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1 | // SPDX-FileCopyrightText: 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
2 | // | |
3 | // SPDX-License-Identifier: LGPL-2.1-or-later | |
4 | ||
d3bfcb24 MD |
5 | #ifndef _URCU_STATIC_LFSTACK_H |
6 | #define _URCU_STATIC_LFSTACK_H | |
7 | ||
8 | /* | |
d3bfcb24 MD |
9 | * Userspace RCU library - Lock-Free Stack |
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 | ||
7294103b MD |
15 | #include <stdbool.h> |
16 | #include <pthread.h> | |
01477510 | 17 | #include <urcu/assert.h> |
d3bfcb24 MD |
18 | #include <urcu/uatomic.h> |
19 | #include <urcu-pointer.h> | |
20 | ||
21 | #ifdef __cplusplus | |
22 | extern "C" { | |
23 | #endif | |
24 | ||
7294103b MD |
25 | /* |
26 | * Lock-free stack. | |
27 | * | |
28 | * Stack implementing push, pop, pop_all operations, as well as iterator | |
29 | * on the stack head returned by pop_all. | |
30 | * | |
31 | * Synchronization table: | |
32 | * | |
33 | * External synchronization techniques described in the API below is | |
34 | * required between pairs marked with "X". No external synchronization | |
35 | * required between pairs marked with "-". | |
36 | * | |
37 | * cds_lfs_push __cds_lfs_pop __cds_lfs_pop_all | |
38 | * cds_lfs_push - - - | |
39 | * __cds_lfs_pop - X X | |
40 | * __cds_lfs_pop_all - X - | |
41 | * | |
42 | * cds_lfs_pop_blocking and cds_lfs_pop_all_blocking use an internal | |
43 | * mutex to provide synchronization. | |
44 | */ | |
45 | ||
46 | /* | |
47 | * cds_lfs_node_init: initialize lock-free stack node. | |
48 | */ | |
d3bfcb24 | 49 | static inline |
70469b43 | 50 | void _cds_lfs_node_init(struct cds_lfs_node *node __attribute__((unused))) |
d3bfcb24 MD |
51 | { |
52 | } | |
53 | ||
7294103b | 54 | /* |
200d100e MD |
55 | * cds_lfs_init: initialize lock-free stack (with lock). Pair with |
56 | * cds_lfs_destroy(). | |
7294103b | 57 | */ |
d3bfcb24 MD |
58 | static inline |
59 | void _cds_lfs_init(struct cds_lfs_stack *s) | |
60 | { | |
7294103b MD |
61 | int ret; |
62 | ||
d3bfcb24 | 63 | s->head = NULL; |
7294103b | 64 | ret = pthread_mutex_init(&s->lock, NULL); |
01477510 | 65 | urcu_posix_assert(!ret); |
7294103b MD |
66 | } |
67 | ||
48a8832b | 68 | /* |
200d100e MD |
69 | * cds_lfs_destroy: destroy lock-free stack (with lock). Pair with |
70 | * cds_lfs_init(). | |
71 | */ | |
72 | static inline | |
73 | void _cds_lfs_destroy(struct cds_lfs_stack *s) | |
74 | { | |
75 | int ret = pthread_mutex_destroy(&s->lock); | |
01477510 | 76 | urcu_posix_assert(!ret); |
200d100e MD |
77 | } |
78 | ||
79 | /* | |
80 | * ___cds_lfs_init: initialize lock-free stack (without lock). | |
81 | * Don't pair with any destroy function. | |
48a8832b MD |
82 | */ |
83 | static inline | |
84 | void ___cds_lfs_init(struct __cds_lfs_stack *s) | |
85 | { | |
86 | s->head = NULL; | |
87 | } | |
88 | ||
7294103b MD |
89 | static inline |
90 | bool ___cds_lfs_empty_head(struct cds_lfs_head *head) | |
91 | { | |
92 | return head == NULL; | |
93 | } | |
94 | ||
95 | /* | |
96 | * cds_lfs_empty: return whether lock-free stack is empty. | |
97 | * | |
98 | * No memory barrier is issued. No mutual exclusion is required. | |
