1 /*
2 * Copyright (c) 2001, 2020, 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.
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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
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23 */
24
25 #ifndef SHARE_GC_SHARED_TASKQUEUE_HPP
26 #define SHARE_GC_SHARED_TASKQUEUE_HPP
27
28 #include "memory/allocation.hpp"
29 #include "memory/padded.hpp"
30 #include "oops/oopsHierarchy.hpp"
31 #include "runtime/atomic.hpp"
32 #include "utilities/debug.hpp"
33 #include "utilities/globalDefinitions.hpp"
34 #include "utilities/ostream.hpp"
35 #include "utilities/stack.hpp"
36
37 // Simple TaskQueue stats that are collected by default in debug builds.
38
39 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
40 #define TASKQUEUE_STATS 1
41 #elif !defined(TASKQUEUE_STATS)
42 #define TASKQUEUE_STATS 0
43 #endif
44
45 #if TASKQUEUE_STATS
46 #define TASKQUEUE_STATS_ONLY(code) code
47 #else
48 #define TASKQUEUE_STATS_ONLY(code)
49 #endif // TASKQUEUE_STATS
50
51 #if TASKQUEUE_STATS
52 class TaskQueueStats {
53 public:
54 enum StatId {
55 push, // number of taskqueue pushes
56 pop, // number of taskqueue pops
57 pop_slow, // subset of taskqueue pops that were done slow-path
58 steal_attempt, // number of taskqueue steal attempts
59 steal, // number of taskqueue steals
60 overflow, // number of overflow pushes
61 overflow_max_len, // max length of overflow stack
62 last_stat_id
63 };
64
65 public:
66 inline TaskQueueStats() { reset(); }
67
68 inline void record_push() { ++_stats[push]; }
69 inline void record_pop() { ++_stats[pop]; }
70 inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }
71 inline void record_steal_attempt() { ++_stats[steal_attempt]; }
72 inline void record_steal() { ++_stats[steal]; }
73 inline void record_overflow(size_t new_length);
74
75 TaskQueueStats & operator +=(const TaskQueueStats & addend);
76
77 inline size_t get(StatId id) const { return _stats[id]; }
78 inline const size_t* get() const { return _stats; }
79
80 inline void reset();
81
82 // Print the specified line of the header (does not include a line separator).
83 static void print_header(unsigned int line, outputStream* const stream = tty,
84 unsigned int width = 10);
85 // Print the statistics (does not include a line separator).
86 void print(outputStream* const stream = tty, unsigned int width = 10) const;
87
88 DEBUG_ONLY(void verify() const;)
89
90 private:
91 size_t _stats[last_stat_id];
92 static const char * const _names[last_stat_id];
93 };
94
95 void TaskQueueStats::record_overflow(size_t new_len) {
96 ++_stats[overflow];
97 if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
98 }
99
100 void TaskQueueStats::reset() {
101 memset(_stats, 0, sizeof(_stats));
102 }
103 #endif // TASKQUEUE_STATS
104
105 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances.
106
107 template <unsigned int N, MEMFLAGS F>
108 class TaskQueueSuper: public CHeapObj<F> {
109 protected:
110 // Internal type for indexing the queue; also used for the tag.
111 typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
112 STATIC_ASSERT(N == idx_t(N)); // Ensure N fits in an idx_t.
113
114 // N must be a power of 2 for computing modulo via masking.
115 // N must be >= 2 for the algorithm to work at all, though larger is better.
116 // C++11: is_power_of_2 is not (yet) constexpr.
