1 /*
2 * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/isGCActiveMark.hpp"
41 #include "gc_interface/collectedHeap.inline.hpp"
42 #include "memory/cardTableRS.hpp"
43 #include "memory/collectorPolicy.hpp"
44 #include "memory/gcLocker.inline.hpp"
45 #include "memory/genCollectedHeap.hpp"
46 #include "memory/genMarkSweep.hpp"
47 #include "memory/genOopClosures.inline.hpp"
48 #include "memory/iterator.hpp"
49 #include "memory/referencePolicy.hpp"
50 #include "memory/resourceArea.hpp"
51 #include "oops/oop.inline.hpp"
52 #include "prims/jvmtiExport.hpp"
53 #include "runtime/globals_extension.hpp"
54 #include "runtime/handles.inline.hpp"
55 #include "runtime/java.hpp"
56 #include "runtime/vmThread.hpp"
57 #include "services/memoryService.hpp"
58 #include "services/runtimeService.hpp"
59
60 // statics
61 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
62 bool CMSCollector::_full_gc_requested = false;
63
64 //////////////////////////////////////////////////////////////////
65 // In support of CMS/VM thread synchronization
66 //////////////////////////////////////////////////////////////////
67 // We split use of the CGC_lock into 2 "levels".
68 // The low-level locking is of the usual CGC_lock monitor. We introduce
69 // a higher level "token" (hereafter "CMS token") built on top of the
70 // low level monitor (hereafter "CGC lock").
71 // The token-passing protocol gives priority to the VM thread. The
72 // CMS-lock doesn't provide any fairness guarantees, but clients
73 // should ensure that it is only held for very short, bounded
74 // durations.
75 //
76 // When either of the CMS thread or the VM thread is involved in
77 // collection operations during which it does not want the other
78 // thread to interfere, it obtains the CMS token.
79 //
80 // If either thread tries to get the token while the other has
81 // it, that thread waits. However, if the VM thread and CMS thread
82 // both want the token, then the VM thread gets priority while the
83 // CMS thread waits. This ensures, for instance, that the "concurrent"
84 // phases of the CMS thread's work do not block out the VM thread
85 // for long periods of time as the CMS thread continues to hog
86 // the token. (See bug 4616232).
87 //
88 // The baton-passing functions are, however, controlled by the
89 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
90 // and here the low-level CMS lock, not the high level token,
91 // ensures mutual exclusion.
92 //
93 // Two important conditions that we have to satisfy:
94 // 1. if a thread does a low-level wait on the CMS lock, then it
95 // relinquishes the CMS token if it were holding that token
96 // when it acquired the low-level CMS lock.
97 // 2. any low-level notifications on the low-level lock
98 // should only be sent when a thread has relinquished the token.
99 //
100 // In the absence of either property, we'd have potential deadlock.
101 //
102 // We protect each of the CMS (concurrent and sequential) phases
103 // with the CMS _token_, not the CMS _lock_.
104 //
105 // The only code protected by CMS lock is the token acquisition code
106 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
107 // baton-passing code.
108 //
109 // Unfortunately, i couldn't come up with a good abstraction to factor and
110 // hide the naked CGC_lock manipulation in the baton-passing code
111 // further below. That's something we should try to do. Also, the proof
112 // of correctness of this 2-level locking scheme is far from obvious,
113 // and potentially quite slippery. We have an uneasy supsicion, for instance,
114 // that there may be a theoretical possibility of delay/starvation in the
115 // low-level lock/wait/notify scheme used for the baton-passing because of
116 // potential intereference with the priority scheme embodied in the
117 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
118 // invocation further below and marked with "XXX 20011219YSR".
119 // Indeed, as we note elsewhere, this may become yet more slippery
120 // in the presence of multiple CMS and/or multiple VM threads. XXX
121
122 class CMSTokenSync: public StackObj {
123 private:
124 bool _is_cms_thread;
125 public:
126 CMSTokenSync(bool is_cms_thread):
127 _is_cms_thread(is_cms_thread) {
128 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
129 "Incorrect argument to constructor");
130 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
131 }
132
133 ~CMSTokenSync() {
134 assert(_is_cms_thread ?
135 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
136 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
137 "Incorrect state");
138 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
139 }
140 };
141
142 // Convenience class that does a CMSTokenSync, and then acquires
143 // upto three locks.
144 class CMSTokenSyncWithLocks: public CMSTokenSync {
145 private:
146 // Note: locks are acquired in textual declaration order
147 // and released in the opposite order
148 MutexLockerEx _locker1, _locker2, _locker3;
149 public:
150 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
151 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
152 CMSTokenSync(is_cms_thread),
153 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
154 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
155 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
156 { }
157 };
158
159
160 // Wrapper class to temporarily disable icms during a foreground cms collection.
161 class ICMSDisabler: public StackObj {
162 public:
163 // The ctor disables icms and wakes up the thread so it notices the change;
164 // the dtor re-enables icms. Note that the CMSCollector methods will check
165 // CMSIncrementalMode.
166 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
167 ~ICMSDisabler() { CMSCollector::enable_icms(); }
168 };
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
190 ReservedSpace rs, size_t initial_byte_size, int level,
191 CardTableRS* ct, bool use_adaptive_freelists,
192 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
193 CardGeneration(rs, initial_byte_size, level, ct),
194 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
195 _debug_collection_type(Concurrent_collection_type)
196 {
197 HeapWord* bottom = (HeapWord*) _virtual_space.low();
198 HeapWord* end = (HeapWord*) _virtual_space.high();
199
200 _direct_allocated_words = 0;
201 NOT_PRODUCT(
202 _numObjectsPromoted = 0;
203 _numWordsPromoted = 0;
204 _numObjectsAllocated = 0;
205 _numWordsAllocated = 0;
206 )
207
208 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
209 use_adaptive_freelists,
210 dictionaryChoice);
211 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
212 if (_cmsSpace == NULL) {
213 vm_exit_during_initialization(
214 "CompactibleFreeListSpace allocation failure");
215 }
216 _cmsSpace->_gen = this;
217
218 _gc_stats = new CMSGCStats();
219
220 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
221 // offsets match. The ability to tell free chunks from objects
222 // depends on this property.
223 debug_only(
224 FreeChunk* junk = NULL;
225 assert(UseCompressedOops ||
226 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
227 "Offset of FreeChunk::_prev within FreeChunk must match"
228 " that of OopDesc::_klass within OopDesc");
229 )
230 if (CollectedHeap::use_parallel_gc_threads()) {
231 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
232 _par_gc_thread_states =
233 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
234 if (_par_gc_thread_states == NULL) {
235 vm_exit_during_initialization("Could not allocate par gc structs");
236 }
237 for (uint i = 0; i < ParallelGCThreads; i++) {
238 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
239 if (_par_gc_thread_states[i] == NULL) {
240 vm_exit_during_initialization("Could not allocate par gc structs");
241 }
242 }
243 } else {
244 _par_gc_thread_states = NULL;
245 }
246 _incremental_collection_failed = false;
247 // The "dilatation_factor" is the expansion that can occur on
248 // account of the fact that the minimum object size in the CMS
249 // generation may be larger than that in, say, a contiguous young
250 // generation.
251 // Ideally, in the calculation below, we'd compute the dilatation
252 // factor as: MinChunkSize/(promoting_gen's min object size)
253 // Since we do not have such a general query interface for the
254 // promoting generation, we'll instead just use the mimimum
255 // object size (which today is a header's worth of space);
256 // note that all arithmetic is in units of HeapWords.
257 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
258 assert(_dilatation_factor >= 1.0, "from previous assert");
259 }
260
261
262 // The field "_initiating_occupancy" represents the occupancy percentage
263 // at which we trigger a new collection cycle. Unless explicitly specified
264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
265 // is calculated by:
266 //
267 // Let "f" be MinHeapFreeRatio in
268 //
269 // _intiating_occupancy = 100-f +
270 // f * (CMSTriggerRatio/100)
271 // where CMSTriggerRatio is the argument "tr" below.
272 //
273 // That is, if we assume the heap is at its desired maximum occupancy at the
274 // end of a collection, we let CMSTriggerRatio of the (purported) free
275 // space be allocated before initiating a new collection cycle.
276 //
277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
278 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
279 if (io >= 0) {
280 _initiating_occupancy = (double)io / 100.0;
281 } else {
282 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
283 (double)(tr * MinHeapFreeRatio) / 100.0)
284 / 100.0;
285 }
286 }
287
288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
289 assert(collector() != NULL, "no collector");
290 collector()->ref_processor_init();
291 }
292
293 void CMSCollector::ref_processor_init() {
294 if (_ref_processor == NULL) {
295 // Allocate and initialize a reference processor
296 _ref_processor =
297 new ReferenceProcessor(_span, // span
298 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
299 (int) ParallelGCThreads, // mt processing degree
300 _cmsGen->refs_discovery_is_mt(), // mt discovery
301 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
302 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
303 &_is_alive_closure, // closure for liveness info
304 false); // next field updates do not need write barrier
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
312 GenCollectedHeap* gch = GenCollectedHeap::heap();
313 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
314 "Wrong type of heap");
315 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
316 gch->gen_policy()->size_policy();
317 assert(sp->is_gc_cms_adaptive_size_policy(),
318 "Wrong type of size policy");
319 return sp;
320 }
321
322 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
323 CMSGCAdaptivePolicyCounters* results =
324 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
325 assert(
326 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
327 "Wrong gc policy counter kind");
328 return results;
329 }
330
331
332 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
333
334 const char* gen_name = "old";
335
336 // Generation Counters - generation 1, 1 subspace
337 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
338
339 _space_counters = new GSpaceCounters(gen_name, 0,
340 _virtual_space.reserved_size(),
341 this, _gen_counters);
342 }
343
344 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
345 _cms_gen(cms_gen)
346 {
347 assert(alpha <= 100, "bad value");
348 _saved_alpha = alpha;
349
350 // Initialize the alphas to the bootstrap value of 100.
351 _gc0_alpha = _cms_alpha = 100;
352
353 _cms_begin_time.update();
354 _cms_end_time.update();
355
356 _gc0_duration = 0.0;
357 _gc0_period = 0.0;
358 _gc0_promoted = 0;
359
360 _cms_duration = 0.0;
361 _cms_period = 0.0;
362 _cms_allocated = 0;
363
364 _cms_used_at_gc0_begin = 0;
365 _cms_used_at_gc0_end = 0;
366 _allow_duty_cycle_reduction = false;
367 _valid_bits = 0;
368 _icms_duty_cycle = CMSIncrementalDutyCycle;
369 }
370
371 double CMSStats::cms_free_adjustment_factor(size_t free) const {
372 // TBD: CR 6909490
373 return 1.0;
374 }
375
376 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
377 }
378
379 // If promotion failure handling is on use
380 // the padded average size of the promotion for each
381 // young generation collection.
382 double CMSStats::time_until_cms_gen_full() const {
383 size_t cms_free = _cms_gen->cmsSpace()->free();
384 GenCollectedHeap* gch = GenCollectedHeap::heap();
385 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
386 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
387 if (cms_free > expected_promotion) {
388 // Start a cms collection if there isn't enough space to promote
389 // for the next minor collection. Use the padded average as
390 // a safety factor.
391 cms_free -= expected_promotion;
392
393 // Adjust by the safety factor.
394 double cms_free_dbl = (double)cms_free;
395 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
396 // Apply a further correction factor which tries to adjust
397 // for recent occurance of concurrent mode failures.
398 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
399 cms_free_dbl = cms_free_dbl * cms_adjustment;
400
401 if (PrintGCDetails && Verbose) {
402 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
403 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
404 cms_free, expected_promotion);
405 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
406 cms_free_dbl, cms_consumption_rate() + 1.0);
407 }
408 // Add 1 in case the consumption rate goes to zero.
409 return cms_free_dbl / (cms_consumption_rate() + 1.0);
410 }
411 return 0.0;
412 }
413
414 // Compare the duration of the cms collection to the
415 // time remaining before the cms generation is empty.
416 // Note that the time from the start of the cms collection
417 // to the start of the cms sweep (less than the total
418 // duration of the cms collection) can be used. This
419 // has been tried and some applications experienced
420 // promotion failures early in execution. This was
421 // possibly because the averages were not accurate
422 // enough at the beginning.
423 double CMSStats::time_until_cms_start() const {
424 // We add "gc0_period" to the "work" calculation
425 // below because this query is done (mostly) at the
426 // end of a scavenge, so we need to conservatively
427 // account for that much possible delay
428 // in the query so as to avoid concurrent mode failures
429 // due to starting the collection just a wee bit too
430 // late.
431 double work = cms_duration() + gc0_period();
432 double deadline = time_until_cms_gen_full();
433 // If a concurrent mode failure occurred recently, we want to be
434 // more conservative and halve our expected time_until_cms_gen_full()
435 if (work > deadline) {
436 if (Verbose && PrintGCDetails) {
437 gclog_or_tty->print(
438 " CMSCollector: collect because of anticipated promotion "
439 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
440 gc0_period(), time_until_cms_gen_full());
441 }
442 return 0.0;
443 }
444 return work - deadline;
445 }
446
447 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
448 // amount of change to prevent wild oscillation.
449 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
450 unsigned int new_duty_cycle) {
451 assert(old_duty_cycle <= 100, "bad input value");
452 assert(new_duty_cycle <= 100, "bad input value");
453
454 // Note: use subtraction with caution since it may underflow (values are
455 // unsigned). Addition is safe since we're in the range 0-100.
456 unsigned int damped_duty_cycle = new_duty_cycle;
457 if (new_duty_cycle < old_duty_cycle) {
458 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
459 if (new_duty_cycle + largest_delta < old_duty_cycle) {
460 damped_duty_cycle = old_duty_cycle - largest_delta;
461 }
462 } else if (new_duty_cycle > old_duty_cycle) {
463 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
464 if (new_duty_cycle > old_duty_cycle + largest_delta) {
465 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
466 }
467 }
468 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
469
470 if (CMSTraceIncrementalPacing) {
471 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
472 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
473 }
474 return damped_duty_cycle;
475 }
476
477 unsigned int CMSStats::icms_update_duty_cycle_impl() {
478 assert(CMSIncrementalPacing && valid(),
479 "should be handled in icms_update_duty_cycle()");
480
481 double cms_time_so_far = cms_timer().seconds();
482 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
483 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
484
485 // Avoid division by 0.
486 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
487 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
488
489 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
490 if (new_duty_cycle > _icms_duty_cycle) {
491 // Avoid very small duty cycles (1 or 2); 0 is allowed.
492 if (new_duty_cycle > 2) {
493 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
494 new_duty_cycle);
495 }
496 } else if (_allow_duty_cycle_reduction) {
497 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
498 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
499 // Respect the minimum duty cycle.
500 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
501 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
502 }
503
504 if (PrintGCDetails || CMSTraceIncrementalPacing) {
505 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
506 }
507
508 _allow_duty_cycle_reduction = false;
509 return _icms_duty_cycle;
510 }
511
512 #ifndef PRODUCT
513 void CMSStats::print_on(outputStream *st) const {
514 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
515 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
516 gc0_duration(), gc0_period(), gc0_promoted());
517 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
518 cms_duration(), cms_duration_per_mb(),
519 cms_period(), cms_allocated());
520 st->print(",cms_since_beg=%g,cms_since_end=%g",
521 cms_time_since_begin(), cms_time_since_end());
522 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
523 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
524 if (CMSIncrementalMode) {
525 st->print(",dc=%d", icms_duty_cycle());
526 }
527
528 if (valid()) {
529 st->print(",promo_rate=%g,cms_alloc_rate=%g",
530 promotion_rate(), cms_allocation_rate());
531 st->print(",cms_consumption_rate=%g,time_until_full=%g",
532 cms_consumption_rate(), time_until_cms_gen_full());
533 }
534 st->print(" ");
535 }
536 #endif // #ifndef PRODUCT
537
538 CMSCollector::CollectorState CMSCollector::_collectorState =
539 CMSCollector::Idling;
540 bool CMSCollector::_foregroundGCIsActive = false;
541 bool CMSCollector::_foregroundGCShouldWait = false;
542
543 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
544 CardTableRS* ct,
545 ConcurrentMarkSweepPolicy* cp):
546 _cmsGen(cmsGen),
547 _ct(ct),
548 _ref_processor(NULL), // will be set later
549 _conc_workers(NULL), // may be set later
550 _abort_preclean(false),
551 _start_sampling(false),
552 _between_prologue_and_epilogue(false),
553 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
554 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
555 -1 /* lock-free */, "No_lock" /* dummy */),
556 _modUnionClosure(&_modUnionTable),
557 _modUnionClosurePar(&_modUnionTable),
558 // Adjust my span to cover old (cms) gen
559 _span(cmsGen->reserved()),
560 // Construct the is_alive_closure with _span & markBitMap
561 _is_alive_closure(_span, &_markBitMap),
562 _restart_addr(NULL),
563 _overflow_list(NULL),
564 _stats(cmsGen),
565 _eden_chunk_array(NULL), // may be set in ctor body
566 _eden_chunk_capacity(0), // -- ditto --
567 _eden_chunk_index(0), // -- ditto --
568 _survivor_plab_array(NULL), // -- ditto --
569 _survivor_chunk_array(NULL), // -- ditto --
570 _survivor_chunk_capacity(0), // -- ditto --
571 _survivor_chunk_index(0), // -- ditto --
572 _ser_pmc_preclean_ovflw(0),
573 _ser_kac_preclean_ovflw(0),
574 _ser_pmc_remark_ovflw(0),
575 _par_pmc_remark_ovflw(0),
576 _ser_kac_ovflw(0),
577 _par_kac_ovflw(0),
578 #ifndef PRODUCT
579 _num_par_pushes(0),
580 #endif
581 _collection_count_start(0),
582 _verifying(false),
583 _icms_start_limit(NULL),
584 _icms_stop_limit(NULL),
585 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
586 _completed_initialization(false),
587 _collector_policy(cp),
588 _should_unload_classes(false),
589 _concurrent_cycles_since_last_unload(0),
590 _roots_scanning_options(0),
591 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
592 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
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)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
694 /(double)100;
695
696 _full_gcs_since_conc_gc = 0;
697
698 // Now tell CMS generations the identity of their collector
699 ConcurrentMarkSweepGeneration::set_collector(this);
700
701 // Create & start a CMS thread for this CMS collector
702 _cmsThread = ConcurrentMarkSweepThread::start(this);
703 assert(cmsThread() != NULL, "CMS Thread should have been created");
704 assert(cmsThread()->collector() == this,
705 "CMS Thread should refer to this gen");
706 assert(CGC_lock != NULL, "Where's the CGC_lock?");
707
708 // Support for parallelizing young gen rescan
709 GenCollectedHeap* gch = GenCollectedHeap::heap();
710 _young_gen = gch->prev_gen(_cmsGen);
711 if (gch->supports_inline_contig_alloc()) {
712 _top_addr = gch->top_addr();
713 _end_addr = gch->end_addr();
714 assert(_young_gen != NULL, "no _young_gen");
715 _eden_chunk_index = 0;
716 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
717 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
718 if (_eden_chunk_array == NULL) {
719 _eden_chunk_capacity = 0;
720 warning("GC/CMS: _eden_chunk_array allocation failure");
721 }
722 }
723 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
724
725 // Support for parallelizing survivor space rescan
726 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
727 const size_t max_plab_samples =
728 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
729
730 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
731 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
732 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
733 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
734 || _cursor == NULL) {
735 warning("Failed to allocate survivor plab/chunk array");
736 if (_survivor_plab_array != NULL) {
737 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
738 _survivor_plab_array = NULL;
739 }
740 if (_survivor_chunk_array != NULL) {
741 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
742 _survivor_chunk_array = NULL;
743 }
744 if (_cursor != NULL) {
745 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
746 _cursor = NULL;
747 }
748 } else {
749 _survivor_chunk_capacity = 2*max_plab_samples;
750 for (uint i = 0; i < ParallelGCThreads; i++) {
751 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
752 if (vec == NULL) {
753 warning("Failed to allocate survivor plab array");
754 for (int j = i; j > 0; j--) {
755 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
756 }
757 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
758 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
759 _survivor_plab_array = NULL;
760 _survivor_chunk_array = NULL;
761 _survivor_chunk_capacity = 0;
762 break;
763 } else {
764 ChunkArray* cur =
765 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
766 max_plab_samples);
767 assert(cur->end() == 0, "Should be 0");
768 assert(cur->array() == vec, "Should be vec");
769 assert(cur->capacity() == max_plab_samples, "Error");
770 }
771 }
772 }
773 }
774 assert( ( _survivor_plab_array != NULL
775 && _survivor_chunk_array != NULL)
776 || ( _survivor_chunk_capacity == 0
777 && _survivor_chunk_index == 0),
778 "Error");
779
780 // Choose what strong roots should be scanned depending on verification options
781 if (!CMSClassUnloadingEnabled) {
782 // If class unloading is disabled we want to include all classes into the root set.
783 add_root_scanning_option(SharedHeap::SO_AllClasses);
784 } else {
785 add_root_scanning_option(SharedHeap::SO_SystemClasses);
786 }
787
788 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
789 _gc_counters = new CollectorCounters("CMS", 1);
790 _completed_initialization = true;
791 _inter_sweep_timer.start(); // start of time
792 #ifdef SPARC
793 // Issue a stern warning, but allow use for experimentation and debugging.
794 if (VM_Version::is_sun4v() && UseMemSetInBOT) {
795 assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
796 warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
797 " on sun4v; please understand that you are using at your own risk!");
798 }
799 #endif
800 }
801
802 const char* ConcurrentMarkSweepGeneration::name() const {
803 return "concurrent mark-sweep generation";
804 }
805 void ConcurrentMarkSweepGeneration::update_counters() {
806 if (UsePerfData) {
807 _space_counters->update_all();
808 _gen_counters->update_all();
809 }
810 }
811
812 // this is an optimized version of update_counters(). it takes the
813 // used value as a parameter rather than computing it.
814 //
815 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
816 if (UsePerfData) {
817 _space_counters->update_used(used);
818 _space_counters->update_capacity();
819 _gen_counters->update_all();
820 }
821 }
822
823 void ConcurrentMarkSweepGeneration::print() const {
824 Generation::print();
825 cmsSpace()->print();
826 }
827
828 #ifndef PRODUCT
829 void ConcurrentMarkSweepGeneration::print_statistics() {
830 cmsSpace()->printFLCensus(0);
831 }
832 #endif
833
834 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
835 GenCollectedHeap* gch = GenCollectedHeap::heap();
836 if (PrintGCDetails) {
837 if (Verbose) {
838 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
839 level(), short_name(), s, used(), capacity());
840 } else {
841 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
842 level(), short_name(), s, used() / K, capacity() / K);
843 }
844 }
845 if (Verbose) {
846 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
847 gch->used(), gch->capacity());
848 } else {
849 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
850 gch->used() / K, gch->capacity() / K);
851 }
852 }
853
854 size_t
855 ConcurrentMarkSweepGeneration::contiguous_available() const {
856 // dld proposes an improvement in precision here. If the committed
857 // part of the space ends in a free block we should add that to
858 // uncommitted size in the calculation below. Will make this
859 // change later, staying with the approximation below for the
860 // time being. -- ysr.
861 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
862 }
863
864 size_t
865 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
866 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
867 }
868
869 size_t ConcurrentMarkSweepGeneration::max_available() const {
870 return free() + _virtual_space.uncommitted_size();
871 }
872
873 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
874 size_t available = max_available();
875 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
876 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
877 if (Verbose && PrintGCDetails) {
878 gclog_or_tty->print_cr(
879 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
880 "max_promo("SIZE_FORMAT")",
881 res? "":" not", available, res? ">=":"<",
882 av_promo, max_promotion_in_bytes);
883 }
884 return res;
885 }
886
887 // At a promotion failure dump information on block layout in heap
888 // (cms old generation).
889 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
890 if (CMSDumpAtPromotionFailure) {
891 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
892 }
893 }
894
895 CompactibleSpace*
896 ConcurrentMarkSweepGeneration::first_compaction_space() const {
897 return _cmsSpace;
898 }
899
900 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
901 // Clear the promotion information. These pointers can be adjusted
902 // along with all the other pointers into the heap but
903 // compaction is expected to be a rare event with
904 // a heap using cms so don't do it without seeing the need.
905 if (CollectedHeap::use_parallel_gc_threads()) {
906 for (uint i = 0; i < ParallelGCThreads; i++) {
907 _par_gc_thread_states[i]->promo.reset();
908 }
909 }
910 }
911
912 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
913 blk->do_space(_cmsSpace);
914 }
915
916 void ConcurrentMarkSweepGeneration::compute_new_size() {
917 assert_locked_or_safepoint(Heap_lock);
918
919 // If incremental collection failed, we just want to expand
920 // to the limit.
921 if (incremental_collection_failed()) {
922 clear_incremental_collection_failed();
923 grow_to_reserved();
924 return;
925 }
926
927 size_t expand_bytes = 0;
928 double free_percentage = ((double) free()) / capacity();
929 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
930 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
931
932 // compute expansion delta needed for reaching desired free percentage
933 if (free_percentage < desired_free_percentage) {
934 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
935 assert(desired_capacity >= capacity(), "invalid expansion size");
936 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
937 }
938 if (expand_bytes > 0) {
939 if (PrintGCDetails && Verbose) {
940 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
941 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
942 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
943 gclog_or_tty->print_cr(" Desired free fraction %f",
944 desired_free_percentage);
945 gclog_or_tty->print_cr(" Maximum free fraction %f",
946 maximum_free_percentage);
947 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
948 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
949 desired_capacity/1000);
950 int prev_level = level() - 1;
951 if (prev_level >= 0) {
952 size_t prev_size = 0;
953 GenCollectedHeap* gch = GenCollectedHeap::heap();
954 Generation* prev_gen = gch->_gens[prev_level];
955 prev_size = prev_gen->capacity();
956 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
957 prev_size/1000);
958 }
959 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
960 unsafe_max_alloc_nogc()/1000);
961 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
962 contiguous_available()/1000);
963 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
964 expand_bytes);
965 }
966 // safe if expansion fails
967 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
968 if (PrintGCDetails && Verbose) {
969 gclog_or_tty->print_cr(" Expanded free fraction %f",
970 ((double) free()) / capacity());
971 }
972 }
973 }
974
975 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
976 return cmsSpace()->freelistLock();
977 }
978
979 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
980 bool tlab) {
981 CMSSynchronousYieldRequest yr;
982 MutexLockerEx x(freelistLock(),
983 Mutex::_no_safepoint_check_flag);
984 return have_lock_and_allocate(size, tlab);
985 }
986
987 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
988 bool tlab /* ignored */) {
989 assert_lock_strong(freelistLock());
990 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
991 HeapWord* res = cmsSpace()->allocate(adjustedSize);
992 // Allocate the object live (grey) if the background collector has
993 // started marking. This is necessary because the marker may
994 // have passed this address and consequently this object will
995 // not otherwise be greyed and would be incorrectly swept up.
996 // Note that if this object contains references, the writing
997 // of those references will dirty the card containing this object
998 // allowing the object to be blackened (and its references scanned)
999 // either during a preclean phase or at the final checkpoint.
1000 if (res != NULL) {
1001 // We may block here with an uninitialized object with
1002 // its mark-bit or P-bits not yet set. Such objects need
1003 // to be safely navigable by block_start().
1004 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1005 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1006 collector()->direct_allocated(res, adjustedSize);
1007 _direct_allocated_words += adjustedSize;
1008 // allocation counters
1009 NOT_PRODUCT(
1010 _numObjectsAllocated++;
1011 _numWordsAllocated += (int)adjustedSize;
1012 )
1013 }
1014 return res;
1015 }
1016
1017 // In the case of direct allocation by mutators in a generation that
1018 // is being concurrently collected, the object must be allocated
1019 // live (grey) if the background collector has started marking.
1020 // This is necessary because the marker may
1021 // have passed this address and consequently this object will
1022 // not otherwise be greyed and would be incorrectly swept up.
1023 // Note that if this object contains references, the writing
1024 // of those references will dirty the card containing this object
1025 // allowing the object to be blackened (and its references scanned)
1026 // either during a preclean phase or at the final checkpoint.
1027 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1028 assert(_markBitMap.covers(start, size), "Out of bounds");
1029 if (_collectorState >= Marking) {
1030 MutexLockerEx y(_markBitMap.lock(),
1031 Mutex::_no_safepoint_check_flag);
1032 // [see comments preceding SweepClosure::do_blk() below for details]
1033 //
1034 // Can the P-bits be deleted now? JJJ
1035 //
1036 // 1. need to mark the object as live so it isn't collected
1037 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1038 // 3. need to mark the end of the object so marking, precleaning or sweeping
1039 // can skip over uninitialized or unparsable objects. An allocated
1040 // object is considered uninitialized for our purposes as long as
1041 // its klass word is NULL. All old gen objects are parsable
1042 // as soon as they are initialized.)
1043 _markBitMap.mark(start); // object is live
1044 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1045 _markBitMap.mark(start + size - 1);
1046 // mark end of object
1047 }
1048 // check that oop looks uninitialized
1049 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1050 }
1051
1052 void CMSCollector::promoted(bool par, HeapWord* start,
1053 bool is_obj_array, size_t obj_size) {
1054 assert(_markBitMap.covers(start), "Out of bounds");
1055 // See comment in direct_allocated() about when objects should
1056 // be allocated live.
1057 if (_collectorState >= Marking) {
1058 // we already hold the marking bit map lock, taken in
1059 // the prologue
1060 if (par) {
1061 _markBitMap.par_mark(start);
1062 } else {
1063 _markBitMap.mark(start);
1064 }
1065 // We don't need to mark the object as uninitialized (as
1066 // in direct_allocated above) because this is being done with the
1067 // world stopped and the object will be initialized by the
1068 // time the marking, precleaning or sweeping get to look at it.
1069 // But see the code for copying objects into the CMS generation,
1070 // where we need to ensure that concurrent readers of the
1071 // block offset table are able to safely navigate a block that
1072 // is in flux from being free to being allocated (and in
1073 // transition while being copied into) and subsequently
1074 // becoming a bona-fide object when the copy/promotion is complete.
1075 assert(SafepointSynchronize::is_at_safepoint(),
1076 "expect promotion only at safepoints");
1077
1078 if (_collectorState < Sweeping) {
1079 // Mark the appropriate cards in the modUnionTable, so that
1080 // this object gets scanned before the sweep. If this is
1081 // not done, CMS generation references in the object might
1082 // not get marked.
1083 // For the case of arrays, which are otherwise precisely
1084 // marked, we need to dirty the entire array, not just its head.
1085 if (is_obj_array) {
1086 // The [par_]mark_range() method expects mr.end() below to
1087 // be aligned to the granularity of a bit's representation
1088 // in the heap. In the case of the MUT below, that's a
1089 // card size.
1090 MemRegion mr(start,
1091 (HeapWord*)round_to((intptr_t)(start + obj_size),
1092 CardTableModRefBS::card_size /* bytes */));
1093 if (par) {
1094 _modUnionTable.par_mark_range(mr);
1095 } else {
1096 _modUnionTable.mark_range(mr);
1097 }
1098 } else { // not an obj array; we can just mark the head
1099 if (par) {
1100 _modUnionTable.par_mark(start);
1101 } else {
1102 _modUnionTable.mark(start);
1103 }
1104 }
1105 }
1106 }
1107 }
1108
1109 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1110 {
1111 size_t delta = pointer_delta(addr, space->bottom());
1112 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1113 }
1114
1115 void CMSCollector::icms_update_allocation_limits()
1116 {
1117 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1118 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1119
1120 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1121 if (CMSTraceIncrementalPacing) {
1122 stats().print();
1123 }
1124
1125 assert(duty_cycle <= 100, "invalid duty cycle");
1126 if (duty_cycle != 0) {
1127 // The duty_cycle is a percentage between 0 and 100; convert to words and
1128 // then compute the offset from the endpoints of the space.
1129 size_t free_words = eden->free() / HeapWordSize;
1130 double free_words_dbl = (double)free_words;
1131 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1132 size_t offset_words = (free_words - duty_cycle_words) / 2;
1133
1134 _icms_start_limit = eden->top() + offset_words;
1135 _icms_stop_limit = eden->end() - offset_words;
1136
1137 // The limits may be adjusted (shifted to the right) by
1138 // CMSIncrementalOffset, to allow the application more mutator time after a
1139 // young gen gc (when all mutators were stopped) and before CMS starts and
1140 // takes away one or more cpus.
1141 if (CMSIncrementalOffset != 0) {
1142 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1143 size_t adjustment = (size_t)adjustment_dbl;
1144 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1145 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1146 _icms_start_limit += adjustment;
1147 _icms_stop_limit = tmp_stop;
1148 }
1149 }
1150 }
1151 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1152 _icms_start_limit = _icms_stop_limit = eden->end();
1153 }
1154
1155 // Install the new start limit.
1156 eden->set_soft_end(_icms_start_limit);
1157
1158 if (CMSTraceIncrementalMode) {
1159 gclog_or_tty->print(" icms alloc limits: "
1160 PTR_FORMAT "," PTR_FORMAT
1161 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1162 _icms_start_limit, _icms_stop_limit,
1163 percent_of_space(eden, _icms_start_limit),
1164 percent_of_space(eden, _icms_stop_limit));
1165 if (Verbose) {
1166 gclog_or_tty->print("eden: ");
1167 eden->print_on(gclog_or_tty);
1168 }
1169 }
1170 }
1171
1172 // Any changes here should try to maintain the invariant
1173 // that if this method is called with _icms_start_limit
1174 // and _icms_stop_limit both NULL, then it should return NULL
1175 // and not notify the icms thread.
1176 HeapWord*
1177 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1178 size_t word_size)
1179 {
1180 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1181 // nop.
1182 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1183 if (top <= _icms_start_limit) {
1184 if (CMSTraceIncrementalMode) {
1185 space->print_on(gclog_or_tty);
1186 gclog_or_tty->stamp();
1187 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1188 ", new limit=" PTR_FORMAT
1189 " (" SIZE_FORMAT "%%)",
1190 top, _icms_stop_limit,
1191 percent_of_space(space, _icms_stop_limit));
1192 }
1193 ConcurrentMarkSweepThread::start_icms();
1194 assert(top < _icms_stop_limit, "Tautology");
1195 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1196 return _icms_stop_limit;
1197 }
1198
1199 // The allocation will cross both the _start and _stop limits, so do the
1200 // stop notification also and return end().
1201 if (CMSTraceIncrementalMode) {
1202 space->print_on(gclog_or_tty);
1203 gclog_or_tty->stamp();
1204 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1205 ", new limit=" PTR_FORMAT
1206 " (" SIZE_FORMAT "%%)",
1207 top, space->end(),
1208 percent_of_space(space, space->end()));
1209 }
1210 ConcurrentMarkSweepThread::stop_icms();
1211 return space->end();
1212 }
1213
1214 if (top <= _icms_stop_limit) {
1215 if (CMSTraceIncrementalMode) {
1216 space->print_on(gclog_or_tty);
1217 gclog_or_tty->stamp();
1218 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1219 ", new limit=" PTR_FORMAT
1220 " (" SIZE_FORMAT "%%)",
1221 top, space->end(),
1222 percent_of_space(space, space->end()));
1223 }
1224 ConcurrentMarkSweepThread::stop_icms();
1225 return space->end();
1226 }
1227
1228 if (CMSTraceIncrementalMode) {
1229 space->print_on(gclog_or_tty);
1230 gclog_or_tty->stamp();
1231 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1232 ", new limit=" PTR_FORMAT,
1233 top, NULL);
1234 }
1235 }
1236
1237 return NULL;
1238 }
1239
1240 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1241 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1242 // allocate, copy and if necessary update promoinfo --
1243 // delegate to underlying space.
1244 assert_lock_strong(freelistLock());
1245
1246 #ifndef PRODUCT
1247 if (Universe::heap()->promotion_should_fail()) {
1248 return NULL;
1249 }
1250 #endif // #ifndef PRODUCT
1251
1252 oop res = _cmsSpace->promote(obj, obj_size);
1253 if (res == NULL) {
1254 // expand and retry
1255 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1256 expand(s*HeapWordSize, MinHeapDeltaBytes,
1257 CMSExpansionCause::_satisfy_promotion);
1258 // Since there's currently no next generation, we don't try to promote
1259 // into a more senior generation.
1260 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1261 "is made to pass on a possibly failing "
1262 "promotion to next generation");
1263 res = _cmsSpace->promote(obj, obj_size);
1264 }
1265 if (res != NULL) {
1266 // See comment in allocate() about when objects should
1267 // be allocated live.
1268 assert(obj->is_oop(), "Will dereference klass pointer below");
1269 collector()->promoted(false, // Not parallel
1270 (HeapWord*)res, obj->is_objArray(), obj_size);
1271 // promotion counters
1272 NOT_PRODUCT(
1273 _numObjectsPromoted++;
1274 _numWordsPromoted +=
1275 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1276 )
1277 }
1278 return res;
1279 }
1280
1281
1282 HeapWord*
1283 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1284 HeapWord* top,
1285 size_t word_sz)
1286 {
1287 return collector()->allocation_limit_reached(space, top, word_sz);
1288 }
1289
1290 // IMPORTANT: Notes on object size recognition in CMS.
1291 // ---------------------------------------------------
1292 // A block of storage in the CMS generation is always in
1293 // one of three states. A free block (FREE), an allocated
1294 // object (OBJECT) whose size() method reports the correct size,
1295 // and an intermediate state (TRANSIENT) in which its size cannot
1296 // be accurately determined.
1297 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1298 // -----------------------------------------------------
1299 // FREE: klass_word & 1 == 1; mark_word holds block size
1300 //
1301 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1302 // obj->size() computes correct size
1303 //
1304 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1305 //
1306 // STATE IDENTIFICATION: (64 bit+COOPS)
1307 // ------------------------------------
1308 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1309 //
1310 // OBJECT: klass_word installed; klass_word != 0;
1311 // obj->size() computes correct size
1312 //
1313 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1314 //
1315 //
1316 // STATE TRANSITION DIAGRAM
1317 //
1318 // mut / parnew mut / parnew
1319 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1320 // ^ |
1321 // |------------------------ DEAD <------------------------------------|
1322 // sweep mut
1323 //
1324 // While a block is in TRANSIENT state its size cannot be determined
1325 // so readers will either need to come back later or stall until
1326 // the size can be determined. Note that for the case of direct
1327 // allocation, P-bits, when available, may be used to determine the
1328 // size of an object that may not yet have been initialized.
1329
1330 // Things to support parallel young-gen collection.
1331 oop
1332 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1333 oop old, markOop m,
1334 size_t word_sz) {
1335 #ifndef PRODUCT
1336 if (Universe::heap()->promotion_should_fail()) {
1337 return NULL;
1338 }
1339 #endif // #ifndef PRODUCT
1340
1341 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1342 PromotionInfo* promoInfo = &ps->promo;
1343 // if we are tracking promotions, then first ensure space for
1344 // promotion (including spooling space for saving header if necessary).
1345 // then allocate and copy, then track promoted info if needed.
1346 // When tracking (see PromotionInfo::track()), the mark word may
1347 // be displaced and in this case restoration of the mark word
1348 // occurs in the (oop_since_save_marks_)iterate phase.
1349 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1350 // Out of space for allocating spooling buffers;
1351 // try expanding and allocating spooling buffers.
