failure && !result) {
887 // Full promotion is not guaranteed because fragmentation
888 // of the cms generation can prevent the full promotion.
889 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
890
891 if (!result) {
892 // With promotion failure handling the test for the ability
893 // to support the promotion does not have to be guaranteed.
894 // Use an average of the amount promoted.
895 result = max_available() >= (size_t)
896 gc_stats()->avg_promoted()->padded_average();
897 if (PrintGC && Verbose && result) {
898 gclog_or_tty->print_cr(
899 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
900 " max_available: " SIZE_FORMAT
901 " avg_promoted: " SIZE_FORMAT,
902 max_available(), (size_t)
903 gc_stats()->avg_promoted()->padded_average());
904 }
905 } else {
906 if (PrintGC && Verbose) {
907 gclog_or_tty->print_cr(
908 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
909 " max_available: " SIZE_FORMAT
910 " adj_max_promo_bytes: " SIZE_FORMAT,
911 max_available(), (size_t)adjusted_max_promo_bytes);
912 }
913 }
914 } else {
915 if (PrintGC && Verbose) {
916 gclog_or_tty->print_cr(
917 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
918 " contiguous_available: " SIZE_FORMAT
919 " adj_max_promo_bytes: " SIZE_FORMAT,
920 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
921 }
922 }
923 return result;
924 }
925
926 // At a promotion failure dump information on block layout in heap
927 // (cms old generation).
928 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
929 if (CMSDumpAtPromotionFailure) {
930 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
931 }
932 }
933
934 CompactibleSpace*
935 ConcurrentMarkSweepGeneration::first_compaction_space() const {
936 return _cmsSpace;
937 }
938
939 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
940 // Clear the promotion information. These pointers can be adjusted
941 // along with all the other pointers into the heap but
942 // compaction is expected to be a rare event with
943 // a heap using cms so don't do it without seeing the need.
944 if (ParallelGCThreads > 0) {
945 for (uint i = 0; i < ParallelGCThreads; i++) {
946 _par_gc_thread_states[i]->promo.reset();
947 }
948 }
949 }
950
951 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
952 blk->do_space(_cmsSpace);
953 }
954
955 void ConcurrentMarkSweepGeneration::compute_new_size() {
956 assert_locked_or_safepoint(Heap_lock);
957
958 // If incremental collection failed, we just want to expand
959 // to the limit.
960 if (incremental_collection_failed()) {
961 clear_incremental_collection_failed();
962 grow_to_reserved();
963 return;
964 }
965
966 size_t expand_bytes = 0;
967 double free_percentage = ((double) free()) / capacity();
968 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
969 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
970
971 // compute expansion delta needed for reaching desired free percentage
972 if (free_percentage < desired_free_percentage) {
973 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
974 assert(desired_capacity >= capacity(), "invalid expansion size");
975 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
976 }
977 if (expand_bytes > 0) {
978 if (PrintGCDetails && Verbose) {
979 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
980 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
981 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
982 gclog_or_tty->print_cr(" Desired free fraction %f",
983 desired_free_percentage);
984 gclog_or_tty->print_cr(" Maximum free fraction %f",
985 maximum_free_percentage);
986 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
987 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
988 desired_capacity/1000);
989 int prev_level = level() - 1;
990 if (prev_level >= 0) {
991 size_t prev_size = 0;
992 GenCollectedHeap* gch = GenCollectedHeap::heap();
993 Generation* prev_gen = gch->_gens[prev_level];
994 prev_size = prev_gen->capacity();
995 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
996 prev_size/1000);
997 }
998 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
999 unsafe_max_alloc_nogc()/1000);
1000 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
1001 contiguous_available()/1000);
1002 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
1003 expand_bytes);
1004 }
1005 // safe if expansion fails
1006 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
1007 if (PrintGCDetails && Verbose) {
1008 gclog_or_tty->print_cr(" Expanded free fraction %f",
1009 ((double) free()) / capacity());
1010 }
1011 }
1012 }
1013
1014 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1015 return cmsSpace()->freelistLock();
1016 }
1017
1018 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1019 bool tlab) {
1020 CMSSynchronousYieldRequest yr;
1021 MutexLockerEx x(freelistLock(),
1022 Mutex::_no_safepoint_check_flag);
1023 return have_lock_and_allocate(size, tlab);
1024 }
1025
1026 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1027 bool tlab) {
1028 assert_lock_strong(freelistLock());
1029 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1030 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1031 // Allocate the object live (grey) if the background collector has
1032 // started marking. This is necessary because the marker may
1033 // have passed this address and consequently this object will
1034 // not otherwise be greyed and would be incorrectly swept up.
1035 // Note that if this object contains references, the writing
1036 // of those references will dirty the card containing this object
1037 // allowing the object to be blackened (and its references scanned)
1038 // either during a preclean phase or at the final checkpoint.
1039 if (res != NULL) {
1040 collector()->direct_allocated(res, adjustedSize);
1041 _direct_allocated_words += adjustedSize;
1042 // allocation counters
1043 NOT_PRODUCT(
1044 _numObjectsAllocated++;
1045 _numWordsAllocated += (int)adjustedSize;
1046 )
1047 }
1048 return res;
1049 }
1050
1051 // In the case of direct allocation by mutators in a generation that
1052 // is being concurrently collected, the object must be allocated
1053 // live (grey) if the background collector has started marking.
1054 // This is necessary because the marker may
1055 // have passed this address and consequently this object will
1056 // not otherwise be greyed and would be incorrectly swept up.
1057 // Note that if this object contains references, the writing
1058 // of those references will dirty the card containing this object
1059 // allowing the object to be blackened (and its references scanned)
1060 // either during a preclean phase or at the final checkpoint.
1061 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1062 assert(_markBitMap.covers(start, size), "Out of bounds");
1063 if (_collectorState >= Marking) {
1064 MutexLockerEx y(_markBitMap.lock(),
1065 Mutex::_no_safepoint_check_flag);
1066 // [see comments preceding SweepClosure::do_blk() below for details]
1067 // 1. need to mark the object as live so it isn't collected
1068 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1069 // 3. need to mark the end of the object so sweeper can skip over it
1070 // if it's uninitialized when the sweeper reaches it.
1071 _markBitMap.mark(start); // object is live
1072 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1073 _markBitMap.mark(start + size - 1);
1074 // mark end of object
1075 }
1076 // check that oop looks uninitialized
1077 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1078 }
1079
1080 void CMSCollector::promoted(bool par, HeapWord* start,
1081 bool is_obj_array, size_t obj_size) {
1082 assert(_markBitMap.covers(start), "Out of bounds");
1083 // See comment in direct_allocated() about when objects should
1084 // be allocated live.
1085 if (_collectorState >= Marking) {
1086 // we already hold the marking bit map lock, taken in
1087 // the prologue
1088 if (par) {
1089 _markBitMap.par_mark(start);
1090 } else {
1091 _markBitMap.mark(start);
1092 }
1093 // We don't need to mark the object as uninitialized (as
1094 // in direct_allocated above) because this is being done with the
1095 // world stopped and the object will be initialized by the
1096 // time the sweeper gets to look at it.
1097 assert(SafepointSynchronize::is_at_safepoint(),
1098 "expect promotion only at safepoints");
1099
1100 if (_collectorState < Sweeping) {
1101 // Mark the appropriate cards in the modUnionTable, so that
1102 // this object gets scanned before the sweep. If this is
1103 // not done, CMS generation references in the object might
1104 // not get marked.
1105 // For the case of arrays, which are otherwise precisely
1106 // marked, we need to dirty the entire array, not just its head.
1107 if (is_obj_array) {
1108 // The [par_]mark_range() method expects mr.end() below to
1109 // be aligned to the granularity of a bit's representation
1110 // in the heap. In the case of the MUT below, that's a
1111 // card size.
1112 MemRegion mr(start,
1113 (HeapWord*)round_to((intptr_t)(start + obj_size),
1114 CardTableModRefBS::card_size /* bytes */));
1115 if (par) {
1116 _modUnionTable.par_mark_range(mr);
1117 } else {
1118 _modUnionTable.mark_range(mr);
1119 }
1120 } else { // not an obj array; we can just mark the head
1121 if (par) {
1122 _modUnionTable.par_mark(start);
1123 } else {
1124 _modUnionTable.mark(start);
1125 }
1126 }
1127 }
1128 }
1129 }
1130
1131 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1132 {
1133 size_t delta = pointer_delta(addr, space->bottom());
1134 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1135 }
1136
1137 void CMSCollector::icms_update_allocation_limits()
1138 {
1139 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1140 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1141
1142 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1143 if (CMSTraceIncrementalPacing) {
1144 stats().print();
1145 }
1146
1147 assert(duty_cycle <= 100, "invalid duty cycle");
1148 if (duty_cycle != 0) {
1149 // The duty_cycle is a percentage between 0 and 100; convert to words and
1150 // then compute the offset from the endpoints of the space.
1151 size_t free_words = eden->free() / HeapWordSize;
1152 double free_words_dbl = (double)free_words;
1153 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1154 size_t offset_words = (free_words - duty_cycle_words) / 2;
1155
1156 _icms_start_limit = eden->top() + offset_words;
1157 _icms_stop_limit = eden->end() - offset_words;
1158
1159 // The limits may be adjusted (shifted to the right) by
1160 // CMSIncrementalOffset, to allow the application more mutator time after a
1161 // young gen gc (when all mutators were stopped) and before CMS starts and
1162 // takes away one or more cpus.
1163 if (CMSIncrementalOffset != 0) {
1164 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1165 size_t adjustment = (size_t)adjustment_dbl;
1166 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1167 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1168 _icms_start_limit += adjustment;
1169 _icms_stop_limit = tmp_stop;
1170 }
1171 }
1172 }
1173 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1174 _icms_start_limit = _icms_stop_limit = eden->end();
1175 }
1176
1177 // Install the new start limit.
1178 eden->set_soft_end(_icms_start_limit);
1179
1180 if (CMSTraceIncrementalMode) {
1181 gclog_or_tty->print(" icms alloc limits: "
1182 PTR_FORMAT "," PTR_FORMAT
1183 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1184 _icms_start_limit, _icms_stop_limit,
1185 percent_of_space(eden, _icms_start_limit),
1186 percent_of_space(eden, _icms_stop_limit));
1187 if (Verbose) {
1188 gclog_or_tty->print("eden: ");
1189 eden->print_on(gclog_or_tty);
1190 }
1191 }
1192 }
1193
1194 // Any changes here should try to maintain the invariant
1195 // that if this method is called with _icms_start_limit
1196 // and _icms_stop_limit both NULL, then it should return NULL
1197 // and not notify the icms thread.
1198 HeapWord*
1199 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1200 size_t word_size)
1201 {
1202 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1203 // nop.
1204 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1205 if (top <= _icms_start_limit) {
1206 if (CMSTraceIncrementalMode) {
1207 space->print_on(gclog_or_tty);
1208 gclog_or_tty->stamp();
1209 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1210 ", new limit=" PTR_FORMAT
1211 " (" SIZE_FORMAT "%%)",
1212 top, _icms_stop_limit,
1213 percent_of_space(space, _icms_stop_limit));
1214 }
1215 ConcurrentMarkSweepThread::start_icms();
1216 assert(top < _icms_stop_limit, "Tautology");
1217 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1218 return _icms_stop_limit;
1219 }
1220
1221 // The allocation will cross both the _start and _stop limits, so do the
1222 // stop notification also and return end().
1223 if (CMSTraceIncrementalMode) {
1224 space->print_on(gclog_or_tty);
1225 gclog_or_tty->stamp();
1226 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1227 ", new limit=" PTR_FORMAT
1228 " (" SIZE_FORMAT "%%)",
1229 top, space->end(),
1230 percent_of_space(space, space->end()));
1231 }
1232 ConcurrentMarkSweepThread::stop_icms();
1233 return space->end();
1234 }
1235
1236 if (top <= _icms_stop_limit) {
1237 if (CMSTraceIncrementalMode) {
1238 space->print_on(gclog_or_tty);
1239 gclog_or_tty->stamp();
1240 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1241 ", new limit=" PTR_FORMAT
1242 " (" SIZE_FORMAT "%%)",
1243 top, space->end(),
1244 percent_of_space(space, space->end()));
1245 }
1246 ConcurrentMarkSweepThread::stop_icms();
1247 return space->end();
1248 }
1249
1250 if (CMSTraceIncrementalMode) {
1251 space->print_on(gclog_or_tty);
1252 gclog_or_tty->stamp();
1253 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1254 ", new limit=" PTR_FORMAT,
1255 top, NULL);
1256 }
1257 }
1258
1259 return NULL;
1260 }
1261
1262 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1263 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1264 // allocate, copy and if necessary update promoinfo --
1265 // delegate to underlying space.
1266 assert_lock_strong(freelistLock());
1267
1268 #ifndef PRODUCT
1269 if (Universe::heap()->promotion_should_fail()) {
1270 return NULL;
1271 }
1272 #endif // #ifndef PRODUCT
1273
1274 oop res = _cmsSpace->promote(obj, obj_size);
1275 if (res == NULL) {
1276 // expand and retry
1277 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1278 expand(s*HeapWordSize, MinHeapDeltaBytes,
1279 CMSExpansionCause::_satisfy_promotion);
1280 // Since there's currently no next generation, we don't try to promote
1281 // into a more senior generation.
1282 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1283 "is made to pass on a possibly failing "
1284 "promotion to next generation");
1285 res = _cmsSpace->promote(obj, obj_size);
1286 }
1287 if (res != NULL) {
1288 // See comment in allocate() about when objects should
1289 // be allocated live.
1290 assert(obj->is_oop(), "Will dereference klass pointer below");
1291 collector()->promoted(false, // Not parallel
1292 (HeapWord*)res, obj->is_objArray(), obj_size);
1293 // promotion counters
1294 NOT_PRODUCT(
1295 _numObjectsPromoted++;
1296 _numWordsPromoted +=
1297 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1298 )
1299 }
1300 return res;
1301 }
1302
1303
1304 HeapWord*
1305 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1306 HeapWord* top,
1307 size_t word_sz)
1308 {
1309 return collector()->allocation_limit_reached(space, top, word_sz);
1310 }
1311
1312 // Things to support parallel young-gen collection.
1313 oop
1314 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1315 oop old, markOop m,
1316 size_t word_sz) {
1317 #ifndef PRODUCT
1318 if (Universe::heap()->promotion_should_fail()) {
1319 return NULL;
1320 }
1321 #endif // #ifndef PRODUCT
1322
1323 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1324 PromotionInfo* promoInfo = &ps->promo;
1325 // if we are tracking promotions, then first ensure space for
1326 // promotion (including spooling space for saving header if necessary).
1327 // then allocate and copy, then track promoted info if needed.
1328 // When tracking (see PromotionInfo::track()), the mark word may
1329 // be displaced and in this case restoration of the mark word
1330 // occurs in the (oop_since_save_marks_)iterate phase.
1331 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1332 // Out of space for allocating spooling buffers;
1333 // try expanding and allocating spooling buffers.
1334 if (!expand_and_ensure_spooling_space(promoInfo)) {
1335 return NULL;
1336 }
1337 }
1338 assert(promoInfo->has_spooling_space(), "Control point invariant");
1339 HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1340 if (obj_ptr == NULL) {
1341 obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1342 if (obj_ptr == NULL) {
1343 return NULL;
1344 }
1345 }
1346 oop obj = oop(obj_ptr);
1347 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1348 // Otherwise, copy the object. Here we must be careful to insert the
1349 // klass pointer last, since this marks the block as an allocated object.
1350 // Except with compressed oops it's the mark word.
1351 HeapWord* old_ptr = (HeapWord*)old;
1352 if (word_sz > (size_t)oopDesc::header_size()) {
1353 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1354 obj_ptr + oopDesc::header_size(),
1355 word_sz - oopDesc::header_size());
1356 }
1357
1358 if (UseCompressedOops) {
1359 // Copy gap missed by (aligned) header size calculation above
1360 obj->set_klass_gap(old->klass_gap());
1361 }
1362
1363 // Restore the mark word copied above.
1364 obj->set_mark(m);
1365
1366 // Now we can track the promoted object, if necessary. We take care
1367 // to delay the transition from uninitialized to full object
1368 // (i.e., insertion of klass pointer) until after, so that it
1369 // atomically becomes a promoted object.
1370 if (promoInfo->tracking()) {
1371 promoInfo->track((PromotedObject*)obj, old->klass());
1372 }
1373
1374 // Finally, install the klass pointer (this should be volatile).
1375 obj->set_klass(old->klass());
1376
1377 assert(old->is_oop(), "Will dereference klass ptr below");
1378 collector()->promoted(true, // parallel
1379 obj_ptr, old->is_objArray(), word_sz);
1380
1381 NOT_PRODUCT(
1382 Atomic::inc(&_numObjectsPromoted);
1383 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1384 &_numWordsPromoted);
1385 )
1386
1387 return obj;
1388 }
1389
1390 void
1391 ConcurrentMarkSweepGeneration::
1392 par_promote_alloc_undo(int thread_num,
1393 HeapWord* obj, size_t word_sz) {
1394 // CMS does not support promotion undo.
1395 ShouldNotReachHere();
1396 }
1397
1398 void
1399 ConcurrentMarkSweepGeneration::
1400 par_promote_alloc_done(int thread_num) {
1401 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1402 ps->lab.retire(thread_num);
1403 }
1404
1405 void
1406 ConcurrentMarkSweepGeneration::
1407 par_oop_since_save_marks_iterate_done(int thread_num) {
1408 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1409 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1410 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1411 }
1412
1413 // XXXPERM
1414 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1415 size_t size,
1416 bool tlab)
1417 {
1418 // We allow a STW collection only if a full
1419 // collection was requested.
1420 return full || should_allocate(size, tlab); // FIX ME !!!
1421 // This and promotion failure handling are connected at the
1422 // hip and should be fixed by untying them.
1423 }
1424
1425 bool CMSCollector::shouldConcurrentCollect() {
1426 if (_full_gc_requested) {
1427 if (Verbose && PrintGCDetails) {
1428 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1429 " gc request (or gc_locker)");
1430 }
1431 return true;
1432 }
1433
1434 // For debugging purposes, change the type of collection.
1435 // If the rotation is not on the concurrent collection
1436 // type, don't start a concurrent collection.
1437 NOT_PRODUCT(
1438 if (RotateCMSCollectionTypes &&
1439 (_cmsGen->debug_collection_type() !=
1440 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1441 assert(_cmsGen->debug_collection_type() !=
1442 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1443 "Bad cms collection type");
1444 return false;
1445 }
1446 )
1447
1448 FreelistLocker x(this);
1449 // ------------------------------------------------------------------
1450 // Print out lots of information which affects the initiation of
1451 // a collection.
1452 if (PrintCMSInitiationStatistics && stats().valid()) {
1453 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1454 gclog_or_tty->stamp();
1455 gclog_or_tty->print_cr("");
1456 stats().print_on(gclog_or_tty);
1457 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1458 stats().time_until_cms_gen_full());
1459 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1460 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1461 _cmsGen->contiguous_available());
1462 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1463 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1464 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1465 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1466 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1467 }
1468 // ------------------------------------------------------------------
1469
1470 // If the estimated time to complete a cms collection (cms_duration())
1471 // is less than the estimated time remaining until the cms generation
1472 // is full, start a collection.
1473 if (!UseCMSInitiatingOccupancyOnly) {
1474 if (stats().valid()) {
1475 if (stats().time_until_cms_start() == 0.0) {
1476 return true;
1477 }
1478 } else {
1479 // We want to conservatively collect somewhat early in order
1480 // to try and "bootstrap" our CMS/promotion statistics;
1481 // this branch will not fire after the first successful CMS
1482 // collection because the stats should then be valid.
1483 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1484 if (Verbose && PrintGCDetails) {
1485 gclog_or_tty->print_cr(
1486 " CMSCollector: collect for bootstrapping statistics:"
1487 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1488 _bootstrap_occupancy);
1489 }
1490 return true;
1491 }
1492 }
1493 }
1494
1495 // Otherwise, we start a collection cycle if either the perm gen or
1496 // old gen want a collection cycle started. Each may use
1497 // an appropriate criterion for making this decision.
1498 // XXX We need to make sure that the gen expansion
1499 // criterion dovetails well with this. XXX NEED TO FIX THIS
1500 if (_cmsGen->should_concurrent_collect()) {
1501 if (Verbose && PrintGCDetails) {
1502 gclog_or_tty->print_cr("CMS old gen initiated");
1503 }
1504 return true;
1505 }
1506
1507 // We start a collection if we believe an incremental collection may fail;
1508 // this is not likely to be productive in practice because it's probably too
1509 // late anyway.
1510 GenCollectedHeap* gch = GenCollectedHeap::heap();
1511 assert(gch->collector_policy()->is_two_generation_policy(),
1512 "You may want to check the correctness of the following");
1513 if (gch->incremental_collection_will_fail()) {
1514 if (PrintGCDetails && Verbose) {
1515 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1516 }
1517 return true;
1518 }
1519
1520 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1521 bool res = update_should_unload_classes();
1522 if (res) {
1523 if (Verbose && PrintGCDetails) {
1524 gclog_or_tty->print_cr("CMS perm gen initiated");
1525 }
1526 return true;
1527 }
1528 }
1529 return false;
1530 }
1531
1532 // Clear _expansion_cause fields of constituent generations
1533 void CMSCollector::clear_expansion_cause() {
1534 _cmsGen->clear_expansion_cause();
1535 _permGen->clear_expansion_cause();
1536 }
1537
1538 // We should be conservative in starting a collection cycle. To
1539 // start too eagerly runs the risk of collecting too often in the
1540 // extreme. To collect too rarely falls back on full collections,
1541 // which works, even if not optimum in terms of concurrent work.
1542 // As a work around for too eagerly collecting, use the flag
1543 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1544 // giving the user an easily understandable way of controlling the
1545 // collections.
1546 // We want to start a new collection cycle if any of the following
1547 // conditions hold:
1548 // . our current occupancy exceeds the configured initiating occupancy
1549 // for this generation, or
1550 // . we recently needed to expand this space and have not, since that
1551 // expansion, done a collection of this generation, or
1552 // . the underlying space believes that it may be a good idea to initiate
1553 // a concurrent collection (this may be based on criteria such as the
1554 // following: the space uses linear allocation and linear allocation is
1555 // going to fail, or there is believed to be excessive fragmentation in
1556 // the generation, etc... or ...
1557 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1558 // the case of the old generation, not the perm generation; see CR 6543076):
1559 // we may be approaching a point at which allocation requests may fail because
1560 // we will be out of sufficient free space given allocation rate estimates.]
1561 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1562
1563 assert_lock_strong(freelistLock());
1564 if (occupancy() > initiating_occupancy()) {
1565 if (PrintGCDetails && Verbose) {
1566 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1567 short_name(), occupancy(), initiating_occupancy());
1568 }
1569 return true;
1570 }
1571 if (UseCMSInitiatingOccupancyOnly) {
1572 return false;
1573 }
1574 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1575 if (PrintGCDetails && Verbose) {
1576 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1577 short_name());
1578 }
1579 return true;
1580 }
1581 if (_cmsSpace->should_concurrent_collect()) {
1582 if (PrintGCDetails && Verbose) {
1583 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1584 short_name());
1585 }
1586 return true;
1587 }
1588 return false;
1589 }
1590
1591 void ConcurrentMarkSweepGeneration::collect(bool full,
1592 bool clear_all_soft_refs,
1593 size_t size,
1594 bool tlab)
1595 {
1596 collector()->collect(full, clear_all_soft_refs, size, tlab);
1597 }
1598
1599 void CMSCollector::collect(bool full,
1600 bool clear_all_soft_refs,
1601 size_t size,
1602 bool tlab)
1603 {
1604 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1605 // For debugging purposes skip the collection if the state
1606 // is not currently idle
1607 if (TraceCMSState) {
1608 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1609 Thread::current(), full, _collectorState);
1610 }
1611 return;
1612 }
1613
1614 // The following "if" branch is present for defensive reasons.
1615 // In the current uses of this interface, it can be replaced with:
1616 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1617 // But I am not placing that assert here to allow future
1618 // generality in invoking this interface.
1619 if (GC_locker::is_active()) {
1620 // A consistency test for GC_locker
1621 assert(GC_locker::needs_gc(), "Should have been set already");
1622 // Skip this foreground collection, instead
1623 // expanding the heap if necessary.
1624 // Need the free list locks for the call to free() in compute_new_size()
1625 compute_new_size();
1626 return;
1627 }
1628 acquire_control_and_collect(full, clear_all_soft_refs);
1629 _full_gcs_since_conc_gc++;
1630
1631 }
1632
1633 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1634 GenCollectedHeap* gch = GenCollectedHeap::heap();
1635 unsigned int gc_count = gch->total_full_collections();
1636 if (gc_count == full_gc_count) {
1637 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1638 _full_gc_requested = true;
1639 CGC_lock->notify(); // nudge CMS thread
1640 }
1641 }
1642
1643
1644 // The foreground and background collectors need to coordinate in order
1645 // to make sure that they do not mutually interfere with CMS collections.
1646 // When a background collection is active,
1647 // the foreground collector may need to take over (preempt) and
1648 // synchronously complete an ongoing collection. Depending on the
1649 // frequency of the background collections and the heap usage
1650 // of the application, this preemption can be seldom or frequent.
1651 // There are only certain
1652 // points in the background collection that the "collection-baton"
1653 // can be passed to the foreground collector.
1654 //
1655 // The foreground collector will wait for the baton before
1656 // starting any part of the collection. The foreground collector
1657 // will only wait at one location.
1658 //
1659 // The background collector will yield the baton before starting a new
1660 // phase of the collection (e.g., before initial marking, marking from roots,
1661 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1662 // of the loop which switches the phases. The background collector does some
1663 // of the phases (initial mark, final re-mark) with the world stopped.
1664 // Because of locking involved in stopping the world,
1665 // the foreground collector should not block waiting for the background
1666 // collector when it is doing a stop-the-world phase. The background
1667 // collector will yield the baton at an additional point just before
1668 // it enters a stop-the-world phase. Once the world is stopped, the
1669 // background collector checks the phase of the collection. If the
1670 // phase has not changed, it proceeds with the collection. If the
1671 // phase has changed, it skips that phase of the collection. See
1672 // the comments on the use of the Heap_lock in collect_in_background().
1673 //
1674 // Variable used in baton passing.
1675 // _foregroundGCIsActive - Set to true by the foreground collector when
1676 // it wants the baton. The foreground clears it when it has finished
1677 // the collection.
1678 // _foregroundGCShouldWait - Set to true by the background collector
1679 // when it is running. The foreground collector waits while
1680 // _foregroundGCShouldWait is true.
1681 // CGC_lock - monitor used to protect access to the above variables
1682 // and to notify the foreground and background collectors.
1683 // _collectorState - current state of the CMS collection.
1684 //
1685 // The foreground collector
1686 // acquires the CGC_lock
1687 // sets _foregroundGCIsActive
1688 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1689 // various locks acquired in preparation for the collection
1690 // are released so as not to block the background collector
1691 // that is in the midst of a collection
1692 // proceeds with the collection
1693 // clears _foregroundGCIsActive
1694 // returns
1695 //
1696 // The background collector in a loop iterating on the phases of the
1697 // collection
1698 // acquires the CGC_lock
1699 // sets _foregroundGCShouldWait
1700 // if _foregroundGCIsActive is set
1701 // clears _foregroundGCShouldWait, notifies _CGC_lock
1702 // waits on _CGC_lock for _foregroundGCIsActive to become false
1703 // and exits the loop.
1704 // otherwise
1705 // proceed with that phase of the collection
1706 // if the phase is a stop-the-world phase,
1707 // yield the baton once more just before enqueueing
1708 // the stop-world CMS operation (executed by the VM thread).
1709 // returns after all phases of the collection are done
1710 //
1711
1712 void CMSCollector::acquire_control_and_collect(bool full,
1713 bool clear_all_soft_refs) {
1714 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1715 assert(!Thread::current()->is_ConcurrentGC_thread(),
1716 "shouldn't try to acquire control from self!");
1717
1718 // Start the protocol for acquiring control of the
1719 // collection from the background collector (aka CMS thread).
1720 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1721 "VM thread should have CMS token");
1722 // Remember the possibly interrupted state of an ongoing
1723 // concurrent collection
1724 CollectorState first_state = _collectorState;
1725
1726 // Signal to a possibly ongoing concurrent collection that
1727 // we want to do a foreground collection.
1728 _foregroundGCIsActive = true;
1729
1730 // Disable incremental mode during a foreground collection.
1731 ICMSDisabler icms_disabler;
1732
1733 // release locks and wait for a notify from the background collector
1734 // releasing the locks in only necessary for phases which
1735 // do yields to improve the granularity of the collection.
1736 assert_lock_strong(bitMapLock());
1737 // We need to lock the Free list lock for the space that we are
1738 // currently collecting.
1739 assert(haveFreelistLocks(), "Must be holding free list locks");
1740 bitMapLock()->unlock();
1741 releaseFreelistLocks();
1742 {
1743 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1744 if (_foregroundGCShouldWait) {
1745 // We are going to be waiting for action for the CMS thread;
1746 // it had better not be gone (for instance at shutdown)!
1747 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1748 "CMS thread must be running");
1749 // Wait here until the background collector gives us the go-ahead
1750 ConcurrentMarkSweepThread::clear_CMS_flag(
1751 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1752 // Get a possibly blocked CMS thread going:
1753 // Note that we set _foregroundGCIsActive true above,
1754 // without protection of the CGC_lock.
1755 CGC_lock->notify();
1756 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1757 "Possible deadlock");
1758 while (_foregroundGCShouldWait) {
1759 // wait for notification
1760 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1761 // Possibility of delay/starvation here, since CMS token does
1762 // not know to give priority to VM thread? Actually, i think
1763 // there wouldn't be any delay/starvation, but the proof of
1764 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1765 }
1766 ConcurrentMarkSweepThread::set_CMS_flag(
1767 ConcurrentMarkSweepThread::CMS_vm_has_token);
1768 }
1769 }
1770 // The CMS_token is already held. Get back the other locks.
1771 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1772 "VM thread should have CMS token");
1773 getFreelistLocks();
1774 bitMapLock()->lock_without_safepoint_check();
1775 if (TraceCMSState) {
1776 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1777 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1778 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1779 }
1780
1781 // Check if we need to do a compaction, or if not, whether
1782 // we need to start the mark-sweep from scratch.
1783 bool should_compact = false;
1784 bool should_start_over = false;
1785 decide_foreground_collection_type(clear_all_soft_refs,
1786 &should_compact, &should_start_over);
1787
1788 NOT_PRODUCT(
1789 if (RotateCMSCollectionTypes) {
1790 if (_cmsGen->debug_collection_type() ==
1791 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1792 should_compact = true;
1793 } else if (_cmsGen->debug_collection_type() ==
1794 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1795 should_compact = false;
1796 }
1797 }
1798 )
1799
1800 if (PrintGCDetails && first_state > Idling) {
1801 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1802 if (GCCause::is_user_requested_gc(cause) ||
1803 GCCause::is_serviceability_requested_gc(cause)) {
1804 gclog_or_tty->print(" (concurrent mode interrupted)");
1805 } else {
1806 gclog_or_tty->print(" (concurrent mode failure)");
1807 }
1808 }
1809
1810 if (should_compact) {
1811 // If the collection is being acquired from the background
1812 // collector, there may be references on the discovered
1813 // references lists that have NULL referents (being those
1814 // that were concurrently cleared by a mutator) or
1815 // that are no longer active (having been enqueued concurrently
1816 // by the mutator).
1817 // Scrub the list of those references because Mark-Sweep-Compact
1818 // code assumes referents are not NULL and that all discovered
1819 // Reference objects are active.
1820 ref_processor()->clean_up_discovered_references();
1821
1822 do_compaction_work(clear_all_soft_refs);
1823
1824 // Has the GC time limit been exceeded?
1825 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1826 size_t max_eden_size = young_gen->max_capacity() -
1827 young_gen->to()->capacity() -
1828 young_gen->from()->capacity();
1829 GenCollectedHeap* gch = GenCollectedHeap::heap();
1830 GCCause::Cause gc_cause = gch->gc_cause();
1831 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1832 young_gen->eden()->used(),
1833 _cmsGen->max_capacity(),
1834 max_eden_size,
1835 full,
1836 gc_cause,
1837 gch->collector_policy());
1838 } else {
1839 do_mark_sweep_work(clear_all_soft_refs, first_state,
1840 should_start_over);
1841 }
1842 // Reset the expansion cause, now that we just completed
1843 // a collection cycle.
1844 clear_expansion_cause();
1845 _foregroundGCIsActive = false;
1846 return;
1847 }
1848
1849 // Resize the perm generation and the tenured generation
1850 // after obtaining the free list locks for the
1851 // two generations.
1852 void CMSCollector::compute_new_size() {
1853 assert_locked_or_safepoint(Heap_lock);
1854 FreelistLocker z(this);
1855 _permGen->compute_new_size();
1856 _cmsGen->compute_new_size();
1857 }
1858
1859 // A work method used by foreground collection to determine
1860 // what type of collection (compacting or not, continuing or fresh)
1861 // it should do.
1862 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1863 // and CMSCompactWhenClearAllSoftRefs the default in the future
1864 // and do away with the flags after a suitable period.
1865 void CMSCollector::decide_foreground_collection_type(
1866 bool clear_all_soft_refs, bool* should_compact,
1867 bool* should_start_over) {
1868 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1869 // flag is set, and we have either requested a System.gc() or
1870 // the number of full gc's since the last concurrent cycle
1871 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1872 // or if an incremental collection has failed
1873 GenCollectedHeap* gch = GenCollectedHeap::heap();
1874 assert(gch->collector_policy()->is_two_generation_policy(),
1875 "You may want to check the correctness of the following");
1876 // Inform cms gen if this was due to partial collection failing.
1877 // The CMS gen may use this fact to determine its expansion policy.
1878 if (gch->incremental_collection_will_fail()) {
1879 assert(!_cmsGen->incremental_collection_failed(),
1880 "Should have been noticed, reacted to and cleared");
1881 _cmsGen->set_incremental_collection_failed();
1882 }
1883 *should_compact =
1884 UseCMSCompactAtFullCollection &&
1885 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1886 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1887 gch->incremental_collection_will_fail());
1888 *should_start_over = false;
1889 if (clear_all_soft_refs && !*should_compact) {
1890 // We are about to do a last ditch collection attempt
1891 // so it would normally make sense to do a compaction
1892 // to reclaim as much space as possible.
1893 if (CMSCompactWhenClearAllSoftRefs) {
1894 // Default: The rationale is that in this case either
1895 // we are past the final marking phase, in which case
1896 // we'd have to start over, or so little has been done
1897 // that there's little point in saving that work. Compaction
1898 // appears to be the sensible choice in either case.
1899 *should_compact = true;
1900 } else {
1901 // We have been asked to clear all soft refs, but not to
1902 // compact. Make sure that we aren't past the final checkpoint
1903 // phase, for that is where we process soft refs. If we are already
1904 // past that phase, we'll need to redo the refs discovery phase and
1905 // if necessary clear soft refs that weren't previously
1906 // cleared. We do so by remembering the phase in which
1907 // we came in, and if we are past the refs processing
1908 // phase, we'll choose to just redo the mark-sweep
1909 // collection from scratch.
1910 if (_collectorState > FinalMarking) {
1911 // We are past the refs processing phase;
1912 // start over and do a fresh synchronous CMS cycle
1913 _collectorState = Resetting; // skip to reset to start new cycle
1914 reset(false /* == !asynch */);
1915 *should_start_over = true;
1916 } // else we can continue a possibly ongoing current cycle
1917 }
1918 }
1919 }
1920
1921 // A work method used by the foreground collector to do
1922 // a mark-sweep-compact.
1923 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1924 GenCollectedHeap* gch = GenCollectedHeap::heap();
1925 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1926 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1927 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1928 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1929 }
1930
1931 // Sample collection interval time and reset for collection pause.
1932 if (UseAdaptiveSizePolicy) {
1933 size_policy()->msc_collection_begin();
1934 }
1935
1936 // Temporarily widen the span of the weak reference processing to
1937 // the entire heap.
1938 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1939 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1940
1941 // Temporarily, clear the "is_alive_non_header" field of the
1942 // reference processor.
1943 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1944
1945 // Temporarily make reference _processing_ single threaded (non-MT).