117 STATIC_ASSERT((N >= 2) && ((N & (N - 1)) == 0));
118 static const uint MOD_N_MASK = N - 1;
119
120 class Age {
121 friend class TaskQueueSuper;
122
123 public:
124 explicit Age(size_t data = 0) : _data(data) {}
125 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
126
127 idx_t top() const { return _fields._top; }
128 idx_t tag() const { return _fields._tag; }
129
130 bool operator ==(const Age& other) const { return _data == other._data; }
131
132 private:
133 struct fields {
134 idx_t _top;
135 idx_t _tag;
136 };
137 union {
138 size_t _data;
139 fields _fields;
140 };
141 STATIC_ASSERT(sizeof(size_t) >= sizeof(fields));
142 };
143
144 uint bottom_relaxed() const {
145 return Atomic::load(&_bottom);
146 }
147
148 uint bottom_acquire() const {
149 return Atomic::load_acquire(&_bottom);
150 }
151
152 void set_bottom_relaxed(uint new_bottom) {
153 Atomic::store(&_bottom, new_bottom);
154 }
155
156 void release_set_bottom(uint new_bottom) {
157 Atomic::release_store(&_bottom, new_bottom);
158 }
159
160 Age age_relaxed() const {
161 return Age(Atomic::load(&_age._data));
162 }
163
164 void set_age_relaxed(Age new_age) {
165 Atomic::store(&_age._data, new_age._data);
166 }
167
168 Age cmpxchg_age(Age old_age, Age new_age) {
169 return Age(Atomic::cmpxchg(&_age._data, old_age._data, new_age._data));
170 }
171
172 idx_t age_top_relaxed() const {
173 // Atomically accessing a subfield of an "atomic" member.
174 return Atomic::load(&_age._fields._top);
175 }
176
177 // These both operate mod N.
178 static uint increment_index(uint ind) {
179 return (ind + 1) & MOD_N_MASK;
180 }
181 static uint decrement_index(uint ind) {
182 return (ind - 1) & MOD_N_MASK;
183 }
184
185 // Returns a number in the range [0..N). If the result is "N-1", it should be
186 // interpreted as 0.
187 uint dirty_size(uint bot, uint top) const {
188 return (bot - top) & MOD_N_MASK;
189 }
190
191 // Returns the size corresponding to the given "bot" and "top".
192 uint clean_size(uint bot, uint top) const {
193 uint sz = dirty_size(bot, top);
194 // Has the queue "wrapped", so that bottom is less than top? There's a
195 // complicated special case here. A pair of threads could perform pop_local
196 // and pop_global operations concurrently, starting from a state in which
197 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
198 // and the pop_global in incrementing _top (in which case the pop_global
199 // will be awarded the contested queue element.) The resulting state must
200 // be interpreted as an empty queue. (We only need to worry about one such
201 // event: only the queue owner performs pop_local's, and several concurrent
202 // threads attempting to perform the pop_global will all perform the same
203 // CAS, and only one can succeed.) Any stealing thread that reads after
204 // either the increment or decrement will see an empty queue, and will not
205 // join the competitors. The "sz == -1" / "sz == N-1" state will not be
206 // modified by concurrent threads, so the owner thread can reset the state
207 // to _bottom == top so subsequent pushes will be performed normally.
208 return (sz == N - 1) ? 0 : sz;
209 }
210
211 // Assert that we're not in the underflow state where bottom has
212 // been decremented past top, so that _bottom+1 mod N == top. See
213 // the discussion in clean_size.
214
215 void assert_not_underflow(uint bot, uint top) const {
216 assert_not_underflow(dirty_size(bot, top));
217 }
218
219 void assert_not_underflow(uint dirty_size) const {
220 assert(dirty_size != N - 1, "invariant");
221 }
222
223 private:
224 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0);
225
226 // Index of the first free element after the last one pushed (mod N).
227 volatile uint _bottom;
228 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(uint));
229
230 // top() is the index of the oldest pushed element (mod N), and tag()
231 // is the associated epoch, to distinguish different modifications of
232 // the age. There is no available element if top() == _bottom or
233 // (_bottom - top()) mod N == N-1; the latter indicates underflow
234 // during concurrent pop_local/pop_global.
235 volatile Age _age;
236 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(Age));
237
238 NONCOPYABLE(TaskQueueSuper);
239
240 public:
241 TaskQueueSuper() : _bottom(0), _age() {}
242
243 // Assert the queue is empty.
244 // Unreliable if there are concurrent pushes or pops.
245 void assert_empty() const {
246 assert(bottom_relaxed() == age_top_relaxed(), "not empty");
247 }
248
249 bool is_empty() const {
250 return size() == 0;
251 }
252
253 // Return an estimate of the number of elements in the queue.
254 // Treats pop_local/pop_global race that underflows as empty.
255 uint size() const {
256 return clean_size(bottom_relaxed(), age_top_relaxed());
257 }
258
259 // Discard the contents of the queue.
