1 /*
2 * Copyright (c) 2001, 2017, 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 "gc/cms/compactibleFreeListSpace.hpp"
27 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
28 #include "gc/cms/parNewGeneration.inline.hpp"
29 #include "gc/cms/parOopClosures.inline.hpp"
30 #include "gc/serial/defNewGeneration.inline.hpp"
31 #include "gc/shared/adaptiveSizePolicy.hpp"
32 #include "gc/shared/ageTable.inline.hpp"
33 #include "gc/shared/copyFailedInfo.hpp"
34 #include "gc/shared/gcHeapSummary.hpp"
35 #include "gc/shared/gcTimer.hpp"
36 #include "gc/shared/gcTrace.hpp"
37 #include "gc/shared/gcTraceTime.inline.hpp"
38 #include "gc/shared/genCollectedHeap.hpp"
39 #include "gc/shared/genOopClosures.inline.hpp"
40 #include "gc/shared/generation.hpp"
41 #include "gc/shared/plab.inline.hpp"
42 #include "gc/shared/preservedMarks.inline.hpp"
43 #include "gc/shared/referencePolicy.hpp"
44 #include "gc/shared/space.hpp"
45 #include "gc/shared/spaceDecorator.hpp"
46 #include "gc/shared/strongRootsScope.hpp"
47 #include "gc/shared/taskqueue.inline.hpp"
48 #include "gc/shared/weakProcessor.hpp"
49 #include "gc/shared/workgroup.hpp"
50 #include "logging/log.hpp"
51 #include "logging/logStream.hpp"
52 #include "memory/resourceArea.hpp"
53 #include "oops/objArrayOop.hpp"
54 #include "oops/oop.inline.hpp"
55 #include "runtime/atomic.hpp"
56 #include "runtime/handles.hpp"
57 #include "runtime/handles.inline.hpp"
58 #include "runtime/java.hpp"
59 #include "runtime/thread.inline.hpp"
60 #include "utilities/copy.hpp"
61 #include "utilities/globalDefinitions.hpp"
62 #include "utilities/stack.inline.hpp"
63
64 ParScanThreadState::ParScanThreadState(Space* to_space_,
65 ParNewGeneration* young_gen_,
66 Generation* old_gen_,
67 int thread_num_,
68 ObjToScanQueueSet* work_queue_set_,
69 Stack<oop, mtGC>* overflow_stacks_,
70 PreservedMarks* preserved_marks_,
71 size_t desired_plab_sz_,
72 ParallelTaskTerminator& term_) :
73 _to_space(to_space_),
74 _old_gen(old_gen_),
75 _young_gen(young_gen_),
76 _thread_num(thread_num_),
77 _work_queue(work_queue_set_->queue(thread_num_)),
78 _to_space_full(false),
79 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
80 _preserved_marks(preserved_marks_),
81 _ageTable(false), // false ==> not the global age table, no perf data.
82 _to_space_alloc_buffer(desired_plab_sz_),
83 _to_space_closure(young_gen_, this),
84 _old_gen_closure(young_gen_, this),
85 _to_space_root_closure(young_gen_, this),
86 _old_gen_root_closure(young_gen_, this),
87 _older_gen_closure(young_gen_, this),
88 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
89 &_to_space_root_closure, young_gen_, &_old_gen_root_closure,
90 work_queue_set_, &term_),
91 _is_alive_closure(young_gen_),
92 _scan_weak_ref_closure(young_gen_, this),
93 _keep_alive_closure(&_scan_weak_ref_closure),
94 _strong_roots_time(0.0),
95 _term_time(0.0)
96 {
97 #if TASKQUEUE_STATS
98 _term_attempts = 0;
99 _overflow_refills = 0;
100 _overflow_refill_objs = 0;
101 #endif // TASKQUEUE_STATS
102
103 _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num());
104 _hash_seed = 17; // Might want to take time-based random value.
105 _start = os::elapsedTime();
106 _old_gen_closure.set_generation(old_gen_);
107 _old_gen_root_closure.set_generation(old_gen_);
108 }
109
110 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
111 size_t plab_word_size) {
112 ChunkArray* sca = survivor_chunk_array();
113 if (sca != NULL) {
114 // A non-null SCA implies that we want the PLAB data recorded.
115 sca->record_sample(plab_start, plab_word_size);
116 }
117 }
118
119 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
120 return new_obj->is_objArray() &&
121 arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
122 new_obj != old_obj;
123 }
124
125 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
126 assert(old->is_objArray(), "must be obj array");
127 assert(old->is_forwarded(), "must be forwarded");
128 assert(GenCollectedHeap::heap()->is_in_reserved(old), "must be in heap.");
129 assert(!old_gen()->is_in(old), "must be in young generation.");
130
131 objArrayOop obj = objArrayOop(old->forwardee());
132 // Process ParGCArrayScanChunk elements now
133 // and push the remainder back onto queue
134 int start = arrayOop(old)->length();
135 int end = obj->length();
136 int remainder = end - start;
137 assert(start <= end, "just checking");
138 if (remainder > 2 * ParGCArrayScanChunk) {
139 // Test above combines last partial chunk with a full chunk
140 end = start + ParGCArrayScanChunk;
141 arrayOop(old)->set_length(end);
142 // Push remainder.
143 bool ok = work_queue()->push(old);
144 assert(ok, "just popped, push must be okay");
145 } else {
146 // Restore length so that it can be used if there
147 // is a promotion failure and forwarding pointers
148 // must be removed.
149 arrayOop(old)->set_length(end);
150 }
151
152 // process our set of indices (include header in first chunk)
153 // should make sure end is even (aligned to HeapWord in case of compressed oops)
154 if ((HeapWord *)obj < young_old_boundary()) {
155 // object is in to_space
156 obj->oop_iterate_range(&_to_space_closure, start, end);
157 } else {
158 // object is in old generation
159 obj->oop_iterate_range(&_old_gen_closure, start, end);
160 }
161 }
162
163 void ParScanThreadState::trim_queues(int max_size) {
164 ObjToScanQueue* queue = work_queue();
165 do {
166 while (queue->size() > (juint)max_size) {
167 oop obj_to_scan;
168 if (queue->pop_local(obj_to_scan)) {
169 if ((HeapWord *)obj_to_scan < young_old_boundary()) {
170 if (obj_to_scan->is_objArray() &&
171 obj_to_scan->is_forwarded() &&
172 obj_to_scan->forwardee() != obj_to_scan) {
173 scan_partial_array_and_push_remainder(obj_to_scan);
174 } else {
175 // object is in to_space
176 obj_to_scan->oop_iterate(&_to_space_closure);
177 }
178 } else {
179 // object is in old generation
180 obj_to_scan->oop_iterate(&_old_gen_closure);
181 }
182 }
183 }
184 // For the case of compressed oops, we have a private, non-shared
185 // overflow stack, so we eagerly drain it so as to more evenly
186 // distribute load early. Note: this may be good to do in
187 // general rather than delay for the final stealing phase.
