1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
179
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
183
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
185
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
192
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
198
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
210
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
218
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
228
229 _gc_stats = new CMSGCStats();
230
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the minimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
271
272
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _initiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
298
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
303
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
317
318 }
319 }
320
321 AdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 return gch->gen_policy()->size_policy();
326 }
327
328 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
329
330 const char* gen_name = "old";
331
332 // Generation Counters - generation 1, 1 subspace
333 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
334
335 _space_counters = new GSpaceCounters(gen_name, 0,
336 _virtual_space.reserved_size(),
337 this, _gen_counters);
338 }
339
340 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
341 _cms_gen(cms_gen)
342 {
343 assert(alpha <= 100, "bad value");
344 _saved_alpha = alpha;
345
346 // Initialize the alphas to the bootstrap value of 100.
347 _gc0_alpha = _cms_alpha = 100;
348
349 _cms_begin_time.update();
350 _cms_end_time.update();
351
352 _gc0_duration = 0.0;
353 _gc0_period = 0.0;
354 _gc0_promoted = 0;
355
356 _cms_duration = 0.0;
357 _cms_period = 0.0;
358 _cms_allocated = 0;
359
360 _cms_used_at_gc0_begin = 0;
361 _cms_used_at_gc0_end = 0;
362 _allow_duty_cycle_reduction = false;
363 _valid_bits = 0;
364 _icms_duty_cycle = CMSIncrementalDutyCycle;
365 }
366
367 double CMSStats::cms_free_adjustment_factor(size_t free) const {
368 // TBD: CR 6909490
369 return 1.0;
370 }
371
372 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
373 }
374
375 // If promotion failure handling is on use
376 // the padded average size of the promotion for each
377 // young generation collection.
378 double CMSStats::time_until_cms_gen_full() const {
379 size_t cms_free = _cms_gen->cmsSpace()->free();
380 GenCollectedHeap* gch = GenCollectedHeap::heap();
381 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
382 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
383 if (cms_free > expected_promotion) {
384 // Start a cms collection if there isn't enough space to promote
385 // for the next minor collection. Use the padded average as
386 // a safety factor.
387 cms_free -= expected_promotion;
388
389 // Adjust by the safety factor.
390 double cms_free_dbl = (double)cms_free;
391 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
392 // Apply a further correction factor which tries to adjust
393 // for recent occurance of concurrent mode failures.
394 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
395 cms_free_dbl = cms_free_dbl * cms_adjustment;
396
397 if (PrintGCDetails && Verbose) {
398 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
399 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
400 cms_free, expected_promotion);
401 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
402 cms_free_dbl, cms_consumption_rate() + 1.0);
403 }
404 // Add 1 in case the consumption rate goes to zero.
405 return cms_free_dbl / (cms_consumption_rate() + 1.0);
406 }
407 return 0.0;
408 }
409
410 // Compare the duration of the cms collection to the
411 // time remaining before the cms generation is empty.
412 // Note that the time from the start of the cms collection
413 // to the start of the cms sweep (less than the total
414 // duration of the cms collection) can be used. This
415 // has been tried and some applications experienced
416 // promotion failures early in execution. This was
417 // possibly because the averages were not accurate
418 // enough at the beginning.
419 double CMSStats::time_until_cms_start() const {
420 // We add "gc0_period" to the "work" calculation
421 // below because this query is done (mostly) at the
422 // end of a scavenge, so we need to conservatively
423 // account for that much possible delay
424 // in the query so as to avoid concurrent mode failures
425 // due to starting the collection just a wee bit too
426 // late.
427 double work = cms_duration() + gc0_period();
428 double deadline = time_until_cms_gen_full();
429 // If a concurrent mode failure occurred recently, we want to be
430 // more conservative and halve our expected time_until_cms_gen_full()
431 if (work > deadline) {
432 if (Verbose && PrintGCDetails) {
433 gclog_or_tty->print(
434 " CMSCollector: collect because of anticipated promotion "
435 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
436 gc0_period(), time_until_cms_gen_full());
437 }
438 return 0.0;
439 }
440 return work - deadline;
441 }
442
443 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
444 // amount of change to prevent wild oscillation.
445 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
446 unsigned int new_duty_cycle) {
447 assert(old_duty_cycle <= 100, "bad input value");
448 assert(new_duty_cycle <= 100, "bad input value");
449
450 // Note: use subtraction with caution since it may underflow (values are
451 // unsigned). Addition is safe since we're in the range 0-100.
452 unsigned int damped_duty_cycle = new_duty_cycle;
453 if (new_duty_cycle < old_duty_cycle) {
454 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
455 if (new_duty_cycle + largest_delta < old_duty_cycle) {
456 damped_duty_cycle = old_duty_cycle - largest_delta;
457 }
458 } else if (new_duty_cycle > old_duty_cycle) {
459 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
460 if (new_duty_cycle > old_duty_cycle + largest_delta) {
461 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
462 }
463 }
464 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
465
466 if (CMSTraceIncrementalPacing) {
467 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
468 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
469 }
470 return damped_duty_cycle;
471 }
472
473 unsigned int CMSStats::icms_update_duty_cycle_impl() {
474 assert(CMSIncrementalPacing && valid(),
475 "should be handled in icms_update_duty_cycle()");
476
477 double cms_time_so_far = cms_timer().seconds();
478 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
479 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
480
481 // Avoid division by 0.
482 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
483 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
484
485 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
486 if (new_duty_cycle > _icms_duty_cycle) {
487 // Avoid very small duty cycles (1 or 2); 0 is allowed.
488 if (new_duty_cycle > 2) {
489 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
490 new_duty_cycle);
491 }
492 } else if (_allow_duty_cycle_reduction) {
493 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
494 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
495 // Respect the minimum duty cycle.
496 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
497 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
498 }
499
500 if (PrintGCDetails || CMSTraceIncrementalPacing) {
501 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
502 }
503
504 _allow_duty_cycle_reduction = false;
505 return _icms_duty_cycle;
506 }
507
508 #ifndef PRODUCT
509 void CMSStats::print_on(outputStream *st) const {
510 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
511 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
512 gc0_duration(), gc0_period(), gc0_promoted());
513 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
514 cms_duration(), cms_duration_per_mb(),
515 cms_period(), cms_allocated());
516 st->print(",cms_since_beg=%g,cms_since_end=%g",
517 cms_time_since_begin(), cms_time_since_end());
518 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
519 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
520 if (CMSIncrementalMode) {
521 st->print(",dc=%d", icms_duty_cycle());
522 }
523
524 if (valid()) {
525 st->print(",promo_rate=%g,cms_alloc_rate=%g",
526 promotion_rate(), cms_allocation_rate());
527 st->print(",cms_consumption_rate=%g,time_until_full=%g",
528 cms_consumption_rate(), time_until_cms_gen_full());
529 }
530 st->print(" ");
531 }
532 #endif // #ifndef PRODUCT
533
534 CMSCollector::CollectorState CMSCollector::_collectorState =
535 CMSCollector::Idling;
536 bool CMSCollector::_foregroundGCIsActive = false;
537 bool CMSCollector::_foregroundGCShouldWait = false;
538
539 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
540 CardTableRS* ct,
541 ConcurrentMarkSweepPolicy* cp):
542 _cmsGen(cmsGen),
543 _ct(ct),
544 _ref_processor(NULL), // will be set later
545 _conc_workers(NULL), // may be set later
546 _abort_preclean(false),
547 _start_sampling(false),
548 _between_prologue_and_epilogue(false),
549 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
550 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
551 -1 /* lock-free */, "No_lock" /* dummy */),
552 _modUnionClosure(&_modUnionTable),
553 _modUnionClosurePar(&_modUnionTable),
554 // Adjust my span to cover old (cms) gen
555 _span(cmsGen->reserved()),
556 // Construct the is_alive_closure with _span & markBitMap
557 _is_alive_closure(_span, &_markBitMap),
558 _restart_addr(NULL),
559 _overflow_list(NULL),
560 _stats(cmsGen),
561 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
562 _eden_chunk_array(NULL), // may be set in ctor body
563 _eden_chunk_capacity(0), // -- ditto --
564 _eden_chunk_index(0), // -- ditto --
565 _survivor_plab_array(NULL), // -- ditto --
566 _survivor_chunk_array(NULL), // -- ditto --
567 _survivor_chunk_capacity(0), // -- ditto --
568 _survivor_chunk_index(0), // -- ditto --
569 _ser_pmc_preclean_ovflw(0),
570 _ser_kac_preclean_ovflw(0),
571 _ser_pmc_remark_ovflw(0),
572 _par_pmc_remark_ovflw(0),
573 _ser_kac_ovflw(0),
574 _par_kac_ovflw(0),
575 #ifndef PRODUCT
576 _num_par_pushes(0),
577 #endif
578 _collection_count_start(0),
579 _verifying(false),
580 _icms_start_limit(NULL),
581 _icms_stop_limit(NULL),
582 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
583 _completed_initialization(false),
584 _collector_policy(cp),
585 _should_unload_classes(CMSClassUnloadingEnabled),
586 _concurrent_cycles_since_last_unload(0),
587 _roots_scanning_options(SharedHeap::SO_None),
588 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
589 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
590 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
591 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
592 _cms_start_registered(false)
593 {
594 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
595 ExplicitGCInvokesConcurrent = true;
596 }
597 // Now expand the span and allocate the collection support structures
598 // (MUT, marking bit map etc.) to cover both generations subject to
599 // collection.
600
601 // For use by dirty card to oop closures.
602 _cmsGen->cmsSpace()->set_collector(this);
603
604 // Allocate MUT and marking bit map
605 {
606 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
607 if (!_markBitMap.allocate(_span)) {
608 warning("Failed to allocate CMS Bit Map");
609 return;
610 }
611 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
612 }
613 {
614 _modUnionTable.allocate(_span);
615 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
616 }
617
618 if (!_markStack.allocate(MarkStackSize)) {
619 warning("Failed to allocate CMS Marking Stack");
620 return;
621 }
622
623 // Support for multi-threaded concurrent phases
624 if (CMSConcurrentMTEnabled) {
625 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
626 // just for now
627 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
628 }
629 if (ConcGCThreads > 1) {
630 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
631 ConcGCThreads, true);
632 if (_conc_workers == NULL) {
633 warning("GC/CMS: _conc_workers allocation failure: "
634 "forcing -CMSConcurrentMTEnabled");
635 CMSConcurrentMTEnabled = false;
636 } else {
637 _conc_workers->initialize_workers();
638 }
639 } else {
640 CMSConcurrentMTEnabled = false;
641 }
642 }
643 if (!CMSConcurrentMTEnabled) {
644 ConcGCThreads = 0;
645 } else {
646 // Turn off CMSCleanOnEnter optimization temporarily for
647 // the MT case where it's not fixed yet; see 6178663.
648 CMSCleanOnEnter = false;
649 }
650 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
651 "Inconsistency");
652
653 // Parallel task queues; these are shared for the
654 // concurrent and stop-world phases of CMS, but
655 // are not shared with parallel scavenge (ParNew).
656 {
657 uint i;
658 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
659
660 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
661 || ParallelRefProcEnabled)
662 && num_queues > 0) {
663 _task_queues = new OopTaskQueueSet(num_queues);
664 if (_task_queues == NULL) {
665 warning("task_queues allocation failure.");
666 return;
667 }
668 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
669 if (_hash_seed == NULL) {
670 warning("_hash_seed array allocation failure");
671 return;
672 }
673
674 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
675 for (i = 0; i < num_queues; i++) {
676 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
677 if (q == NULL) {
678 warning("work_queue allocation failure.");
679 return;
680 }
681 _task_queues->register_queue(i, q);
682 }
683 for (i = 0; i < num_queues; i++) {
684 _task_queues->queue(i)->initialize();
685 _hash_seed[i] = 17; // copied from ParNew
686 }
687 }
688 }
689
690 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
691
692 // Clip CMSBootstrapOccupancy between 0 and 100.
693 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
694
695 _full_gcs_since_conc_gc = 0;
696
697 // Now tell CMS generations the identity of their collector
698 ConcurrentMarkSweepGeneration::set_collector(this);
699
700 // Create & start a CMS thread for this CMS collector
701 _cmsThread = ConcurrentMarkSweepThread::start(this);
702 assert(cmsThread() != NULL, "CMS Thread should have been created");
703 assert(cmsThread()->collector() == this,
704 "CMS Thread should refer to this gen");
705 assert(CGC_lock != NULL, "Where's the CGC_lock?");
706
707 // Support for parallelizing young gen rescan
708 GenCollectedHeap* gch = GenCollectedHeap::heap();
709 _young_gen = gch->prev_gen(_cmsGen);
710 if (gch->supports_inline_contig_alloc()) {
711 _top_addr = gch->top_addr();
712 _end_addr = gch->end_addr();
713 assert(_young_gen != NULL, "no _young_gen");
714 _eden_chunk_index = 0;
715 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
716 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
717 if (_eden_chunk_array == NULL) {
718 _eden_chunk_capacity = 0;
719 warning("GC/CMS: _eden_chunk_array allocation failure");
720 }
721 }
722 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
723
724 // Support for parallelizing survivor space rescan
725 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
726 const size_t max_plab_samples =
727 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
728
729 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
730 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
731 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
732 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
733 || _cursor == NULL) {
734 warning("Failed to allocate survivor plab/chunk array");
735 if (_survivor_plab_array != NULL) {
736 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
737 _survivor_plab_array = NULL;
738 }
739 if (_survivor_chunk_array != NULL) {
740 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
741 _survivor_chunk_array = NULL;
742 }
743 if (_cursor != NULL) {
744 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
745 _cursor = NULL;
746 }
747 } else {
748 _survivor_chunk_capacity = 2*max_plab_samples;
749 for (uint i = 0; i < ParallelGCThreads; i++) {
750 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
751 if (vec == NULL) {
752 warning("Failed to allocate survivor plab array");
753 for (int j = i; j > 0; j--) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
755 }
756 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
757 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
758 _survivor_plab_array = NULL;
759 _survivor_chunk_array = NULL;
760 _survivor_chunk_capacity = 0;
761 break;
762 } else {
763 ChunkArray* cur =
764 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
765 max_plab_samples);
766 assert(cur->end() == 0, "Should be 0");
767 assert(cur->array() == vec, "Should be vec");
768 assert(cur->capacity() == max_plab_samples, "Error");
769 }
770 }
771 }
772 }
773 assert( ( _survivor_plab_array != NULL
774 && _survivor_chunk_array != NULL)
775 || ( _survivor_chunk_capacity == 0
776 && _survivor_chunk_index == 0),
777 "Error");
778
779 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
780 _gc_counters = new CollectorCounters("CMS", 1);
781 _completed_initialization = true;
782 _inter_sweep_timer.start(); // start of time
783 }
784
785 const char* ConcurrentMarkSweepGeneration::name() const {
786 return "concurrent mark-sweep generation";
787 }
788 void ConcurrentMarkSweepGeneration::update_counters() {
789 if (UsePerfData) {
790 _space_counters->update_all();
791 _gen_counters->update_all();
792 }
793 }
794
795 // this is an optimized version of update_counters(). it takes the
796 // used value as a parameter rather than computing it.
797 //
798 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
799 if (UsePerfData) {
800 _space_counters->update_used(used);
801 _space_counters->update_capacity();
802 _gen_counters->update_all();
803 }
804 }
805
806 void ConcurrentMarkSweepGeneration::print() const {
807 Generation::print();
808 cmsSpace()->print();
809 }
810
811 #ifndef PRODUCT
812 void ConcurrentMarkSweepGeneration::print_statistics() {
813 cmsSpace()->printFLCensus(0);
814 }
815 #endif
816
817 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
818 GenCollectedHeap* gch = GenCollectedHeap::heap();
819 if (PrintGCDetails) {
820 if (Verbose) {
821 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
822 level(), short_name(), s, used(), capacity());
823 } else {
824 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
825 level(), short_name(), s, used() / K, capacity() / K);
826 }
827 }
828 if (Verbose) {
829 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
830 gch->used(), gch->capacity());
831 } else {
832 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
833 gch->used() / K, gch->capacity() / K);
834 }
835 }
836
837 size_t
838 ConcurrentMarkSweepGeneration::contiguous_available() const {
839 // dld proposes an improvement in precision here. If the committed
840 // part of the space ends in a free block we should add that to
841 // uncommitted size in the calculation below. Will make this
842 // change later, staying with the approximation below for the
843 // time being. -- ysr.
844 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
845 }
846
847 size_t
848 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
849 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
850 }
851
852 size_t ConcurrentMarkSweepGeneration::max_available() const {
853 return free() + _virtual_space.uncommitted_size();
854 }
855
856 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
857 size_t available = max_available();
858 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
859 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
860 if (Verbose && PrintGCDetails) {
861 gclog_or_tty->print_cr(
862 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
863 "max_promo("SIZE_FORMAT")",
864 res? "":" not", available, res? ">=":"<",
865 av_promo, max_promotion_in_bytes);
866 }
867 return res;
868 }
869
870 // At a promotion failure dump information on block layout in heap
871 // (cms old generation).
872 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
873 if (CMSDumpAtPromotionFailure) {
874 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
875 }
876 }
877
878 CompactibleSpace*
879 ConcurrentMarkSweepGeneration::first_compaction_space() const {
880 return _cmsSpace;
881 }
882
883 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
884 // Clear the promotion information. These pointers can be adjusted
885 // along with all the other pointers into the heap but
886 // compaction is expected to be a rare event with
887 // a heap using cms so don't do it without seeing the need.
888 if (CollectedHeap::use_parallel_gc_threads()) {
889 for (uint i = 0; i < ParallelGCThreads; i++) {
890 _par_gc_thread_states[i]->promo.reset();
891 }
892 }
893 }
894
895 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
896 blk->do_space(_cmsSpace);
897 }
898
899 void ConcurrentMarkSweepGeneration::compute_new_size() {
900 assert_locked_or_safepoint(Heap_lock);
901
902 // If incremental collection failed, we just want to expand
903 // to the limit.
904 if (incremental_collection_failed()) {
905 clear_incremental_collection_failed();
906 grow_to_reserved();
907 return;
908 }
909
910 // The heap has been compacted but not reset yet.
911 // Any metric such as free() or used() will be incorrect.
912
913 CardGeneration::compute_new_size();
914
915 // Reset again after a possible resizing
916 if (did_compact()) {
917 cmsSpace()->reset_after_compaction();
918 }
919 }
920
921 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
922 assert_locked_or_safepoint(Heap_lock);
923
924 // If incremental collection failed, we just want to expand
925 // to the limit.
926 if (incremental_collection_failed()) {
927 clear_incremental_collection_failed();
928 grow_to_reserved();
929 return;
930 }
931
932 double free_percentage = ((double) free()) / capacity();
933 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
934 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
935
936 // compute expansion delta needed for reaching desired free percentage
937 if (free_percentage < desired_free_percentage) {
938 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
939 assert(desired_capacity >= capacity(), "invalid expansion size");
940 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
941 if (PrintGCDetails && Verbose) {
942 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
943 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
944 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
945 gclog_or_tty->print_cr(" Desired free fraction %f",
946 desired_free_percentage);
947 gclog_or_tty->print_cr(" Maximum free fraction %f",
948 maximum_free_percentage);
949 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
950 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
951 desired_capacity/1000);
952 int prev_level = level() - 1;
953 if (prev_level >= 0) {
954 size_t prev_size = 0;
955 GenCollectedHeap* gch = GenCollectedHeap::heap();
956 Generation* prev_gen = gch->_gens[prev_level];
957 prev_size = prev_gen->capacity();
958 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
959 prev_size/1000);
960 }
961 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
962 unsafe_max_alloc_nogc()/1000);
963 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
964 contiguous_available()/1000);
965 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
966 expand_bytes);
967 }
968 // safe if expansion fails
969 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
970 if (PrintGCDetails && Verbose) {
971 gclog_or_tty->print_cr(" Expanded free fraction %f",
972 ((double) free()) / capacity());
973 }
974 } else {
975 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
976 assert(desired_capacity <= capacity(), "invalid expansion size");
977 size_t shrink_bytes = capacity() - desired_capacity;
978 // Don't shrink unless the delta is greater than the minimum shrink we want
979 if (shrink_bytes >= MinHeapDeltaBytes) {
980 shrink_free_list_by(shrink_bytes);
981 }
982 }
983 }
984
985 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
986 return cmsSpace()->freelistLock();
987 }
988
989 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
990 bool tlab) {
991 CMSSynchronousYieldRequest yr;
992 MutexLockerEx x(freelistLock(),
993 Mutex::_no_safepoint_check_flag);
994 return have_lock_and_allocate(size, tlab);
995 }
996
997 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
998 bool tlab /* ignored */) {
999 assert_lock_strong(freelistLock());
1000 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1001 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1002 // Allocate the object live (grey) if the background collector has
1003 // started marking. This is necessary because the marker may
1004 // have passed this address and consequently this object will
1005 // not otherwise be greyed and would be incorrectly swept up.
1006 // Note that if this object contains references, the writing
1007 // of those references will dirty the card containing this object
1008 // allowing the object to be blackened (and its references scanned)
1009 // either during a preclean phase or at the final checkpoint.
1010 if (res != NULL) {
1011 // We may block here with an uninitialized object with
1012 // its mark-bit or P-bits not yet set. Such objects need
1013 // to be safely navigable by block_start().
1014 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1015 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1016 collector()->direct_allocated(res, adjustedSize);
1017 _direct_allocated_words += adjustedSize;
1018 // allocation counters
1019 NOT_PRODUCT(
1020 _numObjectsAllocated++;
1021 _numWordsAllocated += (int)adjustedSize;
1022 )
1023 }
1024 return res;
1025 }
1026
1027 // In the case of direct allocation by mutators in a generation that
1028 // is being concurrently collected, the object must be allocated
1029 // live (grey) if the background collector has started marking.
1030 // This is necessary because the marker may
1031 // have passed this address and consequently this object will
1032 // not otherwise be greyed and would be incorrectly swept up.
1033 // Note that if this object contains references, the writing
1034 // of those references will dirty the card containing this object
1035 // allowing the object to be blackened (and its references scanned)
1036 // either during a preclean phase or at the final checkpoint.
1037 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1038 assert(_markBitMap.covers(start, size), "Out of bounds");
1039 if (_collectorState >= Marking) {
1040 MutexLockerEx y(_markBitMap.lock(),
1041 Mutex::_no_safepoint_check_flag);
1042 // [see comments preceding SweepClosure::do_blk() below for details]
1043 //
1044 // Can the P-bits be deleted now? JJJ
1045 //
1046 // 1. need to mark the object as live so it isn't collected
1047 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1048 // 3. need to mark the end of the object so marking, precleaning or sweeping
1049 // can skip over uninitialized or unparsable objects. An allocated
1050 // object is considered uninitialized for our purposes as long as
1051 // its klass word is NULL. All old gen objects are parsable
1052 // as soon as they are initialized.)
1053 _markBitMap.mark(start); // object is live
1054 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1055 _markBitMap.mark(start + size - 1);
1056 // mark end of object
1057 }
1058 // check that oop looks uninitialized
1059 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1060 }
1061
1062 void CMSCollector::promoted(bool par, HeapWord* start,
1063 bool is_obj_array, size_t obj_size) {
1064 assert(_markBitMap.covers(start), "Out of bounds");
1065 // See comment in direct_allocated() about when objects should
1066 // be allocated live.
1067 if (_collectorState >= Marking) {
1068 // we already hold the marking bit map lock, taken in
1069 // the prologue
1070 if (par) {
1071 _markBitMap.par_mark(start);
1072 } else {
1073 _markBitMap.mark(start);
1074 }
1075 // We don't need to mark the object as uninitialized (as
1076 // in direct_allocated above) because this is being done with the
1077 // world stopped and the object will be initialized by the
1078 // time the marking, precleaning or sweeping get to look at it.
1079 // But see the code for copying objects into the CMS generation,
1080 // where we need to ensure that concurrent readers of the
1081 // block offset table are able to safely navigate a block that
1082 // is in flux from being free to being allocated (and in
1083 // transition while being copied into) and subsequently
1084 // becoming a bona-fide object when the copy/promotion is complete.
1085 assert(SafepointSynchronize::is_at_safepoint(),
1086 "expect promotion only at safepoints");
1087
1088 if (_collectorState < Sweeping) {
1089 // Mark the appropriate cards in the modUnionTable, so that
1090 // this object gets scanned before the sweep. If this is
1091 // not done, CMS generation references in the object might
1092 // not get marked.
1093 // For the case of arrays, which are otherwise precisely
1094 // marked, we need to dirty the entire array, not just its head.
1095 if (is_obj_array) {
1096 // The [par_]mark_range() method expects mr.end() below to
1097 // be aligned to the granularity of a bit's representation
1098 // in the heap. In the case of the MUT below, that's a
1099 // card size.
1100 MemRegion mr(start,
1101 (HeapWord*)round_to((intptr_t)(start + obj_size),
1102 CardTableModRefBS::card_size /* bytes */));
1103 if (par) {
1104 _modUnionTable.par_mark_range(mr);
1105 } else {
1106 _modUnionTable.mark_range(mr);
1107 }
1108 } else { // not an obj array; we can just mark the head
1109 if (par) {
1110 _modUnionTable.par_mark(start);
1111 } else {
1112 _modUnionTable.mark(start);
1113 }
1114 }
1115 }
1116 }
1117 }
1118
1119 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1120 {
1121 size_t delta = pointer_delta(addr, space->bottom());
1122 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1123 }
1124
1125 void CMSCollector::icms_update_allocation_limits()
1126 {
1127 Generation* young = GenCollectedHeap::heap()->get_gen(0);
1128 EdenSpace* eden = young->as_DefNewGeneration()->eden();
1129
1130 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1131 if (CMSTraceIncrementalPacing) {
1132 stats().print();
1133 }
1134
1135 assert(duty_cycle <= 100, "invalid duty cycle");
1136 if (duty_cycle != 0) {
1137 // The duty_cycle is a percentage between 0 and 100; convert to words and
1138 // then compute the offset from the endpoints of the space.
1139 size_t free_words = eden->free() / HeapWordSize;
1140 double free_words_dbl = (double)free_words;
1141 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1142 size_t offset_words = (free_words - duty_cycle_words) / 2;
1143
1144 _icms_start_limit = eden->top() + offset_words;
1145 _icms_stop_limit = eden->end() - offset_words;
1146
1147 // The limits may be adjusted (shifted to the right) by
1148 // CMSIncrementalOffset, to allow the application more mutator time after a
1149 // young gen gc (when all mutators were stopped) and before CMS starts and
1150 // takes away one or more cpus.
1151 if (CMSIncrementalOffset != 0) {
1152 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1153 size_t adjustment = (size_t)adjustment_dbl;
1154 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1155 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1156 _icms_start_limit += adjustment;
1157 _icms_stop_limit = tmp_stop;
1158 }
1159 }
1160 }
1161 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1162 _icms_start_limit = _icms_stop_limit = eden->end();
1163 }
1164
1165 // Install the new start limit.
1166 eden->set_soft_end(_icms_start_limit);
1167
1168 if (CMSTraceIncrementalMode) {
1169 gclog_or_tty->print(" icms alloc limits: "
1170 PTR_FORMAT "," PTR_FORMAT
1171 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1172 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1173 percent_of_space(eden, _icms_start_limit),
1174 percent_of_space(eden, _icms_stop_limit));
1175 if (Verbose) {
1176 gclog_or_tty->print("eden: ");
1177 eden->print_on(gclog_or_tty);
1178 }
1179 }
1180 }
1181
1182 // Any changes here should try to maintain the invariant
1183 // that if this method is called with _icms_start_limit
1184 // and _icms_stop_limit both NULL, then it should return NULL
1185 // and not notify the icms thread.
1186 HeapWord*
1187 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1188 size_t word_size)
1189 {
1190 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1191 // nop.
1192 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1193 if (top <= _icms_start_limit) {
1194 if (CMSTraceIncrementalMode) {
1195 space->print_on(gclog_or_tty);
1196 gclog_or_tty->stamp();
1197 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1198 ", new limit=" PTR_FORMAT
1199 " (" SIZE_FORMAT "%%)",
1200 p2i(top), p2i(_icms_stop_limit),
1201 percent_of_space(space, _icms_stop_limit));
1202 }
1203 ConcurrentMarkSweepThread::start_icms();
1204 assert(top < _icms_stop_limit, "Tautology");
1205 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1206 return _icms_stop_limit;
1207 }
1208
1209 // The allocation will cross both the _start and _stop limits, so do the
1210 // stop notification also and return end().
1211 if (CMSTraceIncrementalMode) {
1212 space->print_on(gclog_or_tty);
1213 gclog_or_tty->stamp();
1214 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1215 ", new limit=" PTR_FORMAT
1216 " (" SIZE_FORMAT "%%)",
1217 p2i(top), p2i(space->end()),
1218 percent_of_space(space, space->end()));
1219 }
1220 ConcurrentMarkSweepThread::stop_icms();
1221 return space->end();
1222 }
1223
1224 if (top <= _icms_stop_limit) {
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 top, space->end(),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1237
1238 if (CMSTraceIncrementalMode) {
1239 space->print_on(gclog_or_tty);
1240 gclog_or_tty->stamp();
1241 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1242 ", new limit=" PTR_FORMAT,
1243 top, NULL);
1244 }
1245 }
1246
1247 return NULL;
1248 }
1249
1250 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1251 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1252 // allocate, copy and if necessary update promoinfo --
1253 // delegate to underlying space.
1254 assert_lock_strong(freelistLock());
1255
1256 #ifndef PRODUCT
1257 if (Universe::heap()->promotion_should_fail()) {
1258 return NULL;
1259 }
1260 #endif // #ifndef PRODUCT
1261
1262 oop res = _cmsSpace->promote(obj, obj_size);
1263 if (res == NULL) {
1264 // expand and retry
1265 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1266 expand(s*HeapWordSize, MinHeapDeltaBytes,
1267 CMSExpansionCause::_satisfy_promotion);
1268 // Since there's currently no next generation, we don't try to promote
1269 // into a more senior generation.
1270 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1271 "is made to pass on a possibly failing "
1272 "promotion to next generation");
1273 res = _cmsSpace->promote(obj, obj_size);
1274 }
1275 if (res != NULL) {
1276 // See comment in allocate() about when objects should
1277 // be allocated live.
1278 assert(obj->is_oop(), "Will dereference klass pointer below");
1279 collector()->promoted(false, // Not parallel
1280 (HeapWord*)res, obj->is_objArray(), obj_size);
1281 // promotion counters
1282 NOT_PRODUCT(
1283 _numObjectsPromoted++;
1284 _numWordsPromoted +=
1285 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1286 )
1287 }
1288 return res;
1289 }
1290
1291
1292 HeapWord*
1293 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1294 HeapWord* top,
1295 size_t word_sz)
1296 {
1297 return collector()->allocation_limit_reached(space, top, word_sz);
1298 }
1299
1300 // IMPORTANT: Notes on object size recognition in CMS.
1301 // ---------------------------------------------------
1302 // A block of storage in the CMS generation is always in
1303 // one of three states. A free block (FREE), an allocated
1304 // object (OBJECT) whose size() method reports the correct size,
1305 // and an intermediate state (TRANSIENT) in which its size cannot
1306 // be accurately determined.
1307 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1308 // -----------------------------------------------------
1309 // FREE: klass_word & 1 == 1; mark_word holds block size
1310 //
1311 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1312 // obj->size() computes correct size
1313 //
1314 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1315 //
1316 // STATE IDENTIFICATION: (64 bit+COOPS)
1317 // ------------------------------------
1318 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1319 //
1320 // OBJECT: klass_word installed; klass_word != 0;
1321 // obj->size() computes correct size
1322 //
1323 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1324 //
1325 //
1326 // STATE TRANSITION DIAGRAM
1327 //
1328 // mut / parnew mut / parnew
1329 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1330 // ^ |
1331 // |------------------------ DEAD <------------------------------------|
1332 // sweep mut
1333 //
1334 // While a block is in TRANSIENT state its size cannot be determined
1335 // so readers will either need to come back later or stall until
1336 // the size can be determined. Note that for the case of direct
1337 // allocation, P-bits, when available, may be used to determine the
1338 // size of an object that may not yet have been initialized.
1339
1340 // Things to support parallel young-gen collection.
1341 oop
1342 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1343 oop old, markOop m,
1344 size_t word_sz) {
1345 #ifndef PRODUCT
1346 if (Universe::heap()->promotion_should_fail()) {
1347 return NULL;
1348 }
1349 #endif // #ifndef PRODUCT
1350
1351 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1352 PromotionInfo* promoInfo = &ps->promo;
1353 // if we are tracking promotions, then first ensure space for
1354 // promotion (including spooling space for saving header if necessary).
1355 // then allocate and copy, then track promoted info if needed.
1356 // When tracking (see PromotionInfo::track()), the mark word may
1357 // be displaced and in this case restoration of the mark word
1358 // occurs in the (oop_since_save_marks_)iterate phase.
1359 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1360 // Out of space for allocating spooling buffers;
1361 // try expanding and allocating spooling buffers.
1362 if (!expand_and_ensure_spooling_space(promoInfo)) {
1363 return NULL;
1364 }
1365 }
1366 assert(promoInfo->has_spooling_space(), "Control point invariant");
1367 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1368 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1369 if (obj_ptr == NULL) {
1370 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1371 if (obj_ptr == NULL) {
1372 return NULL;
1373 }
1374 }
1375 oop obj = oop(obj_ptr);
1376 OrderAccess::storestore();
1377 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1378 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1379 // IMPORTANT: See note on object initialization for CMS above.
1380 // Otherwise, copy the object. Here we must be careful to insert the
1381 // klass pointer last, since this marks the block as an allocated object.
1382 // Except with compressed oops it's the mark word.
1383 HeapWord* old_ptr = (HeapWord*)old;
1384 // Restore the mark word copied above.
1385 obj->set_mark(m);
1386 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1387 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1388 OrderAccess::storestore();
1389
1390 if (UseCompressedClassPointers) {
1391 // Copy gap missed by (aligned) header size calculation below
1392 obj->set_klass_gap(old->klass_gap());
1393 }
1394 if (word_sz > (size_t)oopDesc::header_size()) {
1395 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1396 obj_ptr + oopDesc::header_size(),
1397 word_sz - oopDesc::header_size());
1398 }
1399
1400 // Now we can track the promoted object, if necessary. We take care
1401 // to delay the transition from uninitialized to full object
1402 // (i.e., insertion of klass pointer) until after, so that it
1403 // atomically becomes a promoted object.
1404 if (promoInfo->tracking()) {
1405 promoInfo->track((PromotedObject*)obj, old->klass());
1406 }
1407 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1408 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1409 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1410
1411 // Finally, install the klass pointer (this should be volatile).
1412 OrderAccess::storestore();
1413 obj->set_klass(old->klass());
1414 // We should now be able to calculate the right size for this object
1415 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1416
1417 collector()->promoted(true, // parallel
1418 obj_ptr, old->is_objArray(), word_sz);
1419
1420 NOT_PRODUCT(
1421 Atomic::inc_ptr(&_numObjectsPromoted);
1422 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1423 )
1424
1425 return obj;
1426 }
1427
1428 void
1429 ConcurrentMarkSweepGeneration::
1430 par_promote_alloc_undo(int thread_num,
1431 HeapWord* obj, size_t word_sz) {
1432 // CMS does not support promotion undo.
1433 ShouldNotReachHere();
1434 }
1435
1436 void
1437 ConcurrentMarkSweepGeneration::
1438 par_promote_alloc_done(int thread_num) {
1439 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1440 ps->lab.retire(thread_num);
1441 }
1442
1443 void
1444 ConcurrentMarkSweepGeneration::
1445 par_oop_since_save_marks_iterate_done(int thread_num) {
1446 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1447 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1448 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1449 }
1450
1451 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1452 size_t size,
1453 bool tlab)
1454 {
1455 // We allow a STW collection only if a full
1456 // collection was requested.
1457 return full || should_allocate(size, tlab); // FIX ME !!!
1458 // This and promotion failure handling are connected at the
1459 // hip and should be fixed by untying them.
1460 }
1461
1462 bool CMSCollector::shouldConcurrentCollect() {
1463 if (_full_gc_requested) {
1464 if (Verbose && PrintGCDetails) {
1465 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1466 " gc request (or gc_locker)");
1467 }
1468 return true;
1469 }
1470
1471 // For debugging purposes, change the type of collection.
1472 // If the rotation is not on the concurrent collection
1473 // type, don't start a concurrent collection.
1474 NOT_PRODUCT(
1475 if (RotateCMSCollectionTypes &&
1476 (_cmsGen->debug_collection_type() !=
1477 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1478 assert(_cmsGen->debug_collection_type() !=
1479 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1480 "Bad cms collection type");
1481 return false;
1482 }
1483 )
1484
1485 FreelistLocker x(this);
1486 // ------------------------------------------------------------------
1487 // Print out lots of information which affects the initiation of
1488 // a collection.
1489 if (PrintCMSInitiationStatistics && stats().valid()) {
1490 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1491 gclog_or_tty->stamp();
1492 gclog_or_tty->cr();
1493 stats().print_on(gclog_or_tty);
1494 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1495 stats().time_until_cms_gen_full());
1496 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1497 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1498 _cmsGen->contiguous_available());
1499 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1500 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1501 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1502 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1503 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1504 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1505 gclog_or_tty->print_cr("metadata initialized %d",
1506 MetaspaceGC::should_concurrent_collect());
1507 }
1508 // ------------------------------------------------------------------
1509
1510 // If the estimated time to complete a cms collection (cms_duration())
1511 // is less than the estimated time remaining until the cms generation
1512 // is full, start a collection.
1513 if (!UseCMSInitiatingOccupancyOnly) {
1514 if (stats().valid()) {
1515 if (stats().time_until_cms_start() == 0.0) {
1516 return true;
1517 }
1518 } else {
1519 // We want to conservatively collect somewhat early in order
1520 // to try and "bootstrap" our CMS/promotion statistics;
1521 // this branch will not fire after the first successful CMS
1522 // collection because the stats should then be valid.
