1 /*
2 * Copyright (c) 2001, 2016, 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 *
110 _discovery_is_mt = mt_discovery;
111 _num_q = MAX2(1U, mt_processing_degree);
112 _max_num_q = MAX2(_num_q, mt_discovery_degree);
113 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
114 _max_num_q * number_of_subclasses_of_ref(), mtGC);
115
116 if (_discovered_refs == NULL) {
117 vm_exit_during_initialization("Could not allocated RefProc Array");
118 }
119 _discoveredSoftRefs = &_discovered_refs[0];
120 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
121 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
122 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
123
124 // Initialize all entries to NULL
125 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
126 _discovered_refs[i].set_head(NULL);
127 _discovered_refs[i].set_length(0);
128 }
129
130 setup_policy(false /* default soft ref policy */);
131 }
132
133 #ifndef PRODUCT
134 void ReferenceProcessor::verify_no_references_recorded() {
135 guarantee(!_discovering_refs, "Discovering refs?");
136 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
137 guarantee(_discovered_refs[i].is_empty(),
138 "Found non-empty discovered list at %u", i);
139 }
140 }
141 #endif
142
143 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
144 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
145 if (UseCompressedOops) {
146 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
147 } else {
148 f->do_oop((oop*)_discovered_refs[i].adr_head());
149 }
191 BoolObjectClosure* is_alive,
192 OopClosure* keep_alive,
193 VoidClosure* complete_gc,
194 AbstractRefProcTaskExecutor* task_executor,
195 GCTimer* gc_timer) {
196
197 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
198 // Stop treating discovered references specially.
199 disable_discovery();
200
201 // If discovery was concurrent, someone could have modified
202 // the value of the static field in the j.l.r.SoftReference
203 // class that holds the soft reference timestamp clock using
204 // reflection or Unsafe between when discovery was enabled and
205 // now. Unconditionally update the static field in ReferenceProcessor
206 // here so that we use the new value during processing of the
207 // discovered soft refs.
208
209 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
210
211 ReferenceProcessorStats stats(
212 total_count(_discoveredSoftRefs),
213 total_count(_discoveredWeakRefs),
214 total_count(_discoveredFinalRefs),
215 total_count(_discoveredPhantomRefs));
216
217 // Soft references
218 {
219 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);
220 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
221 is_alive, keep_alive, complete_gc, task_executor);
222 }
223
224 update_soft_ref_master_clock();
225
226 // Weak references
227 {
228 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);
229 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
230 is_alive, keep_alive, complete_gc, task_executor);
231 }
232
233 // Final references
234 {
235 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);
236 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
237 is_alive, keep_alive, complete_gc, task_executor);
238 }
239
240 // Phantom references
241 {
242 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);
243 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
244 is_alive, keep_alive, complete_gc, task_executor);
245 }
246
247 // Weak global JNI references. It would make more sense (semantically) to
248 // traverse these simultaneously with the regular weak references above, but
249 // that is not how the JDK1.2 specification is. See #4126360. Native code can
250 // thus use JNI weak references to circumvent the phantom references and
251 // resurrect a "post-mortem" object.
252 {
253 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
254 if (task_executor != NULL) {
255 task_executor->set_single_threaded_mode();
256 }
257 process_phaseJNI(is_alive, keep_alive, complete_gc);
258 }
259
260 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,
261 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());
262 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
263
264 return stats;
265 }
266
267 #ifndef PRODUCT
268 // Calculate the number of jni handles.
269 size_t ReferenceProcessor::count_jni_refs() {
270 class CountHandleClosure: public OopClosure {
271 private:
272 size_t _count;
273 public:
274 CountHandleClosure(): _count(0) {}
275 void do_oop(oop* unused) { _count++; }
276 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
277 size_t count() { return _count; }
278 };
279 CountHandleClosure global_handle_count;
280 JNIHandles::weak_oops_do(&global_handle_count);
281 return global_handle_count.count();
282 }
283 #endif
284
285 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
286 OopClosure* keep_alive,
287 VoidClosure* complete_gc) {
288 JNIHandles::weak_oops_do(is_alive, keep_alive);
289 complete_gc->do_void();
290 }
291
292 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
293 // Enqueue references that are not made active again, and
294 // clear the decks for the next collection (cycle).