188 // If applicable, we'll transfer a set of objects over to our
189 // work queue, allowing them to be stolen and draining our
190 // private overflow stack.
191 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
192 }
193
194 bool ParScanThreadState::take_from_overflow_stack() {
195 assert(ParGCUseLocalOverflow, "Else should not call");
196 assert(young_gen()->overflow_list() == NULL, "Error");
197 ObjToScanQueue* queue = work_queue();
198 Stack<oop, mtGC>* const of_stack = overflow_stack();
199 const size_t num_overflow_elems = of_stack->size();
200 const size_t space_available = queue->max_elems() - queue->size();
201 const size_t num_take_elems = MIN3(space_available / 4,
202 ParGCDesiredObjsFromOverflowList,
203 num_overflow_elems);
204 // Transfer the most recent num_take_elems from the overflow
205 // stack to our work queue.
206 for (size_t i = 0; i != num_take_elems; i++) {
207 oop cur = of_stack->pop();
208 oop obj_to_push = cur->forwardee();
209 assert(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap");
210 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
211 assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap");
212 if (should_be_partially_scanned(obj_to_push, cur)) {
213 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
214 obj_to_push = cur;
215 }
216 bool ok = queue->push(obj_to_push);
217 assert(ok, "Should have succeeded");
218 }
219 assert(young_gen()->overflow_list() == NULL, "Error");
220 return num_take_elems > 0; // was something transferred?
221 }
222
223 void ParScanThreadState::push_on_overflow_stack(oop p) {
224 assert(ParGCUseLocalOverflow, "Else should not call");
225 overflow_stack()->push(p);
226 assert(young_gen()->overflow_list() == NULL, "Error");
227 }
228
229 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
230 // If the object is small enough, try to reallocate the buffer.
231 HeapWord* obj = NULL;
232 if (!_to_space_full) {
233 PLAB* const plab = to_space_alloc_buffer();
234 Space* const sp = to_space();
235 if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) {
236 // Is small enough; abandon this buffer and start a new one.
237 plab->retire();
238 // The minimum size has to be twice SurvivorAlignmentInBytes to
239 // allow for padding used in the alignment of 1 word. A padding
240 // of 1 is too small for a filler word so the padding size will
241 // be increased by SurvivorAlignmentInBytes.
242 size_t min_usable_size = 2 * static_cast<size_t>(SurvivorAlignmentInBytes >> LogHeapWordSize);
243 size_t buf_size = MAX2(plab->word_sz(), min_usable_size);
244 HeapWord* buf_space = sp->par_allocate(buf_size);
245 if (buf_space == NULL) {
246 const size_t min_bytes = MAX2(PLAB::min_size(), min_usable_size) << LogHeapWordSize;
247 size_t free_bytes = sp->free();
248 while(buf_space == NULL && free_bytes >= min_bytes) {
249 buf_size = free_bytes >> LogHeapWordSize;
250 assert(buf_size == (size_t)align_object_size(buf_size), "Invariant");
251 buf_space = sp->par_allocate(buf_size);
252 free_bytes = sp->free();
253 }
254 }
255 if (buf_space != NULL) {
256 plab->set_buf(buf_space, buf_size);
257 record_survivor_plab(buf_space, buf_size);
258 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
259 // Note that we cannot compare buf_size < word_sz below
260 // because of AlignmentReserve (see PLAB::allocate()).
261 assert(obj != NULL || plab->words_remaining() < word_sz,
262 "Else should have been able to allocate requested object size "
263 SIZE_FORMAT ", PLAB size " SIZE_FORMAT ", SurvivorAlignmentInBytes "
264 SIZE_FORMAT ", words_remaining " SIZE_FORMAT,
265 word_sz, buf_size, SurvivorAlignmentInBytes, plab->words_remaining());
266 // It's conceivable that we may be able to use the
267 // buffer we just grabbed for subsequent small requests
268 // even if not for this one.
269 } else {
270 // We're used up.
271 _to_space_full = true;
272 }
273 } else {
274 // Too large; allocate the object individually.
275 obj = sp->par_allocate(word_sz);
276 }
277 }
278 return obj;
279 }
280
281 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) {
282 to_space_alloc_buffer()->undo_allocation(obj, word_sz);
283 }
284
285 void ParScanThreadState::print_promotion_failure_size() {
286 if (_promotion_failed_info.has_failed()) {
287 log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ",
288 _thread_num, _promotion_failed_info.first_size());
289 }
290 }
291
292 class ParScanThreadStateSet: StackObj {
293 public:
294 // Initializes states for the specified number of threads;
295 ParScanThreadStateSet(int num_threads,
296 Space& to_space,
297 ParNewGeneration& young_gen,
298 Generation& old_gen,
299 ObjToScanQueueSet& queue_set,
300 Stack<oop, mtGC>* overflow_stacks_,
301 PreservedMarksSet& preserved_marks_set,
302 size_t desired_plab_sz,
303 ParallelTaskTerminator& term);
304
305 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
306
307 inline ParScanThreadState& thread_state(int i);
308
309 void trace_promotion_failed(const YoungGCTracer* gc_tracer);
310 void reset(uint active_workers, bool promotion_failed);
311 void flush();
312
313 #if TASKQUEUE_STATS
314 static void
315 print_termination_stats_hdr(outputStream* const st);
316 void print_termination_stats();
317 static void
318 print_taskqueue_stats_hdr(outputStream* const st);
319 void print_taskqueue_stats();
320 void reset_stats();
321 #endif // TASKQUEUE_STATS
322
323 private:
324 ParallelTaskTerminator& _term;
325 ParNewGeneration& _young_gen;
326 Generation& _old_gen;
327 ParScanThreadState* _per_thread_states;
328 const int _num_threads;
329 public:
330 bool is_valid(int id) const { return id < _num_threads; }
331 ParallelTaskTerminator* terminator() { return &_term; }
332 };
333
334 ParScanThreadStateSet::ParScanThreadStateSet(int num_threads,
335 Space& to_space,
336 ParNewGeneration& young_gen,
337 Generation& old_gen,
338 ObjToScanQueueSet& queue_set,
339 Stack<oop, mtGC>* overflow_stacks,
340 PreservedMarksSet& preserved_marks_set,
341 size_t desired_plab_sz,
342 ParallelTaskTerminator& term)
343 : _young_gen(young_gen),
344 _old_gen(old_gen),
345 _term(term),
346 _per_thread_states(NEW_RESOURCE_ARRAY(ParScanThreadState, num_threads)),
347 _num_threads(num_threads)
348 {
349 assert(num_threads > 0, "sanity check!");
350 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
351 "overflow_stack allocation mismatch");
352 // Initialize states.
