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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 | ||
32921450 MD |
39 | #define CDS_LFS_END NULL |
40 | ||
7294103b MD |
41 | /* |
42 | * Lock-free stack. | |
43 | * | |
44 | * Stack implementing push, pop, pop_all operations, as well as iterator | |
45 | * on the stack head returned by pop_all. | |
46 | * | |
47 | * Synchronization table: | |
48 | * | |
49 | * External synchronization techniques described in the API below is | |
50 | * required between pairs marked with "X". No external synchronization | |
51 | * required between pairs marked with "-". | |
52 | * | |
53 | * cds_lfs_push __cds_lfs_pop __cds_lfs_pop_all | |
54 | * cds_lfs_push - - - | |
55 | * __cds_lfs_pop - X X | |
56 | * __cds_lfs_pop_all - X - | |
57 | * | |
58 | * cds_lfs_pop_blocking and cds_lfs_pop_all_blocking use an internal | |
59 | * mutex to provide synchronization. | |
60 | */ | |
61 | ||
62 | /* | |
63 | * cds_lfs_node_init: initialize lock-free stack node. | |
64 | */ | |
d3bfcb24 MD |
65 | static inline |
66 | void _cds_lfs_node_init(struct cds_lfs_node *node) | |
67 | { | |
68 | } | |
69 | ||
7294103b MD |
70 | /* |
71 | * cds_lfs_init: initialize lock-free stack. | |
72 | */ | |
d3bfcb24 MD |
73 | static inline |
74 | void _cds_lfs_init(struct cds_lfs_stack *s) | |
75 | { | |
7294103b MD |
76 | int ret; |
77 | ||
32921450 | 78 | s->head = CDS_LFS_END; |
7294103b MD |
79 | ret = pthread_mutex_init(&s->lock, NULL); |
80 | assert(!ret); | |
81 | } | |
82 | ||
48a8832b MD |
83 | /* |
84 | * ___cds_lfs_init: initialize lock-free stack. | |
85 | */ | |
86 | static inline | |
87 | void ___cds_lfs_init(struct __cds_lfs_stack *s) | |
88 | { | |
32921450 | 89 | s->head = CDS_LFS_END; |
48a8832b MD |
90 | } |
91 | ||
7294103b MD |
92 | static inline |
93 | bool ___cds_lfs_empty_head(struct cds_lfs_head *head) | |
94 | { | |
32921450 | 95 | return head == CDS_LFS_END; |
7294103b MD |
96 | } |
97 | ||
98 | /* | |
99 | * cds_lfs_empty: return whether lock-free stack is empty. | |
100 | * | |
101 | * No memory barrier is issued. No mutual exclusion is required. | |
102 | */ | |
103 | static inline | |
48a8832b | 104 | bool _cds_lfs_empty(cds_lfs_stack_ptr_t s) |
7294103b | 105 | { |
48a8832b | 106 | return ___cds_lfs_empty_head(CMM_LOAD_SHARED(s._s->head)); |
d3bfcb24 MD |
107 | } |
108 | ||
109 | /* | |
110 | * cds_lfs_push: push a node into the stack. | |
111 | * | |
112 | * Does not require any synchronization with other push nor pop. | |
113 | * | |
114 | * Lock-free stack push is not subject to ABA problem, so no need to | |
115 | * take the RCU read-side lock. Even if "head" changes between two | |
116 | * uatomic_cmpxchg() invocations here (being popped, and then pushed | |
117 | * again by one or more concurrent threads), the second | |
118 | * uatomic_cmpxchg() invocation only cares about pushing a new entry at | |
119 | * the head of the stack, ensuring consistency by making sure the new | |
120 | * node->next is the same pointer value as the value replaced as head. | |
121 | * It does not care about the content of the actual next node, so it can | |
122 | * very well be reallocated between the two uatomic_cmpxchg(). | |
123 | * | |
124 | * We take the approach of expecting the stack to be usually empty, so | |
125 | * we first try an initial uatomic_cmpxchg() on a NULL old_head, and | |
126 | * retry if the old head was non-NULL (the value read by the first | |
127 | * uatomic_cmpxchg() is used as old head for the following loop). The | |
128 | * upside of this scheme is to minimize the amount of cacheline traffic, | |
129 | * always performing an exclusive cacheline access, rather than doing | |
130 | * non-exclusive followed by exclusive cacheline access (which would be | |
131 | * required if we first read the old head value). This design decision | |
ffa11a18 | 132 | * might be revisited after more thorough benchmarking on various |
d3bfcb24 MD |
133 | * platforms. |
134 | * | |
135 | * Returns 0 if the stack was empty prior to adding the node. | |
136 | * Returns non-zero otherwise. | |
137 | */ | |
138 | static inline | |
48a8832b | 139 | bool _cds_lfs_push(cds_lfs_stack_ptr_t u_s, |
d3bfcb24 MD |
140 | struct cds_lfs_node *node) |
141 | { | |
48a8832b | 142 | struct __cds_lfs_stack *s = u_s._s; |
32921450 | 143 | struct cds_lfs_head *head = CDS_LFS_END; |
7294103b MD |
144 | struct cds_lfs_head *new_head = |
145 | caa_container_of(node, struct cds_lfs_head, node); | |
d3bfcb24 MD |
146 | |
147 | for (;;) { | |
7294103b | 148 | struct cds_lfs_head *old_head = head; |
d3bfcb24 MD |
149 | |
150 | /* | |
151 | * node->next is still private at this point, no need to | |
152 | * perform a _CMM_STORE_SHARED(). | |
153 | */ | |
7294103b | 154 | node->next = &head->node; |
d3bfcb24 MD |
155 | /* |
156 | * uatomic_cmpxchg() implicit memory barrier orders earlier | |
157 | * stores to node before publication. | |
158 | */ | |
7294103b | 159 | head = uatomic_cmpxchg(&s->head, old_head, new_head); |
d3bfcb24 MD |
160 | if (old_head == head) |
161 | break; | |
162 | } | |
7294103b | 163 | return ___cds_lfs_empty_head(head); |
d3bfcb24 MD |
164 | } |
165 | ||
166 | /* | |
7294103b | 167 | * __cds_lfs_pop: pop a node from the stack. |
d3bfcb24 MD |
168 | * |
169 | * Returns NULL if stack is empty. | |
170 | * | |
7294103b | 171 | * __cds_lfs_pop needs to be synchronized using one of the following |
d3bfcb24 MD |
172 | * techniques: |
173 | * | |
7294103b | 174 | * 1) Calling __cds_lfs_pop under rcu read lock critical section. The |
d3bfcb24 MD |
175 | * caller must wait for a grace period to pass before freeing the |
176 | * returned node or modifying the cds_lfs_node structure. | |
7294103b MD |
177 | * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop |
178 | * and __cds_lfs_pop_all callers. | |
179 | * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and | |
180 | * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme). | |
d3bfcb24 MD |
181 | */ |
182 | static inline | |
48a8832b | 183 | struct cds_lfs_node *___cds_lfs_pop(cds_lfs_stack_ptr_t u_s) |
d3bfcb24 | 184 | { |
48a8832b MD |
185 | struct __cds_lfs_stack *s = u_s._s; |
186 | ||
d3bfcb24 | 187 | for (;;) { |
7294103b MD |
188 | struct cds_lfs_head *head, *next_head; |
189 | struct cds_lfs_node *next; | |
d3bfcb24 MD |
190 | |
191 | head = _CMM_LOAD_SHARED(s->head); | |
7294103b MD |
192 | if (___cds_lfs_empty_head(head)) |
193 | return NULL; /* Empty stack */ | |
194 | ||
195 | /* | |
196 | * Read head before head->next. Matches the implicit | |
197 | * memory barrier before uatomic_cmpxchg() in | |
198 | * cds_lfs_push. | |
199 | */ | |
200 | cmm_smp_read_barrier_depends(); | |
201 | next = _CMM_LOAD_SHARED(head->node.next); | |
202 | next_head = caa_container_of(next, | |
203 | struct cds_lfs_head, node); | |
204 | if (uatomic_cmpxchg(&s->head, head, next_head) == head) | |
205 | return &head->node; | |
206 | /* busy-loop if head changed under us */ | |
d3bfcb24 MD |
207 | } |
208 | } | |
209 | ||
7294103b MD |
210 | /* |
211 | * __cds_lfs_pop_all: pop all nodes from a stack. | |
212 | * | |
213 | * __cds_lfs_pop_all does not require any synchronization with other | |
214 | * push, nor with other __cds_lfs_pop_all, but requires synchronization | |
215 | * matching the technique used to synchronize __cds_lfs_pop: | |
216 | * | |
217 | * 1) If __cds_lfs_pop is called under rcu read lock critical section, | |
218 | * both __cds_lfs_pop and cds_lfs_pop_all callers must wait for a | |
219 | * grace period to pass before freeing the returned node or modifying | |
220 | * the cds_lfs_node structure. However, no RCU read-side critical | |
221 | * section is needed around __cds_lfs_pop_all. | |
222 | * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop and | |
223 | * __cds_lfs_pop_all callers. | |
224 | * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and | |
225 | * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme). | |
226 | */ | |
227 | static inline | |
48a8832b | 228 | struct cds_lfs_head *___cds_lfs_pop_all(cds_lfs_stack_ptr_t u_s) |
7294103b | 229 | { |
48a8832b MD |
230 | struct __cds_lfs_stack *s = u_s._s; |
231 | ||
7294103b MD |
232 | /* |
233 | * Implicit memory barrier after uatomic_xchg() matches implicit | |
234 | * memory barrier before uatomic_cmpxchg() in cds_lfs_push. It | |
235 | * ensures that all nodes of the returned list are consistent. | |
236 | * There is no need to issue memory barriers when iterating on | |
237 | * the returned list, because the full memory barrier issued | |
238 | * prior to each uatomic_cmpxchg, which each write to head, are | |
239 | * taking care to order writes to each node prior to the full | |
240 | * memory barrier after this uatomic_xchg(). | |
241 | */ | |
32921450 | 242 | return uatomic_xchg(&s->head, CDS_LFS_END); |
7294103b MD |
243 | } |
244 | ||
245 | /* | |
246 | * cds_lfs_pop_lock: lock stack pop-protection mutex. | |
247 | */ | |
248 | static inline void _cds_lfs_pop_lock(struct cds_lfs_stack *s) | |
249 | { | |
250 | int ret; | |
251 | ||
252 | ret = pthread_mutex_lock(&s->lock); | |
253 | assert(!ret); | |
254 | } | |
255 | ||
256 | /* | |
257 | * cds_lfs_pop_unlock: unlock stack pop-protection mutex. | |
258 | */ | |
259 | static inline void _cds_lfs_pop_unlock(struct cds_lfs_stack *s) | |
260 | { | |
261 | int ret; | |
262 | ||
263 | ret = pthread_mutex_unlock(&s->lock); | |
264 | assert(!ret); | |
265 | } | |
266 | ||
267 | /* | |
268 | * Call __cds_lfs_pop with an internal pop mutex held. | |
269 | */ | |
270 | static inline | |
271 | struct cds_lfs_node * | |
272 | _cds_lfs_pop_blocking(struct cds_lfs_stack *s) | |
273 | { | |
274 | struct cds_lfs_node *retnode; | |
275 | ||
276 | _cds_lfs_pop_lock(s); | |
277 | retnode = ___cds_lfs_pop(s); | |
278 | _cds_lfs_pop_unlock(s); | |
279 | return retnode; | |
280 | } | |
281 | ||
282 | /* | |
283 | * Call __cds_lfs_pop_all with an internal pop mutex held. | |
284 | */ | |
285 | static inline | |
286 | struct cds_lfs_head * | |
287 | _cds_lfs_pop_all_blocking(struct cds_lfs_stack *s) | |
288 | { | |
289 | struct cds_lfs_head *rethead; | |
290 | ||
291 | _cds_lfs_pop_lock(s); | |
292 | rethead = ___cds_lfs_pop_all(s); | |
293 | _cds_lfs_pop_unlock(s); | |
294 | return rethead; | |
295 | } | |
296 | ||
d3bfcb24 MD |
297 | #ifdef __cplusplus |
298 | } | |
299 | #endif | |
300 | ||
301 | #endif /* _URCU_STATIC_LFSTACK_H */ |