295 enqueue_discovered_reflists(task_executor);
296
297 // Stop treating discovered references specially.
298 disable_discovery();
299 }
300
301 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) {
302 // Given a list of refs linked through the "discovered" field
303 // (java.lang.ref.Reference.discovered), self-loop their "next" field
304 // thus distinguishing them from active References, then
305 // prepend them to the pending list.
306 //
307 // The Java threads will see the Reference objects linked together through
308 // the discovered field. Instead of trying to do the write barrier updates
309 // in all places in the reference processor where we manipulate the discovered
310 // field we make sure to do the barrier here where we anyway iterate through
311 // all linked Reference objects. Note that it is important to not dirty any
312 // cards during reference processing since this will cause card table
313 // verification to fail for G1.
314 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
315
333 // This is the last object.
334 // Swap refs_list into pending list and set obj's
335 // discovered to what we read from the pending list.
336 oop old = Universe::swap_reference_pending_list(refs_list.head());
337 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
338 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
339 }
340 }
341 }
342
343 // Parallel enqueue task
344 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
345 public:
346 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
347 DiscoveredList discovered_refs[],
348 int n_queues)
349 : EnqueueTask(ref_processor, discovered_refs, n_queues)
350 { }
351
352 virtual void work(unsigned int work_id) {
353 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
354 // Simplest first cut: static partitioning.
355 int index = work_id;
356 // The increment on "index" must correspond to the maximum number of queues
357 // (n_queues) with which that ReferenceProcessor was created. That
358 // is because of the "clever" way the discovered references lists were
359 // allocated and are indexed into.
360 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
361 for (int j = 0;
362 j < ReferenceProcessor::number_of_subclasses_of_ref();
363 j++, index += _n_queues) {
364 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]);
365 _refs_lists[index].set_head(NULL);
366 _refs_lists[index].set_length(0);
367 }
368 }
369 };
370
371 // Enqueue references that are not made active again
372 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor) {
373 if (_processing_is_mt && task_executor != NULL) {
374 // Parallel code
375 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q);
376 task_executor->execute(tsk);
377 } else {
378 // Serial code: call the parent class's implementation
379 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
380 enqueue_discovered_reflist(_discovered_refs[i]);
381 _discovered_refs[i].set_head(NULL);
382 _discovered_refs[i].set_length(0);
383 }
384 }
385 }
386
387 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
388 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
389 oop discovered = java_lang_ref_Reference::discovered(_ref);
390 assert(_discovered_addr && discovered->is_oop_or_null(),
391 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
392 _next = discovered;
452 while (iter.has_next()) {
453 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
454 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
455 if (referent_is_dead &&
456 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
457 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
458 p2i(iter.obj()), iter.obj()->klass()->internal_name());
459 // Remove Reference object from list
460 iter.remove();
461 // keep the referent around
462 iter.make_referent_alive();
463 iter.move_to_next();
464 } else {
465 iter.next();
466 }
467 }
468 // Close the reachable set
469 complete_gc->do_void();
470 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
471 iter.removed(), iter.processed(), p2i(&refs_list));
472 }
473
474 // Traverse the list and remove any Refs that are not active, or
475 // whose referents are either alive or NULL.
476 void
477 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
478 BoolObjectClosure* is_alive,
479 OopClosure* keep_alive) {
480 assert(discovery_is_atomic(), "Error");
481 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
482 while (iter.has_next()) {
483 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
484 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
485 assert(next == NULL, "Should not discover inactive Reference");
486 if (iter.is_referent_alive()) {
487 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
488 p2i(iter.obj()), iter.obj()->klass()->internal_name());
489 // The referent is reachable after all.
490 // Remove Reference object from list.
