1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "gc/shared/collectedHeap.inline.hpp"
30 #include "gc/shared/gcTimer.hpp"
31 #include "gc/shared/gcTraceTime.hpp"
32 #include "gc/shared/referencePolicy.hpp"
33 #include "gc/shared/referenceProcessor.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/java.hpp"
36 #include "runtime/jniHandles.hpp"
37
38 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
39 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
40 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
41
42 void referenceProcessor_init() {
43 ReferenceProcessor::init_statics();
44 }
45
46 void ReferenceProcessor::init_statics() {
47 // We need a monotonically non-decreasing time in ms but
48 // os::javaTimeMillis() does not guarantee monotonicity.
49 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
50
51 // Initialize the soft ref timestamp clock.
52 _soft_ref_timestamp_clock = now;
53 // Also update the soft ref clock in j.l.r.SoftReference
54 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
55
56 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
57 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
58 NOT_COMPILER2(LRUCurrentHeapPolicy());
59 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
60 vm_exit_during_initialization("Could not allocate reference policy object");
61 }
62 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
63 RefDiscoveryPolicy == ReferentBasedDiscovery,
64 "Unrecognized RefDiscoveryPolicy");
65 }
66
67 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
68 #ifdef ASSERT
69 // Verify that we're not currently discovering refs
70 assert(!_discovering_refs, "nested call?");
71
72 if (check_no_refs) {
73 // Verify that the discovered lists are empty
74 verify_no_references_recorded();
75 }
76 #endif // ASSERT
77
78 // Someone could have modified the value of the static
79 // field in the j.l.r.SoftReference class that holds the
80 // soft reference timestamp clock using reflection or
81 // Unsafe between GCs. Unconditionally update the static
82 // field in ReferenceProcessor here so that we use the new
83 // value during reference discovery.
84
85 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
86 _discovering_refs = true;
87 }
88
89 ReferenceProcessor::ReferenceProcessor(MemRegion span,
90 bool mt_processing,
91 uint mt_processing_degree,
92 bool mt_discovery,
93 uint mt_discovery_degree,
94 bool atomic_discovery,
95 BoolObjectClosure* is_alive_non_header) :
96 _discovering_refs(false),
97 _enqueuing_is_done(false),
98 _is_alive_non_header(is_alive_non_header),
99 _processing_is_mt(mt_processing),
100 _next_id(0)
101 {
102 _span = span;
103 _discovery_is_atomic = atomic_discovery;
104 _discovery_is_mt = mt_discovery;
105 _num_q = MAX2(1U, mt_processing_degree);
106 _max_num_q = MAX2(_num_q, mt_discovery_degree);
107 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
108 _max_num_q * number_of_subclasses_of_ref(), mtGC);
109
110 if (_discovered_refs == NULL) {
111 vm_exit_during_initialization("Could not allocated RefProc Array");
112 }
113 _discoveredSoftRefs = &_discovered_refs[0];
114 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
115 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
116 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
117 _discoveredCleanerRefs = &_discoveredPhantomRefs[_max_num_q];
118
119 // Initialize all entries to NULL
120 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
121 _discovered_refs[i].set_head(NULL);
122 _discovered_refs[i].set_length(0);
123 }
124
125 setup_policy(false /* default soft ref policy */);
126 }
127
128 #ifndef PRODUCT
129 void ReferenceProcessor::verify_no_references_recorded() {
130 guarantee(!_discovering_refs, "Discovering refs?");
131 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
132 guarantee(_discovered_refs[i].is_empty(),
133 "Found non-empty discovered list");
134 }
135 }
136 #endif
137
138 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
139 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
140 if (UseCompressedOops) {
141 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
142 } else {
143 f->do_oop((oop*)_discovered_refs[i].adr_head());
144 }
145 }
146 }
147
148 void ReferenceProcessor::update_soft_ref_master_clock() {
149 // Update (advance) the soft ref master clock field. This must be done
150 // after processing the soft ref list.
151
152 // We need a monotonically non-decreasing time in ms but
153 // os::javaTimeMillis() does not guarantee monotonicity.
154 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
155 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
156 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
157
158 NOT_PRODUCT(
159 if (now < _soft_ref_timestamp_clock) {
160 warning("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
161 _soft_ref_timestamp_clock, now);
162 }
163 )
164 // The values of now and _soft_ref_timestamp_clock are set using
165 // javaTimeNanos(), which is guaranteed to be monotonically
166 // non-decreasing provided the underlying platform provides such
167 // a time source (and it is bug free).
168 // In product mode, however, protect ourselves from non-monotonicity.
169 if (now > _soft_ref_timestamp_clock) {
170 _soft_ref_timestamp_clock = now;
171 java_lang_ref_SoftReference::set_clock(now);
172 }
173 // Else leave clock stalled at its old value until time progresses
174 // past clock value.
175 }
176
177 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
178 size_t total = 0;
179 for (uint i = 0; i < _max_num_q; ++i) {
180 total += lists[i].length();
181 }
182 return total;
183 }
184
185 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
186 BoolObjectClosure* is_alive,
187 OopClosure* keep_alive,
188 VoidClosure* complete_gc,
189 AbstractRefProcTaskExecutor* task_executor,
190 GCTimer* gc_timer,
191 GCId gc_id) {
192
193 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
194 // Stop treating discovered references specially.
