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_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
579 _eden_chunk_array(NULL), // may be set in ctor body
580 _eden_chunk_capacity(0), // -- ditto --
581 _eden_chunk_index(0), // -- ditto --
582 _survivor_plab_array(NULL), // -- ditto --
583 _survivor_chunk_array(NULL), // -- ditto --
584 _survivor_chunk_capacity(0), // -- ditto --
585 _survivor_chunk_index(0), // -- ditto --
586 _ser_pmc_preclean_ovflw(0),
587 _ser_kac_preclean_ovflw(0),
588 _ser_pmc_remark_ovflw(0),
589 _par_pmc_remark_ovflw(0),
590 _ser_kac_ovflw(0),
591 _par_kac_ovflw(0),
592 #ifndef PRODUCT
593 _num_par_pushes(0),
594 #endif
595 _collection_count_start(0),
596 _verifying(false),
597 _icms_start_limit(NULL),
598 _icms_stop_limit(NULL),
599 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
600 _completed_initialization(false),
601 _collector_policy(cp),
602 _should_unload_classes(false),
603 _concurrent_cycles_since_last_unload(0),
604 _roots_scanning_options(0),
605 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
606 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
607 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
608 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
609 _cms_start_registered(false)
610 {
611 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
612 ExplicitGCInvokesConcurrent = true;
613 }
614 // Now expand the span and allocate the collection support structures
615 // (MUT, marking bit map etc.) to cover both generations subject to
616 // collection.
617
618 // First check that _permGen is adjacent to _cmsGen and above it.
619 assert( _cmsGen->reserved().word_size() > 0
620 && _permGen->reserved().word_size() > 0,
621 "generations should not be of zero size");
622 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
623 "_cmsGen and _permGen should not overlap");
624 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
625 "_cmsGen->end() different from _permGen->start()");
626
627 // For use by dirty card to oop closures.
628 _cmsGen->cmsSpace()->set_collector(this);
629 _permGen->cmsSpace()->set_collector(this);
630
631 // Allocate MUT and marking bit map
632 {
633 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
634 if (!_markBitMap.allocate(_span)) {
635 warning("Failed to allocate CMS Bit Map");
636 return;
637 }
638 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
639 }
640 {
641 _modUnionTable.allocate(_span);
642 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
643 }
644
645 if (!_markStack.allocate(MarkStackSize)) {
646 warning("Failed to allocate CMS Marking Stack");
647 return;
648 }
649 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
650 warning("Failed to allocate CMS Revisit Stack");
651 return;
652 }
653
654 // Support for multi-threaded concurrent phases
655 if (CMSConcurrentMTEnabled) {
656 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
657 // just for now
658 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
659 }
660 if (ConcGCThreads > 1) {
661 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
662 ConcGCThreads, true);
663 if (_conc_workers == NULL) {
664 warning("GC/CMS: _conc_workers allocation failure: "
665 "forcing -CMSConcurrentMTEnabled");
666 CMSConcurrentMTEnabled = false;
667 } else {
668 _conc_workers->initialize_workers();
669 }
670 } else {
671 CMSConcurrentMTEnabled = false;
672 }
673 }
674 if (!CMSConcurrentMTEnabled) {
675 ConcGCThreads = 0;
676 } else {
677 // Turn off CMSCleanOnEnter optimization temporarily for
678 // the MT case where it's not fixed yet; see 6178663.
679 CMSCleanOnEnter = false;
680 }
681 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
682 "Inconsistency");
683
684 // Parallel task queues; these are shared for the
685 // concurrent and stop-world phases of CMS, but
686 // are not shared with parallel scavenge (ParNew).
687 {
688 uint i;
689 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
690
691 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
692 || ParallelRefProcEnabled)
693 && num_queues > 0) {
694 _task_queues = new OopTaskQueueSet(num_queues);
695 if (_task_queues == NULL) {
696 warning("task_queues allocation failure.");
697 return;
698 }
699 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
700 if (_hash_seed == NULL) {
701 warning("_hash_seed array allocation failure");
702 return;
703 }
704
705 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
706 for (i = 0; i < num_queues; i++) {
707 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
708 if (q == NULL) {
709 warning("work_queue allocation failure.");
710 return;
711 }
712 _task_queues->register_queue(i, q);
713 }
714 for (i = 0; i < num_queues; i++) {
715 _task_queues->queue(i)->initialize();
716 _hash_seed[i] = 17; // copied from ParNew
717 }
718 }
719 }
720
721 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
722 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
723
724 // Clip CMSBootstrapOccupancy between 0 and 100.
725 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
726 /(double)100;
727
728 _full_gcs_since_conc_gc = 0;
729
730 // Now tell CMS generations the identity of their collector
731 ConcurrentMarkSweepGeneration::set_collector(this);
732
733 // Create & start a CMS thread for this CMS collector
734 _cmsThread = ConcurrentMarkSweepThread::start(this);
735 assert(cmsThread() != NULL, "CMS Thread should have been created");
736 assert(cmsThread()->collector() == this,
737 "CMS Thread should refer to this gen");
738 assert(CGC_lock != NULL, "Where's the CGC_lock?");
739
740 // Support for parallelizing young gen rescan
741 GenCollectedHeap* gch = GenCollectedHeap::heap();
742 _young_gen = gch->prev_gen(_cmsGen);
743 if (gch->supports_inline_contig_alloc()) {
744 _top_addr = gch->top_addr();
745 _end_addr = gch->end_addr();
746 assert(_young_gen != NULL, "no _young_gen");
747 _eden_chunk_index = 0;
748 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
749 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
750 if (_eden_chunk_array == NULL) {
751 _eden_chunk_capacity = 0;
752 warning("GC/CMS: _eden_chunk_array allocation failure");
753 }
754 }
755 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
756
757 // Support for parallelizing survivor space rescan
758 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
759 const size_t max_plab_samples =
760 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
761
762 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
763 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
764 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
765 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
766 || _cursor == NULL) {
767 warning("Failed to allocate survivor plab/chunk array");
768 if (_survivor_plab_array != NULL) {
769 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
770 _survivor_plab_array = NULL;
771 }
772 if (_survivor_chunk_array != NULL) {
773 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
774 _survivor_chunk_array = NULL;
775 }
776 if (_cursor != NULL) {
777 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
778 _cursor = NULL;
779 }
780 } else {
781 _survivor_chunk_capacity = 2*max_plab_samples;
782 for (uint i = 0; i < ParallelGCThreads; i++) {
783 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
784 if (vec == NULL) {
785 warning("Failed to allocate survivor plab array");
786 for (int j = i; j > 0; j--) {
787 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
788 }
789 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
790 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
791 _survivor_plab_array = NULL;
792 _survivor_chunk_array = NULL;
793 _survivor_chunk_capacity = 0;
794 break;
795 } else {
796 ChunkArray* cur =
797 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
798 max_plab_samples);
799 assert(cur->end() == 0, "Should be 0");
800 assert(cur->array() == vec, "Should be vec");
801 assert(cur->capacity() == max_plab_samples, "Error");
802 }
803 }
804 }
805 }
806 assert( ( _survivor_plab_array != NULL
807 && _survivor_chunk_array != NULL)
808 || ( _survivor_chunk_capacity == 0
809 && _survivor_chunk_index == 0),
810 "Error");
811
812 // Choose what strong roots should be scanned depending on verification options
813 // and perm gen collection mode.
814 if (!CMSClassUnloadingEnabled) {
815 // If class unloading is disabled we want to include all classes into the root set.
816 add_root_scanning_option(SharedHeap::SO_AllClasses);
817 } else {
818 add_root_scanning_option(SharedHeap::SO_SystemClasses);
819 }
820
821 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
822 _gc_counters = new CollectorCounters("CMS", 1);
823 _completed_initialization = true;
824 _inter_sweep_timer.start(); // start of time
825 }
826
827 const char* ConcurrentMarkSweepGeneration::name() const {
828 return "concurrent mark-sweep generation";
829 }
830 void ConcurrentMarkSweepGeneration::update_counters() {
831 if (UsePerfData) {
832 _space_counters->update_all();
833 _gen_counters->update_all();
834 }
835 }
836
837 // this is an optimized version of update_counters(). it takes the
838 // used value as a parameter rather than computing it.
839 //
840 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
841 if (UsePerfData) {
842 _space_counters->update_used(used);
843 _space_counters->update_capacity();
844 _gen_counters->update_all();
845 }
846 }
847
848 void ConcurrentMarkSweepGeneration::print() const {
849 Generation::print();
850 cmsSpace()->print();
851 }
852
853 #ifndef PRODUCT
854 void ConcurrentMarkSweepGeneration::print_statistics() {
855 cmsSpace()->printFLCensus(0);
856 }
857 #endif
858
859 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
860 GenCollectedHeap* gch = GenCollectedHeap::heap();
861 if (PrintGCDetails) {
862 if (Verbose) {
863 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
864 level(), short_name(), s, used(), capacity());
865 } else {
866 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
867 level(), short_name(), s, used() / K, capacity() / K);
868 }
869 }
870 if (Verbose) {
871 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
872 gch->used(), gch->capacity());
873 } else {
874 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
875 gch->used() / K, gch->capacity() / K);
876 }
877 }
878
879 size_t
880 ConcurrentMarkSweepGeneration::contiguous_available() const {
881 // dld proposes an improvement in precision here. If the committed
882 // part of the space ends in a free block we should add that to
883 // uncommitted size in the calculation below. Will make this
884 // change later, staying with the approximation below for the
885 // time being. -- ysr.
886 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
887 }
888
889 size_t
890 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
891 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
892 }
893
894 size_t ConcurrentMarkSweepGeneration::max_available() const {
895 return free() + _virtual_space.uncommitted_size();
896 }
897
898 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
899 size_t available = max_available();
900 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
901 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
902 if (Verbose && PrintGCDetails) {
903 gclog_or_tty->print_cr(
904 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
905 "max_promo("SIZE_FORMAT")",
906 res? "":" not", available, res? ">=":"<",
907 av_promo, max_promotion_in_bytes);
908 }
909 return res;
910 }
911
912 // At a promotion failure dump information on block layout in heap
913 // (cms old generation).
914 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
915 if (CMSDumpAtPromotionFailure) {
916 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
917 }
918 }
919
920 CompactibleSpace*
921 ConcurrentMarkSweepGeneration::first_compaction_space() const {
922 return _cmsSpace;
923 }
924
925 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
926 // Clear the promotion information. These pointers can be adjusted
927 // along with all the other pointers into the heap but
928 // compaction is expected to be a rare event with
929 // a heap using cms so don't do it without seeing the need.
930 if (CollectedHeap::use_parallel_gc_threads()) {
931 for (uint i = 0; i < ParallelGCThreads; i++) {
932 _par_gc_thread_states[i]->promo.reset();
933 }
934 }
935 }
936
937 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
938 blk->do_space(_cmsSpace);
939 }
940
941 void ConcurrentMarkSweepGeneration::compute_new_size() {
942 assert_locked_or_safepoint(Heap_lock);
943
944 // If incremental collection failed, we just want to expand
945 // to the limit.
946 if (incremental_collection_failed()) {
947 clear_incremental_collection_failed();
948 grow_to_reserved();
949 return;
950 }
951
952 size_t expand_bytes = 0;
953 double free_percentage = ((double) free()) / capacity();
954 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
955 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
956
957 // compute expansion delta needed for reaching desired free percentage
958 if (free_percentage < desired_free_percentage) {
959 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
960 assert(desired_capacity >= capacity(), "invalid expansion size");
961 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
962 }
963 if (expand_bytes > 0) {
964 if (PrintGCDetails && Verbose) {
965 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
966 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
967 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
968 gclog_or_tty->print_cr(" Desired free fraction %f",
969 desired_free_percentage);
970 gclog_or_tty->print_cr(" Maximum free fraction %f",
971 maximum_free_percentage);
972 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
973 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
974 desired_capacity/1000);
975 int prev_level = level() - 1;
976 if (prev_level >= 0) {
977 size_t prev_size = 0;
978 GenCollectedHeap* gch = GenCollectedHeap::heap();
979 Generation* prev_gen = gch->_gens[prev_level];
980 prev_size = prev_gen->capacity();
981 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
982 prev_size/1000);
983 }
984 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
985 unsafe_max_alloc_nogc()/1000);
986 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
987 contiguous_available()/1000);
988 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
989 expand_bytes);
990 }
991 // safe if expansion fails
992 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
993 if (PrintGCDetails && Verbose) {
994 gclog_or_tty->print_cr(" Expanded free fraction %f",
995 ((double) free()) / capacity());
996 }
997 }
998 }
999
1000 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1001 return cmsSpace()->freelistLock();
1002 }
1003
1004 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1005 bool tlab) {
1006 CMSSynchronousYieldRequest yr;
1007 MutexLockerEx x(freelistLock(),
1008 Mutex::_no_safepoint_check_flag);
1009 return have_lock_and_allocate(size, tlab);
1010 }
1011
1012 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1013 bool tlab /* ignored */) {
1014 assert_lock_strong(freelistLock());
1015 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1016 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1017 // Allocate the object live (grey) if the background collector has
1018 // started marking. This is necessary because the marker may
1019 // have passed this address and consequently this object will
1020 // not otherwise be greyed and would be incorrectly swept up.
1021 // Note that if this object contains references, the writing
1022 // of those references will dirty the card containing this object
1023 // allowing the object to be blackened (and its references scanned)
1024 // either during a preclean phase or at the final checkpoint.
1025 if (res != NULL) {
1026 // We may block here with an uninitialized object with
1027 // its mark-bit or P-bits not yet set. Such objects need
1028 // to be safely navigable by block_start().
1029 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1030 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1031 collector()->direct_allocated(res, adjustedSize);
1032 _direct_allocated_words += adjustedSize;
1033 // allocation counters
1034 NOT_PRODUCT(
1035 _numObjectsAllocated++;
1036 _numWordsAllocated += (int)adjustedSize;
1037 )
1038 }
1039 return res;
1040 }
1041
1042 // In the case of direct allocation by mutators in a generation that
1043 // is being concurrently collected, the object must be allocated
1044 // live (grey) if the background collector has started marking.
1045 // This is necessary because the marker may
1046 // have passed this address and consequently this object will
1047 // not otherwise be greyed and would be incorrectly swept up.
1048 // Note that if this object contains references, the writing
1049 // of those references will dirty the card containing this object
1050 // allowing the object to be blackened (and its references scanned)
1051 // either during a preclean phase or at the final checkpoint.
1052 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1053 assert(_markBitMap.covers(start, size), "Out of bounds");
1054 if (_collectorState >= Marking) {
1055 MutexLockerEx y(_markBitMap.lock(),
1056 Mutex::_no_safepoint_check_flag);
1057 // [see comments preceding SweepClosure::do_blk() below for details]
1058 // 1. need to mark the object as live so it isn't collected
1059 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1060 // 3. need to mark the end of the object so marking, precleaning or sweeping
1061 // can skip over uninitialized or unparsable objects. An allocated
1062 // object is considered uninitialized for our purposes as long as
1063 // its klass word is NULL. (Unparsable objects are those which are
1064 // initialized in the sense just described, but whose sizes can still
1065 // not be correctly determined. Note that the class of unparsable objects
1066 // can only occur in the perm gen. All old gen objects are parsable
1067 // as soon as they are initialized.)
1068 _markBitMap.mark(start); // object is live
1069 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1070 _markBitMap.mark(start + size - 1);
1071 // mark end of object
1072 }
1073 // check that oop looks uninitialized
1074 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1075 }
1076
1077 void CMSCollector::promoted(bool par, HeapWord* start,
1078 bool is_obj_array, size_t obj_size) {
1079 assert(_markBitMap.covers(start), "Out of bounds");
1080 // See comment in direct_allocated() about when objects should
1081 // be allocated live.
1082 if (_collectorState >= Marking) {
1083 // we already hold the marking bit map lock, taken in
1084 // the prologue
1085 if (par) {
1086 _markBitMap.par_mark(start);
1087 } else {
1088 _markBitMap.mark(start);
1089 }
1090 // We don't need to mark the object as uninitialized (as
1091 // in direct_allocated above) because this is being done with the
1092 // world stopped and the object will be initialized by the
1093 // time the marking, precleaning or sweeping get to look at it.
1094 // But see the code for copying objects into the CMS generation,
1095 // where we need to ensure that concurrent readers of the
1096 // block offset table are able to safely navigate a block that
1097 // is in flux from being free to being allocated (and in
1098 // transition while being copied into) and subsequently
1099 // becoming a bona-fide object when the copy/promotion is complete.
1100 assert(SafepointSynchronize::is_at_safepoint(),
1101 "expect promotion only at safepoints");
1102
1103 if (_collectorState < Sweeping) {
1104 // Mark the appropriate cards in the modUnionTable, so that
1105 // this object gets scanned before the sweep. If this is
1106 // not done, CMS generation references in the object might
1107 // not get marked.
1108 // For the case of arrays, which are otherwise precisely
1109 // marked, we need to dirty the entire array, not just its head.
1110 if (is_obj_array) {
1111 // The [par_]mark_range() method expects mr.end() below to
1112 // be aligned to the granularity of a bit's representation
1113 // in the heap. In the case of the MUT below, that's a
1114 // card size.
1115 MemRegion mr(start,
1116 (HeapWord*)round_to((intptr_t)(start + obj_size),
1117 CardTableModRefBS::card_size /* bytes */));
1118 if (par) {
1119 _modUnionTable.par_mark_range(mr);
1120 } else {
1121 _modUnionTable.mark_range(mr);
1122 }
1123 } else { // not an obj array; we can just mark the head
1124 if (par) {
1125 _modUnionTable.par_mark(start);
1126 } else {
1127 _modUnionTable.mark(start);
1128 }
1129 }
1130 }
1131 }
1132 }
1133
1134 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1135 {
1136 size_t delta = pointer_delta(addr, space->bottom());
1137 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1138 }
1139
1140 void CMSCollector::icms_update_allocation_limits()
1141 {
1142 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1143 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1144
1145 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1146 if (CMSTraceIncrementalPacing) {
1147 stats().print();
1148 }
1149
1150 assert(duty_cycle <= 100, "invalid duty cycle");
1151 if (duty_cycle != 0) {
1152 // The duty_cycle is a percentage between 0 and 100; convert to words and
1153 // then compute the offset from the endpoints of the space.
1154 size_t free_words = eden->free() / HeapWordSize;
1155 double free_words_dbl = (double)free_words;
1156 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1157 size_t offset_words = (free_words - duty_cycle_words) / 2;
1158
1159 _icms_start_limit = eden->top() + offset_words;
1160 _icms_stop_limit = eden->end() - offset_words;
1161
1162 // The limits may be adjusted (shifted to the right) by
1163 // CMSIncrementalOffset, to allow the application more mutator time after a
1164 // young gen gc (when all mutators were stopped) and before CMS starts and
1165 // takes away one or more cpus.
1166 if (CMSIncrementalOffset != 0) {
1167 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1168 size_t adjustment = (size_t)adjustment_dbl;
1169 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1170 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1171 _icms_start_limit += adjustment;
1172 _icms_stop_limit = tmp_stop;
1173 }
1174 }
1175 }
1176 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1177 _icms_start_limit = _icms_stop_limit = eden->end();
1178 }
1179
1180 // Install the new start limit.
1181 eden->set_soft_end(_icms_start_limit);
1182
1183 if (CMSTraceIncrementalMode) {
1184 gclog_or_tty->print(" icms alloc limits: "
1185 PTR_FORMAT "," PTR_FORMAT
1186 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1187 _icms_start_limit, _icms_stop_limit,
1188 percent_of_space(eden, _icms_start_limit),
1189 percent_of_space(eden, _icms_stop_limit));
1190 if (Verbose) {
1191 gclog_or_tty->print("eden: ");
1192 eden->print_on(gclog_or_tty);
1193 }
1194 }
1195 }
1196
1197 // Any changes here should try to maintain the invariant
1198 // that if this method is called with _icms_start_limit
1199 // and _icms_stop_limit both NULL, then it should return NULL
1200 // and not notify the icms thread.
1201 HeapWord*
1202 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1203 size_t word_size)
1204 {
1205 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1206 // nop.
1207 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1208 if (top <= _icms_start_limit) {
1209 if (CMSTraceIncrementalMode) {
1210 space->print_on(gclog_or_tty);
1211 gclog_or_tty->stamp();
1212 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1213 ", new limit=" PTR_FORMAT
1214 " (" SIZE_FORMAT "%%)",
1215 top, _icms_stop_limit,
1216 percent_of_space(space, _icms_stop_limit));
1217 }
1218 ConcurrentMarkSweepThread::start_icms();
1219 assert(top < _icms_stop_limit, "Tautology");
1220 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1221 return _icms_stop_limit;
1222 }
1223
1224 // The allocation will cross both the _start and _stop limits, so do the
1225 // stop notification also and return end().
1226 if (CMSTraceIncrementalMode) {
1227 space->print_on(gclog_or_tty);
1228 gclog_or_tty->stamp();
1229 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1230 ", new limit=" PTR_FORMAT
1231 " (" SIZE_FORMAT "%%)",
1232 top, space->end(),
1233 percent_of_space(space, space->end()));
1234 }
1235 ConcurrentMarkSweepThread::stop_icms();
1236 return space->end();
1237 }
1238
1239 if (top <= _icms_stop_limit) {
1240 if (CMSTraceIncrementalMode) {
1241 space->print_on(gclog_or_tty);
1242 gclog_or_tty->stamp();
1243 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1244 ", new limit=" PTR_FORMAT
1245 " (" SIZE_FORMAT "%%)",
1246 top, space->end(),
1247 percent_of_space(space, space->end()));
1248 }
1249 ConcurrentMarkSweepThread::stop_icms();
1250 return space->end();
1251 }
1252
1253 if (CMSTraceIncrementalMode) {
1254 space->print_on(gclog_or_tty);
1255 gclog_or_tty->stamp();
1256 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1257 ", new limit=" PTR_FORMAT,
1258 top, NULL);
1259 }
1260 }
1261
1262 return NULL;
1263 }
1264
1265 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1266 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1267 // allocate, copy and if necessary update promoinfo --
1268 // delegate to underlying space.
1269 assert_lock_strong(freelistLock());
1270
1271 #ifndef PRODUCT
1272 if (Universe::heap()->promotion_should_fail()) {
1273 return NULL;
1274 }
1275 #endif // #ifndef PRODUCT
1276
1277 oop res = _cmsSpace->promote(obj, obj_size);
1278 if (res == NULL) {
1279 // expand and retry
1280 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1281 expand(s*HeapWordSize, MinHeapDeltaBytes,
1282 CMSExpansionCause::_satisfy_promotion);
1283 // Since there's currently no next generation, we don't try to promote
1284 // into a more senior generation.
1285 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1286 "is made to pass on a possibly failing "
1287 "promotion to next generation");
1288 res = _cmsSpace->promote(obj, obj_size);
1289 }
1290 if (res != NULL) {
1291 // See comment in allocate() about when objects should
1292 // be allocated live.
1293 assert(obj->is_oop(), "Will dereference klass pointer below");
1294 collector()->promoted(false, // Not parallel
1295 (HeapWord*)res, obj->is_objArray(), obj_size);
1296 // promotion counters
1297 NOT_PRODUCT(
1298 _numObjectsPromoted++;
1299 _numWordsPromoted +=
1300 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1301 )
1302 }
1303 return res;
1304 }
1305
1306
1307 HeapWord*
1308 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1309 HeapWord* top,
1310 size_t word_sz)
1311 {
1312 return collector()->allocation_limit_reached(space, top, word_sz);
1313 }
1314
1315 // IMPORTANT: Notes on object size recognition in CMS.
1316 // ---------------------------------------------------
1317 // A block of storage in the CMS generation is always in
1318 // one of three states. A free block (FREE), an allocated
1319 // object (OBJECT) whose size() method reports the correct size,
1320 // and an intermediate state (TRANSIENT) in which its size cannot
1321 // be accurately determined.
1322 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1323 // -----------------------------------------------------
1324 // FREE: klass_word & 1 == 1; mark_word holds block size
1325 //
1326 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1327 // obj->size() computes correct size
1328 // [Perm Gen objects needs to be "parsable" before they can be navigated]
1329 //
1330 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1331 //
1332 // STATE IDENTIFICATION: (64 bit+COOPS)
1333 // ------------------------------------
1334 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1335 //
1336 // OBJECT: klass_word installed; klass_word != 0;
1337 // obj->size() computes correct size
1338 // [Perm Gen comment above continues to hold]
1339 //
1340 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1341 //
1342 //
1343 // STATE TRANSITION DIAGRAM
1344 //
1345 // mut / parnew mut / parnew
1346 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1347 // ^ |
1348 // |------------------------ DEAD <------------------------------------|
1349 // sweep mut
1350 //
1351 // While a block is in TRANSIENT state its size cannot be determined
1352 // so readers will either need to come back later or stall until
1353 // the size can be determined. Note that for the case of direct
1354 // allocation, P-bits, when available, may be used to determine the
1355 // size of an object that may not yet have been initialized.
1356
1357 // Things to support parallel young-gen collection.
1358 oop
1359 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1360 oop old, markOop m,
1361 size_t word_sz) {
1362 #ifndef PRODUCT
1363 if (Universe::heap()->promotion_should_fail()) {
1364 return NULL;
1365 }
1366 #endif // #ifndef PRODUCT
1367
1368 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1369 PromotionInfo* promoInfo = &ps->promo;
1370 // if we are tracking promotions, then first ensure space for
1371 // promotion (including spooling space for saving header if necessary).
1372 // then allocate and copy, then track promoted info if needed.
1373 // When tracking (see PromotionInfo::track()), the mark word may
1374 // be displaced and in this case restoration of the mark word
1375 // occurs in the (oop_since_save_marks_)iterate phase.
1376 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1377 // Out of space for allocating spooling buffers;
1378 // try expanding and allocating spooling buffers.
1379 if (!expand_and_ensure_spooling_space(promoInfo)) {
1380 return NULL;
1381 }
1382 }
1383 assert(promoInfo->has_spooling_space(), "Control point invariant");
1384 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1385 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1386 if (obj_ptr == NULL) {
1387 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1388 if (obj_ptr == NULL) {
1389 return NULL;
1390 }
1391 }
1392 oop obj = oop(obj_ptr);
1393 OrderAccess::storestore();
1394 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1395 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1396 // IMPORTANT: See note on object initialization for CMS above.
1397 // Otherwise, copy the object. Here we must be careful to insert the
1398 // klass pointer last, since this marks the block as an allocated object.
1399 // Except with compressed oops it's the mark word.
1400 HeapWord* old_ptr = (HeapWord*)old;
1401 // Restore the mark word copied above.
1402 obj->set_mark(m);
1403 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1404 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1405 OrderAccess::storestore();
1406
1407 if (UseCompressedOops) {
1408 // Copy gap missed by (aligned) header size calculation below
1409 obj->set_klass_gap(old->klass_gap());
1410 }
1411 if (word_sz > (size_t)oopDesc::header_size()) {
1412 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1413 obj_ptr + oopDesc::header_size(),
1414 word_sz - oopDesc::header_size());
1415 }
1416
1417 // Now we can track the promoted object, if necessary. We take care
1418 // to delay the transition from uninitialized to full object
1419 // (i.e., insertion of klass pointer) until after, so that it
1420 // atomically becomes a promoted object.
1421 if (promoInfo->tracking()) {
1422 promoInfo->track((PromotedObject*)obj, old->klass());
1423 }
1424 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1425 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1426 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1427
1428 // Finally, install the klass pointer (this should be volatile).
1429 OrderAccess::storestore();
1430 obj->set_klass(old->klass());
1431 // We should now be able to calculate the right size for this object
1432 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1433
1434 collector()->promoted(true, // parallel
1435 obj_ptr, old->is_objArray(), word_sz);
1436
1437 NOT_PRODUCT(
1438 Atomic::inc_ptr(&_numObjectsPromoted);
1439 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1440 )
1441
1442 return obj;
1443 }
1444
1445 void
1446 ConcurrentMarkSweepGeneration::
1447 par_promote_alloc_undo(int thread_num,
1448 HeapWord* obj, size_t word_sz) {
1449 // CMS does not support promotion undo.
1450 ShouldNotReachHere();
1451 }
1452
1453 void
1454 ConcurrentMarkSweepGeneration::
1455 par_promote_alloc_done(int thread_num) {
1456 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1457 ps->lab.retire(thread_num);
1458 }
1459
1460 void
1461 ConcurrentMarkSweepGeneration::
1462 par_oop_since_save_marks_iterate_done(int thread_num) {
1463 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1464 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1465 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1466 }
1467
1468 // XXXPERM
1469 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1470 size_t size,
1471 bool tlab)
1472 {
1473 // We allow a STW collection only if a full
1474 // collection was requested.
1475 return full || should_allocate(size, tlab); // FIX ME !!!
1476 // This and promotion failure handling are connected at the
1477 // hip and should be fixed by untying them.
1478 }
1479
1480 bool CMSCollector::shouldConcurrentCollect() {
1481 if (_full_gc_requested) {
1482 if (Verbose && PrintGCDetails) {
1483 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1484 " gc request (or gc_locker)");
1485 }
1486 return true;
1487 }
1488
1489 // For debugging purposes, change the type of collection.
1490 // If the rotation is not on the concurrent collection
1491 // type, don't start a concurrent collection.
1492 NOT_PRODUCT(
1493 if (RotateCMSCollectionTypes &&
1494 (_cmsGen->debug_collection_type() !=
1495 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1496 assert(_cmsGen->debug_collection_type() !=
1497 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1498 "Bad cms collection type");
1499 return false;
1500 }
1501 )
1502
1503 FreelistLocker x(this);
1504 // ------------------------------------------------------------------
1505 // Print out lots of information which affects the initiation of
1506 // a collection.
1507 if (PrintCMSInitiationStatistics && stats().valid()) {
1508 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1509 gclog_or_tty->stamp();
1510 gclog_or_tty->print_cr("");
1511 stats().print_on(gclog_or_tty);
1512 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1513 stats().time_until_cms_gen_full());
1514 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1515 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1516 _cmsGen->contiguous_available());
1517 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1518 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1519 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1520 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1521 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1522 }
1523 // ------------------------------------------------------------------
1524
1525 // If the estimated time to complete a cms collection (cms_duration())
1526 // is less than the estimated time remaining until the cms generation
1527 // is full, start a collection.
1528 if (!UseCMSInitiatingOccupancyOnly) {
1529 if (stats().valid()) {
1530 if (stats().time_until_cms_start() == 0.0) {
1531 return true;
1532 }
1533 } else {
1534 // We want to conservatively collect somewhat early in order
1535 // to try and "bootstrap" our CMS/promotion statistics;
1536 // this branch will not fire after the first successful CMS
1537 // collection because the stats should then be valid.
1538 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1539 if (Verbose && PrintGCDetails) {
1540 gclog_or_tty->print_cr(
1541 " CMSCollector: collect for bootstrapping statistics:"
1542 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1543 _bootstrap_occupancy);
1544 }
1545 return true;
1546 }
1547 }
1548 }
1549
1550 // Otherwise, we start a collection cycle if either the perm gen or
1551 // old gen want a collection cycle started. Each may use
1552 // an appropriate criterion for making this decision.
1553 // XXX We need to make sure that the gen expansion
1554 // criterion dovetails well with this. XXX NEED TO FIX THIS
1555 if (_cmsGen->should_concurrent_collect()) {
1556 if (Verbose && PrintGCDetails) {
1557 gclog_or_tty->print_cr("CMS old gen initiated");
1558 }
1559 return true;
1560 }
1561
1562 // We start a collection if we believe an incremental collection may fail;
1563 // this is not likely to be productive in practice because it's probably too
1564 // late anyway.
1565 GenCollectedHeap* gch = GenCollectedHeap::heap();
1566 assert(gch->collector_policy()->is_two_generation_policy(),
1567 "You may want to check the correctness of the following");
1568 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1569 if (Verbose && PrintGCDetails) {
1570 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1571 }
1572 return true;
1573 }
1574
1575 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1576 bool res = update_should_unload_classes();
1577 if (res) {
1578 if (Verbose && PrintGCDetails) {
1579 gclog_or_tty->print_cr("CMS perm gen initiated");
1580 }
1581 return true;
1582 }
1583 }
1584 return false;
1585 }
1586
1587 // Clear _expansion_cause fields of constituent generations
1588 void CMSCollector::clear_expansion_cause() {
1589 _cmsGen->clear_expansion_cause();
1590 _permGen->clear_expansion_cause();
1591 }
1592
1593 // We should be conservative in starting a collection cycle. To
1594 // start too eagerly runs the risk of collecting too often in the
1595 // extreme. To collect too rarely falls back on full collections,
1596 // which works, even if not optimum in terms of concurrent work.
1597 // As a work around for too eagerly collecting, use the flag
1598 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1599 // giving the user an easily understandable way of controlling the
1600 // collections.
1601 // We want to start a new collection cycle if any of the following
1602 // conditions hold:
1603 // . our current occupancy exceeds the configured initiating occupancy
1604 // for this generation, or
1605 // . we recently needed to expand this space and have not, since that
1606 // expansion, done a collection of this generation, or
1607 // . the underlying space believes that it may be a good idea to initiate
1608 // a concurrent collection (this may be based on criteria such as the
1609 // following: the space uses linear allocation and linear allocation is
1610 // going to fail, or there is believed to be excessive fragmentation in
1611 // the generation, etc... or ...
1612 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1613 // the case of the old generation, not the perm generation; see CR 6543076):
1614 // we may be approaching a point at which allocation requests may fail because
1615 // we will be out of sufficient free space given allocation rate estimates.]
1616 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1617
1618 assert_lock_strong(freelistLock());
1619 if (occupancy() > initiating_occupancy()) {
1620 if (PrintGCDetails && Verbose) {
1621 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1622 short_name(), occupancy(), initiating_occupancy());
1623 }
1624 return true;
1625 }
1626 if (UseCMSInitiatingOccupancyOnly) {
1627 return false;
1628 }
1629 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1630 if (PrintGCDetails && Verbose) {
1631 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1632 short_name());
1633 }
1634 return true;
1635 }
1636 if (_cmsSpace->should_concurrent_collect()) {
1637 if (PrintGCDetails && Verbose) {
1638 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1639 short_name());
1640 }
1641 return true;
1642 }
1643 return false;
1644 }
1645
1646 void ConcurrentMarkSweepGeneration::collect(bool full,
1647 bool clear_all_soft_refs,
1648 size_t size,
1649 bool tlab)
1650 {
1651 collector()->collect(full, clear_all_soft_refs, size, tlab);
1652 }
1653
1654 void CMSCollector::collect(bool full,
1655 bool clear_all_soft_refs,
1656 size_t size,
1657 bool tlab)
1658 {
1659 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1660 // For debugging purposes skip the collection if the state
1661 // is not currently idle
1662 if (TraceCMSState) {
1663 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1664 Thread::current(), full, _collectorState);
1665 }
1666 return;
1667 }
1668
1669 // The following "if" branch is present for defensive reasons.
1670 // In the current uses of this interface, it can be replaced with:
1671 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1672 // But I am not placing that assert here to allow future
1673 // generality in invoking this interface.
1674 if (GC_locker::is_active()) {
1675 // A consistency test for GC_locker
1676 assert(GC_locker::needs_gc(), "Should have been set already");
1677 // Skip this foreground collection, instead
1678 // expanding the heap if necessary.
1679 // Need the free list locks for the call to free() in compute_new_size()
1680 compute_new_size();
1681 return;
1682 }
1683 acquire_control_and_collect(full, clear_all_soft_refs);
1684 _full_gcs_since_conc_gc++;
1685
1686 }
1687
1688 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1689 GenCollectedHeap* gch = GenCollectedHeap::heap();
1690 unsigned int gc_count = gch->total_full_collections();
1691 if (gc_count == full_gc_count) {
1692 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1693 _full_gc_requested = true;
1694 _full_gc_cause = cause;
1695 CGC_lock->notify(); // nudge CMS thread
1696 } else {
1697 assert(gc_count > full_gc_count, "Error: causal loop");
1698 }
1699 }
1700
1701 bool CMSCollector::is_external_interruption() {
1702 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1703 return GCCause::is_user_requested_gc(cause) ||
1704 GCCause::is_serviceability_requested_gc(cause);
1705 }
1706
1707 void CMSCollector::report_concurrent_mode_interruption() {
1708 if (is_external_interruption()) {
1709 if (PrintGCDetails) {
1710 gclog_or_tty->print(" (concurrent mode interrupted)");
1711 }
1712 } else {
1713 if (PrintGCDetails) {
1714 gclog_or_tty->print(" (concurrent mode failure)");
1715 }
1716 _gc_tracer_cm->report_concurrent_mode_failure();
1717 }
1718 }
1719
1720 // The foreground and background collectors need to coordinate in order
1721 // to make sure that they do not mutually interfere with CMS collections.
1722 // When a background collection is active,
1723 // the foreground collector may need to take over (preempt) and
1724 // synchronously complete an ongoing collection. Depending on the
1725 // frequency of the background collections and the heap usage
1726 // of the application, this preemption can be seldom or frequent.
1727 // There are only certain
1728 // points in the background collection that the "collection-baton"
1729 // can be passed to the foreground collector.
1730 //
1731 // The foreground collector will wait for the baton before
1732 // starting any part of the collection. The foreground collector
1733 // will only wait at one location.
1734 //
1735 // The background collector will yield the baton before starting a new
1736 // phase of the collection (e.g., before initial marking, marking from roots,
1737 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1738 // of the loop which switches the phases. The background collector does some
1739 // of the phases (initial mark, final re-mark) with the world stopped.
1740 // Because of locking involved in stopping the world,
1741 // the foreground collector should not block waiting for the background
1742 // collector when it is doing a stop-the-world phase. The background
1743 // collector will yield the baton at an additional point just before
1744 // it enters a stop-the-world phase. Once the world is stopped, the
1745 // background collector checks the phase of the collection. If the
1746 // phase has not changed, it proceeds with the collection. If the
1747 // phase has changed, it skips that phase of the collection. See
1748 // the comments on the use of the Heap_lock in collect_in_background().
1749 //
1750 // Variable used in baton passing.
1751 // _foregroundGCIsActive - Set to true by the foreground collector when
1752 // it wants the baton. The foreground clears it when it has finished
1753 // the collection.
1754 // _foregroundGCShouldWait - Set to true by the background collector
1755 // when it is running. The foreground collector waits while
1756 // _foregroundGCShouldWait is true.
1757 // CGC_lock - monitor used to protect access to the above variables
1758 // and to notify the foreground and background collectors.
1759 // _collectorState - current state of the CMS collection.
1760 //
1761 // The foreground collector
1762 // acquires the CGC_lock
1763 // sets _foregroundGCIsActive
1764 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1765 // various locks acquired in preparation for the collection
1766 // are released so as not to block the background collector
1767 // that is in the midst of a collection
1768 // proceeds with the collection
1769 // clears _foregroundGCIsActive
1770 // returns
1771 //
1772 // The background collector in a loop iterating on the phases of the
1773 // collection
1774 // acquires the CGC_lock
1775 // sets _foregroundGCShouldWait
1776 // if _foregroundGCIsActive is set
1777 // clears _foregroundGCShouldWait, notifies _CGC_lock
1778 // waits on _CGC_lock for _foregroundGCIsActive to become false
1779 // and exits the loop.
