1 /*
2 * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/symbolTable.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "code/codeCache.hpp"
29 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.hpp"
52 #include "memory/referencePolicy.hpp"
53 #include "memory/resourceArea.hpp"
54 #include "oops/oop.inline.hpp"
55 #include "prims/jvmtiExport.hpp"
56 #include "runtime/globals_extension.hpp"
57 #include "runtime/handles.inline.hpp"
58 #include "runtime/java.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "services/memoryService.hpp"
61 #include "services/runtimeService.hpp"
62
63 // statics
64 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
65 bool CMSCollector::_full_gc_requested = false;
66 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
67
68 //////////////////////////////////////////////////////////////////
69 // In support of CMS/VM thread synchronization
70 //////////////////////////////////////////////////////////////////
71 // We split use of the CGC_lock into 2 "levels".
72 // The low-level locking is of the usual CGC_lock monitor. We introduce
73 // a higher level "token" (hereafter "CMS token") built on top of the
74 // low level monitor (hereafter "CGC lock").
75 // The token-passing protocol gives priority to the VM thread. The
76 // CMS-lock doesn't provide any fairness guarantees, but clients
77 // should ensure that it is only held for very short, bounded
78 // durations.
79 //
80 // When either of the CMS thread or the VM thread is involved in
81 // collection operations during which it does not want the other
82 // thread to interfere, it obtains the CMS token.
83 //
84 // If either thread tries to get the token while the other has
85 // it, that thread waits. However, if the VM thread and CMS thread
86 // both want the token, then the VM thread gets priority while the
87 // CMS thread waits. This ensures, for instance, that the "concurrent"
88 // phases of the CMS thread's work do not block out the VM thread
89 // for long periods of time as the CMS thread continues to hog
90 // the token. (See bug 4616232).
91 //
92 // The baton-passing functions are, however, controlled by the
93 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
94 // and here the low-level CMS lock, not the high level token,
95 // ensures mutual exclusion.
96 //
97 // Two important conditions that we have to satisfy:
98 // 1. if a thread does a low-level wait on the CMS lock, then it
99 // relinquishes the CMS token if it were holding that token
100 // when it acquired the low-level CMS lock.
101 // 2. any low-level notifications on the low-level lock
102 // should only be sent when a thread has relinquished the token.
103 //
104 // In the absence of either property, we'd have potential deadlock.
105 //
106 // We protect each of the CMS (concurrent and sequential) phases
107 // with the CMS _token_, not the CMS _lock_.
108 //
109 // The only code protected by CMS lock is the token acquisition code
110 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
111 // baton-passing code.
112 //
113 // Unfortunately, i couldn't come up with a good abstraction to factor and
114 // hide the naked CGC_lock manipulation in the baton-passing code
115 // further below. That's something we should try to do. Also, the proof
116 // of correctness of this 2-level locking scheme is far from obvious,
117 // and potentially quite slippery. We have an uneasy supsicion, for instance,
118 // that there may be a theoretical possibility of delay/starvation in the
119 // low-level lock/wait/notify scheme used for the baton-passing because of
120 // potential intereference with the priority scheme embodied in the
121 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
122 // invocation further below and marked with "XXX 20011219YSR".
123 // Indeed, as we note elsewhere, this may become yet more slippery
124 // in the presence of multiple CMS and/or multiple VM threads. XXX
125
126 class CMSTokenSync: public StackObj {
127 private:
128 bool _is_cms_thread;
129 public:
130 CMSTokenSync(bool is_cms_thread):
131 _is_cms_thread(is_cms_thread) {
132 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
133 "Incorrect argument to constructor");
134 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
135 }
136
137 ~CMSTokenSync() {
138 assert(_is_cms_thread ?
139 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
140 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
141 "Incorrect state");
142 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
143 }
144 };
145
146 // Convenience class that does a CMSTokenSync, and then acquires
147 // upto three locks.
148 class CMSTokenSyncWithLocks: public CMSTokenSync {
149 private:
150 // Note: locks are acquired in textual declaration order
151 // and released in the opposite order
152 MutexLockerEx _locker1, _locker2, _locker3;
153 public:
154 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
155 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
156 CMSTokenSync(is_cms_thread),
157 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
158 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
159 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
160 { }
161 };
162
163
164 // Wrapper class to temporarily disable icms during a foreground cms collection.
165 class ICMSDisabler: public StackObj {
166 public:
167 // The ctor disables icms and wakes up the thread so it notices the change;
168 // the dtor re-enables icms. Note that the CMSCollector methods will check
169 // CMSIncrementalMode.
170 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
171 ~ICMSDisabler() { CMSCollector::enable_icms(); }
172 };
173
174 //////////////////////////////////////////////////////////////////
175 // Concurrent Mark-Sweep Generation /////////////////////////////
176 //////////////////////////////////////////////////////////////////
177
178 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
179
180 // This struct contains per-thread things necessary to support parallel
181 // young-gen collection.
182 class CMSParGCThreadState: public CHeapObj<mtGC> {
183 public:
184 CFLS_LAB lab;
185 PromotionInfo promo;
186
187 // Constructor.
188 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
189 promo.setSpace(cfls);
190 }
191 };
192
193 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
194 ReservedSpace rs, size_t initial_byte_size, int level,
195 CardTableRS* ct, bool use_adaptive_freelists,
196 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
197 CardGeneration(rs, initial_byte_size, level, ct),
198 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
199 _debug_collection_type(Concurrent_collection_type)
200 {
201 HeapWord* bottom = (HeapWord*) _virtual_space.low();
202 HeapWord* end = (HeapWord*) _virtual_space.high();
203
204 _direct_allocated_words = 0;
205 NOT_PRODUCT(
206 _numObjectsPromoted = 0;
207 _numWordsPromoted = 0;
208 _numObjectsAllocated = 0;
209 _numWordsAllocated = 0;
210 )
211
212 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
213 use_adaptive_freelists,
214 dictionaryChoice);
215 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
216 if (_cmsSpace == NULL) {
217 vm_exit_during_initialization(
218 "CompactibleFreeListSpace allocation failure");
219 }
220 _cmsSpace->_gen = this;
221
222 _gc_stats = new CMSGCStats();
223
224 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
225 // offsets match. The ability to tell free chunks from objects
226 // depends on this property.
227 debug_only(
228 FreeChunk* junk = NULL;
229 assert(UseCompressedOops ||
230 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
231 "Offset of FreeChunk::_prev within FreeChunk must match"
232 " that of OopDesc::_klass within OopDesc");
233 )
234 if (CollectedHeap::use_parallel_gc_threads()) {
235 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
236 _par_gc_thread_states =
237 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
238 if (_par_gc_thread_states == NULL) {
239 vm_exit_during_initialization("Could not allocate par gc structs");
240 }
241 for (uint i = 0; i < ParallelGCThreads; i++) {
242 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
243 if (_par_gc_thread_states[i] == NULL) {
244 vm_exit_during_initialization("Could not allocate par gc structs");
245 }
246 }
247 } else {
248 _par_gc_thread_states = NULL;
249 }
250 _incremental_collection_failed = false;
251 // The "dilatation_factor" is the expansion that can occur on
252 // account of the fact that the minimum object size in the CMS
253 // generation may be larger than that in, say, a contiguous young
254 // generation.
255 // Ideally, in the calculation below, we'd compute the dilatation
256 // factor as: MinChunkSize/(promoting_gen's min object size)
257 // Since we do not have such a general query interface for the
258 // promoting generation, we'll instead just use the mimimum
259 // object size (which today is a header's worth of space);
260 // note that all arithmetic is in units of HeapWords.
261 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
262 assert(_dilatation_factor >= 1.0, "from previous assert");
263 }
264
265
266 // The field "_initiating_occupancy" represents the occupancy percentage
267 // at which we trigger a new collection cycle. Unless explicitly specified
268 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
269 // is calculated by:
270 //
271 // Let "f" be MinHeapFreeRatio in
272 //
273 // _intiating_occupancy = 100-f +
274 // f * (CMSTrigger[Perm]Ratio/100)
275 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
276 //
277 // That is, if we assume the heap is at its desired maximum occupancy at the
278 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
279 // space be allocated before initiating a new collection cycle.
280 //
281 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
282 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
283 if (io >= 0) {
284 _initiating_occupancy = (double)io / 100.0;
285 } else {
286 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
287 (double)(tr * MinHeapFreeRatio) / 100.0)
288 / 100.0;
289 }
290 }
291
292 void ConcurrentMarkSweepGeneration::ref_processor_init() {
293 assert(collector() != NULL, "no collector");
294 collector()->ref_processor_init();
295 }
296
297 void CMSCollector::ref_processor_init() {
298 if (_ref_processor == NULL) {
299 // Allocate and initialize a reference processor
300 _ref_processor =
301 new ReferenceProcessor(_span, // span
302 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
303 (int) ParallelGCThreads, // mt processing degree
304 _cmsGen->refs_discovery_is_mt(), // mt discovery
305 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
306 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
307 &_is_alive_closure, // closure for liveness info
308 false); // next field updates do not need write barrier
309 // Initialize the _ref_processor field of CMSGen
310 _cmsGen->set_ref_processor(_ref_processor);
311
312 // Allocate a dummy ref processor for perm gen.
313 ReferenceProcessor* rp2 = new ReferenceProcessor();
314 if (rp2 == NULL) {
315 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
316 }
317 _permGen->set_ref_processor(rp2);
318 }
319 }
320
321 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
326 gch->gen_policy()->size_policy();
327 assert(sp->is_gc_cms_adaptive_size_policy(),
328 "Wrong type of size policy");
329 return sp;
330 }
331
332 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
333 CMSGCAdaptivePolicyCounters* results =
334 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
335 assert(
336 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
337 "Wrong gc policy counter kind");
338 return results;
339 }
340
341
342 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
343
344 const char* gen_name = "old";
345
346 // Generation Counters - generation 1, 1 subspace
347 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
348
349 _space_counters = new GSpaceCounters(gen_name, 0,
350 _virtual_space.reserved_size(),
351 this, _gen_counters);
352 }
353
354 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
355 _cms_gen(cms_gen)
356 {
357 assert(alpha <= 100, "bad value");
358 _saved_alpha = alpha;
359
360 // Initialize the alphas to the bootstrap value of 100.
361 _gc0_alpha = _cms_alpha = 100;
362
363 _cms_begin_time.update();
364 _cms_end_time.update();
365
366 _gc0_duration = 0.0;
367 _gc0_period = 0.0;
368 _gc0_promoted = 0;
369
370 _cms_duration = 0.0;
371 _cms_period = 0.0;
372 _cms_allocated = 0;
373
374 _cms_used_at_gc0_begin = 0;
375 _cms_used_at_gc0_end = 0;
376 _allow_duty_cycle_reduction = false;
377 _valid_bits = 0;
378 _icms_duty_cycle = CMSIncrementalDutyCycle;
379 }
380
381 double CMSStats::cms_free_adjustment_factor(size_t free) const {
382 // TBD: CR 6909490
383 return 1.0;
384 }
385
386 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
387 }
388
389 // If promotion failure handling is on use
390 // the padded average size of the promotion for each
391 // young generation collection.
392 double CMSStats::time_until_cms_gen_full() const {
393 size_t cms_free = _cms_gen->cmsSpace()->free();
394 GenCollectedHeap* gch = GenCollectedHeap::heap();
395 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
396 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
397 if (cms_free > expected_promotion) {
398 // Start a cms collection if there isn't enough space to promote
399 // for the next minor collection. Use the padded average as
400 // a safety factor.
401 cms_free -= expected_promotion;
402
403 // Adjust by the safety factor.
404 double cms_free_dbl = (double)cms_free;
405 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
406 // Apply a further correction factor which tries to adjust
407 // for recent occurance of concurrent mode failures.
408 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
409 cms_free_dbl = cms_free_dbl * cms_adjustment;
410
411 if (PrintGCDetails && Verbose) {
412 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
413 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
414 cms_free, expected_promotion);
415 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
416 cms_free_dbl, cms_consumption_rate() + 1.0);
417 }
418 // Add 1 in case the consumption rate goes to zero.
419 return cms_free_dbl / (cms_consumption_rate() + 1.0);
420 }
421 return 0.0;
422 }
423
424 // Compare the duration of the cms collection to the
425 // time remaining before the cms generation is empty.
426 // Note that the time from the start of the cms collection
427 // to the start of the cms sweep (less than the total
428 // duration of the cms collection) can be used. This
429 // has been tried and some applications experienced
430 // promotion failures early in execution. This was
431 // possibly because the averages were not accurate
432 // enough at the beginning.
433 double CMSStats::time_until_cms_start() const {
434 // We add "gc0_period" to the "work" calculation
435 // below because this query is done (mostly) at the
436 // end of a scavenge, so we need to conservatively
437 // account for that much possible delay
438 // in the query so as to avoid concurrent mode failures
439 // due to starting the collection just a wee bit too
440 // late.
441 double work = cms_duration() + gc0_period();
442 double deadline = time_until_cms_gen_full();
443 // If a concurrent mode failure occurred recently, we want to be
444 // more conservative and halve our expected time_until_cms_gen_full()
445 if (work > deadline) {
446 if (Verbose && PrintGCDetails) {
447 gclog_or_tty->print(
448 " CMSCollector: collect because of anticipated promotion "
449 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
450 gc0_period(), time_until_cms_gen_full());
451 }
452 return 0.0;
453 }
454 return work - deadline;
455 }
456
457 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
458 // amount of change to prevent wild oscillation.
459 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
460 unsigned int new_duty_cycle) {
461 assert(old_duty_cycle <= 100, "bad input value");
462 assert(new_duty_cycle <= 100, "bad input value");
463
464 // Note: use subtraction with caution since it may underflow (values are
465 // unsigned). Addition is safe since we're in the range 0-100.
466 unsigned int damped_duty_cycle = new_duty_cycle;
467 if (new_duty_cycle < old_duty_cycle) {
468 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
469 if (new_duty_cycle + largest_delta < old_duty_cycle) {
470 damped_duty_cycle = old_duty_cycle - largest_delta;
471 }
472 } else if (new_duty_cycle > old_duty_cycle) {
473 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
474 if (new_duty_cycle > old_duty_cycle + largest_delta) {
475 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
476 }
477 }
478 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
479
480 if (CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
482 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
483 }
484 return damped_duty_cycle;
485 }
486
487 unsigned int CMSStats::icms_update_duty_cycle_impl() {
488 assert(CMSIncrementalPacing && valid(),
489 "should be handled in icms_update_duty_cycle()");
490
491 double cms_time_so_far = cms_timer().seconds();
492 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
493 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
494
495 // Avoid division by 0.
496 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
497 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
498
499 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
500 if (new_duty_cycle > _icms_duty_cycle) {
501 // Avoid very small duty cycles (1 or 2); 0 is allowed.
502 if (new_duty_cycle > 2) {
503 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
504 new_duty_cycle);
505 }
506 } else if (_allow_duty_cycle_reduction) {
507 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
508 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
509 // Respect the minimum duty cycle.
510 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
511 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
512 }
513
514 if (PrintGCDetails || CMSTraceIncrementalPacing) {
515 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
516 }
517
518 _allow_duty_cycle_reduction = false;
519 return _icms_duty_cycle;
520 }
521
522 #ifndef PRODUCT
523 void CMSStats::print_on(outputStream *st) const {
524 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
525 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
526 gc0_duration(), gc0_period(), gc0_promoted());
527 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
528 cms_duration(), cms_duration_per_mb(),
529 cms_period(), cms_allocated());
530 st->print(",cms_since_beg=%g,cms_since_end=%g",
531 cms_time_since_begin(), cms_time_since_end());
532 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
533 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
534 if (CMSIncrementalMode) {
535 st->print(",dc=%d", icms_duty_cycle());
536 }
537
538 if (valid()) {
539 st->print(",promo_rate=%g,cms_alloc_rate=%g",
540 promotion_rate(), cms_allocation_rate());
541 st->print(",cms_consumption_rate=%g,time_until_full=%g",
542 cms_consumption_rate(), time_until_cms_gen_full());
543 }
544 st->print(" ");
545 }
546 #endif // #ifndef PRODUCT
547
548 CMSCollector::CollectorState CMSCollector::_collectorState =
549 CMSCollector::Idling;
550 bool CMSCollector::_foregroundGCIsActive = false;
551 bool CMSCollector::_foregroundGCShouldWait = false;
552
553 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
554 ConcurrentMarkSweepGeneration* permGen,
555 CardTableRS* ct,
556 ConcurrentMarkSweepPolicy* cp):
557 _cmsGen(cmsGen),
558 _permGen(permGen),
559 _ct(ct),
560 _ref_processor(NULL), // will be set later
561 _conc_workers(NULL), // may be set later
562 _abort_preclean(false),
563 _start_sampling(false),
564 _between_prologue_and_epilogue(false),
565 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
566 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
567 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
568 -1 /* lock-free */, "No_lock" /* dummy */),
569 _modUnionClosure(&_modUnionTable),
570 _modUnionClosurePar(&_modUnionTable),
571 // Adjust my span to cover old (cms) gen and perm gen
572 _span(cmsGen->reserved()._union(permGen->reserved())),
573 // Construct the is_alive_closure with _span & markBitMap
574 _is_alive_closure(_span, &_markBitMap),
575 _restart_addr(NULL),
576 _overflow_list(NULL),
577 _stats(cmsGen),
578 _eden_chunk_array(NULL), // may be set in ctor body
579 _eden_chunk_capacity(0), // -- ditto --
580 _eden_chunk_index(0), // -- ditto --
581 _survivor_plab_array(NULL), // -- ditto --
582 _survivor_chunk_array(NULL), // -- ditto --
583 _survivor_chunk_capacity(0), // -- ditto --
584 _survivor_chunk_index(0), // -- ditto --
585 _ser_pmc_preclean_ovflw(0),
586 _ser_kac_preclean_ovflw(0),
587 _ser_pmc_remark_ovflw(0),
588 _par_pmc_remark_ovflw(0),
589 _ser_kac_ovflw(0),
590 _par_kac_ovflw(0),
591 #ifndef PRODUCT
592 _num_par_pushes(0),
593 #endif
594 _collection_count_start(0),
595 _verifying(false),
596 _icms_start_limit(NULL),
597 _icms_stop_limit(NULL),
598 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
599 _completed_initialization(false),
600 _collector_policy(cp),
601 _should_unload_classes(false),
602 _concurrent_cycles_since_last_unload(0),
603 _roots_scanning_options(0),
604 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
605 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
606 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
607 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
608 _cms_start_registered(false)
609 {
610 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
611 ExplicitGCInvokesConcurrent = true;
612 }
613 // Now expand the span and allocate the collection support structures
614 // (MUT, marking bit map etc.) to cover both generations subject to
615 // collection.
616
617 // First check that _permGen is adjacent to _cmsGen and above it.
618 assert( _cmsGen->reserved().word_size() > 0
619 && _permGen->reserved().word_size() > 0,
620 "generations should not be of zero size");
621 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
622 "_cmsGen and _permGen should not overlap");
623 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
624 "_cmsGen->end() different from _permGen->start()");
625
626 // For use by dirty card to oop closures.
627 _cmsGen->cmsSpace()->set_collector(this);
628 _permGen->cmsSpace()->set_collector(this);
629
630 // Allocate MUT and marking bit map
631 {
632 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
633 if (!_markBitMap.allocate(_span)) {
634 warning("Failed to allocate CMS Bit Map");
635 return;
636 }
637 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
638 }
639 {
640 _modUnionTable.allocate(_span);
641 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
642 }
643
644 if (!_markStack.allocate(MarkStackSize)) {
645 warning("Failed to allocate CMS Marking Stack");
646 return;
647 }
648 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
649 warning("Failed to allocate CMS Revisit Stack");
650 return;
651 }
652
653 // Support for multi-threaded concurrent phases
654 if (CMSConcurrentMTEnabled) {
655 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
656 // just for now
657 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
658 }
659 if (ConcGCThreads > 1) {
660 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
661 ConcGCThreads, true);
662 if (_conc_workers == NULL) {
663 warning("GC/CMS: _conc_workers allocation failure: "
664 "forcing -CMSConcurrentMTEnabled");
665 CMSConcurrentMTEnabled = false;
666 } else {
667 _conc_workers->initialize_workers();
668 }
669 } else {
670 CMSConcurrentMTEnabled = false;
671 }
672 }
673 if (!CMSConcurrentMTEnabled) {
674 ConcGCThreads = 0;
675 } else {
676 // Turn off CMSCleanOnEnter optimization temporarily for
677 // the MT case where it's not fixed yet; see 6178663.
678 CMSCleanOnEnter = false;
679 }
680 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
681 "Inconsistency");
682
683 // Parallel task queues; these are shared for the
684 // concurrent and stop-world phases of CMS, but
685 // are not shared with parallel scavenge (ParNew).
686 {
687 uint i;
688 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
689
690 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
691 || ParallelRefProcEnabled)
692 && num_queues > 0) {
693 _task_queues = new OopTaskQueueSet(num_queues);
694 if (_task_queues == NULL) {
695 warning("task_queues allocation failure.");
696 return;
697 }
698 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
699 if (_hash_seed == NULL) {
700 warning("_hash_seed array allocation failure");
701 return;
702 }
703
704 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
705 for (i = 0; i < num_queues; i++) {
706 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
707 if (q == NULL) {
708 warning("work_queue allocation failure.");
709 return;
710 }
711 _task_queues->register_queue(i, q);
712 }
713 for (i = 0; i < num_queues; i++) {
714 _task_queues->queue(i)->initialize();
715 _hash_seed[i] = 17; // copied from ParNew
716 }
717 }
718 }
719
720 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
721 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
722
723 // Clip CMSBootstrapOccupancy between 0 and 100.
724 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
725 /(double)100;
726
727 _full_gcs_since_conc_gc = 0;
728
729 // Now tell CMS generations the identity of their collector
730 ConcurrentMarkSweepGeneration::set_collector(this);
731
732 // Create & start a CMS thread for this CMS collector
733 _cmsThread = ConcurrentMarkSweepThread::start(this);
734 assert(cmsThread() != NULL, "CMS Thread should have been created");
735 assert(cmsThread()->collector() == this,
736 "CMS Thread should refer to this gen");
737 assert(CGC_lock != NULL, "Where's the CGC_lock?");
738
739 // Support for parallelizing young gen rescan
740 GenCollectedHeap* gch = GenCollectedHeap::heap();
741 _young_gen = gch->prev_gen(_cmsGen);
742 if (gch->supports_inline_contig_alloc()) {
743 _top_addr = gch->top_addr();
744 _end_addr = gch->end_addr();
745 assert(_young_gen != NULL, "no _young_gen");
746 _eden_chunk_index = 0;
747 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
748 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
749 if (_eden_chunk_array == NULL) {
750 _eden_chunk_capacity = 0;
751 warning("GC/CMS: _eden_chunk_array allocation failure");
752 }
753 }
754 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
755
756 // Support for parallelizing survivor space rescan
757 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
758 const size_t max_plab_samples =
759 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
760
761 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
762 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
763 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
764 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
765 || _cursor == NULL) {
766 warning("Failed to allocate survivor plab/chunk array");
767 if (_survivor_plab_array != NULL) {
768 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
769 _survivor_plab_array = NULL;
770 }
771 if (_survivor_chunk_array != NULL) {
772 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
773 _survivor_chunk_array = NULL;
774 }
775 if (_cursor != NULL) {
776 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
777 _cursor = NULL;
778 }
779 } else {
780 _survivor_chunk_capacity = 2*max_plab_samples;
781 for (uint i = 0; i < ParallelGCThreads; i++) {
782 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
783 if (vec == NULL) {
784 warning("Failed to allocate survivor plab array");
785 for (int j = i; j > 0; j--) {
786 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
787 }
788 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
789 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
790 _survivor_plab_array = NULL;
791 _survivor_chunk_array = NULL;
792 _survivor_chunk_capacity = 0;
793 break;
794 } else {
795 ChunkArray* cur =
796 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
797 max_plab_samples);
798 assert(cur->end() == 0, "Should be 0");
799 assert(cur->array() == vec, "Should be vec");
800 assert(cur->capacity() == max_plab_samples, "Error");
801 }
802 }
803 }
804 }
805 assert( ( _survivor_plab_array != NULL
806 && _survivor_chunk_array != NULL)
807 || ( _survivor_chunk_capacity == 0
808 && _survivor_chunk_index == 0),
809 "Error");
810
811 // Choose what strong roots should be scanned depending on verification options
812 // and perm gen collection mode.
813 if (!CMSClassUnloadingEnabled) {
814 // If class unloading is disabled we want to include all classes into the root set.
815 add_root_scanning_option(SharedHeap::SO_AllClasses);
816 } else {
817 add_root_scanning_option(SharedHeap::SO_SystemClasses);
818 }
819
820 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
821 _gc_counters = new CollectorCounters("CMS", 1);
822 _completed_initialization = true;
823 _inter_sweep_timer.start(); // start of time
824 }
825
826 const char* ConcurrentMarkSweepGeneration::name() const {
827 return "concurrent mark-sweep generation";
828 }
829 void ConcurrentMarkSweepGeneration::update_counters() {
830 if (UsePerfData) {
831 _space_counters->update_all();
832 _gen_counters->update_all();
833 }
834 }
835
836 // this is an optimized version of update_counters(). it takes the
837 // used value as a parameter rather than computing it.
838 //
839 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
840 if (UsePerfData) {
841 _space_counters->update_used(used);
842 _space_counters->update_capacity();
843 _gen_counters->update_all();
844 }
845 }
846
847 void ConcurrentMarkSweepGeneration::print() const {
848 Generation::print();
849 cmsSpace()->print();
850 }
851
852 #ifndef PRODUCT
853 void ConcurrentMarkSweepGeneration::print_statistics() {
854 cmsSpace()->printFLCensus(0);
855 }
856 #endif
857
858 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
859 GenCollectedHeap* gch = GenCollectedHeap::heap();
860 if (PrintGCDetails) {
861 if (Verbose) {
862 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
863 level(), short_name(), s, used(), capacity());
864 } else {
865 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
866 level(), short_name(), s, used() / K, capacity() / K);
867 }
868 }
869 if (Verbose) {
870 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
871 gch->used(), gch->capacity());
872 } else {
873 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
874 gch->used() / K, gch->capacity() / K);
875 }
876 }
877
878 size_t
879 ConcurrentMarkSweepGeneration::contiguous_available() const {
880 // dld proposes an improvement in precision here. If the committed
881 // part of the space ends in a free block we should add that to
882 // uncommitted size in the calculation below. Will make this
883 // change later, staying with the approximation below for the
884 // time being. -- ysr.
885 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
886 }
887
888 size_t
889 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
890 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
891 }
892
893 size_t ConcurrentMarkSweepGeneration::max_available() const {
894 return free() + _virtual_space.uncommitted_size();
895 }
896
897 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
898 size_t available = max_available();
899 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
900 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
901 if (Verbose && PrintGCDetails) {
902 gclog_or_tty->print_cr(
903 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
904 "max_promo("SIZE_FORMAT")",
905 res? "":" not", available, res? ">=":"<",
906 av_promo, max_promotion_in_bytes);
907 }
908 return res;
909 }
910
911 // At a promotion failure dump information on block layout in heap
912 // (cms old generation).
913 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
914 if (CMSDumpAtPromotionFailure) {
915 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
916 }
917 }
918
919 CompactibleSpace*
920 ConcurrentMarkSweepGeneration::first_compaction_space() const {
921 return _cmsSpace;
922 }
923
924 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
925 // Clear the promotion information. These pointers can be adjusted
926 // along with all the other pointers into the heap but
927 // compaction is expected to be a rare event with
928 // a heap using cms so don't do it without seeing the need.
929 if (CollectedHeap::use_parallel_gc_threads()) {
930 for (uint i = 0; i < ParallelGCThreads; i++) {
931 _par_gc_thread_states[i]->promo.reset();
932 }
933 }
934 }
935
936 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
937 blk->do_space(_cmsSpace);
938 }
939
940 void ConcurrentMarkSweepGeneration::compute_new_size() {
941 assert_locked_or_safepoint(Heap_lock);
942
943 // If incremental collection failed, we just want to expand
944 // to the limit.
945 if (incremental_collection_failed()) {
946 clear_incremental_collection_failed();
947 grow_to_reserved();
948 return;
949 }
950
951 size_t expand_bytes = 0;
952 double free_percentage = ((double) free()) / capacity();
953 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
954 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
955
956 // compute expansion delta needed for reaching desired free percentage
957 if (free_percentage < desired_free_percentage) {
958 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
959 assert(desired_capacity >= capacity(), "invalid expansion size");
960 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
961 }
962 if (expand_bytes > 0) {
963 if (PrintGCDetails && Verbose) {
964 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
965 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
966 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
967 gclog_or_tty->print_cr(" Desired free fraction %f",
968 desired_free_percentage);
969 gclog_or_tty->print_cr(" Maximum free fraction %f",
970 maximum_free_percentage);
971 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
972 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
973 desired_capacity/1000);
974 int prev_level = level() - 1;
975 if (prev_level >= 0) {
976 size_t prev_size = 0;
977 GenCollectedHeap* gch = GenCollectedHeap::heap();
978 Generation* prev_gen = gch->_gens[prev_level];
979 prev_size = prev_gen->capacity();
980 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
981 prev_size/1000);
982 }
983 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
984 unsafe_max_alloc_nogc()/1000);
985 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
986 contiguous_available()/1000);
987 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
988 expand_bytes);
989 }
990 // safe if expansion fails
991 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
992 if (PrintGCDetails && Verbose) {
993 gclog_or_tty->print_cr(" Expanded free fraction %f",
994 ((double) free()) / capacity());
995 }
996 }
997 }
998
999 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1000 return cmsSpace()->freelistLock();
1001 }
1002
1003 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1004 bool tlab) {
1005 CMSSynchronousYieldRequest yr;
1006 MutexLockerEx x(freelistLock(),
1007 Mutex::_no_safepoint_check_flag);
1008 return have_lock_and_allocate(size, tlab);
1009 }
1010
1011 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1012 bool tlab /* ignored */) {
1013 assert_lock_strong(freelistLock());
1014 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1015 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1016 // Allocate the object live (grey) if the background collector has
1017 // started marking. This is necessary because the marker may
1018 // have passed this address and consequently this object will
1019 // not otherwise be greyed and would be incorrectly swept up.
1020 // Note that if this object contains references, the writing
1021 // of those references will dirty the card containing this object
1022 // allowing the object to be blackened (and its references scanned)
1023 // either during a preclean phase or at the final checkpoint.
1024 if (res != NULL) {
1025 // We may block here with an uninitialized object with
1026 // its mark-bit or P-bits not yet set. Such objects need
1027 // to be safely navigable by block_start().
1028 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1029 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1030 collector()->direct_allocated(res, adjustedSize);
1031 _direct_allocated_words += adjustedSize;
1032 // allocation counters
1033 NOT_PRODUCT(
1034 _numObjectsAllocated++;
1035 _numWordsAllocated += (int)adjustedSize;
1036 )
1037 }
1038 return res;
1039 }
1040
1041 // In the case of direct allocation by mutators in a generation that
1042 // is being concurrently collected, the object must be allocated
1043 // live (grey) if the background collector has started marking.
1044 // This is necessary because the marker may
1045 // have passed this address and consequently this object will
1046 // not otherwise be greyed and would be incorrectly swept up.
1047 // Note that if this object contains references, the writing
1048 // of those references will dirty the card containing this object
1049 // allowing the object to be blackened (and its references scanned)
1050 // either during a preclean phase or at the final checkpoint.
1051 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1052 assert(_markBitMap.covers(start, size), "Out of bounds");
1053 if (_collectorState >= Marking) {
1054 MutexLockerEx y(_markBitMap.lock(),
1055 Mutex::_no_safepoint_check_flag);
1056 // [see comments preceding SweepClosure::do_blk() below for details]
1057 // 1. need to mark the object as live so it isn't collected
1058 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1059 // 3. need to mark the end of the object so marking, precleaning or sweeping
1060 // can skip over uninitialized or unparsable objects. An allocated
1061 // object is considered uninitialized for our purposes as long as
1062 // its klass word is NULL. (Unparsable objects are those which are
1063 // initialized in the sense just described, but whose sizes can still
1064 // not be correctly determined. Note that the class of unparsable objects
1065 // can only occur in the perm gen. All old gen objects are parsable
1066 // as soon as they are initialized.)
1067 _markBitMap.mark(start); // object is live
1068 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1069 _markBitMap.mark(start + size - 1);
1070 // mark end of object
1071 }
1072 // check that oop looks uninitialized
1073 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1074 }
1075
1076 void CMSCollector::promoted(bool par, HeapWord* start,
1077 bool is_obj_array, size_t obj_size) {
1078 assert(_markBitMap.covers(start), "Out of bounds");
1079 // See comment in direct_allocated() about when objects should
1080 // be allocated live.
1081 if (_collectorState >= Marking) {
1082 // we already hold the marking bit map lock, taken in
1083 // the prologue
1084 if (par) {
1085 _markBitMap.par_mark(start);
1086 } else {
1087 _markBitMap.mark(start);
1088 }
1089 // We don't need to mark the object as uninitialized (as
1090 // in direct_allocated above) because this is being done with the
1091 // world stopped and the object will be initialized by the
1092 // time the marking, precleaning or sweeping get to look at it.
1093 // But see the code for copying objects into the CMS generation,
1094 // where we need to ensure that concurrent readers of the
1095 // block offset table are able to safely navigate a block that
1096 // is in flux from being free to being allocated (and in
1097 // transition while being copied into) and subsequently
1098 // becoming a bona-fide object when the copy/promotion is complete.
1099 assert(SafepointSynchronize::is_at_safepoint(),
1100 "expect promotion only at safepoints");
1101
1102 if (_collectorState < Sweeping) {
1103 // Mark the appropriate cards in the modUnionTable, so that
1104 // this object gets scanned before the sweep. If this is
1105 // not done, CMS generation references in the object might
1106 // not get marked.
1107 // For the case of arrays, which are otherwise precisely
1108 // marked, we need to dirty the entire array, not just its head.
1109 if (is_obj_array) {
1110 // The [par_]mark_range() method expects mr.end() below to
1111 // be aligned to the granularity of a bit's representation
1112 // in the heap. In the case of the MUT below, that's a
1113 // card size.
1114 MemRegion mr(start,
1115 (HeapWord*)round_to((intptr_t)(start + obj_size),
1116 CardTableModRefBS::card_size /* bytes */));
1117 if (par) {
1118 _modUnionTable.par_mark_range(mr);
1119 } else {
1120 _modUnionTable.mark_range(mr);
1121 }
1122 } else { // not an obj array; we can just mark the head
1123 if (par) {
1124 _modUnionTable.par_mark(start);
1125 } else {
1126 _modUnionTable.mark(start);
1127 }
1128 }
1129 }
1130 }
1131 }
1132
1133 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1134 {
1135 size_t delta = pointer_delta(addr, space->bottom());
1136 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1137 }
1138
1139 void CMSCollector::icms_update_allocation_limits()
1140 {
1141 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1142 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1143
1144 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1145 if (CMSTraceIncrementalPacing) {
1146 stats().print();
1147 }
1148
1149 assert(duty_cycle <= 100, "invalid duty cycle");
1150 if (duty_cycle != 0) {
1151 // The duty_cycle is a percentage between 0 and 100; convert to words and
1152 // then compute the offset from the endpoints of the space.
1153 size_t free_words = eden->free() / HeapWordSize;
1154 double free_words_dbl = (double)free_words;
1155 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1156 size_t offset_words = (free_words - duty_cycle_words) / 2;
1157
1158 _icms_start_limit = eden->top() + offset_words;
1159 _icms_stop_limit = eden->end() - offset_words;
1160
1161 // The limits may be adjusted (shifted to the right) by
1162 // CMSIncrementalOffset, to allow the application more mutator time after a
1163 // young gen gc (when all mutators were stopped) and before CMS starts and
1164 // takes away one or more cpus.
1165 if (CMSIncrementalOffset != 0) {
1166 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1167 size_t adjustment = (size_t)adjustment_dbl;
1168 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1169 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1170 _icms_start_limit += adjustment;
1171 _icms_stop_limit = tmp_stop;
1172 }
1173 }
1174 }
1175 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1176 _icms_start_limit = _icms_stop_limit = eden->end();
1177 }
1178
1179 // Install the new start limit.
1180 eden->set_soft_end(_icms_start_limit);
1181
1182 if (CMSTraceIncrementalMode) {
1183 gclog_or_tty->print(" icms alloc limits: "
1184 PTR_FORMAT "," PTR_FORMAT
1185 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1186 _icms_start_limit, _icms_stop_limit,
1187 percent_of_space(eden, _icms_start_limit),
1188 percent_of_space(eden, _icms_stop_limit));
1189 if (Verbose) {
1190 gclog_or_tty->print("eden: ");
1191 eden->print_on(gclog_or_tty);
1192 }
1193 }
1194 }
1195
1196 // Any changes here should try to maintain the invariant
1197 // that if this method is called with _icms_start_limit
1198 // and _icms_stop_limit both NULL, then it should return NULL
1199 // and not notify the icms thread.
1200 HeapWord*
1201 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1202 size_t word_size)
1203 {
1204 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1205 // nop.
1206 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1207 if (top <= _icms_start_limit) {
1208 if (CMSTraceIncrementalMode) {
1209 space->print_on(gclog_or_tty);
1210 gclog_or_tty->stamp();
1211 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1212 ", new limit=" PTR_FORMAT
1213 " (" SIZE_FORMAT "%%)",
1214 top, _icms_stop_limit,
1215 percent_of_space(space, _icms_stop_limit));
1216 }
1217 ConcurrentMarkSweepThread::start_icms();
1218 assert(top < _icms_stop_limit, "Tautology");
1219 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1220 return _icms_stop_limit;
1221 }
1222
1223 // The allocation will cross both the _start and _stop limits, so do the
1224 // stop notification also and return end().
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 top, space->end(),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1237
1238 if (top <= _icms_stop_limit) {
1239 if (CMSTraceIncrementalMode) {
1240 space->print_on(gclog_or_tty);
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1243 ", new limit=" PTR_FORMAT
1244 " (" SIZE_FORMAT "%%)",
1245 top, space->end(),
1246 percent_of_space(space, space->end()));
1247 }
1248 ConcurrentMarkSweepThread::stop_icms();
1249 return space->end();
1250 }
1251
1252 if (CMSTraceIncrementalMode) {
1253 space->print_on(gclog_or_tty);
1254 gclog_or_tty->stamp();
1255 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1256 ", new limit=" PTR_FORMAT,
1257 top, NULL);
1258 }
1259 }
1260
1261 return NULL;
1262 }
1263
1264 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1265 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1266 // allocate, copy and if necessary update promoinfo --
1267 // delegate to underlying space.
1268 assert_lock_strong(freelistLock());
1269
1270 #ifndef PRODUCT
1271 if (Universe::heap()->promotion_should_fail()) {
1272 return NULL;
1273 }
1274 #endif // #ifndef PRODUCT
1275
1276 oop res = _cmsSpace->promote(obj, obj_size);
1277 if (res == NULL) {
1278 // expand and retry
1279 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1280 expand(s*HeapWordSize, MinHeapDeltaBytes,
1281 CMSExpansionCause::_satisfy_promotion);
1282 // Since there's currently no next generation, we don't try to promote
1283 // into a more senior generation.
1284 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1285 "is made to pass on a possibly failing "
1286 "promotion to next generation");
1287 res = _cmsSpace->promote(obj, obj_size);
1288 }
1289 if (res != NULL) {
1290 // See comment in allocate() about when objects should
1291 // be allocated live.
1292 assert(obj->is_oop(), "Will dereference klass pointer below");
1293 collector()->promoted(false, // Not parallel
1294 (HeapWord*)res, obj->is_objArray(), obj_size);
1295 // promotion counters
1296 NOT_PRODUCT(
1297 _numObjectsPromoted++;
1298 _numWordsPromoted +=
1299 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1300 )
1301 }
1302 return res;
1303 }
1304
1305
1306 HeapWord*
1307 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1308 HeapWord* top,
1309 size_t word_sz)
1310 {
1311 return collector()->allocation_limit_reached(space, top, word_sz);
1312 }
1313
1314 // IMPORTANT: Notes on object size recognition in CMS.
1315 // ---------------------------------------------------
1316 // A block of storage in the CMS generation is always in
1317 // one of three states. A free block (FREE), an allocated
1318 // object (OBJECT) whose size() method reports the correct size,
1319 // and an intermediate state (TRANSIENT) in which its size cannot
1320 // be accurately determined.
