Commit | Line | Data |
---|---|---|
8ad4ce58 MD |
1 | #ifndef _URCU_WFCQUEUE_STATIC_H |
2 | #define _URCU_WFCQUEUE_STATIC_H | |
3 | ||
4 | /* | |
5 | * wfcqueue-static.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 wfcqueue.h for linking | |
10 | * 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 | * | |
ebfd2673 MD |
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. | |
8ad4ce58 MD |
48 | * |
49 | * Mutual exclusion of __cds_wfcq_* API | |
50 | * | |
51 | * Unless otherwise stated, the caller must ensure mutual exclusion of | |
52 | * queue update operations "dequeue" and "splice" (for source queue). | |
f94061a3 MD |
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. | |
8ad4ce58 MD |
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(). | |
59 | * | |
60 | * For convenience, cds_wfcq_dequeue_blocking() and | |
61 | * cds_wfcq_splice_blocking() hold the dequeue lock. | |
1fe734e1 MD |
62 | * |
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. | |
8ad4ce58 MD |
66 | */ |
67 | ||
68 | #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */ | |
69 | #define WFCQ_WAIT 10 /* Wait 10 ms if being set */ | |
70 | ||
71 | /* | |
72 | * cds_wfcq_node_init: initialize wait-free queue node. | |
73 | */ | |
74 | static inline void _cds_wfcq_node_init(struct cds_wfcq_node *node) | |
75 | { | |
76 | node->next = NULL; | |
77 | } | |
78 | ||
79 | /* | |
80 | * cds_wfcq_init: initialize wait-free queue. | |
81 | */ | |
82 | static inline void _cds_wfcq_init(struct cds_wfcq_head *head, | |
83 | struct cds_wfcq_tail *tail) | |
84 | { | |
85 | int ret; | |
86 | ||
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); | |
91 | assert(!ret); | |
92 | } | |
93 | ||
94 | /* | |
95 | * cds_wfcq_empty: return whether wait-free queue is empty. | |
96 | * | |
97 | * No memory barrier is issued. No mutual exclusion is required. | |
98 | */ | |
99 | static inline bool _cds_wfcq_empty(struct cds_wfcq_head *head, | |
100 | struct cds_wfcq_tail *tail) | |
101 | { | |
102 | /* | |
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. | |
108 | */ | |
109 | return CMM_LOAD_SHARED(head->node.next) == NULL | |
110 | && CMM_LOAD_SHARED(tail->p) == &head->node; | |
111 | } | |
112 | ||
113 | static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head *head, | |
114 | struct cds_wfcq_tail *tail) | |
115 | { | |
116 | int ret; | |
117 | ||
118 | ret = pthread_mutex_lock(&head->lock); | |
119 | assert(!ret); | |
120 | } | |
121 | ||
122 | static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head, | |
123 | struct cds_wfcq_tail *tail) | |
124 | { | |
125 | int ret; | |
126 | ||
127 | ret = pthread_mutex_unlock(&head->lock); | |
128 | assert(!ret); | |
129 | } | |
130 | ||
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) | |
135 | { | |
136 | struct cds_wfcq_node *old_tail; | |
137 | ||
138 | /* | |
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. | |
142 | */ | |
143 | old_tail = uatomic_xchg(&tail->p, new_tail); | |
144 | ||
145 | /* | |
146 | * Implicit memory barrier after uatomic_xchg() orders store to | |
147 | * q->tail before store to old_tail->next. | |
148 | * | |
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 | |
152 | * perspective. | |
153 | */ | |
154 | CMM_STORE_SHARED(old_tail->next, new_head); | |
155 | } | |
156 | ||
157 | /* | |
158 | * cds_wfcq_enqueue: enqueue a node into a wait-free queue. | |
159 | * | |
160 | * Issues a full memory barrier before enqueue. No mutual exclusion is | |
161 | * required. | |
162 | */ | |
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) | |
166 | { | |
167 | ___cds_wfcq_append(head, tail, new_tail, new_tail); | |
168 | } | |
169 | ||
170 | /* | |
171 | * Waiting for enqueuer to complete enqueue and return the next node. | |
172 | */ | |
173 | static inline struct cds_wfcq_node * | |
174 | ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node) | |
175 | { | |
