1 /*
2 * Copyright (c) 2001, 2014, 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_implementation/shared/gcTimer.hpp"
29 #include "gc_implementation/shared/gcTraceTime.hpp"
30 #include "gc_interface/collectedHeap.hpp"
31 #include "gc_interface/collectedHeap.inline.hpp"
32 #include "memory/referencePolicy.hpp"
33 #include "memory/referenceProcessor.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/java.hpp"
36 #include "runtime/jniHandles.hpp"
37
38 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
39
40 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
41 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
42 bool ReferenceProcessor::_pending_list_uses_discovered_field = false;
43 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
44
45 void referenceProcessor_init() {
46 ReferenceProcessor::init_statics();
47 }
48
49 void ReferenceProcessor::init_statics() {
50 // We need a monotonically non-decreasing time in ms but
51 // os::javaTimeMillis() does not guarantee monotonicity.
52 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
53
54 // Initialize the soft ref timestamp clock.
55 _soft_ref_timestamp_clock = now;
56 // Also update the soft ref clock in j.l.r.SoftReference
57 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
58
59 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
60 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
61 NOT_COMPILER2(LRUCurrentHeapPolicy());
62 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
63 vm_exit_during_initialization("Could not allocate reference policy object");
64 }
65 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
66 RefDiscoveryPolicy == ReferentBasedDiscovery,
67 "Unrecognized RefDiscoveryPolicy");
68 _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field();
69 }
70
71 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
72 #ifdef ASSERT
73 // Verify that we're not currently discovering refs
74 assert(!_discovering_refs, "nested call?");
75
76 if (check_no_refs) {
77 // Verify that the discovered lists are empty
78 verify_no_references_recorded();
79 }
80 #endif // ASSERT
81
82 // Someone could have modified the value of the static
83 // field in the j.l.r.SoftReference class that holds the
84 // soft reference timestamp clock using reflection or
85 // Unsafe between GCs. Unconditionally update the static
86 // field in ReferenceProcessor here so that we use the new
87 // value during reference discovery.
88
89 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
90 _discovering_refs = true;
91 }
92
93 ReferenceProcessor::ReferenceProcessor(MemRegion span,
94 bool mt_processing,
95 uint mt_processing_degree,
96 bool mt_discovery,
97 uint mt_discovery_degree,
98 bool atomic_discovery,
99 BoolObjectClosure* is_alive_non_header) :
100 _discovering_refs(false),
101 _enqueuing_is_done(false),
102 _is_alive_non_header(is_alive_non_header),
103 _processing_is_mt(mt_processing),
104 _next_id(0)
105 {
106 _span = span;
107 _discovery_is_atomic = atomic_discovery;
108 _discovery_is_mt = mt_discovery;
109 _num_q = MAX2(1U, mt_processing_degree);
110 _max_num_q = MAX2(_num_q, mt_discovery_degree);
111 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
112 _max_num_q * number_of_subclasses_of_ref(), mtGC);
113
114 if (_discovered_refs == NULL) {
115 vm_exit_during_initialization("Could not allocated RefProc Array");
116 }
117 _discoveredSoftRefs = &_discovered_refs[0];
118 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
119 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
120 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
121 _discoveredCleanerRefs = &_discoveredPhantomRefs[_max_num_q];
122
123 // Initialize all entries to NULL
124 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
125 _discovered_refs[i].set_head(NULL);
126 _discovered_refs[i].set_length(0);
127 }
128
129 setup_policy(false /* default soft ref policy */);
130 }
131
132 #ifndef PRODUCT
133 void ReferenceProcessor::verify_no_references_recorded() {
134 guarantee(!_discovering_refs, "Discovering refs?");
135 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
136 guarantee(_discovered_refs[i].is_empty(),
137 "Found non-empty discovered list");
138 }
139 }
140 #endif
141
142 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
143 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
144 if (UseCompressedOops) {
145 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
146 } else {
147 f->do_oop((oop*)_discovered_refs[i].adr_head());
148 }
149 }
150 }
151
152 void ReferenceProcessor::update_soft_ref_master_clock() {
153 // Update (advance) the soft ref master clock field. This must be done
154 // after processing the soft ref list.
155
156 // We need a monotonically non-decreasing time in ms but
157 // os::javaTimeMillis() does not guarantee monotonicity.
158 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
159 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
160 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
161
162 NOT_PRODUCT(
163 if (now < _soft_ref_timestamp_clock) {
164 warning("time warp: "INT64_FORMAT" to "INT64_FORMAT,
165 _soft_ref_timestamp_clock, now);
166 }
167 )
168 // The values of now and _soft_ref_timestamp_clock are set using
169 // javaTimeNanos(), which is guaranteed to be monotonically
170 // non-decreasing provided the underlying platform provides such
171 // a time source (and it is bug free).
172 // In product mode, however, protect ourselves from non-monotonicity.
173 if (now > _soft_ref_timestamp_clock) {
174 _soft_ref_timestamp_clock = now;
175 java_lang_ref_SoftReference::set_clock(now);
176 }
177 // Else leave clock stalled at its old value until time progresses
178 // past clock value.
