db0d5b8b1abda178f7cf0e14a0530d5bae43f8aa
[urcu.git] / urcu / static / wfstack.h
1 #ifndef _URCU_STATIC_WFSTACK_H
2 #define _URCU_STATIC_WFSTACK_H
3
4 /*
5 * urcu/static/wfstack.h
6 *
7 * Userspace RCU library - Stack with with wait-free push, blocking traversal.
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for
10 * linking dynamically with the userspace rcu library.
11 *
12 * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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>
30 #include <assert.h>
31 #include <poll.h>
32 #include <stdbool.h>
33 #include <urcu/compiler.h>
34 #include <urcu/uatomic.h>
35
36 #ifdef __cplusplus
37 extern "C" {
38 #endif
39
40 #define CDS_WFS_END ((void *) 0x1UL)
41 #define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
42 #define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */
43
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 *
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.
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 */
73 static inline
74 void _cds_wfs_node_init(struct cds_wfs_node *node)
75 {
76 node->next = NULL;
77 }
78
79 /*
80 * cds_wfs_init: initialize wait-free stack.
81 */
82 static inline
83 void _cds_wfs_init(struct cds_wfs_stack *s)
84 {
85 int ret;
86
87 s->head = CDS_WFS_END;
88 ret = pthread_mutex_init(&s->lock, NULL);
89 assert(!ret);
90 }
91
92 static inline bool ___cds_wfs_end(void *node)
93 {
94 return node == CDS_WFS_END;
95 }
96
97 /*
98 * cds_wfs_empty: return whether wait-free stack is empty.
99 *
100 * No memory barrier is issued. No mutual exclusion is required.
101 */
102 static inline bool _cds_wfs_empty(struct cds_wfs_stack *s)
103 {
104 return ___cds_wfs_end(CMM_LOAD_SHARED(s->head));
105 }
106
107 /*
108 * cds_wfs_push: push a node into the stack.
109 *
110 * Issues a full memory barrier before push. No mutual exclusion is
111 * required.
112 *
113 * Returns 0 if the stack was empty prior to adding the node.
114 * Returns non-zero otherwise.
115 */
116 static inline
117 int _cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node)
118 {
119 struct cds_wfs_head *old_head, *new_head;
120
121 assert(node->next == NULL);
122 new_head = caa_container_of(node, struct cds_wfs_head, node);
123 /*
124 * uatomic_xchg() implicit memory barrier orders earlier stores
125 * to node (setting it to NULL) before publication.
126 */
127 old_head = uatomic_xchg(&s->head, new_head);
128 /*
129 * At this point, dequeuers see a NULL node->next, they should
130 * busy-wait until node->next is set to old_head.
131 */
132 CMM_STORE_SHARED(node->next, &old_head->node);
133 return !___cds_wfs_end(old_head);
134 }
135
136 /*
137 * Waiting for push to complete enqueue and return the next node.
138 */
139 static inline struct cds_wfs_node *
140 ___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
141 {
142 struct cds_wfs_node *next;
143 int attempt = 0;
144
145 /*
146 * Adaptative busy-looping waiting for push to complete.
147 */
148 while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
149 if (!blocking)
150 return CDS_WFS_WOULDBLOCK;
151 if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
152 poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */
153 attempt = 0;
154 } else {
155 caa_cpu_relax();
156 }
157 }
158
159 return next;
160 }
161
162 static inline
163 struct cds_wfs_node *
164 ___cds_wfs_pop(struct cds_wfs_stack *s, int *state, int blocking)
165 {
166 struct cds_wfs_head *head, *new_head;
167 struct cds_wfs_node *next;
168
169 if (state)
170 *state = 0;
171 for (;;) {
172 head = CMM_LOAD_SHARED(s->head);
173 if (___cds_wfs_end(head)) {
174 return NULL;
175 }
176 next = ___cds_wfs_node_sync_next(&head->node, blocking);
177 if (!blocking && next == CDS_WFS_WOULDBLOCK) {
178 return CDS_WFS_WOULDBLOCK;
179 }
180 new_head = caa_container_of(next, struct cds_wfs_head, node);
181 if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
182 if (state && ___cds_wfs_end(new_head))
183 *state |= CDS_WFS_STATE_LAST;
184 return &head->node;
185 }
186 if (!blocking) {
187 return CDS_WFS_WOULDBLOCK;
188 }
189 /* busy-loop if head changed under us */
190 }
191 }
192
193 /*
194 * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
195 *
196 * Returns NULL if stack is empty.
197 *
198 * __cds_wfs_pop_blocking needs to be synchronized using one of the
199 * following techniques:
200 *
201 * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
202 * section. The caller must wait for a grace period to pass before
203 * freeing the returned node or modifying the cds_wfs_node structure.
204 * 2) Using mutual exclusion (e.g. mutexes) to protect
205 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
206 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
207 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
208 *
209 * "state" saves state flags atomically sampled with pop operation.
210 */
211 static inline
212 struct cds_wfs_node *
213 ___cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
214 {
215 return ___cds_wfs_pop(s, state, 1);
216 }
217
218 static inline
219 struct cds_wfs_node *
220 ___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
221 {
222 return ___cds_wfs_pop_with_state_blocking(s, NULL);
223 }
224
225 /*
226 * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
227 *
228 * Same as __cds_wfs_pop_with_state_blocking, but returns
229 * CDS_WFS_WOULDBLOCK if it needs to block.
230 *
231 * "state" saves state flags atomically sampled with pop operation.
232 */
233 static inline
234 struct cds_wfs_node *
235 ___cds_wfs_pop_with_state_nonblocking(struct cds_wfs_stack *s, int *state)
236 {
237 return ___cds_wfs_pop(s, state, 0);
238 }
239
240 /*
241 * __cds_wfs_pop_nonblocking: pop a node from the stack.