99 | */ | |
100 | static inline | |
48a8832b | 101 | bool _cds_lfs_empty(cds_lfs_stack_ptr_t s) |
7294103b | 102 | { |
0e2125fb | 103 | return ___cds_lfs_empty_head(uatomic_load(&s._s->head, CMM_RELAXED)); |
d3bfcb24 MD |
104 | } |
105 | ||
106 | /* | |
107 | * cds_lfs_push: push a node into the stack. | |
108 | * | |
109 | * Does not require any synchronization with other push nor pop. | |
110 | * | |
0e2125fb OD |
111 | * Operations before push are consistent when observed after associated pop. |
112 | * | |
d3bfcb24 MD |
113 | * Lock-free stack push is not subject to ABA problem, so no need to |
114 | * take the RCU read-side lock. Even if "head" changes between two | |
115 | * uatomic_cmpxchg() invocations here (being popped, and then pushed | |
116 | * again by one or more concurrent threads), the second | |
117 | * uatomic_cmpxchg() invocation only cares about pushing a new entry at | |
118 | * the head of the stack, ensuring consistency by making sure the new | |
119 | * node->next is the same pointer value as the value replaced as head. | |
120 | * It does not care about the content of the actual next node, so it can | |
121 | * very well be reallocated between the two uatomic_cmpxchg(). | |
122 | * | |
123 | * We take the approach of expecting the stack to be usually empty, so | |
124 | * we first try an initial uatomic_cmpxchg() on a NULL old_head, and | |
125 | * retry if the old head was non-NULL (the value read by the first | |
126 | * uatomic_cmpxchg() is used as old head for the following loop). The | |
127 | * upside of this scheme is to minimize the amount of cacheline traffic, | |
128 | * always performing an exclusive cacheline access, rather than doing | |
129 | * non-exclusive followed by exclusive cacheline access (which would be | |
130 | * required if we first read the old head value). This design decision | |
ffa11a18 | 131 | * might be revisited after more thorough benchmarking on various |
d3bfcb24 MD |
132 | * platforms. |
133 | * | |
134 | * Returns 0 if the stack was empty prior to adding the node. | |
135 | * Returns non-zero otherwise. | |
136 | */ | |
137 | static inline | |
48a8832b | 138 | bool _cds_lfs_push(cds_lfs_stack_ptr_t u_s, |
d3bfcb24 MD |
139 | struct cds_lfs_node *node) |
140 | { | |
48a8832b | 141 | struct __cds_lfs_stack *s = u_s._s; |
7294103b MD |
142 | struct cds_lfs_head *head = NULL; |
143 | struct cds_lfs_head *new_head = | |
144 | caa_container_of(node, struct cds_lfs_head, node); | |
d3bfcb24 MD |
145 | |
146 | for (;;) { | |
7294103b | 147 | struct cds_lfs_head *old_head = head; |
d3bfcb24 MD |
148 | |
149 | /* | |
150 | * node->next is still private at this point, no need to | |
151 | * perform a _CMM_STORE_SHARED(). | |
152 | */ | |
7294103b | 153 | node->next = &head->node; |
d3bfcb24 MD |
154 | /* |
155 | * uatomic_cmpxchg() implicit memory barrier orders earlier | |
156 | * stores to node before publication. | |
157 | */ | |
0e2125fb OD |
158 | cmm_emit_legacy_smp_mb(); |
159 | head = uatomic_cmpxchg_mo(&s->head, old_head, new_head, | |
160 | CMM_SEQ_CST, CMM_SEQ_CST); | |
d3bfcb24 MD |
161 | if (old_head == head) |
162 | break; | |
163 | } | |
