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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 | 48 | * |
f878b49e MD |
49 | * Mutual exclusion of cds_wfcq_* / __cds_wfcq_* API |
50 | * | |
51 | * Synchronization table: | |
52 | * | |
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 "-". | |
56 | * | |
57 | * Legend: | |
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 | |
63 | * [6] __cds_wfcq_next | |
64 | * | |
65 | * [1] [2] [3] [4] [5] [6] | |
66 | * [1] - - - - - - | |
67 | * [2] - - - - - - | |
68 | * [3] - - X X X X | |
69 | * [4] - - X - X X | |
70 | * [5] - - X X - - | |
71 | * [6] - - X X - - | |
8ad4ce58 | 72 | * |
8ad4ce58 MD |
73 | * Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock(). |
74 | * | |
75 | * For convenience, cds_wfcq_dequeue_blocking() and | |
76 | * cds_wfcq_splice_blocking() hold the dequeue lock. | |
1fe734e1 MD |
77 | * |
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. | |
8ad4ce58 MD |
81 | */ |
82 | ||
83 | #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */ | |
84 | #define WFCQ_WAIT 10 /* Wait 10 ms if being set */ | |
85 | ||
86 | /* | |
87 | * cds_wfcq_node_init: initialize wait-free queue node. | |
88 | */ | |
89 | static inline void _cds_wfcq_node_init(struct cds_wfcq_node *node) | |
90 | { | |
91 | node->next = NULL; | |
92 | } | |
93 | ||
94 | /* | |
200d100e MD |
95 | * cds_wfcq_init: initialize wait-free queue (with lock). Pair with |
96 | * cds_wfcq_destroy(). | |
8ad4ce58 MD |
97 | */ |
98 | static inline void _cds_wfcq_init(struct cds_wfcq_head *head, | |
99 | struct cds_wfcq_tail *tail) | |
100 | { | |
101 | int ret; | |
102 | ||
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 | assert(!ret); | |
108 | } | |
109 | ||
f637f191 | 110 | /* |
200d100e MD |
111 | * cds_wfcq_destroy: destroy wait-free queue (with lock). Pair with |
112 | * cds_wfcq_init(). | |
113 | */ | |
114 | static inline void _cds_wfcq_destroy(struct cds_wfcq_head *head, | |
115 | struct cds_wfcq_tail *tail) | |
116 | { | |
117 | int ret = pthread_mutex_destroy(&head->lock); | |
118 | assert(!ret); | |
119 | } | |
120 | ||
121 | /* | |
122 | * __cds_wfcq_init: initialize wait-free queue (without lock). Don't | |
123 | * pair with any destroy function. | |
f637f191 MD |
124 | */ |
125 | static inline void ___cds_wfcq_init(struct __cds_wfcq_head *head, | |
126 | struct cds_wfcq_tail *tail) | |
127 | { | |
128 | /* Set queue head and tail */ | |
129 | _cds_wfcq_node_init(&head->node); | |
130 | tail->p = &head->node; | |
131 | } | |
132 | ||
8ad4ce58 MD |
133 | /* |
134 | * cds_wfcq_empty: return whether wait-free queue is empty. | |
135 | * | |
136 | * No memory barrier is issued. No mutual exclusion is required. | |
6d5729f7 MD |
137 | * |
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. | |
8ad4ce58 | 144 | */ |
f637f191 | 145 | static inline bool _cds_wfcq_empty(cds_wfcq_head_ptr_t u_head, |
8ad4ce58 MD |
146 | struct cds_wfcq_tail *tail) |
147 | { | |
f637f191 | 148 | struct __cds_wfcq_head *head = u_head._h; |
8ad4ce58 MD |
149 | /* |
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. | |
155 | */ | |
156 | return CMM_LOAD_SHARED(head->node.next) == NULL | |
157 | && CMM_LOAD_SHARED(tail->p) == &head->node; | |
158 | } | |
159 | ||
160 | static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head *head, | |