176 | struct cds_wfcq_node *next; | |
177 | int attempt = 0; | |
178 | ||
179 | /* | |
180 | * Adaptative busy-looping waiting for enqueuer to complete enqueue. | |
181 | */ | |
182 | while ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
183 | if (++attempt >= WFCQ_ADAPT_ATTEMPTS) { | |
184 | poll(NULL, 0, WFCQ_WAIT); /* Wait for 10ms */ | |
185 | attempt = 0; | |
186 | } else { | |
187 | caa_cpu_relax(); | |
188 | } | |
189 | } | |
190 | ||
191 | return next; | |
192 | } | |
193 | ||
194 | /* | |
195 | * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing. | |
196 | * | |
197 | * Content written into the node before enqueue is guaranteed to be | |
198 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 MD |
199 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
200 | * caller. | |
f94061a3 MD |
201 | * |
202 | * Used by for-like iteration macros in urcu/wfqueue.h: | |
203 | * __cds_wfcq_for_each_blocking() | |
204 | * __cds_wfcq_for_each_blocking_safe() | |
8ad4ce58 MD |
205 | */ |
206 | static inline struct cds_wfcq_node * | |
207 | ___cds_wfcq_first_blocking(struct cds_wfcq_head *head, | |
208 | struct cds_wfcq_tail *tail) | |
209 | { | |
210 | struct cds_wfcq_node *node; | |
211 | ||
212 | if (_cds_wfcq_empty(head, tail)) | |
213 | return NULL; | |
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(); | |
217 | return node; | |
218 | } | |
219 | ||
220 | /* | |
221 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. | |
222 | * | |
223 | * Content written into the node before enqueue is guaranteed to be | |
224 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 MD |
225 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
226 | * caller. | |
f94061a3 MD |
227 | * |
228 | * Used by for-like iteration macros in urcu/wfqueue.h: | |
229 | * __cds_wfcq_for_each_blocking() | |
230 | * __cds_wfcq_for_each_blocking_safe() | |
8ad4ce58 MD |
231 | */ |
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) | |
236 | { | |
237 | struct cds_wfcq_node *next; | |
238 | ||
239 | /* | |
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. | |
244 | */ | |
245 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
246 | /* Load node->next before tail->p */ | |
247 | cmm_smp_rmb(); | |
248 | if (CMM_LOAD_SHARED(tail->p) == node) | |
249 | return NULL; | |
250 | next = ___cds_wfcq_node_sync_next(node); | |
251 | } | |
252 | /* Load node->next before loading next's content */ | |
253 | cmm_smp_read_barrier_depends(); | |
254 | return next; | |
255 | } | |
256 | ||
257 | /* | |
258 | * __cds_wfcq_dequeue_blocking: dequeue a node from the queue. | |
259 | * | |
8ad4ce58 MD |
260 | * Content written into the node before enqueue is guaranteed to be |
261 | * consistent, but no other memory ordering is ensured. | |
262 | * It is valid to reuse and free a dequeued node immediately. | |
1fe734e1 MD |
263 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
264 | * caller. | |
8ad4ce58 MD |
265 | */ |
266 | static inline struct cds_wfcq_node * | |
267 | ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head, | |
268 | struct cds_wfcq_tail *tail) | |
269 | { | |
270 | struct cds_wfcq_node *node, *next; | |
271 | ||
272 | if (_cds_wfcq_empty(head, tail)) | |
273 | return NULL; | |
274 | ||
275 | node = ___cds_wfcq_node_sync_next(&head->node); | |
276 | ||
277 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
278 | /* | |
279 | * @node is probably the only node in the queue. | |
280 | * Try to move the tail to &q->head. | |
281 | * q->head.next is set to NULL here, and stays | |
282 | * NULL if the cmpxchg succeeds. Should the | |
283 | * cmpxchg fail due to a concurrent enqueue, the | |
284 | * q->head.next will be set to the next node. | |
285 | * The implicit memory barrier before | |
286 | * uatomic_cmpxchg() orders load node->next | |
287 | * before loading q->tail. | |
288 | * The implicit memory barrier before uatomic_cmpxchg | |
