1 #ifndef _URCU_WFCQUEUE_STATIC_H
2 #define _URCU_WFCQUEUE_STATIC_H
5 * urcu/static/wfcqueue.h
7 * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfcqueue.h for
10 * linking dynamically with the userspace rcu library.
12 * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright 2011-2012 - Lai Jiangshan <laijs@cn.fujitsu.com>
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.
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.
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
33 #include <urcu/assert.h>
34 #include <urcu/compiler.h>
35 #include <urcu/uatomic.h>
42 * Concurrent queue with wait-free enqueue/blocking dequeue.
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.
49 * Mutual exclusion of cds_wfcq_* / __cds_wfcq_* API
51 * Synchronization table:
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 "-".
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
65 * [1] [2] [3] [4] [5] [6]
73 * Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock().
75 * For convenience, cds_wfcq_dequeue_blocking() and
76 * cds_wfcq_splice_blocking() hold the dequeue lock.
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.
83 #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
84 #define WFCQ_WAIT 10 /* Wait 10 ms if being set */
87 * cds_wfcq_node_init: initialize wait-free queue node.
89 static inline void _cds_wfcq_node_init(struct cds_wfcq_node
*node
)
95 * cds_wfcq_init: initialize wait-free queue (with lock). Pair with
98 static inline void _cds_wfcq_init(struct cds_wfcq_head
*head
,
99 struct cds_wfcq_tail
*tail
)
103 /* Set queue head and tail */
104 _cds_wfcq_node_init(&head
->node
);
105 tail
->p
= &head
->node
;
106 ret
= pthread_mutex_init(&head
->lock
, NULL
);
107 urcu_posix_assert(!ret
);
111 * cds_wfcq_destroy: destroy wait-free queue (with lock). Pair with
114 static inline void _cds_wfcq_destroy(struct cds_wfcq_head
*head
,
115 struct cds_wfcq_tail
*tail
__attribute__((unused
)))
117 int ret
= pthread_mutex_destroy(&head
->lock
);
118 urcu_posix_assert(!ret
);
122 * __cds_wfcq_init: initialize wait-free queue (without lock). Don't
123 * pair with any destroy function.
125 static inline void ___cds_wfcq_init(struct __cds_wfcq_head
*head
,
126 struct cds_wfcq_tail
*tail
)
128 /* Set queue head and tail */
129 _cds_wfcq_node_init(&head
->node
);
130 tail
->p
= &head
->node
;
134 * cds_wfcq_empty: return whether wait-free queue is empty.
136 * No memory barrier is issued. No mutual exclusion is required.
138 * We perform the test on head->node.next to check if the queue is
139 * possibly empty, but we confirm this by checking if the tail pointer
140 * points to the head node because the tail pointer is the linearisation
141 * point of the enqueuers. Just checking the head next pointer could
142 * make a queue appear empty if an enqueuer is preempted for a long time
143 * between xchg() and setting the previous node's next pointer.
145 static inline bool _cds_wfcq_empty(cds_wfcq_head_ptr_t u_head
,
146 struct cds_wfcq_tail
*tail
)
148 struct __cds_wfcq_head
*head
= u_head
._h
;
150 * Queue is empty if no node is pointed by head->node.next nor
151 * tail->p. Even though the tail->p check is sufficient to find
152 * out of the queue is empty, we first check head->node.next as a
153 * common case to ensure that dequeuers do not frequently access
154 * enqueuer's tail->p cache line.
156 return CMM_LOAD_SHARED(head
->node
.next
) == NULL
157 && CMM_LOAD_SHARED(tail
->p
) == &head
->node
;
160 static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head
*head
,
161 struct cds_wfcq_tail
*tail
__attribute__((unused
)))
165 ret
= pthread_mutex_lock(&head
->lock
);
166 urcu_posix_assert(!ret
);
169 static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head
*head
,
170 struct cds_wfcq_tail
*tail
__attribute__((unused
)))
174 ret
= pthread_mutex_unlock(&head
->lock
);
175 urcu_posix_assert(!ret
);
178 static inline bool ___cds_wfcq_append(cds_wfcq_head_ptr_t u_head
,
179 struct cds_wfcq_tail
*tail
,
180 struct cds_wfcq_node
*new_head
,
181 struct cds_wfcq_node
*new_tail
)
183 struct __cds_wfcq_head
*head
= u_head
._h
;
184 struct cds_wfcq_node
*old_tail
;
187 * Implicit memory barrier before uatomic_xchg() orders earlier
188 * stores to data structure containing node and setting
189 * node->next to NULL before publication.
