Fix: add missing destroy functions to queues/stack APIs
[urcu.git] / urcu / static / lfstack.h
1 #ifndef _URCU_STATIC_LFSTACK_H
2 #define _URCU_STATIC_LFSTACK_H
3
4 /*
5 * urcu/static/lfstack.h
6 *
7 * Userspace RCU library - Lock-Free Stack
8 *
9 * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
10 *
11 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/lfstack.h for
12 * linking dynamically with the userspace rcu library.
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 <stdbool.h>
30 #include <pthread.h>
31 #include <assert.h>
32 #include <urcu/uatomic.h>
33 #include <urcu-pointer.h>
34
35 #ifdef __cplusplus
36 extern "C" {
37 #endif
38
39 /*
40 * Lock-free stack.
41 *
42 * Stack implementing push, pop, pop_all operations, as well as iterator
43 * on the stack head returned by pop_all.
44 *
45 * Synchronization table:
46 *
47 * External synchronization techniques described in the API below is
48 * required between pairs marked with "X". No external synchronization
49 * required between pairs marked with "-".
50 *
51 * cds_lfs_push __cds_lfs_pop __cds_lfs_pop_all
52 * cds_lfs_push - - -
53 * __cds_lfs_pop - X X
54 * __cds_lfs_pop_all - X -
55 *
56 * cds_lfs_pop_blocking and cds_lfs_pop_all_blocking use an internal
57 * mutex to provide synchronization.
58 */
59
60 /*
61 * cds_lfs_node_init: initialize lock-free stack node.
62 */
63 static inline
64 void _cds_lfs_node_init(struct cds_lfs_node *node)
65 {
66 }
67
68 /*
69 * cds_lfs_init: initialize lock-free stack (with lock). Pair with
70 * cds_lfs_destroy().
71 */
72 static inline
73 void _cds_lfs_init(struct cds_lfs_stack *s)
74 {
75 int ret;
76
77 s->head = NULL;
78 ret = pthread_mutex_init(&s->lock, NULL);
79 assert(!ret);
80 }
81
82 /*
83 * cds_lfs_destroy: destroy lock-free stack (with lock). Pair with
84 * cds_lfs_init().
85 */
86 static inline
87 void _cds_lfs_destroy(struct cds_lfs_stack *s)
88 {
89 int ret = pthread_mutex_destroy(&s->lock);
90 assert(!ret);
91 }
92
93 /*
94 * ___cds_lfs_init: initialize lock-free stack (without lock).
95 * Don't pair with any destroy function.
96 */
97 static inline
98 void ___cds_lfs_init(struct __cds_lfs_stack *s)
99 {
100 s->head = NULL;
101 }
102
103 static inline
104 bool ___cds_lfs_empty_head(struct cds_lfs_head *head)
105 {
106 return head == NULL;
107 }
108
109 /*
110 * cds_lfs_empty: return whether lock-free stack is empty.
111 *
112 * No memory barrier is issued. No mutual exclusion is required.
113 */
114 static inline
115 bool _cds_lfs_empty(cds_lfs_stack_ptr_t s)
116 {
117 return ___cds_lfs_empty_head(CMM_LOAD_SHARED(s._s->head));
118 }
119
120 /*
121 * cds_lfs_push: push a node into the stack.
122 *
123 * Does not require any synchronization with other push nor pop.
124 *
125 * Lock-free stack push is not subject to ABA problem, so no need to
126 * take the RCU read-side lock. Even if "head" changes between two
127 * uatomic_cmpxchg() invocations here (being popped, and then pushed
128 * again by one or more concurrent threads), the second
129 * uatomic_cmpxchg() invocation only cares about pushing a new entry at
130 * the head of the stack, ensuring consistency by making sure the new
131 * node->next is the same pointer value as the value replaced as head.
132 * It does not care about the content of the actual next node, so it can
133 * very well be reallocated between the two uatomic_cmpxchg().
134 *
135 * We take the approach of expecting the stack to be usually empty, so
136 * we first try an initial uatomic_cmpxchg() on a NULL old_head, and
137 * retry if the old head was non-NULL (the value read by the first
138 * uatomic_cmpxchg() is used as old head for the following loop). The
139 * upside of this scheme is to minimize the amount of cacheline traffic,
140 * always performing an exclusive cacheline access, rather than doing
141 * non-exclusive followed by exclusive cacheline access (which would be
142 * required if we first read the old head value). This design decision
143 * might be revisited after more thorough benchmarking on various
144 * platforms.
145 *
146 * Returns 0 if the stack was empty prior to adding the node.
147 * Returns non-zero otherwise.
148 */
149 static inline
150 bool _cds_lfs_push(cds_lfs_stack_ptr_t u_s,
151 struct cds_lfs_node *node)
152 {
153 struct __cds_lfs_stack *s = u_s._s;
154 struct cds_lfs_head *head = NULL;
155 struct cds_lfs_head *new_head =
156 caa_container_of(node, struct cds_lfs_head, node);
157
158 for (;;) {
159 struct cds_lfs_head *old_head = head;
160
161 /*
162 * node->next is still private at this point, no need to
163 * perform a _CMM_STORE_SHARED().
164 */
165 node->next = &head->node;
166 /*
167 * uatomic_cmpxchg() implicit memory barrier orders earlier
168 * stores to node before publication.
