| 1 | #ifndef _URCU_WFCQUEUE_STATIC_H |
| 2 | #define _URCU_WFCQUEUE_STATIC_H |
| 3 | |
| 4 | /* |
| 5 | * urcu/static/wfcqueue.h |
| 6 | * |
| 7 | * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue |
| 8 | * |
| 9 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfcqueue.h for |
| 10 | * linking dynamically with the userspace rcu library. |
| 11 | * |
| 12 | * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 13 | * Copyright 2011-2012 - Lai Jiangshan <laijs@cn.fujitsu.com> |
| 14 | * |
| 15 | * This library is free software; you can redistribute it and/or |
| 16 | * modify it under the terms of the GNU Lesser General Public |
| 17 | * License as published by the Free Software Foundation; either |
| 18 | * version 2.1 of the License, or (at your option) any later version. |
| 19 | * |
| 20 | * This library is distributed in the hope that it will be useful, |
| 21 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 22 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 23 | * Lesser General Public License for more details. |
| 24 | * |
| 25 | * You should have received a copy of the GNU Lesser General Public |
| 26 | * License along with this library; if not, write to the Free Software |
| 27 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 28 | */ |
| 29 | |
| 30 | #include <pthread.h> |
| 31 | #include <assert.h> |
| 32 | #include <poll.h> |
| 33 | #include <stdbool.h> |
| 34 | #include <urcu/compiler.h> |
| 35 | #include <urcu/uatomic.h> |
| 36 | |
| 37 | #ifdef __cplusplus |
| 38 | extern "C" { |
| 39 | #endif |
| 40 | |
| 41 | /* |
| 42 | * Concurrent queue with wait-free enqueue/blocking dequeue. |
| 43 | * |
| 44 | * This queue has been designed and implemented collaboratively by |
| 45 | * Mathieu Desnoyers and Lai Jiangshan. Inspired from |
| 46 | * half-wait-free/half-blocking queue implementation done by Paul E. |
| 47 | * McKenney. |
| 48 | * |
| 49 | * Mutual exclusion of cds_wfcq_* / __cds_wfcq_* API |
| 50 | * |
| 51 | * Synchronization table: |
| 52 | * |
| 53 | * External synchronization techniques described in the API below is |
| 54 | * required between pairs marked with "X". No external synchronization |
| 55 | * required between pairs marked with "-". |
| 56 | * |
| 57 | * Legend: |
| 58 | * [1] cds_wfcq_enqueue |
| 59 | * [2] __cds_wfcq_splice (destination queue) |
| 60 | * [3] __cds_wfcq_dequeue |
| 61 | * [4] __cds_wfcq_splice (source queue) |
| 62 | * [5] __cds_wfcq_first |
| 63 | * [6] __cds_wfcq_next |
| 64 | * |
| 65 | * [1] [2] [3] [4] [5] [6] |
| 66 | * [1] - - - - - - |
| 67 | * [2] - - - - - - |
| 68 | * [3] - - X X X X |
| 69 | * [4] - - X - X X |
| 70 | * [5] - - X X - - |
| 71 | * [6] - - X X - - |
| 72 | * |
| 73 | * Mutual exclusion can be ensured by holding cds_wfcq_dequeue_lock(). |
| 74 | * |
| 75 | * For convenience, cds_wfcq_dequeue_blocking() and |
| 76 | * cds_wfcq_splice_blocking() hold the dequeue lock. |
| 77 | * |
| 78 | * Besides locking, mutual exclusion of dequeue, splice and iteration |
| 79 | * can be ensured by performing all of those operations from a single |
| 80 | * thread, without requiring any lock. |
| 81 | */ |
| 82 | |
| 83 | #define WFCQ_ADAPT_ATTEMPTS 10 /* Retry if being set */ |