191 old_tail
= uatomic_xchg(&tail
->p
, new_tail
);
194 * Implicit memory barrier after uatomic_xchg() orders store to
195 * q->tail before store to old_tail->next.
197 * At this point, dequeuers see a NULL tail->p->next, which
198 * indicates that the queue is being appended to. The following
199 * store will append "node" to the queue from a dequeuer
202 CMM_STORE_SHARED(old_tail
->next
, new_head
);
204 * Return false if queue was empty prior to adding the node,
207 return old_tail
!= &head
->node
;
211 * cds_wfcq_enqueue: enqueue a node into a wait-free queue.
213 * Issues a full memory barrier before enqueue. No mutual exclusion is
216 * Returns false if the queue was empty prior to adding the node.
217 * Returns true otherwise.
219 static inline bool _cds_wfcq_enqueue(cds_wfcq_head_ptr_t head
,
220 struct cds_wfcq_tail
*tail
,
221 struct cds_wfcq_node
*new_tail
)
223 return ___cds_wfcq_append(head
, tail
, new_tail
, new_tail
);
227 * CDS_WFCQ_WAIT_SLEEP:
229 * By default, this sleeps for the given @msec milliseconds.
230 * This is a macro which LGPL users may #define themselves before
231 * including wfcqueue.h to override the default behavior (e.g.
232 * to log a warning or perform other background work).
234 #ifndef CDS_WFCQ_WAIT_SLEEP
235 #define CDS_WFCQ_WAIT_SLEEP(msec) ___cds_wfcq_wait_sleep(msec)
238 static inline void ___cds_wfcq_wait_sleep(int msec
)
240 (void) poll(NULL
, 0, msec
);
244 * ___cds_wfcq_busy_wait: adaptative busy-wait.
246 * Returns 1 if nonblocking and needs to block, 0 otherwise.
249 ___cds_wfcq_busy_wait(int *attempt
, int blocking
)
253 if (++(*attempt
) >= WFCQ_ADAPT_ATTEMPTS
) {
254 CDS_WFCQ_WAIT_SLEEP(WFCQ_WAIT
); /* Wait for 10ms */
263 * Waiting for enqueuer to complete enqueue and return the next node.
265 static inline struct cds_wfcq_node
*
266 ___cds_wfcq_node_sync_next(struct cds_wfcq_node
*node
, int blocking
)
268 struct cds_wfcq_node
*next
;
272 * Adaptative busy-looping waiting for enqueuer to complete enqueue.
274 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
275 if (___cds_wfcq_busy_wait(&attempt
, blocking
))
276 return CDS_WFCQ_WOULDBLOCK
;
282 static inline struct cds_wfcq_node
*
283 ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head
,
284 struct cds_wfcq_tail
*tail
,
287 struct __cds_wfcq_head
*head
= u_head
._h
;
288 struct cds_wfcq_node
*node
;
290 if (_cds_wfcq_empty(__cds_wfcq_head_cast(head
), tail
))
292 node
= ___cds_wfcq_node_sync_next(&head
->node
, blocking
);
293 /* Load head->node.next before loading node's content */
294 cmm_smp_read_barrier_depends();
299 * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
301 * Content written into the node before enqueue is guaranteed to be
302 * consistent, but no other memory ordering is ensured.
303 * Dequeue/splice/iteration mutual exclusion should be ensured by the
306 * Used by for-like iteration macros in urcu/wfqueue.h:
307 * __cds_wfcq_for_each_blocking()
308 * __cds_wfcq_for_each_blocking_safe()
310 * Returns NULL if queue is empty, first node otherwise.
312 static inline struct cds_wfcq_node
*
313 ___cds_wfcq_first_blocking(cds_wfcq_head_ptr_t head
,
314 struct cds_wfcq_tail
*tail
)
316 return ___cds_wfcq_first(head
, tail
, 1);
321 * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing.
