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: stable/12/sys/sys/refcount.h 367457 2020-11-07 18:10:59Z dim $
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 #include <stdbool.h>
40 #define KASSERT(exp, msg) /* */
41 #endif
42
43 static __inline void
44 refcount_init(volatile u_int *count, u_int value)
45 {
46
47 *count = value;
48 }
49
50 static __inline void
51 refcount_acquire(volatile u_int *count)
52 {
53
54 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
55 atomic_add_int(count, 1);
56 }
57
58 static __inline __result_use_check bool
59 refcount_acquire_checked(volatile u_int *count)
60 {
61 u_int lcount;
62
63 for (lcount = *count;;) {
64 if (__predict_false(lcount + 1 < lcount))
65 return (false);
66 if (__predict_true(atomic_fcmpset_int(count, &lcount,
67 lcount + 1) == 1))
68 return (true);
69 }
70 }
71
72 static __inline bool
73 refcount_release(volatile u_int *count)
74 {
75 u_int old;
76
77 atomic_thread_fence_rel();
78 old = atomic_fetchadd_int(count, -1);
79 KASSERT(old > 0, ("refcount %p is zero", count));
80 if (old > 1)
81 return (false);
82
83 /*
84 * Last reference. Signal the user to call the destructor.
85 *
86 * Ensure that the destructor sees all updates. The fence_rel
87 * at the start of the function synchronized with this fence.
88 */
89 atomic_thread_fence_acq();
90 return (true);
91 }
92
93 /*
94 * This functions returns non-zero if the refcount was
95 * incremented. Else zero is returned.
96 *
97 * A temporary hack until refcount_* APIs are sorted out.
98 */
99 static __inline __result_use_check bool
100 refcount_acquire_if_not_zero(volatile u_int *count)
101 {
102 u_int old;
103
104 old = *count;
105 for (;;) {
106 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count));
107 if (old == 0)
108 return (false);
109 if (atomic_fcmpset_int(count, &old, old + 1))
110 return (true);
111 }
112 }
113
114 static __inline __result_use_check bool
115 refcount_release_if_not_last(volatile u_int *count)
116 {
117 u_int old;
118
119 old = *count;
120 for (;;) {
121 KASSERT(old > 0, ("refcount %p is zero", count));
122 if (old == 1)
123 return (false);
124 if (atomic_fcmpset_int(count, &old, old - 1))
125 return (true);
126 }
127 }
128
129 #endif /* ! __SYS_REFCOUNT_H__ */
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