179 }
180
181 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
182 size_t total = 0;
183 for (uint i = 0; i < _max_num_q; ++i) {
184 total += lists[i].length();
185 }
186 return total;
187 }
188
189 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
190 BoolObjectClosure* is_alive,
191 OopClosure* keep_alive,
192 VoidClosure* complete_gc,
193 AbstractRefProcTaskExecutor* task_executor,
194 GCTimer* gc_timer,
195 GCId gc_id) {
196 NOT_PRODUCT(verify_ok_to_handle_reflists());
197
198 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
199 // Stop treating discovered references specially.
200 disable_discovery();
201
202 // If discovery was concurrent, someone could have modified
203 // the value of the static field in the j.l.r.SoftReference
204 // class that holds the soft reference timestamp clock using
205 // reflection or Unsafe between when discovery was enabled and
206 // now. Unconditionally update the static field in ReferenceProcessor
207 // here so that we use the new value during processing of the
208 // discovered soft refs.
209
210 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
211
212 bool trace_time = PrintGCDetails && PrintReferenceGC;
213
214 // Soft references
215 size_t soft_count = 0;
216 {
217 GCTraceTime tt("SoftReference", trace_time, false, gc_timer, gc_id);
218 soft_count =
219 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
220 is_alive, keep_alive, complete_gc, task_executor);
221 }
222
223 update_soft_ref_master_clock();
224
225 // Weak references
226 size_t weak_count = 0;
227 {
228 GCTraceTime tt("WeakReference", trace_time, false, gc_timer, gc_id);
229 weak_count =
230 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
231 is_alive, keep_alive, complete_gc, task_executor);
232 }
233
234 // Final references
235 size_t final_count = 0;
236 {
237 GCTraceTime tt("FinalReference", trace_time, false, gc_timer, gc_id);
238 final_count =
239 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
240 is_alive, keep_alive, complete_gc, task_executor);
241 }
242
243 // Phantom references
244 size_t phantom_count = 0;
245 {
246 GCTraceTime tt("PhantomReference", trace_time, false, gc_timer, gc_id);
247 phantom_count =
248 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
249 is_alive, keep_alive, complete_gc, task_executor);
250
251 // Process cleaners, but include them in phantom statistics. We expect
252 // Cleaner references to be temporary, and don't want to deal with
253 // possible incompatibilities arising from making it more visible.
254 phantom_count +=
255 process_discovered_reflist(_discoveredCleanerRefs, NULL, false,
256 is_alive, keep_alive, complete_gc, task_executor);
257 }
258
259 // Weak global JNI references. It would make more sense (semantically) to
260 // traverse these simultaneously with the regular weak references above, but
261 // that is not how the JDK1.2 specification is. See #4126360. Native code can
262 // thus use JNI weak references to circumvent the phantom references and
263 // resurrect a "post-mortem" object.
264 {
265 GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id);
266 if (task_executor != NULL) {
267 task_executor->set_single_threaded_mode();
268 }
269 process_phaseJNI(is_alive, keep_alive, complete_gc);
270 }
271
272 return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_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 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
300 OopClosure* keep_alive,
301 VoidClosure* complete_gc) {
302 #ifndef PRODUCT
303 if (PrintGCDetails && PrintReferenceGC) {
304 unsigned int count = count_jni_refs();
305 gclog_or_tty->print(", %u refs", count);
306 }
307 #endif
308 JNIHandles::weak_oops_do(is_alive, keep_alive);
309 complete_gc->do_void();
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 NOT_PRODUCT(verify_ok_to_handle_reflists());
337 if (UseCompressedOops) {
338 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
339 } else {
340 return enqueue_discovered_ref_helper<oop>(this, task_executor);
341 }
342 }
343
344 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
345 HeapWord* pending_list_addr) {
346 // Given a list of refs linked through the "discovered" field
347 // (java.lang.ref.Reference.discovered), self-loop their "next" field
348 // thus distinguishing them from active References, then
349 // prepend them to the pending list.
350 //
351 // The Java threads will see the Reference objects linked together through
352 // the discovered field. Instead of trying to do the write barrier updates
353 // in all places in the reference processor where we manipulate the discovered
354 // field we make sure to do the barrier here where we anyway iterate through
355 // all linked Reference objects. Note that it is important to not dirty any
356 // cards during reference processing since this will cause card table
357 // verification to fail for G1.
358 //
359 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777),
360 // the "next" field is used to chain the pending list, not the discovered
361 // field.
362 if (TraceReferenceGC && PrintGCDetails) {
363 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
364 INTPTR_FORMAT, (address)refs_list.head());
365 }
366
367 oop obj = NULL;
368 oop next_d = refs_list.head();
369 if (pending_list_uses_discovered_field()) { // New behavior
370 // Walk down the list, self-looping the next field
371 // so that the References are not considered active.
372 while (obj != next_d) {
373 obj = next_d;
374 assert(obj->is_instanceRef(), "should be reference object");
375 next_d = java_lang_ref_Reference::discovered(obj);
376 if (TraceReferenceGC && PrintGCDetails) {
377 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
378 (void *)obj, (void *)next_d);
379 }
380 assert(java_lang_ref_Reference::next(obj) == NULL,
381 "Reference not active; should not be discovered");
382 // Self-loop next, so as to make Ref not active.
383 java_lang_ref_Reference::set_next_raw(obj, obj);
384 if (next_d != obj) {
385 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
386 } else {
387 // This is the last object.
388 // Swap refs_list into pending_list_addr and
389 // set obj's discovered to what we read from pending_list_addr.
390 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
391 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
392 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
393 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
394 }
395 }
396 } else { // Old behavior
397 // Walk down the list, copying the discovered field into
398 // the next field and clearing the discovered field.