| 84 | #define WFCQ_WAIT 10 /* Wait 10 ms if being set */ |
| 85 | |
| 86 | /* |
| 87 | * cds_wfcq_node_init: initialize wait-free queue node. |
| 88 | */ |
| 89 | static inline void _cds_wfcq_node_init(struct cds_wfcq_node *node) |
| 90 | { |
| 91 | node->next = NULL; |
| 92 | } |
| 93 | |
| 94 | /* |
| 95 | * cds_wfcq_init: initialize wait-free queue (with lock). Pair with |
| 96 | * cds_wfcq_destroy(). |
| 97 | */ |
| 98 | static inline void _cds_wfcq_init(struct cds_wfcq_head *head, |
| 99 | struct cds_wfcq_tail *tail) |
| 100 | { |
| 101 | int ret; |
| 102 | |
| 103 | /* Set queue head and tail */ |
| 104 | _cds_wfcq_node_init(&head->node); |
| 105 | tail->p = &head->node; |
| 106 | ret = pthread_mutex_init(&head->lock, NULL); |
| 107 | assert(!ret); |
| 108 | } |
| 109 | |
| 110 | /* |
| 111 | * cds_wfcq_destroy: destroy wait-free queue (with lock). Pair with |
| 112 | * cds_wfcq_init(). |
| 113 | */ |
| 114 | static inline void _cds_wfcq_destroy(struct cds_wfcq_head *head, |
| 115 | struct cds_wfcq_tail *tail __attribute__((unused))) |
| 116 | { |
| 117 | int ret = pthread_mutex_destroy(&head->lock); |
| 118 | assert(!ret); |
| 119 | } |
| 120 | |
| 121 | /* |
| 122 | * __cds_wfcq_init: initialize wait-free queue (without lock). Don't |
| 123 | * pair with any destroy function. |
| 124 | */ |
| 125 | static inline void ___cds_wfcq_init(struct __cds_wfcq_head *head, |
| 126 | struct cds_wfcq_tail *tail) |
| 127 | { |
| 128 | /* Set queue head and tail */ |
| 129 | _cds_wfcq_node_init(&head->node); |
| 130 | tail->p = &head->node; |
| 131 | } |
| 132 | |
| 133 | /* |
| 134 | * cds_wfcq_empty: return whether wait-free queue is empty. |
| 135 | * |
| 136 | * No memory barrier is issued. No mutual exclusion is required. |
| 137 | * |
| 138 | * We perform the test on head->node.next to check if the queue is |
| 139 | * possibly empty, but we confirm this by checking if the tail pointer |
| 140 | * points to the head node because the tail pointer is the linearisation |
| 141 | * point of the enqueuers. Just checking the head next pointer could |
| 142 | * make a queue appear empty if an enqueuer is preempted for a long time |
| 143 | * between xchg() and setting the previous node's next pointer. |
| 144 | */ |
| 145 | static inline bool _cds_wfcq_empty(cds_wfcq_head_ptr_t u_head, |
| 146 | struct cds_wfcq_tail *tail) |
| 147 | { |
| 148 | struct __cds_wfcq_head *head = u_head._h; |
| 149 | /* |
| 150 | * Queue is empty if no node is pointed by head->node.next nor |
| 151 | * tail->p. Even though the tail->p check is sufficient to find |
| 152 | * out of the queue is empty, we first check head->node.next as a |
| 153 | * common case to ensure that dequeuers do not frequently access |
| 154 | * enqueuer's tail->p cache line. |
| 155 | */ |
| 156 | return CMM_LOAD_SHARED(head->node.next) == NULL |
| 157 | && CMM_LOAD_SHARED(tail->p) == &head->node; |
| 158 | } |
| 159 | |
| 160 | static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head *head, |
| 161 | struct cds_wfcq_tail *tail __attribute__((unused))) |
| 162 | { |
| 163 | int ret; |
| 164 | |
| 165 | ret = pthread_mutex_lock(&head->lock); |
| 166 | assert(!ret); |
| 167 | } |
