| 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 */ |