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 }
247
248 // Cleaners
249 size_t cleaner_count = 0;
250 {
251 GCTraceTime tt("Cleaners", trace_time, false, gc_timer, gc_id);
252 cleaner_count =
253 process_discovered_reflist(_discoveredCleanerRefs, NULL, true,
254 is_alive, keep_alive, complete_gc, task_executor);
255 }
256
257 // Weak global JNI references. It would make more sense (semantically) to
258 // traverse these simultaneously with the regular weak references above, but
259 // that is not how the JDK1.2 specification is. See #4126360. Native code can
260 // thus use JNI weak references to circumvent the phantom references and
261 // resurrect a "post-mortem" object.
262 size_t jni_weak_ref_count = 0;
263 {
264 GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id);
265 if (task_executor != NULL) {
266 task_executor->set_single_threaded_mode();
267 }
268 jni_weak_ref_count =
269 process_phaseJNI(is_alive, keep_alive, complete_gc);
270 }
271
272 return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count, cleaner_count, jni_weak_ref_count);
273 }
274
275 #ifndef PRODUCT
276 // Calculate the number of jni handles.
277 uint ReferenceProcessor::count_jni_refs() {
278 class AlwaysAliveClosure: public BoolObjectClosure {
279 public:
280 virtual bool do_object_b(oop obj) { return true; }
281 };
282
283 class CountHandleClosure: public OopClosure {
284 private:
285 int _count;
286 public:
287 CountHandleClosure(): _count(0) {}
288 void do_oop(oop* unused) { _count++; }
289 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
290 int count() { return _count; }
291 };
292 CountHandleClosure global_handle_count;
293 AlwaysAliveClosure always_alive;
294 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
295 return global_handle_count.count();
296 }
297 #endif
298
299 size_t ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
300 OopClosure* keep_alive,
301 VoidClosure* complete_gc) {
302 DEBUG_ONLY(size_t check_count = count_jni_refs();)
303 size_t count = JNIHandles::weak_oops_do(is_alive, keep_alive);
304 assert(count == check_count, "Counts didn't match");
305 complete_gc->do_void();
306 if (PrintGCDetails && PrintReferenceGC) {
307 gclog_or_tty->print(", " SIZE_FORMAT " refs", count);
308 }
309 return count;
310 }
311
312
313 template <class T>
314 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
315 AbstractRefProcTaskExecutor* task_executor) {
316
317 // Remember old value of pending references list
318 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
319 T old_pending_list_value = *pending_list_addr;
320
321 // Enqueue references that are not made active again, and
322 // clear the decks for the next collection (cycle).
323 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
324 // Do the post-barrier on pending_list_addr missed in
325 // enqueue_discovered_reflist.
326 oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
327
328 // Stop treating discovered references specially.
329 ref->disable_discovery();
330
331 // Return true if new pending references were added
332 return old_pending_list_value != *pending_list_addr;
333 }
334
335 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
336 if (UseCompressedOops) {
337 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
338 } else {
339 return enqueue_discovered_ref_helper<oop>(this, task_executor);
340 }
341 }
342
343 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
344 HeapWord* pending_list_addr) {
345 // Given a list of refs linked through the "discovered" field
346 // (java.lang.ref.Reference.discovered), self-loop their "next" field
347 // thus distinguishing them from active References, then
348 // prepend them to the pending list.
349 //
350 // The Java threads will see the Reference objects linked together through
351 // the discovered field. Instead of trying to do the write barrier updates
352 // in all places in the reference processor where we manipulate the discovered
353 // field we make sure to do the barrier here where we anyway iterate through
354 // all linked Reference objects. Note that it is important to not dirty any
355 // cards during reference processing since this will cause card table
356 // verification to fail for G1.
357 if (TraceReferenceGC && PrintGCDetails) {
358 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
359 INTPTR_FORMAT, p2i(refs_list.head()));
360 }
361
362 oop obj = NULL;
363 oop next_d = refs_list.head();
364 // Walk down the list, self-looping the next field
365 // so that the References are not considered active.
366 while (obj != next_d) {
367 obj = next_d;
368 assert(obj->is_instanceRef(), "should be reference object");
369 next_d = java_lang_ref_Reference::discovered(obj);
370 if (TraceReferenceGC && PrintGCDetails) {
371 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
372 p2i(obj), p2i(next_d));
373 }
374 assert(java_lang_ref_Reference::next(obj) == NULL,
375 "Reference not active; should not be discovered");
376 // Self-loop next, so as to make Ref not active.
