wfcqueue: Implement mutex-free wfcqueue head with transparent union
[urcu.git] / urcu / static / wfcqueue.h
1 #ifndef _URCU_WFCQUEUE_STATIC_H
2 #define _URCU_WFCQUEUE_STATIC_H
3
4 /*
5 * urcu/static/wfcqueue.h
6 *
7 * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfcqueue.h for
10 * linking dynamically with the userspace rcu library.
11 *
12 * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright 2011-2012 - Lai Jiangshan <laijs@cn.fujitsu.com>
14 *
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
19 *
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
24 *
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
28 */
29
30 #include <pthread.h>
31 #include <assert.h>
32 #include <poll.h>
33 #include <stdbool.h>
34 #include <urcu/compiler.h>
35 #include <urcu/uatomic.h>
36
37 #ifdef __cplusplus
38 extern "C" {
39 #endif
40
41 /*
42 * Concurrent queue with wait-free enqueue/blocking dequeue.
43 *
44 * This queue has been designed and implemented collaboratively by
45 * Mathieu Desnoyers and Lai Jiangshan. Inspired from
46 * half-wait-free/half-blocking queue implementation done by Paul E.
47 * McKenney.
48 *
49 * Mutual exclusion of cds_wfcq_* / __cds_wfcq_* API
50 *
51 * Synchronization table:
52 *
53 * External synchronization techniques described in the API below is
54 * required between pairs marked with "X". No external synchronization
55 * required between pairs marked with "-".
56 *
57 * Legend:
58 * [1] cds_wfcq_enqueue
59 * [2] __cds_wfcq_splice (destination queue)
60 * [3] __cds_wfcq_dequeue
61 * [4] __cds_wfcq_splice (source queue)
62 * [5] __cds_wfcq_first
63 * [6] __cds_wfcq_next
64 *
65 * [1] [2] [3] [4] [5] [6]
66 * [1] - - - - - -
67 * [2] - - - - - -
68 * [3] - - X X X X
69 * [4] - - X - X X
70 * [5] - - X X - -
71 * [6] - - X X - -
72 *
73 * Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock().
74 *
75 * For convenience, cds_wfcq_dequeue_blocking() and
76 * cds_wfcq_splice_blocking() hold the dequeue lock.
77 *
78 * Besides locking, mutual exclusion of dequeue, splice and iteration
79 * can be ensured by performing all of those operations from a single
80 * thread, without requiring any lock.
81 */
82
83 #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
84 #define WFCQ_WAIT 10 /* Wait 10 ms if being set */
85
86 /*
87 * cds_wfcq_node_init: initialize wait-free queue node.
88 */
89 static inline void _cds_wfcq_node_init(struct cds_wfcq_node *node)
90 {
91 node->next = NULL;
92 }
93
94 /*
95 * cds_wfcq_init: initialize wait-free queue.
96 */
97 static inline void _cds_wfcq_init(struct cds_wfcq_head *head,
98 struct cds_wfcq_tail *tail)
99 {
100 int ret;
101
102 /* Set queue head and tail */
103 _cds_wfcq_node_init(&head->node);
104 tail->p = &head->node;
105 ret = pthread_mutex_init(&head->lock, NULL);
106 assert(!ret);
107 }
108
109 /*
110 * __cds_wfcq_init: initialize wait-free queue.
111 */
112 static inline void ___cds_wfcq_init(struct __cds_wfcq_head *head,
113 struct cds_wfcq_tail *tail)
114 {
115 /* Set queue head and tail */
116 _cds_wfcq_node_init(&head->node);
117 tail->p = &head->node;
118 }
119
120 /*
121 * cds_wfcq_empty: return whether wait-free queue is empty.
122 *
123 * No memory barrier is issued. No mutual exclusion is required.
124 *
125 * We perform the test on head->node.next to check if the queue is
126 * possibly empty, but we confirm this by checking if the tail pointer
127 * points to the head node because the tail pointer is the linearisation
128 * point of the enqueuers. Just checking the head next pointer could
129 * make a queue appear empty if an enqueuer is preempted for a long time
130 * between xchg() and setting the previous node's next pointer.
131 */
132 static inline bool _cds_wfcq_empty(cds_wfcq_head_ptr_t u_head,
133 struct cds_wfcq_tail *tail)
134 {
135 struct __cds_wfcq_head *head = u_head._h;
136 /*
137 * Queue is empty if no node is pointed by head->node.next nor
138 * tail->p. Even though the tail->p check is sufficient to find
139 * out of the queue is empty, we first check head->node.next as a
140 * common case to ensure that dequeuers do not frequently access
141 * enqueuer's tail->p cache line.