195 disable_discovery();
196
197 // If discovery was concurrent, someone could have modified
198 // the value of the static field in the j.l.r.SoftReference
199 // class that holds the soft reference timestamp clock using
200 // reflection or Unsafe between when discovery was enabled and
201 // now. Unconditionally update the static field in ReferenceProcessor
202 // here so that we use the new value during processing of the
203 // discovered soft refs.
204
205 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
206
207 bool trace_time = PrintGCDetails && PrintReferenceGC;
208
209 // Soft references
210 size_t soft_count = 0;
211 {
212 GCTraceTime tt("SoftReference", trace_time, false, gc_timer, gc_id);
213 soft_count =
214 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
215 is_alive, keep_alive, complete_gc, task_executor);
216 }
217
218 update_soft_ref_master_clock();
219
220 // Weak references
221 size_t weak_count = 0;
222 {
223 GCTraceTime tt("WeakReference", trace_time, false, gc_timer, gc_id);
224 weak_count =
225 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
226 is_alive, keep_alive, complete_gc, task_executor);
227 }
228
229 // Final references
230 size_t final_count = 0;
231 {
232 GCTraceTime tt("FinalReference", trace_time, false, gc_timer, gc_id);
233 final_count =
234 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
235 is_alive, keep_alive, complete_gc, task_executor);
236 }
237
238 // Phantom references
239 size_t phantom_count = 0;
240 {
241 GCTraceTime tt("PhantomReference", trace_time, false, gc_timer, gc_id);
242 phantom_count =
243 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
244 is_alive, keep_alive, complete_gc, task_executor);
245
246 // Process cleaners, but include them in phantom statistics. We expect
247 // Cleaner references to be temporary, and don't want to deal with
248 // possible incompatibilities arising from making it more visible.
249 phantom_count +=
250 process_discovered_reflist(_discoveredCleanerRefs, NULL, true,
251 is_alive, keep_alive, complete_gc, task_executor);
252 }
253
254 // Weak global JNI references. It would make more sense (semantically) to
255 // traverse these simultaneously with the regular weak references above, but
256 // that is not how the JDK1.2 specification is. See #4126360. Native code can
257 // thus use JNI weak references to circumvent the phantom references and
258 // resurrect a "post-mortem" object.
259 {
260 GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id);
261 if (task_executor != NULL) {
262 task_executor->set_single_threaded_mode();
263 }
264 process_phaseJNI(is_alive, keep_alive, complete_gc);
265 }
266
267 return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count);
268 }
269
270 #ifndef PRODUCT
271 // Calculate the number of jni handles.
272 uint ReferenceProcessor::count_jni_refs() {
273 class AlwaysAliveClosure: public BoolObjectClosure {
274 public:
275 virtual bool do_object_b(oop obj) { return true; }
276 };
277
278 class CountHandleClosure: public OopClosure {
279 private:
280 int _count;
281 public:
282 CountHandleClosure(): _count(0) {}
283 void do_oop(oop* unused) { _count++; }
284 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
285 int count() { return _count; }
286 };
287 CountHandleClosure global_handle_count;
288 AlwaysAliveClosure always_alive;
289 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
290 return global_handle_count.count();
291 }
292 #endif
293
294 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
295 OopClosure* keep_alive,
296 VoidClosure* complete_gc) {
297 #ifndef PRODUCT
298 if (PrintGCDetails && PrintReferenceGC) {
299 unsigned int count = count_jni_refs();
300 gclog_or_tty->print(", %u refs", count);
301 }
302 #endif
303 JNIHandles::weak_oops_do(is_alive, keep_alive);
304 complete_gc->do_void();
305 }
306
307
308 template <class T>
309 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
310 AbstractRefProcTaskExecutor* task_executor) {
311
312 // Remember old value of pending references list
313 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
314 T old_pending_list_value = *pending_list_addr;
315
316 // Enqueue references that are not made active again, and
317 // clear the decks for the next collection (cycle).
318 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
319 // Do the post-barrier on pending_list_addr missed in
320 // enqueue_discovered_reflist.
321 oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
322
323 // Stop treating discovered references specially.
324 ref->disable_discovery();
325
326 // Return true if new pending references were added
327 return old_pending_list_value != *pending_list_addr;
328 }
329
330 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
331 if (UseCompressedOops) {
332 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
333 } else {
334 return enqueue_discovered_ref_helper<oop>(this, task_executor);
335 }
336 }
337
338 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
339 HeapWord* pending_list_addr) {
340 // Given a list of refs linked through the "discovered" field
341 // (java.lang.ref.Reference.discovered), self-loop their "next" field
342 // thus distinguishing them from active References, then
343 // prepend them to the pending list.
344 //
345 // The Java threads will see the Reference objects linked together through
346 // the discovered field. Instead of trying to do the write barrier updates
347 // in all places in the reference processor where we manipulate the discovered
348 // field we make sure to do the barrier here where we anyway iterate through
349 // all linked Reference objects. Note that it is important to not dirty any
350 // cards during reference processing since this will cause card table
351 // verification to fail for G1.
