Fix: uatomic arm32: add missing release barrier before uatomic_xchg
[urcu.git] / include / 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 <limits.h>
20 #include <stdlib.h>
21 #include <urcu/uatomic.h>
22
23 struct urcu_ref {
24 long refcount; /* ATOMIC */
25 };
26
27 static inline void urcu_ref_set(struct urcu_ref *ref, long val)
28 {
29 uatomic_set(&ref->refcount, val);
30 }
31
32 static inline void urcu_ref_init(struct urcu_ref *ref)
33 {
34 urcu_ref_set(ref, 1);
35 }
36
37 static inline bool __attribute__((warn_unused_result))
38 urcu_ref_get_safe(struct urcu_ref *ref)
39 {
40 long old, _new, res;
41
42 old = uatomic_read(&ref->refcount);
43 for (;;) {
44 if (old == LONG_MAX) {
45 return false; /* Failure. */
46 }
47 _new = old + 1;
48 res = uatomic_cmpxchg(&ref->refcount, old, _new);
49 if (res == old) {
50 return true; /* Success. */
51 }
52 old = res;
53 }
54 }
55
56 static inline void urcu_ref_get(struct urcu_ref *ref)
57 {
58 if (!urcu_ref_get_safe(ref))
59 abort();
60 }
61
62 static inline void urcu_ref_put(struct urcu_ref *ref,
63 void (*release)(struct urcu_ref *))
64 {
65 long res = uatomic_sub_return(&ref->refcount, 1);
66 assert (res >= 0);
67 if (res == 0)
68 release(ref);
69 }
70
71 /*
72 * urcu_ref_get_unless_zero
73 *
74 * Allows getting a reference atomically if the reference count is not
75 * zero. Returns true if the reference is taken, false otherwise. This
76 * needs to be used in conjunction with another synchronization
77 * technique (e.g. RCU or mutex) to ensure existence of the reference
78 * count. False is also returned in case incrementing the refcount would
79 * result in an overflow.
80 */
81 static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
82 {
83 long old, _new, res;
84
85 old = uatomic_read(&ref->refcount);
86 for (;;) {
87 if (old == 0 || old == LONG_MAX)
88 return false; /* Failure. */
89 _new = old + 1;
90 res = uatomic_cmpxchg(&ref->refcount, old, _new);
91 if (res == old) {
92 return true; /* Success. */
93 }
94 old = res;
95 }
96 }
97
98 #endif /* _URCU_REF_H */
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