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[urcu.git] / include / urcu / static / wfstack.h
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1#ifndef _URCU_STATIC_WFSTACK_H
2#define _URCU_STATIC_WFSTACK_H
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3
4/*
edac6b69 5 * urcu/static/wfstack.h
294d3396 6 *
edac6b69 7 * Userspace RCU library - Stack with with wait-free push, blocking traversal.
294d3396 8 *
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9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for
10 * linking dynamically with the userspace rcu library.
294d3396 11 *
a03a0f42 12 * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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13 *
14 * This library is free software; you can redistribute it and/or
15 * modify it under the terms of the GNU Lesser General Public
16 * License as published by the Free Software Foundation; either
17 * version 2.1 of the License, or (at your option) any later version.
18 *
19 * This library is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
22 * Lesser General Public License for more details.
23 *
24 * You should have received a copy of the GNU Lesser General Public
25 * License along with this library; if not, write to the Free Software
26 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
27 */
28
29#include <pthread.h>
b57aee66 30#include <poll.h>
edac6b69 31#include <stdbool.h>
01477510 32#include <urcu/assert.h>
294d3396 33#include <urcu/compiler.h>
a2e7bf9c 34#include <urcu/uatomic.h>
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35
36#ifdef __cplusplus
37extern "C" {
38#endif
39
edac6b69 40#define CDS_WFS_END ((void *) 0x1UL)
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41#define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
42#define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */
294d3396 43
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44/*
45 * Stack with wait-free push, blocking traversal.
46 *
47 * Stack implementing push, pop, pop_all operations, as well as iterator
48 * on the stack head returned by pop_all.
49 *
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50 * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
51 * cds_wfs_first.
52 * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
53 * iteration on stack head returned by pop_all.
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54 *
55 * Synchronization table:
56 *
57 * External synchronization techniques described in the API below is
58 * required between pairs marked with "X". No external synchronization
59 * required between pairs marked with "-".
60 *
61 * cds_wfs_push __cds_wfs_pop __cds_wfs_pop_all
62 * cds_wfs_push - - -
63 * __cds_wfs_pop - X X
64 * __cds_wfs_pop_all - X -
65 *
66 * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
67 * synchronization.
68 */
69
70/*
71 * cds_wfs_node_init: initialize wait-free stack node.
72 */
756a0322 73static inline
16aa9ee8 74void _cds_wfs_node_init(struct cds_wfs_node *node)
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75{
76 node->next = NULL;
77}
78
718eb63e 79/*
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80 * __cds_wfs_init: initialize wait-free stack. Don't pair with
81 * any destroy function.
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82 */
83static inline void ___cds_wfs_init(struct __cds_wfs_stack *s)
84{
85 s->head = CDS_WFS_END;
86}
87
edac6b69 88/*
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89 * cds_wfs_init: initialize wait-free stack. Pair with
90 * cds_wfs_destroy().
edac6b69 91 */
756a0322 92static inline
16aa9ee8 93void _cds_wfs_init(struct cds_wfs_stack *s)
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94{
95 int ret;
96
edac6b69 97 s->head = CDS_WFS_END;
294d3396 98 ret = pthread_mutex_init(&s->lock, NULL);
01477510 99 urcu_posix_assert(!ret);
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100}
101
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102/*
103 * cds_wfs_destroy: destroy wait-free stack. Pair with
104 * cds_wfs_init().
105 */
106static inline
107void _cds_wfs_destroy(struct cds_wfs_stack *s)
108{
109 int ret = pthread_mutex_destroy(&s->lock);
01477510 110 urcu_posix_assert(!ret);
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111}
112
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113static inline bool ___cds_wfs_end(void *node)
114{
115 return node == CDS_WFS_END;
116}
117
191098fc 118/*
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119 * cds_wfs_empty: return whether wait-free stack is empty.
120 *
121 * No memory barrier is issued. No mutual exclusion is required.
122 */
718eb63e 123static inline bool _cds_wfs_empty(cds_wfs_stack_ptr_t u_stack)
edac6b69 124{
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125 struct __cds_wfs_stack *s = u_stack._s;
126
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127 return ___cds_wfs_end(CMM_LOAD_SHARED(s->head));
128}
129
130/*
131 * cds_wfs_push: push a node into the stack.
132 *
133 * Issues a full memory barrier before push. No mutual exclusion is
134 * required.
135 *
136 * Returns 0 if the stack was empty prior to adding the node.
137 * Returns non-zero otherwise.
191098fc 138 */
756a0322 139static inline
718eb63e 140int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack, struct cds_wfs_node *node)
294d3396 141{
718eb63e 142 struct __cds_wfs_stack *s = u_stack._s;
edac6b69 143 struct cds_wfs_head *old_head, *new_head;
294d3396 144
01477510 145 urcu_posix_assert(node->next == NULL);
edac6b69 146 new_head = caa_container_of(node, struct cds_wfs_head, node);
294d3396 147 /*
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148 * uatomic_xchg() implicit memory barrier orders earlier stores
149 * to node (setting it to NULL) before publication.