352 if (TraceReferenceGC && PrintGCDetails) {
353 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
354 INTPTR_FORMAT, p2i(refs_list.head()));
355 }
356
357 oop obj = NULL;
358 oop next_d = refs_list.head();
359 // Walk down the list, self-looping the next field
360 // so that the References are not considered active.
361 while (obj != next_d) {
362 obj = next_d;
363 assert(obj->is_instanceRef(), "should be reference object");
364 next_d = java_lang_ref_Reference::discovered(obj);
365 if (TraceReferenceGC && PrintGCDetails) {
366 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
367 p2i(obj), p2i(next_d));
368 }
369 assert(java_lang_ref_Reference::next(obj) == NULL,
370 "Reference not active; should not be discovered");
371 // Self-loop next, so as to make Ref not active.
372 java_lang_ref_Reference::set_next_raw(obj, obj);
373 if (next_d != obj) {
374 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
375 } else {
376 // This is the last object.
377 // Swap refs_list into pending_list_addr and
378 // set obj's discovered to what we read from pending_list_addr.
379 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
380 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
381 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
382 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
383 }
384 }
385 }
386
387 // Parallel enqueue task
388 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
389 public:
390 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
391 DiscoveredList discovered_refs[],
392 HeapWord* pending_list_addr,
393 int n_queues)
394 : EnqueueTask(ref_processor, discovered_refs,
395 pending_list_addr, n_queues)
396 { }
397
398 virtual void work(unsigned int work_id) {
399 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
400 // Simplest first cut: static partitioning.
401 int index = work_id;
402 // The increment on "index" must correspond to the maximum number of queues
403 // (n_queues) with which that ReferenceProcessor was created. That
404 // is because of the "clever" way the discovered references lists were
405 // allocated and are indexed into.
406 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
407 for (int j = 0;
408 j < ReferenceProcessor::number_of_subclasses_of_ref();
409 j++, index += _n_queues) {
410 _ref_processor.enqueue_discovered_reflist(
411 _refs_lists[index], _pending_list_addr);
412 _refs_lists[index].set_head(NULL);
413 _refs_lists[index].set_length(0);
414 }
415 }
416 };
417
418 // Enqueue references that are not made active again
419 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
420 AbstractRefProcTaskExecutor* task_executor) {
421 if (_processing_is_mt && task_executor != NULL) {
422 // Parallel code
423 RefProcEnqueueTask tsk(*this, _discovered_refs,
424 pending_list_addr, _max_num_q);
425 task_executor->execute(tsk);
426 } else {
427 // Serial code: call the parent class's implementation
428 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
429 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
430 _discovered_refs[i].set_head(NULL);
431 _discovered_refs[i].set_length(0);
432 }
433 }
434 }
435
436 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
437 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
438 oop discovered = java_lang_ref_Reference::discovered(_ref);
439 assert(_discovered_addr && discovered->is_oop_or_null(),
440 err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
441 _next = discovered;
442 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
443 _referent = java_lang_ref_Reference::referent(_ref);
444 assert(Universe::heap()->is_in_reserved_or_null(_referent),
445 "Wrong oop found in java.lang.Reference object");
446 assert(allow_null_referent ?
447 _referent->is_oop_or_null()
448 : _referent->is_oop(),
449 err_msg("Expected an oop%s for referent field at " PTR_FORMAT,
450 (allow_null_referent ? " or NULL" : ""),
451 p2i(_referent)));
452 }
453
454 void DiscoveredListIterator::remove() {
455 assert(_ref->is_oop(), "Dropping a bad reference");
456 oop_store_raw(_discovered_addr, NULL);
457
458 // First _prev_next ref actually points into DiscoveredList (gross).
459 oop new_next;
460 if (_next == _ref) {
461 // At the end of the list, we should make _prev point to itself.
462 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
463 // and _prev will be NULL.
464 new_next = _prev;
465 } else {
466 new_next = _next;
467 }
468 // Remove Reference object from discovered list. Note that G1 does not need a
469 // pre-barrier here because we know the Reference has already been found/marked,
470 // that's how it ended up in the discovered list in the first place.
471 oop_store_raw(_prev_next, new_next);
472 NOT_PRODUCT(_removed++);
473 _refs_list.dec_length(1);
474 }
475
476 void DiscoveredListIterator::clear_referent() {
477 oop_store_raw(_referent_addr, NULL);
478 }
479
480 // NOTE: process_phase*() are largely similar, and at a high level
481 // merely iterate over the extant list applying a predicate to
482 // each of its elements and possibly removing that element from the
483 // list and applying some further closures to that element.
484 // We should consider the possibility of replacing these
485 // process_phase*() methods by abstracting them into
486 // a single general iterator invocation that receives appropriate
487 // closures that accomplish this work.
488
489 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
490 // referents are not alive, but that should be kept alive for policy reasons.
491 // Keep alive the transitive closure of all such referents.