491 iter.remove();
492 // Update the referent pointer as necessary: Note that this
594 if ((i % _max_num_q) == 0) {
595 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
596 }
597 clear_discovered_references(_discovered_refs[i]);
598 }
599 }
600
601 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
602 public:
603 RefProcPhase1Task(ReferenceProcessor& ref_processor,
604 DiscoveredList refs_lists[],
605 ReferencePolicy* policy,
606 bool marks_oops_alive)
607 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
608 _policy(policy)
609 { }
610 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
611 OopClosure& keep_alive,
612 VoidClosure& complete_gc)
613 {
614 _ref_processor.process_phase1(_refs_lists[i], _policy,
615 &is_alive, &keep_alive, &complete_gc);
616 }
617 private:
618 ReferencePolicy* _policy;
619 };
620
621 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
622 public:
623 RefProcPhase2Task(ReferenceProcessor& ref_processor,
624 DiscoveredList refs_lists[],
625 bool marks_oops_alive)
626 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
627 { }
628 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
629 OopClosure& keep_alive,
630 VoidClosure& complete_gc)
631 {
632 _ref_processor.process_phase2(_refs_lists[i],
633 &is_alive, &keep_alive, &complete_gc);
634 }
635 };
636
637 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
638 public:
639 RefProcPhase3Task(ReferenceProcessor& ref_processor,
640 DiscoveredList refs_lists[],
641 bool clear_referent,
642 bool marks_oops_alive)
643 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
644 _clear_referent(clear_referent)
645 { }
646 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
647 OopClosure& keep_alive,
648 VoidClosure& complete_gc)
649 {
650 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
651 &is_alive, &keep_alive, &complete_gc);
652 }
653 private:
654 bool _clear_referent;
655 };
656
657 #ifndef PRODUCT
658 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) {
659 if (!log_is_enabled(Trace, gc, ref)) {
660 return;
661 }
662
663 stringStream st;
664 for (uint i = 0; i < active_length; ++i) {
665 st.print(SIZE_FORMAT " ", ref_lists[i].length());
666 }
667 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
668 #ifdef ASSERT
669 for (uint i = active_length; i < _max_num_q; i++) {
759 }
760 log_reflist_counts(ref_lists, _num_q, balanced_total_refs);
761 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
762 #endif
763 }
764
765 void ReferenceProcessor::balance_all_queues() {
766 balance_queues(_discoveredSoftRefs);
767 balance_queues(_discoveredWeakRefs);
768 balance_queues(_discoveredFinalRefs);
769 balance_queues(_discoveredPhantomRefs);
770 }
771
772 void ReferenceProcessor::process_discovered_reflist(
773 DiscoveredList refs_lists[],
774 ReferencePolicy* policy,
775 bool clear_referent,
776 BoolObjectClosure* is_alive,
777 OopClosure* keep_alive,
778 VoidClosure* complete_gc,
779 AbstractRefProcTaskExecutor* task_executor)
780 {
781 bool mt_processing = task_executor != NULL && _processing_is_mt;
782 // If discovery used MT and a dynamic number of GC threads, then
783 // the queues must be balanced for correctness if fewer than the
784 // maximum number of queues were used. The number of queue used
785 // during discovery may be different than the number to be used
786 // for processing so don't depend of _num_q < _max_num_q as part
787 // of the test.
788 bool must_balance = _discovery_is_mt;
789
790 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
791 must_balance) {
792 balance_queues(refs_lists);
793 }
794
795 // Phase 1 (soft refs only):
796 // . Traverse the list and remove any SoftReferences whose
797 // referents are not alive, but that should be kept alive for
798 // policy reasons. Keep alive the transitive closure of all
799 // such referents.
800 if (policy != NULL) {
801 if (mt_processing) {
802 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
803 task_executor->execute(phase1);
804 } else {
805 for (uint i = 0; i < _max_num_q; i++) {
806 process_phase1(refs_lists[i], policy,
807 is_alive, keep_alive, complete_gc);
808 }
809 }
810 } else { // policy == NULL
811 assert(refs_lists != _discoveredSoftRefs,
812 "Policy must be specified for soft references.");
813 }
814
815 // Phase 2:
816 // . Traverse the list and remove any refs whose referents are alive.
817 if (mt_processing) {
818 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
819 task_executor->execute(phase2);
820 } else {
821 for (uint i = 0; i < _max_num_q; i++) {
822 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
823 }
824 }
825
826 // Phase 3:
827 // . Traverse the list and process referents as appropriate.
828 if (mt_processing) {
829 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
830 task_executor->execute(phase3);
831 } else {
832 for (uint i = 0; i < _max_num_q; i++) {
833 process_phase3(refs_lists[i], clear_referent,
834 is_alive, keep_alive, complete_gc);
835 }
836 }
837 }
838
839 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
840 uint id = 0;
841 // Determine the queue index to use for this object.