353 for (int i = 0; i < num_threads; ++i) {
354 new(_per_thread_states + i)
355 ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set,
356 overflow_stacks, preserved_marks_set.get(i),
357 desired_plab_sz, term);
358 }
359 }
360
361 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) {
362 assert(i >= 0 && i < _num_threads, "sanity check!");
363 return _per_thread_states[i];
364 }
365
366 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {
367 for (int i = 0; i < _num_threads; ++i) {
368 if (thread_state(i).promotion_failed()) {
369 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());
370 thread_state(i).promotion_failed_info().reset();
371 }
372 }
373 }
374
375 void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) {
376 _term.reset_for_reuse(active_threads);
377 if (promotion_failed) {
378 for (int i = 0; i < _num_threads; ++i) {
379 thread_state(i).print_promotion_failure_size();
380 }
381 }
382 }
383
384 #if TASKQUEUE_STATS
385 void ParScanThreadState::reset_stats() {
386 taskqueue_stats().reset();
387 _term_attempts = 0;
388 _overflow_refills = 0;
389 _overflow_refill_objs = 0;
390 }
391
392 void ParScanThreadStateSet::reset_stats() {
393 for (int i = 0; i < _num_threads; ++i) {
394 thread_state(i).reset_stats();
395 }
396 }
397
398 void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) {
399 st->print_raw_cr("GC Termination Stats");
400 st->print_raw_cr(" elapsed --strong roots-- -------termination-------");
401 st->print_raw_cr("thr ms ms % ms % attempts");
402 st->print_raw_cr("--- --------- --------- ------ --------- ------ --------");
403 }
404
405 void ParScanThreadStateSet::print_termination_stats() {
406 Log(gc, task, stats) log;
407 if (!log.is_debug()) {
408 return;
409 }
410
411 ResourceMark rm;
412 LogStream ls(log.debug());
413 outputStream* st = &ls;
414
415 print_termination_stats_hdr(st);
416
417 for (int i = 0; i < _num_threads; ++i) {
418 const ParScanThreadState & pss = thread_state(i);
419 const double elapsed_ms = pss.elapsed_time() * 1000.0;
420 const double s_roots_ms = pss.strong_roots_time() * 1000.0;
421 const double term_ms = pss.term_time() * 1000.0;
422 st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8),
423 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
424 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
425 }
426 }
427
428 // Print stats related to work queue activity.
429 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) {
430 st->print_raw_cr("GC Task Stats");
431 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
432 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
433 }
434
435 void ParScanThreadStateSet::print_taskqueue_stats() {
436 if (!log_develop_is_enabled(Trace, gc, task, stats)) {
437 return;
438 }
439 Log(gc, task, stats) log;
440 ResourceMark rm;
441 LogStream ls(log.trace());
442 outputStream* st = &ls;
443 print_taskqueue_stats_hdr(st);
444
445 TaskQueueStats totals;
446 for (int i = 0; i < _num_threads; ++i) {
447 const ParScanThreadState & pss = thread_state(i);
448 const TaskQueueStats & stats = pss.taskqueue_stats();
449 st->print("%3d ", i); stats.print(st); st->cr();
450 totals += stats;
451
452 if (pss.overflow_refills() > 0) {
453 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills "
454 SIZE_FORMAT_W(10) " overflow objects",
455 pss.overflow_refills(), pss.overflow_refill_objs());
456 }
457 }
458 st->print("tot "); totals.print(st); st->cr();
459
460 DEBUG_ONLY(totals.verify());
461 }
462 #endif // TASKQUEUE_STATS
463
464 void ParScanThreadStateSet::flush() {
465 // Work in this loop should be kept as lightweight as
466 // possible since this might otherwise become a bottleneck
467 // to scaling. Should we add heavy-weight work into this
468 // loop, consider parallelizing the loop into the worker threads.
469 for (int i = 0; i < _num_threads; ++i) {
470 ParScanThreadState& par_scan_state = thread_state(i);
471
472 // Flush stats related to To-space PLAB activity and
473 // retire the last buffer.
474 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats());
475
476 // Every thread has its own age table. We need to merge
477 // them all into one.
478 AgeTable *local_table = par_scan_state.age_table();
479 _young_gen.age_table()->merge(local_table);
480
481 // Inform old gen that we're done.
482 _old_gen.par_promote_alloc_done(i);
483 }
484
485 if (UseConcMarkSweepGC) {
486 // We need to call this even when ResizeOldPLAB is disabled
487 // so as to avoid breaking some asserts. While we may be able
488 // to avoid this by reorganizing the code a bit, I am loathe
489 // to do that unless we find cases where ergo leads to bad
490 // performance.
491 CompactibleFreeListSpaceLAB::compute_desired_plab_size();
492 }
493 }
494
495 ParScanClosure::ParScanClosure(ParNewGeneration* g,
496 ParScanThreadState* par_scan_state) :
497 OopsInClassLoaderDataOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) {
498 _boundary = _g->reserved().end();
499 }
500
501 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); }
502 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
503
504 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); }
505 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
506
507 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); }
508 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
509
510 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); }
511 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
512
513 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
514 ParScanThreadState* par_scan_state)
515 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
516 {}
517
518 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); }
519 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
520
521 #ifdef WIN32
522 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
523 #endif
524
525 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
526 ParScanThreadState* par_scan_state_,
527 ParScanWithoutBarrierClosure* to_space_closure_,
528 ParScanWithBarrierClosure* old_gen_closure_,
529 ParRootScanWithoutBarrierClosure* to_space_root_closure_,
530 ParNewGeneration* par_gen_,
531 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
532 ObjToScanQueueSet* task_queues_,
533 ParallelTaskTerminator* terminator_) :
534
535 _par_scan_state(par_scan_state_),
536 _to_space_closure(to_space_closure_),
537 _old_gen_closure(old_gen_closure_),
538 _to_space_root_closure(to_space_root_closure_),
539 _old_gen_root_closure(old_gen_root_closure_),
540 _par_gen(par_gen_),
541 _task_queues(task_queues_),
542 _terminator(terminator_)
543 {}
544
545 void ParEvacuateFollowersClosure::do_void() {
546 ObjToScanQueue* work_q = par_scan_state()->work_queue();
547
548 while (true) {
549 // Scan to-space and old-gen objs until we run out of both.
