urcu/static/wfcqueue.h

   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.
  96  */
  97 static inline void _cds_wfcq_init(struct cds_wfcq_head *head,
  98                 struct cds_wfcq_tail *tail)
  99 {
 100         int ret;
 101
 102         /* Set queue head and tail */
 103         _cds_wfcq_node_init(&head->node);
 104         tail->p = &head->node;
 105         ret = pthread_mutex_init(&head->lock, NULL);
 106         assert(!ret);
 107 }
 108
 109 /*
 110  * __cds_wfcq_init: initialize wait-free queue.
 111  */
 112 static inline void ___cds_wfcq_init(struct __cds_wfcq_head *head,
 113                 struct cds_wfcq_tail *tail)
 114 {
 115         /* Set queue head and tail */
 116         _cds_wfcq_node_init(&head->node);
 117         tail->p = &head->node;
 118 }
 119
 120 /*
 121  * cds_wfcq_empty: return whether wait-free queue is empty.
 122  *
 123  * No memory barrier is issued. No mutual exclusion is required.
 124  *
 125  * We perform the test on head->node.next to check if the queue is
 126  * possibly empty, but we confirm this by checking if the tail pointer
 127  * points to the head node because the tail pointer is the linearisation
 128  * point of the enqueuers. Just checking the head next pointer could
 129  * make a queue appear empty if an enqueuer is preempted for a long time
 130  * between xchg() and setting the previous node's next pointer.
 131  */
 132 static inline bool _cds_wfcq_empty(cds_wfcq_head_ptr_t u_head,
 133                 struct cds_wfcq_tail *tail)
 134 {
 135         struct __cds_wfcq_head *head = u_head._h;
 136         /*
 137          * Queue is empty if no node is pointed by head->node.next nor
 138          * tail->p. Even though the tail->p check is sufficient to find
 139          * out of the queue is empty, we first check head->node.next as a
 140          * common case to ensure that dequeuers do not frequently access
 141          * enqueuer's tail->p cache line.
 142          */
 143         return CMM_LOAD_SHARED(head->node.next) == NULL
 144                 && CMM_LOAD_SHARED(tail->p) == &head->node;
 145 }
 146
 147 static inline void _cds_wfcq_dequeue_lock(struct cds_wfcq_head *head,
 148                 struct cds_wfcq_tail *tail)
 149 {
 150         int ret;
 151
 152         ret = pthread_mutex_lock(&head->lock);
 153         assert(!ret);
 154 }
 155
 156 static inline void _cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head,
 157                 struct cds_wfcq_tail *tail)
 158 {
 159         int ret;
 160
 161         ret = pthread_mutex_unlock(&head->lock);
 162         assert(!ret);
 163 }
 164
 165 static inline bool ___cds_wfcq_append(cds_wfcq_head_ptr_t u_head,
 166                 struct cds_wfcq_tail *tail,
 167                 struct cds_wfcq_node *new_head,
 168                 struct cds_wfcq_node *new_tail)
 169 {
 170         struct __cds_wfcq_head *head = u_head._h;
 171         struct cds_wfcq_node *old_tail;
 172
 173         /*
 174          * Implicit memory barrier before uatomic_xchg() orders earlier
 175          * stores to data structure containing node and setting
 176          * node->next to NULL before publication.
 177          */
 178         old_tail = uatomic_xchg(&tail->p, new_tail);
 179
 180         /*
 181          * Implicit memory barrier after uatomic_xchg() orders store to
 182          * q->tail before store to old_tail->next.
 183          *
 184          * At this point, dequeuers see a NULL tail->p->next, which
 185          * indicates that the queue is being appended to. The following
 186          * store will append "node" to the queue from a dequeuer
 187          * perspective.
 188          */
 189         CMM_STORE_SHARED(old_tail->next, new_head);
 190         /*
 191          * Return false if queue was empty prior to adding the node,
 192          * else return true.
 193          */
 194         return old_tail != &head->node;
 195 }
 196
 197 /*
 198  * cds_wfcq_enqueue: enqueue a node into a wait-free queue.
 199  *
 200  * Issues a full memory barrier before enqueue. No mutual exclusion is
 201  * required.
 202  *
 203  * Returns false if the queue was empty prior to adding the node.
 204  * Returns true otherwise.
 205  */
 206 static inline bool _cds_wfcq_enqueue(cds_wfcq_head_ptr_t head,
 207                 struct cds_wfcq_tail *tail,
 208                 struct cds_wfcq_node *new_tail)
 209 {
 210         return ___cds_wfcq_append(head, tail, new_tail, new_tail);
 211 }
 212
 213 /*
 214  * ___cds_wfcq_busy_wait: adaptative busy-wait.