| 168 | |
| 169 | static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head, |
| 170 | struct cds_wfcq_tail *tail __attribute__((unused))) |
| 171 | { |
| 172 | int ret; |
| 173 | |
| 174 | ret = pthread_mutex_unlock(&head->lock); |
| 175 | assert(!ret); |
| 176 | } |
| 177 | |
| 178 | static inline bool ___cds_wfcq_append(cds_wfcq_head_ptr_t u_head, |
| 179 | struct cds_wfcq_tail *tail, |
| 180 | struct cds_wfcq_node *new_head, |
| 181 | struct cds_wfcq_node *new_tail) |
| 182 | { |
| 183 | struct __cds_wfcq_head *head = u_head._h; |
| 184 | struct cds_wfcq_node *old_tail; |
| 185 | |
| 186 | /* |
| 187 | * Implicit memory barrier before uatomic_xchg() orders earlier |
| 188 | * stores to data structure containing node and setting |
| 189 | * node->next to NULL before publication. |
| 190 | */ |
| 191 | old_tail = uatomic_xchg(&tail->p, new_tail); |
| 192 | |
| 193 | /* |
| 194 | * Implicit memory barrier after uatomic_xchg() orders store to |
| 195 | * q->tail before store to old_tail->next. |
| 196 | * |
| 197 | * At this point, dequeuers see a NULL tail->p->next, which |
| 198 | * indicates that the queue is being appended to. The following |
| 199 | * store will append "node" to the queue from a dequeuer |
| 200 | * perspective. |
| 201 | */ |
| 202 | CMM_STORE_SHARED(old_tail->next, new_head); |
| 203 | /* |
| 204 | * Return false if queue was empty prior to adding the node, |
| 205 | * else return true. |
| 206 | */ |
| 207 | return old_tail != &head->node; |
| 208 | } |
| 209 | |
| 210 | /* |
| 211 | * cds_wfcq_enqueue: enqueue a node into a wait-free queue. |
| 212 | * |
| 213 | * Issues a full memory barrier before enqueue. No mutual exclusion is |
| 214 | * required. |
| 215 | * |
| 216 | * Returns false if the queue was empty prior to adding the node. |
| 217 | * Returns true otherwise. |
| 218 | */ |
| 219 | static inline bool _cds_wfcq_enqueue(cds_wfcq_head_ptr_t head, |
| 220 | struct cds_wfcq_tail *tail, |
| 221 | struct cds_wfcq_node *new_tail) |
| 222 | { |
| 223 | return ___cds_wfcq_append(head, tail, new_tail, new_tail); |
| 224 | } |
| 225 | |
| 226 | /* |
| 227 | * CDS_WFCQ_WAIT_SLEEP: |
| 228 | * |
| 229 | * By default, this sleeps for the given @msec milliseconds. |
| 230 | * This is a macro which LGPL users may #define themselves before |
| 231 | * including wfcqueue.h to override the default behavior (e.g. |
| 232 | * to log a warning or perform other background work). |
| 233 | */ |
| 234 | #ifndef CDS_WFCQ_WAIT_SLEEP |
| 235 | #define CDS_WFCQ_WAIT_SLEEP(msec) ___cds_wfcq_wait_sleep(msec) |
| 236 | #endif |
| 237 | |
| 238 | static inline void ___cds_wfcq_wait_sleep(int msec) |
| 239 | { |
| 240 | (void) poll(NULL, 0, msec); |
| 241 | } |
| 242 | |
| 243 | /* |
| 244 | * ___cds_wfcq_busy_wait: adaptative busy-wait. |
| 245 | * |
| 246 | * Returns 1 if nonblocking and needs to block, 0 otherwise. |
| 247 | */ |
| 248 | static inline bool |
| 249 | ___cds_wfcq_busy_wait(int *attempt, int blocking) |
| 250 | { |
| 251 | if (!blocking) |
| 252 | return 1; |
| 253 | if (++(*attempt) >= WFCQ_ADAPT_ATTEMPTS) { |
| 254 | CDS_WFCQ_WAIT_SLEEP(WFCQ_WAIT); /* Wait for 10ms */ |
| 255 | *attempt = 0; |
| 256 | } else { |
