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.
82 static inline void ___cds_wfs_init(struct __cds_wfs_stack
*s
)
84 s
->head
= CDS_WFS_END
;
88 * cds_wfs_init: initialize wait-free stack.
91 void _cds_wfs_init(struct cds_wfs_stack
*s
)
95 s
->head
= CDS_WFS_END
;
96 ret
= pthread_mutex_init(&s
->lock
, NULL
);
100 static inline bool ___cds_wfs_end(void *node
)
102 return node
== CDS_WFS_END
;
106 * cds_wfs_empty: return whether wait-free stack is empty.
108 * No memory barrier is issued. No mutual exclusion is required.
110 static inline bool _cds_wfs_empty(cds_wfs_stack_ptr_t u_stack
)
112 struct __cds_wfs_stack
*s
= u_stack
._s
;
114 return ___cds_wfs_end(CMM_LOAD_SHARED(s
->head
));
118 * cds_wfs_push: push a node into the stack.
120 * Issues a full memory barrier before push. No mutual exclusion is
123 * Returns 0 if the stack was empty prior to adding the node.
124 * Returns non-zero otherwise.
127 int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack
, struct cds_wfs_node
*node
)
129 struct __cds_wfs_stack
*s
= u_stack
._s
;
130 struct cds_wfs_head
*old_head
, *new_head
;
132 assert(node
->next
== NULL
);
133 new_head
= caa_container_of(node
, struct cds_wfs_head
, node
);
135 * uatomic_xchg() implicit memory barrier orders earlier stores
136 * to node (setting it to NULL) before publication.
138 old_head
= uatomic_xchg(&s
->head
, new_head
);
140 * At this point, dequeuers see a NULL node->next, they should
141 * busy-wait until node->next is set to old_head.
143 CMM_STORE_SHARED(node
->next
, &old_head
->node
);
144 return !___cds_wfs_end(old_head
);
148 * Waiting for push to complete enqueue and return the next node.
150 static inline struct cds_wfs_node
*
151 ___cds_wfs_node_sync_next(struct cds_wfs_node
*node
, int blocking
)
153 struct cds_wfs_node
*next
;
157 * Adaptative busy-looping waiting for push to complete.
159 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
161 return CDS_WFS_WOULDBLOCK
;
162 if (++attempt
>= CDS_WFS_ADAPT_ATTEMPTS
) {
163 poll(NULL
, 0, CDS_WFS_WAIT
); /* Wait for 10ms */
174 struct cds_wfs_node
*
175 ___cds_wfs_pop(struct cds_wfs_stack
*s
, int *state
, int blocking
)
177 struct cds_wfs_head
*head
, *new_head
;
178 struct cds_wfs_node
*next
;
183 head
= CMM_LOAD_SHARED(s
->head
);
184 if (___cds_wfs_end(head
)) {
187 next
= ___cds_wfs_node_sync_next(&head
->node
, blocking
);
188 if (!blocking
&& next
== CDS_WFS_WOULDBLOCK
) {
189 return CDS_WFS_WOULDBLOCK
;
191 new_head
= caa_container_of(next
, struct cds_wfs_head
, node
);
192 if (uatomic_cmpxchg(&s
->head
, head
, new_head
) == head
) {
193 if (state
&& ___cds_wfs_end(new_head
))
194 *state
|= CDS_WFS_STATE_LAST
;
198 return CDS_WFS_WOULDBLOCK
;
200 /* busy-loop if head changed under us */
205 * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
207 * Returns NULL if stack is empty.
209 * __cds_wfs_pop_blocking needs to be synchronized using one of the
210 * following techniques:
212 * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
213 * section. The caller must wait for a grace period to pass before
214 * freeing the returned node or modifying the cds_wfs_node structure.
215 * 2) Using mutual exclusion (e.g. mutexes) to protect
216 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
217 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
218 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
220 * "state" saves state flags atomically sampled with pop operation.
223 struct cds_wfs_node
*
224 ___cds_wfs_pop_with_state_blocking(struct cds_wfs_stack
*s
, int *state
)
226 return ___cds_wfs_pop(s
, state
, 1);
230 struct cds_wfs_node
*
231 ___cds_wfs_pop_blocking(struct cds_wfs_stack
*s
)
233 return ___cds_wfs_pop_with_state_blocking(s
, NULL
);
237 * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
239 * Same as __cds_wfs_pop_with_state_blocking, but returns
240 * CDS_WFS_WOULDBLOCK if it needs to block.
242 * "state" saves state flags atomically sampled with pop operation.
245 struct cds_wfs_node
*
246 ___cds_wfs_pop_with_state_nonblocking(struct cds_wfs_stack
*s
, int *state
)
248 return ___cds_wfs_pop(s
, state
, 0);
252 * __cds_wfs_pop_nonblocking: pop a node from the stack.