 215  *
 216  * Returns 1 if nonblocking and needs to block, 0 otherwise.
 217  */
 218 static inline bool
 219 ___cds_wfcq_busy_wait(int *attempt, int blocking)
 220 {
 221         if (!blocking)
 222                 return 1;
 223         if (++(*attempt) >= WFCQ_ADAPT_ATTEMPTS) {
 224                 poll(NULL, 0, WFCQ_WAIT);       /* Wait for 10ms */
 225                 *attempt = 0;
 226         } else {
 227                 caa_cpu_relax();
 228         }
 229         return 0;
 230 }
 231
 232 /*
 233  * Waiting for enqueuer to complete enqueue and return the next node.
 234  */
 235 static inline struct cds_wfcq_node *
 236 ___cds_wfcq_node_sync_next(struct cds_wfcq_node *node, int blocking)
 237 {
 238         struct cds_wfcq_node *next;
 239         int attempt = 0;
 240
 241         /*
 242          * Adaptative busy-looping waiting for enqueuer to complete enqueue.
 243          */
 244         while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
 245                 if (___cds_wfcq_busy_wait(&attempt, blocking))
 246                         return CDS_WFCQ_WOULDBLOCK;
 247         }
 248
 249         return next;
 250 }
 251
 252 static inline struct cds_wfcq_node *
 253 ___cds_wfcq_first(cds_wfcq_head_ptr_t u_head,
 254                 struct cds_wfcq_tail *tail,
 255                 int blocking)
 256 {
 257         struct __cds_wfcq_head *head = u_head._h;
 258         struct cds_wfcq_node *node;
 259
 260         if (_cds_wfcq_empty(head, tail))
 261                 return NULL;
 262         node = ___cds_wfcq_node_sync_next(&head->node, blocking);
 263         /* Load head->node.next before loading node's content */
 264         cmm_smp_read_barrier_depends();
 265         return node;
 266 }
 267
 268 /*
 269  * __cds_wfcq_first_blocking: get first node of a queue, without dequeuing.
 270  *
 271  * Content written into the node before enqueue is guaranteed to be
 272  * consistent, but no other memory ordering is ensured.
 273  * Dequeue/splice/iteration mutual exclusion should be ensured by the
 274  * caller.
 275  *
 276  * Used by for-like iteration macros in urcu/wfqueue.h:
 277  * __cds_wfcq_for_each_blocking()
 278  * __cds_wfcq_for_each_blocking_safe()
 279  *
 280  * Returns NULL if queue is empty, first node otherwise.
 281  */
 282 static inline struct cds_wfcq_node *
 283 ___cds_wfcq_first_blocking(cds_wfcq_head_ptr_t head,
 284                 struct cds_wfcq_tail *tail)
 285 {
 286         return ___cds_wfcq_first(head, tail, 1);
 287 }
 288
 289
 290 /*
 291  * __cds_wfcq_first_nonblocking: get first node of a queue, without dequeuing.
 292  *
 293  * Same as __cds_wfcq_first_blocking, but returns CDS_WFCQ_WOULDBLOCK if
 294  * it needs to block.
 295  */
 296 static inline struct cds_wfcq_node *
 297 ___cds_wfcq_first_nonblocking(cds_wfcq_head_ptr_t head,
 298                 struct cds_wfcq_tail *tail)
 299 {
 300         return ___cds_wfcq_first(head, tail, 0);
 301 }
 302
 303 static inline struct cds_wfcq_node *
 304 ___cds_wfcq_next(cds_wfcq_head_ptr_t head,
 305                 struct cds_wfcq_tail *tail,
 306                 struct cds_wfcq_node *node,
 307                 int blocking)
 308 {
 309         struct cds_wfcq_node *next;
 310
 311         /*
 312          * Even though the following tail->p check is sufficient to find
 313          * out if we reached the end of the queue, we first check
 314          * node->next as a common case to ensure that iteration on nodes
 315          * do not frequently access enqueuer's tail->p cache line.
 316          */
 317         if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
 318                 /* Load node->next before tail->p */
 319                 cmm_smp_rmb();
 320                 if (CMM_LOAD_SHARED(tail->p) == node)
 321                         return NULL;
 322                 next = ___cds_wfcq_node_sync_next(node, blocking);
 323         }
 324         /* Load node->next before loading next's content */
 325         cmm_smp_read_barrier_depends();
 326         return next;
 327 }
 328
 329 /*
 330  * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
 331  *
 332  * Content written into the node before enqueue is guaranteed to be
 333  * consistent, but no other memory ordering is ensured.