1523 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1524 if (Verbose && PrintGCDetails) {
1525 gclog_or_tty->print_cr(
1526 " CMSCollector: collect for bootstrapping statistics:"
1527 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1528 _bootstrap_occupancy);
1529 }
1530 return true;
1531 }
1532 }
1533 }
1534
1535 // Otherwise, we start a collection cycle if
1536 // old gen want a collection cycle started. Each may use
1537 // an appropriate criterion for making this decision.
1538 // XXX We need to make sure that the gen expansion
1539 // criterion dovetails well with this. XXX NEED TO FIX THIS
1540 if (_cmsGen->should_concurrent_collect()) {
1541 if (Verbose && PrintGCDetails) {
1542 gclog_or_tty->print_cr("CMS old gen initiated");
1543 }
1544 return true;
1545 }
1546
1547 // We start a collection if we believe an incremental collection may fail;
1548 // this is not likely to be productive in practice because it's probably too
1549 // late anyway.
1550 GenCollectedHeap* gch = GenCollectedHeap::heap();
1551 assert(gch->collector_policy()->is_generation_policy(),
1552 "You may want to check the correctness of the following");
1553 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1554 if (Verbose && PrintGCDetails) {
1555 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1556 }
1557 return true;
1558 }
1559
1560 if (MetaspaceGC::should_concurrent_collect()) {
1561 if (Verbose && PrintGCDetails) {
1562 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1563 }
1564 return true;
1565 }
1566
1567 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1568 if (CMSTriggerInterval >= 0) {
1569 if (CMSTriggerInterval == 0) {
1570 // Trigger always
1571 return true;
1572 }
1573
1574 // Check the CMS time since begin (we do not check the stats validity
1575 // as we want to be able to trigger the first CMS cycle as well)
1576 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1577 if (Verbose && PrintGCDetails) {
1578 if (stats().valid()) {
1579 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1580 stats().cms_time_since_begin());
1581 } else {
1582 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1583 }
1584 }
1585 return true;
1586 }
1587 }
1588
1589 return false;
1590 }
1591
1592 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1593
1594 // Clear _expansion_cause fields of constituent generations
1595 void CMSCollector::clear_expansion_cause() {
1596 _cmsGen->clear_expansion_cause();
1597 }
1598
1599 // We should be conservative in starting a collection cycle. To
1600 // start too eagerly runs the risk of collecting too often in the
1601 // extreme. To collect too rarely falls back on full collections,
1602 // which works, even if not optimum in terms of concurrent work.
1603 // As a work around for too eagerly collecting, use the flag
1604 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1605 // giving the user an easily understandable way of controlling the
1606 // collections.
1607 // We want to start a new collection cycle if any of the following
1608 // conditions hold:
1609 // . our current occupancy exceeds the configured initiating occupancy
1610 // for this generation, or
1611 // . we recently needed to expand this space and have not, since that
1612 // expansion, done a collection of this generation, or
1613 // . the underlying space believes that it may be a good idea to initiate
1614 // a concurrent collection (this may be based on criteria such as the
1615 // following: the space uses linear allocation and linear allocation is
1616 // going to fail, or there is believed to be excessive fragmentation in
1617 // the generation, etc... or ...
1618 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1619 // the case of the old generation; see CR 6543076):
1620 // we may be approaching a point at which allocation requests may fail because
1621 // we will be out of sufficient free space given allocation rate estimates.]
1622 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1623
1624 assert_lock_strong(freelistLock());
1625 if (occupancy() > initiating_occupancy()) {
1626 if (PrintGCDetails && Verbose) {
1627 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1628 short_name(), occupancy(), initiating_occupancy());
1629 }
1630 return true;
1631 }
1632 if (UseCMSInitiatingOccupancyOnly) {
1633 return false;
1634 }
1635 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1636 if (PrintGCDetails && Verbose) {
1637 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1638 short_name());
1639 }
1640 return true;
1641 }
1642 if (_cmsSpace->should_concurrent_collect()) {
1643 if (PrintGCDetails && Verbose) {
1644 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1645 short_name());
1646 }
1647 return true;
1648 }
1649 return false;
1650 }
1651
1652 void ConcurrentMarkSweepGeneration::collect(bool full,
1653 bool clear_all_soft_refs,
1654 size_t size,
1655 bool tlab)
1656 {
1657 collector()->collect(full, clear_all_soft_refs, size, tlab);
1658 }
1659
1660 void CMSCollector::collect(bool full,
1661 bool clear_all_soft_refs,
1662 size_t size,
1663 bool tlab)
1664 {
1665 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1666 // For debugging purposes skip the collection if the state
1667 // is not currently idle
1668 if (TraceCMSState) {
1669 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1670 Thread::current(), full, _collectorState);
1671 }
1672 return;
1673 }
1674
1675 // The following "if" branch is present for defensive reasons.
1676 // In the current uses of this interface, it can be replaced with:
1677 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1678 // But I am not placing that assert here to allow future
1679 // generality in invoking this interface.
1680 if (GC_locker::is_active()) {
1681 // A consistency test for GC_locker
1682 assert(GC_locker::needs_gc(), "Should have been set already");
1683 // Skip this foreground collection, instead
1684 // expanding the heap if necessary.
1685 // Need the free list locks for the call to free() in compute_new_size()
1686 compute_new_size();
1687 return;
1688 }
1689 acquire_control_and_collect(full, clear_all_soft_refs);
1690 _full_gcs_since_conc_gc++;
1691 }
1692
1693 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1694 GenCollectedHeap* gch = GenCollectedHeap::heap();
1695 unsigned int gc_count = gch->total_full_collections();
1696 if (gc_count == full_gc_count) {
1697 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1698 _full_gc_requested = true;
1699 _full_gc_cause = cause;
1700 CGC_lock->notify(); // nudge CMS thread
1701 } else {
1702 assert(gc_count > full_gc_count, "Error: causal loop");
1703 }
1704 }
1705
1706 bool CMSCollector::is_external_interruption() {
1707 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1708 return GCCause::is_user_requested_gc(cause) ||
1709 GCCause::is_serviceability_requested_gc(cause);
1710 }
1711
1712 void CMSCollector::report_concurrent_mode_interruption() {
1713 if (is_external_interruption()) {
1714 if (PrintGCDetails) {
1715 gclog_or_tty->print(" (concurrent mode interrupted)");
1716 }
1717 } else {
1718 if (PrintGCDetails) {
1719 gclog_or_tty->print(" (concurrent mode failure)");
1720 }
1721 _gc_tracer_cm->report_concurrent_mode_failure();
1722 }
1723 }
1724
1725
1726 // The foreground and background collectors need to coordinate in order
1727 // to make sure that they do not mutually interfere with CMS collections.
1728 // When a background collection is active,
1729 // the foreground collector may need to take over (preempt) and
1730 // synchronously complete an ongoing collection. Depending on the
1731 // frequency of the background collections and the heap usage
1732 // of the application, this preemption can be seldom or frequent.
1733 // There are only certain
1734 // points in the background collection that the "collection-baton"
1735 // can be passed to the foreground collector.
1736 //
1737 // The foreground collector will wait for the baton before
1738 // starting any part of the collection. The foreground collector
1739 // will only wait at one location.
1740 //
1741 // The background collector will yield the baton before starting a new
1742 // phase of the collection (e.g., before initial marking, marking from roots,
1743 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1744 // of the loop which switches the phases. The background collector does some
1745 // of the phases (initial mark, final re-mark) with the world stopped.
1746 // Because of locking involved in stopping the world,
1747 // the foreground collector should not block waiting for the background
1748 // collector when it is doing a stop-the-world phase. The background
1749 // collector will yield the baton at an additional point just before
1750 // it enters a stop-the-world phase. Once the world is stopped, the
1751 // background collector checks the phase of the collection. If the
1752 // phase has not changed, it proceeds with the collection. If the
1753 // phase has changed, it skips that phase of the collection. See
1754 // the comments on the use of the Heap_lock in collect_in_background().
1755 //
1756 // Variable used in baton passing.
1757 // _foregroundGCIsActive - Set to true by the foreground collector when
1758 // it wants the baton. The foreground clears it when it has finished
1759 // the collection.
1760 // _foregroundGCShouldWait - Set to true by the background collector
1761 // when it is running. The foreground collector waits while
1762 // _foregroundGCShouldWait is true.
1763 // CGC_lock - monitor used to protect access to the above variables
1764 // and to notify the foreground and background collectors.
1765 // _collectorState - current state of the CMS collection.
1766 //
1767 // The foreground collector
1768 // acquires the CGC_lock
1769 // sets _foregroundGCIsActive
1770 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1771 // various locks acquired in preparation for the collection
1772 // are released so as not to block the background collector
1773 // that is in the midst of a collection
1774 // proceeds with the collection
1775 // clears _foregroundGCIsActive
1776 // returns
1777 //
1778 // The background collector in a loop iterating on the phases of the
1779 // collection
1780 // acquires the CGC_lock
1781 // sets _foregroundGCShouldWait
1782 // if _foregroundGCIsActive is set
1783 // clears _foregroundGCShouldWait, notifies _CGC_lock
1784 // waits on _CGC_lock for _foregroundGCIsActive to become false
1785 // and exits the loop.
1786 // otherwise
1787 // proceed with that phase of the collection
1788 // if the phase is a stop-the-world phase,
1789 // yield the baton once more just before enqueueing
1790 // the stop-world CMS operation (executed by the VM thread).
1791 // returns after all phases of the collection are done
1792 //
1793
1794 void CMSCollector::acquire_control_and_collect(bool full,
1795 bool clear_all_soft_refs) {
1796 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1797 assert(!Thread::current()->is_ConcurrentGC_thread(),
1798 "shouldn't try to acquire control from self!");
1799
1800 // Start the protocol for acquiring control of the
1801 // collection from the background collector (aka CMS thread).
1802 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1803 "VM thread should have CMS token");
1804 // Remember the possibly interrupted state of an ongoing
1805 // concurrent collection
1806 CollectorState first_state = _collectorState;
1807
1808 // Signal to a possibly ongoing concurrent collection that
1809 // we want to do a foreground collection.
1810 _foregroundGCIsActive = true;
1811
1812 // Disable incremental mode during a foreground collection.
1813 ICMSDisabler icms_disabler;
1814
1815 // release locks and wait for a notify from the background collector
1816 // releasing the locks in only necessary for phases which
1817 // do yields to improve the granularity of the collection.
1818 assert_lock_strong(bitMapLock());
1819 // We need to lock the Free list lock for the space that we are
1820 // currently collecting.
1821 assert(haveFreelistLocks(), "Must be holding free list locks");
1822 bitMapLock()->unlock();
1823 releaseFreelistLocks();
1824 {
1825 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1826 if (_foregroundGCShouldWait) {
1827 // We are going to be waiting for action for the CMS thread;
1828 // it had better not be gone (for instance at shutdown)!
1829 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1830 "CMS thread must be running");
1831 // Wait here until the background collector gives us the go-ahead
1832 ConcurrentMarkSweepThread::clear_CMS_flag(
1833 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1834 // Get a possibly blocked CMS thread going:
1835 // Note that we set _foregroundGCIsActive true above,
1836 // without protection of the CGC_lock.
1837 CGC_lock->notify();
1838 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1839 "Possible deadlock");
1840 while (_foregroundGCShouldWait) {
1841 // wait for notification
1842 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1843 // Possibility of delay/starvation here, since CMS token does
1844 // not know to give priority to VM thread? Actually, i think
1845 // there wouldn't be any delay/starvation, but the proof of
1846 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1847 }
1848 ConcurrentMarkSweepThread::set_CMS_flag(
1849 ConcurrentMarkSweepThread::CMS_vm_has_token);
1850 }
1851 }
1852 // The CMS_token is already held. Get back the other locks.
1853 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1854 "VM thread should have CMS token");
1855 getFreelistLocks();
1856 bitMapLock()->lock_without_safepoint_check();
1857 if (TraceCMSState) {
1858 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1859 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1860 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1861 }
1862
1863 // Check if we need to do a compaction, or if not, whether
1864 // we need to start the mark-sweep from scratch.
1865 bool should_compact = false;
1866 bool should_start_over = false;
1867 decide_foreground_collection_type(clear_all_soft_refs,
1868 &should_compact, &should_start_over);
1869
1870 NOT_PRODUCT(
1871 if (RotateCMSCollectionTypes) {
1872 if (_cmsGen->debug_collection_type() ==
1873 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1874 should_compact = true;
1875 } else if (_cmsGen->debug_collection_type() ==
1876 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1877 should_compact = false;
1878 }
1879 }
1880 )
1881
1882 if (first_state > Idling) {
1883 report_concurrent_mode_interruption();
1884 }
1885
1886 set_did_compact(should_compact);
1887 if (should_compact) {
1888 // If the collection is being acquired from the background
1889 // collector, there may be references on the discovered
1890 // references lists that have NULL referents (being those
1891 // that were concurrently cleared by a mutator) or
1892 // that are no longer active (having been enqueued concurrently
1893 // by the mutator).
1894 // Scrub the list of those references because Mark-Sweep-Compact
1895 // code assumes referents are not NULL and that all discovered
1896 // Reference objects are active.
1897 ref_processor()->clean_up_discovered_references();
1898
1899 if (first_state > Idling) {
1900 save_heap_summary();
1901 }
1902
1903 do_compaction_work(clear_all_soft_refs);
1904
1905 // Has the GC time limit been exceeded?
1906 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1907 size_t max_eden_size = young_gen->max_capacity() -
1908 young_gen->to()->capacity() -
1909 young_gen->from()->capacity();
1910 GenCollectedHeap* gch = GenCollectedHeap::heap();
1911 GCCause::Cause gc_cause = gch->gc_cause();
1912 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1913 young_gen->eden()->used(),
1914 _cmsGen->max_capacity(),
1915 max_eden_size,
1916 full,
1917 gc_cause,
1918 gch->collector_policy());
1919 } else {
1920 do_mark_sweep_work(clear_all_soft_refs, first_state,
1921 should_start_over);
1922 }
1923 // Reset the expansion cause, now that we just completed
1924 // a collection cycle.
1925 clear_expansion_cause();
1926 _foregroundGCIsActive = false;
1927 return;
1928 }
1929
1930 // Resize the tenured generation
1931 // after obtaining the free list locks for the
1932 // two generations.
1933 void CMSCollector::compute_new_size() {
1934 assert_locked_or_safepoint(Heap_lock);
1935 FreelistLocker z(this);
1936 MetaspaceGC::compute_new_size();
1937 _cmsGen->compute_new_size_free_list();
1938 }
1939
1940 // A work method used by foreground collection to determine
1941 // what type of collection (compacting or not, continuing or fresh)
1942 // it should do.
1943 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1944 // and CMSCompactWhenClearAllSoftRefs the default in the future
1945 // and do away with the flags after a suitable period.
1946 void CMSCollector::decide_foreground_collection_type(
1947 bool clear_all_soft_refs, bool* should_compact,
1948 bool* should_start_over) {
1949 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1950 // flag is set, and we have either requested a System.gc() or
1951 // the number of full gc's since the last concurrent cycle
1952 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1953 // or if an incremental collection has failed
1954 GenCollectedHeap* gch = GenCollectedHeap::heap();
1955 assert(gch->collector_policy()->is_generation_policy(),
1956 "You may want to check the correctness of the following");
1957 // Inform cms gen if this was due to partial collection failing.
1958 // The CMS gen may use this fact to determine its expansion policy.
1959 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1960 assert(!_cmsGen->incremental_collection_failed(),
1961 "Should have been noticed, reacted to and cleared");
1962 _cmsGen->set_incremental_collection_failed();
1963 }
1964 *should_compact =
1965 UseCMSCompactAtFullCollection &&
1966 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1967 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1968 gch->incremental_collection_will_fail(true /* consult_young */));
1969 *should_start_over = false;
1970 if (clear_all_soft_refs && !*should_compact) {
1971 // We are about to do a last ditch collection attempt
1972 // so it would normally make sense to do a compaction
1973 // to reclaim as much space as possible.
1974 if (CMSCompactWhenClearAllSoftRefs) {
1975 // Default: The rationale is that in this case either
1976 // we are past the final marking phase, in which case
1977 // we'd have to start over, or so little has been done
1978 // that there's little point in saving that work. Compaction
1979 // appears to be the sensible choice in either case.
1980 *should_compact = true;
1981 } else {
1982 // We have been asked to clear all soft refs, but not to
1983 // compact. Make sure that we aren't past the final checkpoint
1984 // phase, for that is where we process soft refs. If we are already
1985 // past that phase, we'll need to redo the refs discovery phase and
1986 // if necessary clear soft refs that weren't previously
1987 // cleared. We do so by remembering the phase in which
1988 // we came in, and if we are past the refs processing
1989 // phase, we'll choose to just redo the mark-sweep
1990 // collection from scratch.
1991 if (_collectorState > FinalMarking) {
1992 // We are past the refs processing phase;
1993 // start over and do a fresh synchronous CMS cycle
1994 _collectorState = Resetting; // skip to reset to start new cycle
1995 reset(false /* == !asynch */);
1996 *should_start_over = true;
1997 } // else we can continue a possibly ongoing current cycle
1998 }
1999 }
2000 }
2001
2002 // A work method used by the foreground collector to do
2003 // a mark-sweep-compact.
2004 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2005 GenCollectedHeap* gch = GenCollectedHeap::heap();
2006
2007 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2008 gc_timer->register_gc_start();
2009
2010 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2011 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2012
2013 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2014 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2015 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2016 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2017 }
2018
2019 // Temporarily widen the span of the weak reference processing to
2020 // the entire heap.
2021 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2022 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2023 // Temporarily, clear the "is_alive_non_header" field of the
2024 // reference processor.
2025 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2026 // Temporarily make reference _processing_ single threaded (non-MT).
2027 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2028 // Temporarily make refs discovery atomic
2029 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2030 // Temporarily make reference _discovery_ single threaded (non-MT)
2031 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2032
2033 ref_processor()->set_enqueuing_is_done(false);
2034 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2035 ref_processor()->setup_policy(clear_all_soft_refs);
2036 // If an asynchronous collection finishes, the _modUnionTable is
2037 // all clear. If we are assuming the collection from an asynchronous
2038 // collection, clear the _modUnionTable.
2039 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2040 "_modUnionTable should be clear if the baton was not passed");
2041 _modUnionTable.clear_all();
2042 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2043 "mod union for klasses should be clear if the baton was passed");
2044 _ct->klass_rem_set()->clear_mod_union();
2045
2046 // We must adjust the allocation statistics being maintained
2047 // in the free list space. We do so by reading and clearing
2048 // the sweep timer and updating the block flux rate estimates below.
2049 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2050 if (_inter_sweep_timer.is_active()) {
2051 _inter_sweep_timer.stop();
2052 // Note that we do not use this sample to update the _inter_sweep_estimate.
2053 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2054 _inter_sweep_estimate.padded_average(),
2055 _intra_sweep_estimate.padded_average());
2056 }
2057
2058 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2059 ref_processor(), clear_all_soft_refs);
2060 #ifdef ASSERT
2061 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2062 size_t free_size = cms_space->free();
2063 assert(free_size ==
2064 pointer_delta(cms_space->end(), cms_space->compaction_top())
2065 * HeapWordSize,
2066 "All the free space should be compacted into one chunk at top");
2067 assert(cms_space->dictionary()->total_chunk_size(
2068 debug_only(cms_space->freelistLock())) == 0 ||
2069 cms_space->totalSizeInIndexedFreeLists() == 0,
2070 "All the free space should be in a single chunk");
2071 size_t num = cms_space->totalCount();
2072 assert((free_size == 0 && num == 0) ||
2073 (free_size > 0 && (num == 1 || num == 2)),
2074 "There should be at most 2 free chunks after compaction");
2075 #endif // ASSERT
2076 _collectorState = Resetting;
2077 assert(_restart_addr == NULL,
2078 "Should have been NULL'd before baton was passed");
2079 reset(false /* == !asynch */);
2080 _cmsGen->reset_after_compaction();
2081 _concurrent_cycles_since_last_unload = 0;
2082
2083 // Clear any data recorded in the PLAB chunk arrays.
2084 if (_survivor_plab_array != NULL) {
2085 reset_survivor_plab_arrays();
2086 }
2087
2088 // Adjust the per-size allocation stats for the next epoch.
2089 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2090 // Restart the "inter sweep timer" for the next epoch.
2091 _inter_sweep_timer.reset();
2092 _inter_sweep_timer.start();
2093
2094 gc_timer->register_gc_end();
2095
2096 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2097
2098 // For a mark-sweep-compact, compute_new_size() will be called
2099 // in the heap's do_collection() method.
2100 }
2101
2102 // A work method used by the foreground collector to do
2103 // a mark-sweep, after taking over from a possibly on-going
2104 // concurrent mark-sweep collection.
2105 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2106 CollectorState first_state, bool should_start_over) {
2107 if (PrintGC && Verbose) {
2108 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2109 "collector with count %d",
2110 _full_gcs_since_conc_gc);
2111 }
2112 switch (_collectorState) {
2113 case Idling:
2114 if (first_state == Idling || should_start_over) {
2115 // The background GC was not active, or should
2116 // restarted from scratch; start the cycle.
2117 _collectorState = InitialMarking;
2118 }
2119 // If first_state was not Idling, then a background GC
2120 // was in progress and has now finished. No need to do it
2121 // again. Leave the state as Idling.
2122 break;
2123 case Precleaning:
2124 // In the foreground case don't do the precleaning since
2125 // it is not done concurrently and there is extra work
2126 // required.
2127 _collectorState = FinalMarking;
2128 }
2129 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2130
2131 // For a mark-sweep, compute_new_size() will be called
2132 // in the heap's do_collection() method.
2133 }
2134
2135
2136 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2137 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2138 EdenSpace* eden_space = dng->eden();
2139 ContiguousSpace* from_space = dng->from();
2140 ContiguousSpace* to_space = dng->to();
2141 // Eden
2142 if (_eden_chunk_array != NULL) {
2143 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2144 eden_space->bottom(), eden_space->top(),
2145 eden_space->end(), eden_space->capacity());
2146 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2147 "_eden_chunk_capacity=" SIZE_FORMAT,
2148 _eden_chunk_index, _eden_chunk_capacity);
2149 for (size_t i = 0; i < _eden_chunk_index; i++) {
2150 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2151 i, _eden_chunk_array[i]);
2152 }
2153 }
2154 // Survivor
2155 if (_survivor_chunk_array != NULL) {
2156 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2157 from_space->bottom(), from_space->top(),
2158 from_space->end(), from_space->capacity());
2159 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2160 "_survivor_chunk_capacity=" SIZE_FORMAT,
2161 _survivor_chunk_index, _survivor_chunk_capacity);
2162 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2163 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2164 i, _survivor_chunk_array[i]);
2165 }
2166 }
2167 }
2168
2169 void CMSCollector::getFreelistLocks() const {
2170 // Get locks for all free lists in all generations that this
2171 // collector is responsible for
2172 _cmsGen->freelistLock()->lock_without_safepoint_check();
2173 }
2174
2175 void CMSCollector::releaseFreelistLocks() const {
2176 // Release locks for all free lists in all generations that this
2177 // collector is responsible for
2178 _cmsGen->freelistLock()->unlock();
2179 }
2180
2181 bool CMSCollector::haveFreelistLocks() const {
2182 // Check locks for all free lists in all generations that this
2183 // collector is responsible for
2184 assert_lock_strong(_cmsGen->freelistLock());
2185 PRODUCT_ONLY(ShouldNotReachHere());
2186 return true;
2187 }
2188
2189 // A utility class that is used by the CMS collector to
2190 // temporarily "release" the foreground collector from its
2191 // usual obligation to wait for the background collector to
2192 // complete an ongoing phase before proceeding.
2193 class ReleaseForegroundGC: public StackObj {
2194 private:
2195 CMSCollector* _c;
2196 public:
2197 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2198 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2199 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2200 // allow a potentially blocked foreground collector to proceed
2201 _c->_foregroundGCShouldWait = false;
2202 if (_c->_foregroundGCIsActive) {
2203 CGC_lock->notify();
2204 }
2205 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2206 "Possible deadlock");
2207 }
2208
2209 ~ReleaseForegroundGC() {
2210 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2211 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2212 _c->_foregroundGCShouldWait = true;
2213 }
2214 };
2215
2216 // There are separate collect_in_background and collect_in_foreground because of
2217 // the different locking requirements of the background collector and the
2218 // foreground collector. There was originally an attempt to share
2219 // one "collect" method between the background collector and the foreground
2220 // collector but the if-then-else required made it cleaner to have
2221 // separate methods.
2222 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2223 assert(Thread::current()->is_ConcurrentGC_thread(),
2224 "A CMS asynchronous collection is only allowed on a CMS thread.");
2225
2226 GenCollectedHeap* gch = GenCollectedHeap::heap();
2227 {
2228 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2229 MutexLockerEx hl(Heap_lock, safepoint_check);
2230 FreelistLocker fll(this);
2231 MutexLockerEx x(CGC_lock, safepoint_check);
2232 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2233 // The foreground collector is active or we're
2234 // not using asynchronous collections. Skip this
2235 // background collection.
2236 assert(!_foregroundGCShouldWait, "Should be clear");
2237 return;
2238 } else {
2239 assert(_collectorState == Idling, "Should be idling before start.");
2240 _collectorState = InitialMarking;
2241 register_gc_start(cause);
2242 // Reset the expansion cause, now that we are about to begin
2243 // a new cycle.
2244 clear_expansion_cause();
2245
2246 // Clear the MetaspaceGC flag since a concurrent collection
2247 // is starting but also clear it after the collection.
2248 MetaspaceGC::set_should_concurrent_collect(false);
2249 }
2250 // Decide if we want to enable class unloading as part of the
2251 // ensuing concurrent GC cycle.
2252 update_should_unload_classes();
2253 _full_gc_requested = false; // acks all outstanding full gc requests
2254 _full_gc_cause = GCCause::_no_gc;
2255 // Signal that we are about to start a collection
2256 gch->increment_total_full_collections(); // ... starting a collection cycle
2257 _collection_count_start = gch->total_full_collections();
2258 }
2259
2260 // Used for PrintGC
2261 size_t prev_used;
2262 if (PrintGC && Verbose) {
2263 prev_used = _cmsGen->used(); // XXXPERM
2264 }
2265
2266 // The change of the collection state is normally done at this level;
2267 // the exceptions are phases that are executed while the world is
2268 // stopped. For those phases the change of state is done while the
2269 // world is stopped. For baton passing purposes this allows the
2270 // background collector to finish the phase and change state atomically.
2271 // The foreground collector cannot wait on a phase that is done
2272 // while the world is stopped because the foreground collector already
2273 // has the world stopped and would deadlock.
2274 while (_collectorState != Idling) {
2275 if (TraceCMSState) {
2276 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2277 Thread::current(), _collectorState);
2278 }
2279 // The foreground collector
2280 // holds the Heap_lock throughout its collection.
2281 // holds the CMS token (but not the lock)
2282 // except while it is waiting for the background collector to yield.
2283 //
2284 // The foreground collector should be blocked (not for long)
2285 // if the background collector is about to start a phase
2286 // executed with world stopped. If the background
2287 // collector has already started such a phase, the
2288 // foreground collector is blocked waiting for the
2289 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2290 // are executed in the VM thread.
2291 //
2292 // The locking order is
2293 // PendingListLock (PLL) -- if applicable (FinalMarking)
2294 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2295 // CMS token (claimed in
2296 // stop_world_and_do() -->
2297 // safepoint_synchronize() -->
2298 // CMSThread::synchronize())
2299
2300 {
2301 // Check if the FG collector wants us to yield.
2302 CMSTokenSync x(true); // is cms thread
2303 if (waitForForegroundGC()) {
2304 // We yielded to a foreground GC, nothing more to be
2305 // done this round.
2306 assert(_foregroundGCShouldWait == false, "We set it to false in "
2307 "waitForForegroundGC()");
2308 if (TraceCMSState) {
2309 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2310 " exiting collection CMS state %d",
2311 Thread::current(), _collectorState);
2312 }
2313 return;
2314 } else {
2315 // The background collector can run but check to see if the
2316 // foreground collector has done a collection while the
2317 // background collector was waiting to get the CGC_lock
2318 // above. If yes, break so that _foregroundGCShouldWait
2319 // is cleared before returning.
2320 if (_collectorState == Idling) {
2321 break;
2322 }
2323 }
2324 }
2325
2326 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2327 "should be waiting");
2328
2329 switch (_collectorState) {
2330 case InitialMarking:
2331 {
2332 ReleaseForegroundGC x(this);
2333 stats().record_cms_begin();
2334 VM_CMS_Initial_Mark initial_mark_op(this);
2335 VMThread::execute(&initial_mark_op);
2336 }
2337 // The collector state may be any legal state at this point
2338 // since the background collector may have yielded to the
2339 // foreground collector.
2340 break;
2341 case Marking:
2342 // initial marking in checkpointRootsInitialWork has been completed
2343 if (markFromRoots(true)) { // we were successful
2344 assert(_collectorState == Precleaning, "Collector state should "
2345 "have changed");
2346 } else {
2347 assert(_foregroundGCIsActive, "Internal state inconsistency");
2348 }
2349 break;
2350 case Precleaning:
2351 // marking from roots in markFromRoots has been completed
2352 preclean();
2353 assert(_collectorState == AbortablePreclean ||
2354 _collectorState == FinalMarking,
2355 "Collector state should have changed");
2356 break;
2357 case AbortablePreclean:
2358 abortable_preclean();
2359 assert(_collectorState == FinalMarking, "Collector state should "
2360 "have changed");
2361 break;
2362 case FinalMarking:
2363 {
2364 ReleaseForegroundGC x(this);
2365
2366 VM_CMS_Final_Remark final_remark_op(this);
2367 VMThread::execute(&final_remark_op);
2368 }
2369 assert(_foregroundGCShouldWait, "block post-condition");
2370 break;
2371 case Sweeping:
2372 // final marking in checkpointRootsFinal has been completed
2373 sweep(true);
2374 assert(_collectorState == Resizing, "Collector state change "
2375 "to Resizing must be done under the free_list_lock");
2376 _full_gcs_since_conc_gc = 0;
2377
2378 case Resizing: {
2379 // Sweeping has been completed...
2380 // At this point the background collection has completed.
2381 // Don't move the call to compute_new_size() down
2382 // into code that might be executed if the background
2383 // collection was preempted.
2384 {
2385 ReleaseForegroundGC x(this); // unblock FG collection
2386 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2387 CMSTokenSync z(true); // not strictly needed.
2388 if (_collectorState == Resizing) {
2389 compute_new_size();
2390 save_heap_summary();
2391 _collectorState = Resetting;
2392 } else {
2393 assert(_collectorState == Idling, "The state should only change"
2394 " because the foreground collector has finished the collection");
2395 }
2396 }
2397 break;
2398 }
2399 case Resetting:
2400 // CMS heap resizing has been completed
2401 reset(true);
2402 assert(_collectorState == Idling, "Collector state should "
2403 "have changed");
2404
2405 MetaspaceGC::set_should_concurrent_collect(false);
2406
2407 stats().record_cms_end();
2408 // Don't move the concurrent_phases_end() and compute_new_size()
2409 // calls to here because a preempted background collection
2410 // has it's state set to "Resetting".
2411 break;
2412 case Idling:
2413 default:
2414 ShouldNotReachHere();
2415 break;
2416 }
2417 if (TraceCMSState) {
2418 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2419 Thread::current(), _collectorState);
2420 }
2421 assert(_foregroundGCShouldWait, "block post-condition");
2422 }
2423
2424 // Should this be in gc_epilogue?
2425 collector_policy()->counters()->update_counters();
2426
2427 {
2428 // Clear _foregroundGCShouldWait and, in the event that the
2429 // foreground collector is waiting, notify it, before
2430 // returning.
2431 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2432 _foregroundGCShouldWait = false;
2433 if (_foregroundGCIsActive) {
2434 CGC_lock->notify();
2435 }
2436 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2437 "Possible deadlock");
2438 }
2439 if (TraceCMSState) {
2440 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2441 " exiting collection CMS state %d",
2442 Thread::current(), _collectorState);
2443 }
2444 if (PrintGC && Verbose) {
2445 _cmsGen->print_heap_change(prev_used);
2446 }
2447 }
2448
2449 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2450 if (!_cms_start_registered) {
2451 register_gc_start(cause);
2452 }
2453 }
2454
2455 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2456 _cms_start_registered = true;
2457 _gc_timer_cm->register_gc_start();
2458 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2459 }
2460
2461 void CMSCollector::register_gc_end() {
2462 if (_cms_start_registered) {
2463 report_heap_summary(GCWhen::AfterGC);
2464
2465 _gc_timer_cm->register_gc_end();
2466 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2467 _cms_start_registered = false;
2468 }
2469 }
2470
2471 void CMSCollector::save_heap_summary() {
2472 GenCollectedHeap* gch = GenCollectedHeap::heap();
2473 _last_heap_summary = gch->create_heap_summary();
2474 _last_metaspace_summary = gch->create_metaspace_summary();
2475 }
2476
2477 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2478 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2479 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2480 }
2481
2482 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2483 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2484 "Foreground collector should be waiting, not executing");
2485 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2486 "may only be done by the VM Thread with the world stopped");
2487 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2488 "VM thread should have CMS token");
2489
2490 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2491 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2492 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2493 true, NULL, gc_id);)
2494 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2495
2496 HandleMark hm; // Discard invalid handles created during verification
2497
2498 if (VerifyBeforeGC &&
2499 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2500 Universe::verify();
2501 }
2502
2503 // Snapshot the soft reference policy to be used in this collection cycle.
2504 ref_processor()->setup_policy(clear_all_soft_refs);
2505
2506 // Decide if class unloading should be done
2507 update_should_unload_classes();
2508
2509 bool init_mark_was_synchronous = false; // until proven otherwise
2510 while (_collectorState != Idling) {
2511 if (TraceCMSState) {
2512 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2513 Thread::current(), _collectorState);
2514 }
2515 switch (_collectorState) {
2516 case InitialMarking:
2517 register_foreground_gc_start(cause);
2518 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2519 checkpointRootsInitial(false);
2520 assert(_collectorState == Marking, "Collector state should have changed"
2521 " within checkpointRootsInitial()");
2522 break;
2523 case Marking:
2524 // initial marking in checkpointRootsInitialWork has been completed
2525 if (VerifyDuringGC &&
2526 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2527 Universe::verify("Verify before initial mark: ");
2528 }
2529 {
2530 bool res = markFromRoots(false);
2531 assert(res && _collectorState == FinalMarking, "Collector state should "
2532 "have changed");
2533 break;
2534 }
2535 case FinalMarking:
2536 if (VerifyDuringGC &&
2537 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2538 Universe::verify("Verify before re-mark: ");
2539 }
2540 checkpointRootsFinal(false, clear_all_soft_refs,
2541 init_mark_was_synchronous);
2542 assert(_collectorState == Sweeping, "Collector state should not "
2543 "have changed within checkpointRootsFinal()");
2544 break;
2545 case Sweeping:
2546 // final marking in checkpointRootsFinal has been completed
2547 if (VerifyDuringGC &&
2548 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2549 Universe::verify("Verify before sweep: ");
2550 }
2551 sweep(false);
2552 assert(_collectorState == Resizing, "Incorrect state");
2553 break;
2554 case Resizing: {
2555 // Sweeping has been completed; the actual resize in this case
2556 // is done separately; nothing to be done in this state.
2557 _collectorState = Resetting;
2558 break;
2559 }
2560 case Resetting:
2561 // The heap has been resized.
2562 if (VerifyDuringGC &&
2563 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2564 Universe::verify("Verify before reset: ");
2565 }
2566 save_heap_summary();
2567 reset(false);
2568 assert(_collectorState == Idling, "Collector state should "
2569 "have changed");
2570 break;
2571 case Precleaning:
2572 case AbortablePreclean:
2573 // Elide the preclean phase
2574 _collectorState = FinalMarking;
2575 break;
2576 default:
2577 ShouldNotReachHere();
2578 }
2579 if (TraceCMSState) {
2580 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2581 Thread::current(), _collectorState);
2582 }
2583 }
2584
2585 if (VerifyAfterGC &&
2586 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2587 Universe::verify();
2588 }
2589 if (TraceCMSState) {
2590 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2591 " exiting collection CMS state %d",
2592 Thread::current(), _collectorState);
2593 }
2594 }
2595
2596 bool CMSCollector::waitForForegroundGC() {
2597 bool res = false;
2598 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2599 "CMS thread should have CMS token");
2600 // Block the foreground collector until the
2601 // background collectors decides whether to
2602 // yield.
2603 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2604 _foregroundGCShouldWait = true;
2605 if (_foregroundGCIsActive) {
2606 // The background collector yields to the
2607 // foreground collector and returns a value
2608 // indicating that it has yielded. The foreground
2609 // collector can proceed.
2610 res = true;
2611 _foregroundGCShouldWait = false;
2612 ConcurrentMarkSweepThread::clear_CMS_flag(
2613 ConcurrentMarkSweepThread::CMS_cms_has_token);
2614 ConcurrentMarkSweepThread::set_CMS_flag(
2615 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2616 // Get a possibly blocked foreground thread going
2617 CGC_lock->notify();
2618 if (TraceCMSState) {
2619 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2620 Thread::current(), _collectorState);
2621 }
2622 while (_foregroundGCIsActive) {
2623 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2624 }
2625 ConcurrentMarkSweepThread::set_CMS_flag(
2626 ConcurrentMarkSweepThread::CMS_cms_has_token);
2627 ConcurrentMarkSweepThread::clear_CMS_flag(
2628 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2629 }
2630 if (TraceCMSState) {
2631 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2632 Thread::current(), _collectorState);
2633 }
2634 return res;
2635 }
2636
2637 // Because of the need to lock the free lists and other structures in
2638 // the collector, common to all the generations that the collector is
2639 // collecting, we need the gc_prologues of individual CMS generations
2640 // delegate to their collector. It may have been simpler had the
2641 // current infrastructure allowed one to call a prologue on a
2642 // collector. In the absence of that we have the generation's
2643 // prologue delegate to the collector, which delegates back
2644 // some "local" work to a worker method in the individual generations
2645 // that it's responsible for collecting, while itself doing any
2646 // work common to all generations it's responsible for. A similar
2647 // comment applies to the gc_epilogue()'s.
