Phase 1 of deprecating liburcu-signal
[urcu.git] / include / urcu / ref.h
1 // SPDX-FileCopyrightText: 2009 Novell Inc.
2 // SPDX-FileCopyrightText: 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
3 //
4 // SPDX-License-Identifier: LGPL-2.1-only
5
6 #ifndef _URCU_REF_H
7 #define _URCU_REF_H
8
9 /*
10 * Userspace RCU - Reference counting
11 *
12 * Author: Jan Blunck <jblunck@suse.de>
13 */
14
15 #include <stdbool.h>
16 #include <limits.h>
17 #include <stdlib.h>
18 #include <urcu/assert.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 bool __attribute__((warn_unused_result))
36 urcu_ref_get_safe(struct urcu_ref *ref)
37 {
38 long old, _new, res;
39
40 old = uatomic_read(&ref->refcount);
41 for (;;) {
42 if (old == LONG_MAX) {
43 return false; /* Failure. */
44 }
45 _new = old + 1;
46 res = uatomic_cmpxchg(&ref->refcount, old, _new);
47 if (res == old) {
48 return true; /* Success. */
49 }
50 old = res;
51 }
52 }
53
54 static inline void urcu_ref_get(struct urcu_ref *ref)
55 {
56 if (!urcu_ref_get_safe(ref))
57 abort();
58 }
59
60 static inline void urcu_ref_put(struct urcu_ref *ref,
61 void (*release)(struct urcu_ref *))
62 {
63 long res = uatomic_sub_return(&ref->refcount, 1);
64 urcu_posix_assert(res >= 0);
65 if (res == 0)
66 release(ref);
67 }
68
69 /*
70 * urcu_ref_get_unless_zero
71 *
72 * Allows getting a reference atomically if the reference count is not
73 * zero. Returns true if the reference is taken, false otherwise. This
74 * needs to be used in conjunction with another synchronization
75 * technique (e.g. RCU or mutex) to ensure existence of the reference
76 * count. False is also returned in case incrementing the refcount would
77 * result in an overflow.
78 */
79 static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
80 {
81 long old, _new, res;
82
83 old = uatomic_read(&ref->refcount);
84 for (;;) {
85 if (old == 0 || old == LONG_MAX)
86 return false; /* Failure. */
87 _new = old + 1;
88 res = uatomic_cmpxchg(&ref->refcount, old, _new);
89 if (res == old) {
90 return true; /* Success. */
91 }
92 old = res;
93 }
94 }
95
96 #endif /* _URCU_REF_H */
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