323 * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if
326 static inline struct cds_wfcq_node
*
327 ___cds_wfcq_first_nonblocking(cds_wfcq_head_ptr_t head
,
328 struct cds_wfcq_tail
*tail
)
330 return ___cds_wfcq_first(head
, tail
, 0);
333 static inline struct cds_wfcq_node
*
334 ___cds_wfcq_next(cds_wfcq_head_ptr_t head
__attribute__((unused
)),
335 struct cds_wfcq_tail
*tail
,
336 struct cds_wfcq_node
*node
,
339 struct cds_wfcq_node
*next
;
342 * Even though the following tail->p check is sufficient to find
343 * out if we reached the end of the queue, we first check
344 * node->next as a common case to ensure that iteration on nodes
345 * do not frequently access enqueuer's tail->p cache line.
347 if ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
348 /* Load node->next before tail->p */
350 if (CMM_LOAD_SHARED(tail
->p
) == node
)
352 next
= ___cds_wfcq_node_sync_next(node
, blocking
);
354 /* Load node->next before loading next's content */
355 cmm_smp_read_barrier_depends();
360 * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
362 * Content written into the node before enqueue is guaranteed to be
363 * consistent, but no other memory ordering is ensured.
364 * Dequeue/splice/iteration mutual exclusion should be ensured by the
367 * Used by for-like iteration macros in urcu/wfqueue.h:
368 * __cds_wfcq_for_each_blocking()
369 * __cds_wfcq_for_each_blocking_safe()
371 * Returns NULL if reached end of queue, non-NULL next queue node
374 static inline struct cds_wfcq_node
*
375 ___cds_wfcq_next_blocking(cds_wfcq_head_ptr_t head
,
376 struct cds_wfcq_tail
*tail
,
377 struct cds_wfcq_node
*node
)
379 return ___cds_wfcq_next(head
, tail
, node
, 1);
383 * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
385 * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if
388 static inline struct cds_wfcq_node
*
389 ___cds_wfcq_next_nonblocking(cds_wfcq_head_ptr_t head
,
390 struct cds_wfcq_tail
*tail
,
391 struct cds_wfcq_node
*node
)
393 return ___cds_wfcq_next(head
, tail
, node
, 0);
396 static inline struct cds_wfcq_node
*
397 ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head
,
398 struct cds_wfcq_tail
*tail
,
402 struct __cds_wfcq_head
*head
= u_head
._h
;
403 struct cds_wfcq_node
*node
, *next
;
408 if (_cds_wfcq_empty(__cds_wfcq_head_cast(head
), tail
)) {
412 node
= ___cds_wfcq_node_sync_next(&head
->node
, blocking
);
413 if (!blocking
&& node
== CDS_WFCQ_WOULDBLOCK
) {
414 return CDS_WFCQ_WOULDBLOCK
;
417 if ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
419 * @node is probably the only node in the queue.
420 * Try to move the tail to &q->head.
421 * q->head.next is set to NULL here, and stays
422 * NULL if the cmpxchg succeeds. Should the
423 * cmpxchg fail due to a concurrent enqueue, the
424 * q->head.next will be set to the next node.
425 * The implicit memory barrier before
426 * uatomic_cmpxchg() orders load node->next
427 * before loading q->tail.
428 * The implicit memory barrier before uatomic_cmpxchg
429 * orders load q->head.next before loading node's
432 _cds_wfcq_node_init(&head
->node
);
433 if (uatomic_cmpxchg(&tail
->p
, node
, &head
->node
) == node
) {
435 *state
|= CDS_WFCQ_STATE_LAST
;
438 next
= ___cds_wfcq_node_sync_next(node
, blocking
);
440 * In nonblocking mode, if we would need to block to
441 * get node's next, set the head next node pointer
442 * (currently NULL) back to its original value.
444 if (!blocking
&& next
== CDS_WFCQ_WOULDBLOCK
) {
445 head
->node
.next
= node
;
446 return CDS_WFCQ_WOULDBLOCK
;
451 * Move queue head forward.
453 head
->node
.next
= next
;
455 /* Load q->head.next before loading node's content */
456 cmm_smp_read_barrier_depends();
461 * __cds_wfcq_dequeue_with_state_blocking: dequeue node from queue, with state.