550 oop obj_to_scan;
551 par_scan_state()->trim_queues(0);
552
553 // We have no local work, attempt to steal from other threads.
554
555 // Attempt to steal work from promoted.
556 if (task_queues()->steal(par_scan_state()->thread_num(),
557 par_scan_state()->hash_seed(),
558 obj_to_scan)) {
559 bool res = work_q->push(obj_to_scan);
560 assert(res, "Empty queue should have room for a push.");
561
562 // If successful, goto Start.
563 continue;
564
565 // Try global overflow list.
566 } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
567 continue;
568 }
569
570 // Otherwise, offer termination.
571 par_scan_state()->start_term_time();
572 if (terminator()->offer_termination()) break;
573 par_scan_state()->end_term_time();
574 }
575 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
576 "Broken overflow list?");
577 // Finish the last termination pause.
578 par_scan_state()->end_term_time();
579 }
580
581 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen,
582 Generation* old_gen,
583 HeapWord* young_old_boundary,
584 ParScanThreadStateSet* state_set,
585 StrongRootsScope* strong_roots_scope) :
586 AbstractGangTask("ParNewGeneration collection"),
587 _young_gen(young_gen), _old_gen(old_gen),
588 _young_old_boundary(young_old_boundary),
589 _state_set(state_set),
590 _strong_roots_scope(strong_roots_scope)
591 {}
592
593 void ParNewGenTask::work(uint worker_id) {
594 GenCollectedHeap* gch = GenCollectedHeap::heap();
595 // Since this is being done in a separate thread, need new resource
596 // and handle marks.
597 ResourceMark rm;
598 HandleMark hm;
599
600 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
601 assert(_state_set->is_valid(worker_id), "Should not have been called");
602
603 par_scan_state.set_young_old_boundary(_young_old_boundary);
604
605 CLDScanClosure cld_scan_closure(&par_scan_state.to_space_root_closure(),
606 gch->rem_set()->cld_rem_set()->accumulate_modified_oops());
607
608 par_scan_state.start_strong_roots();
609 gch->young_process_roots(_strong_roots_scope,
610 &par_scan_state.to_space_root_closure(),
611 &par_scan_state.older_gen_closure(),
612 &cld_scan_closure);
613
614 par_scan_state.end_strong_roots();
615
616 // "evacuate followers".
617 par_scan_state.evacuate_followers_closure().do_void();
618
619 // This will collapse this worker's promoted object list that's
620 // created during the main ParNew parallel phase of ParNew. This has
621 // to be called after all workers have finished promoting objects
622 // and scanning promoted objects. It should be safe calling it from
623 // here, given that we can only reach here after all thread have
624 // offered termination, i.e., after there is no more work to be
625 // done. It will also disable promotion tracking for the rest of
626 // this GC as it's not necessary to be on during reference processing.
627 _old_gen->par_oop_since_save_marks_iterate_done((int) worker_id);
628 }
629
630 ParNewGeneration::ParNewGeneration(ReservedSpace rs, size_t initial_byte_size)
631 : DefNewGeneration(rs, initial_byte_size, "PCopy"),
632 _overflow_list(NULL),
633 _is_alive_closure(this),
634 _plab_stats("Young", YoungPLABSize, PLABWeight)
635 {
636 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
637 NOT_PRODUCT(_num_par_pushes = 0;)
638 _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
639 guarantee(_task_queues != NULL, "task_queues allocation failure.");
640
641 for (uint i = 0; i < ParallelGCThreads; i++) {
642 ObjToScanQueue *q = new ObjToScanQueue();
643 guarantee(q != NULL, "work_queue Allocation failure.");
644 _task_queues->register_queue(i, q);
645 }
646
647 for (uint i = 0; i < ParallelGCThreads; i++) {
648 _task_queues->queue(i)->initialize();
649 }
650
651 _overflow_stacks = NULL;
652 if (ParGCUseLocalOverflow) {
653 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ','
654 typedef Stack<oop, mtGC> GCOopStack;
655
656 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
657 for (size_t i = 0; i < ParallelGCThreads; ++i) {
658 new (_overflow_stacks + i) Stack<oop, mtGC>();
659 }
660 }
661
662 if (UsePerfData) {
663 EXCEPTION_MARK;
664 ResourceMark rm;
665
666 const char* cname =
667 PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
668 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
669 ParallelGCThreads, CHECK);
670 }
671 }
672
673 // ParNewGeneration::
674 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
675 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
676
677 template <class T>
678 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
679 #ifdef ASSERT
680 {
681 assert(!oopDesc::is_null(*p), "expected non-null ref");
682 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
683 // We never expect to see a null reference being processed
684 // as a weak reference.
685 assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");
686 }
687 #endif // ASSERT
688
689 _par_cl->do_oop_nv(p);
690
691 if (GenCollectedHeap::heap()->is_in_reserved(p)) {
692 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
693 _rs->write_ref_field_gc_par(p, obj);
694 }
695 }
696
697 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); }
698 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
699
700 // ParNewGeneration::
701 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
702 DefNewGeneration::KeepAliveClosure(cl) {}
703
704 template <class T>
705 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
706 #ifdef ASSERT
707 {
708 assert(!oopDesc::is_null(*p), "expected non-null ref");
709 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
710 // We never expect to see a null reference being processed
711 // as a weak reference.
712 assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");
713 }
714 #endif // ASSERT
715
716 _cl->do_oop_nv(p);
717
718 if (GenCollectedHeap::heap()->is_in_reserved(p)) {
719 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
720 _rs->write_ref_field_gc_par(p, obj);
721 }
722 }
723
724 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); }
725 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
726
727 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
728 T heap_oop = oopDesc::load_heap_oop(p);
729 if (!oopDesc::is_null(heap_oop)) {
730 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
731 if ((HeapWord*)obj < _boundary) {
732 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
733 oop new_obj = obj->is_forwarded()
734 ? obj->forwardee()
735 : _g->DefNewGeneration::copy_to_survivor_space(obj);
736 oopDesc::encode_store_heap_oop_not_null(p, new_obj);
737 }
738 if (_gc_barrier) {
739 // If p points to a younger generation, mark the card.
