1 #ifdef USE_PRAGMA_IDENT_SRC
2 #pragma ident "@(#)referenceProcessor.cpp 1.57 07/08/17 12:30:18 JVM"
3 #endif
4 /*
5 * Copyright 2001-2008 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
24 * have any questions.
25 *
26 */
27
28 # include "incls/_precompiled.incl"
29 # include "incls/_referenceProcessor.cpp.incl"
30
31 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
32 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
33 oop ReferenceProcessor::_sentinelRef = NULL;
34 const int subclasses_of_ref = REF_PHANTOM - REF_OTHER;
35
36 // List of discovered references.
37 class DiscoveredList {
38 public:
39 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
40 oop head() const {
41 return UseCompressedOops ? oopDesc::decode_heap_oop_not_null(_compressed_head) :
42 _oop_head;
43 }
44 HeapWord* adr_head() {
45 return UseCompressedOops ? (HeapWord*)&_compressed_head :
46 (HeapWord*)&_oop_head;
47 }
48 void set_head(oop o) {
49 if (UseCompressedOops) {
50 // Must compress the head ptr.
51 _compressed_head = oopDesc::encode_heap_oop_not_null(o);
52 } else {
53 _oop_head = o;
54 }
55 }
56 bool empty() const { return head() == ReferenceProcessor::sentinel_ref(); }
57 size_t length() { return _len; }
58 void set_length(size_t len) { _len = len; }
59 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
60 void dec_length(size_t dec) { _len -= dec; }
61 private:
62 // Set value depending on UseCompressedOops. This could be a template class
63 // but then we have to fix all the instantiations and declarations that use this class.
64 oop _oop_head;
65 narrowOop _compressed_head;
66 size_t _len;
67 };
68
69 void referenceProcessor_init() {
70 ReferenceProcessor::init_statics();
71 }
72
73 void ReferenceProcessor::init_statics() {
74 assert(_sentinelRef == NULL, "should be initialized precisely once");
75 EXCEPTION_MARK;
76 _sentinelRef = instanceKlass::cast(
77 SystemDictionary::reference_klass())->
78 allocate_permanent_instance(THREAD);
79
80 // Initialize the master soft ref clock.
81 java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
82
83 if (HAS_PENDING_EXCEPTION) {
84 Handle ex(THREAD, PENDING_EXCEPTION);
85 vm_exit_during_initialization(ex);
86 }
87 assert(_sentinelRef != NULL && _sentinelRef->is_oop(),
88 "Just constructed it!");
89 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
90 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
91 NOT_COMPILER2(LRUCurrentHeapPolicy());
92 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
93 vm_exit_during_initialization("Could not allocate reference policy object");
94 }
95 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
96 RefDiscoveryPolicy == ReferentBasedDiscovery,
97 "Unrecongnized RefDiscoveryPolicy");
98 }
99
100 ReferenceProcessor*
101 ReferenceProcessor::create_ref_processor(MemRegion span,
102 bool atomic_discovery,
103 bool mt_discovery,
104 BoolObjectClosure* is_alive_non_header,
105 int parallel_gc_threads,
106 bool mt_processing,
107 bool dl_needs_barrier) {
108 int mt_degree = 1;
109 if (parallel_gc_threads > 1) {
110 mt_degree = parallel_gc_threads;
111 }
112 ReferenceProcessor* rp =
113 new ReferenceProcessor(span, atomic_discovery,
114 mt_discovery, mt_degree,
115 mt_processing && (parallel_gc_threads > 0),
116 dl_needs_barrier);
117 if (rp == NULL) {
118 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
119 }
120 rp->set_is_alive_non_header(is_alive_non_header);
121 rp->setup_policy(false /* default soft ref policy */);
122 return rp;
123 }
124
125 ReferenceProcessor::ReferenceProcessor(MemRegion span,
126 bool atomic_discovery,
127 bool mt_discovery,
128 int mt_degree,
129 bool mt_processing,
130 bool discovered_list_needs_barrier) :
131 _discovering_refs(false),
132 _enqueuing_is_done(false),
133 _is_alive_non_header(NULL),
134 _discovered_list_needs_barrier(discovered_list_needs_barrier),
135 _bs(NULL),
136 _processing_is_mt(mt_processing),
137 _next_id(0)
138 {
139 _span = span;
140 _discovery_is_atomic = atomic_discovery;
141 _discovery_is_mt = mt_discovery;
142 _num_q = mt_degree;
143 _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref);
144 if (_discoveredSoftRefs == NULL) {
145 vm_exit_during_initialization("Could not allocated RefProc Array");
146 }
147 _discoveredWeakRefs = &_discoveredSoftRefs[_num_q];
148 _discoveredFinalRefs = &_discoveredWeakRefs[_num_q];
149 _discoveredPhantomRefs = &_discoveredFinalRefs[_num_q];
150 assert(sentinel_ref() != NULL, "_sentinelRef is NULL");
151 // Initialized all entries to _sentinelRef
152 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
153 _discoveredSoftRefs[i].set_head(sentinel_ref());
154 _discoveredSoftRefs[i].set_length(0);
155 }
156 // If we do barreirs, cache a copy of the barrier set.
157 if (discovered_list_needs_barrier) {
158 _bs = Universe::heap()->barrier_set();
159 }
160 }
161
162 #ifndef PRODUCT
163 void ReferenceProcessor::verify_no_references_recorded() {
164 guarantee(!_discovering_refs, "Discovering refs?");
165 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
166 guarantee(_discoveredSoftRefs[i].empty(),
167 "Found non-empty discovered list");
168 }
169 }
170 #endif
171
172 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
173 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
174 if (UseCompressedOops) {
175 f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head());
176 } else {
177 f->do_oop((oop*)_discoveredSoftRefs[i].adr_head());
178 }
179 }
180 }
181
182 void ReferenceProcessor::oops_do(OopClosure* f) {
183 f->do_oop(adr_sentinel_ref());
184 }
185
186 void ReferenceProcessor::update_soft_ref_master_clock() {
187 // Update (advance) the soft ref master clock field. This must be done
188 // after processing the soft ref list.
