1 /*
2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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23 */
24
25 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
27
28 #include "memory/referencePolicy.hpp"
29 #include "memory/referenceProcessorStats.hpp"
30 #include "memory/referenceType.hpp"
31 #include "oops/instanceRefKlass.hpp"
32
33 class GCTimer;
34
35 // ReferenceProcessor class encapsulates the per-"collector" processing
36 // of java.lang.Reference objects for GC. The interface is useful for supporting
37 // a generational abstraction, in particular when there are multiple
38 // generations that are being independently collected -- possibly
39 // concurrently and/or incrementally. Note, however, that the
40 // ReferenceProcessor class abstracts away from a generational setting
41 // by using only a heap interval (called "span" below), thus allowing
42 // its use in a straightforward manner in a general, non-generational
43 // setting.
44 //
45 // The basic idea is that each ReferenceProcessor object concerns
46 // itself with ("weak") reference processing in a specific "span"
47 // of the heap of interest to a specific collector. Currently,
48 // the span is a convex interval of the heap, but, efficiency
49 // apart, there seems to be no reason it couldn't be extended
50 // (with appropriate modifications) to any "non-convex interval".
51
52 // forward references
53 class ReferencePolicy;
54 class AbstractRefProcTaskExecutor;
55
56 // List of discovered references.
57 class DiscoveredList {
58 public:
59 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
60 oop head() const {
61 return UseCompressedOops ? oopDesc::decode_heap_oop(_compressed_head) :
62 _oop_head;
63 }
64 HeapWord* adr_head() {
65 return UseCompressedOops ? (HeapWord*)&_compressed_head :
66 (HeapWord*)&_oop_head;
67 }
68 void set_head(oop o) {
69 if (UseCompressedOops) {
70 // Must compress the head ptr.
71 _compressed_head = oopDesc::encode_heap_oop(o);
72 } else {
73 _oop_head = o;
74 }
75 }
76 bool is_empty() const { return head() == NULL; }
77 size_t length() { return _len; }
78 void set_length(size_t len) { _len = len; }
79 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
80 void dec_length(size_t dec) { _len -= dec; }
81 private:
82 // Set value depending on UseCompressedOops. This could be a template class
83 // but then we have to fix all the instantiations and declarations that use this class.
84 oop _oop_head;
85 narrowOop _compressed_head;
86 size_t _len;
87 };
88
89 // Iterator for the list of discovered references.
90 class DiscoveredListIterator {
91 private:
92 DiscoveredList& _refs_list;
93 HeapWord* _prev_next;
94 oop _prev;
95 oop _ref;
96 HeapWord* _discovered_addr;
97 oop _next;
98 HeapWord* _referent_addr;
99 oop _referent;
100 OopClosure* _keep_alive;
101 BoolObjectClosure* _is_alive;
102
103 DEBUG_ONLY(
104 oop _first_seen; // cyclic linked list check
105 )
106
107 NOT_PRODUCT(
108 size_t _processed;
109 size_t _removed;
110 )
111
112 public:
113 inline DiscoveredListIterator(DiscoveredList& refs_list,
114 OopClosure* keep_alive,
115 BoolObjectClosure* is_alive):
116 _refs_list(refs_list),
117 _prev_next(refs_list.adr_head()),
118 _prev(NULL),
119 _ref(refs_list.head()),
120 #ifdef ASSERT
121 _first_seen(refs_list.head()),
122 #endif
123 #ifndef PRODUCT
124 _processed(0),
125 _removed(0),
126 #endif
127 _next(NULL),
128 _keep_alive(keep_alive),
129 _is_alive(is_alive)
130 { }
131
132 // End Of List.
133 inline bool has_next() const { return _ref != NULL; }
134
135 // Get oop to the Reference object.
136 inline oop obj() const { return _ref; }
137
138 // Get oop to the referent object.
139 inline oop referent() const { return _referent; }
140
141 // Returns true if referent is alive.
142 inline bool is_referent_alive() const {
143 return _is_alive->do_object_b(_referent);
144 }
145
146 // Loads data for the current reference.
147 // The "allow_null_referent" argument tells us to allow for the possibility
148 // of a NULL referent in the discovered Reference object. This typically
149 // happens in the case of concurrent collectors that may have done the
150 // discovery concurrently, or interleaved, with mutator execution.
151 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
152
153 // Move to the next discovered reference.
154 inline void next() {
155 _prev_next = _discovered_addr;
156 _prev = _ref;
157 move_to_next();
158 }
159
160 // Remove the current reference from the list
161 void remove();
162
163 // Make the Reference object active again.
164 void make_active();
165
166 // Make the referent alive.
