2c8c447fd591f46fa213bb6573c79d2a8293316f
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.
64 #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
65 #define WFCQ_WAIT 10 /* Wait 10 ms if being set */
68 * cds_wfcq_node_init: initialize wait-free queue node.
70 static inline void _cds_wfcq_node_init(struct cds_wfcq_node
*node
)
76 * cds_wfcq_init: initialize wait-free queue.
78 static inline void _cds_wfcq_init(struct cds_wfcq_head
*head
,
79 struct cds_wfcq_tail
*tail
)
83 /* Set queue head and tail */
84 _cds_wfcq_node_init(&head
->node
);
85 tail
->p
= &head
->node
;
86 ret
= pthread_mutex_init(&head
->lock
, NULL
);
91 * cds_wfcq_empty: return whether wait-free queue is empty.
93 * No memory barrier is issued. No mutual exclusion is required.
95 static inline bool _cds_wfcq_empty(struct cds_wfcq_head
*head
,
96 struct cds_wfcq_tail
*tail
)
99 * Queue is empty if no node is pointed by head->node.next nor
100 * tail->p. Even though the tail->p check is sufficient to find
101 * out of the queue is empty, we first check head->node.next as a
102 * common case to ensure that dequeuers do not frequently access
103 * enqueuer's tail->p cache line.
105 return CMM_LOAD_SHARED(head
->node
.next
) == NULL
106 && CMM_LOAD_SHARED(tail
->p
) == &head
->node
;
109 static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head
*head
,
110 struct cds_wfcq_tail
*tail
)
114 ret
= pthread_mutex_lock(&head
->lock
);
118 static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head
*head
,
119 struct cds_wfcq_tail
*tail
)
123 ret
= pthread_mutex_unlock(&head
->lock
);
127 static inline void ___cds_wfcq_append(struct cds_wfcq_head
*head
,
128 struct cds_wfcq_tail
*tail
,
129 struct cds_wfcq_node
*new_head
,
130 struct cds_wfcq_node
*new_tail
)
132 struct cds_wfcq_node
*old_tail
;
135 * Implicit memory barrier before uatomic_xchg() orders earlier
136 * stores to data structure containing node and setting
137 * node->next to NULL before publication.
139 old_tail
= uatomic_xchg(&tail
->p
, new_tail
);
142 * Implicit memory barrier after uatomic_xchg() orders store to
143 * q->tail before store to old_tail->next.
145 * At this point, dequeuers see a NULL tail->p->next, which
146 * indicates that the queue is being appended to. The following
147 * store will append "node" to the queue from a dequeuer
150 CMM_STORE_SHARED(old_tail
->next
, new_head
);
154 * cds_wfcq_enqueue: enqueue a node into a wait-free queue.
156 * Issues a full memory barrier before enqueue. No mutual exclusion is
159 static inline void _cds_wfcq_enqueue(struct cds_wfcq_head
*head
,
160 struct cds_wfcq_tail
*tail
,
161 struct cds_wfcq_node
*new_tail
)
163 ___cds_wfcq_append(head
, tail
, new_tail
, new_tail
);
167 * Waiting for enqueuer to complete enqueue and return the next node.
169 static inline struct cds_wfcq_node
*
170 ___cds_wfcq_node_sync_next(struct cds_wfcq_node
*node
)
172 struct cds_wfcq_node
*next
;
176 * Adaptative busy-looping waiting for enqueuer to complete enqueue.
178 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
179 if (++attempt
>= WFCQ_ADAPT_ATTEMPTS
) {
180 poll(NULL
, 0, WFCQ_WAIT
); /* Wait for 10ms */
191 * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
193 * Content written into the node before enqueue is guaranteed to be
194 * consistent, but no other memory ordering is ensured.
195 * Should be called with cds_wfcq_dequeue_lock() held.
197 * Used by for-like iteration macros in urcu/wfqueue.h:
198 * __cds_wfcq_for_each_blocking()
199 * __cds_wfcq_for_each_blocking_safe()
201 static inline struct cds_wfcq_node
*
202 ___cds_wfcq_first_blocking(struct cds_wfcq_head
*head
,
203 struct cds_wfcq_tail
*tail
)
205 struct cds_wfcq_node
*node
;
207 if (_cds_wfcq_empty(head
, tail
))
209 node
= ___cds_wfcq_node_sync_next(&head
->node
);
210 /* Load head->node.next before loading node's content */
211 cmm_smp_read_barrier_depends();
216 * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
218 * Content written into the node before enqueue is guaranteed to be
219 * consistent, but no other memory ordering is ensured.
220 * Should be called with cds_wfcq_dequeue_lock() held.
222 * Used by for-like iteration macros in urcu/wfqueue.h:
223 * __cds_wfcq_for_each_blocking()
224 * __cds_wfcq_for_each_blocking_safe()
226 static inline struct cds_wfcq_node
*
227 ___cds_wfcq_next_blocking(struct cds_wfcq_head
*head
,
228 struct cds_wfcq_tail
*tail
,
229 struct cds_wfcq_node
*node
)
231 struct cds_wfcq_node
*next
;
234 * Even though the following tail->p check is sufficient to find
235 * out if we reached the end of the queue, we first check
236 * node->next as a common case to ensure that iteration on nodes
237 * do not frequently access enqueuer's tail->p cache line.
239 if ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
240 /* Load node->next before tail->p */
242 if (CMM_LOAD_SHARED(tail
->p
) == node
)
244 next
= ___cds_wfcq_node_sync_next(node
);
246 /* Load node->next before loading next's content */
247 cmm_smp_read_barrier_depends();
252 * __cds_wfcq_dequeue_blocking: dequeue a node from the queue.
254 * No need to go on a waitqueue here, as there is no possible state in which the
255 * list could cause dequeue to busy-loop needlessly while waiting for another
256 * thread to be scheduled. The queue appears empty until tail->next is set by
259 * Content written into the node before enqueue is guaranteed to be
260 * consistent, but no other memory ordering is ensured.
261 * It is valid to reuse and free a dequeued node immediately.
262 * Should be called with cds_wfcq_dequeue_lock() held.
264 static inline struct cds_wfcq_node
*
265 ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head
*head
,
266 struct cds_wfcq_tail
*tail
)
268 struct cds_wfcq_node
*node
, *next
;
270 if (_cds_wfcq_empty(head
, tail
))
273 node
= ___cds_wfcq_node_sync_next(&head
->node
);
275 if ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
277 * @node is probably the only node in the queue.
278 * Try to move the tail to &q->head.
279 * q->head.next is set to NULL here, and stays
280 * NULL if the cmpxchg succeeds. Should the
281 * cmpxchg fail due to a concurrent enqueue, the
282 * q->head.next will be set to the next node.
283 * The implicit memory barrier before
284 * uatomic_cmpxchg() orders load node->next
285 * before loading q->tail.
286 * The implicit memory barrier before uatomic_cmpxchg
287 * orders load q->head.next before loading node's
290 _cds_wfcq_node_init(&head
->node
);
291 if (uatomic_cmpxchg(&tail
->p
, node
, &head
->node
) == node
)
293 next
= ___cds_wfcq_node_sync_next(node
);
297 * Move queue head forward.
299 head
->node
.next
= next
;
301 /* Load q->head.next before loading node's content */
302 cmm_smp_read_barrier_depends();
307 * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
309 * Dequeue all nodes from src_q.
310 * dest_q must be already initialized.
311 * Should be called with cds_wfcq_dequeue_lock() held on src_q.
314 ___cds_wfcq_splice_blocking(
315 struct cds_wfcq_head
*dest_q_head
,
316 struct cds_wfcq_tail
*dest_q_tail
,
317 struct cds_wfcq_head
*src_q_head
,
318 struct cds_wfcq_tail
*src_q_tail
)
320 struct cds_wfcq_node
*head
, *tail
;
322 if (_cds_wfcq_empty(src_q_head
, src_q_tail
))
325 head
= ___cds_wfcq_node_sync_next(&src_q_head
->node
);
326 _cds_wfcq_node_init(&src_q_head
->node
);
329 * Memory barrier implied before uatomic_xchg() orders store to
330 * src_q->head before store to src_q->tail. This is required by
331 * concurrent enqueue on src_q, which exchanges the tail before
332 * updating the previous tail's next pointer.
334 tail
= uatomic_xchg(&src_q_tail
->p
, &src_q_head
->node
);
337 * Append the spliced content of src_q into dest_q. Does not
338 * require mutual exclusion on dest_q (wait-free).
340 ___cds_wfcq_append(dest_q_head
, dest_q_tail
, head
, tail
);
344 * cds_wfcq_dequeue_blocking: dequeue a node from a wait-free queue.
346 * Content written into the node before enqueue is guaranteed to be
347 * consistent, but no other memory ordering is ensured.
348 * Mutual exlusion with (and only with) cds_wfcq_splice_blocking is
350 * It is valid to reuse and free a dequeued node immediately.
352 static inline struct cds_wfcq_node
*
353 _cds_wfcq_dequeue_blocking(struct cds_wfcq_head
*head
,
354 struct cds_wfcq_tail
*tail
)
356 struct cds_wfcq_node
*retval
;
358 _cds_wfcq_dequeue_lock(head
, tail
);
359 retval
= ___cds_wfcq_dequeue_blocking(head
, tail
);
360 _cds_wfcq_dequeue_unlock(head
, tail
);
365 * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
367 * Dequeue all nodes from src_q.
368 * dest_q must be already initialized.
369 * Content written into the node before enqueue is guaranteed to be
370 * consistent, but no other memory ordering is ensured.
371 * Mutual exlusion with (and only with) cds_wfcq_dequeue_blocking is
375 _cds_wfcq_splice_blocking(
376 struct cds_wfcq_head
*dest_q_head
,
377 struct cds_wfcq_tail
*dest_q_tail
,
378 struct cds_wfcq_head
*src_q_head
,
379 struct cds_wfcq_tail
*src_q_tail
)
381 _cds_wfcq_dequeue_lock(src_q_head
, src_q_tail
);
382 ___cds_wfcq_splice_blocking(dest_q_head
, dest_q_tail
,
383 src_q_head
, src_q_tail
);
384 _cds_wfcq_dequeue_unlock(src_q_head
, src_q_tail
);
391 #endif /* _URCU_WFCQUEUE_STATIC_H */
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