 334  * Dequeue/splice/iteration mutual exclusion should be ensured by the
 335  * caller.
 336  *
 337  * Used by for-like iteration macros in urcu/wfqueue.h:
 338  * __cds_wfcq_for_each_blocking()
 339  * __cds_wfcq_for_each_blocking_safe()
 340  *
 341  * Returns NULL if reached end of queue, non-NULL next queue node
 342  * otherwise.
 343  */
 344 static inline struct cds_wfcq_node *
 345 ___cds_wfcq_next_blocking(cds_wfcq_head_ptr_t head,
 346                 struct cds_wfcq_tail *tail,
 347                 struct cds_wfcq_node *node)
 348 {
 349         return ___cds_wfcq_next(head, tail, node, 1);
 350 }
 351
 352 /*
 353  * __cds_wfcq_next_blocking: get next node of a queue, without dequeuing.
 354  *
 355  * Same as __cds_wfcq_next_blocking, but returns CDS_WFCQ_WOULDBLOCK if
 356  * it needs to block.
 357  */
 358 static inline struct cds_wfcq_node *
 359 ___cds_wfcq_next_nonblocking(cds_wfcq_head_ptr_t head,
 360                 struct cds_wfcq_tail *tail,
 361                 struct cds_wfcq_node *node)
 362 {
 363         return ___cds_wfcq_next(head, tail, node, 0);
 364 }
 365
 366 static inline struct cds_wfcq_node *
 367 ___cds_wfcq_dequeue_with_state(cds_wfcq_head_ptr_t u_head,
 368                 struct cds_wfcq_tail *tail,
 369                 int *state,
 370                 int blocking)
 371 {
 372         struct __cds_wfcq_head *head = u_head._h;
 373         struct cds_wfcq_node *node, *next;
 374
 375         if (state)
 376                 *state = 0;
 377
 378         if (_cds_wfcq_empty(head, tail)) {
 379                 return NULL;
 380         }
 381
 382         node = ___cds_wfcq_node_sync_next(&head->node, blocking);
 383         if (!blocking && node == CDS_WFCQ_WOULDBLOCK) {
 384                 return CDS_WFCQ_WOULDBLOCK;
 385         }
 386
 387         if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
 388                 /*
 389                  * @node is probably the only node in the queue.
 390                  * Try to move the tail to &q->head.
 391                  * q->head.next is set to NULL here, and stays
 392                  * NULL if the cmpxchg succeeds. Should the
 393                  * cmpxchg fail due to a concurrent enqueue, the
 394                  * q->head.next will be set to the next node.
 395                  * The implicit memory barrier before
 396                  * uatomic_cmpxchg() orders load node->next
 397                  * before loading q->tail.
 398                  * The implicit memory barrier before uatomic_cmpxchg
 399                  * orders load q->head.next before loading node's
 400                  * content.
 401                  */
 402                 _cds_wfcq_node_init(&head->node);
 403                 if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) {
 404                         if (state)
 405                                 *state |= CDS_WFCQ_STATE_LAST;
 406                         return node;
 407                 }
 408                 next = ___cds_wfcq_node_sync_next(node, blocking);
 409                 /*
 410                  * In nonblocking mode, if we would need to block to
 411                  * get node's next, set the head next node pointer
 412                  * (currently NULL) back to its original value.
 413                  */
 414                 if (!blocking && next == CDS_WFCQ_WOULDBLOCK) {
 415                         head->node.next = node;
 416                         return CDS_WFCQ_WOULDBLOCK;
 417                 }
 418         }
 419
 420         /*
 421          * Move queue head forward.
 422          */
 423         head->node.next = next;
 424
 425         /* Load q->head.next before loading node's content */
 426         cmm_smp_read_barrier_depends();
 427         return node;
 428 }
 429
 430 /*
 431  * __cds_wfcq_dequeue_with_state_blocking: dequeue node from queue, with state.
 432  *
 433  * Content written into the node before enqueue is guaranteed to be
 434  * consistent, but no other memory ordering is ensured.
 435  * It is valid to reuse and free a dequeued node immediately.
 436  * Dequeue/splice/iteration mutual exclusion should be ensured by the
 437  * caller.
 438  */
 439 static inline struct cds_wfcq_node *
 440 ___cds_wfcq_dequeue_with_state_blocking(cds_wfcq_head_ptr_t head,
 441                 struct cds_wfcq_tail *tail, int *state)
 442 {
 443         return ___cds_wfcq_dequeue_with_state(head, tail, state, 1);
 444 }
 445
 446 /*
 447  * ___cds_wfcq_dequeue_blocking: dequeue node from queue.
