projects / userspace-rcu.git / blame
| Commit | Line | Data |
|---|---|---|
| d3d3857f MJ |
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 | ||
| 453629a9 MD |
6 | #ifndef _URCU_REF_H |
| 7 | #define _URCU_REF_H | |
| 8 | ||
| 9 | /* | |
| 10 | * Userspace RCU - Reference counting | |
| 11 | * | |
| 453629a9 | 12 | * Author: Jan Blunck <jblunck@suse.de> |
| 453629a9 MD |
13 | */ |
| 14 | ||
| cd21955a | 15 | #include <stdbool.h> |
| 7ce99d02 MD |
16 | #include <limits.h> |
| 17 | #include <stdlib.h> | |
| 01477510 | 18 | #include <urcu/assert.h> |
| a2e7bf9c | 19 | #include <urcu/uatomic.h> |
| 453629a9 MD |
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 | ||
| 8b4b5a1a MD |
35 | static inline bool __attribute__((warn_unused_result)) |
| 36 | urcu_ref_get_safe(struct urcu_ref *ref) | |
| 453629a9 | 37 | { |
| 7ce99d02 MD |
38 | long old, _new, res; |
| 39 | ||
| 40 | old = uatomic_read(&ref->refcount); | |
| 41 | for (;;) { | |
| 42 | if (old == LONG_MAX) { | |
| 8b4b5a1a | 43 | return false; /* Failure. */ |
| 7ce99d02 MD |
44 | } |
| 45 | _new = old + 1; | |
| 46 | res = uatomic_cmpxchg(&ref->refcount, old, _new); | |
| 47 | if (res == old) { | |
| 8b4b5a1a | 48 | return true; /* Success. */ |
| 7ce99d02 MD |
49 | } |
| 50 | old = res; | |
| 51 | } | |
| 453629a9 MD |
52 | } |
| 53 | ||
| 8b4b5a1a MD |
54 | static inline void urcu_ref_get(struct urcu_ref *ref) |
| 55 | { | |
| 56 | if (!urcu_ref_get_safe(ref)) | |
| 57 | abort(); | |
| 58 | } | |
| 59 | ||
| 453629a9 MD |
60 | static inline void urcu_ref_put(struct urcu_ref *ref, |
| 61 | void (*release)(struct urcu_ref *)) | |
| 62 | { | |
| bf27322d | 63 | long res = uatomic_sub_return(&ref->refcount, 1); |
| 01477510 | 64 | urcu_posix_assert(res >= 0); |
| bf27322d | 65 | if (res == 0) |
| 453629a9 MD |
66 | release(ref); |
| 67 | } | |
| 68 | ||
| cd21955a MD |
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 | |
| 7ce99d02 MD |
76 | * count. False is also returned in case incrementing the refcount would |
| 77 | * result in an overflow. | |
| cd21955a MD |
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 (;;) { | |
| 7ce99d02 | 85 | if (old == 0 || old == LONG_MAX) |
| cd21955a MD |
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 | ||
| 453629a9 | 96 | #endif /* _URCU_REF_H */ |