1352 if (!expand_and_ensure_spooling_space(promoInfo)) {
1353 return NULL;
1354 }
1355 }
1356 assert(promoInfo->has_spooling_space(), "Control point invariant");
1357 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1358 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1359 if (obj_ptr == NULL) {
1360 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1361 if (obj_ptr == NULL) {
1362 return NULL;
1363 }
1364 }
1365 oop obj = oop(obj_ptr);
1366 OrderAccess::storestore();
1367 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1368 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1369 // IMPORTANT: See note on object initialization for CMS above.
1370 // Otherwise, copy the object. Here we must be careful to insert the
1371 // klass pointer last, since this marks the block as an allocated object.
1372 // Except with compressed oops it's the mark word.
1373 HeapWord* old_ptr = (HeapWord*)old;
1374 // Restore the mark word copied above.
1375 obj->set_mark(m);
1376 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1377 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1378 OrderAccess::storestore();
1379
1380 if (UseCompressedKlassPointers) {
1381 // Copy gap missed by (aligned) header size calculation below
1382 obj->set_klass_gap(old->klass_gap());
1383 }
1384 if (word_sz > (size_t)oopDesc::header_size()) {
1385 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1386 obj_ptr + oopDesc::header_size(),
1387 word_sz - oopDesc::header_size());
1388 }
1389
1390 // Now we can track the promoted object, if necessary. We take care
1391 // to delay the transition from uninitialized to full object
1392 // (i.e., insertion of klass pointer) until after, so that it
1393 // atomically becomes a promoted object.
1394 if (promoInfo->tracking()) {
1395 promoInfo->track((PromotedObject*)obj, old->klass());
1396 }
1397 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1398 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1399 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1400
1401 // Finally, install the klass pointer (this should be volatile).
1402 OrderAccess::storestore();
1403 obj->set_klass(old->klass());
1404 // We should now be able to calculate the right size for this object
1405 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1406
1407 collector()->promoted(true, // parallel
1408 obj_ptr, old->is_objArray(), word_sz);
1409
1410 NOT_PRODUCT(
1411 Atomic::inc_ptr(&_numObjectsPromoted);
1412 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1413 )
1414
1415 return obj;
1416 }
1417
1418 void
1419 ConcurrentMarkSweepGeneration::
1420 par_promote_alloc_undo(int thread_num,
1421 HeapWord* obj, size_t word_sz) {
1422 // CMS does not support promotion undo.
1423 ShouldNotReachHere();
1424 }
1425
1426 void
1427 ConcurrentMarkSweepGeneration::
1428 par_promote_alloc_done(int thread_num) {
1429 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1430 ps->lab.retire(thread_num);
1431 }
1432
1433 void
1434 ConcurrentMarkSweepGeneration::
1435 par_oop_since_save_marks_iterate_done(int thread_num) {
1436 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1437 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1438 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1439 }
1440
1441 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1442 size_t size,
1443 bool tlab)
1444 {
1445 // We allow a STW collection only if a full
1446 // collection was requested.
1447 return full || should_allocate(size, tlab); // FIX ME !!!
1448 // This and promotion failure handling are connected at the
1449 // hip and should be fixed by untying them.
1450 }
1451
1452 bool CMSCollector::shouldConcurrentCollect() {
1453 if (_full_gc_requested) {
1454 if (Verbose && PrintGCDetails) {
1455 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1456 " gc request (or gc_locker)");
1457 }
1458 return true;
1459 }
1460
1461 // For debugging purposes, change the type of collection.
1462 // If the rotation is not on the concurrent collection
1463 // type, don't start a concurrent collection.
1464 NOT_PRODUCT(
1465 if (RotateCMSCollectionTypes &&
1466 (_cmsGen->debug_collection_type() !=
1467 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1468 assert(_cmsGen->debug_collection_type() !=
1469 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1470 "Bad cms collection type");
1471 return false;
1472 }
1473 )
1474
1475 FreelistLocker x(this);
1476 // ------------------------------------------------------------------
1477 // Print out lots of information which affects the initiation of
1478 // a collection.
1479 if (PrintCMSInitiationStatistics && stats().valid()) {
1480 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1481 gclog_or_tty->stamp();
1482 gclog_or_tty->print_cr("");
1483 stats().print_on(gclog_or_tty);
1484 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1485 stats().time_until_cms_gen_full());
1486 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1487 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1488 _cmsGen->contiguous_available());
1489 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1490 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1491 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1492 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1493 gclog_or_tty->print_cr("metadata initialized %d",
1494 MetaspaceGC::should_concurrent_collect());
1495 }
1496 // ------------------------------------------------------------------
1497
1498 // If the estimated time to complete a cms collection (cms_duration())
1499 // is less than the estimated time remaining until the cms generation
1500 // is full, start a collection.
1501 if (!UseCMSInitiatingOccupancyOnly) {
1502 if (stats().valid()) {
1503 if (stats().time_until_cms_start() == 0.0) {
1504 return true;
1505 }
1506 } else {
1507 // We want to conservatively collect somewhat early in order
1508 // to try and "bootstrap" our CMS/promotion statistics;
1509 // this branch will not fire after the first successful CMS
1510 // collection because the stats should then be valid.
1511 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1512 if (Verbose && PrintGCDetails) {
1513 gclog_or_tty->print_cr(
1514 " CMSCollector: collect for bootstrapping statistics:"
1515 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1516 _bootstrap_occupancy);
1517 }
1518 return true;
1519 }
1520 }
1521 }
1522
1523 // Otherwise, we start a collection cycle if
1524 // old gen want a collection cycle started. Each may use
1525 // an appropriate criterion for making this decision.
1526 // XXX We need to make sure that the gen expansion
1527 // criterion dovetails well with this. XXX NEED TO FIX THIS
1528 if (_cmsGen->should_concurrent_collect()) {
1529 if (Verbose && PrintGCDetails) {
1530 gclog_or_tty->print_cr("CMS old gen initiated");
1531 }
1532 return true;
1533 }
1534
1535 // We start a collection if we believe an incremental collection may fail;
1536 // this is not likely to be productive in practice because it's probably too
1537 // late anyway.
1538 GenCollectedHeap* gch = GenCollectedHeap::heap();
1539 assert(gch->collector_policy()->is_two_generation_policy(),
1540 "You may want to check the correctness of the following");
1541 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1542 if (Verbose && PrintGCDetails) {
1543 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1544 }
1545 return true;
1546 }
1547
1548 if (MetaspaceGC::should_concurrent_collect()) {
1549 if (Verbose && PrintGCDetails) {
1550 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1551 }
1552 return true;
1553 }
1554
1555 return false;
1556 }
1557
1558 // Clear _expansion_cause fields of constituent generations
1559 void CMSCollector::clear_expansion_cause() {
1560 _cmsGen->clear_expansion_cause();
1561 }
1562
1563 // We should be conservative in starting a collection cycle. To
1564 // start too eagerly runs the risk of collecting too often in the
1565 // extreme. To collect too rarely falls back on full collections,
1566 // which works, even if not optimum in terms of concurrent work.
1567 // As a work around for too eagerly collecting, use the flag
1568 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1569 // giving the user an easily understandable way of controlling the
1570 // collections.
1571 // We want to start a new collection cycle if any of the following
1572 // conditions hold:
1573 // . our current occupancy exceeds the configured initiating occupancy
1574 // for this generation, or
1575 // . we recently needed to expand this space and have not, since that
1576 // expansion, done a collection of this generation, or
1577 // . the underlying space believes that it may be a good idea to initiate
1578 // a concurrent collection (this may be based on criteria such as the
1579 // following: the space uses linear allocation and linear allocation is
1580 // going to fail, or there is believed to be excessive fragmentation in
1581 // the generation, etc... or ...
1582 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1583 // the case of the old generation; see CR 6543076):
1584 // we may be approaching a point at which allocation requests may fail because
1585 // we will be out of sufficient free space given allocation rate estimates.]
1586 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1587
1588 assert_lock_strong(freelistLock());
1589 if (occupancy() > initiating_occupancy()) {
1590 if (PrintGCDetails && Verbose) {
1591 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1592 short_name(), occupancy(), initiating_occupancy());
1593 }
1594 return true;
1595 }
1596 if (UseCMSInitiatingOccupancyOnly) {
1597 return false;
1598 }
1599 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1600 if (PrintGCDetails && Verbose) {
1601 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1602 short_name());
1603 }
1604 return true;
1605 }
1606 if (_cmsSpace->should_concurrent_collect()) {
1607 if (PrintGCDetails && Verbose) {
1608 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1609 short_name());
1610 }
1611 return true;
1612 }
1613 return false;
1614 }
1615
1616 void ConcurrentMarkSweepGeneration::collect(bool full,
1617 bool clear_all_soft_refs,
1618 size_t size,
1619 bool tlab)
1620 {
1621 collector()->collect(full, clear_all_soft_refs, size, tlab);
1622 }
1623
1624 void CMSCollector::collect(bool full,
1625 bool clear_all_soft_refs,
1626 size_t size,
1627 bool tlab)
1628 {
1629 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1630 // For debugging purposes skip the collection if the state
1631 // is not currently idle
1632 if (TraceCMSState) {
1633 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1634 Thread::current(), full, _collectorState);
1635 }
1636 return;
1637 }
1638
1639 // The following "if" branch is present for defensive reasons.
1640 // In the current uses of this interface, it can be replaced with:
1641 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1642 // But I am not placing that assert here to allow future
1643 // generality in invoking this interface.
1644 if (GC_locker::is_active()) {
1645 // A consistency test for GC_locker
1646 assert(GC_locker::needs_gc(), "Should have been set already");
1647 // Skip this foreground collection, instead
1648 // expanding the heap if necessary.
1649 // Need the free list locks for the call to free() in compute_new_size()
1650 compute_new_size();
1651 return;
1652 }
1653 acquire_control_and_collect(full, clear_all_soft_refs);
1654 _full_gcs_since_conc_gc++;
1655
1656 }
1657
1658 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1659 GenCollectedHeap* gch = GenCollectedHeap::heap();
1660 unsigned int gc_count = gch->total_full_collections();
1661 if (gc_count == full_gc_count) {
1662 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1663 _full_gc_requested = true;
1664 CGC_lock->notify(); // nudge CMS thread
1665 } else {
1666 assert(gc_count > full_gc_count, "Error: causal loop");
1667 }
1668 }
1669
1670
1671 // The foreground and background collectors need to coordinate in order
1672 // to make sure that they do not mutually interfere with CMS collections.
1673 // When a background collection is active,
1674 // the foreground collector may need to take over (preempt) and
1675 // synchronously complete an ongoing collection. Depending on the
1676 // frequency of the background collections and the heap usage
1677 // of the application, this preemption can be seldom or frequent.
1678 // There are only certain
1679 // points in the background collection that the "collection-baton"
1680 // can be passed to the foreground collector.
1681 //
1682 // The foreground collector will wait for the baton before
1683 // starting any part of the collection. The foreground collector
1684 // will only wait at one location.
1685 //
1686 // The background collector will yield the baton before starting a new
1687 // phase of the collection (e.g., before initial marking, marking from roots,
1688 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1689 // of the loop which switches the phases. The background collector does some
1690 // of the phases (initial mark, final re-mark) with the world stopped.
1691 // Because of locking involved in stopping the world,
1692 // the foreground collector should not block waiting for the background
1693 // collector when it is doing a stop-the-world phase. The background
1694 // collector will yield the baton at an additional point just before
1695 // it enters a stop-the-world phase. Once the world is stopped, the
1696 // background collector checks the phase of the collection. If the
1697 // phase has not changed, it proceeds with the collection. If the
1698 // phase has changed, it skips that phase of the collection. See
1699 // the comments on the use of the Heap_lock in collect_in_background().
1700 //
1701 // Variable used in baton passing.
1702 // _foregroundGCIsActive - Set to true by the foreground collector when
1703 // it wants the baton. The foreground clears it when it has finished
1704 // the collection.
1705 // _foregroundGCShouldWait - Set to true by the background collector
1706 // when it is running. The foreground collector waits while
1707 // _foregroundGCShouldWait is true.
1708 // CGC_lock - monitor used to protect access to the above variables
1709 // and to notify the foreground and background collectors.
1710 // _collectorState - current state of the CMS collection.
1711 //
1712 // The foreground collector
1713 // acquires the CGC_lock
1714 // sets _foregroundGCIsActive
1715 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1716 // various locks acquired in preparation for the collection
1717 // are released so as not to block the background collector
1718 // that is in the midst of a collection
1719 // proceeds with the collection
1720 // clears _foregroundGCIsActive
1721 // returns
1722 //
1723 // The background collector in a loop iterating on the phases of the
1724 // collection
1725 // acquires the CGC_lock
1726 // sets _foregroundGCShouldWait
1727 // if _foregroundGCIsActive is set
1728 // clears _foregroundGCShouldWait, notifies _CGC_lock
1729 // waits on _CGC_lock for _foregroundGCIsActive to become false
1730 // and exits the loop.
1731 // otherwise
1732 // proceed with that phase of the collection
1733 // if the phase is a stop-the-world phase,
1734 // yield the baton once more just before enqueueing
1735 // the stop-world CMS operation (executed by the VM thread).
1736 // returns after all phases of the collection are done
1737 //
1738
1739 void CMSCollector::acquire_control_and_collect(bool full,
1740 bool clear_all_soft_refs) {
1741 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1742 assert(!Thread::current()->is_ConcurrentGC_thread(),
1743 "shouldn't try to acquire control from self!");
1744
1745 // Start the protocol for acquiring control of the
1746 // collection from the background collector (aka CMS thread).
1747 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1748 "VM thread should have CMS token");
1749 // Remember the possibly interrupted state of an ongoing
1750 // concurrent collection
1751 CollectorState first_state = _collectorState;
1752
1753 // Signal to a possibly ongoing concurrent collection that
1754 // we want to do a foreground collection.
1755 _foregroundGCIsActive = true;
1756
1757 // Disable incremental mode during a foreground collection.
1758 ICMSDisabler icms_disabler;
1759
1760 // release locks and wait for a notify from the background collector
1761 // releasing the locks in only necessary for phases which
1762 // do yields to improve the granularity of the collection.
1763 assert_lock_strong(bitMapLock());
1764 // We need to lock the Free list lock for the space that we are
1765 // currently collecting.
1766 assert(haveFreelistLocks(), "Must be holding free list locks");
1767 bitMapLock()->unlock();
1768 releaseFreelistLocks();
1769 {
1770 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1771 if (_foregroundGCShouldWait) {
1772 // We are going to be waiting for action for the CMS thread;
1773 // it had better not be gone (for instance at shutdown)!
1774 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1775 "CMS thread must be running");
1776 // Wait here until the background collector gives us the go-ahead
1777 ConcurrentMarkSweepThread::clear_CMS_flag(
1778 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1779 // Get a possibly blocked CMS thread going:
1780 // Note that we set _foregroundGCIsActive true above,
1781 // without protection of the CGC_lock.
1782 CGC_lock->notify();
1783 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1784 "Possible deadlock");
1785 while (_foregroundGCShouldWait) {
1786 // wait for notification
1787 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1788 // Possibility of delay/starvation here, since CMS token does
1789 // not know to give priority to VM thread? Actually, i think
1790 // there wouldn't be any delay/starvation, but the proof of
1791 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1792 }
1793 ConcurrentMarkSweepThread::set_CMS_flag(
1794 ConcurrentMarkSweepThread::CMS_vm_has_token);
1795 }
1796 }
1797 // The CMS_token is already held. Get back the other locks.
1798 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1799 "VM thread should have CMS token");
1800 getFreelistLocks();
1801 bitMapLock()->lock_without_safepoint_check();
1802 if (TraceCMSState) {
1803 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1804 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1805 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1806 }
1807
1808 // Check if we need to do a compaction, or if not, whether
1809 // we need to start the mark-sweep from scratch.
1810 bool should_compact = false;
1811 bool should_start_over = false;
1812 decide_foreground_collection_type(clear_all_soft_refs,
1813 &should_compact, &should_start_over);
1814
1815 NOT_PRODUCT(
1816 if (RotateCMSCollectionTypes) {
1817 if (_cmsGen->debug_collection_type() ==
1818 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1819 should_compact = true;
1820 } else if (_cmsGen->debug_collection_type() ==
1821 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1822 should_compact = false;
1823 }
1824 }
1825 )
1826
1827 if (PrintGCDetails && first_state > Idling) {
1828 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1829 if (GCCause::is_user_requested_gc(cause) ||
1830 GCCause::is_serviceability_requested_gc(cause)) {
1831 gclog_or_tty->print(" (concurrent mode interrupted)");
1832 } else {
1833 gclog_or_tty->print(" (concurrent mode failure)");
1834 }
1835 }
1836
1837 if (should_compact) {
1838 // If the collection is being acquired from the background
1839 // collector, there may be references on the discovered
1840 // references lists that have NULL referents (being those
1841 // that were concurrently cleared by a mutator) or
1842 // that are no longer active (having been enqueued concurrently
1843 // by the mutator).
1844 // Scrub the list of those references because Mark-Sweep-Compact
1845 // code assumes referents are not NULL and that all discovered
1846 // Reference objects are active.
1847 ref_processor()->clean_up_discovered_references();
1848
1849 do_compaction_work(clear_all_soft_refs);
1850
1851 // Has the GC time limit been exceeded?
1852 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1853 size_t max_eden_size = young_gen->max_capacity() -
1854 young_gen->to()->capacity() -
1855 young_gen->from()->capacity();
1856 GenCollectedHeap* gch = GenCollectedHeap::heap();
1857 GCCause::Cause gc_cause = gch->gc_cause();
1858 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1859 young_gen->eden()->used(),
1860 _cmsGen->max_capacity(),
1861 max_eden_size,
1862 full,
1863 gc_cause,
1864 gch->collector_policy());
1865 } else {
1866 do_mark_sweep_work(clear_all_soft_refs, first_state,
1867 should_start_over);
1868 }
1869 // Reset the expansion cause, now that we just completed
1870 // a collection cycle.
1871 clear_expansion_cause();
1872 _foregroundGCIsActive = false;
1873 return;
1874 }
1875
1876 // Resize the tenured generation
1877 // after obtaining the free list locks for the
1878 // two generations.
1879 void CMSCollector::compute_new_size() {
1880 assert_locked_or_safepoint(Heap_lock);
1881 FreelistLocker z(this);
1882 MetaspaceGC::compute_new_size();
1883 _cmsGen->compute_new_size();
1884 }
1885
1886 // A work method used by foreground collection to determine
1887 // what type of collection (compacting or not, continuing or fresh)
1888 // it should do.
1889 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1890 // and CMSCompactWhenClearAllSoftRefs the default in the future
1891 // and do away with the flags after a suitable period.
1892 void CMSCollector::decide_foreground_collection_type(
1893 bool clear_all_soft_refs, bool* should_compact,
1894 bool* should_start_over) {
1895 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1896 // flag is set, and we have either requested a System.gc() or
1897 // the number of full gc's since the last concurrent cycle
1898 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1899 // or if an incremental collection has failed
1900 GenCollectedHeap* gch = GenCollectedHeap::heap();
1901 assert(gch->collector_policy()->is_two_generation_policy(),
1902 "You may want to check the correctness of the following");
1903 // Inform cms gen if this was due to partial collection failing.
1904 // The CMS gen may use this fact to determine its expansion policy.
1905 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1906 assert(!_cmsGen->incremental_collection_failed(),
1907 "Should have been noticed, reacted to and cleared");
1908 _cmsGen->set_incremental_collection_failed();
1909 }
1910 *should_compact =
1911 UseCMSCompactAtFullCollection &&
1912 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1913 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1914 gch->incremental_collection_will_fail(true /* consult_young */));
1915 *should_start_over = false;
1916 if (clear_all_soft_refs && !*should_compact) {
1917 // We are about to do a last ditch collection attempt
1918 // so it would normally make sense to do a compaction
1919 // to reclaim as much space as possible.
1920 if (CMSCompactWhenClearAllSoftRefs) {
1921 // Default: The rationale is that in this case either
1922 // we are past the final marking phase, in which case
1923 // we'd have to start over, or so little has been done
1924 // that there's little point in saving that work. Compaction
1925 // appears to be the sensible choice in either case.
1926 *should_compact = true;
1927 } else {
1928 // We have been asked to clear all soft refs, but not to
1929 // compact. Make sure that we aren't past the final checkpoint
1930 // phase, for that is where we process soft refs. If we are already
1931 // past that phase, we'll need to redo the refs discovery phase and
1932 // if necessary clear soft refs that weren't previously
1933 // cleared. We do so by remembering the phase in which
1934 // we came in, and if we are past the refs processing
1935 // phase, we'll choose to just redo the mark-sweep
1936 // collection from scratch.
1937 if (_collectorState > FinalMarking) {
1938 // We are past the refs processing phase;
1939 // start over and do a fresh synchronous CMS cycle
1940 _collectorState = Resetting; // skip to reset to start new cycle
1941 reset(false /* == !asynch */);
1942 *should_start_over = true;
1943 } // else we can continue a possibly ongoing current cycle
1944 }
1945 }
1946 }
1947
1948 // A work method used by the foreground collector to do
1949 // a mark-sweep-compact.
1950 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1951 GenCollectedHeap* gch = GenCollectedHeap::heap();
1952 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1953 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1954 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1955 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1956 }
1957
1958 // Sample collection interval time and reset for collection pause.
1959 if (UseAdaptiveSizePolicy) {
1960 size_policy()->msc_collection_begin();
1961 }
1962
1963 // Temporarily widen the span of the weak reference processing to
1964 // the entire heap.
1965 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1966 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1967 // Temporarily, clear the "is_alive_non_header" field of the
1968 // reference processor.
1969 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1970 // Temporarily make reference _processing_ single threaded (non-MT).
1971 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1972 // Temporarily make refs discovery atomic
1973 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1974 // Temporarily make reference _discovery_ single threaded (non-MT)
1975 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1976
1977 ref_processor()->set_enqueuing_is_done(false);
1978 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1979 ref_processor()->setup_policy(clear_all_soft_refs);
1980 // If an asynchronous collection finishes, the _modUnionTable is
1981 // all clear. If we are assuming the collection from an asynchronous
1982 // collection, clear the _modUnionTable.
1983 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1984 "_modUnionTable should be clear if the baton was not passed");
1985 _modUnionTable.clear_all();
1986 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1987 "mod union for klasses should be clear if the baton was passed");
1988 _ct->klass_rem_set()->clear_mod_union();
1989
1990 // We must adjust the allocation statistics being maintained
1991 // in the free list space. We do so by reading and clearing
1992 // the sweep timer and updating the block flux rate estimates below.
1993 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1994 if (_inter_sweep_timer.is_active()) {
1995 _inter_sweep_timer.stop();
1996 // Note that we do not use this sample to update the _inter_sweep_estimate.
1997 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1998 _inter_sweep_estimate.padded_average(),
1999 _intra_sweep_estimate.padded_average());
2000 }
2001
2002 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2003 ref_processor(), clear_all_soft_refs);
2004 #ifdef ASSERT
2005 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2006 size_t free_size = cms_space->free();
2007 assert(free_size ==
2008 pointer_delta(cms_space->end(), cms_space->compaction_top())
2009 * HeapWordSize,
2010 "All the free space should be compacted into one chunk at top");
2011 assert(cms_space->dictionary()->total_chunk_size(
2012 debug_only(cms_space->freelistLock())) == 0 ||
2013 cms_space->totalSizeInIndexedFreeLists() == 0,
2014 "All the free space should be in a single chunk");
2015 size_t num = cms_space->totalCount();
2016 assert((free_size == 0 && num == 0) ||
2017 (free_size > 0 && (num == 1 || num == 2)),
2018 "There should be at most 2 free chunks after compaction");
2019 #endif // ASSERT
2020 _collectorState = Resetting;
2021 assert(_restart_addr == NULL,
2022 "Should have been NULL'd before baton was passed");
2023 reset(false /* == !asynch */);
2024 _cmsGen->reset_after_compaction();
2025 _concurrent_cycles_since_last_unload = 0;
2026
2027 // Clear any data recorded in the PLAB chunk arrays.
2028 if (_survivor_plab_array != NULL) {
2029 reset_survivor_plab_arrays();
2030 }
2031
2032 // Adjust the per-size allocation stats for the next epoch.
2033 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2034 // Restart the "inter sweep timer" for the next epoch.
2035 _inter_sweep_timer.reset();
2036 _inter_sweep_timer.start();
2037
2038 // Sample collection pause time and reset for collection interval.
2039 if (UseAdaptiveSizePolicy) {
2040 size_policy()->msc_collection_end(gch->gc_cause());
2041 }
2042
2043 // For a mark-sweep-compact, compute_new_size() will be called
2044 // in the heap's do_collection() method.
2045 }
2046
2047 // A work method used by the foreground collector to do
2048 // a mark-sweep, after taking over from a possibly on-going
2049 // concurrent mark-sweep collection.
2050 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2051 CollectorState first_state, bool should_start_over) {
2052 if (PrintGC && Verbose) {
2053 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2054 "collector with count %d",
2055 _full_gcs_since_conc_gc);
2056 }
2057 switch (_collectorState) {
2058 case Idling:
2059 if (first_state == Idling || should_start_over) {
2060 // The background GC was not active, or should
2061 // restarted from scratch; start the cycle.
2062 _collectorState = InitialMarking;
2063 }
2064 // If first_state was not Idling, then a background GC
2065 // was in progress and has now finished. No need to do it
2066 // again. Leave the state as Idling.
2067 break;
2068 case Precleaning:
2069 // In the foreground case don't do the precleaning since
2070 // it is not done concurrently and there is extra work
2071 // required.
2072 _collectorState = FinalMarking;
2073 }
2074 if (PrintGCDetails &&
2075 (_collectorState > Idling ||
2076 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2077 gclog_or_tty->print(" (concurrent mode failure)");
2078 }
2079 collect_in_foreground(clear_all_soft_refs);
2080
2081 // For a mark-sweep, compute_new_size() will be called
2082 // in the heap's do_collection() method.
2083 }
2084
2085
2086 void CMSCollector::getFreelistLocks() const {
2087 // Get locks for all free lists in all generations that this
2088 // collector is responsible for
2089 _cmsGen->freelistLock()->lock_without_safepoint_check();
2090 }
2091
2092 void CMSCollector::releaseFreelistLocks() const {
2093 // Release locks for all free lists in all generations that this
2094 // collector is responsible for
2095 _cmsGen->freelistLock()->unlock();
2096 }
2097
2098 bool CMSCollector::haveFreelistLocks() const {
2099 // Check locks for all free lists in all generations that this
2100 // collector is responsible for
2101 assert_lock_strong(_cmsGen->freelistLock());
2102 PRODUCT_ONLY(ShouldNotReachHere());
2103 return true;
2104 }
2105
2106 // A utility class that is used by the CMS collector to
2107 // temporarily "release" the foreground collector from its
2108 // usual obligation to wait for the background collector to
2109 // complete an ongoing phase before proceeding.
2110 class ReleaseForegroundGC: public StackObj {
2111 private:
2112 CMSCollector* _c;
2113 public:
2114 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2115 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2116 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2117 // allow a potentially blocked foreground collector to proceed
2118 _c->_foregroundGCShouldWait = false;
2119 if (_c->_foregroundGCIsActive) {
2120 CGC_lock->notify();
2121 }
2122 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2123 "Possible deadlock");
2124 }
2125
2126 ~ReleaseForegroundGC() {
2127 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2128 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2129 _c->_foregroundGCShouldWait = true;
2130 }
2131 };
2132
2133 // There are separate collect_in_background and collect_in_foreground because of
2134 // the different locking requirements of the background collector and the
2135 // foreground collector. There was originally an attempt to share
2136 // one "collect" method between the background collector and the foreground
2137 // collector but the if-then-else required made it cleaner to have
2138 // separate methods.
2139 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2140 assert(Thread::current()->is_ConcurrentGC_thread(),
2141 "A CMS asynchronous collection is only allowed on a CMS thread.");
2142
2143 GenCollectedHeap* gch = GenCollectedHeap::heap();
2144 {
2145 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2146 MutexLockerEx hl(Heap_lock, safepoint_check);
2147 FreelistLocker fll(this);
2148 MutexLockerEx x(CGC_lock, safepoint_check);
2149 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2150 // The foreground collector is active or we're
2151 // not using asynchronous collections. Skip this
2152 // background collection.
2153 assert(!_foregroundGCShouldWait, "Should be clear");
2154 return;
2155 } else {
2156 assert(_collectorState == Idling, "Should be idling before start.");
2157 _collectorState = InitialMarking;
2158 // Reset the expansion cause, now that we are about to begin
2159 // a new cycle.
2160 clear_expansion_cause();
2161
2162 // Clear the MetaspaceGC flag since a concurrent collection
2163 // is starting but also clear it after the collection.
2164 MetaspaceGC::set_should_concurrent_collect(false);
2165 }
2166 // Decide if we want to enable class unloading as part of the
2167 // ensuing concurrent GC cycle.
2168 update_should_unload_classes();
2169 _full_gc_requested = false; // acks all outstanding full gc requests
2170 // Signal that we are about to start a collection
2171 gch->increment_total_full_collections(); // ... starting a collection cycle
2172 _collection_count_start = gch->total_full_collections();
2173 }
2174
2175 // Used for PrintGC
2176 size_t prev_used;
2177 if (PrintGC && Verbose) {
2178 prev_used = _cmsGen->used(); // XXXPERM
2179 }
2180
2181 // The change of the collection state is normally done at this level;
2182 // the exceptions are phases that are executed while the world is
2183 // stopped. For those phases the change of state is done while the
2184 // world is stopped. For baton passing purposes this allows the
2185 // background collector to finish the phase and change state atomically.
2186 // The foreground collector cannot wait on a phase that is done
2187 // while the world is stopped because the foreground collector already
2188 // has the world stopped and would deadlock.
2189 while (_collectorState != Idling) {
2190 if (TraceCMSState) {
2191 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2192 Thread::current(), _collectorState);
2193 }
2194 // The foreground collector
2195 // holds the Heap_lock throughout its collection.
2196 // holds the CMS token (but not the lock)
2197 // except while it is waiting for the background collector to yield.
2198 //
2199 // The foreground collector should be blocked (not for long)
2200 // if the background collector is about to start a phase
2201 // executed with world stopped. If the background
2202 // collector has already started such a phase, the
2203 // foreground collector is blocked waiting for the
2204 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2205 // are executed in the VM thread.
2206 //
2207 // The locking order is
2208 // PendingListLock (PLL) -- if applicable (FinalMarking)
2209 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2210 // CMS token (claimed in
2211 // stop_world_and_do() -->
2212 // safepoint_synchronize() -->
2213 // CMSThread::synchronize())
2214
2215 {
2216 // Check if the FG collector wants us to yield.
2217 CMSTokenSync x(true); // is cms thread
2218 if (waitForForegroundGC()) {
2219 // We yielded to a foreground GC, nothing more to be
2220 // done this round.
2221 assert(_foregroundGCShouldWait == false, "We set it to false in "
2222 "waitForForegroundGC()");
2223 if (TraceCMSState) {
2224 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2225 " exiting collection CMS state %d",
2226 Thread::current(), _collectorState);
2227 }
2228 return;
2229 } else {
2230 // The background collector can run but check to see if the
2231 // foreground collector has done a collection while the
2232 // background collector was waiting to get the CGC_lock
2233 // above. If yes, break so that _foregroundGCShouldWait
2234 // is cleared before returning.
2235 if (_collectorState == Idling) {
2236 break;
2237 }
2238 }
2239 }
2240
2241 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2242 "should be waiting");
2243
2244 switch (_collectorState) {
2245 case InitialMarking:
2246 {
2247 ReleaseForegroundGC x(this);
2248 stats().record_cms_begin();
2249
2250 VM_CMS_Initial_Mark initial_mark_op(this);
2251 VMThread::execute(&initial_mark_op);
2252 }
2253 // The collector state may be any legal state at this point
2254 // since the background collector may have yielded to the
2255 // foreground collector.
2256 break;
2257 case Marking:
2258 // initial marking in checkpointRootsInitialWork has been completed
2259 if (markFromRoots(true)) { // we were successful
2260 assert(_collectorState == Precleaning, "Collector state should "
2261 "have changed");
2262 } else {
2263 assert(_foregroundGCIsActive, "Internal state inconsistency");
2264 }
2265 break;
2266 case Precleaning:
2267 if (UseAdaptiveSizePolicy) {
2268 size_policy()->concurrent_precleaning_begin();
2269 }
2270 // marking from roots in markFromRoots has been completed
2271 preclean();
2272 if (UseAdaptiveSizePolicy) {
2273 size_policy()->concurrent_precleaning_end();
2274 }
2275 assert(_collectorState == AbortablePreclean ||
2276 _collectorState == FinalMarking,
2277 "Collector state should have changed");
2278 break;
2279 case AbortablePreclean:
2280 if (UseAdaptiveSizePolicy) {
2281 size_policy()->concurrent_phases_resume();
2282 }
2283 abortable_preclean();
2284 if (UseAdaptiveSizePolicy) {
2285 size_policy()->concurrent_precleaning_end();
2286 }
2287 assert(_collectorState == FinalMarking, "Collector state should "
2288 "have changed");
2289 break;
2290 case FinalMarking:
2291 {
2292 ReleaseForegroundGC x(this);
2293
2294 VM_CMS_Final_Remark final_remark_op(this);
2295 VMThread::execute(&final_remark_op);
2296 }
2297 assert(_foregroundGCShouldWait, "block post-condition");
2298 break;
2299 case Sweeping:
2300 if (UseAdaptiveSizePolicy) {
2301 size_policy()->concurrent_sweeping_begin();
2302 }
2303 // final marking in checkpointRootsFinal has been completed
2304 sweep(true);
2305 assert(_collectorState == Resizing, "Collector state change "
2306 "to Resizing must be done under the free_list_lock");
2307 _full_gcs_since_conc_gc = 0;
2308
2309 // Stop the timers for adaptive size policy for the concurrent phases
2310 if (UseAdaptiveSizePolicy) {
2311 size_policy()->concurrent_sweeping_end();
2312 size_policy()->concurrent_phases_end(gch->gc_cause(),
2313 gch->prev_gen(_cmsGen)->capacity(),
2314 _cmsGen->free());
2315 }
2316
2317 case Resizing: {
2318 // Sweeping has been completed...
2319 // At this point the background collection has completed.
2320 // Don't move the call to compute_new_size() down
2321 // into code that might be executed if the background
2322 // collection was preempted.
2323 {
2324 ReleaseForegroundGC x(this); // unblock FG collection
2325 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2326 CMSTokenSync z(true); // not strictly needed.
2327 if (_collectorState == Resizing) {
2328 compute_new_size();
2329 _collectorState = Resetting;
2330 } else {
2331 assert(_collectorState == Idling, "The state should only change"
2332 " because the foreground collector has finished the collection");
2333 }
2334 }
2335 break;
2336 }
2337 case Resetting:
2338 // CMS heap resizing has been completed
2339 reset(true);
2340 assert(_collectorState == Idling, "Collector state should "
2341 "have changed");
2342
2343 MetaspaceGC::set_should_concurrent_collect(false);
2344
2345 stats().record_cms_end();
2346 // Don't move the concurrent_phases_end() and compute_new_size()
2347 // calls to here because a preempted background collection
2348 // has it's state set to "Resetting".
2349 break;
2350 case Idling:
2351 default:
2352 ShouldNotReachHere();
2353 break;
2354 }
2355 if (TraceCMSState) {
2356 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2357 Thread::current(), _collectorState);
2358 }
2359 assert(_foregroundGCShouldWait, "block post-condition");
2360 }
2361
2362 // Should this be in gc_epilogue?
2363 collector_policy()->counters()->update_counters();
2364
2365 {
2366 // Clear _foregroundGCShouldWait and, in the event that the
2367 // foreground collector is waiting, notify it, before
2368 // returning.
2369 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2370 _foregroundGCShouldWait = false;
2371 if (_foregroundGCIsActive) {
2372 CGC_lock->notify();
2373 }
2374 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2375 "Possible deadlock");
2376 }
2377 if (TraceCMSState) {
2378 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2379 " exiting collection CMS state %d",
2380 Thread::current(), _collectorState);
2381 }
2382 if (PrintGC && Verbose) {
2383 _cmsGen->print_heap_change(prev_used);
2384 }
2385 }
2386
2387 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2388 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2389 "Foreground collector should be waiting, not executing");
2390 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2391 "may only be done by the VM Thread with the world stopped");
2392 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2393 "VM thread should have CMS token");
2394
2395 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2396 true, gclog_or_tty);)
2397 if (UseAdaptiveSizePolicy) {
2398 size_policy()->ms_collection_begin();
2399 }
2400 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2401
2402 HandleMark hm; // Discard invalid handles created during verification
2403
2404 if (VerifyBeforeGC &&
2405 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2406 Universe::verify(true);
2407 }
2408
2409 // Snapshot the soft reference policy to be used in this collection cycle.
2410 ref_processor()->setup_policy(clear_all_soft_refs);
2411
2412 bool init_mark_was_synchronous = false; // until proven otherwise
2413 while (_collectorState != Idling) {
2414 if (TraceCMSState) {
2415 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2416 Thread::current(), _collectorState);
2417 }
2418 switch (_collectorState) {
2419 case InitialMarking:
2420 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2421 checkpointRootsInitial(false);
2422 assert(_collectorState == Marking, "Collector state should have changed"
2423 " within checkpointRootsInitial()");
2424 break;
2425 case Marking:
2426 // initial marking in checkpointRootsInitialWork has been completed
2427 if (VerifyDuringGC &&
2428 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2429 gclog_or_tty->print("Verify before initial mark: ");
2430 Universe::verify(true);
2431 }
2432 {
2433 bool res = markFromRoots(false);
2434 assert(res && _collectorState == FinalMarking, "Collector state should "
2435 "have changed");
2436 break;
2437 }
2438 case FinalMarking:
2439 if (VerifyDuringGC &&
2440 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2441 gclog_or_tty->print("Verify before re-mark: ");
2442 Universe::verify(true);
2443 }
2444 checkpointRootsFinal(false, clear_all_soft_refs,
2445 init_mark_was_synchronous);
2446 assert(_collectorState == Sweeping, "Collector state should not "
2447 "have changed within checkpointRootsFinal()");
2448 break;
2449 case Sweeping:
2450 // final marking in checkpointRootsFinal has been completed
2451 if (VerifyDuringGC &&
2452 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2453 gclog_or_tty->print("Verify before sweep: ");
2454 Universe::verify(true);
2455 }
2456 sweep(false);
2457 assert(_collectorState == Resizing, "Incorrect state");
2458 break;
2459 case Resizing: {
2460 // Sweeping has been completed; the actual resize in this case
2461 // is done separately; nothing to be done in this state.
2462 _collectorState = Resetting;
2463 break;
2464 }
2465 case Resetting:
2466 // The heap has been resized.
2467 if (VerifyDuringGC &&
2468 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2469 gclog_or_tty->print("Verify before reset: ");
2470 Universe::verify(true);
2471 }
2472 reset(false);
2473 assert(_collectorState == Idling, "Collector state should "
2474 "have changed");
2475 break;
2476 case Precleaning:
2477 case AbortablePreclean:
2478 // Elide the preclean phase
2479 _collectorState = FinalMarking;
2480 break;
2481 default:
2482 ShouldNotReachHere();
2483 }
2484 if (TraceCMSState) {
2485 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2486 Thread::current(), _collectorState);
2487 }
2488 }
2489
2490 if (UseAdaptiveSizePolicy) {
2491 GenCollectedHeap* gch = GenCollectedHeap::heap();
2492 size_policy()->ms_collection_end(gch->gc_cause());
2493 }
2494
2495 if (VerifyAfterGC &&
2496 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2497 Universe::verify(true);
2498 }
2499 if (TraceCMSState) {
2500 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2501 " exiting collection CMS state %d",
2502 Thread::current(), _collectorState);
2503 }
2504 }
2505
2506 bool CMSCollector::waitForForegroundGC() {
2507 bool res = false;
2508 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2509 "CMS thread should have CMS token");
2510 // Block the foreground collector until the
2511 // background collectors decides whether to
2512 // yield.
