1 /*
2 * Copyright (c) 2015, 2023, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2020, 2021, Red Hat, Inc. and/or its affiliates.
4 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 *
7 * This code is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 only, as
9 * published by the Free Software Foundation.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 *
25 */
26
27 #include "precompiled.hpp"
28 #include "classfile/javaClasses.hpp"
29 #include "gc/shared/workerThread.hpp"
30 #include "gc/shenandoah/shenandoahGeneration.hpp"
31 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
32 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
33 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp"
34 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"
35 #include "gc/shenandoah/shenandoahUtils.hpp"
36 #include "runtime/atomic.hpp"
37 #include "logging/log.hpp"
38
39 static ReferenceType reference_type(oop reference) {
40 return InstanceKlass::cast(reference->klass())->reference_type();
41 }
42
43 static const char* reference_type_name(ReferenceType type) {
44 switch (type) {
45 case REF_SOFT:
46 return "Soft";
47
48 case REF_WEAK:
49 return "Weak";
50
51 case REF_FINAL:
52 return "Final";
53
54 case REF_PHANTOM:
55 return "Phantom";
56
57 default:
58 ShouldNotReachHere();
59 return nullptr;
60 }
61 }
62
63 template <typename T>
64 static void card_mark_barrier(T* field, oop value) {
65 assert(ShenandoahCardBarrier, "Card-mark barrier should be on");
66 ShenandoahGenerationalHeap* heap = ShenandoahGenerationalHeap::heap();
67 assert(heap->is_in_or_null(value), "Should be in heap");
68 if (heap->is_in_old(field) && heap->is_in_young(value)) {
69 // For Shenandoah, each generation collects all the _referents_ that belong to the
70 // collected generation. We can end up with discovered lists that contain a mixture
71 // of old and young _references_. These references are linked together through the
72 // discovered field in java.lang.Reference. In some cases, creating or editing this
73 // list may result in the creation of _new_ old-to-young pointers which must dirty
74 // the corresponding card. Failing to do this may cause heap verification errors and
75 // lead to incorrect GC behavior.
76 heap->old_generation()->mark_card_as_dirty(field);
77 }
78 }
79
80 template <typename T>
81 static void set_oop_field(T* field, oop value);
82
83 template <>
84 void set_oop_field<oop>(oop* field, oop value) {
85 *field = value;
86 if (ShenandoahCardBarrier) {
87 card_mark_barrier(field, value);
88 }
89 }
90
91 template <>
92 void set_oop_field<narrowOop>(narrowOop* field, oop value) {
93 *field = CompressedOops::encode(value);
94 if (ShenandoahCardBarrier) {
95 card_mark_barrier(field, value);
96 }
97 }
98
99 static oop lrb(oop obj) {
100 if (obj != nullptr && ShenandoahHeap::heap()->marking_context()->is_marked(obj)) {
101 return ShenandoahBarrierSet::barrier_set()->load_reference_barrier(obj);
102 } else {
103 return obj;
104 }
105 }
106
107 template <typename T>
108 static volatile T* reference_referent_addr(oop reference) {
109 return (volatile T*)java_lang_ref_Reference::referent_addr_raw(reference);
110 }
111
112 template <typename T>
113 static oop reference_referent(oop reference) {
114 T heap_oop = Atomic::load(reference_referent_addr<T>(reference));
115 return CompressedOops::decode(heap_oop);
116 }
117
118 static void reference_clear_referent(oop reference) {
119 java_lang_ref_Reference::clear_referent_raw(reference);
120 }
121
122 template <typename T>
123 static T* reference_discovered_addr(oop reference) {
124 return reinterpret_cast<T*>(java_lang_ref_Reference::discovered_addr_raw(reference));
125 }
126
127 template <typename T>
128 static oop reference_discovered(oop reference) {
129 T heap_oop = *reference_discovered_addr<T>(reference);
130 return lrb(CompressedOops::decode(heap_oop));
131 }
132
133 template <typename T>
134 static void reference_set_discovered(oop reference, oop discovered);
135
136 template <>
137 void reference_set_discovered<oop>(oop reference, oop discovered) {
