1 #ifdef USE_PRAGMA_IDENT_HDR
2 #pragma ident "@(#)referenceProcessor.hpp 1.43 07/05/05 17:05:54 JVM"
3 #endif
4 /*
5 * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
24 * have any questions.
25 *
26 */
27
28 // ReferenceProcessor class encapsulates the per-"collector" processing
29 // of "weak" references for GC. The interface is useful for supporting
30 // a generational abstraction, in particular when there are multiple
31 // generations that are being independently collected -- possibly
32 // concurrently and/or incrementally. Note, however, that the
33 // ReferenceProcessor class abstracts away from a generational setting
34 // by using only a heap interval (called "span" below), thus allowing
35 // its use in a straightforward manner in a general, non-generational
36 // setting.
37 //
38 // The basic idea is that each ReferenceProcessor object concerns
39 // itself with ("weak") reference processing in a specific "span"
40 // of the heap of interest to a specific collector. Currently,
41 // the span is a convex interval of the heap, but, efficiency
42 // apart, there seems to be no reason it couldn't be extended
43 // (with appropriate modifications) to any "non-convex interval".
44
45 // forward references
46 class ReferencePolicy;
47 class AbstractRefProcTaskExecutor;
48 class DiscoveredList;
49
50 class ReferenceProcessor : public CHeapObj {
51 friend class DiscoveredList;
52 friend class DiscoveredListIterator;
53 protected:
54 // End of list marker
55 static oop _sentinelRef;
56 MemRegion _span; // (right-open) interval of heap
57 // subject to wkref discovery
58 bool _discovering_refs; // true when discovery enabled
59 bool _discovery_is_atomic; // if discovery is atomic wrt
60 // other collectors in configuration
61 bool _discovery_is_mt; // true if reference discovery is MT.
62 bool _enqueuing_is_done; // true if all weak references enqueued
63 bool _processing_is_mt; // true during phases when
64 // reference processing is MT.
65 int _next_id; // round-robin counter in
66 // support of work distribution
67
68 // For collectors that do not keep GC marking information
69 // in the object header, this field holds a closure that
70 // helps the reference processor determine the reachability
71 // of an oop (the field is currently initialized to NULL for
72 // all collectors but the CMS collector).
73 BoolObjectClosure* _is_alive_non_header;
74
75 // The discovered ref lists themselves
76 int _num_q; // the MT'ness degree of the queues below
77 DiscoveredList* _discoveredSoftRefs; // pointer to array of oops
78 DiscoveredList* _discoveredWeakRefs;
79 DiscoveredList* _discoveredFinalRefs;
80 DiscoveredList* _discoveredPhantomRefs;
81
82 public:
83 int num_q() { return _num_q; }
84 DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
85 static oop* sentinel_ref() { return &_sentinelRef; }
86
87 public:
88 // Process references with a certain reachability level.
89 void process_discovered_reflist(DiscoveredList refs_lists[],
90 ReferencePolicy* policy,
91 bool clear_referent,
92 BoolObjectClosure* is_alive,
93 OopClosure* keep_alive,
94 VoidClosure* complete_gc,
95 AbstractRefProcTaskExecutor* task_executor);
96
97 void process_phaseJNI(BoolObjectClosure* is_alive,
98 OopClosure* keep_alive,
99 VoidClosure* complete_gc);
100
101 // Work methods used by the method process_discovered_reflist
102 // Phase1: keep alive all those referents that are otherwise
103 // dead but which must be kept alive by policy (and their closure).
104 void process_phase1(DiscoveredList& refs_list_addr,
105 ReferencePolicy* policy,
106 BoolObjectClosure* is_alive,
107 OopClosure* keep_alive,
108 VoidClosure* complete_gc);
109 // Phase2: remove all those references whose referents are
110 // reachable.
111 inline void process_phase2(DiscoveredList& refs_list_addr,
112 BoolObjectClosure* is_alive,
113 OopClosure* keep_alive,
114 VoidClosure* complete_gc) {
115 if (discovery_is_atomic()) {
116 // complete_gc is ignored in this case for this phase
117 pp2_work(refs_list_addr, is_alive, keep_alive);
118 } else {
119 assert(complete_gc != NULL, "Error");
120 pp2_work_concurrent_discovery(refs_list_addr, is_alive,
121 keep_alive, complete_gc);
122 }
123 }
124 // Work methods in support of process_phase2
125 void pp2_work(DiscoveredList& refs_list_addr,
126 BoolObjectClosure* is_alive,
127 OopClosure* keep_alive);
128 void pp2_work_concurrent_discovery(
129 DiscoveredList& refs_list_addr,
130 BoolObjectClosure* is_alive,
131 OopClosure* keep_alive,
132 VoidClosure* complete_gc);
133 // Phase3: process the referents by either clearing them
134 // or keeping them alive (and their closure)
135 void process_phase3(DiscoveredList& refs_list_addr,
136 bool clear_referent,
137 BoolObjectClosure* is_alive,
138 OopClosure* keep_alive,
139 VoidClosure* complete_gc);
140
141 // Enqueue references with a certain reachability level
142 void enqueue_discovered_reflist(DiscoveredList& refs_list, oop* pending_list_addr);
143
144 // "Preclean" all the discovered reference lists
145 // by removing references with strongly reachable referents.
146 // The first argument is a predicate on an oop that indicates
147 // its (strong) reachability and the second is a closure that
148 // may be used to incrementalize or abort the precleaning process.
149 // The caller is responsible for taking care of potential
150 // interference with concurrent operations on these lists
151 // (or predicates involved) by other threads. Currently
152 // only used by the CMS collector.
153 void preclean_discovered_references(BoolObjectClosure* is_alive,
154 OopClosure* keep_alive,
155 VoidClosure* complete_gc,
156 YieldClosure* yield);
157
158 // Delete entries in the discovered lists that have
159 // either a null referent or are not active. Such
160 // Reference objects can result from the clearing
161 // or enqueueing of Reference objects concurrent
162 // with their discovery by a (concurrent) collector.
163 // For a definition of "active" see java.lang.ref.Reference;
164 // Refs are born active, become inactive when enqueued,
165 // and never become active again. The state of being
166 // active is encoded as follows: A Ref is active
167 // if and only if its "next" field is NULL.
168 void clean_up_discovered_references();
169 void clean_up_discovered_reflist(DiscoveredList& refs_list);
170
171 // Returns the name of the discovered reference list
172 // occupying the i / _num_q slot.
173 const char* list_name(int i);
174
175 protected:
176 // "Preclean" the given discovered reference list
177 // by removing references with strongly reachable referents.
178 // Currently used in support of CMS only.
179 void preclean_discovered_reflist(DiscoveredList& refs_list,
180 BoolObjectClosure* is_alive,
181 OopClosure* keep_alive,
182 VoidClosure* complete_gc,
183 YieldClosure* yield);
184
185 void enqueue_discovered_reflists(oop* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
186 int next_id() {
187 int id = _next_id;
188 if (++_next_id == _num_q) {
189 _next_id = 0;
190 }
191 return id;
192 }
193 DiscoveredList* get_discovered_list(ReferenceType rt);
194 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
195 oop* discovered_addr);
196 void verify_ok_to_handle_reflists() PRODUCT_RETURN;
197
198 void abandon_partial_discovered_list(DiscoveredList& refs_list);
199 void abandon_partial_discovered_list_arr(DiscoveredList refs_lists[]);
200
201 // Calculate the number of jni handles.
202 unsigned int count_jni_refs();
203
204 // Balances reference queues.
205 void balance_queues(DiscoveredList ref_lists[]);
206
207 // Update (advance) the soft ref master clock field.
208 void update_soft_ref_master_clock();
209
210 public:
211 // constructor
212 ReferenceProcessor():
213 _span((HeapWord*)NULL, (HeapWord*)NULL),
214 _discoveredSoftRefs(NULL), _discoveredWeakRefs(NULL),
215 _discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),
216 _discovering_refs(false),
217 _discovery_is_atomic(true),
218 _enqueuing_is_done(false),
219 _discovery_is_mt(false),
220 _is_alive_non_header(NULL),
221 _num_q(0),
222 _processing_is_mt(false),
223 _next_id(0)
224 {}
225
226 ReferenceProcessor(MemRegion span, bool atomic_discovery,
227 bool mt_discovery, int mt_degree = 1,
228 bool mt_processing = false);
229
230 // Allocates and initializes a reference processor.
231 static ReferenceProcessor* create_ref_processor(
232 MemRegion span,
233 bool atomic_discovery,
234 bool mt_discovery,
235 BoolObjectClosure* is_alive_non_header = NULL,
236 int parallel_gc_threads = 1,
237 bool mt_processing = false);
238
239 // RefDiscoveryPolicy values
240 enum {
241 ReferenceBasedDiscovery = 0,
242 ReferentBasedDiscovery = 1
243 };
244
245 static void init_statics();
246
247 public:
248 // get and set "is_alive_non_header" field
249 BoolObjectClosure* is_alive_non_header() {
250 return _is_alive_non_header;
251 }
252 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
253 _is_alive_non_header = is_alive_non_header;
254 }
255
256 // get and set span
257 MemRegion span() { return _span; }
258 void set_span(MemRegion span) { _span = span; }
259
260 // start and stop weak ref discovery
261 void enable_discovery() { _discovering_refs = true; }
262 void disable_discovery() { _discovering_refs = false; }
263 bool discovery_enabled() { return _discovering_refs; }
264
265 // whether discovery is atomic wrt other collectors
266 bool discovery_is_atomic() const { return _discovery_is_atomic; }
267 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
268
269 // whether discovery is done by multiple threads same-old-timeously
270 bool discovery_is_mt() const { return _discovery_is_mt; }
271 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
272
273 // Whether we are in a phase when _processing_ is MT.
274 bool processing_is_mt() const { return _processing_is_mt; }
275 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
276
277 // whether all enqueuing of weak references is complete
278 bool enqueuing_is_done() { return _enqueuing_is_done; }
279 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
280
281 // iterate over oops
282 void weak_oops_do(OopClosure* f); // weak roots
283 static void oops_do(OopClosure* f); // strong root(s)
284
285 // Discover a Reference object, using appropriate discovery criteria
286 bool discover_reference(oop obj, ReferenceType rt);
287
288 // Process references found during GC (called by the garbage collector)
289 void process_discovered_references(ReferencePolicy* policy,
290 BoolObjectClosure* is_alive,
291 OopClosure* keep_alive,
292 VoidClosure* complete_gc,
293 AbstractRefProcTaskExecutor* task_executor);
294
295 public:
296 // Enqueue references at end of GC (called by the garbage collector)
297 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
298
299 // debugging
300 void verify_no_references_recorded() PRODUCT_RETURN;
301 static void verify();
302
303 // clear the discovered lists (unlinking each entry).
304 void clear_discovered_references() PRODUCT_RETURN;
305 };
306
307 // A utility class to disable reference discovery in
308 // the scope which contains it, for given ReferenceProcessor.
309 class NoRefDiscovery: StackObj {
310 private:
311 ReferenceProcessor* _rp;
312 bool _was_discovering_refs;
313 public:
314 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
315 if (_was_discovering_refs = _rp->discovery_enabled()) {
316 _rp->disable_discovery();
317 }
318 }
319
320 ~NoRefDiscovery() {
321 if (_was_discovering_refs) {
322 _rp->enable_discovery();
323 }
324 }
325 };
326
327
328 // A utility class to temporarily mutate the span of the
329 // given ReferenceProcessor in the scope that contains it.
330 class ReferenceProcessorSpanMutator: StackObj {
331 private:
332 ReferenceProcessor* _rp;
333 MemRegion _saved_span;
334
335 public:
336 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
337 MemRegion span):
338 _rp(rp) {
339 _saved_span = _rp->span();
340 _rp->set_span(span);
341 }
342
343 ~ReferenceProcessorSpanMutator() {
344 _rp->set_span(_saved_span);
345 }
346 };
347
348 // A utility class to temporarily change the MT'ness of
349 // reference discovery for the given ReferenceProcessor
350 // in the scope that contains it.
351 class ReferenceProcessorMTMutator: StackObj {
352 private:
353 ReferenceProcessor* _rp;
354 bool _saved_mt;
355
356 public:
357 ReferenceProcessorMTMutator(ReferenceProcessor* rp,
358 bool mt):
359 _rp(rp) {
360 _saved_mt = _rp->discovery_is_mt();
361 _rp->set_mt_discovery(mt);
362 }
363
364 ~ReferenceProcessorMTMutator() {
365 _rp->set_mt_discovery(_saved_mt);
366 }
367 };
368
369
370 // A utility class to temporarily change the disposition
371 // of the "is_alive_non_header" closure field of the
372 // given ReferenceProcessor in the scope that contains it.
373 class ReferenceProcessorIsAliveMutator: StackObj {
374 private:
375 ReferenceProcessor* _rp;
376 BoolObjectClosure* _saved_cl;
377
378 public:
379 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
380 BoolObjectClosure* cl):
381 _rp(rp) {
382 _saved_cl = _rp->is_alive_non_header();
383 _rp->set_is_alive_non_header(cl);
384 }
385
386 ~ReferenceProcessorIsAliveMutator() {
387 _rp->set_is_alive_non_header(_saved_cl);
388 }
389 };
390
391 // A utility class to temporarily change the disposition
392 // of the "discovery_is_atomic" field of the
393 // given ReferenceProcessor in the scope that contains it.
394 class ReferenceProcessorAtomicMutator: StackObj {
395 private:
396 ReferenceProcessor* _rp;
397 bool _saved_atomic_discovery;
398
399 public:
400 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
401 bool atomic):
402 _rp(rp) {
403 _saved_atomic_discovery = _rp->discovery_is_atomic();
404 _rp->set_atomic_discovery(atomic);
405 }
406
407 ~ReferenceProcessorAtomicMutator() {
408 _rp->set_atomic_discovery(_saved_atomic_discovery);
409 }
410 };
411
412
413 // A utility class to temporarily change the MT processing
414 // disposition of the given ReferenceProcessor instance
415 // in the scope that contains it.
416 class ReferenceProcessorMTProcMutator: StackObj {
417 private:
418 ReferenceProcessor* _rp;
419 bool _saved_mt;
420
421 public:
422 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
423 bool mt):
424 _rp(rp) {
425 _saved_mt = _rp->processing_is_mt();
426 _rp->set_mt_processing(mt);
427 }
428
429 ~ReferenceProcessorMTProcMutator() {
430 _rp->set_mt_processing(_saved_mt);
431 }
432 };
433
434
435 // This class is an interface used to implement task execution for the
436 // reference processing.
437 class AbstractRefProcTaskExecutor {
438 public:
439
440 // Abstract tasks to execute.
441 class ProcessTask;
442 class EnqueueTask;
443
444 // Executes a task using worker threads.
445 virtual void execute(ProcessTask& task) = 0;
446 virtual void execute(EnqueueTask& task) = 0;
447
448 // Switch to single threaded mode.
449 virtual void set_single_threaded_mode() { };
450 };
451
452 // Abstract reference processing task to execute.
453 class AbstractRefProcTaskExecutor::ProcessTask {
454 protected:
455 ProcessTask(ReferenceProcessor& ref_processor,
456 DiscoveredList refs_lists[],
457 bool marks_oops_alive)
458 : _ref_processor(ref_processor),
459 _refs_lists(refs_lists),
460 _marks_oops_alive(marks_oops_alive)
461 { }
462
463 public:
464 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
465 OopClosure& keep_alive,
466 VoidClosure& complete_gc) = 0;
467
468 // Returns true if a task marks some oops as alive.
469 bool marks_oops_alive() const
470 { return _marks_oops_alive; }
471
472 protected:
473 ReferenceProcessor& _ref_processor;
474 DiscoveredList* _refs_lists;
475 const bool _marks_oops_alive;
476 };
477
478 // Abstract reference processing task to execute.
479 class AbstractRefProcTaskExecutor::EnqueueTask {
480 protected:
481 EnqueueTask(ReferenceProcessor& ref_processor,
482 DiscoveredList refs_lists[],
483 oop* pending_list_addr,
484 oop sentinel_ref,
485 int n_queues)
486 : _ref_processor(ref_processor),
487 _refs_lists(refs_lists),
488 _pending_list_addr(pending_list_addr),
489 _sentinel_ref(sentinel_ref),
490 _n_queues(n_queues)
491 { }
492
493 public:
494 virtual void work(unsigned int work_id) = 0;
495
496 protected:
497 ReferenceProcessor& _ref_processor;
498 DiscoveredList* _refs_lists;
499 oop* _pending_list_addr;
500 oop _sentinel_ref;
501 int _n_queues;
502 };
503