161 | struct cds_wfcq_tail *tail) | |
162 | { | |
163 | int ret; | |
164 | ||
165 | ret = pthread_mutex_lock(&head->lock); | |
166 | assert(!ret); | |
167 | } | |
168 | ||
169 | static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head, | |
170 | struct cds_wfcq_tail *tail) | |
171 | { | |
172 | int ret; | |
173 | ||
174 | ret = pthread_mutex_unlock(&head->lock); | |
175 | assert(!ret); | |
176 | } | |
177 | ||
f637f191 | 178 | static inline bool ___cds_wfcq_append(cds_wfcq_head_ptr_t u_head, |
8ad4ce58 MD |
179 | struct cds_wfcq_tail *tail, |
180 | struct cds_wfcq_node *new_head, | |
181 | struct cds_wfcq_node *new_tail) | |
182 | { | |
f637f191 | 183 | struct __cds_wfcq_head *head = u_head._h; |
8ad4ce58 MD |
184 | struct cds_wfcq_node *old_tail; |
185 | ||
186 | /* | |
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. | |
190 | */ | |
191 | old_tail = uatomic_xchg(&tail->p, new_tail); | |
192 | ||
193 | /* | |
194 | * Implicit memory barrier after uatomic_xchg() orders store to | |
195 | * q->tail before store to old_tail->next. | |
196 | * | |
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 | |
200 | * perspective. | |
201 | */ | |
202 | CMM_STORE_SHARED(old_tail->next, new_head); | |
23773356 MD |
203 | /* |
204 | * Return false if queue was empty prior to adding the node, | |
205 | * else return true. | |
206 | */ | |
207 | return old_tail != &head->node; | |
8ad4ce58 MD |
208 | } |
209 | ||
210 | /* | |
211 | * cds_wfcq_enqueue: enqueue a node into a wait-free queue. | |
212 | * | |
213 | * Issues a full memory barrier before enqueue. No mutual exclusion is | |
214 | * required. | |
23773356 MD |
215 | * |
216 | * Returns false if the queue was empty prior to adding the node. | |
217 | * Returns true otherwise. | |
8ad4ce58 | 218 | */ |
f637f191 | 219 | static inline bool _cds_wfcq_enqueue(cds_wfcq_head_ptr_t head, |
8ad4ce58 MD |
220 | struct cds_wfcq_tail *tail, |
221 | struct cds_wfcq_node *new_tail) | |
222 | { | |
23773356 | 223 | return ___cds_wfcq_append(head, tail, new_tail, new_tail); |
8ad4ce58 MD |
224 | } |
225 | ||
f878b49e MD |
226 | /* |
227 | * ___cds_wfcq_busy_wait: adaptative busy-wait. | |
228 | * | |
229 | * Returns 1 if nonblocking and needs to block, 0 otherwise. | |
230 | */ | |
231 | static inline bool | |
232 | ___cds_wfcq_busy_wait(int *attempt, int blocking) | |
233 | { | |
234 | if (!blocking) | |
235 | return 1; | |
236 | if (++(*attempt) >= WFCQ_ADAPT_ATTEMPTS) { | |
d8a93add | 237 | (void) poll(NULL, 0, WFCQ_WAIT); /* Wait for 10ms */ |
f878b49e MD |
238 | *attempt = 0; |
239 | } else { | |
240 | caa_cpu_relax(); | |
241 | } | |
242 | return 0; | |
243 | } | |
244 | ||
8ad4ce58 MD |
245 | /* |
246 | * Waiting for enqueuer to complete enqueue and return the next node. | |
247 | */ | |
248 | static inline struct cds_wfcq_node * | |
47215721 | 249 | ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking) |
8ad4ce58 MD |
250 | { |
251 | struct cds_wfcq_node *next; | |
252 | int attempt = 0; | |
253 | ||
254 | /* | |
255 | * Adaptative busy-looping waiting for enqueuer to complete enqueue. | |
256 | */ | |
257 | while ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
f878b49e | 258 | if (___cds_wfcq_busy_wait(&attempt, blocking)) |
47215721 | 259 | return CDS_WFCQ_WOULDBLOCK; |
8ad4ce58 MD |
260 | } |
261 | ||
262 | return next; | |
263 | } | |