492 void
493 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
494 ReferencePolicy* policy,
495 BoolObjectClosure* is_alive,
496 OopClosure* keep_alive,
497 VoidClosure* complete_gc) {
498 assert(policy != NULL, "Must have a non-NULL policy");
499 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
500 // Decide which softly reachable refs should be kept alive.
501 while (iter.has_next()) {
502 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
503 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
504 if (referent_is_dead &&
505 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
506 if (TraceReferenceGC) {
507 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
508 p2i(iter.obj()), iter.obj()->klass()->internal_name());
509 }
510 // Remove Reference object from list
511 iter.remove();
512 // keep the referent around
513 iter.make_referent_alive();
514 iter.move_to_next();
515 } else {
516 iter.next();
517 }
518 }
519 // Close the reachable set
520 complete_gc->do_void();
521 NOT_PRODUCT(
522 if (PrintGCDetails && TraceReferenceGC) {
523 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT
524 " discovered Refs by policy, from list " INTPTR_FORMAT,
525 iter.removed(), iter.processed(), p2i(refs_list.head()));
526 }
527 )
528 }
529
530 // Traverse the list and remove any Refs that are not active, or
531 // whose referents are either alive or NULL.
532 void
533 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
534 BoolObjectClosure* is_alive,
535 OopClosure* keep_alive) {
536 assert(discovery_is_atomic(), "Error");
537 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
538 while (iter.has_next()) {
539 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
540 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
541 assert(next == NULL, "Should not discover inactive Reference");
542 if (iter.is_referent_alive()) {
543 if (TraceReferenceGC) {
544 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
545 p2i(iter.obj()), iter.obj()->klass()->internal_name());
546 }
547 // The referent is reachable after all.
548 // Remove Reference object from list.
549 iter.remove();
550 // Update the referent pointer as necessary: Note that this
551 // should not entail any recursive marking because the
552 // referent must already have been traversed.
553 iter.make_referent_alive();
554 iter.move_to_next();
555 } else {
556 iter.next();
557 }
558 }
559 NOT_PRODUCT(
560 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
561 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
562 " Refs in discovered list " INTPTR_FORMAT,
563 iter.removed(), iter.processed(), p2i(refs_list.head()));
564 }
565 )
566 }
567
568 void
569 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
570 BoolObjectClosure* is_alive,
571 OopClosure* keep_alive,
572 VoidClosure* complete_gc) {
573 assert(!discovery_is_atomic(), "Error");
574 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
575 while (iter.has_next()) {
576 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
577 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
578 oop next = java_lang_ref_Reference::next(iter.obj());
579 if ((iter.referent() == NULL || iter.is_referent_alive() ||
580 next != NULL)) {
581 assert(next->is_oop_or_null(), err_msg("Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)));
582 // Remove Reference object from list
583 iter.remove();
584 // Trace the cohorts
585 iter.make_referent_alive();
586 if (UseCompressedOops) {
587 keep_alive->do_oop((narrowOop*)next_addr);
588 } else {
589 keep_alive->do_oop((oop*)next_addr);
590 }
591 iter.move_to_next();
592 } else {
593 iter.next();
594 }
595 }
596 // Now close the newly reachable set
597 complete_gc->do_void();
598 NOT_PRODUCT(
599 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
600 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
601 " Refs in discovered list " INTPTR_FORMAT,
602 iter.removed(), iter.processed(), p2i(refs_list.head()));
603 }
604 )
605 }
606
607 // Traverse the list and process the referents, by either
608 // clearing them or keeping them (and their reachable
609 // closure) alive.
610 void
611 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
612 bool clear_referent,
613 BoolObjectClosure* is_alive,
614 OopClosure* keep_alive,
615 VoidClosure* complete_gc) {
616 ResourceMark rm;
617 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
618 while (iter.has_next()) {
619 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
620 if (clear_referent) {
621 // NULL out referent pointer
622 iter.clear_referent();
623 } else {
624 // keep the referent around
625 iter.make_referent_alive();
626 }
627 if (TraceReferenceGC) {
628 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
629 clear_referent ? "cleared " : "",
630 p2i(iter.obj()), iter.obj()->klass()->internal_name());
631 }
632 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
633 iter.next();
634 }
635 // Close the reachable set
636 complete_gc->do_void();
637 }
638
639 void
640 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
641 oop obj = NULL;
642 oop next = refs_list.head();
643 while (next != obj) {
644 obj = next;
645 next = java_lang_ref_Reference::discovered(obj);
646 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
647 }
648 refs_list.set_head(NULL);
649 refs_list.set_length(0);
650 }
651
652 void ReferenceProcessor::abandon_partial_discovery() {
653 // loop over the lists
654 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
655 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
656 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i));
657 }
658 clear_discovered_references(_discovered_refs[i]);
659 }
660 }
661
662 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
663 public:
664 RefProcPhase1Task(ReferenceProcessor& ref_processor,
665 DiscoveredList refs_lists[],
666 ReferencePolicy* policy,
667 bool marks_oops_alive)
668 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
669 _policy(policy)
670 { }
671 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
672 OopClosure& keep_alive,
673 VoidClosure& complete_gc)
674 {
675 Thread* thr = Thread::current();
676 int refs_list_index = ((WorkerThread*)thr)->id();
677 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
678 &is_alive, &keep_alive, &complete_gc);
679 }
680 private:
681 ReferencePolicy* _policy;
682 };
683
684 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
685 public:
686 RefProcPhase2Task(ReferenceProcessor& ref_processor,
687 DiscoveredList refs_lists[],
688 bool marks_oops_alive)
689 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
690 { }
691 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
692 OopClosure& keep_alive,
693 VoidClosure& complete_gc)
694 {
695 _ref_processor.process_phase2(_refs_lists[i],
696 &is_alive, &keep_alive, &complete_gc);
697 }
698 };
699
700 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
701 public:
702 RefProcPhase3Task(ReferenceProcessor& ref_processor,
703 DiscoveredList refs_lists[],
704 bool clear_referent,
705 bool marks_oops_alive)
706 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
707 _clear_referent(clear_referent)
708 { }
709 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
710 OopClosure& keep_alive,
711 VoidClosure& complete_gc)
712 {
713 // Don't use "refs_list_index" calculated in this way because
714 // balance_queues() has moved the Ref's into the first n queues.