1321 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1322 // -----------------------------------------------------
1323 // FREE: klass_word & 1 == 1; mark_word holds block size
1324 //
1325 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1326 // obj->size() computes correct size
1327 // [Perm Gen objects needs to be "parsable" before they can be navigated]
1328 //
1329 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1330 //
1331 // STATE IDENTIFICATION: (64 bit+COOPS)
1332 // ------------------------------------
1333 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1334 //
1335 // OBJECT: klass_word installed; klass_word != 0;
1336 // obj->size() computes correct size
1337 // [Perm Gen comment above continues to hold]
1338 //
1339 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1340 //
1341 //
1342 // STATE TRANSITION DIAGRAM
1343 //
1344 // mut / parnew mut / parnew
1345 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1346 // ^ |
1347 // |------------------------ DEAD <------------------------------------|
1348 // sweep mut
1349 //
1350 // While a block is in TRANSIENT state its size cannot be determined
1351 // so readers will either need to come back later or stall until
1352 // the size can be determined. Note that for the case of direct
1353 // allocation, P-bits, when available, may be used to determine the
1354 // size of an object that may not yet have been initialized.
1355
1356 // Things to support parallel young-gen collection.
1357 oop
1358 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1359 oop old, markOop m,
1360 size_t word_sz) {
1361 #ifndef PRODUCT
1362 if (Universe::heap()->promotion_should_fail()) {
1363 return NULL;
1364 }
1365 #endif // #ifndef PRODUCT
1366
1367 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1368 PromotionInfo* promoInfo = &ps->promo;
1369 // if we are tracking promotions, then first ensure space for
1370 // promotion (including spooling space for saving header if necessary).
1371 // then allocate and copy, then track promoted info if needed.
1372 // When tracking (see PromotionInfo::track()), the mark word may
1373 // be displaced and in this case restoration of the mark word
1374 // occurs in the (oop_since_save_marks_)iterate phase.
1375 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1376 // Out of space for allocating spooling buffers;
1377 // try expanding and allocating spooling buffers.
1378 if (!expand_and_ensure_spooling_space(promoInfo)) {
1379 return NULL;
1380 }
1381 }
1382 assert(promoInfo->has_spooling_space(), "Control point invariant");
1383 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1384 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1385 if (obj_ptr == NULL) {
1386 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1387 if (obj_ptr == NULL) {
1388 return NULL;
1389 }
1390 }
1391 oop obj = oop(obj_ptr);
1392 OrderAccess::storestore();
1393 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1394 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1395 // IMPORTANT: See note on object initialization for CMS above.
1396 // Otherwise, copy the object. Here we must be careful to insert the
1397 // klass pointer last, since this marks the block as an allocated object.
1398 // Except with compressed oops it's the mark word.
1399 HeapWord* old_ptr = (HeapWord*)old;
1400 // Restore the mark word copied above.
1401 obj->set_mark(m);
1402 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1403 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1404 OrderAccess::storestore();
1405
1406 if (UseCompressedOops) {
1407 // Copy gap missed by (aligned) header size calculation below
1408 obj->set_klass_gap(old->klass_gap());
1409 }
1410 if (word_sz > (size_t)oopDesc::header_size()) {
1411 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1412 obj_ptr + oopDesc::header_size(),
1413 word_sz - oopDesc::header_size());
1414 }
1415
1416 // Now we can track the promoted object, if necessary. We take care
1417 // to delay the transition from uninitialized to full object
1418 // (i.e., insertion of klass pointer) until after, so that it
1419 // atomically becomes a promoted object.
1420 if (promoInfo->tracking()) {
1421 promoInfo->track((PromotedObject*)obj, old->klass());
1422 }
1423 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1424 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1425 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1426
1427 // Finally, install the klass pointer (this should be volatile).
1428 OrderAccess::storestore();
1429 obj->set_klass(old->klass());
1430 // We should now be able to calculate the right size for this object
1431 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1432
1433 collector()->promoted(true, // parallel
1434 obj_ptr, old->is_objArray(), word_sz);
1435
1436 NOT_PRODUCT(
1437 Atomic::inc_ptr(&_numObjectsPromoted);
1438 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1439 )
1440
1441 return obj;
1442 }
1443
1444 void
1445 ConcurrentMarkSweepGeneration::
1446 par_promote_alloc_undo(int thread_num,
1447 HeapWord* obj, size_t word_sz) {
1448 // CMS does not support promotion undo.
1449 ShouldNotReachHere();
1450 }
1451
1452 void
1453 ConcurrentMarkSweepGeneration::
1454 par_promote_alloc_done(int thread_num) {
1455 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1456 ps->lab.retire(thread_num);
1457 }
1458
1459 void
1460 ConcurrentMarkSweepGeneration::
1461 par_oop_since_save_marks_iterate_done(int thread_num) {
1462 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1463 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1464 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1465 }
1466
1467 // XXXPERM
1468 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1469 size_t size,
1470 bool tlab)
1471 {
1472 // We allow a STW collection only if a full
1473 // collection was requested.
1474 return full || should_allocate(size, tlab); // FIX ME !!!
1475 // This and promotion failure handling are connected at the
1476 // hip and should be fixed by untying them.
1477 }
1478
1479 bool CMSCollector::shouldConcurrentCollect() {
1480 if (_full_gc_requested) {
1481 if (Verbose && PrintGCDetails) {
1482 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1483 " gc request (or gc_locker)");
1484 }
1485 return true;
1486 }
1487
1488 // For debugging purposes, change the type of collection.
1489 // If the rotation is not on the concurrent collection
1490 // type, don't start a concurrent collection.
1491 NOT_PRODUCT(
1492 if (RotateCMSCollectionTypes &&
1493 (_cmsGen->debug_collection_type() !=
1494 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1495 assert(_cmsGen->debug_collection_type() !=
1496 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1497 "Bad cms collection type");
1498 return false;
1499 }
1500 )
1501
1502 FreelistLocker x(this);
1503 // ------------------------------------------------------------------
1504 // Print out lots of information which affects the initiation of
1505 // a collection.
1506 if (PrintCMSInitiationStatistics && stats().valid()) {
1507 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1508 gclog_or_tty->stamp();
1509 gclog_or_tty->print_cr("");
1510 stats().print_on(gclog_or_tty);
1511 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1512 stats().time_until_cms_gen_full());
1513 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1514 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1515 _cmsGen->contiguous_available());
1516 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1517 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1518 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1519 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1520 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1521 }
1522 // ------------------------------------------------------------------
1523
1524 // If the estimated time to complete a cms collection (cms_duration())
1525 // is less than the estimated time remaining until the cms generation
1526 // is full, start a collection.
1527 if (!UseCMSInitiatingOccupancyOnly) {
1528 if (stats().valid()) {
1529 if (stats().time_until_cms_start() == 0.0) {
1530 return true;
1531 }
1532 } else {
1533 // We want to conservatively collect somewhat early in order
1534 // to try and "bootstrap" our CMS/promotion statistics;
1535 // this branch will not fire after the first successful CMS
1536 // collection because the stats should then be valid.
1537 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1538 if (Verbose && PrintGCDetails) {
1539 gclog_or_tty->print_cr(
1540 " CMSCollector: collect for bootstrapping statistics:"
1541 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1542 _bootstrap_occupancy);
1543 }
1544 return true;
1545 }
1546 }
1547 }
1548
1549 // Otherwise, we start a collection cycle if either the perm gen or
1550 // old gen want a collection cycle started. Each may use
1551 // an appropriate criterion for making this decision.
1552 // XXX We need to make sure that the gen expansion
1553 // criterion dovetails well with this. XXX NEED TO FIX THIS
1554 if (_cmsGen->should_concurrent_collect()) {
1555 if (Verbose && PrintGCDetails) {
1556 gclog_or_tty->print_cr("CMS old gen initiated");
1557 }
1558 return true;
1559 }
1560
1561 // We start a collection if we believe an incremental collection may fail;
1562 // this is not likely to be productive in practice because it's probably too
1563 // late anyway.
1564 GenCollectedHeap* gch = GenCollectedHeap::heap();
1565 assert(gch->collector_policy()->is_two_generation_policy(),
1566 "You may want to check the correctness of the following");
1567 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1568 if (Verbose && PrintGCDetails) {
1569 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1570 }
1571 return true;
1572 }
1573
1574 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1575 bool res = update_should_unload_classes();
1576 if (res) {
1577 if (Verbose && PrintGCDetails) {
1578 gclog_or_tty->print_cr("CMS perm gen initiated");
1579 }
1580 return true;
1581 }
1582 }
1583 return false;
1584 }
1585
1586 // Clear _expansion_cause fields of constituent generations
1587 void CMSCollector::clear_expansion_cause() {
1588 _cmsGen->clear_expansion_cause();
1589 _permGen->clear_expansion_cause();
1590 }
1591
1592 // We should be conservative in starting a collection cycle. To
1593 // start too eagerly runs the risk of collecting too often in the
1594 // extreme. To collect too rarely falls back on full collections,
1595 // which works, even if not optimum in terms of concurrent work.
1596 // As a work around for too eagerly collecting, use the flag
1597 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1598 // giving the user an easily understandable way of controlling the
1599 // collections.
1600 // We want to start a new collection cycle if any of the following
1601 // conditions hold:
1602 // . our current occupancy exceeds the configured initiating occupancy
1603 // for this generation, or
1604 // . we recently needed to expand this space and have not, since that
1605 // expansion, done a collection of this generation, or
1606 // . the underlying space believes that it may be a good idea to initiate
1607 // a concurrent collection (this may be based on criteria such as the
1608 // following: the space uses linear allocation and linear allocation is
1609 // going to fail, or there is believed to be excessive fragmentation in
1610 // the generation, etc... or ...
1611 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1612 // the case of the old generation, not the perm generation; see CR 6543076):
1613 // we may be approaching a point at which allocation requests may fail because
1614 // we will be out of sufficient free space given allocation rate estimates.]
1615 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1616
1617 assert_lock_strong(freelistLock());
1618 if (occupancy() > initiating_occupancy()) {
1619 if (PrintGCDetails && Verbose) {
1620 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1621 short_name(), occupancy(), initiating_occupancy());
1622 }
1623 return true;
1624 }
1625 if (UseCMSInitiatingOccupancyOnly) {
1626 return false;
1627 }
1628 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1629 if (PrintGCDetails && Verbose) {
1630 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1631 short_name());
1632 }
1633 return true;
1634 }
1635 if (_cmsSpace->should_concurrent_collect()) {
1636 if (PrintGCDetails && Verbose) {
1637 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1638 short_name());
1639 }
1640 return true;
1641 }
1642 return false;
1643 }
1644
1645 void ConcurrentMarkSweepGeneration::collect(bool full,
1646 bool clear_all_soft_refs,
1647 size_t size,
1648 bool tlab)
1649 {
1650 collector()->collect(full, clear_all_soft_refs, size, tlab);
1651 }
1652
1653 void CMSCollector::collect(bool full,
1654 bool clear_all_soft_refs,
1655 size_t size,
1656 bool tlab)
1657 {
1658 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1659 // For debugging purposes skip the collection if the state
1660 // is not currently idle
1661 if (TraceCMSState) {
1662 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1663 Thread::current(), full, _collectorState);
1664 }
1665 return;
1666 }
1667
1668 // The following "if" branch is present for defensive reasons.
1669 // In the current uses of this interface, it can be replaced with:
1670 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1671 // But I am not placing that assert here to allow future
1672 // generality in invoking this interface.
1673 if (GC_locker::is_active()) {
1674 // A consistency test for GC_locker
1675 assert(GC_locker::needs_gc(), "Should have been set already");
1676 // Skip this foreground collection, instead
1677 // expanding the heap if necessary.
1678 // Need the free list locks for the call to free() in compute_new_size()
1679 compute_new_size();
1680 return;
1681 }
1682 acquire_control_and_collect(full, clear_all_soft_refs);
1683 _full_gcs_since_conc_gc++;
1684
1685 }
1686
1687 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1688 GenCollectedHeap* gch = GenCollectedHeap::heap();
1689 unsigned int gc_count = gch->total_full_collections();
1690 if (gc_count == full_gc_count) {
1691 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1692 _full_gc_requested = true;
1693 _full_gc_cause = cause;
1694 CGC_lock->notify(); // nudge CMS thread
1695 } else {
1696 assert(gc_count > full_gc_count, "Error: causal loop");
1697 }
1698 }
1699
1700 bool CMSCollector::is_external_interruption() {
1701 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1702 return GCCause::is_user_requested_gc(cause) ||
1703 GCCause::is_serviceability_requested_gc(cause);
1704 }
1705
1706 void CMSCollector::report_concurrent_mode_interruption() {
1707 if (is_external_interruption()) {
1708 if (PrintGCDetails) {
1709 gclog_or_tty->print(" (concurrent mode interrupted)");
1710 }
1711 } else {
1712 if (PrintGCDetails) {
1713 gclog_or_tty->print(" (concurrent mode failure)");
1714 }
1715 _gc_tracer_cm->report_concurrent_mode_failure();
1716 }
1717 }
1718
1719 // The foreground and background collectors need to coordinate in order
1720 // to make sure that they do not mutually interfere with CMS collections.
1721 // When a background collection is active,
1722 // the foreground collector may need to take over (preempt) and
1723 // synchronously complete an ongoing collection. Depending on the
1724 // frequency of the background collections and the heap usage
1725 // of the application, this preemption can be seldom or frequent.
1726 // There are only certain
1727 // points in the background collection that the "collection-baton"
1728 // can be passed to the foreground collector.
1729 //
1730 // The foreground collector will wait for the baton before
1731 // starting any part of the collection. The foreground collector
1732 // will only wait at one location.
1733 //
1734 // The background collector will yield the baton before starting a new
1735 // phase of the collection (e.g., before initial marking, marking from roots,
1736 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1737 // of the loop which switches the phases. The background collector does some
1738 // of the phases (initial mark, final re-mark) with the world stopped.
1739 // Because of locking involved in stopping the world,
1740 // the foreground collector should not block waiting for the background
1741 // collector when it is doing a stop-the-world phase. The background
1742 // collector will yield the baton at an additional point just before
1743 // it enters a stop-the-world phase. Once the world is stopped, the
1744 // background collector checks the phase of the collection. If the
1745 // phase has not changed, it proceeds with the collection. If the
1746 // phase has changed, it skips that phase of the collection. See
1747 // the comments on the use of the Heap_lock in collect_in_background().
1748 //
1749 // Variable used in baton passing.
1750 // _foregroundGCIsActive - Set to true by the foreground collector when
1751 // it wants the baton. The foreground clears it when it has finished
1752 // the collection.
1753 // _foregroundGCShouldWait - Set to true by the background collector
1754 // when it is running. The foreground collector waits while
1755 // _foregroundGCShouldWait is true.
1756 // CGC_lock - monitor used to protect access to the above variables
1757 // and to notify the foreground and background collectors.
1758 // _collectorState - current state of the CMS collection.
1759 //
1760 // The foreground collector
1761 // acquires the CGC_lock
1762 // sets _foregroundGCIsActive
1763 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1764 // various locks acquired in preparation for the collection
1765 // are released so as not to block the background collector
1766 // that is in the midst of a collection
1767 // proceeds with the collection
1768 // clears _foregroundGCIsActive
1769 // returns
1770 //
1771 // The background collector in a loop iterating on the phases of the
1772 // collection
1773 // acquires the CGC_lock
1774 // sets _foregroundGCShouldWait
1775 // if _foregroundGCIsActive is set
1776 // clears _foregroundGCShouldWait, notifies _CGC_lock
1777 // waits on _CGC_lock for _foregroundGCIsActive to become false
1778 // and exits the loop.
1779 // otherwise
1780 // proceed with that phase of the collection
1781 // if the phase is a stop-the-world phase,
1782 // yield the baton once more just before enqueueing
1783 // the stop-world CMS operation (executed by the VM thread).
1784 // returns after all phases of the collection are done
1785 //
1786
1787 void CMSCollector::acquire_control_and_collect(bool full,
1788 bool clear_all_soft_refs) {
1789 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1790 assert(!Thread::current()->is_ConcurrentGC_thread(),
1791 "shouldn't try to acquire control from self!");
1792
1793 // Start the protocol for acquiring control of the
1794 // collection from the background collector (aka CMS thread).
1795 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1796 "VM thread should have CMS token");
1797 // Remember the possibly interrupted state of an ongoing
1798 // concurrent collection
1799 CollectorState first_state = _collectorState;
1800
1801 // Signal to a possibly ongoing concurrent collection that
1802 // we want to do a foreground collection.
1803 _foregroundGCIsActive = true;
1804
1805 // Disable incremental mode during a foreground collection.
1806 ICMSDisabler icms_disabler;
1807
1808 // release locks and wait for a notify from the background collector
1809 // releasing the locks in only necessary for phases which
1810 // do yields to improve the granularity of the collection.
1811 assert_lock_strong(bitMapLock());
1812 // We need to lock the Free list lock for the space that we are
1813 // currently collecting.
1814 assert(haveFreelistLocks(), "Must be holding free list locks");
1815 bitMapLock()->unlock();
1816 releaseFreelistLocks();
1817 {
1818 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1819 if (_foregroundGCShouldWait) {
1820 // We are going to be waiting for action for the CMS thread;
1821 // it had better not be gone (for instance at shutdown)!
1822 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1823 "CMS thread must be running");
1824 // Wait here until the background collector gives us the go-ahead
1825 ConcurrentMarkSweepThread::clear_CMS_flag(
1826 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1827 // Get a possibly blocked CMS thread going:
1828 // Note that we set _foregroundGCIsActive true above,
1829 // without protection of the CGC_lock.
1830 CGC_lock->notify();
1831 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1832 "Possible deadlock");
1833 while (_foregroundGCShouldWait) {
1834 // wait for notification
1835 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1836 // Possibility of delay/starvation here, since CMS token does
1837 // not know to give priority to VM thread? Actually, i think
1838 // there wouldn't be any delay/starvation, but the proof of
1839 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1840 }
1841 ConcurrentMarkSweepThread::set_CMS_flag(
1842 ConcurrentMarkSweepThread::CMS_vm_has_token);
1843 }
1844 }
1845 // The CMS_token is already held. Get back the other locks.
1846 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1847 "VM thread should have CMS token");
1848 getFreelistLocks();
1849 bitMapLock()->lock_without_safepoint_check();
1850 if (TraceCMSState) {
1851 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1852 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1853 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1854 }
1855
1856 // Check if we need to do a compaction, or if not, whether
1857 // we need to start the mark-sweep from scratch.
1858 bool should_compact = false;
1859 bool should_start_over = false;
1860 decide_foreground_collection_type(clear_all_soft_refs,
1861 &should_compact, &should_start_over);
1862
1863 NOT_PRODUCT(
1864 if (RotateCMSCollectionTypes) {
1865 if (_cmsGen->debug_collection_type() ==
1866 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1867 should_compact = true;
1868 } else if (_cmsGen->debug_collection_type() ==
1869 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1870 should_compact = false;
1871 }
1872 }
1873 )
1874
1875 if (first_state > Idling) {
1876 report_concurrent_mode_interruption();
1877 }
1878
1879 if (should_compact) {
1880 // If the collection is being acquired from the background
1881 // collector, there may be references on the discovered
1882 // references lists that have NULL referents (being those
1883 // that were concurrently cleared by a mutator) or
1884 // that are no longer active (having been enqueued concurrently
1885 // by the mutator).
1886 // Scrub the list of those references because Mark-Sweep-Compact
1887 // code assumes referents are not NULL and that all discovered
1888 // Reference objects are active.
1889 ref_processor()->clean_up_discovered_references();
1890
1891 if (first_state > Idling) {
1892 save_heap_summary();
1893 }
1894
1895 if (first_state > Idling) {
1896 save_heap_summary();
1897 }
1898
1899 do_compaction_work(clear_all_soft_refs);
1900
1901 // Has the GC time limit been exceeded?
1902 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1903 size_t max_eden_size = young_gen->max_capacity() -
1904 young_gen->to()->capacity() -
1905 young_gen->from()->capacity();
1906 GenCollectedHeap* gch = GenCollectedHeap::heap();
1907 GCCause::Cause gc_cause = gch->gc_cause();
1908 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1909 young_gen->eden()->used(),
1910 _cmsGen->max_capacity(),
1911 max_eden_size,
1912 full,
1913 gc_cause,
1914 gch->collector_policy());
1915 } else {
1916 do_mark_sweep_work(clear_all_soft_refs, first_state,
1917 should_start_over);
1918 }
1919 // Reset the expansion cause, now that we just completed
1920 // a collection cycle.
1921 clear_expansion_cause();
1922 _foregroundGCIsActive = false;
1923 return;
1924 }
1925
1926 // Resize the perm generation and the tenured generation
1927 // after obtaining the free list locks for the
1928 // two generations.
1929 void CMSCollector::compute_new_size() {
1930 assert_locked_or_safepoint(Heap_lock);
1931 FreelistLocker z(this);
1932 _permGen->compute_new_size();
1933 _cmsGen->compute_new_size();
1934 }
1935
1936 // A work method used by foreground collection to determine
1937 // what type of collection (compacting or not, continuing or fresh)
1938 // it should do.
1939 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1940 // and CMSCompactWhenClearAllSoftRefs the default in the future
1941 // and do away with the flags after a suitable period.
1942 void CMSCollector::decide_foreground_collection_type(
1943 bool clear_all_soft_refs, bool* should_compact,
1944 bool* should_start_over) {
1945 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1946 // flag is set, and we have either requested a System.gc() or
1947 // the number of full gc's since the last concurrent cycle
1948 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1949 // or if an incremental collection has failed
1950 GenCollectedHeap* gch = GenCollectedHeap::heap();
1951 assert(gch->collector_policy()->is_two_generation_policy(),
1952 "You may want to check the correctness of the following");
1953 // Inform cms gen if this was due to partial collection failing.
1954 // The CMS gen may use this fact to determine its expansion policy.
1955 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1956 assert(!_cmsGen->incremental_collection_failed(),
1957 "Should have been noticed, reacted to and cleared");
1958 _cmsGen->set_incremental_collection_failed();
1959 }
1960 *should_compact =
1961 UseCMSCompactAtFullCollection &&
1962 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1963 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1964 gch->incremental_collection_will_fail(true /* consult_young */));
1965 *should_start_over = false;
1966 if (clear_all_soft_refs && !*should_compact) {
1967 // We are about to do a last ditch collection attempt
1968 // so it would normally make sense to do a compaction
1969 // to reclaim as much space as possible.
1970 if (CMSCompactWhenClearAllSoftRefs) {
1971 // Default: The rationale is that in this case either
1972 // we are past the final marking phase, in which case
1973 // we'd have to start over, or so little has been done
1974 // that there's little point in saving that work. Compaction
1975 // appears to be the sensible choice in either case.
1976 *should_compact = true;
1977 } else {
1978 // We have been asked to clear all soft refs, but not to
1979 // compact. Make sure that we aren't past the final checkpoint
1980 // phase, for that is where we process soft refs. If we are already
1981 // past that phase, we'll need to redo the refs discovery phase and
1982 // if necessary clear soft refs that weren't previously
1983 // cleared. We do so by remembering the phase in which
1984 // we came in, and if we are past the refs processing
1985 // phase, we'll choose to just redo the mark-sweep
1986 // collection from scratch.
1987 if (_collectorState > FinalMarking) {
1988 // We are past the refs processing phase;
1989 // start over and do a fresh synchronous CMS cycle
1990 _collectorState = Resetting; // skip to reset to start new cycle
1991 reset(false /* == !asynch */);
1992 *should_start_over = true;
1993 } // else we can continue a possibly ongoing current cycle
1994 }
1995 }
1996 }
1997
1998 // A work method used by the foreground collector to do
1999 // a mark-sweep-compact.
2000 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2001 GenCollectedHeap* gch = GenCollectedHeap::heap();
2002
2003 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2004 gc_timer->register_gc_start(os::elapsed_counter());
2005
2006 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2007 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2008
2009 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2010 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2011 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2012 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2013 }
2014
2015 // Sample collection interval time and reset for collection pause.
2016 if (UseAdaptiveSizePolicy) {
2017 size_policy()->msc_collection_begin();
2018 }
2019
2020 // Temporarily widen the span of the weak reference processing to
2021 // the entire heap.
2022 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2023 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2024 // Temporarily, clear the "is_alive_non_header" field of the
2025 // reference processor.
2026 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2027 // Temporarily make reference _processing_ single threaded (non-MT).
2028 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2029 // Temporarily make refs discovery atomic
2030 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2031 // Temporarily make reference _discovery_ single threaded (non-MT)
2032 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2033
2034 ref_processor()->set_enqueuing_is_done(false);
2035 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2036 ref_processor()->setup_policy(clear_all_soft_refs);
2037 // If an asynchronous collection finishes, the _modUnionTable is
2038 // all clear. If we are assuming the collection from an asynchronous
2039 // collection, clear the _modUnionTable.
2040 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2041 "_modUnionTable should be clear if the baton was not passed");
2042 _modUnionTable.clear_all();
2043
2044 // We must adjust the allocation statistics being maintained
2045 // in the free list space. We do so by reading and clearing
2046 // the sweep timer and updating the block flux rate estimates below.
2047 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2048 if (_inter_sweep_timer.is_active()) {
2049 _inter_sweep_timer.stop();
2050 // Note that we do not use this sample to update the _inter_sweep_estimate.
2051 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2052 _inter_sweep_estimate.padded_average(),
2053 _intra_sweep_estimate.padded_average());
2054 }
2055
2056 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2057 ref_processor(), clear_all_soft_refs);
2058 #ifdef ASSERT
2059 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2060 size_t free_size = cms_space->free();
2061 assert(free_size ==
2062 pointer_delta(cms_space->end(), cms_space->compaction_top())
2063 * HeapWordSize,
2064 "All the free space should be compacted into one chunk at top");
2065 assert(cms_space->dictionary()->total_chunk_size(
2066 debug_only(cms_space->freelistLock())) == 0 ||
2067 cms_space->totalSizeInIndexedFreeLists() == 0,
2068 "All the free space should be in a single chunk");
2069 size_t num = cms_space->totalCount();
2070 assert((free_size == 0 && num == 0) ||
2071 (free_size > 0 && (num == 1 || num == 2)),
2072 "There should be at most 2 free chunks after compaction");
2073 #endif // ASSERT
2074 _collectorState = Resetting;
2075 assert(_restart_addr == NULL,
2076 "Should have been NULL'd before baton was passed");
2077 reset(false /* == !asynch */);
2078 _cmsGen->reset_after_compaction();
2079 _concurrent_cycles_since_last_unload = 0;
2080
2081 if (verifying() && !should_unload_classes()) {
2082 perm_gen_verify_bit_map()->clear_all();
2083 }
2084
2085 // Clear any data recorded in the PLAB chunk arrays.
2086 if (_survivor_plab_array != NULL) {
2087 reset_survivor_plab_arrays();
2088 }
2089
2090 // Adjust the per-size allocation stats for the next epoch.
2091 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2092 // Restart the "inter sweep timer" for the next epoch.
2093 _inter_sweep_timer.reset();
2094 _inter_sweep_timer.start();
2095
2096 // Sample collection pause time and reset for collection interval.
2097 if (UseAdaptiveSizePolicy) {
2098 size_policy()->msc_collection_end(gch->gc_cause());
2099 }
2100
2101 gc_timer->register_gc_end(os::elapsed_counter());
2102
2103 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2104
2105 // For a mark-sweep-compact, compute_new_size() will be called
2106 // in the heap's do_collection() method.
2107 }
2108
2109 // A work method used by the foreground collector to do
2110 // a mark-sweep, after taking over from a possibly on-going
2111 // concurrent mark-sweep collection.
2112 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2113 CollectorState first_state, bool should_start_over) {
2114 if (PrintGC && Verbose) {
2115 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2116 "collector with count %d",
2117 _full_gcs_since_conc_gc);
2118 }
2119 switch (_collectorState) {
2120 case Idling:
2121 if (first_state == Idling || should_start_over) {
2122 // The background GC was not active, or should
2123 // restarted from scratch; start the cycle.
2124 _collectorState = InitialMarking;
2125 }
2126 // If first_state was not Idling, then a background GC
2127 // was in progress and has now finished. No need to do it
2128 // again. Leave the state as Idling.
2129 break;
2130 case Precleaning:
2131 // In the foreground case don't do the precleaning since
2132 // it is not done concurrently and there is extra work
2133 // required.
2134 _collectorState = FinalMarking;
2135 }
2136 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2137
2138 // For a mark-sweep, compute_new_size() will be called
2139 // in the heap's do_collection() method.
2140 }
2141
2142
2143 void CMSCollector::getFreelistLocks() const {
2144 // Get locks for all free lists in all generations that this
2145 // collector is responsible for
2146 _cmsGen->freelistLock()->lock_without_safepoint_check();
2147 _permGen->freelistLock()->lock_without_safepoint_check();
2148 }
2149
2150 void CMSCollector::releaseFreelistLocks() const {
2151 // Release locks for all free lists in all generations that this
2152 // collector is responsible for
2153 _cmsGen->freelistLock()->unlock();
2154 _permGen->freelistLock()->unlock();
2155 }
2156
2157 bool CMSCollector::haveFreelistLocks() const {
2158 // Check locks for all free lists in all generations that this
2159 // collector is responsible for
2160 assert_lock_strong(_cmsGen->freelistLock());
2161 assert_lock_strong(_permGen->freelistLock());
2162 PRODUCT_ONLY(ShouldNotReachHere());
2163 return true;
2164 }
2165
2166 // A utility class that is used by the CMS collector to
2167 // temporarily "release" the foreground collector from its
2168 // usual obligation to wait for the background collector to
2169 // complete an ongoing phase before proceeding.
2170 class ReleaseForegroundGC: public StackObj {
2171 private:
2172 CMSCollector* _c;
2173 public:
2174 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2175 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2176 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2177 // allow a potentially blocked foreground collector to proceed
2178 _c->_foregroundGCShouldWait = false;
2179 if (_c->_foregroundGCIsActive) {
2180 CGC_lock->notify();
2181 }
2182 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2183 "Possible deadlock");
2184 }
2185
2186 ~ReleaseForegroundGC() {
2187 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2188 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2189 _c->_foregroundGCShouldWait = true;
2190 }
2191 };
2192
2193 // There are separate collect_in_background and collect_in_foreground because of
2194 // the different locking requirements of the background collector and the
2195 // foreground collector. There was originally an attempt to share
2196 // one "collect" method between the background collector and the foreground
2197 // collector but the if-then-else required made it cleaner to have
2198 // separate methods.
2199 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2200 assert(Thread::current()->is_ConcurrentGC_thread(),
2201 "A CMS asynchronous collection is only allowed on a CMS thread.");
2202
2203 GenCollectedHeap* gch = GenCollectedHeap::heap();
2204 {
2205 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2206 MutexLockerEx hl(Heap_lock, safepoint_check);
2207 FreelistLocker fll(this);
2208 MutexLockerEx x(CGC_lock, safepoint_check);
2209 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2210 // The foreground collector is active or we're
2211 // not using asynchronous collections. Skip this
2212 // background collection.
2213 assert(!_foregroundGCShouldWait, "Should be clear");
2214 return;
2215 } else {
2216 assert(_collectorState == Idling, "Should be idling before start.");
2217 _collectorState = InitialMarking;
2218 register_gc_start(cause);
2219 // Reset the expansion cause, now that we are about to begin
2220 // a new cycle.
2221 clear_expansion_cause();
2222 }
2223 // Decide if we want to enable class unloading as part of the
2224 // ensuing concurrent GC cycle.
2225 update_should_unload_classes();
2226 _full_gc_requested = false; // acks all outstanding full gc requests
2227 _full_gc_cause = GCCause::_no_gc;
2228 // Signal that we are about to start a collection
2229 gch->increment_total_full_collections(); // ... starting a collection cycle
2230 _collection_count_start = gch->total_full_collections();
2231 }
2232
2233 // Used for PrintGC
2234 size_t prev_used;
2235 if (PrintGC && Verbose) {
2236 prev_used = _cmsGen->used(); // XXXPERM
2237 }
2238
2239 // The change of the collection state is normally done at this level;
2240 // the exceptions are phases that are executed while the world is
2241 // stopped. For those phases the change of state is done while the
2242 // world is stopped. For baton passing purposes this allows the
2243 // background collector to finish the phase and change state atomically.
2244 // The foreground collector cannot wait on a phase that is done
2245 // while the world is stopped because the foreground collector already
2246 // has the world stopped and would deadlock.
2247 while (_collectorState != Idling) {
2248 if (TraceCMSState) {
2249 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2250 Thread::current(), _collectorState);
2251 }
2252 // The foreground collector
2253 // holds the Heap_lock throughout its collection.
2254 // holds the CMS token (but not the lock)
2255 // except while it is waiting for the background collector to yield.
2256 //
2257 // The foreground collector should be blocked (not for long)
2258 // if the background collector is about to start a phase
2259 // executed with world stopped. If the background
2260 // collector has already started such a phase, the
2261 // foreground collector is blocked waiting for the
2262 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2263 // are executed in the VM thread.
2264 //
2265 // The locking order is
2266 // PendingListLock (PLL) -- if applicable (FinalMarking)
2267 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2268 // CMS token (claimed in
2269 // stop_world_and_do() -->
2270 // safepoint_synchronize() -->
2271 // CMSThread::synchronize())
2272
2273 {
2274 // Check if the FG collector wants us to yield.
2275 CMSTokenSync x(true); // is cms thread
2276 if (waitForForegroundGC()) {
2277 // We yielded to a foreground GC, nothing more to be
2278 // done this round.
2279 assert(_foregroundGCShouldWait == false, "We set it to false in "
2280 "waitForForegroundGC()");
2281 if (TraceCMSState) {
2282 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2283 " exiting collection CMS state %d",
2284 Thread::current(), _collectorState);
2285 }
2286 return;
2287 } else {
2288 // The background collector can run but check to see if the
2289 // foreground collector has done a collection while the
2290 // background collector was waiting to get the CGC_lock
2291 // above. If yes, break so that _foregroundGCShouldWait
2292 // is cleared before returning.
2293 if (_collectorState == Idling) {
2294 break;
2295 }
2296 }
2297 }
2298
2299 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2300 "should be waiting");
2301
2302 switch (_collectorState) {
2303 case InitialMarking:
2304 {
2305 ReleaseForegroundGC x(this);
2306 stats().record_cms_begin();
2307 VM_CMS_Initial_Mark initial_mark_op(this);
2308 VMThread::execute(&initial_mark_op);
2309 }
2310 // The collector state may be any legal state at this point
2311 // since the background collector may have yielded to the
2312 // foreground collector.
2313 break;
2314 case Marking:
2315 // initial marking in checkpointRootsInitialWork has been completed
2316 if (markFromRoots(true)) { // we were successful
2317 assert(_collectorState == Precleaning, "Collector state should "
2318 "have changed");
2319 } else {
2320 assert(_foregroundGCIsActive, "Internal state inconsistency");
2321 }
2322 break;
2323 case Precleaning:
2324 if (UseAdaptiveSizePolicy) {
2325 size_policy()->concurrent_precleaning_begin();
2326 }
2327 // marking from roots in markFromRoots has been completed
2328 preclean();
2329 if (UseAdaptiveSizePolicy) {
2330 size_policy()->concurrent_precleaning_end();
2331 }
2332 assert(_collectorState == AbortablePreclean ||
2333 _collectorState == FinalMarking,
2334 "Collector state should have changed");
2335 break;
2336 case AbortablePreclean:
2337 if (UseAdaptiveSizePolicy) {
2338 size_policy()->concurrent_phases_resume();
2339 }
2340 abortable_preclean();
2341 if (UseAdaptiveSizePolicy) {
2342 size_policy()->concurrent_precleaning_end();
2343 }
2344 assert(_collectorState == FinalMarking, "Collector state should "
2345 "have changed");
2346 break;
2347 case FinalMarking:
2348 {
2349 ReleaseForegroundGC x(this);
2350
2351 VM_CMS_Final_Remark final_remark_op(this);
2352 VMThread::execute(&final_remark_op);
2353 }
2354 assert(_foregroundGCShouldWait, "block post-condition");
2355 break;
2356 case Sweeping:
2357 if (UseAdaptiveSizePolicy) {
2358 size_policy()->concurrent_sweeping_begin();
2359 }
2360 // final marking in checkpointRootsFinal has been completed
2361 sweep(true);
2362 assert(_collectorState == Resizing, "Collector state change "
2363 "to Resizing must be done under the free_list_lock");
2364 _full_gcs_since_conc_gc = 0;
2365
2366 // Stop the timers for adaptive size policy for the concurrent phases
2367 if (UseAdaptiveSizePolicy) {
2368 size_policy()->concurrent_sweeping_end();
2369 size_policy()->concurrent_phases_end(gch->gc_cause(),
2370 gch->prev_gen(_cmsGen)->capacity(),
2371 _cmsGen->free());
2372 }
2373
2374 case Resizing: {
2375 // Sweeping has been completed...
2376 // At this point the background collection has completed.
2377 // Don't move the call to compute_new_size() down
2378 // into code that might be executed if the background
2379 // collection was preempted.
2380 {
2381 ReleaseForegroundGC x(this); // unblock FG collection
2382 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2383 CMSTokenSync z(true); // not strictly needed.
2384 if (_collectorState == Resizing) {
2385 compute_new_size();
2386 save_heap_summary();
2387 _collectorState = Resetting;
2388 } else {
2389 assert(_collectorState == Idling, "The state should only change"
2390 " because the foreground collector has finished the collection");
2391 }
2392 }
2393 break;
2394 }
2395 case Resetting:
2396 // CMS heap resizing has been completed
2397 reset(true);
2398 assert(_collectorState == Idling, "Collector state should "
2399 "have changed");
2400 stats().record_cms_end();
2401 // Don't move the concurrent_phases_end() and compute_new_size()
2402 // calls to here because a preempted background collection
2403 // has it's state set to "Resetting".
2404 break;
2405 case Idling:
2406 default:
2407 ShouldNotReachHere();
2408 break;
2409 }
2410 if (TraceCMSState) {
2411 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2412 Thread::current(), _collectorState);
2413 }
2414 assert(_foregroundGCShouldWait, "block post-condition");
2415 }
2416
2417 // Should this be in gc_epilogue?
2418 collector_policy()->counters()->update_counters();
2419
2420 {
2421 // Clear _foregroundGCShouldWait and, in the event that the
2422 // foreground collector is waiting, notify it, before
2423 // returning.
2424 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2425 _foregroundGCShouldWait = false;
2426 if (_foregroundGCIsActive) {
2427 CGC_lock->notify();
2428 }
2429 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2430 "Possible deadlock");
2431 }
2432 if (TraceCMSState) {
2433 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2434 " exiting collection CMS state %d",
2435 Thread::current(), _collectorState);
2436 }
2437 if (PrintGC && Verbose) {
2438 _cmsGen->print_heap_change(prev_used);
2439 }
2440 }
2441
2442 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2443 if (!_cms_start_registered) {
2444 register_gc_start(cause);
2445 }
2446 }
2447
2448 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2449 _cms_start_registered = true;
2450 _gc_timer_cm->register_gc_start(os::elapsed_counter());
2451 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2452 }
2453
2454 void CMSCollector::register_gc_end() {
2455 if (_cms_start_registered) {
2456 report_heap_summary(GCWhen::AfterGC);
2457
2458 _gc_timer_cm->register_gc_end(os::elapsed_counter());
2459 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2460 _cms_start_registered = false;
2461 }
2462 }
2463
2464 void CMSCollector::save_heap_summary() {
2465 GenCollectedHeap* gch = GenCollectedHeap::heap();
2466 _last_heap_summary = gch->create_heap_summary();
2467 _last_perm_gen_summary = gch->create_perm_gen_summary();
2468 }
2469
2470 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2471 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_perm_gen_summary);
2472 }
2473
2474 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2475 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2476 "Foreground collector should be waiting, not executing");
2477 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2478 "may only be done by the VM Thread with the world stopped");
2479 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2480 "VM thread should have CMS token");
2481
2482 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2483 true, NULL);)
2484 if (UseAdaptiveSizePolicy) {
2485 size_policy()->ms_collection_begin();
2486 }
2487 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2488
2489 HandleMark hm; // Discard invalid handles created during verification
2490
2491 if (VerifyBeforeGC &&
2492 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2493 Universe::verify();
2494 }
2495
2496 // Snapshot the soft reference policy to be used in this collection cycle.