377 java_lang_ref_Reference::set_next_raw(obj, obj);
378 if (next_d != obj) {
379 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
380 } else {
381 // This is the last object.
382 // Swap refs_list into pending_list_addr and
383 // set obj's discovered to what we read from pending_list_addr.
384 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
385 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
386 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
387 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
388 }
389 }
390 }
391
392 // Parallel enqueue task
393 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
394 public:
395 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
396 DiscoveredList discovered_refs[],
397 HeapWord* pending_list_addr,
398 int n_queues)
399 : EnqueueTask(ref_processor, discovered_refs,
400 pending_list_addr, n_queues)
401 { }
402
403 virtual void work(unsigned int work_id) {
404 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
405 // Simplest first cut: static partitioning.
406 int index = work_id;
407 // The increment on "index" must correspond to the maximum number of queues
408 // (n_queues) with which that ReferenceProcessor was created. That
409 // is because of the "clever" way the discovered references lists were
410 // allocated and are indexed into.
411 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
412 for (int j = 0;
413 j < ReferenceProcessor::number_of_subclasses_of_ref();
414 j++, index += _n_queues) {
415 _ref_processor.enqueue_discovered_reflist(
416 _refs_lists[index], _pending_list_addr);
417 _refs_lists[index].set_head(NULL);
418 _refs_lists[index].set_length(0);
419 }
420 }
421 };
422
423 // Enqueue references that are not made active again
424 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
425 AbstractRefProcTaskExecutor* task_executor) {
426 if (_processing_is_mt && task_executor != NULL) {
427 // Parallel code
428 RefProcEnqueueTask tsk(*this, _discovered_refs,
429 pending_list_addr, _max_num_q);
430 task_executor->execute(tsk);
431 } else {
432 // Serial code: call the parent class's implementation
433 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
434 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
435 _discovered_refs[i].set_head(NULL);
436 _discovered_refs[i].set_length(0);
437 }
438 }
439 }
440
441 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
442 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
443 oop discovered = java_lang_ref_Reference::discovered(_ref);
444 assert(_discovered_addr && discovered->is_oop_or_null(),
445 err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
446 _next = discovered;
447 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
448 _referent = java_lang_ref_Reference::referent(_ref);
449 assert(_referent == oopDesc::bs()->resolve_oop(_referent), "expect forwarded referent");
450 assert(Universe::heap()->is_in_reserved_or_null(_referent),
451 "Wrong oop found in java.lang.Reference object");
452 assert(allow_null_referent ?
453 _referent->is_oop_or_null()
454 : _referent->is_oop(),
455 err_msg("Expected an oop%s for referent field at " PTR_FORMAT,
456 (allow_null_referent ? " or NULL" : ""),
457 p2i(_referent)));
458 }
459
460 void DiscoveredListIterator::remove() {
461 assert(_ref->is_oop(), "Dropping a bad reference");
462 oop_store_raw(_discovered_addr, NULL);
463
464 // First _prev_next ref actually points into DiscoveredList (gross).
465 oop new_next;
466 if (_next == _ref) {
467 // At the end of the list, we should make _prev point to itself.
468 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
469 // and _prev will be NULL.
470 new_next = _prev;
471 } else {
472 new_next = _next;
473 }
474 // Remove Reference object from discovered list. Note that G1 does not need a
475 // pre-barrier here because we know the Reference has already been found/marked,
476 // that's how it ended up in the discovered list in the first place.
477 oop_store_raw(_prev_next, new_next);
478 NOT_PRODUCT(_removed++);
479 _refs_list.dec_length(1);
480 }
481
482 void DiscoveredListIterator::clear_referent() {
483 oop_store_raw(_referent_addr, NULL);
484 }
485
486 // NOTE: process_phase*() are largely similar, and at a high level
487 // merely iterate over the extant list applying a predicate to
488 // each of its elements and possibly removing that element from the
489 // list and applying some further closures to that element.
490 // We should consider the possibility of replacing these
491 // process_phase*() methods by abstracting them into
492 // a single general iterator invocation that receives appropriate
493 // closures that accomplish this work.
494
495 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
496 // referents are not alive, but that should be kept alive for policy reasons.
497 // Keep alive the transitive closure of all such referents.