1946 ReferenceProcessorMTProcMutator z(ref_processor(), false);
1947
1948 // Temporarily make refs discovery atomic
1949 ReferenceProcessorAtomicMutator w(ref_processor(), true);
1950
1951 ref_processor()->set_enqueuing_is_done(false);
1952 ref_processor()->enable_discovery();
1953 ref_processor()->setup_policy(clear_all_soft_refs);
1954 // If an asynchronous collection finishes, the _modUnionTable is
1955 // all clear. If we are assuming the collection from an asynchronous
1956 // collection, clear the _modUnionTable.
1957 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1958 "_modUnionTable should be clear if the baton was not passed");
1959 _modUnionTable.clear_all();
1960
1961 // We must adjust the allocation statistics being maintained
1962 // in the free list space. We do so by reading and clearing
1963 // the sweep timer and updating the block flux rate estimates below.
1964 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1965 if (_inter_sweep_timer.is_active()) {
1966 _inter_sweep_timer.stop();
1967 // Note that we do not use this sample to update the _inter_sweep_estimate.
1968 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1969 _inter_sweep_estimate.padded_average(),
1970 _intra_sweep_estimate.padded_average());
1971 }
1972
1973 {
1974 TraceCMSMemoryManagerStats();
1975 }
1976 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1977 ref_processor(), clear_all_soft_refs);
1978 #ifdef ASSERT
1979 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1980 size_t free_size = cms_space->free();
1981 assert(free_size ==
1982 pointer_delta(cms_space->end(), cms_space->compaction_top())
1983 * HeapWordSize,
1984 "All the free space should be compacted into one chunk at top");
1985 assert(cms_space->dictionary()->totalChunkSize(
1986 debug_only(cms_space->freelistLock())) == 0 ||
1987 cms_space->totalSizeInIndexedFreeLists() == 0,
1988 "All the free space should be in a single chunk");
1989 size_t num = cms_space->totalCount();
1990 assert((free_size == 0 && num == 0) ||
1991 (free_size > 0 && (num == 1 || num == 2)),
1992 "There should be at most 2 free chunks after compaction");
1993 #endif // ASSERT
1994 _collectorState = Resetting;
1995 assert(_restart_addr == NULL,
1996 "Should have been NULL'd before baton was passed");
1997 reset(false /* == !asynch */);
1998 _cmsGen->reset_after_compaction();
1999 _concurrent_cycles_since_last_unload = 0;
2000
2001 if (verifying() && !should_unload_classes()) {
2002 perm_gen_verify_bit_map()->clear_all();
2003 }
2004
2005 // Clear any data recorded in the PLAB chunk arrays.
2006 if (_survivor_plab_array != NULL) {
2007 reset_survivor_plab_arrays();
2008 }
2009
2010 // Adjust the per-size allocation stats for the next epoch.
2011 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2012 // Restart the "inter sweep timer" for the next epoch.
2013 _inter_sweep_timer.reset();
2014 _inter_sweep_timer.start();
2015
2016 // Sample collection pause time and reset for collection interval.
2017 if (UseAdaptiveSizePolicy) {
2018 size_policy()->msc_collection_end(gch->gc_cause());
2019 }
2020
2021 // For a mark-sweep-compact, compute_new_size() will be called
2022 // in the heap's do_collection() method.
2023 }
2024
2025 // A work method used by the foreground collector to do
2026 // a mark-sweep, after taking over from a possibly on-going
2027 // concurrent mark-sweep collection.
2028 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2029 CollectorState first_state, bool should_start_over) {
2030 if (PrintGC && Verbose) {
2031 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2032 "collector with count %d",
2033 _full_gcs_since_conc_gc);
2034 }
2035 switch (_collectorState) {
2036 case Idling:
2037 if (first_state == Idling || should_start_over) {
2038 // The background GC was not active, or should
2039 // restarted from scratch; start the cycle.
2040 _collectorState = InitialMarking;
2041 }
2042 // If first_state was not Idling, then a background GC
2043 // was in progress and has now finished. No need to do it
2044 // again. Leave the state as Idling.
2045 break;
2046 case Precleaning:
2047 // In the foreground case don't do the precleaning since
2048 // it is not done concurrently and there is extra work
2049 // required.
2050 _collectorState = FinalMarking;
2051 }
2052 if (PrintGCDetails &&
2053 (_collectorState > Idling ||
2054 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2055 gclog_or_tty->print(" (concurrent mode failure)");
2056 }
2057 collect_in_foreground(clear_all_soft_refs);
2058
2059 // For a mark-sweep, compute_new_size() will be called
2060 // in the heap's do_collection() method.
2061 }
2062
2063
2064 void CMSCollector::getFreelistLocks() const {
2065 // Get locks for all free lists in all generations that this
2066 // collector is responsible for
2067 _cmsGen->freelistLock()->lock_without_safepoint_check();
2068 _permGen->freelistLock()->lock_without_safepoint_check();
2069 }
2070
2071 void CMSCollector::releaseFreelistLocks() const {
2072 // Release locks for all free lists in all generations that this
2073 // collector is responsible for
2074 _cmsGen->freelistLock()->unlock();
2075 _permGen->freelistLock()->unlock();
2076 }
2077
2078 bool CMSCollector::haveFreelistLocks() const {
2079 // Check locks for all free lists in all generations that this
2080 // collector is responsible for
2081 assert_lock_strong(_cmsGen->freelistLock());
2082 assert_lock_strong(_permGen->freelistLock());
2083 PRODUCT_ONLY(ShouldNotReachHere());
2084 return true;
2085 }
2086
2087 // A utility class that is used by the CMS collector to
2088 // temporarily "release" the foreground collector from its
2089 // usual obligation to wait for the background collector to
2090 // complete an ongoing phase before proceeding.
2091 class ReleaseForegroundGC: public StackObj {
2092 private:
2093 CMSCollector* _c;
2094 public:
2095 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2096 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2097 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2098 // allow a potentially blocked foreground collector to proceed
2099 _c->_foregroundGCShouldWait = false;
2100 if (_c->_foregroundGCIsActive) {
2101 CGC_lock->notify();
2102 }
2103 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2104 "Possible deadlock");
2105 }
2106
2107 ~ReleaseForegroundGC() {
2108 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2109 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2110 _c->_foregroundGCShouldWait = true;
2111 }
2112 };
2113
2114 // There are separate collect_in_background and collect_in_foreground because of
2115 // the different locking requirements of the background collector and the
2116 // foreground collector. There was originally an attempt to share
2117 // one "collect" method between the background collector and the foreground
2118 // collector but the if-then-else required made it cleaner to have
2119 // separate methods.
2120 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2121 assert(Thread::current()->is_ConcurrentGC_thread(),
2122 "A CMS asynchronous collection is only allowed on a CMS thread.");
2123
2124 GenCollectedHeap* gch = GenCollectedHeap::heap();
2125 {
2126 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2127 MutexLockerEx hl(Heap_lock, safepoint_check);
2128 FreelistLocker fll(this);
2129 MutexLockerEx x(CGC_lock, safepoint_check);
2130 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2131 // The foreground collector is active or we're
2132 // not using asynchronous collections. Skip this
2133 // background collection.
2134 assert(!_foregroundGCShouldWait, "Should be clear");
2135 return;
2136 } else {
2137 assert(_collectorState == Idling, "Should be idling before start.");
2138 _collectorState = InitialMarking;
2139 // Reset the expansion cause, now that we are about to begin
2140 // a new cycle.
2141 clear_expansion_cause();
2142 }
2143 // Decide if we want to enable class unloading as part of the
2144 // ensuing concurrent GC cycle.
2145 update_should_unload_classes();
2146 _full_gc_requested = false; // acks all outstanding full gc requests
2147 // Signal that we are about to start a collection
2148 gch->increment_total_full_collections(); // ... starting a collection cycle
2149 _collection_count_start = gch->total_full_collections();
2150 }
2151
2152 // Used for PrintGC
2153 size_t prev_used;
2154 if (PrintGC && Verbose) {
2155 prev_used = _cmsGen->used(); // XXXPERM
2156 }
2157
2158 // The change of the collection state is normally done at this level;
2159 // the exceptions are phases that are executed while the world is
2160 // stopped. For those phases the change of state is done while the
2161 // world is stopped. For baton passing purposes this allows the
2162 // background collector to finish the phase and change state atomically.
2163 // The foreground collector cannot wait on a phase that is done
2164 // while the world is stopped because the foreground collector already
2165 // has the world stopped and would deadlock.
2166 while (_collectorState != Idling) {
2167 if (TraceCMSState) {
2168 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2169 Thread::current(), _collectorState);
2170 }
2171 // The foreground collector
2172 // holds the Heap_lock throughout its collection.
2173 // holds the CMS token (but not the lock)
2174 // except while it is waiting for the background collector to yield.
2175 //
2176 // The foreground collector should be blocked (not for long)
2177 // if the background collector is about to start a phase
2178 // executed with world stopped. If the background
2179 // collector has already started such a phase, the
2180 // foreground collector is blocked waiting for the
2181 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2182 // are executed in the VM thread.
2183 //
2184 // The locking order is
2185 // PendingListLock (PLL) -- if applicable (FinalMarking)
2186 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2187 // CMS token (claimed in
2188 // stop_world_and_do() -->
2189 // safepoint_synchronize() -->
2190 // CMSThread::synchronize())
2191
2192 {
2193 // Check if the FG collector wants us to yield.
2194 CMSTokenSync x(true); // is cms thread
2195 if (waitForForegroundGC()) {
2196 // We yielded to a foreground GC, nothing more to be
2197 // done this round.
2198 assert(_foregroundGCShouldWait == false, "We set it to false in "
2199 "waitForForegroundGC()");
2200 if (TraceCMSState) {
2201 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2202 " exiting collection CMS state %d",
2203 Thread::current(), _collectorState);
2204 }
2205 return;
2206 } else {
2207 // The background collector can run but check to see if the
2208 // foreground collector has done a collection while the
2209 // background collector was waiting to get the CGC_lock
2210 // above. If yes, break so that _foregroundGCShouldWait
2211 // is cleared before returning.
2212 if (_collectorState == Idling) {
2213 break;
2214 }
2215 }
2216 }
2217
2218 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2219 "should be waiting");
2220
2221 switch (_collectorState) {
2222 case InitialMarking:
2223 {
2224 ReleaseForegroundGC x(this);
2225 stats().record_cms_begin();
2226
2227 VM_CMS_Initial_Mark initial_mark_op(this);
2228 VMThread::execute(&initial_mark_op);
2229 }
2230 // The collector state may be any legal state at this point
2231 // since the background collector may have yielded to the
2232 // foreground collector.
2233 break;
2234 case Marking:
2235 // initial marking in checkpointRootsInitialWork has been completed
2236 if (markFromRoots(true)) { // we were successful
2237 assert(_collectorState == Precleaning, "Collector state should "
2238 "have changed");
2239 } else {
2240 assert(_foregroundGCIsActive, "Internal state inconsistency");
2241 }
2242 break;
2243 case Precleaning:
2244 if (UseAdaptiveSizePolicy) {
2245 size_policy()->concurrent_precleaning_begin();
2246 }
2247 // marking from roots in markFromRoots has been completed
2248 preclean();
2249 if (UseAdaptiveSizePolicy) {
2250 size_policy()->concurrent_precleaning_end();
2251 }
2252 assert(_collectorState == AbortablePreclean ||
2253 _collectorState == FinalMarking,
2254 "Collector state should have changed");
2255 break;
2256 case AbortablePreclean:
2257 if (UseAdaptiveSizePolicy) {
2258 size_policy()->concurrent_phases_resume();
2259 }
2260 abortable_preclean();
2261 if (UseAdaptiveSizePolicy) {
2262 size_policy()->concurrent_precleaning_end();
2263 }
2264 assert(_collectorState == FinalMarking, "Collector state should "
2265 "have changed");
2266 break;
2267 case FinalMarking:
2268 {
2269 ReleaseForegroundGC x(this);
2270
2271 VM_CMS_Final_Remark final_remark_op(this);
2272 VMThread::execute(&final_remark_op);
2273 }
2274 assert(_foregroundGCShouldWait, "block post-condition");
2275 break;
2276 case Sweeping:
2277 if (UseAdaptiveSizePolicy) {
2278 size_policy()->concurrent_sweeping_begin();
2279 }
2280 // final marking in checkpointRootsFinal has been completed
2281 sweep(true);
2282 assert(_collectorState == Resizing, "Collector state change "
2283 "to Resizing must be done under the free_list_lock");
2284 _full_gcs_since_conc_gc = 0;
2285
2286 // Stop the timers for adaptive size policy for the concurrent phases
2287 if (UseAdaptiveSizePolicy) {
2288 size_policy()->concurrent_sweeping_end();
2289 size_policy()->concurrent_phases_end(gch->gc_cause(),
2290 gch->prev_gen(_cmsGen)->capacity(),
2291 _cmsGen->free());
2292 }
2293
2294 case Resizing: {
2295 // Sweeping has been completed...
2296 // At this point the background collection has completed.
2297 // Don't move the call to compute_new_size() down
2298 // into code that might be executed if the background
2299 // collection was preempted.
2300 {
2301 ReleaseForegroundGC x(this); // unblock FG collection
2302 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2303 CMSTokenSync z(true); // not strictly needed.
2304 if (_collectorState == Resizing) {
2305 compute_new_size();
2306 _collectorState = Resetting;
2307 } else {
2308 assert(_collectorState == Idling, "The state should only change"
2309 " because the foreground collector has finished the collection");
2310 }
2311 }
2312 break;
2313 }
2314 case Resetting:
2315 // CMS heap resizing has been completed
2316 reset(true);
2317 assert(_collectorState == Idling, "Collector state should "
2318 "have changed");
2319 stats().record_cms_end();
2320 // Don't move the concurrent_phases_end() and compute_new_size()
2321 // calls to here because a preempted background collection
2322 // has it's state set to "Resetting".
2323 break;
2324 case Idling:
2325 default:
2326 ShouldNotReachHere();
2327 break;
2328 }
2329 if (TraceCMSState) {
2330 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2331 Thread::current(), _collectorState);
2332 }
2333 assert(_foregroundGCShouldWait, "block post-condition");
2334 }
2335
2336 // Should this be in gc_epilogue?
2337 collector_policy()->counters()->update_counters();
2338
2339 {
2340 // Clear _foregroundGCShouldWait and, in the event that the
2341 // foreground collector is waiting, notify it, before
2342 // returning.
2343 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2344 _foregroundGCShouldWait = false;
2345 if (_foregroundGCIsActive) {
2346 CGC_lock->notify();
2347 }
2348 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2349 "Possible deadlock");
2350 }
2351 if (TraceCMSState) {
2352 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2353 " exiting collection CMS state %d",
2354 Thread::current(), _collectorState);
2355 }
2356 if (PrintGC && Verbose) {
2357 _cmsGen->print_heap_change(prev_used);
2358 }
2359 }
2360
2361 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2362 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2363 "Foreground collector should be waiting, not executing");
2364 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2365 "may only be done by the VM Thread with the world stopped");
2366 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2367 "VM thread should have CMS token");
2368
2369 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2370 true, gclog_or_tty);)
2371 if (UseAdaptiveSizePolicy) {
2372 size_policy()->ms_collection_begin();
2373 }
2374 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2375
2376 HandleMark hm; // Discard invalid handles created during verification
2377
2378 if (VerifyBeforeGC &&
2379 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2380 Universe::verify(true);
2381 }
2382
2383 // Snapshot the soft reference policy to be used in this collection cycle.
2384 ref_processor()->setup_policy(clear_all_soft_refs);
2385
2386 bool init_mark_was_synchronous = false; // until proven otherwise
2387 while (_collectorState != Idling) {
2388 if (TraceCMSState) {
2389 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2390 Thread::current(), _collectorState);
2391 }
2392 switch (_collectorState) {
2393 case InitialMarking:
2394 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2395 checkpointRootsInitial(false);
2396 assert(_collectorState == Marking, "Collector state should have changed"
2397 " within checkpointRootsInitial()");
2398 break;
2399 case Marking:
2400 // initial marking in checkpointRootsInitialWork has been completed
2401 if (VerifyDuringGC &&
2402 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2403 gclog_or_tty->print("Verify before initial mark: ");
2404 Universe::verify(true);
2405 }
2406 {
2407 bool res = markFromRoots(false);
2408 assert(res && _collectorState == FinalMarking, "Collector state should "
2409 "have changed");
2410 break;
2411 }
2412 case FinalMarking:
2413 if (VerifyDuringGC &&
2414 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2415 gclog_or_tty->print("Verify before re-mark: ");
2416 Universe::verify(true);
2417 }
2418 checkpointRootsFinal(false, clear_all_soft_refs,
2419 init_mark_was_synchronous);
2420 assert(_collectorState == Sweeping, "Collector state should not "
2421 "have changed within checkpointRootsFinal()");
2422 break;
2423 case Sweeping:
2424 // final marking in checkpointRootsFinal has been completed
2425 if (VerifyDuringGC &&
2426 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2427 gclog_or_tty->print("Verify before sweep: ");
2428 Universe::verify(true);
2429 }
2430 sweep(false);
2431 assert(_collectorState == Resizing, "Incorrect state");
2432 break;
2433 case Resizing: {
2434 // Sweeping has been completed; the actual resize in this case
2435 // is done separately; nothing to be done in this state.
2436 _collectorState = Resetting;
2437 break;
2438 }
2439 case Resetting:
2440 // The heap has been resized.
2441 if (VerifyDuringGC &&
2442 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2443 gclog_or_tty->print("Verify before reset: ");
2444 Universe::verify(true);
2445 }
2446 reset(false);
2447 assert(_collectorState == Idling, "Collector state should "
2448 "have changed");
2449 break;
2450 case Precleaning:
2451 case AbortablePreclean:
2452 // Elide the preclean phase
2453 _collectorState = FinalMarking;
2454 break;
2455 default:
2456 ShouldNotReachHere();
2457 }
2458 if (TraceCMSState) {
2459 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2460 Thread::current(), _collectorState);
2461 }
2462 }
2463
2464 if (UseAdaptiveSizePolicy) {
2465 GenCollectedHeap* gch = GenCollectedHeap::heap();
2466 size_policy()->ms_collection_end(gch->gc_cause());
2467 }
2468
2469 if (VerifyAfterGC &&
2470 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2471 Universe::verify(true);
2472 }
2473 if (TraceCMSState) {
2474 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2475 " exiting collection CMS state %d",
2476 Thread::current(), _collectorState);
2477 }
2478 }
2479
2480 bool CMSCollector::waitForForegroundGC() {
2481 bool res = false;
2482 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2483 "CMS thread should have CMS token");
2484 // Block the foreground collector until the
2485 // background collectors decides whether to
2486 // yield.
2487 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2488 _foregroundGCShouldWait = true;
2489 if (_foregroundGCIsActive) {
2490 // The background collector yields to the
2491 // foreground collector and returns a value
2492 // indicating that it has yielded. The foreground
2493 // collector can proceed.
2494 res = true;
2495 _foregroundGCShouldWait = false;
2496 ConcurrentMarkSweepThread::clear_CMS_flag(
2497 ConcurrentMarkSweepThread::CMS_cms_has_token);
2498 ConcurrentMarkSweepThread::set_CMS_flag(
2499 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2500 // Get a possibly blocked foreground thread going
2501 CGC_lock->notify();
2502 if (TraceCMSState) {
2503 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2504 Thread::current(), _collectorState);
2505 }
2506 while (_foregroundGCIsActive) {
2507 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2508 }
2509 ConcurrentMarkSweepThread::set_CMS_flag(
2510 ConcurrentMarkSweepThread::CMS_cms_has_token);
2511 ConcurrentMarkSweepThread::clear_CMS_flag(
2512 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2513 }
2514 if (TraceCMSState) {
2515 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2516 Thread::current(), _collectorState);
2517 }
2518 return res;
2519 }
2520
2521 // Because of the need to lock the free lists and other structures in
2522 // the collector, common to all the generations that the collector is
2523 // collecting, we need the gc_prologues of individual CMS generations
2524 // delegate to their collector. It may have been simpler had the
2525 // current infrastructure allowed one to call a prologue on a
2526 // collector. In the absence of that we have the generation's
2527 // prologue delegate to the collector, which delegates back
2528 // some "local" work to a worker method in the individual generations
2529 // that it's responsible for collecting, while itself doing any
2530 // work common to all generations it's responsible for. A similar
2531 // comment applies to the gc_epilogue()'s.
2532 // The role of the varaible _between_prologue_and_epilogue is to
2533 // enforce the invocation protocol.
2534 void CMSCollector::gc_prologue(bool full) {
2535 // Call gc_prologue_work() for each CMSGen and PermGen that
2536 // we are responsible for.
2537
2538 // The following locking discipline assumes that we are only called
2539 // when the world is stopped.
2540 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2541
2542 // The CMSCollector prologue must call the gc_prologues for the
2543 // "generations" (including PermGen if any) that it's responsible
2544 // for.
2545
2546 assert( Thread::current()->is_VM_thread()
2547 || ( CMSScavengeBeforeRemark
2548 && Thread::current()->is_ConcurrentGC_thread()),
2549 "Incorrect thread type for prologue execution");
2550
2551 if (_between_prologue_and_epilogue) {
2552 // We have already been invoked; this is a gc_prologue delegation
2553 // from yet another CMS generation that we are responsible for, just
2554 // ignore it since all relevant work has already been done.
2555 return;
2556 }
2557
2558 // set a bit saying prologue has been called; cleared in epilogue
2559 _between_prologue_and_epilogue = true;
2560 // Claim locks for common data structures, then call gc_prologue_work()
2561 // for each CMSGen and PermGen that we are responsible for.
2562
2563 getFreelistLocks(); // gets free list locks on constituent spaces
2564 bitMapLock()->lock_without_safepoint_check();
2565
2566 // Should call gc_prologue_work() for all cms gens we are responsible for
2567 bool registerClosure = _collectorState >= Marking
2568 && _collectorState < Sweeping;
2569 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2570 : &_modUnionClosure;
2571 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2572 _permGen->gc_prologue_work(full, registerClosure, muc);
2573
2574 if (!full) {
2575 stats().record_gc0_begin();
2576 }
2577 }
2578
2579 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2580 // Delegate to CMScollector which knows how to coordinate between
2581 // this and any other CMS generations that it is responsible for
2582 // collecting.
2583 collector()->gc_prologue(full);
2584 }
2585
2586 // This is a "private" interface for use by this generation's CMSCollector.
2587 // Not to be called directly by any other entity (for instance,
2588 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2589 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2590 bool registerClosure, ModUnionClosure* modUnionClosure) {
2591 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2592 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2593 "Should be NULL");
2594 if (registerClosure) {
2595 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2596 }
2597 cmsSpace()->gc_prologue();
2598 // Clear stat counters
2599 NOT_PRODUCT(
2600 assert(_numObjectsPromoted == 0, "check");
2601 assert(_numWordsPromoted == 0, "check");
2602 if (Verbose && PrintGC) {
2603 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2604 SIZE_FORMAT" bytes concurrently",
2605 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2606 }
2607 _numObjectsAllocated = 0;
2608 _numWordsAllocated = 0;
2609 )
2610 }
2611
2612 void CMSCollector::gc_epilogue(bool full) {
2613 // The following locking discipline assumes that we are only called
2614 // when the world is stopped.
2615 assert(SafepointSynchronize::is_at_safepoint(),
2616 "world is stopped assumption");
2617
2618 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2619 // if linear allocation blocks need to be appropriately marked to allow the
2620 // the blocks to be parsable. We also check here whether we need to nudge the
2621 // CMS collector thread to start a new cycle (if it's not already active).
2622 assert( Thread::current()->is_VM_thread()
2623 || ( CMSScavengeBeforeRemark
2624 && Thread::current()->is_ConcurrentGC_thread()),
2625 "Incorrect thread type for epilogue execution");
2626
2627 if (!_between_prologue_and_epilogue) {
2628 // We have already been invoked; this is a gc_epilogue delegation
2629 // from yet another CMS generation that we are responsible for, just
2630 // ignore it since all relevant work has already been done.
2631 return;
2632 }
2633 assert(haveFreelistLocks(), "must have freelist locks");
2634 assert_lock_strong(bitMapLock());
2635
2636 _cmsGen->gc_epilogue_work(full);
2637 _permGen->gc_epilogue_work(full);
2638
2639 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2640 // in case sampling was not already enabled, enable it
2641 _start_sampling = true;
2642 }
2643 // reset _eden_chunk_array so sampling starts afresh
2644 _eden_chunk_index = 0;
2645
2646 size_t cms_used = _cmsGen->cmsSpace()->used();
2647 size_t perm_used = _permGen->cmsSpace()->used();
2648
2649 // update performance counters - this uses a special version of
2650 // update_counters() that allows the utilization to be passed as a
2651 // parameter, avoiding multiple calls to used().
2652 //
2653 _cmsGen->update_counters(cms_used);
2654 _permGen->update_counters(perm_used);
2655
2656 if (CMSIncrementalMode) {
2657 icms_update_allocation_limits();
2658 }
2659
2660 bitMapLock()->unlock();
2661 releaseFreelistLocks();
2662
2663 _between_prologue_and_epilogue = false; // ready for next cycle
2664 }
2665
2666 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2667 collector()->gc_epilogue(full);
2668
2669 // Also reset promotion tracking in par gc thread states.
2670 if (ParallelGCThreads > 0) {
2671 for (uint i = 0; i < ParallelGCThreads; i++) {
2672 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2673 }
2674 }
2675 }
2676
2677 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2678 assert(!incremental_collection_failed(), "Should have been cleared");
2679 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2680 cmsSpace()->gc_epilogue();
2681 // Print stat counters
2682 NOT_PRODUCT(
2683 assert(_numObjectsAllocated == 0, "check");
2684 assert(_numWordsAllocated == 0, "check");
2685 if (Verbose && PrintGC) {
2686 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2687 SIZE_FORMAT" bytes",
2688 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2689 }
2690 _numObjectsPromoted = 0;
2691 _numWordsPromoted = 0;
2692 )
2693
2694 if (PrintGC && Verbose) {
2695 // Call down the chain in contiguous_available needs the freelistLock
2696 // so print this out before releasing the freeListLock.
2697 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2698 contiguous_available());
2699 }
2700 }
2701
2702 #ifndef PRODUCT
2703 bool CMSCollector::have_cms_token() {
2704 Thread* thr = Thread::current();
2705 if (thr->is_VM_thread()) {
2706 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2707 } else if (thr->is_ConcurrentGC_thread()) {
2708 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2709 } else if (thr->is_GC_task_thread()) {
2710 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2711 ParGCRareEvent_lock->owned_by_self();
2712 }
2713 return false;
2714 }
2715 #endif
2716
2717 // Check reachability of the given heap address in CMS generation,
2718 // treating all other generations as roots.
2719 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2720 // We could "guarantee" below, rather than assert, but i'll
2721 // leave these as "asserts" so that an adventurous debugger
2722 // could try this in the product build provided some subset of
2723 // the conditions were met, provided they were intersted in the
2724 // results and knew that the computation below wouldn't interfere
2725 // with other concurrent computations mutating the structures
2726 // being read or written.
2727 assert(SafepointSynchronize::is_at_safepoint(),
2728 "Else mutations in object graph will make answer suspect");
2729 assert(have_cms_token(), "Should hold cms token");
2730 assert(haveFreelistLocks(), "must hold free list locks");
2731 assert_lock_strong(bitMapLock());
2732
2733 // Clear the marking bit map array before starting, but, just
2734 // for kicks, first report if the given address is already marked
2735 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2736 _markBitMap.isMarked(addr) ? "" : " not");
2737
2738 if (verify_after_remark()) {
2739 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2740 bool result = verification_mark_bm()->isMarked(addr);
2741 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2742 result ? "IS" : "is NOT");
2743 return result;
2744 } else {
2745 gclog_or_tty->print_cr("Could not compute result");
2746 return false;
2747 }
2748 }
2749
2750 ////////////////////////////////////////////////////////
2751 // CMS Verification Support
2752 ////////////////////////////////////////////////////////
2753 // Following the remark phase, the following invariant
2754 // should hold -- each object in the CMS heap which is
2755 // marked in markBitMap() should be marked in the verification_mark_bm().
2756
2757 class VerifyMarkedClosure: public BitMapClosure {
2758 CMSBitMap* _marks;
2759 bool _failed;
2760
2761 public:
2762 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2763
2764 bool do_bit(size_t offset) {
2765 HeapWord* addr = _marks->offsetToHeapWord(offset);
2766 if (!_marks->isMarked(addr)) {
2767 oop(addr)->print_on(gclog_or_tty);
2768 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2769 _failed = true;
2770 }
2771 return true;
2772 }
2773
2774 bool failed() { return _failed; }
2775 };
2776
2777 bool CMSCollector::verify_after_remark() {
2778 gclog_or_tty->print(" [Verifying CMS Marking... ");
2779 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2780 static bool init = false;
2781
2782 assert(SafepointSynchronize::is_at_safepoint(),
2783 "Else mutations in object graph will make answer suspect");
2784 assert(have_cms_token(),
2785 "Else there may be mutual interference in use of "
2786 " verification data structures");
2787 assert(_collectorState > Marking && _collectorState <= Sweeping,
2788 "Else marking info checked here may be obsolete");
2789 assert(haveFreelistLocks(), "must hold free list locks");
2790 assert_lock_strong(bitMapLock());
2791
2792
2793 // Allocate marking bit map if not already allocated
2794 if (!init) { // first time
2795 if (!verification_mark_bm()->allocate(_span)) {
2796 return false;
2797 }
2798 init = true;
2799 }
2800
2801 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2802
2803 // Turn off refs discovery -- so we will be tracing through refs.
2804 // This is as intended, because by this time
2805 // GC must already have cleared any refs that need to be cleared,
2806 // and traced those that need to be marked; moreover,
2807 // the marking done here is not going to intefere in any
2808 // way with the marking information used by GC.
2809 NoRefDiscovery no_discovery(ref_processor());
2810
2811 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2812
2813 // Clear any marks from a previous round
2814 verification_mark_bm()->clear_all();
2815 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2816 verify_work_stacks_empty();
2817
2818 GenCollectedHeap* gch = GenCollectedHeap::heap();
2819 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2820 // Update the saved marks which may affect the root scans.
2821 gch->save_marks();
2822
2823 if (CMSRemarkVerifyVariant == 1) {
2824 // In this first variant of verification, we complete
2825 // all marking, then check if the new marks-verctor is
2826 // a subset of the CMS marks-vector.
2827 verify_after_remark_work_1();
2828 } else if (CMSRemarkVerifyVariant == 2) {
2829 // In this second variant of verification, we flag an error
2830 // (i.e. an object reachable in the new marks-vector not reachable
2831 // in the CMS marks-vector) immediately, also indicating the
2832 // identify of an object (A) that references the unmarked object (B) --
2833 // presumably, a mutation to A failed to be picked up by preclean/remark?
2834 verify_after_remark_work_2();
2835 } else {
2836 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2837 CMSRemarkVerifyVariant);
2838 }
2839 gclog_or_tty->print(" done] ");
2840 return true;
2841 }
2842
2843 void CMSCollector::verify_after_remark_work_1() {
2844 ResourceMark rm;
2845 HandleMark hm;
2846 GenCollectedHeap* gch = GenCollectedHeap::heap();
2847
2848 // Mark from roots one level into CMS
2849 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2850 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2851
2852 gch->gen_process_strong_roots(_cmsGen->level(),
2853 true, // younger gens are roots
2854 true, // activate StrongRootsScope
2855 true, // collecting perm gen
2856 SharedHeap::ScanningOption(roots_scanning_options()),
2857 ¬Older,
2858 true, // walk code active on stacks
2859 NULL);
2860
2861 // Now mark from the roots
2862 assert(_revisitStack.isEmpty(), "Should be empty");
2863 MarkFromRootsClosure markFromRootsClosure(this, _span,
2864 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2865 false /* don't yield */, true /* verifying */);
2866 assert(_restart_addr == NULL, "Expected pre-condition");
2867 verification_mark_bm()->iterate(&markFromRootsClosure);
2868 while (_restart_addr != NULL) {
2869 // Deal with stack overflow: by restarting at the indicated
2870 // address.
2871 HeapWord* ra = _restart_addr;
2872 markFromRootsClosure.reset(ra);
2873 _restart_addr = NULL;
2874 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2875 }
2876 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2877 verify_work_stacks_empty();
2878 // Should reset the revisit stack above, since no class tree
2879 // surgery is forthcoming.
2880 _revisitStack.reset(); // throwing away all contents
2881
2882 // Marking completed -- now verify that each bit marked in
2883 // verification_mark_bm() is also marked in markBitMap(); flag all
2884 // errors by printing corresponding objects.
2885 VerifyMarkedClosure vcl(markBitMap());
2886 verification_mark_bm()->iterate(&vcl);
2887 if (vcl.failed()) {
2888 gclog_or_tty->print("Verification failed");
2889 Universe::heap()->print_on(gclog_or_tty);
2890 fatal("CMS: failed marking verification after remark");
2891 }
2892 }
2893
2894 void CMSCollector::verify_after_remark_work_2() {
2895 ResourceMark rm;
2896 HandleMark hm;
2897 GenCollectedHeap* gch = GenCollectedHeap::heap();
2898
2899 // Mark from roots one level into CMS
2900 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2901 markBitMap());
2902 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2903 gch->gen_process_strong_roots(_cmsGen->level(),
2904 true, // younger gens are roots
2905 true, // activate StrongRootsScope
2906 true, // collecting perm gen
2907 SharedHeap::ScanningOption(roots_scanning_options()),
2908 ¬Older,
2909 true, // walk code active on stacks
2910 NULL);
2911
2912 // Now mark from the roots
2913 assert(_revisitStack.isEmpty(), "Should be empty");
2914 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2915 verification_mark_bm(), markBitMap(), verification_mark_stack());
2916 assert(_restart_addr == NULL, "Expected pre-condition");
2917 verification_mark_bm()->iterate(&markFromRootsClosure);
2918 while (_restart_addr != NULL) {
2919 // Deal with stack overflow: by restarting at the indicated
2920 // address.
2921 HeapWord* ra = _restart_addr;
2922 markFromRootsClosure.reset(ra);
2923 _restart_addr = NULL;
2924 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2925 }
2926 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2927 verify_work_stacks_empty();
2928 // Should reset the revisit stack above, since no class tree
2929 // surgery is forthcoming.
2930 _revisitStack.reset(); // throwing away all contents
2931
2932 // Marking completed -- now verify that each bit marked in
2933 // verification_mark_bm() is also marked in markBitMap(); flag all
2934 // errors by printing corresponding objects.
2935 VerifyMarkedClosure vcl(markBitMap());
2936 verification_mark_bm()->iterate(&vcl);
2937 assert(!vcl.failed(), "Else verification above should not have succeeded");
2938 }
2939
2940 void ConcurrentMarkSweepGeneration::save_marks() {
2941 // delegate to CMS space
2942 cmsSpace()->save_marks();
2943 for (uint i = 0; i < ParallelGCThreads; i++) {
2944 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2945 }
2946 }
2947
2948 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2949 return cmsSpace()->no_allocs_since_save_marks();
2950 }
2951
2952 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2953 \
2954 void ConcurrentMarkSweepGeneration:: \
2955 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2956 cl->set_generation(this); \
2957 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2958 cl->reset_generation(); \
2959 save_marks(); \
2960 }
2961
2962 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2963
2964 void
2965 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2966 {
2967 // Not currently implemented; need to do the following. -- ysr.
2968 // dld -- I think that is used for some sort of allocation profiler. So it
2969 // really means the objects allocated by the mutator since the last
2970 // GC. We could potentially implement this cheaply by recording only
2971 // the direct allocations in a side data structure.
2972 //
2973 // I think we probably ought not to be required to support these
2974 // iterations at any arbitrary point; I think there ought to be some
2975 // call to enable/disable allocation profiling in a generation/space,
2976 // and the iterator ought to return the objects allocated in the
2977 // gen/space since the enable call, or the last iterator call (which
2978 // will probably be at a GC.) That way, for gens like CM&S that would
2979 // require some extra data structure to support this, we only pay the
2980 // cost when it's in use...