294d3396 150 */
edac6b69 151 old_head = uatomic_xchg(&s->head, new_head);
294d3396 152 /*
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153 * At this point, dequeuers see a NULL node->next, they should
154 * busy-wait until node->next is set to old_head.
294d3396 155 */
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156 CMM_STORE_SHARED(node->next, &old_head->node);
157 return !___cds_wfs_end(old_head);
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158}
159
160/*
edac6b69 161 * Waiting for push to complete enqueue and return the next node.
294d3396 162 */
edac6b69 163static inline struct cds_wfs_node *
af67624d 164___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
294d3396 165{
edac6b69 166 struct cds_wfs_node *next;
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167 int attempt = 0;
168
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169 /*
170 * Adaptative busy-looping waiting for push to complete.
171 */
edac6b69 172 while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
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173 if (!blocking)
174 return CDS_WFS_WOULDBLOCK;
16aa9ee8 175 if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
d8a93add 176 (void) poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */
294d3396 177 attempt = 0;
edac6b69 178 } else {
06f22bdb 179 caa_cpu_relax();
edac6b69 180 }
294d3396 181 }
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182
183 return next;
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184}
185
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186static inline
187struct cds_wfs_node *
711ff0f9 188___cds_wfs_pop(cds_wfs_stack_ptr_t u_stack, int *state, int blocking)
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189{
190 struct cds_wfs_head *head, *new_head;
191 struct cds_wfs_node *next;
711ff0f9 192 struct __cds_wfs_stack *s = u_stack._s;
af67624d 193
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194 if (state)
195 *state = 0;
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196 for (;;) {
197 head = CMM_LOAD_SHARED(s->head);
c8975b94 198 if (___cds_wfs_end(head)) {
af67624d 199 return NULL;
c8975b94 200 }
af67624d 201 next = ___cds_wfs_node_sync_next(&head->node, blocking);
c8975b94 202 if (!blocking && next == CDS_WFS_WOULDBLOCK) {
af67624d 203 return CDS_WFS_WOULDBLOCK;
c8975b94 204 }
af67624d 205 new_head = caa_container_of(next, struct cds_wfs_head, node);
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206 if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
207 if (state && ___cds_wfs_end(new_head))
208 *state |= CDS_WFS_STATE_LAST;
af67624d 209 return &head->node;
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210 }
211 if (!blocking) {
af67624d 212 return CDS_WFS_WOULDBLOCK;
c8975b94 213 }
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214 /* busy-loop if head changed under us */
215 }
216}
217
edac6b69 218/*
c8975b94 219 * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
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220 *
221 * Returns NULL if stack is empty.
222 *
223 * __cds_wfs_pop_blocking needs to be synchronized using one of the
224 * following techniques:
225 *
226 * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
227 * section. The caller must wait for a grace period to pass before
228 * freeing the returned node or modifying the cds_wfs_node structure.
229 * 2) Using mutual exclusion (e.g. mutexes) to protect
230 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
231 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
232 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
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233 *
234 * "state" saves state flags atomically sampled with pop operation.
edac6b69 235 */
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236static inline
237struct cds_wfs_node *
711ff0f9 238___cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack, int *state)
c8975b94 239{
711ff0f9 240 return ___cds_wfs_pop(u_stack, state, 1);
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241}
242
756a0322 243static inline
16aa9ee8 244struct cds_wfs_node *
711ff0f9 245___cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack)
edac6b69 246{
711ff0f9 247 return ___cds_wfs_pop_with_state_blocking(u_stack, NULL);
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248}
249
250/*
251 * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
252 *
253 * Same as __cds_wfs_pop_with_state_blocking, but returns
254 * CDS_WFS_WOULDBLOCK if it needs to block.
255 *
256 * "state" saves state flags atomically sampled with pop operation.
257 */
258static inline
259struct cds_wfs_node *
711ff0f9 260___cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack, int *state)
c8975b94 261{
711ff0f9 262 return ___cds_wfs_pop(u_stack, state, 0);
af67624d 263}
edac6b69 264
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265/*
266 * __cds_wfs_pop_nonblocking: pop a node from the stack.
267 *
268 * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
269 * it needs to block.
270 */
271static inline
272struct cds_wfs_node *
711ff0f9 273___cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack)
af67624d 274{
711ff0f9 275 return ___cds_wfs_pop_with_state_nonblocking(u_stack, NULL);
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276}
277
278/*
279 * __cds_wfs_pop_all: pop all nodes from a stack.
280 *
281 * __cds_wfs_pop_all does not require any synchronization with other
282 * push, nor with other __cds_wfs_pop_all, but requires synchronization
283 * matching the technique used to synchronize __cds_wfs_pop_blocking:
284 *
285 * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
286 * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
287 * must wait for a grace period to pass before freeing the returned
288 * node or modifying the cds_wfs_node structure. However, no RCU
289 * read-side critical section is needed around __cds_wfs_pop_all.
