Fix undefined NULL pointer arithmetic
[urcu.git] / 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>
30#include <assert.h>
b57aee66 31#include <poll.h>
edac6b69 32#include <stdbool.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
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79/*
80 * cds_wfs_init: initialize wait-free stack.
81 */
756a0322 82static inline
16aa9ee8 83void _cds_wfs_init(struct cds_wfs_stack *s)
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84{
85 int ret;
86
edac6b69 87 s->head = CDS_WFS_END;
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88 ret = pthread_mutex_init(&s->lock, NULL);
89 assert(!ret);
90}
91
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92static inline bool ___cds_wfs_end(void *node)
93{
94 return node == CDS_WFS_END;
95}
96
191098fc 97/*
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98 * cds_wfs_empty: return whether wait-free stack is empty.
99 *
100 * No memory barrier is issued. No mutual exclusion is required.
101 */
102static 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.
191098fc 115 */
756a0322 116static inline
191098fc 117int _cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node)
294d3396 118{
edac6b69 119 struct cds_wfs_head *old_head, *new_head;
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120
121 assert(node->next == NULL);
edac6b69 122 new_head = caa_container_of(node, struct cds_wfs_head, node);
294d3396 123 /*
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124 * uatomic_xchg() implicit memory barrier orders earlier stores
125 * to node (setting it to NULL) before publication.
294d3396 126 */
edac6b69 127 old_head = uatomic_xchg(&s->head, new_head);
294d3396 128 /*
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129 * At this point, dequeuers see a NULL node->next, they should
130 * busy-wait until node->next is set to old_head.
294d3396 131 */
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132 CMM_STORE_SHARED(node->next, &old_head->node);
133 return !___cds_wfs_end(old_head);
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134}
135
136/*
edac6b69 137 * Waiting for push to complete enqueue and return the next node.
294d3396 138 */
edac6b69 139static inline struct cds_wfs_node *
af67624d 140___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
294d3396 141{
edac6b69 142 struct cds_wfs_node *next;
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143 int attempt = 0;
144
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145 /*
146 * Adaptative busy-looping waiting for push to complete.
147 */
edac6b69 148 while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
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149 if (!blocking)
150 return CDS_WFS_WOULDBLOCK;
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151 if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
152 poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */
294d3396 153 attempt = 0;
edac6b69 154 } else {
06f22bdb 155 caa_cpu_relax();
edac6b69 156 }
294d3396 157 }
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158
159 return next;
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160}
161
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162static inline
163struct cds_wfs_node *
c8975b94 164___cds_wfs_pop(struct cds_wfs_stack *s, int *state, int blocking)
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165{
166 struct cds_wfs_head *head, *new_head;
167 struct cds_wfs_node *next;
168
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169 if (state)
170 *state = 0;
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171 for (;;) {
172 head = CMM_LOAD_SHARED(s->head);
c8975b94 173 if (___cds_wfs_end(head)) {
af67624d 174 return NULL;
c8975b94 175 }
af67624d 176 next = ___cds_wfs_node_sync_next(&head->node, blocking);
c8975b94 177 if (!blocking && next == CDS_WFS_WOULDBLOCK) {
af67624d 178 return CDS_WFS_WOULDBLOCK;
c8975b94 179 }
af67624d 180 new_head = caa_container_of(next, struct cds_wfs_head, node);
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181 if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
182 if (state && ___cds_wfs_end(new_head))
183 *state |= CDS_WFS_STATE_LAST;
af67624d 184 return &head->node;
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185 }
186 if (!blocking) {
af67624d 187 return CDS_WFS_WOULDBLOCK;
c8975b94 188 }
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189 /* busy-loop if head changed under us */
190 }
191}
192
edac6b69 193/*
c8975b94 194 * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
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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).
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208 *
209 * "state" saves state flags atomically sampled with pop operation.
edac6b69 210 */
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211static inline
212struct 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
756a0322 218static inline
16aa9ee8 219struct cds_wfs_node *
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220___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
221{
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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 */
233static inline
234struct 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);
af67624d 238}
edac6b69 239
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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 */
246static inline
247struct cds_wfs_node *
248___cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
249{
c8975b94 250 return ___cds_wfs_pop_with_state_nonblocking(s, NULL);
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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 */
270static inline
271struct 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 */
295static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s)
294d3396 296{
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297 int ret;
298
299 ret = pthread_mutex_lock(&s->lock);
300 assert(!ret);
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301}
302
303/*
304 * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
305 */
306static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
307{
308 int ret;
309
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310 ret = pthread_mutex_unlock(&s->lock);
311 assert(!ret);
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312}
313
314/*
c8975b94 315 * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
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316 */
317static inline
318struct cds_wfs_node *
c8975b94 319_cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
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320{
321 struct cds_wfs_node *retnode;
322
323 _cds_wfs_pop_lock(s);
c8975b94 324 retnode = ___cds_wfs_pop_with_state_blocking(s, state);
edac6b69 325 _cds_wfs_pop_unlock(s);
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326 return retnode;
327}
328
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329/*
330 * Call _cds_wfs_pop_with_state_blocking without saving any state.
331 */
332static inline
333struct 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
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339/*
340 * Call __cds_wfs_pop_all with an internal pop mutex held.
341 */
342static inline
343struct 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/*
c7ba06ba 355 * cds_wfs_first: get first node of a popped stack.
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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()
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363 *
364 * Returns NULL if popped stack is empty, top stack node otherwise.
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365 */
366static inline struct cds_wfs_node *
c7ba06ba 367_cds_wfs_first(struct cds_wfs_head *head)
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368{
369 if (___cds_wfs_end(head))
370 return NULL;
371 return &head->node;
372}
373
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374static 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
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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()
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399 *
400 * Returns NULL if reached end of popped stack, non-NULL next stack
401 * node otherwise.
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402 */
403static inline struct cds_wfs_node *
404_cds_wfs_next_blocking(struct cds_wfs_node *node)
405{
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406 return ___cds_wfs_next(node, 1);
407}
edac6b69 408
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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 */
416static inline struct cds_wfs_node *
417_cds_wfs_next_nonblocking(struct cds_wfs_node *node)
418{
419 return ___cds_wfs_next(node, 0);
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420}
421
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422#ifdef __cplusplus
423}
424#endif
425
edac6b69 426#endif /* _URCU_STATIC_WFSTACK_H */
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