1 /*
2 * Copyright (c) 2015, 2019, 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 #include "precompiled.hpp"
25 #include "classfile/javaClasses.inline.hpp"
26 #include "gc/shared/referencePolicy.hpp"
27 #include "gc/shared/referenceProcessorStats.hpp"
28 #include "gc/z/zHeap.inline.hpp"
29 #include "gc/z/zOopClosures.inline.hpp"
30 #include "gc/z/zReferenceProcessor.hpp"
31 #include "gc/z/zStat.hpp"
32 #include "gc/z/zTask.hpp"
33 #include "gc/z/zTracer.inline.hpp"
34 #include "gc/z/zUtils.inline.hpp"
35 #include "gc/z/zValue.inline.hpp"
36 #include "memory/universe.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "runtime/os.hpp"
39
40 static const ZStatSubPhase ZSubPhaseConcurrentReferencesProcess("Concurrent References Process");
41 static const ZStatSubPhase ZSubPhaseConcurrentReferencesEnqueue("Concurrent References Enqueue");
42
43 static ReferenceType reference_type(oop reference) {
44 return InstanceKlass::cast(reference->klass())->reference_type();
45 }
46
47 static const char* reference_type_name(ReferenceType type) {
48 switch (type) {
49 case REF_SOFT:
50 return "Soft";
51
52 case REF_WEAK:
53 return "Weak";
54
55 case REF_FINAL:
56 return "Final";
57
58 case REF_PHANTOM:
59 return "Phantom";
60
61 default:
62 ShouldNotReachHere();
63 return NULL;
64 }
65 }
66
67 static volatile oop* reference_referent_addr(oop reference) {
68 return (volatile oop*)java_lang_ref_Reference::referent_addr_raw(reference);
69 }
70
71 static oop reference_referent(oop reference) {
72 return *reference_referent_addr(reference);
73 }
74
75 static void reference_set_referent(oop reference, oop referent) {
76 java_lang_ref_Reference::set_referent_raw(reference, referent);
77 }
78
79 static oop* reference_discovered_addr(oop reference) {
80 return (oop*)java_lang_ref_Reference::discovered_addr_raw(reference);
81 }
82
83 static oop reference_discovered(oop reference) {
84 return *reference_discovered_addr(reference);
85 }
86
87 static void reference_set_discovered(oop reference, oop discovered) {
88 java_lang_ref_Reference::set_discovered_raw(reference, discovered);
89 }
90
91 static oop* reference_next_addr(oop reference) {
92 return (oop*)java_lang_ref_Reference::next_addr_raw(reference);
93 }
94
95 static oop reference_next(oop reference) {
96 return *reference_next_addr(reference);
97 }
98
99 static void reference_set_next(oop reference, oop next) {
100 java_lang_ref_Reference::set_next_raw(reference, next);
101 }
102
103 static void soft_reference_update_clock() {
104 const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
105 java_lang_ref_SoftReference::set_clock(now);
106 }
107
108 ZReferenceProcessor::ZReferenceProcessor(ZWorkers* workers) :
109 _workers(workers),
110 _soft_reference_policy(NULL),
111 _encountered_count(),
112 _discovered_count(),
113 _enqueued_count(),
114 _discovered_list(NULL),
115 _pending_list(NULL),
116 _pending_list_tail(_pending_list.addr()) {}
117
118 void ZReferenceProcessor::set_soft_reference_policy(bool clear) {
119 static AlwaysClearPolicy always_clear_policy;
120 static LRUMaxHeapPolicy lru_max_heap_policy;
121
122 if (clear) {
123 log_info(gc, ref)("Clearing All SoftReferences");
124 _soft_reference_policy = &always_clear_policy;
125 } else {
126 _soft_reference_policy = &lru_max_heap_policy;
127 }
128
129 _soft_reference_policy->setup();
130 }
131
132 bool ZReferenceProcessor::is_inactive(oop reference, oop referent, ReferenceType type) const {
133 if (type == REF_FINAL) {
134 // A FinalReference is inactive if its next field is non-null. An application can't
135 // call enqueue() or clear() on a FinalReference.
136 return reference_next(reference) != NULL;
137 } else {
138 // A non-FinalReference is inactive if the referent is null. The referent can only
139 // be null if the application called Reference.enqueue() or Reference.clear().