189 jlong now = os::javaTimeMillis();
190 jlong clock = java_lang_ref_SoftReference::clock();
191 NOT_PRODUCT(
192 if (now < clock) {
193 warning("time warp: %d to %d", clock, now);
194 }
195 )
196 // In product mode, protect ourselves from system time being adjusted
197 // externally and going backward; see note in the implementation of
198 // GenCollectedHeap::time_since_last_gc() for the right way to fix
199 // this uniformly throughout the VM; see bug-id 4741166. XXX
200 if (now > clock) {
201 java_lang_ref_SoftReference::set_clock(now);
202 }
203 // Else leave clock stalled at its old value until time progresses
204 // past clock value.
205 }
206
207 void ReferenceProcessor::process_discovered_references(
208 BoolObjectClosure* is_alive,
209 OopClosure* keep_alive,
210 VoidClosure* complete_gc,
211 AbstractRefProcTaskExecutor* task_executor) {
212 NOT_PRODUCT(verify_ok_to_handle_reflists());
213
214 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
215 // Stop treating discovered references specially.
216 disable_discovery();
217
218 bool trace_time = PrintGCDetails && PrintReferenceGC;
219 // Soft references
220 {
221 TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);
222 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
223 is_alive, keep_alive, complete_gc, task_executor);
224 }
225
226 update_soft_ref_master_clock();
227
228 // Weak references
229 {
230 TraceTime tt("WeakReference", trace_time, false, gclog_or_tty);
231 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
232 is_alive, keep_alive, complete_gc, task_executor);
233 }
234
235 // Final references
236 {
237 TraceTime tt("FinalReference", trace_time, false, gclog_or_tty);
238 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
239 is_alive, keep_alive, complete_gc, task_executor);
240 }
241
242 // Phantom references
243 {
244 TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty);
245 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
246 is_alive, keep_alive, complete_gc, task_executor);
247 }
248
249 // Weak global JNI references. It would make more sense (semantically) to
250 // traverse these simultaneously with the regular weak references above, but
251 // that is not how the JDK1.2 specification is. See #4126360. Native code can
252 // thus use JNI weak references to circumvent the phantom references and
253 // resurrect a "post-mortem" object.
254 {
255 TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty);
256 if (task_executor != NULL) {
257 task_executor->set_single_threaded_mode();
258 }
259 process_phaseJNI(is_alive, keep_alive, complete_gc);
260 }
261 }
262
263 #ifndef PRODUCT
264 // Calculate the number of jni handles.
265 uint ReferenceProcessor::count_jni_refs() {
266 class AlwaysAliveClosure: public BoolObjectClosure {
267 public:
268 virtual bool do_object_b(oop obj) { return true; }
269 virtual void do_object(oop obj) { assert(false, "Don't call"); }
270 };
271
272 class CountHandleClosure: public OopClosure {
273 private:
274 int _count;
275 public:
276 CountHandleClosure(): _count(0) {}
277 void do_oop(oop* unused) { _count++; }
278 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
279 int count() { return _count; }
280 };
281 CountHandleClosure global_handle_count;
282 AlwaysAliveClosure always_alive;
283 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
284 return global_handle_count.count();
285 }
286 #endif
287
288 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
289 OopClosure* keep_alive,
290 VoidClosure* complete_gc) {
291 #ifndef PRODUCT
292 if (PrintGCDetails && PrintReferenceGC) {
293 unsigned int count = count_jni_refs();
294 gclog_or_tty->print(", %u refs", count);
295 }
296 #endif
297 JNIHandles::weak_oops_do(is_alive, keep_alive);
298 // Finally remember to keep sentinel around
299 keep_alive->do_oop(adr_sentinel_ref());
300 complete_gc->do_void();
301 }
302
303
304 template <class T>
305 static bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
306 AbstractRefProcTaskExecutor* task_executor) {
307
308 // Remember old value of pending references list
309 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
310 T old_pending_list_value = *pending_list_addr;
311
312 // Enqueue references that are not made active again, and
313 // clear the decks for the next collection (cycle).
314 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
315 // Do the oop-check on pending_list_addr missed in
316 // enqueue_discovered_reflist. We should probably
317 // do a raw oop_check so that future such idempotent
318 // oop_stores relying on the oop-check side-effect
319 // may be elided automatically and safely without
320 // affecting correctness.
321 oop_store(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 NOT_PRODUCT(verify_ok_to_handle_reflists());
332 if (UseCompressedOops) {
333 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
334 } else {
335 return enqueue_discovered_ref_helper<oop>(this, task_executor);
336 }
337 }
338
339 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
340 HeapWord* pending_list_addr) {
341 // Given a list of refs linked through the "discovered" field
342 // (java.lang.ref.Reference.discovered) chain them through the
343 // "next" field (java.lang.ref.Reference.next) and prepend
344 // to the pending list.
345 if (TraceReferenceGC && PrintGCDetails) {
346 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
347 INTPTR_FORMAT, (address)refs_list.head());
348 }
349 oop obj = refs_list.head();
350 // Walk down the list, copying the discovered field into
351 // the next field and clearing it (except for the last
352 // non-sentinel object which is treated specially to avoid
353 // confusion with an active reference).
