Commit | Line | Data |
---|---|---|
d3bfcb24 MD |
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 | * | |
07c2a4fd MD |
11 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/lfstack.h for |
12 | * linking dynamically with the userspace rcu library. | |
d3bfcb24 MD |
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 | ||
7294103b MD |
29 | #include <stdbool.h> |
30 | #include <pthread.h> | |
31 | #include <assert.h> | |
d3bfcb24 MD |
32 | #include <urcu/uatomic.h> |
33 | #include <urcu-pointer.h> | |
34 | ||
35 | #ifdef __cplusplus | |
36 | extern "C" { | |
37 | #endif | |
38 | ||
7294103b MD |
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 | */ | |
d3bfcb24 | 63 | static inline |
70469b43 | 64 | void _cds_lfs_node_init(struct cds_lfs_node *node __attribute__((unused))) |
d3bfcb24 MD |
65 | { |
66 | } | |
67 | ||
7294103b | 68 | /* |
200d100e MD |
69 | * cds_lfs_init: initialize lock-free stack (with lock). Pair with |
70 | * cds_lfs_destroy(). | |
7294103b | 71 | */ |
d3bfcb24 MD |
72 | static inline |
73 | void _cds_lfs_init(struct cds_lfs_stack *s) | |
74 | { | |
7294103b MD |
75 | int ret; |
76 | ||
d3bfcb24 | 77 | s->head = NULL; |
7294103b MD |
78 | ret = pthread_mutex_init(&s->lock, NULL); |
79 | assert(!ret); | |
80 | } | |
81 | ||
48a8832b | 82 | /* |
200d100e MD |
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. | |
48a8832b MD |
96 | */ |
97 | static inline | |
98 | void ___cds_lfs_init(struct __cds_lfs_stack *s) | |
99 | { | |
100 | s->head = NULL; | |
101 | } | |
102 | ||
7294103b MD |
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 | |
48a8832b | 115 | bool _cds_lfs_empty(cds_lfs_stack_ptr_t s) |
7294103b | 116 | { |
48a8832b | 117 | return ___cds_lfs_empty_head(CMM_LOAD_SHARED(s._s->head)); |
d3bfcb24 MD |
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 | |
ffa11a18 | 143 | * might be revisited after more thorough benchmarking on various |
d3bfcb24 MD |
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 | |
48a8832b | 150 | bool _cds_lfs_push(cds_lfs_stack_ptr_t u_s, |
d3bfcb24 MD |
151 | struct cds_lfs_node *node) |
152 | { | |
48a8832b | 153 | struct __cds_lfs_stack *s = u_s._s; |
7294103b MD |
154 | struct cds_lfs_head *head = NULL; |
155 | struct cds_lfs_head *new_head = | |
156 | caa_container_of(node, struct cds_lfs_head, node); | |
d3bfcb24 MD |
157 | |
158 | for (;;) { | |
7294103b | 159 | struct cds_lfs_head *old_head = head; |
d3bfcb24 MD |
160 | |
161 | /* | |
162 | * node->next is still private at this point, no need to | |
163 | * perform a _CMM_STORE_SHARED(). | |
164 | */ | |
7294103b | 165 | node->next = &head->node; |
d3bfcb24 MD |
166 | /* |
167 | * uatomic_cmpxchg() implicit memory barrier orders earlier | |
168 | * stores to node before publication. | |
169 | */ | |
7294103b | 170 | head = uatomic_cmpxchg(&s->head, old_head, new_head); |
d3bfcb24 MD |
171 | if (old_head == head) |
172 | break; | |
173 | } | |
e47048cc | 174 | return !___cds_lfs_empty_head(head); |
d3bfcb24 MD |
175 | } |
176 | ||
177 | /* | |
7294103b | 178 | * __cds_lfs_pop: pop a node from the stack. |
d3bfcb24 MD |
179 | * |
180 | * Returns NULL if stack is empty. | |
181 | * | |
7294103b | 182 | * __cds_lfs_pop needs to be synchronized using one of the following |
d3bfcb24 MD |
183 | * techniques: |
184 | * | |
f9b5c2b6 MD |
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. | |
7294103b MD |
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). | |
d3bfcb24 MD |
196 | */ |
197 | static inline | |
48a8832b | 198 | struct cds_lfs_node *___cds_lfs_pop(cds_lfs_stack_ptr_t u_s) |
d3bfcb24 | 199 | { |
48a8832b MD |
200 | struct __cds_lfs_stack *s = u_s._s; |
201 | ||
d3bfcb24 | 202 | for (;;) { |
7294103b MD |
203 | struct cds_lfs_head *head, *next_head; |
204 | struct cds_lfs_node *next; | |
d3bfcb24 MD |
205 | |
206 | head = _CMM_LOAD_SHARED(s->head); | |
7294103b MD |
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 */ | |
d3bfcb24 MD |
222 | } |
223 | } | |
224 | ||
7294103b MD |
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, | |
f9b5c2b6 MD |
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. | |
7294103b MD |
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 | |
48a8832b | 245 | struct cds_lfs_head *___cds_lfs_pop_all(cds_lfs_stack_ptr_t u_s) |
7294103b | 246 | { |
48a8832b MD |
247 | struct __cds_lfs_stack *s = u_s._s; |
248 | ||
7294103b MD |
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 | ||
d3bfcb24 MD |
314 | #ifdef __cplusplus |
315 | } | |
316 | #endif | |
317 | ||
318 | #endif /* _URCU_STATIC_LFSTACK_H */ |