urcu/rculfstack.h

   1 /*
   2  * rculfstack.h
   3  *
   4  * Userspace RCU library - Lock-Free RCU Stack
   5  *
   6  * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
  24 #error "Dynamic loader LGPL wrappers not implemented yet"
  25 #endif
  26
  27 struct rcu_lfs_node {
  28         struct rcu_lfs_node *next;
  29 };
  30
  31 struct rcu_lfs_stack {
  32         struct rcu_lfs_node *head;
  33 };
  34
  35 void rcu_lfs_node_init(struct rcu_lfs_node *node)
  36 {
  37 }
  38
  39 void rcu_lfs_init(struct rcu_lfs_stack *s)
  40 {
  41         s->head = NULL;
  42 }
  43
  44 void rcu_lfs_push(struct rcu_lfs_stack *s, struct rcu_lfs_node *node)
  45 {
  46         for (;;) {
  47                 struct rcu_lfs_node *head;
  48
  49                 rcu_read_lock();
  50                 head = rcu_dereference(s->head);
  51                 node->next = head;
  52                 /*
  53                  * uatomic_cmpxchg() implicit memory barrier orders earlier
  54                  * stores to node before publication.
  55                  */
  56                 if (uatomic_cmpxchg(&s->head, head, node) == head) {
  57                         rcu_read_unlock();
  58                         return;
  59                 } else {
  60                         /* Failure to prepend. Retry. */
  61                         rcu_read_unlock();
  62                         continue;
  63                 }
  64         }
  65 }
  66
  67 /*
  68  * The caller must wait for a grace period to pass before freeing the returned
  69  * node.
  70  * Returns NULL if stack is empty.
  71  */
  72 struct rcu_lfs_node *
  73 rcu_lfs_pop(struct rcu_lfs_stack *s)
  74 {
  75         for (;;) {
  76                 struct rcu_lfs_node *head;
  77
  78                 rcu_read_lock();
  79                 head = rcu_dereference(s->head);
  80                 if (head) {
  81                         struct rcu_lfs_node *next = rcu_dereference(head->next);
  82
  83                         if (uatomic_cmpxchg(&s->head, head, next) == head) {
  84                                 rcu_read_unlock();
  85                                 return head;
  86                         } else {
  87                                 /* Concurrent modification. Retry. */
  88                                 rcu_read_unlock();
  89                                 continue;
  90                         }
  91                 } else {
  92                         /* Empty stack */
  93                         rcu_read_unlock();
  94                         return NULL;
  95                 }
  96         }
  97 }