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