740 if ((HeapWord*)obj < _gen_boundary) {
741 _rs->write_ref_field_gc_par(p, obj);
742 }
743 }
744 }
745 }
746
747 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
748 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
749
750 class ParNewRefProcTaskProxy: public AbstractGangTask {
751 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
752 public:
753 ParNewRefProcTaskProxy(ProcessTask& task,
754 ParNewGeneration& young_gen,
755 Generation& old_gen,
756 HeapWord* young_old_boundary,
757 ParScanThreadStateSet& state_set);
758
759 private:
760 virtual void work(uint worker_id);
761 private:
762 ParNewGeneration& _young_gen;
763 ProcessTask& _task;
764 Generation& _old_gen;
765 HeapWord* _young_old_boundary;
766 ParScanThreadStateSet& _state_set;
767 };
768
769 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,
770 ParNewGeneration& young_gen,
771 Generation& old_gen,
772 HeapWord* young_old_boundary,
773 ParScanThreadStateSet& state_set)
774 : AbstractGangTask("ParNewGeneration parallel reference processing"),
775 _young_gen(young_gen),
776 _task(task),
777 _old_gen(old_gen),
778 _young_old_boundary(young_old_boundary),
779 _state_set(state_set)
780 { }
781
782 void ParNewRefProcTaskProxy::work(uint worker_id) {
783 ResourceMark rm;
784 HandleMark hm;
785 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
786 par_scan_state.set_young_old_boundary(_young_old_boundary);
787 _task.work(worker_id, par_scan_state.is_alive_closure(),
788 par_scan_state.keep_alive_closure(),
789 par_scan_state.evacuate_followers_closure());
790 }
791
792 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
793 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
794 EnqueueTask& _task;
795
796 public:
797 ParNewRefEnqueueTaskProxy(EnqueueTask& task)
798 : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
799 _task(task)
800 { }
801
802 virtual void work(uint worker_id) {
803 _task.work(worker_id);
804 }
805 };
806
807 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) {
808 GenCollectedHeap* gch = GenCollectedHeap::heap();
809 WorkGang* workers = gch->workers();
810 assert(workers != NULL, "Need parallel worker threads.");
811 _state_set.reset(workers->active_workers(), _young_gen.promotion_failed());
812 ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,
813 _young_gen.reserved().end(), _state_set);
814 workers->run_task(&rp_task);
815 _state_set.reset(0 /* bad value in debug if not reset */,
816 _young_gen.promotion_failed());
817 }
818
819 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) {
820 GenCollectedHeap* gch = GenCollectedHeap::heap();
821 WorkGang* workers = gch->workers();
822 assert(workers != NULL, "Need parallel worker threads.");
823 ParNewRefEnqueueTaskProxy enq_task(task);
824 workers->run_task(&enq_task);
825 }
826
827 void ParNewRefProcTaskExecutor::set_single_threaded_mode() {
828 _state_set.flush();
829 GenCollectedHeap* gch = GenCollectedHeap::heap();
830 gch->save_marks();
831 }
832
833 ScanClosureWithParBarrier::
834 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
835 ScanClosure(g, gc_barrier)
836 { }
837
838 EvacuateFollowersClosureGeneral::
839 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch,
840 OopsInGenClosure* cur,
841 OopsInGenClosure* older) :
842 _gch(gch),
843 _scan_cur_or_nonheap(cur), _scan_older(older)
844 { }
845
846 void EvacuateFollowersClosureGeneral::do_void() {
847 do {
848 // Beware: this call will lead to closure applications via virtual
849 // calls.
850 _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen,
851 _scan_cur_or_nonheap,
852 _scan_older);
853 } while (!_gch->no_allocs_since_save_marks());
854 }
855
856 // A Generation that does parallel young-gen collection.
857
858 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) {
859 assert(_promo_failure_scan_stack.is_empty(), "post condition");
860 _promo_failure_scan_stack.clear(true); // Clear cached segments.
861
862 remove_forwarding_pointers();
863 log_info(gc, promotion)("Promotion failed");
864 // All the spaces are in play for mark-sweep.
865 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690.
866 from()->set_next_compaction_space(to());
867 gch->set_incremental_collection_failed();
868 // Inform the next generation that a promotion failure occurred.
869 _old_gen->promotion_failure_occurred();
870
871 // Trace promotion failure in the parallel GC threads
872 thread_state_set.trace_promotion_failed(gc_tracer());
873 // Single threaded code may have reported promotion failure to the global state
874 if (_promotion_failed_info.has_failed()) {
875 _gc_tracer.report_promotion_failed(_promotion_failed_info);
876 }
877 // Reset the PromotionFailureALot counters.
878 NOT_PRODUCT(gch->reset_promotion_should_fail();)
879 }
880
881 void ParNewGeneration::collect(bool full,
882 bool clear_all_soft_refs,
883 size_t size,
884 bool is_tlab) {
885 assert(full || size > 0, "otherwise we don't want to collect");
886
887 GenCollectedHeap* gch = GenCollectedHeap::heap();
888
889 _gc_timer->register_gc_start();
890
891 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
892 WorkGang* workers = gch->workers();
893 assert(workers != NULL, "Need workgang for parallel work");
894 uint active_workers =
895 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
896 workers->active_workers(),
897 Threads::number_of_non_daemon_threads());
898 active_workers = workers->update_active_workers(active_workers);
899 log_info(gc,task)("Using %u workers of %u for evacuation", active_workers, workers->total_workers());
900
901 _old_gen = gch->old_gen();
902
903 // If the next generation is too full to accommodate worst-case promotion
904 // from this generation, pass on collection; let the next generation
905 // do it.
906 if (!collection_attempt_is_safe()) {
907 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one
908 return;
909 }
910 assert(to()->is_empty(), "Else not collection_attempt_is_safe");
911
912 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
913 gch->trace_heap_before_gc(gc_tracer());
914
915 init_assuming_no_promotion_failure();
916
917 if (UseAdaptiveSizePolicy) {
918 set_survivor_overflow(false);
919 size_policy->minor_collection_begin();
920 }
921
922 GCTraceTime(Trace, gc, phases) t1("ParNew", NULL, gch->gc_cause());
923
924 age_table()->clear();
925 to()->clear(SpaceDecorator::Mangle);
926
927 gch->save_marks();
928
929 // Set the correct parallelism (number of queues) in the reference processor
930 ref_processor()->set_active_mt_degree(active_workers);
931
932 // Need to initialize the preserved marks before the ThreadStateSet c'tor.
933 _preserved_marks_set.init(active_workers);
934
935 // Always set the terminator for the active number of workers
936 // because only those workers go through the termination protocol.
937 ParallelTaskTerminator _term(active_workers, task_queues());
938 ParScanThreadStateSet thread_state_set(active_workers,
939 *to(), *this, *_old_gen, *task_queues(),
940 _overflow_stacks, _preserved_marks_set,
941 desired_plab_sz(), _term);
942
943 thread_state_set.reset(active_workers, promotion_failed());
944
945 {
946 StrongRootsScope srs(active_workers);
947
948 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);
949 gch->rem_set()->prepare_for_younger_refs_iterate(true);
950 // It turns out that even when we're using 1 thread, doing the work in a
951 // separate thread causes wide variance in run times. We can't help this
952 // in the multi-threaded case, but we special-case n=1 here to get
953 // repeatable measurements of the 1-thread overhead of the parallel code.
954 // Might multiple workers ever be used? If yes, initialization
955 // has been done such that the single threaded path should not be used.
956 if (workers->total_workers() > 1) {
957 workers->run_task(&tsk);
958 } else {
959 tsk.work(0);
960 }
961 }
962
963 thread_state_set.reset(0 /* Bad value in debug if not reset */,
964 promotion_failed());
965
966 // Trace and reset failed promotion info.
967 if (promotion_failed()) {
968 thread_state_set.trace_promotion_failed(gc_tracer());
969 }
970
971 // Process (weak) reference objects found during scavenge.
972 ReferenceProcessor* rp = ref_processor();
973 IsAliveClosure is_alive(this);
974 ScanWeakRefClosure scan_weak_ref(this);
975 KeepAliveClosure keep_alive(&scan_weak_ref);
976 ScanClosure scan_without_gc_barrier(this, false);
977 ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
978 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
979 EvacuateFollowersClosureGeneral evacuate_followers(gch,
980 &scan_without_gc_barrier, &scan_with_gc_barrier);
981 rp->setup_policy(clear_all_soft_refs);
982 // Can the mt_degree be set later (at run_task() time would be best)?
983 rp->set_active_mt_degree(active_workers);
984 ReferenceProcessorStats stats;
985 ReferenceProcessorPhaseTimes pt(_gc_timer, rp->num_q());
986 if (rp->processing_is_mt()) {
987 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
988 stats = rp->process_discovered_references(&is_alive, &keep_alive,
989 &evacuate_followers, &task_executor,
990 &pt);
991 } else {
992 thread_state_set.flush();
993 gch->save_marks();
994 stats = rp->process_discovered_references(&is_alive, &keep_alive,
995 &evacuate_followers, NULL,
996 &pt);
997 }
998 _gc_tracer.report_gc_reference_stats(stats);
999 _gc_tracer.report_tenuring_threshold(tenuring_threshold());
1000 pt.print_all_references();
1001
1002 WeakProcessor::unlink_or_oops_do(&is_alive, &keep_alive);
1003
1004 if (!promotion_failed()) {
1005 // Swap the survivor spaces.
1006 eden()->clear(SpaceDecorator::Mangle);
1007 from()->clear(SpaceDecorator::Mangle);
1008 if (ZapUnusedHeapArea) {
1009 // This is now done here because of the piece-meal mangling which
1010 // can check for valid mangling at intermediate points in the
1011 // collection(s). When a young collection fails to collect
1012 // sufficient space resizing of the young generation can occur
1013 // and redistribute the spaces in the young generation. Mangle
1014 // here so that unzapped regions don't get distributed to
1015 // other spaces.
1016 to()->mangle_unused_area();
1017 }
1018 swap_spaces();
1019
1020 // A successful scavenge should restart the GC time limit count which is
1021 // for full GC's.
1022 size_policy->reset_gc_overhead_limit_count();
1023
1024 assert(to()->is_empty(), "to space should be empty now");
1025
1026 adjust_desired_tenuring_threshold();
1027 } else {
1028 handle_promotion_failed(gch, thread_state_set);
1029 }
1030 _preserved_marks_set.reclaim();
1031 // set new iteration safe limit for the survivor spaces
1032 from()->set_concurrent_iteration_safe_limit(from()->top());
1033 to()->set_concurrent_iteration_safe_limit(to()->top());
1034
1035 plab_stats()->adjust_desired_plab_sz();
1036
1037 TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
1038 TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
1039
1040 if (UseAdaptiveSizePolicy) {
1041 size_policy->minor_collection_end(gch->gc_cause());
1042 size_policy->avg_survived()->sample(from()->used());
1043 }
1044
1045 // We need to use a monotonically non-decreasing time in ms
1046 // or we will see time-warp warnings and os::javaTimeMillis()
1047 // does not guarantee monotonicity.
1048 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1049 update_time_of_last_gc(now);
1050
1051 rp->set_enqueuing_is_done(true);
1052 if (rp->processing_is_mt()) {
1053 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
1054 rp->enqueue_discovered_references(&task_executor, &pt);
1055 } else {
1056 rp->enqueue_discovered_references(NULL, &pt);
1057 }
1058 rp->verify_no_references_recorded();
1059
1060 gch->trace_heap_after_gc(gc_tracer());
1061
1062 pt.print_enqueue_phase();
1063
1064 _gc_timer->register_gc_end();
1065
1066 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1067 }
1068
1069 size_t ParNewGeneration::desired_plab_sz() {
1070 return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers());
1071 }
1072
1073 static int sum;
1074 void ParNewGeneration::waste_some_time() {
1075 for (int i = 0; i < 100; i++) {
1076 sum += i;
1077 }
1078 }
1079
1080 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1081
1082 // Because of concurrency, there are times where an object for which
1083 // "is_forwarded()" is true contains an "interim" forwarding pointer
1084 // value. Such a value will soon be overwritten with a real value.
1085 // This method requires "obj" to have a forwarding pointer, and waits, if
1086 // necessary for a real one to be inserted, and returns it.
1087
1088 oop ParNewGeneration::real_forwardee(oop obj) {
1089 oop forward_ptr = obj->forwardee();
1090 if (forward_ptr != ClaimedForwardPtr) {
1091 return forward_ptr;
1092 } else {
1093 return real_forwardee_slow(obj);
1094 }
1095 }
1096
1097 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1098 // Spin-read if it is claimed but not yet written by another thread.
1099 oop forward_ptr = obj->forwardee();
1100 while (forward_ptr == ClaimedForwardPtr) {
1101 waste_some_time();
1102 assert(obj->is_forwarded(), "precondition");
1103 forward_ptr = obj->forwardee();
1104 }
1105 return forward_ptr;
1106 }
1107
1108 // Multiple GC threads may try to promote an object. If the object
1109 // is successfully promoted, a forwarding pointer will be installed in
1110 // the object in the young generation. This method claims the right
1111 // to install the forwarding pointer before it copies the object,
1112 // thus avoiding the need to undo the copy as in
1113 // copy_to_survivor_space_avoiding_with_undo.
1114
1115 oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state,
1116 oop old,
1117 size_t sz,
1118 markOop m) {
1119 // In the sequential version, this assert also says that the object is
1120 // not forwarded. That might not be the case here. It is the case that
1121 // the caller observed it to be not forwarded at some time in the past.
1122 assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1123
1124 // The sequential code read "old->age()" below. That doesn't work here,
1125 // since the age is in the mark word, and that might be overwritten with
1126 // a forwarding pointer by a parallel thread. So we must save the mark
1127 // word in a local and then analyze it.
1128 oopDesc dummyOld;
1129 dummyOld.set_mark(m);
1130 assert(!dummyOld.is_forwarded(),
1131 "should not be called with forwarding pointer mark word.");
1132
1133 oop new_obj = NULL;
1134 oop forward_ptr;
1135
1136 // Try allocating obj in to-space (unless too old)
1137 if (dummyOld.age() < tenuring_threshold()) {
1138 new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1139 if (new_obj == NULL) {
1140 set_survivor_overflow(true);
1141 }
1142 }
1143
1144 if (new_obj == NULL) {
1145 // Either to-space is full or we decided to promote try allocating obj tenured
1146
1147 // Attempt to install a null forwarding pointer (atomically),
1148 // to claim the right to install the real forwarding pointer.
1149 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1150 if (forward_ptr != NULL) {
1151 // someone else beat us to it.
1152 return real_forwardee(old);
1153 }
1154
1155 if (!_promotion_failed) {
1156 new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1157 old, m, sz);
1158 }
1159
1160 if (new_obj == NULL) {
1161 // promotion failed, forward to self
1162 _promotion_failed = true;
1163 new_obj = old;
1164
1165 par_scan_state->preserved_marks()->push_if_necessary(old, m);
1166 par_scan_state->register_promotion_failure(sz);
1167 }
1168
1169 old->forward_to(new_obj);
1170 forward_ptr = NULL;
1171 } else {
1172 // Is in to-space; do copying ourselves.
1173 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1174 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");
1175 forward_ptr = old->forward_to_atomic(new_obj);
1176 // Restore the mark word copied above.
1177 new_obj->set_mark(m);
1178 // Increment age if obj still in new generation
1179 new_obj->incr_age();
1180 par_scan_state->age_table()->add(new_obj, sz);
1181 }
1182 assert(new_obj != NULL, "just checking");
1183
1184 // This code must come after the CAS test, or it will print incorrect
1185 // information.
1186 log_develop_trace(gc, scavenge)("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1187 is_in_reserved(new_obj) ? "copying" : "tenuring",
1188 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size());
1189
1190 if (forward_ptr == NULL) {
1191 oop obj_to_push = new_obj;
1192 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1193 // Length field used as index of next element to be scanned.
1194 // Real length can be obtained from real_forwardee()
1195 arrayOop(old)->set_length(0);
1196 obj_to_push = old;
1197 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1198 "push forwarded object");
1199 }
1200 // Push it on one of the queues of to-be-scanned objects.
1201 bool simulate_overflow = false;
1202 NOT_PRODUCT(
1203 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1204 // simulate a stack overflow
1205 simulate_overflow = true;
1206 }
1207 )
1208 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1209 // Add stats for overflow pushes.
1210 log_develop_trace(gc)("Queue Overflow");
1211 push_on_overflow_list(old, par_scan_state);
1212 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1213 }
1214
1215 return new_obj;
1216 }
1217
1218 // Oops. Someone beat us to it. Undo the allocation. Where did we
1219 // allocate it?
1220 if (is_in_reserved(new_obj)) {
1221 // Must be in to_space.
1222 assert(to()->is_in_reserved(new_obj), "Checking");
1223 if (forward_ptr == ClaimedForwardPtr) {
1224 // Wait to get the real forwarding pointer value.
1225 forward_ptr = real_forwardee(old);
1226 }
1227 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1228 }
1229
1230 return forward_ptr;
1231 }
1232
1233 #ifndef PRODUCT
1234 // It's OK to call this multi-threaded; the worst thing
1235 // that can happen is that we'll get a bunch of closely
1236 // spaced simulated overflows, but that's OK, in fact
1237 // probably good as it would exercise the overflow code
1238 // under contention.
1239 bool ParNewGeneration::should_simulate_overflow() {
1240 if (_overflow_counter-- <= 0) { // just being defensive
1241 _overflow_counter = ParGCWorkQueueOverflowInterval;
1242 return true;
1243 } else {
1244 return false;
1245 }
1246 }
1247 #endif
1248
1249 // In case we are using compressed oops, we need to be careful.
1250 // If the object being pushed is an object array, then its length
1251 // field keeps track of the "grey boundary" at which the next
1252 // incremental scan will be done (see ParGCArrayScanChunk).
1253 // When using compressed oops, this length field is kept in the
1254 // lower 32 bits of the erstwhile klass word and cannot be used
1255 // for the overflow chaining pointer (OCP below). As such the OCP
1256 // would itself need to be compressed into the top 32-bits in this
1257 // case. Unfortunately, see below, in the event that we have a
1258 // promotion failure, the node to be pushed on the list can be
1259 // outside of the Java heap, so the heap-based pointer compression
1260 // would not work (we would have potential aliasing between C-heap
1261 // and Java-heap pointers). For this reason, when using compressed
1262 // oops, we simply use a worker-thread-local, non-shared overflow
1263 // list in the form of a growable array, with a slightly different
1264 // overflow stack draining strategy. If/when we start using fat
1265 // stacks here, we can go back to using (fat) pointer chains
1266 // (although some performance comparisons would be useful since
1267 // single global lists have their own performance disadvantages
1268 // as we were made painfully aware not long ago, see 6786503).
1269 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1270 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1271 assert(is_in_reserved(from_space_obj), "Should be from this generation");
1272 if (ParGCUseLocalOverflow) {
1273 // In the case of compressed oops, we use a private, not-shared
1274 // overflow stack.
1275 par_scan_state->push_on_overflow_stack(from_space_obj);
1276 } else {
1277 assert(!UseCompressedOops, "Error");
1278 // if the object has been forwarded to itself, then we cannot
1279 // use the klass pointer for the linked list. Instead we have
1280 // to allocate an oopDesc in the C-Heap and use that for the linked list.
1281 // XXX This is horribly inefficient when a promotion failure occurs
1282 // and should be fixed. XXX FIX ME !!!