289 | * orders load q->head.next before loading node's | |
290 | * content. | |
291 | */ | |
292 | _cds_wfcq_node_init(&head->node); | |
293 | if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) | |
294 | return node; | |
295 | next = ___cds_wfcq_node_sync_next(node); | |
296 | } | |
297 | ||
298 | /* | |
299 | * Move queue head forward. | |
300 | */ | |
301 | head->node.next = next; | |
302 | ||
303 | /* Load q->head.next before loading node's content */ | |
304 | cmm_smp_read_barrier_depends(); | |
305 | return node; | |
306 | } | |
307 | ||
308 | /* | |
309 | * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. | |
310 | * | |
311 | * Dequeue all nodes from src_q. | |
312 | * dest_q must be already initialized. | |
1fe734e1 MD |
313 | * Dequeue/splice/iteration mutual exclusion for src_q should be ensured |
314 | * by the caller. | |
8ad4ce58 MD |
315 | */ |
316 | static inline void | |
317 | ___cds_wfcq_splice_blocking( | |
318 | struct cds_wfcq_head *dest_q_head, | |
319 | struct cds_wfcq_tail *dest_q_tail, | |
320 | struct cds_wfcq_head *src_q_head, | |
321 | struct cds_wfcq_tail *src_q_tail) | |
322 | { | |
323 | struct cds_wfcq_node *head, *tail; | |
324 | ||
325 | if (_cds_wfcq_empty(src_q_head, src_q_tail)) | |
326 | return; | |
327 | ||
328 | head = ___cds_wfcq_node_sync_next(&src_q_head->node); | |
329 | _cds_wfcq_node_init(&src_q_head->node); | |
330 | ||
331 | /* | |
332 | * Memory barrier implied before uatomic_xchg() orders store to | |
333 | * src_q->head before store to src_q->tail. This is required by | |
334 | * concurrent enqueue on src_q, which exchanges the tail before | |
335 | * updating the previous tail's next pointer. | |
336 | */ | |
337 | tail = uatomic_xchg(&src_q_tail->p, &src_q_head->node); | |
338 | ||
339 | /* | |
340 | * Append the spliced content of src_q into dest_q. Does not | |
341 | * require mutual exclusion on dest_q (wait-free). | |
342 | */ | |
343 | ___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail); | |
344 | } | |
345 | ||
346 | /* | |
347 | * cds_wfcq_dequeue_blocking: dequeue a node from a wait-free queue. | |
348 | * | |
349 | * Content written into the node before enqueue is guaranteed to be | |
350 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 | 351 | * Mutual exlusion with cds_wfcq_splice_blocking and dequeue lock is |
8ad4ce58 MD |
352 | * ensured. |
353 | * It is valid to reuse and free a dequeued node immediately. | |
354 | */ | |
355 | static inline struct cds_wfcq_node * | |
356 | _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head, | |
357 | struct cds_wfcq_tail *tail) | |
358 | { | |
359 | struct cds_wfcq_node *retval; | |
360 | ||
361 | _cds_wfcq_dequeue_lock(head, tail); | |
362 | retval = ___cds_wfcq_dequeue_blocking(head, tail); | |
363 | _cds_wfcq_dequeue_unlock(head, tail); | |
364 | return retval; | |
365 | } | |
366 | ||
367 | /* | |
368 | * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. | |
369 | * | |
370 | * Dequeue all nodes from src_q. | |
371 | * dest_q must be already initialized. | |
372 | * Content written into the node before enqueue is guaranteed to be | |
373 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 | 374 | * Mutual exlusion with cds_wfcq_dequeue_blocking and dequeue lock is |
8ad4ce58 MD |
375 | * ensured. |
376 | */ | |
377 | static inline void | |
378 | _cds_wfcq_splice_blocking( | |
379 | struct cds_wfcq_head *dest_q_head, | |
380 | struct cds_wfcq_tail *dest_q_tail, | |
381 | struct cds_wfcq_head *src_q_head, | |
382 | struct cds_wfcq_tail *src_q_tail) | |
383 | { | |
384 | _cds_wfcq_dequeue_lock(src_q_head, src_q_tail); | |
385 | ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail, | |
386 | src_q_head, src_q_tail); | |
387 | _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail); | |
388 | } | |
389 | ||
390 | #ifdef __cplusplus | |
391 | } | |
392 | #endif | |
393 | ||
394 | #endif /* _URCU_WFCQUEUE_STATIC_H */ |