260 void set_empty() {
261 set_bottom_relaxed(0);
262 set_age_relaxed(Age());
263 }
264
265 // Maximum number of elements allowed in the queue. This is two less
266 // than the actual queue size, so that a full queue can be distinguished
267 // from underflow involving pop_local and concurrent pop_global operations
268 // in GenericTaskQueue.
269 uint max_elems() const { return N - 2; }
270
271 TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
272 };
273
274 //
275 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-
276 // ended-queue (deque), intended for use in work stealing. Queue operations
277 // are non-blocking.
278 //
279 // A queue owner thread performs push() and pop_local() operations on one end
280 // of the queue, while other threads may steal work using the pop_global()
281 // method.
282 //
283 // The main difference to the original algorithm is that this
284 // implementation allows wrap-around at the end of its allocated
285 // storage, which is an array.
286 //
287 // The original paper is:
288 //
289 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G.
290 // Thread scheduling for multiprogrammed multiprocessors.
291 // Theory of Computing Systems 34, 2 (2001), 115-144.
292 //
293 // The following paper provides an correctness proof and an
294 // implementation for weakly ordered memory models including (pseudo-)
295 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is
296 // similar to ABP, with the main difference that it allows resizing of the
297 // underlying storage:
298 //
299 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.
300 // Correct and efficient work-stealing for weak memory models
301 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and
302 // practice of parallel programming (PPoPP 2013), 69-80
303 //
304
305 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
306 class GenericTaskQueue: public TaskQueueSuper<N, F> {
307 protected:
308 typedef typename TaskQueueSuper<N, F>::Age Age;
309 typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
310
311 using TaskQueueSuper<N, F>::MOD_N_MASK;
312
313 using TaskQueueSuper<N, F>::bottom_relaxed;
314 using TaskQueueSuper<N, F>::bottom_acquire;
315
316 using TaskQueueSuper<N, F>::set_bottom_relaxed;
317 using TaskQueueSuper<N, F>::release_set_bottom;
318
319 using TaskQueueSuper<N, F>::age_relaxed;
320 using TaskQueueSuper<N, F>::set_age_relaxed;
321 using TaskQueueSuper<N, F>::cmpxchg_age;
322 using TaskQueueSuper<N, F>::age_top_relaxed;
323
324 using TaskQueueSuper<N, F>::increment_index;
325 using TaskQueueSuper<N, F>::decrement_index;
326 using TaskQueueSuper<N, F>::dirty_size;
327 using TaskQueueSuper<N, F>::clean_size;
328 using TaskQueueSuper<N, F>::assert_not_underflow;
329
330 public:
331 using TaskQueueSuper<N, F>::max_elems;
332 using TaskQueueSuper<N, F>::size;
333
334 #if TASKQUEUE_STATS
335 using TaskQueueSuper<N, F>::stats;
336 #endif
337
338 private:
339 // Slow path for pop_local, dealing with possible conflict with pop_global.
340 bool pop_local_slow(uint localBot, Age oldAge);
341
342 public:
343 typedef E element_type;
344
345 // Initializes the queue to empty.
346 GenericTaskQueue();
347
348 void initialize();
349
350 // Push the task "t" on the queue. Returns "false" iff the queue is full.
351 inline bool push(E t);
352
353 // Attempts to claim a task from the "local" end of the queue (the most
354 // recently pushed) as long as the number of entries exceeds the threshold.
355 // If successfully claims a task, returns true and sets t to the task;
356 // otherwise, returns false and t is unspecified. May fail and return
357 // false because of a successful steal by pop_global.
358 inline bool pop_local(E& t, uint threshold = 0);
359
360 // Like pop_local(), but uses the "global" end of the queue (the least
361 // recently pushed).
362 bool pop_global(E& t);
363
364 // Delete any resource associated with the queue.
365 ~GenericTaskQueue();
366
367 // Apply fn to each element in the task queue. The queue must not
368 // be modified while iterating.
369 template<typename Fn> void iterate(Fn fn);
370
371 private:
372 // Base class has trailing padding.
373
374 // Element array.
375 E* _elems;
376
377 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(E*));
378 // Queue owner local variables. Not to be accessed by other threads.
379
380 static const uint InvalidQueueId = uint(-1);
381 uint _last_stolen_queue_id; // The id of the queue we last stole from
382
383 int _seed; // Current random seed used for selecting a random queue during stealing.