2648 // The role of the variable _between_prologue_and_epilogue is to
2649 // enforce the invocation protocol.
2650 void CMSCollector::gc_prologue(bool full) {
2651 // Call gc_prologue_work() for the CMSGen
2652 // we are responsible for.
2653
2654 // The following locking discipline assumes that we are only called
2655 // when the world is stopped.
2656 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2657
2658 // The CMSCollector prologue must call the gc_prologues for the
2659 // "generations" that it's responsible
2660 // for.
2661
2662 assert( Thread::current()->is_VM_thread()
2663 || ( CMSScavengeBeforeRemark
2664 && Thread::current()->is_ConcurrentGC_thread()),
2665 "Incorrect thread type for prologue execution");
2666
2667 if (_between_prologue_and_epilogue) {
2668 // We have already been invoked; this is a gc_prologue delegation
2669 // from yet another CMS generation that we are responsible for, just
2670 // ignore it since all relevant work has already been done.
2671 return;
2672 }
2673
2674 // set a bit saying prologue has been called; cleared in epilogue
2675 _between_prologue_and_epilogue = true;
2676 // Claim locks for common data structures, then call gc_prologue_work()
2677 // for each CMSGen.
2678
2679 getFreelistLocks(); // gets free list locks on constituent spaces
2680 bitMapLock()->lock_without_safepoint_check();
2681
2682 // Should call gc_prologue_work() for all cms gens we are responsible for
2683 bool duringMarking = _collectorState >= Marking
2684 && _collectorState < Sweeping;
2685
2686 // The young collections clear the modified oops state, which tells if
2687 // there are any modified oops in the class. The remark phase also needs
2688 // that information. Tell the young collection to save the union of all
2689 // modified klasses.
2690 if (duringMarking) {
2691 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2692 }
2693
2694 bool registerClosure = duringMarking;
2695
2696 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2697 &_modUnionClosurePar
2698 : &_modUnionClosure;
2699 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2700
2701 if (!full) {
2702 stats().record_gc0_begin();
2703 }
2704 }
2705
2706 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2707
2708 _capacity_at_prologue = capacity();
2709 _used_at_prologue = used();
2710
2711 // Delegate to CMScollector which knows how to coordinate between
2712 // this and any other CMS generations that it is responsible for
2713 // collecting.
2714 collector()->gc_prologue(full);
2715 }
2716
2717 // This is a "private" interface for use by this generation's CMSCollector.
2718 // Not to be called directly by any other entity (for instance,
2719 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2720 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2721 bool registerClosure, ModUnionClosure* modUnionClosure) {
2722 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2723 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2724 "Should be NULL");
2725 if (registerClosure) {
2726 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2727 }
2728 cmsSpace()->gc_prologue();
2729 // Clear stat counters
2730 NOT_PRODUCT(
2731 assert(_numObjectsPromoted == 0, "check");
2732 assert(_numWordsPromoted == 0, "check");
2733 if (Verbose && PrintGC) {
2734 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2735 SIZE_FORMAT" bytes concurrently",
2736 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2737 }
2738 _numObjectsAllocated = 0;
2739 _numWordsAllocated = 0;
2740 )
2741 }
2742
2743 void CMSCollector::gc_epilogue(bool full) {
2744 // The following locking discipline assumes that we are only called
2745 // when the world is stopped.
2746 assert(SafepointSynchronize::is_at_safepoint(),
2747 "world is stopped assumption");
2748
2749 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2750 // if linear allocation blocks need to be appropriately marked to allow the
2751 // the blocks to be parsable. We also check here whether we need to nudge the
2752 // CMS collector thread to start a new cycle (if it's not already active).
2753 assert( Thread::current()->is_VM_thread()
2754 || ( CMSScavengeBeforeRemark
2755 && Thread::current()->is_ConcurrentGC_thread()),
2756 "Incorrect thread type for epilogue execution");
2757
2758 if (!_between_prologue_and_epilogue) {
2759 // We have already been invoked; this is a gc_epilogue delegation
2760 // from yet another CMS generation that we are responsible for, just
2761 // ignore it since all relevant work has already been done.
2762 return;
2763 }
2764 assert(haveFreelistLocks(), "must have freelist locks");
2765 assert_lock_strong(bitMapLock());
2766
2767 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2768
2769 _cmsGen->gc_epilogue_work(full);
2770
2771 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2772 // in case sampling was not already enabled, enable it
2773 _start_sampling = true;
2774 }
2775 // reset _eden_chunk_array so sampling starts afresh
2776 _eden_chunk_index = 0;
2777
2778 size_t cms_used = _cmsGen->cmsSpace()->used();
2779
2780 // update performance counters - this uses a special version of
2781 // update_counters() that allows the utilization to be passed as a
2782 // parameter, avoiding multiple calls to used().
2783 //
2784 _cmsGen->update_counters(cms_used);
2785
2786 if (CMSIncrementalMode) {
2787 icms_update_allocation_limits();
2788 }
2789
2790 bitMapLock()->unlock();
2791 releaseFreelistLocks();
2792
2793 if (!CleanChunkPoolAsync) {
2794 Chunk::clean_chunk_pool();
2795 }
2796
2797 set_did_compact(false);
2798 _between_prologue_and_epilogue = false; // ready for next cycle
2799 }
2800
2801 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2802 collector()->gc_epilogue(full);
2803
2804 // Also reset promotion tracking in par gc thread states.
2805 if (CollectedHeap::use_parallel_gc_threads()) {
2806 for (uint i = 0; i < ParallelGCThreads; i++) {
2807 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2808 }
2809 }
2810 }
2811
2812 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2813 assert(!incremental_collection_failed(), "Should have been cleared");
2814 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2815 cmsSpace()->gc_epilogue();
2816 // Print stat counters
2817 NOT_PRODUCT(
2818 assert(_numObjectsAllocated == 0, "check");
2819 assert(_numWordsAllocated == 0, "check");
2820 if (Verbose && PrintGC) {
2821 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2822 SIZE_FORMAT" bytes",
2823 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2824 }
2825 _numObjectsPromoted = 0;
2826 _numWordsPromoted = 0;
2827 )
2828
2829 if (PrintGC && Verbose) {
2830 // Call down the chain in contiguous_available needs the freelistLock
2831 // so print this out before releasing the freeListLock.
2832 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2833 contiguous_available());
2834 }
2835 }
2836
2837 #ifndef PRODUCT
2838 bool CMSCollector::have_cms_token() {
2839 Thread* thr = Thread::current();
2840 if (thr->is_VM_thread()) {
2841 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2842 } else if (thr->is_ConcurrentGC_thread()) {
2843 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2844 } else if (thr->is_GC_task_thread()) {
2845 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2846 ParGCRareEvent_lock->owned_by_self();
2847 }
2848 return false;
2849 }
2850 #endif
2851
2852 // Check reachability of the given heap address in CMS generation,
2853 // treating all other generations as roots.
2854 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2855 // We could "guarantee" below, rather than assert, but I'll
2856 // leave these as "asserts" so that an adventurous debugger
2857 // could try this in the product build provided some subset of
2858 // the conditions were met, provided they were interested in the
2859 // results and knew that the computation below wouldn't interfere
2860 // with other concurrent computations mutating the structures
2861 // being read or written.
2862 assert(SafepointSynchronize::is_at_safepoint(),
2863 "Else mutations in object graph will make answer suspect");
2864 assert(have_cms_token(), "Should hold cms token");
2865 assert(haveFreelistLocks(), "must hold free list locks");
2866 assert_lock_strong(bitMapLock());
2867
2868 // Clear the marking bit map array before starting, but, just
2869 // for kicks, first report if the given address is already marked
2870 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2871 _markBitMap.isMarked(addr) ? "" : " not");
2872
2873 if (verify_after_remark()) {
2874 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2875 bool result = verification_mark_bm()->isMarked(addr);
2876 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2877 result ? "IS" : "is NOT");
2878 return result;
2879 } else {
2880 gclog_or_tty->print_cr("Could not compute result");
2881 return false;
2882 }
2883 }
2884
2885
2886 void
2887 CMSCollector::print_on_error(outputStream* st) {
2888 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2889 if (collector != NULL) {
2890 CMSBitMap* bitmap = &collector->_markBitMap;
2891 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2892 bitmap->print_on_error(st, " Bits: ");
2893
2894 st->cr();
2895
2896 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2897 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2898 mut_bitmap->print_on_error(st, " Bits: ");
2899 }
2900 }
2901
2902 ////////////////////////////////////////////////////////
2903 // CMS Verification Support
2904 ////////////////////////////////////////////////////////
2905 // Following the remark phase, the following invariant
2906 // should hold -- each object in the CMS heap which is
2907 // marked in markBitMap() should be marked in the verification_mark_bm().
2908
2909 class VerifyMarkedClosure: public BitMapClosure {
2910 CMSBitMap* _marks;
2911 bool _failed;
2912
2913 public:
2914 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2915
2916 bool do_bit(size_t offset) {
2917 HeapWord* addr = _marks->offsetToHeapWord(offset);
2918 if (!_marks->isMarked(addr)) {
2919 oop(addr)->print_on(gclog_or_tty);
2920 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2921 _failed = true;
2922 }
2923 return true;
2924 }
2925
2926 bool failed() { return _failed; }
2927 };
2928
2929 bool CMSCollector::verify_after_remark(bool silent) {
2930 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2931 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2932 static bool init = false;
2933
2934 assert(SafepointSynchronize::is_at_safepoint(),
2935 "Else mutations in object graph will make answer suspect");
2936 assert(have_cms_token(),
2937 "Else there may be mutual interference in use of "
2938 " verification data structures");
2939 assert(_collectorState > Marking && _collectorState <= Sweeping,
2940 "Else marking info checked here may be obsolete");
2941 assert(haveFreelistLocks(), "must hold free list locks");
2942 assert_lock_strong(bitMapLock());
2943
2944
2945 // Allocate marking bit map if not already allocated
2946 if (!init) { // first time
2947 if (!verification_mark_bm()->allocate(_span)) {
2948 return false;
2949 }
2950 init = true;
2951 }
2952
2953 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2954
2955 // Turn off refs discovery -- so we will be tracing through refs.
2956 // This is as intended, because by this time
2957 // GC must already have cleared any refs that need to be cleared,
2958 // and traced those that need to be marked; moreover,
2959 // the marking done here is not going to interfere in any
2960 // way with the marking information used by GC.
2961 NoRefDiscovery no_discovery(ref_processor());
2962
2963 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2964
2965 // Clear any marks from a previous round
2966 verification_mark_bm()->clear_all();
2967 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2968 verify_work_stacks_empty();
2969
2970 GenCollectedHeap* gch = GenCollectedHeap::heap();
2971 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2972 // Update the saved marks which may affect the root scans.
2973 gch->save_marks();
2974
2975 if (CMSRemarkVerifyVariant == 1) {
2976 // In this first variant of verification, we complete
2977 // all marking, then check if the new marks-vector is
2978 // a subset of the CMS marks-vector.
2979 verify_after_remark_work_1();
2980 } else if (CMSRemarkVerifyVariant == 2) {
2981 // In this second variant of verification, we flag an error
2982 // (i.e. an object reachable in the new marks-vector not reachable
2983 // in the CMS marks-vector) immediately, also indicating the
2984 // identify of an object (A) that references the unmarked object (B) --
2985 // presumably, a mutation to A failed to be picked up by preclean/remark?
2986 verify_after_remark_work_2();
2987 } else {
2988 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2989 CMSRemarkVerifyVariant);
2990 }
2991 if (!silent) gclog_or_tty->print(" done] ");
2992 return true;
2993 }
2994
2995 void CMSCollector::verify_after_remark_work_1() {
2996 ResourceMark rm;
2997 HandleMark hm;
2998 GenCollectedHeap* gch = GenCollectedHeap::heap();
2999
3000 // Get a clear set of claim bits for the strong roots processing to work with.
3001 ClassLoaderDataGraph::clear_claimed_marks();
3002
3003 // Mark from roots one level into CMS
3004 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3005 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3006
3007 gch->gen_process_strong_roots(_cmsGen->level(),
3008 true, // younger gens are roots
3009 true, // activate StrongRootsScope
3010 SharedHeap::ScanningOption(roots_scanning_options()),
3011 ¬Older,
3012 NULL,
3013 NULL); // SSS: Provide correct closure
3014
3015 // Now mark from the roots
3016 MarkFromRootsClosure markFromRootsClosure(this, _span,
3017 verification_mark_bm(), verification_mark_stack(),
3018 false /* don't yield */, true /* verifying */);
3019 assert(_restart_addr == NULL, "Expected pre-condition");
3020 verification_mark_bm()->iterate(&markFromRootsClosure);
3021 while (_restart_addr != NULL) {
3022 // Deal with stack overflow: by restarting at the indicated
3023 // address.
3024 HeapWord* ra = _restart_addr;
3025 markFromRootsClosure.reset(ra);
3026 _restart_addr = NULL;
3027 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3028 }
3029 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3030 verify_work_stacks_empty();
3031
3032 // Marking completed -- now verify that each bit marked in
3033 // verification_mark_bm() is also marked in markBitMap(); flag all
3034 // errors by printing corresponding objects.
3035 VerifyMarkedClosure vcl(markBitMap());
3036 verification_mark_bm()->iterate(&vcl);
3037 if (vcl.failed()) {
3038 gclog_or_tty->print("Verification failed");
3039 Universe::heap()->print_on(gclog_or_tty);
3040 fatal("CMS: failed marking verification after remark");
3041 }
3042 }
3043
3044 class VerifyKlassOopsKlassClosure : public KlassClosure {
3045 class VerifyKlassOopsClosure : public OopClosure {
3046 CMSBitMap* _bitmap;
3047 public:
3048 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3049 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3050 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3051 } _oop_closure;
3052 public:
3053 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3054 void do_klass(Klass* k) {
3055 k->oops_do(&_oop_closure);
3056 }
3057 };
3058
3059 void CMSCollector::verify_after_remark_work_2() {
3060 ResourceMark rm;
3061 HandleMark hm;
3062 GenCollectedHeap* gch = GenCollectedHeap::heap();
3063
3064 // Get a clear set of claim bits for the strong roots processing to work with.
3065 ClassLoaderDataGraph::clear_claimed_marks();
3066
3067 // Mark from roots one level into CMS
3068 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3069 markBitMap());
3070 KlassToOopClosure klass_closure(¬Older);
3071
3072 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3073 gch->gen_process_strong_roots(_cmsGen->level(),
3074 true, // younger gens are roots
3075 true, // activate StrongRootsScope
3076 SharedHeap::ScanningOption(roots_scanning_options()),
3077 ¬Older,
3078 NULL,
3079 &klass_closure);
3080
3081 // Now mark from the roots
3082 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3083 verification_mark_bm(), markBitMap(), verification_mark_stack());
3084 assert(_restart_addr == NULL, "Expected pre-condition");
3085 verification_mark_bm()->iterate(&markFromRootsClosure);
3086 while (_restart_addr != NULL) {
3087 // Deal with stack overflow: by restarting at the indicated
3088 // address.
3089 HeapWord* ra = _restart_addr;
3090 markFromRootsClosure.reset(ra);
3091 _restart_addr = NULL;
3092 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3093 }
3094 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3095 verify_work_stacks_empty();
3096
3097 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3098 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3099
3100 // Marking completed -- now verify that each bit marked in
3101 // verification_mark_bm() is also marked in markBitMap(); flag all
3102 // errors by printing corresponding objects.
3103 VerifyMarkedClosure vcl(markBitMap());
3104 verification_mark_bm()->iterate(&vcl);
3105 assert(!vcl.failed(), "Else verification above should not have succeeded");
3106 }
3107
3108 void ConcurrentMarkSweepGeneration::save_marks() {
3109 // delegate to CMS space
3110 cmsSpace()->save_marks();
3111 for (uint i = 0; i < ParallelGCThreads; i++) {
3112 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3113 }
3114 }
3115
3116 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3117 return cmsSpace()->no_allocs_since_save_marks();
3118 }
3119
3120 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3121 \
3122 void ConcurrentMarkSweepGeneration:: \
3123 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3124 cl->set_generation(this); \
3125 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3126 cl->reset_generation(); \
3127 save_marks(); \
3128 }
3129
3130 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3131
3132 void
3133 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3134 cl->set_generation(this);
3135 younger_refs_in_space_iterate(_cmsSpace, cl);
3136 cl->reset_generation();
3137 }
3138
3139 void
3140 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3141 if (freelistLock()->owned_by_self()) {
3142 Generation::oop_iterate(cl);
3143 } else {
3144 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3145 Generation::oop_iterate(cl);
3146 }
3147 }
3148
3149 void
3150 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3151 if (freelistLock()->owned_by_self()) {
3152 Generation::object_iterate(cl);
3153 } else {
3154 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3155 Generation::object_iterate(cl);
3156 }
3157 }
3158
3159 void
3160 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3161 if (freelistLock()->owned_by_self()) {
3162 Generation::safe_object_iterate(cl);
3163 } else {
3164 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3165 Generation::safe_object_iterate(cl);
3166 }
3167 }
3168
3169 void
3170 ConcurrentMarkSweepGeneration::post_compact() {
3171 }
3172
3173 void
3174 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3175 // Fix the linear allocation blocks to look like free blocks.
3176
3177 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3178 // are not called when the heap is verified during universe initialization and
3179 // at vm shutdown.
3180 if (freelistLock()->owned_by_self()) {
3181 cmsSpace()->prepare_for_verify();
3182 } else {
3183 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3184 cmsSpace()->prepare_for_verify();
3185 }
3186 }
3187
3188 void
3189 ConcurrentMarkSweepGeneration::verify() {
3190 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3191 // are not called when the heap is verified during universe initialization and
3192 // at vm shutdown.
3193 if (freelistLock()->owned_by_self()) {
3194 cmsSpace()->verify();
3195 } else {
3196 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3197 cmsSpace()->verify();
3198 }
3199 }
3200
3201 void CMSCollector::verify() {
3202 _cmsGen->verify();
3203 }
3204
3205 #ifndef PRODUCT
3206 bool CMSCollector::overflow_list_is_empty() const {
3207 assert(_num_par_pushes >= 0, "Inconsistency");
3208 if (_overflow_list == NULL) {
3209 assert(_num_par_pushes == 0, "Inconsistency");
3210 }
3211 return _overflow_list == NULL;
3212 }
3213
3214 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3215 // merely consolidate assertion checks that appear to occur together frequently.
3216 void CMSCollector::verify_work_stacks_empty() const {
3217 assert(_markStack.isEmpty(), "Marking stack should be empty");
3218 assert(overflow_list_is_empty(), "Overflow list should be empty");
3219 }
3220
3221 void CMSCollector::verify_overflow_empty() const {
3222 assert(overflow_list_is_empty(), "Overflow list should be empty");
3223 assert(no_preserved_marks(), "No preserved marks");
3224 }
3225 #endif // PRODUCT
3226
3227 // Decide if we want to enable class unloading as part of the
3228 // ensuing concurrent GC cycle. We will collect and
3229 // unload classes if it's the case that:
3230 // (1) an explicit gc request has been made and the flag
3231 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3232 // (2) (a) class unloading is enabled at the command line, and
3233 // (b) old gen is getting really full
3234 // NOTE: Provided there is no change in the state of the heap between
3235 // calls to this method, it should have idempotent results. Moreover,
3236 // its results should be monotonically increasing (i.e. going from 0 to 1,
3237 // but not 1 to 0) between successive calls between which the heap was
3238 // not collected. For the implementation below, it must thus rely on
3239 // the property that concurrent_cycles_since_last_unload()
3240 // will not decrease unless a collection cycle happened and that
3241 // _cmsGen->is_too_full() are
3242 // themselves also monotonic in that sense. See check_monotonicity()
3243 // below.
3244 void CMSCollector::update_should_unload_classes() {
3245 _should_unload_classes = false;
3246 // Condition 1 above
3247 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3248 _should_unload_classes = true;
3249 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3250 // Disjuncts 2.b.(i,ii,iii) above
3251 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3252 CMSClassUnloadingMaxInterval)
3253 || _cmsGen->is_too_full();
3254 }
3255 }
3256
3257 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3258 bool res = should_concurrent_collect();
3259 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3260 return res;
3261 }
3262
3263 void CMSCollector::setup_cms_unloading_and_verification_state() {
3264 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3265 || VerifyBeforeExit;
3266 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_AllCodeCache;
3267
3268 // We set the proper root for this CMS cycle here.
3269 if (should_unload_classes()) { // Should unload classes this cycle
3270 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3271 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3272 remove_root_scanning_option(rso); // Shrink the root set appropriately
3273 set_verifying(should_verify); // Set verification state for this cycle
3274 return; // Nothing else needs to be done at this time
3275 }
3276
3277 // Not unloading classes this cycle
3278 assert(!should_unload_classes(), "Inconsistency!");
3279 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3280 add_root_scanning_option(SharedHeap::SO_AllClasses);
3281
3282 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3283 // Include symbols, strings and code cache elements to prevent their resurrection.
3284 add_root_scanning_option(rso);
3285 set_verifying(true);
3286 } else if (verifying() && !should_verify) {
3287 // We were verifying, but some verification flags got disabled.
3288 set_verifying(false);
3289 // Exclude symbols, strings and code cache elements from root scanning to
3290 // reduce IM and RM pauses.
3291 remove_root_scanning_option(rso);
3292 }
3293 }
3294
3295
3296 #ifndef PRODUCT
3297 HeapWord* CMSCollector::block_start(const void* p) const {
3298 const HeapWord* addr = (HeapWord*)p;
3299 if (_span.contains(p)) {
3300 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3301 return _cmsGen->cmsSpace()->block_start(p);
3302 }
3303 }
3304 return NULL;
3305 }
3306 #endif
3307
3308 HeapWord*
3309 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3310 bool tlab,
3311 bool parallel) {
3312 CMSSynchronousYieldRequest yr;
3313 assert(!tlab, "Can't deal with TLAB allocation");
3314 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3315 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3316 CMSExpansionCause::_satisfy_allocation);
3317 if (GCExpandToAllocateDelayMillis > 0) {
3318 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3319 }
3320 return have_lock_and_allocate(word_size, tlab);
3321 }
3322
3323 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3324 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3325 // to CardGeneration and share it...
3326 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3327 return CardGeneration::expand(bytes, expand_bytes);
3328 }
3329
3330 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3331 CMSExpansionCause::Cause cause)
3332 {
3333
3334 bool success = expand(bytes, expand_bytes);
3335
3336 // remember why we expanded; this information is used
3337 // by shouldConcurrentCollect() when making decisions on whether to start
3338 // a new CMS cycle.
3339 if (success) {
3340 set_expansion_cause(cause);
3341 if (PrintGCDetails && Verbose) {
3342 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3343 CMSExpansionCause::to_string(cause));
3344 }
3345 }
3346 }
3347
3348 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3349 HeapWord* res = NULL;
3350 MutexLocker x(ParGCRareEvent_lock);
3351 while (true) {
3352 // Expansion by some other thread might make alloc OK now:
3353 res = ps->lab.alloc(word_sz);
3354 if (res != NULL) return res;
3355 // If there's not enough expansion space available, give up.
3356 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3357 return NULL;
3358 }
3359 // Otherwise, we try expansion.
3360 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3361 CMSExpansionCause::_allocate_par_lab);
3362 // Now go around the loop and try alloc again;
3363 // A competing par_promote might beat us to the expansion space,
3364 // so we may go around the loop again if promotion fails again.
3365 if (GCExpandToAllocateDelayMillis > 0) {
3366 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3367 }
3368 }
3369 }
3370
3371
3372 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3373 PromotionInfo* promo) {
3374 MutexLocker x(ParGCRareEvent_lock);
3375 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3376 while (true) {
3377 // Expansion by some other thread might make alloc OK now:
3378 if (promo->ensure_spooling_space()) {
3379 assert(promo->has_spooling_space(),
3380 "Post-condition of successful ensure_spooling_space()");
3381 return true;
3382 }
3383 // If there's not enough expansion space available, give up.
3384 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3385 return false;
3386 }
3387 // Otherwise, we try expansion.
3388 expand(refill_size_bytes, MinHeapDeltaBytes,
3389 CMSExpansionCause::_allocate_par_spooling_space);
3390 // Now go around the loop and try alloc again;
3391 // A competing allocation might beat us to the expansion space,
3392 // so we may go around the loop again if allocation fails again.
3393 if (GCExpandToAllocateDelayMillis > 0) {
3394 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3395 }
3396 }
3397 }
3398
3399
3400 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3401 assert_locked_or_safepoint(ExpandHeap_lock);
3402 // Shrink committed space
3403 _virtual_space.shrink_by(bytes);
3404 // Shrink space; this also shrinks the space's BOT
3405 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3406 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3407 // Shrink the shared block offset array
3408 _bts->resize(new_word_size);
3409 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3410 // Shrink the card table
3411 Universe::heap()->barrier_set()->resize_covered_region(mr);
3412
3413 if (Verbose && PrintGC) {
3414 size_t new_mem_size = _virtual_space.committed_size();
3415 size_t old_mem_size = new_mem_size + bytes;
3416 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3417 name(), old_mem_size/K, new_mem_size/K);
3418 }
3419 }
3420
3421 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3422 assert_locked_or_safepoint(Heap_lock);
3423 size_t size = ReservedSpace::page_align_size_down(bytes);
3424 // Only shrink if a compaction was done so that all the free space
3425 // in the generation is in a contiguous block at the end.
3426 if (size > 0 && did_compact()) {
3427 shrink_by(size);
3428 }
3429 }
3430
3431 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3432 assert_locked_or_safepoint(Heap_lock);
3433 bool result = _virtual_space.expand_by(bytes);
3434 if (result) {
3435 size_t new_word_size =
3436 heap_word_size(_virtual_space.committed_size());
3437 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3438 _bts->resize(new_word_size); // resize the block offset shared array
3439 Universe::heap()->barrier_set()->resize_covered_region(mr);
3440 // Hmmmm... why doesn't CFLS::set_end verify locking?
3441 // This is quite ugly; FIX ME XXX
3442 _cmsSpace->assert_locked(freelistLock());
3443 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3444
3445 // update the space and generation capacity counters
3446 if (UsePerfData) {
3447 _space_counters->update_capacity();
3448 _gen_counters->update_all();
3449 }
3450
3451 if (Verbose && PrintGC) {
3452 size_t new_mem_size = _virtual_space.committed_size();
3453 size_t old_mem_size = new_mem_size - bytes;
3454 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3455 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3456 }
3457 }
3458 return result;
3459 }
3460
3461 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3462 assert_locked_or_safepoint(Heap_lock);
3463 bool success = true;
3464 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3465 if (remaining_bytes > 0) {
3466 success = grow_by(remaining_bytes);
3467 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3468 }
3469 return success;
3470 }
3471
3472 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3473 assert_locked_or_safepoint(Heap_lock);
3474 assert_lock_strong(freelistLock());
3475 if (PrintGCDetails && Verbose) {
3476 warning("Shrinking of CMS not yet implemented");
3477 }
3478 return;
3479 }
3480
3481
3482 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3483 // phases.
3484 class CMSPhaseAccounting: public StackObj {
3485 public:
3486 CMSPhaseAccounting(CMSCollector *collector,
3487 const char *phase,
3488 const GCId gc_id,
3489 bool print_cr = true);
3490 ~CMSPhaseAccounting();
3491
3492 private:
3493 CMSCollector *_collector;
3494 const char *_phase;
3495 elapsedTimer _wallclock;
3496 bool _print_cr;
3497 const GCId _gc_id;
3498
3499 public:
3500 // Not MT-safe; so do not pass around these StackObj's
3501 // where they may be accessed by other threads.
3502 jlong wallclock_millis() {
3503 assert(_wallclock.is_active(), "Wall clock should not stop");
3504 _wallclock.stop(); // to record time
3505 jlong ret = _wallclock.milliseconds();
3506 _wallclock.start(); // restart
3507 return ret;
3508 }
3509 };
3510
3511 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3512 const char *phase,
3513 const GCId gc_id,
3514 bool print_cr) :
3515 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3516
3517 if (PrintCMSStatistics != 0) {
3518 _collector->resetYields();
3519 }
3520 if (PrintGCDetails) {
3521 gclog_or_tty->gclog_stamp(_gc_id);
3522 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3523 _collector->cmsGen()->short_name(), _phase);
3524 }
3525 _collector->resetTimer();
3526 _wallclock.start();
3527 _collector->startTimer();
3528 }
3529
3530 CMSPhaseAccounting::~CMSPhaseAccounting() {
3531 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3532 _collector->stopTimer();
3533 _wallclock.stop();
3534 if (PrintGCDetails) {
3535 gclog_or_tty->gclog_stamp(_gc_id);
3536 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3537 _collector->cmsGen()->short_name(),
3538 _phase, _collector->timerValue(), _wallclock.seconds());
3539 if (_print_cr) {
3540 gclog_or_tty->cr();
3541 }
3542 if (PrintCMSStatistics != 0) {
3543 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3544 _collector->yields());
3545 }
3546 }
3547 }
3548
3549 // CMS work
3550
3551 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3552 class CMSParMarkTask : public AbstractGangTask {
3553 protected:
3554 CMSCollector* _collector;
3555 int _n_workers;
3556 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3557 AbstractGangTask(name),
3558 _collector(collector),
3559 _n_workers(n_workers) {}
3560 // Work method in support of parallel rescan ... of young gen spaces
3561 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3562 ContiguousSpace* space,
3563 HeapWord** chunk_array, size_t chunk_top);
3564 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3565 };
3566
3567 // Parallel initial mark task
3568 class CMSParInitialMarkTask: public CMSParMarkTask {
3569 public:
3570 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3571 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3572 collector, n_workers) {}
3573 void work(uint worker_id);
3574 };
3575
3576 // Checkpoint the roots into this generation from outside
3577 // this generation. [Note this initial checkpoint need only
3578 // be approximate -- we'll do a catch up phase subsequently.]
3579 void CMSCollector::checkpointRootsInitial(bool asynch) {
3580 assert(_collectorState == InitialMarking, "Wrong collector state");
3581 check_correct_thread_executing();
3582 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3583
3584 save_heap_summary();
3585 report_heap_summary(GCWhen::BeforeGC);
3586
3587 ReferenceProcessor* rp = ref_processor();
3588 SpecializationStats::clear();
3589 assert(_restart_addr == NULL, "Control point invariant");
3590 if (asynch) {
3591 // acquire locks for subsequent manipulations
3592 MutexLockerEx x(bitMapLock(),
3593 Mutex::_no_safepoint_check_flag);
3594 checkpointRootsInitialWork(asynch);
3595 // enable ("weak") refs discovery
3596 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3597 _collectorState = Marking;
3598 } else {
3599 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3600 // which recognizes if we are a CMS generation, and doesn't try to turn on
3601 // discovery; verify that they aren't meddling.
3602 assert(!rp->discovery_is_atomic(),
3603 "incorrect setting of discovery predicate");
3604 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3605 "ref discovery for this generation kind");
3606 // already have locks
3607 checkpointRootsInitialWork(asynch);
3608 // now enable ("weak") refs discovery
3609 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3610 _collectorState = Marking;
3611 }
3612 SpecializationStats::print();
3613 }
3614
3615 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3616 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3617 assert(_collectorState == InitialMarking, "just checking");
3618
3619 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3620 // precede our marking with a collection of all
3621 // younger generations to keep floating garbage to a minimum.
3622 // XXX: we won't do this for now -- it's an optimization to be done later.
3623
3624 // already have locks
3625 assert_lock_strong(bitMapLock());
3626 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3627
3628 // Setup the verification and class unloading state for this
3629 // CMS collection cycle.
3630 setup_cms_unloading_and_verification_state();
3631
3632 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3633 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3634
3635 // Reset all the PLAB chunk arrays if necessary.
3636 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3637 reset_survivor_plab_arrays();
3638 }
3639
3640 ResourceMark rm;
3641 HandleMark hm;
3642
3643 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3644 GenCollectedHeap* gch = GenCollectedHeap::heap();
3645
3646 verify_work_stacks_empty();
3647 verify_overflow_empty();
3648
3649 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3650 // Update the saved marks which may affect the root scans.
3651 gch->save_marks();
3652
3653 // weak reference processing has not started yet.
3654 ref_processor()->set_enqueuing_is_done(false);
3655
3656 // Need to remember all newly created CLDs,
3657 // so that we can guarantee that the remark finds them.
3658 ClassLoaderDataGraph::remember_new_clds(true);
3659
3660 // Whenever a CLD is found, it will be claimed before proceeding to mark
3661 // the klasses. The claimed marks need to be cleared before marking starts.
3662 ClassLoaderDataGraph::clear_claimed_marks();
3663
3664 if (CMSPrintEdenSurvivorChunks) {
3665 print_eden_and_survivor_chunk_arrays();
3666 }
3667
3668 {
3669 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3670 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3671 // The parallel version.
3672 FlexibleWorkGang* workers = gch->workers();
3673 assert(workers != NULL, "Need parallel worker threads.");
3674 int n_workers = workers->active_workers();
3675 CMSParInitialMarkTask tsk(this, n_workers);
3676 gch->set_par_threads(n_workers);
3677 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3678 if (n_workers > 1) {
3679 GenCollectedHeap::StrongRootsScope srs(gch);
3680 workers->run_task(&tsk);
3681 } else {
3682 GenCollectedHeap::StrongRootsScope srs(gch);
3683 tsk.work(0);
3684 }
3685 gch->set_par_threads(0);
3686 } else {
3687 // The serial version.
3688 KlassToOopClosure klass_closure(¬Older);
3689 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3690 gch->gen_process_strong_roots(_cmsGen->level(),
3691 true, // younger gens are roots
3692 true, // activate StrongRootsScope
3693 SharedHeap::ScanningOption(roots_scanning_options()),
3694 ¬Older,
3695 NULL,
3696 &klass_closure);
3697 }
3698 }
3699
3700 // Clear mod-union table; it will be dirtied in the prologue of
3701 // CMS generation per each younger generation collection.
3702
3703 assert(_modUnionTable.isAllClear(),
3704 "Was cleared in most recent final checkpoint phase"
3705 " or no bits are set in the gc_prologue before the start of the next "
3706 "subsequent marking phase.");
3707
3708 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3709
3710 // Save the end of the used_region of the constituent generations
3711 // to be used to limit the extent of sweep in each generation.
3712 save_sweep_limits();
3713 verify_overflow_empty();
3714 }
3715
3716 bool CMSCollector::markFromRoots(bool asynch) {
3717 // we might be tempted to assert that:
3718 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3719 // "inconsistent argument?");
3720 // However that wouldn't be right, because it's possible that
3721 // a safepoint is indeed in progress as a younger generation
3722 // stop-the-world GC happens even as we mark in this generation.
3723 assert(_collectorState == Marking, "inconsistent state?");
3724 check_correct_thread_executing();
3725 verify_overflow_empty();
3726
3727 bool res;
3728 if (asynch) {
3729 // Weak ref discovery note: We may be discovering weak
3730 // refs in this generation concurrent (but interleaved) with
3731 // weak ref discovery by a younger generation collector.
3732
3733 CMSTokenSyncWithLocks ts(true, bitMapLock());
3734 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3735 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3736 res = markFromRootsWork(asynch);
3737 if (res) {
3738 _collectorState = Precleaning;
3739 } else { // We failed and a foreground collection wants to take over
3740 assert(_foregroundGCIsActive, "internal state inconsistency");
3741 assert(_restart_addr == NULL, "foreground will restart from scratch");
3742 if (PrintGCDetails) {
3743 gclog_or_tty->print_cr("bailing out to foreground collection");
3744 }
3745 }
3746 } else {
3747 assert(SafepointSynchronize::is_at_safepoint(),
3748 "inconsistent with asynch == false");
3749 // already have locks
3750 res = markFromRootsWork(asynch);
3751 _collectorState = FinalMarking;
3752 }
3753 verify_overflow_empty();
3754 return res;
3755 }
3756
3757 bool CMSCollector::markFromRootsWork(bool asynch) {
3758 // iterate over marked bits in bit map, doing a full scan and mark
3759 // from these roots using the following algorithm:
3760 // . if oop is to the right of the current scan pointer,
3761 // mark corresponding bit (we'll process it later)
3762 // . else (oop is to left of current scan pointer)
3763 // push oop on marking stack
3764 // . drain the marking stack
3765
3766 // Note that when we do a marking step we need to hold the
3767 // bit map lock -- recall that direct allocation (by mutators)
3768 // and promotion (by younger generation collectors) is also
3769 // marking the bit map. [the so-called allocate live policy.]
3770 // Because the implementation of bit map marking is not
3771 // robust wrt simultaneous marking of bits in the same word,
3772 // we need to make sure that there is no such interference
3773 // between concurrent such updates.
3774
3775 // already have locks
3776 assert_lock_strong(bitMapLock());
3777
3778 verify_work_stacks_empty();
3779 verify_overflow_empty();
3780 bool result = false;
3781 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3782 result = do_marking_mt(asynch);
3783 } else {
3784 result = do_marking_st(asynch);
3785 }
3786 return result;
3787 }
3788
3789 // Forward decl
3790 class CMSConcMarkingTask;
3791
3792 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3793 CMSCollector* _collector;
3794 CMSConcMarkingTask* _task;
3795 public:
3796 virtual void yield();
3797
3798 // "n_threads" is the number of threads to be terminated.
3799 // "queue_set" is a set of work queues of other threads.
3800 // "collector" is the CMS collector associated with this task terminator.
3801 // "yield" indicates whether we need the gang as a whole to yield.
3802 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3803 ParallelTaskTerminator(n_threads, queue_set),
3804 _collector(collector) { }
3805
3806 void set_task(CMSConcMarkingTask* task) {
3807 _task = task;
3808 }
3809 };
3810
3811 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3812 CMSConcMarkingTask* _task;
3813 public:
3814 bool should_exit_termination();
3815 void set_task(CMSConcMarkingTask* task) {
3816 _task = task;
3817 }
3818 };
3819
3820 // MT Concurrent Marking Task
3821 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3822 CMSCollector* _collector;
3823 int _n_workers; // requested/desired # workers
3824 bool _asynch;
3825 bool _result;
3826 CompactibleFreeListSpace* _cms_space;
3827 char _pad_front[64]; // padding to ...