463 * Content written into the node before enqueue is guaranteed to be
464 * consistent, but no other memory ordering is ensured.
465 * It is valid to reuse and free a dequeued node immediately.
466 * Dequeue/splice/iteration mutual exclusion should be ensured by the
469 static inline struct cds_wfcq_node
*
470 ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_ptr_t head
,
471 struct cds_wfcq_tail
*tail
, int *state
)
473 return ___cds_wfcq_dequeue_with_state(head
, tail
, state
, 1);
477 * ___cds_wfcq_dequeue_blocking: dequeue node from queue.
479 * Same as __cds_wfcq_dequeue_with_state_blocking, but without saving
482 static inline struct cds_wfcq_node
*
483 ___cds_wfcq_dequeue_blocking(cds_wfcq_head_ptr_t head
,
484 struct cds_wfcq_tail
*tail
)
486 return ___cds_wfcq_dequeue_with_state_blocking(head
, tail
, NULL
);
490 * __cds_wfcq_dequeue_with_state_nonblocking: dequeue node, with state.
492 * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK
493 * if it needs to block.
495 static inline struct cds_wfcq_node
*
496 ___cds_wfcq_dequeue_with_state_nonblocking(cds_wfcq_head_ptr_t head
,
497 struct cds_wfcq_tail
*tail
, int *state
)
499 return ___cds_wfcq_dequeue_with_state(head
, tail
, state
, 0);
503 * ___cds_wfcq_dequeue_nonblocking: dequeue node from queue.
505 * Same as __cds_wfcq_dequeue_with_state_nonblocking, but without saving
508 static inline struct cds_wfcq_node
*
509 ___cds_wfcq_dequeue_nonblocking(cds_wfcq_head_ptr_t head
,
510 struct cds_wfcq_tail
*tail
)
512 return ___cds_wfcq_dequeue_with_state_nonblocking(head
, tail
, NULL
);
516 * __cds_wfcq_splice: enqueue all src_q nodes at the end of dest_q.
518 * Dequeue all nodes from src_q.
519 * dest_q must be already initialized.
520 * Mutual exclusion for src_q should be ensured by the caller as
521 * specified in the "Synchronisation table".
522 * Returns enum cds_wfcq_ret which indicates the state of the src or
525 static inline enum cds_wfcq_ret
527 cds_wfcq_head_ptr_t u_dest_q_head
,
528 struct cds_wfcq_tail
*dest_q_tail
,
529 cds_wfcq_head_ptr_t u_src_q_head
,
530 struct cds_wfcq_tail
*src_q_tail
,
533 struct __cds_wfcq_head
*dest_q_head
= u_dest_q_head
._h
;
534 struct __cds_wfcq_head
*src_q_head
= u_src_q_head
._h
;
535 struct cds_wfcq_node
*head
, *tail
;
539 * Initial emptiness check to speed up cases where queue is
540 * empty: only require loads to check if queue is empty.
542 if (_cds_wfcq_empty(__cds_wfcq_head_cast(src_q_head
), src_q_tail
))
543 return CDS_WFCQ_RET_SRC_EMPTY
;
547 * Open-coded _cds_wfcq_empty() by testing result of
548 * uatomic_xchg, as well as tail pointer vs head node
551 head
= uatomic_xchg(&src_q_head
->node
.next
, NULL
);
553 break; /* non-empty */
554 if (CMM_LOAD_SHARED(src_q_tail
->p
) == &src_q_head
->node
)
555 return CDS_WFCQ_RET_SRC_EMPTY
;
556 if (___cds_wfcq_busy_wait(&attempt
, blocking
))
557 return CDS_WFCQ_RET_WOULDBLOCK
;
561 * Memory barrier implied before uatomic_xchg() orders store to
562 * src_q->head before store to src_q->tail. This is required by
563 * concurrent enqueue on src_q, which exchanges the tail before
564 * updating the previous tail's next pointer.
566 tail
= uatomic_xchg(&src_q_tail
->p
, &src_q_head
->node
);
569 * Append the spliced content of src_q into dest_q. Does not
570 * require mutual exclusion on dest_q (wait-free).