354 while (obj != sentinel_ref()) {
355 assert(obj->is_instanceRef(), "should be reference object");
356 oop next = java_lang_ref_Reference::discovered(obj);
357 if (TraceReferenceGC && PrintGCDetails) {
358 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT,
359 obj, next);
360 }
361 assert(java_lang_ref_Reference::next(obj) == NULL,
362 "The reference should not be enqueued");
363 if (next == sentinel_ref()) { // obj is last
364 // Swap refs_list into pendling_list_addr and
365 // set obj's next to what we read from pending_list_addr.
366 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
367 // Need oop_check on pending_list_addr above;
368 // see special oop-check code at the end of
369 // enqueue_discovered_reflists() further below.
370 if (old == NULL) {
371 // obj should be made to point to itself, since
372 // pending list was empty.
373 java_lang_ref_Reference::set_next(obj, obj);
374 } else {
375 java_lang_ref_Reference::set_next(obj, old);
376 }
377 } else {
378 java_lang_ref_Reference::set_next(obj, next);
379 }
380 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
381 obj = next;
382 }
383 }
384
385 // Parallel enqueue task
386 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
387 public:
388 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
389 DiscoveredList discovered_refs[],
390 HeapWord* pending_list_addr,
391 oop sentinel_ref,
392 int n_queues)
393 : EnqueueTask(ref_processor, discovered_refs,
394 pending_list_addr, sentinel_ref, n_queues)
395 { }
396
397 virtual void work(unsigned int work_id) {
398 assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds");
399 // Simplest first cut: static partitioning.
400 int index = work_id;
401 for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) {
402 _ref_processor.enqueue_discovered_reflist(
403 _refs_lists[index], _pending_list_addr);
404 _refs_lists[index].set_head(_sentinel_ref);
405 _refs_lists[index].set_length(0);
406 }
407 }
408 };
409
410 // Enqueue references that are not made active again
411 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
412 AbstractRefProcTaskExecutor* task_executor) {
413 if (_processing_is_mt && task_executor != NULL) {
414 // Parallel code
415 RefProcEnqueueTask tsk(*this, _discoveredSoftRefs,
416 pending_list_addr, sentinel_ref(), _num_q);
417 task_executor->execute(tsk);
418 } else {
419 // Serial code: call the parent class's implementation
420 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
421 enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr);
422 _discoveredSoftRefs[i].set_head(sentinel_ref());
423 _discoveredSoftRefs[i].set_length(0);
424 }
425 }
426 }
427
428 // Iterator for the list of discovered references.
429 class DiscoveredListIterator {
430 public:
431 inline DiscoveredListIterator(DiscoveredList& refs_list,
432 OopClosure* keep_alive,
433 BoolObjectClosure* is_alive);
434
435 // End Of List.
436 inline bool has_next() const { return _next != ReferenceProcessor::sentinel_ref(); }
437
438 // Get oop to the Reference object.
439 inline oop obj() const { return _ref; }
440
441 // Get oop to the referent object.
442 inline oop referent() const { return _referent; }
443
444 // Returns true if referent is alive.
445 inline bool is_referent_alive() const;
446
447 // Loads data for the current reference.
448 // The "allow_null_referent" argument tells us to allow for the possibility
449 // of a NULL referent in the discovered Reference object. This typically
450 // happens in the case of concurrent collectors that may have done the
451 // discovery concurrently, or interleaved, with mutator execution.
452 inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
453
454 // Move to the next discovered reference.
455 inline void next();
456
457 // Remove the current reference from the list
458 inline void remove();
459
460 // Make the Reference object active again.
461 inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); }
462
463 // Make the referent alive.
464 inline void make_referent_alive() {
465 if (UseCompressedOops) {
466 _keep_alive->do_oop((narrowOop*)_referent_addr);
467 } else {
468 _keep_alive->do_oop((oop*)_referent_addr);
469 }
470 }
471
472 // Update the discovered field.
473 inline void update_discovered() {
474 // First _prev_next ref actually points into DiscoveredList (gross).
475 if (UseCompressedOops) {
476 _keep_alive->do_oop((narrowOop*)_prev_next);
477 } else {
478 _keep_alive->do_oop((oop*)_prev_next);
479 }
480 }
481
482 // NULL out referent pointer.
483 inline void clear_referent() { oop_store_raw(_referent_addr, NULL); }
484
485 // Statistics
486 NOT_PRODUCT(
487 inline size_t processed() const { return _processed; }
488 inline size_t removed() const { return _removed; }
489 )
490
491 inline void move_to_next();
492
493 private:
494 DiscoveredList& _refs_list;
495 HeapWord* _prev_next;
496 oop _ref;
497 HeapWord* _discovered_addr;
498 oop _next;
499 HeapWord* _referent_addr;
500 oop _referent;
501 OopClosure* _keep_alive;
502 BoolObjectClosure* _is_alive;
503 DEBUG_ONLY(
504 oop _first_seen; // cyclic linked list check
505 )
506 NOT_PRODUCT(
507 size_t _processed;
508 size_t _removed;
509 )
510 };
511
512 inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list,
513 OopClosure* keep_alive,
514 BoolObjectClosure* is_alive)
515 : _refs_list(refs_list),
516 _prev_next(refs_list.adr_head()),
517 _ref(refs_list.head()),
518 #ifdef ASSERT
519 _first_seen(refs_list.head()),
520 #endif
521 #ifndef PRODUCT
522 _processed(0),
523 _removed(0),
524 #endif
525 _next(refs_list.head()),
526 _keep_alive(keep_alive),
527 _is_alive(is_alive)
528 { }
529
530 inline bool DiscoveredListIterator::is_referent_alive() const {
531 return _is_alive->do_object_b(_referent);
532 }
533
534 inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
535 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
536 oop discovered = java_lang_ref_Reference::discovered(_ref);
537 assert(_discovered_addr && discovered->is_oop_or_null(),
538 "discovered field is bad");
539 _next = discovered;
540 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
541 _referent = java_lang_ref_Reference::referent(_ref);
542 assert(Universe::heap()->is_in_reserved_or_null(_referent),
543 "Wrong oop found in java.lang.Reference object");
544 assert(allow_null_referent ?