167 inline void make_referent_alive() {
168 if (UseCompressedOops) {
169 _keep_alive->do_oop((narrowOop*)_referent_addr);
170 } else {
171 _keep_alive->do_oop((oop*)_referent_addr);
172 }
173 }
174
175 // Update the discovered field.
176 inline void update_discovered() {
177 // First _prev_next ref actually points into DiscoveredList (gross).
178 if (UseCompressedOops) {
179 if (!oopDesc::is_null(*(narrowOop*)_prev_next)) {
180 _keep_alive->do_oop((narrowOop*)_prev_next);
181 }
182 } else {
183 if (!oopDesc::is_null(*(oop*)_prev_next)) {
184 _keep_alive->do_oop((oop*)_prev_next);
185 }
186 }
187 }
188
189 // NULL out referent pointer.
190 void clear_referent();
191
192 // Statistics
193 NOT_PRODUCT(
194 inline size_t processed() const { return _processed; }
195 inline size_t removed() const { return _removed; }
196 )
197
198 inline void move_to_next() {
199 if (_ref == _next) {
200 // End of the list.
201 _ref = NULL;
202 } else {
203 _ref = _next;
204 }
205 assert(_ref != _first_seen, "cyclic ref_list found");
206 NOT_PRODUCT(_processed++);
207 }
208 };
209
210 class ReferenceProcessor : public CHeapObj<mtGC> {
211
212 private:
213 size_t total_count(DiscoveredList lists[]);
214
215 protected:
216 // Compatibility with pre-4965777 JDK's
217 static bool _pending_list_uses_discovered_field;
218
219 // The SoftReference master timestamp clock
220 static jlong _soft_ref_timestamp_clock;
221
222 MemRegion _span; // (right-open) interval of heap
223 // subject to wkref discovery
224
225 bool _discovering_refs; // true when discovery enabled
226 bool _discovery_is_atomic; // if discovery is atomic wrt
227 // other collectors in configuration
228 bool _discovery_is_mt; // true if reference discovery is MT.
229
230 bool _enqueuing_is_done; // true if all weak references enqueued
231 bool _processing_is_mt; // true during phases when
232 // reference processing is MT.
233 uint _next_id; // round-robin mod _num_q counter in
234 // support of work distribution
235
236 // For collectors that do not keep GC liveness information
237 // in the object header, this field holds a closure that
238 // helps the reference processor determine the reachability
239 // of an oop. It is currently initialized to NULL for all
240 // collectors except for CMS and G1.
241 BoolObjectClosure* _is_alive_non_header;
242
243 // Soft ref clearing policies
244 // . the default policy
245 static ReferencePolicy* _default_soft_ref_policy;
246 // . the "clear all" policy
247 static ReferencePolicy* _always_clear_soft_ref_policy;
248 // . the current policy below is either one of the above
249 ReferencePolicy* _current_soft_ref_policy;
250
251 // The discovered ref lists themselves
252
253 // The active MT'ness degree of the queues below
254 uint _num_q;
255 // The maximum MT'ness degree of the queues below
256 uint _max_num_q;
257
258 // Master array of discovered oops
259 DiscoveredList* _discovered_refs;
260
261 // Arrays of lists of oops, one per thread (pointers into master array above)
262 DiscoveredList* _discoveredSoftRefs;
263 DiscoveredList* _discoveredWeakRefs;
264 DiscoveredList* _discoveredFinalRefs;
265 DiscoveredList* _discoveredPhantomRefs;
266
267 public:
268 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
269
270 uint num_q() { return _num_q; }
271 uint max_num_q() { return _max_num_q; }
272 void set_active_mt_degree(uint v) { _num_q = v; }
273
274 DiscoveredList* discovered_refs() { return _discovered_refs; }
275
276 ReferencePolicy* setup_policy(bool always_clear) {
277 _current_soft_ref_policy = always_clear ?
278 _always_clear_soft_ref_policy : _default_soft_ref_policy;
279 _current_soft_ref_policy->setup(); // snapshot the policy threshold
280 return _current_soft_ref_policy;
281 }
282
283 // Process references with a certain reachability level.
284 size_t process_discovered_reflist(DiscoveredList refs_lists[],
285 ReferencePolicy* policy,
286 bool clear_referent,
287 BoolObjectClosure* is_alive,
288 OopClosure* keep_alive,
289 VoidClosure* complete_gc,
290 AbstractRefProcTaskExecutor* task_executor);
291
292 void process_phaseJNI(BoolObjectClosure* is_alive,
293 OopClosure* keep_alive,
294 VoidClosure* complete_gc);
295
296 // Work methods used by the method process_discovered_reflist
297 // Phase1: keep alive all those referents that are otherwise
298 // dead but which must be kept alive by policy (and their closure).