254 * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
258 struct cds_wfs_node
*
259 ___cds_wfs_pop_nonblocking(struct cds_wfs_stack
*s
)
261 return ___cds_wfs_pop_with_state_nonblocking(s
, NULL
);
265 * __cds_wfs_pop_all: pop all nodes from a stack.
267 * __cds_wfs_pop_all does not require any synchronization with other
268 * push, nor with other __cds_wfs_pop_all, but requires synchronization
269 * matching the technique used to synchronize __cds_wfs_pop_blocking:
271 * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
272 * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
273 * must wait for a grace period to pass before freeing the returned
274 * node or modifying the cds_wfs_node structure. However, no RCU
275 * read-side critical section is needed around __cds_wfs_pop_all.
276 * 2) Using mutual exclusion (e.g. mutexes) to protect
277 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
278 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
279 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
282 struct cds_wfs_head
*
283 ___cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack
)
285 struct __cds_wfs_stack
*s
= u_stack
._s
;
286 struct cds_wfs_head
*head
;
289 * Implicit memory barrier after uatomic_xchg() matches implicit
290 * memory barrier before uatomic_xchg() in cds_wfs_push. It
291 * ensures that all nodes of the returned list are consistent.
292 * There is no need to issue memory barriers when iterating on
293 * the returned list, because the full memory barrier issued
294 * prior to each uatomic_cmpxchg, which each write to head, are
295 * taking care to order writes to each node prior to the full
296 * memory barrier after this uatomic_xchg().
298 head
= uatomic_xchg(&s
->head
, CDS_WFS_END
);
299 if (___cds_wfs_end(head
))
305 * cds_wfs_pop_lock: lock stack pop-protection mutex.
307 static inline void _cds_wfs_pop_lock(struct cds_wfs_stack
*s
)
311 ret
= pthread_mutex_lock(&s
->lock
);
316 * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
318 static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack
*s
)
322 ret
= pthread_mutex_unlock(&s
->lock
);
327 * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
330 struct cds_wfs_node
*
331 _cds_wfs_pop_with_state_blocking(struct cds_wfs_stack
*s
, int *state
)
333 struct cds_wfs_node
*retnode
;
335 _cds_wfs_pop_lock(s
);
336 retnode
= ___cds_wfs_pop_with_state_blocking(s
, state
);
337 _cds_wfs_pop_unlock(s
);
342 * Call _cds_wfs_pop_with_state_blocking without saving any state.
345 struct cds_wfs_node
*
346 _cds_wfs_pop_blocking(struct cds_wfs_stack
*s
)
348 return _cds_wfs_pop_with_state_blocking(s
, NULL
);
352 * Call __cds_wfs_pop_all with an internal pop mutex held.
355 struct cds_wfs_head
*
356 _cds_wfs_pop_all_blocking(struct cds_wfs_stack
*s
)
358 struct cds_wfs_head
*rethead
;
360 _cds_wfs_pop_lock(s
);
361 rethead
= ___cds_wfs_pop_all(s
);
362 _cds_wfs_pop_unlock(s
);
367 * cds_wfs_first: get first node of a popped stack.
369 * Content written into the node before enqueue is guaranteed to be
370 * consistent, but no other memory ordering is ensured.
372 * Used by for-like iteration macros in urcu/wfstack.h:
373 * cds_wfs_for_each_blocking()
374 * cds_wfs_for_each_blocking_safe()
376 * Returns NULL if popped stack is empty, top stack node otherwise.
378 static inline struct cds_wfs_node
*
379 _cds_wfs_first(struct cds_wfs_head
*head
)
381 if (___cds_wfs_end(head
))
386 static inline struct cds_wfs_node
*
387 ___cds_wfs_next(struct cds_wfs_node
*node
, int blocking
)
389 struct cds_wfs_node
*next
;
391 next
= ___cds_wfs_node_sync_next(node
, blocking
);
393 * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
394 * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
395 * and still return CDS_WFS_WOULDBLOCK.
397 if (___cds_wfs_end(next
))
403 * cds_wfs_next_blocking: get next node of a popped stack.
405 * Content written into the node before enqueue is guaranteed to be
406 * consistent, but no other memory ordering is ensured.
408 * Used by for-like iteration macros in urcu/wfstack.h:
409 * cds_wfs_for_each_blocking()
410 * cds_wfs_for_each_blocking_safe()
412 * Returns NULL if reached end of popped stack, non-NULL next stack
415 static inline struct cds_wfs_node
*
416 _cds_wfs_next_blocking(struct cds_wfs_node
*node
)
418 return ___cds_wfs_next(node
, 1);
423 * cds_wfs_next_nonblocking: get next node of a popped stack.
425 * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
428 static inline struct cds_wfs_node
*
429 _cds_wfs_next_nonblocking(struct cds_wfs_node
*node
)
431 return ___cds_wfs_next(node
, 0);
438 #endif /* _URCU_STATIC_WFSTACK_H */