include/urcu/static/wfstack.h

   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, cds_wfs_empty,
  51  *                       cds_wfs_first.
  52  * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
  53  *                      iteration on stack head returned by pop_all.
  54  *
  55  * Synchronization table:
  56  *
  57  * External synchronization techniques described in the API below is
  58  * required between pairs marked with "X". No external synchronization
  59  * required between pairs marked with "-".
  60  *
  61  *                      cds_wfs_push  __cds_wfs_pop  __cds_wfs_pop_all
  62  * cds_wfs_push               -              -                  -
  63  * __cds_wfs_pop              -              X                  X
  64  * __cds_wfs_pop_all          -              X                  -
  65  *
  66  * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
  67  * synchronization.
  68  */
  69
  70 /*
  71  * cds_wfs_node_init: initialize wait-free stack node.
  72  */
  73 static inline
  74 void _cds_wfs_node_init(struct cds_wfs_node *node)
  75 {
  76         node->next = NULL;
  77 }
  78
  79 /*
  80  * __cds_wfs_init: initialize wait-free stack. Don't pair with
  81  * any destroy function.
  82  */
  83 static inline void ___cds_wfs_init(struct __cds_wfs_stack *s)
  84 {
  85         s->head = CDS_WFS_END;
  86 }
  87
  88 /*
  89  * cds_wfs_init: initialize wait-free stack. Pair with
  90  * cds_wfs_destroy().
  91  */
  92 static inline
  93 void _cds_wfs_init(struct cds_wfs_stack *s)
  94 {
  95         int ret;
  96
  97         s->head = CDS_WFS_END;
  98         ret = pthread_mutex_init(&s->lock, NULL);
  99         assert(!ret);
 100 }
 101
 102 /*
 103  * cds_wfs_destroy: destroy wait-free stack. Pair with
 104  * cds_wfs_init().
 105  */
 106 static inline
 107 void _cds_wfs_destroy(struct cds_wfs_stack *s)
 108 {
 109         int ret = pthread_mutex_destroy(&s->lock);
 110         assert(!ret);
 111 }
 112
 113 static inline bool ___cds_wfs_end(void *node)
 114 {
 115         return node == CDS_WFS_END;
 116 }
 117
 118 /*
 119  * cds_wfs_empty: return whether wait-free stack is empty.
 120  *
 121  * No memory barrier is issued. No mutual exclusion is required.
 122  */
 123 static inline bool _cds_wfs_empty(cds_wfs_stack_ptr_t u_stack)
 124 {
 125         struct __cds_wfs_stack *s = u_stack._s;
 126
 127         return ___cds_wfs_end(CMM_LOAD_SHARED(s->head));
 128 }
 129
 130 /*
 131  * cds_wfs_push: push a node into the stack.
 132  *
 133  * Issues a full memory barrier before push. No mutual exclusion is
 134  * required.
 135  *
 136  * Returns 0 if the stack was empty prior to adding the node.
 137  * Returns non-zero otherwise.
 138  */
 139 static inline
 140 int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack, struct cds_wfs_node *node)
 141 {
 142         struct __cds_wfs_stack *s = u_stack._s;
 143         struct cds_wfs_head *old_head, *new_head;
 144
 145         assert(node->next == NULL);
 146         new_head = caa_container_of(node, struct cds_wfs_head, node);
 147         /*
 148          * uatomic_xchg() implicit memory barrier orders earlier stores
 149          * to node (setting it to NULL) before publication.
 150          */
 151         old_head = uatomic_xchg(&s->head, new_head);
 152         /*
 153          * At this point, dequeuers see a NULL node->next, they should
 154          * busy-wait until node->next is set to old_head.
 155          */
 156         CMM_STORE_SHARED(node->next, &old_head->node);
 157         return !___cds_wfs_end(old_head);
 158 }
 159
 160 /*
 161  * Waiting for push to complete enqueue and return the next node.
 162  */
 163 static inline struct cds_wfs_node *
 164 ___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
 165 {
 166         struct cds_wfs_node *next;
 167         int attempt = 0;
 168
 169         /*
 170          * Adaptative busy-looping waiting for push to complete.