| 257 | caa_cpu_relax(); |
| 258 | } |
| 259 | return 0; |
| 260 | } |
| 261 | |
| 262 | /* |
| 263 | * Waiting for enqueuer to complete enqueue and return the next node. |
| 264 | */ |
| 265 | static inline struct cds_wfcq_node * |
| 266 | ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking) |
| 267 | { |
| 268 | struct cds_wfcq_node *next; |
| 269 | int attempt = 0; |
| 270 | |
| 271 | /* |
| 272 | * Adaptative busy-looping waiting for enqueuer to complete enqueue. |
| 273 | */ |
| 274 | while ((next = CMM_LOAD_SHARED(node->next)) == NULL) { |
| 275 | if (___cds_wfcq_busy_wait(&attempt, blocking)) |
| 276 | return CDS_WFCQ_WOULDBLOCK; |
| 277 | } |
| 278 | |
| 279 | return next; |
| 280 | } |
| 281 | |
| 282 | static inline struct cds_wfcq_node * |
| 283 | ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head, |
| 284 | struct cds_wfcq_tail *tail, |
| 285 | int blocking) |
| 286 | { |
| 287 | struct __cds_wfcq_head *head = u_head._h; |
| 288 | struct cds_wfcq_node *node; |
| 289 | |
| 290 | if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail)) |
| 291 | return NULL; |
| 292 | node = ___cds_wfcq_node_sync_next(&head->node, blocking); |
| 293 | /* Load head->node.next before loading node's content */ |
| 294 | cmm_smp_read_barrier_depends(); |
| 295 | return node; |
| 296 | } |
| 297 | |
| 298 | /* |
| 299 | * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing. |
| 300 | * |
| 301 | * Content written into the node before enqueue is guaranteed to be |
| 302 | * consistent, but no other memory ordering is ensured. |
| 303 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
| 304 | * caller. |
| 305 | * |
| 306 | * Used by for-like iteration macros in urcu/wfqueue.h: |
| 307 | * __cds_wfcq_for_each_blocking() |
| 308 | * __cds_wfcq_for_each_blocking_safe() |
| 309 | * |
| 310 | * Returns NULL if queue is empty, first node otherwise. |
| 311 | */ |
| 312 | static inline struct cds_wfcq_node * |
| 313 | ___cds_wfcq_first_blocking(cds_wfcq_head_ptr_t head, |
| 314 | struct cds_wfcq_tail *tail) |
| 315 | { |
| 316 | return ___cds_wfcq_first(head, tail, 1); |
| 317 | } |
| 318 | |
| 319 | |
| 320 | /* |
| 321 | * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing. |
| 322 | * |
| 323 | * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if |
| 324 | * it needs to block. |
| 325 | */ |
| 326 | static inline struct cds_wfcq_node * |
| 327 | ___cds_wfcq_first_nonblocking(cds_wfcq_head_ptr_t head, |
| 328 | struct cds_wfcq_tail *tail) |
| 329 | { |
| 330 | return ___cds_wfcq_first(head, tail, 0); |
| 331 | } |
| 332 | |
| 333 | static inline struct cds_wfcq_node * |
| 334 | ___cds_wfcq_next(cds_wfcq_head_ptr_t head __attribute__((unused)), |
| 335 | struct cds_wfcq_tail *tail, |
| 336 | struct cds_wfcq_node *node, |
| 337 | int blocking) |
| 338 | { |
| 339 | struct cds_wfcq_node *next; |
| 340 | |
| 341 | /* |
| 342 | * Even though the following tail->p check is sufficient to find |
| 343 | * out if we reached the end of the queue, we first check |
| 344 | * node->next as a common case to ensure that iteration on nodes |
| 345 | * do not frequently access enqueuer's tail->p cache line. |
| 346 | */ |
| 347 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { |
| 348 | /* Load node->next before tail->p */ |
| 349 | cmm_smp_rmb(); |
| 350 | if (CMM_LOAD_SHARED(tail->p) == node) |
| 351 | return NULL; |
| 352 | next = ___cds_wfcq_node_sync_next(node, blocking); |
| 353 | } |
| 354 | /* Load node->next before loading next's content */ |
| 355 | cmm_smp_read_barrier_depends(); |
| 356 | return next; |
| 357 | } |
| 358 | |
| 359 | /* |
| 360 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. |
| 361 | * |
| 362 | * Content written into the node before enqueue is guaranteed to be |
| 363 | * consistent, but no other memory ordering is ensured. |
| 364 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
| 365 | * caller. |
| 366 | * |
| 367 | * Used by for-like iteration macros in urcu/wfqueue.h: |
| 368 | * __cds_wfcq_for_each_blocking() |
| 369 | * __cds_wfcq_for_each_blocking_safe() |
| 370 | * |
| 371 | * Returns NULL if reached end of queue, non-NULL next queue node |
| 372 | * otherwise. |
| 373 | */ |
| 374 | static inline struct cds_wfcq_node * |
| 375 | ___cds_wfcq_next_blocking(cds_wfcq_head_ptr_t head, |
| 376 | struct cds_wfcq_tail *tail, |
| 377 | struct cds_wfcq_node *node) |
| 378 | { |
| 379 | return ___cds_wfcq_next(head, tail, node, 1); |
| 380 | } |
| 381 | |
| 382 | /* |
| 383 | * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing. |
| 384 | * |
| 385 | * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if |
| 386 | * it needs to block. |
| 387 | */ |
| 388 | static inline struct cds_wfcq_node * |
| 389 | ___cds_wfcq_next_nonblocking(cds_wfcq_head_ptr_t head, |
| 390 | struct cds_wfcq_tail *tail, |
| 391 | struct cds_wfcq_node *node) |
| 392 | { |
| 393 | return ___cds_wfcq_next(head, tail, node, 0); |
| 394 | } |
| 395 | |
| 396 | static inline struct cds_wfcq_node * |
| 397 | ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head, |
| 398 | struct cds_wfcq_tail *tail, |
| 399 | int *state, |
| 400 | int blocking) |
| 401 | { |
| 402 | struct __cds_wfcq_head *head = u_head._h; |
| 403 | struct cds_wfcq_node *node, *next; |
| 404 | |
| 405 | if (state) |
| 406 | *state = 0; |
| 407 | |
| 408 | if (_cds_wfcq_empty(__cds_wfcq_head_cast(head), tail)) { |
| 409 | return NULL; |
| 410 | } |
| 411 | |
| 412 | node = ___cds_wfcq_node_sync_next(&head->node, blocking); |
| 413 | if (!blocking && node == CDS_WFCQ_WOULDBLOCK) { |
| 414 | return CDS_WFCQ_WOULDBLOCK; |
| 415 | } |
| 416 | |
| 417 | if ((next = CMM_LOAD_SHARED(node->next)) == NULL) { |
| 418 | /* |
| 419 | * @node is probably the only node in the queue. |
| 420 | * Try to move the tail to &q->head. |
| 421 | * q->head.next is set to NULL here, and stays |
| 422 | * NULL if the cmpxchg succeeds. Should the |
| 423 | * cmpxchg fail due to a concurrent enqueue, the |
| 424 | * q->head.next will be set to the next node. |
| 425 | * The implicit memory barrier before |
| 426 | * uatomic_cmpxchg() orders load node->next |
| 427 | * before loading q->tail. |
| 428 | * The implicit memory barrier before uatomic_cmpxchg |
| 429 | * orders load q->head.next before loading node's |
| 430 | * content. |
| 431 | */ |
| 432 | _cds_wfcq_node_init(&head->node); |
| 433 | if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) { |
| 434 | if (state) |
| 435 | *state |= CDS_WFCQ_STATE_LAST; |
| 436 | return node; |
| 437 | } |
| 438 | next = ___cds_wfcq_node_sync_next(node, blocking); |
| 439 | /* |
| 440 | * In nonblocking mode, if we would need to block to |
| 441 | * get node's next, set the head next node pointer |
| 442 | * (currently NULL) back to its original value. |
| 443 | */ |
| 444 | if (!blocking && next == CDS_WFCQ_WOULDBLOCK) { |
| 445 | head->node.next = node; |
| 446 | return CDS_WFCQ_WOULDBLOCK; |
| 447 | } |
| 448 | } |
| 449 | |
| 450 | /* |
| 451 | * Move queue head forward. |
| 452 | */ |
| 453 | head->node.next = next; |
| 454 | |
| 455 | /* Load q->head.next before loading node's content */ |
| 456 | cmm_smp_read_barrier_depends(); |
| 457 | return node; |
| 458 | } |
| 459 | |
| 460 | /* |
| 461 | * __cds_wfcq_dequeue_with_state_blocking: dequeue node from queue, with state. |
| 462 | * |
| 463 | * Content written into the node before enqueue is guaranteed to be |
| 464 | * consistent, but no other memory ordering is ensured. |
| 465 | * It is valid to reuse and free a dequeued node immediately. |
| 466 | * Dequeue/splice/iteration mutual exclusion should be ensured by the |
| 467 | * caller. |
| 468 | */ |
| 469 | static inline struct cds_wfcq_node * |
| 470 | ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_ptr_t head, |
| 471 | struct cds_wfcq_tail *tail, int *state) |
| 472 | { |
| 473 | return ___cds_wfcq_dequeue_with_state(head, tail, state, 1); |
| 474 | } |
| 475 | |
| 476 | /* |
| 477 | * ___cds_wfcq_dequeue_blocking: dequeue node from queue. |
| 478 | * |
| 479 | * Same as __cds_wfcq_dequeue_with_state_blocking, but without saving |
| 480 | * state. |
| 481 | */ |
| 482 | static inline struct cds_wfcq_node * |
| 483 | ___cds_wfcq_dequeue_blocking(cds_wfcq_head_ptr_t head, |
| 484 | struct cds_wfcq_tail *tail) |
| 485 | { |
| 486 | return ___cds_wfcq_dequeue_with_state_blocking(head, tail, NULL); |
| 487 | } |
| 488 | |
| 489 | /* |
| 490 | * __cds_wfcq_dequeue_with_state_nonblocking: dequeue node, with state. |
| 491 | * |
| 492 | * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK |
| 493 | * if it needs to block. |
| 494 | */ |
| 495 | static inline struct cds_wfcq_node * |
| 496 | ___cds_wfcq_dequeue_with_state_nonblocking(cds_wfcq_head_ptr_t head, |
| 497 | struct cds_wfcq_tail *tail, int *state) |
| 498 | { |
| 499 | return ___cds_wfcq_dequeue_with_state(head, tail, state, 0); |
| 500 | } |
| 501 | |
| 502 | /* |
| 503 | * ___cds_wfcq_dequeue_nonblocking: dequeue node from queue. |
| 504 | * |
| 505 | * Same as __cds_wfcq_dequeue_with_state_nonblocking, but without saving |
| 506 | * state. |
| 507 | */ |
| 508 | static inline struct cds_wfcq_node * |
| 509 | ___cds_wfcq_dequeue_nonblocking(cds_wfcq_head_ptr_t head, |
| 510 | struct cds_wfcq_tail *tail) |
| 511 | { |
| 512 | return ___cds_wfcq_dequeue_with_state_nonblocking(head, tail, NULL); |
| 513 | } |
| 514 | |
| 515 | /* |
| 516 | * __cds_wfcq_splice: enqueue all src_q nodes at the end of dest_q. |
| 517 | * |
| 518 | * Dequeue all nodes from src_q. |
| 519 | * dest_q must be already initialized. |
| 520 | * Mutual exclusion for src_q should be ensured by the caller as |