1780 // otherwise
1781 // proceed with that phase of the collection
1782 // if the phase is a stop-the-world phase,
1783 // yield the baton once more just before enqueueing
1784 // the stop-world CMS operation (executed by the VM thread).
1785 // returns after all phases of the collection are done
1786 //
1787
1788 void CMSCollector::acquire_control_and_collect(bool full,
1789 bool clear_all_soft_refs) {
1790 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1791 assert(!Thread::current()->is_ConcurrentGC_thread(),
1792 "shouldn't try to acquire control from self!");
1793
1794 // Start the protocol for acquiring control of the
1795 // collection from the background collector (aka CMS thread).
1796 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1797 "VM thread should have CMS token");
1798 // Remember the possibly interrupted state of an ongoing
1799 // concurrent collection
1800 CollectorState first_state = _collectorState;
1801
1802 // Signal to a possibly ongoing concurrent collection that
1803 // we want to do a foreground collection.
1804 _foregroundGCIsActive = true;
1805
1806 // Disable incremental mode during a foreground collection.
1807 ICMSDisabler icms_disabler;
1808
1809 // release locks and wait for a notify from the background collector
1810 // releasing the locks in only necessary for phases which
1811 // do yields to improve the granularity of the collection.
1812 assert_lock_strong(bitMapLock());
1813 // We need to lock the Free list lock for the space that we are
1814 // currently collecting.
1815 assert(haveFreelistLocks(), "Must be holding free list locks");
1816 bitMapLock()->unlock();
1817 releaseFreelistLocks();
1818 {
1819 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1820 if (_foregroundGCShouldWait) {
1821 // We are going to be waiting for action for the CMS thread;
1822 // it had better not be gone (for instance at shutdown)!
1823 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1824 "CMS thread must be running");
1825 // Wait here until the background collector gives us the go-ahead
1826 ConcurrentMarkSweepThread::clear_CMS_flag(
1827 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1828 // Get a possibly blocked CMS thread going:
1829 // Note that we set _foregroundGCIsActive true above,
1830 // without protection of the CGC_lock.
1831 CGC_lock->notify();
1832 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1833 "Possible deadlock");
1834 while (_foregroundGCShouldWait) {
1835 // wait for notification
1836 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1837 // Possibility of delay/starvation here, since CMS token does
1838 // not know to give priority to VM thread? Actually, i think
1839 // there wouldn't be any delay/starvation, but the proof of
1840 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1841 }
1842 ConcurrentMarkSweepThread::set_CMS_flag(
1843 ConcurrentMarkSweepThread::CMS_vm_has_token);
1844 }
1845 }
1846 // The CMS_token is already held. Get back the other locks.
1847 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1848 "VM thread should have CMS token");
1849 getFreelistLocks();
1850 bitMapLock()->lock_without_safepoint_check();
1851 if (TraceCMSState) {
1852 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1853 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1854 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1855 }
1856
1857 // Check if we need to do a compaction, or if not, whether
1858 // we need to start the mark-sweep from scratch.
1859 bool should_compact = false;
1860 bool should_start_over = false;
1861 decide_foreground_collection_type(clear_all_soft_refs,
1862 &should_compact, &should_start_over);
1863
1864 NOT_PRODUCT(
1865 if (RotateCMSCollectionTypes) {
1866 if (_cmsGen->debug_collection_type() ==
1867 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1868 should_compact = true;
1869 } else if (_cmsGen->debug_collection_type() ==
1870 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1871 should_compact = false;
1872 }
1873 }
1874 )
1875
1876 if (first_state > Idling) {
1877 report_concurrent_mode_interruption();
1878 }
1879
1880 if (should_compact) {
1881 // If the collection is being acquired from the background
1882 // collector, there may be references on the discovered
1883 // references lists that have NULL referents (being those
1884 // that were concurrently cleared by a mutator) or
1885 // that are no longer active (having been enqueued concurrently
1886 // by the mutator).
1887 // Scrub the list of those references because Mark-Sweep-Compact
1888 // code assumes referents are not NULL and that all discovered
1889 // Reference objects are active.
1890 ref_processor()->clean_up_discovered_references();
1891
1892 if (first_state > Idling) {
1893 save_heap_summary();
1894 }
1895
1896 do_compaction_work(clear_all_soft_refs);
1897
1898 // Has the GC time limit been exceeded?
1899 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1900 size_t max_eden_size = young_gen->max_capacity() -
1901 young_gen->to()->capacity() -
1902 young_gen->from()->capacity();
1903 GenCollectedHeap* gch = GenCollectedHeap::heap();
1904 GCCause::Cause gc_cause = gch->gc_cause();
1905 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1906 young_gen->eden()->used(),
1907 _cmsGen->max_capacity(),
1908 max_eden_size,
1909 full,
1910 gc_cause,
1911 gch->collector_policy());
1912 } else {
1913 do_mark_sweep_work(clear_all_soft_refs, first_state,
1914 should_start_over);
1915 }
1916 // Reset the expansion cause, now that we just completed
1917 // a collection cycle.
1918 clear_expansion_cause();
1919 _foregroundGCIsActive = false;
1920 return;
1921 }
1922
1923 // Resize the perm generation and the tenured generation
1924 // after obtaining the free list locks for the
1925 // two generations.
1926 void CMSCollector::compute_new_size() {
1927 assert_locked_or_safepoint(Heap_lock);
1928 FreelistLocker z(this);
1929 _permGen->compute_new_size();
1930 _cmsGen->compute_new_size();
1931 }
1932
1933 // A work method used by foreground collection to determine
1934 // what type of collection (compacting or not, continuing or fresh)
1935 // it should do.
1936 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1937 // and CMSCompactWhenClearAllSoftRefs the default in the future
1938 // and do away with the flags after a suitable period.
1939 void CMSCollector::decide_foreground_collection_type(
1940 bool clear_all_soft_refs, bool* should_compact,
1941 bool* should_start_over) {
1942 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1943 // flag is set, and we have either requested a System.gc() or
1944 // the number of full gc's since the last concurrent cycle
1945 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1946 // or if an incremental collection has failed
1947 GenCollectedHeap* gch = GenCollectedHeap::heap();
1948 assert(gch->collector_policy()->is_two_generation_policy(),
1949 "You may want to check the correctness of the following");
1950 // Inform cms gen if this was due to partial collection failing.
1951 // The CMS gen may use this fact to determine its expansion policy.
1952 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1953 assert(!_cmsGen->incremental_collection_failed(),
1954 "Should have been noticed, reacted to and cleared");
1955 _cmsGen->set_incremental_collection_failed();
1956 }
1957 *should_compact =
1958 UseCMSCompactAtFullCollection &&
1959 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1960 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1961 gch->incremental_collection_will_fail(true /* consult_young */));
1962 *should_start_over = false;
1963 if (clear_all_soft_refs && !*should_compact) {
1964 // We are about to do a last ditch collection attempt
1965 // so it would normally make sense to do a compaction
1966 // to reclaim as much space as possible.
1967 if (CMSCompactWhenClearAllSoftRefs) {
1968 // Default: The rationale is that in this case either
1969 // we are past the final marking phase, in which case
1970 // we'd have to start over, or so little has been done
1971 // that there's little point in saving that work. Compaction
1972 // appears to be the sensible choice in either case.
1973 *should_compact = true;
1974 } else {
1975 // We have been asked to clear all soft refs, but not to
1976 // compact. Make sure that we aren't past the final checkpoint
1977 // phase, for that is where we process soft refs. If we are already
1978 // past that phase, we'll need to redo the refs discovery phase and
1979 // if necessary clear soft refs that weren't previously
1980 // cleared. We do so by remembering the phase in which
1981 // we came in, and if we are past the refs processing
1982 // phase, we'll choose to just redo the mark-sweep
1983 // collection from scratch.
1984 if (_collectorState > FinalMarking) {
1985 // We are past the refs processing phase;
1986 // start over and do a fresh synchronous CMS cycle
1987 _collectorState = Resetting; // skip to reset to start new cycle
1988 reset(false /* == !asynch */);
1989 *should_start_over = true;
1990 } // else we can continue a possibly ongoing current cycle
1991 }
1992 }
1993 }
1994
1995 // A work method used by the foreground collector to do
1996 // a mark-sweep-compact.
1997 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1998 GenCollectedHeap* gch = GenCollectedHeap::heap();
1999
2000 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2001 gc_timer->register_gc_start();
2002
2003 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2004 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2005
2006 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2007 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2008 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2009 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2010 }
2011
2012 // Sample collection interval time and reset for collection pause.
2013 if (UseAdaptiveSizePolicy) {
2014 size_policy()->msc_collection_begin();
2015 }
2016
2017 // Temporarily widen the span of the weak reference processing to
2018 // the entire heap.
2019 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2020 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2021 // Temporarily, clear the "is_alive_non_header" field of the
2022 // reference processor.
2023 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2024 // Temporarily make reference _processing_ single threaded (non-MT).
2025 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2026 // Temporarily make refs discovery atomic
2027 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2028 // Temporarily make reference _discovery_ single threaded (non-MT)
2029 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2030
2031 ref_processor()->set_enqueuing_is_done(false);
2032 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2033 ref_processor()->setup_policy(clear_all_soft_refs);
2034 // If an asynchronous collection finishes, the _modUnionTable is
2035 // all clear. If we are assuming the collection from an asynchronous
2036 // collection, clear the _modUnionTable.
2037 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2038 "_modUnionTable should be clear if the baton was not passed");
2039 _modUnionTable.clear_all();
2040
2041 // We must adjust the allocation statistics being maintained
2042 // in the free list space. We do so by reading and clearing
2043 // the sweep timer and updating the block flux rate estimates below.
2044 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2045 if (_inter_sweep_timer.is_active()) {
2046 _inter_sweep_timer.stop();
2047 // Note that we do not use this sample to update the _inter_sweep_estimate.
2048 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2049 _inter_sweep_estimate.padded_average(),
2050 _intra_sweep_estimate.padded_average());
2051 }
2052
2053 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2054 ref_processor(), clear_all_soft_refs);
2055 #ifdef ASSERT
2056 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2057 size_t free_size = cms_space->free();
2058 assert(free_size ==
2059 pointer_delta(cms_space->end(), cms_space->compaction_top())
2060 * HeapWordSize,
2061 "All the free space should be compacted into one chunk at top");
2062 assert(cms_space->dictionary()->total_chunk_size(
2063 debug_only(cms_space->freelistLock())) == 0 ||
2064 cms_space->totalSizeInIndexedFreeLists() == 0,
2065 "All the free space should be in a single chunk");
2066 size_t num = cms_space->totalCount();
2067 assert((free_size == 0 && num == 0) ||
2068 (free_size > 0 && (num == 1 || num == 2)),
2069 "There should be at most 2 free chunks after compaction");
2070 #endif // ASSERT
2071 _collectorState = Resetting;
2072 assert(_restart_addr == NULL,
2073 "Should have been NULL'd before baton was passed");
2074 reset(false /* == !asynch */);
2075 _cmsGen->reset_after_compaction();
2076 _concurrent_cycles_since_last_unload = 0;
2077
2078 if (verifying() && !should_unload_classes()) {
2079 perm_gen_verify_bit_map()->clear_all();
2080 }
2081
2082 // Clear any data recorded in the PLAB chunk arrays.
2083 if (_survivor_plab_array != NULL) {
2084 reset_survivor_plab_arrays();
2085 }
2086
2087 // Adjust the per-size allocation stats for the next epoch.
2088 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2089 // Restart the "inter sweep timer" for the next epoch.
2090 _inter_sweep_timer.reset();
2091 _inter_sweep_timer.start();
2092
2093 // Sample collection pause time and reset for collection interval.
2094 if (UseAdaptiveSizePolicy) {
2095 size_policy()->msc_collection_end(gch->gc_cause());
2096 }
2097
2098 gc_timer->register_gc_end();
2099
2100 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2101
2102 // For a mark-sweep-compact, compute_new_size() will be called
2103 // in the heap's do_collection() method.
2104 }
2105
2106 // A work method used by the foreground collector to do
2107 // a mark-sweep, after taking over from a possibly on-going
2108 // concurrent mark-sweep collection.
2109 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2110 CollectorState first_state, bool should_start_over) {
2111 if (PrintGC && Verbose) {
2112 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2113 "collector with count %d",
2114 _full_gcs_since_conc_gc);
2115 }
2116 switch (_collectorState) {
2117 case Idling:
2118 if (first_state == Idling || should_start_over) {
2119 // The background GC was not active, or should
2120 // restarted from scratch; start the cycle.
2121 _collectorState = InitialMarking;
2122 }
2123 // If first_state was not Idling, then a background GC
2124 // was in progress and has now finished. No need to do it
2125 // again. Leave the state as Idling.
2126 break;
2127 case Precleaning:
2128 // In the foreground case don't do the precleaning since
2129 // it is not done concurrently and there is extra work
2130 // required.
2131 _collectorState = FinalMarking;
2132 }
2133 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2134
2135 // For a mark-sweep, compute_new_size() will be called
2136 // in the heap's do_collection() method.
2137 }
2138
2139
2140 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2141 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2142 EdenSpace* eden_space = dng->eden();
2143 ContiguousSpace* from_space = dng->from();
2144 ContiguousSpace* to_space = dng->to();
2145 // Eden
2146 if (_eden_chunk_array != NULL) {
2147 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2148 eden_space->bottom(), eden_space->top(),
2149 eden_space->end(), eden_space->capacity());
2150 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2151 "_eden_chunk_capacity=" SIZE_FORMAT,
2152 _eden_chunk_index, _eden_chunk_capacity);
2153 for (size_t i = 0; i < _eden_chunk_index; i++) {
2154 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2155 i, _eden_chunk_array[i]);
2156 }
2157 }
2158 // Survivor
2159 if (_survivor_chunk_array != NULL) {
2160 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2161 from_space->bottom(), from_space->top(),
2162 from_space->end(), from_space->capacity());
2163 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2164 "_survivor_chunk_capacity=" SIZE_FORMAT,
2165 _survivor_chunk_index, _survivor_chunk_capacity);
2166 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2167 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2168 i, _survivor_chunk_array[i]);
2169 }
2170 }
2171 }
2172
2173 void CMSCollector::getFreelistLocks() const {
2174 // Get locks for all free lists in all generations that this
2175 // collector is responsible for
2176 _cmsGen->freelistLock()->lock_without_safepoint_check();
2177 _permGen->freelistLock()->lock_without_safepoint_check();
2178 }
2179
2180 void CMSCollector::releaseFreelistLocks() const {
2181 // Release locks for all free lists in all generations that this
2182 // collector is responsible for
2183 _cmsGen->freelistLock()->unlock();
2184 _permGen->freelistLock()->unlock();
2185 }
2186
2187 bool CMSCollector::haveFreelistLocks() const {
2188 // Check locks for all free lists in all generations that this
2189 // collector is responsible for
2190 assert_lock_strong(_cmsGen->freelistLock());
2191 assert_lock_strong(_permGen->freelistLock());
2192 PRODUCT_ONLY(ShouldNotReachHere());
2193 return true;
2194 }
2195
2196 // A utility class that is used by the CMS collector to
2197 // temporarily "release" the foreground collector from its
2198 // usual obligation to wait for the background collector to
2199 // complete an ongoing phase before proceeding.
2200 class ReleaseForegroundGC: public StackObj {
2201 private:
2202 CMSCollector* _c;
2203 public:
2204 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2205 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2206 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2207 // allow a potentially blocked foreground collector to proceed
2208 _c->_foregroundGCShouldWait = false;
2209 if (_c->_foregroundGCIsActive) {
2210 CGC_lock->notify();
2211 }
2212 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2213 "Possible deadlock");
2214 }
2215
2216 ~ReleaseForegroundGC() {
2217 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2218 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2219 _c->_foregroundGCShouldWait = true;
2220 }
2221 };
2222
2223 // There are separate collect_in_background and collect_in_foreground because of
2224 // the different locking requirements of the background collector and the
2225 // foreground collector. There was originally an attempt to share
2226 // one "collect" method between the background collector and the foreground
2227 // collector but the if-then-else required made it cleaner to have
2228 // separate methods.
2229 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2230 assert(Thread::current()->is_ConcurrentGC_thread(),
2231 "A CMS asynchronous collection is only allowed on a CMS thread.");
2232
2233 GenCollectedHeap* gch = GenCollectedHeap::heap();
2234 {
2235 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2236 MutexLockerEx hl(Heap_lock, safepoint_check);
2237 FreelistLocker fll(this);
2238 MutexLockerEx x(CGC_lock, safepoint_check);
2239 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2240 // The foreground collector is active or we're
2241 // not using asynchronous collections. Skip this
2242 // background collection.
2243 assert(!_foregroundGCShouldWait, "Should be clear");
2244 return;
2245 } else {
2246 assert(_collectorState == Idling, "Should be idling before start.");
2247 _collectorState = InitialMarking;
2248 register_gc_start(cause);
2249 // Reset the expansion cause, now that we are about to begin
2250 // a new cycle.
2251 clear_expansion_cause();
2252 }
2253 // Decide if we want to enable class unloading as part of the
2254 // ensuing concurrent GC cycle.
2255 update_should_unload_classes();
2256 _full_gc_requested = false; // acks all outstanding full gc requests
2257 _full_gc_cause = GCCause::_no_gc;
2258 // Signal that we are about to start a collection
2259 gch->increment_total_full_collections(); // ... starting a collection cycle
2260 _collection_count_start = gch->total_full_collections();
2261 }
2262
2263 // Used for PrintGC
2264 size_t prev_used;
2265 if (PrintGC && Verbose) {
2266 prev_used = _cmsGen->used(); // XXXPERM
2267 }
2268
2269 // The change of the collection state is normally done at this level;
2270 // the exceptions are phases that are executed while the world is
2271 // stopped. For those phases the change of state is done while the
2272 // world is stopped. For baton passing purposes this allows the
2273 // background collector to finish the phase and change state atomically.
2274 // The foreground collector cannot wait on a phase that is done
2275 // while the world is stopped because the foreground collector already
2276 // has the world stopped and would deadlock.
2277 while (_collectorState != Idling) {
2278 if (TraceCMSState) {
2279 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2280 Thread::current(), _collectorState);
2281 }
2282 // The foreground collector
2283 // holds the Heap_lock throughout its collection.
2284 // holds the CMS token (but not the lock)
2285 // except while it is waiting for the background collector to yield.
2286 //
2287 // The foreground collector should be blocked (not for long)
2288 // if the background collector is about to start a phase
2289 // executed with world stopped. If the background
2290 // collector has already started such a phase, the
2291 // foreground collector is blocked waiting for the
2292 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2293 // are executed in the VM thread.
2294 //
2295 // The locking order is
2296 // PendingListLock (PLL) -- if applicable (FinalMarking)
2297 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2298 // CMS token (claimed in
2299 // stop_world_and_do() -->
2300 // safepoint_synchronize() -->
2301 // CMSThread::synchronize())
2302
2303 {
2304 // Check if the FG collector wants us to yield.
2305 CMSTokenSync x(true); // is cms thread
2306 if (waitForForegroundGC()) {
2307 // We yielded to a foreground GC, nothing more to be
2308 // done this round.
2309 assert(_foregroundGCShouldWait == false, "We set it to false in "
2310 "waitForForegroundGC()");
2311 if (TraceCMSState) {
2312 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2313 " exiting collection CMS state %d",
2314 Thread::current(), _collectorState);
2315 }
2316 return;
2317 } else {
2318 // The background collector can run but check to see if the
2319 // foreground collector has done a collection while the
2320 // background collector was waiting to get the CGC_lock
2321 // above. If yes, break so that _foregroundGCShouldWait
2322 // is cleared before returning.
2323 if (_collectorState == Idling) {
2324 break;
2325 }
2326 }
2327 }
2328
2329 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2330 "should be waiting");
2331
2332 switch (_collectorState) {
2333 case InitialMarking:
2334 {
2335 ReleaseForegroundGC x(this);
2336 stats().record_cms_begin();
2337 VM_CMS_Initial_Mark initial_mark_op(this);
2338 VMThread::execute(&initial_mark_op);
2339 }
2340 // The collector state may be any legal state at this point
2341 // since the background collector may have yielded to the
2342 // foreground collector.
2343 break;
2344 case Marking:
2345 // initial marking in checkpointRootsInitialWork has been completed
2346 if (markFromRoots(true)) { // we were successful
2347 assert(_collectorState == Precleaning, "Collector state should "
2348 "have changed");
2349 } else {
2350 assert(_foregroundGCIsActive, "Internal state inconsistency");
2351 }
2352 break;
2353 case Precleaning:
2354 if (UseAdaptiveSizePolicy) {
2355 size_policy()->concurrent_precleaning_begin();
2356 }
2357 // marking from roots in markFromRoots has been completed
2358 preclean();
2359 if (UseAdaptiveSizePolicy) {
2360 size_policy()->concurrent_precleaning_end();
2361 }
2362 assert(_collectorState == AbortablePreclean ||
2363 _collectorState == FinalMarking,
2364 "Collector state should have changed");
2365 break;
2366 case AbortablePreclean:
2367 if (UseAdaptiveSizePolicy) {
2368 size_policy()->concurrent_phases_resume();
2369 }
2370 abortable_preclean();
2371 if (UseAdaptiveSizePolicy) {
2372 size_policy()->concurrent_precleaning_end();
2373 }
2374 assert(_collectorState == FinalMarking, "Collector state should "
2375 "have changed");
2376 break;
2377 case FinalMarking:
2378 {
2379 ReleaseForegroundGC x(this);
2380
2381 VM_CMS_Final_Remark final_remark_op(this);
2382 VMThread::execute(&final_remark_op);
2383 }
2384 assert(_foregroundGCShouldWait, "block post-condition");
2385 break;
2386 case Sweeping:
2387 if (UseAdaptiveSizePolicy) {
2388 size_policy()->concurrent_sweeping_begin();
2389 }
2390 // final marking in checkpointRootsFinal has been completed
2391 sweep(true);
2392 assert(_collectorState == Resizing, "Collector state change "
2393 "to Resizing must be done under the free_list_lock");
2394 _full_gcs_since_conc_gc = 0;
2395
2396 // Stop the timers for adaptive size policy for the concurrent phases
2397 if (UseAdaptiveSizePolicy) {
2398 size_policy()->concurrent_sweeping_end();
2399 size_policy()->concurrent_phases_end(gch->gc_cause(),
2400 gch->prev_gen(_cmsGen)->capacity(),
2401 _cmsGen->free());
2402 }
2403
2404 case Resizing: {
2405 // Sweeping has been completed...
2406 // At this point the background collection has completed.
2407 // Don't move the call to compute_new_size() down
2408 // into code that might be executed if the background
2409 // collection was preempted.
2410 {
2411 ReleaseForegroundGC x(this); // unblock FG collection
2412 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2413 CMSTokenSync z(true); // not strictly needed.
2414 if (_collectorState == Resizing) {
2415 compute_new_size();
2416 save_heap_summary();
2417 _collectorState = Resetting;
2418 } else {
2419 assert(_collectorState == Idling, "The state should only change"
2420 " because the foreground collector has finished the collection");
2421 }
2422 }
2423 break;
2424 }
2425 case Resetting:
2426 // CMS heap resizing has been completed
2427 reset(true);
2428 assert(_collectorState == Idling, "Collector state should "
2429 "have changed");
2430 stats().record_cms_end();
2431 // Don't move the concurrent_phases_end() and compute_new_size()
2432 // calls to here because a preempted background collection
2433 // has it's state set to "Resetting".
2434 break;
2435 case Idling:
2436 default:
2437 ShouldNotReachHere();
2438 break;
2439 }
2440 if (TraceCMSState) {
2441 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2442 Thread::current(), _collectorState);
2443 }
2444 assert(_foregroundGCShouldWait, "block post-condition");
2445 }
2446
2447 // Should this be in gc_epilogue?
2448 collector_policy()->counters()->update_counters();
2449
2450 {
2451 // Clear _foregroundGCShouldWait and, in the event that the
2452 // foreground collector is waiting, notify it, before
2453 // returning.
2454 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2455 _foregroundGCShouldWait = false;
2456 if (_foregroundGCIsActive) {
2457 CGC_lock->notify();
2458 }
2459 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2460 "Possible deadlock");
2461 }
2462 if (TraceCMSState) {
2463 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2464 " exiting collection CMS state %d",
2465 Thread::current(), _collectorState);
2466 }
2467 if (PrintGC && Verbose) {
2468 _cmsGen->print_heap_change(prev_used);
2469 }
2470 }
2471
2472 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2473 if (!_cms_start_registered) {
2474 register_gc_start(cause);
2475 }
2476 }
2477
2478 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2479 _cms_start_registered = true;
2480 _gc_timer_cm->register_gc_start();
2481 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2482 }
2483
2484 void CMSCollector::register_gc_end() {
2485 if (_cms_start_registered) {
2486 report_heap_summary(GCWhen::AfterGC);
2487
2488 _gc_timer_cm->register_gc_end();
2489 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2490 _cms_start_registered = false;
2491 }
2492 }
2493
2494 void CMSCollector::save_heap_summary() {
2495 GenCollectedHeap* gch = GenCollectedHeap::heap();
2496 _last_heap_summary = gch->create_heap_summary();
2497 _last_perm_gen_summary = gch->create_perm_gen_summary();
2498 }
2499
2500 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2501 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_perm_gen_summary);
2502 }
2503
2504 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2505 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2506 "Foreground collector should be waiting, not executing");
2507 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2508 "may only be done by the VM Thread with the world stopped");
2509 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2510 "VM thread should have CMS token");
2511
2512 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2513 true, NULL);)
2514 if (UseAdaptiveSizePolicy) {
2515 size_policy()->ms_collection_begin();
2516 }
2517 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2518
2519 HandleMark hm; // Discard invalid handles created during verification
2520
2521 if (VerifyBeforeGC &&
2522 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2523 Universe::verify();
2524 }
2525
2526 // Snapshot the soft reference policy to be used in this collection cycle.
2527 ref_processor()->setup_policy(clear_all_soft_refs);
2528
2529 bool init_mark_was_synchronous = false; // until proven otherwise
2530 while (_collectorState != Idling) {
2531 if (TraceCMSState) {
2532 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2533 Thread::current(), _collectorState);
2534 }
2535 switch (_collectorState) {
2536 case InitialMarking:
2537 register_foreground_gc_start(cause);
2538 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2539 checkpointRootsInitial(false);
2540 assert(_collectorState == Marking, "Collector state should have changed"
2541 " within checkpointRootsInitial()");
2542 break;
2543 case Marking:
2544 // initial marking in checkpointRootsInitialWork has been completed
2545 if (VerifyDuringGC &&
2546 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2547 Universe::verify("Verify before initial mark: ");
2548 }
2549 {
2550 bool res = markFromRoots(false);
2551 assert(res && _collectorState == FinalMarking, "Collector state should "
2552 "have changed");
2553 break;
2554 }
2555 case FinalMarking:
2556 if (VerifyDuringGC &&
2557 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2558 Universe::verify("Verify before re-mark: ");
2559 }
2560 checkpointRootsFinal(false, clear_all_soft_refs,
2561 init_mark_was_synchronous);
2562 assert(_collectorState == Sweeping, "Collector state should not "
2563 "have changed within checkpointRootsFinal()");
2564 break;
2565 case Sweeping:
2566 // final marking in checkpointRootsFinal has been completed
2567 if (VerifyDuringGC &&
2568 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2569 Universe::verify("Verify before sweep: ");
2570 }
2571 sweep(false);
2572 assert(_collectorState == Resizing, "Incorrect state");
2573 break;
2574 case Resizing: {
2575 // Sweeping has been completed; the actual resize in this case
2576 // is done separately; nothing to be done in this state.
2577 _collectorState = Resetting;
2578 break;
2579 }
2580 case Resetting:
2581 // The heap has been resized.
2582 if (VerifyDuringGC &&
2583 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2584 Universe::verify("Verify before reset: ");
2585 }
2586 save_heap_summary();
2587 reset(false);
2588 assert(_collectorState == Idling, "Collector state should "
2589 "have changed");
2590 break;
2591 case Precleaning:
2592 case AbortablePreclean:
2593 // Elide the preclean phase
2594 _collectorState = FinalMarking;
2595 break;
2596 default:
2597 ShouldNotReachHere();
2598 }
2599 if (TraceCMSState) {
2600 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2601 Thread::current(), _collectorState);
2602 }
2603 }
2604
2605 if (UseAdaptiveSizePolicy) {
2606 GenCollectedHeap* gch = GenCollectedHeap::heap();
2607 size_policy()->ms_collection_end(gch->gc_cause());
2608 }
2609
2610 if (VerifyAfterGC &&
2611 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2612 Universe::verify();
2613 }
2614 if (TraceCMSState) {
2615 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2616 " exiting collection CMS state %d",
2617 Thread::current(), _collectorState);
2618 }
2619 }
2620
2621 bool CMSCollector::waitForForegroundGC() {
2622 bool res = false;
2623 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2624 "CMS thread should have CMS token");
2625 // Block the foreground collector until the
2626 // background collectors decides whether to
2627 // yield.
2628 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2629 _foregroundGCShouldWait = true;
2630 if (_foregroundGCIsActive) {
2631 // The background collector yields to the
2632 // foreground collector and returns a value
2633 // indicating that it has yielded. The foreground
2634 // collector can proceed.
2635 res = true;
2636 _foregroundGCShouldWait = false;
2637 ConcurrentMarkSweepThread::clear_CMS_flag(
2638 ConcurrentMarkSweepThread::CMS_cms_has_token);
2639 ConcurrentMarkSweepThread::set_CMS_flag(
2640 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2641 // Get a possibly blocked foreground thread going
2642 CGC_lock->notify();
2643 if (TraceCMSState) {
2644 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2645 Thread::current(), _collectorState);
2646 }
2647 while (_foregroundGCIsActive) {
2648 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2649 }
2650 ConcurrentMarkSweepThread::set_CMS_flag(
2651 ConcurrentMarkSweepThread::CMS_cms_has_token);
2652 ConcurrentMarkSweepThread::clear_CMS_flag(
2653 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2654 }
2655 if (TraceCMSState) {
2656 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2657 Thread::current(), _collectorState);
2658 }
2659 return res;
2660 }
2661
2662 // Because of the need to lock the free lists and other structures in
2663 // the collector, common to all the generations that the collector is
2664 // collecting, we need the gc_prologues of individual CMS generations
2665 // delegate to their collector. It may have been simpler had the
2666 // current infrastructure allowed one to call a prologue on a
2667 // collector. In the absence of that we have the generation's
2668 // prologue delegate to the collector, which delegates back
2669 // some "local" work to a worker method in the individual generations
2670 // that it's responsible for collecting, while itself doing any
2671 // work common to all generations it's responsible for. A similar
2672 // comment applies to the gc_epilogue()'s.
2673 // The role of the varaible _between_prologue_and_epilogue is to
2674 // enforce the invocation protocol.
2675 void CMSCollector::gc_prologue(bool full) {
2676 // Call gc_prologue_work() for each CMSGen and PermGen that
2677 // we are responsible for.
2678
2679 // The following locking discipline assumes that we are only called
2680 // when the world is stopped.
2681 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2682
2683 // The CMSCollector prologue must call the gc_prologues for the
2684 // "generations" (including PermGen if any) that it's responsible
2685 // for.
2686
2687 assert( Thread::current()->is_VM_thread()
2688 || ( CMSScavengeBeforeRemark
2689 && Thread::current()->is_ConcurrentGC_thread()),
2690 "Incorrect thread type for prologue execution");
2691
2692 if (_between_prologue_and_epilogue) {
2693 // We have already been invoked; this is a gc_prologue delegation
2694 // from yet another CMS generation that we are responsible for, just
2695 // ignore it since all relevant work has already been done.
2696 return;
2697 }
2698
2699 // set a bit saying prologue has been called; cleared in epilogue
2700 _between_prologue_and_epilogue = true;
2701 // Claim locks for common data structures, then call gc_prologue_work()
2702 // for each CMSGen and PermGen that we are responsible for.
2703
2704 getFreelistLocks(); // gets free list locks on constituent spaces
2705 bitMapLock()->lock_without_safepoint_check();
2706
2707 // Should call gc_prologue_work() for all cms gens we are responsible for
2708 bool registerClosure = _collectorState >= Marking
2709 && _collectorState < Sweeping;
2710 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2711 &_modUnionClosurePar
2712 : &_modUnionClosure;
2713 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2714 _permGen->gc_prologue_work(full, registerClosure, muc);
2715
2716 if (!full) {
2717 stats().record_gc0_begin();
2718 }
2719 }
2720
2721 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2722 // Delegate to CMScollector which knows how to coordinate between
2723 // this and any other CMS generations that it is responsible for
2724 // collecting.
2725 collector()->gc_prologue(full);
2726 }
2727
2728 // This is a "private" interface for use by this generation's CMSCollector.
2729 // Not to be called directly by any other entity (for instance,
2730 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2731 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2732 bool registerClosure, ModUnionClosure* modUnionClosure) {
2733 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2734 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2735 "Should be NULL");
2736 if (registerClosure) {
2737 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2738 }
2739 cmsSpace()->gc_prologue();
2740 // Clear stat counters
2741 NOT_PRODUCT(
2742 assert(_numObjectsPromoted == 0, "check");
2743 assert(_numWordsPromoted == 0, "check");
2744 if (Verbose && PrintGC) {
2745 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2746 SIZE_FORMAT" bytes concurrently",
2747 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2748 }
2749 _numObjectsAllocated = 0;
2750 _numWordsAllocated = 0;
2751 )
2752 }
2753
2754 void CMSCollector::gc_epilogue(bool full) {
2755 // The following locking discipline assumes that we are only called
2756 // when the world is stopped.
2757 assert(SafepointSynchronize::is_at_safepoint(),
2758 "world is stopped assumption");
2759
2760 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2761 // if linear allocation blocks need to be appropriately marked to allow the
2762 // the blocks to be parsable. We also check here whether we need to nudge the
2763 // CMS collector thread to start a new cycle (if it's not already active).
2764 assert( Thread::current()->is_VM_thread()
2765 || ( CMSScavengeBeforeRemark
2766 && Thread::current()->is_ConcurrentGC_thread()),
2767 "Incorrect thread type for epilogue execution");
2768
2769 if (!_between_prologue_and_epilogue) {
2770 // We have already been invoked; this is a gc_epilogue delegation
2771 // from yet another CMS generation that we are responsible for, just
2772 // ignore it since all relevant work has already been done.
2773 return;
2774 }
2775 assert(haveFreelistLocks(), "must have freelist locks");
2776 assert_lock_strong(bitMapLock());
2777
2778 _cmsGen->gc_epilogue_work(full);
2779 _permGen->gc_epilogue_work(full);
2780
2781 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2782 // in case sampling was not already enabled, enable it
2783 _start_sampling = true;
2784 }
2785 // reset _eden_chunk_array so sampling starts afresh
2786 _eden_chunk_index = 0;
2787
2788 size_t cms_used = _cmsGen->cmsSpace()->used();
2789 size_t perm_used = _permGen->cmsSpace()->used();
2790
2791 // update performance counters - this uses a special version of
2792 // update_counters() that allows the utilization to be passed as a
2793 // parameter, avoiding multiple calls to used().
2794 //
2795 _cmsGen->update_counters(cms_used);
2796 _permGen->update_counters(perm_used);
2797
2798 if (CMSIncrementalMode) {
2799 icms_update_allocation_limits();
2800 }
2801
2802 bitMapLock()->unlock();
2803 releaseFreelistLocks();
2804
2805 if (!CleanChunkPoolAsync) {
2806 Chunk::clean_chunk_pool();
2807 }
2808
2809 _between_prologue_and_epilogue = false; // ready for next cycle
2810 }
2811
2812 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2813 collector()->gc_epilogue(full);
2814
2815 // Also reset promotion tracking in par gc thread states.
2816 if (CollectedHeap::use_parallel_gc_threads()) {
2817 for (uint i = 0; i < ParallelGCThreads; i++) {
2818 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2819 }
2820 }
2821 }
2822
2823 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2824 assert(!incremental_collection_failed(), "Should have been cleared");
2825 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2826 cmsSpace()->gc_epilogue();
2827 // Print stat counters
2828 NOT_PRODUCT(
2829 assert(_numObjectsAllocated == 0, "check");
2830 assert(_numWordsAllocated == 0, "check");
2831 if (Verbose && PrintGC) {
2832 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2833 SIZE_FORMAT" bytes",
2834 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2835 }
2836 _numObjectsPromoted = 0;
2837 _numWordsPromoted = 0;
2838 )
2839
2840 if (PrintGC && Verbose) {
2841 // Call down the chain in contiguous_available needs the freelistLock
2842 // so print this out before releasing the freeListLock.
2843 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2844 contiguous_available());
2845 }
2846 }
2847
2848 #ifndef PRODUCT
2849 bool CMSCollector::have_cms_token() {
2850 Thread* thr = Thread::current();
2851 if (thr->is_VM_thread()) {
2852 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2853 } else if (thr->is_ConcurrentGC_thread()) {
2854 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2855 } else if (thr->is_GC_task_thread()) {
2856 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2857 ParGCRareEvent_lock->owned_by_self();
2858 }
2859 return false;
2860 }
2861 #endif
2862
2863 // Check reachability of the given heap address in CMS generation,
2864 // treating all other generations as roots.
2865 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2866 // We could "guarantee" below, rather than assert, but i'll
2867 // leave these as "asserts" so that an adventurous debugger
2868 // could try this in the product build provided some subset of
2869 // the conditions were met, provided they were intersted in the
2870 // results and knew that the computation below wouldn't interfere
2871 // with other concurrent computations mutating the structures
2872 // being read or written.
2873 assert(SafepointSynchronize::is_at_safepoint(),
2874 "Else mutations in object graph will make answer suspect");
2875 assert(have_cms_token(), "Should hold cms token");
2876 assert(haveFreelistLocks(), "must hold free list locks");
2877 assert_lock_strong(bitMapLock());
2878
2879 // Clear the marking bit map array before starting, but, just
2880 // for kicks, first report if the given address is already marked
2881 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2882 _markBitMap.isMarked(addr) ? "" : " not");
2883
2884 if (verify_after_remark()) {
2885 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2886 bool result = verification_mark_bm()->isMarked(addr);
2887 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2888 result ? "IS" : "is NOT");
2889 return result;
2890 } else {
2891 gclog_or_tty->print_cr("Could not compute result");
2892 return false;
2893 }
2894 }
2895
2896 ////////////////////////////////////////////////////////
2897 // CMS Verification Support
2898 ////////////////////////////////////////////////////////
2899 // Following the remark phase, the following invariant
2900 // should hold -- each object in the CMS heap which is
2901 // marked in markBitMap() should be marked in the verification_mark_bm().