169 */
170 head = uatomic_cmpxchg(&s->head, old_head, new_head);
171 if (old_head == head)
172 break;
173 }
174 return !___cds_lfs_empty_head(head);
175 }
176
177 /*
178 * __cds_lfs_pop: pop a node from the stack.
179 *
180 * Returns NULL if stack is empty.
181 *
182 * __cds_lfs_pop needs to be synchronized using one of the following
183 * techniques:
184 *
185 * 1) Calling __cds_lfs_pop under rcu read lock critical section.
186 * Both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a
187 * grace period to pass before freeing the returned node or pushing
188 * the node back into the stack. It is valid to overwrite the content
189 * of cds_lfs_node immediately after __cds_lfs_pop and
190 * __cds_lfs_pop_all. No RCU read-side critical section is needed
191 * around __cds_lfs_pop_all.
192 * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop
193 * and __cds_lfs_pop_all callers.
194 * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and
195 * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme).
196 */
197 static inline
198 struct cds_lfs_node *___cds_lfs_pop(cds_lfs_stack_ptr_t u_s)
199 {
200 struct __cds_lfs_stack *s = u_s._s;
201
202 for (;;) {
203 struct cds_lfs_head *head, *next_head;
204 struct cds_lfs_node *next;
205
206 head = _CMM_LOAD_SHARED(s->head);
207 if (___cds_lfs_empty_head(head))
208 return NULL; /* Empty stack */
209
210 /*
211 * Read head before head->next. Matches the implicit
212 * memory barrier before uatomic_cmpxchg() in
213 * cds_lfs_push.
214 */
215 cmm_smp_read_barrier_depends();
216 next = _CMM_LOAD_SHARED(head->node.next);
217 next_head = caa_container_of(next,
218 struct cds_lfs_head, node);
219 if (uatomic_cmpxchg(&s->head, head, next_head) == head)
220 return &head->node;
221 /* busy-loop if head changed under us */
222 }
223 }
224
225 /*
226 * __cds_lfs_pop_all: pop all nodes from a stack.
227 *
228 * __cds_lfs_pop_all does not require any synchronization with other
229 * push, nor with other __cds_lfs_pop_all, but requires synchronization
230 * matching the technique used to synchronize __cds_lfs_pop:
231 *
232 * 1) If __cds_lfs_pop is called under rcu read lock critical section,
233 * both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a
234 * grace period to pass before freeing the returned node or pushing
235 * the node back into the stack. It is valid to overwrite the content
236 * of cds_lfs_node immediately after __cds_lfs_pop and
237 * __cds_lfs_pop_all. No RCU read-side critical section is needed
238 * around __cds_lfs_pop_all.
239 * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop and
240 * __cds_lfs_pop_all callers.
241 * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and
242 * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme).
243 */
244 static inline
245 struct cds_lfs_head *___cds_lfs_pop_all(cds_lfs_stack_ptr_t u_s)
246 {
247 struct __cds_lfs_stack *s = u_s._s;
248
249 /*
250 * Implicit memory barrier after uatomic_xchg() matches implicit
251 * memory barrier before uatomic_cmpxchg() in cds_lfs_push. It
252 * ensures that all nodes of the returned list are consistent.
253 * There is no need to issue memory barriers when iterating on
254 * the returned list, because the full memory barrier issued
255 * prior to each uatomic_cmpxchg, which each write to head, are
256 * taking care to order writes to each node prior to the full
257 * memory barrier after this uatomic_xchg().
258 */
259 return uatomic_xchg(&s->head, NULL);
260 }
261
262 /*
263 * cds_lfs_pop_lock: lock stack pop-protection mutex.
264 */
265 static inline void _cds_lfs_pop_lock(struct cds_lfs_stack *s)
266 {
267 int ret;
268
269 ret = pthread_mutex_lock(&s->lock);
270 assert(!ret);
271 }
272
273 /*
274 * cds_lfs_pop_unlock: unlock stack pop-protection mutex.
275 */
276 static inline void _cds_lfs_pop_unlock(struct cds_lfs_stack *s)
277 {
278 int ret;
279
280 ret = pthread_mutex_unlock(&s->lock);
281 assert(!ret);
282 }
283
284 /*
285 * Call __cds_lfs_pop with an internal pop mutex held.
286 */
287 static inline
288 struct cds_lfs_node *
289 _cds_lfs_pop_blocking(struct cds_lfs_stack *s)
290 {
291 struct cds_lfs_node *retnode;
292
293 _cds_lfs_pop_lock(s);
294 retnode = ___cds_lfs_pop(s);
295 _cds_lfs_pop_unlock(s);
296 return retnode;
297 }
298
299 /*
300 * Call __cds_lfs_pop_all with an internal pop mutex held.
301 */
302 static inline
303 struct cds_lfs_head *
304 _cds_lfs_pop_all_blocking(struct cds_lfs_stack *s)
305 {
306 struct cds_lfs_head *rethead;
307
308 _cds_lfs_pop_lock(s);
309 rethead = ___cds_lfs_pop_all(s);
310 _cds_lfs_pop_unlock(s);
311 return rethead;
312 }
313
314 #ifdef __cplusplus
315 }
316 #endif
317
318 #endif /* _URCU_STATIC_LFSTACK_H */
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