2513 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2514 _foregroundGCShouldWait = true;
2515 if (_foregroundGCIsActive) {
2516 // The background collector yields to the
2517 // foreground collector and returns a value
2518 // indicating that it has yielded. The foreground
2519 // collector can proceed.
2520 res = true;
2521 _foregroundGCShouldWait = false;
2522 ConcurrentMarkSweepThread::clear_CMS_flag(
2523 ConcurrentMarkSweepThread::CMS_cms_has_token);
2524 ConcurrentMarkSweepThread::set_CMS_flag(
2525 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2526 // Get a possibly blocked foreground thread going
2527 CGC_lock->notify();
2528 if (TraceCMSState) {
2529 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2530 Thread::current(), _collectorState);
2531 }
2532 while (_foregroundGCIsActive) {
2533 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2534 }
2535 ConcurrentMarkSweepThread::set_CMS_flag(
2536 ConcurrentMarkSweepThread::CMS_cms_has_token);
2537 ConcurrentMarkSweepThread::clear_CMS_flag(
2538 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2539 }
2540 if (TraceCMSState) {
2541 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2542 Thread::current(), _collectorState);
2543 }
2544 return res;
2545 }
2546
2547 // Because of the need to lock the free lists and other structures in
2548 // the collector, common to all the generations that the collector is
2549 // collecting, we need the gc_prologues of individual CMS generations
2550 // delegate to their collector. It may have been simpler had the
2551 // current infrastructure allowed one to call a prologue on a
2552 // collector. In the absence of that we have the generation's
2553 // prologue delegate to the collector, which delegates back
2554 // some "local" work to a worker method in the individual generations
2555 // that it's responsible for collecting, while itself doing any
2556 // work common to all generations it's responsible for. A similar
2557 // comment applies to the gc_epilogue()'s.
2558 // The role of the varaible _between_prologue_and_epilogue is to
2559 // enforce the invocation protocol.
2560 void CMSCollector::gc_prologue(bool full) {
2561 // Call gc_prologue_work() for the CMSGen
2562 // we are responsible for.
2563
2564 // The following locking discipline assumes that we are only called
2565 // when the world is stopped.
2566 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2567
2568 // The CMSCollector prologue must call the gc_prologues for the
2569 // "generations" that it's responsible
2570 // for.
2571
2572 assert( Thread::current()->is_VM_thread()
2573 || ( CMSScavengeBeforeRemark
2574 && Thread::current()->is_ConcurrentGC_thread()),
2575 "Incorrect thread type for prologue execution");
2576
2577 if (_between_prologue_and_epilogue) {
2578 // We have already been invoked; this is a gc_prologue delegation
2579 // from yet another CMS generation that we are responsible for, just
2580 // ignore it since all relevant work has already been done.
2581 return;
2582 }
2583
2584 // set a bit saying prologue has been called; cleared in epilogue
2585 _between_prologue_and_epilogue = true;
2586 // Claim locks for common data structures, then call gc_prologue_work()
2587 // for each CMSGen.
2588
2589 getFreelistLocks(); // gets free list locks on constituent spaces
2590 bitMapLock()->lock_without_safepoint_check();
2591
2592 // Should call gc_prologue_work() for all cms gens we are responsible for
2593 bool duringMarking = _collectorState >= Marking
2594 && _collectorState < Sweeping;
2595
2596 // The young collections clear the modified oops state, which tells if
2597 // there are any modified oops in the class. The remark phase also needs
2598 // that information. Tell the young collection to save the union of all
2599 // modified klasses.
2600 if (duringMarking) {
2601 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2602 }
2603
2604 bool registerClosure = duringMarking;
2605
2606 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2607 &_modUnionClosurePar
2608 : &_modUnionClosure;
2609 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2610
2611 if (!full) {
2612 stats().record_gc0_begin();
2613 }
2614 }
2615
2616 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2617 // Delegate to CMScollector which knows how to coordinate between
2618 // this and any other CMS generations that it is responsible for
2619 // collecting.
2620 collector()->gc_prologue(full);
2621 }
2622
2623 // This is a "private" interface for use by this generation's CMSCollector.
2624 // Not to be called directly by any other entity (for instance,
2625 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2626 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2627 bool registerClosure, ModUnionClosure* modUnionClosure) {
2628 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2629 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2630 "Should be NULL");
2631 if (registerClosure) {
2632 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2633 }
2634 cmsSpace()->gc_prologue();
2635 // Clear stat counters
2636 NOT_PRODUCT(
2637 assert(_numObjectsPromoted == 0, "check");
2638 assert(_numWordsPromoted == 0, "check");
2639 if (Verbose && PrintGC) {
2640 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2641 SIZE_FORMAT" bytes concurrently",
2642 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2643 }
2644 _numObjectsAllocated = 0;
2645 _numWordsAllocated = 0;
2646 )
2647 }
2648
2649 void CMSCollector::gc_epilogue(bool full) {
2650 // The following locking discipline assumes that we are only called
2651 // when the world is stopped.
2652 assert(SafepointSynchronize::is_at_safepoint(),
2653 "world is stopped assumption");
2654
2655 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2656 // if linear allocation blocks need to be appropriately marked to allow the
2657 // the blocks to be parsable. We also check here whether we need to nudge the
2658 // CMS collector thread to start a new cycle (if it's not already active).
2659 assert( Thread::current()->is_VM_thread()
2660 || ( CMSScavengeBeforeRemark
2661 && Thread::current()->is_ConcurrentGC_thread()),
2662 "Incorrect thread type for epilogue execution");
2663
2664 if (!_between_prologue_and_epilogue) {
2665 // We have already been invoked; this is a gc_epilogue delegation
2666 // from yet another CMS generation that we are responsible for, just
2667 // ignore it since all relevant work has already been done.
2668 return;
2669 }
2670 assert(haveFreelistLocks(), "must have freelist locks");
2671 assert_lock_strong(bitMapLock());
2672
2673 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2674
2675 _cmsGen->gc_epilogue_work(full);
2676
2677 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2678 // in case sampling was not already enabled, enable it
2679 _start_sampling = true;
2680 }
2681 // reset _eden_chunk_array so sampling starts afresh
2682 _eden_chunk_index = 0;
2683
2684 size_t cms_used = _cmsGen->cmsSpace()->used();
2685
2686 // update performance counters - this uses a special version of
2687 // update_counters() that allows the utilization to be passed as a
2688 // parameter, avoiding multiple calls to used().
2689 //
2690 _cmsGen->update_counters(cms_used);
2691
2692 if (CMSIncrementalMode) {
2693 icms_update_allocation_limits();
2694 }
2695
2696 bitMapLock()->unlock();
2697 releaseFreelistLocks();
2698
2699 if (!CleanChunkPoolAsync) {
2700 Chunk::clean_chunk_pool();
2701 }
2702
2703 _between_prologue_and_epilogue = false; // ready for next cycle
2704 }
2705
2706 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2707 collector()->gc_epilogue(full);
2708
2709 // Also reset promotion tracking in par gc thread states.
2710 if (CollectedHeap::use_parallel_gc_threads()) {
2711 for (uint i = 0; i < ParallelGCThreads; i++) {
2712 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2713 }
2714 }
2715 }
2716
2717 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2718 assert(!incremental_collection_failed(), "Should have been cleared");
2719 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2720 cmsSpace()->gc_epilogue();
2721 // Print stat counters
2722 NOT_PRODUCT(
2723 assert(_numObjectsAllocated == 0, "check");
2724 assert(_numWordsAllocated == 0, "check");
2725 if (Verbose && PrintGC) {
2726 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2727 SIZE_FORMAT" bytes",
2728 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2729 }
2730 _numObjectsPromoted = 0;
2731 _numWordsPromoted = 0;
2732 )
2733
2734 if (PrintGC && Verbose) {
2735 // Call down the chain in contiguous_available needs the freelistLock
2736 // so print this out before releasing the freeListLock.
2737 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2738 contiguous_available());
2739 }
2740 }
2741
2742 #ifndef PRODUCT
2743 bool CMSCollector::have_cms_token() {
2744 Thread* thr = Thread::current();
2745 if (thr->is_VM_thread()) {
2746 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2747 } else if (thr->is_ConcurrentGC_thread()) {
2748 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2749 } else if (thr->is_GC_task_thread()) {
2750 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2751 ParGCRareEvent_lock->owned_by_self();
2752 }
2753 return false;
2754 }
2755 #endif
2756
2757 // Check reachability of the given heap address in CMS generation,
2758 // treating all other generations as roots.
2759 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2760 // We could "guarantee" below, rather than assert, but i'll
2761 // leave these as "asserts" so that an adventurous debugger
2762 // could try this in the product build provided some subset of
2763 // the conditions were met, provided they were intersted in the
2764 // results and knew that the computation below wouldn't interfere
2765 // with other concurrent computations mutating the structures
2766 // being read or written.
2767 assert(SafepointSynchronize::is_at_safepoint(),
2768 "Else mutations in object graph will make answer suspect");
2769 assert(have_cms_token(), "Should hold cms token");
2770 assert(haveFreelistLocks(), "must hold free list locks");
2771 assert_lock_strong(bitMapLock());
2772
2773 // Clear the marking bit map array before starting, but, just
2774 // for kicks, first report if the given address is already marked
2775 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2776 _markBitMap.isMarked(addr) ? "" : " not");
2777
2778 if (verify_after_remark()) {
2779 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2780 bool result = verification_mark_bm()->isMarked(addr);
2781 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2782 result ? "IS" : "is NOT");
2783 return result;
2784 } else {
2785 gclog_or_tty->print_cr("Could not compute result");
2786 return false;
2787 }
2788 }
2789
2790 ////////////////////////////////////////////////////////
2791 // CMS Verification Support
2792 ////////////////////////////////////////////////////////
2793 // Following the remark phase, the following invariant
2794 // should hold -- each object in the CMS heap which is
2795 // marked in markBitMap() should be marked in the verification_mark_bm().
2796
2797 class VerifyMarkedClosure: public BitMapClosure {
2798 CMSBitMap* _marks;
2799 bool _failed;
2800
2801 public:
2802 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2803
2804 bool do_bit(size_t offset) {
2805 HeapWord* addr = _marks->offsetToHeapWord(offset);
2806 if (!_marks->isMarked(addr)) {
2807 oop(addr)->print_on(gclog_or_tty);
2808 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2809 _failed = true;
2810 }
2811 return true;
2812 }
2813
2814 bool failed() { return _failed; }
2815 };
2816
2817 bool CMSCollector::verify_after_remark() {
2818 gclog_or_tty->print(" [Verifying CMS Marking... ");
2819 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2820 static bool init = false;
2821
2822 assert(SafepointSynchronize::is_at_safepoint(),
2823 "Else mutations in object graph will make answer suspect");
2824 assert(have_cms_token(),
2825 "Else there may be mutual interference in use of "
2826 " verification data structures");
2827 assert(_collectorState > Marking && _collectorState <= Sweeping,
2828 "Else marking info checked here may be obsolete");
2829 assert(haveFreelistLocks(), "must hold free list locks");
2830 assert_lock_strong(bitMapLock());
2831
2832
2833 // Allocate marking bit map if not already allocated
2834 if (!init) { // first time
2835 if (!verification_mark_bm()->allocate(_span)) {
2836 return false;
2837 }
2838 init = true;
2839 }
2840
2841 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2842
2843 // Turn off refs discovery -- so we will be tracing through refs.
2844 // This is as intended, because by this time
2845 // GC must already have cleared any refs that need to be cleared,
2846 // and traced those that need to be marked; moreover,
2847 // the marking done here is not going to intefere in any
2848 // way with the marking information used by GC.
2849 NoRefDiscovery no_discovery(ref_processor());
2850
2851 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2852
2853 // Clear any marks from a previous round
2854 verification_mark_bm()->clear_all();
2855 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2856 verify_work_stacks_empty();
2857
2858 GenCollectedHeap* gch = GenCollectedHeap::heap();
2859 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2860 // Update the saved marks which may affect the root scans.
2861 gch->save_marks();
2862
2863 if (CMSRemarkVerifyVariant == 1) {
2864 // In this first variant of verification, we complete
2865 // all marking, then check if the new marks-verctor is
2866 // a subset of the CMS marks-vector.
2867 verify_after_remark_work_1();
2868 } else if (CMSRemarkVerifyVariant == 2) {
2869 // In this second variant of verification, we flag an error
2870 // (i.e. an object reachable in the new marks-vector not reachable
2871 // in the CMS marks-vector) immediately, also indicating the
2872 // identify of an object (A) that references the unmarked object (B) --
2873 // presumably, a mutation to A failed to be picked up by preclean/remark?
2874 verify_after_remark_work_2();
2875 } else {
2876 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2877 CMSRemarkVerifyVariant);
2878 }
2879 gclog_or_tty->print(" done] ");
2880 return true;
2881 }
2882
2883 void CMSCollector::verify_after_remark_work_1() {
2884 ResourceMark rm;
2885 HandleMark hm;
2886 GenCollectedHeap* gch = GenCollectedHeap::heap();
2887
2888 // Get a clear set of claim bits for the strong roots processing to work with.
2889 ClassLoaderDataGraph::clear_claimed_marks();
2890
2891 // Mark from roots one level into CMS
2892 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2893 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2894
2895 gch->gen_process_strong_roots(_cmsGen->level(),
2896 true, // younger gens are roots
2897 true, // activate StrongRootsScope
2898 false, // not scavenging
2899 SharedHeap::ScanningOption(roots_scanning_options()),
2900 ¬Older,
2901 true, // walk code active on stacks
2902 NULL,
2903 NULL); // SSS: Provide correct closure
2904
2905 // Now mark from the roots
2906 MarkFromRootsClosure markFromRootsClosure(this, _span,
2907 verification_mark_bm(), verification_mark_stack(),
2908 false /* don't yield */, true /* verifying */);
2909 assert(_restart_addr == NULL, "Expected pre-condition");
2910 verification_mark_bm()->iterate(&markFromRootsClosure);
2911 while (_restart_addr != NULL) {
2912 // Deal with stack overflow: by restarting at the indicated
2913 // address.
2914 HeapWord* ra = _restart_addr;
2915 markFromRootsClosure.reset(ra);
2916 _restart_addr = NULL;
2917 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2918 }
2919 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2920 verify_work_stacks_empty();
2921
2922 // Marking completed -- now verify that each bit marked in
2923 // verification_mark_bm() is also marked in markBitMap(); flag all
2924 // errors by printing corresponding objects.
2925 VerifyMarkedClosure vcl(markBitMap());
2926 verification_mark_bm()->iterate(&vcl);
2927 if (vcl.failed()) {
2928 gclog_or_tty->print("Verification failed");
2929 Universe::heap()->print_on(gclog_or_tty);
2930 fatal("CMS: failed marking verification after remark");
2931 }
2932 }
2933
2934 class VerifyKlassOopsKlassClosure : public KlassClosure {
2935 class VerifyKlassOopsClosure : public OopClosure {
2936 CMSBitMap* _bitmap;
2937 public:
2938 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2939 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2940 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2941 } _oop_closure;
2942 public:
2943 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2944 void do_klass(Klass* k) {
2945 k->oops_do(&_oop_closure);
2946 }
2947 };
2948
2949 void CMSCollector::verify_after_remark_work_2() {
2950 ResourceMark rm;
2951 HandleMark hm;
2952 GenCollectedHeap* gch = GenCollectedHeap::heap();
2953
2954 // Get a clear set of claim bits for the strong roots processing to work with.
2955 ClassLoaderDataGraph::clear_claimed_marks();
2956
2957 // Mark from roots one level into CMS
2958 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2959 markBitMap());
2960 CMKlassClosure klass_closure(¬Older);
2961
2962 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2963 gch->gen_process_strong_roots(_cmsGen->level(),
2964 true, // younger gens are roots
2965 true, // activate StrongRootsScope
2966 false, // not scavenging
2967 SharedHeap::ScanningOption(roots_scanning_options()),
2968 ¬Older,
2969 true, // walk code active on stacks
2970 NULL,
2971 &klass_closure);
2972
2973 // Now mark from the roots
2974 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2975 verification_mark_bm(), markBitMap(), verification_mark_stack());
2976 assert(_restart_addr == NULL, "Expected pre-condition");
2977 verification_mark_bm()->iterate(&markFromRootsClosure);
2978 while (_restart_addr != NULL) {
2979 // Deal with stack overflow: by restarting at the indicated
2980 // address.
2981 HeapWord* ra = _restart_addr;
2982 markFromRootsClosure.reset(ra);
2983 _restart_addr = NULL;
2984 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2985 }
2986 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2987 verify_work_stacks_empty();
2988
2989 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2990 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2991
2992 // Marking completed -- now verify that each bit marked in
2993 // verification_mark_bm() is also marked in markBitMap(); flag all
2994 // errors by printing corresponding objects.
2995 VerifyMarkedClosure vcl(markBitMap());
2996 verification_mark_bm()->iterate(&vcl);
2997 assert(!vcl.failed(), "Else verification above should not have succeeded");
2998 }
2999
3000 void ConcurrentMarkSweepGeneration::save_marks() {
3001 // delegate to CMS space
3002 cmsSpace()->save_marks();
3003 for (uint i = 0; i < ParallelGCThreads; i++) {
3004 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3005 }
3006 }
3007
3008 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3009 return cmsSpace()->no_allocs_since_save_marks();
3010 }
3011
3012 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3013 \
3014 void ConcurrentMarkSweepGeneration:: \
3015 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3016 cl->set_generation(this); \
3017 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3018 cl->reset_generation(); \
3019 save_marks(); \
3020 }
3021
3022 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3023
3024 void
3025 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3026 {
3027 // Not currently implemented; need to do the following. -- ysr.
3028 // dld -- I think that is used for some sort of allocation profiler. So it
3029 // really means the objects allocated by the mutator since the last
3030 // GC. We could potentially implement this cheaply by recording only
3031 // the direct allocations in a side data structure.
3032 //
3033 // I think we probably ought not to be required to support these
3034 // iterations at any arbitrary point; I think there ought to be some
3035 // call to enable/disable allocation profiling in a generation/space,
3036 // and the iterator ought to return the objects allocated in the
3037 // gen/space since the enable call, or the last iterator call (which
3038 // will probably be at a GC.) That way, for gens like CM&S that would
3039 // require some extra data structure to support this, we only pay the
3040 // cost when it's in use...
3041 cmsSpace()->object_iterate_since_last_GC(blk);
3042 }
3043
3044 void
3045 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3046 cl->set_generation(this);
3047 younger_refs_in_space_iterate(_cmsSpace, cl);
3048 cl->reset_generation();
3049 }
3050
3051 void
3052 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3053 if (freelistLock()->owned_by_self()) {
3054 Generation::oop_iterate(mr, cl);
3055 } else {
3056 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3057 Generation::oop_iterate(mr, cl);
3058 }
3059 }
3060
3061 void
3062 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3063 if (freelistLock()->owned_by_self()) {
3064 Generation::oop_iterate(cl);
3065 } else {
3066 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3067 Generation::oop_iterate(cl);
3068 }
3069 }
3070
3071 void
3072 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3073 if (freelistLock()->owned_by_self()) {
3074 Generation::object_iterate(cl);
3075 } else {
3076 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3077 Generation::object_iterate(cl);
3078 }
3079 }
3080
3081 void
3082 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3083 if (freelistLock()->owned_by_self()) {
3084 Generation::safe_object_iterate(cl);
3085 } else {
3086 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3087 Generation::safe_object_iterate(cl);
3088 }
3089 }
3090
3091 void
3092 ConcurrentMarkSweepGeneration::post_compact() {
3093 }
3094
3095 void
3096 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3097 // Fix the linear allocation blocks to look like free blocks.
3098
3099 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3100 // are not called when the heap is verified during universe initialization and
3101 // at vm shutdown.
3102 if (freelistLock()->owned_by_self()) {
3103 cmsSpace()->prepare_for_verify();
3104 } else {
3105 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3106 cmsSpace()->prepare_for_verify();
3107 }
3108 }
3109
3110 void
3111 ConcurrentMarkSweepGeneration::verify() {
3112 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3113 // are not called when the heap is verified during universe initialization and
3114 // at vm shutdown.
3115 if (freelistLock()->owned_by_self()) {
3116 cmsSpace()->verify();
3117 } else {
3118 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3119 cmsSpace()->verify();
3120 }
3121 }
3122
3123 void CMSCollector::verify() {
3124 _cmsGen->verify();
3125 }
3126
3127 #ifndef PRODUCT
3128 bool CMSCollector::overflow_list_is_empty() const {
3129 assert(_num_par_pushes >= 0, "Inconsistency");
3130 if (_overflow_list == NULL) {
3131 assert(_num_par_pushes == 0, "Inconsistency");
3132 }
3133 return _overflow_list == NULL;
3134 }
3135
3136 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3137 // merely consolidate assertion checks that appear to occur together frequently.
3138 void CMSCollector::verify_work_stacks_empty() const {
3139 assert(_markStack.isEmpty(), "Marking stack should be empty");
3140 assert(overflow_list_is_empty(), "Overflow list should be empty");
3141 }
3142
3143 void CMSCollector::verify_overflow_empty() const {
3144 assert(overflow_list_is_empty(), "Overflow list should be empty");
3145 assert(no_preserved_marks(), "No preserved marks");
3146 }
3147 #endif // PRODUCT
3148
3149 // Decide if we want to enable class unloading as part of the
3150 // ensuing concurrent GC cycle. We will collect and
3151 // unload classes if it's the case that:
3152 // (1) an explicit gc request has been made and the flag
3153 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3154 // (2) (a) class unloading is enabled at the command line, and
3155 // (b) old gen is getting really full
3156 // NOTE: Provided there is no change in the state of the heap between
3157 // calls to this method, it should have idempotent results. Moreover,
3158 // its results should be monotonically increasing (i.e. going from 0 to 1,
3159 // but not 1 to 0) between successive calls between which the heap was
3160 // not collected. For the implementation below, it must thus rely on
3161 // the property that concurrent_cycles_since_last_unload()
3162 // will not decrease unless a collection cycle happened and that
3163 // _cmsGen->is_too_full() are
3164 // themselves also monotonic in that sense. See check_monotonicity()
3165 // below.
3166 void CMSCollector::update_should_unload_classes() {
3167 _should_unload_classes = false;
3168 // Condition 1 above
3169 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3170 _should_unload_classes = true;
3171 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3172 // Disjuncts 2.b.(i,ii,iii) above
3173 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3174 CMSClassUnloadingMaxInterval)
3175 || _cmsGen->is_too_full();
3176 }
3177 }
3178
3179 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3180 bool res = should_concurrent_collect();
3181 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3182 return res;
3183 }
3184
3185 void CMSCollector::setup_cms_unloading_and_verification_state() {
3186 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3187 || VerifyBeforeExit;
3188 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3189
3190 if (should_unload_classes()) { // Should unload classes this cycle
3191 remove_root_scanning_option(rso); // Shrink the root set appropriately
3192 set_verifying(should_verify); // Set verification state for this cycle
3193 return; // Nothing else needs to be done at this time
3194 }
3195
3196 // Not unloading classes this cycle
3197 assert(!should_unload_classes(), "Inconsitency!");
3198 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3199 // Include symbols, strings and code cache elements to prevent their resurrection.
3200 add_root_scanning_option(rso);
3201 set_verifying(true);
3202 } else if (verifying() && !should_verify) {
3203 // We were verifying, but some verification flags got disabled.
3204 set_verifying(false);
3205 // Exclude symbols, strings and code cache elements from root scanning to
3206 // reduce IM and RM pauses.
3207 remove_root_scanning_option(rso);
3208 }
3209 }
3210
3211
3212 #ifndef PRODUCT
3213 HeapWord* CMSCollector::block_start(const void* p) const {
3214 const HeapWord* addr = (HeapWord*)p;
3215 if (_span.contains(p)) {
3216 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3217 return _cmsGen->cmsSpace()->block_start(p);
3218 }
3219 }
3220 return NULL;
3221 }
3222 #endif
3223
3224 HeapWord*
3225 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3226 bool tlab,
3227 bool parallel) {
3228 CMSSynchronousYieldRequest yr;
3229 assert(!tlab, "Can't deal with TLAB allocation");
3230 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3231 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3232 CMSExpansionCause::_satisfy_allocation);
3233 if (GCExpandToAllocateDelayMillis > 0) {
3234 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3235 }
3236 return have_lock_and_allocate(word_size, tlab);
3237 }
3238
3239 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3240 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3241 // to CardGeneration and share it...
3242 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3243 return CardGeneration::expand(bytes, expand_bytes);
3244 }
3245
3246 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3247 CMSExpansionCause::Cause cause)
3248 {
3249
3250 bool success = expand(bytes, expand_bytes);
3251
3252 // remember why we expanded; this information is used
3253 // by shouldConcurrentCollect() when making decisions on whether to start
3254 // a new CMS cycle.
3255 if (success) {
3256 set_expansion_cause(cause);
3257 if (PrintGCDetails && Verbose) {
3258 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3259 CMSExpansionCause::to_string(cause));
3260 }
3261 }
3262 }
3263
3264 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3265 HeapWord* res = NULL;
3266 MutexLocker x(ParGCRareEvent_lock);
3267 while (true) {
3268 // Expansion by some other thread might make alloc OK now:
3269 res = ps->lab.alloc(word_sz);
3270 if (res != NULL) return res;
3271 // If there's not enough expansion space available, give up.
3272 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3273 return NULL;
3274 }
3275 // Otherwise, we try expansion.
3276 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3277 CMSExpansionCause::_allocate_par_lab);
3278 // Now go around the loop and try alloc again;
3279 // A competing par_promote might beat us to the expansion space,
3280 // so we may go around the loop again if promotion fails agaion.
3281 if (GCExpandToAllocateDelayMillis > 0) {
3282 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3283 }
3284 }
3285 }
3286
3287
3288 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3289 PromotionInfo* promo) {
3290 MutexLocker x(ParGCRareEvent_lock);
3291 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3292 while (true) {
3293 // Expansion by some other thread might make alloc OK now:
3294 if (promo->ensure_spooling_space()) {
3295 assert(promo->has_spooling_space(),
3296 "Post-condition of successful ensure_spooling_space()");
3297 return true;
3298 }
3299 // If there's not enough expansion space available, give up.
3300 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3301 return false;
3302 }
3303 // Otherwise, we try expansion.
3304 expand(refill_size_bytes, MinHeapDeltaBytes,
3305 CMSExpansionCause::_allocate_par_spooling_space);
3306 // Now go around the loop and try alloc again;
3307 // A competing allocation might beat us to the expansion space,
3308 // so we may go around the loop again if allocation fails again.
3309 if (GCExpandToAllocateDelayMillis > 0) {
3310 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3311 }
3312 }
3313 }
3314
3315
3316
3317 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3318 assert_locked_or_safepoint(Heap_lock);
3319 size_t size = ReservedSpace::page_align_size_down(bytes);
3320 if (size > 0) {
3321 shrink_by(size);
3322 }
3323 }
3324
3325 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3326 assert_locked_or_safepoint(Heap_lock);
3327 bool result = _virtual_space.expand_by(bytes);
3328 if (result) {
3329 HeapWord* old_end = _cmsSpace->end();
3330 size_t new_word_size =
3331 heap_word_size(_virtual_space.committed_size());
3332 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3333 _bts->resize(new_word_size); // resize the block offset shared array
3334 Universe::heap()->barrier_set()->resize_covered_region(mr);
3335 // Hmmmm... why doesn't CFLS::set_end verify locking?
3336 // This is quite ugly; FIX ME XXX
3337 _cmsSpace->assert_locked(freelistLock());
3338 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3339
3340 // update the space and generation capacity counters
3341 if (UsePerfData) {
3342 _space_counters->update_capacity();
3343 _gen_counters->update_all();
3344 }
3345
3346 if (Verbose && PrintGC) {
3347 size_t new_mem_size = _virtual_space.committed_size();
3348 size_t old_mem_size = new_mem_size - bytes;
3349 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3350 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3351 }
3352 }
3353 return result;
3354 }
3355
3356 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3357 assert_locked_or_safepoint(Heap_lock);
3358 bool success = true;
3359 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3360 if (remaining_bytes > 0) {
3361 success = grow_by(remaining_bytes);
3362 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3363 }
3364 return success;
3365 }
3366
3367 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3368 assert_locked_or_safepoint(Heap_lock);
3369 assert_lock_strong(freelistLock());
3370 // XXX Fix when compaction is implemented.
3371 warning("Shrinking of CMS not yet implemented");
3372 return;
3373 }
3374
3375
3376 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3377 // phases.
3378 class CMSPhaseAccounting: public StackObj {
3379 public:
3380 CMSPhaseAccounting(CMSCollector *collector,
3381 const char *phase,
3382 bool print_cr = true);
3383 ~CMSPhaseAccounting();
3384
3385 private:
3386 CMSCollector *_collector;
3387 const char *_phase;
3388 elapsedTimer _wallclock;
3389 bool _print_cr;
3390
3391 public:
3392 // Not MT-safe; so do not pass around these StackObj's
3393 // where they may be accessed by other threads.
3394 jlong wallclock_millis() {
3395 assert(_wallclock.is_active(), "Wall clock should not stop");
3396 _wallclock.stop(); // to record time
3397 jlong ret = _wallclock.milliseconds();
3398 _wallclock.start(); // restart
3399 return ret;
3400 }
3401 };
3402
3403 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3404 const char *phase,
3405 bool print_cr) :
3406 _collector(collector), _phase(phase), _print_cr(print_cr) {
3407
3408 if (PrintCMSStatistics != 0) {
3409 _collector->resetYields();
3410 }
3411 if (PrintGCDetails && PrintGCTimeStamps) {
3412 gclog_or_tty->date_stamp(PrintGCDateStamps);
3413 gclog_or_tty->stamp();
3414 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3415 _collector->cmsGen()->short_name(), _phase);
3416 }
3417 _collector->resetTimer();
3418 _wallclock.start();
3419 _collector->startTimer();
3420 }
3421
3422 CMSPhaseAccounting::~CMSPhaseAccounting() {
3423 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3424 _collector->stopTimer();
3425 _wallclock.stop();
3426 if (PrintGCDetails) {
3427 gclog_or_tty->date_stamp(PrintGCDateStamps);
3428 if (PrintGCTimeStamps) {
3429 gclog_or_tty->stamp();
3430 gclog_or_tty->print(": ");
3431 }
3432 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3433 _collector->cmsGen()->short_name(),
3434 _phase, _collector->timerValue(), _wallclock.seconds());
3435 if (_print_cr) {
3436 gclog_or_tty->print_cr("");
3437 }
3438 if (PrintCMSStatistics != 0) {
3439 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3440 _collector->yields());
3441 }
3442 }
3443 }
3444
3445 // CMS work
3446
3447 // Checkpoint the roots into this generation from outside
3448 // this generation. [Note this initial checkpoint need only
3449 // be approximate -- we'll do a catch up phase subsequently.]
3450 void CMSCollector::checkpointRootsInitial(bool asynch) {
3451 assert(_collectorState == InitialMarking, "Wrong collector state");
3452 check_correct_thread_executing();
3453 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3454
3455 ReferenceProcessor* rp = ref_processor();
3456 SpecializationStats::clear();
3457 assert(_restart_addr == NULL, "Control point invariant");
3458 if (asynch) {
3459 // acquire locks for subsequent manipulations
3460 MutexLockerEx x(bitMapLock(),
3461 Mutex::_no_safepoint_check_flag);
3462 checkpointRootsInitialWork(asynch);
3463 // enable ("weak") refs discovery
3464 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3465 _collectorState = Marking;
3466 } else {
3467 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3468 // which recognizes if we are a CMS generation, and doesn't try to turn on
3469 // discovery; verify that they aren't meddling.
3470 assert(!rp->discovery_is_atomic(),
3471 "incorrect setting of discovery predicate");
3472 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3473 "ref discovery for this generation kind");
3474 // already have locks
3475 checkpointRootsInitialWork(asynch);
3476 // now enable ("weak") refs discovery
3477 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3478 _collectorState = Marking;
3479 }
3480 SpecializationStats::print();
3481 }
3482
3483 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3484 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3485 assert(_collectorState == InitialMarking, "just checking");
3486
3487 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3488 // precede our marking with a collection of all
3489 // younger generations to keep floating garbage to a minimum.
3490 // XXX: we won't do this for now -- it's an optimization to be done later.
3491
3492 // already have locks
3493 assert_lock_strong(bitMapLock());
3494 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3495
3496 // Setup the verification and class unloading state for this
3497 // CMS collection cycle.
3498 setup_cms_unloading_and_verification_state();
3499
3500 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3501 PrintGCDetails && Verbose, true, gclog_or_tty);)
3502 if (UseAdaptiveSizePolicy) {
3503 size_policy()->checkpoint_roots_initial_begin();
3504 }
3505
3506 // Reset all the PLAB chunk arrays if necessary.
3507 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3508 reset_survivor_plab_arrays();
3509 }
3510
3511 ResourceMark rm;
3512 HandleMark hm;
3513
3514 FalseClosure falseClosure;
3515 // In the case of a synchronous collection, we will elide the
3516 // remark step, so it's important to catch all the nmethod oops
3517 // in this step.
3518 // The final 'true' flag to gen_process_strong_roots will ensure this.
3519 // If 'async' is true, we can relax the nmethod tracing.
3520 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3521 GenCollectedHeap* gch = GenCollectedHeap::heap();
3522
3523 verify_work_stacks_empty();
3524 verify_overflow_empty();
3525
3526 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3527 // Update the saved marks which may affect the root scans.
3528 gch->save_marks();
3529
3530 // weak reference processing has not started yet.
3531 ref_processor()->set_enqueuing_is_done(false);
3532
3533 // Need to remember all newly created CLDs,
3534 // so that we can guarantee that the remark finds them.
3535 ClassLoaderDataGraph::remember_new_clds(true);
3536
3537 // Whenever a CLD is found, it will be claimed before proceeding to mark
3538 // the klasses. The claimed marks need to be cleared before marking starts.
3539 ClassLoaderDataGraph::clear_claimed_marks();
3540
3541 CMKlassClosure klass_closure(¬Older);
3542 {
3543 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3544 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3545 gch->gen_process_strong_roots(_cmsGen->level(),
3546 true, // younger gens are roots
3547 true, // activate StrongRootsScope
3548 false, // not scavenging
3549 SharedHeap::ScanningOption(roots_scanning_options()),
3550 ¬Older,
3551 true, // walk all of code cache if (so & SO_CodeCache)
3552 NULL,
3553 &klass_closure);
3554 }
3555
3556 // Clear mod-union table; it will be dirtied in the prologue of
3557 // CMS generation per each younger generation collection.
3558
3559 assert(_modUnionTable.isAllClear(),
3560 "Was cleared in most recent final checkpoint phase"
3561 " or no bits are set in the gc_prologue before the start of the next "
3562 "subsequent marking phase.");
3563
3564 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3565
3566 // Save the end of the used_region of the constituent generations
3567 // to be used to limit the extent of sweep in each generation.
3568 save_sweep_limits();
3569 if (UseAdaptiveSizePolicy) {
3570 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3571 }
3572 verify_overflow_empty();
3573 }
3574
3575 bool CMSCollector::markFromRoots(bool asynch) {
3576 // we might be tempted to assert that:
3577 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3578 // "inconsistent argument?");
3579 // However that wouldn't be right, because it's possible that
3580 // a safepoint is indeed in progress as a younger generation
3581 // stop-the-world GC happens even as we mark in this generation.
3582 assert(_collectorState == Marking, "inconsistent state?");
3583 check_correct_thread_executing();
3584 verify_overflow_empty();
3585
3586 bool res;
3587 if (asynch) {
3588
3589 // Start the timers for adaptive size policy for the concurrent phases
3590 // Do it here so that the foreground MS can use the concurrent
3591 // timer since a foreground MS might has the sweep done concurrently
3592 // or STW.
3593 if (UseAdaptiveSizePolicy) {
3594 size_policy()->concurrent_marking_begin();
3595 }
3596
3597 // Weak ref discovery note: We may be discovering weak
3598 // refs in this generation concurrent (but interleaved) with
3599 // weak ref discovery by a younger generation collector.
3600
3601 CMSTokenSyncWithLocks ts(true, bitMapLock());
3602 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3603 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3604 res = markFromRootsWork(asynch);
3605 if (res) {
3606 _collectorState = Precleaning;
3607 } else { // We failed and a foreground collection wants to take over
3608 assert(_foregroundGCIsActive, "internal state inconsistency");
3609 assert(_restart_addr == NULL, "foreground will restart from scratch");
3610 if (PrintGCDetails) {
3611 gclog_or_tty->print_cr("bailing out to foreground collection");
3612 }
3613 }
3614 if (UseAdaptiveSizePolicy) {
3615 size_policy()->concurrent_marking_end();
3616 }
3617 } else {
3618 assert(SafepointSynchronize::is_at_safepoint(),
3619 "inconsistent with asynch == false");
3620 if (UseAdaptiveSizePolicy) {
3621 size_policy()->ms_collection_marking_begin();
3622 }
3623 // already have locks
3624 res = markFromRootsWork(asynch);
3625 _collectorState = FinalMarking;
3626 if (UseAdaptiveSizePolicy) {
3627 GenCollectedHeap* gch = GenCollectedHeap::heap();
3628 size_policy()->ms_collection_marking_end(gch->gc_cause());
3629 }
3630 }
3631 verify_overflow_empty();
3632 return res;
3633 }
3634
3635 bool CMSCollector::markFromRootsWork(bool asynch) {
3636 // iterate over marked bits in bit map, doing a full scan and mark
3637 // from these roots using the following algorithm:
3638 // . if oop is to the right of the current scan pointer,
3639 // mark corresponding bit (we'll process it later)
3640 // . else (oop is to left of current scan pointer)
3641 // push oop on marking stack
3642 // . drain the marking stack
3643
3644 // Note that when we do a marking step we need to hold the
3645 // bit map lock -- recall that direct allocation (by mutators)
3646 // and promotion (by younger generation collectors) is also
3647 // marking the bit map. [the so-called allocate live policy.]
3648 // Because the implementation of bit map marking is not
3649 // robust wrt simultaneous marking of bits in the same word,
3650 // we need to make sure that there is no such interference
3651 // between concurrent such updates.
3652
3653 // already have locks
3654 assert_lock_strong(bitMapLock());
3655
3656 verify_work_stacks_empty();
3657 verify_overflow_empty();
3658 bool result = false;
3659 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3660 result = do_marking_mt(asynch);
3661 } else {
3662 result = do_marking_st(asynch);
3663 }
3664 return result;
3665 }
3666
3667 // Forward decl
3668 class CMSConcMarkingTask;
3669
3670 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3671 CMSCollector* _collector;
3672 CMSConcMarkingTask* _task;
3673 public:
3674 virtual void yield();
3675
3676 // "n_threads" is the number of threads to be terminated.
3677 // "queue_set" is a set of work queues of other threads.
3678 // "collector" is the CMS collector associated with this task terminator.
3679 // "yield" indicates whether we need the gang as a whole to yield.