2981 cmsSpace()->object_iterate_since_last_GC(blk);
2982 }
2983
2984 void
2985 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2986 cl->set_generation(this);
2987 younger_refs_in_space_iterate(_cmsSpace, cl);
2988 cl->reset_generation();
2989 }
2990
2991 void
2992 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2993 if (freelistLock()->owned_by_self()) {
2994 Generation::oop_iterate(mr, cl);
2995 } else {
2996 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2997 Generation::oop_iterate(mr, cl);
2998 }
2999 }
3000
3001 void
3002 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3003 if (freelistLock()->owned_by_self()) {
3004 Generation::oop_iterate(cl);
3005 } else {
3006 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3007 Generation::oop_iterate(cl);
3008 }
3009 }
3010
3011 void
3012 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3013 if (freelistLock()->owned_by_self()) {
3014 Generation::object_iterate(cl);
3015 } else {
3016 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3017 Generation::object_iterate(cl);
3018 }
3019 }
3020
3021 void
3022 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3023 if (freelistLock()->owned_by_self()) {
3024 Generation::safe_object_iterate(cl);
3025 } else {
3026 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3027 Generation::safe_object_iterate(cl);
3028 }
3029 }
3030
3031 void
3032 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3033 }
3034
3035 void
3036 ConcurrentMarkSweepGeneration::post_compact() {
3037 }
3038
3039 void
3040 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3041 // Fix the linear allocation blocks to look like free blocks.
3042
3043 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3044 // are not called when the heap is verified during universe initialization and
3045 // at vm shutdown.
3046 if (freelistLock()->owned_by_self()) {
3047 cmsSpace()->prepare_for_verify();
3048 } else {
3049 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3050 cmsSpace()->prepare_for_verify();
3051 }
3052 }
3053
3054 void
3055 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3056 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3057 // are not called when the heap is verified during universe initialization and
3058 // at vm shutdown.
3059 if (freelistLock()->owned_by_self()) {
3060 cmsSpace()->verify(false /* ignored */);
3061 } else {
3062 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3063 cmsSpace()->verify(false /* ignored */);
3064 }
3065 }
3066
3067 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3068 _cmsGen->verify(allow_dirty);
3069 _permGen->verify(allow_dirty);
3070 }
3071
3072 #ifndef PRODUCT
3073 bool CMSCollector::overflow_list_is_empty() const {
3074 assert(_num_par_pushes >= 0, "Inconsistency");
3075 if (_overflow_list == NULL) {
3076 assert(_num_par_pushes == 0, "Inconsistency");
3077 }
3078 return _overflow_list == NULL;
3079 }
3080
3081 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3082 // merely consolidate assertion checks that appear to occur together frequently.
3083 void CMSCollector::verify_work_stacks_empty() const {
3084 assert(_markStack.isEmpty(), "Marking stack should be empty");
3085 assert(overflow_list_is_empty(), "Overflow list should be empty");
3086 }
3087
3088 void CMSCollector::verify_overflow_empty() const {
3089 assert(overflow_list_is_empty(), "Overflow list should be empty");
3090 assert(no_preserved_marks(), "No preserved marks");
3091 }
3092 #endif // PRODUCT
3093
3094 // Decide if we want to enable class unloading as part of the
3095 // ensuing concurrent GC cycle. We will collect the perm gen and
3096 // unload classes if it's the case that:
3097 // (1) an explicit gc request has been made and the flag
3098 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3099 // (2) (a) class unloading is enabled at the command line, and
3100 // (b) (i) perm gen threshold has been crossed, or
3101 // (ii) old gen is getting really full, or
3102 // (iii) the previous N CMS collections did not collect the
3103 // perm gen
3104 // NOTE: Provided there is no change in the state of the heap between
3105 // calls to this method, it should have idempotent results. Moreover,
3106 // its results should be monotonically increasing (i.e. going from 0 to 1,
3107 // but not 1 to 0) between successive calls between which the heap was
3108 // not collected. For the implementation below, it must thus rely on
3109 // the property that concurrent_cycles_since_last_unload()
3110 // will not decrease unless a collection cycle happened and that
3111 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3112 // themselves also monotonic in that sense. See check_monotonicity()
3113 // below.
3114 bool CMSCollector::update_should_unload_classes() {
3115 _should_unload_classes = false;
3116 // Condition 1 above
3117 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3118 _should_unload_classes = true;
3119 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3120 // Disjuncts 2.b.(i,ii,iii) above
3121 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3122 CMSClassUnloadingMaxInterval)
3123 || _permGen->should_concurrent_collect()
3124 || _cmsGen->is_too_full();
3125 }
3126 return _should_unload_classes;
3127 }
3128
3129 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3130 bool res = should_concurrent_collect();
3131 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3132 return res;
3133 }
3134
3135 void CMSCollector::setup_cms_unloading_and_verification_state() {
3136 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3137 || VerifyBeforeExit;
3138 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3139 | SharedHeap::SO_CodeCache;
3140
3141 if (should_unload_classes()) { // Should unload classes this cycle
3142 remove_root_scanning_option(rso); // Shrink the root set appropriately
3143 set_verifying(should_verify); // Set verification state for this cycle
3144 return; // Nothing else needs to be done at this time
3145 }
3146
3147 // Not unloading classes this cycle
3148 assert(!should_unload_classes(), "Inconsitency!");
3149 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3150 // We were not verifying, or we _were_ unloading classes in the last cycle,
3151 // AND some verification options are enabled this cycle; in this case,
3152 // we must make sure that the deadness map is allocated if not already so,
3153 // and cleared (if already allocated previously --
3154 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3155 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3156 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3157 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3158 "permanent generation verification disabled");
3159 return; // Note that we leave verification disabled, so we'll retry this
3160 // allocation next cycle. We _could_ remember this failure
3161 // and skip further attempts and permanently disable verification
3162 // attempts if that is considered more desirable.
3163 }
3164 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3165 "_perm_gen_ver_bit_map inconsistency?");
3166 } else {
3167 perm_gen_verify_bit_map()->clear_all();
3168 }
3169 // Include symbols, strings and code cache elements to prevent their resurrection.
3170 add_root_scanning_option(rso);
3171 set_verifying(true);
3172 } else if (verifying() && !should_verify) {
3173 // We were verifying, but some verification flags got disabled.
3174 set_verifying(false);
3175 // Exclude symbols, strings and code cache elements from root scanning to
3176 // reduce IM and RM pauses.
3177 remove_root_scanning_option(rso);
3178 }
3179 }
3180
3181
3182 #ifndef PRODUCT
3183 HeapWord* CMSCollector::block_start(const void* p) const {
3184 const HeapWord* addr = (HeapWord*)p;
3185 if (_span.contains(p)) {
3186 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3187 return _cmsGen->cmsSpace()->block_start(p);
3188 } else {
3189 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3190 "Inconsistent _span?");
3191 return _permGen->cmsSpace()->block_start(p);
3192 }
3193 }
3194 return NULL;
3195 }
3196 #endif
3197
3198 HeapWord*
3199 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3200 bool tlab,
3201 bool parallel) {
3202 assert(!tlab, "Can't deal with TLAB allocation");
3203 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3204 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3205 CMSExpansionCause::_satisfy_allocation);
3206 if (GCExpandToAllocateDelayMillis > 0) {
3207 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3208 }
3209 return have_lock_and_allocate(word_size, tlab);
3210 }
3211
3212 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3213 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3214 // to CardGeneration and share it...
3215 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3216 return CardGeneration::expand(bytes, expand_bytes);
3217 }
3218
3219 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3220 CMSExpansionCause::Cause cause)
3221 {
3222
3223 bool success = expand(bytes, expand_bytes);
3224
3225 // remember why we expanded; this information is used
3226 // by shouldConcurrentCollect() when making decisions on whether to start
3227 // a new CMS cycle.
3228 if (success) {
3229 set_expansion_cause(cause);
3230 if (PrintGCDetails && Verbose) {
3231 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3232 CMSExpansionCause::to_string(cause));
3233 }
3234 }
3235 }
3236
3237 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3238 HeapWord* res = NULL;
3239 MutexLocker x(ParGCRareEvent_lock);
3240 while (true) {
3241 // Expansion by some other thread might make alloc OK now:
3242 res = ps->lab.alloc(word_sz);
3243 if (res != NULL) return res;
3244 // If there's not enough expansion space available, give up.
3245 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3246 return NULL;
3247 }
3248 // Otherwise, we try expansion.
3249 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3250 CMSExpansionCause::_allocate_par_lab);
3251 // Now go around the loop and try alloc again;
3252 // A competing par_promote might beat us to the expansion space,
3253 // so we may go around the loop again if promotion fails agaion.
3254 if (GCExpandToAllocateDelayMillis > 0) {
3255 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3256 }
3257 }
3258 }
3259
3260
3261 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3262 PromotionInfo* promo) {
3263 MutexLocker x(ParGCRareEvent_lock);
3264 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3265 while (true) {
3266 // Expansion by some other thread might make alloc OK now:
3267 if (promo->ensure_spooling_space()) {
3268 assert(promo->has_spooling_space(),
3269 "Post-condition of successful ensure_spooling_space()");
3270 return true;
3271 }
3272 // If there's not enough expansion space available, give up.
3273 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3274 return false;
3275 }
3276 // Otherwise, we try expansion.
3277 expand(refill_size_bytes, MinHeapDeltaBytes,
3278 CMSExpansionCause::_allocate_par_spooling_space);
3279 // Now go around the loop and try alloc again;
3280 // A competing allocation might beat us to the expansion space,
3281 // so we may go around the loop again if allocation fails again.
3282 if (GCExpandToAllocateDelayMillis > 0) {
3283 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3284 }
3285 }
3286 }
3287
3288
3289
3290 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3291 assert_locked_or_safepoint(Heap_lock);
3292 size_t size = ReservedSpace::page_align_size_down(bytes);
3293 if (size > 0) {
3294 shrink_by(size);
3295 }
3296 }
3297
3298 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3299 assert_locked_or_safepoint(Heap_lock);
3300 bool result = _virtual_space.expand_by(bytes);
3301 if (result) {
3302 HeapWord* old_end = _cmsSpace->end();
3303 size_t new_word_size =
3304 heap_word_size(_virtual_space.committed_size());
3305 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3306 _bts->resize(new_word_size); // resize the block offset shared array
3307 Universe::heap()->barrier_set()->resize_covered_region(mr);
3308 // Hmmmm... why doesn't CFLS::set_end verify locking?
3309 // This is quite ugly; FIX ME XXX
3310 _cmsSpace->assert_locked(freelistLock());
3311 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3312
3313 // update the space and generation capacity counters
3314 if (UsePerfData) {
3315 _space_counters->update_capacity();
3316 _gen_counters->update_all();
3317 }
3318
3319 if (Verbose && PrintGC) {
3320 size_t new_mem_size = _virtual_space.committed_size();
3321 size_t old_mem_size = new_mem_size - bytes;
3322 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3323 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3324 }
3325 }
3326 return result;
3327 }
3328
3329 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3330 assert_locked_or_safepoint(Heap_lock);
3331 bool success = true;
3332 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3333 if (remaining_bytes > 0) {
3334 success = grow_by(remaining_bytes);
3335 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3336 }
3337 return success;
3338 }
3339
3340 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3341 assert_locked_or_safepoint(Heap_lock);
3342 assert_lock_strong(freelistLock());
3343 // XXX Fix when compaction is implemented.
3344 warning("Shrinking of CMS not yet implemented");
3345 return;
3346 }
3347
3348
3349 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3350 // phases.
3351 class CMSPhaseAccounting: public StackObj {
3352 public:
3353 CMSPhaseAccounting(CMSCollector *collector,
3354 const char *phase,
3355 bool print_cr = true);
3356 ~CMSPhaseAccounting();
3357
3358 private:
3359 CMSCollector *_collector;
3360 const char *_phase;
3361 elapsedTimer _wallclock;
3362 bool _print_cr;
3363
3364 public:
3365 // Not MT-safe; so do not pass around these StackObj's
3366 // where they may be accessed by other threads.
3367 jlong wallclock_millis() {
3368 assert(_wallclock.is_active(), "Wall clock should not stop");
3369 _wallclock.stop(); // to record time
3370 jlong ret = _wallclock.milliseconds();
3371 _wallclock.start(); // restart
3372 return ret;
3373 }
3374 };
3375
3376 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3377 const char *phase,
3378 bool print_cr) :
3379 _collector(collector), _phase(phase), _print_cr(print_cr) {
3380
3381 if (PrintCMSStatistics != 0) {
3382 _collector->resetYields();
3383 }
3384 if (PrintGCDetails && PrintGCTimeStamps) {
3385 gclog_or_tty->date_stamp(PrintGCDateStamps);
3386 gclog_or_tty->stamp();
3387 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3388 _collector->cmsGen()->short_name(), _phase);
3389 }
3390 _collector->resetTimer();
3391 _wallclock.start();
3392 _collector->startTimer();
3393 }
3394
3395 CMSPhaseAccounting::~CMSPhaseAccounting() {
3396 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3397 _collector->stopTimer();
3398 _wallclock.stop();
3399 if (PrintGCDetails) {
3400 gclog_or_tty->date_stamp(PrintGCDateStamps);
3401 if (PrintGCTimeStamps) {
3402 gclog_or_tty->stamp();
3403 gclog_or_tty->print(": ");
3404 }
3405 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3406 _collector->cmsGen()->short_name(),
3407 _phase, _collector->timerValue(), _wallclock.seconds());
3408 if (_print_cr) {
3409 gclog_or_tty->print_cr("");
3410 }
3411 if (PrintCMSStatistics != 0) {
3412 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3413 _collector->yields());
3414 }
3415 }
3416 }
3417
3418 // CMS work
3419
3420 // Checkpoint the roots into this generation from outside
3421 // this generation. [Note this initial checkpoint need only
3422 // be approximate -- we'll do a catch up phase subsequently.]
3423 void CMSCollector::checkpointRootsInitial(bool asynch) {
3424 assert(_collectorState == InitialMarking, "Wrong collector state");
3425 check_correct_thread_executing();
3426 TraceCMSMemoryManagerStats tms(_collectorState);
3427 ReferenceProcessor* rp = ref_processor();
3428 SpecializationStats::clear();
3429 assert(_restart_addr == NULL, "Control point invariant");
3430 if (asynch) {
3431 // acquire locks for subsequent manipulations
3432 MutexLockerEx x(bitMapLock(),
3433 Mutex::_no_safepoint_check_flag);
3434 checkpointRootsInitialWork(asynch);
3435 rp->verify_no_references_recorded();
3436 rp->enable_discovery(); // enable ("weak") refs discovery
3437 _collectorState = Marking;
3438 } else {
3439 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3440 // which recognizes if we are a CMS generation, and doesn't try to turn on
3441 // discovery; verify that they aren't meddling.
3442 assert(!rp->discovery_is_atomic(),
3443 "incorrect setting of discovery predicate");
3444 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3445 "ref discovery for this generation kind");
3446 // already have locks
3447 checkpointRootsInitialWork(asynch);
3448 rp->enable_discovery(); // now enable ("weak") refs discovery
3449 _collectorState = Marking;
3450 }
3451 SpecializationStats::print();
3452 }
3453
3454 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3455 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3456 assert(_collectorState == InitialMarking, "just checking");
3457
3458 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3459 // precede our marking with a collection of all
3460 // younger generations to keep floating garbage to a minimum.
3461 // XXX: we won't do this for now -- it's an optimization to be done later.
3462
3463 // already have locks
3464 assert_lock_strong(bitMapLock());
3465 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3466
3467 // Setup the verification and class unloading state for this
3468 // CMS collection cycle.
3469 setup_cms_unloading_and_verification_state();
3470
3471 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3472 PrintGCDetails && Verbose, true, gclog_or_tty);)
3473 if (UseAdaptiveSizePolicy) {
3474 size_policy()->checkpoint_roots_initial_begin();
3475 }
3476
3477 // Reset all the PLAB chunk arrays if necessary.
3478 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3479 reset_survivor_plab_arrays();
3480 }
3481
3482 ResourceMark rm;
3483 HandleMark hm;
3484
3485 FalseClosure falseClosure;
3486 // In the case of a synchronous collection, we will elide the
3487 // remark step, so it's important to catch all the nmethod oops
3488 // in this step.
3489 // The final 'true' flag to gen_process_strong_roots will ensure this.
3490 // If 'async' is true, we can relax the nmethod tracing.
3491 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3492 GenCollectedHeap* gch = GenCollectedHeap::heap();
3493
3494 verify_work_stacks_empty();
3495 verify_overflow_empty();
3496
3497 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3498 // Update the saved marks which may affect the root scans.
3499 gch->save_marks();
3500
3501 // weak reference processing has not started yet.
3502 ref_processor()->set_enqueuing_is_done(false);
3503
3504 {
3505 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3506 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3507 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3508 gch->gen_process_strong_roots(_cmsGen->level(),
3509 true, // younger gens are roots
3510 true, // activate StrongRootsScope
3511 true, // collecting perm gen
3512 SharedHeap::ScanningOption(roots_scanning_options()),
3513 ¬Older,
3514 true, // walk all of code cache if (so & SO_CodeCache)
3515 NULL);
3516 }
3517
3518 // Clear mod-union table; it will be dirtied in the prologue of
3519 // CMS generation per each younger generation collection.
3520
3521 assert(_modUnionTable.isAllClear(),
3522 "Was cleared in most recent final checkpoint phase"
3523 " or no bits are set in the gc_prologue before the start of the next "
3524 "subsequent marking phase.");
3525
3526 // Temporarily disabled, since pre/post-consumption closures don't
3527 // care about precleaned cards
3528 #if 0
3529 {
3530 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3531 (HeapWord*)_virtual_space.high());
3532 _ct->ct_bs()->preclean_dirty_cards(mr);
3533 }
3534 #endif
3535
3536 // Save the end of the used_region of the constituent generations
3537 // to be used to limit the extent of sweep in each generation.
3538 save_sweep_limits();
3539 if (UseAdaptiveSizePolicy) {
3540 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3541 }
3542 verify_overflow_empty();
3543 }
3544
3545 bool CMSCollector::markFromRoots(bool asynch) {
3546 // we might be tempted to assert that:
3547 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3548 // "inconsistent argument?");
3549 // However that wouldn't be right, because it's possible that
3550 // a safepoint is indeed in progress as a younger generation
3551 // stop-the-world GC happens even as we mark in this generation.
3552 assert(_collectorState == Marking, "inconsistent state?");
3553 check_correct_thread_executing();
3554 verify_overflow_empty();
3555
3556 bool res;
3557 if (asynch) {
3558
3559 // Start the timers for adaptive size policy for the concurrent phases
3560 // Do it here so that the foreground MS can use the concurrent
3561 // timer since a foreground MS might has the sweep done concurrently
3562 // or STW.
3563 if (UseAdaptiveSizePolicy) {
3564 size_policy()->concurrent_marking_begin();
3565 }
3566
3567 // Weak ref discovery note: We may be discovering weak
3568 // refs in this generation concurrent (but interleaved) with
3569 // weak ref discovery by a younger generation collector.
3570
3571 CMSTokenSyncWithLocks ts(true, bitMapLock());
3572 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3573 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3574 res = markFromRootsWork(asynch);
3575 if (res) {
3576 _collectorState = Precleaning;
3577 } else { // We failed and a foreground collection wants to take over
3578 assert(_foregroundGCIsActive, "internal state inconsistency");
3579 assert(_restart_addr == NULL, "foreground will restart from scratch");
3580 if (PrintGCDetails) {
3581 gclog_or_tty->print_cr("bailing out to foreground collection");
3582 }
3583 }
3584 if (UseAdaptiveSizePolicy) {
3585 size_policy()->concurrent_marking_end();
3586 }
3587 } else {
3588 assert(SafepointSynchronize::is_at_safepoint(),
3589 "inconsistent with asynch == false");
3590 if (UseAdaptiveSizePolicy) {
3591 size_policy()->ms_collection_marking_begin();
3592 }
3593 // already have locks
3594 res = markFromRootsWork(asynch);
3595 _collectorState = FinalMarking;
3596 if (UseAdaptiveSizePolicy) {
3597 GenCollectedHeap* gch = GenCollectedHeap::heap();
3598 size_policy()->ms_collection_marking_end(gch->gc_cause());
3599 }
3600 }
3601 verify_overflow_empty();
3602 return res;
3603 }
3604
3605 bool CMSCollector::markFromRootsWork(bool asynch) {
3606 // iterate over marked bits in bit map, doing a full scan and mark
3607 // from these roots using the following algorithm:
3608 // . if oop is to the right of the current scan pointer,
3609 // mark corresponding bit (we'll process it later)
3610 // . else (oop is to left of current scan pointer)
3611 // push oop on marking stack
3612 // . drain the marking stack
3613
3614 // Note that when we do a marking step we need to hold the
3615 // bit map lock -- recall that direct allocation (by mutators)
3616 // and promotion (by younger generation collectors) is also
3617 // marking the bit map. [the so-called allocate live policy.]
3618 // Because the implementation of bit map marking is not
3619 // robust wrt simultaneous marking of bits in the same word,
3620 // we need to make sure that there is no such interference
3621 // between concurrent such updates.
3622
3623 // already have locks
3624 assert_lock_strong(bitMapLock());
3625
3626 // Clear the revisit stack, just in case there are any
3627 // obsolete contents from a short-circuited previous CMS cycle.
3628 _revisitStack.reset();
3629 verify_work_stacks_empty();
3630 verify_overflow_empty();
3631 assert(_revisitStack.isEmpty(), "tabula rasa");
3632 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3633 bool result = false;
3634 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3635 result = do_marking_mt(asynch);
3636 } else {
3637 result = do_marking_st(asynch);
3638 }
3639 return result;
3640 }
3641
3642 // Forward decl
3643 class CMSConcMarkingTask;
3644
3645 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3646 CMSCollector* _collector;
3647 CMSConcMarkingTask* _task;
3648 bool _yield;
3649 protected:
3650 virtual void yield();
3651 public:
3652 // "n_threads" is the number of threads to be terminated.
3653 // "queue_set" is a set of work queues of other threads.
3654 // "collector" is the CMS collector associated with this task terminator.
3655 // "yield" indicates whether we need the gang as a whole to yield.
3656 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3657 CMSCollector* collector, bool yield) :
3658 ParallelTaskTerminator(n_threads, queue_set),
3659 _collector(collector),
3660 _yield(yield) { }
3661
3662 void set_task(CMSConcMarkingTask* task) {
3663 _task = task;
3664 }
3665 };
3666
3667 // MT Concurrent Marking Task
3668 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3669 CMSCollector* _collector;
3670 YieldingFlexibleWorkGang* _workers; // the whole gang
3671 int _n_workers; // requested/desired # workers
3672 bool _asynch;
3673 bool _result;
3674 CompactibleFreeListSpace* _cms_space;
3675 CompactibleFreeListSpace* _perm_space;
3676 HeapWord* _global_finger;
3677 HeapWord* _restart_addr;
3678
3679 // Exposed here for yielding support
3680 Mutex* const _bit_map_lock;
3681
3682 // The per thread work queues, available here for stealing
3683 OopTaskQueueSet* _task_queues;
3684 CMSConcMarkingTerminator _term;
3685
3686 public:
3687 CMSConcMarkingTask(CMSCollector* collector,
3688 CompactibleFreeListSpace* cms_space,
3689 CompactibleFreeListSpace* perm_space,
3690 bool asynch, int n_workers,
3691 YieldingFlexibleWorkGang* workers,
3692 OopTaskQueueSet* task_queues):
3693 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3694 _collector(collector),
3695 _cms_space(cms_space),
3696 _perm_space(perm_space),
3697 _asynch(asynch), _n_workers(n_workers), _result(true),
3698 _workers(workers), _task_queues(task_queues),
3699 _term(n_workers, task_queues, _collector, asynch),
3700 _bit_map_lock(collector->bitMapLock())
3701 {
3702 assert(n_workers <= workers->total_workers(),
3703 "Else termination won't work correctly today"); // XXX FIX ME!
3704 _requested_size = n_workers;
3705 _term.set_task(this);
3706 assert(_cms_space->bottom() < _perm_space->bottom(),
3707 "Finger incorrectly initialized below");
3708 _restart_addr = _global_finger = _cms_space->bottom();
3709 }
3710
3711
3712 OopTaskQueueSet* task_queues() { return _task_queues; }
3713
3714 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3715
3716 HeapWord** global_finger_addr() { return &_global_finger; }
3717
3718 CMSConcMarkingTerminator* terminator() { return &_term; }
3719
3720 void work(int i);
3721
3722 virtual void coordinator_yield(); // stuff done by coordinator
3723 bool result() { return _result; }
3724
3725 void reset(HeapWord* ra) {
3726 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3727 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3728 assert(ra < _perm_space->end(), "ra too large");
3729 _restart_addr = _global_finger = ra;
3730 _term.reset_for_reuse();
3731 }
3732
3733 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3734 OopTaskQueue* work_q);
3735
3736 private:
3737 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3738 void do_work_steal(int i);
3739 void bump_global_finger(HeapWord* f);
3740 };
3741
3742 void CMSConcMarkingTerminator::yield() {
3743 if (ConcurrentMarkSweepThread::should_yield() &&
3744 !_collector->foregroundGCIsActive() &&
3745 _yield) {
3746 _task->yield();
3747 } else {
3748 ParallelTaskTerminator::yield();
3749 }
3750 }
3751
3752 ////////////////////////////////////////////////////////////////
3753 // Concurrent Marking Algorithm Sketch
3754 ////////////////////////////////////////////////////////////////
3755 // Until all tasks exhausted (both spaces):
3756 // -- claim next available chunk
3757 // -- bump global finger via CAS
3758 // -- find first object that starts in this chunk
3759 // and start scanning bitmap from that position
3760 // -- scan marked objects for oops
3761 // -- CAS-mark target, and if successful:
3762 // . if target oop is above global finger (volatile read)
3763 // nothing to do
3764 // . if target oop is in chunk and above local finger
3765 // then nothing to do
3766 // . else push on work-queue
3767 // -- Deal with possible overflow issues:
3768 // . local work-queue overflow causes stuff to be pushed on
3769 // global (common) overflow queue
3770 // . always first empty local work queue
3771 // . then get a batch of oops from global work queue if any
3772 // . then do work stealing
3773 // -- When all tasks claimed (both spaces)
3774 // and local work queue empty,
3775 // then in a loop do:
3776 // . check global overflow stack; steal a batch of oops and trace
3777 // . try to steal from other threads oif GOS is empty
3778 // . if neither is available, offer termination
3779 // -- Terminate and return result
3780 //
3781 void CMSConcMarkingTask::work(int i) {
3782 elapsedTimer _timer;
3783 ResourceMark rm;
3784 HandleMark hm;
3785
3786 DEBUG_ONLY(_collector->verify_overflow_empty();)
3787
3788 // Before we begin work, our work queue should be empty
3789 assert(work_queue(i)->size() == 0, "Expected to be empty");
3790 // Scan the bitmap covering _cms_space, tracing through grey objects.
3791 _timer.start();
3792 do_scan_and_mark(i, _cms_space);
3793 _timer.stop();
3794 if (PrintCMSStatistics != 0) {
3795 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3796 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3797 }
3798
3799 // ... do the same for the _perm_space
3800 _timer.reset();
3801 _timer.start();
3802 do_scan_and_mark(i, _perm_space);
3803 _timer.stop();
3804 if (PrintCMSStatistics != 0) {
3805 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3806 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3807 }
3808
3809 // ... do work stealing
3810 _timer.reset();
3811 _timer.start();
3812 do_work_steal(i);
3813 _timer.stop();
3814 if (PrintCMSStatistics != 0) {
3815 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3816 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3817 }
3818 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3819 assert(work_queue(i)->size() == 0, "Should have been emptied");
3820 // Note that under the current task protocol, the
3821 // following assertion is true even of the spaces
3822 // expanded since the completion of the concurrent
3823 // marking. XXX This will likely change under a strict
3824 // ABORT semantics.
3825 assert(_global_finger > _cms_space->end() &&
3826 _global_finger >= _perm_space->end(),
3827 "All tasks have been completed");
3828 DEBUG_ONLY(_collector->verify_overflow_empty();)
3829 }
3830
3831 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3832 HeapWord* read = _global_finger;
3833 HeapWord* cur = read;
3834 while (f > read) {
3835 cur = read;
3836 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3837 if (cur == read) {
3838 // our cas succeeded
3839 assert(_global_finger >= f, "protocol consistency");
3840 break;
3841 }
3842 }
3843 }
3844
3845 // This is really inefficient, and should be redone by
3846 // using (not yet available) block-read and -write interfaces to the
3847 // stack and the work_queue. XXX FIX ME !!!
3848 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3849 OopTaskQueue* work_q) {
3850 // Fast lock-free check
3851 if (ovflw_stk->length() == 0) {
3852 return false;
3853 }
3854 assert(work_q->size() == 0, "Shouldn't steal");
3855 MutexLockerEx ml(ovflw_stk->par_lock(),
3856 Mutex::_no_safepoint_check_flag);
3857 // Grab up to 1/4 the size of the work queue
3858 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3859 (size_t)ParGCDesiredObjsFromOverflowList);
3860 num = MIN2(num, ovflw_stk->length());
3861 for (int i = (int) num; i > 0; i--) {
3862 oop cur = ovflw_stk->pop();
3863 assert(cur != NULL, "Counted wrong?");
3864 work_q->push(cur);
3865 }
3866 return num > 0;
3867 }
3868
3869 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3870 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3871 int n_tasks = pst->n_tasks();
3872 // We allow that there may be no tasks to do here because
3873 // we are restarting after a stack overflow.
3874 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3875 int nth_task = 0;
3876
3877 HeapWord* aligned_start = sp->bottom();
3878 if (sp->used_region().contains(_restart_addr)) {
3879 // Align down to a card boundary for the start of 0th task
3880 // for this space.
3881 aligned_start =
3882 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3883 CardTableModRefBS::card_size);
3884 }
3885
3886 size_t chunk_size = sp->marking_task_size();
3887 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3888 // Having claimed the nth task in this space,
3889 // compute the chunk that it corresponds to:
3890 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3891 aligned_start + (nth_task+1)*chunk_size);
3892 // Try and bump the global finger via a CAS;
3893 // note that we need to do the global finger bump
3894 // _before_ taking the intersection below, because
3895 // the task corresponding to that region will be
3896 // deemed done even if the used_region() expands
3897 // because of allocation -- as it almost certainly will
3898 // during start-up while the threads yield in the
3899 // closure below.
3900 HeapWord* finger = span.end();
3901 bump_global_finger(finger); // atomically
3902 // There are null tasks here corresponding to chunks
3903 // beyond the "top" address of the space.
3904 span = span.intersection(sp->used_region());
3905 if (!span.is_empty()) { // Non-null task
3906 HeapWord* prev_obj;
3907 assert(!span.contains(_restart_addr) || nth_task == 0,
3908 "Inconsistency");
3909 if (nth_task == 0) {
3910 // For the 0th task, we'll not need to compute a block_start.
3911 if (span.contains(_restart_addr)) {
3912 // In the case of a restart because of stack overflow,
3913 // we might additionally skip a chunk prefix.
3914 prev_obj = _restart_addr;
3915 } else {
3916 prev_obj = span.start();
3917 }
3918 } else {
3919 // We want to skip the first object because
3920 // the protocol is to scan any object in its entirety
3921 // that _starts_ in this span; a fortiori, any
3922 // object starting in an earlier span is scanned
3923 // as part of an earlier claimed task.
3924 // Below we use the "careful" version of block_start
3925 // so we do not try to navigate uninitialized objects.
3926 prev_obj = sp->block_start_careful(span.start());
3927 // Below we use a variant of block_size that uses the
3928 // Printezis bits to avoid waiting for allocated
3929 // objects to become initialized/parsable.
3930 while (prev_obj < span.start()) {
3931 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3932 if (sz > 0) {
3933 prev_obj += sz;
3934 } else {
3935 // In this case we may end up doing a bit of redundant
3936 // scanning, but that appears unavoidable, short of
3937 // locking the free list locks; see bug 6324141.
3938 break;
3939 }
3940 }
3941 }
3942 if (prev_obj < span.end()) {
3943 MemRegion my_span = MemRegion(prev_obj, span.end());
3944 // Do the marking work within a non-empty span --
3945 // the last argument to the constructor indicates whether the
3946 // iteration should be incremental with periodic yields.
3947 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3948 &_collector->_markBitMap,
3949 work_queue(i),
3950 &_collector->_markStack,
3951 &_collector->_revisitStack,
3952 _asynch);
3953 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3954 } // else nothing to do for this task
3955 } // else nothing to do for this task
3956 }
3957 // We'd be tempted to assert here that since there are no
3958 // more tasks left to claim in this space, the global_finger
3959 // must exceed space->top() and a fortiori space->end(). However,
3960 // that would not quite be correct because the bumping of
3961 // global_finger occurs strictly after the claiming of a task,
3962 // so by the time we reach here the global finger may not yet
3963 // have been bumped up by the thread that claimed the last
3964 // task.
3965 pst->all_tasks_completed();
3966 }
3967
3968 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
3969 private:
3970 MemRegion _span;
3971 CMSBitMap* _bit_map;
3972 CMSMarkStack* _overflow_stack;
3973 OopTaskQueue* _work_queue;
3974 protected:
3975 DO_OOP_WORK_DEFN
3976 public:
3977 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3978 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
3979 CMSMarkStack* revisit_stack):
3980 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
3981 _span(_collector->_span),
3982 _work_queue(work_queue),
3983 _bit_map(bit_map),
3984 _overflow_stack(overflow_stack)
3985 { }
3986 virtual void do_oop(oop* p);
3987 virtual void do_oop(narrowOop* p);
3988 void trim_queue(size_t max);
3989 void handle_stack_overflow(HeapWord* lost);
3990 };
3991
3992 // Grey object scanning during work stealing phase --
3993 // the salient assumption here is that any references
3994 // that are in these stolen objects being scanned must
3995 // already have been initialized (else they would not have
3996 // been published), so we do not need to check for
3997 // uninitialized objects before pushing here.
3998 void Par_ConcMarkingClosure::do_oop(oop obj) {
3999 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4000 HeapWord* addr = (HeapWord*)obj;
4001 // Check if oop points into the CMS generation
4002 // and is not marked
4003 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4004 // a white object ...
4005 // If we manage to "claim" the object, by being the
4006 // first thread to mark it, then we push it on our
4007 // marking stack
4008 if (_bit_map->par_mark(addr)) { // ... now grey
4009 // push on work queue (grey set)
4010 bool simulate_overflow = false;
4011 NOT_PRODUCT(
4012 if (CMSMarkStackOverflowALot &&
4013 _collector->simulate_overflow()) {
4014 // simulate a stack overflow
4015 simulate_overflow = true;
4016 }
4017 )
4018 if (simulate_overflow ||
4019 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4020 // stack overflow
4021 if (PrintCMSStatistics != 0) {
4022 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4023 SIZE_FORMAT, _overflow_stack->capacity());
4024 }
4025 // We cannot assert that the overflow stack is full because
4026 // it may have been emptied since.
4027 assert(simulate_overflow ||
4028 _work_queue->size() == _work_queue->max_elems(),
4029 "Else push should have succeeded");
4030 handle_stack_overflow(addr);
4031 }
4032 } // Else, some other thread got there first
4033 }
4034 }
4035
4036 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4037 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4038
4039 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4040 while (_work_queue->size() > max) {
4041 oop new_oop;
4042 if (_work_queue->pop_local(new_oop)) {
4043 assert(new_oop->is_oop(), "Should be an oop");
4044 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4045 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4046 assert(new_oop->is_parsable(), "Should be parsable");
4047 new_oop->oop_iterate(this); // do_oop() above
4048 }
4049 }
4050 }
4051
4052 // Upon stack overflow, we discard (part of) the stack,
4053 // remembering the least address amongst those discarded
4054 // in CMSCollector's _restart_address.
4055 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4056 // We need to do this under a mutex to prevent other
4057 // workers from interfering with the work done below.
4058 MutexLockerEx ml(_overflow_stack->par_lock(),
4059 Mutex::_no_safepoint_check_flag);
4060 // Remember the least grey address discarded
4061 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4062 _collector->lower_restart_addr(ra);
4063 _overflow_stack->reset(); // discard stack contents
4064 _overflow_stack->expand(); // expand the stack if possible
4065 }
4066
4067
4068 void CMSConcMarkingTask::do_work_steal(int i) {
4069 OopTaskQueue* work_q = work_queue(i);
4070 oop obj_to_scan;
4071 CMSBitMap* bm = &(_collector->_markBitMap);
4072 CMSMarkStack* ovflw = &(_collector->_markStack);
4073 CMSMarkStack* revisit = &(_collector->_revisitStack);
4074 int* seed = _collector->hash_seed(i);
4075 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw, revisit);
4076 while (true) {
4077 cl.trim_queue(0);
4078 assert(work_q->size() == 0, "Should have been emptied above");
4079 if (get_work_from_overflow_stack(ovflw, work_q)) {
4080 // Can't assert below because the work obtained from the
4081 // overflow stack may already have been stolen from us.