138 *reference_discovered_addr<oop>(reference) = discovered;
139 }
140
141 template <>
142 void reference_set_discovered<narrowOop>(oop reference, oop discovered) {
143 *reference_discovered_addr<narrowOop>(reference) = CompressedOops::encode(discovered);
144 }
145
146 template<typename T>
147 static bool reference_cas_discovered(oop reference, oop discovered) {
148 T* addr = reinterpret_cast<T *>(java_lang_ref_Reference::discovered_addr_raw(reference));
149 return ShenandoahHeap::atomic_update_oop_check(discovered, addr, nullptr);
150 }
151
152 template <typename T>
153 static T* reference_next_addr(oop reference) {
154 return reinterpret_cast<T*>(java_lang_ref_Reference::next_addr_raw(reference));
155 }
156
157 template <typename T>
158 static oop reference_next(oop reference) {
159 T heap_oop = RawAccess<>::oop_load(reference_next_addr<T>(reference));
160 return lrb(CompressedOops::decode(heap_oop));
161 }
162
163 static void reference_set_next(oop reference, oop next) {
164 java_lang_ref_Reference::set_next_raw(reference, next);
165 }
166
167 static void soft_reference_update_clock() {
168 const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
169 java_lang_ref_SoftReference::set_clock(now);
170 }
171
172 ShenandoahRefProcThreadLocal::ShenandoahRefProcThreadLocal() :
173 _discovered_list(nullptr),
174 _encountered_count(),
175 _discovered_count(),
176 _enqueued_count() {
177 }
178
179 void ShenandoahRefProcThreadLocal::reset() {
180 _discovered_list = nullptr;
181 _mark_closure = nullptr;
182 for (uint i = 0; i < reference_type_count; i++) {
183 _encountered_count[i] = 0;
184 _discovered_count[i] = 0;
185 _enqueued_count[i] = 0;
186 }
187 }
188
189 template <typename T>
190 T* ShenandoahRefProcThreadLocal::discovered_list_addr() {
191 return reinterpret_cast<T*>(&_discovered_list);
192 }
193
194 template <>
195 oop ShenandoahRefProcThreadLocal::discovered_list_head<oop>() const {
196 return *reinterpret_cast<const oop*>(&_discovered_list);
197 }
198
199 template <>
200 oop ShenandoahRefProcThreadLocal::discovered_list_head<narrowOop>() const {
201 return CompressedOops::decode(*reinterpret_cast<const narrowOop*>(&_discovered_list));
202 }
203
204 template <>
205 void ShenandoahRefProcThreadLocal::set_discovered_list_head<narrowOop>(oop head) {
206 *discovered_list_addr<narrowOop>() = CompressedOops::encode(head);
207 }
208
209 template <>
210 void ShenandoahRefProcThreadLocal::set_discovered_list_head<oop>(oop head) {
211 *discovered_list_addr<oop>() = head;
212 }
213
214 ShenandoahReferenceProcessor::ShenandoahReferenceProcessor(uint max_workers) :
215 _soft_reference_policy(nullptr),
216 _ref_proc_thread_locals(NEW_C_HEAP_ARRAY(ShenandoahRefProcThreadLocal, max_workers, mtGC)),
217 _pending_list(nullptr),
218 _pending_list_tail(&_pending_list),
219 _iterate_discovered_list_id(0U),
220 _stats() {
221 for (size_t i = 0; i < max_workers; i++) {
222 _ref_proc_thread_locals[i].reset();
223 }
224 }
225
226 void ShenandoahReferenceProcessor::reset_thread_locals() {
227 uint max_workers = ShenandoahHeap::heap()->max_workers();
228 for (uint i = 0; i < max_workers; i++) {
229 _ref_proc_thread_locals[i].reset();
230 }
231 }
232
233 void ShenandoahReferenceProcessor::set_mark_closure(uint worker_id, ShenandoahMarkRefsSuperClosure* mark_closure) {
234 _ref_proc_thread_locals[worker_id].set_mark_closure(mark_closure);
235 }
236
237 void ShenandoahReferenceProcessor::set_soft_reference_policy(bool clear) {
238 static AlwaysClearPolicy always_clear_policy;
239 static LRUMaxHeapPolicy lru_max_heap_policy;
240
241 if (clear) {
242 log_info(gc, ref)("Clearing All SoftReferences");
243 _soft_reference_policy = &always_clear_policy;
244 } else {
245 _soft_reference_policy = &lru_max_heap_policy;
246 }
247
248 _soft_reference_policy->setup();
249 }
250
251 template <typename T>
252 bool ShenandoahReferenceProcessor::is_inactive(oop reference, oop referent, ReferenceType type) const {
253 if (type == REF_FINAL) {
254 // A FinalReference is inactive if its next field is non-null. An application can't
255 // call enqueue() or clear() on a FinalReference.
