| 1 | #ifndef _URCU_STATIC_WFSTACK_H |
| 2 | #define _URCU_STATIC_WFSTACK_H |
| 3 | |
| 4 | /* |
| 5 | * urcu/static/wfstack.h |
| 6 | * |
| 7 | * Userspace RCU library - Stack with with wait-free push, blocking traversal. |
| 8 | * |
| 9 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for |
| 10 | * linking dynamically with the userspace rcu library. |
| 11 | * |
| 12 | * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 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 <pthread.h> |
| 30 | #include <assert.h> |
| 31 | #include <poll.h> |
| 32 | #include <stdbool.h> |
| 33 | #include <urcu/compiler.h> |
| 34 | #include <urcu/uatomic.h> |
| 35 | |
| 36 | #ifdef __cplusplus |
| 37 | extern "C" { |
| 38 | #endif |
| 39 | |
| 40 | #define CDS_WFS_END ((void *) 0x1UL) |
| 41 | #define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */ |
| 42 | #define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */ |
| 43 | |
| 44 | /* |
| 45 | * Stack with wait-free push, blocking traversal. |
| 46 | * |
| 47 | * Stack implementing push, pop, pop_all operations, as well as iterator |
| 48 | * on the stack head returned by pop_all. |
| 49 | * |
| 50 | * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all. |
| 51 | * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, iteration on stack |
| 52 | * head returned by pop_all. |
| 53 | * |
| 54 | * Synchronization table: |
| 55 | * |
| 56 | * External synchronization techniques described in the API below is |
| 57 | * required between pairs marked with "X". No external synchronization |
| 58 | * required between pairs marked with "-". |
| 59 | * |
| 60 | * cds_wfs_push __cds_wfs_pop __cds_wfs_pop_all |
| 61 | * cds_wfs_push - - - |
| 62 | * __cds_wfs_pop - X X |
| 63 | * __cds_wfs_pop_all - X - |
| 64 | * |
| 65 | * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide |
| 66 | * synchronization. |
| 67 | */ |
| 68 | |
| 69 | /* |
| 70 | * cds_wfs_node_init: initialize wait-free stack node. |
| 71 | */ |
| 72 | static inline |
| 73 | void _cds_wfs_node_init(struct cds_wfs_node *node) |
| 74 | { |
| 75 | node->next = NULL; |
| 76 | } |
| 77 | |
| 78 | /* |
| 79 | * cds_wfs_init: initialize wait-free stack. |
| 80 | */ |
| 81 | static inline |
| 82 | void _cds_wfs_init(struct cds_wfs_stack *s) |
| 83 | { |
| 84 | int ret; |
| 85 | |
| 86 | s->head = CDS_WFS_END; |
| 87 | ret = pthread_mutex_init(&s->lock, NULL); |
| 88 | assert(!ret); |
| 89 | } |
| 90 | |
| 91 | static inline bool ___cds_wfs_end(void *node) |
| 92 | { |
| 93 | return node == CDS_WFS_END; |
| 94 | } |
| 95 | |
| 96 | /* |
| 97 | * cds_wfs_empty: return whether wait-free stack is empty. |
| 98 | * |
| 99 | * No memory barrier is issued. No mutual exclusion is required. |
| 100 | */ |
| 101 | static inline bool _cds_wfs_empty(struct cds_wfs_stack *s) |
| 102 | { |
| 103 | return ___cds_wfs_end(CMM_LOAD_SHARED(s->head)); |
| 104 | } |
| 105 | |
| 106 | /* |
| 107 | * cds_wfs_push: push a node into the stack. |
| 108 | * |
| 109 | * Issues a full memory barrier before push. No mutual exclusion is |
| 110 | * required. |
| 111 | * |
| 112 | * Returns 0 if the stack was empty prior to adding the node. |
| 113 | * Returns non-zero otherwise. |
| 114 | */ |
| 115 | static inline |
| 116 | int _cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node) |
| 117 | { |
| 118 | struct cds_wfs_head *old_head, *new_head; |
| 119 | |
| 120 | assert(node->next == NULL); |
| 121 | new_head = caa_container_of(node, struct cds_wfs_head, node); |
| 122 | /* |
| 123 | * uatomic_xchg() implicit memory barrier orders earlier stores |
| 124 | * to node (setting it to NULL) before publication. |
| 125 | */ |