4082 // assert(work_q->size() > 0, "Work from overflow stack");
4083 continue;
4084 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4085 assert(obj_to_scan->is_oop(), "Should be an oop");
4086 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4087 obj_to_scan->oop_iterate(&cl);
4088 } else if (terminator()->offer_termination()) {
4089 assert(work_q->size() == 0, "Impossible!");
4090 break;
4091 }
4092 }
4093 }
4094
4095 // This is run by the CMS (coordinator) thread.
4096 void CMSConcMarkingTask::coordinator_yield() {
4097 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4098 "CMS thread should hold CMS token");
4099 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4100 // First give up the locks, then yield, then re-lock
4101 // We should probably use a constructor/destructor idiom to
4102 // do this unlock/lock or modify the MutexUnlocker class to
4103 // serve our purpose. XXX
4104 assert_lock_strong(_bit_map_lock);
4105 _bit_map_lock->unlock();
4106 ConcurrentMarkSweepThread::desynchronize(true);
4107 ConcurrentMarkSweepThread::acknowledge_yield_request();
4108 _collector->stopTimer();
4109 if (PrintCMSStatistics != 0) {
4110 _collector->incrementYields();
4111 }
4112 _collector->icms_wait();
4113
4114 // It is possible for whichever thread initiated the yield request
4115 // not to get a chance to wake up and take the bitmap lock between
4116 // this thread releasing it and reacquiring it. So, while the
4117 // should_yield() flag is on, let's sleep for a bit to give the
4118 // other thread a chance to wake up. The limit imposed on the number
4119 // of iterations is defensive, to avoid any unforseen circumstances
4120 // putting us into an infinite loop. Since it's always been this
4121 // (coordinator_yield()) method that was observed to cause the
4122 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4123 // which is by default non-zero. For the other seven methods that
4124 // also perform the yield operation, as are using a different
4125 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4126 // can enable the sleeping for those methods too, if necessary.
4127 // See 6442774.
4128 //
4129 // We really need to reconsider the synchronization between the GC
4130 // thread and the yield-requesting threads in the future and we
4131 // should really use wait/notify, which is the recommended
4132 // way of doing this type of interaction. Additionally, we should
4133 // consolidate the eight methods that do the yield operation and they
4134 // are almost identical into one for better maintenability and
4135 // readability. See 6445193.
4136 //
4137 // Tony 2006.06.29
4138 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4139 ConcurrentMarkSweepThread::should_yield() &&
4140 !CMSCollector::foregroundGCIsActive(); ++i) {
4141 os::sleep(Thread::current(), 1, false);
4142 ConcurrentMarkSweepThread::acknowledge_yield_request();
4143 }
4144
4145 ConcurrentMarkSweepThread::synchronize(true);
4146 _bit_map_lock->lock_without_safepoint_check();
4147 _collector->startTimer();
4148 }
4149
4150 bool CMSCollector::do_marking_mt(bool asynch) {
4151 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4152 // In the future this would be determined ergonomically, based
4153 // on #cpu's, # active mutator threads (and load), and mutation rate.
4154 int num_workers = ConcGCThreads;
4155
4156 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4157 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4158
4159 CMSConcMarkingTask tsk(this, cms_space, perm_space,
4160 asynch, num_workers /* number requested XXX */,
4161 conc_workers(), task_queues());
4162
4163 // Since the actual number of workers we get may be different
4164 // from the number we requested above, do we need to do anything different
4165 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4166 // class?? XXX
4167 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4168 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4169
4170 // Refs discovery is already non-atomic.
4171 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4172 // Mutate the Refs discovery so it is MT during the
4173 // multi-threaded marking phase.
4174 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4175 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4176 conc_workers()->start_task(&tsk);
4177 while (tsk.yielded()) {
4178 tsk.coordinator_yield();
4179 conc_workers()->continue_task(&tsk);
4180 }
4181 // If the task was aborted, _restart_addr will be non-NULL
4182 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4183 while (_restart_addr != NULL) {
4184 // XXX For now we do not make use of ABORTED state and have not
4185 // yet implemented the right abort semantics (even in the original
4186 // single-threaded CMS case). That needs some more investigation
4187 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4188 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4189 // If _restart_addr is non-NULL, a marking stack overflow
4190 // occurred; we need to do a fresh marking iteration from the
4191 // indicated restart address.
4192 if (_foregroundGCIsActive && asynch) {
4193 // We may be running into repeated stack overflows, having
4194 // reached the limit of the stack size, while making very
4195 // slow forward progress. It may be best to bail out and
4196 // let the foreground collector do its job.
4197 // Clear _restart_addr, so that foreground GC
4198 // works from scratch. This avoids the headache of
4199 // a "rescan" which would otherwise be needed because
4200 // of the dirty mod union table & card table.
4201 _restart_addr = NULL;
4202 return false;
4203 }
4204 // Adjust the task to restart from _restart_addr
4205 tsk.reset(_restart_addr);
4206 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4207 _restart_addr);
4208 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4209 _restart_addr);
4210 _restart_addr = NULL;
4211 // Get the workers going again
4212 conc_workers()->start_task(&tsk);
4213 while (tsk.yielded()) {
4214 tsk.coordinator_yield();
4215 conc_workers()->continue_task(&tsk);
4216 }
4217 }
4218 assert(tsk.completed(), "Inconsistency");
4219 assert(tsk.result() == true, "Inconsistency");
4220 return true;
4221 }
4222
4223 bool CMSCollector::do_marking_st(bool asynch) {
4224 ResourceMark rm;
4225 HandleMark hm;
4226
4227 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4228 &_markStack, &_revisitStack, CMSYield && asynch);
4229 // the last argument to iterate indicates whether the iteration
4230 // should be incremental with periodic yields.
4231 _markBitMap.iterate(&markFromRootsClosure);
4232 // If _restart_addr is non-NULL, a marking stack overflow
4233 // occurred; we need to do a fresh iteration from the
4234 // indicated restart address.
4235 while (_restart_addr != NULL) {
4236 if (_foregroundGCIsActive && asynch) {
4237 // We may be running into repeated stack overflows, having
4238 // reached the limit of the stack size, while making very
4239 // slow forward progress. It may be best to bail out and
4240 // let the foreground collector do its job.
4241 // Clear _restart_addr, so that foreground GC
4242 // works from scratch. This avoids the headache of
4243 // a "rescan" which would otherwise be needed because
4244 // of the dirty mod union table & card table.
4245 _restart_addr = NULL;
4246 return false; // indicating failure to complete marking
4247 }
4248 // Deal with stack overflow:
4249 // we restart marking from _restart_addr
4250 HeapWord* ra = _restart_addr;
4251 markFromRootsClosure.reset(ra);
4252 _restart_addr = NULL;
4253 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4254 }
4255 return true;
4256 }
4257
4258 void CMSCollector::preclean() {
4259 check_correct_thread_executing();
4260 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4261 verify_work_stacks_empty();
4262 verify_overflow_empty();
4263 _abort_preclean = false;
4264 if (CMSPrecleaningEnabled) {
4265 _eden_chunk_index = 0;
4266 size_t used = get_eden_used();
4267 size_t capacity = get_eden_capacity();
4268 // Don't start sampling unless we will get sufficiently
4269 // many samples.
4270 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4271 * CMSScheduleRemarkEdenPenetration)) {
4272 _start_sampling = true;
4273 } else {
4274 _start_sampling = false;
4275 }
4276 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4277 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4278 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4279 }
4280 CMSTokenSync x(true); // is cms thread
4281 if (CMSPrecleaningEnabled) {
4282 sample_eden();
4283 _collectorState = AbortablePreclean;
4284 } else {
4285 _collectorState = FinalMarking;
4286 }
4287 verify_work_stacks_empty();
4288 verify_overflow_empty();
4289 }
4290
4291 // Try and schedule the remark such that young gen
4292 // occupancy is CMSScheduleRemarkEdenPenetration %.
4293 void CMSCollector::abortable_preclean() {
4294 check_correct_thread_executing();
4295 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4296 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4297
4298 // If Eden's current occupancy is below this threshold,
4299 // immediately schedule the remark; else preclean
4300 // past the next scavenge in an effort to
4301 // schedule the pause as described avove. By choosing
4302 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4303 // we will never do an actual abortable preclean cycle.
4304 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4305 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4306 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4307 // We need more smarts in the abortable preclean
4308 // loop below to deal with cases where allocation
4309 // in young gen is very very slow, and our precleaning
4310 // is running a losing race against a horde of
4311 // mutators intent on flooding us with CMS updates
4312 // (dirty cards).
4313 // One, admittedly dumb, strategy is to give up
4314 // after a certain number of abortable precleaning loops
4315 // or after a certain maximum time. We want to make
4316 // this smarter in the next iteration.
4317 // XXX FIX ME!!! YSR
4318 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4319 while (!(should_abort_preclean() ||
4320 ConcurrentMarkSweepThread::should_terminate())) {
4321 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4322 cumworkdone += workdone;
4323 loops++;
4324 // Voluntarily terminate abortable preclean phase if we have
4325 // been at it for too long.
4326 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4327 loops >= CMSMaxAbortablePrecleanLoops) {
4328 if (PrintGCDetails) {
4329 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4330 }
4331 break;
4332 }
4333 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4334 if (PrintGCDetails) {
4335 gclog_or_tty->print(" CMS: abort preclean due to time ");
4336 }
4337 break;
4338 }
4339 // If we are doing little work each iteration, we should
4340 // take a short break.
4341 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4342 // Sleep for some time, waiting for work to accumulate
4343 stopTimer();
4344 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4345 startTimer();
4346 waited++;
4347 }
4348 }
4349 if (PrintCMSStatistics > 0) {
4350 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4351 loops, waited, cumworkdone);
4352 }
4353 }
4354 CMSTokenSync x(true); // is cms thread
4355 if (_collectorState != Idling) {
4356 assert(_collectorState == AbortablePreclean,
4357 "Spontaneous state transition?");
4358 _collectorState = FinalMarking;
4359 } // Else, a foreground collection completed this CMS cycle.
4360 return;
4361 }
4362
4363 // Respond to an Eden sampling opportunity
4364 void CMSCollector::sample_eden() {
4365 // Make sure a young gc cannot sneak in between our
4366 // reading and recording of a sample.
4367 assert(Thread::current()->is_ConcurrentGC_thread(),
4368 "Only the cms thread may collect Eden samples");
4369 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4370 "Should collect samples while holding CMS token");
4371 if (!_start_sampling) {
4372 return;
4373 }
4374 if (_eden_chunk_array) {
4375 if (_eden_chunk_index < _eden_chunk_capacity) {
4376 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4377 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4378 "Unexpected state of Eden");
4379 // We'd like to check that what we just sampled is an oop-start address;
4380 // however, we cannot do that here since the object may not yet have been
4381 // initialized. So we'll instead do the check when we _use_ this sample
4382 // later.
4383 if (_eden_chunk_index == 0 ||
4384 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4385 _eden_chunk_array[_eden_chunk_index-1])
4386 >= CMSSamplingGrain)) {
4387 _eden_chunk_index++; // commit sample
4388 }
4389 }
4390 }
4391 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4392 size_t used = get_eden_used();
4393 size_t capacity = get_eden_capacity();
4394 assert(used <= capacity, "Unexpected state of Eden");
4395 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4396 _abort_preclean = true;
4397 }
4398 }
4399 }
4400
4401
4402 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4403 assert(_collectorState == Precleaning ||
4404 _collectorState == AbortablePreclean, "incorrect state");
4405 ResourceMark rm;
4406 HandleMark hm;
4407 // Do one pass of scrubbing the discovered reference lists
4408 // to remove any reference objects with strongly-reachable
4409 // referents.
4410 if (clean_refs) {
4411 ReferenceProcessor* rp = ref_processor();
4412 CMSPrecleanRefsYieldClosure yield_cl(this);
4413 assert(rp->span().equals(_span), "Spans should be equal");
4414 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4415 &_markStack, &_revisitStack,
4416 true /* preclean */);
4417 CMSDrainMarkingStackClosure complete_trace(this,
4418 _span, &_markBitMap, &_markStack,
4419 &keep_alive, true /* preclean */);
4420
4421 // We don't want this step to interfere with a young
4422 // collection because we don't want to take CPU
4423 // or memory bandwidth away from the young GC threads
4424 // (which may be as many as there are CPUs).
4425 // Note that we don't need to protect ourselves from
4426 // interference with mutators because they can't
4427 // manipulate the discovered reference lists nor affect
4428 // the computed reachability of the referents, the
4429 // only properties manipulated by the precleaning
4430 // of these reference lists.
4431 stopTimer();
4432 CMSTokenSyncWithLocks x(true /* is cms thread */,
4433 bitMapLock());
4434 startTimer();
4435 sample_eden();
4436
4437 // The following will yield to allow foreground
4438 // collection to proceed promptly. XXX YSR:
4439 // The code in this method may need further
4440 // tweaking for better performance and some restructuring
4441 // for cleaner interfaces.
4442 rp->preclean_discovered_references(
4443 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4444 &yield_cl, should_unload_classes());
4445 }
4446
4447 if (clean_survivor) { // preclean the active survivor space(s)
4448 assert(_young_gen->kind() == Generation::DefNew ||
4449 _young_gen->kind() == Generation::ParNew ||
4450 _young_gen->kind() == Generation::ASParNew,
4451 "incorrect type for cast");
4452 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4453 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4454 &_markBitMap, &_modUnionTable,
4455 &_markStack, &_revisitStack,
4456 true /* precleaning phase */);
4457 stopTimer();
4458 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4459 bitMapLock());
4460 startTimer();
4461 unsigned int before_count =
4462 GenCollectedHeap::heap()->total_collections();
4463 SurvivorSpacePrecleanClosure
4464 sss_cl(this, _span, &_markBitMap, &_markStack,
4465 &pam_cl, before_count, CMSYield);
4466 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4467 dng->from()->object_iterate_careful(&sss_cl);
4468 dng->to()->object_iterate_careful(&sss_cl);
4469 }
4470 MarkRefsIntoAndScanClosure
4471 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4472 &_markStack, &_revisitStack, this, CMSYield,
4473 true /* precleaning phase */);
4474 // CAUTION: The following closure has persistent state that may need to
4475 // be reset upon a decrease in the sequence of addresses it
4476 // processes.
4477 ScanMarkedObjectsAgainCarefullyClosure
4478 smoac_cl(this, _span,
4479 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4480
4481 // Preclean dirty cards in ModUnionTable and CardTable using
4482 // appropriate convergence criterion;
4483 // repeat CMSPrecleanIter times unless we find that
4484 // we are losing.
4485 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4486 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4487 "Bad convergence multiplier");
4488 assert(CMSPrecleanThreshold >= 100,
4489 "Unreasonably low CMSPrecleanThreshold");
4490
4491 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4492 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4493 numIter < CMSPrecleanIter;
4494 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4495 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4496 if (CMSPermGenPrecleaningEnabled) {
4497 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4498 }
4499 if (Verbose && PrintGCDetails) {
4500 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4501 }
4502 // Either there are very few dirty cards, so re-mark
4503 // pause will be small anyway, or our pre-cleaning isn't
4504 // that much faster than the rate at which cards are being
4505 // dirtied, so we might as well stop and re-mark since
4506 // precleaning won't improve our re-mark time by much.
4507 if (curNumCards <= CMSPrecleanThreshold ||
4508 (numIter > 0 &&
4509 (curNumCards * CMSPrecleanDenominator >
4510 lastNumCards * CMSPrecleanNumerator))) {
4511 numIter++;
4512 cumNumCards += curNumCards;
4513 break;
4514 }
4515 }
4516 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4517 if (CMSPermGenPrecleaningEnabled) {
4518 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4519 }
4520 cumNumCards += curNumCards;
4521 if (PrintGCDetails && PrintCMSStatistics != 0) {
4522 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4523 curNumCards, cumNumCards, numIter);
4524 }
4525 return cumNumCards; // as a measure of useful work done
4526 }
4527
4528 // PRECLEANING NOTES:
4529 // Precleaning involves:
4530 // . reading the bits of the modUnionTable and clearing the set bits.
4531 // . For the cards corresponding to the set bits, we scan the
4532 // objects on those cards. This means we need the free_list_lock
4533 // so that we can safely iterate over the CMS space when scanning
4534 // for oops.
4535 // . When we scan the objects, we'll be both reading and setting
4536 // marks in the marking bit map, so we'll need the marking bit map.
4537 // . For protecting _collector_state transitions, we take the CGC_lock.
4538 // Note that any races in the reading of of card table entries by the
4539 // CMS thread on the one hand and the clearing of those entries by the
4540 // VM thread or the setting of those entries by the mutator threads on the
4541 // other are quite benign. However, for efficiency it makes sense to keep
4542 // the VM thread from racing with the CMS thread while the latter is
4543 // dirty card info to the modUnionTable. We therefore also use the
4544 // CGC_lock to protect the reading of the card table and the mod union
4545 // table by the CM thread.
4546 // . We run concurrently with mutator updates, so scanning
4547 // needs to be done carefully -- we should not try to scan
4548 // potentially uninitialized objects.
4549 //
4550 // Locking strategy: While holding the CGC_lock, we scan over and
4551 // reset a maximal dirty range of the mod union / card tables, then lock
4552 // the free_list_lock and bitmap lock to do a full marking, then
4553 // release these locks; and repeat the cycle. This allows for a
4554 // certain amount of fairness in the sharing of these locks between
4555 // the CMS collector on the one hand, and the VM thread and the
4556 // mutators on the other.
4557
4558 // NOTE: preclean_mod_union_table() and preclean_card_table()
4559 // further below are largely identical; if you need to modify
4560 // one of these methods, please check the other method too.
4561
4562 size_t CMSCollector::preclean_mod_union_table(
4563 ConcurrentMarkSweepGeneration* gen,
4564 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4565 verify_work_stacks_empty();
4566 verify_overflow_empty();
4567
4568 // Turn off checking for this method but turn it back on
4569 // selectively. There are yield points in this method
4570 // but it is difficult to turn the checking off just around
4571 // the yield points. It is simpler to selectively turn
4572 // it on.
4573 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4574
4575 // strategy: starting with the first card, accumulate contiguous
4576 // ranges of dirty cards; clear these cards, then scan the region
4577 // covered by these cards.
4578
4579 // Since all of the MUT is committed ahead, we can just use
4580 // that, in case the generations expand while we are precleaning.
4581 // It might also be fine to just use the committed part of the
4582 // generation, but we might potentially miss cards when the
4583 // generation is rapidly expanding while we are in the midst
4584 // of precleaning.
4585 HeapWord* startAddr = gen->reserved().start();
4586 HeapWord* endAddr = gen->reserved().end();
4587
4588 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4589
4590 size_t numDirtyCards, cumNumDirtyCards;
4591 HeapWord *nextAddr, *lastAddr;
4592 for (cumNumDirtyCards = numDirtyCards = 0,
4593 nextAddr = lastAddr = startAddr;
4594 nextAddr < endAddr;
4595 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4596
4597 ResourceMark rm;
4598 HandleMark hm;
4599
4600 MemRegion dirtyRegion;
4601 {
4602 stopTimer();
4603 // Potential yield point
4604 CMSTokenSync ts(true);
4605 startTimer();
4606 sample_eden();
4607 // Get dirty region starting at nextOffset (inclusive),
4608 // simultaneously clearing it.
4609 dirtyRegion =
4610 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4611 assert(dirtyRegion.start() >= nextAddr,
4612 "returned region inconsistent?");
4613 }
4614 // Remember where the next search should begin.
4615 // The returned region (if non-empty) is a right open interval,
4616 // so lastOffset is obtained from the right end of that
4617 // interval.
4618 lastAddr = dirtyRegion.end();
4619 // Should do something more transparent and less hacky XXX
4620 numDirtyCards =
4621 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4622
4623 // We'll scan the cards in the dirty region (with periodic
4624 // yields for foreground GC as needed).
4625 if (!dirtyRegion.is_empty()) {
4626 assert(numDirtyCards > 0, "consistency check");
4627 HeapWord* stop_point = NULL;
4628 stopTimer();
4629 // Potential yield point
4630 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4631 bitMapLock());
4632 startTimer();
4633 {
4634 verify_work_stacks_empty();
4635 verify_overflow_empty();
4636 sample_eden();
4637 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4638 stop_point =
4639 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4640 }
4641 if (stop_point != NULL) {
4642 // The careful iteration stopped early either because it found an
4643 // uninitialized object, or because we were in the midst of an
4644 // "abortable preclean", which should now be aborted. Redirty
4645 // the bits corresponding to the partially-scanned or unscanned
4646 // cards. We'll either restart at the next block boundary or
4647 // abort the preclean.
4648 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4649 (_collectorState == AbortablePreclean && should_abort_preclean()),
4650 "Unparsable objects should only be in perm gen.");
4651 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4652 if (should_abort_preclean()) {
4653 break; // out of preclean loop
4654 } else {
4655 // Compute the next address at which preclean should pick up;
4656 // might need bitMapLock in order to read P-bits.
4657 lastAddr = next_card_start_after_block(stop_point);
4658 }
4659 }
4660 } else {
4661 assert(lastAddr == endAddr, "consistency check");
4662 assert(numDirtyCards == 0, "consistency check");
4663 break;
4664 }
4665 }
4666 verify_work_stacks_empty();
4667 verify_overflow_empty();
4668 return cumNumDirtyCards;
4669 }
4670
4671 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4672 // below are largely identical; if you need to modify
4673 // one of these methods, please check the other method too.
4674
4675 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4676 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4677 // strategy: it's similar to precleamModUnionTable above, in that
4678 // we accumulate contiguous ranges of dirty cards, mark these cards
4679 // precleaned, then scan the region covered by these cards.
4680 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4681 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4682
4683 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4684
4685 size_t numDirtyCards, cumNumDirtyCards;
4686 HeapWord *lastAddr, *nextAddr;
4687
4688 for (cumNumDirtyCards = numDirtyCards = 0,
4689 nextAddr = lastAddr = startAddr;
4690 nextAddr < endAddr;
4691 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4692
4693 ResourceMark rm;
4694 HandleMark hm;
4695
4696 MemRegion dirtyRegion;
4697 {
4698 // See comments in "Precleaning notes" above on why we
4699 // do this locking. XXX Could the locking overheads be
4700 // too high when dirty cards are sparse? [I don't think so.]
4701 stopTimer();
4702 CMSTokenSync x(true); // is cms thread
4703 startTimer();
4704 sample_eden();
4705 // Get and clear dirty region from card table
4706 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4707 MemRegion(nextAddr, endAddr),
4708 true,
4709 CardTableModRefBS::precleaned_card_val());
4710
4711 assert(dirtyRegion.start() >= nextAddr,
4712 "returned region inconsistent?");
4713 }
4714 lastAddr = dirtyRegion.end();
4715 numDirtyCards =
4716 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4717
4718 if (!dirtyRegion.is_empty()) {
4719 stopTimer();
4720 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4721 startTimer();
4722 sample_eden();
4723 verify_work_stacks_empty();
4724 verify_overflow_empty();
4725 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4726 HeapWord* stop_point =
4727 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4728 if (stop_point != NULL) {
4729 // The careful iteration stopped early because it found an
4730 // uninitialized object. Redirty the bits corresponding to the
4731 // partially-scanned or unscanned cards, and start again at the
4732 // next block boundary.
4733 assert(CMSPermGenPrecleaningEnabled ||
4734 (_collectorState == AbortablePreclean && should_abort_preclean()),
4735 "Unparsable objects should only be in perm gen.");
4736 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4737 if (should_abort_preclean()) {
4738 break; // out of preclean loop
4739 } else {
4740 // Compute the next address at which preclean should pick up.
4741 lastAddr = next_card_start_after_block(stop_point);
4742 }
4743 }
4744 } else {
4745 break;
4746 }
4747 }
4748 verify_work_stacks_empty();
4749 verify_overflow_empty();
4750 return cumNumDirtyCards;
4751 }
4752
4753 void CMSCollector::checkpointRootsFinal(bool asynch,
4754 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4755 assert(_collectorState == FinalMarking, "incorrect state transition?");
4756 check_correct_thread_executing();
4757 // world is stopped at this checkpoint
4758 assert(SafepointSynchronize::is_at_safepoint(),
4759 "world should be stopped");
4760 TraceCMSMemoryManagerStats tms(_collectorState);
4761 verify_work_stacks_empty();
4762 verify_overflow_empty();
4763
4764 SpecializationStats::clear();
4765 if (PrintGCDetails) {
4766 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4767 _young_gen->used() / K,
4768 _young_gen->capacity() / K);
4769 }
4770 if (asynch) {
4771 if (CMSScavengeBeforeRemark) {
4772 GenCollectedHeap* gch = GenCollectedHeap::heap();
4773 // Temporarily set flag to false, GCH->do_collection will
4774 // expect it to be false and set to true
4775 FlagSetting fl(gch->_is_gc_active, false);
4776 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4777 PrintGCDetails && Verbose, true, gclog_or_tty);)
4778 int level = _cmsGen->level() - 1;
4779 if (level >= 0) {
4780 gch->do_collection(true, // full (i.e. force, see below)
4781 false, // !clear_all_soft_refs
4782 0, // size
4783 false, // is_tlab
4784 level // max_level
4785 );
4786 }
4787 }
4788 FreelistLocker x(this);
4789 MutexLockerEx y(bitMapLock(),
4790 Mutex::_no_safepoint_check_flag);
4791 assert(!init_mark_was_synchronous, "but that's impossible!");
4792 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4793 } else {
4794 // already have all the locks
4795 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4796 init_mark_was_synchronous);
4797 }
4798 verify_work_stacks_empty();
4799 verify_overflow_empty();
4800 SpecializationStats::print();
4801 }
4802
4803 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4804 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4805
4806 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4807
4808 assert(haveFreelistLocks(), "must have free list locks");
4809 assert_lock_strong(bitMapLock());
4810
4811 if (UseAdaptiveSizePolicy) {
4812 size_policy()->checkpoint_roots_final_begin();
4813 }
4814
4815 ResourceMark rm;
4816 HandleMark hm;
4817
4818 GenCollectedHeap* gch = GenCollectedHeap::heap();
4819
4820 if (should_unload_classes()) {
4821 CodeCache::gc_prologue();
4822 }
4823 assert(haveFreelistLocks(), "must have free list locks");
4824 assert_lock_strong(bitMapLock());
4825
4826 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4827 if (!init_mark_was_synchronous) {
4828 // We might assume that we need not fill TLAB's when
4829 // CMSScavengeBeforeRemark is set, because we may have just done
4830 // a scavenge which would have filled all TLAB's -- and besides
4831 // Eden would be empty. This however may not always be the case --
4832 // for instance although we asked for a scavenge, it may not have
4833 // happened because of a JNI critical section. We probably need
4834 // a policy for deciding whether we can in that case wait until
4835 // the critical section releases and then do the remark following
4836 // the scavenge, and skip it here. In the absence of that policy,
4837 // or of an indication of whether the scavenge did indeed occur,
4838 // we cannot rely on TLAB's having been filled and must do
4839 // so here just in case a scavenge did not happen.
4840 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4841 // Update the saved marks which may affect the root scans.
4842 gch->save_marks();
4843
4844 {
4845 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4846
4847 // Note on the role of the mod union table:
4848 // Since the marker in "markFromRoots" marks concurrently with
4849 // mutators, it is possible for some reachable objects not to have been
4850 // scanned. For instance, an only reference to an object A was
4851 // placed in object B after the marker scanned B. Unless B is rescanned,
4852 // A would be collected. Such updates to references in marked objects
4853 // are detected via the mod union table which is the set of all cards
4854 // dirtied since the first checkpoint in this GC cycle and prior to
4855 // the most recent young generation GC, minus those cleaned up by the
4856 // concurrent precleaning.
4857 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4858 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4859 do_remark_parallel();
4860 } else {
4861 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4862 gclog_or_tty);
4863 do_remark_non_parallel();
4864 }
4865 }
4866 } else {
4867 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4868 // The initial mark was stop-world, so there's no rescanning to
4869 // do; go straight on to the next step below.
4870 }
4871 verify_work_stacks_empty();
4872 verify_overflow_empty();
4873
4874 {
4875 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4876 refProcessingWork(asynch, clear_all_soft_refs);
4877 }
4878 verify_work_stacks_empty();
4879 verify_overflow_empty();
4880
4881 if (should_unload_classes()) {
4882 CodeCache::gc_epilogue();
4883 }
4884
4885 // If we encountered any (marking stack / work queue) overflow
4886 // events during the current CMS cycle, take appropriate
4887 // remedial measures, where possible, so as to try and avoid
4888 // recurrence of that condition.
4889 assert(_markStack.isEmpty(), "No grey objects");
4890 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4891 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4892 if (ser_ovflw > 0) {
4893 if (PrintCMSStatistics != 0) {
4894 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4895 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4896 ", kac_preclean="SIZE_FORMAT")",
4897 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4898 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4899 }
4900 _markStack.expand();
4901 _ser_pmc_remark_ovflw = 0;
4902 _ser_pmc_preclean_ovflw = 0;
4903 _ser_kac_preclean_ovflw = 0;
4904 _ser_kac_ovflw = 0;
4905 }
4906 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4907 if (PrintCMSStatistics != 0) {
4908 gclog_or_tty->print_cr("Work queue overflow (benign) "
4909 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4910 _par_pmc_remark_ovflw, _par_kac_ovflw);
4911 }
4912 _par_pmc_remark_ovflw = 0;
4913 _par_kac_ovflw = 0;
4914 }
4915 if (PrintCMSStatistics != 0) {
4916 if (_markStack._hit_limit > 0) {
4917 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4918 _markStack._hit_limit);
4919 }
4920 if (_markStack._failed_double > 0) {
4921 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4922 " current capacity "SIZE_FORMAT,
4923 _markStack._failed_double,
4924 _markStack.capacity());
4925 }
4926 }
4927 _markStack._hit_limit = 0;
4928 _markStack._failed_double = 0;
4929
4930 // Check that all the klasses have been checked
4931 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
4932
4933 if ((VerifyAfterGC || VerifyDuringGC) &&
4934 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4935 verify_after_remark();
4936 }
4937
4938 // Change under the freelistLocks.
4939 _collectorState = Sweeping;
4940 // Call isAllClear() under bitMapLock
4941 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4942 " final marking");
4943 if (UseAdaptiveSizePolicy) {
4944 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4945 }
4946 }
4947
4948 // Parallel remark task
4949 class CMSParRemarkTask: public AbstractGangTask {
4950 CMSCollector* _collector;
4951 WorkGang* _workers;
4952 int _n_workers;
4953 CompactibleFreeListSpace* _cms_space;
4954 CompactibleFreeListSpace* _perm_space;
4955
4956 // The per-thread work queues, available here for stealing.
4957 OopTaskQueueSet* _task_queues;
4958 ParallelTaskTerminator _term;
4959
4960 public:
4961 CMSParRemarkTask(CMSCollector* collector,
4962 CompactibleFreeListSpace* cms_space,
4963 CompactibleFreeListSpace* perm_space,
4964 int n_workers, WorkGang* workers,
4965 OopTaskQueueSet* task_queues):
4966 AbstractGangTask("Rescan roots and grey objects in parallel"),
4967 _collector(collector),
4968 _cms_space(cms_space), _perm_space(perm_space),
4969 _n_workers(n_workers),
4970 _workers(workers),
4971 _task_queues(task_queues),
4972 _term(workers->total_workers(), task_queues) { }
4973
4974 OopTaskQueueSet* task_queues() { return _task_queues; }
4975
4976 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4977
4978 ParallelTaskTerminator* terminator() { return &_term; }
4979
4980 void work(int i);
4981
4982 private:
4983 // Work method in support of parallel rescan ... of young gen spaces
4984 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4985 ContiguousSpace* space,
4986 HeapWord** chunk_array, size_t chunk_top);
4987
4988 // ... of dirty cards in old space
4989 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4990 Par_MarkRefsIntoAndScanClosure* cl);
4991
4992 // ... work stealing for the above
4993 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4994 };
4995
4996 void CMSParRemarkTask::work(int i) {
4997 elapsedTimer _timer;
4998 ResourceMark rm;
4999 HandleMark hm;
5000
5001 // ---------- rescan from roots --------------
5002 _timer.start();
5003 GenCollectedHeap* gch = GenCollectedHeap::heap();
5004 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5005 _collector->_span, _collector->ref_processor(),
5006 &(_collector->_markBitMap),
5007 work_queue(i), &(_collector->_revisitStack));
5008
5009 // Rescan young gen roots first since these are likely
5010 // coarsely partitioned and may, on that account, constitute
5011 // the critical path; thus, it's best to start off that
5012 // work first.
5013 // ---------- young gen roots --------------
5014 {
5015 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5016 EdenSpace* eden_space = dng->eden();
5017 ContiguousSpace* from_space = dng->from();
5018 ContiguousSpace* to_space = dng->to();
5019
5020 HeapWord** eca = _collector->_eden_chunk_array;
5021 size_t ect = _collector->_eden_chunk_index;
5022 HeapWord** sca = _collector->_survivor_chunk_array;
5023 size_t sct = _collector->_survivor_chunk_index;
5024
5025 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5026 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5027
5028 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
5029 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
5030 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
5031
5032 _timer.stop();
5033 if (PrintCMSStatistics != 0) {
5034 gclog_or_tty->print_cr(
5035 "Finished young gen rescan work in %dth thread: %3.3f sec",
5036 i, _timer.seconds());
5037 }
5038 }
5039
5040 // ---------- remaining roots --------------
5041 _timer.reset();
5042 _timer.start();
5043 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5044 false, // yg was scanned above
5045 false, // this is parallel code
5046 true, // collecting perm gen
5047 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5048 &par_mrias_cl,
5049 true, // walk all of code cache if (so & SO_CodeCache)
5050 NULL);
5051 assert(_collector->should_unload_classes()
5052 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5053 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5054 _timer.stop();
5055 if (PrintCMSStatistics != 0) {
5056 gclog_or_tty->print_cr(
5057 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5058 i, _timer.seconds());
5059 }
5060
5061 // ---------- rescan dirty cards ------------
5062 _timer.reset();
5063 _timer.start();
5064
5065 // Do the rescan tasks for each of the two spaces
5066 // (cms_space and perm_space) in turn.
5067 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
5068 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
5069 _timer.stop();
5070 if (PrintCMSStatistics != 0) {
5071 gclog_or_tty->print_cr(
5072 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5073 i, _timer.seconds());
5074 }
5075
5076 // ---------- steal work from other threads ...
5077 // ---------- ... and drain overflow list.
5078 _timer.reset();
5079 _timer.start();
5080 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5081 _timer.stop();
5082 if (PrintCMSStatistics != 0) {
5083 gclog_or_tty->print_cr(
5084 "Finished work stealing in %dth thread: %3.3f sec",
5085 i, _timer.seconds());
5086 }
5087 }
5088
5089 void
5090 CMSParRemarkTask::do_young_space_rescan(int i,
5091 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5092 HeapWord** chunk_array, size_t chunk_top) {
5093 // Until all tasks completed:
5094 // . claim an unclaimed task
5095 // . compute region boundaries corresponding to task claimed
5096 // using chunk_array
5097 // . par_oop_iterate(cl) over that region
5098
5099 ResourceMark rm;
5100 HandleMark hm;
5101
5102 SequentialSubTasksDone* pst = space->par_seq_tasks();
5103 assert(pst->valid(), "Uninitialized use?");
5104
5105 int nth_task = 0;
5106 int n_tasks = pst->n_tasks();
5107
5108 HeapWord *start, *end;
5109 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5110 // We claimed task # nth_task; compute its boundaries.