2902
2903 class VerifyMarkedClosure: public BitMapClosure {
2904 CMSBitMap* _marks;
2905 bool _failed;
2906
2907 public:
2908 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2909
2910 bool do_bit(size_t offset) {
2911 HeapWord* addr = _marks->offsetToHeapWord(offset);
2912 if (!_marks->isMarked(addr)) {
2913 oop(addr)->print_on(gclog_or_tty);
2914 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2915 _failed = true;
2916 }
2917 return true;
2918 }
2919
2920 bool failed() { return _failed; }
2921 };
2922
2923 bool CMSCollector::verify_after_remark(bool silent) {
2924 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2925 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2926 static bool init = false;
2927
2928 assert(SafepointSynchronize::is_at_safepoint(),
2929 "Else mutations in object graph will make answer suspect");
2930 assert(have_cms_token(),
2931 "Else there may be mutual interference in use of "
2932 " verification data structures");
2933 assert(_collectorState > Marking && _collectorState <= Sweeping,
2934 "Else marking info checked here may be obsolete");
2935 assert(haveFreelistLocks(), "must hold free list locks");
2936 assert_lock_strong(bitMapLock());
2937
2938
2939 // Allocate marking bit map if not already allocated
2940 if (!init) { // first time
2941 if (!verification_mark_bm()->allocate(_span)) {
2942 return false;
2943 }
2944 init = true;
2945 }
2946
2947 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2948
2949 // Turn off refs discovery -- so we will be tracing through refs.
2950 // This is as intended, because by this time
2951 // GC must already have cleared any refs that need to be cleared,
2952 // and traced those that need to be marked; moreover,
2953 // the marking done here is not going to intefere in any
2954 // way with the marking information used by GC.
2955 NoRefDiscovery no_discovery(ref_processor());
2956
2957 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2958
2959 // Clear any marks from a previous round
2960 verification_mark_bm()->clear_all();
2961 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2962 verify_work_stacks_empty();
2963
2964 GenCollectedHeap* gch = GenCollectedHeap::heap();
2965 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2966 // Update the saved marks which may affect the root scans.
2967 gch->save_marks();
2968
2969 if (CMSRemarkVerifyVariant == 1) {
2970 // In this first variant of verification, we complete
2971 // all marking, then check if the new marks-verctor is
2972 // a subset of the CMS marks-vector.
2973 verify_after_remark_work_1();
2974 } else if (CMSRemarkVerifyVariant == 2) {
2975 // In this second variant of verification, we flag an error
2976 // (i.e. an object reachable in the new marks-vector not reachable
2977 // in the CMS marks-vector) immediately, also indicating the
2978 // identify of an object (A) that references the unmarked object (B) --
2979 // presumably, a mutation to A failed to be picked up by preclean/remark?
2980 verify_after_remark_work_2();
2981 } else {
2982 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2983 CMSRemarkVerifyVariant);
2984 }
2985 if (!silent) gclog_or_tty->print(" done] ");
2986 return true;
2987 }
2988
2989 void CMSCollector::verify_after_remark_work_1() {
2990 ResourceMark rm;
2991 HandleMark hm;
2992 GenCollectedHeap* gch = GenCollectedHeap::heap();
2993
2994 // Mark from roots one level into CMS
2995 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2996 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2997
2998 gch->gen_process_strong_roots(_cmsGen->level(),
2999 true, // younger gens are roots
3000 true, // activate StrongRootsScope
3001 true, // collecting perm gen
3002 SharedHeap::ScanningOption(roots_scanning_options()),
3003 ¬Older,
3004 true, // walk code active on stacks
3005 NULL);
3006
3007 // Now mark from the roots
3008 assert(_revisitStack.isEmpty(), "Should be empty");
3009 MarkFromRootsClosure markFromRootsClosure(this, _span,
3010 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
3011 false /* don't yield */, true /* verifying */);
3012 assert(_restart_addr == NULL, "Expected pre-condition");
3013 verification_mark_bm()->iterate(&markFromRootsClosure);
3014 while (_restart_addr != NULL) {
3015 // Deal with stack overflow: by restarting at the indicated
3016 // address.
3017 HeapWord* ra = _restart_addr;
3018 markFromRootsClosure.reset(ra);
3019 _restart_addr = NULL;
3020 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3021 }
3022 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3023 verify_work_stacks_empty();
3024 // Should reset the revisit stack above, since no class tree
3025 // surgery is forthcoming.
3026 _revisitStack.reset(); // throwing away all contents
3027
3028 // Marking completed -- now verify that each bit marked in
3029 // verification_mark_bm() is also marked in markBitMap(); flag all
3030 // errors by printing corresponding objects.
3031 VerifyMarkedClosure vcl(markBitMap());
3032 verification_mark_bm()->iterate(&vcl);
3033 if (vcl.failed()) {
3034 gclog_or_tty->print("Verification failed");
3035 Universe::heap()->print_on(gclog_or_tty);
3036 fatal("CMS: failed marking verification after remark");
3037 }
3038 }
3039
3040 void CMSCollector::verify_after_remark_work_2() {
3041 ResourceMark rm;
3042 HandleMark hm;
3043 GenCollectedHeap* gch = GenCollectedHeap::heap();
3044
3045 // Mark from roots one level into CMS
3046 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3047 markBitMap());
3048 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3049 gch->gen_process_strong_roots(_cmsGen->level(),
3050 true, // younger gens are roots
3051 true, // activate StrongRootsScope
3052 true, // collecting perm gen
3053 SharedHeap::ScanningOption(roots_scanning_options()),
3054 ¬Older,
3055 true, // walk code active on stacks
3056 NULL);
3057
3058 // Now mark from the roots
3059 assert(_revisitStack.isEmpty(), "Should be empty");
3060 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3061 verification_mark_bm(), markBitMap(), verification_mark_stack());
3062 assert(_restart_addr == NULL, "Expected pre-condition");
3063 verification_mark_bm()->iterate(&markFromRootsClosure);
3064 while (_restart_addr != NULL) {
3065 // Deal with stack overflow: by restarting at the indicated
3066 // address.
3067 HeapWord* ra = _restart_addr;
3068 markFromRootsClosure.reset(ra);
3069 _restart_addr = NULL;
3070 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3071 }
3072 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3073 verify_work_stacks_empty();
3074 // Should reset the revisit stack above, since no class tree
3075 // surgery is forthcoming.
3076 _revisitStack.reset(); // throwing away all contents
3077
3078 // Marking completed -- now verify that each bit marked in
3079 // verification_mark_bm() is also marked in markBitMap(); flag all
3080 // errors by printing corresponding objects.
3081 VerifyMarkedClosure vcl(markBitMap());
3082 verification_mark_bm()->iterate(&vcl);
3083 assert(!vcl.failed(), "Else verification above should not have succeeded");
3084 }
3085
3086 void ConcurrentMarkSweepGeneration::save_marks() {
3087 // delegate to CMS space
3088 cmsSpace()->save_marks();
3089 for (uint i = 0; i < ParallelGCThreads; i++) {
3090 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3091 }
3092 }
3093
3094 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3095 return cmsSpace()->no_allocs_since_save_marks();
3096 }
3097
3098 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3099 \
3100 void ConcurrentMarkSweepGeneration:: \
3101 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3102 cl->set_generation(this); \
3103 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3104 cl->reset_generation(); \
3105 save_marks(); \
3106 }
3107
3108 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3109
3110 void
3111 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3112 {
3113 // Not currently implemented; need to do the following. -- ysr.
3114 // dld -- I think that is used for some sort of allocation profiler. So it
3115 // really means the objects allocated by the mutator since the last
3116 // GC. We could potentially implement this cheaply by recording only
3117 // the direct allocations in a side data structure.
3118 //
3119 // I think we probably ought not to be required to support these
3120 // iterations at any arbitrary point; I think there ought to be some
3121 // call to enable/disable allocation profiling in a generation/space,
3122 // and the iterator ought to return the objects allocated in the
3123 // gen/space since the enable call, or the last iterator call (which
3124 // will probably be at a GC.) That way, for gens like CM&S that would
3125 // require some extra data structure to support this, we only pay the
3126 // cost when it's in use...
3127 cmsSpace()->object_iterate_since_last_GC(blk);
3128 }
3129
3130 void
3131 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3132 cl->set_generation(this);
3133 younger_refs_in_space_iterate(_cmsSpace, cl);
3134 cl->reset_generation();
3135 }
3136
3137 void
3138 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3139 if (freelistLock()->owned_by_self()) {
3140 Generation::oop_iterate(mr, cl);
3141 } else {
3142 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3143 Generation::oop_iterate(mr, cl);
3144 }
3145 }
3146
3147 void
3148 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3149 if (freelistLock()->owned_by_self()) {
3150 Generation::oop_iterate(cl);
3151 } else {
3152 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3153 Generation::oop_iterate(cl);
3154 }
3155 }
3156
3157 void
3158 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3159 if (freelistLock()->owned_by_self()) {
3160 Generation::object_iterate(cl);
3161 } else {
3162 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3163 Generation::object_iterate(cl);
3164 }
3165 }
3166
3167 void
3168 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3169 if (freelistLock()->owned_by_self()) {
3170 Generation::safe_object_iterate(cl);
3171 } else {
3172 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3173 Generation::safe_object_iterate(cl);
3174 }
3175 }
3176
3177 void
3178 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3179 }
3180
3181 void
3182 ConcurrentMarkSweepGeneration::post_compact() {
3183 }
3184
3185 void
3186 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3187 // Fix the linear allocation blocks to look like free blocks.
3188
3189 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3190 // are not called when the heap is verified during universe initialization and
3191 // at vm shutdown.
3192 if (freelistLock()->owned_by_self()) {
3193 cmsSpace()->prepare_for_verify();
3194 } else {
3195 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3196 cmsSpace()->prepare_for_verify();
3197 }
3198 }
3199
3200 void
3201 ConcurrentMarkSweepGeneration::verify() {
3202 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3203 // are not called when the heap is verified during universe initialization and
3204 // at vm shutdown.
3205 if (freelistLock()->owned_by_self()) {
3206 cmsSpace()->verify();
3207 } else {
3208 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3209 cmsSpace()->verify();
3210 }
3211 }
3212
3213 void CMSCollector::verify() {
3214 _cmsGen->verify();
3215 _permGen->verify();
3216 }
3217
3218 #ifndef PRODUCT
3219 bool CMSCollector::overflow_list_is_empty() const {
3220 assert(_num_par_pushes >= 0, "Inconsistency");
3221 if (_overflow_list == NULL) {
3222 assert(_num_par_pushes == 0, "Inconsistency");
3223 }
3224 return _overflow_list == NULL;
3225 }
3226
3227 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3228 // merely consolidate assertion checks that appear to occur together frequently.
3229 void CMSCollector::verify_work_stacks_empty() const {
3230 assert(_markStack.isEmpty(), "Marking stack should be empty");
3231 assert(overflow_list_is_empty(), "Overflow list should be empty");
3232 }
3233
3234 void CMSCollector::verify_overflow_empty() const {
3235 assert(overflow_list_is_empty(), "Overflow list should be empty");
3236 assert(no_preserved_marks(), "No preserved marks");
3237 }
3238 #endif // PRODUCT
3239
3240 // Decide if we want to enable class unloading as part of the
3241 // ensuing concurrent GC cycle. We will collect the perm gen and
3242 // unload classes if it's the case that:
3243 // (1) an explicit gc request has been made and the flag
3244 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3245 // (2) (a) class unloading is enabled at the command line, and
3246 // (b) (i) perm gen threshold has been crossed, or
3247 // (ii) old gen is getting really full, or
3248 // (iii) the previous N CMS collections did not collect the
3249 // perm gen
3250 // NOTE: Provided there is no change in the state of the heap between
3251 // calls to this method, it should have idempotent results. Moreover,
3252 // its results should be monotonically increasing (i.e. going from 0 to 1,
3253 // but not 1 to 0) between successive calls between which the heap was
3254 // not collected. For the implementation below, it must thus rely on
3255 // the property that concurrent_cycles_since_last_unload()
3256 // will not decrease unless a collection cycle happened and that
3257 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3258 // themselves also monotonic in that sense. See check_monotonicity()
3259 // below.
3260 bool CMSCollector::update_should_unload_classes() {
3261 _should_unload_classes = false;
3262 // Condition 1 above
3263 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3264 _should_unload_classes = true;
3265 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3266 // Disjuncts 2.b.(i,ii,iii) above
3267 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3268 CMSClassUnloadingMaxInterval)
3269 || _permGen->should_concurrent_collect()
3270 || _cmsGen->is_too_full();
3271 }
3272 return _should_unload_classes;
3273 }
3274
3275 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3276 bool res = should_concurrent_collect();
3277 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3278 return res;
3279 }
3280
3281 void CMSCollector::setup_cms_unloading_and_verification_state() {
3282 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3283 || VerifyBeforeExit;
3284 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3285
3286 if (should_unload_classes()) { // Should unload classes this cycle
3287 remove_root_scanning_option(rso); // Shrink the root set appropriately
3288 set_verifying(should_verify); // Set verification state for this cycle
3289 return; // Nothing else needs to be done at this time
3290 }
3291
3292 // Not unloading classes this cycle
3293 assert(!should_unload_classes(), "Inconsitency!");
3294 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3295 // We were not verifying, or we _were_ unloading classes in the last cycle,
3296 // AND some verification options are enabled this cycle; in this case,
3297 // we must make sure that the deadness map is allocated if not already so,
3298 // and cleared (if already allocated previously --
3299 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3300 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3301 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3302 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3303 "permanent generation verification disabled");
3304 return; // Note that we leave verification disabled, so we'll retry this
3305 // allocation next cycle. We _could_ remember this failure
3306 // and skip further attempts and permanently disable verification
3307 // attempts if that is considered more desirable.
3308 }
3309 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3310 "_perm_gen_ver_bit_map inconsistency?");
3311 } else {
3312 perm_gen_verify_bit_map()->clear_all();
3313 }
3314 // Include symbols, strings and code cache elements to prevent their resurrection.
3315 add_root_scanning_option(rso);
3316 set_verifying(true);
3317 } else if (verifying() && !should_verify) {
3318 // We were verifying, but some verification flags got disabled.
3319 set_verifying(false);
3320 // Exclude symbols, strings and code cache elements from root scanning to
3321 // reduce IM and RM pauses.
3322 remove_root_scanning_option(rso);
3323 }
3324 }
3325
3326
3327 #ifndef PRODUCT
3328 HeapWord* CMSCollector::block_start(const void* p) const {
3329 const HeapWord* addr = (HeapWord*)p;
3330 if (_span.contains(p)) {
3331 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3332 return _cmsGen->cmsSpace()->block_start(p);
3333 } else {
3334 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3335 "Inconsistent _span?");
3336 return _permGen->cmsSpace()->block_start(p);
3337 }
3338 }
3339 return NULL;
3340 }
3341 #endif
3342
3343 HeapWord*
3344 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3345 bool tlab,
3346 bool parallel) {
3347 CMSSynchronousYieldRequest yr;
3348 assert(!tlab, "Can't deal with TLAB allocation");
3349 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3350 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3351 CMSExpansionCause::_satisfy_allocation);
3352 if (GCExpandToAllocateDelayMillis > 0) {
3353 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3354 }
3355 return have_lock_and_allocate(word_size, tlab);
3356 }
3357
3358 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3359 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3360 // to CardGeneration and share it...
3361 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3362 return CardGeneration::expand(bytes, expand_bytes);
3363 }
3364
3365 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3366 CMSExpansionCause::Cause cause)
3367 {
3368
3369 bool success = expand(bytes, expand_bytes);
3370
3371 // remember why we expanded; this information is used
3372 // by shouldConcurrentCollect() when making decisions on whether to start
3373 // a new CMS cycle.
3374 if (success) {
3375 set_expansion_cause(cause);
3376 if (PrintGCDetails && Verbose) {
3377 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3378 CMSExpansionCause::to_string(cause));
3379 }
3380 }
3381 }
3382
3383 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3384 HeapWord* res = NULL;
3385 MutexLocker x(ParGCRareEvent_lock);
3386 while (true) {
3387 // Expansion by some other thread might make alloc OK now:
3388 res = ps->lab.alloc(word_sz);
3389 if (res != NULL) return res;
3390 // If there's not enough expansion space available, give up.
3391 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3392 return NULL;
3393 }
3394 // Otherwise, we try expansion.
3395 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3396 CMSExpansionCause::_allocate_par_lab);
3397 // Now go around the loop and try alloc again;
3398 // A competing par_promote might beat us to the expansion space,
3399 // so we may go around the loop again if promotion fails agaion.
3400 if (GCExpandToAllocateDelayMillis > 0) {
3401 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3402 }
3403 }
3404 }
3405
3406
3407 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3408 PromotionInfo* promo) {
3409 MutexLocker x(ParGCRareEvent_lock);
3410 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3411 while (true) {
3412 // Expansion by some other thread might make alloc OK now:
3413 if (promo->ensure_spooling_space()) {
3414 assert(promo->has_spooling_space(),
3415 "Post-condition of successful ensure_spooling_space()");
3416 return true;
3417 }
3418 // If there's not enough expansion space available, give up.
3419 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3420 return false;
3421 }
3422 // Otherwise, we try expansion.
3423 expand(refill_size_bytes, MinHeapDeltaBytes,
3424 CMSExpansionCause::_allocate_par_spooling_space);
3425 // Now go around the loop and try alloc again;
3426 // A competing allocation might beat us to the expansion space,
3427 // so we may go around the loop again if allocation fails again.
3428 if (GCExpandToAllocateDelayMillis > 0) {
3429 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3430 }
3431 }
3432 }
3433
3434
3435
3436 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3437 assert_locked_or_safepoint(Heap_lock);
3438 size_t size = ReservedSpace::page_align_size_down(bytes);
3439 if (size > 0) {
3440 shrink_by(size);
3441 }
3442 }
3443
3444 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3445 assert_locked_or_safepoint(Heap_lock);
3446 bool result = _virtual_space.expand_by(bytes);
3447 if (result) {
3448 HeapWord* old_end = _cmsSpace->end();
3449 size_t new_word_size =
3450 heap_word_size(_virtual_space.committed_size());
3451 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3452 _bts->resize(new_word_size); // resize the block offset shared array
3453 Universe::heap()->barrier_set()->resize_covered_region(mr);
3454 // Hmmmm... why doesn't CFLS::set_end verify locking?
3455 // This is quite ugly; FIX ME XXX
3456 _cmsSpace->assert_locked(freelistLock());
3457 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3458
3459 // update the space and generation capacity counters
3460 if (UsePerfData) {
3461 _space_counters->update_capacity();
3462 _gen_counters->update_all();
3463 }
3464
3465 if (Verbose && PrintGC) {
3466 size_t new_mem_size = _virtual_space.committed_size();
3467 size_t old_mem_size = new_mem_size - bytes;
3468 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3469 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3470 }
3471 }
3472 return result;
3473 }
3474
3475 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3476 assert_locked_or_safepoint(Heap_lock);
3477 bool success = true;
3478 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3479 if (remaining_bytes > 0) {
3480 success = grow_by(remaining_bytes);
3481 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3482 }
3483 return success;
3484 }
3485
3486 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3487 assert_locked_or_safepoint(Heap_lock);
3488 assert_lock_strong(freelistLock());
3489 // XXX Fix when compaction is implemented.
3490 warning("Shrinking of CMS not yet implemented");
3491 return;
3492 }
3493
3494
3495 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3496 // phases.
3497 class CMSPhaseAccounting: public StackObj {
3498 public:
3499 CMSPhaseAccounting(CMSCollector *collector,
3500 const char *phase,
3501 bool print_cr = true);
3502 ~CMSPhaseAccounting();
3503
3504 private:
3505 CMSCollector *_collector;
3506 const char *_phase;
3507 elapsedTimer _wallclock;
3508 bool _print_cr;
3509
3510 public:
3511 // Not MT-safe; so do not pass around these StackObj's
3512 // where they may be accessed by other threads.
3513 jlong wallclock_millis() {
3514 assert(_wallclock.is_active(), "Wall clock should not stop");
3515 _wallclock.stop(); // to record time
3516 jlong ret = _wallclock.milliseconds();
3517 _wallclock.start(); // restart
3518 return ret;
3519 }
3520 };
3521
3522 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3523 const char *phase,
3524 bool print_cr) :
3525 _collector(collector), _phase(phase), _print_cr(print_cr) {
3526
3527 if (PrintCMSStatistics != 0) {
3528 _collector->resetYields();
3529 }
3530 if (PrintGCDetails && PrintGCTimeStamps) {
3531 gclog_or_tty->date_stamp(PrintGCDateStamps);
3532 gclog_or_tty->stamp();
3533 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3534 _collector->cmsGen()->short_name(), _phase);
3535 }
3536 _collector->resetTimer();
3537 _wallclock.start();
3538 _collector->startTimer();
3539 }
3540
3541 CMSPhaseAccounting::~CMSPhaseAccounting() {
3542 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3543 _collector->stopTimer();
3544 _wallclock.stop();
3545 if (PrintGCDetails) {
3546 gclog_or_tty->date_stamp(PrintGCDateStamps);
3547 gclog_or_tty->stamp(PrintGCTimeStamps);
3548 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3549 _collector->cmsGen()->short_name(),
3550 _phase, _collector->timerValue(), _wallclock.seconds());
3551 if (_print_cr) {
3552 gclog_or_tty->print_cr("");
3553 }
3554 if (PrintCMSStatistics != 0) {
3555 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3556 _collector->yields());
3557 }
3558 }
3559 }
3560
3561 // CMS work
3562
3563 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3564 class CMSParMarkTask : public AbstractGangTask {
3565 protected:
3566 CMSCollector* _collector;
3567 int _n_workers;
3568 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3569 AbstractGangTask(name),
3570 _collector(collector),
3571 _n_workers(n_workers) {}
3572 // Work method in support of parallel rescan ... of young gen spaces
3573 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3574 ContiguousSpace* space,
3575 HeapWord** chunk_array, size_t chunk_top);
3576 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3577 };
3578
3579 // Parallel initial mark task
3580 class CMSParInitialMarkTask: public CMSParMarkTask {
3581 public:
3582 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3583 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3584 collector, n_workers) {}
3585 void work(uint worker_id);
3586 };
3587
3588 // Checkpoint the roots into this generation from outside
3589 // this generation. [Note this initial checkpoint need only
3590 // be approximate -- we'll do a catch up phase subsequently.]
3591 void CMSCollector::checkpointRootsInitial(bool asynch) {
3592 assert(_collectorState == InitialMarking, "Wrong collector state");
3593 check_correct_thread_executing();
3594 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3595
3596 save_heap_summary();
3597 report_heap_summary(GCWhen::BeforeGC);
3598
3599 ReferenceProcessor* rp = ref_processor();
3600 SpecializationStats::clear();
3601 assert(_restart_addr == NULL, "Control point invariant");
3602 if (asynch) {
3603 // acquire locks for subsequent manipulations
3604 MutexLockerEx x(bitMapLock(),
3605 Mutex::_no_safepoint_check_flag);
3606 checkpointRootsInitialWork(asynch);
3607 // enable ("weak") refs discovery
3608 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3609 _collectorState = Marking;
3610 } else {
3611 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3612 // which recognizes if we are a CMS generation, and doesn't try to turn on
3613 // discovery; verify that they aren't meddling.
3614 assert(!rp->discovery_is_atomic(),
3615 "incorrect setting of discovery predicate");
3616 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3617 "ref discovery for this generation kind");
3618 // already have locks
3619 checkpointRootsInitialWork(asynch);
3620 // now enable ("weak") refs discovery
3621 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3622 _collectorState = Marking;
3623 }
3624 SpecializationStats::print();
3625 }
3626
3627 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3628 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3629 assert(_collectorState == InitialMarking, "just checking");
3630
3631 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3632 // precede our marking with a collection of all
3633 // younger generations to keep floating garbage to a minimum.
3634 // XXX: we won't do this for now -- it's an optimization to be done later.
3635
3636 // already have locks
3637 assert_lock_strong(bitMapLock());
3638 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3639
3640 // Setup the verification and class unloading state for this
3641 // CMS collection cycle.
3642 setup_cms_unloading_and_verification_state();
3643
3644 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3645 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3646 if (UseAdaptiveSizePolicy) {
3647 size_policy()->checkpoint_roots_initial_begin();
3648 }
3649
3650 // Reset all the PLAB chunk arrays if necessary.
3651 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3652 reset_survivor_plab_arrays();
3653 }
3654
3655 ResourceMark rm;
3656 HandleMark hm;
3657
3658 FalseClosure falseClosure;
3659 // In the case of a synchronous collection, we will elide the
3660 // remark step, so it's important to catch all the nmethod oops
3661 // in this step.
3662 // The final 'true' flag to gen_process_strong_roots will ensure this.
3663 // If 'async' is true, we can relax the nmethod tracing.
3664 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3665 GenCollectedHeap* gch = GenCollectedHeap::heap();
3666
3667 verify_work_stacks_empty();
3668 verify_overflow_empty();
3669
3670 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3671 // Update the saved marks which may affect the root scans.
3672 gch->save_marks();
3673
3674 // weak reference processing has not started yet.
3675 ref_processor()->set_enqueuing_is_done(false);
3676
3677 if (CMSPrintEdenSurvivorChunks) {
3678 print_eden_and_survivor_chunk_arrays();
3679 }
3680
3681 {
3682 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3683 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3684 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3685 // The parallel version.
3686 FlexibleWorkGang* workers = gch->workers();
3687 assert(workers != NULL, "Need parallel worker threads.");
3688 int n_workers = workers->active_workers();
3689 CMSParInitialMarkTask tsk(this, n_workers);
3690 gch->set_par_threads(n_workers);
3691 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3692 if (n_workers > 1) {
3693 GenCollectedHeap::StrongRootsScope srs(gch);
3694 workers->run_task(&tsk);
3695 } else {
3696 GenCollectedHeap::StrongRootsScope srs(gch);
3697 tsk.work(0);
3698 }
3699 gch->set_par_threads(0);
3700 } else {
3701 // The serial version.
3702 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3703 gch->gen_process_strong_roots(_cmsGen->level(),
3704 true, // younger gens are roots
3705 true, // activate StrongRootsScope
3706 true, // collecting perm gen
3707 SharedHeap::ScanningOption(roots_scanning_options()),
3708 ¬Older,
3709 true, // walk all of code cache if (so & SO_CodeCache)
3710 NULL);
3711 }
3712 }
3713 // Clear mod-union table; it will be dirtied in the prologue of
3714 // CMS generation per each younger generation collection.
3715
3716 assert(_modUnionTable.isAllClear(),
3717 "Was cleared in most recent final checkpoint phase"
3718 " or no bits are set in the gc_prologue before the start of the next "
3719 "subsequent marking phase.");
3720
3721 // Save the end of the used_region of the constituent generations
3722 // to be used to limit the extent of sweep in each generation.
3723 save_sweep_limits();
3724 if (UseAdaptiveSizePolicy) {
3725 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3726 }
3727 verify_overflow_empty();
3728 }
3729
3730 bool CMSCollector::markFromRoots(bool asynch) {
3731 // we might be tempted to assert that:
3732 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3733 // "inconsistent argument?");
3734 // However that wouldn't be right, because it's possible that
3735 // a safepoint is indeed in progress as a younger generation
3736 // stop-the-world GC happens even as we mark in this generation.
3737 assert(_collectorState == Marking, "inconsistent state?");
3738 check_correct_thread_executing();
3739 verify_overflow_empty();
3740
3741 bool res;
3742 if (asynch) {
3743
3744 // Start the timers for adaptive size policy for the concurrent phases
3745 // Do it here so that the foreground MS can use the concurrent
3746 // timer since a foreground MS might has the sweep done concurrently
3747 // or STW.
3748 if (UseAdaptiveSizePolicy) {
3749 size_policy()->concurrent_marking_begin();
3750 }
3751
3752 // Weak ref discovery note: We may be discovering weak
3753 // refs in this generation concurrent (but interleaved) with
3754 // weak ref discovery by a younger generation collector.
3755
3756 CMSTokenSyncWithLocks ts(true, bitMapLock());
3757 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3758 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3759 res = markFromRootsWork(asynch);
3760 if (res) {
3761 _collectorState = Precleaning;
3762 } else { // We failed and a foreground collection wants to take over
3763 assert(_foregroundGCIsActive, "internal state inconsistency");
3764 assert(_restart_addr == NULL, "foreground will restart from scratch");
3765 if (PrintGCDetails) {
3766 gclog_or_tty->print_cr("bailing out to foreground collection");
3767 }
3768 }
3769 if (UseAdaptiveSizePolicy) {
3770 size_policy()->concurrent_marking_end();
3771 }
3772 } else {
3773 assert(SafepointSynchronize::is_at_safepoint(),
3774 "inconsistent with asynch == false");
3775 if (UseAdaptiveSizePolicy) {
3776 size_policy()->ms_collection_marking_begin();
3777 }
3778 // already have locks
3779 res = markFromRootsWork(asynch);
3780 _collectorState = FinalMarking;
3781 if (UseAdaptiveSizePolicy) {
3782 GenCollectedHeap* gch = GenCollectedHeap::heap();
3783 size_policy()->ms_collection_marking_end(gch->gc_cause());
3784 }
3785 }
3786 verify_overflow_empty();
3787 return res;
3788 }
3789
3790 bool CMSCollector::markFromRootsWork(bool asynch) {
3791 // iterate over marked bits in bit map, doing a full scan and mark
3792 // from these roots using the following algorithm:
3793 // . if oop is to the right of the current scan pointer,
3794 // mark corresponding bit (we'll process it later)
3795 // . else (oop is to left of current scan pointer)
3796 // push oop on marking stack
3797 // . drain the marking stack
3798
3799 // Note that when we do a marking step we need to hold the
3800 // bit map lock -- recall that direct allocation (by mutators)
3801 // and promotion (by younger generation collectors) is also
3802 // marking the bit map. [the so-called allocate live policy.]
3803 // Because the implementation of bit map marking is not
3804 // robust wrt simultaneous marking of bits in the same word,
3805 // we need to make sure that there is no such interference
3806 // between concurrent such updates.
3807
3808 // already have locks
3809 assert_lock_strong(bitMapLock());
3810
3811 // Clear the revisit stack, just in case there are any
3812 // obsolete contents from a short-circuited previous CMS cycle.
3813 _revisitStack.reset();
3814 verify_work_stacks_empty();
3815 verify_overflow_empty();
3816 assert(_revisitStack.isEmpty(), "tabula rasa");
3817 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3818 bool result = false;
3819 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3820 result = do_marking_mt(asynch);
3821 } else {
3822 result = do_marking_st(asynch);
3823 }
3824 return result;
3825 }
3826
3827 // Forward decl
3828 class CMSConcMarkingTask;
3829
3830 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3831 CMSCollector* _collector;
3832 CMSConcMarkingTask* _task;
3833 public:
3834 virtual void yield();
3835
3836 // "n_threads" is the number of threads to be terminated.
3837 // "queue_set" is a set of work queues of other threads.
3838 // "collector" is the CMS collector associated with this task terminator.
3839 // "yield" indicates whether we need the gang as a whole to yield.
3840 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3841 ParallelTaskTerminator(n_threads, queue_set),
3842 _collector(collector) { }
3843
3844 void set_task(CMSConcMarkingTask* task) {
3845 _task = task;
3846 }
3847 };
3848
3849 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3850 CMSConcMarkingTask* _task;
3851 public:
3852 bool should_exit_termination();
3853 void set_task(CMSConcMarkingTask* task) {
3854 _task = task;
3855 }
3856 };
3857
3858 // MT Concurrent Marking Task
3859 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3860 CMSCollector* _collector;
3861 int _n_workers; // requested/desired # workers
3862 bool _asynch;
3863 bool _result;
3864 CompactibleFreeListSpace* _cms_space;
3865 CompactibleFreeListSpace* _perm_space;
3866 char _pad_front[64]; // padding to ...
3867 HeapWord* _global_finger; // ... avoid sharing cache line
3868 char _pad_back[64];
3869 HeapWord* _restart_addr;
3870
3871 // Exposed here for yielding support
3872 Mutex* const _bit_map_lock;
3873
3874 // The per thread work queues, available here for stealing
3875 OopTaskQueueSet* _task_queues;
3876
3877 // Termination (and yielding) support
3878 CMSConcMarkingTerminator _term;
3879 CMSConcMarkingTerminatorTerminator _term_term;
3880
3881 public:
3882 CMSConcMarkingTask(CMSCollector* collector,
3883 CompactibleFreeListSpace* cms_space,
3884 CompactibleFreeListSpace* perm_space,
3885 bool asynch,
3886 YieldingFlexibleWorkGang* workers,
3887 OopTaskQueueSet* task_queues):
3888 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3889 _collector(collector),
3890 _cms_space(cms_space),
3891 _perm_space(perm_space),
3892 _asynch(asynch), _n_workers(0), _result(true),
3893 _task_queues(task_queues),
3894 _term(_n_workers, task_queues, _collector),
3895 _bit_map_lock(collector->bitMapLock())
3896 {
3897 _requested_size = _n_workers;
3898 _term.set_task(this);
3899 _term_term.set_task(this);
3900 assert(_cms_space->bottom() < _perm_space->bottom(),
3901 "Finger incorrectly initialized below");
3902 _restart_addr = _global_finger = _cms_space->bottom();
3903 }
3904
3905
3906 OopTaskQueueSet* task_queues() { return _task_queues; }
3907
3908 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3909
3910 HeapWord** global_finger_addr() { return &_global_finger; }
3911
3912 CMSConcMarkingTerminator* terminator() { return &_term; }
3913
3914 virtual void set_for_termination(int active_workers) {
3915 terminator()->reset_for_reuse(active_workers);
3916 }
3917
3918 void work(uint worker_id);
3919 bool should_yield() {
3920 return ConcurrentMarkSweepThread::should_yield()
3921 && !_collector->foregroundGCIsActive()
3922 && _asynch;
3923 }
3924
3925 virtual void coordinator_yield(); // stuff done by coordinator
3926 bool result() { return _result; }
3927
3928 void reset(HeapWord* ra) {
3929 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3930 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3931 assert(ra < _perm_space->end(), "ra too large");
3932 _restart_addr = _global_finger = ra;
3933 _term.reset_for_reuse();
3934 }
3935
3936 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3937 OopTaskQueue* work_q);
3938
3939 private:
3940 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3941 void do_work_steal(int i);
3942 void bump_global_finger(HeapWord* f);
3943 };
3944
3945 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3946 assert(_task != NULL, "Error");
3947 return _task->yielding();
3948 // Note that we do not need the disjunct || _task->should_yield() above
3949 // because we want terminating threads to yield only if the task
3950 // is already in the midst of yielding, which happens only after at least one
3951 // thread has yielded.
3952 }
3953
3954 void CMSConcMarkingTerminator::yield() {
3955 if (_task->should_yield()) {
3956 _task->yield();
3957 } else {
3958 ParallelTaskTerminator::yield();
3959 }
3960 }
3961
3962 ////////////////////////////////////////////////////////////////
3963 // Concurrent Marking Algorithm Sketch
3964 ////////////////////////////////////////////////////////////////
3965 // Until all tasks exhausted (both spaces):
3966 // -- claim next available chunk
3967 // -- bump global finger via CAS
3968 // -- find first object that starts in this chunk
3969 // and start scanning bitmap from that position
3970 // -- scan marked objects for oops
3971 // -- CAS-mark target, and if successful:
3972 // . if target oop is above global finger (volatile read)
3973 // nothing to do
3974 // . if target oop is in chunk and above local finger
3975 // then nothing to do
3976 // . else push on work-queue
3977 // -- Deal with possible overflow issues:
3978 // . local work-queue overflow causes stuff to be pushed on
3979 // global (common) overflow queue
3980 // . always first empty local work queue
3981 // . then get a batch of oops from global work queue if any
3982 // . then do work stealing
3983 // -- When all tasks claimed (both spaces)
3984 // and local work queue empty,
3985 // then in a loop do:
3986 // . check global overflow stack; steal a batch of oops and trace
3987 // . try to steal from other threads oif GOS is empty
3988 // . if neither is available, offer termination
3989 // -- Terminate and return result
3990 //
3991 void CMSConcMarkingTask::work(uint worker_id) {
3992 elapsedTimer _timer;
3993 ResourceMark rm;
3994 HandleMark hm;
3995
3996 DEBUG_ONLY(_collector->verify_overflow_empty();)
3997
3998 // Before we begin work, our work queue should be empty
3999 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4000 // Scan the bitmap covering _cms_space, tracing through grey objects.
4001 _timer.start();
4002 do_scan_and_mark(worker_id, _cms_space);
4003 _timer.stop();
4004 if (PrintCMSStatistics != 0) {
4005 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4006 worker_id, _timer.seconds());
4007 // XXX: need xxx/xxx type of notation, two timers
4008 }
4009
4010 // ... do the same for the _perm_space
4011 _timer.reset();
4012 _timer.start();
4013 do_scan_and_mark(worker_id, _perm_space);
4014 _timer.stop();
4015 if (PrintCMSStatistics != 0) {
4016 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
4017 worker_id, _timer.seconds());
4018 // XXX: need xxx/xxx type of notation, two timers
4019 }
4020
4021 // ... do work stealing
4022 _timer.reset();
4023 _timer.start();
4024 do_work_steal(worker_id);
4025 _timer.stop();
4026 if (PrintCMSStatistics != 0) {
4027 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4028 worker_id, _timer.seconds());
4029 // XXX: need xxx/xxx type of notation, two timers
4030 }
4031 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4032 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4033 // Note that under the current task protocol, the
4034 // following assertion is true even of the spaces
4035 // expanded since the completion of the concurrent
4036 // marking. XXX This will likely change under a strict
4037 // ABORT semantics.
4038 assert(_global_finger > _cms_space->end() &&
4039 _global_finger >= _perm_space->end(),
4040 "All tasks have been completed");
4041 DEBUG_ONLY(_collector->verify_overflow_empty();)
4042 }
4043
4044 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4045 HeapWord* read = _global_finger;
4046 HeapWord* cur = read;
4047 while (f > read) {
4048 cur = read;
4049 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4050 if (cur == read) {
4051 // our cas succeeded
4052 assert(_global_finger >= f, "protocol consistency");
4053 break;
4054 }
4055 }
4056 }
4057
4058 // This is really inefficient, and should be redone by
4059 // using (not yet available) block-read and -write interfaces to the
4060 // stack and the work_queue. XXX FIX ME !!!