299 void process_phase1(DiscoveredList& refs_list,
300 ReferencePolicy* policy,
301 BoolObjectClosure* is_alive,
302 OopClosure* keep_alive,
303 VoidClosure* complete_gc);
304 // Phase2: remove all those references whose referents are
305 // reachable.
306 inline void process_phase2(DiscoveredList& refs_list,
307 BoolObjectClosure* is_alive,
308 OopClosure* keep_alive,
309 VoidClosure* complete_gc) {
310 if (discovery_is_atomic()) {
311 // complete_gc is ignored in this case for this phase
312 pp2_work(refs_list, is_alive, keep_alive);
313 } else {
314 assert(complete_gc != NULL, "Error");
315 pp2_work_concurrent_discovery(refs_list, is_alive,
316 keep_alive, complete_gc);
317 }
318 }
319 // Work methods in support of process_phase2
320 void pp2_work(DiscoveredList& refs_list,
321 BoolObjectClosure* is_alive,
322 OopClosure* keep_alive);
323 void pp2_work_concurrent_discovery(
324 DiscoveredList& refs_list,
325 BoolObjectClosure* is_alive,
326 OopClosure* keep_alive,
327 VoidClosure* complete_gc);
328 // Phase3: process the referents by either clearing them
329 // or keeping them alive (and their closure)
330 void process_phase3(DiscoveredList& refs_list,
331 bool clear_referent,
332 BoolObjectClosure* is_alive,
333 OopClosure* keep_alive,
334 VoidClosure* complete_gc);
335
336 // Enqueue references with a certain reachability level
337 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
338
339 // "Preclean" all the discovered reference lists
340 // by removing references with strongly reachable referents.
341 // The first argument is a predicate on an oop that indicates
342 // its (strong) reachability and the second is a closure that
343 // may be used to incrementalize or abort the precleaning process.
344 // The caller is responsible for taking care of potential
345 // interference with concurrent operations on these lists
346 // (or predicates involved) by other threads. Currently
347 // only used by the CMS collector.
348 void preclean_discovered_references(BoolObjectClosure* is_alive,
349 OopClosure* keep_alive,
350 VoidClosure* complete_gc,
351 YieldClosure* yield,
352 GCTimer* gc_timer);
353
354 // Delete entries in the discovered lists that have
355 // either a null referent or are not active. Such
356 // Reference objects can result from the clearing
357 // or enqueueing of Reference objects concurrent
358 // with their discovery by a (concurrent) collector.
359 // For a definition of "active" see java.lang.ref.Reference;
360 // Refs are born active, become inactive when enqueued,
361 // and never become active again. The state of being
362 // active is encoded as follows: A Ref is active
363 // if and only if its "next" field is NULL.
364 void clean_up_discovered_references();
365 void clean_up_discovered_reflist(DiscoveredList& refs_list);
366
367 // Returns the name of the discovered reference list
368 // occupying the i / _num_q slot.
369 const char* list_name(uint i);
370
371 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
372
373 protected:
374 // "Preclean" the given discovered reference list
375 // by removing references with strongly reachable referents.
376 // Currently used in support of CMS only.
377 void preclean_discovered_reflist(DiscoveredList& refs_list,
378 BoolObjectClosure* is_alive,
379 OopClosure* keep_alive,
380 VoidClosure* complete_gc,
381 YieldClosure* yield);
382
383 // round-robin mod _num_q (not: _not_ mode _max_num_q)
384 uint next_id() {
385 uint id = _next_id;
386 if (++_next_id == _num_q) {
387 _next_id = 0;
388 }
389 return id;
390 }
391 DiscoveredList* get_discovered_list(ReferenceType rt);
392 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
393 HeapWord* discovered_addr);
394 void verify_ok_to_handle_reflists() PRODUCT_RETURN;
395
396 void clear_discovered_references(DiscoveredList& refs_list);
397 void abandon_partial_discovered_list(DiscoveredList& refs_list);
398
399 // Calculate the number of jni handles.
400 unsigned int count_jni_refs();
401
402 // Balances reference queues.
403 void balance_queues(DiscoveredList ref_lists[]);
404
405 // Update (advance) the soft ref master clock field.
406 void update_soft_ref_master_clock();
407
408 public:
409 // Default parameters give you a vanilla reference processor.
