urcu/rculfstack.h

   1 #ifndef _URCU_RCULFSTACK_H
   2 #define _URCU_RCULFSTACK_H
   3
   4 /*
   5  * rculfstack.h
   6  *
   7  * Userspace RCU library - Lock-Free RCU Stack
   8  *
   9  * Copyright 2010 - 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 #ifdef __cplusplus
  27 extern "C" {
  28 #endif
  29
  30 #if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
  31 #error "Dynamic loader LGPL wrappers not implemented yet"
  32 #endif
  33
  34 struct rcu_lfs_node {
  35         struct rcu_lfs_node *next;
  36 };
  37
  38 struct rcu_lfs_stack {
  39         struct rcu_lfs_node *head;
  40 };
  41
  42 void rcu_lfs_node_init(struct rcu_lfs_node *node)
  43 {
  44 }
  45
  46 void rcu_lfs_init(struct rcu_lfs_stack *s)
  47 {
  48         s->head = NULL;
  49 }
  50
  51 void rcu_lfs_push(struct rcu_lfs_stack *s, struct rcu_lfs_node *node)
  52 {
  53         for (;;) {
  54                 struct rcu_lfs_node *head;
  55
  56                 rcu_read_lock();
  57                 head = rcu_dereference(s->head);
  58                 node->next = head;
  59                 /*
  60                  * uatomic_cmpxchg() implicit memory barrier orders earlier
  61                  * stores to node before publication.
  62                  */
  63                 if (uatomic_cmpxchg(&s->head, head, node) == head) {
  64                         rcu_read_unlock();
  65                         return;
  66                 } else {
  67                         /* Failure to prepend. Retry. */
  68                         rcu_read_unlock();
  69                         continue;
  70                 }
  71         }
  72 }
  73
  74 /*
  75  * The caller must wait for a grace period to pass before freeing the returned
  76  * node or modifying the rcu_lfs_node structure.
  77  * Returns NULL if stack is empty.
  78  */
  79 struct rcu_lfs_node *
  80 rcu_lfs_pop(struct rcu_lfs_stack *s)
  81 {
  82         for (;;) {
  83                 struct rcu_lfs_node *head;
  84
  85                 rcu_read_lock();
  86                 head = rcu_dereference(s->head);
  87                 if (head) {
  88                         struct rcu_lfs_node *next = rcu_dereference(head->next);
  89
  90                         if (uatomic_cmpxchg(&s->head, head, next) == head) {
  91                                 rcu_read_unlock();
  92                                 return head;
  93                         } else {
  94                                 /* Concurrent modification. Retry. */
  95                                 rcu_read_unlock();
  96                                 continue;
  97                         }
  98                 } else {
  99                         /* Empty stack */
 100                         rcu_read_unlock();
 101                         return NULL;
 102                 }
 103         }
 104 }
 105
 106 #ifdef __cplusplus
 107 }
 108 #endif
 109
 110 #endif /* _URCU_RCULFSTACK_H */