842 if (_discovery_is_mt) {
843 // During a multi-threaded discovery phase,
844 // each thread saves to its "own" list.
845 Thread* thr = Thread::current();
846 id = thr->as_Worker_thread()->id();
847 } else {
848 // single-threaded discovery, we save in round-robin
849 // fashion to each of the lists.
850 if (_processing_is_mt) {
851 id = next_id();
852 }
853 }
854 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q);
855
856 // Get the discovered queue to which we will add
1179 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1180 iter.removed(), iter.processed(), p2i(&refs_list));
1181 }
1182 )
1183 }
1184
1185 const char* ReferenceProcessor::list_name(uint i) {
1186 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1187 "Out of bounds index");
1188
1189 int j = i / _max_num_q;
1190 switch (j) {
1191 case 0: return "SoftRef";
1192 case 1: return "WeakRef";
1193 case 2: return "FinalRef";
1194 case 3: return "PhantomRef";
1195 }
1196 ShouldNotReachHere();
1197 return NULL;
1198 }
1199
|
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 *
110 _discovery_is_mt = mt_discovery;
111 _num_q = MAX2(1U, mt_processing_degree);
112 _max_num_q = MAX2(_num_q, mt_discovery_degree);
113 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
114 _max_num_q * number_of_subclasses_of_ref(), mtGC);
115
116 if (_discovered_refs == NULL) {
117 vm_exit_during_initialization("Could not allocated RefProc Array");
118 }
119 _discoveredSoftRefs = &_discovered_refs[0];
120 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
121 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
122 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
123
124 // Initialize all entries to NULL
125 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
126 _discovered_refs[i].set_head(NULL);
127 _discovered_refs[i].set_length(0);
128 }
129
130 _phase_times = new ReferenceProcessorPhaseTimes(_num_q, _processing_is_mt);
131
132 setup_policy(false /* default soft ref policy */);
133 }
134
135 #ifndef PRODUCT
136 void ReferenceProcessor::verify_no_references_recorded() {
137 guarantee(!_discovering_refs, "Discovering refs?");
138 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
139 guarantee(_discovered_refs[i].is_empty(),
140 "Found non-empty discovered list at %u", i);
141 }
142 }
143 #endif
144
145 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
146 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
147 if (UseCompressedOops) {
148 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
149 } else {
150 f->do_oop((oop*)_discovered_refs[i].adr_head());
151 }
193 BoolObjectClosure* is_alive,
194 OopClosure* keep_alive,
195 VoidClosure* complete_gc,
196 AbstractRefProcTaskExecutor* task_executor,
197 GCTimer* gc_timer) {
198
199 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
200 // Stop treating discovered references specially.
201 disable_discovery();
202
203 // If discovery was concurrent, someone could have modified
204 // the value of the static field in the j.l.r.SoftReference
205 // class that holds the soft reference timestamp clock using
206 // reflection or Unsafe between when discovery was enabled and
207 // now. Unconditionally update the static field in ReferenceProcessor
208 // here so that we use the new value during processing of the
209 // discovered soft refs.
210
211 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
212
213 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
214 total_count(_discoveredWeakRefs),
215 total_count(_discoveredFinalRefs),
216 total_count(_discoveredPhantomRefs));
217
218 // Soft references
219 {
220 RefProcPhaseTimesLogger tt("SoftReference", phase_times(), _discoveredSoftRefs, gc_timer);
221 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
222 is_alive, keep_alive, complete_gc, task_executor, gc_timer);
223 }
224
225 update_soft_ref_master_clock();
226
227 // Weak references
228 {
229 RefProcPhaseTimesLogger tt("WeakReference", phase_times(), _discoveredWeakRefs, gc_timer);
230 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
231 is_alive, keep_alive, complete_gc, task_executor, gc_timer);
232 }
233
234 // Final references
235 {
236 RefProcPhaseTimesLogger tt("FinalReference", phase_times(), _discoveredFinalRefs, gc_timer);
237 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
238 is_alive, keep_alive, complete_gc, task_executor, gc_timer);
239 }
240
241 // Phantom references
242 {
243 RefProcPhaseTimesLogger tt("PhantomReference", phase_times(), _discoveredPhantomRefs, gc_timer);
244 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
245 is_alive, keep_alive, complete_gc, task_executor, gc_timer);
246 }
247
248 // Weak global JNI references. It would make more sense (semantically) to
249 // traverse these simultaneously with the regular weak references above, but
250 // that is not how the JDK1.2 specification is. See #4126360. Native code can
251 // thus use JNI weak references to circumvent the phantom references and
252 // resurrect a "post-mortem" object.