399 while (obj != next_d) {
400 obj = next_d;
401 assert(obj->is_instanceRef(), "should be reference object");
402 next_d = java_lang_ref_Reference::discovered(obj);
403 if (TraceReferenceGC && PrintGCDetails) {
404 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
405 (void *)obj, (void *)next_d);
406 }
407 assert(java_lang_ref_Reference::next(obj) == NULL,
408 "The reference should not be enqueued");
409 if (next_d == obj) { // obj is last
410 // Swap refs_list into pending_list_addr and
411 // set obj's next to what we read from pending_list_addr.
412 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
413 // Need oop_check on pending_list_addr above;
414 // see special oop-check code at the end of
415 // enqueue_discovered_reflists() further below.
416 if (old == NULL) {
417 // obj should be made to point to itself, since
418 // pending list was empty.
419 java_lang_ref_Reference::set_next(obj, obj);
420 } else {
421 java_lang_ref_Reference::set_next(obj, old);
422 }
423 } else {
424 java_lang_ref_Reference::set_next(obj, next_d);
425 }
426 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
427 }
428 }
429 }
430
431 // Parallel enqueue task
432 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
433 public:
434 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
435 DiscoveredList discovered_refs[],
436 HeapWord* pending_list_addr,
437 int n_queues)
438 : EnqueueTask(ref_processor, discovered_refs,
439 pending_list_addr, n_queues)
440 { }
441
442 virtual void work(unsigned int work_id) {
443 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
444 // Simplest first cut: static partitioning.
445 int index = work_id;
446 // The increment on "index" must correspond to the maximum number of queues
447 // (n_queues) with which that ReferenceProcessor was created. That
448 // is because of the "clever" way the discovered references lists were
449 // allocated and are indexed into.
450 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
451 for (int j = 0;
452 j < ReferenceProcessor::number_of_subclasses_of_ref();
453 j++, index += _n_queues) {
454 _ref_processor.enqueue_discovered_reflist(
455 _refs_lists[index], _pending_list_addr);
456 _refs_lists[index].set_head(NULL);
457 _refs_lists[index].set_length(0);
458 }
459 }
460 };
461
462 // Enqueue references that are not made active again
463 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
464 AbstractRefProcTaskExecutor* task_executor) {
465 if (_processing_is_mt && task_executor != NULL) {
466 // Parallel code
467 RefProcEnqueueTask tsk(*this, _discovered_refs,
468 pending_list_addr, _max_num_q);
469 task_executor->execute(tsk);
470 } else {
471 // Serial code: call the parent class's implementation
472 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
473 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
474 _discovered_refs[i].set_head(NULL);
475 _discovered_refs[i].set_length(0);
476 }
477 }
478 }
479
480 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
481 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
482 oop discovered = java_lang_ref_Reference::discovered(_ref);
483 assert(_discovered_addr && discovered->is_oop_or_null(),
484 err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
485 _next = discovered;
486 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
487 _referent = java_lang_ref_Reference::referent(_ref);
488 assert(Universe::heap()->is_in_reserved_or_null(_referent),
489 "Wrong oop found in java.lang.Reference object");
490 assert(allow_null_referent ?
491 _referent->is_oop_or_null()
492 : _referent->is_oop(),
493 err_msg("Expected an oop%s for referent field at " PTR_FORMAT,
494 (allow_null_referent ? " or NULL" : ""),
495 p2i(_referent)));
496 }
497
498 void DiscoveredListIterator::remove() {
499 assert(_ref->is_oop(), "Dropping a bad reference");
500 oop_store_raw(_discovered_addr, NULL);
501
502 // First _prev_next ref actually points into DiscoveredList (gross).
503 oop new_next;
504 if (_next == _ref) {
505 // At the end of the list, we should make _prev point to itself.
506 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
507 // and _prev will be NULL.
508 new_next = _prev;
509 } else {
510 new_next = _next;
511 }
512 // Remove Reference object from discovered list. Note that G1 does not need a
513 // pre-barrier here because we know the Reference has already been found/marked,
514 // that's how it ended up in the discovered list in the first place.
515 oop_store_raw(_prev_next, new_next);
516 NOT_PRODUCT(_removed++);
517 _refs_list.dec_length(1);
518 }
519
520 // Make the Reference object active again.
521 void DiscoveredListIterator::make_active() {
522 // The pre barrier for G1 is probably just needed for the old
523 // reference processing behavior. Should we guard this with
524 // ReferenceProcessor::pending_list_uses_discovered_field() ?
525 if (UseG1GC) {
526 HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref);
527 if (UseCompressedOops) {
528 oopDesc::bs()->write_ref_field_pre((narrowOop*)next_addr, NULL);
529 } else {
530 oopDesc::bs()->write_ref_field_pre((oop*)next_addr, NULL);
531 }
532 }
533 java_lang_ref_Reference::set_next_raw(_ref, NULL);
534 }
535
536 void DiscoveredListIterator::clear_referent() {
537 oop_store_raw(_referent_addr, NULL);
538 }
539
540 // NOTE: process_phase*() are largely similar, and at a high level
541 // merely iterate over the extant list applying a predicate to
542 // each of its elements and possibly removing that element from the
543 // list and applying some further closures to that element.
544 // We should consider the possibility of replacing these
545 // process_phase*() methods by abstracting them into
546 // a single general iterator invocation that receives appropriate
547 // closures that accomplish this work.