 448  *
 449  * Same as __cds_wfcq_dequeue_with_state_blocking, but without saving
 450  * state.
 451  */
 452 static inline struct cds_wfcq_node *
 453 ___cds_wfcq_dequeue_blocking(cds_wfcq_head_ptr_t head,
 454                 struct cds_wfcq_tail *tail)
 455 {
 456         return ___cds_wfcq_dequeue_with_state_blocking(head, tail, NULL);
 457 }
 458
 459 /*
 460  * __cds_wfcq_dequeue_with_state_nonblocking: dequeue node, with state.
 461  *
 462  * Same as __cds_wfcq_dequeue_blocking, but returns CDS_WFCQ_WOULDBLOCK
 463  * if it needs to block.
 464  */
 465 static inline struct cds_wfcq_node *
 466 ___cds_wfcq_dequeue_with_state_nonblocking(cds_wfcq_head_ptr_t head,
 467                 struct cds_wfcq_tail *tail, int *state)
 468 {
 469         return ___cds_wfcq_dequeue_with_state(head, tail, state, 0);
 470 }
 471
 472 /*
 473  * ___cds_wfcq_dequeue_nonblocking: dequeue node from queue.
 474  *
 475  * Same as __cds_wfcq_dequeue_with_state_nonblocking, but without saving
 476  * state.
 477  */
 478 static inline struct cds_wfcq_node *
 479 ___cds_wfcq_dequeue_nonblocking(cds_wfcq_head_ptr_t head,
 480                 struct cds_wfcq_tail *tail)
 481 {
 482         return ___cds_wfcq_dequeue_with_state_nonblocking(head, tail, NULL);
 483 }
 484
 485 /*
 486  * __cds_wfcq_splice: enqueue all src_q nodes at the end of dest_q.
 487  *
 488  * Dequeue all nodes from src_q.
 489  * dest_q must be already initialized.
 490  * Mutual exclusion for src_q should be ensured by the caller as
 491  * specified in the "Synchronisation table".
 492  * Returns enum cds_wfcq_ret which indicates the state of the src or
 493  * dest queue.
 494  */
 495 static inline enum cds_wfcq_ret
 496 ___cds_wfcq_splice(
 497                 cds_wfcq_head_ptr_t u_dest_q_head,
 498                 struct cds_wfcq_tail *dest_q_tail,
 499                 cds_wfcq_head_ptr_t u_src_q_head,
 500                 struct cds_wfcq_tail *src_q_tail,
 501                 int blocking)
 502 {
 503         struct __cds_wfcq_head *dest_q_head = u_dest_q_head._h;
 504         struct __cds_wfcq_head *src_q_head = u_src_q_head._h;
 505         struct cds_wfcq_node *head, *tail;
 506         int attempt = 0;
 507
 508         /*
 509          * Initial emptiness check to speed up cases where queue is
 510          * empty: only require loads to check if queue is empty.
 511          */
 512         if (_cds_wfcq_empty(src_q_head, src_q_tail))
 513                 return CDS_WFCQ_RET_SRC_EMPTY;
 514
 515         for (;;) {
 516                 /*
 517                  * Open-coded _cds_wfcq_empty() by testing result of
 518                  * uatomic_xchg, as well as tail pointer vs head node
 519                  * address.
 520                  */
 521                 head = uatomic_xchg(&src_q_head->node.next, NULL);
 522                 if (head)
 523                         break;  /* non-empty */
 524                 if (CMM_LOAD_SHARED(src_q_tail->p) == &src_q_head->node)
 525                         return CDS_WFCQ_RET_SRC_EMPTY;
 526                 if (___cds_wfcq_busy_wait(&attempt, blocking))
 527                         return CDS_WFCQ_RET_WOULDBLOCK;
 528         }
 529
 530         /*
 531          * Memory barrier implied before uatomic_xchg() orders store to
 532          * src_q->head before store to src_q->tail. This is required by
 533          * concurrent enqueue on src_q, which exchanges the tail before
 534          * updating the previous tail's next pointer.
 535          */
 536         tail = uatomic_xchg(&src_q_tail->p, &src_q_head->node);
 537
 538         /*
 539          * Append the spliced content of src_q into dest_q. Does not
 540          * require mutual exclusion on dest_q (wait-free).
 541          */
 542         if (___cds_wfcq_append(dest_q_head, dest_q_tail, head, tail))
 543                 return CDS_WFCQ_RET_DEST_NON_EMPTY;
 544         else
 545                 return CDS_WFCQ_RET_DEST_EMPTY;
 546 }
 547
 548 /*
 549  * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
 550  *
 551  * Dequeue all nodes from src_q.