264 | ||
8ad4ce58 | 265 | static inline struct cds_wfcq_node * |
f637f191 | 266 | ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head, |
47215721 MD |
267 | struct cds_wfcq_tail *tail, |
268 | int blocking) | |
8ad4ce58 | 269 | { |
f637f191 | 270 | struct __cds_wfcq_head *head = u_head._h; |
8ad4ce58 MD |
271 | struct cds_wfcq_node *node; |
272 | ||
4d0d7cbc | 273 | if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail)) |
8ad4ce58 | 274 | return NULL; |
47215721 | 275 | node = ___cds_wfcq_node_sync_next(&head->node, blocking); |
8ad4ce58 MD |
276 | /* Load head->node.next before loading node's content */ |
277 | cmm_smp_read_barrier_depends(); | |
278 | return node; | |
279 | } | |
280 | ||
281 | /* | |
47215721 | 282 | * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing. |
8ad4ce58 MD |
283 | * |
284 | * Content written into the node before enqueue is guaranteed to be | |
285 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 MD |
286 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
287 | * caller. | |
f94061a3 MD |
288 | * |
289 | * Used by for-like iteration macros in urcu/wfqueue.h: | |
290 | * __cds_wfcq_for_each_blocking() | |
291 | * __cds_wfcq_for_each_blocking_safe() | |
131a29a6 MD |
292 | * |
293 | * Returns NULL if queue is empty, first node otherwise. | |
8ad4ce58 MD |
294 | */ |
295 | static inline struct cds_wfcq_node * | |
f637f191 | 296 | ___cds_wfcq_first_blocking(cds_wfcq_head_ptr_t head, |
47215721 MD |
297 | struct cds_wfcq_tail *tail) |
298 | { | |
299 | return ___cds_wfcq_first(head, tail, 1); | |
300 | } | |
301 | ||
302 | ||
303 | /* | |
304 | * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing. | |
305 | * | |
306 | * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if | |
307 | * it needs to block. | |
308 | */ | |
309 | static inline struct cds_wfcq_node * | |
f637f191 | 310 | ___cds_wfcq_first_nonblocking(cds_wfcq_head_ptr_t head, |
47215721 MD |
311 | struct cds_wfcq_tail *tail) |
312 | { | |
313 | return ___cds_wfcq_first(head, tail, 0); | |
314 | } | |
315 | ||
316 | static inline struct cds_wfcq_node * | |
f637f191 | 317 | ___cds_wfcq_next(cds_wfcq_head_ptr_t head, |
8ad4ce58 | 318 | struct cds_wfcq_tail *tail, |
47215721 MD |
319 | struct cds_wfcq_node *node, |
320 | int blocking) | |
8ad4ce58 MD |
321 | { |
322 | struct cds_wfcq_node *next; | |
323 | ||
324 | /* | |
325 | * Even though the following tail->p check is sufficient to find | |
326 | * out if we reached the end of the queue, we first check | |
327 | * node->next as a common case to ensure that iteration on nodes | |
328 | * do not frequently access enqueuer's tail->p cache line. | |
329 | */ | |
330 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
331 | /* Load node->next before tail->p */ | |
332 | cmm_smp_rmb(); | |
333 | if (CMM_LOAD_SHARED(tail->p) == node) | |
334 | return NULL; | |
47215721 | 335 | next = ___cds_wfcq_node_sync_next(node, blocking); |
8ad4ce58 MD |
336 | } |
337 | /* Load node->next before loading next's content */ | |
338 | cmm_smp_read_barrier_depends(); | |
339 | return next; | |
340 | } | |
341 | ||
342 | /* | |
47215721 | 343 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. |
8ad4ce58 | 344 | * |
8ad4ce58 MD |
345 | * Content written into the node before enqueue is guaranteed to be |
346 | * consistent, but no other memory ordering is ensured. | |
