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453629a9 MD |
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> | |
cd21955a | 18 | #include <stdbool.h> |
7ce99d02 MD |
19 | #include <limits.h> |
20 | #include <stdlib.h> | |
a2e7bf9c | 21 | #include <urcu/uatomic.h> |
453629a9 MD |
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 | ||
8b4b5a1a MD |
37 | static inline bool __attribute__((warn_unused_result)) |
38 | urcu_ref_get_safe(struct urcu_ref *ref) | |
453629a9 | 39 | { |
7ce99d02 MD |
40 | long old, _new, res; |
41 | ||
42 | old = uatomic_read(&ref->refcount); | |
43 | for (;;) { | |
44 | if (old == LONG_MAX) { | |
8b4b5a1a | 45 | return false; /* Failure. */ |
7ce99d02 MD |
46 | } |
47 | _new = old + 1; | |
48 | res = uatomic_cmpxchg(&ref->refcount, old, _new); | |
49 | if (res == old) { | |
8b4b5a1a | 50 | return true; /* Success. */ |
7ce99d02 MD |
51 | } |
52 | old = res; | |
53 | } | |
453629a9 MD |
54 | } |
55 | ||
8b4b5a1a MD |
56 | static inline void urcu_ref_get(struct urcu_ref *ref) |
57 | { | |
58 | if (!urcu_ref_get_safe(ref)) | |
59 | abort(); | |
60 | } | |
61 | ||
453629a9 MD |
62 | static inline void urcu_ref_put(struct urcu_ref *ref, |
63 | void (*release)(struct urcu_ref *)) | |
64 | { | |
bf27322d PB |
65 | long res = uatomic_sub_return(&ref->refcount, 1); |
66 | assert (res >= 0); | |
67 | if (res == 0) | |
453629a9 MD |
68 | release(ref); |
69 | } | |
70 | ||
cd21955a MD |
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 | |
7ce99d02 MD |
78 | * count. False is also returned in case incrementing the refcount would |
79 | * result in an overflow. | |
cd21955a MD |
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 (;;) { | |
7ce99d02 | 87 | if (old == 0 || old == LONG_MAX) |
cd21955a MD |
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 | ||
453629a9 | 98 | #endif /* _URCU_REF_H */ |