urcu/wfstack.h

   1 #ifndef _URCU_WFSTACK_H
   2 #define _URCU_WFSTACK_H
   3
   4 /*
   5  * urcu/wfstack.h
   6  *
   7  * Userspace RCU library - Stack with wait-free push, blocking traversal.
   8  *
   9  * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  10  *
  11  * This library is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU Lesser General Public
  13  * License as published by the Free Software Foundation; either
  14  * version 2.1 of the License, or (at your option) any later version.
  15  *
  16  * This library is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  * Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public
  22  * License along with this library; if not, write to the Free Software
  23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  24  */
  25
  26 #include <pthread.h>
  27 #include <assert.h>
  28 #include <stdbool.h>
  29 #include <urcu/compiler.h>
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 /*
  36  * Stack with wait-free push, blocking traversal.
  37  *
  38  * Stack implementing push, pop, pop_all operations, as well as iterator
  39  * on the stack head returned by pop_all.
  40  *
  41  * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
  42  *                       cds_wfs_first.
  43  * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
  44  *                      iteration on stack head returned by pop_all.
  45  *
  46  * Synchronization table:
  47  *
  48  * External synchronization techniques described in the API below is
  49  * required between pairs marked with "X". No external synchronization
  50  * required between pairs marked with "-".
  51  *
  52  *                      cds_wfs_push  __cds_wfs_pop  __cds_wfs_pop_all
  53  * cds_wfs_push               -              -                  -
  54  * __cds_wfs_pop              -              X                  X
  55  * __cds_wfs_pop_all          -              X                  -
  56  *
  57  * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
  58  * synchronization.
  59  */
  60
  61 #define CDS_WFS_WOULDBLOCK      ((void *) -1UL)
  62
  63 /*
  64  * struct cds_wfs_node is returned by __cds_wfs_pop, and also used as
  65  * iterator on stack. It is not safe to dereference the node next
  66  * pointer when returned by __cds_wfs_pop_blocking.
  67  */
  68 struct cds_wfs_node {
  69         struct cds_wfs_node *next;
  70 };
  71
  72 /*
  73  * struct cds_wfs_head is returned by __cds_wfs_pop_all, and can be used
  74  * to begin iteration on the stack. "node" needs to be the first field of
  75  * cds_wfs_head, so the end-of-stack pointer value can be used for both
  76  * types.
  77  */
  78 struct cds_wfs_head {
  79         struct cds_wfs_node node;
  80 };
  81
  82 struct cds_wfs_stack {
  83         struct cds_wfs_head *head;
  84         pthread_mutex_t lock;
  85 };
  86
  87 #ifdef _LGPL_SOURCE
  88
  89 #include <urcu/static/wfstack.h>
  90
  91 #define cds_wfs_node_init               _cds_wfs_node_init
  92 #define cds_wfs_init                    _cds_wfs_init
  93 #define cds_wfs_empty                   _cds_wfs_empty
  94 #define cds_wfs_push                    _cds_wfs_push
  95
  96 /* Locking performed internally */
  97 #define cds_wfs_pop_blocking            _cds_wfs_pop_blocking
  98 #define cds_wfs_pop_all_blocking        _cds_wfs_pop_all_blocking
  99
 100 /*
 101  * For iteration on cds_wfs_head returned by __cds_wfs_pop_all or
 102  * cds_wfs_pop_all_blocking.
 103  */
 104 #define cds_wfs_first                   _cds_wfs_first
 105 #define cds_wfs_next_blocking           _cds_wfs_next_blocking
 106
 107 /* Pop locking with internal mutex */
 108 #define cds_wfs_pop_lock                _cds_wfs_pop_lock
 109 #define cds_wfs_pop_unlock              _cds_wfs_pop_unlock
 110
 111 /* Synchronization ensured by the caller. See synchronization table. */
 112 #define __cds_wfs_pop_blocking          ___cds_wfs_pop_blocking
 113 #define __cds_wfs_pop_all               ___cds_wfs_pop_all
 114
 115 #else /* !_LGPL_SOURCE */
 116
 117 /*
 118  * cds_wfs_node_init: initialize wait-free stack node.
 119  */
 120 extern void cds_wfs_node_init(struct cds_wfs_node *node);
 121
 122 /*
 123  * cds_wfs_init: initialize wait-free stack.
 124  */
 125 extern void cds_wfs_init(struct cds_wfs_stack *s);
 126
 127 /*
 128  * cds_wfs_empty: return whether wait-free stack is empty.
 129  *
 130  * No memory barrier is issued. No mutual exclusion is required.
 131  */
 132 extern bool cds_wfs_empty(struct cds_wfs_stack *s);
 133
 134 /*
 135  * cds_wfs_push: push a node into the stack.
 136  *
 137  * Issues a full memory barrier before push. No mutual exclusion is
 138  * required.
 139  *
 140  * Returns 0 if the stack was empty prior to adding the node.
 141  * Returns non-zero otherwise.
 142  */
 143 extern int cds_wfs_push(struct cds_wfs_stack *s, struct cds_wfs_node *node);
 144
 145 /*
 146  * cds_wfs_pop_blocking: pop a node from the stack.
 147  *
 148  * Calls __cds_wfs_pop_blocking with an internal pop mutex held.
 149  */
 150 extern struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s);
 151
 152 /*
 153  * cds_wfs_pop_all_blocking: pop all nodes from a stack.