1fe734e1 MD |
347 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
348 | * caller. | |
47215721 MD |
349 | * |
350 | * Used by for-like iteration macros in urcu/wfqueue.h: | |
351 | * __cds_wfcq_for_each_blocking() | |
352 | * __cds_wfcq_for_each_blocking_safe() | |
131a29a6 MD |
353 | * |
354 | * Returns NULL if reached end of queue, non-NULL next queue node | |
355 | * otherwise. | |
8ad4ce58 MD |
356 | */ |
357 | static inline struct cds_wfcq_node * | |
f637f191 | 358 | ___cds_wfcq_next_blocking(cds_wfcq_head_ptr_t head, |
47215721 MD |
359 | struct cds_wfcq_tail *tail, |
360 | struct cds_wfcq_node *node) | |
361 | { | |
362 | return ___cds_wfcq_next(head, tail, node, 1); | |
363 | } | |
364 | ||
365 | /* | |
366 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. | |
367 | * | |
368 | * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if | |
369 | * it needs to block. | |
370 | */ | |
371 | static inline struct cds_wfcq_node * | |
f637f191 | 372 | ___cds_wfcq_next_nonblocking(cds_wfcq_head_ptr_t head, |
47215721 MD |
373 | struct cds_wfcq_tail *tail, |
374 | struct cds_wfcq_node *node) | |
375 | { | |
376 | return ___cds_wfcq_next(head, tail, node, 0); | |
377 | } | |
378 | ||
379 | static inline struct cds_wfcq_node * | |
f637f191 | 380 | ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head, |
47215721 | 381 | struct cds_wfcq_tail *tail, |
eec791af | 382 | int *state, |
47215721 | 383 | int blocking) |
8ad4ce58 | 384 | { |
f637f191 | 385 | struct __cds_wfcq_head *head = u_head._h; |
8ad4ce58 MD |
386 | struct cds_wfcq_node *node, *next; |
387 | ||
eec791af MD |
388 | if (state) |
389 | *state = 0; | |
390 | ||
4d0d7cbc | 391 | if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail)) { |
8ad4ce58 | 392 | return NULL; |
eec791af | 393 | } |
8ad4ce58 | 394 | |
47215721 | 395 | node = ___cds_wfcq_node_sync_next(&head->node, blocking); |
eec791af | 396 | if (!blocking && node == CDS_WFCQ_WOULDBLOCK) { |
dfb65fd3 | 397 | return CDS_WFCQ_WOULDBLOCK; |
eec791af | 398 | } |
8ad4ce58 MD |
399 | |
400 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { | |
401 | /* | |
402 | * @node is probably the only node in the queue. | |
403 | * Try to move the tail to &q->head. | |
404 | * q->head.next is set to NULL here, and stays | |
405 | * NULL if the cmpxchg succeeds. Should the | |
406 | * cmpxchg fail due to a concurrent enqueue, the | |
407 | * q->head.next will be set to the next node. | |
408 | * The implicit memory barrier before | |
409 | * uatomic_cmpxchg() orders load node->next | |
410 | * before loading q->tail. | |
411 | * The implicit memory barrier before uatomic_cmpxchg | |
412 | * orders load q->head.next before loading node's | |
413 | * content. | |
414 | */ | |
415 | _cds_wfcq_node_init(&head->node); | |
eec791af MD |
416 | if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) { |
417 | if (state) | |
418 | *state |= CDS_WFCQ_STATE_LAST; | |
8ad4ce58 | 419 | return node; |
eec791af | 420 | } |
47215721 | 421 | next = ___cds_wfcq_node_sync_next(node, blocking); |
dfb65fd3 MD |
422 | /* |
423 | * In nonblocking mode, if we would need to block to | |
424 | * get node's next, set the head next node pointer | |
425 | * (currently NULL) back to its original value. | |
426 | */ | |
427 | if (!blocking && next == CDS_WFCQ_WOULDBLOCK) { | |