498 void
499 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
500 ReferencePolicy* policy,
501 BoolObjectClosure* is_alive,
502 OopClosure* keep_alive,
503 VoidClosure* complete_gc) {
504 assert(policy != NULL, "Must have a non-NULL policy");
505 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
506 // Decide which softly reachable refs should be kept alive.
507 while (iter.has_next()) {
508 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
509 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
510 if (referent_is_dead &&
511 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
512 if (TraceReferenceGC) {
513 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
514 p2i(iter.obj()), iter.obj()->klass()->internal_name());
515 }
516 // Remove Reference object from list
517 iter.remove();
518 // keep the referent around
519 iter.make_referent_alive();
520 iter.move_to_next();
521 } else {
522 iter.next();
523 }
524 }
525 // Close the reachable set
526 complete_gc->do_void();
527 NOT_PRODUCT(
528 if (PrintGCDetails && TraceReferenceGC) {
529 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT
530 " discovered Refs by policy, from list " INTPTR_FORMAT,
531 iter.removed(), iter.processed(), p2i(refs_list.head()));
532 }
533 )
534 }
535
536 // Traverse the list and remove any Refs that are not active, or
537 // whose referents are either alive or NULL.
538 void
539 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
540 BoolObjectClosure* is_alive,
541 OopClosure* keep_alive) {
542 assert(discovery_is_atomic(), "Error");
543 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
544 while (iter.has_next()) {
545 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
546 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
547 assert(next == NULL, "Should not discover inactive Reference");
548 if (iter.is_referent_alive()) {
549 if (TraceReferenceGC) {
550 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
551 p2i(iter.obj()), iter.obj()->klass()->internal_name());
552 }
553 // The referent is reachable after all.
554 // Remove Reference object from list.
555 iter.remove();
556 // Update the referent pointer as necessary: Note that this
557 // should not entail any recursive marking because the
558 // referent must already have been traversed.
559 iter.make_referent_alive();
560 iter.move_to_next();
561 } else {
562 iter.next();
563 }
564 }
565 NOT_PRODUCT(
566 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
567 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
568 " Refs in discovered list " INTPTR_FORMAT,
569 iter.removed(), iter.processed(), p2i(refs_list.head()));
570 }
571 )
572 }
573
574 void
575 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
576 BoolObjectClosure* is_alive,
577 OopClosure* keep_alive,
578 VoidClosure* complete_gc) {
579 assert(!discovery_is_atomic(), "Error");
580 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
581 while (iter.has_next()) {
582 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
583 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
584 oop next = java_lang_ref_Reference::next(iter.obj());
585 if ((iter.referent() == NULL || iter.is_referent_alive() ||
586 next != NULL)) {
587 assert(next->is_oop_or_null(), err_msg("Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)));
588 // Remove Reference object from list
589 iter.remove();
590 // Trace the cohorts
591 iter.make_referent_alive();
592 if (UseCompressedOops) {
593 keep_alive->do_oop((narrowOop*)next_addr);
594 } else {
595 keep_alive->do_oop((oop*)next_addr);
596 }
597 iter.move_to_next();
598 } else {
599 iter.next();
600 }
601 }
602 // Now close the newly reachable set
603 complete_gc->do_void();
604 NOT_PRODUCT(
605 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
606 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
607 " Refs in discovered list " INTPTR_FORMAT,
608 iter.removed(), iter.processed(), p2i(refs_list.head()));
609 }
610 )
611 }
612
613 // Traverse the list and process the referents, by either
614 // clearing them or keeping them (and their reachable
615 // closure) alive.
