1 /*
2 * Copyright (c) 2015, 2017, 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 volatile oop* ZReferenceProcessor::reference_referent_addr(oop obj) const {
81 return (volatile oop*)java_lang_ref_Reference::referent_addr(obj);
82 }
83
84 oop ZReferenceProcessor::reference_referent(oop obj) const {
85 return *reference_referent_addr(obj);
86 }
87
88 bool ZReferenceProcessor::is_referent_alive_or_null(oop obj, ReferenceType type) const {
89 volatile oop* const p = reference_referent_addr(obj);
90
91 // Check if the referent is alive or null, in which case we don't want to discover
92 // the reference. It can only be null if the application called Reference.clear().
93 if (type == REF_PHANTOM) {
94 const oop o = ZBarrier::weak_load_barrier_on_phantom_oop_field(p);
95 return o == NULL || ZHeap::heap()->is_object_live(ZOop::to_address(o));
96 } else {
97 const oop o = ZBarrier::weak_load_barrier_on_weak_oop_field(p);
98 return o == NULL || ZHeap::heap()->is_object_strongly_live(ZOop::to_address(o));
99 }
100 }
101
102 bool ZReferenceProcessor::is_referent_softly_alive(oop obj, ReferenceType type) const {
103 if (type != REF_SOFT) {
104 // Not a soft reference
105 return false;
106 }
107
108 // Ask soft reference policy
109 const jlong clock = java_lang_ref_SoftReference::clock();
110 assert(clock != 0, "Clock not initialized");
111 assert(_soft_reference_policy != NULL, "Policy not initialized");
112 return !_soft_reference_policy->should_clear_reference(obj, clock);
113 }
114
115 bool ZReferenceProcessor::should_drop_reference(oop obj, ReferenceType type) const {
116 // This check is racing with a call to Reference.clear() from the application.
117 // If the application clears the reference after this check it will still end
118 // up on the pending list, and there's nothing we can do about that without
119 // changing the Reference.clear() API.
120 const oop o = reference_referent(obj);
121 if (o == NULL) {
122 // Reference has already been cleared, by an application call to
123 // Reference.clear(), which means we should drop the reference.
124 return true;
125 }
126
127 // Check if the referent is still alive, in which case we should
128 // drop the reference.
129 if (type == REF_PHANTOM) {
130 return ZBarrier::is_alive_barrier_on_phantom_oop(o);
131 } else {
132 return ZBarrier::is_alive_barrier_on_weak_oop(o);
133 }
134 }
135
136 bool ZReferenceProcessor::should_mark_referent(ReferenceType type) const {
137 // Referents of final references (and its reachable sub graph) are
138 // always marked finalizable during discovery. This avoids the problem
139 // of later having to mark those objects if the referent is still final
140 // reachable during processing.