545 _referent->is_oop_or_null()
546 : _referent->is_oop(),
547 "bad referent");
548 }
549
550 inline void DiscoveredListIterator::next() {
551 _prev_next = _discovered_addr;
552 move_to_next();
553 }
554
555 inline void DiscoveredListIterator::remove() {
556 assert(_ref->is_oop(), "Dropping a bad reference");
557 oop_store_raw(_discovered_addr, NULL);
558 // First _prev_next ref actually points into DiscoveredList (gross).
559 if (UseCompressedOops) {
560 // Remove Reference object from list.
561 oopDesc::encode_store_heap_oop_not_null((narrowOop*)_prev_next, _next);
562 } else {
563 // Remove Reference object from list.
564 oopDesc::store_heap_oop((oop*)_prev_next, _next);
565 }
566 NOT_PRODUCT(_removed++);
567 _refs_list.dec_length(1);
568 }
569
570 inline void DiscoveredListIterator::move_to_next() {
571 _ref = _next;
572 assert(_ref != _first_seen, "cyclic ref_list found");
573 NOT_PRODUCT(_processed++);
574 }
575
576 // NOTE: process_phase*() are largely similar, and at a high level
577 // merely iterate over the extant list applying a predicate to
578 // each of its elements and possibly removing that element from the
579 // list and applying some further closures to that element.
580 // We should consider the possibility of replacing these
581 // process_phase*() methods by abstracting them into
582 // a single general iterator invocation that receives appropriate
583 // closures that accomplish this work.
584
585 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
586 // referents are not alive, but that should be kept alive for policy reasons.
587 // Keep alive the transitive closure of all such referents.
588 void
589 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
590 ReferencePolicy* policy,
591 BoolObjectClosure* is_alive,
592 OopClosure* keep_alive,
593 VoidClosure* complete_gc) {
594 assert(policy != NULL, "Must have a non-NULL policy");
595 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
596 // Decide which softly reachable refs should be kept alive.
597 while (iter.has_next()) {
598 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
599 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
600 if (referent_is_dead && !policy->should_clear_reference(iter.obj())) {
601 if (TraceReferenceGC) {
602 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
603 iter.obj(), iter.obj()->blueprint()->internal_name());
604 }
605 // Remove Reference object from list
606 iter.remove();
607 // Make the Reference object active again
608 iter.make_active();
609 // keep the referent around
610 iter.make_referent_alive();
611 iter.move_to_next();
612 } else {
613 iter.next();
614 }
615 }
616 // Close the reachable set
617 complete_gc->do_void();
618 NOT_PRODUCT(
619 if (PrintGCDetails && TraceReferenceGC) {
620 gclog_or_tty->print(" Dropped %d dead Refs out of %d "
621 "discovered Refs by policy ", iter.removed(), iter.processed());
622 }
623 )
624 }
625
626 // Traverse the list and remove any Refs that are not active, or
627 // whose referents are either alive or NULL.
628 void
629 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
630 BoolObjectClosure* is_alive,
631 OopClosure* keep_alive) {
632 assert(discovery_is_atomic(), "Error");
633 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
634 while (iter.has_next()) {
635 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
636 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
637 assert(next == NULL, "Should not discover inactive Reference");
638 if (iter.is_referent_alive()) {
639 if (TraceReferenceGC) {
640 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
641 iter.obj(), iter.obj()->blueprint()->internal_name());
642 }
643 // The referent is reachable after all.
644 // Remove Reference object from list.
645 iter.remove();
646 // Update the referent pointer as necessary: Note that this
647 // should not entail any recursive marking because the
648 // referent must already have been traversed.
649 iter.make_referent_alive();
650 iter.move_to_next();
651 } else {
652 iter.next();
653 }
654 }
655 NOT_PRODUCT(
656 if (PrintGCDetails && TraceReferenceGC) {
657 gclog_or_tty->print(" Dropped %d active Refs out of %d "
658 "Refs in discovered list ", iter.removed(), iter.processed());
659 }
660 )
661 }
662
663 void
664 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
665 BoolObjectClosure* is_alive,
666 OopClosure* keep_alive,
667 VoidClosure* complete_gc) {
668 assert(!discovery_is_atomic(), "Error");
669 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
670 while (iter.has_next()) {
671 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
672 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
673 oop next = java_lang_ref_Reference::next(iter.obj());
674 if ((iter.referent() == NULL || iter.is_referent_alive() ||
675 next != NULL)) {
676 assert(next->is_oop_or_null(), "bad next field");
677 // Remove Reference object from list
678 iter.remove();
679 // Trace the cohorts
680 iter.make_referent_alive();
681 if (UseCompressedOops) {
682 keep_alive->do_oop((narrowOop*)next_addr);
683 } else {
684 keep_alive->do_oop((oop*)next_addr);
685 }
686 iter.move_to_next();
687 } else {
688 iter.next();
689 }
690 }
691 // Now close the newly reachable set
692 complete_gc->do_void();
693 NOT_PRODUCT(
694 if (PrintGCDetails && TraceReferenceGC) {
695 gclog_or_tty->print(" Dropped %d active Refs out of %d "
696 "Refs in discovered list ", iter.removed(), iter.processed());
697 }
698 )
699 }
700
701 // Traverse the list and process the referents, by either
702 // clearing them or keeping them (and their reachable
703 // closure) alive.