5111 if (chunk_top == 0) { // no samples were taken
5112 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5113 start = space->bottom();
5114 end = space->top();
5115 } else if (nth_task == 0) {
5116 start = space->bottom();
5117 end = chunk_array[nth_task];
5118 } else if (nth_task < (jint)chunk_top) {
5119 assert(nth_task >= 1, "Control point invariant");
5120 start = chunk_array[nth_task - 1];
5121 end = chunk_array[nth_task];
5122 } else {
5123 assert(nth_task == (jint)chunk_top, "Control point invariant");
5124 start = chunk_array[chunk_top - 1];
5125 end = space->top();
5126 }
5127 MemRegion mr(start, end);
5128 // Verify that mr is in space
5129 assert(mr.is_empty() || space->used_region().contains(mr),
5130 "Should be in space");
5131 // Verify that "start" is an object boundary
5132 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5133 "Should be an oop");
5134 space->par_oop_iterate(mr, cl);
5135 }
5136 pst->all_tasks_completed();
5137 }
5138
5139 void
5140 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5141 CompactibleFreeListSpace* sp, int i,
5142 Par_MarkRefsIntoAndScanClosure* cl) {
5143 // Until all tasks completed:
5144 // . claim an unclaimed task
5145 // . compute region boundaries corresponding to task claimed
5146 // . transfer dirty bits ct->mut for that region
5147 // . apply rescanclosure to dirty mut bits for that region
5148
5149 ResourceMark rm;
5150 HandleMark hm;
5151
5152 OopTaskQueue* work_q = work_queue(i);
5153 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5154 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5155 // CAUTION: This closure has state that persists across calls to
5156 // the work method dirty_range_iterate_clear() in that it has
5157 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5158 // use of that state in the imbedded UpwardsObjectClosure instance
5159 // assumes that the cards are always iterated (even if in parallel
5160 // by several threads) in monotonically increasing order per each
5161 // thread. This is true of the implementation below which picks
5162 // card ranges (chunks) in monotonically increasing order globally
5163 // and, a-fortiori, in monotonically increasing order per thread
5164 // (the latter order being a subsequence of the former).
5165 // If the work code below is ever reorganized into a more chaotic
5166 // work-partitioning form than the current "sequential tasks"
5167 // paradigm, the use of that persistent state will have to be
5168 // revisited and modified appropriately. See also related
5169 // bug 4756801 work on which should examine this code to make
5170 // sure that the changes there do not run counter to the
5171 // assumptions made here and necessary for correctness and
5172 // efficiency. Note also that this code might yield inefficient
5173 // behaviour in the case of very large objects that span one or
5174 // more work chunks. Such objects would potentially be scanned
5175 // several times redundantly. Work on 4756801 should try and
5176 // address that performance anomaly if at all possible. XXX
5177 MemRegion full_span = _collector->_span;
5178 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5179 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5180 MarkFromDirtyCardsClosure
5181 greyRescanClosure(_collector, full_span, // entire span of interest
5182 sp, bm, work_q, rs, cl);
5183
5184 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5185 assert(pst->valid(), "Uninitialized use?");
5186 int nth_task = 0;
5187 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5188 MemRegion span = sp->used_region();
5189 HeapWord* start_addr = span.start();
5190 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5191 alignment);
5192 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5193 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5194 start_addr, "Check alignment");
5195 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5196 chunk_size, "Check alignment");
5197
5198 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5199 // Having claimed the nth_task, compute corresponding mem-region,
5200 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5201 // The alignment restriction ensures that we do not need any
5202 // synchronization with other gang-workers while setting or
5203 // clearing bits in thus chunk of the MUT.
5204 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5205 start_addr + (nth_task+1)*chunk_size);
5206 // The last chunk's end might be way beyond end of the
5207 // used region. In that case pull back appropriately.
5208 if (this_span.end() > end_addr) {
5209 this_span.set_end(end_addr);
5210 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5211 }
5212 // Iterate over the dirty cards covering this chunk, marking them
5213 // precleaned, and setting the corresponding bits in the mod union
5214 // table. Since we have been careful to partition at Card and MUT-word
5215 // boundaries no synchronization is needed between parallel threads.
5216 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5217 &modUnionClosure);
5218
5219 // Having transferred these marks into the modUnionTable,
5220 // rescan the marked objects on the dirty cards in the modUnionTable.
5221 // Even if this is at a synchronous collection, the initial marking
5222 // may have been done during an asynchronous collection so there
5223 // may be dirty bits in the mod-union table.
5224 _collector->_modUnionTable.dirty_range_iterate_clear(
5225 this_span, &greyRescanClosure);
5226 _collector->_modUnionTable.verifyNoOneBitsInRange(
5227 this_span.start(),
5228 this_span.end());
5229 }
5230 pst->all_tasks_completed(); // declare that i am done
5231 }
5232
5233 // . see if we can share work_queues with ParNew? XXX
5234 void
5235 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5236 int* seed) {
5237 OopTaskQueue* work_q = work_queue(i);
5238 NOT_PRODUCT(int num_steals = 0;)
5239 oop obj_to_scan;
5240 CMSBitMap* bm = &(_collector->_markBitMap);
5241
5242 while (true) {
5243 // Completely finish any left over work from (an) earlier round(s)
5244 cl->trim_queue(0);
5245 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5246 (size_t)ParGCDesiredObjsFromOverflowList);
5247 // Now check if there's any work in the overflow list
5248 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5249 work_q)) {
5250 // found something in global overflow list;
5251 // not yet ready to go stealing work from others.
5252 // We'd like to assert(work_q->size() != 0, ...)
5253 // because we just took work from the overflow list,
5254 // but of course we can't since all of that could have
5255 // been already stolen from us.
5256 // "He giveth and He taketh away."
5257 continue;
5258 }
5259 // Verify that we have no work before we resort to stealing
5260 assert(work_q->size() == 0, "Have work, shouldn't steal");
5261 // Try to steal from other queues that have work
5262 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5263 NOT_PRODUCT(num_steals++;)
5264 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5265 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5266 // Do scanning work
5267 obj_to_scan->oop_iterate(cl);
5268 // Loop around, finish this work, and try to steal some more
5269 } else if (terminator()->offer_termination()) {
5270 break; // nirvana from the infinite cycle
5271 }
5272 }
5273 NOT_PRODUCT(
5274 if (PrintCMSStatistics != 0) {
5275 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5276 }
5277 )
5278 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5279 "Else our work is not yet done");
5280 }
5281
5282 // Return a thread-local PLAB recording array, as appropriate.
5283 void* CMSCollector::get_data_recorder(int thr_num) {
5284 if (_survivor_plab_array != NULL &&
5285 (CMSPLABRecordAlways ||
5286 (_collectorState > Marking && _collectorState < FinalMarking))) {
5287 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5288 ChunkArray* ca = &_survivor_plab_array[thr_num];
5289 ca->reset(); // clear it so that fresh data is recorded
5290 return (void*) ca;
5291 } else {
5292 return NULL;
5293 }
5294 }
5295
5296 // Reset all the thread-local PLAB recording arrays
5297 void CMSCollector::reset_survivor_plab_arrays() {
5298 for (uint i = 0; i < ParallelGCThreads; i++) {
5299 _survivor_plab_array[i].reset();
5300 }
5301 }
5302
5303 // Merge the per-thread plab arrays into the global survivor chunk
5304 // array which will provide the partitioning of the survivor space
5305 // for CMS rescan.
5306 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5307 assert(_survivor_plab_array != NULL, "Error");
5308 assert(_survivor_chunk_array != NULL, "Error");
5309 assert(_collectorState == FinalMarking, "Error");
5310 for (uint j = 0; j < ParallelGCThreads; j++) {
5311 _cursor[j] = 0;
5312 }
5313 HeapWord* top = surv->top();
5314 size_t i;
5315 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5316 HeapWord* min_val = top; // Higher than any PLAB address
5317 uint min_tid = 0; // position of min_val this round
5318 for (uint j = 0; j < ParallelGCThreads; j++) {
5319 ChunkArray* cur_sca = &_survivor_plab_array[j];
5320 if (_cursor[j] == cur_sca->end()) {
5321 continue;
5322 }
5323 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5324 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5325 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5326 if (cur_val < min_val) {
5327 min_tid = j;
5328 min_val = cur_val;
5329 } else {
5330 assert(cur_val < top, "All recorded addresses should be less");
5331 }
5332 }
5333 // At this point min_val and min_tid are respectively
5334 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5335 // and the thread (j) that witnesses that address.
5336 // We record this address in the _survivor_chunk_array[i]
5337 // and increment _cursor[min_tid] prior to the next round i.
5338 if (min_val == top) {
5339 break;
5340 }
5341 _survivor_chunk_array[i] = min_val;
5342 _cursor[min_tid]++;
5343 }
5344 // We are all done; record the size of the _survivor_chunk_array
5345 _survivor_chunk_index = i; // exclusive: [0, i)
5346 if (PrintCMSStatistics > 0) {
5347 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5348 }
5349 // Verify that we used up all the recorded entries
5350 #ifdef ASSERT
5351 size_t total = 0;
5352 for (uint j = 0; j < ParallelGCThreads; j++) {
5353 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5354 total += _cursor[j];
5355 }
5356 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5357 // Check that the merged array is in sorted order
5358 if (total > 0) {
5359 for (size_t i = 0; i < total - 1; i++) {
5360 if (PrintCMSStatistics > 0) {
5361 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5362 i, _survivor_chunk_array[i]);
5363 }
5364 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5365 "Not sorted");
5366 }
5367 }
5368 #endif // ASSERT
5369 }
5370
5371 // Set up the space's par_seq_tasks structure for work claiming
5372 // for parallel rescan of young gen.
5373 // See ParRescanTask where this is currently used.
5374 void
5375 CMSCollector::
5376 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5377 assert(n_threads > 0, "Unexpected n_threads argument");
5378 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5379
5380 // Eden space
5381 {
5382 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5383 assert(!pst->valid(), "Clobbering existing data?");
5384 // Each valid entry in [0, _eden_chunk_index) represents a task.
5385 size_t n_tasks = _eden_chunk_index + 1;
5386 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5387 pst->set_par_threads(n_threads);
5388 pst->set_n_tasks((int)n_tasks);
5389 }
5390
5391 // Merge the survivor plab arrays into _survivor_chunk_array
5392 if (_survivor_plab_array != NULL) {
5393 merge_survivor_plab_arrays(dng->from());
5394 } else {
5395 assert(_survivor_chunk_index == 0, "Error");
5396 }
5397
5398 // To space
5399 {
5400 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5401 assert(!pst->valid(), "Clobbering existing data?");
5402 pst->set_par_threads(n_threads);
5403 pst->set_n_tasks(1);
5404 assert(pst->valid(), "Error");
5405 }
5406
5407 // From space
5408 {
5409 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5410 assert(!pst->valid(), "Clobbering existing data?");
5411 size_t n_tasks = _survivor_chunk_index + 1;
5412 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5413 pst->set_par_threads(n_threads);
5414 pst->set_n_tasks((int)n_tasks);
5415 assert(pst->valid(), "Error");
5416 }
5417 }
5418
5419 // Parallel version of remark
5420 void CMSCollector::do_remark_parallel() {
5421 GenCollectedHeap* gch = GenCollectedHeap::heap();
5422 WorkGang* workers = gch->workers();
5423 assert(workers != NULL, "Need parallel worker threads.");
5424 int n_workers = workers->total_workers();
5425 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5426 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5427
5428 CMSParRemarkTask tsk(this,
5429 cms_space, perm_space,
5430 n_workers, workers, task_queues());
5431
5432 // Set up for parallel process_strong_roots work.
5433 gch->set_par_threads(n_workers);
5434 // We won't be iterating over the cards in the card table updating
5435 // the younger_gen cards, so we shouldn't call the following else
5436 // the verification code as well as subsequent younger_refs_iterate
5437 // code would get confused. XXX
5438 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5439
5440 // The young gen rescan work will not be done as part of
5441 // process_strong_roots (which currently doesn't knw how to
5442 // parallelize such a scan), but rather will be broken up into
5443 // a set of parallel tasks (via the sampling that the [abortable]
5444 // preclean phase did of EdenSpace, plus the [two] tasks of
5445 // scanning the [two] survivor spaces. Further fine-grain
5446 // parallelization of the scanning of the survivor spaces
5447 // themselves, and of precleaning of the younger gen itself
5448 // is deferred to the future.
5449 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5450
5451 // The dirty card rescan work is broken up into a "sequence"
5452 // of parallel tasks (per constituent space) that are dynamically
5453 // claimed by the parallel threads.
5454 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5455 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5456
5457 // It turns out that even when we're using 1 thread, doing the work in a
5458 // separate thread causes wide variance in run times. We can't help this
5459 // in the multi-threaded case, but we special-case n=1 here to get
5460 // repeatable measurements of the 1-thread overhead of the parallel code.
5461 if (n_workers > 1) {
5462 // Make refs discovery MT-safe
5463 ReferenceProcessorMTMutator mt(ref_processor(), true);
5464 GenCollectedHeap::StrongRootsScope srs(gch);
5465 workers->run_task(&tsk);
5466 } else {
5467 GenCollectedHeap::StrongRootsScope srs(gch);
5468 tsk.work(0);
5469 }
5470 gch->set_par_threads(0); // 0 ==> non-parallel.
5471 // restore, single-threaded for now, any preserved marks
5472 // as a result of work_q overflow
5473 restore_preserved_marks_if_any();
5474 }
5475
5476 // Non-parallel version of remark
5477 void CMSCollector::do_remark_non_parallel() {
5478 ResourceMark rm;
5479 HandleMark hm;
5480 GenCollectedHeap* gch = GenCollectedHeap::heap();
5481 MarkRefsIntoAndScanClosure
5482 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5483 &_markStack, &_revisitStack, this,
5484 false /* should_yield */, false /* not precleaning */);
5485 MarkFromDirtyCardsClosure
5486 markFromDirtyCardsClosure(this, _span,
5487 NULL, // space is set further below
5488 &_markBitMap, &_markStack, &_revisitStack,
5489 &mrias_cl);
5490 {
5491 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5492 // Iterate over the dirty cards, setting the corresponding bits in the
5493 // mod union table.
5494 {
5495 ModUnionClosure modUnionClosure(&_modUnionTable);
5496 _ct->ct_bs()->dirty_card_iterate(
5497 _cmsGen->used_region(),
5498 &modUnionClosure);
5499 _ct->ct_bs()->dirty_card_iterate(
5500 _permGen->used_region(),
5501 &modUnionClosure);
5502 }
5503 // Having transferred these marks into the modUnionTable, we just need
5504 // to rescan the marked objects on the dirty cards in the modUnionTable.
5505 // The initial marking may have been done during an asynchronous
5506 // collection so there may be dirty bits in the mod-union table.
5507 const int alignment =
5508 CardTableModRefBS::card_size * BitsPerWord;
5509 {
5510 // ... First handle dirty cards in CMS gen
5511 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5512 MemRegion ur = _cmsGen->used_region();
5513 HeapWord* lb = ur.start();
5514 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5515 MemRegion cms_span(lb, ub);
5516 _modUnionTable.dirty_range_iterate_clear(cms_span,
5517 &markFromDirtyCardsClosure);
5518 verify_work_stacks_empty();
5519 if (PrintCMSStatistics != 0) {
5520 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5521 markFromDirtyCardsClosure.num_dirty_cards());
5522 }
5523 }
5524 {
5525 // .. and then repeat for dirty cards in perm gen
5526 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5527 MemRegion ur = _permGen->used_region();
5528 HeapWord* lb = ur.start();
5529 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5530 MemRegion perm_span(lb, ub);
5531 _modUnionTable.dirty_range_iterate_clear(perm_span,
5532 &markFromDirtyCardsClosure);
5533 verify_work_stacks_empty();
5534 if (PrintCMSStatistics != 0) {
5535 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5536 markFromDirtyCardsClosure.num_dirty_cards());
5537 }
5538 }
5539 }
5540 if (VerifyDuringGC &&
5541 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5542 HandleMark hm; // Discard invalid handles created during verification
5543 Universe::verify(true);
5544 }
5545 {
5546 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5547
5548 verify_work_stacks_empty();
5549
5550 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5551 GenCollectedHeap::StrongRootsScope srs(gch);
5552 gch->gen_process_strong_roots(_cmsGen->level(),
5553 true, // younger gens as roots
5554 false, // use the local StrongRootsScope
5555 true, // collecting perm gen
5556 SharedHeap::ScanningOption(roots_scanning_options()),
5557 &mrias_cl,
5558 true, // walk code active on stacks
5559 NULL);
5560 assert(should_unload_classes()
5561 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5562 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5563 }
5564 verify_work_stacks_empty();
5565 // Restore evacuated mark words, if any, used for overflow list links
5566 if (!CMSOverflowEarlyRestoration) {
5567 restore_preserved_marks_if_any();
5568 }
5569 verify_overflow_empty();
5570 }
5571
5572 ////////////////////////////////////////////////////////
5573 // Parallel Reference Processing Task Proxy Class
5574 ////////////////////////////////////////////////////////
5575 class CMSRefProcTaskProxy: public AbstractGangTask {
5576 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5577 CMSCollector* _collector;
5578 CMSBitMap* _mark_bit_map;
5579 const MemRegion _span;
5580 OopTaskQueueSet* _task_queues;
5581 ParallelTaskTerminator _term;
5582 ProcessTask& _task;
5583
5584 public:
5585 CMSRefProcTaskProxy(ProcessTask& task,
5586 CMSCollector* collector,
5587 const MemRegion& span,
5588 CMSBitMap* mark_bit_map,
5589 int total_workers,
5590 OopTaskQueueSet* task_queues):
5591 AbstractGangTask("Process referents by policy in parallel"),
5592 _task(task),
5593 _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5594 _task_queues(task_queues),
5595 _term(total_workers, task_queues)
5596 {
5597 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5598 "Inconsistency in _span");
5599 }
5600
5601 OopTaskQueueSet* task_queues() { return _task_queues; }
5602
5603 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5604
5605 ParallelTaskTerminator* terminator() { return &_term; }
5606
5607 void do_work_steal(int i,
5608 CMSParDrainMarkingStackClosure* drain,
5609 CMSParKeepAliveClosure* keep_alive,
5610 int* seed);
5611
5612 virtual void work(int i);
5613 };
5614
5615 void CMSRefProcTaskProxy::work(int i) {
5616 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5617 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5618 _mark_bit_map,
5619 &_collector->_revisitStack,
5620 work_queue(i));
5621 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5622 _mark_bit_map,
5623 &_collector->_revisitStack,
5624 work_queue(i));
5625 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5626 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5627 if (_task.marks_oops_alive()) {
5628 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5629 _collector->hash_seed(i));
5630 }
5631 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5632 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5633 }
5634
5635 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5636 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5637 EnqueueTask& _task;
5638
5639 public:
5640 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5641 : AbstractGangTask("Enqueue reference objects in parallel"),
5642 _task(task)
5643 { }
5644
5645 virtual void work(int i)
5646 {
5647 _task.work(i);
5648 }
5649 };
5650
5651 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5652 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5653 OopTaskQueue* work_queue):
5654 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5655 _span(span),
5656 _bit_map(bit_map),
5657 _work_queue(work_queue),
5658 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5659 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5660 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5661 { }
5662
5663 // . see if we can share work_queues with ParNew? XXX
5664 void CMSRefProcTaskProxy::do_work_steal(int i,
5665 CMSParDrainMarkingStackClosure* drain,
5666 CMSParKeepAliveClosure* keep_alive,
5667 int* seed) {
5668 OopTaskQueue* work_q = work_queue(i);
5669 NOT_PRODUCT(int num_steals = 0;)
5670 oop obj_to_scan;
5671
5672 while (true) {
5673 // Completely finish any left over work from (an) earlier round(s)
5674 drain->trim_queue(0);
5675 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5676 (size_t)ParGCDesiredObjsFromOverflowList);
5677 // Now check if there's any work in the overflow list
5678 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5679 work_q)) {
5680 // Found something in global overflow list;
5681 // not yet ready to go stealing work from others.
5682 // We'd like to assert(work_q->size() != 0, ...)
5683 // because we just took work from the overflow list,
5684 // but of course we can't, since all of that might have
5685 // been already stolen from us.
5686 continue;
5687 }
5688 // Verify that we have no work before we resort to stealing
5689 assert(work_q->size() == 0, "Have work, shouldn't steal");
5690 // Try to steal from other queues that have work
5691 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5692 NOT_PRODUCT(num_steals++;)
5693 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5694 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5695 // Do scanning work
5696 obj_to_scan->oop_iterate(keep_alive);
5697 // Loop around, finish this work, and try to steal some more
5698 } else if (terminator()->offer_termination()) {
5699 break; // nirvana from the infinite cycle
5700 }
5701 }
5702 NOT_PRODUCT(
5703 if (PrintCMSStatistics != 0) {
5704 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5705 }
5706 )
5707 }
5708
5709 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5710 {
5711 GenCollectedHeap* gch = GenCollectedHeap::heap();
5712 WorkGang* workers = gch->workers();
5713 assert(workers != NULL, "Need parallel worker threads.");
5714 int n_workers = workers->total_workers();
5715 CMSRefProcTaskProxy rp_task(task, &_collector,
5716 _collector.ref_processor()->span(),
5717 _collector.markBitMap(),
5718 n_workers, _collector.task_queues());
5719 workers->run_task(&rp_task);
5720 }
5721
5722 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5723 {
5724
5725 GenCollectedHeap* gch = GenCollectedHeap::heap();
5726 WorkGang* workers = gch->workers();
5727 assert(workers != NULL, "Need parallel worker threads.");
5728 CMSRefEnqueueTaskProxy enq_task(task);
5729 workers->run_task(&enq_task);
5730 }
5731
5732 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5733
5734 ResourceMark rm;
5735 HandleMark hm;
5736
5737 ReferenceProcessor* rp = ref_processor();
5738 assert(rp->span().equals(_span), "Spans should be equal");
5739 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5740 // Process weak references.
5741 rp->setup_policy(clear_all_soft_refs);
5742 verify_work_stacks_empty();
5743
5744 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5745 &_markStack, &_revisitStack,
5746 false /* !preclean */);
5747 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5748 _span, &_markBitMap, &_markStack,
5749 &cmsKeepAliveClosure, false /* !preclean */);
5750 {
5751 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5752 if (rp->processing_is_mt()) {
5753 CMSRefProcTaskExecutor task_executor(*this);
5754 rp->process_discovered_references(&_is_alive_closure,
5755 &cmsKeepAliveClosure,
5756 &cmsDrainMarkingStackClosure,
5757 &task_executor);
5758 } else {
5759 rp->process_discovered_references(&_is_alive_closure,
5760 &cmsKeepAliveClosure,
5761 &cmsDrainMarkingStackClosure,
5762 NULL);
5763 }
5764 verify_work_stacks_empty();
5765 }
5766
5767 if (should_unload_classes()) {
5768 {
5769 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5770
5771 // Follow SystemDictionary roots and unload classes
5772 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5773
5774 // Follow CodeCache roots and unload any methods marked for unloading
5775 CodeCache::do_unloading(&_is_alive_closure,
5776 &cmsKeepAliveClosure,
5777 purged_class);
5778
5779 cmsDrainMarkingStackClosure.do_void();
5780 verify_work_stacks_empty();
5781
5782 // Update subklass/sibling/implementor links in KlassKlass descendants
5783 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5784 oop k;
5785 while ((k = _revisitStack.pop()) != NULL) {
5786 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5787 &_is_alive_closure,
5788 &cmsKeepAliveClosure);
5789 }
5790 assert(!ClassUnloading ||
5791 (_markStack.isEmpty() && overflow_list_is_empty()),
5792 "Should not have found new reachable objects");
5793 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5794 cmsDrainMarkingStackClosure.do_void();
5795 verify_work_stacks_empty();
5796 }
5797
5798 {
5799 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5800 // Now clean up stale oops in SymbolTable and StringTable
5801 SymbolTable::unlink(&_is_alive_closure);
5802 StringTable::unlink(&_is_alive_closure);
5803 }
5804 }
5805
5806 verify_work_stacks_empty();
5807 // Restore any preserved marks as a result of mark stack or
5808 // work queue overflow
5809 restore_preserved_marks_if_any(); // done single-threaded for now
5810
5811 rp->set_enqueuing_is_done(true);
5812 if (rp->processing_is_mt()) {
5813 CMSRefProcTaskExecutor task_executor(*this);
5814 rp->enqueue_discovered_references(&task_executor);
5815 } else {
5816 rp->enqueue_discovered_references(NULL);
5817 }
5818 rp->verify_no_references_recorded();
5819 assert(!rp->discovery_enabled(), "should have been disabled");
5820
5821 // JVMTI object tagging is based on JNI weak refs. If any of these
5822 // refs were cleared then JVMTI needs to update its maps and
5823 // maybe post ObjectFrees to agents.
5824 JvmtiExport::cms_ref_processing_epilogue();
5825 }
5826
5827 #ifndef PRODUCT
5828 void CMSCollector::check_correct_thread_executing() {
5829 Thread* t = Thread::current();
5830 // Only the VM thread or the CMS thread should be here.
5831 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5832 "Unexpected thread type");
5833 // If this is the vm thread, the foreground process
5834 // should not be waiting. Note that _foregroundGCIsActive is
5835 // true while the foreground collector is waiting.
5836 if (_foregroundGCShouldWait) {
5837 // We cannot be the VM thread
5838 assert(t->is_ConcurrentGC_thread(),
5839 "Should be CMS thread");
5840 } else {
5841 // We can be the CMS thread only if we are in a stop-world
5842 // phase of CMS collection.
5843 if (t->is_ConcurrentGC_thread()) {
5844 assert(_collectorState == InitialMarking ||
5845 _collectorState == FinalMarking,
5846 "Should be a stop-world phase");
5847 // The CMS thread should be holding the CMS_token.
5848 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5849 "Potential interference with concurrently "
5850 "executing VM thread");
5851 }
5852 }
5853 }
5854 #endif
5855
5856 void CMSCollector::sweep(bool asynch) {
5857 assert(_collectorState == Sweeping, "just checking");
5858 check_correct_thread_executing();
5859 verify_work_stacks_empty();
5860 verify_overflow_empty();
5861 increment_sweep_count();
5862 TraceCMSMemoryManagerStats tms(_collectorState);
5863
5864 _inter_sweep_timer.stop();
5865 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5866 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5867
5868 // PermGen verification support: If perm gen sweeping is disabled in
5869 // this cycle, we preserve the perm gen object "deadness" information
5870 // in the perm_gen_verify_bit_map. In order to do that we traverse
5871 // all blocks in perm gen and mark all dead objects.
5872 if (verifying() && !should_unload_classes()) {
5873 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5874 "Should have already been allocated");
5875 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5876 markBitMap(), perm_gen_verify_bit_map());
5877 if (asynch) {
5878 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5879 bitMapLock());
5880 _permGen->cmsSpace()->blk_iterate(&mdo);
5881 } else {
5882 // In the case of synchronous sweep, we already have
5883 // the requisite locks/tokens.
5884 _permGen->cmsSpace()->blk_iterate(&mdo);
5885 }
5886 }
5887
5888 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5889 _intra_sweep_timer.reset();
5890 _intra_sweep_timer.start();
5891 if (asynch) {
5892 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5893 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5894 // First sweep the old gen then the perm gen
5895 {
5896 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5897 bitMapLock());
5898 sweepWork(_cmsGen, asynch);
5899 }
5900
5901 // Now repeat for perm gen
5902 if (should_unload_classes()) {
5903 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5904 bitMapLock());
5905 sweepWork(_permGen, asynch);
5906 }
5907
5908 // Update Universe::_heap_*_at_gc figures.
5909 // We need all the free list locks to make the abstract state
5910 // transition from Sweeping to Resetting. See detailed note
5911 // further below.
5912 {
5913 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5914 _permGen->freelistLock());
5915 // Update heap occupancy information which is used as
5916 // input to soft ref clearing policy at the next gc.
5917 Universe::update_heap_info_at_gc();
5918 _collectorState = Resizing;
5919 }
5920 } else {
5921 // already have needed locks
5922 sweepWork(_cmsGen, asynch);
5923
5924 if (should_unload_classes()) {
5925 sweepWork(_permGen, asynch);
5926 }
5927 // Update heap occupancy information which is used as
5928 // input to soft ref clearing policy at the next gc.
5929 Universe::update_heap_info_at_gc();
5930 _collectorState = Resizing;
5931 }
5932 verify_work_stacks_empty();
5933 verify_overflow_empty();
5934
5935 _intra_sweep_timer.stop();
5936 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5937
5938 _inter_sweep_timer.reset();
5939 _inter_sweep_timer.start();
5940
5941 update_time_of_last_gc(os::javaTimeMillis());
5942
5943 // NOTE on abstract state transitions:
5944 // Mutators allocate-live and/or mark the mod-union table dirty
5945 // based on the state of the collection. The former is done in
5946 // the interval [Marking, Sweeping] and the latter in the interval
5947 // [Marking, Sweeping). Thus the transitions into the Marking state
5948 // and out of the Sweeping state must be synchronously visible
5949 // globally to the mutators.
5950 // The transition into the Marking state happens with the world
5951 // stopped so the mutators will globally see it. Sweeping is
5952 // done asynchronously by the background collector so the transition
5953 // from the Sweeping state to the Resizing state must be done
5954 // under the freelistLock (as is the check for whether to
5955 // allocate-live and whether to dirty the mod-union table).
5956 assert(_collectorState == Resizing, "Change of collector state to"
5957 " Resizing must be done under the freelistLocks (plural)");
5958
5959 // Now that sweeping has been completed, if the GCH's
5960 // incremental_collection_will_fail flag is set, clear it,
5961 // thus inviting a younger gen collection to promote into
5962 // this generation. If such a promotion may still fail,
5963 // the flag will be set again when a young collection is
5964 // attempted.
5965 // I think the incremental_collection_will_fail flag's use
5966 // is specific to a 2 generation collection policy, so i'll
5967 // assert that that's the configuration we are operating within.
5968 // The use of the flag can and should be generalized appropriately
5969 // in the future to deal with a general n-generation system.
5970
5971 GenCollectedHeap* gch = GenCollectedHeap::heap();
5972 assert(gch->collector_policy()->is_two_generation_policy(),
5973 "Resetting of incremental_collection_will_fail flag"
5974 " may be incorrect otherwise");
5975 gch->clear_incremental_collection_will_fail();
5976 gch->update_full_collections_completed(_collection_count_start);
5977 }
5978
5979 // FIX ME!!! Looks like this belongs in CFLSpace, with
5980 // CMSGen merely delegating to it.
5981 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5982 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5983 HeapWord* minAddr = _cmsSpace->bottom();
5984 HeapWord* largestAddr =
5985 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5986 if (largestAddr == NULL) {
5987 // The dictionary appears to be empty. In this case
5988 // try to coalesce at the end of the heap.
5989 largestAddr = _cmsSpace->end();
5990 }
5991 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5992 size_t nearLargestOffset =
5993 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5994 if (PrintFLSStatistics != 0) {
5995 gclog_or_tty->print_cr(
5996 "CMS: Large Block: " PTR_FORMAT ";"
5997 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5998 largestAddr,
5999 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6000 }
6001 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6002 }
6003
6004 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6005 return addr >= _cmsSpace->nearLargestChunk();
6006 }
6007
6008 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6009 return _cmsSpace->find_chunk_at_end();
6010 }
6011
6012 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6013 bool full) {
6014 // The next lower level has been collected. Gather any statistics
6015 // that are of interest at this point.
6016 if (!full && (current_level + 1) == level()) {
6017 // Gather statistics on the young generation collection.
6018 collector()->stats().record_gc0_end(used());
6019 }
6020 }
6021
6022 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6023 GenCollectedHeap* gch = GenCollectedHeap::heap();
6024 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6025 "Wrong type of heap");
6026 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6027 gch->gen_policy()->size_policy();
6028 assert(sp->is_gc_cms_adaptive_size_policy(),
6029 "Wrong type of size policy");
6030 return sp;
6031 }
6032
6033 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6034 if (PrintGCDetails && Verbose) {
6035 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6036 }
6037 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6038 _debug_collection_type =
6039 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6040 if (PrintGCDetails && Verbose) {
6041 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6042 }
6043 }
6044
6045 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6046 bool asynch) {
6047 // We iterate over the space(s) underlying this generation,
6048 // checking the mark bit map to see if the bits corresponding
6049 // to specific blocks are marked or not. Blocks that are
6050 // marked are live and are not swept up. All remaining blocks
6051 // are swept up, with coalescing on-the-fly as we sweep up
6052 // contiguous free and/or garbage blocks:
6053 // We need to ensure that the sweeper synchronizes with allocators
6054 // and stop-the-world collectors. In particular, the following
6055 // locks are used:
6056 // . CMS token: if this is held, a stop the world collection cannot occur
6057 // . freelistLock: if this is held no allocation can occur from this
6058 // generation by another thread
6059 // . bitMapLock: if this is held, no other thread can access or update
6060 //
6061
6062 // Note that we need to hold the freelistLock if we use
6063 // block iterate below; else the iterator might go awry if
6064 // a mutator (or promotion) causes block contents to change
6065 // (for instance if the allocator divvies up a block).
6066 // If we hold the free list lock, for all practical purposes
6067 // young generation GC's can't occur (they'll usually need to
6068 // promote), so we might as well prevent all young generation
6069 // GC's while we do a sweeping step. For the same reason, we might
6070 // as well take the bit map lock for the entire duration
6071
6072 // check that we hold the requisite locks
6073 assert(have_cms_token(), "Should hold cms token");
6074 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6075 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6076 "Should possess CMS token to sweep");
6077 assert_lock_strong(gen->freelistLock());
6078 assert_lock_strong(bitMapLock());
6079
6080 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6081 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6082 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6083 _inter_sweep_estimate.padded_average(),
6084 _intra_sweep_estimate.padded_average());
6085 gen->setNearLargestChunk();
6086
6087 {
6088 SweepClosure sweepClosure(this, gen, &_markBitMap,
6089 CMSYield && asynch);
6090 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6091 // We need to free-up/coalesce garbage/blocks from a
6092 // co-terminal free run. This is done in the SweepClosure
6093 // destructor; so, do not remove this scope, else the
6094 // end-of-sweep-census below will be off by a little bit.
6095 }
6096 gen->cmsSpace()->sweep_completed();
6097 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6098 if (should_unload_classes()) { // unloaded classes this cycle,
6099 _concurrent_cycles_since_last_unload = 0; // ... reset count
6100 } else { // did not unload classes,
6101 _concurrent_cycles_since_last_unload++; // ... increment count
6102 }
6103 }
6104
6105 // Reset CMS data structures (for now just the marking bit map)
6106 // preparatory for the next cycle.
6107 void CMSCollector::reset(bool asynch) {
6108 GenCollectedHeap* gch = GenCollectedHeap::heap();
6109 CMSAdaptiveSizePolicy* sp = size_policy();
6110 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6111 if (asynch) {
6112 CMSTokenSyncWithLocks ts(true, bitMapLock());
6113
6114 // If the state is not "Resetting", the foreground thread
6115 // has done a collection and the resetting.
6116 if (_collectorState != Resetting) {
6117 assert(_collectorState == Idling, "The state should only change"
6118 " because the foreground collector has finished the collection");
6119 return;
6120 }
6121
6122 // Clear the mark bitmap (no grey objects to start with)
6123 // for the next cycle.
6124 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6125 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6126
6127 HeapWord* curAddr = _markBitMap.startWord();
6128 while (curAddr < _markBitMap.endWord()) {
6129 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6130 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6131 _markBitMap.clear_large_range(chunk);
6132 if (ConcurrentMarkSweepThread::should_yield() &&
6133 !foregroundGCIsActive() &&
6134 CMSYield) {
6135 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6136 "CMS thread should hold CMS token");
6137 assert_lock_strong(bitMapLock());
6138 bitMapLock()->unlock();
6139 ConcurrentMarkSweepThread::desynchronize(true);
6140 ConcurrentMarkSweepThread::acknowledge_yield_request();
6141 stopTimer();
6142 if (PrintCMSStatistics != 0) {
6143 incrementYields();
6144 }
6145 icms_wait();
6146
6147 // See the comment in coordinator_yield()
6148 for (unsigned i = 0; i < CMSYieldSleepCount &&
6149 ConcurrentMarkSweepThread::should_yield() &&
6150 !CMSCollector::foregroundGCIsActive(); ++i) {
6151 os::sleep(Thread::current(), 1, false);
6152 ConcurrentMarkSweepThread::acknowledge_yield_request();
6153 }
6154
6155 ConcurrentMarkSweepThread::synchronize(true);
6156 bitMapLock()->lock_without_safepoint_check();
6157 startTimer();
6158 }
6159 curAddr = chunk.end();
6160 }
6161 // A successful mostly concurrent collection has been done.