3680 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3681 ParallelTaskTerminator(n_threads, queue_set),
3682 _collector(collector) { }
3683
3684 void set_task(CMSConcMarkingTask* task) {
3685 _task = task;
3686 }
3687 };
3688
3689 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3690 CMSConcMarkingTask* _task;
3691 public:
3692 bool should_exit_termination();
3693 void set_task(CMSConcMarkingTask* task) {
3694 _task = task;
3695 }
3696 };
3697
3698 // MT Concurrent Marking Task
3699 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3700 CMSCollector* _collector;
3701 int _n_workers; // requested/desired # workers
3702 bool _asynch;
3703 bool _result;
3704 CompactibleFreeListSpace* _cms_space;
3705 char _pad_front[64]; // padding to ...
3706 HeapWord* _global_finger; // ... avoid sharing cache line
3707 char _pad_back[64];
3708 HeapWord* _restart_addr;
3709
3710 // Exposed here for yielding support
3711 Mutex* const _bit_map_lock;
3712
3713 // The per thread work queues, available here for stealing
3714 OopTaskQueueSet* _task_queues;
3715
3716 // Termination (and yielding) support
3717 CMSConcMarkingTerminator _term;
3718 CMSConcMarkingTerminatorTerminator _term_term;
3719
3720 public:
3721 CMSConcMarkingTask(CMSCollector* collector,
3722 CompactibleFreeListSpace* cms_space,
3723 bool asynch,
3724 YieldingFlexibleWorkGang* workers,
3725 OopTaskQueueSet* task_queues):
3726 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3727 _collector(collector),
3728 _cms_space(cms_space),
3729 _asynch(asynch), _n_workers(0), _result(true),
3730 _task_queues(task_queues),
3731 _term(_n_workers, task_queues, _collector),
3732 _bit_map_lock(collector->bitMapLock())
3733 {
3734 _requested_size = _n_workers;
3735 _term.set_task(this);
3736 _term_term.set_task(this);
3737 _restart_addr = _global_finger = _cms_space->bottom();
3738 }
3739
3740
3741 OopTaskQueueSet* task_queues() { return _task_queues; }
3742
3743 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3744
3745 HeapWord** global_finger_addr() { return &_global_finger; }
3746
3747 CMSConcMarkingTerminator* terminator() { return &_term; }
3748
3749 virtual void set_for_termination(int active_workers) {
3750 terminator()->reset_for_reuse(active_workers);
3751 }
3752
3753 void work(uint worker_id);
3754 bool should_yield() {
3755 return ConcurrentMarkSweepThread::should_yield()
3756 && !_collector->foregroundGCIsActive()
3757 && _asynch;
3758 }
3759
3760 virtual void coordinator_yield(); // stuff done by coordinator
3761 bool result() { return _result; }
3762
3763 void reset(HeapWord* ra) {
3764 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3765 _restart_addr = _global_finger = ra;
3766 _term.reset_for_reuse();
3767 }
3768
3769 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3770 OopTaskQueue* work_q);
3771
3772 private:
3773 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3774 void do_work_steal(int i);
3775 void bump_global_finger(HeapWord* f);
3776 };
3777
3778 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3779 assert(_task != NULL, "Error");
3780 return _task->yielding();
3781 // Note that we do not need the disjunct || _task->should_yield() above
3782 // because we want terminating threads to yield only if the task
3783 // is already in the midst of yielding, which happens only after at least one
3784 // thread has yielded.
3785 }
3786
3787 void CMSConcMarkingTerminator::yield() {
3788 if (_task->should_yield()) {
3789 _task->yield();
3790 } else {
3791 ParallelTaskTerminator::yield();
3792 }
3793 }
3794
3795 ////////////////////////////////////////////////////////////////
3796 // Concurrent Marking Algorithm Sketch
3797 ////////////////////////////////////////////////////////////////
3798 // Until all tasks exhausted (both spaces):
3799 // -- claim next available chunk
3800 // -- bump global finger via CAS
3801 // -- find first object that starts in this chunk
3802 // and start scanning bitmap from that position
3803 // -- scan marked objects for oops
3804 // -- CAS-mark target, and if successful:
3805 // . if target oop is above global finger (volatile read)
3806 // nothing to do
3807 // . if target oop is in chunk and above local finger
3808 // then nothing to do
3809 // . else push on work-queue
3810 // -- Deal with possible overflow issues:
3811 // . local work-queue overflow causes stuff to be pushed on
3812 // global (common) overflow queue
3813 // . always first empty local work queue
3814 // . then get a batch of oops from global work queue if any
3815 // . then do work stealing
3816 // -- When all tasks claimed (both spaces)
3817 // and local work queue empty,
3818 // then in a loop do:
3819 // . check global overflow stack; steal a batch of oops and trace
3820 // . try to steal from other threads oif GOS is empty
3821 // . if neither is available, offer termination
3822 // -- Terminate and return result
3823 //
3824 void CMSConcMarkingTask::work(uint worker_id) {
3825 elapsedTimer _timer;
3826 ResourceMark rm;
3827 HandleMark hm;
3828
3829 DEBUG_ONLY(_collector->verify_overflow_empty();)
3830
3831 // Before we begin work, our work queue should be empty
3832 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3833 // Scan the bitmap covering _cms_space, tracing through grey objects.
3834 _timer.start();
3835 do_scan_and_mark(worker_id, _cms_space);
3836 _timer.stop();
3837 if (PrintCMSStatistics != 0) {
3838 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3839 worker_id, _timer.seconds());
3840 // XXX: need xxx/xxx type of notation, two timers
3841 }
3842
3843 // ... do work stealing
3844 _timer.reset();
3845 _timer.start();
3846 do_work_steal(worker_id);
3847 _timer.stop();
3848 if (PrintCMSStatistics != 0) {
3849 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3850 worker_id, _timer.seconds());
3851 // XXX: need xxx/xxx type of notation, two timers
3852 }
3853 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3854 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3855 // Note that under the current task protocol, the
3856 // following assertion is true even of the spaces
3857 // expanded since the completion of the concurrent
3858 // marking. XXX This will likely change under a strict
3859 // ABORT semantics.
3860 // After perm removal the comparison was changed to
3861 // greater than or equal to from strictly greater than.
3862 // Before perm removal the highest address sweep would
3863 // have been at the end of perm gen but now is at the
3864 // end of the tenured gen.
3865 assert(_global_finger >= _cms_space->end(),
3866 "All tasks have been completed");
3867 DEBUG_ONLY(_collector->verify_overflow_empty();)
3868 }
3869
3870 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3871 HeapWord* read = _global_finger;
3872 HeapWord* cur = read;
3873 while (f > read) {
3874 cur = read;
3875 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3876 if (cur == read) {
3877 // our cas succeeded
3878 assert(_global_finger >= f, "protocol consistency");
3879 break;
3880 }
3881 }
3882 }
3883
3884 // This is really inefficient, and should be redone by
3885 // using (not yet available) block-read and -write interfaces to the
3886 // stack and the work_queue. XXX FIX ME !!!
3887 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3888 OopTaskQueue* work_q) {
3889 // Fast lock-free check
3890 if (ovflw_stk->length() == 0) {
3891 return false;
3892 }
3893 assert(work_q->size() == 0, "Shouldn't steal");
3894 MutexLockerEx ml(ovflw_stk->par_lock(),
3895 Mutex::_no_safepoint_check_flag);
3896 // Grab up to 1/4 the size of the work queue
3897 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3898 (size_t)ParGCDesiredObjsFromOverflowList);
3899 num = MIN2(num, ovflw_stk->length());
3900 for (int i = (int) num; i > 0; i--) {
3901 oop cur = ovflw_stk->pop();
3902 assert(cur != NULL, "Counted wrong?");
3903 work_q->push(cur);
3904 }
3905 return num > 0;
3906 }
3907
3908 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3909 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3910 int n_tasks = pst->n_tasks();
3911 // We allow that there may be no tasks to do here because
3912 // we are restarting after a stack overflow.
3913 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3914 uint nth_task = 0;
3915
3916 HeapWord* aligned_start = sp->bottom();
3917 if (sp->used_region().contains(_restart_addr)) {
3918 // Align down to a card boundary for the start of 0th task
3919 // for this space.
3920 aligned_start =
3921 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3922 CardTableModRefBS::card_size);
3923 }
3924
3925 size_t chunk_size = sp->marking_task_size();
3926 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3927 // Having claimed the nth task in this space,
3928 // compute the chunk that it corresponds to:
3929 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3930 aligned_start + (nth_task+1)*chunk_size);
3931 // Try and bump the global finger via a CAS;
3932 // note that we need to do the global finger bump
3933 // _before_ taking the intersection below, because
3934 // the task corresponding to that region will be
3935 // deemed done even if the used_region() expands
3936 // because of allocation -- as it almost certainly will
3937 // during start-up while the threads yield in the
3938 // closure below.
3939 HeapWord* finger = span.end();
3940 bump_global_finger(finger); // atomically
3941 // There are null tasks here corresponding to chunks
3942 // beyond the "top" address of the space.
3943 span = span.intersection(sp->used_region());
3944 if (!span.is_empty()) { // Non-null task
3945 HeapWord* prev_obj;
3946 assert(!span.contains(_restart_addr) || nth_task == 0,
3947 "Inconsistency");
3948 if (nth_task == 0) {
3949 // For the 0th task, we'll not need to compute a block_start.
3950 if (span.contains(_restart_addr)) {
3951 // In the case of a restart because of stack overflow,
3952 // we might additionally skip a chunk prefix.
3953 prev_obj = _restart_addr;
3954 } else {
3955 prev_obj = span.start();
3956 }
3957 } else {
3958 // We want to skip the first object because
3959 // the protocol is to scan any object in its entirety
3960 // that _starts_ in this span; a fortiori, any
3961 // object starting in an earlier span is scanned
3962 // as part of an earlier claimed task.
3963 // Below we use the "careful" version of block_start
3964 // so we do not try to navigate uninitialized objects.
3965 prev_obj = sp->block_start_careful(span.start());
3966 // Below we use a variant of block_size that uses the
3967 // Printezis bits to avoid waiting for allocated
3968 // objects to become initialized/parsable.
3969 while (prev_obj < span.start()) {
3970 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3971 if (sz > 0) {
3972 prev_obj += sz;
3973 } else {
3974 // In this case we may end up doing a bit of redundant
3975 // scanning, but that appears unavoidable, short of
3976 // locking the free list locks; see bug 6324141.
3977 break;
3978 }
3979 }
3980 }
3981 if (prev_obj < span.end()) {
3982 MemRegion my_span = MemRegion(prev_obj, span.end());
3983 // Do the marking work within a non-empty span --
3984 // the last argument to the constructor indicates whether the
3985 // iteration should be incremental with periodic yields.
3986 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3987 &_collector->_markBitMap,
3988 work_queue(i),
3989 &_collector->_markStack,
3990 _asynch);
3991 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3992 } // else nothing to do for this task
3993 } // else nothing to do for this task
3994 }
3995 // We'd be tempted to assert here that since there are no
3996 // more tasks left to claim in this space, the global_finger
3997 // must exceed space->top() and a fortiori space->end(). However,
3998 // that would not quite be correct because the bumping of
3999 // global_finger occurs strictly after the claiming of a task,
4000 // so by the time we reach here the global finger may not yet
4001 // have been bumped up by the thread that claimed the last
4002 // task.
4003 pst->all_tasks_completed();
4004 }
4005
4006 class Par_ConcMarkingClosure: public CMSOopClosure {
4007 private:
4008 CMSCollector* _collector;
4009 CMSConcMarkingTask* _task;
4010 MemRegion _span;
4011 CMSBitMap* _bit_map;
4012 CMSMarkStack* _overflow_stack;
4013 OopTaskQueue* _work_queue;
4014 protected:
4015 DO_OOP_WORK_DEFN
4016 public:
4017 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4018 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4019 CMSOopClosure(collector->ref_processor()),
4020 _collector(collector),
4021 _task(task),
4022 _span(collector->_span),
4023 _work_queue(work_queue),
4024 _bit_map(bit_map),
4025 _overflow_stack(overflow_stack)
4026 { }
4027 virtual void do_oop(oop* p);
4028 virtual void do_oop(narrowOop* p);
4029
4030 void trim_queue(size_t max);
4031 void handle_stack_overflow(HeapWord* lost);
4032 void do_yield_check() {
4033 if (_task->should_yield()) {
4034 _task->yield();
4035 }
4036 }
4037 };
4038
4039 // Grey object scanning during work stealing phase --
4040 // the salient assumption here is that any references
4041 // that are in these stolen objects being scanned must
4042 // already have been initialized (else they would not have
4043 // been published), so we do not need to check for
4044 // uninitialized objects before pushing here.
4045 void Par_ConcMarkingClosure::do_oop(oop obj) {
4046 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4047 HeapWord* addr = (HeapWord*)obj;
4048 // Check if oop points into the CMS generation
4049 // and is not marked
4050 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4051 // a white object ...
4052 // If we manage to "claim" the object, by being the
4053 // first thread to mark it, then we push it on our
4054 // marking stack
4055 if (_bit_map->par_mark(addr)) { // ... now grey
4056 // push on work queue (grey set)
4057 bool simulate_overflow = false;
4058 NOT_PRODUCT(
4059 if (CMSMarkStackOverflowALot &&
4060 _collector->simulate_overflow()) {
4061 // simulate a stack overflow
4062 simulate_overflow = true;
4063 }
4064 )
4065 if (simulate_overflow ||
4066 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4067 // stack overflow
4068 if (PrintCMSStatistics != 0) {
4069 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4070 SIZE_FORMAT, _overflow_stack->capacity());
4071 }
4072 // We cannot assert that the overflow stack is full because
4073 // it may have been emptied since.
4074 assert(simulate_overflow ||
4075 _work_queue->size() == _work_queue->max_elems(),
4076 "Else push should have succeeded");
4077 handle_stack_overflow(addr);
4078 }
4079 } // Else, some other thread got there first
4080 do_yield_check();
4081 }
4082 }
4083
4084 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4085 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4086
4087 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4088 while (_work_queue->size() > max) {
4089 oop new_oop;
4090 if (_work_queue->pop_local(new_oop)) {
4091 assert(new_oop->is_oop(), "Should be an oop");
4092 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4093 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4094 new_oop->oop_iterate(this); // do_oop() above
4095 do_yield_check();
4096 }
4097 }
4098 }
4099
4100 // Upon stack overflow, we discard (part of) the stack,
4101 // remembering the least address amongst those discarded
4102 // in CMSCollector's _restart_address.
4103 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4104 // We need to do this under a mutex to prevent other
4105 // workers from interfering with the work done below.
4106 MutexLockerEx ml(_overflow_stack->par_lock(),
4107 Mutex::_no_safepoint_check_flag);
4108 // Remember the least grey address discarded
4109 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4110 _collector->lower_restart_addr(ra);
4111 _overflow_stack->reset(); // discard stack contents
4112 _overflow_stack->expand(); // expand the stack if possible
4113 }
4114
4115
4116 void CMSConcMarkingTask::do_work_steal(int i) {
4117 OopTaskQueue* work_q = work_queue(i);
4118 oop obj_to_scan;
4119 CMSBitMap* bm = &(_collector->_markBitMap);
4120 CMSMarkStack* ovflw = &(_collector->_markStack);
4121 int* seed = _collector->hash_seed(i);
4122 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4123 while (true) {
4124 cl.trim_queue(0);
4125 assert(work_q->size() == 0, "Should have been emptied above");
4126 if (get_work_from_overflow_stack(ovflw, work_q)) {
4127 // Can't assert below because the work obtained from the
4128 // overflow stack may already have been stolen from us.
4129 // assert(work_q->size() > 0, "Work from overflow stack");
4130 continue;
4131 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4132 assert(obj_to_scan->is_oop(), "Should be an oop");
4133 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4134 obj_to_scan->oop_iterate(&cl);
4135 } else if (terminator()->offer_termination(&_term_term)) {
4136 assert(work_q->size() == 0, "Impossible!");
4137 break;
4138 } else if (yielding() || should_yield()) {
4139 yield();
4140 }
4141 }
4142 }
4143
4144 // This is run by the CMS (coordinator) thread.
4145 void CMSConcMarkingTask::coordinator_yield() {
4146 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4147 "CMS thread should hold CMS token");
4148 // First give up the locks, then yield, then re-lock
4149 // We should probably use a constructor/destructor idiom to
4150 // do this unlock/lock or modify the MutexUnlocker class to
4151 // serve our purpose. XXX
4152 assert_lock_strong(_bit_map_lock);
4153 _bit_map_lock->unlock();
4154 ConcurrentMarkSweepThread::desynchronize(true);
4155 ConcurrentMarkSweepThread::acknowledge_yield_request();
4156 _collector->stopTimer();
4157 if (PrintCMSStatistics != 0) {
4158 _collector->incrementYields();
4159 }
4160 _collector->icms_wait();
4161
4162 // It is possible for whichever thread initiated the yield request
4163 // not to get a chance to wake up and take the bitmap lock between
4164 // this thread releasing it and reacquiring it. So, while the
4165 // should_yield() flag is on, let's sleep for a bit to give the
4166 // other thread a chance to wake up. The limit imposed on the number
4167 // of iterations is defensive, to avoid any unforseen circumstances
4168 // putting us into an infinite loop. Since it's always been this
4169 // (coordinator_yield()) method that was observed to cause the
4170 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4171 // which is by default non-zero. For the other seven methods that
4172 // also perform the yield operation, as are using a different
4173 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4174 // can enable the sleeping for those methods too, if necessary.
4175 // See 6442774.
4176 //
4177 // We really need to reconsider the synchronization between the GC
4178 // thread and the yield-requesting threads in the future and we
4179 // should really use wait/notify, which is the recommended
4180 // way of doing this type of interaction. Additionally, we should
4181 // consolidate the eight methods that do the yield operation and they
4182 // are almost identical into one for better maintenability and
4183 // readability. See 6445193.
4184 //
4185 // Tony 2006.06.29
4186 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4187 ConcurrentMarkSweepThread::should_yield() &&
4188 !CMSCollector::foregroundGCIsActive(); ++i) {
4189 os::sleep(Thread::current(), 1, false);
4190 ConcurrentMarkSweepThread::acknowledge_yield_request();
4191 }
4192
4193 ConcurrentMarkSweepThread::synchronize(true);
4194 _bit_map_lock->lock_without_safepoint_check();
4195 _collector->startTimer();
4196 }
4197
4198 bool CMSCollector::do_marking_mt(bool asynch) {
4199 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4200 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4201 conc_workers()->total_workers(),
4202 conc_workers()->active_workers(),
4203 Threads::number_of_non_daemon_threads());
4204 conc_workers()->set_active_workers(num_workers);
4205
4206 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4207
4208 CMSConcMarkingTask tsk(this,
4209 cms_space,
4210 asynch,
4211 conc_workers(),
4212 task_queues());
4213
4214 // Since the actual number of workers we get may be different
4215 // from the number we requested above, do we need to do anything different
4216 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4217 // class?? XXX
4218 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4219
4220 // Refs discovery is already non-atomic.
4221 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4222 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4223 conc_workers()->start_task(&tsk);
4224 while (tsk.yielded()) {
4225 tsk.coordinator_yield();
4226 conc_workers()->continue_task(&tsk);
4227 }
4228 // If the task was aborted, _restart_addr will be non-NULL
4229 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4230 while (_restart_addr != NULL) {
4231 // XXX For now we do not make use of ABORTED state and have not
4232 // yet implemented the right abort semantics (even in the original
4233 // single-threaded CMS case). That needs some more investigation
4234 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4235 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4236 // If _restart_addr is non-NULL, a marking stack overflow
4237 // occurred; we need to do a fresh marking iteration from the
4238 // indicated restart address.
4239 if (_foregroundGCIsActive && asynch) {
4240 // We may be running into repeated stack overflows, having
4241 // reached the limit of the stack size, while making very
4242 // slow forward progress. It may be best to bail out and
4243 // let the foreground collector do its job.
4244 // Clear _restart_addr, so that foreground GC
4245 // works from scratch. This avoids the headache of
4246 // a "rescan" which would otherwise be needed because
4247 // of the dirty mod union table & card table.
4248 _restart_addr = NULL;
4249 return false;
4250 }
4251 // Adjust the task to restart from _restart_addr
4252 tsk.reset(_restart_addr);
4253 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4254 _restart_addr);
4255 _restart_addr = NULL;
4256 // Get the workers going again
4257 conc_workers()->start_task(&tsk);
4258 while (tsk.yielded()) {
4259 tsk.coordinator_yield();
4260 conc_workers()->continue_task(&tsk);
4261 }
4262 }
4263 assert(tsk.completed(), "Inconsistency");
4264 assert(tsk.result() == true, "Inconsistency");
4265 return true;
4266 }
4267
4268 bool CMSCollector::do_marking_st(bool asynch) {
4269 ResourceMark rm;
4270 HandleMark hm;
4271
4272 // Temporarily make refs discovery single threaded (non-MT)
4273 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4274 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4275 &_markStack, CMSYield && asynch);
4276 // the last argument to iterate indicates whether the iteration
4277 // should be incremental with periodic yields.
4278 _markBitMap.iterate(&markFromRootsClosure);
4279 // If _restart_addr is non-NULL, a marking stack overflow
4280 // occurred; we need to do a fresh iteration from the
4281 // indicated restart address.
4282 while (_restart_addr != NULL) {
4283 if (_foregroundGCIsActive && asynch) {
4284 // We may be running into repeated stack overflows, having
4285 // reached the limit of the stack size, while making very
4286 // slow forward progress. It may be best to bail out and
4287 // let the foreground collector do its job.
4288 // Clear _restart_addr, so that foreground GC
4289 // works from scratch. This avoids the headache of
4290 // a "rescan" which would otherwise be needed because
4291 // of the dirty mod union table & card table.
4292 _restart_addr = NULL;
4293 return false; // indicating failure to complete marking
4294 }
4295 // Deal with stack overflow:
4296 // we restart marking from _restart_addr
4297 HeapWord* ra = _restart_addr;
4298 markFromRootsClosure.reset(ra);
4299 _restart_addr = NULL;
4300 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4301 }
4302 return true;
4303 }
4304
4305 void CMSCollector::preclean() {
4306 check_correct_thread_executing();
4307 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4308 verify_work_stacks_empty();
4309 verify_overflow_empty();
4310 _abort_preclean = false;
4311 if (CMSPrecleaningEnabled) {
4312 _eden_chunk_index = 0;
4313 size_t used = get_eden_used();
4314 size_t capacity = get_eden_capacity();
4315 // Don't start sampling unless we will get sufficiently
4316 // many samples.
4317 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4318 * CMSScheduleRemarkEdenPenetration)) {
4319 _start_sampling = true;
4320 } else {
4321 _start_sampling = false;
4322 }
4323 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4324 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4325 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4326 }
4327 CMSTokenSync x(true); // is cms thread
4328 if (CMSPrecleaningEnabled) {
4329 sample_eden();
4330 _collectorState = AbortablePreclean;
4331 } else {
4332 _collectorState = FinalMarking;
4333 }
4334 verify_work_stacks_empty();
4335 verify_overflow_empty();
4336 }
4337
4338 // Try and schedule the remark such that young gen
4339 // occupancy is CMSScheduleRemarkEdenPenetration %.
4340 void CMSCollector::abortable_preclean() {
4341 check_correct_thread_executing();
4342 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4343 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4344
4345 // If Eden's current occupancy is below this threshold,
4346 // immediately schedule the remark; else preclean
4347 // past the next scavenge in an effort to
4348 // schedule the pause as described avove. By choosing
4349 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4350 // we will never do an actual abortable preclean cycle.
4351 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4352 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4353 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4354 // We need more smarts in the abortable preclean
4355 // loop below to deal with cases where allocation
4356 // in young gen is very very slow, and our precleaning
4357 // is running a losing race against a horde of
4358 // mutators intent on flooding us with CMS updates
4359 // (dirty cards).
4360 // One, admittedly dumb, strategy is to give up
4361 // after a certain number of abortable precleaning loops
4362 // or after a certain maximum time. We want to make
4363 // this smarter in the next iteration.
4364 // XXX FIX ME!!! YSR
4365 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4366 while (!(should_abort_preclean() ||
4367 ConcurrentMarkSweepThread::should_terminate())) {
4368 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4369 cumworkdone += workdone;
4370 loops++;
4371 // Voluntarily terminate abortable preclean phase if we have
4372 // been at it for too long.
4373 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4374 loops >= CMSMaxAbortablePrecleanLoops) {
4375 if (PrintGCDetails) {
4376 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4377 }
4378 break;
4379 }
4380 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4381 if (PrintGCDetails) {
4382 gclog_or_tty->print(" CMS: abort preclean due to time ");
4383 }
4384 break;
4385 }
4386 // If we are doing little work each iteration, we should
4387 // take a short break.
4388 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4389 // Sleep for some time, waiting for work to accumulate
4390 stopTimer();
4391 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4392 startTimer();
4393 waited++;
4394 }
4395 }
4396 if (PrintCMSStatistics > 0) {
4397 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4398 loops, waited, cumworkdone);
4399 }
4400 }
4401 CMSTokenSync x(true); // is cms thread
4402 if (_collectorState != Idling) {
4403 assert(_collectorState == AbortablePreclean,
4404 "Spontaneous state transition?");
4405 _collectorState = FinalMarking;
4406 } // Else, a foreground collection completed this CMS cycle.
4407 return;
4408 }
4409
4410 // Respond to an Eden sampling opportunity
4411 void CMSCollector::sample_eden() {
4412 // Make sure a young gc cannot sneak in between our
4413 // reading and recording of a sample.
4414 assert(Thread::current()->is_ConcurrentGC_thread(),
4415 "Only the cms thread may collect Eden samples");
4416 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4417 "Should collect samples while holding CMS token");
4418 if (!_start_sampling) {
4419 return;
4420 }
4421 if (_eden_chunk_array) {
4422 if (_eden_chunk_index < _eden_chunk_capacity) {
4423 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4424 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4425 "Unexpected state of Eden");
4426 // We'd like to check that what we just sampled is an oop-start address;
4427 // however, we cannot do that here since the object may not yet have been
4428 // initialized. So we'll instead do the check when we _use_ this sample
4429 // later.
4430 if (_eden_chunk_index == 0 ||
4431 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4432 _eden_chunk_array[_eden_chunk_index-1])
4433 >= CMSSamplingGrain)) {
4434 _eden_chunk_index++; // commit sample
4435 }
4436 }
4437 }
4438 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4439 size_t used = get_eden_used();
4440 size_t capacity = get_eden_capacity();
4441 assert(used <= capacity, "Unexpected state of Eden");
4442 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4443 _abort_preclean = true;
4444 }
4445 }
4446 }
4447
4448
4449 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4450 assert(_collectorState == Precleaning ||
4451 _collectorState == AbortablePreclean, "incorrect state");
4452 ResourceMark rm;
4453 HandleMark hm;
4454
4455 // Precleaning is currently not MT but the reference processor
4456 // may be set for MT. Disable it temporarily here.
4457 ReferenceProcessor* rp = ref_processor();
4458 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4459
4460 // Do one pass of scrubbing the discovered reference lists
4461 // to remove any reference objects with strongly-reachable
4462 // referents.
4463 if (clean_refs) {
4464 CMSPrecleanRefsYieldClosure yield_cl(this);
4465 assert(rp->span().equals(_span), "Spans should be equal");
4466 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4467 &_markStack, true /* preclean */);
4468 CMSDrainMarkingStackClosure complete_trace(this,
4469 _span, &_markBitMap, &_markStack,
4470 &keep_alive, true /* preclean */);
4471
4472 // We don't want this step to interfere with a young
4473 // collection because we don't want to take CPU
4474 // or memory bandwidth away from the young GC threads
4475 // (which may be as many as there are CPUs).
4476 // Note that we don't need to protect ourselves from
4477 // interference with mutators because they can't
4478 // manipulate the discovered reference lists nor affect
4479 // the computed reachability of the referents, the
4480 // only properties manipulated by the precleaning
4481 // of these reference lists.
4482 stopTimer();
4483 CMSTokenSyncWithLocks x(true /* is cms thread */,
4484 bitMapLock());
4485 startTimer();
4486 sample_eden();
4487
4488 // The following will yield to allow foreground
4489 // collection to proceed promptly. XXX YSR:
4490 // The code in this method may need further
4491 // tweaking for better performance and some restructuring
4492 // for cleaner interfaces.
4493 rp->preclean_discovered_references(
4494 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl);
4495 }
4496
4497 if (clean_survivor) { // preclean the active survivor space(s)
4498 assert(_young_gen->kind() == Generation::DefNew ||
4499 _young_gen->kind() == Generation::ParNew ||
4500 _young_gen->kind() == Generation::ASParNew,
4501 "incorrect type for cast");
4502 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4503 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4504 &_markBitMap, &_modUnionTable,
4505 &_markStack, true /* precleaning phase */);
4506 stopTimer();
4507 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4508 bitMapLock());
4509 startTimer();
4510 unsigned int before_count =
4511 GenCollectedHeap::heap()->total_collections();
4512 SurvivorSpacePrecleanClosure
4513 sss_cl(this, _span, &_markBitMap, &_markStack,
4514 &pam_cl, before_count, CMSYield);
4515 dng->from()->object_iterate_careful(&sss_cl);
4516 dng->to()->object_iterate_careful(&sss_cl);
4517 }
4518 MarkRefsIntoAndScanClosure
4519 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4520 &_markStack, this, CMSYield,
4521 true /* precleaning phase */);
4522 // CAUTION: The following closure has persistent state that may need to
4523 // be reset upon a decrease in the sequence of addresses it
4524 // processes.
4525 ScanMarkedObjectsAgainCarefullyClosure
4526 smoac_cl(this, _span,
4527 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4528
4529 // Preclean dirty cards in ModUnionTable and CardTable using
4530 // appropriate convergence criterion;
4531 // repeat CMSPrecleanIter times unless we find that
4532 // we are losing.
4533 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4534 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4535 "Bad convergence multiplier");
4536 assert(CMSPrecleanThreshold >= 100,
4537 "Unreasonably low CMSPrecleanThreshold");
4538
4539 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4540 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4541 numIter < CMSPrecleanIter;
4542 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4543 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4544 if (Verbose && PrintGCDetails) {
4545 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4546 }
4547 // Either there are very few dirty cards, so re-mark
4548 // pause will be small anyway, or our pre-cleaning isn't
4549 // that much faster than the rate at which cards are being
4550 // dirtied, so we might as well stop and re-mark since
4551 // precleaning won't improve our re-mark time by much.
4552 if (curNumCards <= CMSPrecleanThreshold ||
4553 (numIter > 0 &&
4554 (curNumCards * CMSPrecleanDenominator >
4555 lastNumCards * CMSPrecleanNumerator))) {
4556 numIter++;
4557 cumNumCards += curNumCards;
4558 break;
4559 }
4560 }
4561
4562 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4563
4564 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4565 cumNumCards += curNumCards;
4566 if (PrintGCDetails && PrintCMSStatistics != 0) {
4567 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4568 curNumCards, cumNumCards, numIter);
4569 }
4570 return cumNumCards; // as a measure of useful work done
4571 }
4572
4573 // PRECLEANING NOTES:
4574 // Precleaning involves:
4575 // . reading the bits of the modUnionTable and clearing the set bits.
4576 // . For the cards corresponding to the set bits, we scan the
4577 // objects on those cards. This means we need the free_list_lock
4578 // so that we can safely iterate over the CMS space when scanning
4579 // for oops.
4580 // . When we scan the objects, we'll be both reading and setting
4581 // marks in the marking bit map, so we'll need the marking bit map.
4582 // . For protecting _collector_state transitions, we take the CGC_lock.
4583 // Note that any races in the reading of of card table entries by the
4584 // CMS thread on the one hand and the clearing of those entries by the
4585 // VM thread or the setting of those entries by the mutator threads on the
4586 // other are quite benign. However, for efficiency it makes sense to keep
4587 // the VM thread from racing with the CMS thread while the latter is
4588 // dirty card info to the modUnionTable. We therefore also use the
4589 // CGC_lock to protect the reading of the card table and the mod union
4590 // table by the CM thread.
4591 // . We run concurrently with mutator updates, so scanning
4592 // needs to be done carefully -- we should not try to scan
4593 // potentially uninitialized objects.
4594 //
4595 // Locking strategy: While holding the CGC_lock, we scan over and
4596 // reset a maximal dirty range of the mod union / card tables, then lock
4597 // the free_list_lock and bitmap lock to do a full marking, then
4598 // release these locks; and repeat the cycle. This allows for a
4599 // certain amount of fairness in the sharing of these locks between
4600 // the CMS collector on the one hand, and the VM thread and the
4601 // mutators on the other.
4602
4603 // NOTE: preclean_mod_union_table() and preclean_card_table()
4604 // further below are largely identical; if you need to modify
4605 // one of these methods, please check the other method too.
4606
4607 size_t CMSCollector::preclean_mod_union_table(
4608 ConcurrentMarkSweepGeneration* gen,
4609 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4610 verify_work_stacks_empty();
4611 verify_overflow_empty();
4612
4613 // strategy: starting with the first card, accumulate contiguous
4614 // ranges of dirty cards; clear these cards, then scan the region
4615 // covered by these cards.
4616
4617 // Since all of the MUT is committed ahead, we can just use
4618 // that, in case the generations expand while we are precleaning.
4619 // It might also be fine to just use the committed part of the
4620 // generation, but we might potentially miss cards when the
4621 // generation is rapidly expanding while we are in the midst
4622 // of precleaning.
4623 HeapWord* startAddr = gen->reserved().start();
4624 HeapWord* endAddr = gen->reserved().end();
4625
4626 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4627
4628 size_t numDirtyCards, cumNumDirtyCards;
4629 HeapWord *nextAddr, *lastAddr;
4630 for (cumNumDirtyCards = numDirtyCards = 0,
4631 nextAddr = lastAddr = startAddr;
4632 nextAddr < endAddr;
4633 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4634
4635 ResourceMark rm;
4636 HandleMark hm;
4637
4638 MemRegion dirtyRegion;
4639 {
4640 stopTimer();
4641 // Potential yield point
4642 CMSTokenSync ts(true);
4643 startTimer();
4644 sample_eden();
4645 // Get dirty region starting at nextOffset (inclusive),
4646 // simultaneously clearing it.
4647 dirtyRegion =
4648 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4649 assert(dirtyRegion.start() >= nextAddr,
4650 "returned region inconsistent?");
4651 }
4652 // Remember where the next search should begin.
4653 // The returned region (if non-empty) is a right open interval,
4654 // so lastOffset is obtained from the right end of that
4655 // interval.
4656 lastAddr = dirtyRegion.end();
4657 // Should do something more transparent and less hacky XXX
4658 numDirtyCards =
4659 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4660
4661 // We'll scan the cards in the dirty region (with periodic
4662 // yields for foreground GC as needed).
4663 if (!dirtyRegion.is_empty()) {
4664 assert(numDirtyCards > 0, "consistency check");
4665 HeapWord* stop_point = NULL;
4666 stopTimer();
4667 // Potential yield point
4668 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4669 bitMapLock());
4670 startTimer();
4671 {
4672 verify_work_stacks_empty();
4673 verify_overflow_empty();
4674 sample_eden();
4675 stop_point =
4676 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4677 }
4678 if (stop_point != NULL) {
4679 // The careful iteration stopped early either because it found an
4680 // uninitialized object, or because we were in the midst of an
4681 // "abortable preclean", which should now be aborted. Redirty
4682 // the bits corresponding to the partially-scanned or unscanned
4683 // cards. We'll either restart at the next block boundary or
4684 // abort the preclean.
4685 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4686 "Should only be AbortablePreclean.");
4687 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4688 if (should_abort_preclean()) {
4689 break; // out of preclean loop
4690 } else {
4691 // Compute the next address at which preclean should pick up;
4692 // might need bitMapLock in order to read P-bits.
4693 lastAddr = next_card_start_after_block(stop_point);
4694 }
4695 }
4696 } else {
4697 assert(lastAddr == endAddr, "consistency check");
4698 assert(numDirtyCards == 0, "consistency check");
4699 break;
4700 }
4701 }
4702 verify_work_stacks_empty();
4703 verify_overflow_empty();
4704 return cumNumDirtyCards;
4705 }
4706
4707 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4708 // below are largely identical; if you need to modify
4709 // one of these methods, please check the other method too.
4710
4711 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4712 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4713 // strategy: it's similar to precleamModUnionTable above, in that
4714 // we accumulate contiguous ranges of dirty cards, mark these cards
4715 // precleaned, then scan the region covered by these cards.
4716 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4717 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4718
4719 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4720
4721 size_t numDirtyCards, cumNumDirtyCards;
4722 HeapWord *lastAddr, *nextAddr;
4723
4724 for (cumNumDirtyCards = numDirtyCards = 0,
4725 nextAddr = lastAddr = startAddr;
4726 nextAddr < endAddr;
4727 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4728
4729 ResourceMark rm;
4730 HandleMark hm;
4731
4732 MemRegion dirtyRegion;
4733 {
4734 // See comments in "Precleaning notes" above on why we
4735 // do this locking. XXX Could the locking overheads be
4736 // too high when dirty cards are sparse? [I don't think so.]
4737 stopTimer();
4738 CMSTokenSync x(true); // is cms thread
4739 startTimer();
4740 sample_eden();
4741 // Get and clear dirty region from card table
4742 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4743 MemRegion(nextAddr, endAddr),
4744 true,
4745 CardTableModRefBS::precleaned_card_val());
4746
4747 assert(dirtyRegion.start() >= nextAddr,
4748 "returned region inconsistent?");
4749 }
4750 lastAddr = dirtyRegion.end();
4751 numDirtyCards =
4752 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4753
4754 if (!dirtyRegion.is_empty()) {
4755 stopTimer();
4756 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4757 startTimer();
4758 sample_eden();
4759 verify_work_stacks_empty();
4760 verify_overflow_empty();
4761 HeapWord* stop_point =
4762 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4763 if (stop_point != NULL) {
4764 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4765 "Should only be AbortablePreclean.");
4766 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4767 if (should_abort_preclean()) {
4768 break; // out of preclean loop
4769 } else {
4770 // Compute the next address at which preclean should pick up.
4771 lastAddr = next_card_start_after_block(stop_point);
4772 }
4773 }
4774 } else {
4775 break;
4776 }
4777 }
4778 verify_work_stacks_empty();
4779 verify_overflow_empty();
4780 return cumNumDirtyCards;
4781 }
4782
4783 class PrecleanKlassClosure : public KlassClosure {
4784 CMKlassClosure _cm_klass_closure;
4785 public:
4786 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4787 void do_klass(Klass* k) {
4788 if (k->has_accumulated_modified_oops()) {
4789 k->clear_accumulated_modified_oops();
4790
4791 _cm_klass_closure.do_klass(k);
4792 }
4793 }
4794 };
4795
4796 // The freelist lock is needed to prevent asserts, is it really needed?