 154  *
 155  * Calls __cds_wfs_pop_all with an internal pop mutex held.
 156  */
 157 extern struct cds_wfs_head *cds_wfs_pop_all_blocking(struct cds_wfs_stack *s);
 158
 159 /*
 160  * cds_wfs_first: get first node of a popped stack.
 161  *
 162  * Content written into the node before enqueue is guaranteed to be
 163  * consistent, but no other memory ordering is ensured.
 164  *
 165  * Used by for-like iteration macros in urcu/wfstack.h:
 166  * cds_wfs_for_each_blocking()
 167  * cds_wfs_for_each_blocking_safe()
 168  *
 169  * Returns NULL if popped stack is empty, top stack node otherwise.
 170  */
 171 extern struct cds_wfs_node *cds_wfs_first(struct cds_wfs_head *head);
 172
 173 /*
 174  * cds_wfs_next_blocking: get next node of a popped stack.
 175  *
 176  * Content written into the node before enqueue is guaranteed to be
 177  * consistent, but no other memory ordering is ensured.
 178  *
 179  * Used by for-like iteration macros in urcu/wfstack.h:
 180  * cds_wfs_for_each_blocking()
 181  * cds_wfs_for_each_blocking_safe()
 182  *
 183  * Returns NULL if reached end of popped stack, non-NULL next stack
 184  * node otherwise.
 185  */
 186 extern struct cds_wfs_node *cds_wfs_next_blocking(struct cds_wfs_node *node);
 187
 188 /*
 189  * cds_wfs_next_nonblocking: get next node of a popped stack.
 190  *
 191  * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
 192  * needs to block.
 193  */
 194 extern struct cds_wfs_node *cds_wfs_next_nonblocking(struct cds_wfs_node *node);
 195
 196 /*
 197  * cds_wfs_pop_lock: lock stack pop-protection mutex.
 198  */
 199 extern void cds_wfs_pop_lock(struct cds_wfs_stack *s);
 200
 201 /*
 202  * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
 203  */
 204 extern void cds_wfs_pop_unlock(struct cds_wfs_stack *s);
 205
 206 /*
 207  * __cds_wfs_pop_blocking: pop a node from the stack.
 208  *
 209  * Returns NULL if stack is empty.
 210  *
 211  * __cds_wfs_pop_blocking needs to be synchronized using one of the
 212  * following techniques:
 213  *
 214  * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
 215  *    section. The caller must wait for a grace period to pass before
 216  *    freeing the returned node or modifying the cds_wfs_node structure.
 217  * 2) Using mutual exclusion (e.g. mutexes) to protect
 218  *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
 219  * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
 220  *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
 221  */
 222 extern struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s);
 223
 224 /*
 225  * __cds_wfs_pop_nonblocking: pop a node from the stack.
 226  *
 227  * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
 228  * it needs to block.
 229  */
 230 extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack *s);
 231
 232 /*
 233  * __cds_wfs_pop_all: pop all nodes from a stack.
 234  *
 235  * __cds_wfs_pop_all does not require any synchronization with other
 236  * push, nor with other __cds_wfs_pop_all, but requires synchronization
 237  * matching the technique used to synchronize __cds_wfs_pop_blocking:
 238  *
 239  * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
 240  *    section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
 241  *    must wait for a grace period to pass before freeing the returned
 242  *    node or modifying the cds_wfs_node structure. However, no RCU
 243  *    read-side critical section is needed around __cds_wfs_pop_all.
 244  * 2) Using mutual exclusion (e.g. mutexes) to protect
 245  *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
 246  * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
 247  *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
 248  */
 249 extern struct cds_wfs_head *__cds_wfs_pop_all(struct cds_wfs_stack *s);
 250
 251 #endif /* !_LGPL_SOURCE */
 252
 253 #ifdef __cplusplus
 254 }
 255 #endif
 256
 257 /*
 258  * cds_wfs_for_each_blocking: Iterate over all nodes returned by
 259  * __cds_wfs_pop_all().
 260  * @head: head of the queue (struct cds_wfs_head pointer).
 261  * @node: iterator (struct cds_wfs_node pointer).
 262  *
 263  * Content written into each node before enqueue is guaranteed to be
 264  * consistent, but no other memory ordering is ensured.
 265  */
 266 #define cds_wfs_for_each_blocking(head, node)                   \
 267         for (node = cds_wfs_first(head);                        \
 268                 node != NULL;                                   \
 269                 node = cds_wfs_next_blocking(node))
 270
 271 /*
 272  * cds_wfs_for_each_blocking_safe: Iterate over all nodes returned by
 273  * __cds_wfs_pop_all(). Safe against deletion.
 274  * @head: head of the queue (struct cds_wfs_head pointer).
 275  * @node: iterator (struct cds_wfs_node pointer).
 276  * @n: struct cds_wfs_node pointer holding the next pointer (used
 277  *     internally).
 278  *
 279  * Content written into each node before enqueue is guaranteed to be
 280  * consistent, but no other memory ordering is ensured.
 281  */
 282 #define cds_wfs_for_each_blocking_safe(head, node, n)                      \
 283         for (node = cds_wfs_first(head),                                   \
 284                         n = (node ? cds_wfs_next_blocking(node) : NULL);   \
 285                 node != NULL;                                              \
 286                 node = n, n = (node ? cds_wfs_next_blocking(node) : NULL))
 287
 288 #endif /* _URCU_WFSTACK_H */