256 return reference_next<T>(reference) != nullptr;
257 } else {
258 // A non-FinalReference is inactive if the referent is null. The referent can only
259 // be null if the application called Reference.enqueue() or Reference.clear().
260 return referent == nullptr;
261 }
262 }
263
264 bool ShenandoahReferenceProcessor::is_strongly_live(oop referent) const {
265 return ShenandoahHeap::heap()->marking_context()->is_marked_strong(referent);
266 }
267
268 bool ShenandoahReferenceProcessor::is_softly_live(oop reference, ReferenceType type) const {
269 if (type != REF_SOFT) {
270 // Not a SoftReference
271 return false;
272 }
273
274 // Ask SoftReference policy
275 const jlong clock = java_lang_ref_SoftReference::clock();
276 assert(clock != 0, "Clock not initialized");
277 assert(_soft_reference_policy != nullptr, "Policy not initialized");
278 return !_soft_reference_policy->should_clear_reference(reference, clock);
279 }
280
281 template <typename T>
282 bool ShenandoahReferenceProcessor::should_discover(oop reference, ReferenceType type) const {
283 T* referent_addr = (T*) java_lang_ref_Reference::referent_addr_raw(reference);
284 T heap_oop = RawAccess<>::oop_load(referent_addr);
285 oop referent = CompressedOops::decode(heap_oop);
286 ShenandoahHeap* heap = ShenandoahHeap::heap();
287
288 if (is_inactive<T>(reference, referent, type)) {
289 log_trace(gc,ref)("Reference inactive: " PTR_FORMAT, p2i(reference));
290 return false;
291 }
292
293 if (is_strongly_live(referent)) {
294 log_trace(gc,ref)("Reference strongly live: " PTR_FORMAT, p2i(reference));
295 return false;
296 }
297
298 if (is_softly_live(reference, type)) {
299 log_trace(gc,ref)("Reference softly live: " PTR_FORMAT, p2i(reference));
300 return false;
301 }
302
303 if (!heap->is_in_active_generation(referent)) {
304 log_trace(gc,ref)("Referent outside of active generation: " PTR_FORMAT, p2i(referent));
305 return false;
306 }
307
308 return true;
309 }
310
311 template <typename T>
312 bool ShenandoahReferenceProcessor::should_drop(oop reference, ReferenceType type) const {
313 const oop referent = reference_referent<T>(reference);
314 if (referent == nullptr) {
315 // Reference has been cleared, by a call to Reference.enqueue()
316 // or Reference.clear() from the application, which means we
317 // should drop the reference.
318 return true;
319 }
320
321 // Check if the referent is still alive, in which case we should
322 // drop the reference.