140 return referent == NULL;
141 }
142 }
143
144 bool ZReferenceProcessor::is_strongly_live(oop referent) const {
145 return ZHeap::heap()->is_object_strongly_live(ZOop::to_address(referent));
146 }
147
148 bool ZReferenceProcessor::is_softly_live(oop reference, ReferenceType type) const {
149 if (type != REF_SOFT) {
150 // Not a SoftReference
151 return false;
152 }
153
154 // Ask SoftReference policy
155 const jlong clock = java_lang_ref_SoftReference::clock();
156 assert(clock != 0, "Clock not initialized");
157 assert(_soft_reference_policy != NULL, "Policy not initialized");
158 return !_soft_reference_policy->should_clear_reference(reference, clock);
159 }
160
161 bool ZReferenceProcessor::should_discover(oop reference, ReferenceType type) const {
162 volatile oop* const referent_addr = reference_referent_addr(reference);
163 const oop referent = ZBarrier::weak_load_barrier_on_oop_field(referent_addr);
164
165 if (is_inactive(reference, referent, type)) {
166 return false;
167 }
168
169 if (is_strongly_live(referent)) {
170 return false;
171 }
172
173 if (is_softly_live(reference, type)) {
174 return false;
175 }
176
177 // PhantomReferences with finalizable marked referents should technically not have
178 // to be discovered. However, InstanceRefKlass::oop_oop_iterate_ref_processing()
179 // does not know about the finalizable mark concept, and will therefore mark
180 // referents in non-discovered PhantomReferences as strongly live. To prevent
181 // this, we always discover PhantomReferences with finalizable marked referents.
182 // They will automatically be dropped during the reference processing phase.
183 return true;
184 }
185
186 bool ZReferenceProcessor::should_drop(oop reference, ReferenceType type) const {
187 // This check is racing with a call to Reference.clear() from the application.
188 // If the application clears the reference after this check it will still end
189 // up on the pending list, and there's nothing we can do about that without
190 // changing the Reference.clear() API. This check is also racing with a call
191 // to Reference.enqueue() from the application, which is unproblematic, since
192 // the application wants the reference to be enqueued anyway.
193 const oop referent = reference_referent(reference);
194 if (referent == NULL) {
195 // Reference has been cleared, by a call to Reference.enqueue()
196 // or Reference.clear() from the application, which means we
197 // should drop the reference.
198 return true;
199 }
200
201 // Check if the referent is still alive, in which case we should
202 // drop the reference.
203 if (type == REF_PHANTOM) {
204 return ZBarrier::is_alive_barrier_on_phantom_oop(referent);
205 } else {
206 return ZBarrier::is_alive_barrier_on_weak_oop(referent);
207 }
208 }
209
210 void ZReferenceProcessor::keep_alive(oop reference, ReferenceType type) const {
211 volatile oop* const p = reference_referent_addr(reference);
212 if (type == REF_PHANTOM) {
213 ZBarrier::keep_alive_barrier_on_phantom_oop_field(p);
214 } else {
215 ZBarrier::keep_alive_barrier_on_weak_oop_field(p);
216 }
217 }
218
219 void ZReferenceProcessor::make_inactive(oop reference, ReferenceType type) const {
220 if (type == REF_FINAL) {
221 // Don't clear referent. It is needed by the Finalizer thread to make the call
222 // to finalize(). A FinalReference is instead made inactive by self-looping the
223 // next field. An application can't call FinalReference.enqueue(), so there is
224 // no race to worry about when setting the next field.
225 assert(reference_next(reference) == NULL, "Already inactive");
226 reference_set_next(reference, reference);
227 } else {
228 // Clear referent
229 reference_set_referent(reference, NULL);
230 }
231 }
232
233 void ZReferenceProcessor::discover(oop reference, ReferenceType type) {
234 log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
235
236 // Update statistics
237 _discovered_count.get()[type]++;
238
239 if (type == REF_FINAL) {
240 // Mark referent (and its reachable subgraph) finalizable. This avoids
241 // the problem of later having to mark those objects if the referent is
242 // still final reachable during processing.
243 volatile oop* const referent_addr = reference_referent_addr(reference);
244 ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);
245 }
246
247 // Add reference to discovered list
248 assert(reference_discovered(reference) == NULL, "Already discovered");
249 oop* const list = _discovered_list.addr();
250 reference_set_discovered(reference, *list);
251 *list = reference;
252 }
253
254 bool ZReferenceProcessor::discover_reference(oop reference, ReferenceType type) {
255 if (!RegisterReferences) {
256 // Reference processing disabled
257 return false;
258 }
259
260 log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
261
262 // Update statistics
263 _encountered_count.get()[type]++;
264
265 if (!should_discover(reference, type)) {
266 // Not discovered
267 return false;
268 }
269
270 discover(reference, type);
271
272 // Discovered
273 return true;
274 }
275
276 oop ZReferenceProcessor::drop(oop reference, ReferenceType type) {
277 log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
278
279 // Keep referent alive
280 keep_alive(reference, type);
281
282 // Unlink and return next in list
283 const oop next = reference_discovered(reference);
284 reference_set_discovered(reference, NULL);
285 return next;
286 }
287
288 oop* ZReferenceProcessor::keep(oop reference, ReferenceType type) {
289 log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
290
291 // Update statistics
292 _enqueued_count.get()[type]++;
293
294 // Make reference inactive
295 make_inactive(reference, type);
296
297 // Return next in list
298 return reference_discovered_addr(reference);
299 }
300
301 void ZReferenceProcessor::work() {
302 // Process discovered references
303 oop* const list = _discovered_list.addr();
304 oop* p = list;
305
306 while (*p != NULL) {
307 const oop reference = *p;
308 const ReferenceType type = reference_type(reference);
309
310 if (should_drop(reference, type)) {
311 *p = drop(reference, type);
312 } else {
313 p = keep(reference, type);
314 }
315 }
316
317 // Prepend discovered references to internal pending list
318 if (*list != NULL) {
319 *p = Atomic::xchg(_pending_list.addr(), *list);
320 if (*p == NULL) {
321 // First to prepend to list, record tail
322 _pending_list_tail = p;
323 }
324
325 // Clear discovered list
326 *list = NULL;
327 }
328 }
329
330 bool ZReferenceProcessor::is_empty() const {
331 ZPerWorkerConstIterator<oop> iter(&_discovered_list);
332 for (const oop* list; iter.next(&list);) {
333 if (*list != NULL) {
334 return false;
335 }
336 }
337
338 if (_pending_list.get() != NULL) {
339 return false;
340 }
341
342 return true;
343 }
344
345 void ZReferenceProcessor::reset_statistics() {
346 assert(is_empty(), "Should be empty");
347
348 // Reset encountered
349 ZPerWorkerIterator<Counters> iter_encountered(&_encountered_count);
350 for (Counters* counters; iter_encountered.next(&counters);) {
351 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
352 (*counters)[i] = 0;
353 }
354 }
355
356 // Reset discovered
357 ZPerWorkerIterator<Counters> iter_discovered(&_discovered_count);
358 for (Counters* counters; iter_discovered.next(&counters);) {
359 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
360 (*counters)[i] = 0;
361 }
362 }
363
364 // Reset enqueued
365 ZPerWorkerIterator<Counters> iter_enqueued(&_enqueued_count);
366 for (Counters* counters; iter_enqueued.next(&counters);) {
367 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
368 (*counters)[i] = 0;
369 }
370 }
371 }
372
373 void ZReferenceProcessor::collect_statistics() {
374 Counters encountered = {};
375 Counters discovered = {};
376 Counters enqueued = {};
377
378 // Sum encountered
379 ZPerWorkerConstIterator<Counters> iter_encountered(&_encountered_count);
380 for (const Counters* counters; iter_encountered.next(&counters);) {
381 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
382 encountered[i] += (*counters)[i];
383 }
384 }
385
386 // Sum discovered
387 ZPerWorkerConstIterator<Counters> iter_discovered(&_discovered_count);
388 for (const Counters* counters; iter_discovered.next(&counters);) {
389 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
390 discovered[i] += (*counters)[i];
391 }
392 }
393
394 // Sum enqueued
395 ZPerWorkerConstIterator<Counters> iter_enqueued(&_enqueued_count);
396 for (const Counters* counters; iter_enqueued.next(&counters);) {
397 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
398 enqueued[i] += (*counters)[i];
399 }
400 }
401
402 // Update statistics
403 ZStatReferences::set_soft(encountered[REF_SOFT], discovered[REF_SOFT], enqueued[REF_SOFT]);
404 ZStatReferences::set_weak(encountered[REF_WEAK], discovered[REF_WEAK], enqueued[REF_WEAK]);
405 ZStatReferences::set_final(encountered[REF_FINAL], discovered[REF_FINAL], enqueued[REF_FINAL]);
406 ZStatReferences::set_phantom(encountered[REF_PHANTOM], discovered[REF_PHANTOM], enqueued[REF_PHANTOM]);
407
408 // Trace statistics
409 const ReferenceProcessorStats stats(discovered[REF_SOFT],
410 discovered[REF_WEAK],
411 discovered[REF_FINAL],
412 discovered[REF_PHANTOM]);
413 ZTracer::tracer()->report_gc_reference_stats(stats);
414 }
415
416 class ZReferenceProcessorTask : public ZTask {
417 private:
418 ZReferenceProcessor* const _reference_processor;
419
420 public:
421 ZReferenceProcessorTask(ZReferenceProcessor* reference_processor) :
422 ZTask("ZReferenceProcessorTask"),
423 _reference_processor(reference_processor) {}
424
425 virtual void work() {
426 _reference_processor->work();
427 }
428 };
429
430 void ZReferenceProcessor::process_references() {
431 ZStatTimer timer(ZSubPhaseConcurrentReferencesProcess);
432
433 // Process discovered lists
434 ZReferenceProcessorTask task(this);
435 _workers->run_concurrent(&task);
436
437 // Update SoftReference clock
438 soft_reference_update_clock();
439
440 // Collect, log and trace statistics
441 collect_statistics();
442 }
443
444 void ZReferenceProcessor::enqueue_references() {
445 ZStatTimer timer(ZSubPhaseConcurrentReferencesEnqueue);
446
447 if (_pending_list.get() == NULL) {
448 // Nothing to enqueue
449 return;
450 }
451
452 {
453 // Heap_lock protects external pending list
454 MonitorLocker ml(Heap_lock);
455
456 // Prepend internal pending list to external pending list
457 *_pending_list_tail = Universe::swap_reference_pending_list(_pending_list.get());
458
459 // Notify ReferenceHandler thread
460 ml.notify_all();
461 }
462
463 // Reset internal pending list
464 _pending_list.set(NULL);
465 _pending_list_tail = _pending_list.addr();
466 }