4061 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4062 OopTaskQueue* work_q) {
4063 // Fast lock-free check
4064 if (ovflw_stk->length() == 0) {
4065 return false;
4066 }
4067 assert(work_q->size() == 0, "Shouldn't steal");
4068 MutexLockerEx ml(ovflw_stk->par_lock(),
4069 Mutex::_no_safepoint_check_flag);
4070 // Grab up to 1/4 the size of the work queue
4071 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4072 (size_t)ParGCDesiredObjsFromOverflowList);
4073 num = MIN2(num, ovflw_stk->length());
4074 for (int i = (int) num; i > 0; i--) {
4075 oop cur = ovflw_stk->pop();
4076 assert(cur != NULL, "Counted wrong?");
4077 work_q->push(cur);
4078 }
4079 return num > 0;
4080 }
4081
4082 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4083 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4084 int n_tasks = pst->n_tasks();
4085 // We allow that there may be no tasks to do here because
4086 // we are restarting after a stack overflow.
4087 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4088 uint nth_task = 0;
4089
4090 HeapWord* aligned_start = sp->bottom();
4091 if (sp->used_region().contains(_restart_addr)) {
4092 // Align down to a card boundary for the start of 0th task
4093 // for this space.
4094 aligned_start =
4095 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4096 CardTableModRefBS::card_size);
4097 }
4098
4099 size_t chunk_size = sp->marking_task_size();
4100 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4101 // Having claimed the nth task in this space,
4102 // compute the chunk that it corresponds to:
4103 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4104 aligned_start + (nth_task+1)*chunk_size);
4105 // Try and bump the global finger via a CAS;
4106 // note that we need to do the global finger bump
4107 // _before_ taking the intersection below, because
4108 // the task corresponding to that region will be
4109 // deemed done even if the used_region() expands
4110 // because of allocation -- as it almost certainly will
4111 // during start-up while the threads yield in the
4112 // closure below.
4113 HeapWord* finger = span.end();
4114 bump_global_finger(finger); // atomically
4115 // There are null tasks here corresponding to chunks
4116 // beyond the "top" address of the space.
4117 span = span.intersection(sp->used_region());
4118 if (!span.is_empty()) { // Non-null task
4119 HeapWord* prev_obj;
4120 assert(!span.contains(_restart_addr) || nth_task == 0,
4121 "Inconsistency");
4122 if (nth_task == 0) {
4123 // For the 0th task, we'll not need to compute a block_start.
4124 if (span.contains(_restart_addr)) {
4125 // In the case of a restart because of stack overflow,
4126 // we might additionally skip a chunk prefix.
4127 prev_obj = _restart_addr;
4128 } else {
4129 prev_obj = span.start();
4130 }
4131 } else {
4132 // We want to skip the first object because
4133 // the protocol is to scan any object in its entirety
4134 // that _starts_ in this span; a fortiori, any
4135 // object starting in an earlier span is scanned
4136 // as part of an earlier claimed task.
4137 // Below we use the "careful" version of block_start
4138 // so we do not try to navigate uninitialized objects.
4139 prev_obj = sp->block_start_careful(span.start());
4140 // Below we use a variant of block_size that uses the
4141 // Printezis bits to avoid waiting for allocated
4142 // objects to become initialized/parsable.
4143 while (prev_obj < span.start()) {
4144 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4145 if (sz > 0) {
4146 prev_obj += sz;
4147 } else {
4148 // In this case we may end up doing a bit of redundant
4149 // scanning, but that appears unavoidable, short of
4150 // locking the free list locks; see bug 6324141.
4151 break;
4152 }
4153 }
4154 }
4155 if (prev_obj < span.end()) {
4156 MemRegion my_span = MemRegion(prev_obj, span.end());
4157 // Do the marking work within a non-empty span --
4158 // the last argument to the constructor indicates whether the
4159 // iteration should be incremental with periodic yields.
4160 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4161 &_collector->_markBitMap,
4162 work_queue(i),
4163 &_collector->_markStack,
4164 &_collector->_revisitStack,
4165 _asynch);
4166 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4167 } // else nothing to do for this task
4168 } // else nothing to do for this task
4169 }
4170 // We'd be tempted to assert here that since there are no
4171 // more tasks left to claim in this space, the global_finger
4172 // must exceed space->top() and a fortiori space->end(). However,
4173 // that would not quite be correct because the bumping of
4174 // global_finger occurs strictly after the claiming of a task,
4175 // so by the time we reach here the global finger may not yet
4176 // have been bumped up by the thread that claimed the last
4177 // task.
4178 pst->all_tasks_completed();
4179 }
4180
4181 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4182 private:
4183 CMSConcMarkingTask* _task;
4184 MemRegion _span;
4185 CMSBitMap* _bit_map;
4186 CMSMarkStack* _overflow_stack;
4187 OopTaskQueue* _work_queue;
4188 protected:
4189 DO_OOP_WORK_DEFN
4190 public:
4191 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4192 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4193 CMSMarkStack* revisit_stack):
4194 Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4195 _task(task),
4196 _span(collector->_span),
4197 _work_queue(work_queue),
4198 _bit_map(bit_map),
4199 _overflow_stack(overflow_stack)
4200 { }
4201 virtual void do_oop(oop* p);
4202 virtual void do_oop(narrowOop* p);
4203 void trim_queue(size_t max);
4204 void handle_stack_overflow(HeapWord* lost);
4205 void do_yield_check() {
4206 if (_task->should_yield()) {
4207 _task->yield();
4208 }
4209 }
4210 };
4211
4212 // Grey object scanning during work stealing phase --
4213 // the salient assumption here is that any references
4214 // that are in these stolen objects being scanned must
4215 // already have been initialized (else they would not have
4216 // been published), so we do not need to check for
4217 // uninitialized objects before pushing here.
4218 void Par_ConcMarkingClosure::do_oop(oop obj) {
4219 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4220 HeapWord* addr = (HeapWord*)obj;
4221 // Check if oop points into the CMS generation
4222 // and is not marked
4223 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4224 // a white object ...
4225 // If we manage to "claim" the object, by being the
4226 // first thread to mark it, then we push it on our
4227 // marking stack
4228 if (_bit_map->par_mark(addr)) { // ... now grey
4229 // push on work queue (grey set)
4230 bool simulate_overflow = false;
4231 NOT_PRODUCT(
4232 if (CMSMarkStackOverflowALot &&
4233 _collector->simulate_overflow()) {
4234 // simulate a stack overflow
4235 simulate_overflow = true;
4236 }
4237 )
4238 if (simulate_overflow ||
4239 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4240 // stack overflow
4241 if (PrintCMSStatistics != 0) {
4242 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4243 SIZE_FORMAT, _overflow_stack->capacity());
4244 }
4245 // We cannot assert that the overflow stack is full because
4246 // it may have been emptied since.
4247 assert(simulate_overflow ||
4248 _work_queue->size() == _work_queue->max_elems(),
4249 "Else push should have succeeded");
4250 handle_stack_overflow(addr);
4251 }
4252 } // Else, some other thread got there first
4253 do_yield_check();
4254 }
4255 }
4256
4257 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4258 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4259
4260 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4261 while (_work_queue->size() > max) {
4262 oop new_oop;
4263 if (_work_queue->pop_local(new_oop)) {
4264 assert(new_oop->is_oop(), "Should be an oop");
4265 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4266 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4267 assert(new_oop->is_parsable(), "Should be parsable");
4268 new_oop->oop_iterate(this); // do_oop() above
4269 do_yield_check();
4270 }
4271 }
4272 }
4273
4274 // Upon stack overflow, we discard (part of) the stack,
4275 // remembering the least address amongst those discarded
4276 // in CMSCollector's _restart_address.
4277 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4278 // We need to do this under a mutex to prevent other
4279 // workers from interfering with the work done below.
4280 MutexLockerEx ml(_overflow_stack->par_lock(),
4281 Mutex::_no_safepoint_check_flag);
4282 // Remember the least grey address discarded
4283 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4284 _collector->lower_restart_addr(ra);
4285 _overflow_stack->reset(); // discard stack contents
4286 _overflow_stack->expand(); // expand the stack if possible
4287 }
4288
4289
4290 void CMSConcMarkingTask::do_work_steal(int i) {
4291 OopTaskQueue* work_q = work_queue(i);
4292 oop obj_to_scan;
4293 CMSBitMap* bm = &(_collector->_markBitMap);
4294 CMSMarkStack* ovflw = &(_collector->_markStack);
4295 CMSMarkStack* revisit = &(_collector->_revisitStack);
4296 int* seed = _collector->hash_seed(i);
4297 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4298 while (true) {
4299 cl.trim_queue(0);
4300 assert(work_q->size() == 0, "Should have been emptied above");
4301 if (get_work_from_overflow_stack(ovflw, work_q)) {
4302 // Can't assert below because the work obtained from the
4303 // overflow stack may already have been stolen from us.
4304 // assert(work_q->size() > 0, "Work from overflow stack");
4305 continue;
4306 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4307 assert(obj_to_scan->is_oop(), "Should be an oop");
4308 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4309 obj_to_scan->oop_iterate(&cl);
4310 } else if (terminator()->offer_termination(&_term_term)) {
4311 assert(work_q->size() == 0, "Impossible!");
4312 break;
4313 } else if (yielding() || should_yield()) {
4314 yield();
4315 }
4316 }
4317 }
4318
4319 // This is run by the CMS (coordinator) thread.
4320 void CMSConcMarkingTask::coordinator_yield() {
4321 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4322 "CMS thread should hold CMS token");
4323 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4324 // First give up the locks, then yield, then re-lock
4325 // We should probably use a constructor/destructor idiom to
4326 // do this unlock/lock or modify the MutexUnlocker class to
4327 // serve our purpose. XXX
4328 assert_lock_strong(_bit_map_lock);
4329 _bit_map_lock->unlock();
4330 ConcurrentMarkSweepThread::desynchronize(true);
4331 ConcurrentMarkSweepThread::acknowledge_yield_request();
4332 _collector->stopTimer();
4333 if (PrintCMSStatistics != 0) {
4334 _collector->incrementYields();
4335 }
4336 _collector->icms_wait();
4337
4338 // It is possible for whichever thread initiated the yield request
4339 // not to get a chance to wake up and take the bitmap lock between
4340 // this thread releasing it and reacquiring it. So, while the
4341 // should_yield() flag is on, let's sleep for a bit to give the
4342 // other thread a chance to wake up. The limit imposed on the number
4343 // of iterations is defensive, to avoid any unforseen circumstances
4344 // putting us into an infinite loop. Since it's always been this
4345 // (coordinator_yield()) method that was observed to cause the
4346 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4347 // which is by default non-zero. For the other seven methods that
4348 // also perform the yield operation, as are using a different
4349 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4350 // can enable the sleeping for those methods too, if necessary.
4351 // See 6442774.
4352 //
4353 // We really need to reconsider the synchronization between the GC
4354 // thread and the yield-requesting threads in the future and we
4355 // should really use wait/notify, which is the recommended
4356 // way of doing this type of interaction. Additionally, we should
4357 // consolidate the eight methods that do the yield operation and they
4358 // are almost identical into one for better maintenability and
4359 // readability. See 6445193.
4360 //
4361 // Tony 2006.06.29
4362 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4363 ConcurrentMarkSweepThread::should_yield() &&
4364 !CMSCollector::foregroundGCIsActive(); ++i) {
4365 os::sleep(Thread::current(), 1, false);
4366 ConcurrentMarkSweepThread::acknowledge_yield_request();
4367 }
4368
4369 ConcurrentMarkSweepThread::synchronize(true);
4370 _bit_map_lock->lock_without_safepoint_check();
4371 _collector->startTimer();
4372 }
4373
4374 bool CMSCollector::do_marking_mt(bool asynch) {
4375 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4376 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4377 conc_workers()->total_workers(),
4378 conc_workers()->active_workers(),
4379 Threads::number_of_non_daemon_threads());
4380 conc_workers()->set_active_workers(num_workers);
4381
4382 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4383 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4384
4385 CMSConcMarkingTask tsk(this,
4386 cms_space,
4387 perm_space,
4388 asynch,
4389 conc_workers(),
4390 task_queues());
4391
4392 // Since the actual number of workers we get may be different
4393 // from the number we requested above, do we need to do anything different
4394 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4395 // class?? XXX
4396 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4397 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4398
4399 // Refs discovery is already non-atomic.
4400 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4401 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4402 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4403 conc_workers()->start_task(&tsk);
4404 while (tsk.yielded()) {
4405 tsk.coordinator_yield();
4406 conc_workers()->continue_task(&tsk);
4407 }
4408 // If the task was aborted, _restart_addr will be non-NULL
4409 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4410 while (_restart_addr != NULL) {
4411 // XXX For now we do not make use of ABORTED state and have not
4412 // yet implemented the right abort semantics (even in the original
4413 // single-threaded CMS case). That needs some more investigation
4414 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4415 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4416 // If _restart_addr is non-NULL, a marking stack overflow
4417 // occurred; we need to do a fresh marking iteration from the
4418 // indicated restart address.
4419 if (_foregroundGCIsActive && asynch) {
4420 // We may be running into repeated stack overflows, having
4421 // reached the limit of the stack size, while making very
4422 // slow forward progress. It may be best to bail out and
4423 // let the foreground collector do its job.
4424 // Clear _restart_addr, so that foreground GC
4425 // works from scratch. This avoids the headache of
4426 // a "rescan" which would otherwise be needed because
4427 // of the dirty mod union table & card table.
4428 _restart_addr = NULL;
4429 return false;
4430 }
4431 // Adjust the task to restart from _restart_addr
4432 tsk.reset(_restart_addr);
4433 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4434 _restart_addr);
4435 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4436 _restart_addr);
4437 _restart_addr = NULL;
4438 // Get the workers going again
4439 conc_workers()->start_task(&tsk);
4440 while (tsk.yielded()) {
4441 tsk.coordinator_yield();
4442 conc_workers()->continue_task(&tsk);
4443 }
4444 }
4445 assert(tsk.completed(), "Inconsistency");
4446 assert(tsk.result() == true, "Inconsistency");
4447 return true;
4448 }
4449
4450 bool CMSCollector::do_marking_st(bool asynch) {
4451 ResourceMark rm;
4452 HandleMark hm;
4453
4454 // Temporarily make refs discovery single threaded (non-MT)
4455 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4456 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4457 &_markStack, &_revisitStack, CMSYield && asynch);
4458 // the last argument to iterate indicates whether the iteration
4459 // should be incremental with periodic yields.
4460 _markBitMap.iterate(&markFromRootsClosure);
4461 // If _restart_addr is non-NULL, a marking stack overflow
4462 // occurred; we need to do a fresh iteration from the
4463 // indicated restart address.
4464 while (_restart_addr != NULL) {
4465 if (_foregroundGCIsActive && asynch) {
4466 // We may be running into repeated stack overflows, having
4467 // reached the limit of the stack size, while making very
4468 // slow forward progress. It may be best to bail out and
4469 // let the foreground collector do its job.
4470 // Clear _restart_addr, so that foreground GC
4471 // works from scratch. This avoids the headache of
4472 // a "rescan" which would otherwise be needed because
4473 // of the dirty mod union table & card table.
4474 _restart_addr = NULL;
4475 return false; // indicating failure to complete marking
4476 }
4477 // Deal with stack overflow:
4478 // we restart marking from _restart_addr
4479 HeapWord* ra = _restart_addr;
4480 markFromRootsClosure.reset(ra);
4481 _restart_addr = NULL;
4482 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4483 }
4484 return true;
4485 }
4486
4487 void CMSCollector::preclean() {
4488 check_correct_thread_executing();
4489 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4490 verify_work_stacks_empty();
4491 verify_overflow_empty();
4492 _abort_preclean = false;
4493 if (CMSPrecleaningEnabled) {
4494 if (!CMSEdenChunksRecordAlways) {
4495 _eden_chunk_index = 0;
4496 }
4497 size_t used = get_eden_used();
4498 size_t capacity = get_eden_capacity();
4499 // Don't start sampling unless we will get sufficiently
4500 // many samples.
4501 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4502 * CMSScheduleRemarkEdenPenetration)) {
4503 _start_sampling = true;
4504 } else {
4505 _start_sampling = false;
4506 }
4507 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4508 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4509 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4510 }
4511 CMSTokenSync x(true); // is cms thread
4512 if (CMSPrecleaningEnabled) {
4513 sample_eden();
4514 _collectorState = AbortablePreclean;
4515 } else {
4516 _collectorState = FinalMarking;
4517 }
4518 verify_work_stacks_empty();
4519 verify_overflow_empty();
4520 }
4521
4522 // Try and schedule the remark such that young gen
4523 // occupancy is CMSScheduleRemarkEdenPenetration %.
4524 void CMSCollector::abortable_preclean() {
4525 check_correct_thread_executing();
4526 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4527 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4528
4529 // If Eden's current occupancy is below this threshold,
4530 // immediately schedule the remark; else preclean
4531 // past the next scavenge in an effort to
4532 // schedule the pause as described avove. By choosing
4533 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4534 // we will never do an actual abortable preclean cycle.
4535 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4536 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4537 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4538 // We need more smarts in the abortable preclean
4539 // loop below to deal with cases where allocation
4540 // in young gen is very very slow, and our precleaning
4541 // is running a losing race against a horde of
4542 // mutators intent on flooding us with CMS updates
4543 // (dirty cards).
4544 // One, admittedly dumb, strategy is to give up
4545 // after a certain number of abortable precleaning loops
4546 // or after a certain maximum time. We want to make
4547 // this smarter in the next iteration.
4548 // XXX FIX ME!!! YSR
4549 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4550 while (!(should_abort_preclean() ||
4551 ConcurrentMarkSweepThread::should_terminate())) {
4552 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4553 cumworkdone += workdone;
4554 loops++;
4555 // Voluntarily terminate abortable preclean phase if we have
4556 // been at it for too long.
4557 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4558 loops >= CMSMaxAbortablePrecleanLoops) {
4559 if (PrintGCDetails) {
4560 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4561 }
4562 break;
4563 }
4564 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4565 if (PrintGCDetails) {
4566 gclog_or_tty->print(" CMS: abort preclean due to time ");
4567 }
4568 break;
4569 }
4570 // If we are doing little work each iteration, we should
4571 // take a short break.
4572 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4573 // Sleep for some time, waiting for work to accumulate
4574 stopTimer();
4575 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4576 startTimer();
4577 waited++;
4578 }
4579 }
4580 if (PrintCMSStatistics > 0) {
4581 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4582 loops, waited, cumworkdone);
4583 }
4584 }
4585 CMSTokenSync x(true); // is cms thread
4586 if (_collectorState != Idling) {
4587 assert(_collectorState == AbortablePreclean,
4588 "Spontaneous state transition?");
4589 _collectorState = FinalMarking;
4590 } // Else, a foreground collection completed this CMS cycle.
4591 return;
4592 }
4593
4594 // Respond to an Eden sampling opportunity
4595 void CMSCollector::sample_eden() {
4596 // Make sure a young gc cannot sneak in between our
4597 // reading and recording of a sample.
4598 assert(Thread::current()->is_ConcurrentGC_thread(),
4599 "Only the cms thread may collect Eden samples");
4600 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4601 "Should collect samples while holding CMS token");
4602 if (!_start_sampling) {
4603 return;
4604 }
4605 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4606 // is populated by the young generation.
4607 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4608 if (_eden_chunk_index < _eden_chunk_capacity) {
4609 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4610 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4611 "Unexpected state of Eden");
4612 // We'd like to check that what we just sampled is an oop-start address;
4613 // however, we cannot do that here since the object may not yet have been
4614 // initialized. So we'll instead do the check when we _use_ this sample
4615 // later.
4616 if (_eden_chunk_index == 0 ||
4617 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4618 _eden_chunk_array[_eden_chunk_index-1])
4619 >= CMSSamplingGrain)) {
4620 _eden_chunk_index++; // commit sample
4621 }
4622 }
4623 }
4624 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4625 size_t used = get_eden_used();
4626 size_t capacity = get_eden_capacity();
4627 assert(used <= capacity, "Unexpected state of Eden");
4628 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4629 _abort_preclean = true;
4630 }
4631 }
4632 }
4633
4634
4635 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4636 assert(_collectorState == Precleaning ||
4637 _collectorState == AbortablePreclean, "incorrect state");
4638 ResourceMark rm;
4639 HandleMark hm;
4640
4641 // Precleaning is currently not MT but the reference processor
4642 // may be set for MT. Disable it temporarily here.
4643 ReferenceProcessor* rp = ref_processor();
4644 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4645
4646 // Do one pass of scrubbing the discovered reference lists
4647 // to remove any reference objects with strongly-reachable
4648 // referents.
4649 if (clean_refs) {
4650 CMSPrecleanRefsYieldClosure yield_cl(this);
4651 assert(rp->span().equals(_span), "Spans should be equal");
4652 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4653 &_markStack, &_revisitStack,
4654 true /* preclean */);
4655 CMSDrainMarkingStackClosure complete_trace(this,
4656 _span, &_markBitMap, &_markStack,
4657 &keep_alive, true /* preclean */);
4658
4659 // We don't want this step to interfere with a young
4660 // collection because we don't want to take CPU
4661 // or memory bandwidth away from the young GC threads
4662 // (which may be as many as there are CPUs).
4663 // Note that we don't need to protect ourselves from
4664 // interference with mutators because they can't
4665 // manipulate the discovered reference lists nor affect
4666 // the computed reachability of the referents, the
4667 // only properties manipulated by the precleaning
4668 // of these reference lists.
4669 stopTimer();
4670 CMSTokenSyncWithLocks x(true /* is cms thread */,
4671 bitMapLock());
4672 startTimer();
4673 sample_eden();
4674
4675 // The following will yield to allow foreground
4676 // collection to proceed promptly. XXX YSR:
4677 // The code in this method may need further
4678 // tweaking for better performance and some restructuring
4679 // for cleaner interfaces.
4680 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4681 rp->preclean_discovered_references(
4682 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4683 &yield_cl, should_unload_classes(), gc_timer);
4684 }
4685
4686 if (clean_survivor) { // preclean the active survivor space(s)
4687 assert(_young_gen->kind() == Generation::DefNew ||
4688 _young_gen->kind() == Generation::ParNew ||
4689 _young_gen->kind() == Generation::ASParNew,
4690 "incorrect type for cast");
4691 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4692 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4693 &_markBitMap, &_modUnionTable,
4694 &_markStack, &_revisitStack,
4695 true /* precleaning phase */);
4696 stopTimer();
4697 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4698 bitMapLock());
4699 startTimer();
4700 unsigned int before_count =
4701 GenCollectedHeap::heap()->total_collections();
4702 SurvivorSpacePrecleanClosure
4703 sss_cl(this, _span, &_markBitMap, &_markStack,
4704 &pam_cl, before_count, CMSYield);
4705 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4706 dng->from()->object_iterate_careful(&sss_cl);
4707 dng->to()->object_iterate_careful(&sss_cl);
4708 }
4709 MarkRefsIntoAndScanClosure
4710 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4711 &_markStack, &_revisitStack, this, CMSYield,
4712 true /* precleaning phase */);
4713 // CAUTION: The following closure has persistent state that may need to
4714 // be reset upon a decrease in the sequence of addresses it
4715 // processes.
4716 ScanMarkedObjectsAgainCarefullyClosure
4717 smoac_cl(this, _span,
4718 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4719
4720 // Preclean dirty cards in ModUnionTable and CardTable using
4721 // appropriate convergence criterion;
4722 // repeat CMSPrecleanIter times unless we find that
4723 // we are losing.
4724 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4725 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4726 "Bad convergence multiplier");
4727 assert(CMSPrecleanThreshold >= 100,
4728 "Unreasonably low CMSPrecleanThreshold");
4729
4730 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4731 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4732 numIter < CMSPrecleanIter;
4733 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4734 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4735 if (CMSPermGenPrecleaningEnabled) {
4736 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4737 }
4738 if (Verbose && PrintGCDetails) {
4739 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4740 }
4741 // Either there are very few dirty cards, so re-mark
4742 // pause will be small anyway, or our pre-cleaning isn't
4743 // that much faster than the rate at which cards are being
4744 // dirtied, so we might as well stop and re-mark since
4745 // precleaning won't improve our re-mark time by much.
4746 if (curNumCards <= CMSPrecleanThreshold ||
4747 (numIter > 0 &&
4748 (curNumCards * CMSPrecleanDenominator >
4749 lastNumCards * CMSPrecleanNumerator))) {
4750 numIter++;
4751 cumNumCards += curNumCards;
4752 break;
4753 }
4754 }
4755 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4756 if (CMSPermGenPrecleaningEnabled) {
4757 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4758 }
4759 cumNumCards += curNumCards;
4760 if (PrintGCDetails && PrintCMSStatistics != 0) {
4761 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4762 curNumCards, cumNumCards, numIter);
4763 }
4764 return cumNumCards; // as a measure of useful work done
4765 }
4766
4767 // PRECLEANING NOTES:
4768 // Precleaning involves:
4769 // . reading the bits of the modUnionTable and clearing the set bits.
4770 // . For the cards corresponding to the set bits, we scan the
4771 // objects on those cards. This means we need the free_list_lock
4772 // so that we can safely iterate over the CMS space when scanning
4773 // for oops.
4774 // . When we scan the objects, we'll be both reading and setting
4775 // marks in the marking bit map, so we'll need the marking bit map.
4776 // . For protecting _collector_state transitions, we take the CGC_lock.
4777 // Note that any races in the reading of of card table entries by the
4778 // CMS thread on the one hand and the clearing of those entries by the
4779 // VM thread or the setting of those entries by the mutator threads on the
4780 // other are quite benign. However, for efficiency it makes sense to keep
4781 // the VM thread from racing with the CMS thread while the latter is
4782 // dirty card info to the modUnionTable. We therefore also use the
4783 // CGC_lock to protect the reading of the card table and the mod union
4784 // table by the CM thread.
4785 // . We run concurrently with mutator updates, so scanning
4786 // needs to be done carefully -- we should not try to scan
4787 // potentially uninitialized objects.
4788 //
4789 // Locking strategy: While holding the CGC_lock, we scan over and
4790 // reset a maximal dirty range of the mod union / card tables, then lock
4791 // the free_list_lock and bitmap lock to do a full marking, then
4792 // release these locks; and repeat the cycle. This allows for a
4793 // certain amount of fairness in the sharing of these locks between
4794 // the CMS collector on the one hand, and the VM thread and the
4795 // mutators on the other.
4796
4797 // NOTE: preclean_mod_union_table() and preclean_card_table()
4798 // further below are largely identical; if you need to modify
4799 // one of these methods, please check the other method too.
4800
4801 size_t CMSCollector::preclean_mod_union_table(
4802 ConcurrentMarkSweepGeneration* gen,
4803 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4804 verify_work_stacks_empty();
4805 verify_overflow_empty();
4806
4807 // Turn off checking for this method but turn it back on
4808 // selectively. There are yield points in this method
4809 // but it is difficult to turn the checking off just around
4810 // the yield points. It is simpler to selectively turn
4811 // it on.
4812 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4813
4814 // strategy: starting with the first card, accumulate contiguous
4815 // ranges of dirty cards; clear these cards, then scan the region
4816 // covered by these cards.
4817
4818 // Since all of the MUT is committed ahead, we can just use
4819 // that, in case the generations expand while we are precleaning.
4820 // It might also be fine to just use the committed part of the
4821 // generation, but we might potentially miss cards when the
4822 // generation is rapidly expanding while we are in the midst
4823 // of precleaning.
4824 HeapWord* startAddr = gen->reserved().start();
4825 HeapWord* endAddr = gen->reserved().end();
4826
4827 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4828
4829 size_t numDirtyCards, cumNumDirtyCards;
4830 HeapWord *nextAddr, *lastAddr;
4831 for (cumNumDirtyCards = numDirtyCards = 0,
4832 nextAddr = lastAddr = startAddr;
4833 nextAddr < endAddr;
4834 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4835
4836 ResourceMark rm;
4837 HandleMark hm;
4838
4839 MemRegion dirtyRegion;
4840 {
4841 stopTimer();
4842 // Potential yield point
4843 CMSTokenSync ts(true);
4844 startTimer();
4845 sample_eden();
4846 // Get dirty region starting at nextOffset (inclusive),
4847 // simultaneously clearing it.
4848 dirtyRegion =
4849 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4850 assert(dirtyRegion.start() >= nextAddr,
4851 "returned region inconsistent?");
4852 }
4853 // Remember where the next search should begin.
4854 // The returned region (if non-empty) is a right open interval,
4855 // so lastOffset is obtained from the right end of that
4856 // interval.
4857 lastAddr = dirtyRegion.end();
4858 // Should do something more transparent and less hacky XXX
4859 numDirtyCards =
4860 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4861
4862 // We'll scan the cards in the dirty region (with periodic
4863 // yields for foreground GC as needed).
4864 if (!dirtyRegion.is_empty()) {
4865 assert(numDirtyCards > 0, "consistency check");
4866 HeapWord* stop_point = NULL;
4867 stopTimer();
4868 // Potential yield point
4869 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4870 bitMapLock());
4871 startTimer();
4872 {
4873 verify_work_stacks_empty();
4874 verify_overflow_empty();
4875 sample_eden();
4876 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4877 stop_point =
4878 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4879 }
4880 if (stop_point != NULL) {
4881 // The careful iteration stopped early either because it found an
4882 // uninitialized object, or because we were in the midst of an
4883 // "abortable preclean", which should now be aborted. Redirty
4884 // the bits corresponding to the partially-scanned or unscanned
4885 // cards. We'll either restart at the next block boundary or
4886 // abort the preclean.
4887 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4888 (_collectorState == AbortablePreclean && should_abort_preclean()),
4889 "Unparsable objects should only be in perm gen.");
4890 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4891 if (should_abort_preclean()) {
4892 break; // out of preclean loop
4893 } else {
4894 // Compute the next address at which preclean should pick up;
4895 // might need bitMapLock in order to read P-bits.
4896 lastAddr = next_card_start_after_block(stop_point);
4897 }
4898 }
4899 } else {
4900 assert(lastAddr == endAddr, "consistency check");
4901 assert(numDirtyCards == 0, "consistency check");
4902 break;
4903 }
4904 }
4905 verify_work_stacks_empty();
4906 verify_overflow_empty();
4907 return cumNumDirtyCards;
4908 }
4909
4910 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4911 // below are largely identical; if you need to modify
4912 // one of these methods, please check the other method too.
4913
4914 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4915 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4916 // strategy: it's similar to precleamModUnionTable above, in that
4917 // we accumulate contiguous ranges of dirty cards, mark these cards
4918 // precleaned, then scan the region covered by these cards.
4919 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4920 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4921
4922 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4923
4924 size_t numDirtyCards, cumNumDirtyCards;
4925 HeapWord *lastAddr, *nextAddr;
4926
4927 for (cumNumDirtyCards = numDirtyCards = 0,
4928 nextAddr = lastAddr = startAddr;
4929 nextAddr < endAddr;
4930 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4931
4932 ResourceMark rm;
4933 HandleMark hm;
4934
4935 MemRegion dirtyRegion;
4936 {
4937 // See comments in "Precleaning notes" above on why we
4938 // do this locking. XXX Could the locking overheads be
4939 // too high when dirty cards are sparse? [I don't think so.]
4940 stopTimer();
4941 CMSTokenSync x(true); // is cms thread
4942 startTimer();
4943 sample_eden();
4944 // Get and clear dirty region from card table
4945 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4946 MemRegion(nextAddr, endAddr),
4947 true,
4948 CardTableModRefBS::precleaned_card_val());
4949
4950 assert(dirtyRegion.start() >= nextAddr,
4951 "returned region inconsistent?");
4952 }
4953 lastAddr = dirtyRegion.end();
4954 numDirtyCards =
4955 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4956
4957 if (!dirtyRegion.is_empty()) {
4958 stopTimer();
4959 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4960 startTimer();
4961 sample_eden();
4962 verify_work_stacks_empty();
4963 verify_overflow_empty();
4964 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4965 HeapWord* stop_point =
4966 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4967 if (stop_point != NULL) {
4968 // The careful iteration stopped early because it found an
4969 // uninitialized object. Redirty the bits corresponding to the
4970 // partially-scanned or unscanned cards, and start again at the
4971 // next block boundary.
4972 assert(CMSPermGenPrecleaningEnabled ||
4973 (_collectorState == AbortablePreclean && should_abort_preclean()),
4974 "Unparsable objects should only be in perm gen.");
4975 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4976 if (should_abort_preclean()) {
4977 break; // out of preclean loop
4978 } else {
4979 // Compute the next address at which preclean should pick up.
4980 lastAddr = next_card_start_after_block(stop_point);
4981 }
4982 }
4983 } else {
4984 break;
4985 }
4986 }
4987 verify_work_stacks_empty();
4988 verify_overflow_empty();
4989 return cumNumDirtyCards;
4990 }
4991
4992 void CMSCollector::checkpointRootsFinal(bool asynch,
4993 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4994 assert(_collectorState == FinalMarking, "incorrect state transition?");
4995 check_correct_thread_executing();
4996 // world is stopped at this checkpoint
4997 assert(SafepointSynchronize::is_at_safepoint(),
4998 "world should be stopped");
4999 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5000
5001 verify_work_stacks_empty();
5002 verify_overflow_empty();
5003
5004 SpecializationStats::clear();
5005 if (PrintGCDetails) {
5006 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5007 _young_gen->used() / K,
5008 _young_gen->capacity() / K);
5009 }
5010 if (asynch) {
5011 if (CMSScavengeBeforeRemark) {
5012 GenCollectedHeap* gch = GenCollectedHeap::heap();
5013 // Temporarily set flag to false, GCH->do_collection will
5014 // expect it to be false and set to true
5015 FlagSetting fl(gch->_is_gc_active, false);
5016 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5017 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5018 int level = _cmsGen->level() - 1;
5019 if (level >= 0) {
5020 gch->do_collection(true, // full (i.e. force, see below)
5021 false, // !clear_all_soft_refs
5022 0, // size
5023 false, // is_tlab
5024 level // max_level
5025 );
5026 }
5027 }
5028 FreelistLocker x(this);
5029 MutexLockerEx y(bitMapLock(),
5030 Mutex::_no_safepoint_check_flag);
5031 assert(!init_mark_was_synchronous, "but that's impossible!");
5032 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5033 } else {
5034 // already have all the locks
5035 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5036 init_mark_was_synchronous);
5037 }
5038 verify_work_stacks_empty();
5039 verify_overflow_empty();
5040 SpecializationStats::print();
5041 }
5042
5043 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5044 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5045
5046 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5047
5048 assert(haveFreelistLocks(), "must have free list locks");
5049 assert_lock_strong(bitMapLock());
5050
5051 if (UseAdaptiveSizePolicy) {
5052 size_policy()->checkpoint_roots_final_begin();
5053 }
5054
5055 ResourceMark rm;
5056 HandleMark hm;
5057
5058 GenCollectedHeap* gch = GenCollectedHeap::heap();
5059
5060 if (should_unload_classes()) {
5061 CodeCache::gc_prologue();
5062 }
5063 assert(haveFreelistLocks(), "must have free list locks");
5064 assert_lock_strong(bitMapLock());
5065
5066 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
5067 if (!init_mark_was_synchronous) {
5068 // We might assume that we need not fill TLAB's when
5069 // CMSScavengeBeforeRemark is set, because we may have just done
5070 // a scavenge which would have filled all TLAB's -- and besides
5071 // Eden would be empty. This however may not always be the case --
5072 // for instance although we asked for a scavenge, it may not have
5073 // happened because of a JNI critical section. We probably need
5074 // a policy for deciding whether we can in that case wait until
5075 // the critical section releases and then do the remark following
5076 // the scavenge, and skip it here. In the absence of that policy,
5077 // or of an indication of whether the scavenge did indeed occur,
5078 // we cannot rely on TLAB's having been filled and must do
5079 // so here just in case a scavenge did not happen.
5080 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5081 // Update the saved marks which may affect the root scans.
5082 gch->save_marks();
5083
5084 if (CMSPrintEdenSurvivorChunks) {
5085 print_eden_and_survivor_chunk_arrays();
5086 }
5087
5088 {
5089 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5090
5091 // Note on the role of the mod union table:
5092 // Since the marker in "markFromRoots" marks concurrently with
5093 // mutators, it is possible for some reachable objects not to have been
5094 // scanned. For instance, an only reference to an object A was
5095 // placed in object B after the marker scanned B. Unless B is rescanned,
5096 // A would be collected. Such updates to references in marked objects
5097 // are detected via the mod union table which is the set of all cards
5098 // dirtied since the first checkpoint in this GC cycle and prior to
5099 // the most recent young generation GC, minus those cleaned up by the
5100 // concurrent precleaning.
5101 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5102 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5103 do_remark_parallel();
5104 } else {
5105 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5106 _gc_timer_cm);
5107 do_remark_non_parallel();
5108 }
5109 }
5110 } else {
5111 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5112 // The initial mark was stop-world, so there's no rescanning to
5113 // do; go straight on to the next step below.
5114 }
5115 verify_work_stacks_empty();
5116 verify_overflow_empty();
5117
5118 {
5119 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5120 refProcessingWork(asynch, clear_all_soft_refs);
5121 }
5122 verify_work_stacks_empty();
5123 verify_overflow_empty();
5124
5125 if (should_unload_classes()) {
5126 CodeCache::gc_epilogue();
5127 }
5128 JvmtiExport::gc_epilogue();
5129
5130 // If we encountered any (marking stack / work queue) overflow
5131 // events during the current CMS cycle, take appropriate
5132 // remedial measures, where possible, so as to try and avoid
5133 // recurrence of that condition.
5134 assert(_markStack.isEmpty(), "No grey objects");
5135 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5136 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5137 if (ser_ovflw > 0) {
5138 if (PrintCMSStatistics != 0) {
5139 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5140 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5141 ", kac_preclean="SIZE_FORMAT")",
5142 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5143 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5144 }
5145 _markStack.expand();
5146 _ser_pmc_remark_ovflw = 0;
5147 _ser_pmc_preclean_ovflw = 0;
5148 _ser_kac_preclean_ovflw = 0;
5149 _ser_kac_ovflw = 0;
5150 }
5151 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5152 if (PrintCMSStatistics != 0) {
5153 gclog_or_tty->print_cr("Work queue overflow (benign) "
5154 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5155 _par_pmc_remark_ovflw, _par_kac_ovflw);
5156 }
5157 _par_pmc_remark_ovflw = 0;
5158 _par_kac_ovflw = 0;
5159 }
5160 if (PrintCMSStatistics != 0) {
5161 if (_markStack._hit_limit > 0) {
5162 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5163 _markStack._hit_limit);
5164 }
5165 if (_markStack._failed_double > 0) {
5166 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5167 " current capacity "SIZE_FORMAT,
5168 _markStack._failed_double,
5169 _markStack.capacity());
5170 }
5171 }
5172 _markStack._hit_limit = 0;
5173 _markStack._failed_double = 0;
5174
5175 // Check that all the klasses have been checked
5176 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5177
5178 if ((VerifyAfterGC || VerifyDuringGC) &&
5179 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5180 verify_after_remark();
5181 }
5182
5183 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5184
5185 // Change under the freelistLocks.
5186 _collectorState = Sweeping;
5187 // Call isAllClear() under bitMapLock
5188 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5189 " final marking");
5190 if (UseAdaptiveSizePolicy) {
5191 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5192 }
5193 }
5194
5195 void CMSParInitialMarkTask::work(uint worker_id) {
5196 elapsedTimer _timer;
5197 ResourceMark rm;
5198 HandleMark hm;
5199
5200 // ---------- scan from roots --------------
5201 _timer.start();
5202 GenCollectedHeap* gch = GenCollectedHeap::heap();
5203 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5204
5205 // ---------- young gen roots --------------
5206 {
5207 work_on_young_gen_roots(worker_id, &par_mri_cl);
5208 _timer.stop();
5209 if (PrintCMSStatistics != 0) {
5210 gclog_or_tty->print_cr(
5211 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5212 worker_id, _timer.seconds());
5213 }
5214 }
5215
5216 // ---------- remaining roots --------------
5217 _timer.reset();
5218 _timer.start();
5219 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5220 false, // yg was scanned above
5221 false, // this is parallel code
5222 true, // collecting perm gen
5223 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5224 &par_mri_cl,
5225 true, // walk all of code cache if (so & SO_CodeCache)
5226 NULL);
5227 assert(_collector->should_unload_classes()
5228 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5229 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5230 _timer.stop();
5231 if (PrintCMSStatistics != 0) {
5232 gclog_or_tty->print_cr(
5233 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5234 worker_id, _timer.seconds());
5235 }
5236 }
5237
5238 // Parallel remark task
5239 class CMSParRemarkTask: public CMSParMarkTask {
5240 CompactibleFreeListSpace* _cms_space;
5241 CompactibleFreeListSpace* _perm_space;
5242
5243 // The per-thread work queues, available here for stealing.
5244 OopTaskQueueSet* _task_queues;
5245 ParallelTaskTerminator _term;
5246
5247 public:
5248 // A value of 0 passed to n_workers will cause the number of
5249 // workers to be taken from the active workers in the work gang.
5250 CMSParRemarkTask(CMSCollector* collector,
5251 CompactibleFreeListSpace* cms_space,
5252 CompactibleFreeListSpace* perm_space,
5253 int n_workers, FlexibleWorkGang* workers,
5254 OopTaskQueueSet* task_queues):
5255 CMSParMarkTask("Rescan roots and grey objects in parallel",
5256 collector, n_workers),
5257 _cms_space(cms_space), _perm_space(perm_space),
5258 _task_queues(task_queues),
5259 _term(n_workers, task_queues) { }
5260
5261 OopTaskQueueSet* task_queues() { return _task_queues; }
5262
5263 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5264
5265 ParallelTaskTerminator* terminator() { return &_term; }
5266 int n_workers() { return _n_workers; }
5267
5268 void work(uint worker_id);
5269
5270 private:
5271 // ... of dirty cards in old space
5272 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5273 Par_MarkRefsIntoAndScanClosure* cl);
5274
5275 // ... work stealing for the above
5276 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5277 };
5278
5279 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5280 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5281 EdenSpace* eden_space = dng->eden();
5282 ContiguousSpace* from_space = dng->from();
5283 ContiguousSpace* to_space = dng->to();
5284
5285 HeapWord** eca = _collector->_eden_chunk_array;
5286 size_t ect = _collector->_eden_chunk_index;
5287 HeapWord** sca = _collector->_survivor_chunk_array;
5288 size_t sct = _collector->_survivor_chunk_index;
5289
5290 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5291 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5292
5293 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5294 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5295 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5296 }
5297
5298 // work_queue(i) is passed to the closure
5299 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5300 // also is passed to do_dirty_card_rescan_tasks() and to
5301 // do_work_steal() to select the i-th task_queue.
5302
5303 void CMSParRemarkTask::work(uint worker_id) {
5304 elapsedTimer _timer;
5305 ResourceMark rm;
5306 HandleMark hm;
5307
5308 // ---------- rescan from roots --------------
5309 _timer.start();
5310 GenCollectedHeap* gch = GenCollectedHeap::heap();
5311 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5312 _collector->_span, _collector->ref_processor(),
5313 &(_collector->_markBitMap),
5314 work_queue(worker_id), &(_collector->_revisitStack));
5315
5316 // Rescan young gen roots first since these are likely
5317 // coarsely partitioned and may, on that account, constitute
5318 // the critical path; thus, it's best to start off that
5319 // work first.
5320 // ---------- young gen roots --------------
5321 {
5322 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5323 _timer.stop();
5324 if (PrintCMSStatistics != 0) {
5325 gclog_or_tty->print_cr(
5326 "Finished young gen rescan work in %dth thread: %3.3f sec",
5327 worker_id, _timer.seconds());
5328 }
5329 }
5330
5331 // ---------- remaining roots --------------
5332 _timer.reset();
5333 _timer.start();
5334 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5335 false, // yg was scanned above
5336 false, // this is parallel code
5337 true, // collecting perm gen
5338 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5339 &par_mrias_cl,
5340 true, // walk all of code cache if (so & SO_CodeCache)
5341 NULL);
5342 assert(_collector->should_unload_classes()
5343 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5344 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5345 _timer.stop();
5346 if (PrintCMSStatistics != 0) {
5347 gclog_or_tty->print_cr(
5348 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5349 worker_id, _timer.seconds());
5350 }
5351
5352 // ---------- rescan dirty cards ------------
5353 _timer.reset();
5354 _timer.start();
5355
5356 // Do the rescan tasks for each of the two spaces
5357 // (cms_space and perm_space) in turn.
5358 // "worker_id" is passed to select the task_queue for "worker_id"
5359 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5360 do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5361 _timer.stop();
5362 if (PrintCMSStatistics != 0) {
5363 gclog_or_tty->print_cr(
5364 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5365 worker_id, _timer.seconds());
5366 }
5367
5368 // ---------- steal work from other threads ...
5369 // ---------- ... and drain overflow list.
5370 _timer.reset();
5371 _timer.start();
5372 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5373 _timer.stop();
5374 if (PrintCMSStatistics != 0) {
5375 gclog_or_tty->print_cr(
5376 "Finished work stealing in %dth thread: %3.3f sec",
5377 worker_id, _timer.seconds());
5378 }
5379 }
5380
5381 // Note that parameter "i" is not used.
5382 void
5383 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5384 OopsInGenClosure* cl, ContiguousSpace* space,
5385 HeapWord** chunk_array, size_t chunk_top) {
5386 // Until all tasks completed:
5387 // . claim an unclaimed task
5388 // . compute region boundaries corresponding to task claimed
5389 // using chunk_array
5390 // . par_oop_iterate(cl) over that region
5391
5392 ResourceMark rm;
5393 HandleMark hm;
5394
5395 SequentialSubTasksDone* pst = space->par_seq_tasks();
5396 assert(pst->valid(), "Uninitialized use?");
5397
5398 uint nth_task = 0;
5399 uint n_tasks = pst->n_tasks();
5400
5401 HeapWord *start, *end;
5402 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5403 // We claimed task # nth_task; compute its boundaries.
5404 if (chunk_top == 0) { // no samples were taken
5405 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5406 start = space->bottom();
5407 end = space->top();
5408 } else if (nth_task == 0) {
5409 start = space->bottom();
5410 end = chunk_array[nth_task];
5411 } else if (nth_task < (uint)chunk_top) {
5412 assert(nth_task >= 1, "Control point invariant");
5413 start = chunk_array[nth_task - 1];
5414 end = chunk_array[nth_task];
5415 } else {
5416 assert(nth_task == (uint)chunk_top, "Control point invariant");
5417 start = chunk_array[chunk_top - 1];
5418 end = space->top();
5419 }
5420 MemRegion mr(start, end);
5421 // Verify that mr is in space
5422 assert(mr.is_empty() || space->used_region().contains(mr),
5423 "Should be in space");
5424 // Verify that "start" is an object boundary
5425 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5426 "Should be an oop");
5427 space->par_oop_iterate(mr, cl);
5428 }
5429 pst->all_tasks_completed();
5430 }
5431
5432 void
5433 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5434 CompactibleFreeListSpace* sp, int i,
5435 Par_MarkRefsIntoAndScanClosure* cl) {
5436 // Until all tasks completed:
5437 // . claim an unclaimed task
5438 // . compute region boundaries corresponding to task claimed
5439 // . transfer dirty bits ct->mut for that region
5440 // . apply rescanclosure to dirty mut bits for that region
5441
5442 ResourceMark rm;
5443 HandleMark hm;
5444
5445 OopTaskQueue* work_q = work_queue(i);
5446 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5447 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5448 // CAUTION: This closure has state that persists across calls to
5449 // the work method dirty_range_iterate_clear() in that it has
5450 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5451 // use of that state in the imbedded UpwardsObjectClosure instance
5452 // assumes that the cards are always iterated (even if in parallel
5453 // by several threads) in monotonically increasing order per each
5454 // thread. This is true of the implementation below which picks
5455 // card ranges (chunks) in monotonically increasing order globally
5456 // and, a-fortiori, in monotonically increasing order per thread
5457 // (the latter order being a subsequence of the former).
5458 // If the work code below is ever reorganized into a more chaotic
5459 // work-partitioning form than the current "sequential tasks"
5460 // paradigm, the use of that persistent state will have to be
5461 // revisited and modified appropriately. See also related
5462 // bug 4756801 work on which should examine this code to make
5463 // sure that the changes there do not run counter to the
5464 // assumptions made here and necessary for correctness and
5465 // efficiency. Note also that this code might yield inefficient
5466 // behaviour in the case of very large objects that span one or
5467 // more work chunks. Such objects would potentially be scanned
5468 // several times redundantly. Work on 4756801 should try and
5469 // address that performance anomaly if at all possible. XXX
5470 MemRegion full_span = _collector->_span;
5471 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5472 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5473 MarkFromDirtyCardsClosure
5474 greyRescanClosure(_collector, full_span, // entire span of interest
5475 sp, bm, work_q, rs, cl);
5476
5477 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5478 assert(pst->valid(), "Uninitialized use?");
5479 uint nth_task = 0;
5480 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5481 MemRegion span = sp->used_region();
5482 HeapWord* start_addr = span.start();
5483 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5484 alignment);
5485 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5486 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5487 start_addr, "Check alignment");
5488 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5489 chunk_size, "Check alignment");
5490
5491 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5492 // Having claimed the nth_task, compute corresponding mem-region,
5493 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5494 // The alignment restriction ensures that we do not need any
5495 // synchronization with other gang-workers while setting or
5496 // clearing bits in thus chunk of the MUT.
5497 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5498 start_addr + (nth_task+1)*chunk_size);
5499 // The last chunk's end might be way beyond end of the
5500 // used region. In that case pull back appropriately.
5501 if (this_span.end() > end_addr) {
5502 this_span.set_end(end_addr);
5503 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5504 }
5505 // Iterate over the dirty cards covering this chunk, marking them
5506 // precleaned, and setting the corresponding bits in the mod union
5507 // table. Since we have been careful to partition at Card and MUT-word
5508 // boundaries no synchronization is needed between parallel threads.
5509 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5510 &modUnionClosure);
5511
5512 // Having transferred these marks into the modUnionTable,
5513 // rescan the marked objects on the dirty cards in the modUnionTable.
5514 // Even if this is at a synchronous collection, the initial marking
5515 // may have been done during an asynchronous collection so there
5516 // may be dirty bits in the mod-union table.
5517 _collector->_modUnionTable.dirty_range_iterate_clear(
5518 this_span, &greyRescanClosure);
5519 _collector->_modUnionTable.verifyNoOneBitsInRange(
5520 this_span.start(),
5521 this_span.end());
5522 }
5523 pst->all_tasks_completed(); // declare that i am done
5524 }
5525
5526 // . see if we can share work_queues with ParNew? XXX
5527 void
5528 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5529 int* seed) {
5530 OopTaskQueue* work_q = work_queue(i);
5531 NOT_PRODUCT(int num_steals = 0;)
5532 oop obj_to_scan;
5533 CMSBitMap* bm = &(_collector->_markBitMap);
5534
5535 while (true) {
5536 // Completely finish any left over work from (an) earlier round(s)
5537 cl->trim_queue(0);
5538 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5539 (size_t)ParGCDesiredObjsFromOverflowList);
5540 // Now check if there's any work in the overflow list
5541 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5542 // only affects the number of attempts made to get work from the
5543 // overflow list and does not affect the number of workers. Just
5544 // pass ParallelGCThreads so this behavior is unchanged.
5545 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5546 work_q,
5547 ParallelGCThreads)) {
5548 // found something in global overflow list;
5549 // not yet ready to go stealing work from others.
5550 // We'd like to assert(work_q->size() != 0, ...)
5551 // because we just took work from the overflow list,
5552 // but of course we can't since all of that could have
5553 // been already stolen from us.
5554 // "He giveth and He taketh away."
5555 continue;
5556 }
5557 // Verify that we have no work before we resort to stealing
5558 assert(work_q->size() == 0, "Have work, shouldn't steal");
5559 // Try to steal from other queues that have work
5560 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5561 NOT_PRODUCT(num_steals++;)
5562 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5563 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5564 // Do scanning work
5565 obj_to_scan->oop_iterate(cl);
5566 // Loop around, finish this work, and try to steal some more
5567 } else if (terminator()->offer_termination()) {
5568 break; // nirvana from the infinite cycle
5569 }
5570 }
5571 NOT_PRODUCT(
5572 if (PrintCMSStatistics != 0) {
5573 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5574 }
5575 )
5576 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5577 "Else our work is not yet done");
5578 }
5579
5580 // Record object boundaries in _eden_chunk_array by sampling the eden
5581 // top in the slow-path eden object allocation code path and record
5582 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5583 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5584 // sampling in sample_eden() that activates during the part of the
5585 // preclean phase.
5586 void CMSCollector::sample_eden_chunk() {
5587 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5588 if (_eden_chunk_lock->try_lock()) {
5589 // Record a sample. This is the critical section. The contents
5590 // of the _eden_chunk_array have to be non-decreasing in the
5591 // address order.
5592 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5593 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5594 "Unexpected state of Eden");
5595 if (_eden_chunk_index == 0 ||
5596 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5597 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5598 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5599 _eden_chunk_index++; // commit sample
5600 }
5601 _eden_chunk_lock->unlock();
5602 }
5603 }
5604 }
5605
5606 // Return a thread-local PLAB recording array, as appropriate.
5607 void* CMSCollector::get_data_recorder(int thr_num) {
5608 if (_survivor_plab_array != NULL &&
5609 (CMSPLABRecordAlways ||
5610 (_collectorState > Marking && _collectorState < FinalMarking))) {
5611 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5612 ChunkArray* ca = &_survivor_plab_array[thr_num];
5613 ca->reset(); // clear it so that fresh data is recorded
5614 return (void*) ca;
5615 } else {
5616 return NULL;
5617 }
5618 }
5619
5620 // Reset all the thread-local PLAB recording arrays
5621 void CMSCollector::reset_survivor_plab_arrays() {
5622 for (uint i = 0; i < ParallelGCThreads; i++) {
5623 _survivor_plab_array[i].reset();
5624 }
5625 }
5626
5627 // Merge the per-thread plab arrays into the global survivor chunk
5628 // array which will provide the partitioning of the survivor space
5629 // for CMS initial scan and rescan.
5630 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5631 int no_of_gc_threads) {
5632 assert(_survivor_plab_array != NULL, "Error");
5633 assert(_survivor_chunk_array != NULL, "Error");
5634 assert(_collectorState == FinalMarking ||
5635 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5636 for (int j = 0; j < no_of_gc_threads; j++) {
5637 _cursor[j] = 0;
5638 }
5639 HeapWord* top = surv->top();
5640 size_t i;
5641 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5642 HeapWord* min_val = top; // Higher than any PLAB address
5643 uint min_tid = 0; // position of min_val this round
5644 for (int j = 0; j < no_of_gc_threads; j++) {
5645 ChunkArray* cur_sca = &_survivor_plab_array[j];
5646 if (_cursor[j] == cur_sca->end()) {
5647 continue;
5648 }
5649 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5650 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5651 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5652 if (cur_val < min_val) {
5653 min_tid = j;
5654 min_val = cur_val;
5655 } else {
5656 assert(cur_val < top, "All recorded addresses should be less");
5657 }
5658 }
5659 // At this point min_val and min_tid are respectively
5660 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5661 // and the thread (j) that witnesses that address.
5662 // We record this address in the _survivor_chunk_array[i]
5663 // and increment _cursor[min_tid] prior to the next round i.
5664 if (min_val == top) {
5665 break;
5666 }
5667 _survivor_chunk_array[i] = min_val;
5668 _cursor[min_tid]++;
5669 }
5670 // We are all done; record the size of the _survivor_chunk_array
5671 _survivor_chunk_index = i; // exclusive: [0, i)
5672 if (PrintCMSStatistics > 0) {
5673 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5674 }
5675 // Verify that we used up all the recorded entries
5676 #ifdef ASSERT
5677 size_t total = 0;
5678 for (int j = 0; j < no_of_gc_threads; j++) {
5679 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5680 total += _cursor[j];
5681 }
5682 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5683 // Check that the merged array is in sorted order
5684 if (total > 0) {
5685 for (size_t i = 0; i < total - 1; i++) {
5686 if (PrintCMSStatistics > 0) {
5687 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5688 i, _survivor_chunk_array[i]);
5689 }
5690 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5691 "Not sorted");
5692 }
5693 }
5694 #endif // ASSERT
5695 }
5696
5697 // Set up the space's par_seq_tasks structure for work claiming
5698 // for parallel initial scan and rescan of young gen.
5699 // See ParRescanTask where this is currently used.
5700 void
5701 CMSCollector::
5702 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5703 assert(n_threads > 0, "Unexpected n_threads argument");
5704 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5705
5706 // Eden space
5707 {
5708 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5709 assert(!pst->valid(), "Clobbering existing data?");
5710 // Each valid entry in [0, _eden_chunk_index) represents a task.
5711 size_t n_tasks = _eden_chunk_index + 1;
5712 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5713 // Sets the condition for completion of the subtask (how many threads
5714 // need to finish in order to be done).
5715 pst->set_n_threads(n_threads);
5716 pst->set_n_tasks((int)n_tasks);
5717 }
5718
5719 // Merge the survivor plab arrays into _survivor_chunk_array
5720 if (_survivor_plab_array != NULL) {
5721 merge_survivor_plab_arrays(dng->from(), n_threads);
5722 } else {
5723 assert(_survivor_chunk_index == 0, "Error");
5724 }
5725
5726 // To space
5727 {
5728 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5729 assert(!pst->valid(), "Clobbering existing data?");
5730 // Sets the condition for completion of the subtask (how many threads
5731 // need to finish in order to be done).
5732 pst->set_n_threads(n_threads);
5733 pst->set_n_tasks(1);
5734 assert(pst->valid(), "Error");
5735 }
5736
5737 // From space
5738 {
5739 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5740 assert(!pst->valid(), "Clobbering existing data?");
5741 size_t n_tasks = _survivor_chunk_index + 1;
5742 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5743 // Sets the condition for completion of the subtask (how many threads
5744 // need to finish in order to be done).
5745 pst->set_n_threads(n_threads);
5746 pst->set_n_tasks((int)n_tasks);
5747 assert(pst->valid(), "Error");
5748 }
5749 }
5750
5751 // Parallel version of remark
5752 void CMSCollector::do_remark_parallel() {
5753 GenCollectedHeap* gch = GenCollectedHeap::heap();
5754 FlexibleWorkGang* workers = gch->workers();
5755 assert(workers != NULL, "Need parallel worker threads.");
5756 // Choose to use the number of GC workers most recently set
5757 // into "active_workers". If active_workers is not set, set it
5758 // to ParallelGCThreads.
5759 int n_workers = workers->active_workers();
5760 if (n_workers == 0) {
5761 assert(n_workers > 0, "Should have been set during scavenge");
5762 n_workers = ParallelGCThreads;
5763 workers->set_active_workers(n_workers);
5764 }
5765 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5766 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5767
5768 CMSParRemarkTask tsk(this,
5769 cms_space, perm_space,
5770 n_workers, workers, task_queues());
5771
5772 // Set up for parallel process_strong_roots work.
5773 gch->set_par_threads(n_workers);
5774 // We won't be iterating over the cards in the card table updating
5775 // the younger_gen cards, so we shouldn't call the following else
5776 // the verification code as well as subsequent younger_refs_iterate
5777 // code would get confused. XXX
5778 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5779
5780 // The young gen rescan work will not be done as part of
5781 // process_strong_roots (which currently doesn't knw how to
5782 // parallelize such a scan), but rather will be broken up into
5783 // a set of parallel tasks (via the sampling that the [abortable]
5784 // preclean phase did of EdenSpace, plus the [two] tasks of
5785 // scanning the [two] survivor spaces. Further fine-grain
5786 // parallelization of the scanning of the survivor spaces
5787 // themselves, and of precleaning of the younger gen itself
5788 // is deferred to the future.
5789 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5790
5791 // The dirty card rescan work is broken up into a "sequence"
5792 // of parallel tasks (per constituent space) that are dynamically
5793 // claimed by the parallel threads.
5794 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5795 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5796
5797 // It turns out that even when we're using 1 thread, doing the work in a
5798 // separate thread causes wide variance in run times. We can't help this
5799 // in the multi-threaded case, but we special-case n=1 here to get
5800 // repeatable measurements of the 1-thread overhead of the parallel code.
5801 if (n_workers > 1) {
5802 // Make refs discovery MT-safe, if it isn't already: it may not
5803 // necessarily be so, since it's possible that we are doing
5804 // ST marking.
5805 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5806 GenCollectedHeap::StrongRootsScope srs(gch);
5807 workers->run_task(&tsk);
5808 } else {
5809 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5810 GenCollectedHeap::StrongRootsScope srs(gch);
5811 tsk.work(0);
5812 }
5813 gch->set_par_threads(0); // 0 ==> non-parallel.
5814 // restore, single-threaded for now, any preserved marks
5815 // as a result of work_q overflow
5816 restore_preserved_marks_if_any();
5817 }
5818
5819 // Non-parallel version of remark
5820 void CMSCollector::do_remark_non_parallel() {
5821 ResourceMark rm;
5822 HandleMark hm;
5823 GenCollectedHeap* gch = GenCollectedHeap::heap();
5824 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5825
5826 MarkRefsIntoAndScanClosure
5827 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5828 &_markStack, &_revisitStack, this,
5829 false /* should_yield */, false /* not precleaning */);
5830 MarkFromDirtyCardsClosure
5831 markFromDirtyCardsClosure(this, _span,
5832 NULL, // space is set further below
5833 &_markBitMap, &_markStack, &_revisitStack,
5834 &mrias_cl);
5835 {
5836 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5837 // Iterate over the dirty cards, setting the corresponding bits in the
5838 // mod union table.
5839 {
5840 ModUnionClosure modUnionClosure(&_modUnionTable);
5841 _ct->ct_bs()->dirty_card_iterate(
5842 _cmsGen->used_region(),
5843 &modUnionClosure);
5844 _ct->ct_bs()->dirty_card_iterate(
5845 _permGen->used_region(),
5846 &modUnionClosure);
5847 }
5848 // Having transferred these marks into the modUnionTable, we just need
5849 // to rescan the marked objects on the dirty cards in the modUnionTable.
5850 // The initial marking may have been done during an asynchronous
5851 // collection so there may be dirty bits in the mod-union table.
5852 const int alignment =
5853 CardTableModRefBS::card_size * BitsPerWord;
5854 {
5855 // ... First handle dirty cards in CMS gen
5856 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5857 MemRegion ur = _cmsGen->used_region();
5858 HeapWord* lb = ur.start();
5859 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5860 MemRegion cms_span(lb, ub);
5861 _modUnionTable.dirty_range_iterate_clear(cms_span,
5862 &markFromDirtyCardsClosure);
5863 verify_work_stacks_empty();
5864 if (PrintCMSStatistics != 0) {
5865 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5866 markFromDirtyCardsClosure.num_dirty_cards());
5867 }
5868 }
5869 {
5870 // .. and then repeat for dirty cards in perm gen
5871 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5872 MemRegion ur = _permGen->used_region();
5873 HeapWord* lb = ur.start();
5874 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5875 MemRegion perm_span(lb, ub);
5876 _modUnionTable.dirty_range_iterate_clear(perm_span,
5877 &markFromDirtyCardsClosure);
5878 verify_work_stacks_empty();
5879 if (PrintCMSStatistics != 0) {
5880 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5881 markFromDirtyCardsClosure.num_dirty_cards());
5882 }
5883 }
5884 }
5885 if (VerifyDuringGC &&
5886 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5887 HandleMark hm; // Discard invalid handles created during verification
5888 Universe::verify();
5889 }
5890 {
5891 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5892
5893 verify_work_stacks_empty();
5894
5895 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5896 GenCollectedHeap::StrongRootsScope srs(gch);
5897 gch->gen_process_strong_roots(_cmsGen->level(),
5898 true, // younger gens as roots
5899 false, // use the local StrongRootsScope
5900 true, // collecting perm gen
5901 SharedHeap::ScanningOption(roots_scanning_options()),
5902 &mrias_cl,
5903 true, // walk code active on stacks
5904 NULL);
5905 assert(should_unload_classes()
5906 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5907 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5908 }
5909 verify_work_stacks_empty();
5910 // Restore evacuated mark words, if any, used for overflow list links
5911 if (!CMSOverflowEarlyRestoration) {
5912 restore_preserved_marks_if_any();
5913 }
5914 verify_overflow_empty();
5915 }
5916
5917 ////////////////////////////////////////////////////////
5918 // Parallel Reference Processing Task Proxy Class
5919 ////////////////////////////////////////////////////////
5920 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5921 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5922 CMSCollector* _collector;
5923 CMSBitMap* _mark_bit_map;
5924 const MemRegion _span;
5925 ProcessTask& _task;
5926
5927 public:
5928 CMSRefProcTaskProxy(ProcessTask& task,
5929 CMSCollector* collector,
5930 const MemRegion& span,
5931 CMSBitMap* mark_bit_map,
5932 AbstractWorkGang* workers,
5933 OopTaskQueueSet* task_queues):
5934 // XXX Should superclass AGTWOQ also know about AWG since it knows
5935 // about the task_queues used by the AWG? Then it could initialize
5936 // the terminator() object. See 6984287. The set_for_termination()
5937 // below is a temporary band-aid for the regression in 6984287.
5938 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5939 task_queues),
5940 _task(task),
5941 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5942 {
5943 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5944 "Inconsistency in _span");
5945 set_for_termination(workers->active_workers());
5946 }
5947
5948 OopTaskQueueSet* task_queues() { return queues(); }
5949
5950 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5951
5952 void do_work_steal(int i,
5953 CMSParDrainMarkingStackClosure* drain,
5954 CMSParKeepAliveClosure* keep_alive,
5955 int* seed);
5956
5957 virtual void work(uint worker_id);
5958 };
5959
5960 void CMSRefProcTaskProxy::work(uint worker_id) {
5961 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5962 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5963 _mark_bit_map,
5964 &_collector->_revisitStack,
5965 work_queue(worker_id));
5966 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5967 _mark_bit_map,
5968 &_collector->_revisitStack,
5969 work_queue(worker_id));
5970 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5971 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5972 if (_task.marks_oops_alive()) {
5973 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5974 _collector->hash_seed(worker_id));
5975 }
5976 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5977 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5978 }
5979
5980 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5981 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5982 EnqueueTask& _task;
5983
5984 public:
5985 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5986 : AbstractGangTask("Enqueue reference objects in parallel"),
5987 _task(task)
5988 { }
5989
5990 virtual void work(uint worker_id)
5991 {
5992 _task.work(worker_id);
5993 }
5994 };
5995
5996 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5997 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5998 OopTaskQueue* work_queue):
5999 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
6000 _span(span),
6001 _bit_map(bit_map),
6002 _work_queue(work_queue),
6003 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
6004 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6005 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6006 { }
6007
6008 // . see if we can share work_queues with ParNew? XXX
6009 void CMSRefProcTaskProxy::do_work_steal(int i,
6010 CMSParDrainMarkingStackClosure* drain,
6011 CMSParKeepAliveClosure* keep_alive,
6012 int* seed) {
6013 OopTaskQueue* work_q = work_queue(i);
6014 NOT_PRODUCT(int num_steals = 0;)
6015 oop obj_to_scan;
6016
6017 while (true) {
6018 // Completely finish any left over work from (an) earlier round(s)
6019 drain->trim_queue(0);
6020 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6021 (size_t)ParGCDesiredObjsFromOverflowList);
6022 // Now check if there's any work in the overflow list
6023 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6024 // only affects the number of attempts made to get work from the
6025 // overflow list and does not affect the number of workers. Just
6026 // pass ParallelGCThreads so this behavior is unchanged.
6027 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6028 work_q,
6029 ParallelGCThreads)) {
6030 // Found something in global overflow list;
6031 // not yet ready to go stealing work from others.
6032 // We'd like to assert(work_q->size() != 0, ...)
6033 // because we just took work from the overflow list,
6034 // but of course we can't, since all of that might have
6035 // been already stolen from us.
6036 continue;
6037 }
6038 // Verify that we have no work before we resort to stealing
6039 assert(work_q->size() == 0, "Have work, shouldn't steal");
6040 // Try to steal from other queues that have work
6041 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6042 NOT_PRODUCT(num_steals++;)
6043 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6044 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6045 // Do scanning work
6046 obj_to_scan->oop_iterate(keep_alive);
6047 // Loop around, finish this work, and try to steal some more
6048 } else if (terminator()->offer_termination()) {
6049 break; // nirvana from the infinite cycle
6050 }
6051 }
6052 NOT_PRODUCT(
6053 if (PrintCMSStatistics != 0) {
6054 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6055 }
6056 )
6057 }
6058
6059 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6060 {
6061 GenCollectedHeap* gch = GenCollectedHeap::heap();
6062 FlexibleWorkGang* workers = gch->workers();
6063 assert(workers != NULL, "Need parallel worker threads.");
6064 CMSRefProcTaskProxy rp_task(task, &_collector,
6065 _collector.ref_processor()->span(),
6066 _collector.markBitMap(),
6067 workers, _collector.task_queues());
6068 workers->run_task(&rp_task);
6069 }
6070
6071 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6072 {
6073
6074 GenCollectedHeap* gch = GenCollectedHeap::heap();
6075 FlexibleWorkGang* workers = gch->workers();
6076 assert(workers != NULL, "Need parallel worker threads.");
6077 CMSRefEnqueueTaskProxy enq_task(task);
6078 workers->run_task(&enq_task);
6079 }
6080
6081 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6082
6083 ResourceMark rm;
6084 HandleMark hm;
6085
6086 ReferenceProcessor* rp = ref_processor();
6087 assert(rp->span().equals(_span), "Spans should be equal");
6088 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6089 // Process weak references.
6090 rp->setup_policy(clear_all_soft_refs);
6091 verify_work_stacks_empty();
6092
6093 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6094 &_markStack, &_revisitStack,
6095 false /* !preclean */);
6096 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6097 _span, &_markBitMap, &_markStack,
6098 &cmsKeepAliveClosure, false /* !preclean */);
6099 {
6100 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6101
6102 ReferenceProcessorStats stats;
6103 if (rp->processing_is_mt()) {
6104 // Set the degree of MT here. If the discovery is done MT, there
6105 // may have been a different number of threads doing the discovery
6106 // and a different number of discovered lists may have Ref objects.
6107 // That is OK as long as the Reference lists are balanced (see
6108 // balance_all_queues() and balance_queues()).
6109 GenCollectedHeap* gch = GenCollectedHeap::heap();
6110 int active_workers = ParallelGCThreads;
6111 FlexibleWorkGang* workers = gch->workers();
6112 if (workers != NULL) {
6113 active_workers = workers->active_workers();
6114 // The expectation is that active_workers will have already
6115 // been set to a reasonable value. If it has not been set,
6116 // investigate.
6117 assert(active_workers > 0, "Should have been set during scavenge");
6118 }
6119 rp->set_active_mt_degree(active_workers);
6120 CMSRefProcTaskExecutor task_executor(*this);
6121 stats = rp->process_discovered_references(&_is_alive_closure,
6122 &cmsKeepAliveClosure,
6123 &cmsDrainMarkingStackClosure,
6124 &task_executor,
6125 _gc_timer_cm);
6126 } else {
6127 stats = rp->process_discovered_references(&_is_alive_closure,
6128 &cmsKeepAliveClosure,
6129 &cmsDrainMarkingStackClosure,
6130 NULL,
6131 _gc_timer_cm);
6132 }
6133 _gc_tracer_cm->report_gc_reference_stats(stats);
6134
6135 verify_work_stacks_empty();
6136 }
6137
6138 if (should_unload_classes()) {
6139 {
6140 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6141
6142 // Follow SystemDictionary roots and unload classes
6143 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6144
6145 // Follow CodeCache roots and unload any methods marked for unloading
6146 CodeCache::do_unloading(&_is_alive_closure,
6147 &cmsKeepAliveClosure,
6148 purged_class);
6149
6150 cmsDrainMarkingStackClosure.do_void();
6151 verify_work_stacks_empty();
6152
6153 // Update subklass/sibling/implementor links in KlassKlass descendants
6154 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
6155 oop k;
6156 while ((k = _revisitStack.pop()) != NULL) {
6157 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
6158 &_is_alive_closure,
6159 &cmsKeepAliveClosure);
6160 }
6161 assert(!ClassUnloading ||
6162 (_markStack.isEmpty() && overflow_list_is_empty()),
6163 "Should not have found new reachable objects");
6164 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
6165 cmsDrainMarkingStackClosure.do_void();
6166 verify_work_stacks_empty();
6167 }
6168
6169 {
6170 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6171 // Clean up unreferenced symbols in symbol table.
6172 SymbolTable::unlink();
6173 }
6174 }
6175
6176 if (should_unload_classes() || !JavaObjectsInPerm) {
6177 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6178 // Now clean up stale oops in StringTable
6179 StringTable::unlink(&_is_alive_closure);
6180 }
6181
6182 verify_work_stacks_empty();
6183 // Restore any preserved marks as a result of mark stack or
6184 // work queue overflow
6185 restore_preserved_marks_if_any(); // done single-threaded for now
6186
6187 rp->set_enqueuing_is_done(true);
6188 if (rp->processing_is_mt()) {
6189 rp->balance_all_queues();
6190 CMSRefProcTaskExecutor task_executor(*this);
6191 rp->enqueue_discovered_references(&task_executor);
6192 } else {
6193 rp->enqueue_discovered_references(NULL);
6194 }
6195 rp->verify_no_references_recorded();
6196 assert(!rp->discovery_enabled(), "should have been disabled");
6197 }
6198
6199 #ifndef PRODUCT
6200 void CMSCollector::check_correct_thread_executing() {
6201 Thread* t = Thread::current();
6202 // Only the VM thread or the CMS thread should be here.
6203 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6204 "Unexpected thread type");
6205 // If this is the vm thread, the foreground process
6206 // should not be waiting. Note that _foregroundGCIsActive is
6207 // true while the foreground collector is waiting.
6208 if (_foregroundGCShouldWait) {
6209 // We cannot be the VM thread
6210 assert(t->is_ConcurrentGC_thread(),
6211 "Should be CMS thread");
6212 } else {
6213 // We can be the CMS thread only if we are in a stop-world
6214 // phase of CMS collection.
6215 if (t->is_ConcurrentGC_thread()) {
6216 assert(_collectorState == InitialMarking ||
6217 _collectorState == FinalMarking,
6218 "Should be a stop-world phase");
6219 // The CMS thread should be holding the CMS_token.
6220 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6221 "Potential interference with concurrently "
6222 "executing VM thread");
6223 }
6224 }
6225 }
6226 #endif
6227
6228 void CMSCollector::sweep(bool asynch) {
6229 assert(_collectorState == Sweeping, "just checking");
6230 check_correct_thread_executing();
6231 verify_work_stacks_empty();
6232 verify_overflow_empty();
6233 increment_sweep_count();
6234 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6235
6236 _inter_sweep_timer.stop();
6237 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6238 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6239
6240 // PermGen verification support: If perm gen sweeping is disabled in
6241 // this cycle, we preserve the perm gen object "deadness" information
6242 // in the perm_gen_verify_bit_map. In order to do that we traverse
6243 // all blocks in perm gen and mark all dead objects.
6244 if (verifying() && !should_unload_classes()) {
6245 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6246 "Should have already been allocated");
6247 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6248 markBitMap(), perm_gen_verify_bit_map());
6249 if (asynch) {
6250 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6251 bitMapLock());
6252 _permGen->cmsSpace()->blk_iterate(&mdo);
6253 } else {
6254 // In the case of synchronous sweep, we already have
6255 // the requisite locks/tokens.
6256 _permGen->cmsSpace()->blk_iterate(&mdo);
6257 }
6258 }
6259
6260 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6261 _intra_sweep_timer.reset();
6262 _intra_sweep_timer.start();
6263 if (asynch) {
6264 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6265 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6266 // First sweep the old gen then the perm gen
6267 {
6268 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6269 bitMapLock());
6270 sweepWork(_cmsGen, asynch);
6271 }
6272
6273 // Now repeat for perm gen
6274 if (should_unload_classes()) {
6275 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6276 bitMapLock());
6277 sweepWork(_permGen, asynch);
6278 }
6279
6280 // Update Universe::_heap_*_at_gc figures.
6281 // We need all the free list locks to make the abstract state
6282 // transition from Sweeping to Resetting. See detailed note
6283 // further below.
6284 {
6285 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6286 _permGen->freelistLock());
6287 // Update heap occupancy information which is used as
6288 // input to soft ref clearing policy at the next gc.
6289 Universe::update_heap_info_at_gc();
6290 _collectorState = Resizing;
6291 }
6292 } else {
6293 // already have needed locks
6294 sweepWork(_cmsGen, asynch);
6295
6296 if (should_unload_classes()) {
6297 sweepWork(_permGen, asynch);
6298 }
6299 // Update heap occupancy information which is used as
6300 // input to soft ref clearing policy at the next gc.
6301 Universe::update_heap_info_at_gc();
6302 _collectorState = Resizing;
6303 }
6304 verify_work_stacks_empty();
6305 verify_overflow_empty();
6306
6307 _intra_sweep_timer.stop();
6308 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6309
6310 _inter_sweep_timer.reset();
6311 _inter_sweep_timer.start();
6312
6313 // We need to use a monotonically non-deccreasing time in ms
6314 // or we will see time-warp warnings and os::javaTimeMillis()
6315 // does not guarantee monotonicity.
6316 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6317 update_time_of_last_gc(now);
6318
6319 // NOTE on abstract state transitions:
6320 // Mutators allocate-live and/or mark the mod-union table dirty
6321 // based on the state of the collection. The former is done in
6322 // the interval [Marking, Sweeping] and the latter in the interval
6323 // [Marking, Sweeping). Thus the transitions into the Marking state
6324 // and out of the Sweeping state must be synchronously visible
6325 // globally to the mutators.