141 return type == REF_FINAL;
142 }
143
144 bool ZReferenceProcessor::should_clear_referent(ReferenceType type) const {
145 // Referents that were not marked must be cleared
146 return !should_mark_referent(type);
147 }
148
149 void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const {
150 volatile oop* const p = reference_referent_addr(obj);
151 if (type == REF_PHANTOM) {
152 ZBarrier::keep_alive_barrier_on_phantom_oop_field(p);
153 } else {
154 ZBarrier::keep_alive_barrier_on_weak_oop_field(p);
155 }
156 }
157
158 bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {
159 if (!RegisterReferences) {
160 // Reference processing disabled
161 return false;
162 }
163
164 // Update statistics
165 _encountered_count.get()[type]++;
166
167 if (is_reference_inactive(obj) ||
168 is_referent_alive_or_null(obj, type) ||
169 is_referent_softly_alive(obj, type)) {
170 // Not discovered
171 return false;
172 }
173
174 discover(obj, type);
175
176 // Discovered
177 return true;
178 }
179
180 void ZReferenceProcessor::discover(oop obj, ReferenceType type) {
181 log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(obj), ReferenceTypeName[type]);
182
183 // Update statistics
184 _discovered_count.get()[type]++;
185
186 // Mark referent finalizable
187 if (should_mark_referent(type)) {
188 oop* const referent_addr = (oop*)java_lang_ref_Reference::referent_addr(obj);
189 ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);
190 }
191
192 // Add reference to discovered list
193 assert(java_lang_ref_Reference::discovered(obj) == NULL, "Already discovered");
194 oop* const list = _discovered_list.addr();
195 java_lang_ref_Reference::set_discovered(obj, *list);
196 *list = obj;
197 }
198
199 oop ZReferenceProcessor::drop(oop obj, ReferenceType type) {
200 log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(obj), ReferenceTypeName[type]);
201
202 // Keep referent alive
203 keep_referent_alive(obj, type);
204
205 // Unlink and return next in list
206 const oop next = java_lang_ref_Reference::discovered(obj);
207 java_lang_ref_Reference::set_discovered(obj, NULL);
208 return next;
209 }
210
211 oop* ZReferenceProcessor::keep(oop obj, ReferenceType type) {
212 log_trace(gc, ref)("Pending Reference: " PTR_FORMAT " (%s)", p2i(obj), ReferenceTypeName[type]);
213
214 // Update statistics
215 _enqueued_count.get()[type]++;
216
217 // Clear referent
218 if (should_clear_referent(type)) {
219 java_lang_ref_Reference::set_referent(obj, NULL);
220 }
221
222 // Make reference inactive by self-looping the next field. We could be racing with a
223 // call to Reference.enqueue() from the application, which is why we are using a CAS
224 // to make sure we change the next field only if it is NULL. A failing CAS means the
225 // reference has already been enqueued. However, we don't check the result of the CAS,
226 // since we still have no option other than keeping the reference on the pending list.
227 // It's ok to have the reference both on the pending list and enqueued at the same
228 // time (the pending list is linked through the discovered field, while the reference
229 // queue is linked through the next field). When the ReferenceHandler thread later
230 // calls Reference.enqueue() we detect that it has already been enqueued and drop it.
231 oop* const next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
232 Atomic::cmpxchg(obj, next_addr, oop(NULL));
233
234 // Return next in list
235 return (oop*)java_lang_ref_Reference::discovered_addr(obj);
236 }
237
238 void ZReferenceProcessor::work() {
239 // Process discovered references
240 oop* const list = _discovered_list.addr();
241 oop* p = list;
242
243 while (*p != NULL) {
244 const oop obj = *p;
245 const ReferenceType type = reference_type(obj);
246
247 if (should_drop_reference(obj, type)) {
248 *p = drop(obj, type);
249 } else {
250 p = keep(obj, type);
251 }
252 }
253
254 // Prepend discovered references to internal pending list
255 if (*list != NULL) {
256 *p = Atomic::xchg(*list, _pending_list.addr());
257 if (*p == NULL) {
258 // First to prepend to list, record tail
259 _pending_list_tail = p;
260 }
261
262 // Clear discovered list
263 *list = NULL;
264 }
265 }
266
267 bool ZReferenceProcessor::is_empty() const {
