1 // SPDX-FileCopyrightText: 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 // SPDX-License-Identifier: LGPL-2.1-or-later
5 #ifndef _URCU_STATIC_WFSTACK_H
6 #define _URCU_STATIC_WFSTACK_H
9 * Userspace RCU library - Stack with with wait-free push, blocking traversal.
11 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for
12 * linking dynamically with the userspace rcu library.
18 #include <urcu/assert.h>
19 #include <urcu/compiler.h>
20 #include <urcu/uatomic.h>
26 #define CDS_WFS_END ((struct cds_wfs_head *) 0x1UL)
27 #define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
28 #define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */
31 * Stack with wait-free push, blocking traversal.
33 * Stack implementing push, pop, pop_all operations, as well as iterator
34 * on the stack head returned by pop_all.
36 * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
38 * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
39 * iteration on stack head returned by pop_all.
41 * Synchronization table:
43 * External synchronization techniques described in the API below is
44 * required between pairs marked with "X". No external synchronization
45 * required between pairs marked with "-".
47 * cds_wfs_push __cds_wfs_pop __cds_wfs_pop_all
50 * __cds_wfs_pop_all - X -
52 * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
57 * cds_wfs_node_init: initialize wait-free stack node.
60 void _cds_wfs_node_init(struct cds_wfs_node
*node
)
66 * __cds_wfs_init: initialize wait-free stack. Don't pair with
67 * any destroy function.
69 static inline void ___cds_wfs_init(struct __cds_wfs_stack
*s
)
71 s
->head
= CDS_WFS_END
;
75 * cds_wfs_init: initialize wait-free stack. Pair with
79 void _cds_wfs_init(struct cds_wfs_stack
*s
)
83 s
->head
= CDS_WFS_END
;
84 ret
= pthread_mutex_init(&s
->lock
, NULL
);
85 urcu_posix_assert(!ret
);
89 * cds_wfs_destroy: destroy wait-free stack. Pair with
93 void _cds_wfs_destroy(struct cds_wfs_stack
*s
)
95 int ret
= pthread_mutex_destroy(&s
->lock
);
96 urcu_posix_assert(!ret
);
99 static inline bool ___cds_wfs_end(void *node
)
101 return node
== CDS_WFS_END
;
105 * cds_wfs_empty: return whether wait-free stack is empty.
107 * No memory barrier is issued. No mutual exclusion is required.
109 static inline bool _cds_wfs_empty(cds_wfs_stack_ptr_t u_stack
)
111 struct __cds_wfs_stack
*s
= u_stack
._s
;
113 return ___cds_wfs_end(CMM_LOAD_SHARED(s
->head
));
117 * cds_wfs_push: push a node into the stack.
119 * Issues a full memory barrier before push. No mutual exclusion is
122 * Returns 0 if the stack was empty prior to adding the node.
123 * Returns non-zero otherwise.
126 int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack
, struct cds_wfs_node
*node
)
128 struct __cds_wfs_stack
*s
= u_stack
._s
;
129 struct cds_wfs_head
*old_head
, *new_head
;
131 urcu_posix_assert(node
->next
== NULL
);
132 new_head
= caa_container_of(node
, struct cds_wfs_head
, node
);
134 * uatomic_xchg() implicit memory barrier orders earlier stores
135 * to node (setting it to NULL) before publication.
137 old_head
= uatomic_xchg(&s
->head
, new_head
);
139 * At this point, dequeuers see a NULL node->next, they should
140 * busy-wait until node->next is set to old_head.
142 CMM_STORE_SHARED(node
->next
, &old_head
->node
);
143 return !___cds_wfs_end(old_head
);
147 * Waiting for push to complete enqueue and return the next node.
149 static inline struct cds_wfs_node
*
150 ___cds_wfs_node_sync_next(struct cds_wfs_node
*node
, int blocking
)
152 struct cds_wfs_node
*next
;
156 * Adaptative busy-looping waiting for push to complete.