572 if (___cds_wfcq_append(__cds_wfcq_head_cast(dest_q_head
), dest_q_tail
,
574 return CDS_WFCQ_RET_DEST_NON_EMPTY
;
576 return CDS_WFCQ_RET_DEST_EMPTY
;
580 * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
582 * Dequeue all nodes from src_q.
583 * dest_q must be already initialized.
584 * Mutual exclusion for src_q should be ensured by the caller as
585 * specified in the "Synchronisation table".
586 * Returns enum cds_wfcq_ret which indicates the state of the src or
587 * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK.
589 static inline enum cds_wfcq_ret
590 ___cds_wfcq_splice_blocking(
591 cds_wfcq_head_ptr_t dest_q_head
,
592 struct cds_wfcq_tail
*dest_q_tail
,
593 cds_wfcq_head_ptr_t src_q_head
,
594 struct cds_wfcq_tail
*src_q_tail
)
596 return ___cds_wfcq_splice(dest_q_head
, dest_q_tail
,
597 src_q_head
, src_q_tail
, 1);
601 * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q.
603 * Same as __cds_wfcq_splice_blocking, but returns
604 * CDS_WFCQ_RET_WOULDBLOCK if it needs to block.
606 static inline enum cds_wfcq_ret
607 ___cds_wfcq_splice_nonblocking(
608 cds_wfcq_head_ptr_t dest_q_head
,
609 struct cds_wfcq_tail
*dest_q_tail
,
610 cds_wfcq_head_ptr_t src_q_head
,
611 struct cds_wfcq_tail
*src_q_tail
)
613 return ___cds_wfcq_splice(dest_q_head
, dest_q_tail
,
614 src_q_head
, src_q_tail
, 0);
618 * cds_wfcq_dequeue_with_state_blocking: dequeue a node from a wait-free queue.
620 * Content written into the node before enqueue is guaranteed to be
621 * consistent, but no other memory ordering is ensured.
622 * Mutual exclusion with cds_wfcq_splice_blocking and dequeue lock is
624 * It is valid to reuse and free a dequeued node immediately.
626 static inline struct cds_wfcq_node
*
627 _cds_wfcq_dequeue_with_state_blocking(struct cds_wfcq_head
*head
,
628 struct cds_wfcq_tail
*tail
, int *state
)
630 struct cds_wfcq_node
*retval
;
632 _cds_wfcq_dequeue_lock(head
, tail
);
633 retval
= ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_cast(head
),
635 _cds_wfcq_dequeue_unlock(head
, tail
);
640 * cds_wfcq_dequeue_blocking: dequeue node from queue.
642 * Same as cds_wfcq_dequeue_blocking, but without saving state.
644 static inline struct cds_wfcq_node
*
645 _cds_wfcq_dequeue_blocking(struct cds_wfcq_head
*head
,
646 struct cds_wfcq_tail
*tail
)
648 return _cds_wfcq_dequeue_with_state_blocking(head
, tail
, NULL
);
652 * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
654 * Dequeue all nodes from src_q.
655 * dest_q must be already initialized.
656 * Content written into the node before enqueue is guaranteed to be
657 * consistent, but no other memory ordering is ensured.
658 * Mutual exclusion with cds_wfcq_dequeue_blocking and dequeue lock is
660 * Returns enum cds_wfcq_ret which indicates the state of the src or
661 * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK.
663 static inline enum cds_wfcq_ret
664 _cds_wfcq_splice_blocking(
665 struct cds_wfcq_head
*dest_q_head
,
666 struct cds_wfcq_tail
*dest_q_tail
,
667 struct cds_wfcq_head
*src_q_head
,
668 struct cds_wfcq_tail
*src_q_tail
)
670 enum cds_wfcq_ret ret
;
672 _cds_wfcq_dequeue_lock(src_q_head
, src_q_tail
);
673 ret
= ___cds_wfcq_splice_blocking(cds_wfcq_head_cast(dest_q_head
), dest_q_tail
,
674 cds_wfcq_head_cast(src_q_head
), src_q_tail
);
675 _cds_wfcq_dequeue_unlock(src_q_head
, src_q_tail
);
683 #endif /* _URCU_WFCQUEUE_STATIC_H */