548
549 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
550 // referents are not alive, but that should be kept alive for policy reasons.
551 // Keep alive the transitive closure of all such referents.
552 void
553 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
554 ReferencePolicy* policy,
555 BoolObjectClosure* is_alive,
556 OopClosure* keep_alive,
557 VoidClosure* complete_gc) {
558 assert(policy != NULL, "Must have a non-NULL policy");
559 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
560 // Decide which softly reachable refs should be kept alive.
561 while (iter.has_next()) {
562 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
563 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
564 if (referent_is_dead &&
565 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
566 if (TraceReferenceGC) {
567 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
568 (void *)iter.obj(), iter.obj()->klass()->internal_name());
569 }
570 // Remove Reference object from list
571 iter.remove();
572 // Make the Reference object active again
573 iter.make_active();
574 // keep the referent around
575 iter.make_referent_alive();
576 iter.move_to_next();
577 } else {
578 iter.next();
579 }
580 }
581 // Close the reachable set
582 complete_gc->do_void();
583 NOT_PRODUCT(
584 if (PrintGCDetails && TraceReferenceGC) {
585 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d "
586 "discovered Refs by policy, from list " INTPTR_FORMAT,
587 iter.removed(), iter.processed(), (address)refs_list.head());
588 }
589 )
590 }
591
592 // Traverse the list and remove any Refs that are not active, or
593 // whose referents are either alive or NULL.
594 void
595 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
596 BoolObjectClosure* is_alive,
597 OopClosure* keep_alive) {
598 assert(discovery_is_atomic(), "Error");
599 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
600 while (iter.has_next()) {
601 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
602 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
603 assert(next == NULL, "Should not discover inactive Reference");
604 if (iter.is_referent_alive()) {
605 if (TraceReferenceGC) {
606 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
607 (void *)iter.obj(), iter.obj()->klass()->internal_name());
608 }
609 // The referent is reachable after all.
610 // Remove Reference object from list.
611 iter.remove();
612 // Update the referent pointer as necessary: Note that this
613 // should not entail any recursive marking because the
614 // referent must already have been traversed.
615 iter.make_referent_alive();
616 iter.move_to_next();
617 } else {
618 iter.next();
619 }
620 }
621 NOT_PRODUCT(
622 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
623 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
624 "Refs in discovered list " INTPTR_FORMAT,
625 iter.removed(), iter.processed(), (address)refs_list.head());
626 }
627 )
628 }
629
630 void
631 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
632 BoolObjectClosure* is_alive,
633 OopClosure* keep_alive,
634 VoidClosure* complete_gc) {
635 assert(!discovery_is_atomic(), "Error");
636 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
637 while (iter.has_next()) {
638 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
639 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
640 oop next = java_lang_ref_Reference::next(iter.obj());
641 if ((iter.referent() == NULL || iter.is_referent_alive() ||
642 next != NULL)) {
643 assert(next->is_oop_or_null(), err_msg("Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)));
644 // Remove Reference object from list
645 iter.remove();
646 // Trace the cohorts
647 iter.make_referent_alive();
648 if (UseCompressedOops) {
649 keep_alive->do_oop((narrowOop*)next_addr);
650 } else {
651 keep_alive->do_oop((oop*)next_addr);
652 }
653 iter.move_to_next();
654 } else {
655 iter.next();
656 }
657 }
658 // Now close the newly reachable set
659 complete_gc->do_void();
660 NOT_PRODUCT(
661 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
662 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
663 "Refs in discovered list " INTPTR_FORMAT,
664 iter.removed(), iter.processed(), (address)refs_list.head());
665 }
666 )
667 }
668
669 // Traverse the list and process the referents, by either
670 // clearing them or keeping them (and their reachable
671 // closure) alive.
672 void
673 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
674 bool clear_referent,
675 BoolObjectClosure* is_alive,
676 OopClosure* keep_alive,
677 VoidClosure* complete_gc) {
678 ResourceMark rm;
679 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
680 while (iter.has_next()) {
681 iter.update_discovered();
682 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
683 if (clear_referent) {
684 // NULL out referent pointer
685 iter.clear_referent();
686 } else {
687 // keep the referent around
688 iter.make_referent_alive();
689 }
690 if (TraceReferenceGC) {
691 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
692 clear_referent ? "cleared " : "",
693 (void *)iter.obj(), iter.obj()->klass()->internal_name());
694 }
695 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
696 iter.next();
697 }
698 // Remember to update the next pointer of the last ref.
