urcu/ref.h

   1 #ifndef _URCU_REF_H
   2 #define _URCU_REF_H
   3
   4 /*
   5  * Userspace RCU - Reference counting
   6  *
   7  * Copyright (C) 2009 Novell Inc.
   8  * Copyright (C) 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   9  *
  10  * Author: Jan Blunck <jblunck@suse.de>
  11  *
  12  * This program is free software; you can redistribute it and/or modify it
  13  * under the terms of the GNU Lesser General Public License version 2.1 as
  14  * published by the Free  Software Foundation.
  15  */
  16
  17 #include <assert.h>
  18 #include <stdbool.h>
  19 #include <urcu/uatomic.h>
  20
  21 struct urcu_ref {
  22         long refcount; /* ATOMIC */
  23 };
  24
  25 static inline void urcu_ref_set(struct urcu_ref *ref, long val)
  26 {
  27         uatomic_set(&ref->refcount, val);
  28 }
  29
  30 static inline void urcu_ref_init(struct urcu_ref *ref)
  31 {
  32         urcu_ref_set(ref, 1);
  33 }
  34
  35 static inline void urcu_ref_get(struct urcu_ref *ref)
  36 {
  37         uatomic_add(&ref->refcount, 1);
  38 }
  39
  40 static inline void urcu_ref_put(struct urcu_ref *ref,
  41                                 void (*release)(struct urcu_ref *))
  42 {
  43         long res = uatomic_sub_return(&ref->refcount, 1);
  44         assert (res >= 0);
  45         if (res == 0)
  46                 release(ref);
  47 }
  48
  49 /*
  50  * urcu_ref_get_unless_zero
  51  *
  52  * Allows getting a reference atomically if the reference count is not
  53  * zero. Returns true if the reference is taken, false otherwise. This
  54  * needs to be used in conjunction with another synchronization
  55  * technique (e.g.  RCU or mutex) to ensure existence of the reference
  56  * count.
  57  */
  58 static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
  59 {
  60         long old, _new, res;
  61
  62         old = uatomic_read(&ref->refcount);
  63         for (;;) {
  64                 if (old == 0)
  65                         return false;   /* Failure. */
  66                 _new = old + 1;
  67                 res = uatomic_cmpxchg(&ref->refcount, old, _new);
  68                 if (res == old) {
  69                         return true;    /* Success. */
  70                 }
  71                 old = res;
  72         }
  73 }
  74
  75 #endif /* _URCU_REF_H */