1 /*
2 * Copyright (c) 2001, 2016, 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,
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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
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23 */
24
25 #ifndef SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
27
28 #include "gc/shared/referencePolicy.hpp"
29 #include "gc/shared/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 inline oop head() const;
61 HeapWord* adr_head() {
62 return UseCompressedOops ? (HeapWord*)&_compressed_head :
63 (HeapWord*)&_oop_head;
64 }
65 inline void set_head(oop o);
66 inline bool is_empty() const;
67 size_t length() { return _len; }
68 void set_length(size_t len) { _len = len; }
69 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
70 void dec_length(size_t dec) { _len -= dec; }
71 private:
72 // Set value depending on UseCompressedOops. This could be a template class
73 // but then we have to fix all the instantiations and declarations that use this class.
74 oop _oop_head;
75 narrowOop _compressed_head;
76 size_t _len;
77 };
78
79 // Iterator for the list of discovered references.
80 class DiscoveredListIterator {
81 private:
82 DiscoveredList& _refs_list;
83 HeapWord* _prev_next;
84 oop _prev;
85 oop _ref;
86 HeapWord* _discovered_addr;
87 oop _next;
88 HeapWord* _referent_addr;
89 oop _referent;
90 OopClosure* _keep_alive;
91 BoolObjectClosure* _is_alive;
92
93 DEBUG_ONLY(
94 oop _first_seen; // cyclic linked list check
95 )
96
97 NOT_PRODUCT(
98 size_t _processed;
99 size_t _removed;
100 )
101
102 public:
103 inline DiscoveredListIterator(DiscoveredList& refs_list,
104 OopClosure* keep_alive,
105 BoolObjectClosure* is_alive);
106
107 // End Of List.
108 inline bool has_next() const { return _ref != NULL; }
109
110 // Get oop to the Reference object.
111 inline oop obj() const { return _ref; }
112
113 // Get oop to the referent object.
114 inline oop referent() const { return _referent; }
115
116 // Returns true if referent is alive.
117 inline bool is_referent_alive() const {
118 return _is_alive->do_object_b(_referent);
119 }
120
121 // Loads data for the current reference.
122 // The "allow_null_referent" argument tells us to allow for the possibility
123 // of a NULL referent in the discovered Reference object. This typically
124 // happens in the case of concurrent collectors that may have done the
125 // discovery concurrently, or interleaved, with mutator execution.
126 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
127
128 // Move to the next discovered reference.
129 inline void next() {
130 _prev_next = _discovered_addr;
131 _prev = _ref;
132 move_to_next();
133 }
134
135 // Remove the current reference from the list
136 void remove();
137
138 // Make the referent alive.
139 inline void make_referent_alive() {
140 if (UseCompressedOops) {
141 _keep_alive->do_oop((narrowOop*)_referent_addr);
142 } else {
143 _keep_alive->do_oop((oop*)_referent_addr);
144 }
145 }
146
147 // NULL out referent pointer.
148 void clear_referent();
149
150 // Statistics
151 NOT_PRODUCT(
152 inline size_t processed() const { return _processed; }
153 inline size_t removed() const { return _removed; }
154 )
155
156 inline void move_to_next() {
157 if (_ref == _next) {
158 // End of the list.
159 _ref = NULL;
160 } else {
161 _ref = _next;
162 }
163 assert(_ref != _first_seen, "cyclic ref_list found");
164 NOT_PRODUCT(_processed++);
165 }
166 };
167
168 class ReferenceProcessor : public CHeapObj<mtGC> {
169
170 private:
171 size_t total_count(DiscoveredList lists[]);
172
173 protected:
174 // The SoftReference master timestamp clock
175 static jlong _soft_ref_timestamp_clock;
176
177 MemRegion _span; // (right-open) interval of heap
178 // subject to wkref discovery
179
180 bool _discovering_refs; // true when discovery enabled
181 bool _discovery_is_atomic; // if discovery is atomic wrt
182 // other collectors in configuration
183 bool _discovery_is_mt; // true if reference discovery is MT.
184
185 bool _enqueuing_is_done; // true if all weak references enqueued
186 bool _processing_is_mt; // true during phases when
187 // reference processing is MT.
188 uint _next_id; // round-robin mod _num_q counter in
189 // support of work distribution
190
191 // For collectors that do not keep GC liveness information
192 // in the object header, this field holds a closure that
193 // helps the reference processor determine the reachability
194 // of an oop. It is currently initialized to NULL for all
195 // collectors except for CMS and G1.
196 BoolObjectClosure* _is_alive_non_header;
197
198 // Soft ref clearing policies
199 // . the default policy
200 static ReferencePolicy* _default_soft_ref_policy;
201 // . the "clear all" policy
202 static ReferencePolicy* _always_clear_soft_ref_policy;
203 // . the current policy below is either one of the above
204 ReferencePolicy* _current_soft_ref_policy;
205
206 // The discovered ref lists themselves
207
208 // The active MT'ness degree of the queues below
209 uint _num_q;
210 // The maximum MT'ness degree of the queues below
211 uint _max_num_q;
212
213 // Master array of discovered oops
214 DiscoveredList* _discovered_refs;
215
216 // Arrays of lists of oops, one per thread (pointers into master array above)
217 DiscoveredList* _discoveredSoftRefs;
218 DiscoveredList* _discoveredWeakRefs;
219 DiscoveredList* _discoveredFinalRefs;
220 DiscoveredList* _discoveredPhantomRefs;
221
222 public:
223 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
224
225 uint num_q() { return _num_q; }
226 uint max_num_q() { return _max_num_q; }
227 void set_active_mt_degree(uint v);
228
229 DiscoveredList* discovered_refs() { return _discovered_refs; }
230
231 ReferencePolicy* setup_policy(bool always_clear) {
232 _current_soft_ref_policy = always_clear ?
233 _always_clear_soft_ref_policy : _default_soft_ref_policy;
234 _current_soft_ref_policy->setup(); // snapshot the policy threshold
235 return _current_soft_ref_policy;
236 }
237
238 // Process references with a certain reachability level.
239 void process_discovered_reflist(DiscoveredList refs_lists[],
240 ReferencePolicy* policy,
241 bool clear_referent,
242 BoolObjectClosure* is_alive,
243 OopClosure* keep_alive,
244 VoidClosure* complete_gc,
245 AbstractRefProcTaskExecutor* task_executor);
246
247 void process_phaseJNI(BoolObjectClosure* is_alive,
248 OopClosure* keep_alive,
249 VoidClosure* complete_gc);
250
251 // Work methods used by the method process_discovered_reflist
252 // Phase1: keep alive all those referents that are otherwise
253 // dead but which must be kept alive by policy (and their closure).
254 void process_phase1(DiscoveredList& refs_list,
255 ReferencePolicy* policy,
256 BoolObjectClosure* is_alive,
257 OopClosure* keep_alive,
258 VoidClosure* complete_gc);
259 // Phase2: remove all those references whose referents are
260 // reachable.
261 inline void process_phase2(DiscoveredList& refs_list,
262 BoolObjectClosure* is_alive,
263 OopClosure* keep_alive,
264 VoidClosure* complete_gc) {
265 if (discovery_is_atomic()) {
266 // complete_gc is ignored in this case for this phase
267 pp2_work(refs_list, is_alive, keep_alive);
268 } else {
269 assert(complete_gc != NULL, "Error");
270 pp2_work_concurrent_discovery(refs_list, is_alive,
271 keep_alive, complete_gc);
272 }
273 }
274 // Work methods in support of process_phase2
275 void pp2_work(DiscoveredList& refs_list,
276 BoolObjectClosure* is_alive,
277 OopClosure* keep_alive);
278 void pp2_work_concurrent_discovery(
279 DiscoveredList& refs_list,
280 BoolObjectClosure* is_alive,
281 OopClosure* keep_alive,
282 VoidClosure* complete_gc);
283 // Phase3: process the referents by either clearing them
284 // or keeping them alive (and their closure)
285 void process_phase3(DiscoveredList& refs_list,
286 bool clear_referent,
287 BoolObjectClosure* is_alive,
288 OopClosure* keep_alive,
289 VoidClosure* complete_gc);
290
291 // Enqueue references with a certain reachability level
292 void enqueue_discovered_reflist(DiscoveredList& refs_list);
293
294 // "Preclean" all the discovered reference lists
295 // by removing references with strongly reachable referents.
296 // The first argument is a predicate on an oop that indicates
297 // its (strong) reachability and the second is a closure that
298 // may be used to incrementalize or abort the precleaning process.
299 // The caller is responsible for taking care of potential
300 // interference with concurrent operations on these lists
301 // (or predicates involved) by other threads. Currently
302 // only used by the CMS collector.
303 void preclean_discovered_references(BoolObjectClosure* is_alive,
304 OopClosure* keep_alive,
305 VoidClosure* complete_gc,
306 YieldClosure* yield,
307 GCTimer* gc_timer);
308
309 // Returns the name of the discovered reference list
310 // occupying the i / _num_q slot.
311 const char* list_name(uint i);
312
313 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor);
314
315 protected:
316 // "Preclean" the given discovered reference list
317 // by removing references with strongly reachable referents.
318 // Currently used in support of CMS only.
319 void preclean_discovered_reflist(DiscoveredList& refs_list,
320 BoolObjectClosure* is_alive,
321 OopClosure* keep_alive,
322 VoidClosure* complete_gc,
323 YieldClosure* yield);
324
325 // round-robin mod _num_q (not: _not_ mode _max_num_q)
326 uint next_id() {
327 uint id = _next_id;
328 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
329 if (++_next_id == _num_q) {
330 _next_id = 0;
331 }
332 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q);
333 return id;
334 }
335 DiscoveredList* get_discovered_list(ReferenceType rt);
336 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
337 HeapWord* discovered_addr);
338
339 void clear_discovered_references(DiscoveredList& refs_list);
340
341 // Calculate the number of jni handles.
342 size_t count_jni_refs();
343
344 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
345
346 // Balances reference queues.
347 void balance_queues(DiscoveredList ref_lists[]);
348
349 // Update (advance) the soft ref master clock field.
350 void update_soft_ref_master_clock();
351
352 public:
353 // Default parameters give you a vanilla reference processor.
354 ReferenceProcessor(MemRegion span,
355 bool mt_processing = false, uint mt_processing_degree = 1,
356 bool mt_discovery = false, uint mt_discovery_degree = 1,
357 bool atomic_discovery = true,
358 BoolObjectClosure* is_alive_non_header = NULL);
359
360 // RefDiscoveryPolicy values
361 enum DiscoveryPolicy {
362 ReferenceBasedDiscovery = 0,
363 ReferentBasedDiscovery = 1,
364 DiscoveryPolicyMin = ReferenceBasedDiscovery,
365 DiscoveryPolicyMax = ReferentBasedDiscovery
366 };
367
368 static void init_statics();
369
370 public:
371 // get and set "is_alive_non_header" field
372 BoolObjectClosure* is_alive_non_header() {
373 return _is_alive_non_header;
374 }
375 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
376 _is_alive_non_header = is_alive_non_header;
377 }
378
379 // get and set span
380 MemRegion span() { return _span; }
381 void set_span(MemRegion span) { _span = span; }
382
383 // start and stop weak ref discovery
384 void enable_discovery(bool check_no_refs = true);
385 void disable_discovery() { _discovering_refs = false; }
386 bool discovery_enabled() { return _discovering_refs; }
387
388 // whether discovery is atomic wrt other collectors
389 bool discovery_is_atomic() const { return _discovery_is_atomic; }
390 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
391
392 // whether discovery is done by multiple threads same-old-timeously
393 bool discovery_is_mt() const { return _discovery_is_mt; }
394 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
395
396 // Whether we are in a phase when _processing_ is MT.
397 bool processing_is_mt() const { return _processing_is_mt; }
398 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
399
400 // whether all enqueueing of weak references is complete
401 bool enqueuing_is_done() { return _enqueuing_is_done; }
402 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
403
404 // iterate over oops
405 void weak_oops_do(OopClosure* f); // weak roots
406
407 // Balance each of the discovered lists.
408 void balance_all_queues();
409 void verify_list(DiscoveredList& ref_list);
410
411 // Discover a Reference object, using appropriate discovery criteria
412 bool discover_reference(oop obj, ReferenceType rt);
413
414 // Has discovered references that need handling
415 bool has_discovered_references();
416
417 // Process references found during GC (called by the garbage collector)
418 ReferenceProcessorStats
419 process_discovered_references(BoolObjectClosure* is_alive,
420 OopClosure* keep_alive,
421 VoidClosure* complete_gc,
422 AbstractRefProcTaskExecutor* task_executor,
423 GCTimer *gc_timer);
424
425 // Enqueue references at end of GC (called by the garbage collector)
426 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
427
428 // If a discovery is in process that is being superceded, abandon it: all
429 // the discovered lists will be empty, and all the objects on them will
430 // have NULL discovered fields. Must be called only at a safepoint.
431 void abandon_partial_discovery();
432
433 // debugging
434 void verify_no_references_recorded() PRODUCT_RETURN;
435 void verify_referent(oop obj) PRODUCT_RETURN;
436 };
437
438 // A utility class to disable reference discovery in
439 // the scope which contains it, for given ReferenceProcessor.
440 class NoRefDiscovery: StackObj {
441 private:
442 ReferenceProcessor* _rp;
443 bool _was_discovering_refs;
444 public:
445 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
446 _was_discovering_refs = _rp->discovery_enabled();
447 if (_was_discovering_refs) {
448 _rp->disable_discovery();
449 }
450 }
451
452 ~NoRefDiscovery() {
453 if (_was_discovering_refs) {
454 _rp->enable_discovery(false /*check_no_refs*/);
455 }
456 }
457 };
458
459
460 // A utility class to temporarily mutate the span of the
461 // given ReferenceProcessor in the scope that contains it.
462 class ReferenceProcessorSpanMutator: StackObj {
463 private:
464 ReferenceProcessor* _rp;
465 MemRegion _saved_span;
466
467 public:
468 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
469 MemRegion span):
470 _rp(rp) {
471 _saved_span = _rp->span();
472 _rp->set_span(span);
473 }
474
475 ~ReferenceProcessorSpanMutator() {
476 _rp->set_span(_saved_span);
477 }
478 };
479
480 // A utility class to temporarily change the MT'ness of
481 // reference discovery for the given ReferenceProcessor
482 // in the scope that contains it.
483 class ReferenceProcessorMTDiscoveryMutator: StackObj {
484 private:
485 ReferenceProcessor* _rp;
486 bool _saved_mt;
487
488 public:
489 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
490 bool mt):
491 _rp(rp) {
492 _saved_mt = _rp->discovery_is_mt();
493 _rp->set_mt_discovery(mt);
494 }
495
496 ~ReferenceProcessorMTDiscoveryMutator() {
497 _rp->set_mt_discovery(_saved_mt);
498 }
499 };
500
501
502 // A utility class to temporarily change the disposition
503 // of the "is_alive_non_header" closure field of the
504 // given ReferenceProcessor in the scope that contains it.
505 class ReferenceProcessorIsAliveMutator: StackObj {
506 private:
507 ReferenceProcessor* _rp;
508 BoolObjectClosure* _saved_cl;
509
510 public:
511 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
512 BoolObjectClosure* cl):
513 _rp(rp) {
514 _saved_cl = _rp->is_alive_non_header();
515 _rp->set_is_alive_non_header(cl);
516 }
517
518 ~ReferenceProcessorIsAliveMutator() {
519 _rp->set_is_alive_non_header(_saved_cl);
520 }
521 };
522
523 // A utility class to temporarily change the disposition
524 // of the "discovery_is_atomic" field of the
525 // given ReferenceProcessor in the scope that contains it.
526 class ReferenceProcessorAtomicMutator: StackObj {
527 private:
528 ReferenceProcessor* _rp;
529 bool _saved_atomic_discovery;
530
531 public:
532 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
533 bool atomic):
534 _rp(rp) {
535 _saved_atomic_discovery = _rp->discovery_is_atomic();
536 _rp->set_atomic_discovery(atomic);
537 }
538
539 ~ReferenceProcessorAtomicMutator() {
540 _rp->set_atomic_discovery(_saved_atomic_discovery);
541 }
542 };
543
544
545 // A utility class to temporarily change the MT processing
546 // disposition of the given ReferenceProcessor instance
547 // in the scope that contains it.
548 class ReferenceProcessorMTProcMutator: StackObj {
549 private:
550 ReferenceProcessor* _rp;
551 bool _saved_mt;
552
553 public:
554 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
555 bool mt):
556 _rp(rp) {
557 _saved_mt = _rp->processing_is_mt();
558 _rp->set_mt_processing(mt);
559 }
560
561 ~ReferenceProcessorMTProcMutator() {
562 _rp->set_mt_processing(_saved_mt);
563 }
564 };
565
566
567 // This class is an interface used to implement task execution for the
568 // reference processing.
569 class AbstractRefProcTaskExecutor {
570 public:
571
572 // Abstract tasks to execute.
573 class ProcessTask;
574 class EnqueueTask;
575
576 // Executes a task using worker threads.
577 virtual void execute(ProcessTask& task) = 0;
578 virtual void execute(EnqueueTask& task) = 0;
579
580 // Switch to single threaded mode.
581 virtual void set_single_threaded_mode() { };
582 };
583
584 // Abstract reference processing task to execute.
585 class AbstractRefProcTaskExecutor::ProcessTask {
586 protected:
587 ProcessTask(ReferenceProcessor& ref_processor,
588 DiscoveredList refs_lists[],
589 bool marks_oops_alive)
590 : _ref_processor(ref_processor),
591 _refs_lists(refs_lists),
592 _marks_oops_alive(marks_oops_alive)
593 { }
594
595 public:
596 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
597 OopClosure& keep_alive,
598 VoidClosure& complete_gc) = 0;
599
600 // Returns true if a task marks some oops as alive.
601 bool marks_oops_alive() const
602 { return _marks_oops_alive; }
603
604 protected:
605 ReferenceProcessor& _ref_processor;
606 DiscoveredList* _refs_lists;
607 const bool _marks_oops_alive;
608 };
609
610 // Abstract reference processing task to execute.
611 class AbstractRefProcTaskExecutor::EnqueueTask {
612 protected:
613 EnqueueTask(ReferenceProcessor& ref_processor,
614 DiscoveredList refs_lists[],
615 int n_queues)
616 : _ref_processor(ref_processor),
617 _refs_lists(refs_lists),
618 _n_queues(n_queues)
619 { }
620
621 public:
622 virtual void work(unsigned int work_id) = 0;
623
624 protected:
625 ReferenceProcessor& _ref_processor;
626 DiscoveredList* _refs_lists;
627 int _n_queues;
628 };
629
630 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP