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8ad4ce58 MD |
1 | #ifndef _URCU_WFCQUEUE_STATIC_H |
2 | #define _URCU_WFCQUEUE_STATIC_H | |
3 | ||
4 | /* | |
47215721 | 5 | * urcu/static/wfcqueue.h |
8ad4ce58 MD |
6 | * |
7 | * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue | |
8 | * | |
07c2a4fd MD |
9 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfcqueue.h for |
10 | * linking dynamically with the userspace rcu library. | |
8ad4ce58 MD |
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 * | |
47215721 | 174 | ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking) |
8ad4ce58 MD |
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) { | |
47215721 MD |
183 | if (!blocking) |
184 | return CDS_WFCQ_WOULDBLOCK; | |
8ad4ce58 MD |
185 | if (++attempt >= WFCQ_ADAPT_ATTEMPTS) { |
186 | poll(NULL, 0, WFCQ_WAIT); /* Wait for 10ms */ | |
187 | attempt = 0; | |
188 | } else { | |
189 | caa_cpu_relax(); | |
190 | } | |
191 | } | |
192 | ||
193 | return next; | |
194 | } | |
195 | ||
8ad4ce58 | 196 | static inline struct cds_wfcq_node * |
47215721 MD |
197 | ___cds_wfcq_first(struct cds_wfcq_head *head, |
198 | struct cds_wfcq_tail *tail, | |
199 | int blocking) | |
8ad4ce58 MD |
200 | { |
201 | struct cds_wfcq_node *node; | |
202 | ||
203 | if (_cds_wfcq_empty(head, tail)) | |
204 | return NULL; | |
47215721 | 205 | node = ___cds_wfcq_node_sync_next(&head->node, blocking); |
8ad4ce58 MD |
206 | /* Load head->node.next before loading node's content */ |
207 | cmm_smp_read_barrier_depends(); | |
208 | return node; | |
209 | } | |
210 | ||
211 | /* | |
47215721 | 212 | * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing. |
8ad4ce58 MD |
213 | * |
214 | * Content written into the node before enqueue is guaranteed to be | |
215 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 MD |
216 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
217 | * caller. | |
f94061a3 MD |
218 | * |
219 | * Used by for-like iteration macros in urcu/wfqueue.h: | |
220 | * __cds_wfcq_for_each_blocking() | |
221 | * __cds_wfcq_for_each_blocking_safe() | |
8ad4ce58 MD |
222 | */ |
223 | static inline struct cds_wfcq_node * | |
47215721 MD |
224 | ___cds_wfcq_first_blocking(struct cds_wfcq_head *head, |
225 | struct cds_wfcq_tail *tail) | |
226 | { | |
227 | return ___cds_wfcq_first(head, tail, 1); | |
228 | } | |
229 | ||
230 | ||
231 | /* | |
232 | * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing. | |
233 | * | |
234 | * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if | |
235 | * it needs to block. | |
236 | */ | |
237 | static inline struct cds_wfcq_node * | |
238 | ___cds_wfcq_first_nonblocking(struct cds_wfcq_head *head, | |
239 | struct cds_wfcq_tail *tail) | |
240 | { | |
241 | return ___cds_wfcq_first(head, tail, 0); | |
242 | } | |
243 | ||
244 | static inline struct cds_wfcq_node * | |
245 | ___cds_wfcq_next(struct cds_wfcq_head *head, | |
8ad4ce58 | 246 | struct cds_wfcq_tail *tail, |
47215721 MD |
247 | struct cds_wfcq_node *node, |
248 | int blocking) | |
8ad4ce58 MD |
249 | { |
250 | struct cds_wfcq_node *next; | |
251 | ||
252 | /* | |
253 | * Even though the following tail->p check is sufficient to find | |
254 | * out if we reached the end of the queue, we first check | |
255 | * node->next as a common case to ensure that iteration on nodes | |
256 | * do not frequently access enqueuer's tail->p cache line. | |
257 | */ | |
258 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
259 | /* Load node->next before tail->p */ | |
260 | cmm_smp_rmb(); | |
261 | if (CMM_LOAD_SHARED(tail->p) == node) | |
262 | return NULL; | |
47215721 | 263 | next = ___cds_wfcq_node_sync_next(node, blocking); |
8ad4ce58 MD |
264 | } |
265 | /* Load node->next before loading next's content */ | |
266 | cmm_smp_read_barrier_depends(); | |
267 | return next; | |
268 | } | |
269 | ||
270 | /* | |
47215721 | 271 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. |
8ad4ce58 | 272 | * |
8ad4ce58 MD |
273 | * Content written into the node before enqueue is guaranteed to be |
274 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 MD |
275 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
276 | * caller. | |
47215721 MD |
277 | * |
278 | * Used by for-like iteration macros in urcu/wfqueue.h: | |
279 | * __cds_wfcq_for_each_blocking() | |
280 | * __cds_wfcq_for_each_blocking_safe() | |
8ad4ce58 MD |
281 | */ |
282 | static inline struct cds_wfcq_node * | |
47215721 MD |
283 | ___cds_wfcq_next_blocking(struct cds_wfcq_head *head, |
284 | struct cds_wfcq_tail *tail, | |
285 | struct cds_wfcq_node *node) | |
286 | { | |
287 | return ___cds_wfcq_next(head, tail, node, 1); | |
288 | } | |
289 | ||
290 | /* | |
291 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. | |
292 | * | |
293 | * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if | |
294 | * it needs to block. | |
295 | */ | |
296 | static inline struct cds_wfcq_node * | |
297 | ___cds_wfcq_next_nonblocking(struct cds_wfcq_head *head, | |
298 | struct cds_wfcq_tail *tail, | |
299 | struct cds_wfcq_node *node) | |
300 | { | |
301 | return ___cds_wfcq_next(head, tail, node, 0); | |
302 | } | |
303 | ||
304 | static inline struct cds_wfcq_node * | |
305 | ___cds_wfcq_dequeue(struct cds_wfcq_head *head, | |
306 | struct cds_wfcq_tail *tail, | |
307 | int blocking) | |
8ad4ce58 MD |
308 | { |
309 | struct cds_wfcq_node *node, *next; | |
310 | ||
311 | if (_cds_wfcq_empty(head, tail)) | |
312 | return NULL; | |
313 | ||
47215721 | 314 | node = ___cds_wfcq_node_sync_next(&head->node, blocking); |
8ad4ce58 MD |
315 | |
316 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
317 | /* | |
318 | * @node is probably the only node in the queue. | |
319 | * Try to move the tail to &q->head. | |
320 | * q->head.next is set to NULL here, and stays | |
321 | * NULL if the cmpxchg succeeds. Should the | |
322 | * cmpxchg fail due to a concurrent enqueue, the | |
323 | * q->head.next will be set to the next node. | |
324 | * The implicit memory barrier before | |
325 | * uatomic_cmpxchg() orders load node->next | |
326 | * before loading q->tail. | |
327 | * The implicit memory barrier before uatomic_cmpxchg | |
328 | * orders load q->head.next before loading node's | |
329 | * content. | |
330 | */ | |
331 | _cds_wfcq_node_init(&head->node); | |
332 | if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) | |
333 | return node; | |
47215721 | 334 | next = ___cds_wfcq_node_sync_next(node, blocking); |
8ad4ce58 MD |
335 | } |
336 | ||
337 | /* | |
338 | * Move queue head forward. | |
339 | */ | |
340 | head->node.next = next; | |
341 | ||
342 | /* Load q->head.next before loading node's content */ | |
343 | cmm_smp_read_barrier_depends(); | |
344 | return node; | |
345 | } | |
346 | ||
347 | /* | |
47215721 | 348 | * __cds_wfcq_dequeue_blocking: dequeue a node from the queue. |
8ad4ce58 | 349 | * |
47215721 MD |
350 | * Content written into the node before enqueue is guaranteed to be |
351 | * consistent, but no other memory ordering is ensured. | |
352 | * It is valid to reuse and free a dequeued node immediately. | |
353 | * Dequeue/splice/iteration mutual exclusion should be ensured by the | |
354 | * caller. | |
8ad4ce58 | 355 | */ |
47215721 MD |
356 | static inline struct cds_wfcq_node * |
357 | ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head, | |
358 | struct cds_wfcq_tail *tail) | |
359 | { | |
360 | return ___cds_wfcq_dequeue(head, tail, 1); | |
361 | } | |
362 | ||
363 | /* | |
364 | * __cds_wfcq_dequeue_nonblocking: dequeue a node from a wait-free queue. | |
365 | * | |
366 | * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK | |
367 | * if it needs to block. | |
368 | */ | |
369 | static inline struct cds_wfcq_node * | |
370 | ___cds_wfcq_dequeue_nonblocking(struct cds_wfcq_head *head, | |
371 | struct cds_wfcq_tail *tail) | |
372 | { | |
373 | return ___cds_wfcq_dequeue(head, tail, 0); | |
374 | } | |
375 | ||
376 | static inline int | |
377 | ___cds_wfcq_splice( | |
8ad4ce58 MD |
378 | struct cds_wfcq_head *dest_q_head, |
379 | struct cds_wfcq_tail *dest_q_tail, | |
380 | struct cds_wfcq_head *src_q_head, | |
47215721 MD |
381 | struct cds_wfcq_tail *src_q_tail, |
382 | int blocking) | |
8ad4ce58 MD |
383 | { |
384 | struct cds_wfcq_node *head, *tail; | |
385 | ||
