2ca9eebe649d9436f7584c1f898e0d29524207b9
1 #ifndef _URCU_WFCQUEUE_STATIC_H
2 #define _URCU_WFCQUEUE_STATIC_H
7 * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfcqueue.h for linking
10 * 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
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_* API
51 * Unless otherwise stated, the caller must ensure mutual exclusion of
52 * queue update operations "dequeue" and "splice" (for source queue).
53 * Queue read operations "first" and "next", which are used by
54 * "for_each" iterations, need to be protected against concurrent
55 * "dequeue" and "splice" (for source queue) by the caller.
56 * "enqueue", "splice" (for destination queue), and "empty" are the only
57 * operations that can be used without any mutual exclusion.
58 * Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock().
60 * For convenience, cds_wfcq_dequeue_blocking() and
61 * cds_wfcq_splice_blocking() hold the dequeue lock.
63 * Besides locking, mutual exclusion of dequeue, splice and iteration
64 * can be ensured by performing all of those operations from a single
65 * thread, without requiring any lock.
68 #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
69 #define WFCQ_WAIT 10 /* Wait 10 ms if being set */
72 * cds_wfcq_node_init: initialize wait-free queue node.
74 static inline void _cds_wfcq_node_init(struct cds_wfcq_node
*node
)
80 * cds_wfcq_init: initialize wait-free queue.
82 static inline void _cds_wfcq_init(struct cds_wfcq_head
*head
,
83 struct cds_wfcq_tail
*tail
)
87 /* Set queue head and tail */
88 _cds_wfcq_node_init(&head
->node
);
89 tail
->p
= &head
->node
;
90 ret
= pthread_mutex_init(&head
->lock
, NULL
);
95 * cds_wfcq_empty: return whether wait-free queue is empty.
97 * No memory barrier is issued. No mutual exclusion is required.
99 static inline bool _cds_wfcq_empty(struct cds_wfcq_head
*head
,
100 struct cds_wfcq_tail
*tail
)
103 * Queue is empty if no node is pointed by head->node.next nor
104 * tail->p. Even though the tail->p check is sufficient to find
105 * out of the queue is empty, we first check head->node.next as a
106 * common case to ensure that dequeuers do not frequently access
107 * enqueuer's tail->p cache line.
109 return CMM_LOAD_SHARED(head
->node
.next
) == NULL
110 && CMM_LOAD_SHARED(tail
->p
) == &head
->node
;
113 static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head
*head
,
114 struct cds_wfcq_tail
*tail
)
118 ret
= pthread_mutex_lock(&head
->lock
);
122 static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head
*head
,
123 struct cds_wfcq_tail
*tail
)
127 ret
= pthread_mutex_unlock(&head
->lock
);
131 static inline void ___cds_wfcq_append(struct cds_wfcq_head
*head
,
132 struct cds_wfcq_tail
*tail
,
133 struct cds_wfcq_node
*new_head
,
134 struct cds_wfcq_node
*new_tail
)
136 struct cds_wfcq_node
*old_tail
;
139 * Implicit memory barrier before uatomic_xchg() orders earlier
140 * stores to data structure containing node and setting
141 * node->next to NULL before publication.
143 old_tail
= uatomic_xchg(&tail
->p
, new_tail
);
146 * Implicit memory barrier after uatomic_xchg() orders store to
147 * q->tail before store to old_tail->next.
149 * At this point, dequeuers see a NULL tail->p->next, which
150 * indicates that the queue is being appended to. The following
151 * store will append "node" to the queue from a dequeuer
154 CMM_STORE_SHARED(old_tail
->next
, new_head
);
158 * cds_wfcq_enqueue: enqueue a node into a wait-free queue.
160 * Issues a full memory barrier before enqueue. No mutual exclusion is
163 static inline void _cds_wfcq_enqueue(struct cds_wfcq_head
*head
,
164 struct cds_wfcq_tail
*tail
,
165 struct cds_wfcq_node
*new_tail
)
167 ___cds_wfcq_append(head
, tail
, new_tail
, new_tail
);
171 * Waiting for enqueuer to complete enqueue and return the next node.
173 static inline struct cds_wfcq_node
*
174 ___cds_wfcq_node_sync_next(struct cds_wfcq_node
*node
)
176 struct cds_wfcq_node
*next
;
180 * Adaptative busy-looping waiting for enqueuer to complete enqueue.
182 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
183 if (++attempt
>= WFCQ_ADAPT_ATTEMPTS
) {
184 poll(NULL
, 0, WFCQ_WAIT
); /* Wait for 10ms */
195 * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
197 * Content written into the node before enqueue is guaranteed to be
198 * consistent, but no other memory ordering is ensured.
199 * Dequeue/splice/iteration mutual exclusion should be ensured by the
202 * Used by for-like iteration macros in urcu/wfqueue.h:
203 * __cds_wfcq_for_each_blocking()
204 * __cds_wfcq_for_each_blocking_safe()
206 static inline struct cds_wfcq_node
*
207 ___cds_wfcq_first_blocking(struct cds_wfcq_head
*head
,
208 struct cds_wfcq_tail
*tail
)
210 struct cds_wfcq_node
*node
;
212 if (_cds_wfcq_empty(head
, tail
))
214 node
= ___cds_wfcq_node_sync_next(&head
->node
);
215 /* Load head->node.next before loading node's content */
216 cmm_smp_read_barrier_depends();
221 * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
223 * Content written into the node before enqueue is guaranteed to be
224 * consistent, but no other memory ordering is ensured.