6326 // The transition into the Marking state happens with the world
6327 // stopped so the mutators will globally see it. Sweeping is
6328 // done asynchronously by the background collector so the transition
6329 // from the Sweeping state to the Resizing state must be done
6330 // under the freelistLock (as is the check for whether to
6331 // allocate-live and whether to dirty the mod-union table).
6332 assert(_collectorState == Resizing, "Change of collector state to"
6333 " Resizing must be done under the freelistLocks (plural)");
6334
6335 // Now that sweeping has been completed, we clear
6336 // the incremental_collection_failed flag,
6337 // thus inviting a younger gen collection to promote into
6338 // this generation. If such a promotion may still fail,
6339 // the flag will be set again when a young collection is
6340 // attempted.
6341 GenCollectedHeap* gch = GenCollectedHeap::heap();
6342 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6343 gch->update_full_collections_completed(_collection_count_start);
6344 }
6345
6346 // FIX ME!!! Looks like this belongs in CFLSpace, with
6347 // CMSGen merely delegating to it.
6348 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6349 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6350 HeapWord* minAddr = _cmsSpace->bottom();
6351 HeapWord* largestAddr =
6352 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6353 if (largestAddr == NULL) {
6354 // The dictionary appears to be empty. In this case
6355 // try to coalesce at the end of the heap.
6356 largestAddr = _cmsSpace->end();
6357 }
6358 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6359 size_t nearLargestOffset =
6360 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6361 if (PrintFLSStatistics != 0) {
6362 gclog_or_tty->print_cr(
6363 "CMS: Large Block: " PTR_FORMAT ";"
6364 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6365 largestAddr,
6366 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6367 }
6368 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6369 }
6370
6371 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6372 return addr >= _cmsSpace->nearLargestChunk();
6373 }
6374
6375 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6376 return _cmsSpace->find_chunk_at_end();
6377 }
6378
6379 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6380 bool full) {
6381 // The next lower level has been collected. Gather any statistics
6382 // that are of interest at this point.
6383 if (!full && (current_level + 1) == level()) {
6384 // Gather statistics on the young generation collection.
6385 collector()->stats().record_gc0_end(used());
6386 }
6387 }
6388
6389 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6390 GenCollectedHeap* gch = GenCollectedHeap::heap();
6391 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6392 "Wrong type of heap");
6393 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6394 gch->gen_policy()->size_policy();
6395 assert(sp->is_gc_cms_adaptive_size_policy(),
6396 "Wrong type of size policy");
6397 return sp;
6398 }
6399
6400 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6401 if (PrintGCDetails && Verbose) {
6402 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6403 }
6404 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6405 _debug_collection_type =
6406 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6407 if (PrintGCDetails && Verbose) {
6408 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6409 }
6410 }
6411
6412 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6413 bool asynch) {
6414 // We iterate over the space(s) underlying this generation,
6415 // checking the mark bit map to see if the bits corresponding
6416 // to specific blocks are marked or not. Blocks that are
6417 // marked are live and are not swept up. All remaining blocks
6418 // are swept up, with coalescing on-the-fly as we sweep up
6419 // contiguous free and/or garbage blocks:
6420 // We need to ensure that the sweeper synchronizes with allocators
6421 // and stop-the-world collectors. In particular, the following
6422 // locks are used:
6423 // . CMS token: if this is held, a stop the world collection cannot occur
6424 // . freelistLock: if this is held no allocation can occur from this
6425 // generation by another thread
6426 // . bitMapLock: if this is held, no other thread can access or update
6427 //
6428
6429 // Note that we need to hold the freelistLock if we use
6430 // block iterate below; else the iterator might go awry if
6431 // a mutator (or promotion) causes block contents to change
6432 // (for instance if the allocator divvies up a block).
6433 // If we hold the free list lock, for all practical purposes
6434 // young generation GC's can't occur (they'll usually need to
6435 // promote), so we might as well prevent all young generation
6436 // GC's while we do a sweeping step. For the same reason, we might
6437 // as well take the bit map lock for the entire duration
6438
6439 // check that we hold the requisite locks
6440 assert(have_cms_token(), "Should hold cms token");
6441 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6442 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6443 "Should possess CMS token to sweep");
6444 assert_lock_strong(gen->freelistLock());
6445 assert_lock_strong(bitMapLock());
6446
6447 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6448 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6449 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6450 _inter_sweep_estimate.padded_average(),
6451 _intra_sweep_estimate.padded_average());
6452 gen->setNearLargestChunk();
6453
6454 {
6455 SweepClosure sweepClosure(this, gen, &_markBitMap,
6456 CMSYield && asynch);
6457 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6458 // We need to free-up/coalesce garbage/blocks from a
6459 // co-terminal free run. This is done in the SweepClosure
6460 // destructor; so, do not remove this scope, else the
6461 // end-of-sweep-census below will be off by a little bit.
6462 }
6463 gen->cmsSpace()->sweep_completed();
6464 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6465 if (should_unload_classes()) { // unloaded classes this cycle,
6466 _concurrent_cycles_since_last_unload = 0; // ... reset count
6467 } else { // did not unload classes,
6468 _concurrent_cycles_since_last_unload++; // ... increment count
6469 }
6470 }
6471
6472 // Reset CMS data structures (for now just the marking bit map)
6473 // preparatory for the next cycle.
6474 void CMSCollector::reset(bool asynch) {
6475 GenCollectedHeap* gch = GenCollectedHeap::heap();
6476 CMSAdaptiveSizePolicy* sp = size_policy();
6477 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6478 if (asynch) {
6479 CMSTokenSyncWithLocks ts(true, bitMapLock());
6480
6481 // If the state is not "Resetting", the foreground thread
6482 // has done a collection and the resetting.
6483 if (_collectorState != Resetting) {
6484 assert(_collectorState == Idling, "The state should only change"
6485 " because the foreground collector has finished the collection");
6486 return;
6487 }
6488
6489 // Clear the mark bitmap (no grey objects to start with)
6490 // for the next cycle.
6491 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6492 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6493
6494 HeapWord* curAddr = _markBitMap.startWord();
6495 while (curAddr < _markBitMap.endWord()) {
6496 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6497 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6498 _markBitMap.clear_large_range(chunk);
6499 if (ConcurrentMarkSweepThread::should_yield() &&
6500 !foregroundGCIsActive() &&
6501 CMSYield) {
6502 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6503 "CMS thread should hold CMS token");
6504 assert_lock_strong(bitMapLock());
6505 bitMapLock()->unlock();
6506 ConcurrentMarkSweepThread::desynchronize(true);
6507 ConcurrentMarkSweepThread::acknowledge_yield_request();
6508 stopTimer();
6509 if (PrintCMSStatistics != 0) {
6510 incrementYields();
6511 }
6512 icms_wait();
6513
6514 // See the comment in coordinator_yield()
6515 for (unsigned i = 0; i < CMSYieldSleepCount &&
6516 ConcurrentMarkSweepThread::should_yield() &&
6517 !CMSCollector::foregroundGCIsActive(); ++i) {
6518 os::sleep(Thread::current(), 1, false);
6519 ConcurrentMarkSweepThread::acknowledge_yield_request();
6520 }
6521
6522 ConcurrentMarkSweepThread::synchronize(true);
6523 bitMapLock()->lock_without_safepoint_check();
6524 startTimer();
6525 }
6526 curAddr = chunk.end();
6527 }
6528 // A successful mostly concurrent collection has been done.
6529 // Because only the full (i.e., concurrent mode failure) collections
6530 // are being measured for gc overhead limits, clean the "near" flag
6531 // and count.
6532 sp->reset_gc_overhead_limit_count();
6533 _collectorState = Idling;
6534 } else {
6535 // already have the lock
6536 assert(_collectorState == Resetting, "just checking");
6537 assert_lock_strong(bitMapLock());
6538 _markBitMap.clear_all();
6539 _collectorState = Idling;
6540 }
6541
6542 // Stop incremental mode after a cycle completes, so that any future cycles
6543 // are triggered by allocation.
6544 stop_icms();
6545
6546 NOT_PRODUCT(
6547 if (RotateCMSCollectionTypes) {
6548 _cmsGen->rotate_debug_collection_type();
6549 }
6550 )
6551
6552 register_gc_end();
6553 }
6554
6555 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6556 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6557 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6558 TraceCollectorStats tcs(counters());
6559
6560 switch (op) {
6561 case CMS_op_checkpointRootsInitial: {
6562 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6563 checkpointRootsInitial(true); // asynch
6564 if (PrintGC) {
6565 _cmsGen->printOccupancy("initial-mark");
6566 }
6567 break;
6568 }
6569 case CMS_op_checkpointRootsFinal: {
6570 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6571 checkpointRootsFinal(true, // asynch
6572 false, // !clear_all_soft_refs
6573 false); // !init_mark_was_synchronous
6574 if (PrintGC) {
6575 _cmsGen->printOccupancy("remark");
6576 }
6577 break;
6578 }
6579 default:
6580 fatal("No such CMS_op");
6581 }
6582 }
6583
6584 #ifndef PRODUCT
6585 size_t const CMSCollector::skip_header_HeapWords() {
6586 return FreeChunk::header_size();
6587 }
6588
6589 // Try and collect here conditions that should hold when
6590 // CMS thread is exiting. The idea is that the foreground GC
6591 // thread should not be blocked if it wants to terminate
6592 // the CMS thread and yet continue to run the VM for a while
6593 // after that.
6594 void CMSCollector::verify_ok_to_terminate() const {
6595 assert(Thread::current()->is_ConcurrentGC_thread(),
6596 "should be called by CMS thread");
6597 assert(!_foregroundGCShouldWait, "should be false");
6598 // We could check here that all the various low-level locks
6599 // are not held by the CMS thread, but that is overkill; see
6600 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6601 // is checked.
6602 }
6603 #endif
6604
6605 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6606 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6607 "missing Printezis mark?");
6608 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6609 size_t size = pointer_delta(nextOneAddr + 1, addr);
6610 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6611 "alignment problem");
6612 assert(size >= 3, "Necessary for Printezis marks to work");
6613 return size;
6614 }
6615
6616 // A variant of the above (block_size_using_printezis_bits()) except
6617 // that we return 0 if the P-bits are not yet set.
6618 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6619 if (_markBitMap.isMarked(addr + 1)) {
6620 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6621 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6622 size_t size = pointer_delta(nextOneAddr + 1, addr);
6623 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6624 "alignment problem");
6625 assert(size >= 3, "Necessary for Printezis marks to work");
6626 return size;
6627 }
6628 return 0;
6629 }
6630
6631 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6632 size_t sz = 0;
6633 oop p = (oop)addr;
6634 if (p->klass_or_null() != NULL && p->is_parsable()) {
6635 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6636 } else {
6637 sz = block_size_using_printezis_bits(addr);
6638 }
6639 assert(sz > 0, "size must be nonzero");
6640 HeapWord* next_block = addr + sz;
6641 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6642 CardTableModRefBS::card_size);
6643 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6644 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6645 "must be different cards");
6646 return next_card;
6647 }
6648
6649
6650 // CMS Bit Map Wrapper /////////////////////////////////////////
6651
6652 // Construct a CMS bit map infrastructure, but don't create the
6653 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6654 // further below.
6655 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6656 _bm(),
6657 _shifter(shifter),
6658 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6659 {
6660 _bmStartWord = 0;
6661 _bmWordSize = 0;
6662 }
6663
6664 bool CMSBitMap::allocate(MemRegion mr) {
6665 _bmStartWord = mr.start();
6666 _bmWordSize = mr.word_size();
6667 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6668 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6669 if (!brs.is_reserved()) {
6670 warning("CMS bit map allocation failure");
6671 return false;
6672 }
6673 // For now we'll just commit all of the bit map up fromt.
6674 // Later on we'll try to be more parsimonious with swap.
6675 if (!_virtual_space.initialize(brs, brs.size())) {
6676 warning("CMS bit map backing store failure");
6677 return false;
6678 }
6679 assert(_virtual_space.committed_size() == brs.size(),
6680 "didn't reserve backing store for all of CMS bit map?");
6681 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6682 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6683 _bmWordSize, "inconsistency in bit map sizing");
6684 _bm.set_size(_bmWordSize >> _shifter);
6685
6686 // bm.clear(); // can we rely on getting zero'd memory? verify below
6687 assert(isAllClear(),
6688 "Expected zero'd memory from ReservedSpace constructor");
6689 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6690 "consistency check");
6691 return true;
6692 }
6693
6694 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6695 HeapWord *next_addr, *end_addr, *last_addr;
6696 assert_locked();
6697 assert(covers(mr), "out-of-range error");
6698 // XXX assert that start and end are appropriately aligned
6699 for (next_addr = mr.start(), end_addr = mr.end();
6700 next_addr < end_addr; next_addr = last_addr) {
6701 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6702 last_addr = dirty_region.end();
6703 if (!dirty_region.is_empty()) {
6704 cl->do_MemRegion(dirty_region);
6705 } else {
6706 assert(last_addr == end_addr, "program logic");
6707 return;
6708 }
6709 }
6710 }
6711
6712 #ifndef PRODUCT
6713 void CMSBitMap::assert_locked() const {
6714 CMSLockVerifier::assert_locked(lock());
6715 }
6716
6717 bool CMSBitMap::covers(MemRegion mr) const {
6718 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6719 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6720 "size inconsistency");
6721 return (mr.start() >= _bmStartWord) &&
6722 (mr.end() <= endWord());
6723 }
6724
6725 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6726 return (start >= _bmStartWord && (start + size) <= endWord());
6727 }
6728
6729 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6730 // verify that there are no 1 bits in the interval [left, right)
6731 FalseBitMapClosure falseBitMapClosure;
6732 iterate(&falseBitMapClosure, left, right);
6733 }
6734
6735 void CMSBitMap::region_invariant(MemRegion mr)
6736 {
6737 assert_locked();
6738 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6739 assert(!mr.is_empty(), "unexpected empty region");
6740 assert(covers(mr), "mr should be covered by bit map");
6741 // convert address range into offset range
6742 size_t start_ofs = heapWordToOffset(mr.start());
6743 // Make sure that end() is appropriately aligned
6744 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6745 (1 << (_shifter+LogHeapWordSize))),
6746 "Misaligned mr.end()");
6747 size_t end_ofs = heapWordToOffset(mr.end());
6748 assert(end_ofs > start_ofs, "Should mark at least one bit");
6749 }
6750
6751 #endif
6752
6753 bool CMSMarkStack::allocate(size_t size) {
6754 // allocate a stack of the requisite depth
6755 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6756 size * sizeof(oop)));
6757 if (!rs.is_reserved()) {
6758 warning("CMSMarkStack allocation failure");
6759 return false;
6760 }
6761 if (!_virtual_space.initialize(rs, rs.size())) {
6762 warning("CMSMarkStack backing store failure");
6763 return false;
6764 }
6765 assert(_virtual_space.committed_size() == rs.size(),
6766 "didn't reserve backing store for all of CMS stack?");
6767 _base = (oop*)(_virtual_space.low());
6768 _index = 0;
6769 _capacity = size;
6770 NOT_PRODUCT(_max_depth = 0);
6771 return true;
6772 }
6773
6774 // XXX FIX ME !!! In the MT case we come in here holding a
6775 // leaf lock. For printing we need to take a further lock
6776 // which has lower rank. We need to recallibrate the two
6777 // lock-ranks involved in order to be able to rpint the
6778 // messages below. (Or defer the printing to the caller.
6779 // For now we take the expedient path of just disabling the
6780 // messages for the problematic case.)
6781 void CMSMarkStack::expand() {
6782 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6783 if (_capacity == MarkStackSizeMax) {
6784 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6785 // We print a warning message only once per CMS cycle.
6786 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6787 }
6788 return;
6789 }
6790 // Double capacity if possible
6791 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6792 // Do not give up existing stack until we have managed to
6793 // get the double capacity that we desired.
6794 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6795 new_capacity * sizeof(oop)));
6796 if (rs.is_reserved()) {
6797 // Release the backing store associated with old stack
6798 _virtual_space.release();
6799 // Reinitialize virtual space for new stack
6800 if (!_virtual_space.initialize(rs, rs.size())) {
6801 fatal("Not enough swap for expanded marking stack");
6802 }
6803 _base = (oop*)(_virtual_space.low());
6804 _index = 0;
6805 _capacity = new_capacity;
6806 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6807 // Failed to double capacity, continue;
6808 // we print a detail message only once per CMS cycle.
6809 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6810 SIZE_FORMAT"K",
6811 _capacity / K, new_capacity / K);
6812 }
6813 }
6814
6815
6816 // Closures
6817 // XXX: there seems to be a lot of code duplication here;
6818 // should refactor and consolidate common code.
6819
6820 // This closure is used to mark refs into the CMS generation in
6821 // the CMS bit map. Called at the first checkpoint. This closure
6822 // assumes that we do not need to re-mark dirty cards; if the CMS
6823 // generation on which this is used is not an oldest (modulo perm gen)
6824 // generation then this will lose younger_gen cards!
6825
6826 MarkRefsIntoClosure::MarkRefsIntoClosure(
6827 MemRegion span, CMSBitMap* bitMap):
6828 _span(span),
6829 _bitMap(bitMap)
6830 {
6831 assert(_ref_processor == NULL, "deliberately left NULL");
6832 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6833 }
6834
6835 void MarkRefsIntoClosure::do_oop(oop obj) {
6836 // if p points into _span, then mark corresponding bit in _markBitMap
6837 assert(obj->is_oop(), "expected an oop");
6838 HeapWord* addr = (HeapWord*)obj;
6839 if (_span.contains(addr)) {
6840 // this should be made more efficient
6841 _bitMap->mark(addr);
6842 }
6843 }
6844
6845 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6846 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6847
6848 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6849 MemRegion span, CMSBitMap* bitMap):
6850 _span(span),
6851 _bitMap(bitMap)
6852 {
6853 assert(_ref_processor == NULL, "deliberately left NULL");
6854 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6855 }
6856
6857 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6858 // if p points into _span, then mark corresponding bit in _markBitMap
6859 assert(obj->is_oop(), "expected an oop");
6860 HeapWord* addr = (HeapWord*)obj;
6861 if (_span.contains(addr)) {
6862 // this should be made more efficient
6863 _bitMap->par_mark(addr);
6864 }
6865 }
6866
6867 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6868 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6869
6870 // A variant of the above, used for CMS marking verification.
6871 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6872 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6873 _span(span),
6874 _verification_bm(verification_bm),
6875 _cms_bm(cms_bm)
6876 {
6877 assert(_ref_processor == NULL, "deliberately left NULL");
6878 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6879 }
6880
6881 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6882 // if p points into _span, then mark corresponding bit in _markBitMap
6883 assert(obj->is_oop(), "expected an oop");
6884 HeapWord* addr = (HeapWord*)obj;
6885 if (_span.contains(addr)) {
6886 _verification_bm->mark(addr);
6887 if (!_cms_bm->isMarked(addr)) {
6888 oop(addr)->print();
6889 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6890 fatal("... aborting");
6891 }
6892 }
6893 }
6894
6895 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6896 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6897
6898 //////////////////////////////////////////////////
6899 // MarkRefsIntoAndScanClosure
6900 //////////////////////////////////////////////////
6901
6902 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6903 ReferenceProcessor* rp,
6904 CMSBitMap* bit_map,
6905 CMSBitMap* mod_union_table,
6906 CMSMarkStack* mark_stack,
6907 CMSMarkStack* revisit_stack,
6908 CMSCollector* collector,
6909 bool should_yield,
6910 bool concurrent_precleaning):
6911 _collector(collector),
6912 _span(span),
6913 _bit_map(bit_map),
6914 _mark_stack(mark_stack),
6915 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6916 mark_stack, revisit_stack, concurrent_precleaning),
6917 _yield(should_yield),
6918 _concurrent_precleaning(concurrent_precleaning),
6919 _freelistLock(NULL)
6920 {
6921 _ref_processor = rp;
6922 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6923 }
6924
6925 // This closure is used to mark refs into the CMS generation at the
6926 // second (final) checkpoint, and to scan and transitively follow
6927 // the unmarked oops. It is also used during the concurrent precleaning
6928 // phase while scanning objects on dirty cards in the CMS generation.
6929 // The marks are made in the marking bit map and the marking stack is
6930 // used for keeping the (newly) grey objects during the scan.
6931 // The parallel version (Par_...) appears further below.
6932 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6933 if (obj != NULL) {
6934 assert(obj->is_oop(), "expected an oop");
6935 HeapWord* addr = (HeapWord*)obj;
6936 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6937 assert(_collector->overflow_list_is_empty(),
6938 "overflow list should be empty");
6939 if (_span.contains(addr) &&
6940 !_bit_map->isMarked(addr)) {
6941 // mark bit map (object is now grey)
6942 _bit_map->mark(addr);
6943 // push on marking stack (stack should be empty), and drain the
6944 // stack by applying this closure to the oops in the oops popped
6945 // from the stack (i.e. blacken the grey objects)
6946 bool res = _mark_stack->push(obj);
6947 assert(res, "Should have space to push on empty stack");
6948 do {
6949 oop new_oop = _mark_stack->pop();
6950 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6951 assert(new_oop->is_parsable(), "Found unparsable oop");
6952 assert(_bit_map->isMarked((HeapWord*)new_oop),
6953 "only grey objects on this stack");
6954 // iterate over the oops in this oop, marking and pushing
6955 // the ones in CMS heap (i.e. in _span).
6956 new_oop->oop_iterate(&_pushAndMarkClosure);
6957 // check if it's time to yield
6958 do_yield_check();
6959 } while (!_mark_stack->isEmpty() ||
6960 (!_concurrent_precleaning && take_from_overflow_list()));
6961 // if marking stack is empty, and we are not doing this
6962 // during precleaning, then check the overflow list
6963 }
6964 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6965 assert(_collector->overflow_list_is_empty(),
6966 "overflow list was drained above");
6967 // We could restore evacuated mark words, if any, used for
6968 // overflow list links here because the overflow list is
6969 // provably empty here. That would reduce the maximum
6970 // size requirements for preserved_{oop,mark}_stack.
6971 // But we'll just postpone it until we are all done
6972 // so we can just stream through.
6973 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6974 _collector->restore_preserved_marks_if_any();
6975 assert(_collector->no_preserved_marks(), "No preserved marks");
6976 }
6977 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6978 "All preserved marks should have been restored above");
6979 }
6980 }
6981
6982 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6983 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6984
6985 void MarkRefsIntoAndScanClosure::do_yield_work() {
6986 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6987 "CMS thread should hold CMS token");
6988 assert_lock_strong(_freelistLock);
6989 assert_lock_strong(_bit_map->lock());
6990 // relinquish the free_list_lock and bitMaplock()
6991 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6992 _bit_map->lock()->unlock();
6993 _freelistLock->unlock();
6994 ConcurrentMarkSweepThread::desynchronize(true);
6995 ConcurrentMarkSweepThread::acknowledge_yield_request();
6996 _collector->stopTimer();
6997 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6998 if (PrintCMSStatistics != 0) {
6999 _collector->incrementYields();
7000 }
7001 _collector->icms_wait();
7002
7003 // See the comment in coordinator_yield()
7004 for (unsigned i = 0;
7005 i < CMSYieldSleepCount &&
7006 ConcurrentMarkSweepThread::should_yield() &&
7007 !CMSCollector::foregroundGCIsActive();
7008 ++i) {
7009 os::sleep(Thread::current(), 1, false);
7010 ConcurrentMarkSweepThread::acknowledge_yield_request();
7011 }
7012
7013 ConcurrentMarkSweepThread::synchronize(true);
7014 _freelistLock->lock_without_safepoint_check();
7015 _bit_map->lock()->lock_without_safepoint_check();
7016 _collector->startTimer();
7017 }
7018
7019 ///////////////////////////////////////////////////////////
7020 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7021 // MarkRefsIntoAndScanClosure
7022 ///////////////////////////////////////////////////////////
7023 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7024 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7025 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
7026 _span(span),
7027 _bit_map(bit_map),
7028 _work_queue(work_queue),
7029 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7030 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7031 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
7032 revisit_stack)
7033 {
7034 _ref_processor = rp;
7035 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7036 }
7037
7038 // This closure is used to mark refs into the CMS generation at the
7039 // second (final) checkpoint, and to scan and transitively follow
7040 // the unmarked oops. The marks are made in the marking bit map and
7041 // the work_queue is used for keeping the (newly) grey objects during
7042 // the scan phase whence they are also available for stealing by parallel
7043 // threads. Since the marking bit map is shared, updates are
7044 // synchronized (via CAS).
7045 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7046 if (obj != NULL) {
7047 // Ignore mark word because this could be an already marked oop
7048 // that may be chained at the end of the overflow list.
7049 assert(obj->is_oop(true), "expected an oop");
7050 HeapWord* addr = (HeapWord*)obj;
7051 if (_span.contains(addr) &&
7052 !_bit_map->isMarked(addr)) {
7053 // mark bit map (object will become grey):
7054 // It is possible for several threads to be
7055 // trying to "claim" this object concurrently;
7056 // the unique thread that succeeds in marking the
7057 // object first will do the subsequent push on
7058 // to the work queue (or overflow list).
7059 if (_bit_map->par_mark(addr)) {
7060 // push on work_queue (which may not be empty), and trim the
7061 // queue to an appropriate length by applying this closure to
7062 // the oops in the oops popped from the stack (i.e. blacken the
7063 // grey objects)
7064 bool res = _work_queue->push(obj);
7065 assert(res, "Low water mark should be less than capacity?");
7066 trim_queue(_low_water_mark);
7067 } // Else, another thread claimed the object
7068 }
7069 }
7070 }
7071
7072 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7073 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7074
7075 // This closure is used to rescan the marked objects on the dirty cards
7076 // in the mod union table and the card table proper.
7077 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7078 oop p, MemRegion mr) {
7079
7080 size_t size = 0;
7081 HeapWord* addr = (HeapWord*)p;
7082 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7083 assert(_span.contains(addr), "we are scanning the CMS generation");
7084 // check if it's time to yield
7085 if (do_yield_check()) {
7086 // We yielded for some foreground stop-world work,
7087 // and we have been asked to abort this ongoing preclean cycle.
7088 return 0;
7089 }
7090 if (_bitMap->isMarked(addr)) {
7091 // it's marked; is it potentially uninitialized?
7092 if (p->klass_or_null() != NULL) {
7093 // If is_conc_safe is false, the object may be undergoing
7094 // change by the VM outside a safepoint. Don't try to
7095 // scan it, but rather leave it for the remark phase.
7096 if (CMSPermGenPrecleaningEnabled &&
7097 (!p->is_conc_safe() || !p->is_parsable())) {
7098 // Signal precleaning to redirty the card since
7099 // the klass pointer is already installed.
7100 assert(size == 0, "Initial value");
7101 } else {
7102 assert(p->is_parsable(), "must be parsable.");
7103 // an initialized object; ignore mark word in verification below
7104 // since we are running concurrent with mutators
7105 assert(p->is_oop(true), "should be an oop");
7106 if (p->is_objArray()) {
7107 // objArrays are precisely marked; restrict scanning
7108 // to dirty cards only.
7109 size = CompactibleFreeListSpace::adjustObjectSize(
7110 p->oop_iterate(_scanningClosure, mr));
7111 } else {
7112 // A non-array may have been imprecisely marked; we need
7113 // to scan object in its entirety.
7114 size = CompactibleFreeListSpace::adjustObjectSize(
7115 p->oop_iterate(_scanningClosure));
7116 }
7117 #ifdef DEBUG
7118 size_t direct_size =
7119 CompactibleFreeListSpace::adjustObjectSize(p->size());
7120 assert(size == direct_size, "Inconsistency in size");
7121 assert(size >= 3, "Necessary for Printezis marks to work");
7122 if (!_bitMap->isMarked(addr+1)) {
7123 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7124 } else {
7125 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7126 assert(_bitMap->isMarked(addr+size-1),
7127 "inconsistent Printezis mark");
7128 }
7129 #endif // DEBUG
7130 }
7131 } else {
7132 // an unitialized object
7133 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7134 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7135 size = pointer_delta(nextOneAddr + 1, addr);
7136 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7137 "alignment problem");
7138 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7139 // will dirty the card when the klass pointer is installed in the
7140 // object (signalling the completion of initialization).
7141 }
7142 } else {
7143 // Either a not yet marked object or an uninitialized object
7144 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7145 // An uninitialized object, skip to the next card, since
7146 // we may not be able to read its P-bits yet.
7147 assert(size == 0, "Initial value");
7148 } else {
7149 // An object not (yet) reached by marking: we merely need to
7150 // compute its size so as to go look at the next block.
7151 assert(p->is_oop(true), "should be an oop");
7152 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7153 }
7154 }
7155 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7156 return size;
7157 }
7158
7159 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7160 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7161 "CMS thread should hold CMS token");
7162 assert_lock_strong(_freelistLock);
7163 assert_lock_strong(_bitMap->lock());
7164 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7165 // relinquish the free_list_lock and bitMaplock()
7166 _bitMap->lock()->unlock();
7167 _freelistLock->unlock();
7168 ConcurrentMarkSweepThread::desynchronize(true);
7169 ConcurrentMarkSweepThread::acknowledge_yield_request();
7170 _collector->stopTimer();
7171 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7172 if (PrintCMSStatistics != 0) {
7173 _collector->incrementYields();
7174 }
7175 _collector->icms_wait();
7176
7177 // See the comment in coordinator_yield()
7178 for (unsigned i = 0; i < CMSYieldSleepCount &&
7179 ConcurrentMarkSweepThread::should_yield() &&
7180 !CMSCollector::foregroundGCIsActive(); ++i) {
7181 os::sleep(Thread::current(), 1, false);
7182 ConcurrentMarkSweepThread::acknowledge_yield_request();
7183 }
7184
7185 ConcurrentMarkSweepThread::synchronize(true);
7186 _freelistLock->lock_without_safepoint_check();
7187 _bitMap->lock()->lock_without_safepoint_check();
7188 _collector->startTimer();
7189 }
7190
7191
7192 //////////////////////////////////////////////////////////////////
7193 // SurvivorSpacePrecleanClosure
7194 //////////////////////////////////////////////////////////////////
7195 // This (single-threaded) closure is used to preclean the oops in
7196 // the survivor spaces.
7197 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7198
7199 HeapWord* addr = (HeapWord*)p;
7200 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7201 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7202 assert(p->klass_or_null() != NULL, "object should be initializd");
7203 assert(p->is_parsable(), "must be parsable.");
7204 // an initialized object; ignore mark word in verification below
7205 // since we are running concurrent with mutators
7206 assert(p->is_oop(true), "should be an oop");
7207 // Note that we do not yield while we iterate over
7208 // the interior oops of p, pushing the relevant ones
7209 // on our marking stack.
7210 size_t size = p->oop_iterate(_scanning_closure);
7211 do_yield_check();
7212 // Observe that below, we do not abandon the preclean
7213 // phase as soon as we should; rather we empty the
7214 // marking stack before returning. This is to satisfy
7215 // some existing assertions. In general, it may be a
7216 // good idea to abort immediately and complete the marking
7217 // from the grey objects at a later time.
7218 while (!_mark_stack->isEmpty()) {
7219 oop new_oop = _mark_stack->pop();
7220 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7221 assert(new_oop->is_parsable(), "Found unparsable oop");
7222 assert(_bit_map->isMarked((HeapWord*)new_oop),
7223 "only grey objects on this stack");
7224 // iterate over the oops in this oop, marking and pushing
7225 // the ones in CMS heap (i.e. in _span).
7226 new_oop->oop_iterate(_scanning_closure);
7227 // check if it's time to yield
7228 do_yield_check();
7229 }
7230 unsigned int after_count =
7231 GenCollectedHeap::heap()->total_collections();
7232 bool abort = (_before_count != after_count) ||
7233 _collector->should_abort_preclean();
7234 return abort ? 0 : size;
7235 }
7236
7237 void SurvivorSpacePrecleanClosure::do_yield_work() {
7238 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7239 "CMS thread should hold CMS token");
7240 assert_lock_strong(_bit_map->lock());
7241 DEBUG_ONLY(RememberKlassesChecker smx(false);)
7242 // Relinquish the bit map lock
7243 _bit_map->lock()->unlock();
7244 ConcurrentMarkSweepThread::desynchronize(true);
7245 ConcurrentMarkSweepThread::acknowledge_yield_request();
7246 _collector->stopTimer();
7247 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7248 if (PrintCMSStatistics != 0) {
7249 _collector->incrementYields();
7250 }
7251 _collector->icms_wait();
7252
7253 // See the comment in coordinator_yield()
7254 for (unsigned i = 0; i < CMSYieldSleepCount &&
7255 ConcurrentMarkSweepThread::should_yield() &&
7256 !CMSCollector::foregroundGCIsActive(); ++i) {
7257 os::sleep(Thread::current(), 1, false);
7258 ConcurrentMarkSweepThread::acknowledge_yield_request();
7259 }
7260
7261 ConcurrentMarkSweepThread::synchronize(true);
7262 _bit_map->lock()->lock_without_safepoint_check();
7263 _collector->startTimer();
7264 }
7265
7266 // This closure is used to rescan the marked objects on the dirty cards
7267 // in the mod union table and the card table proper. In the parallel
7268 // case, although the bitMap is shared, we do a single read so the
7269 // isMarked() query is "safe".
7270 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7271 // Ignore mark word because we are running concurrent with mutators
7272 assert(p->is_oop_or_null(true), "expected an oop or null");
7273 HeapWord* addr = (HeapWord*)p;
7274 assert(_span.contains(addr), "we are scanning the CMS generation");
7275 bool is_obj_array = false;
7276 #ifdef DEBUG
7277 if (!_parallel) {
7278 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7279 assert(_collector->overflow_list_is_empty(),
7280 "overflow list should be empty");
7281
7282 }
7283 #endif // DEBUG
7284 if (_bit_map->isMarked(addr)) {
7285 // Obj arrays are precisely marked, non-arrays are not;
7286 // so we scan objArrays precisely and non-arrays in their
7287 // entirety.
7288 if (p->is_objArray()) {
7289 is_obj_array = true;
7290 if (_parallel) {
7291 p->oop_iterate(_par_scan_closure, mr);
7292 } else {
7293 p->oop_iterate(_scan_closure, mr);
7294 }
7295 } else {
7296 if (_parallel) {
7297 p->oop_iterate(_par_scan_closure);
7298 } else {
7299 p->oop_iterate(_scan_closure);
7300 }
7301 }
7302 }
7303 #ifdef DEBUG
7304 if (!_parallel) {
7305 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7306 assert(_collector->overflow_list_is_empty(),
7307 "overflow list should be empty");
7308
7309 }
7310 #endif // DEBUG
7311 return is_obj_array;
7312 }
7313
7314 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7315 MemRegion span,
7316 CMSBitMap* bitMap, CMSMarkStack* markStack,
7317 CMSMarkStack* revisitStack,
7318 bool should_yield, bool verifying):
7319 _collector(collector),
7320 _span(span),
7321 _bitMap(bitMap),
7322 _mut(&collector->_modUnionTable),
7323 _markStack(markStack),
7324 _revisitStack(revisitStack),
7325 _yield(should_yield),
7326 _skipBits(0)
7327 {
7328 assert(_markStack->isEmpty(), "stack should be empty");
7329 _finger = _bitMap->startWord();
7330 _threshold = _finger;
7331 assert(_collector->_restart_addr == NULL, "Sanity check");
7332 assert(_span.contains(_finger), "Out of bounds _finger?");
7333 DEBUG_ONLY(_verifying = verifying;)
7334 }
7335
7336 void MarkFromRootsClosure::reset(HeapWord* addr) {
7337 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7338 assert(_span.contains(addr), "Out of bounds _finger?");
7339 _finger = addr;
7340 _threshold = (HeapWord*)round_to(
7341 (intptr_t)_finger, CardTableModRefBS::card_size);
7342 }
7343
7344 // Should revisit to see if this should be restructured for
7345 // greater efficiency.
7346 bool MarkFromRootsClosure::do_bit(size_t offset) {
7347 if (_skipBits > 0) {
7348 _skipBits--;
7349 return true;
7350 }
7351 // convert offset into a HeapWord*
7352 HeapWord* addr = _bitMap->startWord() + offset;
7353 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7354 "address out of range");
7355 assert(_bitMap->isMarked(addr), "tautology");
7356 if (_bitMap->isMarked(addr+1)) {
7357 // this is an allocated but not yet initialized object
7358 assert(_skipBits == 0, "tautology");
7359 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7360 oop p = oop(addr);
7361 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7362 DEBUG_ONLY(if (!_verifying) {)
7363 // We re-dirty the cards on which this object lies and increase
7364 // the _threshold so that we'll come back to scan this object
7365 // during the preclean or remark phase. (CMSCleanOnEnter)
7366 if (CMSCleanOnEnter) {
7367 size_t sz = _collector->block_size_using_printezis_bits(addr);
7368 HeapWord* end_card_addr = (HeapWord*)round_to(
7369 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7370 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7371 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7372 // Bump _threshold to end_card_addr; note that
7373 // _threshold cannot possibly exceed end_card_addr, anyhow.
7374 // This prevents future clearing of the card as the scan proceeds
7375 // to the right.
7376 assert(_threshold <= end_card_addr,
7377 "Because we are just scanning into this object");
7378 if (_threshold < end_card_addr) {
7379 _threshold = end_card_addr;
7380 }
7381 if (p->klass_or_null() != NULL) {
7382 // Redirty the range of cards...
7383 _mut->mark_range(redirty_range);
7384 } // ...else the setting of klass will dirty the card anyway.
7385 }
7386 DEBUG_ONLY(})
7387 return true;
7388 }
7389 }
7390 scanOopsInOop(addr);
7391 return true;
7392 }
7393
7394 // We take a break if we've been at this for a while,
7395 // so as to avoid monopolizing the locks involved.
7396 void MarkFromRootsClosure::do_yield_work() {
7397 // First give up the locks, then yield, then re-lock
7398 // We should probably use a constructor/destructor idiom to
7399 // do this unlock/lock or modify the MutexUnlocker class to
7400 // serve our purpose. XXX
7401 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7402 "CMS thread should hold CMS token");
7403 assert_lock_strong(_bitMap->lock());
7404 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7405 _bitMap->lock()->unlock();
7406 ConcurrentMarkSweepThread::desynchronize(true);
7407 ConcurrentMarkSweepThread::acknowledge_yield_request();
7408 _collector->stopTimer();
7409 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7410 if (PrintCMSStatistics != 0) {
7411 _collector->incrementYields();
7412 }
7413 _collector->icms_wait();
7414
7415 // See the comment in coordinator_yield()
7416 for (unsigned i = 0; i < CMSYieldSleepCount &&
7417 ConcurrentMarkSweepThread::should_yield() &&
7418 !CMSCollector::foregroundGCIsActive(); ++i) {
7419 os::sleep(Thread::current(), 1, false);
7420 ConcurrentMarkSweepThread::acknowledge_yield_request();
7421 }
7422
7423 ConcurrentMarkSweepThread::synchronize(true);
7424 _bitMap->lock()->lock_without_safepoint_check();
7425 _collector->startTimer();
7426 }
7427
7428 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7429 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7430 assert(_markStack->isEmpty(),
7431 "should drain stack to limit stack usage");
7432 // convert ptr to an oop preparatory to scanning
7433 oop obj = oop(ptr);
7434 // Ignore mark word in verification below, since we
7435 // may be running concurrent with mutators.