410 ReferenceProcessor(MemRegion span,
411 bool mt_processing = false, uint mt_processing_degree = 1,
412 bool mt_discovery = false, uint mt_discovery_degree = 1,
413 bool atomic_discovery = true,
414 BoolObjectClosure* is_alive_non_header = NULL);
415
416 // RefDiscoveryPolicy values
417 enum DiscoveryPolicy {
418 ReferenceBasedDiscovery = 0,
419 ReferentBasedDiscovery = 1,
420 DiscoveryPolicyMin = ReferenceBasedDiscovery,
421 DiscoveryPolicyMax = ReferentBasedDiscovery
422 };
423
424 static void init_statics();
425
426 public:
427 // get and set "is_alive_non_header" field
428 BoolObjectClosure* is_alive_non_header() {
429 return _is_alive_non_header;
430 }
431 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
432 _is_alive_non_header = is_alive_non_header;
433 }
434
435 // get and set span
436 MemRegion span() { return _span; }
437 void set_span(MemRegion span) { _span = span; }
438
439 // start and stop weak ref discovery
440 void enable_discovery(bool verify_disabled, bool check_no_refs);
441 void disable_discovery() { _discovering_refs = false; }
442 bool discovery_enabled() { return _discovering_refs; }
443
444 // whether discovery is atomic wrt other collectors
445 bool discovery_is_atomic() const { return _discovery_is_atomic; }
446 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
447
448 // whether the JDK in which we are embedded is a pre-4965777 JDK,
449 // and thus whether or not it uses the discovered field to chain
450 // the entries in the pending list.
451 static bool pending_list_uses_discovered_field() {
452 return _pending_list_uses_discovered_field;
453 }
454
455 // whether discovery is done by multiple threads same-old-timeously
456 bool discovery_is_mt() const { return _discovery_is_mt; }
457 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
458
459 // Whether we are in a phase when _processing_ is MT.
460 bool processing_is_mt() const { return _processing_is_mt; }
461 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
462
463 // whether all enqueueing of weak references is complete
464 bool enqueuing_is_done() { return _enqueuing_is_done; }
465 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
466
467 // iterate over oops
468 void weak_oops_do(OopClosure* f); // weak roots
469
470 // Balance each of the discovered lists.
471 void balance_all_queues();
472 void verify_list(DiscoveredList& ref_list);
473
474 // Discover a Reference object, using appropriate discovery criteria
475 bool discover_reference(oop obj, ReferenceType rt);
476
477 // Process references found during GC (called by the garbage collector)
478 ReferenceProcessorStats
479 process_discovered_references(BoolObjectClosure* is_alive,
480 OopClosure* keep_alive,
481 VoidClosure* complete_gc,
482 AbstractRefProcTaskExecutor* task_executor,
483 GCTimer *gc_timer);
484
485 // Enqueue references at end of GC (called by the garbage collector)
486 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
487
488 // If a discovery is in process that is being superceded, abandon it: all
489 // the discovered lists will be empty, and all the objects on them will
490 // have NULL discovered fields. Must be called only at a safepoint.
491 void abandon_partial_discovery();
492
493 // debugging
494 void verify_no_references_recorded() PRODUCT_RETURN;
495 void verify_referent(oop obj) PRODUCT_RETURN;
496
497 // clear the discovered lists (unlinking each entry).
498 void clear_discovered_references() PRODUCT_RETURN;
499 };
500
501 // A utility class to disable reference discovery in
502 // the scope which contains it, for given ReferenceProcessor.
503 class NoRefDiscovery: StackObj {
504 private:
505 ReferenceProcessor* _rp;
506 bool _was_discovering_refs;
507 public:
508 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
509 _was_discovering_refs = _rp->discovery_enabled();
510 if (_was_discovering_refs) {
511 _rp->disable_discovery();
512 }
513 }
514
515 ~NoRefDiscovery() {
516 if (_was_discovering_refs) {
517 _rp->enable_discovery(true /*verify_disabled*/, false /*check_no_refs*/);
518 }
519 }
520 };
521
522
523 // A utility class to temporarily mutate the span of the
524 // given ReferenceProcessor in the scope that contains it.
525 class ReferenceProcessorSpanMutator: StackObj {
526 private:
527 ReferenceProcessor* _rp;
528 MemRegion _saved_span;
529
530 public:
531 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
532 MemRegion span):
533 _rp(rp) {
534 _saved_span = _rp->span();
535 _rp->set_span(span);
536 }
537
538 ~ReferenceProcessorSpanMutator() {
539 _rp->set_span(_saved_span);
540 }
541 };
542
543 // A utility class to temporarily change the MT'ness of
544 // reference discovery for the given ReferenceProcessor
545 // in the scope that contains it.
