urcu/rculfqueue.h

   1 #ifndef _URCU_RCULFQUEUE_H
   2 #define _URCU_RCULFQUEUE_H
   3
   4 /*
   5  * rculfqueue.h
   6  *
   7  * Userspace RCU library - Lock-Free RCU Queue
   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 #include <urcu/urcu_ref.h>
  27 #include <assert.h>
  28
  29 #ifdef __cplusplus
  30 extern "C" {
  31 #endif
  32
  33 /*
  34  * Lock-free RCU queue using reference counting. Enqueue and dequeue operations
  35  * hold a RCU read lock to deal with cmpxchg ABA problem. This implementation
  36  * keeps a dummy head node to ensure we can always update the queue locklessly.
  37  * Given that this is a queue, the dummy head node must always advance as we
  38  * dequeue entries. Therefore, we keep a reference count on each entry we are
  39  * dequeueing, so they can be kept as dummy head node until the next dequeue, at
  40  * which point their reference count will be decremented.
  41  */
  42
  43 struct rcu_lfq_node {
  44         struct rcu_lfq_node *next;
  45         struct urcu_ref ref;
  46 };
  47
  48 struct rcu_lfq_queue {
  49         struct rcu_lfq_node *head, *tail;
  50         struct rcu_lfq_node init;       /* Dummy initialization node */
  51 };
  52
  53 #ifdef _LGPL_SOURCE
  54
  55 #include <urcu/rculfqueue-static.h>
  56
  57 #define rcu_lfq_node_init       _rcu_lfq_node_init
  58 #define rcu_lfq_init            _rcu_lfq_init
  59 #define rcu_lfq_enqueue         _rcu_lfq_enqueue
  60 #define rcu_lfq_dequeue         _rcu_lfq_dequeue
  61
  62 #else /* !_LGPL_SOURCE */
  63
  64 extern void rcu_lfq_node_init(struct rcu_lfq_node *node);
  65 extern void rcu_lfq_init(struct rcu_lfq_queue *q);
  66 extern void rcu_lfq_enqueue(struct rcu_lfq_queue *q, struct rcu_lfq_node *node);
  67
  68 /*
  69  * The entry returned by dequeue must be taken care of by doing a urcu_ref_put,
  70  * which calls the release primitive when the reference count drops to zero. A
  71  * grace period must be waited after execution of the release callback before
  72  * performing the actual memory reclamation or modifying the rcu_lfq_node
  73  * structure.
  74  * In other words, the entry lfq node returned by dequeue must not be
  75  * modified/re-used/freed until the reference count reaches zero and a grace
  76  * period has elapsed (after the refcount reached 0).
  77  */
  78 extern struct rcu_lfq_node *
  79 rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *));
  80
  81 #endif /* !_LGPL_SOURCE */
  82
  83 #ifdef __cplusplus
  84 }
  85 #endif
  86
  87 #endif /* _URCU_RCULFQUEUE_H */