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