6162 // Because only the full (i.e., concurrent mode failure) collections
6163 // are being measured for gc overhead limits, clean the "near" flag
6164 // and count.
6165 sp->reset_gc_overhead_limit_count();
6166 _collectorState = Idling;
6167 } else {
6168 // already have the lock
6169 assert(_collectorState == Resetting, "just checking");
6170 assert_lock_strong(bitMapLock());
6171 _markBitMap.clear_all();
6172 _collectorState = Idling;
6173 }
6174
6175 // Stop incremental mode after a cycle completes, so that any future cycles
6176 // are triggered by allocation.
6177 stop_icms();
6178
6179 NOT_PRODUCT(
6180 if (RotateCMSCollectionTypes) {
6181 _cmsGen->rotate_debug_collection_type();
6182 }
6183 )
6184 }
6185
6186 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6187 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6188 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6189 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6190 TraceCollectorStats tcs(counters());
6191
6192 switch (op) {
6193 case CMS_op_checkpointRootsInitial: {
6194 checkpointRootsInitial(true); // asynch
6195 if (PrintGC) {
6196 _cmsGen->printOccupancy("initial-mark");
6197 }
6198 break;
6199 }
6200 case CMS_op_checkpointRootsFinal: {
6201 checkpointRootsFinal(true, // asynch
6202 false, // !clear_all_soft_refs
6203 false); // !init_mark_was_synchronous
6204 if (PrintGC) {
6205 _cmsGen->printOccupancy("remark");
6206 }
6207 break;
6208 }
6209 default:
6210 fatal("No such CMS_op");
6211 }
6212 }
6213
6214 #ifndef PRODUCT
6215 size_t const CMSCollector::skip_header_HeapWords() {
6216 return FreeChunk::header_size();
6217 }
6218
6219 // Try and collect here conditions that should hold when
6220 // CMS thread is exiting. The idea is that the foreground GC
6221 // thread should not be blocked if it wants to terminate
6222 // the CMS thread and yet continue to run the VM for a while
6223 // after that.
6224 void CMSCollector::verify_ok_to_terminate() const {
6225 assert(Thread::current()->is_ConcurrentGC_thread(),
6226 "should be called by CMS thread");
6227 assert(!_foregroundGCShouldWait, "should be false");
6228 // We could check here that all the various low-level locks
6229 // are not held by the CMS thread, but that is overkill; see
6230 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6231 // is checked.
6232 }
6233 #endif
6234
6235 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6236 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6237 "missing Printezis mark?");
6238 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6239 size_t size = pointer_delta(nextOneAddr + 1, addr);
6240 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6241 "alignment problem");
6242 assert(size >= 3, "Necessary for Printezis marks to work");
6243 return size;
6244 }
6245
6246 // A variant of the above (block_size_using_printezis_bits()) except
6247 // that we return 0 if the P-bits are not yet set.
6248 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6249 if (_markBitMap.isMarked(addr)) {
6250 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6251 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6252 size_t size = pointer_delta(nextOneAddr + 1, addr);
6253 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6254 "alignment problem");
6255 assert(size >= 3, "Necessary for Printezis marks to work");
6256 return size;
6257 } else {
6258 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6259 return 0;
6260 }
6261 }
6262
6263 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6264 size_t sz = 0;
6265 oop p = (oop)addr;
6266 if (p->klass_or_null() != NULL && p->is_parsable()) {
6267 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6268 } else {
6269 sz = block_size_using_printezis_bits(addr);
6270 }
6271 assert(sz > 0, "size must be nonzero");
6272 HeapWord* next_block = addr + sz;
6273 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6274 CardTableModRefBS::card_size);
6275 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6276 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6277 "must be different cards");
6278 return next_card;
6279 }
6280
6281
6282 // CMS Bit Map Wrapper /////////////////////////////////////////
6283
6284 // Construct a CMS bit map infrastructure, but don't create the
6285 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6286 // further below.
6287 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6288 _bm(),
6289 _shifter(shifter),
6290 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6291 {
6292 _bmStartWord = 0;
6293 _bmWordSize = 0;
6294 }
6295
6296 bool CMSBitMap::allocate(MemRegion mr) {
6297 _bmStartWord = mr.start();
6298 _bmWordSize = mr.word_size();
6299 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6300 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6301 if (!brs.is_reserved()) {
6302 warning("CMS bit map allocation failure");
6303 return false;
6304 }
6305 // For now we'll just commit all of the bit map up fromt.
6306 // Later on we'll try to be more parsimonious with swap.
6307 if (!_virtual_space.initialize(brs, brs.size())) {
6308 warning("CMS bit map backing store failure");
6309 return false;
6310 }
6311 assert(_virtual_space.committed_size() == brs.size(),
6312 "didn't reserve backing store for all of CMS bit map?");
6313 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6314 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6315 _bmWordSize, "inconsistency in bit map sizing");
6316 _bm.set_size(_bmWordSize >> _shifter);
6317
6318 // bm.clear(); // can we rely on getting zero'd memory? verify below
6319 assert(isAllClear(),
6320 "Expected zero'd memory from ReservedSpace constructor");
6321 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6322 "consistency check");
6323 return true;
6324 }
6325
6326 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6327 HeapWord *next_addr, *end_addr, *last_addr;
6328 assert_locked();
6329 assert(covers(mr), "out-of-range error");
6330 // XXX assert that start and end are appropriately aligned
6331 for (next_addr = mr.start(), end_addr = mr.end();
6332 next_addr < end_addr; next_addr = last_addr) {
6333 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6334 last_addr = dirty_region.end();
6335 if (!dirty_region.is_empty()) {
6336 cl->do_MemRegion(dirty_region);
6337 } else {
6338 assert(last_addr == end_addr, "program logic");
6339 return;
6340 }
6341 }
6342 }
6343
6344 #ifndef PRODUCT
6345 void CMSBitMap::assert_locked() const {
6346 CMSLockVerifier::assert_locked(lock());
6347 }
6348
6349 bool CMSBitMap::covers(MemRegion mr) const {
6350 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6351 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6352 "size inconsistency");
6353 return (mr.start() >= _bmStartWord) &&
6354 (mr.end() <= endWord());
6355 }
6356
6357 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6358 return (start >= _bmStartWord && (start + size) <= endWord());
6359 }
6360
6361 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6362 // verify that there are no 1 bits in the interval [left, right)
6363 FalseBitMapClosure falseBitMapClosure;
6364 iterate(&falseBitMapClosure, left, right);
6365 }
6366
6367 void CMSBitMap::region_invariant(MemRegion mr)
6368 {
6369 assert_locked();
6370 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6371 assert(!mr.is_empty(), "unexpected empty region");
6372 assert(covers(mr), "mr should be covered by bit map");
6373 // convert address range into offset range
6374 size_t start_ofs = heapWordToOffset(mr.start());
6375 // Make sure that end() is appropriately aligned
6376 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6377 (1 << (_shifter+LogHeapWordSize))),
6378 "Misaligned mr.end()");
6379 size_t end_ofs = heapWordToOffset(mr.end());
6380 assert(end_ofs > start_ofs, "Should mark at least one bit");
6381 }
6382
6383 #endif
6384
6385 bool CMSMarkStack::allocate(size_t size) {
6386 // allocate a stack of the requisite depth
6387 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6388 size * sizeof(oop)));
6389 if (!rs.is_reserved()) {
6390 warning("CMSMarkStack allocation failure");
6391 return false;
6392 }
6393 if (!_virtual_space.initialize(rs, rs.size())) {
6394 warning("CMSMarkStack backing store failure");
6395 return false;
6396 }
6397 assert(_virtual_space.committed_size() == rs.size(),
6398 "didn't reserve backing store for all of CMS stack?");
6399 _base = (oop*)(_virtual_space.low());
6400 _index = 0;
6401 _capacity = size;
6402 NOT_PRODUCT(_max_depth = 0);
6403 return true;
6404 }
6405
6406 // XXX FIX ME !!! In the MT case we come in here holding a
6407 // leaf lock. For printing we need to take a further lock
6408 // which has lower rank. We need to recallibrate the two
6409 // lock-ranks involved in order to be able to rpint the
6410 // messages below. (Or defer the printing to the caller.
6411 // For now we take the expedient path of just disabling the
6412 // messages for the problematic case.)
6413 void CMSMarkStack::expand() {
6414 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6415 if (_capacity == MarkStackSizeMax) {
6416 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6417 // We print a warning message only once per CMS cycle.
6418 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6419 }
6420 return;
6421 }
6422 // Double capacity if possible
6423 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6424 // Do not give up existing stack until we have managed to
6425 // get the double capacity that we desired.
6426 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6427 new_capacity * sizeof(oop)));
6428 if (rs.is_reserved()) {
6429 // Release the backing store associated with old stack
6430 _virtual_space.release();
6431 // Reinitialize virtual space for new stack
6432 if (!_virtual_space.initialize(rs, rs.size())) {
6433 fatal("Not enough swap for expanded marking stack");
6434 }
6435 _base = (oop*)(_virtual_space.low());
6436 _index = 0;
6437 _capacity = new_capacity;
6438 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6439 // Failed to double capacity, continue;
6440 // we print a detail message only once per CMS cycle.
6441 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6442 SIZE_FORMAT"K",
6443 _capacity / K, new_capacity / K);
6444 }
6445 }
6446
6447
6448 // Closures
6449 // XXX: there seems to be a lot of code duplication here;
6450 // should refactor and consolidate common code.
6451
6452 // This closure is used to mark refs into the CMS generation in
6453 // the CMS bit map. Called at the first checkpoint. This closure
6454 // assumes that we do not need to re-mark dirty cards; if the CMS
6455 // generation on which this is used is not an oldest (modulo perm gen)
6456 // generation then this will lose younger_gen cards!
6457
6458 MarkRefsIntoClosure::MarkRefsIntoClosure(
6459 MemRegion span, CMSBitMap* bitMap):
6460 _span(span),
6461 _bitMap(bitMap)
6462 {
6463 assert(_ref_processor == NULL, "deliberately left NULL");
6464 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6465 }
6466
6467 void MarkRefsIntoClosure::do_oop(oop obj) {
6468 // if p points into _span, then mark corresponding bit in _markBitMap
6469 assert(obj->is_oop(), "expected an oop");
6470 HeapWord* addr = (HeapWord*)obj;
6471 if (_span.contains(addr)) {
6472 // this should be made more efficient
6473 _bitMap->mark(addr);
6474 }
6475 }
6476
6477 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6478 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6479
6480 // A variant of the above, used for CMS marking verification.
6481 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6482 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6483 _span(span),
6484 _verification_bm(verification_bm),
6485 _cms_bm(cms_bm)
6486 {
6487 assert(_ref_processor == NULL, "deliberately left NULL");
6488 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6489 }
6490
6491 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6492 // if p points into _span, then mark corresponding bit in _markBitMap
6493 assert(obj->is_oop(), "expected an oop");
6494 HeapWord* addr = (HeapWord*)obj;
6495 if (_span.contains(addr)) {
6496 _verification_bm->mark(addr);
6497 if (!_cms_bm->isMarked(addr)) {
6498 oop(addr)->print();
6499 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6500 fatal("... aborting");
6501 }
6502 }
6503 }
6504
6505 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6506 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6507
6508 //////////////////////////////////////////////////
6509 // MarkRefsIntoAndScanClosure
6510 //////////////////////////////////////////////////
6511
6512 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6513 ReferenceProcessor* rp,
6514 CMSBitMap* bit_map,
6515 CMSBitMap* mod_union_table,
6516 CMSMarkStack* mark_stack,
6517 CMSMarkStack* revisit_stack,
6518 CMSCollector* collector,
6519 bool should_yield,
6520 bool concurrent_precleaning):
6521 _collector(collector),
6522 _span(span),
6523 _bit_map(bit_map),
6524 _mark_stack(mark_stack),
6525 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6526 mark_stack, revisit_stack, concurrent_precleaning),
6527 _yield(should_yield),
6528 _concurrent_precleaning(concurrent_precleaning),
6529 _freelistLock(NULL)
6530 {
6531 _ref_processor = rp;
6532 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6533 }
6534
6535 // This closure is used to mark refs into the CMS generation at the
6536 // second (final) checkpoint, and to scan and transitively follow
6537 // the unmarked oops. It is also used during the concurrent precleaning
6538 // phase while scanning objects on dirty cards in the CMS generation.
6539 // The marks are made in the marking bit map and the marking stack is
6540 // used for keeping the (newly) grey objects during the scan.
6541 // The parallel version (Par_...) appears further below.
6542 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6543 if (obj != NULL) {
6544 assert(obj->is_oop(), "expected an oop");
6545 HeapWord* addr = (HeapWord*)obj;
6546 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6547 assert(_collector->overflow_list_is_empty(),
6548 "overflow list should be empty");
6549 if (_span.contains(addr) &&
6550 !_bit_map->isMarked(addr)) {
6551 // mark bit map (object is now grey)
6552 _bit_map->mark(addr);
6553 // push on marking stack (stack should be empty), and drain the
6554 // stack by applying this closure to the oops in the oops popped
6555 // from the stack (i.e. blacken the grey objects)
6556 bool res = _mark_stack->push(obj);
6557 assert(res, "Should have space to push on empty stack");
6558 do {
6559 oop new_oop = _mark_stack->pop();
6560 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6561 assert(new_oop->is_parsable(), "Found unparsable oop");
6562 assert(_bit_map->isMarked((HeapWord*)new_oop),
6563 "only grey objects on this stack");
6564 // iterate over the oops in this oop, marking and pushing
6565 // the ones in CMS heap (i.e. in _span).
6566 new_oop->oop_iterate(&_pushAndMarkClosure);
6567 // check if it's time to yield
6568 do_yield_check();
6569 } while (!_mark_stack->isEmpty() ||
6570 (!_concurrent_precleaning && take_from_overflow_list()));
6571 // if marking stack is empty, and we are not doing this
6572 // during precleaning, then check the overflow list
6573 }
6574 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6575 assert(_collector->overflow_list_is_empty(),
6576 "overflow list was drained above");
6577 // We could restore evacuated mark words, if any, used for
6578 // overflow list links here because the overflow list is
6579 // provably empty here. That would reduce the maximum
6580 // size requirements for preserved_{oop,mark}_stack.
6581 // But we'll just postpone it until we are all done
6582 // so we can just stream through.
6583 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6584 _collector->restore_preserved_marks_if_any();
6585 assert(_collector->no_preserved_marks(), "No preserved marks");
6586 }
6587 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6588 "All preserved marks should have been restored above");
6589 }
6590 }
6591
6592 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6593 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6594
6595 void MarkRefsIntoAndScanClosure::do_yield_work() {
6596 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6597 "CMS thread should hold CMS token");
6598 assert_lock_strong(_freelistLock);
6599 assert_lock_strong(_bit_map->lock());
6600 // relinquish the free_list_lock and bitMaplock()
6601 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6602 _bit_map->lock()->unlock();
6603 _freelistLock->unlock();
6604 ConcurrentMarkSweepThread::desynchronize(true);
6605 ConcurrentMarkSweepThread::acknowledge_yield_request();
6606 _collector->stopTimer();
6607 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6608 if (PrintCMSStatistics != 0) {
6609 _collector->incrementYields();
6610 }
6611 _collector->icms_wait();
6612
6613 // See the comment in coordinator_yield()
6614 for (unsigned i = 0;
6615 i < CMSYieldSleepCount &&
6616 ConcurrentMarkSweepThread::should_yield() &&
6617 !CMSCollector::foregroundGCIsActive();
6618 ++i) {
6619 os::sleep(Thread::current(), 1, false);
6620 ConcurrentMarkSweepThread::acknowledge_yield_request();
6621 }
6622
6623 ConcurrentMarkSweepThread::synchronize(true);
6624 _freelistLock->lock_without_safepoint_check();
6625 _bit_map->lock()->lock_without_safepoint_check();
6626 _collector->startTimer();
6627 }
6628
6629 ///////////////////////////////////////////////////////////
6630 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6631 // MarkRefsIntoAndScanClosure
6632 ///////////////////////////////////////////////////////////
6633 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6634 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6635 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6636 _span(span),
6637 _bit_map(bit_map),
6638 _work_queue(work_queue),
6639 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6640 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6641 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6642 revisit_stack)
6643 {
6644 _ref_processor = rp;
6645 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6646 }
6647
6648 // This closure is used to mark refs into the CMS generation at the
6649 // second (final) checkpoint, and to scan and transitively follow
6650 // the unmarked oops. The marks are made in the marking bit map and
6651 // the work_queue is used for keeping the (newly) grey objects during
6652 // the scan phase whence they are also available for stealing by parallel
6653 // threads. Since the marking bit map is shared, updates are
6654 // synchronized (via CAS).
6655 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6656 if (obj != NULL) {
6657 // Ignore mark word because this could be an already marked oop
6658 // that may be chained at the end of the overflow list.
6659 assert(obj->is_oop(true), "expected an oop");
6660 HeapWord* addr = (HeapWord*)obj;
6661 if (_span.contains(addr) &&
6662 !_bit_map->isMarked(addr)) {
6663 // mark bit map (object will become grey):
6664 // It is possible for several threads to be
6665 // trying to "claim" this object concurrently;
6666 // the unique thread that succeeds in marking the
6667 // object first will do the subsequent push on
6668 // to the work queue (or overflow list).
6669 if (_bit_map->par_mark(addr)) {
6670 // push on work_queue (which may not be empty), and trim the
6671 // queue to an appropriate length by applying this closure to
6672 // the oops in the oops popped from the stack (i.e. blacken the
6673 // grey objects)
6674 bool res = _work_queue->push(obj);
6675 assert(res, "Low water mark should be less than capacity?");
6676 trim_queue(_low_water_mark);
6677 } // Else, another thread claimed the object
6678 }
6679 }
6680 }
6681
6682 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6683 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6684
6685 // This closure is used to rescan the marked objects on the dirty cards
6686 // in the mod union table and the card table proper.
6687 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6688 oop p, MemRegion mr) {
6689
6690 size_t size = 0;
6691 HeapWord* addr = (HeapWord*)p;
6692 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6693 assert(_span.contains(addr), "we are scanning the CMS generation");
6694 // check if it's time to yield
6695 if (do_yield_check()) {
6696 // We yielded for some foreground stop-world work,
6697 // and we have been asked to abort this ongoing preclean cycle.
6698 return 0;
6699 }
6700 if (_bitMap->isMarked(addr)) {
6701 // it's marked; is it potentially uninitialized?
6702 if (p->klass_or_null() != NULL) {
6703 // If is_conc_safe is false, the object may be undergoing
6704 // change by the VM outside a safepoint. Don't try to
6705 // scan it, but rather leave it for the remark phase.
6706 if (CMSPermGenPrecleaningEnabled &&
6707 (!p->is_conc_safe() || !p->is_parsable())) {
6708 // Signal precleaning to redirty the card since
6709 // the klass pointer is already installed.
6710 assert(size == 0, "Initial value");
6711 } else {
6712 assert(p->is_parsable(), "must be parsable.");
6713 // an initialized object; ignore mark word in verification below
6714 // since we are running concurrent with mutators
6715 assert(p->is_oop(true), "should be an oop");
6716 if (p->is_objArray()) {
6717 // objArrays are precisely marked; restrict scanning
6718 // to dirty cards only.
6719 size = CompactibleFreeListSpace::adjustObjectSize(
6720 p->oop_iterate(_scanningClosure, mr));
6721 } else {
6722 // A non-array may have been imprecisely marked; we need
6723 // to scan object in its entirety.
6724 size = CompactibleFreeListSpace::adjustObjectSize(
6725 p->oop_iterate(_scanningClosure));
6726 }
6727 #ifdef DEBUG
6728 size_t direct_size =
6729 CompactibleFreeListSpace::adjustObjectSize(p->size());
6730 assert(size == direct_size, "Inconsistency in size");
6731 assert(size >= 3, "Necessary for Printezis marks to work");
6732 if (!_bitMap->isMarked(addr+1)) {
6733 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6734 } else {
6735 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6736 assert(_bitMap->isMarked(addr+size-1),
6737 "inconsistent Printezis mark");
6738 }
6739 #endif // DEBUG
6740 }
6741 } else {
6742 // an unitialized object
6743 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6744 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6745 size = pointer_delta(nextOneAddr + 1, addr);
6746 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6747 "alignment problem");
6748 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6749 // will dirty the card when the klass pointer is installed in the
6750 // object (signalling the completion of initialization).
6751 }
6752 } else {
6753 // Either a not yet marked object or an uninitialized object
6754 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6755 // An uninitialized object, skip to the next card, since
6756 // we may not be able to read its P-bits yet.
6757 assert(size == 0, "Initial value");
6758 } else {
6759 // An object not (yet) reached by marking: we merely need to
6760 // compute its size so as to go look at the next block.
6761 assert(p->is_oop(true), "should be an oop");
6762 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6763 }
6764 }
6765 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6766 return size;
6767 }
6768
6769 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6770 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6771 "CMS thread should hold CMS token");
6772 assert_lock_strong(_freelistLock);
6773 assert_lock_strong(_bitMap->lock());
6774 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6775 // relinquish the free_list_lock and bitMaplock()
6776 _bitMap->lock()->unlock();
6777 _freelistLock->unlock();
6778 ConcurrentMarkSweepThread::desynchronize(true);
6779 ConcurrentMarkSweepThread::acknowledge_yield_request();
6780 _collector->stopTimer();
6781 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6782 if (PrintCMSStatistics != 0) {
6783 _collector->incrementYields();
6784 }
6785 _collector->icms_wait();
6786
6787 // See the comment in coordinator_yield()
6788 for (unsigned i = 0; i < CMSYieldSleepCount &&
6789 ConcurrentMarkSweepThread::should_yield() &&
6790 !CMSCollector::foregroundGCIsActive(); ++i) {
6791 os::sleep(Thread::current(), 1, false);
6792 ConcurrentMarkSweepThread::acknowledge_yield_request();
6793 }
6794
6795 ConcurrentMarkSweepThread::synchronize(true);
6796 _freelistLock->lock_without_safepoint_check();
6797 _bitMap->lock()->lock_without_safepoint_check();
6798 _collector->startTimer();
6799 }
6800
6801
6802 //////////////////////////////////////////////////////////////////
6803 // SurvivorSpacePrecleanClosure
6804 //////////////////////////////////////////////////////////////////
6805 // This (single-threaded) closure is used to preclean the oops in
6806 // the survivor spaces.
6807 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6808
6809 HeapWord* addr = (HeapWord*)p;
6810 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6811 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6812 assert(p->klass_or_null() != NULL, "object should be initializd");
6813 assert(p->is_parsable(), "must be parsable.");
6814 // an initialized object; ignore mark word in verification below
6815 // since we are running concurrent with mutators
6816 assert(p->is_oop(true), "should be an oop");
6817 // Note that we do not yield while we iterate over
6818 // the interior oops of p, pushing the relevant ones
6819 // on our marking stack.
6820 size_t size = p->oop_iterate(_scanning_closure);
6821 do_yield_check();
6822 // Observe that below, we do not abandon the preclean
6823 // phase as soon as we should; rather we empty the
6824 // marking stack before returning. This is to satisfy
6825 // some existing assertions. In general, it may be a
6826 // good idea to abort immediately and complete the marking
6827 // from the grey objects at a later time.
6828 while (!_mark_stack->isEmpty()) {
6829 oop new_oop = _mark_stack->pop();
6830 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6831 assert(new_oop->is_parsable(), "Found unparsable oop");
6832 assert(_bit_map->isMarked((HeapWord*)new_oop),
6833 "only grey objects on this stack");
6834 // iterate over the oops in this oop, marking and pushing
6835 // the ones in CMS heap (i.e. in _span).
6836 new_oop->oop_iterate(_scanning_closure);
6837 // check if it's time to yield
6838 do_yield_check();
6839 }
6840 unsigned int after_count =
6841 GenCollectedHeap::heap()->total_collections();
6842 bool abort = (_before_count != after_count) ||
6843 _collector->should_abort_preclean();
6844 return abort ? 0 : size;
6845 }
6846
6847 void SurvivorSpacePrecleanClosure::do_yield_work() {
6848 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6849 "CMS thread should hold CMS token");
6850 assert_lock_strong(_bit_map->lock());
6851 DEBUG_ONLY(RememberKlassesChecker smx(false);)
6852 // Relinquish the bit map lock
6853 _bit_map->lock()->unlock();
6854 ConcurrentMarkSweepThread::desynchronize(true);
6855 ConcurrentMarkSweepThread::acknowledge_yield_request();
6856 _collector->stopTimer();
6857 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6858 if (PrintCMSStatistics != 0) {
6859 _collector->incrementYields();
6860 }
6861 _collector->icms_wait();
6862
6863 // See the comment in coordinator_yield()
6864 for (unsigned i = 0; i < CMSYieldSleepCount &&
6865 ConcurrentMarkSweepThread::should_yield() &&
6866 !CMSCollector::foregroundGCIsActive(); ++i) {
6867 os::sleep(Thread::current(), 1, false);
6868 ConcurrentMarkSweepThread::acknowledge_yield_request();
6869 }
6870
6871 ConcurrentMarkSweepThread::synchronize(true);
6872 _bit_map->lock()->lock_without_safepoint_check();
6873 _collector->startTimer();
6874 }
6875
6876 // This closure is used to rescan the marked objects on the dirty cards
6877 // in the mod union table and the card table proper. In the parallel
6878 // case, although the bitMap is shared, we do a single read so the
6879 // isMarked() query is "safe".
6880 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6881 // Ignore mark word because we are running concurrent with mutators
6882 assert(p->is_oop_or_null(true), "expected an oop or null");
6883 HeapWord* addr = (HeapWord*)p;
6884 assert(_span.contains(addr), "we are scanning the CMS generation");
6885 bool is_obj_array = false;
6886 #ifdef DEBUG
6887 if (!_parallel) {
6888 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6889 assert(_collector->overflow_list_is_empty(),
6890 "overflow list should be empty");
6891
6892 }
6893 #endif // DEBUG
6894 if (_bit_map->isMarked(addr)) {
6895 // Obj arrays are precisely marked, non-arrays are not;
6896 // so we scan objArrays precisely and non-arrays in their
6897 // entirety.
6898 if (p->is_objArray()) {
6899 is_obj_array = true;
6900 if (_parallel) {
6901 p->oop_iterate(_par_scan_closure, mr);
6902 } else {
6903 p->oop_iterate(_scan_closure, mr);
6904 }
6905 } else {
6906 if (_parallel) {
6907 p->oop_iterate(_par_scan_closure);
6908 } else {
6909 p->oop_iterate(_scan_closure);
6910 }
6911 }
6912 }
6913 #ifdef DEBUG
6914 if (!_parallel) {
6915 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6916 assert(_collector->overflow_list_is_empty(),
6917 "overflow list should be empty");
6918
6919 }
6920 #endif // DEBUG
6921 return is_obj_array;
6922 }
6923
6924 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6925 MemRegion span,
6926 CMSBitMap* bitMap, CMSMarkStack* markStack,
6927 CMSMarkStack* revisitStack,
6928 bool should_yield, bool verifying):
6929 _collector(collector),
6930 _span(span),
6931 _bitMap(bitMap),
6932 _mut(&collector->_modUnionTable),
6933 _markStack(markStack),
6934 _revisitStack(revisitStack),
6935 _yield(should_yield),
6936 _skipBits(0)
6937 {
6938 assert(_markStack->isEmpty(), "stack should be empty");
6939 _finger = _bitMap->startWord();
6940 _threshold = _finger;
6941 assert(_collector->_restart_addr == NULL, "Sanity check");
6942 assert(_span.contains(_finger), "Out of bounds _finger?");
6943 DEBUG_ONLY(_verifying = verifying;)
6944 }
6945
6946 void MarkFromRootsClosure::reset(HeapWord* addr) {
6947 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6948 assert(_span.contains(addr), "Out of bounds _finger?");
6949 _finger = addr;
6950 _threshold = (HeapWord*)round_to(
6951 (intptr_t)_finger, CardTableModRefBS::card_size);
6952 }
6953
6954 // Should revisit to see if this should be restructured for
6955 // greater efficiency.
6956 bool MarkFromRootsClosure::do_bit(size_t offset) {
6957 if (_skipBits > 0) {
6958 _skipBits--;
6959 return true;
6960 }
6961 // convert offset into a HeapWord*
6962 HeapWord* addr = _bitMap->startWord() + offset;
6963 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6964 "address out of range");
6965 assert(_bitMap->isMarked(addr), "tautology");
6966 if (_bitMap->isMarked(addr+1)) {
6967 // this is an allocated but not yet initialized object
6968 assert(_skipBits == 0, "tautology");
6969 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6970 oop p = oop(addr);
6971 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6972 DEBUG_ONLY(if (!_verifying) {)
6973 // We re-dirty the cards on which this object lies and increase
6974 // the _threshold so that we'll come back to scan this object
6975 // during the preclean or remark phase. (CMSCleanOnEnter)
6976 if (CMSCleanOnEnter) {
6977 size_t sz = _collector->block_size_using_printezis_bits(addr);
6978 HeapWord* end_card_addr = (HeapWord*)round_to(
6979 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6980 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6981 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6982 // Bump _threshold to end_card_addr; note that
6983 // _threshold cannot possibly exceed end_card_addr, anyhow.
6984 // This prevents future clearing of the card as the scan proceeds
6985 // to the right.
6986 assert(_threshold <= end_card_addr,
6987 "Because we are just scanning into this object");
6988 if (_threshold < end_card_addr) {
6989 _threshold = end_card_addr;
6990 }
6991 if (p->klass_or_null() != NULL) {
6992 // Redirty the range of cards...
6993 _mut->mark_range(redirty_range);
6994 } // ...else the setting of klass will dirty the card anyway.
6995 }
6996 DEBUG_ONLY(})
6997 return true;
6998 }
6999 }
7000 scanOopsInOop(addr);
7001 return true;
7002 }
7003
7004 // We take a break if we've been at this for a while,
7005 // so as to avoid monopolizing the locks involved.
7006 void MarkFromRootsClosure::do_yield_work() {
7007 // First give up the locks, then yield, then re-lock
7008 // We should probably use a constructor/destructor idiom to
7009 // do this unlock/lock or modify the MutexUnlocker class to
7010 // serve our purpose. XXX
7011 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7012 "CMS thread should hold CMS token");
7013 assert_lock_strong(_bitMap->lock());
7014 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7015 _bitMap->lock()->unlock();
7016 ConcurrentMarkSweepThread::desynchronize(true);
7017 ConcurrentMarkSweepThread::acknowledge_yield_request();
7018 _collector->stopTimer();
7019 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7020 if (PrintCMSStatistics != 0) {
7021 _collector->incrementYields();
7022 }
7023 _collector->icms_wait();
7024
7025 // See the comment in coordinator_yield()
7026 for (unsigned i = 0; i < CMSYieldSleepCount &&
7027 ConcurrentMarkSweepThread::should_yield() &&
7028 !CMSCollector::foregroundGCIsActive(); ++i) {
7029 os::sleep(Thread::current(), 1, false);
7030 ConcurrentMarkSweepThread::acknowledge_yield_request();
7031 }
7032
7033 ConcurrentMarkSweepThread::synchronize(true);
7034 _bitMap->lock()->lock_without_safepoint_check();
7035 _collector->startTimer();
7036 }
7037
7038 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7039 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7040 assert(_markStack->isEmpty(),
7041 "should drain stack to limit stack usage");
7042 // convert ptr to an oop preparatory to scanning
7043 oop obj = oop(ptr);
7044 // Ignore mark word in verification below, since we
7045 // may be running concurrent with mutators.
7046 assert(obj->is_oop(true), "should be an oop");
7047 assert(_finger <= ptr, "_finger runneth ahead");
7048 // advance the finger to right end of this object
7049 _finger = ptr + obj->size();
7050 assert(_finger > ptr, "we just incremented it above");
7051 // On large heaps, it may take us some time to get through
7052 // the marking phase (especially if running iCMS). During
7053 // this time it's possible that a lot of mutations have
7054 // accumulated in the card table and the mod union table --
7055 // these mutation records are redundant until we have
7056 // actually traced into the corresponding card.
7057 // Here, we check whether advancing the finger would make
7058 // us cross into a new card, and if so clear corresponding
7059 // cards in the MUT (preclean them in the card-table in the
7060 // future).
7061
7062 DEBUG_ONLY(if (!_verifying) {)
7063 // The clean-on-enter optimization is disabled by default,
7064 // until we fix 6178663.
7065 if (CMSCleanOnEnter && (_finger > _threshold)) {
7066 // [_threshold, _finger) represents the interval
7067 // of cards to be cleared in MUT (or precleaned in card table).
7068 // The set of cards to be cleared is all those that overlap
7069 // with the interval [_threshold, _finger); note that
7070 // _threshold is always kept card-aligned but _finger isn't
7071 // always card-aligned.
7072 HeapWord* old_threshold = _threshold;
7073 assert(old_threshold == (HeapWord*)round_to(
7074 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7075 "_threshold should always be card-aligned");
7076 _threshold = (HeapWord*)round_to(
7077 (intptr_t)_finger, CardTableModRefBS::card_size);
7078 MemRegion mr(old_threshold, _threshold);
7079 assert(!mr.is_empty(), "Control point invariant");
7080 assert(_span.contains(mr), "Should clear within span");
7081 // XXX When _finger crosses from old gen into perm gen
7082 // we may be doing unnecessary cleaning; do better in the
7083 // future by detecting that condition and clearing fewer
7084 // MUT/CT entries.
7085 _mut->clear_range(mr);
7086 }
7087 DEBUG_ONLY(})
7088 // Note: the finger doesn't advance while we drain
7089 // the stack below.
7090 PushOrMarkClosure pushOrMarkClosure(_collector,
7091 _span, _bitMap, _markStack,
7092 _revisitStack,
7093 _finger, this);
7094 bool res = _markStack->push(obj);
7095 assert(res, "Empty non-zero size stack should have space for single push");
7096 while (!_markStack->isEmpty()) {
7097 oop new_oop = _markStack->pop();
7098 // Skip verifying header mark word below because we are
7099 // running concurrent with mutators.
7100 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7101 // now scan this oop's oops
7102 new_oop->oop_iterate(&pushOrMarkClosure);
7103 do_yield_check();
7104 }
7105 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7106 }
7107
7108 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7109 CMSCollector* collector, MemRegion span,
7110 CMSBitMap* bit_map,
7111 OopTaskQueue* work_queue,
7112 CMSMarkStack* overflow_stack,
7113 CMSMarkStack* revisit_stack,
7114 bool should_yield):
7115 _collector(collector),
7116 _whole_span(collector->_span),
7117 _span(span),
7118 _bit_map(bit_map),
7119 _mut(&collector->_modUnionTable),
7120 _work_queue(work_queue),
7121 _overflow_stack(overflow_stack),
7122 _revisit_stack(revisit_stack),
7123 _yield(should_yield),
7124 _skip_bits(0),
7125 _task(task)
7126 {
7127 assert(_work_queue->size() == 0, "work_queue should be empty");
7128 _finger = span.start();
7129 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7130 assert(_span.contains(_finger), "Out of bounds _finger?");
7131 }
7132
7133 // Should revisit to see if this should be restructured for
7134 // greater efficiency.
7135 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7136 if (_skip_bits > 0) {
7137 _skip_bits--;
7138 return true;
7139 }
7140 // convert offset into a HeapWord*
7141 HeapWord* addr = _bit_map->startWord() + offset;
7142 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7143 "address out of range");
7144 assert(_bit_map->isMarked(addr), "tautology");
7145 if (_bit_map->isMarked(addr+1)) {
7146 // this is an allocated object that might not yet be initialized
7147 assert(_skip_bits == 0, "tautology");
7148 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7149 oop p = oop(addr);
7150 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7151 // in the case of Clean-on-Enter optimization, redirty card
7152 // and avoid clearing card by increasing the threshold.
7153 return true;
7154 }
7155 }
7156 scan_oops_in_oop(addr);
7157 return true;
7158 }
7159
7160 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7161 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7162 // Should we assert that our work queue is empty or
7163 // below some drain limit?
7164 assert(_work_queue->size() == 0,
7165 "should drain stack to limit stack usage");
7166 // convert ptr to an oop preparatory to scanning
7167 oop obj = oop(ptr);
7168 // Ignore mark word in verification below, since we
7169 // may be running concurrent with mutators.