3828 HeapWord* _global_finger; // ... avoid sharing cache line
3829 char _pad_back[64];
3830 HeapWord* _restart_addr;
3831
3832 // Exposed here for yielding support
3833 Mutex* const _bit_map_lock;
3834
3835 // The per thread work queues, available here for stealing
3836 OopTaskQueueSet* _task_queues;
3837
3838 // Termination (and yielding) support
3839 CMSConcMarkingTerminator _term;
3840 CMSConcMarkingTerminatorTerminator _term_term;
3841
3842 public:
3843 CMSConcMarkingTask(CMSCollector* collector,
3844 CompactibleFreeListSpace* cms_space,
3845 bool asynch,
3846 YieldingFlexibleWorkGang* workers,
3847 OopTaskQueueSet* task_queues):
3848 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3849 _collector(collector),
3850 _cms_space(cms_space),
3851 _asynch(asynch), _n_workers(0), _result(true),
3852 _task_queues(task_queues),
3853 _term(_n_workers, task_queues, _collector),
3854 _bit_map_lock(collector->bitMapLock())
3855 {
3856 _requested_size = _n_workers;
3857 _term.set_task(this);
3858 _term_term.set_task(this);
3859 _restart_addr = _global_finger = _cms_space->bottom();
3860 }
3861
3862
3863 OopTaskQueueSet* task_queues() { return _task_queues; }
3864
3865 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3866
3867 HeapWord** global_finger_addr() { return &_global_finger; }
3868
3869 CMSConcMarkingTerminator* terminator() { return &_term; }
3870
3871 virtual void set_for_termination(int active_workers) {
3872 terminator()->reset_for_reuse(active_workers);
3873 }
3874
3875 void work(uint worker_id);
3876 bool should_yield() {
3877 return ConcurrentMarkSweepThread::should_yield()
3878 && !_collector->foregroundGCIsActive()
3879 && _asynch;
3880 }
3881
3882 virtual void coordinator_yield(); // stuff done by coordinator
3883 bool result() { return _result; }
3884
3885 void reset(HeapWord* ra) {
3886 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3887 _restart_addr = _global_finger = ra;
3888 _term.reset_for_reuse();
3889 }
3890
3891 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3892 OopTaskQueue* work_q);
3893
3894 private:
3895 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3896 void do_work_steal(int i);
3897 void bump_global_finger(HeapWord* f);
3898 };
3899
3900 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3901 assert(_task != NULL, "Error");
3902 return _task->yielding();
3903 // Note that we do not need the disjunct || _task->should_yield() above
3904 // because we want terminating threads to yield only if the task
3905 // is already in the midst of yielding, which happens only after at least one
3906 // thread has yielded.
3907 }
3908
3909 void CMSConcMarkingTerminator::yield() {
3910 if (_task->should_yield()) {
3911 _task->yield();
3912 } else {
3913 ParallelTaskTerminator::yield();
3914 }
3915 }
3916
3917 ////////////////////////////////////////////////////////////////
3918 // Concurrent Marking Algorithm Sketch
3919 ////////////////////////////////////////////////////////////////
3920 // Until all tasks exhausted (both spaces):
3921 // -- claim next available chunk
3922 // -- bump global finger via CAS
3923 // -- find first object that starts in this chunk
3924 // and start scanning bitmap from that position
3925 // -- scan marked objects for oops
3926 // -- CAS-mark target, and if successful:
3927 // . if target oop is above global finger (volatile read)
3928 // nothing to do
3929 // . if target oop is in chunk and above local finger
3930 // then nothing to do
3931 // . else push on work-queue
3932 // -- Deal with possible overflow issues:
3933 // . local work-queue overflow causes stuff to be pushed on
3934 // global (common) overflow queue
3935 // . always first empty local work queue
3936 // . then get a batch of oops from global work queue if any
3937 // . then do work stealing
3938 // -- When all tasks claimed (both spaces)
3939 // and local work queue empty,
3940 // then in a loop do:
3941 // . check global overflow stack; steal a batch of oops and trace
3942 // . try to steal from other threads oif GOS is empty
3943 // . if neither is available, offer termination
3944 // -- Terminate and return result
3945 //
3946 void CMSConcMarkingTask::work(uint worker_id) {
3947 elapsedTimer _timer;
3948 ResourceMark rm;
3949 HandleMark hm;
3950
3951 DEBUG_ONLY(_collector->verify_overflow_empty();)
3952
3953 // Before we begin work, our work queue should be empty
3954 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3955 // Scan the bitmap covering _cms_space, tracing through grey objects.
3956 _timer.start();
3957 do_scan_and_mark(worker_id, _cms_space);
3958 _timer.stop();
3959 if (PrintCMSStatistics != 0) {
3960 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3961 worker_id, _timer.seconds());
3962 // XXX: need xxx/xxx type of notation, two timers
3963 }
3964
3965 // ... do work stealing
3966 _timer.reset();
3967 _timer.start();
3968 do_work_steal(worker_id);
3969 _timer.stop();
3970 if (PrintCMSStatistics != 0) {
3971 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3972 worker_id, _timer.seconds());
3973 // XXX: need xxx/xxx type of notation, two timers
3974 }
3975 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3976 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3977 // Note that under the current task protocol, the
3978 // following assertion is true even of the spaces
3979 // expanded since the completion of the concurrent
3980 // marking. XXX This will likely change under a strict
3981 // ABORT semantics.
3982 // After perm removal the comparison was changed to
3983 // greater than or equal to from strictly greater than.
3984 // Before perm removal the highest address sweep would
3985 // have been at the end of perm gen but now is at the
3986 // end of the tenured gen.
3987 assert(_global_finger >= _cms_space->end(),
3988 "All tasks have been completed");
3989 DEBUG_ONLY(_collector->verify_overflow_empty();)
3990 }
3991
3992 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3993 HeapWord* read = _global_finger;
3994 HeapWord* cur = read;
3995 while (f > read) {
3996 cur = read;
3997 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3998 if (cur == read) {
3999 // our cas succeeded
4000 assert(_global_finger >= f, "protocol consistency");
4001 break;
4002 }
4003 }
4004 }
4005
4006 // This is really inefficient, and should be redone by
4007 // using (not yet available) block-read and -write interfaces to the
4008 // stack and the work_queue. XXX FIX ME !!!
4009 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4010 OopTaskQueue* work_q) {
4011 // Fast lock-free check
4012 if (ovflw_stk->length() == 0) {
4013 return false;
4014 }
4015 assert(work_q->size() == 0, "Shouldn't steal");
4016 MutexLockerEx ml(ovflw_stk->par_lock(),
4017 Mutex::_no_safepoint_check_flag);
4018 // Grab up to 1/4 the size of the work queue
4019 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4020 (size_t)ParGCDesiredObjsFromOverflowList);
4021 num = MIN2(num, ovflw_stk->length());
4022 for (int i = (int) num; i > 0; i--) {
4023 oop cur = ovflw_stk->pop();
4024 assert(cur != NULL, "Counted wrong?");
4025 work_q->push(cur);
4026 }
4027 return num > 0;
4028 }
4029
4030 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4031 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4032 int n_tasks = pst->n_tasks();
4033 // We allow that there may be no tasks to do here because
4034 // we are restarting after a stack overflow.
4035 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4036 uint nth_task = 0;
4037
4038 HeapWord* aligned_start = sp->bottom();
4039 if (sp->used_region().contains(_restart_addr)) {
4040 // Align down to a card boundary for the start of 0th task
4041 // for this space.
4042 aligned_start =
4043 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4044 CardTableModRefBS::card_size);
4045 }
4046
4047 size_t chunk_size = sp->marking_task_size();
4048 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4049 // Having claimed the nth task in this space,
4050 // compute the chunk that it corresponds to:
4051 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4052 aligned_start + (nth_task+1)*chunk_size);
4053 // Try and bump the global finger via a CAS;
4054 // note that we need to do the global finger bump
4055 // _before_ taking the intersection below, because
4056 // the task corresponding to that region will be
4057 // deemed done even if the used_region() expands
4058 // because of allocation -- as it almost certainly will
4059 // during start-up while the threads yield in the
4060 // closure below.
4061 HeapWord* finger = span.end();
4062 bump_global_finger(finger); // atomically
4063 // There are null tasks here corresponding to chunks
4064 // beyond the "top" address of the space.
4065 span = span.intersection(sp->used_region());
4066 if (!span.is_empty()) { // Non-null task
4067 HeapWord* prev_obj;
4068 assert(!span.contains(_restart_addr) || nth_task == 0,
4069 "Inconsistency");
4070 if (nth_task == 0) {
4071 // For the 0th task, we'll not need to compute a block_start.
4072 if (span.contains(_restart_addr)) {
4073 // In the case of a restart because of stack overflow,
4074 // we might additionally skip a chunk prefix.
4075 prev_obj = _restart_addr;
4076 } else {
4077 prev_obj = span.start();
4078 }
4079 } else {
4080 // We want to skip the first object because
4081 // the protocol is to scan any object in its entirety
4082 // that _starts_ in this span; a fortiori, any
4083 // object starting in an earlier span is scanned
4084 // as part of an earlier claimed task.
4085 // Below we use the "careful" version of block_start
4086 // so we do not try to navigate uninitialized objects.
4087 prev_obj = sp->block_start_careful(span.start());
4088 // Below we use a variant of block_size that uses the
4089 // Printezis bits to avoid waiting for allocated
4090 // objects to become initialized/parsable.
4091 while (prev_obj < span.start()) {
4092 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4093 if (sz > 0) {
4094 prev_obj += sz;
4095 } else {
4096 // In this case we may end up doing a bit of redundant
4097 // scanning, but that appears unavoidable, short of
4098 // locking the free list locks; see bug 6324141.
4099 break;
4100 }
4101 }
4102 }
4103 if (prev_obj < span.end()) {
4104 MemRegion my_span = MemRegion(prev_obj, span.end());
4105 // Do the marking work within a non-empty span --
4106 // the last argument to the constructor indicates whether the
4107 // iteration should be incremental with periodic yields.
4108 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4109 &_collector->_markBitMap,
4110 work_queue(i),
4111 &_collector->_markStack,
4112 _asynch);
4113 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4114 } // else nothing to do for this task
4115 } // else nothing to do for this task
4116 }
4117 // We'd be tempted to assert here that since there are no
4118 // more tasks left to claim in this space, the global_finger
4119 // must exceed space->top() and a fortiori space->end(). However,
4120 // that would not quite be correct because the bumping of
4121 // global_finger occurs strictly after the claiming of a task,
4122 // so by the time we reach here the global finger may not yet
4123 // have been bumped up by the thread that claimed the last
4124 // task.
4125 pst->all_tasks_completed();
4126 }
4127
4128 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4129 private:
4130 CMSCollector* _collector;
4131 CMSConcMarkingTask* _task;
4132 MemRegion _span;
4133 CMSBitMap* _bit_map;
4134 CMSMarkStack* _overflow_stack;
4135 OopTaskQueue* _work_queue;
4136 protected:
4137 DO_OOP_WORK_DEFN
4138 public:
4139 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4140 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4141 MetadataAwareOopClosure(collector->ref_processor()),
4142 _collector(collector),
4143 _task(task),
4144 _span(collector->_span),
4145 _work_queue(work_queue),
4146 _bit_map(bit_map),
4147 _overflow_stack(overflow_stack)
4148 { }
4149 virtual void do_oop(oop* p);
4150 virtual void do_oop(narrowOop* p);
4151
4152 void trim_queue(size_t max);
4153 void handle_stack_overflow(HeapWord* lost);
4154 void do_yield_check() {
4155 if (_task->should_yield()) {
4156 _task->yield();
4157 }
4158 }
4159 };
4160
4161 // Grey object scanning during work stealing phase --
4162 // the salient assumption here is that any references
4163 // that are in these stolen objects being scanned must
4164 // already have been initialized (else they would not have
4165 // been published), so we do not need to check for
4166 // uninitialized objects before pushing here.
4167 void Par_ConcMarkingClosure::do_oop(oop obj) {
4168 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4169 HeapWord* addr = (HeapWord*)obj;
4170 // Check if oop points into the CMS generation
4171 // and is not marked
4172 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4173 // a white object ...
4174 // If we manage to "claim" the object, by being the
4175 // first thread to mark it, then we push it on our
4176 // marking stack
4177 if (_bit_map->par_mark(addr)) { // ... now grey
4178 // push on work queue (grey set)
4179 bool simulate_overflow = false;
4180 NOT_PRODUCT(
4181 if (CMSMarkStackOverflowALot &&
4182 _collector->simulate_overflow()) {
4183 // simulate a stack overflow
4184 simulate_overflow = true;
4185 }
4186 )
4187 if (simulate_overflow ||
4188 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4189 // stack overflow
4190 if (PrintCMSStatistics != 0) {
4191 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4192 SIZE_FORMAT, _overflow_stack->capacity());
4193 }
4194 // We cannot assert that the overflow stack is full because
4195 // it may have been emptied since.
4196 assert(simulate_overflow ||
4197 _work_queue->size() == _work_queue->max_elems(),
4198 "Else push should have succeeded");
4199 handle_stack_overflow(addr);
4200 }
4201 } // Else, some other thread got there first
4202 do_yield_check();
4203 }
4204 }
4205
4206 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4207 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4208
4209 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4210 while (_work_queue->size() > max) {
4211 oop new_oop;
4212 if (_work_queue->pop_local(new_oop)) {
4213 assert(new_oop->is_oop(), "Should be an oop");
4214 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4215 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4216 new_oop->oop_iterate(this); // do_oop() above
4217 do_yield_check();
4218 }
4219 }
4220 }
4221
4222 // Upon stack overflow, we discard (part of) the stack,
4223 // remembering the least address amongst those discarded
4224 // in CMSCollector's _restart_address.
4225 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4226 // We need to do this under a mutex to prevent other
4227 // workers from interfering with the work done below.
4228 MutexLockerEx ml(_overflow_stack->par_lock(),
4229 Mutex::_no_safepoint_check_flag);
4230 // Remember the least grey address discarded
4231 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4232 _collector->lower_restart_addr(ra);
4233 _overflow_stack->reset(); // discard stack contents
4234 _overflow_stack->expand(); // expand the stack if possible
4235 }
4236
4237
4238 void CMSConcMarkingTask::do_work_steal(int i) {
4239 OopTaskQueue* work_q = work_queue(i);
4240 oop obj_to_scan;
4241 CMSBitMap* bm = &(_collector->_markBitMap);
4242 CMSMarkStack* ovflw = &(_collector->_markStack);
4243 int* seed = _collector->hash_seed(i);
4244 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4245 while (true) {
4246 cl.trim_queue(0);
4247 assert(work_q->size() == 0, "Should have been emptied above");
4248 if (get_work_from_overflow_stack(ovflw, work_q)) {
4249 // Can't assert below because the work obtained from the
4250 // overflow stack may already have been stolen from us.
4251 // assert(work_q->size() > 0, "Work from overflow stack");
4252 continue;
4253 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4254 assert(obj_to_scan->is_oop(), "Should be an oop");
4255 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4256 obj_to_scan->oop_iterate(&cl);
4257 } else if (terminator()->offer_termination(&_term_term)) {
4258 assert(work_q->size() == 0, "Impossible!");
4259 break;
4260 } else if (yielding() || should_yield()) {
4261 yield();
4262 }
4263 }
4264 }
4265
4266 // This is run by the CMS (coordinator) thread.
4267 void CMSConcMarkingTask::coordinator_yield() {
4268 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4269 "CMS thread should hold CMS token");
4270 // First give up the locks, then yield, then re-lock
4271 // We should probably use a constructor/destructor idiom to
4272 // do this unlock/lock or modify the MutexUnlocker class to
4273 // serve our purpose. XXX
4274 assert_lock_strong(_bit_map_lock);
4275 _bit_map_lock->unlock();
4276 ConcurrentMarkSweepThread::desynchronize(true);
4277 ConcurrentMarkSweepThread::acknowledge_yield_request();
4278 _collector->stopTimer();
4279 if (PrintCMSStatistics != 0) {
4280 _collector->incrementYields();
4281 }
4282 _collector->icms_wait();
4283
4284 // It is possible for whichever thread initiated the yield request
4285 // not to get a chance to wake up and take the bitmap lock between
4286 // this thread releasing it and reacquiring it. So, while the
4287 // should_yield() flag is on, let's sleep for a bit to give the
4288 // other thread a chance to wake up. The limit imposed on the number
4289 // of iterations is defensive, to avoid any unforseen circumstances
4290 // putting us into an infinite loop. Since it's always been this
4291 // (coordinator_yield()) method that was observed to cause the
4292 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4293 // which is by default non-zero. For the other seven methods that
4294 // also perform the yield operation, as are using a different
4295 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4296 // can enable the sleeping for those methods too, if necessary.
4297 // See 6442774.
4298 //
4299 // We really need to reconsider the synchronization between the GC
4300 // thread and the yield-requesting threads in the future and we
4301 // should really use wait/notify, which is the recommended
4302 // way of doing this type of interaction. Additionally, we should
4303 // consolidate the eight methods that do the yield operation and they
4304 // are almost identical into one for better maintainability and
4305 // readability. See 6445193.
4306 //
4307 // Tony 2006.06.29
4308 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4309 ConcurrentMarkSweepThread::should_yield() &&
4310 !CMSCollector::foregroundGCIsActive(); ++i) {
4311 os::sleep(Thread::current(), 1, false);
4312 ConcurrentMarkSweepThread::acknowledge_yield_request();
4313 }
4314
4315 ConcurrentMarkSweepThread::synchronize(true);
4316 _bit_map_lock->lock_without_safepoint_check();
4317 _collector->startTimer();
4318 }
4319
4320 bool CMSCollector::do_marking_mt(bool asynch) {
4321 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4322 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4323 conc_workers()->total_workers(),
4324 conc_workers()->active_workers(),
4325 Threads::number_of_non_daemon_threads());
4326 conc_workers()->set_active_workers(num_workers);
4327
4328 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4329
4330 CMSConcMarkingTask tsk(this,
4331 cms_space,
4332 asynch,
4333 conc_workers(),
4334 task_queues());
4335
4336 // Since the actual number of workers we get may be different
4337 // from the number we requested above, do we need to do anything different
4338 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4339 // class?? XXX
4340 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4341
4342 // Refs discovery is already non-atomic.
4343 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4344 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4345 conc_workers()->start_task(&tsk);
4346 while (tsk.yielded()) {
4347 tsk.coordinator_yield();
4348 conc_workers()->continue_task(&tsk);
4349 }
4350 // If the task was aborted, _restart_addr will be non-NULL
4351 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4352 while (_restart_addr != NULL) {
4353 // XXX For now we do not make use of ABORTED state and have not
4354 // yet implemented the right abort semantics (even in the original
4355 // single-threaded CMS case). That needs some more investigation
4356 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4357 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4358 // If _restart_addr is non-NULL, a marking stack overflow
4359 // occurred; we need to do a fresh marking iteration from the
4360 // indicated restart address.
4361 if (_foregroundGCIsActive && asynch) {
4362 // We may be running into repeated stack overflows, having
4363 // reached the limit of the stack size, while making very
4364 // slow forward progress. It may be best to bail out and
4365 // let the foreground collector do its job.
4366 // Clear _restart_addr, so that foreground GC
4367 // works from scratch. This avoids the headache of
4368 // a "rescan" which would otherwise be needed because
4369 // of the dirty mod union table & card table.
4370 _restart_addr = NULL;
4371 return false;
4372 }
4373 // Adjust the task to restart from _restart_addr
4374 tsk.reset(_restart_addr);
4375 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4376 _restart_addr);
4377 _restart_addr = NULL;
4378 // Get the workers going again
4379 conc_workers()->start_task(&tsk);
4380 while (tsk.yielded()) {
4381 tsk.coordinator_yield();
4382 conc_workers()->continue_task(&tsk);
4383 }
4384 }
4385 assert(tsk.completed(), "Inconsistency");
4386 assert(tsk.result() == true, "Inconsistency");
4387 return true;
4388 }
4389
4390 bool CMSCollector::do_marking_st(bool asynch) {
4391 ResourceMark rm;
4392 HandleMark hm;
4393
4394 // Temporarily make refs discovery single threaded (non-MT)
4395 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4396 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4397 &_markStack, CMSYield && asynch);
4398 // the last argument to iterate indicates whether the iteration
4399 // should be incremental with periodic yields.
4400 _markBitMap.iterate(&markFromRootsClosure);
4401 // If _restart_addr is non-NULL, a marking stack overflow
4402 // occurred; we need to do a fresh iteration from the
4403 // indicated restart address.
4404 while (_restart_addr != NULL) {
4405 if (_foregroundGCIsActive && asynch) {
4406 // We may be running into repeated stack overflows, having
4407 // reached the limit of the stack size, while making very
4408 // slow forward progress. It may be best to bail out and
4409 // let the foreground collector do its job.
4410 // Clear _restart_addr, so that foreground GC
4411 // works from scratch. This avoids the headache of
4412 // a "rescan" which would otherwise be needed because
4413 // of the dirty mod union table & card table.
4414 _restart_addr = NULL;
4415 return false; // indicating failure to complete marking
4416 }
4417 // Deal with stack overflow:
4418 // we restart marking from _restart_addr
4419 HeapWord* ra = _restart_addr;
4420 markFromRootsClosure.reset(ra);
4421 _restart_addr = NULL;
4422 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4423 }
4424 return true;
4425 }
4426
4427 void CMSCollector::preclean() {
4428 check_correct_thread_executing();
4429 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4430 verify_work_stacks_empty();
4431 verify_overflow_empty();
4432 _abort_preclean = false;
4433 if (CMSPrecleaningEnabled) {
4434 if (!CMSEdenChunksRecordAlways) {
4435 _eden_chunk_index = 0;
4436 }
4437 size_t used = get_eden_used();
4438 size_t capacity = get_eden_capacity();
4439 // Don't start sampling unless we will get sufficiently
4440 // many samples.
4441 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4442 * CMSScheduleRemarkEdenPenetration)) {
4443 _start_sampling = true;
4444 } else {
4445 _start_sampling = false;
4446 }
4447 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4448 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4449 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4450 }
4451 CMSTokenSync x(true); // is cms thread
4452 if (CMSPrecleaningEnabled) {
4453 sample_eden();
4454 _collectorState = AbortablePreclean;
4455 } else {
4456 _collectorState = FinalMarking;
4457 }
4458 verify_work_stacks_empty();
4459 verify_overflow_empty();
4460 }
4461
4462 // Try and schedule the remark such that young gen
4463 // occupancy is CMSScheduleRemarkEdenPenetration %.
4464 void CMSCollector::abortable_preclean() {
4465 check_correct_thread_executing();
4466 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4467 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4468
4469 // If Eden's current occupancy is below this threshold,
4470 // immediately schedule the remark; else preclean
4471 // past the next scavenge in an effort to
4472 // schedule the pause as described above. By choosing
4473 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4474 // we will never do an actual abortable preclean cycle.
4475 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4476 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4477 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4478 // We need more smarts in the abortable preclean
4479 // loop below to deal with cases where allocation
4480 // in young gen is very very slow, and our precleaning
4481 // is running a losing race against a horde of
4482 // mutators intent on flooding us with CMS updates
4483 // (dirty cards).
4484 // One, admittedly dumb, strategy is to give up
4485 // after a certain number of abortable precleaning loops
4486 // or after a certain maximum time. We want to make
4487 // this smarter in the next iteration.
4488 // XXX FIX ME!!! YSR
4489 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4490 while (!(should_abort_preclean() ||
4491 ConcurrentMarkSweepThread::should_terminate())) {
4492 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4493 cumworkdone += workdone;
4494 loops++;
4495 // Voluntarily terminate abortable preclean phase if we have
4496 // been at it for too long.
4497 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4498 loops >= CMSMaxAbortablePrecleanLoops) {
4499 if (PrintGCDetails) {
4500 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4501 }
4502 break;
4503 }
4504 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4505 if (PrintGCDetails) {
4506 gclog_or_tty->print(" CMS: abort preclean due to time ");
4507 }
4508 break;
4509 }
4510 // If we are doing little work each iteration, we should
4511 // take a short break.
4512 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4513 // Sleep for some time, waiting for work to accumulate
4514 stopTimer();
4515 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4516 startTimer();
4517 waited++;
4518 }
4519 }
4520 if (PrintCMSStatistics > 0) {
4521 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4522 loops, waited, cumworkdone);
4523 }
4524 }
4525 CMSTokenSync x(true); // is cms thread
4526 if (_collectorState != Idling) {
4527 assert(_collectorState == AbortablePreclean,
4528 "Spontaneous state transition?");
4529 _collectorState = FinalMarking;
4530 } // Else, a foreground collection completed this CMS cycle.
4531 return;
4532 }
4533
4534 // Respond to an Eden sampling opportunity
4535 void CMSCollector::sample_eden() {
4536 // Make sure a young gc cannot sneak in between our
4537 // reading and recording of a sample.
4538 assert(Thread::current()->is_ConcurrentGC_thread(),
4539 "Only the cms thread may collect Eden samples");
4540 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4541 "Should collect samples while holding CMS token");
4542 if (!_start_sampling) {
4543 return;
4544 }
4545 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4546 // is populated by the young generation.
4547 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4548 if (_eden_chunk_index < _eden_chunk_capacity) {
4549 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4550 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4551 "Unexpected state of Eden");
4552 // We'd like to check that what we just sampled is an oop-start address;
4553 // however, we cannot do that here since the object may not yet have been
4554 // initialized. So we'll instead do the check when we _use_ this sample
4555 // later.
4556 if (_eden_chunk_index == 0 ||
4557 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4558 _eden_chunk_array[_eden_chunk_index-1])
4559 >= CMSSamplingGrain)) {
4560 _eden_chunk_index++; // commit sample
4561 }
4562 }
4563 }
4564 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4565 size_t used = get_eden_used();
4566 size_t capacity = get_eden_capacity();
4567 assert(used <= capacity, "Unexpected state of Eden");
4568 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4569 _abort_preclean = true;
4570 }
4571 }
4572 }
4573
4574
4575 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4576 assert(_collectorState == Precleaning ||
4577 _collectorState == AbortablePreclean, "incorrect state");
4578 ResourceMark rm;
4579 HandleMark hm;
4580
4581 // Precleaning is currently not MT but the reference processor
4582 // may be set for MT. Disable it temporarily here.
4583 ReferenceProcessor* rp = ref_processor();
4584 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4585
4586 // Do one pass of scrubbing the discovered reference lists
4587 // to remove any reference objects with strongly-reachable
4588 // referents.
4589 if (clean_refs) {
4590 CMSPrecleanRefsYieldClosure yield_cl(this);
4591 assert(rp->span().equals(_span), "Spans should be equal");
4592 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4593 &_markStack, true /* preclean */);
4594 CMSDrainMarkingStackClosure complete_trace(this,
4595 _span, &_markBitMap, &_markStack,
4596 &keep_alive, true /* preclean */);
4597
4598 // We don't want this step to interfere with a young
4599 // collection because we don't want to take CPU
4600 // or memory bandwidth away from the young GC threads
4601 // (which may be as many as there are CPUs).
4602 // Note that we don't need to protect ourselves from
4603 // interference with mutators because they can't
4604 // manipulate the discovered reference lists nor affect
4605 // the computed reachability of the referents, the
4606 // only properties manipulated by the precleaning
4607 // of these reference lists.
4608 stopTimer();
4609 CMSTokenSyncWithLocks x(true /* is cms thread */,
4610 bitMapLock());
4611 startTimer();
4612 sample_eden();
4613
4614 // The following will yield to allow foreground
4615 // collection to proceed promptly. XXX YSR:
4616 // The code in this method may need further
4617 // tweaking for better performance and some restructuring
4618 // for cleaner interfaces.
4619 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4620 rp->preclean_discovered_references(
4621 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4622 gc_timer, _gc_tracer_cm->gc_id());
4623 }
4624
4625 if (clean_survivor) { // preclean the active survivor space(s)
4626 assert(_young_gen->kind() == Generation::DefNew ||
4627 _young_gen->kind() == Generation::ParNew,
4628 "incorrect type for cast");
4629 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4630 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4631 &_markBitMap, &_modUnionTable,
4632 &_markStack, true /* precleaning phase */);
4633 stopTimer();
4634 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4635 bitMapLock());
4636 startTimer();
4637 unsigned int before_count =
4638 GenCollectedHeap::heap()->total_collections();
4639 SurvivorSpacePrecleanClosure
4640 sss_cl(this, _span, &_markBitMap, &_markStack,
4641 &pam_cl, before_count, CMSYield);
4642 dng->from()->object_iterate_careful(&sss_cl);
4643 dng->to()->object_iterate_careful(&sss_cl);
4644 }
4645 MarkRefsIntoAndScanClosure
4646 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4647 &_markStack, this, CMSYield,
4648 true /* precleaning phase */);
4649 // CAUTION: The following closure has persistent state that may need to
4650 // be reset upon a decrease in the sequence of addresses it
4651 // processes.
4652 ScanMarkedObjectsAgainCarefullyClosure
4653 smoac_cl(this, _span,
4654 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4655
4656 // Preclean dirty cards in ModUnionTable and CardTable using
4657 // appropriate convergence criterion;
4658 // repeat CMSPrecleanIter times unless we find that
4659 // we are losing.
4660 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4661 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4662 "Bad convergence multiplier");
4663 assert(CMSPrecleanThreshold >= 100,
4664 "Unreasonably low CMSPrecleanThreshold");
4665
4666 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4667 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4668 numIter < CMSPrecleanIter;
4669 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4670 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4671 if (Verbose && PrintGCDetails) {
4672 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4673 }
4674 // Either there are very few dirty cards, so re-mark
4675 // pause will be small anyway, or our pre-cleaning isn't
4676 // that much faster than the rate at which cards are being
4677 // dirtied, so we might as well stop and re-mark since
4678 // precleaning won't improve our re-mark time by much.
4679 if (curNumCards <= CMSPrecleanThreshold ||
4680 (numIter > 0 &&
4681 (curNumCards * CMSPrecleanDenominator >
4682 lastNumCards * CMSPrecleanNumerator))) {
4683 numIter++;
4684 cumNumCards += curNumCards;
4685 break;
4686 }
4687 }
4688
4689 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4690
4691 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4692 cumNumCards += curNumCards;
4693 if (PrintGCDetails && PrintCMSStatistics != 0) {
4694 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4695 curNumCards, cumNumCards, numIter);
4696 }
4697 return cumNumCards; // as a measure of useful work done
4698 }
4699
4700 // PRECLEANING NOTES:
4701 // Precleaning involves:
4702 // . reading the bits of the modUnionTable and clearing the set bits.
4703 // . For the cards corresponding to the set bits, we scan the
4704 // objects on those cards. This means we need the free_list_lock
4705 // so that we can safely iterate over the CMS space when scanning
4706 // for oops.
4707 // . When we scan the objects, we'll be both reading and setting
4708 // marks in the marking bit map, so we'll need the marking bit map.
4709 // . For protecting _collector_state transitions, we take the CGC_lock.
4710 // Note that any races in the reading of of card table entries by the
4711 // CMS thread on the one hand and the clearing of those entries by the
4712 // VM thread or the setting of those entries by the mutator threads on the
4713 // other are quite benign. However, for efficiency it makes sense to keep
4714 // the VM thread from racing with the CMS thread while the latter is
4715 // dirty card info to the modUnionTable. We therefore also use the
4716 // CGC_lock to protect the reading of the card table and the mod union
4717 // table by the CM thread.
4718 // . We run concurrently with mutator updates, so scanning
4719 // needs to be done carefully -- we should not try to scan
4720 // potentially uninitialized objects.
4721 //
4722 // Locking strategy: While holding the CGC_lock, we scan over and
4723 // reset a maximal dirty range of the mod union / card tables, then lock
4724 // the free_list_lock and bitmap lock to do a full marking, then
4725 // release these locks; and repeat the cycle. This allows for a
4726 // certain amount of fairness in the sharing of these locks between
4727 // the CMS collector on the one hand, and the VM thread and the
4728 // mutators on the other.
4729
4730 // NOTE: preclean_mod_union_table() and preclean_card_table()
4731 // further below are largely identical; if you need to modify
4732 // one of these methods, please check the other method too.
4733
4734 size_t CMSCollector::preclean_mod_union_table(
4735 ConcurrentMarkSweepGeneration* gen,
4736 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4737 verify_work_stacks_empty();
4738 verify_overflow_empty();
4739
4740 // strategy: starting with the first card, accumulate contiguous
4741 // ranges of dirty cards; clear these cards, then scan the region
4742 // covered by these cards.
4743
4744 // Since all of the MUT is committed ahead, we can just use
4745 // that, in case the generations expand while we are precleaning.
4746 // It might also be fine to just use the committed part of the
4747 // generation, but we might potentially miss cards when the
4748 // generation is rapidly expanding while we are in the midst
4749 // of precleaning.
4750 HeapWord* startAddr = gen->reserved().start();
4751 HeapWord* endAddr = gen->reserved().end();
4752
4753 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4754
4755 size_t numDirtyCards, cumNumDirtyCards;
4756 HeapWord *nextAddr, *lastAddr;
4757 for (cumNumDirtyCards = numDirtyCards = 0,
4758 nextAddr = lastAddr = startAddr;
4759 nextAddr < endAddr;
4760 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4761
4762 ResourceMark rm;
4763 HandleMark hm;
4764
4765 MemRegion dirtyRegion;
4766 {
4767 stopTimer();
4768 // Potential yield point
4769 CMSTokenSync ts(true);
4770 startTimer();
4771 sample_eden();
4772 // Get dirty region starting at nextOffset (inclusive),
4773 // simultaneously clearing it.
4774 dirtyRegion =
4775 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4776 assert(dirtyRegion.start() >= nextAddr,
4777 "returned region inconsistent?");
4778 }
4779 // Remember where the next search should begin.
4780 // The returned region (if non-empty) is a right open interval,
4781 // so lastOffset is obtained from the right end of that
4782 // interval.
4783 lastAddr = dirtyRegion.end();
4784 // Should do something more transparent and less hacky XXX
4785 numDirtyCards =
4786 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4787
4788 // We'll scan the cards in the dirty region (with periodic
4789 // yields for foreground GC as needed).
4790 if (!dirtyRegion.is_empty()) {
4791 assert(numDirtyCards > 0, "consistency check");
4792 HeapWord* stop_point = NULL;
4793 stopTimer();
4794 // Potential yield point
4795 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4796 bitMapLock());
4797 startTimer();
4798 {
4799 verify_work_stacks_empty();
4800 verify_overflow_empty();
4801 sample_eden();
4802 stop_point =
4803 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4804 }
4805 if (stop_point != NULL) {
4806 // The careful iteration stopped early either because it found an
4807 // uninitialized object, or because we were in the midst of an
4808 // "abortable preclean", which should now be aborted. Redirty
4809 // the bits corresponding to the partially-scanned or unscanned
4810 // cards. We'll either restart at the next block boundary or
4811 // abort the preclean.
4812 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4813 "Should only be AbortablePreclean.");
4814 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4815 if (should_abort_preclean()) {
4816 break; // out of preclean loop
4817 } else {
4818 // Compute the next address at which preclean should pick up;
4819 // might need bitMapLock in order to read P-bits.
4820 lastAddr = next_card_start_after_block(stop_point);
4821 }
4822 }
4823 } else {
4824 assert(lastAddr == endAddr, "consistency check");
4825 assert(numDirtyCards == 0, "consistency check");
4826 break;
4827 }
4828 }
4829 verify_work_stacks_empty();
4830 verify_overflow_empty();
4831 return cumNumDirtyCards;
4832 }
4833
4834 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4835 // below are largely identical; if you need to modify
4836 // one of these methods, please check the other method too.
4837
4838 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4839 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4840 // strategy: it's similar to precleamModUnionTable above, in that
4841 // we accumulate contiguous ranges of dirty cards, mark these cards
4842 // precleaned, then scan the region covered by these cards.
4843 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4844 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4845
4846 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4847
4848 size_t numDirtyCards, cumNumDirtyCards;
4849 HeapWord *lastAddr, *nextAddr;
4850
4851 for (cumNumDirtyCards = numDirtyCards = 0,
4852 nextAddr = lastAddr = startAddr;
4853 nextAddr < endAddr;
4854 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4855
4856 ResourceMark rm;
4857 HandleMark hm;
4858
4859 MemRegion dirtyRegion;
4860 {
4861 // See comments in "Precleaning notes" above on why we
4862 // do this locking. XXX Could the locking overheads be
4863 // too high when dirty cards are sparse? [I don't think so.]
4864 stopTimer();
4865 CMSTokenSync x(true); // is cms thread
4866 startTimer();
4867 sample_eden();
4868 // Get and clear dirty region from card table
4869 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4870 MemRegion(nextAddr, endAddr),
4871 true,
4872 CardTableModRefBS::precleaned_card_val());
4873
4874 assert(dirtyRegion.start() >= nextAddr,
4875 "returned region inconsistent?");
4876 }
4877 lastAddr = dirtyRegion.end();
4878 numDirtyCards =
4879 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4880
4881 if (!dirtyRegion.is_empty()) {
4882 stopTimer();
4883 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4884 startTimer();
4885 sample_eden();
4886 verify_work_stacks_empty();
4887 verify_overflow_empty();
4888 HeapWord* stop_point =
4889 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4890 if (stop_point != NULL) {
4891 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4892 "Should only be AbortablePreclean.");
4893 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4894 if (should_abort_preclean()) {
4895 break; // out of preclean loop
4896 } else {
4897 // Compute the next address at which preclean should pick up.
4898 lastAddr = next_card_start_after_block(stop_point);
4899 }
4900 }
4901 } else {
4902 break;
4903 }
4904 }
4905 verify_work_stacks_empty();
4906 verify_overflow_empty();
4907 return cumNumDirtyCards;
4908 }
4909
4910 class PrecleanKlassClosure : public KlassClosure {
4911 KlassToOopClosure _cm_klass_closure;
4912 public:
4913 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4914 void do_klass(Klass* k) {
4915 if (k->has_accumulated_modified_oops()) {
4916 k->clear_accumulated_modified_oops();
4917
4918 _cm_klass_closure.do_klass(k);
4919 }
4920 }
4921 };
4922
4923 // The freelist lock is needed to prevent asserts, is it really needed?