428 | head->node.next = node; | |
429 | return CDS_WFCQ_WOULDBLOCK; | |
430 | } | |
8ad4ce58 MD |
431 | } |
432 | ||
433 | /* | |
434 | * Move queue head forward. | |
435 | */ | |
436 | head->node.next = next; | |
437 | ||
438 | /* Load q->head.next before loading node's content */ | |
439 | cmm_smp_read_barrier_depends(); | |
440 | return node; | |
441 | } | |
442 | ||
443 | /* | |
eec791af | 444 | * __cds_wfcq_dequeue_with_state_blocking: dequeue node from queue, with state. |
8ad4ce58 | 445 | * |
47215721 MD |
446 | * Content written into the node before enqueue is guaranteed to be |
447 | * consistent, but no other memory ordering is ensured. | |
448 | * It is valid to reuse and free a dequeued node immediately. | |
449 | * Dequeue/splice/iteration mutual exclusion should be ensured by the | |
450 | * caller. | |
8ad4ce58 | 451 | */ |
47215721 | 452 | static inline struct cds_wfcq_node * |
f637f191 | 453 | ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_ptr_t head, |
eec791af MD |
454 | struct cds_wfcq_tail *tail, int *state) |
455 | { | |
456 | return ___cds_wfcq_dequeue_with_state(head, tail, state, 1); | |
457 | } | |
458 | ||
459 | /* | |
460 | * ___cds_wfcq_dequeue_blocking: dequeue node from queue. | |
461 | * | |
462 | * Same as __cds_wfcq_dequeue_with_state_blocking, but without saving | |
463 | * state. | |
464 | */ | |
465 | static inline struct cds_wfcq_node * | |
f637f191 | 466 | ___cds_wfcq_dequeue_blocking(cds_wfcq_head_ptr_t head, |
47215721 MD |
467 | struct cds_wfcq_tail *tail) |
468 | { | |
eec791af | 469 | return ___cds_wfcq_dequeue_with_state_blocking(head, tail, NULL); |
47215721 MD |
470 | } |
471 | ||
472 | /* | |
eec791af | 473 | * __cds_wfcq_dequeue_with_state_nonblocking: dequeue node, with state. |
47215721 MD |
474 | * |
475 | * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK | |
476 | * if it needs to block. | |
477 | */ | |
478 | static inline struct cds_wfcq_node * | |
f637f191 | 479 | ___cds_wfcq_dequeue_with_state_nonblocking(cds_wfcq_head_ptr_t head, |
eec791af MD |
480 | struct cds_wfcq_tail *tail, int *state) |
481 | { | |
482 | return ___cds_wfcq_dequeue_with_state(head, tail, state, 0); | |
483 | } | |
484 | ||
485 | /* | |
486 | * ___cds_wfcq_dequeue_nonblocking: dequeue node from queue. | |
487 | * | |
488 | * Same as __cds_wfcq_dequeue_with_state_nonblocking, but without saving | |
489 | * state. | |
490 | */ | |
491 | static inline struct cds_wfcq_node * | |
f637f191 | 492 | ___cds_wfcq_dequeue_nonblocking(cds_wfcq_head_ptr_t head, |
47215721 MD |
493 | struct cds_wfcq_tail *tail) |
494 | { | |
eec791af | 495 | return ___cds_wfcq_dequeue_with_state_nonblocking(head, tail, NULL); |
47215721 MD |
496 | } |
497 | ||
f878b49e MD |
498 | /* |
499 | * __cds_wfcq_splice: enqueue all src_q nodes at the end of dest_q. | |
500 | * | |
501 | * Dequeue all nodes from src_q. | |
502 | * dest_q must be already initialized. | |
503 | * Mutual exclusion for src_q should be ensured by the caller as | |
504 | * specified in the "Synchronisation table". | |
505 | * Returns enum cds_wfcq_ret which indicates the state of the src or | |
506 | * dest queue. | |
507 | */ | |
23773356 | 508 | static inline enum cds_wfcq_ret |
47215721 | 509 | ___cds_wfcq_splice( |
f637f191 | 510 | cds_wfcq_head_ptr_t u_dest_q_head, |
8ad4ce58 | 511 | struct cds_wfcq_tail *dest_q_tail, |