142 */
143 return CMM_LOAD_SHARED(head->node.next) == NULL
144 && CMM_LOAD_SHARED(tail->p) == &head->node;
145 }
146
147 static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head *head,
148 struct cds_wfcq_tail *tail)
149 {
150 int ret;
151
152 ret = pthread_mutex_lock(&head->lock);
153 assert(!ret);
154 }
155
156 static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head,
157 struct cds_wfcq_tail *tail)
158 {
159 int ret;
160
161 ret = pthread_mutex_unlock(&head->lock);
162 assert(!ret);
163 }
164
165 static inline bool ___cds_wfcq_append(cds_wfcq_head_ptr_t u_head,
166 struct cds_wfcq_tail *tail,
167 struct cds_wfcq_node *new_head,
168 struct cds_wfcq_node *new_tail)
169 {
170 struct __cds_wfcq_head *head = u_head._h;
171 struct cds_wfcq_node *old_tail;
172
173 /*
174 * Implicit memory barrier before uatomic_xchg() orders earlier
175 * stores to data structure containing node and setting
176 * node->next to NULL before publication.
177 */
178 old_tail = uatomic_xchg(&tail->p, new_tail);
179
180 /*
181 * Implicit memory barrier after uatomic_xchg() orders store to
182 * q->tail before store to old_tail->next.
183 *
184 * At this point, dequeuers see a NULL tail->p->next, which
185 * indicates that the queue is being appended to. The following
186 * store will append "node" to the queue from a dequeuer
187 * perspective.
188 */
189 CMM_STORE_SHARED(old_tail->next, new_head);
190 /*
191 * Return false if queue was empty prior to adding the node,
192 * else return true.
193 */
194 return old_tail != &head->node;
195 }
196
197 /*
198 * cds_wfcq_enqueue: enqueue a node into a wait-free queue.
199 *
200 * Issues a full memory barrier before enqueue. No mutual exclusion is
201 * required.
202 *
203 * Returns false if the queue was empty prior to adding the node.
204 * Returns true otherwise.
205 */
206 static inline bool _cds_wfcq_enqueue(cds_wfcq_head_ptr_t head,
207 struct cds_wfcq_tail *tail,
208 struct cds_wfcq_node *new_tail)
209 {
210 return ___cds_wfcq_append(head, tail, new_tail, new_tail);
211 }
212
213 /*
214 * ___cds_wfcq_busy_wait: adaptative busy-wait.
215 *
216 * Returns 1 if nonblocking and needs to block, 0 otherwise.
217 */
218 static inline bool
219 ___cds_wfcq_busy_wait(int *attempt, int blocking)
220 {
221 if (!blocking)
222 return 1;
223 if (++(*attempt) >= WFCQ_ADAPT_ATTEMPTS) {
224 poll(NULL, 0, WFCQ_WAIT); /* Wait for 10ms */
225 *attempt = 0;
226 } else {
227 caa_cpu_relax();
228 }
229 return 0;
230 }
231
232 /*
233 * Waiting for enqueuer to complete enqueue and return the next node.
234 */
235 static inline struct cds_wfcq_node *
236 ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking)
237 {
238 struct cds_wfcq_node *next;
239 int attempt = 0;
240
241 /*
242 * Adaptative busy-looping waiting for enqueuer to complete enqueue.
243 */
244 while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
245 if (___cds_wfcq_busy_wait(&attempt, blocking))
246 return CDS_WFCQ_WOULDBLOCK;
247 }
248
249 return next;
250 }
251
252 static inline struct cds_wfcq_node *
253 ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head,
254 struct cds_wfcq_tail *tail,
255 int blocking)
256 {
257 struct __cds_wfcq_head *head = u_head._h;
258 struct cds_wfcq_node *node;
259
260 if (_cds_wfcq_empty(head, tail))
261 return NULL;
262 node = ___cds_wfcq_node_sync_next(&head->node, blocking);
263 /* Load head->node.next before loading node's content */
264 cmm_smp_read_barrier_depends();
265 return node;
266 }
267
268 /*
269 * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
270 *
271 * Content written into the node before enqueue is guaranteed to be
272 * consistent, but no other memory ordering is ensured.
273 * Dequeue/splice/iteration mutual exclusion should be ensured by the
274 * caller.
275 *
276 * Used by for-like iteration macros in urcu/wfqueue.h:
277 * __cds_wfcq_for_each_blocking()
278 * __cds_wfcq_for_each_blocking_safe()
279 *
280 * Returns NULL if queue is empty, first node otherwise.