4924 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4925
4926 cl->set_freelistLock(freelistLock);
4927
4928 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4929
4930 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4931 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4932 PrecleanKlassClosure preclean_klass_closure(cl);
4933 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4934
4935 verify_work_stacks_empty();
4936 verify_overflow_empty();
4937 }
4938
4939 void CMSCollector::checkpointRootsFinal(bool asynch,
4940 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4941 assert(_collectorState == FinalMarking, "incorrect state transition?");
4942 check_correct_thread_executing();
4943 // world is stopped at this checkpoint
4944 assert(SafepointSynchronize::is_at_safepoint(),
4945 "world should be stopped");
4946 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4947
4948 verify_work_stacks_empty();
4949 verify_overflow_empty();
4950
4951 SpecializationStats::clear();
4952 if (PrintGCDetails) {
4953 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4954 _young_gen->used() / K,
4955 _young_gen->capacity() / K);
4956 }
4957 if (asynch) {
4958 if (CMSScavengeBeforeRemark) {
4959 GenCollectedHeap* gch = GenCollectedHeap::heap();
4960 // Temporarily set flag to false, GCH->do_collection will
4961 // expect it to be false and set to true
4962 FlagSetting fl(gch->_is_gc_active, false);
4963 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4964 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4965 int level = _cmsGen->level() - 1;
4966 if (level >= 0) {
4967 gch->do_collection(true, // full (i.e. force, see below)
4968 false, // !clear_all_soft_refs
4969 0, // size
4970 false, // is_tlab
4971 level // max_level
4972 );
4973 }
4974 }
4975 FreelistLocker x(this);
4976 MutexLockerEx y(bitMapLock(),
4977 Mutex::_no_safepoint_check_flag);
4978 assert(!init_mark_was_synchronous, "but that's impossible!");
4979 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4980 } else {
4981 // already have all the locks
4982 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4983 init_mark_was_synchronous);
4984 }
4985 verify_work_stacks_empty();
4986 verify_overflow_empty();
4987 SpecializationStats::print();
4988 }
4989
4990 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4991 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4992
4993 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4994
4995 assert(haveFreelistLocks(), "must have free list locks");
4996 assert_lock_strong(bitMapLock());
4997
4998 ResourceMark rm;
4999 HandleMark hm;
5000
5001 GenCollectedHeap* gch = GenCollectedHeap::heap();
5002
5003 if (should_unload_classes()) {
5004 CodeCache::gc_prologue();
5005 }
5006 assert(haveFreelistLocks(), "must have free list locks");
5007 assert_lock_strong(bitMapLock());
5008
5009 if (!init_mark_was_synchronous) {
5010 // We might assume that we need not fill TLAB's when
5011 // CMSScavengeBeforeRemark is set, because we may have just done
5012 // a scavenge which would have filled all TLAB's -- and besides
5013 // Eden would be empty. This however may not always be the case --
5014 // for instance although we asked for a scavenge, it may not have
5015 // happened because of a JNI critical section. We probably need
5016 // a policy for deciding whether we can in that case wait until
5017 // the critical section releases and then do the remark following
5018 // the scavenge, and skip it here. In the absence of that policy,
5019 // or of an indication of whether the scavenge did indeed occur,
5020 // we cannot rely on TLAB's having been filled and must do
5021 // so here just in case a scavenge did not happen.
5022 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5023 // Update the saved marks which may affect the root scans.
5024 gch->save_marks();
5025
5026 if (CMSPrintEdenSurvivorChunks) {
5027 print_eden_and_survivor_chunk_arrays();
5028 }
5029
5030 {
5031 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5032
5033 // Note on the role of the mod union table:
5034 // Since the marker in "markFromRoots" marks concurrently with
5035 // mutators, it is possible for some reachable objects not to have been
5036 // scanned. For instance, an only reference to an object A was
5037 // placed in object B after the marker scanned B. Unless B is rescanned,
5038 // A would be collected. Such updates to references in marked objects
5039 // are detected via the mod union table which is the set of all cards
5040 // dirtied since the first checkpoint in this GC cycle and prior to
5041 // the most recent young generation GC, minus those cleaned up by the
5042 // concurrent precleaning.
5043 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5044 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5045 do_remark_parallel();
5046 } else {
5047 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5048 _gc_timer_cm, _gc_tracer_cm->gc_id());
5049 do_remark_non_parallel();
5050 }
5051 }
5052 } else {
5053 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5054 // The initial mark was stop-world, so there's no rescanning to
5055 // do; go straight on to the next step below.
5056 }
5057 verify_work_stacks_empty();
5058 verify_overflow_empty();
5059
5060 {
5061 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5062 refProcessingWork(asynch, clear_all_soft_refs);
5063 }
5064 verify_work_stacks_empty();
5065 verify_overflow_empty();
5066
5067 if (should_unload_classes()) {
5068 CodeCache::gc_epilogue();
5069 }
5070 JvmtiExport::gc_epilogue();
5071
5072 // If we encountered any (marking stack / work queue) overflow
5073 // events during the current CMS cycle, take appropriate
5074 // remedial measures, where possible, so as to try and avoid
5075 // recurrence of that condition.
5076 assert(_markStack.isEmpty(), "No grey objects");
5077 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5078 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5079 if (ser_ovflw > 0) {
5080 if (PrintCMSStatistics != 0) {
5081 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5082 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5083 ", kac_preclean="SIZE_FORMAT")",
5084 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5085 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5086 }
5087 _markStack.expand();
5088 _ser_pmc_remark_ovflw = 0;
5089 _ser_pmc_preclean_ovflw = 0;
5090 _ser_kac_preclean_ovflw = 0;
5091 _ser_kac_ovflw = 0;
5092 }
5093 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5094 if (PrintCMSStatistics != 0) {
5095 gclog_or_tty->print_cr("Work queue overflow (benign) "
5096 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5097 _par_pmc_remark_ovflw, _par_kac_ovflw);
5098 }
5099 _par_pmc_remark_ovflw = 0;
5100 _par_kac_ovflw = 0;
5101 }
5102 if (PrintCMSStatistics != 0) {
5103 if (_markStack._hit_limit > 0) {
5104 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5105 _markStack._hit_limit);
5106 }
5107 if (_markStack._failed_double > 0) {
5108 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5109 " current capacity "SIZE_FORMAT,
5110 _markStack._failed_double,
5111 _markStack.capacity());
5112 }
5113 }
5114 _markStack._hit_limit = 0;
5115 _markStack._failed_double = 0;
5116
5117 if ((VerifyAfterGC || VerifyDuringGC) &&
5118 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5119 verify_after_remark();
5120 }
5121
5122 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5123
5124 // Change under the freelistLocks.
5125 _collectorState = Sweeping;
5126 // Call isAllClear() under bitMapLock
5127 assert(_modUnionTable.isAllClear(),
5128 "Should be clear by end of the final marking");
5129 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5130 "Should be clear by end of the final marking");
5131 }
5132
5133 void CMSParInitialMarkTask::work(uint worker_id) {
5134 elapsedTimer _timer;
5135 ResourceMark rm;
5136 HandleMark hm;
5137
5138 // ---------- scan from roots --------------
5139 _timer.start();
5140 GenCollectedHeap* gch = GenCollectedHeap::heap();
5141 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5142 KlassToOopClosure klass_closure(&par_mri_cl);
5143
5144 // ---------- young gen roots --------------
5145 {
5146 work_on_young_gen_roots(worker_id, &par_mri_cl);
5147 _timer.stop();
5148 if (PrintCMSStatistics != 0) {
5149 gclog_or_tty->print_cr(
5150 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5151 worker_id, _timer.seconds());
5152 }
5153 }
5154
5155 // ---------- remaining roots --------------
5156 _timer.reset();
5157 _timer.start();
5158 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5159 false, // yg was scanned above
5160 false, // this is parallel code
5161 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5162 &par_mri_cl,
5163 NULL,
5164 &klass_closure);
5165 assert(_collector->should_unload_classes()
5166 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5167 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5168 _timer.stop();
5169 if (PrintCMSStatistics != 0) {
5170 gclog_or_tty->print_cr(
5171 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5172 worker_id, _timer.seconds());
5173 }
5174 }
5175
5176 // Parallel remark task
5177 class CMSParRemarkTask: public CMSParMarkTask {
5178 CompactibleFreeListSpace* _cms_space;
5179
5180 // The per-thread work queues, available here for stealing.
5181 OopTaskQueueSet* _task_queues;
5182 ParallelTaskTerminator _term;
5183
5184 public:
5185 // A value of 0 passed to n_workers will cause the number of
5186 // workers to be taken from the active workers in the work gang.
5187 CMSParRemarkTask(CMSCollector* collector,
5188 CompactibleFreeListSpace* cms_space,
5189 int n_workers, FlexibleWorkGang* workers,
5190 OopTaskQueueSet* task_queues):
5191 CMSParMarkTask("Rescan roots and grey objects in parallel",
5192 collector, n_workers),
5193 _cms_space(cms_space),
5194 _task_queues(task_queues),
5195 _term(n_workers, task_queues) { }
5196
5197 OopTaskQueueSet* task_queues() { return _task_queues; }
5198
5199 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5200
5201 ParallelTaskTerminator* terminator() { return &_term; }
5202 int n_workers() { return _n_workers; }
5203
5204 void work(uint worker_id);
5205
5206 private:
5207 // ... of dirty cards in old space
5208 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5209 Par_MarkRefsIntoAndScanClosure* cl);
5210
5211 // ... work stealing for the above
5212 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5213 };
5214
5215 class RemarkKlassClosure : public KlassClosure {
5216 KlassToOopClosure _cm_klass_closure;
5217 public:
5218 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5219 void do_klass(Klass* k) {
5220 // Check if we have modified any oops in the Klass during the concurrent marking.
5221 if (k->has_accumulated_modified_oops()) {
5222 k->clear_accumulated_modified_oops();
5223
5224 // We could have transfered the current modified marks to the accumulated marks,
5225 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5226 } else if (k->has_modified_oops()) {
5227 // Don't clear anything, this info is needed by the next young collection.
5228 } else {
5229 // No modified oops in the Klass.
5230 return;
5231 }
5232
5233 // The klass has modified fields, need to scan the klass.
5234 _cm_klass_closure.do_klass(k);
5235 }
5236 };
5237
5238 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5239 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5240 EdenSpace* eden_space = dng->eden();
5241 ContiguousSpace* from_space = dng->from();
5242 ContiguousSpace* to_space = dng->to();
5243
5244 HeapWord** eca = _collector->_eden_chunk_array;
5245 size_t ect = _collector->_eden_chunk_index;
5246 HeapWord** sca = _collector->_survivor_chunk_array;
5247 size_t sct = _collector->_survivor_chunk_index;
5248
5249 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5250 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5251
5252 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5253 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5254 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5255 }
5256
5257 // work_queue(i) is passed to the closure
5258 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5259 // also is passed to do_dirty_card_rescan_tasks() and to
5260 // do_work_steal() to select the i-th task_queue.
5261
5262 void CMSParRemarkTask::work(uint worker_id) {
5263 elapsedTimer _timer;
5264 ResourceMark rm;
5265 HandleMark hm;
5266
5267 // ---------- rescan from roots --------------
5268 _timer.start();
5269 GenCollectedHeap* gch = GenCollectedHeap::heap();
5270 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5271 _collector->_span, _collector->ref_processor(),
5272 &(_collector->_markBitMap),
5273 work_queue(worker_id));
5274
5275 // Rescan young gen roots first since these are likely
5276 // coarsely partitioned and may, on that account, constitute
5277 // the critical path; thus, it's best to start off that
5278 // work first.
5279 // ---------- young gen roots --------------
5280 {
5281 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5282 _timer.stop();
5283 if (PrintCMSStatistics != 0) {
5284 gclog_or_tty->print_cr(
5285 "Finished young gen rescan work in %dth thread: %3.3f sec",
5286 worker_id, _timer.seconds());
5287 }
5288 }
5289
5290 // ---------- remaining roots --------------
5291 _timer.reset();
5292 _timer.start();
5293 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5294 false, // yg was scanned above
5295 false, // this is parallel code
5296 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5297 &par_mrias_cl,
5298 NULL,
5299 NULL); // The dirty klasses will be handled below
5300 assert(_collector->should_unload_classes()
5301 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5302 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5303 _timer.stop();
5304 if (PrintCMSStatistics != 0) {
5305 gclog_or_tty->print_cr(
5306 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5307 worker_id, _timer.seconds());
5308 }
5309
5310 // ---------- unhandled CLD scanning ----------
5311 if (worker_id == 0) { // Single threaded at the moment.
5312 _timer.reset();
5313 _timer.start();
5314
5315 // Scan all new class loader data objects and new dependencies that were
5316 // introduced during concurrent marking.
5317 ResourceMark rm;
5318 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5319 for (int i = 0; i < array->length(); i++) {
5320 par_mrias_cl.do_class_loader_data(array->at(i));
5321 }
5322
5323 // We don't need to keep track of new CLDs anymore.
5324 ClassLoaderDataGraph::remember_new_clds(false);
5325
5326 _timer.stop();
5327 if (PrintCMSStatistics != 0) {
5328 gclog_or_tty->print_cr(
5329 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5330 worker_id, _timer.seconds());
5331 }
5332 }
5333
5334 // ---------- dirty klass scanning ----------
5335 if (worker_id == 0) { // Single threaded at the moment.
5336 _timer.reset();
5337 _timer.start();
5338
5339 // Scan all classes that was dirtied during the concurrent marking phase.
5340 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5341 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5342
5343 _timer.stop();
5344 if (PrintCMSStatistics != 0) {
5345 gclog_or_tty->print_cr(
5346 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5347 worker_id, _timer.seconds());
5348 }
5349 }
5350
5351 // We might have added oops to ClassLoaderData::_handles during the
5352 // concurrent marking phase. These oops point to newly allocated objects
5353 // that are guaranteed to be kept alive. Either by the direct allocation
5354 // code, or when the young collector processes the strong roots. Hence,
5355 // we don't have to revisit the _handles block during the remark phase.
5356
5357 // ---------- rescan dirty cards ------------
5358 _timer.reset();
5359 _timer.start();
5360
5361 // Do the rescan tasks for each of the two spaces
5362 // (cms_space) in turn.
5363 // "worker_id" is passed to select the task_queue for "worker_id"
5364 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5365 _timer.stop();
5366 if (PrintCMSStatistics != 0) {
5367 gclog_or_tty->print_cr(
5368 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5369 worker_id, _timer.seconds());
5370 }
5371
5372 // ---------- steal work from other threads ...
5373 // ---------- ... and drain overflow list.
5374 _timer.reset();
5375 _timer.start();
5376 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5377 _timer.stop();
5378 if (PrintCMSStatistics != 0) {
5379 gclog_or_tty->print_cr(
5380 "Finished work stealing in %dth thread: %3.3f sec",
5381 worker_id, _timer.seconds());
5382 }
5383 }
5384
5385 // Note that parameter "i" is not used.
5386 void
5387 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5388 OopsInGenClosure* cl, ContiguousSpace* space,
5389 HeapWord** chunk_array, size_t chunk_top) {
5390 // Until all tasks completed:
5391 // . claim an unclaimed task
5392 // . compute region boundaries corresponding to task claimed
5393 // using chunk_array
5394 // . par_oop_iterate(cl) over that region
5395
5396 ResourceMark rm;
5397 HandleMark hm;
5398
5399 SequentialSubTasksDone* pst = space->par_seq_tasks();
5400
5401 uint nth_task = 0;
5402 uint n_tasks = pst->n_tasks();
5403
5404 if (n_tasks > 0) {
5405 assert(pst->valid(), "Uninitialized use?");
5406 HeapWord *start, *end;
5407 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5408 // We claimed task # nth_task; compute its boundaries.
5409 if (chunk_top == 0) { // no samples were taken
5410 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5411 start = space->bottom();
5412 end = space->top();
5413 } else if (nth_task == 0) {
5414 start = space->bottom();
5415 end = chunk_array[nth_task];
5416 } else if (nth_task < (uint)chunk_top) {
5417 assert(nth_task >= 1, "Control point invariant");
5418 start = chunk_array[nth_task - 1];
5419 end = chunk_array[nth_task];
5420 } else {
5421 assert(nth_task == (uint)chunk_top, "Control point invariant");
5422 start = chunk_array[chunk_top - 1];
5423 end = space->top();
5424 }
5425 MemRegion mr(start, end);
5426 // Verify that mr is in space
5427 assert(mr.is_empty() || space->used_region().contains(mr),
5428 "Should be in space");
5429 // Verify that "start" is an object boundary
5430 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5431 "Should be an oop");
5432 space->par_oop_iterate(mr, cl);
5433 }
5434 pst->all_tasks_completed();
5435 }
5436 }
5437
5438 void
5439 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5440 CompactibleFreeListSpace* sp, int i,
5441 Par_MarkRefsIntoAndScanClosure* cl) {
5442 // Until all tasks completed:
5443 // . claim an unclaimed task
5444 // . compute region boundaries corresponding to task claimed
5445 // . transfer dirty bits ct->mut for that region
5446 // . apply rescanclosure to dirty mut bits for that region
5447
5448 ResourceMark rm;
5449 HandleMark hm;
5450
5451 OopTaskQueue* work_q = work_queue(i);
5452 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5453 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5454 // CAUTION: This closure has state that persists across calls to
5455 // the work method dirty_range_iterate_clear() in that it has
5456 // embedded in it a (subtype of) UpwardsObjectClosure. The
5457 // use of that state in the embedded UpwardsObjectClosure instance
5458 // assumes that the cards are always iterated (even if in parallel
5459 // by several threads) in monotonically increasing order per each
5460 // thread. This is true of the implementation below which picks
5461 // card ranges (chunks) in monotonically increasing order globally
5462 // and, a-fortiori, in monotonically increasing order per thread
5463 // (the latter order being a subsequence of the former).
5464 // If the work code below is ever reorganized into a more chaotic
5465 // work-partitioning form than the current "sequential tasks"
5466 // paradigm, the use of that persistent state will have to be
5467 // revisited and modified appropriately. See also related
5468 // bug 4756801 work on which should examine this code to make
5469 // sure that the changes there do not run counter to the
5470 // assumptions made here and necessary for correctness and
5471 // efficiency. Note also that this code might yield inefficient
5472 // behavior in the case of very large objects that span one or
5473 // more work chunks. Such objects would potentially be scanned
5474 // several times redundantly. Work on 4756801 should try and
5475 // address that performance anomaly if at all possible. XXX
5476 MemRegion full_span = _collector->_span;
5477 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5478 MarkFromDirtyCardsClosure
5479 greyRescanClosure(_collector, full_span, // entire span of interest
5480 sp, bm, work_q, cl);
5481
5482 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5483 assert(pst->valid(), "Uninitialized use?");
5484 uint nth_task = 0;
5485 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5486 MemRegion span = sp->used_region();
5487 HeapWord* start_addr = span.start();
5488 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5489 alignment);
5490 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5491 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5492 start_addr, "Check alignment");
5493 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5494 chunk_size, "Check alignment");
5495
5496 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5497 // Having claimed the nth_task, compute corresponding mem-region,
5498 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5499 // The alignment restriction ensures that we do not need any
5500 // synchronization with other gang-workers while setting or
5501 // clearing bits in thus chunk of the MUT.
5502 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5503 start_addr + (nth_task+1)*chunk_size);
5504 // The last chunk's end might be way beyond end of the
5505 // used region. In that case pull back appropriately.
5506 if (this_span.end() > end_addr) {
5507 this_span.set_end(end_addr);
5508 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5509 }
5510 // Iterate over the dirty cards covering this chunk, marking them
5511 // precleaned, and setting the corresponding bits in the mod union
5512 // table. Since we have been careful to partition at Card and MUT-word
5513 // boundaries no synchronization is needed between parallel threads.
5514 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5515 &modUnionClosure);
5516
5517 // Having transferred these marks into the modUnionTable,
5518 // rescan the marked objects on the dirty cards in the modUnionTable.
5519 // Even if this is at a synchronous collection, the initial marking
5520 // may have been done during an asynchronous collection so there
5521 // may be dirty bits in the mod-union table.
5522 _collector->_modUnionTable.dirty_range_iterate_clear(
5523 this_span, &greyRescanClosure);
5524 _collector->_modUnionTable.verifyNoOneBitsInRange(
5525 this_span.start(),
5526 this_span.end());
5527 }
5528 pst->all_tasks_completed(); // declare that i am done
5529 }
5530
5531 // . see if we can share work_queues with ParNew? XXX
5532 void
5533 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5534 int* seed) {
5535 OopTaskQueue* work_q = work_queue(i);
5536 NOT_PRODUCT(int num_steals = 0;)
5537 oop obj_to_scan;
5538 CMSBitMap* bm = &(_collector->_markBitMap);
5539
5540 while (true) {
5541 // Completely finish any left over work from (an) earlier round(s)
5542 cl->trim_queue(0);
5543 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5544 (size_t)ParGCDesiredObjsFromOverflowList);
5545 // Now check if there's any work in the overflow list
5546 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5547 // only affects the number of attempts made to get work from the
5548 // overflow list and does not affect the number of workers. Just
5549 // pass ParallelGCThreads so this behavior is unchanged.
5550 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5551 work_q,
5552 ParallelGCThreads)) {
5553 // found something in global overflow list;
5554 // not yet ready to go stealing work from others.
5555 // We'd like to assert(work_q->size() != 0, ...)
5556 // because we just took work from the overflow list,
5557 // but of course we can't since all of that could have
5558 // been already stolen from us.
5559 // "He giveth and He taketh away."
5560 continue;
5561 }
5562 // Verify that we have no work before we resort to stealing
5563 assert(work_q->size() == 0, "Have work, shouldn't steal");
5564 // Try to steal from other queues that have work
5565 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5566 NOT_PRODUCT(num_steals++;)
5567 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5568 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5569 // Do scanning work
5570 obj_to_scan->oop_iterate(cl);
5571 // Loop around, finish this work, and try to steal some more
5572 } else if (terminator()->offer_termination()) {
5573 break; // nirvana from the infinite cycle
5574 }
5575 }
5576 NOT_PRODUCT(
5577 if (PrintCMSStatistics != 0) {
5578 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5579 }
5580 )
5581 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5582 "Else our work is not yet done");
5583 }
5584
5585 // Record object boundaries in _eden_chunk_array by sampling the eden
5586 // top in the slow-path eden object allocation code path and record
5587 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5588 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5589 // sampling in sample_eden() that activates during the part of the
5590 // preclean phase.
5591 void CMSCollector::sample_eden_chunk() {
5592 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5593 if (_eden_chunk_lock->try_lock()) {
5594 // Record a sample. This is the critical section. The contents
5595 // of the _eden_chunk_array have to be non-decreasing in the
5596 // address order.
5597 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5598 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5599 "Unexpected state of Eden");
5600 if (_eden_chunk_index == 0 ||
5601 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5602 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5603 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5604 _eden_chunk_index++; // commit sample
5605 }
5606 _eden_chunk_lock->unlock();
5607 }
5608 }
5609 }
5610
5611 // Return a thread-local PLAB recording array, as appropriate.
5612 void* CMSCollector::get_data_recorder(int thr_num) {
5613 if (_survivor_plab_array != NULL &&
5614 (CMSPLABRecordAlways ||
5615 (_collectorState > Marking && _collectorState < FinalMarking))) {
5616 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5617 ChunkArray* ca = &_survivor_plab_array[thr_num];
5618 ca->reset(); // clear it so that fresh data is recorded
5619 return (void*) ca;
5620 } else {
5621 return NULL;
5622 }
5623 }
5624
5625 // Reset all the thread-local PLAB recording arrays
5626 void CMSCollector::reset_survivor_plab_arrays() {
5627 for (uint i = 0; i < ParallelGCThreads; i++) {
5628 _survivor_plab_array[i].reset();
5629 }
5630 }
5631
5632 // Merge the per-thread plab arrays into the global survivor chunk
5633 // array which will provide the partitioning of the survivor space
5634 // for CMS initial scan and rescan.
5635 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5636 int no_of_gc_threads) {
5637 assert(_survivor_plab_array != NULL, "Error");
5638 assert(_survivor_chunk_array != NULL, "Error");
5639 assert(_collectorState == FinalMarking ||
5640 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5641 for (int j = 0; j < no_of_gc_threads; j++) {
5642 _cursor[j] = 0;
5643 }
5644 HeapWord* top = surv->top();
5645 size_t i;
5646 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5647 HeapWord* min_val = top; // Higher than any PLAB address
5648 uint min_tid = 0; // position of min_val this round
5649 for (int j = 0; j < no_of_gc_threads; j++) {
5650 ChunkArray* cur_sca = &_survivor_plab_array[j];
5651 if (_cursor[j] == cur_sca->end()) {
5652 continue;
5653 }
5654 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5655 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5656 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5657 if (cur_val < min_val) {
5658 min_tid = j;
5659 min_val = cur_val;
5660 } else {
5661 assert(cur_val < top, "All recorded addresses should be less");
5662 }
5663 }
5664 // At this point min_val and min_tid are respectively
5665 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5666 // and the thread (j) that witnesses that address.
5667 // We record this address in the _survivor_chunk_array[i]
5668 // and increment _cursor[min_tid] prior to the next round i.
5669 if (min_val == top) {
5670 break;
5671 }
5672 _survivor_chunk_array[i] = min_val;
5673 _cursor[min_tid]++;
5674 }
5675 // We are all done; record the size of the _survivor_chunk_array
5676 _survivor_chunk_index = i; // exclusive: [0, i)
5677 if (PrintCMSStatistics > 0) {
5678 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5679 }
5680 // Verify that we used up all the recorded entries
5681 #ifdef ASSERT
5682 size_t total = 0;
5683 for (int j = 0; j < no_of_gc_threads; j++) {
5684 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5685 total += _cursor[j];
5686 }
5687 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5688 // Check that the merged array is in sorted order
5689 if (total > 0) {
5690 for (size_t i = 0; i < total - 1; i++) {
5691 if (PrintCMSStatistics > 0) {
5692 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5693 i, _survivor_chunk_array[i]);
5694 }
5695 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5696 "Not sorted");
5697 }
5698 }
5699 #endif // ASSERT
5700 }
5701
5702 // Set up the space's par_seq_tasks structure for work claiming
5703 // for parallel initial scan and rescan of young gen.
5704 // See ParRescanTask where this is currently used.
5705 void
5706 CMSCollector::
5707 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5708 assert(n_threads > 0, "Unexpected n_threads argument");
5709 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5710
5711 // Eden space
5712 if (!dng->eden()->is_empty()) {
5713 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5714 assert(!pst->valid(), "Clobbering existing data?");
5715 // Each valid entry in [0, _eden_chunk_index) represents a task.
5716 size_t n_tasks = _eden_chunk_index + 1;
5717 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5718 // Sets the condition for completion of the subtask (how many threads
5719 // need to finish in order to be done).
5720 pst->set_n_threads(n_threads);
5721 pst->set_n_tasks((int)n_tasks);
5722 }
5723
5724 // Merge the survivor plab arrays into _survivor_chunk_array
5725 if (_survivor_plab_array != NULL) {
5726 merge_survivor_plab_arrays(dng->from(), n_threads);
5727 } else {
5728 assert(_survivor_chunk_index == 0, "Error");
5729 }
5730
5731 // To space
5732 {
5733 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5734 assert(!pst->valid(), "Clobbering existing data?");
5735 // Sets the condition for completion of the subtask (how many threads
5736 // need to finish in order to be done).
5737 pst->set_n_threads(n_threads);
5738 pst->set_n_tasks(1);
5739 assert(pst->valid(), "Error");
5740 }
5741
5742 // From space
5743 {
5744 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5745 assert(!pst->valid(), "Clobbering existing data?");
5746 size_t n_tasks = _survivor_chunk_index + 1;
5747 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5748 // Sets the condition for completion of the subtask (how many threads
5749 // need to finish in order to be done).
5750 pst->set_n_threads(n_threads);
5751 pst->set_n_tasks((int)n_tasks);
5752 assert(pst->valid(), "Error");
5753 }
5754 }
5755
5756 // Parallel version of remark
5757 void CMSCollector::do_remark_parallel() {
5758 GenCollectedHeap* gch = GenCollectedHeap::heap();
5759 FlexibleWorkGang* workers = gch->workers();
5760 assert(workers != NULL, "Need parallel worker threads.");
5761 // Choose to use the number of GC workers most recently set
5762 // into "active_workers". If active_workers is not set, set it
5763 // to ParallelGCThreads.
5764 int n_workers = workers->active_workers();
5765 if (n_workers == 0) {
5766 assert(n_workers > 0, "Should have been set during scavenge");
5767 n_workers = ParallelGCThreads;
5768 workers->set_active_workers(n_workers);
5769 }
5770 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5771
5772 CMSParRemarkTask tsk(this,
5773 cms_space,
5774 n_workers, workers, task_queues());
5775
5776 // Set up for parallel process_strong_roots work.
5777 gch->set_par_threads(n_workers);
5778 // We won't be iterating over the cards in the card table updating
5779 // the younger_gen cards, so we shouldn't call the following else
5780 // the verification code as well as subsequent younger_refs_iterate
5781 // code would get confused. XXX
5782 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5783
5784 // The young gen rescan work will not be done as part of
5785 // process_strong_roots (which currently doesn't knw how to
5786 // parallelize such a scan), but rather will be broken up into
5787 // a set of parallel tasks (via the sampling that the [abortable]
5788 // preclean phase did of EdenSpace, plus the [two] tasks of
5789 // scanning the [two] survivor spaces. Further fine-grain
5790 // parallelization of the scanning of the survivor spaces
5791 // themselves, and of precleaning of the younger gen itself
5792 // is deferred to the future.
5793 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5794
5795 // The dirty card rescan work is broken up into a "sequence"
5796 // of parallel tasks (per constituent space) that are dynamically
5797 // claimed by the parallel threads.
5798 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5799
5800 // It turns out that even when we're using 1 thread, doing the work in a
5801 // separate thread causes wide variance in run times. We can't help this
5802 // in the multi-threaded case, but we special-case n=1 here to get
5803 // repeatable measurements of the 1-thread overhead of the parallel code.
5804 if (n_workers > 1) {
5805 // Make refs discovery MT-safe, if it isn't already: it may not
5806 // necessarily be so, since it's possible that we are doing
5807 // ST marking.
5808 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5809 GenCollectedHeap::StrongRootsScope srs(gch);
5810 workers->run_task(&tsk);
5811 } else {
5812 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5813 GenCollectedHeap::StrongRootsScope srs(gch);
5814 tsk.work(0);
5815 }
5816
5817 gch->set_par_threads(0); // 0 ==> non-parallel.
5818 // restore, single-threaded for now, any preserved marks
5819 // as a result of work_q overflow
5820 restore_preserved_marks_if_any();
5821 }
5822
5823 // Non-parallel version of remark
5824 void CMSCollector::do_remark_non_parallel() {
5825 ResourceMark rm;
5826 HandleMark hm;
5827 GenCollectedHeap* gch = GenCollectedHeap::heap();
5828 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5829
5830 MarkRefsIntoAndScanClosure
5831 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5832 &_markStack, this,
5833 false /* should_yield */, false /* not precleaning */);
5834 MarkFromDirtyCardsClosure
5835 markFromDirtyCardsClosure(this, _span,
5836 NULL, // space is set further below
5837 &_markBitMap, &_markStack, &mrias_cl);
5838 {
5839 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5840 // Iterate over the dirty cards, setting the corresponding bits in the
5841 // mod union table.
5842 {
5843 ModUnionClosure modUnionClosure(&_modUnionTable);
5844 _ct->ct_bs()->dirty_card_iterate(
5845 _cmsGen->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 if (VerifyDuringGC &&
5871 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5872 HandleMark hm; // Discard invalid handles created during verification
5873 Universe::verify();
5874 }
5875 {
5876 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5877
5878 verify_work_stacks_empty();
5879
5880 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5881 GenCollectedHeap::StrongRootsScope srs(gch);
5882 gch->gen_process_strong_roots(_cmsGen->level(),
5883 true, // younger gens as roots
5884 false, // use the local StrongRootsScope
5885 SharedHeap::ScanningOption(roots_scanning_options()),
5886 &mrias_cl,
5887 NULL,
5888 NULL); // The dirty klasses will be handled below
5889
5890 assert(should_unload_classes()
5891 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5892 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5893 }
5894
5895 {
5896 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5897
5898 verify_work_stacks_empty();
5899
5900 // Scan all class loader data objects that might have been introduced
5901 // during concurrent marking.
5902 ResourceMark rm;
5903 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5904 for (int i = 0; i < array->length(); i++) {
5905 mrias_cl.do_class_loader_data(array->at(i));
5906 }
5907
5908 // We don't need to keep track of new CLDs anymore.
5909 ClassLoaderDataGraph::remember_new_clds(false);
5910
5911 verify_work_stacks_empty();
5912 }
5913
5914 {
5915 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5916
5917 verify_work_stacks_empty();
5918
5919 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5920 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5921
5922 verify_work_stacks_empty();
5923 }
5924
5925 // We might have added oops to ClassLoaderData::_handles during the
5926 // concurrent marking phase. These oops point to newly allocated objects
5927 // that are guaranteed to be kept alive. Either by the direct allocation
5928 // code, or when the young collector processes the strong roots. Hence,
5929 // we don't have to revisit the _handles block during the remark phase.
5930
5931 verify_work_stacks_empty();
5932 // Restore evacuated mark words, if any, used for overflow list links
5933 if (!CMSOverflowEarlyRestoration) {
5934 restore_preserved_marks_if_any();
5935 }
5936 verify_overflow_empty();
5937 }
5938
5939 ////////////////////////////////////////////////////////
5940 // Parallel Reference Processing Task Proxy Class
5941 ////////////////////////////////////////////////////////
5942 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5943 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5944 CMSCollector* _collector;
5945 CMSBitMap* _mark_bit_map;
5946 const MemRegion _span;
5947 ProcessTask& _task;
5948
5949 public:
5950 CMSRefProcTaskProxy(ProcessTask& task,
5951 CMSCollector* collector,
5952 const MemRegion& span,
5953 CMSBitMap* mark_bit_map,
5954 AbstractWorkGang* workers,
5955 OopTaskQueueSet* task_queues):
5956 // XXX Should superclass AGTWOQ also know about AWG since it knows
5957 // about the task_queues used by the AWG? Then it could initialize
5958 // the terminator() object. See 6984287. The set_for_termination()
5959 // below is a temporary band-aid for the regression in 6984287.
5960 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5961 task_queues),
5962 _task(task),
5963 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5964 {
5965 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5966 "Inconsistency in _span");
5967 set_for_termination(workers->active_workers());
5968 }
5969
5970 OopTaskQueueSet* task_queues() { return queues(); }
5971
5972 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5973
5974 void do_work_steal(int i,
5975 CMSParDrainMarkingStackClosure* drain,
5976 CMSParKeepAliveClosure* keep_alive,
5977 int* seed);
5978
5979 virtual void work(uint worker_id);
5980 };
5981
5982 void CMSRefProcTaskProxy::work(uint worker_id) {
5983 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5984 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5985 _mark_bit_map,
5986 work_queue(worker_id));
5987 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5988 _mark_bit_map,
5989 work_queue(worker_id));
5990 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5991 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5992 if (_task.marks_oops_alive()) {
5993 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5994 _collector->hash_seed(worker_id));
5995 }
5996 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5997 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5998 }
5999
6000 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6001 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6002 EnqueueTask& _task;
6003
6004 public:
6005 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6006 : AbstractGangTask("Enqueue reference objects in parallel"),
6007 _task(task)
6008 { }
6009
6010 virtual void work(uint worker_id)
6011 {
6012 _task.work(worker_id);
6013 }
6014 };
6015
6016 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6017 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6018 _span(span),
6019 _bit_map(bit_map),
6020 _work_queue(work_queue),
6021 _mark_and_push(collector, span, bit_map, work_queue),
6022 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6023 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6024 { }
6025
6026 // . see if we can share work_queues with ParNew? XXX
6027 void CMSRefProcTaskProxy::do_work_steal(int i,
6028 CMSParDrainMarkingStackClosure* drain,
6029 CMSParKeepAliveClosure* keep_alive,
6030 int* seed) {
6031 OopTaskQueue* work_q = work_queue(i);
6032 NOT_PRODUCT(int num_steals = 0;)
6033 oop obj_to_scan;
6034
6035 while (true) {
6036 // Completely finish any left over work from (an) earlier round(s)
6037 drain->trim_queue(0);
6038 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6039 (size_t)ParGCDesiredObjsFromOverflowList);
6040 // Now check if there's any work in the overflow list
6041 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6042 // only affects the number of attempts made to get work from the
6043 // overflow list and does not affect the number of workers. Just
6044 // pass ParallelGCThreads so this behavior is unchanged.
6045 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6046 work_q,
6047 ParallelGCThreads)) {
6048 // Found something in global overflow list;
6049 // not yet ready to go stealing work from others.
6050 // We'd like to assert(work_q->size() != 0, ...)
6051 // because we just took work from the overflow list,
6052 // but of course we can't, since all of that might have
6053 // been already stolen from us.
6054 continue;
6055 }
6056 // Verify that we have no work before we resort to stealing
6057 assert(work_q->size() == 0, "Have work, shouldn't steal");
6058 // Try to steal from other queues that have work
6059 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6060 NOT_PRODUCT(num_steals++;)
6061 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6062 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6063 // Do scanning work
6064 obj_to_scan->oop_iterate(keep_alive);
6065 // Loop around, finish this work, and try to steal some more
6066 } else if (terminator()->offer_termination()) {
6067 break; // nirvana from the infinite cycle
6068 }
6069 }
6070 NOT_PRODUCT(
6071 if (PrintCMSStatistics != 0) {
6072 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6073 }
6074 )
6075 }
6076
6077 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6078 {
6079 GenCollectedHeap* gch = GenCollectedHeap::heap();
6080 FlexibleWorkGang* workers = gch->workers();
6081 assert(workers != NULL, "Need parallel worker threads.");
6082 CMSRefProcTaskProxy rp_task(task, &_collector,
6083 _collector.ref_processor()->span(),
6084 _collector.markBitMap(),
6085 workers, _collector.task_queues());
6086 workers->run_task(&rp_task);
6087 }
6088
6089 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6090 {
6091
6092 GenCollectedHeap* gch = GenCollectedHeap::heap();
6093 FlexibleWorkGang* workers = gch->workers();
6094 assert(workers != NULL, "Need parallel worker threads.");
6095 CMSRefEnqueueTaskProxy enq_task(task);
6096 workers->run_task(&enq_task);
6097 }
6098
6099 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6100
6101 ResourceMark rm;
6102 HandleMark hm;
6103
6104 ReferenceProcessor* rp = ref_processor();
6105 assert(rp->span().equals(_span), "Spans should be equal");
6106 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6107 // Process weak references.