323 if (type == REF_PHANTOM) {
324 return ShenandoahHeap::heap()->complete_marking_context()->is_marked(referent);
325 } else {
326 return ShenandoahHeap::heap()->complete_marking_context()->is_marked_strong(referent);
327 }
328 }
329
330 template <typename T>
331 void ShenandoahReferenceProcessor::make_inactive(oop reference, ReferenceType type) const {
332 if (type == REF_FINAL) {
333 // Don't clear referent. It is needed by the Finalizer thread to make the call
334 // to finalize(). A FinalReference is instead made inactive by self-looping the
335 // next field. An application can't call FinalReference.enqueue(), so there is
336 // no race to worry about when setting the next field.
337 assert(reference_next<T>(reference) == nullptr, "Already inactive");
338 assert(ShenandoahHeap::heap()->marking_context()->is_marked(reference_referent<T>(reference)), "only make inactive final refs with alive referents");
339 reference_set_next(reference, reference);
340 } else {
341 // Clear referent
342 reference_clear_referent(reference);
343 }
344 }
345
346 template <typename T>
347 bool ShenandoahReferenceProcessor::discover(oop reference, ReferenceType type, uint worker_id) {
348 if (!should_discover<T>(reference, type)) {
349 // Not discovered
350 return false;
351 }
352
353 if (reference_discovered<T>(reference) != nullptr) {
354 // Already discovered. This can happen if the reference is marked finalizable first, and then strong,
355 // in which case it will be seen 2x by marking.
356 log_trace(gc,ref)("Reference already discovered: " PTR_FORMAT, p2i(reference));
357 return true;
358 }
359
360 if (type == REF_FINAL) {
361 ShenandoahMarkRefsSuperClosure* cl = _ref_proc_thread_locals[worker_id].mark_closure();
362 bool weak = cl->is_weak();
363 cl->set_weak(true);
364 if (UseCompressedOops) {
365 cl->do_oop(reinterpret_cast<narrowOop*>(java_lang_ref_Reference::referent_addr_raw(reference)));
366 } else {
367 cl->do_oop(reinterpret_cast<oop*>(java_lang_ref_Reference::referent_addr_raw(reference)));
368 }
369 cl->set_weak(weak);
370 }
371
372 // Add reference to discovered list
373 // Each worker thread has a private copy of refproc_data, which includes a private discovered list. This means
374 // there's no risk that a different worker thread will try to manipulate my discovered list head while I'm making
375 // reference the head of my discovered list.
376 ShenandoahRefProcThreadLocal& refproc_data = _ref_proc_thread_locals[worker_id];
377 oop discovered_head = refproc_data.discovered_list_head<T>();
378 if (discovered_head == nullptr) {
379 // Self-loop tail of list. We distinguish discovered from not-discovered references by looking at their
380 // discovered field: if it is null, then it is not-yet discovered, otherwise it is discovered
381 discovered_head = reference;
382 }
383 if (reference_cas_discovered<T>(reference, discovered_head)) {
384 // We successfully set this reference object's next pointer to discovered_head. This marks reference as discovered.
385 // If reference_cas_discovered fails, that means some other worker thread took credit for discovery of this reference,
386 // and that other thread will place reference on its discovered list, so I can ignore reference.
387
388 // In case we have created an interesting pointer, mark the remembered set card as dirty.
389 if (ShenandoahCardBarrier) {
390 T* addr = reinterpret_cast<T*>(java_lang_ref_Reference::discovered_addr_raw(reference));
391 card_mark_barrier(addr, discovered_head);
392 }
393
394 // Make the discovered_list_head point to reference.