616 void
617 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
618 bool clear_referent,
619 BoolObjectClosure* is_alive,
620 OopClosure* keep_alive,
621 VoidClosure* complete_gc) {
622 ResourceMark rm;
623 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
624 while (iter.has_next()) {
625 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
626 if (clear_referent) {
627 // NULL out referent pointer
628 iter.clear_referent();
629 } else {
630 // keep the referent around
631 iter.make_referent_alive();
632 }
633 if (TraceReferenceGC) {
634 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
635 clear_referent ? "cleared " : "",
636 p2i(iter.obj()), iter.obj()->klass()->internal_name());
637 }
638 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
639 iter.next();
640 }
641 // Close the reachable set
642 complete_gc->do_void();
643 }
644
645 void
646 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
647 oop obj = NULL;
648 oop next = refs_list.head();
649 while (next != obj) {
650 obj = next;
651 assert(obj == oopDesc::bs()->resolve_oop(obj), "expect forwarded obj");
652 next = java_lang_ref_Reference::discovered(obj);
653 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
654 }
655 refs_list.set_head(NULL);
656 refs_list.set_length(0);
657 }
658
659 void ReferenceProcessor::abandon_partial_discovery() {
660 // loop over the lists
661 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
662 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
663 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i));
664 }
665 clear_discovered_references(_discovered_refs[i]);
666 }
667 }
668
669 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
670 public:
671 RefProcPhase1Task(ReferenceProcessor& ref_processor,
672 DiscoveredList refs_lists[],
673 ReferencePolicy* policy,
674 bool marks_oops_alive)
675 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
676 _policy(policy)
677 { }
678 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
679 OopClosure& keep_alive,
680 VoidClosure& complete_gc)
681 {
682 Thread* thr = Thread::current();
683 int refs_list_index = ((WorkerThread*)thr)->id();
684 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
685 &is_alive, &keep_alive, &complete_gc);
686 }
687 private:
688 ReferencePolicy* _policy;
689 };
690
691 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
692 public:
693 RefProcPhase2Task(ReferenceProcessor& ref_processor,
694 DiscoveredList refs_lists[],
695 bool marks_oops_alive)
696 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
697 { }
698 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
699 OopClosure& keep_alive,
700 VoidClosure& complete_gc)
701 {
702 _ref_processor.process_phase2(_refs_lists[i],
703 &is_alive, &keep_alive, &complete_gc);
704 }
705 };
706
707 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
708 public:
709 RefProcPhase3Task(ReferenceProcessor& ref_processor,
710 DiscoveredList refs_lists[],
711 bool clear_referent,
712 bool marks_oops_alive)
713 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
714 _clear_referent(clear_referent)
715 { }
716 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
717 OopClosure& keep_alive,
718 VoidClosure& complete_gc)
719 {
720 // Don't use "refs_list_index" calculated in this way because
721 // balance_queues() has moved the Ref's into the first n queues.
722 // Thread* thr = Thread::current();
723 // int refs_list_index = ((WorkerThread*)thr)->id();
724 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
725 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
726 &is_alive, &keep_alive, &complete_gc);
727 }
728 private:
729 bool _clear_referent;
730 };
731
732 // Balances reference queues.
733 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
734 // queues[0, 1, ..., _num_q-1] because only the first _num_q
735 // corresponding to the active workers will be processed.
736 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
737 {
738 // calculate total length
739 size_t total_refs = 0;
740 if (TraceReferenceGC && PrintGCDetails) {
741 gclog_or_tty->print_cr("\nBalance ref_lists ");
742 }
743
744 for (uint i = 0; i < _max_num_q; ++i) {
745 total_refs += ref_lists[i].length();
746 if (TraceReferenceGC && PrintGCDetails) {
747 gclog_or_tty->print(SIZE_FORMAT " ", ref_lists[i].length());
748 }
749 }
750 if (TraceReferenceGC && PrintGCDetails) {
751 gclog_or_tty->print_cr(" = " SIZE_FORMAT, total_refs);
752 }
753 size_t avg_refs = total_refs / _num_q + 1;
754 uint to_idx = 0;
755 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
756 bool move_all = false;
757 if (from_idx >= _num_q) {
758 move_all = ref_lists[from_idx].length() > 0;
759 }
760 while ((ref_lists[from_idx].length() > avg_refs) ||
761 move_all) {
762 assert(to_idx < _num_q, "Sanity Check!");
763 if (ref_lists[to_idx].length() < avg_refs) {
764 // move superfluous refs
765 size_t refs_to_move;
766 // Move all the Ref's if the from queue will not be processed.
767 if (move_all) {
768 refs_to_move = MIN2(ref_lists[from_idx].length(),
769 avg_refs - ref_lists[to_idx].length());
770 } else {
771 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
772 avg_refs - ref_lists[to_idx].length());
773 }
774
775 assert(refs_to_move > 0, "otherwise the code below will fail");
776
777 oop move_head = ref_lists[from_idx].head();
778 oop move_tail = move_head;
779 oop new_head = move_head;
780 // find an element to split the list on
781 for (size_t j = 0; j < refs_to_move; ++j) {
782 move_tail = new_head;
783 new_head = java_lang_ref_Reference::discovered(new_head);
784 }
785
786 // Add the chain to the to list.