6108 rp->setup_policy(clear_all_soft_refs);
6109 verify_work_stacks_empty();
6110
6111 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6112 &_markStack, false /* !preclean */);
6113 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6114 _span, &_markBitMap, &_markStack,
6115 &cmsKeepAliveClosure, false /* !preclean */);
6116 {
6117 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6118
6119 ReferenceProcessorStats stats;
6120 if (rp->processing_is_mt()) {
6121 // Set the degree of MT here. If the discovery is done MT, there
6122 // may have been a different number of threads doing the discovery
6123 // and a different number of discovered lists may have Ref objects.
6124 // That is OK as long as the Reference lists are balanced (see
6125 // balance_all_queues() and balance_queues()).
6126 GenCollectedHeap* gch = GenCollectedHeap::heap();
6127 int active_workers = ParallelGCThreads;
6128 FlexibleWorkGang* workers = gch->workers();
6129 if (workers != NULL) {
6130 active_workers = workers->active_workers();
6131 // The expectation is that active_workers will have already
6132 // been set to a reasonable value. If it has not been set,
6133 // investigate.
6134 assert(active_workers > 0, "Should have been set during scavenge");
6135 }
6136 rp->set_active_mt_degree(active_workers);
6137 CMSRefProcTaskExecutor task_executor(*this);
6138 stats = rp->process_discovered_references(&_is_alive_closure,
6139 &cmsKeepAliveClosure,
6140 &cmsDrainMarkingStackClosure,
6141 &task_executor,
6142 _gc_timer_cm,
6143 _gc_tracer_cm->gc_id());
6144 } else {
6145 stats = rp->process_discovered_references(&_is_alive_closure,
6146 &cmsKeepAliveClosure,
6147 &cmsDrainMarkingStackClosure,
6148 NULL,
6149 _gc_timer_cm,
6150 _gc_tracer_cm->gc_id());
6151 }
6152 _gc_tracer_cm->report_gc_reference_stats(stats);
6153
6154 }
6155
6156 // This is the point where the entire marking should have completed.
6157 verify_work_stacks_empty();
6158
6159 if (should_unload_classes()) {
6160 {
6161 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6162
6163 // Unload classes and purge the SystemDictionary.
6164 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6165
6166 // Unload nmethods.
6167 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6168
6169 // Prune dead klasses from subklass/sibling/implementor lists.
6170 Klass::clean_weak_klass_links(&_is_alive_closure);
6171 }
6172
6173 {
6174 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6175 // Clean up unreferenced symbols in symbol table.
6176 SymbolTable::unlink();
6177 }
6178 }
6179
6180 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6181 // Need to check if we really scanned the StringTable.
6182 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6183 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6184 // Delete entries for dead interned strings.
6185 StringTable::unlink(&_is_alive_closure);
6186 }
6187
6188 // Restore any preserved marks as a result of mark stack or
6189 // work queue overflow
6190 restore_preserved_marks_if_any(); // done single-threaded for now
6191
6192 rp->set_enqueuing_is_done(true);
6193 if (rp->processing_is_mt()) {
6194 rp->balance_all_queues();
6195 CMSRefProcTaskExecutor task_executor(*this);
6196 rp->enqueue_discovered_references(&task_executor);
6197 } else {
6198 rp->enqueue_discovered_references(NULL);
6199 }
6200 rp->verify_no_references_recorded();
6201 assert(!rp->discovery_enabled(), "should have been disabled");
6202 }
6203
6204 #ifndef PRODUCT
6205 void CMSCollector::check_correct_thread_executing() {
6206 Thread* t = Thread::current();
6207 // Only the VM thread or the CMS thread should be here.
6208 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6209 "Unexpected thread type");
6210 // If this is the vm thread, the foreground process
6211 // should not be waiting. Note that _foregroundGCIsActive is
6212 // true while the foreground collector is waiting.
6213 if (_foregroundGCShouldWait) {
6214 // We cannot be the VM thread
6215 assert(t->is_ConcurrentGC_thread(),
6216 "Should be CMS thread");
6217 } else {
6218 // We can be the CMS thread only if we are in a stop-world
6219 // phase of CMS collection.
6220 if (t->is_ConcurrentGC_thread()) {
6221 assert(_collectorState == InitialMarking ||
6222 _collectorState == FinalMarking,
6223 "Should be a stop-world phase");
6224 // The CMS thread should be holding the CMS_token.
6225 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6226 "Potential interference with concurrently "
6227 "executing VM thread");
6228 }
6229 }
6230 }
6231 #endif
6232
6233 void CMSCollector::sweep(bool asynch) {
6234 assert(_collectorState == Sweeping, "just checking");
6235 check_correct_thread_executing();
6236 verify_work_stacks_empty();
6237 verify_overflow_empty();
6238 increment_sweep_count();
6239 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6240
6241 _inter_sweep_timer.stop();
6242 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6243
6244 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6245 _intra_sweep_timer.reset();
6246 _intra_sweep_timer.start();
6247 if (asynch) {
6248 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6249 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6250 // First sweep the old gen
6251 {
6252 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6253 bitMapLock());
6254 sweepWork(_cmsGen, asynch);
6255 }
6256
6257 // Update Universe::_heap_*_at_gc figures.
6258 // We need all the free list locks to make the abstract state
6259 // transition from Sweeping to Resetting. See detailed note
6260 // further below.
6261 {
6262 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6263 // Update heap occupancy information which is used as
6264 // input to soft ref clearing policy at the next gc.
6265 Universe::update_heap_info_at_gc();
6266 _collectorState = Resizing;
6267 }
6268 } else {
6269 // already have needed locks
6270 sweepWork(_cmsGen, asynch);
6271 // Update heap occupancy information which is used as
6272 // input to soft ref clearing policy at the next gc.
6273 Universe::update_heap_info_at_gc();
6274 _collectorState = Resizing;
6275 }
6276 verify_work_stacks_empty();
6277 verify_overflow_empty();
6278
6279 if (should_unload_classes()) {
6280 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6281 // requires that the virtual spaces are stable and not deleted.
6282 ClassLoaderDataGraph::set_should_purge(true);
6283 }
6284
6285 _intra_sweep_timer.stop();
6286 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6287
6288 _inter_sweep_timer.reset();
6289 _inter_sweep_timer.start();
6290
6291 // We need to use a monotonically non-decreasing time in ms
6292 // or we will see time-warp warnings and os::javaTimeMillis()
6293 // does not guarantee monotonicity.
6294 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6295 update_time_of_last_gc(now);
6296
6297 // NOTE on abstract state transitions:
6298 // Mutators allocate-live and/or mark the mod-union table dirty
6299 // based on the state of the collection. The former is done in
6300 // the interval [Marking, Sweeping] and the latter in the interval
6301 // [Marking, Sweeping). Thus the transitions into the Marking state
6302 // and out of the Sweeping state must be synchronously visible
6303 // globally to the mutators.
6304 // The transition into the Marking state happens with the world
6305 // stopped so the mutators will globally see it. Sweeping is
6306 // done asynchronously by the background collector so the transition
6307 // from the Sweeping state to the Resizing state must be done
6308 // under the freelistLock (as is the check for whether to
6309 // allocate-live and whether to dirty the mod-union table).
6310 assert(_collectorState == Resizing, "Change of collector state to"
6311 " Resizing must be done under the freelistLocks (plural)");
6312
6313 // Now that sweeping has been completed, we clear
6314 // the incremental_collection_failed flag,
6315 // thus inviting a younger gen collection to promote into
6316 // this generation. If such a promotion may still fail,
6317 // the flag will be set again when a young collection is
6318 // attempted.
6319 GenCollectedHeap* gch = GenCollectedHeap::heap();
6320 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6321 gch->update_full_collections_completed(_collection_count_start);
6322 }
6323
6324 // FIX ME!!! Looks like this belongs in CFLSpace, with
6325 // CMSGen merely delegating to it.
6326 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6327 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6328 HeapWord* minAddr = _cmsSpace->bottom();
6329 HeapWord* largestAddr =
6330 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6331 if (largestAddr == NULL) {
6332 // The dictionary appears to be empty. In this case
6333 // try to coalesce at the end of the heap.
6334 largestAddr = _cmsSpace->end();
6335 }
6336 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6337 size_t nearLargestOffset =
6338 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6339 if (PrintFLSStatistics != 0) {
6340 gclog_or_tty->print_cr(
6341 "CMS: Large Block: " PTR_FORMAT ";"
6342 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6343 largestAddr,
6344 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6345 }
6346 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6347 }
6348
6349 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6350 return addr >= _cmsSpace->nearLargestChunk();
6351 }
6352
6353 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6354 return _cmsSpace->find_chunk_at_end();
6355 }
6356
6357 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6358 bool full) {
6359 // The next lower level has been collected. Gather any statistics
6360 // that are of interest at this point.
6361 if (!full && (current_level + 1) == level()) {
6362 // Gather statistics on the young generation collection.
6363 collector()->stats().record_gc0_end(used());
6364 }
6365 }
6366
6367 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6368 if (PrintGCDetails && Verbose) {
6369 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6370 }
6371 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6372 _debug_collection_type =
6373 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6374 if (PrintGCDetails && Verbose) {
6375 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6376 }
6377 }
6378
6379 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6380 bool asynch) {
6381 // We iterate over the space(s) underlying this generation,
6382 // checking the mark bit map to see if the bits corresponding
6383 // to specific blocks are marked or not. Blocks that are
6384 // marked are live and are not swept up. All remaining blocks
6385 // are swept up, with coalescing on-the-fly as we sweep up
6386 // contiguous free and/or garbage blocks:
6387 // We need to ensure that the sweeper synchronizes with allocators
6388 // and stop-the-world collectors. In particular, the following
6389 // locks are used:
6390 // . CMS token: if this is held, a stop the world collection cannot occur
6391 // . freelistLock: if this is held no allocation can occur from this
6392 // generation by another thread
6393 // . bitMapLock: if this is held, no other thread can access or update
6394 //
6395
6396 // Note that we need to hold the freelistLock if we use
6397 // block iterate below; else the iterator might go awry if
6398 // a mutator (or promotion) causes block contents to change
6399 // (for instance if the allocator divvies up a block).
6400 // If we hold the free list lock, for all practical purposes
6401 // young generation GC's can't occur (they'll usually need to
6402 // promote), so we might as well prevent all young generation
6403 // GC's while we do a sweeping step. For the same reason, we might
6404 // as well take the bit map lock for the entire duration
6405
6406 // check that we hold the requisite locks
6407 assert(have_cms_token(), "Should hold cms token");
6408 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6409 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6410 "Should possess CMS token to sweep");
6411 assert_lock_strong(gen->freelistLock());
6412 assert_lock_strong(bitMapLock());
6413
6414 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6415 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6416 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6417 _inter_sweep_estimate.padded_average(),
6418 _intra_sweep_estimate.padded_average());
6419 gen->setNearLargestChunk();
6420
6421 {
6422 SweepClosure sweepClosure(this, gen, &_markBitMap,
6423 CMSYield && asynch);
6424 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6425 // We need to free-up/coalesce garbage/blocks from a
6426 // co-terminal free run. This is done in the SweepClosure
6427 // destructor; so, do not remove this scope, else the
6428 // end-of-sweep-census below will be off by a little bit.
6429 }
6430 gen->cmsSpace()->sweep_completed();
6431 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6432 if (should_unload_classes()) { // unloaded classes this cycle,
6433 _concurrent_cycles_since_last_unload = 0; // ... reset count
6434 } else { // did not unload classes,
6435 _concurrent_cycles_since_last_unload++; // ... increment count
6436 }
6437 }
6438
6439 // Reset CMS data structures (for now just the marking bit map)
6440 // preparatory for the next cycle.
6441 void CMSCollector::reset(bool asynch) {
6442 if (asynch) {
6443 CMSTokenSyncWithLocks ts(true, bitMapLock());
6444
6445 // If the state is not "Resetting", the foreground thread
6446 // has done a collection and the resetting.
6447 if (_collectorState != Resetting) {
6448 assert(_collectorState == Idling, "The state should only change"
6449 " because the foreground collector has finished the collection");
6450 return;
6451 }
6452
6453 // Clear the mark bitmap (no grey objects to start with)
6454 // for the next cycle.
6455 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6456 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6457
6458 HeapWord* curAddr = _markBitMap.startWord();
6459 while (curAddr < _markBitMap.endWord()) {
6460 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6461 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6462 _markBitMap.clear_large_range(chunk);
6463 if (ConcurrentMarkSweepThread::should_yield() &&
6464 !foregroundGCIsActive() &&
6465 CMSYield) {
6466 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6467 "CMS thread should hold CMS token");
6468 assert_lock_strong(bitMapLock());
6469 bitMapLock()->unlock();
6470 ConcurrentMarkSweepThread::desynchronize(true);
6471 ConcurrentMarkSweepThread::acknowledge_yield_request();
6472 stopTimer();
6473 if (PrintCMSStatistics != 0) {
6474 incrementYields();
6475 }
6476 icms_wait();
6477
6478 // See the comment in coordinator_yield()
6479 for (unsigned i = 0; i < CMSYieldSleepCount &&
6480 ConcurrentMarkSweepThread::should_yield() &&
6481 !CMSCollector::foregroundGCIsActive(); ++i) {
6482 os::sleep(Thread::current(), 1, false);
6483 ConcurrentMarkSweepThread::acknowledge_yield_request();
6484 }
6485
6486 ConcurrentMarkSweepThread::synchronize(true);
6487 bitMapLock()->lock_without_safepoint_check();
6488 startTimer();
6489 }
6490 curAddr = chunk.end();
6491 }
6492 // A successful mostly concurrent collection has been done.
6493 // Because only the full (i.e., concurrent mode failure) collections
6494 // are being measured for gc overhead limits, clean the "near" flag
6495 // and count.
6496 size_policy()->reset_gc_overhead_limit_count();
6497 _collectorState = Idling;
6498 } else {
6499 // already have the lock
6500 assert(_collectorState == Resetting, "just checking");
6501 assert_lock_strong(bitMapLock());
6502 _markBitMap.clear_all();
6503 _collectorState = Idling;
6504 }
6505
6506 // Stop incremental mode after a cycle completes, so that any future cycles
6507 // are triggered by allocation.
6508 stop_icms();
6509
6510 NOT_PRODUCT(
6511 if (RotateCMSCollectionTypes) {
6512 _cmsGen->rotate_debug_collection_type();
6513 }
6514 )
6515
6516 register_gc_end();
6517 }
6518
6519 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6520 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6521 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6522 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6523 TraceCollectorStats tcs(counters());
6524
6525 switch (op) {
6526 case CMS_op_checkpointRootsInitial: {
6527 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6528 checkpointRootsInitial(true); // asynch
6529 if (PrintGC) {
6530 _cmsGen->printOccupancy("initial-mark");
6531 }
6532 break;
6533 }
6534 case CMS_op_checkpointRootsFinal: {
6535 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6536 checkpointRootsFinal(true, // asynch
6537 false, // !clear_all_soft_refs
6538 false); // !init_mark_was_synchronous
6539 if (PrintGC) {
6540 _cmsGen->printOccupancy("remark");
6541 }
6542 break;
6543 }
6544 default:
6545 fatal("No such CMS_op");
6546 }
6547 }
6548
6549 #ifndef PRODUCT
6550 size_t const CMSCollector::skip_header_HeapWords() {
6551 return FreeChunk::header_size();
6552 }
6553
6554 // Try and collect here conditions that should hold when
6555 // CMS thread is exiting. The idea is that the foreground GC
6556 // thread should not be blocked if it wants to terminate
6557 // the CMS thread and yet continue to run the VM for a while
6558 // after that.
6559 void CMSCollector::verify_ok_to_terminate() const {
6560 assert(Thread::current()->is_ConcurrentGC_thread(),
6561 "should be called by CMS thread");
6562 assert(!_foregroundGCShouldWait, "should be false");
6563 // We could check here that all the various low-level locks
6564 // are not held by the CMS thread, but that is overkill; see
6565 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6566 // is checked.
6567 }
6568 #endif
6569
6570 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6571 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6572 "missing Printezis mark?");
6573 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6574 size_t size = pointer_delta(nextOneAddr + 1, addr);
6575 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6576 "alignment problem");
6577 assert(size >= 3, "Necessary for Printezis marks to work");
6578 return size;
6579 }
6580
6581 // A variant of the above (block_size_using_printezis_bits()) except
6582 // that we return 0 if the P-bits are not yet set.
6583 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6584 if (_markBitMap.isMarked(addr + 1)) {
6585 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6586 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6587 size_t size = pointer_delta(nextOneAddr + 1, addr);
6588 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6589 "alignment problem");
6590 assert(size >= 3, "Necessary for Printezis marks to work");
6591 return size;
6592 }
6593 return 0;
6594 }
6595
6596 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6597 size_t sz = 0;
6598 oop p = (oop)addr;
6599 if (p->klass_or_null() != NULL) {
6600 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6601 } else {
6602 sz = block_size_using_printezis_bits(addr);
6603 }
6604 assert(sz > 0, "size must be nonzero");
6605 HeapWord* next_block = addr + sz;
6606 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6607 CardTableModRefBS::card_size);
6608 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6609 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6610 "must be different cards");
6611 return next_card;
6612 }
6613
6614
6615 // CMS Bit Map Wrapper /////////////////////////////////////////
6616
6617 // Construct a CMS bit map infrastructure, but don't create the
6618 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6619 // further below.
6620 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6621 _bm(),
6622 _shifter(shifter),
6623 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6624 {
6625 _bmStartWord = 0;
6626 _bmWordSize = 0;
6627 }
6628
6629 bool CMSBitMap::allocate(MemRegion mr) {
6630 _bmStartWord = mr.start();
6631 _bmWordSize = mr.word_size();
6632 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6633 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6634 if (!brs.is_reserved()) {
6635 warning("CMS bit map allocation failure");
6636 return false;
6637 }
6638 // For now we'll just commit all of the bit map up front.
6639 // Later on we'll try to be more parsimonious with swap.
6640 if (!_virtual_space.initialize(brs, brs.size())) {
6641 warning("CMS bit map backing store failure");
6642 return false;
6643 }
6644 assert(_virtual_space.committed_size() == brs.size(),
6645 "didn't reserve backing store for all of CMS bit map?");
6646 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6647 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6648 _bmWordSize, "inconsistency in bit map sizing");
6649 _bm.set_size(_bmWordSize >> _shifter);
6650
6651 // bm.clear(); // can we rely on getting zero'd memory? verify below
6652 assert(isAllClear(),
6653 "Expected zero'd memory from ReservedSpace constructor");
6654 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6655 "consistency check");
6656 return true;
6657 }
6658
6659 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6660 HeapWord *next_addr, *end_addr, *last_addr;
6661 assert_locked();
6662 assert(covers(mr), "out-of-range error");
6663 // XXX assert that start and end are appropriately aligned
6664 for (next_addr = mr.start(), end_addr = mr.end();
6665 next_addr < end_addr; next_addr = last_addr) {
6666 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6667 last_addr = dirty_region.end();
6668 if (!dirty_region.is_empty()) {
6669 cl->do_MemRegion(dirty_region);
6670 } else {
6671 assert(last_addr == end_addr, "program logic");
6672 return;
6673 }
6674 }
6675 }
6676
6677 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6678 _bm.print_on_error(st, prefix);
6679 }
6680
6681 #ifndef PRODUCT
6682 void CMSBitMap::assert_locked() const {
6683 CMSLockVerifier::assert_locked(lock());
6684 }
6685
6686 bool CMSBitMap::covers(MemRegion mr) const {
6687 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6688 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6689 "size inconsistency");
6690 return (mr.start() >= _bmStartWord) &&
6691 (mr.end() <= endWord());
6692 }
6693
6694 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6695 return (start >= _bmStartWord && (start + size) <= endWord());
6696 }
6697
6698 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6699 // verify that there are no 1 bits in the interval [left, right)
6700 FalseBitMapClosure falseBitMapClosure;
6701 iterate(&falseBitMapClosure, left, right);
6702 }
6703
6704 void CMSBitMap::region_invariant(MemRegion mr)
6705 {
6706 assert_locked();
6707 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6708 assert(!mr.is_empty(), "unexpected empty region");
6709 assert(covers(mr), "mr should be covered by bit map");
6710 // convert address range into offset range
6711 size_t start_ofs = heapWordToOffset(mr.start());
6712 // Make sure that end() is appropriately aligned
6713 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6714 (1 << (_shifter+LogHeapWordSize))),
6715 "Misaligned mr.end()");
6716 size_t end_ofs = heapWordToOffset(mr.end());
6717 assert(end_ofs > start_ofs, "Should mark at least one bit");
6718 }
6719
6720 #endif
6721
6722 bool CMSMarkStack::allocate(size_t size) {
6723 // allocate a stack of the requisite depth
6724 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6725 size * sizeof(oop)));
6726 if (!rs.is_reserved()) {
6727 warning("CMSMarkStack allocation failure");
6728 return false;
6729 }
6730 if (!_virtual_space.initialize(rs, rs.size())) {
6731 warning("CMSMarkStack backing store failure");
6732 return false;
6733 }
6734 assert(_virtual_space.committed_size() == rs.size(),
6735 "didn't reserve backing store for all of CMS stack?");
6736 _base = (oop*)(_virtual_space.low());
6737 _index = 0;
6738 _capacity = size;
6739 NOT_PRODUCT(_max_depth = 0);
6740 return true;
6741 }
6742
6743 // XXX FIX ME !!! In the MT case we come in here holding a
6744 // leaf lock. For printing we need to take a further lock
6745 // which has lower rank. We need to recalibrate the two
6746 // lock-ranks involved in order to be able to print the
6747 // messages below. (Or defer the printing to the caller.
6748 // For now we take the expedient path of just disabling the
6749 // messages for the problematic case.)
6750 void CMSMarkStack::expand() {
6751 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6752 if (_capacity == MarkStackSizeMax) {
6753 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6754 // We print a warning message only once per CMS cycle.
6755 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6756 }
6757 return;
6758 }
6759 // Double capacity if possible
6760 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6761 // Do not give up existing stack until we have managed to
6762 // get the double capacity that we desired.
6763 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6764 new_capacity * sizeof(oop)));
6765 if (rs.is_reserved()) {
6766 // Release the backing store associated with old stack
6767 _virtual_space.release();
6768 // Reinitialize virtual space for new stack
6769 if (!_virtual_space.initialize(rs, rs.size())) {
6770 fatal("Not enough swap for expanded marking stack");
6771 }
6772 _base = (oop*)(_virtual_space.low());
6773 _index = 0;
6774 _capacity = new_capacity;
6775 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6776 // Failed to double capacity, continue;
6777 // we print a detail message only once per CMS cycle.
6778 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6779 SIZE_FORMAT"K",
6780 _capacity / K, new_capacity / K);
6781 }
6782 }
6783
6784
6785 // Closures
6786 // XXX: there seems to be a lot of code duplication here;
6787 // should refactor and consolidate common code.
6788
6789 // This closure is used to mark refs into the CMS generation in
6790 // the CMS bit map. Called at the first checkpoint. This closure
6791 // assumes that we do not need to re-mark dirty cards; if the CMS
6792 // generation on which this is used is not an oldest
6793 // generation then this will lose younger_gen cards!
6794
6795 MarkRefsIntoClosure::MarkRefsIntoClosure(
6796 MemRegion span, CMSBitMap* bitMap):
6797 _span(span),
6798 _bitMap(bitMap)
6799 {
6800 assert(_ref_processor == NULL, "deliberately left NULL");
6801 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6802 }
6803
6804 void MarkRefsIntoClosure::do_oop(oop obj) {
6805 // if p points into _span, then mark corresponding bit in _markBitMap
6806 assert(obj->is_oop(), "expected an oop");
6807 HeapWord* addr = (HeapWord*)obj;
6808 if (_span.contains(addr)) {
6809 // this should be made more efficient
6810 _bitMap->mark(addr);
6811 }
6812 }
6813
6814 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6815 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6816
6817 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6818 MemRegion span, CMSBitMap* bitMap):
6819 _span(span),
6820 _bitMap(bitMap)
6821 {
6822 assert(_ref_processor == NULL, "deliberately left NULL");
6823 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6824 }
6825
6826 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6827 // if p points into _span, then mark corresponding bit in _markBitMap
6828 assert(obj->is_oop(), "expected an oop");
6829 HeapWord* addr = (HeapWord*)obj;
6830 if (_span.contains(addr)) {
6831 // this should be made more efficient
6832 _bitMap->par_mark(addr);
6833 }
6834 }
6835
6836 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6837 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6838
6839 // A variant of the above, used for CMS marking verification.
6840 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6841 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6842 _span(span),
6843 _verification_bm(verification_bm),
6844 _cms_bm(cms_bm)
6845 {
6846 assert(_ref_processor == NULL, "deliberately left NULL");
6847 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6848 }
6849
6850 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6851 // if p points into _span, then mark corresponding bit in _markBitMap
6852 assert(obj->is_oop(), "expected an oop");
6853 HeapWord* addr = (HeapWord*)obj;
6854 if (_span.contains(addr)) {
6855 _verification_bm->mark(addr);
6856 if (!_cms_bm->isMarked(addr)) {
6857 oop(addr)->print();
6858 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6859 fatal("... aborting");
6860 }
6861 }
6862 }
6863
6864 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6865 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6866
6867 //////////////////////////////////////////////////
6868 // MarkRefsIntoAndScanClosure
6869 //////////////////////////////////////////////////
6870
6871 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6872 ReferenceProcessor* rp,
6873 CMSBitMap* bit_map,
6874 CMSBitMap* mod_union_table,
6875 CMSMarkStack* mark_stack,
6876 CMSCollector* collector,
6877 bool should_yield,
6878 bool concurrent_precleaning):
6879 _collector(collector),
6880 _span(span),
6881 _bit_map(bit_map),
6882 _mark_stack(mark_stack),
6883 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6884 mark_stack, concurrent_precleaning),
6885 _yield(should_yield),
6886 _concurrent_precleaning(concurrent_precleaning),
6887 _freelistLock(NULL)
6888 {
6889 _ref_processor = rp;
6890 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6891 }
6892
6893 // This closure is used to mark refs into the CMS generation at the
6894 // second (final) checkpoint, and to scan and transitively follow
6895 // the unmarked oops. It is also used during the concurrent precleaning
6896 // phase while scanning objects on dirty cards in the CMS generation.
6897 // The marks are made in the marking bit map and the marking stack is
6898 // used for keeping the (newly) grey objects during the scan.
6899 // The parallel version (Par_...) appears further below.
6900 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6901 if (obj != NULL) {
6902 assert(obj->is_oop(), "expected an oop");
6903 HeapWord* addr = (HeapWord*)obj;
6904 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6905 assert(_collector->overflow_list_is_empty(),
6906 "overflow list should be empty");
6907 if (_span.contains(addr) &&
6908 !_bit_map->isMarked(addr)) {
6909 // mark bit map (object is now grey)
6910 _bit_map->mark(addr);
6911 // push on marking stack (stack should be empty), and drain the
6912 // stack by applying this closure to the oops in the oops popped
6913 // from the stack (i.e. blacken the grey objects)
6914 bool res = _mark_stack->push(obj);
6915 assert(res, "Should have space to push on empty stack");
6916 do {
6917 oop new_oop = _mark_stack->pop();
6918 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6919 assert(_bit_map->isMarked((HeapWord*)new_oop),
6920 "only grey objects on this stack");
6921 // iterate over the oops in this oop, marking and pushing
6922 // the ones in CMS heap (i.e. in _span).
6923 new_oop->oop_iterate(&_pushAndMarkClosure);
6924 // check if it's time to yield
6925 do_yield_check();
6926 } while (!_mark_stack->isEmpty() ||
6927 (!_concurrent_precleaning && take_from_overflow_list()));
6928 // if marking stack is empty, and we are not doing this
6929 // during precleaning, then check the overflow list
6930 }
6931 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6932 assert(_collector->overflow_list_is_empty(),
6933 "overflow list was drained above");
6934 // We could restore evacuated mark words, if any, used for
6935 // overflow list links here because the overflow list is
6936 // provably empty here. That would reduce the maximum
6937 // size requirements for preserved_{oop,mark}_stack.
6938 // But we'll just postpone it until we are all done
6939 // so we can just stream through.
6940 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6941 _collector->restore_preserved_marks_if_any();
6942 assert(_collector->no_preserved_marks(), "No preserved marks");
6943 }
6944 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6945 "All preserved marks should have been restored above");
6946 }
6947 }
6948
6949 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6950 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6951
6952 void MarkRefsIntoAndScanClosure::do_yield_work() {
6953 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6954 "CMS thread should hold CMS token");
6955 assert_lock_strong(_freelistLock);
6956 assert_lock_strong(_bit_map->lock());
6957 // relinquish the free_list_lock and bitMaplock()
6958 _bit_map->lock()->unlock();
6959 _freelistLock->unlock();
6960 ConcurrentMarkSweepThread::desynchronize(true);
6961 ConcurrentMarkSweepThread::acknowledge_yield_request();
6962 _collector->stopTimer();
6963 if (PrintCMSStatistics != 0) {
6964 _collector->incrementYields();
6965 }
6966 _collector->icms_wait();
6967
6968 // See the comment in coordinator_yield()
6969 for (unsigned i = 0;
6970 i < CMSYieldSleepCount &&
6971 ConcurrentMarkSweepThread::should_yield() &&
6972 !CMSCollector::foregroundGCIsActive();
6973 ++i) {
6974 os::sleep(Thread::current(), 1, false);
6975 ConcurrentMarkSweepThread::acknowledge_yield_request();
6976 }
6977
6978 ConcurrentMarkSweepThread::synchronize(true);
6979 _freelistLock->lock_without_safepoint_check();
6980 _bit_map->lock()->lock_without_safepoint_check();
6981 _collector->startTimer();
6982 }
6983
6984 ///////////////////////////////////////////////////////////
6985 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6986 // MarkRefsIntoAndScanClosure
6987 ///////////////////////////////////////////////////////////
6988 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6989 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6990 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6991 _span(span),
6992 _bit_map(bit_map),
6993 _work_queue(work_queue),
6994 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6995 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6996 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6997 {
6998 _ref_processor = rp;
6999 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7000 }
7001
7002 // This closure is used to mark refs into the CMS generation at the
7003 // second (final) checkpoint, and to scan and transitively follow
7004 // the unmarked oops. The marks are made in the marking bit map and
7005 // the work_queue is used for keeping the (newly) grey objects during
7006 // the scan phase whence they are also available for stealing by parallel
7007 // threads. Since the marking bit map is shared, updates are
7008 // synchronized (via CAS).
7009 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7010 if (obj != NULL) {
7011 // Ignore mark word because this could be an already marked oop
7012 // that may be chained at the end of the overflow list.
7013 assert(obj->is_oop(true), "expected an oop");
7014 HeapWord* addr = (HeapWord*)obj;
7015 if (_span.contains(addr) &&
7016 !_bit_map->isMarked(addr)) {
7017 // mark bit map (object will become grey):
7018 // It is possible for several threads to be
7019 // trying to "claim" this object concurrently;
7020 // the unique thread that succeeds in marking the
7021 // object first will do the subsequent push on
7022 // to the work queue (or overflow list).
7023 if (_bit_map->par_mark(addr)) {
7024 // push on work_queue (which may not be empty), and trim the
7025 // queue to an appropriate length by applying this closure to
7026 // the oops in the oops popped from the stack (i.e. blacken the
7027 // grey objects)
7028 bool res = _work_queue->push(obj);
7029 assert(res, "Low water mark should be less than capacity?");
7030 trim_queue(_low_water_mark);
7031 } // Else, another thread claimed the object
7032 }
7033 }
7034 }
7035
7036 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7037 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7038
7039 // This closure is used to rescan the marked objects on the dirty cards
7040 // in the mod union table and the card table proper.
7041 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7042 oop p, MemRegion mr) {
7043
7044 size_t size = 0;
7045 HeapWord* addr = (HeapWord*)p;
7046 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7047 assert(_span.contains(addr), "we are scanning the CMS generation");
7048 // check if it's time to yield
7049 if (do_yield_check()) {
7050 // We yielded for some foreground stop-world work,
7051 // and we have been asked to abort this ongoing preclean cycle.
7052 return 0;
7053 }
7054 if (_bitMap->isMarked(addr)) {
7055 // it's marked; is it potentially uninitialized?
7056 if (p->klass_or_null() != NULL) {
7057 // an initialized object; ignore mark word in verification below
7058 // since we are running concurrent with mutators
7059 assert(p->is_oop(true), "should be an oop");
7060 if (p->is_objArray()) {
7061 // objArrays are precisely marked; restrict scanning
7062 // to dirty cards only.
7063 size = CompactibleFreeListSpace::adjustObjectSize(
7064 p->oop_iterate(_scanningClosure, mr));
7065 } else {
7066 // A non-array may have been imprecisely marked; we need
7067 // to scan object in its entirety.
7068 size = CompactibleFreeListSpace::adjustObjectSize(
7069 p->oop_iterate(_scanningClosure));
7070 }
7071 #ifdef ASSERT
7072 size_t direct_size =
7073 CompactibleFreeListSpace::adjustObjectSize(p->size());
7074 assert(size == direct_size, "Inconsistency in size");
7075 assert(size >= 3, "Necessary for Printezis marks to work");
7076 if (!_bitMap->isMarked(addr+1)) {
7077 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7078 } else {
7079 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7080 assert(_bitMap->isMarked(addr+size-1),
7081 "inconsistent Printezis mark");
7082 }
7083 #endif // ASSERT
7084 } else {
7085 // An uninitialized object.
7086 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7087 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7088 size = pointer_delta(nextOneAddr + 1, addr);
7089 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7090 "alignment problem");
7091 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7092 // will dirty the card when the klass pointer is installed in the
7093 // object (signaling the completion of initialization).
7094 }
7095 } else {
7096 // Either a not yet marked object or an uninitialized object
7097 if (p->klass_or_null() == NULL) {
7098 // An uninitialized object, skip to the next card, since
7099 // we may not be able to read its P-bits yet.
7100 assert(size == 0, "Initial value");
7101 } else {
7102 // An object not (yet) reached by marking: we merely need to
7103 // compute its size so as to go look at the next block.
7104 assert(p->is_oop(true), "should be an oop");
7105 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7106 }
7107 }
7108 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7109 return size;
7110 }
7111
7112 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7113 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7114 "CMS thread should hold CMS token");
7115 assert_lock_strong(_freelistLock);
7116 assert_lock_strong(_bitMap->lock());
7117 // relinquish the free_list_lock and bitMaplock()
7118 _bitMap->lock()->unlock();
7119 _freelistLock->unlock();
7120 ConcurrentMarkSweepThread::desynchronize(true);
7121 ConcurrentMarkSweepThread::acknowledge_yield_request();
7122 _collector->stopTimer();
7123 if (PrintCMSStatistics != 0) {
7124 _collector->incrementYields();
7125 }
7126 _collector->icms_wait();
7127
7128 // See the comment in coordinator_yield()
7129 for (unsigned i = 0; i < CMSYieldSleepCount &&
7130 ConcurrentMarkSweepThread::should_yield() &&
7131 !CMSCollector::foregroundGCIsActive(); ++i) {
7132 os::sleep(Thread::current(), 1, false);
7133 ConcurrentMarkSweepThread::acknowledge_yield_request();
7134 }
7135
7136 ConcurrentMarkSweepThread::synchronize(true);
7137 _freelistLock->lock_without_safepoint_check();
7138 _bitMap->lock()->lock_without_safepoint_check();
7139 _collector->startTimer();
7140 }
7141
7142
7143 //////////////////////////////////////////////////////////////////
7144 // SurvivorSpacePrecleanClosure
7145 //////////////////////////////////////////////////////////////////
7146 // This (single-threaded) closure is used to preclean the oops in
7147 // the survivor spaces.
7148 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7149
7150 HeapWord* addr = (HeapWord*)p;
7151 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7152 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7153 assert(p->klass_or_null() != NULL, "object should be initialized");
7154 // an initialized object; ignore mark word in verification below
7155 // since we are running concurrent with mutators
7156 assert(p->is_oop(true), "should be an oop");
7157 // Note that we do not yield while we iterate over
7158 // the interior oops of p, pushing the relevant ones
7159 // on our marking stack.
7160 size_t size = p->oop_iterate(_scanning_closure);
7161 do_yield_check();
7162 // Observe that below, we do not abandon the preclean
7163 // phase as soon as we should; rather we empty the
7164 // marking stack before returning. This is to satisfy
7165 // some existing assertions. In general, it may be a
7166 // good idea to abort immediately and complete the marking
7167 // from the grey objects at a later time.
7168 while (!_mark_stack->isEmpty()) {
7169 oop new_oop = _mark_stack->pop();
7170 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7171 assert(_bit_map->isMarked((HeapWord*)new_oop),
7172 "only grey objects on this stack");
7173 // iterate over the oops in this oop, marking and pushing
7174 // the ones in CMS heap (i.e. in _span).