384
385 DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(uint) + sizeof(int));
386 public:
387 int next_random_queue_id();
388
389 void set_last_stolen_queue_id(uint id) { _last_stolen_queue_id = id; }
390 uint last_stolen_queue_id() const { return _last_stolen_queue_id; }
391 bool is_last_stolen_queue_id_valid() const { return _last_stolen_queue_id != InvalidQueueId; }
392 void invalidate_last_stolen_queue_id() { _last_stolen_queue_id = InvalidQueueId; }
393 };
394
395 template<class E, MEMFLAGS F, unsigned int N>
396 GenericTaskQueue<E, F, N>::GenericTaskQueue() : _last_stolen_queue_id(InvalidQueueId), _seed(17 /* random number */) {
397 assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
398 }
399
400 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
401 // elements that do not fit in the TaskQueue.
402 //
403 // This class hides two methods from super classes:
404 //
405 // push() - push onto the task queue or, if that fails, onto the overflow stack
406 // is_empty() - return true if both the TaskQueue and overflow stack are empty
407 //
408 // Note that size() is not hidden--it returns the number of elements in the
409 // TaskQueue, and does not include the size of the overflow stack. This
410 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
411 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
412 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
413 {
414 public:
415 typedef Stack<E, F> overflow_t;
416 typedef GenericTaskQueue<E, F, N> taskqueue_t;
417
418 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
419
420 // Push task t onto the queue or onto the overflow stack. Return true.
421 inline bool push(E t);
422 // Try to push task t onto the queue only. Returns true if successful, false otherwise.
423 inline bool try_push_to_taskqueue(E t);
424
425 // Attempt to pop from the overflow stack; return true if anything was popped.
426 inline bool pop_overflow(E& t);
427
428 inline overflow_t* overflow_stack() { return &_overflow_stack; }
429
430 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
431 inline bool overflow_empty() const { return _overflow_stack.is_empty(); }
432 inline bool is_empty() const {
433 return taskqueue_empty() && overflow_empty();
434 }
435
436 private:
437 overflow_t _overflow_stack;
438 };
439
440 class TaskQueueSetSuper {
441 public:
442 // Assert all queues in the set are empty.
443 NOT_DEBUG(void assert_empty() const {})
444 DEBUG_ONLY(virtual void assert_empty() const = 0;)
445
446 // Tasks in queue
447 virtual uint tasks() const = 0;
448 };
449
450 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
451 };
452
453 template<class T, MEMFLAGS F>
454 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
455 public:
456 typedef typename T::element_type E;
457
458 private:
459 uint _n;
460 T** _queues;
461
462 bool steal_best_of_2(uint queue_num, E& t);
463
464 public:
465 GenericTaskQueueSet(uint n);
466 ~GenericTaskQueueSet();
467
468 void register_queue(uint i, T* q);
469
470 T* queue(uint n);
471
472 // Try to steal a task from some other queue than queue_num. It may perform several attempts at doing so.
473 // Returns if stealing succeeds, and sets "t" to the stolen task.
474 bool steal(uint queue_num, E& t);
475
476 DEBUG_ONLY(virtual void assert_empty() const;)
477
478 virtual uint tasks() const;
479
480 uint size() const { return _n; }
481 };
482
483 template<class T, MEMFLAGS F> void
484 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
485 assert(i < _n, "index out of range.");
486 _queues[i] = q;
487 }
488
489 template<class T, MEMFLAGS F> T*
490 GenericTaskQueueSet<T, F>::queue(uint i) {
491 return _queues[i];
492 }
493
494 #ifdef ASSERT
495 template<class T, MEMFLAGS F>
496 void GenericTaskQueueSet<T, F>::assert_empty() const {
497 for (uint j = 0; j < _n; j++) {
498 _queues[j]->assert_empty();
499 }
500 }
501 #endif // ASSERT
502
503 template<class T, MEMFLAGS F>
504 uint GenericTaskQueueSet<T, F>::tasks() const {
505 uint n = 0;
506 for (uint j = 0; j < _n; j++) {
507 n += _queues[j]->size();
508 }
509 return n;
510 }
511
512 // When to terminate from the termination protocol.
513 class TerminatorTerminator: public CHeapObj<mtInternal> {
514 public:
515 virtual bool should_exit_termination() = 0;
516 };
517
518 // This is a container class for either an oop* or a narrowOop*.