699 iter.update_discovered();
700 // Close the reachable set
701 complete_gc->do_void();
702 }
703
704 void
705 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
706 oop obj = NULL;
707 oop next = refs_list.head();
708 while (next != obj) {
709 obj = next;
710 next = java_lang_ref_Reference::discovered(obj);
711 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
712 }
713 refs_list.set_head(NULL);
714 refs_list.set_length(0);
715 }
716
717 void
718 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
719 clear_discovered_references(refs_list);
720 }
721
722 void ReferenceProcessor::abandon_partial_discovery() {
723 // loop over the lists
724 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
725 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
726 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i));
727 }
728 abandon_partial_discovered_list(_discovered_refs[i]);
729 }
730 }
731
732 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
733 public:
734 RefProcPhase1Task(ReferenceProcessor& ref_processor,
735 DiscoveredList refs_lists[],
736 ReferencePolicy* policy,
737 bool marks_oops_alive)
738 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
739 _policy(policy)
740 { }
741 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
742 OopClosure& keep_alive,
743 VoidClosure& complete_gc)
744 {
745 Thread* thr = Thread::current();
746 int refs_list_index = ((WorkerThread*)thr)->id();
747 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
748 &is_alive, &keep_alive, &complete_gc);
749 }
750 private:
751 ReferencePolicy* _policy;
752 };
753
754 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
755 public:
756 RefProcPhase2Task(ReferenceProcessor& ref_processor,
757 DiscoveredList refs_lists[],
758 bool marks_oops_alive)
759 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
760 { }
761 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
762 OopClosure& keep_alive,
763 VoidClosure& complete_gc)
764 {
765 _ref_processor.process_phase2(_refs_lists[i],
766 &is_alive, &keep_alive, &complete_gc);
767 }
768 };
769
770 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
771 public:
772 RefProcPhase3Task(ReferenceProcessor& ref_processor,
773 DiscoveredList refs_lists[],
774 bool clear_referent,
775 bool marks_oops_alive)
776 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
777 _clear_referent(clear_referent)
778 { }
779 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
780 OopClosure& keep_alive,
781 VoidClosure& complete_gc)
782 {
783 // Don't use "refs_list_index" calculated in this way because
784 // balance_queues() has moved the Ref's into the first n queues.
785 // Thread* thr = Thread::current();
786 // int refs_list_index = ((WorkerThread*)thr)->id();
787 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
788 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
789 &is_alive, &keep_alive, &complete_gc);
790 }
791 private:
792 bool _clear_referent;
793 };
794
795 // Balances reference queues.
796 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
797 // queues[0, 1, ..., _num_q-1] because only the first _num_q
798 // corresponding to the active workers will be processed.
799 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
800 {
801 // calculate total length
802 size_t total_refs = 0;
803 if (TraceReferenceGC && PrintGCDetails) {
804 gclog_or_tty->print_cr("\nBalance ref_lists ");
805 }
806
807 for (uint i = 0; i < _max_num_q; ++i) {
808 total_refs += ref_lists[i].length();
809 if (TraceReferenceGC && PrintGCDetails) {
810 gclog_or_tty->print("%d ", ref_lists[i].length());
811 }
812 }
813 if (TraceReferenceGC && PrintGCDetails) {
814 gclog_or_tty->print_cr(" = %d", total_refs);
815 }
816 size_t avg_refs = total_refs / _num_q + 1;
817 uint to_idx = 0;
818 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
819 bool move_all = false;
820 if (from_idx >= _num_q) {
821 move_all = ref_lists[from_idx].length() > 0;
822 }
823 while ((ref_lists[from_idx].length() > avg_refs) ||
824 move_all) {
825 assert(to_idx < _num_q, "Sanity Check!");
826 if (ref_lists[to_idx].length() < avg_refs) {
827 // move superfluous refs
828 size_t refs_to_move;
829 // Move all the Ref's if the from queue will not be processed.
830 if (move_all) {
831 refs_to_move = MIN2(ref_lists[from_idx].length(),
832 avg_refs - ref_lists[to_idx].length());
833 } else {
834 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
835 avg_refs - ref_lists[to_idx].length());
836 }
837
838 assert(refs_to_move > 0, "otherwise the code below will fail");
839
840 oop move_head = ref_lists[from_idx].head();
841 oop move_tail = move_head;
842 oop new_head = move_head;
843 // find an element to split the list on
844 for (size_t j = 0; j < refs_to_move; ++j) {
845 move_tail = new_head;
846 new_head = java_lang_ref_Reference::discovered(new_head);
847 }
848
849 // Add the chain to the to list.
850 if (ref_lists[to_idx].head() == NULL) {
851 // to list is empty. Make a loop at the end.
852 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
853 } else {
854 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
855 }
856 ref_lists[to_idx].set_head(move_head);
857 ref_lists[to_idx].inc_length(refs_to_move);
858
859 // Remove the chain from the from list.
860 if (move_tail == new_head) {
861 // We found the end of the from list.
862 ref_lists[from_idx].set_head(NULL);
863 } else {
864 ref_lists[from_idx].set_head(new_head);
865 }
866 ref_lists[from_idx].dec_length(refs_to_move);
867 if (ref_lists[from_idx].length() == 0) {
868 break;
869 }
870 } else {
871 to_idx = (to_idx + 1) % _num_q;
872 }
873 }
874 }
875 #ifdef ASSERT
876 size_t balanced_total_refs = 0;
877 for (uint i = 0; i < _max_num_q; ++i) {
878 balanced_total_refs += ref_lists[i].length();
879 if (TraceReferenceGC && PrintGCDetails) {
880 gclog_or_tty->print("%d ", ref_lists[i].length());
881 }
882 }
883 if (TraceReferenceGC && PrintGCDetails) {
884 gclog_or_tty->print_cr(" = %d", balanced_total_refs);
885 gclog_or_tty->flush();
886 }
887 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
888 #endif
889 }
890
891 void ReferenceProcessor::balance_all_queues() {
892 balance_queues(_discoveredSoftRefs);
893 balance_queues(_discoveredWeakRefs);
894 balance_queues(_discoveredFinalRefs);
895 balance_queues(_discoveredPhantomRefs);
896 balance_queues(_discoveredCleanerRefs);
897 }
898
899 size_t
900 ReferenceProcessor::process_discovered_reflist(
901 DiscoveredList refs_lists[],
902 ReferencePolicy* policy,
903 bool clear_referent,
904 BoolObjectClosure* is_alive,
905 OopClosure* keep_alive,
906 VoidClosure* complete_gc,
907 AbstractRefProcTaskExecutor* task_executor)
908 {
909 bool mt_processing = task_executor != NULL && _processing_is_mt;
910 // If discovery used MT and a dynamic number of GC threads, then
911 // the queues must be balanced for correctness if fewer than the
912 // maximum number of queues were used. The number of queue used
913 // during discovery may be different than the number to be used
914 // for processing so don't depend of _num_q < _max_num_q as part
915 // of the test.