253 {
254 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
255 if (task_executor != NULL) {
256 task_executor->set_single_threaded_mode();
257 }
258 process_phaseJNI(is_alive, keep_alive, complete_gc);
259 }
260
261 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
262
263 return stats;
264 }
265
266 #ifndef PRODUCT
267 // Calculate the number of jni handles.
268 size_t ReferenceProcessor::count_jni_refs() {
269 class CountHandleClosure: public OopClosure {
270 private:
271 size_t _count;
272 public:
273 CountHandleClosure(): _count(0) {}
274 void do_oop(oop* unused) { _count++; }
275 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
276 size_t count() { return _count; }
277 };
278 CountHandleClosure global_handle_count;
279 JNIHandles::weak_oops_do(&global_handle_count);
280 return global_handle_count.count();
281 }
282 #endif
283
284 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
285 OopClosure* keep_alive,
286 VoidClosure* complete_gc) {
287 JNIHandles::weak_oops_do(is_alive, keep_alive);
288 complete_gc->do_void();
289 }
290
291 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor, GCTimer* gc_timer) {
292 // Enqueue references that are not made active again, and
293 // clear the decks for the next collection (cycle).
294 enqueue_discovered_reflists(task_executor, gc_timer);
295
296 // Stop treating discovered references specially.
297 disable_discovery();
298 }
299
300 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) {
301 // Given a list of refs linked through the "discovered" field
302 // (java.lang.ref.Reference.discovered), self-loop their "next" field
303 // thus distinguishing them from active References, then
304 // prepend them to the pending list.
305 //
306 // The Java threads will see the Reference objects linked together through
307 // the discovered field. Instead of trying to do the write barrier updates
308 // in all places in the reference processor where we manipulate the discovered
309 // field we make sure to do the barrier here where we anyway iterate through
310 // all linked Reference objects. Note that it is important to not dirty any
311 // cards during reference processing since this will cause card table
312 // verification to fail for G1.
313 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
314
332 // This is the last object.
333 // Swap refs_list into pending list and set obj's
334 // discovered to what we read from the pending list.
335 oop old = Universe::swap_reference_pending_list(refs_list.head());
336 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
337 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
338 }
339 }
340 }
341
342 // Parallel enqueue task
343 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
344 public:
345 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
346 DiscoveredList discovered_refs[],
347 int n_queues)
348 : EnqueueTask(ref_processor, discovered_refs, n_queues)
349 { }
350
351 virtual void work(unsigned int work_id) {
352 RefProcWorkerTimeTracker tt(_ref_processor.phase_times()->worker_time_sec(ReferenceProcessorPhaseTimes::RefEnqueue), work_id);
353
354 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
355 // Simplest first cut: static partitioning.
356 int index = work_id;
357 // The increment on "index" must correspond to the maximum number of queues
358 // (n_queues) with which that ReferenceProcessor was created. That
359 // is because of the "clever" way the discovered references lists were
360 // allocated and are indexed into.