| 521 | * specified in the "Synchronisation table". |
| 522 | * Returns enum cds_wfcq_ret which indicates the state of the src or |
| 523 | * dest queue. |
| 524 | */ |
| 525 | static inline enum cds_wfcq_ret |
| 526 | ___cds_wfcq_splice( |
| 527 | cds_wfcq_head_ptr_t u_dest_q_head, |
| 528 | struct cds_wfcq_tail *dest_q_tail, |
| 529 | cds_wfcq_head_ptr_t u_src_q_head, |
| 530 | struct cds_wfcq_tail *src_q_tail, |
| 531 | int blocking) |
| 532 | { |
| 533 | struct __cds_wfcq_head *dest_q_head = u_dest_q_head._h; |
| 534 | struct __cds_wfcq_head *src_q_head = u_src_q_head._h; |
| 535 | struct cds_wfcq_node *head, *tail; |
| 536 | int attempt = 0; |
| 537 | |
| 538 | /* |
| 539 | * Initial emptiness check to speed up cases where queue is |
| 540 | * empty: only require loads to check if queue is empty. |
| 541 | */ |
| 542 | if (_cds_wfcq_empty(__cds_wfcq_head_cast(src_q_head), src_q_tail)) |
| 543 | return CDS_WFCQ_RET_SRC_EMPTY; |
| 544 | |
| 545 | for (;;) { |
| 546 | /* |
| 547 | * Open-coded _cds_wfcq_empty() by testing result of |
| 548 | * uatomic_xchg, as well as tail pointer vs head node |
| 549 | * address. |
| 550 | */ |
| 551 | head = uatomic_xchg(&src_q_head->node.next, NULL); |
| 552 | if (head) |
| 553 | break; /* non-empty */ |
| 554 | if (CMM_LOAD_SHARED(src_q_tail->p) == &src_q_head->node) |
| 555 | return CDS_WFCQ_RET_SRC_EMPTY; |
| 556 | if (___cds_wfcq_busy_wait(&attempt, blocking)) |
| 557 | return CDS_WFCQ_RET_WOULDBLOCK; |
| 558 | } |
| 559 | |
| 560 | /* |
| 561 | * Memory barrier implied before uatomic_xchg() orders store to |
| 562 | * src_q->head before store to src_q->tail. This is required by |
| 563 | * concurrent enqueue on src_q, which exchanges the tail before |
| 564 | * updating the previous tail's next pointer. |
| 565 | */ |
| 566 | tail = uatomic_xchg(&src_q_tail->p, &src_q_head->node); |
| 567 | |
| 568 | /* |
| 569 | * Append the spliced content of src_q into dest_q. Does not |
| 570 | * require mutual exclusion on dest_q (wait-free). |
| 571 | */ |
| 572 | if (___cds_wfcq_append(__cds_wfcq_head_cast(dest_q_head), dest_q_tail, |
| 573 | head, tail)) |
| 574 | return CDS_WFCQ_RET_DEST_NON_EMPTY; |
| 575 | else |
| 576 | return CDS_WFCQ_RET_DEST_EMPTY; |
| 577 | } |
| 578 | |
| 579 | /* |
| 580 | * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. |
| 581 | * |
| 582 | * Dequeue all nodes from src_q. |
| 583 | * dest_q must be already initialized. |
| 584 | * Mutual exclusion for src_q should be ensured by the caller as |
| 585 | * specified in the "Synchronisation table". |
| 586 | * Returns enum cds_wfcq_ret which indicates the state of the src or |
| 587 | * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK. |
| 588 | */ |
| 589 | static inline enum cds_wfcq_ret |
| 590 | ___cds_wfcq_splice_blocking( |
| 591 | cds_wfcq_head_ptr_t dest_q_head, |
| 592 | struct cds_wfcq_tail *dest_q_tail, |
| 593 | cds_wfcq_head_ptr_t src_q_head, |
| 594 | struct cds_wfcq_tail *src_q_tail) |
| 595 | { |
| 596 | return ___cds_wfcq_splice(dest_q_head, dest_q_tail, |
| 597 | src_q_head, src_q_tail, 1); |
| 598 | } |
| 599 | |
| 600 | /* |
| 601 | * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q. |
| 602 | * |