787 if (ref_lists[to_idx].head() == NULL) {
788 // to list is empty. Make a loop at the end.
789 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
790 } else {
791 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
792 }
793 ref_lists[to_idx].set_head(move_head);
794 ref_lists[to_idx].inc_length(refs_to_move);
795
796 // Remove the chain from the from list.
797 if (move_tail == new_head) {
798 // We found the end of the from list.
799 ref_lists[from_idx].set_head(NULL);
800 } else {
801 ref_lists[from_idx].set_head(new_head);
802 }
803 ref_lists[from_idx].dec_length(refs_to_move);
804 if (ref_lists[from_idx].length() == 0) {
805 break;
806 }
807 } else {
808 to_idx = (to_idx + 1) % _num_q;
809 }
810 }
811 }
812 #ifdef ASSERT
813 size_t balanced_total_refs = 0;
814 for (uint i = 0; i < _max_num_q; ++i) {
815 balanced_total_refs += ref_lists[i].length();
816 if (TraceReferenceGC && PrintGCDetails) {
817 gclog_or_tty->print(SIZE_FORMAT " ", ref_lists[i].length());
818 }
819 }
820 if (TraceReferenceGC && PrintGCDetails) {
821 gclog_or_tty->print_cr(" = " SIZE_FORMAT, balanced_total_refs);
822 gclog_or_tty->flush();
823 }
824 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
825 #endif
826 }
827
828 void ReferenceProcessor::balance_all_queues() {
829 balance_queues(_discoveredSoftRefs);
830 balance_queues(_discoveredWeakRefs);
831 balance_queues(_discoveredFinalRefs);
832 balance_queues(_discoveredPhantomRefs);
833 balance_queues(_discoveredCleanerRefs);
834 }
835
836 size_t
837 ReferenceProcessor::process_discovered_reflist(
838 DiscoveredList refs_lists[],
839 ReferencePolicy* policy,
840 bool clear_referent,
841 BoolObjectClosure* is_alive,
842 OopClosure* keep_alive,
843 VoidClosure* complete_gc,
844 AbstractRefProcTaskExecutor* task_executor)
845 {
846 bool mt_processing = task_executor != NULL && _processing_is_mt;
847 // If discovery used MT and a dynamic number of GC threads, then
848 // the queues must be balanced for correctness if fewer than the
849 // maximum number of queues were used. The number of queue used
850 // during discovery may be different than the number to be used
851 // for processing so don't depend of _num_q < _max_num_q as part
852 // of the test.
853 bool must_balance = _discovery_is_mt;
854
855 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
856 must_balance) {
857 balance_queues(refs_lists);
858 }
859
860 size_t total_list_count = total_count(refs_lists);
861
862 if (PrintReferenceGC && PrintGCDetails) {
863 gclog_or_tty->print(", " SIZE_FORMAT " refs", total_list_count);
864 }
865
866 // Phase 1 (soft refs only):
867 // . Traverse the list and remove any SoftReferences whose
868 // referents are not alive, but that should be kept alive for
869 // policy reasons. Keep alive the transitive closure of all
870 // such referents.
871 if (policy != NULL) {
872 if (mt_processing) {
873 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
874 task_executor->execute(phase1);
875 } else {
876 for (uint i = 0; i < _max_num_q; i++) {
877 process_phase1(refs_lists[i], policy,
878 is_alive, keep_alive, complete_gc);
879 }
880 }
881 } else { // policy == NULL
882 assert(refs_lists != _discoveredSoftRefs,
883 "Policy must be specified for soft references.");
884 }
885
886 // Phase 2:
887 // . Traverse the list and remove any refs whose referents are alive.
888 if (mt_processing) {
889 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
890 task_executor->execute(phase2);
891 } else {
892 for (uint i = 0; i < _max_num_q; i++) {
893 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
894 }
895 }
896
897 // Phase 3:
898 // . Traverse the list and process referents as appropriate.
899 if (mt_processing) {
900 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
901 task_executor->execute(phase3);
902 } else {
903 for (uint i = 0; i < _max_num_q; i++) {
904 process_phase3(refs_lists[i], clear_referent,
905 is_alive, keep_alive, complete_gc);
906 }
907 }
908
909 return total_list_count;
910 }
911
912 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
913 uint id = 0;
914 // Determine the queue index to use for this object.