395 refproc_data.set_discovered_list_head<T>(reference);
396 assert(refproc_data.discovered_list_head<T>() == reference, "reference must be new discovered head");
397 log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
398 _ref_proc_thread_locals[worker_id].inc_discovered(type);
399 }
400 return true;
401 }
402
403 bool ShenandoahReferenceProcessor::discover_reference(oop reference, ReferenceType type) {
404 if (!RegisterReferences) {
405 // Reference processing disabled
406 return false;
407 }
408
409 log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s, %s)",
410 p2i(reference), reference_type_name(type), ShenandoahHeap::heap()->heap_region_containing(reference)->affiliation_name());
411 uint worker_id = WorkerThread::worker_id();
412 _ref_proc_thread_locals[worker_id].inc_encountered(type);
413
414 if (UseCompressedOops) {
415 return discover<narrowOop>(reference, type, worker_id);
416 } else {
417 return discover<oop>(reference, type, worker_id);
418 }
419 }
420
421 template <typename T>
422 oop ShenandoahReferenceProcessor::drop(oop reference, ReferenceType type) {
423 log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
424
425 ShenandoahHeap* heap = ShenandoahHeap::heap();
426 oop referent = reference_referent<T>(reference);
427 assert(referent == nullptr || heap->marking_context()->is_marked(referent), "only drop references with alive referents");
428
429 // Unlink and return next in list
430 oop next = reference_discovered<T>(reference);
431 reference_set_discovered<T>(reference, nullptr);
432 // When this reference was discovered, it would not have been marked. If it ends up surviving
433 // the cycle, we need to dirty the card if the reference is old and the referent is young. Note
434 // that if the reference is not dropped, then its pointer to the referent will be nulled before
435 // evacuation begins so card does not need to be dirtied.
436 if (heap->mode()->is_generational() && heap->is_in_old(reference) && heap->is_in_young(referent)) {
437 // Note: would be sufficient to mark only the card that holds the start of this Reference object.
438 heap->old_generation()->card_scan()->mark_range_as_dirty(cast_from_oop<HeapWord*>(reference), reference->size());
439 }
440 return next;
441 }
442
443 template <typename T>
444 T* ShenandoahReferenceProcessor::keep(oop reference, ReferenceType type, uint worker_id) {
445 log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(reference), reference_type_name(type));
446
447 // Update statistics
448 _ref_proc_thread_locals[worker_id].inc_enqueued(type);
449
450 // Make reference inactive
451 make_inactive<T>(reference, type);
452
453 // Return next in list
454 return reference_discovered_addr<T>(reference);
455 }
456
457 template <typename T>
458 void ShenandoahReferenceProcessor::process_references(ShenandoahRefProcThreadLocal& refproc_data, uint worker_id) {
459 log_trace(gc, ref)("Processing discovered list #%u : " PTR_FORMAT, worker_id, p2i(refproc_data.discovered_list_head<T>()));
460 T* list = refproc_data.discovered_list_addr<T>();
461 // The list head is basically a GC root, we need to resolve and update it,
462 // otherwise we will later swap a from-space ref into Universe::pending_list().
463 if (!CompressedOops::is_null(*list)) {
464 oop first_resolved = lrb(CompressedOops::decode_not_null(*list));
465 set_oop_field(list, first_resolved);
466 }
467 T* p = list;
468 while (true) {
469 const oop reference = lrb(CompressedOops::decode(*p));
470 if (reference == nullptr) {
471 break;
472 }
473 log_trace(gc, ref)("Processing reference: " PTR_FORMAT, p2i(reference));
474 const ReferenceType type = reference_type(reference);
475
476 if (should_drop<T>(reference, type)) {
477 set_oop_field(p, drop<T>(reference, type));
478 } else {
479 p = keep<T>(reference, type, worker_id);
480 }
481
482 const oop discovered = lrb(reference_discovered<T>(reference));
483 if (reference == discovered) {
484 // Reset terminating self-loop to null
485 reference_set_discovered<T>(reference, oop(nullptr));
486 break;
487 }
488 }
489
490 // Prepend discovered references to internal pending list
491 // set_oop_field maintains the card mark barrier as this list is constructed.