158 while ((next
= CMM_LOAD_SHARED(node
->next
)) == NULL
) {
160 return CDS_WFS_WOULDBLOCK
;
161 if (++attempt
>= CDS_WFS_ADAPT_ATTEMPTS
) {
162 (void) poll(NULL
, 0, CDS_WFS_WAIT
); /* Wait for 10ms */
173 struct cds_wfs_node
*
174 ___cds_wfs_pop(cds_wfs_stack_ptr_t u_stack
, int *state
, int blocking
)
176 struct cds_wfs_head
*head
, *new_head
;
177 struct cds_wfs_node
*next
;
178 struct __cds_wfs_stack
*s
= u_stack
._s
;
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(cds_wfs_stack_ptr_t u_stack
, int *state
)
226 return ___cds_wfs_pop(u_stack
, state
, 1);
230 struct cds_wfs_node
*
231 ___cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack
)
233 return ___cds_wfs_pop_with_state_blocking(u_stack
, 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(cds_wfs_stack_ptr_t u_stack
, int *state
)
248 return ___cds_wfs_pop(u_stack
, 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(cds_wfs_stack_ptr_t u_stack
)
261 return ___cds_wfs_pop_with_state_nonblocking(u_stack
, 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
);
312 urcu_posix_assert(!ret
);
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
);
323 urcu_posix_assert(!ret
);
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
;
334 cds_wfs_stack_ptr_t stack
;
336 _cds_wfs_pop_lock(s
);
338 retnode
= ___cds_wfs_pop_with_state_blocking(stack
, state
);
339 _cds_wfs_pop_unlock(s
);
344 * Call _cds_wfs_pop_with_state_blocking without saving any state.
347 struct cds_wfs_node
*
348 _cds_wfs_pop_blocking(struct cds_wfs_stack
*s
)
350 return _cds_wfs_pop_with_state_blocking(s
, NULL
);
354 * Call __cds_wfs_pop_all with an internal pop mutex held.
357 struct cds_wfs_head
*
358 _cds_wfs_pop_all_blocking(struct cds_wfs_stack
*s
)
360 struct cds_wfs_head
*rethead
;
361 cds_wfs_stack_ptr_t stack
;
363 _cds_wfs_pop_lock(s
);
365 rethead
= ___cds_wfs_pop_all(stack
);
366 _cds_wfs_pop_unlock(s
);
371 * cds_wfs_first: get first node of a popped stack.
373 * Content written into the node before enqueue is guaranteed to be
374 * consistent, but no other memory ordering is ensured.
376 * Used by for-like iteration macros in urcu/wfstack.h:
377 * cds_wfs_for_each_blocking()
378 * cds_wfs_for_each_blocking_safe()
380 * Returns NULL if popped stack is empty, top stack node otherwise.
382 static inline struct cds_wfs_node
*
383 _cds_wfs_first(struct cds_wfs_head
*head
)
385 if (___cds_wfs_end(head
))
390 static inline struct cds_wfs_node
*
391 ___cds_wfs_next(struct cds_wfs_node
*node
, int blocking
)
393 struct cds_wfs_node
*next
;
395 next
= ___cds_wfs_node_sync_next(node
, blocking
);
397 * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
398 * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
399 * and still return CDS_WFS_WOULDBLOCK.
401 if (___cds_wfs_end(next
))
407 * cds_wfs_next_blocking: get next node of a popped stack.
409 * Content written into the node before enqueue is guaranteed to be
410 * consistent, but no other memory ordering is ensured.
412 * Used by for-like iteration macros in urcu/wfstack.h:
413 * cds_wfs_for_each_blocking()
414 * cds_wfs_for_each_blocking_safe()
416 * Returns NULL if reached end of popped stack, non-NULL next stack
419 static inline struct cds_wfs_node
*
420 _cds_wfs_next_blocking(struct cds_wfs_node
*node
)
422 return ___cds_wfs_next(node
, 1);
427 * cds_wfs_next_nonblocking: get next node of a popped stack.
429 * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
432 static inline struct cds_wfs_node
*
433 _cds_wfs_next_nonblocking(struct cds_wfs_node
*node
)
435 return ___cds_wfs_next(node
, 0);
442 #endif /* _URCU_STATIC_WFSTACK_H */