915 if (_discovery_is_mt) {
916 // During a multi-threaded discovery phase,
917 // each thread saves to its "own" list.
918 Thread* thr = Thread::current();
919 id = thr->as_Worker_thread()->id();
920 } else {
921 // single-threaded discovery, we save in round-robin
922 // fashion to each of the lists.
923 if (_processing_is_mt) {
924 id = next_id();
925 }
926 }
927 assert(id < _max_num_q, "Id is out-of-bounds (call Freud?)");
928
929 // Get the discovered queue to which we will add
930 DiscoveredList* list = NULL;
931 switch (rt) {
932 case REF_OTHER:
933 // Unknown reference type, no special treatment
934 break;
935 case REF_SOFT:
936 list = &_discoveredSoftRefs[id];
937 break;
938 case REF_WEAK:
939 list = &_discoveredWeakRefs[id];
940 break;
941 case REF_FINAL:
942 list = &_discoveredFinalRefs[id];
943 break;
944 case REF_PHANTOM:
945 list = &_discoveredPhantomRefs[id];
946 break;
947 case REF_CLEANER:
948 list = &_discoveredCleanerRefs[id];
949 break;
950 case REF_NONE:
951 case REF_JNI:
952 // we should not reach here if we are an InstanceRefKlass
953 default:
954 guarantee(false, err_msg("rt should not be %d", rt));
955 }
956 if (TraceReferenceGC && PrintGCDetails) {
957 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
958 }
959 return list;
960 }
961
962 inline void
963 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
964 oop obj,
965 HeapWord* discovered_addr) {
966 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
967 // First we must make sure this object is only enqueued once. CAS in a non null
968 // discovered_addr.
969 oop current_head = refs_list.head();
970 // The last ref must have its discovered field pointing to itself.
971 oop next_discovered = (current_head != NULL) ? current_head : obj;
972
973 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
974 NULL);
975 if (retest == NULL) {
976 // This thread just won the right to enqueue the object.
977 // We have separate lists for enqueueing, so no synchronization
978 // is necessary.
979 refs_list.set_head(obj);
980 refs_list.inc_length(1);
981
982 if (TraceReferenceGC) {
983 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
984 p2i(obj), obj->klass()->internal_name());
985 }
986 } else {
987 // If retest was non NULL, another thread beat us to it:
988 // The reference has already been discovered...
989 if (TraceReferenceGC) {
990 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
991 p2i(obj), obj->klass()->internal_name());
992 }
993 }
994 }
995
996 #ifndef PRODUCT
997 // Non-atomic (i.e. concurrent) discovery might allow us
998 // to observe j.l.References with NULL referents, being those
999 // cleared concurrently by mutators during (or after) discovery.
1000 void ReferenceProcessor::verify_referent(oop obj) {
1001 bool da = discovery_is_atomic();
1002 oop referent = java_lang_ref_Reference::referent(obj);
1003 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
1004 err_msg("Bad referent " INTPTR_FORMAT " found in Reference "
1005 INTPTR_FORMAT " during %satomic discovery ",
1006 p2i(referent), p2i(obj), da ? "" : "non-"));
1007 }
1008 #endif
1009
1010 // We mention two of several possible choices here:
1011 // #0: if the reference object is not in the "originating generation"
1012 // (or part of the heap being collected, indicated by our "span"
1013 // we don't treat it specially (i.e. we scan it as we would
1014 // a normal oop, treating its references as strong references).
1015 // This means that references can't be discovered unless their
1016 // referent is also in the same span. This is the simplest,
1017 // most "local" and most conservative approach, albeit one
1018 // that may cause weak references to be enqueued least promptly.
1019 // We call this choice the "ReferenceBasedDiscovery" policy.
1020 // #1: the reference object may be in any generation (span), but if
1021 // the referent is in the generation (span) being currently collected
1022 // then we can discover the reference object, provided
1023 // the object has not already been discovered by
1024 // a different concurrently running collector (as may be the
1025 // case, for instance, if the reference object is in CMS and
1026 // the referent in DefNewGeneration), and provided the processing
1027 // of this reference object by the current collector will
1028 // appear atomic to every other collector in the system.