7436 assert(obj->is_oop(true), "should be an oop");
7437 assert(_finger <= ptr, "_finger runneth ahead");
7438 // advance the finger to right end of this object
7439 _finger = ptr + obj->size();
7440 assert(_finger > ptr, "we just incremented it above");
7441 // On large heaps, it may take us some time to get through
7442 // the marking phase (especially if running iCMS). During
7443 // this time it's possible that a lot of mutations have
7444 // accumulated in the card table and the mod union table --
7445 // these mutation records are redundant until we have
7446 // actually traced into the corresponding card.
7447 // Here, we check whether advancing the finger would make
7448 // us cross into a new card, and if so clear corresponding
7449 // cards in the MUT (preclean them in the card-table in the
7450 // future).
7451
7452 DEBUG_ONLY(if (!_verifying) {)
7453 // The clean-on-enter optimization is disabled by default,
7454 // until we fix 6178663.
7455 if (CMSCleanOnEnter && (_finger > _threshold)) {
7456 // [_threshold, _finger) represents the interval
7457 // of cards to be cleared in MUT (or precleaned in card table).
7458 // The set of cards to be cleared is all those that overlap
7459 // with the interval [_threshold, _finger); note that
7460 // _threshold is always kept card-aligned but _finger isn't
7461 // always card-aligned.
7462 HeapWord* old_threshold = _threshold;
7463 assert(old_threshold == (HeapWord*)round_to(
7464 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7465 "_threshold should always be card-aligned");
7466 _threshold = (HeapWord*)round_to(
7467 (intptr_t)_finger, CardTableModRefBS::card_size);
7468 MemRegion mr(old_threshold, _threshold);
7469 assert(!mr.is_empty(), "Control point invariant");
7470 assert(_span.contains(mr), "Should clear within span");
7471 // XXX When _finger crosses from old gen into perm gen
7472 // we may be doing unnecessary cleaning; do better in the
7473 // future by detecting that condition and clearing fewer
7474 // MUT/CT entries.
7475 _mut->clear_range(mr);
7476 }
7477 DEBUG_ONLY(})
7478 // Note: the finger doesn't advance while we drain
7479 // the stack below.
7480 PushOrMarkClosure pushOrMarkClosure(_collector,
7481 _span, _bitMap, _markStack,
7482 _revisitStack,
7483 _finger, this);
7484 bool res = _markStack->push(obj);
7485 assert(res, "Empty non-zero size stack should have space for single push");
7486 while (!_markStack->isEmpty()) {
7487 oop new_oop = _markStack->pop();
7488 // Skip verifying header mark word below because we are
7489 // running concurrent with mutators.
7490 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7491 // now scan this oop's oops
7492 new_oop->oop_iterate(&pushOrMarkClosure);
7493 do_yield_check();
7494 }
7495 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7496 }
7497
7498 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7499 CMSCollector* collector, MemRegion span,
7500 CMSBitMap* bit_map,
7501 OopTaskQueue* work_queue,
7502 CMSMarkStack* overflow_stack,
7503 CMSMarkStack* revisit_stack,
7504 bool should_yield):
7505 _collector(collector),
7506 _whole_span(collector->_span),
7507 _span(span),
7508 _bit_map(bit_map),
7509 _mut(&collector->_modUnionTable),
7510 _work_queue(work_queue),
7511 _overflow_stack(overflow_stack),
7512 _revisit_stack(revisit_stack),
7513 _yield(should_yield),
7514 _skip_bits(0),
7515 _task(task)
7516 {
7517 assert(_work_queue->size() == 0, "work_queue should be empty");
7518 _finger = span.start();
7519 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7520 assert(_span.contains(_finger), "Out of bounds _finger?");
7521 }
7522
7523 // Should revisit to see if this should be restructured for
7524 // greater efficiency.
7525 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7526 if (_skip_bits > 0) {
7527 _skip_bits--;
7528 return true;
7529 }
7530 // convert offset into a HeapWord*
7531 HeapWord* addr = _bit_map->startWord() + offset;
7532 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7533 "address out of range");
7534 assert(_bit_map->isMarked(addr), "tautology");
7535 if (_bit_map->isMarked(addr+1)) {
7536 // this is an allocated object that might not yet be initialized
7537 assert(_skip_bits == 0, "tautology");
7538 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7539 oop p = oop(addr);
7540 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7541 // in the case of Clean-on-Enter optimization, redirty card
7542 // and avoid clearing card by increasing the threshold.
7543 return true;
7544 }
7545 }
7546 scan_oops_in_oop(addr);
7547 return true;
7548 }
7549
7550 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7551 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7552 // Should we assert that our work queue is empty or
7553 // below some drain limit?
7554 assert(_work_queue->size() == 0,
7555 "should drain stack to limit stack usage");
7556 // convert ptr to an oop preparatory to scanning
7557 oop obj = oop(ptr);
7558 // Ignore mark word in verification below, since we
7559 // may be running concurrent with mutators.
7560 assert(obj->is_oop(true), "should be an oop");
7561 assert(_finger <= ptr, "_finger runneth ahead");
7562 // advance the finger to right end of this object
7563 _finger = ptr + obj->size();
7564 assert(_finger > ptr, "we just incremented it above");
7565 // On large heaps, it may take us some time to get through
7566 // the marking phase (especially if running iCMS). During
7567 // this time it's possible that a lot of mutations have
7568 // accumulated in the card table and the mod union table --
7569 // these mutation records are redundant until we have
7570 // actually traced into the corresponding card.
7571 // Here, we check whether advancing the finger would make
7572 // us cross into a new card, and if so clear corresponding
7573 // cards in the MUT (preclean them in the card-table in the
7574 // future).
7575
7576 // The clean-on-enter optimization is disabled by default,
7577 // until we fix 6178663.
7578 if (CMSCleanOnEnter && (_finger > _threshold)) {
7579 // [_threshold, _finger) represents the interval
7580 // of cards to be cleared in MUT (or precleaned in card table).
7581 // The set of cards to be cleared is all those that overlap
7582 // with the interval [_threshold, _finger); note that
7583 // _threshold is always kept card-aligned but _finger isn't
7584 // always card-aligned.
7585 HeapWord* old_threshold = _threshold;
7586 assert(old_threshold == (HeapWord*)round_to(
7587 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7588 "_threshold should always be card-aligned");
7589 _threshold = (HeapWord*)round_to(
7590 (intptr_t)_finger, CardTableModRefBS::card_size);
7591 MemRegion mr(old_threshold, _threshold);
7592 assert(!mr.is_empty(), "Control point invariant");
7593 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7594 // XXX When _finger crosses from old gen into perm gen
7595 // we may be doing unnecessary cleaning; do better in the
7596 // future by detecting that condition and clearing fewer
7597 // MUT/CT entries.
7598 _mut->clear_range(mr);
7599 }
7600
7601 // Note: the local finger doesn't advance while we drain
7602 // the stack below, but the global finger sure can and will.
7603 HeapWord** gfa = _task->global_finger_addr();
7604 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7605 _span, _bit_map,
7606 _work_queue,
7607 _overflow_stack,
7608 _revisit_stack,
7609 _finger,
7610 gfa, this);
7611 bool res = _work_queue->push(obj); // overflow could occur here
7612 assert(res, "Will hold once we use workqueues");
7613 while (true) {
7614 oop new_oop;
7615 if (!_work_queue->pop_local(new_oop)) {
7616 // We emptied our work_queue; check if there's stuff that can
7617 // be gotten from the overflow stack.
7618 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7619 _overflow_stack, _work_queue)) {
7620 do_yield_check();
7621 continue;
7622 } else { // done
7623 break;
7624 }
7625 }
7626 // Skip verifying header mark word below because we are
7627 // running concurrent with mutators.
7628 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7629 // now scan this oop's oops
7630 new_oop->oop_iterate(&pushOrMarkClosure);
7631 do_yield_check();
7632 }
7633 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7634 }
7635
7636 // Yield in response to a request from VM Thread or
7637 // from mutators.
7638 void Par_MarkFromRootsClosure::do_yield_work() {
7639 assert(_task != NULL, "sanity");
7640 _task->yield();
7641 }
7642
7643 // A variant of the above used for verifying CMS marking work.
7644 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7645 MemRegion span,
7646 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7647 CMSMarkStack* mark_stack):
7648 _collector(collector),
7649 _span(span),
7650 _verification_bm(verification_bm),
7651 _cms_bm(cms_bm),
7652 _mark_stack(mark_stack),
7653 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7654 mark_stack)
7655 {
7656 assert(_mark_stack->isEmpty(), "stack should be empty");
7657 _finger = _verification_bm->startWord();
7658 assert(_collector->_restart_addr == NULL, "Sanity check");
7659 assert(_span.contains(_finger), "Out of bounds _finger?");
7660 }
7661
7662 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7663 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7664 assert(_span.contains(addr), "Out of bounds _finger?");
7665 _finger = addr;
7666 }
7667
7668 // Should revisit to see if this should be restructured for
7669 // greater efficiency.
7670 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7671 // convert offset into a HeapWord*
7672 HeapWord* addr = _verification_bm->startWord() + offset;
7673 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7674 "address out of range");
7675 assert(_verification_bm->isMarked(addr), "tautology");
7676 assert(_cms_bm->isMarked(addr), "tautology");
7677
7678 assert(_mark_stack->isEmpty(),
7679 "should drain stack to limit stack usage");
7680 // convert addr to an oop preparatory to scanning
7681 oop obj = oop(addr);
7682 assert(obj->is_oop(), "should be an oop");
7683 assert(_finger <= addr, "_finger runneth ahead");
7684 // advance the finger to right end of this object
7685 _finger = addr + obj->size();
7686 assert(_finger > addr, "we just incremented it above");
7687 // Note: the finger doesn't advance while we drain
7688 // the stack below.
7689 bool res = _mark_stack->push(obj);
7690 assert(res, "Empty non-zero size stack should have space for single push");
7691 while (!_mark_stack->isEmpty()) {
7692 oop new_oop = _mark_stack->pop();
7693 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7694 // now scan this oop's oops
7695 new_oop->oop_iterate(&_pam_verify_closure);
7696 }
7697 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7698 return true;
7699 }
7700
7701 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7702 CMSCollector* collector, MemRegion span,
7703 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7704 CMSMarkStack* mark_stack):
7705 OopClosure(collector->ref_processor()),
7706 _collector(collector),
7707 _span(span),
7708 _verification_bm(verification_bm),
7709 _cms_bm(cms_bm),
7710 _mark_stack(mark_stack)
7711 { }
7712
7713 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7714 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7715
7716 // Upon stack overflow, we discard (part of) the stack,
7717 // remembering the least address amongst those discarded
7718 // in CMSCollector's _restart_address.
7719 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7720 // Remember the least grey address discarded
7721 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7722 _collector->lower_restart_addr(ra);
7723 _mark_stack->reset(); // discard stack contents
7724 _mark_stack->expand(); // expand the stack if possible
7725 }
7726
7727 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7728 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7729 HeapWord* addr = (HeapWord*)obj;
7730 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7731 // Oop lies in _span and isn't yet grey or black
7732 _verification_bm->mark(addr); // now grey
7733 if (!_cms_bm->isMarked(addr)) {
7734 oop(addr)->print();
7735 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7736 addr);
7737 fatal("... aborting");
7738 }
7739
7740 if (!_mark_stack->push(obj)) { // stack overflow
7741 if (PrintCMSStatistics != 0) {
7742 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7743 SIZE_FORMAT, _mark_stack->capacity());
7744 }
7745 assert(_mark_stack->isFull(), "Else push should have succeeded");
7746 handle_stack_overflow(addr);
7747 }
7748 // anything including and to the right of _finger
7749 // will be scanned as we iterate over the remainder of the
7750 // bit map
7751 }
7752 }
7753
7754 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7755 MemRegion span,
7756 CMSBitMap* bitMap, CMSMarkStack* markStack,
7757 CMSMarkStack* revisitStack,
7758 HeapWord* finger, MarkFromRootsClosure* parent) :
7759 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7760 _span(span),
7761 _bitMap(bitMap),
7762 _markStack(markStack),
7763 _finger(finger),
7764 _parent(parent)
7765 { }
7766
7767 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7768 MemRegion span,
7769 CMSBitMap* bit_map,
7770 OopTaskQueue* work_queue,
7771 CMSMarkStack* overflow_stack,
7772 CMSMarkStack* revisit_stack,
7773 HeapWord* finger,
7774 HeapWord** global_finger_addr,
7775 Par_MarkFromRootsClosure* parent) :
7776 Par_KlassRememberingOopClosure(collector,
7777 collector->ref_processor(),
7778 revisit_stack),
7779 _whole_span(collector->_span),
7780 _span(span),
7781 _bit_map(bit_map),
7782 _work_queue(work_queue),
7783 _overflow_stack(overflow_stack),
7784 _finger(finger),
7785 _global_finger_addr(global_finger_addr),
7786 _parent(parent)
7787 { }
7788
7789 // Assumes thread-safe access by callers, who are
7790 // responsible for mutual exclusion.
7791 void CMSCollector::lower_restart_addr(HeapWord* low) {
7792 assert(_span.contains(low), "Out of bounds addr");
7793 if (_restart_addr == NULL) {
7794 _restart_addr = low;
7795 } else {
7796 _restart_addr = MIN2(_restart_addr, low);
7797 }
7798 }
7799
7800 // Upon stack overflow, we discard (part of) the stack,
7801 // remembering the least address amongst those discarded
7802 // in CMSCollector's _restart_address.
7803 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7804 // Remember the least grey address discarded
7805 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7806 _collector->lower_restart_addr(ra);
7807 _markStack->reset(); // discard stack contents
7808 _markStack->expand(); // expand the stack if possible
7809 }
7810
7811 // Upon stack overflow, we discard (part of) the stack,
7812 // remembering the least address amongst those discarded
7813 // in CMSCollector's _restart_address.
7814 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7815 // We need to do this under a mutex to prevent other
7816 // workers from interfering with the work done below.
7817 MutexLockerEx ml(_overflow_stack->par_lock(),
7818 Mutex::_no_safepoint_check_flag);
7819 // Remember the least grey address discarded
7820 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7821 _collector->lower_restart_addr(ra);
7822 _overflow_stack->reset(); // discard stack contents
7823 _overflow_stack->expand(); // expand the stack if possible
7824 }
7825
7826 void PushOrMarkClosure::do_oop(oop obj) {
7827 // Ignore mark word because we are running concurrent with mutators.
7828 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7829 HeapWord* addr = (HeapWord*)obj;
7830 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7831 // Oop lies in _span and isn't yet grey or black
7832 _bitMap->mark(addr); // now grey
7833 if (addr < _finger) {
7834 // the bit map iteration has already either passed, or
7835 // sampled, this bit in the bit map; we'll need to
7836 // use the marking stack to scan this oop's oops.
7837 bool simulate_overflow = false;
7838 NOT_PRODUCT(
7839 if (CMSMarkStackOverflowALot &&
7840 _collector->simulate_overflow()) {
7841 // simulate a stack overflow
7842 simulate_overflow = true;
7843 }
7844 )
7845 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7846 if (PrintCMSStatistics != 0) {
7847 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7848 SIZE_FORMAT, _markStack->capacity());
7849 }
7850 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7851 handle_stack_overflow(addr);
7852 }
7853 }
7854 // anything including and to the right of _finger
7855 // will be scanned as we iterate over the remainder of the
7856 // bit map
7857 do_yield_check();
7858 }
7859 }
7860
7861 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7862 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7863
7864 void Par_PushOrMarkClosure::do_oop(oop obj) {
7865 // Ignore mark word because we are running concurrent with mutators.
7866 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7867 HeapWord* addr = (HeapWord*)obj;
7868 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7869 // Oop lies in _span and isn't yet grey or black
7870 // We read the global_finger (volatile read) strictly after marking oop
7871 bool res = _bit_map->par_mark(addr); // now grey
7872 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7873 // Should we push this marked oop on our stack?
7874 // -- if someone else marked it, nothing to do
7875 // -- if target oop is above global finger nothing to do
7876 // -- if target oop is in chunk and above local finger
7877 // then nothing to do
7878 // -- else push on work queue
7879 if ( !res // someone else marked it, they will deal with it
7880 || (addr >= *gfa) // will be scanned in a later task
7881 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7882 return;
7883 }
7884 // the bit map iteration has already either passed, or
7885 // sampled, this bit in the bit map; we'll need to
7886 // use the marking stack to scan this oop's oops.
7887 bool simulate_overflow = false;
7888 NOT_PRODUCT(
7889 if (CMSMarkStackOverflowALot &&
7890 _collector->simulate_overflow()) {
7891 // simulate a stack overflow
7892 simulate_overflow = true;
7893 }
7894 )
7895 if (simulate_overflow ||
7896 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7897 // stack overflow
7898 if (PrintCMSStatistics != 0) {
7899 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7900 SIZE_FORMAT, _overflow_stack->capacity());
7901 }
7902 // We cannot assert that the overflow stack is full because
7903 // it may have been emptied since.
7904 assert(simulate_overflow ||
7905 _work_queue->size() == _work_queue->max_elems(),
7906 "Else push should have succeeded");
7907 handle_stack_overflow(addr);
7908 }
7909 do_yield_check();
7910 }
7911 }
7912
7913 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7914 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7915
7916 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7917 ReferenceProcessor* rp,
7918 CMSMarkStack* revisit_stack) :
7919 OopClosure(rp),
7920 _collector(collector),
7921 _revisit_stack(revisit_stack),
7922 _should_remember_klasses(collector->should_unload_classes()) {}
7923
7924 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7925 MemRegion span,
7926 ReferenceProcessor* rp,
7927 CMSBitMap* bit_map,
7928 CMSBitMap* mod_union_table,
7929 CMSMarkStack* mark_stack,
7930 CMSMarkStack* revisit_stack,
7931 bool concurrent_precleaning):
7932 KlassRememberingOopClosure(collector, rp, revisit_stack),
7933 _span(span),
7934 _bit_map(bit_map),
7935 _mod_union_table(mod_union_table),
7936 _mark_stack(mark_stack),
7937 _concurrent_precleaning(concurrent_precleaning)
7938 {
7939 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7940 }
7941
7942 // Grey object rescan during pre-cleaning and second checkpoint phases --
7943 // the non-parallel version (the parallel version appears further below.)
7944 void PushAndMarkClosure::do_oop(oop obj) {
7945 // Ignore mark word verification. If during concurrent precleaning,
7946 // the object monitor may be locked. If during the checkpoint
7947 // phases, the object may already have been reached by a different
7948 // path and may be at the end of the global overflow list (so
7949 // the mark word may be NULL).
7950 assert(obj->is_oop_or_null(true /* ignore mark word */),
7951 "expected an oop or NULL");
7952 HeapWord* addr = (HeapWord*)obj;
7953 // Check if oop points into the CMS generation
7954 // and is not marked
7955 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7956 // a white object ...
7957 _bit_map->mark(addr); // ... now grey
7958 // push on the marking stack (grey set)
7959 bool simulate_overflow = false;
7960 NOT_PRODUCT(
7961 if (CMSMarkStackOverflowALot &&
7962 _collector->simulate_overflow()) {
7963 // simulate a stack overflow
7964 simulate_overflow = true;
7965 }
7966 )
7967 if (simulate_overflow || !_mark_stack->push(obj)) {
7968 if (_concurrent_precleaning) {
7969 // During precleaning we can just dirty the appropriate card(s)
7970 // in the mod union table, thus ensuring that the object remains
7971 // in the grey set and continue. In the case of object arrays
7972 // we need to dirty all of the cards that the object spans,
7973 // since the rescan of object arrays will be limited to the
7974 // dirty cards.
7975 // Note that no one can be intefering with us in this action
7976 // of dirtying the mod union table, so no locking or atomics
7977 // are required.
7978 if (obj->is_objArray()) {
7979 size_t sz = obj->size();
7980 HeapWord* end_card_addr = (HeapWord*)round_to(
7981 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7982 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7983 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7984 _mod_union_table->mark_range(redirty_range);
7985 } else {
7986 _mod_union_table->mark(addr);
7987 }
7988 _collector->_ser_pmc_preclean_ovflw++;
7989 } else {
7990 // During the remark phase, we need to remember this oop
7991 // in the overflow list.
7992 _collector->push_on_overflow_list(obj);
7993 _collector->_ser_pmc_remark_ovflw++;
7994 }
7995 }
7996 }
7997 }
7998
7999 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8000 MemRegion span,
8001 ReferenceProcessor* rp,
8002 CMSBitMap* bit_map,
8003 OopTaskQueue* work_queue,
8004 CMSMarkStack* revisit_stack):
8005 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
8006 _span(span),
8007 _bit_map(bit_map),
8008 _work_queue(work_queue)
8009 {
8010 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8011 }
8012
8013 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8014 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8015
8016 // Grey object rescan during second checkpoint phase --
8017 // the parallel version.
8018 void Par_PushAndMarkClosure::do_oop(oop obj) {
8019 // In the assert below, we ignore the mark word because
8020 // this oop may point to an already visited object that is
8021 // on the overflow stack (in which case the mark word has
8022 // been hijacked for chaining into the overflow stack --
8023 // if this is the last object in the overflow stack then
8024 // its mark word will be NULL). Because this object may
8025 // have been subsequently popped off the global overflow
8026 // stack, and the mark word possibly restored to the prototypical
8027 // value, by the time we get to examined this failing assert in
8028 // the debugger, is_oop_or_null(false) may subsequently start
8029 // to hold.
8030 assert(obj->is_oop_or_null(true),
8031 "expected an oop or NULL");
8032 HeapWord* addr = (HeapWord*)obj;
8033 // Check if oop points into the CMS generation
8034 // and is not marked
8035 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8036 // a white object ...
8037 // If we manage to "claim" the object, by being the
8038 // first thread to mark it, then we push it on our
8039 // marking stack
8040 if (_bit_map->par_mark(addr)) { // ... now grey
8041 // push on work queue (grey set)
8042 bool simulate_overflow = false;
8043 NOT_PRODUCT(
8044 if (CMSMarkStackOverflowALot &&
8045 _collector->par_simulate_overflow()) {
8046 // simulate a stack overflow
8047 simulate_overflow = true;
8048 }
8049 )
8050 if (simulate_overflow || !_work_queue->push(obj)) {
8051 _collector->par_push_on_overflow_list(obj);
8052 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8053 }
8054 } // Else, some other thread got there first
8055 }
8056 }
8057
8058 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8059 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8060
8061 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
8062 // TBD
8063 }
8064
8065 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
8066 // TBD
8067 }
8068
8069 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8070 DEBUG_ONLY(RememberKlassesChecker mux(false);)
8071 Mutex* bml = _collector->bitMapLock();
8072 assert_lock_strong(bml);
8073 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8074 "CMS thread should hold CMS token");
8075
8076 bml->unlock();
8077 ConcurrentMarkSweepThread::desynchronize(true);
8078
8079 ConcurrentMarkSweepThread::acknowledge_yield_request();
8080
8081 _collector->stopTimer();
8082 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8083 if (PrintCMSStatistics != 0) {
8084 _collector->incrementYields();
8085 }
8086 _collector->icms_wait();
8087
8088 // See the comment in coordinator_yield()
8089 for (unsigned i = 0; i < CMSYieldSleepCount &&
8090 ConcurrentMarkSweepThread::should_yield() &&
8091 !CMSCollector::foregroundGCIsActive(); ++i) {
8092 os::sleep(Thread::current(), 1, false);
8093 ConcurrentMarkSweepThread::acknowledge_yield_request();
8094 }
8095
8096 ConcurrentMarkSweepThread::synchronize(true);
8097 bml->lock();
8098
8099 _collector->startTimer();
8100 }
8101
8102 bool CMSPrecleanRefsYieldClosure::should_return() {
8103 if (ConcurrentMarkSweepThread::should_yield()) {
8104 do_yield_work();
8105 }
8106 return _collector->foregroundGCIsActive();
8107 }
8108
8109 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8110 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8111 "mr should be aligned to start at a card boundary");
8112 // We'd like to assert:
8113 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8114 // "mr should be a range of cards");
8115 // However, that would be too strong in one case -- the last
8116 // partition ends at _unallocated_block which, in general, can be
8117 // an arbitrary boundary, not necessarily card aligned.
8118 if (PrintCMSStatistics != 0) {
8119 _num_dirty_cards +=
8120 mr.word_size()/CardTableModRefBS::card_size_in_words;
8121 }
8122 _space->object_iterate_mem(mr, &_scan_cl);
8123 }
8124
8125 SweepClosure::SweepClosure(CMSCollector* collector,
8126 ConcurrentMarkSweepGeneration* g,
8127 CMSBitMap* bitMap, bool should_yield) :
8128 _collector(collector),
8129 _g(g),
8130 _sp(g->cmsSpace()),
8131 _limit(_sp->sweep_limit()),
8132 _freelistLock(_sp->freelistLock()),
8133 _bitMap(bitMap),
8134 _yield(should_yield),
8135 _inFreeRange(false), // No free range at beginning of sweep
8136 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8137 _lastFreeRangeCoalesced(false),
8138 _freeFinger(g->used_region().start())
8139 {
8140 NOT_PRODUCT(
8141 _numObjectsFreed = 0;
8142 _numWordsFreed = 0;
8143 _numObjectsLive = 0;
8144 _numWordsLive = 0;
8145 _numObjectsAlreadyFree = 0;
8146 _numWordsAlreadyFree = 0;
8147 _last_fc = NULL;
8148
8149 _sp->initializeIndexedFreeListArrayReturnedBytes();
8150 _sp->dictionary()->initialize_dict_returned_bytes();
8151 )
8152 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8153 "sweep _limit out of bounds");
8154 if (CMSTraceSweeper) {
8155 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8156 _limit);
8157 }
8158 }
8159
8160 void SweepClosure::print_on(outputStream* st) const {
8161 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8162 _sp->bottom(), _sp->end());
8163 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8164 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8165 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8166 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8167 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8168 }
8169
8170 #ifndef PRODUCT
8171 // Assertion checking only: no useful work in product mode --
8172 // however, if any of the flags below become product flags,
8173 // you may need to review this code to see if it needs to be
8174 // enabled in product mode.
8175 SweepClosure::~SweepClosure() {
8176 assert_lock_strong(_freelistLock);
8177 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8178 "sweep _limit out of bounds");
8179 if (inFreeRange()) {
8180 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8181 print();
8182 ShouldNotReachHere();
8183 }
8184 if (Verbose && PrintGC) {
8185 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8186 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8187 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8188 SIZE_FORMAT" bytes "
8189 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8190 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8191 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8192 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8193 * sizeof(HeapWord);
8194 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8195
8196 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8197 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8198 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8199 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8200 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8201 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8202 indexListReturnedBytes);
8203 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8204 dict_returned_bytes);
8205 }
8206 }
8207 if (CMSTraceSweeper) {
8208 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8209 _limit);
8210 }
8211 }
8212 #endif // PRODUCT
8213
8214 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8215 bool freeRangeInFreeLists) {
8216 if (CMSTraceSweeper) {
8217 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8218 freeFinger, freeRangeInFreeLists);
8219 }
8220 assert(!inFreeRange(), "Trampling existing free range");
8221 set_inFreeRange(true);
8222 set_lastFreeRangeCoalesced(false);
8223
8224 set_freeFinger(freeFinger);
8225 set_freeRangeInFreeLists(freeRangeInFreeLists);
8226 if (CMSTestInFreeList) {
8227 if (freeRangeInFreeLists) {
8228 FreeChunk* fc = (FreeChunk*) freeFinger;
8229 assert(fc->is_free(), "A chunk on the free list should be free.");
8230 assert(fc->size() > 0, "Free range should have a size");
8231 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8232 }
8233 }
8234 }
8235
8236 // Note that the sweeper runs concurrently with mutators. Thus,
8237 // it is possible for direct allocation in this generation to happen
8238 // in the middle of the sweep. Note that the sweeper also coalesces
8239 // contiguous free blocks. Thus, unless the sweeper and the allocator
8240 // synchronize appropriately freshly allocated blocks may get swept up.
8241 // This is accomplished by the sweeper locking the free lists while
8242 // it is sweeping. Thus blocks that are determined to be free are
8243 // indeed free. There is however one additional complication:
8244 // blocks that have been allocated since the final checkpoint and
8245 // mark, will not have been marked and so would be treated as
8246 // unreachable and swept up. To prevent this, the allocator marks
8247 // the bit map when allocating during the sweep phase. This leads,
8248 // however, to a further complication -- objects may have been allocated
8249 // but not yet initialized -- in the sense that the header isn't yet
8250 // installed. The sweeper can not then determine the size of the block
8251 // in order to skip over it. To deal with this case, we use a technique
8252 // (due to Printezis) to encode such uninitialized block sizes in the
8253 // bit map. Since the bit map uses a bit per every HeapWord, but the
8254 // CMS generation has a minimum object size of 3 HeapWords, it follows
8255 // that "normal marks" won't be adjacent in the bit map (there will
8256 // always be at least two 0 bits between successive 1 bits). We make use
8257 // of these "unused" bits to represent uninitialized blocks -- the bit
8258 // corresponding to the start of the uninitialized object and the next
8259 // bit are both set. Finally, a 1 bit marks the end of the object that
8260 // started with the two consecutive 1 bits to indicate its potentially
8261 // uninitialized state.
8262
8263 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8264 FreeChunk* fc = (FreeChunk*)addr;
8265 size_t res;
8266
8267 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8268 // than "addr == _limit" because although _limit was a block boundary when
8269 // we started the sweep, it may no longer be one because heap expansion
8270 // may have caused us to coalesce the block ending at the address _limit
8271 // with a newly expanded chunk (this happens when _limit was set to the
8272 // previous _end of the space), so we may have stepped past _limit:
8273 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8274 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8275 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8276 "sweep _limit out of bounds");
8277 assert(addr < _sp->end(), "addr out of bounds");
8278 // Flush any free range we might be holding as a single
8279 // coalesced chunk to the appropriate free list.
8280 if (inFreeRange()) {
8281 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8282 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8283 flush_cur_free_chunk(freeFinger(),
8284 pointer_delta(addr, freeFinger()));
8285 if (CMSTraceSweeper) {
8286 gclog_or_tty->print("Sweep: last chunk: ");
8287 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8288 "[coalesced:"SIZE_FORMAT"]\n",
8289 freeFinger(), pointer_delta(addr, freeFinger()),
8290 lastFreeRangeCoalesced());
8291 }
8292 }
8293
8294 // help the iterator loop finish
8295 return pointer_delta(_sp->end(), addr);
8296 }
8297
8298 assert(addr < _limit, "sweep invariant");
8299 // check if we should yield
8300 do_yield_check(addr);
8301 if (fc->is_free()) {
8302 // Chunk that is already free
8303 res = fc->size();
8304 do_already_free_chunk(fc);
8305 debug_only(_sp->verifyFreeLists());
8306 // If we flush the chunk at hand in lookahead_and_flush()
8307 // and it's coalesced with a preceding chunk, then the
8308 // process of "mangling" the payload of the coalesced block
8309 // will cause erasure of the size information from the
8310 // (erstwhile) header of all the coalesced blocks but the
8311 // first, so the first disjunct in the assert will not hold
8312 // in that specific case (in which case the second disjunct
8313 // will hold).
8314 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8315 "Otherwise the size info doesn't change at this step");
8316 NOT_PRODUCT(
8317 _numObjectsAlreadyFree++;
8318 _numWordsAlreadyFree += res;
8319 )
8320 NOT_PRODUCT(_last_fc = fc;)
8321 } else if (!_bitMap->isMarked(addr)) {
8322 // Chunk is fresh garbage
8323 res = do_garbage_chunk(fc);
8324 debug_only(_sp->verifyFreeLists());
8325 NOT_PRODUCT(
8326 _numObjectsFreed++;
8327 _numWordsFreed += res;
8328 )
8329 } else {
8330 // Chunk that is alive.
8331 res = do_live_chunk(fc);
8332 debug_only(_sp->verifyFreeLists());
8333 NOT_PRODUCT(
8334 _numObjectsLive++;
8335 _numWordsLive += res;
8336 )
8337 }
8338 return res;
8339 }
8340
8341 // For the smart allocation, record following
8342 // split deaths - a free chunk is removed from its free list because
8343 // it is being split into two or more chunks.
8344 // split birth - a free chunk is being added to its free list because
8345 // a larger free chunk has been split and resulted in this free chunk.
8346 // coal death - a free chunk is being removed from its free list because
8347 // it is being coalesced into a large free chunk.
8348 // coal birth - a free chunk is being added to its free list because
8349 // it was created when two or more free chunks where coalesced into
8350 // this free chunk.
8351 //
8352 // These statistics are used to determine the desired number of free
8353 // chunks of a given size. The desired number is chosen to be relative
8354 // to the end of a CMS sweep. The desired number at the end of a sweep
8355 // is the
8356 // count-at-end-of-previous-sweep (an amount that was enough)
8357 // - count-at-beginning-of-current-sweep (the excess)
8358 // + split-births (gains in this size during interval)
8359 // - split-deaths (demands on this size during interval)
8360 // where the interval is from the end of one sweep to the end of the
8361 // next.
8362 //
8363 // When sweeping the sweeper maintains an accumulated chunk which is
8364 // the chunk that is made up of chunks that have been coalesced. That
8365 // will be termed the left-hand chunk. A new chunk of garbage that
8366 // is being considered for coalescing will be referred to as the
8367 // right-hand chunk.
8368 //
8369 // When making a decision on whether to coalesce a right-hand chunk with
8370 // the current left-hand chunk, the current count vs. the desired count
8371 // of the left-hand chunk is considered. Also if the right-hand chunk
8372 // is near the large chunk at the end of the heap (see
8373 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8374 // left-hand chunk is coalesced.
8375 //
8376 // When making a decision about whether to split a chunk, the desired count
8377 // vs. the current count of the candidate to be split is also considered.
8378 // If the candidate is underpopulated (currently fewer chunks than desired)
8379 // a chunk of an overpopulated (currently more chunks than desired) size may
8380 // be chosen. The "hint" associated with a free list, if non-null, points
8381 // to a free list which may be overpopulated.
8382 //
8383
8384 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8385 const size_t size = fc->size();
8386 // Chunks that cannot be coalesced are not in the
8387 // free lists.
8388 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8389 assert(_sp->verify_chunk_in_free_list(fc),
8390 "free chunk should be in free lists");
8391 }
8392 // a chunk that is already free, should not have been
8393 // marked in the bit map
8394 HeapWord* const addr = (HeapWord*) fc;
8395 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8396 // Verify that the bit map has no bits marked between
8397 // addr and purported end of this block.
8398 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8399
8400 // Some chunks cannot be coalesced under any circumstances.
8401 // See the definition of cantCoalesce().
8402 if (!fc->cantCoalesce()) {
8403 // This chunk can potentially be coalesced.
8404 if (_sp->adaptive_freelists()) {
8405 // All the work is done in
8406 do_post_free_or_garbage_chunk(fc, size);
8407 } else { // Not adaptive free lists
8408 // this is a free chunk that can potentially be coalesced by the sweeper;
8409 if (!inFreeRange()) {
8410 // if the next chunk is a free block that can't be coalesced
8411 // it doesn't make sense to remove this chunk from the free lists
8412 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8413 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8414 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8415 nextChunk->is_free() && // ... which is free...
8416 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8417 // nothing to do
8418 } else {
8419 // Potentially the start of a new free range:
8420 // Don't eagerly remove it from the free lists.
8421 // No need to remove it if it will just be put
8422 // back again. (Also from a pragmatic point of view
8423 // if it is a free block in a region that is beyond
8424 // any allocated blocks, an assertion will fail)
8425 // Remember the start of a free run.
8426 initialize_free_range(addr, true);
8427 // end - can coalesce with next chunk
8428 }
8429 } else {
8430 // the midst of a free range, we are coalescing
8431 print_free_block_coalesced(fc);
8432 if (CMSTraceSweeper) {
8433 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8434 }
8435 // remove it from the free lists
8436 _sp->removeFreeChunkFromFreeLists(fc);
8437 set_lastFreeRangeCoalesced(true);
8438 // If the chunk is being coalesced and the current free range is
8439 // in the free lists, remove the current free range so that it
8440 // will be returned to the free lists in its entirety - all
8441 // the coalesced pieces included.
8442 if (freeRangeInFreeLists()) {
8443 FreeChunk* ffc = (FreeChunk*) freeFinger();
8444 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8445 "Size of free range is inconsistent with chunk size.");
8446 if (CMSTestInFreeList) {
8447 assert(_sp->verify_chunk_in_free_list(ffc),
8448 "free range is not in free lists");
8449 }
8450 _sp->removeFreeChunkFromFreeLists(ffc);
8451 set_freeRangeInFreeLists(false);
8452 }
8453 }
8454 }
8455 // Note that if the chunk is not coalescable (the else arm
8456 // below), we unconditionally flush, without needing to do
8457 // a "lookahead," as we do below.
8458 if (inFreeRange()) lookahead_and_flush(fc, size);
8459 } else {
8460 // Code path common to both original and adaptive free lists.
8461
8462 // cant coalesce with previous block; this should be treated
8463 // as the end of a free run if any
8464 if (inFreeRange()) {
8465 // we kicked some butt; time to pick up the garbage
8466 assert(freeFinger() < addr, "freeFinger points too high");
8467 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8468 }
8469 // else, nothing to do, just continue
8470 }
8471 }
8472
8473 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8474 // This is a chunk of garbage. It is not in any free list.
8475 // Add it to a free list or let it possibly be coalesced into
8476 // a larger chunk.
8477 HeapWord* const addr = (HeapWord*) fc;
8478 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8479
8480 if (_sp->adaptive_freelists()) {
8481 // Verify that the bit map has no bits marked between
8482 // addr and purported end of just dead object.
8483 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8484
8485 do_post_free_or_garbage_chunk(fc, size);
8486 } else {
8487 if (!inFreeRange()) {
8488 // start of a new free range
8489 assert(size > 0, "A free range should have a size");
8490 initialize_free_range(addr, false);
8491 } else {
8492 // this will be swept up when we hit the end of the
8493 // free range
8494 if (CMSTraceSweeper) {
8495 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8496 }
8497 // If the chunk is being coalesced and the current free range is
8498 // in the free lists, remove the current free range so that it
8499 // will be returned to the free lists in its entirety - all
8500 // the coalesced pieces included.