 171          */
 172         while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
 173                 if (!blocking)
 174                         return CDS_WFS_WOULDBLOCK;
 175                 if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
 176                         (void) poll(NULL, 0, CDS_WFS_WAIT);     /* Wait for 10ms */
 177                         attempt = 0;
 178                 } else {
 179                         caa_cpu_relax();
 180                 }
 181         }
 182
 183         return next;
 184 }
 185
 186 static inline
 187 struct cds_wfs_node *
 188 ___cds_wfs_pop(cds_wfs_stack_ptr_t u_stack, int *state, int blocking)
 189 {
 190         struct cds_wfs_head *head, *new_head;
 191         struct cds_wfs_node *next;
 192         struct __cds_wfs_stack *s = u_stack._s;
 193
 194         if (state)
 195                 *state = 0;
 196         for (;;) {
 197                 head = CMM_LOAD_SHARED(s->head);
 198                 if (___cds_wfs_end(head)) {
 199                         return NULL;
 200                 }
 201                 next = ___cds_wfs_node_sync_next(&head->node, blocking);
 202                 if (!blocking && next == CDS_WFS_WOULDBLOCK) {
 203                         return CDS_WFS_WOULDBLOCK;
 204                 }
 205                 new_head = caa_container_of(next, struct cds_wfs_head, node);
 206                 if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
 207                         if (state && ___cds_wfs_end(new_head))
 208                                 *state |= CDS_WFS_STATE_LAST;
 209                         return &head->node;
 210                 }
 211                 if (!blocking) {
 212                         return CDS_WFS_WOULDBLOCK;
 213                 }
 214                 /* busy-loop if head changed under us */
 215         }
 216 }
 217
 218 /*
 219  * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
 220  *
 221  * Returns NULL if stack is empty.
 222  *
 223  * __cds_wfs_pop_blocking needs to be synchronized using one of the
 224  * following techniques:
 225  *
 226  * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
 227  *    section. The caller must wait for a grace period to pass before
 228  *    freeing the returned node or modifying the cds_wfs_node structure.
 229  * 2) Using mutual exclusion (e.g. mutexes) to protect
 230  *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
 231  * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
 232  *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
 233  *
 234  * "state" saves state flags atomically sampled with pop operation.
 235  */
 236 static inline
 237 struct cds_wfs_node *
 238 ___cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack, int *state)
 239 {
 240         return ___cds_wfs_pop(u_stack, state, 1);
 241 }
 242
 243 static inline
 244 struct cds_wfs_node *
 245 ___cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack)
 246 {
 247         return ___cds_wfs_pop_with_state_blocking(u_stack, NULL);
 248 }
 249
 250 /*
 251  * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
 252  *
 253  * Same as __cds_wfs_pop_with_state_blocking, but returns
 254  * CDS_WFS_WOULDBLOCK if it needs to block.
 255  *
 256  * "state" saves state flags atomically sampled with pop operation.
 257  */
 258 static inline
 259 struct cds_wfs_node *
 260 ___cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack, int *state)
 261 {
 262         return ___cds_wfs_pop(u_stack, state, 0);
 263 }
 264
 265 /*
 266  * __cds_wfs_pop_nonblocking: pop a node from the stack.
 267  *
 268  * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
 269  * it needs to block.
 270  */
 271 static inline
 272 struct cds_wfs_node *
 273 ___cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack)
 274 {
 275         return ___cds_wfs_pop_with_state_nonblocking(u_stack, NULL);
 276 }
 277
 278 /*
 279  * __cds_wfs_pop_all: pop all nodes from a stack.
 280  *
 281  * __cds_wfs_pop_all does not require any synchronization with other
 282  * push, nor with other __cds_wfs_pop_all, but requires synchronization
 283  * matching the technique used to synchronize __cds_wfs_pop_blocking:
 284  *
 285  * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
 286  *    section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
 287  *    must wait for a grace period to pass before freeing the returned
 288  *    node or modifying the cds_wfs_node structure. However, no RCU
 289  *    read-side critical section is needed around __cds_wfs_pop_all.
 290  * 2) Using mutual exclusion (e.g. mutexes) to protect
 291  *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
 292  * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
 293  *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
 294  */
 295 static inline
 296 struct cds_wfs_head *
 297 ___cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack)
 298 {
 299         struct __cds_wfs_stack *s = u_stack._s;
 300         struct cds_wfs_head *head;
 301
 302         /*
 303          * Implicit memory barrier after uatomic_xchg() matches implicit
 304          * memory barrier before uatomic_xchg() in cds_wfs_push. It
 305          * ensures that all nodes of the returned list are consistent.
 306          * There is no need to issue memory barriers when iterating on
 307          * the returned list, because the full memory barrier issued
 308          * prior to each uatomic_cmpxchg, which each write to head, are
 309          * taking care to order writes to each node prior to the full
 310          * memory barrier after this uatomic_xchg().