225 * Dequeue/splice/iteration mutual exclusion should be ensured by the
228 * Used by for-like iteration macros in urcu/wfqueue.h:
229 * __cds_wfcq_for_each_blocking()
230 * __cds_wfcq_for_each_blocking_safe()
232 static inline struct cds_wfcq_node
*
233 ___cds_wfcq_next_blocking(struct cds_wfcq_head
*head
,
234 struct cds_wfcq_tail
*tail
,
235 struct cds_wfcq_node
*node
)
237 struct cds_wfcq_node
*next
;
240 * Even though the following tail->p check is sufficient to find
241 * out if we reached the end of the queue, we first check
242 * node->next as a common case to ensure that iteration on nodes
243 * do not frequently access enqueuer's tail->p cache line.
245 if ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
246 /* Load node->next before tail->p */
248 if (CMM_LOAD_SHARED(tail
->p
) == node
)
250 next
= ___cds_wfcq_node_sync_next(node
);
252 /* Load node->next before loading next's content */
253 cmm_smp_read_barrier_depends();
258 * __cds_wfcq_dequeue_blocking: dequeue a node from the queue.
260 * No need to go on a waitqueue here, as there is no possible state in which the
261 * list could cause dequeue to busy-loop needlessly while waiting for another
262 * thread to be scheduled. The queue appears empty until tail->next is set by
265 * Content written into the node before enqueue is guaranteed to be
266 * consistent, but no other memory ordering is ensured.
267 * It is valid to reuse and free a dequeued node immediately.
268 * Dequeue/splice/iteration mutual exclusion should be ensured by the
271 static inline struct cds_wfcq_node
*
272 ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head
*head
,
273 struct cds_wfcq_tail
*tail
)
275 struct cds_wfcq_node
*node
, *next
;
277 if (_cds_wfcq_empty(head
, tail
))
280 node
= ___cds_wfcq_node_sync_next(&head
->node
);
282 if ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
284 * @node is probably the only node in the queue.
285 * Try to move the tail to &q->head.
286 * q->head.next is set to NULL here, and stays
287 * NULL if the cmpxchg succeeds. Should the
288 * cmpxchg fail due to a concurrent enqueue, the
289 * q->head.next will be set to the next node.
290 * The implicit memory barrier before
291 * uatomic_cmpxchg() orders load node->next
292 * before loading q->tail.
293 * The implicit memory barrier before uatomic_cmpxchg
294 * orders load q->head.next before loading node's
297 _cds_wfcq_node_init(&head
->node
);
298 if (uatomic_cmpxchg(&tail
->p
, node
, &head
->node
) == node
)
300 next
= ___cds_wfcq_node_sync_next(node
);
304 * Move queue head forward.
306 head
->node
.next
= next
;
308 /* Load q->head.next before loading node's content */
309 cmm_smp_read_barrier_depends();
314 * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
316 * Dequeue all nodes from src_q.
317 * dest_q must be already initialized.
318 * Dequeue/splice/iteration mutual exclusion for src_q should be ensured
322 ___cds_wfcq_splice_blocking(
323 struct cds_wfcq_head
*dest_q_head
,
324 struct cds_wfcq_tail
*dest_q_tail
,
325 struct cds_wfcq_head
*src_q_head
,
326 struct cds_wfcq_tail
*src_q_tail
)
328 struct cds_wfcq_node
*head
, *tail
;
330 if (_cds_wfcq_empty(src_q_head
, src_q_tail
))
333 head
= ___cds_wfcq_node_sync_next(&src_q_head
->node
);
334 _cds_wfcq_node_init(&src_q_head
->node
);
337 * Memory barrier implied before uatomic_xchg() orders store to
338 * src_q->head before store to src_q->tail. This is required by
339 * concurrent enqueue on src_q, which exchanges the tail before
340 * updating the previous tail's next pointer.
342 tail
= uatomic_xchg(&src_q_tail
->p
, &src_q_head
->node
);
345 * Append the spliced content of src_q into dest_q. Does not
346 * require mutual exclusion on dest_q (wait-free).
348 ___cds_wfcq_append(dest_q_head
, dest_q_tail
, head
, tail
);
352 * cds_wfcq_dequeue_blocking: dequeue a node from a wait-free queue.
354 * Content written into the node before enqueue is guaranteed to be
355 * consistent, but no other memory ordering is ensured.
356 * Mutual exlusion with cds_wfcq_splice_blocking and dequeue lock is
358 * It is valid to reuse and free a dequeued node immediately.
360 static inline struct cds_wfcq_node
*
361 _cds_wfcq_dequeue_blocking(struct cds_wfcq_head
*head
,
362 struct cds_wfcq_tail
*tail
)
364 struct cds_wfcq_node
*retval
;
366 _cds_wfcq_dequeue_lock(head
, tail
);
367 retval
= ___cds_wfcq_dequeue_blocking(head
, tail
);
368 _cds_wfcq_dequeue_unlock(head
, tail
);
373 * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
375 * Dequeue all nodes from src_q.
376 * dest_q must be already initialized.
377 * Content written into the node before enqueue is guaranteed to be
378 * consistent, but no other memory ordering is ensured.
379 * Mutual exlusion with cds_wfcq_dequeue_blocking and dequeue lock is
383 _cds_wfcq_splice_blocking(
384 struct cds_wfcq_head
*dest_q_head
,
385 struct cds_wfcq_tail
*dest_q_tail
,
386 struct cds_wfcq_head
*src_q_head
,
387 struct cds_wfcq_tail
*src_q_tail
)
389 _cds_wfcq_dequeue_lock(src_q_head
, src_q_tail
);
390 ___cds_wfcq_splice_blocking(dest_q_head
, dest_q_tail
,
391 src_q_head
, src_q_tail
);
392 _cds_wfcq_dequeue_unlock(src_q_head
, src_q_tail
);
399 #endif /* _URCU_WFCQUEUE_STATIC_H */
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