4797 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4798
4799 cl->set_freelistLock(freelistLock);
4800
4801 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4802
4803 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4804 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4805 PrecleanKlassClosure preclean_klass_closure(cl);
4806 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4807
4808 verify_work_stacks_empty();
4809 verify_overflow_empty();
4810 }
4811
4812 void CMSCollector::checkpointRootsFinal(bool asynch,
4813 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4814 assert(_collectorState == FinalMarking, "incorrect state transition?");
4815 check_correct_thread_executing();
4816 // world is stopped at this checkpoint
4817 assert(SafepointSynchronize::is_at_safepoint(),
4818 "world should be stopped");
4819 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4820
4821 verify_work_stacks_empty();
4822 verify_overflow_empty();
4823
4824 SpecializationStats::clear();
4825 if (PrintGCDetails) {
4826 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4827 _young_gen->used() / K,
4828 _young_gen->capacity() / K);
4829 }
4830 if (asynch) {
4831 if (CMSScavengeBeforeRemark) {
4832 GenCollectedHeap* gch = GenCollectedHeap::heap();
4833 // Temporarily set flag to false, GCH->do_collection will
4834 // expect it to be false and set to true
4835 FlagSetting fl(gch->_is_gc_active, false);
4836 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4837 PrintGCDetails && Verbose, true, gclog_or_tty);)
4838 int level = _cmsGen->level() - 1;
4839 if (level >= 0) {
4840 gch->do_collection(true, // full (i.e. force, see below)
4841 false, // !clear_all_soft_refs
4842 0, // size
4843 false, // is_tlab
4844 level // max_level
4845 );
4846 }
4847 }
4848 FreelistLocker x(this);
4849 MutexLockerEx y(bitMapLock(),
4850 Mutex::_no_safepoint_check_flag);
4851 assert(!init_mark_was_synchronous, "but that's impossible!");
4852 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4853 } else {
4854 // already have all the locks
4855 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4856 init_mark_was_synchronous);
4857 }
4858 verify_work_stacks_empty();
4859 verify_overflow_empty();
4860 SpecializationStats::print();
4861 }
4862
4863 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4864 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4865
4866 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4867
4868 assert(haveFreelistLocks(), "must have free list locks");
4869 assert_lock_strong(bitMapLock());
4870
4871 if (UseAdaptiveSizePolicy) {
4872 size_policy()->checkpoint_roots_final_begin();
4873 }
4874
4875 ResourceMark rm;
4876 HandleMark hm;
4877
4878 GenCollectedHeap* gch = GenCollectedHeap::heap();
4879
4880 if (should_unload_classes()) {
4881 CodeCache::gc_prologue();
4882 }
4883 assert(haveFreelistLocks(), "must have free list locks");
4884 assert_lock_strong(bitMapLock());
4885
4886 if (!init_mark_was_synchronous) {
4887 // We might assume that we need not fill TLAB's when
4888 // CMSScavengeBeforeRemark is set, because we may have just done
4889 // a scavenge which would have filled all TLAB's -- and besides
4890 // Eden would be empty. This however may not always be the case --
4891 // for instance although we asked for a scavenge, it may not have
4892 // happened because of a JNI critical section. We probably need
4893 // a policy for deciding whether we can in that case wait until
4894 // the critical section releases and then do the remark following
4895 // the scavenge, and skip it here. In the absence of that policy,
4896 // or of an indication of whether the scavenge did indeed occur,
4897 // we cannot rely on TLAB's having been filled and must do
4898 // so here just in case a scavenge did not happen.
4899 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4900 // Update the saved marks which may affect the root scans.
4901 gch->save_marks();
4902
4903 {
4904 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4905
4906 // Note on the role of the mod union table:
4907 // Since the marker in "markFromRoots" marks concurrently with
4908 // mutators, it is possible for some reachable objects not to have been
4909 // scanned. For instance, an only reference to an object A was
4910 // placed in object B after the marker scanned B. Unless B is rescanned,
4911 // A would be collected. Such updates to references in marked objects
4912 // are detected via the mod union table which is the set of all cards
4913 // dirtied since the first checkpoint in this GC cycle and prior to
4914 // the most recent young generation GC, minus those cleaned up by the
4915 // concurrent precleaning.
4916 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4917 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4918 do_remark_parallel();
4919 } else {
4920 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4921 gclog_or_tty);
4922 do_remark_non_parallel();
4923 }
4924 }
4925 } else {
4926 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4927 // The initial mark was stop-world, so there's no rescanning to
4928 // do; go straight on to the next step below.
4929 }
4930 verify_work_stacks_empty();
4931 verify_overflow_empty();
4932
4933 {
4934 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4935 refProcessingWork(asynch, clear_all_soft_refs);
4936 }
4937 verify_work_stacks_empty();
4938 verify_overflow_empty();
4939
4940 if (should_unload_classes()) {
4941 CodeCache::gc_epilogue();
4942 }
4943 JvmtiExport::gc_epilogue();
4944
4945 // If we encountered any (marking stack / work queue) overflow
4946 // events during the current CMS cycle, take appropriate
4947 // remedial measures, where possible, so as to try and avoid
4948 // recurrence of that condition.
4949 assert(_markStack.isEmpty(), "No grey objects");
4950 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4951 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4952 if (ser_ovflw > 0) {
4953 if (PrintCMSStatistics != 0) {
4954 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4955 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4956 ", kac_preclean="SIZE_FORMAT")",
4957 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4958 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4959 }
4960 _markStack.expand();
4961 _ser_pmc_remark_ovflw = 0;
4962 _ser_pmc_preclean_ovflw = 0;
4963 _ser_kac_preclean_ovflw = 0;
4964 _ser_kac_ovflw = 0;
4965 }
4966 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4967 if (PrintCMSStatistics != 0) {
4968 gclog_or_tty->print_cr("Work queue overflow (benign) "
4969 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4970 _par_pmc_remark_ovflw, _par_kac_ovflw);
4971 }
4972 _par_pmc_remark_ovflw = 0;
4973 _par_kac_ovflw = 0;
4974 }
4975 if (PrintCMSStatistics != 0) {
4976 if (_markStack._hit_limit > 0) {
4977 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4978 _markStack._hit_limit);
4979 }
4980 if (_markStack._failed_double > 0) {
4981 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4982 " current capacity "SIZE_FORMAT,
4983 _markStack._failed_double,
4984 _markStack.capacity());
4985 }
4986 }
4987 _markStack._hit_limit = 0;
4988 _markStack._failed_double = 0;
4989
4990 if ((VerifyAfterGC || VerifyDuringGC) &&
4991 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4992 verify_after_remark();
4993 }
4994
4995 // Change under the freelistLocks.
4996 _collectorState = Sweeping;
4997 // Call isAllClear() under bitMapLock
4998 assert(_modUnionTable.isAllClear(),
4999 "Should be clear by end of the final marking");
5000 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5001 "Should be clear by end of the final marking");
5002 if (UseAdaptiveSizePolicy) {
5003 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5004 }
5005 }
5006
5007 // Parallel remark task
5008 class CMSParRemarkTask: public AbstractGangTask {
5009 CMSCollector* _collector;
5010 int _n_workers;
5011 CompactibleFreeListSpace* _cms_space;
5012
5013 // The per-thread work queues, available here for stealing.
5014 OopTaskQueueSet* _task_queues;
5015 ParallelTaskTerminator _term;
5016
5017 public:
5018 // A value of 0 passed to n_workers will cause the number of
5019 // workers to be taken from the active workers in the work gang.
5020 CMSParRemarkTask(CMSCollector* collector,
5021 CompactibleFreeListSpace* cms_space,
5022 int n_workers, FlexibleWorkGang* workers,
5023 OopTaskQueueSet* task_queues):
5024 AbstractGangTask("Rescan roots and grey objects in parallel"),
5025 _collector(collector),
5026 _cms_space(cms_space),
5027 _n_workers(n_workers),
5028 _task_queues(task_queues),
5029 _term(n_workers, task_queues) { }
5030
5031 OopTaskQueueSet* task_queues() { return _task_queues; }
5032
5033 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5034
5035 ParallelTaskTerminator* terminator() { return &_term; }
5036 int n_workers() { return _n_workers; }
5037
5038 void work(uint worker_id);
5039
5040 private:
5041 // Work method in support of parallel rescan ... of young gen spaces
5042 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5043 ContiguousSpace* space,
5044 HeapWord** chunk_array, size_t chunk_top);
5045
5046 // ... of dirty cards in old space
5047 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5048 Par_MarkRefsIntoAndScanClosure* cl);
5049
5050 // ... work stealing for the above
5051 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5052 };
5053
5054 class RemarkKlassClosure : public KlassClosure {
5055 CMKlassClosure _cm_klass_closure;
5056 public:
5057 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5058 void do_klass(Klass* k) {
5059 // Check if we have modified any oops in the Klass during the concurrent marking.
5060 if (k->has_accumulated_modified_oops()) {
5061 k->clear_accumulated_modified_oops();
5062
5063 // We could have transfered the current modified marks to the accumulated marks,
5064 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5065 } else if (k->has_modified_oops()) {
5066 // Don't clear anything, this info is needed by the next young collection.
5067 } else {
5068 // No modified oops in the Klass.
5069 return;
5070 }
5071
5072 // The klass has modified fields, need to scan the klass.
5073 _cm_klass_closure.do_klass(k);
5074 }
5075 };
5076
5077 // work_queue(i) is passed to the closure
5078 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5079 // also is passed to do_dirty_card_rescan_tasks() and to
5080 // do_work_steal() to select the i-th task_queue.
5081
5082 void CMSParRemarkTask::work(uint worker_id) {
5083 elapsedTimer _timer;
5084 ResourceMark rm;
5085 HandleMark hm;
5086
5087 // ---------- rescan from roots --------------
5088 _timer.start();
5089 GenCollectedHeap* gch = GenCollectedHeap::heap();
5090 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5091 _collector->_span, _collector->ref_processor(),
5092 &(_collector->_markBitMap),
5093 work_queue(worker_id));
5094
5095 // Rescan young gen roots first since these are likely
5096 // coarsely partitioned and may, on that account, constitute
5097 // the critical path; thus, it's best to start off that
5098 // work first.
5099 // ---------- young gen roots --------------
5100 {
5101 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5102 EdenSpace* eden_space = dng->eden();
5103 ContiguousSpace* from_space = dng->from();
5104 ContiguousSpace* to_space = dng->to();
5105
5106 HeapWord** eca = _collector->_eden_chunk_array;
5107 size_t ect = _collector->_eden_chunk_index;
5108 HeapWord** sca = _collector->_survivor_chunk_array;
5109 size_t sct = _collector->_survivor_chunk_index;
5110
5111 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5112 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5113
5114 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5115 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5116 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5117
5118 _timer.stop();
5119 if (PrintCMSStatistics != 0) {
5120 gclog_or_tty->print_cr(
5121 "Finished young gen rescan work in %dth thread: %3.3f sec",
5122 worker_id, _timer.seconds());
5123 }
5124 }
5125
5126 // ---------- remaining roots --------------
5127 _timer.reset();
5128 _timer.start();
5129 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5130 false, // yg was scanned above
5131 false, // this is parallel code
5132 false, // not scavenging
5133 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5134 &par_mrias_cl,
5135 true, // walk all of code cache if (so & SO_CodeCache)
5136 NULL,
5137 NULL); // The dirty klasses will be handled below
5138 assert(_collector->should_unload_classes()
5139 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5140 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5141 _timer.stop();
5142 if (PrintCMSStatistics != 0) {
5143 gclog_or_tty->print_cr(
5144 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5145 worker_id, _timer.seconds());
5146 }
5147
5148 // ---------- unhandled CLD scanning ----------
5149 if (worker_id == 0) { // Single threaded at the moment.
5150 _timer.reset();
5151 _timer.start();
5152
5153 // Scan all new class loader data objects and new dependencies that were
5154 // introduced during concurrent marking.
5155 ResourceMark rm;
5156 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5157 for (int i = 0; i < array->length(); i++) {
5158 par_mrias_cl.do_class_loader_data(array->at(i));
5159 }
5160
5161 // We don't need to keep track of new CLDs anymore.
5162 ClassLoaderDataGraph::remember_new_clds(false);
5163
5164 _timer.stop();
5165 if (PrintCMSStatistics != 0) {
5166 gclog_or_tty->print_cr(
5167 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5168 worker_id, _timer.seconds());
5169 }
5170 }
5171
5172 // ---------- dirty klass scanning ----------
5173 if (worker_id == 0) { // Single threaded at the moment.
5174 _timer.reset();
5175 _timer.start();
5176
5177 // Scan all classes that was dirtied during the concurrent marking phase.
5178 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5179 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5180
5181 _timer.stop();
5182 if (PrintCMSStatistics != 0) {
5183 gclog_or_tty->print_cr(
5184 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5185 worker_id, _timer.seconds());
5186 }
5187 }
5188
5189 // We might have added oops to ClassLoaderData::_handles during the
5190 // concurrent marking phase. These oops point to newly allocated objects
5191 // that are guaranteed to be kept alive. Either by the direct allocation
5192 // code, or when the young collector processes the strong roots. Hence,
5193 // we don't have to revisit the _handles block during the remark phase.
5194
5195 // ---------- rescan dirty cards ------------
5196 _timer.reset();
5197 _timer.start();
5198
5199 // Do the rescan tasks for each of the two spaces
5200 // (cms_space) in turn.
5201 // "worker_id" is passed to select the task_queue for "worker_id"
5202 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5203 _timer.stop();
5204 if (PrintCMSStatistics != 0) {
5205 gclog_or_tty->print_cr(
5206 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5207 worker_id, _timer.seconds());
5208 }
5209
5210 // ---------- steal work from other threads ...
5211 // ---------- ... and drain overflow list.
5212 _timer.reset();
5213 _timer.start();
5214 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5215 _timer.stop();
5216 if (PrintCMSStatistics != 0) {
5217 gclog_or_tty->print_cr(
5218 "Finished work stealing in %dth thread: %3.3f sec",
5219 worker_id, _timer.seconds());
5220 }
5221 }
5222
5223 // Note that parameter "i" is not used.
5224 void
5225 CMSParRemarkTask::do_young_space_rescan(int i,
5226 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5227 HeapWord** chunk_array, size_t chunk_top) {
5228 // Until all tasks completed:
5229 // . claim an unclaimed task
5230 // . compute region boundaries corresponding to task claimed
5231 // using chunk_array
5232 // . par_oop_iterate(cl) over that region
5233
5234 ResourceMark rm;
5235 HandleMark hm;
5236
5237 SequentialSubTasksDone* pst = space->par_seq_tasks();
5238 assert(pst->valid(), "Uninitialized use?");
5239
5240 uint nth_task = 0;
5241 uint n_tasks = pst->n_tasks();
5242
5243 HeapWord *start, *end;
5244 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5245 // We claimed task # nth_task; compute its boundaries.
5246 if (chunk_top == 0) { // no samples were taken
5247 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5248 start = space->bottom();
5249 end = space->top();
5250 } else if (nth_task == 0) {
5251 start = space->bottom();
5252 end = chunk_array[nth_task];
5253 } else if (nth_task < (uint)chunk_top) {
5254 assert(nth_task >= 1, "Control point invariant");
5255 start = chunk_array[nth_task - 1];
5256 end = chunk_array[nth_task];
5257 } else {
5258 assert(nth_task == (uint)chunk_top, "Control point invariant");
5259 start = chunk_array[chunk_top - 1];
5260 end = space->top();
5261 }
5262 MemRegion mr(start, end);
5263 // Verify that mr is in space
5264 assert(mr.is_empty() || space->used_region().contains(mr),
5265 "Should be in space");
5266 // Verify that "start" is an object boundary
5267 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5268 "Should be an oop");
5269 space->par_oop_iterate(mr, cl);
5270 }
5271 pst->all_tasks_completed();
5272 }
5273
5274 void
5275 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5276 CompactibleFreeListSpace* sp, int i,
5277 Par_MarkRefsIntoAndScanClosure* cl) {
5278 // Until all tasks completed:
5279 // . claim an unclaimed task
5280 // . compute region boundaries corresponding to task claimed
5281 // . transfer dirty bits ct->mut for that region
5282 // . apply rescanclosure to dirty mut bits for that region
5283
5284 ResourceMark rm;
5285 HandleMark hm;
5286
5287 OopTaskQueue* work_q = work_queue(i);
5288 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5289 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5290 // CAUTION: This closure has state that persists across calls to
5291 // the work method dirty_range_iterate_clear() in that it has
5292 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5293 // use of that state in the imbedded UpwardsObjectClosure instance
5294 // assumes that the cards are always iterated (even if in parallel
5295 // by several threads) in monotonically increasing order per each
5296 // thread. This is true of the implementation below which picks
5297 // card ranges (chunks) in monotonically increasing order globally
5298 // and, a-fortiori, in monotonically increasing order per thread
5299 // (the latter order being a subsequence of the former).
5300 // If the work code below is ever reorganized into a more chaotic
5301 // work-partitioning form than the current "sequential tasks"
5302 // paradigm, the use of that persistent state will have to be
5303 // revisited and modified appropriately. See also related
5304 // bug 4756801 work on which should examine this code to make
5305 // sure that the changes there do not run counter to the
5306 // assumptions made here and necessary for correctness and
5307 // efficiency. Note also that this code might yield inefficient
5308 // behaviour in the case of very large objects that span one or
5309 // more work chunks. Such objects would potentially be scanned
5310 // several times redundantly. Work on 4756801 should try and
5311 // address that performance anomaly if at all possible. XXX
5312 MemRegion full_span = _collector->_span;
5313 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5314 MarkFromDirtyCardsClosure
5315 greyRescanClosure(_collector, full_span, // entire span of interest
5316 sp, bm, work_q, cl);
5317
5318 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5319 assert(pst->valid(), "Uninitialized use?");
5320 uint nth_task = 0;
5321 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5322 MemRegion span = sp->used_region();
5323 HeapWord* start_addr = span.start();
5324 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5325 alignment);
5326 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5327 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5328 start_addr, "Check alignment");
5329 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5330 chunk_size, "Check alignment");
5331
5332 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5333 // Having claimed the nth_task, compute corresponding mem-region,
5334 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5335 // The alignment restriction ensures that we do not need any
5336 // synchronization with other gang-workers while setting or
5337 // clearing bits in thus chunk of the MUT.
5338 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5339 start_addr + (nth_task+1)*chunk_size);
5340 // The last chunk's end might be way beyond end of the
5341 // used region. In that case pull back appropriately.
5342 if (this_span.end() > end_addr) {
5343 this_span.set_end(end_addr);
5344 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5345 }
5346 // Iterate over the dirty cards covering this chunk, marking them
5347 // precleaned, and setting the corresponding bits in the mod union
5348 // table. Since we have been careful to partition at Card and MUT-word
5349 // boundaries no synchronization is needed between parallel threads.
5350 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5351 &modUnionClosure);
5352
5353 // Having transferred these marks into the modUnionTable,
5354 // rescan the marked objects on the dirty cards in the modUnionTable.
5355 // Even if this is at a synchronous collection, the initial marking
5356 // may have been done during an asynchronous collection so there
5357 // may be dirty bits in the mod-union table.
5358 _collector->_modUnionTable.dirty_range_iterate_clear(
5359 this_span, &greyRescanClosure);
5360 _collector->_modUnionTable.verifyNoOneBitsInRange(
5361 this_span.start(),
5362 this_span.end());
5363 }
5364 pst->all_tasks_completed(); // declare that i am done
5365 }
5366
5367 // . see if we can share work_queues with ParNew? XXX
5368 void
5369 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5370 int* seed) {
5371 OopTaskQueue* work_q = work_queue(i);
5372 NOT_PRODUCT(int num_steals = 0;)
5373 oop obj_to_scan;
5374 CMSBitMap* bm = &(_collector->_markBitMap);
5375
5376 while (true) {
5377 // Completely finish any left over work from (an) earlier round(s)
5378 cl->trim_queue(0);
5379 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5380 (size_t)ParGCDesiredObjsFromOverflowList);
5381 // Now check if there's any work in the overflow list
5382 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5383 // only affects the number of attempts made to get work from the
5384 // overflow list and does not affect the number of workers. Just
5385 // pass ParallelGCThreads so this behavior is unchanged.
5386 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5387 work_q,
5388 ParallelGCThreads)) {
5389 // found something in global overflow list;
5390 // not yet ready to go stealing work from others.
5391 // We'd like to assert(work_q->size() != 0, ...)
5392 // because we just took work from the overflow list,
5393 // but of course we can't since all of that could have
5394 // been already stolen from us.
5395 // "He giveth and He taketh away."
5396 continue;
5397 }
5398 // Verify that we have no work before we resort to stealing
5399 assert(work_q->size() == 0, "Have work, shouldn't steal");
5400 // Try to steal from other queues that have work
5401 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5402 NOT_PRODUCT(num_steals++;)
5403 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5404 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5405 // Do scanning work
5406 obj_to_scan->oop_iterate(cl);
5407 // Loop around, finish this work, and try to steal some more
5408 } else if (terminator()->offer_termination()) {
5409 break; // nirvana from the infinite cycle
5410 }
5411 }
5412 NOT_PRODUCT(
5413 if (PrintCMSStatistics != 0) {
5414 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5415 }
5416 )
5417 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5418 "Else our work is not yet done");
5419 }
5420
5421 // Return a thread-local PLAB recording array, as appropriate.
5422 void* CMSCollector::get_data_recorder(int thr_num) {
5423 if (_survivor_plab_array != NULL &&
5424 (CMSPLABRecordAlways ||
5425 (_collectorState > Marking && _collectorState < FinalMarking))) {
5426 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5427 ChunkArray* ca = &_survivor_plab_array[thr_num];
5428 ca->reset(); // clear it so that fresh data is recorded
5429 return (void*) ca;
5430 } else {
5431 return NULL;
5432 }
5433 }
5434
5435 // Reset all the thread-local PLAB recording arrays
5436 void CMSCollector::reset_survivor_plab_arrays() {
5437 for (uint i = 0; i < ParallelGCThreads; i++) {
5438 _survivor_plab_array[i].reset();
5439 }
5440 }
5441
5442 // Merge the per-thread plab arrays into the global survivor chunk
5443 // array which will provide the partitioning of the survivor space
5444 // for CMS rescan.
5445 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5446 int no_of_gc_threads) {
5447 assert(_survivor_plab_array != NULL, "Error");
5448 assert(_survivor_chunk_array != NULL, "Error");
5449 assert(_collectorState == FinalMarking, "Error");
5450 for (int j = 0; j < no_of_gc_threads; j++) {
5451 _cursor[j] = 0;
5452 }
5453 HeapWord* top = surv->top();
5454 size_t i;
5455 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5456 HeapWord* min_val = top; // Higher than any PLAB address
5457 uint min_tid = 0; // position of min_val this round
5458 for (int j = 0; j < no_of_gc_threads; j++) {
5459 ChunkArray* cur_sca = &_survivor_plab_array[j];
5460 if (_cursor[j] == cur_sca->end()) {
5461 continue;
5462 }
5463 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5464 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5465 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5466 if (cur_val < min_val) {
5467 min_tid = j;
5468 min_val = cur_val;
5469 } else {
5470 assert(cur_val < top, "All recorded addresses should be less");
5471 }
5472 }
5473 // At this point min_val and min_tid are respectively
5474 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5475 // and the thread (j) that witnesses that address.
5476 // We record this address in the _survivor_chunk_array[i]
5477 // and increment _cursor[min_tid] prior to the next round i.
5478 if (min_val == top) {
5479 break;
5480 }
5481 _survivor_chunk_array[i] = min_val;
5482 _cursor[min_tid]++;
5483 }
5484 // We are all done; record the size of the _survivor_chunk_array
5485 _survivor_chunk_index = i; // exclusive: [0, i)
5486 if (PrintCMSStatistics > 0) {
5487 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5488 }
5489 // Verify that we used up all the recorded entries
5490 #ifdef ASSERT
5491 size_t total = 0;
5492 for (int j = 0; j < no_of_gc_threads; j++) {
5493 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5494 total += _cursor[j];
5495 }
5496 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5497 // Check that the merged array is in sorted order
5498 if (total > 0) {
5499 for (size_t i = 0; i < total - 1; i++) {
5500 if (PrintCMSStatistics > 0) {
5501 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5502 i, _survivor_chunk_array[i]);
5503 }
5504 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5505 "Not sorted");
5506 }
5507 }
5508 #endif // ASSERT
5509 }
5510
5511 // Set up the space's par_seq_tasks structure for work claiming
5512 // for parallel rescan of young gen.
5513 // See ParRescanTask where this is currently used.
5514 void
5515 CMSCollector::
5516 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5517 assert(n_threads > 0, "Unexpected n_threads argument");
5518 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5519
5520 // Eden space
5521 {
5522 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5523 assert(!pst->valid(), "Clobbering existing data?");
5524 // Each valid entry in [0, _eden_chunk_index) represents a task.
5525 size_t n_tasks = _eden_chunk_index + 1;
5526 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5527 // Sets the condition for completion of the subtask (how many threads
5528 // need to finish in order to be done).
5529 pst->set_n_threads(n_threads);
5530 pst->set_n_tasks((int)n_tasks);
5531 }
5532
5533 // Merge the survivor plab arrays into _survivor_chunk_array
5534 if (_survivor_plab_array != NULL) {
5535 merge_survivor_plab_arrays(dng->from(), n_threads);
5536 } else {
5537 assert(_survivor_chunk_index == 0, "Error");
5538 }
5539
5540 // To space
5541 {
5542 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5543 assert(!pst->valid(), "Clobbering existing data?");
5544 // Sets the condition for completion of the subtask (how many threads
5545 // need to finish in order to be done).
5546 pst->set_n_threads(n_threads);
5547 pst->set_n_tasks(1);
5548 assert(pst->valid(), "Error");
5549 }
5550
5551 // From space
5552 {
5553 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5554 assert(!pst->valid(), "Clobbering existing data?");
5555 size_t n_tasks = _survivor_chunk_index + 1;
5556 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5557 // Sets the condition for completion of the subtask (how many threads
5558 // need to finish in order to be done).
5559 pst->set_n_threads(n_threads);
5560 pst->set_n_tasks((int)n_tasks);
5561 assert(pst->valid(), "Error");
5562 }
5563 }
5564
5565 // Parallel version of remark
5566 void CMSCollector::do_remark_parallel() {
5567 GenCollectedHeap* gch = GenCollectedHeap::heap();
5568 FlexibleWorkGang* workers = gch->workers();
5569 assert(workers != NULL, "Need parallel worker threads.");
5570 // Choose to use the number of GC workers most recently set
5571 // into "active_workers". If active_workers is not set, set it
5572 // to ParallelGCThreads.
5573 int n_workers = workers->active_workers();
5574 if (n_workers == 0) {
5575 assert(n_workers > 0, "Should have been set during scavenge");
5576 n_workers = ParallelGCThreads;
5577 workers->set_active_workers(n_workers);
5578 }
5579 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5580
5581 CMSParRemarkTask tsk(this,
5582 cms_space,
5583 n_workers, workers, task_queues());
5584
5585 // Set up for parallel process_strong_roots work.
5586 gch->set_par_threads(n_workers);
5587 // We won't be iterating over the cards in the card table updating
5588 // the younger_gen cards, so we shouldn't call the following else
5589 // the verification code as well as subsequent younger_refs_iterate
5590 // code would get confused. XXX
5591 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5592
5593 // The young gen rescan work will not be done as part of
5594 // process_strong_roots (which currently doesn't knw how to
5595 // parallelize such a scan), but rather will be broken up into
5596 // a set of parallel tasks (via the sampling that the [abortable]
5597 // preclean phase did of EdenSpace, plus the [two] tasks of
5598 // scanning the [two] survivor spaces. Further fine-grain
5599 // parallelization of the scanning of the survivor spaces
5600 // themselves, and of precleaning of the younger gen itself
5601 // is deferred to the future.
5602 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5603
5604 // The dirty card rescan work is broken up into a "sequence"
5605 // of parallel tasks (per constituent space) that are dynamically
5606 // claimed by the parallel threads.
5607 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5608
5609 // It turns out that even when we're using 1 thread, doing the work in a
5610 // separate thread causes wide variance in run times. We can't help this
5611 // in the multi-threaded case, but we special-case n=1 here to get
5612 // repeatable measurements of the 1-thread overhead of the parallel code.
5613 if (n_workers > 1) {
5614 // Make refs discovery MT-safe, if it isn't already: it may not
5615 // necessarily be so, since it's possible that we are doing
5616 // ST marking.
5617 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5618 GenCollectedHeap::StrongRootsScope srs(gch);
5619 workers->run_task(&tsk);
5620 } else {
5621 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5622 GenCollectedHeap::StrongRootsScope srs(gch);
5623 tsk.work(0);
5624 }
5625
5626 gch->set_par_threads(0); // 0 ==> non-parallel.
5627 // restore, single-threaded for now, any preserved marks
5628 // as a result of work_q overflow
5629 restore_preserved_marks_if_any();
5630 }
5631
5632 // Non-parallel version of remark
5633 void CMSCollector::do_remark_non_parallel() {
5634 ResourceMark rm;
5635 HandleMark hm;
5636 GenCollectedHeap* gch = GenCollectedHeap::heap();
5637 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5638
5639 MarkRefsIntoAndScanClosure
5640 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5641 &_markStack, this,
5642 false /* should_yield */, false /* not precleaning */);
5643 MarkFromDirtyCardsClosure
5644 markFromDirtyCardsClosure(this, _span,
5645 NULL, // space is set further below
5646 &_markBitMap, &_markStack, &mrias_cl);
5647 {
5648 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5649 // Iterate over the dirty cards, setting the corresponding bits in the
5650 // mod union table.
5651 {
5652 ModUnionClosure modUnionClosure(&_modUnionTable);
5653 _ct->ct_bs()->dirty_card_iterate(
5654 _cmsGen->used_region(),
5655 &modUnionClosure);
5656 }
5657 // Having transferred these marks into the modUnionTable, we just need
5658 // to rescan the marked objects on the dirty cards in the modUnionTable.
5659 // The initial marking may have been done during an asynchronous
5660 // collection so there may be dirty bits in the mod-union table.
5661 const int alignment =
5662 CardTableModRefBS::card_size * BitsPerWord;
5663 {
5664 // ... First handle dirty cards in CMS gen
5665 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5666 MemRegion ur = _cmsGen->used_region();
5667 HeapWord* lb = ur.start();
5668 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5669 MemRegion cms_span(lb, ub);
5670 _modUnionTable.dirty_range_iterate_clear(cms_span,
5671 &markFromDirtyCardsClosure);
5672 verify_work_stacks_empty();
5673 if (PrintCMSStatistics != 0) {
5674 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5675 markFromDirtyCardsClosure.num_dirty_cards());
5676 }
5677 }
5678 }
5679 if (VerifyDuringGC &&
5680 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5681 HandleMark hm; // Discard invalid handles created during verification
5682 Universe::verify(true);
5683 }
5684 {
5685 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5686
5687 verify_work_stacks_empty();
5688
5689 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5690 GenCollectedHeap::StrongRootsScope srs(gch);
5691 gch->gen_process_strong_roots(_cmsGen->level(),
5692 true, // younger gens as roots
5693 false, // use the local StrongRootsScope
5694 false, // not scavenging
5695 SharedHeap::ScanningOption(roots_scanning_options()),
5696 &mrias_cl,
5697 true, // walk code active on stacks
5698 NULL,
5699 NULL); // The dirty klasses will be handled below
5700
5701 assert(should_unload_classes()
5702 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5703 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5704 }
5705
5706 {
5707 TraceTime t("visit unhandled CLDs", PrintGCDetails, false, gclog_or_tty);
5708
5709 verify_work_stacks_empty();
5710
5711 // Scan all class loader data objects that might have been introduced
5712 // during concurrent marking.
5713 ResourceMark rm;
5714 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5715 for (int i = 0; i < array->length(); i++) {
5716 mrias_cl.do_class_loader_data(array->at(i));
5717 }
5718
5719 // We don't need to keep track of new CLDs anymore.
5720 ClassLoaderDataGraph::remember_new_clds(false);
5721
5722 verify_work_stacks_empty();
5723 }
5724
5725 {
5726 TraceTime t("dirty klass scan", PrintGCDetails, false, gclog_or_tty);
5727
5728 verify_work_stacks_empty();
5729
5730 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5731 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5732
5733 verify_work_stacks_empty();
5734 }
5735
5736 // We might have added oops to ClassLoaderData::_handles during the
5737 // concurrent marking phase. These oops point to newly allocated objects
5738 // that are guaranteed to be kept alive. Either by the direct allocation
5739 // code, or when the young collector processes the strong roots. Hence,
5740 // we don't have to revisit the _handles block during the remark phase.
5741
5742 verify_work_stacks_empty();
5743 // Restore evacuated mark words, if any, used for overflow list links
5744 if (!CMSOverflowEarlyRestoration) {
5745 restore_preserved_marks_if_any();
5746 }
5747 verify_overflow_empty();
5748 }
5749
5750 ////////////////////////////////////////////////////////
5751 // Parallel Reference Processing Task Proxy Class
5752 ////////////////////////////////////////////////////////
5753 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5754 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5755 CMSCollector* _collector;
5756 CMSBitMap* _mark_bit_map;
5757 const MemRegion _span;
5758 ProcessTask& _task;
5759
5760 public:
5761 CMSRefProcTaskProxy(ProcessTask& task,
5762 CMSCollector* collector,
5763 const MemRegion& span,
5764 CMSBitMap* mark_bit_map,
5765 AbstractWorkGang* workers,
5766 OopTaskQueueSet* task_queues):
5767 // XXX Should superclass AGTWOQ also know about AWG since it knows
5768 // about the task_queues used by the AWG? Then it could initialize
5769 // the terminator() object. See 6984287. The set_for_termination()
5770 // below is a temporary band-aid for the regression in 6984287.
5771 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5772 task_queues),
5773 _task(task),
5774 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5775 {
5776 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5777 "Inconsistency in _span");
5778 set_for_termination(workers->active_workers());
5779 }
5780
5781 OopTaskQueueSet* task_queues() { return queues(); }
5782
5783 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5784
5785 void do_work_steal(int i,
5786 CMSParDrainMarkingStackClosure* drain,
5787 CMSParKeepAliveClosure* keep_alive,
5788 int* seed);
5789
5790 virtual void work(uint worker_id);
5791 };
5792
5793 void CMSRefProcTaskProxy::work(uint worker_id) {
5794 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5795 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5796 _mark_bit_map,
5797 work_queue(worker_id));
5798 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5799 _mark_bit_map,
5800 work_queue(worker_id));
5801 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5802 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5803 if (_task.marks_oops_alive()) {
5804 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5805 _collector->hash_seed(worker_id));
5806 }
5807 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5808 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5809 }
5810
5811 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5812 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5813 EnqueueTask& _task;
5814
5815 public:
5816 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5817 : AbstractGangTask("Enqueue reference objects in parallel"),
5818 _task(task)
5819 { }
5820
5821 virtual void work(uint worker_id)
5822 {
5823 _task.work(worker_id);
5824 }
5825 };
5826
5827 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5828 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5829 _span(span),
5830 _bit_map(bit_map),
5831 _work_queue(work_queue),
5832 _mark_and_push(collector, span, bit_map, work_queue),
5833 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5834 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5835 { }
5836
5837 // . see if we can share work_queues with ParNew? XXX
5838 void CMSRefProcTaskProxy::do_work_steal(int i,
5839 CMSParDrainMarkingStackClosure* drain,
5840 CMSParKeepAliveClosure* keep_alive,
5841 int* seed) {
5842 OopTaskQueue* work_q = work_queue(i);
5843 NOT_PRODUCT(int num_steals = 0;)
5844 oop obj_to_scan;
5845
5846 while (true) {
5847 // Completely finish any left over work from (an) earlier round(s)
5848 drain->trim_queue(0);
5849 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5850 (size_t)ParGCDesiredObjsFromOverflowList);
5851 // Now check if there's any work in the overflow list
5852 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5853 // only affects the number of attempts made to get work from the
5854 // overflow list and does not affect the number of workers. Just
5855 // pass ParallelGCThreads so this behavior is unchanged.
5856 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5857 work_q,
5858 ParallelGCThreads)) {
5859 // Found something in global overflow list;
5860 // not yet ready to go stealing work from others.
5861 // We'd like to assert(work_q->size() != 0, ...)
5862 // because we just took work from the overflow list,
5863 // but of course we can't, since all of that might have
5864 // been already stolen from us.
5865 continue;
5866 }
5867 // Verify that we have no work before we resort to stealing
5868 assert(work_q->size() == 0, "Have work, shouldn't steal");
5869 // Try to steal from other queues that have work
5870 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5871 NOT_PRODUCT(num_steals++;)
5872 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5873 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5874 // Do scanning work
5875 obj_to_scan->oop_iterate(keep_alive);
5876 // Loop around, finish this work, and try to steal some more
5877 } else if (terminator()->offer_termination()) {
5878 break; // nirvana from the infinite cycle
5879 }
5880 }
5881 NOT_PRODUCT(
5882 if (PrintCMSStatistics != 0) {
5883 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5884 }
5885 )
5886 }
5887
5888 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5889 {
5890 GenCollectedHeap* gch = GenCollectedHeap::heap();
5891 FlexibleWorkGang* workers = gch->workers();
5892 assert(workers != NULL, "Need parallel worker threads.");
5893 CMSRefProcTaskProxy rp_task(task, &_collector,
5894 _collector.ref_processor()->span(),
5895 _collector.markBitMap(),
5896 workers, _collector.task_queues());
5897 workers->run_task(&rp_task);
5898 }
5899
5900 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5901 {
5902
5903 GenCollectedHeap* gch = GenCollectedHeap::heap();
5904 FlexibleWorkGang* workers = gch->workers();
5905 assert(workers != NULL, "Need parallel worker threads.");
5906 CMSRefEnqueueTaskProxy enq_task(task);
5907 workers->run_task(&enq_task);
5908 }
5909
5910 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5911
5912 ResourceMark rm;
5913 HandleMark hm;
5914
5915 ReferenceProcessor* rp = ref_processor();
5916 assert(rp->span().equals(_span), "Spans should be equal");
5917 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5918 // Process weak references.
5919 rp->setup_policy(clear_all_soft_refs);
5920 verify_work_stacks_empty();
5921
5922 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5923 &_markStack, false /* !preclean */);
5924 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5925 _span, &_markBitMap, &_markStack,
5926 &cmsKeepAliveClosure, false /* !preclean */);
5927 {
5928 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5929 if (rp->processing_is_mt()) {
5930 // Set the degree of MT here. If the discovery is done MT, there
5931 // may have been a different number of threads doing the discovery
5932 // and a different number of discovered lists may have Ref objects.
5933 // That is OK as long as the Reference lists are balanced (see
5934 // balance_all_queues() and balance_queues()).
5935 GenCollectedHeap* gch = GenCollectedHeap::heap();
5936 int active_workers = ParallelGCThreads;
5937 FlexibleWorkGang* workers = gch->workers();
5938 if (workers != NULL) {
5939 active_workers = workers->active_workers();
5940 // The expectation is that active_workers will have already
5941 // been set to a reasonable value. If it has not been set,
5942 // investigate.
5943 assert(active_workers > 0, "Should have been set during scavenge");
5944 }
5945 rp->set_active_mt_degree(active_workers);
5946 CMSRefProcTaskExecutor task_executor(*this);
5947 rp->process_discovered_references(&_is_alive_closure,
5948 &cmsKeepAliveClosure,
5949 &cmsDrainMarkingStackClosure,
5950 &task_executor);
5951 } else {
5952 rp->process_discovered_references(&_is_alive_closure,
5953 &cmsKeepAliveClosure,
5954 &cmsDrainMarkingStackClosure,
5955 NULL);
5956 }
5957 verify_work_stacks_empty();
5958 }
5959
5960 if (should_unload_classes()) {
5961 {
5962 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5963
5964 // Follow SystemDictionary roots and unload classes
5965 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5966
5967 // Follow CodeCache roots and unload any methods marked for unloading
5968 CodeCache::do_unloading(&_is_alive_closure,
5969 &cmsKeepAliveClosure,
5970 purged_class);
5971
5972 cmsDrainMarkingStackClosure.do_void();
5973 verify_work_stacks_empty();
5974
5975 // Update subklass/sibling/implementor links in KlassKlass descendants
5976 Klass::clean_weak_klass_links(&_is_alive_closure);
5977 // Nothing should have been pushed onto the working stacks.