 311          */
 312         head = uatomic_xchg(&s->head, CDS_WFS_END);
 313         if (___cds_wfs_end(head))
 314                 return NULL;
 315         return head;
 316 }
 317
 318 /*
 319  * cds_wfs_pop_lock: lock stack pop-protection mutex.
 320  */
 321 static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s)
 322 {
 323         int ret;
 324
 325         ret = pthread_mutex_lock(&s->lock);
 326         assert(!ret);
 327 }
 328
 329 /*
 330  * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
 331  */
 332 static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
 333 {
 334         int ret;
 335
 336         ret = pthread_mutex_unlock(&s->lock);
 337         assert(!ret);
 338 }
 339
 340 /*
 341  * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
 342  */
 343 static inline
 344 struct cds_wfs_node *
 345 _cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
 346 {
 347         struct cds_wfs_node *retnode;
 348
 349         _cds_wfs_pop_lock(s);
 350         retnode = ___cds_wfs_pop_with_state_blocking(s, state);
 351         _cds_wfs_pop_unlock(s);
 352         return retnode;
 353 }
 354
 355 /*
 356  * Call _cds_wfs_pop_with_state_blocking without saving any state.
 357  */
 358 static inline
 359 struct cds_wfs_node *
 360 _cds_wfs_pop_blocking(struct cds_wfs_stack *s)
 361 {
 362         return _cds_wfs_pop_with_state_blocking(s, NULL);
 363 }
 364
 365 /*
 366  * Call __cds_wfs_pop_all with an internal pop mutex held.
 367  */
 368 static inline
 369 struct cds_wfs_head *
 370 _cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
 371 {
 372         struct cds_wfs_head *rethead;
 373
 374         _cds_wfs_pop_lock(s);
 375         rethead = ___cds_wfs_pop_all(s);
 376         _cds_wfs_pop_unlock(s);
 377         return rethead;
 378 }
 379
 380 /*
 381  * cds_wfs_first: get first node of a popped stack.
 382  *
 383  * Content written into the node before enqueue is guaranteed to be
 384  * consistent, but no other memory ordering is ensured.
 385  *
 386  * Used by for-like iteration macros in urcu/wfstack.h:
 387  * cds_wfs_for_each_blocking()
 388  * cds_wfs_for_each_blocking_safe()
 389  *
 390  * Returns NULL if popped stack is empty, top stack node otherwise.
 391  */
 392 static inline struct cds_wfs_node *
 393 _cds_wfs_first(struct cds_wfs_head *head)
 394 {
 395         if (___cds_wfs_end(head))
 396                 return NULL;
 397         return &head->node;
 398 }
 399
 400 static inline struct cds_wfs_node *
 401 ___cds_wfs_next(struct cds_wfs_node *node, int blocking)
 402 {
 403         struct cds_wfs_node *next;
 404
 405         next = ___cds_wfs_node_sync_next(node, blocking);
 406         /*
 407          * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
 408          * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
 409          * and still return CDS_WFS_WOULDBLOCK.
 410          */
 411         if (___cds_wfs_end(next))
 412                 return NULL;
 413         return next;
 414 }
 415
 416 /*
 417  * cds_wfs_next_blocking: get next node of a popped stack.
 418  *
 419  * Content written into the node before enqueue is guaranteed to be
 420  * consistent, but no other memory ordering is ensured.
 421  *
 422  * Used by for-like iteration macros in urcu/wfstack.h:
 423  * cds_wfs_for_each_blocking()
 424  * cds_wfs_for_each_blocking_safe()
 425  *
 426  * Returns NULL if reached end of popped stack, non-NULL next stack
 427  * node otherwise.
 428  */
 429 static inline struct cds_wfs_node *
 430 _cds_wfs_next_blocking(struct cds_wfs_node *node)
 431 {
 432         return ___cds_wfs_next(node, 1);
 433 }
 434
 435
 436 /*
 437  * cds_wfs_next_nonblocking: get next node of a popped stack.
 438  *
 439  * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
 440  * needs to block.
 441  */
 442 static inline struct cds_wfs_node *
 443 _cds_wfs_next_nonblocking(struct cds_wfs_node *node)
 444 {
 445         return ___cds_wfs_next(node, 0);
 446 }
 447
 448 #ifdef __cplusplus
 449 }
 450 #endif
 451
 452 #endif /* _URCU_STATIC_WFSTACK_H */