268 ZPerWorkerConstIterator<oop> iter(&_discovered_list);
269 for (const oop* list; iter.next(&list);) {
270 if (*list != NULL) {
271 return false;
272 }
273 }
274
275 if (_pending_list.get() != NULL) {
276 return false;
277 }
278
279 return true;
280 }
281
282 void ZReferenceProcessor::reset_statistics() {
283 assert(is_empty(), "Should be empty");
284
285 // Reset encountered
286 ZPerWorkerIterator<Counters> iter_encountered(&_encountered_count);
287 for (Counters* counters; iter_encountered.next(&counters);) {
288 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
289 (*counters)[i] = 0;
290 }
291 }
292
293 // Reset discovered
294 ZPerWorkerIterator<Counters> iter_discovered(&_discovered_count);
295 for (Counters* counters; iter_discovered.next(&counters);) {
296 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
297 (*counters)[i] = 0;
298 }
299 }
300
301 // Reset enqueued
302 ZPerWorkerIterator<Counters> iter_enqueued(&_enqueued_count);
303 for (Counters* counters; iter_enqueued.next(&counters);) {
304 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
305 (*counters)[i] = 0;
306 }
307 }
308 }
309
310 void ZReferenceProcessor::collect_statistics() {
311 Counters encountered = {};
312 Counters discovered = {};
313 Counters enqueued = {};
314
315 // Sum encountered
316 ZPerWorkerConstIterator<Counters> iter_encountered(&_encountered_count);
317 for (const Counters* counters; iter_encountered.next(&counters);) {
318 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
319 encountered[i] += (*counters)[i];
320 }
321 }
322
323 // Sum discovered
324 ZPerWorkerConstIterator<Counters> iter_discovered(&_discovered_count);
325 for (const Counters* counters; iter_discovered.next(&counters);) {
326 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
327 discovered[i] += (*counters)[i];
328 }
329 }
330
331 // Sum enqueued
332 ZPerWorkerConstIterator<Counters> iter_enqueued(&_enqueued_count);
333 for (const Counters* counters; iter_enqueued.next(&counters);) {
334 for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
335 enqueued[i] += (*counters)[i];
336 }
337 }
338
339 // Update statistics
340 ZStatReferences::set_soft(encountered[REF_SOFT], discovered[REF_SOFT], enqueued[REF_SOFT]);
341 ZStatReferences::set_weak(encountered[REF_WEAK], discovered[REF_WEAK], enqueued[REF_WEAK]);
342 ZStatReferences::set_final(encountered[REF_FINAL], discovered[REF_FINAL], enqueued[REF_FINAL]);
343 ZStatReferences::set_phantom(encountered[REF_PHANTOM], discovered[REF_PHANTOM], enqueued[REF_PHANTOM]);
344
345 // Trace statistics
346 const ReferenceProcessorStats stats(discovered[REF_SOFT],
347 discovered[REF_WEAK],
348 discovered[REF_FINAL],
349 discovered[REF_PHANTOM]);
350 ZTracer::tracer()->report_gc_reference_stats(stats);
351 }
352
353 class ZReferenceProcessorTask : public ZTask {
354 private:
355 ZReferenceProcessor* const _reference_processor;
356
357 public:
358 ZReferenceProcessorTask(ZReferenceProcessor* reference_processor) :
359 ZTask("ZReferenceProcessorTask"),
360 _reference_processor(reference_processor) {}
361
362 virtual void work() {
363 _reference_processor->work();
364 }
365 };
366
367 void ZReferenceProcessor::process_references() {
368 ZStatTimer timer(ZSubPhaseConcurrentReferencesProcess);
369
370 // Process discovered lists
371 ZReferenceProcessorTask task(this);
372 _workers->run_concurrent(&task);
373
374 // Update soft reference clock
375 update_soft_reference_clock();
376
377 // Collect, log and trace statistics
378 collect_statistics();
379 }
380
381 void ZReferenceProcessor::enqueue_references() {
382 ZStatTimer timer(ZSubPhaseConcurrentReferencesEnqueue);
383
384 if (_pending_list.get() == NULL) {
385 // Nothing to enqueue
386 return;
387 }
388
389 {
390 // Heap_lock protects external pending list
391 MonitorLockerEx ml(Heap_lock);
392
393 // Prepend internal pending list to external pending list
394 *_pending_list_tail = Universe::swap_reference_pending_list(_pending_list.get());
395
396 // Notify ReferenceHandler thread
397 ml.notify_all();
398 }
399
400 // Reset internal pending list
401 _pending_list.set(NULL);
402 _pending_list_tail = _pending_list.addr();
403 }
404
405 void ZReferenceProcessor::process_and_enqueue_references() {
406 process_references();
407 enqueue_references();
408 }