704 void
705 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
706 bool clear_referent,
707 BoolObjectClosure* is_alive,
708 OopClosure* keep_alive,
709 VoidClosure* complete_gc) {
710 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
711 while (iter.has_next()) {
712 iter.update_discovered();
713 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
714 if (clear_referent) {
715 // NULL out referent pointer
716 iter.clear_referent();
717 } else {
718 // keep the referent around
719 iter.make_referent_alive();
720 }
721 if (TraceReferenceGC) {
722 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
723 clear_referent ? "cleared " : "",
724 iter.obj(), iter.obj()->blueprint()->internal_name());
725 }
726 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
727 // If discovery is concurrent, we may have objects with null referents,
728 // being those that were concurrently cleared after they were discovered
729 // (and not subsequently precleaned).
730 assert( (discovery_is_atomic() && iter.referent()->is_oop())
731 || (!discovery_is_atomic() && iter.referent()->is_oop_or_null(UseConcMarkSweepGC)),
732 "Adding a bad referent");
733 iter.next();
734 }
735 // Remember to keep sentinel pointer around
736 iter.update_discovered();
737 // Close the reachable set
738 complete_gc->do_void();
739 }
740
741 void
742 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
743 oop obj = refs_list.head();
744 while (obj != sentinel_ref()) {
745 oop discovered = java_lang_ref_Reference::discovered(obj);
746 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
747 obj = discovered;
748 }
749 refs_list.set_head(sentinel_ref());
750 refs_list.set_length(0);
751 }
752
753 void ReferenceProcessor::abandon_partial_discovery() {
754 // loop over the lists
755 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
756 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
757 gclog_or_tty->print_cr(
758 "\nAbandoning %s discovered list",
759 list_name(i));
760 }
761 abandon_partial_discovered_list(_discoveredSoftRefs[i]);
762 }
763 }
764
765 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
766 public:
767 RefProcPhase1Task(ReferenceProcessor& ref_processor,
768 DiscoveredList refs_lists[],
769 ReferencePolicy* policy,
770 bool marks_oops_alive)
771 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
772 _policy(policy)
773 { }
774 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
775 OopClosure& keep_alive,
776 VoidClosure& complete_gc)
777 {
778 _ref_processor.process_phase1(_refs_lists[i], _policy,
779 &is_alive, &keep_alive, &complete_gc);
780 }
781 private:
782 ReferencePolicy* _policy;
783 };
784
785 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
786 public:
787 RefProcPhase2Task(ReferenceProcessor& ref_processor,
788 DiscoveredList refs_lists[],
789 bool marks_oops_alive)
790 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
791 { }
792 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
793 OopClosure& keep_alive,
794 VoidClosure& complete_gc)
795 {
796 _ref_processor.process_phase2(_refs_lists[i],
797 &is_alive, &keep_alive, &complete_gc);
798 }
799 };
800
801 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
802 public:
803 RefProcPhase3Task(ReferenceProcessor& ref_processor,
804 DiscoveredList refs_lists[],
805 bool clear_referent,
806 bool marks_oops_alive)
807 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
808 _clear_referent(clear_referent)
809 { }
810 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
811 OopClosure& keep_alive,
812 VoidClosure& complete_gc)
813 {
814 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
815 &is_alive, &keep_alive, &complete_gc);
816 }
817 private:
818 bool _clear_referent;
819 };
820
821 // Balances reference queues.
822 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
823 {
824 // calculate total length
825 size_t total_refs = 0;
826 for (int i = 0; i < _num_q; ++i) {
827 total_refs += ref_lists[i].length();
828 }
829 size_t avg_refs = total_refs / _num_q + 1;
830 int to_idx = 0;
831 for (int from_idx = 0; from_idx < _num_q; from_idx++) {
832 while (ref_lists[from_idx].length() > avg_refs) {
833 assert(to_idx < _num_q, "Sanity Check!");
834 if (ref_lists[to_idx].length() < avg_refs) {
835 // move superfluous refs
836 size_t refs_to_move =
837 MIN2(ref_lists[from_idx].length() - avg_refs,
838 avg_refs - ref_lists[to_idx].length());
839 oop move_head = ref_lists[from_idx].head();
840 oop move_tail = move_head;
841 oop new_head = move_head;
842 // find an element to split the list on
843 for (size_t j = 0; j < refs_to_move; ++j) {
844 move_tail = new_head;
845 new_head = java_lang_ref_Reference::discovered(new_head);
846 }
847 java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head());
848 ref_lists[to_idx].set_head(move_head);
849 ref_lists[to_idx].inc_length(refs_to_move);
850 ref_lists[from_idx].set_head(new_head);
851 ref_lists[from_idx].dec_length(refs_to_move);
852 } else {
853 ++to_idx;
854 }
855 }
856 }
857 }
858
859 void
860 ReferenceProcessor::process_discovered_reflist(
861 DiscoveredList refs_lists[],
862 ReferencePolicy* policy,
863 bool clear_referent,
864 BoolObjectClosure* is_alive,
865 OopClosure* keep_alive,
866 VoidClosure* complete_gc,
867 AbstractRefProcTaskExecutor* task_executor)
868 {
869 bool mt = task_executor != NULL && _processing_is_mt;
870 if (mt && ParallelRefProcBalancingEnabled) {
871 balance_queues(refs_lists);
872 }
873 if (PrintReferenceGC && PrintGCDetails) {
874 size_t total = 0;
875 for (int i = 0; i < _num_q; ++i) {
876 total += refs_lists[i].length();
877 }
878 gclog_or_tty->print(", %u refs", total);
879 }
880
881 // Phase 1 (soft refs only):
882 // . Traverse the list and remove any SoftReferences whose
883 // referents are not alive, but that should be kept alive for
884 // policy reasons. Keep alive the transitive closure of all
885 // such referents.