7170 assert(obj->is_oop(true), "should be an oop");
7171 assert(_finger <= ptr, "_finger runneth ahead");
7172 // advance the finger to right end of this object
7173 _finger = ptr + obj->size();
7174 assert(_finger > ptr, "we just incremented it above");
7175 // On large heaps, it may take us some time to get through
7176 // the marking phase (especially if running iCMS). During
7177 // this time it's possible that a lot of mutations have
7178 // accumulated in the card table and the mod union table --
7179 // these mutation records are redundant until we have
7180 // actually traced into the corresponding card.
7181 // Here, we check whether advancing the finger would make
7182 // us cross into a new card, and if so clear corresponding
7183 // cards in the MUT (preclean them in the card-table in the
7184 // future).
7185
7186 // The clean-on-enter optimization is disabled by default,
7187 // until we fix 6178663.
7188 if (CMSCleanOnEnter && (_finger > _threshold)) {
7189 // [_threshold, _finger) represents the interval
7190 // of cards to be cleared in MUT (or precleaned in card table).
7191 // The set of cards to be cleared is all those that overlap
7192 // with the interval [_threshold, _finger); note that
7193 // _threshold is always kept card-aligned but _finger isn't
7194 // always card-aligned.
7195 HeapWord* old_threshold = _threshold;
7196 assert(old_threshold == (HeapWord*)round_to(
7197 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7198 "_threshold should always be card-aligned");
7199 _threshold = (HeapWord*)round_to(
7200 (intptr_t)_finger, CardTableModRefBS::card_size);
7201 MemRegion mr(old_threshold, _threshold);
7202 assert(!mr.is_empty(), "Control point invariant");
7203 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7204 // XXX When _finger crosses from old gen into perm gen
7205 // we may be doing unnecessary cleaning; do better in the
7206 // future by detecting that condition and clearing fewer
7207 // MUT/CT entries.
7208 _mut->clear_range(mr);
7209 }
7210
7211 // Note: the local finger doesn't advance while we drain
7212 // the stack below, but the global finger sure can and will.
7213 HeapWord** gfa = _task->global_finger_addr();
7214 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7215 _span, _bit_map,
7216 _work_queue,
7217 _overflow_stack,
7218 _revisit_stack,
7219 _finger,
7220 gfa, this);
7221 bool res = _work_queue->push(obj); // overflow could occur here
7222 assert(res, "Will hold once we use workqueues");
7223 while (true) {
7224 oop new_oop;
7225 if (!_work_queue->pop_local(new_oop)) {
7226 // We emptied our work_queue; check if there's stuff that can
7227 // be gotten from the overflow stack.
7228 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7229 _overflow_stack, _work_queue)) {
7230 do_yield_check();
7231 continue;
7232 } else { // done
7233 break;
7234 }
7235 }
7236 // Skip verifying header mark word below because we are
7237 // running concurrent with mutators.
7238 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7239 // now scan this oop's oops
7240 new_oop->oop_iterate(&pushOrMarkClosure);
7241 do_yield_check();
7242 }
7243 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7244 }
7245
7246 // Yield in response to a request from VM Thread or
7247 // from mutators.
7248 void Par_MarkFromRootsClosure::do_yield_work() {
7249 assert(_task != NULL, "sanity");
7250 _task->yield();
7251 }
7252
7253 // A variant of the above used for verifying CMS marking work.
7254 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7255 MemRegion span,
7256 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7257 CMSMarkStack* mark_stack):
7258 _collector(collector),
7259 _span(span),
7260 _verification_bm(verification_bm),
7261 _cms_bm(cms_bm),
7262 _mark_stack(mark_stack),
7263 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7264 mark_stack)
7265 {
7266 assert(_mark_stack->isEmpty(), "stack should be empty");
7267 _finger = _verification_bm->startWord();
7268 assert(_collector->_restart_addr == NULL, "Sanity check");
7269 assert(_span.contains(_finger), "Out of bounds _finger?");
7270 }
7271
7272 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7273 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7274 assert(_span.contains(addr), "Out of bounds _finger?");
7275 _finger = addr;
7276 }
7277
7278 // Should revisit to see if this should be restructured for
7279 // greater efficiency.
7280 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7281 // convert offset into a HeapWord*
7282 HeapWord* addr = _verification_bm->startWord() + offset;
7283 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7284 "address out of range");
7285 assert(_verification_bm->isMarked(addr), "tautology");
7286 assert(_cms_bm->isMarked(addr), "tautology");
7287
7288 assert(_mark_stack->isEmpty(),
7289 "should drain stack to limit stack usage");
7290 // convert addr to an oop preparatory to scanning
7291 oop obj = oop(addr);
7292 assert(obj->is_oop(), "should be an oop");
7293 assert(_finger <= addr, "_finger runneth ahead");
7294 // advance the finger to right end of this object
7295 _finger = addr + obj->size();
7296 assert(_finger > addr, "we just incremented it above");
7297 // Note: the finger doesn't advance while we drain
7298 // the stack below.
7299 bool res = _mark_stack->push(obj);
7300 assert(res, "Empty non-zero size stack should have space for single push");
7301 while (!_mark_stack->isEmpty()) {
7302 oop new_oop = _mark_stack->pop();
7303 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7304 // now scan this oop's oops
7305 new_oop->oop_iterate(&_pam_verify_closure);
7306 }
7307 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7308 return true;
7309 }
7310
7311 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7312 CMSCollector* collector, MemRegion span,
7313 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7314 CMSMarkStack* mark_stack):
7315 OopClosure(collector->ref_processor()),
7316 _collector(collector),
7317 _span(span),
7318 _verification_bm(verification_bm),
7319 _cms_bm(cms_bm),
7320 _mark_stack(mark_stack)
7321 { }
7322
7323 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7324 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7325
7326 // Upon stack overflow, we discard (part of) the stack,
7327 // remembering the least address amongst those discarded
7328 // in CMSCollector's _restart_address.
7329 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7330 // Remember the least grey address discarded
7331 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7332 _collector->lower_restart_addr(ra);
7333 _mark_stack->reset(); // discard stack contents
7334 _mark_stack->expand(); // expand the stack if possible
7335 }
7336
7337 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7338 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7339 HeapWord* addr = (HeapWord*)obj;
7340 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7341 // Oop lies in _span and isn't yet grey or black
7342 _verification_bm->mark(addr); // now grey
7343 if (!_cms_bm->isMarked(addr)) {
7344 oop(addr)->print();
7345 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7346 addr);
7347 fatal("... aborting");
7348 }
7349
7350 if (!_mark_stack->push(obj)) { // stack overflow
7351 if (PrintCMSStatistics != 0) {
7352 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7353 SIZE_FORMAT, _mark_stack->capacity());
7354 }
7355 assert(_mark_stack->isFull(), "Else push should have succeeded");
7356 handle_stack_overflow(addr);
7357 }
7358 // anything including and to the right of _finger
7359 // will be scanned as we iterate over the remainder of the
7360 // bit map
7361 }
7362 }
7363
7364 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7365 MemRegion span,
7366 CMSBitMap* bitMap, CMSMarkStack* markStack,
7367 CMSMarkStack* revisitStack,
7368 HeapWord* finger, MarkFromRootsClosure* parent) :
7369 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7370 _span(span),
7371 _bitMap(bitMap),
7372 _markStack(markStack),
7373 _finger(finger),
7374 _parent(parent)
7375 { }
7376
7377 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7378 MemRegion span,
7379 CMSBitMap* bit_map,
7380 OopTaskQueue* work_queue,
7381 CMSMarkStack* overflow_stack,
7382 CMSMarkStack* revisit_stack,
7383 HeapWord* finger,
7384 HeapWord** global_finger_addr,
7385 Par_MarkFromRootsClosure* parent) :
7386 Par_KlassRememberingOopClosure(collector,
7387 collector->ref_processor(),
7388 revisit_stack),
7389 _whole_span(collector->_span),
7390 _span(span),
7391 _bit_map(bit_map),
7392 _work_queue(work_queue),
7393 _overflow_stack(overflow_stack),
7394 _finger(finger),
7395 _global_finger_addr(global_finger_addr),
7396 _parent(parent)
7397 { }
7398
7399 // Assumes thread-safe access by callers, who are
7400 // responsible for mutual exclusion.
7401 void CMSCollector::lower_restart_addr(HeapWord* low) {
7402 assert(_span.contains(low), "Out of bounds addr");
7403 if (_restart_addr == NULL) {
7404 _restart_addr = low;
7405 } else {
7406 _restart_addr = MIN2(_restart_addr, low);
7407 }
7408 }
7409
7410 // Upon stack overflow, we discard (part of) the stack,
7411 // remembering the least address amongst those discarded
7412 // in CMSCollector's _restart_address.
7413 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7414 // Remember the least grey address discarded
7415 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7416 _collector->lower_restart_addr(ra);
7417 _markStack->reset(); // discard stack contents
7418 _markStack->expand(); // expand the stack if possible
7419 }
7420
7421 // Upon stack overflow, we discard (part of) the stack,
7422 // remembering the least address amongst those discarded
7423 // in CMSCollector's _restart_address.
7424 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7425 // We need to do this under a mutex to prevent other
7426 // workers from interfering with the work done below.
7427 MutexLockerEx ml(_overflow_stack->par_lock(),
7428 Mutex::_no_safepoint_check_flag);
7429 // Remember the least grey address discarded
7430 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7431 _collector->lower_restart_addr(ra);
7432 _overflow_stack->reset(); // discard stack contents
7433 _overflow_stack->expand(); // expand the stack if possible
7434 }
7435
7436 void PushOrMarkClosure::do_oop(oop obj) {
7437 // Ignore mark word because we are running concurrent with mutators.
7438 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7439 HeapWord* addr = (HeapWord*)obj;
7440 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7441 // Oop lies in _span and isn't yet grey or black
7442 _bitMap->mark(addr); // now grey
7443 if (addr < _finger) {
7444 // the bit map iteration has already either passed, or
7445 // sampled, this bit in the bit map; we'll need to
7446 // use the marking stack to scan this oop's oops.
7447 bool simulate_overflow = false;
7448 NOT_PRODUCT(
7449 if (CMSMarkStackOverflowALot &&
7450 _collector->simulate_overflow()) {
7451 // simulate a stack overflow
7452 simulate_overflow = true;
7453 }
7454 )
7455 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7456 if (PrintCMSStatistics != 0) {
7457 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7458 SIZE_FORMAT, _markStack->capacity());
7459 }
7460 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7461 handle_stack_overflow(addr);
7462 }
7463 }
7464 // anything including and to the right of _finger
7465 // will be scanned as we iterate over the remainder of the
7466 // bit map
7467 do_yield_check();
7468 }
7469 }
7470
7471 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7472 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7473
7474 void Par_PushOrMarkClosure::do_oop(oop obj) {
7475 // Ignore mark word because we are running concurrent with mutators.
7476 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7477 HeapWord* addr = (HeapWord*)obj;
7478 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7479 // Oop lies in _span and isn't yet grey or black
7480 // We read the global_finger (volatile read) strictly after marking oop
7481 bool res = _bit_map->par_mark(addr); // now grey
7482 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7483 // Should we push this marked oop on our stack?
7484 // -- if someone else marked it, nothing to do
7485 // -- if target oop is above global finger nothing to do
7486 // -- if target oop is in chunk and above local finger
7487 // then nothing to do
7488 // -- else push on work queue
7489 if ( !res // someone else marked it, they will deal with it
7490 || (addr >= *gfa) // will be scanned in a later task
7491 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7492 return;
7493 }
7494 // the bit map iteration has already either passed, or
7495 // sampled, this bit in the bit map; we'll need to
7496 // use the marking stack to scan this oop's oops.
7497 bool simulate_overflow = false;
7498 NOT_PRODUCT(
7499 if (CMSMarkStackOverflowALot &&
7500 _collector->simulate_overflow()) {
7501 // simulate a stack overflow
7502 simulate_overflow = true;
7503 }
7504 )
7505 if (simulate_overflow ||
7506 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7507 // stack overflow
7508 if (PrintCMSStatistics != 0) {
7509 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7510 SIZE_FORMAT, _overflow_stack->capacity());
7511 }
7512 // We cannot assert that the overflow stack is full because
7513 // it may have been emptied since.
7514 assert(simulate_overflow ||
7515 _work_queue->size() == _work_queue->max_elems(),
7516 "Else push should have succeeded");
7517 handle_stack_overflow(addr);
7518 }
7519 do_yield_check();
7520 }
7521 }
7522
7523 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7524 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7525
7526 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7527 ReferenceProcessor* rp,
7528 CMSMarkStack* revisit_stack) :
7529 OopClosure(rp),
7530 _collector(collector),
7531 _revisit_stack(revisit_stack),
7532 _should_remember_klasses(collector->should_unload_classes()) {}
7533
7534 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7535 MemRegion span,
7536 ReferenceProcessor* rp,
7537 CMSBitMap* bit_map,
7538 CMSBitMap* mod_union_table,
7539 CMSMarkStack* mark_stack,
7540 CMSMarkStack* revisit_stack,
7541 bool concurrent_precleaning):
7542 KlassRememberingOopClosure(collector, rp, revisit_stack),
7543 _span(span),
7544 _bit_map(bit_map),
7545 _mod_union_table(mod_union_table),
7546 _mark_stack(mark_stack),
7547 _concurrent_precleaning(concurrent_precleaning)
7548 {
7549 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7550 }
7551
7552 // Grey object rescan during pre-cleaning and second checkpoint phases --
7553 // the non-parallel version (the parallel version appears further below.)
7554 void PushAndMarkClosure::do_oop(oop obj) {
7555 // Ignore mark word verification. If during concurrent precleaning,
7556 // the object monitor may be locked. If during the checkpoint
7557 // phases, the object may already have been reached by a different
7558 // path and may be at the end of the global overflow list (so
7559 // the mark word may be NULL).
7560 assert(obj->is_oop_or_null(true /* ignore mark word */),
7561 "expected an oop or NULL");
7562 HeapWord* addr = (HeapWord*)obj;
7563 // Check if oop points into the CMS generation
7564 // and is not marked
7565 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7566 // a white object ...
7567 _bit_map->mark(addr); // ... now grey
7568 // push on the marking stack (grey set)
7569 bool simulate_overflow = false;
7570 NOT_PRODUCT(
7571 if (CMSMarkStackOverflowALot &&
7572 _collector->simulate_overflow()) {
7573 // simulate a stack overflow
7574 simulate_overflow = true;
7575 }
7576 )
7577 if (simulate_overflow || !_mark_stack->push(obj)) {
7578 if (_concurrent_precleaning) {
7579 // During precleaning we can just dirty the appropriate card(s)
7580 // in the mod union table, thus ensuring that the object remains
7581 // in the grey set and continue. In the case of object arrays
7582 // we need to dirty all of the cards that the object spans,
7583 // since the rescan of object arrays will be limited to the
7584 // dirty cards.
7585 // Note that no one can be intefering with us in this action
7586 // of dirtying the mod union table, so no locking or atomics
7587 // are required.
7588 if (obj->is_objArray()) {
7589 size_t sz = obj->size();
7590 HeapWord* end_card_addr = (HeapWord*)round_to(
7591 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7592 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7593 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7594 _mod_union_table->mark_range(redirty_range);
7595 } else {
7596 _mod_union_table->mark(addr);
7597 }
7598 _collector->_ser_pmc_preclean_ovflw++;
7599 } else {
7600 // During the remark phase, we need to remember this oop
7601 // in the overflow list.
7602 _collector->push_on_overflow_list(obj);
7603 _collector->_ser_pmc_remark_ovflw++;
7604 }
7605 }
7606 }
7607 }
7608
7609 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7610 MemRegion span,
7611 ReferenceProcessor* rp,
7612 CMSBitMap* bit_map,
7613 OopTaskQueue* work_queue,
7614 CMSMarkStack* revisit_stack):
7615 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7616 _span(span),
7617 _bit_map(bit_map),
7618 _work_queue(work_queue)
7619 {
7620 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7621 }
7622
7623 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7624 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7625
7626 // Grey object rescan during second checkpoint phase --
7627 // the parallel version.
7628 void Par_PushAndMarkClosure::do_oop(oop obj) {
7629 // In the assert below, we ignore the mark word because
7630 // this oop may point to an already visited object that is
7631 // on the overflow stack (in which case the mark word has
7632 // been hijacked for chaining into the overflow stack --
7633 // if this is the last object in the overflow stack then
7634 // its mark word will be NULL). Because this object may
7635 // have been subsequently popped off the global overflow
7636 // stack, and the mark word possibly restored to the prototypical
7637 // value, by the time we get to examined this failing assert in
7638 // the debugger, is_oop_or_null(false) may subsequently start
7639 // to hold.
7640 assert(obj->is_oop_or_null(true),
7641 "expected an oop or NULL");
7642 HeapWord* addr = (HeapWord*)obj;
7643 // Check if oop points into the CMS generation
7644 // and is not marked
7645 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7646 // a white object ...
7647 // If we manage to "claim" the object, by being the
7648 // first thread to mark it, then we push it on our
7649 // marking stack
7650 if (_bit_map->par_mark(addr)) { // ... now grey
7651 // push on work queue (grey set)
7652 bool simulate_overflow = false;
7653 NOT_PRODUCT(
7654 if (CMSMarkStackOverflowALot &&
7655 _collector->par_simulate_overflow()) {
7656 // simulate a stack overflow
7657 simulate_overflow = true;
7658 }
7659 )
7660 if (simulate_overflow || !_work_queue->push(obj)) {
7661 _collector->par_push_on_overflow_list(obj);
7662 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7663 }
7664 } // Else, some other thread got there first
7665 }
7666 }
7667
7668 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7669 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7670
7671 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7672 // TBD
7673 }
7674
7675 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7676 // TBD
7677 }
7678
7679 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7680 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7681 Mutex* bml = _collector->bitMapLock();
7682 assert_lock_strong(bml);
7683 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7684 "CMS thread should hold CMS token");
7685
7686 bml->unlock();
7687 ConcurrentMarkSweepThread::desynchronize(true);
7688
7689 ConcurrentMarkSweepThread::acknowledge_yield_request();
7690
7691 _collector->stopTimer();
7692 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7693 if (PrintCMSStatistics != 0) {
7694 _collector->incrementYields();
7695 }
7696 _collector->icms_wait();
7697
7698 // See the comment in coordinator_yield()
7699 for (unsigned i = 0; i < CMSYieldSleepCount &&
7700 ConcurrentMarkSweepThread::should_yield() &&
7701 !CMSCollector::foregroundGCIsActive(); ++i) {
7702 os::sleep(Thread::current(), 1, false);
7703 ConcurrentMarkSweepThread::acknowledge_yield_request();
7704 }
7705
7706 ConcurrentMarkSweepThread::synchronize(true);
7707 bml->lock();
7708
7709 _collector->startTimer();
7710 }
7711
7712 bool CMSPrecleanRefsYieldClosure::should_return() {
7713 if (ConcurrentMarkSweepThread::should_yield()) {
7714 do_yield_work();
7715 }
7716 return _collector->foregroundGCIsActive();
7717 }
7718
7719 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7720 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7721 "mr should be aligned to start at a card boundary");
7722 // We'd like to assert:
7723 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7724 // "mr should be a range of cards");
7725 // However, that would be too strong in one case -- the last
7726 // partition ends at _unallocated_block which, in general, can be
7727 // an arbitrary boundary, not necessarily card aligned.
7728 if (PrintCMSStatistics != 0) {
7729 _num_dirty_cards +=
7730 mr.word_size()/CardTableModRefBS::card_size_in_words;
7731 }
7732 _space->object_iterate_mem(mr, &_scan_cl);
7733 }
7734
7735 SweepClosure::SweepClosure(CMSCollector* collector,
7736 ConcurrentMarkSweepGeneration* g,
7737 CMSBitMap* bitMap, bool should_yield) :
7738 _collector(collector),
7739 _g(g),
7740 _sp(g->cmsSpace()),
7741 _limit(_sp->sweep_limit()),
7742 _freelistLock(_sp->freelistLock()),
7743 _bitMap(bitMap),
7744 _yield(should_yield),
7745 _inFreeRange(false), // No free range at beginning of sweep
7746 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7747 _lastFreeRangeCoalesced(false),
7748 _freeFinger(g->used_region().start())
7749 {
7750 NOT_PRODUCT(
7751 _numObjectsFreed = 0;
7752 _numWordsFreed = 0;
7753 _numObjectsLive = 0;
7754 _numWordsLive = 0;
7755 _numObjectsAlreadyFree = 0;
7756 _numWordsAlreadyFree = 0;
7757 _last_fc = NULL;
7758
7759 _sp->initializeIndexedFreeListArrayReturnedBytes();
7760 _sp->dictionary()->initializeDictReturnedBytes();
7761 )
7762 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7763 "sweep _limit out of bounds");
7764 if (CMSTraceSweeper) {
7765 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7766 }
7767 }
7768
7769 // We need this destructor to reclaim any space at the end
7770 // of the space, which do_blk below may not have added back to
7771 // the free lists. [basically dealing with the "fringe effect"]
7772 SweepClosure::~SweepClosure() {
7773 assert_lock_strong(_freelistLock);
7774 // this should be treated as the end of a free run if any
7775 // The current free range should be returned to the free lists
7776 // as one coalesced chunk.
7777 if (inFreeRange()) {
7778 flushCurFreeChunk(freeFinger(),
7779 pointer_delta(_limit, freeFinger()));
7780 assert(freeFinger() < _limit, "the finger pointeth off base");
7781 if (CMSTraceSweeper) {
7782 gclog_or_tty->print("destructor:");
7783 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7784 "[coalesced:"SIZE_FORMAT"]\n",
7785 freeFinger(), pointer_delta(_limit, freeFinger()),
7786 lastFreeRangeCoalesced());
7787 }
7788 }
7789 NOT_PRODUCT(
7790 if (Verbose && PrintGC) {
7791 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7792 SIZE_FORMAT " bytes",
7793 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7794 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7795 SIZE_FORMAT" bytes "
7796 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7797 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7798 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7799 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7800 sizeof(HeapWord);
7801 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7802
7803 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7804 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7805 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7806 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7807 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7808 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7809 indexListReturnedBytes);
7810 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7811 dictReturnedBytes);
7812 }
7813 }
7814 )
7815 // Now, in debug mode, just null out the sweep_limit
7816 NOT_PRODUCT(_sp->clear_sweep_limit();)
7817 if (CMSTraceSweeper) {
7818 gclog_or_tty->print("end of sweep\n================\n");
7819 }
7820 }
7821
7822 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7823 bool freeRangeInFreeLists) {
7824 if (CMSTraceSweeper) {
7825 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7826 freeFinger, _sp->block_size(freeFinger),
7827 freeRangeInFreeLists);
7828 }
7829 assert(!inFreeRange(), "Trampling existing free range");
7830 set_inFreeRange(true);
7831 set_lastFreeRangeCoalesced(false);
7832
7833 set_freeFinger(freeFinger);
7834 set_freeRangeInFreeLists(freeRangeInFreeLists);
7835 if (CMSTestInFreeList) {
7836 if (freeRangeInFreeLists) {
7837 FreeChunk* fc = (FreeChunk*) freeFinger;
7838 assert(fc->isFree(), "A chunk on the free list should be free.");
7839 assert(fc->size() > 0, "Free range should have a size");
7840 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7841 }
7842 }
7843 }
7844
7845 // Note that the sweeper runs concurrently with mutators. Thus,
7846 // it is possible for direct allocation in this generation to happen
7847 // in the middle of the sweep. Note that the sweeper also coalesces
7848 // contiguous free blocks. Thus, unless the sweeper and the allocator
7849 // synchronize appropriately freshly allocated blocks may get swept up.
7850 // This is accomplished by the sweeper locking the free lists while
7851 // it is sweeping. Thus blocks that are determined to be free are
7852 // indeed free. There is however one additional complication:
7853 // blocks that have been allocated since the final checkpoint and
7854 // mark, will not have been marked and so would be treated as
7855 // unreachable and swept up. To prevent this, the allocator marks
7856 // the bit map when allocating during the sweep phase. This leads,
7857 // however, to a further complication -- objects may have been allocated
7858 // but not yet initialized -- in the sense that the header isn't yet
7859 // installed. The sweeper can not then determine the size of the block
7860 // in order to skip over it. To deal with this case, we use a technique
7861 // (due to Printezis) to encode such uninitialized block sizes in the
7862 // bit map. Since the bit map uses a bit per every HeapWord, but the
7863 // CMS generation has a minimum object size of 3 HeapWords, it follows
7864 // that "normal marks" won't be adjacent in the bit map (there will
7865 // always be at least two 0 bits between successive 1 bits). We make use
7866 // of these "unused" bits to represent uninitialized blocks -- the bit
7867 // corresponding to the start of the uninitialized object and the next
7868 // bit are both set. Finally, a 1 bit marks the end of the object that
7869 // started with the two consecutive 1 bits to indicate its potentially
7870 // uninitialized state.
7871
7872 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7873 FreeChunk* fc = (FreeChunk*)addr;
7874 size_t res;
7875
7876 // check if we are done sweepinrg
7877 if (addr == _limit) { // we have swept up to the limit, do nothing more
7878 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7879 "sweep _limit out of bounds");
7880 // help the closure application finish
7881 return pointer_delta(_sp->end(), _limit);
7882 }
7883 assert(addr <= _limit, "sweep invariant");
7884
7885 // check if we should yield
7886 do_yield_check(addr);
7887 if (fc->isFree()) {
7888 // Chunk that is already free
7889 res = fc->size();
7890 doAlreadyFreeChunk(fc);
7891 debug_only(_sp->verifyFreeLists());
7892 assert(res == fc->size(), "Don't expect the size to change");
7893 NOT_PRODUCT(
7894 _numObjectsAlreadyFree++;
7895 _numWordsAlreadyFree += res;
7896 )
7897 NOT_PRODUCT(_last_fc = fc;)
7898 } else if (!_bitMap->isMarked(addr)) {
7899 // Chunk is fresh garbage
7900 res = doGarbageChunk(fc);
7901 debug_only(_sp->verifyFreeLists());
7902 NOT_PRODUCT(
7903 _numObjectsFreed++;
7904 _numWordsFreed += res;
7905 )
7906 } else {
7907 // Chunk that is alive.
7908 res = doLiveChunk(fc);
7909 debug_only(_sp->verifyFreeLists());
7910 NOT_PRODUCT(
7911 _numObjectsLive++;
7912 _numWordsLive += res;
7913 )
7914 }
7915 return res;
7916 }
7917
7918 // For the smart allocation, record following
7919 // split deaths - a free chunk is removed from its free list because
7920 // it is being split into two or more chunks.
7921 // split birth - a free chunk is being added to its free list because
7922 // a larger free chunk has been split and resulted in this free chunk.
7923 // coal death - a free chunk is being removed from its free list because
7924 // it is being coalesced into a large free chunk.
7925 // coal birth - a free chunk is being added to its free list because
7926 // it was created when two or more free chunks where coalesced into
7927 // this free chunk.
7928 //
7929 // These statistics are used to determine the desired number of free
7930 // chunks of a given size. The desired number is chosen to be relative
7931 // to the end of a CMS sweep. The desired number at the end of a sweep
7932 // is the
7933 // count-at-end-of-previous-sweep (an amount that was enough)
7934 // - count-at-beginning-of-current-sweep (the excess)
7935 // + split-births (gains in this size during interval)
7936 // - split-deaths (demands on this size during interval)
7937 // where the interval is from the end of one sweep to the end of the
7938 // next.
7939 //
7940 // When sweeping the sweeper maintains an accumulated chunk which is
7941 // the chunk that is made up of chunks that have been coalesced. That
7942 // will be termed the left-hand chunk. A new chunk of garbage that
7943 // is being considered for coalescing will be referred to as the
7944 // right-hand chunk.
7945 //
7946 // When making a decision on whether to coalesce a right-hand chunk with
7947 // the current left-hand chunk, the current count vs. the desired count
7948 // of the left-hand chunk is considered. Also if the right-hand chunk
7949 // is near the large chunk at the end of the heap (see
7950 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7951 // left-hand chunk is coalesced.
7952 //
7953 // When making a decision about whether to split a chunk, the desired count
7954 // vs. the current count of the candidate to be split is also considered.
7955 // If the candidate is underpopulated (currently fewer chunks than desired)
7956 // a chunk of an overpopulated (currently more chunks than desired) size may
7957 // be chosen. The "hint" associated with a free list, if non-null, points
7958 // to a free list which may be overpopulated.
7959 //
7960
7961 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7962 size_t size = fc->size();
7963 // Chunks that cannot be coalesced are not in the
7964 // free lists.
7965 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7966 assert(_sp->verifyChunkInFreeLists(fc),
7967 "free chunk should be in free lists");
7968 }
7969 // a chunk that is already free, should not have been
7970 // marked in the bit map
7971 HeapWord* addr = (HeapWord*) fc;
7972 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7973 // Verify that the bit map has no bits marked between
7974 // addr and purported end of this block.
7975 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7976
7977 // Some chunks cannot be coalesced in under any circumstances.
7978 // See the definition of cantCoalesce().
7979 if (!fc->cantCoalesce()) {
7980 // This chunk can potentially be coalesced.
7981 if (_sp->adaptive_freelists()) {
7982 // All the work is done in
7983 doPostIsFreeOrGarbageChunk(fc, size);
7984 } else { // Not adaptive free lists
7985 // this is a free chunk that can potentially be coalesced by the sweeper;
7986 if (!inFreeRange()) {
7987 // if the next chunk is a free block that can't be coalesced
7988 // it doesn't make sense to remove this chunk from the free lists
7989 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7990 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7991 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
7992 nextChunk->isFree() && // which is free...
7993 nextChunk->cantCoalesce()) { // ... but cant be coalesced
7994 // nothing to do
7995 } else {
7996 // Potentially the start of a new free range:
7997 // Don't eagerly remove it from the free lists.
7998 // No need to remove it if it will just be put
7999 // back again. (Also from a pragmatic point of view
8000 // if it is a free block in a region that is beyond
8001 // any allocated blocks, an assertion will fail)
8002 // Remember the start of a free run.
8003 initialize_free_range(addr, true);
8004 // end - can coalesce with next chunk
8005 }
8006 } else {
8007 // the midst of a free range, we are coalescing
8008 debug_only(record_free_block_coalesced(fc);)
8009 if (CMSTraceSweeper) {
8010 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8011 }
8012 // remove it from the free lists
8013 _sp->removeFreeChunkFromFreeLists(fc);
8014 set_lastFreeRangeCoalesced(true);
8015 // If the chunk is being coalesced and the current free range is
8016 // in the free lists, remove the current free range so that it
8017 // will be returned to the free lists in its entirety - all
8018 // the coalesced pieces included.
8019 if (freeRangeInFreeLists()) {
8020 FreeChunk* ffc = (FreeChunk*) freeFinger();
8021 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8022 "Size of free range is inconsistent with chunk size.");
8023 if (CMSTestInFreeList) {
8024 assert(_sp->verifyChunkInFreeLists(ffc),
8025 "free range is not in free lists");
8026 }
8027 _sp->removeFreeChunkFromFreeLists(ffc);
8028 set_freeRangeInFreeLists(false);
8029 }
8030 }
8031 }
8032 } else {
8033 // Code path common to both original and adaptive free lists.
8034
8035 // cant coalesce with previous block; this should be treated
8036 // as the end of a free run if any
8037 if (inFreeRange()) {
8038 // we kicked some butt; time to pick up the garbage
8039 assert(freeFinger() < addr, "the finger pointeth off base");
8040 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8041 }
8042 // else, nothing to do, just continue
8043 }
8044 }
8045
8046 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
8047 // This is a chunk of garbage. It is not in any free list.
8048 // Add it to a free list or let it possibly be coalesced into
8049 // a larger chunk.
8050 HeapWord* addr = (HeapWord*) fc;
8051 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8052
8053 if (_sp->adaptive_freelists()) {
8054 // Verify that the bit map has no bits marked between
8055 // addr and purported end of just dead object.
8056 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8057
8058 doPostIsFreeOrGarbageChunk(fc, size);
8059 } else {
8060 if (!inFreeRange()) {
8061 // start of a new free range
8062 assert(size > 0, "A free range should have a size");
8063 initialize_free_range(addr, false);
8064
8065 } else {
8066 // this will be swept up when we hit the end of the
8067 // free range
8068 if (CMSTraceSweeper) {
8069 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8070 }
8071 // If the chunk is being coalesced and the current free range is
8072 // in the free lists, remove the current free range so that it
8073 // will be returned to the free lists in its entirety - all
8074 // the coalesced pieces included.
8075 if (freeRangeInFreeLists()) {
8076 FreeChunk* ffc = (FreeChunk*)freeFinger();
8077 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8078 "Size of free range is inconsistent with chunk size.");
8079 if (CMSTestInFreeList) {
8080 assert(_sp->verifyChunkInFreeLists(ffc),
8081 "free range is not in free lists");
8082 }
8083 _sp->removeFreeChunkFromFreeLists(ffc);
8084 set_freeRangeInFreeLists(false);
8085 }
8086 set_lastFreeRangeCoalesced(true);
8087 }
8088 // this will be swept up when we hit the end of the free range
8089
8090 // Verify that the bit map has no bits marked between
8091 // addr and purported end of just dead object.
8092 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8093 }
8094 return size;
8095 }
8096
8097 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
8098 HeapWord* addr = (HeapWord*) fc;
8099 // The sweeper has just found a live object. Return any accumulated
8100 // left hand chunk to the free lists.
8101 if (inFreeRange()) {
8102 if (_sp->adaptive_freelists()) {
8103 flushCurFreeChunk(freeFinger(),
8104 pointer_delta(addr, freeFinger()));
8105 } else { // not adaptive freelists
8106 set_inFreeRange(false);
8107 // Add the free range back to the free list if it is not already
8108 // there.
8109 if (!freeRangeInFreeLists()) {
8110 assert(freeFinger() < addr, "the finger pointeth off base");
8111 if (CMSTraceSweeper) {
8112 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
8113 "[coalesced:%d]\n",
8114 freeFinger(), pointer_delta(addr, freeFinger()),
8115 lastFreeRangeCoalesced());
8116 }
8117 _sp->addChunkAndRepairOffsetTable(freeFinger(),
8118 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8119 }
8120 }
8121 }
8122
8123 // Common code path for original and adaptive free lists.
8124
8125 // this object is live: we'd normally expect this to be
8126 // an oop, and like to assert the following:
8127 // assert(oop(addr)->is_oop(), "live block should be an oop");
8128 // However, as we commented above, this may be an object whose
8129 // header hasn't yet been initialized.
8130 size_t size;
8131 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8132 if (_bitMap->isMarked(addr + 1)) {
8133 // Determine the size from the bit map, rather than trying to
8134 // compute it from the object header.
8135 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8136 size = pointer_delta(nextOneAddr + 1, addr);
8137 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8138 "alignment problem");
8139
8140 #ifdef DEBUG
8141 if (oop(addr)->klass_or_null() != NULL &&
8142 ( !_collector->should_unload_classes()
8143 || (oop(addr)->is_parsable()) &&
8144 oop(addr)->is_conc_safe())) {
8145 // Ignore mark word because we are running concurrent with mutators
8146 assert(oop(addr)->is_oop(true), "live block should be an oop");
8147 // is_conc_safe is checked before performing this assertion
8148 // because an object that is not is_conc_safe may yet have
8149 // the return from size() correct.
8150 assert(size ==
8151 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8152 "P-mark and computed size do not agree");
8153 }
8154 #endif
8155
8156 } else {
8157 // This should be an initialized object that's alive.
8158 assert(oop(addr)->klass_or_null() != NULL &&
8159 (!_collector->should_unload_classes()
8160 || oop(addr)->is_parsable()),
8161 "Should be an initialized object");
8162 // Note that there are objects used during class redefinition
8163 // (e.g., merge_cp in VM_RedefineClasses::merge_cp_and_rewrite()
8164 // which are discarded with their is_conc_safe state still
8165 // false. These object may be floating garbage so may be
8166 // seen here. If they are floating garbage their size
8167 // should be attainable from their klass. Do not that
8168 // is_conc_safe() is true for oop(addr).
8169 // Ignore mark word because we are running concurrent with mutators
8170 assert(oop(addr)->is_oop(true), "live block should be an oop");
8171 // Verify that the bit map has no bits marked between
8172 // addr and purported end of this block.