492 if (!CompressedOops::is_null(*list)) {
493 oop head = lrb(CompressedOops::decode_not_null(*list));
494 shenandoah_assert_not_in_cset_except(&head, head, ShenandoahHeap::heap()->cancelled_gc() || !ShenandoahLoadRefBarrier);
495 oop prev = Atomic::xchg(&_pending_list, head);
496 set_oop_field(p, prev);
497 if (prev == nullptr) {
498 // First to prepend to list, record tail
499 _pending_list_tail = reinterpret_cast<void*>(p);
500 }
501
502 // Clear discovered list
503 set_oop_field(list, oop(nullptr));
504 }
505 }
506
507 void ShenandoahReferenceProcessor::work() {
508 // Process discovered references
509 uint max_workers = ShenandoahHeap::heap()->max_workers();
510 uint worker_id = Atomic::add(&_iterate_discovered_list_id, 1U, memory_order_relaxed) - 1;
511 while (worker_id < max_workers) {
512 if (UseCompressedOops) {
513 process_references<narrowOop>(_ref_proc_thread_locals[worker_id], worker_id);
514 } else {
515 process_references<oop>(_ref_proc_thread_locals[worker_id], worker_id);
516 }
517 worker_id = Atomic::add(&_iterate_discovered_list_id, 1U, memory_order_relaxed) - 1;
518 }
519 }
520
521 class ShenandoahReferenceProcessorTask : public WorkerTask {
522 private:
523 bool const _concurrent;
524 ShenandoahPhaseTimings::Phase const _phase;
525 ShenandoahReferenceProcessor* const _reference_processor;
526
527 public:
528 ShenandoahReferenceProcessorTask(ShenandoahPhaseTimings::Phase phase, bool concurrent, ShenandoahReferenceProcessor* reference_processor) :
529 WorkerTask("ShenandoahReferenceProcessorTask"),
530 _concurrent(concurrent),
531 _phase(phase),
532 _reference_processor(reference_processor) {
533 }
534
535 virtual void work(uint worker_id) {
536 if (_concurrent) {
537 ShenandoahConcurrentWorkerSession worker_session(worker_id);
538 ShenandoahWorkerTimingsTracker x(_phase, ShenandoahPhaseTimings::WeakRefProc, worker_id);
539 _reference_processor->work();
540 } else {
541 ShenandoahParallelWorkerSession worker_session(worker_id);
542 ShenandoahWorkerTimingsTracker x(_phase, ShenandoahPhaseTimings::WeakRefProc, worker_id);
543 _reference_processor->work();
544 }
545 }
546 };
547
548 void ShenandoahReferenceProcessor::process_references(ShenandoahPhaseTimings::Phase phase, WorkerThreads* workers, bool concurrent) {
549
550 Atomic::release_store_fence(&_iterate_discovered_list_id, 0U);
551
552 // Process discovered lists
553 ShenandoahReferenceProcessorTask task(phase, concurrent, this);
554 workers->run_task(&task);
555
556 // Update SoftReference clock
557 soft_reference_update_clock();
558
559 // Collect, log and trace statistics
560 collect_statistics();
561
562 enqueue_references(concurrent);
563 }
564
565 void ShenandoahReferenceProcessor::enqueue_references_locked() {
566 // Prepend internal pending list to external pending list
567 shenandoah_assert_not_in_cset_except(&_pending_list, _pending_list, ShenandoahHeap::heap()->cancelled_gc() || !ShenandoahLoadRefBarrier);
568
569 // During reference processing, we maintain a local list of references that are identified by
570 // _pending_list and _pending_list_tail. _pending_list_tail points to the next field of the last Reference object on
571 // the local list.