1029 // (Thus, for instance, a concurrent collector may not
1030 // discover references in other generations even if the
1031 // referent is in its own generation). This policy may,
1032 // in certain cases, enqueue references somewhat sooner than
1033 // might Policy #0 above, but at marginally increased cost
1034 // and complexity in processing these references.
1035 // We call this choice the "RefeferentBasedDiscovery" policy.
1036 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1037 // Make sure we are discovering refs (rather than processing discovered refs).
1038 if (!_discovering_refs || !RegisterReferences) {
1039 return false;
1040 }
1041 // We only discover active references.
1042 oop next = java_lang_ref_Reference::next(obj);
1043 if (next != NULL) { // Ref is no longer active
1044 return false;
1045 }
1046
1047 HeapWord* obj_addr = (HeapWord*)obj;
1048 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1049 !_span.contains(obj_addr)) {
1050 // Reference is not in the originating generation;
1051 // don't treat it specially (i.e. we want to scan it as a normal
1052 // object with strong references).
1053 return false;
1054 }
1055
1056 // We only discover references whose referents are not (yet)
1057 // known to be strongly reachable.
1058 if (is_alive_non_header() != NULL) {
1059 verify_referent(obj);
1060 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1061 return false; // referent is reachable
1062 }
1063 }
1064 if (rt == REF_SOFT) {
1065 // For soft refs we can decide now if these are not
1066 // current candidates for clearing, in which case we
1067 // can mark through them now, rather than delaying that
1068 // to the reference-processing phase. Since all current
1069 // time-stamp policies advance the soft-ref clock only
1070 // at a full collection cycle, this is always currently
1071 // accurate.
1072 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1073 return false;
1074 }
1075 }
1076
1077 ResourceMark rm; // Needed for tracing.
1078
1079 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1080 const oop discovered = java_lang_ref_Reference::discovered(obj);
1081 assert(discovered->is_oop_or_null(), err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
1082 if (discovered != NULL) {
1083 // The reference has already been discovered...
1084 if (TraceReferenceGC) {
1085 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
1086 p2i(obj), obj->klass()->internal_name());
1087 }
1088 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1089 // assumes that an object is not processed twice;
1090 // if it's been already discovered it must be on another
1091 // generation's discovered list; so we won't discover it.
1092 return false;
1093 } else {
1094 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1095 "Unrecognized policy");
1096 // Check assumption that an object is not potentially
1097 // discovered twice except by concurrent collectors that potentially
1098 // trace the same Reference object twice.
1099 assert(UseConcMarkSweepGC || UseG1GC || UseShenandoahGC,
1100 "Only possible with a concurrent marking collector");
1101 return true;
1102 }
1103 }
1104
1105 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1106 verify_referent(obj);
1107 // Discover if and only if EITHER:
1108 // .. reference is in our span, OR
1109 // .. we are an atomic collector and referent is in our span
1110 if (_span.contains(obj_addr) ||
1111 (discovery_is_atomic() &&
1112 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1113 // should_enqueue = true;
1114 } else {
1115 return false;
1116 }
1117 } else {
1118 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1119 _span.contains(obj_addr), "code inconsistency");
1120 }
1121
1122 // Get the right type of discovered queue head.
1123 DiscoveredList* list = get_discovered_list(rt);
1124 if (list == NULL) {
1125 return false; // nothing special needs to be done
1126 }
1127
1128 if (_discovery_is_mt) {
1129 add_to_discovered_list_mt(*list, obj, discovered_addr);
1130 } else {
1131 // We do a raw store here: the field will be visited later when processing
1132 // the discovered references.
1133 oop current_head = list->head();
1134 // The last ref must have its discovered field pointing to itself.
1135 oop next_discovered = (current_head != NULL) ? current_head : obj;
1136
1137 assert(discovered == NULL, "control point invariant");
1138 oop_store_raw(discovered_addr, next_discovered);
1139 list->set_head(obj);
1140 list->inc_length(1);
1141
1142 if (TraceReferenceGC) {
1143 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)",
1144 p2i(obj), obj->klass()->internal_name());
1145 }
1146 }
1147 assert(obj->is_oop(), "Discovered a bad reference");
1148 verify_referent(obj);
1149 return true;
1150 }
1151
1152 // Preclean the discovered references by removing those
1153 // whose referents are alive, and by marking from those that
1154 // are not active. These lists can be handled here
1155 // in any order and, indeed, concurrently.