e47048cc | 164 | return !___cds_lfs_empty_head(head); |
d3bfcb24 MD |
165 | } |
166 | ||
167 | /* | |
7294103b | 168 | * __cds_lfs_pop: pop a node from the stack. |
d3bfcb24 MD |
169 | * |
170 | * Returns NULL if stack is empty. | |
171 | * | |
0e2125fb OD |
172 | * Operations after pop are consistent when observed before associated push. |
173 | * | |
7294103b | 174 | * __cds_lfs_pop needs to be synchronized using one of the following |
d3bfcb24 MD |
175 | * techniques: |
176 | * | |
f9b5c2b6 MD |
177 | * 1) Calling __cds_lfs_pop under rcu read lock critical section. |
178 | * Both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a | |
179 | * grace period to pass before freeing the returned node or pushing | |
180 | * the node back into the stack. It is valid to overwrite the content | |
181 | * of cds_lfs_node immediately after __cds_lfs_pop and | |
182 | * __cds_lfs_pop_all. No RCU read-side critical section is needed | |
183 | * around __cds_lfs_pop_all. | |
7294103b MD |
184 | * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop |
185 | * and __cds_lfs_pop_all callers. | |
186 | * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and | |
187 | * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme). | |
d3bfcb24 MD |
188 | */ |
189 | static inline | |
48a8832b | 190 | struct cds_lfs_node *___cds_lfs_pop(cds_lfs_stack_ptr_t u_s) |
d3bfcb24 | 191 | { |
48a8832b MD |
192 | struct __cds_lfs_stack *s = u_s._s; |
193 | ||
d3bfcb24 | 194 | for (;;) { |
7294103b MD |
195 | struct cds_lfs_head *head, *next_head; |
196 | struct cds_lfs_node *next; | |
d3bfcb24 | 197 | |
0e2125fb | 198 | head = uatomic_load(&s->head, CMM_CONSUME); |
7294103b MD |
199 | if (___cds_lfs_empty_head(head)) |
200 | return NULL; /* Empty stack */ | |
201 | ||
202 | /* | |
203 | * Read head before head->next. Matches the implicit | |
204 | * memory barrier before uatomic_cmpxchg() in | |
205 | * cds_lfs_push. | |
206 | */ | |
0e2125fb | 207 | next = uatomic_load(&head->node.next, CMM_RELAXED); |
7294103b MD |
208 | next_head = caa_container_of(next, |
209 | struct cds_lfs_head, node); | |
0e2125fb OD |
210 | if (uatomic_cmpxchg_mo(&s->head, head, next_head, |
211 | CMM_SEQ_CST, CMM_SEQ_CST) == head){ | |
212 | cmm_emit_legacy_smp_mb(); | |
7294103b | 213 | return &head->node; |
0e2125fb | 214 | } |
7294103b | 215 | /* busy-loop if head changed under us */ |
d3bfcb24 MD |
216 | } |
217 | } | |
218 | ||
7294103b MD |
219 | /* |
220 | * __cds_lfs_pop_all: pop all nodes from a stack. | |
221 | * | |
222 | * __cds_lfs_pop_all does not require any synchronization with other | |
223 | * push, nor with other __cds_lfs_pop_all, but requires synchronization | |
224 | * matching the technique used to synchronize __cds_lfs_pop: | |
225 | * | |
226 | * 1) If __cds_lfs_pop is called under rcu read lock critical section, | |
f9b5c2b6 MD |
227 | * both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a |
228 | * grace period to pass before freeing the returned node or pushing | |
229 | * the node back into the stack. It is valid to overwrite the content | |
230 | * of cds_lfs_node immediately after __cds_lfs_pop and | |
231 | * __cds_lfs_pop_all. No RCU read-side critical section is needed | |
232 | * around __cds_lfs_pop_all. | |
7294103b MD |
233 | * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop and |
234 | * __cds_lfs_pop_all callers. | |
235 | * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and | |
236 | * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme). | |
237 | */ | |
238 | static inline | |
48a8832b | 239 | struct cds_lfs_head *___cds_lfs_pop_all(cds_lfs_stack_ptr_t u_s) |
7294103b | 240 | { |
48a8832b | 241 | struct __cds_lfs_stack *s = u_s._s; |
0e2125fb | 242 | struct cds_lfs_head *head; |
48a8832b | 243 | |
7294103b MD |
244 | /* |
245 | * Implicit memory barrier after uatomic_xchg() matches implicit | |
246 | * memory barrier before uatomic_cmpxchg() in cds_lfs_push. It | |
247 | * ensures that all nodes of the returned list are consistent. | |
248 | * There is no need to issue memory barriers when iterating on | |
249 | * the returned list, because the full memory barrier issued | |
250 | * prior to each uatomic_cmpxchg, which each write to head, are | |
251 | * taking care to order writes to each node prior to the full | |
252 | * memory barrier after this uatomic_xchg(). | |
253 | */ | |
0e2125fb OD |
254 | head = uatomic_xchg_mo(&s->head, NULL, CMM_SEQ_CST); |
255 | cmm_emit_legacy_smp_mb(); | |
256 | return head; | |
7294103b MD |
257 | } |
258 | ||
259 | /* | |
260 | * cds_lfs_pop_lock: lock stack pop-protection mutex. | |
261 | */ | |
262 | static inline void _cds_lfs_pop_lock(struct cds_lfs_stack *s) | |
263 | { | |
264 | int ret; | |
265 | ||
266 | ret = pthread_mutex_lock(&s->lock); | |
01477510 | 267 | urcu_posix_assert(!ret); |
7294103b MD |
268 | } |
269 | ||
270 | /* | |
271 | * cds_lfs_pop_unlock: unlock stack pop-protection mutex. | |
272 | */ | |
273 | static inline void _cds_lfs_pop_unlock(struct cds_lfs_stack *s) | |
274 | { | |
275 | int ret; | |
276 | ||
277 | ret = pthread_mutex_unlock(&s->lock); | |
01477510 | 278 | urcu_posix_assert(!ret); |
7294103b MD |
279 | } |
280 | ||
281 | /* | |
282 | * Call __cds_lfs_pop with an internal pop mutex held. | |
283 | */ | |
284 | static inline | |
285 | struct cds_lfs_node * | |
286 | _cds_lfs_pop_blocking(struct cds_lfs_stack *s) | |
287 | { | |
288 | struct cds_lfs_node *retnode; | |
28757437 | 289 | cds_lfs_stack_ptr_t stack; |
7294103b MD |
290 | |
291 | _cds_lfs_pop_lock(s); | |
28757437 SM |
292 | stack.s = s; |
293 | retnode = ___cds_lfs_pop(stack); | |
7294103b MD |
294 | _cds_lfs_pop_unlock(s); |
295 | return retnode; | |
296 | } | |
297 | ||
298 | /* | |
299 | * Call __cds_lfs_pop_all with an internal pop mutex held. | |
300 | */ | |
301 | static inline | |
302 | struct cds_lfs_head * | |
303 | _cds_lfs_pop_all_blocking(struct cds_lfs_stack *s) | |
304 | { | |
305 | struct cds_lfs_head *rethead; | |
28757437 | 306 | cds_lfs_stack_ptr_t stack; |
7294103b MD |
307 | |
308 | _cds_lfs_pop_lock(s); | |
28757437 SM |
309 | stack.s = s; |
310 | rethead = ___cds_lfs_pop_all(stack); | |
7294103b MD |
311 | _cds_lfs_pop_unlock(s); |
312 | return rethead; | |
313 | } | |
314 | ||
d3bfcb24 MD |
315 | #ifdef __cplusplus |
316 | } | |
317 | #endif | |
318 | ||
319 | #endif /* _URCU_STATIC_LFSTACK_H */ |