886 if (policy != NULL) {
887 if (mt) {
888 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
889 task_executor->execute(phase1);
890 } else {
891 for (int i = 0; i < _num_q; i++) {
892 process_phase1(refs_lists[i], policy,
893 is_alive, keep_alive, complete_gc);
894 }
895 }
896 } else { // policy == NULL
897 assert(refs_lists != _discoveredSoftRefs,
898 "Policy must be specified for soft references.");
899 }
900
901 // Phase 2:
902 // . Traverse the list and remove any refs whose referents are alive.
903 if (mt) {
904 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
905 task_executor->execute(phase2);
906 } else {
907 for (int i = 0; i < _num_q; i++) {
908 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
909 }
910 }
911
912 // Phase 3:
913 // . Traverse the list and process referents as appropriate.
914 if (mt) {
915 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
916 task_executor->execute(phase3);
917 } else {
918 for (int i = 0; i < _num_q; i++) {
919 process_phase3(refs_lists[i], clear_referent,
920 is_alive, keep_alive, complete_gc);
921 }
922 }
923 }
924
925 void ReferenceProcessor::clean_up_discovered_references() {
926 // loop over the lists
927 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
928 if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
929 gclog_or_tty->print_cr(
930 "\nScrubbing %s discovered list of Null referents",
931 list_name(i));
932 }
933 clean_up_discovered_reflist(_discoveredSoftRefs[i]);
934 }
935 }
936
937 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
938 assert(!discovery_is_atomic(), "Else why call this method?");
939 DiscoveredListIterator iter(refs_list, NULL, NULL);
940 while (iter.has_next()) {
941 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
942 oop next = java_lang_ref_Reference::next(iter.obj());
943 assert(next->is_oop_or_null(), "bad next field");
944 // If referent has been cleared or Reference is not active,
945 // drop it.
946 if (iter.referent() == NULL || next != NULL) {
947 debug_only(
948 if (PrintGCDetails && TraceReferenceGC) {
949 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: "
950 INTPTR_FORMAT " with next field: " INTPTR_FORMAT
951 " and referent: " INTPTR_FORMAT,
952 iter.obj(), next, iter.referent());
953 }
954 )
955 // Remove Reference object from list
956 iter.remove();
957 iter.move_to_next();
958 } else {
959 iter.next();
960 }
961 }
962 NOT_PRODUCT(
963 if (PrintGCDetails && TraceReferenceGC) {
964 gclog_or_tty->print(
965 " Removed %d Refs with NULL referents out of %d discovered Refs",
966 iter.removed(), iter.processed());
967 }
968 )
969 }
970
971 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
972 int id = 0;
973 // Determine the queue index to use for this object.
974 if (_discovery_is_mt) {
975 // During a multi-threaded discovery phase,
976 // each thread saves to its "own" list.
977 Thread* thr = Thread::current();
978 assert(thr->is_GC_task_thread(),
979 "Dubious cast from Thread* to WorkerThread*?");
980 id = ((WorkerThread*)thr)->id();
981 } else {
982 // single-threaded discovery, we save in round-robin
983 // fashion to each of the lists.
984 if (_processing_is_mt) {
985 id = next_id();
986 }
987 }
988 assert(0 <= id && id < _num_q, "Id is out-of-bounds (call Freud?)");
989
990 // Get the discovered queue to which we will add
991 DiscoveredList* list = NULL;
992 switch (rt) {
993 case REF_OTHER:
994 // Unknown reference type, no special treatment
995 break;
996 case REF_SOFT:
997 list = &_discoveredSoftRefs[id];
998 break;
999 case REF_WEAK:
1000 list = &_discoveredWeakRefs[id];
1001 break;
1002 case REF_FINAL:
1003 list = &_discoveredFinalRefs[id];
1004 break;
1005 case REF_PHANTOM:
1006 list = &_discoveredPhantomRefs[id];
1007 break;
1008 case REF_NONE:
1009 // we should not reach here if we are an instanceRefKlass
1010 default:
1011 ShouldNotReachHere();
1012 }
1013 return list;
1014 }
1015
1016 inline void
1017 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
1018 oop obj,
1019 HeapWord* discovered_addr) {
1020 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
1021 // First we must make sure this object is only enqueued once. CAS in a non null
1022 // discovered_addr.
1023 oop current_head = refs_list.head();
1024
1025 // Note: In the case of G1, this pre-barrier is strictly
1026 // not necessary because the only case we are interested in
1027 // here is when *discovered_addr is NULL, so this will expand to
1028 // nothing. As a result, I am just manually eliding this out for G1.
1029 if (_discovered_list_needs_barrier && !UseG1GC) {
1030 _bs->write_ref_field_pre((void*)discovered_addr, current_head); guarantee(false, "Needs to be fixed: YSR");
1031 }
1032 oop retest = oopDesc::atomic_compare_exchange_oop(current_head, discovered_addr,
1033 NULL);
1034 if (retest == NULL) {
1035 // This thread just won the right to enqueue the object.
1036 // We have separate lists for enqueueing so no synchronization
1037 // is necessary.
1038 refs_list.set_head(obj);
1039 refs_list.inc_length(1);
1040 if (_discovered_list_needs_barrier) {
1041 _bs->write_ref_field((void*)discovered_addr, current_head); guarantee(false, "Needs to be fixed: YSR");
1042 }
1043
1044 } else {
1045 // If retest was non NULL, another thread beat us to it:
1046 // The reference has already been discovered...
1047 if (TraceReferenceGC) {
1048 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
1049 obj, obj->blueprint()->internal_name());
1050 }
1051 }
1052 }
1053
1054 // We mention two of several possible choices here:
1055 // #0: if the reference object is not in the "originating generation"
1056 // (or part of the heap being collected, indicated by our "span"
1057 // we don't treat it specially (i.e. we scan it as we would
1058 // a normal oop, treating its references as strong references).