| 126 | old_head = uatomic_xchg(&s->head, new_head); |
| 127 | /* |
| 128 | * At this point, dequeuers see a NULL node->next, they should |
| 129 | * busy-wait until node->next is set to old_head. |
| 130 | */ |
| 131 | CMM_STORE_SHARED(node->next, &old_head->node); |
| 132 | return !___cds_wfs_end(old_head); |
| 133 | } |
| 134 | |
| 135 | /* |
| 136 | * Waiting for push to complete enqueue and return the next node. |
| 137 | */ |
| 138 | static inline struct cds_wfs_node * |
| 139 | ___cds_wfs_node_sync_next(struct cds_wfs_node *node) |
| 140 | { |
| 141 | struct cds_wfs_node *next; |
| 142 | int attempt = 0; |
| 143 | |
| 144 | /* |
| 145 | * Adaptative busy-looping waiting for push to complete. |
| 146 | */ |
| 147 | while ((next = CMM_LOAD_SHARED(node->next)) == NULL) { |
| 148 | if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) { |
| 149 | poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */ |
| 150 | attempt = 0; |
| 151 | } else { |
| 152 | caa_cpu_relax(); |
| 153 | } |
| 154 | } |
| 155 | |
| 156 | return next; |
| 157 | } |
| 158 | |
| 159 | /* |
| 160 | * __cds_wfs_pop_blocking: pop a node from the stack. |
| 161 | * |
| 162 | * Returns NULL if stack is empty. |
| 163 | * |
| 164 | * __cds_wfs_pop_blocking needs to be synchronized using one of the |
| 165 | * following techniques: |
| 166 | * |
| 167 | * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical |
| 168 | * section. The caller must wait for a grace period to pass before |
| 169 | * freeing the returned node or modifying the cds_wfs_node structure. |
| 170 | * 2) Using mutual exclusion (e.g. mutexes) to protect |
| 171 | * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers. |
| 172 | * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking() |
| 173 | * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme). |
| 174 | */ |
| 175 | static inline |
| 176 | struct cds_wfs_node * |
| 177 | ___cds_wfs_pop_blocking(struct cds_wfs_stack *s) |
| 178 | { |
| 179 | struct cds_wfs_head *head, *new_head; |
| 180 | struct cds_wfs_node *next; |
| 181 | |
| 182 | for (;;) { |
| 183 | head = CMM_LOAD_SHARED(s->head); |
| 184 | if (___cds_wfs_end(head)) |
| 185 | return NULL; |
| 186 | next = ___cds_wfs_node_sync_next(&head->node); |
| 187 | new_head = caa_container_of(next, struct cds_wfs_head, node); |
| 188 | if (uatomic_cmpxchg(&s->head, head, new_head) == head) |
| 189 | return &head->node; |
| 190 | /* busy-loop if head changed under us */ |
| 191 | } |
| 192 | } |
| 193 | |
| 194 | /* |
| 195 | * __cds_wfs_pop_all: pop all nodes from a stack. |
| 196 | * |
| 197 | * __cds_wfs_pop_all does not require any synchronization with other |
| 198 | * push, nor with other __cds_wfs_pop_all, but requires synchronization |
| 199 | * matching the technique used to synchronize __cds_wfs_pop_blocking: |
| 200 | * |
| 201 | * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical |
| 202 | * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers |
| 203 | * must wait for a grace period to pass before freeing the returned |
| 204 | * node or modifying the cds_wfs_node structure. However, no RCU |
| 205 | * read-side critical section is needed around __cds_wfs_pop_all. |
| 206 | * 2) Using mutual exclusion (e.g. mutexes) to protect |
| 207 | * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers. |
| 208 | * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking() |
| 209 | * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme). |
| 210 | */ |
| 211 | static inline |
| 212 | struct cds_wfs_head * |
| 213 | ___cds_wfs_pop_all(struct cds_wfs_stack *s) |
| 214 | { |
| 215 | struct cds_wfs_head *head; |
| 216 | |
| 217 | /* |