f637f191 | 512 | cds_wfcq_head_ptr_t u_src_q_head, |
47215721 MD |
513 | struct cds_wfcq_tail *src_q_tail, |
514 | int blocking) | |
8ad4ce58 | 515 | { |
f637f191 MD |
516 | struct __cds_wfcq_head *dest_q_head = u_dest_q_head._h; |
517 | struct __cds_wfcq_head *src_q_head = u_src_q_head._h; | |
8ad4ce58 | 518 | struct cds_wfcq_node *head, *tail; |
f878b49e | 519 | int attempt = 0; |
8ad4ce58 | 520 | |
f878b49e MD |
521 | /* |
522 | * Initial emptiness check to speed up cases where queue is | |
523 | * empty: only require loads to check if queue is empty. | |
524 | */ | |
4d0d7cbc | 525 | if (_cds_wfcq_empty(__cds_wfcq_head_cast(src_q_head), src_q_tail)) |
23773356 | 526 | return CDS_WFCQ_RET_SRC_EMPTY; |
8ad4ce58 | 527 | |
f878b49e MD |
528 | for (;;) { |
529 | /* | |
530 | * Open-coded _cds_wfcq_empty() by testing result of | |
531 | * uatomic_xchg, as well as tail pointer vs head node | |
532 | * address. | |
533 | */ | |
534 | head = uatomic_xchg(&src_q_head->node.next, NULL); | |
535 | if (head) | |
536 | break; /* non-empty */ | |
537 | if (CMM_LOAD_SHARED(src_q_tail->p) == &src_q_head->node) | |
538 | return CDS_WFCQ_RET_SRC_EMPTY; | |
539 | if (___cds_wfcq_busy_wait(&attempt, blocking)) | |
540 | return CDS_WFCQ_RET_WOULDBLOCK; | |
541 | } | |
8ad4ce58 MD |
542 | |
543 | /* | |
544 | * Memory barrier implied before uatomic_xchg() orders store to | |
545 | * src_q->head before store to src_q->tail. This is required by | |
546 | * concurrent enqueue on src_q, which exchanges the tail before | |
547 | * updating the previous tail's next pointer. | |
548 | */ | |
549 | tail = uatomic_xchg(&src_q_tail->p, &src_q_head->node); | |
550 | ||
551 | /* | |
552 | * Append the spliced content of src_q into dest_q. Does not | |
553 | * require mutual exclusion on dest_q (wait-free). | |
554 | */ | |
4d0d7cbc MD |
555 | if (___cds_wfcq_append(__cds_wfcq_head_cast(dest_q_head), dest_q_tail, |
556 | head, tail)) | |
23773356 MD |
557 | return CDS_WFCQ_RET_DEST_NON_EMPTY; |
558 | else | |
559 | return CDS_WFCQ_RET_DEST_EMPTY; | |
47215721 MD |
560 | } |
561 | ||
47215721 MD |
562 | /* |
563 | * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. | |
564 | * | |
565 | * Dequeue all nodes from src_q. | |
566 | * dest_q must be already initialized. | |
f878b49e MD |
567 | * Mutual exclusion for src_q should be ensured by the caller as |
568 | * specified in the "Synchronisation table". | |
23773356 MD |
569 | * Returns enum cds_wfcq_ret which indicates the state of the src or |
570 | * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK. | |
47215721 | 571 | */ |
23773356 | 572 | static inline enum cds_wfcq_ret |
47215721 | 573 | ___cds_wfcq_splice_blocking( |
f637f191 | 574 | cds_wfcq_head_ptr_t dest_q_head, |
47215721 | 575 | struct cds_wfcq_tail *dest_q_tail, |
f637f191 | 576 | cds_wfcq_head_ptr_t src_q_head, |
47215721 MD |
577 | struct cds_wfcq_tail *src_q_tail) |
578 | { | |
23773356 | 579 | return ___cds_wfcq_splice(dest_q_head, dest_q_tail, |
47215721 MD |
580 | src_q_head, src_q_tail, 1); |
581 | } | |
582 | ||
583 | /* | |
584 | * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q. | |
585 | * | |
23773356 MD |
586 | * Same as __cds_wfcq_splice_blocking, but returns |
587 | * CDS_WFCQ_RET_WOULDBLOCK if it needs to block. | |
47215721 | 588 | */ |
23773356 | 589 | static inline enum cds_wfcq_ret |
