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