290 * 2) Using mutual exclusion (e.g. mutexes) to protect
291 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
292 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
293 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
294 */
295static inline
296struct cds_wfs_head *
718eb63e 297___cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack)
edac6b69 298{
718eb63e 299 struct __cds_wfs_stack *s = u_stack._s;
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300 struct cds_wfs_head *head;
301
302 /*
303 * Implicit memory barrier after uatomic_xchg() matches implicit
304 * memory barrier before uatomic_xchg() in cds_wfs_push. It
305 * ensures that all nodes of the returned list are consistent.
306 * There is no need to issue memory barriers when iterating on
307 * the returned list, because the full memory barrier issued
308 * prior to each uatomic_cmpxchg, which each write to head, are
309 * taking care to order writes to each node prior to the full
310 * memory barrier after this uatomic_xchg().
311 */
312 head = uatomic_xchg(&s->head, CDS_WFS_END);
313 if (___cds_wfs_end(head))
314 return NULL;
315 return head;
316}
317
318/*
319 * cds_wfs_pop_lock: lock stack pop-protection mutex.
320 */
321static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s)
294d3396 322{
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323 int ret;
324
325 ret = pthread_mutex_lock(&s->lock);
01477510 326 urcu_posix_assert(!ret);
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327}
328
329/*
330 * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
331 */
332static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
333{
334 int ret;
335
294d3396 336 ret = pthread_mutex_unlock(&s->lock);
01477510 337 urcu_posix_assert(!ret);
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338}
339
340/*
c8975b94 341 * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
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342 */
343static inline
344struct cds_wfs_node *
c8975b94 345_cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
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346{
347 struct cds_wfs_node *retnode;
348
349 _cds_wfs_pop_lock(s);
c8975b94 350 retnode = ___cds_wfs_pop_with_state_blocking(s, state);
edac6b69 351 _cds_wfs_pop_unlock(s);
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352 return retnode;
353}
354
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355/*
356 * Call _cds_wfs_pop_with_state_blocking without saving any state.
357 */
358static inline
359struct cds_wfs_node *
360_cds_wfs_pop_blocking(struct cds_wfs_stack *s)
361{
362 return _cds_wfs_pop_with_state_blocking(s, NULL);
363}
364
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365/*
366 * Call __cds_wfs_pop_all with an internal pop mutex held.
367 */
368static inline
369struct cds_wfs_head *
370_cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
371{
372 struct cds_wfs_head *rethead;
373
374 _cds_wfs_pop_lock(s);
375 rethead = ___cds_wfs_pop_all(s);
376 _cds_wfs_pop_unlock(s);
377 return rethead;
378}
379
380/*
c7ba06ba 381 * cds_wfs_first: get first node of a popped stack.
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382 *
383 * Content written into the node before enqueue is guaranteed to be
384 * consistent, but no other memory ordering is ensured.
385 *
386 * Used by for-like iteration macros in urcu/wfstack.h:
387 * cds_wfs_for_each_blocking()
388 * cds_wfs_for_each_blocking_safe()
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389 *
390 * Returns NULL if popped stack is empty, top stack node otherwise.
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391 */
392static inline struct cds_wfs_node *
c7ba06ba 393_cds_wfs_first(struct cds_wfs_head *head)
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394{
395 if (___cds_wfs_end(head))
396 return NULL;
397 return &head->node;
398}
399
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400static inline struct cds_wfs_node *
401___cds_wfs_next(struct cds_wfs_node *node, int blocking)
402{
403 struct cds_wfs_node *next;
404
405 next = ___cds_wfs_node_sync_next(node, blocking);
406 /*
407 * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
408 * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
409 * and still return CDS_WFS_WOULDBLOCK.
410 */
411 if (___cds_wfs_end(next))
412 return NULL;
413 return next;
414}
415
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416/*
417 * cds_wfs_next_blocking: get next node of a popped stack.
418 *
419 * Content written into the node before enqueue is guaranteed to be
420 * consistent, but no other memory ordering is ensured.
421 *
422 * Used by for-like iteration macros in urcu/wfstack.h:
423 * cds_wfs_for_each_blocking()
424 * cds_wfs_for_each_blocking_safe()
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425 *
426 * Returns NULL if reached end of popped stack, non-NULL next stack
427 * node otherwise.
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428 */
429static inline struct cds_wfs_node *
430_cds_wfs_next_blocking(struct cds_wfs_node *node)
431{
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432 return ___cds_wfs_next(node, 1);
433}
edac6b69 434
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435
436/*
437 * cds_wfs_next_nonblocking: get next node of a popped stack.
438 *
439 * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
440 * needs to block.
441 */
442static inline struct cds_wfs_node *
443_cds_wfs_next_nonblocking(struct cds_wfs_node *node)
444{
445 return ___cds_wfs_next(node, 0);
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446}
447
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448#ifdef __cplusplus
449}
450#endif
451
edac6b69 452#endif /* _URCU_STATIC_WFSTACK_H */
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