281 */
282 static inline struct cds_wfcq_node *
283 ___cds_wfcq_first_blocking(cds_wfcq_head_ptr_t head,
284 struct cds_wfcq_tail *tail)
285 {
286 return ___cds_wfcq_first(head, tail, 1);
287 }
288
289
290 /*
291 * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing.
292 *
293 * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if
294 * it needs to block.
295 */
296 static inline struct cds_wfcq_node *
297 ___cds_wfcq_first_nonblocking(cds_wfcq_head_ptr_t head,
298 struct cds_wfcq_tail *tail)
299 {
300 return ___cds_wfcq_first(head, tail, 0);
301 }
302
303 static inline struct cds_wfcq_node *
304 ___cds_wfcq_next(cds_wfcq_head_ptr_t head,
305 struct cds_wfcq_tail *tail,
306 struct cds_wfcq_node *node,
307 int blocking)
308 {
309 struct cds_wfcq_node *next;
310
311 /*
312 * Even though the following tail->p check is sufficient to find
313 * out if we reached the end of the queue, we first check
314 * node->next as a common case to ensure that iteration on nodes
315 * do not frequently access enqueuer's tail->p cache line.
316 */
317 if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
318 /* Load node->next before tail->p */
319 cmm_smp_rmb();
320 if (CMM_LOAD_SHARED(tail->p) == node)
321 return NULL;
322 next = ___cds_wfcq_node_sync_next(node, blocking);
323 }
324 /* Load node->next before loading next's content */
325 cmm_smp_read_barrier_depends();
326 return next;
327 }
328
329 /*
330 * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
331 *
332 * Content written into the node before enqueue is guaranteed to be
333 * consistent, but no other memory ordering is ensured.
334 * Dequeue/splice/iteration mutual exclusion should be ensured by the
335 * caller.
336 *
337 * Used by for-like iteration macros in urcu/wfqueue.h:
338 * __cds_wfcq_for_each_blocking()
339 * __cds_wfcq_for_each_blocking_safe()
340 *
341 * Returns NULL if reached end of queue, non-NULL next queue node
342 * otherwise.
343 */
344 static inline struct cds_wfcq_node *
345 ___cds_wfcq_next_blocking(cds_wfcq_head_ptr_t head,
346 struct cds_wfcq_tail *tail,
347 struct cds_wfcq_node *node)
348 {
349 return ___cds_wfcq_next(head, tail, node, 1);
350 }
351
352 /*
353 * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
354 *
355 * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if
356 * it needs to block.
357 */
358 static inline struct cds_wfcq_node *
359 ___cds_wfcq_next_nonblocking(cds_wfcq_head_ptr_t head,
360 struct cds_wfcq_tail *tail,
361 struct cds_wfcq_node *node)
362 {
363 return ___cds_wfcq_next(head, tail, node, 0);
364 }
365
366 static inline struct cds_wfcq_node *
367 ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head,
368 struct cds_wfcq_tail *tail,
369 int *state,
370 int blocking)
371 {
372 struct __cds_wfcq_head *head = u_head._h;
373 struct cds_wfcq_node *node, *next;
374
375 if (state)
376 *state = 0;
377
378 if (_cds_wfcq_empty(head, tail)) {
379 return NULL;
380 }
381
382 node = ___cds_wfcq_node_sync_next(&head->node, blocking);
383 if (!blocking && node == CDS_WFCQ_WOULDBLOCK) {
384 return CDS_WFCQ_WOULDBLOCK;
385 }
386
387 if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
388 /*
389 * @node is probably the only node in the queue.
390 * Try to move the tail to &q->head.
391 * q->head.next is set to NULL here, and stays
392 * NULL if the cmpxchg succeeds. Should the
393 * cmpxchg fail due to a concurrent enqueue, the
394 * q->head.next will be set to the next node.
395 * The implicit memory barrier before
396 * uatomic_cmpxchg() orders load node->next
397 * before loading q->tail.
398 * The implicit memory barrier before uatomic_cmpxchg
399 * orders load q->head.next before loading node's
400 * content.
401 */
402 _cds_wfcq_node_init(&head->node);
403 if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) {
404 if (state)
405 *state |= CDS_WFCQ_STATE_LAST;
406 return node;
407 }
408 next = ___cds_wfcq_node_sync_next(node, blocking);
409 /*
410 * In nonblocking mode, if we would need to block to
411 * get node's next, set the head next node pointer
412 * (currently NULL) back to its original value.