2497 ref_processor()->setup_policy(clear_all_soft_refs);
2498
2499 bool init_mark_was_synchronous = false; // until proven otherwise
2500 while (_collectorState != Idling) {
2501 if (TraceCMSState) {
2502 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2503 Thread::current(), _collectorState);
2504 }
2505 switch (_collectorState) {
2506 case InitialMarking:
2507 register_foreground_gc_start(cause);
2508 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2509 checkpointRootsInitial(false);
2510 assert(_collectorState == Marking, "Collector state should have changed"
2511 " within checkpointRootsInitial()");
2512 break;
2513 case Marking:
2514 // initial marking in checkpointRootsInitialWork has been completed
2515 if (VerifyDuringGC &&
2516 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2517 gclog_or_tty->print("Verify before initial mark: ");
2518 Universe::verify();
2519 }
2520 {
2521 bool res = markFromRoots(false);
2522 assert(res && _collectorState == FinalMarking, "Collector state should "
2523 "have changed");
2524 break;
2525 }
2526 case FinalMarking:
2527 if (VerifyDuringGC &&
2528 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2529 gclog_or_tty->print("Verify before re-mark: ");
2530 Universe::verify();
2531 }
2532 checkpointRootsFinal(false, clear_all_soft_refs,
2533 init_mark_was_synchronous);
2534 assert(_collectorState == Sweeping, "Collector state should not "
2535 "have changed within checkpointRootsFinal()");
2536 break;
2537 case Sweeping:
2538 // final marking in checkpointRootsFinal has been completed
2539 if (VerifyDuringGC &&
2540 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2541 gclog_or_tty->print("Verify before sweep: ");
2542 Universe::verify();
2543 }
2544 sweep(false);
2545 assert(_collectorState == Resizing, "Incorrect state");
2546 break;
2547 case Resizing: {
2548 // Sweeping has been completed; the actual resize in this case
2549 // is done separately; nothing to be done in this state.
2550 _collectorState = Resetting;
2551 break;
2552 }
2553 case Resetting:
2554 // The heap has been resized.
2555 if (VerifyDuringGC &&
2556 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2557 gclog_or_tty->print("Verify before reset: ");
2558 Universe::verify();
2559 }
2560 save_heap_summary();
2561 reset(false);
2562 assert(_collectorState == Idling, "Collector state should "
2563 "have changed");
2564 break;
2565 case Precleaning:
2566 case AbortablePreclean:
2567 // Elide the preclean phase
2568 _collectorState = FinalMarking;
2569 break;
2570 default:
2571 ShouldNotReachHere();
2572 }
2573 if (TraceCMSState) {
2574 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2575 Thread::current(), _collectorState);
2576 }
2577 }
2578
2579 if (UseAdaptiveSizePolicy) {
2580 GenCollectedHeap* gch = GenCollectedHeap::heap();
2581 size_policy()->ms_collection_end(gch->gc_cause());
2582 }
2583
2584 if (VerifyAfterGC &&
2585 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2586 Universe::verify();
2587 }
2588 if (TraceCMSState) {
2589 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2590 " exiting collection CMS state %d",
2591 Thread::current(), _collectorState);
2592 }
2593 }
2594
2595 bool CMSCollector::waitForForegroundGC() {
2596 bool res = false;
2597 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2598 "CMS thread should have CMS token");
2599 // Block the foreground collector until the
2600 // background collectors decides whether to
2601 // yield.
2602 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2603 _foregroundGCShouldWait = true;
2604 if (_foregroundGCIsActive) {
2605 // The background collector yields to the
2606 // foreground collector and returns a value
2607 // indicating that it has yielded. The foreground
2608 // collector can proceed.
2609 res = true;
2610 _foregroundGCShouldWait = false;
2611 ConcurrentMarkSweepThread::clear_CMS_flag(
2612 ConcurrentMarkSweepThread::CMS_cms_has_token);
2613 ConcurrentMarkSweepThread::set_CMS_flag(
2614 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2615 // Get a possibly blocked foreground thread going
2616 CGC_lock->notify();
2617 if (TraceCMSState) {
2618 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2619 Thread::current(), _collectorState);
2620 }
2621 while (_foregroundGCIsActive) {
2622 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2623 }
2624 ConcurrentMarkSweepThread::set_CMS_flag(
2625 ConcurrentMarkSweepThread::CMS_cms_has_token);
2626 ConcurrentMarkSweepThread::clear_CMS_flag(
2627 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2628 }
2629 if (TraceCMSState) {
2630 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2631 Thread::current(), _collectorState);
2632 }
2633 return res;
2634 }
2635
2636 // Because of the need to lock the free lists and other structures in
2637 // the collector, common to all the generations that the collector is
2638 // collecting, we need the gc_prologues of individual CMS generations
2639 // delegate to their collector. It may have been simpler had the
2640 // current infrastructure allowed one to call a prologue on a
2641 // collector. In the absence of that we have the generation's
2642 // prologue delegate to the collector, which delegates back
2643 // some "local" work to a worker method in the individual generations
2644 // that it's responsible for collecting, while itself doing any
2645 // work common to all generations it's responsible for. A similar
2646 // comment applies to the gc_epilogue()'s.
2647 // The role of the varaible _between_prologue_and_epilogue is to
2648 // enforce the invocation protocol.
2649 void CMSCollector::gc_prologue(bool full) {
2650 // Call gc_prologue_work() for each CMSGen and PermGen that
2651 // we are responsible for.
2652
2653 // The following locking discipline assumes that we are only called
2654 // when the world is stopped.
2655 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2656
2657 // The CMSCollector prologue must call the gc_prologues for the
2658 // "generations" (including PermGen if any) that it's responsible
2659 // for.
2660
2661 assert( Thread::current()->is_VM_thread()
2662 || ( CMSScavengeBeforeRemark
2663 && Thread::current()->is_ConcurrentGC_thread()),
2664 "Incorrect thread type for prologue execution");
2665
2666 if (_between_prologue_and_epilogue) {
2667 // We have already been invoked; this is a gc_prologue delegation
2668 // from yet another CMS generation that we are responsible for, just
2669 // ignore it since all relevant work has already been done.
2670 return;
2671 }
2672
2673 // set a bit saying prologue has been called; cleared in epilogue
2674 _between_prologue_and_epilogue = true;
2675 // Claim locks for common data structures, then call gc_prologue_work()
2676 // for each CMSGen and PermGen that we are responsible for.
2677
2678 getFreelistLocks(); // gets free list locks on constituent spaces
2679 bitMapLock()->lock_without_safepoint_check();
2680
2681 // Should call gc_prologue_work() for all cms gens we are responsible for
2682 bool registerClosure = _collectorState >= Marking
2683 && _collectorState < Sweeping;
2684 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2685 &_modUnionClosurePar
2686 : &_modUnionClosure;
2687 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2688 _permGen->gc_prologue_work(full, registerClosure, muc);
2689
2690 if (!full) {
2691 stats().record_gc0_begin();
2692 }
2693 }
2694
2695 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2696 // Delegate to CMScollector which knows how to coordinate between
2697 // this and any other CMS generations that it is responsible for
2698 // collecting.
2699 collector()->gc_prologue(full);
2700 }
2701
2702 // This is a "private" interface for use by this generation's CMSCollector.
2703 // Not to be called directly by any other entity (for instance,
2704 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2705 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2706 bool registerClosure, ModUnionClosure* modUnionClosure) {
2707 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2708 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2709 "Should be NULL");
2710 if (registerClosure) {
2711 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2712 }
2713 cmsSpace()->gc_prologue();
2714 // Clear stat counters
2715 NOT_PRODUCT(
2716 assert(_numObjectsPromoted == 0, "check");
2717 assert(_numWordsPromoted == 0, "check");
2718 if (Verbose && PrintGC) {
2719 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2720 SIZE_FORMAT" bytes concurrently",
2721 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2722 }
2723 _numObjectsAllocated = 0;
2724 _numWordsAllocated = 0;
2725 )
2726 }
2727
2728 void CMSCollector::gc_epilogue(bool full) {
2729 // The following locking discipline assumes that we are only called
2730 // when the world is stopped.
2731 assert(SafepointSynchronize::is_at_safepoint(),
2732 "world is stopped assumption");
2733
2734 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2735 // if linear allocation blocks need to be appropriately marked to allow the
2736 // the blocks to be parsable. We also check here whether we need to nudge the
2737 // CMS collector thread to start a new cycle (if it's not already active).
2738 assert( Thread::current()->is_VM_thread()
2739 || ( CMSScavengeBeforeRemark
2740 && Thread::current()->is_ConcurrentGC_thread()),
2741 "Incorrect thread type for epilogue execution");
2742
2743 if (!_between_prologue_and_epilogue) {
2744 // We have already been invoked; this is a gc_epilogue delegation
2745 // from yet another CMS generation that we are responsible for, just
2746 // ignore it since all relevant work has already been done.
2747 return;
2748 }
2749 assert(haveFreelistLocks(), "must have freelist locks");
2750 assert_lock_strong(bitMapLock());
2751
2752 _cmsGen->gc_epilogue_work(full);
2753 _permGen->gc_epilogue_work(full);
2754
2755 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2756 // in case sampling was not already enabled, enable it
2757 _start_sampling = true;
2758 }
2759 // reset _eden_chunk_array so sampling starts afresh
2760 _eden_chunk_index = 0;
2761
2762 size_t cms_used = _cmsGen->cmsSpace()->used();
2763 size_t perm_used = _permGen->cmsSpace()->used();
2764
2765 // update performance counters - this uses a special version of
2766 // update_counters() that allows the utilization to be passed as a
2767 // parameter, avoiding multiple calls to used().
2768 //
2769 _cmsGen->update_counters(cms_used);
2770 _permGen->update_counters(perm_used);
2771
2772 if (CMSIncrementalMode) {
2773 icms_update_allocation_limits();
2774 }
2775
2776 bitMapLock()->unlock();
2777 releaseFreelistLocks();
2778
2779 if (!CleanChunkPoolAsync) {
2780 Chunk::clean_chunk_pool();
2781 }
2782
2783 _between_prologue_and_epilogue = false; // ready for next cycle
2784 }
2785
2786 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2787 collector()->gc_epilogue(full);
2788
2789 // Also reset promotion tracking in par gc thread states.
2790 if (CollectedHeap::use_parallel_gc_threads()) {
2791 for (uint i = 0; i < ParallelGCThreads; i++) {
2792 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2793 }
2794 }
2795 }
2796
2797 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2798 assert(!incremental_collection_failed(), "Should have been cleared");
2799 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2800 cmsSpace()->gc_epilogue();
2801 // Print stat counters
2802 NOT_PRODUCT(
2803 assert(_numObjectsAllocated == 0, "check");
2804 assert(_numWordsAllocated == 0, "check");
2805 if (Verbose && PrintGC) {
2806 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2807 SIZE_FORMAT" bytes",
2808 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2809 }
2810 _numObjectsPromoted = 0;
2811 _numWordsPromoted = 0;
2812 )
2813
2814 if (PrintGC && Verbose) {
2815 // Call down the chain in contiguous_available needs the freelistLock
2816 // so print this out before releasing the freeListLock.
2817 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2818 contiguous_available());
2819 }
2820 }
2821
2822 #ifndef PRODUCT
2823 bool CMSCollector::have_cms_token() {
2824 Thread* thr = Thread::current();
2825 if (thr->is_VM_thread()) {
2826 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2827 } else if (thr->is_ConcurrentGC_thread()) {
2828 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2829 } else if (thr->is_GC_task_thread()) {
2830 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2831 ParGCRareEvent_lock->owned_by_self();
2832 }
2833 return false;
2834 }
2835 #endif
2836
2837 // Check reachability of the given heap address in CMS generation,
2838 // treating all other generations as roots.
2839 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2840 // We could "guarantee" below, rather than assert, but i'll
2841 // leave these as "asserts" so that an adventurous debugger
2842 // could try this in the product build provided some subset of
2843 // the conditions were met, provided they were intersted in the
2844 // results and knew that the computation below wouldn't interfere
2845 // with other concurrent computations mutating the structures
2846 // being read or written.
2847 assert(SafepointSynchronize::is_at_safepoint(),
2848 "Else mutations in object graph will make answer suspect");
2849 assert(have_cms_token(), "Should hold cms token");
2850 assert(haveFreelistLocks(), "must hold free list locks");
2851 assert_lock_strong(bitMapLock());
2852
2853 // Clear the marking bit map array before starting, but, just
2854 // for kicks, first report if the given address is already marked
2855 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2856 _markBitMap.isMarked(addr) ? "" : " not");
2857
2858 if (verify_after_remark()) {
2859 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2860 bool result = verification_mark_bm()->isMarked(addr);
2861 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2862 result ? "IS" : "is NOT");
2863 return result;
2864 } else {
2865 gclog_or_tty->print_cr("Could not compute result");
2866 return false;
2867 }
2868 }
2869
2870 ////////////////////////////////////////////////////////
2871 // CMS Verification Support
2872 ////////////////////////////////////////////////////////
2873 // Following the remark phase, the following invariant
2874 // should hold -- each object in the CMS heap which is
2875 // marked in markBitMap() should be marked in the verification_mark_bm().
2876
2877 class VerifyMarkedClosure: public BitMapClosure {
2878 CMSBitMap* _marks;
2879 bool _failed;
2880
2881 public:
2882 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2883
2884 bool do_bit(size_t offset) {
2885 HeapWord* addr = _marks->offsetToHeapWord(offset);
2886 if (!_marks->isMarked(addr)) {
2887 oop(addr)->print_on(gclog_or_tty);
2888 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2889 _failed = true;
2890 }
2891 return true;
2892 }
2893
2894 bool failed() { return _failed; }
2895 };
2896
2897 bool CMSCollector::verify_after_remark() {
2898 gclog_or_tty->print(" [Verifying CMS Marking... ");
2899 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2900 static bool init = false;
2901
2902 assert(SafepointSynchronize::is_at_safepoint(),
2903 "Else mutations in object graph will make answer suspect");
2904 assert(have_cms_token(),
2905 "Else there may be mutual interference in use of "
2906 " verification data structures");
2907 assert(_collectorState > Marking && _collectorState <= Sweeping,
2908 "Else marking info checked here may be obsolete");
2909 assert(haveFreelistLocks(), "must hold free list locks");
2910 assert_lock_strong(bitMapLock());
2911
2912
2913 // Allocate marking bit map if not already allocated
2914 if (!init) { // first time
2915 if (!verification_mark_bm()->allocate(_span)) {
2916 return false;
2917 }
2918 init = true;
2919 }
2920
2921 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2922
2923 // Turn off refs discovery -- so we will be tracing through refs.
2924 // This is as intended, because by this time
2925 // GC must already have cleared any refs that need to be cleared,
2926 // and traced those that need to be marked; moreover,
2927 // the marking done here is not going to intefere in any
2928 // way with the marking information used by GC.
2929 NoRefDiscovery no_discovery(ref_processor());
2930
2931 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2932
2933 // Clear any marks from a previous round
2934 verification_mark_bm()->clear_all();
2935 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2936 verify_work_stacks_empty();
2937
2938 GenCollectedHeap* gch = GenCollectedHeap::heap();
2939 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2940 // Update the saved marks which may affect the root scans.
2941 gch->save_marks();
2942
2943 if (CMSRemarkVerifyVariant == 1) {
2944 // In this first variant of verification, we complete
2945 // all marking, then check if the new marks-verctor is
2946 // a subset of the CMS marks-vector.
2947 verify_after_remark_work_1();
2948 } else if (CMSRemarkVerifyVariant == 2) {
2949 // In this second variant of verification, we flag an error
2950 // (i.e. an object reachable in the new marks-vector not reachable
2951 // in the CMS marks-vector) immediately, also indicating the
2952 // identify of an object (A) that references the unmarked object (B) --
2953 // presumably, a mutation to A failed to be picked up by preclean/remark?
2954 verify_after_remark_work_2();
2955 } else {
2956 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2957 CMSRemarkVerifyVariant);
2958 }
2959 gclog_or_tty->print(" done] ");
2960 return true;
2961 }
2962
2963 void CMSCollector::verify_after_remark_work_1() {
2964 ResourceMark rm;
2965 HandleMark hm;
2966 GenCollectedHeap* gch = GenCollectedHeap::heap();
2967
2968 // Mark from roots one level into CMS
2969 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2970 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2971
2972 gch->gen_process_strong_roots(_cmsGen->level(),
2973 true, // younger gens are roots
2974 true, // activate StrongRootsScope
2975 true, // collecting perm gen
2976 SharedHeap::ScanningOption(roots_scanning_options()),
2977 ¬Older,
2978 true, // walk code active on stacks
2979 NULL);
2980
2981 // Now mark from the roots
2982 assert(_revisitStack.isEmpty(), "Should be empty");
2983 MarkFromRootsClosure markFromRootsClosure(this, _span,
2984 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2985 false /* don't yield */, true /* verifying */);
2986 assert(_restart_addr == NULL, "Expected pre-condition");
2987 verification_mark_bm()->iterate(&markFromRootsClosure);
2988 while (_restart_addr != NULL) {
2989 // Deal with stack overflow: by restarting at the indicated
2990 // address.
2991 HeapWord* ra = _restart_addr;
2992 markFromRootsClosure.reset(ra);
2993 _restart_addr = NULL;
2994 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2995 }
2996 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2997 verify_work_stacks_empty();
2998 // Should reset the revisit stack above, since no class tree
2999 // surgery is forthcoming.
3000 _revisitStack.reset(); // throwing away all contents
3001
3002 // Marking completed -- now verify that each bit marked in
3003 // verification_mark_bm() is also marked in markBitMap(); flag all
3004 // errors by printing corresponding objects.
3005 VerifyMarkedClosure vcl(markBitMap());
3006 verification_mark_bm()->iterate(&vcl);
3007 if (vcl.failed()) {
3008 gclog_or_tty->print("Verification failed");
3009 Universe::heap()->print_on(gclog_or_tty);
3010 fatal("CMS: failed marking verification after remark");
3011 }
3012 }
3013
3014 void CMSCollector::verify_after_remark_work_2() {
3015 ResourceMark rm;
3016 HandleMark hm;
3017 GenCollectedHeap* gch = GenCollectedHeap::heap();
3018
3019 // Mark from roots one level into CMS
3020 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3021 markBitMap());
3022 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3023 gch->gen_process_strong_roots(_cmsGen->level(),
3024 true, // younger gens are roots
3025 true, // activate StrongRootsScope
3026 true, // collecting perm gen
3027 SharedHeap::ScanningOption(roots_scanning_options()),
3028 ¬Older,
3029 true, // walk code active on stacks
3030 NULL);
3031
3032 // Now mark from the roots
3033 assert(_revisitStack.isEmpty(), "Should be empty");
3034 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3035 verification_mark_bm(), markBitMap(), verification_mark_stack());
3036 assert(_restart_addr == NULL, "Expected pre-condition");
3037 verification_mark_bm()->iterate(&markFromRootsClosure);
3038 while (_restart_addr != NULL) {
3039 // Deal with stack overflow: by restarting at the indicated
3040 // address.
3041 HeapWord* ra = _restart_addr;
3042 markFromRootsClosure.reset(ra);
3043 _restart_addr = NULL;
3044 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3045 }
3046 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3047 verify_work_stacks_empty();
3048 // Should reset the revisit stack above, since no class tree
3049 // surgery is forthcoming.
3050 _revisitStack.reset(); // throwing away all contents
3051
3052 // Marking completed -- now verify that each bit marked in
3053 // verification_mark_bm() is also marked in markBitMap(); flag all
3054 // errors by printing corresponding objects.
3055 VerifyMarkedClosure vcl(markBitMap());
3056 verification_mark_bm()->iterate(&vcl);
3057 assert(!vcl.failed(), "Else verification above should not have succeeded");
3058 }
3059
3060 void ConcurrentMarkSweepGeneration::save_marks() {
3061 // delegate to CMS space
3062 cmsSpace()->save_marks();
3063 for (uint i = 0; i < ParallelGCThreads; i++) {
3064 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3065 }
3066 }
3067
3068 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3069 return cmsSpace()->no_allocs_since_save_marks();
3070 }
3071
3072 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3073 \
3074 void ConcurrentMarkSweepGeneration:: \
3075 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3076 cl->set_generation(this); \
3077 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3078 cl->reset_generation(); \
3079 save_marks(); \
3080 }
3081
3082 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3083
3084 void
3085 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3086 {
3087 // Not currently implemented; need to do the following. -- ysr.
3088 // dld -- I think that is used for some sort of allocation profiler. So it
3089 // really means the objects allocated by the mutator since the last
3090 // GC. We could potentially implement this cheaply by recording only
3091 // the direct allocations in a side data structure.
3092 //
3093 // I think we probably ought not to be required to support these
3094 // iterations at any arbitrary point; I think there ought to be some
3095 // call to enable/disable allocation profiling in a generation/space,
3096 // and the iterator ought to return the objects allocated in the
3097 // gen/space since the enable call, or the last iterator call (which
3098 // will probably be at a GC.) That way, for gens like CM&S that would
3099 // require some extra data structure to support this, we only pay the
3100 // cost when it's in use...
3101 cmsSpace()->object_iterate_since_last_GC(blk);
3102 }
3103
3104 void
3105 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3106 cl->set_generation(this);
3107 younger_refs_in_space_iterate(_cmsSpace, cl);
3108 cl->reset_generation();
3109 }
3110
3111 void
3112 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3113 if (freelistLock()->owned_by_self()) {
3114 Generation::oop_iterate(mr, cl);
3115 } else {
3116 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3117 Generation::oop_iterate(mr, cl);
3118 }
3119 }
3120
3121 void
3122 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3123 if (freelistLock()->owned_by_self()) {
3124 Generation::oop_iterate(cl);
3125 } else {
3126 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3127 Generation::oop_iterate(cl);
3128 }
3129 }
3130
3131 void
3132 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3133 if (freelistLock()->owned_by_self()) {
3134 Generation::object_iterate(cl);
3135 } else {
3136 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3137 Generation::object_iterate(cl);
3138 }
3139 }
3140
3141 void
3142 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3143 if (freelistLock()->owned_by_self()) {
3144 Generation::safe_object_iterate(cl);
3145 } else {
3146 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3147 Generation::safe_object_iterate(cl);
3148 }
3149 }
3150
3151 void
3152 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3153 }
3154
3155 void
3156 ConcurrentMarkSweepGeneration::post_compact() {
3157 }
3158
3159 void
3160 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3161 // Fix the linear allocation blocks to look like free blocks.
3162
3163 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3164 // are not called when the heap is verified during universe initialization and
3165 // at vm shutdown.
3166 if (freelistLock()->owned_by_self()) {
3167 cmsSpace()->prepare_for_verify();
3168 } else {
3169 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3170 cmsSpace()->prepare_for_verify();
3171 }
3172 }
3173
3174 void
3175 ConcurrentMarkSweepGeneration::verify() {
3176 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3177 // are not called when the heap is verified during universe initialization and
3178 // at vm shutdown.
3179 if (freelistLock()->owned_by_self()) {
3180 cmsSpace()->verify();
3181 } else {
3182 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3183 cmsSpace()->verify();
3184 }
3185 }
3186
3187 void CMSCollector::verify() {
3188 _cmsGen->verify();
3189 _permGen->verify();
3190 }
3191
3192 #ifndef PRODUCT
3193 bool CMSCollector::overflow_list_is_empty() const {
3194 assert(_num_par_pushes >= 0, "Inconsistency");
3195 if (_overflow_list == NULL) {
3196 assert(_num_par_pushes == 0, "Inconsistency");
3197 }
3198 return _overflow_list == NULL;
3199 }
3200
3201 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3202 // merely consolidate assertion checks that appear to occur together frequently.
3203 void CMSCollector::verify_work_stacks_empty() const {
3204 assert(_markStack.isEmpty(), "Marking stack should be empty");
3205 assert(overflow_list_is_empty(), "Overflow list should be empty");
3206 }
3207
3208 void CMSCollector::verify_overflow_empty() const {
3209 assert(overflow_list_is_empty(), "Overflow list should be empty");
3210 assert(no_preserved_marks(), "No preserved marks");
3211 }
3212 #endif // PRODUCT
3213
3214 // Decide if we want to enable class unloading as part of the
3215 // ensuing concurrent GC cycle. We will collect the perm gen and
3216 // unload classes if it's the case that:
3217 // (1) an explicit gc request has been made and the flag
3218 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3219 // (2) (a) class unloading is enabled at the command line, and
3220 // (b) (i) perm gen threshold has been crossed, or
3221 // (ii) old gen is getting really full, or
3222 // (iii) the previous N CMS collections did not collect the
3223 // perm gen
3224 // NOTE: Provided there is no change in the state of the heap between
3225 // calls to this method, it should have idempotent results. Moreover,
3226 // its results should be monotonically increasing (i.e. going from 0 to 1,
3227 // but not 1 to 0) between successive calls between which the heap was
3228 // not collected. For the implementation below, it must thus rely on
3229 // the property that concurrent_cycles_since_last_unload()
3230 // will not decrease unless a collection cycle happened and that
3231 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3232 // themselves also monotonic in that sense. See check_monotonicity()
3233 // below.
3234 bool CMSCollector::update_should_unload_classes() {
3235 _should_unload_classes = false;
3236 // Condition 1 above
3237 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3238 _should_unload_classes = true;
3239 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3240 // Disjuncts 2.b.(i,ii,iii) above
3241 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3242 CMSClassUnloadingMaxInterval)
3243 || _permGen->should_concurrent_collect()
3244 || _cmsGen->is_too_full();
3245 }
3246 return _should_unload_classes;
3247 }
3248
3249 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3250 bool res = should_concurrent_collect();
3251 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3252 return res;
3253 }
3254
3255 void CMSCollector::setup_cms_unloading_and_verification_state() {
3256 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3257 || VerifyBeforeExit;
3258 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3259
3260 if (should_unload_classes()) { // Should unload classes this cycle
3261 remove_root_scanning_option(rso); // Shrink the root set appropriately
3262 set_verifying(should_verify); // Set verification state for this cycle
3263 return; // Nothing else needs to be done at this time
3264 }
3265
3266 // Not unloading classes this cycle
3267 assert(!should_unload_classes(), "Inconsitency!");
3268 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3269 // We were not verifying, or we _were_ unloading classes in the last cycle,
3270 // AND some verification options are enabled this cycle; in this case,
3271 // we must make sure that the deadness map is allocated if not already so,
3272 // and cleared (if already allocated previously --
3273 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3274 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3275 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3276 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3277 "permanent generation verification disabled");
3278 return; // Note that we leave verification disabled, so we'll retry this
3279 // allocation next cycle. We _could_ remember this failure
3280 // and skip further attempts and permanently disable verification
3281 // attempts if that is considered more desirable.
3282 }
3283 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3284 "_perm_gen_ver_bit_map inconsistency?");
3285 } else {
3286 perm_gen_verify_bit_map()->clear_all();
3287 }
3288 // Include symbols, strings and code cache elements to prevent their resurrection.
3289 add_root_scanning_option(rso);
3290 set_verifying(true);
3291 } else if (verifying() && !should_verify) {
3292 // We were verifying, but some verification flags got disabled.
3293 set_verifying(false);
3294 // Exclude symbols, strings and code cache elements from root scanning to
3295 // reduce IM and RM pauses.
3296 remove_root_scanning_option(rso);
3297 }
3298 }
3299
3300
3301 #ifndef PRODUCT
3302 HeapWord* CMSCollector::block_start(const void* p) const {
3303 const HeapWord* addr = (HeapWord*)p;
3304 if (_span.contains(p)) {
3305 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3306 return _cmsGen->cmsSpace()->block_start(p);
3307 } else {
3308 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3309 "Inconsistent _span?");
3310 return _permGen->cmsSpace()->block_start(p);
3311 }
3312 }
3313 return NULL;
3314 }
3315 #endif
3316
3317 HeapWord*
3318 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3319 bool tlab,
3320 bool parallel) {
3321 CMSSynchronousYieldRequest yr;
3322 assert(!tlab, "Can't deal with TLAB allocation");
3323 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3324 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3325 CMSExpansionCause::_satisfy_allocation);
3326 if (GCExpandToAllocateDelayMillis > 0) {
3327 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3328 }
3329 return have_lock_and_allocate(word_size, tlab);
3330 }
3331
3332 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3333 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3334 // to CardGeneration and share it...
3335 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3336 return CardGeneration::expand(bytes, expand_bytes);
3337 }
3338
3339 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3340 CMSExpansionCause::Cause cause)
3341 {
3342
3343 bool success = expand(bytes, expand_bytes);
3344
3345 // remember why we expanded; this information is used
3346 // by shouldConcurrentCollect() when making decisions on whether to start
3347 // a new CMS cycle.
3348 if (success) {
3349 set_expansion_cause(cause);
3350 if (PrintGCDetails && Verbose) {
3351 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3352 CMSExpansionCause::to_string(cause));
3353 }
3354 }
3355 }
3356
3357 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3358 HeapWord* res = NULL;
3359 MutexLocker x(ParGCRareEvent_lock);
3360 while (true) {
3361 // Expansion by some other thread might make alloc OK now:
3362 res = ps->lab.alloc(word_sz);
3363 if (res != NULL) return res;
3364 // If there's not enough expansion space available, give up.
3365 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3366 return NULL;
3367 }
3368 // Otherwise, we try expansion.
3369 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3370 CMSExpansionCause::_allocate_par_lab);
3371 // Now go around the loop and try alloc again;
3372 // A competing par_promote might beat us to the expansion space,
3373 // so we may go around the loop again if promotion fails agaion.
3374 if (GCExpandToAllocateDelayMillis > 0) {
3375 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3376 }
3377 }
3378 }
3379
3380
3381 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3382 PromotionInfo* promo) {
3383 MutexLocker x(ParGCRareEvent_lock);
3384 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3385 while (true) {
3386 // Expansion by some other thread might make alloc OK now:
3387 if (promo->ensure_spooling_space()) {
3388 assert(promo->has_spooling_space(),
3389 "Post-condition of successful ensure_spooling_space()");
3390 return true;
3391 }
3392 // If there's not enough expansion space available, give up.
3393 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3394 return false;
3395 }
3396 // Otherwise, we try expansion.
3397 expand(refill_size_bytes, MinHeapDeltaBytes,
3398 CMSExpansionCause::_allocate_par_spooling_space);
3399 // Now go around the loop and try alloc again;
3400 // A competing allocation might beat us to the expansion space,
3401 // so we may go around the loop again if allocation fails again.
3402 if (GCExpandToAllocateDelayMillis > 0) {
3403 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3404 }
3405 }
3406 }
3407
3408
3409
3410 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3411 assert_locked_or_safepoint(Heap_lock);
3412 size_t size = ReservedSpace::page_align_size_down(bytes);
3413 if (size > 0) {
3414 shrink_by(size);
3415 }
3416 }
3417
3418 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3419 assert_locked_or_safepoint(Heap_lock);
3420 bool result = _virtual_space.expand_by(bytes);
3421 if (result) {
3422 HeapWord* old_end = _cmsSpace->end();
3423 size_t new_word_size =
3424 heap_word_size(_virtual_space.committed_size());
3425 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3426 _bts->resize(new_word_size); // resize the block offset shared array
3427 Universe::heap()->barrier_set()->resize_covered_region(mr);
3428 // Hmmmm... why doesn't CFLS::set_end verify locking?
3429 // This is quite ugly; FIX ME XXX
3430 _cmsSpace->assert_locked(freelistLock());
3431 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3432
3433 // update the space and generation capacity counters
3434 if (UsePerfData) {
3435 _space_counters->update_capacity();
3436 _gen_counters->update_all();
3437 }
3438
3439 if (Verbose && PrintGC) {
3440 size_t new_mem_size = _virtual_space.committed_size();
3441 size_t old_mem_size = new_mem_size - bytes;
3442 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3443 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3444 }
3445 }
3446 return result;
3447 }
3448
3449 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3450 assert_locked_or_safepoint(Heap_lock);
3451 bool success = true;
3452 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3453 if (remaining_bytes > 0) {
3454 success = grow_by(remaining_bytes);
3455 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3456 }
3457 return success;
3458 }
3459
3460 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3461 assert_locked_or_safepoint(Heap_lock);
3462 assert_lock_strong(freelistLock());
3463 // XXX Fix when compaction is implemented.
3464 warning("Shrinking of CMS not yet implemented");
3465 return;
3466 }
3467
3468
3469 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3470 // phases.
3471 class CMSPhaseAccounting: public StackObj {
3472 public:
3473 CMSPhaseAccounting(CMSCollector *collector,
3474 const char *phase,
3475 bool print_cr = true);
3476 ~CMSPhaseAccounting();
3477
3478 private:
3479 CMSCollector *_collector;
3480 const char *_phase;
3481 elapsedTimer _wallclock;
3482 bool _print_cr;
3483
3484 public:
3485 // Not MT-safe; so do not pass around these StackObj's
3486 // where they may be accessed by other threads.
3487 jlong wallclock_millis() {
3488 assert(_wallclock.is_active(), "Wall clock should not stop");
3489 _wallclock.stop(); // to record time
3490 jlong ret = _wallclock.milliseconds();
3491 _wallclock.start(); // restart
3492 return ret;
3493 }
3494 };
3495
3496 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3497 const char *phase,
3498 bool print_cr) :
3499 _collector(collector), _phase(phase), _print_cr(print_cr) {
3500
3501 if (PrintCMSStatistics != 0) {
3502 _collector->resetYields();
3503 }
3504 if (PrintGCDetails && PrintGCTimeStamps) {
3505 gclog_or_tty->date_stamp(PrintGCDateStamps);
3506 gclog_or_tty->stamp();
3507 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3508 _collector->cmsGen()->short_name(), _phase);
3509 }
3510 _collector->resetTimer();
3511 _wallclock.start();
3512 _collector->startTimer();
3513 }
3514
3515 CMSPhaseAccounting::~CMSPhaseAccounting() {
3516 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3517 _collector->stopTimer();
3518 _wallclock.stop();
3519 if (PrintGCDetails) {
3520 gclog_or_tty->date_stamp(PrintGCDateStamps);
3521 gclog_or_tty->stamp(PrintGCTimeStamps);
3522 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3523 _collector->cmsGen()->short_name(),
3524 _phase, _collector->timerValue(), _wallclock.seconds());
3525 if (_print_cr) {
3526 gclog_or_tty->print_cr("");
3527 }
3528 if (PrintCMSStatistics != 0) {
3529 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3530 _collector->yields());
3531 }
3532 }
3533 }
3534
3535 // CMS work
3536
3537 // Checkpoint the roots into this generation from outside
3538 // this generation. [Note this initial checkpoint need only
3539 // be approximate -- we'll do a catch up phase subsequently.]
3540 void CMSCollector::checkpointRootsInitial(bool asynch) {
3541 assert(_collectorState == InitialMarking, "Wrong collector state");
3542 check_correct_thread_executing();
3543 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3544
3545 save_heap_summary();
3546 report_heap_summary(GCWhen::BeforeGC);
3547
3548 ReferenceProcessor* rp = ref_processor();
3549 SpecializationStats::clear();
3550 assert(_restart_addr == NULL, "Control point invariant");
3551 if (asynch) {
3552 // acquire locks for subsequent manipulations
3553 MutexLockerEx x(bitMapLock(),
3554 Mutex::_no_safepoint_check_flag);
3555 checkpointRootsInitialWork(asynch);
3556 // enable ("weak") refs discovery
3557 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3558 _collectorState = Marking;
3559 } else {
3560 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3561 // which recognizes if we are a CMS generation, and doesn't try to turn on
3562 // discovery; verify that they aren't meddling.
3563 assert(!rp->discovery_is_atomic(),
3564 "incorrect setting of discovery predicate");
3565 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3566 "ref discovery for this generation kind");
3567 // already have locks
3568 checkpointRootsInitialWork(asynch);
3569 // now enable ("weak") refs discovery
3570 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3571 _collectorState = Marking;
3572 }
3573 SpecializationStats::print();
3574 }
3575
3576 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3577 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3578 assert(_collectorState == InitialMarking, "just checking");
3579
3580 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3581 // precede our marking with a collection of all
3582 // younger generations to keep floating garbage to a minimum.
3583 // XXX: we won't do this for now -- it's an optimization to be done later.
3584
3585 // already have locks
3586 assert_lock_strong(bitMapLock());
3587 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3588
3589 // Setup the verification and class unloading state for this
3590 // CMS collection cycle.
3591 setup_cms_unloading_and_verification_state();
3592
3593 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3594 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3595 if (UseAdaptiveSizePolicy) {
3596 size_policy()->checkpoint_roots_initial_begin();
3597 }
3598
3599 // Reset all the PLAB chunk arrays if necessary.
3600 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3601 reset_survivor_plab_arrays();
3602 }
3603
3604 ResourceMark rm;
3605 HandleMark hm;
3606
3607 FalseClosure falseClosure;
3608 // In the case of a synchronous collection, we will elide the
3609 // remark step, so it's important to catch all the nmethod oops
3610 // in this step.
3611 // The final 'true' flag to gen_process_strong_roots will ensure this.
3612 // If 'async' is true, we can relax the nmethod tracing.
3613 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3614 GenCollectedHeap* gch = GenCollectedHeap::heap();
3615
3616 verify_work_stacks_empty();
3617 verify_overflow_empty();
3618
3619 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3620 // Update the saved marks which may affect the root scans.
3621 gch->save_marks();
3622
3623 // weak reference processing has not started yet.
3624 ref_processor()->set_enqueuing_is_done(false);
3625
3626 {
3627 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3628 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3629 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3630 gch->gen_process_strong_roots(_cmsGen->level(),
3631 true, // younger gens are roots
3632 true, // activate StrongRootsScope
3633 true, // collecting perm gen
3634 SharedHeap::ScanningOption(roots_scanning_options()),
3635 ¬Older,
3636 true, // walk all of code cache if (so & SO_CodeCache)
3637 NULL);
3638 }
3639
3640 // Clear mod-union table; it will be dirtied in the prologue of
3641 // CMS generation per each younger generation collection.
3642
3643 assert(_modUnionTable.isAllClear(),
3644 "Was cleared in most recent final checkpoint phase"
3645 " or no bits are set in the gc_prologue before the start of the next "
3646 "subsequent marking phase.");
3647
3648 // Save the end of the used_region of the constituent generations
3649 // to be used to limit the extent of sweep in each generation.
3650 save_sweep_limits();
3651 if (UseAdaptiveSizePolicy) {
3652 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3653 }
3654 verify_overflow_empty();
3655 }
3656
3657 bool CMSCollector::markFromRoots(bool asynch) {
3658 // we might be tempted to assert that:
3659 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3660 // "inconsistent argument?");
3661 // However that wouldn't be right, because it's possible that
3662 // a safepoint is indeed in progress as a younger generation
3663 // stop-the-world GC happens even as we mark in this generation.
3664 assert(_collectorState == Marking, "inconsistent state?");
3665 check_correct_thread_executing();
3666 verify_overflow_empty();
3667
3668 bool res;
3669 if (asynch) {
3670
3671 // Start the timers for adaptive size policy for the concurrent phases
3672 // Do it here so that the foreground MS can use the concurrent
3673 // timer since a foreground MS might has the sweep done concurrently
3674 // or STW.
3675 if (UseAdaptiveSizePolicy) {
3676 size_policy()->concurrent_marking_begin();
3677 }
3678
3679 // Weak ref discovery note: We may be discovering weak
3680 // refs in this generation concurrent (but interleaved) with
3681 // weak ref discovery by a younger generation collector.