242 *
243 * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
244 * it needs to block.
245 */
246 static inline
247 struct cds_wfs_node *
248 ___cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
249 {
250 return ___cds_wfs_pop_with_state_nonblocking(s, NULL);
251 }
252
253 /*
254 * __cds_wfs_pop_all: pop all nodes from a stack.
255 *
256 * __cds_wfs_pop_all does not require any synchronization with other
257 * push, nor with other __cds_wfs_pop_all, but requires synchronization
258 * matching the technique used to synchronize __cds_wfs_pop_blocking:
259 *
260 * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
261 * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
262 * must wait for a grace period to pass before freeing the returned
263 * node or modifying the cds_wfs_node structure. However, no RCU
264 * read-side critical section is needed around __cds_wfs_pop_all.
265 * 2) Using mutual exclusion (e.g. mutexes) to protect
266 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
267 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
268 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
269 */
270 static inline
271 struct cds_wfs_head *
272 ___cds_wfs_pop_all(struct cds_wfs_stack *s)
273 {
274 struct cds_wfs_head *head;
275
276 /*
277 * Implicit memory barrier after uatomic_xchg() matches implicit
278 * memory barrier before uatomic_xchg() in cds_wfs_push. It
279 * ensures that all nodes of the returned list are consistent.
280 * There is no need to issue memory barriers when iterating on
281 * the returned list, because the full memory barrier issued
282 * prior to each uatomic_cmpxchg, which each write to head, are
283 * taking care to order writes to each node prior to the full
284 * memory barrier after this uatomic_xchg().
285 */
286 head = uatomic_xchg(&s->head, CDS_WFS_END);
287 if (___cds_wfs_end(head))
288 return NULL;
289 return head;
290 }
291
292 /*
293 * cds_wfs_pop_lock: lock stack pop-protection mutex.
294 */
295 static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s)
296 {
297 int ret;
298
299 ret = pthread_mutex_lock(&s->lock);
300 assert(!ret);
301 }
302
303 /*
304 * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
305 */
306 static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
307 {
308 int ret;
309
310 ret = pthread_mutex_unlock(&s->lock);
311 assert(!ret);
312 }
313
314 /*
315 * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
316 */
317 static inline
318 struct cds_wfs_node *
319 _cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
320 {
321 struct cds_wfs_node *retnode;
322
323 _cds_wfs_pop_lock(s);
324 retnode = ___cds_wfs_pop_with_state_blocking(s, state);
325 _cds_wfs_pop_unlock(s);
326 return retnode;
327 }
328
329 /*
330 * Call _cds_wfs_pop_with_state_blocking without saving any state.
331 */
332 static inline
333 struct cds_wfs_node *
334 _cds_wfs_pop_blocking(struct cds_wfs_stack *s)
335 {
336 return _cds_wfs_pop_with_state_blocking(s, NULL);
337 }
338
339 /*
340 * Call __cds_wfs_pop_all with an internal pop mutex held.
341 */
342 static inline
343 struct cds_wfs_head *
344 _cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
345 {
346 struct cds_wfs_head *rethead;
347
348 _cds_wfs_pop_lock(s);
349 rethead = ___cds_wfs_pop_all(s);
350 _cds_wfs_pop_unlock(s);
351 return rethead;
352 }
353
354 /*
355 * cds_wfs_first: get first node of a popped stack.
356 *
357 * Content written into the node before enqueue is guaranteed to be
358 * consistent, but no other memory ordering is ensured.
359 *
360 * Used by for-like iteration macros in urcu/wfstack.h:
361 * cds_wfs_for_each_blocking()
362 * cds_wfs_for_each_blocking_safe()
363 *
364 * Returns NULL if popped stack is empty, top stack node otherwise.
365 */
366 static inline struct cds_wfs_node *
367 _cds_wfs_first(struct cds_wfs_head *head)
368 {
369 if (___cds_wfs_end(head))
370 return NULL;
371 return &head->node;
372 }
373
374 static inline struct cds_wfs_node *
375 ___cds_wfs_next(struct cds_wfs_node *node, int blocking)
376 {
377 struct cds_wfs_node *next;
378
379 next = ___cds_wfs_node_sync_next(node, blocking);
380 /*
381 * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
382 * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
383 * and still return CDS_WFS_WOULDBLOCK.
384 */
385 if (___cds_wfs_end(next))
386 return NULL;
387 return next;
388 }
389
390 /*
391 * cds_wfs_next_blocking: get next node of a popped stack.
392 *
393 * Content written into the node before enqueue is guaranteed to be
394 * consistent, but no other memory ordering is ensured.
395 *
396 * Used by for-like iteration macros in urcu/wfstack.h:
397 * cds_wfs_for_each_blocking()
398 * cds_wfs_for_each_blocking_safe()
399 *
400 * Returns NULL if reached end of popped stack, non-NULL next stack
401 * node otherwise.
402 */
403 static inline struct cds_wfs_node *
404 _cds_wfs_next_blocking(struct cds_wfs_node *node)
405 {
406 return ___cds_wfs_next(node, 1);
407 }
408
409
410 /*
411 * cds_wfs_next_nonblocking: get next node of a popped stack.
412 *
413 * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
414 * needs to block.
415 */
416 static inline struct cds_wfs_node *
417 _cds_wfs_next_nonblocking(struct cds_wfs_node *node)
418 {
419 return ___cds_wfs_next(node, 0);
420 }
421
422 #ifdef __cplusplus
423 }
424 #endif
425
426 #endif /* _URCU_STATIC_WFSTACK_H */
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