916 bool must_balance = _discovery_is_mt;
917
918 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
919 must_balance) {
920 balance_queues(refs_lists);
921 }
922
923 size_t total_list_count = total_count(refs_lists);
924
925 if (PrintReferenceGC && PrintGCDetails) {
926 gclog_or_tty->print(", %u refs", total_list_count);
927 }
928
929 // Phase 1 (soft refs only):
930 // . Traverse the list and remove any SoftReferences whose
931 // referents are not alive, but that should be kept alive for
932 // policy reasons. Keep alive the transitive closure of all
933 // such referents.
934 if (policy != NULL) {
935 if (mt_processing) {
936 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
937 task_executor->execute(phase1);
938 } else {
939 for (uint i = 0; i < _max_num_q; i++) {
940 process_phase1(refs_lists[i], policy,
941 is_alive, keep_alive, complete_gc);
942 }
943 }
944 } else { // policy == NULL
945 assert(refs_lists != _discoveredSoftRefs,
946 "Policy must be specified for soft references.");
947 }
948
949 // Phase 2:
950 // . Traverse the list and remove any refs whose referents are alive.
951 if (mt_processing) {
952 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
953 task_executor->execute(phase2);
954 } else {
955 for (uint i = 0; i < _max_num_q; i++) {
956 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
957 }
958 }
959
960 // Phase 3:
961 // . Traverse the list and process referents as appropriate.
962 if (mt_processing) {
963 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
964 task_executor->execute(phase3);
965 } else {
966 for (uint i = 0; i < _max_num_q; i++) {
967 process_phase3(refs_lists[i], clear_referent,
968 is_alive, keep_alive, complete_gc);
969 }
970 }
971
972 return total_list_count;
973 }
974
975 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
976 uint id = 0;
977 // Determine the queue index to use for this object.
978 if (_discovery_is_mt) {
979 // During a multi-threaded discovery phase,
980 // each thread saves to its "own" list.
981 Thread* thr = Thread::current();
982 id = thr->as_Worker_thread()->id();
983 } else {
984 // single-threaded discovery, we save in round-robin
985 // fashion to each of the lists.
986 if (_processing_is_mt) {
987 id = next_id();
988 }
989 }
990 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)");
991
992 // Get the discovered queue to which we will add
993 DiscoveredList* list = NULL;
994 switch (rt) {
995 case REF_OTHER:
996 // Unknown reference type, no special treatment
997 break;
998 case REF_SOFT:
999 list = &_discoveredSoftRefs[id];
1000 break;
1001 case REF_WEAK:
1002 list = &_discoveredWeakRefs[id];
1003 break;
1004 case REF_FINAL:
1005 list = &_discoveredFinalRefs[id];
1006 break;
1007 case REF_PHANTOM:
1008 list = &_discoveredPhantomRefs[id];
1009 break;
1010 case REF_CLEANER:
1011 list = &_discoveredCleanerRefs[id];
1012 break;
1013 case REF_NONE:
1014 // we should not reach here if we are an InstanceRefKlass
1015 default:
1016 ShouldNotReachHere();
1017 }
1018 if (TraceReferenceGC && PrintGCDetails) {
1019 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list);
1020 }
1021 return list;
1022 }
1023
1024 inline void
1025 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
1026 oop obj,
1027 HeapWord* discovered_addr) {
1028 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
1029 // First we must make sure this object is only enqueued once. CAS in a non null
1030 // discovered_addr.
1031 oop current_head = refs_list.head();
1032 // The last ref must have its discovered field pointing to itself.
1033 oop next_discovered = (current_head != NULL) ? current_head : obj;
1034
1035 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
1036 NULL);
1037 if (retest == NULL) {
1038 // This thread just won the right to enqueue the object.
1039 // We have separate lists for enqueueing, so no synchronization
1040 // is necessary.
1041 refs_list.set_head(obj);
1042 refs_list.inc_length(1);
1043
1044 if (TraceReferenceGC) {
1045 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
1046 (void *)obj, obj->klass()->internal_name());
1047 }
1048 } else {
1049 // If retest was non NULL, another thread beat us to it:
1050 // The reference has already been discovered...
1051 if (TraceReferenceGC) {
1052 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
1053 (void *)obj, obj->klass()->internal_name());
1054 }
1055 }
1056 }
1057
1058 #ifndef PRODUCT
1059 // Non-atomic (i.e. concurrent) discovery might allow us
1060 // to observe j.l.References with NULL referents, being those
1061 // cleared concurrently by mutators during (or after) discovery.