3682
3683 CMSTokenSyncWithLocks ts(true, bitMapLock());
3684 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3685 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3686 res = markFromRootsWork(asynch);
3687 if (res) {
3688 _collectorState = Precleaning;
3689 } else { // We failed and a foreground collection wants to take over
3690 assert(_foregroundGCIsActive, "internal state inconsistency");
3691 assert(_restart_addr == NULL, "foreground will restart from scratch");
3692 if (PrintGCDetails) {
3693 gclog_or_tty->print_cr("bailing out to foreground collection");
3694 }
3695 }
3696 if (UseAdaptiveSizePolicy) {
3697 size_policy()->concurrent_marking_end();
3698 }
3699 } else {
3700 assert(SafepointSynchronize::is_at_safepoint(),
3701 "inconsistent with asynch == false");
3702 if (UseAdaptiveSizePolicy) {
3703 size_policy()->ms_collection_marking_begin();
3704 }
3705 // already have locks
3706 res = markFromRootsWork(asynch);
3707 _collectorState = FinalMarking;
3708 if (UseAdaptiveSizePolicy) {
3709 GenCollectedHeap* gch = GenCollectedHeap::heap();
3710 size_policy()->ms_collection_marking_end(gch->gc_cause());
3711 }
3712 }
3713 verify_overflow_empty();
3714 return res;
3715 }
3716
3717 bool CMSCollector::markFromRootsWork(bool asynch) {
3718 // iterate over marked bits in bit map, doing a full scan and mark
3719 // from these roots using the following algorithm:
3720 // . if oop is to the right of the current scan pointer,
3721 // mark corresponding bit (we'll process it later)
3722 // . else (oop is to left of current scan pointer)
3723 // push oop on marking stack
3724 // . drain the marking stack
3725
3726 // Note that when we do a marking step we need to hold the
3727 // bit map lock -- recall that direct allocation (by mutators)
3728 // and promotion (by younger generation collectors) is also
3729 // marking the bit map. [the so-called allocate live policy.]
3730 // Because the implementation of bit map marking is not
3731 // robust wrt simultaneous marking of bits in the same word,
3732 // we need to make sure that there is no such interference
3733 // between concurrent such updates.
3734
3735 // already have locks
3736 assert_lock_strong(bitMapLock());
3737
3738 // Clear the revisit stack, just in case there are any
3739 // obsolete contents from a short-circuited previous CMS cycle.
3740 _revisitStack.reset();
3741 verify_work_stacks_empty();
3742 verify_overflow_empty();
3743 assert(_revisitStack.isEmpty(), "tabula rasa");
3744 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3745 bool result = false;
3746 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3747 result = do_marking_mt(asynch);
3748 } else {
3749 result = do_marking_st(asynch);
3750 }
3751 return result;
3752 }
3753
3754 // Forward decl
3755 class CMSConcMarkingTask;
3756
3757 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3758 CMSCollector* _collector;
3759 CMSConcMarkingTask* _task;
3760 public:
3761 virtual void yield();
3762
3763 // "n_threads" is the number of threads to be terminated.
3764 // "queue_set" is a set of work queues of other threads.
3765 // "collector" is the CMS collector associated with this task terminator.
3766 // "yield" indicates whether we need the gang as a whole to yield.
3767 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3768 ParallelTaskTerminator(n_threads, queue_set),
3769 _collector(collector) { }
3770
3771 void set_task(CMSConcMarkingTask* task) {
3772 _task = task;
3773 }
3774 };
3775
3776 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3777 CMSConcMarkingTask* _task;
3778 public:
3779 bool should_exit_termination();
3780 void set_task(CMSConcMarkingTask* task) {
3781 _task = task;
3782 }
3783 };
3784
3785 // MT Concurrent Marking Task
3786 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3787 CMSCollector* _collector;
3788 int _n_workers; // requested/desired # workers
3789 bool _asynch;
3790 bool _result;
3791 CompactibleFreeListSpace* _cms_space;
3792 CompactibleFreeListSpace* _perm_space;
3793 char _pad_front[64]; // padding to ...
3794 HeapWord* _global_finger; // ... avoid sharing cache line
3795 char _pad_back[64];
3796 HeapWord* _restart_addr;
3797
3798 // Exposed here for yielding support
3799 Mutex* const _bit_map_lock;
3800
3801 // The per thread work queues, available here for stealing
3802 OopTaskQueueSet* _task_queues;
3803
3804 // Termination (and yielding) support
3805 CMSConcMarkingTerminator _term;
3806 CMSConcMarkingTerminatorTerminator _term_term;
3807
3808 public:
3809 CMSConcMarkingTask(CMSCollector* collector,
3810 CompactibleFreeListSpace* cms_space,
3811 CompactibleFreeListSpace* perm_space,
3812 bool asynch,
3813 YieldingFlexibleWorkGang* workers,
3814 OopTaskQueueSet* task_queues):
3815 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3816 _collector(collector),
3817 _cms_space(cms_space),
3818 _perm_space(perm_space),
3819 _asynch(asynch), _n_workers(0), _result(true),
3820 _task_queues(task_queues),
3821 _term(_n_workers, task_queues, _collector),
3822 _bit_map_lock(collector->bitMapLock())
3823 {
3824 _requested_size = _n_workers;
3825 _term.set_task(this);
3826 _term_term.set_task(this);
3827 assert(_cms_space->bottom() < _perm_space->bottom(),
3828 "Finger incorrectly initialized below");
3829 _restart_addr = _global_finger = _cms_space->bottom();
3830 }
3831
3832
3833 OopTaskQueueSet* task_queues() { return _task_queues; }
3834
3835 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3836
3837 HeapWord** global_finger_addr() { return &_global_finger; }
3838
3839 CMSConcMarkingTerminator* terminator() { return &_term; }
3840
3841 virtual void set_for_termination(int active_workers) {
3842 terminator()->reset_for_reuse(active_workers);
3843 }
3844
3845 void work(uint worker_id);
3846 bool should_yield() {
3847 return ConcurrentMarkSweepThread::should_yield()
3848 && !_collector->foregroundGCIsActive()
3849 && _asynch;
3850 }
3851
3852 virtual void coordinator_yield(); // stuff done by coordinator
3853 bool result() { return _result; }
3854
3855 void reset(HeapWord* ra) {
3856 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3857 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3858 assert(ra < _perm_space->end(), "ra too large");
3859 _restart_addr = _global_finger = ra;
3860 _term.reset_for_reuse();
3861 }
3862
3863 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3864 OopTaskQueue* work_q);
3865
3866 private:
3867 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3868 void do_work_steal(int i);
3869 void bump_global_finger(HeapWord* f);
3870 };
3871
3872 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3873 assert(_task != NULL, "Error");
3874 return _task->yielding();
3875 // Note that we do not need the disjunct || _task->should_yield() above
3876 // because we want terminating threads to yield only if the task
3877 // is already in the midst of yielding, which happens only after at least one
3878 // thread has yielded.
3879 }
3880
3881 void CMSConcMarkingTerminator::yield() {
3882 if (_task->should_yield()) {
3883 _task->yield();
3884 } else {
3885 ParallelTaskTerminator::yield();
3886 }
3887 }
3888
3889 ////////////////////////////////////////////////////////////////
3890 // Concurrent Marking Algorithm Sketch
3891 ////////////////////////////////////////////////////////////////
3892 // Until all tasks exhausted (both spaces):
3893 // -- claim next available chunk
3894 // -- bump global finger via CAS
3895 // -- find first object that starts in this chunk
3896 // and start scanning bitmap from that position
3897 // -- scan marked objects for oops
3898 // -- CAS-mark target, and if successful:
3899 // . if target oop is above global finger (volatile read)
3900 // nothing to do
3901 // . if target oop is in chunk and above local finger
3902 // then nothing to do
3903 // . else push on work-queue
3904 // -- Deal with possible overflow issues:
3905 // . local work-queue overflow causes stuff to be pushed on
3906 // global (common) overflow queue
3907 // . always first empty local work queue
3908 // . then get a batch of oops from global work queue if any
3909 // . then do work stealing
3910 // -- When all tasks claimed (both spaces)
3911 // and local work queue empty,
3912 // then in a loop do:
3913 // . check global overflow stack; steal a batch of oops and trace
3914 // . try to steal from other threads oif GOS is empty
3915 // . if neither is available, offer termination
3916 // -- Terminate and return result
3917 //
3918 void CMSConcMarkingTask::work(uint worker_id) {
3919 elapsedTimer _timer;
3920 ResourceMark rm;
3921 HandleMark hm;
3922
3923 DEBUG_ONLY(_collector->verify_overflow_empty();)
3924
3925 // Before we begin work, our work queue should be empty
3926 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3927 // Scan the bitmap covering _cms_space, tracing through grey objects.
3928 _timer.start();
3929 do_scan_and_mark(worker_id, _cms_space);
3930 _timer.stop();
3931 if (PrintCMSStatistics != 0) {
3932 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3933 worker_id, _timer.seconds());
3934 // XXX: need xxx/xxx type of notation, two timers
3935 }
3936
3937 // ... do the same for the _perm_space
3938 _timer.reset();
3939 _timer.start();
3940 do_scan_and_mark(worker_id, _perm_space);
3941 _timer.stop();
3942 if (PrintCMSStatistics != 0) {
3943 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3944 worker_id, _timer.seconds());
3945 // XXX: need xxx/xxx type of notation, two timers
3946 }
3947
3948 // ... do work stealing
3949 _timer.reset();
3950 _timer.start();
3951 do_work_steal(worker_id);
3952 _timer.stop();
3953 if (PrintCMSStatistics != 0) {
3954 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3955 worker_id, _timer.seconds());
3956 // XXX: need xxx/xxx type of notation, two timers
3957 }
3958 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3959 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3960 // Note that under the current task protocol, the
3961 // following assertion is true even of the spaces
3962 // expanded since the completion of the concurrent
3963 // marking. XXX This will likely change under a strict
3964 // ABORT semantics.
3965 assert(_global_finger > _cms_space->end() &&
3966 _global_finger >= _perm_space->end(),
3967 "All tasks have been completed");
3968 DEBUG_ONLY(_collector->verify_overflow_empty();)
3969 }
3970
3971 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3972 HeapWord* read = _global_finger;
3973 HeapWord* cur = read;
3974 while (f > read) {
3975 cur = read;
3976 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3977 if (cur == read) {
3978 // our cas succeeded
3979 assert(_global_finger >= f, "protocol consistency");
3980 break;
3981 }
3982 }
3983 }
3984
3985 // This is really inefficient, and should be redone by
3986 // using (not yet available) block-read and -write interfaces to the
3987 // stack and the work_queue. XXX FIX ME !!!
3988 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3989 OopTaskQueue* work_q) {
3990 // Fast lock-free check
3991 if (ovflw_stk->length() == 0) {
3992 return false;
3993 }
3994 assert(work_q->size() == 0, "Shouldn't steal");
3995 MutexLockerEx ml(ovflw_stk->par_lock(),
3996 Mutex::_no_safepoint_check_flag);
3997 // Grab up to 1/4 the size of the work queue
3998 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3999 (size_t)ParGCDesiredObjsFromOverflowList);
4000 num = MIN2(num, ovflw_stk->length());
4001 for (int i = (int) num; i > 0; i--) {
4002 oop cur = ovflw_stk->pop();
4003 assert(cur != NULL, "Counted wrong?");
4004 work_q->push(cur);
4005 }
4006 return num > 0;
4007 }
4008
4009 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4010 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4011 int n_tasks = pst->n_tasks();
4012 // We allow that there may be no tasks to do here because
4013 // we are restarting after a stack overflow.
4014 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4015 uint nth_task = 0;
4016
4017 HeapWord* aligned_start = sp->bottom();
4018 if (sp->used_region().contains(_restart_addr)) {
4019 // Align down to a card boundary for the start of 0th task
4020 // for this space.
4021 aligned_start =
4022 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4023 CardTableModRefBS::card_size);
4024 }
4025
4026 size_t chunk_size = sp->marking_task_size();
4027 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4028 // Having claimed the nth task in this space,
4029 // compute the chunk that it corresponds to:
4030 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4031 aligned_start + (nth_task+1)*chunk_size);
4032 // Try and bump the global finger via a CAS;
4033 // note that we need to do the global finger bump
4034 // _before_ taking the intersection below, because
4035 // the task corresponding to that region will be
4036 // deemed done even if the used_region() expands
4037 // because of allocation -- as it almost certainly will
4038 // during start-up while the threads yield in the
4039 // closure below.
4040 HeapWord* finger = span.end();
4041 bump_global_finger(finger); // atomically
4042 // There are null tasks here corresponding to chunks
4043 // beyond the "top" address of the space.
4044 span = span.intersection(sp->used_region());
4045 if (!span.is_empty()) { // Non-null task
4046 HeapWord* prev_obj;
4047 assert(!span.contains(_restart_addr) || nth_task == 0,
4048 "Inconsistency");
4049 if (nth_task == 0) {
4050 // For the 0th task, we'll not need to compute a block_start.
4051 if (span.contains(_restart_addr)) {
4052 // In the case of a restart because of stack overflow,
4053 // we might additionally skip a chunk prefix.
4054 prev_obj = _restart_addr;
4055 } else {
4056 prev_obj = span.start();
4057 }
4058 } else {
4059 // We want to skip the first object because
4060 // the protocol is to scan any object in its entirety
4061 // that _starts_ in this span; a fortiori, any
4062 // object starting in an earlier span is scanned
4063 // as part of an earlier claimed task.
4064 // Below we use the "careful" version of block_start
4065 // so we do not try to navigate uninitialized objects.
4066 prev_obj = sp->block_start_careful(span.start());
4067 // Below we use a variant of block_size that uses the
4068 // Printezis bits to avoid waiting for allocated
4069 // objects to become initialized/parsable.
4070 while (prev_obj < span.start()) {
4071 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4072 if (sz > 0) {
4073 prev_obj += sz;
4074 } else {
4075 // In this case we may end up doing a bit of redundant
4076 // scanning, but that appears unavoidable, short of
4077 // locking the free list locks; see bug 6324141.
4078 break;
4079 }
4080 }
4081 }
4082 if (prev_obj < span.end()) {
4083 MemRegion my_span = MemRegion(prev_obj, span.end());
4084 // Do the marking work within a non-empty span --
4085 // the last argument to the constructor indicates whether the
4086 // iteration should be incremental with periodic yields.
4087 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4088 &_collector->_markBitMap,
4089 work_queue(i),
4090 &_collector->_markStack,
4091 &_collector->_revisitStack,
4092 _asynch);
4093 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4094 } // else nothing to do for this task
4095 } // else nothing to do for this task
4096 }
4097 // We'd be tempted to assert here that since there are no
4098 // more tasks left to claim in this space, the global_finger
4099 // must exceed space->top() and a fortiori space->end(). However,
4100 // that would not quite be correct because the bumping of
4101 // global_finger occurs strictly after the claiming of a task,
4102 // so by the time we reach here the global finger may not yet
4103 // have been bumped up by the thread that claimed the last
4104 // task.
4105 pst->all_tasks_completed();
4106 }
4107
4108 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4109 private:
4110 CMSConcMarkingTask* _task;
4111 MemRegion _span;
4112 CMSBitMap* _bit_map;
4113 CMSMarkStack* _overflow_stack;
4114 OopTaskQueue* _work_queue;
4115 protected:
4116 DO_OOP_WORK_DEFN
4117 public:
4118 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4119 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4120 CMSMarkStack* revisit_stack):
4121 Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4122 _task(task),
4123 _span(collector->_span),
4124 _work_queue(work_queue),
4125 _bit_map(bit_map),
4126 _overflow_stack(overflow_stack)
4127 { }
4128 virtual void do_oop(oop* p);
4129 virtual void do_oop(narrowOop* p);
4130 void trim_queue(size_t max);
4131 void handle_stack_overflow(HeapWord* lost);
4132 void do_yield_check() {
4133 if (_task->should_yield()) {
4134 _task->yield();
4135 }
4136 }
4137 };
4138
4139 // Grey object scanning during work stealing phase --
4140 // the salient assumption here is that any references
4141 // that are in these stolen objects being scanned must
4142 // already have been initialized (else they would not have
4143 // been published), so we do not need to check for
4144 // uninitialized objects before pushing here.
4145 void Par_ConcMarkingClosure::do_oop(oop obj) {
4146 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4147 HeapWord* addr = (HeapWord*)obj;
4148 // Check if oop points into the CMS generation
4149 // and is not marked
4150 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4151 // a white object ...
4152 // If we manage to "claim" the object, by being the
4153 // first thread to mark it, then we push it on our
4154 // marking stack
4155 if (_bit_map->par_mark(addr)) { // ... now grey
4156 // push on work queue (grey set)
4157 bool simulate_overflow = false;
4158 NOT_PRODUCT(
4159 if (CMSMarkStackOverflowALot &&
4160 _collector->simulate_overflow()) {
4161 // simulate a stack overflow
4162 simulate_overflow = true;
4163 }
4164 )
4165 if (simulate_overflow ||
4166 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4167 // stack overflow
4168 if (PrintCMSStatistics != 0) {
4169 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4170 SIZE_FORMAT, _overflow_stack->capacity());
4171 }
4172 // We cannot assert that the overflow stack is full because
4173 // it may have been emptied since.
4174 assert(simulate_overflow ||
4175 _work_queue->size() == _work_queue->max_elems(),
4176 "Else push should have succeeded");
4177 handle_stack_overflow(addr);
4178 }
4179 } // Else, some other thread got there first
4180 do_yield_check();
4181 }
4182 }
4183
4184 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4185 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4186
4187 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4188 while (_work_queue->size() > max) {
4189 oop new_oop;
4190 if (_work_queue->pop_local(new_oop)) {
4191 assert(new_oop->is_oop(), "Should be an oop");
4192 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4193 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4194 assert(new_oop->is_parsable(), "Should be parsable");
4195 new_oop->oop_iterate(this); // do_oop() above
4196 do_yield_check();
4197 }
4198 }
4199 }
4200
4201 // Upon stack overflow, we discard (part of) the stack,
4202 // remembering the least address amongst those discarded
4203 // in CMSCollector's _restart_address.
4204 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4205 // We need to do this under a mutex to prevent other
4206 // workers from interfering with the work done below.
4207 MutexLockerEx ml(_overflow_stack->par_lock(),
4208 Mutex::_no_safepoint_check_flag);
4209 // Remember the least grey address discarded
4210 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4211 _collector->lower_restart_addr(ra);
4212 _overflow_stack->reset(); // discard stack contents
4213 _overflow_stack->expand(); // expand the stack if possible
4214 }
4215
4216
4217 void CMSConcMarkingTask::do_work_steal(int i) {
4218 OopTaskQueue* work_q = work_queue(i);
4219 oop obj_to_scan;
4220 CMSBitMap* bm = &(_collector->_markBitMap);
4221 CMSMarkStack* ovflw = &(_collector->_markStack);
4222 CMSMarkStack* revisit = &(_collector->_revisitStack);
4223 int* seed = _collector->hash_seed(i);
4224 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4225 while (true) {
4226 cl.trim_queue(0);
4227 assert(work_q->size() == 0, "Should have been emptied above");
4228 if (get_work_from_overflow_stack(ovflw, work_q)) {
4229 // Can't assert below because the work obtained from the
4230 // overflow stack may already have been stolen from us.
4231 // assert(work_q->size() > 0, "Work from overflow stack");
4232 continue;
4233 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4234 assert(obj_to_scan->is_oop(), "Should be an oop");
4235 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4236 obj_to_scan->oop_iterate(&cl);
4237 } else if (terminator()->offer_termination(&_term_term)) {
4238 assert(work_q->size() == 0, "Impossible!");
4239 break;
4240 } else if (yielding() || should_yield()) {
4241 yield();
4242 }
4243 }
4244 }
4245
4246 // This is run by the CMS (coordinator) thread.
4247 void CMSConcMarkingTask::coordinator_yield() {
4248 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4249 "CMS thread should hold CMS token");
4250 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4251 // First give up the locks, then yield, then re-lock
4252 // We should probably use a constructor/destructor idiom to
4253 // do this unlock/lock or modify the MutexUnlocker class to
4254 // serve our purpose. XXX
4255 assert_lock_strong(_bit_map_lock);
4256 _bit_map_lock->unlock();
4257 ConcurrentMarkSweepThread::desynchronize(true);
4258 ConcurrentMarkSweepThread::acknowledge_yield_request();
4259 _collector->stopTimer();
4260 if (PrintCMSStatistics != 0) {
4261 _collector->incrementYields();
4262 }
4263 _collector->icms_wait();
4264
4265 // It is possible for whichever thread initiated the yield request
4266 // not to get a chance to wake up and take the bitmap lock between
4267 // this thread releasing it and reacquiring it. So, while the
4268 // should_yield() flag is on, let's sleep for a bit to give the
4269 // other thread a chance to wake up. The limit imposed on the number
4270 // of iterations is defensive, to avoid any unforseen circumstances
4271 // putting us into an infinite loop. Since it's always been this
4272 // (coordinator_yield()) method that was observed to cause the
4273 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4274 // which is by default non-zero. For the other seven methods that
4275 // also perform the yield operation, as are using a different
4276 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4277 // can enable the sleeping for those methods too, if necessary.
4278 // See 6442774.
4279 //
4280 // We really need to reconsider the synchronization between the GC
4281 // thread and the yield-requesting threads in the future and we
4282 // should really use wait/notify, which is the recommended
4283 // way of doing this type of interaction. Additionally, we should
4284 // consolidate the eight methods that do the yield operation and they
4285 // are almost identical into one for better maintenability and
4286 // readability. See 6445193.
4287 //
4288 // Tony 2006.06.29
4289 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4290 ConcurrentMarkSweepThread::should_yield() &&
4291 !CMSCollector::foregroundGCIsActive(); ++i) {
4292 os::sleep(Thread::current(), 1, false);
4293 ConcurrentMarkSweepThread::acknowledge_yield_request();
4294 }
4295
4296 ConcurrentMarkSweepThread::synchronize(true);
4297 _bit_map_lock->lock_without_safepoint_check();
4298 _collector->startTimer();
4299 }
4300
4301 bool CMSCollector::do_marking_mt(bool asynch) {
4302 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4303 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4304 conc_workers()->total_workers(),
4305 conc_workers()->active_workers(),
4306 Threads::number_of_non_daemon_threads());
4307 conc_workers()->set_active_workers(num_workers);
4308
4309 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4310 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4311
4312 CMSConcMarkingTask tsk(this,
4313 cms_space,
4314 perm_space,
4315 asynch,
4316 conc_workers(),
4317 task_queues());
4318
4319 // Since the actual number of workers we get may be different
4320 // from the number we requested above, do we need to do anything different
4321 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4322 // class?? XXX
4323 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4324 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4325
4326 // Refs discovery is already non-atomic.
4327 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4328 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4329 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4330 conc_workers()->start_task(&tsk);
4331 while (tsk.yielded()) {
4332 tsk.coordinator_yield();
4333 conc_workers()->continue_task(&tsk);
4334 }
4335 // If the task was aborted, _restart_addr will be non-NULL
4336 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4337 while (_restart_addr != NULL) {
4338 // XXX For now we do not make use of ABORTED state and have not
4339 // yet implemented the right abort semantics (even in the original
4340 // single-threaded CMS case). That needs some more investigation
4341 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4342 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4343 // If _restart_addr is non-NULL, a marking stack overflow
4344 // occurred; we need to do a fresh marking iteration from the
4345 // indicated restart address.
4346 if (_foregroundGCIsActive && asynch) {
4347 // We may be running into repeated stack overflows, having
4348 // reached the limit of the stack size, while making very
4349 // slow forward progress. It may be best to bail out and
4350 // let the foreground collector do its job.
4351 // Clear _restart_addr, so that foreground GC
4352 // works from scratch. This avoids the headache of
4353 // a "rescan" which would otherwise be needed because
4354 // of the dirty mod union table & card table.
4355 _restart_addr = NULL;
4356 return false;
4357 }
4358 // Adjust the task to restart from _restart_addr
4359 tsk.reset(_restart_addr);
4360 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4361 _restart_addr);
4362 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4363 _restart_addr);
4364 _restart_addr = NULL;
4365 // Get the workers going again
4366 conc_workers()->start_task(&tsk);
4367 while (tsk.yielded()) {
4368 tsk.coordinator_yield();
4369 conc_workers()->continue_task(&tsk);
4370 }
4371 }
4372 assert(tsk.completed(), "Inconsistency");
4373 assert(tsk.result() == true, "Inconsistency");
4374 return true;
4375 }
4376
4377 bool CMSCollector::do_marking_st(bool asynch) {
4378 ResourceMark rm;
4379 HandleMark hm;
4380
4381 // Temporarily make refs discovery single threaded (non-MT)
4382 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4383 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4384 &_markStack, &_revisitStack, CMSYield && asynch);
4385 // the last argument to iterate indicates whether the iteration
4386 // should be incremental with periodic yields.
4387 _markBitMap.iterate(&markFromRootsClosure);
4388 // If _restart_addr is non-NULL, a marking stack overflow
4389 // occurred; we need to do a fresh iteration from the
4390 // indicated restart address.
4391 while (_restart_addr != NULL) {
4392 if (_foregroundGCIsActive && asynch) {
4393 // We may be running into repeated stack overflows, having
4394 // reached the limit of the stack size, while making very
4395 // slow forward progress. It may be best to bail out and
4396 // let the foreground collector do its job.
4397 // Clear _restart_addr, so that foreground GC
4398 // works from scratch. This avoids the headache of
4399 // a "rescan" which would otherwise be needed because
4400 // of the dirty mod union table & card table.
4401 _restart_addr = NULL;
4402 return false; // indicating failure to complete marking
4403 }
4404 // Deal with stack overflow:
4405 // we restart marking from _restart_addr
4406 HeapWord* ra = _restart_addr;
4407 markFromRootsClosure.reset(ra);
4408 _restart_addr = NULL;
4409 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4410 }
4411 return true;
4412 }
4413
4414 void CMSCollector::preclean() {
4415 check_correct_thread_executing();
4416 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4417 verify_work_stacks_empty();
4418 verify_overflow_empty();
4419 _abort_preclean = false;
4420 if (CMSPrecleaningEnabled) {
4421 _eden_chunk_index = 0;
4422 size_t used = get_eden_used();
4423 size_t capacity = get_eden_capacity();
4424 // Don't start sampling unless we will get sufficiently
4425 // many samples.
4426 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4427 * CMSScheduleRemarkEdenPenetration)) {
4428 _start_sampling = true;
4429 } else {
4430 _start_sampling = false;
4431 }
4432 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4433 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4434 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4435 }
4436 CMSTokenSync x(true); // is cms thread
4437 if (CMSPrecleaningEnabled) {
4438 sample_eden();
4439 _collectorState = AbortablePreclean;
4440 } else {
4441 _collectorState = FinalMarking;
4442 }
4443 verify_work_stacks_empty();
4444 verify_overflow_empty();
4445 }
4446
4447 // Try and schedule the remark such that young gen
4448 // occupancy is CMSScheduleRemarkEdenPenetration %.
4449 void CMSCollector::abortable_preclean() {
4450 check_correct_thread_executing();
4451 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4452 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4453
4454 // If Eden's current occupancy is below this threshold,
4455 // immediately schedule the remark; else preclean
4456 // past the next scavenge in an effort to
4457 // schedule the pause as described avove. By choosing
4458 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4459 // we will never do an actual abortable preclean cycle.
4460 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4461 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4462 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4463 // We need more smarts in the abortable preclean
4464 // loop below to deal with cases where allocation
4465 // in young gen is very very slow, and our precleaning
4466 // is running a losing race against a horde of
4467 // mutators intent on flooding us with CMS updates
4468 // (dirty cards).
4469 // One, admittedly dumb, strategy is to give up
4470 // after a certain number of abortable precleaning loops
4471 // or after a certain maximum time. We want to make
4472 // this smarter in the next iteration.
4473 // XXX FIX ME!!! YSR
4474 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4475 while (!(should_abort_preclean() ||
4476 ConcurrentMarkSweepThread::should_terminate())) {
4477 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4478 cumworkdone += workdone;
4479 loops++;
4480 // Voluntarily terminate abortable preclean phase if we have
4481 // been at it for too long.
4482 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4483 loops >= CMSMaxAbortablePrecleanLoops) {
4484 if (PrintGCDetails) {
4485 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4486 }
4487 break;
4488 }
4489 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4490 if (PrintGCDetails) {
4491 gclog_or_tty->print(" CMS: abort preclean due to time ");
4492 }
4493 break;
4494 }
4495 // If we are doing little work each iteration, we should
4496 // take a short break.
4497 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4498 // Sleep for some time, waiting for work to accumulate
4499 stopTimer();
4500 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4501 startTimer();
4502 waited++;
4503 }
4504 }
4505 if (PrintCMSStatistics > 0) {
4506 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4507 loops, waited, cumworkdone);
4508 }
4509 }
4510 CMSTokenSync x(true); // is cms thread
4511 if (_collectorState != Idling) {
4512 assert(_collectorState == AbortablePreclean,
4513 "Spontaneous state transition?");
4514 _collectorState = FinalMarking;
4515 } // Else, a foreground collection completed this CMS cycle.
4516 return;
4517 }
4518
4519 // Respond to an Eden sampling opportunity
4520 void CMSCollector::sample_eden() {
4521 // Make sure a young gc cannot sneak in between our
4522 // reading and recording of a sample.
4523 assert(Thread::current()->is_ConcurrentGC_thread(),
4524 "Only the cms thread may collect Eden samples");
4525 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4526 "Should collect samples while holding CMS token");
4527 if (!_start_sampling) {
4528 return;
4529 }
4530 if (_eden_chunk_array) {
4531 if (_eden_chunk_index < _eden_chunk_capacity) {
4532 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4533 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4534 "Unexpected state of Eden");
4535 // We'd like to check that what we just sampled is an oop-start address;
4536 // however, we cannot do that here since the object may not yet have been
4537 // initialized. So we'll instead do the check when we _use_ this sample
4538 // later.
4539 if (_eden_chunk_index == 0 ||
4540 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4541 _eden_chunk_array[_eden_chunk_index-1])
4542 >= CMSSamplingGrain)) {
4543 _eden_chunk_index++; // commit sample
4544 }
4545 }
4546 }
4547 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4548 size_t used = get_eden_used();
4549 size_t capacity = get_eden_capacity();
4550 assert(used <= capacity, "Unexpected state of Eden");
4551 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4552 _abort_preclean = true;
4553 }
4554 }
4555 }
4556
4557
4558 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4559 assert(_collectorState == Precleaning ||
4560 _collectorState == AbortablePreclean, "incorrect state");
4561 ResourceMark rm;
4562 HandleMark hm;
4563
4564 // Precleaning is currently not MT but the reference processor
4565 // may be set for MT. Disable it temporarily here.
4566 ReferenceProcessor* rp = ref_processor();
4567 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4568
4569 // Do one pass of scrubbing the discovered reference lists
4570 // to remove any reference objects with strongly-reachable
4571 // referents.
4572 if (clean_refs) {
4573 CMSPrecleanRefsYieldClosure yield_cl(this);
4574 assert(rp->span().equals(_span), "Spans should be equal");
4575 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4576 &_markStack, &_revisitStack,
4577 true /* preclean */);
4578 CMSDrainMarkingStackClosure complete_trace(this,
4579 _span, &_markBitMap, &_markStack,
4580 &keep_alive, true /* preclean */);
4581
4582 // We don't want this step to interfere with a young
4583 // collection because we don't want to take CPU
4584 // or memory bandwidth away from the young GC threads
4585 // (which may be as many as there are CPUs).
4586 // Note that we don't need to protect ourselves from
4587 // interference with mutators because they can't
4588 // manipulate the discovered reference lists nor affect
4589 // the computed reachability of the referents, the
4590 // only properties manipulated by the precleaning
4591 // of these reference lists.
4592 stopTimer();
4593 CMSTokenSyncWithLocks x(true /* is cms thread */,
4594 bitMapLock());
4595 startTimer();
4596 sample_eden();
4597
4598 // The following will yield to allow foreground
4599 // collection to proceed promptly. XXX YSR:
4600 // The code in this method may need further
4601 // tweaking for better performance and some restructuring
4602 // for cleaner interfaces.
4603 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4604 rp->preclean_discovered_references(
4605 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4606 &yield_cl, should_unload_classes(), gc_timer);
4607 }
4608
4609 if (clean_survivor) { // preclean the active survivor space(s)
4610 assert(_young_gen->kind() == Generation::DefNew ||
4611 _young_gen->kind() == Generation::ParNew ||
4612 _young_gen->kind() == Generation::ASParNew,
4613 "incorrect type for cast");
4614 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4615 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4616 &_markBitMap, &_modUnionTable,
4617 &_markStack, &_revisitStack,
4618 true /* precleaning phase */);
4619 stopTimer();
4620 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4621 bitMapLock());
4622 startTimer();
4623 unsigned int before_count =
4624 GenCollectedHeap::heap()->total_collections();
4625 SurvivorSpacePrecleanClosure
4626 sss_cl(this, _span, &_markBitMap, &_markStack,
4627 &pam_cl, before_count, CMSYield);
4628 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4629 dng->from()->object_iterate_careful(&sss_cl);
4630 dng->to()->object_iterate_careful(&sss_cl);
4631 }
4632 MarkRefsIntoAndScanClosure
4633 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4634 &_markStack, &_revisitStack, this, CMSYield,
4635 true /* precleaning phase */);
4636 // CAUTION: The following closure has persistent state that may need to
4637 // be reset upon a decrease in the sequence of addresses it
4638 // processes.
4639 ScanMarkedObjectsAgainCarefullyClosure
4640 smoac_cl(this, _span,
4641 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4642
4643 // Preclean dirty cards in ModUnionTable and CardTable using
4644 // appropriate convergence criterion;
4645 // repeat CMSPrecleanIter times unless we find that
4646 // we are losing.
4647 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4648 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4649 "Bad convergence multiplier");
4650 assert(CMSPrecleanThreshold >= 100,
4651 "Unreasonably low CMSPrecleanThreshold");
4652
4653 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4654 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4655 numIter < CMSPrecleanIter;
4656 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4657 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4658 if (CMSPermGenPrecleaningEnabled) {
4659 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4660 }
4661 if (Verbose && PrintGCDetails) {
4662 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4663 }
4664 // Either there are very few dirty cards, so re-mark
4665 // pause will be small anyway, or our pre-cleaning isn't
4666 // that much faster than the rate at which cards are being
4667 // dirtied, so we might as well stop and re-mark since
4668 // precleaning won't improve our re-mark time by much.
4669 if (curNumCards <= CMSPrecleanThreshold ||
4670 (numIter > 0 &&
4671 (curNumCards * CMSPrecleanDenominator >
4672 lastNumCards * CMSPrecleanNumerator))) {
4673 numIter++;
4674 cumNumCards += curNumCards;
4675 break;
4676 }
4677 }
4678 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4679 if (CMSPermGenPrecleaningEnabled) {
4680 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4681 }
4682 cumNumCards += curNumCards;
4683 if (PrintGCDetails && PrintCMSStatistics != 0) {
4684 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4685 curNumCards, cumNumCards, numIter);
4686 }
4687 return cumNumCards; // as a measure of useful work done
4688 }
4689
4690 // PRECLEANING NOTES:
4691 // Precleaning involves:
4692 // . reading the bits of the modUnionTable and clearing the set bits.
4693 // . For the cards corresponding to the set bits, we scan the
4694 // objects on those cards. This means we need the free_list_lock
4695 // so that we can safely iterate over the CMS space when scanning
4696 // for oops.
4697 // . When we scan the objects, we'll be both reading and setting
4698 // marks in the marking bit map, so we'll need the marking bit map.
4699 // . For protecting _collector_state transitions, we take the CGC_lock.
4700 // Note that any races in the reading of of card table entries by the
4701 // CMS thread on the one hand and the clearing of those entries by the
4702 // VM thread or the setting of those entries by the mutator threads on the
4703 // other are quite benign. However, for efficiency it makes sense to keep
4704 // the VM thread from racing with the CMS thread while the latter is
4705 // dirty card info to the modUnionTable. We therefore also use the
4706 // CGC_lock to protect the reading of the card table and the mod union
4707 // table by the CM thread.
4708 // . We run concurrently with mutator updates, so scanning
4709 // needs to be done carefully -- we should not try to scan
4710 // potentially uninitialized objects.
4711 //
4712 // Locking strategy: While holding the CGC_lock, we scan over and
4713 // reset a maximal dirty range of the mod union / card tables, then lock
4714 // the free_list_lock and bitmap lock to do a full marking, then
4715 // release these locks; and repeat the cycle. This allows for a
4716 // certain amount of fairness in the sharing of these locks between
4717 // the CMS collector on the one hand, and the VM thread and the
4718 // mutators on the other.
4719
4720 // NOTE: preclean_mod_union_table() and preclean_card_table()
4721 // further below are largely identical; if you need to modify
4722 // one of these methods, please check the other method too.
4723
4724 size_t CMSCollector::preclean_mod_union_table(
4725 ConcurrentMarkSweepGeneration* gen,
4726 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4727 verify_work_stacks_empty();
4728 verify_overflow_empty();
4729
4730 // Turn off checking for this method but turn it back on
4731 // selectively. There are yield points in this method
4732 // but it is difficult to turn the checking off just around
4733 // the yield points. It is simpler to selectively turn
4734 // it on.
4735 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4736
4737 // strategy: starting with the first card, accumulate contiguous
4738 // ranges of dirty cards; clear these cards, then scan the region
4739 // covered by these cards.
4740
4741 // Since all of the MUT is committed ahead, we can just use
4742 // that, in case the generations expand while we are precleaning.
4743 // It might also be fine to just use the committed part of the
4744 // generation, but we might potentially miss cards when the
4745 // generation is rapidly expanding while we are in the midst
4746 // of precleaning.
4747 HeapWord* startAddr = gen->reserved().start();
4748 HeapWord* endAddr = gen->reserved().end();
4749
4750 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4751
4752 size_t numDirtyCards, cumNumDirtyCards;
4753 HeapWord *nextAddr, *lastAddr;
4754 for (cumNumDirtyCards = numDirtyCards = 0,
4755 nextAddr = lastAddr = startAddr;
4756 nextAddr < endAddr;
4757 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4758
4759 ResourceMark rm;
4760 HandleMark hm;
4761
4762 MemRegion dirtyRegion;
4763 {
4764 stopTimer();
4765 // Potential yield point
4766 CMSTokenSync ts(true);
4767 startTimer();
4768 sample_eden();
4769 // Get dirty region starting at nextOffset (inclusive),
4770 // simultaneously clearing it.
4771 dirtyRegion =
4772 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4773 assert(dirtyRegion.start() >= nextAddr,
4774 "returned region inconsistent?");
4775 }
4776 // Remember where the next search should begin.
4777 // The returned region (if non-empty) is a right open interval,
4778 // so lastOffset is obtained from the right end of that
4779 // interval.
4780 lastAddr = dirtyRegion.end();
4781 // Should do something more transparent and less hacky XXX
4782 numDirtyCards =
4783 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4784
4785 // We'll scan the cards in the dirty region (with periodic
4786 // yields for foreground GC as needed).
4787 if (!dirtyRegion.is_empty()) {
4788 assert(numDirtyCards > 0, "consistency check");
4789 HeapWord* stop_point = NULL;
4790 stopTimer();
4791 // Potential yield point
4792 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4793 bitMapLock());
4794 startTimer();
4795 {
4796 verify_work_stacks_empty();
4797 verify_overflow_empty();
4798 sample_eden();
4799 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4800 stop_point =
4801 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4802 }
4803 if (stop_point != NULL) {
4804 // The careful iteration stopped early either because it found an
4805 // uninitialized object, or because we were in the midst of an
4806 // "abortable preclean", which should now be aborted. Redirty
4807 // the bits corresponding to the partially-scanned or unscanned
4808 // cards. We'll either restart at the next block boundary or
4809 // abort the preclean.
4810 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4811 (_collectorState == AbortablePreclean && should_abort_preclean()),
4812 "Unparsable objects should only be in perm gen.");
4813 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4814 if (should_abort_preclean()) {
4815 break; // out of preclean loop
4816 } else {
4817 // Compute the next address at which preclean should pick up;
4818 // might need bitMapLock in order to read P-bits.
4819 lastAddr = next_card_start_after_block(stop_point);
4820 }
4821 }
4822 } else {
4823 assert(lastAddr == endAddr, "consistency check");
4824 assert(numDirtyCards == 0, "consistency check");
4825 break;
4826 }
4827 }
4828 verify_work_stacks_empty();
4829 verify_overflow_empty();
4830 return cumNumDirtyCards;
4831 }
4832
4833 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4834 // below are largely identical; if you need to modify
4835 // one of these methods, please check the other method too.
4836
4837 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4838 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4839 // strategy: it's similar to precleamModUnionTable above, in that
4840 // we accumulate contiguous ranges of dirty cards, mark these cards
4841 // precleaned, then scan the region covered by these cards.