7175 new_oop->oop_iterate(_scanning_closure);
7176 // check if it's time to yield
7177 do_yield_check();
7178 }
7179 unsigned int after_count =
7180 GenCollectedHeap::heap()->total_collections();
7181 bool abort = (_before_count != after_count) ||
7182 _collector->should_abort_preclean();
7183 return abort ? 0 : size;
7184 }
7185
7186 void SurvivorSpacePrecleanClosure::do_yield_work() {
7187 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7188 "CMS thread should hold CMS token");
7189 assert_lock_strong(_bit_map->lock());
7190 // Relinquish the bit map lock
7191 _bit_map->lock()->unlock();
7192 ConcurrentMarkSweepThread::desynchronize(true);
7193 ConcurrentMarkSweepThread::acknowledge_yield_request();
7194 _collector->stopTimer();
7195 if (PrintCMSStatistics != 0) {
7196 _collector->incrementYields();
7197 }
7198 _collector->icms_wait();
7199
7200 // See the comment in coordinator_yield()
7201 for (unsigned i = 0; i < CMSYieldSleepCount &&
7202 ConcurrentMarkSweepThread::should_yield() &&
7203 !CMSCollector::foregroundGCIsActive(); ++i) {
7204 os::sleep(Thread::current(), 1, false);
7205 ConcurrentMarkSweepThread::acknowledge_yield_request();
7206 }
7207
7208 ConcurrentMarkSweepThread::synchronize(true);
7209 _bit_map->lock()->lock_without_safepoint_check();
7210 _collector->startTimer();
7211 }
7212
7213 // This closure is used to rescan the marked objects on the dirty cards
7214 // in the mod union table and the card table proper. In the parallel
7215 // case, although the bitMap is shared, we do a single read so the
7216 // isMarked() query is "safe".
7217 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7218 // Ignore mark word because we are running concurrent with mutators
7219 assert(p->is_oop_or_null(true), "expected an oop or null");
7220 HeapWord* addr = (HeapWord*)p;
7221 assert(_span.contains(addr), "we are scanning the CMS generation");
7222 bool is_obj_array = false;
7223 #ifdef ASSERT
7224 if (!_parallel) {
7225 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7226 assert(_collector->overflow_list_is_empty(),
7227 "overflow list should be empty");
7228
7229 }
7230 #endif // ASSERT
7231 if (_bit_map->isMarked(addr)) {
7232 // Obj arrays are precisely marked, non-arrays are not;
7233 // so we scan objArrays precisely and non-arrays in their
7234 // entirety.
7235 if (p->is_objArray()) {
7236 is_obj_array = true;
7237 if (_parallel) {
7238 p->oop_iterate(_par_scan_closure, mr);
7239 } else {
7240 p->oop_iterate(_scan_closure, mr);
7241 }
7242 } else {
7243 if (_parallel) {
7244 p->oop_iterate(_par_scan_closure);
7245 } else {
7246 p->oop_iterate(_scan_closure);
7247 }
7248 }
7249 }
7250 #ifdef ASSERT
7251 if (!_parallel) {
7252 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7253 assert(_collector->overflow_list_is_empty(),
7254 "overflow list should be empty");
7255
7256 }
7257 #endif // ASSERT
7258 return is_obj_array;
7259 }
7260
7261 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7262 MemRegion span,
7263 CMSBitMap* bitMap, CMSMarkStack* markStack,
7264 bool should_yield, bool verifying):
7265 _collector(collector),
7266 _span(span),
7267 _bitMap(bitMap),
7268 _mut(&collector->_modUnionTable),
7269 _markStack(markStack),
7270 _yield(should_yield),
7271 _skipBits(0)
7272 {
7273 assert(_markStack->isEmpty(), "stack should be empty");
7274 _finger = _bitMap->startWord();
7275 _threshold = _finger;
7276 assert(_collector->_restart_addr == NULL, "Sanity check");
7277 assert(_span.contains(_finger), "Out of bounds _finger?");
7278 DEBUG_ONLY(_verifying = verifying;)
7279 }
7280
7281 void MarkFromRootsClosure::reset(HeapWord* addr) {
7282 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7283 assert(_span.contains(addr), "Out of bounds _finger?");
7284 _finger = addr;
7285 _threshold = (HeapWord*)round_to(
7286 (intptr_t)_finger, CardTableModRefBS::card_size);
7287 }
7288
7289 // Should revisit to see if this should be restructured for
7290 // greater efficiency.
7291 bool MarkFromRootsClosure::do_bit(size_t offset) {
7292 if (_skipBits > 0) {
7293 _skipBits--;
7294 return true;
7295 }
7296 // convert offset into a HeapWord*
7297 HeapWord* addr = _bitMap->startWord() + offset;
7298 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7299 "address out of range");
7300 assert(_bitMap->isMarked(addr), "tautology");
7301 if (_bitMap->isMarked(addr+1)) {
7302 // this is an allocated but not yet initialized object
7303 assert(_skipBits == 0, "tautology");
7304 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7305 oop p = oop(addr);
7306 if (p->klass_or_null() == NULL) {
7307 DEBUG_ONLY(if (!_verifying) {)
7308 // We re-dirty the cards on which this object lies and increase
7309 // the _threshold so that we'll come back to scan this object
7310 // during the preclean or remark phase. (CMSCleanOnEnter)
7311 if (CMSCleanOnEnter) {
7312 size_t sz = _collector->block_size_using_printezis_bits(addr);
7313 HeapWord* end_card_addr = (HeapWord*)round_to(
7314 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7315 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7316 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7317 // Bump _threshold to end_card_addr; note that
7318 // _threshold cannot possibly exceed end_card_addr, anyhow.
7319 // This prevents future clearing of the card as the scan proceeds
7320 // to the right.
7321 assert(_threshold <= end_card_addr,
7322 "Because we are just scanning into this object");
7323 if (_threshold < end_card_addr) {
7324 _threshold = end_card_addr;
7325 }
7326 if (p->klass_or_null() != NULL) {
7327 // Redirty the range of cards...
7328 _mut->mark_range(redirty_range);
7329 } // ...else the setting of klass will dirty the card anyway.
7330 }
7331 DEBUG_ONLY(})
7332 return true;
7333 }
7334 }
7335 scanOopsInOop(addr);
7336 return true;
7337 }
7338
7339 // We take a break if we've been at this for a while,
7340 // so as to avoid monopolizing the locks involved.
7341 void MarkFromRootsClosure::do_yield_work() {
7342 // First give up the locks, then yield, then re-lock
7343 // We should probably use a constructor/destructor idiom to
7344 // do this unlock/lock or modify the MutexUnlocker class to
7345 // serve our purpose. XXX
7346 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7347 "CMS thread should hold CMS token");
7348 assert_lock_strong(_bitMap->lock());
7349 _bitMap->lock()->unlock();
7350 ConcurrentMarkSweepThread::desynchronize(true);
7351 ConcurrentMarkSweepThread::acknowledge_yield_request();
7352 _collector->stopTimer();
7353 if (PrintCMSStatistics != 0) {
7354 _collector->incrementYields();
7355 }
7356 _collector->icms_wait();
7357
7358 // See the comment in coordinator_yield()
7359 for (unsigned i = 0; i < CMSYieldSleepCount &&
7360 ConcurrentMarkSweepThread::should_yield() &&
7361 !CMSCollector::foregroundGCIsActive(); ++i) {
7362 os::sleep(Thread::current(), 1, false);
7363 ConcurrentMarkSweepThread::acknowledge_yield_request();
7364 }
7365
7366 ConcurrentMarkSweepThread::synchronize(true);
7367 _bitMap->lock()->lock_without_safepoint_check();
7368 _collector->startTimer();
7369 }
7370
7371 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7372 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7373 assert(_markStack->isEmpty(),
7374 "should drain stack to limit stack usage");
7375 // convert ptr to an oop preparatory to scanning
7376 oop obj = oop(ptr);
7377 // Ignore mark word in verification below, since we
7378 // may be running concurrent with mutators.
7379 assert(obj->is_oop(true), "should be an oop");
7380 assert(_finger <= ptr, "_finger runneth ahead");
7381 // advance the finger to right end of this object
7382 _finger = ptr + obj->size();
7383 assert(_finger > ptr, "we just incremented it above");
7384 // On large heaps, it may take us some time to get through
7385 // the marking phase (especially if running iCMS). During
7386 // this time it's possible that a lot of mutations have
7387 // accumulated in the card table and the mod union table --
7388 // these mutation records are redundant until we have
7389 // actually traced into the corresponding card.
7390 // Here, we check whether advancing the finger would make
7391 // us cross into a new card, and if so clear corresponding
7392 // cards in the MUT (preclean them in the card-table in the
7393 // future).
7394
7395 DEBUG_ONLY(if (!_verifying) {)
7396 // The clean-on-enter optimization is disabled by default,
7397 // until we fix 6178663.
7398 if (CMSCleanOnEnter && (_finger > _threshold)) {
7399 // [_threshold, _finger) represents the interval
7400 // of cards to be cleared in MUT (or precleaned in card table).
7401 // The set of cards to be cleared is all those that overlap
7402 // with the interval [_threshold, _finger); note that
7403 // _threshold is always kept card-aligned but _finger isn't
7404 // always card-aligned.
7405 HeapWord* old_threshold = _threshold;
7406 assert(old_threshold == (HeapWord*)round_to(
7407 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7408 "_threshold should always be card-aligned");
7409 _threshold = (HeapWord*)round_to(
7410 (intptr_t)_finger, CardTableModRefBS::card_size);
7411 MemRegion mr(old_threshold, _threshold);
7412 assert(!mr.is_empty(), "Control point invariant");
7413 assert(_span.contains(mr), "Should clear within span");
7414 _mut->clear_range(mr);
7415 }
7416 DEBUG_ONLY(})
7417 // Note: the finger doesn't advance while we drain
7418 // the stack below.
7419 PushOrMarkClosure pushOrMarkClosure(_collector,
7420 _span, _bitMap, _markStack,
7421 _finger, this);
7422 bool res = _markStack->push(obj);
7423 assert(res, "Empty non-zero size stack should have space for single push");
7424 while (!_markStack->isEmpty()) {
7425 oop new_oop = _markStack->pop();
7426 // Skip verifying header mark word below because we are
7427 // running concurrent with mutators.
7428 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7429 // now scan this oop's oops
7430 new_oop->oop_iterate(&pushOrMarkClosure);
7431 do_yield_check();
7432 }
7433 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7434 }
7435
7436 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7437 CMSCollector* collector, MemRegion span,
7438 CMSBitMap* bit_map,
7439 OopTaskQueue* work_queue,
7440 CMSMarkStack* overflow_stack,
7441 bool should_yield):
7442 _collector(collector),
7443 _whole_span(collector->_span),
7444 _span(span),
7445 _bit_map(bit_map),
7446 _mut(&collector->_modUnionTable),
7447 _work_queue(work_queue),
7448 _overflow_stack(overflow_stack),
7449 _yield(should_yield),
7450 _skip_bits(0),
7451 _task(task)
7452 {
7453 assert(_work_queue->size() == 0, "work_queue should be empty");
7454 _finger = span.start();
7455 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7456 assert(_span.contains(_finger), "Out of bounds _finger?");
7457 }
7458
7459 // Should revisit to see if this should be restructured for
7460 // greater efficiency.
7461 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7462 if (_skip_bits > 0) {
7463 _skip_bits--;
7464 return true;
7465 }
7466 // convert offset into a HeapWord*
7467 HeapWord* addr = _bit_map->startWord() + offset;
7468 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7469 "address out of range");
7470 assert(_bit_map->isMarked(addr), "tautology");
7471 if (_bit_map->isMarked(addr+1)) {
7472 // this is an allocated object that might not yet be initialized
7473 assert(_skip_bits == 0, "tautology");
7474 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7475 oop p = oop(addr);
7476 if (p->klass_or_null() == NULL) {
7477 // in the case of Clean-on-Enter optimization, redirty card
7478 // and avoid clearing card by increasing the threshold.
7479 return true;
7480 }
7481 }
7482 scan_oops_in_oop(addr);
7483 return true;
7484 }
7485
7486 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7487 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7488 // Should we assert that our work queue is empty or
7489 // below some drain limit?
7490 assert(_work_queue->size() == 0,
7491 "should drain stack to limit stack usage");
7492 // convert ptr to an oop preparatory to scanning
7493 oop obj = oop(ptr);
7494 // Ignore mark word in verification below, since we
7495 // may be running concurrent with mutators.
7496 assert(obj->is_oop(true), "should be an oop");
7497 assert(_finger <= ptr, "_finger runneth ahead");
7498 // advance the finger to right end of this object
7499 _finger = ptr + obj->size();
7500 assert(_finger > ptr, "we just incremented it above");
7501 // On large heaps, it may take us some time to get through
7502 // the marking phase (especially if running iCMS). During
7503 // this time it's possible that a lot of mutations have
7504 // accumulated in the card table and the mod union table --
7505 // these mutation records are redundant until we have
7506 // actually traced into the corresponding card.
7507 // Here, we check whether advancing the finger would make
7508 // us cross into a new card, and if so clear corresponding
7509 // cards in the MUT (preclean them in the card-table in the
7510 // future).
7511
7512 // The clean-on-enter optimization is disabled by default,
7513 // until we fix 6178663.
7514 if (CMSCleanOnEnter && (_finger > _threshold)) {
7515 // [_threshold, _finger) represents the interval
7516 // of cards to be cleared in MUT (or precleaned in card table).
7517 // The set of cards to be cleared is all those that overlap
7518 // with the interval [_threshold, _finger); note that
7519 // _threshold is always kept card-aligned but _finger isn't
7520 // always card-aligned.
7521 HeapWord* old_threshold = _threshold;
7522 assert(old_threshold == (HeapWord*)round_to(
7523 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7524 "_threshold should always be card-aligned");
7525 _threshold = (HeapWord*)round_to(
7526 (intptr_t)_finger, CardTableModRefBS::card_size);
7527 MemRegion mr(old_threshold, _threshold);
7528 assert(!mr.is_empty(), "Control point invariant");
7529 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7530 _mut->clear_range(mr);
7531 }
7532
7533 // Note: the local finger doesn't advance while we drain
7534 // the stack below, but the global finger sure can and will.
7535 HeapWord** gfa = _task->global_finger_addr();
7536 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7537 _span, _bit_map,
7538 _work_queue,
7539 _overflow_stack,
7540 _finger,
7541 gfa, this);
7542 bool res = _work_queue->push(obj); // overflow could occur here
7543 assert(res, "Will hold once we use workqueues");
7544 while (true) {
7545 oop new_oop;
7546 if (!_work_queue->pop_local(new_oop)) {
7547 // We emptied our work_queue; check if there's stuff that can
7548 // be gotten from the overflow stack.
7549 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7550 _overflow_stack, _work_queue)) {
7551 do_yield_check();
7552 continue;
7553 } else { // done
7554 break;
7555 }
7556 }
7557 // Skip verifying header mark word below because we are
7558 // running concurrent with mutators.
7559 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7560 // now scan this oop's oops
7561 new_oop->oop_iterate(&pushOrMarkClosure);
7562 do_yield_check();
7563 }
7564 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7565 }
7566
7567 // Yield in response to a request from VM Thread or
7568 // from mutators.
7569 void Par_MarkFromRootsClosure::do_yield_work() {
7570 assert(_task != NULL, "sanity");
7571 _task->yield();
7572 }
7573
7574 // A variant of the above used for verifying CMS marking work.
7575 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7576 MemRegion span,
7577 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7578 CMSMarkStack* mark_stack):
7579 _collector(collector),
7580 _span(span),
7581 _verification_bm(verification_bm),
7582 _cms_bm(cms_bm),
7583 _mark_stack(mark_stack),
7584 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7585 mark_stack)
7586 {
7587 assert(_mark_stack->isEmpty(), "stack should be empty");
7588 _finger = _verification_bm->startWord();
7589 assert(_collector->_restart_addr == NULL, "Sanity check");
7590 assert(_span.contains(_finger), "Out of bounds _finger?");
7591 }
7592
7593 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7594 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7595 assert(_span.contains(addr), "Out of bounds _finger?");
7596 _finger = addr;
7597 }
7598
7599 // Should revisit to see if this should be restructured for
7600 // greater efficiency.
7601 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7602 // convert offset into a HeapWord*
7603 HeapWord* addr = _verification_bm->startWord() + offset;
7604 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7605 "address out of range");
7606 assert(_verification_bm->isMarked(addr), "tautology");
7607 assert(_cms_bm->isMarked(addr), "tautology");
7608
7609 assert(_mark_stack->isEmpty(),
7610 "should drain stack to limit stack usage");
7611 // convert addr to an oop preparatory to scanning
7612 oop obj = oop(addr);
7613 assert(obj->is_oop(), "should be an oop");
7614 assert(_finger <= addr, "_finger runneth ahead");
7615 // advance the finger to right end of this object
7616 _finger = addr + obj->size();
7617 assert(_finger > addr, "we just incremented it above");
7618 // Note: the finger doesn't advance while we drain
7619 // the stack below.
7620 bool res = _mark_stack->push(obj);
7621 assert(res, "Empty non-zero size stack should have space for single push");
7622 while (!_mark_stack->isEmpty()) {
7623 oop new_oop = _mark_stack->pop();
7624 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7625 // now scan this oop's oops
7626 new_oop->oop_iterate(&_pam_verify_closure);
7627 }
7628 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7629 return true;
7630 }
7631
7632 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7633 CMSCollector* collector, MemRegion span,
7634 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7635 CMSMarkStack* mark_stack):
7636 MetadataAwareOopClosure(collector->ref_processor()),
7637 _collector(collector),
7638 _span(span),
7639 _verification_bm(verification_bm),
7640 _cms_bm(cms_bm),
7641 _mark_stack(mark_stack)
7642 { }
7643
7644 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7645 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7646
7647 // Upon stack overflow, we discard (part of) the stack,
7648 // remembering the least address amongst those discarded
7649 // in CMSCollector's _restart_address.
7650 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7651 // Remember the least grey address discarded
7652 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7653 _collector->lower_restart_addr(ra);
7654 _mark_stack->reset(); // discard stack contents
7655 _mark_stack->expand(); // expand the stack if possible
7656 }
7657
7658 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7659 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7660 HeapWord* addr = (HeapWord*)obj;
7661 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7662 // Oop lies in _span and isn't yet grey or black
7663 _verification_bm->mark(addr); // now grey
7664 if (!_cms_bm->isMarked(addr)) {
7665 oop(addr)->print();
7666 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7667 addr);
7668 fatal("... aborting");
7669 }
7670
7671 if (!_mark_stack->push(obj)) { // stack overflow
7672 if (PrintCMSStatistics != 0) {
7673 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7674 SIZE_FORMAT, _mark_stack->capacity());
7675 }
7676 assert(_mark_stack->isFull(), "Else push should have succeeded");
7677 handle_stack_overflow(addr);
7678 }
7679 // anything including and to the right of _finger
7680 // will be scanned as we iterate over the remainder of the
7681 // bit map
7682 }
7683 }
7684
7685 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7686 MemRegion span,
7687 CMSBitMap* bitMap, CMSMarkStack* markStack,
7688 HeapWord* finger, MarkFromRootsClosure* parent) :
7689 MetadataAwareOopClosure(collector->ref_processor()),
7690 _collector(collector),
7691 _span(span),
7692 _bitMap(bitMap),
7693 _markStack(markStack),
7694 _finger(finger),
7695 _parent(parent)
7696 { }
7697
7698 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7699 MemRegion span,
7700 CMSBitMap* bit_map,
7701 OopTaskQueue* work_queue,
7702 CMSMarkStack* overflow_stack,
7703 HeapWord* finger,
7704 HeapWord** global_finger_addr,
7705 Par_MarkFromRootsClosure* parent) :
7706 MetadataAwareOopClosure(collector->ref_processor()),
7707 _collector(collector),
7708 _whole_span(collector->_span),
7709 _span(span),
7710 _bit_map(bit_map),
7711 _work_queue(work_queue),
7712 _overflow_stack(overflow_stack),
7713 _finger(finger),
7714 _global_finger_addr(global_finger_addr),
7715 _parent(parent)
7716 { }
7717
7718 // Assumes thread-safe access by callers, who are
7719 // responsible for mutual exclusion.
7720 void CMSCollector::lower_restart_addr(HeapWord* low) {
7721 assert(_span.contains(low), "Out of bounds addr");
7722 if (_restart_addr == NULL) {
7723 _restart_addr = low;
7724 } else {
7725 _restart_addr = MIN2(_restart_addr, low);
7726 }
7727 }
7728
7729 // Upon stack overflow, we discard (part of) the stack,
7730 // remembering the least address amongst those discarded
7731 // in CMSCollector's _restart_address.
7732 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7733 // Remember the least grey address discarded
7734 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7735 _collector->lower_restart_addr(ra);
7736 _markStack->reset(); // discard stack contents
7737 _markStack->expand(); // expand the stack if possible
7738 }
7739
7740 // Upon stack overflow, we discard (part of) the stack,
7741 // remembering the least address amongst those discarded
7742 // in CMSCollector's _restart_address.
7743 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7744 // We need to do this under a mutex to prevent other
7745 // workers from interfering with the work done below.
7746 MutexLockerEx ml(_overflow_stack->par_lock(),
7747 Mutex::_no_safepoint_check_flag);
7748 // Remember the least grey address discarded
7749 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7750 _collector->lower_restart_addr(ra);
7751 _overflow_stack->reset(); // discard stack contents
7752 _overflow_stack->expand(); // expand the stack if possible
7753 }
7754
7755 void PushOrMarkClosure::do_oop(oop obj) {
7756 // Ignore mark word because we are running concurrent with mutators.
7757 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7758 HeapWord* addr = (HeapWord*)obj;
7759 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7760 // Oop lies in _span and isn't yet grey or black
7761 _bitMap->mark(addr); // now grey
7762 if (addr < _finger) {
7763 // the bit map iteration has already either passed, or
7764 // sampled, this bit in the bit map; we'll need to
7765 // use the marking stack to scan this oop's oops.
7766 bool simulate_overflow = false;
7767 NOT_PRODUCT(
7768 if (CMSMarkStackOverflowALot &&
7769 _collector->simulate_overflow()) {
7770 // simulate a stack overflow
7771 simulate_overflow = true;
7772 }
7773 )
7774 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7775 if (PrintCMSStatistics != 0) {
7776 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7777 SIZE_FORMAT, _markStack->capacity());
7778 }
7779 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7780 handle_stack_overflow(addr);
7781 }
7782 }
7783 // anything including and to the right of _finger
7784 // will be scanned as we iterate over the remainder of the
7785 // bit map
7786 do_yield_check();
7787 }
7788 }
7789
7790 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7791 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7792
7793 void Par_PushOrMarkClosure::do_oop(oop obj) {
7794 // Ignore mark word because we are running concurrent with mutators.
7795 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7796 HeapWord* addr = (HeapWord*)obj;
7797 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7798 // Oop lies in _span and isn't yet grey or black
7799 // We read the global_finger (volatile read) strictly after marking oop
7800 bool res = _bit_map->par_mark(addr); // now grey
7801 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7802 // Should we push this marked oop on our stack?
7803 // -- if someone else marked it, nothing to do
7804 // -- if target oop is above global finger nothing to do
7805 // -- if target oop is in chunk and above local finger
7806 // then nothing to do
7807 // -- else push on work queue
7808 if ( !res // someone else marked it, they will deal with it
7809 || (addr >= *gfa) // will be scanned in a later task
7810 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7811 return;
7812 }
7813 // the bit map iteration has already either passed, or
7814 // sampled, this bit in the bit map; we'll need to
7815 // use the marking stack to scan this oop's oops.
7816 bool simulate_overflow = false;
7817 NOT_PRODUCT(
7818 if (CMSMarkStackOverflowALot &&
7819 _collector->simulate_overflow()) {
7820 // simulate a stack overflow
7821 simulate_overflow = true;
7822 }
7823 )
7824 if (simulate_overflow ||
7825 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7826 // stack overflow
7827 if (PrintCMSStatistics != 0) {
7828 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7829 SIZE_FORMAT, _overflow_stack->capacity());
7830 }
7831 // We cannot assert that the overflow stack is full because
7832 // it may have been emptied since.
7833 assert(simulate_overflow ||
7834 _work_queue->size() == _work_queue->max_elems(),
7835 "Else push should have succeeded");
7836 handle_stack_overflow(addr);
7837 }
7838 do_yield_check();
7839 }
7840 }
7841
7842 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7843 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7844
7845 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7846 MemRegion span,
7847 ReferenceProcessor* rp,
7848 CMSBitMap* bit_map,
7849 CMSBitMap* mod_union_table,
7850 CMSMarkStack* mark_stack,
7851 bool concurrent_precleaning):
7852 MetadataAwareOopClosure(rp),
7853 _collector(collector),
7854 _span(span),
7855 _bit_map(bit_map),
7856 _mod_union_table(mod_union_table),
7857 _mark_stack(mark_stack),
7858 _concurrent_precleaning(concurrent_precleaning)
7859 {
7860 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7861 }
7862
7863 // Grey object rescan during pre-cleaning and second checkpoint phases --
7864 // the non-parallel version (the parallel version appears further below.)
7865 void PushAndMarkClosure::do_oop(oop obj) {
7866 // Ignore mark word verification. If during concurrent precleaning,
7867 // the object monitor may be locked. If during the checkpoint
7868 // phases, the object may already have been reached by a different
7869 // path and may be at the end of the global overflow list (so
7870 // the mark word may be NULL).
7871 assert(obj->is_oop_or_null(true /* ignore mark word */),
7872 "expected an oop or NULL");
7873 HeapWord* addr = (HeapWord*)obj;
7874 // Check if oop points into the CMS generation
7875 // and is not marked
7876 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7877 // a white object ...
7878 _bit_map->mark(addr); // ... now grey
7879 // push on the marking stack (grey set)
7880 bool simulate_overflow = false;
7881 NOT_PRODUCT(
7882 if (CMSMarkStackOverflowALot &&
7883 _collector->simulate_overflow()) {
7884 // simulate a stack overflow
7885 simulate_overflow = true;
7886 }
7887 )
7888 if (simulate_overflow || !_mark_stack->push(obj)) {
7889 if (_concurrent_precleaning) {
7890 // During precleaning we can just dirty the appropriate card(s)
7891 // in the mod union table, thus ensuring that the object remains
7892 // in the grey set and continue. In the case of object arrays
7893 // we need to dirty all of the cards that the object spans,
7894 // since the rescan of object arrays will be limited to the
7895 // dirty cards.
7896 // Note that no one can be interfering with us in this action
7897 // of dirtying the mod union table, so no locking or atomics
7898 // are required.
7899 if (obj->is_objArray()) {
7900 size_t sz = obj->size();
7901 HeapWord* end_card_addr = (HeapWord*)round_to(
7902 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7903 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7904 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7905 _mod_union_table->mark_range(redirty_range);
7906 } else {
7907 _mod_union_table->mark(addr);
7908 }
7909 _collector->_ser_pmc_preclean_ovflw++;
7910 } else {
7911 // During the remark phase, we need to remember this oop
7912 // in the overflow list.
7913 _collector->push_on_overflow_list(obj);
7914 _collector->_ser_pmc_remark_ovflw++;
7915 }
7916 }
7917 }
7918 }
7919
7920 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7921 MemRegion span,
7922 ReferenceProcessor* rp,
7923 CMSBitMap* bit_map,
7924 OopTaskQueue* work_queue):
7925 MetadataAwareOopClosure(rp),
7926 _collector(collector),
7927 _span(span),
7928 _bit_map(bit_map),
7929 _work_queue(work_queue)
7930 {
7931 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7932 }
7933
7934 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7935 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7936
7937 // Grey object rescan during second checkpoint phase --
7938 // the parallel version.
7939 void Par_PushAndMarkClosure::do_oop(oop obj) {
7940 // In the assert below, we ignore the mark word because
7941 // this oop may point to an already visited object that is
7942 // on the overflow stack (in which case the mark word has
7943 // been hijacked for chaining into the overflow stack --
7944 // if this is the last object in the overflow stack then
7945 // its mark word will be NULL). Because this object may
7946 // have been subsequently popped off the global overflow
7947 // stack, and the mark word possibly restored to the prototypical
7948 // value, by the time we get to examined this failing assert in
7949 // the debugger, is_oop_or_null(false) may subsequently start
7950 // to hold.
7951 assert(obj->is_oop_or_null(true),
7952 "expected an oop or NULL");
7953 HeapWord* addr = (HeapWord*)obj;
7954 // Check if oop points into the CMS generation
7955 // and is not marked
7956 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7957 // a white object ...
7958 // If we manage to "claim" the object, by being the
7959 // first thread to mark it, then we push it on our
7960 // marking stack
7961 if (_bit_map->par_mark(addr)) { // ... now grey
7962 // push on work queue (grey set)
7963 bool simulate_overflow = false;
7964 NOT_PRODUCT(
7965 if (CMSMarkStackOverflowALot &&
7966 _collector->par_simulate_overflow()) {
7967 // simulate a stack overflow
7968 simulate_overflow = true;
7969 }
7970 )
7971 if (simulate_overflow || !_work_queue->push(obj)) {
7972 _collector->par_push_on_overflow_list(obj);
7973 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7974 }
7975 } // Else, some other thread got there first
7976 }
7977 }
7978
7979 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7980 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7981
7982 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7983 Mutex* bml = _collector->bitMapLock();
7984 assert_lock_strong(bml);
7985 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7986 "CMS thread should hold CMS token");
7987
7988 bml->unlock();
7989 ConcurrentMarkSweepThread::desynchronize(true);
7990
7991 ConcurrentMarkSweepThread::acknowledge_yield_request();
7992
7993 _collector->stopTimer();
7994 if (PrintCMSStatistics != 0) {
7995 _collector->incrementYields();
7996 }
7997 _collector->icms_wait();
7998
7999 // See the comment in coordinator_yield()
8000 for (unsigned i = 0; i < CMSYieldSleepCount &&
8001 ConcurrentMarkSweepThread::should_yield() &&
8002 !CMSCollector::foregroundGCIsActive(); ++i) {
8003 os::sleep(Thread::current(), 1, false);
8004 ConcurrentMarkSweepThread::acknowledge_yield_request();
8005 }
8006
8007 ConcurrentMarkSweepThread::synchronize(true);
8008 bml->lock();
8009
8010 _collector->startTimer();
8011 }
8012
8013 bool CMSPrecleanRefsYieldClosure::should_return() {
8014 if (ConcurrentMarkSweepThread::should_yield()) {
8015 do_yield_work();
8016 }
8017 return _collector->foregroundGCIsActive();
8018 }
8019
8020 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8021 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8022 "mr should be aligned to start at a card boundary");
8023 // We'd like to assert:
8024 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8025 // "mr should be a range of cards");
8026 // However, that would be too strong in one case -- the last
8027 // partition ends at _unallocated_block which, in general, can be
8028 // an arbitrary boundary, not necessarily card aligned.
8029 if (PrintCMSStatistics != 0) {
8030 _num_dirty_cards +=
8031 mr.word_size()/CardTableModRefBS::card_size_in_words;
8032 }
8033 _space->object_iterate_mem(mr, &_scan_cl);
8034 }
8035
8036 SweepClosure::SweepClosure(CMSCollector* collector,
8037 ConcurrentMarkSweepGeneration* g,
8038 CMSBitMap* bitMap, bool should_yield) :
8039 _collector(collector),
8040 _g(g),
8041 _sp(g->cmsSpace()),
8042 _limit(_sp->sweep_limit()),
8043 _freelistLock(_sp->freelistLock()),
8044 _bitMap(bitMap),
8045 _yield(should_yield),
8046 _inFreeRange(false), // No free range at beginning of sweep
8047 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8048 _lastFreeRangeCoalesced(false),
8049 _freeFinger(g->used_region().start())
8050 {
8051 NOT_PRODUCT(
8052 _numObjectsFreed = 0;
8053 _numWordsFreed = 0;
8054 _numObjectsLive = 0;
8055 _numWordsLive = 0;
8056 _numObjectsAlreadyFree = 0;
8057 _numWordsAlreadyFree = 0;
8058 _last_fc = NULL;
8059
8060 _sp->initializeIndexedFreeListArrayReturnedBytes();
8061 _sp->dictionary()->initialize_dict_returned_bytes();
8062 )
8063 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8064 "sweep _limit out of bounds");
8065 if (CMSTraceSweeper) {
8066 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8067 _limit);
8068 }
8069 }
8070
8071 void SweepClosure::print_on(outputStream* st) const {
8072 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8073 _sp->bottom(), _sp->end());
8074 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8075 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8076 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8077 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8078 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8079 }
8080
8081 #ifndef PRODUCT
8082 // Assertion checking only: no useful work in product mode --
8083 // however, if any of the flags below become product flags,
8084 // you may need to review this code to see if it needs to be
8085 // enabled in product mode.
8086 SweepClosure::~SweepClosure() {
8087 assert_lock_strong(_freelistLock);
8088 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8089 "sweep _limit out of bounds");
8090 if (inFreeRange()) {
8091 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8092 print();
8093 ShouldNotReachHere();
8094 }
8095 if (Verbose && PrintGC) {
8096 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8097 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8098 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8099 SIZE_FORMAT" bytes "
8100 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8101 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8102 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8103 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8104 * sizeof(HeapWord);
8105 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8106
8107 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8108 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8109 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8110 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8111 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8112 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8113 indexListReturnedBytes);
8114 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8115 dict_returned_bytes);
8116 }
8117 }
8118 if (CMSTraceSweeper) {
8119 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8120 _limit);
8121 }
8122 }
8123 #endif // PRODUCT
8124
8125 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8126 bool freeRangeInFreeLists) {
8127 if (CMSTraceSweeper) {
8128 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8129 freeFinger, freeRangeInFreeLists);
8130 }
8131 assert(!inFreeRange(), "Trampling existing free range");
8132 set_inFreeRange(true);
8133 set_lastFreeRangeCoalesced(false);
8134
8135 set_freeFinger(freeFinger);
8136 set_freeRangeInFreeLists(freeRangeInFreeLists);
8137 if (CMSTestInFreeList) {
8138 if (freeRangeInFreeLists) {
8139 FreeChunk* fc = (FreeChunk*) freeFinger;
8140 assert(fc->is_free(), "A chunk on the free list should be free.");
8141 assert(fc->size() > 0, "Free range should have a size");
8142 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8143 }
8144 }
8145 }
8146
8147 // Note that the sweeper runs concurrently with mutators. Thus,
8148 // it is possible for direct allocation in this generation to happen
8149 // in the middle of the sweep. Note that the sweeper also coalesces
8150 // contiguous free blocks. Thus, unless the sweeper and the allocator
8151 // synchronize appropriately freshly allocated blocks may get swept up.
8152 // This is accomplished by the sweeper locking the free lists while
8153 // it is sweeping. Thus blocks that are determined to be free are
8154 // indeed free. There is however one additional complication:
8155 // blocks that have been allocated since the final checkpoint and
8156 // mark, will not have been marked and so would be treated as
8157 // unreachable and swept up. To prevent this, the allocator marks
8158 // the bit map when allocating during the sweep phase. This leads,
8159 // however, to a further complication -- objects may have been allocated
8160 // but not yet initialized -- in the sense that the header isn't yet
8161 // installed. The sweeper can not then determine the size of the block
8162 // in order to skip over it. To deal with this case, we use a technique
8163 // (due to Printezis) to encode such uninitialized block sizes in the
8164 // bit map. Since the bit map uses a bit per every HeapWord, but the
8165 // CMS generation has a minimum object size of 3 HeapWords, it follows
8166 // that "normal marks" won't be adjacent in the bit map (there will
8167 // always be at least two 0 bits between successive 1 bits). We make use
8168 // of these "unused" bits to represent uninitialized blocks -- the bit
8169 // corresponding to the start of the uninitialized object and the next
8170 // bit are both set. Finally, a 1 bit marks the end of the object that
8171 // started with the two consecutive 1 bits to indicate its potentially
8172 // uninitialized state.
8173
8174 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8175 FreeChunk* fc = (FreeChunk*)addr;
8176 size_t res;
8177
8178 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8179 // than "addr == _limit" because although _limit was a block boundary when
8180 // we started the sweep, it may no longer be one because heap expansion
8181 // may have caused us to coalesce the block ending at the address _limit
8182 // with a newly expanded chunk (this happens when _limit was set to the
8183 // previous _end of the space), so we may have stepped past _limit:
8184 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8185 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8186 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8187 "sweep _limit out of bounds");
8188 assert(addr < _sp->end(), "addr out of bounds");
8189 // Flush any free range we might be holding as a single
8190 // coalesced chunk to the appropriate free list.
8191 if (inFreeRange()) {
8192 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8193 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8194 flush_cur_free_chunk(freeFinger(),
8195 pointer_delta(addr, freeFinger()));
8196 if (CMSTraceSweeper) {
8197 gclog_or_tty->print("Sweep: last chunk: ");
8198 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8199 "[coalesced:%d]\n",
8200 freeFinger(), pointer_delta(addr, freeFinger()),
8201 lastFreeRangeCoalesced() ? 1 : 0);
8202 }
8203 }
8204
8205 // help the iterator loop finish
8206 return pointer_delta(_sp->end(), addr);
8207 }
8208
8209 assert(addr < _limit, "sweep invariant");
8210 // check if we should yield
8211 do_yield_check(addr);
8212 if (fc->is_free()) {
8213 // Chunk that is already free
8214 res = fc->size();
8215 do_already_free_chunk(fc);
8216 debug_only(_sp->verifyFreeLists());
8217 // If we flush the chunk at hand in lookahead_and_flush()
8218 // and it's coalesced with a preceding chunk, then the
8219 // process of "mangling" the payload of the coalesced block
8220 // will cause erasure of the size information from the
8221 // (erstwhile) header of all the coalesced blocks but the
8222 // first, so the first disjunct in the assert will not hold
8223 // in that specific case (in which case the second disjunct
8224 // will hold).
8225 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8226 "Otherwise the size info doesn't change at this step");
8227 NOT_PRODUCT(
8228 _numObjectsAlreadyFree++;
8229 _numWordsAlreadyFree += res;
8230 )
8231 NOT_PRODUCT(_last_fc = fc;)
8232 } else if (!_bitMap->isMarked(addr)) {
8233 // Chunk is fresh garbage
8234 res = do_garbage_chunk(fc);
8235 debug_only(_sp->verifyFreeLists());
8236 NOT_PRODUCT(
8237 _numObjectsFreed++;
8238 _numWordsFreed += res;
8239 )
8240 } else {
8241 // Chunk that is alive.
8242 res = do_live_chunk(fc);
8243 debug_only(_sp->verifyFreeLists());
8244 NOT_PRODUCT(
8245 _numObjectsLive++;
8246 _numWordsLive += res;
8247 )
8248 }
8249 return res;
8250 }
8251
8252 // For the smart allocation, record following
8253 // split deaths - a free chunk is removed from its free list because
8254 // it is being split into two or more chunks.