546 class ReferenceProcessorMTDiscoveryMutator: StackObj {
547 private:
548 ReferenceProcessor* _rp;
549 bool _saved_mt;
550
551 public:
552 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
553 bool mt):
554 _rp(rp) {
555 _saved_mt = _rp->discovery_is_mt();
556 _rp->set_mt_discovery(mt);
557 }
558
559 ~ReferenceProcessorMTDiscoveryMutator() {
560 _rp->set_mt_discovery(_saved_mt);
561 }
562 };
563
564
565 // A utility class to temporarily change the disposition
566 // of the "is_alive_non_header" closure field of the
567 // given ReferenceProcessor in the scope that contains it.
568 class ReferenceProcessorIsAliveMutator: StackObj {
569 private:
570 ReferenceProcessor* _rp;
571 BoolObjectClosure* _saved_cl;
572
573 public:
574 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
575 BoolObjectClosure* cl):
576 _rp(rp) {
577 _saved_cl = _rp->is_alive_non_header();
578 _rp->set_is_alive_non_header(cl);
579 }
580
581 ~ReferenceProcessorIsAliveMutator() {
582 _rp->set_is_alive_non_header(_saved_cl);
583 }
584 };
585
586 // A utility class to temporarily change the disposition
587 // of the "discovery_is_atomic" field of the
588 // given ReferenceProcessor in the scope that contains it.
589 class ReferenceProcessorAtomicMutator: StackObj {
590 private:
591 ReferenceProcessor* _rp;
592 bool _saved_atomic_discovery;
593
594 public:
595 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
596 bool atomic):
597 _rp(rp) {
598 _saved_atomic_discovery = _rp->discovery_is_atomic();
599 _rp->set_atomic_discovery(atomic);
600 }
601
602 ~ReferenceProcessorAtomicMutator() {
603 _rp->set_atomic_discovery(_saved_atomic_discovery);
604 }
605 };
606
607
608 // A utility class to temporarily change the MT processing
609 // disposition of the given ReferenceProcessor instance
610 // in the scope that contains it.
611 class ReferenceProcessorMTProcMutator: StackObj {
612 private:
613 ReferenceProcessor* _rp;
614 bool _saved_mt;
615
616 public:
617 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
618 bool mt):
619 _rp(rp) {
620 _saved_mt = _rp->processing_is_mt();
621 _rp->set_mt_processing(mt);
622 }
623
624 ~ReferenceProcessorMTProcMutator() {
625 _rp->set_mt_processing(_saved_mt);
626 }
627 };
628
629
630 // This class is an interface used to implement task execution for the
631 // reference processing.
632 class AbstractRefProcTaskExecutor {
633 public:
634
635 // Abstract tasks to execute.
636 class ProcessTask;
637 class EnqueueTask;
638
639 // Executes a task using worker threads.
640 virtual void execute(ProcessTask& task) = 0;
641 virtual void execute(EnqueueTask& task) = 0;
642
643 // Switch to single threaded mode.
644 virtual void set_single_threaded_mode() { };
645 };
646
647 // Abstract reference processing task to execute.
648 class AbstractRefProcTaskExecutor::ProcessTask {
649 protected:
650 ProcessTask(ReferenceProcessor& ref_processor,
651 DiscoveredList refs_lists[],
652 bool marks_oops_alive)
653 : _ref_processor(ref_processor),
654 _refs_lists(refs_lists),
655 _marks_oops_alive(marks_oops_alive)
656 { }
657
658 public:
659 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
660 OopClosure& keep_alive,
661 VoidClosure& complete_gc) = 0;
662
663 // Returns true if a task marks some oops as alive.
664 bool marks_oops_alive() const
665 { return _marks_oops_alive; }
666
667 protected:
668 ReferenceProcessor& _ref_processor;
669 DiscoveredList* _refs_lists;
670 const bool _marks_oops_alive;
671 };
672
673 // Abstract reference processing task to execute.
674 class AbstractRefProcTaskExecutor::EnqueueTask {
675 protected:
676 EnqueueTask(ReferenceProcessor& ref_processor,
677 DiscoveredList refs_lists[],
678 HeapWord* pending_list_addr,
679 int n_queues)
680 : _ref_processor(ref_processor),
681 _refs_lists(refs_lists),
682 _pending_list_addr(pending_list_addr),
683 _n_queues(n_queues)
684 { }
685
686 public:
687 virtual void work(unsigned int work_id) = 0;
688
689 protected:
690 ReferenceProcessor& _ref_processor;
691 DiscoveredList* _refs_lists;
692 HeapWord* _pending_list_addr;
693 int _n_queues;
694 };
695
696 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP