1 /*
2 * Copyright (c) 2015, 2018, 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 "memory/universe.hpp"
36 #include "runtime/mutexLocker.hpp"
37 #include "runtime/os.hpp"
38
39 static const ZStatSubPhase ZSubPhaseConcurrentReferencesProcess("Concurrent References Process");
40 static const ZStatSubPhase ZSubPhaseConcurrentReferencesEnqueue("Concurrent References Enqueue");
41
42 ZReferenceProcessor::ZReferenceProcessor(ZWorkers* workers) :
43 _workers(workers),
44 _soft_reference_policy(NULL),
45 _encountered_count(),
46 _discovered_count(),
47 _enqueued_count(),
48 _discovered_list(NULL),
49 _pending_list(NULL),
50 _pending_list_tail(_pending_list.addr()) {}
51
52 void ZReferenceProcessor::set_soft_reference_policy(bool clear) {
53 static AlwaysClearPolicy always_clear_policy;
54 static LRUMaxHeapPolicy lru_max_heap_policy;
55
56 if (clear) {
57 log_info(gc, ref)("Clearing All Soft References");
58 _soft_reference_policy = &always_clear_policy;
59 } else {
60 _soft_reference_policy = &lru_max_heap_policy;
61 }
62
63 _soft_reference_policy->setup();
64 }
65
66 void ZReferenceProcessor::update_soft_reference_clock() const {
67 const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
68 java_lang_ref_SoftReference::set_clock(now);
69 }
70
71 bool ZReferenceProcessor::is_reference_inactive(oop obj) const {
72 // A non-null next field means the reference is inactive
73 return java_lang_ref_Reference::next(obj) != NULL;
74 }
75
76 ReferenceType ZReferenceProcessor::reference_type(oop obj) const {
77 return InstanceKlass::cast(obj->klass())->reference_type();
78 }
79
80 const char* ZReferenceProcessor::reference_type_name(ReferenceType type) const {
81 switch (type) {
82 case REF_SOFT:
83 return "Soft";
84
85 case REF_WEAK:
86 return "Weak";
87
88 case REF_FINAL:
89 return "Final";
90
91 case REF_PHANTOM:
92 return "Phantom";
93
94 default:
95 ShouldNotReachHere();
96 return NULL;
97 }
98 }
99
100 volatile oop* ZReferenceProcessor::reference_referent_addr(oop obj) const {
101 return (volatile oop*)java_lang_ref_Reference::referent_addr_raw(obj);
102 }
103
104 oop ZReferenceProcessor::reference_referent(oop obj) const {
105 return *reference_referent_addr(obj);
106 }
107
108 bool ZReferenceProcessor::is_referent_alive_or_null(oop obj, ReferenceType type) const {
109 volatile oop* const p = reference_referent_addr(obj);
110
111 // Check if the referent is alive or null, in which case we don't want to discover
112 // the reference. It can only be null if the application called Reference.enqueue()
113 // or Reference.clear().
114 if (type == REF_PHANTOM) {
115 const oop o = ZBarrier::weak_load_barrier_on_phantom_oop_field(p);
116 return o == NULL || ZHeap::heap()->is_object_live(ZOop::to_address(o));
117 } else {
118 const oop o = ZBarrier::weak_load_barrier_on_weak_oop_field(p);
119 return o == NULL || ZHeap::heap()->is_object_strongly_live(ZOop::to_address(o));
120 }
121 }
122
123 bool ZReferenceProcessor::is_referent_softly_alive(oop obj, ReferenceType type) const {
124 if (type != REF_SOFT) {
125 // Not a soft reference
126 return false;
127 }
128
129 // Ask soft reference policy
130 const jlong clock = java_lang_ref_SoftReference::clock();
131 assert(clock != 0, "Clock not initialized");
132 assert(_soft_reference_policy != NULL, "Policy not initialized");
133 return !_soft_reference_policy->should_clear_reference(obj, clock);
134 }
135
136 bool ZReferenceProcessor::should_drop_reference(oop obj, ReferenceType type) const {
137 // This check is racing with a call to Reference.clear() from the application.
138 // If the application clears the reference after this check it will still end
139 // up on the pending list, and there's nothing we can do about that without
140 // changing the Reference.clear() API. This check is also racing with a call
141 // to Reference.enqueue() from the application, which is unproblematic, since
142 // the application wants the reference to be enqueued anyway.
143 const oop o = reference_referent(obj);
144 if (o == NULL) {
145 // Reference has been cleared, by a call to Reference.enqueue()
146 // or Reference.clear() from the application, which means we
147 // should drop the reference.
148 return true;
149 }
150
151 // Check if the referent is still alive, in which case we should
152 // drop the reference.
153 if (type == REF_PHANTOM) {
154 return ZBarrier::is_alive_barrier_on_phantom_oop(o);
155 } else {
156 return ZBarrier::is_alive_barrier_on_weak_oop(o);
157 }
158 }
159
160 bool ZReferenceProcessor::should_mark_referent(ReferenceType type) const {
161 // Referents of final references (and its reachable sub graph) are
162 // always marked finalizable during discovery. This avoids the problem
163 // of later having to mark those objects if the referent is still final
164 // reachable during processing.
165 return type == REF_FINAL;
166 }
167
168 bool ZReferenceProcessor::should_clear_referent(ReferenceType type) const {
169 // Referents that were not marked must be cleared
170 return !should_mark_referent(type);
171 }
172
173 void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const {
174 volatile oop* const p = reference_referent_addr(obj);
175 if (type == REF_PHANTOM) {
176 ZBarrier::keep_alive_barrier_on_phantom_oop_field(p);
177 } else {
178 ZBarrier::keep_alive_barrier_on_weak_oop_field(p);
179 }
180 }
181
182 bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {
183 if (!RegisterReferences) {
184 // Reference processing disabled
185 return false;
186 }
187
188 log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
189
190 // Update statistics
191 _encountered_count.get()[type]++;
192
193 if (is_reference_inactive(obj) ||
194 is_referent_alive_or_null(obj, type) ||
195 is_referent_softly_alive(obj, type)) {
196 // Not discovered
197 return false;
198 }
199
200 discover(obj, type);
201
202 // Discovered
203 return true;
204 }
205
206 void ZReferenceProcessor::discover(oop obj, ReferenceType type) {
207 log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
208
209 // Update statistics
210 _discovered_count.get()[type]++;
211
212 // Mark referent finalizable
213 if (should_mark_referent(type)) {
214 oop* const referent_addr = (oop*)java_lang_ref_Reference::referent_addr_raw(obj);
215 ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);
216 }
217
218 // Add reference to discovered list
219 assert(java_lang_ref_Reference::discovered(obj) == NULL, "Already discovered");
220 oop* const list = _discovered_list.addr();
221 java_lang_ref_Reference::set_discovered(obj, *list);
222 *list = obj;
223 }
224
225 oop ZReferenceProcessor::drop(oop obj, ReferenceType type) {
226 log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
227
228 // Keep referent alive
229 keep_referent_alive(obj, type);
230
231 // Unlink and return next in list
232 const oop next = java_lang_ref_Reference::discovered(obj);
233 java_lang_ref_Reference::set_discovered(obj, NULL);
234 return next;
235 }
236
237 oop* ZReferenceProcessor::keep(oop obj, ReferenceType type) {
238 log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
239
240 // Update statistics
241 _enqueued_count.get()[type]++;
242
243 // Clear referent
244 if (should_clear_referent(type)) {
245 java_lang_ref_Reference::set_referent(obj, NULL);
246 }
247
248 // Make reference inactive by self-looping the next field. We could be racing with a
249 // call to Reference.enqueue() from the application, which is why we are using a CAS
250 // to make sure we change the next field only if it is NULL. A failing CAS means the
251 // reference has already been enqueued. However, we don't check the result of the CAS,
252 // since we still have no option other than keeping the reference on the pending list.
253 // It's ok to have the reference both on the pending list and enqueued at the same
254 // time (the pending list is linked through the discovered field, while the reference
255 // queue is linked through the next field). When the ReferenceHandler thread later
256 // calls Reference.enqueue() we detect that it has already been enqueued and drop it.
257 oop* const next_addr = (oop*)java_lang_ref_Reference::next_addr_raw(obj);
258 Atomic::cmpxchg(obj, next_addr, oop(NULL));
259
260 // Return next in list
261 return (oop*)java_lang_ref_Reference::discovered_addr_raw(obj);
262 }
263
264 void ZReferenceProcessor::work() {
265 // Process discovered references
266 oop* const list = _discovered_list.addr();
267 oop* p = list;
268
269 while (*p != NULL) {
270 const oop obj = *p;
271 const ReferenceType type = reference_type(obj);
272
273 if (should_drop_reference(obj, type)) {
274 *p = drop(obj, type);
275 } else {
276 p = keep(obj, type);
277 }
278 }
279
280 // Prepend discovered references to internal pending list
281 if (*list != NULL) {
282 *p = Atomic::xchg(*list, _pending_list.addr());
283 if (*p == NULL) {
284 // First to prepend to list, record tail
285 _pending_list_tail = p;
286 }
287
288 // Clear discovered list
289 *list = NULL;
290 }
291 }
292
293 bool ZReferenceProcessor::is_empty() const {
294 ZPerWorkerConstIterator<oop> iter(&_discovered_list);
295 for (const oop* list; iter.next(&list);) {
296 if (*list != NULL) {
297 return false;
298 }
299 }
300
301 if (_pending_list.get() != NULL) {
302 return false;
303 }
304
305 return true;
306 }
307
308 void ZReferenceProcessor::reset_statistics() {
309 assert(is_empty(), "Should be empty");
310
311 // Reset encountered
312 ZPerWorkerIterator<Counters> iter_encountered(&_encountered_count);
313 for (Counters* counters; iter_encountered.next(&counters);) {
314 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
315 (*counters)[i] = 0;
316 }
317 }
318
319 // Reset discovered
320 ZPerWorkerIterator<Counters> iter_discovered(&_discovered_count);
321 for (Counters* counters; iter_discovered.next(&counters);) {
322 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
323 (*counters)[i] = 0;
324 }
325 }
326
327 // Reset enqueued
328 ZPerWorkerIterator<Counters> iter_enqueued(&_enqueued_count);
329 for (Counters* counters; iter_enqueued.next(&counters);) {
330 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
331 (*counters)[i] = 0;
332 }
333 }
334 }
335
336 void ZReferenceProcessor::collect_statistics() {
337 Counters encountered = {};
338 Counters discovered = {};
339 Counters enqueued = {};
340
341 // Sum encountered
342 ZPerWorkerConstIterator<Counters> iter_encountered(&_encountered_count);
343 for (const Counters* counters; iter_encountered.next(&counters);) {
344 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
345 encountered[i] += (*counters)[i];
346 }
347 }
348
349 // Sum discovered
350 ZPerWorkerConstIterator<Counters> iter_discovered(&_discovered_count);
351 for (const Counters* counters; iter_discovered.next(&counters);) {
352 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
353 discovered[i] += (*counters)[i];
354 }
355 }
356
357 // Sum enqueued
358 ZPerWorkerConstIterator<Counters> iter_enqueued(&_enqueued_count);
359 for (const Counters* counters; iter_enqueued.next(&counters);) {
360 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
361 enqueued[i] += (*counters)[i];
362 }
363 }
364
365 // Update statistics
366 ZStatReferences::set_soft(encountered[REF_SOFT], discovered[REF_SOFT], enqueued[REF_SOFT]);
367 ZStatReferences::set_weak(encountered[REF_WEAK], discovered[REF_WEAK], enqueued[REF_WEAK]);
368 ZStatReferences::set_final(encountered[REF_FINAL], discovered[REF_FINAL], enqueued[REF_FINAL]);
369 ZStatReferences::set_phantom(encountered[REF_PHANTOM], discovered[REF_PHANTOM], enqueued[REF_PHANTOM]);
370
371 // Trace statistics
372 const ReferenceProcessorStats stats(discovered[REF_SOFT],
373 discovered[REF_WEAK],
374 discovered[REF_FINAL],
375 discovered[REF_PHANTOM]);
376 ZTracer::tracer()->report_gc_reference_stats(stats);
377 }
378
379 class ZReferenceProcessorTask : public ZTask {
380 private:
381 ZReferenceProcessor* const _reference_processor;
382
383 public:
384 ZReferenceProcessorTask(ZReferenceProcessor* reference_processor) :
385 ZTask("ZReferenceProcessorTask"),
386 _reference_processor(reference_processor) {}
387
388 virtual void work() {
389 _reference_processor->work();
390 }
391 };
392
393 void ZReferenceProcessor::process_references() {
394 ZStatTimer timer(ZSubPhaseConcurrentReferencesProcess);
395
396 // Process discovered lists
397 ZReferenceProcessorTask task(this);
398 _workers->run_concurrent(&task);
399
400 // Update soft reference clock
401 update_soft_reference_clock();
402
403 // Collect, log and trace statistics
404 collect_statistics();
405 }
406
407 void ZReferenceProcessor::enqueue_references() {
408 ZStatTimer timer(ZSubPhaseConcurrentReferencesEnqueue);
409
410 if (_pending_list.get() == NULL) {
411 // Nothing to enqueue
412 return;
413 }
414
415 {
416 // Heap_lock protects external pending list
417 MonitorLockerEx ml(Heap_lock);
418
419 // Prepend internal pending list to external pending list
420 *_pending_list_tail = Universe::swap_reference_pending_list(_pending_list.get());
421
422 // Notify ReferenceHandler thread
423 ml.notify_all();
424 }
425
426 // Reset internal pending list
427 _pending_list.set(NULL);
428 _pending_list_tail = _pending_list.addr();
429 }