4842 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4843 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4844
4845 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4846
4847 size_t numDirtyCards, cumNumDirtyCards;
4848 HeapWord *lastAddr, *nextAddr;
4849
4850 for (cumNumDirtyCards = numDirtyCards = 0,
4851 nextAddr = lastAddr = startAddr;
4852 nextAddr < endAddr;
4853 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4854
4855 ResourceMark rm;
4856 HandleMark hm;
4857
4858 MemRegion dirtyRegion;
4859 {
4860 // See comments in "Precleaning notes" above on why we
4861 // do this locking. XXX Could the locking overheads be
4862 // too high when dirty cards are sparse? [I don't think so.]
4863 stopTimer();
4864 CMSTokenSync x(true); // is cms thread
4865 startTimer();
4866 sample_eden();
4867 // Get and clear dirty region from card table
4868 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4869 MemRegion(nextAddr, endAddr),
4870 true,
4871 CardTableModRefBS::precleaned_card_val());
4872
4873 assert(dirtyRegion.start() >= nextAddr,
4874 "returned region inconsistent?");
4875 }
4876 lastAddr = dirtyRegion.end();
4877 numDirtyCards =
4878 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4879
4880 if (!dirtyRegion.is_empty()) {
4881 stopTimer();
4882 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4883 startTimer();
4884 sample_eden();
4885 verify_work_stacks_empty();
4886 verify_overflow_empty();
4887 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4888 HeapWord* stop_point =
4889 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4890 if (stop_point != NULL) {
4891 // The careful iteration stopped early because it found an
4892 // uninitialized object. Redirty the bits corresponding to the
4893 // partially-scanned or unscanned cards, and start again at the
4894 // next block boundary.
4895 assert(CMSPermGenPrecleaningEnabled ||
4896 (_collectorState == AbortablePreclean && should_abort_preclean()),
4897 "Unparsable objects should only be in perm gen.");
4898 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4899 if (should_abort_preclean()) {
4900 break; // out of preclean loop
4901 } else {
4902 // Compute the next address at which preclean should pick up.
4903 lastAddr = next_card_start_after_block(stop_point);
4904 }
4905 }
4906 } else {
4907 break;
4908 }
4909 }
4910 verify_work_stacks_empty();
4911 verify_overflow_empty();
4912 return cumNumDirtyCards;
4913 }
4914
4915 void CMSCollector::checkpointRootsFinal(bool asynch,
4916 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4917 assert(_collectorState == FinalMarking, "incorrect state transition?");
4918 check_correct_thread_executing();
4919 // world is stopped at this checkpoint
4920 assert(SafepointSynchronize::is_at_safepoint(),
4921 "world should be stopped");
4922 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4923
4924 verify_work_stacks_empty();
4925 verify_overflow_empty();
4926
4927 SpecializationStats::clear();
4928 if (PrintGCDetails) {
4929 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4930 _young_gen->used() / K,
4931 _young_gen->capacity() / K);
4932 }
4933 if (asynch) {
4934 if (CMSScavengeBeforeRemark) {
4935 GenCollectedHeap* gch = GenCollectedHeap::heap();
4936 // Temporarily set flag to false, GCH->do_collection will
4937 // expect it to be false and set to true
4938 FlagSetting fl(gch->_is_gc_active, false);
4939 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4940 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4941 int level = _cmsGen->level() - 1;
4942 if (level >= 0) {
4943 gch->do_collection(true, // full (i.e. force, see below)
4944 false, // !clear_all_soft_refs
4945 0, // size
4946 false, // is_tlab
4947 level // max_level
4948 );
4949 }
4950 }
4951 FreelistLocker x(this);
4952 MutexLockerEx y(bitMapLock(),
4953 Mutex::_no_safepoint_check_flag);
4954 assert(!init_mark_was_synchronous, "but that's impossible!");
4955 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4956 } else {
4957 // already have all the locks
4958 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4959 init_mark_was_synchronous);
4960 }
4961 verify_work_stacks_empty();
4962 verify_overflow_empty();
4963 SpecializationStats::print();
4964 }
4965
4966 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4967 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4968
4969 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4970
4971 assert(haveFreelistLocks(), "must have free list locks");
4972 assert_lock_strong(bitMapLock());
4973
4974 if (UseAdaptiveSizePolicy) {
4975 size_policy()->checkpoint_roots_final_begin();
4976 }
4977
4978 ResourceMark rm;
4979 HandleMark hm;
4980
4981 GenCollectedHeap* gch = GenCollectedHeap::heap();
4982
4983 if (should_unload_classes()) {
4984 CodeCache::gc_prologue();
4985 }
4986 assert(haveFreelistLocks(), "must have free list locks");
4987 assert_lock_strong(bitMapLock());
4988
4989 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4990 if (!init_mark_was_synchronous) {
4991 // We might assume that we need not fill TLAB's when
4992 // CMSScavengeBeforeRemark is set, because we may have just done
4993 // a scavenge which would have filled all TLAB's -- and besides
4994 // Eden would be empty. This however may not always be the case --
4995 // for instance although we asked for a scavenge, it may not have
4996 // happened because of a JNI critical section. We probably need
4997 // a policy for deciding whether we can in that case wait until
4998 // the critical section releases and then do the remark following
4999 // the scavenge, and skip it here. In the absence of that policy,
5000 // or of an indication of whether the scavenge did indeed occur,
5001 // we cannot rely on TLAB's having been filled and must do
5002 // so here just in case a scavenge did not happen.
5003 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5004 // Update the saved marks which may affect the root scans.
5005 gch->save_marks();
5006
5007 {
5008 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5009
5010 // Note on the role of the mod union table:
5011 // Since the marker in "markFromRoots" marks concurrently with
5012 // mutators, it is possible for some reachable objects not to have been
5013 // scanned. For instance, an only reference to an object A was
5014 // placed in object B after the marker scanned B. Unless B is rescanned,
5015 // A would be collected. Such updates to references in marked objects
5016 // are detected via the mod union table which is the set of all cards
5017 // dirtied since the first checkpoint in this GC cycle and prior to
5018 // the most recent young generation GC, minus those cleaned up by the
5019 // concurrent precleaning.
5020 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5021 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5022 do_remark_parallel();
5023 } else {
5024 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5025 _gc_timer_cm);
5026 do_remark_non_parallel();
5027 }
5028 }
5029 } else {
5030 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5031 // The initial mark was stop-world, so there's no rescanning to
5032 // do; go straight on to the next step below.
5033 }
5034 verify_work_stacks_empty();
5035 verify_overflow_empty();
5036
5037 {
5038 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5039 refProcessingWork(asynch, clear_all_soft_refs);
5040 }
5041 verify_work_stacks_empty();
5042 verify_overflow_empty();
5043
5044 if (should_unload_classes()) {
5045 CodeCache::gc_epilogue();
5046 }
5047 JvmtiExport::gc_epilogue();
5048
5049 // If we encountered any (marking stack / work queue) overflow
5050 // events during the current CMS cycle, take appropriate
5051 // remedial measures, where possible, so as to try and avoid
5052 // recurrence of that condition.
5053 assert(_markStack.isEmpty(), "No grey objects");
5054 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5055 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5056 if (ser_ovflw > 0) {
5057 if (PrintCMSStatistics != 0) {
5058 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5059 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5060 ", kac_preclean="SIZE_FORMAT")",
5061 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5062 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5063 }
5064 _markStack.expand();
5065 _ser_pmc_remark_ovflw = 0;
5066 _ser_pmc_preclean_ovflw = 0;
5067 _ser_kac_preclean_ovflw = 0;
5068 _ser_kac_ovflw = 0;
5069 }
5070 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5071 if (PrintCMSStatistics != 0) {
5072 gclog_or_tty->print_cr("Work queue overflow (benign) "
5073 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5074 _par_pmc_remark_ovflw, _par_kac_ovflw);
5075 }
5076 _par_pmc_remark_ovflw = 0;
5077 _par_kac_ovflw = 0;
5078 }
5079 if (PrintCMSStatistics != 0) {
5080 if (_markStack._hit_limit > 0) {
5081 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5082 _markStack._hit_limit);
5083 }
5084 if (_markStack._failed_double > 0) {
5085 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5086 " current capacity "SIZE_FORMAT,
5087 _markStack._failed_double,
5088 _markStack.capacity());
5089 }
5090 }
5091 _markStack._hit_limit = 0;
5092 _markStack._failed_double = 0;
5093
5094 // Check that all the klasses have been checked
5095 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5096
5097 if ((VerifyAfterGC || VerifyDuringGC) &&
5098 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5099 verify_after_remark();
5100 }
5101
5102 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5103
5104 // Change under the freelistLocks.
5105 _collectorState = Sweeping;
5106 // Call isAllClear() under bitMapLock
5107 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5108 " final marking");
5109 if (UseAdaptiveSizePolicy) {
5110 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5111 }
5112 }
5113
5114 // Parallel remark task
5115 class CMSParRemarkTask: public AbstractGangTask {
5116 CMSCollector* _collector;
5117 int _n_workers;
5118 CompactibleFreeListSpace* _cms_space;
5119 CompactibleFreeListSpace* _perm_space;
5120
5121 // The per-thread work queues, available here for stealing.
5122 OopTaskQueueSet* _task_queues;
5123 ParallelTaskTerminator _term;
5124
5125 public:
5126 // A value of 0 passed to n_workers will cause the number of
5127 // workers to be taken from the active workers in the work gang.
5128 CMSParRemarkTask(CMSCollector* collector,
5129 CompactibleFreeListSpace* cms_space,
5130 CompactibleFreeListSpace* perm_space,
5131 int n_workers, FlexibleWorkGang* workers,
5132 OopTaskQueueSet* task_queues):
5133 AbstractGangTask("Rescan roots and grey objects in parallel"),
5134 _collector(collector),
5135 _cms_space(cms_space), _perm_space(perm_space),
5136 _n_workers(n_workers),
5137 _task_queues(task_queues),
5138 _term(n_workers, task_queues) { }
5139
5140 OopTaskQueueSet* task_queues() { return _task_queues; }
5141
5142 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5143
5144 ParallelTaskTerminator* terminator() { return &_term; }
5145 int n_workers() { return _n_workers; }
5146
5147 void work(uint worker_id);
5148
5149 private:
5150 // Work method in support of parallel rescan ... of young gen spaces
5151 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5152 ContiguousSpace* space,
5153 HeapWord** chunk_array, size_t chunk_top);
5154
5155 // ... of dirty cards in old space
5156 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5157 Par_MarkRefsIntoAndScanClosure* cl);
5158
5159 // ... work stealing for the above
5160 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5161 };
5162
5163 // work_queue(i) is passed to the closure
5164 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5165 // also is passed to do_dirty_card_rescan_tasks() and to
5166 // do_work_steal() to select the i-th task_queue.
5167
5168 void CMSParRemarkTask::work(uint worker_id) {
5169 elapsedTimer _timer;
5170 ResourceMark rm;
5171 HandleMark hm;
5172
5173 // ---------- rescan from roots --------------
5174 _timer.start();
5175 GenCollectedHeap* gch = GenCollectedHeap::heap();
5176 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5177 _collector->_span, _collector->ref_processor(),
5178 &(_collector->_markBitMap),
5179 work_queue(worker_id), &(_collector->_revisitStack));
5180
5181 // Rescan young gen roots first since these are likely
5182 // coarsely partitioned and may, on that account, constitute
5183 // the critical path; thus, it's best to start off that
5184 // work first.
5185 // ---------- young gen roots --------------
5186 {
5187 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5188 EdenSpace* eden_space = dng->eden();
5189 ContiguousSpace* from_space = dng->from();
5190 ContiguousSpace* to_space = dng->to();
5191
5192 HeapWord** eca = _collector->_eden_chunk_array;
5193 size_t ect = _collector->_eden_chunk_index;
5194 HeapWord** sca = _collector->_survivor_chunk_array;
5195 size_t sct = _collector->_survivor_chunk_index;
5196
5197 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5198 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5199
5200 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5201 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5202 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5203
5204 _timer.stop();
5205 if (PrintCMSStatistics != 0) {
5206 gclog_or_tty->print_cr(
5207 "Finished young gen rescan work in %dth thread: %3.3f sec",
5208 worker_id, _timer.seconds());
5209 }
5210 }
5211
5212 // ---------- remaining roots --------------
5213 _timer.reset();
5214 _timer.start();
5215 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5216 false, // yg was scanned above
5217 false, // this is parallel code
5218 true, // collecting perm gen
5219 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5220 &par_mrias_cl,
5221 true, // walk all of code cache if (so & SO_CodeCache)
5222 NULL);
5223 assert(_collector->should_unload_classes()
5224 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5225 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5226 _timer.stop();
5227 if (PrintCMSStatistics != 0) {
5228 gclog_or_tty->print_cr(
5229 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5230 worker_id, _timer.seconds());
5231 }
5232
5233 // ---------- rescan dirty cards ------------
5234 _timer.reset();
5235 _timer.start();
5236
5237 // Do the rescan tasks for each of the two spaces
5238 // (cms_space and perm_space) in turn.
5239 // "worker_id" is passed to select the task_queue for "worker_id"
5240 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5241 do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5242 _timer.stop();
5243 if (PrintCMSStatistics != 0) {
5244 gclog_or_tty->print_cr(
5245 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5246 worker_id, _timer.seconds());
5247 }
5248
5249 // ---------- steal work from other threads ...
5250 // ---------- ... and drain overflow list.
5251 _timer.reset();
5252 _timer.start();
5253 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5254 _timer.stop();
5255 if (PrintCMSStatistics != 0) {
5256 gclog_or_tty->print_cr(
5257 "Finished work stealing in %dth thread: %3.3f sec",
5258 worker_id, _timer.seconds());
5259 }
5260 }
5261
5262 // Note that parameter "i" is not used.
5263 void
5264 CMSParRemarkTask::do_young_space_rescan(int i,
5265 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5266 HeapWord** chunk_array, size_t chunk_top) {
5267 // Until all tasks completed:
5268 // . claim an unclaimed task
5269 // . compute region boundaries corresponding to task claimed
5270 // using chunk_array
5271 // . par_oop_iterate(cl) over that region
5272
5273 ResourceMark rm;
5274 HandleMark hm;
5275
5276 SequentialSubTasksDone* pst = space->par_seq_tasks();
5277 assert(pst->valid(), "Uninitialized use?");
5278
5279 uint nth_task = 0;
5280 uint n_tasks = pst->n_tasks();
5281
5282 HeapWord *start, *end;
5283 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5284 // We claimed task # nth_task; compute its boundaries.
5285 if (chunk_top == 0) { // no samples were taken
5286 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5287 start = space->bottom();
5288 end = space->top();
5289 } else if (nth_task == 0) {
5290 start = space->bottom();
5291 end = chunk_array[nth_task];
5292 } else if (nth_task < (uint)chunk_top) {
5293 assert(nth_task >= 1, "Control point invariant");
5294 start = chunk_array[nth_task - 1];
5295 end = chunk_array[nth_task];
5296 } else {
5297 assert(nth_task == (uint)chunk_top, "Control point invariant");
5298 start = chunk_array[chunk_top - 1];
5299 end = space->top();
5300 }
5301 MemRegion mr(start, end);
5302 // Verify that mr is in space
5303 assert(mr.is_empty() || space->used_region().contains(mr),
5304 "Should be in space");
5305 // Verify that "start" is an object boundary
5306 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5307 "Should be an oop");
5308 space->par_oop_iterate(mr, cl);
5309 }
5310 pst->all_tasks_completed();
5311 }
5312
5313 void
5314 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5315 CompactibleFreeListSpace* sp, int i,
5316 Par_MarkRefsIntoAndScanClosure* cl) {
5317 // Until all tasks completed:
5318 // . claim an unclaimed task
5319 // . compute region boundaries corresponding to task claimed
5320 // . transfer dirty bits ct->mut for that region
5321 // . apply rescanclosure to dirty mut bits for that region
5322
5323 ResourceMark rm;
5324 HandleMark hm;
5325
5326 OopTaskQueue* work_q = work_queue(i);
5327 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5328 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5329 // CAUTION: This closure has state that persists across calls to
5330 // the work method dirty_range_iterate_clear() in that it has
5331 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5332 // use of that state in the imbedded UpwardsObjectClosure instance
5333 // assumes that the cards are always iterated (even if in parallel
5334 // by several threads) in monotonically increasing order per each
5335 // thread. This is true of the implementation below which picks
5336 // card ranges (chunks) in monotonically increasing order globally
5337 // and, a-fortiori, in monotonically increasing order per thread
5338 // (the latter order being a subsequence of the former).
5339 // If the work code below is ever reorganized into a more chaotic
5340 // work-partitioning form than the current "sequential tasks"
5341 // paradigm, the use of that persistent state will have to be
5342 // revisited and modified appropriately. See also related
5343 // bug 4756801 work on which should examine this code to make
5344 // sure that the changes there do not run counter to the
5345 // assumptions made here and necessary for correctness and
5346 // efficiency. Note also that this code might yield inefficient
5347 // behaviour in the case of very large objects that span one or
5348 // more work chunks. Such objects would potentially be scanned
5349 // several times redundantly. Work on 4756801 should try and
5350 // address that performance anomaly if at all possible. XXX
5351 MemRegion full_span = _collector->_span;
5352 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5353 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5354 MarkFromDirtyCardsClosure
5355 greyRescanClosure(_collector, full_span, // entire span of interest
5356 sp, bm, work_q, rs, cl);
5357
5358 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5359 assert(pst->valid(), "Uninitialized use?");
5360 uint nth_task = 0;
5361 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5362 MemRegion span = sp->used_region();
5363 HeapWord* start_addr = span.start();
5364 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5365 alignment);
5366 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5367 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5368 start_addr, "Check alignment");
5369 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5370 chunk_size, "Check alignment");
5371
5372 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5373 // Having claimed the nth_task, compute corresponding mem-region,
5374 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5375 // The alignment restriction ensures that we do not need any
5376 // synchronization with other gang-workers while setting or
5377 // clearing bits in thus chunk of the MUT.
5378 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5379 start_addr + (nth_task+1)*chunk_size);
5380 // The last chunk's end might be way beyond end of the
5381 // used region. In that case pull back appropriately.
5382 if (this_span.end() > end_addr) {
5383 this_span.set_end(end_addr);
5384 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5385 }
5386 // Iterate over the dirty cards covering this chunk, marking them
5387 // precleaned, and setting the corresponding bits in the mod union
5388 // table. Since we have been careful to partition at Card and MUT-word
5389 // boundaries no synchronization is needed between parallel threads.
5390 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5391 &modUnionClosure);
5392
5393 // Having transferred these marks into the modUnionTable,
5394 // rescan the marked objects on the dirty cards in the modUnionTable.
5395 // Even if this is at a synchronous collection, the initial marking
5396 // may have been done during an asynchronous collection so there
5397 // may be dirty bits in the mod-union table.
5398 _collector->_modUnionTable.dirty_range_iterate_clear(
5399 this_span, &greyRescanClosure);
5400 _collector->_modUnionTable.verifyNoOneBitsInRange(
5401 this_span.start(),
5402 this_span.end());
5403 }
5404 pst->all_tasks_completed(); // declare that i am done
5405 }
5406
5407 // . see if we can share work_queues with ParNew? XXX
5408 void
5409 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5410 int* seed) {
5411 OopTaskQueue* work_q = work_queue(i);
5412 NOT_PRODUCT(int num_steals = 0;)
5413 oop obj_to_scan;
5414 CMSBitMap* bm = &(_collector->_markBitMap);
5415
5416 while (true) {
5417 // Completely finish any left over work from (an) earlier round(s)
5418 cl->trim_queue(0);
5419 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5420 (size_t)ParGCDesiredObjsFromOverflowList);
5421 // Now check if there's any work in the overflow list
5422 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5423 // only affects the number of attempts made to get work from the
5424 // overflow list and does not affect the number of workers. Just
5425 // pass ParallelGCThreads so this behavior is unchanged.
5426 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5427 work_q,
5428 ParallelGCThreads)) {
5429 // found something in global overflow list;
5430 // not yet ready to go stealing work from others.
5431 // We'd like to assert(work_q->size() != 0, ...)
5432 // because we just took work from the overflow list,
5433 // but of course we can't since all of that could have
5434 // been already stolen from us.
5435 // "He giveth and He taketh away."
5436 continue;
5437 }
5438 // Verify that we have no work before we resort to stealing
5439 assert(work_q->size() == 0, "Have work, shouldn't steal");
5440 // Try to steal from other queues that have work
5441 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5442 NOT_PRODUCT(num_steals++;)
5443 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5444 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5445 // Do scanning work
5446 obj_to_scan->oop_iterate(cl);
5447 // Loop around, finish this work, and try to steal some more
5448 } else if (terminator()->offer_termination()) {
5449 break; // nirvana from the infinite cycle
5450 }
5451 }
5452 NOT_PRODUCT(
5453 if (PrintCMSStatistics != 0) {
5454 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5455 }
5456 )
5457 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5458 "Else our work is not yet done");
5459 }
5460
5461 // Return a thread-local PLAB recording array, as appropriate.
5462 void* CMSCollector::get_data_recorder(int thr_num) {
5463 if (_survivor_plab_array != NULL &&
5464 (CMSPLABRecordAlways ||
5465 (_collectorState > Marking && _collectorState < FinalMarking))) {
5466 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5467 ChunkArray* ca = &_survivor_plab_array[thr_num];
5468 ca->reset(); // clear it so that fresh data is recorded
5469 return (void*) ca;
5470 } else {
5471 return NULL;
5472 }
5473 }
5474
5475 // Reset all the thread-local PLAB recording arrays
5476 void CMSCollector::reset_survivor_plab_arrays() {
5477 for (uint i = 0; i < ParallelGCThreads; i++) {
5478 _survivor_plab_array[i].reset();
5479 }
5480 }
5481
5482 // Merge the per-thread plab arrays into the global survivor chunk
5483 // array which will provide the partitioning of the survivor space
5484 // for CMS rescan.
5485 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5486 int no_of_gc_threads) {
5487 assert(_survivor_plab_array != NULL, "Error");
5488 assert(_survivor_chunk_array != NULL, "Error");
5489 assert(_collectorState == FinalMarking, "Error");
5490 for (int j = 0; j < no_of_gc_threads; j++) {
5491 _cursor[j] = 0;
5492 }
5493 HeapWord* top = surv->top();
5494 size_t i;
5495 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5496 HeapWord* min_val = top; // Higher than any PLAB address
5497 uint min_tid = 0; // position of min_val this round
5498 for (int j = 0; j < no_of_gc_threads; j++) {
5499 ChunkArray* cur_sca = &_survivor_plab_array[j];
5500 if (_cursor[j] == cur_sca->end()) {
5501 continue;
5502 }
5503 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5504 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5505 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5506 if (cur_val < min_val) {
5507 min_tid = j;
5508 min_val = cur_val;
5509 } else {
5510 assert(cur_val < top, "All recorded addresses should be less");
5511 }
5512 }
5513 // At this point min_val and min_tid are respectively
5514 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5515 // and the thread (j) that witnesses that address.
5516 // We record this address in the _survivor_chunk_array[i]
5517 // and increment _cursor[min_tid] prior to the next round i.
5518 if (min_val == top) {
5519 break;
5520 }
5521 _survivor_chunk_array[i] = min_val;
5522 _cursor[min_tid]++;
5523 }
5524 // We are all done; record the size of the _survivor_chunk_array
5525 _survivor_chunk_index = i; // exclusive: [0, i)
5526 if (PrintCMSStatistics > 0) {
5527 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5528 }
5529 // Verify that we used up all the recorded entries
5530 #ifdef ASSERT
5531 size_t total = 0;
5532 for (int j = 0; j < no_of_gc_threads; j++) {
5533 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5534 total += _cursor[j];
5535 }
5536 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5537 // Check that the merged array is in sorted order
5538 if (total > 0) {
5539 for (size_t i = 0; i < total - 1; i++) {
5540 if (PrintCMSStatistics > 0) {
5541 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5542 i, _survivor_chunk_array[i]);
5543 }
5544 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5545 "Not sorted");
5546 }
5547 }
5548 #endif // ASSERT
5549 }
5550
5551 // Set up the space's par_seq_tasks structure for work claiming
5552 // for parallel rescan of young gen.
5553 // See ParRescanTask where this is currently used.
5554 void
5555 CMSCollector::
5556 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5557 assert(n_threads > 0, "Unexpected n_threads argument");
5558 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5559
5560 // Eden space
5561 {
5562 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5563 assert(!pst->valid(), "Clobbering existing data?");
5564 // Each valid entry in [0, _eden_chunk_index) represents a task.
5565 size_t n_tasks = _eden_chunk_index + 1;
5566 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5567 // Sets the condition for completion of the subtask (how many threads
5568 // need to finish in order to be done).
5569 pst->set_n_threads(n_threads);
5570 pst->set_n_tasks((int)n_tasks);
5571 }
5572
5573 // Merge the survivor plab arrays into _survivor_chunk_array
5574 if (_survivor_plab_array != NULL) {
5575 merge_survivor_plab_arrays(dng->from(), n_threads);
5576 } else {
5577 assert(_survivor_chunk_index == 0, "Error");
5578 }
5579
5580 // To space
5581 {
5582 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5583 assert(!pst->valid(), "Clobbering existing data?");
5584 // Sets the condition for completion of the subtask (how many threads
5585 // need to finish in order to be done).
5586 pst->set_n_threads(n_threads);
5587 pst->set_n_tasks(1);
5588 assert(pst->valid(), "Error");
5589 }
5590
5591 // From space
5592 {
5593 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5594 assert(!pst->valid(), "Clobbering existing data?");
5595 size_t n_tasks = _survivor_chunk_index + 1;
5596 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5597 // Sets the condition for completion of the subtask (how many threads
5598 // need to finish in order to be done).
5599 pst->set_n_threads(n_threads);
5600 pst->set_n_tasks((int)n_tasks);
5601 assert(pst->valid(), "Error");
5602 }
5603 }
5604
5605 // Parallel version of remark
5606 void CMSCollector::do_remark_parallel() {
5607 GenCollectedHeap* gch = GenCollectedHeap::heap();
5608 FlexibleWorkGang* workers = gch->workers();
5609 assert(workers != NULL, "Need parallel worker threads.");
5610 // Choose to use the number of GC workers most recently set
5611 // into "active_workers". If active_workers is not set, set it
5612 // to ParallelGCThreads.
5613 int n_workers = workers->active_workers();
5614 if (n_workers == 0) {
5615 assert(n_workers > 0, "Should have been set during scavenge");
5616 n_workers = ParallelGCThreads;
5617 workers->set_active_workers(n_workers);
5618 }
5619 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5620 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5621
5622 CMSParRemarkTask tsk(this,
5623 cms_space, perm_space,
5624 n_workers, workers, task_queues());
5625
5626 // Set up for parallel process_strong_roots work.
5627 gch->set_par_threads(n_workers);
5628 // We won't be iterating over the cards in the card table updating
5629 // the younger_gen cards, so we shouldn't call the following else
5630 // the verification code as well as subsequent younger_refs_iterate
5631 // code would get confused. XXX
5632 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5633
5634 // The young gen rescan work will not be done as part of
5635 // process_strong_roots (which currently doesn't knw how to
5636 // parallelize such a scan), but rather will be broken up into
5637 // a set of parallel tasks (via the sampling that the [abortable]
5638 // preclean phase did of EdenSpace, plus the [two] tasks of
5639 // scanning the [two] survivor spaces. Further fine-grain
5640 // parallelization of the scanning of the survivor spaces
5641 // themselves, and of precleaning of the younger gen itself
5642 // is deferred to the future.
5643 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5644
5645 // The dirty card rescan work is broken up into a "sequence"
5646 // of parallel tasks (per constituent space) that are dynamically
5647 // claimed by the parallel threads.
5648 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5649 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5650
5651 // It turns out that even when we're using 1 thread, doing the work in a
5652 // separate thread causes wide variance in run times. We can't help this
5653 // in the multi-threaded case, but we special-case n=1 here to get
5654 // repeatable measurements of the 1-thread overhead of the parallel code.
5655 if (n_workers > 1) {
5656 // Make refs discovery MT-safe, if it isn't already: it may not
5657 // necessarily be so, since it's possible that we are doing
5658 // ST marking.
5659 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5660 GenCollectedHeap::StrongRootsScope srs(gch);
5661 workers->run_task(&tsk);
5662 } else {
5663 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5664 GenCollectedHeap::StrongRootsScope srs(gch);
5665 tsk.work(0);
5666 }
5667 gch->set_par_threads(0); // 0 ==> non-parallel.
5668 // restore, single-threaded for now, any preserved marks
5669 // as a result of work_q overflow
5670 restore_preserved_marks_if_any();
5671 }
5672
5673 // Non-parallel version of remark
5674 void CMSCollector::do_remark_non_parallel() {
5675 ResourceMark rm;
5676 HandleMark hm;
5677 GenCollectedHeap* gch = GenCollectedHeap::heap();
5678 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5679
5680 MarkRefsIntoAndScanClosure
5681 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5682 &_markStack, &_revisitStack, this,
5683 false /* should_yield */, false /* not precleaning */);
5684 MarkFromDirtyCardsClosure
5685 markFromDirtyCardsClosure(this, _span,
5686 NULL, // space is set further below
5687 &_markBitMap, &_markStack, &_revisitStack,
5688 &mrias_cl);
5689 {
5690 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5691 // Iterate over the dirty cards, setting the corresponding bits in the
5692 // mod union table.
5693 {
5694 ModUnionClosure modUnionClosure(&_modUnionTable);
5695 _ct->ct_bs()->dirty_card_iterate(
5696 _cmsGen->used_region(),
5697 &modUnionClosure);
5698 _ct->ct_bs()->dirty_card_iterate(
5699 _permGen->used_region(),
5700 &modUnionClosure);
5701 }
5702 // Having transferred these marks into the modUnionTable, we just need
5703 // to rescan the marked objects on the dirty cards in the modUnionTable.
5704 // The initial marking may have been done during an asynchronous
5705 // collection so there may be dirty bits in the mod-union table.
5706 const int alignment =
5707 CardTableModRefBS::card_size * BitsPerWord;
5708 {
5709 // ... First handle dirty cards in CMS gen
5710 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5711 MemRegion ur = _cmsGen->used_region();
5712 HeapWord* lb = ur.start();
5713 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5714 MemRegion cms_span(lb, ub);
5715 _modUnionTable.dirty_range_iterate_clear(cms_span,
5716 &markFromDirtyCardsClosure);
5717 verify_work_stacks_empty();
5718 if (PrintCMSStatistics != 0) {
5719 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5720 markFromDirtyCardsClosure.num_dirty_cards());
5721 }
5722 }
5723 {
5724 // .. and then repeat for dirty cards in perm gen
5725 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5726 MemRegion ur = _permGen->used_region();
5727 HeapWord* lb = ur.start();
5728 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5729 MemRegion perm_span(lb, ub);
5730 _modUnionTable.dirty_range_iterate_clear(perm_span,
5731 &markFromDirtyCardsClosure);
5732 verify_work_stacks_empty();
5733 if (PrintCMSStatistics != 0) {
5734 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5735 markFromDirtyCardsClosure.num_dirty_cards());
5736 }
5737 }
5738 }
5739 if (VerifyDuringGC &&
5740 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5741 HandleMark hm; // Discard invalid handles created during verification
5742 Universe::verify();
5743 }
5744 {
5745 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5746
5747 verify_work_stacks_empty();
5748
5749 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5750 GenCollectedHeap::StrongRootsScope srs(gch);
5751 gch->gen_process_strong_roots(_cmsGen->level(),
5752 true, // younger gens as roots
5753 false, // use the local StrongRootsScope
5754 true, // collecting perm gen
5755 SharedHeap::ScanningOption(roots_scanning_options()),
5756 &mrias_cl,
5757 true, // walk code active on stacks
5758 NULL);
5759 assert(should_unload_classes()
5760 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5761 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5762 }
5763 verify_work_stacks_empty();
5764 // Restore evacuated mark words, if any, used for overflow list links
5765 if (!CMSOverflowEarlyRestoration) {
5766 restore_preserved_marks_if_any();
5767 }
5768 verify_overflow_empty();
5769 }
5770
5771 ////////////////////////////////////////////////////////
5772 // Parallel Reference Processing Task Proxy Class
5773 ////////////////////////////////////////////////////////
5774 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5775 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5776 CMSCollector* _collector;
5777 CMSBitMap* _mark_bit_map;
5778 const MemRegion _span;
5779 ProcessTask& _task;
5780
5781 public:
5782 CMSRefProcTaskProxy(ProcessTask& task,
5783 CMSCollector* collector,
5784 const MemRegion& span,
5785 CMSBitMap* mark_bit_map,
5786 AbstractWorkGang* workers,
5787 OopTaskQueueSet* task_queues):
5788 // XXX Should superclass AGTWOQ also know about AWG since it knows
5789 // about the task_queues used by the AWG? Then it could initialize
5790 // the terminator() object. See 6984287. The set_for_termination()
5791 // below is a temporary band-aid for the regression in 6984287.
5792 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5793 task_queues),
5794 _task(task),
5795 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5796 {
5797 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5798 "Inconsistency in _span");
5799 set_for_termination(workers->active_workers());
5800 }
5801
5802 OopTaskQueueSet* task_queues() { return queues(); }
5803
5804 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5805
5806 void do_work_steal(int i,
5807 CMSParDrainMarkingStackClosure* drain,
5808 CMSParKeepAliveClosure* keep_alive,
5809 int* seed);
5810
5811 virtual void work(uint worker_id);
5812 };
5813
5814 void CMSRefProcTaskProxy::work(uint worker_id) {
5815 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5816 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5817 _mark_bit_map,
5818 &_collector->_revisitStack,
5819 work_queue(worker_id));
5820 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5821 _mark_bit_map,
5822 &_collector->_revisitStack,
5823 work_queue(worker_id));
5824 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5825 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5826 if (_task.marks_oops_alive()) {
5827 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5828 _collector->hash_seed(worker_id));
5829 }
5830 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5831 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5832 }
5833
5834 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5835 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5836 EnqueueTask& _task;
5837
5838 public:
5839 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5840 : AbstractGangTask("Enqueue reference objects in parallel"),
5841 _task(task)
5842 { }
5843
5844 virtual void work(uint worker_id)
5845 {
5846 _task.work(worker_id);
5847 }
5848 };
5849
5850 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5851 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5852 OopTaskQueue* work_queue):
5853 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5854 _span(span),
5855 _bit_map(bit_map),
5856 _work_queue(work_queue),
5857 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5858 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5859 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5860 { }
5861
5862 // . see if we can share work_queues with ParNew? XXX
5863 void CMSRefProcTaskProxy::do_work_steal(int i,
5864 CMSParDrainMarkingStackClosure* drain,
5865 CMSParKeepAliveClosure* keep_alive,
5866 int* seed) {
5867 OopTaskQueue* work_q = work_queue(i);
5868 NOT_PRODUCT(int num_steals = 0;)
5869 oop obj_to_scan;
5870
5871 while (true) {
5872 // Completely finish any left over work from (an) earlier round(s)
5873 drain->trim_queue(0);
5874 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5875 (size_t)ParGCDesiredObjsFromOverflowList);
5876 // Now check if there's any work in the overflow list
5877 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5878 // only affects the number of attempts made to get work from the
5879 // overflow list and does not affect the number of workers. Just
5880 // pass ParallelGCThreads so this behavior is unchanged.
5881 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5882 work_q,
5883 ParallelGCThreads)) {
5884 // Found something in global overflow list;
5885 // not yet ready to go stealing work from others.
5886 // We'd like to assert(work_q->size() != 0, ...)
5887 // because we just took work from the overflow list,
5888 // but of course we can't, since all of that might have
5889 // been already stolen from us.
5890 continue;
5891 }
5892 // Verify that we have no work before we resort to stealing
5893 assert(work_q->size() == 0, "Have work, shouldn't steal");
5894 // Try to steal from other queues that have work
5895 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5896 NOT_PRODUCT(num_steals++;)
5897 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5898 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5899 // Do scanning work
5900 obj_to_scan->oop_iterate(keep_alive);
5901 // Loop around, finish this work, and try to steal some more
5902 } else if (terminator()->offer_termination()) {
5903 break; // nirvana from the infinite cycle
5904 }
5905 }
5906 NOT_PRODUCT(
5907 if (PrintCMSStatistics != 0) {
5908 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5909 }
5910 )
5911 }
5912
5913 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5914 {
5915 GenCollectedHeap* gch = GenCollectedHeap::heap();
5916 FlexibleWorkGang* workers = gch->workers();
5917 assert(workers != NULL, "Need parallel worker threads.");
5918 CMSRefProcTaskProxy rp_task(task, &_collector,
5919 _collector.ref_processor()->span(),
5920 _collector.markBitMap(),
5921 workers, _collector.task_queues());
5922 workers->run_task(&rp_task);
5923 }
5924
5925 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5926 {
5927
5928 GenCollectedHeap* gch = GenCollectedHeap::heap();
5929 FlexibleWorkGang* workers = gch->workers();
5930 assert(workers != NULL, "Need parallel worker threads.");
5931 CMSRefEnqueueTaskProxy enq_task(task);
5932 workers->run_task(&enq_task);
5933 }
5934
5935 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5936
5937 ResourceMark rm;
5938 HandleMark hm;
5939
5940 ReferenceProcessor* rp = ref_processor();
5941 assert(rp->span().equals(_span), "Spans should be equal");
5942 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5943 // Process weak references.
5944 rp->setup_policy(clear_all_soft_refs);
5945 verify_work_stacks_empty();
5946
5947 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5948 &_markStack, &_revisitStack,
5949 false /* !preclean */);
5950 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5951 _span, &_markBitMap, &_markStack,
5952 &cmsKeepAliveClosure, false /* !preclean */);
5953 {
5954 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5955
5956 ReferenceProcessorStats stats;
5957 if (rp->processing_is_mt()) {
5958 // Set the degree of MT here. If the discovery is done MT, there
5959 // may have been a different number of threads doing the discovery
5960 // and a different number of discovered lists may have Ref objects.
5961 // That is OK as long as the Reference lists are balanced (see
5962 // balance_all_queues() and balance_queues()).
5963 GenCollectedHeap* gch = GenCollectedHeap::heap();
5964 int active_workers = ParallelGCThreads;
5965 FlexibleWorkGang* workers = gch->workers();
5966 if (workers != NULL) {
5967 active_workers = workers->active_workers();
5968 // The expectation is that active_workers will have already
5969 // been set to a reasonable value. If it has not been set,
5970 // investigate.
5971 assert(active_workers > 0, "Should have been set during scavenge");
5972 }
5973 rp->set_active_mt_degree(active_workers);
5974 CMSRefProcTaskExecutor task_executor(*this);
5975 stats = rp->process_discovered_references(&_is_alive_closure,
5976 &cmsKeepAliveClosure,
5977 &cmsDrainMarkingStackClosure,
5978 &task_executor,
5979 _gc_timer_cm);
5980 } else {
5981 stats = rp->process_discovered_references(&_is_alive_closure,
5982 &cmsKeepAliveClosure,
5983 &cmsDrainMarkingStackClosure,
5984 NULL,
5985 _gc_timer_cm);
5986 }
5987 _gc_tracer_cm->report_gc_reference_stats(stats);
5988
5989 verify_work_stacks_empty();
5990 }
5991
5992 if (should_unload_classes()) {
5993 {
5994 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5995
5996 // Follow SystemDictionary roots and unload classes
5997 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5998
5999 // Follow CodeCache roots and unload any methods marked for unloading
6000 CodeCache::do_unloading(&_is_alive_closure,
6001 &cmsKeepAliveClosure,
6002 purged_class);
6003
6004 cmsDrainMarkingStackClosure.do_void();
6005 verify_work_stacks_empty();
6006
6007 // Update subklass/sibling/implementor links in KlassKlass descendants
6008 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
6009 oop k;
6010 while ((k = _revisitStack.pop()) != NULL) {
6011 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
6012 &_is_alive_closure,
6013 &cmsKeepAliveClosure);
6014 }
6015 assert(!ClassUnloading ||
6016 (_markStack.isEmpty() && overflow_list_is_empty()),
6017 "Should not have found new reachable objects");
6018 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
6019 cmsDrainMarkingStackClosure.do_void();
6020 verify_work_stacks_empty();
6021 }
6022
6023 {
6024 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6025 // Clean up unreferenced symbols in symbol table.