1283 #ifndef PRODUCT
1284 Atomic::inc(&_num_par_pushes);
1285 assert(_num_par_pushes > 0, "Tautology");
1286 #endif
1287 if (from_space_obj->forwardee() == from_space_obj) {
1288 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1289 listhead->forward_to(from_space_obj);
1290 from_space_obj = listhead;
1291 }
1292 oop observed_overflow_list = _overflow_list;
1293 oop cur_overflow_list;
1294 do {
1295 cur_overflow_list = observed_overflow_list;
1296 if (cur_overflow_list != BUSY) {
1297 from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1298 } else {
1299 from_space_obj->set_klass_to_list_ptr(NULL);
1300 }
1301 observed_overflow_list =
1302 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1303 } while (cur_overflow_list != observed_overflow_list);
1304 }
1305 }
1306
1307 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1308 bool res;
1309
1310 if (ParGCUseLocalOverflow) {
1311 res = par_scan_state->take_from_overflow_stack();
1312 } else {
1313 assert(!UseCompressedOops, "Error");
1314 res = take_from_overflow_list_work(par_scan_state);
1315 }
1316 return res;
1317 }
1318
1319
1320 // *NOTE*: The overflow list manipulation code here and
1321 // in CMSCollector:: are very similar in shape,
1322 // except that in the CMS case we thread the objects
1323 // directly into the list via their mark word, and do
1324 // not need to deal with special cases below related
1325 // to chunking of object arrays and promotion failure
1326 // handling.
1327 // CR 6797058 has been filed to attempt consolidation of
1328 // the common code.
1329 // Because of the common code, if you make any changes in
1330 // the code below, please check the CMS version to see if
1331 // similar changes might be needed.
1332 // See CMSCollector::par_take_from_overflow_list() for
1333 // more extensive documentation comments.
1334 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1335 ObjToScanQueue* work_q = par_scan_state->work_queue();
1336 // How many to take?
1337 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1338 (size_t)ParGCDesiredObjsFromOverflowList);
1339
1340 assert(!UseCompressedOops, "Error");
1341 assert(par_scan_state->overflow_stack() == NULL, "Error");
1342 if (_overflow_list == NULL) return false;
1343
1344 // Otherwise, there was something there; try claiming the list.
1345 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1346 // Trim off a prefix of at most objsFromOverflow items
1347 Thread* tid = Thread::current();
1348 size_t spin_count = ParallelGCThreads;
1349 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1350 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1351 // someone grabbed it before we did ...
1352 // ... we spin for a short while...
1353 os::sleep(tid, sleep_time_millis, false);
1354 if (_overflow_list == NULL) {
1355 // nothing left to take
1356 return false;
1357 } else if (_overflow_list != BUSY) {
1358 // try and grab the prefix
1359 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1360 }
1361 }
1362 if (prefix == NULL || prefix == BUSY) {
1363 // Nothing to take or waited long enough
1364 if (prefix == NULL) {
1365 // Write back the NULL in case we overwrote it with BUSY above
1366 // and it is still the same value.
1367 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1368 }
1369 return false;
1370 }
1371 assert(prefix != NULL && prefix != BUSY, "Error");
1372 oop cur = prefix;
1373 for (size_t i = 1; i < objsFromOverflow; ++i) {
1374 oop next = cur->list_ptr_from_klass();
1375 if (next == NULL) break;
1376 cur = next;
1377 }
1378 assert(cur != NULL, "Loop postcondition");
1379
1380 // Reattach remaining (suffix) to overflow list
1381 oop suffix = cur->list_ptr_from_klass();
1382 if (suffix == NULL) {
1383 // Write back the NULL in lieu of the BUSY we wrote
1384 // above and it is still the same value.
1385 if (_overflow_list == BUSY) {
1386 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1387 }
1388 } else {
1389 assert(suffix != BUSY, "Error");
1390 // suffix will be put back on global list
1391 cur->set_klass_to_list_ptr(NULL); // break off suffix
1392 // It's possible that the list is still in the empty(busy) state
1393 // we left it in a short while ago; in that case we may be
1394 // able to place back the suffix.
1395 oop observed_overflow_list = _overflow_list;
1396 oop cur_overflow_list = observed_overflow_list;
1397 bool attached = false;
1398 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1399 observed_overflow_list =
1400 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1401 if (cur_overflow_list == observed_overflow_list) {
1402 attached = true;
1403 break;
1404 } else cur_overflow_list = observed_overflow_list;
1405 }
1406 if (!attached) {
1407 // Too bad, someone else got in in between; we'll need to do a splice.
1408 // Find the last item of suffix list
1409 oop last = suffix;
1410 while (true) {
1411 oop next = last->list_ptr_from_klass();
1412 if (next == NULL) break;
1413 last = next;
1414 }
1415 // Atomically prepend suffix to current overflow list
1416 observed_overflow_list = _overflow_list;
1417 do {
1418 cur_overflow_list = observed_overflow_list;
1419 if (cur_overflow_list != BUSY) {
1420 // Do the splice ...
1421 last->set_klass_to_list_ptr(cur_overflow_list);
1422 } else { // cur_overflow_list == BUSY
1423 last->set_klass_to_list_ptr(NULL);
1424 }
1425 observed_overflow_list =
1426 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1427 } while (cur_overflow_list != observed_overflow_list);
1428 }
1429 }
1430
1431 // Push objects on prefix list onto this thread's work queue
1432 assert(prefix != NULL && prefix != BUSY, "program logic");
1433 cur = prefix;
1434 ssize_t n = 0;
1435 while (cur != NULL) {
1436 oop obj_to_push = cur->forwardee();
1437 oop next = cur->list_ptr_from_klass();
1438 cur->set_klass(obj_to_push->klass());
1439 // This may be an array object that is self-forwarded. In that case, the list pointer
1440 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1441 if (!is_in_reserved(cur)) {
1442 // This can become a scaling bottleneck when there is work queue overflow coincident
1443 // with promotion failure.
1444 oopDesc* f = cur;
1445 FREE_C_HEAP_ARRAY(oopDesc, f);
1446 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1447 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1448 obj_to_push = cur;
1449 }
1450 bool ok = work_q->push(obj_to_push);
1451 assert(ok, "Should have succeeded");
1452 cur = next;
1453 n++;
1454 }
1455 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1456 #ifndef PRODUCT
1457 assert(_num_par_pushes >= n, "Too many pops?");
1458 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1459 #endif
1460 return true;
1461 }
1462 #undef BUSY
1463
1464 void ParNewGeneration::ref_processor_init() {
1465 if (_ref_processor == NULL) {
1466 // Allocate and initialize a reference processor
1467 _ref_processor =
1468 new ReferenceProcessor(_reserved, // span
1469 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1470 ParallelGCThreads, // mt processing degree
1471 refs_discovery_is_mt(), // mt discovery
1472 ParallelGCThreads, // mt discovery degree
1473 refs_discovery_is_atomic(), // atomic_discovery
1474 NULL); // is_alive_non_header
1475 }
1476 }
1477
1478 const char* ParNewGeneration::name() const {
1479 return "par new generation";
1480 }