1156 void ReferenceProcessor::preclean_discovered_references(
1157 BoolObjectClosure* is_alive,
1158 OopClosure* keep_alive,
1159 VoidClosure* complete_gc,
1160 YieldClosure* yield,
1161 GCTimer* gc_timer,
1162 GCId gc_id) {
1163
1164 // Soft references
1165 {
1166 GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
1167 false, gc_timer, gc_id);
1168 for (uint i = 0; i < _max_num_q; i++) {
1169 if (yield->should_return()) {
1170 return;
1171 }
1172 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1173 keep_alive, complete_gc, yield);
1174 }
1175 }
1176
1177 // Weak references
1178 {
1179 GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
1180 false, gc_timer, gc_id);
1181 for (uint i = 0; i < _max_num_q; i++) {
1182 if (yield->should_return()) {
1183 return;
1184 }
1185 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1186 keep_alive, complete_gc, yield);
1187 }
1188 }
1189
1190 // Final references
1191 {
1192 GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
1193 false, gc_timer, gc_id);
1194 for (uint i = 0; i < _max_num_q; i++) {
1195 if (yield->should_return()) {
1196 return;
1197 }
1198 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1199 keep_alive, complete_gc, yield);
1200 }
1201 }
1202
1203 // Phantom references
1204 {
1205 GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
1206 false, gc_timer, gc_id);
1207 for (uint i = 0; i < _max_num_q; i++) {
1208 if (yield->should_return()) {
1209 return;
1210 }
1211 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1212 keep_alive, complete_gc, yield);
1213 }
1214
1215 // Cleaner references. Included in timing for phantom references. We
1216 // expect Cleaner references to be temporary, and don't want to deal with
1217 // possible incompatibilities arising from making it more visible.
1218 for (uint i = 0; i < _max_num_q; i++) {
1219 if (yield->should_return()) {
1220 return;
1221 }
1222 preclean_discovered_reflist(_discoveredCleanerRefs[i], is_alive,
1223 keep_alive, complete_gc, yield);
1224 }
1225 }
1226 }
1227
1228 // Walk the given discovered ref list, and remove all reference objects
1229 // whose referents are still alive, whose referents are NULL or which
1230 // are not active (have a non-NULL next field). NOTE: When we are
1231 // thus precleaning the ref lists (which happens single-threaded today),
1232 // we do not disable refs discovery to honor the correct semantics of
1233 // java.lang.Reference. As a result, we need to be careful below
1234 // that ref removal steps interleave safely with ref discovery steps
1235 // (in this thread).
1236 void
1237 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1238 BoolObjectClosure* is_alive,
1239 OopClosure* keep_alive,
1240 VoidClosure* complete_gc,
1241 YieldClosure* yield) {
1242 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1243 while (iter.has_next()) {
1244 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1245 oop obj = iter.obj();
1246 oop next = java_lang_ref_Reference::next(obj);
1247 if (iter.referent() == NULL || iter.is_referent_alive() ||
1248 next != NULL) {
1249 // The referent has been cleared, or is alive, or the Reference is not
1250 // active; we need to trace and mark its cohort.
1251 if (TraceReferenceGC) {
1252 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1253 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1254 }
1255 // Remove Reference object from list
1256 iter.remove();
1257 // Keep alive its cohort.
1258 iter.make_referent_alive();
1259 if (UseCompressedOops) {
1260 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1261 keep_alive->do_oop(next_addr);
1262 } else {
1263 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1264 keep_alive->do_oop(next_addr);
1265 }
1266 iter.move_to_next();
1267 } else {
1268 iter.next();
1269 }
1270 }
1271 // Close the reachable set
1272 complete_gc->do_void();
1273
1274 NOT_PRODUCT(
1275 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) {
1276 gclog_or_tty->print_cr(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT
1277 " Refs in discovered list " INTPTR_FORMAT,
1278 iter.removed(), iter.processed(), p2i(refs_list.head()));
1279 }
1280 )
1281 }
1282
1283 const char* ReferenceProcessor::list_name(uint i) {
1284 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1285 "Out of bounds index");
1286
1287 int j = i / _max_num_q;
1288 switch (j) {
1289 case 0: return "SoftRef";
1290 case 1: return "WeakRef";
1291 case 2: return "FinalRef";
1292 case 3: return "PhantomRef";
1293 case 4: return "CleanerRef";
1294 }
1295 ShouldNotReachHere();
1296 return NULL;
1297 }
1298