1059 // This means that references can't be enqueued unless their
1060 // referent is also in the same span. This is the simplest,
1061 // most "local" and most conservative approach, albeit one
1062 // that may cause weak references to be enqueued least promptly.
1063 // We call this choice the "ReferenceBasedDiscovery" policy.
1064 // #1: the reference object may be in any generation (span), but if
1065 // the referent is in the generation (span) being currently collected
1066 // then we can discover the reference object, provided
1067 // the object has not already been discovered by
1068 // a different concurrently running collector (as may be the
1069 // case, for instance, if the reference object is in CMS and
1070 // the referent in DefNewGeneration), and provided the processing
1071 // of this reference object by the current collector will
1072 // appear atomic to every other collector in the system.
1073 // (Thus, for instance, a concurrent collector may not
1074 // discover references in other generations even if the
1075 // referent is in its own generation). This policy may,
1076 // in certain cases, enqueue references somewhat sooner than
1077 // might Policy #0 above, but at marginally increased cost
1078 // and complexity in processing these references.
1079 // We call this choice the "RefeferentBasedDiscovery" policy.
1080 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1081 // We enqueue references only if we are discovering refs
1082 // (rather than processing discovered refs).
1083 if (!_discovering_refs || !RegisterReferences) {
1084 return false;
1085 }
1086 // We only enqueue active references.
1087 oop next = java_lang_ref_Reference::next(obj);
1088 if (next != NULL) {
1089 return false;
1090 }
1091
1092 HeapWord* obj_addr = (HeapWord*)obj;
1093 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1094 !_span.contains(obj_addr)) {
1095 // Reference is not in the originating generation;
1096 // don't treat it specially (i.e. we want to scan it as a normal
1097 // object with strong references).
1098 return false;
1099 }
1100
1101 // We only enqueue references whose referents are not (yet) strongly
1102 // reachable.
1103 if (is_alive_non_header() != NULL) {
1104 oop referent = java_lang_ref_Reference::referent(obj);
1105 // In the case of non-concurrent discovery, the last
1106 // disjunct below should hold. It may not hold in the
1107 // case of concurrent discovery because mutators may
1108 // concurrently clear() a Reference.
1109 assert(UseConcMarkSweepGC || UseG1GC || referent != NULL,
1110 "Refs with null referents already filtered");
1111 if (is_alive_non_header()->do_object_b(referent)) {
1112 return false; // referent is reachable
1113 }
1114 }
1115 if (rt == REF_SOFT) {
1116 // For soft refs we can decide now if these are not
1117 // current candidates for clearing, in which case we
1118 // can mark through them now, rather than delaying that
1119 // to the reference-processing phase. Since all current
1120 // time-stamp policies advance the soft-ref clock only
1121 // at a major collection cycle, this is always currently
1122 // accurate.
1123 if (!_current_soft_ref_policy->should_clear_reference(obj)) {
1124 return false;
1125 }
1126 }
1127
1128 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1129 const oop discovered = java_lang_ref_Reference::discovered(obj);
1130 assert(discovered->is_oop_or_null(), "bad discovered field");
1131 if (discovered != NULL) {
1132 // The reference has already been discovered...
1133 if (TraceReferenceGC) {
1134 gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
1135 obj, obj->blueprint()->internal_name());
1136 }
1137 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1138 // assumes that an object is not processed twice;
1139 // if it's been already discovered it must be on another
1140 // generation's discovered list; so we won't discover it.
1141 return false;
1142 } else {
1143 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1144 "Unrecognized policy");
1145 // Check assumption that an object is not potentially
1146 // discovered twice except by concurrent collectors that potentially
1147 // trace the same Reference object twice.
1148 assert(UseConcMarkSweepGC,
1149 "Only possible with an incremental-update concurrent collector");
1150 return true;
1151 }
1152 }
1153
1154 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1155 oop referent = java_lang_ref_Reference::referent(obj);
1156 assert(referent->is_oop(), "bad referent");
1157 // enqueue if and only if either:
1158 // reference is in our span or
1159 // we are an atomic collector and referent is in our span
1160 if (_span.contains(obj_addr) ||
1161 (discovery_is_atomic() && _span.contains(referent))) {
1162 // should_enqueue = true;
1163 } else {
1164 return false;
1165 }
1166 } else {
1167 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1168 _span.contains(obj_addr), "code inconsistency");
1169 }
1170
1171 // Get the right type of discovered queue head.
1172 DiscoveredList* list = get_discovered_list(rt);
1173 if (list == NULL) {
1174 return false; // nothing special needs to be done
1175 }
1176
1177 if (_discovery_is_mt) {
1178 add_to_discovered_list_mt(*list, obj, discovered_addr);
1179 } else {
1180 // If "_discovered_list_needs_barrier", we do write barriers when
1181 // updating the discovered reference list. Otherwise, we do a raw store
1182 // here: the field will be visited later when processing the discovered
1183 // references.
1184 oop current_head = list->head();
1185 // As in the case further above, since we are over-writing a NULL
1186 // pre-value, we can safely elide the pre-barrier here for the case of G1.
1187 assert(discovered == NULL, "control point invariant");
1188 if (_discovered_list_needs_barrier && !UseG1GC) { // safe to elide for G1
1189 _bs->write_ref_field_pre((oop*)discovered_addr, current_head);
1190 }
1191 oop_store_raw(discovered_addr, current_head);
1192 if (_discovered_list_needs_barrier) {
1193 _bs->write_ref_field((oop*)discovered_addr, current_head);
1194 }
1195 list->set_head(obj);
1196 list->inc_length(1);
1197 }
1198
1199 // In the MT discovery case, it is currently possible to see
1200 // the following message multiple times if several threads
1201 // discover a reference about the same time. Only one will
1202 // however have actually added it to the disocvered queue.