413 */
414 if (!blocking && next == CDS_WFCQ_WOULDBLOCK) {
415 head->node.next = node;
416 return CDS_WFCQ_WOULDBLOCK;
417 }
418 }
419
420 /*
421 * Move queue head forward.
422 */
423 head->node.next = next;
424
425 /* Load q->head.next before loading node's content */
426 cmm_smp_read_barrier_depends();
427 return node;
428 }
429
430 /*
431 * __cds_wfcq_dequeue_with_state_blocking: dequeue node from queue, with state.
432 *
433 * Content written into the node before enqueue is guaranteed to be
434 * consistent, but no other memory ordering is ensured.
435 * It is valid to reuse and free a dequeued node immediately.
436 * Dequeue/splice/iteration mutual exclusion should be ensured by the
437 * caller.
438 */
439 static inline struct cds_wfcq_node *
440 ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_ptr_t head,
441 struct cds_wfcq_tail *tail, int *state)
442 {
443 return ___cds_wfcq_dequeue_with_state(head, tail, state, 1);
444 }
445
446 /*
447 * ___cds_wfcq_dequeue_blocking: dequeue node from queue.
448 *
449 * Same as __cds_wfcq_dequeue_with_state_blocking, but without saving
450 * state.
451 */
452 static inline struct cds_wfcq_node *
453 ___cds_wfcq_dequeue_blocking(cds_wfcq_head_ptr_t head,
454 struct cds_wfcq_tail *tail)
455 {
456 return ___cds_wfcq_dequeue_with_state_blocking(head, tail, NULL);
457 }
458
459 /*
460 * __cds_wfcq_dequeue_with_state_nonblocking: dequeue node, with state.
461 *
462 * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK
463 * if it needs to block.
464 */
465 static inline struct cds_wfcq_node *
466 ___cds_wfcq_dequeue_with_state_nonblocking(cds_wfcq_head_ptr_t head,
467 struct cds_wfcq_tail *tail, int *state)
468 {
469 return ___cds_wfcq_dequeue_with_state(head, tail, state, 0);
470 }
471
472 /*
473 * ___cds_wfcq_dequeue_nonblocking: dequeue node from queue.
474 *
475 * Same as __cds_wfcq_dequeue_with_state_nonblocking, but without saving
476 * state.
477 */
478 static inline struct cds_wfcq_node *
479 ___cds_wfcq_dequeue_nonblocking(cds_wfcq_head_ptr_t head,
480 struct cds_wfcq_tail *tail)
481 {
482 return ___cds_wfcq_dequeue_with_state_nonblocking(head, tail, NULL);
483 }
484
485 /*
486 * __cds_wfcq_splice: enqueue all src_q nodes at the end of dest_q.
487 *
488 * Dequeue all nodes from src_q.
489 * dest_q must be already initialized.
490 * Mutual exclusion for src_q should be ensured by the caller as
491 * specified in the "Synchronisation table".
492 * Returns enum cds_wfcq_ret which indicates the state of the src or
493 * dest queue.
494 */
495 static inline enum cds_wfcq_ret
496 ___cds_wfcq_splice(
497 cds_wfcq_head_ptr_t u_dest_q_head,
498 struct cds_wfcq_tail *dest_q_tail,
499 cds_wfcq_head_ptr_t u_src_q_head,
500 struct cds_wfcq_tail *src_q_tail,
501 int blocking)
502 {
503 struct __cds_wfcq_head *dest_q_head = u_dest_q_head._h;
504 struct __cds_wfcq_head *src_q_head = u_src_q_head._h;
505 struct cds_wfcq_node *head, *tail;
506 int attempt = 0;
507
508 /*
509 * Initial emptiness check to speed up cases where queue is
510 * empty: only require loads to check if queue is empty.
511 */
512 if (_cds_wfcq_empty(src_q_head, src_q_tail))
513 return CDS_WFCQ_RET_SRC_EMPTY;
514
515 for (;;) {
516 /*
517 * Open-coded _cds_wfcq_empty() by testing result of
518 * uatomic_xchg, as well as tail pointer vs head node
519 * address.
520 */
521 head = uatomic_xchg(&src_q_head->node.next, NULL);
522 if (head)
523 break; /* non-empty */
524 if (CMM_LOAD_SHARED(src_q_tail->p) == &src_q_head->node)
525 return CDS_WFCQ_RET_SRC_EMPTY;
526 if (___cds_wfcq_busy_wait(&attempt, blocking))
527 return CDS_WFCQ_RET_WOULDBLOCK;
528 }
529
530 /*
531 * Memory barrier implied before uatomic_xchg() orders store to
532 * src_q->head before store to src_q->tail. This is required by
533 * concurrent enqueue on src_q, which exchanges the tail before
534 * updating the previous tail's next pointer.