| 603 | * Same as __cds_wfcq_splice_blocking, but returns |
| 604 | * CDS_WFCQ_RET_WOULDBLOCK if it needs to block. |
| 605 | */ |
| 606 | static inline enum cds_wfcq_ret |
| 607 | ___cds_wfcq_splice_nonblocking( |
| 608 | cds_wfcq_head_ptr_t dest_q_head, |
| 609 | struct cds_wfcq_tail *dest_q_tail, |
| 610 | cds_wfcq_head_ptr_t src_q_head, |
| 611 | struct cds_wfcq_tail *src_q_tail) |
| 612 | { |
| 613 | return ___cds_wfcq_splice(dest_q_head, dest_q_tail, |
| 614 | src_q_head, src_q_tail, 0); |
| 615 | } |
| 616 | |
| 617 | /* |
| 618 | * cds_wfcq_dequeue_with_state_blocking: dequeue a node from a wait-free queue. |
| 619 | * |
| 620 | * Content written into the node before enqueue is guaranteed to be |
| 621 | * consistent, but no other memory ordering is ensured. |
| 622 | * Mutual exclusion with cds_wfcq_splice_blocking and dequeue lock is |
| 623 | * ensured. |
| 624 | * It is valid to reuse and free a dequeued node immediately. |
| 625 | */ |
| 626 | static inline struct cds_wfcq_node * |
| 627 | _cds_wfcq_dequeue_with_state_blocking(struct cds_wfcq_head *head, |
| 628 | struct cds_wfcq_tail *tail, int *state) |
| 629 | { |
| 630 | struct cds_wfcq_node *retval; |
| 631 | |
| 632 | _cds_wfcq_dequeue_lock(head, tail); |
| 633 | retval = ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_cast(head), |
| 634 | tail, state); |
| 635 | _cds_wfcq_dequeue_unlock(head, tail); |
| 636 | return retval; |
| 637 | } |
| 638 | |
| 639 | /* |
| 640 | * cds_wfcq_dequeue_blocking: dequeue node from queue. |
| 641 | * |
| 642 | * Same as cds_wfcq_dequeue_blocking, but without saving state. |
| 643 | */ |
| 644 | static inline struct cds_wfcq_node * |
| 645 | _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head, |
| 646 | struct cds_wfcq_tail *tail) |
| 647 | { |
| 648 | return _cds_wfcq_dequeue_with_state_blocking(head, tail, NULL); |
| 649 | } |
| 650 | |
| 651 | /* |
| 652 | * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q. |
| 653 | * |
| 654 | * Dequeue all nodes from src_q. |
| 655 | * dest_q must be already initialized. |
| 656 | * Content written into the node before enqueue is guaranteed to be |
| 657 | * consistent, but no other memory ordering is ensured. |
| 658 | * Mutual exclusion with cds_wfcq_dequeue_blocking and dequeue lock is |
| 659 | * ensured. |
| 660 | * Returns enum cds_wfcq_ret which indicates the state of the src or |
| 661 | * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK. |
| 662 | */ |
| 663 | static inline enum cds_wfcq_ret |
| 664 | _cds_wfcq_splice_blocking( |
| 665 | struct cds_wfcq_head *dest_q_head, |
| 666 | struct cds_wfcq_tail *dest_q_tail, |
| 667 | struct cds_wfcq_head *src_q_head, |
| 668 | struct cds_wfcq_tail *src_q_tail) |
| 669 | { |
| 670 | enum cds_wfcq_ret ret; |
| 671 | |
| 672 | _cds_wfcq_dequeue_lock(src_q_head, src_q_tail); |
| 673 | ret = ___cds_wfcq_splice_blocking(cds_wfcq_head_cast(dest_q_head), dest_q_tail, |
| 674 | cds_wfcq_head_cast(src_q_head), src_q_tail); |
| 675 | _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail); |
| 676 | return ret; |
| 677 | } |
| 678 | |
| 679 | #ifdef __cplusplus |
| 680 | } |
| 681 | #endif |
| 682 | |
| 683 | #endif /* _URCU_WFCQUEUE_STATIC_H */ |