47215721 | 590 | ___cds_wfcq_splice_nonblocking( |
f637f191 | 591 | cds_wfcq_head_ptr_t dest_q_head, |
47215721 | 592 | struct cds_wfcq_tail *dest_q_tail, |
f637f191 | 593 | cds_wfcq_head_ptr_t src_q_head, |
47215721 MD |
594 | struct cds_wfcq_tail *src_q_tail) |
595 | { | |
596 | return ___cds_wfcq_splice(dest_q_head, dest_q_tail, | |
597 | src_q_head, src_q_tail, 0); | |
8ad4ce58 MD |
598 | } |
599 | ||
600 | /* | |
eec791af | 601 | * cds_wfcq_dequeue_with_state_blocking: dequeue a node from a wait-free queue. |
8ad4ce58 MD |
602 | * |
603 | * Content written into the node before enqueue is guaranteed to be | |
604 | * consistent, but no other memory ordering is ensured. | |
ffa11a18 | 605 | * Mutual exclusion with cds_wfcq_splice_blocking and dequeue lock is |
8ad4ce58 MD |
606 | * ensured. |
607 | * It is valid to reuse and free a dequeued node immediately. | |
608 | */ | |
609 | static inline struct cds_wfcq_node * | |
eec791af MD |
610 | _cds_wfcq_dequeue_with_state_blocking(struct cds_wfcq_head *head, |
611 | struct cds_wfcq_tail *tail, int *state) | |
8ad4ce58 MD |
612 | { |
613 | struct cds_wfcq_node *retval; | |
614 | ||
615 | _cds_wfcq_dequeue_lock(head, tail); | |
4d0d7cbc MD |
616 | retval = ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_cast(head), |
617 | tail, state); | |
8ad4ce58 MD |
618 | _cds_wfcq_dequeue_unlock(head, tail); |
619 | return retval; | |
620 | } | |
621 | ||
eec791af MD |
622 | /* |
623 | * cds_wfcq_dequeue_blocking: dequeue node from queue. | |
624 | * | |
625 | * Same as cds_wfcq_dequeue_blocking, but without saving state. | |
626 | */ | |
627 | static inline struct cds_wfcq_node * | |
628 | _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head, | |
629 | struct cds_wfcq_tail *tail) | |
630 | { | |
631 | return _cds_wfcq_dequeue_with_state_blocking(head, tail, NULL); | |
632 | } | |
633 | ||
8ad4ce58 MD |
634 | /* |
635 | * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. | |
636 | * | |
637 | * Dequeue all nodes from src_q. | |
638 | * dest_q must be already initialized. | |
639 | * Content written into the node before enqueue is guaranteed to be | |
640 | * consistent, but no other memory ordering is ensured. | |
ffa11a18 | 641 | * Mutual exclusion with cds_wfcq_dequeue_blocking and dequeue lock is |
8ad4ce58 | 642 | * ensured. |
23773356 MD |
643 | * Returns enum cds_wfcq_ret which indicates the state of the src or |
644 | * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK. | |
8ad4ce58 | 645 | */ |
23773356 | 646 | static inline enum cds_wfcq_ret |
8ad4ce58 MD |
647 | _cds_wfcq_splice_blocking( |
648 | struct cds_wfcq_head *dest_q_head, | |
649 | struct cds_wfcq_tail *dest_q_tail, | |
650 | struct cds_wfcq_head *src_q_head, | |
651 | struct cds_wfcq_tail *src_q_tail) | |
652 | { | |
23773356 MD |
653 | enum cds_wfcq_ret ret; |
654 | ||
8ad4ce58 | 655 | _cds_wfcq_dequeue_lock(src_q_head, src_q_tail); |
4d0d7cbc MD |
656 | ret = ___cds_wfcq_splice_blocking(cds_wfcq_head_cast(dest_q_head), dest_q_tail, |
657 | cds_wfcq_head_cast(src_q_head), src_q_tail); | |
8ad4ce58 | 658 | _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail); |
23773356 | 659 | return ret; |
8ad4ce58 MD |
660 | } |
661 | ||
662 | #ifdef __cplusplus | |
663 | } | |
664 | #endif | |
665 | ||
666 | #endif /* _URCU_WFCQUEUE_STATIC_H */ |