6026 SymbolTable::unlink();
6027 }
6028 }
6029
6030 if (should_unload_classes() || !JavaObjectsInPerm) {
6031 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6032 // Now clean up stale oops in StringTable
6033 StringTable::unlink(&_is_alive_closure);
6034 }
6035
6036 verify_work_stacks_empty();
6037 // Restore any preserved marks as a result of mark stack or
6038 // work queue overflow
6039 restore_preserved_marks_if_any(); // done single-threaded for now
6040
6041 rp->set_enqueuing_is_done(true);
6042 if (rp->processing_is_mt()) {
6043 rp->balance_all_queues();
6044 CMSRefProcTaskExecutor task_executor(*this);
6045 rp->enqueue_discovered_references(&task_executor);
6046 } else {
6047 rp->enqueue_discovered_references(NULL);
6048 }
6049 rp->verify_no_references_recorded();
6050 assert(!rp->discovery_enabled(), "should have been disabled");
6051 }
6052
6053 #ifndef PRODUCT
6054 void CMSCollector::check_correct_thread_executing() {
6055 Thread* t = Thread::current();
6056 // Only the VM thread or the CMS thread should be here.
6057 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6058 "Unexpected thread type");
6059 // If this is the vm thread, the foreground process
6060 // should not be waiting. Note that _foregroundGCIsActive is
6061 // true while the foreground collector is waiting.
6062 if (_foregroundGCShouldWait) {
6063 // We cannot be the VM thread
6064 assert(t->is_ConcurrentGC_thread(),
6065 "Should be CMS thread");
6066 } else {
6067 // We can be the CMS thread only if we are in a stop-world
6068 // phase of CMS collection.
6069 if (t->is_ConcurrentGC_thread()) {
6070 assert(_collectorState == InitialMarking ||
6071 _collectorState == FinalMarking,
6072 "Should be a stop-world phase");
6073 // The CMS thread should be holding the CMS_token.
6074 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6075 "Potential interference with concurrently "
6076 "executing VM thread");
6077 }
6078 }
6079 }
6080 #endif
6081
6082 void CMSCollector::sweep(bool asynch) {
6083 assert(_collectorState == Sweeping, "just checking");
6084 check_correct_thread_executing();
6085 verify_work_stacks_empty();
6086 verify_overflow_empty();
6087 increment_sweep_count();
6088 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6089
6090 _inter_sweep_timer.stop();
6091 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6092 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6093
6094 // PermGen verification support: If perm gen sweeping is disabled in
6095 // this cycle, we preserve the perm gen object "deadness" information
6096 // in the perm_gen_verify_bit_map. In order to do that we traverse
6097 // all blocks in perm gen and mark all dead objects.
6098 if (verifying() && !should_unload_classes()) {
6099 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6100 "Should have already been allocated");
6101 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6102 markBitMap(), perm_gen_verify_bit_map());
6103 if (asynch) {
6104 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6105 bitMapLock());
6106 _permGen->cmsSpace()->blk_iterate(&mdo);
6107 } else {
6108 // In the case of synchronous sweep, we already have
6109 // the requisite locks/tokens.
6110 _permGen->cmsSpace()->blk_iterate(&mdo);
6111 }
6112 }
6113
6114 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6115 _intra_sweep_timer.reset();
6116 _intra_sweep_timer.start();
6117 if (asynch) {
6118 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6119 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6120 // First sweep the old gen then the perm gen
6121 {
6122 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6123 bitMapLock());
6124 sweepWork(_cmsGen, asynch);
6125 }
6126
6127 // Now repeat for perm gen
6128 if (should_unload_classes()) {
6129 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6130 bitMapLock());
6131 sweepWork(_permGen, asynch);
6132 }
6133
6134 // Update Universe::_heap_*_at_gc figures.
6135 // We need all the free list locks to make the abstract state
6136 // transition from Sweeping to Resetting. See detailed note
6137 // further below.
6138 {
6139 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6140 _permGen->freelistLock());
6141 // Update heap occupancy information which is used as
6142 // input to soft ref clearing policy at the next gc.
6143 Universe::update_heap_info_at_gc();
6144 _collectorState = Resizing;
6145 }
6146 } else {
6147 // already have needed locks
6148 sweepWork(_cmsGen, asynch);
6149
6150 if (should_unload_classes()) {
6151 sweepWork(_permGen, asynch);
6152 }
6153 // Update heap occupancy information which is used as
6154 // input to soft ref clearing policy at the next gc.
6155 Universe::update_heap_info_at_gc();
6156 _collectorState = Resizing;
6157 }
6158 verify_work_stacks_empty();
6159 verify_overflow_empty();
6160
6161 _intra_sweep_timer.stop();
6162 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6163
6164 _inter_sweep_timer.reset();
6165 _inter_sweep_timer.start();
6166
6167 // We need to use a monotonically non-deccreasing time in ms
6168 // or we will see time-warp warnings and os::javaTimeMillis()
6169 // does not guarantee monotonicity.
6170 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6171 update_time_of_last_gc(now);
6172
6173 // NOTE on abstract state transitions:
6174 // Mutators allocate-live and/or mark the mod-union table dirty
6175 // based on the state of the collection. The former is done in
6176 // the interval [Marking, Sweeping] and the latter in the interval
6177 // [Marking, Sweeping). Thus the transitions into the Marking state
6178 // and out of the Sweeping state must be synchronously visible
6179 // globally to the mutators.
6180 // The transition into the Marking state happens with the world
6181 // stopped so the mutators will globally see it. Sweeping is
6182 // done asynchronously by the background collector so the transition
6183 // from the Sweeping state to the Resizing state must be done
6184 // under the freelistLock (as is the check for whether to
6185 // allocate-live and whether to dirty the mod-union table).
6186 assert(_collectorState == Resizing, "Change of collector state to"
6187 " Resizing must be done under the freelistLocks (plural)");
6188
6189 // Now that sweeping has been completed, we clear
6190 // the incremental_collection_failed flag,
6191 // thus inviting a younger gen collection to promote into
6192 // this generation. If such a promotion may still fail,
6193 // the flag will be set again when a young collection is
6194 // attempted.
6195 GenCollectedHeap* gch = GenCollectedHeap::heap();
6196 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6197 gch->update_full_collections_completed(_collection_count_start);
6198 }
6199
6200 // FIX ME!!! Looks like this belongs in CFLSpace, with
6201 // CMSGen merely delegating to it.
6202 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6203 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6204 HeapWord* minAddr = _cmsSpace->bottom();
6205 HeapWord* largestAddr =
6206 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6207 if (largestAddr == NULL) {
6208 // The dictionary appears to be empty. In this case
6209 // try to coalesce at the end of the heap.
6210 largestAddr = _cmsSpace->end();
6211 }
6212 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6213 size_t nearLargestOffset =
6214 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6215 if (PrintFLSStatistics != 0) {
6216 gclog_or_tty->print_cr(
6217 "CMS: Large Block: " PTR_FORMAT ";"
6218 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6219 largestAddr,
6220 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6221 }
6222 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6223 }
6224
6225 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6226 return addr >= _cmsSpace->nearLargestChunk();
6227 }
6228
6229 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6230 return _cmsSpace->find_chunk_at_end();
6231 }
6232
6233 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6234 bool full) {
6235 // The next lower level has been collected. Gather any statistics
6236 // that are of interest at this point.
6237 if (!full && (current_level + 1) == level()) {
6238 // Gather statistics on the young generation collection.
6239 collector()->stats().record_gc0_end(used());
6240 }
6241 }
6242
6243 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6244 GenCollectedHeap* gch = GenCollectedHeap::heap();
6245 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6246 "Wrong type of heap");
6247 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6248 gch->gen_policy()->size_policy();
6249 assert(sp->is_gc_cms_adaptive_size_policy(),
6250 "Wrong type of size policy");
6251 return sp;
6252 }
6253
6254 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6255 if (PrintGCDetails && Verbose) {
6256 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6257 }
6258 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6259 _debug_collection_type =
6260 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6261 if (PrintGCDetails && Verbose) {
6262 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6263 }
6264 }
6265
6266 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6267 bool asynch) {
6268 // We iterate over the space(s) underlying this generation,
6269 // checking the mark bit map to see if the bits corresponding
6270 // to specific blocks are marked or not. Blocks that are
6271 // marked are live and are not swept up. All remaining blocks
6272 // are swept up, with coalescing on-the-fly as we sweep up
6273 // contiguous free and/or garbage blocks:
6274 // We need to ensure that the sweeper synchronizes with allocators
6275 // and stop-the-world collectors. In particular, the following
6276 // locks are used:
6277 // . CMS token: if this is held, a stop the world collection cannot occur
6278 // . freelistLock: if this is held no allocation can occur from this
6279 // generation by another thread
6280 // . bitMapLock: if this is held, no other thread can access or update
6281 //
6282
6283 // Note that we need to hold the freelistLock if we use
6284 // block iterate below; else the iterator might go awry if
6285 // a mutator (or promotion) causes block contents to change
6286 // (for instance if the allocator divvies up a block).
6287 // If we hold the free list lock, for all practical purposes
6288 // young generation GC's can't occur (they'll usually need to
6289 // promote), so we might as well prevent all young generation
6290 // GC's while we do a sweeping step. For the same reason, we might
6291 // as well take the bit map lock for the entire duration
6292
6293 // check that we hold the requisite locks
6294 assert(have_cms_token(), "Should hold cms token");
6295 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6296 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6297 "Should possess CMS token to sweep");
6298 assert_lock_strong(gen->freelistLock());
6299 assert_lock_strong(bitMapLock());
6300
6301 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6302 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6303 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6304 _inter_sweep_estimate.padded_average(),
6305 _intra_sweep_estimate.padded_average());
6306 gen->setNearLargestChunk();
6307
6308 {
6309 SweepClosure sweepClosure(this, gen, &_markBitMap,
6310 CMSYield && asynch);
6311 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6312 // We need to free-up/coalesce garbage/blocks from a
6313 // co-terminal free run. This is done in the SweepClosure
6314 // destructor; so, do not remove this scope, else the
6315 // end-of-sweep-census below will be off by a little bit.
6316 }
6317 gen->cmsSpace()->sweep_completed();
6318 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6319 if (should_unload_classes()) { // unloaded classes this cycle,
6320 _concurrent_cycles_since_last_unload = 0; // ... reset count
6321 } else { // did not unload classes,
6322 _concurrent_cycles_since_last_unload++; // ... increment count
6323 }
6324 }
6325
6326 // Reset CMS data structures (for now just the marking bit map)
6327 // preparatory for the next cycle.
6328 void CMSCollector::reset(bool asynch) {
6329 GenCollectedHeap* gch = GenCollectedHeap::heap();
6330 CMSAdaptiveSizePolicy* sp = size_policy();
6331 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6332 if (asynch) {
6333 CMSTokenSyncWithLocks ts(true, bitMapLock());
6334
6335 // If the state is not "Resetting", the foreground thread
6336 // has done a collection and the resetting.
6337 if (_collectorState != Resetting) {
6338 assert(_collectorState == Idling, "The state should only change"
6339 " because the foreground collector has finished the collection");
6340 return;
6341 }
6342
6343 // Clear the mark bitmap (no grey objects to start with)
6344 // for the next cycle.
6345 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6346 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6347
6348 HeapWord* curAddr = _markBitMap.startWord();
6349 while (curAddr < _markBitMap.endWord()) {
6350 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6351 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6352 _markBitMap.clear_large_range(chunk);
6353 if (ConcurrentMarkSweepThread::should_yield() &&
6354 !foregroundGCIsActive() &&
6355 CMSYield) {
6356 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6357 "CMS thread should hold CMS token");
6358 assert_lock_strong(bitMapLock());
6359 bitMapLock()->unlock();
6360 ConcurrentMarkSweepThread::desynchronize(true);
6361 ConcurrentMarkSweepThread::acknowledge_yield_request();
6362 stopTimer();
6363 if (PrintCMSStatistics != 0) {
6364 incrementYields();
6365 }
6366 icms_wait();
6367
6368 // See the comment in coordinator_yield()
6369 for (unsigned i = 0; i < CMSYieldSleepCount &&
6370 ConcurrentMarkSweepThread::should_yield() &&
6371 !CMSCollector::foregroundGCIsActive(); ++i) {
6372 os::sleep(Thread::current(), 1, false);
6373 ConcurrentMarkSweepThread::acknowledge_yield_request();
6374 }
6375
6376 ConcurrentMarkSweepThread::synchronize(true);
6377 bitMapLock()->lock_without_safepoint_check();
6378 startTimer();
6379 }
6380 curAddr = chunk.end();
6381 }
6382 // A successful mostly concurrent collection has been done.
6383 // Because only the full (i.e., concurrent mode failure) collections
6384 // are being measured for gc overhead limits, clean the "near" flag
6385 // and count.
6386 sp->reset_gc_overhead_limit_count();
6387 _collectorState = Idling;
6388 } else {
6389 // already have the lock
6390 assert(_collectorState == Resetting, "just checking");
6391 assert_lock_strong(bitMapLock());
6392 _markBitMap.clear_all();
6393 _collectorState = Idling;
6394 }
6395
6396 // Stop incremental mode after a cycle completes, so that any future cycles
6397 // are triggered by allocation.
6398 stop_icms();
6399
6400 NOT_PRODUCT(
6401 if (RotateCMSCollectionTypes) {
6402 _cmsGen->rotate_debug_collection_type();
6403 }
6404 )
6405
6406 register_gc_end();
6407 }
6408
6409 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6410 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6411 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6412 TraceCollectorStats tcs(counters());
6413
6414 switch (op) {
6415 case CMS_op_checkpointRootsInitial: {
6416 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6417 checkpointRootsInitial(true); // asynch
6418 if (PrintGC) {
6419 _cmsGen->printOccupancy("initial-mark");
6420 }
6421 break;
6422 }
6423 case CMS_op_checkpointRootsFinal: {
6424 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6425 checkpointRootsFinal(true, // asynch
6426 false, // !clear_all_soft_refs
6427 false); // !init_mark_was_synchronous
6428 if (PrintGC) {
6429 _cmsGen->printOccupancy("remark");
6430 }
6431 break;
6432 }
6433 default:
6434 fatal("No such CMS_op");
6435 }
6436 }
6437
6438 #ifndef PRODUCT
6439 size_t const CMSCollector::skip_header_HeapWords() {
6440 return FreeChunk::header_size();
6441 }
6442
6443 // Try and collect here conditions that should hold when
6444 // CMS thread is exiting. The idea is that the foreground GC
6445 // thread should not be blocked if it wants to terminate
6446 // the CMS thread and yet continue to run the VM for a while
6447 // after that.
6448 void CMSCollector::verify_ok_to_terminate() const {
6449 assert(Thread::current()->is_ConcurrentGC_thread(),
6450 "should be called by CMS thread");
6451 assert(!_foregroundGCShouldWait, "should be false");
6452 // We could check here that all the various low-level locks
6453 // are not held by the CMS thread, but that is overkill; see
6454 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6455 // is checked.
6456 }
6457 #endif
6458
6459 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6460 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6461 "missing Printezis mark?");
6462 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6463 size_t size = pointer_delta(nextOneAddr + 1, addr);
6464 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6465 "alignment problem");
6466 assert(size >= 3, "Necessary for Printezis marks to work");
6467 return size;
6468 }
6469
6470 // A variant of the above (block_size_using_printezis_bits()) except
6471 // that we return 0 if the P-bits are not yet set.
6472 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6473 if (_markBitMap.isMarked(addr + 1)) {
6474 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6475 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6476 size_t size = pointer_delta(nextOneAddr + 1, addr);
6477 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6478 "alignment problem");
6479 assert(size >= 3, "Necessary for Printezis marks to work");
6480 return size;
6481 }
6482 return 0;
6483 }
6484
6485 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6486 size_t sz = 0;
6487 oop p = (oop)addr;
6488 if (p->klass_or_null() != NULL && p->is_parsable()) {
6489 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6490 } else {
6491 sz = block_size_using_printezis_bits(addr);
6492 }
6493 assert(sz > 0, "size must be nonzero");
6494 HeapWord* next_block = addr + sz;
6495 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6496 CardTableModRefBS::card_size);
6497 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6498 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6499 "must be different cards");
6500 return next_card;
6501 }
6502
6503
6504 // CMS Bit Map Wrapper /////////////////////////////////////////
6505
6506 // Construct a CMS bit map infrastructure, but don't create the
6507 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6508 // further below.
6509 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6510 _bm(),
6511 _shifter(shifter),
6512 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6513 {
6514 _bmStartWord = 0;
6515 _bmWordSize = 0;
6516 }
6517
6518 bool CMSBitMap::allocate(MemRegion mr) {
6519 _bmStartWord = mr.start();
6520 _bmWordSize = mr.word_size();
6521 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6522 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6523 if (!brs.is_reserved()) {
6524 warning("CMS bit map allocation failure");
6525 return false;
6526 }
6527 // For now we'll just commit all of the bit map up fromt.
6528 // Later on we'll try to be more parsimonious with swap.
6529 if (!_virtual_space.initialize(brs, brs.size())) {
6530 warning("CMS bit map backing store failure");
6531 return false;
6532 }
6533 assert(_virtual_space.committed_size() == brs.size(),
6534 "didn't reserve backing store for all of CMS bit map?");
6535 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6536 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6537 _bmWordSize, "inconsistency in bit map sizing");
6538 _bm.set_size(_bmWordSize >> _shifter);
6539
6540 // bm.clear(); // can we rely on getting zero'd memory? verify below
6541 assert(isAllClear(),
6542 "Expected zero'd memory from ReservedSpace constructor");
6543 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6544 "consistency check");
6545 return true;
6546 }
6547
6548 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6549 HeapWord *next_addr, *end_addr, *last_addr;
6550 assert_locked();
6551 assert(covers(mr), "out-of-range error");
6552 // XXX assert that start and end are appropriately aligned
6553 for (next_addr = mr.start(), end_addr = mr.end();
6554 next_addr < end_addr; next_addr = last_addr) {
6555 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6556 last_addr = dirty_region.end();
6557 if (!dirty_region.is_empty()) {
6558 cl->do_MemRegion(dirty_region);
6559 } else {
6560 assert(last_addr == end_addr, "program logic");
6561 return;
6562 }
6563 }
6564 }
6565
6566 #ifndef PRODUCT
6567 void CMSBitMap::assert_locked() const {
6568 CMSLockVerifier::assert_locked(lock());
6569 }
6570
6571 bool CMSBitMap::covers(MemRegion mr) const {
6572 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6573 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6574 "size inconsistency");
6575 return (mr.start() >= _bmStartWord) &&
6576 (mr.end() <= endWord());
6577 }
6578
6579 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6580 return (start >= _bmStartWord && (start + size) <= endWord());
6581 }
6582
6583 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6584 // verify that there are no 1 bits in the interval [left, right)
6585 FalseBitMapClosure falseBitMapClosure;
6586 iterate(&falseBitMapClosure, left, right);
6587 }
6588
6589 void CMSBitMap::region_invariant(MemRegion mr)
6590 {
6591 assert_locked();
6592 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6593 assert(!mr.is_empty(), "unexpected empty region");
6594 assert(covers(mr), "mr should be covered by bit map");
6595 // convert address range into offset range
6596 size_t start_ofs = heapWordToOffset(mr.start());
6597 // Make sure that end() is appropriately aligned
6598 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6599 (1 << (_shifter+LogHeapWordSize))),
6600 "Misaligned mr.end()");
6601 size_t end_ofs = heapWordToOffset(mr.end());
6602 assert(end_ofs > start_ofs, "Should mark at least one bit");
6603 }
6604
6605 #endif
6606
6607 bool CMSMarkStack::allocate(size_t size) {
6608 // allocate a stack of the requisite depth
6609 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6610 size * sizeof(oop)));
6611 if (!rs.is_reserved()) {
6612 warning("CMSMarkStack allocation failure");
6613 return false;
6614 }
6615 if (!_virtual_space.initialize(rs, rs.size())) {
6616 warning("CMSMarkStack backing store failure");
6617 return false;
6618 }
6619 assert(_virtual_space.committed_size() == rs.size(),
6620 "didn't reserve backing store for all of CMS stack?");
6621 _base = (oop*)(_virtual_space.low());
6622 _index = 0;
6623 _capacity = size;
6624 NOT_PRODUCT(_max_depth = 0);
6625 return true;
6626 }
6627
6628 // XXX FIX ME !!! In the MT case we come in here holding a
6629 // leaf lock. For printing we need to take a further lock
6630 // which has lower rank. We need to recallibrate the two
6631 // lock-ranks involved in order to be able to rpint the
6632 // messages below. (Or defer the printing to the caller.
6633 // For now we take the expedient path of just disabling the
6634 // messages for the problematic case.)
6635 void CMSMarkStack::expand() {
6636 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6637 if (_capacity == MarkStackSizeMax) {
6638 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6639 // We print a warning message only once per CMS cycle.
6640 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6641 }
6642 return;
6643 }
6644 // Double capacity if possible
6645 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6646 // Do not give up existing stack until we have managed to
6647 // get the double capacity that we desired.
6648 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6649 new_capacity * sizeof(oop)));
6650 if (rs.is_reserved()) {
6651 // Release the backing store associated with old stack
6652 _virtual_space.release();
6653 // Reinitialize virtual space for new stack
6654 if (!_virtual_space.initialize(rs, rs.size())) {
6655 fatal("Not enough swap for expanded marking stack");
6656 }
6657 _base = (oop*)(_virtual_space.low());
6658 _index = 0;
6659 _capacity = new_capacity;
6660 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6661 // Failed to double capacity, continue;
6662 // we print a detail message only once per CMS cycle.
6663 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6664 SIZE_FORMAT"K",
6665 _capacity / K, new_capacity / K);
6666 }
6667 }
6668
6669
6670 // Closures
6671 // XXX: there seems to be a lot of code duplication here;
6672 // should refactor and consolidate common code.
6673
6674 // This closure is used to mark refs into the CMS generation in
6675 // the CMS bit map. Called at the first checkpoint. This closure
6676 // assumes that we do not need to re-mark dirty cards; if the CMS
6677 // generation on which this is used is not an oldest (modulo perm gen)
6678 // generation then this will lose younger_gen cards!
6679
6680 MarkRefsIntoClosure::MarkRefsIntoClosure(
6681 MemRegion span, CMSBitMap* bitMap):
6682 _span(span),
6683 _bitMap(bitMap)
6684 {
6685 assert(_ref_processor == NULL, "deliberately left NULL");
6686 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6687 }
6688
6689 void MarkRefsIntoClosure::do_oop(oop obj) {
6690 // if p points into _span, then mark corresponding bit in _markBitMap
6691 assert(obj->is_oop(), "expected an oop");
6692 HeapWord* addr = (HeapWord*)obj;
6693 if (_span.contains(addr)) {
6694 // this should be made more efficient
6695 _bitMap->mark(addr);
6696 }
6697 }
6698
6699 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6700 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6701
6702 // A variant of the above, used for CMS marking verification.
6703 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6704 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6705 _span(span),
6706 _verification_bm(verification_bm),
6707 _cms_bm(cms_bm)
6708 {
6709 assert(_ref_processor == NULL, "deliberately left NULL");
6710 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6711 }
6712
6713 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6714 // if p points into _span, then mark corresponding bit in _markBitMap
6715 assert(obj->is_oop(), "expected an oop");
6716 HeapWord* addr = (HeapWord*)obj;
6717 if (_span.contains(addr)) {
6718 _verification_bm->mark(addr);
6719 if (!_cms_bm->isMarked(addr)) {
6720 oop(addr)->print();
6721 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6722 fatal("... aborting");
6723 }
6724 }
6725 }
6726
6727 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6728 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6729
6730 //////////////////////////////////////////////////
6731 // MarkRefsIntoAndScanClosure
6732 //////////////////////////////////////////////////
6733
6734 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6735 ReferenceProcessor* rp,
6736 CMSBitMap* bit_map,
6737 CMSBitMap* mod_union_table,
6738 CMSMarkStack* mark_stack,
6739 CMSMarkStack* revisit_stack,
6740 CMSCollector* collector,
6741 bool should_yield,
6742 bool concurrent_precleaning):
6743 _collector(collector),
6744 _span(span),
6745 _bit_map(bit_map),
6746 _mark_stack(mark_stack),
6747 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6748 mark_stack, revisit_stack, concurrent_precleaning),
6749 _yield(should_yield),
6750 _concurrent_precleaning(concurrent_precleaning),
6751 _freelistLock(NULL)
6752 {
6753 _ref_processor = rp;
6754 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6755 }
6756
6757 // This closure is used to mark refs into the CMS generation at the
6758 // second (final) checkpoint, and to scan and transitively follow
6759 // the unmarked oops. It is also used during the concurrent precleaning
6760 // phase while scanning objects on dirty cards in the CMS generation.
6761 // The marks are made in the marking bit map and the marking stack is
6762 // used for keeping the (newly) grey objects during the scan.
6763 // The parallel version (Par_...) appears further below.
6764 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6765 if (obj != NULL) {
6766 assert(obj->is_oop(), "expected an oop");
6767 HeapWord* addr = (HeapWord*)obj;
6768 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6769 assert(_collector->overflow_list_is_empty(),
6770 "overflow list should be empty");
6771 if (_span.contains(addr) &&
6772 !_bit_map->isMarked(addr)) {
6773 // mark bit map (object is now grey)
6774 _bit_map->mark(addr);
6775 // push on marking stack (stack should be empty), and drain the
6776 // stack by applying this closure to the oops in the oops popped
6777 // from the stack (i.e. blacken the grey objects)
6778 bool res = _mark_stack->push(obj);
6779 assert(res, "Should have space to push on empty stack");
6780 do {
6781 oop new_oop = _mark_stack->pop();
6782 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6783 assert(new_oop->is_parsable(), "Found unparsable oop");
6784 assert(_bit_map->isMarked((HeapWord*)new_oop),
6785 "only grey objects on this stack");
6786 // iterate over the oops in this oop, marking and pushing
6787 // the ones in CMS heap (i.e. in _span).
6788 new_oop->oop_iterate(&_pushAndMarkClosure);
6789 // check if it's time to yield
6790 do_yield_check();
6791 } while (!_mark_stack->isEmpty() ||
6792 (!_concurrent_precleaning && take_from_overflow_list()));
6793 // if marking stack is empty, and we are not doing this
6794 // during precleaning, then check the overflow list
6795 }
6796 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6797 assert(_collector->overflow_list_is_empty(),
6798 "overflow list was drained above");
6799 // We could restore evacuated mark words, if any, used for
6800 // overflow list links here because the overflow list is
6801 // provably empty here. That would reduce the maximum
6802 // size requirements for preserved_{oop,mark}_stack.
6803 // But we'll just postpone it until we are all done
6804 // so we can just stream through.
6805 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6806 _collector->restore_preserved_marks_if_any();
6807 assert(_collector->no_preserved_marks(), "No preserved marks");
6808 }
6809 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6810 "All preserved marks should have been restored above");
6811 }
6812 }
6813
6814 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6815 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6816
6817 void MarkRefsIntoAndScanClosure::do_yield_work() {
6818 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6819 "CMS thread should hold CMS token");
6820 assert_lock_strong(_freelistLock);
6821 assert_lock_strong(_bit_map->lock());
6822 // relinquish the free_list_lock and bitMaplock()
6823 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6824 _bit_map->lock()->unlock();
6825 _freelistLock->unlock();
6826 ConcurrentMarkSweepThread::desynchronize(true);
6827 ConcurrentMarkSweepThread::acknowledge_yield_request();
6828 _collector->stopTimer();
6829 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6830 if (PrintCMSStatistics != 0) {
6831 _collector->incrementYields();
6832 }
6833 _collector->icms_wait();
6834
6835 // See the comment in coordinator_yield()
6836 for (unsigned i = 0;
6837 i < CMSYieldSleepCount &&
6838 ConcurrentMarkSweepThread::should_yield() &&
6839 !CMSCollector::foregroundGCIsActive();
6840 ++i) {
6841 os::sleep(Thread::current(), 1, false);
6842 ConcurrentMarkSweepThread::acknowledge_yield_request();
6843 }
6844
6845 ConcurrentMarkSweepThread::synchronize(true);
6846 _freelistLock->lock_without_safepoint_check();
6847 _bit_map->lock()->lock_without_safepoint_check();
6848 _collector->startTimer();
6849 }
6850
6851 ///////////////////////////////////////////////////////////
6852 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6853 // MarkRefsIntoAndScanClosure
6854 ///////////////////////////////////////////////////////////
6855 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6856 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6857 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6858 _span(span),
6859 _bit_map(bit_map),
6860 _work_queue(work_queue),
6861 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6862 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6863 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6864 revisit_stack)
6865 {
6866 _ref_processor = rp;
6867 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6868 }
6869
6870 // This closure is used to mark refs into the CMS generation at the
6871 // second (final) checkpoint, and to scan and transitively follow
6872 // the unmarked oops. The marks are made in the marking bit map and
6873 // the work_queue is used for keeping the (newly) grey objects during
6874 // the scan phase whence they are also available for stealing by parallel
6875 // threads. Since the marking bit map is shared, updates are
6876 // synchronized (via CAS).
6877 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6878 if (obj != NULL) {
6879 // Ignore mark word because this could be an already marked oop
6880 // that may be chained at the end of the overflow list.
6881 assert(obj->is_oop(true), "expected an oop");
6882 HeapWord* addr = (HeapWord*)obj;
6883 if (_span.contains(addr) &&
6884 !_bit_map->isMarked(addr)) {
6885 // mark bit map (object will become grey):
6886 // It is possible for several threads to be
6887 // trying to "claim" this object concurrently;
6888 // the unique thread that succeeds in marking the
6889 // object first will do the subsequent push on
6890 // to the work queue (or overflow list).
6891 if (_bit_map->par_mark(addr)) {
6892 // push on work_queue (which may not be empty), and trim the
6893 // queue to an appropriate length by applying this closure to
6894 // the oops in the oops popped from the stack (i.e. blacken the
6895 // grey objects)
6896 bool res = _work_queue->push(obj);
6897 assert(res, "Low water mark should be less than capacity?");
6898 trim_queue(_low_water_mark);
6899 } // Else, another thread claimed the object
6900 }
6901 }
6902 }
6903
6904 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6905 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6906
6907 // This closure is used to rescan the marked objects on the dirty cards
6908 // in the mod union table and the card table proper.
6909 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6910 oop p, MemRegion mr) {
6911
6912 size_t size = 0;
6913 HeapWord* addr = (HeapWord*)p;
6914 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6915 assert(_span.contains(addr), "we are scanning the CMS generation");
6916 // check if it's time to yield
6917 if (do_yield_check()) {
6918 // We yielded for some foreground stop-world work,
6919 // and we have been asked to abort this ongoing preclean cycle.
6920 return 0;
6921 }
6922 if (_bitMap->isMarked(addr)) {
6923 // it's marked; is it potentially uninitialized?
6924 if (p->klass_or_null() != NULL) {
6925 // If is_conc_safe is false, the object may be undergoing
6926 // change by the VM outside a safepoint. Don't try to
6927 // scan it, but rather leave it for the remark phase.
6928 if (CMSPermGenPrecleaningEnabled &&
6929 (!p->is_conc_safe() || !p->is_parsable())) {
6930 // Signal precleaning to redirty the card since
6931 // the klass pointer is already installed.
6932 assert(size == 0, "Initial value");
6933 } else {
6934 assert(p->is_parsable(), "must be parsable.");
6935 // an initialized object; ignore mark word in verification below
6936 // since we are running concurrent with mutators
6937 assert(p->is_oop(true), "should be an oop");
6938 if (p->is_objArray()) {
6939 // objArrays are precisely marked; restrict scanning
6940 // to dirty cards only.
6941 size = CompactibleFreeListSpace::adjustObjectSize(
6942 p->oop_iterate(_scanningClosure, mr));
6943 } else {
6944 // A non-array may have been imprecisely marked; we need
6945 // to scan object in its entirety.
6946 size = CompactibleFreeListSpace::adjustObjectSize(
6947 p->oop_iterate(_scanningClosure));
6948 }
6949 #ifdef DEBUG
6950 size_t direct_size =
6951 CompactibleFreeListSpace::adjustObjectSize(p->size());
6952 assert(size == direct_size, "Inconsistency in size");
6953 assert(size >= 3, "Necessary for Printezis marks to work");
6954 if (!_bitMap->isMarked(addr+1)) {
6955 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6956 } else {
6957 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6958 assert(_bitMap->isMarked(addr+size-1),
6959 "inconsistent Printezis mark");
6960 }
6961 #endif // DEBUG
6962 }
6963 } else {
6964 // an unitialized object
6965 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6966 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6967 size = pointer_delta(nextOneAddr + 1, addr);
6968 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6969 "alignment problem");
6970 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6971 // will dirty the card when the klass pointer is installed in the
6972 // object (signalling the completion of initialization).
6973 }
6974 } else {
6975 // Either a not yet marked object or an uninitialized object
6976 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6977 // An uninitialized object, skip to the next card, since
6978 // we may not be able to read its P-bits yet.
6979 assert(size == 0, "Initial value");
6980 } else {
6981 // An object not (yet) reached by marking: we merely need to
6982 // compute its size so as to go look at the next block.
6983 assert(p->is_oop(true), "should be an oop");
6984 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6985 }
6986 }
6987 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6988 return size;
6989 }
6990
6991 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6992 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6993 "CMS thread should hold CMS token");
6994 assert_lock_strong(_freelistLock);
6995 assert_lock_strong(_bitMap->lock());
6996 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6997 // relinquish the free_list_lock and bitMaplock()
6998 _bitMap->lock()->unlock();
6999 _freelistLock->unlock();
7000 ConcurrentMarkSweepThread::desynchronize(true);
7001 ConcurrentMarkSweepThread::acknowledge_yield_request();
7002 _collector->stopTimer();
7003 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7004 if (PrintCMSStatistics != 0) {
7005 _collector->incrementYields();
7006 }
7007 _collector->icms_wait();
7008
7009 // See the comment in coordinator_yield()
7010 for (unsigned i = 0; i < CMSYieldSleepCount &&
7011 ConcurrentMarkSweepThread::should_yield() &&
7012 !CMSCollector::foregroundGCIsActive(); ++i) {
7013 os::sleep(Thread::current(), 1, false);
7014 ConcurrentMarkSweepThread::acknowledge_yield_request();
7015 }
7016
7017 ConcurrentMarkSweepThread::synchronize(true);
7018 _freelistLock->lock_without_safepoint_check();
7019 _bitMap->lock()->lock_without_safepoint_check();
7020 _collector->startTimer();
7021 }
7022
7023
7024 //////////////////////////////////////////////////////////////////
7025 // SurvivorSpacePrecleanClosure
7026 //////////////////////////////////////////////////////////////////
7027 // This (single-threaded) closure is used to preclean the oops in
7028 // the survivor spaces.
7029 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7030
7031 HeapWord* addr = (HeapWord*)p;
7032 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7033 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7034 assert(p->klass_or_null() != NULL, "object should be initializd");
7035 assert(p->is_parsable(), "must be parsable.");
7036 // an initialized object; ignore mark word in verification below
7037 // since we are running concurrent with mutators
7038 assert(p->is_oop(true), "should be an oop");
7039 // Note that we do not yield while we iterate over
7040 // the interior oops of p, pushing the relevant ones
7041 // on our marking stack.
7042 size_t size = p->oop_iterate(_scanning_closure);
7043 do_yield_check();
7044 // Observe that below, we do not abandon the preclean
7045 // phase as soon as we should; rather we empty the
7046 // marking stack before returning. This is to satisfy
7047 // some existing assertions. In general, it may be a
7048 // good idea to abort immediately and complete the marking
7049 // from the grey objects at a later time.
7050 while (!_mark_stack->isEmpty()) {
7051 oop new_oop = _mark_stack->pop();
7052 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7053 assert(new_oop->is_parsable(), "Found unparsable oop");
7054 assert(_bit_map->isMarked((HeapWord*)new_oop),
7055 "only grey objects on this stack");
7056 // iterate over the oops in this oop, marking and pushing
7057 // the ones in CMS heap (i.e. in _span).
7058 new_oop->oop_iterate(_scanning_closure);
7059 // check if it's time to yield
7060 do_yield_check();
7061 }
7062 unsigned int after_count =
7063 GenCollectedHeap::heap()->total_collections();
7064 bool abort = (_before_count != after_count) ||
7065 _collector->should_abort_preclean();
7066 return abort ? 0 : size;
7067 }
7068
7069 void SurvivorSpacePrecleanClosure::do_yield_work() {
7070 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7071 "CMS thread should hold CMS token");
7072 assert_lock_strong(_bit_map->lock());
7073 DEBUG_ONLY(RememberKlassesChecker smx(false);)
7074 // Relinquish the bit map lock
7075 _bit_map->lock()->unlock();
7076 ConcurrentMarkSweepThread::desynchronize(true);
7077 ConcurrentMarkSweepThread::acknowledge_yield_request();
7078 _collector->stopTimer();
7079 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7080 if (PrintCMSStatistics != 0) {
7081 _collector->incrementYields();
7082 }
7083 _collector->icms_wait();
7084
7085 // See the comment in coordinator_yield()
7086 for (unsigned i = 0; i < CMSYieldSleepCount &&
7087 ConcurrentMarkSweepThread::should_yield() &&
7088 !CMSCollector::foregroundGCIsActive(); ++i) {
7089 os::sleep(Thread::current(), 1, false);
7090 ConcurrentMarkSweepThread::acknowledge_yield_request();
7091 }
7092
7093 ConcurrentMarkSweepThread::synchronize(true);
7094 _bit_map->lock()->lock_without_safepoint_check();
7095 _collector->startTimer();
7096 }
7097
7098 // This closure is used to rescan the marked objects on the dirty cards
7099 // in the mod union table and the card table proper. In the parallel
7100 // case, although the bitMap is shared, we do a single read so the
7101 // isMarked() query is "safe".
7102 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7103 // Ignore mark word because we are running concurrent with mutators
7104 assert(p->is_oop_or_null(true), "expected an oop or null");
7105 HeapWord* addr = (HeapWord*)p;
7106 assert(_span.contains(addr), "we are scanning the CMS generation");
7107 bool is_obj_array = false;
7108 #ifdef DEBUG
7109 if (!_parallel) {
7110 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7111 assert(_collector->overflow_list_is_empty(),
7112 "overflow list should be empty");
7113
7114 }
7115 #endif // DEBUG
7116 if (_bit_map->isMarked(addr)) {
7117 // Obj arrays are precisely marked, non-arrays are not;
7118 // so we scan objArrays precisely and non-arrays in their
7119 // entirety.
7120 if (p->is_objArray()) {
7121 is_obj_array = true;
7122 if (_parallel) {
7123 p->oop_iterate(_par_scan_closure, mr);
7124 } else {
7125 p->oop_iterate(_scan_closure, mr);
7126 }
7127 } else {
7128 if (_parallel) {
7129 p->oop_iterate(_par_scan_closure);
7130 } else {
7131 p->oop_iterate(_scan_closure);
7132 }
7133 }
7134 }
7135 #ifdef DEBUG
7136 if (!_parallel) {
7137 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7138 assert(_collector->overflow_list_is_empty(),
7139 "overflow list should be empty");
7140
7141 }
7142 #endif // DEBUG
7143 return is_obj_array;
7144 }
7145
7146 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7147 MemRegion span,
7148 CMSBitMap* bitMap, CMSMarkStack* markStack,
7149 CMSMarkStack* revisitStack,
7150 bool should_yield, bool verifying):
7151 _collector(collector),
7152 _span(span),
7153 _bitMap(bitMap),
7154 _mut(&collector->_modUnionTable),
7155 _markStack(markStack),
7156 _revisitStack(revisitStack),
7157 _yield(should_yield),
7158 _skipBits(0)
7159 {
7160 assert(_markStack->isEmpty(), "stack should be empty");
7161 _finger = _bitMap->startWord();
7162 _threshold = _finger;
7163 assert(_collector->_restart_addr == NULL, "Sanity check");
7164 assert(_span.contains(_finger), "Out of bounds _finger?");
7165 DEBUG_ONLY(_verifying = verifying;)
7166 }
7167
7168 void MarkFromRootsClosure::reset(HeapWord* addr) {
7169 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7170 assert(_span.contains(addr), "Out of bounds _finger?");
7171 _finger = addr;
7172 _threshold = (HeapWord*)round_to(
7173 (intptr_t)_finger, CardTableModRefBS::card_size);
7174 }
7175
7176 // Should revisit to see if this should be restructured for
7177 // greater efficiency.