715 // Thread* thr = Thread::current();
716 // int refs_list_index = ((WorkerThread*)thr)->id();
717 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
718 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
719 &is_alive, &keep_alive, &complete_gc);
720 }
721 private:
722 bool _clear_referent;
723 };
724
725 // Balances reference queues.
726 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
727 // queues[0, 1, ..., _num_q-1] because only the first _num_q
728 // corresponding to the active workers will be processed.
729 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
730 {
731 // calculate total length
732 size_t total_refs = 0;
733 if (TraceReferenceGC && PrintGCDetails) {
734 gclog_or_tty->print_cr("\nBalance ref_lists ");
735 }
736
737 for (uint i = 0; i < _max_num_q; ++i) {
738 total_refs += ref_lists[i].length();
739 if (TraceReferenceGC && PrintGCDetails) {
740 gclog_or_tty->print(SIZE_FORMAT " ", ref_lists[i].length());
741 }
742 }
743 if (TraceReferenceGC && PrintGCDetails) {
744 gclog_or_tty->print_cr(" = " SIZE_FORMAT, total_refs);
745 }
746 size_t avg_refs = total_refs / _num_q + 1;
747 uint to_idx = 0;
748 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
749 bool move_all = false;
750 if (from_idx >= _num_q) {
751 move_all = ref_lists[from_idx].length() > 0;
752 }
753 while ((ref_lists[from_idx].length() > avg_refs) ||
754 move_all) {
755 assert(to_idx < _num_q, "Sanity Check!");
756 if (ref_lists[to_idx].length() < avg_refs) {
757 // move superfluous refs
758 size_t refs_to_move;
759 // Move all the Ref's if the from queue will not be processed.
760 if (move_all) {
761 refs_to_move = MIN2(ref_lists[from_idx].length(),
762 avg_refs - ref_lists[to_idx].length());
763 } else {
764 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
765 avg_refs - ref_lists[to_idx].length());
766 }
767
768 assert(refs_to_move > 0, "otherwise the code below will fail");
769
770 oop move_head = ref_lists[from_idx].head();
771 oop move_tail = move_head;
772 oop new_head = move_head;
773 // find an element to split the list on
774 for (size_t j = 0; j < refs_to_move; ++j) {
775 move_tail = new_head;
776 new_head = java_lang_ref_Reference::discovered(new_head);
777 }
778
779 // Add the chain to the to list.
780 if (ref_lists[to_idx].head() == NULL) {
781 // to list is empty. Make a loop at the end.
782 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
783 } else {
784 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
785 }
786 ref_lists[to_idx].set_head(move_head);
787 ref_lists[to_idx].inc_length(refs_to_move);
788
789 // Remove the chain from the from list.
790 if (move_tail == new_head) {
791 // We found the end of the from list.
792 ref_lists[from_idx].set_head(NULL);
793 } else {
794 ref_lists[from_idx].set_head(new_head);
795 }
796 ref_lists[from_idx].dec_length(refs_to_move);
797 if (ref_lists[from_idx].length() == 0) {
798 break;
799 }
800 } else {
801 to_idx = (to_idx + 1) % _num_q;
802 }
803 }
804 }
805 #ifdef ASSERT
806 size_t balanced_total_refs = 0;
807 for (uint i = 0; i < _max_num_q; ++i) {
808 balanced_total_refs += ref_lists[i].length();
809 if (TraceReferenceGC && PrintGCDetails) {
810 gclog_or_tty->print(SIZE_FORMAT " ", ref_lists[i].length());
811 }
812 }
813 if (TraceReferenceGC && PrintGCDetails) {
814 gclog_or_tty->print_cr(" = " SIZE_FORMAT, balanced_total_refs);
815 gclog_or_tty->flush();
816 }
817 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
818 #endif
819 }
820
821 void ReferenceProcessor::balance_all_queues() {
822 balance_queues(_discoveredSoftRefs);
823 balance_queues(_discoveredWeakRefs);
824 balance_queues(_discoveredFinalRefs);
825 balance_queues(_discoveredPhantomRefs);
826 balance_queues(_discoveredCleanerRefs);
827 }
828
829 size_t
830 ReferenceProcessor::process_discovered_reflist(
831 DiscoveredList refs_lists[],
832 ReferencePolicy* policy,
833 bool clear_referent,
834 BoolObjectClosure* is_alive,
835 OopClosure* keep_alive,
836 VoidClosure* complete_gc,
837 AbstractRefProcTaskExecutor* task_executor)
838 {
839 bool mt_processing = task_executor != NULL && _processing_is_mt;
840 // If discovery used MT and a dynamic number of GC threads, then
841 // the queues must be balanced for correctness if fewer than the
842 // maximum number of queues were used. The number of queue used
843 // during discovery may be different than the number to be used
844 // for processing so don't depend of _num_q < _max_num_q as part
845 // of the test.