386 | if (_cds_wfcq_empty(src_q_head, src_q_tail)) | |
47215721 | 387 | return 0; |
8ad4ce58 | 388 | |
47215721 MD |
389 | head = ___cds_wfcq_node_sync_next(&src_q_head->node, blocking); |
390 | if (head == CDS_WFCQ_WOULDBLOCK) | |
391 | return -1; | |
8ad4ce58 MD |
392 | _cds_wfcq_node_init(&src_q_head->node); |
393 | ||
394 | /* | |
395 | * Memory barrier implied before uatomic_xchg() orders store to | |
396 | * src_q->head before store to src_q->tail. This is required by | |
397 | * concurrent enqueue on src_q, which exchanges the tail before | |
398 | * updating the previous tail's next pointer. | |
399 | */ | |
400 | tail = uatomic_xchg(&src_q_tail->p, &src_q_head->node); | |
401 | ||
402 | /* | |
403 | * Append the spliced content of src_q into dest_q. Does not | |
404 | * require mutual exclusion on dest_q (wait-free). | |
405 | */ | |
406 | ___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail); | |
47215721 MD |
407 | return 0; |
408 | } | |
409 | ||
410 | ||
411 | /* | |
412 | * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. | |
413 | * | |
414 | * Dequeue all nodes from src_q. | |
415 | * dest_q must be already initialized. | |
416 | * Dequeue/splice/iteration mutual exclusion for src_q should be ensured | |
417 | * by the caller. | |
418 | */ | |
419 | static inline void | |
420 | ___cds_wfcq_splice_blocking( | |
421 | struct cds_wfcq_head *dest_q_head, | |
422 | struct cds_wfcq_tail *dest_q_tail, | |
423 | struct cds_wfcq_head *src_q_head, | |
424 | struct cds_wfcq_tail *src_q_tail) | |
425 | { | |
426 | (void) ___cds_wfcq_splice(dest_q_head, dest_q_tail, | |
427 | src_q_head, src_q_tail, 1); | |
428 | } | |
429 | ||
430 | /* | |
431 | * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q. | |
432 | * | |
433 | * Same as __cds_wfcq_splice_blocking, but returns nonzero if it needs to | |
434 | * block. | |
435 | */ | |
436 | static inline int | |
437 | ___cds_wfcq_splice_nonblocking( | |
438 | struct cds_wfcq_head *dest_q_head, | |
439 | struct cds_wfcq_tail *dest_q_tail, | |
440 | struct cds_wfcq_head *src_q_head, | |
441 | struct cds_wfcq_tail *src_q_tail) | |
442 | { | |
443 | return ___cds_wfcq_splice(dest_q_head, dest_q_tail, | |
444 | src_q_head, src_q_tail, 0); | |
8ad4ce58 MD |
445 | } |
446 | ||
447 | /* | |
448 | * cds_wfcq_dequeue_blocking: dequeue a node from a wait-free queue. | |
449 | * | |
450 | * Content written into the node before enqueue is guaranteed to be | |
451 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 | 452 | * Mutual exlusion with cds_wfcq_splice_blocking and dequeue lock is |
8ad4ce58 MD |
453 | * ensured. |
454 | * It is valid to reuse and free a dequeued node immediately. | |
455 | */ | |
456 | static inline struct cds_wfcq_node * | |
457 | _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head, | |
458 | struct cds_wfcq_tail *tail) | |
459 | { | |
460 | struct cds_wfcq_node *retval; | |
461 | ||
462 | _cds_wfcq_dequeue_lock(head, tail); | |
463 | retval = ___cds_wfcq_dequeue_blocking(head, tail); | |
464 | _cds_wfcq_dequeue_unlock(head, tail); | |
465 | return retval; | |
466 | } | |
467 | ||
468 | /* | |
469 | * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. | |
470 | * | |
471 | * Dequeue all nodes from src_q. | |
472 | * dest_q must be already initialized. | |
473 | * Content written into the node before enqueue is guaranteed to be | |
474 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 | 475 | * Mutual exlusion with cds_wfcq_dequeue_blocking and dequeue lock is |
8ad4ce58 MD |
476 | * ensured. |
477 | */ | |
478 | static inline void | |
479 | _cds_wfcq_splice_blocking( | |
480 | struct cds_wfcq_head *dest_q_head, | |
481 | struct cds_wfcq_tail *dest_q_tail, | |
482 | struct cds_wfcq_head *src_q_head, | |
483 | struct cds_wfcq_tail *src_q_tail) | |
484 | { | |
485 | _cds_wfcq_dequeue_lock(src_q_head, src_q_tail); | |
486 | ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail, | |
487 | src_q_head, src_q_tail); | |
488 | _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail); | |
489 | } | |
490 | ||
491 | #ifdef __cplusplus | |
492 | } | |
493 | #endif | |
494 | ||
495 | #endif /* _URCU_WFCQUEUE_STATIC_H */ |