24f6cb478447e76ec0be88b6a86beb28b129e83c
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.
51 * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, iteration on stack
52 * head returned by pop_all.
54 * Synchronization table:
56 * External synchronization techniques described in the API below is
57 * required between pairs marked with "X". No external synchronization
58 * required between pairs marked with "-".
60 * cds_wfs_push __cds_wfs_pop __cds_wfs_pop_all
63 * __cds_wfs_pop_all - X -
65 * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
70 * cds_wfs_node_init: initialize wait-free stack node.
73 void _cds_wfs_node_init(struct cds_wfs_node
*node
)
79 * cds_wfs_init: initialize wait-free stack.
82 void _cds_wfs_init(struct cds_wfs_stack
*s
)
86 s
->head
= CDS_WFS_END
;
87 ret
= pthread_mutex_init(&s
->lock
, NULL
);
91 static inline bool ___cds_wfs_end(void *node
)
93 return node
== CDS_WFS_END
;
97 * cds_wfs_empty: return whether wait-free stack is empty.
99 * No memory barrier is issued. No mutual exclusion is required.
101 static inline bool _cds_wfs_empty(struct cds_wfs_stack
*s
)
103 return ___cds_wfs_end(CMM_LOAD_SHARED(s
->head
));
107 * cds_wfs_push: push a node into the stack.
109 * Issues a full memory barrier before push. No mutual exclusion is
112 * Returns 0 if the stack was empty prior to adding the node.
113 * Returns non-zero otherwise.
116 int _cds_wfs_push(struct cds_wfs_stack
*s
, struct cds_wfs_node
*node
)
118 struct cds_wfs_head
*old_head
, *new_head
;
120 assert(node
->next
== NULL
);
121 new_head
= caa_container_of(node
, struct cds_wfs_head
, node
);
123 * uatomic_xchg() implicit memory barrier orders earlier stores
124 * to node (setting it to NULL) before publication.
126 old_head
= uatomic_xchg(&s
->head
, new_head
);
128 * At this point, dequeuers see a NULL node->next, they should
129 * busy-wait until node->next is set to old_head.
131 CMM_STORE_SHARED(node
->next
, &old_head
->node
);
132 return !___cds_wfs_end(old_head
);
136 * Waiting for push to complete enqueue and return the next node.
138 static inline struct cds_wfs_node
*
139 ___cds_wfs_node_sync_next(struct cds_wfs_node
*node
)
141 struct cds_wfs_node
*next
;
145 * Adaptative busy-looping waiting for push to complete.
147 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
148 if (++attempt
>= CDS_WFS_ADAPT_ATTEMPTS
) {
149 poll(NULL
, 0, CDS_WFS_WAIT
); /* Wait for 10ms */
160 * __cds_wfs_pop_blocking: pop a node from the stack.
162 * Returns NULL if stack is empty.
164 * __cds_wfs_pop_blocking needs to be synchronized using one of the
165 * following techniques:
167 * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
168 * section. The caller must wait for a grace period to pass before
169 * freeing the returned node or modifying the cds_wfs_node structure.
170 * 2) Using mutual exclusion (e.g. mutexes) to protect
171 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
172 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
173 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
176 struct cds_wfs_node
*
177 ___cds_wfs_pop_blocking(struct cds_wfs_stack
*s
)
179 struct cds_wfs_head
*head
, *new_head
;
180 struct cds_wfs_node
*next
;
183 head
= CMM_LOAD_SHARED(s
->head
);
184 if (___cds_wfs_end(head
))
186 next
= ___cds_wfs_node_sync_next(&head
->node
);
187 new_head
= caa_container_of(next
, struct cds_wfs_head
, node
);
188 if (uatomic_cmpxchg(&s
->head
, head
, new_head
) == head
)
190 /* busy-loop if head changed under us */
195 * __cds_wfs_pop_all: pop all nodes from a stack.
197 * __cds_wfs_pop_all does not require any synchronization with other
198 * push, nor with other __cds_wfs_pop_all, but requires synchronization
199 * matching the technique used to synchronize __cds_wfs_pop_blocking:
201 * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
202 * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
203 * must wait for a grace period to pass before freeing the returned
204 * node or modifying the cds_wfs_node structure. However, no RCU
205 * read-side critical section is needed around __cds_wfs_pop_all.
206 * 2) Using mutual exclusion (e.g. mutexes) to protect
207 * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
208 * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
209 * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
212 struct cds_wfs_head
*
213 ___cds_wfs_pop_all(struct cds_wfs_stack
*s
)
215 struct cds_wfs_head
*head
;
218 * Implicit memory barrier after uatomic_xchg() matches implicit
219 * memory barrier before uatomic_xchg() in cds_wfs_push. It
220 * ensures that all nodes of the returned list are consistent.
221 * There is no need to issue memory barriers when iterating on
222 * the returned list, because the full memory barrier issued
223 * prior to each uatomic_cmpxchg, which each write to head, are
224 * taking care to order writes to each node prior to the full
225 * memory barrier after this uatomic_xchg().
227 head
= uatomic_xchg(&s
->head
, CDS_WFS_END
);
228 if (___cds_wfs_end(head
))
234 * cds_wfs_pop_lock: lock stack pop-protection mutex.
236 static inline void _cds_wfs_pop_lock(struct cds_wfs_stack
*s
)
240 ret
= pthread_mutex_lock(&s
->lock
);
245 * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
247 static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack
*s
)
251 ret
= pthread_mutex_unlock(&s
->lock
);
256 * Call __cds_wfs_pop_blocking with an internal pop mutex held.
259 struct cds_wfs_node
*
260 _cds_wfs_pop_blocking(struct cds_wfs_stack
*s
)
262 struct cds_wfs_node
*retnode
;
264 _cds_wfs_pop_lock(s
);
265 retnode
= ___cds_wfs_pop_blocking(s
);
266 _cds_wfs_pop_unlock(s
);
271 * Call __cds_wfs_pop_all with an internal pop mutex held.
274 struct cds_wfs_head
*
275 _cds_wfs_pop_all_blocking(struct cds_wfs_stack
*s
)
277 struct cds_wfs_head
*rethead
;
279 _cds_wfs_pop_lock(s
);
280 rethead
= ___cds_wfs_pop_all(s
);
281 _cds_wfs_pop_unlock(s
);
286 * cds_wfs_first_blocking: get first node of a popped stack.
288 * Content written into the node before enqueue is guaranteed to be
289 * consistent, but no other memory ordering is ensured.
291 * Used by for-like iteration macros in urcu/wfstack.h:
292 * cds_wfs_for_each_blocking()
293 * cds_wfs_for_each_blocking_safe()
295 static inline struct cds_wfs_node
*
296 _cds_wfs_first_blocking(struct cds_wfs_head
*head
)
298 if (___cds_wfs_end(head
))
304 * cds_wfs_next_blocking: get next node of a popped stack.
306 * Content written into the node before enqueue is guaranteed to be
307 * consistent, but no other memory ordering is ensured.
309 * Used by for-like iteration macros in urcu/wfstack.h:
310 * cds_wfs_for_each_blocking()
311 * cds_wfs_for_each_blocking_safe()
313 static inline struct cds_wfs_node
*
314 _cds_wfs_next_blocking(struct cds_wfs_node
*node
)
316 struct cds_wfs_node
*next
;
318 next
= ___cds_wfs_node_sync_next(node
);
319 if (___cds_wfs_end(next
))
328 #endif /* _URCU_STATIC_WFSTACK_H */
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