846 bool must_balance = _discovery_is_mt;
847
848 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
849 must_balance) {
850 balance_queues(refs_lists);
851 }
852
853 size_t total_list_count = total_count(refs_lists);
854
855 if (PrintReferenceGC && PrintGCDetails) {
856 gclog_or_tty->print(", " SIZE_FORMAT " refs", total_list_count);
857 }
858
859 // Phase 1 (soft refs only):
860 // . Traverse the list and remove any SoftReferences whose
861 // referents are not alive, but that should be kept alive for
862 // policy reasons. Keep alive the transitive closure of all
863 // such referents.
864 if (policy != NULL) {
865 if (mt_processing) {
866 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
867 task_executor->execute(phase1);
868 } else {
869 for (uint i = 0; i < _max_num_q; i++) {
870 process_phase1(refs_lists[i], policy,
871 is_alive, keep_alive, complete_gc);
872 }
873 }
874 } else { // policy == NULL
875 assert(refs_lists != _discoveredSoftRefs,
876 "Policy must be specified for soft references.");
877 }
878
879 // Phase 2:
880 // . Traverse the list and remove any refs whose referents are alive.
881 if (mt_processing) {
882 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
883 task_executor->execute(phase2);
884 } else {
885 for (uint i = 0; i < _max_num_q; i++) {
886 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
887 }
888 }
889
890 // Phase 3:
891 // . Traverse the list and process referents as appropriate.
892 if (mt_processing) {
893 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
894 task_executor->execute(phase3);
895 } else {
896 for (uint i = 0; i < _max_num_q; i++) {
897 process_phase3(refs_lists[i], clear_referent,
898 is_alive, keep_alive, complete_gc);
899 }
900 }
901
902 return total_list_count;
903 }
904
905 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
906 uint id = 0;
907 // Determine the queue index to use for this object.
908 if (_discovery_is_mt) {
909 // During a multi-threaded discovery phase,
910 // each thread saves to its "own" list.
911 Thread* thr = Thread::current();
912 id = thr->as_Worker_thread()->id();
913 } else {
914 // single-threaded discovery, we save in round-robin
915 // fashion to each of the lists.
916 if (_processing_is_mt) {
917 id = next_id();
918 }
919 }
920 assert(id < _max_num_q, "Id is out-of-bounds (call Freud?)");
921
922 // Get the discovered queue to which we will add
923 DiscoveredList* list = NULL;
924 switch (rt) {
925 case REF_OTHER:
926 // Unknown reference type, no special treatment
927 break;
928 case REF_SOFT:
929 list = &_discoveredSoftRefs[id];
930 break;
931 case REF_WEAK:
932 list = &_discoveredWeakRefs[id];
933 break;
934 case REF_FINAL:
935 list = &_discoveredFinalRefs[id];
936 break;
937 case REF_PHANTOM:
938 list = &_discoveredPhantomRefs[id];
939 break;
940 case REF_CLEANER:
941 list = &_discoveredCleanerRefs[id];
942 break;
943 case REF_NONE:
944 // we should not reach here if we are an InstanceRefKlass
945 default:
946 ShouldNotReachHere();
947 }
948 if (TraceReferenceGC && PrintGCDetails) {
949 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
950 }
951 return list;
952 }
953
954 inline void
955 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
956 oop obj,
957 HeapWord* discovered_addr) {
958 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
959 // First we must make sure this object is only enqueued once. CAS in a non null
960 // discovered_addr.
961 oop current_head = refs_list.head();
962 // The last ref must have its discovered field pointing to itself.
963 oop next_discovered = (current_head != NULL) ? current_head : obj;
964
965 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
966 NULL);
967 if (retest == NULL) {
968 // This thread just won the right to enqueue the object.
969 // We have separate lists for enqueueing, so no synchronization
970 // is necessary.
971 refs_list.set_head(obj);
972 refs_list.inc_length(1);
973
974 if (TraceReferenceGC) {
975 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
976 p2i(obj), obj->klass()->internal_name());
977 }
978 } else {
979 // If retest was non NULL, another thread beat us to it:
980 // The reference has already been discovered...
981 if (TraceReferenceGC) {
982 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
983 p2i(obj), obj->klass()->internal_name());
984 }
985 }
986 }
987
988 #ifndef PRODUCT
989 // Non-atomic (i.e. concurrent) discovery might allow us
990 // to observe j.l.References with NULL referents, being those
991 // cleared concurrently by mutators during (or after) discovery.