519 // Both are pushed onto a task queue and the consumer will test is_narrow()
520 // to determine which should be processed.
521 class StarTask {
522 void* _holder; // either union oop* or narrowOop*
523
524 enum { COMPRESSED_OOP_MASK = 1 };
525
526 public:
527 StarTask(narrowOop* p) {
528 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
529 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
530 }
531 StarTask(oop* p) {
532 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
533 _holder = (void*)p;
534 }
535 StarTask() { _holder = NULL; }
536 // Trivially copyable, for use in GenericTaskQueue.
537
538 operator oop*() { return (oop*)_holder; }
539 operator narrowOop*() {
540 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
541 }
542
543 bool is_narrow() const {
544 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
545 }
546 };
547
548 class ObjArrayTask
549 {
550 public:
551 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
552 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
553 assert(idx <= size_t(max_jint), "too big");
554 }
555 // Trivially copyable, for use in GenericTaskQueue.
556
557 inline oop obj() const { return _obj; }
558 inline int index() const { return _index; }
559
560 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
561
562 private:
563 oop _obj;
564 int _index;
565 };
566
567 // Wrapper over an oop that is a partially scanned array.
568 // Can be converted to a ScannerTask for placement in associated task queues.
569 // Refers to the partially copied source array oop.
570 class PartialArrayScanTask {
571 void* _p;
572
573 public:
574 PartialArrayScanTask() : _p(NULL) {}
575 explicit PartialArrayScanTask(oop src_array) : _p(src_array) {}
576 // Trivially copyable.
577
578 oop to_source_array() const { return oop(_p); }
579 };
580
581 // Discriminated union over oop*, narrowOop*, and PartialArrayScanTask.
582 // Uses a low tag in the associated pointer to identify the category.
583 // Used as a task queue element type.
584 class ScannerTask {
585 void* _p;
586
587 static const uintptr_t OopTag = 0;
588 static const uintptr_t NarrowOopTag = 1;
589 static const uintptr_t PartialArrayTag = 2;
590 static const uintptr_t TagSize = 2;
591 static const uintptr_t TagAlignment = 1 << TagSize;
592 static const uintptr_t TagMask = TagAlignment - 1;
593
594 static void* encode(void* p, uintptr_t tag) {
595 assert(is_aligned(p, TagAlignment), "misaligned: " PTR_FORMAT, p2i(p));
596 return static_cast<char*>(p) + tag;
597 }
598
599 uintptr_t raw_value() const {
600 return reinterpret_cast<uintptr_t>(_p);
601 }
602
603 bool has_tag(uintptr_t tag) const {
604 return (raw_value() & TagMask) == tag;
605 }
606
607 void* decode(uintptr_t tag) const {
608 assert(has_tag(tag), "precondition");
609 return static_cast<char*>(_p) - tag;
610 }
611
612 public:
613 ScannerTask() : _p(NULL) {}
614
615 explicit ScannerTask(oop* p) : _p(encode(p, OopTag)) {}
616
617 explicit ScannerTask(narrowOop* p) : _p(encode(p, NarrowOopTag)) {}
618
619 explicit ScannerTask(PartialArrayScanTask t) :
620 _p(encode(t.to_source_array(), PartialArrayTag)) {}
621
622 // Trivially copyable.
623
624 // Predicate implementations assume OopTag == 0, others are powers of 2.
625
626 bool is_oop_ptr() const {
627 return (raw_value() & (NarrowOopTag | PartialArrayTag)) == 0;
628 }
629
630 bool is_narrow_oop_ptr() const {
631 return (raw_value() & NarrowOopTag) != 0;
632 }
633
634 bool is_partial_array_task() const {
635 return (raw_value() & PartialArrayTag) != 0;
636 }
637
638 oop* to_oop_ptr() const {
639 return static_cast<oop*>(decode(OopTag));
640 }
641
642 narrowOop* to_narrow_oop_ptr() const {
643 return static_cast<narrowOop*>(decode(NarrowOopTag));
644 }
645
646 PartialArrayScanTask to_partial_array_task() const {
647 return PartialArrayScanTask(oop(decode(PartialArrayTag)));
648 }
649 };
650
651 #endif // SHARE_GC_SHARED_TASKQUEUE_HPP