1062 void ReferenceProcessor::verify_referent(oop obj) {
1063 bool da = discovery_is_atomic();
1064 oop referent = java_lang_ref_Reference::referent(obj);
1065 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
1066 err_msg("Bad referent " INTPTR_FORMAT " found in Reference "
1067 INTPTR_FORMAT " during %satomic discovery ",
1068 (void *)referent, (void *)obj, da ? "" : "non-"));
1069 }
1070 #endif
1071
1072 // We mention two of several possible choices here:
1073 // #0: if the reference object is not in the "originating generation"
1074 // (or part of the heap being collected, indicated by our "span"
1075 // we don't treat it specially (i.e. we scan it as we would
1076 // a normal oop, treating its references as strong references).
1077 // This means that references can't be discovered unless their
1078 // referent is also in the same span. This is the simplest,
1079 // most "local" and most conservative approach, albeit one
1080 // that may cause weak references to be enqueued least promptly.
1081 // We call this choice the "ReferenceBasedDiscovery" policy.
1082 // #1: the reference object may be in any generation (span), but if
1083 // the referent is in the generation (span) being currently collected
1084 // then we can discover the reference object, provided
1085 // the object has not already been discovered by
1086 // a different concurrently running collector (as may be the
1087 // case, for instance, if the reference object is in CMS and
1088 // the referent in DefNewGeneration), and provided the processing
1089 // of this reference object by the current collector will
1090 // appear atomic to every other collector in the system.
1091 // (Thus, for instance, a concurrent collector may not
1092 // discover references in other generations even if the
1093 // referent is in its own generation). This policy may,
1094 // in certain cases, enqueue references somewhat sooner than
1095 // might Policy #0 above, but at marginally increased cost
1096 // and complexity in processing these references.
1097 // We call this choice the "RefeferentBasedDiscovery" policy.
1098 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1099 // Make sure we are discovering refs (rather than processing discovered refs).
1100 if (!_discovering_refs || !RegisterReferences) {
1101 return false;
1102 }
1103 // We only discover active references.
1104 oop next = java_lang_ref_Reference::next(obj);
1105 if (next != NULL) { // Ref is no longer active
1106 return false;
1107 }
1108
1109 HeapWord* obj_addr = (HeapWord*)obj;
1110 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1111 !_span.contains(obj_addr)) {
1112 // Reference is not in the originating generation;
1113 // don't treat it specially (i.e. we want to scan it as a normal
1114 // object with strong references).
1115 return false;
1116 }
1117
1118 // We only discover references whose referents are not (yet)
1119 // known to be strongly reachable.
1120 if (is_alive_non_header() != NULL) {
1121 verify_referent(obj);
1122 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1123 return false; // referent is reachable
1124 }
1125 }
1126 if (rt == REF_SOFT) {
1127 // For soft refs we can decide now if these are not
1128 // current candidates for clearing, in which case we
1129 // can mark through them now, rather than delaying that
1130 // to the reference-processing phase. Since all current
1131 // time-stamp policies advance the soft-ref clock only
1132 // at a major collection cycle, this is always currently
1133 // accurate.
1134 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1135 return false;
1136 }
1137 }
1138
1139 ResourceMark rm; // Needed for tracing.
1140
1141 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1142 const oop discovered = java_lang_ref_Reference::discovered(obj);
1143 assert(discovered->is_oop_or_null(), err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
1144 if (discovered != NULL) {
1145 // The reference has already been discovered...
1146 if (TraceReferenceGC) {
1147 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
1148 (void *)obj, obj->klass()->internal_name());
1149 }
1150 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1151 // assumes that an object is not processed twice;
1152 // if it's been already discovered it must be on another
1153 // generation's discovered list; so we won't discover it.
1154 return false;
1155 } else {
1156 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1157 "Unrecognized policy");
1158 // Check assumption that an object is not potentially
1159 // discovered twice except by concurrent collectors that potentially
1160 // trace the same Reference object twice.
1161 assert(UseConcMarkSweepGC || UseG1GC,
1162 "Only possible with a concurrent marking collector");
1163 return true;
1164 }
1165 }
1166
1167 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1168 verify_referent(obj);
1169 // Discover if and only if EITHER:
1170 // .. reference is in our span, OR
1171 // .. we are an atomic collector and referent is in our span
1172 if (_span.contains(obj_addr) ||
1173 (discovery_is_atomic() &&
1174 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1175 // should_enqueue = true;
1176 } else {
1177 return false;
1178 }
1179 } else {
1180 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1181 _span.contains(obj_addr), "code inconsistency");
1182 }
1183
1184 // Get the right type of discovered queue head.
1185 DiscoveredList* list = get_discovered_list(rt);
1186 if (list == NULL) {
1187 return false; // nothing special needs to be done
1188 }
1189
1190 if (_discovery_is_mt) {
1191 add_to_discovered_list_mt(*list, obj, discovered_addr);
1192 } else {
1193 // We do a raw store here: the field will be visited later when processing
1194 // the discovered references.
1195 oop current_head = list->head();
1196 // The last ref must have its discovered field pointing to itself.
1197 oop next_discovered = (current_head != NULL) ? current_head : obj;
1198
1199 assert(discovered == NULL, "control point invariant");
1200 oop_store_raw(discovered_addr, next_discovered);
1201 list->set_head(obj);
1202 list->inc_length(1);
1203
1204 if (TraceReferenceGC) {
1205 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)",
1206 (void *)obj, obj->klass()->internal_name());
1207 }
1208 }
1209 assert(obj->is_oop(), "Discovered a bad reference");
1210 verify_referent(obj);
1211 return true;
1212 }
1213
1214 // Preclean the discovered references by removing those
1215 // whose referents are alive, and by marking from those that
1216 // are not active. These lists can be handled here
1217 // in any order and, indeed, concurrently.