992 void ReferenceProcessor::verify_referent(oop obj) {
993 bool da = discovery_is_atomic();
994 oop referent = java_lang_ref_Reference::referent(obj);
995 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
996 err_msg("Bad referent " INTPTR_FORMAT " found in Reference "
997 INTPTR_FORMAT " during %satomic discovery ",
998 p2i(referent), p2i(obj), da ? "" : "non-"));
999 }
1000 #endif
1001
1002 // We mention two of several possible choices here:
1003 // #0: if the reference object is not in the "originating generation"
1004 // (or part of the heap being collected, indicated by our "span"
1005 // we don't treat it specially (i.e. we scan it as we would
1006 // a normal oop, treating its references as strong references).
1007 // This means that references can't be discovered unless their
1008 // referent is also in the same span. This is the simplest,
1009 // most "local" and most conservative approach, albeit one
1010 // that may cause weak references to be enqueued least promptly.
1011 // We call this choice the "ReferenceBasedDiscovery" policy.
1012 // #1: the reference object may be in any generation (span), but if
1013 // the referent is in the generation (span) being currently collected
1014 // then we can discover the reference object, provided
1015 // the object has not already been discovered by
1016 // a different concurrently running collector (as may be the
1017 // case, for instance, if the reference object is in CMS and
1018 // the referent in DefNewGeneration), and provided the processing
1019 // of this reference object by the current collector will
1020 // appear atomic to every other collector in the system.
1021 // (Thus, for instance, a concurrent collector may not
1022 // discover references in other generations even if the
1023 // referent is in its own generation). This policy may,
1024 // in certain cases, enqueue references somewhat sooner than
1025 // might Policy #0 above, but at marginally increased cost
1026 // and complexity in processing these references.
1027 // We call this choice the "RefeferentBasedDiscovery" policy.
1028 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1029 // Make sure we are discovering refs (rather than processing discovered refs).
1030 if (!_discovering_refs || !RegisterReferences) {
1031 return false;
1032 }
1033 // We only discover active references.
1034 oop next = java_lang_ref_Reference::next(obj);
1035 if (next != NULL) { // Ref is no longer active
1036 return false;
1037 }
1038
1039 HeapWord* obj_addr = (HeapWord*)obj;
1040 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1041 !_span.contains(obj_addr)) {
1042 // Reference is not in the originating generation;
1043 // don't treat it specially (i.e. we want to scan it as a normal
1044 // object with strong references).
1045 return false;
1046 }
1047
1048 // We only discover references whose referents are not (yet)
1049 // known to be strongly reachable.
1050 if (is_alive_non_header() != NULL) {
1051 verify_referent(obj);
1052 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1053 return false; // referent is reachable
1054 }
1055 }
1056 if (rt == REF_SOFT) {
1057 // For soft refs we can decide now if these are not
1058 // current candidates for clearing, in which case we
1059 // can mark through them now, rather than delaying that
1060 // to the reference-processing phase. Since all current
1061 // time-stamp policies advance the soft-ref clock only
1062 // at a major collection cycle, this is always currently
1063 // accurate.
1064 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1065 return false;
1066 }
1067 }
1068
1069 ResourceMark rm; // Needed for tracing.
1070
1071 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1072 const oop discovered = java_lang_ref_Reference::discovered(obj);
1073 assert(discovered->is_oop_or_null(), err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
1074 if (discovered != NULL) {
1075 // The reference has already been discovered...
1076 if (TraceReferenceGC) {
1077 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
1078 p2i(obj), obj->klass()->internal_name());
1079 }
1080 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1081 // assumes that an object is not processed twice;
1082 // if it's been already discovered it must be on another
1083 // generation's discovered list; so we won't discover it.
1084 return false;
1085 } else {
1086 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1087 "Unrecognized policy");
1088 // Check assumption that an object is not potentially
1089 // discovered twice except by concurrent collectors that potentially
1090 // trace the same Reference object twice.
1091 assert(UseConcMarkSweepGC || UseG1GC,
1092 "Only possible with a concurrent marking collector");
1093 return true;
1094 }
1095 }
1096
1097 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1098 verify_referent(obj);
1099 // Discover if and only if EITHER:
1100 // .. reference is in our span, OR
1101 // .. we are an atomic collector and referent is in our span
1102 if (_span.contains(obj_addr) ||
1103 (discovery_is_atomic() &&
1104 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1105 // should_enqueue = true;
1106 } else {
1107 return false;
1108 }
1109 } else {
1110 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1111 _span.contains(obj_addr), "code inconsistency");
1112 }
1113
1114 // Get the right type of discovered queue head.
1115 DiscoveredList* list = get_discovered_list(rt);
1116 if (list == NULL) {
1117 return false; // nothing special needs to be done
1118 }
1119
1120 if (_discovery_is_mt) {
1121 add_to_discovered_list_mt(*list, obj, discovered_addr);
1122 } else {
1123 // We do a raw store here: the field will be visited later when processing
1124 // the discovered references.
1125 oop current_head = list->head();
1126 // The last ref must have its discovered field pointing to itself.