7178 bool MarkFromRootsClosure::do_bit(size_t offset) {
7179 if (_skipBits > 0) {
7180 _skipBits--;
7181 return true;
7182 }
7183 // convert offset into a HeapWord*
7184 HeapWord* addr = _bitMap->startWord() + offset;
7185 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7186 "address out of range");
7187 assert(_bitMap->isMarked(addr), "tautology");
7188 if (_bitMap->isMarked(addr+1)) {
7189 // this is an allocated but not yet initialized object
7190 assert(_skipBits == 0, "tautology");
7191 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7192 oop p = oop(addr);
7193 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7194 DEBUG_ONLY(if (!_verifying) {)
7195 // We re-dirty the cards on which this object lies and increase
7196 // the _threshold so that we'll come back to scan this object
7197 // during the preclean or remark phase. (CMSCleanOnEnter)
7198 if (CMSCleanOnEnter) {
7199 size_t sz = _collector->block_size_using_printezis_bits(addr);
7200 HeapWord* end_card_addr = (HeapWord*)round_to(
7201 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7202 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7203 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7204 // Bump _threshold to end_card_addr; note that
7205 // _threshold cannot possibly exceed end_card_addr, anyhow.
7206 // This prevents future clearing of the card as the scan proceeds
7207 // to the right.
7208 assert(_threshold <= end_card_addr,
7209 "Because we are just scanning into this object");
7210 if (_threshold < end_card_addr) {
7211 _threshold = end_card_addr;
7212 }
7213 if (p->klass_or_null() != NULL) {
7214 // Redirty the range of cards...
7215 _mut->mark_range(redirty_range);
7216 } // ...else the setting of klass will dirty the card anyway.
7217 }
7218 DEBUG_ONLY(})
7219 return true;
7220 }
7221 }
7222 scanOopsInOop(addr);
7223 return true;
7224 }
7225
7226 // We take a break if we've been at this for a while,
7227 // so as to avoid monopolizing the locks involved.
7228 void MarkFromRootsClosure::do_yield_work() {
7229 // First give up the locks, then yield, then re-lock
7230 // We should probably use a constructor/destructor idiom to
7231 // do this unlock/lock or modify the MutexUnlocker class to
7232 // serve our purpose. XXX
7233 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7234 "CMS thread should hold CMS token");
7235 assert_lock_strong(_bitMap->lock());
7236 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7237 _bitMap->lock()->unlock();
7238 ConcurrentMarkSweepThread::desynchronize(true);
7239 ConcurrentMarkSweepThread::acknowledge_yield_request();
7240 _collector->stopTimer();
7241 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7242 if (PrintCMSStatistics != 0) {
7243 _collector->incrementYields();
7244 }
7245 _collector->icms_wait();
7246
7247 // See the comment in coordinator_yield()
7248 for (unsigned i = 0; i < CMSYieldSleepCount &&
7249 ConcurrentMarkSweepThread::should_yield() &&
7250 !CMSCollector::foregroundGCIsActive(); ++i) {
7251 os::sleep(Thread::current(), 1, false);
7252 ConcurrentMarkSweepThread::acknowledge_yield_request();
7253 }
7254
7255 ConcurrentMarkSweepThread::synchronize(true);
7256 _bitMap->lock()->lock_without_safepoint_check();
7257 _collector->startTimer();
7258 }
7259
7260 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7261 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7262 assert(_markStack->isEmpty(),
7263 "should drain stack to limit stack usage");
7264 // convert ptr to an oop preparatory to scanning
7265 oop obj = oop(ptr);
7266 // Ignore mark word in verification below, since we
7267 // may be running concurrent with mutators.
7268 assert(obj->is_oop(true), "should be an oop");
7269 assert(_finger <= ptr, "_finger runneth ahead");
7270 // advance the finger to right end of this object
7271 _finger = ptr + obj->size();
7272 assert(_finger > ptr, "we just incremented it above");
7273 // On large heaps, it may take us some time to get through
7274 // the marking phase (especially if running iCMS). During
7275 // this time it's possible that a lot of mutations have
7276 // accumulated in the card table and the mod union table --
7277 // these mutation records are redundant until we have
7278 // actually traced into the corresponding card.
7279 // Here, we check whether advancing the finger would make
7280 // us cross into a new card, and if so clear corresponding
7281 // cards in the MUT (preclean them in the card-table in the
7282 // future).
7283
7284 DEBUG_ONLY(if (!_verifying) {)
7285 // The clean-on-enter optimization is disabled by default,
7286 // until we fix 6178663.
7287 if (CMSCleanOnEnter && (_finger > _threshold)) {
7288 // [_threshold, _finger) represents the interval
7289 // of cards to be cleared in MUT (or precleaned in card table).
7290 // The set of cards to be cleared is all those that overlap
7291 // with the interval [_threshold, _finger); note that
7292 // _threshold is always kept card-aligned but _finger isn't
7293 // always card-aligned.
7294 HeapWord* old_threshold = _threshold;
7295 assert(old_threshold == (HeapWord*)round_to(
7296 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7297 "_threshold should always be card-aligned");
7298 _threshold = (HeapWord*)round_to(
7299 (intptr_t)_finger, CardTableModRefBS::card_size);
7300 MemRegion mr(old_threshold, _threshold);
7301 assert(!mr.is_empty(), "Control point invariant");
7302 assert(_span.contains(mr), "Should clear within span");
7303 // XXX When _finger crosses from old gen into perm gen
7304 // we may be doing unnecessary cleaning; do better in the
7305 // future by detecting that condition and clearing fewer
7306 // MUT/CT entries.
7307 _mut->clear_range(mr);
7308 }
7309 DEBUG_ONLY(})
7310 // Note: the finger doesn't advance while we drain
7311 // the stack below.
7312 PushOrMarkClosure pushOrMarkClosure(_collector,
7313 _span, _bitMap, _markStack,
7314 _revisitStack,
7315 _finger, this);
7316 bool res = _markStack->push(obj);
7317 assert(res, "Empty non-zero size stack should have space for single push");
7318 while (!_markStack->isEmpty()) {
7319 oop new_oop = _markStack->pop();
7320 // Skip verifying header mark word below because we are
7321 // running concurrent with mutators.
7322 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7323 // now scan this oop's oops
7324 new_oop->oop_iterate(&pushOrMarkClosure);
7325 do_yield_check();
7326 }
7327 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7328 }
7329
7330 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7331 CMSCollector* collector, MemRegion span,
7332 CMSBitMap* bit_map,
7333 OopTaskQueue* work_queue,
7334 CMSMarkStack* overflow_stack,
7335 CMSMarkStack* revisit_stack,
7336 bool should_yield):
7337 _collector(collector),
7338 _whole_span(collector->_span),
7339 _span(span),
7340 _bit_map(bit_map),
7341 _mut(&collector->_modUnionTable),
7342 _work_queue(work_queue),
7343 _overflow_stack(overflow_stack),
7344 _revisit_stack(revisit_stack),
7345 _yield(should_yield),
7346 _skip_bits(0),
7347 _task(task)
7348 {
7349 assert(_work_queue->size() == 0, "work_queue should be empty");
7350 _finger = span.start();
7351 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7352 assert(_span.contains(_finger), "Out of bounds _finger?");
7353 }
7354
7355 // Should revisit to see if this should be restructured for
7356 // greater efficiency.
7357 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7358 if (_skip_bits > 0) {
7359 _skip_bits--;
7360 return true;
7361 }
7362 // convert offset into a HeapWord*
7363 HeapWord* addr = _bit_map->startWord() + offset;
7364 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7365 "address out of range");
7366 assert(_bit_map->isMarked(addr), "tautology");
7367 if (_bit_map->isMarked(addr+1)) {
7368 // this is an allocated object that might not yet be initialized
7369 assert(_skip_bits == 0, "tautology");
7370 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7371 oop p = oop(addr);
7372 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7373 // in the case of Clean-on-Enter optimization, redirty card
7374 // and avoid clearing card by increasing the threshold.
7375 return true;
7376 }
7377 }
7378 scan_oops_in_oop(addr);
7379 return true;
7380 }
7381
7382 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7383 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7384 // Should we assert that our work queue is empty or
7385 // below some drain limit?
7386 assert(_work_queue->size() == 0,
7387 "should drain stack to limit stack usage");
7388 // convert ptr to an oop preparatory to scanning
7389 oop obj = oop(ptr);
7390 // Ignore mark word in verification below, since we
7391 // may be running concurrent with mutators.
7392 assert(obj->is_oop(true), "should be an oop");
7393 assert(_finger <= ptr, "_finger runneth ahead");
7394 // advance the finger to right end of this object
7395 _finger = ptr + obj->size();
7396 assert(_finger > ptr, "we just incremented it above");
7397 // On large heaps, it may take us some time to get through
7398 // the marking phase (especially if running iCMS). During
7399 // this time it's possible that a lot of mutations have
7400 // accumulated in the card table and the mod union table --
7401 // these mutation records are redundant until we have
7402 // actually traced into the corresponding card.
7403 // Here, we check whether advancing the finger would make
7404 // us cross into a new card, and if so clear corresponding
7405 // cards in the MUT (preclean them in the card-table in the
7406 // future).
7407
7408 // The clean-on-enter optimization is disabled by default,
7409 // until we fix 6178663.
7410 if (CMSCleanOnEnter && (_finger > _threshold)) {
7411 // [_threshold, _finger) represents the interval
7412 // of cards to be cleared in MUT (or precleaned in card table).
7413 // The set of cards to be cleared is all those that overlap
7414 // with the interval [_threshold, _finger); note that
7415 // _threshold is always kept card-aligned but _finger isn't
7416 // always card-aligned.
7417 HeapWord* old_threshold = _threshold;
7418 assert(old_threshold == (HeapWord*)round_to(
7419 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7420 "_threshold should always be card-aligned");
7421 _threshold = (HeapWord*)round_to(
7422 (intptr_t)_finger, CardTableModRefBS::card_size);
7423 MemRegion mr(old_threshold, _threshold);
7424 assert(!mr.is_empty(), "Control point invariant");
7425 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7426 // XXX When _finger crosses from old gen into perm gen
7427 // we may be doing unnecessary cleaning; do better in the
7428 // future by detecting that condition and clearing fewer
7429 // MUT/CT entries.
7430 _mut->clear_range(mr);
7431 }
7432
7433 // Note: the local finger doesn't advance while we drain
7434 // the stack below, but the global finger sure can and will.
7435 HeapWord** gfa = _task->global_finger_addr();
7436 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7437 _span, _bit_map,
7438 _work_queue,
7439 _overflow_stack,
7440 _revisit_stack,
7441 _finger,
7442 gfa, this);
7443 bool res = _work_queue->push(obj); // overflow could occur here
7444 assert(res, "Will hold once we use workqueues");
7445 while (true) {
7446 oop new_oop;
7447 if (!_work_queue->pop_local(new_oop)) {
7448 // We emptied our work_queue; check if there's stuff that can
7449 // be gotten from the overflow stack.
7450 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7451 _overflow_stack, _work_queue)) {
7452 do_yield_check();
7453 continue;
7454 } else { // done
7455 break;
7456 }
7457 }
7458 // Skip verifying header mark word below because we are
7459 // running concurrent with mutators.
7460 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7461 // now scan this oop's oops
7462 new_oop->oop_iterate(&pushOrMarkClosure);
7463 do_yield_check();
7464 }
7465 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7466 }
7467
7468 // Yield in response to a request from VM Thread or
7469 // from mutators.
7470 void Par_MarkFromRootsClosure::do_yield_work() {
7471 assert(_task != NULL, "sanity");
7472 _task->yield();
7473 }
7474
7475 // A variant of the above used for verifying CMS marking work.
7476 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7477 MemRegion span,
7478 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7479 CMSMarkStack* mark_stack):
7480 _collector(collector),
7481 _span(span),
7482 _verification_bm(verification_bm),
7483 _cms_bm(cms_bm),
7484 _mark_stack(mark_stack),
7485 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7486 mark_stack)
7487 {
7488 assert(_mark_stack->isEmpty(), "stack should be empty");
7489 _finger = _verification_bm->startWord();
7490 assert(_collector->_restart_addr == NULL, "Sanity check");
7491 assert(_span.contains(_finger), "Out of bounds _finger?");
7492 }
7493
7494 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7495 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7496 assert(_span.contains(addr), "Out of bounds _finger?");
7497 _finger = addr;
7498 }
7499
7500 // Should revisit to see if this should be restructured for
7501 // greater efficiency.
7502 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7503 // convert offset into a HeapWord*
7504 HeapWord* addr = _verification_bm->startWord() + offset;
7505 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7506 "address out of range");
7507 assert(_verification_bm->isMarked(addr), "tautology");
7508 assert(_cms_bm->isMarked(addr), "tautology");
7509
7510 assert(_mark_stack->isEmpty(),
7511 "should drain stack to limit stack usage");
7512 // convert addr to an oop preparatory to scanning
7513 oop obj = oop(addr);
7514 assert(obj->is_oop(), "should be an oop");
7515 assert(_finger <= addr, "_finger runneth ahead");
7516 // advance the finger to right end of this object
7517 _finger = addr + obj->size();
7518 assert(_finger > addr, "we just incremented it above");
7519 // Note: the finger doesn't advance while we drain
7520 // the stack below.
7521 bool res = _mark_stack->push(obj);
7522 assert(res, "Empty non-zero size stack should have space for single push");
7523 while (!_mark_stack->isEmpty()) {
7524 oop new_oop = _mark_stack->pop();
7525 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7526 // now scan this oop's oops
7527 new_oop->oop_iterate(&_pam_verify_closure);
7528 }
7529 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7530 return true;
7531 }
7532
7533 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7534 CMSCollector* collector, MemRegion span,
7535 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7536 CMSMarkStack* mark_stack):
7537 OopClosure(collector->ref_processor()),
7538 _collector(collector),
7539 _span(span),
7540 _verification_bm(verification_bm),
7541 _cms_bm(cms_bm),
7542 _mark_stack(mark_stack)
7543 { }
7544
7545 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7546 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7547
7548 // Upon stack overflow, we discard (part of) the stack,
7549 // remembering the least address amongst those discarded
7550 // in CMSCollector's _restart_address.
7551 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7552 // Remember the least grey address discarded
7553 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7554 _collector->lower_restart_addr(ra);
7555 _mark_stack->reset(); // discard stack contents
7556 _mark_stack->expand(); // expand the stack if possible
7557 }
7558
7559 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7560 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7561 HeapWord* addr = (HeapWord*)obj;
7562 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7563 // Oop lies in _span and isn't yet grey or black
7564 _verification_bm->mark(addr); // now grey
7565 if (!_cms_bm->isMarked(addr)) {
7566 oop(addr)->print();
7567 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7568 addr);
7569 fatal("... aborting");
7570 }
7571
7572 if (!_mark_stack->push(obj)) { // stack overflow
7573 if (PrintCMSStatistics != 0) {
7574 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7575 SIZE_FORMAT, _mark_stack->capacity());
7576 }
7577 assert(_mark_stack->isFull(), "Else push should have succeeded");
7578 handle_stack_overflow(addr);
7579 }
7580 // anything including and to the right of _finger
7581 // will be scanned as we iterate over the remainder of the
7582 // bit map
7583 }
7584 }
7585
7586 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7587 MemRegion span,
7588 CMSBitMap* bitMap, CMSMarkStack* markStack,
7589 CMSMarkStack* revisitStack,
7590 HeapWord* finger, MarkFromRootsClosure* parent) :
7591 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7592 _span(span),
7593 _bitMap(bitMap),
7594 _markStack(markStack),
7595 _finger(finger),
7596 _parent(parent)
7597 { }
7598
7599 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7600 MemRegion span,
7601 CMSBitMap* bit_map,
7602 OopTaskQueue* work_queue,
7603 CMSMarkStack* overflow_stack,
7604 CMSMarkStack* revisit_stack,
7605 HeapWord* finger,
7606 HeapWord** global_finger_addr,
7607 Par_MarkFromRootsClosure* parent) :
7608 Par_KlassRememberingOopClosure(collector,
7609 collector->ref_processor(),
7610 revisit_stack),
7611 _whole_span(collector->_span),
7612 _span(span),
7613 _bit_map(bit_map),
7614 _work_queue(work_queue),
7615 _overflow_stack(overflow_stack),
7616 _finger(finger),
7617 _global_finger_addr(global_finger_addr),
7618 _parent(parent)
7619 { }
7620
7621 // Assumes thread-safe access by callers, who are
7622 // responsible for mutual exclusion.
7623 void CMSCollector::lower_restart_addr(HeapWord* low) {
7624 assert(_span.contains(low), "Out of bounds addr");
7625 if (_restart_addr == NULL) {
7626 _restart_addr = low;
7627 } else {
7628 _restart_addr = MIN2(_restart_addr, low);
7629 }
7630 }
7631
7632 // Upon stack overflow, we discard (part of) the stack,
7633 // remembering the least address amongst those discarded
7634 // in CMSCollector's _restart_address.
7635 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7636 // Remember the least grey address discarded
7637 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7638 _collector->lower_restart_addr(ra);
7639 _markStack->reset(); // discard stack contents
7640 _markStack->expand(); // expand the stack if possible
7641 }
7642
7643 // Upon stack overflow, we discard (part of) the stack,
7644 // remembering the least address amongst those discarded
7645 // in CMSCollector's _restart_address.
7646 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7647 // We need to do this under a mutex to prevent other
7648 // workers from interfering with the work done below.
7649 MutexLockerEx ml(_overflow_stack->par_lock(),
7650 Mutex::_no_safepoint_check_flag);
7651 // Remember the least grey address discarded
7652 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7653 _collector->lower_restart_addr(ra);
7654 _overflow_stack->reset(); // discard stack contents
7655 _overflow_stack->expand(); // expand the stack if possible
7656 }
7657
7658 void PushOrMarkClosure::do_oop(oop obj) {
7659 // Ignore mark word because we are running concurrent with mutators.
7660 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7661 HeapWord* addr = (HeapWord*)obj;
7662 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7663 // Oop lies in _span and isn't yet grey or black
7664 _bitMap->mark(addr); // now grey
7665 if (addr < _finger) {
7666 // the bit map iteration has already either passed, or
7667 // sampled, this bit in the bit map; we'll need to
7668 // use the marking stack to scan this oop's oops.
7669 bool simulate_overflow = false;
7670 NOT_PRODUCT(
7671 if (CMSMarkStackOverflowALot &&
7672 _collector->simulate_overflow()) {
7673 // simulate a stack overflow
7674 simulate_overflow = true;
7675 }
7676 )
7677 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7678 if (PrintCMSStatistics != 0) {
7679 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7680 SIZE_FORMAT, _markStack->capacity());
7681 }
7682 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7683 handle_stack_overflow(addr);
7684 }
7685 }
7686 // anything including and to the right of _finger
7687 // will be scanned as we iterate over the remainder of the
7688 // bit map
7689 do_yield_check();
7690 }
7691 }
7692
7693 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7694 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7695
7696 void Par_PushOrMarkClosure::do_oop(oop obj) {
7697 // Ignore mark word because we are running concurrent with mutators.
7698 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7699 HeapWord* addr = (HeapWord*)obj;
7700 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7701 // Oop lies in _span and isn't yet grey or black
7702 // We read the global_finger (volatile read) strictly after marking oop
7703 bool res = _bit_map->par_mark(addr); // now grey
7704 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7705 // Should we push this marked oop on our stack?
7706 // -- if someone else marked it, nothing to do
7707 // -- if target oop is above global finger nothing to do
7708 // -- if target oop is in chunk and above local finger
7709 // then nothing to do
7710 // -- else push on work queue
7711 if ( !res // someone else marked it, they will deal with it
7712 || (addr >= *gfa) // will be scanned in a later task
7713 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7714 return;
7715 }
7716 // the bit map iteration has already either passed, or
7717 // sampled, this bit in the bit map; we'll need to
7718 // use the marking stack to scan this oop's oops.
7719 bool simulate_overflow = false;
7720 NOT_PRODUCT(
7721 if (CMSMarkStackOverflowALot &&
7722 _collector->simulate_overflow()) {
7723 // simulate a stack overflow
7724 simulate_overflow = true;
7725 }
7726 )
7727 if (simulate_overflow ||
7728 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7729 // stack overflow
7730 if (PrintCMSStatistics != 0) {
7731 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7732 SIZE_FORMAT, _overflow_stack->capacity());
7733 }
7734 // We cannot assert that the overflow stack is full because
7735 // it may have been emptied since.
7736 assert(simulate_overflow ||
7737 _work_queue->size() == _work_queue->max_elems(),
7738 "Else push should have succeeded");
7739 handle_stack_overflow(addr);
7740 }
7741 do_yield_check();
7742 }
7743 }
7744
7745 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7746 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7747
7748 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7749 ReferenceProcessor* rp,
7750 CMSMarkStack* revisit_stack) :
7751 OopClosure(rp),
7752 _collector(collector),
7753 _revisit_stack(revisit_stack),
7754 _should_remember_klasses(collector->should_unload_classes()) {}
7755
7756 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7757 MemRegion span,
7758 ReferenceProcessor* rp,
7759 CMSBitMap* bit_map,
7760 CMSBitMap* mod_union_table,
7761 CMSMarkStack* mark_stack,
7762 CMSMarkStack* revisit_stack,
7763 bool concurrent_precleaning):
7764 KlassRememberingOopClosure(collector, rp, revisit_stack),
7765 _span(span),
7766 _bit_map(bit_map),
7767 _mod_union_table(mod_union_table),
7768 _mark_stack(mark_stack),
7769 _concurrent_precleaning(concurrent_precleaning)
7770 {
7771 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7772 }
7773
7774 // Grey object rescan during pre-cleaning and second checkpoint phases --
7775 // the non-parallel version (the parallel version appears further below.)
7776 void PushAndMarkClosure::do_oop(oop obj) {
7777 // Ignore mark word verification. If during concurrent precleaning,
7778 // the object monitor may be locked. If during the checkpoint
7779 // phases, the object may already have been reached by a different
7780 // path and may be at the end of the global overflow list (so
7781 // the mark word may be NULL).
7782 assert(obj->is_oop_or_null(true /* ignore mark word */),
7783 "expected an oop or NULL");
7784 HeapWord* addr = (HeapWord*)obj;
7785 // Check if oop points into the CMS generation
7786 // and is not marked
7787 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7788 // a white object ...
7789 _bit_map->mark(addr); // ... now grey
7790 // push on the marking stack (grey set)
7791 bool simulate_overflow = false;
7792 NOT_PRODUCT(
7793 if (CMSMarkStackOverflowALot &&
7794 _collector->simulate_overflow()) {
7795 // simulate a stack overflow
7796 simulate_overflow = true;
7797 }
7798 )
7799 if (simulate_overflow || !_mark_stack->push(obj)) {
7800 if (_concurrent_precleaning) {
7801 // During precleaning we can just dirty the appropriate card(s)
7802 // in the mod union table, thus ensuring that the object remains
7803 // in the grey set and continue. In the case of object arrays
7804 // we need to dirty all of the cards that the object spans,
7805 // since the rescan of object arrays will be limited to the
7806 // dirty cards.
7807 // Note that no one can be intefering with us in this action
7808 // of dirtying the mod union table, so no locking or atomics
7809 // are required.
7810 if (obj->is_objArray()) {
7811 size_t sz = obj->size();
7812 HeapWord* end_card_addr = (HeapWord*)round_to(
7813 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7814 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7815 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7816 _mod_union_table->mark_range(redirty_range);
7817 } else {
7818 _mod_union_table->mark(addr);
7819 }
7820 _collector->_ser_pmc_preclean_ovflw++;
7821 } else {
7822 // During the remark phase, we need to remember this oop
7823 // in the overflow list.
7824 _collector->push_on_overflow_list(obj);
7825 _collector->_ser_pmc_remark_ovflw++;
7826 }
7827 }
7828 }
7829 }
7830
7831 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7832 MemRegion span,
7833 ReferenceProcessor* rp,
7834 CMSBitMap* bit_map,
7835 OopTaskQueue* work_queue,
7836 CMSMarkStack* revisit_stack):
7837 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7838 _span(span),
7839 _bit_map(bit_map),
7840 _work_queue(work_queue)
7841 {
7842 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7843 }
7844
7845 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7846 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7847
7848 // Grey object rescan during second checkpoint phase --
7849 // the parallel version.
7850 void Par_PushAndMarkClosure::do_oop(oop obj) {
7851 // In the assert below, we ignore the mark word because
7852 // this oop may point to an already visited object that is
7853 // on the overflow stack (in which case the mark word has
7854 // been hijacked for chaining into the overflow stack --
7855 // if this is the last object in the overflow stack then
7856 // its mark word will be NULL). Because this object may
7857 // have been subsequently popped off the global overflow
7858 // stack, and the mark word possibly restored to the prototypical
7859 // value, by the time we get to examined this failing assert in
7860 // the debugger, is_oop_or_null(false) may subsequently start
7861 // to hold.
7862 assert(obj->is_oop_or_null(true),
7863 "expected an oop or NULL");
7864 HeapWord* addr = (HeapWord*)obj;
7865 // Check if oop points into the CMS generation
7866 // and is not marked
7867 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7868 // a white object ...
7869 // If we manage to "claim" the object, by being the
7870 // first thread to mark it, then we push it on our
7871 // marking stack
7872 if (_bit_map->par_mark(addr)) { // ... now grey
7873 // push on work queue (grey set)
7874 bool simulate_overflow = false;
7875 NOT_PRODUCT(
7876 if (CMSMarkStackOverflowALot &&
7877 _collector->par_simulate_overflow()) {
7878 // simulate a stack overflow
7879 simulate_overflow = true;
7880 }
7881 )
7882 if (simulate_overflow || !_work_queue->push(obj)) {
7883 _collector->par_push_on_overflow_list(obj);
7884 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7885 }
7886 } // Else, some other thread got there first
7887 }
7888 }
7889
7890 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7891 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7892
7893 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7894 // TBD
7895 }
7896
7897 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7898 // TBD
7899 }
7900
7901 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7902 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7903 Mutex* bml = _collector->bitMapLock();
7904 assert_lock_strong(bml);
7905 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7906 "CMS thread should hold CMS token");
7907
7908 bml->unlock();
7909 ConcurrentMarkSweepThread::desynchronize(true);
7910
7911 ConcurrentMarkSweepThread::acknowledge_yield_request();
7912
7913 _collector->stopTimer();
7914 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7915 if (PrintCMSStatistics != 0) {
7916 _collector->incrementYields();
7917 }
7918 _collector->icms_wait();
7919
7920 // See the comment in coordinator_yield()
7921 for (unsigned i = 0; i < CMSYieldSleepCount &&
7922 ConcurrentMarkSweepThread::should_yield() &&
7923 !CMSCollector::foregroundGCIsActive(); ++i) {
7924 os::sleep(Thread::current(), 1, false);
7925 ConcurrentMarkSweepThread::acknowledge_yield_request();
7926 }
7927
7928 ConcurrentMarkSweepThread::synchronize(true);
7929 bml->lock();
7930
7931 _collector->startTimer();
7932 }
7933
7934 bool CMSPrecleanRefsYieldClosure::should_return() {
7935 if (ConcurrentMarkSweepThread::should_yield()) {
7936 do_yield_work();
7937 }
7938 return _collector->foregroundGCIsActive();
7939 }
7940
7941 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7942 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7943 "mr should be aligned to start at a card boundary");
7944 // We'd like to assert:
7945 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7946 // "mr should be a range of cards");
7947 // However, that would be too strong in one case -- the last
7948 // partition ends at _unallocated_block which, in general, can be
7949 // an arbitrary boundary, not necessarily card aligned.
7950 if (PrintCMSStatistics != 0) {
7951 _num_dirty_cards +=
7952 mr.word_size()/CardTableModRefBS::card_size_in_words;
7953 }
7954 _space->object_iterate_mem(mr, &_scan_cl);
7955 }
7956
7957 SweepClosure::SweepClosure(CMSCollector* collector,
7958 ConcurrentMarkSweepGeneration* g,
7959 CMSBitMap* bitMap, bool should_yield) :
7960 _collector(collector),
7961 _g(g),
7962 _sp(g->cmsSpace()),
7963 _limit(_sp->sweep_limit()),
7964 _freelistLock(_sp->freelistLock()),
7965 _bitMap(bitMap),
7966 _yield(should_yield),
7967 _inFreeRange(false), // No free range at beginning of sweep
7968 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7969 _lastFreeRangeCoalesced(false),
7970 _freeFinger(g->used_region().start())
7971 {
7972 NOT_PRODUCT(
7973 _numObjectsFreed = 0;
7974 _numWordsFreed = 0;
7975 _numObjectsLive = 0;
7976 _numWordsLive = 0;
7977 _numObjectsAlreadyFree = 0;
7978 _numWordsAlreadyFree = 0;
7979 _last_fc = NULL;
7980
7981 _sp->initializeIndexedFreeListArrayReturnedBytes();
7982 _sp->dictionary()->initialize_dict_returned_bytes();
7983 )
7984 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7985 "sweep _limit out of bounds");
7986 if (CMSTraceSweeper) {
7987 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7988 _limit);
7989 }
7990 }
7991
7992 void SweepClosure::print_on(outputStream* st) const {
7993 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7994 _sp->bottom(), _sp->end());
7995 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7996 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7997 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7998 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7999 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8000 }
8001
8002 #ifndef PRODUCT
8003 // Assertion checking only: no useful work in product mode --
8004 // however, if any of the flags below become product flags,
8005 // you may need to review this code to see if it needs to be
8006 // enabled in product mode.
8007 SweepClosure::~SweepClosure() {
8008 assert_lock_strong(_freelistLock);
8009 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8010 "sweep _limit out of bounds");
8011 if (inFreeRange()) {
8012 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8013 print();
8014 ShouldNotReachHere();
8015 }
8016 if (Verbose && PrintGC) {
8017 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8018 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8019 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8020 SIZE_FORMAT" bytes "
8021 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8022 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8023 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8024 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8025 * sizeof(HeapWord);
8026 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8027
8028 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8029 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8030 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8031 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8032 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8033 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8034 indexListReturnedBytes);
8035 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8036 dict_returned_bytes);
8037 }
8038 }
8039 if (CMSTraceSweeper) {
8040 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8041 _limit);
8042 }
8043 }
8044 #endif // PRODUCT
8045
8046 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8047 bool freeRangeInFreeLists) {
8048 if (CMSTraceSweeper) {
8049 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8050 freeFinger, freeRangeInFreeLists);
8051 }
8052 assert(!inFreeRange(), "Trampling existing free range");
8053 set_inFreeRange(true);
8054 set_lastFreeRangeCoalesced(false);
8055
8056 set_freeFinger(freeFinger);
8057 set_freeRangeInFreeLists(freeRangeInFreeLists);
8058 if (CMSTestInFreeList) {
8059 if (freeRangeInFreeLists) {
8060 FreeChunk* fc = (FreeChunk*) freeFinger;
8061 assert(fc->is_free(), "A chunk on the free list should be free.");
8062 assert(fc->size() > 0, "Free range should have a size");
8063 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8064 }
8065 }
8066 }
8067
8068 // Note that the sweeper runs concurrently with mutators. Thus,
8069 // it is possible for direct allocation in this generation to happen
8070 // in the middle of the sweep. Note that the sweeper also coalesces
8071 // contiguous free blocks. Thus, unless the sweeper and the allocator
8072 // synchronize appropriately freshly allocated blocks may get swept up.
8073 // This is accomplished by the sweeper locking the free lists while
8074 // it is sweeping. Thus blocks that are determined to be free are
8075 // indeed free. There is however one additional complication:
8076 // blocks that have been allocated since the final checkpoint and
8077 // mark, will not have been marked and so would be treated as
8078 // unreachable and swept up. To prevent this, the allocator marks
8079 // the bit map when allocating during the sweep phase. This leads,
8080 // however, to a further complication -- objects may have been allocated
8081 // but not yet initialized -- in the sense that the header isn't yet
8082 // installed. The sweeper can not then determine the size of the block
8083 // in order to skip over it. To deal with this case, we use a technique
8084 // (due to Printezis) to encode such uninitialized block sizes in the
8085 // bit map. Since the bit map uses a bit per every HeapWord, but the
8086 // CMS generation has a minimum object size of 3 HeapWords, it follows
8087 // that "normal marks" won't be adjacent in the bit map (there will
8088 // always be at least two 0 bits between successive 1 bits). We make use
8089 // of these "unused" bits to represent uninitialized blocks -- the bit
8090 // corresponding to the start of the uninitialized object and the next
8091 // bit are both set. Finally, a 1 bit marks the end of the object that
8092 // started with the two consecutive 1 bits to indicate its potentially
8093 // uninitialized state.
8094
8095 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8096 FreeChunk* fc = (FreeChunk*)addr;
8097 size_t res;
8098
8099 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8100 // than "addr == _limit" because although _limit was a block boundary when
8101 // we started the sweep, it may no longer be one because heap expansion
8102 // may have caused us to coalesce the block ending at the address _limit
8103 // with a newly expanded chunk (this happens when _limit was set to the
8104 // previous _end of the space), so we may have stepped past _limit:
8105 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8106 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8107 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8108 "sweep _limit out of bounds");
8109 assert(addr < _sp->end(), "addr out of bounds");
8110 // Flush any free range we might be holding as a single
8111 // coalesced chunk to the appropriate free list.
8112 if (inFreeRange()) {
8113 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8114 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8115 flush_cur_free_chunk(freeFinger(),
8116 pointer_delta(addr, freeFinger()));
8117 if (CMSTraceSweeper) {
8118 gclog_or_tty->print("Sweep: last chunk: ");
8119 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8120 "[coalesced:"SIZE_FORMAT"]\n",
8121 freeFinger(), pointer_delta(addr, freeFinger()),
8122 lastFreeRangeCoalesced());
8123 }
8124 }
8125
8126 // help the iterator loop finish
8127 return pointer_delta(_sp->end(), addr);
8128 }
8129
8130 assert(addr < _limit, "sweep invariant");
8131 // check if we should yield
8132 do_yield_check(addr);
8133 if (fc->is_free()) {
8134 // Chunk that is already free
8135 res = fc->size();
8136 do_already_free_chunk(fc);
8137 debug_only(_sp->verifyFreeLists());
8138 // If we flush the chunk at hand in lookahead_and_flush()
8139 // and it's coalesced with a preceding chunk, then the
8140 // process of "mangling" the payload of the coalesced block
8141 // will cause erasure of the size information from the
8142 // (erstwhile) header of all the coalesced blocks but the
8143 // first, so the first disjunct in the assert will not hold
8144 // in that specific case (in which case the second disjunct
8145 // will hold).
8146 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8147 "Otherwise the size info doesn't change at this step");
8148 NOT_PRODUCT(
8149 _numObjectsAlreadyFree++;
8150 _numWordsAlreadyFree += res;
8151 )
8152 NOT_PRODUCT(_last_fc = fc;)
8153 } else if (!_bitMap->isMarked(addr)) {
8154 // Chunk is fresh garbage
8155 res = do_garbage_chunk(fc);
8156 debug_only(_sp->verifyFreeLists());
8157 NOT_PRODUCT(
8158 _numObjectsFreed++;
8159 _numWordsFreed += res;
8160 )
8161 } else {
8162 // Chunk that is alive.
8163 res = do_live_chunk(fc);
8164 debug_only(_sp->verifyFreeLists());
8165 NOT_PRODUCT(
8166 _numObjectsLive++;
8167 _numWordsLive += res;
8168 )
8169 }
8170 return res;
8171 }
8172
8173 // For the smart allocation, record following
8174 // split deaths - a free chunk is removed from its free list because
8175 // it is being split into two or more chunks.
8176 // split birth - a free chunk is being added to its free list because
8177 // a larger free chunk has been split and resulted in this free chunk.
8178 // coal death - a free chunk is being removed from its free list because
8179 // it is being coalesced into a large free chunk.
8180 // coal birth - a free chunk is being added to its free list because
8181 // it was created when two or more free chunks where coalesced into
8182 // this free chunk.
8183 //
8184 // These statistics are used to determine the desired number of free
8185 // chunks of a given size. The desired number is chosen to be relative
8186 // to the end of a CMS sweep. The desired number at the end of a sweep
8187 // is the
8188 // count-at-end-of-previous-sweep (an amount that was enough)
8189 // - count-at-beginning-of-current-sweep (the excess)
8190 // + split-births (gains in this size during interval)
8191 // - split-deaths (demands on this size during interval)
8192 // where the interval is from the end of one sweep to the end of the
8193 // next.
8194 //
8195 // When sweeping the sweeper maintains an accumulated chunk which is
8196 // the chunk that is made up of chunks that have been coalesced. That
8197 // will be termed the left-hand chunk. A new chunk of garbage that
8198 // is being considered for coalescing will be referred to as the
8199 // right-hand chunk.
8200 //
8201 // When making a decision on whether to coalesce a right-hand chunk with
8202 // the current left-hand chunk, the current count vs. the desired count
8203 // of the left-hand chunk is considered. Also if the right-hand chunk
8204 // is near the large chunk at the end of the heap (see
8205 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8206 // left-hand chunk is coalesced.
8207 //
8208 // When making a decision about whether to split a chunk, the desired count
8209 // vs. the current count of the candidate to be split is also considered.
8210 // If the candidate is underpopulated (currently fewer chunks than desired)
8211 // a chunk of an overpopulated (currently more chunks than desired) size may
8212 // be chosen. The "hint" associated with a free list, if non-null, points
8213 // to a free list which may be overpopulated.
8214 //
8215
8216 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8217 const size_t size = fc->size();
8218 // Chunks that cannot be coalesced are not in the
8219 // free lists.
8220 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8221 assert(_sp->verify_chunk_in_free_list(fc),
8222 "free chunk should be in free lists");
8223 }
8224 // a chunk that is already free, should not have been
8225 // marked in the bit map
8226 HeapWord* const addr = (HeapWord*) fc;
8227 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8228 // Verify that the bit map has no bits marked between
8229 // addr and purported end of this block.
8230 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8231
8232 // Some chunks cannot be coalesced under any circumstances.
8233 // See the definition of cantCoalesce().
8234 if (!fc->cantCoalesce()) {
8235 // This chunk can potentially be coalesced.
8236 if (_sp->adaptive_freelists()) {
8237 // All the work is done in
8238 do_post_free_or_garbage_chunk(fc, size);
8239 } else { // Not adaptive free lists
8240 // this is a free chunk that can potentially be coalesced by the sweeper;
8241 if (!inFreeRange()) {
8242 // if the next chunk is a free block that can't be coalesced
8243 // it doesn't make sense to remove this chunk from the free lists
8244 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8245 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8246 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8247 nextChunk->is_free() && // ... which is free...
8248 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8249 // nothing to do
8250 } else {
8251 // Potentially the start of a new free range:
8252 // Don't eagerly remove it from the free lists.
8253 // No need to remove it if it will just be put
8254 // back again. (Also from a pragmatic point of view
8255 // if it is a free block in a region that is beyond
8256 // any allocated blocks, an assertion will fail)
8257 // Remember the start of a free run.
8258 initialize_free_range(addr, true);
8259 // end - can coalesce with next chunk
8260 }
8261 } else {
8262 // the midst of a free range, we are coalescing
8263 print_free_block_coalesced(fc);
8264 if (CMSTraceSweeper) {
8265 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8266 }
8267 // remove it from the free lists
8268 _sp->removeFreeChunkFromFreeLists(fc);
8269 set_lastFreeRangeCoalesced(true);
8270 // If the chunk is being coalesced and the current free range is
8271 // in the free lists, remove the current free range so that it
8272 // will be returned to the free lists in its entirety - all
8273 // the coalesced pieces included.
8274 if (freeRangeInFreeLists()) {
8275 FreeChunk* ffc = (FreeChunk*) freeFinger();
8276 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8277 "Size of free range is inconsistent with chunk size.");
8278 if (CMSTestInFreeList) {
8279 assert(_sp->verify_chunk_in_free_list(ffc),
8280 "free range is not in free lists");
8281 }
8282 _sp->removeFreeChunkFromFreeLists(ffc);
8283 set_freeRangeInFreeLists(false);
8284 }
8285 }
8286 }
8287 // Note that if the chunk is not coalescable (the else arm
8288 // below), we unconditionally flush, without needing to do
8289 // a "lookahead," as we do below.
8290 if (inFreeRange()) lookahead_and_flush(fc, size);
8291 } else {
8292 // Code path common to both original and adaptive free lists.