8173 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8174 assert(size >= 3, "Necessary for Printezis marks to work");
8175 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8176 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8177 }
8178 return size;
8179 }
8180
8181 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8182 size_t chunkSize) {
8183 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8184 // scheme.
8185 bool fcInFreeLists = fc->isFree();
8186 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8187 assert((HeapWord*)fc <= _limit, "sweep invariant");
8188 if (CMSTestInFreeList && fcInFreeLists) {
8189 assert(_sp->verifyChunkInFreeLists(fc),
8190 "free chunk is not in free lists");
8191 }
8192
8193
8194 if (CMSTraceSweeper) {
8195 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8196 }
8197
8198 HeapWord* addr = (HeapWord*) fc;
8199
8200 bool coalesce;
8201 size_t left = pointer_delta(addr, freeFinger());
8202 size_t right = chunkSize;
8203 switch (FLSCoalescePolicy) {
8204 // numeric value forms a coalition aggressiveness metric
8205 case 0: { // never coalesce
8206 coalesce = false;
8207 break;
8208 }
8209 case 1: { // coalesce if left & right chunks on overpopulated lists
8210 coalesce = _sp->coalOverPopulated(left) &&
8211 _sp->coalOverPopulated(right);
8212 break;
8213 }
8214 case 2: { // coalesce if left chunk on overpopulated list (default)
8215 coalesce = _sp->coalOverPopulated(left);
8216 break;
8217 }
8218 case 3: { // coalesce if left OR right chunk on overpopulated list
8219 coalesce = _sp->coalOverPopulated(left) ||
8220 _sp->coalOverPopulated(right);
8221 break;
8222 }
8223 case 4: { // always coalesce
8224 coalesce = true;
8225 break;
8226 }
8227 default:
8228 ShouldNotReachHere();
8229 }
8230
8231 // Should the current free range be coalesced?
8232 // If the chunk is in a free range and either we decided to coalesce above
8233 // or the chunk is near the large block at the end of the heap
8234 // (isNearLargestChunk() returns true), then coalesce this chunk.
8235 bool doCoalesce = inFreeRange() &&
8236 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8237 if (doCoalesce) {
8238 // Coalesce the current free range on the left with the new
8239 // chunk on the right. If either is on a free list,
8240 // it must be removed from the list and stashed in the closure.
8241 if (freeRangeInFreeLists()) {
8242 FreeChunk* ffc = (FreeChunk*)freeFinger();
8243 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8244 "Size of free range is inconsistent with chunk size.");
8245 if (CMSTestInFreeList) {
8246 assert(_sp->verifyChunkInFreeLists(ffc),
8247 "Chunk is not in free lists");
8248 }
8249 _sp->coalDeath(ffc->size());
8250 _sp->removeFreeChunkFromFreeLists(ffc);
8251 set_freeRangeInFreeLists(false);
8252 }
8253 if (fcInFreeLists) {
8254 _sp->coalDeath(chunkSize);
8255 assert(fc->size() == chunkSize,
8256 "The chunk has the wrong size or is not in the free lists");
8257 _sp->removeFreeChunkFromFreeLists(fc);
8258 }
8259 set_lastFreeRangeCoalesced(true);
8260 } else { // not in a free range and/or should not coalesce
8261 // Return the current free range and start a new one.
8262 if (inFreeRange()) {
8263 // In a free range but cannot coalesce with the right hand chunk.
8264 // Put the current free range into the free lists.
8265 flushCurFreeChunk(freeFinger(),
8266 pointer_delta(addr, freeFinger()));
8267 }
8268 // Set up for new free range. Pass along whether the right hand
8269 // chunk is in the free lists.
8270 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8271 }
8272 }
8273 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8274 assert(inFreeRange(), "Should only be called if currently in a free range.");
8275 assert(size > 0,
8276 "A zero sized chunk cannot be added to the free lists.");
8277 if (!freeRangeInFreeLists()) {
8278 if(CMSTestInFreeList) {
8279 FreeChunk* fc = (FreeChunk*) chunk;
8280 fc->setSize(size);
8281 assert(!_sp->verifyChunkInFreeLists(fc),
8282 "chunk should not be in free lists yet");
8283 }
8284 if (CMSTraceSweeper) {
8285 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8286 chunk, size);
8287 }
8288 // A new free range is going to be starting. The current
8289 // free range has not been added to the free lists yet or
8290 // was removed so add it back.
8291 // If the current free range was coalesced, then the death
8292 // of the free range was recorded. Record a birth now.
8293 if (lastFreeRangeCoalesced()) {
8294 _sp->coalBirth(size);
8295 }
8296 _sp->addChunkAndRepairOffsetTable(chunk, size,
8297 lastFreeRangeCoalesced());
8298 }
8299 set_inFreeRange(false);
8300 set_freeRangeInFreeLists(false);
8301 }
8302
8303 // We take a break if we've been at this for a while,
8304 // so as to avoid monopolizing the locks involved.
8305 void SweepClosure::do_yield_work(HeapWord* addr) {
8306 // Return current free chunk being used for coalescing (if any)
8307 // to the appropriate freelist. After yielding, the next
8308 // free block encountered will start a coalescing range of
8309 // free blocks. If the next free block is adjacent to the
8310 // chunk just flushed, they will need to wait for the next
8311 // sweep to be coalesced.
8312 if (inFreeRange()) {
8313 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8314 }
8315
8316 // First give up the locks, then yield, then re-lock.
8317 // We should probably use a constructor/destructor idiom to
8318 // do this unlock/lock or modify the MutexUnlocker class to
8319 // serve our purpose. XXX
8320 assert_lock_strong(_bitMap->lock());
8321 assert_lock_strong(_freelistLock);
8322 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8323 "CMS thread should hold CMS token");
8324 _bitMap->lock()->unlock();
8325 _freelistLock->unlock();
8326 ConcurrentMarkSweepThread::desynchronize(true);
8327 ConcurrentMarkSweepThread::acknowledge_yield_request();
8328 _collector->stopTimer();
8329 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8330 if (PrintCMSStatistics != 0) {
8331 _collector->incrementYields();
8332 }
8333 _collector->icms_wait();
8334
8335 // See the comment in coordinator_yield()
8336 for (unsigned i = 0; i < CMSYieldSleepCount &&
8337 ConcurrentMarkSweepThread::should_yield() &&
8338 !CMSCollector::foregroundGCIsActive(); ++i) {
8339 os::sleep(Thread::current(), 1, false);
8340 ConcurrentMarkSweepThread::acknowledge_yield_request();
8341 }
8342
8343 ConcurrentMarkSweepThread::synchronize(true);
8344 _freelistLock->lock();
8345 _bitMap->lock()->lock_without_safepoint_check();
8346 _collector->startTimer();
8347 }
8348
8349 #ifndef PRODUCT
8350 // This is actually very useful in a product build if it can
8351 // be called from the debugger. Compile it into the product
8352 // as needed.
8353 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8354 return debug_cms_space->verifyChunkInFreeLists(fc);
8355 }
8356
8357 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8358 if (CMSTraceSweeper) {
8359 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8360 }
8361 }
8362 #endif
8363
8364 // CMSIsAliveClosure
8365 bool CMSIsAliveClosure::do_object_b(oop obj) {
8366 HeapWord* addr = (HeapWord*)obj;
8367 return addr != NULL &&
8368 (!_span.contains(addr) || _bit_map->isMarked(addr));
8369 }
8370
8371 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8372 MemRegion span,
8373 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8374 CMSMarkStack* revisit_stack, bool cpc):
8375 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8376 _span(span),
8377 _bit_map(bit_map),
8378 _mark_stack(mark_stack),
8379 _concurrent_precleaning(cpc) {
8380 assert(!_span.is_empty(), "Empty span could spell trouble");
8381 }
8382
8383
8384 // CMSKeepAliveClosure: the serial version
8385 void CMSKeepAliveClosure::do_oop(oop obj) {
8386 HeapWord* addr = (HeapWord*)obj;
8387 if (_span.contains(addr) &&
8388 !_bit_map->isMarked(addr)) {
8389 _bit_map->mark(addr);
8390 bool simulate_overflow = false;
8391 NOT_PRODUCT(
8392 if (CMSMarkStackOverflowALot &&
8393 _collector->simulate_overflow()) {
8394 // simulate a stack overflow
8395 simulate_overflow = true;
8396 }
8397 )
8398 if (simulate_overflow || !_mark_stack->push(obj)) {
8399 if (_concurrent_precleaning) {
8400 // We dirty the overflown object and let the remark
8401 // phase deal with it.
8402 assert(_collector->overflow_list_is_empty(), "Error");
8403 // In the case of object arrays, we need to dirty all of
8404 // the cards that the object spans. No locking or atomics
8405 // are needed since no one else can be mutating the mod union
8406 // table.
8407 if (obj->is_objArray()) {
8408 size_t sz = obj->size();
8409 HeapWord* end_card_addr =
8410 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8411 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8412 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8413 _collector->_modUnionTable.mark_range(redirty_range);
8414 } else {
8415 _collector->_modUnionTable.mark(addr);
8416 }
8417 _collector->_ser_kac_preclean_ovflw++;
8418 } else {
8419 _collector->push_on_overflow_list(obj);
8420 _collector->_ser_kac_ovflw++;
8421 }
8422 }
8423 }
8424 }
8425
8426 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8427 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8428
8429 // CMSParKeepAliveClosure: a parallel version of the above.
8430 // The work queues are private to each closure (thread),
8431 // but (may be) available for stealing by other threads.
8432 void CMSParKeepAliveClosure::do_oop(oop obj) {
8433 HeapWord* addr = (HeapWord*)obj;
8434 if (_span.contains(addr) &&
8435 !_bit_map->isMarked(addr)) {
8436 // In general, during recursive tracing, several threads
8437 // may be concurrently getting here; the first one to
8438 // "tag" it, claims it.
8439 if (_bit_map->par_mark(addr)) {
8440 bool res = _work_queue->push(obj);
8441 assert(res, "Low water mark should be much less than capacity");
8442 // Do a recursive trim in the hope that this will keep
8443 // stack usage lower, but leave some oops for potential stealers
8444 trim_queue(_low_water_mark);
8445 } // Else, another thread got there first
8446 }
8447 }
8448
8449 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8450 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8451
8452 void CMSParKeepAliveClosure::trim_queue(uint max) {
8453 while (_work_queue->size() > max) {
8454 oop new_oop;
8455 if (_work_queue->pop_local(new_oop)) {
8456 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8457 assert(_bit_map->isMarked((HeapWord*)new_oop),
8458 "no white objects on this stack!");
8459 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8460 // iterate over the oops in this oop, marking and pushing
8461 // the ones in CMS heap (i.e. in _span).
8462 new_oop->oop_iterate(&_mark_and_push);
8463 }
8464 }
8465 }
8466
8467 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8468 CMSCollector* collector,
8469 MemRegion span, CMSBitMap* bit_map,
8470 CMSMarkStack* revisit_stack,
8471 OopTaskQueue* work_queue):
8472 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8473 _span(span),
8474 _bit_map(bit_map),
8475 _work_queue(work_queue) { }
8476
8477 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8478 HeapWord* addr = (HeapWord*)obj;
8479 if (_span.contains(addr) &&
8480 !_bit_map->isMarked(addr)) {
8481 if (_bit_map->par_mark(addr)) {
8482 bool simulate_overflow = false;
8483 NOT_PRODUCT(
8484 if (CMSMarkStackOverflowALot &&
8485 _collector->par_simulate_overflow()) {
8486 // simulate a stack overflow
8487 simulate_overflow = true;
8488 }
8489 )
8490 if (simulate_overflow || !_work_queue->push(obj)) {
8491 _collector->par_push_on_overflow_list(obj);
8492 _collector->_par_kac_ovflw++;
8493 }
8494 } // Else another thread got there already
8495 }
8496 }
8497
8498 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8499 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8500
8501 //////////////////////////////////////////////////////////////////
8502 // CMSExpansionCause /////////////////////////////
8503 //////////////////////////////////////////////////////////////////
8504 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8505 switch (cause) {
8506 case _no_expansion:
8507 return "No expansion";
8508 case _satisfy_free_ratio:
8509 return "Free ratio";
8510 case _satisfy_promotion:
8511 return "Satisfy promotion";
8512 case _satisfy_allocation:
8513 return "allocation";
8514 case _allocate_par_lab:
8515 return "Par LAB";
8516 case _allocate_par_spooling_space:
8517 return "Par Spooling Space";
8518 case _adaptive_size_policy:
8519 return "Ergonomics";
8520 default:
8521 return "unknown";
8522 }
8523 }
8524
8525 void CMSDrainMarkingStackClosure::do_void() {
8526 // the max number to take from overflow list at a time
8527 const size_t num = _mark_stack->capacity()/4;
8528 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8529 "Overflow list should be NULL during concurrent phases");
8530 while (!_mark_stack->isEmpty() ||
8531 // if stack is empty, check the overflow list
8532 _collector->take_from_overflow_list(num, _mark_stack)) {
8533 oop obj = _mark_stack->pop();
8534 HeapWord* addr = (HeapWord*)obj;
8535 assert(_span.contains(addr), "Should be within span");
8536 assert(_bit_map->isMarked(addr), "Should be marked");
8537 assert(obj->is_oop(), "Should be an oop");
8538 obj->oop_iterate(_keep_alive);
8539 }
8540 }
8541
8542 void CMSParDrainMarkingStackClosure::do_void() {
8543 // drain queue
8544 trim_queue(0);
8545 }
8546
8547 // Trim our work_queue so its length is below max at return
8548 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8549 while (_work_queue->size() > max) {
8550 oop new_oop;
8551 if (_work_queue->pop_local(new_oop)) {
8552 assert(new_oop->is_oop(), "Expected an oop");
8553 assert(_bit_map->isMarked((HeapWord*)new_oop),
8554 "no white objects on this stack!");
8555 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8556 // iterate over the oops in this oop, marking and pushing
8557 // the ones in CMS heap (i.e. in _span).
8558 new_oop->oop_iterate(&_mark_and_push);
8559 }
8560 }
8561 }
8562
8563 ////////////////////////////////////////////////////////////////////
8564 // Support for Marking Stack Overflow list handling and related code
8565 ////////////////////////////////////////////////////////////////////
8566 // Much of the following code is similar in shape and spirit to the
8567 // code used in ParNewGC. We should try and share that code
8568 // as much as possible in the future.
8569
8570 #ifndef PRODUCT
8571 // Debugging support for CMSStackOverflowALot
8572
8573 // It's OK to call this multi-threaded; the worst thing
8574 // that can happen is that we'll get a bunch of closely
8575 // spaced simulated oveflows, but that's OK, in fact
8576 // probably good as it would exercise the overflow code
8577 // under contention.
8578 bool CMSCollector::simulate_overflow() {
8579 if (_overflow_counter-- <= 0) { // just being defensive
8580 _overflow_counter = CMSMarkStackOverflowInterval;
8581 return true;
8582 } else {
8583 return false;
8584 }
8585 }
8586
8587 bool CMSCollector::par_simulate_overflow() {
8588 return simulate_overflow();
8589 }
8590 #endif
8591
8592 // Single-threaded
8593 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8594 assert(stack->isEmpty(), "Expected precondition");
8595 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8596 size_t i = num;
8597 oop cur = _overflow_list;
8598 const markOop proto = markOopDesc::prototype();
8599 NOT_PRODUCT(ssize_t n = 0;)
8600 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8601 next = oop(cur->mark());
8602 cur->set_mark(proto); // until proven otherwise
8603 assert(cur->is_oop(), "Should be an oop");
8604 bool res = stack->push(cur);
8605 assert(res, "Bit off more than can chew?");
8606 NOT_PRODUCT(n++;)
8607 }
8608 _overflow_list = cur;
8609 #ifndef PRODUCT
8610 assert(_num_par_pushes >= n, "Too many pops?");
8611 _num_par_pushes -=n;
8612 #endif
8613 return !stack->isEmpty();
8614 }
8615
8616 #define BUSY (oop(0x1aff1aff))
8617 // (MT-safe) Get a prefix of at most "num" from the list.
8618 // The overflow list is chained through the mark word of
8619 // each object in the list. We fetch the entire list,
8620 // break off a prefix of the right size and return the
8621 // remainder. If other threads try to take objects from
8622 // the overflow list at that time, they will wait for
8623 // some time to see if data becomes available. If (and
8624 // only if) another thread places one or more object(s)
8625 // on the global list before we have returned the suffix
8626 // to the global list, we will walk down our local list
8627 // to find its end and append the global list to
8628 // our suffix before returning it. This suffix walk can
8629 // prove to be expensive (quadratic in the amount of traffic)
8630 // when there are many objects in the overflow list and
8631 // there is much producer-consumer contention on the list.
8632 // *NOTE*: The overflow list manipulation code here and
8633 // in ParNewGeneration:: are very similar in shape,
8634 // except that in the ParNew case we use the old (from/eden)
8635 // copy of the object to thread the list via its klass word.
8636 // Because of the common code, if you make any changes in
8637 // the code below, please check the ParNew version to see if
8638 // similar changes might be needed.
8639 // CR 6797058 has been filed to consolidate the common code.
8640 bool CMSCollector::par_take_from_overflow_list(size_t num,
8641 OopTaskQueue* work_q) {
8642 assert(work_q->size() == 0, "First empty local work queue");
8643 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8644 if (_overflow_list == NULL) {
8645 return false;
8646 }
8647 // Grab the entire list; we'll put back a suffix
8648 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8649 Thread* tid = Thread::current();
8650 size_t CMSOverflowSpinCount = (size_t)ParallelGCThreads;
8651 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8652 // If the list is busy, we spin for a short while,
8653 // sleeping between attempts to get the list.
8654 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8655 os::sleep(tid, sleep_time_millis, false);
8656 if (_overflow_list == NULL) {
8657 // Nothing left to take
8658 return false;
8659 } else if (_overflow_list != BUSY) {
8660 // Try and grab the prefix
8661 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8662 }
8663 }
8664 // If the list was found to be empty, or we spun long
8665 // enough, we give up and return empty-handed. If we leave
8666 // the list in the BUSY state below, it must be the case that
8667 // some other thread holds the overflow list and will set it
8668 // to a non-BUSY state in the future.
8669 if (prefix == NULL || prefix == BUSY) {
8670 // Nothing to take or waited long enough
8671 if (prefix == NULL) {
8672 // Write back the NULL in case we overwrote it with BUSY above
8673 // and it is still the same value.
8674 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8675 }
8676 return false;
8677 }
8678 assert(prefix != NULL && prefix != BUSY, "Error");
8679 size_t i = num;
8680 oop cur = prefix;
8681 // Walk down the first "num" objects, unless we reach the end.
8682 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8683 if (cur->mark() == NULL) {
8684 // We have "num" or fewer elements in the list, so there
8685 // is nothing to return to the global list.
8686 // Write back the NULL in lieu of the BUSY we wrote
8687 // above, if it is still the same value.
8688 if (_overflow_list == BUSY) {
8689 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8690 }
8691 } else {
8692 // Chop off the suffix and rerturn it to the global list.
8693 assert(cur->mark() != BUSY, "Error");
8694 oop suffix_head = cur->mark(); // suffix will be put back on global list
8695 cur->set_mark(NULL); // break off suffix
8696 // It's possible that the list is still in the empty(busy) state
8697 // we left it in a short while ago; in that case we may be
8698 // able to place back the suffix without incurring the cost
8699 // of a walk down the list.
8700 oop observed_overflow_list = _overflow_list;
8701 oop cur_overflow_list = observed_overflow_list;
8702 bool attached = false;
8703 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8704 observed_overflow_list =
8705 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8706 if (cur_overflow_list == observed_overflow_list) {
8707 attached = true;
8708 break;
8709 } else cur_overflow_list = observed_overflow_list;
8710 }
8711 if (!attached) {
8712 // Too bad, someone else sneaked in (at least) an element; we'll need
8713 // to do a splice. Find tail of suffix so we can prepend suffix to global
8714 // list.
8715 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8716 oop suffix_tail = cur;
8717 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8718 "Tautology");
8719 observed_overflow_list = _overflow_list;
8720 do {
8721 cur_overflow_list = observed_overflow_list;
8722 if (cur_overflow_list != BUSY) {
8723 // Do the splice ...
8724 suffix_tail->set_mark(markOop(cur_overflow_list));
8725 } else { // cur_overflow_list == BUSY
8726 suffix_tail->set_mark(NULL);
8727 }
8728 // ... and try to place spliced list back on overflow_list ...
8729 observed_overflow_list =
8730 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8731 } while (cur_overflow_list != observed_overflow_list);
8732 // ... until we have succeeded in doing so.
8733 }
8734 }
8735
8736 // Push the prefix elements on work_q
8737 assert(prefix != NULL, "control point invariant");
8738 const markOop proto = markOopDesc::prototype();
8739 oop next;
8740 NOT_PRODUCT(ssize_t n = 0;)
8741 for (cur = prefix; cur != NULL; cur = next) {
8742 next = oop(cur->mark());
8743 cur->set_mark(proto); // until proven otherwise
8744 assert(cur->is_oop(), "Should be an oop");
8745 bool res = work_q->push(cur);
8746 assert(res, "Bit off more than we can chew?");
8747 NOT_PRODUCT(n++;)
8748 }
8749 #ifndef PRODUCT
8750 assert(_num_par_pushes >= n, "Too many pops?");
8751 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8752 #endif
8753 return true;
8754 }
8755
8756 // Single-threaded
8757 void CMSCollector::push_on_overflow_list(oop p) {
8758 NOT_PRODUCT(_num_par_pushes++;)
8759 assert(p->is_oop(), "Not an oop");
8760 preserve_mark_if_necessary(p);
8761 p->set_mark((markOop)_overflow_list);
8762 _overflow_list = p;
8763 }
8764
8765 // Multi-threaded; use CAS to prepend to overflow list
8766 void CMSCollector::par_push_on_overflow_list(oop p) {
8767 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8768 assert(p->is_oop(), "Not an oop");
8769 par_preserve_mark_if_necessary(p);
8770 oop observed_overflow_list = _overflow_list;
8771 oop cur_overflow_list;
8772 do {
8773 cur_overflow_list = observed_overflow_list;
8774 if (cur_overflow_list != BUSY) {
8775 p->set_mark(markOop(cur_overflow_list));
8776 } else {
8777 p->set_mark(NULL);
8778 }
8779 observed_overflow_list =
8780 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8781 } while (cur_overflow_list != observed_overflow_list);
8782 }
8783 #undef BUSY
8784
8785 // Single threaded
8786 // General Note on GrowableArray: pushes may silently fail
8787 // because we are (temporarily) out of C-heap for expanding
8788 // the stack. The problem is quite ubiquitous and affects
8789 // a lot of code in the JVM. The prudent thing for GrowableArray
8790 // to do (for now) is to exit with an error. However, that may
8791 // be too draconian in some cases because the caller may be
8792 // able to recover without much harm. For such cases, we
8793 // should probably introduce a "soft_push" method which returns
8794 // an indication of success or failure with the assumption that
8795 // the caller may be able to recover from a failure; code in
8796 // the VM can then be changed, incrementally, to deal with such
8797 // failures where possible, thus, incrementally hardening the VM
8798 // in such low resource situations.
8799 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8800 if (_preserved_oop_stack == NULL) {
8801 assert(_preserved_mark_stack == NULL,
8802 "bijection with preserved_oop_stack");
8803 // Allocate the stacks
8804 _preserved_oop_stack = new (ResourceObj::C_HEAP)
8805 GrowableArray<oop>(PreserveMarkStackSize, true);
8806 _preserved_mark_stack = new (ResourceObj::C_HEAP)
8807 GrowableArray<markOop>(PreserveMarkStackSize, true);
8808 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8809 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8810 "Preserved Mark/Oop Stack for CMS (C-heap)");
8811 }
8812 }
8813 _preserved_oop_stack->push(p);
8814 _preserved_mark_stack->push(m);
8815 assert(m == p->mark(), "Mark word changed");
8816 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8817 "bijection");
8818 }
8819
8820 // Single threaded
8821 void CMSCollector::preserve_mark_if_necessary(oop p) {
8822 markOop m = p->mark();
8823 if (m->must_be_preserved(p)) {
8824 preserve_mark_work(p, m);
8825 }
8826 }
8827
8828 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8829 markOop m = p->mark();
8830 if (m->must_be_preserved(p)) {
8831 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8832 // Even though we read the mark word without holding
8833 // the lock, we are assured that it will not change
8834 // because we "own" this oop, so no other thread can
8835 // be trying to push it on the overflow list; see
8836 // the assertion in preserve_mark_work() that checks
8837 // that m == p->mark().
8838 preserve_mark_work(p, m);
8839 }
8840 }
8841
8842 // We should be able to do this multi-threaded,
8843 // a chunk of stack being a task (this is
8844 // correct because each oop only ever appears
8845 // once in the overflow list. However, it's
8846 // not very easy to completely overlap this with
8847 // other operations, so will generally not be done
8848 // until all work's been completed. Because we
8849 // expect the preserved oop stack (set) to be small,
8850 // it's probably fine to do this single-threaded.
8851 // We can explore cleverer concurrent/overlapped/parallel
8852 // processing of preserved marks if we feel the
8853 // need for this in the future. Stack overflow should
8854 // be so rare in practice and, when it happens, its
8855 // effect on performance so great that this will
8856 // likely just be in the noise anyway.
8857 void CMSCollector::restore_preserved_marks_if_any() {
8858 if (_preserved_oop_stack == NULL) {
8859 assert(_preserved_mark_stack == NULL,
8860 "bijection with preserved_oop_stack");
8861 return;
8862 }
8863
8864 assert(SafepointSynchronize::is_at_safepoint(),
8865 "world should be stopped");
8866 assert(Thread::current()->is_ConcurrentGC_thread() ||
8867 Thread::current()->is_VM_thread(),
8868 "should be single-threaded");
8869
8870 int length = _preserved_oop_stack->length();
8871 assert(_preserved_mark_stack->length() == length, "bijection");
8872 for (int i = 0; i < length; i++) {
8873 oop p = _preserved_oop_stack->at(i);
8874 assert(p->is_oop(), "Should be an oop");
8875 assert(_span.contains(p), "oop should be in _span");
8876 assert(p->mark() == markOopDesc::prototype(),
8877 "Set when taken from overflow list");
8878 markOop m = _preserved_mark_stack->at(i);
8879 p->set_mark(m);
8880 }
8881 _preserved_mark_stack->clear();
8882 _preserved_oop_stack->clear();
8883 assert(_preserved_mark_stack->is_empty() &&
8884 _preserved_oop_stack->is_empty(),
8885 "stacks were cleared above");
8886 }
8887
8888 #ifndef PRODUCT
8889 bool CMSCollector::no_preserved_marks() const {
8890 return ( ( _preserved_mark_stack == NULL
8891 && _preserved_oop_stack == NULL)
8892 || ( _preserved_mark_stack->is_empty()
8893 && _preserved_oop_stack->is_empty()));
8894 }
8895 #endif
8896
8897 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8898 {
8899 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8900 CMSAdaptiveSizePolicy* size_policy =
8901 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8902 assert(size_policy->is_gc_cms_adaptive_size_policy(),
8903 "Wrong type for size policy");
8904 return size_policy;
8905 }
8906
8907 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8908 size_t desired_promo_size) {
8909 if (cur_promo_size < desired_promo_size) {
8910 size_t expand_bytes = desired_promo_size - cur_promo_size;
8911 if (PrintAdaptiveSizePolicy && Verbose) {
8912 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8913 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8914 expand_bytes);
8915 }
8916 expand(expand_bytes,
8917 MinHeapDeltaBytes,
8918 CMSExpansionCause::_adaptive_size_policy);
8919 } else if (desired_promo_size < cur_promo_size) {
8920 size_t shrink_bytes = cur_promo_size - desired_promo_size;
8921 if (PrintAdaptiveSizePolicy && Verbose) {
8922 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8923 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8924 shrink_bytes);
8925 }
8926 shrink(shrink_bytes);
8927 }
8928 }
8929
8930 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8931 GenCollectedHeap* gch = GenCollectedHeap::heap();
8932 CMSGCAdaptivePolicyCounters* counters =
8933 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8934 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8935 "Wrong kind of counters");
8936 return counters;
8937 }
8938
8939
8940 void ASConcurrentMarkSweepGeneration::update_counters() {
8941 if (UsePerfData) {
8942 _space_counters->update_all();
8943 _gen_counters->update_all();
8944 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8945 GenCollectedHeap* gch = GenCollectedHeap::heap();
8946 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8947 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8948 "Wrong gc statistics type");
8949 counters->update_counters(gc_stats_l);
8950 }
8951 }
8952
8953 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8954 if (UsePerfData) {
8955 _space_counters->update_used(used);
8956 _space_counters->update_capacity();
8957 _gen_counters->update_all();
8958
8959 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8960 GenCollectedHeap* gch = GenCollectedHeap::heap();
8961 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8962 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8963 "Wrong gc statistics type");
8964 counters->update_counters(gc_stats_l);
8965 }
8966 }
8967
8968 // The desired expansion delta is computed so that:
8969 // . desired free percentage or greater is used
8970 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8971 assert_locked_or_safepoint(Heap_lock);
8972
8973 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8974
8975 // If incremental collection failed, we just want to expand
8976 // to the limit.
8977 if (incremental_collection_failed()) {
8978 clear_incremental_collection_failed();
8979 grow_to_reserved();
8980 return;
8981 }
8982
8983 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8984
8985 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8986 "Wrong type of heap");
8987 int prev_level = level() - 1;
8988 assert(prev_level >= 0, "The cms generation is the lowest generation");
8989 Generation* prev_gen = gch->get_gen(prev_level);
8990 assert(prev_gen->kind() == Generation::ASParNew,
8991 "Wrong type of young generation");
8992 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8993 size_t cur_eden = younger_gen->eden()->capacity();
8994 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8995 size_t cur_promo = free();
8996 size_policy->compute_tenured_generation_free_space(cur_promo,
8997 max_available(),
8998 cur_eden);
8999 resize(cur_promo, size_policy->promo_size());
9000
9001 // Record the new size of the space in the cms generation
9002 // that is available for promotions. This is temporary.
9003 // It should be the desired promo size.
9004 size_policy->avg_cms_promo()->sample(free());
9005 size_policy->avg_old_live()->sample(used());
9006
9007 if (UsePerfData) {
9008 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9009 counters->update_cms_capacity_counter(capacity());
9010 }
9011 }
9012
9013 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9014 assert_locked_or_safepoint(Heap_lock);
9015 assert_lock_strong(freelistLock());
9016 HeapWord* old_end = _cmsSpace->end();
9017 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9018 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9019 FreeChunk* chunk_at_end = find_chunk_at_end();
9020 if (chunk_at_end == NULL) {
9021 // No room to shrink
9022 if (PrintGCDetails && Verbose) {
9023 gclog_or_tty->print_cr("No room to shrink: old_end "
9024 PTR_FORMAT " unallocated_start " PTR_FORMAT
9025 " chunk_at_end " PTR_FORMAT,
9026 old_end, unallocated_start, chunk_at_end);
9027 }
9028 return;
9029 } else {
9030
9031 // Find the chunk at the end of the space and determine
9032 // how much it can be shrunk.
9033 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9034 size_t aligned_shrinkable_size_in_bytes =
9035 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9036 assert(unallocated_start <= chunk_at_end->end(),
9037 "Inconsistent chunk at end of space");
9038 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9039 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9040
9041 // Shrink the underlying space
9042 _virtual_space.shrink_by(bytes);
9043 if (PrintGCDetails && Verbose) {
9044 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9045 " desired_bytes " SIZE_FORMAT
9046 " shrinkable_size_in_bytes " SIZE_FORMAT
9047 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9048 " bytes " SIZE_FORMAT,
9049 desired_bytes, shrinkable_size_in_bytes,
9050 aligned_shrinkable_size_in_bytes, bytes);
9051 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9052 " unallocated_start " SIZE_FORMAT,
9053 old_end, unallocated_start);
9054 }
9055
9056 // If the space did shrink (shrinking is not guaranteed),
9057 // shrink the chunk at the end by the appropriate amount.
9058 if (((HeapWord*)_virtual_space.high()) < old_end) {
9059 size_t new_word_size =
9060 heap_word_size(_virtual_space.committed_size());
9061
9062 // Have to remove the chunk from the dictionary because it is changing
9063 // size and might be someplace elsewhere in the dictionary.
9064
9065 // Get the chunk at end, shrink it, and put it
9066 // back.
9067 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9068 size_t word_size_change = word_size_before - new_word_size;
9069 size_t chunk_at_end_old_size = chunk_at_end->size();
9070 assert(chunk_at_end_old_size >= word_size_change,
9071 "Shrink is too large");
9072 chunk_at_end->setSize(chunk_at_end_old_size -
9073 word_size_change);
9074 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9075 word_size_change);
9076
9077 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9078
9079 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9080 _bts->resize(new_word_size); // resize the block offset shared array
9081 Universe::heap()->barrier_set()->resize_covered_region(mr);
9082 _cmsSpace->assert_locked();
9083 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9084
9085 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9086
9087 // update the space and generation capacity counters
9088 if (UsePerfData) {
9089 _space_counters->update_capacity();
9090 _gen_counters->update_all();
9091 }
9092
9093 if (Verbose && PrintGCDetails) {
9094 size_t new_mem_size = _virtual_space.committed_size();
9095 size_t old_mem_size = new_mem_size + bytes;
9096 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9097 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9098 }
9099 }
9100
9101 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9102 "Inconsistency at end of space");
9103 assert(chunk_at_end->end() == _cmsSpace->end(),
9104 "Shrinking is inconsistent");
9105 return;
9106 }
9107 }
9108
9109 // Transfer some number of overflown objects to usual marking
9110 // stack. Return true if some objects were transferred.
9111 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9112 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9113 (size_t)ParGCDesiredObjsFromOverflowList);
9114
9115 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9116 assert(_collector->overflow_list_is_empty() || res,
9117 "If list is not empty, we should have taken something");
9118 assert(!res || !_mark_stack->isEmpty(),
9119 "If we took something, it should now be on our stack");
9120 return res;
9121 }
9122
9123 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9124 size_t res = _sp->block_size_no_stall(addr, _collector);
9125 assert(res != 0, "Should always be able to compute a size");
9126 if (_sp->block_is_obj(addr)) {
9127 if (_live_bit_map->isMarked(addr)) {
9128 // It can't have been dead in a previous cycle
9129 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9130 } else {
9131 _dead_bit_map->mark(addr); // mark the dead object
9132 }
9133 }
9134 return res;
9135 }
9136
9137 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase): TraceMemoryManagerStats() {
9138
9139 switch (phase) {
9140 case CMSCollector::InitialMarking:
9141 initialize(true /* fullGC */ ,
9142 true /* recordGCBeginTime */,
9143 true /* recordPreGCUsage */,
9144 false /* recordPeakUsage */,
9145 false /* recordPostGCusage */,
9146 true /* recordAccumulatedGCTime */,
9147 false /* recordGCEndTime */,
9148 false /* countCollection */ );
9149 break;
9150
9151 case CMSCollector::FinalMarking:
9152 initialize(true /* fullGC */ ,
9153 false /* recordGCBeginTime */,
9154 false /* recordPreGCUsage */,
9155 false /* recordPeakUsage */,
9156 false /* recordPostGCusage */,
9157 true /* recordAccumulatedGCTime */,
9158 false /* recordGCEndTime */,
9159 false /* countCollection */ );
9160 break;
9161
9162 case CMSCollector::Sweeping:
9163 initialize(true /* fullGC */ ,
9164 false /* recordGCBeginTime */,
9165 false /* recordPreGCUsage */,
9166 true /* recordPeakUsage */,
9167 true /* recordPostGCusage */,
9168 false /* recordAccumulatedGCTime */,
9169 true /* recordGCEndTime */,
9170 true /* countCollection */ );
9171 break;
9172
9173 default:
9174 ShouldNotReachHere();
9175 }
9176 }
9177
9178 // when bailing out of cms in concurrent mode failure
9179 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(): TraceMemoryManagerStats() {
9180 initialize(true /* fullGC */ ,
9181 true /* recordGCBeginTime */,
9182 true /* recordPreGCUsage */,
9183 true /* recordPeakUsage */,
9184 true /* recordPostGCusage */,
9185 true /* recordAccumulatedGCTime */,
9186 true /* recordGCEndTime */,
9187 true /* countCollection */ );
9188 }
9189