572 //
573 // There is also a global list of reference identified by Universe::_reference_pending_list
574
575 // The following code has the effect of:
576 // 1. Making the global Universe::_reference_pending_list point to my local list
577 // 2. Overwriting the next field of the last Reference on my local list to point at the previous head of the
578 // global Universe::_reference_pending_list
579
580 oop former_head_of_global_list = Universe::swap_reference_pending_list(_pending_list);
581 if (UseCompressedOops) {
582 set_oop_field<narrowOop>(reinterpret_cast<narrowOop*>(_pending_list_tail), former_head_of_global_list);
583 } else {
584 set_oop_field<oop>(reinterpret_cast<oop*>(_pending_list_tail), former_head_of_global_list);
585 }
586 }
587
588 void ShenandoahReferenceProcessor::enqueue_references(bool concurrent) {
589 if (_pending_list == nullptr) {
590 // Nothing to enqueue
591 return;
592 }
593 if (!concurrent) {
594 // When called from mark-compact or degen-GC, the locking is done by the VMOperation,
595 enqueue_references_locked();
596 } else {
597 // Heap_lock protects external pending list
598 MonitorLocker ml(Heap_lock);
599
600 enqueue_references_locked();
601
602 // Notify ReferenceHandler thread
603 ml.notify_all();
604 }
605
606 // Reset internal pending list
607 _pending_list = nullptr;
608 _pending_list_tail = &_pending_list;
609 }
610
611 template<typename T>
612 void ShenandoahReferenceProcessor::clean_discovered_list(T* list) {
613 T discovered = *list;
614 while (!CompressedOops::is_null(discovered)) {
615 oop discovered_ref = CompressedOops::decode_not_null(discovered);
616 set_oop_field<T>(list, oop(nullptr));
617 list = reference_discovered_addr<T>(discovered_ref);
618 discovered = *list;
619 }
620 }
621
622 void ShenandoahReferenceProcessor::abandon_partial_discovery() {
623 uint max_workers = ShenandoahHeap::heap()->max_workers();
624 for (uint index = 0; index < max_workers; index++) {
625 if (UseCompressedOops) {
626 clean_discovered_list<narrowOop>(_ref_proc_thread_locals[index].discovered_list_addr<narrowOop>());
627 } else {
628 clean_discovered_list<oop>(_ref_proc_thread_locals[index].discovered_list_addr<oop>());
629 }
630 }
631 if (_pending_list != nullptr) {
632 oop pending = _pending_list;
633 _pending_list = nullptr;
634 if (UseCompressedOops) {
635 narrowOop* list = reference_discovered_addr<narrowOop>(pending);
636 clean_discovered_list<narrowOop>(list);
637 } else {
638 oop* list = reference_discovered_addr<oop>(pending);
639 clean_discovered_list<oop>(list);
640 }
641 }
642 _pending_list_tail = &_pending_list;
643 }
644
645 void ShenandoahReferenceProcessor::collect_statistics() {
646 Counters encountered = {};
647 Counters discovered = {};
648 Counters enqueued = {};
649 uint max_workers = ShenandoahHeap::heap()->max_workers();
650 for (uint i = 0; i < max_workers; i++) {
651 for (size_t type = 0; type < reference_type_count; type++) {
652 encountered[type] += _ref_proc_thread_locals[i].encountered((ReferenceType)type);
653 discovered[type] += _ref_proc_thread_locals[i].discovered((ReferenceType)type);
654 enqueued[type] += _ref_proc_thread_locals[i].enqueued((ReferenceType)type);
655 }
656 }
657
658 _stats = ReferenceProcessorStats(discovered[REF_SOFT],
659 discovered[REF_WEAK],
660 discovered[REF_FINAL],
661 discovered[REF_PHANTOM]);
662
663 log_info(gc,ref)("Encountered references: Soft: " SIZE_FORMAT ", Weak: " SIZE_FORMAT ", Final: " SIZE_FORMAT ", Phantom: " SIZE_FORMAT,
664 encountered[REF_SOFT], encountered[REF_WEAK], encountered[REF_FINAL], encountered[REF_PHANTOM]);
665 log_info(gc,ref)("Discovered references: Soft: " SIZE_FORMAT ", Weak: " SIZE_FORMAT ", Final: " SIZE_FORMAT ", Phantom: " SIZE_FORMAT,
666 discovered[REF_SOFT], discovered[REF_WEAK], discovered[REF_FINAL], discovered[REF_PHANTOM]);
667 log_info(gc,ref)("Enqueued references: Soft: " SIZE_FORMAT ", Weak: " SIZE_FORMAT ", Final: " SIZE_FORMAT ", Phantom: " SIZE_FORMAT,
668 enqueued[REF_SOFT], enqueued[REF_WEAK], enqueued[REF_FINAL], enqueued[REF_PHANTOM]);
669 }