5978 verify_work_stacks_empty();
5979 }
5980
5981 {
5982 TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
5983 // Clean up unreferenced symbols in symbol table.
5984 SymbolTable::unlink();
5985 }
5986 }
5987
5988 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
5989 // Need to check if we really scanned the StringTable.
5990 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
5991 TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
5992 // Now clean up stale oops in StringTable
5993 StringTable::unlink(&_is_alive_closure);
5994 }
5995
5996 verify_work_stacks_empty();
5997 // Restore any preserved marks as a result of mark stack or
5998 // work queue overflow
5999 restore_preserved_marks_if_any(); // done single-threaded for now
6000
6001 rp->set_enqueuing_is_done(true);
6002 if (rp->processing_is_mt()) {
6003 rp->balance_all_queues();
6004 CMSRefProcTaskExecutor task_executor(*this);
6005 rp->enqueue_discovered_references(&task_executor);
6006 } else {
6007 rp->enqueue_discovered_references(NULL);
6008 }
6009 rp->verify_no_references_recorded();
6010 assert(!rp->discovery_enabled(), "should have been disabled");
6011 }
6012
6013 #ifndef PRODUCT
6014 void CMSCollector::check_correct_thread_executing() {
6015 Thread* t = Thread::current();
6016 // Only the VM thread or the CMS thread should be here.
6017 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6018 "Unexpected thread type");
6019 // If this is the vm thread, the foreground process
6020 // should not be waiting. Note that _foregroundGCIsActive is
6021 // true while the foreground collector is waiting.
6022 if (_foregroundGCShouldWait) {
6023 // We cannot be the VM thread
6024 assert(t->is_ConcurrentGC_thread(),
6025 "Should be CMS thread");
6026 } else {
6027 // We can be the CMS thread only if we are in a stop-world
6028 // phase of CMS collection.
6029 if (t->is_ConcurrentGC_thread()) {
6030 assert(_collectorState == InitialMarking ||
6031 _collectorState == FinalMarking,
6032 "Should be a stop-world phase");
6033 // The CMS thread should be holding the CMS_token.
6034 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6035 "Potential interference with concurrently "
6036 "executing VM thread");
6037 }
6038 }
6039 }
6040 #endif
6041
6042 void CMSCollector::sweep(bool asynch) {
6043 assert(_collectorState == Sweeping, "just checking");
6044 check_correct_thread_executing();
6045 verify_work_stacks_empty();
6046 verify_overflow_empty();
6047 increment_sweep_count();
6048 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6049
6050 _inter_sweep_timer.stop();
6051 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6052 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6053
6054 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6055 _intra_sweep_timer.reset();
6056 _intra_sweep_timer.start();
6057 if (asynch) {
6058 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6059 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6060 // First sweep the old gen
6061 {
6062 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6063 bitMapLock());
6064 sweepWork(_cmsGen, asynch);
6065 }
6066
6067 // Update Universe::_heap_*_at_gc figures.
6068 // We need all the free list locks to make the abstract state
6069 // transition from Sweeping to Resetting. See detailed note
6070 // further below.
6071 {
6072 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6073 // Update heap occupancy information which is used as
6074 // input to soft ref clearing policy at the next gc.
6075 Universe::update_heap_info_at_gc();
6076 _collectorState = Resizing;
6077 }
6078 } else {
6079 // already have needed locks
6080 sweepWork(_cmsGen, asynch);
6081 // Update heap occupancy information which is used as
6082 // input to soft ref clearing policy at the next gc.
6083 Universe::update_heap_info_at_gc();
6084 _collectorState = Resizing;
6085 }
6086 verify_work_stacks_empty();
6087 verify_overflow_empty();
6088
6089 _intra_sweep_timer.stop();
6090 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6091
6092 _inter_sweep_timer.reset();
6093 _inter_sweep_timer.start();
6094
6095 // We need to use a monotonically non-deccreasing time in ms
6096 // or we will see time-warp warnings and os::javaTimeMillis()
6097 // does not guarantee monotonicity.
6098 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6099 update_time_of_last_gc(now);
6100
6101 // NOTE on abstract state transitions:
6102 // Mutators allocate-live and/or mark the mod-union table dirty
6103 // based on the state of the collection. The former is done in
6104 // the interval [Marking, Sweeping] and the latter in the interval
6105 // [Marking, Sweeping). Thus the transitions into the Marking state
6106 // and out of the Sweeping state must be synchronously visible
6107 // globally to the mutators.
6108 // The transition into the Marking state happens with the world
6109 // stopped so the mutators will globally see it. Sweeping is
6110 // done asynchronously by the background collector so the transition
6111 // from the Sweeping state to the Resizing state must be done
6112 // under the freelistLock (as is the check for whether to
6113 // allocate-live and whether to dirty the mod-union table).
6114 assert(_collectorState == Resizing, "Change of collector state to"
6115 " Resizing must be done under the freelistLocks (plural)");
6116
6117 // Now that sweeping has been completed, we clear
6118 // the incremental_collection_failed flag,
6119 // thus inviting a younger gen collection to promote into
6120 // this generation. If such a promotion may still fail,
6121 // the flag will be set again when a young collection is
6122 // attempted.
6123 GenCollectedHeap* gch = GenCollectedHeap::heap();
6124 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6125 gch->update_full_collections_completed(_collection_count_start);
6126 }
6127
6128 // FIX ME!!! Looks like this belongs in CFLSpace, with
6129 // CMSGen merely delegating to it.
6130 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6131 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6132 HeapWord* minAddr = _cmsSpace->bottom();
6133 HeapWord* largestAddr =
6134 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6135 if (largestAddr == NULL) {
6136 // The dictionary appears to be empty. In this case
6137 // try to coalesce at the end of the heap.
6138 largestAddr = _cmsSpace->end();
6139 }
6140 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6141 size_t nearLargestOffset =
6142 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6143 if (PrintFLSStatistics != 0) {
6144 gclog_or_tty->print_cr(
6145 "CMS: Large Block: " PTR_FORMAT ";"
6146 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6147 largestAddr,
6148 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6149 }
6150 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6151 }
6152
6153 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6154 return addr >= _cmsSpace->nearLargestChunk();
6155 }
6156
6157 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6158 return _cmsSpace->find_chunk_at_end();
6159 }
6160
6161 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6162 bool full) {
6163 // The next lower level has been collected. Gather any statistics
6164 // that are of interest at this point.
6165 if (!full && (current_level + 1) == level()) {
6166 // Gather statistics on the young generation collection.
6167 collector()->stats().record_gc0_end(used());
6168 }
6169 }
6170
6171 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6172 GenCollectedHeap* gch = GenCollectedHeap::heap();
6173 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6174 "Wrong type of heap");
6175 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6176 gch->gen_policy()->size_policy();
6177 assert(sp->is_gc_cms_adaptive_size_policy(),
6178 "Wrong type of size policy");
6179 return sp;
6180 }
6181
6182 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6183 if (PrintGCDetails && Verbose) {
6184 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6185 }
6186 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6187 _debug_collection_type =
6188 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6189 if (PrintGCDetails && Verbose) {
6190 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6191 }
6192 }
6193
6194 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6195 bool asynch) {
6196 // We iterate over the space(s) underlying this generation,
6197 // checking the mark bit map to see if the bits corresponding
6198 // to specific blocks are marked or not. Blocks that are
6199 // marked are live and are not swept up. All remaining blocks
6200 // are swept up, with coalescing on-the-fly as we sweep up
6201 // contiguous free and/or garbage blocks:
6202 // We need to ensure that the sweeper synchronizes with allocators
6203 // and stop-the-world collectors. In particular, the following
6204 // locks are used:
6205 // . CMS token: if this is held, a stop the world collection cannot occur
6206 // . freelistLock: if this is held no allocation can occur from this
6207 // generation by another thread
6208 // . bitMapLock: if this is held, no other thread can access or update
6209 //
6210
6211 // Note that we need to hold the freelistLock if we use
6212 // block iterate below; else the iterator might go awry if
6213 // a mutator (or promotion) causes block contents to change
6214 // (for instance if the allocator divvies up a block).
6215 // If we hold the free list lock, for all practical purposes
6216 // young generation GC's can't occur (they'll usually need to
6217 // promote), so we might as well prevent all young generation
6218 // GC's while we do a sweeping step. For the same reason, we might
6219 // as well take the bit map lock for the entire duration
6220
6221 // check that we hold the requisite locks
6222 assert(have_cms_token(), "Should hold cms token");
6223 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6224 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6225 "Should possess CMS token to sweep");
6226 assert_lock_strong(gen->freelistLock());
6227 assert_lock_strong(bitMapLock());
6228
6229 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6230 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6231 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6232 _inter_sweep_estimate.padded_average(),
6233 _intra_sweep_estimate.padded_average());
6234 gen->setNearLargestChunk();
6235
6236 {
6237 SweepClosure sweepClosure(this, gen, &_markBitMap,
6238 CMSYield && asynch);
6239 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6240 // We need to free-up/coalesce garbage/blocks from a
6241 // co-terminal free run. This is done in the SweepClosure
6242 // destructor; so, do not remove this scope, else the
6243 // end-of-sweep-census below will be off by a little bit.
6244 }
6245 gen->cmsSpace()->sweep_completed();
6246 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6247 if (should_unload_classes()) { // unloaded classes this cycle,
6248 _concurrent_cycles_since_last_unload = 0; // ... reset count
6249 } else { // did not unload classes,
6250 _concurrent_cycles_since_last_unload++; // ... increment count
6251 }
6252 }
6253
6254 // Reset CMS data structures (for now just the marking bit map)
6255 // preparatory for the next cycle.
6256 void CMSCollector::reset(bool asynch) {
6257 GenCollectedHeap* gch = GenCollectedHeap::heap();
6258 CMSAdaptiveSizePolicy* sp = size_policy();
6259 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6260 if (asynch) {
6261 CMSTokenSyncWithLocks ts(true, bitMapLock());
6262
6263 // If the state is not "Resetting", the foreground thread
6264 // has done a collection and the resetting.
6265 if (_collectorState != Resetting) {
6266 assert(_collectorState == Idling, "The state should only change"
6267 " because the foreground collector has finished the collection");
6268 return;
6269 }
6270
6271 // Clear the mark bitmap (no grey objects to start with)
6272 // for the next cycle.
6273 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6274 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6275
6276 HeapWord* curAddr = _markBitMap.startWord();
6277 while (curAddr < _markBitMap.endWord()) {
6278 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6279 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6280 _markBitMap.clear_large_range(chunk);
6281 if (ConcurrentMarkSweepThread::should_yield() &&
6282 !foregroundGCIsActive() &&
6283 CMSYield) {
6284 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6285 "CMS thread should hold CMS token");
6286 assert_lock_strong(bitMapLock());
6287 bitMapLock()->unlock();
6288 ConcurrentMarkSweepThread::desynchronize(true);
6289 ConcurrentMarkSweepThread::acknowledge_yield_request();
6290 stopTimer();
6291 if (PrintCMSStatistics != 0) {
6292 incrementYields();
6293 }
6294 icms_wait();
6295
6296 // See the comment in coordinator_yield()
6297 for (unsigned i = 0; i < CMSYieldSleepCount &&
6298 ConcurrentMarkSweepThread::should_yield() &&
6299 !CMSCollector::foregroundGCIsActive(); ++i) {
6300 os::sleep(Thread::current(), 1, false);
6301 ConcurrentMarkSweepThread::acknowledge_yield_request();
6302 }
6303
6304 ConcurrentMarkSweepThread::synchronize(true);
6305 bitMapLock()->lock_without_safepoint_check();
6306 startTimer();
6307 }
6308 curAddr = chunk.end();
6309 }
6310 // A successful mostly concurrent collection has been done.
6311 // Because only the full (i.e., concurrent mode failure) collections
6312 // are being measured for gc overhead limits, clean the "near" flag
6313 // and count.
6314 sp->reset_gc_overhead_limit_count();
6315 _collectorState = Idling;
6316 } else {
6317 // already have the lock
6318 assert(_collectorState == Resetting, "just checking");
6319 assert_lock_strong(bitMapLock());
6320 _markBitMap.clear_all();
6321 _collectorState = Idling;
6322 }
6323
6324 // Stop incremental mode after a cycle completes, so that any future cycles
6325 // are triggered by allocation.
6326 stop_icms();
6327
6328 NOT_PRODUCT(
6329 if (RotateCMSCollectionTypes) {
6330 _cmsGen->rotate_debug_collection_type();
6331 }
6332 )
6333 }
6334
6335 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6336 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6337 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6338 TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6339 TraceCollectorStats tcs(counters());
6340
6341 switch (op) {
6342 case CMS_op_checkpointRootsInitial: {
6343 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6344 checkpointRootsInitial(true); // asynch
6345 if (PrintGC) {
6346 _cmsGen->printOccupancy("initial-mark");
6347 }
6348 break;
6349 }
6350 case CMS_op_checkpointRootsFinal: {
6351 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6352 checkpointRootsFinal(true, // asynch
6353 false, // !clear_all_soft_refs
6354 false); // !init_mark_was_synchronous
6355 if (PrintGC) {
6356 _cmsGen->printOccupancy("remark");
6357 }
6358 break;
6359 }
6360 default:
6361 fatal("No such CMS_op");
6362 }
6363 }
6364
6365 #ifndef PRODUCT
6366 size_t const CMSCollector::skip_header_HeapWords() {
6367 return FreeChunk::header_size();
6368 }
6369
6370 // Try and collect here conditions that should hold when
6371 // CMS thread is exiting. The idea is that the foreground GC
6372 // thread should not be blocked if it wants to terminate
6373 // the CMS thread and yet continue to run the VM for a while
6374 // after that.
6375 void CMSCollector::verify_ok_to_terminate() const {
6376 assert(Thread::current()->is_ConcurrentGC_thread(),
6377 "should be called by CMS thread");
6378 assert(!_foregroundGCShouldWait, "should be false");
6379 // We could check here that all the various low-level locks
6380 // are not held by the CMS thread, but that is overkill; see
6381 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6382 // is checked.
6383 }
6384 #endif
6385
6386 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6387 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6388 "missing Printezis mark?");
6389 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6390 size_t size = pointer_delta(nextOneAddr + 1, addr);
6391 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6392 "alignment problem");
6393 assert(size >= 3, "Necessary for Printezis marks to work");
6394 return size;
6395 }
6396
6397 // A variant of the above (block_size_using_printezis_bits()) except
6398 // that we return 0 if the P-bits are not yet set.
6399 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6400 if (_markBitMap.isMarked(addr + 1)) {
6401 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6402 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6403 size_t size = pointer_delta(nextOneAddr + 1, addr);
6404 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6405 "alignment problem");
6406 assert(size >= 3, "Necessary for Printezis marks to work");
6407 return size;
6408 }
6409 return 0;
6410 }
6411
6412 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6413 size_t sz = 0;
6414 oop p = (oop)addr;
6415 if (p->klass_or_null() != NULL) {
6416 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6417 } else {
6418 sz = block_size_using_printezis_bits(addr);
6419 }
6420 assert(sz > 0, "size must be nonzero");
6421 HeapWord* next_block = addr + sz;
6422 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6423 CardTableModRefBS::card_size);
6424 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6425 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6426 "must be different cards");
6427 return next_card;
6428 }
6429
6430
6431 // CMS Bit Map Wrapper /////////////////////////////////////////
6432
6433 // Construct a CMS bit map infrastructure, but don't create the
6434 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6435 // further below.
6436 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6437 _bm(),
6438 _shifter(shifter),
6439 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6440 {
6441 _bmStartWord = 0;
6442 _bmWordSize = 0;
6443 }
6444
6445 bool CMSBitMap::allocate(MemRegion mr) {
6446 _bmStartWord = mr.start();
6447 _bmWordSize = mr.word_size();
6448 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6449 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6450 if (!brs.is_reserved()) {
6451 warning("CMS bit map allocation failure");
6452 return false;
6453 }
6454 // For now we'll just commit all of the bit map up fromt.
6455 // Later on we'll try to be more parsimonious with swap.
6456 if (!_virtual_space.initialize(brs, brs.size())) {
6457 warning("CMS bit map backing store failure");
6458 return false;
6459 }
6460 assert(_virtual_space.committed_size() == brs.size(),
6461 "didn't reserve backing store for all of CMS bit map?");
6462 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6463 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6464 _bmWordSize, "inconsistency in bit map sizing");
6465 _bm.set_size(_bmWordSize >> _shifter);
6466
6467 // bm.clear(); // can we rely on getting zero'd memory? verify below
6468 assert(isAllClear(),
6469 "Expected zero'd memory from ReservedSpace constructor");
6470 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6471 "consistency check");
6472 return true;
6473 }
6474
6475 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6476 HeapWord *next_addr, *end_addr, *last_addr;
6477 assert_locked();
6478 assert(covers(mr), "out-of-range error");
6479 // XXX assert that start and end are appropriately aligned
6480 for (next_addr = mr.start(), end_addr = mr.end();
6481 next_addr < end_addr; next_addr = last_addr) {
6482 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6483 last_addr = dirty_region.end();
6484 if (!dirty_region.is_empty()) {
6485 cl->do_MemRegion(dirty_region);
6486 } else {
6487 assert(last_addr == end_addr, "program logic");
6488 return;
6489 }
6490 }
6491 }
6492
6493 #ifndef PRODUCT
6494 void CMSBitMap::assert_locked() const {
6495 CMSLockVerifier::assert_locked(lock());
6496 }
6497
6498 bool CMSBitMap::covers(MemRegion mr) const {
6499 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6500 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6501 "size inconsistency");
6502 return (mr.start() >= _bmStartWord) &&
6503 (mr.end() <= endWord());
6504 }
6505
6506 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6507 return (start >= _bmStartWord && (start + size) <= endWord());
6508 }
6509
6510 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6511 // verify that there are no 1 bits in the interval [left, right)
6512 FalseBitMapClosure falseBitMapClosure;
6513 iterate(&falseBitMapClosure, left, right);
6514 }
6515
6516 void CMSBitMap::region_invariant(MemRegion mr)
6517 {
6518 assert_locked();
6519 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6520 assert(!mr.is_empty(), "unexpected empty region");
6521 assert(covers(mr), "mr should be covered by bit map");
6522 // convert address range into offset range
6523 size_t start_ofs = heapWordToOffset(mr.start());
6524 // Make sure that end() is appropriately aligned
6525 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6526 (1 << (_shifter+LogHeapWordSize))),
6527 "Misaligned mr.end()");
6528 size_t end_ofs = heapWordToOffset(mr.end());
6529 assert(end_ofs > start_ofs, "Should mark at least one bit");
6530 }
6531
6532 #endif
6533
6534 bool CMSMarkStack::allocate(size_t size) {
6535 // allocate a stack of the requisite depth
6536 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6537 size * sizeof(oop)));
6538 if (!rs.is_reserved()) {
6539 warning("CMSMarkStack allocation failure");
6540 return false;
6541 }
6542 if (!_virtual_space.initialize(rs, rs.size())) {
6543 warning("CMSMarkStack backing store failure");
6544 return false;
6545 }
6546 assert(_virtual_space.committed_size() == rs.size(),
6547 "didn't reserve backing store for all of CMS stack?");
6548 _base = (oop*)(_virtual_space.low());
6549 _index = 0;
6550 _capacity = size;
6551 NOT_PRODUCT(_max_depth = 0);
6552 return true;
6553 }
6554
6555 // XXX FIX ME !!! In the MT case we come in here holding a
6556 // leaf lock. For printing we need to take a further lock
6557 // which has lower rank. We need to recallibrate the two
6558 // lock-ranks involved in order to be able to rpint the
6559 // messages below. (Or defer the printing to the caller.
6560 // For now we take the expedient path of just disabling the
6561 // messages for the problematic case.)
6562 void CMSMarkStack::expand() {
6563 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6564 if (_capacity == MarkStackSizeMax) {
6565 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6566 // We print a warning message only once per CMS cycle.
6567 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6568 }
6569 return;
6570 }
6571 // Double capacity if possible
6572 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6573 // Do not give up existing stack until we have managed to
6574 // get the double capacity that we desired.
6575 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6576 new_capacity * sizeof(oop)));
6577 if (rs.is_reserved()) {
6578 // Release the backing store associated with old stack
6579 _virtual_space.release();
6580 // Reinitialize virtual space for new stack
6581 if (!_virtual_space.initialize(rs, rs.size())) {
6582 fatal("Not enough swap for expanded marking stack");
6583 }
6584 _base = (oop*)(_virtual_space.low());
6585 _index = 0;
6586 _capacity = new_capacity;
6587 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6588 // Failed to double capacity, continue;
6589 // we print a detail message only once per CMS cycle.
6590 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6591 SIZE_FORMAT"K",
6592 _capacity / K, new_capacity / K);
6593 }
6594 }
6595
6596
6597 // Closures
6598 // XXX: there seems to be a lot of code duplication here;
6599 // should refactor and consolidate common code.
6600
6601 // This closure is used to mark refs into the CMS generation in
6602 // the CMS bit map. Called at the first checkpoint. This closure
6603 // assumes that we do not need to re-mark dirty cards; if the CMS
6604 // generation on which this is used is not an oldest
6605 // generation then this will lose younger_gen cards!
6606
6607 MarkRefsIntoClosure::MarkRefsIntoClosure(
6608 MemRegion span, CMSBitMap* bitMap):
6609 _span(span),
6610 _bitMap(bitMap)
6611 {
6612 assert(_ref_processor == NULL, "deliberately left NULL");
6613 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6614 }
6615
6616 void MarkRefsIntoClosure::do_oop(oop obj) {
6617 // if p points into _span, then mark corresponding bit in _markBitMap
6618 assert(obj->is_oop(), "expected an oop");
6619 HeapWord* addr = (HeapWord*)obj;
6620 if (_span.contains(addr)) {
6621 // this should be made more efficient
6622 _bitMap->mark(addr);
6623 }
6624 }
6625
6626 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6627 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6628
6629 // A variant of the above, used for CMS marking verification.
6630 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6631 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6632 _span(span),
6633 _verification_bm(verification_bm),
6634 _cms_bm(cms_bm)
6635 {
6636 assert(_ref_processor == NULL, "deliberately left NULL");
6637 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6638 }
6639
6640 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6641 // if p points into _span, then mark corresponding bit in _markBitMap
6642 assert(obj->is_oop(), "expected an oop");
6643 HeapWord* addr = (HeapWord*)obj;
6644 if (_span.contains(addr)) {
6645 _verification_bm->mark(addr);
6646 if (!_cms_bm->isMarked(addr)) {
6647 oop(addr)->print();
6648 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6649 fatal("... aborting");
6650 }
6651 }
6652 }
6653
6654 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6655 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6656
6657 //////////////////////////////////////////////////
6658 // MarkRefsIntoAndScanClosure
6659 //////////////////////////////////////////////////
6660
6661 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6662 ReferenceProcessor* rp,
6663 CMSBitMap* bit_map,
6664 CMSBitMap* mod_union_table,
6665 CMSMarkStack* mark_stack,
6666 CMSCollector* collector,
6667 bool should_yield,
6668 bool concurrent_precleaning):
6669 _collector(collector),
6670 _span(span),
6671 _bit_map(bit_map),
6672 _mark_stack(mark_stack),
6673 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6674 mark_stack, concurrent_precleaning),
6675 _yield(should_yield),
6676 _concurrent_precleaning(concurrent_precleaning),
6677 _freelistLock(NULL)
6678 {
6679 _ref_processor = rp;
6680 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6681 }
6682
6683 // This closure is used to mark refs into the CMS generation at the
6684 // second (final) checkpoint, and to scan and transitively follow
6685 // the unmarked oops. It is also used during the concurrent precleaning
6686 // phase while scanning objects on dirty cards in the CMS generation.
6687 // The marks are made in the marking bit map and the marking stack is
6688 // used for keeping the (newly) grey objects during the scan.
6689 // The parallel version (Par_...) appears further below.
6690 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6691 if (obj != NULL) {
6692 assert(obj->is_oop(), "expected an oop");
6693 HeapWord* addr = (HeapWord*)obj;
6694 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6695 assert(_collector->overflow_list_is_empty(),
6696 "overflow list should be empty");
6697 if (_span.contains(addr) &&
6698 !_bit_map->isMarked(addr)) {
6699 // mark bit map (object is now grey)
6700 _bit_map->mark(addr);
6701 // push on marking stack (stack should be empty), and drain the
6702 // stack by applying this closure to the oops in the oops popped
6703 // from the stack (i.e. blacken the grey objects)
6704 bool res = _mark_stack->push(obj);
6705 assert(res, "Should have space to push on empty stack");
6706 do {
6707 oop new_oop = _mark_stack->pop();
6708 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6709 assert(_bit_map->isMarked((HeapWord*)new_oop),
6710 "only grey objects on this stack");
6711 // iterate over the oops in this oop, marking and pushing
6712 // the ones in CMS heap (i.e. in _span).
6713 new_oop->oop_iterate(&_pushAndMarkClosure);
6714 // check if it's time to yield
6715 do_yield_check();
6716 } while (!_mark_stack->isEmpty() ||
6717 (!_concurrent_precleaning && take_from_overflow_list()));
6718 // if marking stack is empty, and we are not doing this
6719 // during precleaning, then check the overflow list
6720 }
6721 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6722 assert(_collector->overflow_list_is_empty(),
6723 "overflow list was drained above");
6724 // We could restore evacuated mark words, if any, used for
6725 // overflow list links here because the overflow list is
6726 // provably empty here. That would reduce the maximum
6727 // size requirements for preserved_{oop,mark}_stack.
6728 // But we'll just postpone it until we are all done
6729 // so we can just stream through.
6730 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6731 _collector->restore_preserved_marks_if_any();
6732 assert(_collector->no_preserved_marks(), "No preserved marks");
6733 }
6734 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6735 "All preserved marks should have been restored above");
6736 }
6737 }
6738
6739 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6740 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6741
6742 void MarkRefsIntoAndScanClosure::do_yield_work() {
6743 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6744 "CMS thread should hold CMS token");
6745 assert_lock_strong(_freelistLock);
6746 assert_lock_strong(_bit_map->lock());
6747 // relinquish the free_list_lock and bitMaplock()
6748 _bit_map->lock()->unlock();
6749 _freelistLock->unlock();
6750 ConcurrentMarkSweepThread::desynchronize(true);
6751 ConcurrentMarkSweepThread::acknowledge_yield_request();
6752 _collector->stopTimer();
6753 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6754 if (PrintCMSStatistics != 0) {
6755 _collector->incrementYields();
6756 }
6757 _collector->icms_wait();
6758
6759 // See the comment in coordinator_yield()
6760 for (unsigned i = 0;
6761 i < CMSYieldSleepCount &&
6762 ConcurrentMarkSweepThread::should_yield() &&
6763 !CMSCollector::foregroundGCIsActive();
6764 ++i) {
6765 os::sleep(Thread::current(), 1, false);
6766 ConcurrentMarkSweepThread::acknowledge_yield_request();
6767 }
6768
6769 ConcurrentMarkSweepThread::synchronize(true);
6770 _freelistLock->lock_without_safepoint_check();
6771 _bit_map->lock()->lock_without_safepoint_check();
6772 _collector->startTimer();
6773 }
6774
6775 ///////////////////////////////////////////////////////////
6776 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6777 // MarkRefsIntoAndScanClosure
6778 ///////////////////////////////////////////////////////////
6779 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6780 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6781 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6782 _span(span),
6783 _bit_map(bit_map),
6784 _work_queue(work_queue),
6785 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6786 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6787 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6788 {
6789 _ref_processor = rp;
6790 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6791 }
6792
6793 // This closure is used to mark refs into the CMS generation at the
6794 // second (final) checkpoint, and to scan and transitively follow
6795 // the unmarked oops. The marks are made in the marking bit map and
6796 // the work_queue is used for keeping the (newly) grey objects during
6797 // the scan phase whence they are also available for stealing by parallel
6798 // threads. Since the marking bit map is shared, updates are
6799 // synchronized (via CAS).
6800 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6801 if (obj != NULL) {
6802 // Ignore mark word because this could be an already marked oop
6803 // that may be chained at the end of the overflow list.
6804 assert(obj->is_oop(true), "expected an oop");
6805 HeapWord* addr = (HeapWord*)obj;
6806 if (_span.contains(addr) &&
6807 !_bit_map->isMarked(addr)) {
6808 // mark bit map (object will become grey):
6809 // It is possible for several threads to be
6810 // trying to "claim" this object concurrently;
6811 // the unique thread that succeeds in marking the
6812 // object first will do the subsequent push on
6813 // to the work queue (or overflow list).
6814 if (_bit_map->par_mark(addr)) {
6815 // push on work_queue (which may not be empty), and trim the
6816 // queue to an appropriate length by applying this closure to
6817 // the oops in the oops popped from the stack (i.e. blacken the
6818 // grey objects)
6819 bool res = _work_queue->push(obj);
6820 assert(res, "Low water mark should be less than capacity?");
6821 trim_queue(_low_water_mark);
6822 } // Else, another thread claimed the object
6823 }
6824 }
6825 }
6826
6827 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6828 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6829
6830 // This closure is used to rescan the marked objects on the dirty cards
6831 // in the mod union table and the card table proper.
6832 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6833 oop p, MemRegion mr) {
6834
6835 size_t size = 0;
6836 HeapWord* addr = (HeapWord*)p;
6837 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6838 assert(_span.contains(addr), "we are scanning the CMS generation");
6839 // check if it's time to yield
6840 if (do_yield_check()) {
6841 // We yielded for some foreground stop-world work,
6842 // and we have been asked to abort this ongoing preclean cycle.
6843 return 0;
6844 }
6845 if (_bitMap->isMarked(addr)) {
6846 // it's marked; is it potentially uninitialized?
6847 if (p->klass_or_null() != NULL) {
6848 // an initialized object; ignore mark word in verification below
6849 // since we are running concurrent with mutators
6850 assert(p->is_oop(true), "should be an oop");
6851 if (p->is_objArray()) {
6852 // objArrays are precisely marked; restrict scanning
6853 // to dirty cards only.
6854 size = CompactibleFreeListSpace::adjustObjectSize(
6855 p->oop_iterate(_scanningClosure, mr));
6856 } else {
6857 // A non-array may have been imprecisely marked; we need
6858 // to scan object in its entirety.
6859 size = CompactibleFreeListSpace::adjustObjectSize(
6860 p->oop_iterate(_scanningClosure));
6861 }
6862 #ifdef DEBUG
6863 size_t direct_size =
6864 CompactibleFreeListSpace::adjustObjectSize(p->size());
6865 assert(size == direct_size, "Inconsistency in size");
6866 assert(size >= 3, "Necessary for Printezis marks to work");
6867 if (!_bitMap->isMarked(addr+1)) {
6868 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6869 } else {
6870 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6871 assert(_bitMap->isMarked(addr+size-1),
6872 "inconsistent Printezis mark");
6873 }
6874 #endif // DEBUG
6875 } else {
6876 // an unitialized object
6877 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6878 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6879 size = pointer_delta(nextOneAddr + 1, addr);
6880 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6881 "alignment problem");
6882 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6883 // will dirty the card when the klass pointer is installed in the
6884 // object (signalling the completion of initialization).
6885 }
6886 } else {
6887 // Either a not yet marked object or an uninitialized object
6888 if (p->klass_or_null() == NULL) {
6889 // An uninitialized object, skip to the next card, since
6890 // we may not be able to read its P-bits yet.
6891 assert(size == 0, "Initial value");
6892 } else {
6893 // An object not (yet) reached by marking: we merely need to
6894 // compute its size so as to go look at the next block.
6895 assert(p->is_oop(true), "should be an oop");
6896 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6897 }
6898 }
6899 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6900 return size;
6901 }
6902
6903 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6904 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6905 "CMS thread should hold CMS token");
6906 assert_lock_strong(_freelistLock);
6907 assert_lock_strong(_bitMap->lock());
6908 // relinquish the free_list_lock and bitMaplock()
6909 _bitMap->lock()->unlock();
6910 _freelistLock->unlock();
6911 ConcurrentMarkSweepThread::desynchronize(true);
6912 ConcurrentMarkSweepThread::acknowledge_yield_request();
6913 _collector->stopTimer();
6914 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6915 if (PrintCMSStatistics != 0) {
6916 _collector->incrementYields();
6917 }
6918 _collector->icms_wait();
6919
6920 // See the comment in coordinator_yield()
6921 for (unsigned i = 0; i < CMSYieldSleepCount &&
6922 ConcurrentMarkSweepThread::should_yield() &&
6923 !CMSCollector::foregroundGCIsActive(); ++i) {
6924 os::sleep(Thread::current(), 1, false);
6925 ConcurrentMarkSweepThread::acknowledge_yield_request();
6926 }
6927
6928 ConcurrentMarkSweepThread::synchronize(true);
6929 _freelistLock->lock_without_safepoint_check();
6930 _bitMap->lock()->lock_without_safepoint_check();
6931 _collector->startTimer();
6932 }
6933
6934
6935 //////////////////////////////////////////////////////////////////
6936 // SurvivorSpacePrecleanClosure
6937 //////////////////////////////////////////////////////////////////
6938 // This (single-threaded) closure is used to preclean the oops in
6939 // the survivor spaces.
6940 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6941
6942 HeapWord* addr = (HeapWord*)p;
6943 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6944 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6945 assert(p->klass_or_null() != NULL, "object should be initializd");
6946 // an initialized object; ignore mark word in verification below
6947 // since we are running concurrent with mutators
6948 assert(p->is_oop(true), "should be an oop");
6949 // Note that we do not yield while we iterate over
6950 // the interior oops of p, pushing the relevant ones
6951 // on our marking stack.
6952 size_t size = p->oop_iterate(_scanning_closure);
6953 do_yield_check();
6954 // Observe that below, we do not abandon the preclean
6955 // phase as soon as we should; rather we empty the
6956 // marking stack before returning. This is to satisfy
6957 // some existing assertions. In general, it may be a
6958 // good idea to abort immediately and complete the marking
6959 // from the grey objects at a later time.
6960 while (!_mark_stack->isEmpty()) {
6961 oop new_oop = _mark_stack->pop();
6962 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6963 assert(_bit_map->isMarked((HeapWord*)new_oop),
6964 "only grey objects on this stack");
6965 // iterate over the oops in this oop, marking and pushing
6966 // the ones in CMS heap (i.e. in _span).
6967 new_oop->oop_iterate(_scanning_closure);
6968 // check if it's time to yield
6969 do_yield_check();
6970 }
6971 unsigned int after_count =
6972 GenCollectedHeap::heap()->total_collections();
6973 bool abort = (_before_count != after_count) ||
6974 _collector->should_abort_preclean();
6975 return abort ? 0 : size;
6976 }
6977
6978 void SurvivorSpacePrecleanClosure::do_yield_work() {
6979 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6980 "CMS thread should hold CMS token");
6981 assert_lock_strong(_bit_map->lock());
6982 // Relinquish the bit map lock
6983 _bit_map->lock()->unlock();
6984 ConcurrentMarkSweepThread::desynchronize(true);
6985 ConcurrentMarkSweepThread::acknowledge_yield_request();
6986 _collector->stopTimer();
6987 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6988 if (PrintCMSStatistics != 0) {
6989 _collector->incrementYields();
6990 }
6991 _collector->icms_wait();
6992
6993 // See the comment in coordinator_yield()
6994 for (unsigned i = 0; i < CMSYieldSleepCount &&
6995 ConcurrentMarkSweepThread::should_yield() &&
6996 !CMSCollector::foregroundGCIsActive(); ++i) {
6997 os::sleep(Thread::current(), 1, false);
6998 ConcurrentMarkSweepThread::acknowledge_yield_request();
6999 }
7000
7001 ConcurrentMarkSweepThread::synchronize(true);
7002 _bit_map->lock()->lock_without_safepoint_check();
7003 _collector->startTimer();
7004 }
7005
7006 // This closure is used to rescan the marked objects on the dirty cards
7007 // in the mod union table and the card table proper. In the parallel
7008 // case, although the bitMap is shared, we do a single read so the
7009 // isMarked() query is "safe".
7010 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7011 // Ignore mark word because we are running concurrent with mutators
7012 assert(p->is_oop_or_null(true), "expected an oop or null");
7013 HeapWord* addr = (HeapWord*)p;
7014 assert(_span.contains(addr), "we are scanning the CMS generation");
7015 bool is_obj_array = false;
7016 #ifdef DEBUG
7017 if (!_parallel) {
7018 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7019 assert(_collector->overflow_list_is_empty(),
7020 "overflow list should be empty");
7021
7022 }
7023 #endif // DEBUG
7024 if (_bit_map->isMarked(addr)) {
7025 // Obj arrays are precisely marked, non-arrays are not;
7026 // so we scan objArrays precisely and non-arrays in their
7027 // entirety.
7028 if (p->is_objArray()) {
7029 is_obj_array = true;
7030 if (_parallel) {
7031 p->oop_iterate(_par_scan_closure, mr);
7032 } else {
7033 p->oop_iterate(_scan_closure, mr);
7034 }
7035 } else {
7036 if (_parallel) {
7037 p->oop_iterate(_par_scan_closure);
7038 } else {
7039 p->oop_iterate(_scan_closure);
7040 }
7041 }
7042 }
7043 #ifdef DEBUG
7044 if (!_parallel) {
7045 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7046 assert(_collector->overflow_list_is_empty(),
7047 "overflow list should be empty");
7048
7049 }
7050 #endif // DEBUG
7051 return is_obj_array;
7052 }
7053
7054 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7055 MemRegion span,
7056 CMSBitMap* bitMap, CMSMarkStack* markStack,
7057 bool should_yield, bool verifying):
7058 _collector(collector),
7059 _span(span),
7060 _bitMap(bitMap),
7061 _mut(&collector->_modUnionTable),
7062 _markStack(markStack),
7063 _yield(should_yield),
7064 _skipBits(0)
7065 {
7066 assert(_markStack->isEmpty(), "stack should be empty");
7067 _finger = _bitMap->startWord();
7068 _threshold = _finger;
7069 assert(_collector->_restart_addr == NULL, "Sanity check");
7070 assert(_span.contains(_finger), "Out of bounds _finger?");
7071 DEBUG_ONLY(_verifying = verifying;)
7072 }
7073
7074 void MarkFromRootsClosure::reset(HeapWord* addr) {
7075 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7076 assert(_span.contains(addr), "Out of bounds _finger?");
7077 _finger = addr;
7078 _threshold = (HeapWord*)round_to(
7079 (intptr_t)_finger, CardTableModRefBS::card_size);
7080 }
7081
7082 // Should revisit to see if this should be restructured for
7083 // greater efficiency.