8255 // split birth - a free chunk is being added to its free list because
8256 // a larger free chunk has been split and resulted in this free chunk.
8257 // coal death - a free chunk is being removed from its free list because
8258 // it is being coalesced into a large free chunk.
8259 // coal birth - a free chunk is being added to its free list because
8260 // it was created when two or more free chunks where coalesced into
8261 // this free chunk.
8262 //
8263 // These statistics are used to determine the desired number of free
8264 // chunks of a given size. The desired number is chosen to be relative
8265 // to the end of a CMS sweep. The desired number at the end of a sweep
8266 // is the
8267 // count-at-end-of-previous-sweep (an amount that was enough)
8268 // - count-at-beginning-of-current-sweep (the excess)
8269 // + split-births (gains in this size during interval)
8270 // - split-deaths (demands on this size during interval)
8271 // where the interval is from the end of one sweep to the end of the
8272 // next.
8273 //
8274 // When sweeping the sweeper maintains an accumulated chunk which is
8275 // the chunk that is made up of chunks that have been coalesced. That
8276 // will be termed the left-hand chunk. A new chunk of garbage that
8277 // is being considered for coalescing will be referred to as the
8278 // right-hand chunk.
8279 //
8280 // When making a decision on whether to coalesce a right-hand chunk with
8281 // the current left-hand chunk, the current count vs. the desired count
8282 // of the left-hand chunk is considered. Also if the right-hand chunk
8283 // is near the large chunk at the end of the heap (see
8284 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8285 // left-hand chunk is coalesced.
8286 //
8287 // When making a decision about whether to split a chunk, the desired count
8288 // vs. the current count of the candidate to be split is also considered.
8289 // If the candidate is underpopulated (currently fewer chunks than desired)
8290 // a chunk of an overpopulated (currently more chunks than desired) size may
8291 // be chosen. The "hint" associated with a free list, if non-null, points
8292 // to a free list which may be overpopulated.
8293 //
8294
8295 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8296 const size_t size = fc->size();
8297 // Chunks that cannot be coalesced are not in the
8298 // free lists.
8299 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8300 assert(_sp->verify_chunk_in_free_list(fc),
8301 "free chunk should be in free lists");
8302 }
8303 // a chunk that is already free, should not have been
8304 // marked in the bit map
8305 HeapWord* const addr = (HeapWord*) fc;
8306 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8307 // Verify that the bit map has no bits marked between
8308 // addr and purported end of this block.
8309 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8310
8311 // Some chunks cannot be coalesced under any circumstances.
8312 // See the definition of cantCoalesce().
8313 if (!fc->cantCoalesce()) {
8314 // This chunk can potentially be coalesced.
8315 if (_sp->adaptive_freelists()) {
8316 // All the work is done in
8317 do_post_free_or_garbage_chunk(fc, size);
8318 } else { // Not adaptive free lists
8319 // this is a free chunk that can potentially be coalesced by the sweeper;
8320 if (!inFreeRange()) {
8321 // if the next chunk is a free block that can't be coalesced
8322 // it doesn't make sense to remove this chunk from the free lists
8323 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8324 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8325 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8326 nextChunk->is_free() && // ... which is free...
8327 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8328 // nothing to do
8329 } else {
8330 // Potentially the start of a new free range:
8331 // Don't eagerly remove it from the free lists.
8332 // No need to remove it if it will just be put
8333 // back again. (Also from a pragmatic point of view
8334 // if it is a free block in a region that is beyond
8335 // any allocated blocks, an assertion will fail)
8336 // Remember the start of a free run.
8337 initialize_free_range(addr, true);
8338 // end - can coalesce with next chunk
8339 }
8340 } else {
8341 // the midst of a free range, we are coalescing
8342 print_free_block_coalesced(fc);
8343 if (CMSTraceSweeper) {
8344 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8345 }
8346 // remove it from the free lists
8347 _sp->removeFreeChunkFromFreeLists(fc);
8348 set_lastFreeRangeCoalesced(true);
8349 // If the chunk is being coalesced and the current free range is
8350 // in the free lists, remove the current free range so that it
8351 // will be returned to the free lists in its entirety - all
8352 // the coalesced pieces included.
8353 if (freeRangeInFreeLists()) {
8354 FreeChunk* ffc = (FreeChunk*) freeFinger();
8355 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8356 "Size of free range is inconsistent with chunk size.");
8357 if (CMSTestInFreeList) {
8358 assert(_sp->verify_chunk_in_free_list(ffc),
8359 "free range is not in free lists");
8360 }
8361 _sp->removeFreeChunkFromFreeLists(ffc);
8362 set_freeRangeInFreeLists(false);
8363 }
8364 }
8365 }
8366 // Note that if the chunk is not coalescable (the else arm
8367 // below), we unconditionally flush, without needing to do
8368 // a "lookahead," as we do below.
8369 if (inFreeRange()) lookahead_and_flush(fc, size);
8370 } else {
8371 // Code path common to both original and adaptive free lists.
8372
8373 // cant coalesce with previous block; this should be treated
8374 // as the end of a free run if any
8375 if (inFreeRange()) {
8376 // we kicked some butt; time to pick up the garbage
8377 assert(freeFinger() < addr, "freeFinger points too high");
8378 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8379 }
8380 // else, nothing to do, just continue
8381 }
8382 }
8383
8384 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8385 // This is a chunk of garbage. It is not in any free list.
8386 // Add it to a free list or let it possibly be coalesced into
8387 // a larger chunk.
8388 HeapWord* const addr = (HeapWord*) fc;
8389 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8390
8391 if (_sp->adaptive_freelists()) {
8392 // Verify that the bit map has no bits marked between
8393 // addr and purported end of just dead object.
8394 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8395
8396 do_post_free_or_garbage_chunk(fc, size);
8397 } else {
8398 if (!inFreeRange()) {
8399 // start of a new free range
8400 assert(size > 0, "A free range should have a size");
8401 initialize_free_range(addr, false);
8402 } else {
8403 // this will be swept up when we hit the end of the
8404 // free range
8405 if (CMSTraceSweeper) {
8406 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8407 }
8408 // If the chunk is being coalesced and the current free range is
8409 // in the free lists, remove the current free range so that it
8410 // will be returned to the free lists in its entirety - all
8411 // the coalesced pieces included.
8412 if (freeRangeInFreeLists()) {
8413 FreeChunk* ffc = (FreeChunk*)freeFinger();
8414 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8415 "Size of free range is inconsistent with chunk size.");
8416 if (CMSTestInFreeList) {
8417 assert(_sp->verify_chunk_in_free_list(ffc),
8418 "free range is not in free lists");
8419 }
8420 _sp->removeFreeChunkFromFreeLists(ffc);
8421 set_freeRangeInFreeLists(false);
8422 }
8423 set_lastFreeRangeCoalesced(true);
8424 }
8425 // this will be swept up when we hit the end of the free range
8426
8427 // Verify that the bit map has no bits marked between
8428 // addr and purported end of just dead object.
8429 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8430 }
8431 assert(_limit >= addr + size,
8432 "A freshly garbage chunk can't possibly straddle over _limit");
8433 if (inFreeRange()) lookahead_and_flush(fc, size);
8434 return size;
8435 }
8436
8437 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8438 HeapWord* addr = (HeapWord*) fc;
8439 // The sweeper has just found a live object. Return any accumulated
8440 // left hand chunk to the free lists.
8441 if (inFreeRange()) {
8442 assert(freeFinger() < addr, "freeFinger points too high");
8443 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8444 }
8445
8446 // This object is live: we'd normally expect this to be
8447 // an oop, and like to assert the following:
8448 // assert(oop(addr)->is_oop(), "live block should be an oop");
8449 // However, as we commented above, this may be an object whose
8450 // header hasn't yet been initialized.
8451 size_t size;
8452 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8453 if (_bitMap->isMarked(addr + 1)) {
8454 // Determine the size from the bit map, rather than trying to
8455 // compute it from the object header.
8456 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8457 size = pointer_delta(nextOneAddr + 1, addr);
8458 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8459 "alignment problem");
8460
8461 #ifdef ASSERT
8462 if (oop(addr)->klass_or_null() != NULL) {
8463 // Ignore mark word because we are running concurrent with mutators
8464 assert(oop(addr)->is_oop(true), "live block should be an oop");
8465 assert(size ==
8466 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8467 "P-mark and computed size do not agree");
8468 }
8469 #endif
8470
8471 } else {
8472 // This should be an initialized object that's alive.
8473 assert(oop(addr)->klass_or_null() != NULL,
8474 "Should be an initialized object");
8475 // Ignore mark word because we are running concurrent with mutators
8476 assert(oop(addr)->is_oop(true), "live block should be an oop");
8477 // Verify that the bit map has no bits marked between
8478 // addr and purported end of this block.
8479 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8480 assert(size >= 3, "Necessary for Printezis marks to work");
8481 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8482 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8483 }
8484 return size;
8485 }
8486
8487 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8488 size_t chunkSize) {
8489 // do_post_free_or_garbage_chunk() should only be called in the case
8490 // of the adaptive free list allocator.
8491 const bool fcInFreeLists = fc->is_free();
8492 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8493 assert((HeapWord*)fc <= _limit, "sweep invariant");
8494 if (CMSTestInFreeList && fcInFreeLists) {
8495 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8496 }
8497
8498 if (CMSTraceSweeper) {
8499 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8500 }
8501
8502 HeapWord* const fc_addr = (HeapWord*) fc;
8503
8504 bool coalesce;
8505 const size_t left = pointer_delta(fc_addr, freeFinger());
8506 const size_t right = chunkSize;
8507 switch (FLSCoalescePolicy) {
8508 // numeric value forms a coalition aggressiveness metric
8509 case 0: { // never coalesce
8510 coalesce = false;
8511 break;
8512 }
8513 case 1: { // coalesce if left & right chunks on overpopulated lists
8514 coalesce = _sp->coalOverPopulated(left) &&
8515 _sp->coalOverPopulated(right);
8516 break;
8517 }
8518 case 2: { // coalesce if left chunk on overpopulated list (default)
8519 coalesce = _sp->coalOverPopulated(left);
8520 break;
8521 }
8522 case 3: { // coalesce if left OR right chunk on overpopulated list
8523 coalesce = _sp->coalOverPopulated(left) ||
8524 _sp->coalOverPopulated(right);
8525 break;
8526 }
8527 case 4: { // always coalesce
8528 coalesce = true;
8529 break;
8530 }
8531 default:
8532 ShouldNotReachHere();
8533 }
8534
8535 // Should the current free range be coalesced?
8536 // If the chunk is in a free range and either we decided to coalesce above
8537 // or the chunk is near the large block at the end of the heap
8538 // (isNearLargestChunk() returns true), then coalesce this chunk.
8539 const bool doCoalesce = inFreeRange()
8540 && (coalesce || _g->isNearLargestChunk(fc_addr));
8541 if (doCoalesce) {
8542 // Coalesce the current free range on the left with the new
8543 // chunk on the right. If either is on a free list,
8544 // it must be removed from the list and stashed in the closure.
8545 if (freeRangeInFreeLists()) {
8546 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8547 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8548 "Size of free range is inconsistent with chunk size.");
8549 if (CMSTestInFreeList) {
8550 assert(_sp->verify_chunk_in_free_list(ffc),
8551 "Chunk is not in free lists");
8552 }
8553 _sp->coalDeath(ffc->size());
8554 _sp->removeFreeChunkFromFreeLists(ffc);
8555 set_freeRangeInFreeLists(false);
8556 }
8557 if (fcInFreeLists) {
8558 _sp->coalDeath(chunkSize);
8559 assert(fc->size() == chunkSize,
8560 "The chunk has the wrong size or is not in the free lists");
8561 _sp->removeFreeChunkFromFreeLists(fc);
8562 }
8563 set_lastFreeRangeCoalesced(true);
8564 print_free_block_coalesced(fc);
8565 } else { // not in a free range and/or should not coalesce
8566 // Return the current free range and start a new one.
8567 if (inFreeRange()) {
8568 // In a free range but cannot coalesce with the right hand chunk.
8569 // Put the current free range into the free lists.
8570 flush_cur_free_chunk(freeFinger(),
8571 pointer_delta(fc_addr, freeFinger()));
8572 }
8573 // Set up for new free range. Pass along whether the right hand
8574 // chunk is in the free lists.
8575 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8576 }
8577 }
8578
8579 // Lookahead flush:
8580 // If we are tracking a free range, and this is the last chunk that
8581 // we'll look at because its end crosses past _limit, we'll preemptively
8582 // flush it along with any free range we may be holding on to. Note that
8583 // this can be the case only for an already free or freshly garbage
8584 // chunk. If this block is an object, it can never straddle
8585 // over _limit. The "straddling" occurs when _limit is set at
8586 // the previous end of the space when this cycle started, and
8587 // a subsequent heap expansion caused the previously co-terminal
8588 // free block to be coalesced with the newly expanded portion,
8589 // thus rendering _limit a non-block-boundary making it dangerous
8590 // for the sweeper to step over and examine.
8591 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8592 assert(inFreeRange(), "Should only be called if currently in a free range.");
8593 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8594 assert(_sp->used_region().contains(eob - 1),
8595 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8596 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8597 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8598 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8599 if (eob >= _limit) {
8600 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8601 if (CMSTraceSweeper) {
8602 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8603 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8604 "[" PTR_FORMAT "," PTR_FORMAT ")",
8605 _limit, fc, eob, _sp->bottom(), _sp->end());
8606 }
8607 // Return the storage we are tracking back into the free lists.
8608 if (CMSTraceSweeper) {
8609 gclog_or_tty->print_cr("Flushing ... ");
8610 }
8611 assert(freeFinger() < eob, "Error");
8612 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8613 }
8614 }
8615
8616 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8617 assert(inFreeRange(), "Should only be called if currently in a free range.");
8618 assert(size > 0,
8619 "A zero sized chunk cannot be added to the free lists.");
8620 if (!freeRangeInFreeLists()) {
8621 if (CMSTestInFreeList) {
8622 FreeChunk* fc = (FreeChunk*) chunk;
8623 fc->set_size(size);
8624 assert(!_sp->verify_chunk_in_free_list(fc),
8625 "chunk should not be in free lists yet");
8626 }
8627 if (CMSTraceSweeper) {
8628 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8629 chunk, size);
8630 }
8631 // A new free range is going to be starting. The current
8632 // free range has not been added to the free lists yet or
8633 // was removed so add it back.
8634 // If the current free range was coalesced, then the death
8635 // of the free range was recorded. Record a birth now.
8636 if (lastFreeRangeCoalesced()) {
8637 _sp->coalBirth(size);
8638 }
8639 _sp->addChunkAndRepairOffsetTable(chunk, size,
8640 lastFreeRangeCoalesced());
8641 } else if (CMSTraceSweeper) {
8642 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8643 }
8644 set_inFreeRange(false);
8645 set_freeRangeInFreeLists(false);
8646 }
8647
8648 // We take a break if we've been at this for a while,
8649 // so as to avoid monopolizing the locks involved.
8650 void SweepClosure::do_yield_work(HeapWord* addr) {
8651 // Return current free chunk being used for coalescing (if any)
8652 // to the appropriate freelist. After yielding, the next
8653 // free block encountered will start a coalescing range of
8654 // free blocks. If the next free block is adjacent to the
8655 // chunk just flushed, they will need to wait for the next
8656 // sweep to be coalesced.
8657 if (inFreeRange()) {
8658 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8659 }
8660
8661 // First give up the locks, then yield, then re-lock.
8662 // We should probably use a constructor/destructor idiom to
8663 // do this unlock/lock or modify the MutexUnlocker class to
8664 // serve our purpose. XXX
8665 assert_lock_strong(_bitMap->lock());
8666 assert_lock_strong(_freelistLock);
8667 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8668 "CMS thread should hold CMS token");
8669 _bitMap->lock()->unlock();
8670 _freelistLock->unlock();
8671 ConcurrentMarkSweepThread::desynchronize(true);
8672 ConcurrentMarkSweepThread::acknowledge_yield_request();
8673 _collector->stopTimer();
8674 if (PrintCMSStatistics != 0) {
8675 _collector->incrementYields();
8676 }
8677 _collector->icms_wait();
8678
8679 // See the comment in coordinator_yield()
8680 for (unsigned i = 0; i < CMSYieldSleepCount &&
8681 ConcurrentMarkSweepThread::should_yield() &&
8682 !CMSCollector::foregroundGCIsActive(); ++i) {
8683 os::sleep(Thread::current(), 1, false);
8684 ConcurrentMarkSweepThread::acknowledge_yield_request();
8685 }
8686
8687 ConcurrentMarkSweepThread::synchronize(true);
8688 _freelistLock->lock();
8689 _bitMap->lock()->lock_without_safepoint_check();
8690 _collector->startTimer();
8691 }
8692
8693 #ifndef PRODUCT
8694 // This is actually very useful in a product build if it can
8695 // be called from the debugger. Compile it into the product
8696 // as needed.
8697 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8698 return debug_cms_space->verify_chunk_in_free_list(fc);
8699 }
8700 #endif
8701
8702 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8703 if (CMSTraceSweeper) {
8704 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8705 fc, fc->size());
8706 }
8707 }
8708
8709 // CMSIsAliveClosure
8710 bool CMSIsAliveClosure::do_object_b(oop obj) {
8711 HeapWord* addr = (HeapWord*)obj;
8712 return addr != NULL &&
8713 (!_span.contains(addr) || _bit_map->isMarked(addr));
8714 }
8715
8716
8717 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8718 MemRegion span,
8719 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8720 bool cpc):
8721 _collector(collector),
8722 _span(span),
8723 _bit_map(bit_map),
8724 _mark_stack(mark_stack),
8725 _concurrent_precleaning(cpc) {
8726 assert(!_span.is_empty(), "Empty span could spell trouble");
8727 }
8728
8729
8730 // CMSKeepAliveClosure: the serial version
8731 void CMSKeepAliveClosure::do_oop(oop obj) {
8732 HeapWord* addr = (HeapWord*)obj;
8733 if (_span.contains(addr) &&
8734 !_bit_map->isMarked(addr)) {
8735 _bit_map->mark(addr);
8736 bool simulate_overflow = false;
8737 NOT_PRODUCT(
8738 if (CMSMarkStackOverflowALot &&
8739 _collector->simulate_overflow()) {
8740 // simulate a stack overflow
8741 simulate_overflow = true;
8742 }
8743 )
8744 if (simulate_overflow || !_mark_stack->push(obj)) {
8745 if (_concurrent_precleaning) {
8746 // We dirty the overflown object and let the remark
8747 // phase deal with it.
8748 assert(_collector->overflow_list_is_empty(), "Error");
8749 // In the case of object arrays, we need to dirty all of
8750 // the cards that the object spans. No locking or atomics
8751 // are needed since no one else can be mutating the mod union
8752 // table.
8753 if (obj->is_objArray()) {
8754 size_t sz = obj->size();
8755 HeapWord* end_card_addr =
8756 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8757 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8758 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8759 _collector->_modUnionTable.mark_range(redirty_range);
8760 } else {
8761 _collector->_modUnionTable.mark(addr);
8762 }
8763 _collector->_ser_kac_preclean_ovflw++;
8764 } else {
8765 _collector->push_on_overflow_list(obj);
8766 _collector->_ser_kac_ovflw++;
8767 }
8768 }
8769 }
8770 }
8771
8772 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8773 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8774
8775 // CMSParKeepAliveClosure: a parallel version of the above.
8776 // The work queues are private to each closure (thread),
8777 // but (may be) available for stealing by other threads.
8778 void CMSParKeepAliveClosure::do_oop(oop obj) {
8779 HeapWord* addr = (HeapWord*)obj;
8780 if (_span.contains(addr) &&
8781 !_bit_map->isMarked(addr)) {
8782 // In general, during recursive tracing, several threads
8783 // may be concurrently getting here; the first one to
8784 // "tag" it, claims it.
8785 if (_bit_map->par_mark(addr)) {
8786 bool res = _work_queue->push(obj);
8787 assert(res, "Low water mark should be much less than capacity");
8788 // Do a recursive trim in the hope that this will keep
8789 // stack usage lower, but leave some oops for potential stealers
8790 trim_queue(_low_water_mark);
8791 } // Else, another thread got there first
8792 }
8793 }
8794
8795 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8796 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8797
8798 void CMSParKeepAliveClosure::trim_queue(uint max) {
8799 while (_work_queue->size() > max) {
8800 oop new_oop;
8801 if (_work_queue->pop_local(new_oop)) {
8802 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8803 assert(_bit_map->isMarked((HeapWord*)new_oop),
8804 "no white objects on this stack!");
8805 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8806 // iterate over the oops in this oop, marking and pushing
8807 // the ones in CMS heap (i.e. in _span).
8808 new_oop->oop_iterate(&_mark_and_push);
8809 }
8810 }
8811 }
8812
8813 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8814 CMSCollector* collector,
8815 MemRegion span, CMSBitMap* bit_map,
8816 OopTaskQueue* work_queue):
8817 _collector(collector),
8818 _span(span),
8819 _bit_map(bit_map),
8820 _work_queue(work_queue) { }
8821
8822 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8823 HeapWord* addr = (HeapWord*)obj;
8824 if (_span.contains(addr) &&
8825 !_bit_map->isMarked(addr)) {
8826 if (_bit_map->par_mark(addr)) {
8827 bool simulate_overflow = false;
8828 NOT_PRODUCT(
8829 if (CMSMarkStackOverflowALot &&
8830 _collector->par_simulate_overflow()) {
8831 // simulate a stack overflow
8832 simulate_overflow = true;
8833 }
8834 )
8835 if (simulate_overflow || !_work_queue->push(obj)) {
8836 _collector->par_push_on_overflow_list(obj);
8837 _collector->_par_kac_ovflw++;
8838 }
8839 } // Else another thread got there already
8840 }
8841 }
8842
8843 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8844 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8845
8846 //////////////////////////////////////////////////////////////////
8847 // CMSExpansionCause /////////////////////////////
8848 //////////////////////////////////////////////////////////////////
8849 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8850 switch (cause) {
8851 case _no_expansion:
8852 return "No expansion";
8853 case _satisfy_free_ratio:
8854 return "Free ratio";
8855 case _satisfy_promotion:
8856 return "Satisfy promotion";
8857 case _satisfy_allocation:
8858 return "allocation";
8859 case _allocate_par_lab:
8860 return "Par LAB";
8861 case _allocate_par_spooling_space:
8862 return "Par Spooling Space";
8863 case _adaptive_size_policy:
8864 return "Ergonomics";
8865 default:
8866 return "unknown";
8867 }
8868 }
8869
8870 void CMSDrainMarkingStackClosure::do_void() {
8871 // the max number to take from overflow list at a time
8872 const size_t num = _mark_stack->capacity()/4;
8873 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8874 "Overflow list should be NULL during concurrent phases");
8875 while (!_mark_stack->isEmpty() ||
8876 // if stack is empty, check the overflow list
8877 _collector->take_from_overflow_list(num, _mark_stack)) {
8878 oop obj = _mark_stack->pop();
8879 HeapWord* addr = (HeapWord*)obj;
8880 assert(_span.contains(addr), "Should be within span");
8881 assert(_bit_map->isMarked(addr), "Should be marked");
8882 assert(obj->is_oop(), "Should be an oop");
8883 obj->oop_iterate(_keep_alive);
8884 }
8885 }
8886
8887 void CMSParDrainMarkingStackClosure::do_void() {
8888 // drain queue
8889 trim_queue(0);
8890 }
8891
8892 // Trim our work_queue so its length is below max at return
8893 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8894 while (_work_queue->size() > max) {
8895 oop new_oop;
8896 if (_work_queue->pop_local(new_oop)) {
8897 assert(new_oop->is_oop(), "Expected an oop");
8898 assert(_bit_map->isMarked((HeapWord*)new_oop),
8899 "no white objects on this stack!");
8900 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8901 // iterate over the oops in this oop, marking and pushing
8902 // the ones in CMS heap (i.e. in _span).
8903 new_oop->oop_iterate(&_mark_and_push);
8904 }
8905 }
8906 }
8907
8908 ////////////////////////////////////////////////////////////////////
8909 // Support for Marking Stack Overflow list handling and related code
8910 ////////////////////////////////////////////////////////////////////
8911 // Much of the following code is similar in shape and spirit to the
8912 // code used in ParNewGC. We should try and share that code
8913 // as much as possible in the future.
8914
8915 #ifndef PRODUCT
8916 // Debugging support for CMSStackOverflowALot
8917
8918 // It's OK to call this multi-threaded; the worst thing
8919 // that can happen is that we'll get a bunch of closely
8920 // spaced simulated overflows, but that's OK, in fact
8921 // probably good as it would exercise the overflow code
8922 // under contention.
8923 bool CMSCollector::simulate_overflow() {
8924 if (_overflow_counter-- <= 0) { // just being defensive
8925 _overflow_counter = CMSMarkStackOverflowInterval;
8926 return true;
8927 } else {
8928 return false;
8929 }
8930 }
8931
8932 bool CMSCollector::par_simulate_overflow() {
8933 return simulate_overflow();
8934 }
8935 #endif
8936
8937 // Single-threaded
8938 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8939 assert(stack->isEmpty(), "Expected precondition");
8940 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8941 size_t i = num;
8942 oop cur = _overflow_list;
8943 const markOop proto = markOopDesc::prototype();
8944 NOT_PRODUCT(ssize_t n = 0;)
8945 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8946 next = oop(cur->mark());
8947 cur->set_mark(proto); // until proven otherwise
8948 assert(cur->is_oop(), "Should be an oop");
8949 bool res = stack->push(cur);
8950 assert(res, "Bit off more than can chew?");
8951 NOT_PRODUCT(n++;)
8952 }
8953 _overflow_list = cur;
8954 #ifndef PRODUCT
8955 assert(_num_par_pushes >= n, "Too many pops?");
8956 _num_par_pushes -=n;
8957 #endif
8958 return !stack->isEmpty();
8959 }
8960
8961 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8962 // (MT-safe) Get a prefix of at most "num" from the list.
8963 // The overflow list is chained through the mark word of
8964 // each object in the list. We fetch the entire list,
8965 // break off a prefix of the right size and return the
8966 // remainder. If other threads try to take objects from
8967 // the overflow list at that time, they will wait for
8968 // some time to see if data becomes available. If (and
8969 // only if) another thread places one or more object(s)
8970 // on the global list before we have returned the suffix
8971 // to the global list, we will walk down our local list
8972 // to find its end and append the global list to
8973 // our suffix before returning it. This suffix walk can
8974 // prove to be expensive (quadratic in the amount of traffic)
8975 // when there are many objects in the overflow list and
8976 // there is much producer-consumer contention on the list.
8977 // *NOTE*: The overflow list manipulation code here and
8978 // in ParNewGeneration:: are very similar in shape,
8979 // except that in the ParNew case we use the old (from/eden)
8980 // copy of the object to thread the list via its klass word.
8981 // Because of the common code, if you make any changes in
8982 // the code below, please check the ParNew version to see if
8983 // similar changes might be needed.
8984 // CR 6797058 has been filed to consolidate the common code.
8985 bool CMSCollector::par_take_from_overflow_list(size_t num,
8986 OopTaskQueue* work_q,
8987 int no_of_gc_threads) {
8988 assert(work_q->size() == 0, "First empty local work queue");
8989 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8990 if (_overflow_list == NULL) {
8991 return false;
8992 }
8993 // Grab the entire list; we'll put back a suffix
8994 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8995 Thread* tid = Thread::current();
8996 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8997 // set to ParallelGCThreads.
8998 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8999 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9000 // If the list is busy, we spin for a short while,
9001 // sleeping between attempts to get the list.
9002 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9003 os::sleep(tid, sleep_time_millis, false);
9004 if (_overflow_list == NULL) {
9005 // Nothing left to take
9006 return false;
9007 } else if (_overflow_list != BUSY) {
9008 // Try and grab the prefix
9009 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9010 }
9011 }
9012 // If the list was found to be empty, or we spun long
9013 // enough, we give up and return empty-handed. If we leave
9014 // the list in the BUSY state below, it must be the case that
9015 // some other thread holds the overflow list and will set it
9016 // to a non-BUSY state in the future.
9017 if (prefix == NULL || prefix == BUSY) {
9018 // Nothing to take or waited long enough
9019 if (prefix == NULL) {
9020 // Write back the NULL in case we overwrote it with BUSY above
9021 // and it is still the same value.
9022 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9023 }
9024 return false;
9025 }
9026 assert(prefix != NULL && prefix != BUSY, "Error");
9027 size_t i = num;
9028 oop cur = prefix;
9029 // Walk down the first "num" objects, unless we reach the end.
9030 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9031 if (cur->mark() == NULL) {
9032 // We have "num" or fewer elements in the list, so there
9033 // is nothing to return to the global list.
9034 // Write back the NULL in lieu of the BUSY we wrote
9035 // above, if it is still the same value.
9036 if (_overflow_list == BUSY) {
9037 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9038 }
9039 } else {
9040 // Chop off the suffix and return it to the global list.
9041 assert(cur->mark() != BUSY, "Error");
9042 oop suffix_head = cur->mark(); // suffix will be put back on global list
9043 cur->set_mark(NULL); // break off suffix
9044 // It's possible that the list is still in the empty(busy) state
9045 // we left it in a short while ago; in that case we may be
9046 // able to place back the suffix without incurring the cost
9047 // of a walk down the list.
9048 oop observed_overflow_list = _overflow_list;
9049 oop cur_overflow_list = observed_overflow_list;
9050 bool attached = false;
9051 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9052 observed_overflow_list =
9053 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9054 if (cur_overflow_list == observed_overflow_list) {
9055 attached = true;
9056 break;
9057 } else cur_overflow_list = observed_overflow_list;
9058 }
9059 if (!attached) {
9060 // Too bad, someone else sneaked in (at least) an element; we'll need
9061 // to do a splice. Find tail of suffix so we can prepend suffix to global
9062 // list.
9063 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9064 oop suffix_tail = cur;
9065 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9066 "Tautology");
9067 observed_overflow_list = _overflow_list;
9068 do {
9069 cur_overflow_list = observed_overflow_list;
9070 if (cur_overflow_list != BUSY) {
9071 // Do the splice ...
9072 suffix_tail->set_mark(markOop(cur_overflow_list));
9073 } else { // cur_overflow_list == BUSY
9074 suffix_tail->set_mark(NULL);
9075 }
9076 // ... and try to place spliced list back on overflow_list ...
9077 observed_overflow_list =
9078 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9079 } while (cur_overflow_list != observed_overflow_list);
9080 // ... until we have succeeded in doing so.
9081 }
9082 }
9083
9084 // Push the prefix elements on work_q
9085 assert(prefix != NULL, "control point invariant");
9086 const markOop proto = markOopDesc::prototype();
9087 oop next;
9088 NOT_PRODUCT(ssize_t n = 0;)
9089 for (cur = prefix; cur != NULL; cur = next) {
9090 next = oop(cur->mark());
9091 cur->set_mark(proto); // until proven otherwise
9092 assert(cur->is_oop(), "Should be an oop");
9093 bool res = work_q->push(cur);
9094 assert(res, "Bit off more than we can chew?");
9095 NOT_PRODUCT(n++;)
9096 }
9097 #ifndef PRODUCT
9098 assert(_num_par_pushes >= n, "Too many pops?");
9099 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9100 #endif
9101 return true;
9102 }
9103
9104 // Single-threaded
9105 void CMSCollector::push_on_overflow_list(oop p) {
9106 NOT_PRODUCT(_num_par_pushes++;)
9107 assert(p->is_oop(), "Not an oop");
9108 preserve_mark_if_necessary(p);
9109 p->set_mark((markOop)_overflow_list);
9110 _overflow_list = p;
9111 }
9112
9113 // Multi-threaded; use CAS to prepend to overflow list
9114 void CMSCollector::par_push_on_overflow_list(oop p) {
9115 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9116 assert(p->is_oop(), "Not an oop");
9117 par_preserve_mark_if_necessary(p);
9118 oop observed_overflow_list = _overflow_list;
9119 oop cur_overflow_list;
9120 do {
9121 cur_overflow_list = observed_overflow_list;
9122 if (cur_overflow_list != BUSY) {
9123 p->set_mark(markOop(cur_overflow_list));
9124 } else {
9125 p->set_mark(NULL);
9126 }
9127 observed_overflow_list =
9128 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9129 } while (cur_overflow_list != observed_overflow_list);
9130 }
9131 #undef BUSY
9132
9133 // Single threaded
9134 // General Note on GrowableArray: pushes may silently fail
9135 // because we are (temporarily) out of C-heap for expanding
9136 // the stack. The problem is quite ubiquitous and affects
9137 // a lot of code in the JVM. The prudent thing for GrowableArray
9138 // to do (for now) is to exit with an error. However, that may
9139 // be too draconian in some cases because the caller may be
9140 // able to recover without much harm. For such cases, we
9141 // should probably introduce a "soft_push" method which returns
9142 // an indication of success or failure with the assumption that
9143 // the caller may be able to recover from a failure; code in
9144 // the VM can then be changed, incrementally, to deal with such
9145 // failures where possible, thus, incrementally hardening the VM
9146 // in such low resource situations.
9147 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9148 _preserved_oop_stack.push(p);
9149 _preserved_mark_stack.push(m);
9150 assert(m == p->mark(), "Mark word changed");
9151 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9152 "bijection");
9153 }
9154
9155 // Single threaded
9156 void CMSCollector::preserve_mark_if_necessary(oop p) {
9157 markOop m = p->mark();
9158 if (m->must_be_preserved(p)) {
9159 preserve_mark_work(p, m);
9160 }
9161 }
9162
9163 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9164 markOop m = p->mark();
9165 if (m->must_be_preserved(p)) {
9166 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9167 // Even though we read the mark word without holding
9168 // the lock, we are assured that it will not change
9169 // because we "own" this oop, so no other thread can
9170 // be trying to push it on the overflow list; see
9171 // the assertion in preserve_mark_work() that checks
9172 // that m == p->mark().
9173 preserve_mark_work(p, m);
9174 }
9175 }
9176
9177 // We should be able to do this multi-threaded,
9178 // a chunk of stack being a task (this is
9179 // correct because each oop only ever appears
9180 // once in the overflow list. However, it's
9181 // not very easy to completely overlap this with
9182 // other operations, so will generally not be done
9183 // until all work's been completed. Because we
9184 // expect the preserved oop stack (set) to be small,
9185 // it's probably fine to do this single-threaded.
9186 // We can explore cleverer concurrent/overlapped/parallel
9187 // processing of preserved marks if we feel the
9188 // need for this in the future. Stack overflow should
9189 // be so rare in practice and, when it happens, its
9190 // effect on performance so great that this will
9191 // likely just be in the noise anyway.
9192 void CMSCollector::restore_preserved_marks_if_any() {
9193 assert(SafepointSynchronize::is_at_safepoint(),
9194 "world should be stopped");
9195 assert(Thread::current()->is_ConcurrentGC_thread() ||
9196 Thread::current()->is_VM_thread(),
9197 "should be single-threaded");
9198 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9199 "bijection");
9200
9201 while (!_preserved_oop_stack.is_empty()) {
9202 oop p = _preserved_oop_stack.pop();
9203 assert(p->is_oop(), "Should be an oop");
9204 assert(_span.contains(p), "oop should be in _span");
9205 assert(p->mark() == markOopDesc::prototype(),
9206 "Set when taken from overflow list");
9207 markOop m = _preserved_mark_stack.pop();
9208 p->set_mark(m);
9209 }
9210 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9211 "stacks were cleared above");
9212 }
9213
9214 #ifndef PRODUCT
9215 bool CMSCollector::no_preserved_marks() const {
9216 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9217 }
9218 #endif
9219
9220 // Transfer some number of overflown objects to usual marking
9221 // stack. Return true if some objects were transferred.
9222 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9223 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9224 (size_t)ParGCDesiredObjsFromOverflowList);
9225
9226 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9227 assert(_collector->overflow_list_is_empty() || res,
9228 "If list is not empty, we should have taken something");
9229 assert(!res || !_mark_stack->isEmpty(),
9230 "If we took something, it should now be on our stack");
9231 return res;
9232 }
9233
9234 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9235 size_t res = _sp->block_size_no_stall(addr, _collector);
9236 if (_sp->block_is_obj(addr)) {
9237 if (_live_bit_map->isMarked(addr)) {
9238 // It can't have been dead in a previous cycle
9239 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9240 } else {
9241 _dead_bit_map->mark(addr); // mark the dead object
9242 }
9243 }
9244 // Could be 0, if the block size could not be computed without stalling.
9245 return res;
9246 }
9247
9248 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9249
9250 switch (phase) {
9251 case CMSCollector::InitialMarking:
9252 initialize(true /* fullGC */ ,
9253 cause /* cause of the GC */,
9254 true /* recordGCBeginTime */,
9255 true /* recordPreGCUsage */,
9256 false /* recordPeakUsage */,
9257 false /* recordPostGCusage */,
9258 true /* recordAccumulatedGCTime */,
9259 false /* recordGCEndTime */,
9260 false /* countCollection */ );
9261 break;
9262
9263 case CMSCollector::FinalMarking:
9264 initialize(true /* fullGC */ ,
9265 cause /* cause of the GC */,
9266 false /* recordGCBeginTime */,
9267 false /* recordPreGCUsage */,
9268 false /* recordPeakUsage */,
9269 false /* recordPostGCusage */,
9270 true /* recordAccumulatedGCTime */,
9271 false /* recordGCEndTime */,
9272 false /* countCollection */ );
9273 break;
9274
9275 case CMSCollector::Sweeping:
9276 initialize(true /* fullGC */ ,
9277 cause /* cause of the GC */,
9278 false /* recordGCBeginTime */,
9279 false /* recordPreGCUsage */,
9280 true /* recordPeakUsage */,
9281 true /* recordPostGCusage */,
9282 false /* recordAccumulatedGCTime */,
9283 true /* recordGCEndTime */,
9284 true /* countCollection */ );
9285 break;
9286
9287 default:
9288 ShouldNotReachHere();
9289 }
9290 }