| 218 | * Implicit memory barrier after uatomic_xchg() matches implicit |
| 219 | * memory barrier before uatomic_xchg() in cds_wfs_push. It |
| 220 | * ensures that all nodes of the returned list are consistent. |
| 221 | * There is no need to issue memory barriers when iterating on |
| 222 | * the returned list, because the full memory barrier issued |
| 223 | * prior to each uatomic_cmpxchg, which each write to head, are |
| 224 | * taking care to order writes to each node prior to the full |
| 225 | * memory barrier after this uatomic_xchg(). |
| 226 | */ |
| 227 | head = uatomic_xchg(&s->head, CDS_WFS_END); |
| 228 | if (___cds_wfs_end(head)) |
| 229 | return NULL; |
| 230 | return head; |
| 231 | } |
| 232 | |
| 233 | /* |
| 234 | * cds_wfs_pop_lock: lock stack pop-protection mutex. |
| 235 | */ |
| 236 | static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s) |
| 237 | { |
| 238 | int ret; |
| 239 | |
| 240 | ret = pthread_mutex_lock(&s->lock); |
| 241 | assert(!ret); |
| 242 | } |
| 243 | |
| 244 | /* |
| 245 | * cds_wfs_pop_unlock: unlock stack pop-protection mutex. |
| 246 | */ |
| 247 | static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s) |
| 248 | { |
| 249 | int ret; |
| 250 | |
| 251 | ret = pthread_mutex_unlock(&s->lock); |
| 252 | assert(!ret); |
| 253 | } |
| 254 | |
| 255 | /* |
| 256 | * Call __cds_wfs_pop_blocking with an internal pop mutex held. |
| 257 | */ |
| 258 | static inline |
| 259 | struct cds_wfs_node * |
| 260 | _cds_wfs_pop_blocking(struct cds_wfs_stack *s) |
| 261 | { |
| 262 | struct cds_wfs_node *retnode; |
| 263 | |
| 264 | _cds_wfs_pop_lock(s); |
| 265 | retnode = ___cds_wfs_pop_blocking(s); |
| 266 | _cds_wfs_pop_unlock(s); |
| 267 | return retnode; |
| 268 | } |
| 269 | |
| 270 | /* |
| 271 | * Call __cds_wfs_pop_all with an internal pop mutex held. |
| 272 | */ |
| 273 | static inline |
| 274 | struct cds_wfs_head * |
| 275 | _cds_wfs_pop_all_blocking(struct cds_wfs_stack *s) |
| 276 | { |
| 277 | struct cds_wfs_head *rethead; |
| 278 | |
| 279 | _cds_wfs_pop_lock(s); |
| 280 | rethead = ___cds_wfs_pop_all(s); |
| 281 | _cds_wfs_pop_unlock(s); |
| 282 | return rethead; |
| 283 | } |
| 284 | |
| 285 | /* |
| 286 | * cds_wfs_first_blocking: get first node of a popped stack. |
| 287 | * |
| 288 | * Content written into the node before enqueue is guaranteed to be |
| 289 | * consistent, but no other memory ordering is ensured. |
| 290 | * |
| 291 | * Used by for-like iteration macros in urcu/wfstack.h: |
| 292 | * cds_wfs_for_each_blocking() |
| 293 | * cds_wfs_for_each_blocking_safe() |
| 294 | */ |
| 295 | static inline struct cds_wfs_node * |
| 296 | _cds_wfs_first_blocking(struct cds_wfs_head *head) |
| 297 | { |
| 298 | if (___cds_wfs_end(head)) |
| 299 | return NULL; |
| 300 | return &head->node; |
| 301 | } |
| 302 | |
| 303 | /* |
| 304 | * cds_wfs_next_blocking: get next node of a popped stack. |
| 305 | * |
| 306 | * Content written into the node before enqueue is guaranteed to be |
| 307 | * consistent, but no other memory ordering is ensured. |
| 308 | * |
| 309 | * Used by for-like iteration macros in urcu/wfstack.h: |
| 310 | * cds_wfs_for_each_blocking() |
| 311 | * cds_wfs_for_each_blocking_safe() |
| 312 | */ |
| 313 | static inline struct cds_wfs_node * |
| 314 | _cds_wfs_next_blocking(struct cds_wfs_node *node) |
| 315 | { |
| 316 | struct cds_wfs_node *next; |
| 317 | |
| 318 | next = ___cds_wfs_node_sync_next(node); |
| 319 | if (___cds_wfs_end(next)) |
| 320 | return NULL; |
| 321 | return next; |
| 322 | } |
| 323 | |
| 324 | #ifdef __cplusplus |
| 325 | } |
| 326 | #endif |
| 327 | |
| 328 | #endif /* _URCU_STATIC_WFSTACK_H */ |