361 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
362 for (int j = 0;
363 j < ReferenceProcessor::number_of_subclasses_of_ref();
364 j++, index += _n_queues) {
365 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]);
366 _refs_lists[index].set_head(NULL);
367 _refs_lists[index].set_length(0);
368 }
369 }
370 };
371
372 // Enqueue references that are not made active again
373 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor, GCTimer* gc_timer) {
374
375 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
376 total_count(_discoveredWeakRefs),
377 total_count(_discoveredFinalRefs),
378 total_count(_discoveredPhantomRefs));
379
380 RefProcEnqueueTimeLogger tt(phase_times(), stats, gc_timer);
381
382 if (_processing_is_mt && task_executor != NULL) {
383 // Parallel code
384 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q);
385 task_executor->execute(tsk);
386 } else {
387 // Serial code: call the parent class's implementation
388 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
389 enqueue_discovered_reflist(_discovered_refs[i]);
390 _discovered_refs[i].set_head(NULL);
391 _discovered_refs[i].set_length(0);
392 }
393 }
394 }
395
396 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
397 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
398 oop discovered = java_lang_ref_Reference::discovered(_ref);
399 assert(_discovered_addr && discovered->is_oop_or_null(),
400 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
401 _next = discovered;
461 while (iter.has_next()) {
462 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
463 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
464 if (referent_is_dead &&
465 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
466 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
467 p2i(iter.obj()), iter.obj()->klass()->internal_name());
468 // Remove Reference object from list
469 iter.remove();
470 // keep the referent around
471 iter.make_referent_alive();
472 iter.move_to_next();
473 } else {
474 iter.next();
475 }
476 }
477 // Close the reachable set
478 complete_gc->do_void();
479 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
480 iter.removed(), iter.processed(), p2i(&refs_list));
481 }
482
483 // Traverse the list and remove any Refs that are not active, or
484 // whose referents are either alive or NULL.
485 void
486 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
487 BoolObjectClosure* is_alive,
488 OopClosure* keep_alive) {
489 assert(discovery_is_atomic(), "Error");
490 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
491 while (iter.has_next()) {
492 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
493 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
494 assert(next == NULL, "Should not discover inactive Reference");
495 if (iter.is_referent_alive()) {
496 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
497 p2i(iter.obj()), iter.obj()->klass()->internal_name());
498 // The referent is reachable after all.
499 // Remove Reference object from list.
500 iter.remove();
501 // Update the referent pointer as necessary: Note that this
603 if ((i % _max_num_q) == 0) {
604 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
605 }
606 clear_discovered_references(_discovered_refs[i]);
607 }
608 }
609
610 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
611 public:
612 RefProcPhase1Task(ReferenceProcessor& ref_processor,
613 DiscoveredList refs_lists[],
614 ReferencePolicy* policy,
615 bool marks_oops_alive)
616 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
617 _policy(policy)
618 { }
619 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
620 OopClosure& keep_alive,
621 VoidClosure& complete_gc)
622 {
623 RefProcWorkerTimeTracker tt(_ref_processor.phase_times()->worker_time_sec(ReferenceProcessorPhaseTimes::RefPhase1), i);
624
625 _ref_processor.process_phase1(_refs_lists[i], _policy,
626 &is_alive, &keep_alive, &complete_gc);
627 }
628 private:
629 ReferencePolicy* _policy;
630 };
631
632 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
633 public:
634 RefProcPhase2Task(ReferenceProcessor& ref_processor,
635 DiscoveredList refs_lists[],
636 bool marks_oops_alive)
637 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
638 { }
639 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
640 OopClosure& keep_alive,
641 VoidClosure& complete_gc)
642 {
643 RefProcWorkerTimeTracker tt(_ref_processor.phase_times()->worker_time_sec(ReferenceProcessorPhaseTimes::RefPhase2), i);
644
645 _ref_processor.process_phase2(_refs_lists[i],
646 &is_alive, &keep_alive, &complete_gc);
647 }
648 };
649
650 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
651 public:
652 RefProcPhase3Task(ReferenceProcessor& ref_processor,
653 DiscoveredList refs_lists[],
654 bool clear_referent,
655 bool marks_oops_alive)
656 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
657 _clear_referent(clear_referent)
658 { }
659 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
660 OopClosure& keep_alive,
661 VoidClosure& complete_gc)