535 */
536 tail = uatomic_xchg(&src_q_tail->p, &src_q_head->node);
537
538 /*
539 * Append the spliced content of src_q into dest_q. Does not
540 * require mutual exclusion on dest_q (wait-free).
541 */
542 if (___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail))
543 return CDS_WFCQ_RET_DEST_NON_EMPTY;
544 else
545 return CDS_WFCQ_RET_DEST_EMPTY;
546 }
547
548 /*
549 * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
550 *
551 * Dequeue all nodes from src_q.
552 * dest_q must be already initialized.
553 * Mutual exclusion for src_q should be ensured by the caller as
554 * specified in the "Synchronisation table".
555 * Returns enum cds_wfcq_ret which indicates the state of the src or
556 * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK.
557 */
558 static inline enum cds_wfcq_ret
559 ___cds_wfcq_splice_blocking(
560 cds_wfcq_head_ptr_t dest_q_head,
561 struct cds_wfcq_tail *dest_q_tail,
562 cds_wfcq_head_ptr_t src_q_head,
563 struct cds_wfcq_tail *src_q_tail)
564 {
565 return ___cds_wfcq_splice(dest_q_head, dest_q_tail,
566 src_q_head, src_q_tail, 1);
567 }
568
569 /*
570 * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q.
571 *
572 * Same as __cds_wfcq_splice_blocking, but returns
573 * CDS_WFCQ_RET_WOULDBLOCK if it needs to block.
574 */
575 static inline enum cds_wfcq_ret
576 ___cds_wfcq_splice_nonblocking(
577 cds_wfcq_head_ptr_t dest_q_head,
578 struct cds_wfcq_tail *dest_q_tail,
579 cds_wfcq_head_ptr_t src_q_head,
580 struct cds_wfcq_tail *src_q_tail)
581 {
582 return ___cds_wfcq_splice(dest_q_head, dest_q_tail,
583 src_q_head, src_q_tail, 0);
584 }
585
586 /*
587 * cds_wfcq_dequeue_with_state_blocking: dequeue a node from a wait-free queue.
588 *
589 * Content written into the node before enqueue is guaranteed to be
590 * consistent, but no other memory ordering is ensured.
591 * Mutual exclusion with cds_wfcq_splice_blocking and dequeue lock is
592 * ensured.
593 * It is valid to reuse and free a dequeued node immediately.
594 */
595 static inline struct cds_wfcq_node *
596 _cds_wfcq_dequeue_with_state_blocking(struct cds_wfcq_head *head,
597 struct cds_wfcq_tail *tail, int *state)
598 {
599 struct cds_wfcq_node *retval;
600
601 _cds_wfcq_dequeue_lock(head, tail);
602 retval = ___cds_wfcq_dequeue_with_state_blocking(head, tail, state);
603 _cds_wfcq_dequeue_unlock(head, tail);
604 return retval;
605 }
606
607 /*
608 * cds_wfcq_dequeue_blocking: dequeue node from queue.
609 *
610 * Same as cds_wfcq_dequeue_blocking, but without saving state.
611 */
612 static inline struct cds_wfcq_node *
613 _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
614 struct cds_wfcq_tail *tail)
615 {
616 return _cds_wfcq_dequeue_with_state_blocking(head, tail, NULL);
617 }
618
619 /*
620 * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
621 *
622 * Dequeue all nodes from src_q.
623 * dest_q must be already initialized.
624 * Content written into the node before enqueue is guaranteed to be
625 * consistent, but no other memory ordering is ensured.
626 * Mutual exclusion with cds_wfcq_dequeue_blocking and dequeue lock is
627 * ensured.
628 * Returns enum cds_wfcq_ret which indicates the state of the src or
629 * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK.
630 */
631 static inline enum cds_wfcq_ret
632 _cds_wfcq_splice_blocking(
633 struct cds_wfcq_head *dest_q_head,
634 struct cds_wfcq_tail *dest_q_tail,
635 struct cds_wfcq_head *src_q_head,
636 struct cds_wfcq_tail *src_q_tail)
637 {
638 enum cds_wfcq_ret ret;
639
640 _cds_wfcq_dequeue_lock(src_q_head, src_q_tail);
641 ret = ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail,
642 src_q_head, src_q_tail);
643 _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail);
644 return ret;
645 }
646
647 #ifdef __cplusplus
648 }
649 #endif
650
651 #endif /* _URCU_WFCQUEUE_STATIC_H */
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