1203 // One could let add_to_discovered_list_mt() return an
1204 // indication for success in queueing (by 1 thread) or
1205 // failure (by all other threads), but I decided the extra
1206 // code was not worth the effort for something that is
1207 // only used for debugging support.
1208 if (TraceReferenceGC) {
1209 oop referent = java_lang_ref_Reference::referent(obj);
1210 if (PrintGCDetails) {
1211 gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)",
1212 obj, obj->blueprint()->internal_name());
1213 }
1214 assert(referent->is_oop(), "Enqueued a bad referent");
1215 }
1216 assert(obj->is_oop(), "Enqueued a bad reference");
1217 return true;
1218 }
1219
1220 // Preclean the discovered references by removing those
1221 // whose referents are alive, and by marking from those that
1222 // are not active. These lists can be handled here
1223 // in any order and, indeed, concurrently.
1224 void ReferenceProcessor::preclean_discovered_references(
1225 BoolObjectClosure* is_alive,
1226 OopClosure* keep_alive,
1227 VoidClosure* complete_gc,
1228 YieldClosure* yield) {
1229
1230 NOT_PRODUCT(verify_ok_to_handle_reflists());
1231
1232 // Soft references
1233 {
1234 TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
1235 false, gclog_or_tty);
1236 for (int i = 0; i < _num_q; i++) {
1237 if (yield->should_return()) {
1238 return;
1239 }
1240 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1241 keep_alive, complete_gc, yield);
1242 }
1243 }
1244
1245 // Weak references
1246 {
1247 TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
1248 false, gclog_or_tty);
1249 for (int i = 0; i < _num_q; i++) {
1250 if (yield->should_return()) {
1251 return;
1252 }
1253 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1254 keep_alive, complete_gc, yield);
1255 }
1256 }
1257
1258 // Final references
1259 {
1260 TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
1261 false, gclog_or_tty);
1262 for (int i = 0; i < _num_q; i++) {
1263 if (yield->should_return()) {
1264 return;
1265 }
1266 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1267 keep_alive, complete_gc, yield);
1268 }
1269 }
1270
1271 // Phantom references
1272 {
1273 TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
1274 false, gclog_or_tty);
1275 for (int i = 0; i < _num_q; i++) {
1276 if (yield->should_return()) {
1277 return;
1278 }
1279 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1280 keep_alive, complete_gc, yield);
1281 }
1282 }
1283 }
1284
1285 // Walk the given discovered ref list, and remove all reference objects
1286 // whose referents are still alive, whose referents are NULL or which
1287 // are not active (have a non-NULL next field). NOTE: When we are
1288 // thus precleaning the ref lists (which happens single-threaded today),
1289 // we do not disable refs discovery to honour the correct semantics of
1290 // java.lang.Reference. As a result, we need to be careful below
1291 // that ref removal steps interleave safely with ref discovery steps
1292 // (in this thread).
1293 void
1294 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1295 BoolObjectClosure* is_alive,
1296 OopClosure* keep_alive,
1297 VoidClosure* complete_gc,
1298 YieldClosure* yield) {
1299 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1300 while (iter.has_next()) {
1301 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1302 oop obj = iter.obj();
1303 oop next = java_lang_ref_Reference::next(obj);
1304 if (iter.referent() == NULL || iter.is_referent_alive() ||
1305 next != NULL) {
1306 // The referent has been cleared, or is alive, or the Reference is not
1307 // active; we need to trace and mark its cohort.
1308 if (TraceReferenceGC) {
1309 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1310 iter.obj(), iter.obj()->blueprint()->internal_name());
1311 }
1312 // Remove Reference object from list
1313 iter.remove();
1314 // Keep alive its cohort.
1315 iter.make_referent_alive();
1316 if (UseCompressedOops) {
1317 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1318 keep_alive->do_oop(next_addr);
1319 } else {
1320 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1321 keep_alive->do_oop(next_addr);
1322 }
1323 iter.move_to_next();
1324 } else {
1325 iter.next();
1326 }
1327 }
1328 // Close the reachable set
1329 complete_gc->do_void();
1330
1331 NOT_PRODUCT(
1332 if (PrintGCDetails && PrintReferenceGC) {
1333 gclog_or_tty->print(" Dropped %d Refs out of %d "
1334 "Refs in discovered list ", iter.removed(), iter.processed());
1335 }
1336 )
1337 }
1338
1339 const char* ReferenceProcessor::list_name(int i) {
1340 assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index");
1341 int j = i / _num_q;
1342 switch (j) {
1343 case 0: return "SoftRef";
1344 case 1: return "WeakRef";
1345 case 2: return "FinalRef";
1346 case 3: return "PhantomRef";
1347 }
1348 ShouldNotReachHere();
1349 return NULL;
1350 }
1351
1352 #ifndef PRODUCT
1353 void ReferenceProcessor::verify_ok_to_handle_reflists() {
1354 // empty for now
1355 }
1356 #endif
1357
1358 void ReferenceProcessor::verify() {
1359 guarantee(sentinel_ref() != NULL && sentinel_ref()->is_oop(), "Lost _sentinelRef");
1360 }
1361
1362 #ifndef PRODUCT
1363 void ReferenceProcessor::clear_discovered_references() {
1364 guarantee(!_discovering_refs, "Discovering refs?");
1365 for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
1366 oop obj = _discoveredSoftRefs[i].head();
1367 while (obj != sentinel_ref()) {
1368 oop next = java_lang_ref_Reference::discovered(obj);
1369 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
1370 obj = next;
1371 }
1372 _discoveredSoftRefs[i].set_head(sentinel_ref());
1373 _discoveredSoftRefs[i].set_length(0);
1374 }
1375 }
1376 #endif // PRODUCT