662 {
663 RefProcWorkerTimeTracker tt(_ref_processor.phase_times()->worker_time_sec(ReferenceProcessorPhaseTimes::RefPhase3), i);
664
665 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
666 &is_alive, &keep_alive, &complete_gc);
667 }
668 private:
669 bool _clear_referent;
670 };
671
672 #ifndef PRODUCT
673 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) {
674 if (!log_is_enabled(Trace, gc, ref)) {
675 return;
676 }
677
678 stringStream st;
679 for (uint i = 0; i < active_length; ++i) {
680 st.print(SIZE_FORMAT " ", ref_lists[i].length());
681 }
682 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
683 #ifdef ASSERT
684 for (uint i = active_length; i < _max_num_q; i++) {
774 }
775 log_reflist_counts(ref_lists, _num_q, balanced_total_refs);
776 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
777 #endif
778 }
779
780 void ReferenceProcessor::balance_all_queues() {
781 balance_queues(_discoveredSoftRefs);
782 balance_queues(_discoveredWeakRefs);
783 balance_queues(_discoveredFinalRefs);
784 balance_queues(_discoveredPhantomRefs);
785 }
786
787 void ReferenceProcessor::process_discovered_reflist(
788 DiscoveredList refs_lists[],
789 ReferencePolicy* policy,
790 bool clear_referent,
791 BoolObjectClosure* is_alive,
792 OopClosure* keep_alive,
793 VoidClosure* complete_gc,
794 AbstractRefProcTaskExecutor* task_executor,
795 GCTimer* gc_timer)
796 {
797 bool mt_processing = task_executor != NULL && _processing_is_mt;
798
799 phase_times()->set_processing_is_mt(mt_processing);
800
801 // If discovery used MT and a dynamic number of GC threads, then
802 // the queues must be balanced for correctness if fewer than the
803 // maximum number of queues were used. The number of queue used
804 // during discovery may be different than the number to be used
805 // for processing so don't depend of _num_q < _max_num_q as part
806 // of the test.
807 bool must_balance = _discovery_is_mt;
808
809 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
810 must_balance) {
811 RefProcBalanceQueuesTimeTracker tt(phase_times(), gc_timer);
812 balance_queues(refs_lists);
813 }
814
815 // Phase 1 (soft refs only):
816 // . Traverse the list and remove any SoftReferences whose
817 // referents are not alive, but that should be kept alive for
818 // policy reasons. Keep alive the transitive closure of all
819 // such referents.
820 if (policy != NULL) {
821 RefProcPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, phase_times(), gc_timer);
822
823 if (mt_processing) {
824 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
825 task_executor->execute(phase1);
826 } else {
827 for (uint i = 0; i < _max_num_q; i++) {
828 process_phase1(refs_lists[i], policy,
829 is_alive, keep_alive, complete_gc);
830 }
831 }
832 } else { // policy == NULL
833 assert(refs_lists != _discoveredSoftRefs,
834 "Policy must be specified for soft references.");
835 }
836
837 // Phase 2:
838 // . Traverse the list and remove any refs whose referents are alive.
839 {
840 RefProcPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, phase_times(), gc_timer);
841
842 if (mt_processing) {
843 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
844 task_executor->execute(phase2);
845 } else {
846 for (uint i = 0; i < _max_num_q; i++) {
847 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
848 }
849 }
850 }
851
852 // Phase 3:
853 // . Traverse the list and process referents as appropriate.
854 {
855 RefProcPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, phase_times(), gc_timer);
856
857 if (mt_processing) {
858 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
859 task_executor->execute(phase3);
860 } else {
861 for (uint i = 0; i < _max_num_q; i++) {
862 process_phase3(refs_lists[i], clear_referent,
863 is_alive, keep_alive, complete_gc);
864 }
865 }
866 }
867 }
868
869 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
870 uint id = 0;
871 // Determine the queue index to use for this object.
872 if (_discovery_is_mt) {
873 // During a multi-threaded discovery phase,
874 // each thread saves to its "own" list.
875 Thread* thr = Thread::current();
876 id = thr->as_Worker_thread()->id();
877 } else {
878 // single-threaded discovery, we save in round-robin
879 // fashion to each of the lists.
880 if (_processing_is_mt) {
881 id = next_id();
882 }
883 }
884 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q);
885
886 // Get the discovered queue to which we will add
1209 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1210 iter.removed(), iter.processed(), p2i(&refs_list));
1211 }
1212 )
1213 }
1214
1215 const char* ReferenceProcessor::list_name(uint i) {
1216 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1217 "Out of bounds index");
1218
1219 int j = i / _max_num_q;
1220 switch (j) {
1221 case 0: return "SoftRef";
1222 case 1: return "WeakRef";
1223 case 2: return "FinalRef";
1224 case 3: return "PhantomRef";
1225 }
1226 ShouldNotReachHere();
1227 return NULL;
1228 }
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