1 #ifndef _URCU_STATIC_WFSTACK_H
2 #define _URCU_STATIC_WFSTACK_H
5 * urcu/static/wfstack.h
7 * Userspace RCU library - Stack with with wait-free push, blocking traversal.
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for
10 * linking dynamically with the userspace rcu library.
12 * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.
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.
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
33 #include <urcu/compiler.h>
34 #include <urcu/uatomic.h>
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 */
45 * Stack with wait-free push, blocking traversal.
47 * Stack implementing push, pop, pop_all operations, as well as iterator
48 * on the stack head returned by pop_all.
50 * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
52 * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
53 * iteration on stack head returned by pop_all.
55 * Synchronization table:
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 "-".
61 * cds_wfs_push __cds_wfs_pop __cds_wfs_pop_all
64 * __cds_wfs_pop_all - X -
66 * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
71 * cds_wfs_node_init: initialize wait-free stack node.
74 void _cds_wfs_node_init(struct cds_wfs_node
*node
)
80 * __cds_wfs_init: initialize wait-free stack. Don't pair with
81 * any destroy function.
83 static inline void ___cds_wfs_init(struct __cds_wfs_stack
*s
)
85 s
->head
= CDS_WFS_END
;
89 * cds_wfs_init: initialize wait-free stack. Pair with
93 void _cds_wfs_init(struct cds_wfs_stack
*s
)
97 s
->head
= CDS_WFS_END
;
98 ret
= pthread_mutex_init(&s
->lock
, NULL
);
103 * cds_wfs_destroy: destroy wait-free stack. Pair with
107 void _cds_wfs_destroy(struct cds_wfs_stack
*s
)
109 int ret
= pthread_mutex_destroy(&s
->lock
);
113 static inline bool ___cds_wfs_end(void *node
)
115 return node
== CDS_WFS_END
;
119 * cds_wfs_empty: return whether wait-free stack is empty.
121 * No memory barrier is issued. No mutual exclusion is required.
123 static inline bool _cds_wfs_empty(cds_wfs_stack_ptr_t u_stack
)
125 struct __cds_wfs_stack
*s
= u_stack
._s
;
127 return ___cds_wfs_end(CMM_LOAD_SHARED(s
->head
));
131 * cds_wfs_push: push a node into the stack.
133 * Issues a full memory barrier before push. No mutual exclusion is
136 * Returns 0 if the stack was empty prior to adding the node.
137 * Returns non-zero otherwise.
140 int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack
, struct cds_wfs_node
*node
)
142 struct __cds_wfs_stack
*s
= u_stack
._s
;
143 struct cds_wfs_head
*old_head
, *new_head
;
145 assert(node
->next
== NULL
);
146 new_head
= caa_container_of(node
, struct cds_wfs_head
, node
);
148 * uatomic_xchg() implicit memory barrier orders earlier stores
149 * to node (setting it to NULL) before publication.
151 old_head
= uatomic_xchg(&s
->head
, new_head
);
153 * At this point, dequeuers see a NULL node->next, they should
154 * busy-wait until node->next is set to old_head.
156 CMM_STORE_SHARED(node
->next
, &old_head
->node
);
157 return !___cds_wfs_end(old_head
);
161 * Waiting for push to complete enqueue and return the next node.
163 static inline struct cds_wfs_node
*
164 ___cds_wfs_node_sync_next(struct cds_wfs_node
*node
, int blocking
)
166 struct cds_wfs_node
*next
;
170 * Adaptative busy-looping waiting for push to complete.
172 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
174 return CDS_WFS_WOULDBLOCK
;
175 if (++attempt
>= CDS_WFS_ADAPT_ATTEMPTS
) {
176 (void) poll(NULL
, 0, CDS_WFS_WAIT
); /* Wait for 10ms */
187 struct cds_wfs_node
*
188 ___cds_wfs_pop(cds_wfs_stack_ptr_t u_stack
, int *state
, int blocking
)
190 struct cds_wfs_head
*head
, *new_head
;
191 struct cds_wfs_node
*next
;
192 struct __cds_wfs_stack
*s
= u_stack
._s
;
197 head
= CMM_LOAD_SHARED(s
->head
);
198 if (___cds_wfs_end(head
)) {
201 next
= ___cds_wfs_node_sync_next(&head
->node
, blocking
);
202 if (!blocking
&& next
== CDS_WFS_WOULDBLOCK
) {
203 return CDS_WFS_WOULDBLOCK
;
205 new_head
= caa_container_of(next
, struct cds_wfs_head
, node
);
206 if (uatomic_cmpxchg(&s
->head
, head
, new_head
) == head
) {
207 if (state
&& ___cds_wfs_end(new_head
))
208 *state
|= CDS_WFS_STATE_LAST
;
212 return CDS_WFS_WOULDBLOCK
;
214 /* busy-loop if head changed under us */
219 * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
221 * Returns NULL if stack is empty.
223 * __cds_wfs_pop_blocking needs to be synchronized using one of the
224 * following techniques:
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).
234 * "state" saves state flags atomically sampled with pop operation.
237 struct cds_wfs_node
*
238 ___cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack
, int *state
)
240 return ___cds_wfs_pop(u_stack
, state
, 1);
244 struct cds_wfs_node
*
245 ___cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack
)
247 return ___cds_wfs_pop_with_state_blocking(u_stack
, NULL
);
251 * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
253 * Same as __cds_wfs_pop_with_state_blocking, but returns
254 * CDS_WFS_WOULDBLOCK if it needs to block.
256 * "state" saves state flags atomically sampled with pop operation.
259 struct cds_wfs_node
*
260 ___cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack
, int *state
)
262 return ___cds_wfs_pop(u_stack
, state
, 0);
266 * __cds_wfs_pop_nonblocking: pop a node from the stack.
268 * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
272 struct cds_wfs_node
*
273 ___cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack
)
275 return ___cds_wfs_pop_with_state_nonblocking(u_stack
, NULL
);
279 * __cds_wfs_pop_all: pop all nodes from a stack.
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:
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).
296 struct cds_wfs_head
*
297 ___cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack
)
299 struct __cds_wfs_stack
*s
= u_stack
._s
;
300 struct cds_wfs_head
*head
;
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().
312 head
= uatomic_xchg(&s
->head
, CDS_WFS_END
);
313 if (___cds_wfs_end(head
))
319 * cds_wfs_pop_lock: lock stack pop-protection mutex.
321 static inline void _cds_wfs_pop_lock(struct cds_wfs_stack
*s
)
325 ret
= pthread_mutex_lock(&s
->lock
);
330 * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
332 static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack
*s
)
336 ret
= pthread_mutex_unlock(&s
->lock
);
341 * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
344 struct cds_wfs_node
*
345 _cds_wfs_pop_with_state_blocking(struct cds_wfs_stack
*s
, int *state
)
347 struct cds_wfs_node
*retnode
;
349 _cds_wfs_pop_lock(s
);
350 retnode
= ___cds_wfs_pop_with_state_blocking(s
, state
);
351 _cds_wfs_pop_unlock(s
);
356 * Call _cds_wfs_pop_with_state_blocking without saving any state.
359 struct cds_wfs_node
*
360 _cds_wfs_pop_blocking(struct cds_wfs_stack
*s
)
362 return _cds_wfs_pop_with_state_blocking(s
, NULL
);
366 * Call __cds_wfs_pop_all with an internal pop mutex held.
369 struct cds_wfs_head
*
370 _cds_wfs_pop_all_blocking(struct cds_wfs_stack
*s
)
372 struct cds_wfs_head
*rethead
;
374 _cds_wfs_pop_lock(s
);
375 rethead
= ___cds_wfs_pop_all(s
);
376 _cds_wfs_pop_unlock(s
);
381 * cds_wfs_first: get first node of a popped stack.
383 * Content written into the node before enqueue is guaranteed to be
384 * consistent, but no other memory ordering is ensured.
386 * Used by for-like iteration macros in urcu/wfstack.h:
387 * cds_wfs_for_each_blocking()
388 * cds_wfs_for_each_blocking_safe()
390 * Returns NULL if popped stack is empty, top stack node otherwise.
392 static inline struct cds_wfs_node
*
393 _cds_wfs_first(struct cds_wfs_head
*head
)
395 if (___cds_wfs_end(head
))
400 static inline struct cds_wfs_node
*
401 ___cds_wfs_next(struct cds_wfs_node
*node
, int blocking
)
403 struct cds_wfs_node
*next
;
405 next
= ___cds_wfs_node_sync_next(node
, blocking
);
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.
411 if (___cds_wfs_end(next
))
417 * cds_wfs_next_blocking: get next node of a popped stack.
419 * Content written into the node before enqueue is guaranteed to be
420 * consistent, but no other memory ordering is ensured.
422 * Used by for-like iteration macros in urcu/wfstack.h:
423 * cds_wfs_for_each_blocking()
424 * cds_wfs_for_each_blocking_safe()
426 * Returns NULL if reached end of popped stack, non-NULL next stack
429 static inline struct cds_wfs_node
*
430 _cds_wfs_next_blocking(struct cds_wfs_node
*node
)
432 return ___cds_wfs_next(node
, 1);
437 * cds_wfs_next_nonblocking: get next node of a popped stack.
439 * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
442 static inline struct cds_wfs_node
*
443 _cds_wfs_next_nonblocking(struct cds_wfs_node
*node
)
445 return ___cds_wfs_next(node
, 0);
452 #endif /* _URCU_STATIC_WFSTACK_H */