7084 bool MarkFromRootsClosure::do_bit(size_t offset) {
7085 if (_skipBits > 0) {
7086 _skipBits--;
7087 return true;
7088 }
7089 // convert offset into a HeapWord*
7090 HeapWord* addr = _bitMap->startWord() + offset;
7091 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7092 "address out of range");
7093 assert(_bitMap->isMarked(addr), "tautology");
7094 if (_bitMap->isMarked(addr+1)) {
7095 // this is an allocated but not yet initialized object
7096 assert(_skipBits == 0, "tautology");
7097 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7098 oop p = oop(addr);
7099 if (p->klass_or_null() == NULL) {
7100 DEBUG_ONLY(if (!_verifying) {)
7101 // We re-dirty the cards on which this object lies and increase
7102 // the _threshold so that we'll come back to scan this object
7103 // during the preclean or remark phase. (CMSCleanOnEnter)
7104 if (CMSCleanOnEnter) {
7105 size_t sz = _collector->block_size_using_printezis_bits(addr);
7106 HeapWord* end_card_addr = (HeapWord*)round_to(
7107 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7108 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7109 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7110 // Bump _threshold to end_card_addr; note that
7111 // _threshold cannot possibly exceed end_card_addr, anyhow.
7112 // This prevents future clearing of the card as the scan proceeds
7113 // to the right.
7114 assert(_threshold <= end_card_addr,
7115 "Because we are just scanning into this object");
7116 if (_threshold < end_card_addr) {
7117 _threshold = end_card_addr;
7118 }
7119 if (p->klass_or_null() != NULL) {
7120 // Redirty the range of cards...
7121 _mut->mark_range(redirty_range);
7122 } // ...else the setting of klass will dirty the card anyway.
7123 }
7124 DEBUG_ONLY(})
7125 return true;
7126 }
7127 }
7128 scanOopsInOop(addr);
7129 return true;
7130 }
7131
7132 // We take a break if we've been at this for a while,
7133 // so as to avoid monopolizing the locks involved.
7134 void MarkFromRootsClosure::do_yield_work() {
7135 // First give up the locks, then yield, then re-lock
7136 // We should probably use a constructor/destructor idiom to
7137 // do this unlock/lock or modify the MutexUnlocker class to
7138 // serve our purpose. XXX
7139 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7140 "CMS thread should hold CMS token");
7141 assert_lock_strong(_bitMap->lock());
7142 _bitMap->lock()->unlock();
7143 ConcurrentMarkSweepThread::desynchronize(true);
7144 ConcurrentMarkSweepThread::acknowledge_yield_request();
7145 _collector->stopTimer();
7146 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7147 if (PrintCMSStatistics != 0) {
7148 _collector->incrementYields();
7149 }
7150 _collector->icms_wait();
7151
7152 // See the comment in coordinator_yield()
7153 for (unsigned i = 0; i < CMSYieldSleepCount &&
7154 ConcurrentMarkSweepThread::should_yield() &&
7155 !CMSCollector::foregroundGCIsActive(); ++i) {
7156 os::sleep(Thread::current(), 1, false);
7157 ConcurrentMarkSweepThread::acknowledge_yield_request();
7158 }
7159
7160 ConcurrentMarkSweepThread::synchronize(true);
7161 _bitMap->lock()->lock_without_safepoint_check();
7162 _collector->startTimer();
7163 }
7164
7165 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7166 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7167 assert(_markStack->isEmpty(),
7168 "should drain stack to limit stack usage");
7169 // convert ptr to an oop preparatory to scanning
7170 oop obj = oop(ptr);
7171 // Ignore mark word in verification below, since we
7172 // may be running concurrent with mutators.
7173 assert(obj->is_oop(true), "should be an oop");
7174 assert(_finger <= ptr, "_finger runneth ahead");
7175 // advance the finger to right end of this object
7176 _finger = ptr + obj->size();
7177 assert(_finger > ptr, "we just incremented it above");
7178 // On large heaps, it may take us some time to get through
7179 // the marking phase (especially if running iCMS). During
7180 // this time it's possible that a lot of mutations have
7181 // accumulated in the card table and the mod union table --
7182 // these mutation records are redundant until we have
7183 // actually traced into the corresponding card.
7184 // Here, we check whether advancing the finger would make
7185 // us cross into a new card, and if so clear corresponding
7186 // cards in the MUT (preclean them in the card-table in the
7187 // future).
7188
7189 DEBUG_ONLY(if (!_verifying) {)
7190 // The clean-on-enter optimization is disabled by default,
7191 // until we fix 6178663.
7192 if (CMSCleanOnEnter && (_finger > _threshold)) {
7193 // [_threshold, _finger) represents the interval
7194 // of cards to be cleared in MUT (or precleaned in card table).
7195 // The set of cards to be cleared is all those that overlap
7196 // with the interval [_threshold, _finger); note that
7197 // _threshold is always kept card-aligned but _finger isn't
7198 // always card-aligned.
7199 HeapWord* old_threshold = _threshold;
7200 assert(old_threshold == (HeapWord*)round_to(
7201 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7202 "_threshold should always be card-aligned");
7203 _threshold = (HeapWord*)round_to(
7204 (intptr_t)_finger, CardTableModRefBS::card_size);
7205 MemRegion mr(old_threshold, _threshold);
7206 assert(!mr.is_empty(), "Control point invariant");
7207 assert(_span.contains(mr), "Should clear within span");
7208 _mut->clear_range(mr);
7209 }
7210 DEBUG_ONLY(})
7211 // Note: the finger doesn't advance while we drain
7212 // the stack below.
7213 PushOrMarkClosure pushOrMarkClosure(_collector,
7214 _span, _bitMap, _markStack,
7215 _finger, this);
7216 bool res = _markStack->push(obj);
7217 assert(res, "Empty non-zero size stack should have space for single push");
7218 while (!_markStack->isEmpty()) {
7219 oop new_oop = _markStack->pop();
7220 // Skip verifying header mark word below because we are
7221 // running concurrent with mutators.
7222 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7223 // now scan this oop's oops
7224 new_oop->oop_iterate(&pushOrMarkClosure);
7225 do_yield_check();
7226 }
7227 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7228 }
7229
7230 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7231 CMSCollector* collector, MemRegion span,
7232 CMSBitMap* bit_map,
7233 OopTaskQueue* work_queue,
7234 CMSMarkStack* overflow_stack,
7235 bool should_yield):
7236 _collector(collector),
7237 _whole_span(collector->_span),
7238 _span(span),
7239 _bit_map(bit_map),
7240 _mut(&collector->_modUnionTable),
7241 _work_queue(work_queue),
7242 _overflow_stack(overflow_stack),
7243 _yield(should_yield),
7244 _skip_bits(0),
7245 _task(task)
7246 {
7247 assert(_work_queue->size() == 0, "work_queue should be empty");
7248 _finger = span.start();
7249 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7250 assert(_span.contains(_finger), "Out of bounds _finger?");
7251 }
7252
7253 // Should revisit to see if this should be restructured for
7254 // greater efficiency.
7255 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7256 if (_skip_bits > 0) {
7257 _skip_bits--;
7258 return true;
7259 }
7260 // convert offset into a HeapWord*
7261 HeapWord* addr = _bit_map->startWord() + offset;
7262 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7263 "address out of range");
7264 assert(_bit_map->isMarked(addr), "tautology");
7265 if (_bit_map->isMarked(addr+1)) {
7266 // this is an allocated object that might not yet be initialized
7267 assert(_skip_bits == 0, "tautology");
7268 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7269 oop p = oop(addr);
7270 if (p->klass_or_null() == NULL) {
7271 // in the case of Clean-on-Enter optimization, redirty card
7272 // and avoid clearing card by increasing the threshold.
7273 return true;
7274 }
7275 }
7276 scan_oops_in_oop(addr);
7277 return true;
7278 }
7279
7280 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7281 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7282 // Should we assert that our work queue is empty or
7283 // below some drain limit?
7284 assert(_work_queue->size() == 0,
7285 "should drain stack to limit stack usage");
7286 // convert ptr to an oop preparatory to scanning
7287 oop obj = oop(ptr);
7288 // Ignore mark word in verification below, since we
7289 // may be running concurrent with mutators.
7290 assert(obj->is_oop(true), "should be an oop");
7291 assert(_finger <= ptr, "_finger runneth ahead");
7292 // advance the finger to right end of this object
7293 _finger = ptr + obj->size();
7294 assert(_finger > ptr, "we just incremented it above");
7295 // On large heaps, it may take us some time to get through
7296 // the marking phase (especially if running iCMS). During
7297 // this time it's possible that a lot of mutations have
7298 // accumulated in the card table and the mod union table --
7299 // these mutation records are redundant until we have
7300 // actually traced into the corresponding card.
7301 // Here, we check whether advancing the finger would make
7302 // us cross into a new card, and if so clear corresponding
7303 // cards in the MUT (preclean them in the card-table in the
7304 // future).
7305
7306 // The clean-on-enter optimization is disabled by default,
7307 // until we fix 6178663.
7308 if (CMSCleanOnEnter && (_finger > _threshold)) {
7309 // [_threshold, _finger) represents the interval
7310 // of cards to be cleared in MUT (or precleaned in card table).
7311 // The set of cards to be cleared is all those that overlap
7312 // with the interval [_threshold, _finger); note that
7313 // _threshold is always kept card-aligned but _finger isn't
7314 // always card-aligned.
7315 HeapWord* old_threshold = _threshold;
7316 assert(old_threshold == (HeapWord*)round_to(
7317 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7318 "_threshold should always be card-aligned");
7319 _threshold = (HeapWord*)round_to(
7320 (intptr_t)_finger, CardTableModRefBS::card_size);
7321 MemRegion mr(old_threshold, _threshold);
7322 assert(!mr.is_empty(), "Control point invariant");
7323 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7324 _mut->clear_range(mr);
7325 }
7326
7327 // Note: the local finger doesn't advance while we drain
7328 // the stack below, but the global finger sure can and will.
7329 HeapWord** gfa = _task->global_finger_addr();
7330 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7331 _span, _bit_map,
7332 _work_queue,
7333 _overflow_stack,
7334 _finger,
7335 gfa, this);
7336 bool res = _work_queue->push(obj); // overflow could occur here
7337 assert(res, "Will hold once we use workqueues");
7338 while (true) {
7339 oop new_oop;
7340 if (!_work_queue->pop_local(new_oop)) {
7341 // We emptied our work_queue; check if there's stuff that can
7342 // be gotten from the overflow stack.
7343 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7344 _overflow_stack, _work_queue)) {
7345 do_yield_check();
7346 continue;
7347 } else { // done
7348 break;
7349 }
7350 }
7351 // Skip verifying header mark word below because we are
7352 // running concurrent with mutators.
7353 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7354 // now scan this oop's oops
7355 new_oop->oop_iterate(&pushOrMarkClosure);
7356 do_yield_check();
7357 }
7358 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7359 }
7360
7361 // Yield in response to a request from VM Thread or
7362 // from mutators.
7363 void Par_MarkFromRootsClosure::do_yield_work() {
7364 assert(_task != NULL, "sanity");
7365 _task->yield();
7366 }
7367
7368 // A variant of the above used for verifying CMS marking work.
7369 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7370 MemRegion span,
7371 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7372 CMSMarkStack* mark_stack):
7373 _collector(collector),
7374 _span(span),
7375 _verification_bm(verification_bm),
7376 _cms_bm(cms_bm),
7377 _mark_stack(mark_stack),
7378 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7379 mark_stack)
7380 {
7381 assert(_mark_stack->isEmpty(), "stack should be empty");
7382 _finger = _verification_bm->startWord();
7383 assert(_collector->_restart_addr == NULL, "Sanity check");
7384 assert(_span.contains(_finger), "Out of bounds _finger?");
7385 }
7386
7387 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7388 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7389 assert(_span.contains(addr), "Out of bounds _finger?");
7390 _finger = addr;
7391 }
7392
7393 // Should revisit to see if this should be restructured for
7394 // greater efficiency.
7395 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7396 // convert offset into a HeapWord*
7397 HeapWord* addr = _verification_bm->startWord() + offset;
7398 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7399 "address out of range");
7400 assert(_verification_bm->isMarked(addr), "tautology");
7401 assert(_cms_bm->isMarked(addr), "tautology");
7402
7403 assert(_mark_stack->isEmpty(),
7404 "should drain stack to limit stack usage");
7405 // convert addr to an oop preparatory to scanning
7406 oop obj = oop(addr);
7407 assert(obj->is_oop(), "should be an oop");
7408 assert(_finger <= addr, "_finger runneth ahead");
7409 // advance the finger to right end of this object
7410 _finger = addr + obj->size();
7411 assert(_finger > addr, "we just incremented it above");
7412 // Note: the finger doesn't advance while we drain
7413 // the stack below.
7414 bool res = _mark_stack->push(obj);
7415 assert(res, "Empty non-zero size stack should have space for single push");
7416 while (!_mark_stack->isEmpty()) {
7417 oop new_oop = _mark_stack->pop();
7418 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7419 // now scan this oop's oops
7420 new_oop->oop_iterate(&_pam_verify_closure);
7421 }
7422 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7423 return true;
7424 }
7425
7426 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7427 CMSCollector* collector, MemRegion span,
7428 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7429 CMSMarkStack* mark_stack):
7430 CMSOopClosure(collector->ref_processor()),
7431 _collector(collector),
7432 _span(span),
7433 _verification_bm(verification_bm),
7434 _cms_bm(cms_bm),
7435 _mark_stack(mark_stack)
7436 { }
7437
7438 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7439 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7440
7441 // Upon stack overflow, we discard (part of) the stack,
7442 // remembering the least address amongst those discarded
7443 // in CMSCollector's _restart_address.
7444 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7445 // Remember the least grey address discarded
7446 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7447 _collector->lower_restart_addr(ra);
7448 _mark_stack->reset(); // discard stack contents
7449 _mark_stack->expand(); // expand the stack if possible
7450 }
7451
7452 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7453 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7454 HeapWord* addr = (HeapWord*)obj;
7455 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7456 // Oop lies in _span and isn't yet grey or black
7457 _verification_bm->mark(addr); // now grey
7458 if (!_cms_bm->isMarked(addr)) {
7459 oop(addr)->print();
7460 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7461 addr);
7462 fatal("... aborting");
7463 }
7464
7465 if (!_mark_stack->push(obj)) { // stack overflow
7466 if (PrintCMSStatistics != 0) {
7467 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7468 SIZE_FORMAT, _mark_stack->capacity());
7469 }
7470 assert(_mark_stack->isFull(), "Else push should have succeeded");
7471 handle_stack_overflow(addr);
7472 }
7473 // anything including and to the right of _finger
7474 // will be scanned as we iterate over the remainder of the
7475 // bit map
7476 }
7477 }
7478
7479 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7480 MemRegion span,
7481 CMSBitMap* bitMap, CMSMarkStack* markStack,
7482 HeapWord* finger, MarkFromRootsClosure* parent) :
7483 CMSOopClosure(collector->ref_processor()),
7484 _collector(collector),
7485 _span(span),
7486 _bitMap(bitMap),
7487 _markStack(markStack),
7488 _finger(finger),
7489 _parent(parent)
7490 { }
7491
7492 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7493 MemRegion span,
7494 CMSBitMap* bit_map,
7495 OopTaskQueue* work_queue,
7496 CMSMarkStack* overflow_stack,
7497 HeapWord* finger,
7498 HeapWord** global_finger_addr,
7499 Par_MarkFromRootsClosure* parent) :
7500 CMSOopClosure(collector->ref_processor()),
7501 _collector(collector),
7502 _whole_span(collector->_span),
7503 _span(span),
7504 _bit_map(bit_map),
7505 _work_queue(work_queue),
7506 _overflow_stack(overflow_stack),
7507 _finger(finger),
7508 _global_finger_addr(global_finger_addr),
7509 _parent(parent)
7510 { }
7511
7512 // Assumes thread-safe access by callers, who are
7513 // responsible for mutual exclusion.
7514 void CMSCollector::lower_restart_addr(HeapWord* low) {
7515 assert(_span.contains(low), "Out of bounds addr");
7516 if (_restart_addr == NULL) {
7517 _restart_addr = low;
7518 } else {
7519 _restart_addr = MIN2(_restart_addr, low);
7520 }
7521 }
7522
7523 // Upon stack overflow, we discard (part of) the stack,
7524 // remembering the least address amongst those discarded
7525 // in CMSCollector's _restart_address.
7526 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7527 // Remember the least grey address discarded
7528 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7529 _collector->lower_restart_addr(ra);
7530 _markStack->reset(); // discard stack contents
7531 _markStack->expand(); // expand the stack if possible
7532 }
7533
7534 // Upon stack overflow, we discard (part of) the stack,
7535 // remembering the least address amongst those discarded
7536 // in CMSCollector's _restart_address.
7537 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7538 // We need to do this under a mutex to prevent other
7539 // workers from interfering with the work done below.
7540 MutexLockerEx ml(_overflow_stack->par_lock(),
7541 Mutex::_no_safepoint_check_flag);
7542 // Remember the least grey address discarded
7543 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7544 _collector->lower_restart_addr(ra);
7545 _overflow_stack->reset(); // discard stack contents
7546 _overflow_stack->expand(); // expand the stack if possible
7547 }
7548
7549 void CMKlassClosure::do_klass(Klass* k) {
7550 assert(_oop_closure != NULL, "Not initialized?");
7551 k->oops_do(_oop_closure);
7552 }
7553
7554 void PushOrMarkClosure::do_oop(oop obj) {
7555 // Ignore mark word because we are running concurrent with mutators.
7556 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7557 HeapWord* addr = (HeapWord*)obj;
7558 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7559 // Oop lies in _span and isn't yet grey or black
7560 _bitMap->mark(addr); // now grey
7561 if (addr < _finger) {
7562 // the bit map iteration has already either passed, or
7563 // sampled, this bit in the bit map; we'll need to
7564 // use the marking stack to scan this oop's oops.
7565 bool simulate_overflow = false;
7566 NOT_PRODUCT(
7567 if (CMSMarkStackOverflowALot &&
7568 _collector->simulate_overflow()) {
7569 // simulate a stack overflow
7570 simulate_overflow = true;
7571 }
7572 )
7573 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7574 if (PrintCMSStatistics != 0) {
7575 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7576 SIZE_FORMAT, _markStack->capacity());
7577 }
7578 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7579 handle_stack_overflow(addr);
7580 }
7581 }
7582 // anything including and to the right of _finger
7583 // will be scanned as we iterate over the remainder of the
7584 // bit map
7585 do_yield_check();
7586 }
7587 }
7588
7589 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7590 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7591
7592 void Par_PushOrMarkClosure::do_oop(oop obj) {
7593 // Ignore mark word because we are running concurrent with mutators.
7594 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7595 HeapWord* addr = (HeapWord*)obj;
7596 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7597 // Oop lies in _span and isn't yet grey or black
7598 // We read the global_finger (volatile read) strictly after marking oop
7599 bool res = _bit_map->par_mark(addr); // now grey
7600 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7601 // Should we push this marked oop on our stack?
7602 // -- if someone else marked it, nothing to do
7603 // -- if target oop is above global finger nothing to do
7604 // -- if target oop is in chunk and above local finger
7605 // then nothing to do
7606 // -- else push on work queue
7607 if ( !res // someone else marked it, they will deal with it
7608 || (addr >= *gfa) // will be scanned in a later task
7609 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7610 return;
7611 }
7612 // the bit map iteration has already either passed, or
7613 // sampled, this bit in the bit map; we'll need to
7614 // use the marking stack to scan this oop's oops.
7615 bool simulate_overflow = false;
7616 NOT_PRODUCT(
7617 if (CMSMarkStackOverflowALot &&
7618 _collector->simulate_overflow()) {
7619 // simulate a stack overflow
7620 simulate_overflow = true;
7621 }
7622 )
7623 if (simulate_overflow ||
7624 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7625 // stack overflow
7626 if (PrintCMSStatistics != 0) {
7627 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7628 SIZE_FORMAT, _overflow_stack->capacity());
7629 }
7630 // We cannot assert that the overflow stack is full because
7631 // it may have been emptied since.
7632 assert(simulate_overflow ||
7633 _work_queue->size() == _work_queue->max_elems(),
7634 "Else push should have succeeded");
7635 handle_stack_overflow(addr);
7636 }
7637 do_yield_check();
7638 }
7639 }
7640
7641 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7642 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7643
7644 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7645 MemRegion span,
7646 ReferenceProcessor* rp,
7647 CMSBitMap* bit_map,
7648 CMSBitMap* mod_union_table,
7649 CMSMarkStack* mark_stack,
7650 bool concurrent_precleaning):
7651 CMSOopClosure(rp),
7652 _collector(collector),
7653 _span(span),
7654 _bit_map(bit_map),
7655 _mod_union_table(mod_union_table),
7656 _mark_stack(mark_stack),
7657 _concurrent_precleaning(concurrent_precleaning)
7658 {
7659 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7660 }
7661
7662 // Grey object rescan during pre-cleaning and second checkpoint phases --
7663 // the non-parallel version (the parallel version appears further below.)
7664 void PushAndMarkClosure::do_oop(oop obj) {
7665 // Ignore mark word verification. If during concurrent precleaning,
7666 // the object monitor may be locked. If during the checkpoint
7667 // phases, the object may already have been reached by a different
7668 // path and may be at the end of the global overflow list (so
7669 // the mark word may be NULL).
7670 assert(obj->is_oop_or_null(true /* ignore mark word */),
7671 "expected an oop or NULL");
7672 HeapWord* addr = (HeapWord*)obj;
7673 // Check if oop points into the CMS generation
7674 // and is not marked
7675 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7676 // a white object ...
7677 _bit_map->mark(addr); // ... now grey
7678 // push on the marking stack (grey set)
7679 bool simulate_overflow = false;
7680 NOT_PRODUCT(
7681 if (CMSMarkStackOverflowALot &&
7682 _collector->simulate_overflow()) {
7683 // simulate a stack overflow
7684 simulate_overflow = true;
7685 }
7686 )
7687 if (simulate_overflow || !_mark_stack->push(obj)) {
7688 if (_concurrent_precleaning) {
7689 // During precleaning we can just dirty the appropriate card(s)
7690 // in the mod union table, thus ensuring that the object remains
7691 // in the grey set and continue. In the case of object arrays
7692 // we need to dirty all of the cards that the object spans,
7693 // since the rescan of object arrays will be limited to the
7694 // dirty cards.
7695 // Note that no one can be intefering with us in this action
7696 // of dirtying the mod union table, so no locking or atomics
7697 // are required.
7698 if (obj->is_objArray()) {
7699 size_t sz = obj->size();
7700 HeapWord* end_card_addr = (HeapWord*)round_to(
7701 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7702 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7703 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7704 _mod_union_table->mark_range(redirty_range);
7705 } else {
7706 _mod_union_table->mark(addr);
7707 }
7708 _collector->_ser_pmc_preclean_ovflw++;
7709 } else {
7710 // During the remark phase, we need to remember this oop
7711 // in the overflow list.
7712 _collector->push_on_overflow_list(obj);
7713 _collector->_ser_pmc_remark_ovflw++;
7714 }
7715 }
7716 }
7717 }
7718
7719 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7720 MemRegion span,
7721 ReferenceProcessor* rp,
7722 CMSBitMap* bit_map,
7723 OopTaskQueue* work_queue):
7724 CMSOopClosure(rp),
7725 _collector(collector),
7726 _span(span),
7727 _bit_map(bit_map),
7728 _work_queue(work_queue)
7729 {
7730 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7731 }
7732
7733 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7734 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7735
7736 // Grey object rescan during second checkpoint phase --
7737 // the parallel version.
7738 void Par_PushAndMarkClosure::do_oop(oop obj) {
7739 // In the assert below, we ignore the mark word because
7740 // this oop may point to an already visited object that is
7741 // on the overflow stack (in which case the mark word has
7742 // been hijacked for chaining into the overflow stack --
7743 // if this is the last object in the overflow stack then
7744 // its mark word will be NULL). Because this object may
7745 // have been subsequently popped off the global overflow
7746 // stack, and the mark word possibly restored to the prototypical
7747 // value, by the time we get to examined this failing assert in
7748 // the debugger, is_oop_or_null(false) may subsequently start
7749 // to hold.
7750 assert(obj->is_oop_or_null(true),
7751 "expected an oop or NULL");
7752 HeapWord* addr = (HeapWord*)obj;
7753 // Check if oop points into the CMS generation
7754 // and is not marked
7755 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7756 // a white object ...
7757 // If we manage to "claim" the object, by being the
7758 // first thread to mark it, then we push it on our
7759 // marking stack
7760 if (_bit_map->par_mark(addr)) { // ... now grey
7761 // push on work queue (grey set)
7762 bool simulate_overflow = false;
7763 NOT_PRODUCT(
7764 if (CMSMarkStackOverflowALot &&
7765 _collector->par_simulate_overflow()) {
7766 // simulate a stack overflow
7767 simulate_overflow = true;
7768 }
7769 )
7770 if (simulate_overflow || !_work_queue->push(obj)) {
7771 _collector->par_push_on_overflow_list(obj);
7772 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7773 }
7774 } // Else, some other thread got there first
7775 }
7776 }
7777
7778 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7779 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7780
7781 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7782 Mutex* bml = _collector->bitMapLock();
7783 assert_lock_strong(bml);
7784 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7785 "CMS thread should hold CMS token");
7786
7787 bml->unlock();
7788 ConcurrentMarkSweepThread::desynchronize(true);
7789
7790 ConcurrentMarkSweepThread::acknowledge_yield_request();
7791
7792 _collector->stopTimer();
7793 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7794 if (PrintCMSStatistics != 0) {
7795 _collector->incrementYields();
7796 }
7797 _collector->icms_wait();
7798
7799 // See the comment in coordinator_yield()
7800 for (unsigned i = 0; i < CMSYieldSleepCount &&
7801 ConcurrentMarkSweepThread::should_yield() &&
7802 !CMSCollector::foregroundGCIsActive(); ++i) {
7803 os::sleep(Thread::current(), 1, false);
7804 ConcurrentMarkSweepThread::acknowledge_yield_request();
7805 }
7806
7807 ConcurrentMarkSweepThread::synchronize(true);
7808 bml->lock();
7809
7810 _collector->startTimer();
7811 }
7812
7813 bool CMSPrecleanRefsYieldClosure::should_return() {
7814 if (ConcurrentMarkSweepThread::should_yield()) {
7815 do_yield_work();
7816 }
7817 return _collector->foregroundGCIsActive();
7818 }
7819
7820 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7821 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7822 "mr should be aligned to start at a card boundary");
7823 // We'd like to assert:
7824 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7825 // "mr should be a range of cards");
7826 // However, that would be too strong in one case -- the last
7827 // partition ends at _unallocated_block which, in general, can be
7828 // an arbitrary boundary, not necessarily card aligned.
7829 if (PrintCMSStatistics != 0) {
7830 _num_dirty_cards +=
7831 mr.word_size()/CardTableModRefBS::card_size_in_words;
7832 }
7833 _space->object_iterate_mem(mr, &_scan_cl);
7834 }
7835
7836 SweepClosure::SweepClosure(CMSCollector* collector,
7837 ConcurrentMarkSweepGeneration* g,
7838 CMSBitMap* bitMap, bool should_yield) :
7839 _collector(collector),
7840 _g(g),
7841 _sp(g->cmsSpace()),
7842 _limit(_sp->sweep_limit()),
7843 _freelistLock(_sp->freelistLock()),
7844 _bitMap(bitMap),
7845 _yield(should_yield),
7846 _inFreeRange(false), // No free range at beginning of sweep
7847 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7848 _lastFreeRangeCoalesced(false),
7849 _freeFinger(g->used_region().start())
7850 {
7851 NOT_PRODUCT(
7852 _numObjectsFreed = 0;
7853 _numWordsFreed = 0;
7854 _numObjectsLive = 0;
7855 _numWordsLive = 0;
7856 _numObjectsAlreadyFree = 0;
7857 _numWordsAlreadyFree = 0;
7858 _last_fc = NULL;
7859
7860 _sp->initializeIndexedFreeListArrayReturnedBytes();
7861 _sp->dictionary()->initialize_dict_returned_bytes();
7862 )
7863 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7864 "sweep _limit out of bounds");
7865 if (CMSTraceSweeper) {
7866 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7867 _limit);
7868 }
7869 }
7870
7871 void SweepClosure::print_on(outputStream* st) const {
7872 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7873 _sp->bottom(), _sp->end());
7874 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7875 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7876 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7877 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7878 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7879 }
7880
7881 #ifndef PRODUCT
7882 // Assertion checking only: no useful work in product mode --
7883 // however, if any of the flags below become product flags,
7884 // you may need to review this code to see if it needs to be
7885 // enabled in product mode.
7886 SweepClosure::~SweepClosure() {
7887 assert_lock_strong(_freelistLock);
7888 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7889 "sweep _limit out of bounds");
7890 if (inFreeRange()) {
7891 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7892 print();
7893 ShouldNotReachHere();
7894 }
7895 if (Verbose && PrintGC) {
7896 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7897 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7898 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7899 SIZE_FORMAT" bytes "
7900 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7901 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7902 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7903 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7904 * sizeof(HeapWord);
7905 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7906
7907 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7908 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7909 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7910 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7911 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7912 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7913 indexListReturnedBytes);
7914 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7915 dict_returned_bytes);
7916 }
7917 }
7918 if (CMSTraceSweeper) {
7919 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7920 _limit);
7921 }
7922 }
7923 #endif // PRODUCT
7924
7925 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7926 bool freeRangeInFreeLists) {
7927 if (CMSTraceSweeper) {
7928 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7929 freeFinger, freeRangeInFreeLists);
7930 }
7931 assert(!inFreeRange(), "Trampling existing free range");
7932 set_inFreeRange(true);
7933 set_lastFreeRangeCoalesced(false);
7934
7935 set_freeFinger(freeFinger);
7936 set_freeRangeInFreeLists(freeRangeInFreeLists);
7937 if (CMSTestInFreeList) {
7938 if (freeRangeInFreeLists) {
7939 FreeChunk* fc = (FreeChunk*) freeFinger;
7940 assert(fc->is_free(), "A chunk on the free list should be free.");
7941 assert(fc->size() > 0, "Free range should have a size");
7942 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7943 }
7944 }
7945 }
7946
7947 // Note that the sweeper runs concurrently with mutators. Thus,
7948 // it is possible for direct allocation in this generation to happen
7949 // in the middle of the sweep. Note that the sweeper also coalesces
7950 // contiguous free blocks. Thus, unless the sweeper and the allocator
7951 // synchronize appropriately freshly allocated blocks may get swept up.
7952 // This is accomplished by the sweeper locking the free lists while
7953 // it is sweeping. Thus blocks that are determined to be free are
7954 // indeed free. There is however one additional complication:
7955 // blocks that have been allocated since the final checkpoint and
7956 // mark, will not have been marked and so would be treated as
7957 // unreachable and swept up. To prevent this, the allocator marks
7958 // the bit map when allocating during the sweep phase. This leads,
7959 // however, to a further complication -- objects may have been allocated
7960 // but not yet initialized -- in the sense that the header isn't yet
7961 // installed. The sweeper can not then determine the size of the block
7962 // in order to skip over it. To deal with this case, we use a technique
7963 // (due to Printezis) to encode such uninitialized block sizes in the
7964 // bit map. Since the bit map uses a bit per every HeapWord, but the
7965 // CMS generation has a minimum object size of 3 HeapWords, it follows
7966 // that "normal marks" won't be adjacent in the bit map (there will
7967 // always be at least two 0 bits between successive 1 bits). We make use
7968 // of these "unused" bits to represent uninitialized blocks -- the bit
7969 // corresponding to the start of the uninitialized object and the next
7970 // bit are both set. Finally, a 1 bit marks the end of the object that
7971 // started with the two consecutive 1 bits to indicate its potentially
7972 // uninitialized state.
7973
7974 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7975 FreeChunk* fc = (FreeChunk*)addr;
7976 size_t res;
7977
7978 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7979 // than "addr == _limit" because although _limit was a block boundary when
7980 // we started the sweep, it may no longer be one because heap expansion
7981 // may have caused us to coalesce the block ending at the address _limit
7982 // with a newly expanded chunk (this happens when _limit was set to the
7983 // previous _end of the space), so we may have stepped past _limit:
7984 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7985 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7986 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7987 "sweep _limit out of bounds");
7988 assert(addr < _sp->end(), "addr out of bounds");
7989 // Flush any free range we might be holding as a single
7990 // coalesced chunk to the appropriate free list.
7991 if (inFreeRange()) {
7992 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7993 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7994 flush_cur_free_chunk(freeFinger(),
7995 pointer_delta(addr, freeFinger()));
7996 if (CMSTraceSweeper) {
7997 gclog_or_tty->print("Sweep: last chunk: ");
7998 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
7999 "[coalesced:"SIZE_FORMAT"]\n",
8000 freeFinger(), pointer_delta(addr, freeFinger()),
8001 lastFreeRangeCoalesced());
8002 }
8003 }
8004
8005 // help the iterator loop finish
8006 return pointer_delta(_sp->end(), addr);
8007 }
8008
8009 assert(addr < _limit, "sweep invariant");
8010 // check if we should yield
8011 do_yield_check(addr);
8012 if (fc->is_free()) {
8013 // Chunk that is already free
8014 res = fc->size();
8015 do_already_free_chunk(fc);
8016 debug_only(_sp->verifyFreeLists());
8017 // If we flush the chunk at hand in lookahead_and_flush()
8018 // and it's coalesced with a preceding chunk, then the
8019 // process of "mangling" the payload of the coalesced block
8020 // will cause erasure of the size information from the
8021 // (erstwhile) header of all the coalesced blocks but the
8022 // first, so the first disjunct in the assert will not hold
8023 // in that specific case (in which case the second disjunct
8024 // will hold).
8025 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8026 "Otherwise the size info doesn't change at this step");
8027 NOT_PRODUCT(
8028 _numObjectsAlreadyFree++;
8029 _numWordsAlreadyFree += res;
8030 )
8031 NOT_PRODUCT(_last_fc = fc;)
8032 } else if (!_bitMap->isMarked(addr)) {
8033 // Chunk is fresh garbage
8034 res = do_garbage_chunk(fc);
8035 debug_only(_sp->verifyFreeLists());
8036 NOT_PRODUCT(
8037 _numObjectsFreed++;
8038 _numWordsFreed += res;
8039 )
8040 } else {
8041 // Chunk that is alive.
8042 res = do_live_chunk(fc);
8043 debug_only(_sp->verifyFreeLists());
8044 NOT_PRODUCT(
8045 _numObjectsLive++;
8046 _numWordsLive += res;
8047 )
8048 }
8049 return res;
8050 }
8051
8052 // For the smart allocation, record following
8053 // split deaths - a free chunk is removed from its free list because
8054 // it is being split into two or more chunks.
8055 // split birth - a free chunk is being added to its free list because
8056 // a larger free chunk has been split and resulted in this free chunk.
8057 // coal death - a free chunk is being removed from its free list because
8058 // it is being coalesced into a large free chunk.
8059 // coal birth - a free chunk is being added to its free list because
8060 // it was created when two or more free chunks where coalesced into
8061 // this free chunk.
8062 //
8063 // These statistics are used to determine the desired number of free
8064 // chunks of a given size. The desired number is chosen to be relative
8065 // to the end of a CMS sweep. The desired number at the end of a sweep
8066 // is the
8067 // count-at-end-of-previous-sweep (an amount that was enough)
8068 // - count-at-beginning-of-current-sweep (the excess)
8069 // + split-births (gains in this size during interval)
8070 // - split-deaths (demands on this size during interval)
8071 // where the interval is from the end of one sweep to the end of the
8072 // next.
8073 //
8074 // When sweeping the sweeper maintains an accumulated chunk which is
8075 // the chunk that is made up of chunks that have been coalesced. That
8076 // will be termed the left-hand chunk. A new chunk of garbage that
8077 // is being considered for coalescing will be referred to as the
8078 // right-hand chunk.
8079 //
8080 // When making a decision on whether to coalesce a right-hand chunk with
8081 // the current left-hand chunk, the current count vs. the desired count
8082 // of the left-hand chunk is considered. Also if the right-hand chunk
8083 // is near the large chunk at the end of the heap (see
8084 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8085 // left-hand chunk is coalesced.
8086 //
8087 // When making a decision about whether to split a chunk, the desired count
8088 // vs. the current count of the candidate to be split is also considered.
8089 // If the candidate is underpopulated (currently fewer chunks than desired)
8090 // a chunk of an overpopulated (currently more chunks than desired) size may
8091 // be chosen. The "hint" associated with a free list, if non-null, points
8092 // to a free list which may be overpopulated.
8093 //
8094
8095 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8096 const size_t size = fc->size();
8097 // Chunks that cannot be coalesced are not in the
8098 // free lists.
8099 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8100 assert(_sp->verify_chunk_in_free_list(fc),
8101 "free chunk should be in free lists");
8102 }
8103 // a chunk that is already free, should not have been
8104 // marked in the bit map
8105 HeapWord* const addr = (HeapWord*) fc;
8106 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8107 // Verify that the bit map has no bits marked between
8108 // addr and purported end of this block.
8109 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8110
8111 // Some chunks cannot be coalesced under any circumstances.
8112 // See the definition of cantCoalesce().
8113 if (!fc->cantCoalesce()) {
8114 // This chunk can potentially be coalesced.
8115 if (_sp->adaptive_freelists()) {
8116 // All the work is done in
8117 do_post_free_or_garbage_chunk(fc, size);
8118 } else { // Not adaptive free lists
8119 // this is a free chunk that can potentially be coalesced by the sweeper;
8120 if (!inFreeRange()) {
8121 // if the next chunk is a free block that can't be coalesced
8122 // it doesn't make sense to remove this chunk from the free lists
8123 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8124 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8125 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8126 nextChunk->is_free() && // ... which is free...
8127 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8128 // nothing to do
8129 } else {
8130 // Potentially the start of a new free range:
8131 // Don't eagerly remove it from the free lists.
8132 // No need to remove it if it will just be put
8133 // back again. (Also from a pragmatic point of view
8134 // if it is a free block in a region that is beyond
8135 // any allocated blocks, an assertion will fail)
8136 // Remember the start of a free run.
8137 initialize_free_range(addr, true);
8138 // end - can coalesce with next chunk
8139 }
8140 } else {
8141 // the midst of a free range, we are coalescing
8142 print_free_block_coalesced(fc);
8143 if (CMSTraceSweeper) {
8144 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8145 }
8146 // remove it from the free lists
8147 _sp->removeFreeChunkFromFreeLists(fc);
8148 set_lastFreeRangeCoalesced(true);
8149 // If the chunk is being coalesced and the current free range is
8150 // in the free lists, remove the current free range so that it
8151 // will be returned to the free lists in its entirety - all
8152 // the coalesced pieces included.
8153 if (freeRangeInFreeLists()) {
8154 FreeChunk* ffc = (FreeChunk*) freeFinger();
8155 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8156 "Size of free range is inconsistent with chunk size.");
8157 if (CMSTestInFreeList) {
8158 assert(_sp->verify_chunk_in_free_list(ffc),
8159 "free range is not in free lists");
8160 }
8161 _sp->removeFreeChunkFromFreeLists(ffc);
8162 set_freeRangeInFreeLists(false);
8163 }
8164 }
8165 }
8166 // Note that if the chunk is not coalescable (the else arm
8167 // below), we unconditionally flush, without needing to do
8168 // a "lookahead," as we do below.
8169 if (inFreeRange()) lookahead_and_flush(fc, size);
8170 } else {
8171 // Code path common to both original and adaptive free lists.
8172
8173 // cant coalesce with previous block; this should be treated
8174 // as the end of a free run if any
8175 if (inFreeRange()) {
8176 // we kicked some butt; time to pick up the garbage
8177 assert(freeFinger() < addr, "freeFinger points too high");
8178 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8179 }
8180 // else, nothing to do, just continue
8181 }
8182 }
8183
8184 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8185 // This is a chunk of garbage. It is not in any free list.