8501 if (freeRangeInFreeLists()) {
8502 FreeChunk* ffc = (FreeChunk*)freeFinger();
8503 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8504 "Size of free range is inconsistent with chunk size.");
8505 if (CMSTestInFreeList) {
8506 assert(_sp->verify_chunk_in_free_list(ffc),
8507 "free range is not in free lists");
8508 }
8509 _sp->removeFreeChunkFromFreeLists(ffc);
8510 set_freeRangeInFreeLists(false);
8511 }
8512 set_lastFreeRangeCoalesced(true);
8513 }
8514 // this will be swept up when we hit the end of the free range
8515
8516 // Verify that the bit map has no bits marked between
8517 // addr and purported end of just dead object.
8518 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8519 }
8520 assert(_limit >= addr + size,
8521 "A freshly garbage chunk can't possibly straddle over _limit");
8522 if (inFreeRange()) lookahead_and_flush(fc, size);
8523 return size;
8524 }
8525
8526 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8527 HeapWord* addr = (HeapWord*) fc;
8528 // The sweeper has just found a live object. Return any accumulated
8529 // left hand chunk to the free lists.
8530 if (inFreeRange()) {
8531 assert(freeFinger() < addr, "freeFinger points too high");
8532 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8533 }
8534
8535 // This object is live: we'd normally expect this to be
8536 // an oop, and like to assert the following:
8537 // assert(oop(addr)->is_oop(), "live block should be an oop");
8538 // However, as we commented above, this may be an object whose
8539 // header hasn't yet been initialized.
8540 size_t size;
8541 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8542 if (_bitMap->isMarked(addr + 1)) {
8543 // Determine the size from the bit map, rather than trying to
8544 // compute it from the object header.
8545 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8546 size = pointer_delta(nextOneAddr + 1, addr);
8547 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8548 "alignment problem");
8549
8550 #ifdef DEBUG
8551 if (oop(addr)->klass_or_null() != NULL &&
8552 ( !_collector->should_unload_classes()
8553 || (oop(addr)->is_parsable()) &&
8554 oop(addr)->is_conc_safe())) {
8555 // Ignore mark word because we are running concurrent with mutators
8556 assert(oop(addr)->is_oop(true), "live block should be an oop");
8557 // is_conc_safe is checked before performing this assertion
8558 // because an object that is not is_conc_safe may yet have
8559 // the return from size() correct.
8560 assert(size ==
8561 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8562 "P-mark and computed size do not agree");
8563 }
8564 #endif
8565
8566 } else {
8567 // This should be an initialized object that's alive.
8568 assert(oop(addr)->klass_or_null() != NULL &&
8569 (!_collector->should_unload_classes()
8570 || oop(addr)->is_parsable()),
8571 "Should be an initialized object");
8572 // Note that there are objects used during class redefinition,
8573 // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8574 // which are discarded with their is_conc_safe state still
8575 // false. These object may be floating garbage so may be
8576 // seen here. If they are floating garbage their size
8577 // should be attainable from their klass. Do not that
8578 // is_conc_safe() is true for oop(addr).
8579 // Ignore mark word because we are running concurrent with mutators
8580 assert(oop(addr)->is_oop(true), "live block should be an oop");
8581 // Verify that the bit map has no bits marked between
8582 // addr and purported end of this block.
8583 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8584 assert(size >= 3, "Necessary for Printezis marks to work");
8585 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8586 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8587 }
8588 return size;
8589 }
8590
8591 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8592 size_t chunkSize) {
8593 // do_post_free_or_garbage_chunk() should only be called in the case
8594 // of the adaptive free list allocator.
8595 const bool fcInFreeLists = fc->is_free();
8596 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8597 assert((HeapWord*)fc <= _limit, "sweep invariant");
8598 if (CMSTestInFreeList && fcInFreeLists) {
8599 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8600 }
8601
8602 if (CMSTraceSweeper) {
8603 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8604 }
8605
8606 HeapWord* const fc_addr = (HeapWord*) fc;
8607
8608 bool coalesce;
8609 const size_t left = pointer_delta(fc_addr, freeFinger());
8610 const size_t right = chunkSize;
8611 switch (FLSCoalescePolicy) {
8612 // numeric value forms a coalition aggressiveness metric
8613 case 0: { // never coalesce
8614 coalesce = false;
8615 break;
8616 }
8617 case 1: { // coalesce if left & right chunks on overpopulated lists
8618 coalesce = _sp->coalOverPopulated(left) &&
8619 _sp->coalOverPopulated(right);
8620 break;
8621 }
8622 case 2: { // coalesce if left chunk on overpopulated list (default)
8623 coalesce = _sp->coalOverPopulated(left);
8624 break;
8625 }
8626 case 3: { // coalesce if left OR right chunk on overpopulated list
8627 coalesce = _sp->coalOverPopulated(left) ||
8628 _sp->coalOverPopulated(right);
8629 break;
8630 }
8631 case 4: { // always coalesce
8632 coalesce = true;
8633 break;
8634 }
8635 default:
8636 ShouldNotReachHere();
8637 }
8638
8639 // Should the current free range be coalesced?
8640 // If the chunk is in a free range and either we decided to coalesce above
8641 // or the chunk is near the large block at the end of the heap
8642 // (isNearLargestChunk() returns true), then coalesce this chunk.
8643 const bool doCoalesce = inFreeRange()
8644 && (coalesce || _g->isNearLargestChunk(fc_addr));
8645 if (doCoalesce) {
8646 // Coalesce the current free range on the left with the new
8647 // chunk on the right. If either is on a free list,
8648 // it must be removed from the list and stashed in the closure.
8649 if (freeRangeInFreeLists()) {
8650 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8651 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8652 "Size of free range is inconsistent with chunk size.");
8653 if (CMSTestInFreeList) {
8654 assert(_sp->verify_chunk_in_free_list(ffc),
8655 "Chunk is not in free lists");
8656 }
8657 _sp->coalDeath(ffc->size());
8658 _sp->removeFreeChunkFromFreeLists(ffc);
8659 set_freeRangeInFreeLists(false);
8660 }
8661 if (fcInFreeLists) {
8662 _sp->coalDeath(chunkSize);
8663 assert(fc->size() == chunkSize,
8664 "The chunk has the wrong size or is not in the free lists");
8665 _sp->removeFreeChunkFromFreeLists(fc);
8666 }
8667 set_lastFreeRangeCoalesced(true);
8668 print_free_block_coalesced(fc);
8669 } else { // not in a free range and/or should not coalesce
8670 // Return the current free range and start a new one.
8671 if (inFreeRange()) {
8672 // In a free range but cannot coalesce with the right hand chunk.
8673 // Put the current free range into the free lists.
8674 flush_cur_free_chunk(freeFinger(),
8675 pointer_delta(fc_addr, freeFinger()));
8676 }
8677 // Set up for new free range. Pass along whether the right hand
8678 // chunk is in the free lists.
8679 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8680 }
8681 }
8682
8683 // Lookahead flush:
8684 // If we are tracking a free range, and this is the last chunk that
8685 // we'll look at because its end crosses past _limit, we'll preemptively
8686 // flush it along with any free range we may be holding on to. Note that
8687 // this can be the case only for an already free or freshly garbage
8688 // chunk. If this block is an object, it can never straddle
8689 // over _limit. The "straddling" occurs when _limit is set at
8690 // the previous end of the space when this cycle started, and
8691 // a subsequent heap expansion caused the previously co-terminal
8692 // free block to be coalesced with the newly expanded portion,
8693 // thus rendering _limit a non-block-boundary making it dangerous
8694 // for the sweeper to step over and examine.
8695 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8696 assert(inFreeRange(), "Should only be called if currently in a free range.");
8697 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8698 assert(_sp->used_region().contains(eob - 1),
8699 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8700 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8701 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8702 if (eob >= _limit) {
8703 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8704 if (CMSTraceSweeper) {
8705 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8706 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8707 "[" PTR_FORMAT "," PTR_FORMAT ")",
8708 _limit, fc, eob, _sp->bottom(), _sp->end());
8709 }
8710 // Return the storage we are tracking back into the free lists.
8711 if (CMSTraceSweeper) {
8712 gclog_or_tty->print_cr("Flushing ... ");
8713 }
8714 assert(freeFinger() < eob, "Error");
8715 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8716 }
8717 }
8718
8719 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8720 assert(inFreeRange(), "Should only be called if currently in a free range.");
8721 assert(size > 0,
8722 "A zero sized chunk cannot be added to the free lists.");
8723 if (!freeRangeInFreeLists()) {
8724 if (CMSTestInFreeList) {
8725 FreeChunk* fc = (FreeChunk*) chunk;
8726 fc->set_size(size);
8727 assert(!_sp->verify_chunk_in_free_list(fc),
8728 "chunk should not be in free lists yet");
8729 }
8730 if (CMSTraceSweeper) {
8731 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8732 chunk, size);
8733 }
8734 // A new free range is going to be starting. The current
8735 // free range has not been added to the free lists yet or
8736 // was removed so add it back.
8737 // If the current free range was coalesced, then the death
8738 // of the free range was recorded. Record a birth now.
8739 if (lastFreeRangeCoalesced()) {
8740 _sp->coalBirth(size);
8741 }
8742 _sp->addChunkAndRepairOffsetTable(chunk, size,
8743 lastFreeRangeCoalesced());
8744 } else if (CMSTraceSweeper) {
8745 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8746 }
8747 set_inFreeRange(false);
8748 set_freeRangeInFreeLists(false);
8749 }
8750
8751 // We take a break if we've been at this for a while,
8752 // so as to avoid monopolizing the locks involved.
8753 void SweepClosure::do_yield_work(HeapWord* addr) {
8754 // Return current free chunk being used for coalescing (if any)
8755 // to the appropriate freelist. After yielding, the next
8756 // free block encountered will start a coalescing range of
8757 // free blocks. If the next free block is adjacent to the
8758 // chunk just flushed, they will need to wait for the next
8759 // sweep to be coalesced.
8760 if (inFreeRange()) {
8761 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8762 }
8763
8764 // First give up the locks, then yield, then re-lock.
8765 // We should probably use a constructor/destructor idiom to
8766 // do this unlock/lock or modify the MutexUnlocker class to
8767 // serve our purpose. XXX
8768 assert_lock_strong(_bitMap->lock());
8769 assert_lock_strong(_freelistLock);
8770 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8771 "CMS thread should hold CMS token");
8772 _bitMap->lock()->unlock();
8773 _freelistLock->unlock();
8774 ConcurrentMarkSweepThread::desynchronize(true);
8775 ConcurrentMarkSweepThread::acknowledge_yield_request();
8776 _collector->stopTimer();
8777 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8778 if (PrintCMSStatistics != 0) {
8779 _collector->incrementYields();
8780 }
8781 _collector->icms_wait();
8782
8783 // See the comment in coordinator_yield()
8784 for (unsigned i = 0; i < CMSYieldSleepCount &&
8785 ConcurrentMarkSweepThread::should_yield() &&
8786 !CMSCollector::foregroundGCIsActive(); ++i) {
8787 os::sleep(Thread::current(), 1, false);
8788 ConcurrentMarkSweepThread::acknowledge_yield_request();
8789 }
8790
8791 ConcurrentMarkSweepThread::synchronize(true);
8792 _freelistLock->lock();
8793 _bitMap->lock()->lock_without_safepoint_check();
8794 _collector->startTimer();
8795 }
8796
8797 #ifndef PRODUCT
8798 // This is actually very useful in a product build if it can
8799 // be called from the debugger. Compile it into the product
8800 // as needed.
8801 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8802 return debug_cms_space->verify_chunk_in_free_list(fc);
8803 }
8804 #endif
8805
8806 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8807 if (CMSTraceSweeper) {
8808 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8809 fc, fc->size());
8810 }
8811 }
8812
8813 // CMSIsAliveClosure
8814 bool CMSIsAliveClosure::do_object_b(oop obj) {
8815 HeapWord* addr = (HeapWord*)obj;
8816 return addr != NULL &&
8817 (!_span.contains(addr) || _bit_map->isMarked(addr));
8818 }
8819
8820 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8821 MemRegion span,
8822 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8823 CMSMarkStack* revisit_stack, bool cpc):
8824 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8825 _span(span),
8826 _bit_map(bit_map),
8827 _mark_stack(mark_stack),
8828 _concurrent_precleaning(cpc) {
8829 assert(!_span.is_empty(), "Empty span could spell trouble");
8830 }
8831
8832
8833 // CMSKeepAliveClosure: the serial version
8834 void CMSKeepAliveClosure::do_oop(oop obj) {
8835 HeapWord* addr = (HeapWord*)obj;
8836 if (_span.contains(addr) &&
8837 !_bit_map->isMarked(addr)) {
8838 _bit_map->mark(addr);
8839 bool simulate_overflow = false;
8840 NOT_PRODUCT(
8841 if (CMSMarkStackOverflowALot &&
8842 _collector->simulate_overflow()) {
8843 // simulate a stack overflow
8844 simulate_overflow = true;
8845 }
8846 )
8847 if (simulate_overflow || !_mark_stack->push(obj)) {
8848 if (_concurrent_precleaning) {
8849 // We dirty the overflown object and let the remark
8850 // phase deal with it.
8851 assert(_collector->overflow_list_is_empty(), "Error");
8852 // In the case of object arrays, we need to dirty all of
8853 // the cards that the object spans. No locking or atomics
8854 // are needed since no one else can be mutating the mod union
8855 // table.
8856 if (obj->is_objArray()) {
8857 size_t sz = obj->size();
8858 HeapWord* end_card_addr =
8859 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8860 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8861 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8862 _collector->_modUnionTable.mark_range(redirty_range);
8863 } else {
8864 _collector->_modUnionTable.mark(addr);
8865 }
8866 _collector->_ser_kac_preclean_ovflw++;
8867 } else {
8868 _collector->push_on_overflow_list(obj);
8869 _collector->_ser_kac_ovflw++;
8870 }
8871 }
8872 }
8873 }
8874
8875 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8876 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8877
8878 // CMSParKeepAliveClosure: a parallel version of the above.
8879 // The work queues are private to each closure (thread),
8880 // but (may be) available for stealing by other threads.
8881 void CMSParKeepAliveClosure::do_oop(oop obj) {
8882 HeapWord* addr = (HeapWord*)obj;
8883 if (_span.contains(addr) &&
8884 !_bit_map->isMarked(addr)) {
8885 // In general, during recursive tracing, several threads
8886 // may be concurrently getting here; the first one to
8887 // "tag" it, claims it.
8888 if (_bit_map->par_mark(addr)) {
8889 bool res = _work_queue->push(obj);
8890 assert(res, "Low water mark should be much less than capacity");
8891 // Do a recursive trim in the hope that this will keep
8892 // stack usage lower, but leave some oops for potential stealers
8893 trim_queue(_low_water_mark);
8894 } // Else, another thread got there first
8895 }
8896 }
8897
8898 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8899 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8900
8901 void CMSParKeepAliveClosure::trim_queue(uint max) {
8902 while (_work_queue->size() > max) {
8903 oop new_oop;
8904 if (_work_queue->pop_local(new_oop)) {
8905 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8906 assert(_bit_map->isMarked((HeapWord*)new_oop),
8907 "no white objects on this stack!");
8908 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8909 // iterate over the oops in this oop, marking and pushing
8910 // the ones in CMS heap (i.e. in _span).
8911 new_oop->oop_iterate(&_mark_and_push);
8912 }
8913 }
8914 }
8915
8916 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8917 CMSCollector* collector,
8918 MemRegion span, CMSBitMap* bit_map,
8919 CMSMarkStack* revisit_stack,
8920 OopTaskQueue* work_queue):
8921 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8922 _span(span),
8923 _bit_map(bit_map),
8924 _work_queue(work_queue) { }
8925
8926 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8927 HeapWord* addr = (HeapWord*)obj;
8928 if (_span.contains(addr) &&
8929 !_bit_map->isMarked(addr)) {
8930 if (_bit_map->par_mark(addr)) {
8931 bool simulate_overflow = false;
8932 NOT_PRODUCT(
8933 if (CMSMarkStackOverflowALot &&
8934 _collector->par_simulate_overflow()) {
8935 // simulate a stack overflow
8936 simulate_overflow = true;
8937 }
8938 )
8939 if (simulate_overflow || !_work_queue->push(obj)) {
8940 _collector->par_push_on_overflow_list(obj);
8941 _collector->_par_kac_ovflw++;
8942 }
8943 } // Else another thread got there already
8944 }
8945 }
8946
8947 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8948 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8949
8950 //////////////////////////////////////////////////////////////////
8951 // CMSExpansionCause /////////////////////////////
8952 //////////////////////////////////////////////////////////////////
8953 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8954 switch (cause) {
8955 case _no_expansion:
8956 return "No expansion";
8957 case _satisfy_free_ratio:
8958 return "Free ratio";
8959 case _satisfy_promotion:
8960 return "Satisfy promotion";
8961 case _satisfy_allocation:
8962 return "allocation";
8963 case _allocate_par_lab:
8964 return "Par LAB";
8965 case _allocate_par_spooling_space:
8966 return "Par Spooling Space";
8967 case _adaptive_size_policy:
8968 return "Ergonomics";
8969 default:
8970 return "unknown";
8971 }
8972 }
8973
8974 void CMSDrainMarkingStackClosure::do_void() {
8975 // the max number to take from overflow list at a time
8976 const size_t num = _mark_stack->capacity()/4;
8977 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8978 "Overflow list should be NULL during concurrent phases");
8979 while (!_mark_stack->isEmpty() ||
8980 // if stack is empty, check the overflow list
8981 _collector->take_from_overflow_list(num, _mark_stack)) {
8982 oop obj = _mark_stack->pop();
8983 HeapWord* addr = (HeapWord*)obj;
8984 assert(_span.contains(addr), "Should be within span");
8985 assert(_bit_map->isMarked(addr), "Should be marked");
8986 assert(obj->is_oop(), "Should be an oop");
8987 obj->oop_iterate(_keep_alive);
8988 }
8989 }
8990
8991 void CMSParDrainMarkingStackClosure::do_void() {
8992 // drain queue
8993 trim_queue(0);
8994 }
8995
8996 // Trim our work_queue so its length is below max at return
8997 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8998 while (_work_queue->size() > max) {
8999 oop new_oop;
9000 if (_work_queue->pop_local(new_oop)) {
9001 assert(new_oop->is_oop(), "Expected an oop");
9002 assert(_bit_map->isMarked((HeapWord*)new_oop),
9003 "no white objects on this stack!");
9004 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
9005 // iterate over the oops in this oop, marking and pushing
9006 // the ones in CMS heap (i.e. in _span).
9007 new_oop->oop_iterate(&_mark_and_push);
9008 }
9009 }
9010 }
9011
9012 ////////////////////////////////////////////////////////////////////
9013 // Support for Marking Stack Overflow list handling and related code
9014 ////////////////////////////////////////////////////////////////////
9015 // Much of the following code is similar in shape and spirit to the
9016 // code used in ParNewGC. We should try and share that code
9017 // as much as possible in the future.
9018
9019 #ifndef PRODUCT
9020 // Debugging support for CMSStackOverflowALot
9021
9022 // It's OK to call this multi-threaded; the worst thing
9023 // that can happen is that we'll get a bunch of closely
9024 // spaced simulated oveflows, but that's OK, in fact
9025 // probably good as it would exercise the overflow code
9026 // under contention.
9027 bool CMSCollector::simulate_overflow() {
9028 if (_overflow_counter-- <= 0) { // just being defensive
9029 _overflow_counter = CMSMarkStackOverflowInterval;
9030 return true;
9031 } else {
9032 return false;
9033 }
9034 }
9035
9036 bool CMSCollector::par_simulate_overflow() {
9037 return simulate_overflow();
9038 }
9039 #endif
9040
9041 // Single-threaded
9042 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9043 assert(stack->isEmpty(), "Expected precondition");
9044 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9045 size_t i = num;
9046 oop cur = _overflow_list;
9047 const markOop proto = markOopDesc::prototype();
9048 NOT_PRODUCT(ssize_t n = 0;)
9049 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9050 next = oop(cur->mark());
9051 cur->set_mark(proto); // until proven otherwise
9052 assert(cur->is_oop(), "Should be an oop");
9053 bool res = stack->push(cur);
9054 assert(res, "Bit off more than can chew?");
9055 NOT_PRODUCT(n++;)
9056 }
9057 _overflow_list = cur;
9058 #ifndef PRODUCT
9059 assert(_num_par_pushes >= n, "Too many pops?");
9060 _num_par_pushes -=n;
9061 #endif
9062 return !stack->isEmpty();
9063 }
9064
9065 #define BUSY (oop(0x1aff1aff))
9066 // (MT-safe) Get a prefix of at most "num" from the list.
9067 // The overflow list is chained through the mark word of
9068 // each object in the list. We fetch the entire list,
9069 // break off a prefix of the right size and return the
9070 // remainder. If other threads try to take objects from
9071 // the overflow list at that time, they will wait for
9072 // some time to see if data becomes available. If (and
9073 // only if) another thread places one or more object(s)
9074 // on the global list before we have returned the suffix
9075 // to the global list, we will walk down our local list
9076 // to find its end and append the global list to
9077 // our suffix before returning it. This suffix walk can
9078 // prove to be expensive (quadratic in the amount of traffic)
9079 // when there are many objects in the overflow list and
9080 // there is much producer-consumer contention on the list.
9081 // *NOTE*: The overflow list manipulation code here and
9082 // in ParNewGeneration:: are very similar in shape,
9083 // except that in the ParNew case we use the old (from/eden)
9084 // copy of the object to thread the list via its klass word.
9085 // Because of the common code, if you make any changes in
9086 // the code below, please check the ParNew version to see if
9087 // similar changes might be needed.
9088 // CR 6797058 has been filed to consolidate the common code.
9089 bool CMSCollector::par_take_from_overflow_list(size_t num,
9090 OopTaskQueue* work_q,
9091 int no_of_gc_threads) {
9092 assert(work_q->size() == 0, "First empty local work queue");
9093 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9094 if (_overflow_list == NULL) {
9095 return false;
9096 }
9097 // Grab the entire list; we'll put back a suffix
9098 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
9099 Thread* tid = Thread::current();
9100 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9101 // set to ParallelGCThreads.
9102 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9103 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9104 // If the list is busy, we spin for a short while,
9105 // sleeping between attempts to get the list.
9106 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9107 os::sleep(tid, sleep_time_millis, false);
9108 if (_overflow_list == NULL) {
9109 // Nothing left to take
9110 return false;
9111 } else if (_overflow_list != BUSY) {
9112 // Try and grab the prefix
9113 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
9114 }
9115 }
9116 // If the list was found to be empty, or we spun long
9117 // enough, we give up and return empty-handed. If we leave
9118 // the list in the BUSY state below, it must be the case that
9119 // some other thread holds the overflow list and will set it
9120 // to a non-BUSY state in the future.
9121 if (prefix == NULL || prefix == BUSY) {
9122 // Nothing to take or waited long enough
9123 if (prefix == NULL) {
9124 // Write back the NULL in case we overwrote it with BUSY above
9125 // and it is still the same value.
9126 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9127 }
9128 return false;
9129 }
9130 assert(prefix != NULL && prefix != BUSY, "Error");
9131 size_t i = num;
9132 oop cur = prefix;
9133 // Walk down the first "num" objects, unless we reach the end.
9134 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9135 if (cur->mark() == NULL) {
9136 // We have "num" or fewer elements in the list, so there
9137 // is nothing to return to the global list.
9138 // Write back the NULL in lieu of the BUSY we wrote
9139 // above, if it is still the same value.
9140 if (_overflow_list == BUSY) {
9141 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9142 }
9143 } else {
9144 // Chop off the suffix and rerturn it to the global list.
9145 assert(cur->mark() != BUSY, "Error");
9146 oop suffix_head = cur->mark(); // suffix will be put back on global list
9147 cur->set_mark(NULL); // break off suffix
9148 // It's possible that the list is still in the empty(busy) state
9149 // we left it in a short while ago; in that case we may be
9150 // able to place back the suffix without incurring the cost
9151 // of a walk down the list.
9152 oop observed_overflow_list = _overflow_list;
9153 oop cur_overflow_list = observed_overflow_list;
9154 bool attached = false;
9155 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9156 observed_overflow_list =
9157 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9158 if (cur_overflow_list == observed_overflow_list) {
9159 attached = true;
9160 break;
9161 } else cur_overflow_list = observed_overflow_list;
9162 }
9163 if (!attached) {
9164 // Too bad, someone else sneaked in (at least) an element; we'll need
9165 // to do a splice. Find tail of suffix so we can prepend suffix to global
9166 // list.
9167 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9168 oop suffix_tail = cur;
9169 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9170 "Tautology");
9171 observed_overflow_list = _overflow_list;
9172 do {
9173 cur_overflow_list = observed_overflow_list;
9174 if (cur_overflow_list != BUSY) {
9175 // Do the splice ...
9176 suffix_tail->set_mark(markOop(cur_overflow_list));
9177 } else { // cur_overflow_list == BUSY
9178 suffix_tail->set_mark(NULL);
9179 }
9180 // ... and try to place spliced list back on overflow_list ...
9181 observed_overflow_list =
9182 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9183 } while (cur_overflow_list != observed_overflow_list);
9184 // ... until we have succeeded in doing so.
9185 }
9186 }
9187
9188 // Push the prefix elements on work_q
9189 assert(prefix != NULL, "control point invariant");
9190 const markOop proto = markOopDesc::prototype();
9191 oop next;
9192 NOT_PRODUCT(ssize_t n = 0;)
9193 for (cur = prefix; cur != NULL; cur = next) {
9194 next = oop(cur->mark());
9195 cur->set_mark(proto); // until proven otherwise
9196 assert(cur->is_oop(), "Should be an oop");
9197 bool res = work_q->push(cur);
9198 assert(res, "Bit off more than we can chew?");
9199 NOT_PRODUCT(n++;)
9200 }
9201 #ifndef PRODUCT
9202 assert(_num_par_pushes >= n, "Too many pops?");
9203 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9204 #endif
9205 return true;
9206 }
9207
9208 // Single-threaded
9209 void CMSCollector::push_on_overflow_list(oop p) {
9210 NOT_PRODUCT(_num_par_pushes++;)
9211 assert(p->is_oop(), "Not an oop");
9212 preserve_mark_if_necessary(p);
9213 p->set_mark((markOop)_overflow_list);
9214 _overflow_list = p;
9215 }
9216
9217 // Multi-threaded; use CAS to prepend to overflow list
9218 void CMSCollector::par_push_on_overflow_list(oop p) {
9219 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9220 assert(p->is_oop(), "Not an oop");
9221 par_preserve_mark_if_necessary(p);
9222 oop observed_overflow_list = _overflow_list;
9223 oop cur_overflow_list;
9224 do {
9225 cur_overflow_list = observed_overflow_list;
9226 if (cur_overflow_list != BUSY) {
9227 p->set_mark(markOop(cur_overflow_list));
9228 } else {
9229 p->set_mark(NULL);
9230 }
9231 observed_overflow_list =
9232 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9233 } while (cur_overflow_list != observed_overflow_list);
9234 }
9235 #undef BUSY
9236
9237 // Single threaded
9238 // General Note on GrowableArray: pushes may silently fail
9239 // because we are (temporarily) out of C-heap for expanding
9240 // the stack. The problem is quite ubiquitous and affects
9241 // a lot of code in the JVM. The prudent thing for GrowableArray
9242 // to do (for now) is to exit with an error. However, that may
9243 // be too draconian in some cases because the caller may be
9244 // able to recover without much harm. For such cases, we
9245 // should probably introduce a "soft_push" method which returns
9246 // an indication of success or failure with the assumption that
9247 // the caller may be able to recover from a failure; code in
9248 // the VM can then be changed, incrementally, to deal with such
9249 // failures where possible, thus, incrementally hardening the VM
9250 // in such low resource situations.
9251 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9252 _preserved_oop_stack.push(p);
9253 _preserved_mark_stack.push(m);
9254 assert(m == p->mark(), "Mark word changed");
9255 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9256 "bijection");
9257 }
9258
9259 // Single threaded
9260 void CMSCollector::preserve_mark_if_necessary(oop p) {
9261 markOop m = p->mark();
9262 if (m->must_be_preserved(p)) {
9263 preserve_mark_work(p, m);
9264 }
9265 }
9266
9267 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9268 markOop m = p->mark();
9269 if (m->must_be_preserved(p)) {
9270 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9271 // Even though we read the mark word without holding
9272 // the lock, we are assured that it will not change
9273 // because we "own" this oop, so no other thread can
9274 // be trying to push it on the overflow list; see
9275 // the assertion in preserve_mark_work() that checks
9276 // that m == p->mark().
9277 preserve_mark_work(p, m);
9278 }
9279 }
9280
9281 // We should be able to do this multi-threaded,
9282 // a chunk of stack being a task (this is
9283 // correct because each oop only ever appears
9284 // once in the overflow list. However, it's
9285 // not very easy to completely overlap this with
9286 // other operations, so will generally not be done
9287 // until all work's been completed. Because we
9288 // expect the preserved oop stack (set) to be small,
9289 // it's probably fine to do this single-threaded.
9290 // We can explore cleverer concurrent/overlapped/parallel
9291 // processing of preserved marks if we feel the
9292 // need for this in the future. Stack overflow should
9293 // be so rare in practice and, when it happens, its
9294 // effect on performance so great that this will
9295 // likely just be in the noise anyway.
9296 void CMSCollector::restore_preserved_marks_if_any() {
9297 assert(SafepointSynchronize::is_at_safepoint(),
9298 "world should be stopped");
9299 assert(Thread::current()->is_ConcurrentGC_thread() ||
9300 Thread::current()->is_VM_thread(),
9301 "should be single-threaded");
9302 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9303 "bijection");
9304
9305 while (!_preserved_oop_stack.is_empty()) {
9306 oop p = _preserved_oop_stack.pop();
9307 assert(p->is_oop(), "Should be an oop");
9308 assert(_span.contains(p), "oop should be in _span");
9309 assert(p->mark() == markOopDesc::prototype(),
9310 "Set when taken from overflow list");
9311 markOop m = _preserved_mark_stack.pop();
9312 p->set_mark(m);
9313 }
9314 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9315 "stacks were cleared above");
9316 }
9317
9318 #ifndef PRODUCT
9319 bool CMSCollector::no_preserved_marks() const {
9320 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9321 }
9322 #endif
9323
9324 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9325 {
9326 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9327 CMSAdaptiveSizePolicy* size_policy =
9328 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9329 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9330 "Wrong type for size policy");
9331 return size_policy;
9332 }
9333
9334 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9335 size_t desired_promo_size) {
9336 if (cur_promo_size < desired_promo_size) {
9337 size_t expand_bytes = desired_promo_size - cur_promo_size;
9338 if (PrintAdaptiveSizePolicy && Verbose) {
9339 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9340 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9341 expand_bytes);
9342 }
9343 expand(expand_bytes,
9344 MinHeapDeltaBytes,
9345 CMSExpansionCause::_adaptive_size_policy);
9346 } else if (desired_promo_size < cur_promo_size) {
9347 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9348 if (PrintAdaptiveSizePolicy && Verbose) {
9349 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9350 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9351 shrink_bytes);
9352 }
9353 shrink(shrink_bytes);
9354 }
9355 }
9356
9357 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9358 GenCollectedHeap* gch = GenCollectedHeap::heap();
9359 CMSGCAdaptivePolicyCounters* counters =
9360 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9361 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9362 "Wrong kind of counters");
9363 return counters;
9364 }
9365
9366
9367 void ASConcurrentMarkSweepGeneration::update_counters() {
9368 if (UsePerfData) {
9369 _space_counters->update_all();
9370 _gen_counters->update_all();
9371 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9372 GenCollectedHeap* gch = GenCollectedHeap::heap();
9373 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9374 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9375 "Wrong gc statistics type");
9376 counters->update_counters(gc_stats_l);
9377 }
9378 }
9379
9380 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9381 if (UsePerfData) {
9382 _space_counters->update_used(used);
9383 _space_counters->update_capacity();
9384 _gen_counters->update_all();
9385
9386 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9387 GenCollectedHeap* gch = GenCollectedHeap::heap();
9388 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9389 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9390 "Wrong gc statistics type");
9391 counters->update_counters(gc_stats_l);
9392 }
9393 }
9394
9395 // The desired expansion delta is computed so that:
9396 // . desired free percentage or greater is used
9397 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9398 assert_locked_or_safepoint(Heap_lock);
9399
9400 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9401
9402 // If incremental collection failed, we just want to expand
9403 // to the limit.
9404 if (incremental_collection_failed()) {
9405 clear_incremental_collection_failed();
9406 grow_to_reserved();
9407 return;
9408 }
9409
9410 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9411
9412 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9413 "Wrong type of heap");
9414 int prev_level = level() - 1;
9415 assert(prev_level >= 0, "The cms generation is the lowest generation");
9416 Generation* prev_gen = gch->get_gen(prev_level);
9417 assert(prev_gen->kind() == Generation::ASParNew,
9418 "Wrong type of young generation");
9419 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9420 size_t cur_eden = younger_gen->eden()->capacity();
9421 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9422 size_t cur_promo = free();
9423 size_policy->compute_tenured_generation_free_space(cur_promo,
9424 max_available(),
9425 cur_eden);
9426 resize(cur_promo, size_policy->promo_size());
9427
9428 // Record the new size of the space in the cms generation
9429 // that is available for promotions. This is temporary.
9430 // It should be the desired promo size.
9431 size_policy->avg_cms_promo()->sample(free());
9432 size_policy->avg_old_live()->sample(used());
9433
9434 if (UsePerfData) {
9435 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9436 counters->update_cms_capacity_counter(capacity());
9437 }
9438 }
9439
9440 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9441 assert_locked_or_safepoint(Heap_lock);
9442 assert_lock_strong(freelistLock());
9443 HeapWord* old_end = _cmsSpace->end();
9444 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9445 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9446 FreeChunk* chunk_at_end = find_chunk_at_end();
9447 if (chunk_at_end == NULL) {
9448 // No room to shrink
9449 if (PrintGCDetails && Verbose) {
9450 gclog_or_tty->print_cr("No room to shrink: old_end "
9451 PTR_FORMAT " unallocated_start " PTR_FORMAT
9452 " chunk_at_end " PTR_FORMAT,
9453 old_end, unallocated_start, chunk_at_end);
9454 }
9455 return;
9456 } else {
9457
9458 // Find the chunk at the end of the space and determine
9459 // how much it can be shrunk.
9460 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9461 size_t aligned_shrinkable_size_in_bytes =
9462 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9463 assert(unallocated_start <= chunk_at_end->end(),
9464 "Inconsistent chunk at end of space");
9465 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9466 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9467
9468 // Shrink the underlying space
9469 _virtual_space.shrink_by(bytes);
9470 if (PrintGCDetails && Verbose) {
9471 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9472 " desired_bytes " SIZE_FORMAT
9473 " shrinkable_size_in_bytes " SIZE_FORMAT
9474 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9475 " bytes " SIZE_FORMAT,
9476 desired_bytes, shrinkable_size_in_bytes,
9477 aligned_shrinkable_size_in_bytes, bytes);
9478 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9479 " unallocated_start " SIZE_FORMAT,
9480 old_end, unallocated_start);
9481 }
9482
9483 // If the space did shrink (shrinking is not guaranteed),
9484 // shrink the chunk at the end by the appropriate amount.
9485 if (((HeapWord*)_virtual_space.high()) < old_end) {
9486 size_t new_word_size =
9487 heap_word_size(_virtual_space.committed_size());
9488
9489 // Have to remove the chunk from the dictionary because it is changing
9490 // size and might be someplace elsewhere in the dictionary.
9491
9492 // Get the chunk at end, shrink it, and put it
9493 // back.
9494 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9495 size_t word_size_change = word_size_before - new_word_size;
9496 size_t chunk_at_end_old_size = chunk_at_end->size();
9497 assert(chunk_at_end_old_size >= word_size_change,
9498 "Shrink is too large");
9499 chunk_at_end->set_size(chunk_at_end_old_size -
9500 word_size_change);
9501 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9502 word_size_change);
9503
9504 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9505
9506 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9507 _bts->resize(new_word_size); // resize the block offset shared array
9508 Universe::heap()->barrier_set()->resize_covered_region(mr);
9509 _cmsSpace->assert_locked();
9510 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9511
9512 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9513
9514 // update the space and generation capacity counters
9515 if (UsePerfData) {
9516 _space_counters->update_capacity();
9517 _gen_counters->update_all();
9518 }
9519
9520 if (Verbose && PrintGCDetails) {
9521 size_t new_mem_size = _virtual_space.committed_size();
9522 size_t old_mem_size = new_mem_size + bytes;
9523 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9524 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9525 }
9526 }
9527
9528 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9529 "Inconsistency at end of space");
9530 assert(chunk_at_end->end() == _cmsSpace->end(),
9531 "Shrinking is inconsistent");
9532 return;
9533 }
9534 }
9535 // Transfer some number of overflown objects to usual marking
9536 // stack. Return true if some objects were transferred.
9537 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9538 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9539 (size_t)ParGCDesiredObjsFromOverflowList);
9540
9541 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9542 assert(_collector->overflow_list_is_empty() || res,
9543 "If list is not empty, we should have taken something");
9544 assert(!res || !_mark_stack->isEmpty(),
9545 "If we took something, it should now be on our stack");
9546 return res;
9547 }
9548
9549 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9550 size_t res = _sp->block_size_no_stall(addr, _collector);
9551 if (_sp->block_is_obj(addr)) {
9552 if (_live_bit_map->isMarked(addr)) {
9553 // It can't have been dead in a previous cycle
9554 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9555 } else {
9556 _dead_bit_map->mark(addr); // mark the dead object
9557 }
9558 }
9559 // Could be 0, if the block size could not be computed without stalling.
9560 return res;
9561 }
9562
9563 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9564
9565 switch (phase) {
9566 case CMSCollector::InitialMarking:
9567 initialize(true /* fullGC */ ,
9568 cause /* cause of the GC */,
9569 true /* recordGCBeginTime */,
9570 true /* recordPreGCUsage */,
9571 false /* recordPeakUsage */,
9572 false /* recordPostGCusage */,
9573 true /* recordAccumulatedGCTime */,
9574 false /* recordGCEndTime */,
9575 false /* countCollection */ );
9576 break;
9577
9578 case CMSCollector::FinalMarking:
9579 initialize(true /* fullGC */ ,
9580 cause /* cause of the GC */,
9581 false /* recordGCBeginTime */,
9582 false /* recordPreGCUsage */,
9583 false /* recordPeakUsage */,
9584 false /* recordPostGCusage */,
9585 true /* recordAccumulatedGCTime */,
9586 false /* recordGCEndTime */,
9587 false /* countCollection */ );
9588 break;
9589
9590 case CMSCollector::Sweeping:
9591 initialize(true /* fullGC */ ,
9592 cause /* cause of the GC */,
9593 false /* recordGCBeginTime */,
9594 false /* recordPreGCUsage */,
9595 true /* recordPeakUsage */,
9596 true /* recordPostGCusage */,
9597 false /* recordAccumulatedGCTime */,
9598 true /* recordGCEndTime */,
9599 true /* countCollection */ );
9600 break;
9601
9602 default:
9603 ShouldNotReachHere();
9604 }
9605 }