1127 oop next_discovered = (current_head != NULL) ? current_head : obj;
1128
1129 assert(discovered == NULL, "control point invariant");
1130 oop_store_raw(discovered_addr, next_discovered);
1131 list->set_head(obj);
1132 list->inc_length(1);
1133
1134 if (TraceReferenceGC) {
1135 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)",
1136 p2i(obj), obj->klass()->internal_name());
1137 }
1138 }
1139 assert(obj->is_oop(), "Discovered a bad reference");
1140 verify_referent(obj);
1141 return true;
1142 }
1143
1144 // Preclean the discovered references by removing those
1145 // whose referents are alive, and by marking from those that
1146 // are not active. These lists can be handled here
1147 // in any order and, indeed, concurrently.
1148 void ReferenceProcessor::preclean_discovered_references(
1149 BoolObjectClosure* is_alive,
1150 OopClosure* keep_alive,
1151 VoidClosure* complete_gc,
1152 YieldClosure* yield,
1153 GCTimer* gc_timer,
1154 GCId gc_id) {
1155
1156 // Soft references
1157 {
1158 GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
1159 false, gc_timer, gc_id);
1160 for (uint i = 0; i < _max_num_q; i++) {
1161 if (yield->should_return()) {
1162 return;
1163 }
1164 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1165 keep_alive, complete_gc, yield);
1166 }
1167 }
1168
1169 // Weak references
1170 {
1171 GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
1172 false, gc_timer, gc_id);
1173 for (uint i = 0; i < _max_num_q; i++) {
1174 if (yield->should_return()) {
1175 return;
1176 }
1177 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1178 keep_alive, complete_gc, yield);
1179 }
1180 }
1181
1182 // Final references
1183 {
1184 GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
1185 false, gc_timer, gc_id);
1186 for (uint i = 0; i < _max_num_q; i++) {
1187 if (yield->should_return()) {
1188 return;
1189 }
1190 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1191 keep_alive, complete_gc, yield);
1192 }
1193 }
1194
1195 // Phantom references
1196 {
1197 GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
1198 false, gc_timer, gc_id);
1199 for (uint i = 0; i < _max_num_q; i++) {
1200 if (yield->should_return()) {
1201 return;
1202 }
1203 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1204 keep_alive, complete_gc, yield);
1205 }
1206
1207 // Cleaner references. Included in timing for phantom references. We
1208 // expect Cleaner references to be temporary, and don't want to deal with
1209 // possible incompatibilities arising from making it more visible.
1210 for (uint i = 0; i < _max_num_q; i++) {
1211 if (yield->should_return()) {
1212 return;
1213 }
1214 preclean_discovered_reflist(_discoveredCleanerRefs[i], is_alive,
1215 keep_alive, complete_gc, yield);
1216 }
1217 }
1218 }
1219
1220 // Walk the given discovered ref list, and remove all reference objects
1221 // whose referents are still alive, whose referents are NULL or which
1222 // are not active (have a non-NULL next field). NOTE: When we are
1223 // thus precleaning the ref lists (which happens single-threaded today),
1224 // we do not disable refs discovery to honor the correct semantics of
1225 // java.lang.Reference. As a result, we need to be careful below
1226 // that ref removal steps interleave safely with ref discovery steps
1227 // (in this thread).
1228 void
1229 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1230 BoolObjectClosure* is_alive,
1231 OopClosure* keep_alive,
1232 VoidClosure* complete_gc,
1233 YieldClosure* yield) {
1234 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1235 while (iter.has_next()) {
1236 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1237 oop obj = iter.obj();
1238 oop next = java_lang_ref_Reference::next(obj);
1239 if (iter.referent() == NULL || iter.is_referent_alive() ||
1240 next != NULL) {
1241 // The referent has been cleared, or is alive, or the Reference is not
1242 // active; we need to trace and mark its cohort.
1243 if (TraceReferenceGC) {
1244 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1245 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1246 }
1247 // Remove Reference object from list
1248 iter.remove();
1249 // Keep alive its cohort.
1250 iter.make_referent_alive();
1251 if (UseCompressedOops) {
1252 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1253 keep_alive->do_oop(next_addr);
1254 } else {
1255 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1256 keep_alive->do_oop(next_addr);
1257 }
1258 iter.move_to_next();
1259 } else {
1260 iter.next();
1261 }
1262 }
1263 // Close the reachable set
1264 complete_gc->do_void();
1265
1266 NOT_PRODUCT(
1267 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) {
1268 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT
1269 " Refs in discovered list " INTPTR_FORMAT,
1270 iter.removed(), iter.processed(), p2i(refs_list.head()));
1271 }
1272 )
1273 }
1274
1275 const char* ReferenceProcessor::list_name(uint i) {
1276 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1277 "Out of bounds index");
1278
1279 int j = i / _max_num_q;
1280 switch (j) {
1281 case 0: return "SoftRef";
1282 case 1: return "WeakRef";
1283 case 2: return "FinalRef";
1284 case 3: return "PhantomRef";
1285 case 4: return "CleanerRef";
1286 }
1287 ShouldNotReachHere();
1288 return NULL;
1289 }
1290