8186 // Add it to a free list or let it possibly be coalesced into
8187 // a larger chunk.
8188 HeapWord* const addr = (HeapWord*) fc;
8189 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8190
8191 if (_sp->adaptive_freelists()) {
8192 // Verify that the bit map has no bits marked between
8193 // addr and purported end of just dead object.
8194 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8195
8196 do_post_free_or_garbage_chunk(fc, size);
8197 } else {
8198 if (!inFreeRange()) {
8199 // start of a new free range
8200 assert(size > 0, "A free range should have a size");
8201 initialize_free_range(addr, false);
8202 } else {
8203 // this will be swept up when we hit the end of the
8204 // free range
8205 if (CMSTraceSweeper) {
8206 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8207 }
8208 // If the chunk is being coalesced and the current free range is
8209 // in the free lists, remove the current free range so that it
8210 // will be returned to the free lists in its entirety - all
8211 // the coalesced pieces included.
8212 if (freeRangeInFreeLists()) {
8213 FreeChunk* ffc = (FreeChunk*)freeFinger();
8214 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8215 "Size of free range is inconsistent with chunk size.");
8216 if (CMSTestInFreeList) {
8217 assert(_sp->verify_chunk_in_free_list(ffc),
8218 "free range is not in free lists");
8219 }
8220 _sp->removeFreeChunkFromFreeLists(ffc);
8221 set_freeRangeInFreeLists(false);
8222 }
8223 set_lastFreeRangeCoalesced(true);
8224 }
8225 // this will be swept up when we hit the end of the free range
8226
8227 // Verify that the bit map has no bits marked between
8228 // addr and purported end of just dead object.
8229 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8230 }
8231 assert(_limit >= addr + size,
8232 "A freshly garbage chunk can't possibly straddle over _limit");
8233 if (inFreeRange()) lookahead_and_flush(fc, size);
8234 return size;
8235 }
8236
8237 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8238 HeapWord* addr = (HeapWord*) fc;
8239 // The sweeper has just found a live object. Return any accumulated
8240 // left hand chunk to the free lists.
8241 if (inFreeRange()) {
8242 assert(freeFinger() < addr, "freeFinger points too high");
8243 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8244 }
8245
8246 // This object is live: we'd normally expect this to be
8247 // an oop, and like to assert the following:
8248 // assert(oop(addr)->is_oop(), "live block should be an oop");
8249 // However, as we commented above, this may be an object whose
8250 // header hasn't yet been initialized.
8251 size_t size;
8252 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8253 if (_bitMap->isMarked(addr + 1)) {
8254 // Determine the size from the bit map, rather than trying to
8255 // compute it from the object header.
8256 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8257 size = pointer_delta(nextOneAddr + 1, addr);
8258 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8259 "alignment problem");
8260
8261 #ifdef DEBUG
8262 if (oop(addr)->klass_or_null() != NULL) {
8263 // Ignore mark word because we are running concurrent with mutators
8264 assert(oop(addr)->is_oop(true), "live block should be an oop");
8265 assert(size ==
8266 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8267 "P-mark and computed size do not agree");
8268 }
8269 #endif
8270
8271 } else {
8272 // This should be an initialized object that's alive.
8273 assert(oop(addr)->klass_or_null() != NULL,
8274 "Should be an initialized object");
8275 // Ignore mark word because we are running concurrent with mutators
8276 assert(oop(addr)->is_oop(true), "live block should be an oop");
8277 // Verify that the bit map has no bits marked between
8278 // addr and purported end of this block.
8279 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8280 assert(size >= 3, "Necessary for Printezis marks to work");
8281 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8282 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8283 }
8284 return size;
8285 }
8286
8287 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8288 size_t chunkSize) {
8289 // do_post_free_or_garbage_chunk() should only be called in the case
8290 // of the adaptive free list allocator.
8291 const bool fcInFreeLists = fc->is_free();
8292 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8293 assert((HeapWord*)fc <= _limit, "sweep invariant");
8294 if (CMSTestInFreeList && fcInFreeLists) {
8295 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8296 }
8297
8298 if (CMSTraceSweeper) {
8299 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8300 }
8301
8302 HeapWord* const fc_addr = (HeapWord*) fc;
8303
8304 bool coalesce;
8305 const size_t left = pointer_delta(fc_addr, freeFinger());
8306 const size_t right = chunkSize;
8307 switch (FLSCoalescePolicy) {
8308 // numeric value forms a coalition aggressiveness metric
8309 case 0: { // never coalesce
8310 coalesce = false;
8311 break;
8312 }
8313 case 1: { // coalesce if left & right chunks on overpopulated lists
8314 coalesce = _sp->coalOverPopulated(left) &&
8315 _sp->coalOverPopulated(right);
8316 break;
8317 }
8318 case 2: { // coalesce if left chunk on overpopulated list (default)
8319 coalesce = _sp->coalOverPopulated(left);
8320 break;
8321 }
8322 case 3: { // coalesce if left OR right chunk on overpopulated list
8323 coalesce = _sp->coalOverPopulated(left) ||
8324 _sp->coalOverPopulated(right);
8325 break;
8326 }
8327 case 4: { // always coalesce
8328 coalesce = true;
8329 break;
8330 }
8331 default:
8332 ShouldNotReachHere();
8333 }
8334
8335 // Should the current free range be coalesced?
8336 // If the chunk is in a free range and either we decided to coalesce above
8337 // or the chunk is near the large block at the end of the heap
8338 // (isNearLargestChunk() returns true), then coalesce this chunk.
8339 const bool doCoalesce = inFreeRange()
8340 && (coalesce || _g->isNearLargestChunk(fc_addr));
8341 if (doCoalesce) {
8342 // Coalesce the current free range on the left with the new
8343 // chunk on the right. If either is on a free list,
8344 // it must be removed from the list and stashed in the closure.
8345 if (freeRangeInFreeLists()) {
8346 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8347 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8348 "Size of free range is inconsistent with chunk size.");
8349 if (CMSTestInFreeList) {
8350 assert(_sp->verify_chunk_in_free_list(ffc),
8351 "Chunk is not in free lists");
8352 }
8353 _sp->coalDeath(ffc->size());
8354 _sp->removeFreeChunkFromFreeLists(ffc);
8355 set_freeRangeInFreeLists(false);
8356 }
8357 if (fcInFreeLists) {
8358 _sp->coalDeath(chunkSize);
8359 assert(fc->size() == chunkSize,
8360 "The chunk has the wrong size or is not in the free lists");
8361 _sp->removeFreeChunkFromFreeLists(fc);
8362 }
8363 set_lastFreeRangeCoalesced(true);
8364 print_free_block_coalesced(fc);
8365 } else { // not in a free range and/or should not coalesce
8366 // Return the current free range and start a new one.
8367 if (inFreeRange()) {
8368 // In a free range but cannot coalesce with the right hand chunk.
8369 // Put the current free range into the free lists.
8370 flush_cur_free_chunk(freeFinger(),
8371 pointer_delta(fc_addr, freeFinger()));
8372 }
8373 // Set up for new free range. Pass along whether the right hand
8374 // chunk is in the free lists.
8375 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8376 }
8377 }
8378
8379 // Lookahead flush:
8380 // If we are tracking a free range, and this is the last chunk that
8381 // we'll look at because its end crosses past _limit, we'll preemptively
8382 // flush it along with any free range we may be holding on to. Note that
8383 // this can be the case only for an already free or freshly garbage
8384 // chunk. If this block is an object, it can never straddle
8385 // over _limit. The "straddling" occurs when _limit is set at
8386 // the previous end of the space when this cycle started, and
8387 // a subsequent heap expansion caused the previously co-terminal
8388 // free block to be coalesced with the newly expanded portion,
8389 // thus rendering _limit a non-block-boundary making it dangerous
8390 // for the sweeper to step over and examine.
8391 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8392 assert(inFreeRange(), "Should only be called if currently in a free range.");
8393 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8394 assert(_sp->used_region().contains(eob - 1),
8395 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8396 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8397 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8398 if (eob >= _limit) {
8399 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8400 if (CMSTraceSweeper) {
8401 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8402 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8403 "[" PTR_FORMAT "," PTR_FORMAT ")",
8404 _limit, fc, eob, _sp->bottom(), _sp->end());
8405 }
8406 // Return the storage we are tracking back into the free lists.
8407 if (CMSTraceSweeper) {
8408 gclog_or_tty->print_cr("Flushing ... ");
8409 }
8410 assert(freeFinger() < eob, "Error");
8411 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8412 }
8413 }
8414
8415 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8416 assert(inFreeRange(), "Should only be called if currently in a free range.");
8417 assert(size > 0,
8418 "A zero sized chunk cannot be added to the free lists.");
8419 if (!freeRangeInFreeLists()) {
8420 if (CMSTestInFreeList) {
8421 FreeChunk* fc = (FreeChunk*) chunk;
8422 fc->set_size(size);
8423 assert(!_sp->verify_chunk_in_free_list(fc),
8424 "chunk should not be in free lists yet");
8425 }
8426 if (CMSTraceSweeper) {
8427 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8428 chunk, size);
8429 }
8430 // A new free range is going to be starting. The current
8431 // free range has not been added to the free lists yet or
8432 // was removed so add it back.
8433 // If the current free range was coalesced, then the death
8434 // of the free range was recorded. Record a birth now.
8435 if (lastFreeRangeCoalesced()) {
8436 _sp->coalBirth(size);
8437 }
8438 _sp->addChunkAndRepairOffsetTable(chunk, size,
8439 lastFreeRangeCoalesced());
8440 } else if (CMSTraceSweeper) {
8441 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8442 }
8443 set_inFreeRange(false);
8444 set_freeRangeInFreeLists(false);
8445 }
8446
8447 // We take a break if we've been at this for a while,
8448 // so as to avoid monopolizing the locks involved.
8449 void SweepClosure::do_yield_work(HeapWord* addr) {
8450 // Return current free chunk being used for coalescing (if any)
8451 // to the appropriate freelist. After yielding, the next
8452 // free block encountered will start a coalescing range of
8453 // free blocks. If the next free block is adjacent to the
8454 // chunk just flushed, they will need to wait for the next
8455 // sweep to be coalesced.
8456 if (inFreeRange()) {
8457 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8458 }
8459
8460 // First give up the locks, then yield, then re-lock.
8461 // We should probably use a constructor/destructor idiom to
8462 // do this unlock/lock or modify the MutexUnlocker class to
8463 // serve our purpose. XXX
8464 assert_lock_strong(_bitMap->lock());
8465 assert_lock_strong(_freelistLock);
8466 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8467 "CMS thread should hold CMS token");
8468 _bitMap->lock()->unlock();
8469 _freelistLock->unlock();
8470 ConcurrentMarkSweepThread::desynchronize(true);
8471 ConcurrentMarkSweepThread::acknowledge_yield_request();
8472 _collector->stopTimer();
8473 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8474 if (PrintCMSStatistics != 0) {
8475 _collector->incrementYields();
8476 }
8477 _collector->icms_wait();
8478
8479 // See the comment in coordinator_yield()
8480 for (unsigned i = 0; i < CMSYieldSleepCount &&
8481 ConcurrentMarkSweepThread::should_yield() &&
8482 !CMSCollector::foregroundGCIsActive(); ++i) {
8483 os::sleep(Thread::current(), 1, false);
8484 ConcurrentMarkSweepThread::acknowledge_yield_request();
8485 }
8486
8487 ConcurrentMarkSweepThread::synchronize(true);
8488 _freelistLock->lock();
8489 _bitMap->lock()->lock_without_safepoint_check();
8490 _collector->startTimer();
8491 }
8492
8493 #ifndef PRODUCT
8494 // This is actually very useful in a product build if it can
8495 // be called from the debugger. Compile it into the product
8496 // as needed.
8497 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8498 return debug_cms_space->verify_chunk_in_free_list(fc);
8499 }
8500 #endif
8501
8502 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8503 if (CMSTraceSweeper) {
8504 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8505 fc, fc->size());
8506 }
8507 }
8508
8509 // CMSIsAliveClosure
8510 bool CMSIsAliveClosure::do_object_b(oop obj) {
8511 HeapWord* addr = (HeapWord*)obj;
8512 return addr != NULL &&
8513 (!_span.contains(addr) || _bit_map->isMarked(addr));
8514 }
8515
8516
8517 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8518 MemRegion span,
8519 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8520 bool cpc):
8521 _collector(collector),
8522 _span(span),
8523 _bit_map(bit_map),
8524 _mark_stack(mark_stack),
8525 _concurrent_precleaning(cpc) {
8526 assert(!_span.is_empty(), "Empty span could spell trouble");
8527 }
8528
8529
8530 // CMSKeepAliveClosure: the serial version
8531 void CMSKeepAliveClosure::do_oop(oop obj) {
8532 HeapWord* addr = (HeapWord*)obj;
8533 if (_span.contains(addr) &&
8534 !_bit_map->isMarked(addr)) {
8535 _bit_map->mark(addr);
8536 bool simulate_overflow = false;
8537 NOT_PRODUCT(
8538 if (CMSMarkStackOverflowALot &&
8539 _collector->simulate_overflow()) {
8540 // simulate a stack overflow
8541 simulate_overflow = true;
8542 }
8543 )
8544 if (simulate_overflow || !_mark_stack->push(obj)) {
8545 if (_concurrent_precleaning) {
8546 // We dirty the overflown object and let the remark
8547 // phase deal with it.
8548 assert(_collector->overflow_list_is_empty(), "Error");
8549 // In the case of object arrays, we need to dirty all of
8550 // the cards that the object spans. No locking or atomics
8551 // are needed since no one else can be mutating the mod union
8552 // table.
8553 if (obj->is_objArray()) {
8554 size_t sz = obj->size();
8555 HeapWord* end_card_addr =
8556 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8557 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8558 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8559 _collector->_modUnionTable.mark_range(redirty_range);
8560 } else {
8561 _collector->_modUnionTable.mark(addr);
8562 }
8563 _collector->_ser_kac_preclean_ovflw++;
8564 } else {
8565 _collector->push_on_overflow_list(obj);
8566 _collector->_ser_kac_ovflw++;
8567 }
8568 }
8569 }
8570 }
8571
8572 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8573 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8574
8575 // CMSParKeepAliveClosure: a parallel version of the above.
8576 // The work queues are private to each closure (thread),
8577 // but (may be) available for stealing by other threads.
8578 void CMSParKeepAliveClosure::do_oop(oop obj) {
8579 HeapWord* addr = (HeapWord*)obj;
8580 if (_span.contains(addr) &&
8581 !_bit_map->isMarked(addr)) {
8582 // In general, during recursive tracing, several threads
8583 // may be concurrently getting here; the first one to
8584 // "tag" it, claims it.
8585 if (_bit_map->par_mark(addr)) {
8586 bool res = _work_queue->push(obj);
8587 assert(res, "Low water mark should be much less than capacity");
8588 // Do a recursive trim in the hope that this will keep
8589 // stack usage lower, but leave some oops for potential stealers
8590 trim_queue(_low_water_mark);
8591 } // Else, another thread got there first
8592 }
8593 }
8594
8595 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8596 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8597
8598 void CMSParKeepAliveClosure::trim_queue(uint max) {
8599 while (_work_queue->size() > max) {
8600 oop new_oop;
8601 if (_work_queue->pop_local(new_oop)) {
8602 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8603 assert(_bit_map->isMarked((HeapWord*)new_oop),
8604 "no white objects on this stack!");
8605 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8606 // iterate over the oops in this oop, marking and pushing
8607 // the ones in CMS heap (i.e. in _span).
8608 new_oop->oop_iterate(&_mark_and_push);
8609 }
8610 }
8611 }
8612
8613 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8614 CMSCollector* collector,
8615 MemRegion span, CMSBitMap* bit_map,
8616 OopTaskQueue* work_queue):
8617 _collector(collector),
8618 _span(span),
8619 _bit_map(bit_map),
8620 _work_queue(work_queue) { }
8621
8622 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8623 HeapWord* addr = (HeapWord*)obj;
8624 if (_span.contains(addr) &&
8625 !_bit_map->isMarked(addr)) {
8626 if (_bit_map->par_mark(addr)) {
8627 bool simulate_overflow = false;
8628 NOT_PRODUCT(
8629 if (CMSMarkStackOverflowALot &&
8630 _collector->par_simulate_overflow()) {
8631 // simulate a stack overflow
8632 simulate_overflow = true;
8633 }
8634 )
8635 if (simulate_overflow || !_work_queue->push(obj)) {
8636 _collector->par_push_on_overflow_list(obj);
8637 _collector->_par_kac_ovflw++;
8638 }
8639 } // Else another thread got there already
8640 }
8641 }
8642
8643 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8644 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8645
8646 //////////////////////////////////////////////////////////////////
8647 // CMSExpansionCause /////////////////////////////
8648 //////////////////////////////////////////////////////////////////
8649 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8650 switch (cause) {
8651 case _no_expansion:
8652 return "No expansion";
8653 case _satisfy_free_ratio:
8654 return "Free ratio";
8655 case _satisfy_promotion:
8656 return "Satisfy promotion";
8657 case _satisfy_allocation:
8658 return "allocation";
8659 case _allocate_par_lab:
8660 return "Par LAB";
8661 case _allocate_par_spooling_space:
8662 return "Par Spooling Space";
8663 case _adaptive_size_policy:
8664 return "Ergonomics";
8665 default:
8666 return "unknown";
8667 }
8668 }
8669
8670 void CMSDrainMarkingStackClosure::do_void() {
8671 // the max number to take from overflow list at a time
8672 const size_t num = _mark_stack->capacity()/4;
8673 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8674 "Overflow list should be NULL during concurrent phases");
8675 while (!_mark_stack->isEmpty() ||
8676 // if stack is empty, check the overflow list
8677 _collector->take_from_overflow_list(num, _mark_stack)) {
8678 oop obj = _mark_stack->pop();
8679 HeapWord* addr = (HeapWord*)obj;
8680 assert(_span.contains(addr), "Should be within span");
8681 assert(_bit_map->isMarked(addr), "Should be marked");
8682 assert(obj->is_oop(), "Should be an oop");
8683 obj->oop_iterate(_keep_alive);
8684 }
8685 }
8686
8687 void CMSParDrainMarkingStackClosure::do_void() {
8688 // drain queue
8689 trim_queue(0);
8690 }
8691
8692 // Trim our work_queue so its length is below max at return
8693 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8694 while (_work_queue->size() > max) {
8695 oop new_oop;
8696 if (_work_queue->pop_local(new_oop)) {
8697 assert(new_oop->is_oop(), "Expected an oop");
8698 assert(_bit_map->isMarked((HeapWord*)new_oop),
8699 "no white objects on this stack!");
8700 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8701 // iterate over the oops in this oop, marking and pushing
8702 // the ones in CMS heap (i.e. in _span).
8703 new_oop->oop_iterate(&_mark_and_push);
8704 }
8705 }
8706 }
8707
8708 ////////////////////////////////////////////////////////////////////
8709 // Support for Marking Stack Overflow list handling and related code
8710 ////////////////////////////////////////////////////////////////////
8711 // Much of the following code is similar in shape and spirit to the
8712 // code used in ParNewGC. We should try and share that code
8713 // as much as possible in the future.
8714
8715 #ifndef PRODUCT
8716 // Debugging support for CMSStackOverflowALot
8717
8718 // It's OK to call this multi-threaded; the worst thing
8719 // that can happen is that we'll get a bunch of closely
8720 // spaced simulated oveflows, but that's OK, in fact
8721 // probably good as it would exercise the overflow code
8722 // under contention.
8723 bool CMSCollector::simulate_overflow() {
8724 if (_overflow_counter-- <= 0) { // just being defensive
8725 _overflow_counter = CMSMarkStackOverflowInterval;
8726 return true;
8727 } else {
8728 return false;
8729 }
8730 }
8731
8732 bool CMSCollector::par_simulate_overflow() {
8733 return simulate_overflow();
8734 }
8735 #endif
8736
8737 // Single-threaded
8738 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8739 assert(stack->isEmpty(), "Expected precondition");
8740 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8741 size_t i = num;
8742 oop cur = _overflow_list;
8743 const markOop proto = markOopDesc::prototype();
8744 NOT_PRODUCT(ssize_t n = 0;)
8745 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8746 next = oop(cur->mark());
8747 cur->set_mark(proto); // until proven otherwise
8748 assert(cur->is_oop(), "Should be an oop");
8749 bool res = stack->push(cur);
8750 assert(res, "Bit off more than can chew?");
8751 NOT_PRODUCT(n++;)
8752 }
8753 _overflow_list = cur;
8754 #ifndef PRODUCT
8755 assert(_num_par_pushes >= n, "Too many pops?");
8756 _num_par_pushes -=n;
8757 #endif
8758 return !stack->isEmpty();
8759 }
8760
8761 #define BUSY (oop(0x1aff1aff))
8762 // (MT-safe) Get a prefix of at most "num" from the list.
8763 // The overflow list is chained through the mark word of
8764 // each object in the list. We fetch the entire list,
8765 // break off a prefix of the right size and return the
8766 // remainder. If other threads try to take objects from
8767 // the overflow list at that time, they will wait for
8768 // some time to see if data becomes available. If (and
8769 // only if) another thread places one or more object(s)
8770 // on the global list before we have returned the suffix
8771 // to the global list, we will walk down our local list
8772 // to find its end and append the global list to
8773 // our suffix before returning it. This suffix walk can
8774 // prove to be expensive (quadratic in the amount of traffic)
8775 // when there are many objects in the overflow list and
8776 // there is much producer-consumer contention on the list.
8777 // *NOTE*: The overflow list manipulation code here and
8778 // in ParNewGeneration:: are very similar in shape,
8779 // except that in the ParNew case we use the old (from/eden)
8780 // copy of the object to thread the list via its klass word.
8781 // Because of the common code, if you make any changes in
8782 // the code below, please check the ParNew version to see if
8783 // similar changes might be needed.
8784 // CR 6797058 has been filed to consolidate the common code.
8785 bool CMSCollector::par_take_from_overflow_list(size_t num,
8786 OopTaskQueue* work_q,
8787 int no_of_gc_threads) {
8788 assert(work_q->size() == 0, "First empty local work queue");
8789 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8790 if (_overflow_list == NULL) {
8791 return false;
8792 }
8793 // Grab the entire list; we'll put back a suffix
8794 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8795 Thread* tid = Thread::current();
8796 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8797 // set to ParallelGCThreads.
8798 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8799 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8800 // If the list is busy, we spin for a short while,
8801 // sleeping between attempts to get the list.
8802 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8803 os::sleep(tid, sleep_time_millis, false);
8804 if (_overflow_list == NULL) {
8805 // Nothing left to take
8806 return false;
8807 } else if (_overflow_list != BUSY) {
8808 // Try and grab the prefix
8809 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8810 }
8811 }
8812 // If the list was found to be empty, or we spun long
8813 // enough, we give up and return empty-handed. If we leave
8814 // the list in the BUSY state below, it must be the case that
8815 // some other thread holds the overflow list and will set it
8816 // to a non-BUSY state in the future.
8817 if (prefix == NULL || prefix == BUSY) {
8818 // Nothing to take or waited long enough
8819 if (prefix == NULL) {
8820 // Write back the NULL in case we overwrote it with BUSY above
8821 // and it is still the same value.
8822 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8823 }
8824 return false;
8825 }
8826 assert(prefix != NULL && prefix != BUSY, "Error");
8827 size_t i = num;
8828 oop cur = prefix;
8829 // Walk down the first "num" objects, unless we reach the end.
8830 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8831 if (cur->mark() == NULL) {
8832 // We have "num" or fewer elements in the list, so there
8833 // is nothing to return to the global list.
8834 // Write back the NULL in lieu of the BUSY we wrote
8835 // above, if it is still the same value.
8836 if (_overflow_list == BUSY) {
8837 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8838 }
8839 } else {
8840 // Chop off the suffix and rerturn it to the global list.
8841 assert(cur->mark() != BUSY, "Error");
8842 oop suffix_head = cur->mark(); // suffix will be put back on global list
8843 cur->set_mark(NULL); // break off suffix
8844 // It's possible that the list is still in the empty(busy) state
8845 // we left it in a short while ago; in that case we may be
8846 // able to place back the suffix without incurring the cost
8847 // of a walk down the list.
8848 oop observed_overflow_list = _overflow_list;
8849 oop cur_overflow_list = observed_overflow_list;
8850 bool attached = false;
8851 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8852 observed_overflow_list =
8853 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8854 if (cur_overflow_list == observed_overflow_list) {
8855 attached = true;
8856 break;
8857 } else cur_overflow_list = observed_overflow_list;
8858 }
8859 if (!attached) {
8860 // Too bad, someone else sneaked in (at least) an element; we'll need
8861 // to do a splice. Find tail of suffix so we can prepend suffix to global
8862 // list.
8863 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8864 oop suffix_tail = cur;
8865 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8866 "Tautology");
8867 observed_overflow_list = _overflow_list;
8868 do {
8869 cur_overflow_list = observed_overflow_list;
8870 if (cur_overflow_list != BUSY) {
8871 // Do the splice ...
8872 suffix_tail->set_mark(markOop(cur_overflow_list));
8873 } else { // cur_overflow_list == BUSY
8874 suffix_tail->set_mark(NULL);
8875 }
8876 // ... and try to place spliced list back on overflow_list ...
8877 observed_overflow_list =
8878 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8879 } while (cur_overflow_list != observed_overflow_list);
8880 // ... until we have succeeded in doing so.
8881 }
8882 }
8883
8884 // Push the prefix elements on work_q
8885 assert(prefix != NULL, "control point invariant");
8886 const markOop proto = markOopDesc::prototype();
8887 oop next;
8888 NOT_PRODUCT(ssize_t n = 0;)
8889 for (cur = prefix; cur != NULL; cur = next) {
8890 next = oop(cur->mark());
8891 cur->set_mark(proto); // until proven otherwise
8892 assert(cur->is_oop(), "Should be an oop");
8893 bool res = work_q->push(cur);
8894 assert(res, "Bit off more than we can chew?");
8895 NOT_PRODUCT(n++;)
8896 }
8897 #ifndef PRODUCT
8898 assert(_num_par_pushes >= n, "Too many pops?");
8899 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8900 #endif
8901 return true;
8902 }
8903
8904 // Single-threaded
8905 void CMSCollector::push_on_overflow_list(oop p) {
8906 NOT_PRODUCT(_num_par_pushes++;)
8907 assert(p->is_oop(), "Not an oop");
8908 preserve_mark_if_necessary(p);
8909 p->set_mark((markOop)_overflow_list);
8910 _overflow_list = p;
8911 }
8912
8913 // Multi-threaded; use CAS to prepend to overflow list
8914 void CMSCollector::par_push_on_overflow_list(oop p) {
8915 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8916 assert(p->is_oop(), "Not an oop");
8917 par_preserve_mark_if_necessary(p);
8918 oop observed_overflow_list = _overflow_list;
8919 oop cur_overflow_list;
8920 do {
8921 cur_overflow_list = observed_overflow_list;
8922 if (cur_overflow_list != BUSY) {
8923 p->set_mark(markOop(cur_overflow_list));
8924 } else {
8925 p->set_mark(NULL);
8926 }
8927 observed_overflow_list =
8928 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8929 } while (cur_overflow_list != observed_overflow_list);
8930 }
8931 #undef BUSY
8932
8933 // Single threaded
8934 // General Note on GrowableArray: pushes may silently fail
8935 // because we are (temporarily) out of C-heap for expanding
8936 // the stack. The problem is quite ubiquitous and affects
8937 // a lot of code in the JVM. The prudent thing for GrowableArray
8938 // to do (for now) is to exit with an error. However, that may
8939 // be too draconian in some cases because the caller may be
8940 // able to recover without much harm. For such cases, we
8941 // should probably introduce a "soft_push" method which returns
8942 // an indication of success or failure with the assumption that
8943 // the caller may be able to recover from a failure; code in
8944 // the VM can then be changed, incrementally, to deal with such
8945 // failures where possible, thus, incrementally hardening the VM
8946 // in such low resource situations.
8947 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8948 _preserved_oop_stack.push(p);
8949 _preserved_mark_stack.push(m);
8950 assert(m == p->mark(), "Mark word changed");
8951 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8952 "bijection");
8953 }
8954
8955 // Single threaded
8956 void CMSCollector::preserve_mark_if_necessary(oop p) {
8957 markOop m = p->mark();
8958 if (m->must_be_preserved(p)) {
8959 preserve_mark_work(p, m);
8960 }
8961 }
8962
8963 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8964 markOop m = p->mark();
8965 if (m->must_be_preserved(p)) {
8966 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8967 // Even though we read the mark word without holding
8968 // the lock, we are assured that it will not change
8969 // because we "own" this oop, so no other thread can
8970 // be trying to push it on the overflow list; see
8971 // the assertion in preserve_mark_work() that checks
8972 // that m == p->mark().
8973 preserve_mark_work(p, m);
8974 }
8975 }
8976
8977 // We should be able to do this multi-threaded,
8978 // a chunk of stack being a task (this is
8979 // correct because each oop only ever appears
8980 // once in the overflow list. However, it's
8981 // not very easy to completely overlap this with
8982 // other operations, so will generally not be done
8983 // until all work's been completed. Because we
8984 // expect the preserved oop stack (set) to be small,
8985 // it's probably fine to do this single-threaded.
8986 // We can explore cleverer concurrent/overlapped/parallel
8987 // processing of preserved marks if we feel the
8988 // need for this in the future. Stack overflow should
8989 // be so rare in practice and, when it happens, its
8990 // effect on performance so great that this will
8991 // likely just be in the noise anyway.
8992 void CMSCollector::restore_preserved_marks_if_any() {
8993 assert(SafepointSynchronize::is_at_safepoint(),
8994 "world should be stopped");
8995 assert(Thread::current()->is_ConcurrentGC_thread() ||
8996 Thread::current()->is_VM_thread(),
8997 "should be single-threaded");
8998 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8999 "bijection");
9000
9001 while (!_preserved_oop_stack.is_empty()) {
9002 oop p = _preserved_oop_stack.pop();
9003 assert(p->is_oop(), "Should be an oop");
9004 assert(_span.contains(p), "oop should be in _span");
9005 assert(p->mark() == markOopDesc::prototype(),
9006 "Set when taken from overflow list");
9007 markOop m = _preserved_mark_stack.pop();
9008 p->set_mark(m);
9009 }
9010 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9011 "stacks were cleared above");
9012 }
9013
9014 #ifndef PRODUCT
9015 bool CMSCollector::no_preserved_marks() const {
9016 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9017 }
9018 #endif
9019
9020 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9021 {
9022 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9023 CMSAdaptiveSizePolicy* size_policy =
9024 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9025 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9026 "Wrong type for size policy");
9027 return size_policy;
9028 }
9029
9030 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9031 size_t desired_promo_size) {
9032 if (cur_promo_size < desired_promo_size) {
9033 size_t expand_bytes = desired_promo_size - cur_promo_size;
9034 if (PrintAdaptiveSizePolicy && Verbose) {
9035 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9036 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9037 expand_bytes);
9038 }
9039 expand(expand_bytes,
9040 MinHeapDeltaBytes,
9041 CMSExpansionCause::_adaptive_size_policy);
9042 } else if (desired_promo_size < cur_promo_size) {
9043 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9044 if (PrintAdaptiveSizePolicy && Verbose) {
9045 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9046 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9047 shrink_bytes);
9048 }
9049 shrink(shrink_bytes);
9050 }
9051 }
9052
9053 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9054 GenCollectedHeap* gch = GenCollectedHeap::heap();
9055 CMSGCAdaptivePolicyCounters* counters =
9056 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9057 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9058 "Wrong kind of counters");
9059 return counters;
9060 }
9061
9062
9063 void ASConcurrentMarkSweepGeneration::update_counters() {
9064 if (UsePerfData) {
9065 _space_counters->update_all();
9066 _gen_counters->update_all();
9067 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9068 GenCollectedHeap* gch = GenCollectedHeap::heap();
9069 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9070 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9071 "Wrong gc statistics type");
9072 counters->update_counters(gc_stats_l);
9073 }
9074 }
9075
9076 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9077 if (UsePerfData) {
9078 _space_counters->update_used(used);
9079 _space_counters->update_capacity();
9080 _gen_counters->update_all();
9081
9082 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9083 GenCollectedHeap* gch = GenCollectedHeap::heap();
9084 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9085 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9086 "Wrong gc statistics type");
9087 counters->update_counters(gc_stats_l);
9088 }
9089 }
9090
9091 // The desired expansion delta is computed so that:
9092 // . desired free percentage or greater is used
9093 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9094 assert_locked_or_safepoint(Heap_lock);
9095
9096 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9097
9098 // If incremental collection failed, we just want to expand
9099 // to the limit.
9100 if (incremental_collection_failed()) {
9101 clear_incremental_collection_failed();
9102 grow_to_reserved();
9103 return;
9104 }
9105
9106 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9107
9108 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9109 "Wrong type of heap");
9110 int prev_level = level() - 1;
9111 assert(prev_level >= 0, "The cms generation is the lowest generation");
9112 Generation* prev_gen = gch->get_gen(prev_level);
9113 assert(prev_gen->kind() == Generation::ASParNew,
9114 "Wrong type of young generation");
9115 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9116 size_t cur_eden = younger_gen->eden()->capacity();
9117 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9118 size_t cur_promo = free();
9119 size_policy->compute_tenured_generation_free_space(cur_promo,
9120 max_available(),
9121 cur_eden);
9122 resize(cur_promo, size_policy->promo_size());
9123
9124 // Record the new size of the space in the cms generation
9125 // that is available for promotions. This is temporary.
9126 // It should be the desired promo size.
9127 size_policy->avg_cms_promo()->sample(free());
9128 size_policy->avg_old_live()->sample(used());
9129
9130 if (UsePerfData) {
9131 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9132 counters->update_cms_capacity_counter(capacity());
9133 }
9134 }
9135
9136 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9137 assert_locked_or_safepoint(Heap_lock);
9138 assert_lock_strong(freelistLock());
9139 HeapWord* old_end = _cmsSpace->end();
9140 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9141 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9142 FreeChunk* chunk_at_end = find_chunk_at_end();
9143 if (chunk_at_end == NULL) {
9144 // No room to shrink
9145 if (PrintGCDetails && Verbose) {
9146 gclog_or_tty->print_cr("No room to shrink: old_end "
9147 PTR_FORMAT " unallocated_start " PTR_FORMAT
9148 " chunk_at_end " PTR_FORMAT,
9149 old_end, unallocated_start, chunk_at_end);
9150 }
9151 return;
9152 } else {
9153
9154 // Find the chunk at the end of the space and determine
9155 // how much it can be shrunk.
9156 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9157 size_t aligned_shrinkable_size_in_bytes =
9158 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9159 assert(unallocated_start <= chunk_at_end->end(),
9160 "Inconsistent chunk at end of space");
9161 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9162 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9163
9164 // Shrink the underlying space
9165 _virtual_space.shrink_by(bytes);
9166 if (PrintGCDetails && Verbose) {
9167 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9168 " desired_bytes " SIZE_FORMAT
9169 " shrinkable_size_in_bytes " SIZE_FORMAT
9170 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9171 " bytes " SIZE_FORMAT,
9172 desired_bytes, shrinkable_size_in_bytes,
9173 aligned_shrinkable_size_in_bytes, bytes);
9174 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9175 " unallocated_start " SIZE_FORMAT,
9176 old_end, unallocated_start);
9177 }
9178
9179 // If the space did shrink (shrinking is not guaranteed),
9180 // shrink the chunk at the end by the appropriate amount.
9181 if (((HeapWord*)_virtual_space.high()) < old_end) {
9182 size_t new_word_size =
9183 heap_word_size(_virtual_space.committed_size());
9184
9185 // Have to remove the chunk from the dictionary because it is changing
9186 // size and might be someplace elsewhere in the dictionary.
9187
9188 // Get the chunk at end, shrink it, and put it
9189 // back.
9190 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9191 size_t word_size_change = word_size_before - new_word_size;
9192 size_t chunk_at_end_old_size = chunk_at_end->size();
9193 assert(chunk_at_end_old_size >= word_size_change,
9194 "Shrink is too large");
9195 chunk_at_end->set_size(chunk_at_end_old_size -
9196 word_size_change);
9197 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9198 word_size_change);
9199
9200 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9201
9202 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9203 _bts->resize(new_word_size); // resize the block offset shared array
9204 Universe::heap()->barrier_set()->resize_covered_region(mr);
9205 _cmsSpace->assert_locked();
9206 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9207
9208 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9209
9210 // update the space and generation capacity counters
9211 if (UsePerfData) {
9212 _space_counters->update_capacity();
9213 _gen_counters->update_all();
9214 }
9215
9216 if (Verbose && PrintGCDetails) {
9217 size_t new_mem_size = _virtual_space.committed_size();
9218 size_t old_mem_size = new_mem_size + bytes;
9219 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9220 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9221 }
9222 }
9223
9224 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9225 "Inconsistency at end of space");
9226 assert(chunk_at_end->end() == _cmsSpace->end(),
9227 "Shrinking is inconsistent");
9228 return;
9229 }
9230 }
9231
9232 // Transfer some number of overflown objects to usual marking
9233 // stack. Return true if some objects were transferred.
9234 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9235 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9236 (size_t)ParGCDesiredObjsFromOverflowList);
9237
9238 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9239 assert(_collector->overflow_list_is_empty() || res,
9240 "If list is not empty, we should have taken something");
9241 assert(!res || !_mark_stack->isEmpty(),
9242 "If we took something, it should now be on our stack");
9243 return res;
9244 }
9245
9246 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9247 size_t res = _sp->block_size_no_stall(addr, _collector);
9248 if (_sp->block_is_obj(addr)) {
9249 if (_live_bit_map->isMarked(addr)) {
9250 // It can't have been dead in a previous cycle
9251 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9252 } else {
9253 _dead_bit_map->mark(addr); // mark the dead object
9254 }
9255 }
9256 // Could be 0, if the block size could not be computed without stalling.
9257 return res;
9258 }
9259
9260 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9261
9262 switch (phase) {
9263 case CMSCollector::InitialMarking:
9264 initialize(true /* fullGC */ ,
9265 cause /* cause of the GC */,
9266 true /* recordGCBeginTime */,
9267 true /* recordPreGCUsage */,
9268 false /* recordPeakUsage */,
9269 false /* recordPostGCusage */,
9270 true /* recordAccumulatedGCTime */,
9271 false /* recordGCEndTime */,
9272 false /* countCollection */ );
9273 break;
9274
9275 case CMSCollector::FinalMarking:
9276 initialize(true /* fullGC */ ,
9277 cause /* cause of the GC */,
9278 false /* recordGCBeginTime */,
9279 false /* recordPreGCUsage */,
9280 false /* recordPeakUsage */,
9281 false /* recordPostGCusage */,
9282 true /* recordAccumulatedGCTime */,
9283 false /* recordGCEndTime */,
9284 false /* countCollection */ );
9285 break;
9286
9287 case CMSCollector::Sweeping:
9288 initialize(true /* fullGC */ ,
9289 cause /* cause of the GC */,
9290 false /* recordGCBeginTime */,
9291 false /* recordPreGCUsage */,
9292 true /* recordPeakUsage */,
9293 true /* recordPostGCusage */,
9294 false /* recordAccumulatedGCTime */,
9295 true /* recordGCEndTime */,
9296 true /* countCollection */ );
9297 break;
9298
9299 default:
9300 ShouldNotReachHere();
9301 }
9302 }
9303