FreeBSD/Linux Kernel Cross Reference
sys/sys/refcount.h
1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 *
27 * $FreeBSD: head/sys/sys/refcount.h 344855 2019-03-06 22:11:45Z jhb $
28 */
29
30 #ifndef __SYS_REFCOUNT_H__
31 #define __SYS_REFCOUNT_H__
32
33 #include <sys/limits.h>
34 #include <machine/atomic.h>
35
36 #ifdef _KERNEL
37 #include <sys/systm.h>
38 #else
39 #define KASSERT(exp, msg) /* */
40 #endif
41
42 static __inline void
43 refcount_init(volatile u_int *count, u_int value)
44 {
45
46 *count = value;
47 }
48
49 static __inline void
50 refcount_acquire(volatile u_int *count)
51 {
52
53 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
54 atomic_add_int(count, 1);
55 }
56
57 static __inline int
58 refcount_release(volatile u_int *count)
59 {
60 u_int old;
61
62 atomic_thread_fence_rel();
63 old = atomic_fetchadd_int(count, -1);
64 KASSERT(old > 0, ("refcount %p is zero", count));
65 if (old > 1)
66 return (0);
67
68 /*
69 * Last reference. Signal the user to call the destructor.
70 *
71 * Ensure that the destructor sees all updates. The fence_rel
72 * at the start of the function synchronized with this fence.
73 */
74 atomic_thread_fence_acq();
75 return (1);
76 }
77
78 /*
79 * This functions returns non-zero if the refcount was
80 * incremented. Else zero is returned.
81 */
82 static __inline __result_use_check int
83 refcount_acquire_if_not_zero(volatile u_int *count)
84 {
85 u_int old;
86
87 old = *count;
88 for (;;) {
89 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count));
90 if (old == 0)
91 return (0);
92 if (atomic_fcmpset_int(count, &old, old + 1))
93 return (1);
94 }
95 }
96
97 static __inline __result_use_check int
98 refcount_release_if_not_last(volatile u_int *count)
99 {
100 u_int old;
101
102 old = *count;
103 for (;;) {
104 KASSERT(old > 0, ("refcount %p is zero", count));
105 if (old == 1)
106 return (0);
107 if (atomic_fcmpset_int(count, &old, old - 1))
108 return (1);
109 }
110 }
111
112 #endif /* ! __SYS_REFCOUNT_H__ */
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