 552  * dest_q must be already initialized.
 553  * Mutual exclusion for src_q should be ensured by the caller as
 554  * specified in the "Synchronisation table".
 555  * Returns enum cds_wfcq_ret which indicates the state of the src or
 556  * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK.
 557  */
 558 static inline enum cds_wfcq_ret
 559 ___cds_wfcq_splice_blocking(
 560                 cds_wfcq_head_ptr_t dest_q_head,
 561                 struct cds_wfcq_tail *dest_q_tail,
 562                 cds_wfcq_head_ptr_t src_q_head,
 563                 struct cds_wfcq_tail *src_q_tail)
 564 {
 565         return ___cds_wfcq_splice(dest_q_head, dest_q_tail,
 566                 src_q_head, src_q_tail, 1);
 567 }
 568
 569 /*
 570  * __cds_wfcq_splice_nonblocking: enqueue all src_q nodes at the end of dest_q.
 571  *
 572  * Same as __cds_wfcq_splice_blocking, but returns
 573  * CDS_WFCQ_RET_WOULDBLOCK if it needs to block.
 574  */
 575 static inline enum cds_wfcq_ret
 576 ___cds_wfcq_splice_nonblocking(
 577                 cds_wfcq_head_ptr_t dest_q_head,
 578                 struct cds_wfcq_tail *dest_q_tail,
 579                 cds_wfcq_head_ptr_t src_q_head,
 580                 struct cds_wfcq_tail *src_q_tail)
 581 {
 582         return ___cds_wfcq_splice(dest_q_head, dest_q_tail,
 583                 src_q_head, src_q_tail, 0);
 584 }
 585
 586 /*
 587  * cds_wfcq_dequeue_with_state_blocking: dequeue a node from a wait-free queue.
 588  *
 589  * Content written into the node before enqueue is guaranteed to be
 590  * consistent, but no other memory ordering is ensured.
 591  * Mutual exclusion with cds_wfcq_splice_blocking and dequeue lock is
 592  * ensured.
 593  * It is valid to reuse and free a dequeued node immediately.
 594  */
 595 static inline struct cds_wfcq_node *
 596 _cds_wfcq_dequeue_with_state_blocking(struct cds_wfcq_head *head,
 597                 struct cds_wfcq_tail *tail, int *state)
 598 {
 599         struct cds_wfcq_node *retval;
 600
 601         _cds_wfcq_dequeue_lock(head, tail);
 602         retval = ___cds_wfcq_dequeue_with_state_blocking(head, tail, state);
 603         _cds_wfcq_dequeue_unlock(head, tail);
 604         return retval;
 605 }
 606
 607 /*
 608  * cds_wfcq_dequeue_blocking: dequeue node from queue.
 609  *
 610  * Same as cds_wfcq_dequeue_blocking, but without saving state.
 611  */
 612 static inline struct cds_wfcq_node *
 613 _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
 614                 struct cds_wfcq_tail *tail)
 615 {
 616         return _cds_wfcq_dequeue_with_state_blocking(head, tail, NULL);
 617 }
 618
 619 /*
 620  * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
 621  *
 622  * Dequeue all nodes from src_q.
 623  * dest_q must be already initialized.
 624  * Content written into the node before enqueue is guaranteed to be
 625  * consistent, but no other memory ordering is ensured.
 626  * Mutual exclusion with cds_wfcq_dequeue_blocking and dequeue lock is
 627  * ensured.
 628  * Returns enum cds_wfcq_ret which indicates the state of the src or
 629  * dest queue. Never returns CDS_WFCQ_RET_WOULDBLOCK.
 630  */
 631 static inline enum cds_wfcq_ret
 632 _cds_wfcq_splice_blocking(
 633                 struct cds_wfcq_head *dest_q_head,
 634                 struct cds_wfcq_tail *dest_q_tail,
 635                 struct cds_wfcq_head *src_q_head,
 636                 struct cds_wfcq_tail *src_q_tail)
 637 {
 638         enum cds_wfcq_ret ret;
 639
 640         _cds_wfcq_dequeue_lock(src_q_head, src_q_tail);
 641         ret = ___cds_wfcq_splice_blocking(dest_q_head, dest_q_tail,
 642                         src_q_head, src_q_tail);
 643         _cds_wfcq_dequeue_unlock(src_q_head, src_q_tail);
 644         return ret;
 645 }
 646
 647 #ifdef __cplusplus
 648 }
 649 #endif
 650
 651 #endif /* _URCU_WFCQUEUE_STATIC_H */