8293
8294 // cant coalesce with previous block; this should be treated
8295 // as the end of a free run if any
8296 if (inFreeRange()) {
8297 // we kicked some butt; time to pick up the garbage
8298 assert(freeFinger() < addr, "freeFinger points too high");
8299 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8300 }
8301 // else, nothing to do, just continue
8302 }
8303 }
8304
8305 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8306 // This is a chunk of garbage. It is not in any free list.
8307 // Add it to a free list or let it possibly be coalesced into
8308 // a larger chunk.
8309 HeapWord* const addr = (HeapWord*) fc;
8310 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8311
8312 if (_sp->adaptive_freelists()) {
8313 // Verify that the bit map has no bits marked between
8314 // addr and purported end of just dead object.
8315 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8316
8317 do_post_free_or_garbage_chunk(fc, size);
8318 } else {
8319 if (!inFreeRange()) {
8320 // start of a new free range
8321 assert(size > 0, "A free range should have a size");
8322 initialize_free_range(addr, false);
8323 } else {
8324 // this will be swept up when we hit the end of the
8325 // free range
8326 if (CMSTraceSweeper) {
8327 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8328 }
8329 // If the chunk is being coalesced and the current free range is
8330 // in the free lists, remove the current free range so that it
8331 // will be returned to the free lists in its entirety - all
8332 // the coalesced pieces included.
8333 if (freeRangeInFreeLists()) {
8334 FreeChunk* ffc = (FreeChunk*)freeFinger();
8335 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8336 "Size of free range is inconsistent with chunk size.");
8337 if (CMSTestInFreeList) {
8338 assert(_sp->verify_chunk_in_free_list(ffc),
8339 "free range is not in free lists");
8340 }
8341 _sp->removeFreeChunkFromFreeLists(ffc);
8342 set_freeRangeInFreeLists(false);
8343 }
8344 set_lastFreeRangeCoalesced(true);
8345 }
8346 // this will be swept up when we hit the end of the free range
8347
8348 // Verify that the bit map has no bits marked between
8349 // addr and purported end of just dead object.
8350 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8351 }
8352 assert(_limit >= addr + size,
8353 "A freshly garbage chunk can't possibly straddle over _limit");
8354 if (inFreeRange()) lookahead_and_flush(fc, size);
8355 return size;
8356 }
8357
8358 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8359 HeapWord* addr = (HeapWord*) fc;
8360 // The sweeper has just found a live object. Return any accumulated
8361 // left hand chunk to the free lists.
8362 if (inFreeRange()) {
8363 assert(freeFinger() < addr, "freeFinger points too high");
8364 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8365 }
8366
8367 // This object is live: we'd normally expect this to be
8368 // an oop, and like to assert the following:
8369 // assert(oop(addr)->is_oop(), "live block should be an oop");
8370 // However, as we commented above, this may be an object whose
8371 // header hasn't yet been initialized.
8372 size_t size;
8373 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8374 if (_bitMap->isMarked(addr + 1)) {
8375 // Determine the size from the bit map, rather than trying to
8376 // compute it from the object header.
8377 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8378 size = pointer_delta(nextOneAddr + 1, addr);
8379 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8380 "alignment problem");
8381
8382 #ifdef DEBUG
8383 if (oop(addr)->klass_or_null() != NULL &&
8384 ( !_collector->should_unload_classes()
8385 || (oop(addr)->is_parsable()) &&
8386 oop(addr)->is_conc_safe())) {
8387 // Ignore mark word because we are running concurrent with mutators
8388 assert(oop(addr)->is_oop(true), "live block should be an oop");
8389 // is_conc_safe is checked before performing this assertion
8390 // because an object that is not is_conc_safe may yet have
8391 // the return from size() correct.
8392 assert(size ==
8393 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8394 "P-mark and computed size do not agree");
8395 }
8396 #endif
8397
8398 } else {
8399 // This should be an initialized object that's alive.
8400 assert(oop(addr)->klass_or_null() != NULL &&
8401 (!_collector->should_unload_classes()
8402 || oop(addr)->is_parsable()),
8403 "Should be an initialized object");
8404 // Note that there are objects used during class redefinition,
8405 // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8406 // which are discarded with their is_conc_safe state still
8407 // false. These object may be floating garbage so may be
8408 // seen here. If they are floating garbage their size
8409 // should be attainable from their klass. Do not that
8410 // is_conc_safe() is true for oop(addr).
8411 // Ignore mark word because we are running concurrent with mutators
8412 assert(oop(addr)->is_oop(true), "live block should be an oop");
8413 // Verify that the bit map has no bits marked between
8414 // addr and purported end of this block.
8415 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8416 assert(size >= 3, "Necessary for Printezis marks to work");
8417 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8418 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8419 }
8420 return size;
8421 }
8422
8423 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8424 size_t chunkSize) {
8425 // do_post_free_or_garbage_chunk() should only be called in the case
8426 // of the adaptive free list allocator.
8427 const bool fcInFreeLists = fc->is_free();
8428 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8429 assert((HeapWord*)fc <= _limit, "sweep invariant");
8430 if (CMSTestInFreeList && fcInFreeLists) {
8431 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8432 }
8433
8434 if (CMSTraceSweeper) {
8435 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8436 }
8437
8438 HeapWord* const fc_addr = (HeapWord*) fc;
8439
8440 bool coalesce;
8441 const size_t left = pointer_delta(fc_addr, freeFinger());
8442 const size_t right = chunkSize;
8443 switch (FLSCoalescePolicy) {
8444 // numeric value forms a coalition aggressiveness metric
8445 case 0: { // never coalesce
8446 coalesce = false;
8447 break;
8448 }
8449 case 1: { // coalesce if left & right chunks on overpopulated lists
8450 coalesce = _sp->coalOverPopulated(left) &&
8451 _sp->coalOverPopulated(right);
8452 break;
8453 }
8454 case 2: { // coalesce if left chunk on overpopulated list (default)
8455 coalesce = _sp->coalOverPopulated(left);
8456 break;
8457 }
8458 case 3: { // coalesce if left OR right chunk on overpopulated list
8459 coalesce = _sp->coalOverPopulated(left) ||
8460 _sp->coalOverPopulated(right);
8461 break;
8462 }
8463 case 4: { // always coalesce
8464 coalesce = true;
8465 break;
8466 }
8467 default:
8468 ShouldNotReachHere();
8469 }
8470
8471 // Should the current free range be coalesced?
8472 // If the chunk is in a free range and either we decided to coalesce above
8473 // or the chunk is near the large block at the end of the heap
8474 // (isNearLargestChunk() returns true), then coalesce this chunk.
8475 const bool doCoalesce = inFreeRange()
8476 && (coalesce || _g->isNearLargestChunk(fc_addr));
8477 if (doCoalesce) {
8478 // Coalesce the current free range on the left with the new
8479 // chunk on the right. If either is on a free list,
8480 // it must be removed from the list and stashed in the closure.
8481 if (freeRangeInFreeLists()) {
8482 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8483 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8484 "Size of free range is inconsistent with chunk size.");
8485 if (CMSTestInFreeList) {
8486 assert(_sp->verify_chunk_in_free_list(ffc),
8487 "Chunk is not in free lists");
8488 }
8489 _sp->coalDeath(ffc->size());
8490 _sp->removeFreeChunkFromFreeLists(ffc);
8491 set_freeRangeInFreeLists(false);
8492 }
8493 if (fcInFreeLists) {
8494 _sp->coalDeath(chunkSize);
8495 assert(fc->size() == chunkSize,
8496 "The chunk has the wrong size or is not in the free lists");
8497 _sp->removeFreeChunkFromFreeLists(fc);
8498 }
8499 set_lastFreeRangeCoalesced(true);
8500 print_free_block_coalesced(fc);
8501 } else { // not in a free range and/or should not coalesce
8502 // Return the current free range and start a new one.
8503 if (inFreeRange()) {
8504 // In a free range but cannot coalesce with the right hand chunk.
8505 // Put the current free range into the free lists.
8506 flush_cur_free_chunk(freeFinger(),
8507 pointer_delta(fc_addr, freeFinger()));
8508 }
8509 // Set up for new free range. Pass along whether the right hand
8510 // chunk is in the free lists.
8511 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8512 }
8513 }
8514
8515 // Lookahead flush:
8516 // If we are tracking a free range, and this is the last chunk that
8517 // we'll look at because its end crosses past _limit, we'll preemptively
8518 // flush it along with any free range we may be holding on to. Note that
8519 // this can be the case only for an already free or freshly garbage
8520 // chunk. If this block is an object, it can never straddle
8521 // over _limit. The "straddling" occurs when _limit is set at
8522 // the previous end of the space when this cycle started, and
8523 // a subsequent heap expansion caused the previously co-terminal
8524 // free block to be coalesced with the newly expanded portion,
8525 // thus rendering _limit a non-block-boundary making it dangerous
8526 // for the sweeper to step over and examine.
8527 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8528 assert(inFreeRange(), "Should only be called if currently in a free range.");
8529 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8530 assert(_sp->used_region().contains(eob - 1),
8531 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8532 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8533 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8534 if (eob >= _limit) {
8535 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8536 if (CMSTraceSweeper) {
8537 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8538 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8539 "[" PTR_FORMAT "," PTR_FORMAT ")",
8540 _limit, fc, eob, _sp->bottom(), _sp->end());
8541 }
8542 // Return the storage we are tracking back into the free lists.
8543 if (CMSTraceSweeper) {
8544 gclog_or_tty->print_cr("Flushing ... ");
8545 }
8546 assert(freeFinger() < eob, "Error");
8547 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8548 }
8549 }
8550
8551 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8552 assert(inFreeRange(), "Should only be called if currently in a free range.");
8553 assert(size > 0,
8554 "A zero sized chunk cannot be added to the free lists.");
8555 if (!freeRangeInFreeLists()) {
8556 if (CMSTestInFreeList) {
8557 FreeChunk* fc = (FreeChunk*) chunk;
8558 fc->set_size(size);
8559 assert(!_sp->verify_chunk_in_free_list(fc),
8560 "chunk should not be in free lists yet");
8561 }
8562 if (CMSTraceSweeper) {
8563 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8564 chunk, size);
8565 }
8566 // A new free range is going to be starting. The current
8567 // free range has not been added to the free lists yet or
8568 // was removed so add it back.
8569 // If the current free range was coalesced, then the death
8570 // of the free range was recorded. Record a birth now.
8571 if (lastFreeRangeCoalesced()) {
8572 _sp->coalBirth(size);
8573 }
8574 _sp->addChunkAndRepairOffsetTable(chunk, size,
8575 lastFreeRangeCoalesced());
8576 } else if (CMSTraceSweeper) {
8577 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8578 }
8579 set_inFreeRange(false);
8580 set_freeRangeInFreeLists(false);
8581 }
8582
8583 // We take a break if we've been at this for a while,
8584 // so as to avoid monopolizing the locks involved.
8585 void SweepClosure::do_yield_work(HeapWord* addr) {
8586 // Return current free chunk being used for coalescing (if any)
8587 // to the appropriate freelist. After yielding, the next
8588 // free block encountered will start a coalescing range of
8589 // free blocks. If the next free block is adjacent to the
8590 // chunk just flushed, they will need to wait for the next
8591 // sweep to be coalesced.
8592 if (inFreeRange()) {
8593 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8594 }
8595
8596 // First give up the locks, then yield, then re-lock.
8597 // We should probably use a constructor/destructor idiom to
8598 // do this unlock/lock or modify the MutexUnlocker class to
8599 // serve our purpose. XXX
8600 assert_lock_strong(_bitMap->lock());
8601 assert_lock_strong(_freelistLock);
8602 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8603 "CMS thread should hold CMS token");
8604 _bitMap->lock()->unlock();
8605 _freelistLock->unlock();
8606 ConcurrentMarkSweepThread::desynchronize(true);
8607 ConcurrentMarkSweepThread::acknowledge_yield_request();
8608 _collector->stopTimer();
8609 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8610 if (PrintCMSStatistics != 0) {
8611 _collector->incrementYields();
8612 }
8613 _collector->icms_wait();
8614
8615 // See the comment in coordinator_yield()
8616 for (unsigned i = 0; i < CMSYieldSleepCount &&
8617 ConcurrentMarkSweepThread::should_yield() &&
8618 !CMSCollector::foregroundGCIsActive(); ++i) {
8619 os::sleep(Thread::current(), 1, false);
8620 ConcurrentMarkSweepThread::acknowledge_yield_request();
8621 }
8622
8623 ConcurrentMarkSweepThread::synchronize(true);
8624 _freelistLock->lock();
8625 _bitMap->lock()->lock_without_safepoint_check();
8626 _collector->startTimer();
8627 }
8628
8629 #ifndef PRODUCT
8630 // This is actually very useful in a product build if it can
8631 // be called from the debugger. Compile it into the product
8632 // as needed.
8633 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8634 return debug_cms_space->verify_chunk_in_free_list(fc);
8635 }
8636 #endif
8637
8638 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8639 if (CMSTraceSweeper) {
8640 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8641 fc, fc->size());
8642 }
8643 }
8644
8645 // CMSIsAliveClosure
8646 bool CMSIsAliveClosure::do_object_b(oop obj) {
8647 HeapWord* addr = (HeapWord*)obj;
8648 return addr != NULL &&
8649 (!_span.contains(addr) || _bit_map->isMarked(addr));
8650 }
8651
8652 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8653 MemRegion span,
8654 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8655 CMSMarkStack* revisit_stack, bool cpc):
8656 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8657 _span(span),
8658 _bit_map(bit_map),
8659 _mark_stack(mark_stack),
8660 _concurrent_precleaning(cpc) {
8661 assert(!_span.is_empty(), "Empty span could spell trouble");
8662 }
8663
8664
8665 // CMSKeepAliveClosure: the serial version
8666 void CMSKeepAliveClosure::do_oop(oop obj) {
8667 HeapWord* addr = (HeapWord*)obj;
8668 if (_span.contains(addr) &&
8669 !_bit_map->isMarked(addr)) {
8670 _bit_map->mark(addr);
8671 bool simulate_overflow = false;
8672 NOT_PRODUCT(
8673 if (CMSMarkStackOverflowALot &&
8674 _collector->simulate_overflow()) {
8675 // simulate a stack overflow
8676 simulate_overflow = true;
8677 }
8678 )
8679 if (simulate_overflow || !_mark_stack->push(obj)) {
8680 if (_concurrent_precleaning) {
8681 // We dirty the overflown object and let the remark
8682 // phase deal with it.
8683 assert(_collector->overflow_list_is_empty(), "Error");
8684 // In the case of object arrays, we need to dirty all of
8685 // the cards that the object spans. No locking or atomics
8686 // are needed since no one else can be mutating the mod union
8687 // table.
8688 if (obj->is_objArray()) {
8689 size_t sz = obj->size();
8690 HeapWord* end_card_addr =
8691 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8692 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8693 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8694 _collector->_modUnionTable.mark_range(redirty_range);
8695 } else {
8696 _collector->_modUnionTable.mark(addr);
8697 }
8698 _collector->_ser_kac_preclean_ovflw++;
8699 } else {
8700 _collector->push_on_overflow_list(obj);
8701 _collector->_ser_kac_ovflw++;
8702 }
8703 }
8704 }
8705 }
8706
8707 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8708 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8709
8710 // CMSParKeepAliveClosure: a parallel version of the above.
8711 // The work queues are private to each closure (thread),
8712 // but (may be) available for stealing by other threads.
8713 void CMSParKeepAliveClosure::do_oop(oop obj) {
8714 HeapWord* addr = (HeapWord*)obj;
8715 if (_span.contains(addr) &&
8716 !_bit_map->isMarked(addr)) {
8717 // In general, during recursive tracing, several threads
8718 // may be concurrently getting here; the first one to
8719 // "tag" it, claims it.
8720 if (_bit_map->par_mark(addr)) {
8721 bool res = _work_queue->push(obj);
8722 assert(res, "Low water mark should be much less than capacity");
8723 // Do a recursive trim in the hope that this will keep
8724 // stack usage lower, but leave some oops for potential stealers
8725 trim_queue(_low_water_mark);
8726 } // Else, another thread got there first
8727 }
8728 }
8729
8730 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8731 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8732
8733 void CMSParKeepAliveClosure::trim_queue(uint max) {
8734 while (_work_queue->size() > max) {
8735 oop new_oop;
8736 if (_work_queue->pop_local(new_oop)) {
8737 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8738 assert(_bit_map->isMarked((HeapWord*)new_oop),
8739 "no white objects on this stack!");
8740 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8741 // iterate over the oops in this oop, marking and pushing
8742 // the ones in CMS heap (i.e. in _span).
8743 new_oop->oop_iterate(&_mark_and_push);
8744 }
8745 }
8746 }
8747
8748 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8749 CMSCollector* collector,
8750 MemRegion span, CMSBitMap* bit_map,
8751 CMSMarkStack* revisit_stack,
8752 OopTaskQueue* work_queue):
8753 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8754 _span(span),
8755 _bit_map(bit_map),
8756 _work_queue(work_queue) { }
8757
8758 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8759 HeapWord* addr = (HeapWord*)obj;
8760 if (_span.contains(addr) &&
8761 !_bit_map->isMarked(addr)) {
8762 if (_bit_map->par_mark(addr)) {
8763 bool simulate_overflow = false;
8764 NOT_PRODUCT(
8765 if (CMSMarkStackOverflowALot &&
8766 _collector->par_simulate_overflow()) {
8767 // simulate a stack overflow
8768 simulate_overflow = true;
8769 }
8770 )
8771 if (simulate_overflow || !_work_queue->push(obj)) {
8772 _collector->par_push_on_overflow_list(obj);
8773 _collector->_par_kac_ovflw++;
8774 }
8775 } // Else another thread got there already
8776 }
8777 }
8778
8779 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8780 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8781
8782 //////////////////////////////////////////////////////////////////
8783 // CMSExpansionCause /////////////////////////////
8784 //////////////////////////////////////////////////////////////////
8785 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8786 switch (cause) {
8787 case _no_expansion:
8788 return "No expansion";
8789 case _satisfy_free_ratio:
8790 return "Free ratio";
8791 case _satisfy_promotion:
8792 return "Satisfy promotion";
8793 case _satisfy_allocation:
8794 return "allocation";
8795 case _allocate_par_lab:
8796 return "Par LAB";
8797 case _allocate_par_spooling_space:
8798 return "Par Spooling Space";
8799 case _adaptive_size_policy:
8800 return "Ergonomics";
8801 default:
8802 return "unknown";
8803 }
8804 }
8805
8806 void CMSDrainMarkingStackClosure::do_void() {
8807 // the max number to take from overflow list at a time
8808 const size_t num = _mark_stack->capacity()/4;
8809 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8810 "Overflow list should be NULL during concurrent phases");
8811 while (!_mark_stack->isEmpty() ||
8812 // if stack is empty, check the overflow list
8813 _collector->take_from_overflow_list(num, _mark_stack)) {
8814 oop obj = _mark_stack->pop();
8815 HeapWord* addr = (HeapWord*)obj;
8816 assert(_span.contains(addr), "Should be within span");
8817 assert(_bit_map->isMarked(addr), "Should be marked");
8818 assert(obj->is_oop(), "Should be an oop");
8819 obj->oop_iterate(_keep_alive);
8820 }
8821 }
8822
8823 void CMSParDrainMarkingStackClosure::do_void() {
8824 // drain queue
8825 trim_queue(0);
8826 }
8827
8828 // Trim our work_queue so its length is below max at return
8829 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8830 while (_work_queue->size() > max) {
8831 oop new_oop;
8832 if (_work_queue->pop_local(new_oop)) {
8833 assert(new_oop->is_oop(), "Expected an oop");
8834 assert(_bit_map->isMarked((HeapWord*)new_oop),
8835 "no white objects on this stack!");
8836 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8837 // iterate over the oops in this oop, marking and pushing
8838 // the ones in CMS heap (i.e. in _span).
8839 new_oop->oop_iterate(&_mark_and_push);
8840 }
8841 }
8842 }
8843
8844 ////////////////////////////////////////////////////////////////////
8845 // Support for Marking Stack Overflow list handling and related code
8846 ////////////////////////////////////////////////////////////////////
8847 // Much of the following code is similar in shape and spirit to the
8848 // code used in ParNewGC. We should try and share that code
8849 // as much as possible in the future.
8850
8851 #ifndef PRODUCT
8852 // Debugging support for CMSStackOverflowALot
8853
8854 // It's OK to call this multi-threaded; the worst thing
8855 // that can happen is that we'll get a bunch of closely
8856 // spaced simulated oveflows, but that's OK, in fact
8857 // probably good as it would exercise the overflow code
8858 // under contention.
8859 bool CMSCollector::simulate_overflow() {
8860 if (_overflow_counter-- <= 0) { // just being defensive
8861 _overflow_counter = CMSMarkStackOverflowInterval;
8862 return true;
8863 } else {
8864 return false;
8865 }
8866 }
8867
8868 bool CMSCollector::par_simulate_overflow() {
8869 return simulate_overflow();
8870 }
8871 #endif
8872
8873 // Single-threaded
8874 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8875 assert(stack->isEmpty(), "Expected precondition");
8876 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8877 size_t i = num;
8878 oop cur = _overflow_list;
8879 const markOop proto = markOopDesc::prototype();
8880 NOT_PRODUCT(ssize_t n = 0;)
8881 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8882 next = oop(cur->mark());
8883 cur->set_mark(proto); // until proven otherwise
8884 assert(cur->is_oop(), "Should be an oop");
8885 bool res = stack->push(cur);
8886 assert(res, "Bit off more than can chew?");
8887 NOT_PRODUCT(n++;)
8888 }
8889 _overflow_list = cur;
8890 #ifndef PRODUCT
8891 assert(_num_par_pushes >= n, "Too many pops?");
8892 _num_par_pushes -=n;
8893 #endif
8894 return !stack->isEmpty();
8895 }
8896
8897 #define BUSY (oop(0x1aff1aff))
8898 // (MT-safe) Get a prefix of at most "num" from the list.
8899 // The overflow list is chained through the mark word of
8900 // each object in the list. We fetch the entire list,
8901 // break off a prefix of the right size and return the
8902 // remainder. If other threads try to take objects from
8903 // the overflow list at that time, they will wait for
8904 // some time to see if data becomes available. If (and
8905 // only if) another thread places one or more object(s)
8906 // on the global list before we have returned the suffix
8907 // to the global list, we will walk down our local list
8908 // to find its end and append the global list to
8909 // our suffix before returning it. This suffix walk can
8910 // prove to be expensive (quadratic in the amount of traffic)
8911 // when there are many objects in the overflow list and
8912 // there is much producer-consumer contention on the list.
8913 // *NOTE*: The overflow list manipulation code here and
8914 // in ParNewGeneration:: are very similar in shape,
8915 // except that in the ParNew case we use the old (from/eden)
8916 // copy of the object to thread the list via its klass word.
8917 // Because of the common code, if you make any changes in
8918 // the code below, please check the ParNew version to see if
8919 // similar changes might be needed.
8920 // CR 6797058 has been filed to consolidate the common code.
8921 bool CMSCollector::par_take_from_overflow_list(size_t num,
8922 OopTaskQueue* work_q,
8923 int no_of_gc_threads) {
8924 assert(work_q->size() == 0, "First empty local work queue");
8925 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8926 if (_overflow_list == NULL) {
8927 return false;
8928 }
8929 // Grab the entire list; we'll put back a suffix
8930 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8931 Thread* tid = Thread::current();
8932 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8933 // set to ParallelGCThreads.
8934 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8935 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8936 // If the list is busy, we spin for a short while,
8937 // sleeping between attempts to get the list.
8938 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8939 os::sleep(tid, sleep_time_millis, false);
8940 if (_overflow_list == NULL) {
8941 // Nothing left to take
8942 return false;
8943 } else if (_overflow_list != BUSY) {
8944 // Try and grab the prefix
8945 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8946 }
8947 }
8948 // If the list was found to be empty, or we spun long
8949 // enough, we give up and return empty-handed. If we leave
8950 // the list in the BUSY state below, it must be the case that
8951 // some other thread holds the overflow list and will set it
8952 // to a non-BUSY state in the future.
8953 if (prefix == NULL || prefix == BUSY) {
8954 // Nothing to take or waited long enough
8955 if (prefix == NULL) {
8956 // Write back the NULL in case we overwrote it with BUSY above
8957 // and it is still the same value.
8958 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8959 }
8960 return false;
8961 }
8962 assert(prefix != NULL && prefix != BUSY, "Error");
8963 size_t i = num;
8964 oop cur = prefix;
8965 // Walk down the first "num" objects, unless we reach the end.
8966 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8967 if (cur->mark() == NULL) {
8968 // We have "num" or fewer elements in the list, so there
8969 // is nothing to return to the global list.
8970 // Write back the NULL in lieu of the BUSY we wrote
8971 // above, if it is still the same value.
8972 if (_overflow_list == BUSY) {
8973 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8974 }
8975 } else {
8976 // Chop off the suffix and rerturn it to the global list.
8977 assert(cur->mark() != BUSY, "Error");
8978 oop suffix_head = cur->mark(); // suffix will be put back on global list
8979 cur->set_mark(NULL); // break off suffix
8980 // It's possible that the list is still in the empty(busy) state
8981 // we left it in a short while ago; in that case we may be
8982 // able to place back the suffix without incurring the cost
8983 // of a walk down the list.
8984 oop observed_overflow_list = _overflow_list;
8985 oop cur_overflow_list = observed_overflow_list;
8986 bool attached = false;
8987 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8988 observed_overflow_list =
8989 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8990 if (cur_overflow_list == observed_overflow_list) {
8991 attached = true;
8992 break;
8993 } else cur_overflow_list = observed_overflow_list;
8994 }
8995 if (!attached) {
8996 // Too bad, someone else sneaked in (at least) an element; we'll need
8997 // to do a splice. Find tail of suffix so we can prepend suffix to global
8998 // list.
8999 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9000 oop suffix_tail = cur;
9001 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9002 "Tautology");
9003 observed_overflow_list = _overflow_list;
9004 do {
9005 cur_overflow_list = observed_overflow_list;
9006 if (cur_overflow_list != BUSY) {
9007 // Do the splice ...
9008 suffix_tail->set_mark(markOop(cur_overflow_list));
9009 } else { // cur_overflow_list == BUSY
9010 suffix_tail->set_mark(NULL);
9011 }
9012 // ... and try to place spliced list back on overflow_list ...
9013 observed_overflow_list =
9014 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9015 } while (cur_overflow_list != observed_overflow_list);
9016 // ... until we have succeeded in doing so.
9017 }
9018 }
9019
9020 // Push the prefix elements on work_q
9021 assert(prefix != NULL, "control point invariant");
9022 const markOop proto = markOopDesc::prototype();
9023 oop next;
9024 NOT_PRODUCT(ssize_t n = 0;)
9025 for (cur = prefix; cur != NULL; cur = next) {
9026 next = oop(cur->mark());
9027 cur->set_mark(proto); // until proven otherwise
9028 assert(cur->is_oop(), "Should be an oop");
9029 bool res = work_q->push(cur);
9030 assert(res, "Bit off more than we can chew?");
9031 NOT_PRODUCT(n++;)
9032 }
9033 #ifndef PRODUCT
9034 assert(_num_par_pushes >= n, "Too many pops?");
9035 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9036 #endif
9037 return true;
9038 }
9039
9040 // Single-threaded
9041 void CMSCollector::push_on_overflow_list(oop p) {
9042 NOT_PRODUCT(_num_par_pushes++;)
9043 assert(p->is_oop(), "Not an oop");
9044 preserve_mark_if_necessary(p);
9045 p->set_mark((markOop)_overflow_list);
9046 _overflow_list = p;
9047 }
9048
9049 // Multi-threaded; use CAS to prepend to overflow list
9050 void CMSCollector::par_push_on_overflow_list(oop p) {
9051 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9052 assert(p->is_oop(), "Not an oop");
9053 par_preserve_mark_if_necessary(p);
9054 oop observed_overflow_list = _overflow_list;
9055 oop cur_overflow_list;
9056 do {
9057 cur_overflow_list = observed_overflow_list;
9058 if (cur_overflow_list != BUSY) {
9059 p->set_mark(markOop(cur_overflow_list));
9060 } else {
9061 p->set_mark(NULL);
9062 }
9063 observed_overflow_list =
9064 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9065 } while (cur_overflow_list != observed_overflow_list);
9066 }
9067 #undef BUSY
9068
9069 // Single threaded
9070 // General Note on GrowableArray: pushes may silently fail
9071 // because we are (temporarily) out of C-heap for expanding
9072 // the stack. The problem is quite ubiquitous and affects
9073 // a lot of code in the JVM. The prudent thing for GrowableArray
9074 // to do (for now) is to exit with an error. However, that may
9075 // be too draconian in some cases because the caller may be
9076 // able to recover without much harm. For such cases, we
9077 // should probably introduce a "soft_push" method which returns
9078 // an indication of success or failure with the assumption that
9079 // the caller may be able to recover from a failure; code in
9080 // the VM can then be changed, incrementally, to deal with such
9081 // failures where possible, thus, incrementally hardening the VM
9082 // in such low resource situations.
9083 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9084 _preserved_oop_stack.push(p);
9085 _preserved_mark_stack.push(m);
9086 assert(m == p->mark(), "Mark word changed");
9087 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9088 "bijection");
9089 }
9090
9091 // Single threaded
9092 void CMSCollector::preserve_mark_if_necessary(oop p) {
9093 markOop m = p->mark();
9094 if (m->must_be_preserved(p)) {
9095 preserve_mark_work(p, m);
9096 }
9097 }
9098
9099 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9100 markOop m = p->mark();
9101 if (m->must_be_preserved(p)) {
9102 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9103 // Even though we read the mark word without holding
9104 // the lock, we are assured that it will not change
9105 // because we "own" this oop, so no other thread can
9106 // be trying to push it on the overflow list; see
9107 // the assertion in preserve_mark_work() that checks
9108 // that m == p->mark().
9109 preserve_mark_work(p, m);
9110 }
9111 }
9112
9113 // We should be able to do this multi-threaded,
9114 // a chunk of stack being a task (this is
9115 // correct because each oop only ever appears
9116 // once in the overflow list. However, it's
9117 // not very easy to completely overlap this with
9118 // other operations, so will generally not be done
9119 // until all work's been completed. Because we
9120 // expect the preserved oop stack (set) to be small,
9121 // it's probably fine to do this single-threaded.
9122 // We can explore cleverer concurrent/overlapped/parallel
9123 // processing of preserved marks if we feel the
9124 // need for this in the future. Stack overflow should
9125 // be so rare in practice and, when it happens, its
9126 // effect on performance so great that this will
9127 // likely just be in the noise anyway.
9128 void CMSCollector::restore_preserved_marks_if_any() {
9129 assert(SafepointSynchronize::is_at_safepoint(),
9130 "world should be stopped");
9131 assert(Thread::current()->is_ConcurrentGC_thread() ||
9132 Thread::current()->is_VM_thread(),
9133 "should be single-threaded");
9134 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9135 "bijection");
9136
9137 while (!_preserved_oop_stack.is_empty()) {
9138 oop p = _preserved_oop_stack.pop();
9139 assert(p->is_oop(), "Should be an oop");
9140 assert(_span.contains(p), "oop should be in _span");
9141 assert(p->mark() == markOopDesc::prototype(),
9142 "Set when taken from overflow list");
9143 markOop m = _preserved_mark_stack.pop();
9144 p->set_mark(m);
9145 }
9146 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9147 "stacks were cleared above");
9148 }
9149
9150 #ifndef PRODUCT
9151 bool CMSCollector::no_preserved_marks() const {
9152 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9153 }
9154 #endif
9155
9156 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9157 {
9158 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9159 CMSAdaptiveSizePolicy* size_policy =
9160 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9161 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9162 "Wrong type for size policy");
9163 return size_policy;
9164 }
9165
9166 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9167 size_t desired_promo_size) {
9168 if (cur_promo_size < desired_promo_size) {
9169 size_t expand_bytes = desired_promo_size - cur_promo_size;
9170 if (PrintAdaptiveSizePolicy && Verbose) {
9171 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9172 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9173 expand_bytes);
9174 }
9175 expand(expand_bytes,
9176 MinHeapDeltaBytes,
9177 CMSExpansionCause::_adaptive_size_policy);
9178 } else if (desired_promo_size < cur_promo_size) {
9179 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9180 if (PrintAdaptiveSizePolicy && Verbose) {
9181 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9182 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9183 shrink_bytes);
9184 }
9185 shrink(shrink_bytes);
9186 }
9187 }
9188
9189 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9190 GenCollectedHeap* gch = GenCollectedHeap::heap();
9191 CMSGCAdaptivePolicyCounters* counters =
9192 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9193 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9194 "Wrong kind of counters");
9195 return counters;
9196 }
9197
9198
9199 void ASConcurrentMarkSweepGeneration::update_counters() {
9200 if (UsePerfData) {
9201 _space_counters->update_all();
9202 _gen_counters->update_all();
9203 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9204 GenCollectedHeap* gch = GenCollectedHeap::heap();
9205 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9206 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9207 "Wrong gc statistics type");
9208 counters->update_counters(gc_stats_l);
9209 }
9210 }
9211
9212 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9213 if (UsePerfData) {
9214 _space_counters->update_used(used);
9215 _space_counters->update_capacity();
9216 _gen_counters->update_all();
9217
9218 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9219 GenCollectedHeap* gch = GenCollectedHeap::heap();
9220 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9221 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9222 "Wrong gc statistics type");
9223 counters->update_counters(gc_stats_l);
9224 }
9225 }
9226
9227 // The desired expansion delta is computed so that:
9228 // . desired free percentage or greater is used
9229 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9230 assert_locked_or_safepoint(Heap_lock);
9231
9232 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9233
9234 // If incremental collection failed, we just want to expand
9235 // to the limit.
9236 if (incremental_collection_failed()) {
9237 clear_incremental_collection_failed();
9238 grow_to_reserved();
9239 return;
9240 }
9241
9242 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9243
9244 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9245 "Wrong type of heap");
9246 int prev_level = level() - 1;
9247 assert(prev_level >= 0, "The cms generation is the lowest generation");
9248 Generation* prev_gen = gch->get_gen(prev_level);
9249 assert(prev_gen->kind() == Generation::ASParNew,
9250 "Wrong type of young generation");
9251 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9252 size_t cur_eden = younger_gen->eden()->capacity();
9253 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9254 size_t cur_promo = free();
9255 size_policy->compute_tenured_generation_free_space(cur_promo,
9256 max_available(),
9257 cur_eden);
9258 resize(cur_promo, size_policy->promo_size());
9259
9260 // Record the new size of the space in the cms generation
9261 // that is available for promotions. This is temporary.
9262 // It should be the desired promo size.
9263 size_policy->avg_cms_promo()->sample(free());
9264 size_policy->avg_old_live()->sample(used());
9265
9266 if (UsePerfData) {
9267 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9268 counters->update_cms_capacity_counter(capacity());
9269 }
9270 }
9271
9272 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9273 assert_locked_or_safepoint(Heap_lock);
9274 assert_lock_strong(freelistLock());
9275 HeapWord* old_end = _cmsSpace->end();
9276 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9277 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9278 FreeChunk* chunk_at_end = find_chunk_at_end();
9279 if (chunk_at_end == NULL) {
9280 // No room to shrink
9281 if (PrintGCDetails && Verbose) {
9282 gclog_or_tty->print_cr("No room to shrink: old_end "
9283 PTR_FORMAT " unallocated_start " PTR_FORMAT
9284 " chunk_at_end " PTR_FORMAT,
9285 old_end, unallocated_start, chunk_at_end);
9286 }
9287 return;
9288 } else {
9289
9290 // Find the chunk at the end of the space and determine
9291 // how much it can be shrunk.
9292 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9293 size_t aligned_shrinkable_size_in_bytes =
9294 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9295 assert(unallocated_start <= chunk_at_end->end(),
9296 "Inconsistent chunk at end of space");
9297 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9298 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9299
9300 // Shrink the underlying space
9301 _virtual_space.shrink_by(bytes);
9302 if (PrintGCDetails && Verbose) {
9303 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9304 " desired_bytes " SIZE_FORMAT
9305 " shrinkable_size_in_bytes " SIZE_FORMAT
9306 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9307 " bytes " SIZE_FORMAT,
9308 desired_bytes, shrinkable_size_in_bytes,
9309 aligned_shrinkable_size_in_bytes, bytes);
9310 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9311 " unallocated_start " SIZE_FORMAT,
9312 old_end, unallocated_start);
9313 }
9314
9315 // If the space did shrink (shrinking is not guaranteed),
9316 // shrink the chunk at the end by the appropriate amount.
9317 if (((HeapWord*)_virtual_space.high()) < old_end) {
9318 size_t new_word_size =
9319 heap_word_size(_virtual_space.committed_size());
9320
9321 // Have to remove the chunk from the dictionary because it is changing
9322 // size and might be someplace elsewhere in the dictionary.
9323
9324 // Get the chunk at end, shrink it, and put it
9325 // back.
9326 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9327 size_t word_size_change = word_size_before - new_word_size;
9328 size_t chunk_at_end_old_size = chunk_at_end->size();
9329 assert(chunk_at_end_old_size >= word_size_change,
9330 "Shrink is too large");
9331 chunk_at_end->set_size(chunk_at_end_old_size -
9332 word_size_change);
9333 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9334 word_size_change);
9335
9336 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9337
9338 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9339 _bts->resize(new_word_size); // resize the block offset shared array
9340 Universe::heap()->barrier_set()->resize_covered_region(mr);
9341 _cmsSpace->assert_locked();
9342 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9343
9344 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9345
9346 // update the space and generation capacity counters
9347 if (UsePerfData) {
9348 _space_counters->update_capacity();
9349 _gen_counters->update_all();
9350 }
9351
9352 if (Verbose && PrintGCDetails) {
9353 size_t new_mem_size = _virtual_space.committed_size();
9354 size_t old_mem_size = new_mem_size + bytes;
9355 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9356 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9357 }
9358 }
9359
9360 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9361 "Inconsistency at end of space");
9362 assert(chunk_at_end->end() == _cmsSpace->end(),
9363 "Shrinking is inconsistent");
9364 return;
9365 }
9366 }
9367
9368 // Transfer some number of overflown objects to usual marking
9369 // stack. Return true if some objects were transferred.
9370 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9371 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9372 (size_t)ParGCDesiredObjsFromOverflowList);
9373
9374 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9375 assert(_collector->overflow_list_is_empty() || res,
9376 "If list is not empty, we should have taken something");
9377 assert(!res || !_mark_stack->isEmpty(),
9378 "If we took something, it should now be on our stack");
9379 return res;
9380 }
9381
9382 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9383 size_t res = _sp->block_size_no_stall(addr, _collector);
9384 if (_sp->block_is_obj(addr)) {
9385 if (_live_bit_map->isMarked(addr)) {
9386 // It can't have been dead in a previous cycle
9387 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9388 } else {
9389 _dead_bit_map->mark(addr); // mark the dead object
9390 }
9391 }
9392 // Could be 0, if the block size could not be computed without stalling.
9393 return res;
9394 }
9395
9396 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9397
9398 switch (phase) {
9399 case CMSCollector::InitialMarking:
9400 initialize(true /* fullGC */ ,
9401 cause /* cause of the GC */,
9402 true /* recordGCBeginTime */,
9403 true /* recordPreGCUsage */,
9404 false /* recordPeakUsage */,
9405 false /* recordPostGCusage */,
9406 true /* recordAccumulatedGCTime */,
9407 false /* recordGCEndTime */,
9408 false /* countCollection */ );
9409 break;
9410
9411 case CMSCollector::FinalMarking:
9412 initialize(true /* fullGC */ ,
9413 cause /* cause of the GC */,
9414 false /* recordGCBeginTime */,
9415 false /* recordPreGCUsage */,
9416 false /* recordPeakUsage */,
9417 false /* recordPostGCusage */,
9418 true /* recordAccumulatedGCTime */,
9419 false /* recordGCEndTime */,
9420 false /* countCollection */ );
9421 break;
9422
9423 case CMSCollector::Sweeping:
9424 initialize(true /* fullGC */ ,
9425 cause /* cause of the GC */,
9426 false /* recordGCBeginTime */,
9427 false /* recordPreGCUsage */,
9428 true /* recordPeakUsage */,
9429 true /* recordPostGCusage */,
9430 false /* recordAccumulatedGCTime */,
9431 true /* recordGCEndTime */,
9432 true /* countCollection */ );
9433 break;
9434
9435 default:
9436 ShouldNotReachHere();
9437 }
9438 }
9439