1218 void ReferenceProcessor::preclean_discovered_references(
1219 BoolObjectClosure* is_alive,
1220 OopClosure* keep_alive,
1221 VoidClosure* complete_gc,
1222 YieldClosure* yield,
1223 GCTimer* gc_timer,
1224 GCId gc_id) {
1225
1226 NOT_PRODUCT(verify_ok_to_handle_reflists());
1227
1228 // Soft references
1229 {
1230 GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
1231 false, gc_timer, gc_id);
1232 for (uint i = 0; i < _max_num_q; i++) {
1233 if (yield->should_return()) {
1234 return;
1235 }
1236 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1237 keep_alive, complete_gc, yield);
1238 }
1239 }
1240
1241 // Weak references
1242 {
1243 GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
1244 false, gc_timer, gc_id);
1245 for (uint i = 0; i < _max_num_q; i++) {
1246 if (yield->should_return()) {
1247 return;
1248 }
1249 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1250 keep_alive, complete_gc, yield);
1251 }
1252 }
1253
1254 // Final references
1255 {
1256 GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
1257 false, gc_timer, gc_id);
1258 for (uint i = 0; i < _max_num_q; i++) {
1259 if (yield->should_return()) {
1260 return;
1261 }
1262 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1263 keep_alive, complete_gc, yield);
1264 }
1265 }
1266
1267 // Phantom references
1268 {
1269 GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
1270 false, gc_timer, gc_id);
1271 for (uint i = 0; i < _max_num_q; i++) {
1272 if (yield->should_return()) {
1273 return;
1274 }
1275 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1276 keep_alive, complete_gc, yield);
1277 }
1278
1279 // Cleaner references. Included in timing for phantom references. We
1280 // expect Cleaner references to be temporary, and don't want to deal with
1281 // possible incompatibilities arising from making it more visible.
1282 for (uint i = 0; i < _max_num_q; i++) {
1283 if (yield->should_return()) {
1284 return;
1285 }
1286 preclean_discovered_reflist(_discoveredCleanerRefs[i], is_alive,
1287 keep_alive, complete_gc, yield);
1288 }
1289 }
1290 }
1291
1292 // Walk the given discovered ref list, and remove all reference objects
1293 // whose referents are still alive, whose referents are NULL or which
1294 // are not active (have a non-NULL next field). NOTE: When we are
1295 // thus precleaning the ref lists (which happens single-threaded today),
1296 // we do not disable refs discovery to honor the correct semantics of
1297 // java.lang.Reference. As a result, we need to be careful below
1298 // that ref removal steps interleave safely with ref discovery steps
1299 // (in this thread).
1300 void
1301 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1302 BoolObjectClosure* is_alive,
1303 OopClosure* keep_alive,
1304 VoidClosure* complete_gc,
1305 YieldClosure* yield) {
1306 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1307 while (iter.has_next()) {
1308 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1309 oop obj = iter.obj();
1310 oop next = java_lang_ref_Reference::next(obj);
1311 if (iter.referent() == NULL || iter.is_referent_alive() ||
1312 next != NULL) {
1313 // The referent has been cleared, or is alive, or the Reference is not
1314 // active; we need to trace and mark its cohort.
1315 if (TraceReferenceGC) {
1316 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1317 (void *)iter.obj(), iter.obj()->klass()->internal_name());
1318 }
1319 // Remove Reference object from list
1320 iter.remove();
1321 // Keep alive its cohort.
1322 iter.make_referent_alive();
1323 if (UseCompressedOops) {
1324 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1325 keep_alive->do_oop(next_addr);
1326 } else {
1327 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1328 keep_alive->do_oop(next_addr);
1329 }
1330 iter.move_to_next();
1331 } else {
1332 iter.next();
1333 }
1334 }
1335 // Close the reachable set
1336 complete_gc->do_void();
1337
1338 NOT_PRODUCT(
1339 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) {
1340 gclog_or_tty->print_cr(" Dropped %d Refs out of %d "
1341 "Refs in discovered list " INTPTR_FORMAT,
1342 iter.removed(), iter.processed(), (address)refs_list.head());
1343 }
1344 )
1345 }
1346
1347 const char* ReferenceProcessor::list_name(uint i) {
1348 assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(),
1349 "Out of bounds index");
1350
1351 int j = i / _max_num_q;
1352 switch (j) {
1353 case 0: return "SoftRef";
1354 case 1: return "WeakRef";
1355 case 2: return "FinalRef";
1356 case 3: return "PhantomRef";
1357 case 4: return "CleanerRef";
1358 }
1359 ShouldNotReachHere();
1360 return NULL;
1361 }
1362
1363 #ifndef PRODUCT
1364 void ReferenceProcessor::verify_ok_to_handle_reflists() {
1365 // empty for now
1366 }
1367 #endif
1368
1369 #ifndef PRODUCT
1370 void ReferenceProcessor::clear_discovered_references() {
1371 guarantee(!_discovering_refs, "Discovering refs?");
1372 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
1373 clear_discovered_references(_discovered_refs[i]);
1374 }
1375 }
1376
1377 #endif // PRODUCT